Polyimide film and preparation method thereof, and base film of radio frequency flexible printed circuit

[0036] See figure 1 , figure 1 It is a schematic flow chart of a preparation method of a polyimide film in an embodiment of the present invention, which specifically includes the following steps:

[0037] S11, prepare a polyamic acid resin solution, filter it for use, control the solid content of the polyamic acid resin solution within the range of 15-35wt.%, and control the viscosity within the range of 10-45x10 4 Within mPa·s;

[0038] S12: Weigh a certain amount of polyamic acid resin solution, perform imidization after vacuum degassing, to obtain a self-supporting semi-cured adhesive film;

[0039] S13: Fix the obtained self-supporting semi-cured adhesive film on the frame, heat the self-supporting semi-cured adhesive film to a set temperature, and then cool to room temperature to obtain a polyimide primary film;

[0040] S14, subjecting the obtained primary polyimide film to annealing treatment to obtain a polyimide film.

[0041] See figure 2 In one embodiment, the method for preparing a polyamic acid resin solution in step S11 includes the following steps:

[0042] Weigh a certain amount of aromatic diamine A solid powder, fluorine-containing aromatic diamine B solid powder and aromatic diamine C solid powder, and add them to a certain amount of polar aprotic solvent protected by inert gas In the reactor of, stir and dissolve at room temperature to 60°C to form a homogeneous aromatic diamine solution;

[0043] Weigh a certain amount of aromatic dianhydride powder, add it to the above homogeneous aromatic diamine solution at a temperature of -10°C to 60°C under stirring, and pass the polycondensation reaction of aromatic diamine and aromatic dianhydride A viscous polyamic acid resin (PAA) solution is formed, filtered and set aside.

[0044] See image 3 In another embodiment, the method for preparing a polyamic acid resin solution in step S11 includes the following steps:

[0045] Weigh a certain amount of solid powder of aromatic diamine A and a certain amount of solid powder of fluorine-containing aromatic diamine B, and put them into a reactor protected by inert gas with a certain amount of polar aprotic solvent. Stir and dissolve at a temperature of 60°C to form a homogeneous aromatic diamine solution;

[0046] Weigh a certain amount of aromatic dianhydride powder, add it to the above homogeneous aromatic diamine solution in batches under stirring at a temperature of -10°C to 60°C, stir and react for a certain period of time to form an intermediate resin solution with a certain viscosity ;

[0047] Weigh a certain amount of aromatic diamine C and add it to the intermediate resin solution under stirring, or first dissolve or disperse the aromatic diamine C in a certain amount of polar aprotic solvent to form an aromatic diamine C solution or The suspension is added to the above intermediate resin solution under stirring;

[0048] Weigh a certain amount of aromatic dianhydride powder, add it to the above intermediate resin solution under stirring, and react for a certain period of time to form a viscous polyamic acid resin (PAA) solution, which is filtered for later use;

[0049] The above method for preparing polyamic acid resin solution also includes weighing a certain amount of aromatic dianhydride powder, dissolving or suspending it in a certain amount of polar aprotic solvent to form an aromatic dianhydride solution or suspension, and placing it in It is added to the above polyamic acid resin solution under stirring to adjust the viscosity of the polyamic acid resin (PAA) solution. It is understandable that this step is used to adjust the viscosity of the polyamic acid resin (PAA) solution to meet the process requirements. When the viscosity of the polyamic acid resin (PAA) solution obtained by the above two methods meets the requirements, this step is not necessary . In one embodiment, the aromatic dianhydride powder is pyromellitic dianhydride (PMDA). In another embodiment, phenylenediamine (PDA) can also be added to dissolve or suspend it in a certain amount of polar aprotic solvent to form an aromatic dianhydride solution or suspension, which is added to the above-mentioned polyamide under stirring. In the amic acid resin solution, the viscosity of the polyamic acid resin solution is adjusted.

[0050] The aromatic diamine A in the above method for preparing polyamic acid resin solution includes 4,4'-diaminodiphenyl ether (4,4-ODA), 3,4'-diaminodiphenyl ether (3,4 -ODA), 1,3-bis(4-aminophenoxy)benzene (1,3,4-APB), 1,4-bis(4-aminophenoxy)benzene (1,4,4-APB) ) And 4,4'-diaminodiphenyl sulfone (4,4-DDS) in one or more combinations. In one embodiment, multiple combinations of aromatic diamine A are mixed in any ratio.

[0051] The fluorine-containing aromatic diamine B in the above method for preparing a polyamic acid resin solution includes bis(2-trifluoromethyl-4-aminophenoxy)benzene (6FAPB), bis(2-trifluoromethyl- 4-aminophenoxy)biphenyl (6FBAB), 4,4'-diamino-2,2'-trifluoromethylbiphenyl (TFDB) and bis(4-aminophenoxyphenyl)hexafluoropropane (6FBAPP) one or more combinations. In one embodiment, multiple combinations of fluorine-containing aromatic diamine B are mixed in any ratio.

[0052] The aromatic diamine C in the above method for preparing polyamic acid resin solution includes p-phenylenediamine (PDA), 4,4'-diaminobiphenyl (TMDA) and 4,4'-diamino 2,2' -One or more combinations of dimethyl biphenyl (TMMDA). In one embodiment, multiple combinations of aromatic diamine C are mixed in any ratio.

[0053] The aromatic dianhydride in the above method for preparing polyamic acid resin solution includes pyromellitic dianhydride (PMDA), 3,3',4,4'-bipyromellitic dianhydride (s-BPDA), 2 ,3',3,4'-Bipyromellitic dianhydride (α-BPDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 2,3',3, 4'-benzophenone tetraacid dianhydride (α-BTDA), 3,3',4,4'-benzophenone tetraacid dianhydride (s-ODPA) and 2,3',3,4' -One or more combinations of dimethyl ether tetraacid dianhydride (α-ODPA). In one embodiment, multiple combinations of aromatic dianhydrides are mixed in any ratio.

[0054] The polar aprotic solvent in the above method for preparing polyamic acid resin solution includes N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAC), N,N-dimethylformamide ( One or more combinations of DMF) and dimethyl sulfoxide (DMSO). In one embodiment, multiple combinations of polar aprotic solvents are mixed in any ratio.

[0055] The molar ratio of the aromatic diamine A to the fluorine-containing aromatic diamine B ranges from 1:49 to 49:1, preferably from 10:40 to 40:10.

[0056] The molar ratio of the sum of the aromatic diamine A and the fluorine-containing aromatic diamine B to the aromatic diamine C is 1:99 to 99:1, preferably 30:70 to 70:30.

[0057] The molar ratio of aromatic dianhydride to aromatic diamine A, fluorine-containing aromatic diamine B, and aromatic diamine C is close to 1:1.

[0058] In one embodiment, the method of imidization in step S12 includes the following steps:

[0059] Extrude the polyamic acid resin (PAA) solution through a slit die and coat it on the surface of a support such as a seamless continuous mirror stainless steel belt or glass plate to form a polyamic acid film with a certain thickness;

[0060] Programmatic heating in the drying tunnel or oven to the range of 40℃-250℃. After a certain period of time, the partially imidized polyamic acid film containing part of the solvent is peeled off the surface of the support to obtain a certain strength And tough self-supporting semi-cured film.

[0061] In another embodiment, the method of imidization in step S12 includes the following steps:

[0062] The polyamic acid resin (PAA) solution is stirred and mixed with the chemical imidization reagent at a low temperature of -5℃~5℃, defoamed, and then extruded through a slit die and coated on a seamless continuous mirror stainless steel belt or glass On the surface of supports such as plates, a polyamic acid film with a certain thickness containing chemical imidization reagents is formed;

[0063] Heat to the range of 40℃-250℃ in the drying tunnel or in the oven. After a certain period of time, the partially imidized polyamic acid film containing part of the solvent is peeled off the surface of the support to obtain a certain strength and toughness The self-supporting semi-cured film.

[0064] The above chemical imidization reagent includes an organic acid anhydride dehydrating agent, an organic base catalyst, and an organic solvent. The organic acid anhydride dehydrating agent includes one or more combinations of acetic anhydride, propionic anhydride, butyric anhydride, phthalic anhydride, and maleic anhydride. The organic base catalyst includes one or more combinations of pyridine, 2-picoline, 3-picoline, and isoquinoline. The organic solvent includes one or more combinations of dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), and N-methylpyrrolidone (NMP). The various combinations of the organic acid anhydride dehydrating agent, the organic base catalyst and the organic solvent can be mixed in any ratio. In one embodiment, the molar ratio of the organic acid anhydride dehydrating agent to the organic base catalyst is 1:1-20:1, preferably 1:1-15:1, and the sum of the organic acid anhydride dehydrating agent and the organic base catalyst and the organic solvent The mass ratio is 1:99 to 99:1, preferably 20:80 to 80:20. The above-mentioned imidization method with chemical imidization reagent is more efficient and saves curing time.

[0065] The step S13 is specifically to fix two or four sides of the self-supporting semi-cured adhesive film on a fixed frame, apply a certain stretching tension, and use a programmed heating method in a high-temperature drying tunnel or oven to heat from room temperature to a maximum of 550°C, Then gradually lower the temperature to room temperature to obtain a polyimide primary film.

[0066] The annealing temperature in the step S13 is 300° C. to 550° C., and the annealing temperature is provided with at least three different temperature sections for annealing and heating.

[0067] A polyimide film prepared by the above method has a dielectric constant ≤3.0, a dielectric loss ≤0.008, and a thermal expansion coefficient close to that of metal copper, and can withstand the high temperature process of lead-free solder wave soldering at 280°C without deformation. The above-mentioned polyimide film can be used as a base film of a flexible printed circuit (FPC) for high-frequency and high-speed signal transmission. After the surface of the polyimide film is activated, a seed layer is formed by ion implantation or sputtering, and then a conductive metal layer is formed by electroplating. After washing and drying, a flexible copper clad laminate (FCCL) is obtained. After exposure, development, etching and other manufacturing processes, the flexible copper clad laminate is used to obtain FPC for high frequency and high speed.

[0069] Example 1

[0070] In a 500ml round bottom flask equipped with mechanical stirring and nitrogen inlet and outlet, add 1.3g of 4,4'-diaminodiphenyl ether (4,4-ODA) solid powder and 30.2g of bis(2-trifluoromethyl-4-amino) Phenoxy)benzene (6FAPB) solid powder and 200ml of N,N-dimethylformamide solvent, stirred and dissolved at 35℃ to form a homogeneous aromatic diamine solution; weigh 15.3g of tetrabenzoic acid dianhydride (PMDA ) The solid powder is added to the homogeneous aromatic diamine solution in batches under stirring, and the reaction is stirred at 35°C for 1-24 hours to form an intermediate resin solution; Weigh 5.5g of p-phenylenediamine (PDA) solid powder Add it to the intermediate resin solution under stirring; weigh 11.4g of pyromellitic dianhydride (PMDA) solid powder, add it to the intermediate resin solution under stirring, and react for a certain period of time to form Viscous polyamic acid resin (PAA) solution.

[0071] Weigh 1.1g PMDA, dissolve it in 16.3ml N,N-dimethylformamide solvent, add it to the above polyamic acid resin solution in batches under stirring, and react for 1-24h under stirring to make polyamide The resin solid content in the acid resin solution is controlled at 24wt.%, and the viscosity is controlled at 16×10 4 mPa·s.

[0072] Weigh a sufficient amount of the above polyamic acid resin solution (PAA) solution according to the selected support area and coating thickness, cool it to -5℃~5℃, add the chemical imidization reagent solution under mechanical stirring, and stir it evenly Perform degassing. Then through a slit die extrusion coating on the surface of a seamless continuous mirror stainless steel belt or glass plate and other supports to form a certain thickness of polyamic acid film containing chemical imidization reagent; pass in the drying tunnel or oven Three stages of different temperatures are gradually heated to 130°C. After a certain period of time, the partially imidized adhesive film containing part of the solvent is peeled from the surface of the support to obtain a self-supporting semi-cured resin with certain strength and toughness Adhesive film; fix the two or four sides of the above-mentioned self-supporting semi-cured resin film on the fixed frame, apply a certain stretching tension, and heat it step by step in a high temperature drying tunnel or oven to 550°C, and then gradually reduce the temperature to as low as A primary polyimide film is obtained at room temperature, and the above primary polyimide film is annealed at 300°C-550°C to obtain a low-loss polyimide film. The main properties are as follows: Tensile modulus (Tm): 4.4GPa; Tensile strength (Ts): 162MPa; Coefficient of thermal expansion (CTE, 50-200℃, TMA): 18.0ppm/K; Water absorption (Wa): 0.48%; Dielectric constant (ε, 1KHz): 2.73; Dielectric loss (tanδ, 1KHz): 0.0045; high-frequency transmission loss (40GHz): -11dB; passed the tin drift experiment (300℃/30S).

[0073] Example 2

[0074] In a 500ml round bottom flask equipped with mechanical stirring and nitrogen inlet and outlet, 2.6g 4,4'-diaminodiphenyl ether (4,4-ODA) solid powder, 28.1g bis(2-trifluoromethyl-4- Aminophenoxy)benzene (6FAPB) solid powder and 200ml of N,N-dimethylformamide solvent, stirred and dissolved at 35℃ to form a homogeneous aromatic diamine solution; Weigh 28.5g of tetrabenzoic acid dianhydride ( PMDA) solid powder, add it to the homogeneous aromatic diamine solution in batches under stirring, stir and react at 35°C for 1-24h to form an intermediate resin solution; weigh 5.6g p-phenylenediamine (PDA) solid Powder, dissolve it in 23.6mL DMF solvent, add it to the above-mentioned intermediate resin in batches under stirring, and form a viscous polyamic acid resin solution after reacting for 1-24 hours under stirring. The solid content of the resin is controlled at 23wt.%, the viscosity is controlled at 10×10 4 mPa·s.

[0075] Weigh a sufficient amount of the above polyamic acid resin solution (PAA) solution according to the selected support area and coating thickness, and extrude and coat it on the surface of the support such as seamless continuous mirror stainless steel belt or glass plate through a slit die. A certain thickness of polyamic acid film containing chemical imidization reagent is formed; in the drying tunnel or in the oven, it is gradually heated to 180℃ through 3 stages at different temperatures. After a certain period of time, the part containing part of the solvent will be formed The imidized adhesive film is peeled from the surface of the support to obtain a self-supporting semi-cured resin adhesive film with certain strength and toughness; the two or four sides of the above-mentioned self-supporting semi-cured resin adhesive film are fixed on the fixed frame, and a certain amount is applied In a high-temperature drying tunnel or oven, heat it step by step to 530℃, and then gradually reduce the temperature to room temperature to obtain a polyimide primary film. The above-mentioned polyimide primary film is carried out at 300℃-550℃ Annealing treatment yields low-loss polyimide film. Its main properties are as follows: tensile modulus (Tm): 4.6GPa; tensile strength (Ts): 171MPa; thermal expansion coefficient (CTE, 50-200℃, TMA): 16.5ppm/K; water absorption (Wa): 0.50%; dielectric constant (ε, 1KHz): 2.78; dielectric loss (tanδ, 1KHz): 0.0048; high frequency transmission loss (-dB, 10-40GHz):- 12; Passed the bleaching tin experiment (300℃/30S).