Failure Analysis And Reliability Study Of Nitride-Based LED

Light emitting diode(LED) has the characteristics of long lifetime, energy saving and environment protection, etc. LED has been widely used in the field of lighting and display. Stadies on the LED reliability are the guarantee to realize the wide use of LED in various applications, and play an important role in stady and manufacture of LED. This paper research on the failure analysis and reliability of Nitride-based LED, find out the causes of LED failure, and establish degradation model of optical parameter. The result of this paper is of great importance for LED scientific research and quality inspection in the future.The failure mechanism of white LED negative electrode shedding phenomenon has been investigated in this paper. Scanning Electron Microscopy(SEM) and Energy Dispersive Spectroscopy(EDS) are used as two main techniques to characterize the surface morphology and composition of the chip. SEM shows that the surface of negative electrode dropped off is coarse, and granular crystals are formed in the transparent conductive film. Chlorine element has been detected in both corroded negative electrode part and the packaging glue by EDS testing. It is found that the electrochemical corrosion between chloridion and aluminum is the main reason to result in LED failure.The short circuit failure mechanism of via hole vertica-structured GaN-based LED has been researched. Dark area near the via hole of failure sample has been observed by optical microscope, and center around the via hole. Corss-section combines with SEM are used to analysis the morphology characterization of the section. SEM shows that the GaN epitaxial layer of failure sample is fractured, a large number of voids have been observed in both back gold layer and dia attaching layer. It is found that the existence of voids leads to internal thermal stress and electrical stress in LED, which break the GaN epitaxial layer ultimately and result in short circuit.A reliability evaluation method has been proposed on nonmonotonic degradation law of LED. The acceleeratd degradation test is conducted inorder to obtain luminous flux degradation data. A bi-exponential degradation model is used to fit the lumen maintenance degradation data. The pseudo failure lifetime is tested and analyzed by MATLAB. The distribution type of pseudo failure life is determined by using Kolmogorov-Smirnov test. The results show that the two samples respectively obey Lognormal distribution and Weibull distribution, and the reliability evaluation of LED are made by the corresponding distribution parameters. This method has a certain reference value to reliability evaluation on nonmonotonic degradation law of LED.