A high-performance nano-copper paste with good oxidation resistance

Copper nanoparticles (Cu NPs) are promising candidates for next-generation interconnect materials in power electronics due to their excellent electrical and thermal conductivity and low cost. However, their susceptibility to surface oxidation hinders sintering and device integration. In this work, Cu NPs were synthesized via an alcohol-phase reduction method using 2-pyridinemethanol (2-HMP), a low-boiling-point nitrogen-containing dispersant, to enhance oxidation resistance. The modified Cu NPs showed uniform quasi-spherical morphology (20–30 nm) and were coated with a ∼1.5 nm organic layer. The TEM interplanar spacing and XRD analysis confirmed its identity as pure copper crystal, while FT-IR and XPS analyses verified the surface coordination between Cu and 2-HMP. TG-DSC demonstrated improved thermal stability, with the oxidation onset temperature increasing from 94.8 °C (unmodified) to 141.3 °C (modified). The nanoparticles were formulated into a screen-printable paste and applied to bond AlN chips onto PCB substrates via fluxless sintering at 275 °C. SEM and CSAM images revealed dense joints with minimal porosity, and shear testing yielded high joint strength (85.8 MPa). High-resolution TEM of sintered structures showed grain growth, dislocation interactions, and nano-twin formation, while EBSD analysis confirmed equiaxed grains, abundant low-angle grain boundaries, and isotropic crystallographic orientation. These features explain the superior mechanical properties and reliability of the joints. Synchrotron-based XANES and EXAFS further elucidated the Cu–N coordination mechanism. This work presents a viable surface-modification strategy for oxidation-resistant Cu NPs in power electronic device packaging.