Adhesive-coated metal substrates and laminates

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 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 composition. The adhesive resin composition contains a polyimide resin (A), a maleimide compound (B), a radical initiator and an epoxy resin. 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 content of the epoxy resin to 100 pts.mass of the total of the polyimide resin (A) and the maleimide compound (B) is 1 pts.mass or more and 5 pts.mass or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a metal substrate with an adhesive and a laminate.

Background Art

[0002] In recent years, with the speeding up of transmission signals represented by the fifth-generation mobile communication system (so-called 5G), the high-frequency of signals exceeding 6 GHz has been advancing. Along with this, flexible printed circuit boards (FPCs) for high-speed transmission are required to have low dielectric characteristics (low dielectric constant, low dielectric tangent) in the high-frequency range.

[0003] For example, Patent Document 1 assumes use for a printed wiring board and discloses a laminate in which a resin substrate and a metal substrate are laminated via an adhesive layer. Although the adhesive layer included in the laminate disclosed in Patent Document 1 is in a low-frequency band with respect to the 5G frequency band, its relative dielectric constant at a frequency of 1 MHz is 3.0 or less, and its dielectric tangent is 0.02 or less.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

[0006] As the surface roughness of the metal foil decreases, the anchoring effect becomes less pronounced, and the adhesion between the resin film and the metal foil decreases. In this case, the FPC is prone to circuit delamination, and the circuit is easily detached due to bending stress, which presents a problem.

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

[0008] In other words, the present invention employs the following configuration. [1] A metal substrate with adhesive comprising a metal layer and an adhesive resin layer formed from an adhesive resin composition, wherein the adhesive resin composition comprises a polyimide resin (A), a maleimide compound (B), a radical initiator, and an epoxy resin, 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 content of the epoxy resin per 100 parts by mass of the total of the polyimide resin (A) and the maleimide compound (B) is 1 part by mass or more and 5 parts by mass or less, the metal substrate with adhesive. [2] The adhesive-bonded metal substrate according to [1], wherein the metal layer is a copper foil with a surface roughness of 1.5 μm or less. [3] The adhesive-coated metal substrate according to [1] or [2], wherein the thickness of the adhesive resin layer is 1 μm or more and 15 μm or less. [4] A laminate comprising an adhesive metal substrate according to any one of [1] to [3] 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 metal substrate is in contact with the metal layer, and the resin film is one or more 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. [Effects of the Invention]

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

[0010] [Figure 1] This is a schematic cross-sectional view of an example of an adhesive-coated metal substrate according to this embodiment. [Figure 2] This is a schematic cross-sectional view of an example of the laminate according to this embodiment. [Modes for carrying out the invention]

[0011] <Metal substrate with adhesive> Figure 1 shows a schematic cross-section of the adhesive-coated metal substrate 1 of this embodiment. The adhesive-coated metal substrate 1 comprises a metal layer 10 and an adhesive resin layer 11.

[0012] By thermal laminating an adhesive-backed metal substrate 1 with any low-dielectric substrate, FPCs and rigid substrates for high-speed transmission can be manufactured. By using, for example, a polyimide resin film or a modified polyimide resin film as a low-dielectric substrate, an FPC can be obtained. When using, for example, a prepreg using a polyphenylene ether resin as a low dielectric substrate, a rigid substrate can be manufactured.

[0013] (Metal layer 10) For the metal layer 10, any known conductive material that can be used for a circuit board can be used. Specifically, it is a metal material such as SUS, copper, aluminum, iron, steel, zinc, nickel, etc., or an alloy of the above metal materials. The metal layer 10 is preferably a metal foil, and more preferably a copper foil.

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

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

[0016] The metal layer 10 is preferably a metal foil with a surface roughness of 1.5 μm or less, more preferably 1.4 μm or less, and particularly preferably 1.3 μm or less.

[0017] When the metal layer 10 is a copper foil, it may be a low roughened copper foil or a non-roughened copper foil. The low roughened copper foil is a copper foil with 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 non-roughened copper foil is a copper foil with a surface roughness of 0.85 μm or less, and may be 0.84 μm or less or 0.82 μm or less.

[0018] From the perspective of further improving the performance of 5G wiring boards whose market scale is expected to expand, the adoption of non-roughened copper foils with reduced skin effect is expected compared to low roughened copper foils. In this embodiment, by forming an adhesive resin layer from a specific adhesive resin composition described later, even when an unroughened copper foil is used as the metal layer 10, an adhesive metal base material or a laminate can be obtained that can sufficiently ensure the adhesive strength between the resin film and the metal layer.

[0019] The surface roughness of a metal foil exemplified by a copper foil can be measured, for example, with a laser microscope VK-9700 manufactured by Keyence Corporation. The surface roughness in this specification means the ten-point average roughness.

[0020] 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. Also, the thickness of the metal layer 10 is preferably 20 μm or less, more preferably 19 μm or less, and even more preferably 18 μm or less. The above upper and lower limit values of the thickness of the metal layer 10 can be arbitrarily combined. Examples of the combination are that the thickness of the metal layer 10 is 1 μm or more and 20 μm or less, 2 μm or more and 19 μm or less, 3 μm or more and 18 μm or less.

[0021] (Adhesive resin layer 11) The adhesive resin layer 11 is formed from an adhesive resin composition described later. According to the adhesive metal base material 1, the metal layer 10 and an arbitrary low dielectric base material can be adhered via the adhesive resin layer 11. The thickness of the adhesive resin layer 11 provided in the adhesive metal base material 1 is preferably 1 μm or more and 15 μm or less, more preferably 1.2 μm or more and 12 μm or less, even more preferably 1.4 μm or more and 9 μm or less, and particularly preferably 1.6 μm or more and 7 μm or less.

[0022] When the thickness of the adhesive resin layer 11 is not less than the above lower limit value, the metal layer 10 and the low dielectric base material can be adhered.

[0023] When adhering different materials such as the metal layer 10 and the low dielectric base material, when using a specific adhesive resin composition described later, the adhesive strength tends to improve within the range where the thickness of the adhesive resin layer 11 is not more than the above upper limit value. The reason for this is presumably that if the thickness of the adhesive resin layer 11 is within the range of the above upper limit, dimensional changes due to temperature changes will be less likely to occur.

[0024] FPCs and flexible copper-clad laminates combine dissimilar materials, namely metal and resin, making them susceptible to deformation due to changes in the operating environment, particularly temperature changes. Therefore, using the adhesive-coated metal substrate of this embodiment, which is less prone to dimensional changes due to temperature fluctuations, makes it easier to obtain FPCs and flexible copper-clad laminates that are less susceptible to deformation.

[0025] (Adhesive resin composition) An adhesive resin composition for forming the adhesive resin layer 11 will be described. In this embodiment, by forming an adhesive resin layer 11 using a specific adhesive resin composition, it is possible to provide an adhesive-coated metal substrate and 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, for example, when considering 5G.

[0026] The specific adhesive resin composition described later is thought to exhibit low dielectric properties in the high-frequency range because it contains a specific amount of maleimide compound, which is a precursor of polyimide resin (A). The maleimide group of the maleimide compound maintains a cyclic structure even after crosslinking, and the crosslinking between maleimide groups results in a symmetrical structure. In this case, molecular motion is easily suppressed, and the resulting adhesive resin layer 11 is thought to exhibit low dielectric properties in the high-frequency range.

[0027] The adhesive resin composition comprises a polyimide resin (A), a maleimide compound (B), a radical initiator, and an epoxy resin. As an adhesive resin composition, a resin composition disclosed in International Publication No. 2022 / 004583 with a predetermined amount of epoxy resin added can be used. The details are described below.

[0028] [Polyimide resin (A)] Polyimide resin (A) is either isocyanate-modified polyimide resin (A1) or end-modified isocyanate-modified polyimide resin (A2). Isocyanate-modified polyimide resin (A1) is referred to as "polyimide resin (A1)," and end-modified isocyanate-modified polyimide resin (A2) is referred to as "polyimide resin (A2)."

[0029] • Polyimide resin (A1) Polyimide resin (A1) is obtained by the reaction of diisocyanate compound (a) with an intermediate polyimide resin. Diisocyanate compound (a) is referred to as "component (a)".

[0030] The intermediate polyimide resin is a reaction product of components (b), (c), and (d) shown below. (b) Components: Aliphatic diamino compounds (b) (c) Ingredients: Tetrabasic acid dianhydride (c) (d) Component: Aromatic diamino compound (d)

[0031] The polyimide resin (A1) is a reaction product of the amino group and / or acid anhydride group present at both ends of the intermediate polyimide resin, and the isocyanate group present in component (a).

[0032] The reaction between the intermediate polyimide resin and component (a) is a copolymerization reaction between the amino group or acid anhydride group at the end of the intermediate polyimide resin and the isocyanate group of component (a). In other words, a urea bond is formed by the reaction between the amino group and the isocyanate group, and an imide bond is formed by the reaction between the acid anhydride and the isocyanate group.

[0033] 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 isocyanate groups of component (a) per 1 equivalent of terminal functional groups of the intermediate polyimide resin, more preferably 0.50 to 0.99 equivalents, and even more preferably 0.67 to 0.98 equivalents.

[0034] By setting the amount of component (a) used in the intermediate polyimide resin to the aforementioned range, the polyimide resin (A1) is sufficiently made to have a high molecular weight. Furthermore, the residual rate of unreacted raw materials is reduced, improving various properties such as heat resistance and flexibility of the adhesive resin composition after curing.

[0035] Furthermore, the terminal functional equivalent of the intermediate polyimide resin referred to here means the value calculated from the amount of each raw material used when synthesizing the intermediate polyimide resin.

[0036] Any component (a) used in the synthesis of polyimide resin (A1) can be used as long as it has two isocyanate groups in its molecule, and multiple diisocyanate compounds can be reacted simultaneously.

[0037] (a) The components that are preferred are phenylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate, tetramethyl xylylene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, tridens diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, allylene sulfone ether diisocyanate, allyl cyanide diisocyanate, N-acyl diisocyanate, trimethylhexamethylene diisocyanate, 1,3-bis(isocyanate methyl)cyclohexane, or norbornane-diisocyanate methyl. Among these, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, or isophorone diisocyanate are more preferred because they have an excellent balance of flexibility, adhesion, etc.

[0038] The reaction between the intermediate polyimide resin and component (a) can be carried out using known synthesis methods. Specifically, polyimide resin (A1) can be obtained by adding component (a) to the intermediate polyimide resin solution obtained by the synthesis method described later, and heating and stirring at a temperature of 80°C to 150°C.

[0039] Furthermore, the reaction time for the synthesis reaction of the intermediate polyimide resin and the reaction of the intermediate polyimide resin with component (a) is greatly influenced by the reaction temperature. However, it is preferable to continue the reaction until the viscosity increase 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.

[0040] The isocyanate-modified polyimide resin solution obtained above can also be immersed in a poor solvent such as water, methanol, and hexane to separate the resulting polymer, and then the solid content of the polyimide resin (A1) can be obtained by reprecipitation.

[0041] • Polyimide resin (A2) Polyimide resin (A2) has either an amino group or an acid anhydride group, or both, at both ends. Therefore, by reacting it with a compound that has one functional group that can react with these functional groups, the ends can be modified to prepare a terminally modified isocyanate-modified polyimide resin, i.e., polyimide resin (A2).

[0042] Examples of compounds that can react with either an amino group or an acid anhydride group or both 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.

[0043] By modifying the ends, the ends 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 end modification is performed using hydroxyethyl acrylate, the ends of the isocyanate-modified polyimide resin can be changed to acryloyl groups), making it possible to create compositions in which the compound is combined with a compound that reacts with a functional group other than an amino group or acid anhydride group.

[0044] Intermediate polyimide resin The intermediate polyimide resin is a reaction product of the above-described components (b), (c), and (d). The reaction of components (b), (c), and (d) includes a step of obtaining a polyamic acid through a copolymerization reaction between the amino groups in components (b) and (d) and the acid anhydride groups in component (c), and a step of obtaining an intermediate polyimide resin through a dehydration cyclization reaction (imidization reaction) of the polyamic acid. These two steps may be carried out separately, but it is more efficient to carry them out continuously and in one batch.

[0045] 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.

[0046] 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.

[0047] 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 mass obtained by subtracting the mass of water generated in the dehydration cyclization reaction step during the synthesis of the intermediate polyimide resin from the total mass of components (b), (c), (d) used in the synthesis step of the intermediate polyimide resin and component (a) used in the synthesis step of the above-described polyimide resin (A1) (this mass is substantially equal to the mass of the finally obtained isocyanate-modified polyimide resin).

[0048] 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.

[0049] The 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 diamino compound having 6 to 36 carbon atoms is preferred.

[0050] (b) Specific examples of components include hexamethylenediamine, 1,3-bis(aminomethyl)cyclohexane, C14 branched diamine, C18 branched diamine, dimer amine, and diaminopolysiloxane. These may be used individually or in combination of two or more.

[0051] (b) Dimer amines described as specific examples of components are, in this specification, dimer acids, which are dimers of unsaturated fatty acids such as oleic acid, in which the two carboxyl groups of dimer acid are replaced with primary amino groups (see Japanese Patent Publication No. 9-12712, etc.).

[0052] Specific examples of commercially available dimer amines 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 individually or in combination of two or more.

[0053] 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.

[0054] (c)Specific examples of components 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 acid anhydride, 3a,4,5,9b-tetrahydro-5-(tetrahydro-2,5-dioxo-3-furanyl)--1,3-dione, 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride, bicyclo(2,2,2)-octo-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, and bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic acid dianhydride, 5,5'-((propane-2,2-diylbis(4,1-phenylene))bis(oxy))bis(isobenzofuran-1,3-dione), etc.

[0055] In particular, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, or 3,3',4,4'-diphenylethertetracarboxylic dianhydride are preferred in terms of solvent solubility, adhesion to the substrate, and photosensitivity. These may be used individually or in combination of two or more.

[0056] 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).

[0057] [ka]

[0058] In formula (4), Y represents C(CF3)2, SO2, CO, O, a direct bond, or a divalent linking group represented by formula (5) below. The two linking parts represented by formula (5) are each the parts that bond to phthalic anhydride.

[0059] [ka]

[0060] 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.

[0061] (d)Specific examples of components include m-phenylenediamine, p-phenylenediamine, m-tolylenediamine, 4,4'-diaminodiphenyl ether, 3,3'-dimethyl-4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylthioether, 3,3'-dimethyl-4,4'-diaminodiphenylthioether, 3,3'-diethoxy-4,4'-diaminodiphenylthioether, 3,3 '-diaminodiphenylthioether, 4,4'-diaminobenzophenone, 3,3'-dimethyl-4,4'-diaminobenzophenone, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 3,3'-dimethoxy-4,4'-diaminodiphenylthioether, 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 Examples include 1,3'-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 individually or in combination of two or more.

[0062] 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 formulas (6) and (8).

[0063] [ka]

[0064] In formula (6), R 1 represents a methyl group or a trifluoromethyl group, in formula (8) Z represents CH(CH3), SO2, CH2, O-C6H4-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 linkages represented by formula (5) are the parts that bond to phthalic anhydride, respectively.

[0065] Intermediate polyimide resins can be synthesized by known methods. For example, by adding a solvent, a dehydrating agent, and a catalyst to a mixture of components (b) to (d) used in the synthesis, and heating and stirring at 100 to 300°C under an inert gas atmosphere such as nitrogen, an imidation reaction (a ring-closing reaction accompanied by dehydration) occurs via polyamic acid, yielding an intermediate polyimide resin solution. At this time, the water generated during imidation is removed from the system by distillation, and after the reaction is complete, the dehydrating agent and catalyst are also removed from the system by distillation, thereby obtaining a high-purity intermediate polyimide resin without the need for washing. Examples of dehydrating agents include toluene and xylene, and examples of catalysts include pyridine and triethylamine.

[0066] Solvents that can be used in the synthesis of intermediate polyimide resins 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, phenethole, methyl acetate, ethyl acetate, propyl acetate, iso acetate Examples include, but are not limited to, propyl, 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, and dimethyl sulfoxide. These may be used individually or in combination of two or more.

[0067] [Maleimide compound (B)] Compounds having a maleimide group are not particularly limited as long as they have one or more maleimide groups in one molecule, but compounds having two or more maleimide groups in one molecule are preferred, such as polyfunctional maleimide compounds obtained by the reaction of 3,4,4'-triaminodiphenylmethane, triaminophenol, etc. with maleic anhydride, maleimide compounds obtained by the reaction of tris-(4-aminophenyl)-phosphate, tris(4-aminophenyl)-phosphate, tos(4-aminophenyl)-thiophosphate, trismaleimide compounds such as tris(4-maleimidophenyl)methane, bis(3,4-dimaleimidophenyl)methane, te Examples include tetramaleimide compounds such as tramalemidebenzophenone, tetramaleimidenaphthalene, and maleimide obtained by the reaction of triethylenetetramine with maleic anhydride, phenol novolac type maleimide resins, isopropylidenebis(phenoxyphenylmaleimide)phenylmaleimide alkyl resins, and biphenylene type phenylmaleimide alkyl resins. Commercially available products include MIR-3000, MIR-5000 (both manufactured by Nippon Kayaku Co., Ltd.), BMI-70, BMI-80 (both manufactured by K.I. Chemicals Co., Ltd.), BMI-1000, BMI-2000, and BMI-3000 (all manufactured by Yamato Chemical Industries, Ltd.).

[0068] Compounds containing maleimide groups self-crosslink with each other through the action of a radical initiator. Therefore, a resin composition using an isocyanate-modified polyimide resin having amino groups at its termini, a compound containing maleimide groups, and a radical initiator will undergo self-crosslinking of the maleimide groups upon heating, resulting in a cured product in which the polyimide resin and the maleimide resin are copolymerized.

[0069] [Radical initiator] Radical initiators that can be used for self-crosslinking of 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).

[0070] [Epoxy resin] As the epoxy resin, a bifunctional or more epoxy resin is preferred. Examples include bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin, glycidylamine type epoxy resin, and phenoxy resin, which is a reaction product of a bisphenol type epoxy resin and epichlorohydrin. Examples of such epoxy resins include, but are not limited to, jER(registered trademark) 154, jER157, jER1031, jER1032, jER630, jER1001, jER1256 (Mitsubishi Chemical Corporation), EPICLON(registered trademark) N-740, EPICLON N-770 (DIC Corporation), YDPN-638, YDCN-700, YH-434 (Nippon Steel & Sumitomo Metal Chemical Corporation), TETRAD(registered trademark)-X, and TETRAD-C (Mitsubishi Gas Chemical Corporation).

[0071] In addition, commercially available epoxy resins such as HP-4032D and HP-7200 from DIC Corporation, and NC-3000 from Nippon Kayaku Co., Ltd. can be used.

[0072] The adhesive resin composition used in this embodiment has a weight ratio of polyimide resin (A) to maleimide compound (B) of 10:1 to 3:2, preferably 7:1 to 5:2. When the weight ratio of polyimide resin (A) to maleimide compound (B) is within the above range, it results in an adhesive-bonded metal substrate or laminate with low dielectric properties in the high-frequency range. Furthermore, it adheres easily to metal foils with a surface roughness of 1.5 μm or less, and exhibits high adhesive strength.

[0073] The adhesive resin composition used in this embodiment contains 1 part by mass or more and less than 15 parts by mass of radical initiator per 100 parts by mass of maleimide compound (B), preferably 4 parts by mass or more and 10 parts by mass or less. When the radical initiator content meets the above range, it results in an adhesive-coated metal substrate or laminate that can sufficiently ensure adhesive strength between the resin film and the metal layer. In particular, it adheres well even to low-roughness metal foils with a surface roughness of 1.5 μm or less, and exhibits high adhesive strength.

[0074] The adhesive resin composition used in this embodiment has an epoxy resin content of 1 to 5 parts by mass relative to 100 parts by mass of the total of polyimide resin (A) and maleimide compound (B). If the epoxy resin content is above the lower limit mentioned above, the epoxy groups that have not fully reacted with the polyimide groups of the polyimide resin can chemically bond (e.g., hydrogen bond) with the surface of the metal layer. Therefore, even when uncoated copper is used as the metal layer, the adhesive-coated metal substrate or laminate can be made with sufficient adhesive strength between the resin film and the metal layer. If the epoxy resin content is below the above upper limit, even when using uncoated copper as the metal layer, the resulting adhesive-coated metal substrate or laminate will have sufficient adhesive strength between the resin film and the metal layer while maintaining low dielectric properties.

[0075] The adhesive resin composition may contain an organic solvent. Specific examples of organic solvents include amide solvents such as γ-butyrolactones, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and N,N-dimethylimidazolidinone; sulfones such as tetramethylene sulfone; ether 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 solvents such as methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, and cyclohexanone; and aromatic solvents such as toluene and xylene.

[0076] The organic solvent is preferably used in a proportion such that the solid content concentration in the adhesive resin composition excluding the organic solvent is typically 10% by mass or more and 80% by mass or less, and is between 20% by mass and 70% by mass or less.

[0077] The adhesive resin composition can be manufactured by adding a main component containing a polyimide resin (A) and a maleimide compound (B) to an organic solvent, and then adding a radical initiator and an epoxy resin.

[0078] <Laminate> The laminate of this embodiment comprises a resin film with an adhesive-coated metal substrate of this embodiment on one or both sides. Figure 2 shows a schematic cross-sectional view of the laminate 2 of this embodiment. The laminate 2 comprises a resin film 12 with adhesive-coated metal substrates 1 on both sides. The resin film 12 is laminated on the surface 11a opposite to the surface where the adhesive resin layer 11 of the adhesive-backed metal substrate 1 is in contact with the metal layer 10. In other words, the laminate 2 is constructed by laminating metal layer 10 / adhesive resin layer 11 / resin film 12 / adhesive resin layer 11 / metal layer 10 in this order.

[0079] When the laminate of this embodiment has an adhesive-coated metal substrate of this embodiment on one side of the resin film, the metal layer 10 / adhesive resin layer 11 / resin film 12 are laminated in this order.

[0080] (Resin film) The resin film 12 is preferably one or more selected from the group consisting of modified polyimide resin film, polyester resin film, liquid crystal polymer film, cyclic olefin resin film, polyphenylene ether resin film, polyphenylene sulfide resin film, polyether ether ketone resin film, bismaleimide resin film, triazine resin film, benzocyclobutene resin film, and low dielectric epoxy resin film.

[0081] In the laminate 2, the thickness of the adhesive resin layer 11 is preferably 1 μm or more and 15 μm or less. The thickness of the resin film is preferably 38 μm or more and 100 μm or less. The thickness of the metal layer 10 is preferably 3 μm or more and 18 μm or less.

[0082] 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 relationship shown in (1) below. 1%≦(X / Y)×100≦8% ···(1)

[0083] When X / Y is greater than or equal to the lower limit value, the metal layer 10 and the resin film 12 can be sufficiently bonded together. When X / Y is below the above upper limit, the thickness of the adhesive resin layer 11 is thin relative to the resin film 12, and it is thought that the influence of dimensional changes in the adhesive resin layer 11 due to temperature changes on the resin film 12 will be small. For this reason, it is presumed that the adhesive strength will not decrease easily even after temperature changes.

[0084] An example of laminate 2 is a flexible copper-clad laminate or a copper-clad laminate. [Examples]

[0085] The present invention will be described in more detail below as examples, but it is not limited to these examples.

[0086] <Preparation of adhesive resin composition> ≪Material≫ A polyimide resin (A) and a 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). As the epoxy resin, we used tetrafunctional glycidylamine (TETRAD-X, manufactured by Mitsubishi Gas Chemical Company, Inc.). Anisole was used as the solvent.

[0087] ≪Preparation≫ The polyimide resin (A) and maleimide compound (B) were mixed in a weight ratio of 10:3, and the main component was dissolved. Furthermore, 3 parts by mass of dicumyl peroxide were added to 100 parts by mass of maleimide compound (B), and then epoxy resin was added in proportion to the total 100 parts by mass of polyimide resin (A) and maleimide compound (B) as shown in Table 1, thereby preparing adhesive resin compositions 1 to 4 with a solid content concentration of 20% by mass.

[0088] <Manufacturing of adhesive-coated metal substrates> ≪Material≫ As the unroughened copper foil, electroless copper foil with a surface roughness of 0.85 μm and a thickness of 12 μm (Fukuda Metal Foil & Powder Industry, CF-T9DA-SV-12) was used. As a low-roughness copper foil, electroless copper foil with a surface roughness of 1.2 μm and a thickness of 12 μm (Fukuda Metal Foil & Powder Industry, CF-T49A-DS-HD2-12) was used.

[0089] Adhesive resin compositions 1 to 4 were applied to both unroughened copper foil and lightly roughened copper foil using an applicator. The amount of adhesive resin applied was such that the thickness of the adhesive resin layer after drying was 6 μm. After coating, the adhesive-coated metal substrates of Examples 1-2 and Comparative Examples 1-2 were produced by drying at 120°C for 10 minutes.

[0090] [Table 1]

[0091] <Manufacturing of laminates> A modified polyimide film with a thickness of 38 μm was used as the resin film. The modified polyimide film was pre-dried at 105°C for 60 minutes.

[0092] The adhesive-coated metal substrates of Examples 1-2 and Comparative Examples 1-2 were laminated on both sides of a modified polyimide film in the order of copper foil / adhesive resin layer / modified polyimide film / adhesive resin layer / copper foil. Then, the laminates of Examples 1-2 and Comparative Examples 1-2 were produced by laminating at 200°C for 120 minutes at 3 MPa.

[0093] <Measuring 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 strips 10 mm wide to obtain test specimens. A 90° peel test was performed by attaching the modified polyimide film to an 11 cm diameter ring core and pulling the copper foil portion at a speed of 50 mm / min.

[0094] Based on this measurement, an adhesive strength of 0.7 N / mm or higher for unroughened copper foil was evaluated as "sufficiently ensuring adhesive strength." The adhesive strengths for Examples 1-2 and Comparisons 1-2 are shown in Table 2. For reference, the adhesive strength when using low-roughness copper foil is also shown in Table 2.

[0095] In the case of unroughened copper foil, an adhesive strength of 0.7 N / mm or higher is required as an indicator of the adhesive strength between the resin film and the metal layer, from the viewpoint of preventing the metal layer from peeling off during the FPC manufacturing process. For this reason, 0.7 N / mm was set as the acceptable value.

[0096] [Table 2]

[0097] <Measurement of dielectric properties> Adhesive resin compositions 1 to 4 were applied to a peeled polyimide film using an applicator. The amount of adhesive resin applied was such that the thickness of the adhesive resin layer after drying was 40 μm. After coating, the sheets were dried at 120°C for 10 minutes to obtain single-layer adhesive resin sheets 1-4.

[0098] Of the obtained single-layer sheets 1 to 4, the specimens dried at 135°C for 1 hour were designated as the dried specimens. After drying, the specimens were further left at 23°C and 50% humidity for 24 hours and designated as the conditioned specimens. The dielectric properties of each were measured.

[0099] The dielectric properties were measured at a frequency of 10 GHz using a QWED resonator, employing the split-post dielectric resonator method to determine the relative permittivity and dielectric loss tangent. A relative permittivity of 3.0 or lower was considered "low relative permittivity." For the dielectric loss tangent, a value of 0.003 or less was considered "low dielectric loss tangent" after drying, and a value of 0.005 or less was considered "low dielectric loss tangent" after humidity control. When both the relative permittivity and dielectric loss tangent described above are satisfied, the dielectric properties in the high-frequency range were evaluated as being low.

[0100] [Table 3]

[0101] As shown in Table 3, single-layer sheets 2 and 3 maintained low dielectric properties in the high-frequency range. From the results in Tables 2 and 3, it was confirmed that the laminates of Examples 1 and 2, which have adhesive resin layers corresponding to single-layer sheets 2 and 3, meet the acceptable adhesive strength values ​​while maintaining low dielectric properties in the high-frequency range, even when using low-roughness copper foil. Furthermore, in the case of unroughened copper foil, Example 2 showed improved adhesive strength compared to Example 1.

[0102] This is thought to be because the epoxy groups that remained unreacted with the polyimide groups of the polyimide resin chemically bonded (e.g., hydrogen bonded) with the surface of the metal layer, thus ensuring sufficient adhesive strength between the resin film and the metal layer, even when using uncoated or low-coated copper as the metal layer.

[0103] On the other hand, Comparative Example 1 did not meet the acceptable adhesive strength when using unroughened copper foil. This is thought to be because the adhesive resin layer of Comparative Example 1 did not contain epoxy resin, and therefore could not adhere to the surface of the unroughened copper foil through chemical bonding. In Comparative Example 2, although the adhesive strength met the acceptable value in the case of uncoated copper, the dielectric properties deteriorated. Since epoxy resin has a highly polar molecular structure, it is thought that when the amount added exceeded 5 parts by mass, the dielectric loss tangent did not meet the acceptable value specified herein. [Explanation of symbols]

[0104] 1: Adhesive-backed metal substrate, 2: Laminate, 10: Metal layer, 11: Adhesive resin layer, 12: Resin film

Claims

1. An adhesive-coated 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), a radical initiator, and an epoxy resin. 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. The content of the epoxy resin is 1 part by mass or more and 5 parts by mass or less, relative to 100 parts by mass of the total of the polyimide resin (A) and the maleimide compound (B). The adhesive resin layer has a thickness of 1 μm or more and 15 μm or less, and is provided on an adhesive-coated metal substrate.

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

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

Images