In order to explore the change law of Shore A hardness and surface roughness of silicone rubber and fluorosilicone rubber under continuous low temperature environment, we put the test pieces made of the two raw materials into the low temperature test box, and carried out low temperature ageing test at -50℃ for 0, 48, 96, 144 h, respectively. The change law of Shore A hardness, surface roughness, and surface morphology with low temperature ageing time were studied, and then its principle was analyzed. The results show that at the constant low temperature environment of -50℃, when the ageing time increase from 0 h to 144 h, the Shore A hardness of the two materials increases slowly at first, then increases sharply, and finally decreases slowly. The surface roughness of the two material decreases at first, then increases sharply, and finally increases slowly. Throughout the ageing process, both the Shore A hardness and surface roughness of fluorosilicone rubber are smaller than that of silicone rubber. It shows that under low temperature environment, fluorosilicone rubber is more stable than silicone rubber.

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.

In order to accelerate the dissipation of the surface charge and improve the flashover voltage of insulator, we propose the plasma fluorination modification technology. Changing the surface modification time, the surface physical, chemical, and dielectric properties of epoxy resin sample with the same formula as insulator was test before and after modification. The results show that as a method of both physical and chemical surface modification, plasma modification can introduce hydrophilic groups to the surface of the sample and change its wettability. With the increase of modification time, the surface roughness of the sample increases at first and then decreases. At the same time, the plasma modification can introduce fluorine to the surface of the material, shallow the surface traps, improve the surface conductivity, and reduce the accumulation of surface charge. Under the selected parameters, the surface flashover voltage increases to the maximum after modification for 9 minutes, and the Weibull distribution calculation shows that the increase rate is about 37.17%. After plasma surface modification for too long, the material structure is damaged, the surface traps become deeper, the surface conductivity and surface flashover voltage decrease.

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 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.

By adjusting the structure and composition of different diamine and dianhydride, we realized the controllable preparation of block copolymerized polyimide films. The effects of different composition structure of polyimide on its mechanical properties, thermal properties, and linear expansion coefficient were studied. The results show that according to the difference of rigid components (such as PDA, PMDA) content, the elastic modulus, elongation at break, and tensile strength of the films change regularly. The thermogravimetric analysis and the study of thermal decomposition kinetics show that due to the high phenyl and structural symmetry of the molecular chain of the prepared polymer, PI has excellent thermal stability, and the carbon residue rate is as high as 50% at 900℃. Moreover, its dimensional stability is very good, the linear expansion coefficient is very close to that of Cu, which shows potential application in copper clad plates and flexible devices.

In order to prepare polyimide (PI) films with high order degree and stable thermomechanical properties, pyromellitic dianhydride (PMDA) monomer was introduced into biphenyltetracarboxylic acid dianhydride-p-phenylenediamine (BPDA-PDA) system, and PI films were prepared by random copolymerization method. The aggregation structure and physical properties of the PI films were analyzed by XRD, TMA, DMA, TGA, prism coupling instrument, and universal testing machine. The results show that different dianhydride composition has a significant effect on the aggregation structure and thermal mechanical properties of PI films. With the increase of PMDA-PDA segment composition, the molecular chain order degree increases, and the molecular chain spacing decreases from 0.469 nm to 0.436 nm. The birefringence value shows an upward trend in the range of 0.18‒0.22. The glass transition temperature (T_g) decreases at first and then increases in the range of 379.86‒439.05℃. The thermal expansion coefficient (CTE) increases at first and then decreases in the range of 0‒7×10^-6 K^-1. The tensile strength and 5% thermal decomposition temperature (T_5%) show a downward trend in the range of 166‒225 MPa and 576.8‒590.4℃, respectively. When the mole fraction of PMDA is 60%, the PI film has excellent comprehensive properties with 0.22 of birefringence, 439.05℃ of T_g, 0.012 5×10^-6 K^-1 of CTE, 302.5℃ of heat resistance index(T_HRI) , and 576.8℃ of T_5%.

According to the application requirements of low thermal expansion (low-CTE) for colorless and transparent polyimide (CPI) films, the structural design and synthesis of methyl-substituted aromatic diamine monomers containing rigid amide bonds in the main chain, including 2-methyl-4,4′-diaminobenzanilide (MeDABA) and 2,3′-dimethyl-4,4′-diaminobenzanilide (MMDABA), were performed. Firstly, the dinitro compounds were prepared by the amide reactions using the methyl-substituted p-nitrobenzoic acid or methyl-substituted p-nitroaniline as raw material. Then, a series of new diamine compounds were obtained by the reduction of hydrazine hydrate under the catalysis of Pd/C. The chemical structures of the diamine monomers were characterized by differential scanning calorimetric analysis (DSC), Fourier infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), mass spectrometry (MS), and elemental analysis (EA). The results show that the aromatic diamine monomers with expected structure are prepared successfully.

A novel dianhydride monomer containing alicyclic ring and amide group was synthesized and further polymerized with several diamine monomers to prepare a series of transparent polyimide films. The properties of the films were tested and characterized. The results show that the synthesized polyimide films have excellent optical properties (T₅₅₀>89%), low coefficient of thermal expansion (CTE<17×10^-6 K^-1), and higher glass transition temperature (T_g>320℃) because of introducing trans cyclohexane and amide into the structure of dianhydride at the same time. The introduction of alicyclic structure decreases the formation of charge transfer complex, which increases the transparency of the polyimide films. On the other hand, the introduction of amide structure decreases the coefficient of thermal expansion.

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.