Automated Optical Inspection

What is AOI?

Automated Optical Inspection (AOI) is primarily used to check that electronic components have been placed, and soldered correctly onto a PCB. Most often used in the production of Surface Mount PCBS where small component sizes and high component density are prevalent.

Why use Automated Optical Inspection?

Historically boards have been checked by hand with a human operator using a magnifying system to look at every component on the board to ensure it is correctly placed and soldered. This is fine in a low volume, large component, low density environment but it has been shown that in a medium volume environment the efficiency of an operator changes over the length of a single shift. Also different operators will have differences of judgment, potentially making the results of testing inconsistent and occasionally passing faulty boards. Automated Optical Inspection takes away this variation in the checking process and gives a consistent, repeatable test that can run 24 hours a day if necessary.

How does Automated optical Inspection fit in my process?

Automatic Optical Inspection (AOI) will typically work alongside a quality/re-work operator to check the PCB’s immediately after the soldering process is complete, but it can work pre-re-flow to check placement/rotation/correct part before soldering if required. A Good AOI system will have a software suite that provides re-work capability as well as inspection so all defects can be managed in the AOI database.

How easy is AOI to programme?

This is one of the key differentiators between the many brands of Automated Optical Inspection available on the market. The software provided by DCB Automation is recognised as the easiest to use. With a library based structure based on part number it reduces programming time significantly as the library is built up and expanded with new boards. Initial creation of a test for each part number is also easy, using a graphic driven interface to guide the programmer to make the correct choices.

How long does it take to programme a board?

With any Automatic Optical Inspection (AOI) system this is a difficult question to answer. For a new board, where no components are in the library, it will take longer than one where all the components are in the library (which is a very simple operation taking no more than a few minutes). Also the number of part numbers on the board makes a difference as each part number is set up individually. DCB Automation ensures that the programming of a board is an easy process to follow and is widely recognised as having the best solution to programming issues.

How long does it take to inspect a board?

This is very much size dependant, but typically it will take 4 to 5 frames per second giving speeds of up to 150,000 components per hour achievable in the real world depending on component density and size. Often a single Automatic Optical Inspection (AOI) machine is used to support multiple production lines with rare and manageable bottlenecks, if very high volumes are expected then an in-line solution could be considered where the load/unload time can be controlled as well as inspection times.

What training is needed to use AOI?

Typically a reasonable experienced person can be trained to use DCB Automation Automatic Optical Inspection (AOI) system in 2 days, with some additional support provided to answer queries as they arise. DCB Automation provide 4 days of training with both the EasyVision and UltraVision systems, which would normally be spread over 4-6 weeks to ensure full training and support through the early days following delivery.

What skills are needed to use AOI?

There are different skill levels required depending on the role of the individual in the inspection process. To programme the Automatic Optical Inspection (AOI) machine there is good knowledge required of the issues in inspection as well as components and solder quality. The day-to-day user of the machine however needs a much lower level of skill/experience as they can be trained to test boards very easily, but through system security may have no access to changing or amending the programmes.

What restrictions are there on component size with AOI?

Currently the smallest size components typically being placed are 01005, and DCB’s UltraVision model with its 10uM resolution is capable of inspecting them. Clearly the future may see new developments but it is usually the case that AOI will develop before these are available in the market. Larger components are not an issue, even if they have to be spread across multiple image frames, due to the unique technology available in the DCB machines. Low Cost Automatic Optical Inspection (AOI) machines will typically have less resolution, like DCB's EasyVision provides capability down to 0402 with it's 2MPixel camera.

How does AOI deal with BGA devices?

Clearly use of optical methods alone will not check anything other than presence and rotation on a BGA device. DCB offer a laser height system as standard on the UltraVision, or as an option on EasyVision to help by measuring both absolute height and co-planarity to ensure that a device is laid correctly on the board. There is no substitute for a separate BGA inspection system, but these are often used on a spot check basis only.

How does a vertical camera system check for lifted legs?

Lifted legs are always shown up in a solder check as having poor quality solder as either there is no joint at all, or all the solder is hidden under the leg. If this is flagged to an operator they may not however pick up the issue and could manually pass the joint. The benefit of the DCB laser system is that it can be set to deploy automatically on suspect joints, thus performing a co-planarity check on all the devices legs. If one leg is lifted this will show very clearly and prevent the operator passing this failure unwittingly.

Automatic Optical Inspection (AOI) from DCB Automation - See what you've been missing