**From:** Chris Cheng (*chris.cheng@3pardata.com*)

**Date:** Mon Jul 17 2000 - 13:55:33 PDT

**Next message:**Muranyi, Arpad: "RE: [SI-LIST] : inductance extracted by ansoft SI3D"**Previous message:**Lynne Green: "RE: [SI-LIST] : inductance extracted by ansoft SI3D"**Maybe in reply to:**Ming: "[SI-LIST] : inductance extracted by ansoft SI3D"**Next in thread:**Muranyi, Arpad: "RE: [SI-LIST] : inductance extracted by ansoft SI3D"

i don't know anything about si3d. but here are ways to get via parasitics.

from simulation

roger harrington (of bem/mom fame) used to defined excess inductance and

capacitance as

delta of inductance/capacitance w & w/o the parasitic. if u believe u have

an acurate

simulator, built a 3d structure of the via with signal leads. then build the

structure with

the leads only without the via. subtract the inductance/capacitance between

the two results

and you've got a lump approximation of the parasitic. the original

methodology use a more

elegant technique to only solve for the delta fields to minimize the error

due to trying to

get a small delta out of two larger number.

from measurement

anyone who claims to be able to tdr a single via and get meaningful result

is dreaming.

however, lump parameters can be calculated by following techniques

(i) build two structures, one with a single trace the other with a match

length trace

but with lots > 50 vias uniformly placed on it. use a low speed capacitance

meter and

measure the low speed capacitance of each structure and subtract the

difference and

divide by the # of via.

(ii) once you figure out the lump capacitance, build two structures, one

with single trace

the other with daisy chained vias and match length. tdr the impedance and

use the formula

Z = sqrt( (l+ delta l)/(c+delta c)) to figure out the lump inductance.

and if u have done the above, you will find out those numbers are very small

and lump

models works fine. anyone who thinks u need hfss or whatever full wave

technique is,

again, dreaming.

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**Next message:**Muranyi, Arpad: "RE: [SI-LIST] : inductance extracted by ansoft SI3D"**Previous message:**Lynne Green: "RE: [SI-LIST] : inductance extracted by ansoft SI3D"**Maybe in reply to:**Ming: "[SI-LIST] : inductance extracted by ansoft SI3D"**Next in thread:**Muranyi, Arpad: "RE: [SI-LIST] : inductance extracted by ansoft SI3D"

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