Film for flexible printed wiring boards

Abstract

To provide a film for a flexible printed wiring board which has a low dielectric loss tangent and which can be laminated at a low temperature.SOLUTION: A film for a flexible printed wiring board is composed of a liquid crystal polymer with a crystal melting temperature of 260°C or less and a dielectric loss tangent of 0.0015 or less at 10 GHz measured by a cavity resonator perturbation method.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a film for flexible printed wiring boards that has excellent dielectric properties and interlayer adhesion, and a laminate including the same. [Background technology]

[0002] Electronic devices such as information processing devices and communication devices generally incorporate circuit boards. A circuit board typically has a substrate made of an insulating material and a layer made of a conductive material (hereinafter referred to as a conductor layer) formed on the substrate, and this conductor layer forms a circuit. Various electronic components are mounted on the circuit board by processes such as soldering.

[0003] In response to the demand for smaller and thinner circuit boards used in small electronic devices such as mobile phones, development is underway for circuit boards (flexible printed wiring boards) that use flexible resin films as insulating substrates. Resin films are used as insulating base materials for conductor circuit boards, bonding sheets that join boards with conductor circuits formed on the surface of the base material, and coverlay films that are formed on the surface of circuit layers.

[0004] In recent years, as the speed of transmitted signals has increased, signals have become increasingly frequent, and multilayer circuit boards having multiple conductor layers have come into widespread use.

[0005] Therefore, for flexible printed wiring boards, there is a demand for resin films that have a low dielectric loss tangent to suppress transmission loss in the high frequency range and excellent interlayer adhesion to allow multiple conductor layers to be multilayered.

[0006] Patent Document 1 describes a resin composition for flexible printed wiring boards, which is composed of a urethane resin, an epoxy resin, and a filler, and a sheet or film made from the composition. Patent Document 2 describes a flexible printed wiring board made from a liquid crystal polymer film. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2016 / 129565 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-10967 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the resin composition and sheet or film thereof described in Patent Document 1 have a high dielectric loss tangent and are not suitable for use in high frequency regions. In addition, the long heat curing time required results in a long manufacturing process.

[0009] The flexible printed wiring board made of the liquid crystal polymer film described in Patent Document 2 requires a lamination process at high temperatures to melt the bonding sheet, which causes problems such as warping, voids, thermal expansion, and other shape defects in the flexible printed wiring board. Furthermore, although the dielectric loss tangent is relatively low, it is insufficient for use in the high frequency range, and there is a demand for materials with even lower dielectric loss tangent.

[0010] An object of the present invention is to provide a film for flexible printed wiring boards that has a low dielectric loss tangent and can be laminated at low temperatures. Another object of the present invention is to provide a laminate constituted by the film for flexible printed wiring boards. [Means for solving the problem]

[0011] In view of the above problems, the inventors conducted extensive research and discovered that by using a liquid crystal polymer that satisfies certain conditions, a film for flexible printed wiring boards can be obtained that has a low dielectric tangent and can be laminated at low temperatures, thereby completing the present invention.

[0012] That is, the present invention includes the following preferred embodiments. [1] A film for flexible printed wiring boards, which is composed of a liquid crystal polymer having a crystalline melting temperature of 260°C or less and a dielectric loss tangent of 0.0015 or less at 10 GHz measured by the cavity resonator perturbation method. [2] The liquid crystal polymer is represented by the formulas (I) to (IV) [ka] [In the formula, Ar1 and Ar2 each represent one or more divalent aromatic groups, and p, q, r, and s each represent the composition ratio (mol %) of each repeating unit in the liquid crystal polymer, and satisfy the following condition: 0.5≦p / q≦2.5 0.1≦r≦25, and 0.1≦s≦25] The film according to [1], which is a wholly aromatic liquid crystal polyester containing a repeating unit represented by the formula: [3] In the formula (III) and / or formula (IV), Ar1 and Ar2 are each independently represented by the formulas (1) to (4): [ka] The film according to [2], which is a wholly aromatic liquid crystal polyester containing one or more repeating units which are aromatic groups selected from the group consisting of: [4] The film according to any one of [1] to [3], which is a bonding sheet for a flexible printed wiring board. [5] The film according to any one of [1] to [3], which is a coverlay for a flexible printed wiring board. [6] A laminate comprising the film according to any one of [1] to [5] and a metal layer. [7] A laminate comprising the film according to any one of [1] to [5] and a resin layer. [Effects of the Invention]

[0013] The flexible printed wiring board film of the present invention has a low dielectric loss tangent, can be laminated at low temperatures, and has excellent interlayer adhesion, so it is suitable for use as a flexible printed wiring board material, particularly as a bonding sheet or coverlay. DETAILED DESCRIPTION OF THE INVENTION

[0014] The liquid crystal polymer used in the film for flexible printed wiring boards of the present invention is a liquid crystal polyester or liquid crystal polyester amide that forms an anisotropic molten phase and is called a thermotropic liquid crystal polymer by those skilled in the art.

[0015] The anisotropic melt phase properties of the liquid crystal polymer can be confirmed by a conventional polarized light inspection method using cross polarizers, that is, by observing a sample placed on a hot stage under a nitrogen atmosphere. Examples of repeating units constituting the liquid crystal polymer used in the present invention include aromatic oxycarbonyl repeating units, aromatic dicarbonyl repeating units, aromatic dioxy repeating units, aliphatic dicarbonyl repeating units, aliphatic dioxy repeating units, aromatic aminooxy repeating units, aromatic diamino repeating units, aromatic aminocarbonyl repeating units, and combinations thereof.

[0016] Specific examples of monomers that provide aromatic oxycarbonyl repeating units include aromatic hydroxycarboxylic acids such as 4-hydroxybenzoic acid, 3-hydroxybenzoic acid, 2-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, 5-hydroxy-2-naphthoic acid, 3-hydroxy-2-naphthoic acid, 4'-hydroxyphenyl-4-benzoic acid, 3'-hydroxyphenyl-4-benzoic acid, 4'-hydroxyphenyl-3-benzoic acid, and the like, as well as alkyl, alkoxy, or halogen-substituted derivatives thereof, and ester-forming derivatives thereof such as acylation products, ester derivatives, and acid halides. Among these, 4-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid are preferred because they allow the mechanical properties, heat resistance, crystalline melting temperature, and moldability of the resulting liquid crystal polymer to be easily adjusted to appropriate levels.

[0017] Specific examples of monomers that provide aromatic dicarbonyl repeating units include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, and 4,4'-dicarboxybiphenyl, as well as their alkyl-, alkoxy-, or halogen-substituted derivatives, and their ester-forming derivatives such as ester derivatives and acid halides. Among these, terephthalic acid and 2,6-naphthalenedicarboxylic acid are preferred because they allow the mechanical properties, heat resistance, crystalline melting temperature, and moldability of the resulting liquid crystal polymer to be easily adjusted to appropriate levels.

[0018] Specific examples of monomers that provide aromatic dioxy repeating units include aromatic diols such as hydroquinone, resorcinol, 2,6-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 1,4-dihydroxynaphthalene, 4,4'-dihydroxybiphenyl, 3,3'-dihydroxybiphenyl, 3,4'-dihydroxybiphenyl, and 4,4'-dihydroxybiphenyl ether, as well as their alkyl, alkoxy, or halogen-substituted derivatives and ester-forming derivatives such as acylated derivatives. Among these, hydroquinone and 4,4'-dihydroxybiphenyl are preferred because they allow for easy adjustment of the reactivity during polymerization and the mechanical properties, heat resistance, crystalline melting temperature, and moldability of the resulting liquid crystal polymer to appropriate levels.

[0019] Specific examples of monomers that provide aliphatic dicarbonyl repeating units include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, tetradecanedioic acid, fumaric acid, maleic acid, cyclohexanedicarboxylic acid, and hexahydroterephthalic acid.

[0020] Specific examples of monomers that provide aliphatic dioxy repeating units include ethylene glycol, 1,4-butanediol, 1,6-hexanediol, and acylated products thereof.

[0021] Monomers that provide aromatic aminooxy repeating units, aromatic diamino repeating units and aromatic aminocarbonyl repeating units include aromatic hydroxyamines, aromatic diamines and aromatic aminocarboxylic acids.

[0022] The liquid crystal polymer used in the present invention may contain an aromatic oxydicarbonyl repeating unit or a thioester bond, provided that the object of the present invention is not impaired. Examples of monomers that provide a thioester bond include mercaptoaromatic carboxylic acids, aromatic dithiols, and hydroxyaromatic thiols. The amount of these monomers used is preferably 10 mol % or less based on the total amount of the monomers that provide the aromatic oxycarbonyl repeating unit, aromatic dicarbonyl repeating unit, aromatic dioxy repeating unit, aromatic aminooxy repeating unit, aromatic diamino repeating unit, and aromatic aminocarbonyl repeating unit.

[0023] Among copolymers combining these repeating units, some may form an anisotropic molten phase and some may not, depending on the monomer structure, composition ratio, and sequence distribution of each repeating unit in the copolymer. However, the liquid crystal polymer used in the present invention is limited to copolymers that form an anisotropic molten phase.

[0024] The liquid crystal polymer used in the present invention may be a blend of two or more liquid crystal polymers.

[0025] The crystalline melting temperature of the liquid crystal polymer used in the present invention measured by a differential scanning calorimeter is 260°C or lower, preferably 150 to 250°C, more preferably 170 to 240°C, and even more preferably 190 to 230°C.

[0026] By having a crystalline melting temperature of 260°C or less, the low-temperature lamination processability when manufacturing flexible printed wiring boards is improved, making it easier to suppress the occurrence of shape defects such as warping, voids, and thermal expansion in flexible printed wiring boards.

[0027] In this specification and claims, the term "crystalline melting temperature" refers to the crystalline melting peak temperature measured using a differential scanning calorimeter (DSC) at a heating rate of 20°C / min. More specifically, a liquid crystal polymer sample is measured at a temperature increase rate of 20°C / min from room temperature to reach an endothermic peak temperature (Tm1), then held at a temperature 20-50°C higher than Tm1 for 10 minutes. The sample is then cooled to room temperature at a temperature decrease rate of 20°C / min, and then measured again at a temperature increase rate of 20°C / min. The endothermic peak is observed, and the temperature at the top of this peak is taken as the crystalline melting temperature of the liquid crystal polymer. For example, an Exstar 6000 manufactured by Seiko Instruments Inc. can be used as a measuring instrument.

[0028] The liquid crystal polymer used in the present invention has a dielectric loss tangent at 10 GHz measured by a cavity resonator perturbation method of 0.0015 or less, preferably 0.0013 or less, and more preferably 0.0010 or less.

[0029] By making the dielectric loss tangent at 10 GHz 0.0015 or less, transmission loss in the high frequency range is suppressed, making the film suitable for flexible printed wiring boards for high-speed communication.

[0030] As the liquid crystal polymer used in the present invention, a wholly aromatic liquid crystal polyester is preferably used, and a wholly aromatic liquid crystal polyester containing repeating units represented by formulas (I) to (IV) is more preferably used. [ka] [In the formula, Ar1 and Ar2 each represent one or more divalent aromatic groups, and p, q, r, and s each represent the composition ratio (mol %) of each repeating unit in the wholly aromatic liquid crystal polyester, and satisfy the following conditions: 0.5≦p / q≦2.5 0.1≦r≦25, and 0.1≦s≦25]

[0031] The molar ratio (p / q) of the composition ratio p (mol %) according to the formula (I) to the composition ratio q (mol %) according to the formula (II) is preferably 0.5 to 2.5, more preferably 0.6 to 1.8, and even more preferably 0.8 to 1.6.

[0032] In the above-mentioned wholly aromatic liquid crystal polyesters that are preferably used, the total composition ratio of p and q is preferably 50 to 99.8 mol %, more preferably 60 to 96 mol %, and even more preferably 70 to 90 mol %.

[0033] In the above-mentioned wholly aromatic liquid crystal polyesters that are preferably used, the composition ratio p according to formula (I) and the composition ratio q according to formula (II) are each preferably 20 to 60 mol %, more preferably 30 to 55 mol %.

[0034] In the wholly aromatic liquid crystalline polyester preferably used in the present invention, by containing the repeating units represented by formula (I) and formula (II) at least in the above molar ratio (p / q), and optionally in the above total composition ratio of p and q and / or the individual composition ratios of p and q (mol %), a wholly aromatic liquid crystalline polyester exhibiting a crystalline melting temperature of 260°C or less can be preferably obtained.

[0035] In the wholly aromatic liquid crystal polyester preferably used in the present invention, the composition ratio r according to formula (III) and the composition ratio s according to formula (IV) are each preferably 0.1 to 25 mol %, more preferably 2 to 20 mol %, and even more preferably 5 to 15 mol %. r and s are preferably equimolar amounts.

[0036] In the above repeating unit, for example, when Ar1 (or Ar2) represents two or more divalent aromatic groups, it means that the wholly aromatic liquid crystal polyester contains two or more repeating units represented by formula (III) (or (IV)) according to the type of divalent aromatic group. In this case, the composition ratio r according to formula (III) (or the composition ratio s according to formula (IV)) represents the total composition ratio of the two or more repeating units.

[0037] Specific examples of monomers that provide the repeating unit represented by formula (I) include 4-hydroxybenzoic acid and its ester-forming derivatives such as acylates, ester derivatives and acid halides.

[0038] Specific examples of monomers that provide the repeating unit represented by formula (II) include 6-hydroxy-2-naphthoic acid and its ester-forming derivatives such as acylates, ester derivatives and acid halides.

[0039] Specific examples of monomers that provide the repeating unit represented by formula (III) include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, and 4,4'-dicarboxybiphenyl, as well as alkyl-, alkoxy-, or halogen-substituted derivatives thereof, and ester-forming derivatives thereof such as ester derivatives and acid halides.

[0040] Specific examples of monomers that provide the repeating unit represented by formula (IV) include aromatic diols such as hydroquinone, resorcinol, 2,6-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 1,4-dihydroxynaphthalene, 4,4'-dihydroxybiphenyl, 3,3'-dihydroxybiphenyl, 3,4'-dihydroxybiphenyl, 4,4'-dihydroxybiphenyl ether, alkyl-, alkoxy- or halogen-substituted products thereof, and ester-forming derivatives such as acylated products thereof.

[0041] Furthermore, among the wholly aromatic liquid crystal polyesters that are preferably used in the present invention, wholly aromatic liquid crystal polyesters in which Ar1 and Ar2 in the repeating units represented by formula (III) and formula (IV) each independently contain one or more aromatic groups selected from the group consisting of aromatic groups represented by formulas (1) to (4) are more preferably used. [ka]

[0042] Among these, as the repeating unit represented by formula (III), aromatic groups represented by formulas (1), (2) and (4) are particularly preferred, that is, terephthalic acid, isophthalic acid and 2,6-naphthalenedicarboxylic acid and their ester-forming derivatives are used as monomers that give these repeating units, because the mechanical properties, heat resistance, crystalline melting temperature and molding processability of the resulting wholly aromatic liquid crystal polyester can be easily adjusted to appropriate levels.

[0043] Furthermore, as the repeating unit represented by formula (IV), it is particularly preferred to use aromatic groups represented by formulas (1) and (3), i.e., hydroquinone, 4,4'-dihydroxybiphenyl, and their ester-forming derivatives as monomers that give these repeating units, because this makes it easy to adjust the reactivity during polymerization and the mechanical properties, heat resistance, crystalline melting temperature, and molding processability of the resulting wholly aromatic liquid crystal polyester to appropriate levels.

[0044] In the above repeating units, for example, when Ar1 (or Ar2) contains two or more aromatic groups, this means that the wholly aromatic liquid crystal polyester contains two or more repeating units represented by formula (III) (or (IV)) according to the type of divalent aromatic group. That is, the wholly aromatic liquid crystal polyester preferably contains one or more repeating units in which Ar1 and Ar2 are each independently an aromatic group selected from the group consisting of formulas (1) to (4). In this case, the composition ratio r according to formula (III) (or the composition ratio s according to formula (IV)) represents the total composition ratio of two or more repeating units.

[0045] In the wholly aromatic liquid crystal polyester preferably used in the present invention, the total composition ratio of the repeating units [p+q+r+s] is preferably 100 mol %, but other repeating units may be further contained within a range that does not impair the object of the present invention.

[0046] Examples of monomers that provide other repeating units constituting the wholly aromatic liquid crystal polyester preferably used in the present invention include other aromatic hydroxycarboxylic acids, aromatic hydroxyamines, aromatic diamines, aromatic aminocarboxylic acids, aromatic hydroxydicarboxylic acids, aromatic mercaptocarboxylic acids, aromatic dithiols, aromatic mercaptophenols, and combinations thereof.

[0047] Specific examples of other aromatic hydroxycarboxylic acids include 3-hydroxybenzoic acid, 2-hydroxybenzoic acid, 5-hydroxy-2-naphthoic acid, 3-hydroxy-2-naphthoic acid, 4'-hydroxyphenyl-4-benzoic acid, 3'-hydroxyphenyl-4-benzoic acid, 4'-hydroxyphenyl-3-benzoic acid, and alkyl-, alkoxy-, or halogen-substituted derivatives thereof, as well as ester-forming derivatives thereof such as acylation products, ester derivatives, and acid halides.

[0048] The total composition ratio of the repeating units provided by these other monomer components is preferably 10 mol % or less based on the total repeating units.

[0049] The method for producing the liquid crystal polymer used in the present invention will be described below.

[0050] There are no particular limitations on the method for producing the liquid crystal polymer used in the present invention, and known polycondensation methods for forming ester bonds, amide bonds, etc. from the combination of the above-mentioned monomers, such as melt acidolysis and slurry polymerization, can be used.

[0051] The melt acidolysis method is a preferred method for preparing the liquid crystalline polymers used in the present invention, in which the monomers are first heated to form a melt of reactants, followed by reaction to obtain a molten polymer, and a vacuum may be applied to facilitate removal of volatile by-products (e.g., acetic acid, water, etc.) produced in the final stage of condensation.

[0052] Slurry polymerization is a process in which the reaction is carried out in the presence of a heat exchange fluid, and the solid product is obtained in a state suspended in the heat exchange medium.

[0053] In both the melt acidolysis method and the slurry polymerization method, the polymerizable monomer components used in producing the liquid crystal polymer can be subjected to the reaction at room temperature in a modified form in which the hydroxyl group and / or amino group is acylated, i.e., as a lower acylated product. The lower acyl group preferably has 2 to 5 carbon atoms, more preferably 2 or 3 carbon atoms. Particularly preferred is a method in which an acetylated product of the above-mentioned monomer is used in the reaction.

[0054] The acylated monomer may be one which has been previously synthesized by separate acylation, or may be produced in the reaction system by adding an acylating agent such as acetic anhydride to the monomer during the production of the liquid crystal polymer.

[0055] In either the molten acidolysis method or the slurry polymerization method, a catalyst may be used during the reaction, if necessary.

[0056] Specific examples of the catalyst include organotin compounds (dialkyltin oxides such as dibutyltin oxide, diaryltin oxides, etc.), titanium dioxide, antimony trioxide, organotitanium compounds (alkoxytitanium silicates, titanium alkoxides, etc.), alkali and alkaline earth metal salts of carboxylic acids (potassium acetate, sodium acetate, etc.), Lewis acids (BF3, etc.), gaseous acid catalysts such as hydrogen halides (HCl, etc.), and the like.

[0057] The catalyst is used in an amount of usually 1 to 1000 ppm, preferably 2 to 100 ppm, based on the total amount of monomers.

[0058] The liquid crystal polymer obtained by the polycondensation reaction in this manner is extracted in a molten state from the polymerization reactor, and then processed into pellets, flakes, or powder.

[0059] The liquid crystal polymer used in the present invention may be blended with an inorganic filler and / or an organic filler, if necessary.

[0060] Examples of inorganic and / or organic fillers include one or more selected from the group consisting of talc, mica, graphite, silica, wollastonite, dolomite, clay, glass flakes, glass beads, glass balloons, calcium carbonate, barium sulfate, titanium oxide, glass fiber, silica alumina fiber, alumina fiber, carbon fiber, potassium titanate fiber, aluminum borate fiber, and aramid fiber, etc. Among these, talc, mica, and silica are preferred because of their excellent balance between physical properties and cost.

[0061] When an inorganic filler and / or an organic filler is used, the amount of the filler to be blended is preferably 0.01 to 100 parts by mass, more preferably 0.05 to 50 parts by mass, and even more preferably 0.1 to 30 parts by mass, per 100 parts by mass of the liquid crystal polymer.

[0062] The liquid crystal polymer used in the present invention may further contain other resin components or additives as long as the purpose of the present invention is not impaired. Examples of other resin components include thermoplastic resins and modified products thereof, such as polyolefins such as polypropylene and polyethylene, amorphous polyarylate, polycarbonate, polyamide, other polyesters, polyacetal, polyphenylene ether, polysulfone, polyethersulfone, polyetherimide, and polyamideimide, as well as thermosetting resins such as phenolic resins, epoxy resins, and polyimide resins. Examples of additives include antioxidants, hydrochloric acid absorbers, heat stabilizers, light stabilizers, UV absorbers, lubricants, antistatic agents, flame retardants, nucleating agents, pigments, dyes, dispersants, copper inhibitors, neutralizing agents, foaming agents, plasticizers, anti-foaming agents, crosslinking agents, flow improvers such as peroxides, and anti-blocking agents.

[0063] The other resin components and additives may be blended either alone or in combination of two or more.

[0064] When other resin components are blended, the blending amount of the resin components is preferably 0.1 to 100 parts by mass, more preferably 5 to 80 parts by mass, per 100 parts by mass of the liquid crystal polymer.

[0065] When an additive is added, the amount of the additive added is preferably 0.001 to 5 parts by mass, more preferably 0.01 to 3 parts by mass, per 100 parts by mass of the liquid crystal polymer.

[0066] The flexible printed wiring board film of the present invention can be obtained by subjecting the liquid crystal polymer obtained as described above to known molding methods such as extrusion molding, press molding, and injection molding, among which extrusion molding is preferred. Any method can be used as the extrusion molding method, but well-known methods such as the T-die method, laminate stretching method, and inflation method are industrially advantageous. In particular, the inflation method and laminate stretching method apply stress not only in the mechanical axis direction of the film (or the machining direction, hereinafter abbreviated as MD direction) but also in the direction perpendicular to this (hereinafter abbreviated as TD direction), thereby making it possible to obtain a film with controlled molecular orientation and dielectric properties in the MD and TD directions.

[0067] In extrusion molding, it is preferable to carry out a stretching process to control the orientation. For example, in extrusion molding using a T-die method, the molten sheet extruded from the T-die may be stretched not only in the MD direction of the film but also in both the TD direction and the MD direction simultaneously, or the molten sheet extruded from the T-die may be stretched in the MD direction first and then in the TD direction.

[0068] In addition, in extrusion molding by the inflation method, a cylindrical sheet melt-extruded from a ring die may be stretched at a predetermined draw ratio (corresponding to the stretch ratio in the MD direction: also called the draw-down ratio) and blow ratio (corresponding to the stretch ratio in the TD direction: also called the blow-up ratio).

[0069] The stretching ratio in such extrusion molding, as a stretching ratio (or draw ratio) in the MD direction, may be, for example, about 1.0 to 10, preferably about 1.2 to 8, and more preferably about 1.3 to 7. The stretching ratio (or blow ratio) in the TD direction may be, for example, about 1.5 to 20, preferably about 2 to 15, and more preferably about 2.5 to 14.

[0070] The ratio of the draw ratio in the MD direction to the draw ratio in the TD direction (TD direction / MD direction) may be, for example, 2.6 or less, preferably about 0.4 to 2.5.

[0071] Furthermore, the liquid crystal polymer film may be stretched as needed after extrusion molding. The stretching method itself is known, and either biaxial stretching or uniaxial stretching may be used, but biaxial stretching is preferred because it is easier to control the degree of molecular orientation. Furthermore, for stretching, known uniaxial stretching machines, simultaneous biaxial stretching machines, sequential biaxial stretching machines, etc. may be used.

[0072] If necessary, the melting point and / or thermal expansion coefficient of the liquid crystal polymer film may be adjusted by a known or conventional heat treatment. The heat treatment conditions can be appropriately set depending on the purpose. For example, the melting point (Tm) of the liquid crystal polymer film may be increased by heating for several hours at a temperature equal to or higher than the melting point (Tm0) of the liquid crystal polymer (Tm0) - 10°C (for example, about Tm0 - 10 to Tm0 + 30°C, preferably about Tm0 to Tm0 + 20°C).

[0073] The film for flexible printed wiring boards of the present invention may have any thickness. When a liquid crystal polymer film is used as the electrical insulating layer, the film thickness is preferably in the range of 1 to 1000 μm, more preferably 5 to 500 μm, and even more preferably 10 to 300 μm. If the film thickness is too thin, the rigidity and strength of the film will decrease, so a method of laminating films with thicknesses in the range of 10 to 300 μm to obtain any thickness may be employed.

[0074] The film for flexible printed wiring boards of the present invention thus obtained has low dielectric loss tangent, excellent gas barrier properties, and low moisture absorption. In addition, it can be laminated at low temperatures and has excellent interlayer adhesion, making it suitable for use as a circuit board material.

[0075] Specific examples of circuit board materials include insulating substrates for conductor circuit boards, bonding sheets for joining substrates having conductor circuits formed on the surface of the substrate, and coverlays formed on the surface of circuit layers.

[0076] When two or more unit circuit boards each having a conductor layer are stacked, the bonding sheet is placed between the unit circuit boards, and the coverlay is placed on the top and / or bottom layer of the stack.

[0077] The film for flexible printed wiring boards of the present invention has excellent interlayer adhesion and can therefore be suitably used as a laminate with metals or resins. Examples of metals constituting the film and laminate of the present invention include copper, gold, silver, nickel, and aluminum, with copper being preferred. The metal is preferably used to form the laminate as a metal foil, with copper foil being particularly preferred.

[0078] Examples of resin films that can be used to form a laminate with the film of the present invention include polyolefins such as polypropylene and polyethylene, liquid crystal polymers, amorphous polyarylates, polycarbonates, polyamides, other polyesters, polyacetals, polyphenylene ethers, polysulfones, polyethersulfones, polyetherimides, polyetheretherketones, polyamideimides, fluororesins such as polytetrafluoroethylene, phenolic resins, epoxy resins, polyimide resins, etc. Among these, laminates with a resin film selected from the group consisting of liquid crystal polymer films, polyimide films, polytetrafluoroethylene films, and polyetheretherketones are preferred, laminates with liquid crystal polymer films or polyimide films are more preferred, and laminates with a liquid crystal polymer film are even more preferred.

[0079] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. [Example]

[0080] The crystal melting temperature and dielectric loss tangent in the examples were measured by the methods described below.

[0081] <Measurement of Crystal Melting Temperature> Measurements were performed using a differential scanning calorimeter (DSC) Exstar 6000 manufactured by Seiko Instruments Inc. A sample of liquid crystal polymer was measured under conditions of a temperature increase from room temperature of 20°C / min, and after observing the endothermic peak temperature (Tm1), it was held at a temperature 20 to 50°C higher than Tm1 for 10 minutes. The sample was then cooled to room temperature under conditions of a temperature decrease of 20°C / min, and then measured again under conditions of a temperature increase of 20°C / min, and the endothermic peak was observed. The temperature at which the peak top was reached was taken as the crystalline melting temperature of the liquid crystal polymer.

[0082] <Measurement of dielectric loss tangent> A liquid crystal polymer sample was molded into a stick-shaped test piece measuring 85 mm in length, 1.70 mm in width, and 1.70 mm in thickness using an injection molding machine (NEX-15-1E manufactured by Nissei Plastic Industrial Co., Ltd.) with a mold having a single gate at the longitudinal end. The dielectric loss tangent at 10 GHz was measured using the obtained stick-shaped test piece by the cavity resonator perturbation method using a cavity resonator for dielectric constant measurement (manufactured by Kanto Electronics Application Development Co., Ltd.) and a network analyzer.

[0083] In the examples and comparative examples, the following abbreviations represent the following compounds. LCP: Liquid Crystal Polymer POB: 4-hydroxybenzoic acid BON6: 6-hydroxy-2-naphthoic acid HQ: Hydroquinone BP: 4,4'-dihydroxybiphenyl TPA: Terephthalic acid NDA: 2,6-naphthalenedicarboxylic acid IPA: Isophthalic acid

[0084] [Synthesis Example 1 (Synthesis of LCP-1)] A reaction vessel equipped with a stirrer with a torque meter and a distillation tube was charged with POB, BON6, HQ, and TPA in the composition ratio shown in Table 1 so that the total amount was 6.5 moles. Furthermore, acetic anhydride was charged in an amount of 1.03 times the moles of the hydroxyl groups (moles) of all the monomers, and deacetic acid polymerization was carried out under the following conditions.

[0085] The temperature was raised from room temperature to 145°C in a nitrogen gas atmosphere over 1 hour and maintained at that temperature for 30 minutes. Next, the temperature was raised to 330°C over 7 hours while distilling off the by-product acetic acid, and then the pressure was reduced to 10 mmHg over 80 minutes. The polymerization reaction was terminated when a predetermined torque was reached, and the contents of the reactor were removed and crushed to obtain pellets of LCP-1. The amount of acetic acid distilled during polymerization was nearly the theoretical value.

[0086] The crystalline melting temperature of the obtained LCP-1 measured by DSC was 218°C. In addition, using a stick-shaped test piece molded at a molding temperature of 250°C and a mold temperature of 70°C, the dielectric loss tangent at 10 GHz measured by the cavity resonator perturbation method was 0.0008.

[0087] [Table 1]

[0088] [Synthesis Example 2 (Synthesis of LCP-2)] A reaction vessel equipped with a stirrer with a torque meter and a distillation tube was charged with POB, BON6, BP, NDA, and IPA in the composition ratio shown in Table 2 so that the total amount was 6.5 moles. Furthermore, 1.03 moles of acetic anhydride relative to the amount (moles) of hydroxyl groups in all monomers was charged, and deacetic acid polymerization was carried out under the following conditions.

[0089] The temperature was raised from room temperature to 150°C in a nitrogen gas atmosphere over one hour and maintained at that temperature for 30 minutes. The temperature was then rapidly raised to 210°C while distilling off the by-product acetic acid and maintained at that temperature for 30 minutes. The temperature was then raised to 340°C over four hours, after which the pressure was reduced to 10 mmHg over 80 minutes. The polymerization reaction was terminated when the specified torque was reached, and the contents of the reactor were removed and crushed to obtain LCP-2 pellets. The amount of acetic acid distilled during polymerization was nearly the theoretical value.

[0090] The crystalline melting temperature of the obtained LCP-2 measured by DSC was 183°C. In addition, the dielectric loss tangent at 10 GHz measured by the cavity resonator perturbation method using a stick-shaped test piece molded at a molding temperature of 250°C and a mold temperature of 70°C was 0.0006.

[0091] [Table 2]

[0092] [Synthesis Example 3 (Synthesis of LCP-3)] A reaction vessel equipped with a stirrer with a torque meter and a distillation tube was charged with POB and BON6 in the composition ratio shown in Table 3 so that the total amount was 6.5 moles. Furthermore, acetic anhydride was charged in an amount of 1.03 times the moles of the hydroxyl groups (moles) of all the monomers, and deacetic acid polymerization was carried out under the following conditions.

[0093] The temperature was raised from room temperature to 150°C in a nitrogen gas atmosphere over 1 hour and maintained at that temperature for 30 minutes. The temperature was then rapidly raised to 210°C while distilling off the by-product acetic acid and maintained at that temperature for 30 minutes. The temperature was then raised to 325°C over 5 hours, after which the pressure was reduced to 20 mmHg over 90 minutes. The polymerization reaction was terminated when the specified torque was reached, and the contents of the reactor were removed and crushed to obtain LCP-3 pellets. The amount of acetic acid distilled during polymerization was nearly the theoretical value.

[0094] The crystalline melting temperature of the obtained LCP-3 measured by DSC was 280°C. In addition, the dielectric loss tangent at 10 GHz measured by the cavity resonator perturbation method using a stick-shaped test piece molded at a molding temperature of 300°C and a mold temperature of 70°C was 0.0021.

[0095] [Table 3]

[0096] [Synthesis Example 4 (Synthesis of LCP-4)] A reaction vessel equipped with a stirrer with a torque meter and a distillation tube was charged with BON6, BP, HQ, and TPA in the composition ratio shown in Table 4 so that the total amount was 6.5 moles. Furthermore, acetic anhydride was charged in an amount of 1.03 times the moles of the hydroxyl groups (moles) of all the monomers, and deacetic acid polymerization was carried out under the following conditions.

[0097] The temperature was raised from room temperature to 150°C in a nitrogen gas atmosphere over 1 hour and maintained at that temperature for 60 minutes. The temperature was then raised to 350°C over 7 hours while distilling off the by-product acetic acid, and the pressure was then reduced to 10 mmHg over 90 minutes. The polymerization reaction was terminated when the specified torque was reached, and the contents of the reactor were removed and crushed to obtain LCP-4 pellets. The amount of acetic acid distilled during polymerization was nearly the theoretical value.

[0098] The crystalline melting temperature of the obtained LCP-4 measured by DSC was 338°C. Furthermore, using a stick-shaped test piece molded at a molding temperature of 350°C and a mold temperature of 70°C, the dielectric loss tangent at 10 GHz measured by the cavity resonator perturbation method was 0.0006. LCP-4 was produced to measure the adhesive strength with LCP-1 to LCP-3.

[0099] [Table 4]

[0100] <Measurement of adhesive strength> Adhesion strength with LCP-4 (adhesion strength 1, 2) For LCP-1 to LCP-4, film-like test specimens (length 150 mm x width 13 mm x thickness 0.8 mm) were produced using an injection molding machine (UH1000-110 manufactured by Nissei Plastic Industrial Co., Ltd.) under the following molding conditions. LCP-1 and LCP-2: Molding temperature 250℃, mold temperature 70℃ LCP-3: Molding temperature 300℃, mold temperature 70℃ LCP-4: Molding temperature 350℃, mold temperature 70℃

[0101] Each film specimen of LCP-1 to LCP-3 was placed over an LCP-4 film specimen with an area of ​​70 mm length x 13 mm width and placed in a 250°C oven heater for 60 seconds to bond the film specimens together. The adhesive strength (tensile shear strength) of each specimen was measured in accordance with JIS-K-7162 using a Shimadzu AUTOGRAPH AG-Xplus (Adhesive Strength 1). The adhesive strength was also measured in the same manner, except that the oven heater temperature was changed to 300°C (Adhesive Strength 2).

[0102] Adhesion strength with copper foil (adhesion strength 3, 4) Using a vacuum press and a metal spacer with a 0.7 mm thick metal plate and a 160 mm long x 50 mm wide hole, the LCPs were melted by leaving them at 10 torr for 2 minutes and 30 seconds at 250°C for LCP-1 and LCP-2, and 300°C for LCP-3, and then pressed at 50 MPa for 3 minutes to produce film-like molded pieces of LCP1 to LCP-3 measuring 160 mm long x 50 mm wide x 0.7 mm thick.

[0103] A copper foil (length 200 mm x width 70 mm x thickness 0.05 mm) was placed on a film-shaped piece of LCP integrated with a metal spacer, with the matte side of the copper foil adhering to the LCP. The piece was then placed in a vacuum press at 250°C and left to stand for 2 minutes and 30 seconds at 10 torr, after which it was pressed at 50 MPa for 3 minutes to bond the LCP and copper foil together. The metal spacer was then removed, and a laminated film of LCP and copper foil was produced.

[0104] This laminated film was cut in half lengthwise, and a 10 mm wide slit was made on the copper foil side. Using a Shimadzu AUTOGRAPH AG-Xplus, the peel strength was measured when peeling the copper foil from the LCP film at a peel width of 10 mm, a peel speed of 25 mm / min, and a peel angle of 90° (Adhesion Strength 3). The peel strength was also measured in the same manner, except that the temperature of the vacuum press was changed to 300°C (Adhesion Strength 4).

[0105] [Table 5]

[0106] When the liquid crystal polymers of Examples 1 and 2 were used, the adhesive strength to the copper foil and the liquid crystal polymer film was high, and the dielectric loss tangent was 0.001 or less, indicating that the dielectric properties were excellent.

[0107] On the other hand, when the liquid crystal polymer of Comparative Example 1 was used, the adhesive strength (adhesive strength 3) to the copper foil at low temperature (250°C) was poor, and the liquid crystal polymer film did not adhere under either the conditions of 250°C or 300°C. Furthermore, the dielectric loss tangent was more than 0.002, and the dielectric properties were poor.

Claims

1. A film for flexible printed wiring boards, comprising a liquid crystal polymer having a crystal melting temperature of 260° C. or lower and a dielectric loss tangent of 0.0015 or lower at 10 GHz as measured by a cavity resonator perturbation method.

2. The liquid crystal polymer is represented by the formulas (I) to (IV): 【Chemistry 1】 [In the formula, Ar １ and Ar ２ Each of p, q, r, and s represents a composition ratio (mol %) of each repeating unit in the liquid crystal polymer, and satisfies the following condition: 0.5≦p / q≦2.5 0.1≦r≦25, and 0.1≦s≦25] 2. The film according to claim 1, which is a wholly aromatic liquid crystal polyester containing a repeating unit represented by the following formula:

3. Formula (III) and / or Formula (IV) are Ar １ and Ar ２ are independently represented by the formulas (1) to (4). 【Chemistry 2】 3. The film according to claim 2, which is a wholly aromatic liquid crystal polyester containing one or more repeating units which are aromatic groups selected from the group consisting of:

4. The film according to any one of claims 1 to 3, which is a bonding sheet for a flexible printed wiring board.

5. The film according to any one of claims 1 to 3, which is a coverlay for a flexible printed wiring board.

6. A laminate comprising the film according to any one of claims 1 to 5 and a metal layer.

7. A laminate comprising the film according to any one of claims 1 to 5 and a resin layer.

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