Initiation and propagation of delaminations at the underfill/passivation interface relevant to flip-chip assemblies

A crucial reliability issue for flip-chip microelectronic assemblies is the mechanical integrity of the various bi-material interfaces present. Understanding the mechanics and physics of adhesion is continually reiterated in the International Technology Roadmap for Semiconductors (ITRS). With current trends in the microelectronics industry pushing for smaller and smaller feature sizes, small-scale delamination and initiation are becoming more of a focus in adhesion studies. Our work looks at the application of a stress singularity approach to the initiation problem at various geometric singularities found at interfaces in flip-chip assemblies. Moreover, we compare the adhesion of the same interfaces using standard fracture mechanics. Specifically, several underfill/polyimide interfaces are tested, in both a standard double cantilever beam geometry and a tensile butt joint geometry. The results show a direct correlation between stress intensity values for both the initiation of delaminations and the propagation of existing delaminations. Modified tensile butt joint geometry testing shows an inverse relationship between singularity strength and overall joint strength.