Brazing copper and alumina metallized with Ti-containing Sn0.3Ag0.7Cu metal powder

A Sn-based metallization layer was successfully prepared on the surface of alumina at 900°C by using Ti-containing Sn0.3Ag0.7Cu (SAC, wt.%) metal powder. Reliable alumina/copper joints were obtained by brazing pre-metallized alumina and copper using SAC filler at 580-660°C for 5min. The typical interfacial microstructure of brazed joint was copper/Cu₃Sn layer/Cu₆Sn₅ layer/β-Sn layer containing Ti₆Sn₅ phase and Al₂O₃ particles/alumina. As brazing temperature increased, the Cu-Sn intermetallic layers thickened rapidly and the amount of β-Sn phase reduced. When brazing temperature exceeded 640°C, Kirkendall voids and microcracks formed at copper/Cu₃Sn interface. The joints brazed at 580-620°C possessed high shear strength and the highest average shear strength of 32MPa was achieved when brazed at 620°C. Fracture analyses indicated that the joints mainly fractured inside of the Cu₆Sn₅ layer and β-Sn layer. The joints brazed above 620°C demonstrated low shear strength due to the formation of Kirkendall voids which caused the joints fractured along the Cu/Cu₃Sn interface.