Here's a typical via ...
.035 dia pad top side
.040 dia pad bot side (for min. test via size)
.020 with a +.003/-.020 finished hole size
Regards, Doug McKean
At 04:41 PM 7/8/99 -0700, Fred Balistreri wrote:
>
>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.
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