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AOI is short of automated optical inspection, which is a type of visual inspection method PCB assembly manufacturers used to identify the quality-related defects with cameras and image processing software. AOI performs well in quality control of printed circuit boards (PCB) and PCB assemblies (PCBA).


Modern circuits are much more complicated than years ago as the rapid progress of electronic technologies, and the PCBs are moving toward miniaturization and high-density. The current market strongly demands a reliable and fast inspection method to meet the requirements of modern circuits. AOI test becomes significant in PCB fabrication to ensure the circuit boards provided for customers with high-quality and without manufacturing faults.


What can be identified during the AOI?

AOI can check the surface defects (scratches), dimensional defects (short or open circuits, thinning of the solder), missing or wrong placed components, etc. The details of the defects are divided into two categories.


For the boards (PCB): the violations of line width and spacing, missing pads, excess copper, cuts, short circuits, gold finger damage, hole breakage, and incorrect mounting of components, etc.


For the boards with components (PCBA): area defects, component offset/ polarity/ skew, components presence or absence, excessive or insufficient of the solder joints, height defects, flipped component, insufficient paste around leads, lifted leads, volume defects, wrong parts or damaged components, etc.


What are the advantages of AOI?

AOI is one of the testing methods before the PCBs applying in any electronic device. Although PCB used to be manually inspection, AOI is still necessary because the manual inspection is not enough since the increasing complexity of PCBs. AOI is a more reliable and faster method of testing PCBs and has lots of benefits as below:

l Higher accuracy and reliability

The inspection starts with visual scanning of the board when placing the circuit board under a high-illuminance light source with one or more HD cameras. Then there is a comparison of the captured image of the board and followed a comparison with the ideal board image that has been input into the AOI machine. Therefore, AOI can provide an accurate output of testing.

l Cost-effective

Compared with some other inspection methods such as X-ray inspection, AOI is cost-effective. Besides, AOI is profitable for PCB manufacturers in the long term because it helps prevent recurring defects and increases production value.

l Good flexibility

The most advantage of AOI is that it can be applied and run at any stage of the PCB manufacturing process based on the needs and affordability, and it can be performed as many times as needed.

l Multiple inspection objects

AOI test works for both PCB and PCBA. It can accurately inspect not only the surface defects on the single board but also the defects in PCB components. Inspecting PCBA includes components soldering, determining values, and polarity, etc.


AOI is the crucial step in PCB fabrication and testing circuit boards for PCB assembly manufacturers, PCB fabricators, and service providers. It can check the quality of the boards coming out of the end of the production line in any PCB manufacturing process, and rectify the defects in time. What' s more, an X-ray is also a necessary tool for PCB manufacturers. NEXTPCB has equipped advanced inspection equipment to perform the strictest standards in PCB manufacturing and PCB assembly.


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