Automated Optical Inspection. AOI.

Automated Optical Inspection 1
Automated Optical Inspection

Automated Optical Inspection (AOI) is an automated visual inspection of printed circuit board’s, (PCB’s) (or LCD, transistor) where a camera autonomously scans the device under test for both catastrophic failure (e.g. missing component) and quality defects (e.g. fillet size or shape or component skew). It is commonly used in the manufacturing process because it is a non-contact test method. It is implemented at many stages through the manufacturing process including bare board inspection, solder paste inspection (SPI), pre-reflow and post-reflow as well as other stages. The automatic optical inspection, Automatic Optical Inspection (AOI), is an optical structure test for PCBs can be found in the relatively high number of errors, but less than with the functional test (FT) or the in-circuit test (ICT). For the AOI test is not so costly and time consuming as the other mentioned test procedures.

When AOI test high-resolution photos are taken, so that the test is reproducible. There are also AOI test systems that make stereoscopic recordings or recordings from 360 different angles. The benefit is that you have a high reliability of the picture but lots of rejects because light and colour have their own influence on the comparison.

The AOI test mechanically defective components can be recognized, moreover failures or 3d misprints , assembly errors during the assembly with SMD components and in the through-hole technology (THT), soldering defects and solder joint failures. Any failure can be detected

Automated Optical Inspection 2
Automated Optical Inspection

In addition, can be controlled, which are located below the chip, as in BGA chips with the AOI test no error in covert chip terminals. Another problem is the polarity of components like capacitors or electrolytic capacitors of tantalum, which cannot be detected and controlled from the top view in axial installed components. This problem can be solved with AOI systems that can make shots from different angles. Defective electrical components cannot be detected with the AOI test. Improving end of line process yields and maximising line UP time is the goal for every SMT Process Engineer.

First Article inspection after set up and programming a placement machine is critical, checking the BOM and layout drawing against the first board assembled. Manual inspection on a complex board can take hours and is open to operator fatigue and errors. Using an AOI machine usually requires a trained operator and is an inefficient use of resources.

Scanning AOI systems has been developed by SMT line engineers for SMT line engineers to effortlessly inspect first off assemblies. Based on a professional high resolution (dpi) line scanner the system can recognise board edges or fiducials (auto align) and this automatically aligns with the centroid CAD data from any pick &place format plus the ability to additionally overlay a board map / plan.

Automated Optical Inspection 3
Automated Optical Inspection

The operator, who requires no programming skills, simply steps through the placement program checking off each part and storing a default image (zoom adjustable) at each position. The CAD data can provide part type, part reference, part size and positional location(s), the inspecting operator can further add polarity check marks plus a free text box to add specific comments. On completion of the cycle a “golden reference board” has been created. The reference board and captured images can then be used to compare with other boards produced in the same or future batches; there is an option to add “alternative” images in the event of part type changes. At the end of each inspection cycle a report is generated that can be saved / printed (PDF) for build records and repair.

Repair software is software for registration of who and when wat has to be repaired. ISO AQUAP and SPC quality systems require these kind of registrations.