Power electronic components can generate significant heat during operation. If that heat cannot be transferred away efficiently, the temperature of the component and PCB can rise, potentially affecting electrical performance, component lifetime, and system reliability.

One of the simplest and most widely used PCB thermal-management techniques is the thermal via. Thermal vias create conductive paths between copper layers, allowing heat to move from a component pad or copper region toward an internal or bottom copper plane where it can be distributed and dissipated.

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However, simply placing a large number of vias underneath a power component does not automatically produce the best thermal design. The thermal vias pattern design needs to consider via diameter, spacing, copper thickness, thermal pad geometry, soldering requirements, PCB layer structure, and the actual heat-dissipation path.

This is particularly important for automotive electronics, industrial control systems, power supplies, energy-storage systems, new-energy equipment, and embodied robotics, where PCB thermal performance can directly influence long-term reliability.

What Is a Thermal Via?

A thermal via is a plated through-hole or suitable via structure used to transfer heat between copper layers of a PCB. A typical thermal path can be represented as:

Power Component → Thermal Pad → Thermal Vias → Internal Copper Plane → Bottom Copper / Heat Sink

The thermal vias themselves are only one part of this path. If the receiving copper layer is too small, poorly connected, or thermally isolated, adding more vias may provide limited additional benefit.

Therefore, thermal via design should always be considered as part of the complete thermal path.

Why Is Thermal Via Pattern Design Important?

The purpose of a thermal via pattern is to provide an effective and manufacturable connection between the hot component area and the PCB's copper heat-spreading structure.

A good design should balance:

• Thermal performance

• Electrical requirements

• Soldering reliability

• Manufacturability

• PCB cost

• Available board space

For example, a power MOSFET or other power device may have a large thermal pad.

Instead of placing vias randomly, designers can arrange them in a regular pattern that provides relatively uniform thermal transfer across the pad.

Common patterns include:

• Grid arrays

• Staggered arrays

• Perimeter arrangements

• Via clusters

• Hybrid patterns

The best pattern depends on the component package and PCB construction.

How Many Thermal Vias Should a Power PCB Use?

There is no universal number. A common mistake is to specify something like "20 thermal vias" without considering the component's thermal pad size and the PCB stackup.

The required number depends on:

• Heat generated by the component

• Thermal pad area

• Via diameter

• Via pitch

• PCB copper thickness

• Number of connected copper layers

• Copper plane area

• Heat-sink structure

• Maximum allowable temperature

A better engineering approach is to start with the required thermal path, then determine how many vias can fit while maintaining appropriate manufacturing and assembly clearances.

More vias can improve the available thermal conduction path, but the benefit is not necessarily linear.

What Via Diameter Should Be Used for Thermal Vias?

Via diameter is an important design parameter, but there is no single diameter suitable for every thermal application. Larger vias can provide a larger conductive path, but they also consume more PCB area.

Smaller vias allow a denser array but require tighter drilling and plating control. PCBBUY's stated PCB manufacturing capability includes a minimum hole size of 0.1 mm, but this should not be interpreted as a recommended thermal-via size for every power PCB.

For thermal applications, the appropriate via diameter should be selected based on:

• Component package

• Thermal pad dimensions

• Required via density

• PCB thickness

• Copper thickness

• Plating requirements

• Soldering process

The smallest possible via is not necessarily the best thermal via.

Should Thermal Vias Be Filled?

For a conventional thermal-via array, open plated vias may be sufficient when they are located in an area where solder wicking does not create a problem. However, vias located directly inside a component's solder pad require additional consideration.

During reflow, solder can flow into open vias. This can change the effective solder volume and potentially affect solder-joint formation. For via-in-pad thermal structures, filled and capped vias may therefore be appropriate depending on the package and assembly requirements.

PCBBUY supports resin-filled vias and copper-filled vias, allowing the via structure to be selected according to the specific PCB design.

Should Thermal Vias Be Connected to Multiple Copper Layers?

Generally, a thermal via works best when it has a meaningful thermal destination.

For example:

Thermal Pad → Via → Inner Copper Plane → Bottom Copper

can provide a more effective thermal path than:

Thermal Pad → Via → Small isolated copper area

This is why power PCB stackup design and thermal via design should be developed together.

If the PCB has multiple copper layers available for heat spreading, thermal vias can potentially connect the hot area to those planes.

However, the actual layer assignment must also consider signal integrity, power distribution, isolation, and impedance requirements.

How Does Copper Thickness Affect Thermal Via Performance?

Copper thickness influences both electrical and thermal conduction. PCBBUY's stated capabilities support copper thickness up to 10 oz for heavy-copper PCB applications.

This can be particularly relevant to power electronics where high current and heat generation occur simultaneously. However, heavy copper is not automatically required for every thermal design. A thinner copper structure with a well-designed thermal path can be more appropriate for many applications.

The correct approach is to optimize:

Copper Thickness + Copper Area + Thermal Via Pattern + Layer Connection

as a complete system.

Thermal Via Pattern Design for Different Power Applications

These are engineering considerations rather than fixed design rules. The final thermal-via pattern should be based on the actual component and system requirements.

How Can PCBBUY Support Thermal Via PCB Manufacturing?

For power-electronics PCB applications, PCBBUY's manufacturing capabilities include several technologies relevant to thermal-via structures.

The stated capabilities include:

• Multilayer PCB fabrication up to 26 layers

• Copper thickness up to 10 oz

• Minimum hole size of 0.1 mm

• Copper-filled vias

• Resin-filled vias

• HDI laser drilling

• Sequential lamination

• Controlled impedance

• PCB sizes up to 1000 × 600 mm

• AOI inspection

• Flying-probe testing

• Four-wire low-resistance testing

For designs combining high current, high thermal load, and dense routing, these capabilities can help support different PCB constructions. For example, a power PCB may combine heavy copper in current-carrying regions with thermal via arrays underneath power components, while other areas use finer routing structures.

The final construction should always be confirmed against the Gerber files, stackup, component package, copper requirements, and manufacturing specifications.

How Should Thermal Vias Be Designed Under a Power Component?

A practical workflow is:

Step 1: Identify the actual heat source

Determine which component or pad generates the majority of the heat.

Step 2: Define the thermal destination

Identify the internal copper plane, bottom copper, heat spreader, or heat sink that will receive the heat.

Step 3: Select a suitable via pattern

Choose grid, staggered, or another arrangement based on the available pad area.

Step 4: Check assembly requirements

If vias are located directly in solder pads, evaluate whether via filling or capping is required.

Step 5: Check PCB manufacturability

Verify via diameter, spacing, pad size, copper thickness, drill capability, and layer registration.

Step 6: Evaluate the complete thermal path

Do not evaluate the via array independently. The component, PCB copper, vias, thermal plane, and heat sink should be treated as one thermal system.

What Are Common Thermal Via Design Mistakes?

Using too many vias without a thermal destination

A dense via array cannot compensate for insufficient copper spreading.

Making the vias unnecessarily small

Smaller vias can increase density, but they may also increase manufacturing complexity without providing a proportional thermal advantage.

Ignoring solder wicking

Open vias inside component pads can affect solder volume during reflow.

Focusing only on the top layer

Heat needs somewhere to go. The receiving copper layers are just as important as the via array.

Ignoring mechanical and electrical constraints

Thermal vias can consume routing space and may interact with isolation distances, impedance structures, and power distribution.

Conclusion

Effective thermal vias pattern design for power electronics is not about placing as many vias as possible. The objective is to create a short, continuous, manufacturable thermal path from the heat-generating component to an effective copper heat-spreading structure or external cooling solution.

Grid and staggered patterns are both useful, but the optimal choice depends on the thermal pad, via dimensions, copper layers, component package, and available PCB space. For automotive, industrial control, power, energy-storage, new-energy, and embodied-robotics applications, thermal-via design should also account for long-term reliability, assembly conditions, copper distribution, and operating temperature.

PCBBUY's capabilities in multilayer PCB fabrication, heavy copper up to 10 oz, copper-filled and resin-filled vias, HDI, sequential lamination, and PCB inspection can support a wide range of power-electronics PCB constructions. The most reliable approach is to optimize the component → thermal pad → via array → copper plane → heat sink path as a complete system rather than treating thermal vias as an isolated PCB feature.

FAQ

1. What is a thermal via in a power electronics PCB?

A thermal via is a plated PCB via used to transfer heat from a component or copper region to another copper layer or heat-spreading structure.

2. How many thermal vias should I use?

There is no universal number. The required quantity depends on the thermal pad size, via diameter and pitch, PCB thickness, copper thickness, heat generation, and available heat-spreading area.

3. Is a grid or staggered thermal via pattern better?

Neither is universally better. A grid provides a straightforward and uniform arrangement, while a staggered pattern can make efficient use of certain pad geometries. The best choice depends on the specific component and PCB design.

4. Should thermal vias be placed directly under a thermal pad?

They can be, and this is common in power electronics. However, open vias may allow solder to wick away during reflow, so the assembly process and via filling requirements should be evaluated.

5. Should thermal vias be filled?

Not necessarily. Open thermal vias can be suitable when solder wicking is not a concern. For via-in-pad applications, filled and capped vias may be considered to provide a more controlled soldering surface.

6. Does a larger number of thermal vias always improve cooling?

No. Additional vias can increase the available thermal conduction path, but the overall result depends heavily on the copper planes and heat-dissipation structure connected to the vias.

7. Can thermal vias carry electrical current?

Yes, a plated via is electrically conductive unless an insulating filling or other structure changes its electrical connection. Whether a thermal via should also carry current depends on the circuit design and isolation requirements.

8. What copper thickness is suitable for thermal PCB design?

There is no universal thickness. The appropriate copper weight depends on current, heat generation, PCB construction, and manufacturing requirements. PCBBUY states a heavy-copper capability of up to 10 oz.

9. Does PCBBUY support thermal via structures?

PCBBUY supports relevant PCB technologies including copper-filled vias, resin-filled vias, multilayer fabrication, HDI laser drilling, sequential lamination, and heavy copper up to 10 oz, which can be incorporated into appropriate thermal PCB constructions.

10. What information should I provide when requesting a power PCB quote?

Provide the Gerber files, layer count, copper thickness, thermal pad dimensions, component information, material requirements, via dimensions if specified, and any thermal or assembly requirements. If thermal performance is a critical requirement, providing the expected heat load and cooling method will also help the manufacturer evaluate the PCB construction.