Reliability of stacked ball grid array packages during the solder reflow process

The reliability of a stacked ball grid array (stacked BGA) package during the solder reflow process was examined using the finite element method (FEM). The stress intensity factors (SIFs) at an interfacial crack tip in the stacked BGA package were analyzed. Vapor pressure on the surfaces of an initial crack and thermal stress were considered. The vapor pressure during the solder reflow was estimated by moisture diffusion analysis. Initial cracks were assumed along interfaces between the die-attach paste/film and a solder resist (SR) layer, the epoxy molding encapsulant (EME) and a SR layer, and a cupper layer and a SR layer. The SIFs of these interfacial cracks were compared with the fracture toughnesses of respective interfaces. The effect of the sizes of the initial cracks on the SIFs was investigated. To measure the fracture toughnesses of the respective interfaces, we performed delamination tests. Finally, the crack extension was estimated by comparing the SIFs of each interfacial crack to its fracture toughness. In this study, we clarified that cracks tend to extend on the interface between the EME and a SR layer, and that vapor pressure during the solder reflow process significantly influences the crack propagation.