Printed circuit boards have largely replaced point to point construction and wire wrap that was earlier used for the making of electronic products. Their manufacture has been largely automated and led greatly to miniaturization of electrical components that need to be inspected to ensure the faithfulness of the circuits on the boards.
PCB inspection is essential for any process of their manufacturing and enables faults to be detected before the PCBs are put to use. It has become all the more essential as most modern-day PCBs are highly complex. In earlier days when PCB manufacturing was first undertaken, this inspection was largely visual. As the manufacture of boards was largely repetitive many faults were not spotted and the PCBs made their way into the next stage of production and were detected only when they did not function as they were required to.
This led to the development of automated optical inspection that is even now the preferred method for PCB inspection. In this system, an optical image is taken of the assembly, which is then compared with the assembly of a PCB that has been proved to work. It is an automatic inspection system that has been perfected and is very reliable in operation.
The density of components and circuits on PCBs have been steadily increasing and with newer technologies being used for mounting integrated circuits, not all solder joints are easily visible in the optical system of inspection. The correct soldering of arrays on new boards, and especially new ones has become very vital to the manufacturing process. This led to the development of an inspection system that used X-rays that permitted inspection of the joints that often lay under the chips being joined. This inspection system is expensive and is therefore used sparingly for a smaller proportion of solder joints. As a result, automatic optical systems are widely used for inspection of PCBs while the X-ray method is used for highly complex circuit boards.
The function of any PCB inspection system has to be to highlight defects so that corrections can be made before they leave the production process to move to the next stage. Any system of inspection only becomes effective if it is used to provide proper feedback to the process of manufacturing, so that that there can be a detection of any pattern of faults that indicate some defect in some step of the manufacturing process. Inspection of boards must allow defects in them to be corrected and also the correction of any steps that are leading to faults continually.
It can also help if inspection systems are set up that can carry out the optical process of inspection before the joints in the PCBs are soldered.