Modeling of the Fluid Volume Transferred in Contact Dispensing Processes

In the contact dispensing process, the contact of the fluid with the target board is essentially needed in order to transfer a certain volume of fluid to the board. Due to the action of surface tension, part of the fluid extruded from the needle hangs on the needle after the process, and this causes the difference between the fluid volume extruded and the one transferred to the board. This difference is usually ignored in the literature, yet is critical to the precise process control. In this paper, a model to represent the difference is developed based on the Young-Laplace capillarity equation as well as the boundary conditions established for this particular problem. Experiments and simulations were carried out to verify the model effectiveness as well as to investigate the influence of the fluid volume extruded from the needle, the needle size, and the initial height of the needle on the fluid volume transferred in the contact dispensing process.