Large-area and low-cost Cu–Cu bonding with cold spray deposition, oxidation, and reduction processes under low-temperature conditions

In order to omit the step of removing organic items in Cu–Cu joint with Cu paste and improve the interface of the Cu–Cu bonding, a novel method based on cold spray deposition and subsequent oxidation–reduction process was proposed to achieve solid-state Cu–Cu joint with cheap micro-sized Cu particles at low temperature with different applied pressures. The micro-sized Cu particles were tightly deposited on surface of Cu substrate to make a robust interface. Cu₂O nanoparticles were formed on the surface of Cu particles with the oxidation, which were completely reduced to metal Cu nanoparticles in formic acid atmosphere at 300 °C to realize the Cu–Cu joint with a shear strength of 32.9 MPa. Moreover, due to the stronger interfacial bonding between cold spray deposit and Cu substrate, the joint fracture exhibited ductile fracture feature which is expected to improve the reliability of Cu–Cu joint.