Dopamine polymerization reaction and hydrothermal method were used to prepare nickel coated Al₂O₃ reinforcement phase (Ni/Al₂O₃). Ni/Al₂O₃ reinforced Sn1.0Ag0.5Cu (SAC105) composite solder was prepared using traditional casting method. The result shows that the nickel coating layer is continuous with uneven thickness. The interface between nickel and aluminum oxide exhibits a metallurgical bonding with coherent interface relationship. The strength, toughness and wettability of the SAC105 solder on the substrate are improved, while the conductivity is not decreased significantly. The fracture mode of composites transitions from a mixed toughness-brittleness mode to a purely toughness-dominated mode, characterized by many dimples. The prepared composite brazing material was made into solder paste for copper plate lap joint experiments. The maximum shear strength is achieved when the doping amount was 0.3wt%. The growth index of intermetallic compound at the brazing interface of Ni/Al₂O₃ reinforced SAC105 composite solder is linearly fitted to n=0.39, demonstrating that the growth of intermetallic compound at the interface is a combined effect of grain boundary diffusion and bulk diffusion.