Silicon base LED yield low current high voltage LED development potential - (AddTime -2013-01-29)

LED packaging technology at present mainly to high luminous efficiency, high reliability, high heat capacity and thin turn four direction development, at present, the main window have silicon base LED and high voltage LED, silicon base LED industry has aroused more and more attention, because it than traditional sapphire substrate LED heat dissipation ability stronger, so the power to do more big, Cree will focus on the development of silicon base LED, it present the main problem is that yield is low, lead to cost also is on the high side.

High voltage LED is another big window, because it can dramatically reduce DC - DC decompression circuit of input/output pressure difference, and further enhance the efficiency of LED drive power supply, which can effectively reduce the 200W led Flood light and lanterns to cooling housing demand, so as to reduce the overall cost of the 200W led Flood light and lanterns. At present Cree, Osram and advanced developing high voltage LED technology. Advanced electronic (Everlight) research and development two marshal LinZhiMin said: "the future will expand advanced development and application of high voltage LED products, integrated more components, to create simple application of the tiny light engine, to reduce the cost for solid state lighting lamps and lanterns, the popularity of do a heart."

LED packaging principle

LED packaging is mainly provides LED chip a platform, let the LED chip have better light, electricity, heat performance, good packaging can make LED have better luminous efficiency and good cooling environment, good heat dissipation environment and enhance the service life of LED. LED packaging technology is based on five main factors, and separately for optical extraction efficiency, heat resistance, power dissipation, reliability and performance (Lm / $).

Above each factor in the package is quite important link, for instance, the light extraction efficiency related to the price; Thermal resistance related to reliability and product life; Power dissipation in relation to customer application. On the whole, better packaging technology is we should pay attention to the each point, but the most important thing is to stand in the customer's position thinking, can satisfy and exceed customer demand, is a good package.

According to the LED encapsulation material composition, LinZhiMin detailed explain a way, LED packaging is mainly composed of base plate, chip, solid crystal glue, phosphor, encapsulation adhesive, etc, we will first chip using solid crystal glue paste on the base plate, the use of gold thread will chip and base plate for electrical connection, and then will phosphors and encapsulation adhesive mixed with different phosphor powder proportion, and the appropriate chip wavelength can be a different color and will last a fluorescent powder and packaging glue mixture into the base plate, heating baking make glue material after curing, to complete the most basic LED packaging.

LED packaging four development trend

He pointed out that LED packaging technology is mainly to high luminous efficiency, high reliability, high heat capacity and tropical change development. From the chip to see, at present the most common is horizontal chip, more high-end manufacturers are r&d vertical type chip and flip chip type chip, the original horizontal LED use sapphire substrates, cooling ability is poor, and in high current drive, light extraction efficiency decline range is bigger also. Therefore, in order to reduce the cost of LED, high current density of chip design and in order to get more light output as the main research direction, in this to consider, the use of vertical type package chip has become a topic, this kind of chip using silicon contour cooling base plate, and the high current operating under have better heat dissipation efficiency, so there is a higher light output, but due to the complicated production process, process yield is too low, that can't achieve ideal high performance-to-price ratio, thus it can be seen, in high wattage packaging, process yield caused by the price factor is also a big consideration.

TSMC electronic company is specializing in science and technology in her wafer level high power LED silica encapsulation technology industry. The company in 2010 has penetrated the street lamp market in 2011, and more focus on indoor lighting ball steep light products. Already in science and technology LED technology research and development division chief LiYu hua said, with eight inches epitaxial calculation, at present already in packaging capacity of 2000 pieces, monthly performance is equivalent to 4 million last year, a successful product into the street light products, big time even as high as 70-800000 monthly performance according to the planet.

And general Taiwan LED packaging manufacturers the alumina (sapphire) base plate technology is different, the mining is already a wafer level LED silica encapsulation technology, mining, said her LiYu China silicon base package LED in the heat better than the sapphire substrate, but the price is higher than the sapphire substrate products, however, that LiYu China within this year already, mining silicon-based encapsulation and sapphire substrate product prices will tend to be consistent, adopt more already set a goal, I hope every year cost reduction can reach 30%.

Silicon base plate yield is low

Silicon substrate for the biggest appeal better thermal conductivity, LiYu China further pointed out that the next generation lighting LED packaging needs the most important thing is to heat dissipation problems, estimate hot question 5 years difficult solution, followed by need powerful structure body and stable and reliable material. In addition the light performance is also very important, such as uniformity, light intensity, the efficiency of light is more outstanding and light type performance, the last is the production and cost management.

LED packaging in the 30 years of evolution, the biggest characteristic is more and more small size, so the thermal effect problem in the input drive current high will highlight out. That is to say, now high power LED demand more and more big, when in the small single LED and will power penetration, heat will produce, in order to reduce the heat, the brightness of the light will be reduced, then in order to increase brightness and to import a higher current, high current and will produce more heat, so become a cycle, quantity of heat is increasing. Joint temperature is too high, the result is increased every twenty ℃, LED efficiency will be reduced by 5% (or every increase 1 ℃, efficiency drop 0.25%).

LED produce 90% quantity of heat is going down, so packaging technology, heat dissipation is very important. Overall, selection of high power LED time installed base station (sub - mount) material is ceramic (alumina, aluminum nitride) and silicon. Among them, the aluminum plate have warping problem, and with the coefficient of thermal conductivity and thermal diffusion perspective, silicon is the best choice.

Silicon base LED packaging process for: insulation and metal layer, chip/metal wire bonding and fluorescent material coating, lens assembly, and then cut and testing. Use silicon wafer method can through to control the hole type (single or multiple), thus increasing the light extraction rate, this is ceramic substrates can not. LiYu China and especially points out that mining her sole IC manufacturing compatible wafer level phosphor powder coating technology, can be in LED chip has the top thin and efficient phosphor powder out light layer, can improve HuangYun phenomenon, and this technology can control the consistency of color temperature.

In addition, hemispherical lens for optical design way to add a light rate method, and one of her by sole design of wafer level products, lens are designed to meet the needs of the various forms of light. In addition, the use of different materials of different refractive index, by inside and outside more and more small, can control the light path make it out of the light rate increased, the structure model can improve the light rate more than 7%. Moreover, by phosphors compensation process can achieve close color temperature control, thus yield can be promoted, make originally less than 70% of the yield, through compensation can promote more than 95%, at present already LED by silicon base packaging products have been in the import, including mainland China qinhuangdao, China beijing-shenyang expressway ramp LED street lamp and hsinchu tsinghua university campus, etc.

However, LED silicon base package there are still many technical challenges facing the need to overcome, such as material, silicon material is easy to shatter shortcomings, and institutions strength is also the problem. Fluorescent powder will need to consider its electronic brightness and heat and wet impedance. In addition, the lens refraction and thermal stability, the adhesive property is considered point. Structure, insulating layer, metal layer has its challenges.

Her mining specializes in led lighting, does not currently have entered led large size back light plan. In 2012, Taiwan, Japan, the United States, Canada will begin to disable the incandescent light bulb policies, adopt her, thinks that in 2011 the third season LED warm white ball bubble lamp sales will be explosive growth, the company will also ball steep light products listed in this year's development key.
Flip chip type LED chips encapsulation

In addition to the above vertical type chip outside, flip chip type chip is the development of the industry to target. Flip chip type chip production a multiple-layered many simple, and can avoid off complex process, which greatly improve production feasibility, coupled with the back end chip technology gold fingers and via mature technology aided, previous must planting a golden ball solid crystal mode change for large scale P, N electrode direct stick support, collocation eutectic solid crystal way, more greatly simplified the flip chip type chip package technology sill, moreover, shorten the encapsulation cooling path, compared with horizontal chip has better heat capacity, the driving voltage can also be decreased, LinZhiMin emphasis that, in the future energy saving carbon reduction drive, flip chip type chip package will be very good solution.

Based on the above package consideration, advanced currently USES the main packaging technology for fluorescent powder coating and conversion process. Fluorescent coating is the development of advanced technology, mainly in the chip with a thin layer of fluorescent layer, so greatly improves the luminous efficiency of the components, the last has put this product used in high power piece.

Conversion technology is originally used in small SMT type products above, LinZhiMin ring, said in the product have achieved great success, and further this technology was applied in the high power model, overcome the silicon molding and sticky mold and other technical problems, at present due to TV and backlight module power of ascension and reliability requirements, the traditional PPA reflection GaiJi plate for organic material, can't like silicon or resin provides better heat and light resistance ability, in order to effectively improve reliability, advanced also plans to sell the conversion technology used in backlight module products.

About the package size, at present advanced electronic experiments can reach the minimum high power package body size 3.0 x 3.0 mm, even 2.0 x 2. 0 mm the following sample preparation, however, at present the market the most common specification is 3.5 x 3.5 mm products, this product is widely used, therefore, LinZhiMin ring, said as open solid state lighting era of pioneer molecules, advanced electronics will continue to be small size high power technique is applied to the product, in order to lower the cost of aluminum nitride ceramic substrate with high reflectivity mirrors implementation, make the product the packaging support, and other application were JinGuJing technology, by metal rapid heat LED by center of orientation of high thermal conductivity aluminum nitride ceramics, in order to reduce the LED module operation temperature, achieve high efficiency (150 lm/w), high power (3-5 w operation), long life (60000 HRS), low energy consumption LED products performance.

Moreover, chip choice is very important, LinZhiMin ring, said with global quality partners are committed to the existing chip quality improvement and cost reduction, and new chip structure of rapid development, in order to the lowest cost to the mass production of silicone molding technology, reduce the existing LED chips encapsulation process cost, and with rapid response optical structure design conforms to the new design of die structure take light effect, to achieve the lowest cost of production, the most efficient design goal.

More than twenty w LED packaging

In the LED packaging, COB packaging technology is another big key, in view of this, the flourishing day science and technology ChenZhenLun xing, general manager of that 10 w is not applicable to the following LED COB packaging technology, the field is still the mainstream of the single power package form; More than twenty w leds is suitable for the COB packaging technology. Flourishing day technology focus on high power LED packaging technology development, crystal yuan photoelectric as its original shareholders. Flourishing day at present in China the market management to miner's lamp and architectural lighting is given priority to. ChenZhenLun xing, points out that miners lamp market is relatively stable, although in recent years growth rate is not high, but flourishing day in the field to keep higher share.

In 2010, Japanese led lamp market expansion has become a global led lighting of typical example. At present Japan LED ball steep light market mainly to to COB polycrystalline packaging is given priority to, the traditional power chip and module is mostly used as MR16 LED light source and directivity.

ChenZhenLun xing pointed out that, at present the COB packaging use more is aluminum plate, copper base plate and ceramic base plate, etc. Each material coefficient of thermal conductivity is different, lead to the difference of the thermal conductivity, such as diamond coefficient of thermal conductivity is 1000, followed by silver and copper for 400 or so, and then aluminum is more than 100, and the thermal conductivity of ceramic in August 22 - between. In insulating materials, ceramic coefficient of thermal conductivity have already been regarded as good, and the price cheap, so many packaging choose the ceramic base plate.

The big project technology is active in the LED radiating ceramic substrate r&d and design of one of the industry, the company, using high-tech thick film and film yellow technology and patent electroforming technology, engaged in LED radiating ceramic base plate and the research and development of production, the product line will include high power LED package with radiating ceramic base plate.

High voltage LED packaging

In addition to the high power LED, high voltage LED encapsulation is also a big key. LinZhiMin ring, said the company has developed a series of high voltage LED encapsulation products, across the 1 w, 2 w and 4 w products market, and high pressure, the appearance of the product is a new thinking to solve solid state lighting for decompression circuit caused by the presence of redundant energy consumption problems, and then assist terminal consumers reduce purchase cost. LinZhiMin stressed that high voltage LED product packaging technology focus is to continue the above advantages, in addition we should provide consumers with more convenience, make different area in different voltage operation conditions, can be quick and convenient application. Such as an electron out of the ring 4 w products, can be directly used to PCB line series parallel design to meet the global 110 v and 220 v different voltage source demand. And because of a single component packaging body voltage across the pressure, up to 110 v, 220 v, so all in the development of high voltage LED packaging, advanced electronic insist to use insulation ceramic substrate package body form, in order to reduce small size between positive and negative electrode spark discharge risk.

At the same time, due to the high voltage LED chip itself with sapphire substrates, lateral light more general chip for strong, so in packaging should adopt the whole Angle even with repeated phosphors design, in order to package body in all apparent role in temperature, and enhance the quality of the light.