XNC Format: Gerber Takes Data Into the Future


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Gerber is the world’s favourite data exchange format for PCB image data: it’s easy to use, crystal clear, and gives designers and engineers an unequivocal language with which to communicate with each other. And this grand old man of the PCB industry has remained at the forefront, powered by ongoing developments that add capability and functionality without ever compromising its characteristic simplicity and ease of use.

It’s the ideal solution for transferring drill data too, as can be seen from scanning the specification. And many in the PCB industry use it for just this, but the majority are still transferring their routing and drilling coordinates using NC formats. These were never designed for data transfer, and more often than not create confusion and waste time.

Some argue that Gerber files, unlike NC files, can’t be sent to a drilling machine. True enough, but PCB manufacturers never send their clients’ incoming files to their machines anyway. Instead, the data goes through the CAM process and is then altered and output as is appropriate to the manufacturer’s specific production line. For CAD, the question should not be which format is best for the machines, but rather which format is best for input into CAM. As we’ve said, this is undoubtedly Gerber.

So, why are CAD developers and their users still stuck on NC formats? It’s most likely a question of inertia or tradition. Drill information has been transferred for decades using NC formats, principally Excellon (hence the generic use of the name “Excellon” for “NC files”), that are similar to the 1985 IPC-NC349 specification. Also, there’s still a lot of legacy software out there, so NC files will likely be with us for a while.

The Problem With Existing NC Specifications

The problem is that so many NC files are of deplorable quality because the NC format was never designed as a data transfer format. It has always been a machine driver and contains all sorts of information that a drilling machine needs, but that is irrelevant and confusing for data exchange. For example, CAD software will typically ask users to specify whether routing should be achieved using nibbling or slot creation and which drill feeds and speeds are to be used. These are decisions that only the fabricator can make, and yet many CAD professionals will feel duty bound to give some sort of answer, which will inevitably be wrong.

To read this entire article, which appeared in the April 2019 issue of Design007 Magazine, click here.

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