From: Boris Mohar
Subject: Re: Ground pours on top and bottom layers?
X-Newsreader: Forte Agent 1.92/32.572
Date: Sat, 04 Jan 2003 21:58:43 -0500
NNTP-Posting-Date: Sat, 04 Jan 2003 22:02:01 EST
Organization: Bell Sympatico
On Sun, 05 Jan 2003 02:21:59 GMT, Andy Peters
>I'm just wondering. What's the current thinking regarding grounded
>copper pours on the top and bottom layers of boards that already have a
>power and ground plane?
>My application is a DSP board with an analog audio front-end, a CODEC
>and a processor. My board has four layers: top and bottom are signal,
>layer two is ground, layer three is power.
>The ground layer has a split to separate the analog and digital grounds.
>The power layer has splits to accomodate the different supply voltages.
>Any pros/cons of the added ground pours on the signal layers are welcome.
It has to be done carefully. To want to avoid capacitively coupling two
grounds like this.
Instead place AGND over AGND And DGND over DGND where you can.
There are other ways to screw it up but if done with care it can be
useful. Adding copper also produces what you board shop calls balanced
layout which make is easier to control the etch because you do not have
huge voids with local concentration of high density fine pitch tracks.
Viatrack Printed Circuit Designs