Re: [SI-LIST] : Via Capacitances ...

Fred Balistreri (fred@apsimtech.com)
Thu, 08 Jul 1999 16:41:14 -0700

Douglas McKean wrote:
>
> Could someone give rough estimate
> of via capacitance?
>
> I'm thinking the orientation of the traces
> connected to the via have a major impact.
>
> For instance, an .062 board with a via
> from one side to the other, different
> capacitances would be had with the two
> following constructions ...
>
> I. Top Trace
> -------------
> |via
> -------------
> Bottom Trace
>
> II. Top Trace
> -------------
> |via
> -------------
> Bottom Trace
>
> Ideas? Comments?
>
> Regards, Doug McKean
>
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Hello Doug, more information is needed. The capacitance comes from
two different physical entities of the via. The most contributing factor
is the via pad(s) size. Less important but can also be calculated is
the capacitance of the barrel. If the via goes through any ground or
vcc planes the clearance needs to be known, as this influences the
capacitance calculation as well. One also needs to know the stackup
of the board. That is to say we need to know how far the gnd or vcc
planes are from the various via pads. Once the structure is known then
capacitance can be calculated pretty accurately. If you give me the
various dimentions I can calculate the particular example for you.

Best Regards,

-- 
Fred Balistreri
fred@apsimtech.com

http://www.apsimtech.com

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