Porous low-dielectric polymer films, laminates, and wiring circuit boards

Abstract

Providing porous, low-dielectric polymer films with improved flexibility, etc. [Solution] A porous low-dielectric polymer film, Hollow particles and fine pores are dispersed in a film composed of polymers. A porous, low-dielectric polymer film having a relative permittivity of 2.40 or less.

Description

Technical Field

[0001] The present invention relates to a porous low dielectric polymer film, a laminate, and a wiring circuit board.

Background Art

[0002] Since a porous polymer film can obtain a low dielectric constant by porosity, for example, its use as an insulating layer of FPC (Flexible printed circuits) has been promoted.

[0003] For example, a porous polymer film using a resin composition containing a bismaleimide resin (A) obtained by reacting a tetracarboxylic dianhydride (a1), a diamine (a2) containing a dimer diamine, and maleic anhydride (a3), inorganic hollow particles (B), rubber (C), and a polymerization initiator (D) has been proposed (see Patent Document 1).

[0004] On the other hand, as hollow particles, a shell portion formed of a polymer having a urea bond and / or a urethane bond obtained by the reaction of an isocyanate compound having a plurality of isocyanate groups with an active hydrogen compound having a plurality of amino groups or hydroxy groups and / or water, and a hollow portion surrounded by the shell portion, and the isocyanate compound is a hollow particle of polymeric MDI has been proposed (see Patent Document 2). Further, as a method for producing hollow particles, it has a shell portion formed of a polymer of a monomer component containing a divinyl aromatic compound and a monovinyl aromatic compound, and a hollow portion surrounded by the shell portion, and the dielectric tangent measured by the cavity resonator method (frequency 10 GHz (room temperature)) is 1.00×10 -3A method for producing hollow particles has been proposed, comprising the steps of: (a) mixing the monomer component with a hydrophobic solvent having 9 or more carbon atoms, such as a normal paraffin solvent, an isoparaffin solvent, or a naphthenic solvent, to obtain an oily mixture; (b) mixing the oily mixture with water to obtain an emulsion in which the oily mixture is dispersed in the water; (c) polymerizing the monomer component in the emulsion to form a polymer containing the hydrophobic solvent; and (d) (d1) washing the polymer with water and (d2) washing the polymer with an organic solvent to remove the hydrophobic solvent contained within the polymer (see Patent Document 3). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2023-180707 [Patent Document 2] Patent No. 6924533 [Patent Document 3] Patent No. 7396735 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Porous polymer films containing hollow particles can be manufactured simply by dispersing the hollow particles in a polymer film. Therefore, porous polymer films containing hollow particles can be manufactured using a simple method. On the other hand, porous polymer films containing hollow particles tend to become rigid, resulting in a decrease in flexibility.

[0007] The present invention aims to provide a porous low-dielectric polymer film with improved flexibility, a laminate comprising the porous low-dielectric polymer film, and a wiring circuit board. [Means for solving the problem]

[0008] In other words, the present invention encompasses the following: [1] A porous low-dielectric polymer film, Hollow particles and fine pores are dispersed in a film composed of polymers. A porous, low-dielectric polymer film having a relative permittivity of 2.40 or less. [2] The porous low-dielectric polymer film according to [1], wherein the volume ratio of voids due to hollow particles to the total voids is 10% or more. [3] A porous low-dielectric polymer film according to [1] or [2], wherein the porosity is 10% or more and 35% or less. [4] A laminate comprising, in order in the thickness direction, a porous low-dielectric polymer film and a metal layer as described in any of [1] to [3]. [5] A wiring circuit board comprising, in order in the thickness direction, a porous low-dielectric polymer film and a conductive layer as described in any of [1] to [3]. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a porous low-dielectric polymer film with improved flexibility, a laminate comprising the porous low-dielectric polymer film, and a wiring circuit board. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic cross-sectional view of one embodiment of a porous low-dielectric polymer film. [Figure 2] Figure 2 is a schematic cross-sectional view of one embodiment of the laminate. [Figure 3] Figure 3 is a schematic cross-sectional view of one embodiment of a wiring circuit board. [Modes for carrying out the invention]

[0011] (Porous low-dielectric polymer film) The porous low-dielectric polymer film of the present invention is a film in which hollow particles and fine pores are dispersed in a film composed of a polymer.

[0012] The fine pores are formed, for example, by porosification with a porosifying agent when producing the polymer film.

[0013] Since the porous low-dielectric polymer film not only contains hollow particles but also has fine pores formed by porosification with a porosifying agent, a film with improved flexibility while maintaining low dielectric properties can be obtained.

[0014] The relative dielectric constant of the porous low-dielectric polymer film is 2.40 or less. The lower limit value of the relative dielectric constant is not particularly limited, but for example, the relative dielectric constant is 2.00 or more.

[0015] The dielectric tangent of the porous low-dielectric polymer film is, for example, 0.0025 or less. The lower limit value of the dielectric tangent is not particularly limited, but for example, the dielectric tangent is 0.0010 or more.

[0016] The relative dielectric constant (Dk) and dielectric tangent (Df) are values measured at 10 GHz using a "10 GHz SPDR resonator" manufactured by QWED in accordance with the SPDR method (split post dielectric resonance method) compliant with ASTM D150.

[0017] The porosity of the porous low-dielectric polymer film is not particularly limited, but from the viewpoint of reducing the relative dielectric constant (Dk) and dielectric tangent (Df), 10% or more is preferable, 20% or more is more preferable, and 25% or more is particularly preferable. The upper limit value of the porosity of the porous low-dielectric polymer film is not particularly limited, but from the viewpoint of mechanical properties such as resistance to breakage, 50% or less is preferable, 40% or less is more preferable, and 35% or less is particularly preferable. The porosity can be determined by the method described in the examples. Alternatively, the porosity may be determined by measuring the relative permittivity of the porous sheet and the non-porous sheet, and using the Maxwell-Garn ett model to find the volume percentage of air in the porous sheet (porosity). The non-porous sheet may be manufactured, for example, by hot-pressing the porous sheet.

[0018] In a porous low-dielectric polymer film, the volume ratio of voids due to hollow particles to the total voids is, for example, 99% or less, preferably 95% or less, and more preferably 90% or less. By having a volume ratio of voids due to hollow particles to the total voids of 90% or less, a porous low-dielectric polymer film with improved flexibility can be obtained. In a porous low-dielectric polymer film, there is no particular lower limit to the volume ratio of pores due to hollow particles relative to the total pores, however, the volume ratio of pores due to hollow particles relative to the total pores is preferably 10% or more, more preferably 30% or more, and particularly preferably 50% or more. The volume ratio of voids caused by hollow particles to total voids can be determined, for example, by observing a porous low-dielectric polymer film using X-ray CT (Computed Tomography). X-ray CT observation allows for the distinction between voids caused by hollow particles and voids caused by porosity-enhancing agents. Furthermore, the volume ratio of voids due to hollow particles to the total voids can be calculated, for example, using the porosity of the porous low-dielectric polymer film and the amount of hollow particles added in the production of the porous low-dielectric polymer film.

[0019] <<polymer>> While there are no particular limitations on the polymer that makes up the film, polyimide resins and liquid crystal polymers are preferred because they easily achieve low dielectric properties.

[0020] <<<Polyimide resin>>> Polyimide resins are, for example, condensation polymers of monomer mixtures containing a diamine component and an acid dianhydride component.

[0021] -Diamine components- Examples of diamine components include the diamine represented by the following formula (M1). [ka] (In formula (M1), Y represents a single bond, -O-, -COO-, -S-, -CH2-, -CH(CH3)-, -C(CH3)2-, -CO-, -SO2-, -NH-, or -NHCO-. n represents 0 or 1.)

[0022] As the diamine represented by formula (M1), the diamine represented by the following formula (M1-1) is preferred. [ka] (In formula (M1-1), Y represents a single bond, -O-, -COO-, -S-, -CH2-, -CH(CH3)-, -C(CH3)2-, -CO-, -SO2-, -NH-, or -NHCO-. n represents 0 or 1.)

[0023] The diamine component may include, for example, dimer amine. Dimer amines are obtained by substituting all carboxyl groups of a dimer acid with primary amino groups or primary aminomethyl groups (see, for example, Japanese Patent Publication No. 9-12712). Here, dimer acid mainly consists of C36 dibasic acids obtained by dimerizing unsaturated fatty acids such as oleic acid, linoleic acid, and linolenic acid, and depending on the degree of purification, it also includes C18 monomeric acids, C54 trimeric acids, and C20-90 polymeric fatty acids. Note that the dimer acid contains double bonds, but the degree of unsaturation may be reduced by, for example, a hydrogenation reaction.

[0024] Examples of dimer amines include those represented by the following formula (DDA). In formula (DDA), m+n=6 to 17 is preferred, p+q=8 to 19 is preferred, and the dashed lines represent carbon-carbon single bonds or carbon-carbon double bonds. [ka]

[0025] Furthermore, commercially available dimer amines include "Versamin 551" and "Versamin 552" (both manufactured by Cognics Japan Co., Ltd.), and "PRIAMINE 1073," "PRIAMINE 1074," and "PRIAMINE 1075" (all manufactured by Croda Japan Co., Ltd.). Of these commercially available products, "Versamin 551" and "PRIAMINE 1074" contain a compound represented by the following formula (DDA-1), while "Versamin 552," "PRIAMINE 1073," and "PRIAMINE 1075" are dimer amines that contain a compound represented by the following formula (DDA-2). [ka] [ka]

[0026] Furthermore, the dimer amine may contain amines derived from the monomeric acid, trimer acid, and / or polymerized fatty acid, and the content of these amines is 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less in the dimer amine.

[0027] Furthermore, dimer amine may be used as is, or it may be used after undergoing purification treatment such as distillation.

[0028] The diamine component may include diamines other than those listed above.

[0029] -Acid dianhydride component- Examples of acid dianhydride components include acid dianhydrides represented by the following formula (M2). [ka] (In formula (M2), p -OCO-, or -COO-H2C-HC(-OC(=O)-CH3)-CH2-OCO-, where p is an integer between 1 and 20. -C6H4- represents a phenylene group.

[0030] Examples of acid dianhydrides represented by formula (M2) include the following: • 2,2',3,3'-biphenyltetracarboxylic acid dianhydride • 3,3',4,4'-biphenyltetracarboxylic acid dianhydride • 3,3',4,4'-diphenylsulfonetetracarboxylic acid dianhydride • 3,3',4,4'-Benzophenonetetracarboxylic dianhydride • 3,3',4,4'-diphenyl ether tetracarboxylic acid dianhydride (4,4'-oxydiphthalic acid anhydride) • 2,2-bis(3,3',4,4'-tetracarboxyphenyl)tetrafluoropropane dianhydride · 4,4'-[propane-2,2-diylbis(1,4-phenyleneoxy)]diphthalic acid dianhydride (bisphenol A type dianhydride) 2,2-Bis(2,3-dicarboxyphenyl)propane dianhydride 2,2-Bis(3,4-dicarboxyphenyl)propane dianhydride • 2,2'-Bis(3,4-dicarboxyphenoxyphenyl) sulfone dianhydride

[0031] The acid dianhydride component may include acid dianhydrides other than those listed above.

[0032] The molar proportion of the diamine represented by formula (M1) in the diamine component is not particularly limited, but is preferably 50 mol% or more, more preferably 70 mol% or more, and particularly preferably 80 mol% or more.

[0033] The molar proportion of the acid dianhydride component represented by formula (M2) is not particularly limited, but is preferably 50 mol% or more, more preferably 70 mol% or more, and particularly preferably 80 mol% or more.

[0034] The ratio of the diamine component to the acid dianhydride component is adjusted so that, for example, the molar amounts of the amino group (-NH2) of the diamine component and the acid anhydride group (-CO-O-CO-) of the acid dianhydride component are equal.

[0035] The polyimide resin may or may not contain fluorine, but a polyimide resin that does not contain fluorine is preferred.

[0036] Polyimide resins can be obtained, for example, by imidizing polyamic acid.

[0037] An example of a method for preparing polyacic acid is described below. For example, a diamine component solution is prepared by combining a diamine component with an organic solvent. The organic solvent is not particularly limited and includes, for example, polar aproton solvents such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethyl sulfoxide, such as ether solvents, ester solvents, aliphatic hydrocarbon solvents, and aromatic hydrocarbon solvents. Polar aproton solvents are preferred. The amount of organic solvent per 100 parts by mass of diamine component is, for example, 100 parts by mass or more, and for example, 1,000 parts by mass or less. The percentage of diamine component in the diamine component solution is, for example, 1% by mass or more, and for example, 10% by mass or less. Next, the diamine component solution and the acid dianhydride component are combined to prepare a mixture. If necessary, an appropriate amount of organic solvent can be added to the mixture at this stage. Subsequently, this mixture is heated. This causes a ring-opening polyaddition reaction between the diamine component and the acid dianhydride component, thereby preparing a polyamic acid solution. The heating temperature is, for example, between 50°C and 100°C.

[0038] Next, the polyamic acid solution, hollow particles, and porosity-forming agent are mixed together.

[0039] Subsequently, a polyamic acid solution containing hollow particles and a porosizing agent is applied to a substrate, and then the organic solvent is removed to obtain a film. Next, the porosizing agent is extracted from the film. Then, the film is heated. Upon heating, the polyamic acid undergoes a dehydration cyclization reaction, resulting in imidation of the polyamic acid and obtaining a polyimide resin. Simultaneously, a porous, low-dielectric polymer film is obtained.

[0040] <<<Liquid crystal polymer>>> The liquid crystal polymer is not limited. The liquid crystal polymer is a liquid crystalline thermoplastic resin. Examples of liquid crystal polymers include liquid crystal polyesters, preferably aromatic liquid crystal polyesters. Liquid crystal polymers are specifically described, for example, in Japanese Patent Publication No. 2020-147670 and Japanese Patent Publication No. 2004-189867. Commercially available liquid crystal polymers can be used. Examples of commercially available products include UENO LCP (registered trademark, hereinafter the same) 8100 series (low melting point type, manufactured by Ueno Pharmaceutical Co., Ltd.) and UENO LCP 5000 series (high melting point type, manufactured by Ueno Pharmaceutical Co., Ltd.). Preferably, the UENO LCP 5000 series is used.

[0041] The melting point of the liquid crystal polymer is not limited. The melting point of the liquid crystal polymer is, for example, 200°C or higher, preferably 220°C or higher, more preferably 250°C or higher, and also, for example, 370°C or lower. The melting point of the liquid crystal polymer is determined by differential scanning calorimetry. In differential scanning calorimetry, the heating rate is 10°C / min, and the liquid crystal polymer is heated in a nitrogen atmosphere, for example, by operating in a range from 25°C to 400°C. If the liquid crystal polymer is a commercially available product, the catalog value of the commercially available product can be used as is. If the melting point of the liquid crystal polymer is below the upper limit mentioned above, the porous low-dielectric polymer film has excellent handling and processability. If the melting point of the liquid crystal polymer is above the lower limit mentioned above, the porous low-dielectric polymer film has excellent heat resistance.

[0042] The glass transition temperature of a liquid crystal polymer is not limited. For example, it may be above 80°C, or below 125°C. The glass transition temperature of a liquid crystal polymer is determined by differential scanning calorimetry performed at a heating rate of 10°C / min.

[0043] <<Hollow particles>> The hollow particles are not particularly limited and may be organic or inorganic hollow particles, but organic hollow particles are preferred from the viewpoint of circuit processability. In the case of inorganic hollow particles, when via processing or drilling is performed on the polymer film, fragments of the inorganic material shell may be generated and remain as residue. On the other hand, in the case of organic hollow particles, although the organic resin shell melts or deforms during processing, it is less likely to break, so fragments are less likely to remain as residue.

[0044] <<Organic hollow particles>> Organic hollow particles are hollow particles that have an organic resin shell. The organic resin that constitutes the shell of the organic hollow particles is not particularly limited.

[0045] The organic hollow particle has a shell made of organic resin and a hollow portion surrounded by the shell.

[0046] The organic resin used as the shell in the hollow organic particles may be a thermoplastic resin or a cured product of a thermosetting resin. The organic resin serving as the shell in the hollow organic particles may or may not have a cross-linked structure.

[0047] Examples of organic resins include polymers of monomer components containing divinyl aromatic compounds. Organic resins are, for example, resins having at least one of urea bonds and urethane bonds. Such resins are obtained, for example, by the reaction of an isocyanate compound having multiple isocyanate groups with an active hydrogen compound having multiple amino groups or hydroxyl groups and / or water. Examples of organic hollow particles include the hollow particles described in Japanese Patent Publication No. 6924533 and Japanese Patent Publication No. 7396735.

[0048] The glass transition temperature of the organic resin acting as a shell in the organic hollow particles is not particularly limited, but it is preferable that it be higher than the melting point of the polymer constituting the film. By doing so, when the polymer, porous agent, and organic hollow particles are kneaded together and the organic hollow particles are dispersed in the polymer, the organic hollow particles can be dispersed without deformation or damage.

[0049] <<Inorganic hollow particles>> Inorganic hollow particles are hollow particles that possess a shell made of inorganic material. Examples of inorganic materials that constitute the shells of inorganic hollow particles include silica, alumina, glass, cordierite, silicon oxide, barium sulfate, barium carbonate, talc, clay, mica powder, zinc oxide, hydrotalcite, boehmite, aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, magnesium oxide, boron nitride, aluminum nitride, manganese nitride, aluminum borate, strontium carbonate, strontium titanate, calcium titanate, magnesium titanate, bismuth titanate, titanium dioxide, zirconium oxide, barium titanate, barium zirconate titanate, barium zirconate, calcium zirconate, zirconium phosphate, zirconium tungstate phosphate, and aluminosilicate. Among these, silica is particularly excellent in low dielectric loss tangent, therefore hollow silica is preferred as the inorganic hollow particle.

[0050] The hollowness ratio of the hollow particles is not particularly limited, but is preferably 5% to 80%, more preferably 10% to 75%, and particularly preferably 30% to 70%. The hollow ratio can be calculated, for example, using the following formula. Hollow fraction of a hollow particle (%) = (R1 / R2) 3 ×100 R1: Inner diameter of the hollow particle R2: Outer diameter of hollow particle For example, electron microscope observation is performed to determine the hollowness ratio of any 10 hollow particles, and the arithmetic mean of these ratios is taken as the hollowness ratio.

[0051] The average particle diameter (median diameter) of the hollow particles is not particularly limited, but 50 nm to 500 nm is preferred. The average particle size (median diameter) of the hollow particles is not particularly limited, but it is preferably 0.05% to 50% of the thickness of the porous low-dielectric polymer film. The average particle diameter (median diameter) of hollow particles can be determined, for example, by measurement using a laser diffraction / scattering particle size distribution analyzer, or by particle size measurement using cross-sectional images of polymer films (e.g., scanning electron microscope images).

[0052] The thickness of the porous low-dielectric polymer film is not particularly limited, but for example, it is 0.01 mm to 1 mm, more preferably 0.05 mm to 1 mm, and particularly preferably 0.1 mm to 1 mm.

[0053] <Method for manufacturing porous low-dielectric polymer films> The method for producing a porous, low-dielectric polymer film is not particularly limited, but may include, for example, a film production step and an extraction step.

[0054] <<Film Manufacturing Process>> The film manufacturing process is a process of producing a film of a composition containing a polymer, hollow particles, and a porosity-reducing agent. In one example of a film manufacturing process, for instance, a composition is obtained by mixing hollow particles and a porosity-forming agent with a polymer solution, and then the composition is applied and dried to produce a film. Another example of a film manufacturing process involves, for instance, kneading a polymer, hollow particles, and a porosity-forming agent to obtain a composition, and then forming the composition into a film by pressing, extruding, or injection molding.

[0055] Examples of polymers include those mentioned in the description of porous, low-dielectric polymer films.

[0056] Examples of hollow particles include the hollow particles mentioned in the description of porous, low-dielectric polymer films. In the film manufacturing process, there are no particular restrictions on the amount of hollow particles added to the polymer, but it is preferably 10% to 50% by mass, and more preferably 15% to 45% by mass relative to the polymer.

[0057] <<<Porous agent>>> Porousing agents are components dispersed in polymers when producing porous, low-dielectric polymer films to make polymer films porous. Furthermore, porousing agents undergo phase separation from the polymer, for example, at the kneading temperature. Phase separation involves the agent remaining undissolved in the polymer and maintaining a certain shape within the kneaded mixture.

[0058] The porosizing agent may be a liquid or a solid at room temperature and pressure.

[0059] The porosizing agent may be, for example, an organic porosizing agent or an inorganic porosizing agent.

[0060] -Organic porous agent- Examples of porosity-forming agents that are liquid at room temperature and pressure include low-polarity compounds. Such porosity-forming agents include aliphatic hydrocarbons, fatty acids, and fatty acid esters. Examples of aliphatic hydrocarbons include n-decane, n-undecane, n-dodecane, n-tridecane, n-pentadecane, n-tetradecane, n-hexadecane, n-heptadecane, and liquid paraffin. Examples of fatty acids include saturated fatty acids and unsaturated fatty acids. Examples of saturated fatty acids include butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, and octanoic acid. Examples of unsaturated fatty acids include palmitoleic acid, oleic acid, linoleic acid, and (9,12,15)-linolenic acid. Examples of fatty acid esters include methyl oleate, ethyl oleate, isopropyl isostearate, and methyl linoleate. Examples of solid porosity-forming agents at room temperature and pressure include imide compounds and fluorinated acid anhydrides. Examples of imide compounds include hexahydrophthalimide, succinimide, N-methylsuccinimide, N-hydroxysuccinimide, 1,2,3,6-tetrahydrophthalimide, 5-norbornene-2,3-dicarboximide, N-phenylsuccinimide, 1,2,3,4-cyclobutanetetracarboxylic acid diimide, phthalimide, N-methylphthalimide, N-hydroxyphthalimide, and N-hydroxymethylphthalimide. Examples of fluorinated acid anhydrides include 4,4'-(hexafluoroisopropylidene)diphthalic anhydride and tetrafluorophthalic anhydride.

[0061] Furthermore, polyoxyethylene dimethyl ether can be used as an organic porosizing agent. By using polyoxyethylene dimethyl ether as a porosizing agent, the porous structure of the resulting film can be made into a closed-cell structure. Other organic porous agents, such as polyalkylene glycols including polyethylene glycol and polypropylene glycol; methyl-saturated products of one or both ends of the polyalkylene glycol, or (meth)acrylate-saturated products of one or both ends of the polyalkylene glycol; compounds in which one end of a polyalkylene glycol, such as phenoxypolyethylene glycol (meth)acrylate, is saturated with an alkyl or aryl group and the other end is saturated with (meth)acrylate; urethane prepolymers; polyhydric alcohol poly(meth)acrylates such as trimethylolpropane tri(meth)acrylate and dipentaerythritol hexa(meth)acrylate; (meth)acrylate compounds such as ε-caprolactone (meth)acrylate, urethane (meth)acrylate, epoxy (meth)acrylate, and oligoester (meth)acrylate may be used in combination with polyoxyethylene dimethyl ether, to the extent that the porous structure of the resulting film is a closed-cell structure.

[0062] -Inorganic porous agent- The inorganic compound used as an inorganic porosizing agent is not particularly limited, but examples include inorganic salts, inorganic oxides, inorganic nitrides, and inorganic sulfides. Among these, inorganic salts are preferred because they are easily extracted in the extraction process.

[0063] The inorganic salt may be an anhydrous or hydrated form, but the anhydrous form is preferred. The inorganic salt is not particularly limited, but examples include metal halides, metal nitrates, metal sulfates, and metal carbonates. Among these, metal halides are preferred because they are easily extracted in the extraction process. Examples of halogens in metal halides include fluorine, chlorine, bromine, and iodine. Among these, chlorine and bromine are preferred. The metal in the inorganic salt is not particularly limited, but alkali metals and alkaline earth metals are preferred. Examples of alkali metals include lithium, sodium, potassium, rubidium, cesium, and francium. Among these, lithium, sodium, and potassium are preferred. Examples of alkaline earth metals include beryllium, magnesium, calcium, strontium, barium, and radium. Of these, calcium is preferred.

[0064] The metal halide is preferably at least one of alkali metal halides and alkaline earth metal halides. Examples of alkali metal halides include lithium chloride, sodium chloride, potassium chloride, lithium bromide, sodium bromide, and potassium bromide. Examples of alkaline earth metal halides include calcium chloride and calcium bromide.

[0065] Inorganic compounds are usually subjected to mixing in powder form. The average particle size of the inorganic compound is not particularly limited and can be appropriately determined depending on the degree of porosity, the thickness of the porous low-dielectric polymer film, and other factors. The average particle size of the inorganic compound powder is, for example, 0.001 mm to 0.8 mm, preferably 0.003 mm to 0.6 mm, and more preferably 0.005 mm to 0.4 mm. The average particle size can be measured using a laser diffraction / scattering particle size distribution analyzer.

[0066] The melting point of the inorganic compound is preferably higher than the melting point (Tm) of the polymer, more preferably 10°C or more higher than the melting point of the polymer, and particularly preferably 20°C or more higher than the melting point of the polymer. The melting point of the inorganic compound is preferably, for example, the melting point of the polymer + 600°C or less. The melting point of an inorganic compound can be determined, for example, by the same method used to measure the melting point of a polymer. The temperature range for differential scanning calorimetry in measuring the melting point of an inorganic compound is, for example, 25°C to 1,000°C.

[0067] In the film manufacturing process, there are no particular restrictions on the amount of porosity agent added to the polymer, but 5% to 45% by mass is preferred, and 10% to 35% by mass is more preferred.

[0068] In the film manufacturing process, the mass ratio of hollow particles to porous agent (hollow particles:porous agent) is not particularly limited, but 47:3 to 5:45 is preferred, 45:5 to 10:40 is more preferred, and 40:10 to 15:35 is particularly preferred.

[0069] <<Extraction process>> The extraction process is the process of extracting the porous agent from the film. The extraction method is not particularly limited, and examples include supercritical fluid extraction. The method for supercritical extraction is not particularly limited and can be carried out by referring to, for example, the method described in Japanese Patent Application Publication No. 2022-165325.

[0070] <Other processes> Other processes include, for example, a heating process. Heating is performed, for example, after the extraction process. Heating is performed, for example, when polyimide resin is used as the polymer that makes up the film. Heating after extraction causes the polyamic acid to undergo a dehydration cyclization reaction, resulting in imidization of the polyamic acid and obtaining polyimide resin. There are no particular restrictions on the heating temperature and time.

[0071] <Applications of porous, low-dielectric polymer films> The applications of porous, low-dielectric polymer films are not limited. Examples of applications include insulating layers for wiring circuit boards and antenna substrates for wireless communication.

[0072] Figure 1 shows one embodiment of a porous, low-dielectric polymer film. Figure 1 is a schematic cross-sectional view of one embodiment of a porous low-dielectric polymer film. In the porous low-dielectric polymer film 1, hollow particles 12 and fine pores 13 are dispersed in a film composed of polymer 11.

[0073] (Laminated structure) The laminate of the present invention comprises, in order in the thickness direction, a porous low-dielectric polymer film and a metal layer according to the present invention. The laminate may also include, for example, an adhesive layer. In a laminate, a porous, low-dielectric polymer film serves as an insulating layer.

[0074] <Metal layer> The metal layer has a sheet (plate) shape. The material of the metal layer is not particularly limited and includes, for example, copper, iron, silver, gold, aluminum, nickel, and their alloys (stainless steel, bronze). Copper is preferred.

[0075] The thickness of the metal layer is, for example, 0.1 μm or more, preferably 1 μm or more, and also, for example, 100 μm or less, preferably 50 μm or less.

[0076] <Adhesive layer> The adhesive layer, for example, has a sheet shape that aligns with the surface direction on one surface in the thickness direction of the porous low-dielectric polymer film of the present invention.

[0077] The adhesive layer material is not particularly limited and can be any type of adhesive, such as hot-melt adhesives or thermosetting adhesives. Specifically, it can be an acrylic adhesive, an epoxy adhesive, or a silicone adhesive. An acrylic adhesive is preferred.

[0078] The thickness of the adhesive layer is, for example, 2 μm or more, preferably 5 μm or more, and for example, 50 μm or less, preferably 25 μm or less.

[0079] The thickness of the laminate is, for example, 10 μm or more, preferably 20 μm or more, and also, for example, 5,000 μm or less, preferably 2,000 μm or less.

[0080] The laminate is used in various applications, for example, as a low-dielectric substrate material, and is preferably used in the manufacture of high-frequency antennas and high-speed transmission substrates (such as high-speed transmission FPCs) that conform to fifth-generation (5G) standards. Specifically, the low-dielectric substrate material is used as a substrate material for high-frequency antennas and high-speed FPCs.

[0081] An example of the laminate of the present invention will be explained with reference to the figure. Figure 2 is a schematic cross-sectional view of one embodiment of the laminate. The laminate 20 comprises a porous low-dielectric polymer film 1 and a metal layer 21 in that order. In the porous low-dielectric polymer film 1, hollow particles 12 and fine pores 13 are dispersed in a film composed of polymer 11.

[0082] (Wiring circuit board) The wiring circuit board of the present invention comprises, in order in the thickness direction, a porous low-dielectric polymer film and a conductive layer of the present invention. In a wiring circuit board, a porous, low-dielectric polymer film serves as an insulating layer.

[0083] A wiring circuit board has wiring, for example, as a conductive layer. Examples of wiring include signal wiring, antenna wiring, and ground wiring. Wiring can be formed, for example, by patterning a metal layer using photolithography (e.g., subtractive method).

[0084] An example of a wiring circuit board will be explained using a diagram. Figure 3 is a schematic cross-sectional view of one embodiment of a wiring circuit board. The wiring circuit board 50 has a sheet shape. The wiring circuit board 50 has a porous low-dielectric polymer film 1 and a conductive layer 51 in that order. The conductive layer 51 has a predetermined wiring pattern. The wiring circuit board 50 shown in Figure 3 can be manufactured, for example, as follows. First, prepare the laminate 20 shown in Figure 2. Next, a conductive layer 51 is formed on a porous low-dielectric polymer film 1 by patterning the metal layer 21 of the laminate 20 shown in Figure 2 using photolithography.

[0085] The modified wiring circuit board comprises a conductor layer, an insulating layer, and another conductor layer, arranged sequentially on one side in the thickness direction. The insulating layer is made of the porous, low-dielectric polymer film described above. Each of the two conductor layers is arranged on one side and the other side in the thickness direction of the insulating layer, and has a predetermined wiring pattern. [Examples]

[0086] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to the examples and comparative examples.

[0087] The meanings and structures of the abbreviations for the components used in the synthesis of polyamic acid are as follows: <Diamine component> • ODA: 4,4'-oxydianiline • PDA: p-phenylenediamine APAB: 4-aminophenyl-4-aminobenzoate [ka]

[0088] Priamine 1075: Dimer amine, manufactured by Croda Japan Co., Ltd. Priamine 1075 is a dimer amine containing the compound represented by the following structure. [ka]

[0089] <Tetracarboxylic acid dianhydride component> • s-BPDA: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride • BPADA: Bisphenol A type dianhydride [ka]

[0090] The organic hollow particles used in the examples were those manufactured by Sansui Co., Ltd., as follows. ·Average particle size: 100nm~300nm ·Hollow rate: 40%~60% • Relative permittivity: 1.3 • Dielectric loss tangent: 0.0005 ·Thermal decomposition temperature: 390℃

[0091] The following porous agents were used in the examples. • Porousing agent: NOF Corporation's Uniox MM-400 (polyoxyethylene-dimethyl ether)

[0092] <Synthesis Example 1> Under a nitrogen atmosphere, the diamine components shown in Table 1 and 100 g of anhydrous NMP (N-methyl-2-pyrrolidone) were added to a 300 mL separable flask and stirred at 25°C for 20 minutes. Subsequently, the tetracarboxylic dianhydride components shown in Table 1 and 10 g of anhydrous NMP were added and stirred at 60°C for 10 hours. Stirring was stopped, and the mixture was allowed to cool to prepare a brown polyamic acid solution.

[0093] <Synthesis Example 2> A polyamic acid solution was prepared in the same manner as in Synthesis Example 1, except that the diamine component and the tetracarboxylic dianhydride component were changed to the diamine component and tetracarboxylic dianhydride component shown in Table 1.

[0094] [Table 1]

[0095] <Example 1> To the polyamic acid solution obtained in Synthesis Example 1, 15 parts by mass of hollow particles and 35 parts by mass of a porous agent were added per 100 parts by mass of the solid content of the polyamic acid solution to obtain a solution. The obtained solution was applied to a copper substrate film to form a coating. Subsequently, the coating film was dried at 135°C for 15 minutes to prepare a precursor film. This precursor film was immersed in carbon dioxide pressurized to 30 MPa at 60°C and passed through it for 4 hours to promote the extraction and removal of the porosity-forming agent, phase separation of the remaining NMP, and porosity formation. Subsequently, the carbon dioxide was reduced in pressure. Subsequently, the precursor film was heated under vacuum at a temperature of 390°C for approximately 185 minutes to remove residual components and promote imidization, thereby obtaining a porous low-dielectric polymer film (porous polyimide film) arranged on one side in the thickness direction of the base film. Subsequently, the base film and the porous low-dielectric polymer film were immersed in an FeCl3 solution to remove the base film, obtaining a porous low-dielectric polymer film with a thickness of 48 μm.

[0096] <Examples 2-4> A porous, low-dielectric polymer film with a thickness of 50 μm was obtained in the same manner as in Example 1, except that the amounts of hollow particles and porosity-forming agents were changed to the amounts listed in Table 2-1.

[0097] <Comparative Example 1> To the polyamic acid solution obtained in Synthesis Example 1, 50 parts by mass of hollow particles were added for every 100 parts by mass of solid content in the polyamic acid solution to obtain a solution. The obtained solution was applied to a copper substrate film to form a coating. Subsequently, the coating film was dried at 135°C for 15 minutes to prepare a precursor film. This precursor film was heated under vacuum at a temperature of 390°C for approximately 185 minutes to remove residual components and promote imidization, thereby obtaining a porous, low-dielectric polymer film (porous polyimide film) arranged on one side in the thickness direction of the base film. Subsequently, the base film and the porous low-dielectric polymer film were immersed in an FeCl3 solution to remove the base film, obtaining a porous low-dielectric polymer film with a thickness of 47 μm.

[0098] <Example 5> A porous, low-dielectric polymer film with a thickness of 48 μm was obtained in the same manner as in Example 1, except that 15 parts by mass of hollow particles and 35 parts by mass of a porosizing agent were added to the polyamic acid solution obtained in Synthesis Example 2, per 100 parts by mass of the solid content of the polyamic acid solution, to obtain a solution.

[0099] <Examples 6-8> A porous, low-dielectric polymer film with a thickness of 48 μm was obtained in the same manner as in Example 5, except that the amounts of hollow particles and porosity-forming agents were changed to the amounts listed in Table 2-2.

[0100] <Comparative Example 2> Except for using the polyamic acid solution obtained in Synthesis Example 2, the procedure was the same as in Comparative Example 1, and the thickness was A porous, low-dielectric polymer film with a thickness of 48 μm was obtained.

[0101] [evaluation] <Hollow: Cavity (Volume Ratio)> The volume ratio (hollow:hollow) of voids caused by hollow particles to voids caused by the porous agent was determined by the following method. The results are shown in Tables 2-1 and 2-2. The total volume of voids in a porous low-dielectric polymer film was determined from the porosity obtained using the method described in <Porosity> below. Furthermore, the volume of voids (hollows) caused by the hollow particles in the porous low-dielectric polymer film was determined from the amount of hollow particles added. Here, the total voids in the porous low-dielectric polymer film consist only of voids caused by the hollow particles (hollows) and voids caused by the porosizing agent. From these, the volume ratio (hollows:voids) was determined.

[0102] <Porosity> The porosity was calculated using the following formula. The results are shown in Tables 2-1 and 2-2. Porosity (%) = (1 - specific gravity of porous material / specific gravity of non-porous material) × 100 <<Method for calculating specific gravity>> Porous or non-porous material was cut into 20 x 20 mm pieces, its weight was measured, and the following formula was used to calculate the weight. Specific gravity = (weight (g)) / (area (cm) 2 ) × film thickness (cm) The specific gravity of the porous material was determined using the porous, low-dielectric polymer films produced in each example and comparative example. The specific gravity of the non-porous material was determined using a non-porous polymer film prepared by the following method. <<Fabrication of Non-Porous Polymer Films>> The polyamic acid solution obtained in Synthesis Example 1 or 2 was applied to a copper substrate film to form a coating. Subsequently, the coating film was dried at 135°C for 15 minutes to prepare a precursor film. This precursor film was heated under vacuum at a temperature of 390°C for approximately 185 minutes to remove residual components and promote imidization, thereby obtaining a non-porous polymer film (non-porous polyimide film) arranged on one side in the thickness direction of the base film. Subsequently, the base film and the nonporous polymer film were immersed in an FeCl3 solution to remove the base film and obtain the nonporous polymer film.

[0103] <Dielectric constant> The relative permittivity (Dk) and dielectric loss tangent (Df) of porous low-dielectric polymer films were measured at 10 GHz using the SPDR (Split Post Dielectric Resonance) method compliant with ASTMD150, with a QWED 10 GHz SPDR resonator. The results are shown in Tables 2-1 and 2-2.

[0104] <Flexibility> A porous, low-dielectric polymer film was subjected to the MIT test (JIS C 5016). A strip-shaped test piece (porous, low-dielectric polymer film: 1 cm wide x 8 cm long) was attached to a spring load clamp and bent 135° to the left and right using a bending device while being pulled with a load of 4.9 N. The bending radius was set to 2 mm. The following evaluation criteria were used. The results are shown in Tables 2-1 and 2-2. [Evaluation Criteria] Good: No breakage or cracks after being folded 5 times. Acceptable: No breakage after being folded 5 times, but there are cracks. Failure: The test specimen fractured after being bent four times or less. [Table 2-1]

[0105] [Table 2-2] [Explanation of Symbols]

[0106] 1. Porous low-dielectric polymer film 10 Laminate 11 Polymers 12 Hollow particles 13 Holes 20 Laminate 21 Metal layer 50 Wiring circuit board 51 Conductor layer

Claims

1. A porous, low-dielectric polymer film, Hollow particles and fine pores are dispersed in a film composed of polymers. A porous, low-dielectric polymer film having a relative permittivity of 2.40 or less.

2. The porous low-dielectric polymer film according to claim 1, wherein the volume ratio of voids due to hollow particles to the total voids is 10% or more.

3. A porous low-dielectric polymer film according to claim 1, wherein the porosity is 10% or more and 35% or less.

4. A laminate comprising, in order in the thickness direction, a porous low-dielectric polymer film and a metal layer according to any one of claims 1 to 3.

5. A wiring circuit board comprising, in order in the thickness direction, a porous low-dielectric polymer film and a conductive layer according to any one of claims 1 to 3.

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