Slot-Die Coating Operability Window for Nanoparticle Bed Deposition in a Microscale Selective Laser Sintering Tool

Abstract This work seeks to develop a fundamental understanding of slot-die coating as a nanoparticle bed deposition mechanism for a microscale selective laser sintering (μ-SLS) process. The specific requirements of the μ-SLS process to deposit uniform sub-5 μm metal nanoparticle films while enabling high throughput fabrication make the slot-die coating process a strong candidate for layer-by-layer deposition. The key challenges of a coating system are to enable uniform nanoparticle ink deposition in an intermittent layer-by-layer manner. Identifying the experimental parameters to achieve this using a slot-die coating process is difficult. Therefore, the main contribution of this study is to develop a framework to predict the wet film thickness and onset of coating defects by simulating the experimental conditions of the μ-SLS process. The single-layer deposition characteristics and the operational window for the slot-die coating setup have been investigated through experiments and two-dimensional computational fluid dynamics simulations. The effect of coating parameters such as inlet speed, coating speed, and coating gap on the wet film thickness has been analyzed. For inlet speeds higher than the coating speed, it was found that the meniscus was susceptible to high instabilities leading to coating defects. Additionally, the study outlines the conditions for which the stability of the menisci upstream and downstream of the slot-die coater can affect the uniformity and thickness range of the coating.