Numerical Innovations - Help Center

Typically when the first object of a Positive Gerber file is "clear" it can assumed the intent of the file was to be a negative Gerber file (i.e dark background with clear objects - such as in ground, power plane). 

Truthfully it's bad practice for a PCB CAD tool to output clear objects at the beginning of a Positive Gerber file as they will be invisible and have no effect on the final image.  Typically when a CAD tool outputs Gerber files that begin with "clear objects" the intent was to be a negative layer (as described above), and this detection by FAB 3000/DFM Now has helped many people correctly process their gerber files for manufacturing.

To determine how FAB 3000/DFM Now will process "Polarity Conflicts", go to Gerber Import Settings and view the option "Polarity Conflicts".  

Ignore:

The default is "Ignore" and FAB 3000 will simply load the file exactly as it has been parsed.   

Change Polarity:

The layer polarity will be reversed to align with the first Gerber object polarity.  Thus if the layer is positive polarity, but the first object is clear - a negative layer will be created.  If the layer is negative polarity, but the first object is dark - a positive layer will be created.

Prompt User:

During import a Prompt message will appear and ask whether you wish to change the layer polarity to align with the first Gerber object polarity. 

Thanks for your question.  When creating a Negative Layer you need to have some type of outer boundary - as the negative layer cannot extend to infinity.

Typically this would be the border layer of a PCB, or use the Extents of your design.  If you're not using a PCB, than I'd recommend using the extents of your design and add a little offset.   Here's a tutorial movie showing me perform this task,  

https://numericalsoftware-update.s3.amazonaws.com/tutorials/2019-04-29_12-53-19_negboundary.mp4

If you select PCB border (for the boundary) and you're PCB border layer does not exist; or is not connected as a single entity -  FAB 3000 is trying to create one for you using your existing design.  For more information about generating PCB borders, please search generate border in our support center.   https://support.numericalinnovations.com/support/search?term=generate+border 

You actually should not export Gerber files with an IPNEG in the Header anymore - that's been depreciated by the latest Gerber File Specifications.

Note: We only keep it available for legacy purposes.

If you wish to reverse LPD to LPC, etc.  - then please use the command "Convert to Negative Layer"  (located in the Fabrication menu).  Film wizard can also generate negative layers  (reverse LPD to LPC).