Automated X-ray inspection

Defects are most often detected by visual inspection or automated optical inspection (AOI). Other means of nondestructive evaluation (NDE) include electrical testing, x-ray inspection, and ultrasonic inspection. The preferred NDE inspection technique for BGA and CSP solder joints is x-ray inspection. Automated x-ray inspection equipment is often placed directly into the assembly process line for circuit board products having a large number of area-array components. 

There may be defects that do not show up as faults. Examples are insufficient solder, a misaligned component, a missing bypass capacitor, and an open power pin. Inspection systems such as automated optical inspection (AOI) and automated x-ray inspection (AXI) detect many of the defects and also some of the same faults as electrical test. The definition includes the phrase at the end of the manufacturing process, which is important when compared with potential defect. ... 

After reflow, the main objective k to identify defects so that repair action can take place. For thk manual vkual inspection, AOI post-reflow, or automated x-ray inspection, can be used. Even with good process control, defect levek are hkely to increase, especially for higher-complexity boards. If defect levek are higher, then a good inspection strategy becomes more valuable. 

Automated x-ray inspection of solder joints has the following major advantages ... 

Sack,Thilo, Implementation Strategy for an Automated X-Ray Inspection Machine, Proceedings of Nepcon West Conference, IBM Corporation, Cahners, 1991. 

Paul R. Groome, director of automated X-ray inspection products, Teradyne Inc., may be contacted at (858) 391-3810 e-mail paul. groome Teradyne.com. 

Figure 6.5, left, shows a typical X-ray image of an MID by way of example. Suitable control and systems technology can extend X-ray processing to automated X-ray inspection (AXI), which can also be combined with automated optical inspection (AOI). 

X-ray inspection of baggage can be divided into a number of technologies, depending on the physical principles employed and whether computer automation used for detection. A number of publications have discussed the variety of options available to do this task [52—60]. Many of these technological systems are in common use at airports, government buildings, and other security checkpoints. 

Corporation of San Diego, California, began the development of an automated radiation gauging inspection system for large caliber artillery shell intended to replace the X-ray technique. The system was named AIDECS for Automatic Inspection Device for Explosive Charge in Shell and is still in the process of test and development as of this writing. The ultimate objective is to produce a system capable of making accept/reject decisions on a production basis at a rate of about 1 minute per shell... 

Where is shown after the system investment, add 181,000 for an automated inspection system comprising an X-ray metal detection machine, and 3 machine vision units to verify closure in place and label and bar code are correct and in place. 

Fully automated inspection systems using hght, laser, or x-ray imaging... 

FIGURE 53.11 Schematic of transmission x-ray automated inspection system for solder joint defect detection. The x-ray detector converts a varying amount of x-rays to hght, based on how much various parts of the solder joint absorb. The camera converts the light photons to an image, which is then processed to find solder joint features and flag defects accordingly. 

Application. Cross-sectional x-ray automated inspection systems work well for all types of printed circuit assemblies, including single-sided and double-sided, surface-mount, through-hole, and mixed-technology assemblies. These systems accurately detect the same solder joint and component defects as do transmission x-ray systems, but, in addition, the cross-sectional x-ray systems accurately detect insufficient solder conditions for BGA and pin-through-hole solder joints. 

FIGURE 53.12 Schematic of cross-sectional x-ray automated inspection system for solder joint measurement. Adding images around a circle from a rotating x-ray beam and detector creates a focal plane that captures just the solder joints of interest and nothing else below or above. 

For transmission x-ray automated inspection systems, no components should be opposite or under dense structures, such as transformers, large capacitors, or thick steel heat sinks. 

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