PREDICTED BOW OF PLASTIC PACKAGES OF INTEGRATED-CIRCUIT (IC) DEVICES

In this study, we develop analytical stress models for the evaluation of thermally induced bows in the following two types of plastic packages: thin elongated packages with large chips, known as thin small outline packages (TSOPs), and high lead count large square packages with relatively small chips, known as plastic quad flat packages (PQFPs). In the case of TSOP packages, we consider the package warpage caused by the thermal contraction mismatch of the constituent materials: silicon chip, metal leadframe, and molding compound. The temperature change is assumed to be the same throughout the package. In the case of PQFP packages, we evaluate the bow due to the temperature gradient (non-uniform distribution of temperature) in the through-thickness direction of the molded body. The developed models enable one to evaluate the effect of the package geometry and materials properties on its bow, and more importantly, to design a plastic package with a sufficiently low residual warpage.