[ Date Time : 2010-8-18 ] [ Comments : 0
To complete the requirements of testing printed circuit boards, has produced a wide range of testing equipment. Automatic Optical Inspection (AOI) system is commonly used as the inner layer of pre-test; in after stratification, X-ray system monitoring of the position accuracy and small defects; scanning laser system provides a layer in the back before the test pad Methods. These systems, coupled with production lines and automatic visual detection of components placed on the integrity of test components will help ensure that the final assembly and welding plate reliability.
However, even these efforts will minimize defects, still needs final assembly of printed circuit board inspection, this is perhaps the most important, because it is the product and the process of assessing the final unit.
The final assembly of printed circuit board testing method may be adopted in the action or by the automated system was completed, and the two methods often used together to complete. "Manual" refers to an operator through visual inspection using optical instrument board, and make correct judgments on the defect. Automation system is the use of computer-aided graphical analysis to determine defects, and many people think that automation than manual contains all the optical detection of external detection method.
X-ray technology provides a assessment of solder thickness, distribution, internal cavity, cracks, loose weld and solder balls subsistence (Markstein, 1993). Ultrasonics to detect holes, cracks, and the interface is not connected posts. Automatic optical inspection assessment of external features, such as bridge, volume and shape of molten tin. Laser detection of the external features can provide three-dimensional image. Infrared detection of a known good through and more weld weld heat signals detected within the welding point of failure.
It is noteworthy that these auto-detection technology have been found on the printed circuit board assembly of the limited detection can not find all the defects. Therefore, manual visual detection and automatic detection method must be used in combination, especially for those small number of applications should be so. X-ray inspection and manual optical inspection is to test the combination of best practices assembled plate defect.
Assembly and welding of the printed circuit board vulnerable of the following deficiencies:
1) components missing;
2) component failure;
3) The existence of installation error components, misalignment;
4) component invalid;
5) bad soldering;
7) insufficient solder;
8) over the formation of tin solder ball;
9) the formation of welding pinhole (bubble);
10) the pollutant;
11) improper pad;
12) polarity error;
13) pin float;
14) pin-out is too long;
15) appear cold weld;
16) more solder;
17) Solder empty;
18) have blown holes;
19) printed line structure within a circular fillet poor.