IACS CO., LIMITED (Yiwu Fuwei e-commerce firm)

In the past, in order to profit from the full white LED beam, the LED industry has developed large-size LED chips to try to achieve the desired goal. However, in fact, when the applied power of the white LED continues to exceed 1W, the beam will decrease and the luminous efficiency will be relatively reduced. ~30%, in other words, if the brightness of white LEDs is several times larger than that of traditional LEDs, and the power consumption characteristics are expected to surpass fluorescent lamps, it is necessary to overcome the following four major problems, including suppressing temperature rise, ensuring service life, and improving illumination. Efficiency, and luminescence characteristics are equalized.

1 Solving the heat dissipation problem of the package is the fundamental method

As the increase of power will cause the thermal impedance of the package to drop to below 10K/W, foreign companies have developed high-temperature resistant white LEDs to try to improve the above problems. However, the heat of high-power LEDs is actually higher than that of low-power LEDs. More than ten times, and the temperature rise will make the luminous efficiency drop sharply. Even if the packaging technology allows high heat, the bonding temperature of the LED chip may exceed the allowable value. Finally, the operator finally realized that solving the heat dissipation problem of the package is the fundamental method.

The service life of LEDs, such as the use of silicon packaging materials and ceramic packaging materials, can increase the lifetime of LEDs by a single digit, especially the white LED's emission spectrum contains short wavelengths of light below 450nm, traditional epoxy packaging The material is easily destroyed by short-wavelength light, and the large amount of high-power white LED accelerates the deterioration of the packaging material. According to the test results of the industry, the continuous lighting is less than 10,000 hours, and the brightness of the high-power white LED has been reduced by more than half. The basic requirements for long life of lighting sources.

Regarding the luminous efficiency of the LED, the chip structure and the package structure can be improved to the same level as the low-power white LED. The main reason is that when the current density is increased by more than 2 times, it is not easy to extract light from a large chip, but the result is luminous efficiency. It is not as good as the low-power white LED. If the electrode structure of the chip is improved, the above-mentioned light-taking problem can be solved theoretically.

2 Try to reduce thermal impedance and improve heat dissipation

Regarding the uniformity of the luminescent characteristics, it is generally considered that the above-mentioned problems should be overcome as long as the uniformity of the phosphor material concentration of the white LED and the fabrication technique of the phosphor are improved. While increasing the applied power as described above, it is necessary to reduce the thermal impedance and improve the heat dissipation problem. The specific contents are: reducing the thermal impedance of the chip to the package, suppressing the thermal impedance of the package to the printed circuit board, and improving the heat dissipation of the chip.

In order to reduce the thermal impedance, many foreign LED manufacturers set the LED chips on the surface of the heatsink made of copper and ceramic materials, and then connect the heat-dissipating wires on the printed circuit board to the cooling fan. On the air-cooled fins, according to the results of the German OSRAMOptoSemiconductorsGmb experiment, the thermal impedance of the LED chip to the solder joint of the above structure can be reduced by 9K/W, which is about 1/6 of that of the conventional LED, and when the packaged LED applies 2W of power. The bonding temperature of the LED chip is 18K higher than the solder joint. Even if the temperature of the printed circuit board rises to 500C, the bonding temperature is only about 700C at most. When the thermal impedance is reduced, the bondingtemperature of the LED chip is affected by the printed circuit board. The influence of temperature, in this way, must try to reduce the temperature of the LED chip, in other words, reduce the thermal impedance of the LED chip to the solder joint, which can effectively reduce the burden of cooling the LED chip. On the other hand, even if the white LED has a structure that suppresses the thermal impedance, if the heat cannot be conducted from the package to the printed circuit board, the luminous efficiency of the LED will rise sharply as a result of the rise in the temperature of the LED, so Panasonic Electric Works develops a printed circuit board and package integration technology. The company encapsulates a 1mm square blue LED in a flipchip package on a ceramic substrate, and then attaches the ceramic substrate to the surface of the copper printed circuit board. According to Panasonic, the thermal impedance of the module including the printed circuit board is about 15K/W. .

    3 Various manufacturers show thermal design skills

Because the adhesion between the heat sink fins and the printed circuit board directly affects the heat conduction effect, the design of the printed circuit board becomes very complicated. In view of the lighting equipment and LED package manufacturers such as Lumileds and Japan CITIZEN, high power LEDs are successively developed. With the simple heat-dissipation technology, CITIZEN began to sample the white LED package in 2004. It can discharge the heat of the heat-dissipating fins of about 2?3mm directly to the outside without special bonding technology. According to the CITIZEN, although the LED chips are bonded, The 30K/W thermal impedance of the heat sink fin is larger than the OSK's 9K/W, and the room temperature increases the thermal impedance by about 1W at room temperature, but even if the conventional printed circuit board has no cooling fan forced air cooling, the white light The LED module can also be used for continuous lighting. Lumileds began sampling high-power LED chips in 2005, with a junction temperature of up to +1850C, which is 600C higher than other companies' same-class products. When using the traditional RF4 printed circuit board package, the ambient temperature can be input within 400C. The current of 1.5W power (approximately 400mA). Therefore, Lumileds and CITIZEN made it possible to increase the allowable temperature of the joint. The German OSRAM company set the LED chip on the surface of the heat sink fin to achieve a 9K/W ultra-low thermal impedance record, which is less than the thermal impedance of the OSRAM developed in the past. %, it is worth mentioning that when the LED module is packaged, the same flipchip method as the conventional method is adopted, but when the LED module is bonded with the heat fin, the light emitting layer closest to the LED chip is selected as the bonding surface, thereby making the heat of the light emitting layer It is capable of conducting emissions at the shortest distance. In 2003, Toshiba Lighting used to lay a luminous efficiency of 60lm/W low thermal impedance white LED on a 400mm square aluminum alloy surface. Without a special cooling component such as a cooling fan, the test beam is a 300lm LED module, which is rich in Toshiba Lighting. Trial experience, so the company said that due to advances in analog analysis technology, white LEDs exceeding 60 lm/W after 2006 can easily use lamps and frames to improve thermal conductivity, or use cooling fans to force air cooling to design lighting equipment. The heat dissipation, module structure that does not require special heat dissipation technology can also use white LEDs.

4 Change the packaging material to suppress the deterioration of the material and the decrease of the light transmittance.

Regarding the longevity of LEDs, the current LED manufacturers are taking measures to change the packaging materials and disperse the fluorescent materials in the packaging materials, especially the silicon encapsulating materials than the traditional blue and near-ultraviolet LED chips. It is more effective in suppressing the deterioration of the material and the decrease in the light transmittance. Since the epoxy resin absorbs up to 45% of the wavelength of 400-450 nm, the siliceous encapsulation material is less than 1%, and the halving of the luminance is less than 10,000 hours. The siliceous packaging material can be extended to About 40,000 hours, almost the same as the design life of the lighting equipment, which means that the white LEDs do not need to be replaced during the use of the lighting equipment. However, the siliceous resin is a highly elastic and soft material, and it is necessary to use a manufacturing technique that does not scratch the surface of the siliceous resin. In addition, the siliceous resin is highly liable to adhere to the powder, so it is necessary to develop a technique for improving the surface characteristics in the future.

Although the silicon packaging material can ensure the service life of the LED for 40,000 hours, the lighting equipment industry has different opinions. The main argument is the service life of the traditional incandescent lamp and the fluorescent lamp, which is defined as "the brightness is reduced to below 30%", and the brightness is defined. The LED that has been halved for 40,000 hours is about 20,000 hours if it is converted to a brightness of less than 30%. At present, there are two countermeasures for extending the service life of the components, namely, suppressing the overall temperature rise of the white LED and stopping the use of the resin packaging method.

It is generally believed that if the above two life extension measures are fully implemented, a requirement of 30% brightness for 40,000 hours can be achieved. To suppress the temperature rise of white LEDs, the method of cooling LED packaging printed circuit boards can be adopted. The main reason is that the high temperature state of the encapsulating resin and the strong light irradiation will rapidly deteriorate. According to the Arrhenius law, the temperature reduction of 100C will be extended by 2 times. Discontinuation of the resin package can completely eliminate the deterioration factor, because the light generated by the LED is reflected in the encapsulation resin. If a resin-based reflector that changes the direction of the light on the side of the chip is used, since the reflector absorbs light, the amount of light taken out will be impatient. Sharp reduction, this is the main reason why LED manufacturers consistently use ceramic and metal packaging materials.

Yiwu Fuwei e-commerce firm (IACS Co., Limited) is a very professional Led manufacturer who produces high quality outdoor led light. Our popular products are solar led lights, UFO lights, underwater lights and so on. If you have any question about the led product, please feel free to contact us.