Forced Fluorinated Liquid Cooling for Medium Voltage SiC Power Modules: Concurrently Addressing Electrical and Thermal Challenges

Enhanced insulation and superior thermal characteristics are crucial in advanced packaging for medium voltage (MV) silicon carbide (SiC) power modules. Nonetheless, the reduction in thermal resistance typically compromises insulation level due to the decreased number of insulation layers. In this paper, the forced fluorinated liquid cooling is proposed, whereby fluorinated liquid (3M FC-40) is directed into the power module, substituting silicone gel and diminishing thermal resistance. Through the utilization of forced fluorinated liquid cooling, a reduction of 21°C in junction temperature at full load is demonstrated in the experiment, compared to traditional water cooled power modules. Furthermore, there is a 35.6% reduction observed in the maximum temperature rise ΔT_j. As dissipation power is transferred from the topside of the chip to the fluorinated liquid, the possibility of unlimited stacking of direct bonded copper (DBC) is enabled to lower the electrical field, thereby facilitating insulation at the chip bottom side without any worries regarding heightened thermal resistance. Forced fluorinated liquid cooling resulted in a 39°C reduction in the double-stacked DBC power module. Moreover, partial discharge (PD) detection under square wave revealed that the DBC immersed in the fluorinated liquid remains free from PD at 10 kV, a significantly higher threshold than observed with silicone gel. A higher partial discharge inception voltage (PDIV) is anticipated for double-stacked DBC when immersed in 3M FC-40. Thus, the forced fluorinated liquid cooling can be considered a promising solution for the next generation of MV SiC power modules.