Microstructure evolution, IMC growth, and microhardness of Cu, Ni, Ag-microalloyed Sn–5Sb/Cu solder joints under isothermal aging

In this work, various Cu, Ni, Ag-microalloyed Sn–5Sb/Cu joints, ordinary Sn–5Sb/Cu joints, and low-melting-point Sn–3Ag–0.5Cu (SAC305)/Cu (used for comparison) were prepared, focusing on the influence of Cu, Ni, and Ag on the microstructure evolution, interfacial IMC growth, and microhardness of Sn–5Sb/Cu joint under long-time isothermal aging process. Results showed that the microstructure of microalloyed joints consisted of β-Sn matrix, SbSn, and (Cu, Ni)(6)Sn(5) and Ag(3)Sn compounds. (Cu, Ni)(6)Sn(5) compounds generated a coarsening effect in the aging microalloyed joints, yet its coarsening speed is significantly lower than the ordinary Sn–5Sb/Cu. Meanwhile, the total IMC layer thickness increased with the rising aging time. A single fine dendritic (Cu, Ni)(6)Sn(5) IMC at the interface of microalloyed joint was observed and evolved into a larger scallop or layer-like duplex IMCs ((Cu, Ni)(6)Sn(5) + Cu(3)Sn) after the aging. Considering the combined effect of Cu, Ni, and Ag, the microalloyed joints exhibited the improved microstructure relative to ordinary counterparts and low-melting-point SAC305 materials, significantly inhibiting the interfacial IMC growth, especially Cu(3)Sn. The Cu(3)Sn IMC thickness and diffusion coefficient in the Sn–5Sb–0.5Cu–0.1Ni–0.5Ag/Cu joint were 0.71–2.81 μm and 0.96 × 10(–6) μm·s(−2), respectively. Besides, the precipitation strengthening mechanism triggered by the microalloyed elements was extremely obvious and the soldering and aging joints revealed superior microhardness values of 20–35 HV. This could effectively improve the application range of Sn–5Sb-based materials in higher-temperature package conditions such as third-generation semiconductors.