Study of electromigration behavior of Cu pillar with micro bump on fine pitch chip-to-substrate interconnect

Current-induced failures in fine pitch Sn micro bump with Cu pillar have been investigated under a current density of 3.2×10⁴ A/cm² and temperature of 150°C. This process takes place in 2000 hours of electromigration test. Intermetallic compound formation, kirkendall effect, and crack contributed to this failure. There are two stages of failure mechanism for Cu pillar with micro-bump during current stressing. In first stage, the whole Sn solder was transformed into intermetallic compound and kirkendall voids were formed at the interface between the Cu pillar and Cu₃Sn intermetallic compound. In second stage, the Kirkendall voids coalesced into larger porosities then formed continue crack by current stressing, led to leading bump resistance increased.