Reliability And Failure Analysis Of The High Power Blue LED

With the demand of power saving and the requirement for higher illumination quality, semiconductor lighting sources have been attractive for its excellent characteristics: high efficiency, low power consumption, long source life, color richness and environment friendly etc. As the representative of semiconductor illumination, the performance of high power Light Emitting Diodes (LED) improves quickly resent years and its luminance efficiency has surpassed 50lm/W. Thus high power LED will become the fourth generation lighting source replacing incandescent, fluorescent and high intensity discharge (HID) lamp. Otherwise some key issues should be solved before high power LEDs widely application in general illumination market, such as new package materials, package heat management and suitable measurement method. This thesis focuses on high power LED lighting sources and researches their assembly and typical failure mechanism. Several failure problems occur in the service are also discussed and some methods for improving the reliability of high power LEDs are suggested.The development of LED package and assembly technology is discussed, especially on the application of the high power LED package technique for LED lighting sources. The primary failure problems occur in the packaging and service process are introduced and a typical failure problem had been researched deeply. Consequently, we analyzed and discussed the problems found in this process. Finally, the possible reason of the failure has been given out.On the effect of the high temperature and ultraviolet radiation in the service, the origin of the dark stain on the chip surface could mostly be the degradation of the plastic packaging material close to the chip surface. Oxygen and carbon were found to be concentrated in the degraded regions and was supposed to be principally responsible for the forming of the dark stain. We found that the silica gel has the stronger resist ability to the radial and high temperature than the plastic. It could solve this failure problem very well.The thermal process of high power LEDs in service was simulated to see the thermal distribution of the LED in several different conditions for cooling. For the specifically chip, the primary influence factor of the LED thermal dissipation is the external convective heat transfer coefficient but the external environment temperature.