+3.3,5-board stackup problem

Stuart P. MacEachern ([email protected])
Mon, 7 Jul 1997 10:22:50 -0400

hi ,

Currently we are spinning a set of boards with +3.3v, +5v and gnd.
for planes.
We are looking at 8 layers with a stackup as follows;

1 ----- top or top
2 ----- signal gnd
3 ----- gnd signal
4 ----- +5 +5
5 ----- signal signal
6 ----- +3.3v signal
7 ----- signal +3.3
8 ----- bottom bottom

A manufacturability problem exists with a non-symetrical plane stackup
as shown. In our system , most power runs off the +3.3v plane. (70%)

I have
suggested a mesh for the +5v plane. Does anyone have experience with
mesh type power planes ?

How tight does the mesh have to be ? (for low inductance, good high
freq returns,ect.)

I understand I will be reducing the high frequency capacitance
between the +5v
and the gnd plane, but does anybody have any data indicating what affect
this will have ?, and what can I do to compensate, if anything.
Any papers out there on this subject? I have read some in the past
, but I looking
for current information/references.