gEDA-user: Eliminate separate Vcc planes?

[Bob Paddock <graceindustries@xxxxxxxxx>]

Boss just sent around something he got from a consultant on
doing "proper" EMI design (which I've been doing for years already,
I thought until consultant came up with this):

"Eliminate separate Vcc planes.
This ancient practice is long overdue for an overhaul.  Years ago, the
leaded capacitors were not able to provide a good enough short at VHF
and above, so the reasoning was that the parallel plates of Vcc and
ground made a good UHF capacitor.   The problem with this is twofold:
it takes away one or more ground planes, and more importantly doesn’t
allow the designer to control where the noise current goes.   Noise
follows the path of least impedance, which may be anywhere on the PCB
after you punch holes in the Vcc plane for vias and to route traces
that have no other room to go.  The best way to control noise is to
use a separate trace for Vcc, and apply series and shunt elements to
control the noise currents."

There is no attribution as to were that advice comes from.  The
frequencies in question are 400 MHz to 3 GHz.
To me running Vcc traces all over the board is the surest way to raise
inductance etc., and seems wrong to me.

Want to know what you thought of this consultants advice?

Doesn't cover what happens in multi-rail systems either.


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