Generally, when the power module is operated at a high temperature, the reliability such as occurrence of lowering of the main bonding strength of the power module is significantly reduced due to thermal deformation. In this power module, the main components of the module are joined using eutectic solder with a solidus line above 350 °C. Copper-tungsten (CuW) was selected as the base plate material. Since the Coefficient of Thermal Expansion (CTE) values of CuW and SiN - AMC are close, it is possible to reduce the stress applied to these joints when the temperature changes. In addition, CuW has excellent thermal conductivity and heat capacity and suppresses heat generation of SiC-MOSFET.
To evaluate the performance of this module, a switching test at 100 A was performed at 250 °C. The switching waveform is shown in Fig.2. The turn-off switching time tf was about 10 ns, and the switching surge voltage at that time was about 150 V. The turn-off switching waveform was almost the same from room temperature to 250 °C. As a result, it was shown that this power module can operate at 250 °C and the built-in snubber circuit works effectively at all temperatures.
Acknowledgement
This work was supported by Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), "Next-generation power electronics / Consistent R&D of next-generation SiC power electronics" (funding agency: NEDO).