An Innovative Multilayer PCB Manufacturer

PCB AOI Inspection

AOI Inspection in PCB Manufacturing

Table of Contents

What is AOI Inspection?

Automated Optical Inspection (AOI) is a PCB and PCBA testing method in manufacturing companies. It tests the PCB for possible defects like surface defects, component placement defects, and dimensional defects. 

The basic working principle of AOI is that it uses a camera system that checks for errors or potential defects in the circuit board. 

It integrates the mechanics, electronics control mechanism, optics, and software that has replaced the manual inspection. It mimics the manual inspection system with greater accuracy, consistency, and speed. 

It checks every component during manufacturing and ensures it meets the required design criteria. For example, the post-reflow AOI PCB system detects issues like short circuits, excessive solder, open circuits, and incorrect component placements. 

The process monitors the PCB production process and helps to fix them during the process flow. This helps maintain the quality during the PCB manufacturing and assembly process.

Benefits of AOI Inspection

The benefits of AOI inspection are as follows:

  • Enhanced defect detection accuracy.
  • Improved product quality assurance.
  • Increased productivity and efficiency.
  • Cost savings through reduced rework.
  • Compliance with industry standards and regulations.
  • Data-driven decision-making for process optimization.
  • Real-time feedback loop for proactive defect management

AOI Components

Components of AOI

The major components for AOI inspection are as follows:

Lighting System

Proper illumination is essential for capturing clear and consistent images. Thus, the AOI inspection system employed various lighting techniques, including dark and bright fields and angled lighting. This enhances the contrast and visibility of the defects. 


The significant component of the AOI inspection system is the high-resolution cameras. It captures the detailed images of PCB and other components. An AOI inspection system uses multiple cameras to capture the various angles for inspection.

Conveyor System

With the use of a conveyor system, manufacturers integrated AOI into the production lines. The conveyer ensures the steady flow of PCB or any components throughout the inspection process. It helps in high-throughput inspection.

Software Algorithm for AOI

The performance of AOI machines is highly dependent on the power and precision of the software algorithm. These algorithms analyze the data captured by an optical system and help identify the defects. 

There are several types of software algorithms for AOI inspection systems:

Statistical Pattern Matching

It is one of the most advanced variants of pattern matching. It pays attention to the differences between each good product and figures out what’s typical. Then, it uses math tricks to decide when a product doesn’t look right compared to what it learned. This way, it can tell when something’s off without freaking out over tiny differences that are just natural. So, it’s like having a flexible system that can handle the natural differences between products without freaking out over every little thing.

Pattern Matching Technique

There will be a reference image for the AOI inspection. This system works by comparing the image of a PCB that requires inspection and reference images. It then looks for any kind of deviation. This technique is effective for applications that require a highly consistent system.

Machine Learning Algorithm

It continuously learns from past inspection results. It tries to improve its ability to recognize and classify defects, adapting to evolving production environments and product variations.

Feature Extraction Algorithm

Extracting relevant information from images, this algorithm identifies key features related to defects and enables efficient analysis.

Image Segmentation Algorithm

Dividing images into distinct regions or segments it enhances the precision of defect detection by isolating areas of interest for targeted analysis and evaluation.

AOI Inspection Process

PCB Quality Control: AOI Inspection Process

The primary working principle of AOI inspection is the use of advanced imaging technology and a software algorithm to analyze the visual characteristics of PCBs for defects.

Thus, the AOI inspection system begins with the setup phase, where AOI is programmed with the required inspection criteria. This process includes fine-tuning the system to ensure the accurate detection of defects. 

The AOI inspection system consists of high-resolution cameras that capture detailed images of products under inspection. The images are then processed and analyzed by the software algorithm with pre-defined standards and criteria. 

The software algorithm utilizes various techniques like edge detection, pattern recognition, and statistical analysis. It identifies the deviations from the expected appearance. After detecting the defects by AOI inspection, the system alerts the operator or marks the location of defects for further inspection. 

The operator then reviews the possible issues and takes suitable action, like adjusting the manufacturing process and reworking the product.

Types of AOI Inspection Systems

AOI system is basically of two types;

2D AOI Inspection System

In most manufacturing companies, two two-dimensional AOI systems are common. It uses 2D cameras, which capture the images of components under the inspection process. It is mainly useful in detecting surface-level eros like missing components, soldering defects, incorrect component placement, and misaligned components. 

To perform the inspections, the 2D AOI system implemented pattern recognition and conventional imaging technologies. The methods have already been discussed above. 

The system helps identify the defects on the actual PCB with the help of stored information.

Limitations of 2D AOI System

  • The 2D AOI system may not identify the defects on the 3-dimensional side, such as insufficient solder, lifted components, and more.
  • AOI system could struggle to detect the defects that require additional testing methods like functional testing for electrical faults. 
  • It requires regular maintenance to ensure optimal performance, including cleaning, calibration, software updates, and more, which adds to the operational cost.

3D AOI Inspection System

It is a more advanced form of the AOI system. The system uses 3D imaging technology. 

It can detect defects not only in the surface but also in height dimensions. The system can accurately measure the component height and solder joints, allowing more precise defect detection and reducing false alarms. 

The basic principle of 3D AOI involves capturing detailed three-dimensional images of objects using technologies such as structured light projection or stereo vision. 

The system detects defects with high precision by analyzing the depth information in these images. It improves inspection accuracy and reduces false alarms in manufacturing processes.

Limitations of 3D AOI system

  • The system is more expensive than 2D systems, which can be a barrier for some manufacturers. 
  • The operation and implementation of a 3D AOI system require additional expertise and training due to the complexity of analyzing 3D data.
  • The system is time-consuming and requires regular adjustments.

Choosing the Right AOI Inspection System

aoi inspection system

Choosing the right AOI inspection system requires careful consideration of various factors:

  • Check for a system with high accuracy and precision in defect detection to ensure reliable inspection results. 
  • Consider the system’s flexibility to adapt the various product types, configurations, and sizes.
  • Estimate the system’s inspection speed and throughput to align with your production requirements. 
  • Evaluate the total cost, including initial investment, maintenance, and operational expenses, to ensure the system provides good ROI and aligns with your budget too.
  • Select a reputable manufacturer company with a proven track record of delivering reliable AOI solutions.
  • Estimate the system’s software features, including advanced algorithms, inspection criteria, and reporting tools, to ensure it meets your specific inspection requirements.


AOI system uses 2D and 3D optical systems with unique benefits and limitations. It has already changed the world of PCB manufacturing and is still upgrading to align with the demands of industries worldwide. 

Overall, it provides the solution with precision, speed, and efficiency demands. Its undeniable contribution to boosting productivity, cutting expenses, and enhancing quality has focused on the AOI system in the manufacturing industry.


What are the defects AOI inspection can handle?

AOI can handle a wide variety of defects like:

  • Misalignment: AOI can identify components that are not correctly aligned on a PCB or in an assembly.
  • Soldering Defects: It can detect issues such as insufficient solder, solder bridges, or solder balls (excess solder that can cause short circuits).
  • Component Placement Errors: AOI can spot missing, misplaced, or rotated components on the PCB.
  • Insufficient or Excessive Component Presence: It can detect if certain components are absent or extra components shouldn’t be there.
  • Defective Components: AOI can identify components that are damaged or have quality issues, such as cracks, scratches, or incorrect markings.
  • PCB Damage: It can detect physical damage to the PCB, such as scratches, breaks, or etching errors.
  • Polarity Reversal: AOI can identify instances where components are inserted with the wrong polarity, which can cause malfunctions or failures.

What is the need for AOI?

AOI is useful in various stages of manufacturing and production of PCB. It works well for solder paste inspection, bare board inspection, post-re-flow, and pre-reflow. Every stage can have some defects which, if unsolved on time, will create a lot of issues at the very end, resulting in huge losses. Thus, AOI inspection can help catch these defects before production starts, saving time and cost. 

Is AOI inspection suitable for all types of electronic assemblies?

AOI inspection is commonly used for PCB and other assemblies like hybrid circuits and semiconductor devices. 

Can we use the AOI for quality assurance in other industries?

While AOI is commonly associated with electronics manufacturing, similar optical inspection techniques can be applied in automotive, aerospace, and medical device manufacturing industries for quality assurance.


ELE PCB has got the IS09001:2015, IS013485:2016, ROHS and FCC certifications. We can offer all kinds of services, including PCB manufacturing and PCB assembly, sample orders and batch orders. For PCB assembly, utilizing 7 high-speed SMT PCBA lines from Yamaha and Sony, to meet our customers’ needs. Our extended services include PCB design &PCB Layout, hardware design engineering, firmware &software development, and personalization. ELE company is honored as an excellent supplier from any company all around the world. We deeply believe that our good service and experience will completely meet your needs. Integrality, value and innovation are the forces that drive our success.



We provide technical expertise form prototype through production increasing speed to market by 20%.

                   Contact us below to start discussing your project with our Technical Experts today.

                   Whether you already have Gerber Files, submit a Quick Quote for free estimate.

Is this article useful?

Click on a star to rate it!

Average rating 0 / 5. Vote count: 0

No votes so far! Be the first to rate this post.

Still, need help? Contact Us:

Need a PCB or PCBA quote? Quote now

Get a Quote
About Michael

Michael is the general manager of ELEPCB, a leading PCB design and manufacturing company based in China. He has over 10 years of experience in the PCB industry, and has been involved in various projects.

Recent Posts