High speed laser printing and sintering for flexible electronics
Jetting dynamics of Newtonian and non-Newtonian fluids via LIFT
A computational model is utilized in order to gain more insight on the transfer mechanisms of Newtonian as well as non-Newtonian fluids. The simulation predictions are validated against experimental results, and found to be in good agreement, even in the case of non-Newtonian fluids.
Laser printing and sintering of copper micro-electrodes
Combination of laser printing and laser sintering of Cu nanoparticle inks, for the fast and reproducible additive manufacturing of conductive patterns with design rules that enable the production of on-chip antennas on flexible integrated circuits. The laser printing process has been conducted in high speed (∼1 m/s), and the printed patterns were sufficiently reproducible, with a line width variation of about 5 µm. The laser sintering has been carried out effectively using the same set up as in printing, and the Cu nanoparticle patterns exhibit very low resistivity (3.3 µΩ·cm). The reported process can be readily employed for a variety of flexible Near Field RFID metallic components with form factors in the order of tens of micrometers up to centimeters and complex geometries, highlighting the advantages of laser additive manufacturing.
Influence of the ink's rheological properties, both on the jet propagation and on the spatial and temporal evolution of the printed droplet
A careful choice of the rheological properties of the ink and the wetting properties of the receiver, in combination with an optimization of the laser printing process parameters, is crucial for achieving optimal control of the final printed droplet. Jet dynamics during the printing of six different, in terms of viscosity, inks with two different surface tensions were investigated. Laser fluence and ink viscosity determine the amount of the ejected volume and the jet front velocity, whereas the surface tension of the ink limits the jet stretching and governs the jet's deceleration, thus playing an important role in the determination of the impact velocity. Finally, the analysis of the printed droplet spreading on three different receivers during the wetting phase highlighted the synergetic influence of the ink's surface tension along with the wetting properties of the receiver surfaces.
Laser printing of silver nanoparticles ink to be used as conductive patterns on flexible substrates
Reproducible, circular and uniform Ag droplets could be printed for a wide laser fluence range processing window. In addition, no “coffee ring” effect was observed on the printed droplets from the mixed-solvent-based Ag NPs ink. The ability of LIFT to print both a low and high viscosity ink allows the printing of various ink compositions with high boiling point solvents and thus minimizing or eliminating the “coffee ring” effect. LIFT printed Ag NP lines on SiO2/Si and polyimide substrates cured at a sufficiently low sintering temperature (150 °C for 60 min) exhibited resistivity of 1.8 × 10−5 Ω cm and 8.4 × 10−5 Ω cm, respectively.