RE: [SI-LIST] : inductance extracted by ansoft SI3D

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From: Jeff Walden (jwalden@flash.net)
Date: Mon Jul 17 2000 - 16:45:21 PDT


RE: [SI-LIST] : inductance extracted by ansoft SI3DHassan,
Is it more important to model a stackup like that & try to safely simplify
the model, or could the structure be simplified ... electrically? Keep the
layer stackup the way you want, but use the novel idea that Dan Swanson (of
the RF persuasion) has used which is a 5 wire transmission line structured
out of vias. The return loss can be easily adjusted to below 20dB over a
broad frequency range (sort of a SI interest) ... albeit a loss of board
space.
Below is a feeble attempt describe the geometry. The G's are vias tying the
ground planes together & S is the the signal via. Optimization is needed to
adjust the spacing of the ground vias & possibly adjust the barrel diameter.
To a point, the smaller the via barrels the smaller the radius of the Gs.
G G
    S
G G

You will use a full wave field solver. Technically any will do, BUT a 3D
planar will cut the run time down enormously, i.e. Sonnet EM (RF
persuasion), it may at this time even have an optimization routine built in.
The model then becomes a transmission line ... Zo & Td which is pretty
simple. I would estimate solver run time on the order of several minutes to
a couple of hours + curiosity = a few days to a solution.

Alternatively, one of Dr. Henri Merkelo's (SI persuasion) students published
a paper a few years ago in which he meticulously modeled a via through 3
ground/power layers. I think it was presented at ECTC ~'93 or '94. With
his SPICE model he even successfully represented the mode conversion between
the layers with controlled current source(s). Their tool was a full wave
time domain field solver, written at the U of I, that could also generate a
time transient animation of the charge propagation. (Great visualization
for those of the SI persuasion.) I know of at least 2 commercial full wave
time domain field solvers that can replicate that effort, i.e. Micro-Stripes
from Flomerics & Microwave Studio from CST. With enough "probes" between
layers, near adjacent vias & traces you should be able to successfully
capture most of the important effects ... albeit a loss of (your) time. I
would estimate solver time in days + your time in days = weeks.

-JLW

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