Background Theory > PCB Design > Gerber File History and Future

History

Gerber files play an integral role in transferring PCB designs from designers to fabricators globally, accounting for over 95% of all transfers. These files are generated automatically by most CAD systems, often without requiring designers to understand their intricate workings. This testament to the power and prevalence of the Gerber file format does not negate occasional complications, necessitating some understanding of the format's structure. Furthermore, there are future plans for enhancing the format's utility.

The Gerber file format derives its name from Joe Gerber (1924-1996), a US inventor who escaped from Austria in 1940. During his student years, he was deeply interested in accurate data plotting. In the 1950s, he created the digital XY co-ordinate table, which eventually formed the foundation for his future business, Gerber Scientific. The company's debut product was a digital drafting machine, one of the first of its kind globally. Subsequent products included automatic cloth cutting machinery and computerized spectacle lens machining equipment, both of which are still widely used today.

In the 1960s, Gerber devised a novel application for his XY table - the world's first NC photo-plotter. The device was designed to create photo-tools for producing PCBs, using a moving optical head that exposed pads and drew tracks on the film. This system is why we still refer to "aperture tables," "flashes," and "draws" today. The photo-plotters, known as vector plotters, followed the PCB pattern. The system was based on the RS-274-D format, developed by the US Electronic Industries Association (EIA), and initially operated using punched cards.

The advent of PCB Computer-Aided Design (CAD) systems in the early 1980s began to phase out hand-taped 2: 1 artworks. These CAD systems could output data directly to a photo-plotter, creating photo-tools. At the time, most photo-plotters were Gerber devices. Gerber had published a complete specification of their format in 1980, so Gerber RS-274-D became the universal standard.

The format, however, had one major flaw: the size, shape, and number of apertures were restricted by the physical aperture wheel. This limitation made handling new surface-mount components with varying rectangular pad sizes challenging. The workaround involved "painting" pads with tiny draws. While this strategy worked for simple plane layers, it was ineffective for mixed plane layers or signal layers. These layers required filling with draws, resulting in large images that took hours to plot.

A new format and photo-plotter were conceived as a solution. The raster photo-plotter employed a light source, typically a laser, to raster-scan the film continuously. With this system, any shape could be plotted using raster pixels. This method is now the industry standard for photo-imaging PCBs, with laser photo-plotters capable of resolutions down to 50,000 dots per inch or more.

The advent of this technology allowed for the creation of a more flexible and designer-friendly Gerber format. The Extended Gerber or RS-274X, launched in 1991, allowed users to define and image any shape - a pad, track, or polygon (plane). The aperture definitions were no longer constrained by a physical wheel and could be generated automatically from the CAD job.

RS-274X is the prevailing PCB layer image data transfer format used today. It is transparent, unequivocal, and user-readable. Each file is self-contained and enables the drawing of any desired pad shape or copper area.

However, the old Standard Gerber RS-274-D persists despite its limitations, such as needing a separate aperture table, generating cumbersome files, and potential requirement for the merging of positive and negative images. Most PCB fabricators still accepts this older format for previous jobs but prefers Extended Gerber, RS-274X, due to its lack of these limitations. RS-274X, complete with its embedded aperture definition, is compatible with PCB Visualizer, facilitating all advantages of our advanced data checking technology. Most current and older CAD systems generate RS-274X output. If your CAD system is still producing the old-style Gerber RS-274-D, it may be possible to switch to RS-274X in the output settings, although different systems may use different terminology.

Today

Today, RS-274X serves as the standard data transfer format for PCB layer images. It stands out for its clarity, lack of ambiguity, and readability. Each RS-274X file is self-contained, enabling the depiction of any desired pad shape or copper area.

Despite its limitations, the older Standard Gerber RS-274-D persists. These limitations include a reliance on a separate aperture table that frequently goes missing, creating large and unwieldy files, and potentially necessitating the merging of positive and negative images. The latter can lead to extensive clean-up operations or, even worse, easily overlooked errors.

While Eurocircuits can still process the older RS-274-D format when necessary, for instance, for prior projects, it is incompatible with our PCB Visualizer. As such, we prefer the Extended Gerber, RS-274X. It is free from the constraints of RS-274-D and integrates the aperture definition within the file, making it compatible with the PCB Visualizer. This compatibility unlocks all advantages of our advanced data checking technology. Most present-generation and several older CAD systems generate RS-274X output. If your CAD system still outputs the outdated Gerber RS-274-D, consider reviewing your output settings. It may be feasible to switch from RS-274-D to RS-274X. However, different systems may use different terminologies. If you have any uncertainties, don't hesitate to contact us.

The Future

Extended Gerber, or RS-274X, offers a precise and clear depiction of a PCB's layers. However, it doesn't incorporate all the information necessary for fabrication, particularly for automated data preparation.

Examples of missing information could be:

The function of the layer in question, such as top copper, top solder mask, etc.

Whether the image represents a single PCB or a delivery panel.

The purpose of a particular object, such as whether it's an SMD pad, via pad, fiducial, etc.

The board's profile. Automated recognition software like PCB Visualizer can identify rectangular profiles but struggles with complex shapes.

Drill tolerances for a specific hole. For instance, it might be a press-fit hole.

The tracks requiring impedance control.

The vias that need filling.

The next progression is to integrate such information into the data transfer format. Any extension of the format must remain compatible with the existing format and current CAD systems. While alternative formats incorporating non-image information have been suggested, the Gerber format's widespread use and effectiveness mean it isn't easily replaceable, much like QWERTY, QWERTZ, and AZERTY keyboards.

Today, the Gerber format is managed and evolved by Ucamco, a Belgian company that acquired Gerber Scientific's PCB Division in 1997. Ucamco has recently unveiled the blueprint for the next version of RS-274X, known as Gerber RS-274X2. This iteration introduces attributes into the format that encapsulate the information mentioned above.