Flux-underfill compatibility and failure mode analysis in high yield flip chip processing

The compatibility of flux and underfill material systems significantly contributes to the formation and growth of process-induced defects and further influences flip chip reliability. Various no-clean fluxes, along with a water-soluble flux used as the baseline, are tested with two fast flow, snap cure underfills. Liquid-to-liquid thermal shock and temperature and humidity tests are conducted to evaluate the reliability of each flux-underfill material system. The failure modes, specifically underfill delamination, solder fatigue, and die cracking, are identified and analyzed. The correlation among process manufacturing defects, failure modes, and long-term reliability are determined. Understanding these failure modes will further enable and facilitate the implementation of low cost, high yield flip chip processing in standard surface mount technology.