Integrated Reduced-Expansion Microchannel Cooling for SiC Power Modules

Rising demand for electrified equipment in next-gen naval systems is increasing the pressure on power systems to achieve high power densities. To improve modularity, scalability, and size, weight, and power (SWaP), the Office of Naval Research (ONR) has pursued the development of Power Electronic Building Blocks (PEBBs) for over 25 years. ONR is currently attempting to develop SiC-based DC-DC power converters with power densities of at least 100 kW/L. Attaining these power densities requires higher switching frequencies (>300 kHz) to reduce transformer size, which generates large switching losses in the SiC die: resultant die-level heat fluxes can exceed 1 kW/cm2, but cooling solutions must have minimal impact on SWaP. Given LRU requirements (<35 lbs), power conversion systems must be developed using a highly-integrated co-design process accounting for temperatures, magnetics, electrical parasitics, durability, and system interdynamics. To this end, Micro Cooling Concepts and the University of Arkansas have formed a team using thermal/electrical/mechanical co-design to demonstrate advanced, extremely compact, power conversion technology by developing advanced thermal management solutions which address the needs for both the specific PEBB used in the proposed DC-DC power converter, as well as general high-power semiconductor cooling applications.    The thermal management approach uses a reduced thermal expansion cold plate (baseplate) with integrated microchannel/microimpingement cooling to dissipate SiC power module heat fluxes in excess of 1 kW/cm2. Microchannel cooling has been shown to have extremely low thermal resistances at low pumping powers, and coolers have been exposed to 1000-hour lifetime tests with no significant change in flow or thermal performance. The cold plate is only 3 mm thick and replaces the existing baseplate of the power module, resulting in no net impact on the power converter volume. The baseline cooler material is MoCu, which has roughly half of the expansion of copper, significantly reducing thermal stresses and improving thermomechanical reliability. The overall objectives of the Phase II Base and Phase II Option programs are to: 1) demonstrate a 100 kW high frequency (300 – 500 kHz) power converter packaged in a 1 liter volume; and 2) to develop reduced-expansion cooled baseplates capable of removing waste heat fluxes of >1000 W/cm2, while maintaining SiC junction temperatures below 175 °C and minimizing the volume of the flow system.