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I've seen some designs which have mounting hole included in the schematic. Are there any good reasons of doing that?

I can see one advantage of doing so when you want to connect your mounting holes to some nets (e.g. GND). But what if the holes aren't supposed to be connected to any net?

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Some people/places like everything to be schematic driven. That way the only changes to the design come from one guy/department. So even though you could add mounting holes in layout and connect them to a net, you put them on the schematic instead. That way you don't have to rely on a note to the layout guy to "add four holes and connect them to GND net". You may also have a bunch of predefined holes and you want to make sure that version gets into your layout.

In the case where you are not connecting the holes to any net then you might want to make a mounting hole as a mechanical part (no nets), just so when you push from schematic to layout the mounting holes automatically get pulled in. This is useful not just for board mounting holes but also for say a heat-sink that goes with an IC.

Really it's just a way not to forget about them or to make sure the right holes are associated with the part or board. You might make the decision on what holes to use well before you get into layout so why force yourself to remember. Especially when your boss is screaming at you to get it released :)

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I'm sure it's just to placate the CAD package, which complains less when everything that's on the board is also in the schematic.

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  • \$\begingroup\$ I don't know about other CAD packages, but the one I use (Altium Designer) doesn't have any problems with that, because it doesn't regard holes as being parts/components. \$\endgroup\$ – m.Alin Nov 29 '12 at 14:24
  • \$\begingroup\$ if the same package does schematic and CAD there should be no problem. But exporting a netlist to a specialist PCB layout program, it might be easier to add the holes to the schematic than hack the netlist or add them manually. \$\endgroup\$ – Brian Drummond Nov 29 '12 at 14:33
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    \$\begingroup\$ Also some people/places like everything to be schematic driven. That way the only changes to the design come from one guy/department. So even though you could add mounting holes in layout and connect them to a net, you put them on the schematic instead. That way you don't have to rely on a note to the layout guy to "add four holes and connect them to GND net". You may also have a bunch of predefined holes and you want to make sure that version gets into you layout. \$\endgroup\$ – Some Hardware Guy Nov 29 '12 at 14:45
  • \$\begingroup\$ @SomeHardwareGuy Good points, but what if the whole design is done by one person and the holes aren't connected to any net? \$\endgroup\$ – m.Alin Nov 29 '12 at 14:55
  • \$\begingroup\$ Well in that case you might want to make a mounting hole as a mechanical part (no nets), just so when you push from schematic to layout the mounting holes automatically get pulled in. This is useful not just for board mounting holes but also for say a heat-sink that goes with an IC. Really just a way not to forget about them or to make sure the right holes are associated with the part or board. You might make the decision on what holes to use well before you get into layout so why force yourself to remember. Especially when your boss is screaming at you to get it released :) \$\endgroup\$ – Some Hardware Guy Nov 29 '12 at 15:11

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