A Review on Solder Reflow and Flux Application for Flip Chip

This paper encompassed of the evolution and key findings, critical technical challenges, solutions and bonding equipment of solder reflow in flip chip bonding. Upon scrutinizing researches done by others, it can be deduced that peak temperature, time above liquidus, soak temperature, soak time, cooling rate and reflow environment played a vital role in achieving the desired bonding profile. In addition, flux is also needed with the purpose of removing oxides/contaminations on bump surface as well as to promote wetting of solder balls. Electromigration and warpage are the two main challenges faced by solder reflow process which can be overcome by the advancement in under bump metallization (UBM) and substrate technology. The review is ended with a brief description of the current equipment used in solder reflow process.