Tuesday, May 23rd
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You’ve completed a PCB design and are ready to send the design to be manufactured. Experienced designers understand that PCB manufacturers require the design to be exported to a format like Gerber or ODB++. But the file export process isn’t always straightforward, and, depending on the PCB manufacturer, specific requirements may vary. Here are some helpful design file guidelines that will make the Bay Area Circuits ordering & manufacturing process go smoothly; we’re confident you’ll find these to be useful no matter who is manufacturing your next PCB design project.

PCB Design File Basics

In general, you’ll need to provide your PCB manufacturer with the following files:

Top Silkscreen
Top Soldermask
Top Copper
Bottom Copper
Bottom Soldermask
Bottom Silkscreen
NC Drill
Board Outline (sometimes embedded in another file)
Inner Layers (optional, depending on design)
Fab Drawing (optional, but recommended)
Readme (optional)

Of course, the file requirements will vary depending on the design. For example, a single-sided board with no soldermask will require fewer files, while a multi-layer board with many inner layers will require more files.  It’s a good practice to not include any more files than necessary – don’t submit a soldermask or silkscreen layer if you don’t want soldermask or silkscreen on the board.

The NC Drill file should be included in Excellon, 2.4 trailing format.  Separate files may be provided for plated and non-plated holes, but this is not necessary unless a non-plated hole will be drilled through copper.

Important Tip! Because many PCB design software applications require the Drill file to be exported as a separate process from the rest of the design files, this is the most commonly forgotten file. Be sure to include this file to prevent manufacturing delays.

The Board Outline is another file that is often overlooked. Depending on the PCB design software application used, this file can either be a stand-alone file or be included within other layer files. In any case, the Board Outline identifies the critical outer dimensions of the design and must be known before manufacturing can proceed.

Lastly, some files such as Fab Drawing & Readme are optional but recommended. These can be helpful to explain design requirements that may not otherwise be reflected in the actual design file output, or, to emphasize requirements such as the Board Outline / outer dimensions. Learn more about Fabrication Drawings in our recent post.

 

PCB Design File Extensions

Depending on the software application used for the PCB design, the actual file extensions associated with each element may vary.  Below is a chart that lists a few of the more common extensions.  Other software applications will differ, but all will use a common extension and have a specific name for the designation.

Protel Altium® EAGLE OrCAD™
Top Silkscreen .gto .plc .sst
Top Soldermask .gts .stc .smt
Top Copper .gtl .cmp .top
Bottom Copper .gbl .sol .bot
Bottom Soldermask .gbs .sts .smb
Bottom Silkscreen .gbo .pls .ssb
NC Drill File .txt .drd thruhole.tap
Board Outline .gm1, .gko
Internal Layers .gp1, .g1
Fab Drawing .pdf .pdf .pdf
Readme .txt  .txt  .txt

 

Final Thoughts

Common Tool Settings

In general, we recommend using these basic settings in your PCB design tool:

Units = Inches
Format = 2.3
Embedded Apertures = RS274X

How Files Are Viewed By a PCB Manufacturer

Something important to remember is that the files are viewed from the top down.  This means that the top layers would be right reading while the bottom layer would be mirrored.  For inner layer planes, the image is typically a negative image.  However, for inner layer signal layers the image is typically a positive image.

File Archive

Once all the PCB design files are ready for manufacturing, they should be placed in the root directory of a folder and archived (.ZIP or .RAR for example). Do not send each individual layer file to the PCB manufacturer as a separate attachment, as this slows processing and creates room for error.

Design for Manufacturability (DFM) Check

As a final confirmation prior to submitting design files for PCB fabrication, it’s always a good idea to run a DFM check to ensure your design files are complete and meet your PCB manufacturer’s capabilities. A DFM check may differ substantially from your design software’s design rule check (DRC), even if you have followed all of the manufacturer’s design rules, as a good DFM check is linked directly to the PCB manufacturer’s CAM software.  At Bay Area Circuits, our free InstantDFM tool allows anyone to upload their design and receive an online DFM report within a minute. The resulting DFM report will identify any potential production issues and allow you to address them prior to submitting a design for manufacturing – ultimately saving time and money!

 

We hope you find this information valuable. We’d wish you luck with your next PCB project, but if you follow these guidelines, we doubt you’ll need it!

 

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