The investigation of LED´s reliability through highly accelerated stress testing methods

The white light emitting diode technology is developing rapidly in recent years. Evaluating the lifetime and failure rates of white LED devices in short time periods is still a big problem. We propose to use highly accelerated stress testing (HAST) methods to investigate the reliability of LED devices in 168 hours. Biased highly accelerated temperature and humidity tests are conducted. The present work shows that under HAST conditions, the degradation of optical flux obeys exponential law also. Based on the Arrhenius equation, an accelerating factor of 81.4 is obtained for HAST methods. Normal accelerated life tests are carried out for comparison usage. The lifetimes of 70% lumen maintenance estimated by HAST experiments, normal ALT experiments and the manufacturer are at the same order, implying that highly accelerated stress tests can be an effective way to estimate LED´s lifetime quickly. Finally, a statistical analysis of the lifetime distribution through Nelson estimation and TTT curve indicates that GaN-based wLED fails in an increasing trend. Efforts must be conducted to improve the reliability of GaN-based LEDs.