UV LED applications and protection issues

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UV wavelengths between visible light and X-rays. Wavelength range is 10 ~ 400nm. However, many believe 430nm wavelength optoelectronic manufacturers also belong to ultraviolet light. Although many do not the human eye can see ultraviolet light, a visible part of the spectrum which is still named after the violet, UV LED in the past few years has made considerable progress. It is not only the production of solid-state UV devices of technological progress results also benefited from increased demand for environmentally sound production of UV lamps.

UV LED photoelectric current supply on the market contain a wavelength range of 265 ~ 420nm, there are a variety of packages, such as perforation, surface mount and COB. UV LED generator has a variety of unique applications, however, each generator on the wavelength and output power are independent. Under normal circumstances, use the LED UV light can be divided into three areas. They are defined, respectively, as UV-A (UVA), UV-B (UVB) and U V-C (UVC) (see Figure 2).

Full application

UV A-type device 1990 has already begun production. The LED is generally used in such counterfeit detection or verification (currency, driver's license or file, etc.). These applications require very low power output, wavelength range actually used is in the range 390 ~ 420n m, the lower wavelength product is not suitable applications. Because these LED on the market long life cycle and easy to manufacture, it can be used as a variety of UV light sources and cheapest products.

UVA LED element areas in the past few years has been greatly increased. This wavelength range (about 350 ~ 390nm) is the most commercial and industrial applications in the production of materials such as adhesives, coatings, inks and UV curing. Due to efficiency, cost reduction and system miniaturization, LED lights than traditional curing techniques, such as mercury or fluorescent lamps, it has a greater advantage. Therefore, the supply chain continues to promote the use of LED technology, making use of LED curing the trend becoming increasingly apparent. Although the cost of the product this wavelength range is significantly higher than the UV A region, but steady increase in manufacturing output and rapid technological progress is gradually reduced prices.

Lower UV A and UV B higher wavelength range (approximately 300-350nm) was recently commercialized fields. These devices have great potential to be adapted for a variety of applications, including UV curing, biological medicine, DNA analysis, and various types of sensing. This three ultraviolet spectral range there is a significant overlap. So, the choice, not only to consider what is best for the application, we also need to consider what is the most cost-effective solution. Because the higher wavelength usually means lower cost of LED.

UV B and UV C wavelength range (about 250 ~ 300nm) is a field still in its infancy to a large extent. However, the application of these products in a warm and needs air and water purification system is very strong. Only a few companies have the ability to produce UV LED in this wavelength range, and a smaller number of companies to produce enough life, reliability and performance characteristics of the product. Therefore, the cost UVC / B device is still high, difficult to use in some applications. However, the first commercial UVC LED disinfection system was launched in 2012, which helped push the market forward.

Good protection

A common question about UV LED is: they pose a security risk it? As described above, UV light has various levels. One of the most common source is an ultraviolet lamp black. The product has been used for decades for use in a poster produced luminescent or fluorescent effect, as well as paintings and currency validation. These light bulbs generally produced in the UV A spectral closest to the wavelength of visible light and have lower energy. Despite the high exposure has been linked to skin cancer and other potential problems, such as skin accelerated aging related, but this part of the UVA spectrum of UV light are the three most secure. Light-emitting diodes (relative to a standard incandescent or fluorescent bulbs) are also highly directional, and the viewing angle is very narrow. Look into the UV LED can damage the eyes. Therefore, the user is best to avoid exposure to UVA products.

UV C and most of the UV B light is mainly used for sterilization and disinfection. These wavelengths of light not only harmful microorganisms, if in contact with it, for humans and other life forms are equally dangerous. These LED lights should always be shielded, and never use the naked eye look, even if it is emitting very little. Exposure at these wavelengths of light, can cause skin cancer and temporary or permanent vision loss or impairment.

All UV devices should have warning labels. Also, before you buy UV C or UV B ultraviolet light, many manufacturers require every customer to sign a document stating that they understand and agree to the use of these products and process matters.

Rui Geer medical hospital design

As the project is located on the ground floor, the lighting is not ideal, can only use artificial light as illumination, but in the forest and blue elements added so that this project has an unusual effect. Currently in the design of the hospital basically stereotyped approach, this project seeks to break the conventional design, to customers extraordinary visual effects and experience.

LED display drivers and system architecture

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LED display as a high-tech products has aroused great attention, using computer control, intelligent optical and electrical integration of the full-color display has been applied in a wide range of fields. Its pixels with LED light-emitting diode, a plurality of light emitting diodes arranged in a dot together constitute LED array, and thus constitute the LED screen. Through different LED drive mode, images can be obtained different effects. Therefore, the merits of the LED driver chip, the LED display on the display quality plays an important role. LED driver chips can be divided into general-purpose chips and a dedicated chip.


Universal LED display chip generally used for low-end products, such as indoor single, two-color screens. The most common is a general-purpose chip 74HC595, with 8-bit latch, serial-parallel shift register and the tri-state output. Each non-constant maximum output current of 35mA.

Since the LED is a current characteristic of the device, that is, under the premise of saturated conduction, the brightness change with the current size varies, as does the voltage across its changes. ASIC most important feature is to provide a constant current source output to ensure stable LED driver, LED eliminate flicker. With output current, constant current and other characteristics, suitable for applications requiring high current, high quality occasions, such as outdoor full color, indoor full color and so on.

LED screen with LED driver IC products SMT5026.SMT5026 built-in CMOS shift register and latch function, you can convert serial input data into parallel output data format.

The second part: LED display system composed of architecture


(1) display unit

This is the main part of the LED display screen, a light emitting material and the drive circuit. Indoor screen is the variety of unit display boards, outdoor screen is the unit cabinet.

(2) Host Controller


The role of the input digital RGB video signal buffer, gray transform, reorganize, and generates various control signals.


(3) Switching Power Supply


Use is 220V AC into a variety of DC to the various circuits.

(4) a transmission cable


Display data and various control signals generated by the master device twisted-pair cable to the screen body.


(5) Scan Controller

The board relies on data buffer, generating various scanning signals, and the duty cycle of the control signal gradation.


(6) dedicated graphics card and multimedia card (video card)

LED full color dedicated graphics card in addition to the basic functions of the computer display card, but also simultaneously output digital RGB signals and line field, blanking signal to the master device. Analog Video Signal multimedia card in addition to the above functions can also be input into a digital RGB signals (ie video capture).

(7) other sources and external devices

Including computers, televisions, Blu-ray, DVD, VCD, video camera and so on.

Eight-dimensional analysis of a small pitch LED display engineering advantages

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Small pitch LED display propulsion technology to break the law of the LED display can only be used in outdoor areas, with rising levels of fine quality, high brightness and low ash and other technical problems of cracks, small pitch LED display works indoors display areas, especially in the control room and other high-end display market, launched the attacks.

Engineering mainstream display technology comparison

Indoor display areas in engineering, fine pitch LED display as a latecomer, need to deal with the face of competition from DLP splicing, LCD splicing technology, and in this we have to sort out characteristics of several display technology comparison:

By contrast can be seen in the current mainstream display technology in engineering, fine pitch LED display occupy patchwork, color, uniformity, power and other performance advantages, but the current price is still high, so the market is currently the main assault focused on high-end indoor applications, with the formation of a DLP face competition to some extent.

As we all know, small pitch LED display technology since 2012, was born, in a few years gained rapid growth, many LED display not only became a pioneer in corporate earnings, but also to advance into the market has been DLP splicing, LCD Video technology constituted a threat.

Throughout recent years, large screen display industry, it is easy to see, not the pursuit of the ultimate patchwork, but high-quality large-screen display. In the current mainstream display technology, liquid crystal mosaic patchwork because of the more obvious, and thus more difficult to lead the studio, Bureau of Meteorology and other images of high integrity field attack. The field is also small LED pitch to attack the core DLP battlefield.

As a representative of the new light source, LED display not only has the inherent advantages of seamless, but with excellent brightness, color advantage, along with low power consumption, long life and other characteristics, which is generally good. Therefore, the industry pointed out that the future, as the cost of the screen occupy 70% of the lamp beads falling prices, the performance advantages of a small pitch LED display will become more prominent, the promotion of high-end applications in indoor areas will grow faster.

In fact, a small pitch LED display for all to see good market performance in recent years, and has attracted many big-screen manufacturers and integrators to join some of the traditional big-screen manufacturers even smaller pitch LED screen as a mosaic to keep pace with the DLP product line. Therefore, in the prosperous market behind the industry, competition has become increasingly prominent. In order to seek differentiation, related companies also assumed a different development strategy, which led to the development of diversified small pitch LED display market.

LED lamp beads LED display on eight aspects

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1, viewing angle

LED display depends on the viewing angle LED lamp beads perspective. Currently most use outdoor display horizontal viewing angle 100 ° ;, vertical viewing angle 50 °; oval LED, indoor displays the selected horizontal and vertical are 120 °; SMD LED. Display on the highway because of its particularity is generally used 30 °; viewing angle circular LED enough. Some high-rise on the display for vertical viewing angle higher. Perspective and brightness mutually contradictory perspective is bound to reduce the brightness large. Select the desired viewing angle, depending on the use to decide.

2, brightness

LED brightness is an important determinant of display brightness. LED brightness higher, the greater use of the current balance of power saving, LED maintaining good stability. LED has a different angle, the brightness has been set in the chip case, the smaller the angle, the more LED lights, but the smaller viewing angle of the display. General should be chosen to ensure 100-degree LED display sufficient perspective. Different for different point spacing and line of sight of the display, you should find a balance in brightness, angle and prices.

3, loss of efficiency

Since the full-color display by the tens of thousands or even hundreds of thousands of groups of red, green, and blue LED pixels composed of dots, the failure of any color LED display will affect the overall visual effect. In general, according to industry experience in LED display will begin to assemble the failure rate of aging 72 hours before shipment should be no higher than ten thousandths (of a failure of the LED lamp itself causes).

4, anti-static capability

LED is a semiconductor device, sensitive to static electricity, static electricity can easily lead to failure, so the antistatic ability is critical to the life of the display. Generally speaking, LED body static mode test failure voltage of not less than 2000V.


5, life

Theoretical life of LED devices for 100,000 hours, LED display is much larger than the working life of other components, so long as the LED device quality assurance, appropriate operating current, PCB thermal design reasonable, strict production process display, LED display device will be whole one of the most durable machine parts.


LED devices accounted for 70% LED display prices in proportion, so that the LED device can determine the quality of the merits of the LED display. That country is the largest producer of LED devices, LED display also making gathering. Technically demanding LED display is the future trend of development, LED display high quality requirements, not only with regard to the trend of LED display manufacturers, LED display screen is also implicated in the development of the device manufacturers. From the LED device checks to promote the transformation of China from a manufacturing to a manufacturing power LED display LED display power.

6, the attenuation characteristic

LED display will appear after working long hours brightness decline and display color inconsistencies, mainly due to the brightness of the LED devices attenuation caused. LED brightness decay will cause the entire display screen brightness is reduced. Red, green and blue LED brightness decay magnitude of inconsistency will cause the LED display color inconsistencies, that is, we often say that the phenomenon of flower display. High quality LED device can be well controlled brightness decay magnitude. By 1000 hours at room temperature 20mA standard lighting, red attenuation should be less than 2%, blue, green decay should be less than 10%, so blue, so as not to be used 20mA current green LED in the display design, it is best to use only 70% to 80 % of the rated current.

In addition to the attenuation characteristics of red, green, blue LED characteristics associated itself, the use of electric current, PCB board thermal design, the display using ambient temperature etc. affect attenuation.

7, size

LED device the size of the impact of the LED display pixel distance, or a resolution. 5mm oval lamp is mainly used for more than P16 outdoor display, 3mm oval lamp is mainly used for P12.5, P12, P10 outdoor display, 3528 SMD LED is mainly used for P6, P8 of the households within the display, 2020 SMD LED is mainly used for P2, P3 and other indoor display. Under the premise of constant spacing, LED device size increases, to increase the display area to reduce the grainy, but by reducing the black area will decrease the contrast; the contrary, LED size decreases, reducing the display area, grainy increased , the black area is increased, increasing the contrast.

8, consistency

Full-color display is composed of numerous pixels of red, green and blue LED component makes up each color LED brightness, wavelength determines the consistency of the entire screen brightness uniformity, white balance, consistency, chromaticity consistency sex. Generally, display devices require manufacturers and suppliers to provide a wavelength range of 1 5nm: 1.3 brightness range of LED, these indicators can be component suppliers were graded by machine to achieve spectral separation. Voltage consistency generally not required.

Since the LED is angled, so the full-color LED display also has a directional angle, that when viewed at different angles, its brightness is incremented or decremented. Thus, the red, green and blue LED's perspective of consistency would seriously affect the consistency of different angles, white balance, directly affecting the display of video color fidelity. To do the red, green and blue LED brightness variations at different angles to match the consistency, we need to package the lens design, selection of raw materials on strict scientific design, depending on package vendor technology. Even the best white balance method to monitor the direction, if the LED angle consistency is not good, the entire screen at different angles balance effect will be bad. LED lamp Angle Consistency feature is available LED Tester angle measured for the high-end display is particularly important.

100 kinds of LED package structure distinction Daquan

Elements LED packaging technology are threefold: package design, selection of suitable packaging materials and craftsmanship.

Currently LED packaging structure in the form of 100 kinds, the main package types Lamp series of 40, SMD (chip LED and TOP LED) series over 30 kinds, COB series over 30 kinds, PLCC, power package, light and integrated package modular packaging, etc., the development of packaging technology to keep up with and meet the needs of LED application product development.

The basic contents of LED packaging technology

The basic requirements for LED packaging technology are: to improve light efficiency, high color performance and device reliability.

(1) improve the light efficiency

The optical efficiency of the LED package generally up to 80 to 90%.

① selection of transparency and better packaging materials: Transparency ≥95% (1mm thickness), a refractive index greater than 1.5 and so on.

② selection of high excitation efficiency, high dominant phosphor particle size appropriate.

③ loading substrate (reflector cup) have a high reflectivity, a light high optical design shape.

④ appropriate choice of packaging technology, in particular coating process.

(2) high performance light color

LED light color main technical parameters are: height, glare, color temperature, color, color tolerance, light flicker.

CRI CRI≥70 (outdoor), ≥80 (outdoor), ≥90 (art museum).

Color tolerance ≤3 SDCM≤5 SDCM (whole life period)

The amount of spectrum to be used on the package more color combination to achieve, focus on improving LED radiation distribution SPD, the spectral distribution of the amount of sunlight near. To attach importance to the development and application of fluorescent quantum dots to achieve a better quality of light and color.

(3) LED device reliability

LED reliability under different conditions contained in the LED device performance variation mechanism and failure modes (LED encapsulating material degradation, combined stresses, etc.), which is the main reference characterization value reliability - life, life is generally present LED device 3 to 5 hours, up to 5 to 10 million hours.

① appropriate choice of packaging materials: binding to large and small stress, a good match, good air tightness, temperature, humidity (low water absorption), anti-ultraviolet light.

② package thermal material: a substrate of high thermal conductivity and high electrical conductivity, high thermal conductivity, high strength and high electrical conductivity of solid crystal materials, stress is smaller.

③ suitable packaging process: loading, bonding, packaging and so on with strong, stress should be small, combine to match.

LED light integrated packaging technology

LED light integrated packaging structure of the existing more than 30 types, we are moving towards a systems integration package, the future direction of development of packaging technology.

(1) COB integrated package

COB integrated package existing MCOB, 30 variety of packages structure COMB, MOFB, MLCOB etc, COB packaging technology matures, the advantage of low cost. COB LED light source packaging now accounts for about 40% of the market, luminous efficiency of 160 ~ 178 lm / w, the thermal resistance of up to 2 ℃ / w, COB LED package package is the recent trend of development.

(2) LED Wafer Level Packaging

Wafer level packaging made from the epitaxial LED device as long as a scribe, is a multi-system integration package LED lighting needs, generally silicon substrate material without solid crystal and pressure welding, dispensing and shaping, forming system integrated package , the advantage of good reliability, low cost, is one of the packaging technology development direction.

(3) COF integrated package

COF integrated package is on a flexible substrate, a large area of ​​the assembly power LED chip, which has the advantages of high thermal conductivity, a thin layer of flexible, low cost, light uniformity, high luminous efficiency, flexible surface light source, can provide the source line, surface light source and three-dimensional LED light source of a variety of products, but also to meet the modern LED lighting, personal lighting requirements, but also can be used as general-purpose package assembly, the market prospect.

(4) LED modular integrated package

Generally refers to a modular integrated package LED chips, power supply, the control section (including IP address), and other system components integrated package, referred to as LED module with material savings, lower cost, standardized production and maintain many advantages convenient It is the direction of LED packaging technology development.

(5) flip-chip packaging technology

Flip Chip technology was developed by the chip, the substrate, the bump forming a space, so that the package out of the chip has a small size, high performance, short connections, etc., ceramic substrates, flip-chip, eutectic processes, direct compression together to achieve high power lighting and other performance requirements.

Gold tin alloy chip laminated on a substrate, a plastic alternative to conventional silver technology "directly laminated" alternative past "reflow", with excellent electrical performance and heat transfer area. The high-power LED packaging technology is an important packaging trends.

(6) Free chip packaging technology

Free packaging technology is the integration of a technology, flip-chip, solid crystal without glue, gold wire and bracket are 70 kinds of semiconductor packaging technology in the process of forming one.

PFC-free packaged chip products can improve light efficiency to 200lm / w, light angle greater than 300 degrees ultra-wide-angle optical design of the whole week, do not use the secondary optical lens, the optical efficiency will reduce consumption and reduce costs, but to put expensive equipment.

PFC LED lighting new products hit the market, in particular the application of candle lights on, not only can simulate the shape of incandescent light, and can break through the restrictions heat volume.

(7) LED other package structures

①EMC package structure: embedded integrated package (Embedded LED Chip) does not directly see the LED light source.


②EMC packaging technology: (Epoxy Molding Compound) with epoxy molding compound scaffold packaging technology, with high heat resistance, high integration, anti-UV, small size, etc., but the tightness badly, now in volume production.

③COG Package: (Chip On Glass) LED chips on the glass substrate package.

④QFN packaging technology: When the small spacing display pixel unit is less than or equal to P.1, package adopted, will replace PLCC structure, market prospects.

⑤3D packaging technology: in the form of three-dimensional packaging technology, is being developed.

⑥ power packaging technology framework: (Chip-in-Frame Package) packaged in a small frame-power LED chips, light industrial efficiency has reached 160 ~ 170 lm / w, up to 200 lm / w or more.

LED packaging materials

LED packaging materials many varieties, and are constantly developing, here only briefly.

(1) packaging materials

Epoxy resins, epoxy molding compound, silicone, silicone plastics, technically refractive index, internal stress, adhesion strength, air tightness, high temperature, UV and other required.

(2) solid crystal material

① solid crystal plastic: resins and silicone type, internal filler metal and ceramic materials.

② eutectic: AuSn, SnAg / SnAgCu.

(3) board material: copper, aluminum and other metal alloys

① ceramic materials: Al2O3, AlN, SiC and the like.

② aluminum-based ceramic materials: referred to as the third generation of packaging materials AlSiC, AlSi like.

③SCB board material: multi-layer stamper substrate, heat (thermal conductivity 380w / m.k), and low cost.

④TES polycrystalline semiconductor ceramic substrate, heat and speed.

(4) heat sink material: copper, aluminum and other metal alloys

Graphene composites, thermal conductivity 200 ~ 1500w / m.k.

PCT special high-temperature plastic (polyethylene terephthalate, 1,4-cyclohexane dimethyl ester), plus ceramic fiber, high temperature, low water absorption.

Thermal engineering plastics: Non-isolated thermal plastic, thermal conductivity of 14w / m.k.

Insulated thermal plastic, thermal conductivity 8w / m.k.

LED SMD Epoxy glue and basics

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1, the role of surface mount adhesive glue adhesive (SMA, surface mount adhesives) for wave soldering and reflow soldering, mainly used for the components mounted on the printed circuit board, usually with dispensing or stencil printing method to allocate , to maintain the position of the component on the printed circuit board (PCB) on, to ensure that transfer element in an assembly line process is not lost. After the paste components into the oven or reflow welding heat-curing. It is the so-called paste is not the same, after a heated hardening, reheating does not melt, that is, plastic patch thermosetting process is irreversible. SMT plastic patch effect due to the thermal curing conditions, the linker, the equipment used, different operating environment differ. To be selected patch of plastic production process according to use.


2, most of the surface mount adhesive (SMA) components PCB assembly of glue used are epoxy resin (epoxies), although there are polypropylene (acrylics) are used for special purposes. The introduction of high-speed dispensing system and electronics industries to learn how to deal with a relatively short shelf life of the product after the epoxy glue has become more mainstream technology worldwide. Epoxy resins generally wide boards provide good adhesion, and has very good electrical properties. The main ingredients are: base material (ie, high body material elements), fillers, curing agent and other additives.


3, plastic patch intended use of a. In wave soldering components to prevent falling (wave soldering) b. Reflow soldering components off to prevent the other side of the (double-sided reflow process) c. Prevent displacement and vertical components when at (reflow process, the pre-coating process) d. mark (wave soldering, reflow, the pre-coat), PCB and components batch change, marked with a plastic patch.

4, the use of glue dispensing a classification type: By dispensing device on the printed wiring board sizing. b Squeegee type: sizing by stencil or screen printing copper Scraping way.


5. The method of SMA Epoxy Epoxy can be used syringe method, the needle transfer method or template printing method applied to the PCB. Transfer method using a needle less than 10% of all applications, it is the use of needles arranged array immersed in a plastic tray. Then hanging drops of glue transferred to the board as a whole. The system requires a low viscosity adhesive, but also a good moisture absorption resistance, because of its exposure in the indoor environment. Control the needle transfer Epoxy key factors including needle diameter and style of glue temperature, cycle length and depth of the needle immersed Epoxy (including time delay before the needle PCB exposure and periods). Pool bath temperature should be between 25 ~ 30 ° C, which controls the amount and form of plastic viscosity and gel point.

Templates are widely used in solder paste printing, and distribution of glue can also be used. SMA Although less than 2% of the model is printed, but the interest in this method has increased, the new device is to overcome some of the limitations of earlier. Correct template parameter is the key to achieving good results. For example, contact printing (zero off-board height) may require a delay cycle allows good dot formation. In addition, the polymer template non-contact printing (approximately 1mm gap) requires optimum blade speed and pressure. Thickness of the metal template is generally 0.15 ~ 2.00mm, should be slightly larger than (+ 0.05mm) gap between the component and the PCB.

Finally, viscosity and temperature will affect the shape of the gel-point temperature of most modern dispensing machines rely on the needle mouth or chamber capacity control device to keep the glue temperature above room temperature. However, if the temperature of the PCB is improved from the previous procedure, then the outline of the gel-point may be damaged.

LED chip manufacturing process and testing project analysis

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LED chip is the most important raw material, its quality directly determines the LED performance. Especially high-end LED lighting for automotive or solid state, absolutely no tolerance for defects, that the reliability of such equipment must be very high. However, LED chip packaging factory incoming inspection due to lack of experience and equipment, the chip does not usually perform incoming inspection, after the failure of the chip available, often only eat Yaba Kui. Jin Jian detecting accumulated a large LED failure analysis case based on the introduction of LED chips incoming inspection services, through the use of high-end analytical instruments to identify strengths and weaknesses of the chip. The testing services can complement LED packaging factory / chip proxy factory incoming inspection, to prevent defective chip storage, chip avoid quality problems caused by the loss of the whole lamp beads.

Test items:

First, the performance parameters of the test chip

Wd (dominant wavelength), Iv (brightness), Vf (forward voltage), Ir (leakage), ESD (antistatic ability) and other optoelectronic performance test chip, Jin Jian as a third party testing agencies to identify the supplier offerings whether the data standards.


Second, the chip defect Find


Test content:


1. Measure the chip, the chip size and the size of the electrode meets the requirements, the electrode pattern is complete.

2. Does the presence of the chip solder contamination, damaged joints, damaged grains, grain sizes cutting, cutting tilt grain and other defects.


LED chip LED damage will directly lead to failure, thus improving the reliability critical to the LED chip. Evaporation process is sometimes required spring clip fixed chip, it will produce clip marks. If the job is not fully developed yellow mask and will have holes in the light emitting area of ​​more residual metal. Grains FEOL in the system Cheng Ruqing washing, evaporation, yellow, chemical etching, fusing, grinding and other operations must use forceps and flower baskets, vehicles, etc., so the situation will die electrode scratching occurs.


Influence of electrode pads of the chip: the chip electrode deposition itself is not solid, resulting in loss or injury after the wire electrode; electrode chip itself poor solderability, solder balls can cause Weld; improper storage can cause the chip electrode surface oxidation, surface contamination etc., minor contamination bonding surface may affect the diffusion of metal atoms between the two, resulting in failure or Weld.

3. The chip defect epitaxial region search

LED epitaxial wafer in a high Wenchang Jing process, the substrate, MOCVD reaction chamber residual sediments, ambient gas and Mo sources will introduce impurities which will penetrate the epitaxial layer to prevent the gallium nitride crystal nucleation, formation of various all sorts of epitaxial defects in the epitaxial layer surface eventually form tiny holes, which will seriously affect the quality and performance of the crystal wafer thin film materials. Jin Jian developed a detection method to detect the rapid identification chip epitaxial defect region, at low cost and quickly detect the chip 80 percent of the epitaxial layer epitaxial defect, to help customers choose the high quality LED epitaxial wafers, chip.

4. The chip technology and observe cleanliness

Electrode process is the production of LED chip key processes, including cleaning, deposition, yellow, chemical etching, fusing, grinding, will be exposed to a lot of chemical cleaning agents, if the chip is not clean enough to clean, make the harmful chemical residues. These harmful chemicals in the LED is energized, and the electrode electrochemical reaction, resulting in dead lights, light, dark, bright, black and other phenomena. Therefore, the identification chip chemical residues is critical for LED packaging factory.

Case (a):

A customer red lamp dark light beads found the problem, but no cause has been entrusted Jin Jian analysis of the cause of failure. After a series of instrumental analysis Jin Jian exclude packaging reasons, bare die suppliers for testing, found that the light-emitting region of each chip has an area ranging from pollutants, energy spectrum analysis showed that the pollutants contained C, O two elements, indicating that organic pollutants. We recommend that customers pay attention to the chip manufacturers in production process specifications and workshop environment assessment, and strengthen incoming inspection of chips.

Case (b):

A customer produced a number of lamp beads appear leakage problems, commissioned Jin Jian find out why. Jin Jian by scanning electron microscopy to identify the reasons for the leakage of these lamp beads electrostatic breakdown, and bare die suppliers testing and found the chip surface of epitaxial layer has a large number of black holes, these defects show poor crystal quality epitaxial layers, PN junction internal defects. Empty find help customers define the responsibility of the party responsible for the accident, for customers to recoup their losses.

NOTE: LED chip manufacturing process

LED chip manufacturing process flow diagram

Wafer cleaning → → → plating transparent electrode layer is a transparent electrode pattern photolithographic etching → → → ashing platform graphics photolithography → → dry etching, ashing → → annealing → SiO2 deposition window graphics lithographic etching → → SiO2 ashing → N pole graphics lithographic pre-cleaning → → → coating peeling → annealing → P extremely graphic lithographic coating → → → stripping → cutting → polishing chip → product testing.


Grown into a wafer, the next step began to make LED epitaxial wafers electrode (P pole, N pole), and then they began to use laser or diamond knife cutting LED epitaxial wafers, chip manufactured after, and then on the wafer nine different positions extraction point do parametric testing. This is mainly voltage, wavelength, brightness testing, in line with normal standard parameters wafer shipments continue to the next step, do not meet the requirements, put aside dealt with separately. After the wafer is cut into chips, you need a 100% visual inspection (VI / VC), the operator must be in multiples of 30 visually at a magnification of the microscope. Then using automatic machine classification according to the different voltages, wavelength, brightness prediction parameters for fully automated chip selection, testing and classification. Finally, the LED chip to be checked (VC) and labeling. Chip type, batch number, quantity and optical measurement statistics recorded on the label attached to the back of glossy paper. Blue film chip will make the final mesh detection test, a visual inspection of the same standard with the first, to ensure that chips neatly arranged and quality standards. This is the LED chip manufacturing process.

LED epitaxial wafer growth process solutions

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Today to discuss the growing process of LED epitaxial wafers, integrated circuits in a small early age, making thousands of chips every 6? Epitaxial wafer, now sub-micron large VLSI, each 8? Epitaxial wafer is also completed only a two hundred large chips. Although the epitaxial wafer manufacturing move? Invest tens of billions, but it is the basis for all of the electronics industry.

Czochralski silicon is grown, you first need a very high purity silicon ore into the furnace, and adding predefined metal material, so that arising out of silicon boules have the required electrical characteristics, then you need to all substances melting and then grow into single crystal silicon boules, the following will be all grown boules process do introduction:


Crystal growth main program:

1, melted (MELtDown)

This procedure is placed in a quartz crucible bulk polysilicon heating system 1420 degrees centigrade above its melting temperature, in this phase the most important parameter for the position of the crucible and the supply of heat, if compared with the use of Great power to melt the polycrystalline silicon, quartz crucible of life will deteriorate if the power is too low melting process takes too long, affecting the overall production capacity.

2, neck growth (Neck Growth)

When the silicon melting temperature of the slurry stabilized, gradually injected into the direction of the seed mixture, then the seed crystal pulled up, and down to a certain diameter (about 6mm), to maintain this diameter and stretch 10-20cm, with Elimination row difference (dislocation) seed within such zero emission difference (dislocation-free) control is mainly confined to the row difference in the growth of the neck.


3, Crystal Crown Growth (Crown Growth)


After a long neck, slowly lower the casting speed and temperature, the diameter of the neck is gradually increased to the desired size.

4, crystal growth (Body Growth)

Use of casting speed and temperature adjustment to maintain a fixed late ingot diameter, the crucible must continue to rise to maintain a constant liquid level, and from the crucible and the ingot reached the level of radiation heat will gradually increase, this will cause a radiant heat source-industry interface temperature gradient becomes smaller, it is necessary to gradually reduce the growth stage in the ingot casting speed, in order to avoid distortions of the ingot produced.

5, trailing growth (Tail Growth)

When the crystal growth to a fixed length (required), the diameter of the ingot to be gradually reduced until the separated liquid, which was to avoid thermal stress caused by the difference between the sliding surface discharge phenomenon.

Cutting:

Boule grown since you can cut a piece of it, which is the epitaxial wafer. Chips, discs, is a "chip or" substrate chip semiconductor element, stretching from high-purity silicon element grow boules (Crystal Ingot), the circular sheet called epitaxial wafers (wafer) cut out of the .

Epitaxy:

Arsenide? Epitaxy by different processes can be divided into LPE (liquid phase epitaxy), MOCVD (metal organic vapor phase epitaxy) and MBE (molecular beam epitaxy). Lower LPE technology, mainly used for general light-emitting diodes, and high levels of MBE technology, easy to grow epitaxial thin, and high purity, flatness is good, but the low production capacity, epitaxial growth rate slow. In addition to high purity MOCVD, smooth and good, the production capacity and speed Yijiao MBE epitaxial growth faster, so now it is mostly in MOCVD to produce.

First, the process is expensive GaAs substrate into the organic chemical vapor deposition furnace (Jane the MOCVD, also known as epitaxial furnace), and then passed through III, an alkyl compound of Group II metal element (methyl or ethyl compound) vapor and non-metallic (V or VI elements) hydride (or alkyls) gas at a high temperature, the pyrolysis reaction occurs to form III-V or group II-VI compound deposited on the substrate, a layer grown the compound semiconductor epitaxial layer thickness of only a few microns (1 mm = 1000 microns). Long or GaAs epitaxial layer sheet is often called epitaxial wafer. After the wafer after processing chip, power will be able to send out? Very pure monochromatic light color, such as red, yellow and so on. Different materials, different growing conditions and the different epitaxial layer structure can change the light emission? Color and brightness. In fact, in the epitaxial layer a few microns thick, the real emission also is one of only a few hundred nanometers (1 micron = 1000 nanometers) thick quantum well structure.

Reaction formula: Ga (CH3) 3 PH3 = GaP3CH4

Select the drive power LED lights dimming applications under

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In LED lighting applications more widely, with better than traditional lighting methods unique, in addition to improving the quality of life, improve performance and extend lamp life light source, the use of its unique function dimmable lighting color temperature and brightness changes, and fully achieve energy saving applications for its biggest advantage.

Dimming performance LED lighting but depends on the mix of LED light source and drive power.

Generally speaking, LED light source can be simply divided into two categories: individual LED diode light source with a resistor or diode LED light source, in the application, sometimes LED light source is designed to be embedded DC-DC converter a modular device, such complex module is not within the scope of this article. If the LED light source module or as a separate LED diode itself, the common LED dimming method to adjust the amplitude of the input current, LED driver power supply and therefore the choice should refer to this feature, the company Meanwell HLG / ELG family characteristics current is adjustable, and can only be controlled by the modulation of the output current or external 1-10VDC * 10VPWM pulse width modulation, or even through a simple external variable resistor. And the other with a resistor LED diode light source (generally referred to as LED light bar or LEDSTRIP), LED light strip is widely used is a LED diode resistor in series, the voltage is relatively stable, so users You can access any of the commercially available constant-voltage power supply to drive the LED light bar. Common LED lights generally based on 12VDC or 24VDC drive, but because of the dimming applications LED light bar can be a bit difficult. This article describes the use of the current amplitude dimming drive application of the LED light bar, and also discuss some common dimming issue, and also introduced an adjustable using the output pulse width (PWM) modulated light LED power driver, Ming Wei launched by the company and access to national technology innovation award recognizes a family of PWM, is currently on the market the most appropriate and easiest LED lights dimming scheme.

Common LED dimming poor condition:

Dimming may sound like a simple thing, in fact, want to have a good and smooth dimming performance is the need to consider many factors, the situation is common LED dimming there are many bad


Common dimming problems


When using the LED output current adjustable power driver for LED lights dimming when, deadtravel is a recurring problem. Although when the LED drive power is in fully loaded condition (as illustrated 1-a) can be operated when the ground is very good, but when the LED driver in a non-full, not smooth dimming state is very obvious.

Meanwell LED Driver HLG-100 at different loads (length) coupled to the LED status lights: (a) 100% of full load - can produce the best dimming performance; (b) 70% of the load - it shows the imperfect dimming effect; (c) 30% of the load - shows poor dimming results because dimmable too restrictive.


The output pulse width modulation (output PWM) Solutions

If you are used under full load conditions LED driver power supply LED lights dimming applications, deadtravel problem would not exist. The above argument is true, but not very practical, in fact, LED lights are often used in a variety of applications (Decorative lighting / auxiliary lighting / Advertising Lighting) can not be accurately estimated at length because of circumstances, so the easiest is the best application solutions is the right choice should be an output pulse width of the PWM LED dimming drive power to achieve LED lights dimming requirements. While the output brightness is by virtue of the duty cycle of the dimming signals to achieve lower brightness dimming changes, important parameters of the drive power is dimming resolution and output pulse width modulation PWM frequency, minimum dimming capability should be as low as 0.1 %, in order to achieve 8bit dimming resolution to comply with all LED lights dimming applications, the output pulse width modulation PWM frequency should be able to raise as much as possible, to prevent the table (a) said light flicker problem, according to the relevant Research reported in the literature, the frequency is recommended at least above 1.25kHz, to reduce ghosting visible to human eyes blink.


in conclusion

The best LED lights dimming solution is to use the output pulse width modulation PWM dimming function, to solve common problems deadtravel dimming. Meanwell company provides PWM model covers four series 40/60/90 / 120W, is very suitable for a variety of LED lights dimming LED drive power applications.

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