A low dielectric constant polyimide film and a method for preparing the same

Abstract

This invention provides a low dielectric constant polyimide film and its preparation method. The raw materials for preparing the low dielectric constant polyimide film include a dianhydride monomer, a diamine monomer, and a polyepoxide capping agent. The polyepoxide capping agent includes amino-capped polyepoxide and / or anhydride-capped polyepoxide. The amino-capped polyepoxide has the structure shown in Formula I, and the anhydride-capped polyepoxide has the structure shown in Formula II. By using the above-mentioned amino-capped polyepoxide and / or anhydride-capped polyepoxide with specific structures as capping agents, combined with diamine monomer and dianhydride monomer, the prepared polyimide film can have a porous structure, thereby having a low dielectric constant, making it suitable for applications in the microelectronics field.

Description

[0001] This application is a divisional application. The parent application number is 202310889691.4, the application date is July 19, 2023, and the invention title is "A polyepoxide end-capping agent, a polyimide film with low dielectric constant and its preparation method and application". Technical Field

[0002] This invention belongs to the field of polyimide technology, specifically relating to a polyimide film with low dielectric constant and its preparation method. Background Technology

[0003] Polyimide (PI) films have been widely used in industries such as microelectronics, including alpha particle shielding layers for aerospace and military integrated circuits, antenna materials for 5G mobile phones, and materials used in microelectromechanical systems (MEMS) processes. However, common aromatic PIs have relatively high dielectric constants, typically ranging from 3.1 to 4.8°C. 2 / (N·M 2 The dielectric constant (around 1 GHz) is insufficient to meet the continuously decreasing dielectric performance requirements of the microelectronics industry. Therefore, the development of PI films with low dielectric constant k (k < 3.0) has been a key focus of research.

[0004] The conventional method for preparing PI film involves first preparing a polyamic acid slurry, and then dehydrating the polyamic acid at high temperature to achieve imidization. However, the reaction of polyamic acid is a reversible reaction. Therefore, in order to maintain the stability of polyamic acid, it must be kept at a low temperature. Of course, end-capping agents can be added to slow down the viscosity change of polyamic acid and improve its storage stability, but this often results in a loss of the mechanical properties of polyimide.

[0005] To reduce the dielectric constant of polyimide, a substance with a lower dielectric constant can be added to the polyimide. CN111844976A discloses a method for preparing a polyimide-fluoropolymer insulating composite material, the preparation method, and its application. The method includes the following steps: 1) After treating the surface of a polyimide film with a corona process, a fluoropolymer emulsion is coated on it, and after high-temperature drying and sintering, a fluoropolymer adhesive layer is formed; 2) The surface of the composite material formed in step 1) is hot-pressed with a fluoropolymer insulating outer layer using a bimetallic roller to prepare a composite polyimide-fluoropolymer insulating composite material. The composite material includes: a polyimide insulating base layer, a fluoropolymer adhesive layer, and a fluoropolymer insulating outer layer. At least one side of the surface of the polyimide insulating base layer is connected to the fluoropolymer insulating outer layer through the fluoropolymer adhesive layer. Through the above method, this invention can integrate excellent heat resistance, mechanical properties, electrical properties, waterproof, oil-proof, scratch-resistant, and chemical corrosion-resistant properties. The composite system prepared has strong adhesion. However, the preparation process of this method is relatively complex.

[0006] CN1293129A discloses a method for preparing polyimide / nano silica composite films by sol-gel method, which includes immersing the composite film in an etching solution, and then washing and drying it to prepare a polyimide film containing air pores. This method also requires relatively cumbersome post-processing and has certain limitations in application.

[0007] Therefore, in view of the problems of complex polyimide film preparation process and difficulty in balancing dielectric constant and mechanical properties in the existing technology, this invention proposes a method for preparing low dielectric constant polyimide films based on polyoxyalkylene end-capping agents. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a polyimide film with low dielectric constant and its preparation method. The polyimide film prepared using the polyepoxide end-capping agent has a uniform porous structure, thereby exhibiting a low dielectric constant, making it suitable for applications in the microelectronics field.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a polyepoxide end-capping agent, wherein the polyepoxide end-capping agent comprises amino-terminated polyepoxide and / or anhydride-terminated polyepoxide;

[0011] The amino-terminated polyepoxide has the structure shown in Formula I:

[0012] Formula I;

[0013] The anhydride-terminated polyepoxide has the structure shown in Formula II:

[0014] Formula II;

[0015] In Formula I and Formula II, A is a benzene ring, R1, R2, R3 and R4 are each independently selected from H, halogen, methyl or ethyl, and n is selected from an integer between 2 and 20 (e.g. 4, 6, 8, 10, 12, 14, 16 or 18).

[0016] The polyepoxide end-capping agent provided by this invention includes amino-terminated polyepoxide and / or anhydride-terminated polyepoxide. The amino-terminated polyepoxide has the structure shown in Formula I, and the anhydride-terminated polyepoxide has the structure shown in Formula II. By using the above-mentioned amino-terminated polyepoxide and / or anhydride-terminated polyepoxide with specific structures as end-capping agents, combined with diamine monomers and diacid monomers, not only can the prepared polyamide slurry have excellent storage stability, but the polyepoxide structure therein will also decompose at high temperature to form uniform pores, so that the polyamide film has a porous structure, and thus has a low dielectric constant (k < 3.0), which is suitable for application in the field of microelectronics technology.

[0017] In this invention, the amino-terminated polyepoxide can be prepared by the following method, which includes: reacting the polyepoxide with the corresponding nitrobenzyl chloride derivative at low temperature to prepare an ester and obtain the corresponding intermediate; then dehydrating or reducing the intermediate to obtain the above-mentioned amino-terminated polyepoxide having the structure shown in Formula I.

[0018] In this invention, the anhydride-terminated polyepoxide can be prepared by the following method, which includes: reacting the polyepoxide with the corresponding benzoyl chloride derivative substituted with phthalic anhydride at low temperature to prepare an ester and obtain the corresponding intermediate; then dehydrating or reducing the intermediate to obtain the anhydride-terminated polyepoxide having the structure shown in Formula II.

[0019] Preferably, the number average molecular weight of the amino-terminated polyepoxide and the anhydride-terminated polyepoxide is independently 100 to 2000, such as 200, 400, 600, 800, 1000, 1200, 1400, 1600 or 1800, and more preferably 300 to 1200.

[0020] In a second aspect, the present invention provides a polyimide film with a low dielectric constant, wherein the raw materials for preparing the polyimide film with a low dielectric constant include dianhydride monomers, diamine monomers, and polyoxyalkylene end-capping agents as described in the first aspect.

[0021] The raw materials for preparing the polyimide film provided by the present invention include dianhydride monomer, diamine monomer, and polyepoxide end-capping agent as described in the first aspect. The addition of the polyepoxide end-capping agent as described in the first aspect can significantly improve the storage stability of the polyamic acid slurry. On the other hand, during the process of coating the polyamic acid slurry onto the substrate surface and heating to form a mold, the polyepoxide will decompose to form uniform nanopores, thereby effectively reducing the dielectric constant of the polyimide film obtained after molding. Furthermore, the porosity and pore diameter of the polyimide film can be controlled by adjusting the amount of polyepoxide end-capping agent added.

[0022] In this invention, the reaction mechanism of amino-terminated polyepoxide with diamine monomer and dianhydride monomer is shown in the following diagram:

[0023] .

[0024] In this invention, the reaction mechanism of anhydride-terminated polyepoxide with diamine monomer and dianhydride monomer is shown in the following diagram:

[0025] .

[0026] Preferably, the dianhydride monomer comprises aromatic tetracarboxylic acid dianhydride.

[0027] Preferably, the aromatic tetracarboxylic dianhydride includes 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxobisphthalic anhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, (4-phthalic anhydride)formyloxy-4-phthalate, bis[(3,4-dianhydride)phenyl]terephthalate, 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, and p-phenylenebisbenzotriic acid. The ester dianhydride, 4,4'-terephthalodioxydiphthalic anhydride, pyromellitic dianhydride, 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride, 2,2-bis(4-(3,4-dicarboxyphenoxy)phenyl)hexafluoropropane dianhydride, 2,2-bis(4-(3,4-dicarboxybenzoyloxy)phenyl)hexafluoropropane dianhydride, or 2,2'-bis(trifluoromethyl)-4,4'-bis(3,4-dicarboxyphenoxy)biphenyl anhydride, or a combination of at least two of these.

[0028] Preferably, the diamine monomer includes p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether,

[0029] The first of the following is a combination of any one or at least two of the following: 2,2'-bis(trifluoromethyl)diaminobiphenyl, 4,4'-diaminobenzoylaniline, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, 4,4'-diaminodiphenyl sulfone, 2-(4-aminophenyl)-5-aminobenzimidazole, 2,2-bis(4-hydroxy-3-aminophenyl)propane, 4,4'-bis(3-aminophenoxy)diphenyl sulfone, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, 4,4'-diaminobiphenyl, or 9,9-bis(4-aminophenyl)fluorene.

[0030] Preferably, the porosity of the polyimide film is 10-50%, such as 15%, 20%, 25%, 30%, 35%, 40%, or 45%, and more preferably 25-40%.

[0031] Preferably, the diameter of the pores in the polyimide film is 0.05~50μm, for example 0.1μm.

[0032] The micrometers are 0.5μm, 1μm, 5μm, 10μm, 15μm, 20μm, 30μm or 40μm, and more preferably 2~4μm.

[0033] Thirdly, the present invention provides a method for preparing a polyimide film as described in the second aspect, the method comprising the following steps:

[0034] (1) The diamine monomer, dianhydride monomer and polyepoxide end-capping agent are reacted in a polar solvent to obtain polyamic acid slurry;

[0035] (2) The polyamic acid slurry obtained in step (1) is coated on the substrate and heated to obtain the polyimide film.

[0036] The method for preparing polyimide film provided by the present invention firstly involves reacting diamine monomer, dianhydride monomer, and polyepoxide end-capping agent in a polar solvent to prepare polyamic acid slurry. Then, the obtained polyamic acid slurry is coated on a substrate to form a wet film. Finally, a heat treatment is performed. The heat treatment can remove the polar solvent on the one hand, and on the other hand, the polyepoxide will decompose under heat during the heat treatment process to generate pores, so that the obtained polyimide film has a porous structure.

[0037] Preferably, the polar solvent in step (1) includes any one or a combination of at least two of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, γ-butyrolactone, propylene glycol monomethyl ether, cyclopentanone, cyclohexanone, ethyl acetate, toluene, or methyl ethyl ketone, and more preferably N,N-dimethylformamide and / or N,N-dimethylacetamide.

[0038] Preferably, the reaction in step (1) is carried out under nitrogen protection.

[0039] Preferably, the reaction time in step (1) is no more than 40 h, for example, 35 h, 30 h, 25 h, 20 h, 15 h or 10 h.

[0040] Preferably, the reaction temperature in step (1) is 0~30℃, such as 2℃, 4℃, 6℃, 8℃, 10℃, 12℃, 14℃, 16℃, 18℃, 20℃, 22℃, 24℃, 26℃ or 28℃.

[0041] Preferably, the reaction in step (1) specifically includes: reacting the diamine monomer and the dianhydride monomer first, then adding the polyepoxide end-capping agent to continue the reaction, to obtain the polyamic acid slurry.

[0042] Preferably, the substrate in step (2) includes a glass substrate.

[0043] Preferably, the heating treatment in step (2) is carried out under a phased heating condition.

[0044] Preferably, the staged heating method specifically includes: first heating the system to 75-85℃ (e.g., 77℃, 79℃, 81℃, or 83℃, etc.), holding at this temperature for 10-20 min (e.g., 12 min, 14 min, 16 min, or 18 min, etc.); second heating to 140-160℃ (e.g., 142℃, 144℃, 146℃, 148℃, 150℃, 152℃, 154℃, 156℃, or 158℃, etc.), holding at this temperature for 10-20 min (e.g., 12 min, 14 min, 16 min, or 18 min, etc.); and third heating to 210-230℃ (e.g., 212℃, 214℃, 216℃, 218℃, 220℃, 222℃, 224℃, 226℃, or 228℃, etc.), holding at this temperature for 10-20 min (e.g., 12 min, 14 min, 16 min, or 18 min, etc.). The temperature is raised to 290-310℃ for the fourth time (e.g., 292℃, 294℃, 296℃, 298℃, 300℃, 302℃, 304℃, 306℃, or 308℃, etc.), and held for 10-20 minutes (e.g., 12 minutes, 14 minutes, 16 minutes, or 18 minutes, etc.). The temperature is then raised to 440-460℃ for the fourth time (e.g., 442℃, 444℃, 446℃, 448℃, 450℃, 452℃, 454℃, 456℃, or 458℃, etc.), and held for 20-40 minutes (e.g., 22 minutes, 24 minutes, 26 minutes, 28 minutes, 30 minutes, 32 minutes, 34 minutes, 36 minutes, or 38 minutes, etc.), thus completing the staged heating process.

[0045] Fourthly, the present invention provides an application of a low dielectric constant polyimide film as described in the second aspect in the field of microelectronics.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] The polyepoxide end-capping agent provided by this invention includes amino-terminated polyepoxides and / or anhydride-terminated polyepoxides. The amino-terminated polyepoxides have the structure shown in Formula I, and the anhydride-terminated polyepoxides have the structure shown in Formula II. By using the above-mentioned amino-terminated polyepoxides and / or anhydride-terminated polyepoxides with specific structures as end-capping agents, combined with diamine monomers and diacid monomers, the prepared polyimide film can have a porous structure, thereby having a lower dielectric constant, which is suitable for applications in the microelectronics field. Attached Figure Description

[0048] Figure 1 A planar scanning electron microscope image of the polyimide film provided in Application Example 1 at a magnification of 2250x;

[0049] Figure 2 A planar scanning electron microscope image of the polyimide film provided in Application Example 1 at a magnification of 590x;

[0050] Figure 3 A cross-sectional scanning electron microscope image of the polyimide film provided in Application Example 1. Detailed Implementation

[0051] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0052] Example 1

[0053] A polyoxyethylene end-capping agent M1 has a number-average molecular weight of 720, and its specific structure is shown below:

[0054] ;

[0055] Its preparation method includes the following steps:

[0056] (1) Weigh 60 g (0.1 mol) of polyethylene glycol (molecular weight 600) and add it to a 1 L three-necked reaction flask. Add 500 mL of anhydrous 1,4-dioxane and 0.15 mol of pyridine (Py). Then dissolve 27.75 g (0.15 mol) of p-nitrobenzoyl chloride in 200 mL of anhydrous dichloromethane and add it dropwise to the three-necked flask through a constant pressure dropping funnel. React overnight at 0 °C. Pour the resulting reaction solution into a large amount of petroleum ether. A large amount of white solid precipitates out. Filter and collect the filter cake. Separate and purify the filter cake by GPC. After evaporating the solvent and drying under vacuum, 68.6 g of white intermediate is obtained (yield = 91.4%).

[0057] (2) 68.6 g (0.92 mol) of intermediate was added to ethanol, palladium on carbon was added and reacted at room temperature for 24 h, palladium on carbon was filtered off, and ethanol was dried by rotary evaporation to obtain crude product. The crude product was then purified by GPC to obtain 62.4 g of white solid (yield = 94.6%), which is polyoxyethylene end-capping agent M1.

[0058] The specific chemical formulas for the reaction are shown below:

[0059] .

[0060] Example 2

[0061] A polyoxyethylene end-capping agent M2 has a number-average molecular weight of 1120, and its specific structure is shown below:

[0062] ;

[0063] (1) Weigh 100 g (0.16 mol) of polyethylene glycol (molecular weight 600) and add it to a 1 L three-necked reaction flask. Add 600 mL of anhydrous 1,4-dioxane and 0.15 mol of pyridine (Py). Then dissolve 27.75 g (0.15 mol) of p-nitrobenzoyl chloride in 200 mL of anhydrous dichloromethane and add it dropwise to the three-necked flask through a constant pressure dropping funnel. React overnight at 0 °C. Pour the resulting reaction solution into a large amount of petroleum ether. A large amount of white solid precipitates out. Filter and collect the filter cake. Separate and purify the filter cake by GPC. After evaporating the solvent and drying under vacuum, 106.1 g of white intermediate is obtained (yield = 92.3%).

[0064] (2) 106.1 g (0.92 mol) of intermediate was added to ethanol. After adding palladium on carbon, the reaction was carried out at room temperature for 24 h. The palladium on carbon was filtered off, and the ethanol was dried by rotary evaporation to obtain crude product. The crude product was then separated and purified by GPC to obtain 96.8 g of white solid (yield = 93.7%), namely amino-terminated polyepoxide M2.

[0065] The specific chemical formulas for the reaction are shown below:

[0066] .

[0067] Example 3

[0068] A polyoxyethylene end-capping agent M3 has a number-average molecular weight of 775, and its specific structure is shown below:

[0069] ;

[0070] The preparation method includes the following steps:

[0071] (1) Weigh 60 g (0.1 mol) of polyethylene glycol (molecular weight 600) and add it to a 1 L three-necked reaction flask. Add 500 mL of anhydrous 1,4-dioxane and 0.15 mol of pyridine (Py). Then dissolve 31.58 g (0.15 mol) of 1,2,4-triphenyltriamic anhydride chloride in 200 mL of anhydrous dichloromethane and add it dropwise to the three-necked flask through a constant pressure dropping funnel. React overnight at 0 °C. Pour the resulting reaction solution into a large amount of petroleum ether. A large amount of white solid precipitates out. Filter and collect the filter cake. Separate and purify the filter cake by GPC. After evaporating the solvent and drying under vacuum, 70.6 g of white intermediate (yield = 90.3%) is obtained.

[0072] (2) 70.6 g (0.90 mol) of intermediate was added to 200 g of acetic anhydride and refluxed for 12 hours. The acetic anhydride was dried by rotary evaporation to obtain crude product. The crude product was then purified by GPC to obtain 68.7 g of white solid (yield = 97.3%), namely anhydride-terminated polyepoxide M3.

[0073] The specific chemical formulas for the reaction are shown below:

[0074] .

[0075] Application Example 1

[0076] A polyimide film with low dielectric constant is prepared by the following steps:

[0077] (1) Under nitrogen protection, DMAc (745.74 g) was added to a 2 L three-necked flask, followed by 4,4'-diaminodiphenyl ether (58.87 g, 0.294 mol). Pyromellitic dianhydride (65.44 g, 0.30 mol) was added in portions at 0 °C. After reacting for 18 h, polyoxyethylene end-capping agent M1 (Example 1, 8.64 g) was added.

[0078] 0.012 mol), and continue the reaction at low temperature for 6 h to obtain a polyamic acid slurry with a solid content of 15% and a viscosity of 75600 cp;

[0079] (2) After centrifugation to remove bubbles, the polyamic acid slurry obtained in step (1) is uniformly coated onto a glass plate. Then, it is heated under staged heating conditions. The staged heating method is as follows: the system is first heated to 80°C and held for 15 min, then heated to 150°C and held for 15 min, then heated to 220°C and held for 15 min, then heated to 300°C and held for 15 min, and finally heated to 450°C and held for 30 min to obtain the polyimide film.

[0080] Application Example 2

[0081] A polyimide film with low dielectric constant is prepared by the following steps:

[0082] (1) Under nitrogen protection, DMAc (772.42 g) was added to a 2 L three-necked flask, followed by 4,4'-diaminodiphenyl ether (58.87 g, 0.294 mol). Pyromellitic dianhydride (65.44 g, 0.30 mol) was added in batches at 0 °C. After the two reacted for 18 h, polyoxyethylene end-capping agent M2 (Example 2, 13.44 g, 0.012 mol) was added, and the reaction was continued at low temperature for 6 h to obtain a polyamic acid slurry with a solid content of 15% and a viscosity of 78800 cp.

[0083] (2) After centrifugation to remove bubbles, the polyamic acid slurry obtained in step (1) is uniformly coated onto a glass plate, and then subjected to heat treatment under staged heating conditions (the staged heating method is to heat the system to 75°C for the first time and hold for 20 min, heat it to 140°C for the second time and hold for 20 min, heat it to 210°C for the third time and hold for 20 min, heat it to 290°C for the fourth time and hold for 20 min, and finally heat it to 440°C and hold for 40 min) to obtain the polyimide film.

[0084] Application Example 3

[0085] A polyimide film with low dielectric constant is prepared by the following steps:

[0086] (1) Under nitrogen protection, DMAc (744.6 g) was added to a 2L three-necked flask, followed by 4,4'-diaminodiphenyl ether (60.07 g, 0.30 mol). Pyromellitic dianhydride (64.13 g, 0.294 mol) was added in batches at 0°C. After the two reacted for 18 h, polyoxyethylene end-capping agent M3 (Example 3, 9.3 g, 0.012 mol) was added, and the reaction was continued at low temperature for 6 h to obtain a polyamic acid slurry with a solid content of 15% and a viscosity of 87300 cp.

[0087] (2) After centrifugation to remove bubbles, the polyamic acid slurry obtained in step (1) is uniformly coated onto a glass plate, and then subjected to heat treatment under staged heating conditions (the staged heating method is to heat the system to 75°C for the first time and hold for 20 min, heat it to 140°C for the second time and hold for 20 min, heat it to 210°C for the third time and hold for 20 min, heat it to 290°C for the fourth time and hold for 20 min, and finally heat it to 440°C and hold for 40 min) to obtain the polyimide film.

[0088] Application Example 4

[0089] A polyimide film with low dielectric constant is prepared by the following steps:

[0090] (1) Under nitrogen protection, DMAc (874.9 g) was added to a 2 L three-necked flask, followed by 4,4'-diaminodiphenyl ether (58.87 g, 0.294 mol). 3,3',4,4'-biphenyltetracarboxylic dianhydride (88.26 g, 0.30 mol) was added in batches at 0 °C. After the two reacted for 24 h, polyoxyethylene end-capping agent M1 (Example 1, 8.64 g, 0.012 mol) was added, and the reaction was continued at low temperature for 10 h to obtain a polyamic acid slurry with a solid content of 15% and a viscosity of 48600 cp.

[0091] (2) After centrifugation to remove bubbles, the polyamic acid slurry obtained in step (1) is uniformly coated onto a glass plate, and then subjected to heat treatment under staged heating conditions (the staged heating method is to heat the system to 75°C for the first time and hold for 20 min, heat it to 140°C for the second time and hold for 20 min, heat it to 210°C for the third time and hold for 20 min, heat it to 290°C for the fourth time and hold for 20 min, and finally heat it to 440°C and hold for 40 min) to obtain the polyimide film.

[0092] Application Example 5

[0093] A polyimide film with low dielectric constant is prepared by the following steps:

[0094] (1) Under nitrogen protection, DMAc (908.54 g) was added to a 1 L three-necked flask, followed by 4,4'-diaminodiphenyl ether (58.87 g, 0.294 mol). 3,3',4,4'-biphenyltetracarboxylic dianhydride (88.26 g, 0.30 mol) was added in batches at 0 °C. After the two reacted for 24 h, polyoxyethylene end-capping agent M1 (Example 1, 17.28 g, 0.024 mol) was added, and the reaction was continued at low temperature for 10 h to obtain a polyamic acid slurry with a solid content of 15% and a viscosity of 48600 cp.

[0095] (2) After centrifugation to remove bubbles, the polyamic acid slurry obtained in step (1) is uniformly coated onto a glass plate. Then, it is heated under staged heating conditions. The staged heating method is as follows: the system is first heated to 80°C and held for 15 min, then heated to 150°C and held for 15 min, then heated to 220°C and held for 15 min, then heated to 300°C and held for 15 min, and finally heated to 450°C and held for 30 min to obtain the polyimide film.

[0096] Comparative Application Example 1

[0097] A polyimide film, the preparation method of which includes the following steps:

[0098] (1) Under nitrogen protection, DMAc (704.42 g) was added to a 1 L three-necked flask, followed by 4,4'-diaminodiphenyl ether (58.87 g, 0.294 mol). Pyromellitic dianhydride (65.44 g, 0.30 mol) was added in batches at 0 °C. After the two reacted for 24 h, a polyamic acid slurry with a solid content of 15% and a viscosity of 96500 cp was obtained.

[0099] (2) After centrifugation to remove bubbles, the polyamic acid slurry obtained in step (1) is uniformly coated onto a glass plate. Then, it is heated under staged heating conditions. The staged heating method is as follows: the system is first heated to 80°C and held for 15 min, then heated to 150°C and held for 15 min, then heated to 220°C and held for 15 min, then heated to 300°C and held for 15 min, and finally heated to 450°C and held for 30 min to obtain the polyimide film.

[0100] Comparative Application Example 2

[0101] A polyimide film, the preparation method of which includes the following steps:

[0102] (1) Under nitrogen protection, DMAc (703.8 g) was added to a 1 L three-necked flask, followed by 4,4'-diaminodiphenyl ether (60.07 g, 0.30 mol). Pyromellitic dianhydride (64.13 g, 0.294 mol) was added in batches at 0 °C. After the two reacted for 18 h, a polyamic acid slurry with a solid content of 15% and a viscosity of 67500 cp was obtained.

[0103] (2) After centrifugation to remove bubbles, the polyamic acid slurry obtained in step (1) is uniformly coated onto a glass plate. Then, it is heated under staged heating conditions. The staged heating method is as follows: the system is first heated to 80°C and held for 15 min, then heated to 150°C and held for 15 min, then heated to 220°C and held for 15 min, then heated to 300°C and held for 15 min, and finally heated to 450°C and held for 30 min to obtain the polyimide film.

[0104] Comparative Application Example 3

[0105] A polyimide film, the preparation method of which includes the following steps:

[0106] (1) Under nitrogen protection, DMAc (713.87 g) was added to a 1 L three-necked flask, followed by 4,4'-diaminodiphenyl ether (60.07 g, 0.30 mol). Pyromellitic dianhydride (64.13 g, 0.294 mol) was added in batches at 0 °C. After the two reacted for 18 h, phthalic anhydride end-capping agent (1.77 g, 0.012 mol) was added to obtain a polyamic acid slurry with a solid content of 15% and a viscosity of 86400 cp.

[0107] (2) After centrifugation to remove bubbles, the polyamic acid slurry obtained in step (1) is uniformly coated onto a glass plate. Then, it is heated under staged heating conditions. The staged heating method is as follows: the system is first heated to 80°C and held for 15 min, then heated to 150°C and held for 15 min, then heated to 220°C and held for 15 min, then heated to 300°C and held for 15 min, and finally heated to 450°C and held for 30 min to obtain the polyimide film.

[0108] Comparative Application Example 4

[0109] A polyimide film, the preparation method of which includes the following steps:

[0110] (1) Under nitrogen protection, DMAc (711.24 g) was added to a 1 L three-necked flask, followed by 4,4'-diaminodiphenyl ether (60.07 g, 0.30 mol). Pyromellitic dianhydride (65.44 g, 0.30 mol) was added in batches at 0 °C. After the two reacted for 18 h, polyepoxide (molecular weight 600, added amount 3 g) was added to obtain a polyamic acid slurry with a solid content of 15% and a viscosity of 156700 cp.

[0111] (2) After centrifugation to remove bubbles, the polyamic acid slurry obtained in step (1) is uniformly coated onto a glass plate. Then, it is heated under staged heating conditions. The staged heating method is as follows: the system is first heated to 80°C and held for 15 min, then heated to 150°C and held for 15 min, then heated to 220°C and held for 15 min, then heated to 300°C and held for 15 min, and finally heated to 450°C and held for 30 min to obtain the polyimide film.

[0112] Performance testing:

[0113] (1) Appearance: The polyimide film obtained in Example 1 was tested using a scanning electron microscope (SEM) for both planar and cross-sectional views. The resulting planar SEM images of the polyimide film obtained in Example 1 at a magnification of 2250x are shown below. Figure 1 As shown, a planar scanning electron microscope image of the polyimide film obtained in Application Example 1 with a magnification of 590x is obtained. Figure 2 As shown, a cross-sectional view of the polyimide film obtained in Application Example 1 is shown below. Figure 3 As shown;

[0114] according to Figure 1 and Figure 2 It can be seen that the surface of the polyimide film obtained in Example 1 has uniformly distributed nanopores; according to Figure 3 It can be seen that the polyimide film obtained in Application Example 1 also has pores evenly distributed inside.

[0115] (2) Porosity: The percentage of air bubbles per unit area on the thin film is measured by scanning electron microscopy.

[0116] (3) Dielectric constant: Before testing, the polyimide film is dried at 100℃ for 1 h, and then placed in a desiccator to cool to room temperature before testing. The test is carried out according to GB / T1409. The dielectric constant corresponding to 1 GHz frequency is tested. Five samples are tested for each polyimide film and the average value is taken.

[0117] The polyimide films provided in Test Cases 1-5 and Comparative Application Examples 1-4 were tested according to the above test methods. The test results are shown in Table 1.

[0118] Table 1

[0119]

[0120] According to the data in Table 1:

[0121] The introduction of the polyoxyalkylene end-capping agent provided by the present invention can form pores during the polyimide film formation process, thereby effectively reducing the dielectric constant of the polyimide film.

[0122] Specifically, the polyamide films obtained in Application Examples 1-5 have a porosity of 21-39% and a dielectric constant of 2.566-3.065, while the polyimide films provided in Application Examples 1-4 have a higher dielectric constant (3.355-4.686). This indicates that the present invention effectively improves the dielectric properties of the polyimide films by introducing a polyepoxide end-capping agent.

[0123] The applicant declares that this invention illustrates a low dielectric constant polyimide film and its preparation method through the above embodiments, but this invention is not limited to the above process steps, that is, it does not mean that this invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of the raw materials used in this invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of this invention.

Claims

1. A method for preparing a polyimide film with low dielectric constant, characterized in that, Includes the following steps: 1) Under nitrogen protection, pyromellitic dianhydride, polyoxyethylene end-capping agent M2 and 4,4'-diaminodiphenyl ether react in dimethylacetamide to obtain polyamic acid slurry; 2) After centrifugation to remove bubbles, the polyamic acid slurry obtained in step 1) is uniformly coated onto a glass plate, and then heat-treated under staged heating conditions to obtain the polyimide film. The polyoxyethylene end-capping agent M2 has a number-average molecular weight of 1120, and its specific structure is shown below: ； The staged heating method involves first heating the system to 75-81℃ and holding it for 16-20 minutes, then heating it to 140-150℃ and holding it for 16-20 minutes, then heating it to 210-220℃ and holding it for 16-20 minutes, then heating it to 290-300℃ and holding it for 16-20 minutes, and finally heating it to 440-450℃ and holding it for 30-40 minutes.

2. The method for preparing a low dielectric constant polyimide film according to claim 1, characterized in that, The reaction temperature is 0~10℃, and the reaction time is 15~25h.

3. The method for preparing a low dielectric constant polyimide film according to claim 2, characterized in that, The polyamic acid slurry has a solid content of 15% and a viscosity of 78,800 cp.

4. A polyimide film with low dielectric constant prepared by the preparation method according to any one of claims 1 to 3.

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