The Effect of Thermal Cycling Cycles on the Microstructure and Properties of Cu/In-48Sn-xGNSs/Cu Solder Joints

This study investigates Cu/In-48Sn/Cu and Cu/In-48Sn-0.05GNSs/Cu solder joints, systematically examining the effects of thermal cycles (200, 400, 600, 800, and 1000 cycles) on the microstructure, shear properties, and shear fracture morphology of the joints. The results indicate that as the number of thermal cycles increases, the microstructure of the joints formed by both composite solder alloys gradually coarsens, the thickness of the interfacial intermetallic compounds (IMCs) gradually increases, and the shear strength exhibits a monotonically decreasing trend. During thermal cycling, the grain size of the γ-InSn₄ phase in the In-48Sn solder joints increased from 10.4 μm to 28.6 μm, the IMC thickness increased from 3.639 μm to 5.462 μm, and the shear strength decreased from 7.9 MPa to 3.1 MPa; After adding 0.05 wt.% graphene, the grain size of the γ-InSn₄ phase increased only from 4.1 μm to 13.8 μm, the IMC thickness increased from 3.174 μm to 4.915 μm, and the shear strength decreased from 16.9 MPa to 12.7 MPa. It was concluded that, under the same thermal cycling conditions, both the grain coarsening rate and the intermetallic compound (IMC) growth rate of the In-48Sn-0.05GNS composite solder joints were significantly lower than those of the In-48Sn joints, while still maintaining high shear strength. Analysis of the shear fracture surface morphology revealed that the fracture mechanism of the In-48Sn composite solder joints shifted from ductile fracture to brittle fracture, while that of the In-48Sn-0.05GNS composite solder joints gradually shifted from ductile fracture to a ductile-brittle mixed fracture.