How much should the mask overlap the copper? (if at all?)

[pigeon]

Hello, I’m making some layers for my PCB in Inkscape before bringing them into KiCad,
And from what I understand the convention is to have a small gap of around 0.05 mm as mask opening, so if there is misalignment the pads are not covered in the mask.

But I kind of want to do the reverse, as I have all exposed traces and really don’t want misalignment to result in a gap of exposed FR4 in between the trace and the mask, so thinking having a small overlap will resolve that issue…but how much is a mask going to be off…are we talking in mm?

[eelik]

That value which is published by the manufacturer works both ways. You have to understand it’s an x/y offset, not for shrinkage/expansion.

This means the whole layer is moved a bit in its entirety.

[pigeon]

Ah, thank you for explaining that!

So, I could enlarge my copper or mask by that factor and both ways would alleviate the risk of the exposed board due to a misalinment.

[eelik]

@pigeon

I could enlarge my copper or mask

You can widen the copper track or narrow down the mask graphics on it. See How does solder mask layer work? – the graphics describe the mask opening, so narrower graphic line exposes less copper while wider line may expose the board material, too.

[pigeon]

Thank you, that was an externally helpful read.

As I have nothing too near to each other, I went with bumping the copper up 0.1mm so if the mask is off it should just be exposing more copper.

Maybe showing it in Kicad would be better