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)Sn and AgSn compounds. (Cu, Ni)Sn 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)Sn IMC at the interface of microalloyed joint was observed and evolved into a larger scallop or layer-like duplex IMCs ((Cu, Ni)Sn + CuSn) 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 CuSn. The CuSn 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 μm·s, 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.