RE: [SI-LIST] : Decoupling capacitors (again!)

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From: Istvan Novak - Board Design Technology (inovak@pompom.east.sun.com)
Date: Thu Aug 17 2000 - 16:09:19 PDT


Larry,

If my math is correct, 0.02 ohms at 200MHz represents about 15pH of inductance. Not
easy, but today we can measure such low values with vector network analyzers. With
two-port measurements, the limit is really due to the probe configuration and
connection. With nothing fancy, you can go down to a few picohenrys with the residual
inductance.

Regards

Istvan Novak
SUN Microsystems

        X-Unix-From: ldmiller@nortelnetworks.com Thu Aug 17 17:34:42 2000
        From: "Larry Miller" <ldmiller@nortelnetworks.com>
        To: Martin J Thompson <Martin.J.Thompson@trw.com>, si-list
<si-list@silab.eng.sun.com>
        Subject: RE: [SI-LIST] : Decoupling capacitors (again!)
        Date: Thu, 17 Aug 2000 13:51:49 -0700
        MIME-Version: 1.0
        
        Twenty milli-ohms. 0.02 ohm. At 100 MHz. How does one measure such a
        curiosity?
        
        Thanks,
        
        Larry Miller
        (Not the other Larry)
        
> -----Original Message-----
> From: Martin J Thompson [SMTP:Martin.J.Thompson@trw.com]
> Sent: Wednesday, August 16, 2000 11:58 PM
> To: si-list
> Subject: RE: [SI-LIST] : Decoupling capacitors (again!)
>
> Larry, another question on buried capacitance...
> What is it about Hadco's material that allows you to get 2mils separation?
> Can this not be achieved with straight FR-4?
>
> Thanks,
> Martin
>
> <snipped for context>
> >>> Larry Smith <Larry.Smith@Eng.Sun.COM> 16 August 2000 23:55:52 >>>
> It turns out that the spreading inductance of power planes
> spaced 4 mils apart will give you roughly 20 mOhms at 100 MHz. We are
> using Hadco 'buried capacitance' planes that are 2 mils apart in many
> of our products to get lower impedance.
>
>
>
>
> TRW Automotive Advanced Product Development,
> Stratford Road, Solihull, B90 4GW. UK
> Tel: +44 (0)121-627-3569
> mailto:martin.j.thompson@trw.com
>
>
>
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Istvan Novak Sun Microsystems, Inc.
Istvan.Novak@Sun.Com Workgroup Servers, BDT Group,
                        One Network Drive, Burlington, MA 01803
                        Phone: (781) 442 0340

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