Thermal vias
Rev. 2.11

Calculation of the maximum heat conduct of a plated via in a PCB.

In complex PBA designs too much heat is often generated which the PCB can have difficulty to handle. The heat has to be lead away, for example by a cooling flange. Sometimes it is appropriate to put the components on one side of the board and the cooling flange on the other. As the substrate of the board does not conduct heat so well a good solution is to put vias between the hot component and the cooling flange on the other side.

Most effective is to let the component have good thermal contact to the vias. If it is possible, let the component connect directly to the surface of the vias. Copper conducts heat 1000 times better than air.

The copper plate of small vias conducts most of the heat. Larger vias can be filled with appropriate material, which conduct the largest part of the heat.

The calculation below is based on the physical quantities and characteristics of the used materials. Tolerances and edge effects are not considered. The vias are assumed to be evenly cylindrical plated.

Thickness of the PCB: [mm]
Lamda for filling material, if any: [W/m*K]. (Example: [W/m*K])
Drill diameter of the via: [mm] (PCB thikness/Drill diameter <= 8)
Copper thickness in the via: [um] (Normally related to the PCB thikness.)
Vias per cm2:

Total thermical resistance: [K/W]
Corresponding Lamda value/cm2: [W/m*K]

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Last updated: 2008-06-17
Sören Nilsson