CN115044204B

CN115044204B - Preparation method of low-dielectric all-organic crosslinked polyimide film

Info

Publication number: CN115044204B
Application number: CN202210676361.2A
Authority: CN
Inventors: 曹贤武; 赵婉婧; 何光建; 黄其隆; 卢翀昊
Original assignee: South China University of Technology SCUT
Current assignee: South China University of Technology SCUT
Priority date: 2022-04-24
Filing date: 2022-06-15
Publication date: 2023-02-14
Anticipated expiration: 2042-06-15
Also published as: CN115044204A; CN114685993A

Abstract

The invention discloses a preparation method of a low-dielectric all-organic crosslinked polyimide film. Firstly, synthesizing a covalent organic framework, then modifying the surface of a COFs pore canal with a polyamino functional group, finally inserting the COFs filler with the surface modified with the polyamino functional group into a PI molecular chain, and constructing a cross-linking structure by taking the COFs as a cross-linking point. The COFs can control air to be uniformly dispersed in the PI matrix in a nanometer size, controllability on the size and the dispersion of material holes is high, ultralow dielectric constant and excellent mechanical performance can be achieved, meanwhile, the COFs also improves the thermal conductivity of polyimide, and the problem of heat dissipation of interlayer insulating materials is solved. And the cross-linked structure is beneficial to reducing the thermal expansion coefficient and ensuring the reliability of the device. The invention is expected to produce large-area high-quality low dielectric interlayer insulating dielectric film with outstanding dielectric property, stable comprehensive property and easy use, and promotes the development and application of interlayer insulating dielectric manufacturing technology.

Description

Preparation method of low-dielectric all-organic crosslinked polyimide film

Technical Field

The invention relates to the field of polymer low-dielectric materials, in particular to a preparation method of a low-dielectric all-organic crosslinked polyimide film.

Background

Integration of first blocks since 1985Since the birth of the circuit, the development of the integrated circuit chip basically follows the moore law, the integration level of the integrated circuit is increased by 1 time every 18 months, and the characteristic size is the original one

When the size of the electronic components is reduced to a certain size, the resistance-capacitance effect between the wirings is stronger and stronger, the mutual influence between the currents of the wires is increased, and the problems of signal lag, loss, crosstalk, energy loss and the like are caused and become key factors for limiting the development of the integrated circuit. The following equation clearly describes the relationship between circuit integrity and delay phenomena:

wherein τ is a delay time of the transmission signal; c is a material capacitor; ρ is the wire specific impedance; epsilon is the dielectric constant of the interlayer insulating dielectric material; epsilon ₀ Is a vacuum dielectric constant; l is the length of the wire; t is the wire thickness; and D is the distance between two wires. It can be seen from the formula that the parasitic capacitance can be minimized by lowering the dielectric constant of the interlayer insulating dielectric, thereby reducing signal delay, loss, cross talk, energy loss and allowing higher signal speed and higher efficiency. Therefore, in order to better meet the requirement of high-frequency and high-speed transmission of 5G signals and the rapid development of the microelectronic industry, the development of interlayer insulating dielectric materials with ultra-low dielectric constants is urgent.

The conventional interlayer insulating dielectric material is generally inorganic material such as silicon oxide, silicon nitride and the like, and the inorganic material has the disadvantages of high dielectric constant, poor machinability, hydrophobicity and the like. Compared with inorganic low-dielectric materials, organic polymer materials generally have the advantages of lower dielectric constant, excellent mechanical properties, good hydrophobicity and the like, and are widely researched and applied. Polyimide (PI) is a special engineering plastic with the highest heat-resistant grade, has good thermal stability and low hygroscopicity, has good cohesiveness with different base materials and reaction inertness with a metal conductor at high temperature, and is an ideal material for interlayer insulation. However, polyimides have not been adequate for the requirements of the microelectronics industry and 5G development, including the requirement that the dielectric constant be as low as possible; low dielectric loss and high breakdown field strength are satisfied in electrical characteristics; the mechanical properties need to meet high and low stress and high hardness; in terms of thermal performance, the material needs to have good thermal stability, low thermal expansion coefficient and high thermal conductivity; the chemical properties of the coating are corrosion resistance, good hydrophobicity and the like. However, for interlayer insulating dielectrics, these properties tend to cancel each other out and mutually dominate. Therefore, the development of the ultralow dielectric PI interlayer insulating material with excellent comprehensive performance has very important scientific significance and application prospect, and is one of the key technologies for 5G application and microelectronic product development.

Polyimide (PI) is a high-performance polymer material obtained by condensation reaction of dibasic anhydride and diamine, and the molecular chain of the Polyimide (PI) is composed of repeat units containing imide rings. Because the monomer structure for synthesizing polyimide is various, polyimide can be classified into three major groups according to its chemical structure: aliphatic polyimides, semi-aliphatic polyimides and aromatic polyimides. Aromatic polyimides have higher heat resistance, mechanical strength and chemical stability than the other two, and thus are more widely used. However, with the advent of the 5G era and the rapid development of the microelectronics industry, the development of PI is severely limited by mainly three problems: firstly, the dielectric constant of common polyimide is generally about 3-3.6, which is far away from the requirement of 2010 International Technology Roadmap (ITRS) on the dielectric constant of a future interlayer insulating medium to reach 2.0; secondly, the polyimide has larger thermal resistance due to the disordered form, so that the heat dissipation in the high-power-density chip becomes complicated; third, reliability issues remain one of the great challenges facing microelectronic device packaging materials. The mismatch in Coefficient of Thermal Expansion (CTE) of PI with other materials results in large residual stress of PI after high temperature curing, which can lead to warpage of thin wafers, and the interface of PI with the substrate can crack or even break away. Therefore, the development of the ultralow dielectric PI interlayer insulating material with excellent comprehensive performance to solve the problems has very important scientific significance and application prospect.

In recent years, low dielectric nanoporous materials have attracted much attention from the scientific community due to their excellent properties of low dielectric constant, high porosity, very large specific surface area, low density, light weight, high specific strength, and the like. The low-dielectric nano porous material can not only introduce air into the PI matrix as much as possible, but also obtain good comprehensive properties such as thermal property, mechanical property and the like. Kurinchyselvan et al added amine-modified mesoporous silica (FMCM-41) to a polyimide matrix and found that the lowest dielectric constant value of 2.21 was achieved at 1MHz at 7wt% FMCM-41 loading, but above 10wt% loading, the dielectric constant increased due to agglomeration of the mesoporous silica nanoparticles in the PI matrix. However, since the inorganic nanofiller has high surface energy and poor compatibility with polymers, it is difficult to manufacture a dielectric thin film having a large area and uniform high quality. ( Kurinchyselvan S, sasikumar R, ariraman M, gomathipriya P, alagor M.Low dielectric waveguide of amine functional MCM-41reinformed polyimide nanocomposites 2016. High Performance Polym 2016;28:842-53. )

Disclosure of Invention

In view of the problems of high dielectric constant, high thermal expansion coefficient, high thermal resistance and the like of the polyimide interlayer insulating material in the prior art, the invention aims to provide a preparation method of a full organic crosslinked polyimide film with low dielectric constant, low thermal expansion coefficient and high thermal conductivity. The method can obtain the all-organic low dielectric crosslinked polyimide film.

The technical scheme of the invention is as follows:

a preparation method of a low-dielectric all-organic crosslinked polyimide film comprises the following steps:

(1) Synthesis and modification of organic framework material COF:

1,3, 5-trimethylacylbenzene and 1, 4-diaminobenzene were weighed in an ampoule and dissolved in 1, 4-dioxane, an aqueous acetic acid solution was added, it was frozen in liquid nitrogen, and then vacuum was applied; then putting the ampoule into an oven at 120-122 ℃ for 70-72 hours to obtain COF yellow solid; washing the obtained COF with N, N-dimethylformamide and tetrahydrofuran, and vacuum drying at 78-80 deg.C for 11-12 hr; then, modifying COF by using polyamino cage-like silsesquioxane, and grafting polyamino cage-like silsesquioxane POSS on the surface of the COF to obtain a modified COF @ POSS filler;

(2) Preparation of polyamic acid solution:

adding an aromatic dianhydride monomer and a diamine monomer into an organic solvent under a protective atmosphere to form a mixed solution, stirring the mixed solution to dissolve the dianhydride monomer and the diamine monomer in the organic solvent, and then fully reacting in an ice-water bath to polymerize to generate a polyamic acid solution;

(3) Preparation of COF @ POSS/PI film:

adding COF @ POSS with different mass fractions into a polyamic acid solution under a protective atmosphere and an ice-water bath, and continuously stirring for 1-2h; and then coating the mixed solution on a glass plate, and carrying out thermal imidization to obtain the COF @ POSS/polyimide low-dielectric all-organic crosslinked composite material, namely the low-dielectric all-organic crosslinked polyimide film.

Further, the proportion of the total mole number of diamine monomers to the total mole number of dianhydride monomers in the step (2) is 1-1; the polyamic acid solution is a tetrapolymer.

Further, in the step (2), the protective atmosphere is nitrogen, and the organic solvent is one of N-methylpyrrolidone, N-dimethylacetamide and N, N-dimethylformamide.

Further, the diamine monomer of step (2) comprises: 4,4 '-diamino-2, 2' -bistrifluoromethylbiphenyl, 9 '-bis (4-aminophenyl) fluorene, 4' -diaminodiphenyl ether, 1, 3-bis (4-aminophenoxybenzene).

Further, the dianhydride monomer of step (2) comprises: 3,3',4' -benzophenone tetracarboxylic dianhydride, 3',4,4' -diphenylether tetracarboxylic dianhydride, 2 '-bis [4- (3, 4-dicarboxyphenoxy) phenyl ] propane tetracarboxylic dianhydride, 2' -bis (3, 4-dicarboxyphenyl) hexafluoropropane tetracarboxylic dianhydride, 2, 3',4' -biphenyl tetracarboxylic dianhydride and 3,3',4' -biphenyl tetracarboxylic dianhydride.

Further, in the step (3), the mass fractions of the added COF @ POSS are 2wt%,5wt%,8wt% and 10wt%.

Further, in the step (3), the thermal imidization procedure is 80 ℃/2h;100 ℃/1h;150 ℃/1h;200 ℃/1h;250 ℃/1h;300 ℃/1h.

Further, the thickness of the polyimide film obtained in the step (3) is controlled to be 20-40 μm.

Further, the preparation method of the modified COF @ POSS filler in the step (1) comprises the following steps:

(a) Silane coupling agent pretreatment COF: and (3) dispersing COF in ethanol, and carrying out ultrasonic treatment for 1-1.5h. Then gradually dropwise adding a silane coupling agent into the mixed solution, refluxing for 3.5-4 hours at 83-85 ℃, then aging for one night, washing twice, filtering and drying to obtain COF pretreated by the silane coupling agent;

(b) Preparation of COF @ POSS: mixing COF pretreated by a silane coupling agent and poly-amino cage-like silsesquioxane POSS in tetrahydrofuran; and (3) keeping the mixture stirred and refluxing for 3.5-4 hours at 68-70 ℃, filtering the obtained COF @ POSS, washing with THF and DI water respectively, and drying the obtained powder for 11-12 hours under vacuum to obtain the modified COF @ POSS filler which can be used without further purification.

Further, the silane coupling agent in the step (a) is one of diethoxy (3-glycidyloxypropyl) methylsilane, 3-glycidyloxypropyl trimethoxysilane and triethoxy (3-glycidyloxypropyl) silane.

Further, the polyamino cage-like silsesquioxane POSS in the step (b) is one of tetraamino POSS and octamino POSS.

According to the preparation method of the polyimide film, the COFs can control air to be uniformly dispersed in the PI substrate in a nanometer size, controllability on the size and the dispersion of material holes is strong, the ultralow dielectric constant and the excellent mechanical property can be realized, meanwhile, the COFs also improve the thermal conductivity of the polyimide, and the problem of heat dissipation of the interlayer insulating material is solved. And the cross-linked structure is beneficial to reducing the thermal expansion coefficient and ensuring the reliability of the device.

Compared with the prior art, the invention has the following advantages and beneficial effects:

hair brushObviously, the low-dielectric full-organic crosslinked polyimide film with a compact and flat surface is integrally formed under the condition of not adding an additional process; the polyimide film prepared by the present invention has uniform filler distribution and good compatibility with the substrate, and in the typical embodiment of the present invention, the PI film with the load of 10wt% COF @ POSS-4 can reach the lowest dielectric constant of 1.8 (1 MHz) and good thermal conductivity (2.43 Wm) ^-1 ·K ^-1 ) And a low coefficient of thermal expansion (20 ppm/K). The invention is expected to produce large-area high-quality low dielectric interlayer insulating dielectric film with outstanding dielectric property, stable comprehensive property and easy use, and promotes the development and application of interlayer insulating dielectric manufacturing technology.

Drawings

FIG. 1 is a graph showing the change of dielectric constant with frequency of PI composite films with different content of COF @ POSS-4 after modifying COF with tetraamino POSS in example 1.

FIG. 2 is a graph showing the change of thermal expansion coefficient and thermal conductivity of PI composite films with filler content after the modification of COF by tetraamino POSS in example 1.

FIG. 3 is a graph of the thermal expansion coefficient and thermal conductivity of PI composite films after modifying COF with octamino POSS in example 2 as a function of filler content.

FIG. 4 is an SEM picture of the COF powder obtained in example 3 and a sectional SEM picture of 8wt% COF @ POSS-8/PI composite.

Detailed Description

Example 1

(1) Preparation and modification of COF:

1.5mmol of 1,3, 5-trimethylacylbenzene and 1.5mmol of 1, 4-diaminobenzene were weighed out in an ampoule and dissolved in 3mL of 1, 4-dioxane. 0.6mL of aqueous acetic acid was added to the mixture, which was frozen in liquid nitrogen and then evacuated. The ampoule was then placed in an oven at 122 ℃ for 70 hours to give a yellow solid of COF. The resulting COF was washed with N, N-dimethylformamide and tetrahydrofuran and dried under vacuum at 78 ℃ for 12 hours for use.

The COF was then pretreated with diethoxy (3-glycidyloxypropyl) methylsilane, 0.2g of the COF was dispersed in ethanol and sonicated for 1h. Subsequently, 0.2mL of diethoxy (3-glycidyloxypropyl) methylsilane was added dropwise to the mixed solution, refluxed at 83 ℃ for 3.5 hours, aged for 12 hours, washed with water twice, filtered and dried to obtain a COF after pretreatment of diethoxy (3-glycidyloxypropyl) methylsilane.

Finally, the diethoxy (3-glycidyloxypropyl) methylsilane pretreated COF and tetraamino POSS were mixed in tetrahydrofuran. The mixture was kept under stirring and refluxed at 70 ℃ for 3.5 hours. The obtained COF @ POSS-4 was filtered and washed with THF and DI water, respectively. The resulting powder was dried under vacuum for 12 hours and used without further purification.

(2) Preparation of polyamic acid (PAA) solution:

diamine monomer was added under nitrogen and ice water bath: 3mmol of 4,4' -diamino-2, 2' -bistrifluoromethylbiphenyl, 3mmol of 9,9' -bis (4-aminophenyl) fluorene, then 15mL of N, N-dimethylacetamide was added to dissolve it completely, and a dianhydride monomer was added: 3,3',4' -benzophenone tetracarboxylic dianhydride, 3mmol 3,3',4' -diphenyl ether tetracarboxylic dianhydride, then 15mL N, N-dimethylacetamide is added, and the mixture is stirred and reacted for 5 hours to obtain the PAA solution.

(3) Preparing a COF @ POSS-4/PI film:

adding 0,2wt%,5wt%,8wt% and 10wt% of COF @ POSS-4 into PAA solution, continuously stirring and reacting for 1h, removing bubbles from the obtained COF @ POSS-4/PAA mixed solution in a vacuum oven, coating the mixed solution on a glass plate by using a scraper, and putting the glass plate in the oven for thermal imidization. The thermal imidization process is as follows: 80 ℃/2h,100 ℃/1h,150 ℃/1h,200 ℃/1h,250 ℃/1h and 300 ℃/1h, and finally obtaining the COF @ POSS-4/PI low-dielectric all-organic crosslinked composite film with different filler loading amounts.

The PI composite film prepared in example 1 was cut into small wafers, and the change of the dielectric constant of the porous PI film with the loading of the filler was tested by an impedance analyzer, and a graph of the change of the dielectric constant of the PI composite films with different contents of cof @ poss-4 with frequency is shown in fig. 1. It can be seen that the dielectric constant of the PI composite film decreases with increasing COF @ POSS-4 content, and the lowest dielectric constant of 1.8 (1 MHz) can be achieved with 10wt% loading of the PI film.

The PI composite film prepared in example 1 was measured for thermal conductivity of the composite material by Hot Disk TPS 2500S tester at 25 ℃ and the coefficient of thermal expansion of the material was measured by thermo-mechanical analysis in tensile mode at room temperature. From FIG. 2 it is clear that the thermal conductivity of the material increases with increasing filler loading, while the coefficient of thermal expansion decreases with increasing loading, with 10wt% loading of PI film reaching the highest thermal conductivity (2.43 Wm) ^-1 ·K ^-1 ) And the lowest coefficient of thermal expansion (20 ppm/K).

Example 2

(1) Preparation and modification of COF:

1.5mmol of 1,3, 5-trimethylacylbenzene and 1.5mmol of 1, 4-diaminobenzene were weighed out in an ampoule and dissolved in 3mL of 1, 4-dioxane. 0.6mL of aqueous acetic acid was added to the mixture, which was frozen in liquid nitrogen and then evacuated. The ampoule was then placed in an oven at 120 ℃ for 72 hours to give a yellow solid of COF. The resulting COF was washed with N, N-dimethylformamide and tetrahydrofuran, and dried under vacuum at 80 ℃ for 11 hours for use.

The COF was then pretreated with 3-glycidoxypropyltrimethoxysilane, 0.2g of COF was dispersed in ethanol and sonicated for 1.5h. Then 0.2mL of diethoxy (3-glycidyloxypropyl) methylsilane was added dropwise to the mixed solution, refluxed at 83 ℃ for 4 hours, aged for 12 hours, washed twice with water, filtered and dried to obtain COF after pretreatment of 3-glycidyloxypropyltrimethoxysilane.

Finally, the COF and the octamino POSS after the pretreatment of 3-glycidyloxypropyltrimethoxysilane are mixed in tetrahydrofuran. The mixture was kept under stirring and refluxed at 70 ℃ for 4 hours. The obtained COF @ POSS-8 was filtered and washed with THF and DI water, respectively. The resulting powder was dried under vacuum for 11 hours and used without further purification.

(2) Preparation of Polyamic acid (PAA):

diamine monomer was added under nitrogen and ice water bath: 3mmol of 4,4' -diaminodiphenyl ether and 3mmol of 1, 3-bis (4-aminophenoxybenzene), then 15mL of N-methylpyrrolidone is added until the mixture is completely dissolved, and then dianhydride monomer: 3mmol of 2, 2-bis [4- (3, 4-dicarboxyphenoxy) phenyl ] propane tetracarboxylic dianhydride, 3mmol of 2, 2-bis (3, 4-dicarboxyphenyl) hexafluoropropane tetracarboxylic dianhydride, and then 15mL of N-methylpyrrolidone are added, and the mixture is stirred and reacted for 5 hours to obtain a PAA solution.

(3) Preparation of COF @ POSS-8/PI film:

adding 0,2wt%,5wt%,8wt% and 10wt% of COF @ POSS-8 into PAA solution, continuously stirring for reaction for 1h, removing bubbles from the obtained COF @ POSS-8/PAA mixed solution in a vacuum oven, coating the mixed solution on a glass plate by using a scraper, and putting the glass plate in the oven for thermal imidization. The thermal imidization process comprises the following steps: 80 ℃/2h,100 ℃/1h,150 ℃/1h,200 ℃/1h,250 ℃/1h,300 ℃/1h, and finally obtaining the COF @ POSS-8/PI low-dielectric all-organic crosslinked composite film.

The PI composite film prepared in example 2 was measured for thermal conductivity of the composite material by Hot Disk TPS 2500S tester at 25 ℃ and the coefficient of thermal expansion of the material was measured by thermo-mechanical analysis in tensile mode at room temperature. From FIG. 3, it is clear that the thermal conductivity of the material increases with increasing filler loading, while the coefficient of thermal expansion decreases with increasing loading, with the highest thermal conductivity (2.68 Wm) being achieved for 10wt% loading of PI film, respectively (2.68 Wm) ^-1 ·K ^-1 ) And the lowest coefficient of thermal expansion (18 ppm/K).

Example 3

(1) Preparation and modification of COF:

1.5mmol of 1,3, 5-trimethylacylbenzene and 1.5mmol of 1, 4-diaminobenzene were weighed out in an ampoule and dissolved in 3mL of 1, 4-dioxane. 0.6mL of aqueous acetic acid was added to the mixture, which was frozen in liquid nitrogen and then evacuated. The ampoule was then placed in an oven at 121 ℃ for 71 hours to give a yellow solid of COF. The resulting COF was washed with N, N-dimethylformamide and tetrahydrofuran, and dried under vacuum at 79 ℃ for 12 hours for use.

The COF was then pretreated with triethoxy (3-epoxypropyloxypropyl) silane, 0.2g of COF was dispersed in ethanol and sonicated for 1h. And then, 0.2mL of triethoxy (3-epoxypropyloxypropyl) silane is dropwise added into the mixed solution, refluxing is carried out for 4 hours at 84 ℃, aging is carried out for 12 hours, washing is carried out twice, and filtering and drying are carried out to obtain COF (COF) pretreated by triethoxy (3-epoxypropyloxypropyl) silane.

Finally, the COF pretreated by triethoxy (3-epoxypropyloxypropyl) silane and the octa-amino POSS are mixed in tetrahydrofuran. The mixture was kept under stirring and refluxed at 69 ℃ for 3.5 hours. The resulting COF @ POSS-8 was filtered and washed with THF and DI water, respectively. The resulting powder was dried under vacuum for 12 hours and used without further purification.

(2) Preparation of Polyamic acid (PAA):

under nitrogen and in an ice-water bath, adding 3mmol of diamine monomer of 4,4' -diaminodiphenyl ether and 3mmol of 1, 3-bis (4-aminophenoxybenzene), adding 15mL of N-methylpyrrolidone until the diamine monomer is completely dissolved, and adding dianhydride monomer: 3mmol of 2, 3',4' -biphenyl tetracarboxylic dianhydride, 3mmol of 3,3',4' -biphenyl tetracarboxylic dianhydride, and then 15mL of N-methylpyrrolidone are added, and the mixture is stirred and reacted for 5 hours to obtain the PAA solution.

(3) Preparation of COF @ POSS-8/PI film

Adding 0,2wt%,5wt%,8wt% and 10wt% of COF @ POSS-8 into PAA solution, continuously stirring for reaction for 1h, removing bubbles from the COF @ POSS-8/PAA mixed solution in a vacuum oven, coating the solution on a glass plate by using a scraper, and putting the glass plate in the oven for thermal imidization. The thermal imidization process is as follows: 80 ℃/2h,100 ℃/1h,150 ℃/1h,200 ℃/1h,250 ℃/1h,300 ℃/1h, and finally obtaining the COF @ POSS-8/PI low-dielectric all-organic crosslinked composite film.

Brittle fracture surfaces of the COF powder and the COF @ POSS-8/PI composite material obtained in example 3 were observed and analyzed by a Scanning Electron Microscope (SEM). SEM image of COF powder as shown in (a) of fig. 4, agglomerated spheres of different sizes of nanometer order size can be seen, which is important for lowering the dielectric constant because a large number of voids can be maintained therebetween. SEM image of 8wt% COF @ POSS-8/PI composite As shown in (b) of FIG. 4, it was found that the filler was uniformly dispersed in the PI matrix even at a high loading amount of 8 wt%. The polyimide film prepared by the invention has the characteristics of uniform filler distribution and good compatibility with a matrix.

Claims

1. A preparation method of a low-dielectric all-organic crosslinked polyimide film is characterized by comprising the following steps:

(1) Synthesis and modification of organic framework material COF:

1,3, 5-trimethylacylbenzene and 1, 4-diaminobenzene were weighed in an ampoule and dissolved in 1, 4-dioxane, an aqueous acetic acid solution was added, it was frozen in liquid nitrogen, and then vacuum was applied; then putting the ampoule into an oven for drying, washing the obtained organic framework material COF, and drying in vacuum for later use; then, modifying COF by using polyamino cage-like silsesquioxane, and grafting polyamino cage-like silsesquioxane POSS on the surface of the COF to obtain a modified COF @ POSS filler;

(2) Preparation of polyamic acid solution:

adding an aromatic dianhydride monomer and a diamine monomer into an organic solvent under a protective atmosphere to form a mixed solution, stirring the mixed solution to dissolve the dianhydride monomer and the diamine monomer in the organic solvent, fully reacting in an ice-water bath, and polymerizing to generate a polyamic acid solution;

(3) Preparation of COF @ POSS/PI film:

adding COF @ POSS with different mass fractions into the polyamic acid solution under the protection atmosphere and ice-water bath, and continuously stirring; and then coating the mixed solution on a glass plate, and carrying out thermal imidization to obtain the COF @ POSS/PI low-dielectric all-organic crosslinked composite material, namely the low-dielectric all-organic crosslinked polyimide film.

2. The preparation method of the low dielectric all-organic crosslinked polyimide film according to claim 1, wherein the preparation method of the modified COF @ POSS filler in the step (1) comprises the following steps:

(a) Silane coupling agent pretreatment COF: dispersing COF in ethanol, and carrying out ultrasonic treatment; then, dropwise adding a silane coupling agent into the mixed solution for refluxing, and obtaining COF (chip on film) pretreated by the silane coupling agent through aging, washing, filtering and drying;

(b) Preparation of COF @ POSS: mixing COF pretreated by a silane coupling agent and poly-amino polyhedral oligomeric silsesquioxane POSS in tetrahydrofuran, and keeping stirring and refluxing the mixture; and filtering the obtained COF @ POSS, washing with THF (tetrahydrofuran) and DI (DI) water respectively, and drying the obtained powder in vacuum to obtain the modified COF @ POSS filler.

3. The method as claimed in claim 2, wherein the silane coupling agent in step (a) is one of diethoxy (3-glycidoxypropyl) methylsilane, 3-glycidoxypropyltrimethoxysilane, and triethoxy (3-glycidoxypropyl) silane; and (b) the polyamino cage-like silsesquioxane POSS is one of tetraamino POSS and octamino POSS.

4. The method for preparing a low dielectric all-organic crosslinked polyimide film according to claim 2, wherein the time of the ultrasonic treatment in the step (a) is 1-1.5h; the reflux temperature in the step (a) is 83-85 ℃, and the time is 3.5-4 hours; the reflux temperature in the step (b) is 68-70 ℃, and the time is 3.5-4 hours; the vacuum drying time of the step (b) is 11 to 12 hours.

5. The method for preparing a low dielectric all-organic crosslinked polyimide film according to claim 1, wherein the drying temperature in the oven in step (1) is 120-122 ℃ for 70-72 hours; the temperature of the vacuum drying in the step (1) is 78-80 ℃, and the time is 11-12 hours; and (4) the continuous stirring time in the step (3) is 1-2h.

6. The method for preparing a low dielectric all-organic crosslinked polyimide film according to claim 1, wherein in the step (2), the protective atmosphere is nitrogen, and the organic solution is one of N-methylpyrrolidone, N-dimethylacetamide and N, N-dimethylformamide; the proportion of the total mole number of the diamine monomer to the total mole number of the dianhydride monomer in the step (2) is 1-1; and (3) the polyamic acid solution in the step (2) is a quadripolymer.

7. The method for preparing a low dielectric all-organic crosslinked polyimide film according to claim 1, wherein the diamine monomer of step (2) comprises: 4,4 '-diamino-2, 2' -bistrifluoromethylbiphenyl, 9 '-bis (4-aminophenyl) fluorene, 4' -diaminodiphenyl ether, 1, 3-bis (4-aminophenoxybenzene).

8. The method for preparing a low dielectric all-organic crosslinked polyimide film according to claim 1, wherein the dianhydride monomer of step (2) comprises: 3,3',4' -benzophenone tetracarboxylic dianhydride, 3',4,4' -diphenylether tetracarboxylic dianhydride, 2' -bis [4- (3, 4-dicarboxyphenoxy) phenyl ] propane tetracarboxylic dianhydride, 2-bis (3, 4-dicarboxyphenyl) hexafluoropropane tetracarboxylic dianhydride, 2, 3',4' -biphenyl tetracarboxylic dianhydride and 3,3',4' -biphenyl tetracarboxylic dianhydride.

9. The preparation method of the low dielectric all-organic crosslinked polyimide film according to claim 1, wherein the mass fraction of the cof @ poss added in the step (3) is 2wt%,5wt%,8wt%,10wt%.

10. The method for preparing a low dielectric full organic crosslinked polyimide film according to any one of claims 1-9, wherein the heating procedure of the thermal imidization in step (3) is 80 ℃/2h;100 ℃/1h;150 ℃/1h;200 ℃/1h;250 ℃/1h;300 ℃/1h; and (4) controlling the thickness of the polyimide film obtained in the step (3) to be 20-40 mu m.