Numerical simulations of droplet forming, breaking and depositing behaviors in high-viscosity paste jetting

Drop-on-demand (DOD) printing of high-viscosity pastes can solve the sputtering and low forming efficiency issues in inkjet printing technology, but the irregular deposition morphology of deposited droplets poses a challenge for the printing quality. A computational fluid dynamics (CFD) model was developed to predict the droplet forming, breaking and depositing behaviors during the high-viscosity paste jetting process. The model considers the shear-thinning and viscosity-temperature characteristics of the paste, as well as the shearing effect of needle motion during the droplet formation. The jetting process and deposition morphology were compared with the results obtained by a high-speed camera, and the predictions are consistent with the experiments. According to the CFD simulation, paste suction phenomenon appears when the needle moves upward, and part of the paste flows back into the reservoir when the needle moves downward. In addition, the effects of the input parameters (operating pressure, spring preload angle and fluid pressure) on the droplet volume, deposition diameter and bump height of the deposited paste were revealed. This study provides an in-depth and clear understanding of the high-viscosity droplet formation and also lays the foundation for the morphological control of conductive lines in high-viscosity paste DOD printing.