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AOI ( Automated Optical Inspection) which is based on the optical principle to detect common defects encountered in welding production. At present, the equipment is a more effective method of industrial automation detection. Using machine vision as the detection standard technology.
AOI technology is very extensive. Generalized AOI equipment is a combination of an optical sensing system, signal processing system and analysis software. Its application level can include space exploration, aviation, satellite telemetry, biomedicine, industrial production quality detection, fingerprint comparison, robot control, multimedia technology, LCD/TFT, transistor and PCB industry.
AOI equipment in the narrow sense refers to the urgent need for industrial use in IC and general electronics industry, mechanical tools/automation machinery, motor/electronics industry, metal and steel industry, food processing/packaging industry, textile and leather industry, automobile industry, building materials, maintenance/monitoring system, etc.
Technical principle of AOI:
It is to use high-speed and accurate visual processing technology to detect various kinds of misfit and welding defects on PCB. Because of non-contact inspection, semi-finished products can be inspected in intermediate engineering.
In the process of automatic detection, the machine scans PCB automatically through the camera, collects images, compares the tested solder joints with the qualified parameters in the database, and checks the defects on PCB through image processing. The defect is displayed/marked by display or automatic sign for repairing by maintenance personnel.
AOI system can mainly detect the following errors: component leakage, polarity error of tantalum capacitor, welding foot positioning error or deflection, pin bending or folding, excessive or insufficient solder, welding joint bridging or virtual welding, etc.
AOI can not only inspect defects that can not be detected by manual visual inspection but also detect components and solder joints that can not be touched by needle bed in online testing, so as to improve defect coverage. AOI can also collect the working quality of each process and the types of defects in the production process, and feedback them back to process controllers for analysis and management, so as to reduce the PCB waste rate.
Application of AOI after different production steps on the production line:
1. Mainly used to detect the printing quality of solder paste printing press, whether there is any solder paste offset, missed print, more tin, less tin and other bad.
2. After mounting machine, this kind of inspection is called pre-weld inspection, which is used to detect the improper mounting of components before welding, such as offset, reverse, missing parts, anti-whitening, lateral and other defects of electronic components.
3. Used after the reflow furnace, this kind of inspection is called post-weld inspection, which detects the defective, offset, missing parts of electronic components after the reflow furnace, reverse re-inspection and solder joints with more tin, less tin, and empty soldering.
4. The main function of the application in the PCB industry is to inspect the defects of PCB (such as short circuit, open circuit, etc.) by means of optical scanning after PCB fabrication (etching).
The summary is as follows:
1. Solder paste printing: presence or absence, offset, less tin, more tin, circuit breaking, tin linking, pollution, etc.
2. Part defects: missing parts, offset, skew, stele, side-up, upset parts, wrong parts, OCV, damage, capacitance polarity reversal, etc.
3. Defects of solder joints after wave soldering and furnace soldering. Such as more tin, less tin, virtual soldering, continuous tin, copper foil pollution, etc.