A flexible printed circuit board containing a low dielectric constant high light transmittance polyimide material

Abstract

The application provides a preparation method of a flexible printed circuit board containing a low-dielectric-constant high-transmittance polyimide material. The method mainly synthesizes a novel fluorine-containing dianhydride monomer 5-(4-(2-(4-(1,3-dioxyl-1,3-dihydroisobenzofuran-5-yl)-3-(trifluoromethyl)cyclohex-3-en-1-yl)-9,9'-spirobifluorene-7-yl)-2-(trifluoromethyl)phenyl)isobenzofuran-1,3-dione, and the monomer is used to synthesize a polyimide for modifying the performance of the polyimide. Due to the presence of the bulky fluorine-containing group, the dielectric constant of the material is greatly reduced. Meanwhile, the fluorine element has high electronegativity, can inhibit the formation of charge transfer complexes, and makes the obtained material have excellent optical transmittance. The material is used to prepare a flexible printed circuit board, the dielectric constant and dielectric loss of the flexible printed circuit board are low, and the flexible printed circuit board can be used in the field of high-frequency high-speed communication.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of material modification, in particular to a preparation of a flexible circuit board containing a low dielectric constant and high light transmittance polyimide. BACKGROUND

[0002] Flexible printed circuit board is a kind of printed circuit board with high reliability and excellent flexibility, which is made of polyimide, polyester or polynaphthalene film as insulating layer and copper foil as conductor layer. It has the characteristics of high wiring density, light weight, thin thickness and good bending property. Compared with the other two commonly used insulating substrates of polyester film and polynaphthalene film, polyimide (PI) film has the characteristics of high strength, good toughness and excellent heat resistance, and can withstand 500℃ high temperature in a short time and can be used at 300℃ for a long time. Therefore, the polyimide material used in printed circuit board is the focus of research, development and application in the field of printed circuit board. At present, more than 90% of high-performance flexible copper-clad plate uses polyimide as heat-resistant base film.

[0003] Polyimide refers to a class of polymers containing imide rings in the main chain. Due to its excellent comprehensive performance, it has been widely used in aviation, aerospace, machinery, electronic devices and many other fields. With the rapid development of science and technology, there are higher requirements for the performance of polyimide materials. In particular, in the past two years, 5G technology has developed rapidly. In order to meet the characteristics of high frequency and high speed in 5G field, the performance requirements of high frequency printed circuit board substrate are increasing day by day, among which the dielectric properties of insulating materials need to be further improved. By introducing fluorine element with large volume and low electronic polarizability, the dielectric constant and dielectric loss of polyimide material can be reduced (dielectric constant less than 3.0, dielectric loss factor less than 0.001), which meets the requirements of high frequency and high speed of 5G communication. In addition, flexible OLED display as a new generation of display technology has attracted widespread attention from all walks of life, and there are higher requirements for its light transmittance. Due to the existence of charge transfer complex in polyimide, charge transfer complex is generated, which absorbs light and makes traditional polyimide film present brown or yellow color. By introducing fluorine element with high electronegativity, the formation of charge transfer complex can be inhibited, which greatly improves the light transmittance of polyimide film and meets the requirements for flexible OLED display. Therefore, it is of great significance to develop polyimide material with low dielectric property and high light transmittance and prepare the corresponding flexible printed circuit board. SUMMARY

[0004] In view of the increasing requirements for materials in the fields of high-frequency high-speed communication and flexible OLED display, the application provides a preparation method of a flexible printed circuit board containing a low-dielectric-constant high-transmittance polyimide material. The researchers of the project find that the purpose of the application can be achieved by using the following preparation method: a novel fluorine-containing dianhydride monomer 5-(4-(2-(4-(1,3-dioxo-1,3-dihydroisobenzofuran-5-yl)-3-(trifluoromethyl)cyclohex-3-en-1-yl)-9,9'-spirobifluorene-7-yl)-2-(trifluoromethyl)phenyl)isobenzofuran-1,3-dione is synthesized from raw materials such as 2,7-dibromo-9,9'-spirobifluorene and 4-bromo-3-(trifluoromethyl)phenylboronic acid, and the water is removed by drying treatment. The dried diamine monomer is dissolved in a polar aprotic solution at room temperature. After complete dissolution, the ice water bath is adjusted to 5-10 DEG C, and 5-(4-(2-(4-(1,3-dioxo-1,3-dihydroisobenzofuran-5-yl)-3-(trifluoromethyl)cyclohex-3-en-1-yl)-9,9'-spirobifluorene-7-yl)-2-(trifluoromethyl)phenyl)isobenzofuran-1,3-dione and other dianhydride monomers are added in five times according to the half feeding method. After the last addition is completed, the stirring is continued for 12 hours to obtain a fluorine-containing polyamide acid solution with a certain viscosity. The obtained polyamide acid solution is vacuum defoaming for 0.5 h, and then coated on a glass plate or a steel plate, the thickness is adjusted to about 35 microns, the solvent is removed at 80-150 DEG C, and the imidization treatment is carried out at 180-300 DEG C. After complete imidization, the temperature is lowered to room temperature, and the film is removed by water boiling, so that a polyimide film with low dielectric constant and high transmittance is obtained. The film is dissolved in N-methyl pyrrolidone under the action of ultrasonic waves, uniformly stirred, and a solution with a solid content of 15-20% is formed, and then the solution is coated on the rough surface of a 12-micron-thick electrolytic copper foil, and dried in a vacuum oven at 50-170 DEG C for 1-3 hours, so that the flexible printed circuit board of the application is obtained.

[0005] In the preparation process, the amount of 5-(4-(2-(4-(1,3-dioxo-1,3-dihydroisobenzofuran-5-yl)-3-(trifluoromethyl)cyclohex-3-en-1-yl)-9,9'-spirobifluorene-7-yl)-2-(trifluoromethyl)phenyl)isobenzofuran-1,3-dione is 5%-20% of the total moles of dianhydride monomers, the ratio of the total moles of dianhydride to the total moles of diamine is about 1.02:1, and the solid content (the total mass of dianhydride and diamine monomers accounts for the percentage of the total mass of polyamic acid) is 20%. The polar aprotic solvent used is one of N-methylpyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide. The diamine monomer is one or more of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether, 4,4'-diaminodiphenylmethane, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminobiphenyl, 4,4-(hexafluoroisopropyl)bis(p-phenoxy) diphenylamine, 4,4'-diaminophenyl ether, and p-phenylenediamine. The other dianhydride monomer is one or more of 4,4'-hexafluoroisopropyl phthalic anhydride, 2,3,3',4-biphenyl tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, pyromellitic dianhydride, and 3,3',4,4'-biphenyl tetracarboxylic dianhydride.

[0006] The beneficial effects of the present application: due to the presence of fluorine-containing groups in the novel dianhydride monomer synthesized by the present application, the dielectric constant and dielectric loss of the obtained polyimide material and the finally obtained flexible printed circuit board are reduced, which can meet the requirements of 5G high frequency and high speed communication field. At the same time, the monomer contains large side groups and fluorine elements at the same time, which can more effectively inhibit the formation of charge transfer complex through synergistic effect, so that the light transmittance of the obtained polyimide material is greatly improved, which can meet the requirements of flexible OLED display field. And the preparation process of the flexible printed circuit board described in the present application is simple, which greatly reduces the energy consumption and process flow. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 The synthetic route map of the present application. DETAILED DESCRIPTION

[0008] In order to make the technical means, creative features, purposes and effects realized by the present application easy to understand, the present application will be further described below in combination with specific examples.

[0009] Example 1

[0010] The dry treated 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and 4,4'-diaminophenyl ether are dissolved in polar aprotic solution at room temperature with a molar ratio of 5:5. N-methylpyrrolidone is added and the solution is stirred at room temperature for about 0.5 h. After complete dissolution, the ice water bath is adjusted to 5-10°C, and 5-(4-(2-(4-(1,3-dioxo-1,3-dihydroisobenzofuran-5-yl)-3-(trifluoromethyl)cyclohex-3-en-1-yl)-9,9'-spirobifluorene-7-yl)-2-(trifluoromethyl)phenyl)isobenzofuran-1,3-dione and 3,3',4,4'-benzophenonetetracarboxylic dianhydride are added in five portions by half-feeding method with a molar ratio of 2:8. After the last addition is completed, the stirring is continued for 12 hours, and the solid content is controlled at about 20% by solvent to obtain a fluorine-containing polyamide acid solution with certain viscosity. The obtained polyamide acid solution is vacuum defoamed for 0.5 h, then coated on a glass plate, and the wet film thickness is adjusted to about 35 microns. The solvent is removed by heat treatment at 80°C, 120°C and 150°C for 1 h respectively, and the imidization treatment is carried out at 180°C, 210°C, 240°C, 270°C and 300°C for 1 h respectively. After complete imidization, the temperature is lowered to room temperature, and the film is removed by water boiling to obtain the polyimide film with low dielectric constant and high light transmittance according to the present application, with a dry film thickness of 25 microns. The film is cut into pieces and then dissolved in N-methylpyrrolidone again, and stirred uniformly to form a solution with a solid content of 15%. Then the solution is coated on the rough surface of an electrolytic copper foil with a thickness of 12 microns, and dried in a vacuum oven at 50°C, 120°C and 170°C for 1 h respectively to obtain the flexible printed circuit board according to the present application.

[0011] Example 2

[0012] The dry treated 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and 4,4'-diaminophenyl ether are dissolved in polar aprotic solution at room temperature with a molar ratio of 5:5. N-methylpyrrolidone is added and the solution is stirred at room temperature for about 0.5 h. After complete dissolution, the ice water bath is adjusted to 5-10°C, and 5-(4-(2-(4-(1,3-dioxo-1,3-dihydroisobenzofuran-5-yl)-3-(trifluoromethyl)cyclohex-3-en-1-yl)-9,9'-spirobifluorene-7-yl)-2-(trifluoromethyl)phenyl)isobenzofuran-1,3-dione and 3,3',4,4'-benzophenonetetracarboxylic dianhydride are added in five portions by half-feeding method with a molar ratio of 3:7. After the last addition is completed, the stirring is continued for 12 hours, and the solid content is controlled at about 20% by solvent to obtain a fluorine-containing polyamide acid solution with certain viscosity. The obtained polyamide acid solution is vacuum defoamed for 0.5 h, then coated on a glass plate, and the wet film thickness is adjusted to about 35 microns. The solvent is removed by heat treatment at 80°C, 120°C and 150°C for 1 h respectively, and the imidization treatment is carried out at 180°C, 210°C, 240°C, 270°C and 300°C for 1 h respectively. After complete imidization, the temperature is lowered to room temperature, and the film is removed by water boiling to obtain the polyimide film with low dielectric constant and high light transmittance according to the present application, with a dry film thickness of 25 microns. The film is cut into pieces and then dissolved in N-methylpyrrolidone again, and stirred uniformly to form a solution with a solid content of 15%. Then the solution is coated on the rough surface of an electrolytic copper foil with a thickness of 12 microns, and dried in a vacuum oven at 50°C, 150°C and 170°C for 1 h respectively to obtain the flexible printed circuit board according to the present application.

[0013] Example 3

[0014] The dry treated 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and 4,4'-diaminophenyl ether are dissolved in polar aprotic solution at room temperature with a molar ratio of 5:5. N-methylpyrrolidone is added and the solution is stirred at room temperature for about 0.5 h. After complete dissolution, the ice water bath is adjusted to 5-10°C, and 5-(4-(2-(4-(1,3-dioxo-1,3-dihydroisobenzofuran-5-yl)-3-(trifluoromethyl)cyclohex-3-en-1-yl)-9,9'-spirobifluorene-7-yl)-2-(trifluoromethyl)phenyl)isobenzofuran-1,3-dione and 3,3',4,4'-benzophenonetetracarboxylic dianhydride are added in five portions by half-feeding method with a molar ratio of 1:9. After the last addition is completed, the stirring is continued for 12 hours, and the solid content is controlled at about 20% by solvent to obtain a fluorine-containing polyamide acid solution with certain viscosity. The obtained polyamide acid solution is vacuum defoamed for 0.5 h, then coated on a glass plate, and the wet film thickness is adjusted to about 35 microns. The solvent is removed by heat treatment at 80°C, 120°C and 150°C for 1 h respectively, and the imidization treatment is carried out at 180°C, 210°C, 240°C, 270°C and 300°C for 1 h respectively. After complete imidization, the temperature is lowered to room temperature, and the film is removed by water boiling to obtain the polyimide film with low dielectric constant and high light transmittance according to the present application, with a dry film thickness of 25 microns. The film is cut into pieces and then dissolved in N-methylpyrrolidone again, and stirred uniformly to form a solution with a solid content of 20%. Then the solution is coated on the rough surface of an electrolytic copper foil with a thickness of 12 microns, and dried in a vacuum oven at 50°C, 150°C and 170°C for 1 h respectively to obtain the flexible printed circuit board according to the present application.

[0015] Comparative Example 1

[0016] The dry 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and 4,4'-diaminophenyl ether were dissolved in polar aprotic solvent at room temperature with a molar ratio of 5:5. N-methyl pyrrolidone was added and the solution was stirred at room temperature for about 0.5 h. After complete dissolution, the ice water bath was adjusted to 5-10 °C and 3,3',4,4'-benzophenonetetracarboxylic dianhydride was added in five portions by half-feeding method. After the last addition, the stirring was continued for 12 hours and the solid content was controlled at about 20% by solvent to obtain a solution of fluorine-containing polyamide acid with certain viscosity. The polyamide acid solution was vacuum defoaming for 0.5 h, then coated on a glass plate, the wet film thickness was adjusted to about 35 microns, and the solvent was removed by heating at 80 °C, 120 °C and 150 °C for 1 h, respectively, and imidization treatment was carried out at 180 °C, 210 °C, 240 °C, 270 °C and 300 °C for 1 h, respectively. After complete imidization, the temperature was lowered to room temperature, and the film was removed by water boiling to obtain a polyimide film with a dry film thickness of 25 microns. The film was cut and then dissolved in N-methyl pyrrolidone again, stirred uniformly, and a solution with a solid content of 15% was formed. Then the solution was coated on the rough surface of an electrolytic copper foil with a thickness of 12 microns, and dried in a vacuum oven at 50 °C, 120 °C and 170 °C for 1 h, respectively, to obtain a flexible printed circuit board.

[0017] Comparative Example 2

[0018] The dry 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and 4,4'-diaminophenyl ether were dissolved in polar aprotic solvent at room temperature with a molar ratio of 5:5. N-methyl pyrrolidone was added and the solution was stirred at room temperature for about 0.5 h. After complete dissolution, the ice water bath was adjusted to 5-10 °C and 3,3',4,4'-benzophenonetetracarboxylic dianhydride was added in five portions by half-feeding method. After the last addition, the stirring was continued for 12 hours and the solid content was controlled at about 20% by solvent to obtain a solution of fluorine-containing polyamide acid with certain viscosity. The polyamide acid solution was vacuum defoaming for 0.5 h, then coated on a glass plate, the wet film thickness was adjusted to about 35 microns, and the solvent was removed by heating at 80 °C, 120 °C and 150 °C for 1 h, respectively, and imidization treatment was carried out at 180 °C, 210 °C, 240 °C, 270 °C and 300 °C for 1 h, respectively. After complete imidization, the temperature was lowered to room temperature, and the film was removed by water boiling to obtain a polyimide film with a dry film thickness of 25 microns. The film was cut and then dissolved in N-methyl pyrrolidone again, stirred uniformly, and a solution with a solid content of 15% was formed. Then the solution was coated on the rough surface of an electrolytic copper foil with a thickness of 12 microns, and dried in a vacuum oven at 50 °C, 120 °C and 170 °C for 1 h, respectively, to obtain a flexible printed circuit board.

[0019] Comparative Example 3

[0020] The dry treated 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and 4,4'-diaminophenyl ether were dissolved in polar aprotic solvent at room temperature with a molar ratio of 5:5. N-methylpyrrolidone was added and the solution was stirred at room temperature for about 0.5 h. After complete dissolution, the solution was adjusted to 5-10 °C with an ice water bath and 2,3,3',4-biphenyltetracarboxylic dianhydride was added in five equal portions. After the last addition, the solution was stirred for 12 h and the solid content was controlled at about 20% by solvent. A solution of the fluorine-containing polyamic acid with certain viscosity was obtained. The polyamic acid solution was vacuum degassed for 0.5 h and then coated on a glass plate with a wet film thickness of about 35 microns. The solvent was removed by heat treatment at 80 °C, 120 °C and 150 °C for 1 h, respectively. The imidization was carried out at 180 °C, 210 °C, 240 °C, 270 °C and 300 °C for 1 h, respectively. After complete imidization, the temperature was lowered to room temperature and the film was removed from the water bath. A polyimide film with a dry film thickness of 25 microns was obtained. The film was cut into pieces and dissolved again in N-methylpyrrolidone with rapid stirring to form a solution with a solid content of 15%. The solution was then coated on the rough side of a 12 micron thick electrolytic copper foil and dried in a vacuum oven at 50 °C, 120 °C and 170 °C for 0.5 h, respectively. A flexible printed circuit board was obtained.

[0021] The properties of the materials obtained in this example and comparative examples were tested and are shown in the following table:

[0022]

[0023]

Claims

1. A method for preparing a polyimide film with low dielectric constant and high transmittance, characterized in that: The method comprises the following steps: using 2,7-dibromo-9,9'-spirobifluorene and 4-bromo-3-(trifluoromethyl) phenyl boronic acid as raw materials to synthesize fluorine-containing dianhydride monomer 5-(4-(2-(4-(1,3-dioxo-1,3-dihydroisobenzofuran-5-yl)-3-(trifluoromethyl)cyclohex-3-en-1-yl)-9,9'-spirobifluorene-7-yl)-2-(trifluoromethyl)phenyl)isobenzofuran-1,3-dione, and the fluorine-containing dianhydride monomer is dried to remove water, the dried diamine monomer is dissolved in a polar aprotic solution at room temperature, and after complete dissolution, the solution is cooled to 5-10 DEG C in an ice water bath, 5-(4-(2-(4-(1,3-dioxo-1,3-dihydroisobenzofuran-5-yl)-3-(trifluoromethyl)cyclohex-3-en-1-yl)-9,9'-spirobifluorene-7-yl)-2-(trifluoromethyl)phenyl)isobenzofuran-1,3-dione and other dianhydride monomers are added in five portions by half feeding method, after the last addition is completed, the solution is continuously stirred for 12 hours to obtain a fluorine-containing polyamide acid solution with a certain viscosity, the obtained polyamide acid solution is vacuum defoamed for 0.5 h, and then coated on a glass plate or a steel plate, the thickness is adjusted to 35 microns, the solvent is removed at 80-150 DEG C, and imidization treatment is performed at 180-300 DEG C, after complete imidization, the solution is cooled to room temperature, and then boiled in water to remove the film, thereby obtaining a polyimide film with low dielectric constant and high light transmittance.

2. The method of claim 1, wherein the polyimide film has a low dielectric constant and a high light transmittance. The fluorine-containing dianhydride monomer 5-(4-(2-(4-(1,3-dioxo-1,3-dihydroisobenzofuran-5-yl)-3-(trifluoromethyl)cyclohex-3-en-1-yl)-9,9'-spirobifluorene-7-yl)-2-(trifluoromethyl)phenyl)isobenzofuran-1,3-dione used in the formula (1) is synthesized by the following steps: under nitrogen protection, 2,7-dibromo-9,9'-spirobifluorene, 4-bromo-3-(trifluoromethyl)phenylboronic acid, Pd(PPh3)2Cl2 and PPh3 are added to a reaction bottle containing toluene and water, mixed and heated to reflux for 24 hours, after the reaction is completed, the system is cooled, toluene is removed by a rotary evaporator, extracted with dichloromethane, the obtained organic phase is dried with anhydrous sodium sulfate, filtered, rotary dried, and purified by column chromatography with petroleum ether-dichloromethane as the eluent to obtain 2,7-di(4-bromo-3-(trifluoromethyl)phenyl)-9,9'-spirobifluorene with a yield of 84.1%, under nitrogen protection, the obtained 2,7-di(4-bromo-3-(trifluoromethyl)phenyl)-9,9'-spirobifluorene, 3,4-dimethylphenylboronic acid, Pd(PPh3)2Cl2 and PPh3 are added to a reaction bottle containing toluene and water, mixed and heated to reflux for 24 hours, after the reaction is completed, the system is cooled, toluene is removed by a rotary evaporator, extracted with dichloromethane, the obtained organic phase is dried with anhydrous sodium sulfate, filtered, rotary dried, and purified by column chromatography with petroleum ether-dichloromethane as the eluent to obtain 2,7-di(3',4'-dimethyl-2-(trifluoromethyl)-[1,1'-biphenyl]-4-yl)-9,9'-spirobifluorene with a yield of 79.2%, under nitrogen protection, 2,7-di(3',4'-dimethyl-2-(trifluoromethyl)-[1,1'-biphenyl]-4-yl)-9,9'-spirobifluorene and potassium permanganate are added to a dry reaction bottle containing tert-butyl alcohol and water, reacted at 78°C for 3h, after the reaction is completed, 10mL sodium thiosulfate solution is added to the system, after the tert-butyl alcohol is removed by a rotary evaporator, hydrochloric acid is added to make pH=1, extracted with dichloromethane, the obtained organic phase is dried with anhydrous sodium sulfate, filtered, rotary dried, and purified by column chromatography with dichloromethane-methanol as the eluent to obtain 4',4'''-(9,9'-spiro[fluorene]-2,7-diyl)bis(2'-(trifluoromethyl)-[1,1'-biphenyl]-3,4-dicarboxylic acid), under nitrogen protection, 4',4'''-(9,9'-spiro[fluorene]-2,7-diyl)bis(2'-(trifluoromethyl)-[1,1'-biphenyl]-3,4-dicarboxylic acid) is added to a dry reaction bottle containing acetic anhydride, heated to reflux for 3h, after the reaction is completed, the mixture is cooled, filtered and dried to obtain 5-(4-(2-(4-(1,3-dioxo-1,3-dihydroisobenzofuran-5-yl)-3-(trifluoromethyl)cyclohex-3-en-1-yl)-9,9'-spirobifluorene-7-yl)-2-(trifluoromethyl)phenyl)isobenzofuran-1,3-dione.

3. The method of claim 1, wherein the polyimide film has a low dielectric constant and a high light transmittance. The other dianhydride monomers used are one or more of 4,4'-hexafluoroisopropyl phthalic anhydride, 2,3,3',4-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride.

4. The method of claim 1, wherein the polyimide film has a low dielectric constant and a high light transmittance. The polar aprotic solvent used is one of N-methylpyrrolidone, N,N-dimethylacetamide or N,N-dimethylformamide.

5. The method for preparing a polyimide film with low dielectric constant and high transmittance according to claim 1, wherein: The diamine monomers used are one or more of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether, 4,4'-diaminodiphenylmethane, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl, 4,4-(hexafluoroisopropyl)bis(p-phenoxy) diphenylamine, 4,4'-diaminophenyl ether, p-phenylenediamine.

6. The method for preparing a polyimide film with low dielectric constant and high transmittance as claimed in claim 1, wherein: The ratio of the total moles of dianhydride to the total moles of diamine in the polyamic acid solution is 1.02:1, and the total mass of the dianhydride and diamine monomers accounts for 20% of the total mass of the polyamic acid.

7. The method for preparing a polyimide film with low dielectric constant and high transmittance as claimed in claim 1, characterized in that: The fluorine-containing dianhydride monomer 5-(4-(2-(4-(1,3-dioxo-1,3-dihydroisobenzofuran-5-yl)-3-(trifluoromethyl)cyclohex-3-en-1-yl)-9,9'-spirobifluorene-7-yl)-2-(trifluoromethyl)phenyl)isobenzofuran-1,3-dione is used in an amount of 5%-20% of the total moles of dianhydride monomers.

8. A method for manufacturing a flexible printed circuit board using the low dielectric constant and high transmittance polyimide film obtained by the production method according to claim 1, characterized by, by the following steps Composition: the low dielectric constant and high light transmittance polyimide material obtained by the preparation method of claim 1 is dissolved again in N-methylpyrrolidone under ultrasonic action, stirred quickly and uniformly to form a solution with a solid content of 15-20%, and then the solution is coated on the rough surface of an electrolytic copper foil with a thickness of 12 microns, dried in a vacuum oven at 50-170℃ for 1-3 hours to obtain the flexible printed circuit board.

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