Analysis of ways to improve the thermal performance of LED
About the LED thermal performance analysis of the ways: LED energy-saving lamps, LED related to the use of life, such as the use of silicon packaging materials and ceramic pottery packaging materials, LED life can increase the number of years, in particular White LED’s flash spectrum includes short wavelengths of less than 450nm light, the traditional epoxy natural resin packaging materials can easily be short-wavelength light damage, high-power white LED light more rapid deterioration of packaging materials, LED fluorescent, according to industry testing The final result revealed that re-lighting less than 10,000 hours, high-power white LED brightness has been reduced by more than half, there is no way to meet the basic requirements of the long life of the lighting source. Up to now, there are two ways to extend the life of the components used to survive, respectively, to restrict the temperature rise of white LED groups, and stop using natural resin encapsulation.The use of natural resin encapsulation can completely eliminate the deterioration factor, LED lamp, the LED initiation of light in the package of natural resin reflection, if you can change the chip side of the light advance direction of the natural resin material reflector, the reflector will learn from light , So that the amount of light extraction sharply reduced. Because of this, indispensable way to reduce the temperature of LED chips, in other words, to reduce the thermal resistance of the LED chip to the solder joint, LED tube can reduce the temperature effect of reducing the burden.However, in fact, high-power LED hair card than the low-power LED high number of times more than, and the temperature rise will make the flash rate dropped significantly. LED bulb, the specific content of the specific internal as follows: to reduce the thermal resistance of the chip to the package, the thermal resistance of the package to the printed circuit substrate, the chip heat dissipation smooth patency.Reduce thermal impedance, improve heat dissipationRelated LED flash rate, improve the chip structure and package structure, can be achieved with the same level of low-power white LED. In view of this, the United States Lumileds and Oriental CITIZEN and other lighting facilities, LED packaging manufacturers, followed by a research and development of high-power LED with simple cooling technology, CITIZEN in 2004 to proceed to produce white LED sample package, without special combination of technology can also be thick 2 ~ 3mm The calorie of the heat sink is discharged directly to the outside. According to the CITIZEN report, the 30K W thermal impedance of the junction point of the LED chip to the heat sink is larger than 9K W of the OSRAM, and the room temperature in the ordinary background will increase the thermal resistance by 1W , Even if the traditional printed circuit board cooling fan forced air cooling conditions, the white LED plate can also be reelected use.Related to the special nature of the average flash, the general feeling that as long as the improvement of white LED fluorescent material, the average concentration of liquid and phosphor manufacturing technology, should be able to overcome the above-mentioned siege and disturbance.Because the increase in power will lead to the rapid thermal resistance of the package down to 10K W below, because the overseas industry before the development of high-temperature white LED, intended to improve the above-mentioned problems.Although the silicon packaging materials can guarantee the use of LED 40,000 hours of life, but the lighting industry has revealed a different view, the main argument is the use of traditional light bulbs and fluorescent lamp life, is defined as “brightness down to 30 100% or less. ” Brightness half of the time for the forty thousand hours of the LED, if converted into brightness to 30% below, then only about 20,000 hours or so.General feel that if the full implementation of the above two life extension measures, you can reach 30% of the brightness of 40,000 hours when the request. Because of this, Matsushita Electric Research and Development of printed circuit board and package integration technology, the company will 1mm square blue LED to flip chip package in the form of ceramic ceramic substrate, ceramic substrate and then continue to adhere to the appearance of copper printed circuit board, According to Panasonic reported that inside the printed circuit board with Shunde led display panel, including the thermal resistance of the plate group is about 15K W or so. So Lumileds and CITIZEN is taken to increase the junction temperature allows the German OSRAM LED chips will be set in the cooling device surface, to 9K W ultra-low thermal impedance records, the record than the previous OSRAM products developed similar thermal impedance loss of 40 percent . It is worth mentioning that the LED plate package, that the appropriate use of traditional flip-chip approach with the same form, but the LED plate and the heat sink in conjunction with the often, then pick the closest to the LED chip flash layer as the bonding surface, Flash layer calories can be the shortest distance conduction emissions.LED industry in the past in order to obtain full white LED light beam, large-size LED chip before the development of this plan intended to achieve the purpose of anticipating. Such as growth to give power at the same time, indispensable way to reduce thermal impedance, improve the heat problem. However, in fact, given the white LED power to continue to adhere to more than 1W more than the time will actually decline, the flash rate is relatively reduced by 20 to 30 percent. In other words, the brightness of the white LED if the LED several times larger than the traditional, the special nature of the power consumption of more than fluorescent, it is essential to overcome the following four issues: to limit the temperature, to ensure the use of life, improve the flash rate, and Special properties of the flash are averaged. On the contrary, even if the white LED has a structure to control the thermal impedance, if there is no way to the calories from the packaging conduction to the printed circuit board, LED temperature rose the final result will make the flash rate of rapid decline.Solve the package heat problem is the fundamental wayThe solution to temperature rise is to reduce the thermal impedance of the package; to maintain the life of LED life is to improve the chip shape, that the appropriate use of small-scale chip; LED flash rate improvement approach is to improve the chip structure, The use of small-scale chip; As for the special nature of the flash is the way to improve the average LED packaging methods, these methods have been developed in succession. Because the natural gas epoxy resin reference wavelength of 400 ~ 450nm as high as 45% of the percentage of light, silicone packaging materials are less than 1 percent, half the brightness of time less than 10,000 hours of natural epoxy resin, silicon packaging Materials can be extended to about 40,000 hours, almost the same life with the default life of the lighting, which means that the use of lighting facilities do not need to change white LED.However, the natural silicone resin belongs to the high elasticity and soft material, and the processing is not necessary to use the manufacturing technology which does not scratch the appearance of the natural siliceous resin. In addition, the natural siliceous resin can easily be attached to the crumbs because this future is indispensable. R & D can improve the appearance of the special nature of the technology.Related LED longevity, so far LED manufacturers to take measures to change the packaging materials, while the fluorescent material dispersed in the packaging materials, especially silicon packaging materials than traditional blue, near the top of the ultraviolet LED chip epoxy natural resin Packaging materials, can be more effective control of material deterioration and light penetration rate to reduce the rate.
Change the packaging material control material deterioration and the rate of light penetration rate reducedToshiba Lighting in 2003 before the 400mm square aluminum alloy appearance, shop repair flash rate of 60lm W low thermal resistance white LED, no cooling fan and other special cooling components under the premise of trying to make light beam 300lm LED plate. Mainly by the current density increased by more than 2 times, not only can not help but easy to extract light from a large chip, the end result will lead to flash rate is not as low-power white LED dilemma. According to the results of the German OSRAM Semi conductors GmbH, the thermal resistance of the LED chip to the solder joint can be reduced by 9K W, which is about 1 6 of that of the conventional LED. The LED after encapsulation gives 2W of power , The LED chip bonding temperature 18K higher than the solder joint, even if the printed circuit board temperature rose to 50 ℃, the combination temperature is only about 70 ℃ at most; compared to the past once reduced thermal impedance, LED chip bonding temperature Will suffer from the impact of printed circuit board temperature. Restricted white LED temperature rise can be considered appropriate to use cooling LED packaging printed circuit board approach, the main end is encapsulated by the natural resin at high temperature conditions, coupled with strong light mapping will rapidly deteriorate, followed by the law of Arrhenius temperature 10 ℃ to survive Of life will be extended by 2 times.Because the heat sink and the printed circuit board between the precise precision of the direct left and right thermal effects, because the printed circuit board design becomes very complex. In order to reduce the thermal resistance, many overseas LED manufacturers will LED chip set in the copper and ceramic materials made of heat sink (heat sink) appearance, continue to use the form of welding cooling cable printed circuit board connected to the use of cooling fans Forced air cooling of the cooling device. Because Toshiba Lighting has Haobo try to make the experience, because the expression of the enterprise because the mimic profiling technology advances in 2006, after more than 60lm W of white LED, can easily use the lamp, the box to increase thermal conductivity , Or the use of cooling fans forced air-cooled form of pre-lighting of the heat, without special cooling technology can also use the plate structure of white LED.Lumileds began manufacturing high-power LED chips in 2005, combined with the allowable temperature of up to +185 ℃, LED bulbs, LED lighting products higher than the same level of other enterprises 60 ℃, the use of traditional RF 4 printed circuit board package, A current equivalent to 1.5 W of electric power (about 400 mA) can be inputted in the temperature range of 40 ° C. This is exactly the same as LED manufacturers believe that the use of porcelain pottery and metal-based packaging materials mainly by the end. Even if the packaging technology to allow high-calorie, but the combination of LED chip temperature may exceed the allowable value, and ultimately the industry finally realized that the cooling solution to solve the package is the fundamental way.