Introduction

Gerber files are the standard file format used in the PCB industry to describe the printed circuit board images copper layers, solder mask, legend, and drill/route. When designers send their designs to manufacturers for fabrication, Gerber is the most common format used.

However, many designers make mistakes when generating Gerber files, leading to manufacturing issues, delays, and added costs. In this article, we’ll cover the top 7 most common Gerber File Mistakes and provide tips on how to avoid them.

Mistake #1: Incorrect File Extensions

One of the most basic yet common mistakes is using incorrect file extensions when saving Gerber files. Each Gerber file represents a specific layer and should use the correct extension.

Here are the proper extensions to use:

How to Avoid It

• Double check that you are using the correct file extensions when exporting Gerber files from your PCB design software.
• Refer to the manufacturer’s documentation if you are unsure about which extensions to use.
• Consider using a free Gerber Viewer to check that your exported files are correct before sending them out for production.

Mistake #2: Missing Layers

Another frequent mistake is failing to include all the necessary layers when generating the Gerber files. Omitting a required layer will prevent the board from being manufactured properly.

Essential layers that are commonly forgotten include:

• Solder mask layers
• Silkscreen layers
• Drill files
• Board outline layer

How to Avoid It

• Create a checklist of the required layers for your specific PCB and verify that each one is accounted for before exporting Gerbers.
• Compare the exported Gerber files against your original PCB design to ensure no layers are missing.
• If your design requires unique layers, clearly communicate this to your manufacturer ahead of time and confirm which layers need to be supplied.

Mistake #3: Incorrect Drill File Format

There are two main formats for drill files – Excellon and Sieb & Meyer. Mixing up these formats or using the wrong one for your manufacturer can cause problems.

How to Avoid It

• Clarify with your manufacturer which drill format they prefer and set up your design software to export in that format.
• The Excellon format is most commonly used, but always doublecheck with your fab house to be sure.
• Include details about the drill format along with your Gerber files so there is no ambiguity.

Mistake #4: Insufficient Clearances

PCB designs that have inadequate clearances between traces, pads, and vias often lead to shorts or manufacturing issues. Most manufacturers have specific design rules and minimum clearances that must be adhered to.

How to Avoid It

• Carefully review your manufacturer’s design guidelines and recommended clearances before starting your PCB layout.
• Use your PCB software’s built-in design rule checks (DRC) to verify clearances throughout your design process.
• If your design requires tighter clearances than the typical minimums, discuss this with your manufacturer to see if it’s possible and what the impact on cost or yield may be.

Mistake #5: Overlapping Silk and Mask

Overlapping silkscreen with solder mask openings is a common issue that causes problems during PCB Assembly. Components may be difficult to solder if the silkscreen ink overlaps the pad areas.

How to Avoid It

• Adhere to your manufacturer’s minimum silkscreen width and clearance guidelines. Typically, silkscreen line widths should be at least 0.008″ (0.15mm).
• On dense PCB designs, consider eliminating silkscreen between fine-pitch surface mount pads to avoid overlap issues.
• If your silkscreen is too close to pads, use your PCB software’s solder mask expansion settings to force a clearance between the openings and silk.

Mistake #6: Inaccurate Board Outline

Issues with the board outline layer can lead to fit issues or require manual fixes that impact cost and lead time. Common problems include unclosed outlines, incorrect line widths, and hidden contours.

How to Avoid It

• Ensure your board outline is a fully closed contour on the correct layer (.GKO extension).
• Make the outline easy for your manufacturer to distinguish by using a unique line width (e.g. 0.012″).
• Double check that your design doesn’t include any stray or hidden lines on the outline layer.

Mistake #7: Outdated Gerber Format

While many PCB manufacturers can handle older Gerber formats like RS-274-D, it’s always best to use the more modern RS-274X format. Newer formats allow additional information to be embedded and prevent issues with apertures and drawings.

How to Avoid It

• Set up your PCB design software to export in RS-274X (Extended Gerber) format.
• If you’re unsure which format you’re using, ask your manufacturer for clarification and update your export settings if needed.
• Consider using Gerber X2 if your design software and manufacturer support it.

Frequently Asked Questions

What is the difference between Gerber RS-274-D and RS-274X?

RS-274-D (Standard Gerber) is an older format that has some limitations, such as a lack of embedded aperture definitions. RS-274X (Extended Gerber) is the newer format that allows all the necessary information to be contained in each file, making it easier for manufacturers to process.

How do I check my Gerber files for errors?

Many free Gerber viewer programs are available that will allow you to open and inspect each layer of your design. Some PCB manufacturers also offer free online Gerber viewers that can be used to upload and check your files before placing an order.

What should I do if my manufacturer says my Gerber files have errors?

If your manufacturer reports issues with your Gerber files, first ask them for details about what the specific problems are. Then review each error and make the necessary changes in your PCB design software. Regenerate the updated Gerber files and resubmit them to your manufacturer for verification.

Can I use Gerber files generated from different PCB design software?

Yes, Gerber is a universal format that allows designs to be transferred between different PCB design tools. As long as you are generating valid Gerber files, it does not matter which software you use.

What other PCB Manufacturing files are needed in addition to Gerbers?

In addition to the complete set of Gerber files, most manufacturers will also require the following:

• NC drill file (Excellon or Sieb & Meyer format)
• PDF or drawing of your part placement (component locations)
• Bill of Materials (BOM)
• PCB Stackup information
• Any design notes or special requirements

Conclusion

Avoiding these common Gerber file mistakes will help ensure your PCB design can be manufactured on the first attempt without delays or additional costs. By carefully setting up your design software, adhering to manufacturer guidelines, and double-checking your output, you can produce error-free Gerber files every time.