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AOI Machine: A Comprehensive Overview of Automatic Optical Inspection Systems

Make sure the PCB or Circuit Board you employ in the projects will function properly and satisfy your customers. It’s critical to possess a reliable method for checking PCBs for faults and making sure they work as intended.

The size and complexity of PCBs are both increasing; today’s PCBs can contain numerous soldered joints with a huge number of microscopic components. Errors may occur more frequently as a result of the increased complexity. Automated optical inspection or AOI approaches can give more clarity and accuracy when a typical visual examination is unable to discover minute flaws in a crowded, tightly packed board.

How Does AOI Machine Work?

How can one define AOI? The Automatic optical inspection involves an electronic scanner that employs light imaging to visually check the finished PCB. It assesses the level of craftsmanship to ensure that the Circuits are appropriate for usage and purchase.

A typical AOI system includes several light sources, numerous cameras, and maybe even video cameras. Several light sources from various perspectives illuminate the Circuit board. Moreover, the cameras click videos and photos to produce a complete image for analysis.

Without the requirement for a manual visual inspection, AOI measurement often employs a scanner to autonomously scan the item. The scanner checks for larger problems that would impair the quality of the PCB as well as tiny errors that might result in catastrophic failures, like the lack of a crucial component. Smaller flaws include things like slightly misaligned parts and soldering that creates the incorrect shape or size.

At several phases of the production process, AOI is helpful. It performs well for the inspection of solder paste, bare PCBs, and pre and post-reflow. Each step has the potential to create design flaws in a PCB, and AOI aids in identifying these flaws before production on a defective board continues.

Although, the majority of AOI happens during post-production. This is because the AOI may employ an individual system to simultaneously examine several types of faults. One thorough inspection takes relatively less duration than one inspection after each stage of the procedure. Utilizing AOI for a final verification allows the production process to move quickly and enables it to meet deadlines and higher productivity. Additionally, the problematic boards also go back for repair while the remaining boards proceed if AOI discovers faults during the post-production phase.

The Role Of AOI Machine

PCB manufacturing depends significantly on AOI. It ensures that every board can deliver the high efficiency needed in intricate electrical devices.

When AOI finds a PCB defect, it marks the PCB and sends it back for rework. This procedure may take place in a number of distinct manners. The results of the AOI may not meet some facility specifications, such as all the PCB lines ought to be larger than a particular size. In this situation, people may examine the results and choose which boards need repair. AOI can make a comparison between the actual PCB and a CAD rendering of an ideal PCB. When the real PCB diverts from the desired design, AOI automatically spots those areas and flags the PCB for reworking.

For PCB manufacture, AOI offers the following advantages:

· Ensuring Quality

You may use AOI to verify that the PCB products work as planned. Increasing customer happiness, improving your company’s reputation, and giving clients assurance about the service quality you’re providing all benefit from maintaining the PCB quality.

· Evaluating A Complex Board

A board from Millennium Circuits will automatically go through AOI if it has over 100 components. The naked eye is incapable of inspecting complex PCB layouts with the same level of precision as AOI.

· Improving Processes

If flaws occur from defective processes, grasp them right away using AOI. AOI may assist you in identifying defect patterns and modifying your procedures before producing thousands of PCBs with the same defect. According to the latest study, finding a flaw in a PCB that has just been assembled is just ten times more expensive than finding one in a bare PCB. Yet finding a flaw in a PCB that has already been put to use in the field is around 1,000 times more expensive. Early mistake detection reduces the possibility of future repair and improves the productivity of your manufacturing processes.

· Customizability

Even though AOI operates fully automatically, the operator may still specify the parameters that will inform the scanner where and what to look for. It’s simple to tweak your parameters to locate the defects you need if the design requirements change.

Reviews of AOI Machine


The following constitute a few of the elements evaluated while an AOI:

Soldering Defects

Soldering employs a very low-melting-temp alloy, frequently lead, lead-free or tin alloy, to bond the PCB’s electrical components. With the exception of not melting the electrical components, the procedure is comparable to welding. When the bonds between two electrical components don’t form properly, this is known as a soldering fault.

The following are some typical soldering flaws that AOI might look for:

· Open Circuit

PCB’s open circuits are typically the main problem. The reason is that an incomplete or open circuit stops the current from passing through them. The board won’t operate properly if a circuit is wide open.

Open circuits may arise due to inadequate traces or vias. These improper traces form due to inefficient soldering. An evident open circuit may occasionally be found by eye examination, while AOI can find even marginally open circuit points and mark the PCB for correct circuit closure.

· Solder Bridges Or Solder Shorts

Solder bridges happen when two PCB components are connected electrically, even though they shouldn’t be. These bridges may develop if a board is produced with an excessive amount of solder or if solder leaks into a solder-free section of the PCB.

If the solder paste fails to detach from its tips or leads prior to solidifying, solder bridges frequently happen. The metal pads known as leads are used to link two places on a circuit board. Due to the size of the leads, the amount of paste bonding them to a PCB, or the shallow pitch of the PCB, the solder paste may not separate.

Solder bridges cause problems as they hinder the desired current flow through the circuit. They may short-circuit the PCB or destroy vital components or vias. Additionally, solder bridges are extremely hard to spot with the human eye; even minute solder seepage may allow them to develop. Luckily, AOI scanning may detect even the smallest solder bridges or shorts and return the defective circuit boards for correction.

· Insufficient Solder

When the manufacturing process utilizes insufficient solder to bind various components onto the circuit, an inadequate solder connection develops. Solder skips happen when the solder occasionally fails to join the components completely.

The PCB’s performance will suffer if the connections of components are improperly soldered because they may not produce solid electrical connections. Additionally, the PCB will have missing parts if there is insufficient solder to hold the electrical components in place, which will very certainly lead to catastrophic failure. If a board has to be resoldered, an AOI may scan it, note how much solder is on each electrical component, or compare it to the right picture.

· Excess Solder

When the reverse occurs, that is, when the manufacturing process soldiers the board, excess solder results. Sometimes it happens as a result of using too-wide soldering tips or applying too much heat.

Solder bridges and other defects like excess solder might be problematic. A huge spherical solder ball may form when excessive solder is applied to a board pin during production, making it hard to determine if the board pin is adequately moistened to adhere to the PCB.

Due to their size, solder balls or bridges are generally simple to spot, although a human examiner may skip one after examining hundreds of almost similar boards. With the use of a solder wick or solder sucker, an effective AOI scanner may quickly identify excess solder and return the board for repair.

Component Defects of AOI Machine

Defects in the tiny functional elements connected to a PCB are known as component defects. Here are a few typical PCB component flaws:

· Lifted Lead

When one small metal pad on a circuit doesn’t stick correctly, the lifted lead results. Sometimes a raised lead happens as a result of manufacturing handling, extreme heat, or board flexing. On the other hand, it happens when leads that are excessively long rise once they touch solder.

The instability of lifted leads makes them troublesome. Pins may link to a copper sheet below using the metal pads on the PCB. However, if somehow the lead rises, the pins won’t allow it to do so correctly. Missed connections may harm the operation of the board and lead to component failure.

· Missing Components

A Circuit board may miss an electrical component due to various causes. Inadequate soldering may result in components going missing, or the manufacturing process may omit a crucial component.

A PCB with a missing electrical component has a major fault that might result in catastrophic failure. The naked eye may see the missing part. Yet, since this is a serious flaw, having a trustworthy AOI scanning device is essential for identifying the missing components in PCBs before they reach end users.

· Misaligned & Misplaced Component

 Misplacement or Misalignment can happen when the manufacturing process installs components wrongly or when electrical components move after placement. Due to the ease with which parts can move on top of molten solder due to the solder’s low surface tension, component shifting often occurs during reflow.

The PCB may function even with a misplaced or misaligned component, although it may operate slowly. Or it may not function at all. The ability to detect alignment issues requires a reliable AOI scanner since some alignment issues may be too little to be seen with the human eye.

Comparing AOI Machine With Other Inspection Methods


AOI offers a number of benefits over other procedures for finding PCB flaws. A comparison between AOI and other inspection techniques is described below:

1. Automated X-Ray Inspection (AXI)

Instead of using light scanning to check the PCBs, AXI employs X-rays. AXI is frequently used by businesses to assess boards with especially intricate or thick construction. This is because X-rays can photograph the materials since they pass through them. One component could be able to block others since the light utilized for AOI bounces off surfaces. But an X-ray passes through several layers of substance, precisely imaging each one.

AXI features brand-new, cutting-edge technology, and its biggest drawback is the cost. AXI seems so expensive that, unless a board is exceptionally complex or densely packed, it is frequently not worthwhile to utilize.

2. Automatic Laser Test (ALT) Measurement

Instead of using conventional light imaging, ALT measurement scans and measures PCBs using lasers. The ALT technology uses the placement of the lasers to determine the height and positioning of various components and evaluate their reflectivity when the laser bounces off the components of the PCB. Similar to AOI, the ALT technology may identify any defects by comparing the empirical analysis to a list of requirements or schematic.

Although interference can occasionally result in erroneous results, ALT technology is particularly helpful in determining where and how much solder paste is present.

3. In-Circuit Testing (ICT)

An electric probe is used in in-circuit inspection to assess the performance of a built PCB. Each component’s placement and functionality are checked using a current of electricity. It examines crucial electrical properties, including resistance and capacitance, as well as checks for open and short circuits.

ICT seems to provide less comprehensive soldering data than AOI since it relies on electricity rather than imagery. It can assess the caliber of components and offer details on circuitry-affecting soldering flaws, but it is unable to provide much information regarding inadequate or excess solder.

Particularly for the thinner PCBs being created today, AOI is typically more trustworthy than in-circuit inspection.

4. Manual Visual Inspection (MVI)

Since AOI doesn’t involve touching the PCB, most PCB businesses prefer it to human visual examination. The human examiner must examine the PCB. Moreover, handling may cause an otherwise flawless board to develop flaws. AOI also helps in maintaining PCBs’ structural integrity and scanning their sensitive components without harming them.

A more trustworthy method than a personal visual assessment is AOI. A person may overlook the tiny PCB fault. However, AOI can detect even the smallest mistakes. It can easily scan the PCB in more detail than a human eye is able to see. It is dependably trustworthy throughout all phases of the production process. Its relentless acuity never wanes.


Verifying the PCB’s quality as they leave an assembly line is crucial. This allows for the monitoring of the boards’ quality as well as the early identification and correction of errors to avoid recurrence.

This also shows the significance of an AOI system for a fabrication organization.

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