Interfacial stress analysis and fracture of a bi-material strip with a heterogeneous underfill

Flip chip assemblies used in electronic packaging consist of three main components (layers): chip, underfill, and substrate. In this paper, the flip chip assembly is represented as a bi-material strip consisting of the chip and underfill. Our analysis is focused on delamination along the chip-underfill interface due to thermal loading. The underfill is modeled as a composite material made of a polymer matrix and silica particles. Interfacial stresses are studied for several particle configurations: cases of one, two, or three particles near the interface and 30 different random particle arrangements. Interfacial fracture is investigated by evaluating the J integral and stress intensity factors. Statistics of random particle arrangements in the underfill are also discussed. The interfacial stress and fracture analyses give the same trends.