L=5.08h[ln{4h/d)+1] Unit: nH

ln –> natural logarithm

h — > via length (PCB thickness) Unit: inch

d — > via diameter in inches Unit: inchL=5.08h[ln{4h/d)+1] Unit: nH

ln –> natural logarithm

h — > via length (PCB thickness) Unit: inch

d — > via diameter in inches Unit: inch

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We manufacture 3Gb/s PCB assemblies for broadcast TV. As we rely on a via to connect ICs to power and ground planes, series inductance is of high concern. Typically our PCBs have 1 or 2 power planes at the center with each pwr plane .002″ or .003″ away from a gnd plane. PCB thickness .09. As the power via passes thru the PCB, it will pass thru at least 3 gnd planes, with 0.008 clearance. Will the gnd planes affect the VIA inductance? What is the effect?

For a VIA with 0.020 finished hole, 0.043 long, I calculated 0.493 Nh. Is the VIA inductance really that high?

I believe it is ballpark correct.

If I run a formal 3D analysis tool like Ansoft Q3D, I get 0.37nH for a via which comes out as 0.64nH using the formula here.

Maybe you should use the non-finished size (i.e., the drill size) for the diameter, by the way. It’s probably about 21 or 22 mils. That will reduce the inductance slightly.

I don’t know if the GND planes affect Lseries much. I’d have to do some simulations in Ansoft Q3D to see.

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