Study On Phosphor Conformal Coating For LED Packaging

The human pursuit for bright never stopped. From Edison’s first incandescent to fluorescent later and then the emergence of light-emitting diode (LED) in the20th century, with the technological technology advances, the electro-optical conversion efficiency of the lighting source continues to increase. Compared to the fluorescent and incandescent lights, the smaller size, shock resistance, security stability, environmental protection and energy saving is the favorable performance characteristics of light-emitting diodes. So once there was wide concern and gradually it became the high-tech industries with significant social and economic significance. With the rapid development of industrialization, the semiconductor lighting will eventually enter millions of households and become excellent lighting source.LED light by electron-hole pair recombination, it’s emits the narrow spectrum of light which is not applicable to the lighting. So for white LED the way is that blue LED excitation of yellow YAG phosphor. Domestic white package is mainly dispensing process used in mixed phosphor and silicone or epoxy. The equipment and packaging process are simple, but the color parameter of single device is much discrete and there is a big difference between the devices of the same batch. And due to the change in viscosity of silicone, this process is also difficult to control the performance between the different batches of devices. The packaging cost has a considerable proportion of the total cost of unit’s wattage lamps, still effectively reduce the cost of the package has become a hot issue for the LED packaging industry.This article, based on thin film chip, research on three phosphor conformal coating technology, describes methods improve packaging efficiency and reduce the cost of the package and improve the consistency of performance of the device. The thin film chip is different with the LED chip growing on the sapphire and silicon carbide substrate, its big advantage is phosphor can be directly applied to the surface of the chip and it can be a white point light source, the light source apply the desired the only simple optical design, the light source is more similar to the Lambertian distribution. There is no requirement of large lens even the smaller can also achieve good parallel light, outside the range of light source the stray light is less suited for applications requiring light controllable range of lighting situations, this is the unique advantages of this technology. In addition, when the other substrate are not removed LED package technology roadmap avoids phosphor precipitation, the package of this article, however, want to the phosphor to fully precipitate, improve LED light efficiency and light decay, more, also greatly improve the controllability of the product. Therefore, the full play to the advantage of this technology is the key to improve the competitiveness of this roadmap. Wafer-level phosphor conformal coating and the grinding technique is directly the YAG phosphor layer coated on a wafer, to avoid the complex processes of a single chip coated on with phosphor herein can significantly reduce costs, and can also better control product consistency and quality of the white light spot. Finally, since this chip can easily be solid crystal directly in the heat dissipation substrate, can save a lot of aspects of the package, more importantly, can greatly reduce the thermal resistance; improve product reliability and luminous efficiency. The product, which has certain advantages in performance, is also expected to break the patent blockage of foreign high-end semiconductor lighting products, greatly improving the international competitiveness of Chinese semiconductor lighting products.The main work and conclusions are as follows:1. In order to solve the problem of the dispensing process, carrying out the studies for remote phosphor coating process. Through self-developed phosphor coating device using water glass as a phosphor binder, the phosphor deposited on the glass surface of the wafer to prepare a uniform thickness of the shape controllability and consistent composition, and packaging into the remote phosphor coating device. In this article through self-developed test device it is tested that the color temperature of the phosphor layer on the wafer uniformity prepared by this process. The test results showed that the phosphor layer on a2-inch wafer prepared by the present method is extremely uniform distribution of color temperature distribution variance of only3x102(color temperature difference between the phosphor dispensing the same batch of devices often up to800K), explain the phosphor layer can effectively control the thickness and shape, to produce excellent degree parameter set device.2. For reducing the cost of the package and improving packaging efficiency, we study on the conformal coating process based on the vertical structure of the chip wafer. Deposited water glass and phosphor in a2inch chip wafer coating by self-developed device in this article, baking film deposition and lithography stripped exposed pad, the final wafer cutting to produce a separate phosphor conformal coating white LED chip. And testing the phosphor conformal coating technology LED chip emitting performance.3. The grinding can successfully control of the distribution of the phosphor layer on the chip wafer, to effectively achieve a color temperature control on all chips in the chip wafer. The technology package device crystallized on a ceramic substrate and tests the package structure of the EL performance and chromaticity uniformity in space.