Thermal vias

Heat dissipation through metallised holes

Thermal vias are mechanically drilled through-hole-contacts from TOP to BOTTOM. The vias are ideally placed directly under the components and are exclusively provided for heat dissipation. As a rule, these through-hole-contacts should be specified with an increased copper layer thickness in the barrel (at least 25 µm). This further improves the heat dissipation through the circuit board. An optimum final diameter is 0.30 mm and the ideal distance from hole to hole (pitch) is
0.80 mm. Other diameters are possible for thermal vias. To ensure that the components are securely soldered on to these via areas, the through-hole-contacts should be filled with resin and covered with copper (“filled and capped vias”). Thanks to the filling and capping, the solder surface is completely sealed and solder outflow is prevented. Filled and capped thermal vias are used in circuit board applications which are thicker than 0.7 mm.

The good vertical heat conduction through thermal vias in the Z–axis is especially important to allow a lateral distribution over large areas of the circuit board. These large areas are essential for creating a high potential difference between the heat source and the heat sink and thus ensuring high vertical heat transfer through thermally less conductive materials, such as pre-pregs or cores.

Microvias in combination with buried vias

For complex constructions (multilayers), the combination of microvias (vias drilled by laser) for the exterior layers and buried vias (mechanically drilled vias) for the inner layer is a further option for efficient heat dissipation by circuit boards. As a result of this, the copper content of the circuit board underneath the power components is increased once again. The use of microvias also guarantees good solderability.