Automated Optical Inspection (AOI): 101

Automated Optical Inspection (AOI) is a process that uses digital cameras to inspect every square millimeter of your printed circuit board for defects and errors. In concert with human inspection, AOI machines look at first-articles and final assemblies to find defects that range from insufficient part placement clearance to floating parts, billboarding, tombstoning, misaligned parts, incorrect part placement, etc. With today’s parts shrinking in size below the visual acuity of mortal man, automated optical inspection is more important than ever.

Automated Optical Inspection machines locate parts, capture images, and then analyze one or more images to determine if the part is correctly attached to the printed circuit board. In the past, AOI machine learning algorithms could only learn from a “golden board.” These AOI machines are increasingly able to use cad files to generate the necessary pass/fail parameters.

This article introduces, or refreshes on, the various machinery used within an AOI machine. It begins by discussing the differences in views and distortions made by various lenses and lighting. Then it moves into the processes of verification used with golden boards, potential flaws with processing, and advancements made with machine learning.

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