Research On The Precision Inspection System Of Drillings On The Bare PCB

The topic is derived from the project of "Manufacturing Process Technology of the Circuit with High Speed Interconnection and Electromagnetic Compatibility",which belongs to the National Defense Basic Research during the Twelfth Five-year Plan Period.It does a research on the precision inspection method of drillings on the bare PCB.The existing precision inspection equipment of drillings on the bare PCB uses camera to collect the image to be measured and template image.In this method,the quality of images is susceptible to light intensity and the shooting angle of the camera,which affects the detection accuracy.Therefore,the method that directly compares the scanned image with the design data to improve the inspection precision of drillings on the bare PCB is worth studying.In order to overcome the image deformation and the low quality,a drillings detection method based on the design data and the scanned image is proposed.It analyzes the EDA design files to obtain the design data,uses the scanner to generate the high quality image to be measured,and the image data is directly compared with the design data,which effectively improves the inspection accuracy.At the same time,this paper presents a distance positioning method with low complexity.In this method,the first step is to manually mark all the mounting holes on the image and select two mounting holes located at a diagonal position as image reference points.Then,the system looks for the corresponding points in the EDA design files and uses them as design reference points.Finally,the system locates the drilling areas on the scanned image based on the positional relationships between the design reference points and a drilling in the design files.In addition,by combining the image reference point and the design reference point,this paper presents a hole position deviation calculation method,which calculates the distance between the image reference point and the drilling hole on the image and the distance between the design reference point and the drilling hole in the EDA design file.After the units are unified,the difference is used to characterize the hole deviation.This paper designs and implements a precision inspection system of drillings on the bare PCB based on the above method.The main modules of the system include EDA design files analysis module,parameters configuration module,scanned images preprocessing module,drillings positioning module,drilling parameters calculation module,deviation calculation module and reports generation module.The EDA design files analysis module provides the design data to the drillings positioning module and the deviation calculation module;the scanned images preprocessing module includes grayscale sub-module,brightness enhancement sub-module,tilt correction sub-module,cutting sub-module;the drillings positioning module uses the distance positioning method to quickly locate the image drilling areas;the drilling parameters calculation module includes drilling images preprocessing submodule,edge classification sub-module and parameters fitting sub-module;the deviation calculation module calculates aperture deviation and hole positions deviation according to the design data and the image data.Finally,the function and performance of the system are tested.The test results show that the deviation of the system is less than 5% when inspecting the drillings on the bare PCB of small and medium-sized,which meet the requirements of the mission statement.System's function and performance has reached the design goals.