Compared with other dielectric materials, polymer-based all-organic composite dielectric materials have the advantages of high electrical strength, low dielectric loss, light weight, and excellent mechanical processing performance, and is more suitable for practical applications. In this article, the research progress of polymer-based all-organic composite dielectric materials with the matrix of pure polyvinylidene fluoride (PVDF), PVDF copolymers, and other polymers is reviewed. Some problems still faced in capacitor energy storage and practical application are discussed, and its future development is prospected.

This review mainly discusses the insulating materials adapted in chip packaging process from the perspective of the application of current silicon-based and next-generation silicone carbide (SiC) and other wide-bandgap semiconductor in power electronics packing, and prospects its future research trends towards requirements of high thermal conductivity and high temperature resistance.

A series of thermal insulating EPG composite with high performance and light wight were prepared through solvent-free BMC thermocompression technique using multifunctional group epoxy resin (MF4101) as matrix, methyl tetrahydrophthalic anhydride as curing agent, and hollow glass beads with high strength as filler and thermal insulating phase. And the structure, mechanical properties, and thermal properties of the composite were studied. The results show that the average particle size of hollow glass beads is 25.6 μm, and it remains intact in the composite. When the amount of hollow glass beads is 80, 120, and 140 phr, the density of EPG composite is 0.82, 0.72, and 0.71 g/cm³, respectively; the compressive strength is 105.7, 68.1, and 67.4 MPa, respectively; the thermal conductivity is low, the value is 0.012 9, 0.085 4, and 0.0826 W/(m·K), respectively. Besides, with high glass transition temperatures and epitaxial degradation temperatures (>300℃), the EGP composite material can be used under high temperature and high pressure for a long time.

In recent years, flexible electronic devices have developed rapidly. As a flexible substrate material and dielectric insulating material, polyimide (PI) film has been widely used in the preparation of flexible electronic devices and flexible circuit boards. However, its high thermal expansion coefficient reduces its dimensional stability in the process of variable temperature processing. Therefore, it is necessary to adjust its thermal expansion coefficient to match with other materials of electronic devices. In this paper, the patent status of low expansion polyimide films at home and abroad, the preparation and application research progress of low expansion polyimide composite films were introduced, and the general trend of synthesis, modification and application research of low expansion PI was forecasted.

Two novel diamines contained N-phenyl substituted benzimidazole were synthesized, and their difference was that the ortho-position of N-phenyl was substituted by methyl and fluorine atom, respectively. The novel diamines and commercially available dianhydrides 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 4,4′-oxydiphthalic anhydride (ODPA) were used to prepare poly(benzimidazole-imide) (PBII) films by two-step thermal imidization. The properties of new diamine monomer and PBII films were tested and characterized. The results show that the PBII films exhibit good thermal properties (glass transition temperature T_g=341-381℃) and mechanical properties (σ=95-135 MPa). The N-phenyl groups with different ortho units destroy the effective molecular packing, which improves the solubility and optical transmittance of the PBII films.

A graphene oxide (GO) was synthesized by modified Hummers’ method, and a graphene oxide/polyimide (GO/PI) composite film was prepared by solution blending method. The structure and the properties of the composite film were analyzed by XRD, TMA, TGA. The results show that compared with the PI film without GO, when the mass fraction of GO in composite film is 0.2%, the mechanical properties of the composite film increase obviously, the tensile strength increases by 26.77%, the elongation at break increases by 76.47%, and the elastic modulus changes little basically. When the mass fraction of GO is 0.1%, the maximum value of T₅ and T₁₀ of the composite film are 587.3℃ and 603.3℃, which increase by 2.44% and 1.69% compared with that of the PI film without GO, respectively. It is indicated that the addition of GO with appropriate amount can enhance the mechanical properties and thermal properties of PI films.

According to the application requirements of high-temperature resistant polymers with low dielectric constant (low-D_k) and low dielectric loss factor (low-D_f) for the development of high frequency communication technology, two key diamine monomers for fluoro-containing poly(imide-benzoxazole)s (PIBO), including 2,2-bis[3-(4-aminobenzamide)-4-hydroxylphenyl] hexafluoropropane (p6FAHP) and 2,2-bis[3-(3-aminobenzamide)-4-hydroxyphenyl] hexafluoropropane (m6FAHP) were synthesized. The dinitro compounds containing bis (o-hydroxy substituted benzamide) groups in molecular structure were first prepared by the low temperature reactions of the nitro-substituted benzoyl chloride and 2,2-bis(3-amino-4- hydroxyphenyl)hexafluoro-propane (6FAP) in polar aprotic solvent. Then the diamine monomers were obtained by the reduction of hydrogen under the catalysis of Pd/C. The melting points of the diamines were measured by DSC. The chemical structures of the diamines were characterized by ATR-FTIR, NMR, and elemental analysis (EA). The results show that the aromatic diamine monomers with expected structures are prepared successfully.

A polyamide acid was prepared using 4,4′-diamino-2,2′-bistrifluoromethyl benzene (TFMB) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) as raw materials. The azocyclic quinoline (QL) was used to promote its imidization at lower temperature, and the amount of QL, maximum imidization temperature, and curing time were optimized. The imidization degree of polyimide (PI) film was determined by infrared spectroscopy. The results show that when the molar addition of QL is twice that of BPDA, the polyamide acid is only cured for 4 h at 200℃, the imidization degree is more than 99%. After treated at 250℃ for 0.5 h to remove the residual solvent and QL, the thermal stability of the PI is improved greatly, while its light transmittance is basically unchanged. Compared with the PI film imidized at 300℃, the 5% weight loss temperature (T_5%), glass transition temperature (T_g), and tensile strength of the PI film whose imidization promoted by QL decrease slightly, but the elongation at break increases, and the light transmittance at 400 nm increases from 4.5% to 34.4%.

According to the application requirements of thermoplastic black polyimide film in the field of advanced flexible copper clad laminate (FCCL), three organo-soluble polyimide (SPI) resins were prepared from an aromatic diamine monomer containing chromogenic imine (-NH-) group, 4,4′-diaminodiphenylamine (NDA) and various dianhydrides, including 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), and hydrogenated 3,3′,4,4′- biphenyltetracarboxylic dianhydride (HBPDA) by polymerization. Then PI films were prepared from SPI/DMAc solution at relatively low temperature (80-250℃), and the effects of the above characteristic groups on the optical properties, thermal properties, and electrical properties of PI films were studied systematically. The results show that the SPI resin has good solubility in polar aprotic solvents such as N-methylpyrrolidone (NMP) and N,N-dimethylacetamide (DMAc). The SPI films show intrinsically deep color, the transmittance value at 550 nm of wavelength (T₅₀₀) is lower than 5%, and the lightness (L^*) is below 60. The PI films have good thermal stabilities, the glass transition temperatures (T_g) is up to 375.9℃ and the 5% weight loss temperatures (T_5%) is over 500℃ in nitrogen. Besides, the PI films exhibit good electrical insulating properties, the volume resistivities (ρ_v) is higher than 10¹⁵ Ω·cm.

Under different environmental relative humidity (RH), the corona resistance of polyimide film presents significant differences. In order to understand the effects of RH on the surface corona characteristics and ageing process of film, we monitored the corona discharge process, electrical properties, and surface morphology of the film under different RH, and obtained the effects of RH on the corona ageing of film. The results show that with the increase of RH, the changing trends of the discharge activity at positive and negative half cycle are opposite. When the RH is equal or less than 69%, both the discharge quantity and discharge frequency show rapid growth stage, stationary stage, and secondary development stage with corona time, and when the RH attains 84%, both of them increase linearly with time. The changing rate of moisture content (Δwt%) of the film increases significantly at the beginning of corona ageing and tends to be stable at the middle and later periods, and when the RH attains 84%, the Δwt% increases linearly with the ageing time. It is analyzed that the surface electrothermal damage of film caused by corona discharge is the main cause of the rapid decrease of surface resistivity (ρ_s). With the corona erosion, water penetrate into the film gradually, eventually leading to the sharp decrease of ρ_v till breakdown.