Preparation method of high-end electronic-grade polyimide film

Abstract

The application provides a preparation method of high-end electronic-grade polyimide film, and the film is prepared from diamine monomers, dianhydride monomers and cross-linking fluorine-containing reaction monomers through polymerization, doping, casting, two-way stretching and gradient imidization. The application effectively solves the problems of high thermal expansion coefficient, large high-frequency dielectric loss and poor size stability of the existing polyimide film by introducing rigid cross-linking units containing fluorine into the molecular chain, and combining multi-batch low-temperature polymerization, multi-layer gradient filtration, simultaneous two-way stretching and segmented gradient imidization process. The method is stable in process, the product has excellent comprehensive performance, and is suitable for fields of 5G high-frequency communication flexible copper-clad plate and chip packaging substrate.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and specifically relates to a method for preparing high-end electronic-grade polyimide films. Background Technology

[0002] Polyimide (PI) films are widely used in aerospace, electrical insulation, and microelectronics fields due to their excellent heat resistance, mechanical properties, electrical insulation, and chemical stability. With the development of electronic devices towards thinner, lighter, higher-frequency, and more integrated designs, especially with the advent of the 5G communication era, even more stringent requirements are being placed on polyimide films as substrates for flexible circuit boards.

[0003] High-end electronic-grade polyimide films need to meet the following performance requirements simultaneously: 1. Low coefficient of thermal expansion (CTE): It needs to be compatible with copper foil (CTE about 17ppm / ℃) or silicon chip (CTE about 3-5ppm / ℃) to avoid circuit breakage or device failure due to thermal stress during high-temperature soldering or use.

[0004] 2. Low dielectric constant (Dk) and dielectric loss factor (Df): In high-frequency signal transmission, reducing signal delay and transmission loss requires materials to have stable low dielectric properties over a wide frequency range.

[0005] 3. Low water absorption: The dielectric constant of water is as high as 80, which will significantly degrade the dielectric properties of the material and lead to dimensional instability.

[0006] While traditional polyimide films exhibit excellent heat resistance, their high coefficient of thermal expansion (typically 30-50 ppm / ℃) and dielectric constant of around 3.5 make them unsuitable for high-end electronic packaging and high-frequency communication applications. To address these issues, researchers have undertaken various attempts: Introducing rigid segments: such as using the BPDA / PPD system, can effectively reduce CTE, but often leads to increased film brittleness and decreased processing performance.

[0007] Introducing fluorinated groups: Using fluorinated monomers such as 6FDA can significantly reduce the dielectric constant and water absorption rate. However, fluorinated monomers are expensive and often lead to a decrease in the mechanical strength and heat resistance of the film.

[0008] Composite inorganic fillers: Adding nano-silica can improve dimensional stability, but traditional solid fillers can lead to an increase in dielectric constant and the fillers are prone to agglomeration, affecting the uniformity and mechanical properties of the film.

[0009] Therefore, how to achieve low CTE, low dielectric loss, low water absorption and good mechanical properties, while ensuring the uniformity and process stability of the film, through a synergistic formulation design and optimized preparation process remains a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0010] To address the aforementioned shortcomings, this invention provides a method for preparing high-end electronic-grade polyimide films, solving the problem of balancing low thermal expansion coefficient, low dielectric loss, and high mechanical properties in polyimide films.

[0011] This invention is achieved through the following technical solution: A method for preparing a high-end electronic-grade polyimide film, wherein the raw materials comprise the following components by weight: 100 parts of diamine monomer; 95-110 parts of dianhydride monomer; 5-25 parts of cross-linked fluorinated reactive monomer; 600-1000 parts of polar aprotic solvent; The method for preparing the high-end electronic-grade polyimide film includes the following steps: S1: Dissolve the diamine monomer in a polar aprotic solvent and stir until completely dissolved. The water content of the aprotic solvent is controlled below 100 ppm. Then, cool the reaction system to -5℃ to 10℃ and add the dianhydride monomer and cross-linked fluorinated reactive monomer in 3 to 5 batches, adding one batch every 20 to 40 minutes, controlling the reaction temperature at each addition to not exceed 5℃. After the last batch is added, continue stirring the reaction at 0℃ to 25℃ for 4 to 12 hours to obtain a viscous polyamic acid resin solution. S2: Add surface-modified nanoporous silica filler and heat stabilizer to the polyamic acid resin solution obtained in step S1, and disperse it uniformly in a high-speed disperser at 2000-4000 rpm for 30-90 min. Then, place the mixture in a degassing tank with a vacuum of -0.06 MPa to -0.1 MPa and let it stand to remove bubbles for 2-6 h until there are no visible bubbles in the solution. S3: The degassed adhesive solution is passed through a multi-layer filter screen, which consists of a 300-mesh primary filter screen, a 600-mesh intermediate filter screen, and a 20μm fine filter element. The filtered adhesive solution is then uniformly coated onto a mirror stainless steel support or PET release film through a casting nozzle. The casting thickness is controlled by a metering pump to ensure that the final dry film thickness reaches the target value. The casting area is divided into multiple temperature zones, with temperatures of 60–80℃, 80–100℃, and 100–120℃, respectively. The hot air circulation speed is 1–3 m / s, and the drying time is 5–20 min, causing partial imidization of the adhesive solution to form a self-supporting gel film with a solid content of 50%–70%. S4: Peel the gel film obtained in step S3 from the support and send it into a biaxial tenter frame. Preheat it for 1 to 3 minutes at a preheating temperature of 150 to 200°C. Then, perform simultaneous biaxial stretching in the tenter frame. The longitudinal stretching ratio is 1.1 to 1.6 times, the transverse stretching ratio is 1.1 to 1.6 times, the temperature of the stretching zone is 200 to 280°C, and the stretching rate is 5% to 20% / s. After stretching, perform heat setting. The width of the heat setting zone remains unchanged. The temperature is 250 to 300°C and held for 2 to 5 minutes to eliminate internal stress. S5: The stretched and shaped film is sent to a high-temperature imidization furnace for segmented gradient temperature imidization under high-purity nitrogen protection. First imidization zone: temperature 200-250℃, residence time 10-20min, this stage mainly involves solvent evaporation and preliminary cyclization; Second imidization zone: temperature 300-350℃, residence time 15-25min, deep imidization reaction occurs in this stage; Third imidization zone: temperature 380-420℃, residence time 5-15min, complete imidization is achieved in this stage; Finally, it enters the heat setting zone and is heat-set at 400-450℃ for 5-20 minutes. At the same time, 0.5-1.5% lateral relaxation is applied in the heat setting zone to further reduce the coefficient of thermal expansion. S6: After naturally cooling to room temperature, the film is trimmed, measured, and corona treated before being finally wound up to obtain the finished product.

[0012] This invention introduces rigid segments (BPDA / p-PDA) and flexible segments (PMDA / ODA) and mixes them in a specific ratio to control the rigid-flexibility balance of the molecular chains. Simultaneously, it combines biaxial stretching and heat-setting lateral relaxation to achieve a high degree of molecular chain orientation along the stretching direction, significantly reducing the coefficient of thermal expansion of the film and resulting in excellent thermal compatibility with copper foil. The film prepared by this invention has a tensile strength ≥250MPa, elongation at break ≥30%, glass transition temperature Tg ≥360℃, coefficient of thermal expansion (CTE) ≤12ppm / ℃, dielectric constant (1MHz) ≤3.2, and dielectric loss factor ≤0.002. After treatment at 85℃ / 85%RH for 48 hours, the film exhibits a water absorption rate ≤0.5% and a dimensional change rate ≤0.1%.

[0013] As a further improvement of the present invention, the diamine monomer comprises one or more of the following substances: phenyl 2,2'-bis(trifluoromethyl)-4,4'-diaminobenzoate, 1,4-bis(4-amino-2-trifluoromethylphenoxy)-2,5-di-tert-butylbenzene, p-phenylenediamine, diamine derivatives corresponding to bicyclic [2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, or rigid heterocyclic diamines containing pyridine or pyrimidine rings. The diamine derivative corresponding to the bicyclic [2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride is one of 1,6-diamino-2,2,3,3,4,4,5,5-octafluorohexane or 4,4'-methylenebis(2-methylcyclohexylamine); the rigid heterocyclic diamine containing a pyridine or pyrimidine ring is one of 2,6-bis(4-aminophenyl)-4-phenylpyridine or 2,4,6-triaminopyrimidine.

[0014] The presence of ester bonds in phenyl 2,2'-bis(trifluoromethyl)-4,4'-diaminobenzoate can introduce intramolecular or intermolecular hydrogen bonding interactions, further enhancing the binding force between polymer chains, thus achieving extremely high modulus without the need for external fillers. When polymerized with rigid dianhydrides such as benzoic acid dianhydride, it can significantly reduce the overall CTE of the film at extremely low addition levels, making it particularly suitable for ultrathin film applications requiring precise bonding to inorganic substrates (such as glass substrates).

[0015] 1,4-Bis(4-amino-2-trifluoromethylphenoxy)-2,5-di-tert-butylbenzene has a central benzene ring substituted with two large tert-butyl groups (-C(CH3)3), with the ends connected to an aminobenzene ring containing a trifluoromethyl group via ether bonds. The tert-butyl groups significantly increase the distance between molecular chains, completely suppressing the formation of charge-transfer complexes (CTCs). The resulting polyimide films are nearly completely transparent, and their dielectric constant can be reduced to below 2.5, making them ideal substrates for 5G / 6G communication and optical devices. This achieves a leap in optical and electrical properties while maintaining mechanical strength.

[0016] The diamine derivative of bicyclic [2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride is an alicyclic diamine whose main chain does not contain aromatic rings but is composed of alicyclic or fatty chains. Copolymerizing alicyclic diamines with rigid aromatic dianhydrides (such as PMDA) can produce composite structures that combine a rigid framework with low dielectric constant and high transparency. The absence of aromatic rings in alicyclic diamines means that the film has almost no absorption in the visible and near-infrared regions, exhibits extremely high transparency, and does not yellow; the alicyclic structure is insensitive to ultraviolet radiation, making the film less prone to aging and degradation under long-term outdoor use or strong light exposure.

[0017] Rigid heterocyclic diamines containing pyridine or pyrimidine rings have aromatic heterocycles (pyridine, pyrimidine) in their backbones. The nitrogen atoms in these heterocycles have lone pairs of electrons, which can participate in coordination or form hydrogen bonds. The nitrogen atoms on the heterocycles can form hydrogen bonds with hydrogen atoms on adjacent molecular chains (such as hydrogen atoms on amide acids or imine rings), significantly enhancing intermolecular forces. Introducing a small amount of diamines containing pyridine rings can significantly improve the Tg and modulus retention of films at high temperatures without significantly increasing the CTE, making them particularly suitable for ultrathin films that need to maintain structural stability above 300°C.

[0018] As a further improvement of the present invention, the dianhydride monomer is a mixture of pyromellitic dianhydride (PMDA) and biphenyl dianhydride (BPDA), with a molar mixing ratio of PMDA:BPDA = 1:(0.8~1.2).

[0019] As a further improvement of the present invention, the cross-linked fluorinated reactive monomer is a dicarboxylic acid anhydride or diamine containing trifluoromethyl and ethynyl groups, specifically 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) or an aniline derivative containing ethynyl groups.

[0020] As a further improvement of the present invention, the nanoporous silica filler in step S2 has a particle size of 20-80 nm and a pore size of 2-5 nm, and its surface is hydrophobically treated with a silane coupling agent, the amount of which is 0.5%-3.0% of the solid content of the polyamic acid resin; the silane coupling agent is KH-560.

[0021] As a further improvement of the present invention, the biaxial stretching in step S4 adopts a simultaneous biaxial stretching process, and the thickness of the stretched film is controlled at 12.5μm, 25μm or 50μm, with a thickness tolerance of less than ±3%.

[0022] As a further improvement of the present invention, in the gradient imidization process of step S5, the heating rate is 2-5℃ / min, and high-purity nitrogen is introduced for protection throughout the process, with an oxygen content of less than 50ppm.

[0023] As a further improvement of the present invention, the polar aprotic solvent is one or more combinations of N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP) or N,N-dimethylformamide (DMF).

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention regulates the rigid-flexibility balance of molecular chains by introducing a specific ratio of rigid and flexible segments into the formulation; at the same time, it combines biaxial stretching process and heat setting lateral relaxation to make the molecular chains highly oriented along the stretching direction, which greatly reduces the thermal expansion coefficient of the film and has excellent thermal matching with copper foil.

[0025] 2. This invention introduces a cross-linked fluorine-containing reactive monomer, which utilizes the low polarizability and hydrophobicity of fluorine atoms to reduce intermolecular forces, thereby reducing the intrinsic dielectric constant. At the same time, mesoporous silica is added, and air is introduced through its internal cavity structure to further reduce the overall dielectric constant and dielectric loss of the composite material, making it particularly suitable for 5G high-frequency signal transmission.

[0026] 3. This invention employs a multi-batch feeding and low-temperature polymerization process, ensuring high uniformity of the polyamic acid molecular weight and avoiding localized burst polymerization, thus laying the foundation for the high strength of the final film. The introduction of fluorinated monomers and the hydrophobic surface treatment of nanofillers significantly reduce the water absorption rate of the film, ensuring the stability of the film's dimensions and dielectric properties under humid and hot conditions.

[0027] 4. This invention employs a multi-layer gradient filtration system, effectively removing gel particles, foreign impurities, and undispersed filler agglomerates, resulting in minimal surface defects on the film and meeting the high cleanliness requirements of electronic-grade materials. The gradient imidization process avoids defects such as pinholes and blistering caused by rapid solvent evaporation and vigorous imidization reactions. Detailed Implementation

[0028] The present invention will be further described below with reference to the embodiments. Unless otherwise specified, the technical means used in the embodiments are all conventional technical means in the art.

[0029] Example 1: A method for preparing a high-end electronic-grade polyimide film, wherein the raw materials include the following components by weight: 100 parts of diamine monomer, wherein the diamine monomer is a mixture of 4,4'-diaminodiphenyl ether and p-phenylenediamine, and the molar mixing ratio of 4,4'-diaminodiphenyl ether to p-phenylenediamine is 1:0.2.

[0030] 95 parts of dianhydride monomer, the dianhydride monomer being a mixture of phenyl 2,2'-bis(trifluoromethyl)-4,4'-diaminobenzoate and 1,4-bis(4-amino-2-trifluoromethylphenoxy)-2,5-di-tert-butylbenzene.

[0031] Five parts of cross-linked fluorinated reactive monomer; the cross-linked fluorinated reactive monomer is 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride.

[0032] 600 parts of a polar aprotic solvent; the polar aprotic solvent is N,N-dimethylacetamide.

[0033] The method for preparing the high-end electronic-grade polyimide film includes the following steps: S1: Dissolve the diamine monomer in a polar aprotic solvent and stir until completely dissolved. The water content of the aprotic solvent is controlled below 100 ppm. Then, cool the reaction system to -5°C and add the dianhydride monomer and cross-linked fluorinated reactive monomer in three batches, adding one batch every 20 minutes, controlling the reaction temperature at each addition to not exceed 5°C. After the last batch is added, continue stirring at 0°C for 4 hours to obtain a viscous polyamic acid resin solution.

[0034] S2: Add surface-modified nanoporous silica filler and heat stabilizer to the polyamic acid resin solution obtained in step S1, and disperse it uniformly at 2000 rpm for 30 min in a high-speed disperser. Then, place the mixture in a degassing tank with a vacuum degree of -0.06 MPa and let it stand to remove bubbles for 2 h until there are no visible bubbles in the solution. The nanoporous silica filler has a particle size of 20 nm and a pore size of 2 nm, and its surface is hydrophobically treated with a silane coupling agent. The amount added is 0.5% of the solid content of the polyamic acid resin. The silane coupling agent is KH-560.

[0035] S3: The degassed adhesive solution is passed through a multi-layer filter screen, which consists of a 300-mesh primary filter screen, a 600-mesh intermediate filter screen, and a 20μm fine filter element. The filtered adhesive solution is then uniformly coated onto a mirror stainless steel support or PET release film through a casting nozzle. The casting thickness is controlled by a metering pump to ensure that the final dry film thickness reaches the target value. The casting area is divided into multiple temperature zones with temperatures of 60℃, 80℃, and 100℃, respectively. The hot air circulation speed is 1m / s, and the drying time is 20min, causing partial imidization of the adhesive solution to form a self-supporting gel film with a solid content of 50%.

[0036] S4: Peel the gel film obtained in step S3 from the support and feed it into a biaxial tenter frame. Preheat it for 1 minute at a preheating zone temperature of 150°C. Then, perform simultaneous biaxial stretching in the tenter frame. The longitudinal stretching ratio is 1.1 times, the transverse stretching ratio is 1.1 times, the stretching zone temperature is 200°C, and the stretching rate is 5% / s. After stretching, perform heat setting. The width of the heat setting zone remains unchanged, the temperature is 250°C, and it is held for 5 minutes to eliminate internal stress. The biaxial stretching adopts a simultaneous biaxial stretching process. The thickness of the stretched film is controlled at 12.5 μm, and the thickness tolerance is less than ±3%.

[0037] S5: The stretched and shaped film is sent to a high-temperature imidization furnace for segmented gradient temperature imidization under high-purity nitrogen protection. First imidization zone: temperature 200℃, residence time 20min, this stage mainly involves solvent evaporation and preliminary cyclization; Second imidization zone: temperature 300℃, residence time 25min, deep imidization reaction occurs in this stage; Third imidization zone: temperature 380℃, residence time 15min, complete imidization is achieved in this stage; Finally, it enters the heat setting zone and is heat-set at 400℃ for 20 minutes. At the same time, 0.5% lateral relaxation is applied in the heat setting zone to further reduce the coefficient of thermal expansion. During the gradient imidization process, the heating rate is 2℃ / min, and high-purity nitrogen is introduced throughout the process for protection, with an oxygen content of less than 50ppm.

[0038] S6: After naturally cooling to room temperature, the film is trimmed, measured, and corona treated before being finally wound up to obtain the finished product.

[0039] The performance test results of the finished product prepared in this embodiment are as follows: Tensile strength: 286 MPa.

[0040] Elongation at break: 35%.

[0041] Tg: 372℃.

[0042] CTE (50-250℃): 11 ppm / ℃.

[0043] Dielectric constant (1MHz / 10GHz): 3.1 / 3.0.

[0044] Dielectric loss factor (1MHz / 10GHz): 0.0018 / 0.0020.

[0045] Water absorption rate (85℃ / 85%RH, 48h): 0.45%.

[0046] Example 2: A method for preparing a high-end electronic-grade polyimide film, wherein the raw materials include the following components by weight: 100 parts of diamine monomer, wherein the diamine monomer is a mixture of p-phenylenediamine, 1,6-diamino-2,2,3,3,4,4,5,5-octafluorohexane and 2,6-bis(4-aminophenyl)-4-phenylpyridine.

[0047] 110 parts of dianhydride monomer, which is a mixture of pyromellitic dianhydride and biphenyl dianhydride, with a molar mixing ratio of pyromellitic dianhydride to biphenyl dianhydride of 1:1.2.

[0048] 25 parts of cross-linked fluorinated reactive monomers; the cross-linked fluorinated reactive monomers are aniline derivatives containing acetylene groups.

[0049] 1000 parts of polar aprotic solvent; the polar aprotic solvent is a combination of N-methylpyrrolidone and N,N-dimethylformamide.

[0050] The method for preparing the high-end electronic-grade polyimide film includes the following steps: S1: Dissolve the diamine monomer in a polar aprotic solvent and stir until completely dissolved. The water content of the aprotic solvent is controlled below 100 ppm. Then, cool the reaction system to 10°C and add the dianhydride monomer and cross-linked fluorinated reactive monomer in 5 batches, adding one batch every 20 minutes, controlling the reaction temperature at each addition to not exceed 5°C. After the last batch is added, continue stirring the reaction at 25°C for 12 hours to obtain a viscous polyamic acid resin solution.

[0051] S2: Add surface-modified nanoporous silica filler and heat stabilizer to the polyamic acid resin solution obtained in step S1, and disperse it uniformly at 4000 rpm for 90 min in a high-speed disperser. Then, place the mixture in a degassing tank with a vacuum degree of -0.1 MPa and let it stand to remove bubbles for 6 h until there are no visible bubbles in the solution. The nanoporous silica filler has a particle size of 80 nm and a pore size of 5 nm, and its surface is hydrophobically treated with a silane coupling agent. The amount added is 3.0% of the solid content of the polyamic acid resin. The silane coupling agent is KH-560.

[0052] S3: The degassed adhesive solution is passed through a multi-layer filter screen, which consists of a 300-mesh primary filter screen, a 600-mesh intermediate filter screen, and a 20μm fine filter element. The filtered adhesive solution is then uniformly coated onto a mirror stainless steel support or PET release film through a casting nozzle. The casting thickness is controlled by a metering pump to ensure that the final dry film thickness reaches the target value. The casting area is divided into multiple temperature zones with temperatures of 80℃, 100℃, and 120℃, respectively. The hot air circulation speed is 3m / s, and the drying time is 20min, causing partial imidization of the adhesive solution to form a self-supporting gel film with a solid content of 70%.

[0053] S4: Peel the gel film obtained in step S3 from the support and send it into a biaxial tenter frame. Preheat it for 1 minute at a preheating zone temperature of 200℃. Then, perform simultaneous biaxial stretching in the tenter frame. The longitudinal stretching ratio is 1.6 times, the transverse stretching ratio is 1.6 times, the temperature of the stretching zone is 280℃, and the stretching rate is 20% / s. After stretching, perform heat setting. The width of the heat setting zone remains unchanged, the temperature is 300℃, and it is held for 2 minutes to eliminate internal stress. The biaxial stretching adopts a simultaneous biaxial stretching process. The thickness of the stretched film is controlled at 50μm, and the thickness tolerance is less than ±3%.

[0054] S5: The stretched and shaped film is sent to a high-temperature imidization furnace for segmented gradient temperature imidization under high-purity nitrogen protection. First imidization zone: temperature 250℃, residence time 10min, this stage mainly involves solvent evaporation and preliminary cyclization; Second imidization zone: temperature 350℃, residence time 15min, deep imidization reaction occurs in this stage; Third imidization zone: temperature 420℃, residence time 5min, complete imidization is achieved in this stage; Finally, it enters the heat setting zone and is heat-set at 450℃ for 5 minutes. At the same time, 1.5% lateral relaxation is applied in the heat setting zone to further reduce the coefficient of thermal expansion. During the gradient imidization process, the heating rate is 5℃ / min, and high-purity nitrogen is introduced throughout the process for protection, with an oxygen content of less than 50ppm.

[0055] S6: After naturally cooling to room temperature, the film is trimmed, measured, and corona treated before being finally wound up to obtain the finished product.

[0056] The performance test results of the finished product prepared in this embodiment are as follows: Tensile strength: 265 MPa.

[0057] Elongation at break: 31%.

[0058] Tg: 384℃.

[0059] CTE: 9 ppm / ℃.

[0060] Dielectric constant (10GHz): 2.9.

[0061] Dielectric loss factor (10GHz): 0.0019.

[0062] Water absorption rate (85℃ / 85%RH, 48h): 0.46%.

[0063] Example 3: A method for preparing a high-end electronic-grade polyimide film, wherein the raw materials include the following components by weight: 100 parts of diamine monomer, wherein the diamine monomer is a mixture of phenyl 2,2'-bis(trifluoromethyl)-4,4'-diaminobenzoate and 2,6-bis(4-aminophenyl)-4-phenylpyridine or 2,4,6-triaminopyrimidine.

[0064] 95-110 parts of dianhydride monomer, which is a mixture of pyromellitic dianhydride and biphenyl dianhydride, with a molar mixing ratio of pyromellitic dianhydride to biphenyl dianhydride of 1:1.

[0065] 15 parts of cross-linked fluorinated reactive monomer; 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, a cross-linked fluorinated reactive monomer.

[0066] 800 parts of polar aprotic solvent; the polar aprotic solvent is a combination of N,N-dimethylacetamide and N,N-dimethylformamide.

[0067] The method for preparing the high-end electronic-grade polyimide film includes the following steps: S1: Dissolve the diamine monomer in a polar aprotic solvent and stir until completely dissolved. The water content of the aprotic solvent is controlled below 100 ppm. Then, cool the reaction system to 0°C and add the dianhydride monomer and cross-linked fluorinated reactive monomer in 4 batches, adding one batch every 30 minutes, controlling the reaction temperature at each addition to not exceed 5°C. After the last batch is added, continue stirring at 10°C for 8 hours to obtain a viscous polyamic acid resin solution.

[0068] S2: Add surface-modified nanoporous silica filler and heat stabilizer to the polyamic acid resin solution obtained in step S1, and disperse it uniformly at 3000 rpm for 60 min in a high-speed disperser. Then, place the mixture in a degassing tank with a vacuum degree of -0.08 MPa and let it stand to remove bubbles for 4 h until there are no visible bubbles in the solution. The nanoporous silica filler has a particle size of 50 nm and a pore size of 3 nm, and its surface is hydrophobically treated with a silane coupling agent. The amount added is 1.5% of the solid content of the polyamic acid resin. The silane coupling agent is KH-560.

[0069] S3: The degassed adhesive solution is passed through a multi-layer filter screen, which consists of a 300-mesh primary filter screen, a 600-mesh intermediate filter screen, and a 20μm fine filter element. The filtered adhesive solution is then uniformly coated onto a mirror stainless steel support or PET release film through a casting nozzle. The casting thickness is controlled by a metering pump to ensure that the final dry film thickness reaches the target value. The casting area is divided into multiple temperature zones with temperatures of 70℃, 90℃, and 110℃, respectively. The hot air circulation speed is 2m / s, and the drying time is 10min, causing partial imidization of the adhesive solution to form a self-supporting gel film with a solid content of 65%.

[0070] S4: Peel the gel film obtained in step S3 from the support and feed it into a biaxial tenter frame. Preheat it for 2 minutes at a preheating zone temperature of 180°C. Then, perform simultaneous biaxial stretching in the tenter frame. The longitudinal stretching ratio is 1.4 times, the transverse stretching ratio is 1.4 times, the stretching zone temperature is 250°C, and the stretching rate is 15% / s. After stretching, perform heat setting. The width of the heat setting zone remains unchanged, the temperature is 280°C, and it is held for 3 minutes to eliminate internal stress. The biaxial stretching adopts a simultaneous biaxial stretching process. The thickness of the stretched film is controlled at 25μm, and the thickness tolerance is less than ±3%.

[0071] S5: The stretched and shaped film is sent to a high-temperature imidization furnace for segmented gradient temperature imidization under high-purity nitrogen protection. First imidization zone: temperature 220℃, residence time 15min, this stage mainly involves solvent evaporation and preliminary cyclization; Second imidization zone: temperature 330℃, residence time 20min, deep imidization reaction occurs in this stage; Third imidization zone: temperature 400℃, residence time 10min, complete imidization is achieved in this stage; Finally, it enters the heat setting zone and is heat-set at 435℃ for 10 minutes. At the same time, 1.0% lateral relaxation is applied in the heat setting zone to further reduce the coefficient of thermal expansion. During the gradient imidization process, the heating rate was 3℃ / min, and high-purity nitrogen was introduced throughout the process for protection, with an oxygen content of less than 50ppm.

[0072] S6: After naturally cooling to room temperature, the film is trimmed, measured, and corona treated before being finally wound up to obtain the finished product.

[0073] The performance test results of the finished product prepared in this embodiment are as follows: Tensile strength: 288 MPa.

[0074] Elongation at break: 33%.

[0075] Tg: 380℃.

[0076] CTE: 10 ppm / ℃.

[0077] Dielectric constant (10GHz): 3.0.

[0078] Dielectric loss factor (10GHz): 0.0020.

[0079] Water absorption rate (85℃ / 85%RH, 48h): 0.42%.

[0080] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the present invention. The scope of protection of the present invention is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within its spirit and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of the present invention.

Claims

1. A method for preparing a high-end electronic-grade polyimide film, characterized in that: By weight, the raw materials comprise the following components: 100 parts of diamine monomer; 95-110 parts of dianhydride monomer; 5-25 parts of cross-linked fluorinated reactive monomer; 600-1000 parts of polar aprotic solvent; The method for preparing the high-end electronic-grade polyimide film includes the following steps: S1: Dissolve the diamine monomer in a polar aprotic solvent and stir until completely dissolved. The water content of the aprotic solvent is controlled below 100 ppm. Then, cool the reaction system to -5℃ to 10℃ and add the dianhydride monomer and cross-linked fluorinated reactive monomer in 3 to 5 batches, adding one batch every 20 to 40 minutes, controlling the reaction temperature at each addition to not exceed 5℃. After the last batch is added, continue stirring the reaction at 0℃ to 25℃ for 4 to 12 hours to obtain a viscous polyamic acid resin solution. S2: Add surface-modified nanoporous silica filler and heat stabilizer to the polyamic acid resin solution obtained in step S1, and disperse it uniformly in a high-speed disperser at 2000-4000 rpm for 30-90 min. Then, place the mixture in a degassing tank with a vacuum of -0.06 MPa to -0.1 MPa and let it stand to remove bubbles for 2-6 h until there are no visible bubbles in the solution. S3: The degassed adhesive solution is passed through a multi-layer filter screen, which consists of a 300-mesh primary filter screen, a 600-mesh intermediate filter screen, and a 20μm fine filter element. The filtered adhesive solution is then uniformly coated onto a mirror stainless steel support or PET release film through a casting nozzle. The casting area is divided into multiple temperature zones, with temperatures ranging from 60 to 80°C, 80 to 100°C, and 100 to 120°C, respectively. The hot air circulation speed is 1 to 3 m / s, and the drying time is 5 to 20 minutes, causing partial imidization of the adhesive solution to form a self-supporting gel film with a solid content of 50% to 70%. S4: Peel the gel film obtained in step S3 from the support and send it into a biaxial tenter frame. Preheat it for 1 to 3 minutes at a preheating temperature of 150 to 200°C. Then, perform simultaneous biaxial stretching in the tenter frame. The longitudinal stretching ratio is 1.1 to 1.6 times, the transverse stretching ratio is 1.1 to 1.6 times, the temperature of the stretching zone is 200 to 280°C, and the stretching rate is 5% to 20% / s. After stretching, perform heat setting. The width of the heat setting zone remains unchanged. The temperature is 250 to 300°C and held for 2 to 5 minutes to eliminate internal stress. S5: The stretched and shaped film is sent to a high-temperature imidization furnace for segmented gradient temperature imidization under high-purity nitrogen protection. First imidization zone: temperature 200-250℃, residence time 10-20 min; Second imidization zone: temperature 300-350℃, residence time 15-25 min; Third imidization region: temperature 380-420℃, residence time 5-15 min; Finally, it enters the heat setting zone and is heat-set at 400-450℃ for 5-20 minutes, while applying 0.5-1.5% lateral relaxation in the heat setting zone. S6: After naturally cooling to room temperature, the film is trimmed, measured, and corona treated before being finally wound up to obtain the finished product.

2. The method for preparing high-end electronic-grade polyimide film according to claim 1, characterized in that: The diamine monomer comprises one or more of the following substances: phenyl 2,2'-bis(trifluoromethyl)-4,4'-diaminobenzoate, 1,4-bis(4-amino-2-trifluoromethylphenoxy)-2,5-di-tert-butylbenzene, p-phenylenediamine, diamine derivatives corresponding to bicyclic [2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, or rigid heterocyclic diamines containing pyridine or pyrimidine rings; The diamine derivative corresponding to the bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride is one of 1,6-diamino-2,2,3,3,4,4,5,5-octafluorohexane or 4,4'-methylenebis(2-methylcyclohexylamine); The rigid heterocyclic diamine containing a pyridine or pyrimidine ring is one of 2,6-bis(4-aminophenyl)-4-phenylpyridine or 2,4,6-triaminopyrimidine.

3. The method for preparing high-end electronic-grade polyimide film according to claim 1, characterized in that: The dianhydride monomer is a mixture of pyromellitic dianhydride and biphenyl dianhydride, with a molar mixing ratio of pyromellitic dianhydride to biphenyl dianhydride of 1:(0.8-1.2).

4. The method for preparing high-end electronic-grade polyimide film according to claim 1, characterized in that: The cross-linked fluorinated reactive monomer is a dicarboxylic acid anhydride or diamine containing trifluoromethyl and ethynyl groups, specifically 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride or an aniline derivative containing ethynyl groups.

5. The method for preparing high-end electronic-grade polyimide film according to claim 1, characterized in that: The nanoporous silica filler in step S2 has a particle size of 20-80 nm and a pore size of 2-5 nm, and its surface is hydrophobically treated with a silane coupling agent. The amount added is 0.5%-3.0% of the solid content of the polyamic acid resin. The silane coupling agent is KH-560.

6. The method for preparing high-end electronic-grade polyimide film according to claim 1, characterized in that: The biaxial stretching in step S4 adopts a simultaneous biaxial stretching process, and the thickness of the stretched film is controlled at 12.5μm, 25μm or 50μm, with a thickness tolerance of less than ±3%.

7. The method for preparing high-end electronic-grade polyimide film according to claim 1, characterized in that: During the gradient imidization process in step S5, the heating rate is 2-5℃ / min, and high-purity nitrogen is introduced throughout the process for protection, with an oxygen content of less than 50ppm.

8. The method for preparing high-end electronic-grade polyimide film according to claim 1, characterized in that: The polar aprotic solvent is one or more combinations of N,N-dimethylacetamide, N-methylpyrrolidone, or N,N-dimethylformamide.