Joining of silicon nitride ceramic to oxygen‐free copper using Ag–Cu–TiH₂ filler

Complex liquid–solid reactions occur during brazing. A deep understanding of brazing liquid evolution is therefore of important concern for the bonding between filler and substrates. The joining of gas‐pressure‐sintered silicon nitride (Si 3 N 4 ) ceramic to oxygen‐free copper (OFC) foil was prepared using Ag–Cu–TiH 2 filler at 875°C for 0.5 h. The effect of the Ag:Cu ratio on the interfacial microstructure and peeling strength of the joints was analyzed. The reaction of brazing liquid with Si 3 N 4 ceramic includes reactions with both the β‐Si 3 N 4 and the grain boundary phases (Y–Si–Mg–O–N). The resulting interfacial reaction products include TiN, Ti 5 Si 3 , and potential Cu 3 Ti 3 O. Based on the phase composition and three‐dimensional morphology of the interfacial reaction products in the Si 3 N 4 ceramic/OFC foil joints, a model for the evolution of the brazing liquid as the reaction proceeds was proposed. Peeling test results indicated that the peeling strength of the joints rises unilaterally with the increase of the Ag:Cu ratio in the filler until reaching the peak value of 24.3 N/mm at the maximum Ag:Cu ratio of 90:10. The mechanisms of the joint peeling fracture were discussed in detail.