Thick Al wires bonded on chips of power semiconductor devices were examined for thermal cycle tests, then the bonded joints were cut using microtome method, after that those were observed by scanning electron microscope and analyzed by electron back scattered diffraction. Some cracks were observed between Al wires and the chips, unexpectedly the crack lengths were almost constant for -40/150 °C, -40/200 °C and -40/250 °C tests. It is considered that re-crystallization has been progressed during the high temperature side of the thermal cycle tests. Furthermore, joint samples were prepared using high temperature solders such as Zn-Al and Bi with CuAlMn, Direct Bonded Copper insulated substrates and Mo heatsinks. The fabricated samples were evaluated by scanning acoustic microscope before and after thermal cycle tests. Consequently, almost neither serious damages nor delaminations were observed for -40/200 °C and -40/250 °C tests.
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