Processing and Warpage Evaluation of Package-on-Packages with Various Epoxy Molding Compounds

We fabricated the top packages of Package-on-Packages (PoPs) with various epoxy molding compounds (EMCs) and measured their warpage using the shadow moire method. The warpage was positive (crying shape) at room temperature due to the smaller coefficients of thermal expansion (CTEs) of the EMCs relative to that of the substrate at temperatures below the glass transition temperature T-g. With increasing heating cycle temperature, the warpage decreased and became negative (smiling shape) at approximately 100 degrees C, then increased toward positive (crying shape) with further increasing temperature, and finally reached its peak value at the solder reflow temperature of 260 degrees C. Such warpage variation behavior is closely related to the CTEs of the EMCs being larger than that of the substrate above T-g. Among the packages, the one molded with the EMCs exhibiting the lowest T-g and the largest CTE at temperatures above T-g exhibited the largest warpage at the solder reflow temperature of 260 degrees C.