Porous low dielectric polymer film, laminate, and wiring circuit board

Abstract

This porous low dielectric polymer film is obtained by dispersing hollow particles and fine pores in a film composed of a polymer, and has a relative permittivity of 2.40 or less.

Description

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

[0001] The present invention relates to porous low-dielectric polymer films, laminates, and wiring circuit boards.

[0002] Porous polymer films are increasingly being used as insulating layers in flexible printed circuits (FPCs) because their porous structure allows for a low dielectric constant.

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

[0004] On the other hand, a hollow particle has been proposed in which the hollow particle has a shell portion formed of a polymer having urea bonds and / or urethane bonds, obtained 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, and a hollow portion surrounded by the shell portion, wherein the isocyanate compound is polymeric MDI (see Patent Document 2). Furthermore, a method for producing a hollow particle has been proposed in which the hollow particle has a shell portion formed of a polymer of monomer components including a divinyl aromatic compound and a monovinyl aromatic compound, and a hollow portion surrounded by the shell portion, and the dielectric loss 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).

[0005] Japanese Patent Publication No. 2023-180707, Japanese Patent Publication No. 6924533, Japanese Patent Publication No. 7396735

[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.

[0008] In other words, the present invention encompasses the following: [1] A porous low-dielectric polymer film, wherein hollow particles and fine pores are dispersed in a film composed of a polymer, and the relative dielectric constant is 2.40 or less. [2] The porous low-dielectric polymer film according to [1], wherein the volume ratio of pores due to hollow particles to total pores is 10% or more. [3] The 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 the porous low-dielectric polymer film according to any one of [1] to [3] and a metal layer in order in the thickness direction. [5] A wiring circuit board comprising the porous low-dielectric polymer film according to any one of [1] to [3] and a conductor layer in order in the thickness direction.

[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.

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

[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 polymer.

[0012] Fine pores are formed, for example, by porosity creation using porosizing agents during the manufacturing of polymer films.

[0013] By creating a porous, low-dielectric polymer film that not only contains hollow particles but also has fine pores formed by porosity enhancement with a porosizing agent, it is possible to obtain a film with improved flexibility while maintaining low dielectric properties.

[0014] The relative permittivity of a porous, low-dielectric polymer film is 2.40 or less. There is no particular lower limit to the relative permittivity, but for example, it is 2.00 or more.

[0015] The dielectric loss tangent of a porous, low-dielectric polymer film is, for example, 0.0025 or less. There is no particular lower limit to the dielectric loss tangent, but for example, the dielectric loss tangent is 0.0010 or more.

[0016] The relative permittivity (Dk) and dielectric loss tangent (Df) are values ​​measured at 10 GHz using a QWED 10 GHz SPDR resonator in accordance with the ASTMD150 SPDR method (split-post dielectric resonant method).

[0017] The porosity of the porous low-dielectric polymer film is not particularly limited, but from the viewpoint of reducing the relative permittivity (Dk) and dielectric loss tangent (Df), it is preferably 10% or more, more preferably 20% or more, and particularly preferably 25% or more. The upper limit 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, it is preferably 50% or less, more preferably 40% or less, and particularly preferably 35% or less. 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 determine the volume percentage of air in the porous sheet (porosity). The non-porous sheet may be made, 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. There is no particular lower limit to the volume ratio of voids due to hollow particles to the total voids in a porous low-dielectric polymer film, but it is preferably 10% or more, more preferably 30% or more, and particularly preferably 50% or more. The volume ratio of voids due to hollow particles to the total voids can be determined, for example, by observing the porous low-dielectric polymer film using X-ray CT (Computed Tomography). In X-ray CT observation, for example, voids due to hollow particles and voids due to the porous agent can be observed separately. 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] <<Polymers>> There are no particular limitations on the polymers that make up the film, but polyimide resins and liquid crystal polymers are preferred because they make it easier to achieve low dielectric properties.

[0020] <<<Polyimide resin>>> Polyimide resin is, for example, a condensation polymer of a monomer mixture containing a diamine component and an acid dianhydride component.

[0021] -Diamine component- Examples of diamine components include the diamine represented by the following formula (M1). (In formula (M1), Y is a single bond, -O-, -COO-, -S-, -CH ２ -, -CH(CH ３ )-,-C(CH ３ ) ２ -, -CO-, -SO ２ (This represents -, -NH-, or -NHCO-. n represents 0 or 1.)

[0022] As the diamine represented by the formula (M1), the diamine represented by the following formula (M1-1) is preferable. (In the formula (M1-1), Y represents a single bond, -O-, -COO-, -S-, -CH ２ -, -CH(CH ３ ), -C(CH ３ ) ２ -, -CO-, -SO ２ -, -NH-, or -NHCO-. n represents 0 or 1.)

[0023] As the diamine component, for example, it may contain dimer diamine. The dimer diamine is a substance in which all carboxyl groups of dimer acid are substituted with primary amino groups or primary aminomethyl groups (for example, refer to Japanese Patent Laid-Open No. 9-12712). Here, the dimer acid mainly contains a dibasic acid having 36 carbon atoms obtained by dimerizing unsaturated fatty acids such as oleic acid, linoleic acid, and linolenic acid, and depending on the degree of purification, it contains monomer acid having 18 carbon atoms, trimer acid having 54 carbon atoms, and polymerized fatty acids having 20 to 90 carbon atoms. Although the dimer acid contains double bonds, for example, the degree of unsaturation may be reduced by a hydrogenation reaction.

[0024] Examples of the dimer diamine include those represented by the following formula (DDA). In the formula (DDA), m + n = 6 to 17 is preferable, p + q = 8 to 19 is preferable, and the broken line part means a carbon-carbon single bond or a carbon-carbon double bond.

[0025] In addition, commercially available products of dimer diamine include "Versamine 551", "Versamine (552)" (both manufactured by Cognis Japan Co., Ltd.), "PRIAMINE 1073", "PRIAMINE 1074", "PRIAMINE 1075" (all manufactured by Croda Japan Co., Ltd.), etc. Among these commercially available products, "Versamine 551" and "PRIAMINE 1074" contain the compound represented by the following formula (DDA-1), and "Versamine 552", "PRIAMINE 1073", and "PRIAMINE 1075" are dimer diamines containing the compound represented by the following formula (DDA-2). [[ID=

[23] ]

[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 Components - Examples of acid dianhydride components include the acid dianhydride represented by the following formula (M2). (In equation (M2), X is a single bond, -SO ２ -, -CO-, -O-, -O-C ６ H ４ -C(CH ３ ) ２ -C ６ H ４ -O-, -C(CH ３ ) ２ -, -O-C ６ H ４ -SO ２ -C ６ H ４ -O-, -C(CHF ２ ) ２ -, -COO-(CH ２ ) ｐ -OCO-, or -COO-H ２ C-HC(-OC(=O)-CH ３ ) - CH ２ -OCO- represents a set of integers, where p is an integer between 1 and 20. ) -C ６ H ４ The dash (-) 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 acid dianhydride • 3,3',4,4'-diphenylethertetracarboxylic 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 acid 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 dianhydride represented by formula (M2) in the dianhydride 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.

[0034] The ratio of the diamine component to the acid dianhydride component is the amino group (-NH) of the diamine component. ２ The molar amounts of ) and the molar amounts of the acid anhydride group (-CO-O-CO-) of the acid dianhydride component are adjusted to be, for example, 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, a mixture is prepared by combining the diamine component solution with an acidic dianhydride component. At this time, an appropriate amount of organic solvent can be added to the mixture as needed. After that, this mixture is heated. By doing so, a polyamic acid solution is prepared by a ring-opening polyaddition reaction between the diamine component and the acidic dianhydride component. 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. Commercial liquid crystal polymers can be used. Examples of commercial 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 above upper limit, the porous low-dielectric polymer film has excellent handling and processability. If the melting point of the liquid crystal polymer is above the above lower limit, 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, the glass transition temperature of a liquid crystal polymer may be 80°C or higher, or 125°C or lower. 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>> There are no particular restrictions on the hollow particles; they may be organic hollow particles 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 these fragments may 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. There are no particular limitations on the organic resin that constitutes the shell of the organic hollow particle.

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

[0046] The organic resin serving as the shell in the hollow organic particles may be a thermoplastic resin or a cured thermosetting resin. The organic resin serving as the shell in the hollow organic particles may or may not have a crosslinked 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 can be 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 have a shell made of an inorganic material. Examples of inorganic materials that make up the shell 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 oxide, 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, so hollow silica is preferred as inorganic hollow particles.

[0050] The hollowness ratio of the hollow particle is not particularly limited, but is preferably 5% to 80%, more preferably 10% to 75%, and especially preferably 30% to 70%. The hollowness ratio can be calculated, for example, by the following formula: Hollowness ratio of hollow particle (%) = (R １ / R ２ ) ３ ×100 R １ : Inner diameter R of the hollow particle ２ : Outer diameter of hollow particles For example, observe with an electron microscope to determine the hollowness ratio of any 10 hollow particles, and take the arithmetic mean value as the hollowness ratio.

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

[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 film> The method for manufacturing porous low-dielectric polymer film is not particularly limited, but may include, for example, a film manufacturing step and an extraction step.

[0054] <<Film Manufacturing Process>> The film manufacturing process is the process of producing a film of a composition containing a polymer, hollow particles, and a porosizing agent. In one example of the film manufacturing process, for example, a composition is obtained by mixing a polymer solution with hollow particles and a porosizing agent, and then the composition is applied and dried to produce a film. In another example of the film manufacturing process, for example, a composition is obtained by kneading a polymer, hollow particles, and a porosizing agent, and then the composition is made into a film by pressing, extruding, injection molding, etc.

[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. The amount of hollow particles added to the polymer in the film manufacturing process is not particularly limited, but is preferably 10% to 50% by mass, and more preferably 15% to 45% by mass relative to the polymer.

[0057] <<<Porous Agents>>> Porous agents are components dispersed in polymers when producing porous, low-dielectric polymer films in order to make polymer films porous. Furthermore, porous agents undergo phase separation from the polymer, for example, at the kneading temperature. Phase separation involves not dissolving 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 Agents- Examples of porous agents that are liquid at room temperature and pressure include low-polarity compounds. Examples of such porous 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 Agents - The inorganic compound used as an inorganic porous 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 anhydrous or hydrated, but anhydrous 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 the 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. Among these, calcium is preferred.

[0064] The metal halide is preferably at least one of an alkali metal halide or an alkaline earth metal halide. 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, etc. The average particle size of the powdered inorganic compound 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, and particularly preferably 20°C or more higher. For example, the melting point of the inorganic compound is preferably 600°C or less above the melting point of the polymer. The melting point of the inorganic compound can be determined, for example, by the same method as the method for measuring the melting point of the polymer. The temperature range for differential scanning calorimetry in measuring the melting point of the 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 porous agent added to the polymer, but it is preferably 5% to 45% by mass, and more preferably 10% to 35% by mass relative to the polymer.

[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 a process of extracting the porous agent from the film. The extraction method is not particularly limited, and examples include supercritical extraction. The method of 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 constituting the film. Heating after extraction causes the polyamic acid to be imidized by a dehydration cyclization reaction, and polyimide resin is obtained. There are no particular restrictions on the temperature and time of heating.

[0071] <Applications of Porous Low-Dielectric Polymer Films> The applications of porous low-dielectric polymer films are not limited. Examples of applications for porous low-dielectric polymer films 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] (Laminate) The laminate of the present invention comprises, in order in the thickness direction, a porous low-dielectric polymer film and a metal layer. The laminate also comprises, for example, an adhesive layer as other components. In the laminate, the porous low-dielectric polymer film is 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 for example, 100 μm or less, preferably 50 μm or less.

[0076] <Adhesive Layer> The adhesive layer has a sheet shape that is aligned with the surface direction on one side 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 described with reference to the figures. Figure 2 is a schematic cross-sectional view of one embodiment of the laminate. The laminate 20 has 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 made 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. In the wiring circuit board, the porous low-dielectric polymer film is 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 with reference to the figures. 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, a laminate 20 shown in Figure 2 is prepared. Next, the conductive layer 51 is formed on the 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.

[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 components> ・ODA: 4,4'-oxydianiline ・PDA: p-phenylenediamine ・APAB: 4-aminophenyl-4-aminobenzoate

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

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

[0090] The organic hollow particles used in the examples were manufactured by Sansui Co., Ltd. and had the following characteristics: • Average particle size: 100 nm to 300 nm • Hollowness: 40% to 60% • Relative permittivity: 1.3 • Dielectric loss tangent: 0.0005 • Thermal decomposition temperature: 390°C

[0091] The porous agent used in the examples was the following: • Porous 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]

[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 solids in the polyamic acid solution to obtain a solution. The obtained solution was applied to a copper substrate film to form a coating. The coating was then 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 for 4 hours to promote the extraction and removal of the porous agent, phase separation of the remaining NMP, and the formation of pores. The carbon dioxide was then reduced in pressure. The precursor film was then heated under vacuum at 390°C for approximately 185 minutes to remove remaining 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 substrate film. The substrate film and the porous low-dielectric polymer film were then treated with FeCl ３ The substrate film was removed by immersion in a solution, yielding 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 to 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. The coating was then dried at 135°C for 15 minutes to prepare a precursor film. This precursor film was heated under vacuum at 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 substrate film. Subsequently, the substrate film and the porous low-dielectric polymer film were treated with FeCl ３ The substrate film was removed by immersion in a solution, yielding 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.

[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> A porous, low-dielectric polymer film with a thickness of 48 μm was obtained in the same manner as in Comparative Example 1, except that the polyamic acid solution obtained in Synthesis Example 2 was used.

[0101] [Evaluation] <Hollow:Vacuum (Volume Ratio)> The volume ratio (hollow:vacuum) of vacancies caused by hollow particles and vacancies caused by the porosizing agent was determined by the following method. The results are shown in Tables 2-1 and 2-2. The total volume of vacancies in the porous low-dielectric polymer film was determined from the porosity obtained by the method described in <Porosity> below. In addition, the volume of vacancies caused by hollow particles in the porous low-dielectric polymer film was determined from the amount of hollow particles added. Here, the total vacancies in the porous low-dielectric polymer film consist only of vacancies caused by hollow particles and vacancies caused by the porosizing agent. From these, the volume ratio (hollow:vacuum) 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>> A porous or non-porous material was cut into 20 × 20 mm pieces, its weight was measured, and the specific gravity was calculated using the following formula. Specific gravity = (Weight (g)) / (Area (cm²)) ２ ) × film thickness (cm) The specific gravity of the porous material was determined using the porous low-dielectric polymer film produced in each example and comparative example. The specific gravity of the non-porous material was determined using the non-porous polymer film produced by the following method. <<Preparation of non-porous polymer film>> The polyamic acid solution obtained in Synthesis Example 1 or 2 was applied to a copper substrate film to form a coating film. The coating film was then dried at 135°C for 15 minutes to produce a precursor film. This precursor film was heated under vacuum at 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 substrate film. The substrate film and the non-porous polymer film were then treated with FeCl ３ The substrate film was removed by immersion in a solution to obtain a non-porous polymer film.

[0103] <Dielectric Constant> The relative permittivity (Dk) and dielectric loss tangent (Df) of a porous low-dielectric polymer film at 10 GHz were measured using the SPDR method (split-post dielectric resonant method) compliant with ASTM D150, with a "10 GHz SPDR resonator" manufactured by QWED. 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 to 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 and no cracks after 5 bends. Acceptable: No breakage after 5 bends, but cracks are present. Unacceptable: The test piece broke after 4 or fewer bends.

[0105]

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

Claims

1. A porous low-dielectric polymer film, wherein hollow particles and fine pores are dispersed in a film composed of polymer, and the relative dielectric constant is 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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