Evaluating underfill materials for high reliability applications

This paper outlines the methodology used to screen for high reliability underfills in a recent materials evaluation conducted in our facility. The goal of this selection process was to rank several commercially available underfill materials, from a large number of vendors, based on several reliability and processability criteria. The top candidates from this screening process were then used to manufacture prototype lots of high I/O flip chip devices for further testing. The ranking process was divided into two sections: processability and reliability. The use of interfacial toughness assessment techniques, in conjunction with the more traditional stress testing approach presented here, such as thermal cycling and high moisture stressing, is reviewed as a means to further reduce the time required to select reliable materials for FCIP applications.