PCB Design Limitations Beyond Borders: Extending Past Edge Clearance

Altium Designer
|  Created: February 9, 2018  |  Updated: September 25, 2020

Man sitting over edge of a cliff

Have you ever stood, two feet planted, on the edge of a cliff? No, not a very steep slope that would slightly injure you if you fell, I’m talking about the 90-degree style, 2,000 feet straight down cliffs you see pictures of in National Geographic. Certainly a terrifying experience, no matter how seasoned you are at cliff standing.

The thoughts that race through your mind are non-stop and extremely primal. Will my feet slip if I get too close? What about that gust of wind that I feel at my back? Not exactly my cup of tea, but sometimes you just have to look over the edge.

Similarly, you may find yourself (or your components) standing on the edge (clearance) of your PCB with little room to spare. Sometimes, your components must bear the terrifying experience of standing on the edge of that 2,000 foot (ok, maybe it’s closer to an inch or so) drop only to be subject to operate at peak performance for the remainder of its existence. Oh, what a life!

Whether it be lack of board real estate, a heaping amount of components to cram, or simply the restrictions of the chassis surrounding the board, sometimes you will need to extend your components past acceptable edge clearance tolerances and into the realm of the cliffs. So what factors come into play when extending past these boundaries? The following are some guidelines that will ensure your components don’t go falling off left and right.

In Any PCB Design Limitations, Keep Ample Copper Connections

A rule of thumb for component placement at any position on the board is to first ensure that there is adequate copper enough for a sturdy electro-mechanical connection. While some things may change when you venture past edge clearance tolerances, the rule for copper is no different.

Just like any cliff-stander needs to ensure their feet are firmly planted on the ground, you will need to take similar care with your components. Keep yourself and your design from toppling over by taking the extra precautionary measures to promise the physical, copper connections will be solid throughout.

Manually soldering
Ensure plenty of copper is available to keep your connections sturdy.

Use Beyond Intention: Designing Outside the Box

Of course, when designing your PCB, you’ll expect it to be used in some form or another, and when any product is being used, you can never discount the ingenuity of a consumer to find new ways to use your designs. In other words, when your product is opened up by the intended user, they might be using it for purposes you never thought possible, but the user will still expect your product to hold to their standards.

By looking at the space surrounding potentially hazardous components, you can be proactive about preventing damage even from unintended product uses. Especially if your components are edging closer to the cliffside, you’ll need to consider even outside-the-box use cases of your design. Are there any that if handled aggressively would bend and break? What about being affected by damage to the chassis?

Simply being wise about intended (and unintended) uses of the product and how your components might be affected will answer many of the gray area/edge clearance questions that will arise.

Child playing with a car
Sometimes, you will have no idea how users will treat your product

Manufacturing Limitations and How to Prevent Them

If I had a nickel for every time I told folks to consider limitations of manufacturers prior to design freezes, I could probably build a staircase down from whatever cliff I’m facing. In PCB design software, you can design anything your mind is able to conjure; however, translating it to the real world (manufacturing it) is another feat entirely.

Moving components closer together or closer to the edge clearance of your design will make it that much more difficult for manufacturing teams to incorporate. Depending on the capabilities of your manufacturer’s machines, you may find yourself at a loss when sending out your initial RFQ’s. Before you know it, it’s back to the drawing board.

One way to combat this is by performing an audit and manufacturing facility review before you commit to a manufacturer for your design. You can check the capabilities of your manufacturer, and therefore ensure that they have the capabilities you need for your design to succeed. Reaching out to even a small number of manufacturers will give you an idea of where limitations exist when you’re extending past edge clearances.

Don’t Overthink Your Edge

Moving beyond edge clearance isn’t rocket science, instead, it is a game of risk. The game translates into, “How close can I get to the edge before falling off?” Again, not a question that I like to ask when overlooking thousand-foot drops, but sometimes in our PCB designs we don’t have a choice.

Keeping the aforementioned considerations in mind will benefit your process in small ways that will keep your design churning as long as sales are healthy. For PCB design software which can make these considerations easy through incorporating intuitive rule checking, as well as clear, effective manufacturing output files, consider Altium Designer®. Its unified design environment lets you skirt from schematic to layout to output all on the same platform.

If you are interested in seeing what Altium can do for you in terms of keeping your components from falling off the edge, talk to an Altium expert today.

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About Author

PCB Design Tools for Electronics Design and DFM. Information for EDA Leaders.

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