I have a question about layer stackup and routing.

Most of our designs have a pair of routing layers
sandwiched between planes, one for vertical and
the other for horizontal traces.
Maybe I haven't had enough coffee yet today, but
I started wondering how the return path energy
gets from one plane to the other (unless there
happens to be a decoupling cap nearby?) If both
planes were GND there wouldn't be a problem,
since they would be stitched together in many
places, but one is GND and the other is PWR.

So I started wondering.... Wouldn't it be better to
have one routing layer ABOVE the GND plane and
one BENEATH? In this scheme all the routing would
be straddling the SAME return path and it seems
logical the it would be less noisy. There would never
be a discontiuity from the energy trying to get from
one plane to the other, right?

maybe the gains are not worth the loss in the
overall scheme, though?

onward thru the fog,
Jack

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