PCB Design Glossary

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Active Components

Active components can control the power gain in a circuit, usually with a controlling input.  Examples include transistors, vacuum tubes, thyristors.

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Annular Ring

One of the steps in fabricating a via is to drill holes through a series of parallel circular pads on adjacent layers.  Mathematicians call the copper ring that remains an annulus.  Engineers colloquially call it an annular ring.
From left to right - a buried via, a blind via, a through via, stacked microvia and staggered microvia.


Surrounding every pad is an area with no copper that acts as an insulator.  This is called the anti-pad.


AOI is an initialism that stands for Automated Optical Inspection.  A camera moves rapidly over all areas of the board looking for issue that would affect the quality of the PCB.  If an issue is found, the board is either crossed out or flagged for follow up by a human operator.  

AOI does not detect internal flaws in a PCB.