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Application: UV light source equipment led products knowledg

时间:2016-04-19 10:42来源:sankun点击:

Application: UV light source equipment led products knowledge

  Semiconductor light-emitting devices including semiconductor light-emitting diode (LED), digital tube, pipe, rice word in sign and the matrix display tube) (hereinafter referred to as matrix, etc. In fact, digital tube, pipe, rice word in sign and the matrix in the tube each light emitting unit is a light-emitting diode.

A, semiconductor light-emitting diodes (leds) working principle, characteristics and application
  (a) LED principle
  Light-emitting diodes (leds) by Ⅲ - Ⅳ compounds, such as GaAs (gallium arsenide), GaP (gallium phosphide), GaAsP made of semiconductor such as gallium arsenide (p), its core is the p-n junction. So it is usually I - N characteristics of p-n junction, which is the wizard, reverse blocking, the breakdown characteristic. In addition, under certain conditions, it also has a luminescence properties. Under the forward voltage, the electronic by N area into P area, hole by P area into N area. Part into the area of minority carrier (Jane) with majority carrier (children) composite and glow, as shown in figure 1.
Assume that light is in the P region, then injected electrons and the valence band hole composite and shine directly, or be luminous center after capture, hole composite luminescence again. In addition, this kind of light composite some electrons are not luminous center (the center between the conduction band, interface with near middle) capture, then with hole compound, every time the energy released is not big, could not form visible light. Amount of composite luminescence relative to the amount of light composite, the greater the proportion of light quantum efficiency is higher. Because the compound is glowing in the Jane diffusion zone, so the light only near the surface of p-n junction generated within a few microns.
Theory and practice proves that the peak wavelength lambda light with the light emitting area of semiconductor materials forbidden band width of Eg, namely the lambda material 1240 / Eg (mm) of Eg unit for electron volts (eV). If you can produce visible light wavelength (780 nm to 380 nm violet light red light), Eg of semiconductor materials should be between 3.26 ~ 1.63 eV. Long wavelength than red light for infrared light. Now has the infrared, red, yellow, green and blue leds, but the blue light diode costs, the price is very high, use is not widespread.

(b) the characteristics of the LED
1. The meaning of the limit parameters
  (1) allow power Pm: allow LED on both ends are dc voltage and current flow through the maximum value of product. More than this value, LED fever, damage.
  (2) the biggest positive dc current IFm: allow the biggest positive direct current. More than this value can damage the diodes. ??
  (3) the largest reverse voltage VRm: the biggest reverse voltage is allowed to add. More than this value, light emitting diode can be broken down. ? ?
  (4) work environment topm: light-emitting diodes (leds) working environment temperature range. Below or above this temperature range, the leds will not work properly, the efficiency is greatly reduced.

  2. The significance of electrical parameters
  (1) spectral distribution, and peak wavelength: a light of the light emitting diode is not a single wavelength, the wavelength can press is shown in figure 2. By the chart shows, in the light of the luminous tube light intensity, the largest of a wavelength lambda 0 this wavelength for peak wavelength.
  (2) luminous intensity IV: the luminous intensity of leds, often referred to as normal () refers to the axis of cylindrical luminous tubes on the direction of luminous intensity. If the radiation intensity in the direction of (1/683) W/sr, glow, 1 candela (symbol for CD). Due to the general LED luminous intensity is small, so the luminous intensity candela is commonly used (MCD) as a unit.
  (3) spectrum halfwidth Δ lambda: it says spectral purity of luminous tube. Refer to figure 3 1/2 wavelength two peak intensity in between.
  (4) half value Angle theta 1/2 and perspectives: theta 1/2 refers to half of the axial intensity is a luminous intensity value direction and Angle of optical axis to the (normal).
2 times of the half value Angle view (or a power Angle). Figure 3 shows the Angle of two different types of leds luminous intensity distribution. Midperpendicular (normal) are the coordinates of the AO relative luminous intensity (i.e., the ratio of the luminous intensity and maximum luminous intensity). Obviously, the normal direction on the relative luminous intensity is 1, out of normal direction Angle is larger, the smaller the relative luminous intensity. This figure can get half value Angle or perspective.
  (5) positive working current If: it refers to the normal light-emitting light-emitting diode when the positive current value. In be used actually shall be according to the need to select the IF below 0.6 · IFm.

  (6) positive working voltage VF: parameters of the working voltage is given in the table at a given positive electrical flow. Is usually measured during the IF = 20 ma. Leds are working voltage VF in 1.4 ~ 3 v. At higher temperatures in the world and the VF will decline.
  (7) V - I characteristic: light-emitting diodes (leds) the relationship between voltage and current can be used in figure 4. In the forward voltage is less than a certain value (called threshold), small current, light. When the voltage exceeds a certain value, after the forward current voltage increase rapidly, glow. By the curve of V - I can draw a luminous tube forward voltage, reverse current and reverse voltage and other parameters. Positive luminous tube IR reverse leakage current.

(c) the classification of the LED
  1. According to the luminous tube emitting light colors
According to the luminous tube light color points, can be divided into red, orange, green, yellow green, standards, green and subdivision and pure green), blue, etc. In addition, some leds included in two or three kinds of color chip.
According to the light emitting diode out light scattering or after adding the agent, colored or colorless, the above all sorts of color of leds can also be divided into colored transparent, colorless, transparent, colored and colorless scattering four types. Scattering of light emitting diode and up to do light is used.

  2. According to the luminous tube out smooth feature points According to the luminous tube smooth feature points out round lights, side lights, rectangular, surface light-emitting tube, lateral tube, install with the micro tube surface, etc. Circular lamp according to the diameter from 2 mm, 4.4 mm, from 5 mm, 8 mm and 10 mm and phi phi 20 mm, etc. Abroad usually write phi 3 mm leds for T - 1; Write phi 5 mm T - 1 (3/4); Write phi 4.4 mm T - 1 (1/4).
Can be estimated by half value Angle size round Angle of luminous intensity distribution. From the Angle of luminous intensity distribution to three points:
(1) high directivity. Is commonly pointed epoxy encapsulation, or with metal reflective cavity encapsulation, and do not add scattering agent. Half value Angle of 5 ° ~ 20 ° or less, has the very high directivity, can be used for local lighting light source, or with light detector combined to form an automatic test system.
(2) standard. Usually used as indicator light, the half value Angle of 20 ° to 45 °.
(3) the scattering model. This is a bigger light Angle, half value Angle is 45 ° ~ 90 ° or greater, the amount of scattering agent is bigger.

  3. According to the structure of light emitting diode points?? According to the structure of the light-emitting diodes (leds) have all epoxy coating, metal base epoxy encapsulation, ceramic base epoxy encapsulation, glass encapsulation structure, etc.
4. According to the luminous intensity and working current
According to the luminous intensity and working current are normal brightness LED luminescence intensity (MCD) 100; The luminous intensity between 10 to 100 MCD called high brightness leds.
General LED working current in a dozen mA to dozens of mA, and LED the working current of low current under 2 mA brightness (the same as the ordinary light-emitting tube).
In addition to the above classification method, and the chip materials classification and classified by function method. ??
(d) the application of LED??
Due to the light emitting diode luminescence intensity of the color, size, shape, and transparent situation is different, so using light-emitting diodes (leds) should choose according to actual needs appropriately.
  Because the light emitting diode has the biggest forward current VRm IFm, maximum reverse voltage limit, when used, shall ensure that no more than this value. To be on the safe side, IF the actual current should be below 0.6 IFm; Should make possible VRRm reverse voltage. ?? LED is widely used in electronic instruments and electronic equipment, can be used as the indicator, level indicator or micro light source. Infrared light-emitting tube is often used in TV sets and video recorders, remote control.
  (1) using high brightness or super high brightness leds made flashlight circuit as shown in figure 5. Figure in the resistance R current-limiting resistance, its highest value should guarantee the power supply voltage should be the LED current is less than the maximum permissible current IFm.
  (2) the figure 6 (a), (b), (c), respectively, for the dc power supply, rectifier power supply and ac power circuit. ?? In figure (a) resistance material (E - VF)/IF; ?? In figure (b) R material (1.4 Vi - VF)/IF; ?? In figure (c) R material Vi/IF?? Type Vi - ac voltage RMS.
  (3) single LED level indication circuit. In the amplifier, the output of the oscillator or pulse digital circuit, available LED indicates whether the output signal has the normal, as shown in figure 7. R for current limiting resistor. Only when a LED output voltage is greater than the threshold voltage, LED to shine.
  (4) single LED can be served as a low voltage regulator works. Due to the LED is after the current voltage change very fast, a common voltage regulator tube voltage characteristics. The stability of the light emitting diode voltage between 1.4 ~ 3 v, should according to the need to choose VF, as shown in figure 8.
  (5) the level meter. At present, the extensive use of LED level meter in stereo equipment. More than it is to use light-emitting tube indicates the output signal level, the number of LED light is different, the change of the output level. Figure 9 is composed of five leds level meter. When the input signal level is very low, the light. The input signal level increases, the first LED1 light, then increase the LED2 light... .

(e) light-emitting diode detection

1. Ordinary light-emitting diode detection
  (1) the multimeter test. Using pointer with x 10 k Ω block multimeter can roughly judge of light-emitting diodes (leds). Normal, the diode is proposed.theoretical Ω for decades to 200 k, reverse resistance value is ∝. If positive resistance to 0 or for up, reverse resistance is small or zero, is easy to damage. This kind of detection method, cannot see the luminous tube light field, because x 10 k Ω block cannot provide larger forward current to the LED.
If there are two pieces of pointer multimeter (same) best can better check light-emitting light-emitting diodes (leds). Use a wire to which the "+" terminal of a multimeter and another piece of table "-" terminal connection. The rest of the "-" pen after being measured the positive (P) of the light tube, the rest of the "+" pen by negative (N) of the measured light pipe. Two pieces of multimeter Ω all buy x 10 block. Under normal circumstances, after connect to normal light. If the brightness is very low, not even light, can be both block multimeter to x 1 Ω if, if still very dark, not even light, it shows that the light emitting diode performance undesirable or damage. Should be paid attention to, can't start measuring is put two pieces of multimeter at x 1 Ω, in order to avoid too much electricity, damage the leds.
  (2) an external power measurement. With 3 v voltage source or two series of dry cells and the multimeter can be local (analog or digital) can accurately measure the leds light, electrical characteristics. This may according to the circuit are connected as shown in figure 10. If measured VF between 1.4 ~ 3 v, and the luminous intensity is normal, that light is normal. If the measured VF = 0 or VF material 3 v, and does not shine, luminous tube has been bad. 2. The detection of infrared light-emitting diode
  Due to the infrared light emitting diode, it is 1 ~ 3 microns of infrared light that the human eye can't see. Often single infrared light-emitting diodes transmitted power only for mW, different models of Angle of infrared LED luminous intensity distribution is not the same. The positive pressure drop infrared LED, as a general rule, be from 1.3 V to 2.5 V. It is because of its infrared emission people see, so using visible light the LED test can only determine the p-n junction is, reverse electric properties is normal, and unable to determine its luminous normal or not. To this end, the best prepared a light-sensitive device (such as cr, 2 Dr Type silicon photocell) as a receiver. The change of the multimeter metering on both ends of the battery voltage. Judge whether the infrared leds combined with appropriate after the forward current launch infrared light. The measuring circuit is shown in figure 11.

B, LED display structure and classification
  By appropriate light emitting diode chip connection (including series and parallel), and appropriate optical structure. May constitute a light-emitting display light-emitting section or markers. Consists of the light-emitting section or markers can be digital pipe, symbol, rice word pipe, matrix, level display tube and so on. Usually the digital pipe, symbols and words tube called stroke display, and the stroke display and matrix are collectively referred to as character display.
  (a) structure of LED display
The basic semiconductor digital tube is made up of seven strip light emitting diode chip sorted by figure 12. Can be 0 ~ 9 shows. Its specific structure has "reflector type", "seven stages" bar and "more than monolithic integrated digital" and so on.
  (1) reflector type digital tube is generally made with white plastic reflective cavity seven sections of the shell, a single LED to stick with each other seven reflex reflector cavity counterpoint of printed circuit boards, each reflection cavity at the bottom of the center position is the LED chip. Before install reflector, bonding way between the chip and corresponding metal printed circuit even good phi 30 microns of silicon aluminium wire or metal wire, drip into the epoxy resin in the reflector, and it is an act of printed circuit board and the chip reflector counterpoint glue, and curing.
Reflector type digital tube free way of packaging seal and seal two kinds. Solid seal way with scattering agent of epoxy resin and dye, mainly used for one or two position device. Empty sealing way is on the top cover with filter and optical film, in order to improve the reliability of the device, must be in the chips and base plate coated with transparent insulation adhesive, it can also improve the efficiency of light. This approach is generally used in more than four digital display (or symbols).
  (2) bar seven sections of digital tube belongs to hybrid packaging form. It is the well tube core gallium phosphide or gallium phosphide wafer, as it contains one or several LED bar, and then stick the same seven in stud the kovar "box, even in the good lead by bonding process, using epoxy resin coating.
  (3) more than monolithic integrated digital display is in luminescent material substrate (wafer), using the integrated circuit technology to produce a large number of seven segment digital display graphics, qualified chips selected via scribing, registration on the printed circuit board, with a lead wire bonding process, and then cover them with "fisheye lens" shell. They apply to small digital instrument.
  (4) symbol pipe, rice word production mode is similar to digital tube.

  (5). Lattice matrix tube (light emitting diode) also can be used more than similar to monolithic integrated digital display process.

(b) the LED display
  (1). According to the word high marks: stroke display words high minimum 1 mm high (more than monolithic integrated digital tube words be in commonly 2 ~ 3 mm). Other types of stroke
Display up to 12.7 mm (0.5 inch) or even hundreds of mm.
  (2). According to the color has red, orange, yellow, green and so on several kinds.
  (3). According to the structure, has seven stages and reflector, a single monolithic integrated type.
  (4). From the light-emitting section has a total of common cathode and anode electrode connection points two kinds.
Total Yang way refers to the stroke display paragraphs luminous tube anode (P) is public, the cathode isolation from each other. ?? So-called Yin way is total stroke display paragraphs luminous tube cathode (N) is public, and the anode is isolated from each other. As shown in figure 13.

(c) the parameters of the LED display
   Due to the LED display is based on the LED, so its optical and electrical properties and limit parameters meaning most the same as the light-emitting diodes (oleds). But due to the LED display with multiple leds, so need to have the following specific parameters:

  1. The luminous intensity than?? Paragraphs of the digital tube in the same driving voltage, paragraphs forward current is not the same, so the paragraphs different luminous intensity. All segments of luminous intensity values of the ratio of the maximum and minimum of luminous intensity ratio. Ratio can be between 1.5 ~ 2.3, the biggest can't more than 2.5.
  2. The pulse forward current IF stroke display every typical positive dc working current for the IF, is under the pulse, the forward current can be far greater than the IF. Pulse duty ratio is smaller, the greater the pulse forward current can be.

(d) of the LED display application guide
1. Seven segment digital display
  (1) if the digital agency for a total of anode form, then its driver stage (OC) should be open collector structure, as shown in figure 14 (a). If digital tube for common cathode forms, its output driver stage shall be the emitter or source output circuit, as shown in figure 14 (b). ? Such as domestic TTL integrated circuits CT1049, CT4049 glyph decoding drive circuit for the open collector form seven segment; The CMOS integrated circuit CC4511 seven segment as the source output latch, decoding drive circuit.

(2) control of the control circuit of digital tube driver stage (also known as driving circuit) has two categories, static and dynamic.
  ① Static drive: static drive also calls the dc drive. Static drive is to point to each digital tube with a stroke decoder (such as BCD BCD decoder) decoder driver. Figure 15 is an example of a static digital tube driver. Figure IC TC5002BP contains emitter output driver stage, so using common cathode digital tube. A, B, C, D end for BCD (BCD 8421 yards) input, BL for digital tube out and displays A status control, R for resistance. Figure 16 for the static drive N digits display circuit.
  ② Dynamic driving is all the digital tube dynamic drive: using a special decoding drive, individually controlled in turn make your digital tube display, this is a dynamic drive. Because of the scanning speed. Display effect is the same as the static drive. Figure 17 is a four-digit dynamic drive line of (pulse impulse drive) method. In the figure TC5002BP took a decoder driver circuit. TC4508BP with two latch, each can be latches latch four binary BCD code, corresponding to the four decimal number four groups of BCD input respectively to four latches, four latches, four groups of BCD output in turn by the four latches points into the decoder, enter the digital tube driver stage after decoding integrated circuit TD62505P (input end I1 ~ I7 and output end Q1 to Q7 one-to-one correspondence). Q1 to Q7, respectively to four digital tube a ~ g seven on the anode. TD62003P digital driving circuit is composed of darlington array circuit, which end grounding in Q1 to Q4, four teachers by input I1 ~ I4 DS1 ~ DS4 control "enable" signal. Due to four latches rotation output is controlled by the DS1 ~ DS4 "enable" signal. So the four digital tube electric display in turn. Because take turns to show frequency is higher, so the display of digital not flicker phenomenon.

2.M word pipe, tube display symbols
  Mizi pipe and symbolic structure principle of the camera, so the driving mode is basically the same, just the decoding process of decoding circuit different from seven-segment decoder.
  M word tube can display a variety of symbols, including English letters. Symbol tube is mainly used to display the +, - or + number, etc.

3.LED dot matrix display

  LED dot matrix display by a single light-emitting diodes together with the display, compared with less solder joints, attachment, all in the same plane, brightness uniformity, good appearance, etc.
  Internal LED dot matrix according to its size, the quantity and the size of the luminous intensity, color and so on can be divided into a variety of specifications. Is shown in figure 18 representative P2057A and P2157A phi 5 high brightness orange-red 5 x7 matrix components. Using dual in 14 feet encapsulation, the difference of two kinds of display is the LED polarity is different, as shown in figure 18. The display panels scanning drive mode, select the larger peak current and narrow pulse driving source, each LED the average current should not exceed 20 ma.
  LED dot matrix can replace digital tube, pipe and character symbols. Not only can display the number, also can show all es in letters and symbols. If will block combination, can constitute a large screen display, used to display Chinese characters, graphs, charts, and so on. Is widely used in airport, station, wharf, Banks and many public places the instructions, instructions, advertising, etc.
Figure 19 is an example of a LED dot matrix display driver circuit.

   LED is a kind of can directly convert electrical energy into visible light and radiant energy of the light-emitting device, has low working voltage, small power consumption, high luminous efficiency, light response time is very short, light color purity, firm structure, impact resistant, resistant to vibration, stable and reliable performance, light weight, small volume, low cost of a series of features, the development by leaps and bounds, the entire visible spectrum can already batch production of a variety of colors high brightness, high performance products. Domestic red, green, orange, and yellow LED production accounts for about 12% of the world total, during the period of "15" goal is to achieve the inheritance of 30 billion with an annual output of the ability, realize ultra-high brightness AiGslnP LED epitaxial wafer and the chip production, annual output of more than 1 billion red, orange, Huang Chaogao brightness LED tube core, break through the key technology of GaN material, blue, green and white leds in batch production. It is predicted that by 2005 international LED the market demand of about 200 billion, sales of $80 billion.

Link in LED industry, the upstream is LED chip substrate and substrate production, in the middle of industrialization as the LED chip design and manufacturing, downstream to the LED packaging and testing, research and development of low thermal resistance, excellent optical properties, high reliable packaging technology is a new type LED to practical, to the industrialization path of the market, in a sense is the tie that links to industry and market, only good can be end products, can be put into practical application, to provide customers with service, make the industry chain loops and seamless flow.

2. The particularity of LED packaging
  LED packaging technology are mostly based on discrete device packaging technology development and evolution, but there are a lot of particularity. Under normal circumstances, the discrete device of the tube core is sealed in the packaging, packaging the role of the main is to protect the tube core and electrical interconnection. And LED encapsulation is completed the output electric signal, protection tube core work, output: the function of visible light, both the electric parameters, and the optical parameters of design and technical requirements, cannot simply be discrete device packaging for the LED.
  The core of the LED light-emitting part is composed of p-type and n-type semiconductor pn junction tube core, when the minority carrier injection pn junction with majority carrier compound, can emit visible light, ultraviolet light or near-infrared light. But p-n junction area of photons is directional, to launch the same chance in all directions, therefore, not all of the light tube core can be released, the quality depends mainly on semiconductor materials, the sealed tube core structure and geometric shape, structure and coating materials, application for higher internal and external quantum efficiency of leds. Conventional Φ type 5 mm LED encapsulation is the side length of 0.25 mm square tube core bonding or sintering in lead frame, the positive by the spherical contact point of the tube core with gold, within the bonded to lead connected to a tube feet, the cathode through reflection cup and wire rack connected to another pin, and then the top with epoxy resin coating. Reflection cup is used to collect the light tube core side, interface, to expect the direction Angle of the launch. The top coating of epoxy resin into a certain shape, have this effect: several protection tube core is not affected by the outside world, such as erosion; With different shapes and materials properties (or after adding the bulk toner), lens or diffuse lens function, control the divergence Angle of light; Tube core index related to air refractive index is too big, causing the inside of the tube core total reflection critical Angle is small, its output of light only a fraction of the active layer is removed, most easily inside the tube core is absorbed by multiple reflection, easily lead to too much light in total reflection loss, choose corresponding refractive index of the epoxy resin as the transition, improve the efficiency of light emergent tube core. Epoxy resin is used as a tube and shell should have wet resistance, insulation, mechanical strength, to emit light tube core refractive index and high transmission rate. Choose different refractive index of packaging materials, packaging geometry on the photon escape efficiency is different, the influence of the Angle of the luminous intensity distribution and core tube structure, the light output way, encapsulation used material and shape of the lens. If using pointed resin lens, can make a LED light on the axis direction, the corresponding Angle is smaller; If the top of the resin lens is round or flat type,   its corresponding perspective will be increased.
  In general, the LED light wavelength with the temperature change of 0.2 0.3 nm / ℃, the spectral width will increase, affect the color brilliance.
In addition, when the forward current flows through the p-n junction, and make the junction area produces a febrile loss, temperature near the room temperature, temperature rise per 1 ℃, the luminous intensity of leds will correspondingly reduced about 1%, encapsulation cooling; Keep the color purity and luminous intensity is very important, more than ever driven by reducing its current approach, to reduce the junction temperature, most of the LED drive current limit at about 20 ma. But the LED light output will increase along with the increase of current, at present, a lot of power type LED drive current can reach 70 ma and 100 ma even 1 a, need to improve the encapsulation structure, new LED packaging design concept and low thermal resistance package structure and technology, improve the thermal characteristics. For example, a large chip inversion structure, select well thermal conductive silver glue, increasing the surface area of the metallic stent, solder bumps silicon carrier in a heat sink directly superior method. In addition, in the application design, PCB circuit boards and other thermal design, thermal conductive performance is also very important.
  After entering the 21st century, leds highlyeffective, high brightness, full color, continuous development and innovation, red, orange LED luminous efficiency has reached 100 Im/W, green LED to 501 m/W, single LED luminous flux of dozens of Im. Along the gong LED chip and packaging is no longer the traditional design concept and manufacturing production mode, in the light output of chips, impurities in materials research and development is not only limited to changing the number of lattice defects and dislocation to improve internal efficiency, at the same time, how to improve the tube core and encapsulate internal structure, enhance the LED inside, the danger of the photon emergent to improve photosynthetic efficiency, solve the heat dissipation, light and heat sink optimization design, improve the optical performance, speed up SMT SMD process is the mainstream of the industry development direction.

3. product packaging structure type
  Since the 1990 s, research and development of LED chips and materials technology, has been a number of breakthroughs, transparent substrate trapezoidal structure, texture, surface structure, the structure of the flip chip, the commercialization of ultra-high brightness (1 CD) of red, orange, yellow, green, blue LED products have the introduction, as shown in table 1, 2000 in low, the luminous flux of special lighting applications. Leds, middle industry has been unprecedented attention, further promote the development of downstream encapsulation technology and industry, using different encapsulation structure forms and sizes, different light color tube core and double color, or three color combination, can produce various series of varieties, specifications of the products.
  LED products packaging structure types are shown in table 2, there are also according to the luminous color, chip materials, luminous intensity, size, and so on and so forth features for classification. Single tube core generally constitute a point light source, multiple core tube assembly in general can constitute a plane light source and line source, for information, state directives and display, light emitting display is also with multiple tube core, through the appropriate connection tube core (including series and parallel) with appropriate optical structure combination, constitute a light-emitting display light-emitting section and markers. Surface-mount LED can be gradually replace pin type LED, application design more flexible and has set up a file in the LED display market occupies a share, have accelerated development trend. Some products listed, solid-state lighting source be LED the medium and long-term development direction in the future.

4. pin type packaging
  LED the type USES the lead frame for various packaging shaped pin, were the first to market research and development success of encapsulation structure, the number of varieties is various, technical maturity is higher, package structure and reflector continues to improve. Standard LED display industry is considered by most customers is the most convenient and economical solution, in typical conventional leds can withstand the 0.1 W input power coating, 90% of the heat is distributed by the cathode pin frame to the PCB, and then send out into the air, how to reduce the work of pn junction temperature rise is encapsulation and application must be considered. Coating material with high temperature curing epoxy resin, the optical performance is good, good adaptability to technology, products with high reliability and can be made into colored or colorless transparent or colorless, transparent and colored scattering scattering lens assembly, different lens shape a variety of shapes and sizes, for example, circles are divided into Φ diameter 2 mm, 3 mm and 4.4 mm Φ Φ, 5 mm and 7 mm Φ Φ several kinds, such as the different components of the epoxy resin can produce different luminous effect.
  Point source of design and color has a variety of packaging structure: ceramic base epoxy resin encapsulation has good work performance, pin can be bent into shape, small volume; Metal base plastic packaging is a kind of energy saving lamp reflector type, suitable for power supply instructions; Flashing type CMOS oscillator circuit chip and LED tube core composite packaging, can produce a strong visual impact of the light; Double color type is composed of two different luminous color tube core, packaging in the same epoxy resin lens, in addition to the double color can also be a third of the mixed color, has extensive application in the large screen display system, and packaging of double color display devices; Voltage type constant current source chip and LED tube core composite packaging, can be a direct replacement of 5 to 24 v voltage indicator light. Plane light source is multiple LED chip bonding on the regulation of miniature PCB position, plastic reflection and potting epoxy resin to form a box cover, the different PCB design to determine the outer lead arrangement and connection mode, there are dual in structure with single upright, etc. Point, surface light source has developed hundreds of package shapes and sizes, applies for the market and customers.
  LED display can be made of digital pipe or m words, symbols tubes, rectangular tubes Chen over a variety of products, designed by actual demand into various shape and structure. Digital tube, for example, a reflector type, monolithic integrated type, such as a single seven sections of three kinds of encapsulation structure, the connection mode has a total of anode and cathode two, one is often said of the digital tube, two or more commonly known as the monitor. Reflector type, with large fonts, with makings provinces, hybrid packaging characteristics of flexible assembly, generally made of white plastic into shape shell with reflective cavity seven pieces, will be a single LED chip bonding with seven reflex reflector cavity registration on the PCB board of each other, each reflection cavity at the bottom of the center position is a form of luminous tube core area, bonding with bonding method fuses, within the reflector drops of epoxy resin, and the tube core PCB surface glue, glue and curing. Reflector type is divided into empty seal and seal two kinds, the former with scattering agent and dye of epoxy resin, multi-purpose at unit, on-off device; Which cover with uniform light color filter membrane, and the tube core with transparent insulation glue onto the base plate, improve the efficiency of the light, is generally used in more than four digital display. Monolithic integrated chip is in luminescent material on a large number of seven segment digital display graphics chip, then scribing divided into single chip graphics chip, bonding, bonding and encapsulating the lens (commonly known as the fisheye lens). A single seven stages will have to make a good large LED chips, cross cut into article contains one or more than just the core of light, so the same seven bonding in digital glyph of kovar rack, the bonding, epoxy resin encapsulation. The characteristics of the single chip, a single type is microminiaturization, dual-in-line package can be used, mostly special products. LED light display on the 106 mm length of the circuit board, 101 just core (up to 201 just core), belongs to high density packaging, using optics refraction principle, make the point light through a transparent cover article 13 to 15 grating imaging, finish every just core from dot to line, according to packaging technology is more complicated.
  Electroluminescent mechanism of semiconductor pn junction decision is unlikely to have a continuous spectrum of white light LED, at the same time, single LED is not likely to produce two or more of the high brightness monochromatic light, only in the wrapping with the aid of fluorescent material, blue or uv LED coating phosphors on the tube core, indirectly from broadband spectrum, synthetic white light; Or use several (two, three or more) different colours of tube core is encapsulated within a component shells, consists of a mix of white LED by ray. Both methods have practical application, the Japanese production white LED up to 100 million, 2000, developed into a kind of steady hair white light products, and will be more than white LED assembly design flux requirement is not high, in pairs is given priority to with local adornment effect, the pursuit of new electric light source.

5. Surface-mount packaging
  In 2002, surface-mount package LED (SMD leds) is gradually accepted by the market, and get a certain market share, from pin type packaging to SMD conforms to the whole electronic industry development trend, many manufacturers to launch such products.
  Early SMD LED mostly by modification of the transparent plastic body SOT - 23, shape size 3.04 x 1.11 mm, volume disc braid packaging container.
On the basis of SOT - 23, developed the high brightness SMD with lens SLM - 125 series, SLM - 245 series of LED, the former for monochromatic light, the latter for double color or three colors glow. Development become a hot spot in recent years, SMD LED, well solved the brightness, perspective, flatness, reliability, consistency, use lighter PCB board and reflector material, the display reflector need fill less epoxy resin, pins and remove the heavier carbon steel material, through the smaller size, lower weight, half the weight of the product, and easily will eventually make the application more hasten is perfect, especially suitable for indoor, half outdoor full-color display applications.
  Table 3 shows the SMD LED several kinds of common size, and according to the size (plus the necessary clearance) calculated the best view distance. Welding plate is one of the important channels, its heat dissipation vendors data is 4.0 x 4.0 mm SMD LED welding plate, on the basis of the reflow soldering can designed to solder and lead JiaoXiang, etc. Ultra-high brightness LED products can be used PLCC (laminate with lead chip carrier) - 2 encapsulation, shape size is 3.0 * 2.8 mm, with unique method high brightness tube core assembly, product thermal resistance of 400 k/W, can press welding CECC way, its luminous intensity in 50 ma drive current issued 1250 MCD. Seven sections of one, two, three and four digital characters of SMD LED display device height is 5.08 12.7 mm, wide range of display size selection. PLCC encapsulation to avoid the pin 7 digital display for manual insert and pin alignment process, conform to the requirements of the automatic pick up - SMT equipment production, flexible application design space, display bright and clear. Multicolor PLCC encapsulated with an external reflector, can be easily combined with luminous tube or optical, replace the current transmission type with reflective optical design, to provide uniform illumination for wide area, research and development under the condition of 3.5 V, 1 a drive to work the power type of SMD leds encapsulation.

6. Power type of encapsulation
  LED chip and package to develop in the direction of high power, the big electric flow produce 10 to 20 times larger than 5 mmled Φ luminous flux, must adopt effective heat dissipation and no degradation of the packaging material to solve the problem of light failure, therefore, shell and assembly as well as the key technology, can withstand the number W power LED packaging. 5 W series of white, green, blue, green, and blue type power supply LED from the beginning of 2003, white LED light output up to 1871 m, 44.31 m/W green lighting failure problems, develop sustainable 10 W power leds, large tube; Bi size is 2.5 * 2.5 mm, can be worked in 5 a power flow, light output up to 2001 m, as a solid lighting source has very big development space.
  Luxeon series power LED is A1GalnN power type inversion tube core inversion welding in silicon with solder bumps carrier, and then put the complete inversion welding silicon carrier into heat sink and the shell, the bonding wire for encapsulation. This package to get light efficiency, heat dissipation performance, increase the working current density of the design is the best. Its main features: low thermal resistance, generally is only 14 ℃ / W, only 1/10 of the conventional leds; Fill the sealed high reliability, the stability of the flexible gel, the range - 40-120 ℃, without internal stress caused by temperature shock, make gold and lead frame disconnected, and prevent yellowing epoxy resin lens, lead frame will not defiled by oxidation; Reflected the optimum design for the cup and the lens for radiation pattern control and the optical efficiency is highest. In addition, the output optical power, excellent performance, such as external quantum efficiency will LED solid-state light source development to a new level.
  Norlux series power LED encapsulation structure for the hexagonal aluminum plate base (which is not conductive) multichip combination, base diameter of 31.75 mm, light emitting area is located in the center of the site, (0.375 x 25.4) mm in diam., can accommodate 40 only LED tube core, aluminum plate as a heat sink at the same time. Tube core bonding wire through the base of the contact points of the two connected to the positive and negative, according to the size of the output light power required to determine the base with the number of the tube core, composable encapsulation of ultra-high brightness AlGaInN and AlGaInP tube core, the emission light monochrome, respectively, for the color or synthetic white, with high refractive index material finally according to the shape of optical design for coating. This using conventional tube core density composite packaging, high light efficiency, low thermal resistance, better protection tube core and bonding wire, in large electrical shed have higher optical output power, is also a kind of promising LED solid-state light source.
In the application, can be in already packaging product assembly with an aluminum laminated metal core PCB, form the power density of LED, PCB board as a device of electrode connection wiring, mezzanine can be used for heat sink, aluminum core to obtain high luminous flux and photoelectric conversion efficiency. In addition, the packaging good SMD LED small size, flexible combination, constitute a module type, guide plate type, concentrating, reflective and other colorful lighting light source.
  Thermal characteristics of the power type LED directly affect the LED working temperature, the luminous efficiency, light wavelength, service life, etc., therefore, the power type LED chips encapsulation design, the manufacture technology is more important.

7. LED development and application prospect
  100 times in recent years, LED the luminous efficiency of growth, the falling cost ten times, it is widely used in large areas of graphic display, full color, status indication, signs, lighting, signal display, LCD back light, auto combination tail lights, and interior lighting, and so on, its development prospects attract global illumination are big manufacturer has added to LED light source and market development. Development and application prospect is extremely white LED, as a significant economy of solid-state lighting devices, and better for the environment, and gradually replace the traditional incandescent lamp, the annual growth rate over 20%, us, Japan, Europe and China's Taiwan province launched a semiconductor lighting project. At present, the ordinary white LED light-emitting efficiency of 251 m/W, experts estimate that 2005 May be over 3001 m/W. Power type LED excellent thermal properties and optical properties are more comfortable with general lighting field, is considered by academia and industry is the only way for the LED into the lighting market. To replace fluorescent lamp, white LED must have a 150-2001 m/W lights, and each Im should be significantly lower than the price of 0.015 / Im (present price 0.25 $/ Im, red LED 0.065 / Im), in order to achieve this goal still has a lot of technical problems need to study, but to overcome the solutions to these problems are not very far away. Glow in solid physics, LED luminous efficiency can approximate 100%, therefore, new light source, LED has been hailed as the 21st century is expected to become the incandescent lamp, fluorescent lamp, high intensity discharge lamp after the fourth generation light source.

  In the domestic LED industry has more than 20, development and production units and more than 150 middle after packaging companies, high-end packaging products to market has yet to see. Now done, GaN blue green light LED the middle industrialization technology research, strive to make our products in the short term performance indexes reached the level of similar products abroad at the same time, strive to in a relatively short period of time to produce 10 kk production capacity, development of white light source in lighting power type LED chips and other new products. Ministry of science and technology will invest 80 million yuan of money, start the national semiconductor lighting project, pay attention to the end product, first start from the special product, in the car, urban landscape lighting as a market, put high power, high brightness LED as the prominent position, it will be in the service of the Beijing Olympic Games and Shanghai world expo.    
Undoubtedly, substrate, the extension of industry chain, chips, encapsulation, application need to common development, and interactive cultivating, encapsulation is the essential part of the industrial chain, pay close attention to.

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