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Accurate Gerber files are mission critical for smooth PCB manufacturing

Gerber files can reveal design issues ahead of the quote process and ensure your manufacturer has everything needed to produce your boards correctly. In a recent conversation with our Engineering Support Specialist, Eric Haugen, we explored some best practices for making sure Gerber files are accurate.

Speed is a critical component of the PCB manufacturing process. I spend the bulk of my day receiving files from customers and giving them back quotes in return. Rare is the day when a customer finishes off a quote request with, “Hey, take your time. I’m in no hurry.”

We process dozens of rush quote requests every day and I can assure you we do not like sending them back for more information from the client because crucial information is missing. And I’m pretty certain our customers don’t like getting their quote requests sent back or, worse yet, producing boards that don’t work because a key design element was not relayed to us.

Sometimes this happens for an unavoidable or unforeseeable reason. Other times, it’s purely a function of being in too much of a hurry to measure twice and cut once. We get it. It’s hard to take your foot off the gas when your production lead or your boss is tapping his or her fingers on your desk.

An important thing to remember when you’re deciding whether or not to hit the pause button: Your fabricator cannot read your mind. That’s why, before you hit send on a quote request, it makes sense to take five minutes and be sure you are sending something that’s usable for your manufacturer.

Especially if you’ve been working on it for a long time, viewing your design in the native CAD tool can be overwhelming. You have been zoomed in looking at tiny details for days or weeks. It seems so close to finished, but this is exactly when you should lean back and look at the big picture.

Converting to Gerber provides you with an uncluttered view of your board design. You can see each layer, lined up. This can reveal all sorts of issues that will slow the quote process such as one layer being scaled while others are not or one layer being metric, one not.

 Converting to Gerber offers a double check that can pre-solve problems related to esoteric naming convention, text on silkscreen layer showing up on the copper layer, tolerance issues with traces, and mis-aligned drill holes.

Perform a design rule check before you convert.

You can prevent many issues by using the design rule check (DRC) tool in your CAD software. If you’ve properly configured the DRC tool, questions that often send a quote request back for more information can be answered. Are the layers all there? Are the spaces big enough? Do you have more drill files than copper layers? How are your tolerances?

These answers provide a good foundation for manufacturability, but you still have one very critical job with regard to the DRC. Ask yourself, “Can my fabricator make this design?”

Remember, just because your software will let you design a board in a certain way, that doesn’t mean we can build it. Think about manufacturability as you perform your design rule check before converting to Gerber.

Now let’s check your Gerber files.

Once you’ve converted to Gerber format, you’ll gain a more holistic, simplified view of what’s really going on with your design. Here are some categorized items you can more easily check for and make changes where needed when viewing Gerber files.

Minimum Feature Size

When you carefully scrutinize minimum features size and question what the DRC permits, you can:

  • Find unintentional neck downs.
  • Locate places where traces just barely touch pins.
  • Discover breaks in traces or where ends just barely touch.
  • See where pads are too small.
  • Eliminate small traces or features that can be a needless and major cost driver.
  • Validate minimum drill size, more easily locating unnecessarily small drill holes that can also significantly drive up costs.

Feature spacing

Solve clearance problems before they occur. Upon viewing the Gerber file, you’ll have a sharper view of spacing types and be better able to recognize clearance problems for:

  • Trace/trace
  • Pad/pad
  • Copper/copper
  • Drill/drill
  • Drill/copper
  • Pad/pad

Look at each layer.

 This is really the only way to visually confirm each is correct. And by doing so, you accelerate the quote process and avoid cost overruns during production of the boards. Before submitting your quote request, consider:

  • Does each layer import at correct scale and size?
  • Are the number of copper layers correct?
  • Are the silkscreen and soldermask layer counts accurate?
  • Did the drill file read as intended, as a single file or multiple files? If not, why?
  • Was the drill file updated at the same time as Gerber files?
  • Do drill holes line up with artwork?
  • Were all area fills refreshed just prior to generating Gerber files?
  • Did you intend to have potentially expensive blind vias or buried vias?

Even one misstep in this category can create problems down the road. Though the list may seem long, the potential return on investment of a few minutes can be significant.

Check soldermask layers.

When you are double checking each board layer, pay careful attention to soldermask layers. Oversights here can not only cause delays but result in boards that do not function properly or at all.

  • Do all pins have mask openings?
  • Vias under components should not have mask openings. Do they?
  • Are soldermask openings slightly larger—at least .004”—than component pads?
  • Are plated through-hole pads .015” larger than drill and therefore large enough to avoid breakout?

Leave plenty of breadcrumbs for your fabricator.

Like I said, we can’t read your mind. Fabricator notes can make the difference between a quick turn and a protracted delay. If filenames are just a jumble of numbers or we have questions about what services you want us to perform, the notes are where we can go for guidance.

  • Will the fab notes conflict with your order form?
  • Do notes call for unnecessary services?
  • Do you reference documents that we do not have access to?
  • Does the design service you selected include a technician checking your notes?

Not all quick turn prototyping services offer human intervention. So, if you’re relying on a technician for review of your design files ahead of the quote and production process, be sure to choose a service level that includes it.

Finally, and this may seem obvious, make sure you are sending your fabricator the correct file. You would be surprised how often we receive the wrong files and discover it after production of the PCBs is complete.

So, please invest a few minutes in your design and check your Gerber files before you hit send. We want to help your rush job and help you keep your boss from tapping his fingers impatiently on your desk.

 

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