Boundary element analysis of delamination in IC packages

A crack tip at an interface between two materials has an order of singularity which is a function of the material properties. For accurate analysis, a special variable-order singular boundary element has been developed and used. The effect of defect size and location along the pad-encapsulant interface on interfacial delamination has been studied. It was found that the energy release rate or stress intensity factor increases with defect size as well as proximity to the pad corner. This implies that when a small delamination near a pad corner delaminates, the crack tip nearer the pad corner will propagate first. The analysis also shows that this delamination, once started, will continue until the crack tip reaches the pad corner. If the variation of interface toughness as a function of mode mixity is known, the delamination propagation behaviour can be determined. Depending on the shape of the curve describing the variation of interface toughness with mode mixity, the delamination growth can either be stable, catastrophic or initially unstable followed by stable growth.