Microstructure evolution and mechanical properties of the In-Sn-20Cu composite particles TLP bonding solder joints

In this study, the Cu/In-Sn-20Cu/Cu solder joints were fabricated under the bonding temperature of 260 degrees C, bonding stress of 3 MPa and bonding time of 0.5-60 min by transient liquid phase bonding. The influence of bonding time on the microstructure evolution and the shear strength of the solder joints was investigated. The results indicated that the intermetallic compound in the interface reaction zone was Cu-3(In, Sn) phase, and its thickness was increased continuously with increasing bonding time. The scallop-type Cu-6(In, Sn)(5) phase was formed at the interface of Cu-3(In, Sn)/In-Sn-20Cu composite solder and then gradually grew to connect the island-type Cu-6(In, Sn)(5) phase which formed in the in situ reaction zone. The transformation of Cu-6(In, Sn)(5) phase to Cu-3(In, Sn) phase occurred in the in situ reaction zone after the bonding time reached 15 min. The shear strength of the Cu/In-Sn-20Cu/Cu solder joints was increased first and then decreased with increasing bonding time. The maximum shear strength was 26.54 MPa when the bonding time reached 15 min. The shear fracture mechanism of solder joints transited from brittle fracture to ductile-brittle mixed fracture with increasing bonding time.