Cooling of power electronics by integrating sintered Cu particle wick onto a direct-bond copper substrate

Power electronics devices can be limited in operation, and lifetime by the ability to remove heat and maintain low junction temperatures. A common architecture for power electronics devices is a circuit soldered onto a direct-bonded-copper (DBC) substrate, which is attached to a heat spreader or and heat sink. The removal of some of these interfaces and materials, however, can reduce the overall thermal resistance and allow for the devices to operate at much higher power levels. One approach to do this is to directly cool the backside of the DBC power substrate. By sintering copper particles to the DBC, evaporative cooling can be integrated into the architecture without the need for another bond. In this study heat fluxes up to 75 W/cm2 were applied through a test chip attached to a 15 mm x 17 mm DBC substrate with varying thicknesses of sintered copper particles on the backside. The copper porous layer was partially submerged into deionized (DI) water in order to allow for capillary wicking and evaporative cooling from the backside. Heat was dissipated through the thermal test chip, while the junction temperature was measured. The surface temperature of the porous copper layer was measured with a FLIR thermal camera. From this set-up the evaporative heat transfer coefficient (HTC) was computed and the thermal resistance calculated. The thermal resistance was found to be in good agreement with numerical models. Overall, the thermal resistance was reduced by about half when compared to the conventional packaging design.