Development of a high-throughput fine line metallization process using CFD-simulation

In order to enhance dispensing technology towards an industrial application in Silicon Photovoltaics, in particular throughput rate has to be increased. For this reason, a novel parallel high precision fine line dispensing unit is currently being developed at Fraunhofer ISE providing one nozzle per contact finger and a central Paste supply. In order to ensure a homogeneous paste distribution to all nozzles, the influence of paste rheology on the flow profile of the dispensing nozzles was analyzed. An analytical comparison of two different dispensing pastes with water gave a good insight on the influence of paste rheology on flow patterns inside the dispensing nozzles. Furthermore, numerical CFD-simulation (CFD: Computational Fluid Dynamics) was used to investigate different nozzle geometries and finally print head designs. In various iteration steps, the influence of fabrication tolerances especially concerning the nozzle geometry was isolated and print head designs were optimized based on CFD towards maximum process stability. In the meantime, process optimization using a single nozzle approach led to an average finger width below 35 μm, confirmed by several characterization methods.