I agree with Dave.
We get this question/topic raised/asked about in classes a lot.
There are NOT many cases in the practical design and troubleshooting of
electronic products for electrical noise where edge radiation is a big
worry. And in the circumstances where it is an issue, the 20H idea (why even
call it a rule?) does not seem to have much merit. See these research
papers... they have been peer-reviewed.
Effects of 20-H Rule and Shielding Vias
on Electromagnetic Radiation From Printed Circuit Boards
Huabo Chen, Student Member, IEEE, and Jiayuan Fang, Senior Member, IEEE
Dept. of Electrical Engineering, University of California at Santa Cruz,
Santa Cruz, CA 95064 9th Topical Meeting on Electrical Performance of
Electronic Packaging, EPEP 2000
20-H Rule Modeling and Measurements, Hwan W. Shim, Todd H. Hubing,
Electromagnetic Compatibility Laboratory Department of Electrical and
Computer Engineering University of Missouri - Rolla, Rolla, MO, 65409.
Proceedings of 2001 IEEE International Symposium on EMC
Best Regards
Lee
Lee Hill
Founding Partner
SILENT
10 Northern Boulevard, Suite 1
Amherst, NH 03031
USA
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Dave
Schaefer
Sent: Sunday, November 30, 2008 8:53 PM
To: [log in to unmask]
Subject: Re: [DC] PWR & GND PLANES
Don,
The "rule" for plane separation comes from a text by Mark Montrose , he
refers to the rule as the "20H rule" ... Power Plane should be set back 20 x
the dielectric separation between the planes. Montrose's analysis:
http://www.sigrity.com/papers/epep2000/epep_20h.pdf
Another paper referenced via the Speeding Edge website (Lee Ritchey) focuses
on experimental results and suggests that applying "20H" may actually make
the plane performance worse:
http://ieeexplore.ieee.org/iel5/15/30899/01433046.pdf
More can be found on Si-List:
http://www.freelists.org/post/si-list/20H-Rule-theoretically-investigated-wi
th-simulation,3
Based on my research, I do not employ "20H" in any of my designs.
Hth,
Dave
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