Experimental investigations on the offset correction of transient cooling curves of light emitting diodes based on JESD51-14 and simple semi-empirical approximations

Determination of the thermal resistance of high power light emitting diodes by transient thermal measurements is of rapidly growing interest. Due to electrical disturbances at small delay times, correction algorithms like the offset correction described in JESD51-14 are necessary. A simple model based on a mean temperature is presented which gives insight into the physics of this correction algorithm. It both allows for a rough estimate of time intervals where the correction algorithm is applicable in ideal cases, and it can be used to detect the presence of an interface resistance between the substrate and the package. Measurements and numerical simulations reveal that a significant interface resistance between the epi-layer and the substrate leads to a modification of the thermal transient. Offset correction then leads to an error in the determined thermal resistance in the range of several percent depending on the magnitude of the interface resistance. Additionally some simple semi-empirical approximations for the transient cooling curves are given.