Fluorinated polyimide: High toughness and low dielectric properties pave new path for high-frequency communication materials

Conventional polyimides (PIs) exhibit excellent thermal stability and mechanical performance, yet their dielectric properties (dielectric constant (D_k) > 3.2, dissipation factor (D_f) > 0.005 @ 10 GHz). In previous reports, the introduction of trifluoromethyl reduced the dielectric constant and dissipation factor, but it increased chain rigidity, weakened hydrogen bonds interaction, and reduced free volume, which definitely reduced mechanical performance (such as poor toughness leading to crack risks in advanced packaging). Therefore, it is necessary to design PI materials with high toughness and low dielectric properties to meet the demands of advanced packaging technologies evolving towards millimeter-wave frequencies and heterogeneous integration. A research team has developed a novel fluorinated polyimide that reduces the material's dielectric constant and dissipation factor while enhancing its mechanical properties. Their work is published in the journal Industrial Chemistry & Materials on 03 Jun 2025.

Reducing the dielectric constant of PI materials is a key challenge in developing advanced packaging materials. Common strategies, such as incorporating porous structures, aerogels, or low-k fillers like SiO₂, effectively lower the dielectric constant by increasing porosity or introducing air. However, these methods often come at the expense of mechanical strength and thermal stability, limiting their practical application.

Molecular structure design offers an effective approach to reducing the dielectric constant. By incorporating low-polarizability functional groups or introducing bulky side chains to increase free volume, both dipole and electronic polarization can be effectively suppressed. This strategy enables precise molecular-level control, avoiding common issues like phase separation or filler agglomeration. Additionally, it maintains excellent mechanical integrity and thermal stability, providing a well-balanced solution for achieving low dielectric properties, making it particularly promising for advanced microelectronic applications.

To achieve a low dielectric constant while maintaining robust mechanical properties, the research team designed a novel fluorinated diamine monomer (5FBODA) featuring a pentafluorophenyl side group. This monomer was copolymerized with the fluorinated dianhydride 6FESDA and another fluorinated diamine (HFBAPP) to synthesize an advanced fluorinated polyimide (FPI). The pentafluorophenyl group played a dual role:

lowering polarizability⁠—its strong electron-withdrawing effect reduced molecular polarizability; and suppressing dipole polarization⁠—the bulky structure restricted molecular chain mobility, further decreasing the dielectric constant and dissipation factor.

Meanwhile, the incorporation of flexible ether linkages and optimized intermolecular interactions ensured the material retained excellent mechanical toughness, making it highly suitable for high-performance microelectronic packaging.

The material achieves three major breakthroughs in core performance. The first is low dielectric properties. It’s D_k reduced to 2.60 and D_f as low as 3.37 × 10⁻³, the material shows great potential for significantly reducing high-frequency signal transmission loss. The second is excellent mechanical toughness. It had a remarkable elongation at break of 50.1%, and it exhibited markedly superior performance compared to conventional polyimides. (typically <20%). It demonstrated a strong capacity to withstand mechanical stress. The third is the synergistic optimization of comprehensive properties. While retaining the inherent high thermal and chemical stability of polyimides, the material simultaneously achieved the dual objectives of low D_k/D_f and high toughness. This material offers an effective solution for enhancing the reliability and signal integrity of advanced electronic devices such as high-frequency chip packaging systems.

The FPI also exhibits good transparency and hydrophobicity, making it processable for wafer-level packaging and suitable for applications in 5G communication devices.

Looking ahead, the research team hopes that their work can provide insights into the development and application of high-performance electronic packaging materials.

The research team includes Hangqian Wang, Yao Zhang, Xialei Lv, Jinhui Li, Kuangyu Wang, Guoping Zhang and Rong Sun from the Shenzhen Institutes of Advanced Technology.

This research is funded by the National Natural Science Foundation of China, the Guangdong Basic and Applied Basic Research, the Key Area Research and Development program of Guangdong Province, the Shenzhen Science and Technology Program, the Autonomous deployment project of China National Key Laboratory of Materials for Integrated Circuits, and the SIAT Innovation Program for Excellent Young.

Industrial Chemistry & Materials is a peer-reviewed interdisciplinary academic journal published by Royal Society of Chemistry (RSC) with APCs currently waived. ICM publishes significant innovative research and major technological breakthroughs in all aspects of industrial chemistry and materials, especially the important innovation of the low-carbon chemical industry, energy, and functional materials. Check out the latest ICM news on the blog.