Electromigration-Induced Interfacial Reactions in Cu/Sn/Electroless Ni-P Solder Interconnects

The effect of electromigration (EM) on the interfacial reaction in a line-type Cu/Sn/Ni-P/Al/Ni-P/Sn/Cu interconnect was investigated at 150°C under 5.0 × 10 3 A/cm 2 . When Cu atoms were under downwind diffusion, EM enhanced the cross-solder diffusion of Cu atoms to the opposite Ni-P/Sn (anode) interface compared with the aging case, resulting in the transformation of interfacial intermetallic compound (IMC) from Ni 3 Sn 4 into (Cu,Ni) 6 Sn 5 . However, at the Sn/Cu (cathode) interface, the interfacial IMCs remained as Cu 6 Sn 5 (containing less than 0.2 wt.% Ni) and Cu 3 Sn. When Ni atoms were under downwind diffusion, only a very small quantity of Ni atoms diffused to the opposite Cu/Sn (anode) interface and the interfacial IMCs remained as Cu 6 Sn 5 (containing less than 0.6 wt.% Ni) and Cu 3 Sn. EM significantly accelerated the dissolution of Ni atoms from the Ni-P and the interfacial Ni 3 Sn 4 compared with the aging case, resulting in fast growth of Ni 3 P and Ni 2 SnP, disappearance of interfacial Ni 3 Sn 4 , and congregation of large (Ni,Cu) 3 Sn 4 particles in the Sn solder matrix. The growth kinetics of Ni 3 P and Ni 2 SnP were significantly accelerated after the interfacial Ni 3 Sn 4 IMC completely dissolved into the solder, but still followed the t 1/2 law.