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LED Radiation Cooling Technology and Heat Dissipation Material

Radiation is one of the main factors affecting the LED lamp lighting intensity. LED lamp has higher energy efficiency 80% than traditional incandescent lamp, but its LED components and driver circuit are cursed by large amount of heat. If the heat is not properly discharged out, luminescence and lifetime of LED lamps will fall sharply.

The radiating fins can solve the problem of low illumination LED lamp. Lamps manufacturers can produce 40W LED s and 60W LED replacement lamps. High brightness LED lamp will meet the heat dissipation problem. A heat sink is unable to solve the problem of heat dissipation of 75W or 100W LED lamp.

Demand for the high brightness lighting is obvious, 75W and 100W occupy a large share of lamps lighting market. Markets are keen to use the inherent advantage of the LED lamp energy saving and repair. The United States energy independence and security act in 2007 requires the use of more efficient lighting lamps from 2012. These new requirements urge consumers looking for good quality , high service life and strong illuminance lighting to replace the existing incandescent lamp.

In order to achieve the ideal lighting intensity, we must use the active cooling technology to solve the heat release from LED lamp assembly. Some active cooling solution such as fan’s life is shorter than LED lamps’. In order to give the high brightness LED lamp a practical active cooling solution, cooling technology must be low energy consumption; and is suitable for the small lamp; the cooling system’s life is similar to or higher than the light sources.

Cooling mode

Generally speaking, in accordance with the modes how the heat is taken away from the radiator, the radiator can be divided into active and passive cooling heat dissipation. so-called Passive cooling refers that the heat of the LED light sources naturally emits into the air through the heat sink, heat effect is proportional to heat sink’s size, but because its heat emits naturally, and makes it greatly inefficient, often used in the space which does not have the required equipment, or used for radiating heat small parts, as part of universal motherboard will take passive cooling in the Northbridge. the vast majority takes active cooling type, which takes the heat from the heat sink compulsorily by fan cooling equipment,ect, which is characterized by high heat radiating efficiency, and small equipment volume

Active cooling, from the cooling mode segmentation, can be divided into air cooling, liquid cooling, heat pipe cooling, semiconductor refrigeration, and chemical refrigeration.

The wind cooling

The wind cooling heat is the most common way, by comparison, is a relatively cheap way. In fact, wind cooling/ air Cooling to use the fan to absorb heat away from radiator. Enjoys relatively low prices, is convenient for installation. But relying on relatively high on the environment, such as temperature and when overclocking ,the cooling performance was greatly affected.

Liquid cooling

Liquid cooling is to take away the heat of the radiator through the forced cyclic liquid in the pump drive , and compared with air cooling, it is quiet, can cool stably, has less dependence on the environment and so on. Liquid cooling at higher prices, and the installation is also relatively troublesome. at the same time ,When Installing ,as far as possible in accordance with instructions to guide installation to obtain the best cooling effect. Due to the cost and ease of use into account, liquid cooling usually adopts water as heat conducting liquid, so the liquid cooling radiator is often called the water-cooling radiator.

Heat pipe

Heat pipe is a heat transfer element, it makes full use of the heat conduction principle and the rapid heat transfer properties of the cooling medium, By liquid evaporation and condensation in fully-closed vacuum tube to transfer heat, Heat Pipe enjoys high thermal conductivity, good isothermal, the heat transfer area of hot and cold sides can be arbitrarily changed, long distance heat transfer is available, the temperature can be controlled , and a series of advantages, also the heat exchanger composed of the pipes has the advantages of high heat transfer efficiency, compact structure, small loss of fluid resistance. Its thermal conductivity has been far more than the heat capacity of any known metal.

Semiconductor refrigeration

Semiconductor refrigeration is to use a special semiconductor refrigeration slice energize to refrigeration through temperature difference, as long as the heat at the high temperature end can be effectively dissipated, the low temperature end is constantly being cooling. Have a temperature difference in each semiconductor particles, a refrigeration piece series by dozens of such particles, resulting in the refrigeration piece two is formed on the surface of a temperature difference. By using the temperature difference phenomenon, with the air / water cooling on the hot end temperature, can get excellent radiating effect. Semiconductor refrigeration has the advantages of low refrigerating temperature, higher reliability, cold temperature can reach minus 10 DEG C, but the cost is too high, which may be resulted from the low temperature and short circuited, and now the process of the semiconductor refrigeration piece is not mature, not practical.

Chemical refrigeration

The so-called chemical refrigeration, is to use some cryogenic chemicals which can absorb a lot of heat in the melting time to to reduce the temperature. The more common is to use dry ice and liquid nitrogen. For example ,the dry ice can decrease the temperature to minus 20 degrees Celsius, and some game player using liquid nitrogen make CPU temperature dropped to minus 100 degrees Celsius (in theory) is more "i, of course, because of the expensive price and the short duration , this method is more common in the laboratory or extreme overclocking enthusiasts   

The choice of material

The heat conduction coefficient (unit: W/mK)

  • Silver 429
  • Copper 401
  • Gold 317
  • Aluminum 237
  • Iron 80
  • Lead 34.8
  • 1070 type aluminum alloy 226
  • 1050 type aluminum alloy 209
  • 6063 type aluminum alloy 201
  • 6061 type aluminum alloy 155

Generally speaking, the ordinary air cooling radiator naturally choose metal as a radiator material. On the choice of materials, hope it has high specific heat and high thermal conductivity, as can be seen above, silver and copper conducting material is best, followed by gold and aluminum. But the gold, silver is too expensive, so, the heat sink is mainly composed of aluminum and brass. In contrast, copper and aluminum alloy two , each has its advantages and disadvantages: copper has good thermal conductivity, but the price is more expensive, difficult processing, its weight is too large, and the copper radiator heat capacity is small, and easy oxidation. On the other hand, pure aluminum is too soft, can not directly use, aluminum alloy can be used to provide enough hardness, advantages of aluminum alloy is cheap,enjoys light weight, but its thermal conductivity than copper will be much worse. So the following material products also appeared in the history of the development of the radiator:

Pure aluminum radiator

Pure aluminum radiator is the most common radiator early, the manufacturing process is simple with low cost, so far, pure aluminum radiator still occupy a considerable part of the market. In order to increase its fins’ heat radiating, the most commonly used processing method for pure aluminum radiatoris the aluminum extrusion technology, the main indicators and evaluation of a pure aluminum radiator is the radiator base’s thickness and Pin-Fin ratio. Pin refers to the heat sink fin’s height, Fin refers to the distance between the adjacent two fins. Pin-Fin ratio is Pin height (excluding the base thickness) divided by Fin, the bigger the Pin-Fin ratio is, means the greater the effective heat dissipation area of the radiator will be, also explains the aluminum extrusion technology more advanced.

Copper radiator

Thermal conductivity of copper is 1.69 times higher than that of aluminum, so in under the same conditions, copper radiator more quickly takes heat away from the heat source. But the texture of copper is a problem, a lot of radiator advertised "copper radiator" is not a real 100% copper. In the list of copper, copper containing more than 99% is known as non acid copper, the next grade of copper is named as Dan copper which is content of red copper under 85%. The copper content of pure copper radiator I in between on the market at present. The copper content of some poor copper radiator even is less than 85%, while the cost is very low, but its heat transfer capability is greatly reduced, affecting the heat dissipation. In addition, copper has obvious shortcomings such as high cost, difficult processing, bad radiator quality hinder the application of full copper heat sink. Red bronze ‘s hardness is not good like aluminum alloy AL6063 copper’s, some machining (such as groove etc.) performance is worser than aluminum; the melting point of copper is much higher than aluminum, is not conducive to the extrusion (Extrusion) etc..

Copper aluminum combined technology

Considering the shortcomings of the two kinds of copper and aluminum materials respectively, the current market for high-end part is a copper aluminum combined radiator manufacturing process, these fins’s base are usually made of copper metal, and the radiating fin is made of aluminum alloy, of course, in addition to the copper bottom, also a heat sink using copper pillars or by other methods, the principle is the same. With high thermal conductivity, copper bottom can rapidly absorb the heat released from CPU; aluminum fins can draw support from complex technological means to make the most conducive shape for heat dissipation and also offer larger heat storage space to quickly release heat, which find a balanced point in all aspects.

To enhance the LED luminous efficiency and service life, solving the problem of heat dissipation of LED products is the most important subject at the present stage of development, LED industry also focus on high power, high brightness, small size LED products for the development , therefore, providing heat dissipation substrate with the high radiation performance and precision dimension is the future trend in the LED substrate development. At the present stage, nitrogen aluminum substrate instead of alumina substrate, or by eutectic or flip chip process instead of grain / gold substrate binding mode to improve the luminous efficiency of LED is the mainstream of development. In this development trend, line alignment accuracy of the substrate itself request is extremely harsh, and must have the characteristics like high radiation, small size, metal lines which can be attached good., therefore, thin film ceramic substrates by using Photolithography fabrication, will become one of the important catalyst to promote LED high power.

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