Pcb Gerber File Of Application Research In Optical Detection

The high density, high complexity and high-performance development trend inPrinted Circuit Board (PCB) industry continue to challenge its quality testing,Automatic Optical Inspection (AOI) has become the first choice to replace thetraditional artificial visual for its advantages of high speed, high accuracy, automationand no damage.In PCB production, for confidentiality and other reasons, the PCB designer isgenerally only provide Gerber file to the manufacturing sector. Gerber file describes thebasic physical appearance features of the circuit board like coordinates, shape, size ofthe wires, pads and so on in the PCB but doesn’t contain any information of electricalproperties and electronic components parameters. As the target of PCB opticalinspection is detected the appearance defect information of the board, Gerber file playedan important role in the process. For the above, the following researches have beendone.1. Firstly, based on analyzing the syntax and data structure of Gerber file in thisdissertation, the entities and other relevant information was extracted by the top-downapproach with regular expression and after data were saved by a Map embedded list.2. The graphic described by Gerber file was plotted by Graphics Device Interface(GDI+), and the drawing errors caused by mismatching of pixel coordinates were solvedby Corrosion Expansion Algorithm.3. The standard color of each layer was extracted from the scanned images ofstandard PCBs which are processed by Flat-correction, chromatic aberration-correctionand image enhancement.4. With the help of Alpha Component, standard image was composed aftermatching each standard color to standard graphic in corresponding layer.5. In order to make inspection more targeted in different regions and materials ofPCB, a method for setting defect threshold by layer was proposed based on analysis ofcommon defects. The experimental results show that the method worked accurately and quickly.To our knowledge, the method of setting standard image in Automatic OpticalInspection of PCB by combining the raster graphics parsed from Gerber file and colorinformation extracted from the scanned images of standard PCBs haven’t been reportedin domestic literatures. This method has been used in industrial inspection and usersreflect well.