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.