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.
Miguel Morales, Emre Turkoz, David Munoz-Martin, Carlos Molpeceres, and Craig B. Arnold, "Multiple-pulse effects during printing of silver paste using laser induced forward transfer (Conference Presentation)," Proc. SPIE 10519, Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XXIII, 105190N (Presented at SPIE LASE: January 30, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2290690.5751440556001.
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