Thermal Performance Evaluation of a Two-Layer Wick Vapor Chamber for High Heat Flux Dissipation by Air Cooling

Abstract

Silicon carbide (SiC) semiconductors have been identified to have potential to replace silicon devices due to superior electrical and thermal properties for a range of power conversion applications. For electrified vehicle applications, the device configuration leads to high current rates, and this in turn leads to high heat fluxes (~1 kW/cm2) over large bare dies (~1 cm2). SiC devices are capable of operating at higher junction temperatures than Si devices, which warrants revisiting air-cooling solutions that are more simple and reliable than liquid cooling. To enable air cooling for high heat flux dissipation, transformative heat spreading technologies must be developed to increase the heat sink footprint area considering the relatively low heat transfer coefficients available. An advanced vapor chamber technology is being investigated for spreading the high heat fluxes generated by next-generation wide band-gap power devices. For vapor chamber heat spreaders to operate at very high heat fluxes over large areas, the internal wick layer at the evaporator must simultaneously minimize the device temperature rise and the flow resistance to liquid resupply by capillary action during boiling. In this study, a vapor chamber is investigated having an embedded two-layer evaporator wick designed to decouple the functions of liquid resupply (through a cap layer) and capillary-fed boiling heat transfer (within a base layer). The performance of a 50 mm × 50 mm × 5.5 mm vapor chamber with an embedded two-layer evaporator wick is evaluated as the heat spreader under a straight pin fin heat sink cooled via air jet impingement for a 1 cm2 area heat source. The maximum dryout heat flux and thermal resistance are compared with that of a vapor chamber having a traditional monolayer evaporator wick. At a power dissipation of ~500 W, the air-cooled two-layer wick vapor chamber provides a 12% reduction in the thermal resistance compared to the monolayer wick vapor chamber assembly. The results indicate that the design of the evaporator wick of the vapor chamber plays a critical role in determining the overall thermal resistance of the heat sink plus spreader assembly.