Design of Cu nanoaggregates composed of ultra-small Cu nanoparticles for Cu-Cu thermocompression bonding

In this paper, new type Cu nanoaggregates (Cu NAs) were designed, and the Cu-Cu bonding by Cu NAs was investigated. The Cu NAs were obtained by agglomeration of the synthesized 5 nm Cu nanoparticles (Cu NPs). Compared to ultra-small Cu NPs, the collection difficulties were effectively solved and the antioxidation properties were also enhanced by the formation of Cu NAs. After sintering at 250 °C for 60 min, the Cu NAs film achieved a low electrical resistivity of 4.1 μΩ cm, which is only 2.5 times larger than that of bulk Cu. A high strength Cu-Cu bonding joint of 25.36 MPa can also be achieved via sintering of Cu NAs at 250 °C under a low bonding pressure of 1.08 MPa. After characterizations of Cu-Cu bonding interfaces and fracture structures of bonded joints, the Cu-Cu interconnection was demonstrated to be tightly contacted, sufficiently diffused and with high purity. In addition, a sintering and bonding mechanism by Cu NAs were proposed, explaining the key role played by ultra-small Cu NPs on the shell layer of Cu NAs. According to the advantages, Cu NAs are expected to be ideal substitutes to traditional solders, which have a huge application prospect in electronics packaging.