The influence of phosphor layer and sidecoating on the thermal performance and the structure function of modern waver level high power LEDs

Many modern Waver Level LED Packages (WLP-LEDs) are thin film flip chips with the sapphire substrate attached on top of the epitaxial light emitting layer (EPI). This study targets to investigate the impact of the upstream thermal masses of the sapphire, the phosphor layer (PL) and the side coating (SC) on the transient thermal impedance curve and the cumulative structure function. It is shown that the standard approach to extract thermal properties by features (steps) within the structure function is not appropriate for this kind of LEDs. By transient Finite Element (FE) simulation the transient thermal measurements are analysed to extract information about the thermal parameters and the thermal path. Starting from the analysis of the blue flip chip LED (FC-LED) the FE-model is set up. Stepwise the FE model is extended and the influence of the PL and the SC on the transient thermal measurement is investigated.