γ-ray irradiation, SnBi eutectic solder joints, Oxidation corrosion, Quasi-in-situ characterization, DFT calculation, Materials of engineering and construction. Mechanics of materials, TA401-492

As deep space exploration and extraterrestrial missions increase, the long-term radiation-induced deterioration of solder joint performance has become a critical factor limiting their long-term operational stability. This study employs quasi-in-situ characterization and first-principles calculations to investigates the microstructural evolution and oxidation behavior of SnBi eutectic solder joints under γ-ray irradiation. Sn oxides preferentially form at the Sn/Bi interface, and with prolonged irradiation, Sn and Bi oxides accumulate. After 200 h, the solder joint surface becomes fully covered by Sn oxides. Atomic vacancies induced by γ-ray irradiation enhance the adsorption of O2 molecules on the Sn and Bi surfaces and accelerates the oxidation process. Bi incorporation lowers the work function of the Sn-based solid solution than Bi-based solid solution, making Sn more susceptible to oxidation. Additionally, the low diffusion energy barrier of Sn atoms into SnO2 facilitates their continuous migration across the Sn/SnO2 interface and SnO2, thereby promoting the sustained thickening of the SnO2 oxide layer. The present results provide key insights into microstructural evolution and oxidation processes of the SnBi solder joints, supporting the development of more reliable solder materials for next-generation spaceborne electronic systems.