CN114763436B - Polyimide film with low dielectric loss - Google Patents

Abstract

This application is a low dielectric loss polyimide film, which is made from copolymerized polyamic acid through a chemical cyclization method, in which the copolymerized polyamic acid must have at least 3,3',4,4'- The composition of biphenyltetracarboxylic dianhydride (BPDA), p-phenylene diamine (p-PDA) and the diamine of the following chemical formula (A): Chemical formula (A): Among them, the number of moles of BPDA must account for more than 60% of the total moles of dianhydride of the copolymerized polyamic acid, and the number of moles of p-PDA must account for more than 50% of the total number of moles of diamine of the copolymerized polyamic acid, and The number of moles of chemical formula (A) must account for more than 30% of the total moles of diamine in the copolymerized polyamic acid; and the polyimide film has a glass transition temperature Tg greater than 280°C and a dielectric loss tangent Df (@ 10GHz) is less than 0.008 and the thermal expansion coefficient CTE is less than 12ppm/℃.

Description

A low dielectric loss polyimide film

Technical field

This application relates to a polyimide film with low dielectric loss, specifically a polyimide film with a diameter of 25 microns or more that is chemically manufactured to have lower dielectric loss and lower linear expansion. Coefficient

Background technique

Polyimide has excellent heat resistance, electrical properties and mechanical strength properties and is designed to have low dielectric loss. Polyimide films are often used in flexible circuit board applications with high-temperature processes, and Recently, more designs are used in 5G high-frequency and high-speed application originals. In addition, the currently well-known compounds are composed of 1,2,4,5-pyromellitic anhydride (PMDA) and phenylenediamine (PDA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and Polyimide composed of p-phenylenediamine (PDA). Among them, although PMDA/PDA has excellent thermal properties, its film is very brittle and has poor mechanical and electrical properties. BPDA/PDA not only has excellent heat resistance, but also has excellent mechanical properties and dimensional stability. Therefore, it is preferably used in applications such as flexible printed circuit boards, protective films for semiconductor components, and interlayer insulating films for integrated circuits that require these characteristics. However, its high dielectric loss is not suitable for 5G high-frequency materials. . In addition, because it is rigid and has a straight main structure, the molecules are arranged too densely, making it difficult for solvent vapor to penetrate during the production of the film, causing bubbles to be generated inside and on the surface.

Since this type of polyimide film is prone to bubbles, it was mostly produced using a thermal cyclization process in the past. This is because the thermal cyclization process involves slowly heating and baking the polyamic acid precursor (PAA). The temperature needs to be greater than 300 degrees. In this process, when the polyamic acid precursor (PAA) is in the plastic segment where solvent still exists, its molecular chain segment is nonlinear, so the arrangement is less dense, so there are fewer bubbles, but when the film thickness is thicker There will still be bubbles even if it is thick (>25um). According to Patent Document 1, the polyimide (BPDA-PDA) is manufactured using a co-solvent. The co-solvent utilizes the azeotropic phenomenon produced by solvents with different boiling points to reduce the residual amount of solvent during the same baking process. A bubble-free polyimide film can be obtained, but its disadvantage is that the waste liquid treatment after mass production is cumbersome and increases the cost.

In addition to thermal cyclization, chemical cyclization is also a common film-making process. Chemical cyclization uses dehydrating agents and catalysts to convert polyamic acid precursors into polyimides at low temperatures. Therefore, in When there is a plastic segment in the presence of solvent, since most of the nonlinear polyamic acid segments are converted into linear polyimide segments, the molecular chains are arranged regularly and closely, which is relatively easier and has more Bubbles are generated, but therefore the chemical cyclization method of polyimide will have better mechanical and thermal properties than the thermal cyclization method. Patent Document 2 provides that a small amount of monomers with larger steric hindrances are added to form a polyimide. Imine allows the molecular refining section to have space for the solvent to be discharged more easily without affecting too many mechanical and thermal properties. Although it can effectively eliminate bubbles, it will have a greater impact on electrical properties, resulting in increased dielectric loss and cannot be applied to 5G high-frequency materials.

Patent document 1: CN101802059B

Patent Document 2: TWI448487B

Contents of the invention

Based on this, this application provides a polyimide film, which is prepared from copolymerized polyamic acid through a chemical cyclization method, wherein the copolymerized polyamic acid must have at least 3,3',4,4'-linked The composition of pyromellitic dianhydride (3,3',4,4'-biphenyltetracarboxylic dianhydride; BPDA), p-phenylenediamine (p-phenylene diamine; p-PDA) and the diamine of the following chemical formula (A).

Chemical formula (A):

In the chemical formula (A), R can be -CF3 or -CH3;

The number of moles of BPDA must account for more than 60% of the total number of moles of dianhydride of the polyamic acid, and the number of moles of p-PDA must account for more than 50% of the total number of moles of diamine of the polyamic acid, and the chemical formula The mole number of (A) must account for more than 30% of the total mole number of diamines in the polyimide acid, so that the polyimide film has:

a. Glass transition temperature Tg is greater than 280℃

b. Dielectric loss tangent Df (@10GHz) is less than 0.008

c. The thermal expansion coefficient CTE is less than 12ppm/℃.

Detailed ways

The present application is a polyimide film with low dielectric loss. The thickness of the polyimide film is greater than 25 microns. It is prepared from copolymerized polyamic acid through a chemical cyclization method, wherein the copolymerized polyamic acid is at least Need to have 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and p-phenylene diamine (p-PDA) and the following The composition of the diamine of the chemical formula (A) is as follows:

The mole number of BPDA must account for more than 60% of the total mole number of dianhydrides of the copolymerized polyamic acid, and the mole number of p-PDA must account for more than 50% of the total mole number of diamines of the copolymerized polyamic acid; the chemical formula ( The number of moles of A) must account for more than 30% of the total moles of diamine in the copolymerized polyamic acid; and the polyimide film must have a glass transition temperature Tg greater than 280°C and a dielectric loss tangent Df (@10GHz ) is less than 0.008, and the thermal expansion coefficient CTE is less than 12ppm/℃.

Wherein, in addition to the aromatic polyamic acid obtained by reacting the above-mentioned aromatic diamines and aromatic dianhydrides of PDA, chemical formula (A) and BPDA, the aromatic polyamic acid may also include the following aromatic diamines and dianhydrides: wherein the aromatic diamines and dianhydrides are Amines include 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB), 2,2'-bis[4-(4-aminophenoxyphenyl)]propane (BAPP), 2, 2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane (HFBAPP), p-phenylenediamine (PDA), 4,4'- Bis(4-aminophenoxy)biphenyl (BAPB), 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether (6FODA), 4,4'-diaminobiphenyl ether Phenyl sulfone (44DDS), 4,4'-diaminodiphenyl ether (ODA), 4,4'-diaminobenzoanilide (44DABA), 2,2-bis(4-aminophenyl)hexafluoropropane (Bis-A-AF), m-phenylenediamine (mPDA), 3,5-diaminobenzoic acid (35DABA), 2-(4-aminophenyl)-5-aminobenzoxazole (5BPOA), 1 , 4-bis(4-aminophenoxy)benzene (TPEQ), 4,4'-[1,4-phenylbis(oxy)]bis[3-(trifluoromethyl)aniline] (FAPB).

Among them, R in the chemical formula (A) can be CH3, so that the chemical formula (A) is 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB).

Wherein, R in the chemical formula (A) can be CF3, so that the chemical formula (A) is 2,2-bis(trifluoromethyl)diaminobiphenyl (TFMB).

Among them, the chemical cyclization method is formed by adding a dehydrating agent and a catalyst, wherein the dehydrating agent is acetic anhydride and the catalyst is methylpyridine and isoquinoline.

The dehydrating agent is added in an amount of at least 2 equivalents, and the catalyst is added in an amount of at least 1 equivalent.

Example

<Detection method>

The thermal properties and electrical properties of the polyimide films obtained in the following examples were measured using the following methods.

(1) Dk&Df@10GHz: Measured using the E5071C ENANetwork Analyzer instrument produced by Keysight Technologies.

(2) CTE: Measured in accordance with ASTM D696 specifications using the model Q400TMA instrument produced by TA Instruments. The thermal expansion coefficient of the transparent polyimide film is measured at 50 to 200°C, and the heating rate is set to 10°C/min. In order to remove the stress caused by heat treatment, after removing the residual stress through the first measurement, the second measurement result is used as the actual value.

(3) Thickness: Use the MiniTest 2100 instrument manufactured by Elektro Physik Company

Take measurements.

Example 1

Production of polyamic acid

Add 17.458 grams of p-phenylene diamine (PDA, 0.0161 mole) to 400 grams of N,N-dimethylacetamide (DMAc). After all is dissolved, add 27.174 grams of 3,3',4,4'- biphenyltetracarboxylicdianhydride (BPDA, 0.092 mole), stir for 1 hour and keep the temperature at 25°C, then add 14.688 grams of 2,2'-diMethyl-4,4'-diaMinobiphenyl (m-Tolidine, 0.069 mole), stir until completely dissolved , then slowly add 40.034 grams of BPDA, 0.136 mole, stir for 12 hours to dissolve and react, and maintain the temperature of the solution at 25°C. Then use a trace amount of BPDA to adjust the viscosity to 200,000cps±30,000cps, and finally obtain the solid content It is a 20% copolymer polyamic acid solution.

Production of polyimide film

Take out 58.5 grams of the above copolymerized polyamic acid solution and add 6.5 grams of N,N-dimethylacetamide (DMAc) to dilute the solid content to 18%. After stirring for 10 minutes, add acetic anhydride and DMAc at a ratio of 5 to 1. Dilute 3-methylpyridine and DMAc at a weight ratio of 1:1, then add 6.3 ml of acetic anhydride diluent and 5.3 ml of 3-methylpyridine diluent respectively. After evenly stirring, use a centrifugal degassing machine to degas, apply the degassed solution to the glass plate and use a spatula with a gap of 900 μm for coating. Place the coated sample in an oven at 80°C for 20 minutes, then raise the temperature to 170°C at a rate of 1.8°C/min and bake for 20 minutes, then raise the temperature to 350°C at a rate of 2.0°C/min and bake for 20 minutes. minutes for final processing.

The polyimide film produced above has a thermal expansion coefficient between 50 and 200°C of 9.7ppm/°C, a dielectric loss of Df0.0069, and a Tg of 335°C.

Example 2

Production of polyamic acid

Add 11.898 grams of p-phenylene diamine (PDA, 0.0110 mole) to 400 grams of N,N-dimethylacetamide (DMAc). After all is dissolved, add 16.186 grams of 3,3',4,4'- biphenyltetracarboxylicdianhydride (BPDA, 0.055 mole), stir for 1 hour and keep the temperature at 25°C, then add 23.358 grams of 2,2'-diMethyl-4,4'-diaMinobiphenyl (m-Tolidine, 0.110 mole), stir until completely dissolved , then slowly add 47.586 grams of BPDA, 0.1161 mole, stir for 12 hours to dissolve and react, and maintain the temperature of the solution at 25°C. Then use a trace amount of BPDA to adjust the viscosity to 200,000±30,000cps, and finally obtain a solid content of 20% copolymer polyamic acid solution.

Production of polyimide film

Take out 58.5 grams of the above copolymerized polyamic acid solution and add 6.5 grams of N,N-dimethylacetamide (DMAc) to dilute the solid content to 18%. After stirring for 10 minutes, add acetic anhydride and DMAc at a ratio of 5 to 1. Dilute 3-methylpyridine and DMAc at a weight ratio of 1:1, then add 6.0 ml of acetic anhydride diluent and 5.1 ml of 3-methylpyridine diluent respectively. After evenly stirring, use a centrifugal degassing machine to degas, apply the degassed solution to the glass plate and use a spatula with a gap of 900 μm for coating. Place the coated sample in an oven at 80°C for 20 minutes, then raise the temperature to 170°C at a rate of 1.8°C/min and bake for 20 minutes, then raise the temperature to 350°C at a rate of 2.0°C/min and bake for 20 minutes. minutes for final processing.

The polyimide film produced above has a thermal expansion coefficient between 50 and 200°C of 7.7ppm/°C, a dielectric loss of Df0.0065, and a Tg of 315°C.

Example 3

Production of polyamic acid

Add 12.514 grams of p-phenylene diamine (PDA, 0.0116 mole) to 400 grams of N,N-dimethylacetamide (DMAc). After all is dissolved, add 17.064 grams of 3,3',4,4'- biphenyltetracarboxylicdianhydride (BPDA, 0.058 mole), stir for 1 hour and keep the temperature at 25°C, then add 24.60 grams of 2,2'-diMethyl-4,4'-diaMinobiphenyl (mTB, 0.116 mole), stir until completely dissolved, and then Slowly add 15.156 grams of pyromellitic anhydride (PMDA, 0.0695 mole), stir for 0.5 hours, then slowly add 30.001 grams of BPDA, 0.102 mole, stir for 12 hours until it dissolves and reacts, and The temperature of the solution was maintained at 25°C, and then a trace amount of BPDA was used to adjust the viscosity to 200,000±30,000cps, finally obtaining a copolymer polyamic acid solution with a solid content of 20%.

Production of polyimide film

Take 58.5 grams of the above copolymerized polyamic acid solution and add 6.5 grams of N,N-dimethylacetamide (DMAc) to dilute the solid content to 18%. After stirring for 10 minutes, add acetic anhydride and DMAc at a weight ratio of 5 to 1. Dilute, then dilute 3-methylpyridine and DMAc at a weight ratio of 1:1, then add 6.3 ml of acetic anhydride diluent and 5.3 ml of 3-methylpyridine diluent respectively. After evenly stirring, use a centrifugal degassing machine to degas, apply the degassed solution to the glass plate and use a spatula with a gap of 900 μm for coating. Place the coated sample in an oven at 80°C for 20 minutes, then raise the temperature to 170°C at a rate of 1.8°C/min and bake for 20 minutes, then raise the temperature to 350°C at a rate of 2.0°C/min and bake for 20 minutes. minutes for final processing.

The polyimide film produced above has a thermal expansion coefficient between 50 and 200°C of 8.5ppm/°C, a dielectric loss of Df0.008, and a Tg of 342°C.

Example 4

Production of polyamic acid

Add 11.123 grams of p-phenylene diamine (PDA, 0.103 mole) to 400 grams of N,N-dimethylacetamide (DMAc). After all is dissolved, add 15.151 grams of 3,3',4,4'- biphenyltetracarboxylicdianhydride (BPDA, 0.052 mole), stir the reaction for 1 hour and maintain the temperature at 25°C, then add 24.60 grams of 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB, 0.103 mole), and stir until complete Dissolve, then slowly add 13.472 grams of pyromellitic anhydride (PMDA, 0.062 mole), stir for 0.5 hours, then slowly add 26.666 grams of BPDA, 0.091 mole, stir for 12 hours until it is dissolved and reaction, and the temperature of the solution was maintained at 25°C, and then a trace amount of BPDA was used to adjust the viscosity to 200,000±30,000cps, and finally a copolymerized polyamic acid solution with a solid content of 20% was obtained.

Production of polyimide film

Take 58.5 grams of the above copolymerized polyamic acid solution and add 6.5 grams of N,N-dimethylacetamide (DMAc) to dilute the solid content to 18%. After stirring for 10 minutes, add acetic anhydride and DMAc at a weight ratio of 5 to 1. Dilute, then dilute 3-methylpyridine and DMAc at a weight ratio of 1:1, and then add 5.6 ml of acetic anhydride diluent and 4.7 ml of 3-methylpyridine diluent respectively. After evenly stirring, use a centrifugal degassing machine to degas, apply the degassed solution to the glass plate and use a spatula with a gap of 900 μm for coating. Place the coated sample in an oven at 80°C for 20 minutes, then raise the temperature to 170°C at a rate of 1.8°C/min and bake for 20 minutes, then raise the temperature to 350°C at a rate of 2.0°C/min and bake for 20 minutes. minutes for final processing.

The polyimide film produced above has a thermal expansion coefficient between 50 and 200°C of 11.9ppm/°C, a dielectric loss of Df 0.007, and a Tg of 328°C.

Example 5

Production of copolymerized polyamic acid

Add 10.623 grams of p-phenylene diamine (PDA, 0.098 mole) to 400 grams of N,N-dimethylacetamide (DMAc). After all is dissolved, add 14.470 grams of 3,3',4,4'- biphenyltetracarboxylicdianhydride (BPDA, 0.049 mole), stir the reaction for 1 hour and keep the temperature at 25°C, then add 31.498 grams of 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB, 0.098 mole), and stir until complete Dissolve, then slowly add 42.831 grams of BPDA, 0.146 mole, stir for 12 hours to dissolve and react, and maintain the temperature of the solution at 25°C. Then use a trace amount of BPDA to adjust the viscosity to 200,000±30,000cps, and finally obtain the solid content It is a 20% copolymer polyamic acid solution.

Production of polyimide film

Take 58.5 grams of the above copolymerized polyamic acid solution and add 6.5 grams of N,N-dimethylacetamide (DMAc) to dilute the solid content to 18%. After stirring for 10 minutes, add acetic anhydride and DMAc at a weight ratio of 5 to 1. Dilute, then dilute 3-methylpyridine and DMAc at a weight ratio of 1:1, and then add 5.3 ml of acetic anhydride diluent and 4.5 ml of 3-methylpyridine diluent respectively. After evenly stirring, use a centrifugal degassing machine to degas, apply the degassed solution to the glass plate and use a spatula with a gap of 900 μm for coating. Place the coated sample in an oven at 80°C for 20 minutes, then raise the temperature to 170°C at a rate of 1.8°C/min and bake for 20 minutes, then raise the temperature to 350°C at a rate of 2.0°C/min and bake for 20 minutes. minutes for final processing.

The polyimide film produced above has a thermal expansion coefficient between 50 and 200°C of 11ppm/°C, a dielectric loss of Df0.0075, and a Tg of 300°C.

Example 6

Production of polyamic acid

Add 11.123 grams of p-phenylene diamine (PDA, 0.103 mole) to 400 grams of N,N-dimethylacetamide (DMAc). After all is dissolved, add 15.151 grams of 3,3',4,4'- biphenyltetracarboxylicdianhydride (BPDA, 0.052 mole), stir the reaction for 1 hour and maintain the temperature at 25°C, then add 24.60 grams of 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB, 0.103 mole), and stir until complete Dissolve, then slowly add 13.472 grams of pyromellitic anhydride (PMDA, 0.062 mole), stir for 0.5 hours, then slowly add 26.666 grams of BPDA, 0.091 mole, stir for 0.5 hours until it is dissolved and reaction, and the temperature of the solution was maintained at 25°C, and then a trace amount of BPDA was used to adjust the viscosity to 200,000±30,000cps, and finally a copolymerized polyamic acid solution with a solid content of 20% was obtained.

Production of polyimide film

Take 58.5 mg of the above copolymerized polyamic acid solution and add 6.5 mg of N,N-dimethylacetamide (DMAc) to dilute the solid content to 18%. After stirring for 10 minutes, add acetic anhydride and DMAc at a weight ratio of 5 to 1. Dilute, then dilute 3-methylpyridine and DMAc at a weight ratio of 1:1, and then add 6.1 ml of acetic anhydride diluent and 5.2 ml of 3-methylpyridine diluent respectively. After evenly stirring, use a centrifugal degassing machine to degas, apply the degassed solution to the glass plate and use a spatula with a gap of 900 μm for coating. Place the coated sample in an oven at 80°C for 20 minutes, then raise the temperature to 170°C at a rate of 1.8°C/min and bake for 20 minutes, then raise the temperature to 350°C at a rate of 2.0°C/min and bake for 20 minutes. minutes for final processing.

The polyimide film produced above has a thermal expansion coefficient between 50 and 200°C of 9.0ppm/°C, a dielectric loss of Df0.0080, and a Tg of 325°C.

Comparative example 1

Preparation of polyamic acid solution

Add 20.422 grams of p-phenylene diamine (PDA, 0.189 mole) to 400 grams of N,N-dimethylacetamide (DMAc). After all is dissolved, add 27.817 grams of 3,3',4,4'- biphenyltetracarboxylicdianhydride (BPDA, 0.0945 mole), stir for 1 hour and keep the temperature at 25°C, then add 10.036 grams of 2,2'-diMethyl-4,4'-diaMinobiphenyl (mTB, 0.047 mole), stir until completely dissolved, and then Slowly add 40.682 grams of BPDA (0.138 mole), stir for 12 hours to dissolve and react, and maintain the temperature of the solution at 25°C. Then use a trace amount of BPDA to adjust the viscosity to 200,000±30,000cps, and finally obtain a solid content of 20 % copolymerized polyamic acid solution.

Production of polyimide film

Take 58.5 mg of the above copolymerized polyamic acid solution and add 6.5 mg of N,N-dimethylacetamide (DMAc) to dilute the solid content to 18%. After stirring for 10 minutes, add acetic anhydride and DMAc at a weight ratio of 5 to 1. Dilute, then dilute 3-methylpyridine and DMAc at a weight ratio of 1:1, and then add 6.4 ml of acetic anhydride diluent and 5.4 ml of 3-methylpyridine diluent respectively. After evenly stirring, use a centrifugal degassing machine to degas, apply the degassed solution to the glass plate and use a spatula with a gap of 900 μm for coating. Place the coated sample in an oven at 80°C for 20 minutes, then raise the temperature to 170°C at a rate of 1.8°C/min and bake for 20 minutes, then raise the temperature to 350°C at a rate of 2.0°C/min and bake for 20 minutes. minutes for final processing. The polyimide film produced above has a thermal expansion coefficient between 50 and 200°C of 9.5ppm/°C, a dielectric loss of Df 0.011, and a Tg of 340°C.

Comparative example 2

Add 10.175 grams of p-phenylene diamine (PDA, 0.094 mole) to 400 grams of N,N-dimethylacetamide (DMAc). After all is dissolved, add 13.859 grams of 3,3',4,4'- biphenyltetracarboxylicdianhydride (BPDA, 0.0471 mole), stir the reaction for 1 hour and maintain the temperature at 25°C, then add 10.036 grams of 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB, 0.047 mole), and stir until complete After dissolving, slowly add 12.323 grams of 1,2,4,5-pyromellitic anhydride (PMDA, 0.057 mole), stir for 0.5 hours, and then slowly add 19.614 grams of 4,4'-(4,4'-isopropyl Diphenoxy) diphthalic anhydride (BPADA, 0.038 mole) and 13.028 grams of BPDA (0.044 mole), stir for 12 hours to dissolve and react, and maintain the temperature of the solution at 25°C, and then use a trace amount of BPDA to The viscosity was adjusted to 200,000±30,000cps, and a copolymer polyamic acid solution with a solid content of 20% was finally obtained.

Production of polyimide film

Take 58.5 mg of the above copolymerized polyamic acid solution and add 6.5 mg of N,N-dimethylacetamide (DMAc) to dilute the solid content to 18%. After stirring for 10 minutes, add acetic anhydride and DMAc at a weight ratio of 5 to 1. Dilute, then dilute 3-methylpyridine and DMAc at a weight ratio of 1:1, and then add 5.1 ml of acetic anhydride diluent and 4.3 ml of 3-methylpyridine diluent respectively. After evenly stirring, use a centrifugal degassing machine to degas, apply the degassed solution to the glass plate and use a spatula with a gap of 900 μm for coating. Place the coated sample in an oven at 80°C for 20 minutes, then raise the temperature to 170°C at a rate of 1.8°C/min and bake for 20 minutes, then raise the temperature to 350°C at a rate of 2.0°C/min and bake for 20 minutes. minutes for final processing.

Comparative example 3

Preparation of polyamic acid solution

Add 12.695 grams of p-phenylene diamine (PDA, 0.118 mole) to 400 grams of N,N-dimethylacetamide (DMAc). After all is dissolved, add 17.293 grams of 3,3',4,4'- biphenyltetracarboxylicdianhydride (BPDA, 0.059 mole), stir the reaction for 1 hour and keep the temperature at 25°C, then add 23.510 grams of 4,4'-diaminodiphenyl ether (ODA, 0.118 mole), stir until completely dissolved, and then slowly add 15.375 Grams of 1,2,4,5-pyromellitic anhydride (PMDA, 0.071 mole), stir for 0.5 hours, then slowly add 30.089 grams of BPDA (0.102 mole), stir for 12 hours until it dissolves and reacts, and the solution The temperature was maintained at 25°C, and then a trace amount of BPDA was used to adjust the viscosity to 200,000±30,000cps, finally obtaining a copolymer polyamic acid solution with a solid content of 20%.

Production of polyimide film

Take 58.5 mg of the above copolymerized polyamic acid solution and add 6.5 mg of N,N-dimethylacetamide (DMAc) to dilute the solid content to 18%. After stirring for 10 minutes, add acetic anhydride and DMAc at a weight ratio of 5 to 1. Dilute, then dilute 3-methylpyridine and DMAc at a weight ratio of 1:1, and then add 6.4 ml of acetic anhydride diluent and 5.4 ml of 3-methylpyridine diluent respectively. After evenly stirring, use a centrifugal degassing machine to degas, apply the degassed solution to the glass plate and use a spatula with a gap of 900 μm for coating. Place the coated sample in an oven at 80°C for 20 minutes, then raise the temperature to 170°C at a rate of 1.8°C/min and bake for 20 minutes, then raise the temperature to 350°C at a rate of 2.0°C/min and bake for 20 minutes. minutes for final processing. The polyimide film produced above has a thermal expansion coefficient between 50 and 200°C of 10.0ppm/°C, a dielectric loss of Df 0.012, and a Tg of 340°C.

Comparative example 4

Preparation of polyamic acid solution

Add 26.851 grams of p-phenylene diamine (PDA, 0.249 mole) to 400 grams of N,N-dimethylacetamide (DMAc). After all is dissolved, add 71.686 grams of 3,3',4,4'- When adding biphenyltetracarboxylicdianhydride (BPDA, 0.244 mole), the temperature is controlled at 25°C. The reaction is stirred for 24 hours and the temperature is maintained at 25°C. Then a trace amount of BPDA is used to adjust the viscosity to 200,000±30,000cps, and the final solid content is 20 % copolymerized polyamic acid solution.

Production of polyimide film

Take 58.5 mg of the above copolymerized polyamic acid solution and add 6.5 mg of N,N-dimethylacetamide (DMAc) to dilute the solid content to 18%. After stirring for 10 minutes, add acetic anhydride and DMAc at a weight ratio of 5 to 1. Dilute, then dilute 3-methylpyridine and DMAc at a weight ratio of 1:1, and then add 6.8 ml of acetic anhydride diluent and 5.7 ml of 3-methylpyridine diluent respectively. After evenly stirring, use a centrifugal degassing machine to degas, apply the degassed solution to the glass plate and use a spatula with a gap of 900 μm for coating. Place the coated sample in an oven at 80°C for 20 minutes, then raise the temperature to 170°C at a rate of 1.8°C/min and bake for 20 minutes, then raise the temperature to 350°C at a rate of 2.0°C/min and bake for 20 minutes. minutes for final processing. The polyimide film produced above has a thermal expansion coefficient between 50 and 200°C of 3.5ppm/°C, a dielectric loss of Df 0.013, and a Tg of 360°C.

Table of Examples and Comparative Examples

The content of the above specific embodiments is for the purpose of describing the present application in detail. However, these embodiments are only for illustration and are not intended to limit the present application. Those skilled in the art will understand that various changes or modifications made to this application without departing from the scope defined in the appended patent application are part of this application.

Claims (4)

1. A polyimide film with low dielectric loss. The thickness of the polyimide film is greater than 25 microns. It is prepared from copolymerized polyamic acid through a chemical cyclization method, wherein the copolymerized polyamic acid requires at least It has 3,3',4,4'-biphenyltetracarboxylic dianhydride and p-phenylenediamine and 2,2'-dimethyl-4,4'-diaminobiphenyl; Among them, the number of moles of 3,3',4,4'-biphenyltetracarboxylic dianhydride must account for more than 60% of the total moles of dianhydride of the copolymerized polyamic acid, and the number of moles of p-phenylenediamine must account for more than 60% of the total moles of dianhydride of the copolymerized polyamic acid. The percentage of the total moles of diamines in the polyamic acid is more than 50; the moles of 2,2'-dimethyl-4,4'-diaminobiphenyl need to account for the percentage of the total moles of the diamines in the copolymerized polyamic acid. The reaction composition is more than 30; and the polyimide film has a glass transition temperature Tg greater than 280°C, a dielectric loss tangent Df@10GHz less than 0.008, and a thermal expansion coefficient CTE less than 12 ppm/ ^o C. 2. The low dielectric loss polyimide film according to claim 1, wherein the aromatic polyamic acid contains, in addition to the above-mentioned 3,3',4,4'-biphenyltetracarboxylic dianhydride and terephthalic dianhydride. In addition to amines and aromatic diamines obtained by reacting 2,2'-dimethyl-4,4'-diaminobiphenyl with aromatic dianhydrides, it may also include one of the following aromatic diamines and dianhydrides. One or more kinds: the aromatic diamines include 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, 2,2-bis[4-(4-aminophenoxy)benzene base]-1,1,1,3,3,3-hexafluoropropane, 4,4'-bis(4-aminophenoxy)biphenyl, 2,2'-bis(trifluoromethyl)-4 ,4'-diaminophenyl ether, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl ether, 4,4'-diaminophenyl anilide, 2,2-bis( 4-Aminophenyl)hexafluoropropane, m-phenylenediamine, 3,5-diaminobenzoic acid, 2-(4-aminophenyl)-5-aminobenzoxazole, 1,4-bis(4- Aminophenoxy)benzene, 4,4'-[1,4-phenylbis(oxy)]bis[3-(trifluoromethyl)aniline]. 3. The polyimide film with low dielectric loss as claimed in claim 1, wherein the chemical cyclization method is formed by adding a dehydrating agent and a catalyst, wherein the dehydrating agent is acetic anhydride, and the catalyst is methylpyridine, isopropyl quinoline. 4. The polyimide film with low dielectric loss as claimed in claim 3, wherein the dehydrating agent is added in an amount of at least 2 equivalents, and the catalyst is added in an amount of at least 1 equivalent.