Adhesive-backed metal substrate and laminate

Abstract

To provide a metal substrate with an adhesive and a laminate which have low dielectric characteristics in a high frequency region, and can sufficiently secure an adhesive strength between a resin film and a metal layer.SOLUTION: A metal substrate with an adhesive includes a metal layer, and an adhesive resin layer formed of an adhesive resin. The adhesive resin composition contains a polyimide resin (A), a maleimide compound (B), a radical initiator. A weight ratio of the polyimide resin (A) to the maleimide compound (B) is 10:1 to 3:2. The content of the radical initiator to 100 pts.mass of the maleimide compound (B) is 1 pts.mass or more and less than 15 pts.mass. The thickness of the adhesive resin layer is 1 μm or more and 5 μm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to adhesive-backed metal substrates and laminates. [Background technology]

[0002] In recent years, with the increasing speed of transmission signals, as exemplified by the fifth-generation mobile communication system (so-called 5G), signals are becoming increasingly frequent, exceeding 6 GHz. Accordingly, flexible printed circuits (FPCs) for high-speed transmission are required to have low dielectric properties (low dielectric constant, low dielectric loss tangent) in the high-frequency range.

[0003] For example, Patent Document 1 discloses a laminate in which a resin substrate and a metal substrate are laminated via an adhesive layer, intended for use in printed wiring boards. The adhesive layer of the laminate disclosed in Patent Document 1 is in a low frequency band compared to the 5G frequency band, but has a relative dielectric constant of 3.0 or less and a dielectric loss tangent of 0.02 or less at a frequency of 1 MHz. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-3886 Summary of the Invention [Problem to be solved by the invention]

[0005] In high-frequency transmission, the higher the frequency band, the more the current flows only on the surface of the metal wiring. Therefore, if the surface shape is not smooth, the transmission loss increases. This is a well-known phenomenon called the skin effect. To reduce transmission loss due to the skin effect, for example, there is a trend to use metal foil with a small surface roughness for metal substrates.

[0006] The lower the surface roughness of the metal foil, the harder it is to achieve an anchoring effect, and the lower the adhesion between the resin film and the metal foil. In this case, the FPC is prone to circuit peeling, and the circuit can easily fall off due to bending stress.

[0007] The present invention has been made in view of the above circumstances, and aims to provide an adhesive-backed metal substrate and a laminate that have low dielectric properties in the high frequency range and can ensure sufficient adhesive strength between a resin film and a metal layer. [Means for solving the problem]

[0008] That is, the present invention employs the following configuration. [1] An adhesive-backed metal substrate comprising a metal layer and an adhesive resin layer formed from an adhesive resin composition, wherein the adhesive resin composition contains a polyimide resin (A), a maleimide compound (B), and a radical initiator, the weight ratio of the polyimide resin (A) to the maleimide compound (B) is 10:1 to 3:2, the content of the radical initiator per 100 parts by mass of the maleimide compound (B) is 1 part by mass or more and less than 15 parts by mass, and the thickness of the adhesive resin layer is 1 μm or more and 5 μm or less. [2] The adhesive-backed metal substrate according to [1], wherein the metal layer is a copper foil having a surface roughness of 1.5 μm or less. [3] A laminate comprising an adhesive-backed metal substrate according to claim 1 or 2 on one or both sides of a resin film, wherein the resin film is laminated on the side opposite to the side on which the adhesive resin layer of the adhesive-backed metal substrate contacts the metal layer, and the resin film is one or more selected from the group consisting of modified polyimide resin films, polyester resin films, liquid crystal polymer films, cyclic olefin resin films, polyphenylene ether resin films, polyphenylene sulfide resin films, polyether ether ketone resin films, bismaleimide resin films, triazine resin films, benzocyclobutene resin films, and low dielectric epoxy resin films. [4] The laminate according to [3], wherein the adhesive resin layer has a thickness of 1 μm or more and 5 μm or less, the resin film has a thickness of 38 μm or more and 100 μm or less, and the metal layer has a thickness of 3 μm or more and 18 μm or less, and the following formula (1) is satisfied: 1%≦(X / Y)×100≦8% ···(1) (In (1), X is the thickness (μm) of the adhesive resin layer, and Y is the thickness (μm) of the resin film.) [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an adhesive-backed metal substrate and a laminate that have low dielectric properties in the high frequency range and can ensure sufficient adhesive strength between a resin film and a metal layer. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional schematic view of an example of an adhesive-backed metal substrate of the present embodiment. [Figure 2] FIG. 2 is a cross-sectional view of an example of a laminate according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] <Metal substrate with adhesive> 1 is a schematic cross-sectional view of an adhesive-backed metal substrate 1 of this embodiment. The adhesive-backed metal substrate 1 comprises a metal layer 10 and an adhesive resin layer 11.

[0012] By combining and thermally laminating the adhesive-backed metal substrate 1 with any low-dielectric substrate, it is possible to manufacture FPCs and rigid substrates for high-speed transmission. When a polyimide resin film or a modified polyimide resin film is used as the low dielectric substrate, an FPC can be obtained. For example, if a prepreg using polyphenylene ether resin is used as the low dielectric substrate, a rigid substrate can be manufactured.

[0013] (metal layer 10) Any known conductive material that can be used for circuit boards can be used for the metal layer 10. Specifically, metal materials such as SUS, copper, aluminum, iron, steel, zinc, and nickel, and alloys of the above metal materials can be used. The metal layer 10 is preferably a metal foil, more preferably a copper foil.

[0014] When the metal layer 10 is a copper foil, rolled copper foil or electrolytic copper foil can be used. When excellent flexural properties (for example, flexural properties of 1 million or more times) are required for an FPC, it is preferable to use rolled copper foil.

[0015] Furthermore, the material of the copper foil may be pure copper or a copper alloy in which a small amount of tin (Sn) or silver (Ag) is added to pure copper.

[0016] The metal layer 10 is preferably a metal foil having a surface roughness of 1.5 μm or less, more preferably 1.4 μm or less, and particularly preferably 1.3 μm or less. The metal layer 10 is preferably a copper foil having a surface roughness of 1.5 μm or less, more preferably 1.4 μm or less, and particularly preferably 1.3 μm or less. The surface roughness of a metal foil, such as a copper foil, can be measured using, for example, a laser microscope VK-9700 manufactured by Keyence Corporation.

[0017] The thickness of the metal layer 10 is preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 3 μm or more, and is preferably 20 μm or less, more preferably 19 μm or less, and even more preferably 18 μm or less. The upper and lower limits of the thickness of the metal layer 10 can be combined arbitrarily. Examples of combinations include a thickness of the metal layer 10 of 1 μm or more and 20 μm or less, 2 μm or more and 19 μm or less, and 3 μm or more and 18 μm or less.

[0018] (Adhesive resin layer 11) The adhesive resin layer 11 is formed from an adhesive resin composition described below. According to the adhesive-backed metal substrate 1, the metal layer 10 can be bonded to any low-dielectric substrate via the adhesive resin layer 11. The thickness of the adhesive resin layer 11 provided on the adhesive-backed metal substrate 1 is 1 μm or more and 5 μm or less, preferably 1.2 μm or more and 4.8 μm or less, more preferably 1.4 μm or more and 4.6 μm or less, and even more preferably 1.6 μm or more and 4.5 μm or less.

[0019] When the thickness of the adhesive resin layer 11 is equal to or greater than the above lower limit, the metal layer 10 and the low dielectric substrate can be bonded together.

[0020] In general, it is believed that if the thickness of the adhesive resin layer 11 is made thinner, the adhesive strength between the metal layer 10 and the low-dielectric substrate decreases, and if the thickness is made thicker, the adhesive strength improves.

[0021] However, after extensive research, the inventors have found that when a specific adhesive resin composition described below is used, if the thickness of the adhesive resin layer 11 exceeds the above upper limit, the adhesive strength between the metal layer 10 and the low dielectric substrate decreases. When bonding dissimilar materials, such as a metal layer 10 and a low dielectric substrate, it has been found that when a specific adhesive resin composition described below is used, the adhesive strength is improved when the thickness of the adhesive resin layer 11 is in a range not exceeding the above upper limit value. The reason for this is presumably that when the thickness of the adhesive resin layer 11 is in the range of the above upper limit or less, dimensional changes due to temperature changes are less likely to occur.

[0022] FPCs and flexible copper-clad laminates are made by combining different materials, namely metal and resin, and are therefore prone to distortion due to changes in the environment in which they are used, particularly temperature changes. For this reason, by using the adhesive-backed metal substrate of this embodiment, which is less susceptible to dimensional changes due to temperature changes, it is easier to obtain FPCs and flexible copper-clad laminates that are less susceptible to distortion.

[0023] (Adhesive resin composition) The adhesive resin composition for forming the adhesive resin layer 11 will be described. In this embodiment, by forming the adhesive resin layer 11 using a specific adhesive resin composition, it is possible to provide an adhesive-coated metal substrate and a laminate that can exhibit low dielectric properties in the high frequency range of 10 GHz, which is a frequency band of 6 GHz or higher assuming 5G.

[0024] The specific adhesive resin composition described below contains a specific amount of a maleimide compound, which is one component of the precursor of the polyimide resin (A), and is therefore believed to result in an adhesive resin layer 11 that exhibits low dielectric properties in the high-frequency range. The maleimide groups of the maleimide compound maintain a cyclic structure even after crosslinking, and crosslinking between maleimide groups results in a symmetrical structure. In this case, molecular motion is likely to be suppressed, and it is believed that the adhesive resin layer 11 that is obtained exhibits low dielectric properties in the high-frequency range.

[0025] The adhesive resin composition contains a polyimide resin (A), a maleimide compound (B), and a radical initiator. As the adhesive resin composition, the resin composition disclosed in WO 2022 / 004583 can be used. The details are described below.

[0026] [Polyimide resin (A)] The polyimide resin (A) is an isocyanate-modified polyimide resin (A1) or a terminal-modified isocyanate-modified polyimide resin (A2). The isocyanate-modified polyimide resin (A1) is referred to as "polyimide resin (A1)," and the terminal-modified isocyanate-modified polyimide resin (A2)" is referred to as "polyimide resin (A2)."

[0027] Polyimide resin (A1) The polyimide resin (A1) is obtained by reacting a diisocyanate compound (a) with an intermediate polyimide resin. The diisocyanate compound (a) is referred to as "component (a)."

[0028] The intermediate polyimide resin is a reaction product of the following components (b), (c), and (d). (b) Component: Aliphatic diamino compound (b) (c) Component: tetrabasic acid dianhydride (c) Component (d): Aromatic diamino compound (d)

[0029] The polyimide resin (A1) is a reaction product of either or both of an amino group and an acid anhydride group present at both ends of the intermediate polyimide resin with an isocyanate group present in the component (a).

[0030] The reaction between the intermediate polyimide resin and component (a) is a copolymerization reaction between the amino group or acid anhydride group at the terminal of the intermediate polyimide resin and the isocyanate group of component (a). That is, the reaction between the amino group and the isocyanate group forms a urea bond, and the reaction between the acid anhydride and the isocyanate group forms an imide bond.

[0031] The amount of component (a) used in the copolymerization reaction between the intermediate polyimide resin and component (a) is preferably less than 1 equivalent of the isocyanate group of component (a) relative to 1 equivalent of the terminal functional group of the intermediate polyimide resin, more preferably 0.50 to 0.99 equivalents, and even more preferably 0.67 to 0.98 equivalents.

[0032] By using the component (a) in an amount within the above range relative to the intermediate polyimide resin, the polyimide resin (A1) can be sufficiently polymerized, and the residual proportion of unreacted raw materials can be reduced, improving the properties of the adhesive resin composition after curing, such as heat resistance and flexibility.

[0033] The terminal functional equivalent of the intermediate polyimide resin referred to here means a value calculated from the amounts of each raw material used when synthesizing the intermediate polyimide resin.

[0034] The component (a) used in the synthesis of the polyimide resin (A1) can be any compound having two isocyanate groups in the molecule, and multiple diisocyanate compounds can be reacted simultaneously.

[0035] As component (a), phenylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, tridenediisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, allylene sulfone ether diisocyanate, allyl cyanide diisocyanate, N-acyl diisocyanate, trimethylhexamethylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, or norbornane-diisocyanatomethyl is preferred. Among these, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, or isophorone diisocyanate is more preferred, as they have an excellent balance of flexibility, adhesiveness, etc.

[0036] The reaction between the intermediate polyimide resin and component (a) may be carried out by a known synthesis method. Specifically, the polyimide resin (A1) can be obtained by adding component (a) to an intermediate polyimide resin solution obtained by the synthesis method described below, and heating and stirring at a temperature of 80°C or higher and 150°C or lower.

[0037] The reaction time for the synthesis reaction of the intermediate polyimide resin and the reaction between the intermediate polyimide resin and component (a) is greatly affected by the reaction temperature, but it is preferable to carry out the reaction until the increase in viscosity accompanying the progress of the reaction reaches equilibrium and the maximum molecular weight is obtained, which is usually several tens of minutes to 10 hours.

[0038] The isocyanate-modified polyimide resin solution obtained above can be added to a poor solvent such as water, methanol, or hexane to separate the resulting polymer, and then a solid content of polyimide resin (A1) can be obtained by reprecipitation.

[0039] Polyimide resin (A2) The polyimide resin (A2) has either or both of an amino group and an acid anhydride group at both ends, and therefore, the ends can be modified by reacting it with a compound having a functional group reactive with these functional groups to prepare a terminally modified isocyanate-modified polyimide resin, i.e., polyimide resin (A2).

[0040] Examples of compounds that can react with either or both of an amino group and an acid anhydride group include compounds having an acid anhydride group such as maleic anhydride, compounds having an alcoholic hydroxyl group such as hydroxyethyl acrylate, compounds having a phenolic hydroxyl group such as phenol, compounds having an isocyanate group such as 2-methacryloyloxyethyl isocyanate, and compounds having an epoxy group such as glycidyl methacrylate.

[0041] By modifying the terminals, both terminals of the isocyanate compound of the present invention can be changed to functional groups other than amino groups and acid anhydride groups (for example, when terminal modification is performed with hydroxyethyl acrylate, the terminals of the isocyanate-modified polyimide resin can be changed to acryloyl groups), so it is also possible to prepare a composition in which the compound is combined with a compound that reacts with functional groups other than amino groups or acid anhydride groups.

[0042] ··Intermediate polyimide resin The intermediate polyimide resin is a reaction product of the above-mentioned components (b), (c), and (d). The reaction of components (b), (c), and (d) involves a step of obtaining a polyamic acid by copolymerization of the amino groups in components (b) and (d) with the acid anhydride groups in component (c), and a step of obtaining an intermediate polyimide resin by cyclodehydration (imidization) of the polyamic acid. These two steps may be carried out separately, but it is more efficient to carry them out continuously in one go.

[0043] When the number of moles of component (b) used in the copolymerization reaction is MB, the number of moles of component (c) is MC, and the number of moles of component (d) is MD, if the relationship MB + MD > MC is satisfied, both ends of the resulting intermediate polyimide resin will be amino groups; if the relationship MB + MD < MC is satisfied, both ends of the resulting intermediate polyimide resin will be acid anhydride groups.

[0044] Also, when the relationship MB + MD = MC is satisfied, the resulting intermediate polyimide resin theoretically has an infinite molecular weight and has one amino group and one acid anhydride group at both ends.

[0045] An example of the amount of component (b) used in the copolymerization reaction is an amount in the range of 10% to 50% by mass of the total mass of components (b), (c), and (d) used in the synthesis step of the intermediate polyimide resin and component (a) used in the synthesis step of the above-mentioned polyimide resin (A1), excluding the mass of water generated in the dehydration cyclization reaction step during the synthesis of the intermediate polyimide resin (this mass is substantially equal to the mass of the finally obtained isocyanate-modified polyimide resin).

[0046] If the amount of component (b) is below the above range, the proportion of the aliphatic chain derived from component (b) in the intermediate polyimide resin is too small, resulting in high dielectric constant and dielectric loss tangent. If it exceeds the above range, the proportion of the aliphatic chain derived from component (b) in the intermediate polyimide resin is too large, leading to a decrease in the heat resistance of the cured product.

[0047] Component (b) used in the synthesis of the intermediate polyimide resin is not particularly limited as long as it is an aliphatic compound having two amino groups in one molecule, but an aliphatic diamine compound having 6 to 36 carbon atoms is preferred.

[0048] Specific examples of component (b) include hexamethylenediamine, 1,3-bis(aminomethyl)cyclohexane, C14 branched diamine, C18 branched diamine, dimer diamine, and diaminopolysiloxane. These may be used alone or in combination of two or more.

[0049] The dimer diamine described as a specific example of component (b) in this specification is a dimer acid, which is a dimer of an unsaturated fatty acid such as oleic acid, in which the two carboxy groups of the dimer acid are substituted with primary amino groups (see, for example, JP-A-9-12712).

[0050] Specific examples of commercially available dimer diamines include PRIAMINE 1074 and PRIAMINE 1075 (both manufactured by Croda Japan Co., Ltd.), and Versamin 551 (manufactured by Cognis Japan Co., Ltd.) These may be used alone or in combination of two or more.

[0051] The component (c) used in the synthesis of the intermediate polyimide resin is not particularly limited as long as it has two acid anhydride groups in one molecule.

[0052] Specific examples of component (c) include pyromellitic anhydride, ethylene glycol bis(anhydrotrimellitate), glycerin bis(anhydrotrimellitate) monoacetate, 1,2,3,4-butanetetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-diphenylethertetracarboxylic dianhydride, 5-(2,5-dioxotetrahydro-3-furanyl)-3- Examples include methylcyclohexene-1,2-dicarboxylic anhydride, 3a,4,5,9b-tetrahydro-5-(tetrahydro-2,5-dioxo-3-furanyl)-1,3-dione, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, bicyclo(2,2,2)-oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride, and 5,5'-((propane-2,2-diylbis(4,1-phenylene))bis(oxy))bis(isobenzofuran-1,3-dione).

[0053] Among these, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and 3,3',4,4'-diphenylethertetracarboxylic dianhydride are preferred in terms of solvent solubility, adhesion to substrates, and photosensitivity. These may be used alone or in combination of two or more.

[0054] The component (c) used in the synthesis of the intermediate polyimide resin preferably contains at least one compound selected from the group consisting of the following formulas (1) to (4).

[0055] [ka]

[0056] In formula (4), Y represents C(CF3)2, SO2, CO, O, a direct bond, or a divalent linking group represented by the following formula (5): The two linking moieties represented by formula (5) are each a moiety that bonds to phthalic anhydride.

[0057] [ka]

[0058] The component (d) used in the synthesis of the intermediate polyimide resin is not particularly limited as long as it is an aromatic compound having two amino groups in one molecule.

[0059] Specific examples of component (d) include m-phenylenediamine, p-phenylenediamine, m-tolylenediamine, 4,4'-diaminodiphenyl ether, 3,3'-dimethyl-4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl thioether, 3,3'-dimethyl-4,4'-diaminodiphenyl thioether, 3,3'-diethoxy-4,4'-diaminodiphenyl thioether, and 3,3 '-Diaminodiphenyl thioether, 4,4'-diaminobenzophenone, 3,3'-dimethyl-4,4'-diaminobenzophenone, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 3,3'-dimethoxy-4,4'-diaminodiphenyl thioether, 2,2'-bis(3-aminophenyl)propane, 2,2'-bis(4-aminophenyl)propane, 4,4'-diamino Diphenyl sulfoxide, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, benzidine, 3,3'-dimethylbenzidine, 3,3'-dimethoxybenzidine, 3,3'-diaminobiphenyl, p-xylylenediamine, m-xylylenediamine, o-xylylenediamine, 2,2'-bis(3-aminophenoxyphenyl)propane, 2,2'-bis(4-aminophenoxyphenyl)propane, 1,3-bis(4 bis(4-aminophenoxyphenyl)benzene, 1,3'-bis(3-aminophenoxyphenyl)propane, bis(4-amino-3-methylphenyl)methane, bis(4-amino-3,5-dimethylphenyl)methane, bis(4-amino-3-ethylphenyl)methane, bis(4-amino-3,5-diethylphenyl)methane, bis(4-amino-3-propylphenyl)methane, and bis(4-amino-3,5-dipropylphenyl)methane. These may be used alone or in combination of two or more.

[0060] The component (d) used in the synthesis of the intermediate polyimide resin preferably contains at least one compound selected from the group consisting of the following formulae (6) and (8).

[0061] [ka]

[0062] In formula (6), R 1 represents a methyl group or a trifluoromethyl group, and in formula (8), Z represents CH(CH), SO, CH, O-C H -O, O, a direct bond, or a divalent linking group represented by formula (5) above, R 3 represents a hydrogen atom, a methyl group, an ethyl group, or a trifluoromethyl group. The two linking moieties represented by formula (5) are each bonded to phthalic anhydride.

[0063] The intermediate polyimide resin can be synthesized by a known method. For example, a solvent, dehydrating agent, and catalyst are added to a mixture of components (b) to (d) used in the synthesis, and the mixture is heated and stirred at 100 to 300°C under an inert gas atmosphere such as nitrogen. This causes an imidization reaction (a ring-closing reaction accompanied by dehydration) via polyamic acid, yielding an intermediate polyimide resin solution. The water generated during the imidization is distilled out of the system, and after the reaction is complete, the dehydrating agent and catalyst are also distilled out of the system, allowing for the production of a highly pure intermediate polyimide resin without the need for washing. Examples of dehydrating agents include toluene and xylene, and examples of catalysts include pyridine and triethylamine.

[0064] Solvents that can be used in the synthesis of the intermediate polyimide resin include methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl butyl ketone, methyl isobutyl ketone, methyl n-hexyl ketone, diethyl ketone, diisopropyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, methylcyclohexanone, acetylacetone, γ-butyrolactone, diacetone alcohol, cyclohexen-1-one, dipropyl ether, diisopropyl ether, dibutyl ether, tetrahydrofuran, tetrahydropyran, ethyl isoamyl ether, ethyl-t-butyl ether, ethyl benzyl ether, cresyl methyl ether, anisole, phenetole, methyl acetate, ethyl acetate, propyl acetate, and isoacetate. Propyl acetate, butyl acetate, isobutyl acetate, amyl acetate, isoamyl acetate, 2-ethylhexyl acetate, cyclohexyl acetate, methylcyclohexyl acetate, benzyl acetate, methyl acetoacetate, ethyl acetoacetate, methyl propionate, ethyl propionate, butyl propionate, benzyl propionate, methyl butyrate, ethyl butyrate, isopropyl butyrate, butyl butyrate, isoamyl butyrate, methyl lactate, ethyl lactate, butyl lactate, ethyl isovalerate, isoamyl isovalerate, diethyl oxalate, dibutyl oxalate, methyl benzoate, ethyl benzoate, propyl benzoate, methyl salicylate, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, etc. These may be used alone or in combination of two or more.

[0065] [Maleimide compound (B)] The compound having a maleimide group is not particularly limited as long as it is a compound having one or more maleimide groups in one molecule, but a compound having two or more maleimide groups in one molecule is preferred, and examples thereof include polyfunctional maleimide compounds obtained by reacting 3,4,4'-triaminodiphenylmethane, triaminophenol, or the like with maleic anhydride, maleimide compounds obtained by reacting tris-(4-aminophenyl)-phosphate, tris(4-aminophenyl)-phosphate, or tris(4-aminophenyl)-thiophosphate with maleic anhydride, trismaleimide compounds such as tris(4-maleimidophenyl)methane, bis(3,4-dimaleimidophenyl)methane, tetrahydrofuran ... Examples of suitable phenylmaleimide compounds include tetramaleimide compounds such as tetramaleimide benzophenone, tetramaleimide naphthalene, and maleimides obtained by reacting triethylenetetramine with maleic anhydride; phenol novolac-type maleimide resins; isopropylidenebis(phenoxyphenylmaleimide)phenylmaleimide aralkyl resins; and biphenylene-type phenylmaleimide aralkyl resins. Commercially available products include MIR-3000 and MIR-5000 (all manufactured by Nippon Kayaku Co., Ltd.), BMI-70 and BMI-80 (all manufactured by K.I. Kasei Co., Ltd.), BMI-1000, BMI-2000, and BMI-3000 (all manufactured by Daiwa Kasei Kogyo Co., Ltd.).

[0066] A compound having a maleimide group undergoes self-crosslinking between maleimide groups due to the action of a radical initiator. Therefore, when a resin composition using an isocyanate-modified polyimide resin having an amino group at its terminal, a compound having a maleimide group, and a radical initiator is heated, the maleimide groups undergo self-crosslinking and the polyimide resin and maleimide resin are copolymerized to form a cured product.

[0067] [Radical initiator] Radical initiators that can be used for self-crosslinking between maleimide groups include peroxides such as dicumyl peroxide and dibutyl peroxide, and azo compounds such as 2,2'-azobis(isobutyronitrile) and 2,2'-azobis(2,4-dimethylvaleronitrile).

[0068] In the adhesive resin composition used in this embodiment, the weight ratio of the polyimide resin (A) to the maleimide compound (B) is 10:1 to 3:2, and preferably 7:1 to 5:2. When the weight ratio of the polyimide resin (A) to the maleimide compound (B) is within the above range, the adhesive-coated metal substrate or laminate has low dielectric properties in the high frequency range. Furthermore, it easily adheres to metal foils with a surface roughness of 1.5 μm or less, and exhibits high adhesive strength.

[0069] In the adhesive resin composition used in this embodiment, the content of the radical initiator relative to 100 parts by mass of the maleimide compound (B) is 1 part by mass or more and less than 15 parts by mass, and preferably 4 parts by mass or more and 10 parts by mass or less. When the content of the radical initiator satisfies the above range, the adhesive-coated metal substrate or laminate can ensure sufficient adhesive strength between the resin film and the metal layer. In particular, it is easy to adhere even to metal foils with a low surface roughness of 1.5 μm or less, and it is easy to demonstrate high adhesive strength.

[0070] The adhesive resin composition may contain an organic solvent. Specific examples of organic solvents include amide-based solvents such as γ-butyrolactones, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and N,N-dimethylimidazolidinone; sulfones such as tetramethylene sulfone; ether-based solvents such as diethylene glycol dimethyl ether, diethylene glycol diethyl ether, propylene glycol, propylene glycol monomethyl ether, propylene glycol monomethyl ether monoacetate, and propylene glycol monobutyl ether; ketone-based solvents such as methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, and cyclohexanone; and aromatic solvents such as toluene and xylene.

[0071] The organic solvent is preferably used in a proportion such that the solids concentration in the adhesive resin composition excluding the organic solvent is generally 10% by mass or more and 80% by mass or less, and more preferably 20% by mass or more and 70% by mass or less.

[0072] The adhesive resin composition can be produced by adding a base material containing a polyimide resin (A) and a maleimide compound (B) to an organic solvent, and further adding a radical initiator.

[0073] <Laminate> The laminate of this embodiment comprises the adhesive-backed metal substrate of this embodiment on one or both sides of a resin film. 2 is a schematic cross-sectional view of a laminate 2 of this embodiment. The laminate 2 includes adhesive-backed metal substrates 1 on both sides of a resin film 12. The resin film 12 is laminated on a surface 11 a of the adhesive-coated metal substrate 1 opposite to the surface of the adhesive resin layer 11 that contacts the metal layer 10 . That is, the laminate 2 has the metal layer 10 / adhesive resin layer 11 / resin film 12 / adhesive resin layer 11 / metal layer 10 laminated in this order.

[0074] When the laminate of this embodiment has the adhesive-backed metal substrate of this embodiment on one side of a resin film, the metal layer 10 / adhesive resin layer 11 / resin film 12 are laminated in this order.

[0075] (resin film) The resin film 12 is preferably one or more selected from the group consisting of modified polyimide resin films, polyester resin films, liquid crystal polymer films, cyclic olefin resin films, polyphenylene ether resin films, polyphenylene sulfide resin films, polyether ether ketone resin films, bismaleimide resin films, triazine resin films, benzocyclobutene resin films, and low dielectric epoxy resin films.

[0076] In the laminate 2, the thickness of the adhesive resin layer 11 is preferably 1 μm or more and 5 μm or less, the thickness of the resin film is preferably 38 μm or more and 100 μm or less, and the thickness of the metal layer 10 is preferably 3 μm or more and 18 μm or less.

[0077] It is preferable that the thickness X (μm) of the adhesive resin layer 11 and the thickness Y (μm) of the resin film 12 satisfy the following relationship (1). 1%≦(X / Y)×100≦8% ···(1)

[0078] When X / Y is equal to or greater than the above lower limit, the metal layer 10 and the resin film 12 can be sufficiently bonded to each other. When X / Y is equal to or less than the upper limit, the thickness of the adhesive resin layer 11 is small relative to the resin film 12, and it is thought that the dimensional change of the adhesive resin layer 11 caused by temperature change has a small effect on the resin film 12. For this reason, it is presumed that the adhesive strength is less likely to decrease even after temperature change.

[0079] An example of the laminate 2 is a flexible copper clad laminate or copper clad laminate. [Example]

[0080] The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples.

[0081] <Preparation of Adhesive Resin Composition> ≪Material≫ The polyimide resin (A) and the maleimide compound (B) were mixed in a ratio of polyimide resin (A):maleimide compound (B)=10:3 and used. The radical initiator used was dicumyl peroxide (manufactured by Sigma-Aldrich). Anisole was used as the solvent.

[0082] ≪Preparation≫ The main component and the solvent were mixed so that the weight ratio of the polyimide resin (A) to the maleimide compound (B) was 10:3, and the main component was dissolved. Furthermore, 3 parts by mass of dicumyl peroxide was added to 100 parts by mass of the maleimide compound (B) to prepare an adhesive resin composition 1 having a solid content concentration of 20% by mass.

[0083] <Manufacturing of adhesive-coated metal substrates> Adhesive resin composition 1 was applied to an electroless copper foil (Fukuda Metal Foil & Powder Co., Ltd., CF-T49A-DS-HD2-12) having a surface roughness of 1.2 μm and a thickness of 12 μm using an applicator. The amount of coating was determined so that the adhesive resin layer after drying would have a thickness satisfying each of the thicknesses listed in Table 1. After coating, the coating was dried at 140° C. for 1 minute to produce adhesive-backed metal substrates of Examples 1 and 2 and Comparative Examples 1 and 2.

[0084] [Table 1]

[0085] <Production of laminate> The resin film used was a modified polyimide film with a thickness of 38 μm, which was pre-dried at 105° C. for 60 minutes.

[0086] The adhesive-backed metal substrates of Examples 1 and 2 and Comparative Examples 1 and 2 were laminated on both sides of the modified polyimide film in the following order: copper foil / adhesive resin layer / modified polyimide film / adhesive resin layer / copper foil. Lamination was then performed at 200°C for 120 minutes under a pressure of 3 MPa to produce the laminates of Examples 1 and 2 and Comparative Examples 1 and 2, respectively.

[0087] <x y> For the laminates of Examples 1 and 2 and Comparative Examples 1 and 2, "(X / Y) x 100 (unit: %)" is shown in Table 1. X is the thickness (μm) of the adhesive resin layer, and Y is the thickness (μm) of the resin film.

[0088] <Measurement of adhesive strength> The adhesive strength between the copper foil and the modified polyimide film of the resulting laminate was measured. The resulting laminate was cut into a width of 10 mm to obtain a test piece. The modified polyimide film side was attached to a ring core with a diameter of 11 cm, and a 90° peel test was performed by pulling the copper foil portion at a speed of 50 mm / min. From this measurement, adhesive strength of 0.8 N / mm or more was evaluated as "sufficient adhesive strength." The adhesive strengths of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 2. As an index of adhesive strength between the resin film and the metal layer, an adhesive strength of 0.8 N / mm or more is required from the viewpoint of preventing peeling of the metal layer during the FPC manufacturing process. For this reason, 0.8 N / mm was determined to be the pass value.

[0089] <Measurement of dielectric properties> The copper foil was removed from each of the resulting laminates by etching to obtain test pieces (50 mm wide, 100 mm long) in which adhesive resin layer / modified polyimide film / adhesive resin were laminated in this order. The obtained test pieces were dried at 135°C for 1 hour to be used as dried test pieces. After drying, the test pieces were left to stand for 24 hours under conditions of 23°C and 50% humidity to be used as humidity-conditioned test pieces, and the dielectric properties of each were measured.

[0090] The dielectric properties were measured using a resonator manufactured by QWED Inc. by the split post dielectric resonator method at a frequency of 10 GHz, including the relative permittivity and dielectric loss tangent. When the relative permittivity is 3.5 or less and the dielectric loss tangent is 0.005 or less, the dielectric properties in the high frequency range are evaluated as being low.

[0091] [Table 2]

[0092] As shown in Table 2, Examples 1 and 2 maintained low dielectric properties in the high frequency range of 10 GHz and had adhesive strengths that met the acceptable values. This is thought to be because in Examples 1 and 2, in which the thickness of the adhesive resin layer was 1 μm or more and 5 μm or less, dimensional changes due to temperature changes in the sample production process were unlikely to occur.

[0093] On the other hand, Comparative Examples 1 and 2 had low dielectric properties in the high frequency range, but the adhesive strength was below 0.8 N / mm. [Explanation of symbols]

[0094] 1: adhesive-backed metal substrate, 2: laminate, 10: metal layer, 11: adhesive resin layer, 12: resin film< / x>

Claims

1. An adhesive-backed metal substrate comprising a metal layer and an adhesive resin layer formed from an adhesive resin composition, The adhesive resin composition comprises a polyimide resin (A), a maleimide compound (B), and a radical initiator, the weight ratio of the polyimide resin (A) to the maleimide compound (B) is 10:1 to 3:2; the content of the radical initiator relative to 100 parts by mass of the maleimide compound (B) is 1 part by mass or more and less than 15 parts by mass, The adhesive-coated metal substrate, wherein the adhesive resin layer has a thickness of 1 μm or more and 5 μm or less.

2. 2. The adhesive-backed metal substrate according to claim 1, wherein the metal layer is a copper foil having a surface roughness of 1.5 μm or less.

3. A laminate comprising the adhesive-backed metal substrate according to claim 1 or 2 on one or both sides of a resin film, the resin film is laminated on a surface of the adhesive-backed metal substrate opposite to a surface of the adhesive resin layer that is in contact with the metal layer, The resin film is at least one selected from the group consisting of a modified polyimide resin film, a polyester resin film, a liquid crystal polymer film, a cyclic olefin resin film, a polyphenylene ether resin film, a polyphenylene sulfide resin film, a polyether ether ketone resin film, a bismaleimide resin film, a triazine resin film, a benzocyclobutene resin film, and a low dielectric epoxy resin film.

4. The thickness of the adhesive resin layer is 1 μm or more and 5 μm or less, The thickness of the resin film is 38 μm or more and 100 μm or less, The thickness of the metal layer is 3 μm or more and 18 μm or less, The laminate according to claim 3, which satisfies the following formula (1): 1%≦(X / Y)×100≦8%...(1) (In (1), X is the thickness (μm) of the adhesive resin layer, and Y is the thickness (μm) of the resin film.)

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