1. The Automated Optical Inspection Process
Automated optical inspection is a quality improvement tool which can provide up to 100% inspection of the products as they progress through an SMT process, particularly post print and post reflow. The inspection is done by means of automated equipment fitted with specially designed vision systems which help to highlight process problems.
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2. AOI Applications
AOI is used to ensure the quality of a number of process stages.
Post print inspection can check the printed PCB for solder paste deposition and can identify such problems as bridging, insufficient solder, excess solder, solder volume, solder smearing and debris.
Post reflow inspection checks reflowed PCB's for problems such as component presence, polarity, shift, tombstoning and even for solder fillet quality.
Other AOI applications include post placement and post wave/selective.
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3. AOI Machine Types
There is abroad range of AOI systems on the market ranging from simple scanner/comparator systems to full algorithm driven automatic systems.
Post print inspection systems come in two different styles, the 2d and the 3d inspection system. 2d systems usually incorporate a top down camera system coupled to a vision system and can inspect printed solder quickly for almost everything with the exception of paste volume and shape. This is where a 3d system has an advantage, as these systems either offer multiple cameras or special optics to visualise volume and shape information.
Post Reflow Scanner or comparator systems compare a saved image of a golden board with a scanned image of the PCB under test, and highlight any differences between the two. These systems have a number of limitations which make some advanced inspection tasks impossible.
More advanced post reflow systems incorporate high resolution cameras and powerful software to enable full inspection of assembled PCB's, with the most advanced systems capable of reliable soder fillet inspection as well.
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4. Troubleshooting AOI Problems
The main issue with AOI systems is the elimination of false fails and false passes. The purpose of AOI is to offer you a 100% repeatable inspection of your products without the varaiables of human inspection,
To get repeatable results that you can trust from AOI means a lot of fine tuning of component parameters and vision setings. Without effort in the initial stages of AOI introduction to tighten up your process window and minimise false fails, you will not reap the benefits such systems can offer.
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5. Expert Advice..
Please visit individual supplier websites for further detailed information.
Browse manufacturers automated optical inspection machines (AOI) here
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