Thermosetting adhesive composition, thermosetting adhesive sheet and printed wiring board

Abstract

To provide a thermosetting adhesive composition which has, after thermally cured, a low dielectric constant, a low dielectric loss tangent, a low temperature change rate of the dielectric loss tangent, and good bending resistance.SOLUTION: A thermosetting adhesive composition for bonding between substrates is provided, containing with respect to 100 pts.mass of the total of the thermosetting adhesive composition, 65 to 90 pts.mass of a styrenic elastomer, as crosslinking components, 5 to 20 pts.mass of (A) a modified polyphenylene ether resin having a radical polymerizable group at a molecular terminal, 4 to 10 pts.mass of (B) 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 of the contents of the radical polymerization initiator, the epoxy resin and the epoxy resin curing agent is 10 pts.mass or less, a styrenic elastomer having a styrene ratio of less than 67% is contained as the styrenic elastomer, and the total of the content of the component (A) and the content of the component (B) is 25 pts.mass or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present technology relates to a thermosetting adhesive composition, a thermosetting adhesive sheet, and a printed wiring board. [Background technology]

[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), a resin material for high frequencies, as a guideline.

[0004] The signal transmission loss in a high-frequency circuit depends on its dielectric dissipation factor (tanδ), which is an index of the loss, but the dielectric dissipation factor generally worsens with temperature. Therefore, there is a demand for materials that do not worsen signal transmission loss, i.e., do not significantly increase their dielectric dissipation factor, even in environments where the temperature around the circuit rises 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, nor do they mention or suggest, reducing the rate of change of the dielectric 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 having poor flexibility due to its very high melting point (softening point) and its hard nature 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. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 7351912 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-131866 Summary of the Invention [Problem to be solved by the invention]

[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. [Means for solving the problem]

[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, 5 to 20 parts by mass of (A) a modified polyphenylene ether resin having a radically polymerizable group at a molecular terminal as a crosslinking component, and 4 to 10 parts by mass of (B) 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. [Effects of the Invention]

[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. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view showing an example of the configuration of a printed wiring board. [Figure 2] FIG. 2 is a cross-sectional view showing an example of the configuration of a multilayer printed wiring board. [Figure 3] FIG. 3 is a plan view showing an example of the configuration of a TEG used in a bending resistance test. [Figure 4] FIG. 4 is a perspective view showing a measuring device used in the bending resistance test. DETAILED DESCRIPTION OF THE INVENTION

[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 the Japanese Industrial Standards (JIS Z 8703).

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

[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 (hereinafter also referred to as component (A)) having radically polymerizable groups at the molecular terminals 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 a total amount of 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 a total amount of 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 after curing of less than 0.0030 at both 23°C and 80°C, and can exhibit a rate of change expressed by the following formula 1 of less than 50%. Equation 1: Rate of change (%) = ((Dielectric loss tangent of the cured thermosetting adhesive composition at 80°C) / (Dielectric loss tangent of the cured thermosetting adhesive composition at 23°C) - 1) × 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, the more preferable. 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 components to be mounted or connected to another printed wiring board by a solder reflow process or hot bar soldering process, similar to conventional printed wiring boards, even in high-frequency printed wiring boards. Therefore, the thermosetting adhesive composition according to the present technology can be suitably used for joining substrates, for example, as an adhesive (interlayer adhesive) for flexible printed wiring boards.

[0022] An example of the composition of the thermosetting adhesive composition according to the present technology is described below. The thermosetting adhesive composition according to the present technology contains a styrene-based elastomer, component (A), component (B), a radical polymerization initiator, and an epoxy resin, and may further contain an epoxy resin curing agent as necessary.

[0023] [Styrene-based 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 / 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 elastomers) in which the double bonds of the conjugated diene components 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 per 100 parts by mass of the total thermosetting adhesive composition. By ensuring that the content of the styrene-based elastomer is 65 parts by mass or more, the relative contents of other components (e.g., radical polymerization initiator, epoxy resin, and epoxy resin curing agent) are not too high, and the dielectric constant and dielectric loss tangent of the cured thermosetting adhesive composition, as well as the temperature change rate of the dielectric loss tangent of the cured thermosetting adhesive composition, can be reduced. Furthermore, by ensuring that the content of the styrene-based elastomer is 90 parts by mass or less, the relative contents of other components (e.g., component (A) and component (B)) are not too low, and the temperature change rate of the dielectric loss tangent 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 styrene-based elastomer content 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 elastomer may be used alone or in combination of two or more. When two or more styrene 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 radically polymerizable group at its molecular terminal, is a crosslinking component and has a polyphenylene ether chain in the molecule and a radically polymerizable group at its molecular terminal. As described above, the radically polymerizable group at the molecular terminal of component (A) is crosslinked by the 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 radically 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 terminals. 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] An example of component (A), a modified polyphenylene ether resin having vinylbenzyl groups at both molecular terminals, can be obtained, for example, by vinylbenzyl-etherifying the terminal phenolic hydroxyl groups of a difunctional phenylene ether oligomer obtained by oxidative coupling of a difunctional 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 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] [(B) Component] 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, and a resin having a polybutadiene structure and a polyisoprene structure and a weight-average molecular weight of 10,000 to 50,000, or a combination of these. Furthermore, as long as component (B) contains a butadiene structure or a polyisoprene structure as the main component, it may contain structures other than the butadiene structure and the polyisoprene structure as long as the effects of the present technology are not impaired. However, from the viewpoint of improving the effects of the present technology, compatibility with other components, dispersibility, etc., it is preferable that component (B) is substantially free of other structures (e.g., a styrene structure). From the viewpoint of ease of handling, it is preferable that component (B) be 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] Component (B) may have a functional group that accelerates the curing reaction of the epoxy resin. When component (B) has a functional group that accelerates the curing reaction of the epoxy resin, it also functions as an epoxy resin curing agent, eliminating the need for 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 component (B) 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 ensuring that the weight-average molecular weight of component (B) is 50,000 or less, the crosslink density can be prevented from becoming too low, the rate of change of the dielectric tangent of the cured thermosetting adhesive composition with temperature can be reduced, and compatibility with component (A) can be improved. 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 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 20 parts by mass or more.

[0054] Furthermore, it is preferable that the content of the component (A) and the content of the component (B) satisfy the following formula 2. Equation 2: (Content of component (A) in thermosetting adhesive composition)>(Content of component (B) in 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 cured thermosetting adhesive composition 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 cured thermosetting adhesive composition 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, which results in a half-life of 1 minute, is preferred. Examples of such organic peroxides include dicumyl peroxide (decomposition temperature of 175°C, which results in a half-life of 1 minute), t-butylcumyl peroxide (decomposition temperature of 173°C, which results in a half-life of 1 minute), and 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (decomposition temperature of 194°C, which 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 of 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, 0.5 parts by mass or more, or 1 part by mass or more, or 1 to 5 parts by mass, or 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 of 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 hardener] The epoxy resin curing agent is a catalyst that accelerates 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 life (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 life at room temperature simplifies 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 of 10 parts by mass or less relative to a total of 100 parts by mass of the thermosetting adhesive composition. For example, the content may be 0.1 parts by mass or more, 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] 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 (B) component having a functional group that accelerates the curing reaction of the epoxy resin as the component (B), the (B) component having a functional group that accelerates the curing reaction of the epoxy resin is included in the content of the (B) component described above, but is not included in the content of the epoxy resin curing agent. 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 (B) component 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 the 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 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] Furthermore, in a second aspect of the thermosetting adhesive composition according to the present technology, when the styrene-based elastomer has a functional group that accelerates the curing reaction of the epoxy resin, the thermosetting adhesive composition may or may not contain an epoxy resin curing agent. That is, the thermosetting adhesive composition according to 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 radically 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 ingredients] The thermosetting adhesive composition may further contain other components in addition to the above-mentioned 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. One type of organic solvent may be used alone, or two or more types may be used in combination.

[0072] <Thermosetting adhesive sheet> The thermosetting adhesive sheet according to the present technology has a film shape and includes a substrate and a thermosetting adhesive layer formed thereon, the thermosetting adhesive layer being made of the thermosetting adhesive composition described above. The thermosetting adhesive sheet can be obtained, for example, by diluting the thermosetting adhesive composition described above with a solvent, applying the diluted composition to at least one surface of the substrate using a bar coater, roll coater, or the like so that the dried thickness is 10 to 60 μm, and drying 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 subjected to a release treatment with silicone or the like.

[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 is, for example, a laminate of the wiring pattern side of a wiring substrate having a substrate and a wiring pattern and a coverlay, with a cured product (thermosetting adhesive layer) of the above-mentioned thermosetting adhesive composition interposed therebetween. 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 two together 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] An example of the configuration of a printed wiring board using the thermosetting adhesive composition according to the present technology will be described. 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) comprising 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] Furthermore, the printed wiring board may 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), copper foil 8 (thickness 18 µm), and 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). [Example]

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

[0080] <Styrene-based elastomer> 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 the molecular terminals> OPE-2St2200: Modified polyphenylene ether resin (Mn=2,200) with vinylbenzyl groups at both ends of the molecule, manufactured by Mitsubishi Gas Chemical Company, Inc. SA9000: Modified polyphenylene ether resin (Mw=1,700) with methacryloyl groups at both ends of the molecule, manufactured by SABIC

[0082] <(A') Modified polyphenylene ether resin having no radically polymerizable groups at the molecular terminals> S201A: Polyphenylene ether resin with hydroxyl groups at both ends of the molecule, 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 LIR-30: Liquid polyisoprene (Mw=28,000), manufactured by Kuraray

[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 B-3000: Liquid polybutadiene (Mw=8,000, Mn=3,000), manufactured by Nippon Soda Co., Ltd.

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

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

[0087] <Epoxy resin hardener> Novacure 3941: A microcapsule-type latent curing agent consisting of a core of imidazole modified substance coated with polyurethane, manufactured by Asahi Kasei E-Materials Corporation 2E4MZ: 2-ethyl-4-methylimidazole (non-latent imidazole)

[0088] <Preparation of Thermosetting Adhesive Composition> 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 for "(A) + (B) ≦ 25" states "Satisfied 24," meaning that the total content of component (A) and component (B) is 24 parts by mass, satisfying the above-mentioned formula 1. Furthermore, in Comparative Example 9 in Table 2, the column for "(A) + (B) ≦ 25" states "Not Satisfied 30," meaning that the total content of component (A) and component (B) 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 produce a thermosetting adhesive sheet having a polyethylene terephthalate film and a 25 μm thick thermosetting adhesive layer.

[0090] <Evaluation> <Evaluation of the coating properties (film state) of paints for forming thermosetting adhesive layers> 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 practice, a rating of A is preferable.

[0091] A: The compatibility with the thermosetting adhesive composition is good, and the evaluation described below can be carried out in the film state. B: The compatibility of the thermosetting adhesive composition is poor, making it impossible to perform 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 test pieces for evaluation. The dielectric constants of these test pieces were measured using a dielectric constant measuring device (manufactured by AET) 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 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 as A or B, and more preferably A.

[0095] <Dielectric loss tangent (Df)> The dielectric loss tangent of the evaluation specimen 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 tangent less than 0.0020 B: Dielectric tangent is 0.0020 or more and less than 0.0030 C: Dielectric tangent is 0.0030 or more and less than 0.0050 D: Dielectric tangent is 0.0050 or more

[0097] In practical terms, the dielectric loss tangent is preferably evaluated as A or B, and more preferably 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] <Rate of change of dielectric tangent> The rate of change (%) of the measured value at 80°C 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 temperature change rate between 23℃ and 80℃ is less than 30% B: The rate of change between 23℃ and 80℃ is 30% or more and less than 50% C: Change rate between 23℃ and 80℃ is 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 represented by the above-mentioned formula 1, of less than 50%, and more preferably less than 30%.

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

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

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

[0103] [After reliability testing (85°C, 85% relative humidity, 240 hours (i.e., after thermal curing under the above 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 7N / cm or more B: Peel strength is 5N / cm or more and less than 7N / cm C: Peel strength is 3N / cm or more and less than 5N / cm D: Peel strength is less than 3N / 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, after which the appearance of the samples was visually inspected and evaluated for peeling or swelling according to the following criteria. The results are shown in Tables 1 and 2.

[0106] A: No abnormalities after passing three times B: No abnormalities after two passes, but abnormalities such as peeling or swelling of 0.2 mm or more in diameter occur after the third pass C: No abnormalities after one pass, but abnormalities such as peeling or swelling of 0.2 mm or more in diameter occur after the second pass D: Abnormalities such as peeling or swelling of 0.2 mm or more in diameter occurred on the first try

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

[0108] <Bending resistance> The resulting thermosetting adhesive sheet was cut into strips (1.5 cm x 12 cm) of the specified size. 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 configuration of the TEG for MIT flex resistance testing is shown in Figure 3. TEG11 is a CCL consisting of a liquid crystal polymer film (50 μm thick) as the substrate and rolled copper foil (12 μm thick) to form copper wiring. A coverlay (not shown) is laminated onto the copper wiring of TEG11. In Figure 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). The copper wiring width is 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 Figure 4. The bending angle was 135°, the bending clamp angle R was 0.38, and the test speed was 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: More than 1200 bending times before breaking B: Number of times bent to break is 600 or more but less than 1200 C: Number of times of bending before breaking is 300 or more but less than 600 D: Less than 300 bending times before breaking

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

[0111] <Measurement of glass transition temperature> The thermosetting adhesive sheets were laminated together to create a 600 μm thick test piece. This test piece was then heat-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 using a dynamic viscoelasticity analyzer (TA Instruments) when the temperature was raised from -60°C to 250°C at a rate of 10°C / min. Note that multiple tan δ peaks may be detected in copolymer polymers or mixtures of multiple components. In such cases, the temperature of the tan δ peak with the highest value (the one with the greatest change in elastic modulus) was used as the glass transition temperature. The results are shown in Tables 1 and 2.

[0112] [Table 1]

[0113] [Table 2]

[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 the styrene-based elastomer containing a styrene ratio of less than 67%, and the total content of component (A) and component (B) being 25 parts by mass or less, with respect to a total of 100 parts by mass of the thermosetting adhesive composition, 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 temperature change rate of the dielectric dissipation factor (temperature change rate of the dielectric dissipation factor at 23 to 80°C), and had good flex resistance and heat resistance.

[0115] Regarding the dielectric constant and dielectric dissipation factor after curing, the thermosetting adhesive compositions of Examples 1 to 10 were found to have a dielectric dissipation factor 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, the thermosetting adhesive compositions of Examples 1 to 10 were found to exhibit 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 formula 2, i.e., the content of component (A) is greater than the content of component (B), tend to have lower dielectric tangents after curing and lower rates of change of the dielectric tangent with temperature. Specifically, it was found that the thermosetting adhesive compositions of Examples 1, 3, 5, 6, 7, 9, and 10 had dielectric tangents after curing that were less than 0.0020 at both 23°C and 80°C, and the rate of change represented by formula 1 was less than 30%.

[0117] Furthermore, for example, the results of Example 4 and the other Examples indicate 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, the results of Example 5 and the other Examples show 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, the results of Example 7 and other Examples show that thermosetting adhesive compositions containing a styrene-based elastomer with a styrene ratio of less than 42% (e.g., 12 to 30%) tend to have good dielectric properties as well as better peel strength and flex resistance.

[0120] Furthermore, for example, the results of Example 8 and the other Examples show that when the epoxy resin content is less than 5 parts by mass per 100 parts by mass of the total 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 contained more than 20 parts by mass of component (A), 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 tangent at 80°C, it was also difficult to suppress the rate of change of the dielectric 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] In the thermosetting adhesive composition of Comparative Example 12, the total content of the radical polymerization initiator, epoxy resin, and epoxy resin curing agent was high at more than 10 parts by mass, and it was therefore 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 rather than a radically polymerizable group, so the film was in poor condition and it was found that evaluations (dielectric constant, dielectric tangent, peel strength, temperature change rate of dielectric tangent, heat resistance, and flex resistance) could not be performed. [Explanation of symbols]

[0134] 1 printed wiring board, 2 liquid crystal polymer film, 3 copper foil, 4 liquid crystal polymer film, 5. A cured layer made of an adhesive composition; 6 printed wiring boards, 7 polyimide layer, 8 copper foil, 9 copper plating layer, 10 coverlay, 11 TEG, 12 test specimens, 13 MIT folding fatigue testing machine, 14 plunger, 15 Upper chuck, 16 Rotating chuck, 17 Bending frame

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; As a cross-linking component, (A) 5 to 20 parts by mass of a modified polyphenylene ether resin having a radical polymerizable group at the molecular end, (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, the total content of the radical polymerization initiator, the epoxy resin, and the epoxy resin curing agent is 10 parts by mass or less, The styrene-based elastomer contains a styrene-based elastomer having a styrene ratio of less than 67%, A thermosetting adhesive composition, wherein the total content of the component (A) and the component (B) is 25 parts by mass or less.

2. The dielectric tangent after curing is less than 0.0030 at both 23°C and 80°C, The thermosetting adhesive composition according to claim 1, wherein the rate of change represented by the following formula 1 is less than 50%: Equation 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) × 100

3. 3. The thermosetting adhesive composition according to claim 1, wherein the content of the component (A) and the content of the component (B) satisfy the following formula 2: Equation 2: (Content of component (A) in the thermosetting adhesive composition)>(Content of component (B) in the thermosetting adhesive composition)

4. The 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. 3. The thermosetting adhesive composition according to claim 1, wherein the styrene content 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. 3. The thermosetting adhesive composition according to claim 1, 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. 3. The thermosetting adhesive composition according to claim 1, wherein the styrene-based elastomer contains a styrene-based 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 comprising a resin substrate with wiring, the resin substrate having a substrate and a wiring pattern, and a coverlay laminated on the wiring pattern side of the resin substrate via a cured product of the thermosetting adhesive composition according to claim 1 or 2.

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