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

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From: Kon, Hon Lee ([email protected])
Date: Wed Aug 23 2000 - 17:51:37 PDT

We do design high speed multilayer PCB of up to 16 layers and we normally
use 5mils as the core between the PWR and GND plane. We use multiple Vcc-GND
planes to provide multiple plane capacitance and interdigitated. However, we
have not tried using any dielectric thinner than 3mils as our PCB board
house advicing us not to use it because of leakage and potential shorts due
to the thin prepreg. Special material would have to be used similar to those
used in buried capacitance board which cost a lot more than normal PCB. - my
2cents

        Thank you.

        Regards�
        HL Kon
        Hardware Development Engineer
        iNTEL Test Tooling Operations Malaysia

���
-----Original Message-----
From: Ritchey Lee [mailto:[email protected]]
Sent: Wednesday, August 23, 2000 11:38 PM
To: Barry Ma
Cc: [email protected]; [email protected]
Subject: Re: [SI-LIST] : Decoupling capacitors (again!)

I design lots of high speed multilayer PCBs. I use 3 mils between power
planes to achieve maximum plane capacitance. You can do this reliably so
long as you do you stackup so that the dielectric between the power planes
is the prepreg material.

Lee

Barry Ma wrote:

> Larry,
>
> Thanks a lot for your great note! It is very helpful.
>
> You mentioned small spacing between pwr and gnd planes in the PCB a couple
of times in the discussion. I'd like to add my 2 cents.
>
> In addition to enough capacitance between pwr and gnd planes for high
frequencies noise to go through, the small spacing also makes it possible
for limited decoupling capacitors to be shared by different gates. This is
another important reason why much less numbers of decap can practically work
than calculated numbers.
>
> You suggested 5 mil or so spacing, Prof. Todd Hubing asked for at least <
10 mil. Is there any articles giving quantitative description about the
criteria?
>
> Thanks.
> Best Regards,
> Barry Ma <[email protected]>
> ANRITSU www.anritsu.com
> Morgan Hill, CA 95037
> Tel. 408-778-2000 x 4465
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