Re: [SI-LIST] : 20-H Rule for Power Planes

Michael E Vrbanac (mvrbanac@cisco.com)
Thu, 27 May 1999 14:32:01 -0700 (PDT)

In a multilayer PCB, it is the practice of "indenting" the "non-zero"
voltage planes by 20 times the height of that plane to the "zero"
voltage plane (referenced to the chassis). The purpose being to
provide a measure of field containment at the plane edges by a very
inexpensive technique (usually unless there are 'real estate'
problems). The 20H rule can be modified to suit the amount of field
containment at the plane edges by adjusting the "20" to some other
value which is appropriate for the design. It is particularly
effective when such a method is used in conjunction w/a second "zero
voltage plane" above the "non-zero" voltage plane and "zero voltage
plane" referencing to chassis potential.

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> I've read every post on this subject so far. I still only have a vague
> idea of what the 20H rule is and the assumed conditions under which it is
> applied. Any one want to try a one or two paragraph description?
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