All great info, but I think the thread starter was asking about leaving a thin bit of PCB material between hole and edge, not about copper traces. In other words, I think the question is how much clearance you need between a hole and the board edge.Half a millimetre is a wide trace by today's standards, though around a screw hole it is likely to get "chewed up" which could result in little bits of copper that might cause grief, especially if a lock washer is to be used.
Unless there is a need for electrical connection via the screw, which can be a bit dubious, I prefer screw holes to be unplated and have no annulus. If electrical connection is required, an annulus that extends a bit beyond the head of the screw was my preference. I see lots of computer mother boards with an annulus with a bunch of small vias all the way around.
If you are using a "full service" board house you can have holes left unplated, but exactly how that is done depends on the process and the size of the holes. If the pad is smaller than the hole, the hole might get plated and then the plating etched away. I've use that method with prototype boards, but had inconsistent results from the same board house. Some came back with nice clean holes, some (different batch) came back with a more or less intact barrel through the hole. Unplated holes may be drilled after the board is etched, which may cost a bit extra - it depends on whether the board has to go back to a drilling machine or if they can/must do them on the routing machine. Big holes are usually routed since drills all have 1/8" (3.175 mm) shanks and there is a limit to how much bigger the actual drill is relative to the shank. It is always best to consult the board house in advance.
For general work, "8 and 8" (8 mil tracks, 8 mil spacing; 8 mils = 0.2 mm) is regarded as easy by any reasonable board house unless you are looking for very heavy copper. 4 and 4 is pretty much required for lots of ball grid array parts.
standard .062 inch.It depends.
I've punched holes in CEM-1, which isn't recommended, and have successfully punched within 1.5mm of board edge. Even in cases where the punch crushed board material, a screw could still hold the board in position.
- What is the board thickness? Material?
- How is the hole being made? Drilled or punched?
- Is it the only hole?
- Purpose of the hole? Support board vertically or horizontally?
- Board dimensions?
So 4 holes total?2 holes....the other is about 90 mm away from that hole.
To screw the board down vertically (note that there are 2 additional screw holes that will not have this issue).
Unless there are significant lateral forces on the hole, your the main issue will likely be whether the board house design rules allow it. You could consider using a lock washer to increase the friction between the screw head and board.I told the team that we could just make the hole a U, but they did not like that idea.