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AVI Inspection System

AVI Inspection

Table of Contents

What is PCB Automated Visual Inspection (AVI)?

PCB automated visual inspection is used in PCB manufacturing to examine the circuit board using a computerized system. The system includes various lighting systems, cameras, and computer algorithms. 

The process has replaced manual inspection and involves the image capture of PCB. The system analyzed the captured image for defects such as component misplacement, soldering defects, and surface imperfections. It ensures defect-free PCBs for the final shipping process. 

It is a final step before shipping the PCB to assemblers. The scanner of the AVI inspection system will identify any circuit board that doesn’t align with the requirement guidelines of PCB manufacturers. This will help to increase the quality of PCB. The AVI inspection process is faster and provides a more accurate vision inspection. 

Benefits of Automated Visual Inspection

AVI inspection systems offer various benefits. Some of them are explained below:

  • AVI inspection system uses advanced imaging technology and an algorithm that detects defects with high accuracy and precision.
  • It provided faster inspection time than a manual inspection system. This leads to increased production efficiency and throughput. 
  • It can be programmed to inspect a large range of components and products. This makes the AVI system suitable for a wide range of applications. 
  • AVI inspection system collects and analyzes a large amount of inspection data. It provides valuable insight into production processes and areas for improvement. 
  • It reduces the need for manual handling of the components, enhancing workplace safety. 

How does the AVI Inspection System Work?

Working of AVI Inspection System

Motion System:

  • Manual Type: Simple setup with inspection table and servo motors for x- and y-axis movement.
  • Auto Type: More complex setup with components such as loader, cleaning unit, flipping unit, unloader, sorter, and board handling unit.

Lighting System:

  • Various light sources are used, including LED, halogen lamps, and fluorescent lamps.
  • Different machines use different color lights based on requirements.
  • AOI inspection machines often use infrared light for better distinction between copper and substrate, while AVI inspection machines use white light to capture accurate colors.

Camera System:

  • Formed by cameras and lenses, with color and monochrome options.
  • Monochrome cameras are sufficient for AOI machines, while color cameras are more common in AVI inspection machines for cosmetic inspection.
  • Pixel size is crucial, calculated by scan width divided by the number of pixels.

Computer System:

  • Receives image data from cameras for processing.
  • Requires fast processors and large memory for efficient processing.
  • Often runs on Microsoft Windows or Linux operating systems to prevent virus issues.

Software Components AVI Inspection System

Software:

  • Provides a graphical interface for users to operate and performs internal calculations to identify defects.
  • Utilizes different methods for defect detection, such as pixel-by-pixel comparison or logical methods involving contour comparison and design-based inspection.

Additional Components:

Process Method of the Image:

    • Influences processing time; some machines use pixel-by-pixel comparison for faster processing, while others employ logical methods for more detailed defect detection.
    • It may require faster and more computers for complex processing methods.

How are Defects Found in the AVI Inspection System?

Method #1


In the AVI inspection system, the ability to identify defects depends on two main factors: the size and brightness/color of the defects.

Size of Defects: The pixel size of AVI machines determines the minimum size of defects they can detect. Think of pixel size as the basic unit of the scanned image. So, the smallest defect detectable must be larger or equal to the pixel size. However, even if a defect is the same size as a pixel, it might still be difficult to detect. 

For instance, it’s easier to detect if the defect falls inside a pixel (Case A). But if the defect spans multiple pixels (Case B), each pixel may only capture a portion of it, making detection challenging.

Brightness/Color of Defects: If the brightness or color of defects closely resembles that of the normal area, it becomes difficult for the machine to detect them. Common defects missed by AVI include scratches and dents.

Lighting: AVI machines use both specular and diffuse light. Specular light reflects off surfaces like a mirror, while diffuse light scatters in many directions. A dent’s uneven surface reflects less specular light but still reflects some diffuse light.

Effect of Lighting on Detection: If the diffuse light reflected by a dent is intense, it may appear similar in brightness to the surrounding flat surface, making detection difficult. Conversely, reducing diffuse light intensity may lead to false detections, such as mistaking oxidation or dust for defects.

Motion System: In AVI, the board being inspected typically remains stationary. Universal machines share similar motion system components with AVI machines and can adapt to either system with minor modifications.

AVI Inspection Detect Detection

Method #2

In AVI inspection machines, having a reference image is crucial for identifying defects on the boards.

Types of Reference Images:

  • CAD Data: This is a computer-aided design representation of PCBs, containing detailed information like circuit layout and solder mask layout. CAD data are created using specialized software, and all regions on the PCB are classified.
CAD Image
  • Golden Board Image: This is an image of a flawless board. To ensure its quality, it’s typically manually inspected first using magnifying devices. Then, it’s scanned by AOI/AVI machines to create the golden board image. Sometimes, the golden board image is formed by scanning multiple boards and averaging their images.

Role of Reference Images:

    • CAD Data: If CAD data is used as the reference image, it’s already classified. However, the scanned image needs classification before comparison. This process involves categorizing regions in the scanned image.
    • Golden Board Image: If the reference image is a golden board image, neither the scanned image nor the golden board image is classified. Hence, the scanned image can be directly compared with the golden board image to detect differences.

Classification and Comparison:

Classified Image of AVI Image
  • With CAD Data: The process involves classifying the scanned image, comparing it with the classified CAD data, and analyzing the differences to identify defects.
  • With Golden Board Image: Here, both the scanned image and the golden board image are unclassified. Thus, a direct comparison is made to detect differences, and the golden board image may be classified for further analysis based on the identified differences.

What are the types of Defects AVI Can Detect

Detecting defects in Automated Visual Inspection is crucial for ensuring the quality of PCBs. The ability of AVI systems to identify defects relies on several factors, such as the size and brightness/color of the defects and the performance of the lighting and camera systems.

AVI inspection systems are capable of detecting a wide range of defects, including:

  1. Missing components: AVI inspection can identify instances where components are missing from the PCB, which could lead to functionality issues or electrical failures.
  2. Soldering defects: AVI inspection systems can detect problems with solder joints, such as insufficient solder, solder bridges, or cold solder joints, which may impact the reliability of the PCB.
  3. Component misalignment: AVI is adept at identifying instances where components are not properly aligned on the PCB, which could affect the functionality or performance of the electronic device.
  4. PCB contamination: AVI systems can spot contaminants on the surface of the PCB, such as dust, debris, or foreign substances, which may compromise the integrity of the circuitry.

Difference Between AOI and AVI

AOI (Automated Optical Inspection)

AVI (Automated Visual Inspection)

Uses optical technology to inspect PCBs.

Utilizes cameras and image analysis algorithms.

Is an inspection process during production line

Is the last inspection before shipping

Commonly used for inspecting solder joints.

Suitable for a wide range of defect detection.

 

Conclusion

AVI plays a crucial role in the PCB manufacturing process. It is an automatic system of circuit boards that uses imaging technology and computer algorithms. 

It has largely replaced the manual inspection system by offering large benefits like accuracy, speed, versatility, and consistency. 

AVI inspection system offers large benefits, including product quality, increased production efficiency, valuable insights into the production process for improvements, and more. With advanced technology and an automation system, the AVI system ensures that defect-free PCB is delivered to the customers. 

Working with ElePCB

At ElePCB, we offer the PCB inspection services. We understand how vital the PCB inspection system is to have the proper functionality of the product. We are the experts in this domain and have been providing services for decades. We use cutting-edge technologies. We can customize our services, ensuring they meet your specific requirements. 

We perform various PCB testing and inspection systems. You can discuss your specific PCB inspection needs, and we would love to provide you with the best quality work. Contact us today and request a quote. Our team is always ready to help you in your PCB journey. 

FAQs

What types of defects can AVI detect on PCB?

AVI system can detect various defects, including missing components, soldering defects, component misalignment, PCB contamination, and more.

How does AVI work?

AVI system captures images of PCB using high-resolution cameras. Specialized software will analyzed these images. It compares against the pre-defined criteria to identify the defects. ML algorithms also help to improve defect detection accuracy over time. 

Is AVI suitable for all types of PCBs?

AVI can be used for many PCBs, including single-sided, double-sided, and multi-layer. 

However, the suitability of AVI for specific applications depends on various factors like the complexity of the board, defect types, and the density of components. 

Can AVI detect the hidden defects within the components?

While the AVI focuses on surface-level defects, it can still detect hidden defects like insufficient soldering, internal defects within the components using X-ray inspection techniques, and more.

CONTACT ELE

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.

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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.

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