Abstract
In general, formation and growth of intermetallic compounds (IMCs) play a major role in the reliability of the solder joint in electronics packaging and assembly. The formation of Cu-Sn or Ni-Sn IMCs have been observed at the interface of Sn-rich solders reacted with Cu or Ni substrates. In this study, a nanoindentation technique was employed to investigate nanohardness and reduced elastic moduli of Cu <sub>6</sub> Sn <sub>5</sub> , Cu <sub>5</sub> Sn, and Ni <sub>3</sub> Sn <sub>4</sub> IMCs in the solder joints. The Sn-3.5Ag and Sn-37Pb solder pastes were placed on a Cu/Ti/Si substrate and Ni foil then annealed at 240°C to fabricate solder joints. In Sn-3.5Ag joints, the magnitude of the hardness of the IMCs was in the order Ni <sub>3</sub> Sn <sub>4</sub> > Cu <sub>6</sub> Sn <sub>5</sub> > Cu <sub>3</sub> Sn, and the elastic moduli of Cu <sub>6</sub> Sn <sub>5</sub> , Cu <sub>3</sub> Sn, and Ni <sub>3</sub> Sn <sub>4</sub> were 125 GPa, 136 GPa, and 142 GPa, respectively. In addition, the elastic modulus of the Cu <sub>6</sub> Sn <sub>5</sub> IMC in the Sn-37Pb joint was similar to that for the bulk Cu <sub>6</sub> Sn <sub>5</sub> specimen but less than that in the Sn-3.5Ag joint. This might be attributed to the strengthening effect of the dissolved Ag atoms in the Cu <sub>6</sub> Sn <sub>5</sub> IMC to enhance the elastic modulus in the Sn-3.5Ag/Cu joint.