Author Topic: PCB Slots. Best practices?  (Read 5699 times)

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Offline phil from seattleTopic starter

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PCB Slots. Best practices?
« on: May 25, 2021, 07:12:14 pm »
I suspect the answer will be "depends on your PCB House".

Anyway, I want to make slots in a PCB with KiCad.  In googling I found 2 answers:
  • draw a line on the edge cuts layer with the desired slot thickness.
  • draw a polygon (via lines) on the edge cut layer.

What do other people do for slots in the PCB?  Note, these are just simple slots for things like an air gap or stress isolation. Should be pretty straight forward, eh?

Option one seems a lot easier though I get why option two might be more desirable.  I tried OSHPark and JLCPCB for each. Both seem to like option one (line with thickness). OSHPark and JLCPCB gerber viewers only show the outline of option two (polygon).  However, option one gets a DRC "Board outline does not form a closed polygon" error.  I don't like ignoring DRC errors - too easy to let a real error slip through.

I sent a board off to JLCPCB with  to see what will happen.

[EDIT] This is with Kicad 5.1.9, if that matters...
« Last Edit: May 25, 2021, 07:25:10 pm by phil from seattle »
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Offline mikeselectricstuff

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Re: PCB Slots. Best practices?
« Reply #1 on: May 25, 2021, 08:26:26 pm »
Draw a line showing the outline of the slot on the board layer, the centre of the line indicating the  edge of the cut. The thickness of the line doesn't matter, but should be a sensible size to see on a gerber viewer ( e.g. 0.2mm)
Keep slots 1.6mm or over if possible, as smaller needs smaller tools, which must be run slower. .
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Offline madires

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Re: PCB Slots. Best practices?
« Reply #2 on: May 25, 2021, 08:41:13 pm »
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Offline liteyear

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Re: PCB Slots. Best practices?
« Reply #3 on: May 29, 2023, 01:22:35 am »
I sent a board off to JLCPCB with  to see what will happen.

What did you discover?

I've always done outlines, but am porting an OrCAD project at the moment that uses a "NCROUTE_PATH" element to explicitly specify a 2mm diameter slot using a single stroke. So it got me wondering if my habit was unnecessary.

I think I'll stick with outlines to keep KiCad happy, and perhaps it's slightly superior anyway because the manufacturer is free to create their own NC Route paths, instead of being constrained by some naive designer who thinks a 2mm tool should be used.

For the record, the linked voltlog video says at the 3:06 mark: "[edge cuts] need to describe an enclosed shape. It doesn't work if you just place a single 0.8mm thick line [for KiCad to correctly interpret it] ... The board house may be able to understand a single thicker line but in KiCad you need to have a closed perimeter... [which is a little more work]". So echoing the original post pretty closely, I think.

Offline Infraviolet

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Re: PCB Slots. Best practices?
« Reply #4 on: June 05, 2023, 02:44:15 pm »
In eagle you draw them in the "milling" layer, but I'm not sure how that corresponds to KiCAD's layer names.

Scroll down to "non plated slots" on this page for exmaples:

the trick will be finding KiCAD's equivalent to the "milling layer".

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