Thermomechanical Analysis of Plastic Ball Grid Arrays With Vapor Pressure Effects

This study adopts a mechanism-based computational approach to gain insights into the delamination and cracking of plastic ball grid array (PBGA) packages under moisture sensitivity test (MST) conditions. The possible crack paths in the molding compound are first examined by modeling the fully porous over-mold with void-containing cell elements. These computational cells are governed by a Gurson constitutive relation, extended to account for vapor pressure effects. We show that the corner of the die/die-attach interface presents a likely site for crack initiation under MST conditions. Failure along this interface of interest is then examined by deploying a single row of computational cells along the die/die-attach interface. Under combined thermal and vapor pressure loading, delamination concurrently occurs at both the die corner and the die center; these competing damage sites lead to the rapid and complete delamination of the die/die-attach interfaces.