Influence of properties and microstructures on thermal fatigue testing of high-power LED

The objective of this paper is to investigate the effect of rapid thermal cycling on microstructure and optical property (luminous flux and luminous efficiency) of high power light emitting diode (LED) by thermal fatigue testing from -40 to 125. Under an application of thermal fatigue device as a heating source, the specimens that were being non-operating and thermal fatigue testing in the experiment were rapidly heated and cooled based on a control system that employs a fuzzy logic algorithm, respectively. The optical performances, including luminous flux, luminous efficiency, radiant power and color temperature (CCT) of LED specimens were tested and analyzed. It was found that the rapid thermal cycling have similar evident influence on them. The results showed that the color purity of LED was also descended, the correlated color temperature (CCT) was also risen, but their changing rate and extents are different. The high and low temperature distribution in LED chip was simulated by finite element modeling which is helpful for the failure analysis and design of the reliability of the LED packaging. The microstructures of LED chips are analyzed after different rapid thermal cycling time. The results are showed that rapid thermal cycling can affect greatly the LED properties and interface microstructures. All the results indicate that this approach to rapid thermal cycling by using rapid heating source is feasible to investigate the optical performance of high power LED, so it can also effectively verify the reliability of LED devices.