Abnormal growth of intermetallic compounds in asymmetrical Cu/Sn/Ag couples

The current study revealed that the growth kinetics and the interfacial reaction of the Cu/Sn/Ag couples with different thickness solder. For the Cu/Sn/Ag couples, plate-type Ag₃Sn was firstly formed at the Sn/Cu interface rather than at the Sn/Ag interface for the Cu/Sn/Ag couple at the initial state of the reflow procedure when the solder thicknesses is 150 μm or 300 μm. Besides, the microstructure of the Cu/Sn interface was different from that of Ag/Sn interface for the Cu/Sn (300 μm)/Ag couple. With increasing reflow time to 60 s, plate-type Ag₃Sn was detected at Sn/Ag and Sn/Cu interfaces, and the columnar Cu₆Sn₅ grains were also observed at the Cu/Sn interface for the Ag/Sn (150 μm)/Cu couple under liquid-state condition. However, for the Cu/Sn(40 μm)/Ag couple, columnar Cu₆Sn₅ and plate-type Ag₃Sn were not observed, and few Cu-Sn IMC particles were observed in the solder even after long time aging. The growth kinetics of intermetallic compounds was also investigated for the Cu/Sn/Ag couples with different thickness solder.