| We focus on the delamination of the underfill from the passivation layer of a chip in a flip chip assembly due to thermal loading. We first calculate stresses at the interface between chip and underfill, and then investigate fracture by using the J-integral method and the stress intensity factors, which are determined using crack surface displacements. The finite element method is used for the analysis. We assume that all components of the flip chip assembly are linear elastic and isotropic, and that their properties are temperature independent. Our analysis is conducted in the context of the uncoupled plane thermo-elasticity under a plane strain assumption.; The underfill is usually a composite material consisting of the polymer matrix and silica particles. First, we assume, for simplicity, that the underfill is a homogeneous material having effective properties of a composite. In the parametric study we consider a range of volume fractions of particles in the underfill. The effective properties of underfill are calculated by Mori-Tanaka method. We investigate how the interfacial stresses and fracture at the chip/underfill interface are influenced by varying volume fractions of particles in underfill and by the different geometric models of flip-chip devices such as a finite bi-material strip, a three layer strip, and four three-layer models with different strip lengths and accounting for curvature in the underfill. The interfacial stress analysis is consistent with the fracture analysis for all geometries.; Then, we model the underfill as a composite material consisting of the polymer matrix and silica particles. Interfacial stresses and fracture are studied for several particle arrangements and find the effect of inclusion arrangement in the underfill on stresses and fracture at the chip-underfill interface. The statistics of random particle arrangements are studied. We find that both interfacial stress analysis and fracture give the same trends for all cases including random particle arrangements.; Finally, the experiments are performed to compensate the numerical study. The three-layer samples consisting of chip, underfill and substrate are made and we apply thermal loading and measure displacements using the micro-DAC. The results are in agreement comparing the results from the finite element method. |
