A study on the measurement and prediction of LED junction temperature

Abstract

In this study, an innovative method for the measurement of the LED junction temperature is proposed. In the proposed technique, the temperature values at the LED chip surface, at the solder joint, and at a substrate point in the vicinity of the LED are measured, and the results are compared with the junction temperature measured by transient thermal measurements method. The aforementioned three temperature values are precisely measured via an IR thermometry and thin wire thermocouple. For the demonstration of the feasibility of the IR thermometry to the LED chip surface, the spectral distribution of the LED emission is analyzed using a spectroradiometer. The results show that there is negligible IR irradiation at the LED, suggesting no IR-induced interference is expected for the surface temperature estimation. In order to validate the experimentally obtained temperature distribution, an FEM-based numerical study is also performed. The experimental and numerical results are shown to agree well to each other within 15%. Based on the results, an empirical equations that correlate the junction temperature and the temperature at the solder joint, substrate, and surface of LED are developed. In addition, we show that analyzation of the structure function containing thermal resistance data of LED package obtained from the transient thermal measurement can yield a good interpretation in regard to the thermal resistance of the LED itself. The proposed methodology can act as a good guideline for the thermal management of the LED-related products.