Study on Failure Mechanism of C4 Bump Solder Excursion in CoWoS Package

As Moore's Law reaches its limit, the trend of chip development towards advanced packaging is becoming increasingly evident, with Chip on Wafer on Substrate (CoWoS) packaging (2.5D) technology rapidly being adopted by major IC manufacturers due to its advantages. However, the structure of CoWoS package is more complex than other package, its failure analysis (FA) also facing many challenges. This paper analysis the solder excursion of C4 bump and study its failure mechanism in CoWoS package. The flux residue comes from the substrate causes delamination between the solder mask (SM) and under-fill, resulting in solder excursion.