Wiring board

Abstract

A wiring board comprising: conductor wiring; an insulation layer having a first main surface with which a surface of the conductor wiring is brought into firm contact, and a second main surface on the side opposite to the first main surface; a magnetic layer positioned on the second main surface side of the insulation layer; and a conductor layer positioned on the side opposite to the insulation layer with respect to the magnetic layer. The surface or the first main surface has an arithmetic average roughness of 0.1 μm to 5.0 μm.

Description

wiring board

[0001] The present disclosure relates to a wiring substrate.

[0002] It is known that one of the causes of attenuation of electrical signals in circuit boards is the high surface roughness of conductor layers, including wiring. In particular, when high-frequency electrical signals are used, transmission loss due to high surface roughness of conductor layers is significant. In so-called high-frequency circuit boards that require high-speed transmission of electrical signals, such as those for servers, it is particularly desirable to reduce the surface roughness of conductor layers (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2021-016006

[0004] When a conductor wiring adheres to an insulating layer, the greater the surface roughness of the conductor wiring or insulating layer, the stronger the adhesion between the conductor wiring and the insulating layer due to the anchor effect. However, increasing the surface roughness of the conductor wiring or insulating layer can increase scattering loss. Scattering loss is a phenomenon in which electrical signals are scattered by roughened areas on the surface of the conductor wiring or at the interface between the conductor wiring and the insulating layer, resulting in loss as heat.

[0005] The present disclosure provides a wiring board that can achieve both good adhesion between conductor wiring and an insulating layer and suppression of scattering loss.

[0006] A first aspect of the substrate wiring comprises: a conductor wiring; an insulating layer having a first main surface to which the surface of the conductor wiring is in close contact and a second main surface opposite the first main surface; a magnetic layer located on the second main surface side of the insulating layer; and a conductor layer located on the opposite side of the insulating layer with respect to the magnetic layer, wherein the surface or the first main surface has an arithmetic mean roughness of 0.1 μm or more and 5.0 μm or less.

[0007] A second aspect is the wiring board of the first aspect, wherein the magnetic layer has a thickness of 0.1 μm or more and 100 μm or less.

[0008] A third aspect is the wiring board according to the first or second aspect, wherein the magnetic layer has a relative permeability of 1.5 or more at a frequency of 30 GHz or more.

[0009] A fourth aspect is the wiring board according to any one of the first to third aspects, wherein the magnetic layer has a portion that is wider than the conductor wiring.

[0010] A fifth aspect is the wiring board according to any one of the first to fourth aspects, wherein the insulating layer has a portion that is the same thickness as or thinner than the magnetic layer.

[0011] A sixth aspect is the wiring board according to any one of the first to fifth aspects, further comprising a second insulating layer between the magnetic layer and the conductor layer.

[0012] According to the present disclosure, it is possible to provide a wiring board that can achieve both good adhesion between conductor wiring and an insulating layer and suppression of scattering loss.

[0013] 8 is a diagram for explaining a breakdown of transmission loss. FIG. 9 is a perspective view showing an example of a configuration of the wiring board of the first embodiment. FIG. 10 is a cross-sectional view showing an example of a configuration of the wiring board of the first embodiment. FIG. 11 is a diagram showing an example of a current distribution in conductor wiring when there is no magnetic layer. FIG. 12 is a diagram showing an example of a current distribution in conductor wiring when there is a magnetic layer. FIG. 13 is a cross-sectional view showing an example of a configuration of the wiring board of the second embodiment. FIG. 14 is a diagram for explaining an example of the concept of a scattering loss evaluation method. FIG. 15 is a simulation diagram showing an example of scattering loss calculated using the evaluation method of FIG. 7. FIG. 16 is a table showing an example of calculation results of scattering loss for the wiring board of the first embodiment and a wiring board of a comparative embodiment. FIG. 17 is a graph showing an example of calculation results of scattering loss for the wiring board of the first embodiment and a wiring board of a comparative embodiment. FIG. 18 is a graph showing an example of calculation results of scattering loss for the wiring board of the first embodiment and a wiring board of a comparative embodiment.

[0014] Each embodiment will be described below. In this specification and the drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant description will be omitted.

[0015] To facilitate understanding, the scales of the various parts in the drawings may differ from the actual scales. Directions such as parallel, right-angled, orthogonal, horizontal, vertical, up, down, left, and right are permitted to deviate to the extent that they do not impair the functions and effects of the embodiments. The X-axis, Y-axis, and Z-axis directions represent directions parallel to the X-axis, Y-axis, and Z-axis, respectively. The X-axis, Y-axis, and Z-axis directions are mutually orthogonal. The XY plane, YZ plane, and ZX plane represent imaginary planes parallel to the X-axis and Y-axis directions, imaginary planes parallel to the Y-axis and Z-axis directions, and imaginary planes parallel to the Z-axis and X-axis directions, respectively.

[0016] The term "layer" may encompass not only a structure with a shape formed over the entire surface when observed in a plan view, but also a structure with a shape formed on a portion of the surface. Unless otherwise specified, the materials exemplified below may be used singly or in combination of two or more. When multiple substances corresponding to each component are present in the composition, the content of each component refers to the total amount of the multiple substances present in the composition, unless otherwise specified. Numerical ranges indicated using "to" indicate ranges that include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range may be replaced with the upper or lower limit of the numerical range of another stage. In the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with the values ​​shown in the examples.

[0017] <About Transmission Loss> First, we will explain transmission loss. Transmission loss refers to the degree to which signals such as electrical, optical, or acoustic signals attenuate over distances along a communication path. In the case of a wiring board on which a transmission line such as a microstrip line is formed, the higher the signal frequency, the greater the transmission loss.

[0018] 1 is a diagram for explaining the breakdown of transmission loss, which is equal to the sum of dielectric loss, scattering loss, and conductor loss.

[0019] Dielectric loss is a phenomenon in which, when an AC electric field is applied to a dielectric, part of the electrical energy supplied by the AC electric field is lost as heat inside the dielectric. Dielectric loss depends on the dielectric properties of the dielectric. Specifically, the magnitude of dielectric loss varies depending on the dielectric loss tangent and dielectric constant. The higher the frequency, the greater the dielectric loss, and the greater the dielectric loss tangent or dielectric constant.

[0020] In the case of wiring board 10, conductor wiring 11 is formed on or above and below dielectric substrate 12. When an AC current signal flows through conductor wiring 11, an AC electric field is applied to dielectric substrate 12. When part of the signal energy is lost inside substrate 12 as dielectric loss, the energy of the original signal is attenuated by that amount.

[0021] Conductor loss refers to a phenomenon in which part of the energy of a signal transmitted through the conductor wiring 11 is lost as Joule heat inside the conductor wiring 11 due to the resistance or skin effect of the conductor wiring 11. When the signal current is DC, the higher the resistance of the conductor wiring 11, the greater the Joule heat. Therefore, when a DC current signal is transmitted through the conductor wiring 11, the higher the resistance of the conductor wiring 11, the greater the conductor loss. On the other hand, when the signal current is AC, the higher the frequency of the signal, the shallower the skin depth becomes due to the skin effect. Skin depth is an index that indicates how far below the surface of the conductor the current flows. The shallower the skin depth, the higher the resistance of the conductor wiring 11 for AC signals. Therefore, when an AC current signal is transmitted through the conductor wiring 11, the higher the frequency of the signal, the greater the conductor loss.

[0022] Scattering loss refers to a phenomenon in which, when a high-frequency electric field is applied to the conductor wiring 11, signals transmitted through the conductor wiring 11 are scattered and lost as heat due to roughened portions on the surface of the conductor wiring 11 or on the interface between the conductor wiring 11 and the substrate 12. A roughened portion refers to an uneven portion on the surface or interface.

[0023] In the case of wiring substrate 10, the surface of conductor wiring 11 or the interface between conductor wiring 11 and substrate 12 is often roughened to improve adhesion between conductor wiring 11 and substrate 12. On the other hand, the skin effect increases as the signal frequency increases. Therefore, scattering due to the roughened portion of the surface of conductor wiring 11 or the interface between conductor wiring 11 and substrate 12 can be a major factor affecting transmission loss.

[0024] Some believe that loss due to roughening of the surface or interface of a conductor is included in conductor loss as loss due to the skin effect. However, it is considered easier to understand if the conductor loss, which takes into account the skin depth as an increase in resistance and for which a calculation formula has already been established, and the loss due to roughening, for which a calculation formula is under discussion, are defined separately. Therefore, this disclosure treats scattering loss as a loss different from conductor loss.

[0025] First Embodiment Fig. 2 is a perspective view showing an example of the configuration of a wiring board according to a first embodiment. Fig. 3 is a cross-sectional view showing an example of the configuration of a wiring board according to the first embodiment. Figs. 2 and 3 may show an example of the configuration in which a part of the wiring board according to the first embodiment is cut out. This also applies to the drawings showing other embodiments described later. Hereinafter, the first embodiment will be described with reference to Figs. 2 and 3.

[0026] 2 and 3 includes a substrate 12 and conductive wiring 11. The substrate 12 includes an insulating layer 20, a magnetic layer 30, and a conductive layer 50.

[0027] The conductor wiring 11 is a conductive signal line extending in the Y-axis direction. The conductor wiring 11 has an input end 15 facing the negative Y-axis direction, an output end 16 facing the positive Y-axis direction, an upper surface 14 facing the positive Z-axis direction, and a lower surface 13 facing the negative Z-axis direction. The lower surface 13 is a surface that is in close contact with the first main surface 21 of the insulating layer 20.

[0028] A high-frequency current signal transmitted through the conductor wiring 11 flows from the input terminal 15 to the output terminal 16. The conductor wiring 11 has a wiring length L in the Y-axis direction from the input terminal 15 to the output terminal 16, a wiring width w1 in the X-axis direction from one side surface to the other side surface, and a wiring thickness d1 in the Z-axis direction from the bottom surface 13 to the top surface 14.

[0029] The conductor wiring 11 is a signal line of a transmission line formed on the wiring substrate 101. Examples of the transmission line include a microstrip line, a coplanar line, and a strip line. In Figures 2 and 3, the conductor layer 50 functions as a ground pattern of the transmission line. The conductor wiring 11 is made of a conductive metal such as copper.

[0030] The insulating layer 20 is an insulator extending along the XY plane. The insulating layer 20 has a first main surface 21 facing the positive Z-axis direction and a second main surface 22 facing the negative Z-axis direction. The second main surface 22 is the surface opposite to the first main surface 21 in the Z-axis direction. The insulating layer 20 has a width w2 along the X-axis direction, a length L along the Y-axis direction, and a thickness d2 along the Z-axis direction.

[0031] The thickness d2 of the insulating layer 20 can be appropriately set in accordance with the wiring thickness d1 of the conductor wiring 11 to be formed, and may be, for example, 30 μm or less, 20 μm or less, 10 μm or less, 5 μm or less, or 3 μm or less. The thickness d2 of the insulating layer 20 may be 1 μm or more from the viewpoint of insulation reliability.

[0032] The magnetic layer 30 is a magnetic material that extends along the XY plane and has a relative permeability greater than 1. The magnetic layer 30 is located on the second major surface 22 side of the insulating layer 20 and may be in contact with the second major surface 22. Since the insulating layer 20 is sandwiched between the magnetic layer 30 and the conductor wiring 11, the magnetic layer 30 is not in contact with the conductor wiring 11 and is located at a distance from the conductor wiring 11. The magnetic layer 30 has a width w2 along the X-axis direction, a length L along the Y-axis direction, and a thickness d3 along the Z-axis direction. The magnetic layer 30 is located between the insulating layer 20 and the conductor layer 50.

[0033] The magnetic layer 30 is, for example, an insulating magnetic layer having an insulator containing a magnetic material. An insulator containing a magnetic material is also called a magnetic insulator. The insulating magnetic layer-forming composition will be described later.

[0034] The conductor layer 50 is located on the opposite side of the magnetic layer 30 from the insulating layer 20. The conductor layer 50 is a conductor that extends along the XY plane. The conductor layer 50 functions as a ground pattern for the transmission line formed on the wiring board 101. The conductor layer 50 may be the same type of conductor as the conductor wiring 11, or may be a different type of conductor from the conductor wiring 11. The conductor layer 50 may be in contact with the lower surface of the magnetic layer 30.

[0035] The function of the magnetic layer 30 will now be described with reference to Fig. 4 and Fig. 5. Fig. 4 is a diagram showing an example of current distribution in the conductor wiring 11 when the magnetic layer 30 is not present. Fig. 5 is a diagram showing an example of current distribution in the conductor wiring 11 when the magnetic layer 30 is present. Figs. 4 and 5 are contour diagrams showing the current density in the ZX cross section of the conductor wiring 11 through which a high-frequency current of 0.1 GHz flows. The lower surface 13 of the conductor wiring 11 contacts the first main surface 21 of the insulating layer 20.

[0036] When a high-frequency current flows through the conductor wiring 11, the current density in the conductor wiring 11 increases due to the skin effect, the closer to the surface of the conductor wiring 11. In the case of FIG. 4 , where there is no magnetic layer 30, the current density along the lower surface 13, which is relatively close to the ground pattern, is high. On the other hand, in the case of FIG. 5 , where there is a magnetic layer 30, the presence of the magnetic layer 30 reduces the current density along the lower surface 13, while increasing the current density along the side surfaces, upper surface 14, and upper corners of the conductor wiring 11. Because the current density along the lower surface 13 is reduced, scattering loss caused by roughened portions of the lower surface 13 of the conductor wiring 11 or the interface between the lower surface 13 and the first main surface 21 is suppressed.

[0037] 2 and 3, the lower surface 13 of the conductor wiring 11 or the first main surface 21 of the insulating layer 20 has an arithmetic mean roughness of 0.1 μm or more and 5.0 μm or less. The arithmetic mean roughness is also referred to as Ra.

[0038] When Ra is 0.1 μm or more, the surface roughness of the lower surface 13 or the first main surface 21 is greater than when Ra is less than 0.1 μm. This improves adhesion between the conductor wiring 11 and the insulating layer 20. On the other hand, when Ra is 5.0 μm or less, the surface roughness of the lower surface 13 or the first main surface 21 is smaller than when Ra exceeds 5.0 μm. This reduces scattering loss caused by roughened portions of the lower surface 13 of the conductor wiring 11 or the interface between the lower surface 13 and the first main surface 21. In this way, by having the lower surface 13 of the conductor wiring 11 or the first main surface 21 of the insulating layer 20 have an arithmetic mean roughness of 0.1 μm or more and 5.0 μm or less, it is possible to achieve both adhesion between the conductor wiring 11 and the insulating layer 20 and suppression of scattering loss caused between the conductor wiring 11 and the insulating layer 20.

[0039] In order to improve the adhesion of the lower surface 13 or the first main surface 21, Ra is preferably 0.1 μm or more, more preferably 0.2 μm or more, and even more preferably 0.5 μm or more. In order to suppress scattering loss occurring between the conductor wiring 11 and the insulating layer 20, Ra is preferably 5.0 μm or less, more preferably 3.0 μm or less, and even more preferably 1.0 μm or less.

[0040] Lower surface 13 can ensure adhesion and suppress scattering loss by having a portion where Ra is 0.1 μm or more and 5.0 μm or less in a portion that overlaps first main surface 21 in a plan view of wiring substrate 101 in the Z-axis direction. First main surface 21 can ensure adhesion and suppress scattering loss by having a portion where Ra is 0.1 μm or more and 5.0 μm or less in a portion that overlaps lower surface 13 in a plan view of wiring substrate 101 in the Z-axis direction.

[0041] Ra is measured, for example, in accordance with JIS B0601-2001. The average line for measuring Ra is, for example, a line extending along the Y-axis direction in which a current signal flows through the conductor wiring 11.

[0042] Scattering loss can be suppressed when the magnetic layer 30 has a thickness d3 of 0.1 μm or more and 100 μm or less. From the viewpoint of suppressing scattering loss, the thickness d3 may be 0.2 μm or more and 80 μm or less, or 0.5 μm or more and 60 μm or less.

[0043] When a signal with a frequency of 30 GHz or higher is transmitted through the conductor wiring 11, the magnetic layer 30 can suppress scattering loss if it has a relative permeability of 1.5 or higher. In terms of suppressing scattering loss, when a signal with a frequency of 30 GHz or higher is transmitted through the conductor wiring 11, the relative permeability of the magnetic layer 30 may be 2 or higher, 3 or higher, 10 or higher, or 20 or higher. The upper limit of the relative permeability of the magnetic layer 30 is not particularly limited, but is, for example, a value of 1000 or lower. The frequency of the signal transmitted through the conductor wiring 11 is not particularly limited, but is, for example, a value of 100 GHz or lower.

[0044] Scattering loss can be suppressed if the magnetic layer 30 has a portion wider than the conductor wiring 11. The magnetic layer 30 illustrated in FIGS.

[0045] Scattering loss can be suppressed when the insulating layer 20 has a portion that is the same as or thinner than the thickness d3 of the magnetic layer 30. For example, the insulating layer 20 has a thickness d2 that is the same as or thicker than the thickness d3 of the magnetic layer 30.

[0046] 6 is a cross-sectional view showing a configuration example of a wiring board according to a second embodiment. In the second embodiment, the description of the configuration, operation, and effects similar to those of the first embodiment will be omitted or simplified by invoking the above description.

[0047] The wiring board 102 of the second embodiment shown in Fig. 6 differs from the wiring board 101 of the first embodiment shown in Fig. 3 in that it further includes an insulating layer 40. The wiring board 102 shown in Fig. 6 includes the insulating layer 40 between the magnetic layer 30 and the conductor layer 50.

[0048] The insulating layer 40 is an example of a second insulating layer and is an insulator that extends along the XY plane. The insulating layer 40 has a thickness d4 along the Z-axis direction. The insulating layer 40 may be made of the same type of insulator as the insulating layer 20, or may be made of a different type of insulator from the insulating layer 20. The insulating layer 40 may be in contact with the lower surface of the magnetic layer 30. The insulating layer 40 may be in contact with the upper surface of the conductor layer 50.

[0049] The insulating layer 40 is disposed so as to sandwich the magnetic layer 30 between itself and the insulating layer 20. The insulating layer 40 may be in contact with the magnetic layer 30. The insulating layer 40 has a width w2 in the X-axis direction and a length L in the Y-axis direction.

[0050] For example, a substrate obtained by laminating several sheets of known prepreg together and subjecting them to a pressure and heat treatment can be used as the insulating layer 40. Such prepreg can be produced by a known method in which a prepared resin varnish is impregnated into a fiber substrate (reinforced fiber) such as glass fiber or organic fiber, and examples of such prepreg include glass-epoxy composite substrates. Furthermore, a metal substrate or ceramic substrate may be used as the core material to which the prepreg is bonded. Furthermore, known low-dielectric substrates, such as substrates made of low-dielectric resin materials such as polyimide resin, fluorine-based resin, and liquid crystal polymer (LCP), can be used as the insulating layer 40.

[0051] Examples of the resin material constituting the insulating layer 40 include thermosetting resins, thermoplastic resins, etc. The resin materials may be used alone or in combination of two or more.

[0052] Examples of thermosetting resins include polycarbonate resins, thermosetting polyimide resins, thermosetting fluorinated polyimide resins, epoxy resins, phenolic resins, urea resins, melamine resins, diallyl phthalate resins, silicone resins, thermosetting urethane resins, fluororesins, liquid crystal polymers, etc. Examples of fluororesins include polymers of fluorine-containing olefins such as polytetrafluoroethylene (PTFE).

[0053] Examples of thermoplastic resins include olefin resins, acrylic resins, polystyrene resins, polyester resins, polyacrylonitrile resins, maleimide resins, polyvinyl acetate resins, ethylene-vinyl acetate copolymers, polyvinyl alcohol resins, polyamide resins, polyvinyl chloride resins, polyacetal resins, polyphenylene oxide resins, polyphenylene sulfide resins, polysulfone resins, polyethersulfone resins, polyetheretherketone resins, polyallylsulfone resins, thermoplastic polyimide resins, thermoplastic fluorinated polyimide resins, thermoplastic urethane resins, polyetherimide resins, polymethylpentene resins, cellulose resins, liquid crystal polymers, and ionomers.

[0054] The insulating layer 40 may be a single layer or a multilayer. The insulating layer 40 may have an adhesive layer on the surface.

[0055] The thickness of the insulating layer 40 may be between 10 μm and 1 mm.

[0056] 6 , the lower surface 13 of the conductor wiring 11 or the first main surface 21 of the insulating layer 20 has an arithmetic mean roughness of 0.1 μm to 5.0 μm, which allows for both good adhesion between the conductor wiring 11 and the insulating layer 20 and suppression of scattering loss that occurs between the conductor wiring 11 and the insulating layer 20.

[0057] <Method for Evaluating Scattering Loss> Fig. 7 is a diagram for explaining an example of the concept of a method for evaluating scattering loss. At present, a method for calculating the magnitude of scattering loss has not been established. For this reason, in this specification, as shown in Fig. 7, the loss amount obtained by subtracting the transmission loss amount calculated when the interface has roughness from the transmission loss amount calculated when the interface does not have roughness is defined as the magnitude of scattering loss generated by the roughened portion of the interface.

[0058] 8 is a simulation diagram showing an example of scattering loss calculated using the evaluation method of FIG. 7. S21_rev is a value (=loss amount) obtained by normalizing S21 in consideration of reflection, and "S21 ２ / (1-S11 ２)). S21 is one of the S parameters and represents the transmission coefficient from the input terminal 15 to the output terminal 16 in the conductor wiring 11. S11 is one of the S parameters and represents the input reflection coefficient, which indicates the proportion of a signal reflected at the input terminal 15 in the conductor wiring 11 relative to the signal input to the input terminal 15. The smaller S21_rev is, the greater the transmission loss in the conductor wiring 11. "S21_rev_μ=1.0_Ra=0.0" indicates a case where the relative permeability of the magnetic layer 30 is 1.0 and Ra is 0.0, i.e., represents an example of the amount of transmission loss calculated when there is no interface roughness. "S21_rev_μ=1.0_Ra=1.0" indicates a case where the relative permeability of the magnetic layer 30 is 1.0 and Ra is 1.0, i.e., represents an example of the amount of transmission loss calculated when there is interface roughness. The value obtained by subtracting the amount of transmission loss when "S21_rev_μ=1.0_Ra=0.0" from the amount of transmission loss when "S21_rev_μ=1.0_Ra=1.0" corresponds to the magnitude of scattering loss occurring due to the roughened portion of the interface.

[0059] <Scattering Loss Evaluation Result Example 1> FIG. 9 is a table showing an example of the results of calculating the scattering loss of the wiring board of the first embodiment and the wiring board of the comparative embodiment using the evaluation method shown in FIGS. 7 and 8 . "Scattering loss [dB / mm] magnetic: μ=3" represents the scattering loss when the relative permeability μ of the magnetic layer 30 of the wiring board 101 of the first embodiment shown in FIG. 3 is 3. "Scattering loss [dB / mm] non-magnetic: μ=1" represents the scattering loss of the wiring board of the comparative embodiment, which does not have the magnetic layer 30. The wiring board of the comparative embodiment corresponds to the calculation result when the relative permeability μ of the magnetic layer 30 of the wiring board 101 of the first embodiment shown in FIG. 3 is set to 1. The "loss ratio" represents the degree of reduction in scattering loss of the wiring board 101 of the first embodiment relative to the scattering loss of the wiring board of the comparative embodiment. The smaller the loss ratio, the greater the scattering loss reduction effect.

[0060] Fig. 9 shows the scattering loss calculated for each example dimension of pattern 1 to pattern 9. The dimensions and parameters used in the calculations shown in Fig. 9 are: Wiring width w1: 100 µm Wiring thickness d1: 20 µm Thickness d2 of insulating layer 20: 10 µm, 20 µm, or 30 µm Thickness d3 of magnetic layer 30: 10 µm, 20 µm, or 30 µm Dielectric loss tangent of insulating layer 20: 0.03 @ 60 GHz Relative dielectric constant of insulating layer 20: 5 @ 60 GHz Ra of lower surface 13 or first main surface 21: 0.5 µm

[0061] Fig. 10 is a graph showing an example of calculation results of scattering loss for the wiring board of the first embodiment and a wiring board of a comparative embodiment. Fig. 10 shows simulation results of scattering loss calculated for each dimension example of patterns 1 to 9 shown in Fig. 9. As shown in Figs. 9 and 10, in any of patterns 1 to 9, when the magnetic layer 30 is provided, scattering loss can be suppressed compared to when the magnetic layer 30 is not provided.

[0062] 9 , patterns 1, 2, and 3 are calculation groups in which the thickness d3 of the magnetic layer 30 is fixed at 10 μm, while the thickness d2 of the insulating layer 20 is set to different values. Patterns 4, 5, and 6 are calculation groups in which the thickness d3 of the magnetic layer 30 is fixed at 20 μm, while the thickness d2 of the insulating layer 20 is set to different values. Patterns 7, 8, and 9 are calculation groups in which the thickness d3 of the magnetic layer 30 is fixed at 30 μm, while the thickness d2 of the insulating layer 20 is set to different values. In all calculation groups, the effect of suppressing scattering loss is enhanced by having the thickness d2 of the insulating layer 20 be the same as or thinner than the thickness d3 of the magnetic layer 30.

[0063] <Scattering Loss Evaluation Result Example 2> Figure 11 is a graph showing an example of the calculation results of scattering loss for the wiring board of the first embodiment and the wiring board of the comparative embodiment. "μ = 2.0" represents the scattering loss when the relative permeability μ of the magnetic layer 30 of the wiring board 101 of the first embodiment shown in Figure 3 is 2.0. "μ = 1.0" represents the scattering loss of the wiring board of the comparative embodiment, which does not have the magnetic layer 30. The wiring board of the comparative embodiment corresponds to the calculation results when the relative permeability μ of the magnetic layer 30 of the wiring board 101 of the first embodiment shown in Figure 3 is set to 1.0.

[0064] Fig. 11 shows scattering loss calculated for three different Ra values. The dimensions and parameters used in the calculation shown in Fig. 11 are: Wiring width w1: 100 µm Wiring thickness d1: 20 µm Thickness d2 of insulating layer 20: 20 µm Thickness d3 of magnetic layer 30: 10 µm Dielectric loss tangent of insulating layer 20: 0.03 @ 60 GHz Relative permittivity of insulating layer 20: 5 @ 60 GHz Ra of lower surface 13 or first main surface 21: 0.1 µm, 0.2 µm, or 0.3 µm

[0065] As shown in FIG. 11, it can be confirmed that, in all cases where the Ra is 0.1 μm, 0.2 μm, and 0.3 μm, when the magnetic layer 30 is provided, scattering loss can be suppressed compared to when the magnetic layer 30 is not provided.

[0066] <Scattering Loss Evaluation Result Example 3> Figure 12 is a graph showing an example of the calculation results of scattering loss for the wiring board of the second embodiment and the wiring board of the comparative embodiment. "μ = 2.0" represents the scattering loss when the relative permeability μ of the magnetic layer 30 for the wiring board 102 of the second embodiment shown in Figure 6 is 2.0. "μ = 1.0" represents the scattering loss for the wiring board of the comparative embodiment, which does not have the magnetic layer 30. The wiring board of the comparative embodiment corresponds to the calculation results when the relative permeability μ of the magnetic layer 30 of the wiring board 102 of the second embodiment shown in Figure 6 is set to 1.0.

[0067] Fig. 12 shows scattering loss calculated for three different Ra values. The dimensions and parameters used in the calculations shown in Fig. 12 are: Wiring width w1: 100 µm Wiring thickness d1: 20 µm Thickness d2 of insulating layer 20: 20 µm Thickness d3 of magnetic layer 30: 10 µm Thickness d4 of insulating layer 40: 10 µm Dielectric loss tangent of insulating layer 20: 0.03 @ 60 GHz Relative dielectric constant of insulating layer 20: 5 @ 60 GHz Ra of lower surface 13 or first main surface 21: 0.1 µm, 0.2 µm, or 0.3 µm

[0068] As shown in FIG. 12, it can be confirmed that, in all cases where the Ra is 0.1 μm, 0.2 μm, and 0.3 μm, when the magnetic layer 30 is provided, scattering loss can be suppressed compared to when the magnetic layer 30 is not provided.

[0069] <Insulating Magnetic Layer-Forming Composition> The insulating magnetic layer-forming composition is a curable composition containing a magnetic material. The insulating magnetic layer-forming composition can be formed, for example, by mixing a binder resin varnish with a magnetic powder.

[0070] The magnetic material may be, for example, at least one magnetic powder selected from the group consisting of a metal element, an alloy, and a metal compound. The alloy may include at least one selected from the group consisting of a solid solution, a eutectic, an amorphous metal, and an intermetallic compound. The metal compound may include a metal oxide.

[0071] From the viewpoint of insulating properties, the magnetic material may be a metal oxide, an amorphous metal, or a metallic glass magnetic powder. Examples of the metal oxide include ferrite. Examples of the amorphous metal include an Fe-based nanocrystalline alloy and a Co-based nanocrystalline alloy.

[0072] The magnetic powder may contain one or more metal elements. The metal element contained in the magnetic powder may be, for example, a base metal element, a noble metal element, a transition metal element, or a rare earth element. The metal element contained in the magnetic powder may be, for example, at least one element selected from the group consisting of iron (Fe), copper (Cu), titanium (Ti), manganese (Mn), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), tin (Sn), chromium (Cr), barium (Ba), strontium (Sr), lead (Pb), silver (Ag), praseodymium (Pr), neodymium (Nd), samarium (Sm), and dysprosium (Dy). The magnetic powder may also contain elements other than metal elements. The magnetic powder may also contain, for example, oxygen, boron, or silicon.

[0073] The magnetic powder may be at least one composition selected from the group consisting of Fe—Si alloys, Fe—Si—Al alloys (sendust), Fe—Ni alloys (permalloy), Fe—Cu—Ni alloys (permalloy), Fe—Cr—Si alloys, Fe—Cr alloys, Fe—Ni—Cr alloys (electromagnetic stainless steel), Nd—Fe—B alloys (rare earth magnets), Al—Ni—Co alloys (alnico magnets), and ferrite. The ferrite may be, for example, spinel ferrite, hexagonal ferrite, or garnet ferrite.

[0074] The Fe-based alloy may be an Fe-amorphous alloy. Amorphous Fe alloy powder is an amorphous powder obtained by rapidly quenching an alloy in which the main component Fe, together with other elements such as Si, is melted at high temperature. This amorphous Fe alloy powder is also known as metallic glass. The amorphous Fe alloy powder can be produced according to methods well known in the art. Examples of commercially available amorphous Fe alloy powders include those manufactured by Epson Atmix Corporation under the product names "AW2-08" and "KUAMET-6B2," those manufactured by Daido Steel Co., Ltd. under the product names "DAPMS3," "DAPMS7," "DAPMSA10," "DAPPB," "DAPPC," "DAPMKV49," "DAP410L," "DAP430L," and "DAPHYB Series," and those manufactured by Kobe Steel, Ltd. under the product names "MH45D," "MH28D," "MH25D," and "MH20D."

[0075] The magnetic powder may contain one of the above elements and compositions, or may contain a plurality of the above elements and compositions.

[0076] The magnetic powder may be spherical, approximately spherical, flake-like, or elliptical. The magnetic powder may also have various other shapes, including corners. From the viewpoint of excellent flowability, the magnetic powder may be spherical.

[0077] The average particle size of the magnetic powder may be 0.005 to 50 μm. The "average particle size" described in this specification means the particle size at an integrated value of 50% (volume basis) in the particle size distribution. A mixture of particles with two to three different average particle sizes can be used as the magnetic powder so as to achieve close packing.

[0078] The magnetic powder may have a coating on its surface. The coating may be formed, for example, from an inorganic salt, an acrylic resin, a silicon oxide compound, or the like. The magnetic powder may also be entirely or partially coated with a surface treatment agent. Examples of the surface treatment agent include inorganic oxides, phosphoric acid compounds, phosphate compounds, and inorganic surface treatment agents such as silane coupling agents, organic surface treatment agents such as montan wax, and cured resins. Coupling agents, as described below, can also be used as the surface treatment agent. For example, metal-based magnetic powders such as Fe-based alloys may be entirely or partially coated with an insulating material. Examples of insulating materials include silica, titania, calcium phosphate, montan wax, and cured epoxy resins.

[0079] The magnetic powder may include magnetic powder whose surface is coated with an insulating material (hereinafter referred to as insulating-coated magnetic powder). The insulating-coated magnetic powder may be used alone or in combination of two or more types. The average particle diameters of two or more types of insulating-coated magnetic powder may be the same or different. In addition, insulating-coated magnetic powder may be used in combination with magnetic powder without an insulating coating (hereinafter referred to as uncoated magnetic powder). The average particle diameter of the uncoated magnetic powder may be the same as or different from the average particle diameter of the insulating-coated magnetic powder. For example, from the viewpoint of exhibiting insulating properties, the average particle diameter of the uncoated magnetic powder may be smaller than the average particle diameter of the insulating-coated magnetic powder.

[0080] The insulating coated magnetic powder may be an Fe amorphous alloy powder having an insulating coating. Examples of such insulating coated magnetic powder include commercially available products such as "KUAMET9A4" (Fe-Si-B alloy, D50: 20 μm, with insulating coating) manufactured by Epson Atmix Corporation and "SAP-2D(C)" (Fe-Si-B-PNb-Cr alloy, D50: 2.3 μm, with insulating coating) manufactured by Shinto Kogyo Co., Ltd. Examples of uncoated magnetic powder include commercially available products such as "SAP-2D" (Fe-Si-B-PNb-Cr alloy, D50: 2.3 μm, without insulating coating) manufactured by Shinto Kogyo Co., Ltd. and "BSN-125" (Ni-Zn alloy, D50: 10 μm, without insulating coating) soft ferrite powder manufactured by Toda Kogyo Co., Ltd.

[0081] The content of the magnetic powder in the insulating magnetic layer-forming composition may be 70 to 99 parts by mass, or 80 to 90 parts by mass, when the total mass of the composition is 100 parts by mass.

[0082] The binder resin varnish may be a resin composition.

[0083] The resin composition may contain an epoxy resin.

[0084] Examples of epoxy resins include epoxy resins having a condensed ring structure such as naphthalene type epoxy resins, naphthalene type tetrafunctional epoxy resins, naphthol type epoxy resins, naphthylene ether type epoxy resins, anthracene type epoxy resins, dicyclopentadiene type epoxy resins, naphthalene type epoxy resins, naphthalene type tetrafunctional epoxy resins, naphthol type epoxy resins, naphthylene ether type epoxy resins, and dicyclopentadiene type epoxy resins; bisphenol A type epoxy resins; bisphenol F type epoxy resins; bisphenol S type epoxy resins; bisphenol AF type epoxy resins; and trisphenol type epoxy resins. Resins include novolac-type epoxy resins, naphthol novolac-type epoxy resins, phenol novolac-type epoxy resins, tert-butyl-catechol-type epoxy resins, glycidylamine-type epoxy resins, glycidyl ester-type epoxy resins, cresol novolac-type epoxy resins, biphenyl-type epoxy resins, linear aliphatic epoxy resins, epoxy resins having a butadiene structure, alicyclic epoxy resins, heterocyclic epoxy resins, spiro ring-containing epoxy resins, cyclohexanedimethanol-type epoxy resins, trimethylol-type epoxy resins, tetraphenylethane-type epoxy resins, and bixylenol-type epoxy resins. These may be used alone or in combination of two or more.

[0085] The epoxy resin may be an epoxy resin having two or more epoxy groups in one molecule, and may be in a liquid or solid state at 25°C.

[0086] Examples of epoxy resins that are liquid at 25°C (hereinafter also referred to as "liquid epoxy resins") that can be used include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol AF type epoxy resins, naphthalene type epoxy resins, glycidyl ester type epoxy resins, glycidyl amine type epoxy resins, phenol novolac type epoxy resins, alicyclic epoxy resins having an ester skeleton, cyclohexanedimethanol type epoxy resins, glycidyl amine type epoxy resins, and epoxy resins having a butadiene structure. Liquid epoxy resins include "HP4032," "HP4032D," and "HP4032SS" (naphthalene-type epoxy resins) manufactured by DIC Corporation, "828US," "jER828EL" (bisphenol A-type epoxy resin), "jER807" (bisphenol F-type epoxy resin), "jER152" (phenol novolac-type epoxy resin), "630," and "630LSD" (glycidylamine-type epoxy resin) manufactured by Mitsubishi Chemical Corporation, and "ZX1059" (a mixture of bisphenol A-type epoxy resin and bisphenol F-type epoxy resin) manufactured by Nippon Steel & Sumitomo Metal Chemical Co., Ltd. Commercially available products that can be used include "EX-721" (glycidyl ester type epoxy resin) manufactured by Nagase ChemteX Corporation, "Celloxide 2021P" (alicyclic epoxy resin having an ester skeleton) and "PB-3600" (epoxy resin having a butadiene structure) manufactured by Daicel Corporation, "ZX1658" and "ZX1658GS" (liquid 1,4-glycidylcyclohexane) manufactured by Nippon Steel & Sumikin Chemical Co., Ltd., "630LSD" (glycidylamine type epoxy resin) manufactured by Mitsubishi Chemical Corporation, and "EP-3980S" (glycidylamine type epoxy resin) manufactured by ADEKA Corporation.

[0087] Examples of epoxy resins that are solid at 25°C include naphthalene-type tetrafunctional epoxy resins, cresol novolac-type epoxy resins, dicyclopentadiene-type epoxy resins, trisphenol-type epoxy resins, naphthol-type epoxy resins, biphenyl-type epoxy resins, naphthylene ether-type epoxy resins, anthracene-type epoxy resins, bisphenol A-type epoxy resins, and tetraphenylethane-type epoxy resins. Examples of solid epoxy resins include "HP4032H" (naphthalene-type epoxy resin), "HP-4700", "HP-4710" (naphthalene-type tetrafunctional epoxy resin), "N-690" (cresol novolac-type epoxy resin), "N-695", "N-680" (cresol novolac-type epoxy resin), "HP-7200" (dicyclopentadiene-type epoxy resin), "HP-7200HH", and "HP- 7200H", "EXA-7311", "EXA-7311-G3", "EXA-7311-G4", "EXA-7311-G4S", "HP6000" (naphthylene ether type epoxy resin), Nippon Kayaku's "EPPN-502H" (trisphenol type epoxy resin), "NC7000L" (naphthol novolac type epoxy resin), "NC3000H", "NC3000", "NC3000L", "NC Commercially available epoxy resins that can be used include "3100" (biphenyl-type epoxy resin), "ESN475V" (naphthalene-type epoxy resin), "ESN485" (naphthol novolac-type epoxy resin) manufactured by Nippon Steel & Sumikin Chemical Co., Ltd., "YX4000H", "YL6121" (biphenyl-type epoxy resin), "YX4000HK" (bixylenol-type epoxy resin), and "YX8800" (anthracene-type epoxy resin) manufactured by Mitsubishi Chemical Corporation, "PG-100" and "CG-500" manufactured by Osaka Gas Chemicals Co., Ltd., "YL7760" (bisphenol AF-type epoxy resin), "YL7800" (fluorene-type epoxy resin) manufactured by Mitsubishi Chemical Corporation, and "jER1010" (solid bisphenol A-type epoxy resin), "jER1031S" (tetraphenylethane-type epoxy resin), and "157S70" (novolac-type epoxy resin) manufactured by Mitsubishi Chemical Corporation.

[0088] The resin composition may contain a curing agent. Examples of the curing agent include phenol-based curing agents, naphthol-based curing agents, benzoxazine-based curing agents, and cyanate ester-based curing agents. The curing agents may be used alone or in combination of two or more.

[0089] As the phenol-based curing agent and naphthol-based curing agent, a phenol-based curing agent having a novolac structure, a naphthol-based curing agent having a novolac structure, a nitrogen-containing phenol-based curing agent, and a triazine skeleton-containing phenol-based curing agent can be used.

[0090] Phenol-based curing agents and naphthol-based curing agents include "MEH-7700," "MEH-7810," and "MEH-7851" manufactured by Meiwa Kasei Co., Ltd., "NHN," "CBN," and "GPH" manufactured by Nippon Kayaku Co., Ltd., "SN170," "SN180," "SN190," "SN475," "SN485," "SN495V," "SN375," and "SN395" manufactured by Nippon Steel & Sumikin Chemical Co., Ltd., and "TD2090" manufactured by DIC Corporation. "," "TD2090-60M," "LA-7052," "LA-7054," "LA-1356," "LA-3018," "LA-3018-50P," "EXB-9500," "HPC-9500," "KA-1160," "KA-1163," "KA-1165," and Gun-ei Chemical Co., Ltd.'s "GDP-6115L," "GDP-6115H," and "ELPC75" are commercially available products that can be used.

[0091] As the benzoxazine-based curing agent, commercially available products such as "HFB2006M" manufactured by Showa Highpolymer Co., Ltd., and "Pd" and "Fa" manufactured by Shikoku Chemicals Corporation can be used.

[0092] Examples of cyanate ester curing agents include bifunctional cyanate resins such as bisphenol A dicyanate, polyphenol cyanate, oligo(3-methylene-1,5-phenylene cyanate), 4,4'-methylenebis(2,6-dimethylphenyl cyanate), 4,4'-ethylidene diphenyl dicyanate, hexafluorobisphenol A dicyanate, 2,2-bis(4-cyanate)phenylpropane, 1,1-bis(4-cyanatephenylmethane), bis(4-cyanate-3,5-dimethylphenyl)methane, 1,3-bis(4-cyanatephenyl-1-(methylethylidene))benzene, bis(4-cyanatephenyl)thioether, and bis(4-cyanatephenyl)ether; polyfunctional cyanate resins derived from phenol novolac and cresol novolac; and prepolymers in which these cyanate resins are partially converted to triazine.

[0093] As the cyanate ester curing agent, commercially available products such as "PT30" and "PT60" (both of which are phenol novolac type polyfunctional cyanate ester resins) manufactured by Lonza Japan Co., Ltd., "BA230" and "BA230S75" (prepolymers in which part or all of bisphenol A dicyanate has been converted to triazine and formed into a trimer) can be used.

[0094] The content of the curing agent in the resin composition may be 0.1 parts by mass or more, 0.3 parts by mass or more, or 0.5 parts by mass or more, and may be 5 parts by mass or less, 3 parts by mass or less, or 2 parts by mass or less, when the resin component in the resin composition is 100 parts by mass.

[0095] The resin composition may contain a curing accelerator. Examples of the curing accelerator include phosphorus-based curing accelerators, amine-based curing accelerators, imidazole-based curing accelerators, guanidine-based curing accelerators, and metal-based curing accelerators. Examples of the curing accelerator include phosphorus-based curing accelerators, amine-based curing accelerators, imidazole-based curing accelerators, and metal-based curing accelerators. One type of curing accelerator can be used alone, or two or more types can be used in combination.

[0096] Examples of phosphorus-based curing accelerators include triphenylphosphine, phosphonium borate compounds, tetraphenylphosphonium tetraphenylborate, n-butylphosphonium tetraphenylborate, tetrabutylphosphonium decanoate, (4-methylphenyl)triphenylphosphonium thiocyanate, tetraphenylphosphonium thiocyanate, and butyltriphenylphosphonium thiocyanate.

[0097] Examples of the amine curing accelerator include trialkylamines such as triethylamine and tributylamine, 4-dimethylaminopyridine, benzyldimethylamine, 2,4,6-tris(dimethylaminomethyl)phenol, and 1,8-diazabicyclo(5,4,0)-undecene, and examples thereof include 4-dimethylaminopyridine and 1,8-diazabicyclo(5,4,0)-undecene.

[0098] Examples of the imidazole curing accelerator include 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, and 1-benzyl-2-methylimidazole. Phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazolium trimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl -(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct imidazole compounds such as 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, 2-methylimidazoline, and 2-phenylimidazoline, as well as adducts of imidazole compounds with epoxy resins.

[0099] As the imidazole-based curing accelerator, commercially available products such as "P200-H50" manufactured by Mitsubishi Chemical Corporation can be used.

[0100] Examples of guanidine curing accelerators include dicyandiamide, 1-methylguanidine, 1-ethylguanidine, 1-cyclohexylguanidine, 1-phenylguanidine, 1-(o-tolyl)guanidine, dimethylguanidine, diphenylguanidine, trimethylguanidine, tetramethylguanidine, pentamethylguanidine, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1-methylbiguanide, 1-ethylbiguanide, 1-n-butylbiguanide, 1-n-octadecylbiguanide, 1,1-dimethylbiguanide, 1,1-diethylbiguanide, 1-cyclohexylbiguanide, 1-allylbiguanide, 1-phenylbiguanide, and 1-(o-tolyl)biguanide.

[0101] Examples of metal-based curing accelerators include organometallic complexes or organometallic salts of metals such as cobalt, copper, zinc, iron, nickel, manganese, and tin. Examples of organometallic complexes include organic cobalt complexes such as cobalt(II) acetylacetonate and cobalt(III) acetylacetonate, organic copper complexes such as copper(II) acetylacetonate, organic zinc complexes such as zinc(II) acetylacetonate, organic iron complexes such as iron(III) acetylacetonate, organic nickel complexes such as nickel(II) acetylacetonate, and organic manganese complexes such as manganese(II) acetylacetonate. Examples of organometallic salts include zinc octoate, tin octoate, zinc naphthenate, cobalt naphthenate, tin stearate, and zinc stearate.

[0102] The content of the curing accelerator in the resin composition may be 0.001 parts by mass or more, 0.005 parts by mass or more, or 0.01 parts by mass or more, and may be 0.1 parts by mass or less, 0.08 parts by mass or less, or 0.05 parts by mass or less, when the non-volatile components in the resin composition are taken as 100 parts by mass.

[0103] The resin composition may contain a thermoplastic resin, such as a phenoxy resin, a polyvinyl acetal resin, a polyolefin resin, a polybutadiene resin, a siloxane resin, a poly(meth)acrylic resin, a polyalkylene resin, a polyalkyleneoxy resin, a polyisoprene resin, a polyisobutylene resin, a polyimide resin, a polyamideimide resin, a polyetherimide resin, a polysulfone resin, a polyethersulfone resin, a polyphenylene ether resin, a polycarbonate resin, a polyetheretherketone resin, or a polyester resin.

[0104] Examples of phenoxy resins include "1256" and "4250" (both phenoxy resins containing a bisphenol A structure), "YX8100" (phenoxy resin containing a bisphenol S skeleton), and "YX6954" (phenoxy resin containing a bisphenol acetophenone structure) manufactured by Mitsubishi Chemical Corporation. In addition, commercially available products such as "FX280" and "FX293" manufactured by Nippon Steel & Sumikin Chemical Co., Ltd., and "YX7180," "YX6954," "YX7553," "YX7553BH30," "YL7553BH30," "YL7769," "YL6794," "YL7213," "YL7290," "YL7891," and "YL7482" manufactured by Mitsubishi Chemical Corporation can also be used.

[0105] The thermoplastic resin may have one or more structures selected from a polybutadiene structure, a polysiloxane structure, a poly(meth)acrylate structure, a polyalkylene structure, a polyalkyleneoxy structure, a polyisoprene structure, a polyisobutylene structure, and a polycarbonate structure in its molecule. These structures may be contained in the main chain or in a side chain. The polybutadiene structure may be partially or completely hydrogenated. The polyalkyleneoxy structure may be a polyalkyleneoxy structure having 2 to 15 carbon atoms, a polyalkyleneoxy structure having 3 to 10 carbon atoms, or a polyalkyleneoxy structure having 5 to 6 carbon atoms.

[0106] The thermoplastic resin may have a number average molecular weight (Mn) of 1,000 or more, 1,500 or more, 3,000 or more, or 5,000 or more, and may be 1,000,000 or less, or 900,000 or less. The number average molecular weight (Mn) means the number average molecular weight in terms of polystyrene measured using GPC (gel permeation chromatography).

[0107] The thermoplastic resin may have a functional group capable of reacting with an epoxy resin, which may be one or more functional groups selected from the group consisting of a hydroxy group, a carboxy group, an acid anhydride group, a phenolic hydroxyl group, an epoxy group, an isocyanate group, and a urethane group.

[0108] Examples of the polybutadiene resin that can be used include commercially available products such as "Ricon 130MA8," "Ricon 130MA13," "Ricon 130MA20," "Ricon 131MA5," "Ricon 131MA10," "Ricon 131MA17," "Ricon 131MA20," and "Ricon 184MA6" (acid anhydride group-containing polybutadienes) manufactured by Cray Valley Corporation; "GQ-1000" (hydroxyl- and carboxyl-group-introduced polybutadiene), "G-1000," "G-2000," and "G-3000" (polybutadiene with hydroxyl groups at both ends), "GI-1000," "GI-2000," and "GI-3000" (hydrogenated polybutadiene with hydroxyl groups at both ends) manufactured by Nippon Soda Co., Ltd.; and "FCA-061L" (hydrogenated polybutadiene skeleton epoxy resin) manufactured by Nagase ChemteX Corporation.

[0109] As the poly(meth)acrylic resin, commercially available products such as Teisan Resin manufactured by Nagase ChemteX Corporation, and ME-2000, W-116.3, W-197C, KG-25, and KG-3000 manufactured by Negami Chemical Industrial Co., Ltd. can be used.

[0110] As the polycarbonate resin, commercially available products such as "T6002" and "T6001" (polycarbonate diols) manufactured by Asahi Kasei Chemicals Corporation, and "C-1090", "C-2090", and "C-3090" (polycarbonate diols) manufactured by Kuraray Co., Ltd. can be used.

[0111] Thermoplastic resins include "SMP-2006", "SMP-2003PGMEA", and "SMP-5005PGMEA" manufactured by Shin-Etsu Silicone Co., Ltd., linear polyimides made from amine-terminated polysiloxanes and tetrabasic acid anhydrides (see, for example, International Publication No. 2010 / 053185, JP 2002-12667 A and JP 2000-319386 A), "PTXG-1000" and "PTXG-1800" manufactured by Asahi Kasei Fibers Corporation, "KL-610" and "KL613" manufactured by Kuraray Co., Ltd., "SIBSTAR-073T" (styrene-isobutylene-styrene triblock copolymer) and "SIBSTAR-042D" (styrene-isobutylene diblock copolymer) manufactured by Kaneka Corporation, and "Denka Butyral" manufactured by Denki Kagaku Kogyo Co., Ltd. 4000-2", "Denka Butyral 5000-A", "Denka Butyral 6000-C", "Denka Butyral 6000-EP", Sekisui Chemical Co., Ltd.'s S-LEC BH series, BX series (e.g., BX-5Z), KS series (e.g., KS-1), BL series, BM series, New Japan Chemical Co., Ltd.'s "Rikacoat SN20" and "Rikacoat PN20", Toyobo Co., Ltd.'s "Vylomax HR11NN" and "Vylomax HR16NN", Hitachi Chemical Co., Ltd.'s "KS9100" and "KS9300", Sumitomo Chemical Co., Ltd.'s "PES5003P", Solvay Advanced Polymers' polysulfone "P1700" and "P3500", Ganz Chemical Co., Ltd.'s "AC3832" and other commercially available products may also be used.

[0112] The content of the thermoplastic resin in the resin composition may be 0.1 parts by mass or more, 0.3 parts by mass or more, or 0.5 parts by mass or more, and may be 20 parts by mass or less, 10 parts by mass or less, 5 parts by mass or less, or 3 parts by mass or less, when the non-volatile components in the resin composition are 100 parts by mass.

[0113] The resin composition may contain an active ester compound having one or more active ester groups in one molecule. The active ester compound may be used alone or in combination of two or more.

[0114] As the active ester compound, a compound having two or more highly reactive ester groups per molecule, such as phenol esters, thiophenol esters, N-hydroxyamine esters, esters of heterocyclic hydroxy compounds, etc. Examples of such active ester compounds include those obtained by a condensation reaction between a carboxylic acid compound and / or a thiocarboxylic acid compound and a hydroxy compound and / or a thiol compound.

[0115] From the viewpoint of improving heat resistance, the active ester compound may be an active ester compound obtained from a carboxylic acid compound and a hydroxy compound, or may be an active ester compound obtained from a carboxylic acid compound and a phenol compound and / or a naphthol compound. Examples of the carboxylic acid compound include benzoic acid, acetic acid, succinic acid, maleic acid, itaconic acid, phthalic acid, isophthalic acid, terephthalic acid, and pyromellitic acid. Examples of phenol compounds or naphthol compounds include hydroquinone, resorcinol, bisphenol A, bisphenol F, bisphenol S, phenolphthalene, methylated bisphenol A, methylated bisphenol F, methylated bisphenol S, phenol, o-cresol, m-cresol, p-cresol, catechol, α-naphthol, β-naphthol, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, dihydroxybenzophenone, trihydroxybenzophenone, tetrahydroxybenzophenone, phloroglucin, benzenetriol, dicyclopentadiene-type diphenol compounds, phenol novolak, etc. Here, "dicyclopentadiene-type diphenol compounds" refers to diphenol compounds obtained by condensing one dicyclopentadiene molecule with two phenol molecules.

[0116] Specific examples of the active ester compound include an active ester compound containing a dicyclopentadiene-type diphenol structure, an active ester compound containing a naphthalene structure, an active ester compound containing an acetylated product of phenol novolac, and an active ester compound containing a benzoylated product of phenol novolac. Note that the "dicyclopentadiene-type diphenol structure" refers to a divalent structural unit consisting of phenylene-dicyclopentylene-phenylene.

[0117] Examples of active ester compounds containing a dicyclopentadiene-type diphenol structure include "EXB9451," "EXB9460," "EXB9460S," "HPC-8000-65T," "HPC-8000H-65TM," "EXB-8000L-65TM," and "EXB-8150-65T" (manufactured by DIC Corporation). Examples of active ester compounds containing a naphthalene structure include "EXB9416-70BK" (manufactured by DIC Corporation). Examples of active ester compounds containing an acetylated product of phenol novolac include "DC808 (manufactured by Mitsubishi Chemical Corporation), as an active ester compound containing a benzoylated product of phenol novolac, "YLH1026" (manufactured by Mitsubishi Chemical Corporation), as an active ester compound which is an acetylated product of phenol novolac, "DC808" (manufactured by Mitsubishi Chemical Corporation), and as an active ester-based curing agent which is a benzoylated product of phenol novolac, commercially available products such as "YLH1026" (manufactured by Mitsubishi Chemical Corporation), "YLH1030" (manufactured by Mitsubishi Chemical Corporation), and "YLH1048" (manufactured by Mitsubishi Chemical Corporation) may be used.

[0118] When the resin composition contains an active ester compound and an epoxy resin, the quantitative ratio of the epoxy resin to the active ester compound, expressed as the ratio of [total number of epoxy groups in the epoxy resin]:[total number of active ester groups in the active ester compound], may be 1:0.01 to 1:5, 1:0.05 to 1:3, or 1:0.1 to 1:1.5.

[0119] The content of the active ester compound in the resin composition may be 1 part by mass or more, 1.5 parts by mass or more, or 2 parts by mass or more, and may be 40 parts by mass or less, 30 parts by mass or less, 20 parts by mass or less, 10 parts by mass or less, 8 parts by mass or less, or 5 parts by mass or less, relative to 100 parts by mass of the non-volatile components in the resin composition.

[0120] The resin composition may contain a carbodiimide compound having one or more carbodiimide groups (-N=C=N-) in one molecule. As the carbodiimide compound, a compound having two or more carbodiimide groups in one molecule may be used. The carbodiimide compound may be used alone or in combination of two or more.

[0121] The carbodiimide compound may be a compound having a structure represented by the following formula (A): -(X) ｐ -N=C=N- (A) [In the formula, X represents an alkylene group, a cycloalkylene group, or an arylene group, which may have a substituent. p represents an integer of 1 to 5. When there are multiple Xs, they may be the same or different.] The number of carbon atoms of the alkylene group represented by X (not including the number of carbon atoms of the substituent) may be 1 to 20, 1 to 10, 1 to 6, 1 to 4, or 1 to 3. Examples of the alkylene group include a methylene group, an ethylene group, a propylene group, and a butylene group.

[0122] The number of carbon atoms of the cycloalkylene group represented by X (not including the number of carbon atoms of the substituent) may be 3 to 20, 3 to 12, or 3 to 6. Examples of the cycloalkylene group include a cyclopropylene group, a cyclobutylene group, a cyclopentylene group, and a cyclohexylene group.

[0123] The arylene group represented by X is a group in which two hydrogen atoms on the aromatic ring have been removed from an aromatic hydrocarbon. The number of carbon atoms in the arylene group (not including the number of carbon atoms in the substituent) may be 6 to 24, 6 to 18, 6 to 14, or 6 to 10. Examples of the arylene group include a phenylene group, a naphthylene group, and an anthracenylene group.

[0124] The alkylene group, cycloalkylene group, or aryl group represented by X may have a substituent. Examples of the substituent include a halogen atom, an alkyl group, an alkoxy group, a cycloalkyl group, a cycloalkyloxy group, an aryl group, an aryloxy group, an acyl group, and an acyloxy group. Examples of the halogen atom used as a substituent include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. The alkyl group and alkoxy group as a substituent may be linear or branched, and may have 1 to 20, 1 to 10, 1 to 6, 1 to 4, or 1 to 3 carbon atoms. The cycloalkyl group and cycloalkyloxy group as a substituent may have 3 to 20, 3 to 12, or 3 to 6 carbon atoms. The aryl group as a substituent is a group in which one hydrogen atom on the aromatic ring has been removed from an aromatic hydrocarbon, and may have 6 to 24, 6 to 18, 6 to 14, or 6 to 10 carbon atoms. The aryloxy group as a substituent may have 6 to 24, 6 to 18, 6 to 14, or 6 to 10 carbon atoms. The acyl group as a substituent is represented by the formula: -C(=O)-R １ (wherein R １ represents an alkyl group or an aryl group. １ The alkyl group represented by R may be either linear or branched, and may have 1 to 20, 1 to 10, 1 to 6, 1 to 4, or 1 to 3 carbon atoms. １ The number of carbon atoms in the aryl group represented by the formula: ２ (wherein R ２ represents an alkyl group or an aryl group.

[0125] In formula (A), p represents an integer of 1 to 5. p may be 1 to 4, 2 to 4, 2, or 3.

[0126] The content of the structure represented by formula (A) in the carbodiimide compound may be 50 parts by mass or more, 60 parts by mass or more, 70 parts by mass or more, 80 parts by mass or more, or 90 parts by mass or more, when the mass of the entire molecule of the carbodiimide compound is 100 parts by mass. The carbodiimide compound may essentially consist of the structure represented by formula (A), excluding the terminal structure. Examples of the terminal structure of the carbodiimide compound include an alkyl group, a cycloalkyl group, and an aryl group, which may have a substituent. The alkyl group, cycloalkyl group, and aryl group used as the terminal structure may be the same as the alkyl group, cycloalkyl group, and aryl group described above as the substituent that the group represented by X may have. Furthermore, the substituent that the group used as the terminal structure may have may be the same as the substituent that the group represented by X may have.

[0127] The weight average molecular weight of the carbodiimide compound may be 500 or more, 600 or more, 700 or more, 800 or more, 900 or more, or 1000 or more, and may be 5000 or less, 4500 or less, 4000 or less, 3500 or less, or 3000 or less. The weight average molecular weight of the carbodiimide compound can be measured, for example, by gel permeation chromatography (GPC) (polystyrene equivalent).

[0128] When the carbodiimide compound contains an isocyanate group (—N═C═O) in the molecule, the content of the isocyanate group in the carbodiimide compound (also referred to as the “NCO content”) may be 5% by mass or less, 4% by mass or less, 3% by mass or less, 2% by mass or less, 1% by mass or less, or 0.5% by mass or less.

[0129] As the carbodiimide compound, commercially available products such as Carbodilite (registered trademark) V-02B, V-03, V-04K, V-07, and V-09 manufactured by Nisshinbo Chemical Inc., and Stavaxol (registered trademark) P, P400, and Hi-Kasil 510 manufactured by Rhein Chemie AG may be used.

[0130] The content of the carbodiimide compound in the resin composition may be 0.1 parts by mass or more, 0.3 parts by mass or more, or 0.5 parts by mass or more, and may be 3 parts by mass or less, 2 parts by mass or less, or 1.5 parts by mass or less, based on 100 parts by mass of the non-volatile components in the resin composition.

[0131] The resin composition may further contain other additives as needed, such as flame retardants, organometallic compounds such as organocopper compounds, organozinc compounds, and organocobalt compounds, binders, thickeners, antifoaming agents, leveling agents, adhesion promoters, and colorants.

[0132] The insulating magnetic layer-forming composition may be in the form of a paste (hereinafter referred to as "paste"), and the paste may contain magnetic powder, an epoxy group-containing compound, and a curing agent.

[0133] The magnetic powder may be any of the magnetic powders described above.

[0134] The average particle size of the magnetic powder contained in the paste may be 0.05 to 200 μm, 0.5 to 100 μm, or 1 to 50 μm. If the magnetic powder is coated, the average particle size of the magnetic powder including the coating film may be within the above range.

[0135] The content of the magnetic powder in the paste may be 70% by mass or more, or 80% by mass or more, and 99% by mass or less, or 90% by mass or less, based on the total mass of the paste. The content of the magnetic powder in the paste may be 70 to 99% by mass, or 80 to 90% by mass, based on the total mass of the paste.

[0136] The term "epoxy group-containing compound" refers to a compound having one or more epoxy groups in its molecule, and may take the form of a monomer, or an oligomer or polymer having structural units formed by polymerization of the monomer. The epoxy group-containing compound cures by heat treatment and can function as a binder resin that binds the metal element-containing powder. Examples of epoxy group-containing compounds include oligomers and polymers having two or more epoxy groups in their molecules, commonly known as epoxy resins. Other examples of epoxy group-containing compounds include compounds that have one or more epoxy groups in their molecules but do not contain structural units formed by polymerization (hereinafter referred to as "epoxy compounds"). Such epoxy compounds are generally known as reactive diluents. The epoxy group-containing compound preferably includes at least one selected from the group consisting of epoxy resins and epoxy compounds.

[0137] The epoxy resin may be the same as that blended in the resin composition described above.

[0138] The molecular weight of the epoxy compound may be 100 or more, 150 or more, or 200 or more. When an epoxy compound having a molecular weight of 100 or more is used, volatilization before reaction with a curing agent can be suppressed by setting appropriate curing conditions. In addition, a low molecular weight reduces the occurrence of defects such as a short distance between crosslinking points after reaction, making the cured product prone to cracking. On the other hand, the molecular weight of the epoxy compound may be 700 or less, 500 or less, or 300 or less. When an epoxy compound having a molecular weight of 700 or less is used, an appropriate viscosity can be easily obtained as a diluent.

[0139] The molecular weight of the epoxy compound may be 100 to 700, 150 to 500, or 200 to 300. When an epoxy compound having a molecular weight within such a range is used, it becomes easy to adjust the viscosity of the paste. Unlike components such as organic solvents that volatilize when heated, epoxy compounds harden when heated and are incorporated into the cured product. Therefore, when an epoxy compound is used, it contributes to adjusting the viscosity of the paste while also making it possible to suppress deterioration in the properties of the cured product.

[0140] The epoxy compound may contain one or more epoxy groups in the molecule. The epoxy compound may be, for example, at least one selected from the group consisting of n-butyl glycidyl ether, versatate glycidyl ether, styrene oxide, ethylhexyl glycidyl ether, phenyl glycidyl ether, butylphenyl glycidyl ether, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, diethylene glycol diglycidyl ether, and trimethylolpropane triglycidyl ether. The epoxy compound may have 500 ppm or less of ionic impurities such as free Na ions and free Cl ions.

[0141] The epoxy equivalent of the epoxy group-containing compound may be 80 g / eq to 350 g / eq, 100 g / eq to 300 g / eq, or 120 g / eq to 250 g / eq. When the epoxy equivalent is within the above range, the viscosity of the epoxy group-containing compound itself is low, making it easy to adjust the viscosity of the paste.

[0142] The epoxy group-containing compound preferably contains an epoxy group-containing compound that is liquid at 25°C. In this specification, "liquid at 25°C" means that the viscosity of the epoxy group-containing compound at 25°C is 200 Pa s or less. The viscosity is a value measured using an E-type viscometer under the following conditions: temperature: 25°C, cone plate type: SPP, cone angle: 1°34', and rotation speed: 2.5 rpm. As the E-type viscometer, for example, a TV-33 viscometer manufactured by Toki Sangyo Co., Ltd. can be used.

[0143] When an epoxy group-containing compound that is liquid at 25°C is used, the amount of volatile components, such as organic solvents, typically used to achieve fluidity can be significantly reduced. In one embodiment, a paste that does not contain organic solvents can be formed. Furthermore, the magnetic powder content can be easily increased while maintaining appropriate fluidity as a paste. From these perspectives, the viscosity of the epoxy group-containing compound may be 100 Pa·s or less, 50 Pa·s or less, or 10 Pa·s or less.

[0144] The viscosity of the epoxy compound among the epoxy group-containing compounds may be lower than that of the liquid epoxy resin in order to adjust the paste viscosity. The viscosity of the epoxy compound may be 1 Pa s or less, 0.5 Pa s or less, or 0.1 Pa s or less.

[0145] The epoxy group-containing compound that is liquid at 25° C. may contain at least one selected from the group consisting of epoxy resins that are liquid at 25° C. and epoxy compounds that are liquid at 25° C. The content of the epoxy resin that is liquid at 25° C. may be 50% by mass or more, 70% by mass or more, 90% by mass or more, or 100% by mass based on the total mass of the epoxy group-containing compound.

[0146] The epoxy resin that is liquid at 25°C may contain, for example, at least one liquid epoxy resin selected from bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol AD ​​type epoxy resin, bisphenol S type epoxy resin, naphthalenediol type epoxy resin, hydrogenated bisphenol A type epoxy resin, and aminoglycidyl ether type epoxy resin.

[0147] Epoxy group-containing compounds that are liquid at 25°C are also available as commercial products. For example, they are sold by Nippon Steel Chemical Co., Ltd. as liquid bisphenol A type epoxy resin and liquid bisphenol F type epoxy resin. For example, a liquid bisphenol F type epoxy resin with the product name "YDF-8170C" (epoxy equivalent weight 165, viscosity 1,000 to 1,500 mPa·s) can be used. An example of an epoxy compound is the ADEKA GLYCIROL (product name) series manufactured by ADEKA Corporation. For example, a product with the product name "ADEKA GLYCIROL ED-503G" (epoxy equivalent weight 135, viscosity 15 mPa·s) can be used.

[0148] The paste may further contain other resins in addition to the epoxy group-containing compound. The other resins may include at least one selected from the group consisting of thermosetting resins (excluding epoxy resins) and thermoplastic resins. The thermosetting resin may be, for example, at least one selected from the group consisting of phenolic resins, acrylic resins, polyimide resins, and polyamide-imide resins. When a phenolic resin is used in addition to the epoxy group-containing compound, the phenolic resin can also function as a curing agent for the epoxy group-containing compound.

[0149] The thermoplastic resin may be, for example, at least one selected from the group consisting of acrylic resin, polyethylene, polypropylene, polystyrene, polyvinyl chloride, and polyethylene terephthalate. The resin component may further contain a silicone resin in addition to the epoxy group-containing compound.

[0150] When the paste contains a resin other than the epoxy group-containing compound, it is preferable to adjust the content of the other resin within a range that does not reduce the effect of the epoxy group-containing compound. For example, the content of the other resin may be 50% by mass or less, 30% by mass or less, or 10% by mass or less, based on the total mass of the resins in the paste. The blending amount can be adjusted so that the viscosity of the mixture of the epoxy group-containing compound and the other resin is 50 Pa s or less at 25°C. The viscosity is measured using an E-type viscometer under the following conditions: temperature: 25°C, cone-plate type: SPP, cone angle: 1°34', and rotation speed: 2.5 rpm. As the E-type viscometer, for example, a TV-33 viscometer manufactured by Toki Sangyo Co., Ltd. can be used.

[0151] The curing agent can be a compound that imparts appropriate viscosity to the paste and reacts with the epoxy group of the epoxy group-containing compound to form a cured product. Well-known curing agents commonly used as curing agents for epoxy resins can be used. Examples of curing agents include phenol-based curing agents, acid anhydride-based curing agents, and amine-based curing agents.

[0152] Curing agents are classified into those that cure epoxy resins in a temperature range from low to room temperature and those that cure epoxy resins upon heating. Examples of curing agents that cure epoxy resins in a temperature range from low to room temperature include aliphatic polyamines, polyaminoamides, and polymercaptans. Examples of heat-curing curing agents include aromatic polyamines, acid anhydrides, phenolic novolac resins, and dicyandiamide (DICY). When a curing agent that cures epoxy resins in a temperature range from low to room temperature is used, the glass transition temperature of the cured epoxy resin tends to be low and the cured epoxy resin tends to be soft. As a result, the insulating magnetic layer formed from the paste also tends to be soft. From the viewpoint of improving the heat resistance and mechanical strength of the insulating magnetic layer, it is preferable that the curing agent include a heat-curing curing agent.

[0153] Among heat-curing curing agents, a liquid curing agent at 25°C can be used from the viewpoint of reducing the viscosity of the paste. As the liquid curing agent, for example, at least one selected from the group consisting of aliphatic polyamines, polymercaptans, aromatic polyamines, acid anhydrides, and imidazole-based curing agents can be used. As long as the increase in viscosity of the paste can be suppressed, a solid curing agent at 25°C may be used, or a liquid curing agent and a solid curing agent may be used in combination. As the solid curing agent, for example, dicyandiamide, tertiary amines, imidazole-based curing agents, and imidazoline-based curing agents can be used. The exemplified solid curing agents are polyfunctional or act catalytically, so they can function sufficiently even in small amounts.

[0154] The curing agent may include at least one selected from the group consisting of an amine-based curing agent, an imidazole-based curing agent, and an imidazoline-based curing agent. The curing agent may include at least an amine-based curing agent. The amine-based curing agent (more specifically, a tertiary amine), the imidazole-based curing agent, and the imidazoline-based curing agent may also be used as a curing accelerator in combination with other curing agents.

[0155] The amine curing agent may be a compound having at least two amino groups in the molecule. The amine curing agent includes at least one selected from the group consisting of aliphatic amines and aromatic amines. Examples of aliphatic amine compounds include diethylenetriamine, triethylenetetramine, n-propylamine, 2-hydroxyethylaminopropylamine, cyclohexylamine, and 4,4'-diamino-dicyclohexylmethane. Examples of aromatic amine compounds include 4,4'-diaminodiphenylmethane, 2-methylaniline, amine compounds represented by the following formula (1), and amine compounds represented by the following formula (2).

[0156]

[0157] The imidazole curing agent is a compound having an imidazole skeleton, and may be an imidazole compound in which hydrogen atoms in the molecule are substituted with substituents. The imidazole curing agent may be a compound having an imidazole skeleton, such as an alkyl group-substituted imidazole. Examples of imidazole curing agents include imidazole, 2-methylimidazole, 2-ethylimidazole, and 2-isopropylimidazole. As the imidazole curing agent, commercially available products such as "Curezol 2E4MZ" (2-ethyl-4-methylimidazole) manufactured by Shikoku Chemicals Corporation can be used.

[0158] The imidazoline curing agent is a compound having an imidazoline skeleton, and may be an imidazoline compound in which hydrogen atoms in the molecule are substituted with substituents. The imidazoline curing agent may be a compound having an imidazoline skeleton, such as an alkyl group-substituted imidazoline. Examples of imidazoline curing agents include imidazoline, 2-methylimidazoline, and 2-ethylimidazoline.

[0159] From the viewpoint of compatibility with epoxy resins that are liquid at 25°C and storage stability, the curing agent may contain an aromatic amine. The aromatic ring of the aromatic amine may have a substituent other than an amino group. For example, it may have an alkyl group having 1 to 5 carbon atoms, or an alkyl group having 1 or 3 carbon atoms. The number of aromatic rings in the aromatic amine may be one or two or more. When the number of aromatic rings is two or more, the aromatic rings may be bonded to each other by a single bond or via a linking group such as an alkylene group.

[0160] From the viewpoint of the viscosity of the paste, it is preferable that the curing agent contains a liquid aromatic amine. For example, at least one selected from the group consisting of the compound represented by the above formula (1) and the compound represented by the above formula (2) can be used.

[0161] Liquid aromatic amines that can be used as curing agents are also commercially available, such as those manufactured by Mitsubishi Chemical Corporation under the product name "Grade: jER Cure WA" and those manufactured by Nippon Kayaku Co., Ltd. under the product name "Kayahard AA."

[0162] The content of the curing agent in the paste can be set in consideration of the ratio between the number of equivalents of epoxy groups in the epoxy group-containing compound such as the epoxy resin and the number of equivalents of active groups in the curing agent. For example, the ratio of the curing agent to 1 equivalent of epoxy groups in the epoxy group-containing compound may be 0.5 to 1.5 equivalents, 0.9 to 1.4 equivalents, or 1.0 to 1.2 equivalents.

[0163] When the ratio of active groups in the curing agent is 0.5 equivalents or more, the amount of OH groups per unit weight of the epoxy resin after heat curing is reduced, thereby preventing a decrease in the curing rate of the epoxy resin. Furthermore, a decrease in the glass transition temperature of the resulting cured product and a decrease in the modulus of elasticity of the cured product can be prevented. Furthermore, a decrease in the insulating reliability of the cured product due to unreacted resin components in the binder resin can be prevented. On the other hand, when the ratio of active groups in the curing agent is 1.5 equivalents or less, a decrease in the mechanical strength of the insulating magnetic layer formed from the paste after heat curing can be prevented. Furthermore, a decrease in the insulating properties of the cured product due to unreacted curing agent can be prevented.

[0164] The paste may further include a curing accelerator as needed. The paste may include a magnetic powder, an epoxy group-containing compound, a curing agent, and a curing accelerator. In another embodiment, the paste may further include additives such as a coupling agent and a flame retardant in addition to the above components.

[0165] The curing accelerator is not limited to any compound capable of accelerating the curing reaction between the epoxy resin and the curing agent. Examples of curing accelerators include tertiary amines, imidazole-based curing accelerators, imidazoline-based curing accelerators, and phosphorus compounds. The compounds previously exemplified as imidazole-based curing agents and imidazoline-based curing accelerators may also be used as imidazole-based curing accelerators and imidazoline-based curing accelerators. Among liquid curing agents, when a liquid acid anhydride is used, a curing accelerator can be used in combination. The paste may contain one or more curing accelerators. The use of a curing accelerator improves the mechanical strength of the insulating magnetic layer formed from the paste and easily lowers the curing temperature of the paste.

[0166] The amount of the curing accelerator to be blended is not particularly limited as long as it is an amount that can achieve a curing acceleration effect. However, from the viewpoint of improving the curing property and fluidity of the paste when absorbing moisture, the amount of the curing accelerator to be blended may be 0.001 parts by mass or more relative to 100 parts by mass of the epoxy resin and curing agent combined. The amount of the curing accelerator to be blended may be 0.01 parts by mass or more, or may be 0.1 parts by mass or more. On the other hand, the amount of the curing accelerator to be blended may be 5 parts by mass or less, 4 parts by mass or less, or 3 parts by mass or less. When the amount of the curing accelerator to be blended is 0.001 parts by mass or more, a sufficient curing acceleration effect can be easily obtained. When the amount of the curing accelerator to be blended is 5 parts by mass or less, excellent storage stability can be easily obtained in the paste.

[0167] The use of a coupling agent improves the dispersibility of the magnetic powder in the paste and facilitates control of the paste viscosity. It also facilitates improved adhesion between the binder resin and the magnetic powder. Furthermore, it facilitates improved adhesion, flexibility, and mechanical strength of the insulating magnetic layer formed from the paste to the conductor wiring. The coupling agent may be, for example, at least one selected from the group consisting of silane-based compounds (silane coupling agents), titanium-based compounds, aluminum compounds (aluminum chelates), and aluminum / zirconium-based compounds. The silane coupling agent may be, for example, at least one selected from the group consisting of epoxysilane, mercaptosilane, aminosilane, alkylsilane, ureidosilane, acid anhydride-based silane, and vinylsilane. The silane coupling agent may also be an aminophenyl-based silane coupling agent. The paste may contain at least one of the above coupling agents, or may contain two or more of the above coupling agents.

[0168] To improve the environmental safety, recyclability, moldability, and cost of the paste, the paste may contain a flame retardant. The flame retardant may be, for example, at least one selected from the group consisting of bromine-based flame retardants, phosphorus-based flame retardants, hydrated metal compound-based flame retardants, silicone-based flame retardants, nitrogen-containing compounds, hindered amine compounds, organometallic compounds, and aromatic engineering plastics. The paste may contain one or more of the flame retardants listed above.

[0169] The paste may contain an organic solvent as needed. The organic solvent is not particularly limited. For example, an organic solvent capable of dissolving the binder resin may be used. The organic solvent may be, for example, at least one selected from the group consisting of acetone, methyl ethyl ketone, methyl isobutyl ketone, benzene, toluene, carbitol acetate, butyl carbitol acetate, cyclohexanone, and xylene. From the viewpoint of workability, the organic solvent may be liquid at room temperature (25°C). From the viewpoint of workability, the boiling point of the organic solvent may be 50°C or higher and 160°C or lower.

[0170] When the paste contains an organic solvent, the content thereof may be 5% by mass or less, 3% by mass or less, or 1% by mass or less, based on the total mass of the paste. The paste may be substantially free of organic solvent. In this specification, "substantially free" means that no organic solvent is intentionally added to the paste. Therefore, the paste may contain, for example, an organic solvent that was used during the production of the resin and remains in the resin.

[0171] The viscosity of the paste may be 1 Pa·s or more, 10 Pa·s or more, or 100 Pa·s or more. By adjusting the viscosity to 1 Pa·s or more, dripping after application can be suppressed, and the pattern shape can be easily prevented from collapsing after printing. In addition, settling of the magnetic powder in the paste can be suppressed, and the deterioration of application properties over time after stirring the paste can be easily improved. On the other hand, the viscosity of the paste may be 600 Pa·s or less, 400 Pa·s or less, or 200 Pa·s or less. By adjusting the viscosity to 600 Pa·s or less, the paste becomes fluid, and good application properties can be easily obtained.

[0172] When the paste is used in screen printing, the viscosity of the paste may be 10 Pa·s to 400 Pa·s, 50 Pa·s to 300 Pa·s, or 100 Pa·s to 250 Pa·s. Adjusting the viscosity within the above ranges can prevent the paste from passing through the openings in the plate during screen printing. The viscosity of the paste can be freely adjusted by the structure and properties of the epoxy group-containing compound, the structure and properties of the curing agent, and the combination and blending ratio of these, as well as the structure and blending ratio of additives such as a curing accelerator and a coupling agent. The paste may also contain additives such as a viscosity modifier, a thixotropic agent, and a dispersion stabilizer.

[0173] Although the embodiments have been described above, they are presented as examples and the present invention is not limited to the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims.

[0174] This international application claims priority based on Japanese Patent Application No. 2023-104222, filed on June 26, 2023, the entire contents of which are incorporated herein by reference.

[0175] REFERENCE SIGNS LIST 10 Wiring substrate 11 Conductor wiring 12 Substrate 13 Lower surface 14 Upper surface 15 Input terminal 16 Output terminal 20 Insulating layer 21 First main surface 22 Second main surface 30 Magnetic layer 40 Insulating layer 50 Conductor layer 101, 102 Wiring substrate

Claims

1. A wiring board comprising: a conductor wiring; an insulating layer having a first main surface to which a surface of the conductor wiring is in close contact and a second main surface opposite the first main surface; a magnetic layer located on the second main surface side of the insulating layer; and a conductor layer located on the opposite side of the insulating layer with respect to the magnetic layer, wherein the surface or the first main surface has an arithmetic mean roughness of 0.1 μm or more and 5.0 μm or less.

2. The wiring board according to claim 1, wherein the magnetic layer has a thickness of 0.1 μm or more and 100 μm or less.

3. The wiring board according to claim 1 or 2, wherein the magnetic layer has a relative permeability of 1.5 or more at a frequency of 30 GHz or more.

4. The wiring board according to claim 1, wherein the magnetic layer has a portion that is wider than the conductor wiring.

5. The wiring board according to claim 1, wherein the insulating layer has a portion that is the same thickness as the magnetic layer or that is thinner than the magnetic layer.

6. The wiring board according to claim 1, further comprising a second insulating layer between the magnetic layer and the conductor layer.