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I have a board currently 50x30 mm. And I need to have 4 mounting holes on it.

Bad news is that I don't have enough space to place them in regular way. Now I made the following thing: I placed four 3.2 mm holes with centers within the board edges but big part of the holes appears outside the board:

enter image description here

(white circles are washers edges)

If the manufacturer will be able to do this thing I'm sure that those holes can be used for mounting.

Main reason for this question here is that I'm pretty in rush and if in the Monday morning I will find out that it's not possible I will lost one day for rerouting (and probably to expand the board which is not very good actually). As I don't want to lose a day I came here to have an advise: is it common that this kind of holes can be made? Or maybe there is anything else I'm not aware of?

So if your advise will be to avoid this kind of holes I will have Sunday to make needed changes. What is you opinion?

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  • \$\begingroup\$ It should be possible, but there might be some issues with panelizing the board so that those holes don't overlap other boards. \$\endgroup\$ – Jan Dorniak Jan 16 '16 at 14:11
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    \$\begingroup\$ Could you use clips to hold the board instead? Think of a matchstick with a notch cut in it, but made of plastic, and perhaps a corresponding notch on the PCB to aid in location. \$\endgroup\$ – Andrew Morton Jan 16 '16 at 14:38
  • \$\begingroup\$ @AndrewMorton do you have any picture of such clips? I was never used them. \$\endgroup\$ – Roman Matveev Jan 16 '16 at 14:39
  • \$\begingroup\$ @RomanMatveev I do not. My central heating controller uses them to mount two boards, but I don't want to disassemble it for photography it as the weather is cold here. You could take a piece of round plastic rod and cut a notch in it. The PCB will locate in the notch, and the shaft can go, for example, in a drilled blind hole in the casing. However, it will not be as secure as a screw. \$\endgroup\$ – Andrew Morton Jan 16 '16 at 14:50
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    \$\begingroup\$ I think Andrew means essentracomponents.com.sg/… @RomanMatveev \$\endgroup\$ – Passerby Jan 16 '16 at 14:51
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That's why you should always place the mounting holes before you place your components :)

The good news is that the manufacturer will not have any issues making these holes. The only thing I'd suggest is to remove the plating.

Another way to do this is to define the "mounting slots" on the PCB outline instead of drilling. That way, you'd have greater control over the shape of the holes.

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  • \$\begingroup\$ This placing is not because I forget to place holes. I wanted to save space and make the board as small as possible. Which plating do you suggesting to remove? I did not get this idea :) Mounting slots require PCB milling? Will it make PCB much more expensive? \$\endgroup\$ – Roman Matveev Jan 16 '16 at 14:29
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    \$\begingroup\$ The 3.2mm holes are plated through. You don't have any pads on top (and probably bottom), so the plating is useless. I don't think the price will increase very much, even if they have to mill the holes. \$\endgroup\$ – Armandas Jan 16 '16 at 14:33
  • \$\begingroup\$ +1 for the last paragraph about making gulfs/slots in the outline. \$\endgroup\$ – Nick Alexeev Jan 16 '16 at 19:22
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I would suggest talking to your board vendor. What you propose can certainly be made but different vendors may have different preffered ways of doing it.

Drilling it as a plated hole and then cutting would likely be the cheap and dirty but risks the plating getting ripped off and leaving an ugly mess.

Drilling non-plated holes and then cutting means an extra drilling step which some cheap board vendors may not like.

Drilling may also require bigger gaps to be left between the boards reducing the efficienty of panelisation.

Making it part of the board outline would be a good option if the board vendor intends to mill the board. Some vendors use milling as their default de-panelisation method, for others it may be an extra.

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  • \$\begingroup\$ Thank you Peter for your answer. Let me comment on some points. First: I will definitely talk to the vendor but it will be on Monday :( Second: making the holes plated was definitely my mistake, I already removed plating. \$\endgroup\$ – Roman Matveev Jan 16 '16 at 17:23
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You could ask yourself whether you need mounting holes that big? Apart from the top left corner it looks like you could bring a smaller hole further into the board?

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    \$\begingroup\$ Smaller holes can make sense. But it becomes much harder to find such small screws. 3mm is a kind of a standard. So I tried to use this one. \$\endgroup\$ – Roman Matveev Jan 16 '16 at 14:26
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    \$\begingroup\$ @RomanMatveev 2mm screws and below are not that hard to find, especially as you say in another comment you are making hundreds of these. You'll come up against that again. I'm doing a mechanical project and needed to mount just 2 microswitches. I was faced with the option of buying 100 2mm screws, or an assortment of different sizes. Obviously no-one would sell me just 4 of them. I do think it's a better idea than the kind of rough edges you might get from drilling holes that are partially outside the board area. \$\endgroup\$ – Level River St Jan 17 '16 at 13:19
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I would use a round file to slot the edges of the board. This could be tedious if there were more than 30 boards.

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  • \$\begingroup\$ File is not that precise. But the most important is that there will be hundreds of PCBs :( \$\endgroup\$ – Roman Matveev Jan 16 '16 at 17:36

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