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From: EdV on 15 Jun 2010 11:12
On Jun 14, 12:24 pm, Bill Sloman <bill.slo...(a)ieee.org> wrote:
> On Jun 14, 3:48 pm, EdV <edvoge...(a)gmail.com> wrote:
>
> > I have "inherited" a PCB design from a former contractor at a start up
> > company.  In the process of adding some more circuits to an already
> > crowded board (to me at any rate using Eagle for the first time) I am
> > thinking adding one more route layer might help me make schedule.
> > Currently it is a top and bottom signal layer with a power plane and
> > two separate ground planes.
>
> > In the the past I have been encouraged not to have route layers that
> > are inaccessible by exacto knife.  ;-)
>
> > Any comments, suggestions or horror stories are welcome.
>
> Unless you have worked out how to embed chips inside the board, even
> buried traces are accessible to the "exacto knife" at both ends. You
> may have to bend up the relevant lead on the package tp break the
> connection to the buried trace, but it's always do-able, though often
> not that easy.
>
> And I've certainly worked with circuits where it was a very good idea
> to have a ground plane - or a least a ground or power pour - directly
> under traces carrying fast signals, and on both sides of buried
> traces. Extra layers do cost money, but so do the logic chips that are
> fast enough to need them, and providing a sub-optimal electromagnetic
> environemnt can throw away the money you spent on the faster chips in
> the first place.
>
> --
> Bill Sloman, Nijmegen

I was able to get the last couple traces to route without adding a
signal layer. Regarding the ground planes what I meant to say is
there is a copper pour for ground that is divided by into two areas
one for analog and one for digital as opposes to two actual ground
planes.

Thanks much to all who contributed to my post.

Best,
Ed Vogel
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