Thermal Behavior of Remote Phosphor in Light-Emitting Diode Packages

This letter reports on the detailed thermal behavior of remote type light-emitting diode (LED) packages with different positions of a phosphor layer from the substrate. The temperatures of phosphor layers were directly measured using microthermocouples. It was confirmed by both measurement and simulation, for the investigated LED package structure, the phosphor temperatures are always higher than the junction temperature. Both temperatures are found to change as a function of the phosphor-substrate distance. It is demonstrated that the distance determines the effect of back-scattered photons and the thermal resistance between the phosphor layer and the substrate. From both the experiment and simulation results, it is proposed that there exists an optimal distance of phosphor layer in the remote-type LED package, which is about 320 μ m for the package structure utilized in this study. The package with the optimal position exhibits an optical output which is 6% higher than that from a package where the phosphor layer directly covers LED chip. It is shown that the heating load at the phosphor layer changes with the position of the phosphor layer and must be implemented for the precise thermal analysis of whole LED package.