Mask Gerbers Now Negative Polarity

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1

I just migrated from Kicad 5.x to 7.0. For my entire long career I have always created gerbers where the “printed” areas are the mask openings. However, in Kicad 7.0 it appears that the mask gerbers are output as negative polarity without an option to change the polarity. (I can change the polarity by editing the gerber file with a text editor, but…)

Are manufacturers going to object to this format?
Why was this change made to KiCad?
Is there some way in KiCad to select the polarity of the Gerbers?

2

AFAIK nothing that drastic has occurred. Can you zip up and post your project so that we can look at the gerbers and try to replicate your symptoms?

3

You are right - it is more subtle than that. My earlier files when examined with a text editor also say that they are “Negative”. For some reason my Viewmate Gerber viewer actually treats the new (V7.0) files as negative polarity. But it treats my old (V5.x) files as if they were positive polarity.
I have been using the Viewmate viewer for years with gerbers from various CAD software and the mask has always appeared as a positive.

But perhaps it was V5.x that was wrong?

Header of OLD Gerber:

G04 #@! TF.GenerationSoftware,KiCad,Pcbnew,(5.1.0)-1*
G04 #@! TF.CreationDate,2023-02-02T11:30:01-06:00*
G04 #@! TF.ProjectId,Helen_Proto,48656c65-6e5f-4507-926f-746f2e6b6963,rev?*
G04 #@! TF.SameCoordinates,Original*
G04 #@! TF.FileFunction,Soldermask,Bot*
G04 #@! TF.FilePolarity,Negative*

Header of 7.0 gerber:
%TF.GenerationSoftware,KiCad,Pcbnew,(7.0.0)%
%TF.CreationDate,2023-03-13T21:11:01-05:00%
%TF.ProjectId,Pegasus,50656761-7375-4732-9e6b-696361645f70,rev?%
%TF.SameCoordinates,Original%
%TF.FileFunction,Soldermask,Bot*%
%TF.FilePolarity,Negative*%

4

Those are comments inserted using no-op G04 codes.

What happens if you generate Gerbers with X2 format selected. Maybe Viewmate must have X2? If you don’t have v5.1 around any more, you could try changing "G04 #@! " to “%” to simulate the X2 option selected. Oh, I think you also need to end those metadata lines with %.

5

It does seem that the selection of “X2” was the difference.
And I also edited the old file to format the comments with % and the viewer changed its treatment of the file to match the “New” file.

I guess this is a non-issue. I now wonder if Viewmate was displaying the old files with the incorrect polarity?

Thank you very much for your help - I am reassured.

6

I guess Viewmate didn’t implement a heuristic that if it (looks like it) is a Soldermask layer, then default to Negative.

7

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