Cohesive zone modeling of 3D delamination in encapsulated silicon devices

Interfacial delamination in encapsulated silicon devices has been a great reliability concern in IC packaging. Experimental testing of a transparent Quad Flat No Leads Package (QFN) was carried out with the goal of studying delamination characteristics and investigating the viability of cohesive zone modeling (CZM) in simulating delamination patterns and trends. To simplify the study, the package was molded without the die. The pattern of initiation and propagation of delamination under thermal loading is the focus of this study. A video camera was focused on the interface between the pad and the encapsulant. When the temperature has reached a critical value, delaminations were seen to initiate and propagate in a certain pattern. The experimental setup was then modeled within the finite element framework with the failure of the interface described through a cohesive-zone surface interaction approach. The cohesive-zone approach is ideal as, unlike other fracture mechanics methods, it does not require prior specification of any initial delamination. It was found that the 3D numerical model was able to capture the experimentally observed delamination pattern satisfactorily.