Numerical and Experimental Study on the Transferred Volume in Phosphor Dip-Transfer Coating Process of Light-Emitting Diodes Packaging

Abstract

The phosphor dip-transfer coating method is simple and flexible for transferring a pre-analyzed volume of phosphor gel, which can be beneficial to the high angular color uniformity (ACU) of white light-emitting diodes (LEDs). The crux of this method is the volume control of the phosphor gel; however, the critical factors which influence the volume control remain unrevealed. In this paper, we concentrate on investigating the transferred volume in terms of three parameters: withdrawal speed, post radius, and dipping depth. Numerical simulations were carried out utilizing the volume of fluid (VOF) model combined with the dynamic mesh model. The experiments were also conducted on an optical platform equipped with a high-speed camera. The simulation results coincide well with the experimental results, with the maximum relative difference within 15%. The results show that the transferred volume increases with the increasing withdrawal speed and remains stable when the speed is greater than 1 mm/s, and it shows a linear relationship with the cube of post radius. And the transferred volume will increase with the dipping depth. Based on the experimental and numerically work, it is concluded that the volume of the pre-analyzed phosphor gel can be precisely obtained.

Cylindrical Tuber Encapsulant Layer Realization by Patterned Surface for Chip-on-Board Light-Emitting Diodes Packaging

“…The phosphor layer geometry decides the optical performance of wLEDs such as light efficiency and angular color uniformity [6][7][8]. However, subject to the low surface tension (about 30 mN/m) of phosphor gel, the phosphor gel tends to wet all the substrate surface with a very small contact angle less than 30 deg [9,10], resulting in significant light efficiency droop due to total internal reflection (TIR) [11]. Such situation becomes more serious for chip-on-board LEDs (COB-LEDs) whose size ranging from several centimeters to dozens of centimeters.…”

“…Another feasible method is to guide the light emit out directly through dome-shape encapsulant (silicone) layer [17,18]. However, dome-shape silicone layer realization is a great challenge in LED packaging due to the low surface tension of the silicone [9,10]. In our previous study, we realized a hemispherical encapsulant layer by fabricating patterned LED substrate with both silicone-wetting and silicone-repellency surfaces [18].…”