Cu-Cu bonding enhancement at low temperature by using carboxylic acid surface-modified Cu nanoparticles

•Cu nanoparticles (NPs) were synthesized by water phase reduction method.•The synthesized Cu NPs were surface-modified by carboxylic acid.•Robust Cu-Cu joints using surface-modified Cu NPs were achieved at 250 °C.•The mechanism of carboxylic acid surface-modification was proposed for Cu NPs. The carboxylic acid (formic acid and oxalic acid) surface-modification was applied on Cu nanoparticles (NPs) to remove surface oxidation. The synthesized Cu NPs were soaked in the mixture of carboxylic acid and dehydrated ethanol for surface-modification. The reliable Cu-Cu bonding joints using formic acid and oxalic acid surface-modified Cu NPs were achieved at 250 °C, and the shear strengths were improved to 20.2 MPa and 32.4 MPa, respectively. The bonded Cu NPs layer exhibited obvious sintering necks and ductile characteristics. The experimental results demonstrated that low temperature bonding using carboxylic acid surface-modified Cu NPs had the potential to fulfill the requirements of three-dimensional (3D) integration.