Re: [SI-LIST] : What's your favorite Screwy SI Concept?

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From: rbmccammon@mmm.com
Date: Wed Jan 12 2000 - 06:25:06 PST


Michael E. Vrbanac wrote:

>Starting with two adjacent power/ground distribution planes, the entire
power
>plane perimeter is designed to be smaller than the ground plane by a
factor of
>20 times the distance between the two planes when measured at any point
>along the ground plane perimeter edge.

>To the forum,

>It looks as if we have found what the 20H rule is and who originated it
>and who wrote something about it. That's good progress but we need
>more. It is obvious that its effectiveness is disputed, so let's continue
>to explore the possible reasons why the 20H rule might exist for as long
>as it has. Without making any claims one way or other, I will offer some
>"thought experiments" to hopefully help us along.

>We first have to assume that there was a beneficial intent by the
application
>of the rule and it was thought to have been effective in its original use.
>Otherwise, the whole thing would be an intentional sham and we should
>forget about it altogether. Since there would be no benefit of throwing
it
>out without adequately researching any possible ways it could be of
benefit,
>let's assume that it had some perceived well intended benefit from the
>application of it.

>Then by logical deduction, we could conclude that a few things might
happen
>as a result of this 20H rule (from a general point of view) just from a
>physical description of it and applying some basic knowledge of physics to
>see if there are any plausible avenues of understanding the 20H rule's
usefulness.

And while we consider that, we shoiuld also consider the effect
of backing both the power and ground planes back by 20H.

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