In Situ Observation of Small-Scale Deformation in a Lead-Free Solder Alloy

In situ observation of the local, small-scale deformation behavior of a Sn-Ag-Cu (SAC387) alloy under extremely small strain rates was realized using a custom-designed mechanical testing stage integrated with atomic force microscopy (AFM) and optical microscopy. Grain boundary sliding (GBS) hand in hand with grain boundary decohesion (GBD) is the dominant mechanism in the early stage of deformation (<8.0% local strain) while intragranular slip bands are observed in the large-strain regime for the dendritic microstructure at room temperature. The deformation mechanisms of SAC387 are discussed in detail with reference to its microstructural constituents and mechanical properties.