Joining of Pure Copper Using Cu Nanoparticles Derived from CuO Paste

Abstract

A paste containing CuO particles and polyethylene glycol 1000 as a reducing solvent has been applied to joining pure Cu in electronic applications, and the bondability of the joints and bonding mechanism were investigated. Based on a combination of thermogravimetric and differential thermal analysis, pressurization in the bonding process was determined to be started at temperatures near the exothermal peak of 320°C. Pressurization started at a temperature of 320°C, with the 11 MPa shear strength of the Cu-to-Cu joint being 2.4 times greater than a joint pressed at room temperature. During the bonding process, CuO particles were not directly reduced to Cu, but were instead first reduced to Cu 2 O nanoparticles, which were subsequently reduced to Cu nanoparticles, and an oxide film of a Cu substrate was also reduced, thus ensuring a direct connection between a sintered Cu layer and substrate. The shear strength increases with holding time. Moreover, the shear strength of a joint created with CuO paste and a holding time of 15 min (20 MPa) is in fact higher than what can be achieved using a conventional lead-rich Pb-5Sn solder, thus making it well-suited for use in electronic applications.

Tailoring Fast Directional Mass Transport of Nano-Confined Ag–Cu Alloys upon Heating: Effect of the AlN Barrier Thickness

“…In recent years, various novel bonding technologies have been envisaged as a replacement of conventional Cu- and Ag-based joining technologies. − For example, novel solder pastes constituted of Ag, AgO, or CuO nanoparticles (NPs) (typically coated with an organic solvent) have been developed, which exhibit enhanced sintering kinetics at relatively low temperatures, as driven by very fast surface diffusion in possible combination with surface melting. ,, Joining processes with Ag- and CuO-nanopastes can be performed at temperatures as low as 250 and 400 °C, respectively. , However, broad application of nanopaste technologies suffers from handling, safety, and processing issues, such as NP agglomeration, oxidation (aging), sintering, organic residues, and the need to apply large external pressures to reduce porosity in the joint zone. Surface-activated bonding (SAB) presents an alternative solution for low-temperature bonding ,,, and also (i.e., as for nanopaste) exploits the intrinsically high reactivity of atomically clean metal surfaces.…”

Robust Cu–Cu Bonding with Multiscale Coralloid Nano-Cu3Sn Paste for High-Power Electronics Packaging

“…The increase of resistivity of the film is related to the oxidation of copper and tin at high temperatures in air as Figure b shows (when the stored temperature is above 300 °C). The resistivity of copper oxide and tin oxide is much higher than that of Cu 3 Sn (the resistivity of SnO 2 , CuO, and Cu 3 Sn is 1.0 × 10 4 μΩ·cm, 6.8 × 10 7 μΩ·cm, and 8.8 μΩ·cm, respectively). If the Cu 3 Sn IMC is oxidized, the resistivity of the Cu 3 Sn will increase.…”

“…Therefore, it is urgent to develop an efficient, low-cost, and ecofriendly method to replace the existing production process. Recently, nanopastes prepared with antioxidant nanoparticles and ecofriendly reducing organic solvents could realize direct bonding of bare copper in air, which provides a possible solution to the above problems. − The added reducing organic solvents such as CELTOL-IA, ascorbic acid, glycerol, and polyethylene glycol (PEG) − can alleviate the rapid oxidation of the Cu substrate during the sintering process in air. Inspired by this idea, the antioxidation nano-Cu 3 Sn IMCs with organic solvent PEG-400 are first directly bonded with the bare Cu substrate in air to obtain a full-Cu 3 Sn joint.…”

High-temperature resistant interconnection using Ni nanoparticles and Al microparticles paste sintered in an atmosphere

“…Metal nanoparticle sintered bonding utilizes the low-temperature sintering ability derived from the high surface activity of metal nanoparticles, and although the bonding process temperature is lower than the melting point of the bulk metal, high heat resistance is obtained after bonding. Bonding materials, such as Ag nanoparticles, 17,[27][28][29][30][31][32][33] Cu nanoparticles, [34][35][36][37] combinations of nanoparticles and micro-sized metal particles, 38) and hybrids of dissimilar metal particles have been reported. 39,40) Furthermore, it is a promising technology that has been actively researched as a high heat-resistant mounting technology for power devices using wide bandgap semiconductors.…”