Effect of ZrO2 and CuO nanoparticles on corrosion-induced Sn whisker grwoth from SnAgCu alloys: An experimental and quantum mechanical study

Composite solder joints were produced from 99Sn0.3Ag0.7Cu (SAC0307) solder alloy doped with ZrO2 nano-powder and nano-fiber, and CuO nano-powder in 0.25 and 0.5 wt%. The samples were kept for 4000 h in an 85 °C/85RH% temperature-humidity test to enhance the corrosion-induced Sn whisker growth. SEM investigations revealed that ZrO2 had a positive effect, while CuO had a negative effect on the corrosion susceptibility and corrosion-induced Sn whisker growth. A correlation was found between the grain refinement and the increase in corrosion susceptibility of the composite solder joints. Quantum mechanical study showed that ZrO2=Sn has lower binding energy than the Sn-Sn grain-boundary cohesion, and it could be advantageous, since then debonding occurs more likely under stress, thereby dissipating local strain and suppressing anisotropic deformation such as whisker growth. Coupling Sn with ZrO2 that possesses d-orbitals at the valence band could yield a stable interface, even though a lattice mismatch exists between them. In addition, d-orbitals can distribute the corrosion-induced charges more uniformly across the surface, creating an electric field barrier effect that may counteract corrosion.