摘要
基于节能的需要以及人们对照明质量要求的不断提高,半导体照明光源以其高效节能、长寿命、色彩丰富和环保等特点受到了人们的广泛关注。大功率发光二极管作为半导体照明的代表,其性能近来提高很快,发光效率已接近130 lm/W,有望取代白炽灯、荧光灯和高压放电灯等传统光源,成为人类照明史上的第四代照明光源。目前大功率LED应用于通用照明上还存在着一些问题有待解决,比如新型的封装材料,过高的封装热阻和合适的测试方法等。本文研究了大功率LED光源的封装结构与典型失效机理,对实际服役中出现的失效问题进行了分析和讨论,并提出了改善大功率LED可靠性的建议。
文章首先论述了LED封装与组装技术的发展,对大功率LED芯片封装技术在LED照明光源上的应用作了探讨。接着指出了目前大功率LED在封装和服役过程中所产生的主要失效问题,并就其中一种典型失效进行了探讨。对于实验中所遇到的问题进行分析和讨论,明确了其失效机理。
本文提出大功率蓝光LED在服役过程中由于高温,紫外线辐照等因素导致其封装材料的快速老化而分离出来的C和O元素的沉积是芯片表面发黑失效的原因。发现,采用抗老化能力更强的硅胶作为封装材料以及提高芯片的散热性能将有效的解决这一失效问题。
本文还利用计算机模拟了大功率蓝光LED的热过程以明确在不同的散热条件下大功率LED温度分布的情况。研究表明:在芯片材料一定的情况下,影响LED散热的主要条件为外部对流换热系数的大小,而外界环境温度的影响不大。
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.
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