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. 

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).

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