Designing PCBs for IoT: How to Plan for FCC Certification and Testing

When I worked on my first internet of things (IoT) product, I was at a startup that was just past the two guys in the garage stage. I was literally the third employee. We were all smart, enthusiastic, and entirely focused on the proof of concept of our design. As the newcomer, I assumed that there was a plan in place for finalizing our product, getting any equipment certifications or approvals, and getting it to market. Spoiler alert--I was completely wrong. We learned the hard way that no matter how amazing your IoT product is, no one will appreciate it if you can’t get it certified and on the market.

I knew IoT was everywhere, or it was going to be. You could wear smartwatches or fitness trackers, order detergent from a button in the laundry room, and have your crockpot text you that dinner is ready. Having this equipment at your fingertips is phenomenal! With IoT being ubiquitous in our day-to-day lives, I assumed that gaining any certification would be trivial.

All of these IoT devices depend on being able to transmit their information back to MU-TH-ER, or whatever you call “the cloud” if you’re not an Alien fan. All that radio frequency (RF) transmission is regulated by the Federal Communications Commission (FCC), to ensure that any device isn't encroaching on each others’ approved frequencies or broadcasting at unsafe power levels.

If you only add RF modules on your products, this can lead to enormous fines if your products aren’t properly tested and certified. These fines are often per transmitter per day of a violation, so costs rack up quickly if you’ve already deployed a system.

While we didn’t get fined, we had plenty of other issues with the certification of our equipment. Do not underestimate the importance of planning ahead for certification before your product is launched, or even designed. Certification is expensive and time-consuming. I assure you, you want to design for it on day one and avoid a respin because you didn’t pass the certification testing.

What kind of testing and certification do I need?

Selecting a module depends on your application requirements, and can be an extensive process. There are several online comparison tools to help you identify what will work best for you, like AT&T’s Module . You’ll end up with a module in one of two categories.

Full EMC Compliance Testing and Registration

Any device will require a range of testing to make sure that they are not producing any electromagnetic emission that exceeds the limits set by any FCC rule and requirement. This is followed with paperwork to certify and register your digital device. All receiver designs will need to be fully certified, but you may be able to simplify things for your transmitters with a modular certification.

Modular Certification

Some modules are basically “pre-certified” and have already gone through the most extensive part of the FCC certification process. You still need to get your completed system tested for unintentional emissions, but the bulk of the testing is done. I recommend this approach for a first-time foray into IoT design.

Okay, but how does this affect my design?

There are various flavors of black magic that go into any RF design, like grounding, noise reduction, and impedance matching. It’s also possible for many elements of your system to unintentionally become antennas, transmitting or receiving outside of your design specifications.

This means that small changes to a design can shift the RF emission frequency, cause spurious emissions, change the output power, and have your system producing outputs in places you never expected. Add that all up and you get a failed certification testing.

To eliminate those problems, there are several things to keep in mind as you’re designing your PCB.

• Minimize trace length
• Keep high-speed components close to each other, especially in mixed signal designs
• Use good grounding practices
• Isolate your inputs. High sensitivity inputs may even require a separate routing layer
• Use bypass capacitors to reduce noise around DC components

Smart component selection is as important as your layout

Our first design used commercial sensors from a small company (probably smaller than ours) that was thrilled at a chance to increase their sales. For various reasons, they never certified their sensors. This made for a fun surprise when we connected them to our control board at a prescan (a cheap, unofficial test where they check for obvious problems). The tech said, “Wow. Those things are screaming. That is the worst I’ve ever seen.” Those words carried weight, as he had 12 years of experience testing products. At the time, it felt like the end of the world.

To avoid this scenario, do a little research up front on your components. This will save you from scrambling around trying to find shielding solutions or changing your hardware. Remember to look beyond your PCB and try to eliminate troublesome components in the entire system.

• A single faulty component can be a harmful interference with your whole digital device. Check whether you’re including any components, like sensors with long traces, that can propagate issues to the system as a whole.
• Beware of wires and cables connecting to external components as they can become little electromagnetic radiators of chaos.
• Every single oscillator in your system is a possible source of trouble. Choose components that have been included in other successful designs, and shield them whenever possible to avoid the MHz screams we saw in our test.
• If you are using a modular certification, you can only use the module with antennas that were approved in the original certification or you will have to start from scratch.

Finally, the testing may require you to connect and disconnect any inputs, outputs, or power supplies. Make sure your connectors can survive unplugging without any adverse effects on your board!

Certification can be a confusing process, so it’s important to plan ahead and minimize your issues down the road. Fortunately, there are tools that can help.

Professional PCB Design Software used in conjunction with Altium Vault^® helps you to identify components used successfully used in previous designs, or that meet your specific requirements to pass certification easily. Some RF modules are already included. (The same company, Linx Technologies, also offers a nice overview of certification.)

Once you have a successful design, you can reuse modules from that design for your next IoT product to make both the design and certification easier. If you’re ready to start designing smarter, contact an Altium Designer representative to see how they can help!