Modeling on phosphor sedimentation phenomenon during curing process of high power LED packaging

Abstract

In the LED packaging, the phosphor particles are usually mixed with silicone matrix material, and then dispensed onto the LED chips directly. Since the density of the phosphor particle is bigger than that of the silicone, the phosphor particles may settle in the silicone matrix because of the gravity during dispensing and curing processes. In this paper, a model was developed to investigate the phosphor sedimentation phenomenon in silicone during isothermal curing according to the Stokes’ law, and the size distribution of phosphor particles and the viscosity-time function of silicone during curing were built for the model. We compared the modeling results with the experimental results and found that the model can well simulate the sedimentation phenomenon. The modeling results show that the sedimentation velocity is inversely proportional to the viscosity of silicone and proportional to the size of phosphor particle. Phosphor particles sedimentation lasts for about 5 minutes during isothermal curing at 85°C, and the big particles accumulate in the bottom of the sample.