[SI-LIST] : stackup question

Paul Thompson (crash@apple.com)
Mon, 13 Apr 1998 19:37:19 -0700

I'd like to know what people think about the following stackup for a 10
layer board with 2 power planes and 2 ground planes:

Signal 1
-4 mil-
Ground 1
-5 mil-
Signal 2
-8 mil-
Signal 3
-5 mil-
Power 1
-6 mil-
Power 2
-5 mil-
Signal 4
-8 mil-
Signal 5
-5 mil-
Ground 2
-4 mil-
Signal 6

The idea is first to get the impedance of all layers quite close, and
secondly to get as much of the return currents as possible in the ground
planes rather than the power planes (this is obviously not the case for
signal layers 3 and 4, but I can keep my critical signals off them.

Can anyone think of a better stackup, or are my priorities mixed up for a
high speed (~100 MHz) digital board? Am I sacrificing high speed
decoupling by not putting power and ground planes right next to each other?
(One plane is 5V and the other is 3.3V, BTW)

Regards,

Paul

--
Paul Thompson                                        crash@apple.com
System Integrator, Macintosh Desktop Systems         Apple Computer