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Power LED packaging technology at home and abroad
Published：2013/6/14 10:51:03
Ultra-high brightness LED applications are continuously expanding, first enter the specialty lighting market sectors, and the general lighting market forward. Input power of the LED chip continues to improve, these power LED packaging technology put forward higher requirements. power LED packaging technology should primarily meet the following two requirements: First, packaging structure have high light extraction efficiency, and the second is the thermal resistance as low as possible, so as to ensure power LED photoelectric performance and reliability.
To semiconductor LED as a light source, the luminous flux of conventional products with incandescent and fluorescent light sources such versatility, they are far away. Therefore, LED lighting field to develop, it is critical to its luminous efficiency, luminous flux raised to the level of existing lighting sources. Power LED epitaxial materials used in the MOCVD epitaxial growth technology and multi-quantum well structure, although the internal quantum efficiency should be further improved, but to obtain a high luminous flux remains the biggest obstacle to the light extraction efficiency is the chip is low. Existing power LED has been designed using flip chip new structure to improve light extraction efficiency, improve the thermal characteristics of the chip, and by increasing the chip area, and increase the operating current to improve the photoelectric conversion efficiency of the device to obtain higher luminous flux. In addition to the chip, the device packaging technology is also important. Packaging technology processes are critical:
Cooling technology
Traditional lamp type LED package structure, usually with conductive or non-conductive glue chip mounted on the small size of the reflector cup or slide stage, completed by the gold inside and outside the device connection is made with epoxy resin, the thermal resistance up to 250 ℃ / W ~ 300 ℃ / W, the new power-type chips if using the traditional style of the LED package, will be because of poor heat causes the chip junction temperature rise and rapid yellowing epoxy carbonation, resulting in device accelerated light fades until failure, or because of the rapid thermal expansion caused by the stress generated by open and failure.
Therefore, for large operating current power LED chip, low thermal resistance, good heat dissipation and low stress new power LED package structure is key technology devices. Can be low resistance, high thermal conductivity material bonded chips; the lower part of the chip plus copper or aluminum heat sink, and the use of semi-enclosed structure, accelerate the heat; even secondary cooling device designed to reduce the thermal resistance. Inside the device, filling a flexible transparent silicone rubber, the silicone rubber to withstand the temperature range (typically -40 ℃ ~ 200 ℃), colloidal sudden temperature changes will not cause the device to open, it will not turn yellow phenomenon. Parts and materials should also take full account of its thermal conductivity, thermal characteristics, in order to get a good overall thermal characteristics.
Second optical design technology
In order to improve the light extraction efficiency of the device, the design of the reflector, and multiple additional optical lens.
Power LED white light technology
Common realization of white craft method has the following three kinds:
(1) Apply a YAG phosphor blue chip, chip, phosphor emit blue light excitation 540nm ~ 560nm yellow green, yellow green and blue light synthetic white light. Prepared by this method is relatively simple, efficient, practical. Drawback is the amount of glue consistency is poor, phosphor easy precipitation lead to a smooth poor uniformity, color consistency is not good; high color temperature; CRI is not ideal.
(2) RGB trichromatic multiple chips or multiple devices emitting blending into a white, or yellow with blue + green two-chip complementary colors produce white light. As long as the heat well, the method produces white light stable compared with the previous method, but the driver is more complex, while also taking into account different color chips of different light decay speed.
(3) coated on the ultraviolet-chip RGB phosphor, phosphor excitation using violet mixing generating three primary colors form white light. Due to the current UV chip and RGB phosphor efficiency is low, has not yet reached the practical stage.
We believe that the class W power LED lighting products to achieve the industrialization of technical issues must be addressed as follows:
1, the powder coating quantity control: LED chip + phosphor coating process using the method of the phosphor is usually mixed with the gel to be coated with a dispenser to the chip. In operation, as the carrier plastic viscosity is dynamic parameters, the phosphor to produce larger specific gravity than the carrier gel precipitate and precision dispenser factors, this process is the uniformity of the phosphor coating amount of difficult control, resulting in a white uneven color.
2, the film optical parameters with: semiconductor process determined by the characteristics of the same material the same wafer chip may exist between the optical parameters (such as wavelength, light intensity) and electrical (such as forward voltage) parameter differences. RGB three-color chips even more so, the white color parameters influence. This is the industry must address one of the key technologies.
3, according to the application required to produce the light color parameter control: products for different purposes, the color coordinates of the white LED, color temperature, color, optical power (or intensity), and the spatial distribution of light different requirements. The parameters involved in the control of product structure, process methods, materials and other factors of cooperation. In industrial production, controlling for these factors, to get fit the application requirements, a good product consistency is very important.
Detection Technology and Standards
With the W stage power white LED chip manufacturing technology and the development of technology, LED products is gradually entering the (special) lighting market, display or instruction in the traditional LED product parameters testing standards and testing methods can not meet the needs of lighting applications. Domestic semiconductor equipment and instruments manufacturers have also launched their own test equipment, test instrumentation different principles, conditions and standards there are some differences, increasing the test application, the difficulty of comparing product performance and complicate the issue.
Optics and Optoelectronics Manufactures Association of optoelectronic devices branch of industry associations based LED product development, in 2003 issued a light-emitting diode test methods (Trial), this test method increases the requirements of the LED color parameters. But the LED lighting industry to expand to establish standard LED lighting products are an important means of industrial standardization.
Screening technology and Reliability Assurance
Since the appearance of lamps restrictions LED lighting assembly space sealed and has been limited, sealed and limited space is not conducive to LED cooling, which means that the use of LED lighting environment inferior to conventional display, which indicates that LED products. In addition, LED lighting is in working under high current drive, which raised its higher reliability requirements. In industrial production, for different uses of the products, proper thermal aging, temperature cycling shock load aging process screening test, excluding early failures goods, to ensure product reliability is necessary.
Power protection technology
Since GaN is a wide bandgap material, high resistivity, such chips in the production process due to the induced electrostatic charge does not disappear easily, accumulated to a considerable extent, can generate a high electrostatic voltage. When exceeding the capacity of the material occurs when the breakdown and discharge. Sapphire blue chip chip its positive and negative electrodes are located above the closely spaced; For InGaN / AlGaN / GaN double heterojunction, InGaN thin layer activation only tens of nanometers, for electrostatic capacity of small, vulnerable breakdown by static electricity, so that the device failure.
Therefore, in the industrial production, the electrostatic precautions it properly, a direct impact on product yield, reliability and economic efficiency. Static electricity prevention technology there are several:
1, the production, the use of premises from the human body, and Taiwan, ground, space and product transport, stacking and other aspects of the implementation of prevention, means there are anti-static clothing, gloves, wristbands, shoes, mats, boxes, ion fan, testing instruments.
2, on-chip ESD protection circuit design.
3, LED fitted protection devices.
Related Links
Power LED packaging technology status
Power LED into power LED and W class power LED two. Power LED input power less than 1W (tens of milliwatts power LED exception); W power LED input power level is equal to or greater than 1W.
Foreign power LED packaging technology
(1) Power LED
Earliest HP Company in the 20th century in the early 1990s launched the piranha package structure of the LED, and in 1994 launched improved version of SnapLED, there are two operating current, respectively, 70mA and 150mA, the input power can be up to 0.3W. followed by OSRAM launched PowerTOPLED. then some companies offer a variety of power LED package structure. These structures than the original rack power LED package LED input power is increased several times, reduced to a fraction of the thermal resistance.
(2) W class power LED
W class power LED is the future of lighting a core part of the world's major companies invest so much force, the W-class power LED packaging technology research and development.
Single-chip W-class power LED was first used by Lumileds, launched in 1998 LUXEONLED, the package structure characterized by the use of thermal isolation in the form of silicon carrier will flip chip soldered directly on the heat sink, and the use of reflective glass, optical flexible transparent plastic lenses and other new structures and new materials, we offer single-chip 1W, 3W and 5W high power LED.OSRAM company in 2003 introduced a single-chip GoldenDragon series LED, the structure is characterized by a heat sink and direct contact with the metal circuit board, with good thermal performance, while the input power up to 1W.
Combination of multi-chip package power LED, its structure and package more. U.S. UOE company launched in 2001 a multi-chip package combinations Norlux series LED, the hexagonal structure is the use of aluminum as a substrate. LaninaCeramics company in 2003 introduced the use of the company's unique low-temperature co-fired ceramic substrate metal (LTCC-M) technology packaged high power LED array. Panasonic introduced in 2003 by the 64-chip-packaged high-power white LED. Nichia company launched in 2003 claimed to be the world's most brightest white LED, the luminous flux of up to 600lm, 1000lm output beam is, the power consumption of 30W, maximum input power of 50W, providing exhibition luminous efficiency white LED module 33lm / W.
For a combination of multi-chip high power LED, many companies based on actual market demand, and constantly develop new structures encapsulated many new products, developed very fast.
Domestic power LED packaging technology
Domestic LED packaging more complete variety of products, according to preliminary estimates, the country more than 200 LED packaging factory, packaging capacity of over 20 billion / year, the package is also very strong supporting capacity. But many packaging factory for the private sector, small-scale. But China's Taiwan UEC companies (National League) metal bonding (MetalBonding) technology package MB series is characterized by high-power LED with Si instead of GaAs substrate, heat, and light-reflecting metal bonding layer for layer, increase the light output .
For high-power LED packaging technology research and development, the country has not yet officially supported by investment, domestic research units rarely intervene, packaging businesses to invest in research and development efforts (human and financial) is still not enough to form a domestic packaging technology development is weak situation , packaging technology level and that there is still a considerable gap.
To semiconductor LED as a light source, the luminous flux of conventional products with incandescent and fluorescent light sources such versatility, they are far away. Therefore, LED lighting field to develop, it is critical to its luminous efficiency, luminous flux raised to the level of existing lighting sources. Power LED epitaxial materials used in the MOCVD epitaxial growth technology and multi-quantum well structure, although the internal quantum efficiency should be further improved, but to obtain a high luminous flux remains the biggest obstacle to the light extraction efficiency is the chip is low. Existing power LED has been designed using flip chip new structure to improve light extraction efficiency, improve the thermal characteristics of the chip, and by increasing the chip area, and increase the operating current to improve the photoelectric conversion efficiency of the device to obtain higher luminous flux. In addition to the chip, the device packaging technology is also important. Packaging technology processes are critical:
Cooling technology
Traditional lamp type LED package structure, usually with conductive or non-conductive glue chip mounted on the small size of the reflector cup or slide stage, completed by the gold inside and outside the device connection is made with epoxy resin, the thermal resistance up to 250 ℃ / W ~ 300 ℃ / W, the new power-type chips if using the traditional style of the LED package, will be because of poor heat causes the chip junction temperature rise and rapid yellowing epoxy carbonation, resulting in device accelerated light fades until failure, or because of the rapid thermal expansion caused by the stress generated by open and failure.
Therefore, for large operating current power LED chip, low thermal resistance, good heat dissipation and low stress new power LED package structure is key technology devices. Can be low resistance, high thermal conductivity material bonded chips; the lower part of the chip plus copper or aluminum heat sink, and the use of semi-enclosed structure, accelerate the heat; even secondary cooling device designed to reduce the thermal resistance. Inside the device, filling a flexible transparent silicone rubber, the silicone rubber to withstand the temperature range (typically -40 ℃ ~ 200 ℃), colloidal sudden temperature changes will not cause the device to open, it will not turn yellow phenomenon. Parts and materials should also take full account of its thermal conductivity, thermal characteristics, in order to get a good overall thermal characteristics.
Second optical design technology
In order to improve the light extraction efficiency of the device, the design of the reflector, and multiple additional optical lens.
Power LED white light technology
Common realization of white craft method has the following three kinds:
(1) Apply a YAG phosphor blue chip, chip, phosphor emit blue light excitation 540nm ~ 560nm yellow green, yellow green and blue light synthetic white light. Prepared by this method is relatively simple, efficient, practical. Drawback is the amount of glue consistency is poor, phosphor easy precipitation lead to a smooth poor uniformity, color consistency is not good; high color temperature; CRI is not ideal.
(2) RGB trichromatic multiple chips or multiple devices emitting blending into a white, or yellow with blue + green two-chip complementary colors produce white light. As long as the heat well, the method produces white light stable compared with the previous method, but the driver is more complex, while also taking into account different color chips of different light decay speed.
(3) coated on the ultraviolet-chip RGB phosphor, phosphor excitation using violet mixing generating three primary colors form white light. Due to the current UV chip and RGB phosphor efficiency is low, has not yet reached the practical stage.
We believe that the class W power LED lighting products to achieve the industrialization of technical issues must be addressed as follows:
1, the powder coating quantity control: LED chip + phosphor coating process using the method of the phosphor is usually mixed with the gel to be coated with a dispenser to the chip. In operation, as the carrier plastic viscosity is dynamic parameters, the phosphor to produce larger specific gravity than the carrier gel precipitate and precision dispenser factors, this process is the uniformity of the phosphor coating amount of difficult control, resulting in a white uneven color.
2, the film optical parameters with: semiconductor process determined by the characteristics of the same material the same wafer chip may exist between the optical parameters (such as wavelength, light intensity) and electrical (such as forward voltage) parameter differences. RGB three-color chips even more so, the white color parameters influence. This is the industry must address one of the key technologies.
3, according to the application required to produce the light color parameter control: products for different purposes, the color coordinates of the white LED, color temperature, color, optical power (or intensity), and the spatial distribution of light different requirements. The parameters involved in the control of product structure, process methods, materials and other factors of cooperation. In industrial production, controlling for these factors, to get fit the application requirements, a good product consistency is very important.
Detection Technology and Standards
With the W stage power white LED chip manufacturing technology and the development of technology, LED products is gradually entering the (special) lighting market, display or instruction in the traditional LED product parameters testing standards and testing methods can not meet the needs of lighting applications. Domestic semiconductor equipment and instruments manufacturers have also launched their own test equipment, test instrumentation different principles, conditions and standards there are some differences, increasing the test application, the difficulty of comparing product performance and complicate the issue.
Optics and Optoelectronics Manufactures Association of optoelectronic devices branch of industry associations based LED product development, in 2003 issued a light-emitting diode test methods (Trial), this test method increases the requirements of the LED color parameters. But the LED lighting industry to expand to establish standard LED lighting products are an important means of industrial standardization.
Screening technology and Reliability Assurance
Since the appearance of lamps restrictions LED lighting assembly space sealed and has been limited, sealed and limited space is not conducive to LED cooling, which means that the use of LED lighting environment inferior to conventional display, which indicates that LED products. In addition, LED lighting is in working under high current drive, which raised its higher reliability requirements. In industrial production, for different uses of the products, proper thermal aging, temperature cycling shock load aging process screening test, excluding early failures goods, to ensure product reliability is necessary.
Power protection technology
Since GaN is a wide bandgap material, high resistivity, such chips in the production process due to the induced electrostatic charge does not disappear easily, accumulated to a considerable extent, can generate a high electrostatic voltage. When exceeding the capacity of the material occurs when the breakdown and discharge. Sapphire blue chip chip its positive and negative electrodes are located above the closely spaced; For InGaN / AlGaN / GaN double heterojunction, InGaN thin layer activation only tens of nanometers, for electrostatic capacity of small, vulnerable breakdown by static electricity, so that the device failure.
Therefore, in the industrial production, the electrostatic precautions it properly, a direct impact on product yield, reliability and economic efficiency. Static electricity prevention technology there are several:
1, the production, the use of premises from the human body, and Taiwan, ground, space and product transport, stacking and other aspects of the implementation of prevention, means there are anti-static clothing, gloves, wristbands, shoes, mats, boxes, ion fan, testing instruments.
2, on-chip ESD protection circuit design.
3, LED fitted protection devices.
Related Links
Power LED packaging technology status
Power LED into power LED and W class power LED two. Power LED input power less than 1W (tens of milliwatts power LED exception); W power LED input power level is equal to or greater than 1W.
Foreign power LED packaging technology
(1) Power LED
Earliest HP Company in the 20th century in the early 1990s launched the piranha package structure of the LED, and in 1994 launched improved version of SnapLED, there are two operating current, respectively, 70mA and 150mA, the input power can be up to 0.3W. followed by OSRAM launched PowerTOPLED. then some companies offer a variety of power LED package structure. These structures than the original rack power LED package LED input power is increased several times, reduced to a fraction of the thermal resistance.
(2) W class power LED
W class power LED is the future of lighting a core part of the world's major companies invest so much force, the W-class power LED packaging technology research and development.
Single-chip W-class power LED was first used by Lumileds, launched in 1998 LUXEONLED, the package structure characterized by the use of thermal isolation in the form of silicon carrier will flip chip soldered directly on the heat sink, and the use of reflective glass, optical flexible transparent plastic lenses and other new structures and new materials, we offer single-chip 1W, 3W and 5W high power LED.OSRAM company in 2003 introduced a single-chip GoldenDragon series LED, the structure is characterized by a heat sink and direct contact with the metal circuit board, with good thermal performance, while the input power up to 1W.
Combination of multi-chip package power LED, its structure and package more. U.S. UOE company launched in 2001 a multi-chip package combinations Norlux series LED, the hexagonal structure is the use of aluminum as a substrate. LaninaCeramics company in 2003 introduced the use of the company's unique low-temperature co-fired ceramic substrate metal (LTCC-M) technology packaged high power LED array. Panasonic introduced in 2003 by the 64-chip-packaged high-power white LED. Nichia company launched in 2003 claimed to be the world's most brightest white LED, the luminous flux of up to 600lm, 1000lm output beam is, the power consumption of 30W, maximum input power of 50W, providing exhibition luminous efficiency white LED module 33lm / W.
For a combination of multi-chip high power LED, many companies based on actual market demand, and constantly develop new structures encapsulated many new products, developed very fast.
Domestic power LED packaging technology
Domestic LED packaging more complete variety of products, according to preliminary estimates, the country more than 200 LED packaging factory, packaging capacity of over 20 billion / year, the package is also very strong supporting capacity. But many packaging factory for the private sector, small-scale. But China's Taiwan UEC companies (National League) metal bonding (MetalBonding) technology package MB series is characterized by high-power LED with Si instead of GaAs substrate, heat, and light-reflecting metal bonding layer for layer, increase the light output .
For high-power LED packaging technology research and development, the country has not yet officially supported by investment, domestic research units rarely intervene, packaging businesses to invest in research and development efforts (human and financial) is still not enough to form a domestic packaging technology development is weak situation , packaging technology level and that there is still a considerable gap.
