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

Douglas McKean ([email protected])
Wed, 26 May 1999 11:04:07 -0700

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At 02:44 PM 5/25/99 -0700, Larry Smith wrote:
>I don't believe in the "20-H Rule". Suppose the power plane was at
>3.3V and the ground plane was at 0V. It would be easy to reconfigure
>the system so that the "power" plane is at 0 volts and the"ground"
>plane is at -3.3V. Does this mean that the power plane should now be
>bigger than the ground plane?

I employ the 20-H Rule only in stackups where the
power plane is sandwiched between two ground planes.

Otherwise, I believe your remaining hypothesis
concerning a power plane referenced with only
one ground plane is correct.

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