Nano-sized, nonreacting, noncoarsening SrTiO₃ particles have been incorporated into Sn–3.0wt% Ag–0.5wt% Cu solder alloys and the interfacial microstructure and the shear strength on Au/Ni metallized Cu pads ball grid array substrates investigated as a function of the number of reflow cycles and aging time. At their interfaces, a scallop-shaped ternary Sn–Ni–Cu intermetallic compound layer was found in both plain Sn–Ag–Cu solder joints and solder joints containing SrTiO₃ nano-particles, and the intermetallic compound layer thickness increased with the number of reflow cycles and aging time. After the addition of SrTiO₃ nano-particles, in the solder ball region, a fine microstructure of AuSn₄, Ag₃Sn, Cu₆Sn₅ intermetallic compounds appeared in the β-Sn matrix. In addition, the shear strength of solder joints containing SrTiO₃ nano-particles exhibited a consistently higher value than that of plain Sn–Ag–Cu solder joints due to a second phase dispersion strengthening mechanism as well as a refinement of the intermetallic compounds. The fracture surface of plain Sn–Ag–Cu solder joints exhibited a brittle fracture mode with a smooth surface while Sn–Ag–Cu solder joints containing SrTiO₃ nano-particles showed ductile failure characteristics with rough dimpled surfaces.