Elroy,
     
     I recently attended the University of Wisconsin's "System EMC 
     Compliance through Printed Circuit Design" seminar and was taught that 
     if the external planes are for shielding purposes, it is a good idea 
     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. Tying the IC and Cap ground pins to the external plane only puts 
     noise onto the shield.  The course contained other subtle tricks. Take 
     it if you can get the chance.
     
     Gary Fuller
     Edwards Systems Technology
     Sarasota, Florida 34243
     [log in to unmask]


______________________________ Reply Separator _________________________________
Subject: Internal and external ground planes
Author:  "Elroy A. Tesch; Jr." <[log in to unmask]> at Internet2
Date:    10-22-96 19:37


We design high speed line scan cameras and use internal and 
external ground planes (external for shielding) on our PCB's.  
My question is this-
     
Should the internal and external planes be tied throughout the board (at 
vias, etc.) or should the external planes be tied back only at a single 
soure (power connector) and leave the internal plane(s) for all component 
connections?  I am wondering if there are advantages of one over the other.
     
VIP Lab 
University of Arkansas
     
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