Microstructure evolution and mechanical properties of Sn-Ag based composite solder joints during isothermal aging

The microstructure evolution and mechanical properties of Sn-3.5Ag and its new composite solder containing three different nano-sized polyhedral oligomeric silsesquioxanes (POSS) particulates with the best mass fractions during isothermal aging were studied. All of the above four solder joints were aged at three different temperatures (125℃，150℃，175℃) up to 1000 h and the intermetallic compound growth was measured. The interfacial layers between the solder and the copper substrate were examined using the optical and scanning electronic microscopy. The growth kinetics of intermetallic interfacial layers formed between the solder and the copper substrate was characterized. The growth rate of the intermetallic layers of the composite solders is slower than that of Sn-3.5Ag solder. The activation energies of the composite solders are 80，97 and 77kJ/mol, respectively，and are higher than those of Sn-3.5Ag solder. Besides，the shear strength of the composite solder joints is higher and not so sensitive to the different aging processes.