Integrated Methodology for Warpage Prediction of IC packages

Warpage and residual stress are important issues in integrated circuit encapsulation, especially for thin plastic encapsulated packages. A comprehensive study was performed at material level, bi-material level and package level. It was found that the assumption of stress-free at curing temperature is challenged. The bi-material beam and lead quad flat package (LQFP) warp even at curing temperature and the residual stress exists due to chemical shrinkage. The chemical shrinkage must be considered or warpage cannot be predicted accurately by numerical modeling. Theoretical analysis and different warpage modeling methodologies are developed and compared. The results from theoretical analysis and temperature-independent model could not match well with experimental measurements because they don´t include effects of temperature dependence. Results from temperature-dependent model and viscoelastic model correlate well with experiments when chemical shrinkage is considered. Viscoelastic model is the best choice if detailed material characterization is available. It is the only method which can include both effects of temperature and time.