"The first one, according to plan, we will have another 4 lines around March next year. I also plan to use the other half of the factory for application development, mainly as a bulb, and now this profit is very big." Last year Li Li, who has switched from a trading company to the owner of the LED packaging factory, is sitting in his office in Putian, Shenzhen, and is portraying the LED dream he is building with three other investors. The 1,400 square meter factory is very empty, and the only packaging line only accounts for about 50 square meters. In contrast, the office in the corner of the factory building is a bit cramped. In addition to the two large boss tables, chairs, sofas, coffee tables, and water dispensers, there are scattered industry magazines about LEDs. LED light source and LED bulb.
"It’s not too early for me to enter the LED. But to be honest, this industry is simply too hot. It’s no exaggeration to say that I just put the news out, there are many people who come to me to invest in me, start the funds. The problem was solved quickly."
"This field is really crazy. Many people who don't understand anything at all dare to enter. I heard that a friend is ready to engage in packaging, investors are looking for it, the factory is looking for it, and I contact ASM at startup. I know that even if I pay the full amount now, I will not be able to get the packaging equipment until May and June of 2011. As a result, everything is gone."
From the ordering situation of ASM, everyone can imagine the "heat" of China's LED packaging. "As long as the product that needs to be illuminated is the business opportunity of LED", the attractive LED prospects attract more and more people to fight. After joining the industry. At present, LED's most promising market is undoubtedly a large-size LCD backlight in flat-panel LCD TVs, notebook computers and notebook monitors, but there is no doubt that general lighting is the ultimate development goal of LED. At present, LED bulb replacement lamps will become the most important growth area in the lighting market before the LED general lighting market has actually started. However, is there a large number of LED bulbs on the market that are equivalent to true solid-state lighting (SSL)? Is LED really ready for general lighting?
LED general lighting faces four major challenges first
The US Department of Energy has said that solid-state lighting is the most devastating innovation in the field of lighting for 50 years. Many people in the industry agree with this and believe that LED is a disruptive product, and it is necessary to reform its original product. But in fact, LEDs still face four major challenges in the general lighting market: light quality, light performance, reliability, and simplification.
Zhou Xuejun, Marketing Director of Philips Asia, explained: "The light quality of LEDs still has a gap compared with traditional lighting; there are some applications that cannot be covered by light performance; because LED lighting reliability is made up of chips, electricity, light, heat, machinery Due to a number of factors, such as the interconnection part, it is impossible to maintain sufficient light output lumens to maintain the life; due to the lack of uniform standards, LED lighting products on the market are now diverse, and the complexity also hinders it from being accepted by more audiences in the short term. "So, what are the current solutions on the market to improve LED light quality and light efficiency?
Light quality Generally speaking, the light quality we talk about mainly refers to light distribution, light angle and shadow, and color rendering. Here, Zhou Xuejun particularly emphasizes that designers should pay attention to: Is the color of light between different LED particles consistent? Is the change of different particles consistent with time? Is there a color difference between different LEDs at different angles? How is the color rendering index?
The entire packaging process of LEDs consists of two important steps: bonding the chips and pins with gold wires, and performing phosphor coating. These two steps will cause color difference to the LED, especially the gold wire will block the light path. If improper operation may cause hidden cracks on the chip, thus forming a chip breakage hazard. To solve these problems, Philips Lumileds' latest LUXEON Rebel LED series uses the latest TFFC (film flip chip technology) and the unique Lumiramic fluorescence technology.
According to Zhou Xuejun, the electrode of TFFC technology is behind the board, and there is no vertical and horizontal wiring on the surface, so the physical structure is better. Lumiramic fluorescence technology uses ceramic fluorescent plates instead of phosphors to directly bond to the chip, so that the surface is completely flat without unevenness and unevenness, thus fundamentally avoiding the traditional packaging method caused by uneven phosphor coating. Most LEDs show color inconsistencies at angles that are off the center of the boresight. “In addition, Lumiramic technology can also reduce the range of white light bins (bins) to 1/4 of the original.†Zhou Xuejun added.
At present, the most troublesome problem for the lighting industry, especially lighting design, is bin. For some experienced LED manufacturers, the usual practice is to use the entire output range of white LEDs in all files. However, at a specific CCT (correlated color temperature), it is impossible to produce a white LED having high uniformity at a low cost, mainly because of the wavelength of the blue LED chip and the coating process of the phosphor. As a result, manufacturers may mix multiple LEDs in separate bins, but as a result, the range of applications is limited, increasing the complexity of the production process and generating more inventory. Cree's solution for this is EasyWhite bin, which uses Cree's multi-chip XLamp MC-E LED. The MC-E chip is packaged in a four-core package. Cree selects four white LED chips with different characteristics (overlying fluorescent). Powder) and packaged, the white light output after mixing can reach the expected color temperature, and is much smaller than the standard range specified by ANSI.
Light efficiency is like the Moore's Law of the semiconductor industry. The LED industry also has a Haitz law, that is, the LED brightness is doubled every 18-24 months, and in the next 10 years, the brightness is expected to increase by 20 times, and the cost will be Down to the current 1/10. Today, the market can buy about 100-150 lumens for 1 dollar, and the US Department of Energy estimates that this number will reach 1000 lumens in 2020.
How to improve the LED luminous efficiency? First look at the package. At present, the most common LED light sources on the market are in-line and patch. Zhu Xiaotian, deputy director of technology of Shenzhen Changguang Semiconductor Lighting Technology Co., Ltd., believes that the cooling outlets of these two packages have a small cross-sectional area, and the passage of a single light exit is narrow, and the utilization rate is relatively low. According to the light-emitting characteristics of LEDs, Changguang Semiconductor has designed a flat primary optical channel to form a planar light source array chip, which can minimize optical loss. In this regard, Zhu Xiaotian explained: "SMD's 3528 or 505 light source uses glass fiber or plastic as the substrate, and the bottom is not connected to any metal. The planar light source array chip uses a multi-chip integrated COB direct packaging technology, the light source is used. The aluminum substrate can dissipate more heat through the direct connection heat dissipation. It is reported that the company's LED surface light source technology with completely independent intellectual property rights has reached 130lm/w, and the overall lighting efficiency has been greater than 100lm/w.
In addition to packaging, chip structure, forward voltage and other factors are also critical. If the forward voltage can be controlled within a very small range, good light efficiency can be obtained. In this part, we must pay special attention to how to solve the droop phenomenon. It is well known that an increase in current density causes LEDs (mainly LEDs that use InGaN as a light-emitting layer, such as blue, green, etc.) to emit more light, but at the same time, the light effect is also reduced. Currently, chip design companies are working hard to find a solution that is as close as possible to the increase in light efficiency. That is to say, on a square millimeter area, more light is obtained on the premise that the light is not damaged, instead of increasing the die size. Of course, an increase in the thermal coefficient (LED output ratio at 100 ° C junction temperature and 25 ° C junction temperature) also helps to simplify the heat sink design, thereby reducing the cost per lumen in the final application.
How to solve the "hot" problem?
The importance of LED heat resistance has become the consensus of the industry. This problem also exists for LED general illumination. In this regard, Zhou Xuejun vividly likes to say: "LED is like a snowman. It is very beautiful when it is cold, but it will melt when it gets hot, and it will become very difficult to see."
"The thermal management in LED system design is very important, because a considerable part of the electrical energy is converted into heat." Zheng Zhaoxiong, senior director of global sales and marketing of ON Semiconductor's power and portable products, said, "To solve the heat problem, you need to upgrade the drive power. LEDs that convert energy efficiency and apply higher light efficiency, use LED driver chips that provide strong thermal fault protection performance, and drive chip packages with better heat dissipation performance, LED substrates with better heat dissipation performance, etc. In addition, in order to improve system reliability, Combine other means, such as using better external components with higher rated operating temperatures and using ambient light sensors to reduce power consumption and heat."
Li Zhiyuan, marketing manager for the Asia Pacific region of National Semiconductor (NS), believes that the internal temperature of LEDs may indeed rise to extremely high levels due to the actual operating environment. Once the temperature of the LED rises above the threshold and enters the non-safe area, the life and lighting effects of the LED will be affected. The thermal energy folding circuit can monitor the thermal energy of the system to avoid temperature loss.
NS's LM3424 chip is one such product that sets the temperature and ramp breakpoints for the LEDs of the lighting system to ensure that the LEDs stay in the safe zone. In the event of overheating, the thermal breakback circuit of the LM3424 reduces the regulated current flowing into the LED. The reduced rectification current will also reduce the brightness of the LED, but remain within the engineer's preset range until the operating temperature returns to a safe operating range. In addition, NS also introduced a high-power LED driver LM3464, which can monitor the temperature of the LED heat sink/copper layer by using the chip's overheat protection system solution: if the LED temperature suddenly rises sharply, the overheat protection function will reduce the output current. To avoid overheating and damage of the LED under abnormal conditions, and the LED can maintain a certain brightness.
Mao Yuhai, general manager of Shanghai Longmao Microelectronics Co., Ltd. pointed out that the solution to the 'hot' problem has yet to be improved. Lin Chang, executive vice president of Shenzhen Ruifeng Optoelectronics Co., Ltd., agreed that “To solve the problem of thermal management, we must first improve the light efficiency from the chip side, and the natural heat will be reduced when the light efficiency is improved. Consider how to derive the heat, and also need to solve the heat-resisting problem of the packaging material, the material is not yellow, and the light attenuation is not. What is needed at the application end is how to introduce the heat into the natural environment, which is not hot here. It is the key. The designers in the three aspects must do what they should do. This is the fundamental. The solution must be different for different products.†It is reported that Ruifeng Optoelectronics has been able to do this in the packaging process. 5000H zero attenuation.
LED driver solution
For LED lighting applications, the role of the drive power section is critical, because if the drive power section is not supported, then the higher LED efficacy is waste. It can be said that efficient driving power is a powerful guarantee to improve the efficiency of the lighting system. In this regard, Mao Yuhai specifically pointed out: "The biggest problem in LED design is how to ensure the reliability of the driving power supply to match the long life of the LED. This aspect must deeply understand the design principles and specific methods of reliability, and know how to test the product. reliability."
The reliability of LED driver power is largely related to “heatâ€. If the heat dissipation effect is not good, the life of electrolytic capacitors in the circuit will be greatly reduced, which will seriously affect the life of LED products. We have already discussed the above content. Below we will mainly introduce other possible problems and several latest solutions.
At present, due to the lag of LED lamp standards, the LED driver power supply in the market mainly adopts a customized operation mode. Therefore, LED lamps generally have voltage, current, and power levels that are not standardized, and space is limited, heat dissipation conditions are poor, and power consumption affects lamps. Problems such as ambient temperature. Qian Jiafa, manager of the technology marketing department of Fairchild Semiconductor Shenzhen Branch, said that LED applications with different power levels may encounter different problems. For example, a small power application may be unable to be placed due to too small space, and the safety distance is not enough, the constant current accuracy is not enough, and the temperature is too high. The medium power application usually adopts the PFC+PWM two-level architecture, resulting in The overall cost is too high; while the high-power requirements for PFC and constant current are very high, the direct problems are complicated circuits, many parts, PFC and main current timing need to be controlled, and low efficiency. For a variety of applications, Fairchild has introduced a variety of LED driver solutions, including low-power flyback (PSR & SSR) solutions for indoor lighting, high-power AHB and LLC solutions for outdoor lighting. And multi-channel drive solutions for TV backlighting and more.
Li Zhiyuan pointed out that the two most likely problems encountered by engineers in designing LED drive circuits are: how to pass electromagnetic interference verification, and mutual interference between circuits may cause abnormal work. NS's LM3402/4HV chip targets the DC-DC converter market, which not only has higher power conversion efficiency, but also has strong anti-electromagnetic interference capability. For general-purpose lighting, NS's LM3445 chip can adjust the brightness of LED bulbs with a triac dimmer (TRIAC) dimmer. Li Zhiyuan said: "As long as the LM3445 solution is adopted, conventional bulbs such as A bulbs, PAR bulbs, and ceiling spotlights that are commonly used on the market can be switched to LED bulbs."
This product is similar to the function of ON Semiconductor's NCL3000. The NCL3000 is a single-stage power factor corrected TRIAC dimmable LED driver for residential and commercial AC-DC powered LED lighting applications from 8W to 25W, using a critical conduction mode (CrM) flyback architecture in a single stage The topology provides a high power factor greater than 0.95, thus eliminating the DC-DC conversion section. Constant on-time CrM operation is particularly suitable for isolated flyback LED applications because of its simple control principle and extremely high energy efficiency even at low power levels, which is important in the field of LED lighting in order to comply with the Energy Star. "Solid lighting requirements and other specifications and overall system efficacy requirements.
Another new low-current LED driver solution from the ON Semiconductor, the NSI45 series of dual-ended and three-terminal linear constant current regulators (CCR), uses patent-pending self-biasing transistor (SBT) technology. This solution is simpler and less expensive than a linear regulator, but the performance is greatly improved compared to the resistor scheme, filling the gap in the market. The NSI45 Series maintains constant brightness over a wide voltage range, protects the LED from overdrive when the input voltage is high, and brightens the LED when the input voltage is low, helping to reduce or eliminate LED code inventory and help reduce overall system cost Etc. Ideal for low current LED current applications.
According to Shi Jingyan, Senior Director of Sales and Business Development, Industrial and Diversified Electronics Markets Division of Infineon Technologies (China) Co., Ltd., Infineon has also recently launched an off-line LED driver IC that supports dimming, the ICL8001G. High-efficiency LED bulbs for residential lighting. The product's flexible design replaces all 40W/60W/100W incandescent bulbs and all typical consumer lighting applications. With up to 90% energy savings, the ICL8001G supports a wide range of installed wall dimmers and is the only master-offline LED driver solution with integrated power factor correction (PFC).
Although the LED driver market is mainly occupied by European and American companies such as TI, NS, Avago, Linear, NXP, and Taiwanese manufacturers such as Accumulation, Lijun, Dianjing, and Jingjing, several local companies in China are also performing in this field. Very active. For example, Shanghai Longmao Microelectronics Co., Ltd. has introduced a constant current driving power supply for various power LEDs. "Our advantage is to master the core chip technology. In addition, we also focus on the dimming technology of street lamps, fluorescent lamps, tunnel lights, etc., and have 5 patents." Mao Yuhai said. It is reported that Longkou has mass-produced the step-down high-power LED constant current drive module SLM2842J has received a lot of praise in the industry, the module can drive 10 string 6 and 1W LED, or 10 string 2 and 3W when the input voltage is 36V The LED has a driving power of up to 60W and an efficiency of up to 98%. Only 1.2W of power needs to be dissipated, so the heat is very low, below 60 degrees.
A new generation of LED modules for indoor lighting
Anson's Zheng Zhaoxiong believes that there is another important challenge in the LED lighting design process, which is to maintain the highest possible energy efficiency of different components of the lighting system or light source. “The light source should be seen as a complete system, with LEDs, heat sinks for heat dissipation, optical components, and electronic drive circuitry as a whole, ensuring that each component is designed to provide maximum energy efficiency,†he said.
In actual operation, Ruifeng Optoelectronics has modularized the above concepts and introduced a modular solution for indoor lighting. “Modularization means mass production of light source, heat dissipating components and drive power components, and standardization of LED lighting products through molds.†Liu Xin, head of high-power LED module development at Ruifeng Optoelectronics R&D Center, said, “Despite the current local Enterprises can't bypass the patent barriers of foreign companies in LED epitaxial wafers and chips, but the mass production of modules has a price advantage, which is a good choice for downstream LED lighting application companies."
Nowadays, many companies add 3520, 5050 and other low-power LED light sources to indoor lighting for bulbs, but the products often have problems such as excessive glare, insufficient heat treatment, short life, high cost and large color difference. "We believe that the traditional light bulbs are equipped with LED light sources, which is not the same as semiconductor lighting." Liu Xin said, "If LEDs really want to enter thousands of households, they must exert their advantages, and this should be a systematic project. Including power systems, LED light sources, drive systems, optical systems, exterior structure design, cooling systems, intelligent control systems and many other aspects."
As mentioned earlier, light quality includes color rendering, spatial uniformity, color consistency, and no glare. Ruifeng Optoelectronics' module light source solution enhances the color rendering of the overall light source or a single color rendering by implanting a color LED chip. "Because in the LED spectrum, the red and green segments are relatively low. If the green and red chips are stringed in a white light module, there is a very substantial improvement in color rendering," Liu Xin explained. “Because the overall light effect is enhanced by white light, the color rendering is enhanced by the light of other chips. This also helps to separate the light effect from the color rendering.â€
“Spatial uniformity and color consistency are first improved by selecting and optimizing materials.†Liu Xin said. The material selection here includes phosphors and chips. When packaging, the device can be used to verify the chip and how wide the wavelength of the phosphor feed is to verify that the incoming material meets the requirements. The second is the design of the circuit inside the module power supply, taking into account the string and the situation of the entire module. The third is to carry out strict process control, including the most direct, that is, the way and how much phosphor coating, which has a great impact on color consistency. Finally, material reliability control is also required.
With the improvement of LED light efficiency, Liu Xin believes that the glare problem will be more prominent in the future LED lighting design. The modular power supply is optimized for structural design, such as the use of reflective cups to reduce glare. This is also one of the innovative designs of Ruifeng Optoelectronics. Adding a reflective cup can greatly reduce the loss of light emitted by each LED chip. Similarly, adding a lens and roughening the surface. Etc., combined with the module can improve the light extraction efficiency.
The life of light consists of two parts, one is the brightness life and the other is the color life. Brightness life directly affects the operating cost of the light source. In life control, the first consideration is the heat dissipation design. The module light source solves this problem through structural design. There is a direct relationship between life and heat dissipation, including chips and raw materials. The most direct life impact is from heat. The light-emitting efficiency of blue light and phosphors are all related to the junction temperature. “Under normal circumstances, the LED's junction temperature will increase by half when it rises by 10 degrees.†Liu Xin added, “The module has its advantages in solving the thermal resistance. At present, the thermal resistance of LED application lamps mainly includes LED. Chips, packaging materials, brackets, thermal resistance attached to the circuit board, thermal resistance of the secondary application system, if a certain intermediate link can be omitted, the thermal resistance of the entire application process is saved a large part. The group solution can directly save the thermal resistance of the bracket and the re-chip thermal resistance after the customer buys it back."
summary
In addition to the difficulties and challenges mentioned in the article, LED general lighting is of course inseparable from cost pressure. In this regard, Zhang Sanling, the chief manager of Fairchild's technical marketing department, said: "In the TV market, the cost of LED backlighting is acceptable because the product must meet the requirements of ENERGY STAR and CEC standards to reduce overall power consumption. However, for indoor and outdoor lighting, the cost of LED lighting is still much higher than traditional solutions. High reliability is a key factor in LED lighting applications, but it will also increase system cost pressure."
LED general lighting is still in the early stages of the market, and there are still many difficulties that have been discovered or not yet discovered. With the investment in research and development of LED chips by Chinese local enterprises and the introduction of national standards, China's LED general lighting market will accelerate the development of health and standardization. "At present, LED lighting has solved all applications except the headlamps in the automotive field. If the street lamp application is successful, I believe that the application of the car headlights will be popularized immediately." Ruifeng Optoelectronics executive vice president Lin Chang looked forward. "At that time, LEDs will also enter the home as ordinary lighting. I think this process will be 5-8 years."
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