Create a mounting hole


#1

Hi, I would like to create some mounting holes on my PCB, just like in this picture: https://www.adafruit.com/product/3405

How do I create a hole that looks like the ones next to the micro USB?


#2

Have a look into the mounting hole library.
The _Pad mounting holes are plated.

If you want it connected to some net, you can either use the conn01x01 symbol to connect the plated mounting hole to any net or you can use the same trick as is used for stitching vias. (give the pad the netname you want with the properties dialog in pcb_new)

If you don’t want it connected just place it from within pcb_new and don’t edit anything.

To place a footprint from within pcb_new without it being connected to a symbol look in the right toolbar. There is a symbol that looks like a dip footprint. (tooltip: add footprint)


#3

Thanks!

Quick question - what is the most common reason for having these plated holes? Is normal for these to be connected to, say, GND? Or is the plated ring primarily to make sure the screws don’t bump into any components?


#4

Depending on the project, both reasons are right. Sometimes the screws are connected to GND, sometimes you don’t want them to overlap any signal and the plated ring forces clearance.


#5

Plated through mounting holes are also easier to make for the board manufacturer.
The process is exactly the same as for the via’s and holes for THT components.
If you want the holes to be not plated then the holes will have to be drilled at the end of the board manufactory.
Not a big deal if your PCB outline is routed anyway, but it might be an extra step if your board only uses V-scoring.

Also note that in the KiCad lib of the mounting holes, a lot of the holes have via’s in them.
These via’s are for mechanical toughness of the plating.

Tip:
When designing a PCB with SMD connectors (such as uUSB) it’s always a good idea to draw some via’s under the big mounting pads of the connector.


#6

I have also used a graphic circle on the silkscreen to indicate the location of the fastener head and/or washer. Having some sort of visual feature there not only provides guidance in the layout process, but also guides the assembler with clues about how many screws to insert and where. If you want to get really fancy, graphic techniques like dotted or dashed outlines could be a code for the size or length of screws to be used.

Many incarnations ago a PC layout guy told me that the plated pad under a screw head provided a malleable bearing surface, preventing the screw from chafing away the board surface (and becoming loose) as the board and its mounting experienced thermal cycling. Sounds reasonable, but I don’t recall ever observing the wear problem.

Dale