Index

Electronics basics

    Basics

      Cooling

      Heatsinks are the most basic form of cooling next to simple surface convection in today's electronics devices. If you look inside the average PC, you'll probably find two or three heatsinks: on CPUs, video cards, and even the chipset of a motherboard. Heat sinks are also seen on power electronics devices like power supplies, power amplifiers, light dimmers and electronics power switching components (like SSRs).

      Typically heatsinks appear as nothing fancy: hunks of aluminum with a large number of protrusions. While there are different ways of manufacturing heatsinks, and different philosophies in the way they are shaped, the idea of all of them is the same: increase surface area to increase heat dissipation.

      Not all heat sinks are created equal. The most important factor in a heatsink is, naturally, its ability to dissipate the largest amount of heat in the shortest amount of time. How good the heatsink is in this is typically indicated by how much one watt of power will heat it (C/W rating). The lower the C/W rating, the better the heat sink is at dissipating the heat, given proper ventilation and ambient temperature. Commercially made heat sinks typically have this number listed in their data sheet. This ability to transfer heat away from the component depends on a number of factors. First is material. The vast majority of heatsinks are made out of aluminum. Aluminum is an excellent conductor of heat, and relatively cheap. Roughly speaking, conduction can be understood as the transfer of molecular kinetic energy between solids. Copper is indeed a better conductor than aluminum, but because of it's higher price it is not common.

      The second factor in heatsink effectiveness is, as mentioned above, surface area. The protrusions function to make the exposed surface area many times greater than if the same amount of material was in a solid block. The greater the surface area exposed to the air, the greater the dissipation of heat for a given quantity of metal. The temperature gets out of heatsink through convection and radiation. Convection transfers kinetic energy from solid object into the air. Most solutions now use fans to force larger quantities of air over the surface of a heatsink.

      When heatsink is hot, it also radiates some of the hat as heat radiation, but on low temperatures the heatsinks normally are (typically below 100 degrees celsius) the radiation of heat is quite low. It is true, that the color of heat sink has some effect on radiation, but different color heatsinks are so similar once they're closed up inside your machine that they can be safely ignored.

      Heatsinks are approximately equivalent, in heat dissipation, to a sheet of aluminum 1/8" thick by the dimensions shown below:

      • 12" X 12" = approximately 2.1 degrees C per watt thermal rise (2.1 C/W)
      • 15" X 15" = approximately 1.5 degrees C per watt thermal rise (1.5 C/W)
      • 18" X 18" = approximately 1.0 degrees C per watt thermal rise (1.0 C/W)
      In comparison, twice the amount of steel and four times the amount of stainless steel would be needed to achieve the same effect. Remember that the heatsink removes the heat from the electronic component that needs to be cooled and transfers that heat to the air in the electrical enclosure. In turn, this air must circulate and transfer its heat to the outside ambient. Providing vents and/or forced ventilation is a good way to accomplish this. It is a good idea to have at least one inch below them, so air can enter the finned heat sink area (if you have less free area, the heatsink is less efficient, meaning higher C/W rating). Heatsinks should always have empty space above them so the warm air can exit the heat sink area.

      The heat must be transfered from the electronics component to a heat sink in some way, typically the component is mouted on heatsink (regulators, transistors, thyristors etc.) or heatsink is mounted on the top of the component (typical ICs). The best thermal contact is metal to metal (when the whole metal area touches each other and there is thus no insulating air gaps between metal). The best way of acheiving this is by "lapping" the contact area's together with a fine abrasive. Once your have done this the application of a minute amount of thermal grease improves conductivity by less than 0.5%. We also discovered that applying more than a fine film or grease significantly decreased the conductivity (10% or more). Due to the machining process, just about every heat sink will have a rough surface. To the naked eye it may look flat or even feel smooth, but there are microscopic groves in the surface. These groves will trap air between the heat sink and the CPU or other heat generating electronics component, and cause a poor transfer of heat. Thermal compound (Artic Silver, Nanotherm, etc.) is used to fill these groves and help transfer the heat from the CPU or other electronics part to the heat sink.

      Lots of OEM or low end cooling setups use either a thermal interface pad (TIM) or that white goop (slicon based paste) you get at radio shack. The fact is that neither of those does an excellent job of transferring heat from the processor or other component to the heatsink, they work ok. The problem with current commercial pastes is that they have focused on the thermal conductivity of the material, and not on the fundamental principle of a thermal paste, which is gap filling. Silicone based 'goop' from is fairly thermally conductive, but the size of the particles and the terrible spreadability can cause it to be more of an insulator than a conductor. On the other hand, using something entirely liquid such as mineral oil doesn't cool well either because it isn't conductive enough. Even the very best silver-filled grease is 1/32nd the thermal conductivity of Aluminum. An Indium gasket is probably the best you can do, and is is still very much worse temperature conductor than aluminium. Paste isn't meant to be used like car body filler. The key is to find something with the right balance of conductivity and spreadability. Try to eliminate the gap. Correct application is critical to the effectiveness of thermal goop. The idea is to get a very thin, uncontaminated layer of the stuff between the chip and the heatsink. Any kind of oil, scratches, dust, etc. can cause efficiency to drop.

      ASICs

      High speed digital design

      When designing high speed digital systems, you need to understand much more than just bits. According to the classical view, the days when you could ignore signal integrity issued ended when bus-clock rates passed approximately 50 MHz. At that point, give or take a few megahertz, when you designed buses or interconnects, you had to start taking terminations seriously and stop thinking of reflections as just a little overshoot and ringing on waveform edges at state changes. Because of fundamentally analog SI (signal-integrity) issues that accompany today's higher data / signal rates, digital electronics is now as much analog as it is digital. There are only two kinds of electronics engineers working on this field: those who have had SI problems and those who will. Ideally, all high-speed-logic designs should include tightly coupled bypass capacitors for each IC, and all multilayer pc boards should have power and ground distribution planes. Unfortunately, poor design practices still exist, such as using just one bypass capacitor at the power entrance to a logic board and routing power and ground to the ICs from opposite sides of the board. This faulty distribution scheme creates large spikes on the logic supply voltage and produces significant electromagnetic fields around the board and unstable power for the ICs in the board. High system speeds are making clock design a critical problem: Clock signals distributed within a printed-circuit board andaround a system must be clean, stable, synchronized, and have as near toa 50:50 duty cycle as possible. Historically, designing high-speed signals into small, low-pin-count packages required little attention to impedance matching. Nowadays things have changed. As current and future generations of high-speed devices move into larger and denser packages with longer effective signal paths that approach transmission-line structures, impedance matching becomes more important. During IC/package co-design, IC and package designers often agree on impedance targets and signal configurations.such as single-ended, differential pair, and coplanar.for routing signals between the die and the package pins. At high frequencies also transmission losses can be a serious issue. Two types of transmission losses exist: skin-effect losses and dielectric losses. Skin effect, which is proportional to the square root of frequency, leads to an increase in conductor dissipation. At high frequencies, significant skin-effect losses degrade signal-waveform amplitudes. In lossy materials within substrate layers, the dielectric constant's frequency dependence leads to dielectric leakage at very high frequencies. As a system's switching speed increases, electromagnetic radiation can produce troublesome EMI. Radiated emissions associated with multigigabit-per-second data rates can introduce noise via signal lines, power and ground planes, and traces. This noise can superimpose itself on signals as they travel between nets, between chips in a single system, and between systems. Avoiding EMI through careful planning is easier, less costly, and faster than trying to correct EMI-induced system misbehavior after you discover it.

      • Signal-integrity modeling of gigabit backplanes, cables, and connectors using TDR - The TDR (time-domain-reflectometry) method for signal-integrity analysis can help gigabit-system designers produce more accurate interconnect models, resulting in more reliable and higher performance designs.    Rate this link
      • On-chip bypassing with series termination    Rate this link
      • Beware of analog effects in pc-board conductors of fast digital systems - to avoid crosstalk and reflection problems in high-speed digital systems, you must consider transmission-line effects in the pc-board traces    Rate this link
      • Both-ends termination - Terminations exist to control ringing (sometimes called overshoot or resonance). The best ways to control ringing on very long transmission lines are source termination, end termination, and both-ends termination. The both-ends termination is supremely tolerant of imperfections within the transmission system and within the terminators themselves.    Rate this link
      • Breaking up a pair - The two traces comprising a differential pair, when routed close together, share a certain amount of cross-coupling, what happens when pair is breaking up    Rate this link
      • Characteristic impedance of lossy line - This article illustrates the relative influence of skin-effect and dielectric losses on the characteristic impedance of a lossy transmission line.    Rate this link
      • Choose termination and topology to maximize signal integrity and timing - Termination techniques improve noise margins and reduce signal reflections, but they require that you balance trade-offs among conflicting goals. Understanding your choices and their design impact helps you produce a more reliable and cost-effective design.    Rate this link
      • Clock-jitter propagation - Many control systems exhibit a resonant peak between their tracking and filtering ranges.    Rate this link
      • Constant-resistance equalizer - This article describes how to combines a good termination with a useful equalizing function.    Rate this link
      • Constant-resistance termination - Constant-resistance termination occasionally sees application in digital systems as a terminating network. As long as you scale the components correctly, the rate of decrease in the admittance of the R-C leg precisely matches the rate of increase in the admittance of the L-R leg. The result is that the impedance, Z(f), of the whole circuit remains constant at all frequencies. At least, it remains constant until some limit above which the parasitic aspects of the circuit take over and the C and L components no longer behave like Cs and Ls.    Rate this link
      • Differential-to-common-mode conversion - Any unbalanced circuit element within an otherwise well-balanced transmission channel creates a region of partial coupling between the differential and common modes of transmission at that point. The coupling can translate part of a perfectly good differential signal into a common-mode signal, or vice versa. Such differential-to-common-mode-conversion problems frequently arise in the design of LAN adapters.    Rate this link
      • Driving two loads - The split-tee configuration conveniently drives two CMOS receivers from one output. Any time you build a split-tee, always simulate the circuit with a maximal degree of imbalance. For CMOS loads, that scenario means using the maximum load capacitance at one receiver and the minimum (sometimes zero) at the other. Look at the step response to see whether an observable resonance exists.    Rate this link
      • Analysis and Optimization of Power/Ground Bounce in Digital CMOS Circuits - The high edge speeds and clock frequencies of advanced CMOS technology can produce unwanted oscillations during logic level transitions resulting in random logic bit errors.    Rate this link
      • Grounding Rules for High Speed Circuits - This is a selection of application notes documents from Analog Devices    Rate this link
      • Really cool bus - air-conditioning technicians do some really cool things with their big ductwork and the same principle applied to electrical-bus topologies yields some interesting results    Rate this link
      • Decoupling capacitors: use them or fail - Theory is wonderful, but practicalities have their place. This rule is to use one 0.1-?F ceramic per digital chip, two 0.1-?F ceramics per analog chip (one on each supply), and one 1-?F tantalum per every eight ICs or per IC row.    Rate this link
      • Delivering the High-Speed Clock: It's Not Easy To Be On Time - For the digital system clock in high-speed processors, being late, or even being early, causes serious system problems. By doing your homework and not taking design risks, you can ensure that your clock edges make their transitions in the right time window.    Rate this link
      • Design and layout rules eliminate noise coupling in communication systems - high-speed telecommunication and data-communication schemes, such as SONET/SDH networks, noisy high-speed digital logic often shares board space with sensitive analog circuitry    Rate this link
      • Designing for minimal jitter when using clock buffers - High-speed digital boards leave little room for timing margin, certainly not enough to take jitter performance for granted. Awareness of just a few key factors can yield superior performance by design.    Rate this link
      • Designing with PECL (ECL at +5.0V) - The High Speed Solution for the CMOS/TTL Designer application note that tells that PECL, or Positive Emitter Coupled Logic, is nothing more than standard ECL devices run off of a positive power supply.    Rate this link
      • Differential receivers tolerate high-frequency losses - If you instead select a differential receiver and a differential cabling system, the receiver thresholds more nearly center in the middle of the data pattern, because differential receivers are commonly specified with more accurate switching thresholds than ordinary single-ended logic.    Rate this link
      • Differential signaling - The number of grounds depends on spacing and sizes of the connector pins and how they are bent    Rate this link
      • Don't let rules of thumb set decoupling-capacitor values - Choosing decoupling-capacitor values can seem to be a "no-brainer." Unfortunately, even though the consequences of selecting the wrong values are often serious, the most commonly used methods usually produce the wrong answers.    Rate this link
      • Equalizing cables - This article describes the basics of designing cable equalizers. Either style of fixed equalizer can fix a 6-dB equalization problem on a binary code. The simple fixed equalizer works for any cable length from zero to the maximum length. If, however, you need to fix a more-than-6-dB problem or you are using multilevel coding, then you must implement either an adaptive equalizer or a specific equalizer circuit coded for each cable length.    Rate this link
      • Exploit the potential of high-performance CMOS by selecting best interface - High-speed-bus and point-to-point interfaces between CMOS ASICs are no longer limited to conventional CMOS-level signals. By using low-voltage interfaces in a differential, point-to-point, terminated-transmission-line environment, you can obtain data rates of several hundred Mbps. But, to accomplish this, you need to understand interface characteristics and requirements and the system limitations that affect maximum speed.    Rate this link
      • Eyeing jitter: shaking out why signals shake - Jitter may be the enemy of data integrity, but attacking jitter head-on is only one, and not always the fastest way, to end data corruption. itter has become a hot topic among system designers. Seemingly easy to understand, it provides a quantifiable, thanks to the now-ubiquitous eye-diagram display, graphical indication of the severity of a host of phenomena that damage data integrity. Jitter's importance is undeniable, but whether it deserves all the attention it has been getting is another matter.    Rate this link
      • Ground-current control enhances dynamic range in high-speed circuits - Preserving dynamic range in communications products, as well as minimizing unwanted electromagnetic radiation from digital circuitry, requires careful control of currents flowing through ground returns.    Rate this link
      • Growing your own IC clock tree - Defining the clock-distribution network is one of the most difficult aspects of high-speed digital systems and system-on-a-chip designs. Employing the right design methodology helps you.    Rate this link
      • High-speed connectors' electrical properties eclipse mechanical traits - faster rise times and wider buses have changed all the old rules of thumb, now you must rigorously analyze connectors    Rate this link
      • High-speed-connector systems - In high-speed systems, you can't afford to look at connectors as just blobs of plastic and pins. Instead, adopt a systems approach that takes account of the connectors' complex interaction with other parts of the host-system design.    Rate this link
      • High-Speed Digital Design - site with lots of very good high speed design information    Rate this link
      • How to make a processor with the delay between instructions less than a half nano second in standard 1u CMOS. (GHz instruction frequence)    Rate this link
      • Intentional overshoot - The risks associated with intentional overshoot usually outweigh the benefits, especially when a simple, nonresonant end termination provides an equivalent improvement.    Rate this link
      • Understanding Common-Mode Signals - To understand how common-mode signals are created and then suppressed, you should first understand the interaction of shields and grounds in common cable configurations. The following discussion defines a common-mode signal, reviews the common cable configurations, considers shielded vs. unshielded cables, and describes typical grounding practices. It iscusses methods whereby common-mode signals are created and rejected.    Rate this link
      • Modeling and simulation capabilities smooth signal-integrity problems - Like speed bumps on a road, signal distortion, crosstalk, interconnect delay, and EMI can force you to slow your logic circuits unless you take steps to avoid these problems early in the design cycle. Today?s modeling and simulation EDA capabilities make those steps easier and faster than ever.    Rate this link
      • Mysterious ground - For single-ended measurements, don't depend on mysterious ground connections. Always use a good, short ground connection. A short, explicit ground connection made between the scope ground and the equipment under test shunts L and C components on the measuring cable, eliminating their influence on the measured result and pushing the probe resonance up and out of the band of interest. All good probes come with short, tiny ground attachments to prevent such problems.    Rate this link
      • Negative Delay - The rule of causality prohibits the existence of a negative-delay circuit. This article reveals how to make a negative-delay clock repeater, which is really just a positive-delay circuit with a delay u set to a little less than one clock period. You can easily implement a negative clock delay by using a coaxial cable of a suitable length.    Rate this link
      • PC-board layout eases high-speed transmission - As digital techniques move to higher speeds, designers become aware of the need to treat pc-board traces as RF transmission lines. In these lines, you strive to hold the line impedance, Z0, to a constant value typically, and to terminate the line with the same impedance. Data families such as ECL, PECL, and LVDS send data over a pair of traces known as a balanced transmission line. If the traces are on the top of a board with a ground plane under them, then you can model them as coupled "microstrip" lines and if the traces are in a layer with ground planes above and below them, then you can model them as coupled "striplines". This article gives basic design information and dimensions tables for 50 ohm lines.    Rate this link
      • Practical timing analysis for 100-MHz digital designs - As increasing chip complexity, high clock rates, and analog signal-integrity issues complicate digital design, time-to-market pressures continue to shorten development schedules. These factors present increasing challenges to digital-design engineers. Most technical literature on high-speed design focuses on termination, ringing, and crosstalk. Despite signal integrity's importance, inadequate timing margins cause many more errors in today's 100-MHz digital designs.    Rate this link
      • Protecting high-speed buses at 1 Gbps and beyond - Circuit-protection trade-offs become more challenging as bit rate increases, but layered protection and new devices minimize the downside.    Rate this link
      • Reducing Emissions - Many hardware-design engineers use signal-integrity-analysis software to check every trace on their boards for acceptable ringing, crosstalk, and delay. Often during this process, the termination resistors are changed to ensure that the proper voltage waveforms arrive at every receiver. Once the voltage waveforms are acceptable, the design process is complete. This process is good enough for signal integrity, but it's not good enough for EMI because most radiated-emissions problems depend more on signal currents than on signal voltages.    Rate this link
      • Reducing EMI with differential signaling - Differential signals radiate less than single-ended signals do. That's one of the benefits of differential logic. If the two complementary signals of a differential pair are perfectly balanced, the separation between traces entirely determines the degree of field cancellation. If, however, the two complementary signals are not perfectly balanced, then the degree of attainable field cancellation is limited to a minimum value determined not by the trace spacing, but by the common-mode balance of the differential pair.    Rate this link
      • Signal-integrity modeling of gigabit backplanes, cables, and connectors using TDR - The TDR (time-domain-reflectometry) method for signal-integrity analysis can help gigabit-system designers produce more accurate interconnect models, resulting in more reliable and higher performance designs.    Rate this link
      • Signal Integrity: Words of wisdom - Measure everything. Sit with your layout people. Make your hardware testable.    Rate this link
      • Solving signal-integrity problems in high-speed digital systems - Signal-integrity and transmission-line simulation is a crucial part of high-speed digital design. If you repair signal-integrity and crosstalk problems before building your design, you can eliminate unnecessary design tangents and improve design quality and yield.    Rate this link
      • Testing gigabit serial buses: First, get physical - Verifying product designs that incorporate today's superfast interconnects and buses begins with modeling and simulating the physical layer when only components are available to test. And that testing is just the beginning.    Rate this link
      • The nuts and bolts of signal-integrity analysis - Analyzing signal integrity is not like gazing into a crystal ball or shaking bones over a design to determine its viability. You must implement a set of tools, software, and reporting mechanisms to determine whether a design is acceptable to ship.    Rate this link
      • Understanding common-mode signals - The interactions between shields, grounds, and common cable configurations are central to understanding common-mode signals' creation and their suppression.    Rate this link
      • Use local bypass capacitors to meet rigorous high-speed-system demands - When conductors look like inductors and supply lines must absorb amps of fast-edge glitchiness, low-inductance, locally applied bypass capacitors come to the rescue.    Rate this link
      • When the package means as much as the chip - Successful design of high-speed, high-pin-count ICs requires packaging engineers and chip designers to work closely together throughout the project.    Rate this link
      • Why 50 ohms? - Why do most engineers use 50 ohm pc-board transmission lines on circuit boards and why it is a common coaxial cable type?    Rate this link
      • 50-ohm mailbag - some interesting justifications for the use of 50 Ohm coaxial cabling    Rate this link
      • Ground fill - The "poured-ground" (more commonly called a "ground-fill") technique is useful on two-layer boards that lack solid reference planes. It reduces crosstalk due to electric-field (capacitive) coupling. Ground fill works particularly well in high-impedance analog designs that lack solid planes. For example, your VCR undoubtedly uses the ground-fill and guard-trace concepts to reduce coupling between the digital and analog sections.    Rate this link
      • Analysis of board layout helps cure jitter problems - In a design in which you must reduce tight timing, routing all timing-sensitive lines in buried stripline layers minimizes one source of jitter and lowers the overall required timing budget.    Rate this link
      • On-chip bypassing with end termination    Rate this link
      • What's that glitch?    Rate this link
      • Digital common-mode noise: coupling mechanisms and transfers in the z axis - Digital noise can couple into sensitive circuit regions of an analog/digital board. The process of noise production from the common-mode point of view in the z axis merits careful analysis.    Rate this link
      • Return current matters - Differential architectures sometimes tempt you to ignore return-current issues, assuming that the signal current returns on the other trace. Although in some cases this assumption may provide a useful mental image, it is not true. Even in a differential configuration, current flows separately on the planes under each trace, almost as if they were two independently routed, single-ended signals.    Rate this link

      Analogue-digital conversion

      An analog-to-digital converter (also known as an ADC or an A/D converter) is an electronic circuit that measures a real-world signal (such as temperature, pressure, acceleration, and speed) and converts it to a digital representation of the signal. A/D-converter compares the analog input voltage to a known reference voltage and then produces a digital representation of this analog input. The output of an ADC is a digital binary code. By its nature, an ADC introduces a quantization error. This is simply the information that is lost, because for a continuous analog signal there are an infinite number of voltages but only a finite number of ADC digital codes. By increasing the resolution of the ADC, the number of discrete steps is increased, which reduces quantization errors. Some A/D converters sample the input signal continuously, whereas others sample at specific times. Any A/D converter that uses a track/hold buffer must periodically connect its track/hold capacitor to the input signal, causing a small inrush current. All the sampling processes are limited by Nyquist limit. The Nyquist limit is defined as half of the sampling frequency. The Nyquist limit sets the highest frequency that the system can sample without frequency aliasing. In a sampled data system, when the input signal of interest is sampled at a rate slower than the Nyquist limit (fIN > 0.5fSAMPLE), the signal is effectively "folded back" into the Nyquist band, thus appearing to be at a lower frequency than it actually is. This unwanted signal is indistinguishable from other signals in the desired frequency band (fSAMPLE/2). Usually the signals are prefiltered before they enter the A/D-converter to avoid too high frequency signal components which can cause this kind of unwanted signals. In actual practice, you should sample at a rate much higher than two times the Nyquist limit to minimize sampling errors (general rule of thumb is 5 times higher that highest frequency needed to be analyzed well) or you need to provide a very good filter which filters out those "too high" frequency components from your incoming signal. In some special applications frequency aliasing can also be used in an advantageous manner (generally known as "undersampling" method). A digital-to-analog converter (also known as a DAC or a D/A converter) is an electronic circuit that converts a digital representation of a quantity into a discrete analog value. The input to the DAC is typically a digital binary code, and this code, along with a known reference voltage, results in a voltage or current at the DAC output. The word "discrete" is very important to understand, because a DAC cannot provide a continuous time output signal; rather, it provides analog "steps." The steps can be lowpass-filtered to obtain a continuous signal. In D/A conversion process the output of D/A converter is fed through a filter which will remove the image-frequency information (signal higher than 1/2 of sampling frequency) from the output signal. This image-frequency information can distort the output signal. Two methods exist for removing unwanted image signals from the DAC output to prevent alising in a following ADC. First approach is to use a high-performance lowpass filter (data -> DAC -> high-order lowpass filter). For low pass filtering usually a sixth-order lowpass filter is enough.The second methos is to use digital-interpolation filters and a simple analogue filter (data -> oversampling digital-interpolation filter -> DAC -> low-order lowpass filter). The selection of sampling rate to use is an important decision in any system involving sampling. When selecting a sampling rate, there are usually several competing goals, such as:

      • Sample as fast as possible to obtain greatest accuracy.
      • Sample as slow as possible to conserve processor time.
      • Sample slow enough that noise doesn't dominate the input signal.
      • Sample fast enough to provide adequate response time.
      • Sample at a rate that's a multiple of the control algorithm frequency to minimize jitter.
      The truth is there's usually no best answer for all systems, but there's often one answer that stands out as better than most others when the peculiarities of a specific application and the target hardware are considered.
      • 1-bit converters    Rate this link
      • 16-bit ADC provides 19-bit resolution - Many data-acquisition systems require both high accuracy and a fast acquisition rate. With aid of a programmable amplifier before A/D conversion you can get more relative accuracy to the conversion.    Rate this link
      • ADC grounding - Chip designers often internally partition the ground-reference net (or substrate) for an ADC into isolated analog and digital regions for good reasons.    Rate this link
      • Getting the Most from High Resolution D/A Converters - application note in pdf format    Rate this link
      • How to Choose A Sensible Sampling Rate - Trial-and-error testing is neither the fastest nor the best way to determine the sampling rate for a given application, although it's probably the most common. Systematic engineering analysis, plus a few guided experiments, will help you find a good rate quickly.    Rate this link
      • Improved amplifier drives differential-input ADCs - ADCs with differential inputs are becoming increasingly popular. This popularity isn't surprising, because differential inputs in the ADC offer several advantages: good common-mode noise rejection, a doubling of the available dynamic range without doubling the supply voltage, and cancellation of even-order harmonics that accrue with a single-ended input. This document shows shows two easy ways to create a differential-input differential-output instrumentation amplifier.    Rate this link
      • Maximize performance when driving differential ADCs - Converting a single-ended signal to a differential signal before the analog-to-digital conversion can improve the performance of your data-acquisition system. Using differential signals in data-acquisition systems is becoming increasingly popular because differential signals are highly immune to system noise based on the common-mode rejection of a differential ADC. System noise accumulates in signals as they travel across a pc board or through long cables, but this noise does not interfere with the analog-to-digital conversion because the differential ADC rejects any signal noise that appears as a common-mode voltage. Because differential signals cancel out even-order harmonics, they also provide better distortion performance than do single-ended signals. Another benefit is that differential signals double the ADC's dynamic range.    Rate this link
      • Maximize performance when driving differential ADCs - Converting a single-ended signal to a differential signal before the analog-to-digital conversion can improve the performance of your data-acquisition system.    Rate this link
      • Mixed Signal Circuit Techniques - application note in pdf format    Rate this link
      • Multiple ADC grounding - If you have a lot of ADCs on the same board and they all tie to the same digital ground, then the various ADC grounds must all be somehow tied together. In a low-resolution, 8-bit system, which needs only about 60 dB of noise rejection, you can use one big, solid ground plane for all the analog channels and the digital logic. In higher resolution systems requiring more noise isolation, you might worry about stray digital currents flowing across the analog-ground region of your pc board.    Rate this link
      • Sampling rates for analog sensors - Why use trial-and-error methods to determine sampling rates when you can use science and mathematics? Here are the details of a simple procedure that makes more sense.    Rate this link
      • The alias theorems: practical undersampling for expert engineers - Aliasing, long considered an undesirable artifact of an insufficiently high sampling rate, is in fact a useful tool for lab testing and analysis.    Rate this link
      • The beauty of differential drive - Even when sheer chaos is breaking out around an ADC, differential-drive techniques can make the converter perform quietly    Rate this link
      • Using PWM to Generate Analog Output - Pulse Width Modulation (PWM) modules, which produce basically digital waveforms, can be used as cheap Digital-to-Analog (D/A) converters only a few external components. A wide variety of microcontroller applications exist that need analog output but do not require high resolution D/A converters. Some speech applications (talk back units, speech synthesis systems in toys, etc.) also do not require high resolution D/A converters. For these applications, Pulse Width Modulated outputs may be converted to analog outputs. Conversion of PWM waveforms to analog signals involves the use of analog low-pass filters. This application note describes the design criteria of the analog filters necessary and the requirements of the PWM frequency. Later in this application note, a simple RC low-pass filter is designed to convert PWM speech signals of 4 kHz bandwidth.    Rate this link
      • Multiple ADC grounding - If you have a lot of ADCs on the same board and they all tie to the same digital ground, then the various ADC grounds must all be somehow tied together.    Rate this link
      • What does the ADC SNR mean? - ADC's ideal SNR is 6.02N+1.76 dB (excluding delta-sigma converters). Where does this ideal formula come from, and how do you measure SNR with a real ADC?    Rate this link
      • DDS IC plus frequency-to-voltage converter make low-cost DAC - Precision DACs are essential in many consumer, industrial, and military applications, but high-resolution DACs can be costly. Frequency-to-voltage converters have good nonlinearity specifications?typically, 0.002% for the AD650?and are inherently monotonic. This Design Idea shows how you can use a frequency-to-voltage converter and a DDS (direct-digital-synthesizer) chip for precise digital-to-analog conversion. The DDS chip generates a precision frequency proportional to its digital input. This frequency serves as the input to a voltage-to-frequency converter, thereby generating an 18-bit analog voltage proportional to the original digital input.    Rate this link
      • Buffer adapts single-ended signals for differential inputs - DC coupling of single-ended signals into differential-input, single-supply ADCs can be challenging. The input signal requires level shifting from ground to VS/2 as well as single-ended-to-differential conversion. In addition, you must balance the differential inputs of the ADC to cancel even-order harmonics and common-mode noise. Systems often require this signal translation to take place without injecting dc bias currents back into the signal source. Processing wideband signals with large dynamic range (12- to 14-bit ADCs) can also add to the circuit complexity. Wideband amplifiers address nearly all these issues, but their standard implementation requires the use of ac coupling. This Design Idea describes a new circuit that eliminates this requirement through the use of an external dc feedback loop. It also allows the lower end of the passband to extend to dc. The basis of the circuit is a simple level-shifting circuit.    Rate this link
      • An overview of data converters - Digital communications, digital instruments and displays have created a demand for low cost reliable converters that can convert signal between analogue and digital formats. This application note AN100 from Philips gives you an overview of A/D and D/A conversion technologies.    Rate this link
      • Combine two 8-bit outputs to make one 16-bit DAC - Inexpensive, 16-bit, monolithic DACs can serve almost all applications. However, some applications require unconventional approaches. In this circuit two PWM outputs from a microcontroller combine to form a monotonic 16-bit DAC.    Rate this link

      Protecting ideas and intellectual property

      By 'intellectual property? we mean intangible legal rights which may be protected by patents, copyrights, trademarks, and trade secrets. Today in electronics industry a good engineer needs to know documenting and promoting the protection of intellectual property (IP) associated with a given product line. The major players in the electronics industry realize that to be successful in this business requires that IP be cultivated and harvested in parallel with the technical advances generated by the research and development staff. There are different protection mechanisms:

      • Trade Secret: Trade secret can be a formula, pattern, cimpilation, program, device, method, technique or process that derives independent economic value. The information must kept secret, which can be hard.
      • Copyright: A copyright owner has the exclusive right with respect to the copyrighted work of (a) reproduction, (b) preparation of derivative works, (c) distribution of copies, (d) performance of the work publically, and (e) public display of the work. The rights given to a copyright owner attach on creation or 'fixation? of the work in a tangible medium. Copyright protection may be appropriate for the expression of ideas such as PLD/FPGA source code, schematics, program listings, etc., it is inappropriate to protect the ideas that these entities embody.
      • Trademarks: Trademarks are used within our economy to protect consumers from confusion regarding the source, quality, or origin of goods or services. The right given a trademark owner to exclude others who might use marks which tend to confuse the public is a right which is acquired by use of the mark to which protection is sought.
      • Patents: Patents provide a right of exclusion to prohibit the sale, offer for sale, manufacture, import, or use of a device which is covered by the patent without the permission of the patent holder. While this exclusionary right may be narrowly tailored by the claims in the patent, the goal in any properly written patent is to stake out as broad an area of product coverage as possible. Key to this is a properly written technical description (disclosure) of the invention.
      You must understand those different protection mechanism to be able to understand when to use which.

    Electronics construction

      Soldering

      Soldering is the joining together of two metals to give physical bonding and good electrical conductivity. It is used primarily in electrical and electronic circuitry. Solder is a combination of metals, which are solid at normal room temperatures and become liquid at between 180 and 200 degrees celsius. Solder bonds well to various metals, and extremely well to copper.Soldering is a necessary skill you need to learn to succesfullybuild electronics circuits. It is the primary way how electronics components are connected to circuit boards, wires and sometimes directly to other components.

      To solder you need a soldering iron. A modern basic electrical soldering iron consists of a heating element, a soldering bit (often called the tip), a handle and a power cord. The heating element can be either a resistance wire wound around a ceramic tube, or a thick film resistance element printed onto a ceramic base. The element is then insulated and placed into a metal tube for strength and protection. This is then thermally insulated from the handle. The heating element of soldering iron usually reaches temperatures of around 370 to 400 celsius degrees (higher than neededto melt the solder). The soldering bit is a specially shaped piece of copper plated with iron and then usually plated with chrome or iron. The tip planting makes it very resistant to aggressive solders and fluxes. The strength or power of a soldering iron is usually expressed in Watts. Irons generally used in electronics are typically in the range 12 to 25 Watts. Higher powered iron will not run hotter, but it will have more power available to quickly replace heat drained from the iron during soldering. Most irons are available in a variety of voltages, 12V, 24V, 115V, and 230V are the most popular. Today most laboratories and repair shops use soldering irons which operate at 24V (powered by isolation trasfermer supplied with the soldering iron or by a separate low voltage outlet). You should always use this low voltage where possible, as it is much safer. For advanced soldering work (like very tiny very sensitive electronicscomponents), you will need a soldering iron with a temperature control. In this type of soldering irons the temperature may be usually set between 200 degC and 450 degrees C. Many temperature controlled solderingirons designed for electronics have a power rating of around 40-50W. They will heat fast and give enough power for operation, but are mechanically small (because the temperature controller stops them from overheating when they are not used).

      There are many different kinds of soldering iron tips. The tips vary both in shape and construction. The cheapest soldering irons use just a tip made of a piece copper or similar material. The part where solder should melt is "wetted" by applying solder to it. After some use the other part of the tip generally get oxidised (looks usually black). This kind of just copper tip is cheap, but does not last long. When the copper tip wears out, you can use a metal file to file out the corrided part and make the tip again to right shape and then pre-tin the soldering part of tip.

      Soldering iron tips made for electronics work are generally iron clad coated on copper base. They do wear out with use (but less than tips made of just copper). When the iron clad is worn off, you will see the copper inside. The tip is useable, but not at its peak performance as when the iron clad is still on it. The fix is to replace the worn tip. A Weller tip is made of a copper core which is electro-plated with iron to extend the life of the tip. The non-working end of the tip is plated with nickel for protection against corrosion and then chrome plated to prevent the solder from adhering except where desired. The wettable part is tin covered. Because of the electro-plating Weller tips should never be filed or ground. Filing long-life tips will remove the protective plating and reduce tip life. The solder type, used temperature and flux type affect can affect the soldering iron tip price. Usually soldering iron tip life is prolonged when mildly activated rosin fluxes are selected rather than water soluble or no-clean chemistries. When soldering with temperatures over 665 F (350 C) and after long work pauses (more than 1 hour) the tip should be cleaned and tinned often, otherwise the solder on the tip could oxidize causing unwettability of the tip. To clean the tip use the original synthetic wet sponges (no rags or cloths). When doing rework, special care should be taken for good pretinnng. Usually there are only small amounts of solder used and the tip has to be cleaned often. The tin coating on the tip could disappear rapidly and the tip may become unwettable. To avoid this the tip should be retinned frequently.

      For fast and optimal heat transfer to the solder joint the tip mass should be as large as possible. When choosing a soldering tip always select the largest possible diameter and shortest reach. Use fine-point long reach tips only where access to the work piece is difficult.

      There are also other types of soldering irons in use. You will occasionally see gas-powered soldering irons which use butane rather than the mains electrical supply to operate. They have a catalytic element which, once warmed up, continues to glow hot when gas passes over them. Gas-powered soldering irons are designed for occasional "on the spot" use for quick repairs, rather than for mainstream construction or assembly work.

      There are also solddering guns that can heat up very quicly. Soldering guns should never be used to solder electronic components, such as resistors,capacitors, and transistors, because the heat generated can destroy the components. They should be used only on terminals, splices, and connectors(not the miniature type). Soldering guns have typically power rating of around 100W. The soldering guns work by resistive heating of the soldering tip. Inside soldering gun there is a transformer that feeds a low voltage (typically around 1 volt) high current (typically around 100-150 amperes) AC to through the tip. The transformer steps the volts down and current up. The tip heats up by the large current flowing through it. The tips have a low thermal mass (eg not much metal) so thay they heat up quickly. You can make your own tips for this kind of iron by usign a thick copper wire (about same thickness as original tip) and and shape it like such solder tip.

      You need to be careful in soldering because most electronic components are fragile, and heat sensitive. Usually our biggest concern is heat. Low enough soldering temperature and short enough solvering time keeps components in good shape. Electronics components are designed so that they can take high temperatures on their contacts/wires forsome time without damage (to withstandard the soldering). Prolonged exposure to high temperatus will heat up when inside of the component can cause damage to it.

      The solders designed for electronics work are usually a mixture of tin and lead. Tin melts at 450?F and lead at 621?F. Solder Made from 63% tin and 37% lead melts at 361?F, the lowest melting point for a tin and lead mixture. Solder construction is designated by two numbers representing the percentages of each metal in that specific mix. The first number always refers to the percentage of tin, the second is the percentage of lead. Currently, the best commonly available, workable, and safe solder alloy is 63/37. That is, 63% tin, 37% lead. It is also known as eutectic solder. Its most desirable characteristic is that its solidus ("pasty") state, and its liquid state occur at the same temperature -- 361 degrees F (around 183 ?C). This is the lowest possible temperature for lead and tin combination to melt. You will often find "63/37" solder referred to as a quick set solder or eutectic solder. Other commonly used mixture ration is 60/40, (60% tin/40% lead). Look for solders that are sold as "free of impurities" in the component metals. Impurities cause a "scum" on your solder bead, degrade soldering iron tips, and interfere with the proper soldering. For all electrical work you need to use rosin core solder. In electronics a 60/40 fluxed core solder commonly is used. This consists of 60% Lead and 40% Tin, with flux cores added through the length of the solder.

      The metals involved are not the only things to consider in a solder. Flux is vital to a good solder joint. Flux is an aggressive chemical that removes oxides and impurities from the parts to be soldered. The chemical reactions at the point(s) of connection must take place for the metals to fuse. RMA-type flux (Rosin Mildly Active) is the least corrosive of the readily available materials, and provides an adequate oxide removal. Flux is an integral part of the soldering process to prepare the work surface. Flux is not a cleaning agent! Always clean the work before soldering. Flux is not a part of a soldered connection?it merely aids the soldering process. After soldering, remove any remaining flux. The remaining flux can conduct electricity and couse other problems. Resin flux can be removed with isopropyl or denatured alcohol. A cotton swab is a good tool for applying the alcohol and scrubbing the excess flux away. Commercial flux-removal sprays are available at most electronic-part distributors. There are also solder fluxes that need not be cleared after soldering and also water soluble. Usually soldering iron tip life is prolonged when mildly activated rosin fluxes are selected rather than water soluble or no-clean chemistries.

      Never use acid-core solder for electrical work. It should be used only for plumbing or chassis work. For circuit construction, only use fluxes or solder-flux combinations that are labeled for electronic soldering.

      Nowadays there is tendency to move to use lead free solders, but it will takes years until they will catch on normal soldering work. Lead free solders are nowadays available, but they are generally more expensive and/or harder to work on than tradional solders that have lead in then. Depending on the specific mix of metals, lead free will produce differing liquid, solid, and pasty range temperatures. Check with the solder manufacturers for these specifics.

      There are certain safety measures which you should keep in mind when soldering. The tin material used in soldering contains dangerous substances like lead (40-60% of typical solderin tins are lead and lead is poisonous). Also the varous from the soldering flux can be dangeroous. While it is true that lead does not vaporize at the temperatures at which soldering is typically done, particulate matter is just as dangerous as fumes would be in terms of poisoning and there is particulate lead present to some extent in the fumes from your flux. Composed of rosin-resin and mixed with an activator (halogen organic agent) that, as the temperature increases, generate noxious components such as salicylic acid and pinene commonly seen as smoke rising from the work area. High content ratios of resin generate phinol (C6H5OH) and the activators can emit hydrogen chloride (HCL) and other compounds. The US Government and many other countries have occupational hazard standards controlling the permissible amounts of such compounds in the work area. When soldering keep the room well ventilated and use a small fan or fume trap. A proper fume trap or a fan will keep the most pollution away from your face. Professional electronics workshops use expensive fume extraction systems to protect their workers (needed for working safety resons). Those fume extraction devices have a special filter which filters out the dangerous fumes. If you can connect a duct to the output from the trap to the outside, that would be great. If you can't afford a fume extraction system and do just a little bit "hobby solderdering", then at leadst be sure to use good ventilation. Breathing lead solder fumes is bad.

      Always wash hands prior to smoking, eating, drinking or going to the bathroom. When you handle soldering tin, your hands will pick up lead, which needs to be washed out from it before it gets to your body. Wash you hands well with soap and water after handling anything that contains lead. Do not eat, drink or smoke whilst working with soldering iron. Do not place cups, glasses or a plate of food near your working area. Eating lead is bad for your health. Wash also your working table sometimes. As you solder, at times there will be a bit of spitting and sputtering. If you look you'll see tiny balls of solder that shoot out and can be found on your soldering table.

      The soldering iron will last longer with proper care. Before and during use wipe the bit on a damp sponge. Most bench stands incorporate a sponge for this purpose.When using a new bit, apply solder to it as it heats up. Always keep a hot iron in a bench stand, or suspended by the hook, when not in use. Turn of the iron when you do not use it. Periodically remove the bit and clear away any oxide build up. Regularly check the mains lead for burns or other damage (change mais lead if necessary).

      Copper wires are usually tinned by dipping them into flux (view A of figure 2-25) and then into a solder bath (pot). In the field, copper wires can be tinned with a soldering iron and rosin-core solder. Tin the conductor for about half its exposed length. Tinning or solder on the wire above the barrel causes the wire to be stiff at the point where flexing takes place. This will result in the wire breaking. The flux used in tinning copper wire is a mixture of denatured alcohol and freshly ground rosin. This type of flux may be mixed just prior to use. A premixed paste flux may also be used. The solder used for terminal lugs, splices, and connectors is a mixture of 60-percent tin and 40-percent lead. Maintain the temperature of the solder bath (pot) between 450 and 500 degrees F keeps the solder in a liquid state. Skim the surface of the solder pot, as necessary, with a metal spoon or blade. This keeps the solder clean and free from oxides, dirt, and so forth.

      Nowadays more and more electronics are being manufactured without lead in them. This means moving to use lead free solders. For example modern SnAgCu lead free solders have a melting temperature of around 220 degrees celsius, which is somewhat higher than what traditional solders used to have (usually below 200 degrees celsius). In traditional soldering the solder tip is heated to somewhat higher temperature than the soldering melting point, so the tip has enough energy to melt the solder in use quicly and still not overheat the component. The higher eltin temperature in lead free solders can cause problems with the soldering iron design, because the soldering iron tip can't be at very much higher temperature because most lead free SMD components are rated for maximum 260 degrees celsius soldering temperature.

      Here is a list of some commonly used solders and their melting temperatures (degrees celsius):

      • Sn-0,7Cu = 227 C
      • Sn-3,5Ag = 221 C
      • Sn-3,8Ag-0,7Cu = 217 C
      • Sn-2,8Ag-1Bi = 215 C
      • Sn-3,4Ag-3Bi = 210 C
      • Sn-3,5Ag-6Bi = 206 C
      • 60Si-40Pb = 183 C
      • CASTIN (96.2% tin, 2.5% silver, .8% copper and .5% antimony) = 216 C
      For more than 50 years lead-containing solders have been used almost exclusively throughout the electronics industry for attaching components to printed circuit boards (PCBs). Such solders are inexpensive, perform reliably under a variety of operating conditions, and possess unique characteristics (e.g. low melting point, high strength ductility and fatigue resistance, high thermal cycling and joint integrity) that are well suited for electronics applications. Solder is usually identified by its tin-to-lead composition. If you look at a solder roll, you will probably find the figures 40/60, 50/50, 60/40 or 63/37. These are the ratios of tin-to-lead, given in percent. Solder with a higher tin content melts at a lower temperature, and is usually desirable. The so-called "eutectic alloy" of 63% tin and 37% lead has a melting or eutectic temperature of 361 degrees Fahrenheit (183 degrees celsius). That composition is the standard for electronic purposes, being approximated by 60/40 solder, and has a pronounced melting point. The 60Si-40Pb is the traditional soldering tin used in electronics work. Solders with a 63/37 or 60/40 composition are the most free-flowing kinds and are particularly good for working on delicate printed circuit boards. Other solder compositions have a flexible or plastic range running from the 361 degrees eutectic temperature up to the melting points of either pure lead (621 degrees), or pure tin (450 degrees). Since tin is a more active metallic solvent than lead, the quality of the joint is very closely related to its tin content. The alloy quality curve reaches its peak with about 60% tin, which approximately corresponds to the composition of the eutectic alloy we described.

      Most other solders listed on this list are newer lead free solders. Initially as many as 100 lead-free alloy configurations were being considered, today only a dozen or so are being used, with the general alloy being agreed globally as tin-silver-copper and tin-copper alloys mostly for wave soldering assembly. Eventually, there will be an overall movement to eliminate lead from all aspects of soldering, board coating, and component terminations. Government regulations are becoming more strict, and handling of waste materials are becoming more regulated. Now is the time to take a serious look at alternative (altenative to solders that contain lead) materials for making electrical interconnections. Lead in solder will not meet the same fate as use od lead in paint, plumbing and gasoline. In Europe this has resulted in a move, embodied in European legislation, to ban the use of lead in solders and electronics components in most electronics fields. It is the ROHS proposal that will have the greatest impact on the electronics manufacturing industry. It requires certain substances (including various heavy metals such as Pb, Hg, Cd hexavalent Cr) to be phased out of new equipment by 2008. Although there are some exemptions to this ban on the use of lead (in radiation protection, ceramics etc), lead in soldering is not exempt. Pb-free soldering will become the norm in the next few years. With the Europeans WEEE Directive now mandating a phase out of lead in electronic soldering by July 2006 and Japan's efforts to do the same even sooner, lead-free is rapidly taking on momentum around the world. The process changes are needed to achieve adequate wetting and flow characteristics of lead-free solders.

      Just a good solder does not make good solder joists. Most metals will react with oxygen in the air, particularly so if the metal is heated. Soldering flux is formulated to remove a film of oxides from the metal and make the solder and metal more able to dissolve in each other. Soldering flux is just a safe, convenient acid for dissolving the oxide skin off the metal you want your solder to wet well. Also dissolves oxide off the liquid solder, making it less crusty and therefore more shiny. "Acid" flux is the stronger class of flux; it has something like hydrochloric acid in it. The paste form has zinc chloride. This is good for making difficult oxides dissolve so difficult metals like stainless steel can be solder-wetted. But the acid can hang around later trying to corrode the metal it just cleaned for you. So for electronic stuff we mostly do not use it. The copper traces on the circuit board are thin, and will be quite quicly corrored by stron acids. Acid fluxes should never be used on electronics circuit baords, or for splicing copper leadwires. The paste fluxes, containing chlorides, should not be used under any circumstances for electronics soldering.

      The flux built into most solder wire targeted for elecronics work is called rosin flux. I think it is like a form of organic acid, stuck onto larger molecules that melt only at soldering temperatures. That is the clear yellow-brownish plaque that sits on the solder's surface when you are done. It does the same stuff as acid flux, but it is muchj milder. It is only strong enough to reduce weakly oxidizable metals like copper, tin, lead, silver. And rosin-flux goes back to its plastic-like solid form after use, so it does not act very corrosive to the metals later on. No need to immediately clean it away carefully. But generally it is a good idea to remove it, because it can become partially coductive later on (especially on wet environment). Cleaning of flux residue is necessary to insure reliability. Rosin flux residues can be cleaned away with the right "polar solvents". "Flux remover" is sold in spray-cans for this. Rubbing alcohol with a dash of dish-soap sort of works as well.

      There are also special fluxes called "no clean flux" that do not need to be cleared from cirucit board after soldering. Today most electronics assemblies are soldered using no-clean fluxes. No-clean fluxes have proven to be reliable. There has also been a benefit to the environment by eliminating the cleaning process and its effluents. No-clean fluxes first emerged to market in the mid-eighties due to the elimination of CFC's, electronic assemblers were confronted with not cleaning residues off soldered circuits. The use of no-clean liquid fluxes and no-clean solder pastes were considered by assemblers to be an impossible eariler on. Flux chemistries in no-clean and water washable configurations are nowdays popular.

      Soldering in mass production of electronics devices nowdays use mostly automated reflow and wave soldering. It is unconventional to use a hand held iron in mass produced electronics business unless you are doing board rework.

      Reflow is commonly used method for soldering surface mount devices (SMD). Reflow requires applying a controlled amount of solder and flux to the areas whereconnections are to be made. A common technique is to print a pattern of solder paste on theboard, and then put the components onto their places. They tend to stay in position because ofthe stickiness of the paste. Optionally, components can be held with chip-bonding epoxy.When heat is applied, it must produce a time-temperature profile suitable for accomplishing several process steps. First, solvent evaporation is done at temperatures up to about l00 C. Second, flux reducesmetal oxides as temperature rises to the solder melting point, typically l83 C. Third, astemperature continues to rise, the solder particles in the paste melt and wetting and wickingin the joint area begin. In the next step when temperature reaches a peak around 215 C. The length of time that the work is actually above 200 C is usually limited to one or two minutes to avoid damage. Many plastic encapsulated components canwithstand several minutes of solder-melt temperature when re-flowed. You can view a reflow oven as just a fancy pizza oven. It has a conveyor belt and different zones so you can controll the time/temperature profile of the board as the solder starts to flow (tuning this is an art). There are several techniques for applying the heat needed for re-flow. Two of the most common are infrared and vapor phase. Infrared heat sources operate at very high temperatureand are placed at the inner walls of the chamber, not in contact with the work. Organic materials such as epoxy-based boards tend to absorb the IR radiationand conduct the heat to metal parts which, by themselves, would tend to reflect the IR away. SMT reflow ovens, essentially, are identical to the ovens used in Pizza Hut where they stick a pizza in one end and it is taken through heating zones via a conveyor and pops out the other side done. Reflow ovens have very well controlled thermal profiles, slowly ramping temperature to a plateau, holding, slowly ramping up to final tmep, holding etc. This is done to avoid thermal shock related mechanical failure mechanism that can damage some SMD component. High voltage SMD ceramic capacitors are especially prone to this. In SMT reflow, the zones are controlled in such a manner that the holy 2 degrees C per second maximum heating or cooling rule is never broken (some components can take up to 4 degrees C per second). Most components will stop working at 140C and in the oven they will go over 200C - they will survive, but the PCB should not be powered up until the PCB has cooled to room temperature. Typical process cycle is first heat to dying temperature (100-150 degrees celsius), then dying for 30 seconds to 3 minutes, then ramping temperature to soldering temperature (paste reflow temperature plus 20 degrees celsius typically, usually around 250 degrees celsius) and finally cooling down the circuit board. In order to achieve reliable solders and to minimize thermal stress on components, a precise thermal profile must be used. Quick heating and cooling (within the limits of set by maximum allowed speed) is important (the quicker the better) in order to reduce the thermal stress on the components. Maintaining a homogeneous temperature inside the oven is also important. An accurate temperature and timing regulation is a must in order to guarantee that successive reflows follow the exact same profile. A clean blank PCB, suitable components and suitable soldering paste are extremely important. In order to have a quick heating time, some industrial reflow ovens use infrared heaters. The full soldering cycle takes around 10 min.

      In the vapor-phase soldering process the vapor surrounding the work is maintained at the optimum solder-wetting temperature. This is accomplished by boiling aninert liquid in a tank. The boiling point is approximately 215 degrees C. When the work is held in thevapor just above the liquid, the heat at that temperature is transferred to all surfaces quite uniformly.

      In wave soldering molten solder is applied to the bottom side of a circuit board after a preheating sequence, with cool-down following the soldering. When doing wave soldering all the components have been loosely secured to the board, but they need to be soldered for electrical conductivity. By drawing the board just over the top of a molten solder bath, capillary action draws the solder into all the joints in a single step. The process on how the solder bath works is as follows. The solder bath has to be at a certain temperature and then the flux is added to the set level. The PCB passes over the flux which makes the solder stick to the circuit board. If this is not done correctly it could cause many problems such as solder bridges and dry joints. If the temperature is too high then sensitive components like chips could be blown. Once the process is complete the PCB is then moved onto the next stage of production. The machine needs to be maintained regularly and calibration procedures are followed every time the machine is used.There are variations to the method, mainly characterized by the shape of the solder wave; the choice among them is influenced by the type of assembly and the components being mounted. Solder temperature is typically 260 C. Wave soldering can sometimes cause micro cracks developing at the leads. Resistance to this defect is enhanced when moisture is baked out of the plastic material before soldering by either method; 24 hours at 125 C is usually effective. When soldering SMT components, it is imperative that a component recieves no more than 2 degrees C (about 3 degrees F) a second ramp-up in temperature. This is to prevent thermal shock and damage to the components. It is OK for a component to be exposed to soldering temperatures, ideally for as little as possible; a few seconds. If you do thing in other ways, you might get soldering done but you run a risk of damaging sensitive components. Passive components like SMT resistors, coils, and simple IC's like logic gates generally take the punishment a lot better than film capacitors, PROM's, etc.

      For hand soldering of SMT IC components the following method can be used: Place the IC on the pads; center it up as well as you can. Using a regular soldering iron, "tack" two opposing corners of the IC to the lands with conventional solder. Don't worry about bridging. Then, apply a small amount of liquid solder flux to one side of the IC, bathing the legs. Then, apply a small bead of solder to the end of you iron and GENTLY wipe this bead across all the legs, from pin one to pin whatever. You'll see as if by magic that you'll get very few solder bridges. Apply more flux if required. Clean tip of iron completely of solder, and just touch it to solder bridges. The excess solder will "sweat" to the iron. Clean iron tip again and repeat. When done, clean flux with laquer thinner or similar substance. (If you use no-clean flux, you could just be gross and leave it there if you wished, removing excess with a paper towel.) SMD soldering of discrete components: Make sure that the PCBs are tinned when they are manufactures. Do not put any extra solder on the PCB pads (leave the pads flat). Get a tiny flux dispenser, or flux pen of the type of flux you are using, usuallyWater soluble or no clean. Wipe the pads wet. Put some wet on asurface and dip the resistor or cap terminations in the wet area withthe tweezers. With a tiny tiny drop of solder on a 600 F max tip, place the part flat down in the right spot, and drag the tip of theiron across the face of the part termination. It should sizzle, smoke, and wet, making a perfect solder joint. Do not make bulbous solder joints because they are bad. Once one side is done, if the part did stayflat, drag a tip on the other side with a microdrop on it.Do not overheat the components. Especially do not overheat ceramic caps! They fail! If reflow is required keep it short and accurate. One shot solder up only. Do one side, then the other, and be done. No reflows needed. Think microdrops. Smaller is better.

      Hot air reflow of paste: Using Solder Paste, you can use a hot air gun to place components on a PCB as well. Some people have also used different kind of ovens for the heating (for example some people have used old toaster ovens. When using oven, remeber the following: Solder paste will only stay reliably sticky for 30 minutes. Make sure that you have your components ready and the oven at the primary temperature before you break the seals on the syringe and start applying paste. The PCB should be as dry as possible. Before putting on paste/components. Solder "paste" is made up of finely ground solder held together by flux. Both the solder and the flux are poisenous. An oven used for SMT experiments cannot be used for food preparation afterwards.Solder paste must be capped and refridgerated when not in use. The PCB coming out of the oven is very hot and will take several minutes to cool down. The PCB pads should be "HASL" ("Hot Air Solder Leveled") for best results.

      There is no soldering method that is ideal for all IC packages. Wave soldering is often preferred when through-hole and surface mounted components are mixed on one printed-circuit board. However, wave soldering is not always suitable for surface mounted ICs, or for printed-circuits with high population densities. In these situations reflow soldering is often used. For DIP packages typically the maximum permissible temperature of the solder is 260 ?C when using wave solder or dipping methods; solder at this temperature must not be in contact with the joint for more than 5 seconds. The total contact time of successive solder waves must not exceed 5 seconds. The device may be mounted up to the seating plane, but the temperature of the plastic body must not exceed the specified maximum storage temperature. When repairing the solder joints the temperature of the soldering iron bit is less than 300 ?C it may remain in contact for up to 10 seconds. If the bit temperature is between 300 and 400 ?C, contact may be up to 5 seconds.

      Reflow soldering techniques are suitable for all SO packages. Reflow soldering requires solder paste (a suspension of fine solder particles, flux and binding agent) to be applied to the printed-circuit board by screen printing, stencilling or pressure-syringe dispensing before package placement. Several techniques exist for reflowing; for example, thermal conduction by heated belt. Dwell times vary between 50 and 300 seconds depending on heating method. Typical reflow temperatures range from 215 to 250 ?C. Preheating is necessary to dry the paste and evaporate the binding agent. Preheating duration: 45 minutes at 45 ?C. Wave soldering techniques can be used for all SO packages if the following conditions are observed: A double-wave soldering technique (a turbulent wave with high upward pressure followed by a smooth laminar wave) is used, the longitudinal axis of the package footprint must be parallel to the solder flow and the package footprint must incorporate solder thieves at the downstream end. During placement and before soldering, the package must be fixed with a droplet of adhesive. The adhesive can be applied by screen printing, pin transfer or syringe dispensing. The package can be soldered after the adhesive is cured. Maximum permissible solder temperature is 260 ?C, and maximum duration of package immersion in solder is 10 seconds, if cooled to less than 150 ?C within 6 seconds. Typical dwell time is 4 seconds at 250 ?C. A mildly-activated flux will eliminate the need for removal of corrosive residues in most applications.

      Hand-soldering SO packages: Fix the component by first soldering two diagonallyopposite end leads. Use only a low voltage soldering iron (less than 24 V) applied to the flat part of the lead. Contact time must be limited to 10 seconds at up to 300 ?C. When using a dedicated tool, all other leads can be soldered in one operation within 2 to 5 seconds between 270 and 320 ?C.

      Gerally for SMD IC packages with pins on the sides the method of using lots of flux and a soldering iron works. It is key to use flux so that the solder flows properly. When you want to solder an IC you can run the soldering iron along the side of the IC. Slope the board and then run the soldering iron down the board from the top most pin to the bottom most one and the solder meniscus will stick/flow with the soldering iron. You will end up with the last 2 or 3 pins with a bridge which can easily be removed with solder braid. You do however need to tack the IC down to start off with so that it doesn't move whilst soldering. WHen you learn this technique, it works incredibly well. Especially for 25-50mil pitch QFPs. Sometimes a microscope is required and then occasional washing to remove the solidified gunky flux (wash in ethyl alcohol). Using a suitable flux is always key though! Water soluble if possible as it's easier to clean off. Just wash it and wait for it to dry (no not dry to heat it dry because it can damage soldering joints or components).

      One real issue in SMT soldering is that IC's have to be baked out if they've been sitting in a normal environmnet (humidity) since the epoxy absorbs water. The water then gets heated by the IR reflow process/oven and can cause the IC to crack. The way around this is to heat the IC/components gently to above 100 deg C (125 deg C is OK). This bakes out the water. Usually in an industrial process this is done for about an hour or 2. The IC's are then sealed in a waffle tray and bag with an hydrous silicone crystals to make sure no water gets reabsorbed. You shoudl only be wary of this if your IC's have been lying around in a damp warm atmosphere for a few days. For normal prototyping this is not so much of a problem.

      Hand soldering of discrete SMD componenents is usually hard and can samage some components. Reflow machines are best suited to soldering smt. If you have to do it by hand, the use of hot air is preferred over the traditional soldering iron for most components. Hand soldering can be very hard on SMD ceramic capacitors. The high temperature gradiant created by applying heat suddenly at one end can fracture the ceramic. This can lead to excess noise or a tendency to break down at a lower than rated voltage as moisure gets into the crack(s). The insidious aspect of this kind of damage is that it can show up in the field, quite some time after the parts perform alright in initial testing. The damages created in this way are nearly impossible to see without a microscope, and may not even show with iot. Typically, the micro-cracks do not extend clear thru the part, and they tend to be closed, being held together by the unbroken material. Some components can take hand soldering better than other. When soldering SMD components, contact time must be limited below 10 seconds at up to 300 ?C, and much shorter at slightly higher temperatures. If you need to use a normal soldering iron, get a decent temperature controlled soldering iron, run it at 600F/315C and use low melting point solder. Try to keep the soldering time minimum possible, maximum few seconds. For example for surface mount electrolytics there are recommendations that suggest that if you spend more than 3 seconds on a junction that's too long and you should start over with a new part. Generally there is no need for preheating or any other messing about with most SMD components. For SMD hand soldering work you will usually need a a soldering iron with very smaller iron tip to work with small components. Usually it is a good idea to have another soldering iron with larger tip around for works that need larger tip (soldering ICs, some component removals). A tiny hot air gun is a very good tool as well. There are also special soldering tools with two soldering iron tips (those can solder or desolder both ends of SMD component at the same time).

      You can also get the reflow "hairdryer" kinds of devices. These work well also and are a little bit more controllable than an oven. There are small controlable hot air units that are of side of around a normal soldering iron. In hot air soldering you paste the component pads and just heat around the IC/components until the solder goes shiny. It'll reflow at that point. Let it cool off and check it. In a number of places it was necessary to clean up a few of the traces expecially when soldering ICs with many pins near each other.

      Rework involving removal of chips takes a number of tricks, but primarily remember that you're much more interested in maintaining the PCB in good shape, at the expense of a trashed component. Generally using hot air to heat the component and blocking the air to get to nearby components too much works well. There are also special tips for soldering irons and special irons that match the SMD component shape, and those can be useful when removing different components. When reworking SMD based boards, please note that on some circuit boards chips and other components can be tricky to remove because they are glued in place.

      For years surface-mount technology (SMT) has been the manufacturing technology of choice, particularly because it?s less expensive than classic through-hole processes and because of the reduction in board size. I?m sure you have noticed that SMT is now mandatory for prototypes, even if a project isn?t space-constrained. Many new and exciting components are only available in SMT packages. High-speed designs (using high-speed digital or radio frequencies) won?t work using large through-hole packages. It?s possible to solder the majority of SMT components by hand, but it?s painful and time-consuming. The components must be soldered individually with either a small soldering iron or a hot-air pencil. But small packages like 0603 resistors are likely to fly away when soldered with hot air and stick to the soldering iron at the worst time

      Most hand soldered SMD prototypes are generally unsuited for shipping to the customer due to the rework and handling in engineering test. Generally you should never ship a 'prototype' to anyone.

      With the increasing global demand to eliminate all lead from the electronics industry, we will soon be also faced with the challenge of Lead-Free Rework on all the new circuit boards. The new Lead-Free alloys that are being used in manufacturing have a higher melting temperature and do not wet as well as the tin lead alloy that we have been used to. For hand soldering this will require us to make major changes in our methods of rework.

      Prototyping

      Prototyping electronics devices is a wide topic. Various protyping techniques are generally needed in electronics laboratory. Often used techniques for building electronics device prototypes are breadboard, wire-wrapping, soldering components to prototypingboards (like "vero" coppr stip board) or just using point to point wiring.

      Breadboard protypyping is one way to test small circuits easily. With breadboard you do not need to do any soldering and such. Breadboards are easy to work with, but they have their limitationsa also. You can often make stuff work in quite wide frequency range on a plug in proto board, if you apply some tricks. Just don't expect theprototype to give much of an indication how the same components will work on a printed circuit board.

      Wirewrapping uses special wire wrapped around square pins. A wire wrapped connection is made by coiling the wire around the sharp corners of a terminal under mechanical tension. The corners of the pins dig into the wire, forming an airtight joint. This method of connection was developed by Bell Telephone Laboratories, Western Electric Company. With wire wrapping you can make wire connections to various electronics components without soldering (there are certain limitations to where you can wrap wires to). Wirewrapping is quick and cheap. You can get lots of connections into a very small space. A distinct advantage of wire wrapping is the ease with which a wire may be removed from a terminal to correct errors or modify wiring. This means that used components are re-usable. Solid wire is used for wire wrapped connections. Copper is the most commonly used wire. There are many types of tool available, from a few pounds, up to several hundreds. All usually have some means of stripping the correct length of insulation. When wrapping, push the wire all the way into the tool and then wrap. Properly made withstands vibration well. Regular wrap is here quite good. A modified wrap, where some of the insulation is wrapped around the pin is more vibration proof.

      One method for prototyping is rats nesting. This method involves flattening all ICs legs out, and soldering all the components together so they sit in roughly the same pattern as the circuit diagram. This is sometimes a bit difficult around ICs since circuit diagrams don't usually draw the boxes of ICs with their pin numbers in their physical locations, but generally in logical positions. However, all resistors, capacitors, transistors, and power rails can be positioned this way. This method makes it very easy to check the circuit out with a meter or oscilloscope, since everything is in its logical position, and reference to the circuit diagram is easy.

      One way to build circuits is veroboard. Is is a circuit biard that has holes and copper tracs on it. You sintall the component to right places on board, use the copper traces for wiring and solver everything to place. Usually you need to cut few copper traces and add some jumber wires. Veroboard is a good way to build a simple circuit that you want in a hurry.

      In some cases other methods are needed. Nowadays you can buy adhesive copper strips/tape and conductive ink pens at electronics supliers. You can buy sheet copper foil with sticky stuff on the back it cuts with an exacto knife just fine. This kind of copper sheet or foil is used as prevent RFI. Those might be useful for small repairs and changes on an existing boards, but they are not to recommend for a whole designwork, not even for single prototypes.

      Some people have also mentioned technology where you draw the traces to circuit board with a lead pencil (really graphite). Then electroplating copper to this. You need an agitator, a temperature control, Copper Sulfate and DC voltage (around 1.5V). Copper will be deposited on one lead or another. It takes long time to get enough copper to deposit and without the temp control and constant agitation. The copper grows in weird and unpredictable patterns,but mostly stays near the conductor. I have not used this myself, but some people claim this works.

      Using conductive ink actually, this harks back to the original PRINTED circuit boards. Theywere made with a phenolic insulating board, and conductive inks wereliterally 'printed' on using a printing process. So, yes, it can be done. However, the present thick copper coatings, then etching, makefor a far more reliable circuit. The older, truly printed boards develop cracks easily if the board flexes or changes temperature very much. When they went to the present photo-etched method of making circuitboards they never changed the terminology. We still usually call them printed circuit boards, or PC boards, even though they are no longer printed.

      Nowadays prototyping with small SMD components can be troublesome, because those components are small and only designef for circuit board soldering in mind (meaning you would need to design circuit board for every prototype). Nowadays there are many components you can only get in a small SMD package (for example 16-pin SOIC package). If everything else you do is DIP-based, it seems that what you want is an adapter - ideally a socket that adapts the SMD componenent to DIP/DIL format case. There are commercially available IC adapters avaialble for this both solderless adapters and solderable small circuit board type adapters. The downside of those that they are usually hard to find and quite expensive (easily 100 USD or more for a solderless adapter). There are also snap-apart PC board material with SIOC & DIP patterns which would do much the same thing, those ase somehat chaper but you generally need to biy a whole board with many adapters. You can also make my own PC board if you have the right tools and ready plans or a decent circuit board design package tht you can use to design your own adapter (if you need to go to this route why not design the whole circuit in this way to bord directly). If you want cheap, you'll need to pass on the socket part. Sockets for surface-mount parts simply aren't cheap. For one thing, unlike DIP sockets, they're used only for prototyping and not for production, so the volumes aren't there; for another, they're more complex to make because the shape of the leads is not obliging. There are also methods to convert SMD IC cases to DIL without special adapters. You can for example tack 16 wires on the SOIC and mount it in a 16 pin DIL header. Pot it or cover it with hot melt glue to make it more robust. Or do it "dead bug" by gluing the SOIC to the board upside-down and soldering, say, AWG 30 the legs to the pads.

      If you are not doing any circuit development, but are just building known-working circuits, and you are going to be doing this quite a lot, then it is strongly suggested that you make your own printed circuits based on those designs. Once you know the techniques for doing this, it is not nearly so hard as people imagine, and produces the best quality and most reliable circuits.

      Casing prototype circuits

      Many different types of electrical and electronic devices are both electrically-insulated and protected from the outside environment (heat, moisture, touching, etc.) by putting them to a case. Most cases are made of plastic or metal.

      Plastic cases are used in many electronics circuit projects because they are inexpensive and easy to work with (easi to cut holes etc.). Practically all plastic cases provide a good electrical isolation between the outside world and the elctroni circuit, thus can act as insulator for safety reasons. When using plastic case, select a case made of material suitable for this kind of use. This means that the plastic material is not too flammable.

      Metal cases are used when shielding agains external electical and/or magnetic fields are needed. They are also often used when a very good environmental protection is needed (there are watertight cases). Metal cases are generally more expensive than plastic cases and harder to work with (like making necessary holes). If the circuit in metal case has dangerous voltages in it, the case should be grounded for safety reasons. There are many materials that can be used for making metal cases. Many electronics cases are made of aluminium, because it is quite lightweight and quite easy to work with. Some cases are made of iron/steel. Iron/steel cases are harder to work with (like harder to drill holes etc.), but provide better magnetic shielding than aluminium cases (especially for low frequency magentic fields). Metal case is good for fire safety reason, because metal case does not normally burn (it takes very much heat to make aluminium or iron to burn).

      When very good shielding agains external magnetic field are needed, sometime protection cases made of mu-metal are placed over sensitive components like signal transformer. Mu-metal is a nickel-iron alloy (77% nickel, 15% iron, plus copper and molybdenum) that is very efficient for screening magnetic fields. The name of the material refers to the Greek letter that is the symbol for magnetic permeability. Mu-metal has a high value of magnetic permeability.

      Electronics modules made for very demanding environments (like car electronics) are protected by potting them inside polymeric resins such as acrylics, silicone and urethane. This potting encapsulation is usually done using two-part reactive resins which are mixed then used. Encapsulation involves submerging an assembly into resin (usually epoxy) and allowing the resin to harden.Epoxy potting protects circuit very well. The obvious disadvantage to having circuits potted in epoxy is that they cannot easily be repaired, as the components are inaccessible through the hard potting material. It also works effectively in maintaining the security of the board design.

      There is a near infinite number of circuit casing possibilities for the hobbyist. You can solder scrap circuit board together, and make little boxes. You can put things in tin cans that food originally comes with. For some people, wood is something they can work with easily. If you are fond of metalwork, get a metal brake, and bend sheet metal for your boxes. Electronic equipment that's tossed out can often provide interesting boxes. You can also buy utility boxes (metal or plastic depending on country) that are designed for electrical installation work. Those usually can be used for casing small circuits quite cheaply.

      Circuit board design and making

      Most high quality copper-clad circuit boards are composed of one or more layers of fiberglass or other fibers woven or compressed and then impregnated with an epoxy. The glass fibers (sometimes called E-glass or silica-glass) are treated chemically in a process called silaning (or silane processing) to improve adhesion to the epoxy. FR-4 resin systems are generally green, whereas G-10 is usually tan. The boards are made of woven fiberglass (also called E-glass or silica glass),which is treated chemically to adhere to the epoxy resin. So the materials used in those circuit boards are the fiberglass, epoxy and copper. The typical thickness of the copper on the circuit board is 35 micrometers and 17-18 micrometers.

      There is another commonly used printed circuit. This 'brown stuff' is known as 'paper-phenolic' or 'Pertinax'. It is still in use, and is far more popular than fiberglass especially on cheap consumer equipment. Paper Phenolic is a paper-based high pressure laminate circuit board material. has low moisture absorption and very low cold flow. Parts machined from XX have an excellent appearance and can be hot punched in thicknesses up to .062". There are also board material that is called Synthetic-Resin-Bonded Paper or SRBP (trade name is "Paxolin").

      Fiberglass is absolutely only needed for plated through hole and multilayer. And satisfying the Army - fungus doesn't like it as much as paper. Fiberglass board is also mechanically considerably stronger than pertinax, which is needed property on some applications.

      One of the things that scares people away from doing there own electronics circuits is the fabrication of the circuit board. A custom etched board makes things easy to put together and minimizes wire lengths.

      This section of web page describes how you can design and manufacture your own printed circuit boards (PCBs). There are many techniques for making PCBs, some of them are more suitable for low volume manufacturing and other are better for high volume manufacturing in factories. PCBs are great when mass-producing a device or when the circuit complexity makes point-to-point wiring impractical.

      Please note that making these PCBs involves some potentially hazardous chemicals and tools. It is your own resposibillity to take suitable precautionary actions! If you do not know what these suitable precautionary actions are, DO NOT use these chemicals and tools. I recommend wearing protective goggles, clothing, and chemical resistant gloves all the time when handling these chemicals, tools and PCBs!. In some countries the use of some of the tools and chemicals may be bound to restrictions, such as proper waste disposal and licenses, or may even be forbidden. For example both NaOH (caustic soda) and Iron Cloride are very unhealthy if used carelessly.

      The most commonly used circuit board etching chemical if ferric cloride (FeCL). FeCl method ies easy and cheap, but a little messy. Another possible chemical for the PCB making is Sodium Persulphate. It is somewhat more expensive and less messy and available on some electronics component sources. Sodium Persulphate starts of clear, turns blue like copper sulphate solution. It works quickly and with less mess than FeCl. There is also possibility to use acid based etching solutions (for example 700 ml of water + 200ml 37% HCl + 50ml 30% hydrogen peroxide). A useful tip, etching boards upside down some distance from the bottom is considerably quicker than etching copper side up. Sometimes there could be need to free the bubbles which accumulate under the board from time to time by moving the board. Or you can simply adjust the board holding system to leave the board at a tilt of a few degrees.Standing on edge is probably the ideal for circuit board etching. Now add a bubbler at the low end (something like an aquarium air pump with moderate pressure and a long, fine-pored airstone or a plastic tube with many tiny holes). Adding the bubbler means that the fluid moves a bit more aggressively and keeps the bubbles from settling on any area of the etch. And finally, arrange heat to keep the solution temperature 10C or so above room temp.

      Most circuit boards are nowadays made using photo transfer system. The idea in it is that you design the circuit board with a computer, print it a suitable film (can be made with laser printer to photocopier tranparent overhead projector fim) and then phototansfered to the photo-sensitive coating on the circuit board (put film on top of circuit board and use sutisble UV light source to expose). The photo-sensitive coating is then developed (around 1% NaOH solution). After that the board is ready for etching. If you plan to do this yourself, get ready-made photo-resist coated boards - they make some that expose quickly even with a fluorescent desk-lamp - and they don't cost more than a $ or so more than plain ones.

      Flexible circuits is a technology for building electronic circuits by depositing electronic devices on flexible circuits substrates, such as plastic. In the simplest case, flexible circuits can be made by using the same techniques used for rigid printed circuits boards manufacturing. The only thing in flexible circuits that needs to change is the substrate, being made flexible, rather than rigid. Many modern flexible circuits and circuit boards are manufactured with very thin conducting layers. The film deposited on top of the substrate is usually very thin, on the order of a few micrometers. Flexible circuits is often used as connectors in various applications where flexibility is needed. A common application of flexible circuits is in computer keyboard manufacturing; most keyboards made today use flexible circuits for the switch matrix. You can also see flexible circuits in many consumer equipment: digital cameras, ink jet printer print heads, wiring to DVD-drive read/write head etc.

        General

        • Forming The Conductor Pattern to PCB - how it is done    Rate this link
        • Making your own PCB's at Home - You can make printed circuit boards at home for a modest expense. Invaluable to experimenters and homebrewers.    Rate this link
        • The Printed Circuit Board Primer - A fine printed circuit board (PCB) is a mixture if high art, and solid engineering. Here is a short primer on what goes into the making of a PCB, the terminology, and the features that enhance reliabity, and lower cost.    Rate this link
        • Making your own PCB's is easy with Kinsten    Rate this link
        • How to make your own PCB - There are a handful of ways available to the hobbyist to turn your own designs into PCBs. They yield results of different qualities, where the quality seems to be inversely proportional to the amount of mess you make (in most cases), and amount of money you spend (in all cases). I'll talk a bit about each, and then compare them all at the bottom of the page.    Rate this link
        • Making your own PCB    Rate this link
        • Easy Printed Circuit Board Fabrication Using Laser Printer Toner Transfer - You can easily make your own high-quality PCBs (printed circuit boards), from a laser-printer or copier printout of the desired copper pattern, using an ordinary clothes iron, and, most-importantly, the correct paper type. You can have finished boards in less than an hour, including printing, preparing the copper board, transferring the pattern, removing the paper, etching, and drilling. You can also use this method to print the component markings onto the non-copper side of a single-sided PCB. AND the COST is VERY LOW.    Rate this link
        • Making Your Own Printed Circuit Boards Using the Positive Proof Photo-etching system - The positive-proof photo etching may seem scary at first but once you try it you'll be amazed at just how easy it is. This process is suitable for both single, and multiple board runs; that is you can make only one of the PCB you designed or just keep making essentially as many of the same PCB's as you like - with ease. The big advantage to using photo process etching to make only one PCB is that you can design the board on computer and print it out on a clear acetate, rather than trying to use rub-on transfers or an etch resist pen, etc... The system cannot be done away with if you plan on running off anymore than two of the same board as once you've made the clear acetate and have the involved chemicals, you can "burn" as many boards as you like from the same acetate.    Rate this link
        • How to make a PCB - This project will explain how you make your own PCB. You will be amazed how easy it is and how good the result will be. All you need is so get some basic stuff and time for experimenting.    Rate this link

        Designing info

        There are many things which should be considered when desiging electronics circuit boards.

        Drill size is generally selected to be slightly larger than pin diameter, and pad size larger than this (large neough to be well soldered).If using plated holes, drill size must be enough larger than pin toallow for thickness of plating. Consult your PCB service for their standard drill sizes to avoid "special drill" charge. Generally the drill size should be at least 20% bigger than the pin diameter, to allow for tolerances and reduction in dia from plating. The restring should be 25% of the drill, with a minimum of 12mil and a max of 24mil or so according to your design rules. Drill sizes are most often specified in "finished" hole diameter whichincludes the plating through the hole. So if you specify a 0.8mm holethen thats what you should get, but manufacturers vary on this and itcan be a big potential problem, so check with them first. Typically specify your hole at least 0.1mm extra over the pin size you will be using. Don't try and get a 0.8mm pin into a 0.8mm hole. If a pin is a square in section, the drill size has to be 1.41 larger than the side length of the square. For general purpose axial components like normal resistors and capacitors and also IC's, 0.8mm Hole is a good choice.

        Pad diameter = drill +2 * restring. All manufacturers will have a recommended pad to hole ratio spec. This is typically 1.8, so the pad should be 1.8 times larger than your holesize to allow for any drilling offset errors and plating. Some say your pad should be at least double the hole size. You can goless than this if you need to (check with your manufacturer), but it's a nice rule of thumb. For some components such as power diodes or Transistors you will need to use 1mm or 1.2mm holes. When selecting most suitable hole size, look at the spec for the device leg diameter, plus it's tolerance.Then look at the tolerance in your specifications for a finished hole size. Your drill hole needs to be okay, if a worst case scenario occurs and you have a component leg on the top tolerance, and a drill hole on the bottom tolerance

        For general purpose axial components like normal resistors and capacitors and also IC's, 0.8mm Hole (around 32 thou = 0.032") and 1.75mm or 2mm pad size are generally good choises. This is a reaonable minimum size if you have enough space. Really there is no disadvangate to use larger pad size (uless you go to a very hige side), and they are much easier to work with at hand soldering. If you are using a plated through hole then the PCB manuafacturer is going to drill that hole above your stated size, so that it plates down to your required size. Generally, a manufacturer will either go 0.15 mm above yourstated hole size, or 0.05 mm above your top tolerance. When they do this, your pad needs to be sufficently large enough. This is called the annularring.

        For general purpose designs, at standard PCB manufacturers, aim foran 8 thou (0.008") annular ring. If your working on cutting edge stuff and/or use avery good PCB manufacturer you could design to a 5 thou (0.005") annular ring. It is a good idea to design PCB's using imperial measure, because the vastmajority of components are based on 0.1" pitch or other imperialmeasure. A 2mm pad is 80 thousands of an inch.Normally the PCB design software offers the possibility of AUTO DIAMETER ofPads/Vias. It means, you have to specify the Drill (Hole) size only, therest will be set by software.

        When putting traces and pads to circuit board, you need also keep in mind the separation of different PADs. You need to allow at least 1mm/KV (1inch/27KV)air gap between pads/traces at all times, for traces at differentpotentials, to prevent arcing. This is the minimum. In many cases in safety critical applications, there are safety standards which give very detailed information of needed safety distances (those depend on safety level and environment).There are also other circuit board design considerations, especially on high speed electronics. Some important things to remember are:

        • an inch of #20AWG wire has about 20nH of inductance
        • an inch of 0.030 trace has 10nH
        • a square inch of FR-4 has about 5pF of capacitance.
        • inductance scales by length, capacitance by area.
        At very high frequencies the traces on circuit board act like transmission lines. To determine if a trace or wire is a transmission line, we need to know its electrical length. As the trace length approaches about 1/6 of wavelength it starts to look like a "line". Before that, it doesn't have a characteristic impedance, only a reactance. Besides the length, a transmission line must be homogenous. This means it must be over a continuous return path. Even though a trace isn't a transmission line, failing to put a continuous ground under it can have subtle side effects. Although most PCB traces aren't transmission lines, they act as if they were. Typical Delay Times for Various Types of Transmission Lines: 
        Line type                       picosec/inch
Wire in Air (Vacuum)                 85 
Coax (RG-59A, 75, 66% Propagation)  128 
Coax (RG-58A, 50, 66% Propagation)  128 
Coax (RG-11A, 75, 55% Propagation)  154 
PC Board, Inside Trace (FR-4)       140 
PC Board, Outside Trace (FR-4)      180

        Ideally, all high-speed-logic designs should include tightly coupled bypass capacitors for each IC, and all multilayer pc boards should have power and ground distribution planes. Unfortunately, poor design practices still exist, such as using just one bypass capacitor at the power entrance to a logic board and routing power and ground to the ICs from opposite sides of the board. This faulty distribution scheme creates large spikes on the logic supply voltage and produces significant electromagnetic fields around the board and unstable power for the ICs in the board.

        The copper on circuit board has resistance so it generates heat to circuit board. Too much heat will destroy the board and wiring in it. The power-handling capacity of a PCB trace depends on its cross-sectional area and allowable temperature increase (typically 10 degrees). For a 10 degree C temp rise, minimum track widths are: 

        Current  width in inches
        0.5A      .008"
        0.75A     .012"
        1.25A     .020"
        2.5A      .050"
        4.0A      .100"
        7.0A      .200"
        10.0A     .325"
        For the table above the circuit baord is expected to have normal 35 micrometer copper width. If you use thinner copper, you need to reduce the current ratings according the wire thickness.

      Electronics design

      To be able to understand electronics circuits, and later design your own, you need to be able to know basic electronics componentns and to be able to read schematic diagrams. Learning to read a schematic diagram, is similar to map reading. You need to know which wires connect to which component and where each wire starts and finishes. With a map book this would be equivalent to knowing your origin and destination points and which roads connect to the motorway network, etc. However schematics are a little more complicated as components need to be identified and some are polarity conscious (must be wired up in the circuit the correct way round) in order to work. You do not need to understand what the circuit does, or how it works, in order to read it, but you do need to correctly interpret the schematic.

      Any schematic may be drawn in a number of different ways. Two electrically equivalent circuits may look very different. A well-drawn schematic makes it easy to understand how a circuit works and aids in troubleshooting; a poor schematic only creates confusion. By keeping a few rules and suggestions in mind, you can draw a good schematic in no more time than it takes to draw a poor one.

      • Schematics should be unambiguous. Therefore, pin numbers, parts values, polarities, etc., should be clearly labeled to avoid confusion.
      • A good schematic makes circuit functions clear. Therefore, keep functional areas distinct. A good schematic makes circuit functions clear. Therefore, keep functional areas distinct. There are conventional ways to draw functional subunits, and you should learn and follow those.
      • Wires connecting are indicated by a heavy black dot; wires crossing, but not connecting, have no dot. Please note that four wires must not connect at a point; i.e., wires must not cross and connect
      • Always use the same symbol for the same device
      • Wires and components should be aligned horizontally or vertically, unless there's a good reason to do otherwise.
      • In general, the main signals in a circuit drawing should go from left to right. This makes the circuit easier to read because most of the circuits are drawn in this way.
      • Label pin numbers on the outside of a symbol, signal names on the inside.
      • All parts should have values or types indicated; it's best to give all parts a label that refers to the component list (for example IC1, R3, C2 etc.)
      • It is helpful to bring leads away from components a short distance before making connections or jogs, this makes the circuit diagram easier to to read. It is a good idea to leave some space around circuit symbols to leave room for labels, pin numbers, etc.
      • Use small rectangles, ovals, or circles to indicate card-edge connections, connector pins, etc.
      • Be consistent with the symbols you use.
      • Power-supply connections are normally assumed for op-amps and logic devices ("normal" power supply connection are not always drawn to the schematic). If you are drawing your circuit diagrams and have any doubts should you draw the power connections, then it is best to draw them to your circuit diagram.
      • It is a good idea to include a title area near the bottom of the page, with name of circuit, name of instrument, by whom drawn, by whom designed or checked, date, and assembly number. Also include a revision area, with columns for revision number, date, and subject. Those are often found on the professionally drawn circuit diagrams.
      Sometimes the way a circuit is wired up may compromise its performance. This is particularly important for high frequency and radio circuits, and some high gain audio circuits. Also in audio circuits and other sensitve circuits the wires from one component to another should be kept short to prevent a long wire picking up radio interfereance or mains hum from a transformer. The earth terminal would be connected to the chassis or metal framework of the enclosure in which this circuit is built. Many schematics contain a chassis or earth point. Generally its just to indicate the common reference terminal of the circuit, but in radio work, the earth symbol usually requires a physical connection to a cold water pipe or an earth spike buried in the soil.

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