Effect of viscoelastic behavior of EMC on predicting QFN fatigue life

Epoxy molding compounds (EMCs) are widely used in encapsulation of various semiconductor devices. QFN package has been widely accepted in electronic packaging industry in recent years due to due to its smaller dimension, excellent thermal and electrical performance. In this study, the tensile tests based on Dynamic Mechanical Analyzer (DMA) experiment are employed to investigate the viscoelastic behavior a commercial EMC material. FEM is used to analyze the effect of EMC viscoelasticity by EMC constant elastic and viscoelastic model based on generalized Maxwell model and WLF equation. The results show the difference of von Mises stress for EMC elastic and viscoelastic material models is not obvious while equivalent plastic strain reveals very significant difference. The predicted fatigue life of QFN package is underestimated about 45% if EMC is assumed to be elastic instead of viscoelastic. It is necessary to perform viscoelastic analysis during the prediction of fatigue life.