JP7655752B2 - Polyimide, resin composition, resin film, laminate, coverlay film, resin-coated copper foil, metal-clad laminate, and circuit board - Google Patents

Description

The present invention relates to polyimides, resin compositions, resin films, laminates, coverlay films, resin-coated copper foils, metal-clad laminates, and circuit boards that are useful as adhesives in circuit boards such as printed wiring boards.

In recent years, with the progress of miniaturization, weight saving, and space saving of electronic devices, there is an increasing demand for flexible printed circuits (FPCs) that are thin, lightweight, flexible, and have excellent durability even when repeatedly bent. Because FPCs allow three-dimensional and high-density mounting even in a limited space, their applications are expanding to include wiring for moving parts of electronic devices such as HDDs, DVDs, and mobile phones, as well as components such as cables and connectors.

Polyimide, which has excellent heat resistance, chemical resistance, flexibility, mechanical properties, and electrical properties, is widely used as a material for insulating resin layers that make up circuit boards such as FPCs. In addition, various additives have been added to improve the functionality of polyimide. For example, an adhesive composition that has excellent adhesion, heat resistance, flame retardancy, and handling properties as well as high insulation reliability has been proposed by combining polyimide with a specific phosphorus compound (Patent Document 1).

In addition to higher density, the performance of devices has improved, so there is also a need to accommodate higher frequencies of transmission signals. In information processing and information communication, efforts are being made to increase transmission frequencies in order to transmit and process large volumes of information, and printed circuit board materials are being required to reduce transmission loss by thinning the insulating layer and improving the dielectric properties of the insulating layer. In the future, there will be an increasing demand for the insulating layers (including adhesive layers) that make up FPCs to reduce transmission loss and accommodate higher frequencies. In order to improve the dielectric properties of printed circuit board materials, a resin composition has been proposed that contains a multifunctional vinyl aromatic polymer and a thermosetting compound, but does not contain a radical polymerization initiator (Patent Document 2).

It has been proposed to apply a crosslinked polyimide resin obtained by reacting a thermoplastic polyimide made from a diamine compound derived from a dimer diamine derived from a dimer acid (dimer fatty acid) with an amino compound having at least two primary amino groups as functional groups to the adhesive layer of a coverlay film (Patent Document 3). In the examples of Patent Document 3, it is also disclosed that flaky talc is blended with a thermoplastic polyimide composition made from a dimer diamine. Here, the dimer acid is a dimerized fatty acid obtained by Diels-Alder reaction using natural fatty acids such as soybean oil fatty acid, tall oil fatty acid, rapeseed oil fatty acid, and oleic acid, linoleic acid, linolenic acid, erucic acid, etc., which are refined from these, as raw materials, and it is known that a polybasic acid compound derived from a dimer acid is obtained as a composition of raw fatty acids and fatty acids that are trimerized or higher (Patent Document 4).

Patent No. 6733845 International Publication No. WO2020/175537 Patent No. 5777944 JP 2017-137375 A

Polyimides made from dimer diamine are soluble in solvents, have excellent adhesive properties, and are easy to handle, making them a useful resin material for use as an adhesive. However, to keep up with the increasing demand for higher frequencies in the future, in addition to satisfying the above characteristics, there is a demand for even lower dielectric tangents.

Therefore, the object of the present invention is to provide a polyimide that can be used as a raw material to form a resin film that has both a low dielectric tangent and excellent adhesion.

The polyimide of the present invention is a polyimide containing a tetracarboxylic acid residue derived from a tetracarboxylic acid anhydride component and a diamine residue derived from a diamine component.
The polyimide of the present invention contains, relative to the total diamine residues, 40 mol % or more and 95 mol % or less of diamine residues derived from a dimer diamine composition mainly composed of a dimer diamine in which two terminal carboxylic acid groups of a dimer acid are substituted with primary aminomethyl groups or amino groups.
The polyimide of the present invention contains, relative to all diamine residues, a diamine residue derived from a diamine compound which contains a biphenyl skeleton or a naphthalene skeleton, and the biphenyl skeleton or the naphthalene skeleton has at least one substituent having a carbon-carbon double bond selected from the group consisting of a vinyl group, an acrylic group, a methacrylic group, and an allyl group, in an amount within the range of 5 mol % to 25 mol %.

The resin composition of the present invention comprises the following components (A) and (B):
(A) the polyimide; and (B) a crosslinking agent;
and the content of the (B) component is within the range of 5 parts by weight or more and 30 parts by weight or less per 100 parts by weight of the (A) component.

The resin composition of the present invention further comprises the following component (C):
(C) an elastomer resin,
The content of the (C) component relative to 100 parts by weight of the (A) component may be within the range of 5 parts by weight or more and 100 parts by weight or less.

The resin composition of the present invention further comprises the following component (D):
(D) a polymerization initiator,
The content of the (D) component relative to 100 parts by weight of the (A) component may be within the range of 0.5 parts by weight or more and 2.0 parts by weight or less.

The resin film of the present invention contains the above polyimide.

The resin film of the present invention may have a dielectric loss tangent (Tan δ) of less than 0.002 at 10 GHz measured using a split post dielectric resonator (SPDR) after being conditioned for 24 hours under constant temperature and humidity conditions (normal state) of 23°C and 50% RH.

The laminate of the present invention is a laminate having a substrate and an adhesive layer laminated on at least one surface of the substrate, the adhesive layer being made of the above-mentioned resin film.

The coverlay film of the present invention is a coverlay film having a coverlay film material layer and an adhesive layer laminated on the coverlay film material layer, and the adhesive layer is made of the above-mentioned resin film.

The resin-coated copper foil of the present invention is a resin-coated copper foil in which an adhesive layer and a copper foil are laminated, and the adhesive layer is made of the above-mentioned resin film.

The metal-clad laminate of the present invention is a metal-clad laminate having an insulating resin layer and a metal layer laminated on at least one surface of the insulating resin layer, and at least one layer of the insulating resin layer is made of the above-mentioned resin film.

The circuit board of the present invention is formed by wiring the metal layer of the metal-clad laminate.

The polyimide of the present invention contains a diamine residue derived from a dimer diamine composition and a diamine residue derived from a diamine compound having a substituent with a carbon-carbon double bond, and therefore can form a resin film having excellent high-frequency characteristics as well as sufficient adhesiveness (particularly peel strength), solder heat resistance, and flame retardancy for practical use. Therefore, the resin composition and resin film of the present invention can be particularly suitably used as a circuit board material such as an FPC in electronic devices that require high-speed signal transmission. In addition, by improving the dielectric properties of the resin film, it can be applied to a direct conversion type receiver. Furthermore, as a highly reliable low-dielectric adhesive, it can be applied to electronic devices of any structure.

The following describes an embodiment of the present invention.

[Polyimide]
A polyimide according to an embodiment of the present invention is a polyimide having adhesive properties. Hereinafter, the polyimide according to the present embodiment may be referred to as an "adhesive polyimide". The adhesive polyimide contains a tetracarboxylic acid residue derived from a tetracarboxylic dianhydride component and a diamine residue derived from a diamine component. When the raw materials, tetracarboxylic dianhydride and diamine compound, are reacted in approximately equal moles, the types and molar ratios of the tetracarboxylic acid residues and diamine residues contained in the polyimide can be made to correspond approximately to the types and molar ratios of the raw materials.
In the present invention, the term "polyimide" refers to a resin made of a polymer having an imide group in the molecular structure, such as polyimide, polyamideimide, polyetherimide, polyesterimide, polysiloxaneimide, polybenzimidazoleimide, etc.
The tetracarboxylic acid residue and the diamine residue constituting the adhesive polyimide will be described below together with their raw materials.

(Acid anhydride)
The adhesive polyimide can be made of any tetracarboxylic dianhydride that is generally used as a raw material for polyimide, without any particular limitation. Examples of tetracarboxylic acid residues derived from such tetracarboxylic dianhydrides include 3,3',4,4'-, 2,3',3,4'-, 2,2',3,3'-, or 2,3,3',4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA), 4,4'-oxydiphthalic anhydride (ODPA), 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), p-phenylenebis(trimellitic monoester acid anhydride) (TAHQ), and ethylene glycol. Bisanhydrotrimellitate (TMEG), pyromellitic dianhydride, 2,3',3,4'-biphenyltetracarboxylic dianhydride, 2,3',3,4'-diphenylethertetracarboxylic dianhydride, bis(2,3-dicarboxyphenyl)ether dianhydride, 3,3'',4,4''-, 2,3,3'',4''- or 2,2'',3,3''-p-terphenyltetracarboxylic dianhydride, 2,2-bis(2,3- or 3,4-dicarboxyphenyl)-propane dianhydride, bis(2,3- or 3,4-dicarboxyphenyl)methane dianhydride, bis(2,3- or 3,4-dicarboxyphenyl)methane dianhydride, 1,1-bis(2,3- or 3,4-dicarboxyphenyl)ethane dianhydride, 1,2,7,8-, 1,2,6,7- or 1,2,9,10-phenanthrene tetracarboxylic dianhydride, 2,3,6,7-anthracene tetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)tetrafluoropropane dianhydride, 1,2,5,6-naphthalene tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride, 4,8-dimethyl-1,2,3,5,6, 7-Hexahydronaphthalene-1,2,5,6-tetracarboxylic dianhydride, 2,6- or 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-(or 1,4,5,8-)tetrachloronaphthalene-1,4,5,8-(or 2,3,6,7-)tetracarboxylic dianhydride, 2,3,8,9-, 3,4,9,10-, 4,5,10,11- or 5,6,11,12-perylene-tetracarboxylic dianhydride, pyrazine-2,3,5,6-tetracarboxylic dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic dianhydride, thiophene-2,3,4, tetracarboxylic acid residues derived from aromatic tetracarboxylic acid dianhydrides such as 1,2,3,4-tetracarboxylic acid dianhydride, 1,2,3,4-cyclobutane tetracarboxylic acid dianhydride, 1,2,3,4-cyclopentane tetracarboxylic acid dianhydride, 1,2,4,5-cyclohexane tetracarboxylic acid dianhydride, 1,2,4,5-cycloheptane tetracarboxylic acid dianhydride, 1,2,5,6-cyclooctane tetracarboxylic acid dianhydride, and the like.
Among these, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), which have a large effect of lowering the dielectric tangent, are preferred, and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) are more preferred.

(Diamine)
The adhesive polyimide may use, without any particular limitation, any diamine compound generally used in polyimides as a raw material, but the adhesive polyimide contains 40 mol % or more and 95 mol % or less, preferably 70 to 90 mol %, of diamine residues derived from a dimer diamine composition mainly composed of a dimer diamine in which two terminal carboxylic acid residues of a dimer acid are substituted with primary aminomethyl groups or amino groups, relative to the total diamine residues. By containing the diamine residues derived from the dimer diamine composition within the above range, the solubility of the polyimide can be improved, and the relative dielectric constant and dielectric loss tangent can be reduced.
If the content of the diamine residue derived from the dimer diamine composition is less than 40 mol% relative to the total diamine residue, the relative dielectric constant and dielectric loss tangent tend to increase due to the increase in the polar groups contained in the polyimide. In addition, by containing the diamine residue derived from the dimer diamine composition in the above amount, the glass transition temperature of the polyimide is lowered (lowered Tg), thereby improving the thermocompression bonding properties, and the internal stress is reduced due to the lowered elastic modulus. On the other hand, if the content of the diamine residue derived from the dimer diamine composition is more than 95 mol% relative to the total diamine residue, the mobility of the molecular chain of the polyimide is excessively increased, and the dielectric loss tangent may increase.

The dimer diamine composition is a refined product that contains the following component (a) as the main component, with the amounts of components (b) and (c) controlled.

(a) dimer diamine;
The dimer diamine of the component (a) means a diamine in which two terminal carboxylic acid groups (-COOH) of a dimer acid are replaced by primary aminomethyl groups (-CH ₂ -NH ₂ ) or amino groups (-NH ₂ ). Dimer acid is a known dibasic acid obtained by intermolecular polymerization of unsaturated fatty acids, and its industrial production process is almost standardized in the industry, and is obtained by dimerizing unsaturated fatty acids having 11 to 22 carbon atoms using a clay catalyst or the like. Industrially obtained dimer acid is mainly composed of a dibasic acid having 36 carbon atoms obtained by dimerizing unsaturated fatty acids having 18 carbon atoms, such as oleic acid, linoleic acid, and linolenic acid, but contains any amount of monomer acid (having 18 carbon atoms), trimer acid (having 54 carbon atoms), and other polymerized fatty acids having 20 to 54 carbon atoms depending on the degree of purification. In addition, although double bonds remain after the dimerization reaction, in the present invention, those which have been further subjected to a hydrogenation reaction to reduce the degree of unsaturation are also included in the dimer acid. The dimer diamine of the component (a) can be defined as a diamine compound obtained by substituting the terminal carboxylic acid group of a dibasic acid compound having a carbon number of 18 to 54, preferably 22 to 44, with a primary aminomethyl group or an amino group.

Dimer diamine has the characteristic of being able to impart properties derived from the dimer acid skeleton. In other words, since dimer diamine is an aliphatic macromolecule with a molecular weight of approximately 560 to 620, it can increase the molecular molar volume and relatively reduce the polar groups of the polyimide. It is believed that such characteristics of dimer acid type diamine contribute to improving the dielectric properties by reducing the relative dielectric constant and dielectric tangent while suppressing the deterioration of the heat resistance of the polyimide. In addition, since it has two freely moving hydrophobic chains with 7 to 9 carbon atoms and two chain-like aliphatic amino groups with a length close to 18 carbon atoms, it not only imparts flexibility to the polyimide, but also allows the polyimide to have an asymmetric chemical structure or a non-planar chemical structure, which is believed to enable the polyimide to have a low dielectric constant.

It is advisable to use a dimer diamine composition in which the dimer diamine content of component (a) has been increased to 96% by weight or more, preferably 97% by weight or more, and more preferably 98% by weight or more, by a purification method such as molecular distillation. By increasing the dimer diamine content of component (a) to 96% by weight or more, it is possible to suppress the broadening of the molecular weight distribution of the polyimide. If technically possible, it is best that all of the dimer diamine composition (100% by weight) is composed of component (a) dimer diamine.

(b) a monoamine compound obtained by substituting a terminal carboxylic acid group of a monobasic acid compound having 10 to 40 carbon atoms with a primary aminomethyl group or an amino group;
The monobasic acid compound having 10 to 40 carbon atoms is a mixture of a monobasic unsaturated fatty acid having 10 to 20 carbon atoms derived from the raw material of dimer acid, and a monobasic acid compound having 21 to 40 carbon atoms which is a by-product during the production of dimer acid. The monoamine compound is obtained by substituting the terminal carboxylic acid group of these monobasic acid compounds with a primary aminomethyl group or an amino group.

The monoamine compound of component (b) is a component that suppresses the increase in molecular weight of the polyimide. During polymerization of the polyamic acid or polyimide, the monofunctional amino group of the monoamine compound reacts with the terminal acid anhydride group of the polyamic acid or polyimide, thereby blocking the terminal acid anhydride group and suppressing the increase in molecular weight of the polyamic acid or polyimide.

(c) Amine compounds obtained by substituting the terminal carboxylic acid group of a polybasic acid compound having a hydrocarbon group having 41 to 80 carbon atoms with a primary aminomethyl group or an amino group (excluding the above-mentioned dimer diamine);
The polybasic acid compound having a hydrocarbon group having 41 to 80 carbon atoms is a polybasic acid compound mainly composed of a tribasic acid compound having 41 to 80 carbon atoms, which is a by-product during the production of dimer acid. It may also contain a polymerized fatty acid other than dimer acid having 41 to 80 carbon atoms. The amine compound is obtained by substituting the terminal carboxylic acid group of these polybasic acid compounds with a primary aminomethyl group or an amino group.

The amine compound (c) is a component that promotes an increase in the molecular weight of the polyimide. The tri- or higher functional amino group, the main component of which is a triamine derived from trimer acid, reacts with the terminal acid anhydride group of the polyamic acid or polyimide, rapidly increasing the molecular weight of the polyimide. In addition, amine compounds derived from polymerized fatty acids other than dimer acids having 41 to 80 carbon atoms also increase the molecular weight of the polyimide, causing the polyamic acid or polyimide to gel.

When quantifying each component by measurement using gel permeation chromatography (GPC), in order to facilitate confirmation of the peak start, peak top, and peak end of each component of the dimer diamine composition, a sample of the dimer diamine composition treated with acetic anhydride and pyridine is used, and cyclohexanone is used as an internal standard. Using the sample thus prepared, each component is quantified by the area percentage of the GPC chromatogram. The peak start and peak end of each component are taken as the minimum values of each peak curve, and the area percentage of the chromatogram can be calculated based on this.

In addition, the dimer diamine composition has a total area percentage of components (b) and (c) of 4% or less, preferably less than 4%, in the chromatogram obtained by GPC measurement. By keeping the total area percentage of components (b) and (c) at 4% or less, it is possible to suppress the broadening of the molecular weight distribution of the polyimide.

The area percentage of the chromatogram of component (b) is preferably 3% or less, more preferably 2% or less, and even more preferably 1% or less. By setting it in this range, it is possible to suppress a decrease in the molecular weight of the polyimide, and further to widen the range of the molar ratio of the tetracarboxylic dianhydride component and the diamine component. Note that component (b) does not have to be included in the dimer diamine composition.

The area percentage of the chromatogram of component (c) is 2% or less, preferably 1.8% or less, and more preferably 1.5% or less. By setting it in this range, a sudden increase in the molecular weight of the polyimide can be suppressed, and further, an increase in the dielectric tangent of the resin film over a wide frequency range can be suppressed. Note that component (c) does not have to be included in the dimer diamine composition.

In addition, when the ratio (b/c) of the area percentages of the chromatograms of components (b) and (c) is 1 or more, the molar ratio of the tetracarboxylic dianhydride component and the diamine component (tetracarboxylic dianhydride component/diamine component) is preferably 0.97 or more and less than 1.0, and such a molar ratio makes it easier to control the molecular weight of the polyimide.

In addition, when the ratio (b/c) of the area percentages of the chromatograms of components (b) and (c) is less than 1, the molar ratio of the tetracarboxylic dianhydride component and the diamine component (tetracarboxylic dianhydride component/diamine component) is preferably 0.97 or more and 1.1 or less, and such a molar ratio makes it easier to control the molecular weight of the polyimide.

The dimer diamine composition is available as a commercially available product, and is preferably purified to reduce the amount of components other than the dimer diamine in component (a), for example to make the amount of component (a) 96 area % or more. There are no particular limitations on the purification method, but known methods such as distillation and precipitation purification are suitable. Examples of commercially available dimer diamine compositions include PRIAMINE 1073 (trade name), PRIAMINE 1074 (trade name), and PRIAMINE 1075 (trade name) manufactured by Croda Japan.

The adhesive polyimide also contains, relative to the total diamine residues, a diamine residue derived from a diamine compound (hereinafter sometimes referred to as a "reactive double bond-containing diamine compound") that contains a biphenyl skeleton or a naphthalene skeleton and that has at least one or more substituents having a carbon-carbon double bond selected from the group consisting of a vinyl group, an acrylic group (acrylate group), a methacrylic group (methacrylate group) and an allyl group, in an amount of 5 mol % or more and 25 mol % or less, preferably 10 mol % or more and 20 mol % or less.
By containing the diamine residue derived from the reactive double bond-containing diamine compound within the above range, the adhesive polyimide can have a low dielectric tangent, and the solder heat resistance and flame retardancy can be improved. In addition, by containing a highly reactive double bond, crosslinking can be formed, and the introduction of a flame retardant compound into the polyimide skeleton can be facilitated, so that the solder heat resistance and flame retardancy can be further improved. If the diamine residue derived from the reactive double bond-containing diamine compound is less than 5 mol%, the effect of improving the dielectric properties, solder heat resistance, and flame retardancy may not be exhibited, and if it exceeds 25 mol%, the reactive double bond-containing diamine compounds are more likely to polymerize with each other, making it difficult to form crosslinks.

As a reactive double bond-containing diamine compound, for example, a diamine compound represented by the following general formula (1) or (2) can be preferably used. The diamine compounds represented by general formulas (1) and (2) can increase the aromatic ring concentration of the polyimide due to their basic skeleton and suppress the mobility of the polyimide molecules, thereby contributing to a low dielectric tangent.

一般式（１）及び（２）中、Ｘは、独立にビニル基、アクリル基、メタクリル基又はアリル基を示し、ｍ、ｎは独立に０～３の整数を意味する。ただし、ｍとｎが同時に０である場合を除くものとする。

In the general formulas (1) and (2), X independently represents a vinyl group, an acrylic group, a methacrylic group, or an allyl group, and m and n independently represent integers of 0 to 3, except for the case where m and n are both 0.

Preferred examples of reactive double bond-containing diamine compounds include 2,2'-divinyl-4,4'-diaminobiphenyl (VAB) and 4,8-divinylnaphthalene-2,6-diamine.

Other diamine compounds that can be used in polyimides include aromatic diamine compounds. Specific examples of these include 1,4-diaminobenzene (p-PDA; paraphenylenediamine), 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB), 2,2'-n-propyl-4,4'-diaminobiphenyl (m-NPB), 4-aminophenyl-4'-aminobenzoate (APAB), 2,2-bis-[4-(3-aminophenoxy)phenyl]propane, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)biphenyl, bis[1-(3-aminophenoxy)]biphenyl, bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(3 -aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)]benzophenone, 9,9-bis[4-(3-aminophenoxy)phenyl]fluorene, 2,2-bis-[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis-[4-(3-aminophenoxy)phenyl]hexafluoropropane, 3,3'-dimethyl-4,4'-diaminobiphenyl, 4,4'-methylenedi-o-toluidine, 4,4'-methylenedi-2,6-xylidine, 4,4'-methylene-2,6-diethylaniline, 3,3'-diaminodiphenylethane, 3,3'-diaminobiphenyl, 3 ,3'-Dimethoxybenzidine, 3,3''-Diamino-p-terphenyl, 4,4'-[1,4-phenylenebis(1-methylethylidene)]bisaniline, 4,4'-[1,3-phenylenebis(1-methylethylidene)]bisaniline, bis(p-aminocyclohexyl)methane, bis(p-β-amino-t-butylphenyl)ether, bis(p-β-methyl-δ-aminopentyl)benzene, p-bis(2-methyl-4-aminopentyl)benzene, p-bis(1,1-dimethyl-5-aminopentyl)benzene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,4-bis(β-amino-t -butyl)toluene, 2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine, m-xylylenediamine, p-xylylenediamine, 2,6-diaminopyridine, 2,5-diaminopyridine, 2,5-diamino-1,3,4-oxadiazole, piperazine, 2'-methoxy-4,4'-diaminobenzanilide, 4,4'-diaminobenzanilide, 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene, 6-amino-2-(4-aminophenoxy)benzoxazole, 1,3-bis(3-aminophenoxy)benzene, and other diamine compounds.

Polyimide can be produced by reacting the above tetracarboxylic anhydride component and diamine component in a solvent to produce polyamic acid, which is then heated to close the ring. For example, the tetracarboxylic anhydride component and diamine component are dissolved in approximately equal moles in an organic solvent, and the mixture is stirred at a temperature in the range of 0 to 100°C for 30 minutes to 24 hours to cause a polymerization reaction, resulting in polyamic acid, which is a precursor to polyimide. In the reaction, the reaction components are dissolved so that the resulting precursor is in the range of 5 to 50% by weight, preferably 10 to 40% by weight, in the organic solvent. Examples of organic solvents used in the polymerization reaction include N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2-butanone, dimethylsulfoxide (DMSO), hexamethylphosphoramide, N-methylcaprolactam, dimethyl sulfate, cyclohexanone, methylcyclohexane, dioxane, tetrahydrofuran, diglyme, triglyme, methanol, ethanol, benzyl alcohol, and cresol. Two or more of these solvents can be used in combination, and aromatic hydrocarbons such as xylene and toluene can also be used in combination. The amount of such organic solvents used is not particularly limited, but it is preferable to adjust the amount so that the concentration of the polyamic acid solution obtained by the polymerization reaction is about 5 to 50% by weight.

The synthesized polyamic acid is usually advantageously used as a reaction solvent solution, but it can be concentrated, diluted, or replaced with another organic solvent if necessary. Polyamic acid is also advantageously used because it generally has excellent solvent solubility. The viscosity of the polyamic acid solution is preferably within the range of 500 cps to 100,000 cps. If it is outside this range, defects such as uneven thickness and streaks are likely to occur in the film during coating operations using a coater, etc.

There are no particular limitations on the method for imidizing polyamic acid to form polyimide, and a suitable method is, for example, heat treatment in the solvent at a temperature in the range of 80 to 400°C for 1 to 24 hours. The temperature may be constant, or it may be changed during the process.

In adhesive polyimides, the dielectric properties, thermal expansion coefficient, tensile modulus, glass transition temperature, etc. can be controlled by selecting the type of tetracarboxylic anhydride component and diamine component, or the molar ratio of each when two or more types of tetracarboxylic anhydride components or diamine components are used. In addition, when an adhesive polyimide has multiple polyimide structural units, they may exist as blocks or randomly, but it is preferable that they exist randomly.

The imide group concentration of the adhesive polyimide is preferably 22% by weight or less, more preferably 20% by weight or less. Here, "imide group concentration" means the value obtained by dividing the molecular weight of the imide group (-(CO) ₂ -N-) in the polyimide by the molecular weight of the entire polyimide structure. If the imide group concentration exceeds 22% by weight, the molecular weight of the resin itself decreases, and the low moisture absorption property deteriorates due to an increase in polar groups, and Tg and tensile modulus increase.

The adhesive polyimide is most preferably a completely imidized structure. However, a part of the polyimide may be an amic acid. The imidization rate can be calculated from the absorbance of the C=O stretching derived from the imide group at 1780 cm ^-1 , based on the benzene ring absorber at about 1015 cm- ¹ , by measuring the infrared absorption spectrum of the polyimide thin film by the single reflection ATR method using a Fourier transform infrared spectrophotometer (commercial product: manufactured by JASCO Corporation, product name: FT/IR620).

[Resin composition]
The resin composition according to one embodiment of the present invention comprises the following components (A) and (B):
(A) an adhesive polyimide;
and (B) a crosslinking agent,
Contains:

<Component (A): Adhesive Polyimide>
In the resin composition of the present embodiment, the adhesive polyimide of the component (A) is as described above.

<Component (B): Crosslinking agent>
By including the crosslinking agent of component (B), crosslinking of the adhesive polyimide becomes possible, and the resin film obtained from the resin composition has improved solder heat resistance and flame retardancy, while suppressing bleed-out and reducing the dielectric tangent.
The crosslinking agent of component (B) that can be incorporated into the resin composition may be any compound having a functional group in the molecule that can react with a highly reactive substituent having a carbon-carbon double bond in the adhesive polyimide of component (A) to form a crosslink, and examples of such functional groups include vinyl groups, acrylic groups (acrylate groups), methacrylic groups (methacrylate groups), allyl groups, and acryloyl groups. Examples of compounds having such functional groups include 1,5-hexadiene, triallylamine, and dipentaerythritol hexaacrylate. As shown in the examples below, the crosslinking agent of component (B) may also be a compound containing an atom such as phosphorus in the molecule, and in this case, the effect of further improving the flame retardancy of the resin film after crosslinking can be expected.

The content of the (B) component in the resin composition is preferably in the range of 5 parts by weight to 30 parts by weight, and more preferably in the range of 10 parts by weight to 25 parts by weight, per 100 parts by weight of the (A) component. If the content of the (B) component is less than 5 parts by weight, crosslinking does not proceed sufficiently, making it difficult to improve the solder heat resistance, low dielectric tangent, and flame retardancy. If the content of the (B) component exceeds 30 parts by weight, unreacted crosslinking agent may cause bleeding out, or the adhesiveness may decrease when a resin film is formed, and the (B) components may react with each other, decreasing the handleability.

The crosslinking between component (A) and component (B) is carried out by reacting a substituent having a carbon-carbon double bond in the adhesive polyimide of component (A) with a functional group contained in the crosslinking agent of component (B).
For example, this can be achieved by a method such as (i) synthesis of an adhesive polyimide (imidization), followed by addition of a crosslinking agent of component (B) and heating, or (ii) processing a resin composition containing components (A) and (B) into a predetermined shape (for example, after coating on a substrate or forming into a film) and then heating.
The reaction conditions for crosslinking are not particularly limited, but may be, for example, a method of heating to a temperature within the range of 100 to 220° C., preferably within the range of 120 to 200° C. The reaction time is preferably about 30 minutes to 24 hours. In order to hasten the start of the reaction, a polymerization initiator of component (D), which will be described later, may be used as necessary.

<Component (C): Elastomer resin>
The resin composition may further contain an elastomer resin as component (C). By blending the elastomer resin as component (C), the toughness of the resin film can be increased, and sufficient peel strength and low dielectric tangent can be maintained. The elastomer resin as component (C) is preferably a copolymer of styrene or a derivative thereof with a conjugated diene compound, and includes a hydrogenated product thereof. Here, examples of styrene or a derivative thereof include, but are not limited to, styrene, methylstyrene, butylstyrene, divinylbenzene, vinyltoluene, etc. Furthermore, examples of the conjugated diene compound include, but are not limited to, butadiene, isoprene, 1,3-pentadiene, etc.
In addition, the elastomer resin is preferably hydrogenated, which further improves the thermal stability and makes it less susceptible to deterioration such as decomposition and polymerization, and also enhances the aliphatic properties and improves compatibility with the adhesive polyimide.

The copolymer structure of the elastomer resin of component (C) may be a block structure or a random structure. Preferred examples of the elastomer resin include styrene-butadiene-styrene block copolymer (SBS), styrene-butadiene-butylene-styrene block copolymer (SBBS), styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-ethylene-propylene-styrene block copolymer (SEPS), and styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS), but are not limited to these.

The acid value of the elastomer resin of the (C) component is 10 mgKOH/g or less, preferably 1 mgKOH/g or less, and more preferably 0 mgKOH/g. By blending an elastomer resin with an acid value of 10 mgKOH/g or less into the resin composition, the dielectric tangent when the resin film is formed can be reduced and good peel strength can be maintained. On the other hand, if the acid value exceeds 10 mgKOH/g, the dielectric properties deteriorate due to an increase in polar groups, and the compatibility with the (A) component deteriorates, resulting in a decrease in adhesion when the resin film is formed. Therefore, the lower the acid value, the better, and a non-acid-modified one (i.e., an acid value of 0 mgKOH/g) is most suitable as the (C) component of the present invention. In the present invention, when the adhesive polyimide contains a residue derived from dimer diamine, it is possible to develop excellent adhesion, so that even if a non-acid-modified (i.e., a highly aliphatic) elastomer resin is used, a decrease in adhesive strength can be avoided.

The elastomer resin of component (C) preferably has a content of styrene units _{[ -CH2CH} ( _C6H5 )-] in the range of 10 to 65% by weight, more preferably in the range of 20 to 65% by weight, and most preferably in the range of 30 to 60% by weight. If the content of styrene units in the elastomer resin is less than 10% by weight, the elastic modulus of the resin decreases and the handleability as a film deteriorates, whereas if it exceeds 65% by weight, the resin becomes rigid, making it difficult to use as an adhesive, and the rubber component in the elastomer resin decreases, leading to deterioration of the dielectric properties.
In addition, by having the content ratio of styrene units within the above range, the proportion of aromatic rings in the resin film is increased, so that when via holes (through holes) and blind via holes are formed by laser processing in the process of manufacturing a circuit board using the resin film, it is possible to increase the absorbency in the ultraviolet region and further improve the laser processability.

The weight average molecular weight of the elastomer resin of component (C) is preferably, for example, within the range of 50,000 to 300,000, and more preferably within the range of 80,000 to 270,000. If the weight average molecular weight of component (C) is lower than the above range, the effect of improving the peel strength and dielectric properties may be reduced, and conversely, if it is too high, the viscosity of the resin composition may increase, making it difficult to produce a resin film.

As the elastomer resin of component (C), a commercially available product can be appropriately selected and used as long as the acid value is 10 mgKOH/g or less. As such commercially available elastomer resins, for example, A1535HU (trade name), G1652MU (trade name), G1726VS (trade name), G1645VS (trade name), FG1901GT (trade name), G1650MU (trade name), G1654HU (trade name), G1730VO (trade name), MD1653MO (trade name), etc. manufactured by KRATON can be preferably used.

The content of the (C) component in the resin composition relative to 100 parts by weight of the (A) component is in the range of 5 parts by weight to 100 parts by weight, preferably in the range of 10 parts by weight to 90 parts by weight, and more preferably in the range of 20 parts by weight to 80 parts by weight. If the content of the (C) component relative to 100 parts by weight of the (A) component is less than 5 parts by weight, the peel strength may not be sufficiently expressed. On the other hand, if the weight ratio of the (C) component exceeds 100 parts by weight, the adhesiveness when the resin film is formed decreases, and the solid concentration in the resin composition becomes too high, causing an increase in viscosity and decreasing handleability.

<Component (D): Polymerization initiator>
The resin composition may further contain a polymerization initiator as component (D). As the polymerization initiator of component (D), any one generally used as a radical polymerization initiator may be used without any particular limitation, but preferred examples include dihalogen compounds, azo compounds, and organic peroxides. Among these, organic peroxides are preferred. As the polymerization initiator of component (D), a commercially available product may be appropriately selected and used. As such a commercially available polymerization initiator, for example, Perbutyl (registered trademark) P (manufactured by Nippon Oil & Fats Corporation), Perbutyl (registered trademark) C (manufactured by Nippon Oil & Fats Corporation), etc. are preferred.

The content of the (D) component in the resin composition relative to 100 parts by weight of the (A) component is preferably within the range of 0.5 parts by weight to 2.0 parts by weight. If the content of the (D) component relative to 100 parts by weight of the (A) component is less than 0.5 parts by weight, the effect of adding the polymerization initiator may not be fully manifested. On the other hand, if the weight ratio of the (D) component exceeds 2.0 parts by weight, the dielectric tangent may deteriorate and the storage stability and handling properties of the resin composition may decrease.

In addition, adhesive polyimide can be cured by mixing and curing compounds having unsaturated bonds, such as epoxy resins, epoxy resin curing agents, maleimides, activated ester resins, and resins having a styrene skeleton.

Furthermore, the resin composition of the present embodiment may contain a solvent such as an organic solvent. Since the adhesive polyimide has solvent solubility, the resin composition of the present embodiment may be prepared as a polyimide solution (varnish) containing a solvent. As the organic solvent, for example, it is preferable to use a mixed solvent in which one or more selected from N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2-butanone, dimethylsulfoxide (DMSO), hexamethylphosphoramide, N-methylcaprolactam, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diglyme, triglyme, cresol, etc. are mixed with the aromatic hydrocarbon solvent in any ratio.
The content of the solvent is not particularly limited, but it is preferable to adjust the amount used so that the concentration of the polyamic acid or polyimide becomes about 5 to 30% by weight.

The resin composition of the present embodiment may further contain optional components such as inorganic fillers, organic fillers, plasticizers, curing accelerators, coupling agents, pigments, and flame retardants, as necessary, within the scope of the invention. Examples of inorganic fillers include silicon dioxide, aluminum oxide, beryllium oxide, niobium oxide, titanium oxide, magnesium oxide, boron nitride, aluminum nitride, silicon nitride, aluminum fluoride, calcium fluoride, magnesium fluoride, potassium silicofluoride, and metal phosphinates. These may be used alone or in combination of two or more. Other resin components such as epoxy resins, fluororesins, and olefin-based resins may also be added as optional components.

[viscosity]
The viscosity of the resin composition is preferably within a range of, for example, 3000 cps to 100000 cps, more preferably 5000 cps to 50000 cps, which is a viscosity range that improves the handling property when applying the resin composition and makes it easy to form a coating film of uniform thickness. If the viscosity is outside the above range, defects such as uneven thickness and streaks are likely to occur in the film during application by a coater or the like.

[Preparation of resin composition]
The resin composition can be prepared, for example, by blending and mixing the (B) component and, if necessary, the (C) component, the (D) component, etc., into a resin solution of the adhesive polyimide of the (A) component prepared using any solvent. In this case, in order to mix uniformly, the (B), (C) and (D) components may be mixed in a state of being dissolved in a solvent, or a solvent showing high solubility for the (B), (C) and (D) components may be added.

The resin composition of this embodiment has excellent flexibility and thermoplasticity when used to form an adhesive layer. Therefore, it has favorable properties for applications such as adhesive layer materials in FPCs and rigid-flex circuit boards, and adhesives for coverlay films that protect wiring parts.

[Resin film]
The resin film of the present embodiment is a resin film consisting of a single layer or multiple layers including a polyimide layer, and the polyimide layer is formed by forming the adhesive polyimide or the solid content (the remainder excluding the solvent) of the above-mentioned resin composition into a film as a main component. The resin film of the present embodiment has excellent high-frequency characteristics, as well as sufficient adhesiveness (particularly peel strength), solder heat resistance, and flame retardancy for practical use.

The resin film of this embodiment is not particularly limited as long as it is an insulating resin film containing the above-mentioned thermoplastic resin layer, and may be a film (sheet) made of insulating resin only, or may be an insulating resin film laminated on a substrate such as a resin sheet, such as copper foil, glass plate, polyimide film, polyamide film, or polyester film.

(Dielectric constant)
In order to ensure impedance matching when used in a circuit board such as an FPC and to reduce loss of an electric signal, the resin film of the present embodiment has a relative dielectric constant (ε) at 10 GHz measured by a split post dielectric resonator (SPDR) after 24 hours of humidity control under constant temperature and humidity conditions (normal state) of 23° C. and 50% RH, of preferably 3.3 or less, more preferably 3.1 or less. If the relative dielectric constant exceeds 3.3, problems such as loss of an electric signal are likely to occur on the transmission path of a high-frequency signal when used in a circuit board such as an FPC.

(Dielectric tangent)
In addition, in order to reduce loss of electric signals when the resin film of the present embodiment is used in a circuit board such as an FPC, the dielectric loss tangent (Tan δ) at 10 GHz measured by a split post dielectric resonator (SPDR) after 24 hours of humidity control under constant temperature and humidity conditions (normal state) of 23° C. and 50% RH is preferably less than 0.002, more preferably 0.0017 or less. If the dielectric loss tangent is 0.0020 or more, problems such as loss of electric signals are likely to occur on the transmission path of high frequency signals when the resin film is used in a circuit board such as an FPC.

(Glass Transition Temperature)
The resin film of this embodiment preferably has a glass transition temperature (Tg) of 250° C. or less, more preferably in the range of 40° C. or more and 200° C. or less. By making the Tg of the resin film 250° C. or less, thermocompression bonding at a low temperature is possible, so that the internal stress generated during lamination can be alleviated and dimensional change after circuit processing can be suppressed. If the Tg of the resin film exceeds 250° C., the bonding temperature becomes high, and there is a risk of impairing dimensional stability after circuit processing.

(Thickness)
The thickness of the resin film of the present embodiment is preferably, for example, in the range of 5 μm to 125 μm, and more preferably in the range of 8 μm to 100 μm. If the thickness of the resin film is less than 5 μm, there is a risk of problems such as wrinkles occurring during transportation in the production of the resin film, while if the thickness of the resin film exceeds 125 μm, there is a risk of a decrease in productivity of the resin film.

(Tensile Modulus)
The resin film of the present embodiment preferably has a tensile modulus in the range of 0.1 GPa to 3.0 GPa, more preferably in the range of 0.2 GPa to 2.0 GPa, from the viewpoints of reducing the occurrence of wrinkles, preventing air bubbles from being trapped during lamination, and handling properties.

(Maximum elongation)
From the viewpoints of bendability and crack prevention when applied as an insulating resin layer of an FPC, the resin film of the present embodiment preferably has a maximum elongation within the range of 30% to 250%, and more preferably within the range of 100% to 200%.

The resin film of this embodiment has a low dielectric tangent and excellent adhesion, and is therefore useful as an adhesive layer in coverlay films, circuit boards, multilayer circuit boards, adhesive layers in resin-coated copper foils, bond plies, bonding sheets, etc.

(solder heat resistance)
The resin film of this embodiment preferably has a solder heat resistance (dry) of 280° C. or more, and a solder heat resistance (moisture absorption) of 260° C. or more, as measured by the test method and conditions shown in the Examples below. If swelling occurs at the temperature during solder reflow, wiring misalignment and poor conduction will occur, so by having the solder heat resistance (dry, moisture absorption) at the above temperatures or more, the yield in the mounting process can be increased and the reliability of electronic components can be improved. Until now, when evaluated without performing pretreatment such as prior drying, an adhesive film with high solder heat resistance and low dielectric tangent has not been obtained, so there is a demand for one with high solder heat resistance without pretreatment, and the resin film of this embodiment can satisfy such required characteristics.

(Peel Strength)
The resin film of the present embodiment preferably has a peel strength of 1.0 kN/m or more, as measured by the test method and conditions shown in the Examples below. By having a peel strength of 1.0 kN/m or more, sufficient adhesion for practical use can be obtained between the wiring layer and the resin layer after circuit processing.

[Laminate]
The laminate according to one embodiment of the present invention has a substrate and an adhesive layer laminated on at least one surface of the substrate, the adhesive layer being made of the above-mentioned resin film. The laminate may also include any layer other than the above. Examples of the substrate in the laminate include substrates made of inorganic materials such as copper foil and glass plate, and substrates made of resin materials such as polyimide film, polyamide film, and polyester film.
Preferred embodiments of the laminate include a coverlay film and a resin-coated copper foil.

[Coverlay film]
The coverlay film, which is one embodiment of the laminate, has a coverlay film material layer as a substrate and an adhesive layer laminated on one side of the coverlay film material layer, the adhesive layer being made of the above-mentioned resin film. Note that the coverlay film may include any layer other than those described above.

The material of the coverlay film material layer is not particularly limited, but may be, for example, a polyimide-based film such as polyimide resin, polyetherimide resin, or polyamideimide resin, a polyamide-based film, or a polyester-based film. Of these, it is preferable to use a polyimide-based film with excellent heat resistance. In addition, the coverlay film material may contain a black pigment to effectively exhibit light-shielding properties, concealing properties, design properties, etc., and may contain optional components such as a matte pigment that suppresses surface gloss, as long as the effect of improving the dielectric properties is not impaired.

The thickness of the coverlay film material layer is not particularly limited, but is preferably within the range of, for example, 5 μm or more and 100 μm or less.
The thickness of the adhesive layer is not particularly limited, but is preferably within the range of 10 μm to 75 μm, for example.

The coverlay film of the present embodiment can be produced by the method exemplified below.
First, as a first method, a varnish-like resin composition containing a solvent is applied to one side of a film material layer for a coverlay, and then the composition is dried at a temperature of, for example, 80 to 180°C to form an adhesive layer, thereby forming a coverlay film having a film material layer for a coverlay and an adhesive layer.

As a second method, a varnish-like resin composition containing a solvent is applied onto any substrate, dried at a temperature of, for example, 80 to 180°C, and then peeled off to form a resin film for the adhesive layer. This resin film is then thermocompressed with a film material layer for the coverlay at a temperature of, for example, 60 to 220°C to form a coverlay film.

[Copper foil with resin]
The resin-coated copper foil, which is another embodiment of the laminate, is obtained by laminating an adhesive layer on at least one side of a copper foil as a base material, and the adhesive layer is made of the above-mentioned resin film. Note that the resin-coated copper foil of this embodiment may include any layer other than the above.

The thickness of the adhesive layer in the resin-coated copper foil is preferably within the range of 2 to 125 μm, for example, and more preferably within the range of 2 to 100 μm. If the thickness of the adhesive layer is less than the above lower limit, problems such as inability to ensure sufficient adhesion may occur. On the other hand, if the thickness of the adhesive layer exceeds the above upper limit, problems such as reduced dimensional stability may occur. Also, from the viewpoint of lowering the dielectric constant and the dielectric loss tangent, it is preferable that the thickness of the adhesive layer is 3 μm or more.

The material of the copper foil in the resin-coated copper foil is preferably one whose main component is copper or a copper alloy. The thickness of the copper foil is preferably 35 μm or less, and more preferably in the range of 5 to 25 μm. From the viewpoint of production stability and handling, the lower limit of the copper foil thickness is preferably 5 μm. The copper foil may be a rolled copper foil or an electrolytic copper foil. In addition, commercially available copper foils can be used as the copper foil.

The resin-coated copper foil may be prepared, for example, by sputtering a metal onto a resin film to form a seed layer, and then forming a copper layer, for example, by copper plating, or by laminating a resin film and copper foil by a method such as thermocompression bonding. Furthermore, the resin-coated copper foil may be prepared by casting a coating solution of a resin composition on the copper foil to form an adhesive layer, drying the coating film, and then carrying out the necessary heat treatment.

[Metal-clad laminate]
(First aspect)
The metal-clad laminate according to one embodiment of the present invention includes an insulating resin layer and a metal layer laminated on at least one surface of the insulating resin layer, and at least one of the insulating resin layers is made of the resin film. Note that the metal-clad laminate according to this embodiment may include any layer other than those described above.

(Second Aspect)
The metal-clad laminate according to another embodiment of the present invention is a so-called three-layer metal-clad laminate, which includes, for example, an insulating resin layer, an adhesive layer laminated on at least one side of the insulating resin layer, and a metal layer laminated on the insulating resin layer via the adhesive layer, and the adhesive layer is made of the above-mentioned resin film. The three-layer metal-clad laminate may include any layer other than the above. The three-layer metal-clad laminate may have an adhesive layer on one or both sides of the insulating resin layer, and the metal layer may be provided on one or both sides of the insulating resin layer via the adhesive layer. In other words, the three-layer metal-clad laminate may be a single-sided metal-clad laminate or a double-sided metal-clad laminate. A single-sided or double-sided FPC can be manufactured by etching the metal layer of the three-layer metal-clad laminate to form a wiring circuit.

The insulating resin layer in the three-layer metal-clad laminate is not particularly limited as long as it is made of a resin having electrical insulation properties, and examples of such resins include polyimide, epoxy resin, phenolic resin, polyethylene, polypropylene, polytetrafluoroethylene, silicone, and ETFE, but it is preferably made of polyimide. The polyimide layer constituting the insulating resin layer may be a single layer or multiple layers, but it is preferable that it includes a non-thermoplastic polyimide layer.

The thickness of the insulating resin layer in the three-layer metal-clad laminate is preferably within the range of 1 to 125 μm, and more preferably within the range of 5 to 100 μm. If the thickness of the insulating resin layer is less than the above lower limit, problems such as inability to ensure sufficient electrical insulation may occur. On the other hand, if the thickness of the insulating resin layer exceeds the above upper limit, problems such as the metal-clad laminate becoming more susceptible to warping may occur.

The thickness of the adhesive layer in the three-layer metal-clad laminate is preferably in the range of 0.1 to 125 μm, more preferably in the range of 0.3 to 100 μm. In the three-layer metal-clad laminate of the present embodiment, if the thickness of the adhesive layer is less than the above-mentioned lower limit, problems such as inability to ensure sufficient adhesion may occur. On the other hand, if the thickness of the adhesive layer exceeds the above-mentioned upper limit, problems such as reduced dimensional stability may occur. In addition, from the viewpoint of reducing the dielectric constant and the dielectric loss tangent of the entire insulating layer, which is a laminate of an insulating resin layer and an adhesive layer, the thickness of the adhesive layer is preferably 3 μm or more.
The ratio of the thickness of the insulating resin layer to the thickness of the adhesive layer (thickness of the insulating resin layer/thickness of the adhesive layer) is preferably in the range of 0.1 to 3.0, and more preferably in the range of 0.15 to 2.0. By setting such a ratio, it is possible to suppress warping of the three-layer metal-clad laminate. Furthermore, the insulating resin layer may contain a filler as necessary. Examples of the filler include silicon dioxide, aluminum oxide, magnesium oxide, beryllium oxide, boron nitride, aluminum nitride, silicon nitride, aluminum fluoride, calcium fluoride, and metal salts of organic phosphinic acid. These can be used alone or in combination of two or more.

[Circuit board]
The circuit board according to the embodiment of the present invention is formed by wiring the metal layer of the metal-clad laminate according to any of the above embodiments. One or more metal layers of the metal-clad laminate are patterned by a conventional method to form a wiring layer (conductor circuit layer), thereby manufacturing a circuit board such as an FPC. The circuit board may include a coverlay film that covers the wiring layer.

The following examples are provided to more specifically explain the features of the present invention. However, the scope of the present invention is not limited to the examples. In the following examples, the various measurements and evaluations are as follows, unless otherwise noted.

[Measurement of weight average molecular weight (Mw) of polyimide]
The weight average molecular weight was measured by gel permeation chromatography (manufactured by Tosoh Corporation, product name: HLC-8220GPC was used). Polystyrene was used as a standard substance, and tetrahydrofuran (THF) was used as a developing solvent.

[Hydroxyl equivalent]
The measurement was performed in accordance with JIS K 0070. Specifically, a potentiometric titrator was used, 1,4-dioxane was used as a solvent, acetylation was performed with 1.5 mol/L acetyl chloride, excess acetyl chloride was decomposed with water, and titration was performed with 0.5 mol/L potassium hydroxide.

[Phosphorus content]
Sulfuric acid, hydrochloric acid, and perchloric acid were added to the sample, which was then heated and wet-ashed to convert all phosphorus atoms into orthophosphate. Metavanadate and molybdate were reacted in the sulfuric acid acid solution, and the absorbance of the resulting phosphorus vanadate molybdate complex was measured at 420 nm. The phosphorus atom content was expressed in percentage based on a calibration curve prepared in advance using potassium dihydrogen phosphate.

[Field desorption mass spectrometry (FD-MS)]
The molecular weight was measured using a JEOL JMS-T100GCV.

[Measurement of storage modulus]
The measurement was carried out using a dynamic viscoelasticity measuring device (DMA: manufactured by TA Instruments, product name: RSA-G2).
Polyimides having a storage modulus of 1.0×10 ⁹ Pa or more at 30° C. and a storage modulus of 3.0×10 ⁸ Pa or more at 280° C. were defined as “non-thermoplastic polyimides”, and polyimides having a storage modulus of 1.0×10 ⁸ Pa or more at 30° C. and a storage modulus of less than 3.0×10 ⁷ Pa at 280° C. were defined as “thermoplastic polyimides”.

[Evaluation of dielectric properties]
Using a vector network analyzer (manufactured by Agilent, product name: Vector Network Analyzer E8363C) and an SPDR resonator, the polyimide film (cured polyimide film) was left to stand for 24 hours under conditions of a temperature of 23° C. and a humidity of 50% RH, and then the relative dielectric constant (ε) and dielectric loss tangent (Tan δ) at a frequency of 10 GHz were measured.

[Glass transition temperature (Tg)]
The adhesive sheet was pressed under conditions of temperature: 160°C, pressure: 3.5 MPa, and time: 60 minutes, and cut into test pieces measuring 5 mm x 20 mm. Measurements were performed using a dynamic viscoelasticity measuring device (DMA: manufactured by TA Instruments, product name: RSA-G2) at a heating rate of 4°C/min from 30°C to 200°C and a frequency of 11 Hz, and the temperature at which the change in elastic modulus (tan δ) was maximum was determined as the glass transition temperature.

[Tensile modulus and maximum elongation]
Using a tension tester (Tensilon manufactured by Orientec), a tensile test was carried out at 50 mm/min on a test piece of the resin film (width: 12.7 mm, length: 127 mm) to determine the tensile modulus and maximum elongation at 25°C.

[Solder heat resistance test (dry)]
One of the copper foils of a double-sided copper-clad laminate (manufactured by Nippon Steel Chemical & Material Co., Ltd., product name: ESPANEX MB12-25-12UEG) was etched away, and the other copper foil surface and the adhesive sheet were laminated in a manner sandwiched between the copper foils, and pressed under the conditions of temperature: 160°C, pressure: 3.5 MPa, and time: 60 minutes. The test piece with the copper foil was dried at 135°C/60 minutes, and then immersed for 10 seconds in a solder bath set at each evaluation temperature from 260°C to 300°C in 10°C increments, and the adhesion state was observed to confirm the presence or absence of defects such as foaming, swelling, and peeling. The judgment was ◯ (good) when no defects were observed at 280°C, and × (bad) when defects were observed.

[Solder heat resistance test (moisture absorption)]
The copper foil on one side of a double-sided copper-clad laminate (manufactured by Nippon Steel Chemical & Material Co., Ltd., product name: ESPANEX MB12-25-12UEG) was etched away, and the other copper foil surface and adhesive sheet were laminated in a manner sandwiched between the copper foils, and pressed under the conditions of temperature: 160°C, pressure: 3.5 MPa, and time: 60 minutes. The test piece with the copper foil was left at 40°C and relative humidity: 90% RH for 72 hours, and then immersed in a solder bath set at each evaluation temperature from 240°C to 300°C in 10°C increments for 10 seconds, and the adhesion state was observed to confirm the presence or absence of defects such as foaming, swelling, and peeling. The judgment was ◯ (good) when no defects were observed at 260°C, and × (bad) when defects were observed.

[Peel strength measurement]
A double-sided copper-clad laminate (manufactured by Nippon Steel Chemical & Material Co., Ltd., trade name: Espanex MB12-25-12UEG) was cut to a width of 50 mm and a length of 100 mm, and then the adhesive sheet to be tested was placed on the copper foil side of the sample in which the copper foil on one side had been etched away, and a polyimide film (manufactured by Toray DuPont Co., Ltd., trade name: Kapton 50EN-S) was further laminated on top of this adhesive sheet, and pressed under conditions of temperature: 160 ° C., pressure: 3.5 MPa, and time: 60 minutes to prepare a laminate. This laminate was cut to a width of 5 mm to prepare a test piece, and a tensile tester (manufactured by Toyo Seiki Seisakusho, trade name: Strograph VE) was used to measure the peel strength between the adhesive sheet and the copper foil when the test piece was pulled in the 180 ° direction at a speed of 50 mm / min, and this was taken as the peel strength.

[Method for evaluating film retention]
The adhesive sheet was cut into a test piece 20 mm wide and 20 mm long, folded along the diagonal line to create a crease, and then opened to observe the condition of the film. If the test piece had no cracks even after the crease was created and opened, it was rated as "good," and if it had any cracks even in part, it was rated as "no good."

[Flame retardancy evaluation method]
Flame retardancy was evaluated by the following method. A polyimide film (manufactured by Toray DuPont Co., Ltd., product name: Kapton 50EN-S) was laminated on both sides of two resin films laminated to a thickness of 50 μm, and pressed under the conditions of temperature: 160 ° C., pressure: 3.5 MPa, and time: 60 minutes. A sample was cut to 200 ± 5 mm × 50 ± 1 mm, rolled into a cylindrical shape with a diameter of about 12.7 mm and a length of 200 ± 5 mm, and a test piece conforming to the UL94VTM standard was prepared and a combustion test was performed. If the time until flame extinction was within 11 seconds, it was marked as "○" (good), and if it exceeded 11 seconds, it was marked as "×" (bad).

[Method for measuring amine value]
Approximately 2 g of the dimer diamine composition is weighed into a 200-250 mL Erlenmeyer flask, and phenolphthalein is used as an indicator. A 0.1 mol/L ethanolic potassium hydroxide solution is added dropwise until the solution turns light pink, and the composition is dissolved in approximately 100 mL of neutralized butanol. 3-7 drops of phenolphthalein solution are added thereto, and titration is performed with 0.1 mol/L ethanolic potassium hydroxide solution while stirring until the sample solution turns light pink. Five drops of bromophenol blue solution are added thereto, and titration is performed with 0.2 mol/L hydrochloric acid/isopropanol solution while stirring until the sample solution turns yellow.
The amine value is calculated according to the following formula (1).
Amine value = {(V ₂ × C ₂ ) - (V ₁ × C ₁ )} × M _KOH / m (1)
Here, the amine value is a value expressed in mg-KOH/g, M _KOH is the molecular weight of potassium hydroxide, 56.1, V and C are the volume and concentration of the solution used in the titration, respectively, and the subscripts 1 and 2 represent a 0.1 mol/L ethanolic potassium hydroxide solution and a 0.2 mol/L hydrochloric acid/isopropanol solution, respectively, and m is the sample weight expressed in grams.

[GPC and Chromatogram Area Percentage Calculation]
(a) Dimer diamine; (b) Monoamine compound obtained by substituting a terminal carboxylic acid group of a monobasic acid compound having 10 to 40 carbon atoms with a primary aminomethyl group or an amino group; (c) Amine compound obtained by substituting a terminal carboxylic acid group of a polybasic acid compound having a hydrocarbon group having 41 to 80 carbon atoms with a primary aminomethyl group or an amino group (excluding the above dimer diamine).

For GPC, 20 mg of the dimer diamine composition was pretreated with 200 μL of acetic anhydride, 200 μL of pyridine, and 2 mL of THF to prepare a 100 mg solution, which was then diluted with 10 mL of THF (containing 1000 ppm of cyclohexanone). The prepared sample was measured using a Tosoh Corporation product name: HLC-8220GPC under the following conditions: column: TSK-gel G2000HXL, G1000HXL, flow rate: 1 mL/min, column (oven) temperature: 40°C, injection volume: 50 μL. Cyclohexanone was used as a standard substance to correct the elution time.

In this case, the retention times were adjusted so that the peak top of the cyclohexanone main peak was at a retention time of 27 to 31 minutes, and the period from the peak start to the peak end of the cyclohexanone main peak was 2 minutes, and the peak top of the main peak excluding the cyclohexanone peak was at a retention time of 18 to 19 minutes, and the period from the peak start to the peak end of the main peak excluding the cyclohexanone peak was 2 minutes to 4 minutes 30 seconds.
(a) Component represented by the main peak;
(b) A component represented by a GPC peak detected at a time later than the minimum retention time of the main peak;
(c) a component represented by a GPC peak detected at a time earlier than the minimum retention time of the main peak;
was detected.

The abbreviations used in the examples represent the following compounds.
BTDA: 3,3',4,4'-benzophenonetetracarboxylic dianhydride VAB: 2,2'-divinyl-4,4'-diaminobiphenyl DDA: product name: PRIAMINE 1075, manufactured by Croda Japan Co., Ltd., distilled and purified (component a: 99.2%, component b: 0%, component c: 0.8%, amine value: 210 mgKOH/g)
N-12: dodecanedioic acid dihydrazide NMP: N-methyl-2-pyrrolidone 6FDA: 4,4'-(hexafluoroisopropylidene)diphthalic anhydride BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride Elastomer resin 1: manufactured by KRATON, trade name: A1535HU (hydrogenated polystyrene elastomer resin, styrene unit content: 58% by weight, specific gravity: 0.96, no acid value)
In the above DDA, the "%" of component a, component b, and component c means the area percentage of the chromatogram in GPC measurement. The molecular weight of DDA was calculated by the following formula (1).
Molecular weight = 56.1 × 2 × 1000 / amine value (1)

(Synthesis Example 1)
<Preparation of phosphorus-containing phenol (phosphorus compound A)>
A 2-liter, four-neck flask equipped with a stirrer, a thermometer, and a hydrochloric acid recovery device (a condenser connected to a water scrubber) was charged with 1,500 g of phosphorus oxychloride, 471 g of phenol, and 1.2 g of magnesium chloride as a catalyst.

The resulting mixed solution was gradually heated to 90°C over a period of about 3 hours while stirring to allow the reaction to proceed, and the hydrogen chloride (hydrochloric acid gas) generated was collected using a water scrubber. The pressure inside the flask was then gradually reduced to 12 kPa at 120°C, and unreacted phosphorus oxychloride and phenol, as well as the by-product hydrogen chloride, were removed to obtain 1,055 g of monophenyl phosphorodichloridate (MPC).

A 2-liter, four-neck flask equipped with a stirrer, thermometer, dropping funnel, and condenser was charged with 822 g of 2,3,5-trimethylhydroquinone, 6.3 g of aluminum chloride as a catalyst, and 1,000 g of 1,2-dichlorobenzene as a solvent. The dropping funnel was also charged with 570 g of the above MPC.

The mixed solution in the four-neck flask was heated to 110°C while stirring, and while maintaining the same temperature (110°C), the MPC in the dropping funnel was added dropwise over 2 hours. After the dropwise addition was completed, the mixture was gradually heated to 160°C and stirred for 4 hours to obtain the reaction product. It was then cooled to 105°C, and the pressure in the flask was gradually reduced to 6.3 kPa, and the by-product hydrogen chloride was removed.

The resulting reaction product was washed with dilute hydrochloric acid and water, neutralized and washed with an aqueous sodium carbonate solution, and washed again with water. It was then heated to 150°C and reduced in pressure to 1 kPa to recover water and 1,2-dichlorobenzene. It was then subjected to steam distillation at 110°C under reduced pressure of 1 kPa to remove low boiling points, and cooled to room temperature to obtain 1,195 g of a phosphorus-containing phenolic compound (phosphorus compound A) as a black-brown solid. The phosphorus content of the resulting mixture of phosphorus compound A was 6.5%, and the hydroxyl equivalent was 272 g/eq.

(Synthesis Example 2)
<Preparation of phosphorus-containing vinylbenzyl ether compound (phosphorus compound B)>
In a separable glass flask equipped with a stirrer, a thermometer, and a cooling tube, 200.0 g of phosphorus compound A and 133.2 g of diethylene glycol dimethyl ether were charged and dissolved in a nitrogen atmosphere at 75° C. 134.0 g of CMS-P (trade name, manufactured by AGC Seimi Chemical Co., Ltd.) was added, and after the mixture became uniform, 10.0 g of tetrabutylammonium bromide and 222.4 g of a 50% aqueous potassium carbonate solution were added and reacted for 10 hours.

The reaction solution was then concentrated and dissolved in 674.4 g of toluene, neutralized with a 10% aqueous solution of sodium dihydrogen phosphate, and washed with water. The solution was then dehydrated, filtered, and the solvent was concentrated to obtain 340.0 g of a toluene solution of a phosphorus-containing vinylbenzyl ether compound (phosphorus compound B). The resulting phosphorus compound B was analyzed by FD-MS, and a peak at molecular weight 674 was confirmed, confirming that the compound with the following structure was the main component. The phosphorus content was 4.7%.

(Synthesis Example 3)
<Preparation of phosphorus-containing methacryloyl compound (phosphorus compound C)>
In a glass separable flask equipped with a stirrer, a thermometer, a cooling tube, and a dropping funnel, 200.0 g of phosphorus compound A, 133.2 g of tetrahydrofuran, and 104.0 g of triethylamine were charged and dissolved, and then cooled in an ice bath to 5° C. or less. In a nitrogen atmosphere, 89.6 g of methacryloyl chloride was added dropwise over 1 hour, and the reaction was continued for another 2 hours.

The reaction solution was then concentrated and dissolved in 608.0 g of toluene, and washed in that order with hydrochloric acid, an aqueous sodium carbonate solution, and water. After washing with water, the solution was dehydrated, filtered, and the solvent was further concentrated to obtain 212.64 g of a toluene solution of a phosphorus-containing methacryloyl compound (phosphorus compound C). The resulting phosphorus compound C was analyzed by FD-MS, and a peak at a molecular weight of 578 was confirmed, confirming that the compound of the following structure was the main component. The phosphorus content was also 5.6%.

[Example 1]
A polyamic acid solution was prepared by charging 58.71 g of BTDA (0.1819 mol), 87.01 g of DDA (0.1629 mol), 4.28 g of VAB (0.0181 mol), 210 g of NMP and 140 g of xylene into a 1000 ml separable flask and thoroughly mixing for 1 hour at 40° C. The polyamic acid solution was heated to 190° C., heated and stirred for 10 hours, and 125 g of xylene was added to complete imidization to prepare polyimide solution 1 (solid content: 32.7% by weight, weight average molecular weight: 56,611, thermoplastic polyimide), which was named polyimide varnish 1a.

[Example 2]
To 100 g of the polyimide solution 1 prepared in Example 1, 5.6 g of phosphorus-containing vinylbenzyl ether compound B, 6.5 g of elastomer resin 1, and 0.3 g of Perbutyl P (trade name, manufactured by NOF Corporation) were mixed, and the mixture was diluted with xylene and NMP to a solid content of 30% by weight, followed by stirring to prepare a polyimide varnish 2a.

[Example 3]
A polyamic acid solution was prepared by charging 59.97g of BTDA (0.1857 mol), 83.51g of DDA (0.1563 mol), 6.52g of VAB (0.0276 mol), 210g of NMP and 140g of xylene into a 1000ml separable flask and thoroughly mixing for 1 hour at 40°C. This polyamic acid solution was heated to 190°C, heated and stirred for 10 hours, and 125g of xylene was added to complete imidization to prepare polyimide solution 2 (solid content: 31% by weight, weight average molecular weight: 52,515, thermoplastic polyimide), which was named polyimide varnish 3a.

[Example 4]
5.6 g of phosphorus compound B, 6.5 g of elastomer resin 1, and 0.3 g of perbutyl P were mixed with 100 g of polyimide solution 2 prepared in Example 3, and the mixture was diluted with xylene and NMP to a solid content of 30% by weight, and stirred to prepare polyimide varnish 4a.

[Example 5]
A polyimide varnish 5a was prepared in the same manner as in Example 4, except that the amount of phosphorus compound B was 7.5 g.

[Example 6]
A polyimide varnish 6a was prepared in the same manner as in Example 4, except that 7.5 g of phosphorus compound C was used instead of 5.6 g of phosphorus compound B.

[Example 7]
A 1000 ml separable flask was charged with 71.81 g of 6FDA (0.1613 mol), 72.53 g of DDA (0.1358 mol), 5.66 g of VAB (0.0240 mol), 210 g of NMP and 140 g of xylene, and mixed thoroughly for 1 hour at 40° C. to prepare a polyamic acid solution. The polyamic acid solution was heated to 190° C., heated and stirred for 10 hours, and 125 g of xylene was added to prepare a polyimide solution 3 (solid content: 32.6 wt %, weight average molecular weight: 54,197, thermoplastic polyimide) in which imidization was completed, and this was named polyimide varnish 7a.

[Example 8]
A polyamic acid solution was prepared by charging 56.73 g of BPDA (0.1924 mol), 86.52 g of DDA (0.1619 mol), 6.75 g of VAB (0.0286 mol), 210 g of NMP and 140 g of xylene into a 1000 ml separable flask and thoroughly mixing for 1 hour at 40° C. The polyamic acid solution was heated to 190° C., heated and stirred for 10 hours, and 125 g of xylene was added to complete imidization to prepare polyimide solution 4 (solid content: 32.5% by weight, weight average molecular weight: 55,345, thermoplastic polyimide), which was named polyimide varnish 8a.

[Example 9]
Polyimide varnish 9a was prepared in the same manner as in Example 4, except that elastomer resin 1 was not blended.

Comparative Example 1
A polyamic acid solution was prepared by charging 55.51 g of BTDA (0.1721 mol), 94.49 g of DDA (0.1735 mol), 210 g of NMP, and 140 g of xylene into a 1000 ml separable flask and thoroughly mixing for 1 hour at 40° C. The polyamic acid solution was heated to 190° C., heated and stirred for 10 hours, and 125 g of xylene was added to complete imidization to prepare polyimide solution 5 (solid content: 31% by weight, weight average molecular weight: 80,900, thermoplastic polyimide), which was named polyimide varnish 10a.

Comparative Example 2
1.12 g of N-12 was mixed with 100 g of the polyimide solution 5 prepared in Comparative Example 1, and the mixture was diluted with xylene and NMP so that the solid content became 31% by weight, and stirred to prepare a polyimide varnish 11a.

Table 1 shows the formulations for Examples 1 to 9 and Comparative Examples 1 and 2.

[Example 10]
The polyimide varnish 1a prepared in Example 1 was applied to one side of a release-treated PET film, dried at 100°C for 5 minutes, then dried at 120°C for 10 minutes, and peeled off to prepare a resin sheet 1b (thickness: 25 µm).
The various evaluation results of the adhesive sheet 1b are as follows.
Dielectric constant: 2.7, dielectric loss tangent: 0.0017, flame retardancy: ○

[Example 11]
A resin sheet 2b was prepared in the same manner as in Example 10 using the polyimide varnish 2a.
The various evaluation results of the adhesive sheet 2b are as follows.
Relative dielectric constant: 2.6, dielectric loss tangent: 0.0015, tensile modulus: 0.5 GPa, maximum elongation: 171%, Tg: 44°C, film retention: good, solder heat resistance test (dry): good, solder heat resistance test (moisture absorption): good, peel strength: 1.2 kN/m, flame retardancy: good

[Example 12]
A resin sheet 3b was prepared in the same manner as in Example 10 using the polyimide varnish 3a.
The various evaluation results of the adhesive sheet 3b are as follows.
Dielectric constant: 2.6, dielectric tangent: 0.0016, flame retardancy: ○

[Example 13]
A resin sheet 4b was prepared in the same manner as in Example 10 using the polyimide varnish 4a.
The various evaluation results of the adhesive sheet 4b are as follows.
Relative dielectric constant: 2.6, dielectric loss tangent: 0.0014, tensile modulus: 0.7 GPa, maximum elongation: 199%, Tg: 49°C, film retention: good, solder heat resistance test (dry): good, solder heat resistance test (moisture absorption): good, peel strength: 1.2 kN/m, flame retardancy: good

[Example 14]
A resin sheet 5b was prepared in the same manner as in Example 10 using the polyimide varnish 5a.
The various evaluation results of the adhesive sheet 5b are as follows.
Relative dielectric constant: 2.6, dielectric loss tangent: 0.0014, tensile modulus: 0.7 GPa, maximum elongation: 162%, Tg: 46°C, film retention: good, solder heat resistance test (dry): good, solder heat resistance test (moisture absorption): good, peel strength: 1.1 kN/m, flame retardancy: good

[Example 15]
A resin sheet 6b was prepared in the same manner as in Example 10 using the polyimide varnish 6a.
The various evaluation results of the adhesive sheet 6b are as follows.
Relative dielectric constant: 2.7, dielectric loss tangent: 0.0017, tensile modulus: 0.8 GPa, maximum elongation: 183%, Tg: 49°C, film retention: good, solder heat resistance test (dry): good, solder heat resistance test (moisture absorption): good, peel strength: 1.1 kN/m, flame retardancy: good

[Example 16]
A resin sheet 7b was prepared in the same manner as in Example 10 using the polyimide varnish 7a.
The various evaluation results of the adhesive sheet 7b are as follows.
Dielectric constant: 2.5, dielectric tangent: 0.0014, flame retardancy: ○

[Example 17]
A resin sheet 8b was prepared in the same manner as in Example 10 using the polyimide varnish 8a.
The various evaluation results of the adhesive sheet 8b are as follows.
Dielectric constant: 2.7, dielectric loss tangent: 0.0015, flame retardancy: ○

[Example 18]
A resin sheet 9b was prepared in the same manner as in Example 10 using the polyimide varnish 9a.
The various evaluation results of the adhesive sheet 9b are as follows.
Relative dielectric constant: 2.7, dielectric loss tangent: 0.0016, tensile modulus: 0.9 GPa, maximum elongation: 130%, Tg: 47°C, film retention: good, solder heat resistance test (dry): good, solder heat resistance test (moisture absorption): good, peel strength: 0.5 kN/m, flame retardancy: good

Comparative Example 4
A resin sheet 10b was prepared in the same manner as in Example 10 using the polyimide varnish 10a.
The various evaluation results of the adhesive sheet 10b are as follows.
Dielectric constant: 2.6, dielectric loss tangent: 0.0021, flame retardancy: x

Comparative Example 5
A resin sheet 11b was prepared in the same manner as in Example 10 using the polyimide varnish 11a.
The various evaluation results of the adhesive sheet 11b are as follows.
Relative dielectric constant: 2.6, dielectric loss tangent: 0.0021, tensile modulus: 0.5 GPa, maximum elongation: 119%, Tg: 44°C, film retention: good, solder heat resistance test (dry): x, solder heat resistance test (moisture absorption): x, peel strength: 1.0 kN/m, flame retardancy: x

The above results are summarized in Table 2.

As can be seen from Table 2, compared to resin sheets 10b and 11b of comparative examples 4 and 5, resin sheets 1b to 9b of examples 10 to 18, which had different resins, had a dielectric tangent of 0.0017 or less, high peel strength, and good solder heat resistance and flame retardancy. From these results, it was confirmed that the adhesive sheet as a resin film according to this embodiment can be expected to reduce transmission loss in the high frequency band of, for example, about 10 to 20 GHz, and has excellent peel strength, solder heat resistance, and flame retardancy while maintaining flexibility and film retention.

As shown in the above examples, polyimides made from aliphatic diamines and vinyl-containing diamines showed clear improvements in dielectric properties, and resin compositions using these polyimides also showed improvements in peel strength, solder heat resistance, and flame retardancy.

These results confirm that the resin film according to this embodiment can be used effectively as a material for circuit boards such as high-frequency compatible FPCs, for example in various high-frequency signal transmission devices, such as direct conversion type receivers.

Although the embodiment of the present invention has been described in detail above for the purpose of illustration, the present invention is not limited to the above embodiment, and various modifications are possible.

Claims (11)

A polyimide containing a tetracarboxylic acid residue derived from a tetracarboxylic acid anhydride component and a diamine residue derived from a diamine component,
the diamine residues derived from a dimer diamine composition mainly composed of a dimer diamine in which two terminal carboxylic acid groups of a dimer acid are substituted with primary aminomethyl groups or amino groups are contained in an amount in the range of 40 mol % or more and 95 mol % or less relative to the total diamine residues;
1. A polyimide comprising a diamine compound having a biphenyl skeleton or a naphthalene skeleton, the biphenyl skeleton or the naphthalene skeleton having at least one substituent having a carbon-carbon double bond selected from the group consisting of a vinyl group, an acrylic group, a methacrylic group, and an allyl group, in an amount of 5 mol % or more and 25 mol % or less relative to all diamine residues, the diamine compound having such a diamine residue. 2. A polyimide comprising a diamine compound having a biphenyl skeleton or a naphthalene skeleton, the biphenyl skeleton or the naphthalene skeleton having at least one substituent having a carbon-carbon double bond selected from the group consisting of a vinyl group, an acrylic group, a methacrylic group, and an allyl group, the diamine compound comprising a biphenyl skeleton or a naphthalene skeleton having a biphenyl skeleton or a naphthalene skeleton, the biphenyl skeleton or the naphthalene skeleton having at least one substituent having a carbon-carbon double bond selected from the group consisting of a vinyl group, an acrylic group, a methacrylic group, and an allyl group, the diamine compound having such a diamine residue in an amount of 5 mol % or more and ... The following components (A) and (B):
(A) the polyimide according to claim 1, and (B) a crosslinking agent;
and the content of the (B) component relative to 100 parts by weight of the (A) component is within the range of 5 parts by weight or more and 30 parts by weight or less. Furthermore, the following component (C):
(C) an elastomer resin,
and the content of the (C) component per 100 parts by weight of the (A) component is within the range of 5 parts by weight or more and 100 parts by weight or less. Further, the component (D) is described below:
(D) a polymerization initiator,
and the content of the (D) component is within the range of 0.5 parts by weight or more and 2.0 parts by weight or less per 100 parts by weight of the (A) component. A resin film containing the polyimide according to claim 1. The resin film according to claim 5, characterized in that after 24 hours of conditioning under constant temperature and humidity conditions (normal conditions) of 23°C and 50% RH, the dielectric loss tangent (Tan δ) at 10 GHz measured with a split post dielectric resonator (SPDR) is less than 0.002. A laminate having a substrate and an adhesive layer laminated on at least one surface of the substrate,
A laminate, wherein the adhesive layer is made of the resin film according to claim 5 or 6. A coverlay film having a coverlay film material layer and an adhesive layer laminated on the coverlay film material layer,
A coverlay film, wherein the adhesive layer is made of the resin film according to claim 5 or 6. A resin-coated copper foil in which an adhesive layer and a copper foil are laminated,
7. A resin-coated copper foil, wherein the adhesive layer is made of the resin film according to claim 5 or 6. A metal-clad laminate having an insulating resin layer and a metal layer laminated on at least one surface of the insulating resin layer,
7. A metal-clad laminate, wherein at least one of the insulating resin layers is made of the resin film according to claim 5. A circuit board obtained by wiring the metal layer of the metal-clad laminate described in claim 10.