Quantitative analysis on air-dispensing parameters for manufacturing dome lenses of chip-on-board LED system

Abstract

A COB(chip-on-board) LED(light emitting diode) system has advantages such as low cost and good heat dissipation. LED chips are bonded on PCB(printed circuit board) directly without packaging process in case of COB LED systems. Dome lenses made of polymeric resin are generally covered on the bonded LED chips by air dispensing for preventing mechanical damage and making white light. However, it is hard to control the shape of dome lenses precisely due to viscosity of the polymeric resin. We analyzed the relationship of the shape of dome lenses and experimental conditions of the air dispensing in this study. We introduced a new parameter, air pressure * dispensing time, whose physical meaning is impulse per unit area, and obtained much clear relationship of dispensing parameters and shape parameters of the dome lens. This relationship was similar to viscoelastic behavior. The aspect ratio (height over diameter) was increased as the new parameter increased, and was converged to a certain value. The maximum aspect ratio could be calculated by Young’s equation of contact angle.