How does AOI play a crucial role for the Surface Mount Technology Assembly?

By Mer-Mar Electronics Date posted: Last updated: August 30, 2022

There are several reasons why automated optical inspection (AOI) is increasingly playing a crucial role when it comes to surface mount technology assembly. Notable among them are:

  • Lines on PCB are getting finer.
  • PCBs are getting increasingly miniaturized and there is high component density.

This is besides the fact that, production volumes are typically high, and so are quality expectations. The conventional method of inspection clearly cannot serve the purpose of high-density PCB assembly products. It is for all these reasons that quality control is turning to automated machines for addressing quality issues.

How does AOI Technology work?

Automatic Optical Inspection (AOI), sometimes also referred to as Automated Visual Inspection, is essentially a control process. Simply put, it uses optical methods for inspection. It evaluates the quality of the surface mount technology assembly by way of visual information. With stringent quality benchmarks for electronic devices already laid down, it comes in handy in pointing out any defects.

The key advantage of these systems is that they can detect failures early. What this means is that you do not have to deal with costly errors once the final product is ready to go to the market. Instead, the quality can be checked at each stage of the SMT manufacturing process. This has definite financial advantages, not to mention the fact that you do not have to put your reputation at stake, should any errors crop up once your product reaches the market.

The two commonly used inspection, analysis and judgment methods include:

  • Design Rule Check
  • Computer-Aided Design, Data Comparison

Let us look at both of them in some detail:

Design Rule Check (DRC) Method

This method involves inspecting the design pattern basis some rules. For instance, in inspecting the SMT PCB assembly pattern, the rule that is followed is that all lines should rely on solder joints as terminals and that all lines share the same width and the spacing should be equal or more than the regulated value. The advantages of the DRC method include:

  • Ease of setting up
  • Speed of processing
  • Small volume of programming

The disadvantages of the DRC system, however, lie in:

  • Weakness in determining boundary capacity and boundary position

Computer-Aided Design (CAD) Data Comparison Method

This method involves comparing the image patterns stored in the AOI system with the practical image patterns. The challenge of this method, however, occurs on account of high requirement of data real time processing.

Inspection Functions of AOI Technology

AOI technology can be used for inspection of the following:

  • Bare Boards
  • Solder Paste Printing
  • Component Inspection
  • Solder Joints

When it comes to Bare Boards as well as solder joints, it is important to remember that inspections are not made in real time. For Bare Boards, the AOI items include:

  • Wiretapping
  • Scratches
  • Pinhole
  • Line spacing
  • Edge Roughness, and more

AOI items for solder joints include:

  • Missing components
  • Component placement direction
  • Component Number
  • Solder joint quality, and more

In case of Solder Paste and Component Inspection, the inspections are made in real time.

Structure of an AOI System

For Bare PCBs

It relies on the comparison function. The image signals are sent to the control subsystem that makes its judgment on the defects. Marks are made on the PCB in real time and defects can be magnified and checked. This method allows for high inspection speed.

For Solder Joints

Optical cameras are used to capture 3D images of solder joints that are, in turn, compared with standard solder joint images. This enables the defects to be clearly seen and ascertained.

For Solder Paste Printing

It consists of a camera and optical fiber x-y system for solder paste printing at surface mount technology assembly. It enables the solder paste thickness to be measured. The inspection primarily works on the principle of transforming shapes into optical changes.

To sum up

It is easy to see why AOI is one of the best inspection tools in the surface mount technology environment. Not only is it reliable it is extremely cost-effective too. You can count on it to detect both catastrophic failures as well as quality defects.

We provide SMT PCB assembly for high mechanical strength, flexibility, durability, reliability and high performance. Whether you need a low volume or high volume, semi-automatic or fully automatic SMT PCB assembly, we have a system in line with meeting your throughput & budget requirements.

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