Printed wiring board substrates and multilayer substrates

Abstract

A printed wiring board substrate according to one embodiment is provided with: a base material layer; and a copper foil which is laminated, directly or indirectly, over at least some part of one or both surfaces of the base material layer. The base material layer includes a matrix consisting mainly of a fluororesin and one or a plurality of reinforcing material layers included in the matrix. When the average thickness of the base material layer is represented by A, and the average distance between the copper foil surface facing the matrix, and the reinforcing material layer surface closest to said surface and facing the copper foil is represented by B, the ratio B / A is 0.003 to 0.37.

Description

[Technical Field]

[0001] The present disclosure relates to a substrate for a printed wiring board and a multilayer substrate. This application claims priority to Japanese Application No. 2020-113450, filed on June 30, 2020, and incorporates by reference all of the contents of said Japanese application. [Background technology]

[0002] Printed wiring boards having fluororesin substrates have been known for some time. Because fluororesin has a lower dielectric constant than epoxy resin, printed wiring boards having fluororesin substrates are used in circuit boards for high-frequency signal processing. For such printed wiring boards, it has been proposed to dispose a substrate layer made of glass cloth impregnated with fluororesin on at least one side of a fluororesin sheet (see JP 2002-158415 A). Because an insulating layer is formed by the fluororesin sheet and the substrate layer, this printed wiring board has higher mechanical strength and is less susceptible to warping or distortion of the board compared to printed wiring boards that use a polytetrafluoroethylene (PTFE) sheet alone. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-158415 Summary of the Invention

[0004] A substrate for printed wiring boards according to one embodiment of the present disclosure comprises a base layer and copper foil laminated directly or indirectly on at least a portion of one or both sides of the base layer, the base layer having a matrix containing a fluororesin as a main component and one or more reinforcing material layers contained in the matrix, and when A is the average thickness of the base layer and B is the average distance between a surface of the copper foil facing the matrix and a surface of the reinforcing material layer closest to the base layer facing the copper foil, the ratio B / A is 0.003 or more and 0.37 or less. [Brief explanation of the drawings]

[0005] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a substrate for a printed wiring board according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic cross-sectional view showing a multilayer substrate according to an embodiment of the present disclosure. [Figure 3] FIG. 3 is a schematic cross-sectional view showing a multilayer substrate according to another embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0006] [Problem to be solved by this disclosure] In general, substrates for printed wiring boards are used in a folded state, or may be folded during the manufacturing process when they are incorporated into devices such as mobile phones. However, substrates for printed wiring boards that use fluororesin substrates containing reinforcing materials such as glass cloth may break if they are repeatedly bent.

[0007] The present disclosure has been made in light of the above-mentioned circumstances, and has an object to provide a substrate for a printed wiring board that has excellent bending strength.

[0008] [Effects of this disclosure] The substrate for printed wiring board of the present disclosure has excellent bending strength.

[0009] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described.

[0010] (1) A substrate for printed wiring boards according to one embodiment of the present disclosure comprises a base layer and copper foil laminated directly or indirectly on at least a portion of one or both sides of the base layer, the base layer having a matrix containing a fluororesin as a main component and one or more reinforcing material layers contained in the matrix, and the ratio B / A is 0.003 or more and 0.37 or less, where A is the average thickness of the base layer and B is the average distance between a surface of the copper foil facing the matrix and a surface of the reinforcing material layer closest to the base layer facing the copper foil.

[0011] A printed wiring board substrate used in a multilayer board preferably has a bending strength sufficient to withstand bending 60 or more times. However, when a printed wiring board substrate is bent into a U-shape, peaks and valleys are formed, and the constituent material of the printed wiring board substrate (e.g., fluororesin) is tensioned at the peaks and compressed at the valleys. Generally, a printed wiring board substrate has copper foil on its surface. When a printed wiring board substrate is bent into a U-shape, the copper foil cannot withstand the stress generated by bending and breaks. The present inventors have confirmed that this copper foil breakage tends to occur from both ends of the substrate in a direction perpendicular to the bending direction of the printed wiring board substrate. Therefore, the present inventors speculate that "when a printed wiring board substrate is bent, the fluororesin is compressed at the valleys due to its softness, causing significant strain in the fluororesin. The copper foil bonded to the fluororesin cannot accommodate this strain and breaks." Based on this assumption, the inventors discovered that by reducing the distortion of the fluororesin, i.e., the force that causes the fluororesin to extrude, the bending strength of the substrate for printed wiring boards can be improved and breakage of the substrate for printed wiring boards due to bending can be suppressed. In the substrate for printed wiring board according to one embodiment of the present disclosure, the ratio B / A is 0.003 or more and 0.37 or less, thereby minimizing the outermost matrix (mainly composed of fluororesin), i.e., the matrix (fluororesin layer) between the copper foil and the reinforcing material layer closest to the copper foil. Therefore, when the substrate for printed wiring board according to one embodiment of the present disclosure is bent, the force (matrix distortion) that causes the matrix (fluororesin layer) to protrude is reduced, suppressing the load on the copper foil. Therefore, the substrate for printed wiring board according to one embodiment of the present disclosure has excellent bending strength.

[0012] (2) The ratio B / A may be 0.10 or more and 0.25 or less. If the ratio B / A is 0.10 or more and 0.25 or less, the bending strength is further improved.

[0013] The "major component" is the component with the largest content. The "major component" is, for example, a component with a content of 50% by mass or more, and may be a component with a content of 90% by mass or more. The "average thickness" of the base layer or reinforcing layer is the distance between the mean line of the interface on the front side and the mean line of the interface on the back side within the measurement field of the base layer or reinforcing layer in a cross section cut in the thickness direction of a printed wiring board substrate or multilayer substrate. The cross section is observed using a scanning electron microscope or optical microscope. The size of the observation field is 0.1 μm × 0.1 μm or more and 3 mm × 3 mm or less. The "average line" means an imaginary line drawn along the interface, such that the total area of ​​the peaks (total area above the imaginary line) and the total area of ​​the valleys (total area below the imaginary line) defined by the interface and this imaginary line are equal. The "average distance B" is the average of the five measurements of the distance b between the surface of the copper foil facing the matrix and the surface of the reinforcement layer closest to that surface facing the copper foil, measured at any five points. The average distance B corresponds to the average of the five measurements of the distance between the outermost surface of the reinforcement layer located on both ends of the base layer in the thickness direction and the surface of the copper foil opposite the outermost surface of this reinforcement layer. The distance b is measured by observing a cross section of the printed wiring board substrate or multilayer substrate cut in the thickness direction. The cross section is observed using a scanning electron microscope or optical microscope, with a field of view of 0.1 μm × 0.1 μm or more and 3 mm × 3 mm or less. Furthermore, when copper foils are present on both sides of the base material layer, B can be determined for each copper foil and the reinforcing material layer closest to each copper foil. In the substrate for printed wiring board according to one embodiment of the present disclosure, the ratio B / A for each B is 0.003 or more and 0.37 or less.

[0014] (3) The fluororesin may be any one of tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFE), polytetrafluoroethylene (PTFE), or a combination thereof. By using any one of FEP, PFE, and PTFE as the fluororesin, or a combination thereof, the effect of suppressing transmission loss can be further enhanced.

[0015] (4) The ratio of the total average thickness of the reinforcing material layers to the average thickness of the base material layer may be 0.01 or more and 0.99 or less. (5) The ratio of the total average thickness of the reinforcing material layers to the average thickness of the base material layer may be 0.20 or more and 0.50 or less. (6) The ratio of the total average thickness of the reinforcing material layers to the average thickness of the base material layer may be 0.22 or more and 0.47 or less. (7) The ratio of the total average thickness of the reinforcing material layers to the average thickness of the base material layer may be 0.25 or more and 0.45 or less. When the ratio of the sum of the average thicknesses of the reinforcing material layers to the average thickness of the base layer is 0.01 or more and 0.99 or less, the bending strength and transmission characteristics can be further improved. When the ratio of the sum of the average thicknesses of the reinforcing material layers to the average thickness of the base layer is 0.20 or more and 0.50 or less, the bending strength and transmission characteristics can be further improved. When the ratio of the sum of the average thicknesses of the reinforcing material layers to the average thickness of the base layer is 0.22 or more and 0.47 or less, the bending strength and transmission characteristics can be further improved. When the ratio of the sum of the average thicknesses of the reinforcing material layers to the average thickness of the base layer is 0.25 or more and 0.45 or less, the bending strength and transmission characteristics can be particularly improved. "The sum of the average thicknesses of the reinforcing material layers" refers to the average thickness of the reinforcing material layer when there is one reinforcing material layer, and refers to the sum of the average thicknesses of the reinforcing material layers when there are multiple reinforcing material layers.

[0016] (8) The reinforcing material layer may include glass cloth, a heat-resistant film, a resin cloth, or a nonwoven fabric. When the reinforcing material layer includes glass cloth, a heat-resistant film, a resin cloth, or a nonwoven fabric, the bending strength of the substrate for printed wiring boards can be further improved.

[0017] (9) The copper foil may be an electrolytic copper foil or a rolled copper foil. When the copper foil is an electrolytic copper foil or a rolled copper foil, it is possible to obtain excellent transmission characteristics and better flexibility.

[0018] (10) The matrix may be divided into a plurality of layers. By dividing the matrix into a plurality of layers, the substrate for a printed wiring board can be made even more excellent in bending strength.

[0019] (11) A multilayer substrate according to another aspect of the present disclosure is formed by stacking a plurality of substrates for printed wiring boards according to one aspect of the present disclosure. By stacking a plurality of substrates for printed wiring boards, the multilayer substrate can reduce distortion due to compression of the outermost matrix (fluororesin layer) of the multilayer substrate and suppress the load on the copper foil arranged on the outermost side. Therefore, the multilayer substrate according to another aspect of the present disclosure has excellent bending strength.

[0020] (12) A plurality of the substrates for printed wiring boards may be laminated via an adhesive layer mainly composed of a bonding sheet or a silane coupling agent. By laminating a plurality of substrates for printed wiring boards via an adhesive layer mainly composed of a bonding sheet or a silane coupling agent, good adhesion can be obtained between the plurality of substrates for printed wiring boards.

[0021] (13) A multilayer board according to another aspect of the present disclosure may be formed by laminating a first substrate for printed wiring boards and a second substrate for printed wiring boards. The first substrate for printed wiring boards and the second substrate for printed wiring boards are the substrates for printed wiring boards described in any one of (1) to (10). In the first substrate for printed wiring boards, the copper foil is laminated directly or indirectly on at least a portion of each of both surfaces of the base layer, and in the second substrate for printed wiring boards, the copper foil is laminated directly or indirectly on at least a portion of one surface of the base layer. The copper foil of the first printed wiring board substrate, on which the second printed wiring board substrate is laminated, may be a first copper foil, and the reinforcing material layer of the second printed wiring board substrate closest to the first copper foil may be a first reinforcing material layer. When the average thickness of the base layer of the second printed wiring board substrate is A and the average distance between the surface of the first copper foil facing the matrix of the second printed wiring board substrate and the surface of the first reinforcing material layer facing the first copper foil is D, the ratio D / A may be 0.003 or more and 0.37 or less. This configuration can reduce the load on the copper foil disposed inside the multilayer board. Therefore, this multilayer board has excellent bending strength. The "average distance D" is the average value of five measurements of the distance d between the surface of the first copper foil facing the matrix of the second printed wiring board substrate and the surface of the first reinforcing material layer facing the first copper foil, measured at any five points. The method for measuring the distance d is the same as the method for measuring the distance b.

[0022] [Details of the embodiments of the present disclosure] Hereinafter, a substrate for a printed wiring board according to the present disclosure will be described with reference to the drawings.

[0023] <Printed wiring board substrate> The substrate for printed wiring boards according to the present disclosure includes a base layer and a copper foil laminated directly or indirectly on at least a portion of one or both sides of the base layer. The base layer has a matrix containing a fluororesin as a main component and one or more reinforcing material layers contained in the matrix.

[0024] The substrate 1 for a printed wiring board shown in FIG. 1 includes a base layer 51. The substrate 1 for a printed wiring board also includes copper foils 41 and 42 laminated directly or indirectly on both sides of the base layer 51. The base layer 51, which is mainly composed of a fluororesin, includes reinforcing material layers 31 and 32 and a matrix formed of a fluororesin layer. In FIG. 1, the matrix is ​​divided into three layers, matrices 2a, 2b, and 2c, by the two reinforcing material layers 31 and 32. The matrix 2a is disposed facing the copper foil 41, and the matrix 2c is disposed facing the copper foil 42. The matrix 2b is disposed between the reinforcing material layer 31 and the reinforcing material layer 32.

[0025] [Base material layer] The substrate layer has a matrix and one or more reinforcing material layers contained in the matrix. The matrix is ​​a base material whose main component is fluororesin. The matrix is ​​the portion other than the reinforcing material layers. In FIG. 1, the matrix is ​​made up of three layers (matrices 2a, 2b, and 2c). The reinforcing material layers are disposed between the matrices (matrix layers).

[0026] Fluororesin is a material with a relatively low dielectric constant, and the temperature dependency of the dielectric constant is small. Therefore, when the matrix is ​​mainly composed of fluororesin, the transmission loss of the printed wiring board substrate 1 is effectively suppressed. Furthermore, the crystallinity of the fluororesin is 50% or more and 60% or less. Because the crystallinity of the fluororesin is low, even if a specific change occurs in the crystal structure, it is expected that the change in the electrical properties will be small. Therefore, the temperature dependency of the electrical properties of the fluororesin is good.

[0027] The fluororesin may be any one of tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFE), polytetrafluoroethylene (PTFE), or a combination thereof. When the fluororesin is any one of FEP, PFE, and PTFE, or a combination thereof, the effect of suppressing transmission loss can be further improved.

[0028] The matrix may contain components (optional components) other than the fluororesin. Examples of optional components include resins other than fluororesin, flame retardants, flame retardant auxiliaries, pigments, antioxidants, reflectivity imparting agents, opacifying agents, lubricants, processing stabilizers, plasticizers, foaming agents, heat-dissipating fillers made of alumina, silicon nitride, or the like, and linear expansion reducing particles made of silica, titanium oxide, or the like. The upper limit of the content of optional components contained in the matrix may be 20% by mass or 10% by mass.

[0029] The base layer may have a hollow structure, which can reduce the relative dielectric constant and therefore more effectively suppress transmission loss.

[0030] The upper limit of the dielectric constant of the matrix may be 2.7 or 2.5. The lower limit of the dielectric constant may be 1.2 or 1.4. If the dielectric constant of the matrix exceeds 2.7, the dielectric loss tangent becomes too large, which may result in an insufficient reduction in transmission loss and an insufficient transmission speed. If the dielectric constant of the matrix is ​​2.5 or less, the transmission loss can be further reduced and the transmission speed can be increased. If the dielectric constant of the matrix is ​​less than 1.2, the circuit width may not be sufficiently reduced when etching the copper foil into a pattern to form a circuit on the printed wiring board substrate, and the strength of the printed wiring board substrate may be reduced. If the dielectric constant of the matrix is ​​1.4 or more, it becomes easier to further reduce the circuit width and the strength of the printed wiring board substrate is less likely to be reduced. The dielectric constant is measured using a cavity resonator. The measurement device used is the AET ADMS01Oc, a device for measuring the microwave complex dielectric constant of the object under test. First, a detector is attached to the cavity resonator corresponding to the frequency to be measured using a torque wrench, and the measurement conditions are entered as follows: thickness 0.821 mm, width 3.005 mm, and frequency 10 GHz. After performing a blank measurement without a measurement sample, a reference sample made of polytetrafluoroethylene is placed in the cavity resonator. The dielectric constant of the reference sample is measured and confirmed to be 2.02 ± 0.02. Next, the sample is punched out using a dedicated sample cutter to prepare three rectangular measurement samples, each 3 mm wide and 25 mm long. The thickness of each measurement sample is measured on a surface plate using a Mitutoyo Digimatic Indicator ID-H. The width of each measurement sample is also measured using a Mitutoyo ABS Digimatic Caliper CD-AX. The measurement conditions are the total thickness of the three measurement samples, the average width of the three measurement samples, and a frequency of 10 GHz.Then, the three measurement samples are stacked and attached to the cavity resonator, and the relative permittivity is measured.The measurement is performed 10 times, and the average of the 10 measurements is used as the relative permittivity of the sample.

[0031] The upper limit of the linear expansion coefficient of the matrix is ​​1.2 × 10 -4 / °C. The lower limit of the linear expansion coefficient is 2 × 10 -5 / °C. The linear expansion coefficient of the matrix may be 1.2 × 10 -4 If the linear expansion coefficient of the matrix exceeds 2×10 / °C, the volume of the base layer may change due to temperature changes, and warping may not be effectively suppressed. -5 If it is less than 1 / °C, there may be a problem in terms of cost. The "linear expansion coefficient" is measured as follows. First, the expansion and contraction rates in the machine direction (MD) and the transverse direction (TD) are measured under the following conditions, and the expansion and contraction rate / temperature is measured at 40-50°C, 50-60°C, and . . . in 10°C intervals. This measurement is continued up to 250°C, and the average value of all measurements from 50°C to 250°C is taken as the linear expansion coefficient. Device name: SS7100 manufactured by Hitachi High-Tech Science Corporation Sample length: 10 mm Sample width: 4mm Initial load: 20.4g / mm 2 Heating start temperature: 30℃ End temperature: 255℃ Heating rate: 5℃ / min Atmosphere: Nitrogen

[0032] (reinforcement layer) The reinforcing material layer is a layer made of or containing a reinforcing material. The presence of the reinforcing material layer in the printed wiring board substrate improves the mechanical strength. Examples of the reinforcing material that can be used include films, woven fabrics (hereinafter also referred to as "cloths"), and nonwoven fabrics.

[0033] The reinforcing material is not particularly limited as long as it has a smaller linear expansion coefficient than the matrix. The reinforcing material may have insulating properties, heat resistance such that it does not melt and flow at the melting point of the fluororesin, tensile strength equal to or greater than that of the fluororesin, and corrosion resistance.

[0034] Examples of reinforcing materials include: (a) Glass cloth made by processing glass fibers into a cloth shape; (b) Fluorine resin-containing glass cloth, which is glass cloth made by processing glass fibers into a cloth shape and impregnating it with fluorine resin; (c) Inorganic cloth made by processing inorganic fibers such as metals and ceramics into cloth. (d) Polyimide, aramid, polyether ether ketone, liquid crystal polymer, polyamideimide, polybenzoimide ZoHeat-resistant films mainly composed of polyethylene terephthalate, polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, thermosetting resin, cross-linked resin, etc. (e) Resin cloth or nonwoven fabric made by processing synthetic resin fibers such as polyimide, aramid, polyetheretherketone, liquid crystal polymer (LCP), polyethersulfone, polyamideimide, polysulfone, polytetrafluoroethylene, etc. into a cross shape; Examples include: The resin cloth and the heat-resistant film may have a melting point (or heat distortion temperature) equal to or higher than the temperature of the step of thermocompression bonding in the manufacturing method of the base layer described below. Plain weaving of glass cloth, inorganic cloth, or resin cloth can make the substrate layer thinner. Twill or satin weaving of glass cloth, inorganic cloth, or resin cloth can make the substrate layer flexible. Other known weaving methods can also be used. The reinforcing material may be a glass cloth, a heat-resistant film, a resin cloth, or a nonwoven fabric, from the viewpoint of further improving the bending strength of the substrate for a printed wiring board. The main component of the heat-resistant film may be polyimide, aramid, polyether ether ketone, or a liquid crystal polymer.

[0035] When the reinforcing material is a fluororesin-containing glass cloth, the fluororesin impregnated into the glass cloth may be the same as the fluororesin that is the main component of the matrix of the substrate for printed wiring boards.

[0036] From the viewpoint of further improving the bending strength of the substrate for printed wiring boards, the reinforcing material may be glass cloth, a heat-resistant film mainly composed of polyimide, or a heat-resistant film mainly composed of liquid crystal polymer.

[0037] In the substrate for printed wiring board of the present disclosure, when the average thickness of the base layer is A and the average distance between the surface of the copper foil facing the matrix and the surface of the reinforcing material layer closest to that surface facing the copper foil is B, the ratio B / A is 0.003 or more and 0.37 or less. 1 , when the average thickness of the base layer 51 is A and the average distance between the surface 71 of the copper foil 41 facing the matrix and the surface 61 of the reinforcing material layer closest to the surface 71 facing the copper foil is B, the ratio B / A is 0.003 or more and 0.37 or less. This average distance B is approximately equal to the average thickness of the matrix 2a disposed between the copper foil 41 and the reinforcing material layer 31. Furthermore, when the average thickness of the base layer 51 is A and the average distance between the surface 72 of the copper foil 42 facing the matrix and the surface 62 of the reinforcing material layer closest to surface 72 facing the copper foil is B, the ratio B / A is 0.003 or more and 0.37 or less. This average distance B is approximately equal to the average thickness of the matrix 2c disposed between the copper foil 42 and the reinforcing material layer 32.

[0038] The lower limit of the ratio B / A is 0.003, and may be 0.10. The upper limit of the ratio B / A is 0.37, and may be 0.25. If the ratio B / A is less than 0.003, there is a possibility that the transmission characteristics will be adversely affected. If the ratio B / A is 0.10 or more, the transmission characteristics will be further improved. If the ratio B / A exceeds 0.37, there is a possibility that the bending characteristics will be adversely affected. If the ratio B / A is 0.25 or less, the bending characteristics will be further improved.

[0039] The lower limit of the ratio of the sum of the average thicknesses of the reinforcing material layers to the average thickness of the base material layer may be 0.01, 0.20, 0.22, or 0.25. The upper limit of this ratio may be 0.99, 0.5, 0.47, or 0.45. If this ratio is less than 0.01, the bending strength of the printed wiring board substrate may not be sufficiently improved, and warpage due to residual stress in the copper foil may not be effectively suppressed. If this ratio is 0.20 or more, the bending strength of the printed wiring board substrate can be further improved, and warpage due to residual stress in the copper foil can be more effectively suppressed. If this ratio is 0.22 or more, the bending strength of the printed wiring board substrate can be further improved, and warpage due to residual stress in the copper foil can be more effectively suppressed. If this ratio is 0.25 or more, the bending strength of the printed wiring board substrate can be particularly improved, and warpage due to residual stress in the copper foil can be particularly effectively suppressed. If this ratio exceeds 0.99, there is a possibility that the transmission characteristics and the bendability of the reinforcement layer may be reduced. If this ratio is 0.5 or less, the transmission characteristics and the bendability of the reinforcement layer are further improved. If this ratio is 0.47 or less, the transmission characteristics and the bendability of the reinforcement layer are further improved. If this ratio is 0.45 or less, the transmission characteristics and the bendability of the reinforcement layer are particularly improved.

[0040] The upper limit of the density of the glass fibers that make up the glass cloth is 5 g / m 3 may be 3 g / m 3 The lower limit of the density is 1 g / m 3 2 g / m 3 The density of the glass fiber may be 1 g / m 3 More than 5g / m 3 By setting the density of the glass fiber to 2 g / m or less, the strength and dimensional stability of the base material layer can be improved in a balanced manner, and warping during manufacturing can be suppressed. 3 More than 3g / m 3By setting the density as follows, the strength and dimensional stability of the substrate layer can be improved in a more balanced manner, and warping during manufacturing can be further suppressed. "Glass fiber density" means a value measured in accordance with JIS-L1013:2010 "Testing methods for chemical fiber filament yarns." The "tensile strength of glass fiber" and "maximum elongation of glass fiber" described below are also defined in the same way.

[0041] The upper limit of the tensile strength of the glass fibers forming the glass cloth may be 10 GPa or 5 GPa. The lower limit of the tensile strength may be 1 GPa or 2 GPa. By setting the tensile strength of the glass fibers to 1 GPa or more and 10 GPa or less, the strength and dimensional stability of the base layer can be improved in a balanced manner, and warping during production can be suppressed. By setting the tensile strength of the glass fibers to 2 GPa or more and 5 GPa or less, the strength and dimensional stability of the base layer can be further improved in a balanced manner, and warping during production can be further suppressed.

[0042] The upper limit of the tensile modulus of the glass fibers forming the glass cloth may be 200 GPa or 100 GPa. The lower limit of the tensile modulus may be 10 GPa or 50 GPa. By setting the tensile modulus of the glass fibers to 10 GPa or more and 200 GPa or less, the strength and dimensional stability of the base layer can be improved in a balanced manner, and warping during production can be suppressed. By setting the tensile modulus of the glass fibers to 50 GPa or more and 100 GPa or less, the strength and dimensional stability of the base layer can be further improved in a balanced manner, and warping during production can be further suppressed. "Tensile modulus" refers to the complex modulus of elasticity that represents the relationship between tensile stress and strain, and means a value measured by a tensile tester.

[0043] The upper limit of the maximum elongation of the glass fibers forming the glass cloth may be 20% or 10%. The lower limit of the maximum elongation of the glass fibers may be 1% or 3%. By setting the maximum elongation of the glass fibers to 1% or more and 20% or less, the strength and dimensional stability of the base layer can be improved in a balanced manner, and warping during production can be suppressed. By setting the maximum elongation of the glass fibers to 3% or more and 10% or less, the strength and dimensional stability of the base layer can be improved in a balanced manner, and warping during production can be suppressed.

[0044] The upper limit of the softening point of the glass fiber forming the glass cloth may be 1200°C or 1000°C. The lower limit of the softening point of the glass fiber may be 700°C or 800°C. If the softening point of the glass fiber exceeds 1200°C, the range of material selection may be narrowed. If the softening point of the glass fiber is 1000°C or less, the range of material selection may be further broadened. If the softening point of the glass fiber is less than 700°C, the glass fiber may soften during the production of the base layer, causing warping or the like. If the softening point of the glass fiber is 800°C or higher, the possibility of the glass fiber softening during the production of the base layer causing warping or the like is further reduced. "Softening point" means the softening point measured by the ring and ball method specified in JIS-K7234:1986.

[0045] The upper limit of the dielectric constant of the reinforcing material may be 10, 6, or 5. The lower limit of the dielectric constant may be 1.2, 1.5, or 1.8. If the dielectric constant of the reinforcing material exceeds 10, the dielectric tangent may become large, which may result in an insufficient reduction in transmission loss and an insufficient transmission speed. If the dielectric constant of the reinforcing material is 6 or less, the transmission loss can be further reduced and the transmission speed can be further increased. If the dielectric constant of the reinforcing material is 5 or less, the transmission loss can be further reduced and the transmission speed can be further increased. If the dielectric constant is less than 1.2, the cost may be high. If the dielectric constant of the reinforcing material is 1.5 or more, the cost can be further reduced, and if it is 1.8 or more, the cost can be further reduced.

[0046] The upper limit of the linear expansion coefficient of the reinforcing material is 5 x 10 -5 / °C, may be 4.7 x 10 -5 / °C. The lower limit of the linear expansion coefficient of the reinforcing material is -1 × 10 -4 / °C or 0 / °C. The linear expansion coefficient of the reinforcing material is 5×10 -5 / °C, warping due to temperature changes may not be effectively suppressed. -5 If the linear expansion coefficient of the reinforcing material is -1×10 / °C or less, warping due to temperature changes can be more effectively suppressed. -4 If the coefficient of linear expansion of the reinforcing material is less than 0 / °C, the cost may be high. If the coefficient of linear expansion of the reinforcing material is 0 / °C or more, the cost can be reduced.

[0047] The upper limit of the ratio of the linear expansion coefficient of the reinforcing material to the linear expansion coefficient of the matrix may be 0.95 or 0.1. The lower limit of this ratio may be 0.001 or 0.002. If this ratio exceeds 0.95, warpage of the printed wiring board substrate may not be effectively suppressed. If this ratio is 0.1 or less, warpage of the printed wiring board substrate can be more effectively suppressed. If this ratio is less than 0.001, the cost of the reinforcing material may be high. If this ratio is 0.002 or more, the cost of the reinforcing material can be reduced.

[0048] (copper foil) Copper foil is used as the conductive layer of a substrate for a printed wiring board. In FIG. 1 , the substrate for a printed wiring board has copper foils 41 and 42 laminated directly or indirectly on both sides of a base layer 51. The copper foils 41 and 42 are laminated, for example, via an adhesive layer (the adhesive layer is not shown). Copper foil has excellent conductivity and flexibility, and is cost-effective. The copper foil may be electrolytic copper foil or rolled copper foil. Using electrolytic copper foil or rolled copper foil can achieve excellent transmission characteristics while also achieving better flexibility. The surface of electrolytic copper foil is formed by electrodeposited copper particles, while the surface of rolled copper foil is formed by contact with a rolling roll. Rolled copper foil has smaller surface roughness than electrolytic copper foil and higher strength and flex resistance than electrolytic copper foil.

[0049] The upper limit of the ten-point mean roughness (Rz) of the copper foil may be 4 μm, 1 μm, or 0.6 μm. If the ten-point mean roughness (Rz) of the copper foil exceeds 4 μm, the skin effect will increase the unevenness in the area where the high-frequency signal is concentrated, preventing the current from flowing linearly and potentially resulting in unintended transmission loss. If the ten-point mean roughness (Rz) of the copper foil is 1 μm or less, the current will flow more easily linearly and unintended transmission loss will be less likely to occur. If the ten-point mean roughness (Rz) of the copper foil is 0.6 μm or less, the current will flow even more easily linearly and unintended transmission loss will be less likely to occur. The lower limit of the ten-point mean roughness (Rz) of the copper foil is not particularly limited, but may be 0.01 μm or 0.1 μm. The ten-point mean roughness (Rz) is a value specified in JIS-B-0601 (1994).

[0050] The upper limit of the average thickness of the copper foil may be 300 μm, 200 μm, or 150 μm. The lower limit of the average thickness of the copper foil may be 1 μm, 5 μm, or 10 μm. If the average thickness of the copper foil exceeds 300 μm, it may be difficult to apply the substrate for printed wiring boards of the present disclosure to electronic devices requiring flexibility. If the average thickness of the copper foil is 200 μm or less, the substrate for printed wiring boards of the present disclosure is more easily applied to electronic devices. If the average thickness of the copper foil is 150 μm or less, the substrate for printed wiring boards of the present disclosure is even more easily applied to electronic devices. If the average thickness of the copper foil is less than 1 μm, the resistance of the copper foil may increase. If the average thickness of the copper foil is 5 μm or more, the resistance of the copper foil is further reduced. If the average thickness of the copper foil is 10 μm or more, the resistance of the copper foil is even further reduced.

[0051] The upper limit of the average thickness of the substrate for printed wiring boards may be 2.7 mm, 2.5 mm, or 2.2 mm. The lower limit of the average thickness of the substrate for printed wiring boards may be 1 μm, 1.5 μm, or 2 μm. If the average thickness of the substrate for printed wiring boards exceeds 2.7 mm, sufficient flexibility may not be obtained. If the average thickness of the substrate for printed wiring boards is 2.5 mm or less, flexibility is further improved. If the average thickness of the substrate for printed wiring boards is 2.2 mm or less, flexibility is further improved. If the average thickness of the substrate for printed wiring boards is less than 1 μm, handling may be difficult. If the average thickness of the substrate for printed wiring boards is 1.5 μm or more, handling becomes easier. If the average thickness of the substrate for printed wiring boards is 2 μm or more, handling becomes even easier.

[0052] [Method of manufacturing substrates for printed wiring boards] The method for producing a substrate for a printed wiring board may include, for example, (1) a step of forming a base layer and (2) a step of laminating a copper foil.

[0053] (1) Step of forming a base layer First, a first forming method and a second forming method will be described as examples of methods for forming the base layer. According to the first forming method or the second forming method, the base layer can be formed easily and reliably.

[0054] The first method for forming the base material layer includes a laminating step of laminating resin films containing fluororesin as a main component on both sides of the reinforcing material layer, and a thermocompression bonding step of thermocompression bonding the laminate while vacuum suctioning.

[0055] [Superimposition process]

[0056] In this step, resin films containing fluororesin as a main component are laminated on both sides of the reinforcing material layer. The main component of the resin films is the fluororesin that is the main component of the matrix of the base material layer.

[0057] The volume ratio of the reinforcing material layer in the laminate obtained in the laminating step may be 60 vol%, 40 vol%, or 30 vol%. The lower limit of the volume ratio of the reinforcing material layer may be 10 vol%, 20 vol%, or 25 vol%. By setting the volume ratio of the reinforcing material layer to 10 vol% or more and 60 vol% or less, a good balance can be achieved between the adhesiveness of the base layer, reduced temperature dependence of electrical properties after bonding, and improved transmission properties. By setting the volume ratio of the reinforcing material layer to 20 vol% or more and 40 vol% or less, a better balance can be achieved between the adhesiveness of the base layer, reduced temperature dependence of electrical properties after bonding, and improved transmission properties. By setting the volume ratio of the reinforcing material layer to 25 vol% or more and 35 vol% or less, a better balance can be achieved between the adhesiveness of the base layer, reduced temperature dependence of electrical properties after bonding, and improved transmission properties.

[0058] [Thermocompression bonding process] In this step, the laminate obtained in the laminating step is thermocompression bonded while being vacuum-suctioned. The upper limit of the thermocompression bonding temperature may be 400°C or 300°C. The lower limit of the thermocompression bonding temperature may be the melting point of the fluororesin, which is the main component of the resin film, or the decomposition initiation temperature of the fluororesin. Furthermore, the lower limit of the thermocompression bonding temperature may be a temperature 10°C higher than the melting point of the fluororesin, or a temperature 30°C higher than the melting point of the fluororesin. The lower limit of the thermocompression bonding temperature may be 200°C or 220°C. If the thermocompression bonding temperature exceeds 400°C, the resulting substrate layer may be deformed. If the thermocompression bonding temperature is 300°C or lower, the substrate layer is less likely to deform. If the thermocompression bonding temperature is lower than the melting point of the fluororesin, it may be difficult to obtain a substrate layer in which the reinforcing material layer and the resin film are integrated. If the thermocompression bonding temperature is equal to or higher than the decomposition initiation temperature of the fluororesin, it is easier to obtain a substrate layer in which the reinforcing material layer and the resin film are integrated. When the thermocompression bonding temperature is 10°C higher than the melting point of the fluororesin, it becomes easier to obtain a substrate layer in which the reinforcing material layer and the resin film are integrated. The "decomposition onset temperature" refers to the temperature at which the fluororesin begins to thermally decompose, and the "decomposition temperature" refers to the temperature at which the fluororesin loses 10% of its mass due to thermal decomposition.

[0059] The pressure for thermocompression bonding may be 0.01 MPa or more and 1200 MPa or less. When the pressure for thermocompression bonding is 0.01 MPa or more and 1000 MPa or less, adhesion to the base material layer is improved. The pressure application time for thermocompression bonding may be 5 seconds or more and 10 hours or less. When the pressure application time for thermocompression bonding is 5 seconds or more and 10 hours or less, adhesion between the base material layer and the resin film is improved.

[0060] The upper limit of the degree of vacuum during vacuum suction may be 10 MPa, 1 MPa, or 10 kPa. The lower limit of the degree of vacuum is not particularly limited, but is, for example, 0.01 Pa. By setting the degree of vacuum to 10 MPa or less, the adhesion between the resin film and the reinforcing material layer is improved. If the degree of vacuum is 1 MPa or less, the adhesion between the resin film and the reinforcing material layer is further improved. If the degree of vacuum is 10 kPa or less, the adhesion between the resin film and the reinforcing material layer is further improved. Furthermore, when a woven fabric or nonwoven fabric is used as the reinforcing material layer, the resin of the resin film can be reliably impregnated into the voids in the woven fabric or nonwoven fabric, thereby obtaining a substrate layer in which the reinforcing material layer and the matrix are more firmly integrated.

[0061] In the first method for forming the base material layer, in order to further improve the adhesion between the resin film and the reinforcing material layer, vacuum suction may be started before the start of thermocompression bonding.

[0062] (Second method for forming base layer) The second method for forming the base material layer includes an impregnation step of impregnating the surface and interior of the reinforcing material layer with a composition mainly composed of a fluororesin, and a heating step of heating the impregnated composition. In the second method for forming the base material layer, the reinforcing material layer is a woven fabric or a nonwoven fabric.

[0063] [Impregnation process] In the impregnation step, the surface and interior of the reinforcing material layer are impregnated with a composition mainly composed of a fluororesin. Examples of the composition include a fluororesin dispersion in which fluororesin particles are dispersed in a solvent. Methods for impregnating the surface and interior of the reinforcing material layer with the composition include, for example, a method of applying the composition to the surface of the reinforcing material layer and a method of immersing a glass cloth or a resin cloth in the composition.

[0064] The volume ratio of the reinforcing material to the total of the solid content and the reinforcing material contained in the composition may be 60 volume %, 40 volume %, or 30 volume %. The lower limit of the volume ratio of the reinforcing material may be 10 volume %, 20 volume %, or 25 volume %. By setting the volume ratio of the reinforcing material to 10 volume % or more and 60 volume % or less, a good balance can be achieved between the adhesiveness of the base layer, the reduction in the temperature dependence of the electrical properties after bonding, and the improvement in the transmission properties. By setting the volume ratio of the reinforcing material to 20 volume % or more and 40 volume % or less, a good balance can be achieved between the adhesiveness of the base layer, the reduction in the temperature dependence of the electrical properties after bonding, and the improvement in the transmission properties. By setting the volume ratio of the reinforcing material to 25 volume % or more and 30 volume % or less, a good balance can be achieved between the adhesiveness of the base layer, the reduction in the temperature dependence of the electrical properties after bonding, and the improvement in the transmission properties. "Solid content" refers to the components in the composition other than the solvent.

[0065] [Heating process] In the heating step, the impregnated composition is heated. This heating step corresponds to a baking step in which the impregnated composition is dried and cured. After the heating step, a fluororesin layer is formed on the surface of the reinforcing material layer, and the fluororesin is impregnated into the interior of the reinforcing material layer.

[0066] The upper limit of the temperature in the heating step may be 400°C or 300°C. The lower limit of the temperature in the heating step may be 150°C or 200°C. If the temperature in the heating step is less than 150°C, the impregnated composition may not be sufficiently dried and cured. If the temperature in the heating step is 200°C or higher, the drying and curing of the composition is further accelerated. If the temperature in the heating step exceeds 400°C, the resulting substrate layer may be deformed. If the temperature in the heating step is 300°C or lower, the substrate layer is less likely to deform.

[0067] In the second formation method, after forming a fluororesin layer on a first surface of the reinforcing material layer, another fluororesin layer may be formed on a second surface. In addition, in the second formation method, fluororesin layers may be formed on both surfaces of the reinforcing material layer simultaneously.

[0068] In the second formation method, the impregnation step and the heating step may be repeated two or more times. For example, by repeatedly applying the composition and heating, a fluororesin layer having a predetermined thickness can be easily formed.

[0069] In the second forming method, the surface and interior of the reinforcing material layer are impregnated with a composition mainly composed of a fluororesin, which makes it possible to easily and reliably obtain a substrate layer in which the reinforcing material layer and the matrix are more firmly integrated.

[0070] (2) Copper foil lamination process First, a primer material is applied to the copper foil. When the primer material is a silane coupling agent, the primer material containing the silane coupling agent, alcohol, and water is applied to the copper foil. Next, the copper foil is dried and, if necessary, heated to remove the alcohol in the primer material. After that, a base layer is placed on the surface of the primer material, and the resulting laminate is thermocompression bonded using a press. Thermocompression bonding may be performed under reduced pressure to prevent the formation of bubbles or voids between the copper foil and the base layer. Furthermore, thermocompression bonding may be performed under low-oxygen conditions (e.g., in a nitrogen atmosphere) to suppress oxidation of the copper foil. This results in a printed wiring board substrate having an adhesive layer between the copper foil and the base layer.

[0071] The upper limit of the thermocompression bonding temperature may be 600°C or 500°C. The lower limit of the thermocompression bonding temperature may be the melting point of the fluororesin, which is the main component of the matrix of the substrate layer, or the decomposition initiation temperature of the fluororesin. It may be 30°C higher than the melting point of the fluororesin, or 50°C higher than the melting point of the fluororesin. If the thermocompression bonding temperature exceeds 600°C, unintended deformation may occur during manufacturing. If the thermocompression bonding temperature is 500°C or lower, unintended deformation during manufacturing is less likely to occur. If the thermocompression bonding temperature is lower than the melting point of the fluororesin, the adhesion between the copper foil and the substrate layer may be insufficient. If the thermocompression bonding temperature is equal to or higher than the decomposition initiation temperature of the fluororesin, the adhesion between the copper foil and the substrate layer is further improved. If the thermocompression bonding temperature is equal to or higher than 30°C higher than the melting point of the fluororesin, the adhesion between the copper foil and the substrate layer is further improved. If the thermocompression bonding temperature is equal to or higher than 50°C higher than the melting point of the fluororesin, the adhesion between the copper foil and the substrate layer is further improved.

[0072] The reason for thermocompression bonding at a temperature equal to or higher than the melting point of the fluororesin is that the fluororesin is not activated at temperatures below the melting point. Furthermore, by heating to a temperature equal to or higher than the decomposition temperature of the fluororesin, the carbon atoms of the fluororesin are radicalized, further activating the fluororesin. In other words, it is believed that by setting the thermocompression bonding temperature equal to or higher than the melting point (or decomposition temperature) of the fluororesin, the adhesion between the copper foil and the base layer can be further promoted.

[0073] The pressure of the thermocompression bonding may be 0.01 MPa or more and 1000 MPa or less. If the pressure of the thermocompression bonding is 0.01 MPa or more and 1000 MPa or less, the adhesion between the copper foil and the base layer is improved. Furthermore, the pressure application time of the thermocompression bonding may be 5 seconds or more and 10 hours or less. If the pressure application time of the thermocompression bonding is 5 seconds or more and 10 hours or less, the adhesion between the copper foil and the base layer is improved.

[0074] <Multilayer board> A multilayer board is a laminate of multiple substrates for printed wiring boards. By laminating multiple substrates for printed wiring boards, the multilayer board reduces distortion due to compression of the outermost matrix (fluororesin layer) of the multilayer board, and suppresses the load on the copper foil arranged on the outermost side. Therefore, this multilayer board has excellent bending strength.

[0075] A plurality of substrates for printed wiring boards may be laminated via an adhesive layer mainly composed of a bonding sheet or a silane coupling agent. By laminating a plurality of substrates for printed wiring boards via an adhesive layer mainly composed of a bonding sheet or a silane coupling agent, good adhesion can be obtained between the plurality of substrates for printed wiring boards.

[0076] The bonding sheet is an adhesive formed into a film. The adhesive material is not particularly limited, but may be one with excellent flexibility and heat resistance. Examples of adhesives include resin-based adhesives such as epoxy resin, polyimide, polyester, phenolic resin, polyurethane, acrylic resin, melamine resin, and polyamideimide.

[0077] Silane coupling agents improve adhesion by forming siloxane bonds in the fluororesin, which is the main component of the matrix of the base layer. Silane coupling agents may be those with hydrophilic functional groups in their molecules, or those with hydrolyzable silicon-containing functional groups. Such silane coupling agents chemically bond with the fluororesin contained in the matrix of the base layer. The chemical bond between the silane coupling agent and the fluororesin may consist solely of covalent bonds, or may include covalent bonds and hydrogen bonds. A "hydrophilic functional group" refers to a functional group composed of atoms with high electronegativity that has hydrophilic properties. A "hydrolyzable silicon-containing functional group" refers to a group that can form a silanol group (Si-OH) upon hydrolysis.

[0078] In an adhesive layer containing a silane coupling agent as a main component, the Si atom constituting the siloxane bond (hereinafter, this atom is also referred to as "Si atom of the siloxane bond") is covalently bonded to the C atom of the fluororesin via at least one atom selected from the group consisting of an N atom, a C atom, an O atom, and an S atom. Specifically, the Si atom of the siloxane bond is, for example, -O-, -S-, -SS-, -(CH2) n -, -NH-, -(CH2) n -NH-, -(CH2) n -O-(CH2) m It bonds to a C atom of the fluororesin via an atomic group such as - (n and m are integers of 1 or more).

[0079] The hydrophilic functional group may be any one of a hydroxyl group, a carboxyl group, a carbonyl group, an amino group, an amide group, a sulfide group, a sulfonyl group, a sulfo group, a sulfonyldioxy group, an epoxy group, a methacryl group, and a mercapto group, or a combination thereof. Among these, a hydrophilic functional group containing an N atom and a hydrophilic functional group containing an S atom may be used. These hydrophilic functional groups further improve the adhesion and bonding properties of the surface.

[0080] Furthermore, an adhesive layer containing a silane coupling agent as a main component may contain two or more of these hydrophilic functional groups. By adding hydrophilic functional groups with different properties to an adhesive layer containing a silane coupling agent as a main component, the reactivity of the surface can be diversified. These hydrophilic functional groups can be bonded directly to the Si atom, which is a component of the siloxane bond, or via one or more C atoms.

[0081] The upper limit of the average thickness of the bonding sheet or adhesive layer containing a silane coupling agent as the main component may be 200 nm or 50 nm. The lower limit of the average thickness of the adhesive layer may be 3 nm or 5 nm. If the average thickness of the adhesive layer exceeds 200 nm, the high-frequency characteristics may be insufficient due to the influence of dielectric loss caused by the adhesive layer. If the average thickness of the adhesive layer is 50 nm or less, the high-frequency characteristics are further improved. If the average thickness of the adhesive layer is less than 3 nm, the surface activation effect may be insufficient, and sufficient adhesion and adhesiveness may not be obtained. If the average thickness of the adhesive layer is 5 nm or more, the adhesion and adhesiveness are further improved. In this way, by adjusting the average thickness of the adhesive layer, it is possible to achieve a good balance between the function of suppressing transmission loss and the function of improving adhesion. The average thickness of the adhesive layer can be measured, for example, by X-ray spectroscopy.

[0082] Figure 2 is a schematic cross-sectional view showing a multilayer board according to an embodiment of the present disclosure. The multilayer board 100 shown in Figure 2 is formed by laminating a printed wiring board substrate 1 and a printed wiring board substrate 10 with a bonding sheet 8 interposed therebetween. In Figure 2, the same elements as those in the printed wiring board substrate 1 of Figure 1 are denoted by the same reference numerals, and redundant explanations will be omitted below. The printed wiring board substrate 10 includes a base layer 52 and a copper foil 43 laminated directly or indirectly on one side of the base layer 52. In the substrate 10 for printed wiring boards, when the average thickness of the base layer 52 is A and the average distance between the surface 73 facing the matrix 2f of the copper foil 43 and the surface 63 facing the copper foil 43 of the reinforcing material layer 34 closest to the surface 73 is B, the ratio B / A is 0.003 or more and 0.37 or less. Furthermore, when the average thickness of the base material layer 52 of the printed wiring board substrate 10 is A and the average distance between the surface 74 of the copper foil 42 of the printed wiring board substrate 1 facing the matrix 2d of the printed wiring board substrate 10 and the surface 64 of the reinforcing material layer 33 of the printed wiring board substrate 10 that is closest to the copper foil 42 of the printed wiring board substrate 1 is D, the ratio D / A is 0.003 or more and 0.37 or less.

[0083] FIG. 3 is a schematic cross-sectional view showing a multilayer substrate according to another embodiment of the present disclosure. In FIG. 3, the same elements as those in the printed wiring board substrate 10 of FIG. 2 are designated by the same reference numerals, and redundant description will be omitted below. The printed wiring board substrate 20 includes a base layer 53 and copper foils 44, 45 laminated directly or indirectly on both sides of the base layer 53. The copper foil 45 laminated on the matrix 2i of the printed wiring board substrate 20 has a plurality of through holes 9. An adhesive layer containing a silane coupling agent as a main component is formed on a surface 74 of the copper foil 45 facing the matrix 2d. That is, in the multilayer substrate 200, the copper foil 45 of the printed wiring board substrate 20 and the matrix 2d of the printed wiring board substrate 10 are bonded by thermocompression bonding via an adhesive layer, thereby laminating the printed wiring board substrate 10 and the printed wiring board substrate 20. The printed wiring board substrate 10 and the printed wiring board substrate 20 are laminated by thermocompression bonding, so that the matrix 2d of the printed wiring board substrate 10 and the matrix 2i of the printed wiring board substrate 20 are filled into the through-holes 9. In the substrate 20 for printed wiring boards, when the average thickness of the base material layer 53 is A and the average distance between the surface 76 facing the matrix 2g of the copper foil 44 and the surface 66 facing the copper foil 44 of the reinforcing material layer 37 closest to the surface 76 is B, the ratio B / A is 0.003 or more and 0.37 or less. Furthermore, when the average thickness of the base material layer 53 of the substrate 20 for printed wiring boards is A and the average distance between the surface 75 facing the matrix 2i of the copper foil 45 and the surface 65 facing the copper foil 45 of the reinforcing material layer 36 closest to surface 75 is B, the ratio B / A is 0.003 or more and 0.37 or less. Furthermore, when the average thickness of the base material layer 52 of the printed wiring board substrate 10 is A and the average distance between the surface 74 of the copper foil 45 of the printed wiring board substrate 20 facing the matrix 2d of the printed wiring board substrate 10 and the surface 64 of the reinforcing material layer 33 of the printed wiring board substrate 10 that is closest to the copper foil 45 of the printed wiring board substrate 20 facing the copper foil 45 of the printed wiring board substrate 20 is D, the ratio D / A is 0.003 or more and 0.37 or less.

[0084] [Manufacturing method for multilayer boards] A method for manufacturing a multilayer board includes, for example, a step of laminating a first substrate for printed wiring boards in which copper foil is laminated directly or indirectly on both sides of a base layer and a second substrate for printed wiring boards in which copper foil is laminated directly or indirectly on only one side of a base layer. In the first substrate for printed wiring boards, copper foil may be laminated directly or indirectly on at least a portion of each of both sides of the base layer. In the second substrate for printed wiring boards, copper foil may be laminated directly or indirectly on at least a portion of one side of the base layer.

[0085] The process of laminating a first substrate for printed wiring boards and a second substrate for printed wiring boards via a bonding sheet or an adhesive layer mainly composed of a silane coupling agent can be, for example, the following process. First, a bonding sheet is laminated on the copper foil of the first substrate for printed wiring boards, or a primer material for the silane coupling agent, which is the main component of the adhesive layer, is attached. Then, the base layer of the second substrate for printed wiring boards is placed on the copper foil of the first substrate for printed wiring boards via a bonding sheet or adhesive layer, and thermocompression bonding is performed, thereby laminating the first substrate for printed wiring boards and the second substrate for printed wiring boards. The process of laminating a first substrate for printed wiring boards and a second substrate for printed wiring boards via an adhesive layer mainly composed of a silane coupling agent is the same process as the copper foil lamination process described above.

[0086] Another method for manufacturing a multilayer board may include a step of bonding two substrates for printed wiring boards, each having copper foil laminated directly or indirectly on both sides of a base layer, via a bonding sheet.

[0087] The substrate for printed wiring board according to one embodiment of the present disclosure and the multilayer substrate according to another embodiment of the present disclosure have excellent bending strength, and therefore can be suitably used in, for example, portable devices such as portable information devices and portable communication terminals.

[0088] [Other embodiments] The above-disclosed embodiments should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is not limited to the configurations of the above-disclosed embodiments, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0089] In the above embodiment, the reinforcing material layer is two layers, but it may be one layer or three or more layers. Also, the matrix is ​​three layers, but it may be two layers or four or more layers.

[0090] In the above embodiment, the multilayer substrate has two substrates for printed wiring boards, but it may have three or more substrates for printed wiring boards. [Example]

[0091] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to the following examples.

[0092] <Production of printed wiring board substrates> [Test Example 1] The printed wiring board substrate of Test Example 1 was prepared according to the following procedure. First, a primer material was applied to electrolytic copper foil by dipping, followed by drying and heating at 110°C to form a primer material layer on the copper foil. Then, the electrolytic copper foil, a base layer having a three-layer matrix (fluororesin layer) and two reinforcing material layers, and the electrolytic copper foil were laminated in this order, with the primer material layer facing the base layer. The resulting laminate was thermocompression-bonded using a press to obtain a printed wiring board substrate having an adhesive layer between the copper foil and the base layer. The specific configuration of the base layer was Neoflon FEP (average thickness 20 μm) manufactured by Daikin Industries, Ltd., glass cloth (IPC Standard Style 1015, average thickness 15 μm), Neoflon FEP (average thickness 45 μm) manufactured by Daikin Industries, Ltd., glass cloth (IPC Standard Style 1015, average thickness 15 μm), and Neoflon FEP (average thickness 20 μm) manufactured by Daikin Industries, Ltd. The thermocompression bonding conditions were a temperature of 320°C, a pressure of 6 MPa, and a pressure time of 40 minutes. The average thickness of the substrate layer was 115 μm. The primer material used contained 1% by mass of 3-aminopropyltrimethoxysilane and ethanol. No water was added to the primer material. In other words, the water used was moisture present in the air and moisture contained as an impurity in ethanol.

[0093] [Test Example 2] A printed wiring board substrate of Test Example 2 was produced using the same steps as in Test Example 1, except that rolled copper foil was used instead of electrolytic copper foil, Neoflon PFA (average thickness 20 μm) manufactured by Daikin Industries, Ltd. was used instead of Neoflon FEP (average thickness 20 μm) manufactured by Daikin Industries, Ltd., and Neoflon PFA (average thickness 45 μm) manufactured by Daikin Industries, Ltd. was laminated instead of Neoflon FEP (average thickness 45 μm) manufactured by Daikin Industries, Ltd.

[0094] [Test Example 3] The printed wiring board substrate of Test Example 3 was produced by laminating, in this order, rolled copper foil, NEOFLON FEP (average thickness 7 μm) manufactured by Daikin Industries, Ltd., glass cloth (IPC standard style 1015, average thickness 15 μm), NEOFLON PFA (average thickness 70 μm) manufactured by Daikin Industries, Ltd., glass cloth (IPC standard style 1015, average thickness 15 μm), NEOFLON FEP (average thickness 7 μm) manufactured by Daikin Industries, Ltd., and rolled copper foil. Heat pressing was carried out under the same conditions as Test Example 1.

[0095] [Test Example 4] A rolled copper foil was coated with a water-based PTFE coating adjusted to a solids content of 25% and dried in a nitrogen furnace at 380°C for 10 minutes to prepare a rolled copper foil having a PTFE layer with a coating thickness of approximately 0.3 μm. The PTFE-coated rolled copper foil, glass cloth (IPC Standard Style 1015, average thickness 15 μm), Neoflon FEP (average thickness 85 μm) manufactured by Daikin Industries, Ltd., glass cloth (IPC Standard Style 1015, average thickness 15 μm), and PTFE-coated rolled copper foil were laminated in this order. Heat pressing was performed under the same conditions as in Test Example 1. The printed wiring board substrate of Test Example 4 was fabricated by laminating the PTFE layer facing the glass cloth side.

[0096] [Test Example 5] A substrate for a printed wiring board of Test Example 5 was produced by laminating, in this order, electrolytic copper foil, NEOFLON FEP (average thickness 42.5 μm) manufactured by Daikin Industries, Ltd., glass cloth (IPC standard style 1030, average thickness 30 μm), NEOFLON FEP (average thickness 42.5 μm) manufactured by Daikin Industries, Ltd., and electrolytic copper foil. The heat pressing was carried out under the same conditions as in Test Example 1.

[0097] [Test Example 6] A substrate for a printed wiring board of Test Example 6 was produced by laminating, in this order, electrolytic copper foil, Neoflon FEP (average thickness 46 μm) manufactured by Daikin Industries, Ltd., glass cloth (IPC standard style 1015, average thickness 15 μm), Neoflon FEP (average thickness 46 μm) manufactured by Daikin Industries, Ltd., and electrolytic copper foil. The heat pressing was carried out under the same conditions as in Test Example 1.

[0098] [Test Example 7] An electrolytic copper foil, Neoflon FEP (average thickness 100 μm) manufactured by Daikin Industries, Ltd., and an electrolytic copper foil were laminated in this order to produce a substrate for a printed wiring board of Test Example 7. The heat pressing was carried out under the same conditions as in Test Example 1.

[0099] [Test Example 8] A substrate for a printed wiring board of Test Example 8 was produced by laminating, in this order, rolled copper foil, NEOFLON FEP (average thickness 25 μm) manufactured by Daikin Industries, Ltd., polyimide film (average thickness 25 μm), NEOFLON FEP (average thickness 25 μm) manufactured by Daikin Industries, Ltd., polyimide film (average thickness 25 μm), NEOFLON FEP (average thickness 25 μm) manufactured by Daikin Industries, Ltd., and rolled copper foil. The heat pressing was carried out under the same conditions as in Test Example 1.

[0100] [Test Example 9] A substrate for a printed wiring board of Test Example 9 was produced by laminating, in this order, rolled copper foil, NEOFLON FEP (average thickness 25 μm) manufactured by Daikin Industries, Ltd., a liquid crystal polymer film (average thickness 25 μm), NEOFLON FEP (average thickness 25 μm) manufactured by Daikin Industries, Ltd., a liquid crystal polymer film (average thickness 25 μm), NEOFLON FEP (average thickness 25 μm) manufactured by Daikin Industries, Ltd., and rolled copper foil. The heat pressing was carried out under the same conditions as in Test Example 1.

[0101] [Test Example 10] A substrate for printed wiring board of Test Example 10 was produced by laminating rolled copper foil, NEOFLON FEP (average thickness 25 μm) manufactured by Daikin Industries, Ltd., aramid paper (average thickness 50 μm) manufactured by DuPont Teijin Advanced Papers, NEOFLON FEP (average thickness 25 μm) manufactured by Daikin Industries, Ltd., and rolled copper foil in this order. The heat press was carried out under the same conditions as in Test Example 1.

[0102] <Making a multilayer board> [Test Example 11] A substrate for printed wiring board of Test Example 1 and a substrate for printed wiring board of Test Example 1 in which electrolytic copper foil was not formed on one side were prepared. These substrates for printed wiring board were heat-pressed under the same conditions as in Test Example 1, with bonding sheets made of epoxy resin interposed between them, so that copper foil was arranged on both ends, to produce a multilayer substrate of Test Example 11.

[0103] [Test Example 12] A substrate for printed wiring board of Test Example 6 and a substrate for printed wiring board of Test Example 6 in which electrolytic copper foil was not formed on one side were prepared. These substrates for printed wiring board were heat-pressed under conditions of 180°C, 30 minutes, and 2 MPa via bonding sheets made of epoxy resin so that copper foil was arranged on both ends of the substrate, to produce a multilayer substrate of Test Example 12.

[0104] [evaluation] The printed wiring board substrates of Test Examples 1 to 10 and the multilayer boards of Test Examples 11 and 12 were evaluated for the following items.

[0105] (bending strength) The bending strength was evaluated using the following procedure. Test specimens with long sides of 100 mm and short sides of 25 mm were prepared for each printed wiring board substrate and multilayer substrate of each test example. These test specimens were folded while wrapping the long sides around a metal cylinder with a radius of 2.5 mm until the bending angle reached 90° (normal 90°). Next, the specimens were returned to their original state, and the surface that had not been in contact with the cylinder was folded toward the cylinder, following the same procedure (reverse 90°). After each bending of 90° normal and reverse 90° was counted as one bending, the mountain folds and valley folds of the bent portion were observed under a microscope, and the number of bending cycles until breakage occurred was measured. The evaluation results are shown in Table 1.

[0106] (Warpage after one-sided etching) The prepared substrate was cut into a 100 mm square, Nitto Denko Elep Masking N-380 attached to one side, and immersed in a copper chloride aqueous solution. After the copper foil on the side without the masking had completely dissolved, the substrate was rinsed twice with ion-exchanged water, wiped dry with a rag, and then the masking was removed. The substrate was then placed on a surface plate with the copper foil side facing down, and the height from the surface plate at four points on the 100 mm square was measured with a ruler. If no warping was observed, the measurement was repeated with the fluororesin side facing up. Warping toward the fluororesin side was recorded as a positive value, and warping toward the copper foil side was recorded as a negative value. If the warping was severe and cylindrical, the diameter (φ) of the cylinder was measured.

[0107] [Table 1]

[0108] In Table 1, the portion corresponding to matrix 2a, 2d or 2g is referred to as fluororesin layer 1, the portion corresponding to matrix 2b, 2e or 2h is referred to as fluororesin layer 2, and the portion corresponding to matrix 2c, 2f or 2i is referred to as fluororesin layer 3.

[0109] As shown in Table 1, the substrates for printed wiring boards of Test Examples 1 to 5 and Test Examples 8 to 10, in which the ratio B / A was 0.003 or more and 0.37 or less, and the multilayer substrate of Test Example 11, in which the ratio B / A and the ratio D / A were 0.003 or more and 0.37 or less, had good bending strength and warpage after single-sided etching. The substrates for printed wiring boards of Test Example 6, in which the ratio B / A and the ratio D / A were outside the range of 0.003 or more and 0.37 or less, and Test Example 7, which did not have a reinforcing material layer, had poor bending strength and warpage after single-sided etching. Furthermore, the multilayer substrate of Test Example 12, in which the ratio B / A and the ratio D / A were outside the range of 0.003 or more and 0.37 or less, had poor bending strength.

[0110] The above results demonstrate that the substrate for printed wiring board according to one embodiment of the present disclosure and the multilayer substrate according to another embodiment of the present disclosure are excellent in bending strength and in the effect of suppressing warpage after etching. [Explanation of symbols]

[0111] 1, 10, 20 Printed wiring board substrate 2a, 2b, 2c, 2d, 2e, 2f, 2g, 2h, 2i Matrix of base layer 31, 32, 33, 34, 35, 36 Reinforcement layers 41, 42, 43, 44, 45 Copper foil 51, 52, 53 Base material layer 61, 62, 63, 64, 65, 66 The surface of the reinforcement layer facing the copper foil closest to the surface of the copper foil facing the matrix 71, 72, 73, 74, 75, 76 Surface of copper foil facing the matrix 8 Bonding Sheet 9 Through holes 100, 200 multilayer board A Average thickness of the substrate layer b Distance between the surface of the copper foil facing the matrix and the surface of the reinforcement layer closest to that surface facing the copper foil d: Distance between the surface of the copper foil on which the second printed wiring board substrate is laminated and the surface of the reinforcing material layer of the second printed wiring board substrate closest to the copper foil, facing the copper foil.

Claims

1. A substrate layer and a copper foil directly or indirectly laminated on at least a portion of one or both sides of the substrate layer, the substrate layer has a matrix containing a fluororesin as a main component and one or more reinforcing material layers contained in the matrix, When the average thickness of the base material layer is A and the average distance between the surface of the copper foil facing the matrix and the surface of the reinforcing material layer closest to the surface facing the copper foil is B, the ratio B / A is 0.003 or more and 0.17 or less, A substrate for a printed wiring board, wherein the ratio of the total average thickness of each of the reinforcing material layers to the average thickness of the base material layer is 0.01 or more and 0.26 or less.

2. 2. The substrate for printed wiring boards according to claim 1, wherein the ratio B / A is 0.10 or more and 0.17 or less.

3. 3. The substrate for printed wiring boards according to claim 1, wherein the fluororesin is any one of tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and polytetrafluoroethylene, or a combination thereof.

4. The substrate for printed wiring board according to claim 1 , wherein the reinforcing material layer comprises glass cloth, heat-resistant film, resin cloth, or nonwoven fabric.

5. The substrate for printed wiring board according to any one of claims 1 to 4, wherein the copper foil is an electrolytic copper foil or a rolled copper foil.

6. The substrate for a printed wiring board according to any one of claims 1 to 5, wherein the matrix is ​​divided into a plurality of layers.

7. A multilayer substrate comprising a plurality of substrates for printed wiring boards according to any one of claims 1 to 6 stacked one on top of the other.

8. 8. The multilayer substrate according to claim 7, wherein a plurality of the substrates for printed wiring boards are laminated via a bonding sheet or an adhesive layer containing a silane coupling agent as a main component.

9. 9. The multilayer substrate according to claim 7 or 8, wherein a first substrate for a printed wiring board and a second substrate for a printed wiring board are laminated together, the first printed wiring board substrate and the second printed wiring board substrate are the printed wiring board substrates according to any one of claims 1 to 6, In the first substrate for printed wiring board, the copper foil is laminated directly or indirectly on at least a portion of each of both surfaces of the base material layer, In the second substrate for printed wiring board, the copper foil is laminated directly or indirectly on at least a portion of one surface of the base material layer, Among the copper foils of the first substrate for printed wiring boards, the copper foil on which the second substrate for printed wiring boards is laminated is a first copper foil, the reinforcing material layer of the second printed wiring board substrate closest to the first copper foil is a first reinforcing material layer; A multilayer substrate in which, when the average thickness of the base layer of the second printed wiring board substrate is A and the average distance between the surface of the first copper foil facing the matrix of the second printed wiring board substrate and the surface of the first reinforcing material layer facing the first copper foil is D, the ratio D / A is 0.003 or more and 0.37 or less.

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