Effect of nano-TiO_2 addition on the microstructure and bonding strengths of Sn3.5AgO.5Cu composite solder BGA packages with immersion Sn surface finish

摘要

The effects of nano-TiO_2 particles on the interfacial microstructures and bonding strength of Sn3.5Ag0.5Cu composite solder joints in ball grid array packages with immersion Sn surface finishes have been investigated. Metallography reveals that addition of nano-TiO_2 particle retarded wicker-Cu_6Sn_5 IMC formed in the Sn3.5Ag0.5Cu composite solder joints. The thickness of the interfacial intermetallic compounds of the solder joint was reduced with increased additions of nano-TiO_2 particles (0.25-1.0 wt%), but further additions up to 1.25 wt% decreased the beneficial influence. This indicates that the presence of a small amount of nano-TiO_2 particles is effective in suppressing the growth of the intermetallic compounds layer. In addition, the shear strength of the soldered joints was improved by larger nano-TiO_2 particle additions, with the peak shear strength occurring at 1.0 wt% of nano-TiO_2 particles into the Sn3.5Ag0.5Cu solder. The fracture mode also changed with increased amounts of nano-TiO_2 particles.