Lattice Boltzmann Simulation On Phosphor Coating Process Of High Power White LED Packaging

With advantages of high efficiency, long lifetime and environment protection, light emitting diodes?LEDs? have become the most popular light source in 21 st century. To get white light emission, it's common to use a blue LED chip covered with yellow emitting phosphor via a phosphor coating process. The phosphor coating process combines two-phase flow and heat transfer problems. The heat transfer and flowing in the phosphor layer decide its morphology and properties, then strongly influence both optical and thermal performances of LEDs. Thus, it is important to investigate the rules of heat transfer and fluid flow in the coating process to improve the phosphor coating quality.Based on the lattice Boltzmann method?LBM?, a thermal lattice Boltzmann model for the phosphor/silicone composite and a flow model of phosphor silicone were established to simulate the phosphor coating process.A lattice Boltzmann model was presented to predict the silicone/phosphor composite effective thermal conductivity and based on the prediction model, the influence of phosphor particle size and sedimentation were analyzed. The deviations between simulation and experimental results are less than 7%, when the phosphor volume fraction varies from 0.038 to 0.45. The simulation results also indicate that effective thermal conductivity of the composite with larger particles is higher than that with small particles at the same volume fraction. While mixing these two sizes of phosphor particles provides an extra enhancement for the effective thermal conductivity. And phosphor sedimentation also increases the effective thermal conductivity, especially at a high phosphor volume fraction.Based on the flowing lattice Boltzmann model, the dispensing and forming process of phosphor gel were analyzed on flat surface and square bump structure respectively. Experimental results show that LBM can simulate the dispensing process accurately and predict the morphology. The droplet contact line changes as a power function as?d L / D? ^{t / T} m on flat surface.The flowing of the phosphor microprint process was also simulated. As a result of the pin effect of edges, there exists a critical value both for the influence of chip/mold size ratio?W1/W2? and phosphor gel volume?H/R?. Through adjusting these parameters, different phosphor gel morphology can be realized, such as square, cone and inverted cone. Optimized phosphor layer is achieved as square who has a better color uniformity and the CCT deviation is 850 K.