Laser-Induced Forward Transfer of High Viscous, Non-Newtonian Silver Nanoparticle Inks: Jet Dynamics and Temporal Evolution of the Printed Droplet Study

Current technological trends in the field of microelectronics highlight the requirement to use cost-effective techniques for precise deposition of highly resolved features. Laser-induced forward transfer (LIFT) meets these requirements and is already applied for direct printing of electronic components. However, to improve the process' reproducibility and printing resolution, further research has to be conducted, regarding the rheological characteristics of the printable fluids and their jetting dynamics. Herein, a high-speed imaging setup is used to investigate the liquid jet's propagation during the printing process. Different Ag nanoparticle inks are studied and compared, over a wide range of viscosities and two different values of surface tension. The main focus of this investigation is the influence of the ink's rheological properties, both on the jet propagation and on the spatial and temporal evolution of the printed droplet during the wetting phase on three different receiver substrates (glass, SU-8, and gate dielectric). The results indicate that both the surface tension and the wetting properties of the receiver determine the shape of the printed droplet, whereas the inks' viscosity and laser fluence determine the printed volume.