Ni Barrier Symmetry Effect on Electromigration Failure Mechanism of Cu/Sn–Ag Microbump

Ni barrier symmetry effect on the electromigration (EM) failure mechanism of Cu/Sn–Ag microbump were systematically investigated by studying the intermetallic compound (IMC) growth characteristics at 150 °C with a current density of 1.5 × 10 5 A/cm 2 . In the symmetric Ni barrier structure, Cu diffusion to Sn–Ag solder was restricted by the Ni barrier at both interfaces and the Ni 3 Sn 4 phase formed by the inter-diffusion between Ni and Sn atoms just after bonding, which was gradually transformed to (Ni,Cu) 3 Sn 4 phase and later to (Cu,Ni) 6 Sn 5 during current stressing with relatively slow resistance increase with time. By the way, in the asymmetric structure, extensive Cu 6 Sn 5 phase grew by the inter-diffusion between Cu and Sn atoms due to there is no Ni barrier at the upper interface, which was rapidly transformed into only Cu 6 Sn 5 and Cu 3 Sn IMCs during electron downward flow, with relatively fast resistance increase with time. Therefore, the symmetric Ni barrier structure is very effective in restricting extensive IMC reactions during EM of Cu-solder microbump structure. Graphical Abstract