A Study On Optical Automated Modification Of Copper Residues On PCB

Copper residues make one of the main defects on Printed Circuit Board (PCB). At present, the modification for copper residues is mainly conducted manually with a fixed knife. As the PCB pattern turns to demand higher accuracy and density and stricter Line/Space (L/S), more and more copper residues can’t be modified with the fixed knife. Thus, a study on optical automated modification of copper residues has an important theoretical significance and economic value in light of the production demand for high-quality PCB products.With regards to the current problem of using the fixed knife to modify copper residues, the thesis investigates how to combine the Automatic Optic Inspection (AOI) technology and laser technology to develop a new method of modifying copper residues. The eight-grayscale digital image is absorbed through the image-taking system, Charge Coupled Device (CCD) and Analog to Digital Converter (ADC). In the next stage of image processing, as the image surface only features copper and base material, the gray image gets linearized by dynamic threshold binarization algorithm, then median filter is used for image denoising, Sobel operator to extract the outline and finally more precise image information comes out. The thesis designs a mark hole, which can be used for the alignment of the image with the CAM digital image. The offset of the mark hole can be calculated based on the Hough transform and then offset correction can be made on the image. The thesis draws out a mark desktop to avoid malposition. Information about copper residues can be obtained through the human-computer interaction (HIC) to locate the residual copper ablation area. The thesis makes out a residual copper laser ablation system. The thesis selects the532nm green light laser wave band according to the complementary color theory. The thesis designs a mobile control system and laser ablation system. To ensure the proper work environment in residual copper modification, the thesis formulates the airflow system, temperature control system and humidity control system. The thesis taps into the shortcomings of using the Gaussian beam mode and flat beam mode to modify copper residues and puts forward an optimization scheme. The thesis tests and verifies the effects of using the optimization scheme to modify copper residues. All results show that optical automated modification of copper residues on PCB has higher reliability.