Effect of Underfill Formulation on Large-Die, Flip-Chip Organic Package Reliability: A Systematic Study on Compositional and Assembly Process Variations

Selection of appropriate underfills (or encapsulants) for flip-chip packages is critical to their reliability. In this research article, we present a comprehensive study geared towards the development of such materials. Several underfill formulations were developed based on the target material property guidelines obtained from parametric numerical simulations. Material parameters such as base resin composition, filler particle size, filler particle surface treatment and adhesive strength were modulated to arrive at an optimal composite material composition which facilitated package assembly. The robustness of these formulations was further evaluated by conducting post-assembly thermal cycling tests. Results on the reliability performance of these tailor-made underfills along with the failure analysis studies and correlation with numerical modeling will be presented.