Thermosetting adhesive sheet and printed wiring board

Abstract

The present invention addresses the problem of providing: a thermosetting adhesive sheet that has a low dielectric constant, facilitates positioning work, and has excellent heat resistance; and a printed wiring board including a cured product of the thermosetting adhesive sheet.　The present invention is a thermosetting adhesive sheet having an adhesive layer comprising an adhesive composition, wherein: the adhesive layer contains 75-90 parts by mass of a styrene-based elastomer with respect to 100 parts by mass of the adhesive composition; the styrene-based elastomer contains at least a styrene-based elastomer (A) having a styrene ratio of 30% or more; the adhesive layer contains a polyfunctional resin having, in a structure thereof, at least two functional groups having reactivity; and a cured product of the thermosetting adhesive sheet has a dielectric constant of 1.0-3.0 at 23°C, 50%RH, and a frequency of 28 GHz.

Description

[Technical Field]

[0001] The present invention relates to a thermosetting adhesive sheet and a printed wiring board.

[0002] In recent years, the realization of faster and larger-capacity information communications has led to increasingly higher frequencies of electrical signals. However, as electrical signals become more frequent, their output tends to decrease and dielectric loss increases. Therefore, electronic devices used in high-speed communications require low dielectric properties that enable them to achieve high output and low loss even with high-frequency electrical signals. The printed wiring boards used in electronic devices for high-speed communications also require the aforementioned low dielectric properties, and the constituent materials of flexible printed wiring boards (FPCs) in particular require properties such as low dielectric properties, heat resistance, and processability.

[0003] BACKGROUND ART Thermosetting adhesive sheets with low dielectric constants and dielectric loss tangents have been proposed as constituent materials for flexible printed circuit boards (FPCs) used in high-speed communications (for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-135280 [Patent Document 2] International Publication No. 2021 / 024364 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the thermosetting adhesive sheets disclosed in Documents 1 and 2 have a strong tack, and during the positioning work to check the attachment position of the thermosetting adhesive sheet, the thermosetting adhesive sheet may adhere too strongly to the component, making it difficult to reattach when correcting the attachment position. Also, the thermosetting adhesive sheets disclosed in Documents 1 and 2 may cause swelling and flow in the cured product during the solder reflow process, resulting in insufficient reflow heat resistance.

[0006] Therefore, an object of the present invention is to provide a thermosetting adhesive sheet that has a low dielectric constant, is easy to position, and has excellent heat resistance, and a printed wiring board that includes a cured product of the thermosetting adhesive sheet. [Means for solving the problem]

[0007] The present invention includes the following aspects. [1] A thermosetting adhesive sheet having an adhesive layer made of an adhesive composition, wherein the adhesive layer contains 75 to 90 parts by mass of a styrene-based elastomer per 100 parts by mass of the adhesive composition, and the styrene-based elastomer contains at least a styrene-based elastomer (A) having a styrene ratio of 30% or more, the adhesive layer contains a multifunctional resin having at least two reactive functional groups in its structure, and the cured product of the thermosetting adhesive sheet has a dielectric constant of 1.0 to 3.0 at 23°C, 50% RH, and a frequency of 28 GHz.

[0008] [2] The thermosetting adhesive sheet according to [1] above, wherein the styrene-based elastomer contains a styrene-based elastomer (B) having a styrene ratio of less than 30%.

[0009] [3] The thermosetting adhesive sheet according to [1] or [2], wherein the content of the styrene-based elastomer (A) is 5 parts by mass or more per 100 parts by mass of the adhesive composition.

[0010] [4] The thermosetting adhesive sheet according to [2] or [3], wherein the content of the styrene-based elastomer (B) is 35 parts by mass or more per 100 parts by mass of the adhesive composition.

[0011] [5] The thermosetting adhesive sheet according to any one of [1] to [4], wherein the polyfunctional resin is a modified polyphenylene ether resin having a polymerizable group at its terminal, in an amount of 5 to 20 parts by mass per 100 parts by mass of the adhesive composition.

[0012] [6] The thermosetting adhesive sheet according to any one of [1] to [5], wherein the polyfunctional resin contains an epoxy resin in a total amount of 1 to 15 parts by mass per 100 parts by mass of the adhesive composition.

[0013] [7] The thermosetting adhesive sheet according to any one of [1] to [6], which contains 0.1 to 10 parts by mass of an organic peroxide per 100 parts by mass of the adhesive composition.

[0014] [8] The storage modulus E' of the adhesive layer at 30°C is 1 × 10 6 ~1×10 9 The thermosetting adhesive sheet according to any one of [1] to [7], wherein Pa.

[0015] [9] The thermosetting adhesive sheet according to any one of [1] to [8], wherein the initial adhesive strength of the thermosetting adhesive sheet to polyimide is 0.5 N / mm or less.

[0016]

[10] A thermosetting adhesive sheet according to any one of [1] to [9], wherein the thermosetting adhesive sheet has a T-peel adhesive strength of 0.25 N / mm or more after being attached to a polyimide and cured.

[0017]

[11] The thermosetting adhesive sheet according to any one of [1] to

[10] above, which is used for a printed wiring board.

[0018]

[12] A printed wiring board comprising a cured product of the thermosetting adhesive sheet according to any one of [1] to

[11] above. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a thermosetting adhesive sheet that has a low dielectric constant, weak tack, which makes positioning easy, and excellent heat resistance. DETAILED DESCRIPTION OF THE INVENTION

[0020] The thermosetting adhesive sheet of the present invention will be described in more detail below based on its constituent elements.

[0021] "Thermosetting adhesive sheet" The thermosetting adhesive sheet of the present invention has an adhesive layer made of an adhesive composition. The adhesive layer made of the adhesive composition of the present invention contains, per 100 parts by mass of the adhesive composition, 75 to 90 parts by mass of a styrene-based elastomer and a polyfunctional resin having at least two reactive functional groups in its structure, and the styrene-based elastomer contains at least a styrene-based elastomer (A) having a styrene ratio of 30% or more. By configuring the adhesive composition in this way, a thermosetting adhesive sheet with low tack and excellent heat resistance can be obtained.

[0022] <Adhesive composition> The adhesive composition of the present invention contains 75 to 90 parts by mass of a styrene-based elastomer and a polyfunctional resin having at least two reactive functional groups in its structure, relative to 100 parts by mass of the adhesive composition.

[0023] (styrene elastomer) Styrenic elastomers are copolymers of styrene and olefins (e.g., conjugated dienes such as butadiene and isoprene) and / or hydrogenated products thereof. Styrenic elastomers are block copolymers with styrene as the hard segment and conjugated dienes as the soft segment. Examples of styrene elastomers include styrene AB type diblock copolymers such as styrene-ethylene-butylene copolymer (SEB); styrene-butadiene-styrene copolymer (SBS), hydrogenated SBS (styrene-ethylene-butylene-styrene copolymer (SEBS), styrene-butadiene-butylene-styrene copolymer (SBBS)), styrene-isoprene-styrene copolymer (SIS), hydrogenated SIS (styrene-ethylene-propylene-styrene copolymer (SEPS)), and styrene-isobutylene-styrene copolymer (SIBS); and styrene ABA type triblock copolymers such as styrene-isobutylene-styrene copolymer (SIBS). Styrenic ABAB tetrablock copolymers such as styrene-butadiene-styrene-butadiene (SBSB); styrene-based ABABA pentablock copolymers such as styrene-butadiene-styrene-butadiene-styrene (SBSBS); styrene-based multiblock copolymers having AB repeating units greater than or equal to these; hydrogenated products obtained by hydrogenating the ethylenic double bonds of styrene-based random copolymers such as styrene-butadiene rubber (SBR); terminal amine-modified copolymers obtained by amine-modifying the terminals of these copolymers; and maleic anhydride-modified copolymers obtained by partially modifying these copolymers with maleic anhydride are preferably used. Commercially available styrene elastomers may be used. These may be used alone or in combination of two or more types.

[0024] Among these, it is preferred that the styrene elastomer be at least one selected from the group consisting of hydrogenated SBS, maleic anhydride modified hydrogenated SBS, and terminal amine modified hydrogenated SBS, as this will result in a thermosetting adhesive sheet with weaker tack and better heat resistance, and furthermore, the thermosetting adhesive sheet will exhibit good low dielectric properties.

[0025] The weight-average molecular weight of the styrene-based elastomer is preferably 50,000 or more, more preferably 80,000 to 1,000,000. Setting the weight-average molecular weight of the styrene-based elastomer within this preferred range is preferable in that the thermosetting adhesive sheet has weak tack and can have better heat resistance. When the adhesive composition contains two or more types of styrene-based elastomers as the styrene-based elastomer, the weight-average molecular weight of the styrene-based elastomer refers to the weight-average molecular weight of each of the two or more types of styrene-based elastomers.

[0026] Here, the weight average molecular weight of the styrene elastomer is measured by the GPC method using a GPC device (HLC-8329GPC, manufactured by Tosoh Corporation) and is a value converted into standard polystyrene. The measurement conditions are as follows: -Measurement conditions- Sample concentration: 0.5% by mass (tetrahydrofuran (THF) solution) Sample injection volume: 100 μL ·Eluent:THF ·Flow rate: 1.0mL / min ·Measurement temperature: 40℃ Main column: TSKgel GMHHR-H(20) x 2 Guard column: TSKgel HXL-H Detector: Differential refractometer Standard polystyrene molecular weight: 10,000 to 20 million (Tosoh Corporation)

[0027] The adhesive composition of the present invention contains 75 to 90 parts by mass of the styrene-based elastomer per 100 parts by mass of the adhesive composition. When the adhesive composition contains two or more types of styrene-based elastomers as the styrene-based elastomer, the total content of the two or more types of styrene-based elastomers per 100 parts by mass of the adhesive composition is in the above-mentioned range. In particular, the content of the styrene-based elastomer is more preferably 80 to 90 parts by mass per 100 parts by mass of the adhesive composition. When the content of the styrene-based elastomer is within the above-mentioned preferred range, the thermosetting adhesive sheet has weak tack and can have better heat resistance, and further, the thermosetting adhesive sheet can exhibit good low dielectric properties, which is preferable.

[0028] The styrene elastomer contains at least a styrene elastomer (A) having a styrene ratio of 30% or more. The styrene ratio of the styrene elastomer (A) is preferably 30% or more, more preferably 30 to 80%, and particularly preferably 30 to 70%. This configuration allows for a low dielectric constant, weak tackiness, and improved heat resistance.

[0029] The content of the styrene-based elastomer (A) is preferably 5 parts by mass or more, more preferably 7 to 90 parts by mass, and even more preferably 9 to 50 parts by mass, per 100 parts by mass of the adhesive composition. When the content of the styrene-based elastomer (A) is within the above-mentioned preferred range, the thermosetting adhesive sheet has low tack and good adhesiveness after curing, which is preferable.

[0030] The styrene elastomer may contain two or more styrene elastomers with different styrene ratios. When the styrene elastomer contains two or more styrene elastomers with different styrene ratios, the styrene elastomer preferably further contains, in addition to the styrene elastomer (A) with a styrene ratio of 30% or more, a styrene elastomer (B) with a styrene ratio different from that of the styrene elastomer (A). The use of the styrene elastomer (B) in combination reduces the tack of the thermosetting adhesive sheet and strengthens the adhesiveness after curing.

[0031] When the styrene elastomer (A) and the styrene elastomer (B) are used in combination, the styrene ratio of the styrene elastomer (B) is preferably less than 30%, more preferably 5 to 25%, even more preferably 7 to 20%, and particularly preferably 10 to 15%. When the styrene ratio of the styrene elastomer (B) is within the above range, the adhesiveness of the thermosetting adhesive sheet after curing can be improved.

[0032] When the styrene-based elastomer (A) and the styrene-based elastomer (B) are used in combination, the content of the styrene-based elastomer (B) is preferably 35 parts by mass or more, more preferably 40 to 80 parts by mass, and even more preferably 50 to 75 parts by mass, per 100 parts by mass of the adhesive composition. When the content of the styrene-based elastomer (B) is within the above-mentioned preferred range, the thermosetting adhesive sheet has low tack and can have better heat resistance and adhesiveness after curing, which is preferable.

[0033] When the styrene-based elastomer (A) and the styrene-based elastomer (B) are used in combination, the mass ratio [(A) / (B)] is not particularly limited, but is preferably in the range of 10 / 73 to 48 / 35, more preferably in the range of 17 / 65 to 48 / 35, and even more preferably in the range of 28 / 55 to 48 / 35. A mass ratio in this range is preferred because it can weaken the tack of the thermosetting adhesive sheet and makes it easier to position the thermosetting adhesive sheet when laminating it to an adherend.

[0034] In addition to the styrene-based elastomer, the adhesive composition of the present invention contains a multifunctional resin having at least two reactive functional groups in its structure. The reactive functional groups are not particularly limited as long as they do not impair the effects of the present invention, and examples thereof include hydroxyl groups, halogen groups, amino groups, carboxyl groups, epoxy groups, and functional groups containing ethylenically unsaturated bonds. From the viewpoint of heat resistance after curing of the thermosetting adhesive sheet, functional groups containing amino groups, carboxyl groups, epoxy groups, and ethylenically unsaturated bonds are particularly preferred. Furthermore, the multifunctional resin is not particularly limited as long as it does not impair the effects of the present invention, and examples thereof include modified polyphenylene ether resins and epoxy resins. One or more types of the multifunctional resins may be contained. Furthermore, the adhesive composition of the present invention may contain an organic peroxide as a polymerization initiator for the modified polyphenylene ether resin, and an epoxy resin curing agent as a curing agent for the epoxy resin.

[0035] The content of the polyfunctional resin is preferably 1 to 20 parts by mass, more preferably 2 to 20 parts by mass, even more preferably 5 to 20 parts by mass, and particularly preferably 10 to 20 parts by mass, relative to 100 parts by mass of the adhesive composition. Adjusting the content of the polyfunctional resin within this preferred range is preferable in that when the thermosetting adhesive sheet cures, the polyfunctional resin reacts to form a crosslinked structure, thereby suppressing the fluidity of the cured adhesive layer at high temperatures and improving heat resistance.

[0036] (Modified polyphenylene ether resin) The adhesive composition may contain, for example, one or more modified polyphenylene ether resins as a polyfunctional resin having at least two or more reactive functional groups in its structure. The modified polyphenylene ether resin preferably has a polyphenylene ether chain in its molecule and a polymerizable group at its terminal. The modified polyphenylene ether resin preferably has, as polymerizable groups, two or more of at least one type of functional group containing an epoxy group or an ethylenically unsaturated bond in one molecule. In particular, from the viewpoints of compatibility with the above-mentioned styrene-based elastomer and the dielectric properties of the adhesive composition, the modified polyphenylene ether resin preferably has, at both terminals, at least one type of functional group containing an epoxy group or an ethylenically unsaturated bond. Examples of functional groups containing an ethylenically unsaturated bond include a (meth)acryloyl group and a vinylbenzyl group.

[0037] Among these, modified polyphenylene ether resins having (meth)acryloyl groups at both ends are preferred in that they can improve the heat resistance of the thermosetting adhesive sheet after curing and can also impart excellent low dielectric properties.

[0038] The number-average molecular weight of the modified polyphenylene ether resin is preferably 1,000 to 10,000, more preferably 1,000 to 3,000. Setting the number-average molecular weight of the modified polyphenylene ether resin within the above-mentioned preferred range is preferable in that it improves the heat resistance and adhesiveness of the thermosetting adhesive sheet after curing and also imparts excellent low dielectric properties. The number-average molecular weight of the modified polyphenylene ether resin was measured using gel permeation chromatography (GPC) in terms of standard polystyrene. The measurement conditions were the same as those for measuring the weight-average molecular weight described above.

[0039] When the adhesive composition of the present invention contains a modified polyphenylene ether resin, the content of the modified polyphenylene ether resin is preferably 5 to 20 parts by mass, and particularly preferably 9 to 15 parts by mass, per 100 parts by mass of the adhesive composition. Setting the content of the modified polyphenylene ether resin within the above-mentioned preferred range is preferable in that it improves the heat resistance and adhesion of the thermosetting adhesive sheet after curing and can impart excellent low dielectric properties. In particular, when the thermosetting adhesive sheet cures, the modified polyphenylene ether resin reacts to form a crosslinked structure, which suppresses the fluidity of the cured adhesive layer at high temperatures and improves heat resistance.

[0040] (organic peroxide) Organic peroxides can be used as the polymerization initiator for the modified polyphenylene ether resin described above.As the organic peroxides, for example, dicumyl peroxide, di-tert-butyl peroxide, 2,5-di-(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexyne-3, 1,3-bis(tert-butylperoxyisopropyl)benzene, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, n-butyl-4,4-bis(tert-butylperoxy)valerate, benzoyl peroxide, p-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, tert-butyl peroxybenzoate, ert-butylperoxyisopropyl carbonate, diacetyl peroxide, lauroyl peroxide, tert-butylcumyl peroxide, etc. are preferably used. The organic peroxides may be used alone or in combination of two or more.

[0041] Among these, dicumyl peroxide is preferred because it can improve the heat resistance and adhesiveness of the thermosetting adhesive sheet after curing.

[0042] When the adhesive composition of the present invention contains an organic peroxide, the content of the organic peroxide is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, even more preferably 1 to 5 parts by mass, and particularly preferably 1.5 to 3 parts by mass, per 100 parts by mass of the adhesive composition. Setting the content of the organic peroxide within the above preferred range is preferable in that it can improve the heat resistance and adhesiveness of the thermosetting adhesive sheet after curing, and is particularly preferable in that when the thermosetting adhesive sheet cures, the organic peroxide reacts to form a crosslinked structure, thereby suppressing the fluidity of the cured adhesive layer at high temperatures and improving heat resistance.

[0043] (epoxy resin) The adhesive composition may contain, for example, an epoxy resin as a polyfunctional resin having at least two reactive functional groups in its structure. The epoxy resin may be a compound having two or more epoxy groups per molecule. Examples of suitable epoxy resins include bisphenol-type epoxy resins such as bisphenol A-type epoxy resins and bisphenol F-type epoxy resins, modified resins thereof, dicyclopentadiene-type epoxy resins such as dicyclopentadiene-phenol addition reaction type epoxy resins, biphenyl-type epoxy resins, tetramethylbiphenyl-type epoxy resins, polyhydroxynaphthalene-type epoxy resins, isocyanate-modified epoxy resins, 10-(2,5-dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-modified epoxy resins, phenol novolac-type epoxy resins, cresol novolac-type epoxy resins, triphenylmethane-type epoxy resins, and tetramethylbiphenyl-type epoxy resins. Phenylethane-type epoxy resins, phenol aralkyl-type epoxy resins, naphthol novolac-type epoxy resins, hexanediol-type epoxy resins, naphthol aralkyl-type epoxy resins, naphthol-phenol co-condensed novolac-type epoxy resins, naphthol-cresol co-condensed novolac-type epoxy resins, aromatic hydrocarbon formaldehyde resin-modified phenolic resin-type epoxy resins, biphenyl-modified novolac-type epoxy resins, trimethylolpropane-type epoxy resins, alicyclic epoxy resins, acrylic resins having epoxy groups, polyurethane resins having epoxy groups, polyester resins having epoxy groups, flexible epoxy resins, etc. Epoxy resins may be used alone or in combination of two or more.

[0044] Among these, the use of dicyclopentadiene-type epoxy resins such as dicyclopentadiene-phenol addition reaction type epoxy resins, biphenyl-type epoxy resins, tetramethylbiphenyl-type epoxy resins, and polyhydroxynaphthalene-type epoxy resins is preferred, as they can improve the heat resistance and adhesiveness of the thermosetting adhesive sheet after curing.

[0045] When the adhesive composition of the present invention contains an epoxy resin, the content of the epoxy resin is preferably 1 to 15 parts by mass, more preferably 2 to 10 parts by mass, per 100 parts by mass of the adhesive composition. Setting the content of the epoxy resin within this preferred range is preferable in that it improves the heat resistance of the thermosetting adhesive sheet after curing and can impart excellent low dielectric properties, and is particularly preferable in that when the thermosetting adhesive sheet cures, the epoxy resin reacts to form a crosslinked structure, thereby suppressing the fluidity of the cured adhesive layer at high temperatures and improving heat resistance.

[0046] (epoxy resin hardener) The epoxy resin curing agent can be used as a catalyst to accelerate the curing reaction of the above-mentioned epoxy resin. Examples of epoxy resin curing agents that can be used include imidazole-based, phenol-based, amine-based, acid anhydride-based, and organic peroxide-based agents. In particular, from the viewpoint of the storage stability of the adhesive composition at room temperature, the epoxy resin curing agent is preferably a latent curing agent, and more preferably an encapsulated latent imidazole-based curing agent. The excellent storage stability at room temperature can further simplify the management of the supply and use of the adhesive composition. Specifically, the epoxy resin curing agent can be a microencapsulated latent curing agent, which has a core of a latent imidazole modified substance and whose surface is coated with polyurethane. The epoxy resin curing agent may be used alone or in combination of two or more types.

[0047] When the adhesive composition of the present invention contains an epoxy resin curing agent, the content of the epoxy resin curing agent is preferably 1 to 10 parts by mass, more preferably 1 to 7 parts by mass, even more preferably 2 to 5 parts by mass, and particularly preferably 2 to 3 parts by mass, per 100 parts by mass of the adhesive composition. Setting the content of the epoxy resin curing agent within the above preferred range is preferable in that it can improve the curability of the thermosetting adhesive sheet when heated and the heat resistance after curing, and is particularly preferable in that when the thermosetting adhesive sheet cures, the epoxy resin curing agent reacts to form a crosslinked structure, thereby suppressing the fluidity of the cured adhesive layer at high temperatures and improving heat resistance.

[0048] (Other ingredients) The adhesive composition of the present invention may further contain other components to the extent that the effects of the present invention are not impaired. Examples of other components include tackifying resins; crosslinking agents, antioxidants, UV absorbers, polymerization inhibitors, surface conditioners, antistatic agents, foaming agents, antifoaming agents, viscosity modifiers, light stabilizers, weather stabilizers, heat stabilizers, antioxidants, leveling agents, conductive particles, organic pigments, inorganic pigments, pigment dispersants, silica beads, organic beads, and other additives; and fillers such as silicon oxide, aluminum oxide, titanium oxide, zirconia, and antimony pentoxide. These may be used alone or in combination of two or more. The content of the other components can be appropriately selected within a range that does not impair the effects of the present invention.

[0049] <Adhesive layer> The adhesive layer in the present invention may have a single layer structure or a multi-layer structure of two or more layers.

[0050] The thickness of the adhesive layer in the present invention is not particularly limited as long as it is within a range that does not impair the effects of the present invention, but is preferably 10 to 75 μm, more preferably 15 to 50 μm, and even more preferably 15 to 25 μm. When the thickness of the adhesive layer is within the above-mentioned preferred range, it is preferable in that it is possible to make parts containing a cured product of the thermosetting adhesive sheet, such as a printed wiring board, thin while maintaining good heat resistance and adhesiveness after curing the thermosetting adhesive sheet.

[0051] The adhesive layer in the present invention has a storage modulus E' at 30°C of 1 x 10 6 ~1×10 9 Pa is preferred, and 2×10 6 ~5×10 8 Pa is more preferable, and 1×10 7 ~5×10 8 It is more preferable that the storage modulus E' of the adhesive layer is within this preferable range. When the storage modulus E' of the adhesive layer is within this preferable range, the tackiness of the thermosetting adhesive sheet can be weakened, and the positioning of the thermosetting adhesive sheet when it is attached to the adherend can be facilitated. The storage modulus E' of the adhesive layer at 30°C can be adjusted to within the above-mentioned preferred range, for example, by adjusting the type, styrene ratio, and content of the styrene-based elastomer (A) and styrene-based elastomer (B) contained in the adhesive layer.

[0052] The storage modulus E' of the adhesive layer can be measured by the following method. The adhesive layers of the present invention are stacked to prepare an adhesive layer with a thickness of 100 mm. Next, the adhesive layer is punched out using a dumbbell cutter into the shape of a JIS K 7127 type 5 test piece to prepare a test piece. Next, a tensile viscoelasticity tester (manufactured by Rheometrics, product name: RSA-II) is used to measure under the following conditions. Load mode: sine wave (load change frequency 3.5Hz) Tensile strain: 0.1% Heating rate: 5℃ / min

[0053] The cured product of the adhesive layer in the present invention preferably has a cure rate of 10 to 100%, more preferably 15 to 95%, and even more preferably 30 to 90% after heating the cured product of the adhesive layer at 290°C for 10 minutes. When the cure rate of the cured product of the adhesive layer after heating at 290°C for 10 minutes is set within the above-mentioned preferred range, the fluidity of the cured adhesive layer at high temperatures can be suppressed, and heat resistance can be improved. The curing rate after heating the cured product of the adhesive layer at 290°C for 10 minutes can be adjusted to within the above-mentioned preferred range, for example, by adjusting the type and content of the multifunctional resin contained in the adhesive layer or the type and content of the organic peroxide.

[0054] The degree of cure after heating the cured product of the adhesive layer at 290° C. for 10 minutes is expressed as a gel fraction, and can be measured according to the following method. In the present invention, the adhesive layer is heated at 180°C for 60 minutes to form a cured product, and then the cured product is heated at 290°C for 10 minutes to form a test piece. The test piece is then immersed in a toluene solution adjusted to 23°C for 24 hours, and the mass of the test piece remaining in the solvent after drying and the mass of the test piece before immersion in toluene are used to calculate the value according to the following formula. Gel fraction (mass%) = {(mass of the test piece remaining after immersion in toluene without dissolving after drying) / (mass of the test piece before immersion in toluene)} × 100

[0055] The adhesive layer preferably has a dielectric constant (Dk) of 1.0 to 3.0, more preferably 1.0 to 2.8, after curing. The adhesive layer preferably has a dielectric loss tangent (Df) of 0.01 or less, more preferably 0.0001 to 0.01, even more preferably 0.0001 to 0.005, and particularly preferably 0.0001 to 0.003, after curing. By ensuring that the adhesive layer has a dielectric constant (Dk) and / or a dielectric loss tangent (Df) within the above-mentioned preferred ranges after curing, the adhesive layer can exhibit good low dielectric properties after curing. The dielectric constant (Dk) and dielectric loss tangent (Df) of the adhesive layer after curing can be adjusted to fall within the above-mentioned preferred ranges, for example, by adjusting the type, styrene ratio, and content of the styrene-based elastomer (A) and styrene-based elastomer (B) contained in the adhesive layer.

[0056] The dielectric constant (Dk) and the dielectric loss tangent (Df) can be measured according to the following method. The adhesive layer is cut into a size of 35 mm × 50 mm and cured for 1 hour at 180° C. to prepare an evaluation test piece. The dielectric constant (Dk) and the dielectric loss tangent (Df) of this evaluation test piece are measured at a measurement temperature of 23° C. and a measurement frequency of 28 GHz using a dielectric constant measuring device (Keysight, split cylinder resonator) in an environment of 50% RH.

[0057] <Thermosetting adhesive sheet> The thermosetting adhesive sheet of the present invention has an adhesive layer made of the adhesive composition described above. The thermosetting adhesive sheet of the present invention may be one composed of a single adhesive layer, or one composed of two or more adhesive layers, which may be the same or different, laminated together.

[0058] The thermosetting adhesive sheet of the present invention may be a substrate-less adhesive sheet in which both sides of the adhesive layer are adhesive surfaces of the thermosetting adhesive sheet, or a substrate may be laminated on the adhesive layer. When a substrate is laminated, the thermosetting adhesive sheet of the present invention may be a single-sided adhesive sheet in which the adhesive layer is laminated on one side of the substrate, or a double-sided adhesive sheet in which the adhesive layer is laminated on both sides of the substrate.

[0059] Examples of the substrate include resin films, foam films, paper, cloth, metal foils, and composites thereof. Examples of resin films include polyolefin films such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymers; polyester films such as PET; vinyl chloride resin films; vinyl acetate resin films; polyimide resin films; polyamide resin films; fluororesin films; and cellophane. Examples of paper include Japanese paper, kraft paper, glassine paper, fine paper, synthetic paper, and top-coated paper. Examples of cloth include woven fabrics and nonwoven fabrics made from various fibrous materials, either alone or in combination. Examples of the fibrous materials include cotton, staple fiber, Manila hemp, pulp, rayon, acetate fiber, polyester fiber, polyvinyl alcohol fiber, polyamide fiber, and polyolefin fiber. Examples of rubber sheets include natural rubber sheets and butyl rubber sheets. Examples of foam sheets include foamed polyurethane sheets and foamed polychloroprene rubber sheets. Examples of metal foils include aluminum foil and copper foil.

[0060] The shape and dimensions of the thermosetting adhesive sheet of the present invention are not particularly limited, and include, for example, adhesive sheets having shapes and dimensions suitable for attachment to a specified adherend (e.g., adhesive sheets in a state after being punched), and long sheet-like adhesive sheets (e.g., adhesive sheets before being processed into a specific shape).

[0061] The thickness of the thermosetting adhesive sheet of the present invention is not particularly limited as long as it is within a range that does not impair the effects of the present invention, but is preferably 10 to 150 μm, more preferably 10 to 100 μm, more preferably 10 to 75 μm, even more preferably 15 to 50 μm, and particularly preferably 15 to 25 μm. Setting the thickness of the thermosetting adhesive sheet within this preferred range is advantageous in that it allows the printed wiring board containing the cured product of the thermosetting adhesive sheet to be made thin while maintaining good heat resistance and adhesiveness after curing of the thermosetting adhesive sheet.

[0062] The thermosetting adhesive sheet of the present invention can be firmly bonded to an adherend by being applied to the adherend and then cured. The curing conditions for the thermosetting adhesive sheet of the present invention are not particularly limited and can be appropriately selected from known methods.

[0063] The curing conditions can be appropriately set depending on the type of adhesive composition, etc. The curing temperature is, for example, preferably 100 to 220°C, more preferably 120 to 200°C, and even more preferably 150 to 180°C. The curing time is, for example, preferably 1 to 180 minutes, more preferably 15 to 120 minutes, and even more preferably 30 to 60 minutes. Setting the curing conditions within the preferred ranges is preferable in that strong adhesion to the adherend can be achieved after curing.

[0064] The thermosetting adhesive sheet of the present invention preferably has a dielectric constant (Dk) after curing of 1.0 to 3.0, more preferably 1.0 to 2.8. When the dielectric constant (Dk) of the thermosetting adhesive sheet after curing is within this preferred range, the thermosetting adhesive sheet after curing exhibits good low dielectric properties, and when used in high-frequency components, can exhibit good transmission characteristics. The dielectric constant (Dk) of the thermosetting adhesive sheet after curing can be adjusted to fall within the above-mentioned preferred range, for example, by adjusting the type, styrene ratio, and content of the styrene-based elastomer (A) and styrene-based elastomer (B) contained in the adhesive layer.

[0065] The thermosetting adhesive sheet of the present invention preferably has a dielectric loss tangent (Df) after curing of 0.01 or less, more preferably 0.0001 to 0.01, even more preferably 0.0001 to 0.005, and particularly preferably 0.0001 to 0.003. When the dielectric loss tangent (Df) of the thermosetting adhesive sheet after curing is within the above-mentioned preferred range, the thermosetting adhesive sheet after curing exhibits good low dielectric properties, and when used in high-frequency components, can exhibit good transmission characteristics. The dielectric loss tangent (Df) of the thermosetting adhesive sheet after curing can be adjusted to fall within the above-mentioned preferred range, for example, by adjusting the type, styrene ratio, and content of the styrene-based elastomer (A) and styrene-based elastomer (B) contained in the adhesive layer.

[0066] The dielectric constant (Dk) and the dielectric loss tangent (Df) can be measured according to the following method. The thermosetting adhesive sheet is cut into a size of 35 mm x 50 mm to prepare a test piece. This test piece is cured at 180°C for 1 hour to prepare an evaluation test piece. Using a dielectric constant measuring device (Keysight, split cylinder resonator), the dielectric constant (Dk) and dielectric loss tangent (Df) are measured at a measurement temperature of 23°C and a measurement frequency of 28 GHz under an environment of 50% RH.

[0067] The thermosetting adhesive sheet of the present invention preferably has an initial adhesive strength to polyimide of 0.5 N / mm or less, more preferably 0.46 N / mm or less, even more preferably 0.1 N / mm or less, and particularly preferably 0.05 N / mm or less. When the initial adhesive strength of the thermosetting adhesive sheet to polyimide is within this preferred range, tackiness is weak, making it easier to position the thermosetting adhesive sheet when applying it to an adherend.

[0068] The initial adhesive strength refers to the 90-degree peel adhesive strength of the thermosetting adhesive sheet to polyimide before curing, and can be measured according to the method described below. A test specimen was prepared by bonding both sides of a thermosetting adhesive sheet to a polyimide film (Toray DuPont, Kapton 100H, 0.025 mm thick) at 23°C and 50% RH. The test specimen was cut to a size of 20 mm x 70 mm, pressed back and forth with a 2 kg roller, and cured for 1 hour at 23°C and 50% RH. The polyimide film on one side of the test specimen was fixed to a SUS plate (30 mm x 130 mm). The end of the polyimide film not fixed to the SUS plate was chucked using a tensile tester (A&D Co., Ltd. RTH-1310), and a tensile test was performed in a 90-degree direction at a test speed of 50 mm / min. The value obtained at this time was used to determine the initial adhesive strength of the thermosetting adhesive sheet.

[0069] The thermosetting adhesive sheet of the present invention preferably has a T-peel adhesive strength of 0.25 N / mm or more after being applied to a polyimide and cured, with 0.25 to 4.00 N / mm being preferred, 0.35 to 4.00 N / mm being more preferred, and 0.50 to 4.00 N / mm being even more preferred. When the T-peel adhesive strength of the thermosetting adhesive sheet to the polyimide after curing is within this preferred range, adhesion between the cured thermosetting adhesive sheet and the adherend is good, and when used in high-frequency components, excellent adhesion performance can be achieved while exhibiting good transmission characteristics.

[0070] The T-peel adhesive strength of the thermosetting adhesive sheet to the polyimide after curing can be measured according to the method described below. A test specimen was prepared by bonding both sides of a thermosetting adhesive sheet to a polyimide film (Toray DuPont, Kapton 100H, 0.025 mm thick) at 23°C and 50% RH. The test specimen was then heated to 180°C using a heat press and pressed at 4.0 MPa for 10 minutes. The test specimen was then cured by heating in a dryer at 180°C for 50 minutes to prepare a test specimen for evaluation. The test specimen was then cut to a size of 10 mm x 100 mm. The edges of the polyimide film bonded to both sides of the test specimen were chucked using a tensile tester (A&D Co., Ltd. RTH-1310). A tensile test was then performed in the T-shape at a test speed of 300 mm / min using the tensile tester. The value obtained at this time was used to determine the T-peel adhesive strength of the cured thermosetting adhesive sheet.

[0071] "Another embodiment of the thermosetting adhesive sheet" Another embodiment of the thermosetting adhesive sheet of the present invention is a thermosetting adhesive sheet in which the adhesive layer has a storage modulus E' at 30°C of 1 x 10 6 ~1×10 9 Pa, the initial adhesive strength of the thermosetting adhesive sheet to polyimide is 0.5 N / mm or less, and the cured product of the thermosetting adhesive sheet has a dielectric constant of 1.0 to 3.0 at 23° C., 50% RH, and a frequency of 28 GHz.

[0072] As already explained, the adhesive layer containing 75 to 90 parts by mass of a styrene-based elastomer per 100 parts by mass of the adhesive composition may be referred to as an adhesive layer containing a styrene-based elastomer as the main component.

[0073] The thermosetting adhesive sheet of this embodiment is easy to position when applied to an adherend, can be reapplied, and can be firmly bonded to the adherend by curing after application. Furthermore, the thermosetting adhesive sheet of this embodiment has a low dielectric constant, can exhibit good transmission characteristics when used in parts for high-frequency applications, and further has excellent heat resistance, so it can suppress defects such as swelling caused by exposure to high temperatures during the manufacturing process of the part, such as the reflow process.

[0074] In the thermosetting adhesive sheet of this embodiment, the storage modulus E' of the adhesive layer at 30°C can be set to the same preferred range as the storage modulus E' at 30°C of the adhesive layer whose main component is a styrene-based elastomer as already described.

[0075] The adhesive composition constituting the adhesive layer in this embodiment is not particularly limited as long as it has a composition that can exhibit desired physical properties, and is not limited to adhesive compositions containing the above-mentioned styrene-based elastomer as a main component, but examples thereof include epoxy resins, olefin resins, and polyester resins.

[0076] Other details of the adhesive layer containing a styrene-based elastomer as a main component, which have already been explained in this specification, can also be applied to the adhesive layer in this embodiment.

[0077] The initial adhesive strength of the thermosetting adhesive sheet of this embodiment to polyimide can be set to the same preferred range as the initial adhesive strength of the thermosetting adhesive sheet having an adhesive layer primarily composed of a styrene-based elastomer as described above to polyimide.

[0078] The dielectric constant of the cured product of the thermosetting adhesive sheet of this embodiment at 23°C, 50% RH, and a frequency of 28 GHz can be similar to the preferred range of the dielectric constant of the cured product of the thermosetting adhesive sheet having an adhesive layer primarily composed of the styrene-based elastomer already described, under an environment of 23°C, 50% RH, and at a frequency of 28 GHz.

[0079] Other details of the thermosetting adhesive sheet having an adhesive layer containing a styrene-based elastomer as a main component, which have already been explained in this specification, can also be applied to the thermosetting adhesive sheet of this embodiment.

[0080] "Method of manufacturing thermosetting adhesive sheets" The method for producing the thermosetting adhesive sheet of the present invention is not particularly limited, and can be appropriately selected from known methods.

[0081] The thermosetting adhesive sheet of the present invention can be produced, for example, by forming an adhesive layer made of the above-mentioned adhesive composition in a sheet form on a release liner. The sheet-like adhesive layer can be produced, for example, by diluting the above-mentioned adhesive composition with a solvent, applying it to the surface of the release liner, and drying it. The thickness and physical properties of the thermosetting adhesive sheet described above are those excluding the release liner.

[0082] The release liner is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include paper such as kraft paper, glassine paper, and wood-free paper; resin films such as polyethylene, polypropylene (biaxially oriented polypropylene (OPP), uniaxially oriented polypropylene (CPP)), and polyethylene terephthalate (PET); laminated paper in which the above-mentioned paper and resin film are laminated together; paper that has been sealed with clay, polyvinyl alcohol, or the like; and paper on one or both sides that has been subjected to a release treatment with a silicone-based resin or the like. These may be used alone or in combination of two or more.

[0083] "Uses of thermosetting adhesive sheets" As described above, the thermosetting adhesive sheet of the present invention has low tack before curing, making it easy to position when attaching the thermosetting adhesive sheet to an adherend during the manufacturing process. Furthermore, the cured product of the thermosetting adhesive sheet has a low dielectric constant and dielectric dissipation factor, and also has excellent heat resistance when exposed to very high temperatures. Therefore, the thermosetting adhesive sheet can be used, for example, as an interlayer adhesive for printed wiring boards, or for bonding and fixing terminal portions of printed wiring boards to connecting substrates that back them up. In addition to printed wiring boards, the thermosetting adhesive sheet of the present invention can also be used for high-frequency components such as flexible flat cables and various high-speed communication modules.

[0084] "Printed wiring board" The printed wiring board of the present invention can be produced using a cured product of the thermosetting adhesive sheet. The printed wiring board may be a printed circuit board in which circuits are connected by circuit components such as printed parts and mounted components, or may be a printed wiring board having wiring before the circuit components are formed. The printed wiring board of the present invention may be a rigid printed wiring board having a hard insulating substrate, or may be a flexible printed wiring board having a flexible insulating substrate. Furthermore, it may be a flex-rigid printed wiring board in which the insulating substrate has hard and flexible portions. [Example]

[0085] The present invention will now be described in more detail with reference to the following examples, but the present invention is not limited to these examples. The materials used in the examples and comparative examples are as follows.

[0086] <Component A: Styrene-based elastomer> A-1: Amine-modified hydrogenated styrene elastomer (Tuftec MP10, styrene ratio 30%, manufactured by Asahi Kasei Corporation) A-2: Maleic acid-modified hydrogenated styrene elastomer (Tuftec M1913, styrene ratio 30%, manufactured by Asahi Kasei Corporation) A-3: Hydrogenated styrene elastomer (Tuftec H1221, styrene ratio 12%, manufactured by Asahi Kasei Corporation) A-4: Hydrogenated styrene elastomer (Tuftec H1041, styrene ratio 30%, manufactured by Asahi Kasei Corporation) A-5: Hydrogenated styrene elastomer (Tuftec H1043, styrene ratio 67%, manufactured by Asahi Kasei Corporation)

[0087] <Component B: Modified polyphenylene ether resin> B-1: Modified polyphenylene ether resin with methacryloyl groups at both ends (NORYL SA9000, number average molecular weight 2300, glass transition temperature 160°C, manufactured by SABIC) <Component C: Epoxy resin> C-1: Naphthalene-type epoxy resin (HP4032D, epoxy equivalent weight 136-148g / eq, liquid or crystalline, manufactured by DIC Corporation)

[0088] <Component D: Organic peroxide> D-1: Dicumyl peroxide (Permicle D, decomposition temperature for a half-life of 1 minute is 175°C, manufactured by NOF Corporation)

[0089] [Preparation of adhesive composition] Component A shown in Table 1 was dissolved uniformly in toluene solvent to a concentration of 25% according to the parts by mass shown in Table 1. Then, the other components B to D shown in Table 1 were mixed uniformly according to the parts by mass shown in Table 1 to prepare an adhesive composition.

[0090] [Preparation of thermosetting adhesive sheet] The resulting adhesive composition was applied to a release liner so that the thickness after drying was 25 μm. It was then dried in a dryer at 85°C for 2 minutes to obtain an adhesive layer with a thickness of 25 μm. A release liner was then laminated onto the exposed surface of the adhesive layer to produce a thermosetting adhesive sheet.

[0091] The physical properties of the adhesive layer and thermosetting adhesive sheet prepared by the above method were measured and evaluated according to the following methods. Unless otherwise specified, measurements using a thermosetting adhesive sheet were performed after peeling off the laminated release liner.

[0092] <Dielectric constant (Dk)> The thermosetting adhesive sheets prepared in the examples and comparative examples were cut to a size of 35 mm x 50 mm and cured at 180°C for 1 hour to prepare evaluation test pieces. The dielectric constant (Dk) of these evaluation test pieces was measured at a measurement temperature of 23°C, 50% RH, and a measurement frequency of 28 GHz using a dielectric constant measuring device (Keysight, split cylinder resonator). The results are shown in Table 1.

[0093] <Dielectric loss tangent (Df)> The dielectric loss tangent (Df) of the evaluation specimen was determined in the same manner as in the measurement of the dielectric constant (Dk) described above. The results are shown in Table 1.

[0094] <Storage modulus E'> The adhesive layers prepared in the examples and comparative examples were stacked together to prepare an adhesive layer 100 mm thick. Next, the adhesive layer was punched out using a dumbbell cutter into the shape of a JIS K 7127 Type 5 test piece to prepare a test piece. The storage modulus E' of the obtained test piece was measured using a tensile viscoelasticity tester (manufactured by Rheometrics, product name: RSA-II) under the following conditions. The results are shown in Table 1. Load mode: sine wave (load change frequency 3.5Hz) Tensile strain: 0.1% Heating rate: 5℃ / min

[0095] <Initial adhesive strength to polyimide> Test pieces were prepared by laminating both sides of the thermosetting adhesive sheets prepared in the examples and comparative examples to polyimide film (Kapton 100H, manufactured by DuPont-Toray Co., Ltd.) at 23°C and 50% RH. The test pieces were cut into 20 mm x 70 mm pieces, pressed back and forth with a 2 kg roller once, and left to age for 1 hour at 23°C and 50% RH to prepare test pieces for evaluation.

[0096] The polyimide film on one side of the evaluation test piece was fixed to a SUS plate (30 mm x 130 mm). The end of the polyimide film on the side of the evaluation test piece that was not fixed to the SUS plate was chucked using a tensile tester (RTH-1310 manufactured by A&D Co., Ltd.), and a tensile test was performed in a 90-degree direction at a test speed of 50 mm / min using the tensile tester. The value obtained at this time was taken as the initial adhesive strength of the thermosetting adhesive sheet. The results are shown in Table 1.

[0097] <T-peel adhesive strength after curing of heat-curing adhesive sheet> Test specimens were prepared by bonding both sides of the thermosetting adhesive sheets prepared in the Examples and Comparative Examples to polyimide film (Kapton 100H, manufactured by DuPont-Toray Co., Ltd.) at 23°C and 50% RH. Using a heat press, the test specimens were heated to 180°C and pressed at 4.0 MPa for 10 minutes. The test specimens were then cured by heating in a dryer at 180°C for 50 minutes, producing test specimens for evaluation.

[0098] The test piece was cut to a size of 10 mm x 100 mm, and the edges of the polyimide film attached to both sides of the test piece were chucked using a tensile tester (RTH-1310 manufactured by A&D Co., Ltd.). Using the tensile tester, a tensile test was performed in the T-shape direction at a test speed of 300 mm / min. The value obtained at this time was taken as the T-peel adhesive strength of the thermosetting adhesive sheet after curing. The results are shown in Table 1.

[0099] <Curing rate> The curing rate of the cured adhesive layer prepared in the examples and comparative examples is expressed as a gel fraction, and can be measured according to the following method. The adhesive layers prepared in the Examples and Comparative Examples were heated at 180°C for 60 minutes to form cured products. The cured products were then heated at 290°C for 10 minutes to form test pieces. The test pieces were immersed in a toluene solution adjusted to 23°C for 24 hours, and the mass of the test pieces remaining in the solvent after drying and the mass of the test pieces before immersion in toluene were used to calculate the value according to the following formula.

[0100] Gel fraction (mass%) = {(mass of the test piece remaining after immersion in toluene without dissolving after drying) / (mass of the adhesive layer before immersion in toluene)} × 100 The results are shown in Table 1.

[0101] <Positioning ability> The release liner on one side of the thermosetting adhesive sheet prepared in the Examples and Comparative Examples was peeled off and placed on a polyimide film. Next, with the release liner still laminated on one side of the thermosetting adhesive sheet, the thermosetting adhesive sheet was slid onto the polyimide film and peeled back again to evaluate whether it could be positioned according to the following criteria. The results are shown in Table 1. ◯: The tape did not adhere to the polyimide film and could be slid over, allowing positioning. △: It was able to adhere to the polyimide film and not slide, but it was possible to position it without leaving any adhesive residue when it was peeled off. ×: The adhesive could not be adhered to the polyimide film and could not be slid, and adhesive remained when peeled off, making it unsuitable for positioning.

[0102] <Reflow heat resistance> Both sides of the thermosetting adhesive sheets prepared in the Examples and Comparative Examples were laminated to polyimide or copper foil, and the sheets were heated at 180°C for 60 minutes to produce cured products. The cured products were then heated at 260°C or 290°C for 15 minutes to produce test specimens. The appearance of the test specimens was checked and visually evaluated according to the following criteria. The results are shown in Table 1. ○: No change in the appearance of the test piece △: Blisters occurred on the test piece ×: Resin flow occurred in the test piece

[0103] Based on the results of the reflow heat resistance test, the pass / fail of the reflow heat resistance was judged according to the following criteria. The results are shown in Table 1. Passed: No swelling or resin flow occurred in the test piece before and after heating at 260°C and 290°C. Or, no swelling or resin flow occurred in the test piece before and after heating at 260°C, but swelling or resin flow occurred in the test piece after heating at 290°C. Failed: Blisters and resin flow occurred in the test piece before and after heating at 260℃ and 290℃.

[0104] [Table 1] It should be noted that Examples 1 and 2 are reference examples.

[0105] The results shown in Table 1 indicate that the thermosetting adhesive sheets of the examples had good positioning properties, and also had good adhesive properties and reflow heat resistance after thermal curing.

[0106] The results of Comparative Examples 1 and 2 show that the thermosetting adhesive sheets that did not contain the styrene elastomer (A) with a styrene ratio of 30% or more had high initial adhesive strength to polyimide and poor positioning ability.

[0107] The results of Comparative Example 2 showed that thermosetting adhesive sheets that do not contain polyfunctional resins having at least two reactive functional groups in their structure, such as polyphenylene ether resins and epoxy resins, have high resin fluidity in high-temperature environments of 260°C or higher, making it difficult to maintain heat resistance.

Claims

1. A thermosetting adhesive sheet having an adhesive layer made of an adhesive composition, the adhesive layer contains 75 to 90 parts by mass of a styrene-based elastomer relative to 100 parts by mass of the adhesive composition; The styrene-based elastomer contains at least a styrene-based elastomer (A) having a styrene ratio of 30% or more and a styrene-based elastomer (B) having a styrene ratio of 5 to 15%, a mass ratio of the styrene-based elastomer (A) to the styrene-based elastomer (B) is 10 / 73 to 48 / 35; the adhesive layer contains a polyfunctional resin having at least two reactive functional groups in its structure, The thermosetting adhesive sheet has a dielectric constant of 1.0 to 3.0 at 23°C, 50% RH, and a frequency of 28 GHz.

2. 2. The thermosetting adhesive sheet according to claim 1, wherein the content of the styrene-based elastomer (A) is 5 parts by mass or more per 100 parts by mass of the adhesive composition.

3. The thermosetting adhesive sheet according to claim 1 , wherein the content of the styrene-based elastomer (B) is 35 parts by mass or more per 100 parts by mass of the adhesive composition.

4. 2. The thermosetting adhesive sheet according to claim 1, wherein the polyfunctional resin is a modified polyphenylene ether resin having a polymerizable group at its terminal, in an amount of 5 to 20 parts by mass per 100 parts by mass of the adhesive composition.

5. 2. The thermosetting adhesive sheet according to claim 1, wherein the polyfunctional resin is an epoxy resin in an amount of 1 to 15 parts by mass per 100 parts by mass of the adhesive composition.

6. 2. The thermosetting adhesive sheet according to claim 1, wherein the adhesive composition contains 0.1 to 10 parts by mass of an organic peroxide per 100 parts by mass of the adhesive composition.

7. The adhesive layer has a storage modulus E' of 1 x 10 at 30°C. ６ ~1 x 10 ９ The thermosetting adhesive sheet according to claim 1, wherein the viscosity is 100 psig.

8. 2. The thermosetting adhesive sheet according to claim 1, wherein the initial adhesive strength of the thermosetting adhesive sheet to polyimide is 0.5 N / mm or less.

9. 2. The thermosetting adhesive sheet according to claim 1, wherein the thermosetting adhesive sheet has a T-peel adhesive strength of 0.25 N / mm or more after being applied to a polyimide and cured.

10. The thermosetting adhesive sheet according to claim 1, which is used for a printed wiring board.

11. A printed wiring board comprising the cured thermosetting adhesive sheet of claim 1.

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