7 PCB Design Mistakes That Will Fail Certifications
Certification testing is already time-consuming and expensive, and that’s assuming you pass the first time.
But if your product fails, it can quickly spiral into redesigns, extra testing fees, and long delays.
I’ve seen plenty of designs that were fully functional, and the founder thought they were almost ready for production, but once they hit certification testing, unexpected issues came up and turned into a major roadblock for the project.
If you’re lucky, it might only take a minor layout tweak. But more often, if you haven’t designed with certifications in mind from the start, you’ll be facing major changes that cost serious time and money.
In this article, I’m going to show you 7 PCB and product design mistakes that can lead to certification failures, and how to avoid them early.
Hi, I’m John Teel, a former microchip design engineer who brought my own hardware product to life. Now I help others develop and launch new electronic products.
Mistake #1: Ignoring EMC in Your Layout
Most certification failures come down to one thing: electromagnetic compatibility.
If your design radiates too much noise or is too susceptible to interference, it’s going to fail EMC testing, whether you’re doing FCC, CE, or both.
And a lot of that comes down to layout.
For example, if you run long signal traces without a solid return path underneath, like over a split ground plane or a routed-out area, those traces effectively become antennas.
High-speed signals need a continuous ground reference to prevent radiating noise. Without that, they can leak emissions and fail radiated emissions tests.
Another common issue is ground plane fragmentation. If your ground plane is chopped up by vias or routing, you break the low-impedance return path, which again increases emissions.
And then there’s power input filtering. If you skip ferrite beads, bulk capacitors, or LC filters on power inputs, you’re inviting conducted emissions issues.
Even power supply layout matters. A switching regulator with long loops or poor grounding can radiate across a wide frequency range and tank your EMC results.
So don’t just think about functionality. Think about emissions and immunity, because the test lab will.
Mistake #2: Relying on a Two-Layer Board Without a Solid Ground Plane
Two-layer PCBs are great for quick prototypes and low-cost dev boards. But when it comes to passing certification, they often create more problems than they solve.
Why? Because they almost never provide a clean, continuous ground plane.
In a four-layer board, you typically dedicate an entire internal layer to ground. That gives high-speed signals a consistent return path right underneath their traces, minimizing current loop area and reducing emissions.
But on a two-layer board, you usually end up with a patchwork of copper pours that get chopped up by signal traces, or worse, you just use ground traces to connect everything. That breaks up return paths and increases EMI risk.
Even worse, those chopped-up ground areas can act like unintended antennas, radiating noise instead of containing it. That’s a fast path to failed EMC testing.
If you’re serious about passing certification, using a solid ground plane, ideally on a dedicated internal layer, is one of the best decisions you can make.
Mistake #3: No Shielding or Filtering on External Interfaces
If it connects to the outside world, it needs attention. USB, power jacks, antennas, even GPIOs with long wires these all become potential antennas for noise or interference.
If you skip ferrite beads, ESD protection, or common-mode chokes, you’re going to see problems in emissions testing.
And if your board passes alone but fails when connected to a cable, this is often the reason.
Add filtering. Add protection. And make sure your return paths are solid.
Mistake #4: Thinking You’re Only Certifying the PCB
One of the biggest misconceptions about certification is thinking it only applies to your circuit board.
But that’s not how it works. What actually gets certified is the entire product your PCB, your enclosure, the wiring, the connectors, everything.
So if you design and test the board in isolation, then later put it in a metal enclosure with standoffs, screws, and cables, you might get completely different results in the lab.
Even plastic enclosures can change emissions or susceptibility, especially if they limit ventilation or are packed tightly with other noisy subsystems.
And metal enclosures, if not grounded properly, can create resonance chambers or act like unintended antennas.
The mistake is treating certification like a board-level exercise. It’s not.
Make sure you test your final assembled product, not just the bare board. Include the enclosure, wiring, and anything else the customer will receive.
Mistake #5: Poor Antenna Placement or Grounding
If your product includes Bluetooth, Wi-Fi, or any other wireless radio, you’ll need to pass intentional radiator testing.
And the antenna is often the problem.
If you place it too close to the ground fill, your enclosure, or other noisy components, it can cause performance issues like reduced wireless range or detuned antenna characteristics.
But even more importantly, poor antenna design can lead to failed RF certification due to spurious emissions or insufficient radiated power.
Even worse, if you use a pre-certified module but change the layout around the antenna, especially the ground clearance area or keep-out zone, you might void that certification, forcing full RF testing from scratch.
Always follow the reference layout exactly. Leave the recommended clearance around the antenna, avoid routing signals nearby, and don’t place it under metal parts of the enclosure.
Mistake #6: No Isolation Between High and Low Voltage
If you have any high-voltage circuits AC mains, power conversion, etc. You’ll need to think about safety testing.
That means creepage and clearance. It means isolation. And it means understanding which parts of your board must stay separate.
If you place high-voltage and low-voltage parts too close together, or route signals across isolation boundaries, your board could fail.
Pay attention to trace spacing. Remove copper fills under isolation areas. And follow the standards for your target market.
Mistake #7: Placing Noisy Components Near Sensitive Traces
When it comes to passing EMC and RF certification, component placement is just as important as trace routing.
Placing high-speed or noisy components, like switching regulators, crystal oscillators, or digital buses, too close to sensitive analog traces, antennas, or RF paths can create unexpected interference.
This can result in spurious emissions that show up in radiated emissions tests or degrade the performance of nearby wireless circuits, potentially causing certification failures.
For example, placing a switching regulator too close to an RF trace can inject noise directly into the signal path, especially if there’s inadequate shielding or grounding between them.
Group noisy and quiet sections of your board, use shielding where needed, and pay attention to layout isolation. Keep sensitive analog and RF areas physically separated from high-speed digital sections whenever possible.
