Re: vias between parallel planes and traces?

John Popelish <jpopelish@xxxxxxxx> wrote in
news:7q2dnTuBO82MU1jeRVn-vw@xxxxxxxxxxxx:


> Before I try to answer your ground plane questions, I would like you
> to describe why you have a ground layer. What (and be as specific as
> possible) is it supposed to do for your circuit? Does it do different
> things for different parts of the circuit? You may find that you are
> answering your own questions.
>

OK well the top ground plane is for a very specific purpose: it is directly
below a compass module that is very sensitive to interference and whatnot.
Unfortunately I had to run some signal lines directly beneath it so I moved
them to the bottom layer and then put the ground plane above them on the
top layer to shield the module from the signal lines (they're SPI lines
that will be running at about 5Mhz as I recall). The data*** for the
compass module very specifically stated not to run any traces directly
beneath the module, so this was the best I could do.

The other ground plane is there, to me, for three main reasons:

-simplify layout by making a ground signal always readily available
-give lots of copper to ground signal to decrease resistance
-provide a sort of shield to the circuit board. (this is something I've
always been told)


So with all that said I'm still not entirely sure about how to answer my
questions... Any suggestions?

Thanks,

-Mike
.

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