Automated optical inspection (AOI) is an important inspection in printed circuit board (PCB) manufacture process.  The camera of AOI  scans the test  PCB for both catastrophic failure (e.g. missing component) and quality defects (e.g. fillet size or shape or component skew). It is applied mainly in 3 stages of the manufacturing process: bare board inspection, pre-reflow and post-reflow. Howe choose automated optical inspection AOI is an important question for company.

There are tens of automated optical inspection manufactures in the world. They have released hundreds of automated optical inspection products with different model to market. Normally, we are not sure which one to choose  when we need an automated optical inspection.

Here, we will give you some advises to help choose a suitable AOI  for your PCB line.

1.Resolution in Choose a Automated Optical Inspection AOI

The resolution of AOI for item 01005  should be higher than 12 μm,  while for item 0402 should be higher than 25 μm.
We can calculate the resolution from the pixels of camera and POV. The equation is: Resolution =FOV/Pixels of camera. For example, if a camera has 300,000 (480*640) pixels and the FOV is 12*16mm, The best resolution of this AOI is 12mm/480=25 μm. Thus, this AOI can only used to check item beyond 0402, such as item 0805.  If a camera has 2,000,000 (1200*1600) pixels and the FOV is 12*16mm, The best resolution of this AOI is 12mm/1200=10 μm. Thus, this AOI can only used to check  both item 0201 and 0402, even more item beyond.
Items    Resolution
01005  <=12 μm

0201    <=15 μm

0402    <=25 μm

2. Test PCB Size in Choose a Automated Optical Inspection AOI

Every automated optical inspection have the largest PCB size  it can test.   Before you choose AOI, make sure that the size of PCB pads you will test is smaller than AOI’s largest  test size.

3.Online AOI or Offline AOI 

In the case of sufficient budget, we recommend online AOI.

  • Reason A: The inspection process is almost done in sync with production. From raw materials to inspection, fully automated process production process. Reduced production time.
  • Reason B: Reduced the intermediate links and reduced the input of manpower and material resources. It also reduces the error link in the middle turn.
  • Reason C: From the component patch to monitor the welding quality, from the source to focus on the improvement of defective products and product scrap rate, effectively reduce the number of waste.

However, if you have limited budget, offline AOI is also a better choice than check PCB by human eyes.

4. Special features in Choose a Automated Optical Inspection AOI

If you want to test the PCBA of a multi-connected board, you must choose an AOI detector with a springboard function, that is, an AOI detector with a zone selection function. If you use the AOI detector as a quality process control, then you must choose an AOI detector with RPC capability when selecting an AOI detector, or an AOI detector with real-time process control.

5.CAD in Choose a Automated Optical Inspection AOI

Most AOI detectors now have a CAD data import function, but the use of this function is not very efficient for PCBA boards with fewer devices. The more devices on PCBA boards, the more efficient we can get.

6. SPC selection

SPC is process statistics control. Statistical control does not have real-time process control. RPC important RPC can not only perform real-time statistical analysis but also provide early warning so that the production line can maintain normal working conditions for a long time.

7. Choice of repeat ability, false positive rate and missed rate

The higher the repeat ability, the more stable the performance of the AOI detector. The lower the false positive rate, and the lower the missed rate.

In conclusion, we should choose a Automated optical inspection (AOI) based on Resolution, Test PCB Size, Online AOI or Offline AOI, SPC selection and so on. It is important to choose a suitable and cost-effective automated optical inspection. ZhenHuaXing Provide a series AOI for your requirements. please see VCTA AOI.