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

Abstract

Provided is a resin film (100) comprising a core layer (2) and adhesive resin layers (1) provided on both surfaces of the core layer (2), wherein each adhesive resin layer (1) is constituted from an adhesive resin composition, and the minimum viscosity of the adhesive resin composition from 40°C to 160°C as measured by a rheometer is 500 Pa·s or more.

Description

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

[0001] The present invention relates to a resin film, a multilayer wiring board, a resin-coated copper foil, 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. Therefore, to ensure the insulation of the heat-resistant resin layer, it has been considered to use an interlayer insulating material with a three-layer structure including a core layer and adhesive resin layers on both sides of the core layer. However, it has been found that when a multilayer wiring board using such an interlayer insulating material is subjected to a reflow process, delamination may occur.

[0005] The present invention aims to provide a resin film that can suppress the occurrence of delamination even when subjected to high-temperature heat treatment, as well as a multilayer wiring board, a resin-coated copper foil, 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, multilayer wiring boards, resin-coated copper foils, 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 layers are made of an adhesive resin composition, and the adhesive resin composition has a minimum viscosity of 500 Pa s or more at temperatures from 40°C to 160°C, as measured with a rheometer. [2] The resin film according to [1], wherein the adhesive resin composition contains an epoxy resin, an aromatic amine-based curing agent, and a solvent-soluble polyimide resin. [3] The resin film according to [1] or [2], wherein the core layer is made of a polyimide film. [4] The resin film according to any one of [1] to [3], wherein the adhesive resin composition has a viscosity of 5 x 10 at 60°C, as measured with a rheometer. ５ [1] A resin film having a viscosity of 100 Pa·s or more. [5] A multilayer wiring board comprising an insulating layer formed using the resin film according to any one of [1] to [4]. [6] A resin-coated copper foil comprising the resin film according to any one of [1] to [4] and copper foil laminated on the resin film. [7] A coil structure comprising an insulating layer formed using the resin film according to any one of [1] to [4]. [8] A magnetic device comprising an insulating layer formed using the resin film according to any one of [1] to [4].

[0007] According to the present invention, it is possible to provide a resin film that can suppress the occurrence of delamination even when subjected to high-temperature heat treatment, as well as a multilayer wiring board, a resin-coated copper foil, a coil structure, and a magnetic device that use the resin film.

[0008] FIG. 1 is a schematic diagram showing a resin film according to an embodiment of the present invention. FIG. 2 is an explanatory diagram showing an example of a method for producing a resin film according to an embodiment of the present invention. FIG. 3 is an explanatory diagram showing an example of a method for producing a resin film according to an embodiment of the present invention. FIG. 4 is an explanatory diagram showing an example of a method for producing a resin film according to an embodiment of the present invention. FIG. 5 is an explanatory diagram showing an example of a method for producing a multilayer wiring board according to an embodiment of the present invention. FIG. 6 is an explanatory diagram showing an example of a method for producing a multilayer wiring board according to an embodiment of the present invention. FIG. 7 is a graph showing the results of measuring the viscosity of the adhesive resin compositions of the resin films obtained in Example 1 and Comparative Example 1 at temperatures from 40°C to 170°C using a rheometer.

[0009] The present invention will be described below by taking an embodiment as an example and referring to the drawings. 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. Furthermore, the adhesive resin composition must have a minimum viscosity of 500 Pa·s or more at temperatures between 40° C. and 160° C., as measured with a rheometer. The reason why the resin film 100 according to this embodiment can suppress the occurrence of delamination even when subjected to high-temperature heat treatment is as follows. That is, the inventors speculated that the occurrence of delamination when a multilayer wiring substrate 200 (see FIG. 3C ) is produced using the resin film 100 is due to the influence of viscosity changes during curing of the adhesive resin composition. The adhesive resin composition becomes softer as the temperature increases, but also hardens as it cures due to heat. The present inventors have found that if the minimum viscosity at that time is too low, delamination occurs. As a result of extensive research, they have found that the occurrence of delamination can be suppressed by using an adhesive resin composition whose minimum viscosity at temperatures from 40°C to 160°C, as measured with a rheometer, is 500 Pa s or more.

[0011] The minimum viscosity at temperatures from 40°C to 160°C is preferably 1000 Pa·s or less, and particularly preferably 800 Pa·s or less. If the minimum viscosity is equal to or less than the upper limit, the adhesive properties of the adhesive resin composition can be improved. From the same viewpoint, the temperature at which the minimum viscosity is reached is preferably 130°C or more and 150°C or less, and more preferably 135°C or more and 145°C or less. Furthermore, the viscosity at a temperature of 60°C is 5×10 ５ Pa・s or more 5×10 ６ It is preferable that the viscosity is 1×10 Pa·s or less. ６ Pa・s or more 3×10 ６ It is particularly preferable that the viscosity is not more than Pa·s. If the viscosity is not less than the lower limit, the occurrence of delamination can be more reliably suppressed.

[0012] The viscosity of the adhesive resin layer 1 can be measured as follows. That is, first, an adhesive resin composition for the adhesive resin layer 1 is collected as a sample from the resin film 100. The collected adhesive resin composition is placed in a rheometer (device name "HAAKE MARS III", manufactured by Thermo Fisher Scientific), and the viscosity of the adhesive resin composition is measured when the temperature is changed from 40°C to 160°C while the plate is rotated left and right at a temperature rise rate of 2.5°C / min and a frequency of 1.0 Hz.

[0013] Methods for adjusting the minimum viscosity and degree of viscosity change of the adhesive resin composition to fall within the above-mentioned ranges include the following: The minimum viscosity and degree of viscosity change can be adjusted by changing the types or amounts of the resin and curing agent, or by changing the degree to which the adhesive resin composition is brought into a B-stage (semi-cured).

[0014] (Adhesive Resin Layer) The adhesive resin layer 1 is a layer made of an adhesive resin composition. 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 brought to a B-stage by heat. The coating liquid for the adhesive resin composition preferably contains an epoxy resin, an aromatic amine-based curing agent, and a solvent-soluble polyimide resin. By bringing this adhesive resin composition to a B-stage, the minimum viscosity can be easily adjusted to within the above-mentioned range. The coating liquid for the adhesive resin composition may also contain a filler, a curing accelerator, a flame retardant, a solvent, etc., as necessary.

[0015] Any epoxy resin having two or more glycidyl groups can be used. Suitable epoxy resins include bis-A type epoxy resins, bis-F type epoxy resins, novolac phenol type epoxy resins, biphenyl type epoxy resins, naphthalene type epoxy resins, and dicyclopentadiene type epoxy resins. These may be used alone or in combination of two or more.

[0016] 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.

[0017] When the number of moles of epoxy resin is 1, the amount of aromatic amine curing agent used is preferably 0.3 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] The thickness of the adhesive resin layer 1 varies depending on the copper thickness of the wiring substrate to be bonded and is not particularly limited. For example, when the copper thickness of the wiring substrate is 35 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 20 μm to 50 μm, and particularly preferably 30 μm to 40 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.

[0022] (Core Layer) The core layer 2 is a layer that forms the core at the center of the three-layer resin film 100. This core layer 2 prevents resin outflow and other problems during thermocompression bonding when using the resin film 100 to fabricate a multilayer wiring board or the like. The core layer 2 is preferably made of a resin film with excellent heat resistance. Examples of such resin films include polyimide films, polyetherimide films, polyamide films, polyamideimide films, polymethylpentene films, polyester films, polyetheretherketone films, liquid crystal polymer films, polyphenylene ether films, polyphenylene sulfide films, polyolefin films, syndiotactic polystyrene-based films, fluorine-based resin films, and cycloolefin polymer films. Among these, polyimide films are preferred from the viewpoint of their compatibility with the adhesive resin layer 1.

[0023] The thickness of the core layer 2 varies depending on the configuration of the wiring substrate to be joined 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 10 μm or more and 50 μm or less, and particularly preferably 20 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.

[0024] (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.

[0025] 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 laminating 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.

[0026] 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 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.

[0027] 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. Within this temperature range, the adhesive resin composition can be appropriately brought to a B-stage, and the minimum viscosity of the adhesive resin composition can be adjusted to a suitable range. 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. Within this time range, the adhesive resin composition can be appropriately brought to a B-stage, and the minimum viscosity of the adhesive resin composition can be adjusted to a suitable range.

[0028] In the lamination process, as shown in FIG. 2C , the core layer 2 is sandwiched between two adhesive laminate films obtained in the drying process 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.

[0029] [Multilayer Wiring Board] The multilayer wiring board 200 according to this embodiment includes an insulating layer formed using the resin film 100 according to this embodiment described above. This insulating layer has a three-layer structure, and can suppress the occurrence of delamination even when subjected to high-temperature heat treatment. The multilayer wiring board 200 can be manufactured, for example, as shown in FIGS. 3A to 3C , by a method including the following steps: a release film removal step of removing the release film layer 3 from the resin film 100; a lamination step of sandwiching the resin film 100 from which the release film layer 3 has been removed between two single-layer wiring boards 4 to obtain a wiring laminate; and a heat curing step of 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 200.

[0030] In the release film removing step, as shown in Fig. 3A, the 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.

[0031] In the lamination step, as shown in Fig. 3B, the resin film 100 from which the release film layer 3 has been removed is sandwiched between two single-layer wiring boards 4 to obtain a wiring laminate. The single-layer wiring board 4 includes a base material 41 and wiring 42. The single-layer wiring board 4 may be a double-sided board having wiring 42 on both sides, or may be a single-sided board. Here, the resin film 100 from which the release film layer 3 has been removed is sandwiched between the two single-layer wiring boards 4. Because the adhesive resin layer 1 has adhesive properties, a wiring laminate can be obtained.

[0032] In the thermal curing step, the adhesive resin layer 1 of the wiring laminate obtained in the lamination step is subjected to a thermal curing treatment to obtain the multilayer wiring substrate 200 shown in FIG. 3C . 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 150°C or higher and 200°C or lower, and more preferably 170°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.

[0033] In this manner, the multilayer wiring board 200 according to this embodiment can be fabricated. Even when electronic components are mounted on the wiring 42 of this multilayer wiring board 200 and a reflow process is performed, the occurrence of delamination can be suppressed.

[0034] [Resin-Coated Copper Foil] The resin-coated copper foil according to this embodiment (not shown) comprises the resin film 100 according to this embodiment (from which at least one release film layer 3 has been removed) and copper foil laminated on the resin film 100. This resin-coated copper foil allows another wiring to be built up on the wiring of a wiring board via an insulating layer. The copper foil may be laminated on one side of the resin film 100 or on both sides of the resin film 100.

[0035] [Coil Structure and Magnetic Device] The coil structure (not shown) according to this embodiment includes an insulating layer formed using the resin film 100 according to the embodiment described above. This coil structure can be fabricated by the same method as the multilayer wiring board 200 according to the embodiment described above. That is, the coil structure can be fabricated by using a wiring board having coil-shaped wiring as the single-layer wiring board 4. Furthermore, the magnetic device (not shown) according to this embodiment includes an insulating layer formed using the resin film 100 according to the embodiment described above. This magnetic device can be fabricated by the same method as the multilayer wiring board 200 according to the embodiment described above. That is, the coil structure can be fabricated by using a wiring board having coil-shaped wiring as the single-layer wiring board 4. The magnetic device according to this embodiment includes this coil structure and a core. A known core can be used, such as ferrite.

[0036] [Modifications of the Embodiments] The present invention is not limited to the above-described embodiments, and modifications or improvements within the scope of achieving the object of the present invention are included in the present invention. For example, in the above-described embodiment, the multilayer wiring board 200 is formed by bonding two single-layer wiring boards 4 using the resin film 100, but this is not limiting. For example, the multilayer wiring board 200 may include three or more single-layer wiring boards 4. Furthermore, the multilayer wiring board 200 may further include an FR-4 base material or the like on the outermost layer to improve strength.

[0037] 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.

[0038] 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.

[0039] [Example 1] The resin varnish obtained in Preparation Example 1 was applied onto 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 thickness of the adhesive resin layer was 36 μm. Two PET films with adhesive resin layers were placed with the adhesive resin layers facing each other, and a core layer (polyimide film, thickness: 25 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. Next, two FR-4 substrates (substrate thickness: 0.4 mm) with test patterns (copper foil thickness: 35 μm) were prepared. The two FR-4 substrates were placed with the test patterns facing each other. The release film was then removed from the resulting resin film, which was then sandwiched between the FR-4 substrates and subjected to a heat press treatment to produce a multilayer wiring board. The conditions for the heat press treatment were as follows: in the first stage, the temperature was set at 150° C. and the pressure was 0.5 MPa for 30 minutes; and in the second stage, the temperature was set at 190° C. and the pressure was 2 MPa for 70 minutes.

[0040] Comparative Example 1 A resin film and a multilayer wiring board were produced in the same manner as in Example 1, except that the lamination conditions in the roll laminator were changed to a peak actual temperature of 95° C. and a roll speed of 0.5 m / min.

[0041] [Evaluation of Resin Film] The resin film was evaluated (viscosity of adhesive resin composition, swelling after reflow) using the following method. The results are shown in Table 1. (1) Viscosity of Adhesive Resin Composition An adhesive resin composition for an adhesive resin layer was sampled from the obtained resin film. The sampled adhesive resin composition was placed in a rheometer (device name "HAAKE MARS III", manufactured by Thermo Fisher Scientific), and the viscosity of the adhesive resin composition was measured as the temperature was changed from 40°C to 170°C while the plate was rotated left and right at a heating rate of 2.5°C / min and a frequency of 1.0 Hz. The results are shown in Figure 4. The minimum viscosity (unit: Pa s) from 40°C to 160°C and the temperature at that time were also read from the graph shown in Figure 4. The viscosity (unit: Pa s) at a temperature of 60°C was also read. (2) Blistering after reflow The obtained multilayer wiring board was placed in a reflow furnace (manufactured by Tamura Corporation) and subjected to a reflow process. The reflow conditions were a preheat temperature of 140°C to 160°C (approximately 120 seconds), a time at a temperature of 220°C or higher for approximately 100 seconds, and a peak temperature of 260°C. The multilayer wiring board after reflow was then observed, and the blistering after reflow was evaluated according to the following criteria: A: No blistering occurred. C: Blistering occurred.

[0042]

[0043] As is clear from the results shown in Table 1 and Fig. 4, it was confirmed that the results of the swelling after reflow were good when the minimum viscosity measured by a rheometer from 40°C to 160°C was 500 Pa s or more (Example 1). Therefore, it was confirmed that the resin film according to the present invention can suppress the occurrence of delamination even when subjected to high-temperature heat treatment.

[0044] DESCRIPTION OF SYMBOLS 1... adhesive resin layer 1a... cured resin layer 1b... coating film 2... core layer 3... release film layer 4... single-layer wiring board 41... substrate 42... wiring 100... resin film 200... multi-layer wiring board

Claims

1. A resin film comprising a core layer and an adhesive resin layer provided on each side of the core layer, the adhesive resin layer being made of an adhesive resin composition, the adhesive resin composition having a minimum viscosity of 500 Pa·s or more at temperatures from 40°C to 160°C, as measured using a rheometer.

2. The resin film according to claim 1, wherein the adhesive resin composition contains an epoxy resin, an aromatic amine-based curing agent, and a solvent-soluble polyimide resin.

3. The resin film according to claim 1 or 2, wherein the core layer is made of a polyimide film.

4. The resin film according to claim 1 or 2, wherein the adhesive resin composition has a viscosity of 5×10 at 60° C. as measured by a rheometer. ５ A resin film having a viscosity of Pa·s or more.

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

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

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

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

Images