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Research on the Reliability and Failure Mechanism Analysis of High Power Led

Author: ZhaoALing
Tutor: ChenJianXin
School: Beijing University of Technology
Course: Microelectronics and Solid State Electronics
Keywords: High power LED Reliability Life test Failure mechanism
CLC: TN312.8
Type: Master's thesis
Year: 2010
Downloads: 788
Quote: 1
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Abstract

Light-Emitting-Diode (LED) is a semiconductor light source. Used in a variety of applications ranging from indicator lamp to general illumination, LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater durability and relilance. Compared to incandescent light and fluorescent light, LEDs are especially energy efficient and environmentally sustainable, which lead them to become a main lighting source in the future. For these reasons, LEDs are becoming a research focus of academia, industry and geverment.LEDs provide energy efficiency in illumination. Among the many applications of LEDs, using as a general illumination is the most prosperous application. Semiconductor illumination is now the new industry the governments pay attention to, for which high power LED is the key device. However, the realization of semiconductor illumination depends on the improvement of high power LED reliability. The research on the reliability of LED is the premise and base for the improvement of LED reliability.Based on the above reasons, the main works in the paper can be summarized as following:1. Staring from the working principle of LED, the advantages and disadvantages of LED are introduced. Reviews the reliazation methods and the main application of white LED and the development level of domestic and inaternational research institutes and companies of high power LEDs. The significance of the thesis and main works of this dissertation were explained.2. Reviews the concept and significance of reliablity testing. Discusses the basic methods of the LED reliability testing and accelerated life test. The principle of accelarated life test in which current as accelerated stress was discussed.3. Current stress accelerated life tests were carried out in which 1W and 3W GaN-based white LED were used as test samples. Some key performance parameters change with the aging time were studied, including luminous flux, luminescence efficiency, peak wavelength, voltage, correlated color temperature. The main factors that influence the samples lifetime were analyzed. The lifetime of 1W and 3W LED test samples were estimated respectively. In conclusion, the lifetime of 1W LED in normal condition is 25,565 hours, and the lifetime of 3W LED in normal condition is 37,371 hours. In addition, the errors that introduced in test and lifetime calculation were briefly discussed.4. Based on the test, failure mechanisms of high power white LED are discussed. The main reasons that cause the failure include degradation of encapsulant, phosphor degeneration, poor heat dissipation and electrostatic discharge. Besides, other failure mechanisms of LED include metal electromigration and defects of LED chip. Some improvement measures were suggested.

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