Multiscale simulation study of laser sintering of inkjet-printed silver nanoparticle inks

Abstract

Inkjet printing of metal nanoparticle (NP) inks on various substrates is a novel additive manufacturing technology which has found widespread applications in flexible electronics. The printed NP inks need to be heated through laser sintering to obtain high electrical and mechanical properties. However, the heat transfer and diffusion mechanisms of metal nanoparticles during laser sintering have not been fully understood. In this study, a multiscale model combined transient heat transfer model and molecular dynamics (MD) model is developed to simulate the laser sintering process of silver NP inks. Our simulation results show that the local temperature in printed silver film in the laser spot increases significantly, while the temperature increase in the polyimide (PI) substrate is much lower, demonstrating the feasibility of laser sintering in flexible heat-sensitive substrates. To reveal the micro sintering mechanism, the configurational evolution of silver nanoparticles during laser sintering is observed using MD model. We found that the silver atoms on the nanoparticle surface diffuse into the interfaces between adjacent nanoparticles, forming sintered necks. These necks gradually grow, reducing electrical resistivity of the sintered nanostructures. In addition, the effects of laser parameters on the sintering performance are discussed. Both increasing laser power and decreasing scanning speed can improve sintering performance. However, the laser power is much more efficient than scanning speed in improving sintering performance. Our simulation method could be used to optimize the laser sintering process.