[PCB_FORUM] Power plane -vs- gnd path signal return path
- From: "Jim Wages" <jwages@xxxxxxxxx>
- To: <icu-pcb-forum@xxxxxxxxxxxxx>
- Date: Thu, 13 Mar 2008 09:20:06 -0400
Ok, folks. Let me know if my thinking is wrong here.
I have a 14 layer stack up. External etch layers are adjacent to power
planes, which are adjacent to ground planes. Lyr 2 is a split power plane.
Lyr13 is a solid 3.3V plane.
Do you see any signal "return path" or integrity issues with routing a
critical signal trace on the bottom layer as long as the driver of the
signal was powered by 3.3V. What about a differential pair?
I'm assuming that the power and gnd planes would be perceived as a short to
hi-frequency signals, so that the return path would not have to get to a
ground plane, but would just stay on the 3.3V plane directly beneath the
trace until it returned to the driver.
Thoughts?
Jim S. Wages
SR. PCB Layout Designer
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