Reaction kinetics and mechanical properties in the reactive brazing of copper to aluminum nitride

Aluminum nitride (AlN) is an attractive substrate material for electronic packaging applications because of its high thermal conductivity and electrical resistivity. However, improved metallization of aluminum nitride is required for reliable conductivity and good adhesion to the ceramic substrate. In this study, the kinetics, microstructure, and mechanical strength of Ag–Cu–Ti/AlN reaction couples have been studied in the temperature range of 900–1,050 C and hold time range of 0–1.44 · 104 s using a eutectic silver– copper filler alloy containing titanium within the range of 2–8 wt%. The product layer thickening kinetics has been observed to change from a linear to non-linear thickening mechanism with the increase in holding time and temperature. At shorter hold times at a fixed temperature, the interfacial product layer followed a linear thickening kinetics. With the increase in the hold time, the thickening kinetics of the interface followed a non-linear thickening behavior. The nonlinear thickening mechanism has been approximated as a parabolic thickening mechanism. The interface has been found to be rich in the reactive metal (Ti) content. The mechanical strength of the brazed joints has been analyzed using four-point bend tests. The strength of the brazed joints initially increased and then decreased with an increase in the hold time at a fixed temperature. A maximum strength of 196 MPa has been obtained for a brazed joint heated at 1,000 C for 2,700 s containing 2 wt% Ti in the filler alloy. It was observed that the sample with the maximum strength had a discontinuous interface