Hi,

> I'm new to this layout stuff. Can any of you experts out there tell me if
I
> can use a 10 mil trace, or should I use something larger?


    I do not consider myself an expert but I have done quite a few products
that are on the market and they usually work well :-)

    I would use a much larger power trace.. Remember that even if your
average power consuptiom is 35ma Cmos switches very fast and can "eat" more
than 1 amp when switching. The decoupling capacitors are your main defense
there but "beafier" traces also help a lot, specially ground.

    As a rule of thumb I never use less than 40 mils for vcc and 50 for
ground return. Whenever I have more than a few hundred miliamps I try to
route power directly from the regulator. If I cannot do that I try to
calculate the worst case conditions and use heavier decoupling. That also
helps a lot in emissions control.

    When I have to get the board inside a box that is oversized and has
mouting holes that I have to follow I use much heavier power traces, as
heavy as possible...

    Another layout trick that I find very nice for power traces and really
gives measurable improvement in decoupling is to put the capacitor as close
to the IC ground pin as possible, route vcc to the capacitor with as wide a
trace as possible and than go with a 20 mils trace to the vcc pin. I saw
that in a tip from David Vanhorn, that should still be part of this list and
you can see how better the results are with a good scope. He has a website
that explains it in more details but I do not have the address handy. Nice
tip indeed.

Best regards,
Alexandre Guimaraes

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