Automated optical inspection (AOI) is a machine-based technique used to test and check PCB for potential errors, such as surface defects, dimensional defects, as well as component placement defects. As the circuit board is more and more complicated, it’s hard and impossible to manually check the boards, needless to say, AOI plays an important role in checking the printed circuit board after assembly. What’s more, it does make a great effect on getting the necessary product quality in the production line with low cost.