An analysis of interface delamination in flip-chip packages

Interface delamination is an important failure mode for flip-chip PBGA (plastic ball grid array) packages. It plays a significant role on package performance and reliability. In this paper, a fracture mechanics approach is utilized to evaluate the impact of interface delamination on package reliability. Interface cracks are mixed mode cracks with both mode I (opening mode) and mode II (shear mode) components. To characterize the interfaces in electronic packages, it is essential to define the interfacial toughness as a function of different mode mixity, or loading phase angle. In this paper, interface fracture mechanics is incorporated into finite element analysis to determine the critical interface fracture parameters. The proposed methodology is validated against analytical solutions. A Flip-Chip PBGA package with underfill delamination is studied. The effect of temperature, initial delamination length, package geometry and materials on the fracture parameters is evaluated.