Porous polyimide film as well as preparation method and application thereof

Abstract

The invention discloses a porous polyimide film as well as a preparation method and application thereof, and belongs to the technical field of polyimide film materials, the preparation method comprises the following steps: carrying out esterification reaction on methoxypolyethylene glycol and 3-5-bis (4-nitrophenoxy) benzoic acid to obtain an esterification product; carrying out hydrogenation reaction on the esterification product to obtain a hydrogenated product; polymerizing the hydrogenated product and a dianhydride monomer under the catalytic action of isoquinoline and acetic anhydride to obtain a polyamide-imide solution; the preparation method comprises the following steps: uniformly coating a polyamide-imide solution on a substrate, and then preserving heat at 250-300 DEG C for 3.5-5.0 hours to prepare a porous polyimide film; by designing the structure of polyimide, the dielectric constant of the polyimide film is remarkably reduced to 2.3 or below, and a porous structure is generated in the polyimide film; the porous polyimide film can be used as a flexible dielectric material to be applied to a dielectric layer, a multi-chip module or an integrated circuit chip in the microelectronic industry.

Description

Technical Field

[0001] The invention belongs to the technical field of polyimide film materials, and in particular relates to a porous polyimide film and a preparation method and application thereof. Background Art

[0002] The fifth generation (5G) mobile communication technology has rapidly emerged, and 5G communication technology has attracted people's attention. Driven by this technology, the pursuit of high speed and low latency has become an inevitable trend in the development of 5G communication equipment, which has also prompted communication equipment to continue to evolve towards more excellent performance. For 5G communication devices, the higher dielectric constant makes them bulky and heavier. Studies have shown that the transmission attenuation and delay of signals in material media are related to the dielectric constant of the dielectric material. Reducing the dielectric constant is an important way to reduce signal attenuation and speed up transmission rate.

[0003] PI film has been widely used in the semiconductor and microelectronics fields due to its outstanding comprehensive characteristics and good dielectric properties, especially playing a key role in 5G communication technology. Despite this, traditional PI film cannot fully meet the requirements of microelectronics and 5G communication devices due to its defects such as dark color and high moisture absorption rate, as well as a dielectric constant of 3.0 to 4.0. At present, the dielectric constant of the widely commercialized polyimide film generally falls in the range of 3.2 to 3.8, which does not meet the requirements of microelectronics and optoelectronic devices for lower dielectric constants. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a porous polyimide film and its preparation method and application. By synthesizing a diamine monomer containing thermally decomposable polyethylene glycol, an intrinsic polyimide material is prepared, and its side chain is thermally decomposed to generate a porous structure, thereby significantly reducing the dielectric constant of the polyimide film. The material has good flexibility and low dielectric properties, and is suitable for applications such as dielectric layers, multi-chip modules and integrated circuit chips in the microelectronics industry.

[0005] The technical solution adopted by the present invention is as follows:

[0006] The present invention provides a method for preparing a porous polyimide film, the preparation method comprising the following steps:

[0007] (1) subjecting polyethylene glycol monomethyl ether to an esterification reaction with 3-5-bis(4-nitrophenoxy)benzoic acid to obtain an esterification product;

[0008] (2) subjecting the esterification product obtained in step (1) to a hydrogenation reaction to obtain a hydrogenated product;

[0009] (3) polymerizing the hydrogenated product and the dianhydride monomer under the catalytic action of isoquinoline and acetic anhydride to obtain a polyamide imide solution;

[0010] (4) The polyimide solution is uniformly coated on the substrate, and then kept at 250-300° C. for 3.5-5.0 hours to prepare a porous polyimide film.

[0011] Furthermore, the dianhydride monomer can be any commercial dianhydride monomer, preferably one of 4,4′-(hexafluoroisopropylene) diphthalic anhydride (6FDA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), and pyromellitic dianhydride (PMDA).

[0012] When the dianhydride monomer is 6FDA, BPDA or PMDA, the structural formula of the polyamide imide prepared in step (3) of the preparation method is:

[0013] Among them, B in the structural formula represents n≥5, x≥1.

[0014] The preparation method specifically comprises the following steps:

[0015] (1) dissolving polyethylene glycol monomethyl ether, 3-5-bis(4-nitrophenoxy)benzoic acid, EDCI and DMAP in an organic solvent, reacting at room temperature for 20 to 24 hours under the protection of an inert gas, and post-treating to obtain an esterification product;

[0016] (2) dissolving the esterification product obtained in step (1) in an alcohol solvent, adding palladium carbon, stirring and reacting in a hydrogen atmosphere for 1.5 to 2.5 hours, and post-treating to obtain a hydrogenation product;

[0017] (3) dissolving the hydrogenation product in an organic solvent, adding a dianhydride monomer under the protection of an inert gas and in an ice bath, and when the reaction solution is a yellow, transparent, viscous liquid, adding isoquinoline and acetic anhydride, stirring and reacting for 10 to 12 hours to obtain a polyamide imide solution;

[0018] (4) The polyimide solution is uniformly coated on the substrate, and then kept at 250-300° C. for 3.5-5.0 hours to prepare a porous polyimide film.

[0019] In step (1), the molar ratio of polyethylene glycol monomethyl ether, 3-5-bis(4-nitrophenoxy)benzoic acid, EDCI and DMAP is 1:1.3-1.5:1.8-2.2:0.3-0.7.

[0020] In step (1), the organic solvent is dichloromethane or tetrahydrofuran; the concentration of 3-5-bis(4-nitrophenoxy)benzoic acid in the organic solvent is 0.05-0.1M.

[0021] In step (2), the mass ratio of the esterification product to palladium carbon is 8 to 12:1.

[0022] In step (2), the alcohol solvent is anhydrous ethanol.

[0023] In step (3), the molar ratio of the hydrogenation product to the commercial dianhydride is 1:0.90-1.05.

[0024] In step (3), the organic solvent is one of N,N-dimethylacetamide, N-methylpyrrolidone and N,N-dimethylformamide.

[0025] In the preparation method of the porous polyimide film provided by the present invention, a polyimide polymer with polyethylene glycol (PEG) side chains is first prepared, and the introduction of the PEG side chains increases the free volume between polyimide molecules, thereby reducing the density of the material; then, the polyethylene glycol on the side chains is thermally cracked at 250-300°C, the main chain polyimide is stable at this temperature, a pore structure is generated, and air is introduced into the material to further reduce the dielectric constant, which can be as low as 2.3 or less. This process makes the porous polyimide film have good flexibility and low dielectric properties, and is suitable for applications such as dielectric layers, multi-chip modules and integrated circuit chips in the microelectronics industry.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. Uniform pore formation: The existing technology mainly adopts physical doping and pyrolysis pore formation methods, which are difficult to achieve uniform distribution of pores, resulting in uneven porous structure and affecting material performance. However, the present invention generates pores uniformly in the polyimide film through thermal cracking of polyethylene glycol (PEG) side chains, ensuring the consistency of pore distribution and significantly improving the stability of the dielectric properties of the material.

[0028] 2. Optimized chemical composition, no need for external doping: Different from the traditional method of adding additional exogenous materials to the polyimide matrix to assist in pore formation, the present invention directly synthesizes intrinsic polyimide containing thermally decomposable side chains, simplifies the preparation process, avoids the dispersion and compatibility problems that may be caused by external doping materials, thereby ensuring the mechanical properties and thermal stability of the material.

[0029] 3. Enhanced mechanical and thermal properties: By optimizing the molecular design, the present invention maintains the excellent mechanical strength and thermal stability of polyimide while forming holes, solving the problem in the prior art that porous structures often lead to increased material brittleness, and is suitable for microelectronic devices with higher requirements and high temperature environments.

[0030] 4. Controllable pore size and structural optimization: By utilizing the thermal decomposition of polyethylene glycol side chains, the present invention can control the size and distribution of pores, so as to achieve a low dielectric constant without affecting the structural integrity of the material, while maintaining good durability and electrical properties, thus meeting the strict requirements of high-performance microelectronic devices for low dielectric materials.

[0031] 5. The porous structure of the porous polyimide film provided by the present invention makes the porous polyimide film have potential application value in film lightweighting, adsorption, electromagnetic shielding, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is the H NMR spectrum of the hydrogenated product, i.e., the diamine monomer in Example 1;

[0033] Figure 2 This is the GPC chart of the polyimide solution in step (3) of Example 1;

[0034] Figure 3 The H NMR spectrum of the polyimide powder prepared from the polyimide solution in step (3) of Example 1;

[0035] Figure 4 The following is the appearance change of the polyimide film in Example 1 before and after being kept at a constant temperature of 300°C for 4 hours.

[0036] Figure 5 is a SEM image of the surface of the porous polyimide film in Example 1;

[0037] Figure 6 The dielectric constant test result diagram of the porous polyimide film in Example 1;

[0038] Figure 7 This is the dielectric constant test result of Kapton's PI;

[0039] Figure 8 The tensile properties of the porous polyimide film prepared in Example 1 and the polyimide film prepared at room temperature;

[0040] Fig. 9 The thermal cracking curve of polyethylene glycol monomethyl ether with a number average molecular weight of 350 in Example 1;

[0041] Fig.10 The thermal decomposition curve of the polyimide powder prepared from the polyimide solution in step (3) of Example 1;

[0042] Fig.11 This is the GPC diagram of the polyimide solution in step (1) of Example 2;

[0043] Fig.12is a SEM image of the surface of the porous polyimide film in Example 2;

[0044] Fig.13 The dielectric constant test result diagram of the porous polyimide film in Example 2;

[0045] Fig.14 The tensile properties of the porous polyimide film prepared in Example 2 and the polyimide film prepared at room temperature;

[0046] Fig.15 This is the H-NMR spectrum of the polyimide powder prepared from the polyimide solution in step (1) of Example 2. DETAILED DESCRIPTION

[0047] The present invention is described in detail below with reference to the embodiments.

[0048] Example 1

[0049] A method for preparing a porous polyimide film comprises the following steps:

[0050] (1) 5.74 g (16.41 mmol) of polyethylene glycol monomethyl ether with a number average molecular weight of 350, 5 g (12.62 mmol) of 3-5-bis(4-nitrophenoxy)benzoic acid, 4.84 g (25.24 mmol) of EDCI, and 0.77 g (6.31 mmol) of DMAP were dissolved in 150 mL of anhydrous dichloromethane and reacted for 24 h under nitrogen atmosphere. Subsequently, the solution was concentrated and separated by column chromatography. The eluent was a mixed solvent of DCM and MeOH in a volume ratio of 20:1. The product solution was collected and concentrated to dryness to obtain a slightly yellow oily esterification product.

[0051] (2) 7.0 g of the esterification product obtained in step (1) was weighed and dissolved in 70 mL of anhydrous ethanol, and 700 mg of 10% palladium carbon was added. The mixture was stirred and reacted in a hydrogen atmosphere at 25° C. for 2 h. After the reaction was completed, the mixture was filtered, concentrated, and dried to obtain a hydrogenated product, i.e., a diamine monomer. Its magnetic hydrogen spectrum is as follows: Figure 1 shown.

[0052] (3) 6.5 g (9.72 mmol) of the hydrogenated product was dissolved in 43 mL of N,N-dimethylacetamide, and 2.86 g (9.72 mmol) of biphenyltetracarboxylic dianhydride was added thereto under the protection of nitrogen and in an ice bath to obtain a polyimide precursor solution; 1.98 g (19.44 mmol) of acetic anhydride and 1.25 g (9.72 mmol) of isoquinoline were added thereto, and the mixture was reacted at room temperature for 12 h to obtain a polyimide solution, the GPC diagram of which is shown in FIG. Figure 2 As shown, its molecular weight Mn = 23000, polymer dispersibility index PDI = 1.86;

[0053] (4) The polyimide solution was evenly coated on a glass substrate, kept in an oven at 300°C for 4 hours, and then the heating was turned off. After natural cooling, the film was taken out and the appearance was as follows: Figure 4 As shown in the right figure; the porous polyimide film is obtained, and its SEM morphology is as follows Figure 5 As shown in the figure, it can be seen that there are a large number of evenly distributed holes in the film. Its dielectric constant is characterized by Figure 6 As shown in the figure, it can be seen that the dielectric constant of the porous polyimide film is as low as 2.3, compared with the PI test result of the conventionally purchased Kapton of about 3.6. Figure 7 As shown in Figure 2, there is a significant decrease. The tensile properties test results are shown in Figure 2. Figure 8 As shown in the figure, it can be seen that compared with the film obtained by drying at room temperature, although the tensile strength of the porous polyimide film is reduced, it still has relatively excellent tensile properties.

[0054] The polyimide solution prepared in step (3) was poured into 400 mL of cold methanol, filtered and dried to obtain a polyimide powder, the H NMR spectrum of which was as follows: Figure 2 As shown, it can be seen that step (3) successfully prepared polyimide, and its synthesis route is as follows:

[0055]

[0056] The TGA curve of the polyimide powder further prepared from the polyimide solution prepared in step (3) is as follows: Fig. 9 As shown, the TGA curve of polyethylene glycol monomethyl ether with a number average molecular weight of 350 is as follows Figure 8 As shown, from Figure 8 The TGA curve of PEG shows that PEG begins to decompose at 195°C and 300°C.

[0057] The decomposition reaches its maximum value. Fig. 9 It can be seen that the TGA curve of the polyimide powder further prepared from the polyimide solution prepared in step (3) is divided into two sections. The figure shows that the first decomposition occurs near 300°C, which is the thermal decomposition of PEG on the polyimide side chain; the second decomposition occurs above 400°C, at which time the polyimide main chain begins to thermally decompose. It can be seen that under the conditions in step (4) of this embodiment, the polyimide main chain remains stable when the PEG on the polyimide side chain decomposes, ensuring the excellent mechanical strength of the film.

[0058] The polyimide solution prepared in step (3) is uniformly coated on a glass substrate, and then dried naturally to obtain a polyimide film. Figure 4 As shown on the left, its dielectric constant is characterized as Figure 6 shown; from Figure 4Comparing the left and right pictures in the figure, it can be seen that the film will not break after heating. Figure 6 It can be seen that the dielectric constant of the polyimide film obtained after heating is significantly reduced.

[0059] Example 2

[0060] A method for preparing a porous polyimide film comprises the following steps:

[0061] (1) 7.8 g (11.66 mmol) of the hydrogenation product in Example 1 was dissolved in 65 mL of N,N-dimethylacetamide, and 5.18 g (11.66 mmol) of 6FDA was added thereto under the protection of nitrogen and in an ice bath to obtain a polyamide imide precursor polyamic acid solution; 2.37 g (23.32 mmol) of acetic anhydride and 1.5 g (11.66 mmol) of isoquinoline were added, and the mixture was reacted at room temperature for 12 h to obtain a polyimide solution, the GPC diagram of which is shown in FIG. Fig.11 As shown, its molecular weight Mn = 24000, polymer dispersibility index PDI = 1.78;

[0062] (2) The polyimide solution was uniformly coated on a glass substrate, kept in an oven at 300°C for 4 hours, and then the heating was turned off. After natural cooling, the film was taken out to obtain a porous polyimide film. Its SEM morphology is as follows: Fig.12 As shown in the figure, it can be seen that there are a large number of evenly distributed holes in the film. Its dielectric constant is characterized by Fig.13 As shown in the figure, it can be seen that the dielectric constant of the porous polyimide film is as low as 1.9. It can be seen that the introduction of fluorine atoms further reduces the dielectric constant of the PI film. The tensile performance test results are shown in Fig.14 As shown in the figure, it can be seen that compared with the film obtained by drying at room temperature, although the tensile strength of the porous polyimide film is reduced, it still has relatively excellent tensile properties.

[0063] The polyimide solution prepared in step (1) was poured into 600 mL of cold methanol, filtered and dried to obtain a polyimide powder, the H NMR spectrum of which was as follows: Fig.15 As shown, it can be seen that step (1) successfully prepared polyimide, and its synthesis route is as follows:

[0064]

[0065] The polyimide solution prepared in step (3) is uniformly coated on a glass substrate and then dried naturally to obtain a polyimide film whose dielectric constant is characterized by: Fig.13 shown; from Fig.13 It can be seen that the dielectric constant of the polyimide film obtained after heating is significantly reduced.

[0066] The detailed description of a porous polyimide film and its preparation method and application with reference to the above embodiments is illustrative rather than restrictive. Several embodiments can be listed according to the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a porous polyimide film, characterized in that: The preparation method comprises the following steps: (1) subjecting polyethylene glycol monomethyl ether to an esterification reaction with 3-5-bis(4-nitrophenoxy)benzoic acid to obtain an esterification product; (2) subjecting the esterification product obtained in step (1) to a hydrogenation reaction to obtain a hydrogenated product; (3) polymerizing the hydrogenated product and the dianhydride monomer under the catalytic action of isoquinoline and acetic anhydride to obtain a polyamide imide solution; (4) The polyimide solution is uniformly coated on the substrate, and then kept at 250-300° C. for 3.5-5.0 hours to prepare a porous polyimide film.

2. The preparation method according to claim 1, characterized in that: The dianhydride monomer is any commercial dianhydride monomer.

3. The preparation method according to claim 1, characterized in that: The dianhydride monomer is one of 4,4′-(hexafluoroisopropylene) diphthalic anhydride, 3,3′,4,4′-biphenyltetracarboxylic anhydride and pyromellitic anhydride.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: (1) dissolving polyethylene glycol monomethyl ether, 3-5-bis(4-nitrophenoxy)benzoic acid, EDCI and DMAP in an organic solvent, reacting at room temperature for 20 to 24 hours under the protection of an inert gas, and post-treating to obtain an esterification product; (2) dissolving the esterification product obtained in step (1) in an alcohol solvent, adding palladium carbon, stirring and reacting in a hydrogen atmosphere for 1.5 to 2.5 hours, and post-treating to obtain a hydrogenation product; (3) dissolving the hydrogenation product in an organic solvent, adding a dianhydride monomer under the protection of an inert gas and in an ice bath, and when the reaction solution is a yellow, transparent, viscous liquid, adding isoquinoline and acetic anhydride, stirring and reacting for 10 to 12 hours to obtain a polyamide imide solution; (4) The polyimide solution is uniformly coated on the substrate, and then kept at 250-300° C. for 3.5-5.0 hours to prepare a porous polyimide film.

5. The preparation method according to claim 4, characterized in that: In step (1), the molar ratio of polyethylene glycol monomethyl ether, 3-5-bis(4-nitrophenoxy)benzoic acid, EDCI and DMAP is 1:1.3-1.5:1.8-2.2:0.3-0.

7.

6. The preparation method according to claim 4, characterized in that: In step (2), the mass ratio of the esterification product to palladium carbon is 8 to 12:

1.

7. The preparation method according to claim 4, characterized in that: In step (1), the organic solvent is dichloromethane or tetrahydrofuran; the concentration of 3-5-bis(4-nitrophenoxy)benzoic acid in the organic solvent is 0.05 to 0.1 M; in step (2), the alcohol solvent is anhydrous ethanol; in step (3), the organic solvent is N,N-dimethylacetamide.

8. The preparation method according to claim 4, characterized in that: In step (3), the molar ratio of the hydrogenated product to the dianhydride monomer is 1:0.90-1.

05.

9. The porous polyimide film prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the porous polyimide film as claimed in claim 9 as a flexible dielectric material.

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