Effects of nano-Al2O3 particles on microstructure and mechanical properties of Sn3.5Ag0.5Cu composite solder ball grid array joints on Sn/Cu pads

• Sn3.5Ag0.5Cu–nano-Al2O3 composite solder BGA joints was investigated.
• Both scallop- and prism- modes were observed after reflowing.
• Al2O3 suppressed Cu6Sn5 growth, significantly improving the shear strength.

A Sn3.5Ag0.5Cu (SAC)–XAl2O3 nano-composite solder was prepared by adding 100 nm Al2O3 to SAC (wt.%) solder. The interfacial microstructures and mechanical properties of SAC–XAl2O3 nano-composite solder balls on immersion Sn surface finished BGA joints after multiple reflows was investigated. As a whole, adding Al2O3 nanoparticles to SAC solders significantly changed in the interfacial microstructure, and both scallop-type and prism-type modes were observed in the plain SAC solder and SAC–XAl2O3 nano-composite solder after reflowing, respectively. The nanoparticles suppressed the growth of the Cu6Sn5 layer, significantly improving the shear strength. The fracture surfaces of the plain SAC solder showed a semi-brittle fracture mode, but those of the SAC–XAl2O3 nano-composite solder exhibited typical ductile failures.