I want to make a mounting hole of 2.4 mm diameter for a M2 screw.
I have found three methods used to make mounting holes, none of them is satisfying to me:
[SEE ATTACHED IMAGE]
METHOD 1.
Place a pad on the PCB, set hole size to 2.4mm and annular ring size to less than 2.4mm.
problems:
-if you set annular ring to 0mm you will get manufacturer errors, as you will get a virtual 0mm point surrounded by soldermask clearance ring in gerber files
-if you set annular ring to 2.4mm, same as hole size, you will get a hole with soldermask clearance ring (makes the soldermask susceptible to peeling with screw torque)
-using a PCB template rules from
http://www.eurocircuits.com/Altium-Designer-templates-with-Eurocircuits-design-rules (my fabricator of choice) for Class 6C - 2 layer - 1.55 mm i get an design rule error saying "Hole Size Constraint (Min=0.25mm) (Max=2mm) (All) 4" which means they do holes up to 2mm. Clearly that can not include routing and cutouts. What gives? How do I make a larger hole then?
METHOD 2.
Create a PCB library footprint for the hole (also from a pad). The bonus is that you can add a 3d model of the screw [SEE ATTACHED IMAGE], which makes it much nicer for the final board 3D render. You could add a 3D model to each screw hole in the METHOD 1, but you would have to align it one by one, and here its all pre-done.
problems:
-this METHOD gives errors when processing the PCB as it is an object in the PCB not referenced in the schematic
-I also tried creating a schematic library part, and adding the above mentioned PCB library footprint(pad) and 3D model to it - now I had to hide unnecessary bloat items in the schematic
-same Eurocircuits fabricator problem as above
METHOD 3.
Place a primitive/polygon on a mechanical layer and perform [SEE ATTACHED IMAGE] TOOLS>CONVERT>CREATE BOARD CUTOUT FROM SELECTED PRIMITIVES
problems:
-there is no nice screw model representation like in METHOD 2
-will it generate proper gerber drill data to the manufacturer? I am afraid it will be just a random cutout that they will have to route in some expensive way
-I don't get the nice dimension outlines: screw head (grey circle) and screw clearance (green circle)
-it will not make a plated hole: I have read that its best to keep all holes plated, even mounting ones, as it reduces the tooling overhead. Is that true?
I am offering ten(10) engineer-nice-person points for an elegant solution to this trivial problem!
cheers