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There are many discussions on if mounting holes should be plated or if they should include vias. This is not asking about those issues.

I've seen suggestions to add solder to the annular ring on the mounting holes. This, possibly in conjunction with serrated screw heads, was suggested as a way to lock the screws. I've also seen such solder bumps on some computer motherboards.

Is this actually known to help? What does it help with specifically? Can it hurt? Should it only be on the screw head side?

I can imagine a couple places where this is not wanted; like if you care about accurate dimensions of the holes for mounting heatsinks.

Assuming it is desired, what is the optimal solder pattern? A bunch of bumps around the hole? Or a thin flat solder layer like you'd get with HASL finish?

Also, do different PCB copper finishes/platings change this at all?

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  • \$\begingroup\$ Where have you seen such recommendations? \$\endgroup\$ – Matt Young Jun 28 '17 at 1:31
  • \$\begingroup\$ The place that comes to mind is an answer on this site. I'm not finding it at the moment. \$\endgroup\$ – Cameron Tacklind Jun 28 '17 at 7:45
  • \$\begingroup\$ I just ran across an image of a board with these bumps on plated mounting hole annular rings. I can imagine that they could be helpful creating a low resistance path between the contact surface of the screw and the pad, but the whole thing makes me a bit nervous. I'd be concerned, especially with serrated screws, that as one tightens the screw, the possibility of filing off solder would exist, creating risks for shorts if the solder ends up in the wrong place. \$\endgroup\$ – AJbotic 6 hours ago
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Assuming that the mounting holes are plated and connected to ground, the presence of solder bumps will help in two ways -

  1. The connection to ground can still be maintained even if the screws are not fully tightened.
  2. If somebody over-tightens the screws, the solder bumps will take damage first (they flatten up) before damaging the annular ring on the mounting hole.

The second point will be valid for both plated and non-plated mounting holes.

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  • \$\begingroup\$ Any reason these could hurt? Are there any fatigue or other metal weirdness issues to consider? \$\endgroup\$ – Cameron Tacklind Jul 6 '17 at 5:19

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