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I've already read about reasons for exposing copper at the perimeter of a PCB (i.e. Why do some PCBs have exposed plated perimeters?).

It seems that the main reason to completely expose the copper along the edge is to provide a seamless connection to ground when using shielding covers or shielding metal case soldered/attached to the PCB.

But I wonder why some PCBs have exposed copper (here on top copper layer near the perimeter, contrary to sideplating) even when they are mounted in a plastic enclosure like in the pictures below? (PCB of a Valve Steam Controller)

enter image description here

enter image description here

CatastrophicFailure
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    The edge in your image does not appear to be copper plated. To me that is the base material. Some fr2 material. The soldermask lip away from the routed edge would be to reduce the risk of it being chipped by routing. – Reroute Aug 20 '20 at 08:58
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    I’m voting to close this question because the claimed copper edge doesn't exist, neither in the picture shown nor usually in other devices. – Marcus Müller Aug 20 '20 at 10:15
  • I meant the exposed copper on Top layer near the edge, not the edge itself. Have a look here: [Link 1](https://www.ifixit.com/Teardown/Steam+Controller+Teardown/52578) or here: [Link 2](https://www.allaboutcircuits.com/uploads/articles/Steam_Controller_Main_PCB_tactile_switch_tape.jpg) – CatastrophicFailure Aug 20 '20 at 11:02
  • It could have been put in "just in case" they needed to install a grounded shield of some sort to reduce emissions but when they tested the board found they didn't need it. – td127 Aug 20 '20 at 16:49
  • Can you confirm with a multimeter that the outer egde is connected to GND? – winny Aug 24 '20 at 12:35
  • @winny: Have a look at the bottom picture. There is a white silkscreen marking "GND" beneath a Test Land (Test Point). You can clearly see that there is a direct copper connection between this Test Land and the mentioned exposed copper near the edge. – CatastrophicFailure Aug 24 '20 at 13:26
  • Please test with a multimeter to confirm it. If yes then EMI shield and case closed. No idea why your question was closed. – winny Aug 24 '20 at 15:24
  • @winny: I do not own such a controller myself. Therefore I am unfortunately not able to confirm the connection. But to me it looks pretty obvious that it is connected here. What do you mean by "If yes then EMI shield and case closed"? Also I have no clue why the question was closed... – CatastrophicFailure Aug 25 '20 at 08:22
  • It means if you are able to measure continuity between the GND test point and the boarder of the board, then it’s due to EMI. – winny Aug 25 '20 at 12:14
  • @winny: Thanks for clarification - But my question is actually why does the copper then need to be exposed. Ok td127 has already had a guess but I wonder if there could be additional reasons for doing that... – CatastrophicFailure Aug 25 '20 at 12:34

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