In advanced electronic packaging and thermal management, engineers are constantly looking for materials that combine three key characteristics:

• High thermal conductivity similar to metals

• Excellent electrical insulation like ceramics

• Easy processing and reliability typical of engineering plastics

Finding a material that meets all these requirements simultaneously is extremely challenging.

Polyether Ether Ketone (PEEK), often called the  "gold standard of engineering plastics",is widely used in aerospace, new energy vehicles, and high-end electronics due to its exceptional properties:

• High temperature resistance

• Excellent mechanical strength

• Outstanding chemical stability

• Intrinsic electrical insulation

However, despite these advantages, PEEK has a critical limitation — very low thermal conductivity.

Why Is PEEK's Thermal Conductivity So Low?

PEEK is a semi-crystalline aromatic thermoplastic polymer with a dense molecular structure. While this structure provides excellent mechanical performance and stability, it also restricts heat transfer.

Heat in polymers is mainly carried by phonons, but in PEEK the phonon transport path is extremely short. As a result, the intrinsic thermal conductivity of pure PEEK is only:

~0.21 W/(m·K)

For high-power electronic devices such as:

• CPUs

• LEDs

• IGBT modules

this low thermal conductivity becomes a serious limitation. If heat cannot be removed efficiently, device temperatures increase rapidly, leading to performance degradation and reliability issues.

Therefore, developing PEEK composites with both high thermal conductivity and electrical insulation has become an important research focus.

Challenges in Improving PEEK Thermal Conductivity

Improving the thermal conductivity of PEEK is difficult for two main reasons.

1. Poor Filler Dispersion

Adding high thermal conductivity fillers such as boron nitride (BN) is a common strategy. However, PEEK has very high melt viscosity, which makes it difficult to disperse fillers uniformly using conventional melt blending methods.

As a result:

• Fillers tend to agglomerate

• Continuous thermal conduction networks cannot form

Even with 30 wt% BN filler, thermal conductivity only increases to about 1.01 W/(m·K).

2. Processing Limitations

A more effective way to create oriented thermal pathways is electrospinning, which can align fillers along polymer fibers.

However, electrospinning requires a polymer solution, and PEEK is almost insoluble in common solvents. This makes solution-based microstructure design extremely difficult.

Thus, the key challenge becomes:

How can we build an ordered thermal conduction network without destroying PEEK's intrinsic properties?

Innovative Strategy: "Dissolve First, Restore Later"

To overcome this limitation, researchers developed an innovative approach:

Temporarily modify PEEK to make it soluble, construct the filler network, then restore it to its original structure.

This method allows the advantages of solution processing while preserving the final properties of PEEK.

Key Technology: Electrospinning and Structural Recovery

Soluble PEEK Precursor

Researchers first synthesized a soluble polymer precursor called PEEKt (poly aryl ether ketimine).

In this structure, the ketone group (C=O) in PEEK is replaced with ketimine (C=N) groups, allowing the polymer to dissolve in solvents such as NMP.

Electrospinning to Build Thermal Networks

Functional fillers were introduced into the PEEKt solution:

• Boron nitride nanosheets (fBNNSs)

• Multi-walled carbon nanotubes (fMWCNTs)

During electrospinning, the electric field and shear forces align the fillers along the fiber direction. CNTs act as bridges, connecting BN nanosheets to form an interconnected thermal conduction network.

Acid Hydrolysis to Restore PEEK

The electrospun fibers are then treated in 10 wt% sulfuric acid at 100°C for 24 hours.

During this process:

• The ketimine groups convert back to ketone groups

• The polymer returns to the standard PEEK molecular structure

Importantly, the fiber structure and filler orientation remain intact.

Hot Pressing

Finally, the composite fiber membranes are hot-pressed into dense sheets, forming a stable thermal conduction network.

Performance Improvements

This integrated process — electrospinning + hydrolysis + hot pressing — results in remarkable performance improvements.

High Thermal Conductivity

With 25 wt% boron nitride, in-plane thermal conductivity reaches:

5.09 W/(m·K)
(about 24× higher than pure PEEK)

When 1 wt% CNTs are added as thermal bridges, conductivity further increases to:

6.02 W/(m·K)
(about 28.7× higher than pure PEEK)

Excellent Electrical Insulation

Despite the improved thermal conductivity, the composite maintains excellent insulation:

Volume resistivity: ~10¹⁶ Ω·cm

This is far above the insulation standard of 10⁹ Ω·cm, because CNT content is below the electrical percolation threshold.

High Thermal Stability

The composites retain the outstanding thermal stability of PEEK.

The 5% weight loss temperature (T5%) exceeds 556°C, and filler addition slightly improves stability by restricting polymer chain motion.

Potential Applications

These new PEEK composites combine:

• High thermal conductivity

• Excellent electrical insulation

• Outstanding thermal stability

• Strong mechanical performance

This makes them ideal for demanding thermal management applications.

High-Power LED Cooling

The material can be used as thermal interface films or insulating heat dissipation pads to improve LED lifetime and efficiency.

IGBT Module Packaging

In electric vehicles and rail systems, IGBT modules require materials that provide both heat dissipation and electrical insulation. These composites could serve as alternatives to traditional ceramic substrates.

Consumer Electronics

With increasing power density in 5G and advanced computing devices, the material can be used for:

• Chip thermal interface materials

• RF module packaging

• Electronic heat spreaders

Aerospace Electronics

The combination of lightweight properties and thermal performance makes the material suitable for aerospace electronic systems.

Conclusion

Through a novel soluble precursor – electrospinning – structural recovery strategy, researchers have developed a new approach to overcome the low thermal conductivity of PEEK.

This technology demonstrates how microstructure engineering and reversible molecular modification can dramatically enhance the performance of high-performance polymers.

For industries seeking materials that combine thermal conductivity, electrical insulation, and mechanical reliability, advanced PEEK composites represent a promising solution for next-generation electronic thermal management.