Re: [SI-LIST] : stackup question

Ravinder Ajmani (ajmani@us.ibm.com)
Tue, 14 Apr 1998 11:26:30 -0400

For a high-speed board, it will be necessary to use the stackup that wi=
ll
provide good inter-plane capacitance. I have observed that this capaci=
tance is
most effective for suppression of noise above 200 MHz. Based on this
assumption, I would suggest the following stackup:

Signal
Signal
Power
Ground
Signal
Signal
Power
Ground
Signal
Signal

This stackup provides 4 microstrip layers, and 2 stripline layers for r=
outing
high-speed signals. It also ensures that the two power planes will not=
overlap
each other. You should provide sufficient vias between the two ground =
planes.

Regards,
Ravinder Ajmani

Always do right. This will gratify some people and astonish the rest. =
....
Mark Twain

owner-si-list@silab.Eng.Sun.COM on 04/13/98 07:54:36 PM
Please respond to owner-si-list@silab.Eng.Sun.COM
To: si-list@silab.Eng.Sun.COM
cc:
Subject: [SI-LIST] : stackup question

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 groun=
d
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 ot=
her?
(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

=