barcode scanner input asp.net Post-reflow AOI systems of solder joints have in Software

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Post-reflow AOI systems of solder joints have
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They eliminate visual inspection by automating solder joint defect detection, thereby also reducing unnecessary rework due to false reject calls. They reduce rework analysis time by pinpointing defects to the exact solder joint. They afford real-time process control of all three process steps paste printing, component placement, and solder reflow to lower defect rates and rework costs. They can be used during the lead-free conversion with minimal program tuning. They are a low-cost option for reasonable test coverage.
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Post-reflow AOI systems have the following limitations:
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Test throughput is not always fast enough to allow inspection of all solder joints within the manufacturing cycle time for the printed circuit assembly. A significant learning curve is required to become expert at developing solder joint tests with both low false accept and false reject rates. The ability to inspect hidden (or invisible) joints is not possible with post-reflow AOI.
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Transmission X-Ray Systems 53.10.2.1 Operating Principles. Transmission x-ray systems radiate x-rays from a point source perpendicularly through the printed circuit assembly being inspected, as depicted in Fig. 53.11. An x-ray detector picks up a varying amount of x-rays depending on the thickness of metals that the x-rays are penetrating and converts the x-rays to light photons for a camera to create a grayscale image. The x-ray source is filtered so that metals of only a certain density range lead, tin, gold, and silver will absorb the x-rays. The copper leads and frames of components sitting on top of solder joints do not absorb the x-rays and are therefore practically invisible to the x-ray detector. Thus, x-ray systems can easily see the entire solder joint, no matter what component material may be on top of the joint blocking its optical or visual access. In other words, x-ray is the only automated inspection method equipped to inspect hidden joints such as those found in a BGA or CSP. The resulting x-ray image will be darker wherever the lead or tin solder or lead-free solder is thicker in the solder joint. The image processing capability of the system then searches for features, such as the heel and toe fillets, the sides of the solder joint, and even voids internal to the joint based on grayscale readings of the solder joint x-ray image.The system then uses predetermined decision rules to compare
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X-ray detector Camera Solder joint and component placement measurement Heel Center Toe Heel
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FIGURE 53.11 Schematic of transmission x-ray automated inspection system for solder joint defect detection.The x-ray detector converts a varying amount of x-rays to light, based on how much various parts of the solder joint absorb. The camera converts the light photons to an image, which is then processed to find solder joint features and flag defects accordingly.
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the grayscale readings to acceptance criteria to accept or reject a solder joint automatically. For example, the system might compare the relative grayscale reading for the heel fillet region, the center of the solder joint, and the toe fillet region. The acceptance criteria might state that the heel fillet reading should be twice that of the center and that the toe fillet reading should be 50 percent higher than that of the center. If the actual readings do not meet these criteria, then the solder joint is reported as being defective. The bottom of Fig. 53.11 shows an x-ray image of a gull-wing solder joint that shows the center of the joint as much darker than the heel fillet region. This solder joint is clearly defective, as the heel fillet region should always be darker and have a higher grayscale reading than the center of the joint, where the solder is thinnest for mechanically good solder joints. (The system s image processing capability is able to detect much more subtle changes in grayscales than can the human eye, allowing very accurate relative readings from one solder joint to the next.) 53.10.2.2 Application. Transmission x-ray technology works well for single-sided surfacemount assemblies. These automated inspection systems accurately detect solder joint defects such as opens, insufficient solder, excess solder, bridges, misalignment between pin and pad, and voids for most surface-mount solder joint types, including J-leads, gull-wings, passive chips, and small-outline transistors in hidden and nonhidden joints alike. These systems also detect missing components and reversed tantalum capacitors. Based on trends in grayscale reading, these systems also can accurately detect process drifts through real-time process control charting. For double-sided assemblies, however, the transmission x-ray images of solder joints on the top side will overlap with the images of solder joints on the bottom side. The x-rays are absorbed by any solder in their path through the printed circuit assembly from the source to the detector. These overlapping images make accurate solder joint measurement impossible. Transmission x-ray imaging also cannot easily distinguish between the top, bottom, and barrel of PTH solder joints or the bottom of BGA solder joints. So transmission x-ray systems cannot be used for accurate measurement of and defect detection in solder joints on doublesided assemblies or for PTH and BGA solder joints.
Cross-Sectional X-Ray Systems 53.10.3.1 Operating Principles. Cross-sectional x-ray systems radiate x-rays at an acute angle from vertical through the printed circuit assembly being inspected.As Fig. 53.12 indicates, images from all around the particular view being inspected are added together or integrated essentially to create an x-ray focal plane in space. This focal plane creates a cross-sectional image, approximately 0.2 to 0.4 mm thick, right at the focal plane, by blurring everything above and below the focal plane into the background, or noise, of the image. By moving the top side of an assembly into the focal plane, cross-sectional images of only the solder joints on the top side are created. By moving the bottom side of an assembly into the focal plane, cross-sectional images of only the solder joints on the bottom side are created. Separate images of top and bottom sides are always created, preventing any image overlap from the two sides. 53.10.3.2 Application. Cross-sectional x-ray automated inspection systems work well for all types of printed circuit assemblies, including single-sided and double-sided, surface-mount, through-hole, and mixed-technology assemblies. These systems accurately detect the same solder joint and component defects as do transmission x-ray systems, but, in addition, the cross-sectional x-ray systems accurately detect insufficient solder conditions for BGA and pin-through-hole solder joints. Some cross-sectional x-ray automated inspection systems go beyond just grayscale readings of specific solder joint features. By carefully calibrating grayscale readings to actual solder thickness, it is possible to generate real-world measurements, in physical units rather than grayscale numbers, of fillet heights, solder and void volume, and average solder thickness for
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