Thermosetting adhesive composition, thermosetting adhesive sheet, and printed wiring board

Abstract

Provided is a thermosetting adhesive composition having a low dielectric constant and a low dielectric loss tangent even after thermosetting, a low temperature change rate of a dielectric loss tangent, and favorable bending resistance.　The present technique is a thermosetting adhesive composition for bonding substrates, the thermosetting adhesive composition comprising, with respect to 100 parts by mass of the total amount of the thermosetting adhesive composition: 65-90 parts by mass of a styrene-based elastomer; 5-20 parts by mass of (A) a modified polyphenylene ether resin having a radically polymerizable group at the molecular terminal thereof and 4-10 parts by mass of (B) a polybutadiene and / or polyisoprene having a weight-average molecular weight of 10,000-50,000, as crosslinking components; a radical polymerization initiator; and an epoxy resin, wherein the total content of the radical polymerization initiator, the epoxy resin, and an epoxy resin curing agent is at most 10 parts by mass, a styrene-based elastomer having a styrene ratio of less than 67% is contained as the styrene-based elastomer, and the total of the content of the (A) component and the content of the (B) component is at most 25 parts by mass.

Description

Thermosetting adhesive composition, thermosetting adhesive sheet and printed wiring board

[0001] This application claims priority from Japanese Patent Application No. 2024-055214, filed on March 29, 2024, which is incorporated herein by reference.

[0002] The trend toward higher frequencies for signals transmitted through printed wiring boards is accelerating due to the increasing speed and capacity of information communications. To address this trend, materials (e.g., adhesive compositions) for rigid substrates and flexible printed wiring boards (FPCs) are required to have low dielectric constants and low dielectric loss tangents.

[0003] In particular, the dielectric loss tangent is preferably less than 0.0030, and more preferably less than 0.0020, for example, using liquid crystal polymer (LCP), which is a resin material for high frequencies, as a guideline.

[0004] The signal transmission loss in a high-frequency circuit depends on the dielectric loss tangent (tan δ), which is an index of the loss, and the dielectric loss tangent generally deteriorates depending on the temperature. Therefore, there is a demand for a material that does not deteriorate the signal transmission loss, i.e., does not significantly increase the dielectric loss tangent, even in an environment where the surroundings of the circuit become hot due to the signal processing load of the high-frequency circuit.

[0005] For example, Patent Document 1 discloses an adhesive composition for flexible printed wiring boards, and Patent Document 2 discloses an elastomer composition that has good adhesive strength to polyimide and good high-frequency characteristics. However, the techniques described in Patent Documents 1 and 2 do not take into consideration, and neither mention nor suggest, reducing the rate of change of the dielectric loss tangent with temperature.

[0006] Regarding flexibility, which is essential for flexible printed wiring board applications, polyphenylene ether has many advantages as a substrate material with low dielectric properties, but it has the drawback of being poor in flexibility because it has a very high melting point (softening point) and is hard at room temperature.

[0007] Thus, it is desirable for the adhesive composition to have a low dielectric constant and dielectric loss tangent even after heat curing, a low rate of change of the dielectric loss tangent with temperature, and good flex resistance.

[0008] Japanese Patent No. 7351912 Japanese Patent Application Laid-Open No. 2015-131866

[0009] The present technology has been proposed in view of the above-described conventional situation, and provides an adhesive composition that has a low dielectric constant and dielectric dissipation factor even after heat curing, a low rate of change of the dielectric dissipation factor with respect to temperature, and good flex resistance.

[0010] The present technology is a thermosetting adhesive composition for bonding substrates, which contains, relative to a total of 100 parts by mass of the thermosetting adhesive composition, 65 to 90 parts by mass of a styrene-based elastomer, and as crosslinking components, (A) 5 to 20 parts by mass of a modified polyphenylene ether resin having a radical polymerizable group at a molecular terminal, and (B) 4 to 10 parts by mass of polybutadiene and / or polyisoprene having a weight average molecular weight of 10,000 to 50,000, a radical polymerization initiator, and an epoxy resin, wherein the total content of the radical polymerization initiator, epoxy resin, and epoxy resin curing agent is 10 parts by mass or less, and the styrene-based elastomer contains a styrene ratio of less than 67%, and the total content of the component (A) and the component (B) is 25 parts by mass or less.

[0011] According to the present technology, it is possible to provide an adhesive composition that has a low dielectric constant and dielectric loss tangent even after heat curing, a low rate of change of the dielectric loss tangent with respect to temperature, and good flex resistance.

[0012] Fig. 1 is a cross-sectional view showing an example of the configuration of a printed wiring board. Fig. 2 is a cross-sectional view showing an example of the configuration of a multilayer printed wiring board. Fig. 3 is a plan view showing an example of the configuration of a TEG used in a bending endurance test. Fig. 4 is a perspective view showing a measuring device used in the bending endurance test.

[0013] Hereinafter, embodiments of the present technology will be described. In this specification, room temperature refers to the range of 20°C ± 15°C (5°C to 35°C) as defined by Japanese Industrial Standards (JIS Z 8703).

[0014] In this specification, the values ​​of weight average molecular weight (Mn) and number average molecular weight (Mn) refer to values ​​calculated from the molecular weight converted into standard polystyrene measured by gel permeation chromatography (GPC). Specific measurement conditions for the GPC method are as follows: Solvent: tetrahydrofuran Column: KF-806M, KF-806M, KF-803, KF-801, KF-800D (manufactured by Resonac Corporation) Column temperature: 40°C Sample concentration: 0.25% by mass Detector: RI detector Flow rate (flow rate): 1.0 ml / min Injection volume: 200 μL Calibration curve: A calibration curve using 10 samples of standard polystyrene with Mw = 605 to 5,680,000 was used.

[0015] <Thermosetting Adhesive Composition> The thermosetting adhesive composition according to the present technology contains, relative to a total of 100 parts by mass of the thermosetting adhesive composition, 65 to 90 parts by mass of a styrene-based elastomer, 5 to 20 parts by mass of a modified polyphenylene ether resin having a radical polymerizable group at the molecular end (hereinafter also referred to as component (A)) as a crosslinking component, 4 to 10 parts by mass of polybutadiene and / or polyisoprene (hereinafter also referred to as component (B)) having a weight average molecular weight of 10,000 to 50,000, a radical polymerization initiator, and an epoxy resin. Furthermore, the thermosetting adhesive composition according to the present technology contains the radical polymerization initiator, epoxy resin, and epoxy resin curing agent in total at 10 parts by mass or less. The thermosetting adhesive composition according to the present technology contains, as the styrene-based elastomer, a styrene ratio of less than 67%. The thermosetting adhesive composition according to the present technology contains the styrene-based elastomer in total at 25 parts by mass or less of the content of component (A) and the content of component (B).

[0016] The thermosetting adhesive composition according to the present technology has such a configuration, and therefore can maintain a low dielectric constant and dielectric loss tangent even after thermal curing, and can also reduce the rate of change of the dielectric loss tangent with temperature. Thus, the thermosetting adhesive composition according to the present technology has good dielectric properties after curing.

[0017] The thermosetting adhesive composition according to the present technology has a dielectric loss tangent of less than 0.0030 after curing at both 23°C and 80°C, and can exhibit a rate of change of less than 50%, as expressed by the following formula 1: Rate of change (%) = ((dielectric loss tangent of the thermosetting adhesive composition after curing at 80°C) / (dielectric loss tangent of the thermosetting adhesive composition after curing at 23°C) - 1) x 100

[0018] The dielectric constant of the cured thermosetting adhesive composition is preferably less than 2.40, and more preferably less than 2.30. The dielectric constant of the cured thermosetting adhesive composition can be measured by the method described in the examples below.

[0019] The thermosetting adhesive composition after curing preferably has a dielectric loss tangent of less than 0.0030, more preferably less than 0.0020, at 23° C. Furthermore, the thermosetting adhesive composition after curing preferably has a dielectric loss tangent of less than 0.0030, more preferably less than 0.0020, at 80° C. The dielectric loss tangent of the thermosetting adhesive composition after curing can be measured by the method described in the examples below.

[0020] The smaller the rate of change expressed by Equation 1 for the cured thermosetting adhesive composition, the more preferable, i.e., the smaller the temperature dependency of the dielectric loss tangent. For example, the cured thermosetting adhesive composition preferably exhibits a rate of change expressed by Equation 1 of less than 50%, more preferably less than 40%, and even more preferably less than 30%.

[0021] Furthermore, the thermosetting adhesive composition according to the present technology can adjust the glass transition temperature after curing to, for example, a range of 60 to 150°C, and can maintain good flex resistance and heat resistance (e.g., solder heat resistance) even after heat curing. For example, the good heat resistance of the thermosetting adhesive composition after heat curing allows high-frequency printed wiring boards to be mounted with components or connected to other printed wiring boards by a solder reflow process or hot bar soldering process, similar to conventional processes. Therefore, the thermosetting adhesive composition according to the present technology can be suitably used for bonding substrates, for example, as an adhesive (interlayer adhesive) for flexible printed wiring boards.

[0022]

[0023] The thermosetting adhesive composition according to the present technology includes a styrene-based elastomer, component (A), component (B), a radical polymerization initiator, and an epoxy resin, and may further include an epoxy resin curing agent as needed.

[0023] [Styrene-Based Elastomer] Styrene-based elastomers are copolymers of styrene and olefins (e.g., conjugated dienes such as butadiene and isoprene) and / or hydrogenated products thereof. Styrene-based elastomers are block copolymers with styrene as the hard segment and conjugated dienes as the soft segment. Examples of styrene-based elastomers include styrene / butadiene / styrene block copolymers, styrene / isoprene / styrene block copolymers, styrene / ethylene / butylene / styrene block copolymers, styrene / ethylene / propylene / styrene block copolymers, and styrene / butadiene block copolymers. Furthermore, styrene / ethylene / butylene / styrene block copolymers, styrene / ethylene / propylene / styrene block copolymers, and styrene / butadiene block copolymers (also referred to as hydrogenated styrene-based elastomers) in which the double bonds of the conjugated diene component have been eliminated by hydrogenation may also be used.

[0024] The styrene-based elastomer may have a functional group that accelerates the curing reaction of the epoxy resin. When the styrene-based elastomer has a functional group that accelerates the curing reaction of the epoxy resin, it also has the function of an epoxy resin curing agent, so there is no need to use an epoxy resin curing agent. However, a separate epoxy resin curing agent may be used in combination as long as it does not impair the effects of the present technology.

[0025] Examples of functional groups that accelerate the curing reaction of epoxy resins include functional groups such as amines and acid anhydrides. When using a styrene-based elastomer having a functional group that accelerates the curing reaction of epoxy resins, forming the thermosetting adhesive composition according to the present technology into a film restricts the movement of polymer chains containing the functional group that accelerates the curing reaction of epoxy resins, thereby imparting latency to the polymer side (e.g., styrene-based elastomer). Examples of such styrene-based elastomers include amine-modified styrene-based elastomers and acid-modified styrene-based elastomers.

[0026] The thermosetting adhesive composition according to the present technology contains a styrene-based elastomer having a styrene ratio of less than 67% (e.g., 67% by mass). This allows the thermosetting adhesive composition to have good peel strength and flex resistance after curing. Furthermore, the lower the styrene ratio in the styrene-based elastomer, the better the thermosetting adhesive composition's dielectric constant and dielectric loss tangent after curing, and the better the peel strength and flex resistance.

[0027] The styrene ratio in the styrene-based elastomer may be, for example, 60% or less, 50% or less, 42% or less, less than 42%, 30% or less, 20% or less, 15% or less, 12% or more and less than 67%, 12 to 42%, or 12 to 30%.

[0028] Specific examples of styrene-based elastomers include Tuftec H1221 (styrene ratio 12%, manufactured by Asahi Kasei Corporation), Tuftec MP1911 (styrene ratio 30%, acid-modified styrene-based elastomer, manufactured by Asahi Kasei Corporation), and Tuftec H1051 (styrene ratio 42%, manufactured by Asahi Kasei Corporation).

[0029] The content of the styrene-based elastomer is 65 to 90 parts by mass relative to 100 parts by mass of the total thermosetting adhesive composition. By setting the content of the styrene-based elastomer to 65 parts by mass or more, the content of other components (e.g., radical polymerization initiator, epoxy resin, and epoxy resin curing agent) does not become too high relatively, and the dielectric constant and dielectric dissipation factor of the cured thermosetting adhesive composition, as well as the temperature change rate of the dielectric dissipation factor of the cured thermosetting adhesive composition, can be reduced. Furthermore, by setting the content of the styrene-based elastomer to 90 parts by mass or less, the content of other components (e.g., component (A) and component (B)) does not become too low relatively, and the temperature change rate of the dielectric dissipation factor of the cured thermosetting adhesive composition can be reduced, and the heat resistance of the cured thermosetting adhesive composition can be improved.

[0030] The lower limit of the amount of the styrene-based elastomer may be 68 parts by mass or more, 70 parts by mass or more, 71 parts by mass or more, 75 parts by mass or more, or 76 parts by mass or more, relative to a total of 100 parts by mass of the thermosetting adhesive composition.

[0031] The upper limit of the styrene-based elastomer content may be 85 parts by mass or less, 81 parts by mass or less, or 80 parts by mass or less, per 100 parts by mass of the total of the thermosetting adhesive composition.

[0032] The styrene-based elastomer may be used alone or in combination of two or more. When two or more styrene-based elastomers are used in combination, it is preferable that the total amount thereof satisfies the above-mentioned range of the content.

[0033] As an example of a use embodiment of the styrene-based elastomer, a styrene-based elastomer having a styrene ratio of less than 67% may be used in combination with a styrene-based elastomer having a styrene ratio of 67% or more. In this case, the content of the styrene-based elastomer having a styrene ratio of less than 67% in the thermosetting adhesive composition is preferably 50% by mass or more, and may be 55% by mass or more, 60% by mass or more, 65% by mass or more, 70% by mass or more, 75% by mass or more, 80% by mass or more, 85% by mass or more, 90% by mass or more, 95% by mass or more, or even 99% by mass or more, based on the total amount of the styrene-based elastomer. For example, a styrene-based elastomer having a styrene ratio of 42% or less and a styrene-based elastomer having a styrene ratio of 67% or more may be used in combination. In this case, the content of the styrene-based elastomer having a styrene ratio of 42% or less is preferably 50% by mass or more, based on the total amount of the styrene-based elastomer.

[0034] [Component (A)] Component (A), i.e., a modified polyphenylene ether resin having a radical polymerizable group at the molecular end, is a crosslinking component and has a polyphenylene ether chain in the molecule and a radical polymerizable group at the molecular end. As described above, the radical polymerizable group at the molecular end of component (A) is crosslinked by a radical polymerization initiator in the thermosetting adhesive composition, thereby adjusting the glass transition temperature of the cured thermosetting adhesive composition to, for example, a range of 60 to 150°C, and improving the flex resistance and heat resistance even after thermal curing. Component (A) preferably has, for example, two or more ethylenically unsaturated bonds as radical polymerizable groups per molecule. In particular, from the viewpoints of compatibility with the above-mentioned styrene-based elastomer and the dielectric properties of the cured thermosetting adhesive composition, component (A) preferably has at least one ethylenically unsaturated bond (e.g., a (meth)acryloyl group or a vinylbenzyl group) at both molecular ends. Here, the (meth)acryloyl group includes both an acryloyl group and a methacryloyl group.

[0035] Modified polyphenylene ether resins other than component (A), such as modified polyphenylene ether resins having hydroxyl groups at the molecular terminals, are undesirable because they have too strong a polarity and are therefore poorly compatible with the above-mentioned styrene-based elastomer, which may prevent the thermosetting adhesive composition from being formed into a film.

[0036] A modified polyphenylene ether resin having vinylbenzyl groups at both molecular terminals, which is an example of component (A), can be obtained, for example, by vinylbenzyl-etherifying the terminal phenolic hydroxyl groups of a bifunctional phenylene ether oligomer obtained by oxidative coupling of a bifunctional phenol compound with a monofunctional phenol compound.

[0037] The weight average molecular weight (or number average molecular weight) of component (A) is preferably 1,000 to 3,000 from the viewpoints of compatibility with the above-mentioned styrene-based elastomer and conformability to unevenness when the wiring pattern side of a wiring-equipped resin substrate comprising a substrate and a wiring pattern and the coverlay are thermally cured (pressed) via the cured product of the thermosetting adhesive composition.

[0038] Specific examples of the component (A) that can be used include OPE-2St (a modified polyphenylene ether resin having vinylbenzyl groups at both molecular terminals, manufactured by Mitsubishi Gas Chemical Company, Inc.), OPE-2EA (a modified polyphenylene ether resin having acryloyl groups at both molecular terminals, manufactured by Mitsubishi Gas Chemical Company, Inc.), and Noryl SA9000 (a modified polyphenylene ether resin having methacryloyl groups at both molecular terminals, manufactured by SABIC).

[0039] The content of component (A) is 5 to 20 parts by mass per 100 parts by mass of the total thermosetting adhesive composition. By having the content of component (A) 20 parts by mass or less, it is possible to improve flex resistance. Furthermore, by having the content of component (A) 5 parts by mass or more, it is possible to reduce the dielectric loss tangent of the thermosetting adhesive composition after curing.

[0040] The content of component (A) may be 18 parts by mass or less, 15 parts by mass or less, 13 parts by mass or less, 10 parts by mass or less, or 9 parts by mass or less, relative to a total of 100 parts by mass of the thermosetting adhesive composition.

[0041] The content of component (A) may be 6 parts by mass or more, 8 parts by mass or more, 9 parts by mass or more, or 10 parts by mass or more, relative to a total of 100 parts by mass of the thermosetting adhesive composition.

[0042] The component (A) may be used alone or in combination of two or more. When two or more components (A) are used in combination, it is preferable that the total amount thereof satisfies the above-mentioned range of the content.

[0043] [Component (B)] Component (B) is a crosslinking component and is polybutadiene and / or polyisoprene having a weight-average molecular weight of 10,000 to 50,000. Component (B) is at least one of a polybutadiene resin (resin having only a polybutadiene structure) having a weight-average molecular weight of 10,000 to 50,000, a polyisoprene resin (resin having only a polyisoprene structure) having a weight-average molecular weight of 10,000 to 50,000, or a resin having both a polybutadiene structure and a polyisoprene structure and having a weight-average molecular weight of 10,000 to 50,000, or a combination of these. Furthermore, as long as the component (B) contains a butadiene structure or a polyisoprene structure as a main component, it may contain structures other than the butadiene structure and the polyisoprene structure within a range that does not impair the effects of the present technology, but from the viewpoint of improving the effects of the present technology, compatibility with other components, dispersibility, etc., it is preferable that the component (B) is substantially free of other structures (for example, a styrene structure). From the viewpoint of handleability, the component (B) is preferably liquid at room temperature.

[0044] The polybutadiene may be any resin having a polybutadiene structure, and the polybutadiene structure may be contained in the main chain or in a side chain. The butadiene structure may be partially hydrogenated or may not be hydrogenated.

[0045] The polyisoprene may be any resin having a polyisoprene structure, and the polyisoprene structure may be contained in the main chain or in a side chain. The polyisoprene structure may be partially hydrogenated or may not be hydrogenated.

[0046] The (B) component may have a functional group that accelerates the curing reaction of the epoxy resin. When the (B) component has a functional group that accelerates the curing reaction of the epoxy resin, it also functions as an epoxy resin curing agent, so there is no need to use an epoxy resin curing agent. However, a separate epoxy resin curing agent may be used in combination as long as it does not impair the effects of the present technology. Examples of functional groups that accelerate the curing reaction of the epoxy resin include functional groups such as acid anhydrides. Examples of such a (B) component include acid-modified polybutadiene and acid-modified polyisoprene.

[0047] Regarding the weight-average molecular weight of component (B), by having the weight-average molecular weight of component (B) of 10,000 or more, it is possible to prevent the crosslinking density from becoming too high, and to improve the peel strength and flex resistance of the cured thermosetting adhesive composition. The weight-average molecular weight of component (B) may be 15,000 or more, 20,000 or more, 25,000 or more, 30,000 or more, or 35,000 or more.

[0048] Furthermore, by making the weight-average molecular weight of component (B) 50,000 or less, it is possible to prevent the crosslink density from becoming too small, to reduce the rate of change of the dielectric tangent of the cured thermosetting adhesive composition with respect to temperature, and to improve compatibility with component (A). The weight-average molecular weight of component (B) may be 45,000 or less, 40,000 or less, 35,000 or less, or 30,000 or less.

[0049] The content of component (B) is 4 to 10 parts by mass per 100 parts by mass of the total thermosetting adhesive composition. By having the content of component (B) 10 parts by mass or less, the peel strength and flex resistance of the cured thermosetting adhesive composition can be improved. Furthermore, by having the content of component (B) 4 parts by mass or more, the temperature change rate of the dielectric loss tangent of the cured thermosetting adhesive composition can be reduced.

[0050] The content of component (B) may be 9 parts by mass or less, 8 parts by mass or less, 7 parts by mass or less, 6 parts by mass or less, or 5 parts by mass or less, relative to a total of 100 parts by mass of the thermosetting adhesive composition.

[0051] The content of component (B) may be 5 parts by mass or more, 6 parts by mass or more, 7 parts by mass or more, or 8 parts by mass or more, relative to a total of 100 parts by mass of the thermosetting adhesive composition.

[0052] Furthermore, the total content of the (A) component and the (B) component is 25 parts by mass or less, and may be 24 parts by mass or less, 23 parts by mass or less, 22 parts by mass or less, 21 parts by mass or less, 20 parts by mass or less, 19 parts by mass or less, 18 parts by mass or less, 17 parts by mass or less, or 16 parts by mass or less.

[0053] The lower limit of the total content of the (A) component and the (B) component is not particularly limited as long as it is within a range that satisfies the above-mentioned contents of the (A) component and the (B) component, and can be, for example, 15 parts by mass or more, or alternatively 16 parts by mass or more, or 17 parts by mass or more, or 18 parts by mass or more, or 19 parts by mass or more, or alternatively 20 parts by mass or more.

[0054] Furthermore, the content of the component (A) and the content of the component (B) preferably satisfy the following formula 2: (content of the component (A) in the thermosetting adhesive composition)>(content of the component (B) in the thermosetting adhesive composition).

[0055] When the content of component (A) and the content of component (B) in the thermosetting adhesive composition satisfy formula 2, the dielectric constant and dielectric dissipation factor of the thermosetting adhesive composition after curing can be more effectively reduced, the rate of change of the dielectric dissipation factor with temperature can also be more effectively reduced, and the flex resistance and heat resistance of the thermosetting adhesive composition after curing can be more effectively improved.

[0056] The component (B) may be used alone or in combination of two or more. When two or more components (B) are used in combination, it is preferable that the total amount thereof satisfies the above-mentioned range of the content.

[0057] [Radical Polymerization Initiator] The radical polymerization initiator is a catalyst that promotes the radical curing reaction of unsaturated bonds. For example, the radical polymerization initiator crosslinks the radical polymerizable groups at the molecular terminals of component (A) and the radical polymerizable groups in component (B) through thermal curing. By including a radical polymerization initiator in the thermosetting adhesive composition, the heat resistance of the cured thermosetting adhesive composition can be improved. From the viewpoint of the shelf life (life) of the thermosetting adhesive composition at room temperature, the radical polymerization initiator is preferably a peroxide with a high reaction initiation temperature. For example, an organic peroxide with a decomposition temperature of 170°C or higher that results in a half-life of 1 minute is preferred. Examples of such organic peroxides include dicumyl peroxide (decomposition temperature of 175°C that results in a half-life of 1 minute), t-butylcumyl peroxide (decomposition temperature of 173°C that results in a half-life of 1 minute), and 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (decomposition temperature of 194°C that results in a half-life of 1 minute).

[0058] The content of the radical polymerization initiator is not particularly limited as long as the total content of the radical polymerization initiator, epoxy resin, and epoxy resin curing agent is within a range that satisfies 10 parts by mass or less relative to a total of 100 parts by mass of the thermosetting adhesive composition, and may be, for example, 0.5 parts by mass or more, 1 part by mass or more, 1 to 5 parts by mass, 1 to 4 parts by mass, or 1 to 3 parts by mass.

[0059] The radical polymerization initiator may be used alone or in combination of two or more. When two or more radical polymerization initiators are used in combination, it is preferable that the total amount thereof satisfies the above-mentioned range of the content.

[0060] [Epoxy Resin] Examples of epoxy resins include epoxy resins having a naphthalene skeleton, bisphenol A type epoxy resins, bisphenol F type epoxy resins, phenol novolac type epoxy resins, alicyclic epoxy resins, siloxane type epoxy resins, biphenyl type epoxy resins, glycidyl ester type epoxy resins, glycidyl amine type epoxy resins, hydantoin type epoxy resins, etc. In particular, from the viewpoint of film formability, the epoxy resin is preferably an epoxy resin having a naphthalene skeleton, a bisphenol A type epoxy resin, or a bisphenol F type epoxy resin that is liquid at room temperature.

[0061] The content of the epoxy resin is not particularly limited as long as the total content of the radical polymerization initiator, epoxy resin, and epoxy resin curing agent is within a range that satisfies 10 parts by mass or less relative to a total of 100 parts by mass of the thermosetting adhesive composition; for example, it may be less than 5 parts by mass, 0.5 parts by mass or more, 1 part by mass or more, 1 to 7 parts by mass, 1 to 6 parts by mass, 1 to 5 parts by mass, 1 to 4 parts by mass, or 1 to 3 parts by mass.

[0062] The epoxy resin may be used alone or in combination of two or more. When two or more epoxy resins are used in combination, it is preferable that the total amount thereof satisfies the above-mentioned range of the content.

[0063] [Epoxy Resin Curing Agent] The epoxy resin curing agent is a catalyst that promotes 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 curing agents. In particular, from the viewpoint of the storage stability (life) of the thermosetting 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 improved storage stability at room temperature can simplify the management of the supply and use of the thermosetting 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. A commercially available product such as Novacure 3941 (manufactured by Asahi Kasei E-Materials Corporation) can be used.

[0064] When the thermosetting adhesive composition contains an epoxy resin curing agent, the content of the epoxy resin curing agent is not particularly limited as long as the total content of the radical polymerization initiator, epoxy resin, and epoxy resin curing agent is within a range that satisfies 10 parts by mass or less relative to a total of 100 parts by mass of the thermosetting adhesive composition, and can be, for example, 0.1 parts by mass or more, alternatively 0.5 parts by mass or more, 0.8 parts by mass or more, 1 part by mass or more, 0.1 to 3 parts by mass, or 0.5 to 3 parts by mass.

[0065]

[0013] When the thermosetting adhesive composition contains a styrene-based elastomer having a functional group that accelerates the curing reaction of the epoxy resin as the styrene-based elastomer, the styrene-based elastomer having a functional group that accelerates the curing reaction of the epoxy resin is included in the content of the styrene-based elastomer described above, but is not included in the content of the epoxy resin curing agent. Similarly, when the thermosetting adhesive composition contains a component (B) having a functional group that accelerates the curing reaction of the epoxy resin as the component (B), the component (B) having a functional group that accelerates the curing reaction of the epoxy resin is included in the content of the component (B) described above, but is not included in the content of the epoxy resin curing agent.

[0014] When the thermosetting adhesive composition contains a styrene-based elastomer having a functional group that accelerates the curing reaction of the epoxy resin as the styrene-based elastomer, or when the thermosetting adhesive composition contains a component (B) having a functional group that accelerates the curing reaction of the epoxy resin as the component (B), the thermosetting adhesive composition may or may not contain a separate epoxy resin curing agent.

[0066] The epoxy resin curing agent may be used alone or in combination of two or more. When two or more epoxy resin curing agents are used in combination, it is preferable that the total amount thereof satisfies the above-mentioned range of the content.

[0067] In the thermosetting adhesive composition according to the present technology, the total content of the radical polymerization initiator, epoxy resin, and epoxy resin curing agent is 10 parts by mass or less, alternatively 9 parts by mass or less, or alternatively 5 parts by mass or less, relative to a total of 100 parts by mass of the thermosetting adhesive composition (styrene-based elastomer, component (A), component (B), radical polymerization initiator, epoxy resin, and epoxy resin curing agent). By ensuring that the total content of the radical polymerization initiator, epoxy resin, and epoxy resin curing agent is 10 parts by mass or less, the dielectric properties of the thermosetting adhesive composition after curing can be improved.

[0068] Furthermore, the lower limit of the total content of the radical polymerization initiator, epoxy resin, and epoxy resin curing agent in the thermosetting adhesive composition is not particularly limited, and may be, for example, 0.1 parts by mass or more, 0.5 parts by mass or more, or 1 part by mass or more, relative to a total of 100 parts by mass of the thermosetting adhesive composition.

[0069] As described above, in a first aspect, the thermosetting adhesive composition according to the present technology contains an epoxy resin curing agent when the styrene-based elastomer does not have a functional group that accelerates the curing reaction of the epoxy resin. That is, the thermosetting adhesive composition of the first aspect contains 65 to 90 parts by mass of a styrene-based elastomer, and as crosslinking components, 5 to 20 parts by mass of (A) a modified polyphenylene ether resin having a radical polymerizable group at a molecular terminal and 4 to 10 parts by mass of (B) a polybutadiene and / or polyisoprene having a weight average molecular weight of 10,000 to 50,000, a radical polymerization initiator, an epoxy resin, and an epoxy resin curing agent, wherein the total content of the radical polymerization initiator, epoxy resin, and epoxy resin curing agent is 10 parts by mass or less, and the styrene-based elastomer contains a styrene ratio of less than 67%, and the total content of the component (A) and the component (B) is 25 parts by mass or less.

[0070]

[0013] Furthermore, in a second aspect of the present disclosure, the thermosetting adhesive composition may or may not contain an epoxy resin curing agent when the styrene-based elastomer has a functional group that accelerates the curing reaction of the epoxy resin. That is, the thermosetting adhesive composition of the second aspect contains at least 65 to 90 parts by mass of a styrene-based elastomer, (A) 5 to 20 parts by mass of a modified polyphenylene ether resin having a radical polymerizable group at a molecular terminal as a crosslinking component, and (B) 4 to 10 parts by mass of a polybutadiene and / or polyisoprene having a weight average molecular weight of 10,000 to 50,000, a radical polymerization initiator, and an epoxy resin, wherein the total content of the radical polymerization initiator and the epoxy resin is 10 parts by mass or less, and the styrene-based elastomer contains a styrene ratio of less than 67%, and the total content of the component (A) and the component (B) is 25 parts by mass or less.

[0071] [Other Components] The thermosetting adhesive composition may further contain other components in addition to the above-described components, as long as the effects of the present technology are not impaired. Examples of other components include organic solvents, adhesion promoters such as silane coupling agents, and fillers for adjusting flowability and imparting flame retardancy. The organic solvent is not particularly limited, and examples thereof include alcohol-based solvents, ketone-based solvents, ether-based solvents, aromatic solvents, and ester-based solvents. Among these, aromatic solvents and ester-based solvents are preferred from the viewpoint of solubility. The organic solvent may be used alone or in combination of two or more.

[0072] <Thermosetting Adhesive Sheet> The thermosetting adhesive sheet according to the present technology has a substrate and a thermosetting adhesive layer formed from the above-described thermosetting adhesive composition, and is in the form of a film. The thermosetting adhesive sheet can be obtained, for example, by diluting the above-described thermosetting adhesive composition with a solvent, applying it to at least one surface of the substrate using a bar coater, roll coater, or the like so that the thickness after drying is 10 to 60 μm, and drying it at a temperature of about 50 to 130°C. The substrate can be, for example, a polyethylene terephthalate film, a polyimide film, or the like, and optionally a release substrate that has been treated with a release agent such as silicone.

[0073] The thickness of the thermosetting adhesive layer constituting the thermosetting adhesive sheet can be set appropriately depending on the purpose, and can be, for example, 1 to 100 μm, or can also be 1 to 30 μm.

[0074] The thermosetting adhesive layer constituting the thermosetting adhesive sheet is made of a thermosetting adhesive composition that, as described above, has a low dielectric constant and dielectric loss tangent, a low rate of change of the dielectric loss tangent with temperature, and good flex resistance and heat resistance even after heat curing, and is therefore applicable, for example, to applications such as interlayer adhesives for flexible printed wiring boards and bonding and fixing terminal portions of flexible printed wiring boards to connecting substrates that back them up. In addition, the thermosetting adhesive sheet also has good peel strength and heat resistance after curing, and good storage properties at room temperature.

[0075] <Printed Wiring Board> The printed wiring board according to the present technology includes, for example, a substrate and a wiring pattern side of a wiring substrate having a wiring pattern, and a coverlay laminated together via a cured product (thermosetting adhesive layer) of the above-described thermosetting adhesive composition. The printed wiring board can be obtained, for example, by arranging a thermosetting adhesive layer of a thermosetting adhesive sheet between the wiring pattern side of the wiring substrate and the coverlay, and then thermocompressing the substrate to integrate the wiring substrate and the coverlay. The coverlay is an insulating layer for protecting the wiring pattern of the wiring substrate.

[0076] Like the adhesive composition described above, the wired substrate preferably has excellent electrical properties in the high frequency range, for example, a low dielectric constant and dielectric loss tangent in the frequency range of 1 to 10 GHz. Specific examples of the substrate include substrates whose main component is liquid crystal polymer (LCP), polytetrafluoroethylene, polyimide, or polyethylene naphthalate. Among these substrates, substrates whose main component is liquid crystal polymer (liquid crystal polymer film) are preferred. Liquid crystal polymers have an extremely low moisture absorption rate compared to polyimides, and are less susceptible to the environment in which they are used.

[0077]

[0023] The following describes an example of the configuration of a printed wiring board using the thermosetting adhesive composition according to the present technology. The printed wiring board 1 shown in Fig. 1 is configured such that the copper foil 3 side of a wiring substrate (copper-clad laminate: CCL) including a liquid crystal polymer film 2 and a copper foil (rolled copper foil) 3 is laminated with a liquid crystal polymer film 4 via a cured product layer 5 made of the above-mentioned thermosetting adhesive composition (thermosetting adhesive layer).

[0078] The printed wiring board may also have a multilayer structure as shown in Fig. 2. The printed wiring board 6 shown in Fig. 2 is formed by laminating, for example, the copper plating layer 9 side of a wiring substrate including a polyimide layer 7 (thickness 25 µm), a copper foil 8 (thickness 18 µm), and a copper plating layer 9 (thickness 10 µm) and a coverlay 10 (thickness 25 µm) via a cured product layer 5 (thickness 35 µm) made of the above-mentioned thermosetting adhesive composition (thermosetting adhesive layer) (total thickness 201 µm).

[0079] Hereinafter, examples of the present technology will be described, but the present technology is not limited to these examples.

[0080] <Styrene-based elastomers> Tuftec H1221: hydrogenated styrene-based thermoplastic elastomer (styrene ratio 12%), manufactured by Asahi Kasei Corporation Tuftec M1911: hydrogenated styrene-based thermoplastic elastomer (styrene ratio 30%), manufactured by Asahi Kasei Corporation Tuftec H1051: hydrogenated styrene-based thermoplastic elastomer (styrene ratio 42%), manufactured by Asahi Kasei Corporation Tuftec H1043: hydrogenated styrene-based thermoplastic elastomer (styrene ratio 67%), manufactured by Asahi Kasei Corporation

[0081] <(A) Modified polyphenylene ether resin having radically polymerizable groups at molecular terminals> OPE-2St2200: modified polyphenylene ether resin (Mn=2,200) having vinylbenzyl groups at both molecular terminals, manufactured by Mitsubishi Gas Chemical Company, Inc. SA9000: modified polyphenylene ether resin (Mw=1,700) having methacryloyl groups at both molecular terminals, manufactured by SABIC Corporation

[0082] <(A') Modified polyphenylene ether resin having no radically polymerizable groups at molecular terminals> S201A: polyphenylene ether resin having hydroxyl groups at both molecular terminals, manufactured by Asahi Kasei Corporation

[0083] <(B) Polybutadiene and / or polyisoprene having a weight average molecular weight of 10,000 to 50,000> Ricon 154: liquid polybutadiene (Mw=15,000, Mn=5,200), manufactured by Cray Valley Corporation LIR-30: liquid polyisoprene (Mw=28,000), manufactured by Kuraray Co., Ltd.

[0084] <(B') Polybutadiene and / or polyisoprene having a weight average molecular weight of less than 10,000 or more than 50,000> LIR-50: liquid polyisoprene (Mw=54,000), manufactured by Kuraray Co., Ltd. B-3000: liquid polybutadiene (Mw=8,000, Mn=3,000), manufactured by Nippon Soda Co., Ltd.

[0085] <Radical polymerization initiator> Dicumyl peroxide: (Decomposition temperature for half-life of 1 minute is 175°C) Dilauroyl peroxide: (Decomposition temperature for half-life of 1 minute is 116°C)

[0086] <Epoxy resin> JER828: Epoxy resin, manufactured by Mitsubishi Chemical Corporation 4032D: Naphthalene-type epoxy resin, manufactured by DIC Corporation

[0087] <Epoxy resin curing agent> Novacure 3941: a microcapsule-type latent curing agent having a core of modified imidazole and its surface coated with polyurethane, manufactured by Asahi Kasei E-materials Corporation. 2E4MZ: 2-ethyl-4-methylimidazole (a non-latent imidazole).

[0088] <Preparation of Thermosetting Adhesive Compositions> Each component shown in Tables 1 and 2 was weighed out to the mass shown in Tables 1 and 2, and uniformly mixed in an organic solvent containing toluene and ethyl acetate to prepare a thermosetting adhesive composition (a coating material for forming a thermosetting adhesive layer). Regarding the "relationship between (A) and (B)" in Tables 1 and 2, for example, in Example 1 in Table 1, the column "(A) + (B) ≦ 25" states "Satisfied 24," which means that the total content of the (A) component and the (B) component is 24 parts by mass, satisfying the above-mentioned formula 1. Furthermore, in Comparative Example 9 in Table 2, the column "(A) + (B) ≦ 25" states "Not Satisfied 30," which means that the total content of the (A) component and the (B) component is 30 parts by mass, not satisfying the above-mentioned formula 1.

[0089] <Preparation of Thermosetting Sheet> The obtained thermosetting adhesive composition was applied to a polyethylene terephthalate film that had been subjected to a release treatment, and then dried in a drying oven at 40 to 130°C to prepare a thermosetting adhesive sheet having a polyethylene terephthalate film and a 25 μm-thick thermosetting adhesive layer.

[0090] <Evaluation> <Evaluation of the coatability (film state) of the coating material for forming a thermosetting adhesive layer> When producing the above-mentioned thermosetting adhesive sheet, the coatability of the thermosetting adhesive composition was evaluated according to the following criteria. The results are shown in Tables 1 and 2. In practical terms, a rating of A is preferable.

[0091] A: The compatibility of the thermosetting adhesive composition is good, and it is possible to carry out the evaluation described below in the film state. B: The compatibility of the thermosetting adhesive composition is poor, and it is impossible to carry out the evaluation described below in the film state.

[0092] <Dielectric Constant (Dk)> The thermosetting adhesive sheets prepared in the Examples and Comparative Examples were laminated together to prepare 1 mm thick test pieces, which were then thermally cured at 180°C and 1.0 MPa for 1 hour to prepare evaluation test pieces. The dielectric constants of these evaluation test pieces were measured using a dielectric constant measuring device (manufactured by AET Co., Ltd.) by the cavity resonance perturbation method at measurement temperatures of 23°C and 80°C and a measurement frequency of 10 GHz. The dielectric constants were evaluated according to the following criteria. The results are shown in Tables 1 and 2.

[0093] A: Dielectric constant is less than 2.30 B: Dielectric constant is 2.30 or more and less than 2.40 C: Dielectric constant is 2.40 or more and less than 2.60 D: Dielectric constant is 2.60 or more

[0094] In practice, the dielectric constant is preferably rated A or B, and more preferably A.

[0095] <Dielectric loss tangent (Df)> The dielectric loss tangent of the evaluation test piece was determined in the same manner as in the measurement of the dielectric constant described above. The dielectric loss tangent was evaluated according to the following criteria. The results are shown in Tables 1 and 2.

[0096] A: Dielectric loss tangent is less than 0.0020 B: Dielectric loss tangent is 0.0020 or more and less than 0.0030 C: Dielectric loss tangent is 0.0030 or more and less than 0.0050 D: Dielectric loss tangent is 0.0050 or more

[0097] In practical terms, the dielectric loss tangent is preferably evaluated as A or B, and more preferably as A. That is, the thermosetting adhesive composition has a dielectric loss tangent after curing of preferably less than 0.0030 at both 23°C and 80°C, and more preferably less than 0.0020 at both.

[0098] <Change in dielectric tangent> The change (%) of the measured value at 80°C relative to the measured value at 23°C was determined and evaluated according to the following criteria. The results are shown in Tables 1 and 2. A: The change between 23°C and 80°C was less than 30%. B: The change between 23°C and 80°C was 30% or more but less than 50%. C: The change between 23°C and 80°C was 50% or more.

[0099] In practice, the rate of change in dielectric loss tangent is preferably evaluated as A or B, and more preferably as A. That is, the thermosetting adhesive composition preferably exhibits a rate of change in dielectric loss tangent after curing, as expressed by the above-mentioned formula 1, of less than 50%, and more preferably less than 30%.

[0100] <Peel Strength (Peel)> The obtained thermosetting adhesive sheet was cut into strips (2 cm x 5 cm) of a predetermined size, and the cut thermosetting adhesive layer was temporarily attached to a 2 cm x 7 cm x 50 μm thick liquid crystal polymer film using a laminator set at 100 ° C., and then the substrate (polyethylene terephthalate film) was removed to expose the thermosetting adhesive layer. The exposed thermosetting adhesive layer was then placed on top of the rolled copper foil surface (the surface that had not been roughened) of a copper-clad laminate (CCL consisting of a 12 μm thick rolled copper foil and a 50 μm thick liquid crystal polymer film) of the same size, and thermally cured at 180 ° C. and 1.0 MPa for 1 hour. A sample was thus prepared.

[0101] The obtained samples were subjected to a 90-degree peel test at a peel rate of 50 mm / min, and the force required for peeling (initial peel strength and peel strength after reliability test) was measured. The results are shown in Tables 1 and 2.

[0102] [Initial (measured directly after thermal curing under the above-mentioned conditions of 180°C and 1.0 MPa)] A: Peel strength is 8 N / cm or more B: Peel strength is 6 N / cm or more but less than 8 N / cm C: Peel strength is 4 N / cm or more but less than 6 N / cm D: Peel strength is less than 4 N / cm

[0103] [After reliability test (85°C, 85% relative humidity, 240 hours (i.e., after thermal curing under the above-mentioned conditions of 180°C and 1.0 MPa, the sample was placed in an environment of 85°C and 85% relative humidity for 240 hours, and then removed and measured 3 hours later)] A: Peel strength is 7 N / cm or more B: Peel strength is 5 N / cm or more but less than 7 N / cm C: Peel strength is 3 N / cm or more but less than 5 N / cm D: Peel strength is less than 3 N / cm

[0104] In practice, the evaluation of the initial peel strength and the peel strength after the reliability test is preferably A or B, and A is more preferable.

[0105] <Heat Resistance (Solder Heat Resistance)> The above samples were subjected to a solder float test at 288°C for 10 seconds three times, and the appearance of the samples after the test was visually inspected to determine whether peeling or blistering had occurred, and evaluated according to the following criteria. The results are shown in Tables 1 and 2.

[0106] A: No abnormalities after three passes B: No abnormalities after two passes, but abnormalities such as peeling or a blister with a diameter of 0.2 mm or more occurred after the third pass C: No abnormalities after one pass, but abnormalities such as peeling or a blister with a diameter of 0.2 mm or more occurred after the second pass D: Abnormalities such as peeling or a blister with a diameter of 0.2 mm or more occurred after the first pass

[0107] In practical terms, the heat resistance is preferably evaluated as A or B, and more preferably A.

[0108] <Flexibility> The obtained thermosetting adhesive sheet was cut into strips of a predetermined size (1.5 cm x 12 cm). The cut thermosetting adhesive layer was temporarily attached to a 1.5 cm x 12 cm x 50 μm thick liquid crystal polymer film using a laminator set to 100°C. The substrate (polyethylene terephthalate film) was then removed to expose the thermosetting adhesive layer. An FPC-TEG (Test Elementary Group) for MIT flex resistance testing was then placed on the exposed thermosetting adhesive layer and thermally cured at 180°C and 1.0 MPa for 1 hour to obtain a test specimen. The structure of the TEG for MIT flex resistance testing is shown in Figure 3. TEG 11 was formed by forming copper wiring from a CCL consisting of a liquid crystal polymer film (50 μm thick) as a substrate and rolled copper foil (12 μm thick). A coverlay (not shown) was attached to the copper wiring of TEG 11. In FIG. 3 , “130 mm” represents the overall length of the TEG 11, “120 mm” represents the length of the coverlay (a laminate of a thermosetting adhesive layer and a liquid crystal polymer film), “15 mm” represents the overall width of the TEG 11 and the width of the coverlay, “11 mm” represents the distance between the copper wirings (outside), and “10 mm” represents the distance between the copper wirings (inside), with the copper wiring width being 1 mm. The MIT bending fatigue test was performed by placing the prepared test piece 12 in an MIT bending fatigue tester 13 equipped with a plunger 14, an upper chuck 15, a rotating chuck 16, and a bending roller 17, as shown in FIG. 4 . The test was performed under the conditions of a bending angle of 135°, a bending clamp angle R of 0.38, and a test speed of 175 cpm. The number of bending cycles until the copper wiring broke was confirmed. The results are shown in Tables 1 and 2.

[0109] A: The number of times of bending before breaking is 1200 or more. B: The number of times of bending before breaking is 600 or more but less than 1200. C: The number of times of bending before breaking is 300 or more but less than 600. D: The number of times of bending before breaking is less than 300.

[0110] In practical terms, the bending resistance is preferably evaluated as A or B, and more preferably A.

[0111] <Measurement of Glass Transition Temperature> The prepared thermosetting adhesive sheets were laminated together to prepare a 600 μm thick test piece, which was then thermally cured at 180°C and 1.0 MPa for 1 hour to prepare a test piece for evaluation. The glass transition temperature of this test piece was determined by heating it from -60°C to 250°C at a rate of 10°C / min using a dynamic viscoelasticity measuring device (manufactured by TA Instruments). In the case of copolymerized polymers or mixtures of multiple components, multiple tan δ peaks may be detected. In such cases, the temperature of the tan δ peak showing the higher value (the one with the larger change in elastic modulus) was used as the glass transition temperature. The results are shown in Tables 1 and 2.

[0112]

[0113]

[0114] As in Examples 1 to 10, the thermosetting adhesive composition for bonding substrates contains 65 to 90 parts by mass of a styrene-based elastomer, 5 to 20 parts by mass of component (A) and 4 to 10 parts by mass of component (B) as crosslinking components, a radical polymerization initiator, and an epoxy resin, with the total content of the radical polymerization initiator, epoxy resin, and epoxy resin curing agent being 10 parts by mass or less, and containing a styrene-based elastomer having a styrene ratio of less than 67% as the styrene elastomer, and the total content of the component (A) and the component (B) being 25 parts by mass or less, and it was found that the thermosetting adhesive composition had low dielectric constant and dielectric dissipation factor even after heat curing, and also had a low rate of change of the dielectric dissipation factor with temperature (rate of change of the dielectric dissipation factor with temperature from 23 to 80°C), and had good flex resistance and heat resistance.

[0115] Regarding the dielectric constant and dielectric dissipation factor after curing, it was found that the thermosetting adhesive compositions of Examples 1 to 10 had a dielectric dissipation factor after curing of less than 0.003 at both 23° C. and 80° C. Furthermore, regarding the rate of change of the dielectric dissipation factor with temperature, it was found that the thermosetting adhesive compositions of Examples 1 to 10 exhibited a rate of change expressed by Equation 1 of less than 50%.

[0116] Furthermore, from the results of Example 2 and the other Examples, it was found that thermosetting adhesive compositions in which the contents of components (A) and (B) satisfy Equation 2, i.e., the content of component (A) is greater than the content of component (B), tend to have lower dielectric loss tangents after curing and lower rates of change of the dielectric loss tangent with temperature. Specifically, it was found that the thermosetting adhesive compositions of Examples 1, 3, 5, 6, 7, 9, and 10 had dielectric loss tangents after curing that were less than 0.0020 at both 23°C and 80°C, and the rate of change expressed by Equation 1 was less than 30%.

[0117] Furthermore, for example, from the results of Example 4 and the other Examples, it was found that thermosetting adhesive compositions that do not use polybutadiene and / or polyisoprene having a weight average molecular weight of more than 50,000 in combination with component (B), in other words, thermosetting adhesive compositions that do not contain polybutadiene and / or polyisoprene having a weight average molecular weight of more than 50,000, tend to have lower dielectric tangents and temperature change rates of the dielectric tangents after curing.

[0118] Furthermore, for example, from the results of Example 5 and the other Examples, it was found that thermosetting adhesive compositions that do not use polybutadiene and / or polyisoprene having a weight-average molecular weight of less than 10,000 in combination with component (B), in other words, thermosetting adhesive compositions that do not contain polybutadiene and / or polyisoprene having a weight-average molecular weight of more than 10,000, tend to have better peel strength and flex resistance.

[0119] Furthermore, for example, from the results of Example 7 and the other Examples, it was found that thermosetting adhesive compositions containing a styrene-based elastomer with a styrene ratio of less than 42% (e.g., 12 to 30%) as the styrene-based elastomer tend to have good dielectric properties as well as better peel strength and flex resistance.

[0120] Furthermore, for example, from the results of Example 8 and the other Examples, it was found that when the content of the epoxy resin is less than 5 parts by mass per 100 parts by mass of the total of the thermosetting adhesive composition, the dielectric tangent after curing and the temperature change rate of the dielectric tangent tend to be lower.

[0121] It was found that the thermosetting adhesive composition of Comparative Example 1 did not contain component (B), and therefore it was difficult to suppress the rate of change of the dielectric loss tangent with temperature.

[0122] The thermosetting adhesive composition of Comparative Example 2 did not contain component (B), and in addition, the content of component (A) exceeded 20 parts by mass, making it difficult to suppress the rate of change of the dielectric tangent with temperature.

[0123] The thermosetting adhesive composition of Comparative Example 3 does not contain component (B), in other words, it does not contain component (B) and contains only (B') polybutadiene and / or polyisoprene having a weight average molecular weight of more than 50,000, and therefore it was found that it was difficult to suppress the rate of change of the dielectric tangent with temperature.

[0124] The thermosetting adhesive composition of Comparative Example 4 did not contain component (B), in other words, it did not contain component (B) and contained only (B') polybutadiene and / or polyisoprene having a weight average molecular weight of less than 10,000, and therefore it was found that the peel strength and flex resistance were not good.

[0125] It was found that it was difficult to reduce the dielectric loss tangent of the thermosetting adhesive composition of Comparative Example 5 because it did not contain component (A).

[0126] It was found that the thermosetting adhesive composition of Comparative Example 6 had poor peel strength and flex resistance because the content of component (B) was as high as more than 10 parts by mass.

[0127] It was found that the thermosetting adhesive composition of Comparative Example 7 did not contain a styrene-based elastomer with a styrene ratio of less than 67%, and therefore did not have good peel strength and flex resistance.

[0128] The thermosetting adhesive composition of Comparative Example 8 did not contain a radical polymerization initiator, and therefore it was difficult to reduce the dielectric loss tangent at 80°C, it was also difficult to suppress the rate of change of the dielectric loss tangent with temperature, and it was found that the heat resistance was not good.

[0129] It was found that the thermosetting adhesive composition of Comparative Example 9 did not have good peel strength and flex resistance because the total content of component (A) and component (B) exceeded 25 parts by mass.

[0130] The thermosetting adhesive composition of Comparative Example 10 contained a large amount of styrene-based elastomer, exceeding 90 parts by mass, and therefore contained relatively small amounts of components (A) and (B). As a result, it was found that it was difficult to reduce the dielectric tangent at 80°C, it was also difficult to suppress the rate of change of the dielectric tangent with temperature, and the heat resistance was not good.

[0131] The thermosetting adhesive composition of Comparative Example 11 had a low styrene-based elastomer content of less than 65 parts by mass, and also had a high total content of the radical polymerization initiator, epoxy resin, and epoxy resin curing agent of more than 10 parts by mass. This made it difficult to reduce the dielectric constant and dielectric dissipation factor, and it was also difficult to suppress the rate of change of the dielectric dissipation factor with temperature.

[0132] The thermosetting adhesive composition of Comparative Example 12 had a high total content of the radical polymerization initiator, epoxy resin, and epoxy resin curing agent of more than 10 parts by mass, and therefore it was found that it was difficult to reduce the dielectric constant and dielectric dissipation factor, and it was also difficult to suppress the rate of change of the dielectric dissipation factor with temperature.

[0133] The thermosetting adhesive composition of Comparative Example 13 did not contain component (A), in other words, it used a polyphenylene ether resin having a hydroxyl group at the molecular end instead of a radically polymerizable group, and therefore it was found that the film was in poor condition and could not be evaluated (dielectric constant, dielectric loss tangent, peel strength, rate of change of dielectric loss tangent with temperature, heat resistance, and flex resistance).

[0134] DESCRIPTION OF SYMBOLS 1 Printed wiring board, 2 Liquid crystal polymer film, 3 Copper foil, 4 Liquid crystal polymer film, 5 Cured layer of adhesive composition, 6 Printed wiring board, 7 Polyimide layer, 8 Copper foil, 9 Copper plated layer, 10 Coverlay, 11 TEG, 12 Test piece, 13 MIT folding fatigue tester, 14 Plunger, 15 Upper chuck, 16 Rotating chuck, 17 Bending link

Claims

1. A thermosetting adhesive composition for bonding substrates, comprising, relative to a total of 100 parts by mass of the thermosetting adhesive composition, 65 to 90 parts by mass of a styrene-based elastomer, and as crosslinking components, (A) 5 to 20 parts by mass of a modified polyphenylene ether resin having a radically polymerizable group at the molecular terminal, and (B) 4 to 10 parts by mass of polybutadiene and / or polyisoprene having a weight average molecular weight of 10,000 to 50,000, a radical polymerization initiator, and an epoxy resin, wherein the total content of the radical polymerization initiator, epoxy resin, and epoxy resin curing agent is 10 parts by mass or less, and the styrene-based elastomer contains a styrene ratio of less than 67%, and the total content of the (A) component and the (B) component is 25 parts by mass or less.

2. The thermosetting adhesive composition according to claim 1, wherein the dielectric loss tangent after curing is less than 0.0030 at both 23°C and 80°C, and the rate of change, as expressed by the following formula 1, is less than 50%. Formula 1: Rate of change (%) = ((dielectric loss tangent of the thermosetting adhesive composition after curing at 80°C) / (dielectric loss tangent of the thermosetting adhesive composition after curing at 23°C) - 1) x 100 3. The thermosetting adhesive composition according to claim 1 or 2, wherein the content of the component (A) and the content of the component (B) satisfy the following formula 2: (content of component (A) in the thermosetting adhesive composition) > (content of component (B) in the thermosetting adhesive composition).

4. A thermosetting adhesive composition according to claim 1 or 2, wherein the content of the epoxy resin is less than 5 parts by mass.

5. The thermosetting adhesive composition according to claim 2, wherein the rate of change represented by the above formula 1 is less than 30%.

6. The thermosetting adhesive composition according to claim 1 or 2, wherein the styrene ratio of the styrene-based elastomer is 42% or less.

7. The thermosetting adhesive composition according to claim 1 or 2, further comprising an epoxy resin curing agent.

8. The thermosetting adhesive composition according to claim 1 or 2, wherein the radical polymerization initiator is an organic peroxide having a decomposition temperature of 170°C or higher, which gives a half-life of 1 minute.

9. A thermosetting adhesive composition according to claim 1 or 2, wherein the styrene elastomer contains a styrene elastomer having a functional group that accelerates the curing reaction of the epoxy resin.

10. A thermosetting adhesive sheet comprising a substrate and an adhesive layer formed on the substrate, the adhesive layer comprising the thermosetting adhesive composition according to claim 1 or 2.

11. A printed wiring board in which the wiring pattern side of a wiring-equipped resin substrate having a substrate and a wiring pattern is laminated with a coverlay via a cured product of the thermosetting adhesive composition described in claim 1 or 2.

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