Modeling the influence of mold compound and temperature profile on board level reliability of single die QFN packages

Solder interconnect fatigue in Quad Flat No-Lead (QFN) electronic packages has been shown to be as sensitive to changes in mechanical properties of the mold compound as to the physical dimension of the package itself. In some scenarios, the combination of temperature profile and the mold compound properties can increase solder joint fatigue life. Finite element analysis (FEA) is used to investigate the limits at which the combination of intrinsic and extrinsic factors influences solder joint fatigue in QFN packages. Simulation results indicate increase in solder joint fatigue life for QFN packages with glass transition temperature (Tg) which is lower or within the thermal profile range. A Semi-analytical fatigue life model is developed with an empirical relationship to account for the ramp rate effect. Fatigue life predictions using both semi-analytical model and FEA indicate a similar trend in the influence of ramp rates of 1 °C/minute and below to be as damaging as those in standardized accelerated thermal cycling tests. Fatigue life predictions for several package dimensions and mold compound properties are compared with experimental results available in literature. The results of this study show the significance in interaction of temperature dependent mold compound properties and temperature profile in board level reliability of QFN packages and the ability to predict fatigue of solder interconnects using first order semi-empirical models.