White LED Life
White led detailed graphic analysis, and how to improve white LED package
In order to obtain a sufficient white LED beam, has developed a large-size LED chip, trying in this way to achieve the intended objectives. But will actually applied on the white LED electric power continues to exceed the above 1W beam decreased, the luminous efficiency is relatively reduced by 20% to 30%, to improve the input power and the light emitting efficiency of white LED must be overcome problems are: to suppress the temperature rise; to ensure The life ; improve luminous efficiency; luminescence properties equalization.
The increase in power will use white SMD LED package thermal impedance drops to less than 10K / W and abroad have developed high-temperature white LEDs, an attempt to improve the problem of temperature rise. More due to high power white LED heat than power white LED high number of times, even if the white LED package allows the high-calorie, but allows the temperature of the white light LED chip is certain. Suppress the temperature rise of the specific method is to reduce the thermal resistance of the package.
The specific method to improve white LED service life is to improve the chip shape, a small chip. White LED emission spectrum contains wavelengths below 450nm short wavelength light, the traditional epoxy sealing material can easily be short-wavelength light damage, high power LED light accelerated the deterioration of the sealing material. Switch to the siliceous sealed ceramic package material, white LED life can improve a few.
The specific method to improve white LED luminous efficiency is to improve the chip package structure, to achieve the same level with the low-power white LED, the main reason is the current density is increased by more than 2 times, not only is not easy removed from the large chip light, the result will resulting in luminous efficiency than the low-power white LED, and improving the electrode structure of the chip, in theory, can solve the above-described light extraction.
Luminescent characteristics homogenized specific method is to improve the white LED package, generally considered long as the phosphor material to improve the white LED uniformity of the concentration with the production technology of the phosphor can be overcome the above distress.
Reduce thermal impedance, to improve the heat dissipation problem are:
(1) Reduce the chip-to-package thermal impedance.
(2) Inhibition of the package to the printed circuit board thermal impedance.
(3) Improve the the chips heat dissipation smooth.
In order to reduce the thermal impedance, many foreign led manufacturers LED chip provided in the surface of the cooling fins made of copper with a ceramic material, as shown in Figure 1, by welding the radiating conductor of the printed circuit board connected to the use of the cooling fan forces the air-cooling fin. German OSRAM Opto Semiconductors Gmb experimental results confirmed the above structure of the LED chip to the thermal impedance of the welding points can be reduced 9K / W, approximately about 1/6 of the conventional LED. Encapsulated LED 2W of the electric power applied to the LED chip temperature higher than the welding point 18 ℃, even if the temperature of the printed circuit board to rise to 500 ° C, the temperature of the LED chip is also only about 700 ℃. Once the thermal impedance is reduced, the temperature of the LED chip will be influenced by the temperature of the printed circuit board, this must be to reduce the thermal impedance of the LED chip to the welding point. Conversely, even if the white LED has to suppress the thermal impedance of the structure, if heat from the LED package can not be conducted to the printed circuit board, the LED temperature rise will make the light emitting efficiency decreases, so Panasonic Company developed a printed circuit board and package integration technology, the side length of 1mm square blue LED to overlying chips manner packaged on the ceramic substrate, the ceramic substrate can then paste in the copper surface of the printed circuit boards, including printed circuit boards, including module The overall thermal impedance is about 15K / W.
Longevity problem for white LED, the LED manufacturers in the countermeasures taken is to change the sealing material, while the fluorescent material is dispersed in the sealing material, the material degradation and the rate of decrease of light transmittance can be suppressed more effectively.
As the epoxy absorption wavelength of 400 ~ 450nm light percentage up to 45%, the siliceous sealing material is less than 1%, epoxy luminance half-time of less than 10,000 hours, siliceous sealing material may be extended to 4 million hours (Figure 2), almost the same as with the design life of the lighting device during use, this means that the lighting device without replacing the white LED. However, the the siliceous sealing material is a soft, flexible material, the processing must be used that will not scratch the surface of the sealing material production technology siliceous and easily attached Fenxie addition process on the siliceous sealing materials must be developed in the future can improve the surface characteristics technology.
Although the siliceous sealing material can ensure that the white LED has a service life of 40,000 hours, lighting equipment industry, however, has a different view, the main debate is the life of traditional incandescent and fluorescent lamps is defined as "brightness down to 30% or less", brightness The half-time of 40,000 hours of white light LED, if converted into brightness down to 30% or less, and only about 20,000 hours. There are two longer component life, the countermeasures are:
(1) Inhibit the overall temperature rise of the white LED.
(2) The stop using the resin encapsulation.
The above two countermeasures can reach a brightness reduced to 30% of the requirements of the service life of 40,000 hours. Inhibition of white LED temperature rise the cooling white LED packages The method of the printed circuit board can be used, mainly the encapsulating resin under high temperature, coupled glare rapid deterioration, in accordance with the Porto-Vilnius rule, the temperature is reduced 100 ℃ Life will be extended to 2 times.
Stop using the resin package can completely eliminate the deterioration factors, because the white light generated by the LED light is reflected within the encapsulating resin, if used may change the chip side surface of the light traveling direction of the resin material reflecting plate, the reflecting plate will absorb light, so the amount of light extraction will dropped, and this is the main reason for using a ceramic and metal packaging materials.
There are two methods to improve the luminous efficiency of the white LED chips: one is to use an area 10 times larger than the small chip (1mm2) in a large LED chip; Another is the use of a plurality of small high luminous efficiency of the LED chip are combined into a single The body of the module. Although the large LED chip may obtain a large beam, but the negative impact of increasing the chip area, for example, light-emitting layer within the chip uneven limitation, the light-emitting portion, and the chip internally generated light is emitted to the outside will be severely attenuated. To solve the above problem, through the improvement of the electrode structure of the white LED, overlying a chip package, plus integrated chip surface technology has reached 50lm / W luminous efficiency. Large white LED package shown in Figure 4. About the equality of the light-emitting layer of the chip as a whole, since the emergence of the comb-like grid-like p-type electrode, the electrode also developed optimization direction.
About follow-chip package, due to the light-emitting layer can easily exhaust heat, plus the light emission of the light-emitting layer close to the package end to the external electrode sheltered troubled American Lumileds cooperation Toyota has officially cover a chip package , the processing of the chip surface can prevent the light emitted towards the outside of the chip from the chip's internal reflection occurs at the interface, provided on a sapphire substrate is removed in the light parts of the concavo-convex structure, the chip external light extraction efficiency can be improved about 30%. The chip side improved large LED chip packaging entity emitted light toward the reflection of the package above the plate road, high efficiency to remove the chip internal light package size is 7mm x 7mm.
Small enhancement of the luminous efficiency of the LED chip seems to be more effective than the large LED chip module. For example, Japanese CITIZEN combinations of eight small LED chips reach 60lm / W high luminous efficiency. 0.3mm x 0.3mm Nichia produced small LED chip, a package module uses up to 12 chips, each LED chip using the traditional gold wire bonding package, applied power is about 2W.
The problem of uneven luminance and color temperature of white LED must be screened in the use of optical characteristics similar to the white LED. In fact reduce the unevenness of the white LED light-emitting characteristics of the LED chip emitting characteristics of the same, and the implementation of the concentration of phosphor material uniformly distributed management is very important.
LED chip light-emitting characteristics, the manufacturers are very active chip screening, light-emitting characteristics equal treatment LED light features to reduce the problem of uneven, such as Matsushita Electric Company has reached the same characteristics of the target through the screening of the chip. The follow-chip manner, 64 LED chip package on a substrate, and finally then were covering the phosphor. LED chips during processing first encapsulated in the light emission characteristics of sub-substrate test, followed by the light emitting characteristics of the same chip transplant encapsulated in the main substrate. 8 LED chip on a substrate, even if the light emitting characteristics of the LED chip is not uniform, the total light emission characteristics of the eight LED chips in the package between the unevenness will become very small.
The white LED is usually directly coated LED chip with a sealing resin containing phosphor material, the concentration of the phosphor material in the sealing resin may occur deviation finally result in uneven distribution of the color temperature of white LED. Therefore, the resin sheet containing the phosphor material is combined with the LED chip, through strict management due to the thickness of the sheet, and the concentration of the phosphor material, so the color temperature of the white LED uneven distribution of degree less than the traditional way of 4/5. The industry that the use of the phosphor sheet with the light-emitting properties of the LED chip to change the thickness of the concentration of the phosphor sheet, you can make a white LED color temperature change of control in the expected range.
Although gradually increase the possibility of application of white LED lighting in the area with white LED luminous efficiency, but obviously, single white LED luminous flux is low, so the package unlikely to achieve a single white LED lighting lumens. For this human problem, the solution can be broadly divided into two categories: one is the more traditional use only LED light source module, which each white LED drive power and general use (for 20 to 30mA); another type of method is the use of a larger area of the chip, traditional 0.3mm2 size chip is no longer in use at this time, while the use of a size of 0.6 ~ 1mm2 chip, and use a high driving current to drive so The light-emitting components (typically 150 ~ 350mA, up to 500mA). But no matter which method is used, the will must handle high heat in a tiny LED packaging, if the components can not be dispersed these heat, in addition to a variety of packaging materials will be due to the different expansion coefficient between each other and reliable products issues, the luminous efficiency of the chip as the temperature rises, and has significantly decreased, and causing life shortened significantly. Therefore, how to disperse heat from the component to become the important subject of the current white LED encapsulation technology.
For the white LED, it is most important that the output of the luminous flux and light color, so one end of the white LED must not shading, while the need to use the effect of high transparency of the epoxy resin material coated. However, there is the epoxy almost all thermally non-conductive material, for white LED packaging technology, its white LED chip under metal feet to disperse the heat emitted by the component. Opinion, the current trend, the metal foot is mainly a high thermal conductivity coefficient material mainly consisting of, e.g., aluminum, copper or even ceramic material, etc., but a great difference in coefficient of thermal expansion between these materials and chip, the direct contact, it may be because stress generated between the material at elevated temperatures and cause reliability problems, so usually coupled with a material between the intermediate material of appropriate conductivity and expansion coefficient as the interval. Matsushita Electric company only made of white LED is still in the metal material and the metal line module on a multilayer substrate made of the composite material to form a light source module, the high thermal conductivity of the substrate effect on the use of a light source, so that the output of the light source in the prolonged use able to maintain the stability. Lumileds production of the materials used in the white LED substrate of copper having a high conductivity, and then its connection to a special metal circuit board, it can be both circuit conduction and increase the effect of the heat conduction.
The high-power white LED chip manufacturing technology, packaging technology seems to have become a mainstream technology for high brightness white LED, the largest chip manufacturing technology and packaging technology, however, is not just the chip area bigger, if they want to apply white LED high brightness lighting field, technology has yet to be studied further.
White LED in general lighting field, there are still many problems to be solved, first white LED efficiency, such as the the GaInN Department of the green, blue and near-UV LED efficiency is still a big development margin. In addition, the internal quantum efficiency of the integrated energy efficiency is the most important item, and the internal quantum efficiency by the active layer of the non-light-emitting the percentage light emitting recombination percentage decided, it can lock the focus to this part in the non-light emitting recombination, and managed to reduce the crystal defects. And to reduce the dislocation density of the UV LED can indeed significantly improve internal quantum efficiency, the future need for the UV LED to further reduce the dislocation density. However, this countermeasure of green, blue LED does not have a significant impact.
Green and blue LEDs at low current densities (around 1A/cm2) have the maximum quantum efficiency, the quantum efficiency in the high current density will decrease, as shown in Figure 7. LED can be driven with high current density as possible while increasing the output power of the component, so the early unlock the mechanism and cause of decrease of the quantum efficiency in the green and blue LED high current density from the cost viewpoint, not only is the material The physical characteristics of exploration on the need for future applications, the study also has a key role. The present study shows violet LED (wavelength of 382nm) is applied, the high current density (50A/cm2), the quantum efficiency is not lowered.
The conventional white LED are the side length of 200 to 350 μm square chip packaged into a ball pillar shape, after the required order to obtain the lighting beam, then is encapsulated a plurality of white LED components are arranged in a matrix shape. Simply to high output power for the purpose of especially developed area ratio the conventional chip 6 to 10 times, dimensions up to 500 μm to 1 mm of the white LED Although the package obtained after several hundred milliwatts (tens of lumens) of output power, increase the dimensions of the chip, but the white LED light within the absorption ratio increased external light extraction rate decreased. For example, AlGaInP LED Dimensions of the chip is 0.50mm x 0.50mm, 0.22mm x 0.22mm increase external light extraction rates have reduced by about 20%. If the switch TIP structure, internal result of multiple reflection so that the internal light absorption rate decreased, the external light extraction efficiency is improved significantly. The GaInN LED also has the same effect. How to improve the external light extraction efficiency of the LED chip LED used in the field of general lighting. In addition, the considerable disadvantage of high thermal impedance (150 ~ 200K / W) for the high brightness output. LED internal quantum efficiency of the active layer temperature dependence great addition to the low thermal resistance packaging technology, the use of heat sinks become hot spots for future R & D exclude active layer of heat.
In order to obtain a sufficient white LED beam, has developed a large-size LED chip, trying in this way to achieve the intended objectives. But will actually applied on the white LED electric power continues to exceed the above 1W beam decreased, the luminous efficiency is relatively reduced by 20% to 30%, to improve the input power and the light emitting efficiency of white LED must be overcome problems are: to suppress the temperature rise; to ensure The life ; improve luminous efficiency; luminescence properties equalization.
The increase in power will use white SMD LED package thermal impedance drops to less than 10K / W and abroad have developed high-temperature white LEDs, an attempt to improve the problem of temperature rise. More due to high power white LED heat than power white LED high number of times, even if the white LED package allows the high-calorie, but allows the temperature of the white light LED chip is certain. Suppress the temperature rise of the specific method is to reduce the thermal resistance of the package.
The specific method to improve white LED service life is to improve the chip shape, a small chip. White LED emission spectrum contains wavelengths below 450nm short wavelength light, the traditional epoxy sealing material can easily be short-wavelength light damage, high power LED light accelerated the deterioration of the sealing material. Switch to the siliceous sealed ceramic package material, white LED life can improve a few.
The specific method to improve white LED luminous efficiency is to improve the chip package structure, to achieve the same level with the low-power white LED, the main reason is the current density is increased by more than 2 times, not only is not easy removed from the large chip light, the result will resulting in luminous efficiency than the low-power white LED, and improving the electrode structure of the chip, in theory, can solve the above-described light extraction.
Luminescent characteristics homogenized specific method is to improve the white LED package, generally considered long as the phosphor material to improve the white LED uniformity of the concentration with the production technology of the phosphor can be overcome the above distress.
Reduce thermal impedance, to improve the heat dissipation problem are:
(1) Reduce the chip-to-package thermal impedance.
(2) Inhibition of the package to the printed circuit board thermal impedance.
(3) Improve the the chips heat dissipation smooth.
In order to reduce the thermal impedance, many foreign led manufacturers LED chip provided in the surface of the cooling fins made of copper with a ceramic material, as shown in Figure 1, by welding the radiating conductor of the printed circuit board connected to the use of the cooling fan forces the air-cooling fin. German OSRAM Opto Semiconductors Gmb experimental results confirmed the above structure of the LED chip to the thermal impedance of the welding points can be reduced 9K / W, approximately about 1/6 of the conventional LED. Encapsulated LED 2W of the electric power applied to the LED chip temperature higher than the welding point 18 ℃, even if the temperature of the printed circuit board to rise to 500 ° C, the temperature of the LED chip is also only about 700 ℃. Once the thermal impedance is reduced, the temperature of the LED chip will be influenced by the temperature of the printed circuit board, this must be to reduce the thermal impedance of the LED chip to the welding point. Conversely, even if the white LED has to suppress the thermal impedance of the structure, if heat from the LED package can not be conducted to the printed circuit board, the LED temperature rise will make the light emitting efficiency decreases, so Panasonic Company developed a printed circuit board and package integration technology, the side length of 1mm square blue LED to overlying chips manner packaged on the ceramic substrate, the ceramic substrate can then paste in the copper surface of the printed circuit boards, including printed circuit boards, including module The overall thermal impedance is about 15K / W.
Longevity problem for white LED, the LED manufacturers in the countermeasures taken is to change the sealing material, while the fluorescent material is dispersed in the sealing material, the material degradation and the rate of decrease of light transmittance can be suppressed more effectively.
As the epoxy absorption wavelength of 400 ~ 450nm light percentage up to 45%, the siliceous sealing material is less than 1%, epoxy luminance half-time of less than 10,000 hours, siliceous sealing material may be extended to 4 million hours (Figure 2), almost the same as with the design life of the lighting device during use, this means that the lighting device without replacing the white LED. However, the the siliceous sealing material is a soft, flexible material, the processing must be used that will not scratch the surface of the sealing material production technology siliceous and easily attached Fenxie addition process on the siliceous sealing materials must be developed in the future can improve the surface characteristics technology.
Although the siliceous sealing material can ensure that the white LED has a service life of 40,000 hours, lighting equipment industry, however, has a different view, the main debate is the life of traditional incandescent and fluorescent lamps is defined as "brightness down to 30% or less", brightness The half-time of 40,000 hours of white light LED, if converted into brightness down to 30% or less, and only about 20,000 hours. There are two longer component life, the countermeasures are:
(1) Inhibit the overall temperature rise of the white LED.
(2) The stop using the resin encapsulation.
The above two countermeasures can reach a brightness reduced to 30% of the requirements of the service life of 40,000 hours. Inhibition of white LED temperature rise the cooling white LED packages The method of the printed circuit board can be used, mainly the encapsulating resin under high temperature, coupled glare rapid deterioration, in accordance with the Porto-Vilnius rule, the temperature is reduced 100 ℃ Life will be extended to 2 times.
Stop using the resin package can completely eliminate the deterioration factors, because the white light generated by the LED light is reflected within the encapsulating resin, if used may change the chip side surface of the light traveling direction of the resin material reflecting plate, the reflecting plate will absorb light, so the amount of light extraction will dropped, and this is the main reason for using a ceramic and metal packaging materials.
There are two methods to improve the luminous efficiency of the white LED chips: one is to use an area 10 times larger than the small chip (1mm2) in a large LED chip; Another is the use of a plurality of small high luminous efficiency of the LED chip are combined into a single The body of the module. Although the large LED chip may obtain a large beam, but the negative impact of increasing the chip area, for example, light-emitting layer within the chip uneven limitation, the light-emitting portion, and the chip internally generated light is emitted to the outside will be severely attenuated. To solve the above problem, through the improvement of the electrode structure of the white LED, overlying a chip package, plus integrated chip surface technology has reached 50lm / W luminous efficiency. Large white LED package shown in Figure 4. About the equality of the light-emitting layer of the chip as a whole, since the emergence of the comb-like grid-like p-type electrode, the electrode also developed optimization direction.
About follow-chip package, due to the light-emitting layer can easily exhaust heat, plus the light emission of the light-emitting layer close to the package end to the external electrode sheltered troubled American Lumileds cooperation Toyota has officially cover a chip package , the processing of the chip surface can prevent the light emitted towards the outside of the chip from the chip's internal reflection occurs at the interface, provided on a sapphire substrate is removed in the light parts of the concavo-convex structure, the chip external light extraction efficiency can be improved about 30%. The chip side improved large LED chip packaging entity emitted light toward the reflection of the package above the plate road, high efficiency to remove the chip internal light package size is 7mm x 7mm.
Small enhancement of the luminous efficiency of the LED chip seems to be more effective than the large LED chip module. For example, Japanese CITIZEN combinations of eight small LED chips reach 60lm / W high luminous efficiency. 0.3mm x 0.3mm Nichia produced small LED chip, a package module uses up to 12 chips, each LED chip using the traditional gold wire bonding package, applied power is about 2W.
The problem of uneven luminance and color temperature of white LED must be screened in the use of optical characteristics similar to the white LED. In fact reduce the unevenness of the white LED light-emitting characteristics of the LED chip emitting characteristics of the same, and the implementation of the concentration of phosphor material uniformly distributed management is very important.
LED chip light-emitting characteristics, the manufacturers are very active chip screening, light-emitting characteristics equal treatment LED light features to reduce the problem of uneven, such as Matsushita Electric Company has reached the same characteristics of the target through the screening of the chip. The follow-chip manner, 64 LED chip package on a substrate, and finally then were covering the phosphor. LED chips during processing first encapsulated in the light emission characteristics of sub-substrate test, followed by the light emitting characteristics of the same chip transplant encapsulated in the main substrate. 8 LED chip on a substrate, even if the light emitting characteristics of the LED chip is not uniform, the total light emission characteristics of the eight LED chips in the package between the unevenness will become very small.
The white LED is usually directly coated LED chip with a sealing resin containing phosphor material, the concentration of the phosphor material in the sealing resin may occur deviation finally result in uneven distribution of the color temperature of white LED. Therefore, the resin sheet containing the phosphor material is combined with the LED chip, through strict management due to the thickness of the sheet, and the concentration of the phosphor material, so the color temperature of the white LED uneven distribution of degree less than the traditional way of 4/5. The industry that the use of the phosphor sheet with the light-emitting properties of the LED chip to change the thickness of the concentration of the phosphor sheet, you can make a white LED color temperature change of control in the expected range.
Although gradually increase the possibility of application of white LED lighting in the area with white LED luminous efficiency, but obviously, single white LED luminous flux is low, so the package unlikely to achieve a single white LED lighting lumens. For this human problem, the solution can be broadly divided into two categories: one is the more traditional use only LED light source module, which each white LED drive power and general use (for 20 to 30mA); another type of method is the use of a larger area of the chip, traditional 0.3mm2 size chip is no longer in use at this time, while the use of a size of 0.6 ~ 1mm2 chip, and use a high driving current to drive so The light-emitting components (typically 150 ~ 350mA, up to 500mA). But no matter which method is used, the will must handle high heat in a tiny LED packaging, if the components can not be dispersed these heat, in addition to a variety of packaging materials will be due to the different expansion coefficient between each other and reliable products issues, the luminous efficiency of the chip as the temperature rises, and has significantly decreased, and causing life shortened significantly. Therefore, how to disperse heat from the component to become the important subject of the current white LED encapsulation technology.
For the white LED, it is most important that the output of the luminous flux and light color, so one end of the white LED must not shading, while the need to use the effect of high transparency of the epoxy resin material coated. However, there is the epoxy almost all thermally non-conductive material, for white LED packaging technology, its white LED chip under metal feet to disperse the heat emitted by the component. Opinion, the current trend, the metal foot is mainly a high thermal conductivity coefficient material mainly consisting of, e.g., aluminum, copper or even ceramic material, etc., but a great difference in coefficient of thermal expansion between these materials and chip, the direct contact, it may be because stress generated between the material at elevated temperatures and cause reliability problems, so usually coupled with a material between the intermediate material of appropriate conductivity and expansion coefficient as the interval. Matsushita Electric company only made of white LED is still in the metal material and the metal line module on a multilayer substrate made of the composite material to form a light source module, the high thermal conductivity of the substrate effect on the use of a light source, so that the output of the light source in the prolonged use able to maintain the stability. Lumileds production of the materials used in the white LED substrate of copper having a high conductivity, and then its connection to a special metal circuit board, it can be both circuit conduction and increase the effect of the heat conduction.
The high-power white LED chip manufacturing technology, packaging technology seems to have become a mainstream technology for high brightness white LED, the largest chip manufacturing technology and packaging technology, however, is not just the chip area bigger, if they want to apply white LED high brightness lighting field, technology has yet to be studied further.
White LED in general lighting field, there are still many problems to be solved, first white LED efficiency, such as the the GaInN Department of the green, blue and near-UV LED efficiency is still a big development margin. In addition, the internal quantum efficiency of the integrated energy efficiency is the most important item, and the internal quantum efficiency by the active layer of the non-light-emitting the percentage light emitting recombination percentage decided, it can lock the focus to this part in the non-light emitting recombination, and managed to reduce the crystal defects. And to reduce the dislocation density of the UV LED can indeed significantly improve internal quantum efficiency, the future need for the UV LED to further reduce the dislocation density. However, this countermeasure of green, blue LED does not have a significant impact.
Green and blue LEDs at low current densities (around 1A/cm2) have the maximum quantum efficiency, the quantum efficiency in the high current density will decrease, as shown in Figure 7. LED can be driven with high current density as possible while increasing the output power of the component, so the early unlock the mechanism and cause of decrease of the quantum efficiency in the green and blue LED high current density from the cost viewpoint, not only is the material The physical characteristics of exploration on the need for future applications, the study also has a key role. The present study shows violet LED (wavelength of 382nm) is applied, the high current density (50A/cm2), the quantum efficiency is not lowered.
The conventional white LED are the side length of 200 to 350 μm square chip packaged into a ball pillar shape, after the required order to obtain the lighting beam, then is encapsulated a plurality of white LED components are arranged in a matrix shape. Simply to high output power for the purpose of especially developed area ratio the conventional chip 6 to 10 times, dimensions up to 500 μm to 1 mm of the white LED Although the package obtained after several hundred milliwatts (tens of lumens) of output power, increase the dimensions of the chip, but the white LED light within the absorption ratio increased external light extraction rate decreased. For example, AlGaInP LED Dimensions of the chip is 0.50mm x 0.50mm, 0.22mm x 0.22mm increase external light extraction rates have reduced by about 20%. If the switch TIP structure, internal result of multiple reflection so that the internal light absorption rate decreased, the external light extraction efficiency is improved significantly. The GaInN LED also has the same effect. How to improve the external light extraction efficiency of the LED chip LED used in the field of general lighting. In addition, the considerable disadvantage of high thermal impedance (150 ~ 200K / W) for the high brightness output. LED internal quantum efficiency of the active layer temperature dependence great addition to the low thermal resistance packaging technology, the use of heat sinks become hot spots for future R & D exclude active layer of heat.
