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In the fierce market competition, electronic product PCB manufacturers must ensure the quality of their products. In order to ensure product quality, it is particularly important to monitor the quality of semi-finished or finished products in each production link during the product manufacturing process. Those in the industry know that printed circuit boards assembled and welded are prone to defects, which can be summarized as follows: 1) missing components; 2) component failures; 3) components have installation errors and misalignment; 4) components fail; 5) Poor soldering; 6) Bridging; 7) Insufficient solder; 8) Excessive solder to form solder balls; 9) Formation of solder pinholes (bubbles); 10) Contaminants; 11) Inappropriate pads; 12) Incorrect polarity; 13) pins floating; 14) pins protruding too long; 15) cold solder joints; 16) too much solder; 17) solder voids; 18) blowholes; 19) printed lines Poor internal fillet structure.
1. In order to fulfill the requirements of PCB printed circuit board testing, a variety of testing equipment has been produced. Automatic optical inspection (AOI) systems are usually used to test the inner layer before layering. After layering, the X-ray system monitors the alignment accuracy and small defects. The scanning laser system provides inspection of the pad layer before reflow. method. These systems, combined with the intuitive inspection technology of the production line and the component integrity inspection of the automatic placement of components, all help to ensure the reliability of the final assembly and welding of the board.
However, even if these efforts minimize defects, the final inspection of the assembled printed circuit board is still required, which may be the most important because it is the final unit of product and overall process evaluation.
2. The final inspection of the assembled printed circuit board may be done manually or by an automated system, and the two methods are often used together. "Manual" refers to an operator using optical instruments to visually inspect the board and make a correct judgment about the defect. Automated systems use computer-aided graphic analysis to determine defects. Many people also believe that automated systems include all inspection methods except manual light inspection.
3. X-ray technology provides a method to evaluate solder thickness, distribution, internal voids, cracks, desoldering, and solder balls. Ultrasonics will detect cavities, cracks, and unattached interfaces. Automatic optical inspection evaluates external features, such as bridging, solder melting, and shape. Laser inspection can provide three-dimensional images of external features. Infrared detection compares the thermal signal of the solder joint with a known good solder joint to detect the internal solder joint failure.
It is worth noting that these automatic inspection technologies have found all the defects that cannot be found by the limited inspection of assembled printed PCB boards. Therefore, manual visual inspection methods must be used in conjunction with automatic inspection methods, especially for those few applications. The combination of X-ray inspection and manual optical inspection is the best method for detecting defects in assembled boards.
