Microstructure evolution, grain morphology variation and mechanical property change of Cu-Sn intermetallic joints subjected to high-temperature aging

In this work, the aging treatment was carried out on full Cu₃Sn joints at different temperatures for various durations, the microstructure evolution, grain morphology variation and mechanical property change of joints were investigated. The temperature effects on the growth rate and grain morphology of Cu₄₁Sn₁₁ phase were found: The complete transformation from Cu₃Sn phase to Cu₄₁Sn₁₁ phase in joints needed 300 h at 400 °C, but 4 h at 500 °C. The Cu₄₁Sn₁₁ phase formed at 400 °C consisted of columnar grains with an average width of 23.5 μm, while the Cu₄₁Sn₁₁ phase formed at 500 °C consisted columnar grains with an average width of 8.5 μm. The average hardness and shear strength values of the Cu₄₁Sn₁₁ joints formed at 400 °C were 432.5 HV and 62 MPa, while the joints formed at 500 °C exhibited higher hardness and shear strength (451.5 HV and 65 MPa). Besides, the Cu₄₁Sn₁₁ joint was found to exhibit a combination of transgranular and intergranular fracture during shear test.