What is automatic optical inspection(AOI) of PCB manufacturing?
2023-10-28
When you use printed circuit boards (PCBS) in your projects, you need to make sure they perform well and keep your customers happy. There must be a reliable way to test PCBS for defects and ensure that they operate as expected.
Printed circuit boards are getting smaller and more complex - today's PCBS may contain thousands of welds and many tiny components. This added complexity can lead to a greater potential for error. When standard visual inspection is insufficient to detect tiny defects on densely crowded boards, technologies such as Automated Optical Inspection (AOI) can help provide greater understanding and accuracy.
How do we define automatic optical inspection?
How do we define AOI? Automated optical inspection is the visual inspection of the finished circuit board by a machine scanner using light imaging. It assesses process quality to ensure that PCBS are suitable for purchase and use.
AOI systems typically contain many light sources and multiple cameras, sometimes including cameras. The light source illuminates the PCB from different angles, while the camera takes photos or videos to create a comprehensive image for evaluation.
AOI measurements typically use a machine scanner to automatically scan the equipment without the need for a visual inspection. The scanner can check for defects that could lead to catastrophic failure, such as missing critical components, and can also test for smaller defects that can degrade the quality and performance of the PCB. These smaller defects can include issues such as components that are slightly misaligned or welded to form the wrong size or shape.
AOI is very useful in many different stages of production. It is suitable for bare plate inspection, solder paste inspection, pre-reflux and post-reflux. Each stage introduces defects into the design of the PCB board, and the AOI captures defects before further production on the defective board.
But, in reality, most AOI happens in post-production. The reason is that AOI can use a single system to check for multiple defects simultaneously. The time required to perform a full inspection is less than the time required to perform the inspection after each step of the process. Using AOI as a final check can help speed up production and increase productivity and on-time completion. And, if AOI finds a defect at a later stage of production, the defective board can be returned for rework, while the rest can be moved forward.
The role of AOI
AOI plays a crucial role in PCB production. It ensures that each board meets the high performance required in complex electrical applications.
When AOI finds a defect on the PCB, it flags the board for repair. This process can occur in several different ways. AOI's findings may not meet specific facility requirements, such as the requirement that all lines on a board must exceed a certain size. In this case, the personnel can review the findings and determine which boards should be returned for further work. Or AOI can compare the actual PCB to a computer-aided design (CAD) image of the perfect PCB. AOI can automatically detect where the actual board is deviating from the ideal design and mark it as reprocessable.
AOI brings the following benefits to PCB production:
· Ensure quality: AOI enables you to ensure that your PCB products perform as expected. Ensuring product quality can help you increase customer
satisfaction, enhance your reputation in your business, and reassure you about the value of the service you provide to your customers.
· Evaluate complex boards: At Millenium Circuits, if one of our boards contains more than 100 components, it will do AOI automatically. AOI can examine complex circuit board designs with a precision unmatched by the human eye.
· Improve the process: If a defect is caused by a faulty process, identifying the defect immediately through AOI can help you identify the pattern of the
defect and adjust the process, and then regenerate thousands of boards with the same defect. A new study published in the International Journal of
Engineering and Advanced Technology reports that the cost of finding a fault on a newly assembled circuit board is only ten times higher than the cost of catching a defect on a bare board, but it is 1,000 times more expensive to find a fault in a board already in the field. Catching errors early minimizes the possibility of future rework and makes your production operations more efficient.
· Customizability: AOI is an automated process, but the operator can set parameters to tell the scanner what to check. If your design specifications change, it's easy to adjust the Settings to detect the defects you need to look for.
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