Creating a square soldermask aperture with rounded edges in KiCAD (5.1.5)-3 64-b

Hi all!

Hopefully I am not asking something stupid here, but I could not find this documented anywhere. I am trying to make a rectangular solder mask opening with rounded edges. There will be no component there, it is just an opening to allow some light to shine through the -otherwise black- soldermask.

I proceeded to create a fill plane on the F.Mask layer and set the outline display to “line” and the minimum width to 2mm to create 1mm radiuses. This kind of worked, because the interface is showing what I expected to see:

However, when I previewed it in the viewer of my supplier, the edges did not show rounded, neither do they in KiCADs gerber viewer so something seems to go wrong here:

The strange this is that it does work when a soldermask opening is generated for a pad with rounded edges, as was done elsewhere on the PCB:

Please note that in this case there is actually a copper pad on top. The opening in the soldermask was created to facilitate it. The other opening needs to be a (bit) translucent though, and it is not an option to add a copper pad there. I could remove it afterwards by manually editing the Gerber, but that seems a bit of a hack.

Maybe I needed to set some option somewhere to make the edges of the opening rounded, but I don’t seem to find it. Did anybody else run into this issue (or does anybody know what I am missing here)?

BTW: I am using KiCAD (5.1.5)-3 64-bit on Windows 8


Why not just place a mask only pad? (a pad without copper, paste and without a pad number)

You could also draw a polygon on the mask layer and increase the line’s width to get the desired rounded corners.

Above: Polygon with a line with of 2mm
Below: Non-copper zone, the same result as yours.

Hi guys,

That’s perfect, both methods work just fine! @der.ule: That seems to work, just tested it. I will remember this! @Rene_Poschl: Didn’t see that option, I think I’ll be using your solution in the footprint editor so I can align the silkscreen easier. Thanks guys, you were a great help! :+1: