AOI (Automatic Optical Inspection) is composed of workbench, camera system, electromechanical control and system software. During inspection, the circuit board to be inspected is first placed on the workbench of AOI machine, and the inspection program of the product to be inspected is called out through positioning. The X/Y workbench will send the circuit board under the lens according to the command of the set program. With the assistance of special light source, the lens will capture the image required by AOI system and carry out analytical processing. Then the processor will move the X/Y workbench to the next position to collect and carry out analytical processing on the next image. Through continuous analytical processing on the image, a higher inspection speed can be obtained. AOI image processing in essence is to

digitize the captured images, and then compare them with pre-stored “standards”. After analysis and judgment, if defects are found, their position will be prompted, and image characters will be generated for further confirmation by the operator. Or, the circuit board will be sent to the maintenance platform for maintenance.

AOI used in on-line inspection is mainly for the following two targets:

- -Final quality: monitoring the final state of the product when it goes down the production line. At this time, AOI is usually placed at the end of the production line. In this position, the equipment can obtain a wide range of process control information.

-Process tracking: monitoring the production process by using inspection equipment. It is often required to place the inspection equipment at several positions on the production line to monitor the specific production conditions on-line and provide necessary basis for the adjustment of the production process.

The placement position of AOI can be flexibly arranged according to production requirements, but for its main purposes, three positions are common:

-AOI inspection is arranged after solder paste printing: the AOI inspection is arranged after the solder paste printing, which is a typical arrangement because many defects are caused by poor solder paste printing. Insufficient solder paste may lead to component loss or open circuit.

-AOI inspection is arranged before welding: arrange the inspection before welding and after the patch and plug-in process to inspect defects caused by poor mounting and plug-in.

-AOI inspection is arranged after welding: this is the most common arrangement of AOI, which can inspect defective products in all previous processes to ensure that the final defective products will not be used by customers.