One of hardest tasks when fabricating PCB’s is Printed Circuit Board(PCB) routing. There is no unified rules on how properly board should be routed and it would be impossible to write them as situation on each board is different. One of general rules are that the shortest routes are the best because longer routes tend to generate more noises or pick them up from different sources. It is obvious that every conducting material acts as an antenna no exception with PCB routes. No secret that each route acts as small transmitting and receiving antenna. So one thing is to keep in mid when routing PCB is to route short as possible.

Another concerning area is a cross-talk or cross-coupling between routes. This effect appears when two traces run along each other and energy from one trace route couples to another. This effect is obvious in high frequency digital and analog circuits. This effect can make device dis-functional because only of crosscoupling effect. These defects are hard to determine as electrically circuit board is correct. If this effect is noticed – the only solution is to cut traces off and run separate wires instead. It is better to do keep this in mind while routing the board. Many modern autorouters are quite good at this but again human word is always the last.

If circuit board have many components there is no way to deal with one layer or even two layer boards. So traces will be distributed among several layers that are connected by vias. There is a same rule – less vias is better. Why? One thing is that form more vias PCB fabricating companies charge more. Another thing is that vias or traces next to noisy vias also couple noises. Most autorouters can handle via minimisation.

So good routing always require you to keep in mind all signals of the circuit. Especially when working with sensitive devices keep in mind that higher frequencies, or higher gain the interference sensitivity also increases. If you see circuit with capacitors like several pF or inductors with mH then be sure that routing may be critical task.

Simple example. If you route some sort of amplifier and put input signals near output, then there is a big chance that your amplifier will become an oscillator.

Read more about Avoiding noises in mixed signal design.

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This entry was posted on Monday, May 21st, 2007 at 5:36 pm and is filed under Electronics Tutorial. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.