A numerical analysis of penny-shaped delaminations in an encapsulated silicon module

Abstract

Modeling penny-shaped delaminations in encapsulated silicon devices and modules such as solar photovoltaic modules, multichip modules or plastic quad flat packs (PQFPs) is not straightforward. Due to the geometrical structure of the module or package, a 3D model is the best representation of the problem. The objective of this study is to numerically investigate the 3D fracture mechanics of a penny-shaped delamination at the pad-encapsulant interface near the corner of a pad of a PQFP. For all the cases analyzed, all the 3 modes of fracture are present. The proportion of each mode is dependent on the location of the initial delamination. Generally, mode I is insignificant compared to modes II and III. In the case of delamination along the diagonal and analyzing the variation of the total ERR along the crack front, 2 local maximums are observed, both along the diagonal. The global maximum is usually located at the diagonal point that is furthest away from the center of the package except when the delamination is located very near the edge of the die, albeit separated by the pad. For a point along the crack front of a particular delamination, a longer distance away from the center of the package does not result in a larger ERR. However, if the initial delamination is located nearer to the center of the package, both the local maximums decrease monotonically and the difference between the 2 local maximums decreases. When a delamination is located away from the diagonal, the maximum shifted away from the diagonal as well. The investigation of the ERR along the crack front reveals that its distribution is complex and non-uniform, leading to the conclusion that the delamination propagation characteristics is non self-similar. Hence, a penny-shaped delamination is unlikely to remain penny-shaped after delamination propagation, and the shape of crack front is likely to be dependent on the location of the initial delamination. © 2011 IEEE.