Influence of ink properties on the dynamics of high velocity laser printing

Full text: The deposition of conductive lines of few tens of micrometers width is of prime interest for the manufacturing of electronic devices, especially on flexible substrates. Laser printing, based on LIFT process (Laser-Induced Forward Transfer), always appears very attractive for such application. This technique allows the deposition of silver nanoparticle inks with a wide range of viscosities and the formation of 2D/3D structures with high resolution. The dynamics of formation and expansion of the liquid jet, which is the basic mechanism of the LIFT process in liquid phase, has been extensively studied by means of time-resolved shadowgraphy. Recently, micrometer conductive lines have been laser printed at velocities up to 4m/s in multi-passes configuration with a picosecond laser operating at 500kHz and a scanning mirror to move the laser at the surface of the donor film. Time-resolved shadowgraphy studies showed that the instabilities induced by the interactions between two adjacent cavitation bubbles and/or two adjacent liquid jets prevent the deposition of a continuous line in a single step at high velocity with standard silver nanoparticle inks (20% silver content). In this study, we investigate the influence of silver ink donor film properties (thickness, density, viscosity) on the dynamics of the liquid transfer at high velocity and the morphologies of the printed lines. In particular, we observe a new deposition mechanism when inks with higher densities (40% silver content) are used to print conductive lines at high velocity. All the successive jets are linked together and the specific properties of this ink maintain the stability of this multi-jet structure. In these conditions, we printed 30µm width silver lines at velocities up to 17m/s in a single pass, using a UV picosecond laser operating at 1MHz. (author)