Don,
     
     As long as the return paths are already taken care of, (not 
     unnecessarily breaking up the internal ground plane) having the 
     internal plane contiguous to the guard ring won't put the shield in 
     the return path as long as they are only tied together at the board 
     edge. (At least that's what the instructor said) It's all BLACK MAGIC 
     anyway. 
     
     Gary Fuller
     [log in to unmask]




______________________________ Reply Separator _________________________________
Subject: Re[2]: Internal and external ground planes
Author:  "Walker; Don" <[log in to unmask]> at Internet2
Date:    10-23-96 08:40




This is a good idea.  Especially if you have high speed signals running
near the board edge.  The only problem I see is where you say to "...tie
the external planes and the internal ground plane together..." I think
you probably meant to say "...tie the external planes and the internal
GUARD RINGS together..."  This prevents any possibility of the shield
becoming a part of the return path.

Don Walker
[log in to unmask]

>    to run a guard ring of ground around the periphery of the board on all
>    layers and tie the external planes and the internal ground plane
>    together through closely spaced (.25 inch) vias only at the guard
>    ring.

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