Blog  /  7 Aspects To Help You Learn More About AOI Test

7 Aspects To Help You Learn More About AOI Test

The automated test inspection (AOI) Is a first test used to automatically detect faults or inconsistencies in the manufacture of Printed Circuit Boards (PCB). It is a process in which a high-definition camera effortlessly scans through the device in focus to detect any quality defect that might have.

Manufacturers do make use of various inspection and testing devices to build quality into the manufacturing process. And buyers should not be oblivious of this fact. Hence, the need for this article that aims at intimating you about all you need to know about Automated Optical Testing from 7 different perspectives or aspects.


The automated test inspection AOI Test Is a first test used to automatically detect faults or inconsistencies in the manufacture of Printed Circuit Boards (PCB).

(Optical quality control and assembly inspection of an electronic product in the factory)


1. The Demand For AOL Testing


Over the years, we have improved the requirements of AOI and automatic optical inspection, so we cannot overemphasize it. The introduction of surface mount technology and further reductions in the size of these boards have made them compact, making it easy to miss obvious faults. Several solder joints in the PCB can find most of the errors.

In the past, we have conducted a manual inspection, but the increasing complexities of modern-day PCB tired-out inspectors made manual methods unreliable and, in the end, obsolete. Hence, there is a need to know automated test inspection through the seven aspects of knowing AOI testing procedures.


motion detection system as one of the several applications of Printed Circuit Boards, PCB

 (motion detection system as one of the several applications of Printed Circuit Boards, PCB)


2. Why Are AOI Tests Popular


Printed circuit boards are an integral part of automated optical test inspection. When ordering the board, it should immediately correct its mistake. The financial implications of such things would be disheartening.

As mentioned earlier, due to the increasing complexity of modern circuit boards, manual inspection has become obsolete. TNow points to check the circuit board by soldering automation. Contemporary markets now require high volume, top-notch products that can reach their customers as fast as possible without compromising quality inspection.

An automated test inspection is a fundamental tool in an electronics test strategy to ensure that faults are detected as fast as possible in production for products to reach the market in the shortest time possible.


Printed Circuit Board with many electrical components

(Printed Circuit Board with many electrical components)


3.  AOI Test Detectable Defects


A wide range of errors can be detected using automated inspection test facilities. This involves using different techniques to determine if a printed circuit board fulfills all the conditions of quality or not. Some of these techniques include template matching, pattern matching, and statistical matching.

The template matching compares scanned images with the golden board. Pattern matching compares the information stored on both perfect and faulty systems. The statistical matching uses statistical data to address apparent problems.

Further advanced visual means for scanning a circuit board manufacturing defects. The systems used for fault detection, on the other hand, also make use of images, comparing them with ideal diagrams in a bid to note some glaring faults.

  • Welding defects can be detected in this way, for example, solder bridges, solder short circuits, the solder gap, excess solder, the solder mass, and an open circuit condition.
  • Component defects are also addressed, such as missing components, incorrect component value, improperly placed or misaligned components, faulty parts, lifted lead deficiencies sent when aiming to correct errors in printed circuit boards.
  • Also, BGA shorts and BGA open circuit connections can be detected during the AOI tests in line with approved guidelines.


printed circuit board, digital motherboard chip, and integrated communication processor

 (printed circuit board, digital motherboard chip, and integrated communication processor)


4. The Technology Used When Checking or Testing


There are different technologies or means used for checking or testing for abnormalities in printed circuit boards. Some of these include In-Circuit Testing, which is a robust testing method. Designed for full coverage testing PCB design, and the user is guaranteed about 85-90% coverage that is free from human error compared to other methods.

This test actuates the entire board circuitry, and it also involves the use of probes laid out expertly in a manner that mimics the design of the circuit board. Experts have recommended that this test is ideal for a product that only needs a few revisions.

Other testing methods include:

  • The flying probe test: This is cost-effective when compared to in-circuit testing. It is a non-powered test that is ideal for checking for Shorts, Opens, Resistance, Inductance, Diode issues, and any related checks to be carried out.
  • The Burn-in Testing: This is an intensive test for printed circuit boards.Its designers to detect a load failure
  • The X-Ray inspection testing: This method is the best for detecting soldering defects that are not visible to the naked eyes.
  • Functional testing: This is a test that requires the use of external pieces of equipment, and it ensures that the PCB will power-up to perform its functions.


flying probe test as a method of testing for defects in printed circuit boards

(flying probe test as a method of testing for defects in printed circuit boards)


5. The Type of Lighting Systems Used for AOI Test


Light is one fundamental part of the automatic optical inspection layout. Choosing the most appropriate amidst the available lighting systems is very crucial for easy detection of faults. Recently in lighting technology, we have made some progress. To enhance the image-derived, reduce the time required to develop overall system status, and increase accuracy.

Many AOI systems in use have a well-defined lighting apparatus. Although this solely depends on the type of product to be tested and the operation carried out. Sometimes, when carrying out PCB quality testing, you may need to do some customizations, and the proper understanding of lighting would be required. The types of lighting used include:

  • LED Lighting: An LED lighting system's use means that AOI systems can suitably adopt a stable form of lightning in carrying out random checks. By using LED lighting, we can easily control the light intensity.LEDs are better alternatives to fluorescent and incandescent lights. Although from experience, We noticed that the power of LED lights decreased over time. Nevertheless, we can add circuits to solve the problem.
  • Fluorescent Lighting: This is one of the most widely used light sources for AOIs; adequate lighting means checking defects on PCB. However, the main drawback of this form of lighting is that it degrades over time. It means that the optical detection system may change over time.
  • Ultra-violet or Infra-red light: This is useful to enhance certain defects, and third lighting systems are readily detectable.


Cob LEDs on black carrier trays as a type of lighting used for AOI

(Cob LEDs on black carrier trays as a type of lighting used for AOI)


6. AOI Camera Configuration


One of the fundamental and equally important aspects of the automatic optical inspection system is the image capturing system. It enables capturing the image of the printed circuit boards and its assembly layout that is subsequently analyzed by the related software within the AOI system.

There are different types of AOI camera configurations used for image capture and analysis of the overall AOI system to detect faults in a PCB. Based on examples using this setting, the imaging system may comprise a single camera. There is also the possibility of using multiple cameras to increase the chances of detecting an inherent fault.

A 3D camera provides better imaging. Any camera type used should be able to move under the control of application software to detect the faults. Speed and accuracy are also factors that influence the choice of cameras to use.

Camera types include:

  • The still image-camera system: We need to place it near the target PCB, and its effectiveness depends on the existence of the sound lighting system. The camera might need to be under the control of an audio software system to ensure efficacy.
  • Streaming Video: This is also another type of camera used for optical inspection. From the streaming video, full-frame shots are taken and subsequently analyzed. Conclusion this approach is not definite as it is not so accurate compared with other alternatives, but it possesses an advantage of speed over others.


Circuit boards configured into a mobile device

(Circuit boards configured into a mobile device)


7. AOI Test is Required Whether Prototyped or Soldering Process


Regardless of whether the assembly process follows the prototype, the AOI test is required. Or it is a soldering process. No matter the intricacies involved, the optical inspection system is an automatic quality inspection that is best for checking out for inherent errors of manufacturing or other quality issues. Product quality is the aim in this context, and automated optical inspection systems can ably provide that.




In conclusion, When checking the quality of manufacturing the printed circuit board, it takes a long time to fully accept the automated optical inspection system. The complexities of PCB have grown over time, improving the capacity for optimum functioning of AOIs.

The presence of smaller components and higher densities on contemporary PCB has further prompted the increasing acceptance of automatic checking systems. These facts have been discussed in this article to foster an increased understanding of its role. OurPCB has advanced detection technology; if you need it, you can contact us in time to get service.