With the increasingly serious in energy shortage and environmental pollution, LED lamps (especially for high-brightness LED applications) have become a hot topic among lighting applications providers and customers due to their energy-saving and environmental friendly characteristics. Normally, LED lamps are composed of LED modules, cooling sections, drivers, lens, and other optical/electrical components. It is the cooling section that the most important, since LED lamps with a poor heat dissipation effect will reduce their lifetime. According to the testing report of Cree XLamp XR-E, there is a closed relation between working temperatures and service life of LED lamps. Thus solving the problem of thermal management has become a key point to high-brightness LED applications.
However, the heat generated by LED lighting sources is not the major factor for LED working conditions and service life. The accumulation of heat within chips (hot spots) is a more serious problem for LED lamps. For general standard LED devices, LED modules that have a power consumption of 1W will have a heat flux of 100W/cm2, 300W/ cm2 for 3W LED modules, while the average heat flux of CPU is only 60-130 W/cm2. A large amount of heat concentrated within the small-sized wafer, leading to the increase of temperature, the uneven distribution of thermal stress, and finally the reduction of wafer luminous efficiency and emission efficiency of the fluorescent powder. When the temperature exceeds a certain value (threshold), the failure rate of the device will increase exponentially. When multiple LED lights constitute the entire white light illumination system, the heat dissipation is even more serious.
Heat conduction and heat convection are two main path for heat dissipation of LED devices. Traditionally, the cooling structures of LED lamps include bases, heat sinks and radiators. Bases are directly connected with LED chips and typically used for conducting heat generated by chips, with thermal conductivity but not electrical conductivity. Heat sinks can spread the heat, used to avoid the heat accumulation on LED chips. They can also increase the efficiency of radiators. Heat radiator can effectively dissipate all heat outwards into the air. Among them, it is the base that needs to be taken careful consideration of. Bases made by materials with relatively large thermal conductivity will result in severe self heat effects, which is a devastating impact on the performance and reliability of LED devices.