Warpage Variation Analysis and Model Prediction for Molded Packages

Mechanical simulation model is an effective way to analyze warpage of electronic packages. To establish a reliable numerical model, simulation results are usually calibrated by warpage measurement results. In general, the measured warpage data are collected through averaging the warpage of several samples. Some categories of electronic packages show relatively stable warpage behavior so that the average warpage can eliminate the measurement error. However, in this study, it was observed that samples at different locations of substrate displayed quite different warpage values and shapes, which means the average warpage cannot represent the actual deformation situation. The warpage variation and location dependency were attributed to the shrinkage impact of epoxy molding compound. Therefore, molding shrinkage needs to be considered in simulation models to better predict molded packages. In this work, the molded packages are simulated during reflow profile. The effective strain of molding material, consisting of chemical shrinkage and cooling strain at gel point, is calculated and included in numerical model. By employing different chemical shrinkage strains from different directions, the warpage variation curve was accurately described and simulated by numerical model.