Effect of TiO₂ on the formation of primary and interfacial Cu₆Sn₅ in Sn-0.7wt%Cu and Sn-0.7wt%Cu-0.05wt%Ni solder paste during soldering

This paper investigates the effect of 1 wt% TiO₂ on the formation of primary and interfacial Cu₆Sn₅ in Sn-0.7wt%Cu and Sn-0.7wt%Cu-0.05wt%Ni solder pastes soldered on a Cu substrate using a real-time synchrotron imaging technique. It was found that TiO₂ had altered the nucleation time of the primary Cu₆Sn₅ intermetallics and increased the number of particles observed. In addition, a more planar Cu₆Sn₅ interfacial layer had formed in joints made with TiO₂ reinforced solders. This indicated that TiO₂ promotes nucleation of primary Cu₆Sn₅ intermetallics in the early stages of soldering while being a barrier for further growth of interfacial Cu₆Sn₅ intermetallics. The synchrotron imaging technique provides direct evidence of the sequence of events in the soldering reaction and how these are influenced by TiO₂ reinforcement.