A Study On Phosphor Coating Structure And Processes For White LED

As a new generation of solid-state lighting resource, white light-emitting diodes(WLEDs) possess superior advantages compared to the traditional light sources(filament lamp and fluorescent lamp). Currently, white LEDs are fabricated by three ways, in which the most common method is phosphor-converted LEDs(pc-LEDs), namely the generation of visible lights over a broadband emission spectrum is achieved by exciting YAG: Ce3+ yellow phosphor on blue Ga N-based LED chips. The method not only offers high conversion efficiency, also is favorable for massive production. Due to the structure of phosphor coating layer affect the overall performance of the LED devices, phosphor coating method has become one of the key techniques in the manufacture of WLEDs. However, the conventional coating method lack control in the geometry of phosphor coating layer, this will result in an inhomogeneous distribution of phosphor, thus affecting the spatial color homogeneity of WLEDs.In order to solve the above-mentioned problems, we propose a concept of self-adaptive remote phosphor coating and a newly-developed electrophoretic deposition phosphor method(EPD).In this paper, we have demonstrated a self-adaptive remote phosphor coating method in WLED. With self-exposure process, the pattern of phosphor coating layer can be effectively controlled,the coating layer is a mapping to the intensity distribution of chip-emitting light, and the spatial color homogeneity of WLEDs is improved. With this method, the extraction efficiency of blue light is enhanced, so an increase of luminous efficiency is observed. The exciting results pave the new way to enhance the overall performance of WLEDs packaging.Combined the conventional electrophoresis techniques with advanced conformal coating concepts, we have developed a novel electrophoretic deposition phosphor process in phosphor coating of WLEDs. With this method, we can easily and effectively control the shape and thickness of LED phosphor layer, thereby improving the optical properties of WLED. The involved research work are listed as follows:(1) The development of wafer-level chip scale packaging technique for WLEDs based on EPD method.(2) Discussion of effect of deposition time, voltage and distance between two electrodes in the EPD process on the performance of WLEDs.(3) The development of a nano ATO spray coating for evenly coated transparent conductive layer.(4) The post curing process of phosphor coating layer in EPD process.In this paper,we propose self-adaptive remote phosphor coating method and electrophoretic deposition method. Those new methods greatly improve the light quality of WLEDs.