The fast formation of full Cu3Sn solder joints in Cu/Sn/Cu system by thermal gradient bonding
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To form full intermetallic compounds (IMCs) solder joints becomes widely available for the die bonding of the third generation semiconductor power devices. The fast formation of Cu3Sn in Cu/Sn(10 µm)/Cu solder joints were investigated by thermal compression bonding in a few seconds and under a low pressure of 0.1 MPa at ambient temperature. The results show that the temperature gradient produced by thermal compression bonding contributes to enhancing the interfacial reaction at the liquid Sn/solid Cu metallization interface. The scallop-liked Cu6Sn5 is formed while planar-liked Cu3Sn is formed between Cu and Cu6Sn5 at initial bonding stage. After that, the growth rate of scallop-liked Cu6Sn5 layer from cold end is faster than that from hot end and the thin planar-liked Cu3Sn layer becomes thick. This abnormal growth behavior of Cu6Sn5 is due to the fact that Cu atoms migrate from hot end to cold end by temperature gradient. The middle Sn layer is completely consumed with increasing bonding time. Cu6Sn5 and Cu3Sn are consisted of the solder joints and the planar-liked Cu3Sn grows with a transition to scallop-liked morphology until the full Cu3Sn solder joint is eventually formed, which indicates that the formation time of full IMCs solder joints can be narrowed by temperature gradient. This bonding process provides a new solution for the rapid acquisition of interconnect material for the third generation semiconductor power devices.
This work is supported by the National Natural Science Foundation of China (51174069) and National High Technology Research and Development Program (863 Program) of China (No. 2015AA033304).
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