Study on characterization of light aging of RGB LED packaging materials

Abstract

Based on the advantages of high luminous efficiency, clear color, high color purity and wide color rendering range, RGB LED devices are widely used in full-color display and white light illumination. However, due to different energy from different wavelengths of red, green, and blue light, the degree of aging of the packaging material (mainly epoxy resin) is imparity under the same environmental conditions, resulting in inconsistent light decay of the LEDs of different colors and deviation of the final color development. The common solution is to use multiple current modulation methods, which requires a lot of manpower, material resources, and time costs, limiting the market promotion of RGB LED devices. To deal with the above defect of RGB LED, the first step is to find out its light aging mechanism. In this paper, the aging process of the LEDs packaged by two kinds of common packaging resins(bisphenol-A epoxy resin(6915) and cycloaliphatic epoxy resin(0484)) was studied respectively. And the structural changes of packaging materials after aging was also revealed from the aspect of aging mechanism of materials. Firstly, red, green and blue LED lamps packaged by bisphenol-A epoxy resin and cycloaliphatic epoxy resin were lightened in the environment of normal temperature and normal humidity conditions and aged for more than 1000h under 20mA, during which the photoelectric parameters (IV, VF, WL, etc.) of the LEDs were test by the IS standard test machine every 168 hours. Then attenuated total reflection infrared analysis (ATR-FTIR) was performed on the packaging materials of all above LEDs before and after aging including the characterization of the surface portion and the core portion next to the chip. The relative luminous intensity curves showed that the light aging of RGB LED mainly resulted from the degradation of packaging materials and blue light was the main factor inducing the aging of the packaging materials of RGB LED. The results of the FTIR characterization showed that LED aging mainly occurred on the surface of LED packaging materials. Furthermore, oxidation and chain breaking reaction might happen during the degradation of the packaging materials.