At present, the global LED production capacity breakthrough is quite obvious, and Taiwan, Japan, South Korea and China have a certain degree of mass production capacity and technology improvement. Taking China as an example, the planned industrial target is to produce 30 billion LEDs per year. At the same time, it is hoped to have ultra-high brightness AiGslnP LED wafers and LED dies. In addition to lower-order red LEDs, GaN materials are also planned. The production of blue and white LED products is in mass production. In Japan, high-brightness white light, RGB three-color LEDs, and backlight LEDs have better inking, and the market share is also high.
If we look at the LED industry supply chain, the upstream is LED substrate chip and substrate production, the middle is LED chip design and manufacturing production, the downstream is LED packaging and testing, but as the industry is booming, the integration of the upper, middle and lower reaches is very Obviously, if Japan is Japanese, the upper, middle and lower reaches are all-inclusive, while the Taiwanese manufacturers are divided into upstream and downstream, and the middle reaches are absorbed upstream.
In general, the die of the discrete device is sealed in the package, and the package functions to protect the die and complete the electrical interconnection. The LED package is to complete the output electrical signal, protect the normal operation of the die, output: visible light function, both electrical parameters, optical design and technical requirements, can not simply use the discrete device package for LED. The core light-emitting portion of the LED is a pn crystal grain composed of a p-type and an n-type semiconductor. When a minority carrier injected into the pn junction is combined with a majority carrier, visible light, ultraviolet light or near-infrared light is emitted. However, the photons emitted by the pn junction region are non-directional, that is, the same probability is emitted in all directions. Therefore, not all light generated by the crystal grains can be released, which mainly depends on the quality, grain structure and geometry of the semiconductor material. The internal structure of the package and the encapsulation material are required to improve the internal and external quantum efficiency of the LED. Conventional Φ5mm LED package is to bond or sinter a square die with a side length of 0.25mm on the lead frame. The positive electrode of the die passes through the spherical contact point and the gold wire, and the inner lead is connected to one pin. The negative electrode passes through the reflection. The cup is connected to the other leg of the lead frame and then the top is encapsulated with epoxy.
The function of the reflector cup is to collect the light emitted from the side of the die and the interface and emit it in the desired direction. The top encapsulated epoxy resin is shaped to have several functions: to protect the crystal grains from external corrosion; to use different shapes and material properties (with or without colorants), to act as a lens or diffuse lens Function, control the divergence angle of light; the refractive index of the grain is too much related to the refractive index of the air, so that the critical angle of total reflection inside the grain is small, and a small part of the light generated by the active layer is taken out, most of which are easy to The inside of the grain is absorbed by multiple reflections, and it is easy to cause total reflection to cause excessive light loss. The epoxy resin with corresponding refractive index is used as a transition to improve the light emission efficiency of the crystal grain. The epoxy resin used to form the envelope must have moisture resistance, insulation, mechanical strength, and a high refractive index and transmittance for light emitted from the crystal grains. The choice of packaging materials with different refractive indices, the influence of package geometry on photon emission efficiency is different, and the angular distribution of luminous intensity is also related to the grain structure, light output mode, and the material and shape of the package lens. If a pointed resin lens is used, the light can be concentrated in the axial direction of the LED, and the corresponding viewing angle is small; if the resin lens at the top is circular or planar, the corresponding viewing angle will increase. Under normal circumstances, the LED's emission wavelength changes with temperature by 0.2-0.3nm/°C, and the spectral width increases, which affects the color vividness.
In addition, when the forward current flows through the pn junction, the heating loss causes the junction region to produce a temperature rise. At around 1°C, the luminous intensity of the LED is reduced by about 1%, and the heat dissipation of the package is maintained. Purity and luminescence intensity are very important. In the past, the method of reducing the driving current was used to reduce the junction temperature. The driving current of most LEDs was limited to about 20 mA. However, the light output of LEDs will increase with the increase of current. At present, many power LEDs can drive currents up to 70mA, 100mA or even 1A. It is necessary to improve the package structure, the new LED package design concept and low thermal resistance package structure and Technology to improve thermal properties. For example, a large-area grain flip-chip structure is used, and a silver paste with good thermal conductivity is used to increase the surface area of ​​the metal support, and the silicon carrier of the solder bump is directly mounted on the heat sink. In addition, in the application design, the thermal design and thermal conductivity of the PCB circuit board are also very important. After entering the 21st century, LED's high efficiency, ultra-high brightness, full colorization continue to develop and innovate. Red and orange LED light effects have reached 100Im/W, green LEDs are 501m/W, and the luminous flux of single LEDs has reached dozens. Im.
LED die and package no longer follow the traditional design concept and manufacturing mode of Gong. In terms of increasing the light output of the die, research and development is not limited to changing the amount of impurities in the material, lattice defects and dislocations to improve internal efficiency. How to improve the internal structure of the die and package, enhance the probability of photon emission inside the LED, improve the light efficiency, solve the heat dissipation, take light and heat sink optimization design, improve the optical performance, accelerate the surface adhesion SMD process is the mainstream of the industry research and development direction.
Product packaging structure type Since the 1990s, the development of LED die and material fabrication technology has achieved many breakthroughs, transparent base ladder structure, textured surface structure, die-flip structure, commercial high brightness (1cd or more Red, orange, yellow, green, and blue LED products have been asked one after another. In 2000, they began to be used in special lighting with low and medium light flux. The upper and middle reaches of LED industry have received unprecedented attention, further promoting the downstream packaging technology and industrial development. Different types of packaging structures and sizes, different luminescent color dies and their two-color or three-color combination can produce a variety of Series, variety, specifications of the product.
The type of LED product packaging structure is also classified according to the characteristics of the color of the light, the material of the grain, the brightness of the light, the size and the like. A single die generally constitutes a point source, and a plurality of die assemblies generally constitute a surface source and a line source for information, status indication, and display. The illuminating display also uses a plurality of dies, through appropriate connections of the dies (including series and Parallel) combined with a suitable optical structure to form the illumination segment and the illumination point of the illuminated display. The surface-adhesive LED can gradually replace the lead-type LED, and the application design is more flexible. It has occupied a certain share in the LED display market and has an accelerated development trend.
Some solid-state lighting sources have been launched, which will become the medium and long-term development direction of LEDs in the future. The lead-type package LED foot package adopts the lead frame as the pin of various package appearances. It is the first package structure successfully developed on the market. The variety of products is high, the technology maturity is high, and the structure and reflective layer in the package are still in the package. keep improving. Standard LEDs are considered by most customers to be the most convenient and economical solution in the display industry. Typical LEDs are housed in an enclosure that can withstand 0.1W of input power, 90% of which is pinned by the negative pole. The rack is distributed to the PCB and then released into the air. How to reduce the temperature rise of the pn junction during operation is a must for packaging and application. The encapsulating material is mostly made of high-temperature curing epoxy resin, which has excellent optical rotation performance, good process adaptability, high product reliability, and can be made into colored transparent or colorless transparent and colored scattering or colorless scattering lens package, different lens shapes. A variety of shapes and sizes are formed. For example, the circular shape is divided into several types according to the diameter: Φ2mm, Φ3mm, Φ4.4mm, Φ5mm, Φ7mm, etc., and different components of the epoxy resin can produce different illuminating effects.
The color point light source has a variety of different package structures: the ceramic base epoxy resin package has better working temperature performance, the lead can be bent into a desired shape, and the volume is small; the metal base plastic reflective cover type package is an energy-saving indicator light. Suitable for power indication; flashing CMOS oscillating circuit die and LED die package, can generate self-generated scintillation light with strong visual impact; two-color type consists of two different illuminating color crystal grains, packaged in the same ring In the oxy resin lens, a third mixed color can be obtained in addition to the two colors, which is widely used in a large-screen display system, and can be packaged to form a two-color display device; the voltage type combines a constant current source die with an LED die. The package can directly replace various voltage indicators of 5-24V. The surface light source is formed by bonding a plurality of LED dies to a predetermined position of the micro PCB board, and is formed by using a plastic reflective frame cover and potting the epoxy resin. The different designs of the PCB board determine the arrangement and connection manner of the outer leads, and the double row is straight. Insert and single-row inline and other structural forms. Point and surface light sources have been developed in hundreds of package shapes and sizes for the market and customers.
The LED light-emitting display can be composed of a digital tube or a meter tube, a symbol tube, and a rectangular tube to form various products, and is designed into various shapes and structures according to actual needs. Take the digital tube as an example, there are three kinds of package structures, such as a reflector cover, a single-chip integrated type, and a single seven-segment type. The connection mode includes a common anode and a common cathode. One is a commonly known digital tube, and two or more. Generally referred to as a display. The reflector type has the characteristics of large font, material saving and flexible assembly. It is generally made of white plastic into a seven-section housing with a reflective cavity, and a single LED die is bonded to the seven reflective chambers of the reflector. On the PCB board that is aligned with each other, the center position of the bottom of each reflective cavity is the light-emitting area formed by the die, and the lead wire is bonded by a pressure welding method, and the epoxy resin is dropped in the reflective cover, and the die-bonded PCB board is bonded. Bonded in place and then cured.
The reflector type is divided into two types: air seal and solid seal. The former uses epoxy resin with scattering agent and dye, and is mostly used for unit and double-position devices; the latter covers the color filter and the uniform film, and is in the grain and The bottom plate is coated with transparent insulating glue to improve the light-emitting efficiency, and is generally used for digital display of four or more digits. The monolithic integrated system is to fabricate a large number of seven-segment digital display graphic dies on the luminescent material chip, and then dicing into a single-chip graphic die, bonding, pressure-welding, and encapsulating a lens with a lens (commonly known as a fisheye lens). A single seven-segment type of large-area LED die that has been fabricated into a light-emitting strip containing one or more crystal grains, so that the same seven strips are bonded to the digital-shaped cut-off frame, and are pressure-welded, Epoxy resin package. The monolithic and single strip features are miniaturized and can be used in dual in-line packages, mostly for specialty products.
LED light column display is equipped with 101 crystal grains (up to 201 crystal grains) on a 106mm length circuit board. It is a high-density package. Using optical refraction principle, the point light source passes through 13-15 gratings of transparent cover. Imaging, to complete the display of each die from point to line, the packaging technology is more complicated. The electroluminescence mechanism of the semiconductor pn junction determines that it is impossible for LED to produce white light with continuous spectrum. At the same time, it is impossible for a single LED to produce more than two kinds of high-brightness monochromatic light. The package can be used for packaging with fluorescent substances, blue or ultraviolet LEDs. The phosphor is coated on the crystal grain to indirectly generate a broadband spectrum to synthesize white light; or several (two or three or more) crystals of different color light are packaged in one component casing, and the white light LED is formed by mixing of color lights. . Both methods have been put into practical use. In 2000, Japan produced 100 million white LEDs, which developed into a class of products that stably emit white light. The design of multiple white LEDs was not required to meet the luminous flux. Lord, the pursuit of a new electric light source.
Surface Adhesive Packaging In 2002, surface mount LEDs (SMD LEDs) were gradually accepted by the market and gained a certain market share. From lead package to SMD, it conformed to the development trend of the whole electronics industry. Many manufacturers introduced such products. product. Most of the early SMD LEDs were modified with SOT-23 with a transparent plastic body. The outer dimensions were 3.04×1.11mm, and the reel-type container was taped. Based on SOT-23, the SLM-125 series with high-brightness SMD with lens and SLM-245 series LED are developed. The former is monochromatic illumination, and the latter is two-color or three-color illumination. In recent years, SMD LED has become a development hotspot, which solves the problems of brightness, viewing angle, flatness, reliability, consistency, etc., using a lighter PCB board and reflective layer material to display the ring that needs to be filled in the reflective layer. Less oxygen resin, and remove the heavier carbon steel material pins, can reduce the weight of the product by half, reduce the weight of the product, and finally make the application more perfect, especially suitable for indoor, semi-outdoor full color display application. Table 3 shows several dimensions of common SMD LEDs, as well as the best viewing distance calculated from the dimensions (plus the necessary clearance). The pad is an important channel for heat dissipation. The SMD LED data provided by the manufacturer is based on a 4.0×4.0mm pad. The reflow soldering can be used to design the pad to be equal to the pin.
Ultra-high brightness LED products can be packaged in PLCC (plastic package with lead chip carrier)-2, the external dimensions are 3.0×2.8mm, and the high-brightness die is assembled by a unique method. The thermal resistance of the product is 400K/W, which can be pressed. CECC soldering, its luminous intensity is 1250mcd at 50mA driving current. The seven-segment one, two, three and four digital SMD LED display devices have a character height of 5.08-12.7mm and a wide display size range. The PLCC package avoids the manual insertion and pin alignment processes required for the seven-segment digital display of the pin, and meets the production requirements of the automatic pick-and-stick device. The application design space is flexible and the display is bright and clear. The multi-color PLCC package features an external reflector that can be easily combined with an LED or light guide to replace the current transmissive optical design with a reflective version to provide uniform illumination over a wide area, developed at 3.5V, 1A drive Power SMD LED package operating under conditions. The power-type packaged LED die and package are developed in the direction of high power. Under high current, the luminous flux is 10-20 times larger than that of Φ5mm LED. It is necessary to use effective heat dissipation and non-degrading packaging materials to solve the problem of light decay. Therefore, the package and Packaging is also a key technology, and LED packages capable of withstanding several W power have emerged. 5W series white, green, blue green, blue power LEDs have been available since the beginning of 2003. The white LED light output reaches 1871m, the light efficiency is 44.31m/W green light decay problem, and the LED that can withstand 10W power is developed. The area tube; the size of the crucible is 2.5×2.5mm, it can work under the current of 5A, and the light output reaches 2001m. It has great development space as a solid illumination source.
The Luxeon series power LEDs are flip-chip soldered to A1GalnN power-type flip-chips on a silicon carrier with solder bumps, and then the flip-chip soldered silicon carrier is placed in the heat sink and the package, and the bonding leads are packaged. This package is optimized for light extraction efficiency, heat dissipation performance, and increased operating current density. Its main features: low thermal resistance, generally only 14 ° C / W, with 1/10 of conventional LED; high reliability, flexible gel filled inside the package, in the range of -40-120 ° C, will not cause The internal stress generated by sudden temperature changes disconnects the gold wire from the lead frame and prevents the epoxy lens from turning yellow. The lead frame is not stained by oxidation. The optimal design of the reflector cup and lens makes the radiation pattern controllable. The optical efficiency is the highest. In addition, its output optical power, external quantum efficiency and other properties are excellent, and the LED solid light source has been developed to a new level.
The package structure of the Norlux series of power LEDs is a multi-die combination of a hexagonal aluminum plate as a base (which makes it non-conductive). The base has a diameter of 31.75 mm, and the light-emitting area is located at the center thereof, and the diameter is about (0.375×25.4) mm. It holds 40 LED dies, and the aluminum plate acts as a heat sink at the same time. The bonding wires of the die are connected to the positive and negative electrodes through two contact points made on the base, and the number of arranged crystal grains on the base is determined according to the required output optical power, and the packaged ultra-high brightness AlGaInN and AlGaInP can be combined. The crystal grains, which emit light in a single color, color or synthetic white, are finally encapsulated in an optically designed shape with a material having a high refractive index. The package adopts a conventional high-density combination of crystal grains, has high light extraction efficiency, low thermal resistance, better protection of crystal grains and bonding wires, and high light output power under high current, and is also a promising prospect. LED solid light source. In the application, the packaged product can be assembled on a metal core PCB board with aluminum interlayer to form a power density LED. The PCB board is used as the wiring for connecting the device electrodes, and the aluminum core interlayer can be used as a heat sink. Higher luminous flux and photoelectric conversion efficiency. In addition, the packaged SMD LEDs are small in size and can be flexibly combined to form a variety of illumination sources such as module type, light guide type, concentrating type, and reflective type. The thermal characteristics of power LEDs directly affect the operating temperature, luminous efficiency, wavelength of illumination, and lifetime of LEDs. Therefore, packaging design and manufacturing techniques for power LEDs are particularly important.
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