Heatsink design for direct double-sided liquid cooling of SiC power semiconductors

This article deals with direct double sided liquid cooling and especially the sealing at the surface of the semiconductor considering the limited available space for a power class above 100kW. Several parameters must be taken into account for the seal.

The cooling surface of the power semiconductor should be used as efficiently is possible. It is important to decide whether to seal on the cooling surface or next to it on the mold compound. The advantages and disadvantages with regard to the resulting thermal heat transfer and functional reliability are considered.

Another challenge with a smaller size of the semiconductor is the distance between the cooling surface and the power pins. Liquid based heat sinks are usually made of aluminum to ensure better heat transfer.

Furthermore, they have higher mechanical strength and are watertight. Since aluminum is electrically conductive, the air and creepage path to the power pins must be maintained.

The largest possible cooling surface and the required air and creepage path leads to very little space available for the seal. Therefore, the use of a thin gasket is necessary, which is why the tolerances between the cooling surfaces of the semiconductor and the sealing surfaces of the heat sink must be kept low.

Different designs are compared and evaluated by means of FEM simulation and experimental setups. As a result a possible design for heatsink and gasket according to all electrical and mechanichal compliances is determined.