Usually 3-4 times the height of the
dielectric which is between the GND and PWR plane. The idea is to keep the
radiation lobe of the power plane as tight to the GND plane as possible. You
don’t want the PWR plane to radiate outwards from the edge of the PCB.
There is no long-winded calculation, just a rule-of-thumb. If you want
super-safe and over-kill ? Then pull back more. Then it’s a compromise to
maximizing the PWR plane area. PCB’s are a collection of compromise……..that
does what its suppose to do…….. very well !!!!
TDK
From: DesignerCouncil
[mailto:[log in to unmask]] On Behalf Of
Don Larisey
Sent: Friday, November 28, 2008
8:07 AM
To: [log in to unmask]
Subject: [DC] PWR & GND PLANES
For some time
we have received requests to step back the edge of the PWR Planes from the edge
of the GND Plane around the perimeter of the board. My question is, by how
much? We have a request for 3.00mm pull-back. I forget what Lee Ritchey
recommended many many years ago, and of course, that may not be relevant today.
Is there a spec for this? Are there any rules?
Regards,
Don
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