Author Guan Pin Chemical Research and Development Department - Dr. Ye Shengwei
The problem of severe light decay of LED street lights needs to be solved from the fundamentals of LED heat dissipation technology.
   At present, the growth rate of LED street lamps in China is higher than that of countries. According to statistics, 2010 will still be the first in the global market. Last year, the Ministry of Science and Technology of China decided that the “Ten Cities and Ten Thousand†semiconductor lighting application engineering pilot policy, although it is a model of economic development through market policies to create market demand, but the first-line response to the actual case of the manufacturer is not as expected.
   The gap between policy and market, in addition to the LED standard has not been fully regulated for manufacturers to follow, another latent technical problem is "LED street light severe light decay", resulting in less than one year of installation LED street lights can not pass the use of unit certification acceptance. The aforementioned LED standard specification has unified the formulation of the problem, and it is possible to draw a final decision in the near future. As for the "severe light failure of LED street lamps", it is necessary to solve the problem from the fundamentals of LED heat dissipation technology.
   Discussion on the Causes of LED Road Light Depletion
   Temperature is actually the key issue of LED road lighting, and LED street lights are stuck in this link. Since the LED street lamp has higher luminous power than the household lamp, the manufacturer has painstakingly designed the heat sink substrate fin and the heat dissipation module. The assembly needs to be outside the lamp heat dissipation module to protect the weather from frost. Unexpectedly, this externally protected spray paint sealed the heat of the heat-dissipating module, resulting in poor heat dissipation and LED epitaxial light decay.
   LED epitaxial luminescence heat energy belongs to a small range of concentrated heat energy. In the application of high-power street lamps, the power input power is also large, and the interface temperature of the LED is quite high. If the street lamp continues to work for a long time, if the heat dissipation module cannot effectively dissipate heat, Will affect the LED life and luminescence performance, such as the current LED street lights severe light decay is caused by these factors. LED street lights are used outdoors and have environmental and environmental interference factors. Therefore, most manufacturers use the anode treatment of LED street light radiators to protect them, or spray paint to avoid acid and alkali corrosion. The life of the anode treatment is not long, and it will oxidize and discolor for a long time. If you want to remove the heavy work, not only the time and labor will increase the maintenance cost; the paint protection cost is lower, the protection effect is good, but the general paint does not dissipate heat. Function, the paint itself will form a barrier function, which is equivalent to increase the thermal impedance of the LED street light radiator, which not only does not help, but because the heat energy is blocked in the heat sink, the LED epitaxial light power is reduced, and finally the severe light decay is caused. . The above has been a serious problem in the LED lighting industry, and it is almost the main reason why the public works LED street lights can not pass the procurement unit acceptance.
   LED road light failure solution
   To solve these existing problems, it is recommended that street lamp manufacturers start from the basic materials and solve the problem of high-power LED heat sources from the inside out. For example, when the light-emitting component is bonded to the aluminum substrate, the thermal conductive adhesive plays a key role. Some manufacturers think that the thermal conductivity film or the thermal conductive rubber pad has a good thermal conductivity, and the thicker the film thickness, the better, but the thermal resistance problem is not considered. The thermal conductivity is good, and the thermal resistance of the film thickness is useless. Moreover, the thermal conductive film or the soft thermal conductive gasket does not really adhere to the substrate, and there are actually many voids in the bonding surface. These pores are viewed under an electron microscope, like a hollow cavitation, another form of thermal resistance. In the presence of so many thermal resistances that interfere with heat transfer, the efficiency of heat and heat transfer is virtually reduced.
   The thermal resistance should be low to use the thermal conductive adhesive. It is recommended to use the soft ceramic thermal conductive adhesive for screen printing. The soft ceramic thermal conductive adhesive of screen printing is different from the traditional laminated thermal conductive adhesive film. The soft ceramic thermal conductive adhesive is soft semi-liquid. When the screen printing machine blade is coated on the aluminum substrate, the thermal conductive particles will penetrate into the pores of the substrate surface and Fill it up to full. This results in a completely flat, non-porous plane that will completely conform to the LED epitaxial carrier. In this way, the thermal resistance is reduced to a minimum, and the heat can be quickly conducted, which naturally reduces the ambient temperature of the LED die, and also prolongs the life of the epitaxial crystal and greatly delays the occurrence of light decay. In addition, due to the ductility of the soft ceramic thermal conductive paint applied by screen printing, it will change with the thermal expansion and contraction of the aluminum substrate during high temperature baking or reflow, the stress is very small, and the aluminum substrate will not be bent, nor will it be caused. Will burst.
   In the external protection of LED lamps, LED lamps and soft ceramic heat-dissipating paints are recommended. The spray-type soft ceramic heat-dissipating paint can be directly sprayed on the outside of the LED lamp, and the construction operation is simple, and can be adapted to various shapes of heat-dissipating structures, and can also be adjusted to different colors, in response to the needs of landscape design. The soft ceramic particles in the spray-type heat-dissipating paint are treated by nano-treatment, and the fine particles are not only easy to be sprayed, but also the heat-conducting particles on the same coating area are dense and dense, and the area of ​​the temperature volatilization is also increased. Let the heat of the LED luminaire be quickly conducted. Soft ceramic heat-dissipating paint is a thermosetting material, which is in compliance with RoHS environmental protection safety regulations. The construction procedure is simple and does not require any special equipment. After baking, it is heat-set and can withstand the high temperature of LED for a long time without quality change. LED street lights, landscape lights, or LED advertising billboards used outdoors will also face acid and alkali damage such as wind and rain, acid rain, bird droppings, air dust, black smoke, etc. Therefore, this spray-type soft ceramic heat-dissipating paint must have the characteristics of acid and alkali resistance. The current acid-base resistance value is in the range of PH 3 ~ 11, which can effectively protect the appearance of LED outdoor lamps from being eroded.
   The cost structure of LED lamps has been continuously improved with the development of packaging technology, carrier board design and heat dissipation module structure, and the cost has also decreased with the development of technology and market demand. However, there are not many manufacturers investing in material improvement, which is mainly related to the history and habits of Taiwan's industrial and commercial development. Taiwanese manufacturers are more prone to process and design, and have less ink on material development. Therefore, in the issue of solving technical problems or reducing costs, it is more biased towards purchasing thinking or life management thinking. However, at the first time, US and Japanese manufacturers will think about the application materials, reduce costs, improve quality and increase profits from the perspective of innovation.
   Taiwan's LED industry's output value ranks among the top two in the world. Under the common theme of global warming, energy conservation and carbon reduction, it is an organic and sustainable industrial advantage. If Taiwanese companies can master the current high-quality production technology, advanced processes, and research and development of materials, it is very likely to become the leader in LED applications after the computer industry. At the beginning of 2010, within the foreseeable one or two years, the LED lighting industry will be able to see the economic scale, which is the key opportunity for Taiwanese manufacturers to grasp.
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