Double-Sided Liquid Cooling of a 1.2 kV SiC Three- Phase Traction Inverter Power Stage

To enhance the thermal management of wide-bandgap power semiconductor devices, double-side cooled (DSC) module packaging has been extensively studied. This approach enables higher power density with fewer devices, reducing overall system costs. However, its implementation is constrained by the thermal resistance of conventional liquid cooling, where multiple material layers introduce thermal barriers between the device junction and the cooling medium. Among these, thermal interface materials—used to enhance contact between module substrates and heat sinks—are typically the most resistive. Direct cooling of the outer faces of module substrates eliminates the need for separate cold plates, heat sinks, and low-conductivity thermal interface materials. To explore this concept, a three-phase traction inverter power stage with direct fluid cooling was designed and fabricated, guided by thermal and fluid dynamic simulations. The design featured double-side cooled 1.2 kV SiC phase-leg modules in a sandwich structure, where each MOSFET’s drain was sintered to a SÍ3N4 active metal brazed (AMB) substrate. The module halves were joined using porous silver inter-posts, bridging the device source pads to corresponding pads on the opposite substrate. Three modules were assembled into a cooling manifold, forming a three-phase traction inverter power stage. The manifold consisted of open-face channels that ensured approximately equal water flow across all six cooling faces of the three modules. Heat flux was introduced by controlling each MOSFET’s drain-to-source current (I&) via a gate-source voltage (Vgs) in the ohmic region, allowing precise power dissipation measurements. Pressure drop, average water temperature, and device temperature—estimated via thermistor readings—were recorded for flow rates ranging from 3 to 5 liters per minute through the manifold.