Different hole size

Layout Footprints
1

Can we have different hole size? I mean, is there acceptable by convention / international standard?

  • First hole is just like current one. For drilling before the board is plated. This also for vias and NPTH hole.
  • Second hole size is to make sure the component lead is fitted after board is plated.
2

Best I know, “Hole Size” is generally treated as the “finished hole size”. That means that for plated holes, a hole a bit bigger then what is specified is drilled, and then after the plating it should have the size specified by KiCad. But PCB manufacturing is a jungle and there is no guarantee that each and every manufacturer follows this convention. Usually it also does not matter much. For a dual sided PCB with 35um copper, normally base material is used with a copper thickness of 17um, then the holes are drilled and “made conductive”, and then copper is added though electrolysis. The result is that the plating in the holes is 17um thinner then on the planes. So it’s a diameter difference of 35um.

Sometimes finished hole diameter is important, for example for high density press fit connectors. In such cases it is common to parley with your PCB manufacturer to cut though the jungle and have some insurance of a quality end result.

3

So, most of the time I can specify the hole just as finished? Example when I have 0.7mm lead, I just specify hole diameter as 0.8mm. Then the manufacturer will calculate the drill size before plating.

4

In general, probably yes. However, a square 0.7mm pin won’t fit in a 0.8mm round hole. I am reasonably sure that the https://www.ipc.org/ has guidelines for gaps between pins and holes.

To be precise: because it’s a jungle, you would have to verify with your PCB manufacturer or, in practice, add a bit of tolerance so it does not matter.

5

Ok, thanks.
Actually I have IPC tables from unknown (forgot) source. It has drill size recommendation by class A,B,C and by lead size. Also mention finished hole size.

That one also makes me asks, which one I need to specify in footprint library, the finished size, or real drill size.

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6

My first guess is that KiCad would be straight forward and not “guess” what plating thickness some unknown PCB manufacturer might use, and just puts the numbers from the library into the excellon drill file. But it’s easy enough to check, just create a gerber & drill file set and open it in a text editor.

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7

I think a general recommendation is to have a finished hole 0.3mm bigger that that pin of the component.
So if a lead is 0.7mm, your finished hole should be 1.0mm

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