Low-pressure sintering bonding with Cu and CuO flake paste for power devices

Low-temperature sintering bonding has been proposed as an alternative technique for the soldering to overcome such high operating temperature in wide-gap semiconductor power devices. Ag nanoparticle sintering is one of the candidates in die-attach bonding, but there are certain obstacles for mass production mainly due to the high cost of silver. In addition, metal nano-particle paste including Ag nanoparticle paste bonding needs to apply certain high pressure of MPa order. For mass productions, it is necessary to decrease the applying pressure during the bonding process. In the present study, the authors make flake-shaped Cu based particles by using mechanical milling for improving the contact area between the particles to decrease the required pressure. The die-bonding with Cu flake pastes was carried out at 300 °C with a formic acid. Resulting die-shear strength exceeds 15 MPa for bonded at 300 °C for 60 minutes low pressure (0.4 MPa). Moreover, Cu flake pastes with polyethylene glycol (PEG) solvent showed solid interface layer like bulk Cu. Thus, the Cu flake PEG paste is one of the most promising bonding materials with the remarkably high strength of the sintered bonding.