LED is a light-emitting device made of semiconductor ma […]
LED is a light-emitting device made of semiconductor materials which can emit light when electrified. The material uses III-V chemical elements (such as GaP and GaAs). The principle of light-emitting is to convert electric energy into light, that is, to apply current to compound semiconductors. Through the combination of electrons and holes, excess energy will be in the form of light. Release, achieve the effect of luminescence, belongs to cold luminescence.
The biggest characteristics of LED are: no idling time, fast reaction speed (about 10 ^ - 9 seconds), small size, low power consumption, low pollution, suitable for mass production, high reliability, easy to make minimal or array components to meet the needs of application, wide application range, such as automobile, communication industry, computer, traffic number. Backlight, LED screen, etc. for logo lamp, LCD panel.
The LED industry can be divided into three categories: upper, middle and lower reaches. The upstream is single chip and its extension, the middle is LED chip processing, and the downstream is package testing and application. Among them, the upstream and middle reaches have high technology content and high capital input density. From upstream to downstream, there is a considerable gap in the appearance of products. LED luminous color and brightness are determined by the epitaxy material, and the epitaxy accounts for about 70% of the cost of LED manufacturing, which is very important to the LED industry.
The upstream is made of Lei chips, which are about a circle six to eight centimeters wide in diameter and quite thin in thickness, just like a planar metal. The common epitaxy methods are liquid phase epitaxy (LPE), vapor phase epitaxy (VPE) and metal organic chemical vapor deposition (MOCVD), among which VPE and LPE technologies are quite mature and can be used to grow general brightness LED. The MOCVD method must be used to grow high brightness LED. The upstream epitaxy process sequence is: single chip (III-V family substrate), structure design, crystallization growth, material characteristics/thickness measurement.
Midstream manufacturers design device structure and process according to the performance requirement of LED. They diffuse the epitaxy sheet, then coat metal, then photolithography, heat treatment, forming metal electrode, and then grind and polish the substrate to cut. According to the size of the chip, it can be cut into 20,000 to 40,000 chips. These chips, which look like sand on the beach, are usually fixed with special tape and sent to downstream manufacturers for packaging. The process sequence of midstream chip is: Lei chip, metal film evaporation, mask, etching, heat treatment, cutting, cracking, measurement.
Downstream includes packaging test and application of LED chips. LED packaging refers to connecting external leads to the electrodes of LED chips to form LED devices. Packaging plays a role in protecting the LED chips and improving the efficiency of light extraction. The downstream manufacturers encapsulation processing sequence is: chip, crystallization, adhesion, stringing, resin encapsulation, long baking, tin plating, foot shearing, testing.