In creating a PCB that requires some relatively large (1/4" to 1/2" dia) mounting and clearance holes, I suppose I can either show such holes as pads with holes that either are nearly as big as, or slightly bigger than, the pad, or as cutouts on the 'board layer' using a 'place arc' command with all four quadrants selected. What do fabricators prefer in this case? The holes do not require plating-through. Are board-layer cutouts drilled or routed as one of the final steps; that is, after all the pad holes have been drilled, plated, etc.? I'm concerned that copper 'fill' that covers the mounting hole area may not show the hole properly and it might be overlooked.

Another reason for this question is that I'm planning to make front and back panels for an item out of copper-clad PCB material, as the fabrication of circuit boards with a stick-on plastic label is far less expensive than punched sheet metal with silkscreened graphics. Plating-through is not necessary at all, and the typical solder-plate over the copper makes a good surface for the plastic label.

Many thanks for any tips!

 

What CAD are you using?
You probably have Mounting Holes in your libraries. Look at modifying one of those. There should be a place to increase the clearance of the pad. You can pick very large numbers.

 

Hi, ronsimpson, thanks for the reply. I'm running CircuitMaker 2000, admittedly quite long in the tooth, but I have an extensive user library and the program has served me flawlessly over the past 25 years or so. CM does not include any 'mounting holes' in its native library, but the manual does advise, "Holes can be defined up to 2 mils larger than the pad diameter. This provides a convenient way to define a mechanical hole, with enough tolerance to ensure that it will be free of any copper when manufactured." I'd probably just follow this instruction, but was asked by at least one 'offshore' PCB fabricator to show unplated holes on the 'board layer,' which I take is the layer that defines the outline of the board, and thus is routed-out or drilled in the same final stage of operation as shearing or milling the board away from whatever panelized configuration the fabricator uses.