**From:** Ray Anderson (*raymonda@ha1mpk-mail.eng.sun.com*)

**Date:** Fri Jun 09 2000 - 10:08:50 PDT

**Next message:**Ray Anderson: "RE: [SI-LIST] : Upper limit of interplane capacitance"**Previous message:**Chan, Michael : "RE: [SI-LIST] : Upper limit of interplane capacitance"**Maybe in reply to:**Barry Ma: "[SI-LIST] : Upper limit of interplane capacitance"**Next in thread:**Ray Anderson: "RE: [SI-LIST] : Upper limit of interplane capacitance"

You can calculate the interplane capacitance

(ignoring fringing effects) as

C = (ErEo)/t

Works out to about 225 pF/sq inch for 4 mil FR4

Inductance can be derived from the following

relation:

vel = Co/sqrt(Er) = 1 /sqrt(LC)

Solving for L yields about .13 nH/square for

planes separated by 4 mils.

so Zo = sqrt(L/C) therefore you get .75 ohm-inch

Zo for 4 mil FR4 planes.

We've been able to get very good prediction to measurement correlation

in the lab.

We've created a plane model in spice based on the above relationships.

Simulation of the model provides results with very good correlation

to VNA measurements of actual planes. (i.e. same capacitance,

same inductance, same resonance)

-Ray

*>
*

*> What would people expect the characteristic impedance
*

*> to be of a 4" x 6" x 4mil FR-4 structure?
*

*>
*

*> Parallel plates are just two dimensional transmission
*

*> lines with L and C being in units of H/area and F/area.
*

*> The equations pop out pretty much the same as a one
*

*> dimensional transmission line, i.e.
*

*>
*

*> vprop = 1/sqrt(LC)
*

*> Z0 = sqrt(L/C)
*

*>
*

*> In fact, there's some pretty neat derivations
*

*> for parallel plates such as
*

*>
*

*> Z0 = sqrt(mu/epsilon)*d/w
*

*>
*

*> d = distance of separation
*

*> w = width
*

*>
*

*> ignoring fringing effects.
*

*>
*

*> Just was wondering if anyone has done any
*

*> research into correlating pure theory
*

*> versus reality.
*

*>
*

*> - Doug McKean
*

*>
*

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**Next message:**Ray Anderson: "RE: [SI-LIST] : Upper limit of interplane capacitance"**Previous message:**Chan, Michael : "RE: [SI-LIST] : Upper limit of interplane capacitance"**Maybe in reply to:**Barry Ma: "[SI-LIST] : Upper limit of interplane capacitance"**Next in thread:**Ray Anderson: "RE: [SI-LIST] : Upper limit of interplane capacitance"

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