Liquid crystal polymer film and method for producing the same

Abstract

To provide a liquid crystal polymer film with reduced warping.SOLUTION: There is provided a liquid crystal polymer film in which a difference (ΔL1-ΔL2) between the amount (ΔL1) of a dimensional change of the liquid crystal polymer film when a temperature is increased at the first time from 40°C to 200°C by using a thermomechanical analyzer and then lowered from 200°C to 40°C and the amount (ΔL2) of a dimensional change of the liquid crystal polymer film when the temperature is increased at the second time from 40°C to 200°C by using the thermomechanical analyzer and then lowered from 200°C to 40°C, is 120 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a liquid crystal polymer film, a method for producing the same, and a low dielectric substrate material and a printed circuit board comprising a liquid crystal polymer film. [Background technology]

[0002] Liquid crystal polymers have a low moisture absorption rate and a low dielectric constant, and therefore liquid crystal polymer films using liquid crystal polymers are increasingly being used as insulating layers for flexible printed circuits (FPCs), for example.

[0003] The liquid crystal polymer film as the insulating layer is used by being laminated on a metal foil such as a copper foil, etc. In this case, the metal foil with the insulating layer is required not to warp.

[0004] For example, an extruded LCP film with significantly reduced anisotropy in dimensional change rate has been proposed, which contains a thermoplastic liquid crystal polymer and has a thickness of 15 μm to 300 μm, in which the hardness H1 at a depth of 1 μm located 1 μm from the film surface in the thickness direction and the hardness H2 at the center point of the thickness, measured by nanoindentation on a film cross section parallel to the MD direction, satisfy -10.0≦100×(H2-H1) / H1≦0.0, and the linear expansion coefficients in the MD and TD directions at 23 to 200° C., measured by the TMA method in accordance with JIS K7197, are within the ranges of -30 to 55 ppm / K (see Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2022-91688 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a liquid crystal polymer film with reduced warpage, a method for producing the same, and a low dielectric substrate material and a wiring circuit board including the liquid crystal polymer film. [Means for solving the problem]

[0007] That is, the present invention includes the following.

[0008] [1] A liquid crystal polymer film, A liquid crystal polymer film, in which the difference (ΔL1-ΔL2) between the dimensional change (ΔL1) of the liquid crystal polymer film when the temperature is lowered from 200°C to 40°C after a first heating step in which the temperature is raised from 40°C to 200°C using a thermomechanical analyzer and the dimensional change (ΔL2) of the liquid crystal polymer film when the temperature is lowered from 200°C to 40°C after a second heating step in which the temperature is raised from 40°C to 200°C using the thermomechanical analyzer is 120 μm or less. [2] The liquid crystal polymer film according to [1], which is a rolled film. [3] The liquid crystal polymer film according to [2], wherein the degree of in-plane orientation in the MD direction during rolling is 50% or less. [4] The liquid crystal polymer film according to any one of [1] to [3], which contains 20 volume % to 70 volume % of a filler. [5] The liquid crystal polymer film according to any one of [1] to [4], which has a porosity of 20% to 70%. [6] A low dielectric substrate material having a liquid crystal polymer film according to any one of [1] to [5] and a metal layer in the thickness direction. [7] A wiring circuit board comprising the liquid crystal polymer film according to any one of [1] to [5] and a conductor layer in the thickness direction. [8] A step of rolling a sheet formed from a composition containing a liquid crystal polymer to obtain a rolled film; A step of heat treating the rolled film at a heat treatment temperature that satisfies the following formula (1); A method for producing a liquid crystal polymer film, comprising: T1<Heat treatment temperature (℃)≦T2 Equation (1) T1: a temperature 100° C. lower than the melting point of the liquid crystal polymer T2: Melting point of the liquid crystal polymer [9] The method for producing a liquid crystal polymer film described in [8], wherein the rolling is performed by passing the sheet between a pair of rolls.

[10] The rolling is carried out by passing the laminate between a pair of rolls; The laminate has the sheet, a first film-like substrate arranged in contact with a first surface of the sheet, and a second film-like substrate arranged in contact with a second surface of the sheet. A method for producing a liquid crystal polymer film according to [8]. Effect of the Invention

[0009] According to the present invention, it is possible to provide a liquid crystal polymer film with reduced warpage, a method for producing the same, and a low dielectric substrate material and a wiring circuit board including the liquid crystal polymer film. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic cross-sectional view of one embodiment of a low dielectric substrate material of the present invention. [Diagram 2] FIG. 2 is a schematic cross-sectional view of another embodiment of the low dielectric substrate material of the present invention. [Diagram 3] FIG. 3 is a schematic cross-sectional view of one embodiment of the wired circuit board of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] (Liquid crystal polymer film) In the liquid crystal polymer film of the present invention, the difference (ΔL1-ΔL2) between the dimensional change (ΔL1) and the dimensional change (ΔL2) is 120 μm or less. The dimensional change (ΔL1) is the dimensional change of the liquid crystal polymer film when the temperature is lowered from 200°C to 40°C after the first temperature increase from 40°C to 200°C using a thermomechanical analyzer. The dimensional change (ΔL1) is the difference in the dimensions of the film before and after the first temperature increase and decrease, and the length (L1) of the film after the first temperature increase and decrease after ) and the length of the film before the first heating and cooling (L1 before ) and the difference (L1 after -L1 before ). The dimensional change (ΔL2) is the dimensional change of the liquid crystal polymer film when the temperature is lowered from 200°C to 40°C after the second temperature increase from 40°C to 200°C using a thermomechanical analyzer. The dimensional change (ΔL2) is the difference in the dimensions of the film before and after the second temperature increase and decrease, and the length (L2 after ) and the length of the film before the second heating and cooling (L2 before ) and the difference (L2 after -L2 before ). The method for measuring the amount of dimensional change will be described later in the Examples, but the effective length of the test sample (the length between the chucks) was 24 mm. The dimensional change refers to the amount of change in the length of the film, not the amount of change in the thickness of the film, and the length of the film refers to the length of the film in a direction perpendicular to the thickness direction of the film.

[0012] The present inventors have conducted extensive research in order to obtain a liquid crystal polymer film with reduced warpage. The inventors of the present invention considered that residual stress generated during the production of a liquid crystal polymer film has a large influence on warpage. Therefore, the inventors of the present invention attempted to reduce the residual stress by subjecting the liquid crystal polymer film to a heat treatment, and were able to obtain a liquid crystal polymer film with reduced warpage. Whether the residual stress is relaxed can be known by measuring the dimensional change of the liquid crystal polymer film using a thermomechanical analyzer. However, since the dimensional change of the liquid crystal polymer film also includes dimensional changes caused by noise such as twisting that occurs when the test sample is set in the device, the relaxation of the residual stress cannot be correctly understood by measuring only the dimensional change during the first heating and cooling in the measurement of the dimensional change using a thermomechanical analyzer. Therefore, the inventors focused on the difference (ΔL1-ΔL2) between the dimensional change during the first heating and cooling (ΔL1) and the dimensional change during the second heating and cooling (ΔL2). The dimensional change during the first heating and cooling (ΔL1) includes the dimensional change caused by the residual stress and the dimensional change caused by noise such as twisting that occurs when the test sample is set in the device. On the other hand, because the stress in the test sample is relieved by the first heating and cooling, the dimensional change (ΔL2) during the second heating and cooling includes the dimensional change caused by noise such as twisting that occurs when the test sample is set in the device, but does not include the dimensional change caused by residual stress. Therefore, the difference (ΔL1-ΔL2) is the dimensional change that reflects the residual stress. When the difference (ΔL1−ΔL2) is 120 μm or less, a liquid crystal polymer film with sufficiently reduced warpage can be obtained.

[0013] The difference (ΔL1−ΔL2) is not particularly limited as long as it is 120 μm or less, but is preferably 100 μm or less. The lower limit of the difference (ΔL1-ΔL2) is not particularly limited, but for example, the difference (ΔL1-ΔL2) may be 0 μm or more, 10 μm or more, 20 μm or more, or 40 μm or more.

[0014] The amount of dimensional change (ΔL1) is not particularly limited, but is preferably 150 μm or less, more preferably 130 μm or less, and particularly preferably 110 μm or less. The lower limit of the dimensional change (ΔL1) is not particularly limited, but may be 20 μm or more, 40 μm or more, or 60 μm or more.

[0015] The amount of dimensional change (ΔL2) is not particularly limited, but is preferably 40 μm or less, more preferably 30 μm or less, and particularly preferably 20 μm or less. The lower limit of the dimensional change (ΔL2) is not particularly limited, but may be 0 μm or more, or 1 μm or more.

[0016] The liquid crystal polymer film contains a liquid crystal polymer. The liquid crystal polymer is not limited. The liquid crystal polymer is a liquid crystal thermoplastic resin. Examples of the liquid crystal polymer include liquid crystal polyester, preferably aromatic liquid crystal polyester. The liquid crystal polymer is specifically described in, for example, JP 2020-147670 A and JP 2004-189867 A. The liquid crystal polymer may be a commercially available product. 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.). The UENO LCP 5000 series is preferable.

[0017] The melting point of the liquid crystal polymer is not limited. The melting point of the liquid crystal polymer is, for example, 170°C or higher, preferably 180°C or higher, more preferably 200°C or higher, and 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 temperature is increased at a rate of 10°C / min, and the temperature is controlled in the range of 25°C to 400°C, and the liquid crystal polymer is heated in a nitrogen atmosphere. If the liquid crystal polymer is a commercially available product, the catalog value of the commercially available product can be used as is.

[0018] The glass transition temperature of the liquid crystal polymer is not limited. The glass transition temperature of the liquid crystal polymer is, for example, 80° C. or higher and, for example, 125° C. or lower. The glass transition temperature of the liquid crystal polymer is determined by differential scanning calorimetry performed at a heating rate of 10° C. / min.

[0019] The content of the liquid crystal polymer in the liquid crystal polymer film is not particularly limited, but is preferably 70% by mass or more based on the liquid crystal polymer film.

[0020] The liquid crystal polymer film may contain other components. Examples of other components include fillers, additives, and resins other than the liquid crystal polymer.

[0021] Examples of the filler include inorganic fillers such as silica, alumina, titanium oxide, barium titanate, strontium titanate, aluminum hydroxide, and calcium carbonate; and organic fillers such as cured epoxy resins, crosslinked benzoguanamine resins, and crosslinked acrylic resins. When a filler is contained, the content of the filler in the liquid crystal polymer film is not particularly limited, but is preferably 20% by volume to 70% by volume.

[0022] Examples of the additives include leveling agents, antifoaming agents, antioxidants, ultraviolet absorbers, flame retardants, and colorants. The content of the additive in the liquid crystal polymer film is not particularly limited, but is preferably 0 to 5 parts by mass with respect to 100 parts by mass of the liquid crystal polymer.

[0023] Examples of resins other than liquid crystal polymers include thermoplastic resins such as polypropylene, polyamide, amorphous polyester, polyphenylene sulfide, polyether ketone, polycarbonate, polyether sulfone, polyphenylene ether, and polyether imide; and thermosetting resins such as phenol resin, epoxy resin, polyimide resin, and cyanate resin. The content of the resin other than the liquid crystal polymer is not particularly limited, but is preferably 0 to 20 parts by mass relative to 100 parts by mass of the liquid crystal polymer.

[0024] The liquid crystal polymer film may or may not be porous. When the liquid crystal polymer film is porous, the porosity of the liquid crystal polymer film is not particularly limited, but is preferably 20% to 70%. The method for determining the porosity of the liquid crystal polymer film will be described in the Examples below.

[0025] The thickness of the liquid crystal polymer film is not particularly limited, but is, for example, 2 μm or more, preferably 5 μm or more, and more preferably 10 μm or more, and is, for example, 200 μm or less, preferably 100 μm or less, and more preferably 75 μm or less.

[0026] Residual stress in the liquid crystal polymer film is likely to be generated by rolling. On the other hand, the production of a film by rolling has the advantage that a film can be formed even if the filler content is increased. In this respect, the liquid crystal polymer film is preferably produced by rolling. That is, the liquid crystal polymer film is preferably a rolled film. The liquid crystal polymer film of the present invention is a liquid crystal polymer film with reduced warpage even if it is a rolled film.

[0027] The degree of in-plane orientation in the MD (machine direction) during rolling of the liquid crystal polymer film is not particularly limited, but is preferably 50% or less. The MD direction during rolling refers to the feed direction (conveyance direction) of the film during rolling. The lower limit of the in-plane orientation degree in the MD direction during rolling is not particularly limited, but the in-plane orientation degree in the MD direction during rolling may be, for example, 20% or more. The method for determining the degree of in-plane orientation will be described in the Examples section below.

[0028] The liquid crystal polymer film may or may not be a stretched film. The term "stretching" used here refers to a film manufacturing process in which the film is mechanically stretched in one direction (mainly the longitudinal direction) or in two directions (the longitudinal and transverse directions), as opposed to rolling, i.e., uniaxial or biaxial stretching. On the other hand, it is preferable that the porous liquid crystal polymer film is not a stretched film, and in particular, it is preferable that the porous liquid crystal polymer film produced by using a porosifying agent is not a stretched film.

[0029] (Method of manufacturing liquid crystal polymer film) The method for producing a liquid crystal polymer film of the present invention includes a rolling step and a heat treatment step. The method for producing the liquid crystal polymer film of the present invention is a suitable method for producing the liquid crystal polymer film of the present invention.

[0030] <Rolling process> The rolling step is not particularly limited as long as it is a step of rolling a sheet to obtain a rolled film. The sheet is formed from a composition that includes a liquid crystal polymer.

[0031] The composition contains a liquid crystal polymer. The liquid crystal polymer is not particularly limited, and examples thereof include the liquid crystal polymers described above. The composition may contain other components, such as fillers, additives, and resins other than the liquid crystal polymer.

[0032] When a porous liquid crystal polymer film is to be produced, the composition may further contain a porosifying agent. The porosifying agent may be an inorganic compound or an organic compound. Examples of inorganic compounds include inorganic salts. The inorganic salts may be, for example, sulfates, chlorides, or carbonates. Examples of sulfates are sodium sulfate, potassium sulfate, lithium sulfate, magnesium sulfate, and calcium sulfate. Examples of chlorides are sodium chloride, potassium chloride, lithium chloride, magnesium chloride, and calcium chloride. Examples of carbonates are sodium carbonate, potassium carbonate, lithium carbonate, magnesium carbonate, and calcium carbonate. The organic compound includes, for example, a purine derivative, and preferably, caffeine.

[0033] The content of the porosity agent in the composition is not particularly limited, but the volume ratio of the liquid crystal polymer to the porosity agent (liquid crystal polymer:porosity agent) is preferably 10:90 to 90:10, more preferably 20:80 to 80:20, and particularly preferably 30:70 to 60:40.

[0034] When the composition contains components other than the liquid crystal polymer in addition to the liquid crystal polymer, the composition can be obtained, for example, by kneading raw materials.

[0035] The sheet is formed from a composition that includes a liquid crystal polymer. The method for forming the sheet is not particularly limited, and examples thereof include press molding, extrusion molding, and injection molding.

[0036] The thickness of the sheet before rolling is not particularly limited, but is preferably 100 μm to 1,000 μm, and more preferably 150 μm to 800 μm.

[0037] Rolling refers to, for example, applying linear pressure to a sheet by sandwiching it between a pair of rolls (two rolls) to stretch the sheet. Linear pressure is the value obtained by dividing the load applied to the roll by the face length of the roll. The line pressure during rolling is not particularly limited and can be appropriately selected. The line pressure can be adjusted, for example, by a hydraulic system.

[0038] The thickness of the rolled film after rolling is not particularly limited, but is, for example, 2 μm or more, preferably 5 μm or more, and more preferably 10 μm or more, and is, for example, 200 μm or less, preferably 100 μm or less, and more preferably 75 μm or less. The ratio (T0 / T1) of the thickness (T0) of the sheet before rolling to the thickness (T1) of the rolled film after rolling is not particularly limited, but may be, for example, 2 to 30, or 5 to 20.

[0039] During rolling, the rolls may be heated. The roll temperature is not particularly limited, and may be, for example, 250°C to 450°C, or 300°C to 400°C. The roll temperature is preferably higher than the melting point of the liquid crystal polymer, and is preferably at least 30° C. higher than the melting point of the liquid crystal polymer. The upper limit of the roll temperature is not particularly limited as long as it is appropriately set to a temperature lower than or equal to a temperature at which the liquid crystal polymer is not deteriorated by thermal decomposition, but the roll temperature may be, for example, lower than or equal to a temperature 100° C. higher than the melting point of the liquid crystal polymer. The heating is performed, for example, by using a heating roll. The heating roll may be either one or both of a pair of rolls.

[0040] The rolling is carried out, for example, by passing the sheet between a pair of rolls. The rolling is preferably carried out by passing the laminate between a pair of rolls. The laminate has a sheet, a first film-like substrate arranged in contact with a first surface of the sheet, and a second film-like substrate arranged in contact with a second surface of the sheet. That is, the laminate has the first film-like substrate, the sheet, and the second film-like substrate in this order. The laminate may further have other films or sheets. The rolling is performed by passing the laminate between a pair of rolls, which makes it possible to avoid direct contact of the sheet with the rolls, thereby preventing the sheet from adhering to the rolls and winding around the rolls.

[0041] The rolling step may be performed once or multiple times. The rolling conditions (e.g., line pressure, heating temperature, etc.) in the multiple rolling steps may be the same or different. For example, since it is difficult to reduce a sheet (before rolling) having a thickness of about 1 mm to a thickness of several tens of μm by rolling it once, a sheet (before rolling) having a thickness of about 1 mm may be rolled multiple times to a thickness of several tens of μm.

[0042] There are no particular limitations on the thickness, material, and structure of the first film substrate and the second film substrate. The thickness of the first film-like substrate and the second film-like substrate may be, for example, independently from 10 μm to 200 μm, from 20 μm to 150 μm, or from 50 μm to 100 μm. The material of the first film-shaped substrate and the second film-shaped substrate is not particularly limited, but may be a metal or a thermoplastic resin. Examples of metals include copper, aluminum, and stainless steel. Examples of thermoplastic resins include polyolefin resins such as polyethylene, polypropylene, polymethylpentene, and ethylene-α-olefin copolymers, acrylic resins such as PMMA, polyimide resins, polyamide resins, acrylonitrile-butadiene-styrene copolymers (ABS resins), polystyrene (PS), polyvinyl chloride, polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polycarbonate (PC), polyether ether ketone (PEEK), and polyphenyl sulfide (PPS).

[0043] <Heat treatment process> The heat treatment step is not particularly limited as long as it is a step of heat treating the rolled film at a heat treatment temperature that satisfies the following formula (1). T1<Heat treatment temperature (℃)≦T2 Equation (1) T1: 100°C lower than the melting point of the liquid crystal polymer T2: Melting point of liquid crystal polymer

[0044] The heat treatment relieves the residual stress in the rolled film, resulting in a liquid crystal polymer film with reduced warping. From the viewpoint of not melting the liquid crystal polymer, the heat treatment temperature is preferably below the melting point of the liquid crystal polymer. On the other hand, if the heat treatment temperature is too low, the residual stress is not sufficiently relaxed. Therefore, the heat treatment temperature is preferably a heat treatment temperature that satisfies the formula (1).

[0045] The heat treatment step is preferably a step of heat treating the rolled film at a heat treatment temperature that satisfies the following formula (1-1). T1'≦Heat treatment temperature (℃)≦T2 Formula (1-1) T1': 80°C lower than the melting point of the liquid crystal polymer T2: Melting point of liquid crystal polymer

[0046] The lower limit of the heat treatment temperature in the heat treatment step is not particularly limited as long as the above formula (1) is satisfied, and the heat treatment temperature may be, for example, 150°C or more, 180°C or more, or 200°C or more. The upper limit of the heat treatment temperature in the heat treatment step is not particularly limited as long as the above formula (1) is satisfied, and the heat treatment temperature may be, for example, 350°C or less, 300°C or less, or 250°C or less.

[0047] The heat treatment may be carried out in a batch manner or a continuous manner, for example, in which the rolled film sent out from the rolling process is continuously fed into a heat treatment device in a roll-to-roll manner and heat-treated.

[0048] The heat treatment time is not particularly limited, but may be from 5 seconds to 1 hour.

[0049] <Porous process> When a porous liquid crystal polymer film is produced, the method for producing a liquid crystal polymer film of the present invention may further include a porosity-forming step. The porosity-making step may be carried out before the heat treatment step or after the heat treatment step, so long as it is carried out after the rolling step.

[0050] The porosity-making step is a step of making the rolled film porous. The porosity-providing step is, for example, a step of extracting a porosity-providing agent from a rolled film. The extraction method is not particularly limited, but examples thereof include solvent extraction and supercritical extraction.

[0051] When the porosifying agent is an inorganic salt, the extraction is carried out, for example, with a solvent (eg, water). The extraction can be carried out, for example, by immersing the rolled film in a solvent (eg, ultrapure water). The temperature of the solvent during immersion is not particularly limited, and may be, for example, 10°C to 100°C. The immersion time is not particularly limited, and may be, for example, 10 minutes to 2 hours. The rolled film may be immersed in a solvent under pressure. In this case, the temperature of the solvent may be equal to or higher than the boiling point of the solvent at normal pressure.

[0052] When the porosifying agent is an organic compound, the extraction is performed, for example, using a supercritical fluid. The extraction method using a supercritical fluid is not particularly limited, and examples thereof include the second and third steps described in JP 2022-156865 A.

[0053] (Low dielectric substrate material) The low dielectric substrate material of the present invention comprises the liquid crystal polymer film of the present invention and a metal layer in this order in the thickness direction. The low dielectric substrate material may further include, for example, an adhesive layer. In low dielectric substrate materials, the liquid crystal polymer film is an insulating layer.

[0054] <Metal layer> The metal layer has a sheet (plate) shape. The material of the metal layer is not particularly limited, and examples thereof include copper, iron, silver, gold, aluminum, nickel, and alloys thereof (stainless steel, bronze), etc. Copper is preferable.

[0055] 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.

[0056] <Adhesive layer> The adhesive layer has a sheet shape extending along the surface direction, for example, on one surface in the thickness direction of the liquid crystal polymer film.

[0057] The material of the adhesive layer is not particularly limited, and various types of adhesives such as hot melt adhesives and thermosetting adhesives can be used, and specifically, acrylic adhesives, epoxy adhesives, silicone adhesives, etc. are used. Preferably, acrylic adhesives are used.

[0058] 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.

[0059] The thickness of the low dielectric substrate material is, for example, 10 μm or more, and preferably 20 μm or more, and is, for example, 5,000 μm or less, and preferably 2,000 μm or less.

[0060] The low dielectric substrate material is used for various purposes, and is preferably used for manufacturing high-frequency antennas and high-speed transmission substrates (such as high-speed transmission FPCs) that comply with the fifth generation (5G) standards. Specifically, the low dielectric substrate material is used as a substrate material for high-frequency antennas and high-speed FPCs.

[0061] An example of a low dielectric substrate material will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of one embodiment of a low dielectric substrate material of the present invention. A low dielectric substrate material 1 shown in FIG. 1 has one surface and the other surface opposing each other in the thickness direction, and has a shape extending in a planar direction perpendicular to the thickness direction. The low dielectric substrate material 1 includes a first metal layer 2, a liquid crystal polymer film 3 disposed on one surface in the thickness direction of the first metal layer 2, an adhesive layer 4 disposed on one surface in the thickness direction of the liquid crystal polymer film 3, and a second metal layer 5 disposed on one surface in the thickness direction of the adhesive layer 4. That is, the low dielectric substrate material 1 includes the first metal layer 2, the liquid crystal polymer film 3, the adhesive layer 4, and the second metal layer 5 in this order from the other side to the one side in the thickness direction. Preferably, the low dielectric substrate material 1 includes only the first metal layer 2, the liquid crystal polymer film 3, the adhesive layer 4, and the second metal layer 5.

[0062] In another embodiment of the low dielectric substrate material, as shown in FIG. 2, a low dielectric substrate material 1 includes a liquid crystal polymer film 3 and a metal layer 6 in this order toward one side in the thickness direction.

[0063] (Wired circuit board) The wired circuit board of the present invention comprises the liquid crystal polymer film of the present invention and a conductor layer in this order in the thickness direction. The printed circuit board may further include, for example, an adhesive layer. In the printed circuit board, the liquid crystal polymer film is an insulating layer.

[0064] The wired circuit board has, for example, wiring as a conductor layer. Examples of the wiring include signal wiring, antenna wiring, ground wiring, etc. The wiring can be formed, for example, by patterning a metal layer by photolithography (for example, a subtractive method).

[0065] An example of a printed circuit board will be described with reference to the drawings. FIG. 3 is a schematic cross-sectional view of one embodiment of the wired circuit board of the present invention. The wired circuit board 10 shown in Fig. 3 extends in a planar direction. The wired circuit board 10 has a sheet shape. The wired circuit board 10 includes a liquid crystal polymer film 3 and a conductor layer 7 in this order toward one side in a thickness direction. The conductor layer 7 contacts one surface in the thickness direction of the liquid crystal polymer film 3. The conductor layer 7 has a predetermined wiring pattern. The wired circuit board 10 shown in FIG. 3 can be produced, for example, in the following manner. First, a low dielectric substrate material 1 shown in FIG. 2 is prepared. Next, the metal layer 6 of the low dielectric substrate material 1 shown in FIG. 2 is patterned by photolithography to form a conductor layer 7 on the liquid crystal polymer film 3. EXAMPLES

[0066] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples and comparative examples.

[0067] Example 1 <<First process: kneading>> A composition was prepared by kneading 45 parts by volume of UENO LCP A5000 (melting point 280°C) manufactured by Ueno Pharmaceutical Co., Ltd. as a liquid crystal polymer and 55 parts by volume of sodium sulfate manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. as a porosifying agent using a Labo Plastomill (model number: 4C150) manufactured by Toyo Seiki Co., Ltd. The temperature during kneading was 350°C, and the rotation speed of the screw in the kneading device was adjusted to 30 rpm (revolutions per minute).

[0068] <<Second step: Sheet production>> Next, a non-porous sheet having a thickness of 200 μm to 560 μm was produced from the composition using a manual hydraulic vacuum press (model number: 11FD) manufactured by Imoto Machinery Works. The temperature in the press was 350° C., and the pressure was 4 to 10 MPa.

[0069] <<Third process: rolling>> A rolling machine having a pair of induction heating rolls (two rolls) with a diameter of 300 mm arranged above and below in the compression molding section was used. As a film-like heat-resistant substrate, an ultra-heat-resistant and ultra-cold-resistant polyimide film (Toray DuPont's "Kapton 300H", thickness 75 μm) was prepared on one side and copper foil (CF-T49A-DS-HD2-18) manufactured by Fukuda Metal Foil and Powder Co., Ltd. was prepared on the other side, and a non-porous sheet was sandwiched between them to obtain a laminate. As the first rolling, the following rolling was performed. The laminate was fed to the lower roll so as to be embraced by the roll at an angle of 90°. The roll temperature was 350° C., and the roll load was 2 tonF. As the second rolling, the following rolling was carried out. The laminate that had been subjected to the first rolling was turned 90° and fed to the lower roll so as to be embraced by the lower roll at an angle of 90°. The roll temperature was 350° C. and the roll load was 2 tonF. After passing through the rolls, the film was naturally cooled to room temperature, and then the polyimide film was peeled off.

[0070] <<4th step: Porousization>> Sodium sulfate was extracted from the rolled non-porous sheet into ultrapure water as a solvent by the following method. The temperature of the ultrapure water was 20° C., and the extraction time, which is the time during which the nonporous sheet was immersed in the ultrapure water, was 36 hours. Thereafter, sodium sulfate was extracted with ultrapure water, and the resulting sheet was dried to obtain a porous sheet.

[0071] <<5th step: Heat treatment>> The obtained porous sheet was placed in a muffle furnace (FP300) manufactured by Yamato Scientific Co., Ltd. and subjected to a heat treatment at 260° C. for 30 minutes. Thereafter, the porous sheet was left to stand in the furnace and slowly cooled to room temperature (20°C). As a result, a laminate in which a liquid crystal polymer film was laminated on a copper foil was obtained.

[0072] (Examples 2 to 4 and Comparative Examples 1, 2, 4 and 5) A liquid crystal polymer film was obtained in the same manner as in Example 1, except that the second rolling, the heat treatment, the heat treatment temperature, and the slow cooling were changed to the conditions shown in Table 1-1 or Table 1-2. When slow cooling was not performed after the heat treatment, the porous sheet was removed from the furnace immediately after the heat treatment and left to stand outside the furnace to cool naturally.

[0073] Example 5 <<First step: Sheet production>> UENO LCP A5000 (melting point 280° C.) manufactured by Ueno Pharmaceutical Co., Ltd. was pressed as a liquid crystal polymer using a manual hydraulic vacuum press (model number: 11FD) manufactured by Imoto Manufacturing Co., Ltd. to produce a non-porous sheet (non-porous sheet) having a thickness of 200 μm to 560 μm. The temperature in the press was 350° C., and the pressure was 0.5 to 4 MPa.

[0074] <<Second process: rolling>> A rolling machine having a pair of induction heating rolls (two rolls) with a diameter of 300 mm arranged above and below in the compression molding section was used. As a film-like heat-resistant substrate, an ultra-heat-resistant and ultra-cold-resistant polyimide film (Toray DuPont's "Kapton 300H", thickness 75 μm) was prepared on one side and copper foil (CF-T49A-DS-HD2-18) manufactured by Fukuda Metal Foil and Powder Co., Ltd. was prepared on the other side, and a non-porous sheet was sandwiched between them to obtain a laminate. As the first rolling, the following rolling was performed. The laminate was fed to the lower roll so as to be embraced by the roll at an angle of 90°. The roll temperature was 350° C., and the roll load was 2 tonF. After passing through the rolls, the film was naturally cooled to room temperature, and then the polyimide film was peeled off.

[0075] <<Third process: Heat treatment>> The rolled non-porous sheet was heat-treated in a muffle furnace (FP300) manufactured by Yamato Scientific Co., Ltd. The heat treatment temperature was 260° C., and the heat treatment time was 30 minutes. Immediately after the heat treatment, the porous sheet was removed from the furnace and allowed to stand outside the furnace. As a result, a laminate in which a liquid crystal polymer film was laminated on a copper foil was obtained.

[0076] Comparative Example 3 A liquid crystal polymer film was obtained in the same manner as in Example 5, except that the heat treatment was performed or not and the heat treatment temperature were changed to the conditions shown in Table 1-2.

[0077] (porosity) The porosity was calculated by the following formula: The results are shown in Tables 1-1 and 1-2. Porosity [%]=100×{(M i -M p ) / M i} M i : Specific gravity of liquid crystal polymer M p : Specific gravity of porous sheet

[0078] (Thickness) The thickness of the liquid crystal polymer film was measured using a digital gauge (RI-205) manufactured by Ozaki Manufacturing Co., Ltd. The results are shown in Tables 1-1 and 1-2.

[0079] (TMA (Thermomechanical Analysis)) The copper foil was removed by etching, leaving only the liquid crystal polymer film. The TMA measurement was carried out in accordance with JIS K7197 under the following conditions. The test sample of the liquid crystal polymer film was prepared so that the sheet feed direction (MD) during the first rolling was the longitudinal direction. Sample width: 4mm Effective sample length (length between chucks): 24mm ·Temperature increase / decrease rate: 10℃ / min ·Constant load: 0.020N Temperature range: 40℃ ⇒ 200℃ (actual temperature) ⇒ 40℃ measurement conditions The temperature was raised from 40°C to 200°C, and then changed from 200°C to 40°C. The dimensional change ΔL1 in the sheet feed direction (MD direction) during the first rolling of the liquid crystal polymer film was measured, and the dimensional change ΔL2 when the liquid crystal polymer film was measured again under the same temperature conditions, and the difference between them (ΔL1-ΔL2) were obtained. The results are shown in Table 1-1 and Table 1-2. The amount of dimensional change refers to the difference in dimensions before and after the temperature increase and decrease.

[0080] (Curl evaluation) The "curl" (warpage) can be determined in accordance with JIS C6481, and specifically, the measurement was performed as follows. A laminate (5cm x 5cm) of a liquid crystal polymer film laminated on a copper foil was placed on a horizontal table so that the center of the film was in contact with the table and the four corners were raised above the table, and the maximum distance between the four corners and the table was measured. The maximum value was divided by the length of the side of the film to obtain the percentage warpage (%). The evaluation was performed according to the following criteria, and the results are shown in Tables 1-1 and 1-2. [Evaluation Criteria] ○: Warpage rate is 20% or less △: Warpage rate is over 20% and 30% or less ×: Warpage rate is over 30%

[0081] (Orientation degree) The degree of orientation (%) was measured by X-ray diffraction measurement using a transmission method with a Rigaku X-ray diffractometer (Nano-Viewer). Peak intensity (orientation component) was measured by 2θ / θ scanning. Using the peaks of the obtained profile, the intensity was measured in the azimuth angle direction from 0° to 360° by β scanning. The half-width of each peak of the obtained diffraction intensity distribution curve (β profile) was calculated by waveform separation, and the degree of orientation was calculated according to the following formula. The degree of orientation is the degree of orientation in the sheet feed direction during the first rolling. The results are shown in Tables 1-1 and 1-2. Orientation degree = (360 - (sum of peak half-widths)) / 360 x 100

[0082] [Table 1-1]

[0083] [Table 1-2] [Explanation of symbols]

[0084] 1. Low dielectric substrate material 2 1st metal layer 3 Liquid crystal polymer film 4 Adhesive layer 5 Second metal layer 6 metal layer 7 Conductor Layer 10 Wiring circuit board

Claims

1. A liquid crystal polymer film, A liquid crystal polymer film, wherein the difference (ΔL1-ΔL2) between a dimensional change (ΔL1) of the liquid crystal polymer film when the temperature is lowered from 200°C to 40°C after a first heating step in which the temperature is raised from 40°C to 200°C using a thermomechanical analyzer and a dimensional change (ΔL2) of the liquid crystal polymer film when the temperature is lowered from 200°C to 40°C after a second heating step in which the temperature is raised from 40°C to 200°C using the thermomechanical analyzer is 120 μm or less.

2. The liquid crystal polymer film of claim 1 which is a calendered film.

3. 3. The liquid crystal polymer film according to claim 2, wherein the degree of in-plane orientation in the MD direction during rolling is 50% or less.

4. 2. The liquid crystal polymer film of claim 1, containing 20 to 70 volume percent of a filler.

5. 2. The liquid crystal polymer film according to claim 1, wherein the porosity is 20% to 70%.

6. 6. A low dielectric substrate material comprising the liquid crystal polymer film according to claim 1 and a metal layer in that order in the thickness direction.

7. 6. A wiring circuit board comprising the liquid crystal polymer film according to claim 1 and a conductor layer in that order in the thickness direction.

8. A step of rolling a sheet formed from a composition containing a liquid crystal polymer to obtain a rolled film; A step of heat treating the rolled film at a heat treatment temperature that satisfies the following formula (1); A method for producing a liquid crystal polymer film, comprising: T1<Heat treatment temperature (°C)≦T2 ... Formula (1) T1: a temperature 100° C. lower than the melting point of the liquid crystal polymer T2: melting point of the liquid crystal polymer

9. The method for producing a liquid crystal polymer film according to claim 8, wherein the rolling is performed by passing the sheet between a pair of rolls.

10. The rolling is carried out by passing the laminate between a pair of rolls; The laminate has the sheet, a first film-like substrate arranged in contact with a first surface of the sheet, and a second film-like substrate arranged in contact with a second surface of the sheet. The method for producing the liquid crystal polymer film according to claim 8 .

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