<![CDATA[This study examines how gamma radiation (0–50,000 Gy) affects SAC305 (Sn‑3.0Ag‑0.5Cu) solder. Solder joints were irradiated using a Co‑60 source. Structural changes were evaluated by X‑ray diffraction and microstructural evolution were observed with optical microscopy after etching. XRD of β‑Sn reflections indicates smaller crystallite size with dose, together with higher lattice strain and greater dislocation density, consistent with crystal‑level alteration under irradiation. Microstructure observations show coarsening of β‑Sn grains and thickening of the Cu₆Sn₅ intermetallic (IMC) layer at the Cu/solder interface as dose increases. These outcomes reveal a two‑scale response: nanoscale coherent domains refine due to defect formation and accumulation, while microscale grains grow and the IMC layer thickens due to radiation‑enhanced diffusion, which increases atomic mobility. Recognizing that the system involves different length scales helps resolve the apparent contradiction between the decreasing crystallite size and the increasing grain size. Practically, the combined increases in lattice strain, dislocation density, and IMC thickness may reduce reliability and fatigue life of SAC305 solder joints in high‑radiation environments such as space and nuclear applications]]>
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