Phase transformation and fracture behavior of Cu/In/Cu joints formed by solid–liquid interdiffusion bonding

In this paper, microstructure evolution and phase transformation of Cu–In intermetallic compounds in Cu/In/Cu joints formed by solid–liquid interdiffusion bonding at 260 and 360 °C were investigated respectively. The shearing properties and fracture behaviors of the Cu/In/Cu joints formed under different bonding conditions were also studied. For Cu/In/Cu joints bonded at 260 °C, Cu₁₁In₉ phase firstly generated and then Cu₂In phase formed between Cu₁₁In₉ layer and Cu substrate. For Cu/In/Cu joints bonded at 360 °C, Cu₂In phase firstly formed and then parts of Cu₂In grains transformed to Cu₇In₃ phase, and this transition from incomplete to complete coverage of Cu₂In/Cu₂In grain boundaries by Cu₇In₃ phases was observed with the bonding time increasing. The shear test results show that Cu₂In was high-quality phase which could improve the mechanical properties of Cu/In/Cu joints. After shear test, the fractures in Cu/In/Cu joints bonded at 260 °C were found at Cu₁₁In₉ layers and the fracture mode was cleavage fracture. In the case of the joints bonded at 360 °C, the intergranular fractures were found at the interface between Cu₂In layer and Cu₇In₃ layer while the cleavage fractures were found at Cu₇In₃ layer.