Gerber's new attributes set to transform CAD-to-CAM communication

Ucamco is delighted to present its ground-breaking second extension for the Gerber format. This offers an unequivocal standard for non-image data that is just as simple, practical and universally accessible as the well-known Gerber image data format it now supports.

Ucamco's Managing Director Karel Tavernier comments: "CAD/CAM professionals need to transmit data in a robust, reliable and cost-effective way, something the Gerber image format has been doing for years. It's freely available, simple and to the point. It can be used by everybody, no matter how big or small the CAD or CAM operation is. It's the most practical image description format out there, and by far the most used by our industry – every single day thousands of perfect PCB layer images are reliably transferred all over the world thanks to Gerber".

Indeed, with Gerber, CAD/CAM professionals know that the most critical and fragile part of their archives – the image data – is secure and accurate. But there is another part of the PCB design that images cannot convey. This non-image data includes information about layer order and function, the differentiation between objects like SMD and via pads, and a raft of further information that, together with the image data, helps to translate designers' intentions into high performance products.

The problem is that there is currently no Gerber standard for transferring non-image data, leaving designers to decide for themselves how best to communicate with their manufacturing partners. They might add text files or drawings to their Gerber archive, or they might not, putting the onus on CAM engineers to search for the necessary information, or contact the designer if it's missing. These are error-prone, time-consuming tasks that can end up affecting quality and deadlines, which can translate disastrously into loss of orders, clients and future business, especially in the time-critical context of prototypes and quick-turn boards. Thus whether you are a designer, customer or manufacturer of PCBs, data quality and clarity should be a top priority for you.

This is why Ucamco has developed its Gerber X2 format. X2 offers a series of attributes that provide a standard for describing non-image data – some might rather grandly say that they add intelligence to the image data. Applicable either to a whole file or to individual graphic objects, Gerber's standard attributes can now be used to define

• Gerber file function:  top copper layer, top solder mask,  etc.
• Part: single PCB, customer panel etc.
• Object function: SMD pad, via pad etc
• PCB profile
• Drill tolerances
• Locations of impedance-controlled tracks
• Filled vias
• An MD5 checksum for added security

The attributes have been purposely crafted, from scratch with the sole aim of supporting the transfer of PCB data from design to manufacturing. They are essential, simple and focused rather than a casual smorgasbord of "nice to haves" with unnecessary complexity, not to mention potential bugs. There is no overhead of manufacturing specific attributes as are found in CAM formats. X2 is simple and clean.

The attributes intentionally do not cover all possible non-image data.  Ucamco refrained from adding the netlist to X2 as there is a simple and well-established format adequately describing netlists:  IPC-356-A. Materials were not added as they are not linked to images and can be handled by a subset of IPC-2581 as soon as 2581 is opened up to partial implementations. In this way X2 delivers the best of all worlds: accessibility, simplicity, performance, and tried and tested formats that work for everybody. It's a great combination that gives designers a clear and simple method for ensuring that their manufacturing partners have all the data necessary for efficient, reliable manufacture.  And it eliminates the need to adopt complex new formats wholesale, which is a blessing, as Ucamco R&D engineer Thomas Weyn explains: “Imaging software, notoriously hard to implement, takes forever to debug and field test, especially for images as complex as PCBs. Here, errors are fiendishly difficult to detect and almost inevitably lead to scrap, so it is far preferable to keep what we know works (the Gerber image format) and support it, without disrupting it, with what is missing”.

A prime design goal of X2 is ease of adoption and of implementation. To fully exploit the productivity jump that X2 can bring, CAD and CAM software only requires quite minor updates. Given that the imaging model remains unchanged, it only requires adding a few extra lines with the attributes when writing a Gerber file – it could hardly be simpler. The payback for this is a more versatile product and greater competitivity for systems vendors. The attributes' use is not mandatory: they can be used wholesale, partially or not at all, whichever suits the implementation best. Most importantly, systems that have not been updated will still generate the correct image as Gerber X2 is upward compatible with previous versions of the format as the image is not affected by the attributes. Existing workflows are not broken by introducing X2.

Developed with the support of Eurocircuits, LPKF and AT&S, and currently in draft form, the new specification can be found at www.ucamco.com. Before the final version goes live, Ucamco encourages CAD and CAM professionals to look at it and in particular at the Attributes in Section 5, and participate in its fine-tuning by sending comments to gerber@ucamco.com.

Further reading on Gerber Attributes: Extending the Gerber Format with Attributes