Re: [SI-LIST] : via capacitance

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From: apanella (apanella@enteract.com)
Date: Mon Apr 10 2000 - 20:46:40 PDT


Is this 0.3 pF Assuming that there isn't a current return path (ground) via
near by?

If there is a return path (ground) via near by... one might want to know
the pitch between the vias before using the 0.3 pF value.

For example.. like the vias you might have for the through hole tails of a
connector.. when using the connector to connect two PCBs.

Best Regards,
_gus
apanella@enteract.com

----- Original Message -----
From: Ritchey Lee <leeritchey@earthlink.net>
To: <si-list@silab.eng.sun.com>
Sent: Monday, April 10, 2000 9:15 AM
Subject: Re: [SI-LIST] : via capacitance

> I have done many experiments to determine the capacitance value of vias.
A 13 mil diameter via, 100 mils long has approximately .3 pF of capacitance.
Your traces will average about 3 pF per inch of
> length. The small value of the via capacitance will not be detectable at
edge rates slower than 100 pSEc.
>
> Lee
>
> Sunil Kumar wrote:
>
> > Dear all SI experts.
> >
> > I am using a multilayer board having the following stack-up:
> >
> > LAYER1 TOP LAYER (CONDUCTOR)
> > LAYER2 GND
> > LAYER3 CONDUCTOR
> > LAYER4 CONDUCTOR
> > LAYER5 VCC
> > LAYER6 GND
> > LAYER7 CONDUCTOR
> > LAYER8 CONDUCTOR
> > LAYER9 GND
> > LAYER10 BOTTOM LAYER (CONDUCTOR)
> >
> > A signal trace is going from layer7 to layer8. A through-hole via is
used.
> > The via is having pads on layers 1,7,8,10. There are antipads on the
power
> > planes. Is there any formula/tools to calculate the exact capacitance of
> > the via?? How can I measure it in the board??
> >
> > Sunil Kumar
> > Research Engineer
> > C-DOT
> > INDIA
> >
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