Life and Reliability Evaluation of High-Power LED under Thermal Environment

抄録

Finite element analysis (FEA) is frequently employed by researchers to investigate the mechanics and/or thermal behaviors of high-power LEDs. However, after performing FEA, only a few people continue to discuss the life and reliability of the LED. In this study, a relationship between the junction temperature and the life of a LED is first established based on real test data. FEA is then employed to find the junction temperature of the LED. By using the numerical results of FEA as the input for the relationship mentioned above, one can predict the life of the LED. However, the life is a fixed value under a certain condition, which cannot truly reflect the discrete characteristic in real life testing. Furthermore, it cannot provide extra information such as the reliability and the failure rate of the LED. To the end, this study further accounts for uncertainties coming from parameters such as convection coefficient and photoelectric conversion efficiency, and regards them as random variables. The Monte-Carlo method is used to simulate samples of these random variables when performing FEA and predicting life of the LED. Scattered lives indicating a random sample out of the studied LED are then obtained even under the same temperature and environmental condition. By using the probability plot and statistical analysis, one can find the life distribution and reliability-related quantities of the LED.