However, even if these efforts minimize the defects, the final inspection of the assembled printed circuit board still needs to be performed, which is perhaps the most important because it is the final unit of evaluation of the product and the entire process.
The final inspection of the assembled printed circuit board may be done by a dynamic method or by an automated system, and is often done using both methods. "Manual" means that an operator uses optical instruments to visually inspect the board and make correct judgments about defects. Automated systems use computer-aided graphical analysis to identify defects. Many also believe that automated systems include all detection methods except manual light detection.
X-ray technology provides a way to evaluate solder thickness, distribution, internal voids, cracks, desoldering, and the presence of solder balls (Markstein, 1993). Ultrasonics will detect voids, cracks, and unattached interfaces. Automatic optical inspection evaluates external features such as bridging, tin melting, and shape. Laser detection can provide three-dimensional images of external features. Infrared detection detects the failure of the internal solder joint by comparing the thermal signal of the solder joint with a known good solder joint.
It is worth noting that these automatic detection techniques have been found to have all the drawbacks that cannot be found with the limited detection of printed circuit boards. Therefore, manual visual inspection methods must be used in conjunction with automatic detection methods, especially for those few applications. The combination of X-ray inspection and manual optical inspection is the best way to detect assembly board defects.
Assembled and soldered printed circuit boards are subject to the following defects:
1) The lack of components;
2) Failure of components;
3) There are installation errors and misalignment of components;
4) Component failure;
5) bad tinning;
7) Insufficient solder;
8) Excessive solder ball formation;
9) Forming solder pinholes (bubbles);
10) There is a pollutant;
11) Inappropriate pad;
12) Poor polarity;
13) The pin floats;
14) The pin extends too long;
15) Cold welding points appear;
16) too much solder;
17) solder voids;
18) There are blowholes;
19) The inner circle of the printed wire is poorly angled.