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The perils of long, thin traces?

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juz_ad

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Kind of a general question (if there is a general answer)…

What are some of the main problems associated with long, thin traces on a PCB design?

I'm asking because I recently had to troubleshoot a circuit where the problem seems to be down to 3x traces at approx. 6cm long and 5 mil thick - which was about twice the distance and half the thickness of any of the other traces on the board.

Shorting them with wire solved all the problems - so it seems like a layout problem.

Can anyone offer any insight into that?

Thanks.
 

andre_teprom

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If the current layout clearance support a track thickening, I also would come to the same conclusion that most likely the thickness could be the cause of the problem, although we should not discard interference issues to certain routed paths.
 

ads-ee

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6cm and 5mil isn't all that long, so unless there was a manufacturing issue with the PCB (like over etching) I wouldn't think that would be the source of the problem.

There are quite a few things that could be potential problems and a lot of them are dependent on the board design engineer and the quality of the board designer who did the job.
 

chris.mourad

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Hi

Long and thin PCB traces are usually to avoid, because they tend to increase drastically track resistance.
Long wires on a PCB can also be considered as antennas, and will easily catch a lot of interferences/rubbish.
Moreover, long wires will have a bigger parasitic inductance, creating non-idealities on the dynamic signals.

Now long tracks can be used on a PCB, as long as it is for static logic signals: No current flowing into those tracks.
 

andre_teprom

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A track with 6cm/5mils/0.5Oz yelds less than 0,5 Ohms of resistace, which don´t make any difference for digital circuits and also even for analog circuits.
 

marce

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Do loads of boards with these sort of track sizes, also look at PC motherboards, they are covered in them.... a lot will be 4 mil wide traces for the impedance figures..... DDR interfaces, gigabit Ethernet, PCIe etc.

What is a static logic signal???????

What specifically was the problem.....
 

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