Printed circuit board inspection method
Printed circuit boards, also known as printed circuit boards, are providers of electrical connections for electronic components. In order to meet the requirements of printed circuit board testing, a variety of testing equipment has been produced.
Automated Optical Inspection (AOI) systems are typically used for testing inner layers before layering; after layering, X-ray systems monitor alignment accuracy and small defects; scanning laser systems provide inspection of pad layers prior to reflow method. These systems, combined with line-intuitive inspection technology and component integrity inspection for automated component placement, help ensure final assembled and soldered board reliability.
However, even when defects are minimized, final inspection of the assembled printed circuit board is still required. Final inspection of assembled printed circuit boards may be done by manual methods or by automated systems, and often a combination of both is used.
“Manual inspection” means that an operator uses optical instruments to inspect the board by vision and make correct judgments about defects. Automated systems, which use computer-aided pattern analysis to identify defects, are also considered by many to include all inspection methods except manual light inspection.
Inspection by X-ray technology provides a method for evaluating solder thickness, distribution, internal voids, cracks, desoldering and presence of solder balls. Ultrasonics will detect voids, cracks and unbonded joints. Automated optical inspection evaluates external features such as bridging, solder volume and shape. Laser inspection can provide a three-dimensional image of external features. Infrared inspection detects internal solder joint failures by comparing the thermal signature of a solder joint with a known good solder joint.
Manual visual inspection methods must be used in conjunction with automatic inspection methods, especially for those small number of applications. SMT people have found that these automatic inspection techniques can detect all defects that cannot be found by the limited inspection of assembled printed circuit boards. The combination of X-ray inspection and manual optical inspection is the optimal method for detecting defects in assembled boards.
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