During the etching process, the etching method, the etching rate, the types and pH value of the etchants, or other factors directly affect the quality of the circuits. If these factors are not properly controlled, defects such as short circuits, open circuits, circuit width defects, and copper residues will be caused. Therefore, the boards after etching need to be carefully inspected. Automatic Optical Inspection (AOI) is a common method that can effectively control the scrap rate and improve product quality.
In the AOI process, CAM/CAD data of PCB are often used as references for image comparison. The CAM/CAD data is firstly converted into image data that can be recognized and stored by the AOI machine. Various light sources are filtered by optical lenses and then irradiated on the PCBs to be inspected. The lights are then reflected through various filter lenses to the receiver that generates a corresponding electrical signal according to the intensity of the light signal.
Through its image processing card, the AOI machine converts the electrical signal obtained by the Charge Coupled Device (CCD) camera scanning the board surface into a computer-identifiable binary signal, thus obtaining a binary image of PCB. The binary image will be compared with the board image data converted by the CAM stored in the AOI machine, defects will be reported at the positions of discrepancies. Finally, the inspector confirms the discrepancies to complete the entire inspection process. Automatic optical inspection can detect defects early, so as to effectively prevent defective boards from moving onto the next process, thus reducing material waste and costs.
