Fluid Flow Analysis Of Phosphor Coating Process And Its Engineering Applications In LED Packaging

High-power white light-emitting diode(LED)has many advantages over the conventional incandescent and fluorescent lamps such as light efficiency,lifetime and environmental protection,and has been widely applied in the lighting and display occasions.Phosphor coating is one of the key process in LED packaging,it determines the position,concentration,and geometry of the phosphor layer,and therefore affects the optical and thermal properties of the LEDs.The essence of phosphor coating is the wetting and spreading process of tiny droplet on the tiny solid surface.Therefore,understanding the wetting and spreading process of the phosphor gel is helpful for developing new phosphor coating methods.For this goal,we numerically and experimentally investigated the wetting and spreading process of phosphor gel in this thesis,and developed new phosphor coating methods based on the research results.The main achievements are as follows:(1)A numerical model was established based on the volume of fluid(VOF)method and user defined function(UDF)method and an experimental platform was built to investigate the wetting and spreading process of phosphor gel.The experimental and simulated results show that the numerical model predicts the geometry evolution of the phosphor gel accurately with maximum final contact radius deviation and maximum total spreading time deviation of 6.7% and 5.1%.(2)Two phosphor coating methods were proposed by utilizing the thermosetting property of silicone to enhance the light efficiency of LED:(a)Remote phosphor coating for realizing dome-shaped remote phosphor layer with non-uniform thickness.Compared to the conventional spherical cap phosphor layer,it enhances the light efficiency by 5% and improves the angular color uniformity(ACU)simultaneously.(b)Dispensing phosphor coating for realizing cylindrical tuber phosphor layer.Compared to the conventional flat phosphor layer,it enhances the light efficiency by more than 10% for ~5000 K white chip on board-LED(COB-LED)and more than 60% for pure blue COB-LED.(3)Two phosphor coating methods were proposed by utilizing the wetting behaviors of phosphor on curved surfaces to improve the ACU of LED:(a)Remote phosphor coating for realizing remote phosphor layer with uniform and non-uniform thickness.(b)Dispensing phosphor coating for realizing bell shape phosphor layer.The thickness of the two proposed phosphor layers along the central angle is thicker than that of the edge angle,therefore,they presents higher ACU than the conventional spherical cap geometry.(4)Patterned surfaces with both silicone wetting and silicone repellency area were designed and applied to COB-LED packaging.Silicone repellency surfaces with contact angle higher than 145o were fabricated by coating low surface energy nano-silicon particles with spray coating method.Patterned surfaces were realized by introducing a tailored template into the nano-silicon coating process.The proposed patterned surfaces were applied to the COB-LED packaging to achieve hemispherical and cylindrical tuber phosphor layer.Compared to the conventional flat geometry,the two proposed phosphor layer enhanced the light efficiency by more than 10%.(5)The effect of phosphor sedimentation on the optical performance of LED was investigated by online testing method and optical simulation.The results show that the sedimentation happened above LED chip decreases the correlated color temperature(CCT),while the sedimentation happened above LED substrate increases the CCT.