Preparation of High Shear Strength Self-Reduced Nanocopper Paste and Fracture Behavior Study of Sintering Joint

With the advancement of high-power devices and wide bandgap semiconductors, electronic packaging materials face increasing demands for high temperature and power density performance. Copper nanopaste is promising due to its low cost and high interconnect strength. However, its susceptibility to oxidation in air significantly weakens bonding performance. In this study, copper nanoparticles with high oxidation resistance were prepared via co-treatment with 2-pyridine methanol and oxalic acid. XRD and XPS confirmed the absence of oxides. Rheological and surface profiling determined the optimal mixing ratio, yielding pastes with excellent printability and uniform particle dispersion. Uniform nanoparticle distribution promoted strong Cu-Cu joint formation. Bonding experiments under varying vacuum conditions revealed that insufficient temperature, pressure, or time led to void-rich joints. Optimal bonding at 300 °C, 5 MPa for 40 minutes achieved a shear strength of 120 MPa. EBSD analysis showed nanocrystalline sintered bulks with 96% large-angle grain boundaries and 22.9% twin boundaries, enhancing dislocation resistance and shear performance. Fracture analysis indicated that high-strength joints fractured along the substrate, while low-strength ones cracked within the bulk. This self-reducing Cu nanopaste holds great potential for high-power device packaging.