10 PCB Design Mistakes That Cause Thermal Failures
Thermal issues are one of the biggest killers of electronic products.
Heat degrades components, shortens product lifespan, and can even create dangerous fire situations.
So in this video, I’ll show you 10 common PCB design mistakes that cause thermal failures so you can avoid them in your design.
I’ll be honest, I’ve fallen into some of these traps myself, and I still see them all the time in the designs members share in the Hardware Academy.
Don’t beat yourself up if you recognize a few here. Everyone does. What matters is learning how to avoid them in the future.
Okay, lets get started.
Mistake 1: Undersized Copper Traces for High Current
One of the most basic and most common mistakes is using traces that are too narrow for the current they’re supposed to carry.
If the copper is too thin or too narrow, it heats up as current flows through. This creates localized hot spots, higher resistance, and in the worst case, melted traces or burned PCB substrate.
You might think, “I used 10 mil traces and it worked in my bench test.” But that’s often under ideal conditions not with the enclosure closed, ambient temperature elevated, and other heat sources active.
The IPC-2221 standard gives general current-carrying capacity guidelines for copper traces. But it’s only useful if you actually account for the worst-case operating conditions not just the average.
And don’t forget that copper thickness matters too. A 2 oz copper layer carries twice the current of a 1 oz layer of the same width.
If your trace width is borderline, increase it, and use pours when possible. It’s one of the cheapest and easiest thermal improvements you can make.
Mistake 2: Poor Thermal Via Design
Thermal vias are your best friend when it comes to spreading heat away from hot components, especially things like processors and voltage regulators with exposed thermal pads.
But I still see designs with just one or two tiny vias, or worse, no vias at all.
That traps heat right under the component, with no easy path for it to escape into internal copper planes. The part runs hot, and reliability takes a hit.
The best solution, if your PCB fab supports it, is to use vias-in-pad that are filled and plated so they don’t wick away solder during reflow.
This creates a direct thermal bridge from the component’s pad into the internal copper planes.
If your fab doesn’t support via-in-pad, then connect the exposed pad to a copper pour on the same layer and place multiple thermal vias in that pour, right next to the pad.
It’s not as efficient as via-in-pad, but it still moves heat into the board where it can spread out.
Either way, don’t rely on air cooling alone. The PCB itself needs to act as a heat sink
Mistake 3: No Thermal Relief on Pads
Here’s the opposite problem too much copper, and no thermal relief during soldering.
If a pad is directly connected to a large copper pour without thermal relief spokes, it becomes a heat sink. That might sound good for cooling, but during assembly, it pulls heat away from the pad while soldering making the joint difficult or unreliable.
You get cold solder joints and uneven heating during reflow.
Thermal relief patterns solve this by using thin copper spokes to isolate the pad thermally just enough for proper soldering, while still providing good heat dissipation during operation.
You’ll usually see these on power planes and ground pours. Many PCB tools add them by default, but you should double-check and tune them if needed.
Good thermal relief equals easier soldering and longer-lasting joints.
Mistake 4: Concentrating Heat Sources Together
Another big one grouping multiple heat-generating components in the same small area of the board.
It’s tempting, especially when trying to minimize trace length or keep things compact. But placing two switching regulators side by side, for example, concentrates heat in one small region.
Without good airflow or heat sinking, the temperature rises quickly and both components degrade faster as a result.
Instead, try to spread out power components. Put one regulator on each side of the board if possible. Separate hot areas from temperature-sensitive analog or RF sections.
Mistake 5: Inadequate Copper Pour or Planes
Copper is your #1 tool for spreading and dissipating heat across the board.
But in low-cost or compact designs, people often skimp on copper pours or internal planes.
Without sufficient copper area, hot components remain thermally isolated. Their heat builds up, and performance suffers.
For power components with thermal pads, always connect to a large copper area on the same layer, and then use multiple thermal vias to tie into internal copper planes. Ideally, one of your inner layers should be a solid ground or power plane that can absorb and distribute heat.
Even in two-layer designs, you can use wide copper pours and lots of via stitching to help.
Just be careful: tying everything to a copper plane might solve thermal issues but introduce EMI or noise problems. You always have to balance thermal and electrical requirements.
Engineering is always a balancing act of compromises.
Mistake 6: Ignoring Component Thermal Specs
Every component datasheet includes thermal specs and yet, they’re often ignored or misunderstood.
Take a power regulator with a thermal pad, for example. The datasheet might show a maximum current or power dissipation, but that rating assumes the thermal pad is connected to a large copper area, exactly as shown in the recommended footprint.
If you skip that connection, the chip may work at first, but it will overheat under real-world loads.
Pay attention to the thermal resistance values in the datasheet.
Junction-to-ambient (Theta-JA) tells you how much the junction temperature will rise for each watt of power dissipated.
Lower θJA means the device moves heat into the board and surrounding air more effectively.
Junction-to-case (Theta-JC) tells you how well heat transfers out through the case or exposed pad, which matters if you’re using a heat sink or thermal vias.
Many datasheets also include curves showing how θJA improves as you increase copper area. That’s your guide for how much copper you really need to keep the part cool.
Mistake 7: No Consideration of Airflow
Most PCBs don’t live out in the open. They’re inside plastic or metal enclosures and airflow becomes critical.
If you block natural convection with tall components, ribbon cables, or sideways-mounted heat sinks, the entire thermal system breaks down.
Even in fan-cooled designs, poor layout can trap air or force it to bypass the hot areas entirely.
The solution is simple: think about airflow while placing parts. Align heat sinks vertically if relying on natural convection. Leave channels for air to flow across hot components. Avoid creating heat pockets where air gets trapped.
Even small tweaks can make a huge difference especially in sealed enclosures where heat has nowhere to go.
Mistake 8: Overlooking Board Thickness and Layer Count
This one often comes down to cost. Designers try to cut costs by reducing the layer count or going with thinner copper.
But fewer layers and thinner boards spread heat less effectively.
A 4-layer board with solid inner planes will move heat far better than a 2-layer board with narrow traces. And the added copper thickness alone can be a game-changer for high-current applications.
Yes, you’ll pay more per board. But you may eliminate the need for heat sinks, fans, or thermal redesigns down the road.
For anything above a few watts of power dissipation, don’t assume a thin two-layer board will cut it. Test early and design accordingly.
Mistake 9: Wrong Placement of Temperature-Sensitive Components
Not every component handles heat the same way.
Electrolytic capacitors degrade quickly at elevated temperatures because the electrolyte dries out. Their lifetime roughly halves for every 10°C increase above their rating.
Quartz oscillators are also temperature-sensitive. High sustained temperatures accelerate aging and cause permanent frequency drift.
The same goes for precision analog ICs and lithium coin cells, which lose accuracy or capacity much faster in hot zones.
If you place these parts right next to a MOSFET or buck regulator, they’re going to bake and fail much earlier than expected.
Always keep sensitive components away from known hot areas, and if your board has a clear temperature gradient, put them on the cooler side.
Mistake 10: Skipping Thermal Testing
You can do everything right in layout, but without testing, you’re still flying blind.
But nothing beats real-world testing. Power up your prototype under worst-case loads. Seal it in the enclosure. Use a thermal camera or temperature sensors to see where heat builds up.
Thermal failures often show up after hours or days of use long after your quick bench tests are done.
So don’t skip this step. It’s one of the most critical things you can do for product reliability.
If you’d like help avoiding costly mistakes in your design then we can help you do just that in the Hardware Academy.
And if you liked this video, then check out this video on design mistakes that damage product reliability, or this one where I reveal common mistakes that fail certification.
