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Potential of Zn-Al solder alloy for high temperature SiC power module
Keywords: SiC, power module, Zn-Al solder alloy
We have studied shear strength and a crack growth of die bond layer made from ZnAl solder alloy to realize SiC power module operating at 250C. It is possible to realize a power module with small volume and with high power density by operating at high temperature. Towards high temperature operation, die bond layer is very important. We have reported a ZnAl solder alloy as die bond layer for SiC power module (1). Although it showed sufficient shear strength, but chip cracks were found occasionally since a relatively thin of die bond layer thickness of 10 to 20 micron. In order to improve the crack problem, we have tried to increase a thickness of die bond layer. The thickness of the die bond layer was controlled to 20 micron, 50 micron, and 100 micron by Zr balls. By applying this method, 3 mm square samples with die bond thickness of 50 micron were shown shear strength of 143 MPa. Since samples without Zr ball that had die bond layer of 10 to 20 micron showed shear strength of 150 MPa. This shows that Zr balls hardly affect to shear strength. We applied this method for die bonding process of 6 mm square chips. In order to observe cracks, scanning acoustic tomograph was carried out. Both chip and die bond layer showed no cracks not only after die bonding process but also after 1000 cycle of thermal cycle test between -40C and +250C. This indicates that stress is relaxed by increasing the thickness of the die bond layer. We will use ZnAl solder alloy to fabricate SiC power module.
Hiroshi Sato, Team Leader
National Institute of Advanced Industrial Science and Technology(AIST)
Tsukuba, Ibaraki

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