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pically drilled hole plate than undrilled plate, when AOI detection more complicated. Because after the board drilled holes have a greater impact on the AOI inspection. When the partial hole occurs, breaking the hole, the ring width smaller than the minimum line width of the hole, the hole size and data size is different, the position of the hole with the information recording position has minor deviations, etc., at the location of the hole will report a large number of defects. This paper analyzes the causes of the theoretical principles of the above situation, and by optimizing the detection parameters, to ensure detection reliability while reducing the number of false defects.
AOI (Automated Optical Inspection)
Detectors are widely used in various PCB manufacturers, mainly used to detect surface defects PCB semi-finished products, and process control, to achieve lower costs, quality assurance purposes. Because of different manufacturers of the PCB board, the problems encountered during the actual testing is also different, so the actual detection process needs to be appropriately adjusted parameters, to minimize leakage test and false points, ensure reliability of the detection, the detection time saving.
PCB effects on AOI face detection
The reason is caused by the PCB faces false defects and defect types
Typically, the plate than the hole drilled undrilled plate, when AOI detection more complicated. Because after the board drilling, hole detection have a greater impact on the AOI. In this paper, the company SK-75 model Orbotech AOI inspection machine for analysis, both from the theoretical and experimental study of the effects of PCB face of test results, and by optimizing the detection parameters, to ensure detection reliability while reducing the number of false defects.
SK-75 using direct light and scattered light, is irradiated to the measured surface of the plate, then the plate surface reflected light into an analog electrical signal, converted to gray-scale digital signal, and finally processed into a binary (0,1) of the black and white patterns . The resulting digital data is compared with data in the motherboard logic processor, depending on the parameters of the report set and display defects.
For the wells of the plate surface and the corresponding grommet, during scan testing, after which the reflected light is received, the binary (black and white) obtained by processing the digital data, the hole is processed into black, the grommet were processed into white.
This digital information includes feature type and the grommet hole, the size of the position, shape, hole, aperture width of the rings and other relevant information, in the same manner, information is also recorded in the motherboard information corresponding hole and the grommet. When comparing the logical processor, that is, for such information to be processed.
In the scanning process and PCB board faces the grommet in the process, because of the focus together, threshold gray level and other parameters, the scanned image size and position will have some differences with the plate surface actual situation; in addition, the hole edge of the copper surface (grommet) of the reflected light will define the boundaries of the location of the hole and grommet some impact, which will lead to the resulting hole and grommet size, there are differences with the board position of the actual situation. If this difference value exceeds the allowed tolerance value set, and so it will not match the size of the false report defects.
In addition, the board and the motherboard compare actual data will be there are some differences. Engineering CAM data and information can not be directly used as a mother board, to be compared to the scanned board data, it first needs to be processed, the process and the time of detection of the PCB processing scanned image similar to the way. Motherboard porous layer information is information used borehole data, the pore size is recorded when they drill size, and in the AOI scan, PCB board face after Shen copper electroplating, its size and the presence of certain dimensions of the recorded data difference, which led to the actual size of the face of the PCB motherboard comparative information recorded size is different, so the false reporting of defects will appear.
Shihai often have detected cases:
1. aperture ring width is less than the minimum line width or partial hole, the hole will be reported at the ring width is not enough.
2. have broken hole, the hole will open the report, insufficient width, lack of spacing and other defects.
3. If there are scratches detection platform, often report such defects residual copper in the larger hole.
Parameter optimization method
To alleviate the above drawbacks false, the method may be used to cover the hole. According to the actual situation of the plate surface, the selected pattern size in the range of 0 ~ 100mil.
Most manufacturers during AOI inspection, in order to reduce the possibility of leakage measured, this will delete the file, then the detection plate surface, the design value (line / space) is smaller than the set parameter values (the minimum line width / spacing) of the graphics will still report defects, which is the real false defects.
Acceptance criteria for different manufacturers partial hole, broken hole is different, according to the actual acceptance criteria, select the appropriate shape and size to cover up the graphics, you can greatly reduce the hole caused by the false defects. However, there are imperfections, in the following cases, it may cause some other problems:
1. Assume the hole size is 30mil, 40mil select the size of the circular on the holes covered up. When no partial hole, the hole may be completely filled; If there is partial hole, the graphic will not fully cover up the filling hole, which is because the filling of the hole, the filled hole position is position information recorded on the mother board, rather than the actual hole board position. At this point, will be reported as "open, less width, lack of spacing, hole broken or residual copper" and other false defects. When detecting board and motherboard data alignment is not precise enough, there will be a similar situation.
2. When the panel hole size difference between the larger, more difficult to find a suitable filler size: If the filling hole slightly larger than the maximum size that can be all the holes are filled, but the larger will be the smaller surrounding areas are filled with holes, such small holes around the defect will leak test; if size is less than the maximum filling hole size is larger than the size of the hole will be filled, which would report "insufficient spacing" and other false defects.
When processing data generated motherboard, will produce a material, this material recorded some data in graphical features motherboard design does not meet the rules, the vast majority are insufficient width, spacing less than such defects. When CAM engineering data in graphics design width / spacing is less than the set minimum line width / spacing, in dealing with the motherboard generates comparative information, the software will think it is defective, it will be the location of the defect type and other information recorded to generate a masked file.
If you leave this cover up file, at the time of the detection plate surface, the same defect at the same position with the cover up these files will not be recorded in the report. To minimize false due to the hole caused by the defect, Also used to retain documents and methods for masking motherboard holes filled.
Experimental verification
Selection line and the copper surface mixing pattern, design flaws in various forms open, short, residual copper, holes broken, gaps, or protrusions of different sizes. Then using different methods to analyze its impact on test results.
Effect of hole concealment of test results, when the filling ratio of the hole does not fill the hole, the number of the measured pseudo defect greatly reduced, and the same leak test, the leakage test defect is (a pore size of less than 1.0mil minute defects break, a residual copper), are within the scope of the standard requirements may receive.
Motherboard conceal the impact of information on the test results, test results and remove the motherboard when compared to conceal information, keep this motherboard conceal information, and will not cause leakage test, and that will reduce the number of false defects. The results are shown results consistent with the theoretical analysis to verify the theoretical analysis.
In conclusion
AOI (Automated Optical Inspection)
Detectors are widely used in various PCB manufacturers, mainly used to detect surface defects PCB semi-finished products, and process control, to achieve lower costs, quality assurance purposes. Because of different manufacturers of the PCB board, the problems encountered during the actual testing is also different, so the actual detection process needs to be appropriately adjusted parameters, to minimize leakage test and false points, ensure reliability of the detection, the detection time saving.
PCB effects on AOI face detection
The reason is caused by the PCB faces false defects and defect types
Typically, the plate than the hole drilled undrilled plate, when AOI detection more complicated. Because after the board drilling, hole detection have a greater impact on the AOI. In this paper, the company SK-75 model Orbotech AOI inspection machine for analysis, both from the theoretical and experimental study of the effects of PCB face of test results, and by optimizing the detection parameters, to ensure detection reliability while reducing the number of false defects.
SK-75 using direct light and scattered light, is irradiated to the measured surface of the plate, then the plate surface reflected light into an analog electrical signal, converted to gray-scale digital signal, and finally processed into a binary (0,1) of the black and white patterns . The resulting digital data is compared with data in the motherboard logic processor, depending on the parameters of the report set and display defects.
For the wells of the plate surface and the corresponding grommet, during scan testing, after which the reflected light is received, the binary (black and white) obtained by processing the digital data, the hole is processed into black, the grommet were processed into white.
This digital information includes feature type and the grommet hole, the size of the position, shape, hole, aperture width of the rings and other relevant information, in the same manner, information is also recorded in the motherboard information corresponding hole and the grommet. When comparing the logical processor, that is, for such information to be processed.
In the scanning process and PCB board faces the grommet in the process, because of the focus together, threshold gray level and other parameters, the scanned image size and position will have some differences with the plate surface actual situation; in addition, the hole edge of the copper surface (grommet) of the reflected light will define the boundaries of the location of the hole and grommet some impact, which will lead to the resulting hole and grommet size, there are differences with the board position of the actual situation. If this difference value exceeds the allowed tolerance value set, and so it will not match the size of the false report defects.
In addition, the board and the motherboard compare actual data will be there are some differences. Engineering CAM data and information can not be directly used as a mother board, to be compared to the scanned board data, it first needs to be processed, the process and the time of detection of the PCB processing scanned image similar to the way. Motherboard porous layer information is information used borehole data, the pore size is recorded when they drill size, and in the AOI scan, PCB board face after Shen copper electroplating, its size and the presence of certain dimensions of the recorded data difference, which led to the actual size of the face of the PCB motherboard comparative information recorded size is different, so the false reporting of defects will appear.
Shihai often have detected cases:
1. aperture ring width is less than the minimum line width or partial hole, the hole will be reported at the ring width is not enough.
2. have broken hole, the hole will open the report, insufficient width, lack of spacing and other defects.
3. If there are scratches detection platform, often report such defects residual copper in the larger hole.
Parameter optimization method
To alleviate the above drawbacks false, the method may be used to cover the hole. According to the actual situation of the plate surface, the selected pattern size in the range of 0 ~ 100mil.
Most manufacturers during AOI inspection, in order to reduce the possibility of leakage measured, this will delete the file, then the detection plate surface, the design value (line / space) is smaller than the set parameter values (the minimum line width / spacing) of the graphics will still report defects, which is the real false defects.
Acceptance criteria for different manufacturers partial hole, broken hole is different, according to the actual acceptance criteria, select the appropriate shape and size to cover up the graphics, you can greatly reduce the hole caused by the false defects. However, there are imperfections, in the following cases, it may cause some other problems:
1. Assume the hole size is 30mil, 40mil select the size of the circular on the holes covered up. When no partial hole, the hole may be completely filled; If there is partial hole, the graphic will not fully cover up the filling hole, which is because the filling of the hole, the filled hole position is position information recorded on the mother board, rather than the actual hole board position. At this point, will be reported as "open, less width, lack of spacing, hole broken or residual copper" and other false defects. When detecting board and motherboard data alignment is not precise enough, there will be a similar situation.
2. When the panel hole size difference between the larger, more difficult to find a suitable filler size: If the filling hole slightly larger than the maximum size that can be all the holes are filled, but the larger will be the smaller surrounding areas are filled with holes, such small holes around the defect will leak test; if size is less than the maximum filling hole size is larger than the size of the hole will be filled, which would report "insufficient spacing" and other false defects.
When processing data generated motherboard, will produce a material, this material recorded some data in graphical features motherboard design does not meet the rules, the vast majority are insufficient width, spacing less than such defects. When CAM engineering data in graphics design width / spacing is less than the set minimum line width / spacing, in dealing with the motherboard generates comparative information, the software will think it is defective, it will be the location of the defect type and other information recorded to generate a masked file.
If you leave this cover up file, at the time of the detection plate surface, the same defect at the same position with the cover up these files will not be recorded in the report. To minimize false due to the hole caused by the defect, Also used to retain documents and methods for masking motherboard holes filled.
Experimental verification
Selection line and the copper surface mixing pattern, design flaws in various forms open, short, residual copper, holes broken, gaps, or protrusions of different sizes. Then using different methods to analyze its impact on test results.
Effect of hole concealment of test results, when the filling ratio of the hole does not fill the hole, the number of the measured pseudo defect greatly reduced, and the same leak test, the leakage test defect is (a pore size of less than 1.0mil minute defects break, a residual copper), are within the scope of the standard requirements may receive.
Motherboard conceal the impact of information on the test results, test results and remove the motherboard when compared to conceal information, keep this motherboard conceal information, and will not cause leakage test, and that will reduce the number of false defects. The results are shown results consistent with the theoretical analysis to verify the theoretical analysis.
In conclusion
After the plate surface drilling, hole detection have a greater impact on the AOI, AOI is detected in more complex than some undrilled plates, often report many false defects. To reduce such holes caused by false defects, according to the actual acceptance criteria, to choose the right shape and size to cover up the graphics, for filling holes, while preserving hide files generated motherboard information, which will be produced. With this method, can greatly reduce the false defects caused by the hole, and will not cause leakage test.
Nanjing given surplus electronic Technology Co., Ltd.