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This work was focused on the influence of Ga on the thermal properties, microstructural evolution and interfacial morphology with aging treatment at 150°C of low-silver Sn-0.5Ag-0.7Cu (SAC) lead-free solder. The melting temperature of the SAC-Ga solder was decreased owing to the low melting point element Ga and the formations of intermetallic compound (IMC) and growth at the interfaces of SAC/Cu and SAC-0.5Ga/Cu were studied for different aging time ranging from 0 to 720 h. The results indicated that for both solders, the thickness of the IMC increased with aging time prolonging. However, compared with the interface of SAC/Cu, the thickness of the interface of SAC-Ga/Cu was obviously suppressed and the growing speed was slowed down, which may be attributed to the decreased activity of copper atoms by Ga addition, so that the SAC-Ga solder showed relatively planar-like IMC instead of scallop-like at the interface.

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The effect of trace amount of Ga on the inoxidizability and wettability of Sn-0.5Ag-0.7Cu-0.05Pr solders was investigated systematically by means of microstructure characterizations. The results indicate that the wettability and oxidation resistance properties are remarkably improved with addition of trace amount of Ga. Moreover, it is observed that the trace amount of Ga in Sn-0.5Ag-0.7Cu-0.05Pr solders refines the matrix microstructure. The relationship between wettability and oxidation resistance was put into deep study. And Ga was found to be enriched on the surface of the molten solder, which benefited the properties correspondingly. The results of this study can stimulate the use of low-silver Sn-Ag-Cu-Pr solders for various applications.