Gerber File Extension

For those that are not familiar with the Gerber file extension designation of rs274d vs rs274x we put together some basic information to help you understand the difference and why it is important in the PCB ordering and manufacturing process.

How can just a letter make such a big difference? At first glance the “d” would seem like it would be better than the “x”. After all d is the fourth letter of the alphabet and x usually means something should be canceled or “X’d-out”. Well in this situation that is not the case.

PCB manufacturers use the Gerber File Extension in the manufacturing process of printed circuit boards. The files are used to create photo plots, drill data and other information needed to produce the desired end result.

Design engineers will use a circuit design program to create their PCB design. They will export the files from that program into Gerber format in order to have the circuit boards manufactured. It is at the export function that one of many critical decisions must be made. Do I export in rs274d or rs274x format?

Here is the difference; it is all about apertures. What is an aperture? It is a shape such as square, round, rectangle. They are sometimes called D-codes, because their designators are “D” followed by a number. Of course there are many levels of complexity that are often added in order to produce the exact right shape that is needed in the circuit design. The apertures will designate that a pad or other feature on the board is a square, round, oblong, rectangle or other standard or custom shape.

rs274d vs rs274x

The challenge with the two formats is how that data is exported and then used by the PCB manufacturer.

In the D format the apertures are exported as a separate file. This creates some problems for the PCB Manufacturer’s CAM engineering team.

A Bay Area Circuits’ CAM Engineer says, “Sometimes there is a global aperture list; sometimes there are multiple lists, one for each Gerber layer. Aperture files come in a multitude of types, most of which are proprietary to the software that generates them. Many can only be read by the application that generated them; this leaves the CAM operator with only one option: enter them all in manually. This is time consuming, prone to errors, and sometimes results in the wrong shape pads being used where the aperture definition is unclear.”

So, files in the D format are going to subject to errors and delays in the manufacturing process. However, in the X format things get much easier.

Which is Preferred?

Bay Area Circuits’ engineering manager says, “rs274X is preferred over rs274d because the apertures are embedded into the file data and do not require any manual input from the CAM operators.”

The X format will ensure that a design engineer will be getting exactly what they expect to get. It makes the quote, order and pre-manufacturing process go much faster and smoother for all involved.

Any modern PCB design software package will export in the rs274x format. That will take care of anything new being produced. However, there is a lot of old data still out there that is already in the old format and it has not been updated. In those cases our CAM Department can make those changes. We would recommend though that the data be updated to rs274x format in order to ensure that the circuit can be continued to be manufactured.


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