The Significance of Automatic Optical Inspection in Electronics Printed Circuit Boards

AOI, which is also known as automated automatic inspection or automatic optical inspection is a major technique used for the manufacturing and testing of printed circuit boards or electronics.

Automated optical inspection makes accurate and fast inspection of the assemblies of electronics particularly PCBs to make sure that the product is of high quality. This ensures a high production line and the building of the items will be done correctly and excluding any manufacturing faults.

Importance of Automated Optical Inspection

Even with the huge improvements made, the modern circuits are now much more complicated compared to boards even a few years back. Introducing the surface mount technology, as well as the further size reductions, which means that boards are usually compact. The relatively average board even features many soldered joints, and these joints are where most problems are seen and found.

Increases in the boards’ complexity means that the manual inspection isn’t a reliable and viable option today. Even when the approach was accepted, it was seen that this approach wasn’t as effective as expected. This is because inspectors soon got tired and incorrect and poor construction was missed easily.

Now, with today’s marketplace now needing high volume, high-quality products need to get to the market quickly, there is a need for very fast and reliable methods to make sure that the quality of the product remains high. Automated optical inspection (AOI) is very important for the test strategy of integrated electronics, which ensures that costs remain low. This can happen by detecting the faults very early during production.

The use of automatic or automated optical inspection is one solution. This could be placed in the line of production just after completing the solder process. By so doing, they will be useful in catching problems quickly and early during the production process. Now, this comes with different advantages.

Fixing faults can cost more when the production process has gone further along, this is clearly the best place for you to discover faults. In addition, problems with process in the assembly and solder area could be seen very early during the production and the information used as a feedback. A quick response can make sure that you recognize problems quickly and also rectify them.

What are the Basics of Automatic Optical Inspection?

Automated optical inspection systems make use of visual methods in monitoring defects in printed circuit boards. Also, they can detect different defects of the surface features like stains, scratches, nodules, and other well-known dimensional defects like solder thinning, shorts, and open circuits. Also, they can detect missing components, incorrect components, as well as components that are incorrectly placed. This is why it is possible for them to perform the visual checks initially performed by the manual operators more accurately and swiftly.

This they achieve by scanning the board’s surface visually. Light is given to the board through different light sources. Also, at least one camera of high definition is used. By this, the AOI machine (automated optical inspection) will have the ability of building the board’s picture.

Also, the AOI system (automated optical inspection system? Makes use of this captured image, that is processed and compared with the machine’s knowledge on the way the board ought to look. Making use of the comparison, this AOI system will detect as well as highlight the suspect or defects areas.

Furthermore, automated optical inspection makes use of some techniques to help in analyzing if the board has defects or is satisfactory.

Template Matching

Making use of this to process the automatic optical inspection system helps in comparing the obtained image with that of the golden board.

Statistical Pattern Matching

For this, it makes use of a statistical approach in addressing the issues. When you store the results of different boards as well as different failure types, then it will have the ability of accommodating the minor acceptable deviations

Pattern Matching

With this technique, the automatic optical inspection (AOI system) helps in storing information of the bad and good PCB assemblies, thereby matching these obtained images.

To build the database that the board should have or be both printed circuit board (PCB) design information and status boards are useful. However, with the great improvements in technology, AOI systems have been able to predict the defects accurately and also reduce the possibility of defects. This is why automated optical inspection systems are very important elements in a very sophisticated manufacturing environment.

AOI Image Capturing and Analysis

A key element of automatic optical inspection is its image capture system. It helps in capturing the image of a specific printed circuit board assembly (PCB assembly). The processing software then analyzes it within the aoi systems. Note that, there are lots of variants when we talk of the image capture system. This depends on the application as well as the cost/complexity of that AOI system.

Furthermore, the imaging systems could be just one camera or more. This offers better imaging, as well as the probability of capability. Also, the cameras ought to move under a specific software control. With this, they will be able to move and reach the optimum position for a specific PCB assembly.

Also, this camera type can affect the performance. Accuracy against speed is an important balance you must strike and will determine the type of camera used.

Still image camera system

The system is placed close to that specific PCB (printed circuit board). Due to this it needs a good lighting system. Also, it may be required to move its camera under a specific software control.

Streaming video

The camera type used for automatic optical inspection takes the streaming video from where the complete frames are usually taken. This captured frame allows the generation of still images where the performance of the signal processing takes place. This specific approach isn’t as accurate as the other types of still image systems. However, it has a great benefit due to its extremely high speed.

During a board’s image analysis, the AOI systems checks for different specific features like component size, component placement, reflectivity, background color, label patterns, and board fiducials, etc.

As a significant element of the task, the AOI system also helps in the inspection of the solder joints. This is to make sure that they indicate satisfactory joints. During the analysis of the boards, it is necessary for the AOI system to consider many variations between the good boards.

Components don’t just vary in size considerably between the batches, they also vary in reflectivity and color. Frequently, there are differences in silk screening also where the color typeface and ink thickness may experience a slight change.

The AOI Light Source

One important element in an AOI system is lighting. By selecting the right lighting source, it becomes realistic to highlight the different defects more easily. Also, with great advances in the lighting technology recently, this allowed the use of lighting in enhancing the available images. In return, this allows the highlighting of defects easily and a reduction in the processing necessary as well as an increase in accuracy and speed.

Majority of AOI systems feature a lighting set that is already defined. This involves the required operation as well as the types of products that need to be tested. Usually, these have been optimized to work with the anticipated conditions. Moreover, at times, it may require some customization, and one useful point is understanding what lighting is.

Below are the different types of lighting:

LED Lighting

LED lighting development means that AOI systems can adapt a very stable lighting form; though LED lighting suffers from light output reduction from LEDs overtime. You can get some compensation for this via current increase making use of LED lighting. The lighting level can be controlled as well. Therefore LEDs are more satisfactory than incandescent or fluorescent lights, which were used years back.

Fluorescent Lighting

This is widely useful in applications relating to automatic optical inspection. This is because it offers a very effective lighting form to view PCB defects. One issue with fluorescent lighting for use in AOI applications is that, with time, these lamps degrade. What this means is that, the AOI system is subject to constant change in the light quality as well as levels.

Ultra-violet or Infra-red

 There are cases where ultraviolet or infrared lighting may become necessary in enhancing some defects or enabling the carrying out of automatic optical inspection in order to reveal some defects. Asides from the lighting form, the lighting position for an AOI, automated optical inspection is also very important.

These light sources need positioning not just to make sure that all the areas have enough light, which is very important whenever some components happen to cast shadows, but highlight defects as well. This is why there may be a need for careful adjustment for the different assemblies.


Here comes the end of our article on the importance of automatic optical inspection in the electronics industry. This covers everything that entails accurate inspection, solder paste inspection systems, as well as manual visual inspection.

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