Drop-on-demand jet-based printing and deposition techniques benefit from increased printing resolution compared to inkjet printing. In this study, we present two sets of methods to improve the printing resolution and decrease the laser transfer threshold energy for blister-actuated laser-induced forward transfer (BA-LIFT). In one technique, we examine the steady meniscus formation by fabricating micrometer-sized holes onto the solid polyimide thin film substrate which hosts the donor liquid ink film to be printed. Due to the micrometer size of holes, surface tension effects are enhanced, a steady meniscus is formed at the air-ink interface, and the resulting focused jets are thinner and faster than regular jets. In the other set of techniques, we examine the transient meniscus formation by using Faraday waves to induce a transient meniscus at the air-ink interface. We show that focused jets may have different features compared to regular jets depending on the focusing method. We demonstrate experimentally and computationally that steady and transient meniscus formation enable jetting at lower laser pulse energies and leads to the ejection of smaller droplets.
Laser induced forward transfer (LIFT) technique has been used for printing of various materials ranging from flexible metallic contacts to conductive silver lines. In this study, we are focusing on the printing of an industrial-grade silver paste formulated for the metalization of the front side of solar cells.
Printing of industrial silver pastes using the LIFT technique is challenging because the high viscosity of the silver paste allows only a small window of process parameters for reproducible and well-defined material transfer. In this work, we are examining the multiple-pulse effects during the printing of silver paste. Time-resolved imaging and characterization of the ejected silver paste voxels are performed to examine the influence of process parameters on the morphology of transferred paste dots and lines.
We have observed that by firing repeating laser pulses below the transfer energy threshold it is possible to print smaller volumes of paste, which yields an opportunity to print lines with higher resolution.
We also show that it is possible to print well-defined dots (voxels) of the paste using pulse energies near transfer threshold values. However, regarding the printing of lines, there is a strong interaction effect between adjacent voxels. This influence is so important that a distance between adjacent laser pulses threshold has been evaluated to print lines. The printing of single voxels has been achieved above the evaluated threshold value, while no printing could be achieved below the threshold. This distance threshold represents a limitation to the LIFT process of high viscosity pastes, which indicates that a compromise must be done between voxel size and laser frequency.
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