Interaction of multiple delaminations and die in a plastic IC package

摘要

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. All the delaminations are assumed to be of the same length. In the analyses involving 2 delaminations of length 0.2 mm, it is found that the effect caused by two interacting delaminations is insignificant, the amplification of ERR and the change in phase angle are less than 10%. However, when the length of the 2 delaminations is increased to 0.482 mm, significant amplification effect is observed. With the presence of 3 delaminations of equal lengths, the presence of crack#2 and crack#3 has less effect on the ERR of the crack#1 whereas the impact of crack#1 and crack#3 on crack#2 is more significant. Generally, the presence of more than 1 delamination will aggravate the crack situation as the amplification effect on ERR is evident especially for longer delamin- - ations and the phase angle remains relatively less significant. Besides, it is found that amount of amplification increases with an increase in the number of delaminations at the interface and length of the interacting delaminations while it decreases with distance between the delaminations.