Introduction of heat dissipation technology for high-power LED lighting products
LED lighting application trends and heat dissipation problems Due to the continuous advancement of Solid State Lighting technology, the luminous efficiency of LEDs has improved in recent years, and can gradually replace traditional light sources. At present, the luminous efficiency has surpassed incandescent lamps and halogen lamps and continues to grow upwards.
And some companies have developed LED components with an efficiency exceeding 100lm/W, which also makes LED lighting applications more and more widely used, not only has been used in indoor and outdoor lighting, mobile phone backlight modules and car direction lights, etc., more optimistic It is used in high-wattage projection lamps and street lamps and other strong lighting, large-sized backlight modules, and automotive headlights. Due to the advantages of power saving, environmental protection and long life, the trend of LED light source as the mainstream in the future will become more and more obvious.
In order to make LEDs emit brighter light, it is necessary to input higher power. However, the photoelectric conversion efficiency of high-power LEDs is still limited. Generally, only about 15~25% of the input power becomes light, and the rest is converted into heat energy. . Due to the small area of the LED chip, the heat generation per unit area (heat density) of the high-power LED is very high, even more serious than the general IC component, and the junction temperature of the LED chip is greatly increased, which is easy to cause overheating problems. . Excessive wafer junction temperature will reduce the luminous brightness of LED, among which the attenuation of red light is the most obvious. It will also cause the wavelength shift of the LED to affect the color rendering, and will also cause a significant reduction in the reliability of the LED. Therefore, the heat dissipation technology has become the bottleneck of the current LED technology development.
Therefore, the challenge of heat dissipation design is great. It is necessary to attach great importance to heat dissipation design from the chip level, package level, PCB level to system module level, and seek the best heat dissipation solution. For LED lighting products, the heat dissipation requirements of other levels are more obvious due to the large heat dissipation restrictions on the system side.
For the LED heat transfer problem, the most basic analysis method is to use the thermal resistance network for analysis. That is, a thermal resistance network is constructed from the main heat dissipation path of the LED from the chip heat source to the ambient temperature, and then the characteristics and magnitudes of each thermal resistance value are analyzed. Countermeasures to reduce the thermal resistance value. It should be noted that in actual analysis, a more detailed thermal resistance network can be formed according to the system structure, for example, considering the thermal resistance of interface materials such as Die Attach material and Solder, or the thermal resistance value of the heat dissipation module structure.
Due to the poor thermal conductivity of the Sapphire substrate of the LED chip, the thermal resistance value will be too high. Therefore, the improvement method must replace the Sapphire with a material with high thermal conductivity such as copper, or use the flip chip method to remove the substrate from the heat transfer path to reduce the thermal resistance. value. At present, the heat dissipation design with better performance from the chip to the package level, including the design of the common alloy substrate and the flip chip form, makes the heat transfer from the chip to the package more easily. It is also a feasible direction to increase the wafer size to reduce the heat generation density.
The heat dissipation design of high-power LEDs is very important, which is related to the quality and service life of the LEDs. Through the thermal resistance network, you can quickly analyze the heat dissipation capacity and requirements and find heat dissipation countermeasures. Due to the high heat generation density of high-power LEDs, it is necessary to conduct heat dissipation design from Chip Level, Package Level, Board Level to System Level to reduce thermal resistance. Get the best cooling effect. At present, major LED chip and packaging manufacturers in the world are committed to developing products with higher luminous efficiency. By improving the quantum efficiency of light, the photoelectric conversion efficiency is improved to reduce the heat generation of the chip.
In order to make the development and application of LED products faster, the related heat dissipation technology still needs to be developed simultaneously. Due to the continuous improvement of human's demand for the quality of life, just as the demand for heat dissipation of IC products has always existed, the heat dissipation design will still occupy an important position in the product design of various high-power LEDs.
