Immersion Cooling of Power Electronics in Segregated Hydrofluoroether Liquids Available to Purchase

Passive two-phase immersion cooling with dielectric liquids is a well established method of cooling thyristor type power semiconductors. However, the capabilities of this method for cooling high heat flux power semiconductor devices such as insulated gate bipolar transistors (IGBTs) have not been thoroughly explored. This work quantifies the junction-to-fluid thermal resistance of IGBTs soldered to boilers and immersed in the segregated hydrofluoroether liquid C₃F₇OCH₃, one of a class of new dielectric liquids with a low Global Warming Potential. The boilers were square copper heat spreaders with a microporous metallic boiling enhancement coating applied to the wetted surfaces. Bare 0.54cm² IGBT die were soldered to experimentally-optimized boilers and immersed in saturated C₃F₇OCH₃ liquid at atmospheric pressure. Boiler temperature measurements showed a peak boiler-to-fluid heat transfer coefficient of ∼14W/cm²-K at a die level heat flux of 255 W/cm². Direct junction temperature measurements yielded junction-to-fluid resistivities of 0.15°C/(W/cm²) at this heat flux and 0.20°C/(W/cm²) at 400 W/cm², the maximum heat flux studied. These results, coupled with published data for air cooled condensers, show that passive two-phase cooling of power modules may provide junction-to-ambient thermal resistances approximately 25% those of conventional air cooled modules and junction-to-fluid resistances 30%–50% of conventional liquid cooled modules, and similar to emerging direct substrate liquid cooling schemes.