Polyimide (PI): An In-Depth Look at an Outstanding High-Performance Material

From Aerospace to the 5G Battlefield:

The Evolution and Modification Revolution of Polyimide (PI)

 

In the field of materials science, polyimide (PI) has long been regarded as one of the most demanding polymers in terms of performance. The reputation is well deserved, but rather on the fact that it can withstand both the extreme low temperatures of liquid helium at -269°C and high temperatures of 400°C, while maintaining structural and stable performance. For a long time, PI has played an indispensable role in high-performance materials applications due to its near-limit thermal stability and flame-retardant characteristics (UL94 V-0).

 

 

 

The "tightly bound curse" of traditional PI: the fate of being insoluble and infusible

 

However, traditional PI possesses a physical property that engineers both love and hate: electron charge-transfer interactions. At the microscopic level, the polymer chains of PI are packed so tightly that they seem welded together. While this confers steel-like thermal resistance, it also comes with the burden of being neither soluble nor melt-processable.

 

In the past, processing PI was akin to taming a piece of ceramic, requiring a cumbersome high-temperature imidization process often exceeding 300 °C. This was not only extremely energy-intensive, but also made it challenging for many heat-sensitive precision electronic components to withstand.

 

 

Turning Point: "Process Liberation" through Modification Technology

 

To break free from these constraints, modern materials science has employed molecular-level "tuning" to develop modified polyimides (Modified PI). This is not merely a minor performance adjustment—it represents a revolution in processing:

 

• Enabling low-temperature processing: Modern modified resins are usually pre-imidized before leaving the factory. This means downstream engineers no longer need to push ovens to their limits for curing; processing can be completed at 200 °C or even lower (160–180 °C), which is crucial for protecting heat-sensitive components.
• Diversification of solvent options: Through modification, PI now achieves excellent solubility. The material can be compatible with solvent systems such as MEK (methyl ethyl ketone) or toluene, meeting both handling convenience and evaporation rate requirements.

 

 

A Key Piece in the 5G and High-Frequency Era

 

As we enter the 5G era, the battleground for PI has shifted to signal loss. At high frequencies, traditional materials consume energy heavily, much like a sponge absorbing water, but low dielectric (Low Dk/Df) modified PI doesn't, which fundamentally changes the rules of the game.

 

At high frequencies of 10 GHz, modified PI can reduce the dielectric constant (Dk) to below 2.60 and keep the dielectric loss (Df) under 0.002. Even more remarkably, it overcomes a common issue in high-performance materials—poor adhesion—maintaining excellent electrical properties while achieving copper peel strength exceeding 1.2 kgf/cm, and easily passing 300 °C solder heat resistance tests.

 

 

Versatile Applications: From Ultra-Thin Films to Shielding Barriers

 

Through its evolution, modified PI demonstrates remarkable adaptability in smart devices. In pursuit of extreme thinness, modified PI can be fabricated into insulating protective layers as thin as 2–3 μm, suitable for EMI shielding films or FPCB (flexible printed circuit board) substrates.

 

• For components requiring flexibility, it can achieve elongation at break of up to 90%.
• For designs demanding structural strength, it can exhibit a high modulus of 5.5 GPa.

 

 

"Liquid Steel" in the Materials field

 

If traditional PI is like steel—hard but difficult to shape—then modern modified PI is more akin to "liquid steel," which retains a ceramic-like thermal-resistant framework while possessing fluid-like processing flexibility. It is no longer just an expensive component tucked inside aerospace engines; it has become the thin layer in your smartphone, the substrate beneath touchscreens, and the silent, robust guardian behind 5G signals.

 

For those interested in high-frequency, high-speed electronics, advanced packaging, or next-generation electronic materials, we welcome further discussion on modified PI design and practical implementation experience.

 

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