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LED lighting cooling technology status and progress

LED for its small size, low power consumption, environmental protection, durable and rich color and other characteristics of light. The majority of users of all ages. But the current development of LED lighting is one of the bottlenecks facing the heat, this article will analyze the lighting process of heating problems on the impact of LED to lead the importance of cooling technology in LED lighting, and the current and future cooling technology to do Generalization and analysis.
First, LED lighting problems and the impact of heat
1. LED lighting there is a heat problem
In the use of LED lighting process, and the use of traditional lighting methods, the need to convert electrical energy into light energy. However, neither of these two methods can convert electrical energy into light energy completely, and only a small amount of electric energy can be converted into light energy, and most of the remaining electric energy (60% to 70%) in the LED light, Of the process into heat. Especially for high-power LED devices and lighting fixtures, as the power increases, LED internal chip temperature will gradually increase, and the LED chip and other internal device performance will decrease with the temperature rise, or even Failure. Eventually leading to LED devices can not work. Fundamentally, the rise in junction temperature reduces the probability of PN junctions emitting recombination. The performance of the light source is the luminous brightness decreased, resulting in a saturation phenomenon. So the heat problem is the LED development process to be solved.
2. The Effect of Heating Problem on LED
Fever in the above mentioned problems, heat problems will not only affect the life of LED devices, but also can affect the luminous brightness. Experience has shown that, in particular, the life of high-power LED LED mainly depends on the junction temperature of the chip, the higher the temperature. The lower the reliability, the shorter the service life. So not only from the LED materials, production methods, packaging structure and the principle of light-emitting devices such as integrated design LED, more important is to solve the existing LED devices and lighting in the heat, select the appropriate package structure and reasonable heat dissipation, and Applied to the LED lighting.
Second, LED lighting cooling technology status quo
Aiming at the limitations of LED devices and lamps in converting electrical energy into light energy, the concept of heat dissipation technology is put forward. Heat dissipation is designed to solve the problem of LED lighting, the removal of energy into that part of the light energy, heat from the power into the internal LED chip impact (making the chip performance degradation, aging or even failure).
1, the main factors affect the LED cooling
The main factors affecting the heat properties of materials (thermal conductivity), packaging structure, packaging materials, chip size, chip materials, the chip current density. Under normal circumstances, LED lighting devices and lamps from the chip, circuit board, external heat sink and drive four parts. Therefore, there are two kinds of thermal design: First, reduce the LED devices from the electrical energy into heat, the process needs to improve the internal quantum efficiency of LED devices, thereby improving the efficiency of LED light, and then from the internal solution LED lighting (use) The two sides is from the external design considerations, by changing the LED device and the lamp packaging materials or packaging in order to achieve the purpose of reducing the package thermal resistance, and sometimes need to configure the appropriate heat sink to solve the high Junction temperature problem, and thus to extend the service life of LED devices.
2, the current cooling method
Due to technical limitations, the current use of LED lighting devices to change the external design or use of the radiator method to solve the heat problem. LED lighting devices are currently a variety of cooling methods, can be divided into package-level cooling and lamp-level cooling mode. Package-level cooling, as the name suggests, it is by optimizing the LED internal packaging structure and materials to achieve the effect of reducing package thermal resistance, mainly divided into the packaging structure of the silicon substrate flip chip (FCLED) structure, metal circuit board structure and so on. Materials based on the substrate material and paste the principle of preferred selection of materials.
The main means of heat dissipation from the package substrate to the external heat sink in the transmission process to implement the cooling method, mainly divided into passive cooling and active cooling, active cooling refers to the energy outside the system through the drive, the LED chip and the internal The heat dissipation of the device itself, including the installation of forced cooling fan, liquid cooling, cooling and cooling of semiconductor cooling, ion wind cooling and synthetic jet cooling; and passive cooling is only through the radiator itself, will produce LED lighting process Of the heat out to achieve the effect of reducing the junction temperature, there are direct natural convection heat and heat pipe (flat heat pipe, loop heat pipe and fin heat pipe) technology cooling two.
3, several examples of cooling methods
(1) the principle of selecting the preferred material
In the use of this cooling method is the premise of the package structure has been identified, according to the package structure has been determined to select the most suitable packaging materials to improve the thermal conductivity of the system, thereby reducing the LED lighting package thermal resistance, and ultimately achieve the cooling effect of the system . Packaging materials can be broadly divided into three kinds of substrate materials, adhesive materials and packaging materials.
In the case of substrate materials, the heat dissipation technology involved in LED lighting devices requires substrate materials with high electrical insulation, high stability, high thermal conductivity, and chip-matched thermal expansion coefficients. Commonly used substrate materials are silicon, metal (aluminum, copper, etc.), ceramic (A1N, SiC) and composite materials.
(2) liquid cooling
Liquid cooling is a way to use the liquid in the pump driven by the force of the surface of the way through the radiator, heat dissipation of heat dissipation technology. US manufacturers Etemaleds has introduced a "water-cooled" LED lights - Etemaleds HydraLux one. It uses liquid cooling method, not only eliminates the need for cooling the bulb inside the heat pipes, heat sinks and fans, and not in the upper part of the bulb covered with heat dissipation material, its light radiation angle expanded to 360 degrees, such as Figure 1-1 shows.
From the above description we can see that the cooling liquid cooling is an active cooling method, but the liquid cooling method in the production process is complex and difficult to achieve, the price is high, not suitable for high temperature, vibration and other harsh environments; and liquid cooling in the cooling mode LED lighting device applications, require a high sealing liquid circulating refrigeration device, if the production process in a little improper, it will cause LED device damage.
Third, LED lighting cooling technology
With the current LED lighting technology matures, and the popularity of LED lighting applications, the existing thermal technology is not only based on the package structure, materials, but also based on the energy transfer process. New developments in substrate materials in packaging materials have been made in recent years, and the latest trends point to the development of silicon-on-silicon (GaN-on-silicon). Compared with the existing sapphire substrate, silicon-based gallium nitride has the following characteristics: to reduce the thermal expansion coefficient of difference, to strengthen the LED luminous intensity, low manufacturing cost, heat dissipation effect is remarkable. So silicon-based GaN by the LED manufacturers of all ages.
Fourth, the conclusion
Compared with the traditional lighting technology, LED does not completely replace the traditional light source, which is due to the LED lighting technology, there are still many key issues, one of the main bottleneck is the cooling problem. Although there are many existing cooling methods, but there are limitations, such as the realization of difficulties, high cost, poor thermal conductivity, high environmental requirements, and technical immaturity. So in the LED lighting cooling technology has yet to be in-depth research and development in order to LED-related technology for the mature development and lay the foundation for the extensive application of LED.

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