There is no doubt that this world needs high-brightness light-emitting diode (HB LED), not only high-brightness white LED (HB WLED), also includes high-brightness LED, and from now on the future is more positive efforts and the need for high Brightness LED (UHD LED).
With LED backlight to replace the original handheld device EL backlight, CCFL backlight, not only the circuit design is more simple and easy, and have a high resistance to external force. With LED backlight to replace the original LCD TV CCFL backlight, not only more environmentally friendly and show more realistic bright. LED lighting to replace the white light, halogen and other lighting, not only more bright power, the use of more long-term, and the light reaction faster, for the brake lights can reduce the follow-up rate. Therefore, the LED from the past can only be used in the electronic device status indicator, progress to become a liquid crystal display backlight, and then extended to the electronic lighting and public display, such as vehicle lights, traffic lights, information billboards, large video walls, and even Is the projector's lighting, etc., its application is still continuing to extend. More importantly, the luminous efficiency of the LED is like Moore 's Law, doubling every 24 months, that the white LED can only be used to replace the excessive power consumption of incandescent, halogen, that is, Luminous efficiency in the 10 ~ 30lm / W level, but in the white LED break 60lm / W or even up to 100lm / W, even fluorescent lamps, high pressure gas discharge lamp also began to feel the threat.
Although the LED continues to enhance the brightness and luminous efficiency, but in addition to the core of the fluorescent, mixed light and other patented technology, the package will also be more and more challenges, and is the challenge of double problems, on the one hand the package must LED The maximum light rate, the highest luminous flux, so that light loss to a minimum, but also pay attention to the light divergence angle, light mean, and the light guide plate with the sex. On the other hand, the package must have the best heat dissipation of the LED, especially HB (high brightness) almost means that HP (high power, high power), into and out of the LED current value continues to increase, if not good heat, It will not only reduce the brightness of the LED, but also shorten the life of the LED. Therefore, the continued pursuit of high brightness LED, the use of packaging technology if there is no corresponding enhancement to enhance, then the high brightness performance will be discounted, so this article will be more for HB LED packaging technology for more discussion, including the discussion of light , As well as discussion of thermal conductivity.
Naked crystal layer: "quantum wells, multi-quantum wells" to enhance the "light conversion efficiency"
Although this article is mainly concerned about the LED package to enhance the luminous flux, but also had to first explain the deeper core of the bare crystal part, after all, the improvement of the crystal structure can also make a substantial increase in luminous flux. The first is to strengthen the efficiency of light conversion, which is the most root of the way, the existing LED per watt of electricity, only 15% to 2% was converted into light energy, the rest are converted into heat and dissipate (waste heat) And to enhance the efficiency of this conversion on the pn junction (pn junction), pn junction is the main LED heating position, through the pn junction structure design changes can improve the conversion efficiency. (Quantum Well; QW), in order to enhance the conversion of electricity into the proportion of light energy, and further will be more efforts to dig out the number of efforts, that is, multi-quantum wells (Multiple Quantum Well; MQW) technology.
"Refueling restructuring, light through the light off" pull high "light efficiency"
If the light conversion efficiency is difficult to ask, and further must start from the level of light efficiency, this level of practice quite a lot, depending on the different materials are different, the current HB LED more commonly used two kinds of materials are AlGaInP and GaN / InGaN, the former used to produce high brightness orange, orange, yellow, green, the latter GaN used to produce green, green, blue, and InGaN produce near ultraviolet, blue, blue. The method involves changing the physical geometry (transverse to vertical), changing the material of the substrate (substrate, also known as the substrate), adding a new material layer, changing the bonding of the material layer, different material surface treatment, and the like. However, in any case change, generally not from the two principles: First, reduce the shelter, increase the luminous flux. Second, to strengthen the light refraction, reflection of the utilization rate. As in the past AlGaInP LED, the substrate used in the material for the GaAs, then the black surface of the GaAs to p-n surface of the light emitted by half of the occlusion of absorption, resulting in a waste of light, so use transparent GaP material to do the substrate. Another example is the Nichia Chemical Industry (Nichia), the p-type electrode (p type) part of the mesh pattern (Mesh Pattern), in order to increase the transparency of the p-pole, reduce the optical barrier while enhancing the light penetration. As for the increase in refraction, a layer of DBR (Distributed Bragg Reflector) is added to the structure of AlGaInP, and the other side of the light source is folded to the same side. GaN side of the substrate material will be replaced by sapphire (aluminum oxide) to increase the reflection, while the substrate surface is designed as convex and concave, thereby increasing the light reflection of the scattering angle, and thus to enhance the rate of light. Or such as OSRAM (OSRAM) using SiC substrate, and the substrate is designed to be inclined, but also help to increase the reflection, or add silver, aluminum metal mirror layer.
Packaging layer: anti-aging yellow light, light transmission battle
From the die layer to increase the brightness, and then formally from the packaging level to take over, so that the highest luminous maintenance, light attenuation to a minimum.
To have a high lumen retention rate (Transmittance), the first step is to encapsulate the material. In the past, the most commonly used LED is epoxy, but the aging of epoxy resin will gradually turn yellow, which will affect the bright color, especially the lower the wavelength when the aging faster, especially part of the WLED using near ultraviolet (Near ultraviolet) light , Compared with other visible light and its wavelength is lower, faster aging. The new proposal is to use silicone resin (silicone), such as the United States Lumileds Luxeon series of LED is to change the silicon sealant. Not just Lumileds Luxeon, other companies also have silicone solutions, such as General Electric. Toshiba's InvisiSi1, Toray. Dow Corning's SR 7010, etc. are also LED silicone packaging program.
Silica gel in addition to the low wavelength of a better resistance, less susceptible to aging, the silica gel blocking the UV light to make it leak is also a protection of human health, in addition to silica gel permeability, refractive index, heat resistance Ideal. GE Toshiba's InvisiSi1 has a refractive index of up to 1.5 to 1.53, with a wavelength range of 95% between 350nm and 800nm and 75% to 80% of the wavelength as low as 300nm, reducing the refractive index 1.41, even 300nm wavelength can maintain 95% of the light permeability. Dow Coring Toray SR 7010 in the 405nm wavelength above the 100% transmittance, and hardening after the refractive index is also 1.51, the other heat can also reach 180 ℃ ~ 200 ℃ level. In addition, the industry has proposed a so-called resin-free package, that is, with glass as a coat protection, such as Kyocera Kyocera (Kyocera) proposed ceramic packaging, are designed to anti-aging, which also has a better heat-resistant ceramic.
The reflection and refraction of the transmitted reflector of the lens
After the plastic package, according to the different uses of LED there will be a variety of different methods, such as making a separate package components, the most typical single LED in the past that is the case. The other is to be a number of LED into a whole component, such as seven-segment display, dot-matrix display and so on. In addition, there are two different types of welding pins, namely, Through-Hole Technology and Surface-Mount Technology.
On a separate, separate, discrete packaging, but also due to different applications have different packaging appearance. If the state indicator as a perforated welding is only a lamp (Lamp) type of package (commonly known as "shell type"), even this also has a lens type (Lens Type) difference, such as the typical Lamp, Oval Oval, Oval Oval Super Oval, Flat Flat and so on. And if the surface adhesion type, but also top view Top View, side view Side View, Dome Dome and so on.
Why do you have a variety of different lens shapes? In general, Lamp is used to make lights, Oval for outdoor signs or numbers, Top View used for straight down the backlight, Flat and Side View with guide plate (Guide Plate) for the side into the light Of the backlight, Dome as a small light bulb, small flash and so on. Different appearance, the application of different, light angle of view (View Angle) is different, this part will test the packaging design again. The use of different design methods, you can get a different light angle, light intensity, luminous flux, this common practice there are four: Axial lens Axial lens, flat lens, reflective cup Reflective cup, island reflex cup Reflective cup by Island. The general lamp is used in the central lens method, Dome and Oval / Super Oval, etc. are similar, but the Oval / Super Oval bright than the Lamp is more concentrated in the axial angle. The flat is the use of flat lens method, the advantage of light angle is larger than the central lens method, but the drawback is reduced luminous flux, light intensity weakened. As for the Top View, Side View, etc. are more reflective cup or island reflective cup, this approach is to add a mirror in the package, part of the divergence angle of the beam reflection, refraction and other convergence action, so that the angle and light intensity can be balanced.
For technical difficulties, only the lens of the Axial lens, Flat lens is relatively simple, as long as the transmission and beam divergence, the relative Reflective cup is different, the original transmission, divergence should be considered, but also consider Reflection, refraction and beam convergence, more complex.
Material, the lens part of the lens in addition to the existing material can also be used instead of the original material, because the lens has been more stress and not pay attention to bare crystal protection, so can also take plastic (Plastic), acrylic (Acrylic), glass (Glass), polycarbonate (Polycarbonate), etc., and as mentioned earlier, the permeability and wavelength, different wavelengths of different light penetration, coupled with a different material can be selected, even for Lens color, good increase in light color contrast, or depending on the application of the decorative effect (toys, Christmas tree), as well as the front of the lens, reflective cups and other geometric design, the above constitute the LED light on the fourth subject The
Conclusion
HB LED is emphasized as "green lighting", implied meaning "environmental protection" is its great demands, so not only lead-free (Pb Free) package, but also in line with today's European RoHS (Restriction Hazardous Substances Directive) (PBB), polyBrominated Diphenyl Ether (PBDE) and other environmentally harmful substances, in addition to WEEE (waste), the use of mercury, cadmium, hexavalent chromium (hexavalent chromium), polybrominated biphenyl (PBB) Electronic and electrical equipment directive) and other relevant laws and regulations must also comply.
We have also briefly mentioned in front of the package must be able to block and resist low wavelength, ultraviolet light, but also have a certain degree of hardness to resist mechanical external force, and heat resistance, in addition to insulation, anti-static, moisture must also note. More importantly, whether or not high brightness, must be derived as bright as possible, because, if not faithfully derived light energy, light can be absorbed in the packaging layer, it will be converted into heat, cooling problems for the package added A problem, if the LED heat can not be successfully resolved and reduced, become a heat load, in turn, like to hurt the LED body, including the brightness will be affected, therefore, to achieve the best, the best light is the packaging design is bound to Attention to the subject!