Why AOI is a Must-have for PCB Assembly


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Automated optical inspection (AOI) is the automated visual inspection of a printed circuit board (PCB) assembly in which a camera is used to scan the board in extremely fine detail to check for any defects or failures.

So why is AOI so important?

Assuming your PCB design is correct, if you assemble the right parts in the right place then your product will work.  In production, this means putting a lot of focus on detecting and correcting any manufacturing defects or Manufacturing Defects Analysis (MDA.)

AOI is a vital inspection system which enables you to measure and monitor the quality of your PCB production, and to correct any issues or defects, at any strategic point in the process flow.

Crucially too, it’s the ‘quality gate’ for your PCB, providing peace of mind both for you and your EMS partner.

In many respects, your PCB is the 'brains' of your product and, as such, it’s a critical component with its own precise and rigorous design requirements.

And just as PCBs are getting smaller, they’re also becoming more complex. Even a relatively simple board can be made up of literally thousands of soldered joints, which means it simply isn't practical, or viable, to attempt to inspect manually.

So the sooner in the production process that faults are spotted, the easier and more cost efficient it is to rectify them to avoid replicating the same problem on a larger scale.

Put simply, if you’re in the business of creating PCBs, then a system for AOI should be on your check-list of “must-haves.”

The Role of AOI

The AOI process delivers the real-time inspection required by an EMS as well as providing empirical data that is invaluable for process control and refinement as production volumes increase.

An AOI system uses a number of strategies to analyze whether a PCB has been produced to the required standards.

Pattern matching algorithms keep a record of both successful and unsuccessful PCB assemblies.

And by constantly reviewing and analyzing fault data, your EMS partner can ensure they are identifying trends, enabling improvements in the manufacturing process, minimizing the risk of future rework and increasing the efficiency of production.

Key Questions for Your EMS partner

So what questions should an OEM be asking a prospective EMS partner about their AOI process?

You may be tempted to want to quiz your potential EMS provider on their AOI pass figures. After all, high pass rates equal a great quality product, right? Well, not always.

While in theory a high pass rate figure could suggest your product will be more reliable in the field, in reality it doesn’t necessarily guarantee performance.

Likewise too, a lower pass rate doesn’t mean that the build quality is bad—it may just mean that your EMS partner is being more particular in what they’re asking the AOI system to check for. In the long run, what you want is a high performing product, not a fantastic pass rate at the expense of product performance.

So, are there any limitations to AOI? While it’s an automated system, the inspection windows or parameters are set by the operator. So, the AOI will only inspect what you tell it to—and, conversely, it won’t find what it’s not told to look for.

There are also key elements of the inspection process where other methods of inspection are essential. In some cases, a degree of manual inspection, for example might be required alongside AOI if you’re wanting to check the quality of a solder joint. And X-ray can be invaluable for certain electronic assemblies when you want to check components with ‘hidden’ solder joints.

With the growing demand for higher quality and higher volume products, and an increasingly sophisticated manufacturing environment, it's crucial that any potential problems are identified and corrected as early as possible in the process flow.

As we've explored in this article, AOI has an invaluable role to play in speeding up the process of PCB production, in ensuring extreme precision to catch even the smallest of defects, and in minimizing the potential for time-consuming and costly reworking.

AOI acts as a 'quality gate,' for your PCB production, it’s an invaluable form of process control and it ensures greater reliability of your product ‘in the field’ which will provide peace of mind for both you and your EMS partner.

This article originally appeared on the JJS Manufacturing blog, which can be found here.

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