Curable resin composition for bonding film, bonding film and printed wiring board

Abstract

To provide a curable resin composition for bonding film which has high adhesive force to copper foil with small surface roughness used in high-frequency applications, maintains high adhesive force even after HAST, and whose cured product also has excellent dielectric characteristics.SOLUTION: A curable resin composition for bonding film for adhering copper foil contains: (A) a maleimide compound which is represented by the following formula (1) and has one or more hydrocarbon group derived from a dimer acid skeleton in one molecule (includes at least two kinds, and at least one kind is solid at 25°C), and (B) catalyst. (In the formula (1), A independently denotes a tetravalent organic group having a cyclic structure, B independently denotes a divalent hydrocarbon group having a carbon number 6 to 60 other than a hydrocarbon group derived from dimer acid skeleton, D denotes a hydrocarbon group derived from a dimer acid skeleton, and m and l severally denote 1 to 100)SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a curable resin composition for a bonding film, a bonding film, and a printed wiring board having the bonding film. [Background technology]

[0002] In recent years, the next-generation communication system known as 5G has become popular, starting with the sub-6 band below 6 GHz, and going beyond the millimeter wave band of 26 GHz to 80 GHz. Development of the next-generation communication system known as 6G has also begun, aiming to achieve even faster speeds, larger capacity, and lower latency than current systems. To achieve this, materials for high-frequency bands are required, and reducing transmission loss as a noise countermeasure is essential. Transmission loss is the sum of conductor loss and dielectric loss, and reducing conductor loss requires reducing the surface roughness of the metal foil used, especially copper foil. On the other hand, since dielectric loss is proportional to the product of the square root of the relative dielectric constant and the dielectric loss tangent, there is a demand for the development of insulating materials with excellent dielectric properties (low relative dielectric constant and low dielectric loss tangent). Particularly at high frequencies, the conductor loss is significantly affected by the skin effect, making it essential to use a material with a small surface roughness, and it is particularly preferable to use copper foil with a small surface roughness.

[0003] In order to reduce dielectric loss, materials with low relative permittivity and dielectric dissipation factor have come to be used, such as reactive polyphenylene ether resin (PPE) as a thermosetting resin, liquid crystal polymer (LCP) as a thermoplastic resin, modified polyimide (MPI) with improved properties, and even polytetrafluoroethylene (PTFE).However, these materials generally have low adhesive strength to copper foil with a low surface roughness, and are not suitable for practical use with low-roughness copper foil for high frequencies, so an adhesive with excellent dielectric properties is also required to compensate for the adhesive strength.

[0004] In response to this, it has been reported that maleimide compounds (special maleimide compounds) that essentially have a dimer diamine skeleton are used as the main resin for circuit boards (Patent Documents 1 and 2). Contrary to the properties of typical maleimide resins, special maleimide compounds have a low glass transition temperature (Tg) and a high coefficient of thermal expansion (CTE), but they also have many advantages, such as excellent dielectric properties, flexibility, excellent adhesion to metals, and the possibility of (high) multi-layering because they are thermosetting resins. Research and development on these compounds has been extensively conducted, but specifically, their adhesion to copper foil with a surface roughness (Ra) of approximately 0.5 μm or less has not been particularly studied, and it was unclear whether they could actually be used for high-frequency applications.

[0005] Although the use of build-up films (Patent Documents 3 to 6) is already known as a method for producing substrates, these build-up films have very low adhesive strength to copper foil with Ra of 0.5 μm or less. Therefore, to solve the adhesion problem of build-up films, it is necessary to improve the build-up film itself to have excellent adhesive strength, or to use a bonding film with very high adhesive strength to copper foil in combination. In particular, in high frequency applications, the surface roughness of copper foil tends to become smaller, and since the adhesive strength of the build-up film itself to such copper foil is insufficient, a bonding film with high adhesive strength is required.

[0006] Furthermore, in terms of adhesive strength, taking into consideration long-term reliability and the occurrence of cracks due to the stress of the build-up film mentioned above, a material is required that has high adhesive strength to copper foil with very low surface roughness even when not fully cured, and that also has high adhesive strength after HAST (Highly Accelerated Temperature and Humidity Stress Test), while also having excellent dielectric properties. There is a strong demand for the development of a material that satisfies these requirements. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2016 / 114287 [Patent Document 2] Japanese Patent Application Publication No. 2018-201024 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-90236 [Patent Document 4] Japanese Patent Application Laid-Open No. 2010-90238 [Patent Document 5] Japanese Patent Application Laid-Open No. 2014-5464 [Patent Document 6] Japanese Patent Application Laid-Open No. 2015-101626 Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, an object of the present invention is to provide a curable resin composition for a bonding film that has high adhesive strength to copper foil with a small surface roughness used in high-frequency applications, for example, copper foil with an Ra of 0.5 μm or less, maintains high adhesive strength even after HAST, and produces a cured product with excellent dielectric properties; a bonding film made of the curable resin composition; and a printed wiring board having the bonding film. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to solve the above problems and have found that the following curable resin composition can achieve the above object, thereby completing the present invention.

[0010] That is, the present invention provides the following curable resin composition and the like. [1] (A) A maleimide compound having one or more hydrocarbon groups derived from a dimer acid skeleton in one molecule, represented by the following formula (1), (2), or (3): and (B) Catalyst Contains A curable resin composition for a bonding film for bonding copper foil, wherein the maleimide compound of component (A) contains at least two maleimide compounds represented by formula (1), (2), or (3), and at least one of the maleimide compounds represented by formula (1), (2), or (3) is solid at 25°C. [ka] (In formula (1), A's independently represent tetravalent organic groups having a cyclic structure, B's independently represent divalent hydrocarbon groups having 6 to 60 carbon atoms other than hydrocarbon groups derived from a dimer acid skeleton, D's represent a hydrocarbon group derived from a dimer acid skeleton, m's represent 1 to 100, and l's represent 1 to 100. The order of the repeating units bracketed by m and l's is not limited, and the bonding pattern may be alternating, block, or random.) [ka] (In formula (2), A's independently represent tetravalent organic groups having a cyclic structure, D represents a hydrocarbon group derived from a dimer acid skeleton, and n represents an integer of 1 to 100.) [ka] (In formula (3), D is a hydrocarbon group derived from a dimer acid skeleton.) [2] The curable resin composition according to [1], wherein the content of the maleimide compound that is solid at 25°C in the maleimide compound of component (A) is 60 to 100 mass%. [3] The curable resin composition according to [1] or [2], wherein A in formula (1) and formula (2) is any one of tetravalent organic groups represented by the following structural formulas: [ka] (The bond not bonded to a substituent in the above structural formula is bonded to the carbonyl carbon that forms the cyclic imide structure in formulas (1) and (2).) [4] The curable resin composition according to any one of [1] to [3], which is a thermosetting type. [5] The curable resin composition according to any one of [1] to [4], wherein the catalyst of component (B) is at least one selected from the group consisting of thermal radical polymerization initiators and anionic polymerization initiators. [6] The component (B) is an anionic polymerization initiator, The curable resin composition according to [5], further comprising an epoxy resin having two or more epoxy groups in one molecule. [7] The curable resin composition according to any one of [1] to [6], wherein a cured product of the curable resin composition has a dielectric loss tangent of 0.005 or less at 10 GHz. [8] The curable resin composition according to any one of [1] to [7], wherein a test piece obtained by laminating the curable resin composition on a copper foil having a surface roughness Ra of 0.17 μm, heating at 130°C for 30 minutes, and then further heating at 170°C for 30 minutes to cure the curable resin composition has a peel strength between the cured product of the curable resin composition and the copper foil of 0.8 kN / m or more, as measured in accordance with JIS C 6481, and the test piece has a peel strength between the cured product and the copper foil of 0.3 kN / m or more, as measured in accordance with JIS C 6481, after being left at 130°C and 85% RH for 100 hours. [9] A bonding film made of the curable resin composition according to any one of [1] to [8].

[10] A printed wiring board having the bonding film according to [9]. [Effects of the Invention]

[0011] The curable resin composition of the present invention has high adhesion to low-roughness copper foil, for example, copper foil with a surface roughness Ra of 0.5 μm or less, and can maintain high adhesion even after HAST. The cured product also has excellent dielectric properties. Therefore, the curable resin composition of the present invention is particularly useful for bonding films used in high-frequency applications, and further for printed wiring boards. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in more detail below.

[0013] (A) A maleimide compound having one or more hydrocarbon groups derived from a dimer acid skeleton in one molecule. The component (A) of the present invention is a maleimide compound having one or more hydrocarbon groups derived from a dimer acid skeleton per molecule, as represented by the following formula (1), (2), or (3): Since the component (A) has a hydrocarbon group derived from a dimer acid skeleton, the cured product of a composition containing the component (A) has a low dielectric constant and dielectric dissipation factor, and also exhibits excellent film-forming properties and handleability after curing. Furthermore, since the component (A) has an imide group, the composition containing the component (A) has high insulating properties even when formed into a film (thin film). Furthermore, the maleimide compound of component (A) contains at least two maleimide compounds represented by formula (1), (2), or (3), and at least one of the maleimide compounds represented by formula (1), (2), or (3) is solid at 25° C. By containing, as component (A), at least one maleimide compound represented by formula (1), (2), or (3) that is solid at 25° C., the curable resin composition of the present invention has excellent film properties and reduced tackiness when uncured, and can therefore be suitably used as a curable resin composition for bonding films.

[0014] [ka] (In formula (1), A's independently represent tetravalent organic groups having a cyclic structure, B's independently represent divalent hydrocarbon groups having 6 to 60 carbon atoms other than hydrocarbon groups derived from a dimer acid skeleton, D's represent a hydrocarbon group derived from a dimer acid skeleton, m's represent 1 to 100, and l's represent 1 to 100. The order of the repeating units bracketed by m and l's is not limited, and the bonding pattern may be alternating, block, or random.)

[0015] [ka] (In formula (2), A is a tetravalent organic group having a cyclic structure, as in formula (1), and D is a hydrocarbon group derived from a dimer acid skeleton, as in formula (1). n is 1 to 100.)

[0016] [ka] (In formula (3), D is a hydrocarbon group derived from a dimer acid skeleton, as in formulas (1) and (2).)

[0017] The dimer acid referred to here is a liquid dibasic acid primarily composed of a 36-carbon dicarboxylic acid, produced by dimerization of an 18-carbon unsaturated fatty acid derived from natural sources such as vegetable oils. Dimer acids do not have a single skeleton but rather have multiple structures, resulting in several isomers. Representative dimer acids are classified as linear (a), monocyclic (b), aromatic (c), and polycyclic (d). In this specification, the dimer acid skeleton refers to a group derived from a dimer diamine having a structure in which the carboxyl groups of such a dimer acid are substituted with primary aminomethyl groups. In other words, component (A) preferably has a hydrocarbon group derived from the dimer acid skeleton in one molecule, such as the dimer acids shown below in (a) to (d), in which two carboxyl groups are substituted with methylene groups. Furthermore, from the viewpoint of the heat resistance and reliability of the cured product, it is more preferable that the hydrocarbon group derived from the dimer acid skeleton in the maleimide compound of component (A) has a structure in which the carbon-carbon double bond in the hydrocarbon group derived from the dimer acid skeleton is reduced by a hydrogenation reaction. Generally, dimer acids may contain trimers (trimer acids) due to the use of natural products such as vegetable oils and fats as raw materials, but a high proportion of dimer acid-derived hydrocarbon groups, for example 95% by mass or more, among the hydrocarbon groups derived from dimer acids and trimer acids, is preferred because it results in excellent dielectric properties, a tendency for viscosity to decrease when heated, excellent moldability, and a tendency to be less affected by moisture absorption. In this specification, the dimer acid (trimer acid) skeleton refers to a group derived from a dimer diamine (trimer triamine) having a structure in which the carboxy group of such a dimer acid (trimer acid) is substituted with a primary aminomethyl group.

[0018] [ka] As described above, the dimer acid skeleton has a plurality of structures, and therefore, in this specification, the hydrocarbon group derived from the dimer acid skeleton is referred to as the average structure, i.e., -C 36 H 70 It may be written as -.

[0019] The use of the maleimide compound represented by formula (1) above results in a composition with superior dielectric properties both before and after curing compared to the use of other common maleimide compounds containing many aromatic groups, a high Tg for a maleimide compound having a hydrocarbon group derived from a dimer acid skeleton, and a high reliability. The maleimide compound represented by formula (1) is often solid at room temperature.

[0020] In the formula (1), A independently represents a tetravalent organic group having a cyclic structure, and is preferably any of the tetravalent organic groups represented by the following structural formulas. [ka] (The bond not bonded to a substituent in the above structural formula is bonded to the carbonyl carbon that forms the cyclic imide structure in formula (1).)

[0021] In the formula (1), D is a hydrocarbon group derived from a dimer acid skeleton, and specific examples thereof include groups in which two carboxy groups in each of the dimer acids represented by the formulae (a) to (d) are substituted with methylene groups. In this specification, the hydrocarbon group derived from a dimer acid skeleton represented by D is referred to as -C as its average structure. 36 H 70 It may be written as -.

[0022] In the formula (1), each B is independently a divalent hydrocarbon group having 6 to 60 carbon atoms other than a hydrocarbon group derived from a dimer acid skeleton, preferably a divalent hydrocarbon group having 7 to 40 carbon atoms and having an aromatic ring or a cyclohexane ring, and more preferably a divalent hydrocarbon group having 8 to 30 carbon atoms and having an aromatic ring or a cyclohexane ring. The embodiment having the cyclohexane ring may be one having one cyclohexane ring, or a plurality of cyclohexane rings bonded via a divalent group such as an alkylene group, or a polycyclic ring having a bridged structure. Specific examples of B include divalent hydrocarbon groups represented by the following structural formula: [ka]

[0023] In the formula (1), m is 1 to 100, preferably 1 to 60, and more preferably 2 to 50, and l is 1 to 100, preferably 1 to 50, and more preferably 3 to 40. If m or l is too large, the flowability may decrease, and moldability may be poor. The order of the repeating units enclosed by m and l is not limited, and the bonding pattern may be alternating, block, or random, but a block bond is preferred from the viewpoint of facilitating a high Tg.

[0024] Next, when the maleimide compound represented by the formula (2) is used, the dielectric properties are superior both before and after curing compared to when other common maleimide compounds containing many aromatic groups are used, and it is particularly effective in maintaining the dielectric properties even at high frequencies, resulting in a composition that is superior in flexibility before and after curing compared to when only the maleimide compound represented by formula (1) is used. In particular, the use of the maleimide compound represented by formula (2) is effective in imparting film properties to the composition when uncured.

[0025] In the formula (2), A is the same as A in the formula (1) and independently represents a tetravalent organic group having a cyclic structure, and is preferably any of the tetravalent organic groups represented by the following structural formulas: Depending on the structure of A in the formula (2), the maleimide compound represented by the formula (2) changes its state from a solid to a viscous liquid at 25°C. Therefore, when combining at least two types of component (A), the structure of the tetravalent organic group represented by A may be appropriately selected.

[0026] [ka] (The bond not bonded to a substituent in the above structural formula is bonded to the carbonyl carbon that forms the cyclic imide structure in formula (2).)

[0027] In the formula (2), D is a hydrocarbon group derived from a dimer acid skeleton, similar to D in the formula (1), and specific examples include groups in which two carboxy groups in each of the dimer acids represented by the formulas (a) to (d) above are substituted with methylene groups.

[0028] In the formula (2), n is 1 to 100, preferably 1 to 60, and more preferably 1 to 50. If n is too large, the solubility and flowability may decrease, resulting in poor film-forming properties.

[0029] The maleimide compound represented by formula (3) is a low-viscosity liquid at room temperature (25°C), and when incorporated into a resin composition, it reduces the melt viscosity during molding, improving embeddability and moldability, as well as wettability and adhesive strength. The maleimide represented by formula (3) has a viscosity in the range of 1.5 to 6.0 Pa·s measured at 25°C under the following measurement conditions: Measurement conditions: According to the method described in JIS Z8803:2011, a Brookfield type rotational viscometer is used at the specified measurement temperature, with the spindle rotation speed set to 5 rpm.

[0030] In the formula (3), D is a hydrocarbon group derived from a dimer acid skeleton, similar to D in the formulas (1) and (2). Specific examples include groups in which two carboxy groups in each of the dimer acids represented by the formulas (a) to (d) above are substituted with methylene groups.

[0031] The curable resin composition of the present invention may contain a maleimide compound other than the component (A), i.e., a maleimide compound other than the maleimide compound represented by formula (1), (2), or (3). When a maleimide compound other than the component (A) is contained, the proportion of the component (A) (i.e., the maleimide compound represented by formula (1), (2), or (3)) relative to the total amount of maleimide compounds is preferably 20 to 100 mass%, more preferably 30 to 100 mass%, and even more preferably 40 to 100 mass%.

[0032] The maleimide compound of component (A) includes at least two maleimide compounds represented by formula (1), (2), or (3), and at least one of the maleimide compounds represented by formula (1), (2), or (3) is solid at 25° C. For example, a maleimide compound represented by formula (1) that is solid at 25° C. and a maleimide compound represented by formula (2) that is liquid at 25° C. may be used in combination; a maleimide compound represented by formula (1) that is solid at 25° C. and a maleimide compound represented by formula (2) that is solid at 25° C. may be used in combination; or a maleimide compound represented by formula (1) that is solid at 25° C. and a maleimide compound represented by formula (3) that is liquid at 25° C. may be used in combination. Furthermore, for example, two or more maleimide compounds represented by formula (2) having different structures may be used, in which case at least one is solid at 25° C. Of the maleimide compounds of component (A), the maleimide compounds that are solid at 25° C. preferably account for 60 to 100 mass %, more preferably 70 to 100 mass %.

[0033] (B) Catalyst The component (B) used in the present invention is a catalyst. A catalyst is a general term for anything that initiates or accelerates the reaction of the maleimide group in the maleimide compound (component (A)). There are no particular limitations on the component (B) as long as it initiates or accelerates the reaction of the maleimide group in component (A), but at least one member selected from the group consisting of thermal radical polymerization initiators and anionic polymerization initiators is preferably used.

[0034] Examples of the thermal radical polymerization initiator include organic peroxides and azo polymerization initiators, and organic peroxides are preferably used. Examples of the organic peroxides include dicumyl peroxide, t-butyl peroxybenzoate, t-amyl peroxybenzoate, dibenzoyl peroxide, diuraroyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 1,1-di(t-butylperoxy)cyclohexane, di-t-butyl peroxide, dibenzoyl peroxide, and t-butylperoxy-2-ethylhexyl carbonate.

[0035] It is believed that the anionic polymerization initiator acts on the epoxy groups in the epoxy resin described below, and then the active species attacks the maleimide groups, thereby initiating anionic polymerization. Therefore, when a maleimide compound and an epoxy resin as component (A) are used, it is preferable to use an anionic polymerization initiator as the catalyst for component (B). Examples of the anionic polymerization initiator include imidazole, 2-methylimidazole, 2-ethylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, and 2-phenyl-4,5-dihydroxymethylimidazole. imidazole compounds such as 2-phenyl-4-methyl-5-hydroxymethylimidazole; organophosphorus compounds such as tributylphosphine, tri(p-methylphenyl)phosphine, tri(nonylphenyl)phosphine, triphenylphosphine, triphenylphosphine oxide, triphenylphosphine-triphenylborane, and tetraphenylphosphine-tetraphenylborate; and tertiary amine compounds such as triethylamine, benzyldimethylamine, α-methylbenzyldimethylamine, 1,8-diazabicyclo[5.4.0]undecene, and tris(dimethylaminomethyl)phenol.

[0036] The content of the catalyst for component (B) is preferably 0.1 to 5.0 parts by mass, more preferably 0.2 to 4.5 parts by mass, and even more preferably 0.5 to 4.0 parts by mass, per 100 parts by mass of component (A). If the amount of component (B) is less than 0.1 part by mass per 100 parts by mass of component (A), curing may proceed slowly, while if it is more than 5.0 parts by mass, the composition may lack storage stability. The component (B) may be used alone or in combination with two or more other types. For example, a thermal radical polymerization initiator and an anionic polymerization initiator may be used in combination.

[0037] Other additives The curable resin composition of the present invention may further contain various additives as needed, provided that the effects of the present invention are not impaired. Examples of other additives are listed below.

[0038] Epoxy resin To improve the properties of the curable resin composition of the present invention, an epoxy resin may be further contained. Any epoxy resin having two or more epoxy groups per molecule can be used without particular limitation. Specific examples of epoxy resins include biphenol-type epoxy resins such as bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, 3,3',5,5'-tetramethyl-4,4'-biphenol-type epoxy resins and 4,4'-biphenol-type epoxy resins, phenol novolac-type epoxy resins, cresol novolac-type epoxy resins, bisphenol A novolac-type epoxy resins, naphthalenediol-type epoxy resins, trisphenolmethane-type epoxy resins, trisphenylolmethane-type epoxy resins, tetrakisphenylolethane-type epoxy resins, phenolbiphenyl-type epoxy resins, dicyclopentadiene-type epoxy resins, biphenylaralkyl-type epoxy resins, epoxy resins in which the aromatic rings of phenoldicyclopentadiene novolac-type epoxy resins have been hydrogenated, triazine derivative epoxy resins, and alicyclic epoxy resins.

[0039] When an epoxy resin is blended and an anionic polymerization initiator is used as a catalyst for component (B), the proportion of the epoxy resin per 100 parts by mass of component (A) is preferably 0.1 to 100 parts by mass, and more preferably 0.1 to 50 parts by mass. The amount of the anionic polymerization initiator blended is preferably 0.1 to 5.0 parts by mass, more preferably 0.2 to 4.5 parts by mass, and even more preferably 0.5 to 4.0 parts by mass, per 100 parts by mass of component (A).

[0040] inorganic filler In the present invention, an inorganic filler may be added as needed. The inorganic filler may be blended to increase the strength and rigidity of the cured product of the curable resin composition of the present invention, or to adjust the thermal expansion coefficient and dimensional stability of the cured product. Examples of inorganic fillers that can be used include those typically blended into epoxy resin compositions and silicone resin compositions. Examples include silicas such as spherical silica, fused silica, and crystalline silica, alumina, silicon nitride, aluminum nitride, boron nitride, barium sulfate, talc, clay, aluminum hydroxide, magnesium hydroxide, calcium carbonate, glass fibers, and glass particles. Furthermore, fluorine-containing resin fillers, coating fillers, and / or hollow particles may be used to improve dielectric properties, and conductive fillers such as metal particles, metal-coated inorganic particles, carbon fibers, and carbon nanotubes may be added to impart conductivity. The inorganic fillers may be used alone or in combination of two or more. The amount of inorganic filler added may be 0 to 400 parts by mass, preferably 0 to 300 parts by mass, per 100 parts by mass of component (A).

[0041] The average particle size and shape of the inorganic filler are not particularly limited, but since the curable resin composition of the present invention is used to form a bonding film, spherical silica having an average particle size of 0.5 to 5 μm is particularly preferred. The average particle size is determined by the mass average particle size D 50 (or median diameter).

[0042] Furthermore, in order to improve the properties of the inorganic filler, it is preferable that the inorganic filler is surface-treated with a silane coupling agent having an organic group capable of reacting with a reactive group such as a maleimide group, as already mentioned above. Examples of such silane coupling agents include epoxy group-containing alkoxysilanes, amino group-containing alkoxysilanes, (meth)acrylic group-containing alkoxysilanes, and alkenyl group-containing alkoxysilanes, as mentioned above.

[0043] others In addition to the above, the curable resin composition may contain thermoplastic resins such as styrene-ethylene-butadiene-styrene block copolymers (SEBS), thermoplastic elastomers, organic synthetic rubbers, non-functional silicone oils, reactive diluents, photosensitizers, light stabilizers, polymerization inhibitors, antioxidants, flame retardants, pigments, dyes, adhesion promoters, ion trapping materials, etc. Furthermore, silane coupling agents such as epoxy group-containing alkoxysilanes, amino group-containing alkoxysilanes, (meth)acrylic group-containing alkoxysilanes, and alkenyl group-containing alkoxysilanes, which are used to surface treat the inorganic fillers, may be separately blended into the curable resin composition of the present invention as a type of adhesion promoter.

[0044] From the viewpoint of practical applications, the curable resin composition of the present invention preferably has a low dielectric constant and dielectric dissipation factor, and since, as described above, the dielectric loss is proportional to the product of the square root of the dielectric constant and the dielectric dissipation factor, the dielectric dissipation factor is particularly preferably low. Specifically, the dielectric dissipation factor at 10 GHz of the cured product of the curable resin composition of the present invention is preferably 0.005 or less, more preferably 0.004 or less.

[0045] Bonding Film The curable resin composition of the present invention is suitable for use in producing a bonding film. A bonding film made from the curable resin composition of the present invention may be produced by dissolving the composition in an organic solvent to form a varnish, applying the varnish to a substrate, and volatilizing the organic solvent. Alternatively, the components may be premixed without using an organic solvent and extruded into a sheet or film using a melt kneader. The composition may also be made into a varnish, which may be applied to or impregnated into glass cloth made from E-glass, low-dielectric glass, quartz glass, or the like, followed by drying the organic solvent, and the resulting prepreg containing the curable resin composition in a semi-cured state may be used as a bonding film. Any organic solvent can be used without limitation as long as it dissolves the curable resin (A). Examples include ketone-based organic solvents such as methyl ethyl ketone (MEK) and methyl isobutyl ketone (MIBK); hydrocarbon-based organic solvents such as tetralin, mesitylene, xylene, and toluene; anisole, tetrahydrofuran (THF), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and acetonitrile. However, aromatic organic solvents such as anisole, tetralin, mesitylene, xylene, and toluene are preferred. These organic solvents may be used alone or in combination.

[0046] Such a varnish-like resin composition (resin varnish) is prepared, for example, as follows. First, each component of the resin composition that is soluble in an organic solvent is added to the organic solvent and dissolved. At this time, heating may be performed as necessary. Thereafter, components that are insoluble in the organic solvent, such as an inorganic filler, which are used as needed, are added, and the mixture is dispersed using a ball mill, bead mill, planetary mixer, roll mill, or the like until a predetermined dispersion state is achieved, thereby preparing a varnish-like resin composition.

[0047] Thereafter, for example, a curable resin composition (varnish) dissolved in an organic solvent is applied to a substrate, and the substrate is then heated for 0.5 to 20 minutes at a temperature typically above 80°C, preferably above 100°C, to remove the organic solvent, thereby producing a bonding film. The temperatures in the drying step for removing the organic solvent and the subsequent heat curing step may each be constant, but it is preferable to increase the temperature stepwise. This allows the organic solvent to be efficiently removed from the composition and the resin curing reaction to proceed efficiently. Methods for applying the varnish include, but are not limited to, a spin coater, slit coater, spray, dip coater, bar coater, die coater, etc.

[0048] The coating substrate can be a general resin substrate, such as polyolefin resins such as polyethylene (PE) resin, polypropylene (PP) resin, and polystyrene (PS) resin; or polyester resins such as polyethylene terephthalate (PET) resin, polybutylene terephthalate (PBT) resin, and polycarbonate (PC) resin. The surface of the substrate may be subjected to a release treatment. The thickness of the coating layer (curable resin composition) is not particularly limited, but the thickness after solvent removal is in the range of 1 to 200 μm, preferably 3 to 150 μm. A cover film may also be applied to the coating layer.

[0049] The thickness of the bonding film made of the curable resin composition is generally in the range of 1 to 300 μm, and from the viewpoints of handling, manufacturing method, and adhesive strength stability, it is preferably in the range of 3 to 200 μm.

[0050] Prepreg The prepreg comprises the curable resin composition or a semi-cured product of the curable resin composition and glass cloth. The semi-cured product refers to a resin composition that has been partially cured to the extent that it can be further cured. In other words, the semi-cured product refers to a resin composition that has been semi-cured, or in other words, in a B-stage. On the other hand, the uncured state is sometimes referred to as an A-stage. That is, the curable resin composition in the prepreg may be in either an A-stage or a B-stage state. As mentioned above, examples of glass cloth include E-glass, low-dielectric glass, quartz glass, S-glass, and T-glass. While any type of glass can be used, it is preferable to use quartz glass cloth, which has low dielectric properties, in order to take advantage of the properties of the curable resin composition. The thickness of commonly used glass cloth is, for example, 0.01 mm or more and 0.3 mm or less.

[0051] When producing a prepreg, the curable resin composition is often prepared in a varnish form as described above and used to impregnate a glass cloth, which is a substrate for forming the prepreg. That is, the curable resin composition is usually a resin varnish prepared in a varnish form, and the method for producing the varnish can be mentioned above.

[0052] After impregnating glass cloth with a curable resin composition prepared in a varnish form, the organic solvent is typically dried. The curable resin composition is impregnated into the glass cloth by immersion, coating, or the like. Impregnation can be performed by repeated immersion and / or coating, if necessary. Furthermore, by repeating the impregnation process using multiple resin compositions with different compositions and concentrations, it is possible to adjust the final composition and impregnation amount to the desired level. The glass cloth impregnated with the resin composition (resin varnish) is heated under desired heating conditions, for example, at 80°C to 180°C for 1 minute to 20 minutes. Heating produces a prepreg in an uncured (A-stage) or semi-cured (B-stage) state. The heating volatilizes the organic solvent from the resin varnish, thereby reducing or eliminating the organic solvent.

[0053] printed wiring board The printed wiring board of the present invention has the bonding film. The substrate used for the printed wiring board is preferably copper foil, and from the viewpoint of conductor loss, copper foil with a low surface roughness Ra is preferably used. As described below, the curable resin composition of the present invention has a high initial adhesive strength, particularly to copper foil with a very low surface roughness Ra of 0.17 μm, and maintains a high adhesive strength even after HAST. As a guideline for adhesive strength, a test piece is prepared by laminating the curable resin composition of the present invention onto copper foil having a surface roughness Ra of 0.17 μm, heating the composition at 130°C for 30 minutes, and then further heating it at 170°C for 30 minutes to cure the curable resin composition. The peel strength (initial adhesive strength) between the cured product of the curable resin composition and the copper foil measured in accordance with JIS C 6481 is preferably 0.8 kN / m or more, and the test piece is further left to stand at 130°C and 85% RH for 100 hours, after which the peel strength (adhesion strength after HAST) between the cured product and the copper foil is preferably 0.3 kN / m or more. The surface roughness Ra of the copper foil is a value measured in accordance with JIS B 0601-2001.

[0054] In the step of laminating the curable resin composition onto the copper foil, a lamination method using a roll or press pressure is used because it is easy to obtain a uniform contact state and has good workability. Among these, a vacuum lamination method is preferably used. The lamination method may be a batch method or a continuous method.

[0055] A commercially available vacuum laminator can be used as the vacuum laminator. The heating temperature is preferably 40 to 160°C. Within this range, the curable resin composition softens but is easily pressure-bonded to the substrate without flowing out. The upper and lower layers of the laminator may be set at different temperatures. The pressure is preferably 0.1 to 1.5 MPa. Within this range, the resin composition can be pressure-bonded to the substrate without flowing out. Lamination is preferably performed under reduced pressure with an air pressure of 30 hPa or less.

[0056] The lamination of the curable resin composition on a surface other than the surface on which it is to be laminated to the copper foil can be carried out in the same manner as described above. During lamination, several films of the curable resin composition may be laminated simultaneously, or a film that has already been laminated to a substrate may be laminated with the curable resin composition with a support. The curable resin composition may also be in the form of a prepreg, as described above, further containing glass cloth.

[0057] Regarding the curing of the curable resin composition, thermal curing is preferred from the viewpoint of increasing adhesive strength and workability. The conditions vary depending on the type of component (B) used, but generally, the curing temperature is 120 to 200°C and the curing time is 15 to 600 minutes. However, in the present invention, the adhesive strength of the curable resin composition can be confirmed by measuring the peel strength after curing by heating at 130°C for 30 minutes and then at 170°C for 30 minutes. Note that in the actual manufacturing process of a printed wiring board, curing conditions other than those described above may be used, and the laminate may be cured by further applying pressure or without applying pressure. [Example]

[0058] EXAMPLES The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0059] The components used in the examples and comparative examples are shown below.

[0060] (A-1) Maleimide compound (A-1-1): A bismaleimide compound represented by the following formula (BMI-2500, manufactured by Designer Molecules Inc., solid at 25°C) [ka] -C 36 H 70 - represents a hydrocarbon group derived from a dimer acid skeleton. l≒5 (average value), m≒1 (average value) (A-1-2): A bismaleimide compound represented by the following formula (BMI-1500, manufactured by Designer Molecules Inc., viscous liquid at 25°C) [ka] -C 36 H 70 - represents a hydrocarbon group derived from a dimer acid skeleton. n≒2 (average value) (A-1-3): A bismaleimide compound represented by the following formula (BMI-5000, manufactured by Designer Molecules Inc., solid at 25°C) [ka] -C 36 H 70 - represents a hydrocarbon group derived from a dimer acid skeleton. n≒8 (average value) (A-1-4): Bismaleimide compound represented by the following formula (BMI-689, manufactured by Designer Molecules Inc., liquid at 25°C, 1.5 Pa s) [ka]

[0061] <Other resins> (A-2-1): A bismaleimide compound represented by the following formula (trade name: BMI-6100, manufactured by Designer Molecules Inc.) [ka] l'≒1 (average value), l"≒10 (average value) (A-2-2): 4,4'-diphenylmethane bismaleimide (BMI-1000, manufactured by Daiwa Chemical Industry Co., Ltd.) (A-2-3): Crystalline bisphenol A epoxy resin (YL-6810, manufactured by Mitsubishi Chemical Corporation, epoxy equivalent weight 170) (A-2-4): Solid bisphenol A epoxy resin (jER-1001, manufactured by Mitsubishi Chemical Corporation, epoxy equivalent 475, softening point 64°C) (A-2-5): Trisphenolmethane type epoxy resin (EPPN-501S, manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent 166, softening point 54°C) (A-2-6): Trisphenolmethane type phenolic resin (MEH-7500, manufactured by Meiwa Kasei Co., Ltd., hydroxyl group equivalent weight 97) (A-2-7): Active ester compound (EXB9460S-65T, manufactured by DIC Corporation, active ester equivalent weight 223, toluene solution with solid content of 65% by mass)

[0062] <(B) Catalyst> (B-1): Dicumyl peroxide (Perkadox BC-FF, manufactured by Kayaku Nouryon Co., Ltd., 1-hour half-life temperature 137°C) (B-2): t-butylperoxy-2-ethylhexyl carbonate (Trigonox 117, manufactured by Kayaku Nouryon Co., Ltd., 1-hour half-life temperature 117°C) (B-3): 2-phenyl-4,5-dihydroxymethylimidazole (2PHZ-PW, manufactured by Shikoku Chemicals Corporation) (B-4): Triphenylphosphine (TPP, manufactured by Hokko Chemical Industry Co., Ltd.)

[0063] <(C) Inorganic filler> (C-1): Toluene slurry of spherical silica having an average particle size of 0.5 μm (5SV-CT1, manufactured by Admattex Co., Ltd., solid concentration 75% by mass)

[0064] <Preparation of Resin Varnish> The components shown in Tables 1 and 2 were added to a 500 mL four-neck flask equipped with a Dimroth condenser and a stirrer, and the mixture was stirred at 80°C for 2 hours to obtain a varnish-like resin composition (resin varnish). Comparative Examples 3 and 5 were not evaluated because they were liquids from which the organic solvent had been removed in order to form a film, and could not be treated as a film. Comparative Example 9 was not evaluated because all of the resin components were dissolved, but separation was observed in the varnish.

[0065] <Preparation of uncured resin film> For those resin varnishes that could be produced without any problems using the above procedure, the resin varnish was applied to a 50 μm thick release-treated PET film (TN-010, manufactured by Toyobo STC) using a roller coater and dried at 120°C for 10 minutes to obtain an uncured resin film with a thickness of 50 μm.

[0066] <Peel strength> A 75mm long, 25mm wide, and 1.0mm thick SUS304 board was prepared. The uncured resin film with the PET film was placed on one surface of the board, with the resin film facing the board. Lamination was performed at 100°C, 0.3 MPa, and 60 seconds. After lamination, the PET film was peeled off, and an 18μm thick copper foil (Ra: 0.17μm) was placed on the resin film facing the board. Lamination was performed at 100°C, 0.3 MPa, and 60 seconds. After lamination, the board was heated at 130°C for 30 minutes, and then further heated at 170°C for 30 minutes to cure the laminate. To evaluate adhesion, the 90° peel strength (kN / m) of each adhesive test piece was measured at 23°C and a tensile speed of 50mm / min according to JIS-C-6481 "Test Methods for Copper-Clad Laminates for Printed Wiring Boards." Furthermore, the adhesive test pieces prepared by the above method were left to stand at 130°C and 85% RH for 100 hours, and then the 90° peel adhesive strength (kN / m) was measured when the copper foil of each adhesive test piece was peeled off from the glass slide at a temperature of 23°C and a pulling speed of 50 mm / min, similarly in accordance with JIS-C-6481 "Test Methods for Copper-Clad Laminates for Printed Wiring Boards."

[0067] <Relative permittivity, dielectric loss tangent> The uncured resin film was fixed directly onto a flat plate together with a release-treated PET film and heated at 130°C for 30 minutes, and then further heated at 170°C for 30 minutes to cure the film, yielding a cured resin film. A network analyzer (Keysight, product name: E5063-2D5) was connected to a strip line (Keycom Corporation) to measure the relative permittivity and dielectric loss tangent of the cured resin film at a frequency of 10 GHz.

[0068] [Table 1] *: The number in parentheses for component C indicates the actual amount of inorganic filler in parts.

[0069] [Table 2] **: The numbers in parentheses for component A-2-7 indicate the number of parts of the active ester compound. ***: The number in parentheses for component C indicates the actual amount of inorganic filler in parts.

[0070] In Comparative Examples 1 to 6 and 9, which contained only one maleimide compound as component (A), films could not be formed, or even if they could be formed, the peel strength after HAST was low and the adhesive strength was poor. In Comparative Examples 7 to 8 and 10 to 16, which did not contain a maleimide compound as component (A), some of the films had low initial peel strength and also low peel strength after HAST. On the other hand, in Examples 1 to 11, the compositions could be formed into films, had high initial peel strength against copper foil with a small surface roughness Ra of 0.17 μm, maintained high peel strength even after HAST, and the cured product had excellent dielectric properties. Therefore, it was confirmed that the curable resin composition of the present invention is useful as a curable resin composition for bonding films for bonding copper foil used in high-frequency applications.

Claims

1. (A) A maleimide compound having one or more hydrocarbon groups derived from a dimer acid skeleton in one molecule, represented by the following formula (1), (2), or (3): and (B) an anionic polymerization initiator, and Epoxy resins with two or more epoxy groups in one molecule Contains A curable resin composition for a bonding film for bonding copper foil, wherein the maleimide compound of component (A) comprises at least two maleimide compounds represented by formula (1), (2), or (3), and at least one of the at least two maleimide compounds is solid at 25°C. [Chemical Formula 1] (In formula (1), A's independently represent tetravalent organic groups having a cyclic structure; B's independently represent divalent hydrocarbon groups having 6 to 60 carbon atoms other than hydrocarbon groups derived from a dimer acid skeleton; D's represent a hydrocarbon group derived from a dimer acid skeleton; m's represents 1 to 100; and l's represents 1 to 100. The order of the repeating units bracketed by m and l's is not limited, and the bonding pattern may be alternating, block, or random.) 【Chemistry 2】 (In formula (2), A's independently represent tetravalent organic groups having a cyclic structure, D's represent a hydrocarbon group derived from a dimer acid skeleton, and n's represent a number from 1 to 100.) 【Chemistry 3】 (In formula (3), D is a hydrocarbon group derived from a dimer acid skeleton.)

2. 2. The curable resin composition according to claim 1, wherein the content of the maleimide compound that is solid at 25°C in the maleimide compound of component (A) is 60 to 100 mass%.

3. 2. The curable resin composition according to claim 1, wherein A in formula (1) and formula (2) is any one of tetravalent organic groups represented by the following structural formulas: 【Chemistry 4】 (The bond not bonded to a substituent in the above structural formula is bonded to the carbonyl carbon that forms the cyclic imide structure in formula (1) and formula (2).)

4. The curable resin composition according to claim 1, which is a thermosetting type.

5. The curable resin composition according to claim 1, wherein a cured product of the curable resin composition has a dielectric loss tangent of 0.005 or less at 10 GHz.

6. 2. The curable resin composition according to claim 1, wherein a test piece obtained by laminating the curable resin composition on a copper foil having a surface roughness Ra of 0.17 μm, heating the curable resin composition at 130° C. for 30 minutes, and then further heating at 170° C. for 30 minutes to cure the curable resin composition has a peel strength between the cured product of the curable resin composition and the copper foil of 0.8 kN / m or more, as measured in accordance with JIS C 6481, and the test piece has a peel strength between the cured product and the copper foil of 0.3 kN / m or more, as measured in accordance with JIS C 6481, after being left at 130° C. and 85% RH for 100 hours.

7. A bonding film comprising the curable resin composition according to any one of claims 1 to 6.

8. A printed wiring board having the bonding film according to claim 7.

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