[SI-LIST] Re: How calculate the capacitance between via and plane

Zhangkun Wrote:

 > Hi all
 >
 > I meet one problem and need to calculate the capacitance between via and
> plane. Please give me some advice......
 >
 > Best Regards
 > Zhangkun
 >

 Hi  Zhangkun,

 Howard  W. Johnson and Martin Graham, "High-Speed Digital Design A Handbook
of Black Magic" on Page 257 offer following formula for determining the via
parasitic capacitance to ground:

 C = (1.41 * Er * T * D1)/(D2 - D1)

 Where,

 Er is relative dielectric constant of substrate.
 T is  PCB thickness.
 D1 is  diameter of the via pad.
 D2 is antipad diameter in ground plane(s).

 The accuracy of above formula is within an order of magnitude and
 when  D2, D1 and T are in inches C is in pico Farads.

 If you like to investigate via capacitance using a
 field solver for higher accuracy, I suggest FastCap.
 It is a public domain software obtainable at:

 http://www.fastfieldsolvers.com


 FastCap requires some effort to learn, but there are
 excellent literature and examples available which facilitate
 learning.

 Best Regards,

 Abe Riazi
 ServerWorks



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