Versatile Landscape of Low-k Polyimide: Theories, Synthesis, Synergistic Properties, and Industrial Integration

The development of microelectronics and large-scale intelligence nowadays promotes the integration, miniaturization, and multifunctionality of electronic and devices but also leads to the increment of signal transmission delays, crosstalk, and energy consumption. The exploitation of materials with low permittivity (low-k) is crucial for realizing innovations in microelectronics. However, due to the high permittivity of conventional interlayer dielectric material (k ∼ 4.0), it is difficult to meet the demands of current microelectronic technology development (k < 3.0). Organic dielectric materials have attracted much attention because of their relatively low permittivity owing to their low material density and low single bond polarization. Polyimide (PI) exhibits better application potential based on its well permittivity tunability (k = 1.1-3.2), high thermal stability (>500 °C), and mechanical property (modulus of elasticity up to 3.0-4.0 GPa). In this review, based on the synergistic relationship of dielectric parameters of materials, the development of nearly 20 years on low-k PI is thoroughly summarized. Moreover, process strategies for modifying low-k PI at the molecular level, multiphase recombination, and interface engineering are discussed exhaustively. The industrial application, technological challenges, and future development of low-k PI are also analyzed, which will provide meaningful guidance for the design and practical application of multifunctional low-k materials.

Polyimide Films Based on β-Cyclodextrin Polyrotaxane with Low Dielectric and Excellent Comprehensive Performance

In order to prepare polyimide (PI) films with a low dielectric constant and excellent comprehensive performance, a two-step method was employed in this study to integrate β-cyclodextrin into a semi-aromatic fluorine-containing polyimide ternary system. By introducing trifluoromethyl groups to reduce the dielectric constant, the dielectric constant was further reduced to 2.55 at 10 MHz. Simultaneously, the film exhibited noteworthy thermal stability (a glass transition temperature exceeding 300 °C) and a high coefficient of thermal expansion. The material also demonstrated outstanding mechanical properties, boasting a strength of 122 MPa and a modulus of 2.2 GPa, along with high optical transparency (transmittance reaching up to 89% at 450 nm). Moreover, the inherent high transparency of colorless polyimide (CPI) combined with good stretchability contributed to the attainment of a low dielectric constant. This strategic approach not only opens up new opportunities for novel electroactive polymers but also holds potential applications in flexible displays, circuit printing, and chip packaging.

Research Advances of Porous Polyimide-Based Composites with Low Dielectric Constant

With the burgeoning of the microelectronics industry, in order to improve the transmission speed between chips in large-scale integrated circuits to meet the demands of high integration, it is necessary for interlayer insulation materials to possess a lower dielectric constant (k). Polyimide (PI) has been widely used as interlayer insulation materials for large-scale integrated circuits, and the exploration on reducing their dielectric constant has attracted extensive attention in recent years. In this work, porous PI-based composites with a low dielectric constant are mainly reviewed. The application of porous SiO2, graphene derivatives, polyoxometalates, polyhedral oligomeric silsesquioxane and hyperbranched polysiloxane in reducing the dielectric constant of PI is emphatically introduced. The key technical problems and challenges in the current research of porous polyimide materials are summarized, and the development prospect of low k polyimide is also expounded.

Polyimide/fluorinated silica composite films with low dielectric constant and low water absorption

In this study, KMnO4 was applied as an etchant to partially decompose the silica microspheres into mesoporous structures. 1H,1H,2H,2H-perfluorodecyltriethoxysilane was grafted onto the surface of the hollow silica. A fluorinated silica/polyimide hybrid material was prepared. Meanwhile, the influence of fluorinated silica on the dielectric property and moisture absorption property of the hybrid material was discussed. It is found that the fluorinated silica can lower the dielectric constant and hygroscopicity of the hybrid film. The fluorinated silica is characterized by strong hydrophobicity, good dispersibility, and good thermal stability. Even at a very low filling level of only 2 wt%, the dielectric constant of the polyimide hybrid is significantly reduced to 2.61 without sacrificing thermal stability. The water absorption rate of the polyimide hybrid film is reduced from approximately 3.1% to 2.1 wt%. Moreover, this provides a new idea for reducing the dielectric and water absorption properties of materials.

Facile strategy to prepare polyimide nanofiber assembled aerogel for effective airborne particles filtration

Polyimide nanofiber (PINF) aerogel materials have received extensive attention as heat insulation, sensors and filtration media due to their excellent thermodynamic properties and unique porous structure. However, PINF must be difficult to disperse in organic solvents (dioxane or dimethyl sulfoxide) and dimensional instability has been regarded as issues that limits the preparation of PINF aerogels, especially in the water. So, it is of great significance to prepare polyimide aerogels with stable structure using water as a dispersant. In this work, the electrospun polyimide nanofiber precursor (polyamic acid (PAA) nanofiber (PAANF)) is uniformly dispersed in water, and triethylamine is added to terminated PAA oligomer as a binder. The resultant PINF aerogel has excellent mechanical properties with outstanding elasticity and a maximum compressive stress of 7.03 kpa at 50% strain. Furthermore, due to the extremely high porosity (98.4%) and hierarchical porous structure, the aerogel exhibits a high filtration efficiency (99.83%) for PM2.5, while the pressure drop is lower than that of the corresponding nanofiber membrane materials, which will facilitate its application in high temperature filtration and other fields.

Preparation and properties of adhesive-free double-sided flexible copper clad laminate with outstanding adhesion strength

In this paper, the synthesized thermoplastic polyimide (TPI) precursor is coated on both surfaces of the surface-treated polyimide (PI) base film, and the TPI/PI/TPI multilayer films is obtained by thermal imidization. The mechanical properties, heat resistance, water absorption of the multilayer film and the interface between the TPI and the PI base film were investigated in detail. Then, multilayer film-2 (MF-2) with excellent comprehensive performance and the two copper foils were pressed together to prepare a double-sided flexible copper clad laminate (FCCL) by thermal lamination method, and the properties of FCCL were studied in detail. The results show that the FCCL has a high peel strength of 1.22 N/mm, passed a solder bath test of 288°C, and the surface condition was good under hot-pressing temperature of 360°C, hot-pressing pressure of 15 MPa and hot-pressing time of 60 s. In addition, the SEM and EDS spectra of the stripped copper foil confirmed that the TPI layer was immersed into the interstitial space of the Cu nodules, forming a strong physical bite with the copper foil. The current work provides a promising solution for the design and fabrication of multilayer printed circuit boards with excellent performance.

Sub-10 nm domains in high-performance polyetherimides

After condensation with polystyrene oligomers, ultra-low-molecular-weight polyetherimide-based triblock copolymers form disordered nanostructures with domain sizes less than 8 nm.