Comprehensive introduction of AOI test system for PCB

The precision of PCBA board plays a crucial role in the functionality of electronic equipment. However, this precision also poses a risk of potential failures. As a B2B company that values high-quality products, FS Technology is committed to delivering defect-free products to our clients. Defects can lead to production delays, increased costs, and most importantly, negatively impact our brand image.

To mitigate these negative effects, it is imperative to implement strict testing protocols throughout the PCBA process, including the use of automatic optical inspection (AOI). AOI is a critical PCB testing method that allows us to detect defects in PCBAs and ensure they meet the required standards. This article aims to provide a more comprehensive explanation of the AOI test and its importance in PCBA production. The picture below shows two AOI detectors used in the assembly workshop of FS Technology.

aoi machine for pcb
EKT-VT-680D Vision Inspection AOI Automatic Optical Equipment
SONY automatic optical inspection equipment

What is AOI Inspection

In PCBA production, manufacturers often employ various testing methods to ensure high-quality products. One such method is AOI optical inspection, which is a type of visual inspection that uses advanced equipment to scan the produced board and compare it with the correct PCB to detect any defects or failures in the circuit board and other electronic components. PCB optical inspection is a critical step in the entire service process, including manufacturing (pads, interlayer connections, surface quality, etc.) and assembly (SMT assembly and through hole PCB assembly).

How Automatic Optical Inspection System Works

In the AOI inspection system, any discrepancies that do not comply with the predefined set of criteria are immediately flagged for further investigation. This automated inspection process enables manufacturers to maintain quality control during production runs, thereby preventing costly rework or errors from being passed on to customers. The detection method offered by AOI is a vital tool that allows for the identification of faults before they affect customers. Unlike manual PCB inspections that are prone to human errors caused by fatigue or inattention, the visual inspections performed by AOI equipment are highly accurate.

At FS Technologies, we continuously strive to improve our manufacturing process and reduce costs associated with rework or recall activities. We have invested in state-of-the-art automated optical inspection equipment that enables us to scan all circuit boards before they leave the shop floor. The AOI inspection process includes the following steps:

  1. Reference object: The significance of AOI visual inspection lies in the correct comparison and analysis of boards to determine whether there is a failure. High-precision instruments are required to take images of normal PCBs as reference images for subsequent inspections.
  2. Scanned image: The produced circuit boards are sent to the AOI system along the docking station, where they are quickly scanned and displayed on the screen for inspection.
  3. Image processing: The image processing software that comes with the AOI equipment automatically processes the scanned image, including denoising and contrast enhancement, among others.
  4. Comparison: The processed image is then compared with the prepared reference image to detect whether there are any defects or faults.
  5. Flagging: If any common PCB issues are detected, the test system flags it for further inspection by the operator, ensuring that all products meet the highest quality standards.

The Necessity of Automatic Optical Inspection of PCB

In recent years, the PCBA industry has made significant strides in manufacturing, assembly, and testing technologies, resulting in improved production capacity and more complex circuit structures. As surface mount technology continues to advance, electronic PCBA boards have become increasingly smaller and more sophisticated.

Given the increasing complexity of circuit boards, manual PCB inspection is no longer a viable option. The majority of issues are typically located in the thousands of soldered joints present on even the most typical boards. Despite the fact that manual inspection can occur at any point in the manufacturing process and provides instantaneous results, its efficiency is not high. Even the most experienced inspectors can become fatigued and prone to improper inspection due to the high density of solder fillets. Empirical evidence has shown that this detection method is not reliable, and opting for manual inspection as a cost-saving measure may lead to circuit board failure, resulting in significant losses. Therefore, AOI solder fillet inspection will completely replace manual work, with manual inspection serving as an auxiliary inspection solution. The image below depicts high-density PCBA products tested by AOI automation equipment.

To meet market demands for fast turnaround and high quality, reliable and efficient testing technology is necessary to ensure and improve production levels. AOI Inspection PCB is an integral part of an integrated electronics test strategy that optimizes costs by identifying issues early in the production process. One solution to this challenge is the implementation of automated or automated optical inspection tools. After the soldering process, automated optical inspection equipment can be incorporated into the production line to detect and flag issues at an early stage. This early intervention is critical, as detecting issues deeper in the production process is more costly and time-consuming to correct. Furthermore, early manufacturing difficulties with soldering and PCB assembly can be identified and feedback provided in the early stages to ensure timely resolution. This approach enables rapid response to ensure that problems are detected and addressed immediately, preventing the production of boards with the same problem.

Features of AOI detection

  • High precision: AOI inspection equipment is capable of detecting subtle defects that are as small as a few microns, while minimizing inaccurate inspection results that may occur due to human errors.
  • High efficiency: The automated inspection process is more efficient than manual inspection, allowing for faster turnaround times for PCB assembly.
  • Flexibility: AOI testing offers greater flexibility, as the inspection process can be stopped or started at any time, and manufacturing or assembly settings can be immediately adjusted if a problem is detected. The equipment can also be configured and adjusted to meet specific production line requirements.
  • Recording and tracking: The inspection system is capable of recording the inspection results of each PCB and tracking the occurrence and resolution of problems, allowing production lines to identify the root cause of quality issues and improve the production process.
  • Versatility: AOI system is not limited to detecting basic surface defects and missing components; it can also identify solder voids, incorrectly shaped connectors, and PCB component orientation issues.
  • Multiple options: A variety of reliable AOI inspection equipment brands are available for manufacturers to choose from, including both 2D and 3D options.
  • User-friendly: The inspection machine can generate comprehensive inspection reports to reduce the workload of engineers and improve project operability.
Basic Surface DefectsYesNoYes
Missing ComponentsYesNoYes
Solder Joint IntegrityYesYesNo
Solder Joint LocationYesYesNo
Component Placement ErrorYesNoYes
Component OrientationYesNoYes
Solder Void DetectionYesYesNo
Short Circuit DetectionNoYesYes
Open Circuit DetectionNoYesYes
Reverse PolarityNoYesYes
High Voltage TestingNoYesYes
Functional TestingNoNoYes


In conclusion, AOI is a highly advanced technology that seamlessly integrates optics, mechanics, electrical control, and software to replace manual inspection. With the growing trend towards smaller and more complex PCBs, even the simplest board can have thousands of soldered components, making it crucial to utilize AOI in today’s competitive PCBA production environment. By continuously evaluating production quality and making necessary corrections to the process flow, AOI helps companies achieve cheaper production costs, reduced waste, and increased yields. Investing in AOI systems can provide a significant advantage to businesses seeking to enhance their manufacturing capabilities and remain competitive in the industry.


Does FS Technology provide AOI testing service?

Certainly, at FS Technology, we take pride in our commitment to quality assurance throughout the PCBA production process. Our AOI inspection equipment is strategically placed at critical points in both our manufacturing and assembly workshops, where it performs precision inspections to ensure that every PCB meets the highest quality standards.

Is the test offered free of charge?

This test is basic so it's completely free!

When does the device work?

In the PCB assembly process, it is commonly acknowledged that a majority of failures occur after soldering. Hence, it is crucial to place AOI equipment after the reflow soldering or wave soldering process and connect it with a docking station. This allows for efficient inspection and early identification of any defects, enabling timely corrective action and minimizing any unnecessary waste of resources.

2D or 3D?

Many PCBA companies rely on 2D AOI equipment due to its versatility, which can fulfill most of the manufacturing needs. However, it may not provide enough information for checking the glue dispensing and soldering parts. To ensure higher quality inspections, FS Technology offers both 2D and 3D inspection equipment that provide better inspection control and accuracy.

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