Ucamco Seeks Comments on Gerber Nested Blocks Capabilities

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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. Our work draws on our deep understanding of the needs of the PCB industry and its design and engineering functions, but also on the invaluable feedback that we receive from you as designers and engineers, because your day-to-day experience of what it means to use our hardware and software makes you the real experts.

Now, we welcome your input on our latest proposal, which is to extend the Gerber format with nested blocks capabilities. Our principal aim in doing so is to make panel definition and handling easier and more efficient, and it is most likely that this development will bring additional benefits. Before this goes live, we ask you to read the proposed new draft specification here.


Printed circuit boards are fabricated on production panels, onto which the same PCB is repeated a number of times.  This means that the image file representing the panel must represent all instances of the PCB. One way of doing this is to use a 'flat' file into which the features representing the PCB are copied 'n' times, in all the appropriate places. While this defines the correct image, the resultant file is large, and slow to process in CAM and on the production equipment. A more efficient solution is to store the PCB objects just once, and add an instruction to step-and-repeat the PCB across the panel image. Which is exactly how Gerber's current SR command works, and that takes care of the PCB fabrication panel.

Panel production is so efficient that assemblers are also working increasingly with panels (known as arrays, biscuits or assembly panels), so PCB fabricators are increasingly called upon to ship arrays of PCBs, rather than single PCBs, to their assembly partners. Fabricators therefore need to produce panels carrying repeated arrays of repeated single PCBs. 

The most efficient way to create this two-tier repeat pattern is to use a nested step-and-repeat command. This takes the single PCB image and steps it into an array, then steps the array onto a production panel.  Gerber's SR command cannot do this as it supports just one level of step-and-repeat. This means that fabricators must flatten either the array or the working panel, again creating large files that can be cumbersome when handling small but complex circuits such as those found in smartphones.

We propose to address this issue by extending Gerber to include a nested step-and-repeat command – one that, during extensive tests at Via Mechanics in Japan, has proved to yield dramatic increases in productivity.

We propose that, rather than making it an extension of the existing SR command, nested step-and-repeat should be a totally new command, mainly AB. This is because some legacy Gerber readers do not yet support nested step-and-repeat, and could mistake the two-tier nested step-and-repeat command for a simple one-tier command and generate the wrong image without any form of warning.

By introducing nested step-and-repeat as a new command, we ensure that any reader that does not support it will at least throw an error message, in accordance with the conformance section in the Gerber format specification, which states: “To prepare for future extensions of the format, Gerber file readers must give a warning when encountering an unknown command....”. Indeed, when read on the well-respected GC-Prevue Gerber viewer, the new command initiates an error message.

Another issue is that simple step-and-repeat generates an array made up of regularly-spaced, identically- oriented PCBs. For added flexibility, we have introduced a block aperture that that can be flashed in any location and orientation. The new AB command creates a block aperture that can be mirrored, rotated and scaled using the existing LM, LR and LS aperture options, while the new Part Attributes Value defines unequivocally whether we are dealing with a single PCB, an array or a fabrication panel.

In this way, panelized data can be handled with greater efficiencies, while the block aperture is a powerful general construct that will no doubt have many other applications. Together, nested step-and-repeat and the block aperture form a powerful extension of the Gerber format.

The draft specifications are open for your review and that of your fellow Gerber users before the new features go live. We invite you to evaluate them and welcome all your comments and constructive criticism. E-mail us your comments by clicking here.  

Thank you,

Karel Tavernier
Managing Director, Ucamco





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