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 300h at 400°C, but 4h at 500°C. The Cu41Sn11 phase formed at 400°C consisted of columnar grains with an average width of 23.5μm, while the Cu41Sn11 phase formed at 500°C consisted columnar grains with an average width of 8.5μm. The average hardness and shear strength values of the Cu41Sn11 joints formed at 400°C were 432.5HV and 62MPa, while the joints formed at 500°C exhibited higher hardness and shear strength (451.5HV and 65MPa). Besides, the Cu41Sn11 joint was found to exhibit a combination of transgranular and intergranular fracture during shear test.