WO2025094504A1 - Adhesive composition, and adhesive sheet, laminate and printed wiring board each containing same - Google Patents

Abstract

The present invention provides: an adhesive composition that has excellent solder heat resistance and adhesive strength, and also has excellent dielectric characteristics with low relative permittivity and low loss tangent; and an adhesive sheet, a laminate, and a printed wiring board each containing the adhesive composition.　The adhesive composition according to the present invention comprises a polyimide resin and an epoxy resin (E), and is characterized in that: the epoxy resin (E) includes an epoxy resin (A) represented by formula (I); and the content of a glycidyl ether-type epoxy resin (B) contained as the epoxy resin (E) is 5 parts by mass or less with respect to 100 parts by mass of the polyimide resin. In formula (I), R¹ to R⁵ each independently represent a hydrogen atom or a C_1-10 alkyl group.

Description

Adhesive composition, and adhesive sheet, laminate and printed wiring board containing same

The present invention relates to an adhesive composition. More specifically, the present invention relates to an adhesive composition for printed wiring boards used for bonding a resin substrate to a resin substrate or a metal substrate. In particular, the present invention relates to an adhesive composition for flexible printed wiring boards (hereinafter abbreviated as FPC), as well as an adhesive sheet, a laminate, and a printed wiring board containing the same.

　Since FPCs have excellent flexibility, they can accommodate the multi-functionality and miniaturization of personal computers (PCs) and smartphones, and are often used to incorporate electronic circuit boards into narrow and complex interiors. In recent years, electronic devices have become smaller, lighter, more dense, and more powerful, and the demands for the performance of wiring boards (electronic circuit boards) are becoming increasingly sophisticated. In particular, high-frequency signals are being used to increase transmission speeds. Accordingly, there is an increasing demand for low dielectric properties (low dielectric constant, low dielectric tangent) in the high-frequency range for FPCs. In order to achieve such low dielectric properties, measures have been taken to reduce the dielectric loss of FPC substrates and adhesives, and as for substrates used in FPCs, not only conventional polyimide (PI) and polyethylene terephthalate (PET), but also substrate films such as liquid crystal polymers (LCPs) and fluororesins with low dielectric properties have been proposed. As for adhesives, development of combinations of polyolefin and epoxy (Patent Document 1) and adhesives using polyphenylene ether (Patent Document 2) are being developed.

International Publication No. 2016/047289 International Publication No. 2020/196718

However, the adhesive described in Patent Document 1 is highly polar because it contains an epoxy resin and an epoxy resin curing agent, and does not satisfy the high requirements, particularly for dielectric tangent. The adhesive described in Patent Document 2 cannot be said to have excellent heat resistance as an FPC adhesive, and is also insufficient in terms of dielectric properties.

Furthermore, the reaction between the general epoxy resin and carboxyl group-containing resin described in Patent Document 1 is slow, and when an adhesive sheet is produced by applying the adhesive to a substrate and evaporating the solvent by low-temperature heating, the curing reaction hardly progresses at all. As a result, when using the adhesive sheet, the resin flow (i.e. the fluidity of the resin during lamination) becomes extremely large, hindering the conduction of the circuit, and there are problems with precise control.

The present invention was made against the background of these problems in the conventional technology. That is, the first object of the present invention is to provide an adhesive composition that has excellent solder heat resistance and adhesive strength, and further has excellent dielectric properties such as low relative dielectric constant and dielectric tangent, as well as an adhesive sheet, laminate, and printed wiring board that contain the same.

In addition to the first objective described above, the second objective of the present invention is to provide an adhesive composition that allows the degree of curing to be controlled, as well as an adhesive sheet, a laminate, and a printed wiring board that contain the same.

The present invention may be one that can achieve either the first or second objective, and it would be even better if it could achieve both the first and second objectives.

As a result of extensive research, the inventors discovered that the above problems could be solved by the means described below, and arrived at the present invention. That is, the present invention has the following configuration.

［式（Ｉ）中、Ｒ¹～Ｒ⁵は、それぞれ独立に、水素原子またはＣ_1-10アルキル基を表す。］
［２］　前記エポキシ樹脂（Ａ）の含有量が、前記ポリイミド樹脂１００質量部に対して、０．０１質量部以上２０質量部以下である［１］に記載の接着剤組成物。
［３］　前記ポリイミド樹脂の酸価が１０当量／１０⁶ｇ以上１０００当量／１０⁶ｇ以下である［１］または［２］に記載の接着剤組成物。
［４］　（前記エポキシ樹脂（Ｅ）のエポキシ価の合計／前記ポリイミド樹脂の酸価の合計）で表される比率が０．５以上１０．０以下である［１］～［３］のいずれか１つに記載の接着剤組成物。
［５］　前記エポキシ樹脂（Ａ）の含有量が、前記エポキシ樹脂（Ｅ）１００質量％中、７０質量％以上である［１］～［４］のいずれか１つに記載の接着剤組成物。
［６］　前記エポキシ樹脂（Ｂ）の含有量が、前記エポキシ樹脂（Ｅ）１００質量％中、２５質量％以下である［１］～［５］のいずれか１つに記載の接着剤組成物。
［７］　前記式（Ｉ）において、Ｒ¹及び／又はＲ⁵がＣ_1-10アルキル基である［１］～［６］のいずれか１つに記載の接着剤組成物。
［８］　前記エポキシ樹脂（Ａ）及び前記グリシジルエーテル型エポキシ樹脂（Ｂ）の合計量が、前記エポキシ樹脂（Ｅ）１００質量％中、５０質量％以上である［１］～［７］のいずれか１つに記載の接着剤組成物。
［９］　前記グリシジルエーテル型エポキシ樹脂（Ｂ）は、分子内に式（ＩＩ）または式（ＩＩＩ）で表される化学構造を有するエポキシ樹脂である［１］～［８］のいずれか１つに記載の接着剤組成物。

［式（ＩＩ）中、Ｒ⁶～Ｒ⁹は、それぞれ独立に、水素原子またはＣ_1-10アルキル基を表す。＊は結合手を表す。］

［式（ＩＩＩ）中、Ｒ²⁶～Ｒ²⁹は、それぞれ独立に、水素原子またはＣ_1-10アルキル基を表す。＊は結合手を表す。］
［１０］　前記グリシジルエーテル型エポキシ樹脂（Ｂ）を含まない［１］～［９］のいずれか１つに記載の接着剤組成物。
［１１］　前記グリシジルエーテル型エポキシ樹脂（Ｂ）を含み、
　前記グリシジルエーテル型エポキシ樹脂（Ｂ）の含有量が、前記ポリイミド樹脂１００質量部に対して０．５質量部以上５質量部以下である［１］～［９］のいずれか１つに記載の接着剤組成物。
［１２］　塩素濃度が、接着剤組成物の固形分中、０．０１～３００ｐｐｍである［１］～［１１］のいずれか１つに記載の接着剤組成物。
［１３］　プリント配線板用である［１］～［１２］のいずれか１つに記載の接着剤組成物。
［１４］　樹脂基材、金属基材または紙類である基材と、離型基材とを、［１］～［１２］のいずれか１つに記載の接着剤組成物を介して積層した接着シート。
［１５］　下記式に基づいて算出される誘電正接変化率が８～７０％である［１４］に記載の接着シート。
　　　誘電正接変化率（％）＝（Ｔ_Ｂ－Ｔ_Ｃ）／Ｔ_Ｂ×１００
（上記式中、
　Ｔ_Ｂ：接着剤組成物を厚さ１００μｍのテフロン（登録商標）シートに、乾燥後の厚みが２５μｍとなるように塗布し、１３０℃で３分乾燥して得られたＢステージ品の誘電正接
　Ｔ_Ｃ：前記Ｂステージ品を得た後、１８０℃で３時間熱処理して硬化させて得られたＣステージ品の誘電正接）
［１６］　樹脂基材、金属基材または紙類である基材に、［１］～［１２］のいずれか１つに記載の接着剤組成物が積層された積層体。
［１７］　［１６］に記載の積層体を構成要素として含むプリント配線板。 [1] An adhesive composition comprising a polyimide resin and an epoxy resin (E),
The epoxy resin (E) contains an epoxy resin (A) represented by formula (I),
an adhesive composition in which the content of a glycidyl ether type epoxy resin (B) contained as the epoxy resin (E) is 5 parts by mass or less per 100 parts by mass of the polyimide resin;

[In formula (I), R ¹ to R ⁵ each independently represent a hydrogen atom or a C _1-10 alkyl group.]
[2] The adhesive composition according to [1], wherein the content of the epoxy resin (A) is 0.01 parts by mass or more and 20 parts by mass or less relative to 100 parts by mass of the polyimide resin.
[3] The adhesive composition according to [1] or [2], wherein the acid value of the polyimide resin is from 10 equivalents/10 ⁶ g to 1,000 equivalents/10 ⁶ g.
[4] The adhesive composition according to any one of [1] to [3], wherein a ratio represented by (the sum of the epoxy values of the epoxy resins (E) / the sum of the acid values of the polyimide resins) is 0.5 or more and 10.0 or less.
[5] The adhesive composition according to any one of [1] to [4], wherein the content of the epoxy resin (A) is 70 mass% or more in 100 mass% of the epoxy resin (E).
[6] The adhesive composition according to any one of [1] to [5], wherein the content of the epoxy resin (B) is 25 mass% or less in 100 mass% of the epoxy resin (E).
[7] The adhesive composition according to any one of [1] to [6], wherein, in formula (I), R ¹ and/or R ⁵ is a C _1-10 alkyl group.
[8] The adhesive composition according to any one of [1] to [7], wherein a total amount of the epoxy resin (A) and the glycidyl ether type epoxy resin (B) is 50 mass% or more in 100 mass% of the epoxy resin (E).
[9] The adhesive composition according to any one of [1] to [8], wherein the glycidyl ether type epoxy resin (B) is an epoxy resin having a chemical structure represented by formula (II) or formula (III) in the molecule.

[In formula (II), R ⁶ to R ⁹ each independently represent a hydrogen atom or a C _1-10 alkyl group. * represents a bond.]

[In formula (III), R ²⁶ to R ²⁹ each independently represent a hydrogen atom or a C _1-10 alkyl group. * represents a bond.]
[10] The adhesive composition according to any one of [1] to [9], which does not contain the glycidyl ether type epoxy resin (B).
[11] The glycidyl ether type epoxy resin (B),
The adhesive composition according to any one of [1] to [9], wherein the content of the glycidyl ether type epoxy resin (B) is 0.5 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the polyimide resin.
[12] The adhesive composition according to any one of [1] to [11], having a chlorine concentration of 0.01 to 300 ppm in the solid content of the adhesive composition.
[13] The adhesive composition according to any one of [1] to [12], which is for use in a printed wiring board.
[14] An adhesive sheet obtained by laminating a substrate which is a resin substrate, a metal substrate or a paper substrate and a release substrate via the adhesive composition according to any one of [1] to [12].
[15] The adhesive sheet according to [14], wherein the rate of change in dielectric tangent calculated based on the following formula is 8 to 70%.
Dielectric loss tangent change rate (%) = (T _B - T _C )/T _B ×100
(In the above formula,
T _B : Dielectric loss tangent of a B-stage product obtained by applying the adhesive composition to a 100 μm thick Teflon (registered trademark) sheet so that the thickness after drying would be 25 μm, and drying at 130° C. for 3 minutes. T _C : Dielectric loss tangent of a C-stage product obtained by heat treating the B-stage product for 3 hours at 180° C. for curing.
[16] A laminate in which the adhesive composition according to any one of [1] to [12] is laminated on a substrate which is a resin substrate, a metal substrate or a paper substrate.
[17] A printed wiring board comprising the laminate according to [16] as a component.

The adhesive composition of the present invention has excellent solder heat resistance and adhesive strength, and also has excellent dielectric properties. The adhesive composition of the present invention also allows the degree of curing to be controlled. For this reason, it is suitable for use in adhesives for FPCs, adhesive sheets, laminates, and printed wiring boards in the high frequency range.

Below, one embodiment of the present invention is described in detail. However, the present invention is not limited to this embodiment, and can be implemented in various modified forms within the scope described above.

［式（Ｉ）中、Ｒ¹～Ｒ⁵は、それぞれ独立に、水素原子またはＣ_1-10アルキル基を表す。］ <Adhesive Composition>
The adhesive composition of the present invention is an adhesive composition comprising a polyimide resin and an epoxy resin (E), wherein the epoxy resin (E) comprises an epoxy resin (A) represented by formula (I), and the content of a glycidyl ether type epoxy resin (B) contained as the epoxy resin (E) is 5 parts by mass or less relative to 100 parts by mass of the polyimide resin.

[In formula (I), R ¹ to R ⁵ each independently represent a hydrogen atom or a C _1-10 alkyl group.]

In the present invention, by blending the epoxy resin (A) represented by formula (I) with the polyimide resin and by controlling the content of the glycidyl ether type epoxy resin (B) to a predetermined amount or less, when the carboxyl group in the polyimide resin reacts with the epoxy resin (E), a high-density crosslinked structure is formed, and the movement of the by-product hydroxyl group is suppressed in the crosslinked structure, so that an adhesive composition having excellent solder heat resistance, adhesive strength, and dielectric properties is provided.

<Polyimide resin>
The polyimide resin in the present invention is a polymer having an imide bond in the main chain, and is produced by a method of producing it from a carboxylic acid anhydride component and an isocyanate component (isocyanate method), a method of reacting a polycarboxylic acid component with an amine component to synthesize an amic acid and then ring-closing it (direct method), a method of reacting a compound having a carboxylic acid anhydride and an acid chloride with a diamine, etc. In terms of the number of options for monomer components, the direct method is advantageous.

The polyimide resin of the present invention may also contain bond species resulting from reactions other than imidization, such as amide bonds, ester bonds, and urethane bonds. By containing these bond species, flexibility can be imparted to the resin, and a flexible cured coating film can be formed. On the other hand, since imide bonds are advantageous for low dielectric properties because the polarity is partially canceled due to the symmetry of their structure, it is preferable to keep the content of bond species such as amide bonds, ester bonds, and urethane bonds to the minimum necessary, and in order to improve low dielectric properties, when the total amount of imide bonds, amide bonds, ester bonds, and urethane bonds is taken as 100 mol%, the amount of imide bonds is preferably 50 mol% or more, more preferably 70 mol% or more, and even more preferably 80 mol% or more, and may be 100 mol%.

The carboxylic acid anhydride component constituting the polyimide resin in the present invention is not particularly limited, and examples thereof include pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 1,2,5,6-naphthalene tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride, 3,4,9,10-perylene tetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, 1,1,1,3,3,3-hexafluoro-2,2-bis(2,3- or 3,4-dicarboxyphenyl)propanhydride, and the like. Examples of the tetrabasic acid dianhydride include tetrabasic acid dianhydrides having an aromatic ring, such as 2,2-bis(2,3- or 3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis[4-(2,3- or 3,4-dicarboxyphenoxy)phenyl]propane dianhydride, and the like; aliphatic tetrabasic acid dianhydrides, such as meso-butane-1,2,3,4-tetracarboxylic acid dianhydride and pentane-1,2,4,5-tetracarboxylic acid dianhydride; and alicyclic tetrabasic acid dianhydrides, such as cyclobutane tetracarboxylic acid dianhydride, cyclopentane tetracarboxylic acid dianhydride, dicyclohexyl-3,3',4,4'-tetracarboxylic acid dianhydride, and hydrogenated products of the tetrabasic acid dianhydrides having an aromatic ring. In addition, trimellitic anhydride and trimellitic anhydride derivatives such as alkylene glycol bisanhydrotrimellitate, such as ethylene glycol bisanhydrotrimellitate, propylene glycol bisanhydrotrimellitate, and 1,4-butanediol bisanhydrotrimellitate, may be used. These may be used alone or in combination. From the viewpoint of dielectric properties, tetrabasic acid dianhydrides having an aromatic ring and alicyclic tetrabasic acid dianhydrides are preferred, and 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride and 2,2-bis[4-(2,3- or 3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA) are more preferred.

The isocyanate component constituting the polyimide resin in the present invention is not particularly limited, and examples of diisocyanates having an aromatic ring include tolylene diisocyanate (TDI), 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate and its structural isomers, 3,3'-diethyldiphenylmethane-4,4'-diisocyanate and its structural isomers, diphenylmethane-4,4'-diisocyanate, diphenylmethane-3,3'-diisocyanate, diphenylmethane-3,4'-diisocyanate, and diphenylmethane-2,4'-diisocyanate. Examples of the diisocyanate include diphenylmethane-2,2'-diisocyanate, diphenylether-4,4'-diisocyanate, benzophenone-4,4'-diisocyanate, diphenylsulfone-4,4'-diisocyanate, m-xylylene diisocyanate, p-xylylene diisocyanate, naphthalene-2,6-diisocyanate, 3,3'- or 2,2'-dimethylbiphenyl-4,4'-diisocyanate, 3,3'- or 2,2'-diethylbiphenyl-4,4'-diisocyanate, and 3,3'-dimethoxybiphenyl-4,4'-diisocyanate. Among these, diphenylmethane-4,4'-diisocyanate (MDI) and 3,3'-dimethylbiphenyl-4,4'-diisocyanate (ToDI) are preferred from the viewpoint of polymerizability. These may be used alone or in combination.

As diisocyanates, in addition to those already mentioned that have an aromatic ring, aliphatic or alicyclic diisocyanates can also be used, such as diisocyanates obtained by hydrogenating any of the components listed in the previous section. Other examples include isophorone diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, ethylene diisocyanate, propylene diisocyanate, and hexamethylene diisocyanate.

The amine components constituting the polyimide resin in the present invention are not particularly limited, and examples thereof include dimer diamine, m-phenylenediamine, 2,5-diethyl-6-methyl-1,3-benzenediamine, p-phenylenediamine, 2,5-dimethyl-1,4-phenylenediamine, and 2,3,5,6-tetramethyl-1,4-phenylenediamine. Among these, dimer diamine is preferred from the viewpoint of low dielectric properties.

The polyimide resin in the present invention may contain components other than the above-mentioned carboxylic anhydride component, isocyanate component, and amine component. Examples include aromatic dicarboxylic acid components, aliphatic dicarboxylic acid components, and diol components. Examples of aromatic dicarboxylic acid components include, but are not limited to, terephthalic acid, isophthalic acid, orthophthalic acid, 4,4'-dicarboxybiphenyl, 5-sodium sulfoisophthalic acid, naphthalenedicarboxylic acid, and esters thereof. Examples of aliphatic dicarboxylic acids include, but are not limited to, dimer acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, tetrahydrophthalic acid, methyltetrahydrophthalic acid, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, and hydrogenated naphthalenedicarboxylic acid. Dimer acid is preferable, as it can exhibit excellent dielectric properties. The diol component is not particularly limited, but examples include decanediol, dimer diol, polybutadiene with hydroxyl groups at both ends, hydrogenated polybutadiene with hydroxyl groups at both ends, polyisoprene with hydroxyl groups at both ends, and polyolefin with hydroxyl groups at both ends. Among these, polybutadiene with hydroxyl groups at both ends is preferred because of its excellent dielectric properties.

The number average molecular weight (Mn) of the polyimide resin in the present invention is preferably in the range of 10,000 to 50,000. More preferably, it is in the range of 15,000 to 45,000, and even more preferably, it is in the range of 20,000 to 40,000. By making it equal to or greater than the lower limit, the cohesive force is good and excellent adhesive properties can be achieved. Furthermore, by making it equal to or less than the upper limit, excellent fluidity and operability can be achieved.

The polyimide resin in the present invention preferably has a carboxy group, and the acid value of the polyimide resin is preferably 10 equivalents/10 ⁶ g or more, more preferably 100 equivalents/10 6 g or more, and even more preferably 150 equivalents/10 ⁶ g or more, from the viewpoint of heat resistance and adhesion to a resin substrate or a ^metal substrate. By being equal to or more than the above value, the compatibility with the epoxy resin is improved, the adhesive strength is improved, and the crosslinking density is increased, so that the heat resistance can also be improved. The upper limit is preferably 1000 equivalents/10 ⁶ g or less, more preferably 700 equivalents/10 ⁶ g or less, and even more preferably 500 equivalents/10 ⁶ g or less. When it is equal to or less than the above value, the adhesiveness and low dielectric properties are better.

The glass transition temperature of the polyimide resin in the present invention is preferably -20°C or higher. More preferably, it is 0°C or higher, and even more preferably, it is 20°C or higher. By having a glass transition temperature equal to or higher than the lower limit, it is possible to improve the solder heat resistance. There is no particular upper limit to the glass transition temperature, but in practice it is 300°C or lower, and it may be 200°C or lower.

The polyimide resin in the present invention preferably has a relative dielectric constant (εc) of 3.0 or less at a frequency of 10 GHz. More preferably, it is 2.8 or less, and even more preferably, it is 2.6 or less. There is no particular lower limit, but in practical use, it is 2.0. Furthermore, the relative dielectric constant (εc) in the entire frequency range from 1 GHz to 60 GHz is preferably 3.0 or less, more preferably 2.8 or less, and even more preferably 2.6 or less.

The polyimide resin in the present invention preferably has a dielectric loss tangent (tan δ) of 0.005 or less at a frequency of 10 GHz. More preferably, it is 0.004 or less, and even more preferably, it is 0.003 or less. There is no particular lower limit, but in practical use, it is 0.0001 or more. Furthermore, the dielectric loss tangent (tan δ) over the entire frequency range of 1 GHz to 60 GHz is preferably 0.005 or less, more preferably 0.004 or less, and even more preferably 0.003 or less.

Polyimide resins can be obtained, for example, by dissolving a carboxylic anhydride component and an isocyanate component or an amine component in a solvent and heating the solution. At this time, it is preferable that the molar ratio of the acid anhydride group of the carboxylic anhydride component to the isocyanate group of the isocyanate component or the amino group of the amine component is 100:91 to 100:109. Outside this range, the molecular weight may not increase sufficiently, resulting in insufficient mechanical strength or gelation during polymerization. In addition, from the perspective of the stability of the resin and resin varnish, it is preferable that the imide ring portion of the polyimide resin is 90% or more ring-closed. To achieve this, it is necessary to react sufficiently during polyimide polymerization, and methods such as increasing the reaction temperature or adding a catalyst are available.

Solvents that can be used in the polymerization of the polyimide resin in the present invention include, for example, N-methyl-2-pyrrolidone, γ-butyrolactone, dimethylimidazolidinone, dimethylsulfoxide, dimethylformamide, N-ethyl-2-pyrrolidone, dimethylacetamide, cyclohexanone, cyclopentanone, tetrahydrofuran, and methylcyclohexane, of which cyclohexanone is preferred from the viewpoint of polymerization properties. After polymerization, the non-volatile content and solution viscosity can be adjusted by diluting with the solvent used in the polymerization or another low-boiling point solvent.

Low boiling point solvents include aromatic solvents such as toluene and xylene, aliphatic solvents such as hexane, heptane, and octane, alcohol solvents such as methanol, ethanol, propanol, butanol, and isopropanol, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and cyclopentanone, ether solvents such as diethyl ether and tetrahydrofuran, and ester solvents such as ethyl acetate, butyl acetate, and isobutyl acetate.

In addition, to accelerate the reaction, catalysts such as alkali metals such as sodium fluoride, potassium fluoride, and sodium methoxide, amines such as triethylenediamine, triethylamine, diethanolamine, 1,8-diazabicyclo[5,4,0]-7-undecene, and 1,5-diazabicyclo[4,3,0]-5-nonene, and dibutyltin dilaurate can be used.

The polyimide resin is preferably included as a main component in the adhesive composition. In this specification, the main component in the adhesive composition specifically refers to the component that is contained in the largest amount in the solid content of the adhesive composition. The content of the polyimide resin in the adhesive composition of the present invention is preferably 5% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, based on 100% by mass of the solid content of the adhesive composition. It is also preferably 99% by mass or less, more preferably 95% by mass or less, and even more preferably 90% by mass or less. It is preferable that the content is within the above range because it provides good adhesion and heat resistance.

<Epoxy resin (E)>
The adhesive composition of the present invention contains an epoxy resin (A) represented by formula (I) as the epoxy resin (E). Since the epoxy resin (A) has two epoxy groups, it is advantageous for forming a high-density crosslinked structure. An epoxy resin having three or more epoxy groups is not preferable because some of the epoxy groups may not react and may remain, resulting in a deterioration in the dielectric tangent. Furthermore, since the number of carbon atoms between the nitrogen atom and the epoxy group indirectly bonded thereto is small, the epoxy resin (A) has a large steric hindrance and a structure with poor mobility. Such a structure with large steric hindrance can suppress the movement of atoms, making it ideal for obtaining an adhesive composition with a low dielectric tangent.

［式（Ｉ）中、Ｒ¹～Ｒ⁵は、それぞれ独立に、水素原子またはＣ_1-10アルキル基を表す。］ In addition, the epoxy resin (A) has a dielectric loss tangent of the semi-cured product (B stage product) that decreases as the curing progresses, as a result of the suppression of atomic movement after curing. In addition, the epoxy resin (A) reacts with the polyimide resin more quickly than general epoxy resins (except for the epoxy resin (A)), so the curing reaction gradually progresses at the stage where the adhesive composition is applied to the substrate and the solvent is evaporated by low-temperature heating. As a result, the dielectric loss tangent of the adhesive composition of the present invention is significantly reduced from the B stage product to the C stage product. By utilizing this characteristic, the decrease in the dielectric loss tangent of the adhesive composition after application can be monitored, and the degree of curing (degree of reaction) of the adhesive composition can be grasped from the obtained dielectric loss tangent. The degree of curing of the adhesive composition is related to resin flow and solder heat resistance, which are closely related to the crosslinking state, so grasping the degree of curing of the adhesive composition leads to precise control of these characteristics.

[In formula (I), R ¹ to R ⁵ each independently represent a hydrogen atom or a C _1-10 alkyl group.]

The C _1-10 alkyl group (-C _n H _2n+1 , where n is an integer from 1 to 10) in formula (I) may be linear or branched. The C _1-10 alkyl group is preferably a C _1-6 alkyl group, more preferably a C _1-3 alkyl group, and even more preferably a methyl group or an ethyl group.

In formula (I), it is preferable that 0 to 3 of R ¹ to R ⁵ are C _1-10 alkyl groups and the groups other than the C _1-10 alkyl groups are hydrogen atoms, and it is more preferable that 0 to 1 of R ¹ to R ⁵ is a C _1-10 alkyl group and the groups other than the C _1-10 alkyl groups are hydrogen atoms.

In formula (I), it is preferable that at least ^R1 and/or ^R5 are a _C1-10 alkyl group. If ^R1 and/or ^R5 are a _C1-10 alkyl group, they act as steric hindrances and can inhibit the movement of polar groups, which is effective in obtaining an adhesive composition with a low dielectric tangent.

Examples of epoxy resin (A) include N,N-diglycidylaniline, N,N-(diglycidyl)-o-toluidine, N,N-(diglycidyl)-m-toluidine, and N,N-(diglycidyl)-p-toluidine, with N,N-(diglycidyl)-o-toluidine, N,N-(diglycidyl)-m-toluidine, and N,N-(diglycidyl)-p-toluidine being preferred.

From the viewpoint of heat resistance and adhesion to resin substrates and metal substrates, the epoxy value of the epoxy resin (A) is preferably 5,000 to 12,000 equivalents/10 ⁶ g, more preferably 6,000 to 11,000 equivalents/10 ⁶ g, and even more preferably 7,000 to 10,000 equivalents/10 ⁶ g. When it is equal to or greater than the above value, the adhesive strength is improved and the crosslinking density is increased, thereby improving the heat resistance. When it is equal to or less than the above value, the adhesiveness and low dielectric properties are improved. The epoxy value can be evaluated in accordance with the provisions of JIS K7236 (hereinafter the same).

The content of epoxy resin (A) is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 1 part by mass or more, relative to 100 parts by mass of polyimide resin. By making it equal to or more than the lower limit, a sufficient curing effect can be obtained, and excellent adhesion and solder heat resistance can be exhibited. Also, it is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 6 parts by mass or less. By making it equal to or less than the upper limit, the pot life and low dielectric properties become good. In other words, by making it within the above range, an adhesive composition having excellent low dielectric properties in addition to adhesion and solder heat resistance can be obtained.

The content of epoxy resin (A) is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, based on 100% by mass of epoxy resin (E) contained in the adhesive composition of the present invention. By making it equal to or more than the lower limit, the dielectric properties become extremely good. The upper limit is not particularly limited, but it may be 100% by mass, and 95% by mass is also acceptable.

The adhesive composition of the present invention may contain a small amount of glycidyl ether type epoxy resin (B) as the epoxy resin (E). The glycidyl ether type epoxy resin (B) specifically refers to an epoxy resin containing a glycidyl ether group in the molecule, in which a glycidyl group and an ether group are bonded. The glycidyl ether group has a structure with little steric hindrance and high local mobility. In addition, while two glycidyl groups are bonded to one nitrogen atom in the epoxy resin (A), the glycidyl ether group has only one glycidyl group bonded to one oxygen atom, and has few reaction points. Due to these factors, if the content of the epoxy resin (B) exceeds a predetermined amount, it becomes difficult to obtain an adhesive composition with a low dielectric tangent. Therefore, it is desirable that the adhesive composition of the present invention contains only a small amount of epoxy resin (B) even if it contains epoxy resin (B), or does not contain any epoxy resin (B).

［式（ＩＩ）中、Ｒ⁶～Ｒ⁹は、それぞれ独立に、水素原子またはＣ_1-10アルキル基を表す。＊は結合手を表す。］

［式（ＩＩＩ）中、Ｒ²⁶～Ｒ²⁹は、それぞれ独立に、水素原子またはＣ_1-10アルキル基を表す。＊は結合手を表す。］ The epoxy resin (B) is preferably an epoxy resin (B) having a chemical structure represented by formula (II) or formula (III) in the molecule.

[In formula (II), R ⁶ to R ⁹ each independently represent a hydrogen atom or a C _1-10 alkyl group. * represents a bond.]

[In formula (III), R ²⁶ to R ²⁹ each independently represent a hydrogen atom or a C _1-10 alkyl group. * represents a bond.]

［式（ＩＩ－Ａ）中、Ｒ⁶～Ｒ⁹は前記に同じ。］

［式（ＩＩ－Ｂ）中、Ｒ⁶～Ｒ⁹は前記に同じ。Ｒ¹⁰～Ｒ¹⁵は、それぞれ独立に、水素原子またはＣ_1-10アルキル基を表す。］

［式（ＩＩＩ－Ａ）中、Ｒ²⁶～Ｒ²⁹は前記に同じ。］ As the epoxy resin (B), an epoxy resin represented by formula (II-A), formula (II-B) or formula (III-A) is preferable, and from the viewpoint of low dielectric properties and solder heat resistance, an epoxy resin represented by formula (II-A) or formula (III-A) is more preferable.

[In formula (II-A), R ⁶ to R ⁹ are the same as defined above.]

[In formula (II-B), R ⁶ to R ⁹ are the same as defined above. R ¹⁰ to R ¹⁵ each independently represent a hydrogen atom or a C _1-10 alkyl group.]

[In formula (III-A), R ²⁶ to R ²⁹ are the same as above.]

The C _1-10 alkyl group (-C _n H _2n+1 , where n is an integer from 1 to 10) in formulae (II), (III), (II-A), (II-B) and (III-A) may be linear or branched. The C _1-10 alkyl group is preferably a C _1-6 alkyl group, more preferably a C _1-3 alkyl group, and even more preferably a methyl group or an ethyl group.

Examples of such epoxy resins (B) include the following.

From the viewpoint of heat resistance and adhesion to resin substrates and metal substrates, the epoxy value of the epoxy resin (B) is preferably 3,000 to 13,000 equivalents/10 ⁶ g, more preferably 4,000 to 12,000 equivalents/10 ⁶ g, and even more preferably 5,000 to 11,000 equivalents/10 ⁶ g. When it is equal to or greater than the above value, the adhesive strength is improved and the crosslinking density is increased, thereby improving heat resistance. When it is equal to or less than the above value, the adhesiveness and low dielectric properties are better.

The content of epoxy resin (B) is 5 parts by mass or less, preferably 1 part by mass or less, and more preferably 0 parts by mass, per 100 parts by mass of polyimide resin. By making it below the upper limit, the hydroxyl groups derived from the glycidyl ether groups can be reduced, and low dielectric properties become good. In other words, by using epoxy resin (A) and epoxy resin (B) below the upper limit, an adhesive composition having excellent low dielectric properties in addition to adhesion and solder heat resistance can be obtained. When the adhesive resin composition of the present invention contains epoxy resin (B), the content of epoxy resin (B) is preferably 0.5 parts by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, per 100 parts by mass of polyimide resin.

The content of epoxy resin (B) is preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less, based on 100% by mass of epoxy resin (E) contained in the adhesive composition of the present invention. By keeping it below the upper limit, the dielectric properties become extremely good. The lower limit is not particularly limited, but it may be 0% by mass, and 5% by mass is also acceptable.

The adhesive composition of the present invention may contain, as the epoxy resin (E), an epoxy resin other than the above-mentioned epoxy resin (A) and the above-mentioned epoxy resin (B). The other epoxy resin other than the above-mentioned epoxy resin (A) and the above-mentioned epoxy resin (B) is not particularly limited as long as it has an epoxy group in the molecule, but is preferably a multifunctional epoxy resin having two or more epoxy groups in the molecule. Specific examples include, but are not particularly limited to, biphenyl-type epoxy resin, naphthalene-type epoxy resin, bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, novolac-type epoxy resin, alicyclic epoxy resin, dicyclopentadiene-type epoxy resin, glycidylamine-type epoxy resin, epoxy-modified polybutadiene, glycidyl group-containing isocyanuric acid, etc.

The adhesive composition of the present invention contains 100% by mass of epoxy resin (E), and the total amount of epoxy resin (A) and epoxy resin (B) is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, and may be 100% by mass. By keeping the total amount of epoxy resin (A) and epoxy resin (B) within the above range, it is possible to improve the solder heat resistance, adhesive strength, and dielectric properties.

The total amount of epoxy resin (E) contained in the adhesive composition of the present invention is preferably 0.01 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more, relative to 100 parts by mass of polyimide resin. By making it equal to or more than the lower limit, a sufficient curing effect can be obtained, and excellent adhesion and solder heat resistance can be exhibited. In addition, it is preferably 25 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 7 parts by mass or less. By making it equal to or less than the upper limit, the pot life and low dielectric properties are improved. In other words, by making it within the above range, an adhesive composition having excellent low dielectric properties in addition to adhesion and solder heat resistance can be obtained.

In the adhesive composition of the present invention, it is preferable to adjust the balance between the acid value of the polyimide resin and the epoxy value of the epoxy resin (E) from the viewpoint of improving heat resistance. Specifically, the ratio (hereinafter sometimes referred to as "E/A") expressed by (total epoxy value of epoxy resin (E) / total acid value of polyimide resin) is preferably 0.5 to 10.0, more preferably 1.0 to 5.0, even more preferably 1.5 to 4.0, even more preferably 1.8 to 3.5, and particularly preferably 1.9 to 3.3. By making it equal to or greater than the lower limit, the crosslink density can be increased and the solder heat resistance can be improved. By making it equal to or less than the upper limit, the polar groups in the adhesive can be reduced and the dielectric properties can be improved. In other words, by making the epoxy group value/acid value within the above range, an adhesive composition having a good balance between solder heat resistance and low dielectric properties can be obtained.

However, when epoxy resin (E) is blended, the adhesive composition may contain by-products generated during the production of epoxy resin (E). One such by-product is a chlorine-containing substance having a hydrolyzable chlorine group that cannot be ring-closed by NaOH. The present inventors have conducted extensive research focusing on the amount of chlorine in the adhesive composition, and have found that in the adhesive composition of the present invention containing a polyimide resin, reducing the amount of chlorine in the adhesive composition leads to an improvement in the dielectric tangent, in particular. It is generally believed that reducing the chlorine concentration in the adhesive composition leads to the suppression of ion migration, and as a result, it is known to contribute to improving the insulation reliability. However, it has not been widely known that the chlorine concentration in the adhesive composition affects dielectric properties such as the relative dielectric constant and dielectric tangent that are not related to ion migration. In the frequency band of several tens of GHz, reducing the number of highly polar functional groups is effective in lowering the relative dielectric constant and dielectric loss tangent, but when considering the chlorine concentration, even if the chlorine concentration is low, in an adhesive composition with a high concentration of highly polar functional groups, the insulation reliability can be improved by suppressing ion migration, but the dielectric properties cannot be improved. In other words, focusing on the chlorine concentration is extremely effective from the viewpoint of improving the dielectric properties. The chlorine concentration contained in the adhesive composition of the present invention is, for example, preferably 0.01 to 300 ppm, more preferably 0.1 to 140 ppm, and even more preferably 1 to 100 ppm in the solid content of the adhesive composition. By keeping it within the above range, the influence of chlorine-containing substances can be reduced, and the dielectric properties (especially the dielectric loss tangent) become extremely good.

Methods for reducing the chlorine concentration in the adhesive composition include, for example, a method using an epoxy resin (E) synthesized by an oxidation method that does not use the chlorine-containing substance, and a method using a distilled and purified epoxy resin (E). In particular, the use of an epoxy resin (E) synthesized by an oxidation method is advantageous because it is possible to obtain an adhesive composition with a chlorine concentration of about 0 ppm in the solid content. On the other hand, when an epoxy resin (E) synthesized by an oxidation method is used, low-molecular-weight allyl group-containing substances may be mixed in as impurities, which may adversely affect the dielectric properties. Therefore, from the viewpoint of improving the dielectric properties, an adhesive composition with a chlorine concentration of 0 ppm is ideal, but in reality, the epoxy resin (E) that can achieve this contains low-molecular-weight allyl group-containing substances, so an adhesive composition that does not contain low-molecular-weight allyl group-containing substances is preferable, even if the chlorine concentration is more than 0 ppm. In addition, the distillation method for the epoxy resin (E) includes rotary evaporation, reduced-pressure fractional distillation, short-path distillation, packed column distillation, rotating band distillation column distillation, falling-film distillation, wiper-type thin-film distillation, and reduced-pressure distillation including steam distillation.

<Polycarbodiimide>
The adhesive composition of the present invention may contain polycarbodiimide. The polycarbodiimide is not particularly limited as long as it has two or more carbodiimide bonds in the molecule. By using polycarbodiimide, the carboxy group of the polyimide resin or the epoxy group of the epoxy resin (E) reacts with the carbodiimide bond, thereby improving heat resistance and adhesiveness.

In the adhesive composition of the present invention, the content of polycarbodiimide is preferably 1 part by mass or more, more preferably 3 parts by mass or more, per 100 parts by mass of polyimide resin. By making it equal to or more than the lower limit, the crosslinking density can be increased, and solder heat resistance is improved. Also, it is preferably 20 parts by mass or less, more preferably 10 parts by mass or less. By making it equal to or less than the upper limit, excellent solder heat resistance and low dielectric properties can be achieved. In other words, by making it within the above range, an adhesive composition having excellent solder heat resistance and low dielectric properties can be obtained.

<Unsaturated Hydrocarbons>
The adhesive composition of the present invention may contain an unsaturated hydrocarbon having a terminal unsaturated hydrocarbon group and a 5% weight loss temperature of 260°C or higher. When the unsaturated hydrocarbon contains the terminal unsaturated hydrocarbon group, the crosslink density can be increased by a curing reaction caused by radicals generated by using a radical initiator or the like, thereby improving the solder heat resistance. In addition, since no hydroxyl groups that deteriorate the dielectric properties are generated after the reaction, an adhesive having better dielectric properties can be obtained. It is preferable that one molecule has two or more terminal unsaturated hydrocarbon groups, since this can further increase the crosslink density.

The 5% weight loss temperature of the unsaturated hydrocarbon must be 260°C or higher. It is preferably 270°C or higher, more preferably 280°C or higher, and even more preferably 290°C or higher. By having a 5% weight loss temperature above this value, soldering can be performed without causing appearance defects even at temperatures exceeding the melting point of the solder. There is no particular upper limit, but 500°C is practical.

The unsaturated hydrocarbon preferably has an aromatic ring structure or an alicyclic structure as a structural unit. By having an aromatic ring structure or an alicyclic structure as a structural unit, the solder heat resistance can be improved and the dielectric properties are also excellent. In particular, it is preferable for the unsaturated hydrocarbon to have an aromatic ring structure or an alicyclic structure as the skeleton, and polyphenylene ether or phenol resin is preferable. Specific examples of polyphenylene ethers having terminal unsaturated hydrocarbon groups include SA-9000 from SABIC and OPE-2St from Mitsubishi Gas Chemical Company. In addition, an example of a phenol resin having terminal unsaturated hydrocarbon groups is Resitop FTC-809AE from Gun-ei Chemical Industry Co., Ltd.

The number average molecular weight of the unsaturated hydrocarbon is preferably 500 or more, and more preferably 1,000 or more. It is also preferably 100,000 or less, more preferably 10,000 or less, and even more preferably 5,000 or less. If it is within the above range, it has good solubility in solvents and can form a uniform adhesive coating.

The content of unsaturated hydrocarbons in the adhesive composition of the present invention is preferably 1 part by mass or more, and more preferably 2 parts by mass or more, per 100 parts by mass of polyimide resin. Also, it is preferably 100 parts by mass or less, and more preferably 50 parts by mass or less. Within the above range, both excellent adhesion and solder heat resistance can be achieved.

<Radical Generator>
The adhesive composition of the present invention preferably contains a radical generator. The radicals generated by the radical generator efficiently react the terminal unsaturated hydrocarbon groups of the unsaturated hydrocarbon with each other, increasing the crosslinking density, thereby improving the solder heat resistance and dielectric properties. The radical generator is not particularly limited, but it is preferable to use an organic peroxide. The organic peroxide is not particularly limited, but examples thereof include peroxides such as di-tert-butyl peroxyphthalate, tert-butyl hydroperoxide, dicumyl peroxide, benzoyl peroxide, tert-butyl peroxybenzoate, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxypivalate, methyl ethyl ketone peroxide, di-tert-butyl peroxide, and lauroyl peroxide; and azonitriles such as azobisisobutyronitrile and azobisisopropionitrile.

The one-minute half-life temperature of the radical generator used in the present invention is preferably 140°C or higher. By setting the temperature at 140°C or higher, the initiation of a radical reaction can be prevented when the solvent of the adhesive composition varnish is volatilized to prepare the adhesive sheet, and excellent adhesive properties can be achieved.

The amount of the radical generator used in the present invention is preferably 0.1 parts by mass or more, and more preferably 1 part by mass or more, per 100 parts by mass of the unsaturated hydrocarbon. Also, it is preferably 50 parts by mass or less, and more preferably 10 parts by mass or less. By keeping it within the above range, an optimal crosslink density can be achieved, and both adhesion and solder heat resistance can be achieved.

<Organic Solvent>
The adhesive composition of the present invention may further contain an organic solvent. The organic solvent used in the present invention is not particularly limited as long as it dissolves the polyimide resin and the epoxy resin (E). Specifically, for example, aromatic hydrocarbons such as benzene, toluene, xylene, etc.; aliphatic hydrocarbons such as hexane, heptane, octane, decane, etc.; alicyclic hydrocarbons such as cyclohexane, cyclohexene, methylcyclohexane, ethylcyclohexane, etc.; halogenated hydrocarbons such as trichloroethylene, dichloroethylene, chlorobenzene, chloroform, etc.; alcohol solvents such as methanol, ethanol, isopropyl alcohol, butanol, pentanol, hexanol, propanediol, phenol, etc.; acetone, methyl isobutyl ketone, methyl ethyl ketone, pentanone, hexanone, cyclohexanone, isophorone, acetophenone, etc. ketone-based solvents, cellosolves such as methyl cellosolve and ethyl cellosolve, ester-based solvents such as methyl acetate, ethyl acetate, butyl acetate, methyl propionate and butyl formate, glycol ether-based solvents such as ethylene glycol mono n-butyl ether, ethylene glycol mono iso-butyl ether, ethylene glycol mono tert-butyl ether, diethylene glycol mono n-butyl ether, diethylene glycol mono iso-butyl ether, triethylene glycol mono n-butyl ether and tetraethylene glycol mono n-butyl ether, and the like can be used alone or in combination of two or more of these. In particular, methylcyclohexane and toluene are preferred from the viewpoints of working environment and drying properties.

The organic solvent is preferably in the range of 100 to 1000 parts by mass per 100 parts by mass of the solid content of the adhesive composition. By making it equal to or greater than the lower limit, the liquid state and pot life will be good. In addition, by making it equal to or less than the upper limit, it will be advantageous in terms of manufacturing costs and transportation costs.

The adhesive composition of the present invention may further contain other components as necessary. Specific examples of such components include flame retardants, tackifiers, fillers, antioxidants, silane coupling agents, etc.

<Flame retardants>
The adhesive composition of the present invention may contain a flame retardant as necessary. Examples of flame retardants include bromine-based, phosphorus-based, nitrogen-based, and metal hydroxide compounds. Among them, phosphorus-based flame retardants are preferred, and phosphorus-based flame retardants such as phosphate esters, phosphates, and phosphine oxides can be used. These may be used alone or in any combination of two or more. When a flame retardant is contained, it is preferred to contain the flame retardant in a range of 1 to 200 parts by mass, more preferably 5 to 150 parts by mass, and most preferably 10 to 100 parts by mass, per 100 parts by mass of the polyimide resin and the epoxy resin (E) in total. By keeping the content within the above range, flame retardancy can be expressed while maintaining adhesion, solder heat resistance, and electrical properties.

<Tackifier>
The adhesive composition of the present invention may contain a tackifier as necessary. Examples of tackifiers include polyterpene resins, rosin resins, aliphatic petroleum resins, alicyclic petroleum resins, copolymerized petroleum resins, styrene resins, and hydrogenated petroleum resins, and are used for the purpose of improving adhesive strength. These may be used alone or in any combination of two or more. When a tackifier is contained, it is preferably contained in the range of 1 to 200 parts by mass, more preferably in the range of 5 to 150 parts by mass, and most preferably in the range of 10 to 100 parts by mass, per 100 parts by mass of the polyimide resin and the epoxy resin (E) in total. By keeping it within the above range, the effect of the tackifier can be expressed while maintaining the adhesiveness, solder heat resistance, and electrical properties.

<Filler>
The adhesive composition of the present invention may contain a filler as necessary. Examples of organic fillers include powders of heat-resistant resins such as polyimide, polyamideimide, fluororesin, and liquid crystal polyester. Examples of inorganic fillers include silica (SiO ₂ ), alumina (Al ₂ O ₃ ), titania (TiO ₂ ), tantalum oxide (Ta ₂ O ₅ ), zirconia (ZrO ₂ ), silicon nitride (Si ₃ N ₄ ), boron nitride (BN), calcium carbonate (CaCO ₃ ), calcium sulfate (CaSO ₄ ), zinc oxide (ZnO), magnesium titanate (MgO.TiO ₂ ), barium sulfate (BaSO ₄ ), organic bentonite, clay, mica, aluminum hydroxide, and magnesium hydroxide. Among these, silica is preferred because of its ease of dispersion and heat resistance improvement effect.

Hydrophobic silica and hydrophilic silica are generally known as silica, but in this case, hydrophobic silica treated with dimethyldichlorosilane, hexamethyldisilazane, octylsilane, etc. is better for imparting moisture absorption resistance. When silica is added, the amount of silica added is preferably 1 to 100 parts by mass per 100 parts by mass of polyimide resin and epoxy resin (E) combined. By adding an amount equal to or greater than the lower limit, further heat resistance can be achieved. Also, by adding an amount equal to or less than the upper limit, poor dispersion of silica and excessively high solution viscosity can be prevented, improving workability.

<Antioxidants>
The adhesive composition of the present invention may contain an antioxidant as necessary. By adding an antioxidant, it is possible to suppress the deterioration of properties such as adhesion and dielectric properties even when the adhesive composition is used in a high-temperature environment exposed to air, which is preferable. The antioxidant is not particularly limited, but examples thereof include phenol-based antioxidants, amine-based antioxidants, phosphorus-based antioxidants, and sulfur-based antioxidants. These may be used alone or in combination of two or more.

If the adhesive composition contains an antioxidant, the content is preferably 0.01 to 5 parts by mass, and more preferably 0.1 to 3 parts by mass, per 100 parts by mass of the solid content of the adhesive composition. If the content of the antioxidant is within the above range, it is possible to prevent deterioration of properties such as adhesion and dielectric properties even when the adhesive composition is used in a high-temperature environment exposed to air.

<Silane coupling agent>
The adhesive composition of the present invention may contain a silane coupling agent as necessary. The incorporation of a silane coupling agent is highly preferred because it improves the adhesiveness to metals and heat resistance. The silane coupling agent is not particularly limited, but examples include those having an unsaturated group, those having an epoxy group, and those having an amino group. Among these, silane coupling agents having an epoxy group such as γ-glycidoxypropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and β-(3,4-epoxycyclohexyl)ethyltriethoxysilane are more preferred from the viewpoint of heat resistance. When a silane coupling agent is incorporated, the amount of the silane coupling agent is preferably 0.5 to 20 parts by mass per 100 parts by mass of the total of the polyimide resin and the epoxy resin (E). By keeping the amount within the above range, solder heat resistance and adhesiveness can be improved.

<Laminate>
The laminate of the present invention is a laminate of an adhesive composition on a substrate, specifically, a laminate of an adhesive composition on a substrate (a two-layer laminate of substrate/adhesive layer), or a laminate of a substrate attached thereto (a three-layer laminate of substrate/adhesive layer/substrate). Here, the adhesive layer refers to a layer of the adhesive composition after the adhesive composition of the present invention is applied to a substrate and dried. The adhesive composition of the present invention can be applied to various substrates according to a conventional method, dried, and then laminated with another substrate to obtain the laminate of the present invention.

<Substrate>
In the present invention, the substrate is not particularly limited as long as it is capable of forming an adhesive layer by applying and drying the adhesive composition of the present invention. Examples of the substrate include resin substrates such as film-like resins, metal substrates such as metal plates and metal foils, and papers.

Examples of resin substrates include polyester resins, polyamide resins, polyimide resins, polyamideimide resins, liquid crystal polymers, polyphenylene sulfide, syndiotactic polystyrene, polyolefin resins, and fluorine resins. A film-like resin (hereinafter also referred to as a substrate film layer) is preferred.

Any conventionally known conductive material that can be used for a circuit board can be used as the metal substrate. Examples of materials include various metals such as SUS, copper, aluminum, iron, steel, zinc, and nickel, as well as their alloys, plated products, and metals treated with other metals such as zinc and chromium compounds. Metal foil is preferred, and copper foil is more preferred. There is no particular limitation on the thickness of the metal foil, but it is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 10 μm or more. It is also preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less. If the thickness is too thin, it may be difficult to obtain sufficient electrical performance of the circuit, while if the thickness is too thick, the processing efficiency during circuit fabrication may decrease. Metal foil is usually provided in a rolled form. There is no particular limitation on the form of the metal foil used in manufacturing the printed wiring board of the present invention. When a ribbon-shaped metal foil is used, there is no particular limitation on its length. There is also no particular limitation on its width, but it is preferably about 250 to 500 cm. There are no particular limitations on the surface roughness of the substrate, but it is preferably 3 μm or less, more preferably 2 μm or less, and even more preferably 1.5 μm or less. In practical terms, it is preferably 0.3 μm or more, more preferably 0.5 μm or more, and even more preferably 0.7 μm or more.

Examples of paper include fine paper, craft paper, roll paper, glassine paper, etc. Examples of composite materials include glass epoxy, etc.

In terms of adhesion to the adhesive composition and durability, the substrate is preferably polyester resin, polyamide resin, polyimide resin, polyamideimide resin, liquid crystal polymer, polyphenylene sulfide, syndiotactic polystyrene, polyolefin resin, fluorine resin, SUS steel plate, copper foil, aluminum foil, or glass epoxy.

<Adhesive sheet>
In the present invention, the adhesive sheet is a laminate of the substrate and the release substrate via an adhesive composition. Specific configurations include substrate/adhesive layer/release substrate, or release substrate/adhesive layer/substrate/adhesive layer/release substrate. The release substrate functions as a protective layer for the substrate by laminating it. In addition, by using a release substrate, the release substrate can be released from the adhesive sheet and the adhesive layer can be transferred to another substrate.

The adhesive sheet of the present invention can be obtained by applying the adhesive composition of the present invention to various laminates and drying them in the usual manner. Furthermore, by attaching a release substrate to the adhesive layer after drying, it is possible to wind it up without causing offset onto the substrate, which is excellent in operability, and since the adhesive layer is protected, it is excellent in storage properties and easy to use. Furthermore, if a release substrate is applied and dried, and then another release substrate is attached as necessary, it becomes possible to transfer the adhesive layer itself to another substrate.

The adhesive composition of the present invention preferably has a rate of change in dielectric tangent calculated, for example, by the following formula of 8 to 70%, more preferably 20 to 65%, and even more preferably 30 to 60%. Because the adhesive composition of the present invention contains the epoxy resin (A), the dielectric tangent can be significantly reduced from the B stage product to the C stage product.
Dielectric loss tangent change rate (%) = (T _B - T _C )/T _B ×100
(In the above formula,
T _B : Dielectric loss tangent of a B-stage product obtained by applying the adhesive composition to a 100 μm thick Teflon (registered trademark) sheet so that the thickness after drying would be 25 μm, and drying at 130° C. for 3 minutes. T _C : Dielectric loss tangent of a C-stage product obtained by heat treating the B-stage product for 3 hours at 180° C. for curing.

<Release substrate>
The release substrate is not particularly limited, but examples thereof include those in which a coating layer of a filler such as clay, polyethylene, or polypropylene is provided on both sides of paper such as fine paper, craft paper, roll paper, or glassine paper, and a silicone-based, fluorine-based, or alkyd-based release agent is further applied on each coating layer. Other examples include various olefin films such as polyethylene, polypropylene, ethylene-α-olefin copolymer, and propylene-α-olefin copolymer alone, and films such as polyethylene terephthalate on which the release agent is applied. Due to the release force between the release substrate and the adhesive layer, and the adverse effect of silicone on electrical properties, it is preferable to use a polypropylene-filled coating on both sides of fine paper and an alkyd-based release agent thereon, or an alkyd-based release agent on polyethylene terephthalate.

In the present invention, the method of coating the adhesive composition on the substrate is not particularly limited, but includes a comma coater, a reverse roll coater, a die coater, etc. Alternatively, if necessary, an adhesive layer can be provided directly or by a transfer method on the rolled copper foil or polyimide film that is the printed wiring board constituent material. The thickness of the adhesive layer after drying can be appropriately changed as necessary, but is preferably in the range of 5 to 200 μm. By making the adhesive film thickness 5 μm or more, sufficient adhesive strength can be obtained. In addition, by making it 200 μm or less, it becomes easier to control the amount of residual solvent in the drying process, and blisters are less likely to occur during pressing in the production of printed wiring boards. The drying conditions are not particularly limited, but the residual solvent rate after drying is preferably 1 mass % or less. By making it 1 mass % or less, foaming of the residual solvent is suppressed during pressing of the printed wiring board, and blisters are less likely to occur.

<Printed Wiring Board>
The printed wiring board in the present invention includes, as a component, a laminate formed of a metal foil forming a conductor circuit and a resin substrate. The printed wiring board is manufactured by a conventionally known method such as a subtractive method using a metal-clad laminate. If necessary, the printed wiring board is a general term for so-called flexible circuit boards (FPC), flat cables, circuit boards for tape automated bonding (TAB), etc., in which a conductor circuit formed by a metal foil is partially or entirely covered with a cover film, screen printing ink, etc.

The printed wiring board of the present invention can have any laminated structure that can be used as a printed wiring board. For example, it can be a printed wiring board consisting of four layers: a base film layer, a metal foil layer, an adhesive layer, and a cover film layer. It can also be a printed wiring board consisting of five layers: a base film layer, an adhesive layer, a metal foil layer, an adhesive layer, and a cover film layer.

Furthermore, if necessary, two or more of the above printed wiring boards can be stacked together.

The adhesive composition of the present invention can be suitably used for each adhesive layer of a printed wiring board. In particular, when the adhesive composition of the present invention is used as an adhesive, it has high adhesion not only to conventional polyimide, polyester film, and copper foil that constitute printed wiring boards, but also to low-polarity resin substrates such as LCP, and can provide solder reflow resistance, and the adhesive layer itself has excellent low dielectric properties. Therefore, it is suitable as an adhesive composition for use in coverlay films, laminates, resin-coated copper foil, and bonding sheets.

In the printed wiring board of the present invention, any resin film that has been conventionally used as a substrate for printed wiring boards can be used as the substrate film. Examples of resins for the substrate film include polyester resins, polyamide resins, polyimide resins, polyamideimide resins, liquid crystal polymers, polyphenylene sulfide, syndiotactic polystyrene, polyolefin resins, and fluorine-based resins. In particular, the film has excellent adhesion to low-polarity substrates such as liquid crystal polymers, polyphenylene sulfide, syndiotactic polystyrene, and polyolefin resins.

<Cover film>
As the cover film, any insulating film conventionally known as an insulating film for printed wiring boards can be used. For example, films made of various polymers such as polyimide, polyester, polyphenylene sulfide, polyethersulfone, polyetheretherketone, aramid, polycarbonate, polyarylate, polyamideimide, liquid crystal polymer, syndiotactic polystyrene, and polyolefin resin can be used. More preferably, it is a polyimide film or a liquid crystal polymer film.

The printed wiring board of the present invention can be manufactured using any conventionally known process, except for using the materials for each layer described above.

In a preferred embodiment, a semi-finished product is manufactured in which an adhesive layer is laminated on a cover film layer (hereinafter referred to as a "cover film side semi-finished product"). On the other hand, a semi-finished product is manufactured in which a metal foil layer is laminated on a base film layer to form a desired circuit pattern (hereinafter referred to as a "base film side two-layer semi-finished product"), or a semi-finished product is manufactured in which an adhesive layer is laminated on a base film layer and a metal foil layer is laminated on top of it to form a desired circuit pattern (hereinafter referred to as a "base film side three-layer semi-finished product") (hereinafter, the base film side two-layer semi-finished product and the base film side three-layer semi-finished product are collectively referred to as the "base film side semi-finished product"). By bonding the cover film side semi-finished product thus obtained and the base film side semi-finished product together, a four-layer or five-layer printed wiring board can be obtained.

The semi-finished product on the base film side can be obtained, for example, by a manufacturing method including a process (A) of applying a solution of the resin that will become the base film to the metal foil and initially drying the coating, and a process (B) of heat-treating and drying the laminate of the metal foil and the initially dried coating obtained in (A) (hereinafter referred to as the "heat-treatment/solvent-removal process").

The formation of the circuit in the metal foil layer can be achieved by a conventional method. Either an additive method or a subtractive method can be used. A subtractive method is preferable.

The obtained semi-finished product on the base film side may be used as is for bonding to the semi-finished product on the cover film side, or it may be used for bonding to the semi-finished product on the cover film side after bonding a release film and storing it.

The cover film side semi-finished product is produced, for example, by applying an adhesive to the cover film. If necessary, a crosslinking reaction can be carried out in the applied adhesive. In a preferred embodiment, the adhesive layer is semi-cured.

The obtained semi-finished product on the cover film side may be used as is for bonding to the semi-finished product on the base film side, or it may be used for bonding to the semi-finished product on the base film side after bonding a release film and storing it.

The semi-finished product on the base film side and the semi-finished product on the cover film side are stored, for example, in the form of a roll, and then bonded together to produce a printed wiring board. Any method can be used to bond them together, and for example, they can be bonded together using a press or roll. They can also be bonded together while heating them, for example, using a hot press or a hot roll device.

In the case of a reinforcing material that is soft and can be rolled up, such as a polyimide film, the semi-finished reinforcing material is preferably manufactured by applying an adhesive to the reinforcing material. In the case of a reinforcing plate that is hard and cannot be rolled up, such as a metal plate such as SUS or aluminum, or a plate made of glass fiber cured with epoxy resin (E), it is preferably manufactured by transfer-coating an adhesive that has been applied in advance to a release substrate. If necessary, a crosslinking reaction can be carried out in the applied adhesive. In a preferred embodiment, the adhesive layer is semi-cured.

The obtained semi-finished product on the reinforcing material side may be used as is for bonding to the back surface of a printed wiring board, or it may be used for bonding to the semi-finished product on the base film side after a release film has been applied and stored.

The base film semi-finished product, the cover film semi-finished product, and the reinforcing material semi-finished product are all laminates for printed wiring boards according to the present invention.

This application claims the benefit of priority based on Japanese Patent Application No. 2023-187159, filed on October 31, 2023. The entire contents of the specification of Japanese Patent Application No. 2023-187159, filed on October 31, 2023, are incorporated by reference into this application.

The present invention will be specifically explained below with reference to examples. Note that in these examples and comparative examples, parts simply indicate parts by mass.

<Physical property evaluation method>
(Acid value measurement)
In the present invention, the acid value (equivalent/10 ⁶ g) was measured by dissolving the polyimide resin in toluene and titrating it with a methanol solution of sodium methoxide using phenolphthalein as an indicator.

(Measurement of Glass Transition Temperature)
Measurement was performed using a differential scanning calorimeter (DSC-200, SII). 5 mg of the sample was placed in an aluminum container with a lid and sealed, and cooled to -50°C using liquid nitrogen. The temperature was then increased to 150°C at a rate of 20°C/min, and the glass transition temperature (unit: °C) was determined as the temperature at the intersection of the extension of the baseline before the endothermic peak (below the glass transition temperature) and the tangent to the endothermic peak (the tangent showing the maximum slope between the rising part of the peak and the apex of the peak) in the endothermic curve obtained during the temperature increase process.

(Measurement of chlorine concentration in epoxy resin)
1 g of the epoxy resin used in the examples was dissolved in 25 ml of ethylene glycol monobutyl ether. 25 ml of 1N potassium hydroxide propylene glycol solution was added to the solution, and the mixture was boiled for 20 minutes. The total amount of chlorine in the epoxy resin was titrated with an aqueous silver nitrate solution to determine the chlorine concentration in the epoxy resin.

(Measurement of the amount of allyl group-containing substances contained in epoxy resin)
The amount of allyl group-containing substances in the epoxy resins used in the examples was measured using gas chromatography (Shimadzu Corporation, GC-2010Plus).

Below are examples of the production of adhesive compositions that serve as examples of the present invention, and comparative examples of adhesive compositions.

The polyimide resin was prepared as follows.
(Production Example 1)
A four-neck flask equipped with a thermometer, a condenser, and a nitrogen gas inlet tube was charged with 53 parts of 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 185.5 parts of cyclohexanone, and 37.1 parts of methylcyclohexane, and the solution was heated to 60° C. Then, 85.4 parts of dimer diamine (PRIAMINE 1075, manufactured by Croda) was added dropwise, and the mixture was subjected to an imidization reaction at 140° C. for 1 hour to obtain a polyimide resin solution (glass transition temperature 70° C., acid value 146 equivalents/10 ⁶ g, relative dielectric constant 2.6, dielectric loss tangent 0.0019).

As the epoxy resin (A), the following was used.
Epoxy resin a1: EP-3980S (manufactured by ADEKA Corporation, N,N-(diglycidyl)-O-toluidine, epoxy value 8696 equivalents/10 ⁶ g, chlorine 700 ppm, allyl group-containing substances 0%)

　エポキシ樹脂ｂ２：ＹＬ９８０（三菱ケミカル社製、エポキシ価５３７６当量／１０⁶ｇ、塩素３００ｐｐｍ、アリル基含有物質０％）

As the epoxy resin (B), the following was used.
Epoxy resin b1: EP-3900S (manufactured by ADEKA Corporation, epoxy value 10,000 equivalents/10 ⁶ g, chlorine 1,200 ppm, allyl group-containing substances 0%)

Epoxy resin b2: YL980 (manufactured by Mitsubishi Chemical Corporation, epoxy value 5376 equivalents/10 ⁶ g, chlorine 300 ppm, allyl group-containing substances 0%)

The other components used were as follows:
c1: Silica ("GT3SDC" manufactured by Denka Co., Ltd.)
c2: Phosphine oxide flame retardant (Dai-ichi Kogyo Seiyaku Co., Ltd. "PQ-60")
c3: Phosphorus-based antioxidant ("HOSTANOX (registered trademark) P-EPQ" manufactured by Clariant)

Example 1
100 parts of the polyimide resin and 4 parts of the epoxy resin (A) were mixed and dissolved in toluene to a solids concentration of 30%, to obtain a toluene adhesive composition (S1).
The adhesive composition (S1) thus obtained was evaluated for its relative dielectric constant, dielectric loss tangent, peel strength, and solder heat resistance. The results are shown in Table 1.

<Examples 2 to 6, Comparative Examples 1 to 3>
Adhesive compositions (S2) to (S9) were prepared and evaluated in the same manner as in Example 1, except that the types and amounts of each component of the adhesive composition were changed as shown in Tables 1 and 2. The results are shown in Tables 1 and 2.

<Evaluation of Adhesive Composition>
(Dielectric constant (εc) and dielectric tangent (tan δ))
The adhesive composition was applied to a 100 μm thick Teflon (registered trademark) sheet so that the thickness after drying was 25 μm, and dried at 130° C. for 3 minutes (B stage product). Then, after hardening by heat treatment at 180° C. for 3 hours, the Teflon (registered trademark) sheet was peeled off to obtain an adhesive resin sheet for testing. The obtained adhesive resin sheet for testing was then cut into strips of 8 cm x 3 mm to obtain test samples (C stage product). The relative dielectric constant (εc) and dielectric loss tangent (tan δ) were measured using a network analyzer (manufactured by Anritsu Corporation) by a cavity resonator perturbation method at a temperature of 23° C. and a frequency of 10 GHz.
After the measurement, the dielectric loss tangent of the B stage product was designated as T _B , the dielectric loss tangent of the C stage product was designated as T _C , and the rate of change in dielectric loss tangent was calculated according to the following formula.
Dielectric loss tangent change rate (%) = (T _B - T _C )/T _B ×100
<Evaluation criteria for dielectric constant>
○: Less than 2.5 △: 2.5 or more and 2.7 or less ×: More than 2.7 <Evaluation criteria for dielectric tangent>
○: 0.002 or less △: More than 0.002 and 0.005 or less ×: More than 0.005

(Peel strength (adhesiveness))
The adhesive composition was applied to a 12.5 μm thick polyimide film (Apical (registered trademark), manufactured by Kaneka Corporation) so that the thickness after drying was 25 μm, and dried at 130 ° C for 3 minutes. The adhesive film (B stage product) thus obtained was laminated with a rolled copper foil (ESPANEX series, manufactured by Nippon Steel Chemical & Material Co., Ltd.) having a thickness of 18 μm. The laminate was pressed for 280 seconds at 170 ° C under a pressure of 2 MPa so that the glossy surface of the rolled copper foil was in contact with the adhesive layer, and the adhesive was bonded. The laminate was then heat-treated at 180 ° C for 3 hours to harden the film, and a peel strength evaluation sample was obtained. The peel strength was measured under the conditions of 25 ° C, film pulling, tensile speed 50 mm / min, and 90 ° peeling. This test shows the adhesive strength at room temperature.
<Evaluation criteria>
○: 1.0 N/mm or more △: 0.7 N/mm or more but less than 1.0 N/mm ×: Less than 0.7 N/mm

(solder heat resistance)
An evaluation sample was prepared in the same manner as for measuring the peel strength described above, and a 2.0 cm x 2.0 cm sample piece was immersed in a bath of molten solder at 288°C, and the presence or absence of any change in appearance, such as blistering, was confirmed.
<Evaluation criteria>
○: No swelling for 60 seconds or more △: Swelling occurs for 30 seconds or more but less than 60 seconds ×: Swelling occurs for less than 30 seconds

As is clear from Table 1, Examples 1 to 6 have excellent dielectric properties, peel strength, and solder heat resistance. Comparing Examples 1 to 3, it is clear that the dielectric properties can be changed by changing the content ratio and type of epoxy resin (B).

On the other hand, in Comparative Example 1, since the epoxy resin (A) was not contained and only the epoxy resin (B) was contained, the dielectric tangent was deteriorated.
In Comparative Example 2, since no epoxy resin (A) was contained and the amount of epoxy resin (B) was smaller than that in Comparative Example 1, the dielectric tangent was improved, but the crosslink density was reduced and the solder heat resistance was deteriorated.
In Comparative Example 3, although the epoxy resin (A) was contained, the epoxy resin (B) was contained in a large amount, and therefore the dielectric properties were deteriorated.

It can also be seen that in the adhesive compositions of Examples 1 and 4 to 6, which contain epoxy resin (A), the dielectric tangent drops significantly from the B stage to the C stage. On the other hand, in the adhesive compositions of Comparative Examples 1 and 2, which do not contain epoxy resin (A), and the adhesive composition of Comparative Example 3, which contains a large amount of epoxy resin (B), the effect of the epoxy resin (A) is not fully exerted, so there is almost no change in the dielectric tangent between the B stage and C stage products.

The adhesive composition of the present invention has excellent solder heat resistance, excellent adhesive strength, and good dielectric constant and dielectric loss tangent, and is therefore useful as an adhesive or adhesive sheet for FPCs in the high frequency range.

Claims (17)

An adhesive composition comprising a polyimide resin and an epoxy resin (E),
The epoxy resin (E) contains an epoxy resin (A) represented by formula (I),
an adhesive composition in which the content of a glycidyl ether type epoxy resin (B) contained as the epoxy resin (E) is 5 parts by mass or less per 100 parts by mass of the polyimide resin;

[In formula (I), R ¹ to R ⁵ each independently represent a hydrogen atom or a C _1-10 alkyl group.] The adhesive composition according to claim 1, wherein the content of the epoxy resin (A) is 0.01 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the polyimide resin. 2. The adhesive composition according to claim 1, wherein the polyimide resin has an acid value of 10 equivalents/10 ⁶ g or more and 1,000 equivalents/10 ⁶ g or less. The adhesive composition according to claim 1, in which the ratio represented by (total epoxy value of the epoxy resin (E)/total acid value of the polyimide resin) is 0.5 or more and 10.0 or less. The adhesive composition according to claim 1, wherein the content of the epoxy resin (A) is 70% by mass or more in 100% by mass of the epoxy resin (E). The adhesive composition according to claim 1, wherein the content of the epoxy resin (B) is 25% by mass or less in 100% by mass of the epoxy resin (E). 2. The adhesive composition according to claim 1, wherein in formula (I), R ¹ and/or R ⁵ is a C _1-10 alkyl group. The adhesive composition according to claim 1, wherein the total amount of the epoxy resin (A) and the glycidyl ether type epoxy resin (B) is 50% by mass or more in 100% by mass of the epoxy resin (E). 2. The adhesive composition according to claim 1, wherein the glycidyl ether type epoxy resin (B) is an epoxy resin having a chemical structure represented by formula (II) or formula (III) in the molecule.

[In formula (II), R ⁶ to R ⁹ each independently represent a hydrogen atom or a C _1-10 alkyl group. * represents a bond.]

[In formula (III), R ²⁶ to R ²⁹ each independently represent a hydrogen atom or a C _1-10 alkyl group. * represents a bond.] The adhesive composition according to claim 1, which does not contain the glycidyl ether type epoxy resin (B). The glycidyl ether type epoxy resin (B) is contained,
2. The adhesive composition according to claim 1, wherein the content of the glycidyl ether type epoxy resin (B) is 0.5 parts by mass or more and 5 parts by mass or less based on 100 parts by mass of the polyimide resin. The adhesive composition according to claim 1, wherein the chlorine concentration is 0.01 to 300 ppm in the solid content of the adhesive composition. The adhesive composition according to any one of claims 1 to 12, which is for use on printed wiring boards. An adhesive sheet in which a substrate, which is a resin substrate, a metal substrate, or a paper substrate, and a release substrate are laminated via the adhesive composition according to any one of claims 1 to 12. The adhesive sheet according to claim 14, wherein the rate of change in dielectric tangent calculated based on the following formula is 8 to 70%.
Dielectric loss tangent change rate (%) = (T _B - T _C )/T _B ×100
(In the above formula,
T _B : Dielectric loss tangent of a B-stage product obtained by applying the adhesive composition to a 100 μm thick Teflon (registered trademark) sheet so that the thickness after drying would be 25 μm, and drying at 130° C. for 3 minutes. T _C : Dielectric loss tangent of a C-stage product obtained by heat treating the B-stage product for 3 hours at 180° C. for curing. A laminate in which the adhesive composition according to any one of claims 1 to 12 is laminated onto a substrate that is a resin substrate, a metal substrate, or a paper substrate. A printed wiring board comprising the laminate according to claim 16 as a component.