Is anyone out there investigating or using a conductive Polymer Thick 
     Film layer on the outside of the board to reduce EMI.  Using this PTF 
     allows you to possibly go from a 4 layer board with internal ground 
     planes to a 2 layer board. CHEAPER!!!!!!!!
     
     [log in to unmask]


______________________________ Reply Separator _________________________________
Subject: Re: Internal and external ground planes
Author:  Non-HP-dwalker ([log in to unmask]) at HP-Vancouver,shargw2
Date:    10/23/96 8:38 AM


     
I believe you should tie the external ground plane at one point only.
The return current path often completes a loop antenna - a highly directional 
radiation source - and if, by connecting the components to the outer shield, 
you make the outer plane a part of the current return path you have turned 
your shield into a radiation source.
     
Don Walker
[log in to unmask]
     
> 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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