Novel low temperature active soldering of Ti-MAO/substrate (Si wafer and sapphire) with In49Sn0.5Lu active solder in air

A micro-porous TiO 2 layer was synthesized on Ti sheet (Ti-MAO) using the micro-arc oxidation (MAO) technique. In this paper, the direct ultrasonic-assisted active soldering technology is applied and its feasibility for the Ti-MAO/substrate (Si wafer, sapphire) bonding is investigated for In49Sn0.5Lu active solder (IS) for 30 s at 150°C in air. The results show that the joints were nearly void-free. the Lu migrated to the solder/substrate interface, reacted with the substrate and formed a thin Lu-rich transition layer. According to thermodynamics calculations, the Gibbs free energy value of LuO 2 is one order of magnitude more negative than the substrate (TiO 2 and sapphire). The shear strength of both Ti-MAO/IS/Si and Ti-MAO/IS/sapphire joint were 3.17 ± 0.57 MPa and 4.87 ± 0.61 MPa, respectively.