Electronic – Standard Meaning/Purpose of Exposed Areas on a PCB

pcbstandard

I noticed that on some circuits, there will be dots or rings of exposed circuit material.

Take for instance the back plate of a Nest thermostat:
https://d3nevzfk7ii3be.cloudfront.net/igi/6J2elHPEJArWXaE6.huge

There is a thin ring around the inside, outside, and several dots of exposed brass colored PCB metal.

Is it a fair assumption that these always connect to ground? Or is this something that isn't standard?

Best Answer

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Red arrow: these are targets used by optical sensors in the pick and place machine to detect and register the board so the machine knows exactly where the board is and can place components on it accurately.

Blue arrow: these are test points to probe various signals, either for automated testing of the board before or after assembly, or for manual testing/debugging during design/development or rework/repair.

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