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[SOLVED] What is Via impedance?

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mmitchell

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Hi,

When using Saturn PCB Toolkit to calculate Via parameters, I see an item “Via Impedance” which is tens of thousands times larger than Via’s DC resistance.

SaturnPCB_via_impedance.png

For example, when Via DC Resistance is only 0.00132Ω, the “Via Impedance” is 57.429Ω, 43506.8 times of Via DC Resistance.

Is it the characteristic impedance of Via which is defined as the resistance per unit length? Does anyone know its exact formula?


Matt
 

Inductance is not directly related to the DC resistance, a low dc resistance will not always indicate a low impedance, and for ac signals either the capacitive or inductive reactance will dominate except where the the inductance and capacitance cancel out at the resonant frequency.
To calculate the parameters correctly you require a full 3D field solver, ther is no simple foruma, the Saturn gives a close enough approximation, and unless going into the gigahertz, a via has very little effect on signal integrity.
 
thunderdantheman,

That is a good article, thanks for recommendation.


marce,

Thanks for your comment on calculation methods. I believe Saturn is good enough for me.


Matt
 

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