RE: [SI-LIST] : different 4-layer board Stack up (S-P-G-S) ?

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From: jwalden ([email protected])
Date: Tue Mar 07 2000 - 11:51:49 PST

Adding to the original question; what are the opinions about a P-S-G-S

Keep the spacing between the ground & the signal layers the same and as
close as possible. This will keep a more uniform impedance (whatever it is)
and shorten the via barrel length (and resulting L) for the signal traces.
The signal lines are tightly coupled to the same reference plane ... just
different sides. Might this reduce high frequency mode conversion that
occurs with fast edge rates on longer vias between loosely coupled (or at
least seldom tight enough) layers such as power & ground?

If there are a large amount of outer layer signal lines, then more careful
attention might have to made to ensure that the inner signal lines'
characteristics more closely match the outer. Such as moving the power
plane further away to reduce its effect on the inner signal layer. And,
adjusting the inner layer signal line widths to compensate for being
embedded in the dielectric as well as some effect of the power plane.

Jeff Walden

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