Interfacial bonding mechanisms of sintered Cu nanoparticles on different metallization surfaces

Cu nanoparticle sintering bonding is a low-cost die-attach method compared with Ag nanoparticles for power electronic packaging. The joint strength highly depends on the surface metallization of the devices. In present study, the interfacial sintering behavior of copper nanoparticle film (CNF) on different metallizations (Au, Ag, and Cu) was studied. The CNF exhibited a superior shear strength (115 MPa) on Cu substrates when sintered at 250 °C-15 MPa, much higher than that on Ag and Au metallized substrates. The interface connection ratio of bondline-substrate showed the same trend as the shear strength. The neck formation at the bonding interfaces showed no orientation preference. The lateral diffusion of Cu atoms on substrates dominated the sintering bonding, rather than the longitudinal diffusion. The Cu metallization showed much faster lateral diffusion than the Ag and Au metallization, which was confirmed by the neck growth of monolayer nanoparticle sintering and the molecular dynamics (MD) simulation.