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

Abstract

Provided is a thermosetting adhesive composition that has low dielectric constant and dielectric loss tangent after thermal curing, low temperature change rate of dielectric loss tangent, and good bending resistance. The present technology is a thermosetting adhesive composition for bonding between substrates, which contains, relative to 100 parts by mass of the total thermosetting adhesive composition, 65 to 90 parts by mass of a styrene-based elastomer; as a cross-linking component, 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 a 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, the epoxy resin, and an epoxy resin curing agent is 10 parts by mass or less, as the styrene-based elastomer, a styrene-based elastomer having a styrene ratio of less than 67% is contained, and the total content of the (A) component and the (B) component is 25 parts by mass or less.

Description

Technical Field

[0001] This technology relates to thermosetting adhesive compositions, thermosetting adhesive sheets, and printed circuit boards. This application claims priority based on Japanese Patent Application No. 2024-055214, filed on March 29, 2024, which is incorporated herein by reference. Background Technology

[0002] The high speed and large capacity of information communication have accelerated the trend of higher frequency signals flowing through printed circuit boards. To address this, the materials (such as adhesive compositions) used in the construction of rigid substrates and flexible printed circuit boards (FPCs) are required to have characteristics such as low dielectric constant and low dielectric loss tangent.

[0003] In particular, regarding the dielectric loss tangent, based on liquid crystal polymer (LCP) used as a resin material for high-frequency applications, it is preferably less than 0.0030, and more preferably less than 0.0020.

[0004] The transmission loss of signals in high-frequency circuits depends on the dielectric loss tangent (tanδ), which is typically a metric of the signal loss. However, the dielectric loss tangent usually deteriorates with temperature. Therefore, there is a need for a material that does not worsen the signal transmission loss, i.e., the dielectric loss tangent does not increase significantly, even in environments where the circuit periphery becomes 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 circuit boards, and Patent Document 2 discloses an elastomer composition that exhibits good adhesive strength to polyimide and good high-frequency characteristics. However, the technologies described in Patent Documents 1 and 2 do not consider reducing the temperature change rate of the dielectric loss tangent, nor are they described or suggested.

[0006] In addition, for flexible printed circuit boards, which are indispensable for bending resistance, polyphenylene ether, as a substrate material with low dielectric properties, has many advantages, but its melting point (softening point) is very high and it has a relatively hard property at room temperature, thus having the disadvantage of poor bending resistance.

[0007] Thus, as an adhesive composition, it is ideal to have low dielectric constant and dielectric loss tangent after thermosetting, low temperature change rate of dielectric loss tangent, and good bending resistance.

[0008] Existing technical documents Patent documents Patent Document 1: Japanese Patent No. 7351912 Patent Document 2: Japanese Patent Application Publication No. 2015-131866 Summary of the Invention

[0009] The problem that the invention aims to solve This technology is proposed in view of the existing situation, and provides an adhesive composition that has low dielectric constant and dielectric loss tangent after thermosetting, low temperature change rate of dielectric loss tangent, and good bending resistance.

[0010] Solution for solving the problem This technology is a thermosetting adhesive composition for bonding substrates. Relative to a total of 100 parts by weight of the thermosetting adhesive composition, it contains: 65 to 90 parts by weight of a styrene-based elastomer; 5 to 20 parts by weight of (A) a modified polyphenylene ether resin having free radical polymerizable groups at the molecular ends, and 4 to 10 parts by weight of (B) polybutadiene and / or polyisoprene with a weight average molecular weight of 10,000 to 50,000; a free radical polymerization initiator; and an epoxy resin, wherein the total content of the free radical polymerization initiator, epoxy resin, and epoxy resin curing agent is 10 parts by weight or less, and the styrene-based elastomer contains a styrene ratio of less than 67%, and the total content of component (A) and component (B) is 25 parts by weight or less.

[0011] Invention Effects According to this technology, an adhesive composition can be provided that has low dielectric constant and dielectric loss tangent after thermosetting, low temperature change rate of dielectric loss tangent, and good bending resistance. Attached Figure Description

[0012] Figure 1 This is a cross-sectional view showing an example of the structure of a printed circuit board.

[0013] Figure 2 This is a cross-sectional view showing an example of the structure of a multilayer printed circuit board.

[0014] Figure 3 This is a top view showing an example of the structure of TEG used in the flexural strength test.

[0015] Figure 4 This is a three-dimensional diagram showing the measuring apparatus used in the bending resistance test. Detailed Implementation

[0016] The following describes the implementation of this technology. In this specification, room temperature refers to the range of 20℃±15℃ (5℃~35℃) as specified in Japanese Industrial Standard (JISZ 8703).

[0017] Furthermore, in this specification, the values ​​of weight-average molecular weight (Mn) and number-average molecular weight (Mn) are calculated based on the molecular weight of standard polystyrene determined by gel permeation chromatography (GPC). The specific determination conditions for the GPC method are described below.

[0018] Solvent: Tetrahydrofuran Chromatographic 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: 1.0 ml / min Injection volume: 200μL Calibration curves: Calibration curves were used for 10 samples based on standard polystyrene Mw = 605 to 5,680,000.

[0019] <Thermosetting Adhesive Compositions> The thermosetting adhesive composition of this technology contains, relative to a total of 100 parts by weight of the thermosetting adhesive composition: 65 to 90 parts by weight of a styrene-based elastomer; 5 to 20 parts by weight of a modified polyphenylene ether resin having free radical polymerizable groups at the molecular ends (hereinafter also referred to as component (A)) as a crosslinking component; and 4 to 10 parts by weight of polybutadiene and / or polyisoprene with a weight average molecular weight of 10,000 to 50,000 (hereinafter also referred to as component (B)); a free radical polymerization initiator; and an epoxy resin. Furthermore, in the thermosetting adhesive composition of this technology, the total content of the free radical polymerization initiator, epoxy resin, and epoxy resin curing agent is 10 parts by weight or less. In the thermosetting adhesive composition of this technology, the styrene-based elastomer contains a styrene-based elastomer with a styrene ratio of less than 67%. In the thermosetting adhesive composition of this technology, the total content of component (A) and component (B) is 25 parts by weight or less.

[0020] The thermosetting adhesive composition of this technology, by having a configuration that results in low dielectric constant and low dielectric loss tangent after thermosetting, and also low temperature change rate of the dielectric loss tangent. Thus, the thermosetting adhesive composition of this technology exhibits excellent dielectric properties after curing.

[0021] In the thermosetting adhesive composition of this technology, the dielectric loss tangent after curing is less than 0.0030 at both 23°C and 80°C, and the change rate shown in Formula 1 below is less than 50%.

[0022] Formula 1: Change rate (%) = ((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 The dielectric constant of the cured thermosetting adhesive composition is preferably less than 2.40, more preferably less than 2.30. The dielectric constant of the cured thermosetting adhesive composition can be determined by the method described in the examples below.

[0023] The dielectric loss tangent of the cured thermosetting adhesive composition at 23°C is preferably less than 0.0030°, more preferably less than 0.0020°. Furthermore, the dielectric loss tangent of the cured thermosetting adhesive composition at 80°C is preferably less than 0.0030°, more preferably less than 0.0020°. The dielectric loss tangent of the cured thermosetting adhesive composition can be determined by the method described in the examples below.

[0024] Furthermore, the smaller the rate of change shown in Formula 1 of the cured thermosetting adhesive composition, the better; that is, the smaller the temperature dependence of the dielectric loss tangent, the better. For example, the rate of change shown in Formula 1 of the cured thermosetting adhesive composition preferably shows less than 50%, more preferably less than 40%, and even more preferably less than 30%.

[0025] Furthermore, the thermosetting adhesive composition of this technology can adjust the glass transition temperature after curing to, for example, a range of 60–150°C, resulting in good flexural strength and heat resistance (e.g., solder heat resistance) after thermosetting. For example, due to the good heat resistance of the thermosetting adhesive composition after thermosetting, even in high-frequency printed circuit boards, components can be mounted and connected to other printed circuit boards through solder reflow and hot bar soldering processes, just as in the past. Therefore, the thermosetting adhesive composition of this technology is suitable for use in bonding substrates, for example, it is suitable as an adhesive (interlayer adhesive) for flexible printed circuit boards.

[0026] The following describes an example of the composition of the thermosetting adhesive of this technology. The thermosetting adhesive composition of this technology contains a styrene-based elastomer, component (A), component (B), a free radical polymerization initiator, and an epoxy resin, and may further contain an epoxy resin curing agent as needed.

[0027] [Styrene-based elastomers] Styrene-based elastomers are copolymers of styrene with olefins (such as butadiene, isoprene, and other conjugated dienes) and / or their hydrogenates. Styrene-based elastomers are block copolymers in which styrene is the hard segment and the conjugated diene is the soft segment. Examples of styrene-based elastomers include: styrene / butadiene / styrene block copolymers, styrene / isoprene / styrene block copolymers, styrene / ethylene / butene / styrene block copolymers, styrene / ethylene / propylene / styrene block copolymers, and styrene / butadiene block copolymers. Furthermore, styrene / ethylene / butene / styrene block copolymers, styrene / ethylene / propylene / styrene block copolymers, and styrene / butadiene block copolymers (also known as hydrogenated styrene-based elastomers) can also be used, as these have had the double bonds of the conjugated diene component eliminated through hydrogenation.

[0028] Styrene-based elastomers can also possess functional groups that promote the curing reaction of epoxy resins. When a styrene-based elastomer possesses functional groups that promote the curing reaction of epoxy resins, it also functions as an epoxy resin curing agent. Therefore, it is unnecessary to use an epoxy resin curing agent, but it is permissible to use one separately without compromising the effectiveness of this technology.

[0029] Examples of functional groups that promote the curing reaction of epoxy resins include amines and acid anhydrides. When using a styrene-based elastomer with functional groups that promote the curing reaction of epoxy resins, by film-forming the thermosetting adhesive composition of this technology, the movement of polymer chains containing these functional groups is restricted, thus imparting latency to the polymer side (e.g., the styrene-based elastomer). Examples of such styrene-based elastomers include amine-modified styrene-based elastomers and acid-modified styrene-based elastomers.

[0030] The thermosetting adhesive composition of this technology contains a styrene-based elastomer with a styrene ratio of less than 67% (e.g., 67% by mass). This results in good peel strength and flexural strength of the cured thermosetting adhesive composition. Furthermore, the lower the styrene ratio in the styrene-based elastomer, the more likely the thermosetting adhesive composition will exhibit better dielectric constant and dielectric loss tangent after curing, and also tends to have better peel strength and flexural strength.

[0031] The styrene content in styrene-based elastomers can be, for example, less than 60%, less than 50%, less than 42%, less than 42%, less than 30%, less than 20%, less than 15%, more than 12% and less than 67%, 12% to 42%, or 12% to 30%.

[0032] Specific examples of styrene-based elastomers include: Tuftec H1221 (12% styrene content, manufactured by Asahi Kasei Corporation), Tuftec MP1911 (30% styrene content, acid-modified styrene-based elastomer, manufactured by Asahi Kasei Corporation), and Tuftec H1051 (42% styrene content, manufactured by Asahi Kasei Corporation).

[0033] The content of styrene-based elastomer is 65 to 90 parts by mass relative to the total 100 parts by mass of the thermosetting adhesive composition. By ensuring that the content of styrene-based elastomer is 65 parts by mass or more, the content of other components (e.g., free radical polymerization initiator, epoxy resin, and epoxy resin curing agent) is not relatively excessive, resulting in a lower dielectric constant and dielectric loss tangent, and a lower temperature change rate of the dielectric loss tangent of the cured thermosetting adhesive composition. Furthermore, by ensuring that the content of styrene-based elastomer is 90 parts by mass or less, the content of other components (e.g., components (A) and (B)) is not relatively insufficient, resulting in a lower temperature change rate of the dielectric loss tangent of the cured thermosetting adhesive composition, and also resulting in good heat resistance of the cured thermosetting adhesive composition.

[0034] The minimum content of styrene-based elastomer relative to a total of 100 parts by weight of the thermosetting adhesive composition can be 68 parts by weight or more, or 70 parts by weight or more, or 71 parts by weight or more, or 75 parts by weight or more, or 76 parts by weight or more.

[0035] The upper limit of the content of styrene-based elastomer relative to a total of 100 parts by weight of the thermosetting adhesive composition may be 85 parts by weight or less, or 81 parts by weight or less, or 80 parts by weight or less.

[0036] Styrene-based elastomers can be used alone or in combination with two or more. When using two or more styrene-based elastomers, it is preferable that their total content meets the numerical range mentioned above.

[0037] As an example of the use of styrene-based elastomers, styrene-based elastomers with a styrene ratio of less than 67% and styrene-based elastomers with a styrene ratio of 67% or more can be used together. In this case, in the thermosetting adhesive composition, the content of styrene-based elastomers with a styrene ratio of less than 67% is preferably 50% by mass or more, and may also 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 99% by mass or more. For example, styrene-based elastomers with a styrene ratio of 42% or less and styrene-based elastomers with a styrene ratio of 67% or more can be used together. In this case, the content of styrene-based elastomers with a styrene ratio of 42% or less is preferably 50% by mass or more, relative to the total amount of styrene-based elastomers.

[0038] [(A) Ingredient] Component (A), namely the modified polyphenylene ether resin having free radical polymerizable groups at the molecular ends, is a crosslinking component. It has polyphenylene ether chains in its molecule and free radical polymerizable groups at the molecular ends. As described above, the free radical polymerizable groups at the molecular ends of component (A) are crosslinked by a free 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 60–150°C, resulting in good flexural strength and heat resistance after thermosetting. Component (A) preferably has two or more olefinic unsaturated bonds as free radical polymerizable groups in one molecule. In particular, from the viewpoint of compatibility with the aforementioned styrene-based elastomers and the dielectric properties of the cured thermosetting adhesive composition, component (A) preferably has at least one olefinic unsaturated bond (e.g., (meth)acryloyl, vinylbenzyl) at both molecular ends. Here, (meth)acryloyl refers to both acryloyl and methacryloyl groups.

[0039] It should be noted that modified polyphenylene ether resins other than component (A), such as modified polyphenylene ether resins with hydroxyl groups at the molecular end, are too polar and therefore have poor compatibility with the above-mentioned styrene-based elastomers. They may not be able to film the thermosetting adhesive composition and are therefore not preferred.

[0040] As an example of component (A), a modified polyphenylene ether resin having vinyl benzyl groups at both ends of the molecule is obtained, for example, by vinyl benzyl etherification of the terminal phenolic hydroxyl groups of a difunctional phenylene ether oligomer obtained by oxidative coupling of a difunctional phenolic compound and a monofunctional phenolic compound.

[0041] From the viewpoints of compatibility with the above-mentioned styrene-based elastomers and the ability of the cured product of the thermosetting adhesive composition to follow the height difference when the wiring pattern side of the resin substrate with wiring pattern and the protective layer are thermoset (pressed), the weight average molecular weight (or number average molecular weight) of component (A) is preferably 1000 to 3000.

[0042] Specific examples of component (A) include OPE-2St (a modified polyphenylene ether resin with vinyl benzyl groups at both ends of the molecule, manufactured by Mitsubishi Gas Chemical), OPE-2EA (a modified polyphenylene ether resin with acryloyl groups at both ends of the molecule, manufactured by Mitsubishi Gas Chemical), Noryl SA9000 (a modified polyphenylene ether resin with methacryloyl groups at both ends of the molecule, manufactured by SABIC), etc.

[0043] The content of component (A) is 5 to 20 parts by mass relative to 100 parts by mass of the total thermosetting adhesive composition. A content of component (A) of 20 parts by mass or less results in good flexural resistance. Furthermore, a content of component (A) of 5 parts by mass or more results in a lower dielectric loss tangent in the cured thermosetting adhesive composition.

[0044] The content of component (A) may be less than 18 parts by mass, less than 15 parts by mass, less than 13 parts by mass, less than 10 parts by mass, or less than 9 parts by mass relative to the total 100 parts by mass of the thermosetting adhesive composition.

[0045] The content of component (A) may be 6 or more parts by mass, 8 or more parts by mass, 9 or more parts by mass, or 10 or more parts by mass relative to a total of 100 parts by mass of the thermosetting adhesive composition.

[0046] (A) Component can be used alone or in combination with two or more. When using two or more (A) components, it is preferable that their total amount meets the numerical range of the above content.

[0047] [(B) Component] (B) is a crosslinking component, which is polybutadiene and / or polyisoprene with a weight average molecular weight of 10,000 to 50,000. (B) is at least one of the following: polybutadiene resin (resin having only a polybutadiene structure) with a weight average molecular weight of 10,000 to 50,000; polyisoprene resin (resin having only a polyisoprene structure) with a weight average molecular weight of 10,000 to 50,000; or a resin having both a polybutadiene structure and a polyisoprene structure with a weight average molecular weight of 10,000 to 50,000. Furthermore, as long as (B) contains a butadiene structure or a polyisoprene structure as a main component, it may also contain other structures besides the butadiene structure and the polyisoprene structure, to the extent that it does not impair the effect of the present invention. However, from the viewpoint of improving the effect of the present invention, compatibility with other components, dispersibility, etc., it is preferable that it substantially does not contain other structures (e.g., a styrene structure). From an operational point of view, component (B) is preferably in a liquid state at room temperature.

[0048] Polybutadiene can be any resin that has a polybutadiene structure, which can be contained in the main chain or in the side chain. Part of the butadiene structure may or may not be hydrogenated.

[0049] Polyisoprene can be any resin that has a polyisoprene structure, which can be contained in the main chain or in the side chains. A portion of the polyisoprene structure may or may not be hydrogenated.

[0050] Component (B) may have functional groups that promote the curing reaction of epoxy resin. When component (B) has functional groups that promote the curing reaction of epoxy resin, it also functions as an epoxy resin curing agent, thus eliminating the need for an epoxy resin curing agent. However, an epoxy resin curing agent may be used separately without compromising the effectiveness of this technology. Examples of functional groups that promote the curing reaction of epoxy resin include, for example, acid anhydrides. Examples of such components (B) include acid-modified polybutadiene and acid-modified polyisoprene.

[0051] Regarding the weight-average molecular weight of component (B), a weight-average molecular weight of 10,000 or higher can prevent the crosslinking density from becoming excessive, resulting in good peel strength and flexural strength of the cured thermosetting adhesive composition. The weight-average molecular weight of component (B) can be 15,000 or higher, or 20,000 or higher, or 25,000 or higher, or 30,000 or higher.

[0052] Furthermore, by having a weight-average molecular weight of component (B) of 50,000 or less, it is possible to prevent the crosslinking density from becoming too low, reduce the temperature change rate of the dielectric loss tangent of the cured thermosetting adhesive composition, and ensure good compatibility with component (A). The weight-average molecular weight of component (B) can be 45,000 or less, 40,000 or less, 35,000 or less, or 30,000 or less.

[0053] The content of component (B) is 4 to 10 parts by mass relative to the total 100 parts by mass of the thermosetting adhesive composition. With the content of component (B) being 10 parts by mass or less, the cured thermosetting adhesive composition exhibits good peel strength and flexural strength. Furthermore, with the content of component (B) being 4 parts by mass or more, the temperature change rate of the dielectric loss tangent of the cured thermosetting adhesive composition is reduced.

[0054] 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.

[0055] The content of component (B) may be 5 or more parts by mass, 6 or more parts by mass, 7 or more parts by mass, or 8 or more parts by mass relative to a total of 100 parts by mass of the thermosetting adhesive composition.

[0056] In addition, the total content of component (A) and component (B) is 25 parts by mass or less, or it can be 24 parts by mass or less, or 23 parts by mass or less, or 22 parts by mass or less, or 21 parts by mass or less, or 20 parts by mass or less, or 19 parts by mass or less, or 18 parts by mass or less, or 17 parts by mass or less, or 16 parts by mass or less.

[0057] The lower limit of the total content of component (A) and component (B) is not particularly limited within the range of the content of component (A) and component (B) as described above. For example, it can be set to 15 parts by mass or more, or 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.

[0058] Furthermore, the contents of component (A) and component (B) preferably satisfy the following formula 2.

[0059] Formula 2: (content of component (A) in the thermosetting adhesive composition) > (content of component (B) in the thermosetting adhesive composition) By ensuring that the contents of component (A) and component (B) in the thermosetting adhesive composition satisfy Equation 2, the dielectric constant and dielectric loss tangent of the cured thermosetting adhesive composition can be reduced more effectively, the temperature change rate of the dielectric loss tangent can be reduced more effectively, and the flexural strength and heat resistance of the cured thermosetting adhesive composition can be improved more effectively.

[0060] (B) Component may be used alone or in combination with two or more. When two or more (B) components are used together, it is preferable that their total amount meets the numerical range of the above content.

[0061] [Free radical polymerization initiator] Free radical polymerization initiators are catalysts that promote the free radical curing reaction of unsaturated bonds. For example, free radical polymerization initiators crosslink the free radical polymeric groups at the molecular ends of component (A) and the free radical polymeric groups in component (B) through thermosetting. By including a free 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 (lifetime) of the thermosetting adhesive composition at room temperature, the free 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 is preferred to achieve a half-life of 1 minute. Examples of such organic peroxides include: dicumyl peroxide (decomposition temperature of 175°C for achieving a half-life of 1 minute), tert-butyl peroxide (decomposition temperature of 173°C for achieving a half-life of 1 minute), and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (decomposition temperature of 194°C for achieving a half-life of 1 minute).

[0062] The content of the free radical polymerization initiator is not particularly limited as long as the total content of the free radical polymerization initiator, epoxy resin, and epoxy resin curing agent is less than 10 parts by mass relative to the total of 100 parts by mass of the thermosetting adhesive composition. For example, it can be set to more than 0.5 parts by mass, more than 1 part by mass, 1 to 5 parts by mass, 1 to 4 parts by mass, or 1 to 3 parts by mass.

[0063] Free radical polymerization initiators can be used alone or in combination with two or more. When using two or more free radical polymerization initiators, it is preferable that their total amount meets the numerical range of the above-mentioned content.

[0064] [Epoxy Resin] Examples of epoxy resins include: epoxy resins with a naphthalene skeleton, bisphenol A type epoxy resins, bisphenol F type epoxy resins, phenolic varnish type epoxy resins, alicyclic epoxy resins, siloxane type epoxy resins, biphenyl type epoxy resins, glycidyl ester type epoxy resins, glycidylamine type epoxy resins, and hydantoin type epoxy resins. In particular, from the viewpoint of film formability, epoxy resins are preferably epoxy resins with a naphthalene skeleton, bisphenol A type epoxy resins, or bisphenol F type epoxy resins, and are liquid at room temperature.

[0065] The content of epoxy resin is not particularly limited relative to the total of 100 parts by weight of the thermosetting adhesive composition, as long as the total content of the free radical polymerization initiator, epoxy resin and epoxy resin curing agent is less than 10 parts by weight. For example, it can be less than 5 parts by weight, or more than 0.5 parts by weight, or more than 1 part by weight, or 1 to 7 parts by weight, or 1 to 6 parts by weight, or 1 to 5 parts by weight, or 1 to 4 parts by weight, or 1 to 3 parts by weight.

[0066] Epoxy resin can be used alone or in combination with two or more. When using two or more epoxy resins, it is preferable that their total content meets the numerical range mentioned above.

[0067] [Epoxy resin curing agent] Epoxy resin curing agents are catalysts that promote the curing reaction of the aforementioned epoxy resin. Examples of epoxy resin curing agents include imidazole-based, phenolic, amine-based, acid anhydride-based, and organic peroxide-based agents. In particular, from the viewpoint of the shelf life (lifespan) of the thermosetting adhesive composition at room temperature, epoxy resin curing agents with latent curing properties are preferred, and more preferably imidazole-based curing agents with latent curing properties obtained through encapsulation. Good shelf life at room temperature simplifies the supply and management of the thermosetting adhesive composition. Specifically, microencapsulated latent curing agents, consisting of a latent imidazole modifier as the core and its surface coated with polyurethane, can be used as epoxy resin curing agents. Commercially available examples include Novacure 3941 (manufactured by Asahi Kasei E-Materials Co., Ltd.).

[0068] 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 free radical polymerization initiator, epoxy resin, and epoxy resin curing agent is less than 10 parts by mass relative to the total 100 parts by mass of the thermosetting adhesive composition. For example, it can be set to more than 0.1 parts by mass, more than 0.5 parts by mass, more than 0.8 parts by mass, more than 1 part by mass, or 0.1 to 3 parts by mass, or 0.5 to 3 parts by mass.

[0069] It should be noted that when the thermosetting adhesive composition contains a styrene-based elastomer with functional groups that promote the curing reaction of epoxy resin as the styrene-based elastomer, this styrene-based elastomer with functional groups that promote the curing reaction of epoxy resin is included in the content of the aforementioned styrene-based elastomer, but is not included in the content of the epoxy resin curing agent. Similarly, when the thermosetting adhesive composition contains component (B) with functional groups that promote the curing reaction of epoxy resin as component (B), this component (B) with functional groups that promote the curing reaction of epoxy resin is included in the content of the aforementioned component (B), but is not included in the content of the epoxy resin curing agent. It should be noted that when the thermosetting adhesive composition contains a styrene-based elastomer with functional groups that promote the curing reaction of epoxy resin as a styrene-based elastomer, or when the thermosetting adhesive composition contains component (B) with functional groups that promote the curing reaction of epoxy resin as component (B), the thermosetting adhesive composition may or may not contain an epoxy resin curing agent separately.

[0070] Epoxy resin curing agents can be used alone or in combination with two or more. When using two or more epoxy resin curing agents, it is preferable that their total dosage meets the numerical range of the above-mentioned content.

[0071] In this thermosetting adhesive composition, relative to a total of 100 parts by weight of the thermosetting adhesive composition (styrene-based elastomer, component (A), component (B), free radical polymerization initiator, epoxy resin, and epoxy resin curing agent), the total content of the free radical polymerization initiator, epoxy resin, and epoxy resin curing agent is 10 parts by weight or less, or 9 parts by weight or less, or 5 parts by weight or less. By ensuring that the total content of the free radical polymerization initiator, epoxy resin, and epoxy resin curing agent is 10 parts by weight or less, the cured thermosetting adhesive composition exhibits good dielectric properties.

[0072] Furthermore, there is no particular limitation on the lower limit of the total content of free radical polymerization initiator, epoxy resin, and epoxy resin curing agent in the thermosetting adhesive composition. For example, it may be 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.

[0073] As shown above, in the first embodiment, where the styrene-based elastomer does not have functional groups that promote the curing reaction of epoxy resin, the thermosetting adhesive composition of this technology includes an epoxy resin curing agent. That is, the thermosetting adhesive composition of the first embodiment contains: 65 to 90 parts by weight of a styrene-based elastomer; 5 to 20 parts by weight of (A) a modified polyphenylene ether resin having free radical polymerizable groups at the molecular ends and 4 to 10 parts by weight of (B) polybutadiene and / or polyisoprene with a weight average molecular weight of 10,000 to 50,000 as a crosslinking component; a free radical polymerization initiator; an epoxy resin; and an epoxy resin curing agent, wherein the total content of the free radical polymerization initiator, epoxy resin, and epoxy resin curing agent is 10 parts by weight or less, and the styrene-based elastomer contains a styrene-based elastomer with a styrene ratio of less than 67%, and the total content of component (A) and component (B) is 25 parts by weight or less.

[0074] Furthermore, as a second approach, when the styrene-based elastomer has functional groups that promote the curing reaction of epoxy resin, the thermosetting adhesive composition of this technology may or may not contain an epoxy resin curing agent. Specifically, the thermosetting adhesive composition of the second approach contains at least: 65 to 90 parts by weight of a styrene-based elastomer; 5 to 20 parts by weight of (A) a modified polyphenylene ether resin having free radical polymerizable groups at the molecular ends, and 4 to 10 parts by weight of (B) polybutadiene and / or polyisoprene with a weight average molecular weight of 10,000 to 50,000; a free radical polymerization initiator; and an epoxy resin, wherein the total content of the free radical polymerization initiator and the epoxy resin is 10 parts by weight or less, and the styrene-based elastomer contains a styrene ratio of less than 67%, and the total content of component (A) and component (B) is 25 parts by weight or less.

[0075] [Other ingredients] Without impairing the effectiveness of this technology, the thermosetting adhesive composition may further contain other components besides those described above. Examples of other components include: organic solvents, adhesive agents such as silane coupling agents, and fillers for adjusting flowability and imparting flame retardancy. There are no particular limitations on the organic solvents; examples include: alcohol-based solvents, ketone-based solvents, ether-based solvents, aromatic solvents, and ester-based solvents. From a solubility point of view, aromatic solvents and ester-based solvents are preferred. One organic solvent may be used alone, or two or more may be used in combination.

[0076] <Thermosetting adhesive sheet> The thermosetting adhesive sheet of this technology has a thermosetting adhesive layer formed of the above-described thermosetting adhesive composition on a substrate, and is in the form of a film. The thermosetting adhesive sheet is obtained, for example, by diluting the above-described thermosetting adhesive composition with a solvent, applying it to at least one side of the substrate using a bar coater, roller coater, or the like to a thickness of 10–60 μm after drying, and then drying it at a temperature of approximately 50–130°C. The substrate can be, for example, a release substrate obtained by peeling a substrate such as a polyethylene terephthalate film or a polyimide film with silicone or the like, as needed.

[0077] The thickness of the thermosetting adhesive layer constituting the thermosetting adhesive sheet can be appropriately set according to the purpose. For example, it can be set to 1 to 100 μm or 1 to 30 μm.

[0078] As described above, the thermosetting adhesive layer constituting the thermosetting adhesive sheet is formed from a thermosetting adhesive composition that exhibits low dielectric constant and dielectric loss tangent after thermosetting, low temperature change rate of dielectric loss tangent, and good flexural resistance and heat resistance after thermosetting. Therefore, it can be used, for example, as an interlayer adhesive for flexible printed circuit boards, and for bonding and fixing the terminals of flexible printed circuit boards to a substrate used for their backing. Furthermore, the thermosetting adhesive sheet also exhibits good peel strength, heat resistance, and shelf life at room temperature after curing.

[0079] Printed Circuit Boards The printed circuit board of this technology is, for example, a substrate having a wiring pattern, with the wiring pattern side of the substrate and a protective layer separated by a cured product (thermosetting adhesive layer) of the aforementioned thermosetting adhesive composition. The printed circuit board is also obtained, for example, by thermosetting bonding a thermosetting adhesive sheet between the wiring pattern side of the substrate and the protective layer, thereby integrating the wiring substrate and the protective layer. The protective layer is an insulating layer used to protect the wiring pattern of the wiring substrate.

[0080] Similar to the adhesive composition described above, the substrate with wiring preferably exhibits excellent electrical properties in the high-frequency region; for example, it is preferable to have a low dielectric constant and dielectric loss tangent in the frequency range of 1 to 10 GHz. Specific examples of substrates include those with any one of liquid crystal polymers (LCPs), polytetrafluoroethylene, polyimide, and polyethylene naphthalate as the main component. Among these substrates, those with liquid crystal polymers as the main component (liquid crystal polymer films) are preferred. Compared to polyimide, liquid crystal polymers have a very low moisture absorption rate and are less susceptible to environmental influences.

[0081] An example of the configuration of a printed circuit board using the thermosetting adhesive composition of this technology will be described. Figure 1 In the printed circuit board 1 shown, the copper foil 3 side of the wiring substrate (copper clad laminate: CCL) having liquid crystal polymer film 2 and copper foil (rolled copper foil) 3 is laminated with the liquid crystal polymer film 4 through a cured layer 5 formed by the above-mentioned thermosetting adhesive composition (thermosetting adhesive layer).

[0082] In addition, printed circuit boards can also be, for example, for Figure 2 The multi-layered structure shown. Figure 2 In the printed circuit board 6 shown, for example, the copper plating layer 9 side of the wiring substrate having a polyimide layer 7 (thickness 25 μm), copper foil 8 (thickness 18 μm) and copper plating layer 9 (thickness 10 μm) is stacked with a protective layer 10 (thickness 25 μm) separated by a cured layer 5 (thickness 35 μm) formed by the above-mentioned thermosetting adhesive composition (thermosetting adhesive layer) (total thickness 201 μm).

[0083] Example The following describes embodiments of this technology. It should be noted that this technology is not limited to these embodiments.

[0084] <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 (30% styrene content), manufactured by Asahi Kasei Corporation Tuftec H1051: Hydrogenated styrene-based thermoplastic elastomer (42% styrene content), manufactured by Asahi Kasei Corporation. Tuftec H1043: Hydrogenated styrene-based thermoplastic elastomer (67% styrene content), manufactured by Asahi Kasei Corporation.

[0085] <(A) Modified polyphenylene ether resin with free radical polymerizable groups at the molecular ends> OPE-2St2200: A modified polyphenylene ether resin (Mn=2200) with vinyl benzyl groups at both ends of the molecule, manufactured by Mitsubishi Gas Chemical Co., Ltd. SA9000: A modified polyphenylene ether resin (Mw=1700) with methacrylamide groups at both ends of the molecule, manufactured by SABIC.

[0086] <(A') Modified polyphenylene ether resins that do not have free radical polymerizable groups at the molecular ends> S201A: A polyphenylene ether resin with hydroxyl groups at both ends of the molecule, manufactured by Asahi Kasei Corporation.

[0087] <(B) Polybutadiene and / or polyisoprene with a weight-average molecular weight of 10,000 to 50,000> Ricon154: Liquid polybutadiene (Mw=15000, Mn=5200), manufactured by Cray Valley Corporation. LIR-30: Liquid polyisoprene (Mw=28000), manufactured by Kuraray.

[0088] <(B') Polybutadiene and / or polyisoprene with a weight average molecular weight of less than 10,000 or more than 50,000> LIR-50: Liquid polyisoprene (Mw=54000), manufactured by Kuraray. B-3000: Liquid polybutadiene (Mw=8000, Mn=3000), manufactured by Nippon Soda Co., Ltd.

[0089] <Free radical polymerization initiators> Dicumyl peroxide: (The decomposition temperature is 175°C, used to make the half-life 1 minute) Dilauroyl peroxide: (The decomposition temperature for achieving a half-life of 1 minute is 116°C).

[0090] <Epoxy Resin> JER828: Epoxy resin, manufactured by Mitsubishi Chemical Co., Ltd. 4032D: Naphthalene-type epoxy resin, manufactured by DIC Corporation.

[0091] <Epoxy Resin Curing Agent> Novacure 3941: A microcapsule-type latent curing agent with an imidazole-modified core coated with polyurethane, manufactured by Asahi Kasei E-Materials. 2E4MZ: 2-Ethyl-4-methylimidazole (imidazolium without latency).

[0092] <Preparation of Thermosetting Adhesive Compositions> The components shown in Tables 1 and 2 were weighed in the manner indicated by the masses shown in Tables 1 and 2, and uniformly mixed in an organic solvent containing toluene and ethyl acetate, thereby preparing a thermosetting adhesive composition (a coating for forming a thermosetting adhesive layer). It should be noted that in Tables 1 and 2, regarding the "relationship between (A) and (B)," for example, in Example 1 of Table 1, the column for "(A) + (B) ≤ 25" is recorded as "satisfies 24," which means that the total content of component (A) and component (B) is 24 parts by mass, satisfying Equation 1 above. Furthermore, in Comparative Example 9 of Table 2, the column for "(A) + (B) ≤ 25" is recorded as "does not satisfy 30," which means that the total content of component (A) and component (B) is 30 parts by mass, not satisfying Equation 1 above.

[0093] <The manufacture of thermosetting sheets> The obtained thermosetting adhesive composition was coated onto a polyethylene terephthalate film that had undergone a peeling treatment and dried in a drying oven at 40–130°C, thereby producing a thermosetting adhesive sheet having a polyethylene terephthalate film and a thermosetting adhesive layer with a thickness of 25 μm.

[0094] <Evaluation> Evaluation of the coatability (film state) of coatings for forming thermosetting adhesive layers When manufacturing 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, evaluation A is preferred.

[0095] A: The thermosetting adhesive composition exhibits good compatibility and can be evaluated in film form as described later. B: The thermosetting adhesive composition has poor compatibility and cannot be evaluated in the film state as described later.

[0096] <Dielectric constant (Dk)> The thermosetting adhesive sheets prepared in the examples and comparative examples were laminated together to produce test sheets with a thickness of 1 mm. These test sheets were then thermocured at 180°C and 1.0 MPa for 1 hour to produce evaluation test sheets. The dielectric constant of these evaluation test sheets was determined using a dielectric constant measuring device (manufactured by AET Corporation) at measurement temperatures of 23°C and 80°C and a measurement frequency of 10 GHz via the cavity resonance perturbation method. The dielectric constant was evaluated according to the following criteria. The results are shown in Tables 1 and 2.

[0097] A: Dielectric constant is less than 2.30 B: Dielectric constant is greater than or equal to 2.30 and less than 2.40. C: Dielectric constant is greater than or equal to 2.40 and less than 2.60. D: Dielectric constant is 2.60 or higher.

[0098] In practice, the dielectric constant is preferably evaluated as A or B, with A being more preferred.

[0099] <Dielectric loss tangent (Df)> The dielectric loss tangent was determined for the evaluation test piece using the same method as the dielectric constant determination described above. The dielectric loss tangent was evaluated according to the following criteria. The results are shown in Tables 1 and 2.

[0100] A: The dielectric loss tangent is less than 0.0020°. B: The dielectric loss tangent is greater than or equal to 0.0020° and less than 0.0030°. C: The dielectric loss tangent is greater than or equal to 0.0030° and less than 0.0050°. D: The dielectric loss tangent is above 0.0050°.

[0101] In practice, the dielectric loss tangent is preferably evaluated as A or B, more preferably A. That is, the dielectric loss tangent of the cured thermosetting adhesive composition is preferably less than 0.0030 at both 23°C and 80°C, more preferably less than 0.0020.

[0102] <Rate of change of dielectric loss tangent> Calculate the rate of change (%) of the measured value at 80℃ relative to the measured value at 23℃, and evaluate it according to the following criteria. The results are shown in Tables 1 and 2.

[0103] A: The rate of change between 23℃ and 80℃ is less than 30%. B: The rate of change between 23℃ and 80℃ is greater than 30% and less than 50%. C: The rate of change between 23℃ and 80℃ is over 50%.

[0104] In practice, the evaluation of the rate of change of dielectric loss tangent is preferably A or B, more preferably A. That is, the rate of change of dielectric loss tangent after curing of the thermosetting adhesive composition as shown in Formula 1 above preferably shows less than 50%, more preferably less than 30%.

[0105] <Peel strength> The obtained thermosetting adhesive sheet was cut into strips of a specified size (2cm × 5cm). The cut thermosetting adhesive layer was temporarily bonded to a 2cm × 7cm × 50μm thick liquid crystal polymer film using a laminator set to 100℃. The substrate (polyethylene terephthalate film) was then removed, exposing the thermosetting adhesive layer. For the exposed thermosetting adhesive layer, a copper-clad laminate (CCL) of the same size was superimposed from above, with the rolled copper foil side (the side not roughened) heat-cured at 180℃ and 1.0MPa for 1 hour. This produced a sample.

[0106] The obtained samples were subjected to a 90-degree peel test at a peeling speed 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.

[0107] [Initial state (measured after thermosetting at 180°C and 1.0 MPa as described above, while maintaining this state)] A: Peel strength is above 8 N / cm B: Peel strength is 6 N / cm or higher and less than 8 N / cm. C: Peel strength is 4 N / cm or higher and less than 6 N / cm. D: Peel strength is less than 4 N / cm.

[0108] [After reliability testing (85°C, 85% relative humidity, 240 hours (i.e., after thermosetting under the above conditions of 180°C and 1.0MPa, immerse in an environment of 85°C and 85% relative humidity for 240 hours, and then measure 3 hours after removal))] A: Peel strength is above 7 N / cm B: Peel strength is above 5N / cm and below 7N / cm C: Peel strength is above 3N / cm and less than 5N / cm D: Peel strength is less than 3 N / cm.

[0109] In practice, the evaluation of the initial peel strength and the peel strength after the reliability test is preferably A or B, and more preferably A.

[0110] <Heat Resistance (Solder Heat Resistance)> The samples were subjected to three floating soldering tests at 288°C for 10 seconds each. The appearance of the samples after the tests was visually confirmed, and the absence of peeling or bulging was evaluated according to the following criteria. The results are shown in Tables 1 and 2.

[0111] A: No abnormalities were found after three attempts.

[0112] B: No abnormalities were observed after two treatments, but abnormalities such as peeling and bulging with a diameter of more than 0.2 mm occurred on the third treatment.

[0113] C: No abnormalities were observed after the first treatment, but abnormalities such as peeling and bulging with a diameter of more than 0.2 mm occurred on the second treatment.

[0114] D: The first occurrence of abnormalities such as peeling or bulging with a diameter of more than 0.2 mm.

[0115] In practical applications, the heat resistance rating is preferably A or B, with A being more preferred.

[0116] <Bending resistance> The obtained thermosetting adhesive sheet was cut into strips of a specified size (1.5cm × 12cm). The cut thermosetting adhesive layer was temporarily bonded to a 1.5cm × 12cm × 50μm thick liquid crystal polymer film using a laminator set to 100℃. The substrate (polyethylene terephthalate film) was then removed, exposing the thermosetting adhesive layer. For the exposed thermosetting adhesive layer, an FPC-TEG (Test Elementary Group) for the MIT flexural endurance test was overlapped, and thermosetting was performed at 180℃ and 1.0MPa for 1 hour to obtain the test piece. The composition of the TEG for the MIT flexural endurance test is shown below. Figure 3 TEG11 is formed by creating copper wiring using a CCL (Crystal Liquid Crystal Polymer Film) consisting of a substrate (50 μm thick) and rolled copper foil (12 μm thick). A protective layer (not shown) is bonded to the copper wiring of TEG11. Figure 3 In the diagram, "130mm" refers to the overall length of TEG11, "120mm" to the length of the protective layer (a layer that bonds the thermosetting adhesive layer and the liquid crystal polymer film), "15mm" to the overall width of TEG11 and the width of the protective layer, "11mm" to the spacing between copper wires (outer side), and "10mm" to the spacing between copper wires (inner side). The width of the copper wires is 1mm. The MIT flexural endurance test involves placing the fabricated test piece 12 as shown in the diagram. Figure 4 The test was conducted in an MIT bending fatigue testing machine 13, equipped with a plunger 14, an upper chuck 15, a rotating chuck 16, and a bending stop 17. The test was performed at a bending angle of 135°, a bending fixture angle R = 0.38, and a test speed of 175 cpm. The number of bends required to break the copper wiring was determined. The results are shown in Tables 1 and 2.

[0117] A: The number of bends required before breakage is over 1200. B: The number of bends before breakage is more than 600 but less than 1200. C: The number of bends before breakage is more than 300 but less than 600. D: The number of bends before breakage is less than 300.

[0118] In practical applications, the evaluation of bending resistance is preferably A or B, with A being more preferred.

[0119] <Determination 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 produce an evaluation test piece. For this test piece, a dynamic viscoelasticity measuring device (TA INSTRUMENTS) was used to determine the glass transition temperature at which the temperature increased from -60 °C to 250 °C at a rate of 10 °C / min. It should be noted that in the case of copolymerized polymers or mixtures of multiple components, multiple tanδ peaks may sometimes be detected. In such cases, the temperature of the tanδ peak with the higher value (the one with the greater change in elastic modulus) is taken as the glass transition temperature. The results are shown in Tables 1 and 2. As shown in Examples 1-10, it can be seen that the thermosetting adhesive composition described below has a low dielectric constant and dielectric loss tangent after thermosetting, a low temperature change rate of dielectric loss tangent (temperature change rate of dielectric loss tangent from 23 to 80°C), and good bending resistance and heat resistance. The thermosetting adhesive composition contains, relative to a total of 100 parts by weight of the thermosetting adhesive composition used to bond the substrates, 65-90 parts by weight of a styrene-based elastomer; 5-20 parts by weight of component (A) and 4-10 parts by weight of component (B) as crosslinking components; a free radical polymerization initiator; and an epoxy resin, wherein the total content of the free radical polymerization initiator, epoxy resin, and epoxy resin curing agent is 10 parts by weight or less, and the styrene-based elastomer contains a styrene-based elastomer with a styrene ratio of less than 67%, and the total content of component (A) and component (B) is 25 parts by weight or less.

[0120] Regarding the dielectric constant and dielectric loss tangent after curing, it is known that the dielectric loss tangent of the thermosetting adhesive compositions of Examples 1-10 after curing is less than 0.003 at both 23°C and 80°C. Furthermore, regarding the temperature change rate of the dielectric loss tangent, it is known that the change rate shown in Formula 1 for the thermosetting adhesive compositions of Examples 1-10 is less than 50%.

[0121] Furthermore, based on the results of Example 2 and other examples, it can be seen that the content of components (A) and (B) satisfies Equation 2, that is, the thermosetting adhesive composition with a higher content of component (A) than component (B) tends to have a lower dielectric loss tangent and a lower temperature change rate of the dielectric loss tangent after curing. Specifically, it can be seen that the dielectric loss tangent of the thermosetting adhesive compositions of Examples 1, 3, 5, 6, 7, 9, and 10 after curing is less than 0.0020 at both 23°C and 80°C, and the change rate shown in Equation 1 is less than 30%.

[0122] Furthermore, for example, based on the results of Example 4 and other examples, it can be seen that thermosetting adhesive compositions that do not use polybutadiene and / or polyisoprene with component (B) with a weight average molecular weight exceeding 50,000, in other words, thermosetting adhesive compositions that do not contain polybutadiene and / or polyisoprene with a weight average molecular weight exceeding 50,000, tend to have lower dielectric loss tangent and lower temperature change rate of dielectric loss tangent after curing.

[0123] Furthermore, for example, based on the results of Example 5 and other examples, it can be seen that thermosetting adhesive compositions that do not use polybutadiene and / or polyisoprene with component (B) with a weight average molecular weight of less than 10,000, in other words, thermosetting adhesive compositions that do not contain polybutadiene and / or polyisoprene with a weight average molecular weight of more than 10,000, tend to have better peel strength and flexural strength.

[0124] Furthermore, for example, based on the results of Example 7 and other examples, it can be seen that styrene-based elastomers containing less than 42% styrene (e.g., 12% to 30%) have good dielectric properties as thermosetting adhesive compositions of styrene-based elastomers, and also tend to have better peel strength and flexural strength.

[0125] Furthermore, for example, based on the results of Example 8 and other examples, it can be seen that by having less than 5 parts by mass of epoxy resin relative to a total of 100 parts by mass of the thermosetting adhesive composition, there is a tendency for lower dielectric loss tangent and temperature change rate of dielectric loss tangent after curing.

[0126] It can be seen that the thermosetting adhesive composition of Comparative Example 1 does not contain component (B), and therefore it is difficult to suppress the temperature change rate of dielectric loss tangent.

[0127] It can be seen that the thermosetting adhesive composition of Comparative Example 2 does not contain component (B), and in addition, the content of component (A) also exceeds 20 parts by mass, so it is difficult to suppress the temperature change rate of dielectric loss tangent.

[0128] It can be seen that the thermosetting adhesive composition of Comparative Example 3 does not contain component (B), in other words, it does not contain component (B) but only contains polybutadiene and / or polyisoprene with a weight average molecular weight of more than 50,000 (B'), so it is difficult to suppress the temperature change rate of dielectric loss tangent.

[0129] It can be seen that the thermosetting adhesive composition of Comparative Example 4 does not contain component (B), in other words, it does not contain component (B) but only contains (B') polybutadiene and / or polyisoprene with a weight average molecular weight of less than 10,000. Therefore, its peel strength and flexural strength are poor.

[0130] It can be seen that the thermosetting adhesive composition of Comparative Example 5 does not contain component (A), and therefore it is difficult to reduce the dielectric loss tangent.

[0131] It can be seen that the content of component (B) in the thermosetting adhesive composition of Comparative Example 6 is high, exceeding 10 parts by mass, and therefore the peel strength and flexural strength are poor.

[0132] It can be seen that the thermosetting adhesive composition of Comparative Example 7 does not contain styrene-based elastomers with a styrene ratio of less than 67%, and therefore its peel strength and flexural strength are poor.

[0133] It can be seen that the thermosetting adhesive composition of Comparative Example 8 does not contain a free radical polymerization initiator, so it is difficult to reduce the dielectric loss tangent at 80°C, and it is also difficult to suppress the temperature change rate of the dielectric loss tangent, and the heat resistance is also poor.

[0134] It can be seen that the total content of component (A) and component (B) in the thermosetting adhesive composition of Comparative Example 9 exceeds 25 parts by mass, therefore the peel strength and flexural strength are poor.

[0135] It can be seen that the thermosetting adhesive composition of Comparative Example 10 has a high content of styrene-based elastomer, exceeding 90 parts by mass, while the contents of components (A) and (B) are relatively low. Therefore, it is difficult to reduce the dielectric loss tangent at 80°C, and it is also difficult to suppress the temperature change rate of the dielectric loss tangent. The heat resistance is also poor.

[0136] It can be seen that the thermosetting adhesive composition of Comparative Example 11 contains a small amount of styrene-based elastomer, less than 65 parts by mass. In addition, the total content of free radical polymerization initiator, epoxy resin and epoxy resin curing agent is large, exceeding 10 parts by mass. Therefore, it is difficult to reduce the dielectric constant and dielectric loss tangent, and it is also difficult to suppress the temperature change rate of dielectric loss tangent.

[0137] It can be seen that the total content of free radical polymerization initiator, epoxy resin and epoxy resin curing agent in the thermosetting adhesive composition of Comparative Example 12 is large, exceeding 10 parts by mass. Therefore, it is difficult to reduce the dielectric constant and dielectric loss tangent, and it is also difficult to suppress the temperature change rate of dielectric loss tangent.

[0138] It can be seen that the thermosetting adhesive composition of Comparative Example 13 does not contain component (A), in other words, it uses polyphenylene ether resin with hydroxyl groups at the molecular ends rather than free radical polymerizable groups. Therefore, the film condition is poor and cannot be evaluated (dielectric constant, dielectric loss tangent, peel strength, temperature change rate of dielectric loss tangent, heat resistance, flexural strength).

[0139] Explanation of reference numerals in the attached figures 1: Printed circuit board; 2: Liquid crystal polymer film; 3: Copper foil; 4: Liquid crystal polymer film; 5: Cured layer formed by adhesive composition; 6: Printed circuit board; 7: Polyimide layer; 8: Copper foil; 9: Copper plating layer; 10: Protective layer; 11: TEG; 12: Test piece; 13: MIT flexural fatigue testing machine; 14: Plunger; 15: Upper chuck; 16: Rotary chuck; 17: Bending stop.

Claims

1. A thermosetting adhesive composition for bonding substrates, Relative to a total of 100 parts by weight of the thermosetting adhesive composition, it contains: 65-90 parts by weight of styrene-based elastomers; 5-20 parts by weight of A as a crosslinking component: modified polyphenylene ether resin with free radical polymerizable groups at the molecular ends and 4-10 parts by weight of B: polybutadiene and / or polyisoprene with a weight average molecular weight of 10,000-50,000. Free radical polymerization initiators; as well as Epoxy resin, among which, The total content of the free radical polymerization initiator, the epoxy resin, and the epoxy resin curing agent is less than 10 parts by weight. As the styrene-based elastomer, a styrene-based elastomer containing a styrene ratio of less than 67% is specified. The total content of component A and component B is less than 25 parts by mass.

2. The thermosetting adhesive composition according to claim 1, wherein, The dielectric loss tangent after curing is less than 0.0030°C at both 23°C and 80°C. The rate of change shown in Equation 1 below is less than 50%. Formula 1: Change rate % = ((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.

3. The thermosetting adhesive composition according to claim 1 or 2, wherein, The content of component A and the content of component B satisfy the following formula 2. Formula 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 weight.

5. The thermosetting adhesive composition according to claim 2, wherein, The rate of change shown in Equation 1 is less than 30%.

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

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

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

9. The thermosetting adhesive composition according to claim 1 or 2, wherein, The styrene-based elastomer contains a styrene-based elastomer with functional groups that promote the curing reaction of the epoxy resin.

10. A thermosetting adhesive sheet formed on a substrate having an adhesive layer formed from the thermosetting adhesive composition as described in claim 1 or 2.

11. A printed circuit board comprising a resin substrate having a wiring pattern, wherein the wiring pattern side of the resin substrate having a wiring pattern is laminated with a protective layer separated by a cured product of the thermosetting adhesive composition as described in claim 1 or 2.

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