## 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.

Updates:

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.

**Inputs:
**

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 |

**Notes:
**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

**References:**

[1] "Constructing Your Power Supply - Layout Considerations", by Robert Kollman

http://focus.ti.com/lit/ml/slup230/slup230.pdf

[2] "Current Carrying Capacity of Vias", by Doug Brooks and Dave Graves

http://www.ultracad.com/articles/viacurrents.pdf

## 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 weâ€™ll do what we can to implement them.