Detecting advantages of AOI and X-ray Inspection Equipment

AOI (Auto Optical Inspection), It has been widely used in the circuit board assembly line of the electronics industry, and has replaced the previous manual visual inspection operations.

AOI uses imaging technology, to determine whether the object under test conforms to the standard based on whether there is a large difference, between the object to be measured and the standard image.

Now and In the past Of AOI

Before, AOI was used to detect whether the surface printing of the IC (integrated circuit) package was defective. As the technology evolved, Now it was used to detect the PCB assembly on the quality status of  SMT assembly line, or check whether the solder paste meets the standards after printing.

The biggest advantage of AOI is that it can replace the manual visual inspection before and after SMT reflow soldering, and it can judge the shortcomings of SMT assembly assembly more accurately than the human eye.

As with the human eye, AOI can only perform surface inspection of objects, so as long as it is visible on the surface of the object, it can be checked correctly, but for the welding under the part or the edge of the part.

There may be some unsuccessful points. Of course, many AOIs have been able to make multi-angle photography to increase their ability to detect IC sticks and increase the angle of photography of some shielded components to provide more The detection rate, but the effect is always not ideal, it is difficult to achieve 100% test coverage.

Shortcoming of AOI

In fact, the biggest shortcoming of AOI is that some gray scales or shadows are not obvious (prone to false reject), you may use different colors of light to discriminate, but the most troublesome are those covered by other parts.

The components and the solder joints located underneath the component, the traditional AOI can only detect where the direct light can reach, the For example, the shield frame ribs or the components underneath their edges, which are ignored because the AOI is not detected.

Generally, circuit board assembly lines use AOI to ensure their assembly quality at least. They usually have to be tested by ICT (In-Circuit Test) and functional test (FVT). Some production lines will also be in AXI (Automatic X-ray Inspection). Use X-Ray machine to check the quality of solder joints (such as BGA) under the component.

Detecting advantages of AOI and X-ray Inspection Equipment

The AOI can fully check out the following shortcomings:
  1. Missing
  2. Skew
  3. Tombstone
The X Ray inspection machine can fully check out the following shortcomings:
  1. Defect inspection in IC encapsulation, e.g.: layer separation, cracking, void, and line integrity.
  2. Measuring chip size, measuring line curvature, measuring the proportion of solder area of components.
  3. Possible defects in PCB manufacturing processes, e.g.: misalignment, solder bridge and open.
  4. SMT solder short, cold solder, False Solder, component shifted, solder insufficient, solder void inspection and measurement.
  5. Defect inspection of open, short or abnormal connections that may occur.

Since AOI is subject to factors such as light, angle, resolution etc, the following shortcomings can only be checked under certain conditions, but it is difficult to achieve 100% detection rate.

  1. Wrong component
  2. Wrong polarity
  3. Lead lift, lead defective
  4. Solder bridge
  5. Insufficient solder
  6. False Solder, Cold Solder

In short, although AOI is easy to use, it does have some inherent limitations. However, it is used for preliminary quality analysis of SMT, and immediately feedback the quality status of SMT and improves it, which can effectively increase the output of SMT.

Usually, using an ICT tester to solve the problem and then reacting to SMT is usually a time difference after 24 hours. At that time, SMT conditions usually changed, and even the lines changed.

In addition, with the development of technology and the improvement of MCU computing power, many SMT manufacturers already have AOI equipment. In order to ensure high quality, it is necessary to have MES x ray inspection machine.

Family of Industrial X-ray inspection machine & BGA rework station

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