Studies on a reflowable underfill for flip chip application

This paper presents the material properties, assembly process identification and reliability performance coupled with failure analysis of a newly developed reflowable underfill. The curing profile, glass transition temperature (Tg), coefficient of thermal expansion (CTE) and modules were investigated via differential scanning calorimeter (DSC), thermo-mechanical analyzer (TMA) and dynamic mechanical analyzer (DMA), respectively. The dependence of viscosity on aging time was measured via Brookfield viscometer. Wettability was demonstrated through solder sphere wetting test. In addition, the effect of reflow profile on wettability was evaluated as well, for example, the variation of overall acid number under several reflow profiles was monitored via titration with standard sodium hydroxide (NaOH) solution. After that, approaches to control voids were made by manipulating material aging time and adjusting reflow profile, and the effects were subsequently identified via scanning acoustic microscopy (C-SAM)