Power Type White Led-based Flat Phosphor Coating Of Diazo Photosensitizer

For many years, human beings have been working for finding and developing the source of Solid State Lighting (SSL). Thus, the new concept of lighting—semiconductor illumination—was brought forward, which uses white light-emitting diodes (LEDs) as the light source. LEDs will revolutionize the way we illuminate our homes, work places and public spaces.At present, there are several methods to realize white LED, among which the method of coating YAG:Ce3+ phosphor on GaN chip is widely used due to its low cost. The encapsulation craft employed in domestic industry is that directly dip the mixture of phosphor and silicone on the surface of chip. By the reason of operating by hand work, many problems generated in this process influence the light quality of white LEDs. To overcome these problems, a new coating method should be discovered to achieve phosphor layer of even surface, controllable thickness, and repeatable parameters.The paper just aim at solving problems mentioned above and put forward a new coating technique—conformal phosphor coating which is based on water-soluble photoresist. The content of this paper is mainly about1) The photosensitivity of photoresist consisted of PVA and ADC is investigated, and conformal phosphor coating on LED chip was realized by using self-exposure method.2) The thickness of phosphor layer was controlled by altering the exposure time, which is significant to industrial mass production of high quality and stable performance white LEDs.3) Experimental process is optimized in several aspects to increase luminous efficiency, chromatic uniformity, and correlated color temperature stability of white LEDs.4) The absorption of Cr ion in slurry introduced by ADC is analyzed and discussed. And two ways are put forward to reduce the absorption of Cr ion. Experimental results show that these two methods are feasible to increase luminous efficiency of white LEDs. 5) The conformal phosphor layer of high resolution was achieved by using diazo sensitizer based photoresist.6) The diazo sensitizer is selected to replace ADC for its several advantages such as easily developed, high resolution, low cost, and nontoxic to human and environment. The luminance of white LED is increased by using diazo sensitizer based photoresist.This paper has great significance to improve the light quality of white LEDs, and actualize mass production in industry. Along with the development of this technique, the conformal coating has a far-reaching influence in white LEDs manufacture.