A novel pattern printing method of applying Ag nanoparticles to Cu pads for high density Cu-Cu interconnection

Recently, Low temperature Cu-Cu bonding by nanoparticles has attracted a lot of attention due to a lower temperature, lower pressure and fewer requirements on the surface roughness and purity. However, methods of distributing nanoparticles to the bonding interfaces evenly are an obstacle to make it widely used. In this paper, a novel pattern printing method was proposed and Ag nanoparticles were patterned by means of the different properties of Cu pads and the surface of silicon, which was treated to obtain a superhydrophobic property. The assembly was performed at room temperature and the bonding was implemented by thermo-compression at the bonding temperature of 250 °C and the bonding pressure of 30 MPa for 0.5 h in a N2 atmosphere. The shear strength of bonding joints was about 20 MPa, and the bonding interfaces and fracture interfaces were observed. By the method, Ag nanoparticles can be homogeneously distributed to Cu pads, and the sizes are uniform. Therefore, nanoparticles can be better used in packaging, which requires relatively low experimental conditions.