Abstract: In order to solve the coarsening problem of reinforcing particles in fabrication of traditional composite solders and enhance the properties of lead-free composite solders, the eutectic Sn-3.5Ag and Sn-3.0Ag-0.5Cu were selected as solder matrix, and three different nano-sized polyhedral oligomeric silsesquioxane(POSS) particulates were used as reinforcing particles to form composite solders. The spreadability properties, mechanical performance, and creep rupture lives of solder matrix and their new composite solders with different mass fractions were studied. The experimental results indicate that the new composite solders and their joints show better wettability, mechanical properties, as well as longer creep rupture lives than those of the solder matrix. Besides, Sn-Ag-Cu composite solder joints exhibit better properties compared with Sn-Ag composite solder joints.