On the failure mechanism in lead-free flip-chip interconnects comprising ENIG finish during electromigration

The aim of this research was to investigate the failure mechanism of lead-free (SAC305) flip-chip solder connections subjected to long-term electromigration. Interconnects with a nominal diameter of 60 µm or 50 µm were assembled in flip-chip organic packages with a pitch of 100 µm. The under bump metallization (UBM) and surface finish on PCBs comprised of a 5 µm thick electroless nickel immersion gold (ENIG) layer directly deposited on AlCu0.5 or Cu traces, respectively.