TiO2 nanoparticles functionalized Sn/3.0Ag/0.5Cu lead-free solder

As the development of micro-systems moves towards higher speed and miniaturization, the requirement for interconnection density increases significantly. However, the use of conventional solders will be limited as the increasing I/O density lowers the pitches to very small size. Recently, there have been great developments in nano-composite solders. This paper investigated the influence of nano-titanium dioxide (TiO₂) of 99.9% purity on the wettability, micro-structural, melting and mechanical properties of Sn/3.0Ag/0.5Cu. The composite solder was prepared by mechanically mixing solder paste with TiO₂ nanoparticles for 30 minutes. The TiO₂ nanoparticles, with average diameter of 10 nm, were manufactured by precipitation. The solder paste was SAC305 Type 4. After reflow soldering the wetting angle was measured. The microstructure of the composite solders and TiO₂ was studied by means of scanning electron microscope (SEM). An optical microscope (OM) was employed to observe the fracture mode after shear test. A pull test was performed to investigate the shear strength of all samples with composite solders between two PCBs with Sn coating, both before and after thermal cycling (TC) with range between -40°C and 85°C. Differential scanning caborimetry (DSC) was adopted to analyze the melting point of composite solders. The results indicate that when the TiO₂ content increased from 0.5% to 2%, the wettability of the solder improved, which resulted in higher shear strength and better mechanical behavior.