LED is a light-emitting element made of a semiconductor material that emits light when energized. The material uses III-V chemical elements (such as gallium phosphide (GaP), gallium arsenide (GaAs), etc.), and the principle of light is to convert electrical energy into light. That is, a current is applied to a compound semiconductor, and a combination of electrons and a hole is transmitted, and excess energy is released in the form of light to achieve a luminescent effect, which is a cold luminescence.
The biggest feature of LED is that it does not need idling time, fast reaction speed (about 10^-9 seconds), small size, low power consumption, low pollution, suitable for mass production, high reliability, easy to match. Applications need to be made into very small or array-type components, such as automotive, communications industry, computers, traffic signals, backlights for LCD panels, LED screens, etc.
The LED industry can be divided into three categories: upper, middle and lower. The upstream is a single chip and its extension, the middle reaches for LED chip processing, and the downstream for package testing and application. Among them, the upstream and middle reaches have higher technical content and the capital input density is large. From the upstream to the downstream, the product is quite different in appearance. LED color and brightness are determined by epitaxial materials, and epitaxy accounts for about 70% of LED manufacturing costs, which is extremely important for the LED industry.
The upstream is formed by the epichip, which is roughly a circle with a diameter of six to eight centimeters wide and a relatively thin thickness, like a flat metal. Common epitaxial methods include liquid phase epitaxy (LPE), vapor phase epitaxy (VPE), and metal organic chemical vapor deposition (MOCVD). VPE and LPE technologies are quite mature and can be used to grow general brightness LEDs. The growth of high-brightness LEDs must use the MOCVD method. The upstream epitaxial process sequence is: single chip (III-V substrate), structural design, crystal growth, material properties/thickness measurement.
The midstream manufacturers carry out the device structure and process design according to the performance requirements of the LED, diffuse through the epitaxial wafer, and then metallize the film, then perform photolithography, heat treatment, and form a metal electrode, and then the substrate is polished and polished to be cut. According to the size of the chip, it can be cut into 20,000 to 40,000 chips. These chips look like sand on the beach and are usually fixed with special tape before being sent to downstream manufacturers for packaging. The process sequence of the mid-stream chip is: epitaxial chip, metal film evaporation, photomask, etching, heat treatment, cutting, cracking, measurement.
Downstream includes package testing and application of LED chips. The LED package refers to connecting an external lead to an electrode of the LED chip to form an LED device, and the package functions to protect the LED chip and improve light extraction efficiency. The downstream manufacturers package processing sequence: chip, die bonding, bonding, wire bonding, resin packaging, long baking, tin plating, shearing, testing.
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