Common Problems with Gerber Files and How to Avoid Them!
The PCB manufacturing process is complex. The precision of the manufactured PCBs hinges on many things, but none more important than complete and accurate design or manufacturing data, most often Gerber files. To produce manufacturing data, a wide variety of PCB design software applications are used, and the complexity of each design can vary significantly. As a result, the manufacturing data generated may not always yield the intended results, leading to board failures, manufacturing delays and increased costs.
In this post we will address the most common problems that we encounter with Gerber files and how to avoid them (we’re going to focus on Gerber files because they’re most common but many of these also apply if you generate ODB++ files).
Obsolete File Format
Avoid generating an obsolete file format like Gerber 274D. Gerber 274D is all but extinct today, but be aware that the newer Gerber 274X has also received an update called Gerber X2, and Gerber 274X itself been declared obsolete. This doesn’t mean that Gerber 274X cannot be accepted by your manufacturer (it’s by far the most common format we receive today) but you may want to start looking into the benefits of Gerber X2 – especially if your PCB design software package already supports this format. Interested in more of an education on the Gerber format? Here’s an interview with Ucamco, who owns and maintains the Gerber format.
Confusing File Labels
The naming of each Gerber file should reflect the board layer and be easily interpreted. Each software application may have its own way of exporting the files. That process is fine as long as it either makes obvious sense, or the details of the file names and which layer they correspond to are provided. In most cases these issues can be worked through and figured out, but mistakes can happen when the PCB manufacturer has to interpret & modify data which may results in delays or engineering costs.
Often there are no “Fabrication Drawings” sent with the Gerber files. A fabrication drawing sometimes provides useful information about the desired board characteristics that are not contained within the Gerber files. In addition to displaying the overall dimensions of the board, they will identify any special cut outs or routing. They can also contain any notes related to the fabrication of the boards such as file names, material type, thickness, finish, etc. Not all PCB design software packages include the ability to generate a fabrication drawing; if yours does not, there’s no need to worry, just create and include a document file which lists any board characteristics not included in your Gerber files.
Drill files are often provided without the correct format. Importing the file then becomes “trial and error” to get it right. The header in the file should include information that clearly indicates the format. The proper format is called a NC Drill file. If you are further able to define that file, it’s helpful to add to the software export: 2.4, Absolute, Trailing.
Registration of Layers
When possible, having the Gerber files registered to a common data point is recommended. Some files come in with the layers at a different datum alignment (like a target) which then requires manual alignment of the layers. This can be done, but is an instance which requires additional engineering time and leaves room for error.
Often times Gerber data is provided with no defined outline of the board included. This can be a problem when defining the dimensions of the board per your requirements. The outline can be its own independent file or you can include an outline on each layer in the data set. This is one of the most common mistakes we encounter and is a showstopper; meaning, the PCB manufacturer will put your job on hold until this information is provided.
Often plane layers or layers with shield areas are provided to us filled with 1 mil or 2 mil vectors. This causes the Gerber file to be quite large in size and requires a process to “contourize” the data. When we panelize this type of data, the files often become too large for the plotter (equipment) to digest. It is recommended that for areas to be filled, use “raster” or “contour” data.
Some PCB design software uses composite layers to create one layer. For example, a plane layer with embedded traces will use three layers just to create one layer; first, you have the plane layer, then the clearance layer, then the trace layer. Some layers are positive images while others are negative images. Layers similar to this, should all be combined then output as a single Gerber layer.
Some PCB design software creates surface mount pads with vectorized data, meaning the pad is composed of many small vectors arranged in such a manner as to create a surface mount pad. This requires the CAM operator to substitute all the surface mount pads to create one flash pad. This not only reduces the amount of data, but also helps in the editing of such files. Better to use flash pads if you can.
We trust you have found some helpful suggestions from this three-part series on Gerber file problems. If you have further questions, our experienced team is available to assist on your next project.