What is AOI machine？

AOI (Automated Optical Inspection) machine is an automated testing equipment used for inspecting printed circuit boards (PCBs) for defects or issues, such as missing components, misaligned components, solder bridges, solder voids, and incorrect polarity. AOI uses high-resolution cameras and specialized lighting to capture images of the PCB assembly after the soldering process. The captured images are then analyzed by software algorithms to compare them against a pre-defined set of criteria for acceptability.

AOI Machine Working Principles

The AOI software algorithm uses advanced image processing techniques such as pattern recognition, edge detection, and contrast analysis to detect any anomalies in the image of the PCB assembly. The software then generates a report highlighting the defects found, allowing operators to take corrective action. This process helps to ensure the quality of the PCB assembly and identify defects early in the production process, reducing the likelihood of costly rework or recalls.

For example, when detecting a solder joint, a standard digitized image is established according to a good solder joint, and the actual measured image is compared. The inspection result depends on the standard image, resolution, and detection program. Various algorithms are used in graphic recognition, such as calculating the black-to-white ratio, color analysis, composition, averaging, summation, subtraction, plane fitting, and corner detection.

AOI Testing Scope

In detail, AOI can be used for various tasks during PCBA (Printed Circuit Board Assembly) production, including:

1. Component presence and polarity verification: AOI can verify if all the components have been placed correctly and have the right orientation.
2. Solder joint inspection: AOI can inspect the quality of the solder joints to ensure they meet the necessary standards.
3. Component alignment and placement: AOI can verify if components are properly aligned and placed according to the design.
4. Defect detection: AOI can detect defects such as missing components, lifted leads, short circuits, and incorrect values of components.
5. Barcode and serial number reading: AOI can read the barcodes and serial numbers of the PCBs to ensure traceability and quality control.

AOI Working Steps

The working system of an AOI machine typically involves the following steps:

1. PCB Loading: The operator loads the PCBs onto the AOI machine’s conveyor belt or in the dedicated holder.
2. Image Acquisition: The machine captures high-resolution images of the top and/or bottom sides of the PCB.
3. Image Processing: The machine processes the images, comparing them to a pre-defined standard or reference image to detect any defects or discrepancies.
4. Defect Detection: The machine uses algorithms and machine learning to analyze the images and detect potential defects or issues.
5. Alert and Sorting: The AOI machine identifies any defects or issues and generates an alert for the operator to take corrective action. The machine may also sort the good and defective PCBs based on the inspection result.
6. Inspection Report: The AOI machine generates a report detailing the inspection results, including any defects found and their location on the PCB.

Overall, the working system of an AOI machine helps to ensure the quality and reliability of PCBs during the production process by detecting any potential issues early on and allowing for timely corrective action.

How to use AOI machine in PCB production?

To make the most out of AOI (Automated Optical Inspection) machine during PCBA production, it is recommended to follow these best practices:

1. Define clear inspection criteria: The inspection criteria should be defined beforehand and should be clear and concise. This helps in avoiding confusion during the inspection process.
2. Perform regular maintenance: The AOI machine should be properly maintained and cleaned regularly to ensure that it functions optimally. This helps in reducing false rejects and increases the accuracy of the inspection.
3. Properly calibrate the machine: The machine should be properly calibrated before starting the inspection process. This helps in ensuring that the machine is functioning correctly and the inspection results are accurate.
4. Perform regular inspections: Regular inspections should be conducted to ensure that the machine is working correctly and providing accurate results. This also helps in identifying any issues with the machine before they become major problems.
5. Train operators properly: Operators should be properly trained on how to use the AOI machine and how to interpret the inspection results. This helps in reducing the number of false rejects and increases the overall efficiency of the inspection process.
6. Use in conjunction with other inspection methods: AOI should be used in conjunction with other inspection methods like X-ray inspection, functional testing, and visual inspection to ensure that all defects are identified.

By following these best practices, the use of AOI machine can greatly improve the quality and efficiency of the PCBA production process.

All in all, AOI plays a crucial role in ensuring the quality and reliability of the PCBA by detecting defects and errors that may be difficult to identify manually.