PCB inspection basics
In the early days of PCB manufacture, or the manufacture of any electronics equipment, all inspection was undertaken manually. This was the best option, but was recognised as having only limited value. The repetitive nature of the process meant that many faults were not spotted and passed on into the next stage of production undetected.
There are various methods by which PCB inspection can be achieved:
· Manual PCB inspection : As the name implies, manual inspection involves individual inspectors looking at boards or other assemblies to inspect them for problems. This approach has been proved to be costly, and yielding poor results. Before automation, it was the only way that inspection could be performed.
· AOI PCB inspection: Automatic or automated optical inspection is the preferred method of PCB inspection. It utilises an optical system that takes an image of a good assembly and compares the two images to detect any faults or other issues.
This form of PCB inspection is widely used and has been perfected so that it operates very reliably.
· AXI PCB inspection: With density on PCBs increasing and new IC mounting technologies being used, not all solder joints may be visible. Particularly when new boards are being manufactured and new set-ups being used, it is very important to check that solder joints on packages such as BGAs (Ball Grid Arrays) are being correctly soldered. Optical inspection cannot achieve this because the solder joints are not visible. The only option is to use an X-Ray system - Automated X-Ray Inspection, AXI, that is able to look under the chips to view the solder joints. Although expensive and only used for a small proportion of the solder joints, etc, they are necessary in many instances.
For high volume production these days most manufacturers use AOI systems for their PCB inspection functions. With the increase in the number of BGAs and BGA associated packages being used, AXI is also being increasingly used.