(2) Power LED combination of multi-chip package
The hexagonal aluminum substrate having a diameter of 3.175cm (1.25 inches), the light emitting region is located in its central portion, about 0.9525cm (0.375 inches) in diameter, which can accommodate 40 of the LED chip. The thermal liner, and the chip through bonding wires on a substrate made of the aluminum plate as the two points of contact with the positive electrode and the negative electrode connected. According to the size of the optical power of the desired output to determine the number of the substrate arranged on the die, the combination ultrahigh brightness chip package including AlGaInN and AlGaInP, they emitted light may be monochrome, color (RGB), white (RGB three primaries synthesis or by the blue and yellow binary synthesis). Finally, a high refractive index material to be encapsulated in accordance with the shape of the optical design, not only a high light extraction efficiency, but also to the chip and the bonding of the leads to be protected. 40 AlGaInP (AS) chip combo package LED luminous efficiency of 20lm / W. Using a combination of RGB three primary colors of synthetic white encapsulation module, when the mixing ratio of 0:43 (R) 0:48 (G): 0.009 (B) when a typical value for the luminous flux is 100lm, the the CCT standard color temperature is 4420K, the color coordinates x 0.3529 to 0.3612, y. This shows that this kind of power type LED the conventional chip for high-density combination package can reach a higher level of brightness with low thermal resistance, can work in the high-current and high optical output power.
Portfolio of multi-chip package high power LEDs, its structure and package more. The the American the UOE company in 2001 launched a portfolio of multi-chip package Norlux series LED, its structure is adopted the hexagonal aluminum plate as the substrate. Lanina Ceramics in 2003 to launch a low temperature co-fired ceramic (LTCC-M) technology package on the metal substrate using the company's proprietary high-power LED array. Panasonic introduced in 2003 high power white LED package 64 only chip combination. Nichia launched in 2003, the ultra-high brightness white LED luminous flux of up to 600lm output beam 1000lm, the power consumption of 30W, maximum input power of 50W up to 33lm / W luminous efficiency of white LED module. MB series of high-power LED characteristics of Taiwan UEC (the Guolian) company metal bonding (Metal Bonding) technology package, instead of using Si GaAs substrate, thermal effects, and as the light reflective layer to metal bonding layer to improve light output.
Power type LED thermal characteristics directly affect the LED's operating temperature, luminous efficiency, emission wavelength, life, power type LED chip package design, manufacturing technology is particularly important. The main issues to be considered in the high-power LED packaging:
(1) The cooling. Cooling is essential for power LED devices. If you can not dissipate the heat generated by the current in a timely manner to maintain the junction temperature of the PN junction within the allowable range, would not be able to obtain a stable light output and maintenance of the normal lifetime of the devices.
In the common heat sink material in the highest thermal conductivity of silver, but the high cost of silver, unsuitable for the universal type radiator. The thermal conductivity of copper is close to the silver, and its cost is lower than silver. Although the thermal conductivity of aluminum is lower than copper, but its lowest cost, is conducive to large-scale manufacturing.
After experimental comparison found a more appropriate approach is: connect the chip part of the copper-based or silver-based thermal liner, high thermal conductivity of the thermal liner connection aluminum radiator, ladder-type thermal structure, the use of copper or silver will efficient transfer of heat generated by the chip to the aluminum radiator, aluminum radiator to dissipate the heat (shed by air cooling or heat conduction). The advantages of this approach are: fully consider the value for money of the radiator, and together the different characteristics of the radiator, so that efficient cooling rationalization and cost control.
It should be noted that: the choice of material connected to the copper-based thermal liner with the chip is very important, the LED used in the chip-connecting material is silver glue. However, after a study found that the thermal resistance of the silver colloid is 10 ~ 25W / (m · K), if the use of silver gum as a connecting material, it is equal to artificially coupled with a thermal resistance between the chip and the thermal liner. Further, after curing of the silver plastic inner basic structure the epoxy skeleton + the amalgam fillings thermal conductive structure and a high thermal resistance of such a structure and lower TG point, extremely unfavorable for the stability of the cooling device and physical properties. Practice to solve this problem is: to tin plate welding as the material of the connection between the grain and the thermal liner [tin thermal conductivity of 67W / (m · K)], can be obtained an ideal thermal effects (thermal resistance of about 16 ℃ / W). Tin thermal effects and physical properties far superior to the silver plastic.
(2) the light. Conventional LED device package, only use the chip emits about 50% of the light, due to the refractive index of the semiconductor closed epoxy difference larger, resulting in the internal total reflection critical angle is small, the active layer generates light only small portion is removed, most of the light through multiple reflections inside the chip is absorbed, and this is the fundamental reason of the high brightness LED chip light extraction efficiency is very low. Between different materials of the internal refraction, reflection 50% of the consumed energy be utilized, is the design of the key of the optical coefficients.
Can be more effective than conventional LED chip packaging technology light exit through the chip's flip (Flip Chip) technology. If, however, it is to say in the light-emitting layer and the electrode of the chip below increases the reflective layer to reflect the light energy of a waste, will result in loss of about 8% of the light reflective layer, so the base plate material must be increased. The chip side surface of the light must also be used to heat the lining of the mirror machining method to be reflected, to increase the device out of the light-receiving rate. The optical combination of surface and in the portion of the sapphire substrate of the flip chip with the epoxy resin derivative should be added to a layer of silicone material, to improve the chip out of the refractive index of the light.
After the improvement of the optical packaging technology, can significantly improve the high-power LED devices the Idemitsu rate (flux). Lens optical design of the top of the high-power LED devices is also very important, the usual practice is: and during optical lens design should take full account of the the final lighting fixtures optical design requirements, as far as possible with the application of optical lighting equipment requirements for the design.
Common lens shape: convex lens, a concave cone lens, spherical lens, a Fresnel lens, and a combined lens. Lens with high-power LED devices ideal assembly method is to take a hermetic package, semi-hermetic package can also be taken, if the lens shape. The lens material should be selected high transmittance of synthetic materials such as glass or acrylic, and may also be used conventional epoxy modular package, together with the secondary thermal design which can achieve the effect to improve the light-receiving rate.
3. Power type LED progress
Power type LED development began in the mid-1960s, the GaAs infrared light source, because of its high reliability, small size, light weight, low voltage, first used in military night vision equipment, to replace the original Some incandescent 1980s InGaAsP / InP double heterojunction infrared light source is used for some special test equipment to replace the original volume, short life xenon lamp. This infrared light source DC operating current of up to 1A pulse current up to 24A. Infrared light source fall early power LED, but it has been developed so far, constantly upgrading products more widely, and become light power type LED technology base inheritable.
In 1991, red, orange, yellow the AlGaInP power type of LED practical application of LED from indoor to outdoor, successfully used in a variety of traffic lights, car tail lights, directional lights and outdoor information display. Blue, of green AlGaInN high brightness LED have developed successful, the realization of ultra-high brightness LED full color for lighting, however, is another new field of ultra-high brightness LED expansion, replace incandescent and fluorescent lamps with LED solid-state light LED Development Goals and other traditional glass bulb lighting source has become. Therefore, the power LED R & D and industrialization will become another important direction for future development, the key is to continuously improve the luminous efficiency of each device (component) luminous flux. Power type LED epitaxial material using an MOCVD epitaxial growth techniques and multiple quantum well structure, although the need to further improve the internal quantum efficiency, but the greatest obstacle to obtain a high luminous flux is still very low light extraction efficiency of the chip. Follows traditional indicator LED package structure, the operating current is generally limited to 20mA. According to this conventional concept design and production of power type LED simply can not achieve the requirements of high efficiency and high flux. In order to improve the visible power LED luminous efficiency and luminous flux, must adopt a new design concept, on the one hand, through the design of a new chip architecture to increase light extraction efficiency, on the other hand, by increasing the chip area, and increase the operating current, low thermal resistance The packaging structure to improve the photoelectric conversion efficiency of the device. Therefore, the design and production of the new chip and package structure, and continuously improve the light extraction efficiency of the device and photoelectric conversion efficiency has been a crucial issue in the development of power type LED.
Power type LED greatly expanding the application of LED in the signal display and the field of lighting source, automotive interior and exterior lights and traffic lights, including urban transport, railways, highways, airports, seaports, lighthouses, safety warning lights, etc.. Power white LED as special illumination source has started for the automotive and aircraft reading lights, portable lighting source (such as a key light, flashlight), backlight and miners lamps has also been an increasing number of applications. White addition of synthesized by the three primary colors, but also through a specially designed phosphor coated on the GaN blue or ultraviolet wavelength of the power-type LED chips are formed. Power type LED in building decorative lighting, stage lighting, store windows, lighting, advertising light boxes lighting, garden lawn lighting, city night scene compared to their similar products shows its unique characteristics. Use power type RGB tricolor LED, can be made into a compact structure, the tone light source of high luminous efficiency than traditional incandescent light source digital tune, with computer-controlled technology, can be obtained very colorful glow. Power type LED low voltage, low power consumption, small size, light weight, long life, high reliability, it can also serve as the military field, diving, aerospace, aviation, special solid light source.
Optimize the design of the progress of the power type LED structure, take the heat and light lining continuously improve its luminous efficiency and luminous flux from multiple 5mm LED lamp panel and lamp assembly will be replaced by power type LED assembly wick. From 1970 to 2000, the last 30 years, the luminous flux every 18 to 24 months to 2-fold increase. Since the advent of the 1998 Norlux Series Power LED, luminous flux increasing trend faster.
With the improvement of the performance of power type LED, LED lighting source has attracted greater attention in the field of lighting. General lighting market demand is huge, power white LED technology will be better able to adapt to the application of the general lighting. Sustainable development direction as long as the LED industry, LED solid-state lighting will be achieved in the next five to 10 years, a major breakthrough in the market.
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