Keyword: pcb, pcb board, printed circuit board, assembly PCB plate
To complete the requirements for printed circuit board inspection , there are a wide range of testing equipment PCB. Automatic optical inspection (AOI) systems are commonly used to test the inner layer precursor ; in a layer and thereafter , X-ray system monitoring the accuracy of the position and the smallest defects ; scanning laser system provides a pad layer prior to the reflow test methods . These systems , combined with visual detection technology production lines and automatic placement components components integrity PCB testing will help to ensure that the final assembly and welding board reliability.
However, even these efforts to minimize defects , still need to be assembled final inspection of printed circuit board , which is perhaps the most important because it is the product and the final assessment of the process unit . Final assembly of the printed circuit board by means of the movable detection methods may or by the automation system is completed, and both methods are often used together. " Manually " refers to an operator through visual inspection using an optical instrument board , and make correct judgment about the defects . Automation systems is the use of computer-aided graphical analysis to determine defect , many people also believe that in PCB addition to the manual Automation System contains all of the outside light detection detection method. X-ray technology provides an assessment of solder thickness , distribution printed circuit board, internal voids, cracks , and the ball sealing off existing methods (Markstein, 1993).
Ultrasonics will detect voids printed circuit board, cracks and did not take note of the interface. AOI assess external characteristics, such as bridges , tin melting capacity and shape. External features laser detector can provide a three-dimensional image . Infrared detector and a known good through welding point comparison weld thermal signal is detected within the welding point of failure. It should be noted , it has been found that the automatic detection of the printed circuit board assembly is not limited detect all defects found . Therefore , manual visual inspection method and automated detection method must be used in combination , especially for those few applications even more so . X-ray inspection and manual optical detection assembly PCB plate combination is to detect defects in the optimal way .
Assembled printed circuit board and soldered easily the following defects : 1.Component missing ; 2.component failure ; 3.Component exist installation error , misalignment ; 4.component failure ; 5.wetting bad ; 6.bridge ; 7.insufficient solder ; 8.Excessive formation of solder ball ; 9.form a weld pinholes ( bubbles ) ; 10.for contaminants ; 11.Inappropriate pads ; 12.wrong polarity ; 13.pin float ; 14.pin protruding too long ; 15.appears cold solder joints ; 16.Excessive solder ; 17.solder voids ; 18.There are blowing holes ; 19.traces the inner circle of fillet poor structure .
