Investigation of microstructure and optical property of high power LED based on rapid thermal cycling

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 induction heating. Under an application of induction heating as rapid heating source, the specimens that were being non-operating and operating life tests 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 and radiant power of two kinds of LED specimens were compared 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 (FEM) which is helpful for the failure analysis and design of the reliability of the LED packaging. The microstucrue 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.