Research On The Method Of Removing And Detecting The Surface Pads Of The Through Holes

There will be some pads which are not connected by any lines in external layers in PCB(Printed Circuits Board)designs.They may bring the risk of being broken down in the long term power operation which may cause unstable performance.Therefore,these pads should be removed to ensure product quality and enhance competitiveness.Based on the above,it is necessary to design the right way to remove those unconnected pads.At present,backdrilling and buried vias are two commonly used methods.But they all need to add additional process to the original production process.Not only the cost increase,but also the corresponding quality risk increase.This research is about etching those unconnected pads in original process.The main working principle of this method is as follows.Firstly before etching,those through holes should be plugged with resin ink in case the copper in the through hole wall etched by chemical which may cause layer connection exception.Then using AOI(automatic optical detector)combined with image processing(image sharpening,image binarization,image segmentation,edge detection,etc.)method identifying those plugging holes if their pads need to be removed.Also using AOI based on gray threshold detection checking if the holes are fully filled.Then etching those pads in the external layers and checking whether the pads are removed completely with AOI equipments.