How can thermal via design prevent heat-related PCB failures?

A PCB can work reliably on an open test bench and struggle once it is fitted inside a compact enclosure. Under sustained load, heat builds around power components, temperatures rise and the product may start limiting its performance or shutting down. PCB thermal via design helps give that heat a route away from the components generating it. The result depends on where the vias sit, the copper they connect to and how heat eventually leaves the product. Considering those connections early can reduce the risk of overheating and avoid expensive changes late in development.

Why heat needs a designed path through the PCB

Voltage regulators, power transistors, processors and LEDs all generate heat during operation. If that heat cannot escape quickly enough, their internal temperatures rise. This can affect performance, accelerate ageing and push components beyond their operating limits.

The board itself plays an important part in controlling that temperature. Copper conducts heat far more readily than the insulating material used in a conventional PCB, so the layout needs to make effective use of its copper layers.

Thermal vias are small holes with copper-plated walls that carry heat through the board. They commonly connect a component’s thermal pad to larger copper areas on internal layers or the underside. Those areas spread the heat, allowing it to reach surrounding air or a cooling surface.

The benefit can be substantial. In a Texas Instruments study, moving from a two-layer board to a four-layer design with heavier copper and improved planes reduced resistance to heat flow from chip to surrounding air by approximately 42%. At 2 W of heat dissipation, that equates to a calculated temperature rise about 37°C lower. Both boards used thermal vias, so the improvement reflects the wider board construction. These are results for that particular design, rather than a guaranteed reduction for other products.

This is why thermal vias need to be considered alongside the board’s layer arrangement, available copper area and enclosure. A good connection through the PCB still needs somewhere useful to send the heat.

Via arrays, copper planes and enclosure contact points

Start with the component manufacturer’s recommended layout. For many devices with an exposed thermal pad underneath, placing vias within that pad provides a short route into the board’s copper layers. The pad’s electrical connection also matters: it must connect to the correct circuit potential, which is not always ground.

From there, look at the copper receiving the heat. A via connected to a small, isolated patch has limited opportunity to spread it. Larger, continuous copper areas are generally more useful, provided they also meet the circuit’s electrical requirements. Narrow spoke connections around vias restrict heat flow; TI’s PowerPAD guidance recommends solid connections for its thermal vias.

Adding more vias does not necessarily solve a weak thermal path. In one TI simulation, increasing the additional vias around the main thermal-pad region from zero to 24 improved thermal resistance by only 0.5%. The vias beneath the main pad remained in place. The result illustrates diminishing returns from extra surrounding vias in that layout.

Via diameter, spacing and copper plating all influence the result, but there is no universal arrangement that suits every component and board. The useful question is where another via improves the path from the heat source into copper that can carry the heat away.

Manufacturing needs to be part of that decision. Open vias within a solder pad can draw solder away during assembly, reducing the connection between the component and the PCB. Agree the via treatment and solder-paste stencil design with the fabricator and assembler. Filling or capping may be appropriate, depending on the package and process; covering every opening with solder mask should not become a default fix.

The next connection may be mechanical. If heat is intended to pass from the board into a metal enclosure or heatsink, that route needs a defined contact area and suitable interface material. Assembly tolerances, contact pressure and any required electrical insulation all affect how well it works.

A metal housing close to a hot component is only useful as a cooling surface if the design provides an effective way for heat to reach it.

Testing thermal performance before the product reaches production

Thermal calculations and simulation help compare layout options while changes are still straightforward. Their assumptions need to reflect the intended product, including its copper layers, enclosure and cooling conditions. Nexperia’s thermal studies show how strongly device temperatures depend on the surrounding PCB and cooling arrangement.

Prototype testing should then check those assumptions in the assembled product. Use representative workloads, sustained maximum operating loads and relevant short power peaks. Include the expected upper ambient temperature, mounting orientation and available airflow. Allow enough time for temperatures to settle during sustained-load tests.

A board that passes with the enclosure open may behave differently once the lid is fitted and nearby components warm up.

Thermal imaging can reveal hotspots and show where heat is spreading, but a surface reading does not directly measure the temperature inside a semiconductor. In one TI test at 3 W, the chip’s internal junction was approximately 10°C hotter than the package surface. That difference was specific to the test, but shows why surface measurements need careful interpretation.

Use the component manufacturer’s measurement guidance, suitable sensors and validated calculations to assess internal temperatures. Check the margin below the relevant operating limits, including nearby components that may be heated by the same copper area.

Record the board revision, load, ambient conditions and enclosure configuration alongside the results. If copper thickness, via construction, solder coverage or the enclosure interface changes, review whether thermal performance needs checking again. Those details help ensure that production units reproduce the behaviour demonstrated by the prototype.

For TAD, connecting PCB design, prototyping and manufacturing brings these decisions into the same conversation. Via placement can be reviewed alongside assembly requirements, and thermal testing can inform the design before production begins. That gives teams a practical route from a promising layout to a product that manages heat reliably in use.

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FAQs

What are thermal vias in PCB design?

Thermal vias are copper-plated holes that help transfer heat between PCB layers. They often connect the thermal pad beneath a component to larger copper areas, helping spread heat away from a concentrated source.

How do thermal vias reduce heat?

Thermal vias conduct heat away from a component into other copper layers. They do not reduce the heat being generated. Their effectiveness depends on the complete route through the board and onwards to the air, enclosure or heatsink.

Where should thermal vias be placed?

Place thermal vias according to the component manufacturer’s guidance, commonly beneath an exposed thermal pad or close to the heat source. They should connect to suitable copper areas, respect the pad’s electrical requirements and be compatible with the soldering process.