PCB Assembly AOI

//PCB Assembly AOI

PCB Assembly AOI

Automatic or automated optical inspection, AOI, is a key technique used in the manufacture and test of electronics printed circuit boards, PCBs,PCB assembly. Automatic optical inspection, AOI enables fast and accurate inspection of electronics assemblies and in particular PCBs to ensure that the quality of product leaving the production line is high and the items are built correctly and without manufacturing faults.

Need for AOI, automatic optical inspection

Despite the major improvements that have been made, modern circuits are far more complicated than boards were even a few years ago. The introduction of surface mount technology, and the subsequent further reductions in size mean that boards are particularly compact. Even relatively average boards have thousands of soldered joints, and these are where the majority of problems are found.

This increase in the complexity of boards also means that manual inspection is not a viable option these days. Even when it was an accepted approach, it was realised that it was not particularly effective as inspectors soon tired and poor and incorrect construction was easily missed. With the marketplace now requiring high volume, high quality products to be brought to market very quickly very reliable and fast methods are needed to ensure that product quality remains high. AOI, automatic optical inspection is an essential tool in an integrated electronics test strategy that ensure costs are kept as low as possible by detecting faults early in the production line.

One of the solutions to this is to use automated or automatic optical inspection systems. Automated optical inspection systems can be placed into the production line just after the solder process. In this way they can be used to catch problems early in the production process. This has a number of advantages. With faults costing more to fix the further along the production process they are found, this is obviously the optimum place to find faults. Additionally process problems in the solder and assembly area can be seen early in the production process and information used to feedback quickly to earlier stages. In this way a rapid response can ensure that problems are recognised quickly and rectified before too many boards are built with the same problem

COMPARISON OF THE MAJOR DEFECT DETECTION CAPABILITIES OF AOI, AXI AND ICT
Defect type AOI AXI ICT
Defect type
Open circuits Y Y Y
Solder bridges Y Y Y
Solder shorts Y Y Y
Insufficient solder Y-not heel of joint Y N
Solder void N Y N
Excess solder Y Y N
Solder quality N Y N
Component defects
Lifted lead Y Y Y
Missing component Y Y Y
Misaligned or misplaced component Y Y Y
Incorrect component value N N Y
Faulty component N N Y
BGA and CSP defects
BGA shorts N Y Y
BGA open circuit connections N Y Y

WellerPCB how to make AOI inspection on PCB assembly

All PCBs assembled (PCBA) in WellerPCB SMT production becomes optically inspected by our computer-based AOI system. The AOI-system consists of 15 cameras that takes a high-resolution image of the inspected PCBA.
The image of the PCBA is analyzed against a reference board. In analysis, the AOI system will identify the following types of unacceptable deviations:

  • Wrong components
  • wisted/turned components
  • Tombstoning” (where the component is situated like a tombstone)
  • Wrong text on chips (week code, etc.)
  • Wrong color shades
  • Some of these mistakes is what is termed “false errors” where AOI system iteratively learns new approved week codes, texts, etc.., So the system gets better and better the more we use it.

The data and information we get from the AOI system, is used for multiple purposes in our production process:

  • General debugging
  • Statistics analysis for our internal quality control.
  • Input to improve the processes in SMT production (e.g. attention on specific types of components in the automatic assembly)
  • Optimization of the stencils used for applying solder paste (e.g. reduction of solder paste on specific solder pads)
  • Increases our trace-ability in the production (all PCBAs will be scanned and the data from the AOI system are stored on our servers).This information will also be available to our customers, so they also have the opportunity to optimize their design according to our “Design For Manufacturing” philosophy.All PCBAs are registered in our system. Defective boards will be sent to a separate repair station, where the operator will see the specific error on the inspected PCBA board on the screen of the repair station. Correction of the defective PCBA board will be ery efficient and can be performed in parallel with ongoing production. Once the defective board has been fixed it will once again be checked in AOI system until they finally 100% passed AOI inspection.

For more information about AOI test, you’re expected to contact us through emailing to service@wellerpcb.com and we’re always ready to reply you as soon as possible.

2019-07-24T18:26:49+00:00May 11th, 2017|Uncategorized|