A new one-pot method for the synthesis of Cu nanoparticles for low temperature bonding

Abstract

We developed a new one-pot method for the synthesis of Cu nanoparticles capped with fatty acids and amines from an insoluble salt, such as Cu carbonate and Cu hydroxide, in ethylene glycol. This method could be completed within a short period of time and provides a high collection rate from inexpensive raw materials without impurities. The mean diameter of the Cu nanoparticles was controlled from 93 to 13 nm as the alkyl carbon number increased from C10 to C22. The same fraction of fatty acids and amines used for capping agents was suitable to obtain the minimum size of Cu nanoparticles. The thermal decomposition temperature of the capping layer was lower than 300 °C even in an inert atmosphere. Higher strengths of the Cu plates bonded by the Cu nanoparticles were achieved owing to the more densely packed sintered structures by the smaller Cu nanoparticles. The shear strength of the Cu plates bonded by the Cu nanoparticles was higher than 30 MPa which was the same level as for ordinary solders even though the process temperature of 300 °C was much lower than high-temperature solders. The minimum electrical resistivity of the sintered Cu nanoparticle film was 13 μΩ cm which was obtained after annealing at 300 °C.