Sintering of Cu particles baked by formic acid vapor for Cu–Cu low temperature bonding

Cu particles sintering is considered one of the most suitable connection technologies for power devices, but Cu has poor oxidation resistance and Cu oxides hinder the sintering process. In this paper, formic acid vapor is used for baking Cu paste to achieve high strength Cu–Cu joints at low temperature. The Cu–Cu joint of 33.9 MPa is obtained easily at 200 °C through baking by formic acid vapor at 130 °C for 15 min. Formic acid vapor effectively reduces the Cu oxides on the surface of the Cu particles, improving the sintering performance of the Cu paste. The effects of baking atmosphere, temperature and time on the shear strength on Cu–Cu joints are analyzed. Additionally, the mechanism of formic acid vapor in reducing the sintering temperature of Cu paste is investigated by the analysis of phase composition and thermal behavior. This work further expands the application of Cu paste in the packaging of high-power semiconductor devices.