JP7223569B2 - Adhesive film, adhesive composition and flexible printed circuit board - Google Patents

Description

TECHNICAL FIELD The present invention relates to an adhesive film containing fluororubber, an adhesive composition, and a flexible printed circuit board using the adhesive film or adhesive composition.

As an adhesive composition for printed wiring boards, generally, one containing a thermosetting resin such as an epoxy resin as a main component is used (for example, Patent Document 1). It has also been proposed to use a fluororubber and mix it with an epoxy resin (for example, Patent Document 2).

Japanese Patent No. 3175338 Japanese Patent No. 3555354

However, it has been found that when fluororubber is used, the workability of the printed wiring board is reduced due to the low elastic modulus and high elongation of the fluororubber.
An object of the present invention is to solve the above problems.
That is, it is an object of the present invention to provide an adhesive film and an adhesive composition which contain a fluororubber and a thermosetting resin and have good workability when used for printed wiring boards.

As a result of intensive studies, the inventors have found that the above problems can be solved by the following.
That is, the present invention is as follows.
An adhesive film in which an adhesive layer is laminated on a resin film layer,
The adhesive layer is composed of an adhesive composition containing a fluororubber having an unsaturated bond, a thermosetting resin, and an inorganic filler,
The adhesive layer is in a B-stage state,
The content of the thermosetting resin is 8 parts by mass to 120 parts by mass with respect to 100 parts by mass of the fluororubber having the unsaturated bond,
An adhesive film, wherein the adhesive layer has an elastic modulus of 15 MPa or more and an elongation at break of less than 400%, as measured in accordance with JIS7127 (1999).
The present invention also provides an adhesive composition containing a fluororubber having an unsaturated bond, a thermosetting resin, and an inorganic filler,
The content of the thermosetting resin is 8 parts by mass to 120 parts by mass with respect to 100 parts by mass of the fluororubber having unsaturated bonds.

According to the present invention, it is possible to provide an adhesive film and an adhesive composition that contain a fluororubber and a thermosetting resin and have good workability when used for printed wiring boards. Moreover, according to the present invention, a flexible printed circuit board using the adhesive film or adhesive composition can be provided.

In the present invention, descriptions such as "○○ or more and △▲ or less" and "○○ to △▲" indicating a numerical range are ranges including the lower limit and the upper limit, which are endpoints, unless otherwise specified.
The present invention relates to an adhesive film in which an adhesive layer is laminated on a resin film layer,
The adhesive layer is composed of an adhesive composition containing a fluororubber having an unsaturated bond, a thermosetting resin, and an inorganic filler,
The adhesive layer is in a B-stage state,
The content of the thermosetting resin is 8 parts by mass to 120 parts by mass with respect to 100 parts by mass of the fluororubber having the unsaturated bond,
The adhesive layer has an elastic modulus of 15 MPa or more and an elongation at break of less than 400%, as measured in accordance with JIS7127 (1999).

Each material used in the present invention will be described below.
<Fluorine rubber having unsaturated bond>
The adhesive composition used in the present invention contains fluororubber having unsaturated bonds such as double bonds. A fluororubber having an unsaturated bond can be obtained by introducing an unsaturated bond into a fluororubber by a known method. For example, a method using base denaturation such as alkali denaturation can be used.
By using a fluororubber having an unsaturated bond such as a double bond, a cross-linking point derived from the unsaturated bond can be imparted to the fluororubber, so that a three-dimensional structure can be obtained after curing. Therefore, the adhesive strength at high temperatures, the solder heat resistance, and the adhesive strength after a long-term high-temperature endurance test are improved.

Preferably, the fluororubber having an unsaturated bond is a polymer or copolymer of at least one monomer selected from the group consisting of vinyl fluoride, vinylidene fluoride, hexafluoropropene, tetrafluoroethylene, and the like. Examples include unsaturated bond introductions. More preferably, it is a copolymer of at least one monomer selected from the group consisting of vinylidene fluoride, hexafluoropropene, tetrafluoroethylene, and the like, into which an unsaturated bond is introduced. The copolymer is preferably a copolymer or terpolymer, more preferably a copolymer.
Fluorinated olefins such as ethylene, propylene, alkyl vinyl ether, hexafluoroisobutene and vinyl acetate, olefins, vinyl compounds, and the like may be copolymerized in the copolymer to the extent that the effects of the present invention are not impaired.
Specifically, for example, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropene copolymer, tetrafluoroethylene-hexafluoropropene copolymer, chlorofluoro Unsaturated bond-introduced materials such as ethylene-vinylidene fluoride copolymers can be mentioned.
Preferably, it is a vinylidene fluoride-hexafluoropropene copolymer having an unsaturated bond introduced therein, and the copolymerization ratio (vinylidene fluoride: hexafluoropropene) is preferably 3:7 to 9.5:0 on a mass basis. .5, more preferably 5:5 to 9:1.

The Mooney viscosity (ML ₁₊₁₀ (121° C.)) of the fluororubber having unsaturated bonds is preferably 40-110. Within the above range, the sheet workability is excellent, and the elastic modulus and elongation are within appropriate ranges. And the workability in the B-stage state is improved. Mooney viscosity (ML ₁₊₁₀ (121° C.)) is more preferably 50-100.
The Mooney viscosity can be controlled by, for example, the molecular weight of the material. For example, higher molecular weights can lead to higher Mooney viscosities.
Mooney viscosity is measured according to JIS K 6300-1 (2013). Using a Mooney Viscometer SMV-201 (manufactured by Shimadzu Corporation), the viscosity is measured at a temperature of 121° C. under the conditions of a preheating time of 1 minute and a rotor rotation time of 10 minutes.

If necessary, these polymers or copolymers are treated with an alkaline solvent such as potassium hydroxide, sodium hydroxide, cesium hydroxide, calcium hydroxide, calcium carbonate, or triethylamine in the presence of a ketone solvent such as acetone or methyl ethyl ketone. Depending on the substance, treatment at a temperature of preferably about 20 to 70° C. can cause a dehydrofluorination reaction to form an unsaturated bond in the molecule.
The unsaturated bond content (-CH=CH- content) in the fluororubber having an unsaturated bond is preferably 0.1% by mass to 30% by mass, more preferably 0.5% by mass to 10% by mass. A commercially available fluororubber having an unsaturated bond can also be used.

<Thermosetting resin>
The adhesive composition contains a thermosetting resin. The thermosetting resin preferably has a softening point of 30° C. or higher. That is, it is preferably in a solid state at room temperature (25°C). The softening point is more preferably 30°C to 160°C, still more preferably 40°C to 160°C, still more preferably 50°C to 150°C, and particularly preferably 60°C to 130°C.
In the manufacturing process of a printed wiring board such as a flexible printed circuit board, processing such as drilling for component mounting may be required in the B-stage (semi-cured) state before hot pressing. By using a thermosetting resin that has a softening point in the above range and is in a solid state at room temperature, the mixing property with the fluororubber is improved, and combined with the effect of improving the elastic modulus of the inorganic filler described later, in the B stage state. The processability of is further improved.
The softening point of the resin can be measured by the ring and ball method of JIS K 7234. For the measuring device, for example, a Mettler softening point measuring device (FP900 thermo system) manufactured by Mettler Toledo Corporation can be used.

From the viewpoint of reactivity and heat resistance, the thermosetting resin is preferably a phenol resin, an epoxy resin, or a mixture of two or more of these.
Examples of epoxy resins include bisphenol-type epoxy resins such as bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, and bisphenol S-type epoxy resin; epoxy resins, alicyclic epoxy resins, aliphatic chain epoxy resins, diglycidyl-etherified biphenols, diglycidyl-etherified naphthalene diols, diglycidyl-etherified phenols, diglycidyl-etherified alcohols, and these are exemplified by alkyl-substituted products and hydrogenated products of One type of epoxy resin may be used alone, or two or more types may be mixed and used.

Phenolic resins are obtained by reacting phenols and aldehydes with acid or alkali as a catalyst.
Phenols include phenol, meta-cresol, para-cresol, ortho-cresol, isopropylphenol, nonylphenol and the like.
Examples of aldehydes include formaldehyde, paraformaldehyde, acetaldehyde, paraacetaldehyde, butyraldehyde, octylaldehyde, benzaldehyde and the like. Formaldehyde or paraformaldehyde are commonly used. In addition, a vegetable oil-modified phenolic resin can also be used. The vegetable oil-modified phenolic resin is obtained by reacting phenols and vegetable oil in the presence of an acid catalyst, and then reacting aldehydes in the presence of an alkali catalyst. Examples of acid catalysts include p-toluenesulfonic acid. Alkaline catalysts include amine-based catalysts such as ammonia, trimethylamine, and triethylamine.
As thermosetting resins, xylene resins, guanamine resins, diallyl phthalate resins, vinyl ester resins, unsaturated polyester resins, furan resins, polyimide resins, polyurethane resins, cyanate resins, maleimide resins, benzocyclobutene resins, etc. can be used. can also

The thermosetting resin preferably contains an epoxy resin, preferably an epoxy resin. The epoxy resin is preferably a cresol novolac type epoxy resin, more preferably an o-cresol novolac type epoxy resin. Commercially available epoxy resins may be used, such as YDCN700-10 (Nippon Steel & Sumikin Chemical Co., Ltd.) and N695 (DIC Corporation).
The content of the thermosetting resin must be 8 to 120 parts by mass with respect to 100 parts by mass of the fluororubber having unsaturated bonds. Within the above range, punching workability and adhesive strength at high temperatures are improved. The content is preferably 8 to 110 parts by mass, more preferably 8 to 100 parts by mass.

<Inorganic filler>
The adhesive composition used in the present invention contains an inorganic filler. A known material can be used for the inorganic filler. The inorganic filler is preferably electrically insulating.
For example, silica, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, calcium silicate, aluminum silicate, calcium carbonate, aluminum oxide, magnesium oxide, antimony oxide, tin oxide, titanium oxide, manganese oxide and zirconium oxide, silicon nitride , aluminum nitride, boron nitride, talc, mica, kaolin and the like.

Since the fluororubber has a low elastic modulus, it was found that burrs of the adhesive and adhesion of the adhesive to the processed portion occurred during processing in the B-stage state. On the other hand, by using an inorganic filler in the adhesive composition, the elastic modulus can be improved and the workability is improved.
The inorganic filler preferably has a thixotropic property that tends to aggregate to some extent to increase the elastic modulus. From such a point of view, silica, aluminum hydroxide, talc and the like are preferable. Silica is more preferred. Silica can be used without particular limitation, such as dry silica or wet silica. A commercially available silica can also be used. For example, Aerosil 200 (Nippon Aerosil Industry Co., Ltd.) can be used.

The inorganic filler may be hydrophobized. Hydrophobic treatment includes silicone oil treatment, silane coupling agent treatment, and the like.
The number average particle size of the primary particles of the inorganic filler is preferably 10 nm to 100000 nm, more preferably about 50 nm to 10000 nm.
The content of the inorganic filler is preferably 1 part by mass to 35 parts by mass, more preferably 1 part by mass to 30 parts by mass, and still more preferably 3 parts by mass to 25 parts by mass. Within the above range, in addition to workability, adhesiveness, soldering heat resistance, and high-temperature long-term durability are improved.

<Amine compound>
The adhesive composition may contain an amine compound as a curing agent. The amine compound is preferably an aromatic diamine compound from the viewpoint of curability.
Examples of aromatic diamine compounds include those represented by the following formula (I).

[In formula (I), R ¹ and R ² are each independently an alkyl group having 1 to 6 carbon atoms, R ³ is an alkylene group having 1 to 6 carbon atoms, an aromatic hydrocarbon group, a carbonyl group, It is at least one selected from the group consisting of a fluorene group, a sulfonyl group, an ether group and a sulfide group, and m and n are each an integer of 0 to 4. ]
Alkyl groups are preferably methyl, ethyl and propyl groups. From the viewpoint of curability, the alkyl group is more preferably a methyl group or an ethyl group.
The alkylene group preferably includes a methylene group and an ethylene group. From the viewpoint of curability, the alkylene group is more preferably a methylene group.

Each of m and n is preferably an integer of 0 to 2, more preferably 1 or 2, and even more preferably 2, from the viewpoint of superior storage stability and rapid curability.
In the formula, the configuration of —NH ² is preferably para to R ³ from the viewpoint of curability.
The aromatic hydrocarbon group is not particularly limited as long as it is divalent. Examples include phenylene. Aromatic hydrocarbon groups can have substituents such as, for example, methyl groups.

R ³ may be a substituent in which an aromatic hydrocarbon group and an alkylene group are combined, and the combination of the aromatic hydrocarbon group and the alkylene group is not particularly limited. Examples include an alkylene group having an aromatic hydrocarbon group. Specifically, for example, an aspect in which two alkylene groups are bonded via an aromatic hydrocarbon, an aspect in which an aromatic hydrocarbon is bonded as a side chain of the alkylene group, an aromatic hydrocarbon group and an alkylene group are bonded However, an embodiment in which an aromatic hydrocarbon group and an alkylene group are respectively bonded to two benzene rings represented by formula (I) is exemplified. Examples of aromatic hydrocarbons include benzene rings and naphthalene. Aromatic hydrocarbons can have substituents such as methyl groups.
Among the compounds represented by formula (I), 4,4'-methylenebis(2-ethyl-6-methylaniline) is particularly preferred.
The content of the amine compound is preferably 0.1 to 20 parts by mass, more preferably 1 to 10 parts by mass, per 100 parts by mass of the fluororubber having unsaturated bonds.

<Adhesive composition>
The adhesive composition of the present invention can be obtained by mixing a fluororubber having an unsaturated bond, a thermosetting resin, an inorganic filler, and optionally other additives such as an amine compound. When mixing, you may use an organic solvent as needed.
The adhesive composition of the present invention is preferably for use in manufacturing flexible printed circuit boards.
For example, an adhesive film can be obtained using the adhesive composition and used for the production of flexible printed circuit boards.

<Adhesive film>
The adhesive film of the present invention is an adhesive film in which an adhesive layer is laminated on a resin film layer, and the adhesive layer is composed of the adhesive composition described above. The resin film layer is not particularly limited, and known materials such as polyimide can be used.

The elastic modulus of the adhesive layer (or the elastic modulus when the adhesive composition is in a B-stage state (semi-cured state)) measured in accordance with the JIS7127 tensile property test method must be 15 MPa or more. is. Preferably, it is 20 MPa or more. Although the upper limit is not particularly limited, it is preferably 3000 MPa or less, more preferably 1000 MPa or less, and still more preferably 100 MPa or less.
In addition, the elongation at break of the adhesive layer (or the elongation at break when the adhesive composition is in a B-stage state (semi-cured state)) measured in accordance with JIS7127 (1999) Tensile property test method is 400. % must be less than Preferably less than 300%, more preferably less than 200%. Although the lower limit is not particularly limited, it is preferably 50% or more, more preferably 100% or more.
When the elastic modulus and the elongation at break are within the above ranges, workability is improved. The elastic modulus and elongation at break can be controlled by the softening point of the thermosetting resin, the Mooney viscosity of the fluororubber, the content of the inorganic filler, and the like.

An adhesive film can be manufactured by a well-known method. For example, an organic solvent solution of the adhesive composition is prepared and applied to a resin film layer such as polyimide to form an adhesive layer. Then, it is dried, for example, at 50° C. to 160° C. for 1 minute to 15 minutes to bring the adhesive layer into a B-stage state, thereby obtaining an adhesive film. After that, the obtained adhesive film can be attached to an adherend and cured by heating.
In the production of a flexible printed circuit board, a flexible printed circuit board having an adhesive layer containing a cured product of the adhesive composition is obtained by adhering in the same manner when the above adhesive composition is used for adhesion of a cover film, a carrier film, or the like. be able to. If necessary, drilling or the like can be performed between the B-stage state and the heat curing.

The method of obtaining the B-stage adhesive composition is not particularly limited, and known methods including the method of heat drying as described above can be employed.
The organic solvent is not particularly limited, and known ones can be used. Examples include acetone, methyl ethyl ketone, tetrahydrofuran, chloroform, dimethylformamide, methyl isobutyl ketone (MIBK), and the like. The amount of the organic solvent to be used is not particularly limited, but it may be used within the range of preferably 10% to 70% by mass, more preferably 20% to 40% by mass of solid content.

The configuration of the flexible printed circuit board is not particularly limited. The adhesive film of the present invention can be applied to a flexible printed circuit board having a known structure. Alternatively, an adhesive layer containing a cured product of the adhesive composition of the present invention can be applied to an adhesive layer in a flexible printed circuit board having a known configuration.
For example, a carrier film such as polyimide, an adhesive layer A laminated on one surface of the carrier film, a circuit made of copper foil or the like provided on the adhesive layer A, and a circuit formed on the circuit and the adhesive layer A a flexible printed circuit board having an adhesive layer B formed thereon and a cover film laminated on the adhesive layer B;
At least one or both of the adhesive layer A and the adhesive layer B are preferably adhesive layers containing a cured product of the adhesive composition of the present invention. Each thickness of the adhesive layer A and the adhesive layer B is preferably about 1 μm to 100 μm, more preferably about 10 μm to 50 μm.
Alternatively, the above adhesive film may be used in the production of flexible printed circuit boards. For example, the adhesive film can be used as a carrier film containing the adhesive layer A or a cover film containing the adhesive layer B. By doing so, it is possible to obtain a flexible printed circuit board including an adhesive film in which the adhesive layer contained in the adhesive film is cured.
Materials used for the carrier film, circuit, and cover film are not particularly limited, and known materials can be used. The method of manufacturing the flexible printed circuit board is also not particularly limited, and known methods can be employed.

The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the aspects of the following examples. In addition, in the following formulations, parts are based on mass unless otherwise specified.

First, the test method employed in the examples will be described.
(Adhesion test (23 ° C.))
The solution of the adhesive composition is applied to a polyimide film (Apical NPI manufactured by Kaneka Co., Ltd., thickness 12.5 μm) so that the thickness after drying is 20 μm, dried at 140 ° C. for 3 minutes with a hot air dryer, and semi-cured ( B stage) samples were obtained. The adhesive-applied surface of this B-stage sample and the black-treated surface of copper foil (BHY manufactured by JX Nikko Nisseki Co., Ltd., thickness 18 μm) were thermocompressed under reduced pressure at 160° C. and 3 MPa for 30 seconds using a vacuum press laminator. . After that, it was cured by heating at 160° C. for 10 hours.
The adhesive strength of the cured sample was measured by peeling off the polyimide film in a 90° direction at a rate of 50 mm/min in an atmosphere of 23°C using a tensile tester (Shimadzu Autograph).
A is given when the adhesive strength is 0.5 N/mm or more, B is given when 0.34 N/mm or more and less than 0.5 N/mm, and C is given when less than 0.34 N/mm.

(Adhesion test (150 ° C.))
In the above adhesion test, the polyimide film was peeled off at a speed of 50 mm/min in the direction of 90° C. in an atmosphere of 150° C., and the adhesion strength was measured.
A is given when the adhesive strength is 0.5 N/mm or more, B is given when 0.34 N/mm or more and less than 0.5 N/mm, and C is given when less than 0.34 N/mm.

(solder heat resistance)
A heat-cured sample was prepared in the same manner as in the adhesive evaluation, cut into 20 mm squares, and floated in a solder bath at 300° C. for 10 minutes with the polyimide surface facing up.
A was given when there was no swelling or peeling, B was when there was slight swelling or peeling, and C was when there was noticeable swelling or peeling.

(Adhesive strength after 150°C endurance test)
A sample prepared in the same manner as in the evaluation of adhesion was left in an atmospheric oven at 150° C. for 3000 hours, then allowed to cool at room temperature, and the peel strength was measured in the same manner as in the evaluation of adhesion.

(punching workability)
Using a polyimide film in which the adhesive composition was applied and dried to form a B-stage film, punching workability was evaluated. The punching was performed by shearing using a press machine. 100 round holes with a diameter of 5 mm were punched, the cross section of the punch was observed, and the number of holes with burrs of 100 μm or more was counted. The number of burrs was rated A when 0 to 3, rated B when 4 to 10, and rated C when 11 or more.

(Elastic modulus and elongation in B stage state)
The elastic modulus and elongation at break are measured according to JIS7127 (1999) (Plastics-Testing methods for tensile properties-Part 3: Test conditions for films and sheets). As an apparatus, Shimadzu Corporation desktop type precision universal testing machine AG-IS 10KN is used.
A solution of the adhesive composition obtained in each Example/Comparative Example was applied to a PET film coated with a silicone release agent so that the thickness after drying was 30 μm, and dried (140° C.). for 3 minutes with a hot air dryer). After drying, the adhesive layer composed of the adhesive composition in the B-stage state is peeled off from the PET film and evaluated as a sample. The evaluation is performed under the conditions of a tensile speed of 50 mm/min and a gauge length of 100 mm.

<Example 1>
・ Fluororubber A double bond modified (binary copolymer of vinylidene fluoride and hexafluoropropene (copolymerization ratio: vinylidene fluoride/hexafluoropropene = 8/2) alkali-modified product, Mooney viscosity: 98, Heavy bond content: 4% by mass) 100 parts Silica (fumed silica: Aerosil 200 (Nippon Aerosil Kogyo)) 5 parts Epoxy resin (solid softening point 95 ° C.) o-cresol novolak type epoxy resin (N695 (DIC Co., Ltd.)) 20 parts Amine compound (4,4′-methylenebis(2-ethyl-6-methylaniline) cure hard MED-J) 3 parts Using methyl ethyl ketone (MEK), the solid content is reduced to 30% by mass was dissolved to obtain an adhesive composition. Note that silica was dispersed using a bead mill.
Further, the obtained solution of the adhesive composition was applied to a polyimide film (Apical NPI manufactured by Kaneka Co., Ltd., thickness 12.5 μm) so that the thickness after drying was 20 μm, and dried with a hot air dryer at 140 ° C. for 3 minutes. to obtain a B-stage sample. The adhesive-applied surface of this sample and the black treated surface of copper foil (BHY manufactured by JX Nikko Nisseki Co., Ltd., thickness 18 μm) were thermocompressed under reduced pressure at 160° C. and 3 MPa for 30 seconds using a vacuum press laminator. After that, it was cured by heating at 160° C. for 10 hours, and a test sample of Example 1 was obtained. The above-mentioned evaluation was performed using the obtained test sample. Table 1 shows the results.

<Examples 2 to 11, Comparative Examples 1 to 6>
Adhesive compositions and test samples of Examples 2 to 11 and Comparative Examples 1 to 6 were obtained in the same manner as in Example 1 except that the materials used were changed as shown in Table 1. These evaluation results are shown in Table 1.

Materials other than the above described in the table are as follows.
Fluororubber B Double bond-modified (binary copolymer of vinylidene fluoride and hexafluoropropene (copolymerization ratio: vinylidene fluoride/hexafluoropropene = 8/2) alkali-modified product, Mooney viscosity: 50, double Bond content: 4% by mass)
Fluoroelastomer C Double bond-modified (binary copolymer of vinylidene fluoride and hexafluoropropene (copolymerization ratio: vinylidene fluoride/hexafluoropropene = 8/2) alkali-modified product, Mooney viscosity: 30, double bond Bond content: 4% by mass)
Fluororubber A Unmodified (binary copolymer of vinylidene fluoride and hexafluoropropene (copolymerization ratio: vinylidene fluoride/hexafluoropropene = 8/2, Mooney viscosity: 98)
Epoxy resin (liquid) JER604: Glycidylamine type tetrafunctional epoxy resin (epoxy shell epoxy product Epicoat 604)
Epoxy resin (liquid) EP828: Bisphenol A type epoxy resin (Mitsubishi Chemical Epoxy Co., Ltd.)
Epoxy resin (solid softening point 80 ° C.): o-cresol novolak type epoxy resin (YDCN700-10 (Nippon Steel & Sumikin Chemical))

表中、組成の数値は、質量部である。また、>500%は、500%を超えることを意味する。

In the table, the numerical values of the composition are parts by mass. Also, >500% means greater than 500%.

Claims (20)

An adhesive film in which an adhesive layer is laminated on a resin film layer,
The adhesive layer is composed of an adhesive composition containing a fluororubber having an unsaturated bond, a thermosetting resin, and an inorganic filler,
The adhesive layer is in a B-stage state,
The content of the thermosetting resin is 8 parts by mass to 120 parts by mass with respect to 100 parts by mass of the fluororubber having the unsaturated bond,
An adhesive film, wherein the adhesive layer has an elastic modulus of 15 MPa or more and an elongation at break of less than 400%, as measured in accordance with JIS7127 (1999). The unsaturated bond-containing fluororubber is a polymer or copolymer of at least one monomer selected from the group consisting of vinyl fluoride, vinylidene fluoride, hexafluoropropene, and tetrafluoroethylene. The adhesive film according to claim 1, which is a product. 2. The adhesive film according to claim 1, wherein the unsaturated bond-containing fluororubber is an unsaturated bond-introduced vinylidene fluoride-hexafluoropropene copolymer. The adhesive film according to any one of claims 1 to 3, wherein the thermosetting resin contains an epoxy resin. 5. The adhesive film according to claim 4, wherein the epoxy resin is a cresol novolak type epoxy resin. The adhesive film according to any one of claims 1 to 5, wherein the fluororubber having unsaturated bonds has a Mooney viscosity (ML ₁₊₁₀ (121°C)) of 40-110. The adhesive film according to any one of claims 1 to 6, wherein the thermosetting resin has a softening point of 30°C or higher. The adhesive film according to any one of claims 1 to 7, wherein the content of the inorganic filler is 1 part by mass to 35 parts by mass with respect to 100 parts by mass of the fluororubber having unsaturated bonds. The adhesive film according to any one of claims 1 to 8, wherein the inorganic filler comprises silica. A flexible printed circuit board comprising the adhesive film according to any one of claims 1 to 9,
A flexible printed circuit board in which the adhesive layer is cured. An adhesive composition containing a fluororubber having an unsaturated bond, a thermosetting resin, and an inorganic filler,
The content of the thermosetting resin is 8 parts by mass to 120 parts by mass with respect to 100 parts by mass of the fluororubber having the unsaturated bond,
The adhesive composition has an elastic modulus of 15 MPa or more and a breaking elongation of less than 400% when the adhesive composition is in a B-stage state, as measured in accordance with JIS7127 (1999). adhesive composition. The unsaturated bond-containing fluororubber is a polymer or copolymer of at least one monomer selected from the group consisting of vinyl fluoride, vinylidene fluoride, hexafluoropropene, and tetrafluoroethylene. 12. The adhesive composition according to claim 11, which is a product. 12. The adhesive composition according to claim 11, wherein the unsaturated bond-containing fluororubber is an unsaturated bond-introduced vinylidene fluoride-hexafluoropropene copolymer. The adhesive composition according to any one of claims 11 to 13, wherein said thermosetting resin comprises an epoxy resin. 15. The adhesive composition according to claim 14, wherein the epoxy resin is a cresol novolac type epoxy resin. The adhesive composition according to any one of claims 11 to 15, wherein the fluororubber having unsaturated bonds has a Mooney viscosity (ML ₁₊₁₀ (121°C)) of 40 to 110. The adhesive composition according to any one of claims 11 to 16, wherein the thermosetting resin has a softening point of 30°C or higher. The adhesive composition according to any one of claims 11 to 17, wherein the content of the inorganic filler is 1 part by mass to 35 parts by mass with respect to 100 parts by mass of the fluororubber having an unsaturated bond. . The adhesive composition according to any one of claims 11 to 18, wherein said inorganic filler comprises silica. A flexible printed circuit board having an adhesive layer comprising a cured product of the adhesive composition according to any one of claims 11 to 19 .