Microstructural evolution of 96.5Sn-3.0Ag-0.5Cu (SAC305) solder joints induced by variation doses of gamma-irradiation

Sn-Ag-Cu-based solder alloys are extensively employed in electronic packaging applications, thus necessitating in-depth reliability studies in various environmental conditions. This study investigated the microstructural evolution characteristics of gamma-irradiated 96.5Sn3.0Ag0.5Cu (SAC305) solder joints under varied gamma doses. The findings in this study involved the primary phase beta Sn (β-Sn) and near eutectic phase distributions, intermetallic compound (IMC) layer thickness, and micro-crack occurrences. Therefore, notable phase formation changes in the β-Sn and near eutectic phase distributions occurred following the microstructure changes in the gamma-irradiated solder alloy. Although the SAC305 solder matrix did not demonstrate any new structural phases, the higher radiation exposures increased the β-Sn and Ag₃Sn peak intensities. Furthermore, the microstructure analysis presented a higher near eutectic phase percentage upon initial gamma radiation exposure from 5 to 15 Gy, gradually decreasing from 20 to 50 Gy. The IMC layer thickness was also positively correlated with the gamma doses, while the micro-cracks near the IMC layer-solder bulk interface were evident. Consequently, the microstructural evolution varied under different gamma radiation levels, demonstrating a profound correlation to the mechanical properties of the SAC305 solder joints.