pcb design

During  PCB design  many issues come across and one of them is in the regard of non-plated and plated through holes. What is the difference between them and where should one use which one? is a commonly asked question. Here we will briefly discuss this issue.  Through hole components  have leads(straight or clinched) and these leads are put through holes available or made on the PCB insulating materials and soldered on the other side onto the copper tracks. The  difference between non plated through hole and plated through hole  is the presence of plated copper inside the insulating base material as shown in the pictures below. The presence of this plated through hole has in turn effect on electrical properties and mechanical stability. When component leads is soldered through plated holes then (1)the electrical resistance by the joint formed becomes less and (2) the mechanical stability increases. This is not the case with the non plated holes and hence p...

Cables and Connectors (1) Cables should be grouped according to their function such as power, analog, digital, and RF. (2) Separate connector assemblies should be used for analog and digital signals. (3) Analog and digital connectors should be located as far apart as possible. (4) Analog and digital signal pins should be separated by unused grounded pins when sharing the same I/O connector. (5) Individual pins should be used inside the I/O connector for each signal return so that all return circuits remain separated. (6) Connector crosstalk may be reduced by using separate power and ground pins for each signal and by reducing the circuit’s loading and current flow.   (7) Cable shields should be grounded to equipment housing at the I/O points. (8) Shielded I/O cables are most effective if grounded at both ends. (9) Cable common mode currents should be removed at the equipment’s metal housing prior to internal connections. (10) Cables shou...

Printed Circuit Board Design Guidelines  Below is a list of 16 EMC design guidelines for printed circuit boards along with a short justification for each. 1. The lengths of traces carrying high-speed digital signals or clocks should be minimized. High-speed digital signals and clocks are often the strongest noise sources. The longer these traces are, the more opportunities there will be to couple energy away from these traces. Remember also, that loop area is generally more important than trace length. Make sure that there is a good high-frequency current return path very near each trace. 2. The lengths of traces attached directly to connectors (I/O traces) should be minimized. Traces attached directly to connectors are likely paths for energy to be coupled on or off the board. 3. Signals with high-frequency content should not be routed beneath components used for board I/O . Traces routed under a component can capacitively or inductively couple energy to that compo...

During your PCB design, an important thing to consider is placement of decoupling capacitors on your PCB for EMI. Capacitors do many things. They filter voltage droops, they present a 'brick wall' for transients, and they try their best to kill any EMI noise on your power rails. One of the most common functions though, is this filtering of EMI noise going into and coming out of the chip on your PCB design. It's supposed to be attached as close as possible to the input power pin of your part with the shortest, fattest trace possible, but surely you're already aware of this (it's also supposed to have the shortest current loop possible between the chip and part, but that's beyond the scope of this article).   For the sake of explanation, you can think of a capacitor as really a capacitor in line with an inductor. Crazy? Yes it is, but it's also unavoidable. If you found a wire lying on the ground and pick it up, it is inherently an inductor of some val...

Decoupling, Bypassing and Filtering ( 1) EMI filters can be used as a shunt element to divert electrical currents from a trace or conductor; as a series element to block a trace or conductor current; or they may be used as a combination of these functions.    Selection of the filter elements should always be based on the desired frequency range and component characteristics.    A low pass filter can be useful for reducing most high frequency EMI problems.    It incorporates a capacitive shunt and series resistance or inductance.    However, at frequency extremes, the capacitor can become inductive and the inductor can become capacitive causing the filter to act more like a band-stop filter.     The filter design type should be based on the overall impedance at the circuit’s point of application for proper match.    A T-filter design is effective for most EMI applications and is ideal for analog and digital I/O ports....

EMI/EMC problems may be approached at the component, PC board or enclosure levels.    However, it is much more efficient to deal with these problems as close to the source or susceptible victim as possible.    Therefore, it is important to consider these tips as guidelines for PCB design and layout so that problems may be identified and prevented prior to actual fabrication of the equipment. (1) EMI controls should be applied at the circuit and box levels prior to addressing EMI at the interconnected and system levels. (2) Digital circuits are more likely to be the source of emissions due to the handling of periodic waveforms and the fast clock/switching rates.    Analog circuits are more likely to be the susceptible victims due to higher gain functions. (3) The source or susceptible victim of most EMI problems is typically an electronic component .    Although active components are usually the sources of EMI , passive components ...

As mentioned in my previous Article i am trying to elaborate the EMI source and victims. After seeing the word EMI you must be thinking  what is it? Below is the small definition of EMI. Electromagnetic Interference (EMI) The process where disruptive electromagnetic energy is transmitted from one electronic device to another via radiated or conducted paths. –  Radiated Emissions -The component of RF (roughly 10kHz to 100GHz) energy transmitted through a medium, usually free space (air), as an electromagnetic field. –  Conducted Emissions -The component of RF energy transmitted as a propagating wave generally through a wire or interconnect cable. LCI (Line conducted interference) refers to RF energy in the power cord.   A typical circuit board may have dozens, hundreds or even thousands of circuits. Each circuit is a potential source of energy that might eventually be coupled unintentionally to other circuits or devices. Each circuit is also a poten...