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Keep Your Order on Track - Design tips for layout - by Matt Stevenson
In PCB manufacturing we see hundreds of PCB layouts represented in Gerber format every week. Some of the layouts are really well thought out and ready to roll straight into manufacturing and then there are the layouts from the other end of the spectrum. Sometimes we affectionately refer to these layouts as the Etch A Sketch® designs, meaning that they did not adhere to the same thoughtfulness during the layout phase (yes sometimes it really does look like it was created on a toy and not in a CAD tool).
There are many reasons that we have seen for one of these designs to be submitted, but the main three are lack of layout experience, lack of time spent on the project, or lack of attention to the details. There are some things you can do to avoid scenarios that create issues with your budget, schedule, and life by either causing your design to go on hold or cause yield and reliability issues.
Use the tools in your CAD program
Simply representing a feature in your design, by any means, is not the best way. There are many useful functions in most CAD design tools that help eliminate confusion to your PCB manufacturer. Representing slots as overlapping drilled holes is a common practice in many designs, but it creates two potential issues for the manufacturer: if left as is it can create broken drill bits impacting yields and quality of the product or an inefficient tooling process as the tooler has to correct the issue to make a manufacturable PCB. Most software for PCB layout has the ability to make a slot and have it contained on the drill layer of the Gerber files. Another common representation comes in the form of circles drawn on a layer to represent non-plated mounting holes. Creating these holes in your tool and assigning them the plating type that you need is a much better approach. This will insure that you do not just receive copper circles on your PCB where you wanted to have mounting holes.
Pay attention to your Gerber files
Under many cases, the Gerber files that you submit for manufacturing will be the “gold standard” by which the PCB is created. Many of the higher-end PCB layout tools do a pretty good job of creating Gerbers that do justice to the Layout, but there are certainly exceptions. Utilizing a Gerber viewer to view your files prior to submission, can help you to identify potential issues prior to manufacturing and even limit your need to troubleshoot a completed design and use blue wires to make it work. Some common items that we have seen here are: overlapping thermal connections on adjacent pins (isolating intended connections), drilled holes in an unintended copper feature (like through a trace), oversized or missing solder mask clearances (potential to create solder shorts or un-solderable situations).
"Just because you can......don't mean you should!"
We get the pleasure of seeing designs submitted that are virtually unbuildable due to the blind and or buried vias in the design. Several PCB layout tools are very accommodating and will let you do just about anything digitally but the consequences can be staggering and many times unnecessary. Blind and buried vias are one sure way to drive up the cost, lead time and yield loss on any design so if you do not absolutely need to design with these, you should not. I am sure that none of you fall into this category but we have had several very smart people over the years make comments like “I was able to draw it so you should be able to build it” and be serious about it. PCB manufacturing must adhere to the laws of physics still and that does make some things impossible to build ... at any cost.
At the end of the day...
...it comes down to taking your time, checking your work and applying thoughtful design concepts to your PCB layout project. PCB layout is not rocket science (well, sometimes it actually is) and applying a few concepts and common-sense steps in the design phase can be a serious time saver. It is like the old adage about health, an ounce of prevention is worth a pound of cure.
There are many resources available to help you be successful: YouTube videos, colleagues and your PCB manufacturer just to name a few.
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