Power-type White Led Flat Coating Technology Optimization Study

LED (Light emitting diodes) lighting has been regarded as"green lighting", because of its advantages such as energy saving, long life, flexibility and so on. It is expected to widely take place of incandescent, fluorescent lamp and to be come to the fourth-generation light source. It has shown an extremely rapid development in LED lighting recent years, as tremendous attentions and capital resources have been invested on this field by governments, industries and research institutions. And the progresses in semiconductor technology have also contributed to drive the wheel of LED lighting.Our group has been focusing on the research of phosphor coating several years, which turns to be a key technique in Power White LEDs (PWLEDs) packaging. With PVA+ADC as a water-soluble photoresist, a new kind of conformal coating technique had been proposed and developed in our laborotary. But early research on this technology had just proven the feasibility, a lot of work on such as process stability, highly luminance and uniformity of light output need to be done so as to guarantee the realization of PWLEDs with good performances. In this paper, several factors and important parameters in our processes, which have deep impact on the performance of PWLEDs, had been discussed in detail. And optimized results have been reached through experimental research. the 1W LEDs with luminous efficiency over 100lm/W had been successfully realized during this work. It has shown a bright promise of our process for an industrial application. Some conclusions from this paper are listed as follow:(1) Works focused on achieving stability, uniformity and repeatability of PWLEDs in luminous efficiency and color temperature had been carried out. With optimized parameters proposed in this paper, PWLEDs examples of luminous efficiency over 100lm/W and color temperature between 4000-6000K with highly stability had been successfully worked out in our lab.(2) By introducing Tetra-hydrogen Furan (THF) as a surfactant, a stable PVA + Silicone Multiphase dispersant for phosphor coating had been achieved, and so do the PWLEDs with multiphase phosphor coating. Measurement and analysis have been carried out to give a clear picture of role of THF in the process of forming of a multiphase phosphor coating layer on the LED chip.(3) In order to solve the problem of rapid sediment of large particle phosphor encountered in the coating process, the TiO2 nanoparticle as a sediment resistant had been introduced into the above mentioned slurry e.g. photoresis system. With the increasing of ingredient of TiO2 nanoparticles, the viscosity of slurry can be adjusted effectively to reach a better and homogeneous distribution of phosphor particles in PVA dispersant layer, and no degradation in luminous efficiency of PWLEDs had been observed.In this paper, efforts had been paid on the optimization of arts of phosphor coating process with slurry method. Conclusions and proposals had been put forward for promoting the application of this technology in mass production.