Resin film, resin-equipped copper foil, multilayer wiring board, coil structure, and magnetic device

Abstract

A resin film (100) comprising a core layer (2) and adhesive resin layers (1) which are respectively provided to both sides of the core layer (2), wherein: the adhesive resin layers (1) each comprise an adhesive resin composition that contains an epoxy resin; the dielectric breakdown strength of a cured product of the adhesive resin composition is not less than 300 kV / mm; the core layer (2) comprises a polyimide film; and the dielectric breakdown strength of the polyimide film is not less than 300 kV / mm.

Description

Resin film, resin-coated copper foil, multilayer wiring board, coil structure, and magnetic device

[0001] The present invention relates to a resin film, a resin-coated copper foil, a multilayer wiring board, a coil structure, and a magnetic device.

[0002] As an example of a thin transformer, which is one type of magnetic device, Patent Document 1 describes a thin transformer that includes a printed coil, a core made of a magnetic material, and a terminal base for mounting the printed coil and core. This thin transformer is characterized in that the surface where the conductor of the printed coil is exposed is covered with a heat-resistant resin.

[0003] Japanese Patent Application Publication No. 9-326316

[0004] However, in recent years, magnetic devices have been required to carry higher voltages and larger currents. However, when conventional prepreg (glass cloth substrate / epoxy resin) was used as the heat-resistant resin layer, it was not possible to achieve both sufficient thinness and sufficient voltage resistance. Furthermore, conventional prepreg had the problem of a high dielectric constant.

[0005] The present invention aims to provide a resin film that has excellent voltage resistance, a low dielectric constant, and allows for a thinner insulating layer, as well as a resin-coated copper foil, a multilayer wiring board, a coil structure, and a magnetic device that use the resin film.

[0006] According to the present invention, there are provided the following resin films, resin-coated copper foils, multilayer wiring boards, coil structures, and magnetic devices. [1] A resin film comprising a core layer and adhesive resin layers provided on both sides of the core layer, wherein the adhesive resin layer is made of an adhesive resin composition containing an epoxy resin, and the adhesive resin composition has a cured product with a dielectric breakdown strength of 300 kV / mm or more, and the core layer is made of a polyimide film, and the dielectric breakdown strength of the polyimide film is 300 kV / mm or more. [2] The resin film according to [1], wherein the ratio of the thickness of the adhesive resin layer to the thickness of the core layer is 1 / 2 or more and 4 or less. [3] A resin-coated copper foil comprising the resin film according to [1] or [2] and copper foil laminated on the resin film. [4] A multilayer wiring board comprising an insulating layer formed using the resin film according to [1] or [2]. [5] A coil structure comprising an insulating layer formed using the resin film according to [1] or [2]. [6] A magnetic device comprising an insulating layer formed using the resin film according to [1] or [2].

[0007] According to one aspect of the present invention, it is possible to provide a resin film that has excellent voltage resistance, a low dielectric constant, and allows for a thinner insulating layer, as well as a resin-coated copper foil, a multilayer wiring board, a coil structure, and a magnetic device that use the resin film.

[0008] FIG. 7 is a schematic view showing a resin film according to a first embodiment of the present invention. FIG. 7 is an explanatory view showing an example of a method for manufacturing a resin film according to a first embodiment of the present invention. FIG. 7 is an explanatory view showing an example of a method for manufacturing a resin film according to a first embodiment of the present invention. FIG. 7 is an explanatory view showing an example of a method for manufacturing a resin film according to a first embodiment of the present invention. FIG. 7 is an explanatory view showing an example of a method for manufacturing a resin film according to a first embodiment of the present invention. FIG. 7 is an explanatory view showing an example of a method for manufacturing a resin coated copper foil according to a first embodiment of the present invention. FIG. 7 is an explanatory view showing an example of a method for manufacturing a resin coated copper foil according to a first embodiment of the present invention. FIG. 7 is an explanatory view showing an example of a method for manufacturing a multilayer wiring board according to a first embodiment of the present invention. FIG. 7 is an explanatory view showing an example of a method for manufacturing a multilayer wiring board according to a first embodiment of the present invention. FIG. 7 is an explanatory view showing an example of a method for manufacturing a multilayer wiring board according to a first embodiment of the present invention. FIG. 7 is an explanatory view showing an example of a method for manufacturing a multilayer wiring board according to a second embodiment of the present invention. FIG. 7 is an explanatory view showing an example of a method for manufacturing a multilayer wiring board according to a second embodiment of the present invention. FIG. 7 is an explanatory view showing an example of a method for manufacturing a multilayer wiring board according to a third ...

[0009] [First embodiment] Hereinafter, the present invention will be described with reference to the drawings, taking an embodiment as an example. The present invention is not limited to the content of the embodiment. Note that in the drawings, some parts are illustrated enlarged or reduced in size for ease of explanation.

[0010] (Resin Film) As shown in FIG. 1 , the resin film 100 according to this embodiment includes a core layer 2, an adhesive resin layer 1, and a release film layer 3. The adhesive resin layer 1 is provided on each side of the core layer 2. The release film layer 3 is provided on the adhesive resin layer 1. When using the resin film 100, the release film layer 3 is peeled off from the adhesive resin layer 1. The adhesive resin layer 1 is made of an adhesive resin composition containing an epoxy resin. The cured product of this adhesive resin composition must have a dielectric breakdown strength of 300 kV / mm or more. The core layer 2 is made of a polyimide film. The dielectric breakdown strength of this polyimide film must be 300 kV / mm or more. The resin film 100 according to this embodiment has excellent withstand voltage, a low dielectric constant, and allows for a thinner insulating layer for the following reasons. That is, the resin film 100 includes a core layer 2 made of a polyimide film with a low dielectric constant and high dielectric breakdown strength. The cured product of the adhesive resin layer 1 also has high dielectric breakdown strength. Therefore, it has excellent withstand voltage and low dielectric constant. In addition, since the adhesive resin layer 1 contains an epoxy resin and has sufficient adhesiveness, it is possible to fabricate a multilayer wiring substrate 300 (see FIGS. 4A to 4D) using this resin film 100. Furthermore, since the resin film 100 has high dielectric breakdown strength, it can maintain its withstand voltage even when it is thin, allowing for a thinner film.

[0011] (Adhesive Resin Layer) The adhesive resin layer 1 is a layer made of an adhesive resin composition containing an epoxy resin. The dielectric breakdown strength of the cured product of this adhesive resin composition must be 300 kV / mm or more. If this dielectric breakdown strength is below the lower limit, the withstand voltage of the resin film 100 will be insufficient, and since a film thickness must be ensured to withstand the voltage, it will be difficult to reduce the thickness. From the same perspective, the dielectric breakdown strength of the cured product of the adhesive resin composition is preferably 320 kV / mm or more, more preferably 340 kV / mm or more. The adhesive resin layer 1 may be formed by applying a coating liquid for the adhesive resin composition and drying it. The adhesive resin composition may also be B-staged by heat. The coating liquid for the adhesive resin composition must contain an epoxy resin, and preferably contains an epoxy resin, an aromatic amine-based curing agent, and a solvent-soluble polyimide resin. By B-staging this adhesive resin composition, an adhesive resin layer 1 with sufficient fluidity and adhesiveness can be obtained. Furthermore, the coating liquid for the adhesive resin composition may contain a filler, a curing accelerator, a flame retardant, a solvent, and the like, as required.

[0012] Any epoxy resin having two or more glycidyl groups can be used. Suitable epoxy resins include bisphenol A epoxy resins, bisphenol F epoxy resins, novolac phenol epoxy resins, biphenyl epoxy resins, naphthalene epoxy resins, and dicyclopentadiene epoxy resins. These may be used alone or in combination of two or more.

[0013] The aromatic amine curing agent is not particularly limited as long as it has an aromatic group and an amino group and has the effect of promoting the curing of the epoxy resin when irradiated with light. Examples of the aromatic group include a phenyl group, a biphenyl group, and a fluorenyl group. Examples of aromatic amine curing agents include 4,4'-diaminodiphenylsulfone, 4,4'-bis(4-aminophenoxy)biphenyl, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, bis[4-(4-aminophenoxy)phenyl]sulfone, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, trimethylenebis(4-aminobenzoate), 3,3'-dimethyl-4,4'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, bis[4-(3-aminophenoxy)phenyl]sulfone, 9,9'-bis(4-aminophenyl)fluorene, and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane. These may be used alone or in combination of two or more.

[0014] When the number of moles of epoxy resin is 1, the amount of aromatic amine curing agent used is preferably 0.2 moles or more and 1.5 moles or less. If the amount used is above the lower limit, it tends to be easier to obtain an appropriate thermal expansion coefficient. On the other hand, if the amount used is below the upper limit, it tends to be easier to obtain an appropriate Tg and thermal expansion coefficient.

[0015] The solvent-soluble polyimide resin is a polyimide resin that is soluble in the solvent used to produce the adhesive resin composition according to this embodiment. Suitable solvent-soluble polyimide resins have a high Tg, a low thermal expansion coefficient, excellent film properties, a low dielectric constant, and a low dielectric loss tangent. Examples of solvent-soluble polyimide resins include fully imidized soluble polyimide resins obtained by reacting diaminotrimethylphenylindane with benzophenonetetracarboxylic dianhydride. This compound can improve adhesive strength without the use of an additional adhesion promoter. The number-average molecular weight (Mn) of the solvent-soluble polyimide resin is not particularly limited, but is preferably 10,000 to 50,000, and more preferably 12,000 to 20,000.

[0016] When the total amount of the epoxy resin and aromatic amine-based curing agent is taken as 100 parts by mass, the blending amount of the solvent-soluble polyimide resin is preferably 10 parts by mass or more and 100 parts by mass or less, and particularly preferably 15 parts by mass or more and 100 parts by mass or less. If the blending amount is equal to or more than the lower limit, the effect of improving adhesive strength and flexibility tends to be easily obtained. On the other hand, if the blending amount is equal to or less than the upper limit, the breaking strength of the film tends to be ensured.

[0017] Examples of fillers include silica, alumina, aluminum hydroxide, and magnesium hydroxide. These may be used alone or in combination of two or more. Examples of curing accelerators include imidazoles. These may be used alone or in combination of two or more. Examples of flame retardants include condensed phosphate esters, phosphazenes, polyphosphates, and HCA (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) derivatives. These may be used alone or in combination of two or more. Examples of solvents include NMP (N-methylpyrrolidone), diethylene glycol monomethyl ether acetate, cyclohexanone, and MEK (methyl ethyl ketone). These may be used alone or in combination of two or more.

[0018] The thickness of the adhesive resin layer 1 varies depending on the copper thickness of the wiring board to be bonded and is not particularly limited. For example, when the copper thickness of the wiring board is 25 μm, the thickness of the adhesive resin layer 1 is preferably 5 μm to 100 μm, more preferably 10 μm to 70 μm, even more preferably 15 μm to 50 μm, and particularly preferably 20 μm to 30 μm. If the thickness is equal to or less than the upper limit, the thickness of the resin film 100 can be made thinner. If the thickness is equal to or greater than the lower limit, the adhesiveness of the resin film 100 can be improved.

[0019] (Core Layer) The core layer 2 is a layer made of a polyimide film. The dielectric breakdown strength of this polyimide film must be 300 kV / mm or more. If this dielectric breakdown strength is below the lower limit, the withstand voltage of the resin film 100 will be insufficient, and since a film thickness must be ensured to withstand the voltage, it will be difficult to reduce the thickness. From the same perspective, the dielectric breakdown strength of the core layer 2 is preferably 340 kV / mm or more, and more preferably 370 kV / mm or more. This core layer 2 can improve the withstand voltage of the resin film 100 and reduce the dielectric constant. Furthermore, since this core layer 2 can maintain its withstand voltage even when made thin, it is possible to reduce the thickness of the resin film 100.

[0020] The thickness of the core layer 2 varies depending on the configuration of the wiring board to be bonded and is not particularly limited. For example, the thickness of the core layer 2 is preferably 5 μm or more and 100 μm or less, more preferably 7 μm or more and 50 μm or less, and particularly preferably 10 μm or more and 30 μm or less. If the thickness is equal to or less than the upper limit, the thickness of the resin film 100 can be made thinner. If the thickness is equal to or more than the lower limit, the insulation properties of the resin film 100 can be improved.

[0021] From the viewpoint of balancing the various physical properties of the resin film 100, such as the withstand voltage, dielectric constant, and adhesiveness, the ratio of the thickness of the adhesive resin layer 1 to the thickness of the core layer 2 (thickness of adhesive resin layer 1 / thickness of core layer 2) is preferably 1 / 2 or more and 4 or less, more preferably 2 / 3 or more and 4 or less, even more preferably 1 or more and 3 or less, and particularly preferably 3 / 2 or more and 5 / 2 or less.

[0022] (Release Film Layer) The release film layer 3 is a layer made of a release film provided on the adhesive resin layer 1. When using the resin film 100, the release film layer 3 can be peeled off from the adhesive resin layer 1 and used. In addition, a coating liquid for the adhesive resin composition can be applied to the release film layer 3 to form a film and bring it to a B-stage, so that the adhesive resin layer 1 can be easily formed. The release film layer 3 does not necessarily have to be provided. The release film layer 3 is a member that is provided as needed. Examples of release films include polyethylene terephthalate film (PET film) and polyethylene naphthalate film. The surface of the release film may be subjected to a release treatment.

[0023] (Method for Producing Resin Film) There are no particular limitations on the method for producing the resin film 100 according to this embodiment. For example, as shown in Figures 2A to 2C, the resin film 100 can be produced by a method including a film-forming step of applying a coating liquid for an adhesive resin composition onto a release film layer 3 to form a coating film 1b, a drying step of drying the coating film 1b formed in the film-forming step to form an adhesive resin layer 1 and obtain an adhesive laminate film, and a lamination step of sandwiching a core layer 2 between and laminating the two adhesive laminate films obtained in the drying step to obtain the resin film 100.

[0024] In the film-forming step, as shown in Fig. 2A, a coating liquid for the adhesive resin composition is applied onto the release film layer 3 to form a film. Apparatuses for applying the adhesive resin composition include a bar coater, a die coater, a curtain coater, a spray coater, a roll coater, and a screen printing machine. The coating thickness of the adhesive resin composition is preferably adjusted so that the thickness of the adhesive resin layer 1 falls within the aforementioned range.

[0025] In the drying step, as shown in FIG. 2B , the coating film 1b formed in the film-forming step is dried to form an adhesive resin layer 1, thereby obtaining an adhesive laminate film. The drying temperature is preferably 100°C or higher and 160°C or lower, more preferably 105°C or higher and 155°C or lower, and particularly preferably 110°C or higher and 150°C or lower. If this temperature is within the above range, the adhesive resin composition can be appropriately brought to a B-stage. The drying time is preferably 10 seconds or higher and 600 seconds or lower, more preferably 15 seconds or higher and 500 seconds or lower, and particularly preferably 30 seconds or higher and 500 seconds or lower. If this time is within the above range, the adhesive resin composition can be appropriately brought to a B-stage.

[0026] In the lamination step, as shown in FIG. 2C , the core layer 2 is sandwiched between two adhesive laminate films obtained in the drying step and laminated to obtain a resin film 100. Here, the core layer 2 is sandwiched between two adhesive laminate films with the release film layer 3 of the adhesive laminate film facing outward. Since the adhesive resin layer 1 has adhesive properties, the resin film 100 can be obtained. As the lamination, vacuum pressure lamination, vacuum roll lamination, roll lamination, and the like can be used. In this manner, the resin film 100 according to this embodiment can be produced.

[0027] (Resin-Coated Copper Foil) The resin-coated copper foil 200 according to this embodiment includes the resin film 100 according to this embodiment described above and a copper foil 4 laminated on the resin film 100. The resin-coated copper foil 200 can be produced, for example, as shown in Figures 3A and 3B, by a method including a release film removing step of removing a release film layer 3 from the resin film 100 and a laminating step of laminating a copper foil 4 onto the resin film 100 from which one release film layer 3 has been removed, thereby obtaining the resin-coated copper foil 200.

[0028] In the release film removing step, as shown in Fig. 3A, one release film layer 3 is removed from the resin film 100. The release film layer 3 is for protecting the adhesive resin layer 1 until use, and can be removed by peeling it off from the adhesive resin layer 1.

[0029] In the lamination step, as shown in Fig. 3B, a copper foil 4 is laminated to a resin film 100 from which one release film layer 3 has been removed, to obtain a resin-coated copper foil 200. From the resin film 100 from which one release film layer 3 has been removed, the adhesive resin layer 1 is exposed. The exposed adhesive resin layer 1 and the matte surface of the copper foil 4 are then placed in contact with each other and laminated. The lamination is as described above. Since the adhesive resin layer 1 has adhesive properties, a resin-coated copper foil 200 can be obtained.

[0030] (Multilayer Wiring Board) The multilayer wiring board 300 according to this embodiment includes an insulating layer formed using the resin film 100 according to the embodiment described above. As shown in Figures 4A to 4D, the multilayer wiring board 300 can be manufactured by a method including the following steps: a release film removing step of removing both release film layers 3 from the resin film 100; a lamination step of sandwiching the resin film 100, from which the release film layers 3 have been removed, between two copper foils 4 to obtain a copper-clad laminate; a heat curing step of subjecting the adhesive resin layer 1 of the copper-clad laminate obtained in the lamination step to a heat curing treatment to obtain a copper-clad laminate; and an etching step of etching the copper foil 4 of the copper-clad laminate so as to form wiring 41 in a predetermined pattern to obtain the multilayer wiring board 300.

[0031] In the release film removing step, as shown in FIG. 4A, both release film layers 3 are removed from resin film 100.

[0032] In the lamination step, as shown in Fig. 4B, the resin film 100 from which the release film layer 3 has been removed is sandwiched between two copper foils 4 to obtain a copper clad laminate. It is preferable that one side of the copper foil 4 is matte. It is also preferable that the two copper foils 4 are arranged so that the matte sides of the two copper foils 4 face each other. Here, the resin film 100 from which the release film layer 3 has been removed is sandwiched between the two copper foils 4 and laminated. The lamination is as described above. Since the adhesive resin layer 1 has adhesive properties, a copper clad laminate can be obtained.

[0033] In the thermal curing step, as shown in FIG. 4C , the adhesive resin layer 1 of the copper clad laminate obtained in the lamination step is subjected to a thermal curing treatment to obtain a copper clad laminate substrate. The thermal curing treatment transforms the adhesive resin layer 1 into a cured resin layer 1a consisting of a cured product of the adhesive composition. Examples of the thermal curing treatment include a thermocompression bonding treatment and a heat treatment. The thermal curing treatment may be a one-stage treatment or a two-stage or more treatment. The temperature of the thermal curing treatment is preferably 130°C or higher and 200°C or lower, and more preferably 150°C or higher and 190°C or lower. The pressure of the thermal curing treatment is preferably 0.1 MPa or higher and 10 MPa or lower, and more preferably 0.5 MPa or higher and 4 MPa or lower. The time of the thermal curing treatment is preferably 0.5 hours or higher and 4 hours or lower, and more preferably 1 hour or higher and 3 hours or lower.

[0034] 4D , in the etching step, the copper foil 4 of the copper-clad laminate substrate is etched to form wiring 41 of a predetermined pattern, thereby obtaining a multilayer wiring substrate 300. To form the wiring 41 of the predetermined pattern, for example, an etching resist may be used. Specifically, the wiring 41 of the predetermined pattern can be formed by forming a pattern of etching resist on the copper foil 4 and then performing an etching process.

[0035] In this manner, the multilayer wiring board 300 according to this embodiment can be fabricated. The multilayer wiring board 300 is a wiring board with a two-layer structure having two layers of wiring 41.

[0036] Second Embodiment Next, a second embodiment of the present invention will be described with reference to the drawings. Description of the same configuration as in the first embodiment will be omitted. The multilayer wiring board 300A according to this embodiment is a four-layer wiring board having four layers of wiring 41, as shown in FIG. 5C . The multilayer wiring board 300A can be manufactured, for example, as shown in FIGS. 5A to 5C , by a method including the following steps: preparing two multilayer wiring boards 300 and one resin film 100; removing the release film layer 3 from the resin film 100; sandwiching the resin film 100 from which the release film layer 3 has been removed between the two multilayer wiring boards 300 to obtain a wiring laminate; and subjecting the adhesive resin layer 1 of the wiring laminate obtained in the lamination step to a heat curing treatment to obtain the multilayer wiring board 300A.

[0037] In the release film removing step, as shown in FIG. 5A, two multilayer wiring substrates 300 and one resin film 100 are prepared, and the release film layer 3 is removed from the resin film 100.

[0038] In the lamination process, as shown in FIG. 5B , the resin film 100 from which the release film layer 3 has been removed is sandwiched between two multilayer wiring substrates 300 to obtain a wiring laminate. Here, the resin film 100 from which the release film layer 3 has been removed is sandwiched between two multilayer wiring substrates 300 and laminated. The lamination is as described above. Since the adhesive resin layer 1 has adhesive properties, a copper-clad laminate can be obtained. Note that the thickness of the adhesive resin layer 1 is preferably greater than the thickness of the wiring 41 of the multilayer wiring substrate 300. With this configuration, the wiring 41 can be embedded in the adhesive resin layer 1.

[0039] 5C, in the heat curing step, the adhesive resin layer 1 of the wiring laminate obtained in the lamination step is subjected to a heat curing treatment to obtain a multilayer wiring substrate 300A. The adhesive resin layer 1 becomes a cured resin layer 1a made of a cured product of the adhesive composition by the heat curing treatment. The heat curing treatment is as described above.

[0040] In this manner, the multilayer wiring board 300A according to this embodiment can be fabricated. This multilayer wiring board 300A is a four-layer wiring board having four layers of wiring 41. Furthermore, a wiring board having an even number of layers, that is, six or more layers, can be fabricated by applying the manufacturing method for the multilayer wiring board 300A according to this embodiment.

[0041] Third Embodiment Next, a third embodiment of the present invention will be described with reference to the drawings. Description of components similar to those of the first embodiment will be omitted. The multilayer wiring board 300B according to this embodiment is a three-layer wiring board having three layers of wiring 41, as shown in FIG. 6D . The multilayer wiring board 300B can be manufactured, for example, as shown in FIGS. 6A to 6D , by a method including the following steps: preparing one multilayer wiring board 300 and one resin-coated copper foil 200; removing the release film layer 3 from the resin-coated copper foil 200; laminating the resin-coated copper foil 200 from which the release film layer 3 has been removed onto the multilayer wiring board 300 to obtain a copper foil-coated wiring laminate; subjecting the adhesive resin layer 1 of the copper foil-coated wiring laminate obtained in the lamination step to a heat curing treatment to obtain a copper foil-coated wiring laminate; and etching the copper foil 4 of the copper foil-coated wiring laminate to form wiring 41 in a predetermined pattern, thereby obtaining the multilayer wiring board 300B.

[0042] In the release film removing step, as shown in FIG. 6A, one multilayer wiring substrate 300 and one resin-coated copper foil 200 are prepared, and the release film layer 3 is removed from the resin-coated copper foil 200.

[0043] In the lamination step, as shown in Fig. 6B, the resin-coated copper foil 200 from which the release film layer 3 has been removed is laminated onto a multilayer wiring substrate 300 to obtain a wiring laminate with copper foil. The adhesive resin layer 1 is exposed from the resin-coated copper foil 200 from which the release film layer 3 has been removed. The exposed adhesive resin layer 1 and the multilayer wiring substrate 300 are then placed in contact with each other and laminated. The lamination is as described above. Since the adhesive resin layer 1 has adhesive properties, a wiring laminate with copper foil can be obtained.

[0044] In the heat curing step, as shown in Fig. 6C, the adhesive resin layer 1 of the copper foil-attached wiring laminate obtained in the lamination step is subjected to a heat curing treatment to obtain a copper foil-attached wiring laminate substrate. The adhesive resin layer 1 is converted by the heat curing treatment into a cured resin layer 1a made of a cured product of the adhesive composition. The heat curing treatment is as described above.

[0045] In the etching step, as shown in Fig. 6D, the copper foil 4 of the copper foil-attached wiring laminated substrate is etched so as to form wiring 41 of a predetermined pattern, thereby obtaining a multilayer wiring substrate 300B. The etching is performed as described above.

[0046] In this manner, the multilayer wiring board 300B according to this embodiment can be fabricated. This multilayer wiring board 300B is a three-layer wiring board having three layers of wiring 41. Furthermore, a wiring board having an odd number of layers, that is, five or more layers, can be fabricated by applying the manufacturing method for the multilayer wiring board 300B according to this embodiment.

[0047] Fourth Embodiment Next, a fourth embodiment of the present invention will be described with reference to the drawings. Note that a description of the same configuration as in the first embodiment will be omitted. The coil structure and magnetic device according to this embodiment include an insulating layer formed using the resin film 100 according to the embodiment described above. That is, as shown in FIGS. 7 and 8, the magnetic device 400 according to this embodiment includes a multilayer wiring substrate 300A and a core 5. The multilayer wiring substrate 300A has a coil-shaped pattern of wiring 41 formed thereon. Thus, the multilayer wiring substrate 300A constitutes the coil structure according to this embodiment. The multilayer wiring substrate 300A has a hole in its center, into which the core 5 is inserted. Known cores can be used as the core 5, including magnetic materials such as ferrite, powder magnetic cores, and laminated steel sheets.

[0048] [Modifications of the Embodiments] The present invention is not limited to the above-described embodiments, and includes modifications and improvements within the scope of achieving the object of the present invention. For example, in the above-described embodiments, the multilayer wiring boards 300, 300A, and 300B are wiring boards with two to four layers of wiring 41, but are not limited to this. For example, the multilayer wiring board may be a wiring board with a layer structure having five or more layers.

[0049] Next, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples in any way.

[0050] Preparation Example 1 A mixture consisting of 453 parts by mass of bisphenol A-type epoxy resin "Epiclon 850-S" (manufactured by DIC Corporation, epoxy equivalent: 188), 247 parts by mass of aromatic amine-based curing agent "BAPP" (manufactured by Wakayama Seika Kogyo Co., Ltd., 2,2-bis[4-(4-aminophenoxy)phenyl]propane), 1500 parts by weight of soluble polyimide resin "Q-VR-X0163" (manufactured by PI Technical Research Institute Co., Ltd., resin solids content: 20% by mass), and 0.7 parts by mass of 2-ethyl-4-methylimidazole was prepared, and a resin varnish with a resin solids content of 46% by mass was prepared.

[0051] Example 1 The resin varnish obtained in Preparation Example 1 was applied to a release film (a PET film subjected to a release treatment) and dried at 110°C for 300 seconds to produce a PET film with an adhesive resin layer. The adhesive resin layer had a thickness of 25 μm. Two PET films with adhesive resin layers were arranged with the adhesive resin layers facing each other, and a core layer (polyimide film, thickness: 12.5 μm) was sandwiched between them. The films were then laminated using a roll laminator at a peak actual temperature of 111°C and a roll speed of 0.35 m / min to produce a resin film.

[0052] [Example 2] After removing one of the release films from the resin film obtained in Example 1, the matte side of an electrolytic copper foil (thickness: 35 µm) was laminated to the removed surface under the conditions of a peak actual temperature of 111°C and a roll speed of 0.35 m / min to produce a resin-coated copper foil.

[0053] [Example 3] Two sheets of electrolytic copper foil (thickness: 35 μm) were prepared, and these two sheets of electrolytic copper foil were arranged with their matte surfaces facing each other. Then, both release films were removed from the resin film obtained in Example 1, and the film was sandwiched between the two sheets of electrolytic copper foil and subjected to a heat press treatment to produce a double-sided copper-clad laminate. The heat press treatment conditions were as follows: a first stage was performed at a set temperature of 150°C and a pressure of 0.5 MPa for 30 minutes, and a second stage was performed at a set temperature of 190°C and a pressure of 2 MPa for 70 minutes. A multilayer wiring board was obtained by etching the copper foil of the double-sided copper-clad laminate into a predetermined pattern.

[0054] [Comparative Example 1] Two sheets of electrolytic copper foil (thickness: 35 μm) were prepared, and these two sheets of electrolytic copper foil were arranged with their matte surfaces facing each other. Then, two sheets of prepreg (thickness: 100 μm, "R-1551" manufactured by Panasonic Industries Co., Ltd.) were prepared, and the two prepregs were stacked and sandwiched between the two sheets of electrolytic copper foil, followed by a heat press treatment to produce a double-sided copper-clad laminate. The heat press treatment conditions were as follows: a first stage was performed at a set temperature of 130°C and a pressure of 1.0 MPa for 30 minutes, and a second stage was performed at a set temperature of 180°C and a pressure of 2.0 MPa for 90 minutes.

[0055] Comparative Example 2 A double-sided copper-clad laminate was obtained in the same manner as in Comparative Example 1, except that three prepregs were used.

[0056] [Evaluation of Multilayer Wiring Board] Evaluation of the multilayer wiring board (withstand voltage (dielectric breakdown strength and breakdown voltage of the insulating material), thickness, and relative dielectric constant) was performed using the following method. The obtained results are shown in Table 1. The layer configurations of the insulating material in Example 3 and Comparative Examples 1 and 2 are also shown in Table 1. (1) Withstand Voltage The copper foil of the obtained double-sided copper-clad laminate was completely etched to prepare an insulating material sample. The polyimide film used in the example was used as the core layer sample. The adhesive resin layer used in the example was cured under the same conditions as in Example 3 to prepare the cured resin layer sample. A voltage of 0.5 kV / sec was applied to the obtained sample in the thickness direction over a predetermined area, and the conductive voltage was measured using a "Super High Voltage Withstand Voltage Tester Model 7472" manufactured by Keisoku Gijutsu Kenkyusho Co., Ltd., to calculate the dielectric breakdown strength and dielectric breakdown voltage. (2) Thickness The copper foil of the obtained double-sided copper-clad laminate was completely etched to prepare a sample. The thickness of this sample was measured using a vernier caliper. (3) Dielectric Constant The copper foil of the obtained double-sided copper-clad laminate was completely etched, and then processed into a sample having a size of 20 mm × 20 mm and a thickness of 200 μm. The dielectric constant of the obtained sample at 1 MHz was measured using a measuring device (Keysight RF Impedance / Material Analyzer, Model 4291B, 1.8 GHz).

[0057]

[0058] As is clear from the results shown in Table 1, the multilayer wiring board according to the present invention (Example 3) was confirmed to have good results in terms of withstand voltage, thickness, and dielectric constant. In contrast, the multilayer wiring board using two prepregs (Comparative Example 1) had a breakdown voltage of 20 kV, which was lower than the target of 21 kV, and also had a high dielectric constant. Furthermore, the multilayer wiring board using three prepregs (Comparative Example 2) had an insulating material thickness of 300 μm, which was too thick, and also had a high dielectric constant. Therefore, it was confirmed that the resin film according to the present invention has excellent withstand voltage, a low dielectric constant, and allows for a thinner insulating layer.

[0059] REFERENCE SIGNS LIST 1 adhesive resin layer 1a cured resin layer 1b coating film 2 core layer 3 release film layer 4 copper foil 41 wiring 5 core 100 resin film 200 resin-coated copper foil 300, 300A, 300B multilayer wiring board 400 magnetic device

Claims

1. A resin film comprising a core layer and adhesive resin layers provided on both sides of the core layer, wherein the adhesive resin layer is made of an adhesive resin composition containing an epoxy resin, and the cured product of the adhesive resin composition has a dielectric breakdown strength of 300 kV / mm or more, and the core layer is made of a polyimide film, and the dielectric breakdown strength of the polyimide film is 300 kV / mm or more.

2. A resin film according to claim 1, wherein the ratio of the thickness of said adhesive resin layer to the thickness of said core layer is 1 / 2 or more and 4 or less.

3. A resin-coated copper foil comprising the resin film according to claim 1 or 2 and copper foil laminated on the resin film.

4. A multilayer wiring board comprising an insulating layer formed using the resin film according to claim 1 or 2.

5. A coil structure comprising an insulating layer formed using the resin film according to claim 1 or 2.

6. A magnetic device comprising an insulating layer formed using the resin film according to claim 1 or 2.

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