LED lamp packaging structure, process development status and trends

LED lamp packaging structure, process development status and trends缩略图

The functions of LED package mainly include: 1.

  1. Mechanical protection to improve reliability; 2.
  2. Enhance the heat dissipation, to reduce the chip junction temperature, improve LED performance; 3.
  3. Optical control, to improve the efficiency of light output, optimize the beam distribution; 4.
  4. power supply management, including AC / DC conversion, and power control.

LED packaging is a multidisciplinary (such as optical, thermal, mechanical, electrical, mechanical, materials, semiconductor, etc.) technology. (As shown in Figure 1) from a certain point of view, LED packaging is not only a manufacturing technology (Technology), but also a basic science (Science), excellent packaging engineers need to have a deep understanding of the physical nature of thermal, optical, materials and process mechanics. Recently, chip-scale packaging CSP has attracted everyone's attention, so now and the future of LED packaging technology, the need for LED packaging design and chip design at the same time, and the need for optical, thermal, electrical, structural and other properties of unified consideration. In the encapsulation process, although the material (heat dissipation substrate, phosphor, potting adhesive) selection is very important, but the encapsulation structure (such as thermal interface, optical interface) on the LED luminous efficacy and reliability of the impact is also very large, high-power white LED packaging must be used in the new materials, new technologies, new ideas. Small-pitch or Mini LED packaging technology requires a deeper understanding of flip chip and reflow or eutectic flip chip packaging process. For LED technology practitioners, beyond cost efficiency and reliability, there is a need to integrate light source, heat dissipation, power supply and lamps. This whitepaper discusses the current status and future of LED packaging technology, and analyzes the future trends of LED packaging technology and products.

LED lamp packaging structure, process development status and trends插图

2.LED Technology Development Trends

The selection of LED packaging methods, materials, structures and processes is mainly determined by factors such as chip structure, optoelectronic/mechanical characteristics, specific applications and costs. After more than 40 years of development, LED packaging has gone through the bracket type (LampLED), SMD (S MD LED), power LED (Power LED) and COB and other stages of development.

Development to today, the future will go where? SMD? EMC? COB? or CSP? What is the flip-flop soldering and no package? In the end, LED packaging will go in that direction, there are still many opinions. However, from the historical trend, the package material is less and less, the material thermal conductivity is getting better and better, the power density is getting bigger and bigger, the package process steps to more and more streamlined and fewer and fewer devices is the trend of the future, of course, this can not leave the advancement of chip technology.

It is expected that by the future 2022 will reach the goal of 300 lumens watt, the cost of a single lamp will be less than 10 dollars, which is a very big challenge for the packaging technology, technological advances, cost reductions, Haze's law in the future will continue to dominate the direction of the LED, especially in the LED lighting industry. In the past decade, the improvement of LED chip efficiency will make the chip area continue to reduce, and then drive the LED packaging revolution.

Future chip technology will be to improve efficiency and reduce costs, Perspex technology will improve efficiency and stability and color rendering index as the direction of progress, LED chip efficiency will be improved in stages of growth, from 10lm/w~80lm/w, 80lm/w~100lm/w, 100lm/w~150lm/w, 150lm/w~200lm/w, LED chip efficiency will be improved in stages of growth. …… When the technology advances to 300lm/w compared to the existing chip efficiency increased by 1.5 ~ 2 times, the chip's heat will be greatly reduced (refers to the same volume with the area of comparison), which will lead to a variety of packaging technology for the big competition, all the technology route trend will be more differentiated and diversified, what products use what packaging LED will usher in the mainstream in the pluralistic, pluralistic differentiation, but not far from the mainstream.

LED lamp packaging structure, process development status and trends插图2
  1. is changing and the future is about to change the LED encapsulation technology

With the increasing power density of the chip, especially the development of semiconductor lighting technology needs, the optical, thermal, electrical and mechanical structure of the LED package has put forward new and higher requirements.

From the previous description, the development of high luminous efficiency technology route can be expected to the existing packaging process and packaging materials and can not be applied to the future packaging requirements. Due to the enhancement of quantum efficiency within the chip, so the heat generated will be reduced, the effective current density of the active layer of the chip will rise dramatically. Chip overall heat reduction, so for the package form of heat dissipation area requirements will be reduced, the current use of heavy heat dissipation of the package structure will undergo a major change, so the LED chip efficiency to improve the chip area is greatly reduced, thereby changing the way the package, so that the light output of a single device greatly increased, now, a single high-efficiency LED chip area is greatly reduced (250mil2 =) 60LM). Heat becomes less with the application of a single LED light source of high luminous flux demand for integrated packaging has become mainstream. Integrated package LED device thermal aggregation effect so that the overall thermal conductivity of the LED device becomes extremely important. Can significantly reduce the thermal resistance of the packaging technology may become the mainstream of the LED chip packaging technology, flip-flop reflow soldering technology as long as the solution to the chip yield and cost issues, which will revolutionize the cost of reducing the package will make the non-golden wire soldering technology flip-flop packaging technology for large-scale applications. Of course, imitation PC hardness of silicone molding technology, aspheric secondary optical lens technology and other light technology will become the basis of LED packaging technology. Directional quantitative dispensing process, graphic gluing process, the second electrostatic spraying Perspex process, film lamination method of three-color phosphor coating process, chip deposition and pressurization method and other white light technology will be used in the LED packaging process, will improve the LED device light efficiency and light color distribution.

1.SMD development trend

SMD package, is the abbreviation of Surface Mounted Devices, meaning: Surface Mounted Devices, it is SMT (Surface Mount Technology Chinese: surface adhesion technology) components of a kind. Currently SMD is the packaging technology of the largest products, especially 2835-type package type currently occupies almost the mainstream lighting market, predicted that the next five years SMD will be the mainstream of the LED, but will gradually reduce the ratio, but to maintain half of the river still have the opportunity, the future SMD will have the following trends to meet the competition from other technologies:

a) Medium power to become the mainstream packaging. Currently on the market for high-power LED products or low-power LED products, although they have their own advantages, but also has insurmountable defects. The combination of the two advantages of medium-power LED products came into being, and became the mainstream packaging.

b) The application of new materials in packaging. Due to high temperature resistance, UV resistance and low water absorption and other higher and better environmental tolerance, thermoset materials EMC (Epoxy Molding Compound), thermoplastic PCT, modified PPA and ceramic-like plastics and other materials will be widely used.

c) Compared with PPA or ceramic substrate, EMC packaging program for the use of epoxy resin material-based, easier to achieve large-scale mass production needs, through the expansion of the volume to further compress the manufacturing cost, in addition to the application of epoxy resin material is more flexible, not only the size can be easily re-designed, coupled with the material is smaller and easier to cut the processing of the end-product component design is more flexible, flexible, and made of terminal light source components can be used in the light source components in the light source components in the light source components in the light source components in the light source components in the light source components. Made of terminal light source components can be driven in a small volume of high wattage, especially in the 0.2W ~ 2W or so light source products are very competitive.

2.COB development trend

COB application is gradually gaining popularity, with low thermal resistance, good light type, no welding and low cost advantages, COB applications in the future will continue to penetrate. COB encapsulation process has a lot of advantages, get rid of the bracket table sticker soldering this link, COB encapsulation process is directly fixed to the LED bare chip pad, so the heat dissipation area relative to the traditional encapsulation process to be larger, the material is also a high comprehensive heat conduction coefficient, good heat dissipation. Coefficient is also high, good heat dissipation. This is to ensure that the COB package of high reliability factors in the highest weight of a factor. COB package eliminates the bead surface over the reflow soldering process, no longer caused by the traditional packaging process reflow soldering furnace high temperature on the LED chip and solder line failure. In addition to other components can be integrated with the packaged light engine is also a great advantage of COB, integrated packaged light engine may be one of the mainstream of the future COB technology.

SIP (System in Package) is in recent years in order to adapt to the portable development of the machine and system miniaturization requirements, in the System on Chip (SOC) based on the development of a new type of package integration. For SIP-LED, not only can multiple light-emitting chips be assembled in one package, but also a variety of different types of devices (e.g., power supply, control circuits, optical microstructures, sensors, etc.) can be integrated together to build a more complex and complete system. Compared with other packaging structures, SIP has the advantages of good process compatibility (can utilize existing electronic packaging materials and processes), high integration, low cost, can provide more new functions, easy to block test, short development cycle. Of course, COB in the luminous efficiency and luminous density of the parameters are also more concerned about the focus, according to reports, in the Ra>80, R9>0 under the high quality of the light color, the highest luminous efficiency of the domestic COB data as high as 162lm / W, the highest density of lumens can be reached 88lm/mm2, but in the 105lm / W under the luminous efficacy of the lumen density can reach 220lm/mm2, with the U.S. cree's 280lm/mm2, and the lumen density of the U.S. cree's 280lm/mm2. With the United States of America's cree 280lm/mm2 is still a small gap, but has been close to the level of international manufacturers.

3.CSP development trend

CSP's full name is Chip Scale Package (Chip Scale Package), is currently the packaging industry's most feared packaging process, CSP without stents, gold wire and other traditional packaging process must be the main components of the material and solid crystal, welding gold wire and other packaging equipment. 20%, and the LED can still have a complete function of the packaging device, and CSP technology is pursued in the device volume as much as possible to minimize, reduce, but still have to maintain the same chip should be the light effect, and the key device volume reduction after the most direct characteristics of the practice of low-cost, small light-emitting area, longer component service life of the design purpose, coupled with the small size of the device also indicates that the secondary optics of the relevant optical processing Optimization of higher flexibility, lower processing costs, made of lamps and lanterns products in a very small optical structure to practice the highest brightness and maximum luminous angle.

CSP development to the present, the technology route has always had two directions, single-sided light-emitting and five-sided light-emitting, samsung LED development CSP at the beginning of the use of backlighting for large-size, the use of technology is relatively simple five-side light-emitting technology, the same technology route is the Seoul Semiconductor's WICOP, used to be applied to the general lighting market. Single-sided light-emitting technology has Nichia and bright sharp CSP products, as a result of single-sided light-emitting, so the process is more complex, the need to reflective film plating on the side of the device, the cost will be relatively high, but this product can be used for high-end applications such as automotive lighting and cell phone camera flash, so it is currently the future trend of CSP technology.

At present, Nichia Chemical is in the leading position in the single-sided light-emitting CSP technology, single-sided light-emitting technology relative to SMD, in addition to the price is higher, there are very absolute advantages, can be used in special lighting market applications, such as electronic products, cell phone camera flash and LCD backlighting, automotive headlamps, outdoor lighting, street lamps, tunnel lights and floodlights, and high-density COB products can be used. In the future, with the maturity of high-volume CSP manufacturing technology, CSP will continue to penetrate more lighting applications.

Currently domestic manufacturers of CSP brightness performance has been close to the level of Japan and South Korea, the market can be mass-produced 1W level of luminous efficacy can reach 205lm / W (350mA, cRI 80 +, 5000K), 3W level of the product can also reach 190lm / W (750mA, cRI 70 +, 5000K) luminous efficacy of the 5W package technology can reach 170lm / W (1200mA, CRI 70 +, 5000K), 5W package technology can reach 170lm / W (1200mA, CRI 70 +, 5000K). 1200mA, CRI70+, 5000K) light effect. Cost-effective is to leave Japan and South Korea related products, but due to brand and patent relations, the mainstream applications such as automotive lighting or flash market is still difficult to enter.

  1. General lighting packaging trends in the future

1) Chip ultra-current density will continue to increase.

In the future, the ultra-current density of the chip will develop from 0.5mA/mil2 to 1mA/mil2 or even higher. And the chip demand voltage will be lower, smoother VI curve (low heat), and ESD and VF both.

2) Multi-color LED light source for scenario lighting.

Scenario lighting will be the core competitiveness of LED lighting, and the second take-off of LED lighting in the future will rely on scenario lighting to realize.

3) The demand for luminous efficacy is relatively low, and cost-effectiveness has become a winning strategy for packaging factories.

The future of indoor lighting will not be too concerned about the light effect, but will pay more attention to the quality of light. With the improvement of packaging technology, LED lamps and lanterns cost reduction to replace the traditional lighting source of motion.

4) Go to the power solution (high voltage LED).

Future indoor lighting will pay more attention to the quality, and in the cost factor drive, go to the power program will gradually become an acceptable product, and high-voltage LED fully cater to the go to the power program, but it needs to solve the chip reliability needs to be strengthened.

5) International and domestic standards are further improved.

I believe that with the continuous improvement of LED packaging technology, domestic and international quality standards for LED products will continue to improve.

6) The demand for higher light quality.

Mainly for indoor lighting, companies will be LED indoor lighting products RA to 80 as a standard, RA to 90 as the goal, try to make lighting products close to the Planck curve, so that the light can be uniform, no glare.

LED lamp packaging structure, process development status and trends插图4

The future packaging trend of the display

In the past, the packaging of the display screen has inline, SMD and COB three mainstream directions, but with the increasing demand for small pitch, COB will be more and more of the mainstream in the future. Inline and SMD encapsulation process in the solid crystal welding line and COB encapsulation is no difference, the biggest difference is the use of brackets.

As we all know, the bracket generally has four welding legs, which need to be welded to the PCB board through SMT. Therefore, the COB packaging process compared to inline and SMD packaging process is the biggest difference between the single lamp eliminates a bracket, and therefore saves the bead surface over the reflow soldering machine surface paste welding process. Why COB will be

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