Improved shear property of Sn-3.0Ag-0.5Cu/Ni micro solder joints under thermal shock between 77 K and 423 K by adding TiO₂ nanoparticles

The rapid development of space exploration technology was intensifying the desire for lead-free solders with high performance and reliability under extreme temperature environments. In this study, the influence of TiO₂ nanoparticle addition on the microstructure, growth behavior of interfacial intermetallic compounds (IMCs) and shear property of Sn-3.0Ag-0.5Cu (SAC305)/Ni micro solder joints under thermal shock from 77 K to 423 K was systematically investigated. The results indicated that the grain size of β-Sn, IMC (Ag₃Sn and (Cu,Ni)₆Sn₅) particles inside the solder was refined by adding 0.05 and 0.1 wt% TiO₂ nanoparticles. Due to the spalling of interfacial IMCs into the solder occurring in all micro joints during thermal shock, the thickness of interfacial IMCs did not show a monotony increasing trend with increasing thermal cycles. However, the micro composite solder joint added with 0.05 and 0.1 wt% TiO₂ nanoparticles always exhibited thinner interfacial IMC thickness and higher shear force compared with the plain micro joints during thermal shock. The inhibiting effect of TiO₂ nanoparticles on the interfacial IMC growth could be explained by the adsorption theory and grain boundary pinning theory. The improvement in shear property of micro composite solder joints was primarily induced by the refinement of IMC particles in the solder and the reduced growth rate of interfacial IMCs by adding TiO₂ nanoparticles.