结温与热阻制约大功率LED发展

Junction Temperature and Thermal Resistance Restrict the Developing of High-power LED

LED结温高低直接影响到LED出光效率、器件寿命、可靠性、发射波长等。保持LED结温在允许的范围内,是大功率LED芯片制备、器件封装和器件应用等每个环节都必须重点研究的关键因素,尤其是LED器件封装和器件应用设计必须着重解决的核心问题。首先介绍pn结结温对LED器件性能的影响,接着分析大功率LED结温与器件热阻的关系。基于对器件热阻的分析,得出了结温与热阻已经制约大功率LED进一步向更大功率发展的结论,并提出了如下两个观点:1.要在保持低成本和自然散热方式下提高LED器件的功率,根本的出路是提高光转换效率;2.在目前没有提高光转换效率的情况下,发展超过5 W的大功率器件对工程应用没有实质意义。

The junction temperature of LED has directly influence upon light output efficiency, device life time, reliability, emitting wavelength of LED. With the invention of high-power LEDs, the requirement for drive current has increased significantly, thereby increasing power dissipation. But only approximately 5%-to-10% of the input electrical power in LEDs is dissipated optically while the other portion produces heat energy based on the current technology. Specially, the heat inside high-power LEDs rely mainly on natural cooling, but no active cooling was used because the active cooling will increase the cost, decrease the reliability, and shorten life time of the whole LED lighting system. Only if the cost of each lumen（for example, USD/lm） in the semiconductor lighting is lower than other lighting source, the semiconductor lighting could replace the conventional lighting sources. So, effective thermal management of high-power LEDs must be dealt with by way of low cost and natural cooling. Keeping the junction temperature of LED in the given range is a main research goal of chip fabricating, device packaging and application. Specially, it＇s also a key issue being dealt with during packaging and application of high-power LED. The influences of pn junction temperature on capabilities of LEDs are described in this paper, firstly. And then the relations of junction temperature and thermal resistance of high-power LEDs are analyzed. The conclusion that junction temperature and thermal resistance restrict farther developments of high-power LEDs has been deduced based on the thermal resistance analyses of high-power LEDs. Meanwhile, the following viewpoints is put forward： （a） How to increase light output efficiency is a basic sticking point in process of raising the power of LED devices. （b） There is no point in developing high-power LEDs which go beyond 5 W for engineering applications if the light output efficiency of LEDs has no improvement.