The effect of temperature gradient on interfacial Cu6Sn5 growth during thermal compression bonding
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The growth of Cu6Sn5 intermetallic compound (IMC) in Cu/Sn/Cu sandwich system is investigated by thermal compression bonding under a temperature gradient of 800 °C/cm at 400 °C on the hot end. The results show that the interfacial Cu6Sn5 layer shows symmetrical growth at both sides at initial stage, which means that the growth of the Cu6Sn5 layer is controlled by chemical potential gradient. The growth rate of interfacial Cu6Sn5 layer will gradually decrease with increasing Cu6Sn5 layer thickness, which means that the effect of chemical potential gradient on the growth of interfacial Cu6Sn5 layer is undermined and the effect of temperature gradient on the growth of interfacial Cu6Sn5 layer is enhanced. This is due to the fact that the Cu atoms migrate from hot end toward cold end during temperature gradient, the growth rate of Cu6Sn5 layer at cold end is faster than that at hot end. The consumption rate of Cu layer is 0.3 μm/s under temperature gradient of 800 °C/cm. By knowing the calculated consumption rate of Cu layer, the Cu layer thickness on SiC power device can be designed when evaluating the reliability of power device during thermal compression bonding.
This work is supported by the National Natural Science Foundation of China (51174069), National High Technology Research and Development Program (863 Program) of China (No. 2015AA033304).
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