High-strength AlN/Cu brazed joints using AgCuTi/FeZr2 composite filler with residual-stress mitigation

The AlN/Cu composite substrate is promising for power electronic packaging. However, the large coefficient of thermal expansion (CTE) mismatch among AlN, Cu, and AgCuTi fillers generates high residual stresses, undermining joint reliability. We design AgCuTi/FeZr 2 fillers to lower the CTE of the brazed seam in AlN/Cu joints. Results show that FeZr 2 doping improves joint performance, raising the shear strength to 124.0 MPa at 5 wt.% (≈83% above the undoped joint) and enhancing thermal-shock resistance. Turner-model calculations and finite-element analysis indicate that FeZr 2 lowers the CTE of the composite filler and thus reduces the interfacial residual stress. Microstructure reveals that excessive FeZr 2 results in pronounced thinning and local discontinuity of the TiN reaction layer by reducing the availability of active titanium ([Ti]) involved in the interfacial reaction. These findings demonstrate that AgCuTi/FeZr 2 fillers provide an effective route to low-stress, high-reliability AlN/Cu brazed substrates when the FeZr 2 content is kept at an appropriate level.