Microstructure and shear strength of sintered Cu–Al2O3 composite joined to Cu using Ag–Cu and Cu–Zn filler alloys

The microstructure and shear strength of joints between Cu–Al2O3 (50 vol.% Al2O3) composite and Cu metal brazed with 72Ag–28Cu and 70Cu–30Zn filler metals were characterized. The composite fabricated by the pulsed electric current sintering of Cu-coated alumina particles showed less than 2% residual porosity and interesting thermophysical properties for electronic packaging applications; thus, the adhesion of the composite to copper metal was evaluated. The composite–Cu assemblies were brazed in an inert atmosphere at working temperatures of 10, 60 and 110 °C above the liquidus of the alloys. In the case of Ag–Cu, there was significant diffusion of silver to the composite side, forming a (Ag, Cu) solution. Zinc diffused to the copper side when using the Cu–Zn filler metal, and the formation of fine oxygen-containing Zn precipitates was observed; furthermore, the overheating of the Cu–Zn material originated in interfacial cavities due to evaporation and the zinc deficiency of the fused metal, which reduces its fluidity. The shear strength followed a similar trend with respect to temperature for both joining systems; maximum strengths of 49.9 and 37.1 MPa were obtained for the 72Ag–28Cu and 70Cu–30Zn fillers, respectively, at the intermediate temperatures used. Fracture examination revealed that the brazed arrays failed in all cases on the composite side. The microstructure and strength values indicate a strong adhesion between the parts, which constitutes an important requirement for thermal management in electronic assemblies.