High strength and density Cu-Cu joints formation by low temperature and pressure sintering of different mass ratio of Cu micron-nanoparticles paste

High strength Cu-Cu interconnections of direct bonded copper substrate are achieved by low-temperature and low-pressure sintering of Cu micron-nanoparticles mixed in different mass ratio. The copper micronparticles with a particle size of 1μm and copper nanoparticles with a particle size of 200 nm were mixed in a certain mass ratio (for example, the mass ratio is 0/10, 1/9, 3/7, 5/5, 7/3, 9/1, 10/0). A certain amount of copper micronparticles was added to the Cu nanoparticles solution. After mixing and vacuum homogenization, a copper micron-nanoparticles paste is obtained. When sintering at the temperature of 260°C, a sintering pressure of 2 MPa and a reduced atmosphere of 5 % hydrogen and 95% argon for 30 minutes, the interconnection joints were obtained. The shear test showed the interconnection strength of the 7 different mass ratio copper pastes. Among them, the sintering strength of the copper paste with a mass ratio of 3/7 is 43.66 MPa. In a conclusion, the microstructure analysis demonstrated that the Cu-Cu joints were formed between the copper paste and the pad. Analyzing the shear section, the fracture layer of the copper paste was in a tensile fracture state. The copper paste with a mass ratio of 3/7 had the best sintering performance realizing the dense sintering of the copper paste at low temperature and low pressure, and the shear strength can reach 43.66 MPa.