Investigation on dip-transfer phosphor coating for light-emitting diodes: Experiments and VOF simulations

Dip-transfer phosphor coating method and its benefit on enhancing angular color uniformity (ACU) of white light-emitting diodes (LEDs) were previously reported, however, for applying this method in mass production, its fluid transfer mechanism and packaging consistency needs to be further investigated. The dip-transfer process is divided into two process, they are dipping process and transfer process. In our previous study, the dipping process were studied with experiments and simulations. In this study, we further studied the transfer process with numerical simulations based on combination of the volume of fluid (VOF) method and the dynamic mesh model, four parameters include post radius, withdrawal velocity, transfer height and phosphor gel viscosity were investigated. Besides, the packaging consistency of the dip-transfer phosphor coating method was studied with experiments. The simulated results show that the transfer volume decreases with the post radius, phosphor withdrawal velocity and phosphor gel viscosity, while keep the same with the transfer height. The experimental results show that the packaging consistency is highly rely on the transfer volume, with transfer volume varies from 0.71 μl to 6.12 ul, the maximum transfer volume deviation (MTVD) changes from 6.98% to 2.31%.