Interaction of multiple delaminations in a PQFP

Abstract

To lend more confidence to the engineers adopting the fracture mechanics approach in the study of delamination in IC packages, a series of studies is performed to investigate the interactions of multiple delaminations and the impact of the die edge. Finite element models are constructed and the energy release rate (ERR) of the crack tips calculated using the virtual crack closure method and J-integral. Since the fracture toughness of the interface is dependent on the mode mixity, the mode mixity of the crack tips will be calculated using a method based on the modified virtual crack closure method. The vehicle of study is a plastic quad flat pack (PQFP) and the interface of interest is the pad/encapsulant interface. The interaction of up to 3 delaminations is studied. It is found that for a single long edge delamination, the ERR will peak in the vicinity of the die. As for delamination of identical sizes at different locations, the edge delamination will result in the highest ERR. Hence, in the choice of delaminations to be included in the multiple delamination analyses, the edge delamination is always included (named crack#1) and the other delaminations (crack#2 and crack#3) lie in the vicinity of the die edge. In addition to multiple delaminations of equal length, the interaction among delaminations of unequal length is studied to investigate the shielding or amplification effect. It is found that amplification effect is observed for all the combinations of delamination studied. Both the delamination length and the distance between the crack tips play a part in the influence of the amplification effect.