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Common problems with LED lights
Adddate:2017-09-08 15:56????Hits:
What is 1.LED?
Answer: LED is English Light Emitting Diode, namely a light-emitting diode, is a semiconductor device, which is used as luminescent materials using solid semiconductor chip, when the two ends with forward voltage, carrier in semiconductor composite induced photon emission and light.LED can directly emit red, yellow, blue, green, green, orange, purple, white light. The first commercialdiodes in 1960. Its basic structure is an electroluminescentsemiconductor materials, placed on a wire rack, then sealed with epoxy resin around, to protect the internal core function, so the seismic performance LED good.
2.LED why is the fourth generation light source (green lighting)?
Answer: according to the classification of electric light emitting mechanism: the first generation of light source: resistance such as incandescent lamps. The second generation light source: arc and gas emission such as sodium lamp. The third generation light source light such as fluorescent lamp fluorescent powder. The fourth generation light source: solid light emitting chip such as LED.
What are the light emitting mechanisms and working principles of 3.LED?
Answer: the light emitting diode is composed of III-V compounds, such as GaAs (Shen Huajia), GaP (GAP), GaAsP (P Shen Huajia) as its core is made of a semiconductor, p-n junction. So it has the characteristics of general I-N P-N junction, the forward conduction and reverse cut-off and the breakdown characteristics. In addition, in a certain condition under the,
It also has luminescence characteristics. Under the positive voltage, the electrons are injected into the P region by N region, and the holes are injected into the N region by the P region. The minority carrier (minority) part of the opposing region is combined with the majority carrier (multiple daughter) to emit light
What are the optical characteristics of 4.LED?
Answer: the light that 1.LED sends is neither monochromatic light, also be not broadband light, but balance between two
2.LED light source is like point light source and non point light source
The color of the light emitted by 3.LED varies with the direction of the space
The junction temperature of the LED under 4. constant current operation strongly affects the forward voltage VF.
What forms of 5.LED do you have?
Answer: LED because of its different colors, and its chemical composition is different
Such as: red aluminum indium gallium phosphide
Green and blue: indium gallium nitride
White and other colors are blended in the proper proportion of RGB three primary colors
The manufacturing process of LED is similar to that of semiconductor, but its processing accuracy is not as good as that of semiconductor, and the cost is still higher.
6. what is the luminous wavelength of all colors?
Answer: at present, several domestic color ultra bright LED wavelength distribution is 460 ~ 636nm, from short to long wavelength are presented as blue, green, yellow green, yellow, orange and red. * * typical peak wavelength is LED common color: Blue - 470nm, blue and green 505nm, green 525nm * *, - 590nm, 615nm - 625nm. - orange, red
 
What are the 7.LED packaging methods?
Answer: package: 1, pin type (Lamp) LED package, 2, surface mount (SMD) type (SMT - LED), chip on board package, 3 direct mounted (COB) LED package 4, package type system (SiP) LED package 5. wafer bonding and chip bonding.
What categories of 8.LED do you have?
Answer: according to the 1. LEDs color, can be divided into red, orange and green (yellow and green, and subdivided the standard green and pure green and blue). In addition, some of the light emitting diode contains two or three colors of the light emitting diode chip. According to a light scattering agent, with or without adding color or colorless, the various colors of light-emitting diodes can be divided into colored transparent, colorless transparent, colored and colorless four types of scattering scattering. Scatter led and used as an indicator light
2. according to the characteristics of the luminous surface of the luminous tube, the divided circle lamp, square lamp, rectangle and surface luminous tube, lateral tube, surface mounting micro tube, etc.. According to the circular lamp diameter is Phi 2mm, Phi 4.4mm, Phi 5mm, Phi 8mm, Phi Phi 10mm and 20mm. Usually the foreign Phi 3mm light emitting diode is denoted as T-1; the diameter of 5mm is denoted by T-1 (3/4); the diameter of 4.4mm is denoted by T-1 (1/4) by the half angle size. To estimate the circular luminous intensity angular distribution.
There are three kinds of light intensity angular distribution maps: (1) high directivity, usually pointed epoxy package, or metal reflective cavity package without any scattering agent. The half angle is 5 DEG to 20 DEG or smaller, with very high directivity, can make local lighting light source and light detector, or combined to form an automatic detection system. (2) standard. Usually light, the half value angle of 20 degrees to 45 degrees (3.) scattering type. This is the angle indicator is larger, the half angle of 45 degrees to 90 degrees or more, a large amount of scattering agent.
3. according to the structure of LED, there are all epoxy sealing, metal base, epoxy packaging, ceramic base, epoxy packaging and glass packaging and other structures
4. according to the light intensity and current work with ordinary brightness LED (light emitting intensity >100mcd); the light intensity in the name of high brightness LEDs 10 ~ 100mcd. The general LED working current in 10 mA to tens of mA, while the low current LED working current is below 2mA (brightness and ordinary light emitting tubes of the same). In addition to the above classification method, and according to the chip material classification and methods of classification by function.
What are the production process steps of 9.LED?
Answer: 1. process:
(a) cleaning: use ultrasonic cleaning PCB or LED holder, and dry
(b) a: the LED tube core (wafer) bottom electrode prepared on silver colloid after expansion, will expand after the tube core (wafer) placed in the thorn crystal on the stage, will die a pad installed in the PCB or LED stent on the corresponding crystal pen with barbed in microscope next, followed by sintering the silver adhesive.
(c) pressure welding: the electrode is connected to the LED core by aluminum wire or wire bonder to be used as the lead for the current injection. LED installed directly on the PCB, the general use of aluminum wire welding machine (to make white TOP-LED needs wire welding machine)
(d) encapsulation: protect the LED core and the bonding line by epoxy. The glue on the PCB board has strict requirements on the shape of the solidified colloid, which is directly related to the brightness of the backlight products. This process will also undertake the task of point phosphor (white light LED)
(E) welding: if the backlight is made of SMD-LED or other packaged LED, the LED shall be soldered to the PCB board prior to the assembly process
(f) cutting film: using punching machine, cutting back light source for a variety of diffusion film, reflective film and so on
(g) assembly: according to the drawing requirements, the various materials of the backlight are installed in the right place by hand
(H) test: check the backlight, photoelectric parameters and the uniformity of out light
The encapsulation task of 1.LED
Is the wire connected to the electrode of LED chip, and protect the LED chip, and to improve the light extraction efficiency. The key process for assembling, welding and packaging.
2.LED package LED package can be said to be all kinds of mainly used, corresponding to the dimensions according to different applications, radiating countermeasures and illumination effect according to.LED classification, Lamp-LED package TOP-LED, Side-LED, SMD-LED, High-Power-LED and so on.
3.LED packaging process flow
4. package process description
1. chip test
Microscopic examination: mechanical damage and pitting pit or material surface (lockhill) is the chip size and electrode size, electrode pattern conform to the requirement of process is complete.
2. expansion
As the LED chip is still closely spaced after dicing, the spacing is very small (about 0.1mm), which is not conducive to the operation of the subsequent process. We use the expansion machine to expand the adhesive chip film, which is LED chip spacing stretching to about 0.6mm., can also be manually expanded, but it is easy to cause chip waste, waste and other undesirable problems
3. dispensing
At the corresponding position of the LED stent, silver glue or insulating adhesive is used. (for GaAs, SiC conductive substrate, red, yellow and yellow green chips with back electrode, silver glue is used. For sapphire blue and green LED chips with sapphire insulation substrate, insulating glue is used to fix the chip
Control requirements in the process of colloidal height, dispensing position are detailed. Because silver glue and insulation glue in the storage and use have strict requirements, silver colloid material, mixing, wake up the use time must pay attention to the process.
4. prepare glue
The preparation and dispensing glue is used instead, preparing the silver glue to glue machine on the back of the LED electrode, and then put back with silver colloid LED installed in the LED bracket. The efficiency of preparation is higher than that of the glue dispensing, but not all products are suitable for preparation of adhesive technology.   
   5. hand stabbed
The expansion LED chip (glue or no glue) is placed on the gripper of the thorn table, and the LED bracket is placed under the clamp, and the LED chip is stabbed one by one at the corresponding position with the needle under the microscope
Hand thorn has an advantage compared with the automatic racking, for different chips replaced at any time, suitable for the need to install a variety of chip products.
6. automatic automatic mounting rack is combined with glue (glue) and chip installed two steps, the first in the LED bracket on the silver colloid (insulating glue), then use the vacuum suction nozzle LED chip suction location, and then placed in the bracket on the corresponding position. In the process mainly to automatic familiar with the equipment operation and programming, to adjust the installation precision and glue equipment. In the selection of nozzle on selecting bakelite nozzle, to prevent damage to the surface of the LED chip, especially blue, green chips must use the bakelite. Because the steel nozzle scratches the surface of the chip's current diffusion layer
7. sintering
The purpose is to make the sintered silver glue curing sintering, requirements for temperature monitoring, to prevent the bad. The silver colloid batch sintering temperature control at 150 degrees, 2 hours of sintering time. According to the actual situation can be adjusted to 170 DEG C for 1 hours. The insulation rubber 150 DEG C for 1 hours. The silver colloid sintering oven must according to the requirement of process every 2 hours (or 1 hours) to open the replacement of sintered products, please do not open the middle. Sintering oven shall not for other purposes, to prevent pollution.
8. pressure welding
The purpose of press welding is to lead the electrode onto the LED chip to finish the connection between the inside and outside lead of the product
LED's welding process consists of two kinds of gold wire welding and aluminum wire welding. This is a process of aluminum wire bonding, the first LED chip electrode pressure on the first point, then the aluminum wire to stand above the corresponding pressure on the second points after the break, aluminum wire. In the process of gold wire welding, a ball is fired before the first point of pressure, and the rest of the process is similar
Pressure welding is a key link in the process of LED packaging technology, mainly is the need to monitor the pressure welding wire (Lv Si) arch wire shape, solder joint shape, tension. Research on bonding process involves many aspects, such as gold (aluminum) wire material, ultrasonic power, welding pressure, capillary pressure (steel (steel), a selection of mouth mouth) trajectory and so on. (this is the same condition, the microstructure of the welding spot pictures of two different capillary pressure both in micro structure difference, thus affecting the quality of the products.) here we no longer tired.
9. dispensing package
LED packaging mainly has three kinds of dispensing, potting and molding
Basically, the difficulties in process control are bubbles, missing materials, and black spots
The design is mainly for the selection of materials, the choice of good combination of epoxy and stent (general LED can not pass the air tightness test), such as the right shown TOP-LED and Side-LED apply glue dispensing package.
The manual dispensing package of high demands on the operation level (especially white LED), the main difficulty is to control the dispensing, because in the process of using epoxy will thicken. White LED also causes the dispensing color light precipitate fluorescent powder.
10. glue filling package
Lamp-LED package using potting form. The potting process is first injected in LED liquid epoxy molding cavity, and then insert the pressure LED stent welding, into the oven and let the epoxy curing, the LED cavity is formed from the prolapse.
11. molded package
The pressure LED stent welded into a mould, the upper and lower two sets of mould hydraulic clamping machine and vacuum, the solid epoxy glue injection into the entrance heating road with hydraulic push rod is pressed into the mould rubber road, along the road into the various LED epoxy adhesive curing and molding groove.
12. curing and post curing
Curing refers to the encapsulation of epoxy curing, general epoxy curing conditions at 135 degrees, 1 hours. Molded packaging generally at 150 degrees, 4 minutes
13. post cure
Curing is to allow the epoxy to be fully cured and to heat the LED at the same time. Post cure is very important to improve the bonding strength between epoxy and PCB. The general conditions are 120 degrees centigrade and 4 hours
14. cutting and dicing
Because the LED is linked together in production (not single), the Lamp package LED uses the ribs to cut the tendons of the LED bracket. SMD-LED is on a PCB board that requires a dicing machine to complete the separation
15. test
Test the photoelectric parameters of LED, check the dimensions of the products, and sort the LED products according to the customers' requirements
16. packing
Count the finished packages. Ultra bright LED requires anti-static packaging
 
What are the basic lighting terms for 10.LED?
Answer: common lighting terms
Luminous flux: symbol phi, unit lumen Lm, indicating the total amount of light emitted by each second of a luminous body, that is, the flux of light
Light intensity: the symbol I, unit candela CD luminous body in flux, indicating specific direction within the unit solid angle emission
Illumination: the symbol E, unit Lm/m2 shows light lux, exposure in the luminous flux per unit area of the illuminated objects
Brightness: the symbol L, cd/m2 Nituo unit, that lights in the specific direction of luminous flux per unit area per unit solid angle
Luminous efficiency: the unit is Lm/w per watt lumen, indicating the ability of an electric light source to convert electric energy into light and to indicate the luminous flux divided by the power consumption
Average life: unit hours, indicating the number of bulbs to fifty percent, the number of hours of damage
Economic life: unit hour, indicating that the combined beam output is reduced to a specific number of hours while considering the damage of the bulb and the attenuation of the beam output. This ratio is used for outdoor light sources of seventy percent, for indoor light sources, such as fluorescent lamps, is eighty percent
Color: color and black light in a light radiation temperature is the same, the temperature of the blackbody is called the temperature of the light. The light color temperature of different color, different color temperature, a steady atmosphere below 3300K, warm feeling; color temperature in 3000--5000K as the intermediate color temperature, a refreshing feeling; color have a cold feeling above 5000K. Different color of different light source composed of the best environment,
As table:
Colour temperature >5000k:, light color is cool and cool (bluish white), cool atmosphere effect;
Color temperature in 3300-5000K: light color for the middle (white), refreshing atmosphere effect;
Color temperature <3300K: light color is warm (with red white), sedate atmosphere effect
A. color temperature and high brightness light source color temperature, such as brightness is not high for people who have a gloomy atmosphere; low color temperature light and high brightness will give people a hot feeling.
Comparison of B. color using two color light source in the same big space, the contrast will level effect, color contrast, the brightness level at the same time, and can get the color level. Color: color light is a color index to indicate that it shows the object in the light of color than the quasi optical (sun light) illumination color deviation can comprehensively reflect the color of light source.
There are two colors
Faithful color: the correct expression of the original color of the material, you need to use color rendering index (Ra) high light source, the value is close to 100, the best color rendering
Effect color: to highlight the specific color, the performance of the beauty of life, you can use the additive color method to enhance the effect of color rendering
The composition of light spectrum is different, even the same color, color lights may be different. Luminaire efficiency (also called light output coefficient) is an important standard to measure the light energy utilization efficiency, it is between the light energy and light energy lamp output in the light output ratio.
11. what is a high power LED?
Answer: high-power LED, in broad sense, is a single LED light source power greater than 0.35W (including 0.35W).
Although China has LED city street lighting development and production enterprises, but many small power LED array as the luminous body, solve the problem of radiation, the quantities of LED to a lot of small power LED light, high installation cost; city lighting LED lamp with high power LED is the trend of development, with a few high power LED road lamp luminous body because there is no good solution to power reaches a certain amount, the heat of LED; astigmatism and spotlight LED control problem; equilibrium problem in road lamp illumination range, style and irradiated surface illumination; photoelectric conversion efficiency is too low, only a few lumens per watt etc.. Therefore, product performance is not satisfactory; high performance products and high prices, it is difficult to popularize. Heat dissipation and reliability are the main factors that affect LED applications
LED light source has two practices, one is the use of traditional low-power LED as a combination, generally as many as hundreds or even hundreds of, power design complex. Another is the use of high-power tubes as light source, the price is more expensive. Two methods are inevitably to the thermal design and reliability as the main design considerations, many applied to government demonstration project, the real market operation of the project is very few, this aspect of foreign application more, but its biggest drawback is still reliable, light lumens and prices, because many engineering LED poor quality, not very good to show the advantages of long service life. Also, consider the cost, from the angle of the market, LED as a light source, and the combination of whether the use of solar energy in the design, it needs to take a different route, and not as a single light source development can be done.
LED device products applied to the lamp, special requirements on technology mainly is to combine LED light intensity and light angle to design, also due to multiple combinations of LED optical design to take into account the irradiation area, lighting needs to focus on the effectiveness of radiation. LED street lamp and ordinary street lamp contrast advantages: energy saving, environmental protection, easy and low voltage adaptation, can also be directly matched with solar energy system, without additional inversion and conversion process, can achieve maximum energy utilization. Insufficient: the illumination angle is small and uneven, the color rendering index is low, and the optical and heat dissipation design is complex. Technical deficiencies: the luminous flux under current technology is not enough, the light efficiency is too low, and the quality is difficult to guarantee. Solution: LED products are applied to the road
12.LED color temperature characteristics?
Answer: color temperature refers to the changes in color of human eyes when light waves are at different energies
In the calculation of temperature, is a unit of Kelvin 0Kelvin= black body radiation -273 DEG C as the starting point of the computation. The blackbody heating, with the increase of energy, will enter the field of visible light, for example, at 2800 K, a light bulb and the same, we say that the color is light bulb 2800K.
The temperature change of visible light field, high color temperature is made by low color temperature orange white blue -- > -- >.
Color temperature characteristics
1., in high latitudes, the color temperature is higher, the color is blue
2. in low latitudes, the color temperature is low and the colors seen are red
(C no problem with low color temperature and high color temperature ball)
3. in the course of the day, the temperature also changes, when the sun angle, energy (clouds and air) to absorb more, so the color temperature low. When direct sunlight, less energy is absorbed, so the temperature is high.
The sRGB color model of 4.Windows is based on 6500 K as standard color temperature, expressed in D65
5. the morning color temperature is about 4400 K.
6. mountain color, temperature about 6000 K.
Relative color temperature, light source color temperature in different light sources
Northern clear sky 8000-8500k
Cloudy 6500-7500k
Summer noon sunshine 5500k
Metal halide lamp 4000-4600k
Afternoon sun 4000K
Cool color camp light 4000-5000k
High pressure mercury lamp 3450-3750k
Halogen lamp 3000K
Tungsten filament lamp 2700k
High pressure sodium lamp 1950-2250k
Candle light 2000K
The color temperature of the light source, light color is different, color temperature and stable atmosphere below 3300K, warm feeling; color temperature in the 3000--5000K intermediate color, cool feeling; feeling cold temperature above 5000K. Different colors of different light source composed of the best environment,
For example: color temperature, light color, atmosphere effect
>5000K cool (blue, white) cool atmosphere
The atmosphere of the middle (white) 3300-5000K
13. now, what are the famous brands of LED light sources in the world?
Answer: United States: CREE, LUMILED., Japan: CIZITEN, NICHIA., Germany: ORSAM, etc.
What intellectual property rights does 14.LED have?
Answer: CREE: high power blue chip, Nichia: white phosphor technology.
15. what is a high-power LED lamps?
Answer: an illumination device that uses a high power LED as a light source
What are the advantages of the 16. power LED lamps compared with the traditional lamps?
Answer: 1. high efficiency
2. high energy saving
3. more light colored
4., high safety
5. design shapes for diversity
6. long life
7. fast response
8. lamps and lanterns structure is reasonable
9., environmental protection, environmental protection benefits better
10. high-tech tip
11. low operating costs
12., color temperature changes little, less than 100K, color temperature consistency is good
13. lumen maintenance rate is high, slow decay, use 5000 hours light does not exceed 10百分比.
17. heat LED lamps how to dissipate heat?
Answer: uses the heat pipe to carry on the radiator to the radiator heat which the LED light source produces, then uses the radiator the area to carry on the heat radiation heat dissipation and the air air cooling heat dissipation
18.LED why energy saving?
Answer: high brightness monochromatic light LED has made headway in the market. Although they are compared with the traditional light bulb is more expensive, but their advantages can be offset by its high price, it has a higher price. First, a red light LED consumed at a brightness when the energy is 15 watts, while the traditional lighting to achieve the same brightness to consume up to 150 watts; in addition to the scientists measured LED, electroluminescence, 10百分比 of the electrical energy can be converted into energy, while the conversion efficiency of incandescent bulbs only 7-8百分比, thus, to achieve the same effect of lighting, LED lights the incandescent lamp energy saving is obviously.
Why does 19.LED live long?
Answer: the luminescence mechanism of incandescent lamp is electricity heating and light will shine tungsten, after heating for a long time, tungsten will aging or burn out, so far, the incandescent light bulb life ended, and the luminescence mechanism of light emitting diode is decided by the special structure of diode, diode composed mainly by the crystallization of PN films, electrodes and optical system, when coupled with the forward bias voltage on the electrode, were injected into the P region and N region of the electrons and holes, when non equilibrium minority carriers and majority carrier compound, will form the excess radiation photon energy into light. The luminescence process consists of three parts: carrier injection, recombination radiation and light energy transmission under forward bias. It can be seen that the diode mainly depends on the continuous movement of the carrier, and there is no phenomenon of aging and burning. Its special luminous mechanism determines its luminous lifetime up to 5-10 hours
LED lighting, we must recognize that the concept of single or multiple white LED as light source and lighting are different. At present, the white LED domestic and foreign R & D and production is far to meet the lighting requirements. We should use and play in China to seize the opportunity in the development of all kinds of compact type the fluorescent lamp in the world of advantages and advanced technology, and make a difference in the development of the new solid light source. Some of the major problems faced in the implementation of the white LED lighting lamp and compact fluorescent lamps have been resolved or are faced with problems similar.
1, lamps installed in the AC-DC converter circuit should adapt to the LED current drive features
This power supply should have the forward current output which is close to the constant current required for LED, and also has high conversion rate, so as to ensure the safe and reliable operation of LED, and of course, pay attention to the cost
2, LED lamp reliability
The main factors that affect the reliability of lamps and lanterns are LED devices and the above

 


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