Abstract: Effect of nano-TiO₂ dopant on Cu₆Sn₅ IMC grain ripening growth in Sn-3.0Ag-0.5Cu-xTiO₂ solder joints during reflow process was investigated in this study. Flux-driven ripening (FDR) theoretical model is adopted to analyze the Cu₆Sn₅ IMC grain ripening growth mechanism. Results show that nano-TiO₂ dopant could alter both the morphology and size of Cu₆Sn₅ IMC grain. The size of Cu₆Sn₅ IMC grain in TiO₂-containg solder joints is smaller than that in TiO₂-free solder joints, and the Cu₆Sn₅ IMC grain in TiO₂-containg solder joints is more uniform and evenly distributed than those in TiO₂-free solder joints. The FDR theoretical model was well consistent with the experimental data. The growth exponents of Cu₆Sn₅ IMC grain in Sn-3.0Ag-0.5Cu-xTiO₂ solder joints are 0.346, 0.338, 0.332, and 0.342, respectively. This indicates that Cu₆Sn₅ IMC grain growth is controlled by atomic interdiffusion and grain maturity.