Scaling effect on Ag3Sn growth behaviours in micro-joints for flip chip assemblies

ABSTRACTThe scaling effect on Ag3Sn growth behaviours in Sn–3.0Ag–0.5Cu (SAC305) micro-joints of flip chip assemblies was investigated using thermal shock (TS) tests. After assembly reflow, the large plate-like Ag3Sn compounds only emerged from the Cu interface of small joints, which was strongly related with a higher local Ag concentration in the remaining solder. During TS cycling, the growth of Ag3Sn grains exhibited comparatively more pronounced growth in the solder matrix of small joints, due to the stronger strain-enhanced coarsening induced by more cycle stress and strain. Coarsening kinetic models based on TS experiments were employed to predict Ag3Sn growth, the kinetic constants N were determined to clarify the correlation of the joints scaling and Ag3Sn coarsening in depth.