Abstract: Nano-sized polyhedral oligomeric silsesquioxane-TriSilanol cyclohexyl (POSS) particulates reinforced Sn-3.5Ag composite solder joint could improve mechanical reliability. The 3% fraction of POSS reinforcement is the best weight fraction. The welding characterization of POSS reinforcement in 3% POSS/Sn-Ag composite solder was analyzed through differential scanning calorimeter (DSC) analysis based on former experimental results in this paper. Results indicate that the welding temperature of 3% POSS/Sn-Ag composite solder is similar to that of Sn-3.5Ag eutectic solder, so 3% POSS/Sn-Ag composite solder has acceptable processing property. In addition, according to DSC analysis, 3% POSS/Sn-Ag composite solder has higher activation energy. It demonstrates that POSS reinforcements might be present in the Sn boundaries.