Investigation of brazing joints of Al₂O₃ ceramics to Kovar alloys by Ti+Nb/Mo metallization

Ti+Nb/Mo thin films were deposited onto Al₂O₃ ceramic by magnetron sputtering with a subsequent nickel-plating to ensure the robust brazing of Al₂O₃ ceramic to Kovar alloy using the filler of AgCu28. Microstructures of the metallization layer and the brazing joints of Al₂O₃/Kovar were investigated systematically by scanning electron microscopy (SEM) and energy dispersive X-ray (EDS). The results show that the interfacial reaction layers are created between filler alloys and base materials. Interdiffusion of Ni and Cu at the interface of AgCu/Kovar resulted in the formation of the reaction layer. The metallization layer plays an important role in hindering the formation of intermetallic compounds and relieving residual thermal stress at Al₂O₃/AgCu interface. In addition, the presence of eutectic region arising from nickel-plating can improve the thickness of the brazing seam and therefore a good bonding betweenAl₂O₃ ceramic and Kovar was achieved.