How to detect defects in printed circuit board assembly
To complete the requirements of testing printed circuit boards, has produced a variety of testing equipment. Automatic optical inspection (AOI) systems are commonly used as the inner layer of the test before; in after stratification, X-ray system monitoring the accuracy of the position and small defects; scanning laser system provides a layer in the pad before the detection of reflux methods. These systems, coupled with production lines and automatic visual inspection of components placed on the integrity of components, testing, final assembly and will help to ensure the reliability of welded plates.
The final assembly of printed circuit board testing method may be adopted in the action or by the automated system to complete, and often use two methods work together. "Manual" refers to an operator through visual inspection using optical instrument board, and make correct judgments about the defects. Automation systems is the use of computer-aided graphical analysis to determine defects, and many people also believe that automation than manual contains all the detection of external optical detection methods.
However, even these efforts will minimize defects, still need to assemble the final inspection of printed circuit board, which is perhaps the most important because it is a product and eventually the whole process of evaluation units.
X-ray technology provides a assessment of solder thickness, distribution, internal voids, cracks, sealing off and the ball existing methods (Markstein, 1993). Ultrasonics will detect voids, cracks and did not post then the interface. Automatic optical inspection evaluation of external characteristics, such as bridge, volume and shape of molten tin. The external characteristics of the laser detection can provide three-dimensional images. Infrared detection of a known good through and compare weld weld heat signals detected within the welding point of failure.
It is worth noting, has found that the auto-detection technology to the limited printed circuit board assembly test can not find all the defects. Therefore, the manual method of visual inspection and automated detection methods must be used in combination, especially for those small number of applications and even more so. X-ray inspection and manual optical inspection is to test the combination of best practices assembled plate defects.
