Enhancement and Mechanism of Copper Nanoparticle Sintering in Activated Formic Acid Atmosphere at Low Temperature

Cu nanoparticle paste has become one of the alternative materials for conventional high-temperature packaging, but this sintering process is significantly inhibited by copper oxides. In this paper, the activated formic acid atmosphere was used to achieve high-strength Cu-Cu bonding at low temperature. When sintered at a temperature of 275 degrees C for 30 min with a pressure of 5 MPa, a shear strength of more than 70 MPa was achieved. In contrast to formic acid atmosphere, the hydrogen radicals generated by activated formic acid atmosphere facilitated the rapid evaporation of the solvent during preheating process. Moreover, the hydrogen radicals effectively reduced of the oxides on the surface of the Cu nanoparticle resulting in a higher shear strength. This Cu nanoparticle sintering method has great potential in the field of power device integration in future.