Re: [SI-LIST] : No buried/embedded capacitance?

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From: Larry Smith ([email protected])
Date: Fri Sep 22 2000 - 14:19:17 PDT

Doug - Here is a table of frequency, skin depth and resistivity in

        Freq depth resistivity
        (MHz) (mils) (mOhms/square)
        ------ ------ -------------
        1 1.4 0.49 (thickness of 1 oz copper)
        10 0.823 0.82
        100 0.262 2.59
        1000 0.082 8.25

The thing to notice is that at 100 MHz, the resistivity of the planes
is 5X what it was at DC. At 1 GHz, it is 16X. You have to use
spreading resistance concepts to convert resistivity to resistance.

I use a home grown plane simulator so it was free, except for the
number of hours (probably over 1000) that I have put into it. We have
been using it here at Sun for about 4 years. It is basically a matrix
of spice transmission lines that include the frequency dependent
effects from skin effect and dielectric loss. We mount our high
frequency capacitors on these plane models for simulation.

I will be presenting the power plane spice model together with model to
hardware correlation at the EPEP conference in Phoenix in October. We
feel that it is time to share this with the rest of the industry and it
will be in the public domain after that.

HP has some similar plane modeling tools with their MDS package.
Cadence will be releasing similar models with their Power Plane Builder
software under Spectra Quest.

Larry Smith
Sun Microsystems

> Delivered-To: [email protected]Eng.Sun.COM@fixme
> X-Sender: [email protected]
> Date: Fri, 22 Sep 2000 12:43:58 -0700
> To: Larry Smith <[email protected]>, [email protected]
> From: Doug Brooks <[email protected]>
> Subject: Re: [SI-LIST] : No buried/embedded capacitance?
> Mime-Version: 1.0
> >
> >
> >Another factor is skin effect. The planes are far more resistive at
> >100MHz and 1GHz than you have modeled. Only the skin of the copper
> >planes is conductive. This greatly reduces the Q and therefor the
> >peaks shown in the simulation.
> What (approximate) resistance value would be appropriate for planar
> capacitance in the several hundred MHz area?
> >Bottom line is that you need a plane simulator that accounts for the
> >distributed nature and the frequency dependent loss of the power planes
> >to do power distribution analysis above 100 MHz.
> Out of curiosity, what do plane simulators cost? Whose do you use?
> Doug Brooks
> .
> ************************************************************
> Doug Brooks' book "Electrical Engineering for the Non-Degreed
> Engineer" is now available. See our web site for details.
> .
> Doug Brooks, President [email protected]
> UltraCAD Design, Inc.

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