AOI vs ICT vs AXI and PCB SMT Assembly Inspection
To improve the quality of PCBA production, manufacturers require good inspection of the boards. For efficient and detailed in-depth board inspection, PCB (Printed Circuit Board) SMT (Surface Mount Technology) assembly inspection equipment should be adopted.
AOI, ICT, and AXI will give you the information to optimize your boards and fix errors to provide the highest overall output quality. In this post, we compare AOI vs ICT vs AXI.
AOI (Automated Optical Inspection)
Virtually every current electronic device works with a circuit board. AOI (Automated Optical Inspection) is a type of classical inspection technology that is widely used for PCB SMT assembly inspection.
AOI equipment works effectively by using a rotating camera to capture images that will automatically scan PCB and then compares between tested solder joints and eligible parameters in the database.
What is PCB?
A PCB connects electrical components such as integrated circuits (ICs) that are assembled on bare boards applied in different electronic devices including handheld computers, electronic watches, calculators, electronic communication equipment, and more.
Without AOI processing and testing images, PCBs will be exposed to lead defects which will devalue the system.
AOI performs two major roles, including end quality and process tracking. AOI equipment can be positioned at multiple locations along the manufacturing line; however, the following automated vision inspection positions can be considered if most defects are to be recognized and corrected.
- After Solder Paste Printing
- Before Reflow Soldering
- After Reflow Soldering
ICT or In-circuit Test
When it comes to electrical tests, ICT equipment is the most fundamental device applied. When bed nails come in contact with components that are soldered solidly on simple PCB boards, certain current and voltage are used to test for component defects including solder joint bridging, parameter deviation, displacement, missing, misplacement, opens and shorts, etc.
While bed nails produce high speed and mass volume production at a low cost, it still fails to carry out an appropriate test on some high-density SMT PCB assembly.
There is also the flying probe test which tests the electrical performance of circuits based on a large number of flying probes. However, this prevalent ICT method for PCB SMT assembly inspection is commonly applied in PCB fabrication tests.
ICT equipment consists of a number of elements namely circuit tester, software, and fixture. The software and board will be assembly or board-specific while the tester will be used for a variety of boards. These three elements form the major parts of any ICT system.
- Test results are easy to interpret
- Easy to detect manufacturing defects
- Generating programme is easy
- High defect observation capability
- High test speed
- Fixtures are difficult to update
- Fixtures are expensive
- Test access becoming more difficult
- Main types of ICT machines
- Standard ICT machine
- Manufacturing defect analyzer, MDA
- Flying probe tester
- Cableform tester
AXI is a type of structural test and inspection and the newest developed inspection method among the three.
AXIs are high-energy electromagnetic radiation that is designed to test PCB printed circuit boards containing components with fine pitch packaging or array-style packaging e.g.
CSPs (Chip Size Package), BGAs, CGAs (Column Grid Arrays), etc. They can penetrate the components to check their internal structures.
When PCB boards enter AXI equipment along the rail or when the X-rays pass through a component, the X-rays will be absorbed by the detector allowing different densities within the components to attenuate different amounts of X-rays which results in areas of light and shade on the detection medium.
Since solder joints contain so much lead that can absorb X-rays, AXI can easily detect solder joint defects as well as slag inclusion, incomplete welding, and porosity through image analysis algorithms.
AXI benefits include:
- It contributes to the cost reduction of defects
- Many defects can be detected in the early stage of the PCB assembly process
- AXI prevents defects from flooding among remaining printed circuit board assembly or even clients’ practical projects
Comparing AOI, ICT, AND AXI
For AOI, the advantages include high flexibility and extremely short test programming time. AOI is also capable of accumulating the manufacturing quality of each link and defect type that technology control engineers will use for analysis and management. The biggest disadvantages of AOI solutions are defects that visual inspection fails to inspect, disability to detect unseen solder joints, and failure to detect circuit errors.
ICT comes with a lot of advantages like high test speed and high defect observation. Due to its fast features and convenience, it is mainly adopted by users requiring mass volume products. On the downside, companies requiring low volume and diverse kinds of products may not value ICT because bed nails need to be changed often and it may be difficult to detect defects in complex circuits with more density.
AXI is capable of inspecting solder joints that can’t be seen with naked eyes. Its manufacturing defect rate is as high as 97%. On the downside, when it comes to electrical performance, AXI fails to test defects. Both AXI and AOI belong to the same structural test and inspection category – that is, they capture images for inspection. Nevertheless, the major difference is that AXI depends on X-ray to capture images while AOI machines on the light source.
The Bottom Line
We hope this post shows a clear comparison among AOI, ICT, and AXI, and aids you in making a better decision for your manufacturing business.
To ensure the lowest defect rate, manufacturers should consider tapping into the latest inspection technology for maximum efficiency.
For further enquiries, feel free to get in touch with our specialists.
Cortex Robotics Sdn Bhd.
72-2-6, Arena Curve, Jalan Mahsuri,
11950 Bayan Lepas, Penang, Malaysia.
T: +604 – 611 0110