If you’ve ever held a piece of electronic gear that feels just a little too warm after an hour or two of use—say a gaming laptop, a power supply, or a compact smart device—you’ve felt the quiet, unrelenting problem electronics engineers have chased for decades: heat. For every component crammed into a printed circuit board (PCB), heat is a side effect, and too much of it shortens lifespans, slows performance, or even leads to catastrophic failure. As a PCB supplier who’s worked with engineers and product designers across industries for nearly 12 years, I can tell you one of the most underrated, yet critical, solutions to this problem is the humble thermal via. Let’s break down exactly what thermal vias do, why they matter more than you might think, and how we integrate them into our PCB designs to keep products running cool, reliably, and efficiently. Printed Circuit board
First, let’s get the basics straight. A via, in PCB terms, is a tiny hole drilled through the board, lined with copper, that connects copper traces on different layers of the PCB. Think of a PCB as a stack of thin, insulated layers, each with its own circuit traces, power planes, or ground planes. When a component like a CPU, MOSFET, or power IC dumps heat, it doesn’t just hang out in the layer it’s soldered to—it spreads to adjacent layers, and if there’s nowhere for that heat to go, it builds up like water behind a dam.
A thermal via is a specialized type of via designed explicitly to move that heat away from hot components. The difference between a standard via and a thermal via is intentionality: standard vias are sized and placed for signal or power continuity, while thermal vias are optimized for thermal conductivity. They’re usually grouped in tight clusters under heat-generating components, and their copper lining isn’t just for connecting layers—it’s a direct path for heat to travel from the top layer of the board to the inner layers, and even down to the bottom layer, where it can dissipate into the air or to a heat sink.
Let’s talk about how that heat transfer works at a practical level, not just in textbook terms. Copper is one of the best conductors of heat we use in PCBs; it has a thermal conductivity of around 401 W/m·K, which means it moves heat quickly. Air, by contrast, has a thermal conductivity of just 0.026 W/m·K—so a tiny air gap is a massive insulator. When you have a hot component on the top of a PCB, the heat needs to get past the air between the component’s solder pads and the board, then down through the board’s layers, without getting stuck in insulating materials like fiberglass (FR-4, the most common PCB substrate, has a thermal conductivity of around 0.3 W/m·K, way lower than copper). That’s where thermal vias come in. Each thermal via is a solid (well, almost) column of copper, so instead of heat having to work its way through the FR-4 and air gaps between layers, it jumps directly along copper paths.
For example, take a 10W MOSFET used in a power supply for a home appliance. Without thermal vias, all that heat would have to spread across the top layer’s copper trace, and dissipate only from the edges of the board into the air. A MOSFET rated for 10W would run at a temperature of 80°C or more in that scenario—not dangerous, but it would shorten its operational lifespan by years, as every 10°C increase in temperature cuts semiconductor component life in half. Add 12–15 thermal vias clustered tightly under the MOSFET’s pad, and you create a direct heat path down through the board. The heat spreads not just across the top layer, but into the inner ground plane, which is a large, flat sheet of copper that acts as a heat spreader, and then down to the bottom layer, where it can dissipate into the surrounding air. In that same power supply, the MOSFET’s temperature drops to 55°C, extending its lifespan dramatically and making the whole product more reliable.
Thermal vias aren’t one-size-fits-all, though. The size, spacing, and type of thermal via we specify in our designs depend entirely on the application, the component, and the board’s layers. Let’s walk through the choices our engineering team makes every day.
First, via size. Thermal vias are usually small, ranging from 0.2mm to 0.4mm in diameter, because smaller vias mean we can fit more of them in a tight cluster under a small component pad. But there’s a tradeoff: smaller vias can be harder to line with copper (the plating process has to evenly coat the inside of the hole, and very small holes can have incomplete plating, which kills thermal conductivity). For high-power components, we’ll go with slightly larger vias—0.4mm to 0.6mm—even if that means we need fewer of them, because the copper column is thicker and can carry more heat.
Then there’s spacing. The gap between thermal vias is critical. If vias are too close, they can cause a problem called “copper pooling” during the soldering process, where excess solder from the component pad flows into the vias, leading to bad connections or, worse, a short between layers. If they’re too far apart, there’s not enough copper to carry the heat, so the cluster becomes ineffective. Our sweet spot for most applications is a spacing of 0.5mm to 1mm between vias, adjusted based on component size and power load.
We also have to decide whether to fill the vias with a material or leave them empty. Standard thermal vias are “through-hole” and left empty, with the open top and bottom sometimes covered with a mask to prevent solder from getting in. But for high-performance applications, like automotive PCBs or high-power LED boards, we use filled vias. Filled thermal vias are either solid copper (called “copper filled”) or filled with a epoxy resin that’s then coated with copper. Filled vias don’t have air gaps inside them, so heat can move more freely through the via, and they provide a flat surface for soldering if we need to attach a component or heat sink to the bottom layer. For a power supply in an electric vehicle, where reliability is non-negotiable and temperatures can swing wildly between -40°C and 125°C, filled thermal vias are a must.
Another key design choice is where to route the thermal vias. The worst mistake we see designers make is placing thermal vias too close to signal traces. Even though thermal vias are copper, they can act as parasitic capacitors or inductors, which interfere with high-frequency signals. For RF boards or high-speed data PCBs, we have to keep thermal vias at least 2–3 times their diameter away from signal traces, and sometimes we even add a guard ring of ground around the vias to minimize signal interference. It’s a balancing act: we need maximum heat transfer from the hot component, but we can’t compromise signal integrity. As a supplier that works on a lot of high-speed telecom and IoT boards, this is a detail we obsess over—one misaligned via can turn a perfectly functional design into one that fails signal tests.
Let’s also talk about the common myths about thermal vias. I hear two all the time from new designers: first, that thermal vias are only useful for high-power components, and second, that they’re too expensive to add to a design. Both are wrong. Even low-power components, like the microcontroller on a smart thermostat, generate enough heat over time to affect performance. A microcontroller running at 5V and 100mA might only generate 0.5W of heat, but if it’s sealed inside a plastic casing with no airflow (like a wall-mounted thermostat), that heat can build up, causing the MCU to throttle its processing speed to prevent overheating. Adding four small thermal vias under the MCU cuts its temperature by 10–15°C, eliminating throttling and making the device feel snappier to users. And as for cost? The extra cost per thermal via is negligible—usually less than a cent per via. The savings from avoiding product returns, shortened component lifespans, and design delays far outweigh that tiny added cost.
What about real-world examples, beyond the power supply I mentioned earlier? Let’s take wearable electronics, like wireless earbuds or smart watches. These devices have almost no space for airflow, so all heat has to dissipate through the PCB. The small chip that handles Bluetooth and processing might only generate 0.3W of heat, but if it’s not paired with thermal vias, it can run at 70°C inside a 5mm-thick watch case, which feels hot to the user and can degrade the battery’s lifespan by 20%. We recently designed a PCB for a mid-range smart watch, where we used six 0.25mm thermal vias under the main system-on-chip (SoC), routed them to the inner ground plane, and left the bottom layer vias exposed to the plastic case’s inner wall. The result? The SoC runs at 52°C, feels cool to the touch, and the battery maintains its rated capacity for two full years, well above the industry average.
Another example is automotive ADAS (advanced driver-assistance systems) cameras. These cameras process high-resolution video in real time, so their image sensor and processing chip generate significant heat, and they have to operate reliably in extreme under-hood temperatures. We worked with an automotive startup a couple of years ago that was having issues with their camera failing after 18 months of use, due to overheating. We redesigned their PCB to use a dense cluster of 12 filled thermal vias under the image processor, routed to a thick copper inner heat spreader layer, and added a metal heat sink attached to the exposed bottom vias. After testing, their camera passed 10,000 hours of reliability testing, equivalent to five years of on-road use, and their product launch went off without a hitch.
Now, you might be wondering: how do we make sure thermal vias are working as intended, especially when designs get more complex? As a PCB supplier, we have strict testing protocols to verify thermal performance. We use thermal imaging cameras to map heat distribution across a prototype board, measuring temperatures at the component, the trace, and the via cluster, to make sure our calculations are accurate. We also run thermal simulation software during the design phase, long before we manufacture a prototype, to tweak via size, spacing, and placement. For example, if a simulation shows a hot spot under a MOSFET that’s still too high, we’ll add a few more thermal vias, or switch to a larger via size, before production, saving our customers time and money.
I also want to mention a common pitfall: not accounting for board thickness. Thicker PCBs have more layers, so thermal vias have a longer path to travel through the board. For a 4-layer board (two outer layers, two inner layers), a thermal via might be 1.6mm long, which is manageable, but for an 8-layer board, that same via is 2.4mm long, and heat transfer is slightly less efficient. That’s why, for high-power applications on thicker boards, we often specify a “thermal via stack”: vias that go from the top layer to the inner ground plane, and separate vias that go from the inner ground plane to the bottom layer, creating two shorter, more efficient heat paths instead of one long one.
At the end of the day, thermal vias are a small, unassuming part of a PCB, but they’re one of the most impactful for product performance and reliability. They’re not just a technical detail for engineers—they’re the reason your laptop doesn’t overheat mid-work, why your smart watch stays comfortable on your wrist all day, and why your car’s ADAS system works safely every time you drive. As a PCB supplier, our job isn’t just to drill holes in copper sheets; it’s to solve problems that keep our customers’ products running. That means paying attention to the small stuff: the size of a via, its placement, its ability to move heat where it needs to go, and not interfere with what it shouldn’t.
If you’re working on a new product, troubleshooting overheating issues in an existing design, or just want to make sure your PCB is optimized for reliability, we’re here to help. We’ve designed thermal vias for everything from tiny wearables to heavy-duty industrial power supplies, and we can help you figure out the right setup for your specific application. Connect with our team to discuss your project, and let’s make sure your products stay cool, reliable, and built to last.
Printed Circuit board References
- Tummala, R. R. (2004). Fundamentals of Microsystems Packaging. McGraw-Hill.
- Lau, J. H. (1996). Thermal Stress and Strain in Microelectronics Packaging. Van Nostrand Reinhold.
- Electronic Industries Alliance. (2010). IPC-2221: Generic Standard on Printed Board Design.
- Zhang, Y., & Shih, W. Y. (2018). Thermal Management of Printed Circuit Boards for High-Power Electronics. IEEE Transactions on Components, Packaging, and Manufacturing Technology.
Shenzhen Uniwell Circuits Co., Ltd.
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