AOI, named as automated optical inspection machine includes multi-light source lighting, high-speed digital cameras, high-speed linear motors, precision mechanical transmission structures, and graphics processing software. During the inspection, the AOI automatically scans the PCB through the camera to capture and image the components or features on the PCB (including the status of printed solder paste, surface mount components, solder joint morphology and defects, etc.) through software processing and pass the database. The parameters are comprehensively compared to determine whether the components and their characteristics are qualified, and then the test conclusions are drawn, such as problems, missing components, bridges or solder joint quality.
The working principle of automated optical inspection machine is the same as that of the vision system used in the pick and place machine and the PCB printing machine. Generally, two methods of Design Rule Checking (DRC) and pattern recognition are adopted. The DRC method checks the circuit pattern according to some given rules (such as all wires should use solder joints as endpoints, all lead widths should be no less than 0.127mm, and the spacing between all leads should be no less than 0.102mm, etc.) This methods can guarantee the correctness of the circuit being tested from the algorithm, and also has the characteristics of easy manufacturing, easy algorithm logic, fast processing speed, small program editing amount, small data occupancy, etc. For this reason, this testing method is often used.
The pattern recognition method compares the stored digitized image with the actual image. During the inspection, the comparison is performed according to an intact printed circuit board or an inspection file established according to the model, or according to the inspection program prepared in the computer-assisted design. The accuracy depends on the split rate and the inspection procedures used. It is generally the same as the electronic test system, but the amount of data collected is large and the real-time data processing requirements are high. The pattern recognition method replaces the established design principles in DRC with actual design data, so it has obvious advantages.
Automated optical inspection machine has functions such as component inspection, PCB light board inspection, and post-weld assembly inspection. The general procedure of automated optical inspection machine system for component inspection is: automatic counting of printed circuit boards with installed components and start inspection; check the leaded side of printed circuit boards to ensure proper arrangement and bending of lead ends; check printed Whether there are missing components, wrong components, damaged components, improper component mounting direction, etc. on the front side of the circuit board; check the type, direction, and position of the IC and discrete components connected; check the components marked on the IC components Printing quality inspection, etc. Once the AOI finds a defective component, the system sends a signal to the operator or triggers the actuator to automatically remove the defective component. The system analyzes defects, provides defect types and frequencies to the host computer, and makes necessary adjustments to the manufacturing process. The efficiency and reliability of automated optical inspection machine depends on the integrity of the software used. AO also has the advantages of convenient use, easy adjustment, and no need to program vision system algorithms.
The above is the automated optical inspection machine (AOI), which uses high-speed and high-precision visual processing technology to automatically detect various mounting errors and soldering defects on the PCB. The PCB can range from fine-pitch high-density boards to low-density large-size boards, and can provide online inspection solutions to improve production efficiency and welding quality.
