Low-dielectric polyimide material and preparation method thereof

Abstract

The invention relates to a low-dielectric polyimide material and a preparation method thereof. A fluorine-containing anhydride monomer reacts in an ice-water bath to generate a polyamide acid solution with a certain concentration. And after defoaming treatment, coating a substrate with the obtained product, placing the substrate in a certain appropriate amount of air, aging the substrate for a certain time, and placing the substrate in a water bath for replacement. And taking out and transferring to a high-temperature oven for gradient cyclization to realize complete imidization. According to the method, normal-pressure drying is achieved, and meanwhile the problems of irreversible shrinkage, pore structure collapse and the like caused by traditional normal-pressure drying are avoided; the product has the advantages of smooth appearance, complete and ordered pore structure and low dielectric constant, and can be widely used in the fields of microelectronics, integrated electrical appliances and the like.

Description

Technical Field

[0001] The invention relates to a low dielectric polyimide material and a preparation method thereof, in particular to a fluorine-containing porous polyimide material and a preparation method thereof. Background Art

[0002] With the development of the 5G era, the integration density of the microelectronics field and integrated circuits has increased dramatically, and the transmission delay and propagation loss of electronic signals at high frequencies cannot be ignored. In view of the obvious advantages of dielectric materials with low dielectric constant and low dielectric loss in high-frequency signal transmission, mobile phone antennas and other fields. Polyimide (PI) is widely used in the field of microelectronics due to its excellent thermal stability, corrosion resistance, good mechanical properties and adhesion properties. However, the dielectric constant of ordinary PI film is 3.1 to 3.5, which can no longer meet the needs of integrated circuit process development. Reducing the dielectric constant of PI film for electrical use has been the focus of researchers in this field.

[0003] At present, the methods for reducing the dielectric constant of PI film mainly focus on two aspects: on the one hand, changing the main structure of PI, introducing fluorine atoms or larger side groups in the molecular chain to reduce the polarization ability of the dipole in the molecule; on the other hand, introducing a porous structure in the material system to form pores, thereby reducing the number of polarized molecules per unit volume, and replacing them with air media with a lower dielectric constant, thereby reducing the dielectric constant of the material as a whole. CN116554475A discloses a method for preparing a low-dielectric polyimide film, adding a thermally unstable polymer nanoparticle to a polyamic acid solution, and forming nanopores in the polymer matrix through the decomposition of a low molecular weight polymer at high temperature. In order to achieve the thermal decomposition of nanoparticles in this process, the ambient temperature must be high enough. CN114316591B discloses a method for preparing a dimensionally stable low-dielectric polyimide film. Glycidyl ether oxypropyl caged polysilsesquioxane and triphenylmethane are added to a dianhydride diamine system, and a polyamic acid solution is synthesized in an inert atmosphere, and imidization is performed to obtain the target product. The pore-forming process of this method is obtained by decomposing the cage polymer under certain environmental conditions, so the pH of the solution system is required to be relatively high. CN112646179B uses a template method to prepare a low-dielectric polyimide film. Polyacrylic acid and hexadecyltrimethylammonium bromide are selected as dual template agents, and tetraethyl orthosilicate is used as a silicon source to prepare "core-shell" structure microspheres, and then the template agent is calcined to remove the template agent to obtain porous nanoparticles; the porous nanoparticles are then reacted with an aminosilane coupling agent to obtain porous nanoparticles with surface amino modifications. It is then polymerized with an amine anhydride monomer and imidized to form a film to obtain a film with a low dielectric constant. Since the process involves surface functionalized grafting, there are certain requirements for the preparation environment conditions, and the reaction needs to be carried out under the protection of an inert gas. CN104927082A proposes a porous low-dielectric polyimide film. Calcium carbonate is used as a pore-forming agent raw material, and a porous film is obtained after calcium carbonate is removed with dilute hydrochloric acid. Although the raw materials in this method are simple and easy to obtain, no complicated operation is required. However, since the addition of calcium carbonate will form an isolated phase in the polyamic acid solution and its compatibility with polyamic acid is insufficient, the amount of modified filler added is not large and the reduction in the dielectric constant is relatively limited.

[0004] As a typical polymer aerogel, PI aerogel has excellent thermal stability, mechanical properties and insulation, and has received widespread attention in applications. The key step in the preparation process of aerogel is the drying of wet gel. Since there is no good measure to solve the strong shrinkage problem caused by solvent removal, the current drying of PI aerogel still uses two traditional drying methods: supercritical drying and freeze drying. Compared with the first two drying methods, atmospheric pressure drying does not require higher pressure and temperature to dry the wet gel at normal pressure and better maintain the gel pore structure. However, the difficulty of atmospheric pressure drying is that when the solvent is removed from the wet gel, the surface tension and capillary pressure on the gel surface will cause irreversible shrinkage of the material and collapse of the pore structure. Therefore, how to achieve the integrity of the pore structure of PI aerogel during atmospheric pressure drying has broad engineering significance for the preparation of low dielectric polyimide materials. Summary of the invention

[0005] The purpose of the present invention is to broaden the application of polyimide-based materials in the low dielectric field, and at the same time effectively improve the problems of high shrinkage and easy structural collapse of gel materials during the preparation process, thereby providing a rapid and simple preparation method for gel-state porous structure materials, that is, a preparation method for low dielectric polyimide materials. Another purpose of the present invention is to provide a low dielectric polyimide material prepared by the above method.

[0006] The technical solution of the present invention is: a method for preparing a polyimide aerogel material, and the specific steps are as follows:

[0007] (1) preparing a polyamic acid solution, obtaining a PAA solution with a solid content of 5% to 15%, and degassing;

[0008] (2) Preparation of polyimide aerogel:

[0009] The PAA solution after degassing is coated on a substrate with a certain thickness, and is placed in the air for aging. When the surface shows a certain degree of condensation, it is immersed in pure water and replaced for a certain period of time. The surface is dried at room temperature and placed in a high-temperature oven for dehydration and cyclization to obtain a polyimide aerogel material.

[0010] Preferably, the degassing in step (1) is static degassing or ultrasonic degassing. Preferably, the substrate is glass or ceramic plate. The preparation of the polyamic acid solution in step (1) is carried out in accordance with the patent "A method for preparing a high modulus and low thermal expansion coefficient polyimide hybrid film" (ZL200810236233.6) in an ice-water mixing system to obtain a polyamic acid solution (PAA) with stable performance. The preferred diamines in the preparation are 2,2'-bis(trifluoromethyl)-(1,1'-diphenyl)-4,4'-diamine (TFMB), 9,9-bis(3-fluoro-4-aminophenyl)fluorene (FFDA), 2,2'-bis(trifluoromethyl)-4,4'diaminophenyl ether (6FODA), 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP), 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP), 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (6FAPB), 2,2-bis(4-aminophenyl)hexafluoropropane (FA) or a mixture of two thereof. In the preparation of PAA, the dianhydride is preferably hexafluorodianhydride (6FDA), bisphenol AF dianhydride (FBBBA), 9,9-bis(trifluoromethyl)-2,3,6,7-oxanthene tetracarboxylic dianhydride (6FCDA), 3,6-bis(3',5'-bis(trifluoromethyl)phenyl)pyromellitic dianhydride (12FPMDA), 3,6-bis(4'-trifluoromethylphenyl)pyromellitic dianhydride (6FPMDA), N-[4-[4-[(1,3-dioxy-2-benzofuran-5carbonyl)amino]-2-(trifluoromethyl)phenyl]-3-(trifluoromethyl)phenyl]-1,3-dioxy-2-benzofuran-5-carboxamide (TA-TFMB) or a mixture of two thereof.

[0011] Preferably, the coating thickness in step (2) is 500-1500 microns; the air humidity is 50%-80%; the aging time is 8-24 hours; the degree of coagulation is preferably 40%-95%; and the replacement time is 6-12 hours.

[0012] Preferably, in step (2), the temperature in the high temperature oven is increased gradually at a heating rate of 0.5-3°C / min, the temperature is increased to 85-120°C and kept constant for 50-70min, and the temperature is increased to 200-240°C and kept constant for 50-120min.

[0013] The present invention also provides a polyimide aerogel material prepared by the above method. The prepared polyimide aerogel material has a porosity of 63% to 67% and a pore diameter of 6 to 36 μm.

[0014] The experimental operation process of the present invention is controllable and the implementation conditions are mild. A simple and feasible method is provided for preparing polymer-based aerogel materials. The structural material prepared by the method has a complete pore structure, good controllability, and a low dielectric constant, and can be well applied in the field of low dielectric electronics.

[0015] Beneficial effects:

[0016] 1. The method has mild conditions and controllable process.

[0017] 2. The polyimide aerogel material prepared by this method presents a complete pore structure, and the porosity is stably controlled between 63% and 67%; the pore size can be controlled between 6 and 36 μm.

[0018] 3. The polyimide aerogel material prepared by this method exhibits excellent low dielectric properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The pore structure of Example 1;

[0020] Figure 2 The pore structure of Example 2;

[0021] Figure 3 The pore structure of Example 3;

[0022] Figure 4 The pore structure of Example 4;

[0023] Figure 5 This is the pore structure of Example 5. DETAILED DESCRIPTION

[0024] The calculation method of the degree of coagulation involved in the following embodiments is based on the ratio of the colloidal viscosity of the solution before and after aging; the porosity test method and standard are based on GBT 42697-2023; the dielectric constant test method and standard are based on GBT 31838.6-2021.

[0025] Example 1

[0026] In an ice-water mixture, add 1.0581g 6FODA to 47.5g DMAc solvent, stir to dissolve, then add 1.4419g 6FCDA in equal molar amounts in batches, stir ultrasonically at 40Hz for 7h to form a homogeneous phase, and prepare a PAA solution with a mass concentration of 5%. Stand at room temperature to degas and set aside.

[0027] The PAA solution after degassing was coated on a glass plate with a thickness of 600 microns. It was placed in air with a humidity of 50% for 10 hours, and its surface was milky white with a condensation degree of 40%. It was moved to pure water and replaced for 6 hours. It was taken out and the surface was dried at room temperature, and it was placed in a high-temperature oven for imidization at a heating rate of 3℃ / min (120℃×50min, 200℃×120min), completing the preparation of polyimide aerogel material.

[0028] The PI aerogel obtained in this embodiment has finger-like pores (such as Figure 1 ), with very little thickness and fiber pores, orderly pore distribution and complete structure. The porosity is 63% and the pore size is 36μm. The porous system has a low dielectric constant of 1.93.

[0029] Example 2

[0030] In an ice-water mixture, add 1.8286g of 6FAP to 46g of DMF solvent, stir to dissolve, then add 2.1714g of 6FPMDA in equal molar amounts in batches, and stir at 20Hz for 2h to form a homogeneous phase to obtain a PAA solution with a mass concentration of 8%. Degas by ultrasonic at room temperature and set aside.

[0031] The PAA solution after degassing was coated on a glass plate with a thickness of 500 microns. It was placed in air with a humidity of 65% for 8 hours, and its surface was milky white with a coagulation degree of 55%. It was moved to pure water and replaced for 8 hours. It was taken out and the surface was dried at room temperature, and it was placed in a high-temperature oven for imidization at a heating rate of 1.5℃ / min (85℃×70min, 210℃×90min), completing the preparation of polyimide aerogel material.

[0032] The PI aerogel obtained in this embodiment has finger-like pores (such as Figure 2 ), half of the thickness presents fiber pores, the pores are distributed in an orderly manner, and the structure is complete. The porosity is 64%, and the pore size is 28μm. The porous system has a low dielectric constant of 1.74.

[0033] Example 3

[0034] In an ice-water mixture, add 2.4003g of 6FAPB to 44g of DMF solvent, stir to dissolve, then add 3.5997g of 12FPMDA in equal molar amounts in batches, and stir at 60Hz for 3h to form a homogeneous phase to obtain a PAA solution with a mass concentration of 12%. Stand at room temperature to degas and set aside.

[0035] The PAA solution after degassing was coated on a glass plate with a thickness of 800 microns. It was placed in air with a humidity of 70% for 12 hours, and its surface was milky white with a condensation degree of 75%. It was moved to pure water and replaced for 10 hours. It was taken out and the surface was dried at room temperature, and it was placed in a high-temperature oven for imidization at a heating rate of 0.5℃ / min (100℃×55min, 220℃×70min), completing the preparation of polyimide aerogel material.

[0036] The PI aerogel prepared in this embodiment has finger-like pores (such as Figure 3 ), two-thirds of the thickness presents fiber pores, the pores are distributed in an orderly manner, and the structure is complete. The porosity is 65%, and the pore size is 19μm. The porous system has a low dielectric constant of 1.67.

[0037] Example 4

[0038] In an ice-water mixture, add 2.1468g FA to 45g NMP solvent, stir to dissolve, then add 6FDA in equal molar amounts (2.8532g) in batches, stir ultrasonically at 100Hz for 4h to form a homogeneous phase, and prepare a PAA solution with a mass concentration of 10%. Degas by ultrasonic at room temperature and set aside.

[0039] The PAA solution after degassing was coated on a glass plate with a thickness of 1500 microns. It was placed in air with a humidity of 60% for 18 hours, and its surface was milky white with a coagulation degree of 85%. It was moved to pure water and replaced for 12 hours. It was taken out and the surface was dried at room temperature, and it was placed in a high-temperature oven for imidization at a heating rate of 1°C / min (110°C×65min, 230°C×50min), completing the preparation of polyimide aerogel material.

[0040] The PI aerogel obtained in this embodiment has fiber pores (such as Figure 4 ), the pore structure is complete. The porosity is 66%, and the pore size is 13μm. The porous system has a low dielectric constant of 1.62.

[0041] Example 5

[0042] In an ice-water mixture, add 4.0391g HFBAPP to 42.5g DMAc solvent, stir to dissolve, then add 3.4609g 6FDA in equal molar amounts in batches, stir at 80Hz for 5h to form a homogeneous phase, and prepare a PAA solution with a mass concentration of 15%. Stand at room temperature to degas and set aside.

[0043] The PAA solution after degassing was coated on a glass plate with a thickness of 1000 microns. It was placed in air with a humidity of 80% for 24 hours, and its surface was milky white with a coagulation degree of 95%. It was moved to pure water and replaced for 12 hours. It was taken out and the surface was dried at room temperature, and it was placed in a high-temperature oven for imidization at a heating rate of 2°C / min (100°C×60min, 240°C×60min), completing the preparation of polyimide aerogel material.

[0044] The PI aerogel obtained in this embodiment has fiber pores (such as Figure 5 ), the pores are orderly distributed and the structure is complete. The porosity is 67% and the pore size is 6μm. The porous system has a low dielectric constant of 1.58.

Claims

1. A method for preparing a polyimide aerogel material, the specific steps of which are as follows: (1) preparing a polyamic acid solution, obtaining a PAA solution with a solid content of 5% to 15%, and degassing; (2) Preparation of polyimide aerogel: The PAA solution after degassing is coated on a substrate with a certain thickness, and is placed in the air for aging. When the surface shows a certain degree of condensation, it is immersed in pure water and replaced for a certain period of time. The surface is dried and placed in a high-temperature oven for dehydration and cyclization to obtain a polyimide aerogel material.

2. The method according to claim 1, characterized in that The degassing is static degassing or ultrasonic degassing.

3. The method according to claim 1, characterized in that The coating thickness in step (2) is 500-1500 microns; the air humidity is 50%-80%, the aging time is 8-24h; the degree of coagulation is preferably 40%-95%; and the replacement time is 6-12h.

4. The method according to claim 1, characterized in that In step (2), the temperature in the high temperature oven is gradually increased at a rate of 0.5-3°C / min, the temperature is increased to 85-120°C and kept constant for 50-70min, and the temperature is increased to 200-240°C and kept constant for 50-120min.

5. A polyimide aerogel material prepared by the method according to claims 1 to 4.

6. The polyimide aerogel material according to claim 5, characterized in that The porosity of the polyimide aerogel material is 63% to 67%; the pore diameter is 6 to 36 μm.

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