White LED temperature rise the solution to the problem

19 May

The past LED to take full advantage of the industry white led strip lights, ever developed large size LED chips to way to achieve the expected goal. But, in fact, white LED on the power for more than 1 W above beam may decline, the luminous efficiency relative reduce 20 to 30%. In other words, a white LED brightness if better than the traditional LED tarsus times, power consumption characteristics of fluorescent lamps beyond words, he must overcome the four big subject: inhibition of temperature rise, to ensure that the service life, improve the luminous efficiency, and equal access to shine characteristics.
Temperature rise the solution to the problem is to reduce encapsulates the heat impedance; Maintain LED the service life of method is to improve chip appearance, using small chips; To improve the efficiency of the luminous LED is to improve the structure, using small chips; As for the method of even the light characteristics is to improve the packaging method LED, these methods have been acquired development.
To solve the heat dissipation problems is the fundamental encapsulation method
By increasing the power it will cause encapsulates the heat impedance sharply down to 10 K/W below, therefore the foreign investors ever developed resistance to high temperature white LED, to improve the above problems. However, in fact high power LED calorific value than small high power LED several times above, and temperature rise still can make the luminous efficiency greatly decrease. Even if the packaging technology allow high quantity of heat, but LED chips temperature could engage more than allow value, finally providers to solve encapsulation finally understood the heat dissipation problems is the fundamental method.
The LED the service life, such as switching to siliceous packaging materials and ceramic packaging materials, can make the LED the service life of a digit increase, especially the white LED light spectrum contains less than 450 nm wavelength light wave, the traditional epoxy resin packaging materials can be wave light damage, high power of large amount of light in the white LED more accelerated packaging materials of degradation, according to industry and the test results show that less than ten thousand hours of continuous light, high power white LED brightness has more than halved, cannot satisfy the lighting of the basic requirements of long life.
The luminous efficiency about flexible led strip, improve the structure and packaging structure, can achieve the and low power white LED the same level. The main reason is the current density improve more than two times, not only not easy to take out the light from the large chips, but the result will cause the luminous efficiency as low power white LED dilemma. If improve chip electrode structure, theory can solve the above problem take light.
Try to reduce heat impedance, improve heat dissipation problems
The glowing characteristics uniformity, it is generally thought that as long as the improvement of the fluorescent white LED the material concentration uniformity and fluorescence body production technology, should be able to overcome the above problems. As described above on improving power at the same time, must try to reduce heat impedance, improve heat dissipation problems. Specific content is respectively: reduce chips to encapsulates the heat impedance, inhibition of packaging to printing substrate heat impedance, improve the chip heat flow.
In order to lower the heat impedance, many foreign firms will LED LED Light Bars set in copper and ceramic material made of radiator (heat sink) surface, then again by welding way will print circuit board with wires connected to heat the cooling fan forced air cooling of the radiator. According to German OSRAM Opto Semi conductors Gmb experiment results show, the structure of the LED chips to welding points can reduce the heat impedance 9 K/W, is about traditional LED to about 1/6 of that, after the encapsulation on 2 W LED power, LED chips of joint temperature welding points than high 18 K, even printed circuit boards up to 50 ℃ temperature, temperature 70 ℃ at most only engagement around; Compared with previous heat impedance once reduce words, LED chips of joint temperature will by the influence of the temperature of printed circuit board. Therefore, it is necessary to try to reduce the temperature of the LED chips, in other words, reduce LED chips to welding points of heat impedance, can effectively reduce the burden of the cooling effect LED chips. In turn that even the white LED with the structure of the heat impedance inhibition, if not from the heat conduction printed circuit board words to package, LED the increase of the temperature will still make the luminous efficiency fallen sharply. Therefore, matsushita electric development printed circuit board and packaging integration technology, this company will 1 mm square blue light to flip chip packages LED way in ceramic substrates, then again will ceramic substrates paste in printed circuit board copper surface, according to panasonic reports include printed circuit board, the whole heat impedance module is about 15 K/W or so.
The industry design show heat work force
Due to the radiator and printing circuit board between the density of direct heat transfer effect around, so printed circuit board design become very complex. In view of the American Lumileds and Japan etc lighting equipment, CITIZEN LED packaging manufacturer, has successively developed high power LED with simple cooling technology, CITIZEN in 2004 to start making white LED samples enclosed, do not need special bonding technology can also thick about 2 ~ 3 mm the quantity of heat of radiator directly discharge to external, according to the CITIZEN reported although LED chips juncture to the radiators 30 K/W heat impedance ratio of OSRAM 9 K/W, and in general environment will make the hot impedance increase at about 1 W, even if is the traditional printed circuit board without the cooling fan forced air cooling condition, this white LED module can also be used for lighting.
Lumileds began in 2005 manufacturing of high power LED chip, engage allow up to + 185 ℃ temperature higher than other company the product high 60 ℃, the use of traditional RF 4 printed circuit board packaging, around 40 ℃ environment temperature range can enter the equivalent of 1.5 W power of current (about 400 mA). So Lumileds and CITIZEN is take actions to enhance juncture allow temperature, Germany OSRAM company is will LED chips set in radiator surface to 9 K/W low heat impedance records, this record than the past at the same level of product development OSRAM heat impedance reduced by 40%. It is this LED module package, the traditional method and the same flip chip way, but LED module and radiator joints is select the most close to shine LED chips as the jointing surface layer to make light of the layer heat to the most short conduction emissions.
In 2003, Toshiba Lighting once in 400 mm square aluminum alloy surface, laid the luminous efficiency for 60 lm/W low impedance white LED, without the cooling fan, and other special heat dissipation components premise, manufacture beam for 300 lm LED module. Because Toshiba Lighting has rich experience of manufacture, so the company that the simulation analysis of technology progress, 2006 years after more than 60 lm/W white LED, can easily use lamps, box body improving the heat conductivity, or use of compulsory cooling fan air cooling way design of Lighting equipment cooling, don’t need special cooling technology module structure can also use white LED.
Change packaging materials inhibit material degradation and light transmittance reduce speed
The longevity of the LED, at present, the LED manufacturers is to change the countermeasures of packaging materials, and at the same time will be scattered fluorescent material in packaging materials inside, especially silicon quality packaging materials than traditional blu-ray, nearly ultraviolet light above LED chips epoxy resin packaging materials, we can be more effectively restrain the material degradation and light transmittance reduce speed. Because of the epoxy resin absorption wavelength for 400 ~ 450 nm light percentage reaches as high as 45%, siliceous packaging materials is below 1%, fai degrees in half the time of epoxy resin is less than ten thousand hours, siliceous packaging materials can be extended to forty thousand hours, almost and lighting equipment design life the same, this means that the lighting equipment use period without the need to change the white LED. But siliceous resin belong to high elasticity soft materials, process required to use won’t scratch the surface of the siliceous resin production technology, in addition process siliceous resin easily attached to the powder crumbs, so the future development can improve surface characteristics necessary technology.
Although siliceous packaging materials can ensure that LED to forty thousand hours of service life, however lighting equipment industry there are different views, the main argument is the traditional incandescent lamp and the service life of fluorescent lamp, is defined as “brightness drop to 30% below”. Brightness in half the time for forty thousand hours of LED, if converted to fall to 30% from the following words brightness, with only about twenty thousand hours. There are two prolong the service life of components countermeasures, it is respectively, restrain white LED the rise of temperature of the whole, and stop using resin packaging mode.
Generally think that if thoroughly carry out above two countermeasures and prolong its life, can achieve 30% brightness of forty thousand hours of requirements. Restrain white LED by cooling temperature can be LED encapsulation printed circuit board of method, the main reason is encapsulated under high temperature resin, plus the glare rapid degradation will, in accordance with the law, o ray temperature by 10 ℃ life will extend 2 times. Stop using resin packaging can completely destroy the degradation factors, because of the light from the LED in encapsulated resin internal reflections, if use can change the direction of the light side chip marching resin material reflex plate, the reflex plate can absorb the light, make the light out of quantity sharply down sharply. This is also LED manufacturers use ceramic is consistent with metal is the main reason for packaging materials.


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