Effect of TiO₂ addition concentration on the wettability and intermetallic compounds growth of Sn3.0Ag0.5Cu–xTiO₂ nano-composite solders

In the present study, addition of TiO₂ nanoparticles with a concentration in the range from 0 to 0.75 wt% into eutectic Sn3.0Ag0.5Cu solders were prepared. The effect of TiO₂ addition concentration on intermetallic compounds (IMC) growth in solder matrix, wettability of the composite solder, and interfacial IMC growth at composite solder/Cu interface were studied respectively. The microstructure images show that both IMC growth in solder matrix and interfacial IMC growth at solder/Cu interface were suppressed when TiO₂ nanoparticles are added into the Sn3.0Ag0.5Cu solder system, meanwhile, wettability test results show wetting time reduction and wetting force enlargement with TiO₂ nanoparticles addition concentration increasing. These results reveal that the added TiO₂ nanoparticles in solders work as reinforce agent and enhance solder performance by reducing IMC dimension and improving wettability. However, TiO₂ addition concentration is critical to the improvement extent. The matrix IMC size and interfacial IMC thickness were reduced significantly with the TiO₂ addition concentration increasing in small addition range (0, 0.1 and 0.25 wt%). The most significant suppression appears when TiO₂ concentration is about 0.25 wt%. Beyond this concentration, the matrix IMC size and interfacial IMC thickness increase, but still smaller than non-added Sn3.0Ag0.5Cu solder. Sn–Ag–Cu (SAC)–0.25TiO₂ exhibits most obviously refined solder microstructure. The variation of wetting time and wetting force with the change of TiO₂ concentration are similar. Addition of 0.25 wt% TiO₂ shortens wetting time and strengthens wetting force most effectively. SAC–0.25TiO₂ exhibit best wettability performance as well. The IMC variation consistent with wettability variation revels there is an optimal TiO₂ addition concentration which is about 0.25 wt%. Both insufficient adding and excessive adding will weaken the TiO₂ nanoparticle reinforcement extent. Based on the theory of adsorption and agglomeration, a mechanism of the TiO₂ nanoparticle concentration effect and the optimal addition point was proposed.