The growth of interfacial intermetallic compounds (IMC) and mechanical properties by the widely used Au-Sn solder jointed Cu pillar are studied in this paper. Three concentrations of Sn (15%, 20%, and 25%) are employed to investigate the evolution of IMC growth and mechanical properties. It is found that the initial IMC growth is linear growth and surface reaction domination at the reflow step, as both Au and Sn directly react with Cu to form scallop-like (Au,Cu)Sn. Following the initial growth, IMC gradually becomes thicker, which inhibits Au/Sn penetrating into IMC to react with Cu, thus, at this stage, AuCu instead of (Au,Cu)Sn, forms the IMC and the inter-diffusion of parabolic growth dominates. By increasing HTS time, AuCu3 grows by consuming the AuCu compound. Moreover, the AuSn eutectic precipitations gradually decreased, which resulted in reduced hardness. Ductile fractures appeared among all the samples, and the appropriate IMC thickness improved the adhesion ability of the Au-Sn solder on the Cu pillar.
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