Jul 10, 2023 
The AOI system includes a variety of lighting sources, high-speed digital cameras, high-speed linear motors, precision mechanical transmission structures, and image processing software. During the test, AOI equipment automatically scans through the camera and captures images of the PCB, components on the PCB, or special components (including the state of printed solder paste, SMD components, solder joint shapes, and defects, etc.), and checks the qualified parameters through processing and database software. Compare and comprehensively judge whether the components and characteristics are qualified, and then test the conclusions, such as missing components, bridging, or solder joint quality problems.
AOI works in the same way as the vision systems used in SPI and printing presses in SMT processing, usually using design rule checking (DRC) and pattern recognition. The DRC method checks the circuit pattern against some given rules (all lines should end at solder joints, all leads should be at least 0.127 mm wide, all leads should be at least 0.102 mm apart, etc.). This method can guarantee the correctness of the circuit to be tested from the algorithm and has the characteristics of simple production, simple algorithm logic, fast processing speed, a small amount of program editing, and small space occupied by data, so it is adopted by many people. However, the ability of this method to determine the boundary is poor.
The pattern recognition method compares the stored digital image with the actual image. The inspection is carried out according to the complete printed circuit board, the inspection file established by the model, or the program compiled in the computer-aided design. Its accuracy depends on the licensing rate and inspection procedures adopted, generally the same as the electronic test system, but the amount of data collected is large, and the requirements for real-time data processing are relatively high. The pattern recognition approach has the distinct advantage of utilizing actual design data instead of established design principles in DRC.
AOl has functions such as component detection, PCB board detection, and welding component detection. The general procedure of the AOI inspection system for the detection of SMT processing parts is to automatically count the printed circuit boards with installed components and start inspection; check the lead side of the printed circuit board to ensure that the lead ends are aligned and bent correctly; check for defects Parts, wrong parts, damaged parts, check the type, orientation, and position of installed ICs and discrete devices, and check the quality of mark printing on IC devices. If AOI finds a defective part, the system will send a signal to the operator, or trigger a handler that automatically removes the bad part from the machine. The system analyzes the defects, provides the type and frequency of defects to the host computer, and makes necessary adjustments to the manufacturing process. The efficiency and reliability of AOI inspection depend on the integrity of the software used. AO also has the advantage of being easy to use, easy to tune, and does not require programming algorithms for the visualization system.
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