Effects of service parameters on thermomechanical fatigue behaviors of new nano composite solder joints

Thermomechanical fatigue (TMF) resulted from the mismatch in the coefficient of thermal expansion (CTE) between solder and substrate would degrade the mechanical properties of solder joints during service. In this research, nano-structured polyhedral oligomeric silsesquioxane (POSS) reinforcing particles were incorporated into a promising lead-free solder, eutectic Sn-3.5Ag solder, by mechanically mixing to improve service reliability of the base solder matrix. Three different temperature profiles, with the same temperature extremes of -40degC to 125degC, different dwell times at temperature extremes and ramp rates, were applied in the tests. Microstructural characterization of surface damage and residual shear strength of these solder joints were carried out after 0, 100, 250, 500 and 1000 TMF cycles. Results obtained from this study were used to analyze the effect of service parameters on the TMF behaviors of the nano composite solder joints. Experimental results indicated that the nano composite solder joints exhibited better TMF performance than the eutectic Sn-Ag solder joint. It also proved that the nano composite solder joints that experienced longer dwell time and slower ramp rate exhibited less surface damage accumulation and less decrease in shear strength of solder joints.