AOI, the full name of Automatic Optical Inspection, is automatic optical inspection equipment. It is an efficient intelligent equipment based on simulating human eyes, running machine vision technology, and replacing people in welding process production to detect common missing parts in PCBA.

As PCBs become more and more complex and components become smaller and smaller, traditional ICT and functional tests are becoming more laborious and time-consuming. It is difficult to obtain the physical space of test probes for dense and fine-pitch boards using bed-of-nails testing; for high-density surface mount circuit boards (PCBA), manual visual inspection is neither reliable nor Economical, and in the face of tiny components, such as 0402 type, 01005 type, etc., manual visual inspection has actually lost its meaning. In order to overcome the obstacles above, AOI came into being and is a powerful supplement to online testing (ICT) and functional testing (F/T). It can help PCBA manufacturers improve the pass rate of ICT (F/T), reduce the labor cost of visual inspection and the production cost of ICT fixtures, avoid ICT becoming a capacity bottleneck, shorten the production capacity improvement cycle of new products, and effectively control through statistics Product quality, improve product quality.

AOI technology can be applied to multiple positions in the PCBA production line. ALeader AOI can provide effective and high-quality quality inspection in the following five inspection positions:

1) After solder paste printing: After the solder paste is printed on the printer, defects in the printing process can be detected. Through the detection of the printed solder paste, defects in PCBA production before placement are avoided, and the maintenance cost of the PCBA board is reduced.

2) Before reflow soldering: This position should be after patching and before reflow soldering. This location can detect the quality of solder paste and patch, prevent PCBA defects before reflow soldering, and reduce the maintenance cost of PCBA board.

3) After reflow soldering: This position is the most typical position and indispensable. The biggest advantage of using this position detection is that all defects in the manufacturing process can be detected at this stage, so no defects will flow to the end customer.

4) Red glue inspection after reflow oven: The inspection of this position is mainly for the inspection of red glue board, which can effectively detect whether the red glue is OK or not, reduce its defects after wave soldering, and effectively reduce its labor Visual inspection costs and maintenance costs.

5) After wave crest furnace: This position is mainly for wave soldering inspection, including component inspection and plug-in inspection. This position inspection is an effective supplement to quality inspection and control in the entire wave soldering process.

How to place AOI system in SMT

There are various inspection and testing methods used in the electronics industry. The visual inspection method is the most common and low-cost, but very dependent on the operator. X-ray methods are costly, slow, and have limited capabilities. Automated optical inspection (AOI, automated optical inspection) is fast but expensive. In-circuit test (ICT, in-circuit test) and functional test are sometimes used as inspection tools, but their capabilities are also limited. In this article, I will discuss vision and AOI methods.

AOI, the full name of Automatic Optical Inspection, is automatic optical inspection equipment. It is an efficient intelligent equipment based on simulating human eyes, running machine vision technology, and replacing people in welding process production to detect common missing parts in PCBA.

As PCBs become more and more complex and components become smaller and smaller, traditional ICT and functional tests are becoming more laborious and time-consuming. It is difficult to obtain the physical space of test probes for dense and fine-pitch boards using bed-of-nails testing; for high-density surface mount circuit boards (PCBA), manual visual inspection is neither reliable nor Economical, and in the face of tiny components, such as 0402 type, 01005 type, etc., manual visual inspection has actually lost its meaning. In order to overcome the obstacles above, AOI came into being and is a powerful supplement to online testing (ICT) and functional testing (F/T). It can help PCBA manufacturers improve the pass rate of ICT (F/T), reduce the labor cost of visual inspection and the production cost of ICT fixtures, avoid ICT becoming a capacity bottleneck, shorten the production capacity improvement cycle of new products, and effectively control through statistics Product quality, improve product quality.

AOI technology can be applied to multiple positions in the PCBA production line. ALeader AOI can provide effective and high-quality quality inspection in the following five inspection positions:

1) After solder paste printing: After the solder paste is printed on the printer, defects in the printing process can be detected. Through the detection of the printed solder paste, defects in PCBA production before placement are avoided, and the maintenance cost of the PCBA board is reduced.

2) Before reflow soldering: This position should be after patching and before reflow soldering. This location can detect the quality of solder paste and patch, prevent PCBA defects before reflow soldering, and reduce the maintenance cost of PCBA board.

3) After reflow soldering: This position is the most typical position and indispensable. The biggest advantage of using this position detection is that all defects in the manufacturing process can be detected at this stage, so no defects will flow to the end customer.

4) Red glue inspection after reflow oven: The inspection of this position is mainly for the inspection of red glue board, which can effectively detect whether the red glue is OK or not, reduce its defects after wave soldering, and effectively reduce its labor Visual inspection costs and maintenance costs.

5) After wave crest furnace: This position is mainly for wave soldering inspection, including component inspection and plug-in inspection. This position inspection is an effective supplement to quality inspection and control in the entire wave soldering process.

How to place AOI system in SMT

There are various inspection and testing methods used in the electronics industry. The visual inspection method is the most common and low-cost, but very dependent on the operator. X-ray methods are costly, slow, and have limited capabilities. Automated optical inspection (AOI, automated optical inspection) is fast but expensive. In-circuit test (ICT, in-circuit test) and functional test are sometimes used as inspection tools, but their capabilities are also limited. In this article, I will discuss vision and AOI methods.

Visual inspection

 The most common and widely used inspection method is visual inspection, using a magnifying glass or microscope with a magnification of 2 to 10 times. J-STD-001 requires 2~4 times inspection for all components with a lead pitch greater than 0.020″. For fine-pitch components with a lead pitch of 0.020″ or less, a magnification factor of 10 times is required. The higher magnification factor should only be used as a reference.

The main problem of visual inspection is that it is up to the operator, and therefore, the supervisor. For example, if the same assembly is given to different inspectors, they will report different quality levels. A common response to this situation is to reduce human factors and switch to one of the many automated inspection systems.

Automatic Optical Inspection (AOI)

As electronic industry components enter into more closely spaced ball grid array (BGA) components, visual inspection of tin spots has become difficult or impossible. Also, as discussed earlier, even when feasible, visual inspection is very much up to the operator. Therefore, the industry has moved to automatic inspection systems. There are many systems on the market with a large price range. New machines are constantly being introduced to the market.

When choosing the machine you need, you need to decide what you want the AOI system to do. For example, do you want the machine to point out missing components, component polarity, placement accuracy, solder paste printing or solder joint quality? It is important to remember that most AOI machines are used to confirm wrong polarity or missing components It works fine, but it can be challenging to accurately confirm the quality of solder joints.

Regardless of the type of equipment used, the general AOI system requirements should include accuracy, repeatability, speed, computer-aided design (CAD) compatibility, and false failure and false acceptance (when using a machine for solder point quality inspection) A very common problem).

Sometimes, it is mistaken that the automatic inspection system can be used for process control to correct defects in real time by changing the appropriate variables. For most systems, this may be a promising idea now, because many changes that need to prevent problems require human intervention.

The only way to control the quality of solder joints in real time is if the soldering and inspection systems are integrated. With such an integrated system, the welding point either stops or continues, depending on the heat input requirements of the individual welding point. It is almost impossible in traditional reflow soldering processes such as convection. Laser welding systems with closed-loop inspection features are now commercially available to achieve this goal.

However, there is no system that can really point out a given defect and confirm its cause. Defect analysis may require human intervention and engineering judgment. For example, automatic inspection systems rely heavily on the quality and density of solder joints (less tin, more tin or no tin). However, defects with more than one reason may never be placed in only one of these three categories to meet the needs of automatic inspection systems. Poor tin may be caused by voids, insufficient solder fillet or insufficient solder paste. The improvement actions for these deficiencies are different and require human judgment and intervention.

Check the leading thought

There are two main ideas for inspection: defect prevention or defect discovery. The appropriate method should be the prevention of defects, because the focus is on process control and the implementation of corrective actions to eliminate defects. In such a method, the AOI machine is placed either after the solder paste printer of the SMT production line or after the component placement.

The people who use the discovery philosophy put the inspection machine very far behind the SMT line-behind the reflow oven. This is the final step in the manufacturing process to ensure that no bad products escape the factory.

From the leading ideology, many people do not agree with the preventive method of inspection. If you agree with this idea, where should you place the AOI system in the production line?

The first option is to place the AOI system directly behind the solder paste printing. Because many defects are related to the amount of solder paste and printing quality, this is a good location for the AOI system. What should such a system monitor? Only the X-Y size of solder paste, including misprints or solder paste volume (X-Y-Z)? Solder paste volume measurement will be slower than X-Y measurement, but provides more useful data. This is more critical in some applications than others. For example, for ceramic packaging, the volume of solder paste is critical to achieving the desired solder joint quality.

The second option is to put the AOI system directly after the shooter. Here, you can check the misplaced or misplaced small components, including resistors and capacitors, as well as the quality and volume of the solder paste of BGA and fine-pitch components. These components are mounted by different placement machines after the in-line chip shooter. Using their visualisual inspection

The most common and widely used inspection method is visual inspection, using a magnifying glass or microscope with a magnification of 2 to 10 times. J-STD-001 requires 2~4 times inspection for all components with a lead pitch greater than 0.020″. For fine-pitch components with a lead pitch of 0.020″ or less, a magnification factor of 10 times is required. The higher magnification factor should only be used as a reference.

The main problem of visual inspection is that it is up to the operator, and therefore, the supervisor. For example, if the same assembly is given to different inspectors, they will report different quality levels. A common response to this situation is to reduce human factors and switch to one of the many automated inspection systems.

Automatic Optical Inspection (AOI)

As electronic industry components enter into more closely spaced ball grid array (BGA) components, visual inspection of tin spots has become difficult or impossible. Also, as discussed earlier, even when feasible, visual inspection is very much up to the operator. Therefore, the industry has moved to automatic inspection systems. There are many systems on the market with a large price range. New machines are constantly being introduced to the market.

When choosing the machine you need, you need to decide what you want the AOI system to do. For example, do you want the machine to point out missing components, component polarity, placement accuracy, solder paste printing or solder joint quality? It is important to remember that most AOI machines are used to confirm wrong polarity or missing components It works fine, but it can be challenging to accurately confirm the quality of solder joints.

Regardless of the type of equipment used, the general AOI system requirements should include accuracy, repeatability, speed, computer-aided design (CAD) compatibility, and false failure and false acceptance (when using a machine for solder point quality inspection) A very common problem).

Sometimes, it is mistaken that the automatic inspection system can be used for process control to correct defects in real time by changing the appropriate variables. For most systems, this may be a promising idea now, because many changes that need to prevent problems require human intervention.

 The only way to control the quality of solder joints in real time is if the soldering and inspection systems are integrated. With such an integrated system, the welding point either stops or continues, depending on the heat input requirements of the individual welding point. It is almost impossible in traditional reflow soldering processes such as convection. Laser welding systems with closed-loop inspection features are now commercially available to achieve this goal.

However, there is no system that can really point out a given defect and confirm its cause. Defect analysis may require human intervention and engineering judgment. For example, automatic inspection systems rely heavily on the quality and density of solder joints (less tin, more tin or no tin). However, defects with more than one reason may never be placed in only one of these three categories to meet the needs of automatic inspection systems. Poor tin may be caused by voids, insufficient solder fillet or insufficient solder paste. The improvement actions for these deficiencies are different and require human judgment and intervention.

Check the leading thought

There are two main ideas for inspection: defect prevention or defect discovery. The appropriate method should be the prevention of defects, because the focus is on process control and the implementation of corrective actions to eliminate defects. In such a method, the AOI machine is placed either after the solder paste printer of the SMT production line or after the component placement.

The people who use the discovery philosophy put the inspection machine very far behind the SMT line-behind the reflow oven. This is the final step in the manufacturing process to ensure that no bad products escape the factory.

From the leading ideology, many people do not agree with the preventive method of inspection. If you agree with this idea, where should you place the AOI system in the production line?

The first option is to place the AOI system directly behind the solder paste printing. Because many defects are related to the amount of solder paste and printing quality, this is a good location for the AOI system. What should such a system monitor? Only the X-Y size of solder paste, including misprints or solder paste volume (X-Y-Z)? Solder paste volume measurement will be slower than X-Y measurement, but provides more useful data. This is more critical in some applications than others. For example, for ceramic packaging, the volume of solder paste is critical to achieving the desired solder joint quality.

The second option is to put the AOI system directly after the shooter. Here, you can check the misplaced or misplaced small components, including resistors and capacitors, as well as the quality and volume of the solder paste of BGA and fine-pitch components. These components are mounted by different placement machines after the in-line chip shooter. Using their visua capabilities, they usually have better accuracy for larger packages.

　　 The third option is to place the AOI system behind the fine pitch and BGA placement machine (before reflow) to check for misplaced dense feet, BGA and other large components. This is a good location because most defects are related to dense foot components. These are the choices of the advocates of prevention philosophy.

　　 If you focus on the found method, you have a fourth option-put the AOI system after reflow soldering and look for poor quality solder joints. This is a good method for companies that want to ensure that unacceptable solder joints are discovered before they are shipped to the end user.

　　 The fifth option is to combine the ideas of prevention and discovery, placing the AOI system after every process step-solder paste printing, chip shooting machine, BGA and close-foot mounting, and reflow soldering. This choice may be unaffordable.

　　 Most people have a limited budget and must decide where to place the system on the SMT line. If you only buy an AOI system, you may want to put it directly after the shooter. You can check for two main problems-misplacement or errors of smaller components and the quality of solder paste of BGA and dense-pin components. volume. Also, this is the most critical position that determines the overall quality.

  in conclusion

　　 Tin point inspection is an afterthought. A more effective method is to take preventive measures. That is, implement process control to ensure that problems do not occur. Does this mean that inspection is unnecessary? Not at all. The inspection will have to continue to complete the feedback of defect collection to monitor the process and implement improvement actions, so the problem will not occur.