How to Easily Invert Solder Mask Layer Graphics

[thegrinch]

Hi, I’ve been experimenting with translating some of my silkscreen graphics to the solder-mask layer. I found this is fairly easy to do by copying the silkscreen gerber file’s graphic information to the mask file. However, the mask file is translated as a negative image in production (areas where graphics are present subtract from the solder mask). I was wondering if there was a simple process I could do to invert the values held in the solder mask gerber file to get the same positive image as the silkscreen.

Thanks!

[PCB_Wiz]

@thegrinch

I was wondering if there was a simple process I could do to invert the values held in the solder mask gerber file to get the same positive image as the silkscreen.

Yes, you might like to look at the nifty script linked here

Combine gerbers (useful for negative text)

Further to the topic Enable drill marks for Gerber files I created a script to combine gerber files with positive or negative polarity. You can find it here https://github.com/bobc/kicad-utils/tree/v5/scripts/gerber_combine. Note that the gerbers files must have the same format (ie… inch/metric, number format) as no conversion is performed. For the use case of negative text in a copper fill, you might do something like: python gerber_combine.py ktest4-F.Cu.gbr -s ktest4-Cmts.User.gbr -o ktest…

That allows you to merge gerber files, and define the file polarity, using the plot dark and plot clear features.

Of course, user care is needed, as plot clear first needs a dark area to appear on, and if you were to plot clear across traces, that’s exactly what will happen. DRC cannot help you here…
The results should be Gerber-viewable, so always check the starting and end files…

[thegrinch]

Okay, I tried out this gerber merging software, it seems to be doing the merging thing, but the output looks the same in the gerber viewer as my manual method.

How to import / make a negative with it isn’t really documented at all. Any idea how to do this?

[PCB_Wiz]

@thegrinch

Okay, I tried out this gerber merging software, it seems to be doing the merging thing, but the output looks the same in the gerber viewer as my manual method.

How to import / make a negative with it isn’t really documented at all. Any idea how to do this?

Hmm, I see it is brief - Did you read gerber_combine.py ?

Help says :
Combine Gerber files
-a add (draw positive)
-s subtract (draw clear)
-o output file

and the example given is
e.g.
python gerber_combine.py ktest4-F.Cu.gbr -s ktest4-Cmts.User.gbr -o ktest4-merged.gbr

So you need the graphic info you want negative in the subtract ( -s) file name.