[SI-LIST] Re: EMI and Power plane card edge clearance distance

Greetings,
 There exists a 20-H rule that basically states that you want to keep
the power planes back 20 x the spacing between the power and ground
planes.  The theory is that the field lines from the end of the power
plane will mostly just run into the ground plane instead of being
present beside the edge of the card with the opportunity to excite
another assembly.  If you keep your ground plane quiet and/or use buried
capacitance, I don't really see why it would be necessary - I don't know
of many people who use it (of course, I don't know of many people who
pass EMI the first time around either :o)

Best Regards
Dave Heald

Stacy L Gore wrote:
> 
> I remember reading something (article, e-mail) about the EMI benefits of
> etching  back power/ground sandwich planes at different levels. (i.e. power
> plane back 50 mils from the card edge and the ground plane back 100 mils).
> Anybody know anything about this or have a comment one way or another?
> 
> Stacy L. Gore
> Hardware Engineering Staff
> Raytheon - Garland Site
> Phone - (972) 205-4208
> Fax - (972) 205-8083
> 
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