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PCB Via Calculator March 12, 2006

This Javascript web calculator calculates the resistance, voltage drop, and power loss of printed circuit board vias. Note that vias are made out of plated copper which typically has a resistivity of 1.7E-6 to 2.2E-6 Ohm-cm. The calculator has an input box for the resistivity which defaults to 1.9E-6 Ohm-cm.

May 22, 2006 - Added thermal resistance calculation.
January 19, 2007 - Minor Clarifications.
March 28, 2007 - Updated resistivity. See comment 12.
June 21, 2007 - Added estimated ampacity. See comment 17.


Finished Hole Dia
Plating Thickness
Via Length

Optional Inputs:

Applied Current Amps
Plating Resistivity Ohm-cm

Electrical Results:

Resistance Ohms
Voltage Drop Volts
Power Loss Watts
Estimated Ampacity Amps

Thermal Results:

Thermal Resistance Deg. C/Watt

Resistance = Resistivity*Length/Area
Area = pi*(Inner_dia + Plating_thk)*Plating_thk
Resistivity = 1.9E-6 Ohm-cm (plated copper)
(plated copper is much more resistive than pure copper)
Copper Thermal_Resistivity = 0.249 cm-K/W (at 300K)
Est_Ampacity [Amps] = k*(Temp_Rise [deg C])^b*(Area [mils^2])^c
For IPC-2221 external layers: k = 0.048, b = 0.44, c = 0.725

[1] "Constructing Your Power Supply - Layout Considerations", by Robert Kollman
[2] "Current Carrying Capacity of Vias", by Doug Brooks and Dave Graves

Calculator Wish List March 3, 2006

If there is a calculator that you feel would be a good addition to this site, please add it to the comment section of this post and we’ll do what we can to implement them.