LED Dictionary

Surface mount LEDs appeared in the early 1980s in response to smaller packaging and factory automation. The main reason why manufacturers hesitated in the early days was that the first problem faced by surface mount LEDs was the inability to complete the solder reflow step under high-temperature infrared light. The specific heat of LEDs is lower than that of ICs. When the temperature rises, not only will the brightness decrease, but it will also accelerate the degradation of components when it exceeds 100 degrees Celsius. The resin used in LED packaging absorbs moisture. When these water molecules evaporate rapidly, they will cause cracks in the original packaging resin, affecting the product's benefits. In the early 1990s, HP and Siemens Component Group jointly developed long molecular bond polymers as a design for surface mount LEDs to cooperate with pick-and-place machines. Surface mount LEDs were officially launched at this point.

LED Light Emitting Diode.

LED is an electronic component that emits light when powered on. It is a light-emitting component made of semiconductor materials. The materials use III-V chemical elements (such as gallium phosphide (GaP), gallium arsenide (GaAs), etc.). The principle of light emission is to convert electrical energy into light, that is, to apply current to compound semiconductors. Through the combination of electrons and holes, the excess energy will be released in the form of light to achieve the effect of light emission. It is cold light emission with a lifespan of more than 100,000 hours. The biggest features of LED are: no idling time, fast response speed (about 10^-9 seconds), small size, low power consumption, low pollution, suitable for mass production, high reliability, easy to make extremely small or array components according to application needs, and a wide range of applications, such as automobiles, communications industry, computers, traffic signs, displays, etc.

LED can be divided into upstream, midstream and downstream. From upstream to downstream, the appearance of products is quite different. The upstream is formed by epitaxial chips, which are roughly a circle with a diameter of six to eight centimeters and are very thin, like a flat metal. The color and brightness of LED light are determined by the epitaxial material, and epitaxial accounts for about 70% of the LED manufacturing cost, which is extremely important to the LED industry. The upstream epitaxial process sequence is: single chip (III-V substrate), structural design, crystal growth, material properties/thickness measurement.

Midstream manufacturers cut these chips into tens of thousands of grains. Depending on the size of the chip, it can be cut into 20,000 to 40,000 grains. These grains grow like sand on the beach. They are usually fixed with special tape and then sent to downstream manufacturers for packaging. The midstream grain process sequence is: epitaxial chip, metal film evaporation, mask, etching, heat treatment, cutting, cracking, and measurement. The downstream packaging sequence is: grain, solid crystal, adhesion, wire bonding, resin packaging, long baking, tinning, pin cutting, and testing.

The main domestic LED manufacturers include Dingyuan, Guanglei, Guolian, Everlight and other companies.

Infrared Light Emitting Diode Infrared Light Emitting Diode.

It is mainly developed based on GaAs series materials and is usually produced by LPE liquid phase epitaxy method. The emission wavelength ranges from 850 to 940.

GaP Gallium Phosphide.

Gallium phosphide is a compound of group III-V elements. GaP is an indirect migration semiconductor with low current and high efficiency luminescence characteristics. Its luminescence range covers red to yellow-green, and it is one of the main materials used in LEDs.

GaN Gallium Nitride.

Gallium nitride is a compound of group III-V elements. GaN uses MOVPE technology to produce high-brightness pure blue LEDs and pure green LEDs, and can also be used to produce blue and green laser diodes. Although MOVPE is a mature epitaxial production technology, it still requires considerable expertise, experience and skills to produce GaN blue LEDs.

AlInGaP Aluminum Indium Gallium Phosphide.

AlInGaP is a relatively new material used in the manufacture of high-brightness LEDs in recent years. It is made using the MOVPE epitaxy process. Currently, there are only three companies in the world that supply this product, namely HP in the United States, Toshiba in Japan, and Guolian Optoelectronics in Taiwan.

AlGaAs Aluminum Gallium Arsenide.

It is a mixed crystal of GaAs and AlAs. AlGaAs is suitable for manufacturing high-brightness red and infrared LEDs, and is mainly mass-produced by LPE epitaxy, but because it requires the production of AlGaAs substrates, the technology is difficult.

Reverse mounting type thin chip LED reverse mounting type thin chip LED.

This chip can be bonded to a through-type printed circuit board to reduce the thickness of the LED. It can be mainly used as a backlight source for mobile phone buttons.

Side-emitting right angle LED

This type of LED chip emits light from the top layer, but the light-emitting surface can be rotated and welded. Side-emitting right-angle LEDs are available in two types: ultra-small and high-brightness. The ultra-small type is used for LCD backlights, pagers, and mobile phones; the high-brightness type is used for third brake lights on cars and motorcycles and outdoor displays.

Right angle surface mount LED bulb SIDELED.

Right-angle surface mount LED bulbs do not require additional optical components or reflectors. After welding, the light path can be parallel to each circuit board, giving engineers greater flexibility in design, so they can add this product to the later stage of the design without prior consideration. The product can be used in automatic safety power-off switches, backlight sources and light pipes, etc., as indicator lights for telephones and data processing systems.

Visible light LED Visible light Light Emitting Diode.

There are many types of LEDs (light emitting diodes), which are roughly divided into visible light and invisible light according to the wavelength of light emission. Visible light LED products mainly include traditional LEDs, high-brightness AlGaInP (aluminum gallium indium phosphide) red, yellow, and orange LEDs, InGaN (indium gallium nitride) blue, green LEDs, and white light LEDs. Its products are mainly used for display purposes, and the brightness of one candlelight (1 cd) is used as the dividing point between general LEDs and high-brightness LEDs. General LEDs are widely used in various indoor display purposes; high-brightness LEDs are suitable for outdoor displays, such as car third brake lights, outdoor information billboards, and traffic signs.

Invisible light LED Invisible light Light Emitting Diode.

There are many types of LEDs (light emitting diodes), which are roughly divided into visible light and invisible light according to the wavelength of light emission. Invisible light LEDs have a wavelength of 850 to 1550 nanometers, and their short-wavelength infrared light can be used for infrared wireless communication, such as infrared LEDs used in photocopy paper size detection, home appliance remote controls, factory automatic detection, automatic doors, automatic flushing device control, etc.; long-wavelength infrared light is used in medium and short-distance optical fiber communications as a light source for optical communications.

GaN LED Gallium Nitride Light Emitting Diode.

GaN LED is a direct bandgap semiconductor material with a bandgap of 3.4ev, while AlN is 6.3ev and InN is 2.0ev. When these materials are made into a mixed crystal, the bandgap can be continuously changed from 2.0ev to 6.3ev, so colors ranging from ultraviolet light, purple light, blue light, green light to yellow light can be obtained.

The most successful GaN components at present are high-brightness blue and green LEDs. The successful development of GaN high-brightness blue and green LEDs has made it possible to realize outdoor full-color LED displays and LED traffic signs, and the application of various LEDs has become more extensive. High-brightness blue LEDs can produce white light by stimulating fluorescent materials (phospher). With their low power consumption and long life, they may replace incandescent bulbs for general lighting in the future. The market potential of GaN LEDs is very strong.

OLED OELD. Organic Electro-Luminescence Display. Organic electro-luminescence.

The organic film is driven by electric current to emit light, which can be red, blue, green or even full color. Since the organic compound materials used in OLED can emit light by themselves, it does not need a backlight behind the LCD panel, which can greatly reduce power consumption, simplify the process, and make the panel thinner. The characteristics of OLED are self-luminescence, wide viewing angle, fast response speed, low power consumption, strong contrast, high brightness, thin thickness, full color, and animation display, etc. It is considered to be a flat display technology with great potential. At present, domestic manufacturers such as Rebao, Optoelectronics, TECO Laser, and Hanli Optoelectronics have invested in it.

Indoor LED display board

Regardless of the size, LED display billboards are assembled from single-component LEDs. The single components of LEDs come from downstream packaged dot-matrix LEDs or unit module clusters. The display billboard manufacturers then assemble these single components into various large billboards according to various needs, add control circuits, and then install and test them at various construction sites.

Indoor LED display boards require higher resolution because of the short viewing distance. Dot matrix modules are generally used. Because the indoor environment is more stable, there is less need for waterproof protection devices and heat dissipation measures, and the construction is relatively easy.

Outdoor LED Display Board

Regardless of the size, LED display billboards are assembled from single-component LEDs. The single components of LEDs come from downstream packaged dot-matrix LEDs or unit module clusters. The display billboard manufacturers assemble these single components into various large billboards according to various needs, add control circuits, and then install and test them at various construction sites.

For outdoor LED billboards, the viewing distance is far and the resolution requirement is relatively low, but the requirements for brightness, visibility and weather resistance are relatively high. Therefore, in outdoor construction, it is necessary to consider issues such as heat dissipation and waterproofing.

Large LED display

Large-scale LED display screens require a combination of different components and technologies. It is difficult for a manufacturer to be completely self-sufficient, so the division of labor in the peripheral industry is very important. The components required for large-scale LED display screens include: Driver IC, LED Cluster, Power Supply, Cable and mechanical frame, etc.; technical requirements include: anti-static design, power distribution planning, drive circuit design, drive software design, mechanical structure design (heat dissipation, viewing angle, support, sunshade, moisture-proof, etc.) and brightness and color testing technology.

UV LED Ultraviolet diode

UV LED (ultraviolet light emitting diode) lighting can not only purify the air and save energy, but is also expected to replace existing lighting devices such as fluorescent lamps and incandescent lamps. In addition, the wavelength band that was only 405nm in the past has recently been expanded to 200nm. It is expected that the scope of application will be greatly expanded to sterilization, wastewater treatment, deodorization, medical treatment, skin disease treatment, counterfeit banknote identification and environmental sensors.

Luminous flux (Φ) unit: lumen (lm) All radiant energy emitted by a light source and perceived by the human eye is called luminous flux. Luminous intensity (I) Luminous flux of a light source in a certain direction within a solid angle. Unit: candela (cd) Illuminance (E) unit: lux (lx) Illuminance is the ratio of luminous flux to the illuminated surface. 1 lux is the luminous flux of 1 lumen evenly distributed in an area of ​​1 square meter. Luminance (L) unit: candela per square meter (cd/㎡) The luminance of a light source or an illuminated surface refers to the light intensity density of its unit surface in a certain direction, which can also be said to be the brightness of this light source or illuminated surface perceived by the human eye.

Light Emitting Diode (LED) is a photoelectric semiconductor component that emits light (electric energy → light) by exciting electrons with an external voltage. The luminescence phenomenon is direct luminescence in semiconductors (without the intervention of a third particle). The entire luminescence phenomenon can be divided into three processes (direct luminescence): The electrons in the valence band are excited to the conduction band by external energy (forward bias), and at the same time leave a hole in the valence band to form an electron-hole pair. The excited electrons collide with other particles in the conduction band (scattering), lose some energy, and approach the edge of the conduction band. Once the electrons at the edge of the conduction band find a hole in the valence band, the electrons return from the edge of the conduction band through the trap center (releasing heat energy) or the luminescence center (releasing light energy) to the valence band to recombine with the hole, and the electron-hole pair disappears.

Because LED mainly emits light through the recombination of electrons and holes through the luminescent center, it is a tiny solid-state light source. It is not only small in size, long in life, low in driving voltage, fast in response rate, and excellent in shock resistance, but also can meet the needs of light, thin and miniaturized application equipment, becoming a very common product in daily life.

Different LEDs are designed by using various compound semiconductor materials and component structures. They are divided into visible light and invisible light (infrared light, ultraviolet light) according to their emission wavelength.

Visible light: There are various colors such as red, orange, yellow, green, blue, and purple, and it is mainly used for display purposes. The brightness of 1 candela (cd) is used as the dividing point between general brightness and high brightness. General brightness LEDs are widely used in various indoor display purposes; high brightness LEDs are suitable for outdoor displays, such as: car third brake lights, outdoor information billboards and traffic signs. Invisible light: Short-wavelength infrared light can be used for infrared wireless communication; long-wavelength infrared light is used in medium and short-distance optical fiber communications as a light source for optical communications.

The materials used basically determine the wavelength emitted by the LED. Among them, the materials suitable for making high-brightness LEDs above 1000mcd are, from long wavelength to short wavelength, AlGaAs (aluminum gallium arsenide), AlGaInP (aluminum indium gallium phosphide) and GaInN (indium gallium nitride).

AlGaAs (aluminum gallium arsenide) is suitable for manufacturing high-brightness red and infrared LEDs. It is mainly mass-produced by liquid phase epitaxy (LPE) and mainly uses a double heterojunction structure (DH). However, because the AlGaAs substrate must be made, the technical difficulty is very high, so there are fewer manufacturers investing in development. AlGaInP (aluminum indium gallium phosphide) is suitable for high-brightness red, orange, yellow and yellow-green LEDs. It is mainly mass-produced by metal organic vapor phase epitaxy (MOVPE) and uses a double heterojunction (DH) and quantum well (QW) structure, which improves efficiency. And because the life test results of AlGaInP red LEDs are better than those of AlGaAs red LEDs in high temperature and high humidity environments, there is a trend of becoming the mainstream of red LEDs in the future.

GaInN (indium gallium nitride) is suitable for high-brightness deep green, blue, purple and ultraviolet LEDs. It is mass-produced using high-temperature metal organic vapor phase epitaxy (MOVPE) and also uses double heterojunction (DH) and quantum well (QW) structures. Its efficiency is higher than the aforementioned AlGaAs and AlGaInP. Major manufacturers around the world have actively invested in the research and development of related material component technologies and have made some breakthroughs.

White light LED is made by Nichia Corporation of Japan using blue light LED and yellow fluorescent material. Its photoelectric conversion efficiency has been improved to 15 lumens/watt in April 1998, which is slightly higher than traditional bulbs. Judging from the development history of common lighting fixtures, white light LED has a great chance to become a star product in the lighting industry in the future.

When LED was first designed, it was mainly used for home appliance displays, advertising billboards or decoration. However, due to its fixed wavelength and easy operation, it has gradually been used in plant production research. In 1987, some scholars began to use the fixed wavelength characteristics of LED to study plant geotropism, morphological changes and disease occurrence. Professor Kozai's laboratory at Chiba University in Japan applied it to the production research of tissue bottle seedlings. It is expected to have great application value in light research in the future. Of course, the brightness and price of LED have not yet reached the practical stage. However, due to its great market potential, various research is rapidly developing, and LED is bound to become a new light source for plant growth.

Epitaxial wafer growth The basic principle of epitaxial growth is that on a substrate substrate (mainly ruby ​​and SiC) heated to an appropriate temperature, gaseous substances In, Ga, Al, and P are controlled to be transported to the substrate surface to grow a specific single crystal film. At present, the LED epitaxial wafer growth technology mainly adopts the organic metal chemical vapor deposition method. MOCVD Metal- Organic Chemical Vapor Deposition (MOCVD for short) is a new technology for preparing single compound semiconductor thin films proposed by Rockwell Corporation in the United States in 1968. The equipment integrates precision machinery, semiconductor materials, vacuum electronics, fluid mechanics, optics, chemistry, and computers. It is a high-level automation, expensive, and high-tech integrated cutting-edge optoelectronics special equipment. It is mainly used for the epitaxial growth of GaN (gallium nitride) semiconductor materials and the manufacture of blue, green or ultraviolet light-emitting diode chips. It is also one of the most promising special equipment in the optoelectronics industry.