Why Thermal Conductivity Is Not Enough When Choosing a Thermal Pad?

When selecting a thermal pad, thermal conductivity is often the first specification engineers look at. A material with 10 W/m·K or 15 W/m·K may appear to offer better thermal performance than one rated at 5 W/m·K.

However, thermal conductivity alone does not determine how well a thermal pad performs in a real electronic device.

For applications such as AI servers, GPUs, CPUs, power modules, automotive electronics and battery systems, engineers need to consider several other factors, including thermal resistance, thickness, compressibility, contact pressure, electrical insulation, reliability and application conditions.

1. Thermal Conductivity vs. Thermal Resistance

Thermal conductivity, expressed in W/m·K, describes how effectively a material conducts heat.

But the actual heat-transfer performance of a thermal pad depends on more than conductivity.

A simplified relationship is:

Thermal Resistance ≈ Thickness / (Thermal Conductivity × Contact Area)

This means that a high-conductivity thermal pad may not necessarily provide low thermal resistance if it is too thick or does not achieve good contact with the mating surfaces.

For example, a 15 W/m·K thermal pad with poor surface contact may perform worse than a lower-conductivity pad that conforms closely to the component and heatsink.

Therefore, engineers should evaluate thermal resistance under actual application conditions, rather than comparing W/m·K values alone.

2. Thickness Matters

Thermal pad thickness is another critical factor.

Electronic components and heatsinks rarely have perfectly flat surfaces. A thermal pad is typically used to fill the gap between two surfaces.

If the pad is too thin, it may not adequately compensate for surface irregularities.

If it is too thick, the additional material thickness can increase thermal resistance.

Therefore, selecting the right thickness is a balance between:

• Gap size
• Thermal resistance
• Compressibility
• Surface flatness
• Assembly tolerance

For applications such as GPU thermal management and AI server cooling, precise thickness selection can be particularly important because the available thermal interface gap may be very limited.

3. Compressibility and Conformability

A good thermal pad should be able to conform to the surfaces of the heat source and heatsink.

This is where compressibility becomes important.

A soft and conformable thermal pad can fill microscopic surface irregularities and reduce air gaps. Air has very low thermal conductivity, so minimizing air gaps can significantly improve heat transfer.

However, excessive softness is not always desirable.

The material must also provide sufficient mechanical stability during assembly and long-term operation.

Therefore, engineers should consider:

Compressibility + Contact Pressure + Surface Conformability

rather than simply choosing the material with the highest thermal conductivity.

4. Electrical Insulation Can Be Critical

Many electronic applications require a thermal interface material to provide both thermal conductivity and electrical insulation.

For example, thermal pads may be used around:

• Power semiconductor devices
• MOSFETs
• IGBTs
• GPU modules
• Automotive electronics
• Battery systems
• Power supplies

In these applications, a material with excellent thermal conductivity may not be suitable if it does not meet the required electrical insulation requirements.

Depending on the design, engineers may need to evaluate properties such as:

• Dielectric strength
• Volume resistivity
• Breakdown voltage
• Electrical insulation stability

The ideal thermal pad must therefore meet the electrical and thermal requirements simultaneously.

5. Mechanical Reliability and Compression Set

Electronic devices can operate for thousands of hours under continuous thermal cycling.

During operation, components may repeatedly expand and contract as temperatures change.

A thermal pad must maintain sufficient contact throughout this process.

Important properties can include:

• Compression set
• Tensile strength
• Tear resistance
• Mechanical stability
• Long-term compression behavior

A thermal pad that performs well during initial testing may not maintain the same performance after prolonged thermal cycling if its mechanical properties are not suitable.

This is especially important for automotive electronics, EV battery systems and industrial power electronics, where long-term reliability is a major consideration.

6. Operating Temperature Range

Thermal performance should also be evaluated across the actual operating temperature range.

A thermal pad used in a consumer electronic device may have very different requirements from one used in an automotive or industrial application.

Engineers should consider:

Minimum operating temperature → Normal operating temperature → Maximum operating temperature

The material should maintain its mechanical and thermal properties throughout the required temperature range.

For demanding applications, testing under thermal cycling and accelerated aging conditions can provide additional information about long-term reliability.

7. Processability and Die-Cutting

In mass production, the thermal pad is rarely used simply as a rectangular sheet.

It may need to be converted into a custom shape with:

• Holes
• Slots
• Steps
• Notches
• Multiple dimensions
• Adhesive layers

Therefore, die-cutting capability and dimensional stability can also influence material selection.

A thermal pad with excellent thermal conductivity but poor processing characteristics may increase production complexity or manufacturing costs.

For OEM and ODM applications, customized thermal pads can help simplify assembly and improve consistency.

8. Thermal Pad Selection Should Be Application-Based

There is no single thermal pad that is ideal for every application.

Different devices may prioritize different properties.

This is why thermal pad selection should begin with the actual application requirements, rather than starting with thermal conductivity alone.

How to Choose the Right Thermal Pad?

Before selecting a thermal pad, engineers should consider at least the following parameters:

1. Thermal conductivity
What level of heat transfer is required?

2. Thermal resistance
What is the actual thermal performance at the required thickness and pressure?

3. Gap thickness
What is the actual gap between the heat source and heatsink?

4. Compressibility
How much compression is available during assembly?

5. Electrical insulation
Does the application require dielectric insulation?

6. Operating temperature
What are the minimum and maximum operating temperatures?

7. Mechanical reliability
Can the material maintain performance during long-term compression and thermal cycling?

8. Manufacturing requirements
Does the material need die-cutting, adhesive backing or customized dimensions?

ZIITEK Thermal Pads for Advanced Thermal Management

For demanding applications, ZIITEK provides a range of Thermal Interface Materials (TIMs) designed for electronics thermal management.

ZIITEK thermal pads can be customized according to application requirements such as thermal conductivity, thickness, dimensions, compressibility, electrical insulation and operating temperature.

They can be used in applications including AI servers, GPUs, CPUs, power electronics, automotive electronics, EV battery systems and industrial equipment.

Instead of selecting a thermal pad based only on its W/m·K value, engineers should evaluate the complete thermal interface system—including thermal resistance, thickness, contact conditions, mechanical properties and long-term reliability.

Need Help Selecting the Right Thermal Pad?

Share your application, gap thickness, dimensions, operating temperature and thermal requirements with the ZIITEK team.

We can help you evaluate a suitable thermal pad solution for your application.