High dielectric constant and low dielectric loss tangent polyimide film, multilayer polyimide film, flexible metal clad laminate, and flexible printed circuit board

Abstract

To provide a polyimide film with heat resistance, a high dielectric constant and a low dielectric loss tangent, and a multilayer polyimide film including the same.SOLUTION: A polyimide film has a dielectric loss tangent of 0.006 or less and a dielectric constant of 4 or more at 10 GHz. The polyimide film includes a condensate of an acid dianhydride and a diamine compound, and an inorganic filler with a dielectric constant of 5 or more at 10 GHz. There is also provided a multilayer polyimide film including the same.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyimide film having a high dielectric constant and a low dielectric loss tangent, a multilayer polyimide film, a flexible metal-clad laminate, and a flexible printed circuit board, which can be suitably used for high-frequency circuit boards. [Background technology]

[0002] Polyimide film is widely used as an electronic circuit board material due to its excellent mechanical strength, heat resistance, electrical insulation, and chemical resistance. For example, flexible copper-clad laminates (hereinafter also referred to as FCCLs) are manufactured by laminating copper foil on at least one side of polyimide film as a circuit board material, and flexible printed circuit boards (hereinafter also referred to as FPCs) are manufactured by further fabricating circuits on polyimide film, and these are used in various electronic devices.

[0003] In recent years, the high-speed signal transmission of electronic devices has led to an increase in the frequency of electrical signals propagating through circuits, which has led to an increasing demand for electronic circuit board materials with low dielectric constants and low dielectric dissipation factors. This is because lowering the dielectric constant and dielectric dissipation factor is effective in suppressing transmission loss of electrical signals. In recent years, as we are in the dawn of the IoT society, the trend toward higher frequencies is progressing, and there is a demand for circuit board materials that can suppress transmission loss, even in the range of 10 GHz and above.

[0004] On the other hand, with the trend towards lighter, thinner, and smaller devices, there is also a demand for materials with a high dielectric constant that can shorten the signal propagation wavelength.Ceramics have been used as materials with such high dielectric constants and low dielectric loss tangents, but with the demand for even lower transmission loss and the need for even lower dielectric loss tangents, organic materials are also seen as promising. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] No. 5011697 Summary of the Invention [Problem to be solved by the invention]

[0006] Various methods have been proposed to achieve a high dielectric constant and a low dielectric loss tangent. For example, as in Patent Document 1, there have been many studies on adding inorganic fillers with high dielectric constants to polyimide resins. However, although the film properties such as heat resistance are good, the dielectric loss tangent is not low.

[0007] In view of the above problems, an object of the present invention is to provide a polyimide film that has heat resistance, a high dielectric constant, and a low dielectric loss tangent. [Means for solving the problem]

[0008] In view of the above-mentioned current situation, the present inventors have conducted extensive research and found that the above-mentioned object can be achieved by the following configuration.

[0009] 1) A polyimide film characterized by a dielectric loss tangent of 0.006 or less at 10 GHz and a dielectric constant of 4 or more.

[0010] 2) The polyimide film according to 1), characterized in that the polyimide film comprises a condensation reaction product of an acid dianhydride and a diamine compound, the condensation reaction product having a dielectric loss tangent of 0.004 or less at 10 GHz, and an inorganic filler having a dielectric constant of 5 or more at 10 GHz.

[0011] 3) The polyimide film according to 1) or 2), characterized in that the polyimide dianhydride contains one or more acid dianhydrides selected from 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, pyromellitic dianhydride, and ester group-containing tetracarboxylic dianhydrides, and the diamine compound contains paraphenylenediamine and one or more diamine compounds selected from 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene residue, 1,4-bis(4-aminophenoxy)benzene residue, and 4,4'-diamino-2,2'-dimethylbiphenyl.

[0012] 4) The polyimide film according to any one of 1) to 3), characterized in that it contains paraphenylenediamine in an amount of 75 mol % to 95 mol % when the total amount of all diamine compounds is taken as 100 mol %.

[0013] 5) The polyimide film according to any one of 1) to 4), characterized in that it contains 10 mol% or more and 80 mol% or less of 3,3',4,4'-biphenyltetracarboxylic dianhydride, when the total acid dianhydride is taken as 100 mol%.

[0014] 6) The polyimide film according to any one of 1) to 5), characterized in that the acid dianhydride contains 4,4'-oxydiphthalic anhydride.

[0015] 7) The polyimide film according to any one of 1) to 5), which contains pyromellitic dianhydride as the acid dianhydride.

[0016] 8) The polyimide film according to any one of 1) to 7), which contains 3,3',4,4'-benzophenonetetracarboxylic dianhydride as the acid dianhydride.

[0017] 9) The polyimide film according to any one of 1) to 8), wherein the inorganic filler forms a perovskite-type crystal structure.

[0018] 10) The polyimide film according to any one of 1) to 9), wherein the A-site element of the inorganic filler that forms the perovskite (ABO3) crystal structure is Ca.

[0019] 11) A multilayer polyimide film, characterized in that a thermoplastic polyimide layer is laminated on at least one surface of the polyimide film according to any one of 1) to 10).

[0020] 12) A flexible metal-clad laminate in which a metal layer is provided on the multilayer polyimide film described in 11).

[0021] 13) A flexible printed circuit board having a circuit formed on the metal layer of the flexible metal clad laminate according to 12). [Effects of the Invention]

[0022] According to the present invention, it is possible to provide a polyimide film that has heat resistance, a high dielectric constant, and a low dielectric loss tangent. DETAILED DESCRIPTION OF THE INVENTION

[0023] The polyimide film of the present invention is characterized by having a dielectric loss tangent of 0.006 or less and a dielectric constant of 4 or more at 10 GHz at a temperature of 23° C. and a humidity of 50%.

[0024] The dielectric constant and dielectric loss tangent in the present invention were measured at 10 GHz using a 2 mm × 100 mm sample cut out of a material using a network analyzer (Keysight Corporation, E5071C) and a cavity resonator perturbation method in accordance with ASTM D2520 (JIS C2565).

[0025] The polyimide film of the present invention comprises a condensation reaction product (polyimide) of an acid dianhydride and a diamine compound, the condensation reaction product having a dielectric loss tangent of 0.004 or less at 10 GHz, and an inorganic filler having a dielectric constant of 5 or more at 10 GHz.

[0026] The condensation reaction product (polyimide) of an acid dianhydride and a diamine compound and the inorganic filler having a dielectric constant of 5 or more at 10 GHz according to the present invention will be described below.

[0027] (Condensation reaction product of acid dianhydride and diamine compound) The condensation reaction product of the present invention between an acid dianhydride and a diamine compound preferably contains, as the acid dianhydride, one or more acid dianhydrides selected from 3,3',4,4'-biphenyltetracarboxylic dianhydride (hereinafter sometimes referred to as BPDA), 4,4'-oxydiphthalic anhydride (hereinafter sometimes referred to as ODPA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (hereinafter sometimes referred to as BTDA), pyromellitic dianhydride (hereinafter sometimes referred to as PMDA), and ester group-containing tetracarboxylic dianhydrides, because this has the effect of lowering the dielectric tangent.

[0028] BPDA is an essential component, and the content of BPDA is preferably 10 mol % or more and 80 mol % or less, more preferably 15 mol % or more and 75 mol % or less, and even more preferably 20 mol % or more and 70 mol % or less, when the total acid dianhydride is taken as 100 mol %.

[0029] The ester group-containing tetracarboxylic acid dianhydride is not particularly limited as long as it contains an ester group in its structure. Examples thereof include p-phenylene bis(trimellitic acid monoester anhydride) (hereinafter, sometimes referred to as "TMHQ"), ethylene bis(trimellitic acid monoester anhydride), bisphenol A bis(trimellitic acid monoester anhydride), p-biphenylene bis(trimellitic acid monoester anhydride) (hereinafter, sometimes referred to as "BP-TME"), 4-[4-(1,3-dioxoisobenzofuran-5-ylcarbonyloxy)-2,3,5-trimethylphenyl]-2,3,6-trimethylphenyl 1,3-dioxoisobenzofuran-5-carboxylate, 4-{[4-(1,3-dioxoisobenzofuran-5-ylcarbonyloxy)phenyl]cyclohexyl}phenyl 1,3-dioxoisobenzofuran-5-carboxylate, and derivatives thereof. Among these ester group-containing tetracarboxylic dianhydrides, TMHQ and BP-TME tend to exhibit low dielectric tangents and are therefore particularly preferred.

[0030] Inclusion of an ester group-containing tetracarboxylic acid dianhydride as the tetracarboxylic acid dianhydride component is preferred because the dielectric loss tangent of the resulting polyamic acid or polyimide tends to be reduced. When an ester group-containing tetracarboxylic acid dianhydride is included, the content is preferably 5 mol% to 70 mol%, more preferably 5 mol% to 60 mol%, and even more preferably 10 mol% to 50 mol%, based on the total acid dianhydride content being 100 mol%. In particular, to obtain a polyimide that can reduce the dielectric loss tangent, the total content of BPDA and the ester group-containing tetracarboxylic acid dianhydride is preferably 75 mol% or less, more preferably 70 mol% or less, based on the total tetracarboxylic acid dianhydride components constituting the polyimide precursor and polyimide.

[0031] Furthermore, it is preferable that the diamine compound contains paraphenylenediamine and one or more diamine compounds selected from 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene residue, 1,4-bis(4-aminophenoxy)benzene residue, and 4,4'-diamino-2,2'-dimethylbiphenyl, as this has the effect of lowering the dielectric tangent.

[0032] Furthermore, when the total amount of diamine compounds is taken as 100 mol %, it is preferable to contain paraphenylenediamine in an amount of 75 mol % or more and 95 mol % or less, more preferably 80 mol % or more and 95 mol % or less, since this tends to improve heat resistance, particularly shape retention at 380°C.

[0033] Inclusion of ODPA as a tetracarboxylic dianhydride component is preferred because the dielectric loss tangent of the resulting polyamic acid or polyimide tends to decrease. When ODPA is included, the content is preferably 20 mol% to 60 mol%, more preferably 25 mol% to 60 mol%, and even more preferably 25 mol% to 55 mol%, based on 100 mol% of the total acid dianhydride.

[0034] Inclusion of PMDA as a tetracarboxylic dianhydride component is preferred because it tends to improve the molecular weight of the resulting polyamic acid or polyimide. When PMDA is used as a tetracarboxylic dianhydride component, in order to obtain a polyimide that can further reduce the dielectric tangent while improving heat resistance, the content of PMDA relative to the total tetracarboxylic dianhydride components constituting the polyimide precursor and polyimide is preferably 15 mol % or less, more preferably 12 mol % or less, and even more preferably 10 mol % or less.

[0035] It is also preferred that BTDA is contained as the tetracarboxylic dianhydride component. When ODDA is contained, the content thereof is preferably 5 mol % to 40 mol % inclusive, more preferably 5 mol % to 35 mol % inclusive, and even more preferably 10 mol % to 30 mol % inclusive, based on 100 mol % of the total acid dianhydrides.

[0036] In order to obtain a polyimide that can further reduce the dielectric loss tangent, the ratio of the total amount of substance of all tetradicarboxylic dianhydrides constituting the polyimide precursor and polyimide divided by the total amount of substance of all diamines constituting the polyimide precursor and polyimide is preferably 0.95 or more and 1.05 or less, more preferably 0.97 or more and 1.03 or less, and even more preferably 0.99 or more and 1.01 or less. The polyimide of the present invention may contain components (additives) other than the components constituting the polyimide precursor and polyimide. Examples of additives that can be used include dyes, surfactants, leveling agents, plasticizers, silicones, and sensitizers. The content of the additives in the polyimide is, for example, 30% by weight or less, preferably 20% by weight or less, more preferably 10% by weight or less, and may even be 0% by weight, based on the total amount of the polyimide.

[0037] (Inorganic filler with a dielectric constant of 5 or more at 10 GHz) The inorganic filler of the present invention having a dielectric constant of 5 or more at 10 GHz is not particularly limited, but preferably has a perovskite (ABO3) crystal structure.

[0038] The inorganic filler having a perovskite-type crystal structure of the present invention is not particularly limited, but examples thereof include the following materials.

[0039] It is preferable that the A-site element is at least one selected from the group consisting of Ba, Ca, Mg, and Sr, and the B-site element is at least one selected from the group consisting of Ti and Zr. Specific examples of preferable compositions include BaTiO3, CaTiO3, SrTiO3, Ba x Ca 1-x TiO3 (where x is 0 <x<1)、Ba x Sr 1-x ZrO3 (where x is 0 <x<1)、BaTi x Zr 1-x O3 (where x is 0 <x<1)、Ba x Ca1-x Ti y Zr 1-y O3 (where 0 < x < 1, 0 < y < 1), Ba 1-x-y Ca x Mg y Ti z Zr 1-z O3 (where 0 < x < 1, 0 < y < 1, 0 < z < 1, 0 < x + y < 1), etc. These perovskite-type complex metal oxides may be used alone or in combination of two or more.

[0040] Also, although the reason is not clear, it is most preferable for low dielectric loss tangent that the A-site element is Ca.

[0041] The addition amount of the inorganic filler in the present invention is preferably 10 VOL% or more, more preferably 70% VOL or less. When the addition amount of the inorganic filler in the present invention is 10 VOL% or less, the dielectric constant may not reach 4 or more. Also, when the addition amount is 70 VOL% or more, there are concerns about the reduction of mechanical strength and insulation.

[0042] [[ID=二十七]](Method of containing inorganic filler in polyimide film) The method of containing an inorganic filler in the polyimide film of the present invention will be described. An inorganic filler-containing polyamic acid is synthesized by mixing an inorganic filler into a polyamic acid solution which is a precursor of polyimide, and then an inorganic filler-containing polyimide film can be obtained by converting it into polyimide.

[0043] As the method of mixing the polyamic acid solution and the inorganic filler, a known method can be used and is not particularly limited. For example, before synthesizing the polyamic acid solution, it may be dispersed in a solvent in advance, and the polyamic acid may be synthesized in the dispersion liquid of the inorganic filler, or the synthesized polyamic acid solution and the dispersion liquid of the inorganic filler dispersed in a solvent in advance may be mixed. In order to obtain a polyamic acid solution in which the inorganic filler is uniformly dispersed, it is preferable to mix the synthesized polyamic acid solution and the inorganic filler dispersion liquid.

[0044] Methods for imidizing polyamic acid, a precursor of polyimide, can be broadly divided into thermal imidization and chemical imidization. Thermal imidization is a method in which a polyamic acid solution is cast onto a support as a film-forming dope without using a dehydrating ring-closing agent or the like, and imidization proceeds simply by heating. On the other hand, chemical imidization is a method in which a polyamic acid solution to which at least one of a dehydrating ring-closing agent and a catalyst has been added as an imidization accelerator is used as a film-forming dope to accelerate imidization. Either method can be used, but chemical imidization is superior in productivity.

[0045] As the dehydration ring-closing agent, an acid anhydride such as acetic anhydride can be suitably used. As the catalyst, a tertiary amine such as an aliphatic tertiary amine, an aromatic tertiary amine, or a heterocyclic tertiary amine can be suitably used. Among the tertiary amines, pyridine compounds having alkyl groups at the β- and / or γ-positions, such as β-picoline, γ-picoline, and 3,5-dimethylpyridine, pyridine, and isoquinoline are particularly preferred. Suitable supports for casting the film-forming dope include glass plates, aluminum foils, endless stainless steel belts, stainless steel drums, etc. Heating conditions are set depending on the thickness of the final film to be obtained and the production rate, and the film is partially imidized or dried, and then peeled off from the support to obtain a polyamic acid film (hereinafter referred to as a gel film).

[0046] The gel film is dried by fixing the edges to prevent shrinkage during curing, and water, residual solvent, and imidization accelerator are removed from the gel film, and the remaining amic acid is completely imidized to obtain a polyimide-containing film. The heating conditions can be appropriately set depending on the thickness of the final film to be obtained and the production speed.

[0047] The polyimide film of the present invention is laminated to copper foil via an adhesive to form a flexible Furthermore, a multilayer polyimide film and a copper foil may be laminated together to form a flexible copper-clad laminate. The multilayer polyimide film will now be described.

[0048] (multi-layer polyimide film) The multilayer polyimide film is a multilayer polyimide film having a non-thermoplastic polyimide film and at least one thermoplastic polyimide layer, and a specific example is a multilayer polyimide film having a thermoplastic polyimide layer on one or both sides of a non-thermoplastic polyimide film.

[0049] The polyimide film of the present invention can be used for either a non-thermoplastic polyimide layer or a thermoplastic polyimide layer depending on its properties.

[0050] Flexible printed wiring boards are manufactured by laminating a metal foil layer to an insulating film layer, such as the multilayer polyimide film mentioned above, to produce a flexible metal-clad laminate, and then forming a circuit pattern. Epoxy resins and acrylic resins have traditionally been used for the adhesive layer, but these have poor heat resistance and are therefore limited in their applications. However, two-layer flexible printed wiring boards using thermoplastic polyimide as the adhesive layer are expected to see further growth in demand due to their excellent heat resistance and flexibility.

[0051] In the present invention, the method for producing a multilayer polyimide film comprises the following steps: i) A step of reacting a diamine with an acid dianhydride in an organic solvent to obtain a polyamic acid solution. ii) A step of casting a membrane-forming dope containing the polyamic acid solution onto a support. iii) peeling the gel film from the support after heating on the support. iv) There is a method in which a non-thermoplastic polyimide film is produced by further heating to imidize the remaining polyamic acid and drying the film, and then the non-thermoplastic polyimide film is used as a non-thermoplastic polyimide layer, and an adhesive layer is provided on at least one side of the non-thermoplastic polyimide film by coating or the like.

[0052] In addition, in the above step ii), a co-extrusion die having a plurality of flow paths is used to cast and coat a solution containing a precursor of a polyimide resin for forming the non-thermoplastic polyimide layer and a solution containing a precursor of a polyimide resin for forming the adhesive layer onto a support, thereby simultaneously forming multiple resin layers (co-extrusion casting and coating method).

[0053] In addition, as will be described in detail in the section on flexible metal-clad laminates below, there is also a method (metal foil casting method) in which multiple polyamic acid solutions are sequentially cast onto a metal foil and then imidized to directly form a layer equivalent to a multilayer polyimide film on the metal foil.

[0054] ii) The subsequent steps are broadly divided into thermal imidization and chemical imidization. Thermal imidization is a method in which a polyamic acid solution is used as a film-forming dope and cast onto a support, without using a dehydrating ring-closing agent or the like, and imidization is promoted simply by heating. On the other hand, chemical imidization is a method in which a polyamic acid solution to which at least one of a dehydrating ring-closing agent and a catalyst has been added as an imidization accelerator is used as a film-forming dope to accelerate imidization. Either thermal imidization or chemical imidization may be used, but chemical imidization is more productive.

[0055] As the dehydration ring-closing agent, an acid anhydride such as acetic anhydride can be suitably used. As the catalyst, a tertiary amine such as an aliphatic tertiary amine, an aromatic tertiary amine, or a heterocyclic tertiary amine can be suitably used. Among the tertiary amines, pyridine compounds having alkyl groups at the β- and / or γ-positions, such as β-picoline, γ-picoline, and 3,5-dimethylpyridine, pyridine, and isoquinoline are particularly preferred.

[0056] In the steps iii) and thereafter, the support for casting the film-forming dope can be a glass plate, aluminum foil, an endless stainless steel belt, a stainless steel drum, etc. Heating conditions are set depending on the thickness of the final film to be obtained and the production rate, and the film is partially imidized and / or dried, and then peeled off from the support to obtain a polyamic acid film (hereinafter also referred to as a gel film).

[0057] In the subsequent steps of iv) and iv, the edges of the gel film are fixed to prevent shrinkage during curing, and the film is dried to remove water, residual solvent, and any imidization accelerator remaining in the film, and the remaining polyamic acid is completely imidized to obtain a polyimide film. In addition to fixing the edges of the gel film, the film may also be stretched in the machine direction or perpendicular to the machine direction.

[0058] Since imidization requires extremely high temperatures, when a resin layer other than polyimide is provided, it is preferable to adopt the latter method to suppress thermal decomposition. When providing a thermoplastic polyimide film by coating, a thermoplastic polyimide precursor may be applied and then imidized, or a thermoplastic polyimide solution may be applied and dried. Furthermore, a thermoplastic polyimide film may be obtained by casting a polyimide solution and cooling it instead of casting a polyamic acid solution onto a support in the above-mentioned process.

[0059] (flexible metal laminate) A flexible metal laminate may be produced by forming a layer produced by a dry film-forming method on at least one surface of the polyimide film of the present invention, and then forming a metal layer directly on the polyimide film by forming an electroless plating layer in a subsequent step. Examples of methods for forming a metal layer by dry plating include vacuum deposition, sputtering, ion plating, and CVD.

[0060] Other methods include the following: a) After obtaining a multilayer polyimide film as described above, a metal foil is laminated onto the multilayer polyimide film by heating and pressing to obtain a flexible metal foil laminate. b) A method of casting an organic solvent solution containing polyamic acid onto a metal foil, removing the solvent by heating, and carrying out imidization to obtain a flexible metal foil laminate.

[0061] In the method a), a metal foil is laminated to the obtained multilayer polyimide film by heating and pressing (laminating), thereby obtaining the flexible metal foil laminate of the present invention. The means and conditions for laminating the metal foil may be appropriately selected from those known in the art.

[0062] In the method b), the method for casting the organic solvent solution containing the polyamic acid onto the metal foil is not particularly limited, and conventionally known methods such as a die coater, a comma coater (registered trademark), a reverse coater, a knife coater, etc. Conventionally known methods can also be used as heating means for removing the solvent and performing imidization, such as a hot air oven or a far-infrared oven.

[0063] When the polyimide film of the present invention is to be provided with multiple layers of other polyimide layers or layers of resins other than polyimide, the above-mentioned casting and heating steps can be repeated multiple times, or multiple cast layers can be formed by co-extrusion or continuous casting and then heated all at once.

[0064] In the case of method b), the flexible metal foil laminate of the present invention is obtained simultaneously with the completion of imidization. When metal foil layers are provided on both sides of the resin layer, the metal foil may be laminated to the opposite surface of the resin layer by heating and pressing.

[0065] The metal foil that can be used in the present invention is not particularly limited. However, when the flexible metal-clad laminate of the present invention is used for electronic or electrical equipment applications, examples include foils made of copper or copper alloys, stainless steel or its alloys, nickel or nickel alloys (including 42 alloy), and aluminum or aluminum alloys. Copper foils such as rolled copper foils and electrolytic copper foils are commonly used in general flexible laminates, and they can also be preferably used in the present invention. The surface of these metal foils may be coated with an anti-corrosion layer, a heat-resistant layer, or an adhesive layer. The thickness of the metal foil is not particularly limited, and any thickness that can exhibit sufficient functionality depending on the application may be used.

[0066] (flexible printed circuit board) A flexible printed circuit board obtained by etching the metal layer of the flexible metal clad laminate according to the present invention is a circuit board that can be miniaturized, has low transmission loss, and is suitable for high frequency applications. [Example]

[0067] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The dielectric constant and dielectric loss tangent were evaluated as follows.

[0068] <Measurement of dielectric constant (Dk) and dielectric loss tangent (Df)> The dielectric constant and dielectric loss tangent were measured using a Hewlett-Packard 8719C network analyzer and a Kanto Electronics Application Development Co., Ltd. CP511 cavity resonator vibration method dielectric constant measurement device. Samples were cut into 2 mm x 100 mm pieces and measured after 24 hours of humidity conditioning in a 23°C / 50% RH environment (normal conditions). Measurements were performed at 10 GHz.

[0069] (Synthesis Example 1) In a 500 mL glass flask, 164.2 g of N,N-dimethylformamide (DMF), 3.0 g of 1,3-bis(4-aminophenoxy)benzene (TPE-R), and 6.4 g of p-phenylenediamine (p-PDA) were dissolved. To the resulting solution, 12.2 g of s-biphenyltetracarboxylic dianhydride (s-BPDA) and 7.9 g of 4,4'-oxyphthalic dianhydride (ODPA) were added, and the solution was stirred for 30 minutes to dissolve the components. A separately prepared DMF solution of pyromellitic dianhydride (PMDA) (0.5 g PMDA / 5.8 g DMF) was carefully added to the resulting solution, and the addition was stopped when the viscosity reached approximately 1500 poise. The solution in the flask was then stirred for 1 hour to yield a polyamic acid solution with a solids concentration of approximately 15 wt% and a rotational viscosity of 1500-2000 poise at 23°C.

[0070] (Synthesis Example 2) DMF was added to a reaction vessel and stirred under a nitrogen atmosphere. 100 parts by weight of 2,2'-bis(trifluoromethyl)benzidine (TFMB), 30 parts by weight of p-phenylenebis(trimellitic acid monoester anhydride) (TMHQ), and 70 parts by weight of 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride (6FDA) were added sequentially and stirred under a nitrogen atmosphere for 5 hours to obtain a polyamic acid solution with a solids concentration of 18%. Pyridine was added as an imidization catalyst to the polyamic acid solution, and after complete dispersion, acetic anhydride was added. The solution was stirred at 120°C for 2 hours and then cooled to room temperature. Isopropyl alcohol (IPA) was added while stirring to precipitate the polyimide. The solution was then suction filtered and washed with IPA four times. After drying for 12 hours in a vacuum oven set at 120°C, the polyimide resin was obtained.

[0071] (Reference example 1) To 55 g of the polyamic acid solution obtained in Synthesis Example 1, 27.5 g of a curing agent consisting of 5.15 g of acetic anhydride, 6.01 g of isoquinoline, and 16.34 g of DMF was added. The mixture was stirred and degassed at a temperature below 0°C, and then cast onto aluminum foil using a comma coater. The resulting resin film was dried at 110°C for 133 seconds, after which the gel film was peeled off the aluminum foil and fixed to a metal frame, taking care not to shrink the gel film. The gel film fixed to the metal frame was heated in a preheated hot air circulating oven at 250°C for 15 seconds and 350°C for 79 seconds, and then cut from the frame to obtain a 17 μm-thick polyimide film.

[0072] (Reference example 2) A polyimide solution was prepared by dissolving the polyimide resin obtained in Synthesis Example 2 in methylene chloride to a solids concentration of 12%. Next, this polyimide solution was applied to a glass plate under the following conditions, followed by primary drying on a hot plate and secondary drying in a metal frame at 200°C for 30 minutes, to obtain a polyimide film. Application conditions: Clearance 300 μm, speed 10 mm / sec

[0073] Example 1 A DMF dispersion was prepared by dispersing 18.79 g of inorganic filler (calcium titanate (CT-03)) in 10.0 g of DMF. 28.79 g of the resulting inorganic filler dispersion was added to 55 g of the polyamic acid solution synthesized in Synthesis Example 1 and mixed. 17.5 g of a curing agent consisting of 5.15 g of acetic anhydride, 6.01 g of isoquinoline, and 6.34 g of DMF was added to the resulting inorganic filler-containing polyamic acid solution, stirred and degassed at a temperature below 0°C, and then cast onto aluminum foil using a comma coater. The subsequent procedures were the same as in Reference Example 1 to obtain a polyimide film. The type of inorganic filler, the amount added, the dielectric constant, and the dielectric loss tangent are listed in Table 1. In Table 1, the ratio of Synthesis Example 1:CT-03 = 60:40 refers to vol%.

[0074] (Examples 2 to 4 and Comparative Examples 1 to 3) A polyimide film was obtained in the same manner as in Example 1, except that the type and content of the inorganic filler in Example 1 were changed. The type, amount added, dielectric constant, and dielectric loss tangent of the inorganic filler are shown in Table 1.

[0075] (Comparative Examples 4 and 5) As in Reference Example 2, a polyimide solution was prepared by dissolving the polyimide resin obtained in Synthesis Example 2 and a predetermined amount of inorganic filler: calcium titanate (CT-03) in methylene chloride to a solids concentration of 12%. A polyimide film was then obtained in the same manner as in Reference Example 2. The type, amount added, dielectric constant, and dielectric loss tangent of the inorganic filler are shown in Table 1.

[0076] <Inorganic filler used> CT-03 Calcium titanate manufactured by Sakai Chemical Industry Co., Ltd. CZ-03 Calcium zirconate manufactured by Sakai Chemical Industry Co., Ltd. BT-03 Barium titanate manufactured by Sakai Chemical Industry Co., Ltd. TA-300K Titanium oxide manufactured by Fuji Titanium Industry Co., Ltd. [Table 1]

Claims

1. The dielectric loss tangent at 10 GHz is 0.006 or less and the dielectric constant is 4 or more, a condensation reaction product of an acid dianhydride and a diamine compound, the condensation reaction product having a dielectric loss tangent of 0.004 or less at 10 GHz, and an inorganic filler having a dielectric constant of 5 or more at 10 GHz, the acid dianhydride comprises 3,3',4,4'-biphenyltetracarboxylic dianhydride and one or more selected from 4,4'-oxydiphthalic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, pyromellitic dianhydride and ester group-containing tetracarboxylic dianhydride; The diamine compound includes paraphenylenediamine and at least one selected from 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, and 4,4'-diamino-2,2'-dimethylbiphenyl.

2. 2. The polyimide film according to claim 1, wherein the content of paraphenylenediamine is 75 mol % or more and 95 mol % or less when the total amount of all diamine compounds is taken as 100 mol %.

3. 3. The polyimide film according to claim 1, wherein the content of 3,3',4,4'-biphenyltetracarboxylic dianhydride is 10 mol % or more and 80 mol % or less, when the total acid dianhydride is taken as 100 mol %.

4. 4. The polyimide film according to claim 1, wherein the acid dianhydride includes 4,4'-oxydiphthalic anhydride.

5. A polyimide film described in any one of claims 1 to 4, characterized in that the acid dianhydride includes pyromellitic dianhydride.

6. A polyimide film according to claim 1, wherein the acid dianhydride comprises 3,3',4,4'-benzophenonetetracarboxylic dianhydride.

7. 7. The polyimide film according to claim 1, wherein the inorganic filler forms a perovskite (ABO3) crystal structure.

8. 8. The polyimide film according to claim 7, wherein the A-site element of the inorganic filler that forms the perovskite (ABO3) crystal structure is Ca.

9. A multilayer polyimide film, comprising the polyimide film according to any one of claims 1 to 8 and a thermoplastic polyimide layer laminated on at least one surface of the polyimide film.

10. A flexible metal clad laminate comprising the multilayer polyimide film according to claim 9 and a metal layer provided on the multilayer polyimide film.

11. A flexible printed circuit board comprising a circuit formed on the metal layer of the flexible metal clad laminate according to claim 10.

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