Ucamco Seeks Comments on Adding Netlists to Gerber

Estimated reading time: 2 minutes

At Ucamco, we are dedicated to excellence in everything that we do. That includes our decades-long stewardship of Gerber, the de-facto standard image format for PCB design: our ongoing work on Gerber ensures that this free, open format keeps abreast of, and indeed drives, beneficial developments in PCB design and engineering.

Once again, we welcome your input on our latest proposal, which is to include the CAD netlist in Gerber. Our principal aim in doing so is to make life easier for electronics design, manufacturing and assembly professionals by facilitating clear, unequivocal communications prior to production. Before this goes live, we ask you to read the proposed new draft specification and share your comments and constructive criticism with us.

Further reading

In the new proposal, new X2 object attributes allow the inclusion of CAD netlists in Gerber fabrication data. These enable the following:

• The component reference designator, pin number and net name – a row in the CAD netlist - can be attached to the component pads in the Gerber file.
• The netlist can be attached to any conducting object.
• The component reference can be attached to any object, so it is now possible, for example, to identify all the legend objects belonging to a given component. 

The goal of the Gerber netlist is to facilitate upfront communication between the different parties involved in design, assembly and automation.

To this end, and for example:

• A CAD netlist attached to pads defines the position and orientation of external components, which is essential for assembly and for complete board display.
• By using netlist names, even simple viewers can display netlists without the need for special algorithms to compute connectivity.
• The netlist provides a powerful redundancy check during CAM input, reducing the probability of image errors to virtually zero.

We have taken great care to make this new capability complete yet simple and straightforward in its implementation and adoption. True to the Gerber hallmark of simplicity and power, there are no needless bells and whistles.

The new capability is fully compatible with existing and legacy applications and files as the new attributes do not affect the image. Furthermore, the CAD netlist information and attributes are not mandatory, so if they are not needed to process a Gerber file, they can be skipped and the file remains valid. While these attributes provide very useful fabrication data, it is not necessary to expend any development effort to include them in design and manufacturing processes if they are not seen as bringing any benefit to a particular application.

This proposed new development overlaps to some degree with the venerable IPC-D-356 format, but the design goal is completely different. The 356 format aims to provide a data input method for bare board electrical test. Gerber netlist, rather than to drive testers, aims to facilitate upfront communication, prior to manufacturing proper. Accordingly, it does not contain the adjacency list, fiducials, and other information needed for electrical test. The advantages of the Gerber netlist lie precisely within this limitation as it is easier to understand and implement than 356.

Our sincere thanks go to Jean-Pierre Charras for his insightful comments which contributed so much to this draft.

We are publishing this draft specification to allow the Gerber user community to review and comment on the new feature before it is cast in concrete. To review the specification, click here.  To share your comments and constructive criticism, click here.  

Thank you,

Karel Tavernier
Managing Director
Ucamco