Surface modification of Cu flakes through Ag precipitation for low-temperature pressureless sintering bonding

•Cu flake surface is modified by sub-micron Ag precipitations with green method.•Precipitated Ag on Cu flakes improves anti-oxidation reducing oxygen penetration.•Precipitated Ag NPs transform into bulk-like Ag, providing obvious necking at 250 °C.•Our Ag-precipitated Cu flakes indicate potential applications as metallic fillers.

Cu flakes with surface modified by precipitated Ag nanoparticles (NPs) were investigated for potential use as a sinter joining material. The surface modification was conducted via a simple and green amine treatment process. The precipitated Ag inter-NPs improved the sintering ability of the Cu flakes by increased necking and grain growth at 250 °C. The linked Ag network formed a dense microstructure of the sinter joining layer and contributed to the Cu flake connection. The surface-modified Cu flakes exhibit 30% less oxidation than the original flakes at temperatures as high as 200 °C. The present surface modification expands the application of Cu flake paste to sinter joining for heat-resistant interconnections.