JP7598756B2 - Resin films, metal-clad laminates and circuit boards - Google Patents

Description

The present invention relates to a resin film that is useful, for example, as a circuit board material, and to a metal-clad laminate and a circuit board that use the same.

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 smartphones, as well as components such as cables and connectors.

In addition to higher density, the performance of devices has improved, so there is also a need to accommodate higher frequencies of transmitted signals. When transmitting high-frequency signals, if there is a large transmission loss in the transmission path, problems such as loss of electrical signals and longer signal delay times will occur. For this reason, reducing transmission loss will become important in the future for FPCs as well. In order to accommodate high-frequency signal transmission, it is being considered to use fluororesins with low dielectric constants and low dielectric loss tangents as the dielectric layer of FPC materials (for example, Patent Documents 1 and 2).

Patent Document 1 discloses a CCL with a structure in which a non-thermoplastic polyimide layer is used as a base layer, a fluororesin adhesive layer is laminated on one or both sides of the base layer, and copper foil is further laminated on top of it. However, the laminate structure of Patent Document 1 requires the base layer to ensure dimensional stability, so the thickness of the adhesive layer cannot be made larger than that of the base layer, which is problematic in that there is a limit to the effect of improving the dielectric properties.

Among fluororesins, polytetrafluoroethylene (hereinafter sometimes abbreviated as PTFE) has excellent dielectric properties, but has issues with dimensional stability and low adhesion to other layers. For this reason, Patent Document 2 uses tetrafluoroethylene-hexafluoropropylene copolymer (FEP) and tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA) as fluororesins, and PTFE is positioned as a comparative example with significantly inferior peel strength compared to these.

International Publication No. WO2020/213515 JP 2017-24265 A

The object of the present invention is to provide a resin film, a metal-clad laminate, and a circuit board that use PTFE, can reduce transmission loss even in the transmission of high-frequency signals, and has excellent interlayer adhesion and dimensional stability.

As a result of intensive research, the inventors discovered that the above problems could be solved by forming a resin film with a sandwich structure in which a PTFE layer is sandwiched between adhesive layers having a predetermined storage modulus, and thus completed the present invention.

The resin film of the present invention is a resin film comprising a polytetrafluoroethylene layer, a first adhesive layer laminated on one side of the polytetrafluoroethylene layer, and a second adhesive layer laminated on the side of the polytetrafluoroethylene layer opposite the first adhesive layer.
The resin film of the present invention is characterized in that the storage modulus of the first adhesive layer and the second adhesive layer at 50°C is independently 1800 MPa or less, and the maximum value of the storage modulus at 180 to 260°C is independently 800 MPa or less.

The resin film of the present invention may have a dielectric loss tangent of 0.0016 or less at 10 GHz for the entire resin film.

In the resin film of the present invention, the first adhesive layer and the second adhesive layer may each have a glass transition temperature (Tg) of 180°C or less.

In the resin film of the present invention, the first adhesive layer and the second adhesive layer may contain polyimide as a resin component. In this case, the polyimide may contain an acid anhydride residue derived from a tetracarboxylic acid anhydride component and a diamine residue derived from a diamine component, and may contain 50 mol% or more of diamine residues derived from a diamine derived from a dimer acid in which two terminal carboxylic acid groups of the dimer acid are substituted with primary aminomethyl groups or amino groups, relative to the total diamine residues.

The resin film of the present invention may have the following relationship, where the thickness of the polytetrafluoroethylene layer is TFE, the thickness of the first adhesive layer is T _B1 , and the thickness of the second adhesive layer is T _B2 .
0.15≦(T _B1 +T _B2 )/(T _FE +T _B1 +T _B2 )≦0.70

The metal-clad laminate of the present invention includes a first single-sided metal-clad laminate having a first metal layer and a first insulating resin layer laminated on at least one surface of the first metal layer;
a second single-sided metal-clad laminate having a second metal layer and a second insulating resin layer laminated on at least one surface of the second metal layer;
The metal-clad laminate includes an intermediate resin layer arranged so as to abut the first insulating resin layer and the second insulating resin layer, and laminated between the first single-sided metal-clad laminate and the second single-sided metal-clad laminate.
The metal-clad laminate of the present invention is characterized in that the intermediate resin layer is made of any one of the resin films described above.

The metal-clad laminate of the present invention may have a total thickness T1 of the first insulating resin layer, the intermediate resin layer, and the second insulating resin layer in the range of 50 to 500 μm, and the ratio (T2/T1) of the thickness T2 of the intermediate resin layer to the total thickness T1 may be in the range of 0.50 to 0.90.

In the metal-clad laminate of the present invention, the first insulating resin layer and the second insulating resin layer may both have a multilayer structure in which a thermoplastic polyimide layer, a non-thermoplastic polyimide layer, and a thermoplastic polyimide layer are laminated in this order, and the intermediate resin layer may be provided in contact with the two thermoplastic polyimide layers.

In the metal-clad laminate of the present invention, the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer may contain tetracarboxylic acid residues and diamine residues, and the content of diamine residues derived from a diamine compound represented by the following general formula (A1) may be 80 molar parts or more per 100 molar parts of all diamine residues.

In formula (A1), the linking group Z represents a single bond or -COO-, Y independently represents a monovalent hydrocarbon having 1 to 3 carbon atoms, which may be substituted with a halogen atom or a phenyl group, an alkoxy group having 1 to 3 carbon atoms, a perfluoroalkyl group having 1 to 3 carbon atoms, or an alkenyl group, n represents an integer from 0 to 2, and p and q independently represent integers from 0 to 4.

The circuit board of the present invention includes a first circuit board having a first wiring layer and a first insulating resin layer laminated on at least one surface of the first wiring layer;
a second circuit board having a second wiring layer and a second insulating resin layer laminated on at least one surface of the second wiring layer;
an intermediate resin layer arranged so as to abut the first insulating resin layer and the second insulating resin layer, and laminated between the first circuit board and the second circuit board.
The circuit board of the present invention is characterized in that the intermediate resin layer is made of any one of the resin films described above.

The resin film of the present invention has a sandwich structure in which a polytetrafluoroethylene (PTFE) layer is sandwiched between adhesive layers having a predetermined storage modulus, and therefore has excellent dielectric properties and dimensional stability. That is, even in an environment with large humidity changes, the change in dielectric tangent is small, and when applied as an insulating layer of a circuit board such as a rigid board or a flexible board, the transmission loss can be effectively reduced. In addition, by laminating an adhesive layer having a predetermined storage modulus on the PTFE layer, it is possible to compensate for the shortcomings of the PTFE layer, which has a high thermal expansion coefficient, poor dimensional stability, and low adhesion to other insulating films.
Therefore, in a circuit board using the resin film of the present invention, it is possible to reduce transmission loss during high-frequency signal transmission, and to ensure excellent interlayer adhesion and dimensional stability.
In addition, since the metal-clad laminate of the present invention has a structure in which two single-sided metal-clad laminates are bonded together with the above-mentioned resin film interposed therebetween, it is possible to increase the thickness of the insulating resin layer, thereby reducing transmission loss during high-frequency signal transmission, and also to have excellent dimensional stability.
Therefore, by using the resin film or metal-clad laminate of the present invention, it becomes possible to accommodate higher frequencies in circuit boards, and it is also possible to improve reliability and yield.

1 is a schematic diagram showing a cross-sectional structure of a resin film according to an embodiment of the present invention. 1 is a schematic diagram showing a configuration of a metal-clad laminate according to one embodiment of the present invention. FIG. 1 is a schematic cross-sectional view showing a configuration of a metal-clad laminate according to a preferred embodiment of the present invention.

The embodiment of the present invention will be explained with reference to the drawings as appropriate.

[Resin film]
Fig. 1 is a schematic diagram showing the structure of a resin film (A) according to one embodiment of the present invention. The resin film (A) includes a PTFE layer (FE), a first adhesive layer (B1) laminated on one side of the PTFE layer (FE), and a second adhesive layer (B2) laminated on the opposite side of the PTFE layer (FE) from the first adhesive layer (B1). The resin film (A) has a sandwich structure in which the PTFE layer (FE) is sandwiched between the first adhesive layer (B1) and the second adhesive layer (B2).

[PTFE layer]
The PTFE layer (FE) may be a layer containing PTFE as the main component of the resin component, preferably 70% by weight or more of the resin component, more preferably 90% by weight or more of the resin component, and most preferably the entire resin component. The main component of the resin component means a component contained in more than 50% by weight of the total resin component. PTFE has almost no frequency dependence of the dielectric properties, has very excellent dielectric properties, and also contributes to improving flame retardancy.

In order to improve the dielectric properties of the entire resin film (A), the PTFE layer (FE) should preferably have a relative dielectric constant at 10 GHz in the range of 2.0 to 3.0, more preferably in the range of 2.0 to 2.5, and a dielectric loss tangent of preferably 0.0008 or less, more preferably 0.0003 or less.

In addition, the PTFE film for forming the PTFE layer (FE) is preferably one whose adhesion has been improved by surface treatment in order to ensure ease of handling and adhesion when forming a laminated structure with the first adhesive layer (B1) and the second adhesive layer (B2) by thermocompression bonding.

The PTFE film for forming the PTFE layer (FE) may be subjected to a surface treatment such as plasma treatment, primer treatment, corona treatment, chemical treatment, etc. The surface treatment can enhance adhesion to the first adhesive layer (B1) and the second adhesive layer (B2). However, in the present invention, since the first adhesive layer (B1) and the second adhesive layer (B2) have a predetermined storage modulus, the adhesion to the PTFE layer (FE) is good, and surface treatment is not necessarily required.

The PTFE layer (FE) constituting the resin film (A) may contain optional components such as plasticizers, other resin components such as epoxy resins, hardeners, hardening accelerators, organic fillers, inorganic fillers, coupling agents, and flame retardants.

As the PTFE layer (FE), a commercially available PTFE film can be appropriately selected and used. For example, products manufactured by Chukoh Chemical Industries Co., Ltd. (product names: Skived Tape MSF-100, MSF-200, etc.), products manufactured by Nitto Denko Corporation (product name: Nitoflon (registered trademark)), and products manufactured by Daikin Industries, Ltd. (product name: Polyflon PTFE) are preferably used.

[First adhesive layer and second adhesive layer]
The first adhesive layer (B1) and the second adhesive layer (B2) each independently have a storage modulus of 1800 MPa or less at 50° C., and each independently have a maximum storage modulus of 800 MPa or less at 180 to 260° C., preferably in the range of 500 MPa or less. By setting the storage modulus to such a value, adhesion to the PTFE layer (FE) is ensured, and dimensional stability after circuit processing is maintained by alleviating internal stress during thermocompression bonding, and warping is less likely to occur even after a solder reflow process after circuit processing.
The first adhesive layer (B1) and the second adhesive layer (B2) may be the same or different in terms of thickness, physical properties, material, etc., but it is preferable that they have the same configuration.

In order to maintain good dielectric properties of the entire resin film (A), the first adhesive layer (B1) and the second adhesive layer (B2) each have, as a single layer, a relative dielectric constant at 10 GHz of preferably 2 to 3.5, more preferably 2 to 3, and a dielectric loss tangent of preferably less than 0.003, more preferably 0.0025 or less.

The first adhesive layer (B1) and the second adhesive layer (B2) each preferably have a glass transition temperature (Tg) of 180°C or less, more preferably 160°C or less. By setting the Tg of the first adhesive layer (B1) and the second adhesive layer (B2) to 180°C or less, thermocompression bonding at low temperatures is possible, which can alleviate the internal stress generated during lamination with a metal-clad laminate or the like and suppress dimensional changes after circuit processing. If the Tg of the first adhesive layer (B1) and the second adhesive layer (B2) exceeds 180°C, the thermocompression bonding temperature becomes high when the resin film (A) is interposed between metal-clad laminates or the like and bonded, and dimensional stability after circuit processing may be impaired.

The first adhesive layer (B1) and the second adhesive layer (B2) are preferably polyimide layers containing polyimide as the main resin component, preferably 70% by weight or more of the resin component, more preferably 90% by weight or more of the resin component, and most preferably the entire resin component. The main resin component means a component contained in an amount of more than 50% by weight of the total resin component.
When the first adhesive layer (B1) and the second adhesive layer (B2) are polyimide layers, the polyimide constituting them preferably contains an acid anhydride residue derived from a tetracarboxylic anhydride component and a diamine residue derived from a diamine component, and contains 50 mol% or more of diamine residues derived from a diamine derived from a dimer acid in which two terminal carboxylic acid groups of a dimer acid are substituted with a primary aminomethyl group or an amino group, relative to the total diamine residues. Hereinafter, the polyimide constituting the first adhesive layer (B1) and the second adhesive layer (B2) may be referred to as an "adhesive polyimide". In the present invention, the "tetracarboxylic acid residue" refers to a tetravalent group derived from a tetracarboxylic dianhydride, and the "diamine residue" refers to a divalent group derived from a diamine compound. When the raw materials tetracarboxylic anhydride and diamine compound are reacted in approximately equal moles, the type and molar ratio of the tetracarboxylic acid residue and diamine residue contained in the polyimide can be approximately corresponding to the type and molar ratio 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, and the like.

(Acid anhydride)
The adhesive polyimide may be made of any tetracarboxylic anhydride generally used in thermoplastic polyimides as a raw material, without any particular limitations. However, it is preferable to use a raw material containing 90 mol % or more of tetracarboxylic anhydrides represented by the following general formula (1) and/or (2) in total relative to the total tetracarboxylic anhydride components. In other words, it is preferable for the adhesive polyimide to contain 90 mol % or more of tetracarboxylic acid residues derived from tetracarboxylic anhydrides represented by the following general formula (1) and/or (2) in total relative to the total tetracarboxylic acid residues. By containing 90 mol % or more of tetracarboxylic acid residues derived from tetracarboxylic anhydrides represented by the following general formula (1) and/or (2) in total relative to the total tetracarboxylic acid residues, it is preferable that the adhesive polyimide is easily compatible with flexibility and heat resistance. If the total amount of tetracarboxylic acid residues derived from tetracarboxylic anhydrides represented by the following general formula (1) and/or (2) is less than 90 mol %, the adhesive polyimide tends to have a low solvent solubility.

In general formula (1), X represents a single bond or a divalent group selected from the following formulas, and in general formula (2), the cyclic portion represented by Y represents a cyclic saturated hydrocarbon group selected from a 4-membered ring, a 5-membered ring, a 6-membered ring, a 7-membered ring, or an 8-membered ring.

In the above formula, Z represents —C ₆ H ₄ —, —(CH ₂ )n— or —CH ₂ —CH(—O—C(═O)—CH ₃ )—CH ₂ —, where n represents an integer of 1 to 20.

Examples of tetracarboxylic acid anhydrides represented by the above general formula (1) include 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 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 acid monoester anhydride) (TAHQ), and ethylene glycol bisanhydrotrimellitate (TMEG). Among these, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) is particularly preferred. When BTDA is used, the carbonyl group (ketone group) contributes to adhesion, so the adhesion of the adhesive polyimide can be improved. In addition, the ketone group present in the molecular skeleton of BTDA may react with the amino group of an amino compound for crosslinking, which will be described later, to form a C=N bond, which is likely to produce an effect of improving heat resistance. From this perspective, it is preferable that the tetracarboxylic acid residues derived from BTDA are contained in an amount of preferably 50 mol% or more, more preferably 60 mol% or more, of the total tetracarboxylic acid residues.

Examples of tetracarboxylic acid anhydrides represented by general formula (2) include 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, and 1,2,5,6-cyclooctane tetracarboxylic acid dianhydride.

The adhesive polyimide may contain tetracarboxylic acid residues derived from acid anhydrides other than the tetracarboxylic acid anhydrides represented by the above general formula (1) and general formula (2) within the scope of the invention. There are no particular limitations on such tetracarboxylic acid residues, and examples thereof include pyromellitic dianhydride, 2,3',3,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'- or 2,3,3',4'-benzophenonetetracarboxylic 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, 2,3',3,4''- ...4''-, 2,3',3,4''-, 2,3',3 ,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)sulfone 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-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic 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 acid dianhydride, 2,3,8,9-, 3,4,9,10-, 4,5,10,11- or 5,6,11,12-perylene-tetracarboxylic acid dianhydride, pyrazine-2,3,5,6-tetracarboxylic acid dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic acid dianhydride, thiophene-2,3,4,5-tetracarboxylic acid dianhydride, 4,4'-bis(2,3-dicarboxyphenoxy)diphenylmethane dianhydride, and other aromatic tetracarboxylic acid dianhydrides are included.

(Diamine)
The adhesive polyimide may be made of any diamine compound generally used in thermoplastic polyimides, without any particular limitations, but it is preferable to use a raw material containing 50 mol% or more of diamine derived from dimer acid, in which two terminal carboxylic acid groups of dimer acid are substituted with primary aminomethyl groups or amino groups, relative to the total diamine components. In other words, it is preferable that the adhesive polyimide contains 50 mol% or more of diamine residues derived from diamine derived from dimer acid, in which two terminal carboxylic acid groups of dimer acid are substituted with primary aminomethyl groups or amino groups, relative to the total diamine residues. By containing 50 mol% or more of diamine residues derived from diamine derived from dimer acid, it is possible to lower the dielectric constant and dielectric loss tangent of the adhesive polyimide, and to enhance the adhesiveness.

Since dimer acid-derived diamines are mixtures containing trimer and monomer components other than dimer diamine, it is preferable to purify them before use. Hereinafter, the purified dimer acid-derived diamines may be referred to as "dimer diamine compositions." Dimer diamine compositions are purified products that contain 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 a macromolecular aliphatic molecule with a molecular weight of approximately 560 to 620, it is possible to increase the molecular molar volume and relatively reduce the polar groups of the polyimide. Such characteristics of dimer diamine are thought to 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 is thought that not only does it impart flexibility to the polyimide, but it can also give the polyimide an asymmetrical or non-planar chemical structure, thereby lowering the dielectric constant of the polyimide.

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, the broadening of the molecular weight distribution of the polyimide can be suppressed.

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 anhydride 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 anhydride component and the diamine component (tetracarboxylic anhydride 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 components (b) and (c) in the chromatogram is less than 1, the molar ratio of the tetracarboxylic anhydride component and the diamine component (tetracarboxylic anhydride component/diamine component) is preferably 0.97 or more and 1.1 or less, and by setting such a molar ratio, it becomes easier to control the molecular weight of the polyimide.

Commercially available diamines derived from dimer acid are available, and are preferably purified to reduce the amount of components other than the dimer diamine in component (a), for example to 96% by weight or more of component (a). There are no particular limitations on the purification method, but known methods such as distillation and precipitation purification are suitable. Commercially available diamines derived from dimer acid include, for example, PRIAMINE 1073 (trade name), PRIAMINE 1074 (trade name), and PRIAMINE 1075 (trade name) manufactured by Croda Japan.

The adhesive polyimide may contain diamine residues derived from diamine components other than those mentioned above. As such diamine residues, for example, diamine residues derived from diamine compounds represented by the general formulas (B1) to (B7) are preferred.

In formulae (B1) to (B7), R ₁ independently represents a monovalent hydrocarbon group or alkoxy group having 1 to 6 carbon atoms, linking group A independently represents a divalent group selected from -O-, -S-, -CO-, -SO-, -SO ₂ -, -COO-, -CH ₂ -, -C(CH ₃ ) ₂ -, -NH- or -CONH-, and n ₁ independently represents an integer of 0 to 4. However, formula (B3) excluding those which overlap with formula (B2), and formula (B5) excluding those which overlap with formula (B4). Here, "independently" means that in one or two or more of formulae (B1) to (B7), multiple linking groups A, multiple R _1s or multiple n _1s may be the same or different. In the above formulas (B1) to (B7), the hydrogen atoms in the two terminal amino groups may be substituted, for example, -NR ₂ R ₃ (wherein R ₂ and R ₃ independently represent any substituent such as an alkyl group).

The diamine represented by formula (B1) (hereinafter sometimes referred to as "diamine (B1)") is an aromatic diamine having two benzene rings. In this diamine (B1), since an amino group directly bonded to at least one benzene ring and a divalent linking group A are at meta positions, the degree of freedom of the polyimide molecular chain is increased and the polyimide has high flexibility, which is considered to contribute to improving the flexibility of the polyimide molecular chain. Therefore, by using diamine (B1), the thermoplasticity of the polyimide is increased. Here, as the linking group A, -O-, -CH ₂ -, -C(CH ₃ ) ₂ -, -CO-, -SO ₂ -, and -S- are preferable.

Examples of diamines (B1) include 3,3'-diaminodiphenylmethane, 3,3'-diaminodiphenylpropane, 3,3'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylpropane, 3,4'-diaminodiphenyl sulfide, 3,3'-diaminobenzophenone, and (3,3'-bisamino)diphenylamine.

The diamine represented by formula (B2) (hereinafter sometimes referred to as "diamine (B2)") is an aromatic diamine having three benzene rings. In this diamine (B2), the amino group directly bonded to at least one benzene ring and the divalent linking group A are in the meta position, which increases the degree of freedom of the polyimide molecular chain and gives it high flexibility, which is thought to contribute to improving the flexibility of the polyimide molecular chain. Therefore, the use of diamine (B2) increases the thermoplasticity of the polyimide. Here, -O- is preferable as the linking group A.

Examples of diamines (B2) include 1,4-bis(3-aminophenoxy)benzene, 3-[4-(4-aminophenoxy)phenoxy]benzeneamine, and 3-[3-(4-aminophenoxy)phenoxy]benzeneamine.

The diamine represented by formula (B3) (hereinafter sometimes referred to as "diamine (B3)") is an aromatic diamine having three benzene rings. In this diamine (B3), two divalent linking groups A directly bonded to one benzene ring are in the meta position relative to each other, which increases the degree of freedom of the polyimide molecular chain and gives it high flexibility, which is thought to contribute to improving the flexibility of the polyimide molecular chain. Therefore, the use of diamine (B3) increases the thermoplasticity of the polyimide. Here, -O- is preferred as the linking group A.

Examples of diamines (B3) include 1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,3-bis(3-aminophenoxy)benzene (APB), 4,4'-[2-methyl-(1,3-phenylene)bisoxy]bisaniline, 4,4'-[4-methyl-(1,3-phenylene)bisoxy]bisaniline, and 4,4'-[5-methyl-(1,3-phenylene)bisoxy]bisaniline.

The diamine represented by formula (B4) (hereinafter sometimes referred to as "diamine (B4)") is an aromatic diamine having four benzene rings. This diamine (B4) has high flexibility due to the fact that the amino group directly bonded to at least one benzene ring and the divalent linking group A are at the meta position, and is considered to contribute to improving the flexibility of the polyimide molecular chain. Therefore, the use of diamine (B4) enhances the thermoplasticity of the polyimide. Here, the linking group A is preferably -O-, -CH ₂ -, -C(CH ₃ ) ₂ -, -SO ₂ -, -CO-, or -CONH-.

Examples of diamines (B4) include bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(3-aminophenoxy)phenyl]propane, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)]benzophenone, and bis[4,4'-(3-aminophenoxy)]benzanilide.

The diamine represented by formula (B5) (hereinafter sometimes referred to as "diamine (B5)") is an aromatic diamine having four benzene rings. In this diamine (B5), two divalent linking groups A directly bonded to at least one benzene ring are mutually in meta positions, which increases the degree of freedom of the polyimide molecular chain and gives it high flexibility, which is thought to contribute to improving the flexibility of the polyimide molecular chain. Therefore, the use of diamine (B5) enhances the thermoplasticity of the polyimide. Here, -O- is preferred as the linking group A.

Examples of diamines (B5) include 4-[3-[4-(4-aminophenoxy)phenoxy]phenoxy]aniline, 4,4'-[oxybis(3,1-phenyleneoxy)]bisaniline, etc.

The diamine represented by formula (B6) (hereinafter sometimes referred to as "diamine (B6)") is an aromatic diamine having four benzene rings. This diamine (B6) has high flexibility due to having at least two ether bonds, and is considered to contribute to improving the flexibility of the polyimide molecular chain. Therefore, the use of diamine (B6) enhances the thermoplasticity of the polyimide. Here, the linking group A is preferably -C( _CH3 ) _2- , -O-, _-SO2- , or -CO-.

Examples of diamines (B6) include 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), bis[4-(4-aminophenoxy)phenyl]ether (BAPE), bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS), and bis[4-(4-aminophenoxy)phenyl]ketone (BAPK).

The diamine represented by formula (B7) (hereinafter sometimes referred to as "diamine (B7)") is an aromatic diamine having four benzene rings. This diamine (B7) has a highly flexible divalent linking group A on both sides of the diphenyl skeleton, and is therefore thought to contribute to improving the flexibility of the polyimide molecular chain. Therefore, the use of diamine (B7) enhances the thermoplasticity of the polyimide. Here, -O- is preferred as the linking group A.

Examples of diamines (B7) include bis[4-(3-aminophenoxy)]biphenyl, bis[4-(4-aminophenoxy)]biphenyl, etc.

The adhesive polyimide preferably contains diamine residues derived from at least one diamine compound selected from diamines (B1) to (B7) in an amount of 1 mol % to 50 mol %, more preferably 5 mol % to 35 mol %, based on the total diamine residues. Diamines (B1) to (B7) have flexible molecular structures, so by using at least one diamine compound selected from these in an amount within the above range, the flexibility of the polyimide molecular chain can be improved and thermoplasticity can be imparted.

The adhesive polyimide may further contain diamine residues other than those mentioned above, provided that the effect of the invention is not impaired.

Adhesive polyimide can be produced by reacting the above-mentioned acid anhydride component and diamine component in a solvent to produce polyamic acid, which is then heated to close the ring. For example, the acid anhydride component and diamine component are dissolved in approximately equimolar amounts 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, thereby obtaining polyamic acid, which is a precursor of polyimide. In the reaction, the reaction components are dissolved so that the resulting precursor is in the range of 5 to 50% by weight in the organic solvent, preferably in the range of 10 to 40% by weight. 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 physical properties such as dielectric properties, thermal expansion coefficient, tensile modulus, glass transition temperature, etc. can be controlled by selecting the types of the acid anhydride components and diamine components, and the respective molar ratios when two or more types of acid anhydride components or diamine components are used. In addition, when the adhesive polyimide has multiple structural units, they may be present as blocks or randomly, but it is preferable that they are present randomly.

The weight-average molecular weight of the adhesive polyimide is preferably, for example, in the range of 10,000 to 400,000, and more preferably in the range of 50,000 to 350,000. If the weight-average molecular weight is less than 10,000, the strength of the film tends to decrease and it tends to become brittle. On the other hand, if the weight-average molecular weight exceeds 400,000, the viscosity increases excessively, and defects such as uneven film thickness and streaks tend to occur during the coating process.

(Crosslinking of adhesive polyimide)
When the adhesive polyimide has a ketone group, a crosslinked structure can be formed by reacting the ketone group with a crosslinking agent having a functional group that undergoes a nucleophilic addition reaction. The formation of the crosslinked structure can improve heat resistance. A polyimide having such a crosslinked structure (hereinafter sometimes referred to as "crosslinked polyimide") is an application example of the adhesive polyimide, and is a preferred form.

As the crosslinking agent, for example, an amino compound having at least two primary amino groups as functional groups (hereinafter, sometimes referred to as "amino compound for crosslinking") is preferably used. A crosslinked structure can be formed by reacting the ketone groups of the adhesive polyimide with the amino groups of the amino compound for crosslinking to form a C=N bond. In other words, the two primary amino groups in the amino compound function as functional groups that undergo a nucleophilic addition reaction with the ketone groups.

A preferred tetracarboxylic anhydride for forming an adhesive polyimide having a ketone group is, for example, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), and a preferred diamine compound is, for example, an aromatic diamine such as 4,4'-bis(3-aminophenoxy)benzophenone (BABP) or 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene (BABB). For the purpose of forming a crosslinked structure, it is particularly preferred to allow a crosslinking amino compound to act on the above adhesive polyimide, which contains, with respect to the total tetracarboxylic acid residues, preferably 50 mol % or more, more preferably 60 mol % or more of BTDA residues derived from BTDA. In the present invention, the term "BTDA residue" refers to a tetravalent group derived from BTDA.

Examples of amino compounds for forming crosslinks include (I) dihydrazide compounds, (II) aromatic diamines, and (III) aliphatic amines. Among these, dihydrazide compounds are preferred. Aliphatic amines other than dihydrazide compounds are prone to form crosslinked structures even at room temperature, which raises concerns about the storage stability of the varnish, while aromatic diamines require high temperatures to form crosslinked structures. In this way, when a dihydrazide compound is used, it is possible to achieve both the storage stability of the varnish and a shortened curing time. Examples of dihydrazide compounds include oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, pimelic acid dihydrazide, suberic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, dodecanedioic acid dihydrazide, maleic acid dihydrazide, fumaric acid dihydrazide, diglyceryl ester dihydrazide, ... Dihydrazide compounds such as cholic acid dihydrazide, tartaric acid dihydrazide, malic acid dihydrazide, phthalic acid dihydrazide, isophthalic acid dihydrazide, terephthalic acid dihydrazide, 2,6-naphthoedioic acid dihydrazide, 4,4-bisbenzene dihydrazide, 1,4-naphthoic acid dihydrazide, 2,6-pyridine diacid dihydrazide, and itaconic acid dihydrazide are preferred. The above dihydrazide compounds may be used alone or in combination of two or more.

The above amino compounds, such as (I) dihydrazide compounds, (II) aromatic diamines, and (III) aliphatic amines, can also be used in combination of two or more types beyond the scope of the category, such as a combination of (I) and (II), a combination of (I) and (III), or a combination of (I), (II), and (III).

In order to make the mesh-like structure formed by the crosslinking with the crosslinking amino compound denser, the crosslinking amino compound used in the present invention preferably has a molecular weight (weight average molecular weight when the crosslinking amino compound is an oligomer) of 5,000 or less, more preferably 90 to 2,000, and even more preferably 100 to 1,500. Among these, crosslinking amino compounds having a molecular weight of 100 to 1,000 are particularly preferred. If the molecular weight of the crosslinking amino compound is less than 90, only one amino group of the crosslinking amino compound will form a C=N bond with a ketone group of the adhesive polyimide, and the surroundings of the remaining amino groups will be three-dimensionally bulky, making it difficult for the remaining amino groups to form C=N bonds.

When crosslinking the ketone group in the adhesive polyimide with the crosslinking amino compound, the crosslinking amino compound is added to a resin solution containing the adhesive polyimide to cause a condensation reaction between the ketone group in the adhesive polyimide and the primary amino group of the crosslinking amino compound. This condensation reaction hardens the resin solution to become a hardened product. In this case, the amount of the crosslinking amino compound added can be 0.004 to 1.5 moles, preferably 0.005 to 1.2 moles, more preferably 0.03 to 0.9 moles, and most preferably 0.04 to 0.6 moles of primary amino groups per mole of ketone group. If the amount of crosslinking amino compound added is such that the total number of primary amino groups per mole of ketone groups is less than 0.004 moles, crosslinking by the crosslinking amino compound is insufficient, and heat resistance after curing tends to be difficult to achieve. If the amount of crosslinking amino compound added exceeds 1.5 moles, the unreacted crosslinking amino compound acts as a thermoplasticizer, tending to reduce the heat resistance of the adhesive layer.

A ketone group in the adhesive polyimide and a functional group of the crosslinking agent are subjected to a nucleophilic addition reaction to form a crosslink, resulting in a crosslinked polyimide, which is a cured product. The conditions of the nucleophilic addition reaction for forming the crosslink are not particularly limited and can be selected according to the type of the crosslinking agent. For example, when a primary amino group of an amino compound for forming a crosslink is reacted with a ketone group in the adhesive polyimide, an imine bond (C=N bond) is generated by a condensation reaction by heating, and a crosslinked structure is formed. The conditions of the condensation reaction for forming the crosslink are not particularly limited as long as the ketone group in the adhesive polyimide and the primary amino group of the amino compound for forming the crosslink form an imine bond (C=N bond). The temperature of the heat condensation is preferably within the range of 120 to 220°C, more preferably within the range of 140 to 200°C, for example, in order to release water generated by condensation out of the system, or to simplify the condensation step when a heat condensation reaction is performed subsequently after the synthesis of the adhesive polyimide. The reaction time is preferably about 30 minutes to 24 hours. The end point of the reaction can be confirmed by measuring the infrared absorption spectrum using, for example, a Fourier transform infrared spectrophotometer (commercially available: FT/IR620 manufactured by JASCO Corporation), based on the decrease or disappearance of the absorption peak derived from the ketone group in the polyimide resin at about 1670 cm ^-1 and the appearance of an absorption peak derived from the imine group at about 1635 cm ^-1 .

The thermal condensation of the ketone group of the adhesive polyimide with the primary amino group of the crosslinking amino compound can be carried out, for example, by the following method:
(1) A method in which, following synthesis (imidization) of an adhesive polyimide, an amino compound for crosslinking is added and heated;
(2) A method in which an excess amount of an amino compound is charged in advance as a diamine component, and following the synthesis (imidization) of an adhesive polyimide, the remaining amino compound that is not involved in imidization or amidation is used as an amino compound for crosslinking and heated together with the adhesive polyimide;
Or,
(3) A method in which the adhesive polyimide composition containing the above-mentioned crosslinking amino compound is processed into a predetermined shape (for example, after being applied to a substrate or formed into a film), and then heated;
This can be done by, etc.

In order to impart heat resistance to adhesive polyimide, an example of crosslinked polyimide with a crosslinked structure formed by the formation of imine bonds has been given, but the present invention is not limited to this. As a method for curing polyimide, it is also possible to mix and cure it with compounds having unsaturated bonds, such as epoxy resins, epoxy resin curing agents, maleimides, activated ester resins, and resins having a styrene skeleton.

The first adhesive layer (B1) and the second adhesive layer (B2) constituting the resin film (A) may each contain optional components such as plasticizers, other resin components such as epoxy resins, curing agents, curing accelerators, organic fillers, inorganic fillers, coupling agents, flame retardants, etc.

When the resin film (A) is applied to, for example, a circuit board, in order to suppress deterioration of the dielectric loss, the dielectric tangent (Tan δ) at 10 GHz is preferably 0.0016 or less, more preferably 0.0012 or less, and even more preferably 0.0008 or less. If the dielectric tangent at 10 GHz of the resin film (A) exceeds 0.0016, when the resin film (A) is applied to a circuit board, inconveniences such as loss of electrical signals on the transmission path of high-frequency signals are likely to occur. On the other hand, there is no particular lower limit for the dielectric tangent at 10 GHz of the resin film (A).

When the resin film (A) is applied to, for example, a circuit board, in order to ensure impedance matching, the relative dielectric constant at 10 GHz is preferably 3.0 or less, more preferably 2.8 or less, and even more preferably 2.6 or less. If the relative dielectric constant of the resin film (A) at 10 GHz exceeds 3.0, this leads to a deterioration in the dielectric loss of the resin film (A) when applied to a circuit board, and is likely to cause inconveniences such as loss of electrical signals on the transmission path of high-frequency signals.

When the thickness of the PTFE layer (FE) is T _FE , the thickness of the first adhesive layer (B1) is T _B1 , and the thickness of the second adhesive layer (B2) is T _B2 , the resin film (A) preferably has the following relationship:
0.15≦(T _B1 +T _B2 )/(T _FE +T _B1 +T _B2 )≦0.70
If the ratio of the total thickness of the first adhesive layer (B1) and the second adhesive layer (B2) to the total thickness of the resin film (A) is less than 0.15, the dimensional change rate after heating will be large, and dimensional stability may be impaired. If it is greater than 0.70, it will be difficult to obtain the effect of PTFE in improving the dielectric properties of the entire resin film (A).
Here, the thickness T _FE of the PTFE layer (FE) is not particularly limited, but is preferably within a range of, for example, 25 to 250 μm, and more preferably within a range of 50 to 100 μm. Also, the thickness T _B1 of the first adhesive layer (B1) and the thickness T _B2 of the second adhesive layer (B2) are not particularly limited, but are each preferably within a range of, for example, 1 to 100 μm, and more preferably within a range of 5 to 50 μm.

The resin film (A) may be a film (sheet) consisting of a PTFE layer (FE), a first adhesive layer (B1) and a second adhesive layer (B2), or may be laminated to a substrate made of an inorganic material such as copper foil or a glass plate, or a resin substrate such as a polyimide film, a polyamide film or a polyester film.

The manufacturing method of the resin film (A) in this embodiment is not particularly limited. For example, in the case where the first adhesive layer (B1) and the second adhesive layer (B2) are polyimide layers made of adhesive polyimide, the following methods [1] to [3] can be mentioned.
[1] A method in which an adhesive polyimide is applied in a solution state (for example, in a polyimide composition state) to one side of a PTFE film to form a coating film, which is then dried at a temperature of, for example, 80 to 180°C, and then a coating film of adhesive polyimide is formed on the other side in the same manner, followed by heating and drying to form a resin film (A).
[2] A method in which a solution of a polyamic acid, which is a precursor of an adhesive polyimide, is applied to an arbitrary substrate, dried, imidized to form a film, and then peeled off from the substrate. A PTFE film is sandwiched between two sheets of the polyimide film thus obtained, and the resulting film is heat-pressed to form a resin film (A).
[3] A method in which a solution of polyamic acid, which is a precursor of adhesive polyimide, is applied to an arbitrary substrate, dried, and then a gel film of polyamic acid is peeled off from the substrate. A PTFE film is sandwiched between two sheets of the gel film thus obtained, and the two sheets are thermally pressed to form a resin film (A) at the same time as imidization.
The method for applying the adhesive polyimide solution (or polyamic acid solution) onto the substrate is not particularly limited, and it is possible to apply it using, for example, a coater such as a comma, die, knife or lip coater.

The resin film (A) obtained in the above manner has a sandwich structure in which a PTFE layer (FE) is sandwiched between a first adhesive layer (B1) and a second adhesive layer (B2) having a predetermined storage modulus, and therefore has excellent adhesion, dielectric properties, and dimensional stability. Therefore, the resin film (A) can be preferably used, for example, as an adhesive film (bonding sheet) or an adhesive layer that constitutes a part of an insulating resin layer of a circuit board. By applying the resin film (A), it is possible to reduce transmission loss during high-frequency signal transmission in the circuit board and ensure dimensional stability.

[Metal-clad laminate]
2 is a schematic diagram showing the configuration of a metal-clad laminate according to one embodiment of the present invention. The metal-clad laminate (C) of this embodiment has a structure in which a pair of single-sided metal-clad laminates are bonded together with an adhesive layer (A').
That is, the metal-clad laminate (C) comprises a first single-sided metal-clad laminate (C1), a second single-sided metal-clad laminate (C2), and an adhesive layer (A') laminated between the first single-sided metal-clad laminate (C1) and the second single-sided metal-clad laminate (C2). Here, the adhesive layer (A') is composed of the resin film (A).

The first single-sided metal-clad laminate (C1) has a first metal layer (M1) and a first insulating resin layer (P1) laminated on at least one side of the first metal layer (M1). The second single-sided metal-clad laminate (C2) has a second metal layer (M2) and a second insulating resin layer (P2) laminated on at least one side of the second metal layer (M2). The adhesive layer (A') is arranged so as to abut the first insulating resin layer (P1) and the second insulating resin layer (P2). In other words, the metal-clad laminate (C) has a structure in which the first metal layer (M1) / first insulating resin layer (P1) / adhesive layer (A') / second insulating resin layer (P2) / second metal layer (M2) are laminated in this order. The first metal layer (M1) and the second metal layer (M2) are located on the outermost sides, and the first insulating resin layer (P1) and the second insulating resin layer (P2) are arranged inside them, and an adhesive layer (A') is interposed between the first insulating resin layer (P1) and the second insulating resin layer (P2).

The configuration of the pair of single-sided metal-clad laminates (C1, C2) is not particularly limited, and may be any common FPC material, such as a commercially available copper-clad laminate. The first single-sided metal-clad laminate (C1) and the second single-sided metal-clad laminate (C2) may have the same configuration or different configurations.

(Metal Layer)
The material of the first metal layer (M1) and the second metal layer (M2) is not particularly limited, but examples thereof include copper, stainless steel, iron, nickel, beryllium, aluminum, zinc, indium, silver, gold, tin, zirconium, tantalum, titanium, lead, magnesium, manganese, and alloys thereof. Among these, copper or a copper alloy is particularly preferable. The material of the wiring layer in the circuit board of this embodiment described later is the same as that of the first metal layer (M1) and the second metal layer (M2).

The thickness of the first metal layer (M1) and the second metal layer (M2) is not particularly limited, but when a metal foil such as copper foil is used, it 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, it is preferable that the lower limit of the thickness of the metal foil is 5 μm. When copper foil is used, it may be rolled copper foil or electrolytic copper foil. In addition, commercially available copper foil may be used as the copper foil.

The metal foil may also be surface-treated with, for example, siding, aluminum alcoholate, aluminum chelate, silane coupling agent, etc., for the purpose of, for example, rust prevention or improving adhesion.

(Insulating resin layer)
The first insulating resin layer (P1) and the second insulating resin layer (P2) are not particularly limited as long as they are made of a resin having electrical insulation properties, and examples thereof include polyimide, epoxy resin, phenolic resin, polyethylene, polypropylene, polytetrafluoroethylene, silicone, ETFE, etc., but are preferably made of polyimide. In addition, the first insulating resin layer (P1) and the second insulating resin layer (P2) are not limited to a single layer, and may be a laminate of multiple resin layers.

<Layer thickness>
In the metal-clad laminate (C), when the total thickness T1 of the first insulating resin layer (P1), the adhesive layer (A') and the second insulating resin layer (P2) is defined as T1, the total thickness T1 is in the range of 50 to 500 μm, and preferably in the range of 100 to 300 μm. If the total thickness T1 is less than 50 μm, the effect of reducing transmission loss when used in a circuit board becomes insufficient, and if it exceeds 500 μm, there is a risk of a decrease in flexibility of the circuit board and a decrease in productivity.

Furthermore, the thickness T2 of the adhesive layer (A') (i.e., T _FE +T _B1 +T _B2 in the resin film (A)) is preferably, for example, in the range of 26 to 350 μm, and more preferably in the range of 30 to 250 μm. If the thickness T2 of the adhesive layer (A') is less than the above lower limit, the transmission loss as a high-frequency substrate may increase. On the other hand, if the thickness of the adhesive layer (A') exceeds the above upper limit, problems such as reduced dimensional stability may occur.

The ratio (T2/T1) of the thickness T2 of the adhesive layer (A') to the total thickness T1 is in the range of 0.50 to 0.90, and preferably in the range of 0.50 to 0.80. If the ratio (T2/T1) is less than 0.5, it becomes difficult to make T1 50 μm or more, and the effect of reducing transmission loss when used in a circuit board becomes insufficient, and if it exceeds 0.90, problems such as reduced dimensional stability occur.

The thickness T3 of both the first insulating resin layer (P1) and the second insulating resin layer (P2) is preferably within the range of, for example, 12 to 100 μm, and more preferably within the range of 12 to 50 μm. If the thickness T3 of the first insulating resin layer (P1) and the second insulating resin layer (P2) is less than the above lower limit, problems such as warping of the metal-clad laminate (C) may occur. If the thickness T3 of the first insulating resin layer (P1) and the second insulating resin layer (P2) exceeds the above upper limit, problems such as reduced productivity may occur. Note that the first insulating resin layer (P1) and the second insulating resin layer (P2) do not necessarily have to be the same thickness.

<Thermal expansion coefficient>
The first insulating resin layer (P1) and the second insulating resin layer (P2) have a coefficient of thermal expansion (CTE) of 10 ppm/K or more, preferably in the range of 10 ppm/K to 30 ppm/K, more preferably in the range of 15 ppm/K to 25 ppm/K. If the CTE is less than 10 ppm/K or more than 30 ppm/K, warping occurs or dimensional stability decreases. By appropriately changing the combination of raw materials used, the thickness, and the drying and curing conditions, a polyimide layer having a desired CTE can be obtained.

Because the first adhesive layer (B1) and the second adhesive layer (B2) have low elasticity and low glass transition temperature, even if the CTE of the entire adhesive layer (A') exceeds 30 ppm/K, the internal stress generated during lamination can be alleviated. In addition, the overall coefficient of thermal expansion (CTE) of the first insulating resin layer (P1), the adhesive layer (A') and the second insulating resin layer (P2) is preferably 10 ppm/K or more, preferably in the range of 10 ppm/K to 30 ppm/K, and more preferably in the range of 15 ppm/K to 25 ppm/K. If the CTE of the entire resin layers is less than 10 ppm/K or exceeds 30 ppm/K, warping may occur or dimensional stability may decrease.

<Dielectric tangent>
In order to suppress deterioration of dielectric loss when applied to a circuit board, the first insulating resin layer (P1) and the second insulating resin layer (P2) each have a dielectric loss tangent (Tan δ) at 10 GHz of preferably 0.02 or less, more preferably 0.01 or less, and even more preferably 0.008 or less. If the dielectric loss tangent at 10 GHz of the first insulating resin layer (P1) and the second insulating resin layer (P2) exceeds 0.02, inconveniences such as loss of electrical signals on the transmission path of high-frequency signals are likely to occur when applied to a circuit board. On the other hand, the lower limit of the dielectric loss tangent at 10 GHz of the first insulating resin layer (P1) and the second insulating resin layer (P2) is not particularly limited, but the physical property control as an insulating resin layer of a circuit board is taken into consideration.

<Dielectric constant>
When the first insulating resin layer (P1) and the second insulating resin layer (P2) are applied as insulating resin layers of a circuit board, for example, the insulating resin layer as a whole preferably has a relative dielectric constant of 4.0 or less at 10 GHz in order to ensure impedance matching. If the relative dielectric constant of the first insulating resin layer (P1) and the second insulating resin layer (P2) exceeds 4.0 at 10 GHz, when applied to a circuit board, this leads to deterioration of the dielectric loss of the first insulating resin layer (P1) and the second insulating resin layer (P2), and is likely to cause inconveniences such as loss of electrical signals on the transmission path of high-frequency signals.

<Action>
In the metal-clad laminate (C), a PTFE layer (FE) is provided on the adhesive layer (A') in order to reduce the dielectric tangent of the entire insulating resin layer and to enable high-frequency signal transmission. However, the PTFE layer (FE) has low adhesion and a large dimensional change rate before and after heating, so that increasing the thickness of the PTFE layer (FE) may cause problems such as interlayer peeling due to insufficient adhesion and a decrease in dimensional stability.

Therefore, in the metal-clad laminate (C) of this embodiment, the adhesive layer (A') is sandwiched between the first adhesive layer (B1) and the second adhesive layer (B2) having a low storage modulus, thereby improving adhesion and relieving internal stress caused by heating, thereby ensuring dimensional stability. In particular, when a polyimide containing 50 mol % or more of diamine residues derived from a diamine derived from a dimer acid in which two terminal carboxylic acid groups of the dimer acid are substituted with primary aminomethyl groups or amino groups is used as the material for the first adhesive layer (B1) and the second adhesive layer (B2), it is possible to improve adhesion and dimensional stability without significantly increasing the relative dielectric constant and dielectric loss tangent of the entire adhesive layer (A').

In addition, since the adhesive layer (A') is laminated between the first insulating resin layer (P1) and the second insulating resin layer (P2), it functions as an intermediate layer and suppresses warping and dimensional changes. Furthermore, even during heating processes such as solder reflow when mounting a semiconductor chip, the first insulating resin layer (P1) or the second insulating resin layer (P2) blocks direct contact with heat and oxygen, so the adhesive layer (A') is less susceptible to oxidation degradation and dimensional changes are less likely to occur. In this way, there are also advantages due to the characteristics of the layer structure of the first insulating resin layer (P1), adhesive layer (A'), and second insulating resin layer (P2).

[Production of metal-clad laminate]
The metal-clad laminate (C) can be produced, for example, by a method in which a resin film (A) that becomes an adhesive layer (A') is placed between a first insulating resin layer (P1) of a first single-sided metal-clad laminate (C1) and a second insulating resin layer (P2) of a second single-sided metal-clad laminate (C2), bonded together, and thermocompression bonded.

The metal-clad laminate (C) of this embodiment obtained as described above can be used to manufacture circuit boards such as single-sided FPCs or double-sided FPCs by processing the first metal layer (M1) and/or the second metal layer (M2) into wiring circuits, for example by etching them.

[Preferable configuration example of metal-clad laminate]
Next, the first insulating resin layer (P1), the second insulating resin layer (P2), the adhesive layer (A'), the first metal layer (M1) and the second metal layer (M2) in the metal-clad laminate (C) of this embodiment will be described in more detail.

Figure 3 is a schematic cross-sectional view showing the structure of the metal-clad laminate 100 of this embodiment. As shown in Figure 3, the metal-clad laminate 100 includes metal layers 101, 101 as the first metal layer (M1) and the second metal layer (M2), polyimide layers 110, 110 as the first insulating resin layer (P1) and the second insulating resin layer (P2), and an adhesive layer 120 as the adhesive layer (A'). Here, the metal layer 101 and the polyimide layer 110 form a single-sided metal-clad laminate 130 as the first single-sided metal-clad laminate (C1) or the second single-sided metal-clad laminate (C2). In this embodiment, the first single-sided metal-clad laminate (C1) and the second single-sided metal-clad laminate (C2) have the same configuration.

The polyimide layers 110, 110 may each have a structure in which multiple polyimide layers are laminated. For example, in the embodiment shown in FIG. 3, a three-layer structure is formed with non-thermoplastic polyimide layers 111, 111 made of non-thermoplastic polyimide as a base layer, and thermoplastic polyimide layers 112, 112 made of thermoplastic polyimide provided on both sides of the non-thermoplastic polyimide layers 111, 111, respectively. Note that the polyimide layers 110, 110 are not limited to a three-layer structure.

In the metal-clad laminate 100 shown in FIG. 3, the outer thermoplastic polyimide layers 112, 112 of the two single-sided metal-clad laminates 130, 130 are each bonded to an adhesive layer 120 to form the metal-clad laminate 100. The adhesive layer 120 is an adhesive layer for bonding the two single-sided metal-clad laminates 130, 130 in the metal-clad laminate 100, and is intended to thicken the insulating resin layer of the metal-clad laminate 100 while ensuring dimensional stability. The adhesive layer 120 is as described above for the adhesive layer (A').

Next, the non-thermoplastic polyimide layer 111 and the thermoplastic polyimide layer 112 constituting the polyimide layers 110, 110 will be described. Note that, although the term "non-thermoplastic polyimide" generally refers to a polyimide that does not soften or exhibit adhesiveness even when heated, in the present invention, it refers to a polyimide having a storage modulus of 1.0×10 ⁹ Pa or more at 30° C. and a storage modulus of 1.0×10 ⁸ Pa or more at 350° C., as measured using a dynamic mechanical analyzer (DMA). Furthermore, the term "thermoplastic polyimide" generally refers to a polyimide whose glass transition temperature (Tg) can be clearly confirmed, in the present invention, it refers to a polyimide having a storage modulus of 1.0×10 ⁹ Pa or more at 30° C. and a storage modulus of less than 1.0×10 ⁸ Pa at 350° C., as measured using a DMA.

Non-thermoplastic polyimide layer:
The non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer 111 contains a tetracarboxylic acid residue and a diamine residue. The non-thermoplastic polyimide preferably contains an aromatic tetracarboxylic acid residue derived from an aromatic tetracarboxylic dianhydride and an aromatic diamine residue derived from an aromatic diamine.

(Tetracarboxylic acid residue)
The non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer 111 preferably contains, as a tetracarboxylic acid residue, a tetracarboxylic acid residue derived from at least one of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and 1,4-phenylenebis(trimellitic acid monoester) dianhydride (TAHQ), and a tetracarboxylic acid residue derived from at least one of pyromellitic dianhydride (PMDA) and 2,3,6,7-naphthalenetetracarboxylic dianhydride (NTCDA).

Tetracarboxylic acid residues derived from BPDA (hereinafter also referred to as "BPDA residues") and tetracarboxylic acid residues derived from TAHQ (hereinafter also referred to as "TAHQ residues") tend to form ordered polymer structures and can reduce dielectric tangent and hygroscopicity by suppressing molecular motion. BPDA residues can impart self-supporting properties to the gel film of the polyamic acid of the polyimide precursor, but at the same time, they tend to increase the CTE after imidization and lower the glass transition temperature, thereby reducing heat resistance.

From this viewpoint, the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer 111 is controlled so that the total of BPDA residues and TAHQ residues is preferably within the range of 30 to 60 molar parts, more preferably 40 to 50 molar parts, per 100 molar parts of all tetracarboxylic acid residues. If the total of BPDA residues and TAHQ residues is less than 30 molar parts, the formation of an ordered structure of the polymer will be insufficient, resulting in reduced moisture absorption resistance and insufficient reduction in dielectric tangent. If it exceeds 60 molar parts, there is a risk of an increase in CTE, an increase in the amount of change in in-plane retardation (RO), and reduced heat resistance.

In addition, the tetracarboxylic acid residue derived from pyromellitic dianhydride (hereinafter also referred to as "PMDA residue") and the tetracarboxylic acid residue derived from 2,3,6,7-naphthalenetetracarboxylic dianhydride (hereinafter also referred to as "NTCDA residue") are residues that have rigidity, and therefore increase the in-plane orientation, suppress the CTE low, and also play a role in controlling the in-plane retardation (RO) and the glass transition temperature. On the other hand, since the PMDA residue has a small molecular weight, if the amount of the PMDA residue becomes too large, the imide group concentration of the polymer increases, the polar groups increase, and the hygroscopicity increases, and the dielectric tangent increases due to the influence of moisture inside the molecular chain. In addition, the NTCDA residue tends to make the film brittle due to the highly rigid naphthalene skeleton, and tends to increase the elastic modulus.
Therefore, the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer preferably contains the total of PMDA residues and NTCDA residues in the range of 40 to 70 molar parts, more preferably in the range of 50 to 60 molar parts, and even more preferably in the range of 50 to 55 molar parts, relative to 100 molar parts of all tetracarboxylic acid residues. If the total of PMDA residues and NTCDA residues is less than 40 molar parts, the CTE may increase or the heat resistance may decrease, while if it exceeds 70 molar parts, the imide group concentration of the polymer increases, the polar groups increase, and the low moisture absorption property is impaired, the dielectric loss tangent may increase, or the film may become brittle and the self-supporting property of the film may decrease.

The total amount of at least one of BPDA residues and TAHQ residues and at least one of PMDA residues and NTCDA residues is preferably 80 molar parts or more, and more preferably 90 molar parts or more, per 100 molar parts of all tetracarboxylic acid residues.

In addition, the molar ratio of at least one of BPDA residues and TAHQ residues to at least one of PMDA residues and NTCDA residues {(BPDA residues + TAHQ residues)/(PMDA residues + NTCDA residues)} is set within the range of 0.4 to 1.5, preferably within the range of 0.6 to 1.3, and more preferably within the range of 0.8 to 1.2, to control the CTE and the formation of an ordered structure of the polymer.

PMDA and NTCDA have a rigid skeleton, so compared to other common acid anhydride components, it is possible to control the in-plane orientation of the molecules in the polyimide, suppressing the coefficient of thermal expansion (CTE) and improving the glass transition temperature (Tg). In addition, BPDA and TAHQ have a larger molecular weight than PMDA, so an increase in the charge ratio reduces the imide group concentration, which is effective in reducing the dielectric tangent and moisture absorption rate. On the other hand, if the charge ratio of BPDA and TAHQ is increased, the in-plane orientation of the molecules in the polyimide decreases, leading to an increase in CTE. Furthermore, the formation of an ordered structure in the molecule progresses, and the haze value increases. From this perspective, the total charge amount of PMDA and NTCDA is within the range of 40 to 70 mol parts, preferably within the range of 50 to 60 mol parts, and more preferably within the range of 50 to 55 mol parts, relative to 100 mol parts of the total acid anhydride components of the raw material. If the total amount of PMDA and NTCDA charged is less than 40 molar parts per 100 molar parts of the total acid anhydride components of the raw material, the in-plane orientation of the molecules decreases, making it difficult to achieve a low CTE, and the heat resistance and dimensional stability of the film when heated due to a decrease in Tg. On the other hand, if the total amount of PMDA and NTCDA charged exceeds 70 molar parts, the moisture absorption rate tends to deteriorate and the elastic modulus tends to increase due to an increase in the imide group concentration.

BPDA and TAHQ are effective in suppressing molecular motion and lowering the dielectric tangent and moisture absorption rate by reducing the imide group concentration, but they also increase the CTE of the polyimide film after imidization. From this perspective, the combined amount of BPDA and TAHQ to be charged should be within the range of 30 to 60 molar parts, preferably 40 to 50 molar parts, and more preferably 40 to 45 molar parts, per 100 molar parts of the total acid anhydride components in the raw material.

Examples of tetracarboxylic acid residues other than the BPDA residue, TAHQ residue, PMDA residue, and NTCDA residue contained in the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer 111 include 3,3',4,4'-diphenylsulfonetetracarboxylic acid dianhydride, 4,4'-oxydiphthalic anhydride, 2,3',3,4'-biphenyltetracarboxylic acid dianhydride, 2,2',3,3'-, 2,3,3',4'-, or 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride, 2,3',3,4'-diphenylethertetracarboxylic acid dianhydride, bis(2,3-dicarbazone), 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)sulfone 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-tetracarbo dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)tetrafluoropropane dianhydride, 2,3,5,6-cyclohexane dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic 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-) Examples of the tetracarboxylic acid residues include those derived from aromatic tetracarboxylic acid dianhydrides such as tetrachloronaphthalene-1,4,5,8-(or 2,3,6,7-)tetracarboxylic acid dianhydride, 2,3,8,9-, 3,4,9,10-, 4,5,10,11- or 5,6,11,12-perylene-tetracarboxylic acid dianhydride, cyclopentane-1,2,3,4-tetracarboxylic acid dianhydride, pyrazine-2,3,5,6-tetracarboxylic acid dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic acid dianhydride, thiophene-2,3,4,5-tetracarboxylic acid dianhydride, 4,4'-bis(2,3-dicarboxyphenoxy)diphenylmethane dianhydride, and ethylene glycol bisanhydrotrimellitate.

(Diamine residue)
The diamine residue contained in the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer 111 is preferably a diamine residue derived from a diamine compound represented by the general formula (A1).

In formula (A1), the linking group Z represents a single bond or -COO-, Y independently represents a monovalent hydrocarbon having 1 to 3 carbon atoms, which may be substituted with a halogen atom or a phenyl group, or an alkoxy group having 1 to 3 carbon atoms, or a perfluoroalkyl group having 1 to 3 carbon atoms, or an alkenyl group, n represents an integer of 0 to 2, and p and q independently represent integers of 0 to 4. Here, "independently" means that in formula (A1), the multiple substituents Y, and further the integers p and q, may be the same or different. In formula (A1), the hydrogen atoms in the two amino groups at the ends may be substituted, for example, -NR ₂ R ₃ (wherein R ₂ and R ₃ independently represent any substituent such as an alkyl group).

The diamine compound represented by the general formula (A1) (hereinafter sometimes referred to as "diamine (A1)") is an aromatic diamine having one to three benzene rings. Diamine (A1) has a rigid structure, and therefore has the effect of imparting an orderly structure to the entire polymer. As a result, a polyimide with low gas permeability and low moisture absorption can be obtained, and the moisture inside the molecular chain can be reduced, thereby lowering the dielectric tangent. Here, a single bond is preferable as the linking group Z.

Examples of diamines (A1) include 1,4-diaminobenzene (p-PDA; paraphenylenediamine), 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB), 2,2'-n-propyl-4,4'-diaminobiphenyl (m-NPB), and 4-aminophenyl-4'-aminobenzoate (APAB).

The non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer 111 preferably contains 80 molar parts or more, more preferably 85 molar parts or more, of diamine residues derived from diamine (A1) relative to 100 molar parts of the total diamine residues. By using diamine (A1) in an amount within the above range, an ordered structure is easily formed throughout the polymer due to the rigid structure derived from the monomer, and a non-thermoplastic polyimide with low gas permeability, low moisture absorption, and low dielectric tangent is easily obtained.

When the diamine residues derived from diamine (A1) are within the range of 80 to 85 molar parts per 100 molar parts of all diamine residues in the non-thermoplastic polyimide, it is preferable to use 1,4-diaminobenzene as diamine (A1) from the viewpoint of a structure that is more rigid and has excellent in-plane orientation.

Other diamine residues contained in the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer 111 include, for example, 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 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 Examples of the diamine residues include diamine residues derived from aromatic diamine compounds such as benzene, 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, and 6-amino-2-(4-aminophenoxy)benzoxazole, and diamine residues derived from aliphatic diamine compounds such as diamines derived from dimer acids in which the two terminal carboxylic acid groups of the dimer acid are replaced with primary aminomethyl groups or amino groups.

In non-thermoplastic polyimides, the thermal expansion coefficient, storage modulus, tensile modulus, etc. can be controlled by selecting the types of the tetracarboxylic acid residues and diamine residues, or the molar ratios of two or more types of tetracarboxylic acid residues or diamine residues. In addition, in non-thermoplastic polyimides, when multiple polyimide structural units are used, they may be present as blocks or randomly, but from the viewpoint of suppressing the variation in the in-plane retardation (RO), it is preferable that they are present randomly.

It is preferable that the tetracarboxylic acid residues and diamine residues contained in the non-thermoplastic polyimide are both aromatic groups, since this improves the dimensional accuracy of the polyimide film in a high-temperature environment and reduces the amount of change in the in-plane retardation (RO).

The imide group concentration of the non-thermoplastic polyimide is preferably 33% or less, more preferably 32% 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. When the imide group concentration exceeds 33%, the molecular weight of the resin itself decreases, and the low moisture absorption property also deteriorates due to the increase in polar groups. By selecting the combination of the acid anhydride and the diamine compound, the molecular orientation in the non-thermoplastic polyimide is controlled, thereby suppressing the increase in CTE associated with the decrease in the imide group concentration and ensuring low moisture absorption.

The weight-average molecular weight of the non-thermoplastic polyimide is preferably, for example, in the range of 10,000 to 400,000, and more preferably in the range of 50,000 to 350,000. If the weight-average molecular weight is less than 10,000, the strength of the film tends to decrease and it tends to become brittle. On the other hand, if the weight-average molecular weight exceeds 400,000, the viscosity increases excessively, and defects such as uneven film thickness and streaks tend to occur during the coating process.

The thickness of the non-thermoplastic polyimide layer 111 is preferably in the range of 6 μm to 100 μm, more preferably in the range of 9 μm to 50 μm, in order to ensure the function as a base layer and to facilitate transport during production and during thermoplastic polyimide coating. If the thickness of the non-thermoplastic polyimide layer 111 is less than the lower limit, electrical insulation and handling properties will be insufficient, and if the thickness exceeds the upper limit, productivity will decrease.

From the viewpoint of heat resistance, it is preferable that the non-thermoplastic polyimide layer 111 has a glass transition temperature (Tg) of 280°C or higher.

In addition, from the viewpoint of suppressing warping, the thermal expansion coefficient of the non-thermoplastic polyimide layer 111 is preferably in the range of 1 ppm/K to 30 ppm/K, more preferably in the range of 1 ppm/K to 25 ppm/K, and even more preferably in the range of 10 ppm/K to 20 ppm/K.

The non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer 111 may contain optional components such as plasticizers, other curable resin components such as epoxy resins, curing agents, curing accelerators, coupling agents, fillers, solvents, and flame retardants. However, some plasticizers contain many polar groups, which may promote the diffusion of copper from the copper wiring, so it is preferable to avoid using plasticizers as much as possible.

Thermoplastic polyimide layer:
The thermoplastic polyimide constituting the thermoplastic polyimide layer 112 contains a tetracarboxylic acid residue and a diamine residue, and preferably contains an aromatic tetracarboxylic acid residue derived from an aromatic tetracarboxylic acid dianhydride and an aromatic diamine residue derived from an aromatic diamine.

(Tetracarboxylic acid residue)
As the tetracarboxylic acid residue used in the thermoplastic polyimide constituting the thermoplastic polyimide layer 112, the same ones as those exemplified as the tetracarboxylic acid residue in the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer 111 can be used.

(Diamine residue)
As the diamine residue contained in the thermoplastic polyimide constituting the thermoplastic polyimide layer 112, a diamine residue derived from a diamine compound represented by the general formulas (B1) to (B7) described above with respect to the adhesive polyimide is preferable.

The thermoplastic polyimide constituting the thermoplastic polyimide layer 112 contains 60 or more mol parts, preferably 60 or more 99 or less mol parts, more preferably 70 or more 95 or less mol parts of diamine residues derived from at least one diamine compound selected from diamine (B1) to diamine (B7) per 100 mol parts of all diamine residues. Since diamine (B1) to diamine (B7) have a molecular structure with flexibility, by using at least one diamine compound selected from these in an amount within the above range, the flexibility of the polyimide molecular chain can be improved and thermoplasticity can be imparted. If the total amount of diamine (B1) to diamine (B7) in the raw material is less than 60 mol parts per 100 mol parts of all diamine components, the flexibility of the polyimide resin is insufficient and sufficient thermoplasticity cannot be obtained.

As the diamine residue contained in the thermoplastic polyimide constituting the thermoplastic polyimide layer 112, a diamine residue derived from a diamine compound represented by general formula (A1) is also preferred. The diamine compound represented by formula (A1) [diamine (A1)] is as described in the explanation of non-thermoplastic polyimides. Diamine (A1) has a rigid structure and has the effect of imparting an ordered structure to the entire polymer, so that it is possible to reduce the dielectric tangent and moisture absorption by suppressing the movement of molecules. Furthermore, by using it as a raw material for thermoplastic polyimide, polyimide with low gas permeability and excellent long-term heat-resistant adhesion can be obtained.

The thermoplastic polyimide constituting the thermoplastic polyimide layer 112 may contain diamine residues derived from diamine (A1) in a range of preferably 1 to 40 molar parts, more preferably 5 to 30 molar parts. By using diamine (A1) in an amount within the above range, an ordered structure is formed throughout the polymer due to the rigid structure derived from the monomer, resulting in a polyimide that is thermoplastic yet has low gas permeability and moisture absorption and excellent long-term heat-resistant adhesion.

The thermoplastic polyimide constituting the thermoplastic polyimide layer 112 may contain diamine residues derived from diamine compounds other than the diamines (A1) and (B1) to (B7) as long as the effects of the invention are not impaired.

In thermoplastic polyimides, the thermal expansion coefficient, tensile modulus, glass transition temperature, etc. can be controlled by selecting the types of the tetracarboxylic acid residues and diamine residues, or the molar ratios of two or more types of tetracarboxylic acid residues or diamine residues. In addition, in thermoplastic polyimides, when multiple polyimide structural units are present, they may be present as blocks or randomly, but it is preferable that they are present randomly.

In addition, by making the tetracarboxylic acid residues and diamine residues contained in the thermoplastic polyimide both aromatic groups, the dimensional accuracy of the polyimide film in a high-temperature environment can be improved and the amount of change in the in-plane retardation (RO) can be suppressed.

The imide group concentration of the thermoplastic polyimide is preferably 33% or less, more preferably 32% 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 33%, the molecular weight of the resin itself decreases, and the low moisture absorption property also deteriorates due to an increase in polar groups. By selecting a combination of the above diamine compounds, the molecular orientation in the thermoplastic polyimide is controlled, thereby suppressing the increase in CTE associated with a decrease in the imide group concentration, and ensuring low moisture absorption.

The weight-average molecular weight of the thermoplastic polyimide is preferably, for example, in the range of 10,000 to 400,000, and more preferably in the range of 50,000 to 350,000. If the weight-average molecular weight is less than 10,000, the strength of the film tends to decrease and it tends to become brittle. On the other hand, if the weight-average molecular weight exceeds 400,000, the viscosity increases excessively, and defects such as uneven film thickness and streaks tend to occur during the coating process.

The thermoplastic polyimide constituting the thermoplastic polyimide layer 112 is most preferably a completely imidized structure in order to suppress the diffusion of copper, since it becomes, for example, an adhesive layer in an insulating resin layer of a circuit board. However, a part of the polyimide may be an amic acid. The imidization rate is 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 around 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: FT/IR620 manufactured by JASCO).

From the viewpoint of ensuring adhesive function, the thickness of the thermoplastic polyimide layer 112 is preferably in the range of 1 μm to 10 μm, and more preferably in the range of 1 μm to 5 μm. If the thickness of the thermoplastic polyimide layer 112 is less than the lower limit value, the adhesiveness will be insufficient, and if it exceeds the upper limit value, the dimensional stability will tend to deteriorate.

From the viewpoint of suppressing warping, the thermoplastic polyimide layer 112 should have a thermal expansion coefficient of 30 ppm/K or more, preferably in the range of 30 ppm/K or more and 100 ppm/K or less, and more preferably in the range of 30 ppm/K or more and 80 ppm/K or less.

In addition to polyimide, the resin used for the thermoplastic polyimide layer 112 may contain optional components such as plasticizers, other curable resin components such as epoxy resins, curing agents, curing accelerators, inorganic fillers, coupling agents, bulking agents, solvents, and flame retardants. However, some plasticizers contain a large number of polar groups, which may promote the diffusion of copper from the copper wiring, so it is preferable to avoid using plasticizers as much as possible.

In order to ensure dimensional stability after circuit processing in the metal-clad laminate 100, the overall thermal expansion coefficient of the two polyimide layers 110 and the adhesive layer 120 should be 10 ppm/K or more, preferably in the range of 10 ppm/K or more and 30 ppm/K or less, and more preferably in the range of 15 ppm/K or more and 25 ppm/K or less.
In the metal-clad laminate 100, the total thickness T1 of the two polyimide layers 110 and the adhesive layer 120, the thickness T2 of the adhesive layer 120, and the ratio (T2/T1) of the thickness T2 of the adhesive layer 120 to the total thickness T1 are as described in FIG. 2.

(Synthesis of Polyimide)
The polyimide constituting the polyimide layer 110 can be produced by reacting the acid anhydride and the diamine in a solvent to generate a precursor resin, which is then heated to close the ring. The polyimide can be synthesized in the same manner as described above for the adhesive polyimide.

[Circuit board]
The metal-clad laminate 100 is useful mainly as a circuit board material for FPC, rigid-flex circuit boards, etc. That is, one or both of the two metal layers 101 of the metal-clad laminate 100 are processed into a pattern shape by a conventional method to form a wiring layer, thereby manufacturing a circuit board such as an FPC, which is one embodiment of the present invention. Although not shown in the figure, this circuit board includes a resin laminate in which a first insulating resin layer (P1), an adhesive layer (A'), and a second insulating resin layer (P2) are laminated in this order, and a wiring layer provided on one or both sides of the resin laminate.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In the following examples, various measurements and evaluations are as follows, unless otherwise specified.

[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 = {(V2 x C2) - (V1 x C1)} x MKOH / m ... (1)
Here, the amine value is a value expressed in mg-KOH/g, and MKOH 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. Furthermore, m is the sample weight expressed in grams.

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

[Viscosity measurement]
The viscosity was measured at 25° C. using an E-type viscometer (manufactured by Brookfield, product name: DV-II+Pro). The rotation speed was set so that the torque was 10% to 90%, and the value was read when the viscosity stabilized 2 minutes after the start of the measurement.

[Measurement of coefficient of thermal expansion (CTE)]
A polyimide film having a size of 3 mm x 20 mm was heated at a constant heating rate of 20°C/min from 30°C to 265°C while applying a load of 5.0 g using a thermomechanical analyzer (manufactured by Bruker, product name: 4000SA), and was then held at that temperature for 10 minutes and then cooled at a rate of 5°C/min to determine the average thermal expansion coefficient (thermal expansion coefficient) from 250°C to 100°C.

[Peel strength measurement]
The metal-clad laminate was cut to a width of 8 cm and a length of 4 cm to prepare a measurement sample. The peel strength of the interface between the PTFE film and the adhesive layer of the measurement sample was measured by fixing the copper foil surface of the measurement sample to an aluminum plate with double-sided tape using a Tensilon tester (manufactured by Toyo Seiki Seisakusho, product name: Strograph VE-1D), peeling the adhesive layer in a 180° direction at a rate of 50 mm/min, and determining the median strength when peeled 10 mm from the PTFE layer.

[Measurement of relative permittivity and dielectric loss tangent]
Using a vector network analyzer (manufactured by Agilent, product name: E8363C) and an SPDR resonator, the relative dielectric constant and dielectric loss tangent of the resin sheet (adhesive film, resin laminate) at 10 GHz were measured. The material used for the measurement was left for 24 hours under the conditions of temperature: 24 to 26°C and humidity: 45°C to 55% RH.

[Measurement of storage modulus and glass transition temperature (Tg)]
A sample was cut to 5 mm x 20 mm, and was heated stepwise from 30°C to 400°C at a temperature increase rate of 4°C/min using a dynamic viscoelasticity device (DMA: manufactured by UBM, product name: E4000F), and measurements were performed at a frequency of 11 Hz. The maximum temperature at which the value of Tan δ during the measurement was maximum was defined as Tg.

[Measurement of dimensional change rate]
The measurement of the dimensional change rate was carried out by the following procedure. First, a test piece of 150 mm square was used, and a dry film resist was exposed and developed at intervals of 100 mm to form a target for position measurement. After measuring the dimensions before etching (normal state) in an atmosphere of 23±2°C and 50±5% relative humidity, copper other than the target of the test piece was removed by etching (liquid temperature 40°C or less, time 10 minutes or less). After leaving it for 24±4 hours in an atmosphere of 23±2°C and 50±5% relative humidity, the dimensions after etching were measured. The dimensional change rate was calculated for three points in the MD direction (longitudinal direction) and TD direction (width direction) relative to the normal state, and the average value of each was used as the dimensional change rate after etching. The dimensional change rate after etching was calculated by the following formula.

Dimensional change rate after etching (%) = [(B-A)/A] x 100
A: Distance between targets before etching B: Distance between targets after etching

Next, the test piece is heat-treated in an oven at 250°C for one hour, and the distance between the position targets is then measured. The dimensional change rate after etching is calculated for three locations in each of the MD (longitudinal) and TD (width) directions, and the average value of each is taken as the dimensional change rate after heat treatment. The dimensional change rate due to heating was calculated using the following formula.

Heat dimensional change rate (%) = [(C-B)/B] x 100
B: Target distance after etching C: Target distance after heating

The abbreviations used in the examples represent the following compounds.
PMDA: pyromellitic dianhydride BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride m-TB: 2,2'-dimethyl-4,4'-diaminobiphenyl TPE-R: 1,3-bis(4-aminophenoxy)benzene bisaniline-M: 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene NMP: N-methyl-2-pyrrolidone DMAc: N,N-dimethylacetamide BTDA: 3,3',4,4'-benzophenonetetracarboxylic dianhydride DDA: aliphatic diamine having 36 carbon atoms (manufactured by Croda Japan Co., Ltd., trade name: PRIAMINE 1074, amine value: 205 mg KOH/g, mixture of dimer diamines having a cyclic structure and a chain structure, dimer component content: 95% by weight or more)
N-12: Dodecanedioic acid dihydrazide OP935: Organic phosphinic acid aluminum salt (manufactured by Clariant Japan, product name: Exolit OP935)

(Synthesis Example 1)
<Preparation of Resin Solution for Adhesive Layer>
A 500 mL four-neck flask equipped with a nitrogen inlet tube, a stirrer, a thermocouple, a Dean-Stark trap, and a cooling tube was charged with 44.92 g of BTDA (0.139 mol), 75.08 g of DDA (0.141 mol), 168 g of NMP, and 112 g of xylene, and mixed at 40 ° C for 30 minutes to prepare a polyamic acid solution. The polyamic acid solution was heated to 190 ° C, heated and stirred for 4 hours, and the distilled water and xylene were removed from the system. Thereafter, the solution was cooled to 100 ° C, 112 g of xylene was added and stirred, and further cooled to 30 ° C to prepare a polyimide solution 1 (solid content: 29.5 wt %, weight average molecular weight: 75,700) in which imidization was completed.

(Synthesis Example 2)
<Preparation of polyamic acid solution for insulating resin layer>
In a nitrogen stream, 64.20 g of m-TB (0.302 mol), 5.48 g of bisaniline-M (0.016 mol), and DMAc in an amount such that the solid content concentration after polymerization was 15% by weight were added to the reaction layer, and the mixture was stirred at room temperature to dissolve. Next, 34.20 g of PMDA (0.157 mol) and 46.13 g of BPDA (0.157 mol) were added, and the mixture was stirred at room temperature for 3 hours to carry out a polymerization reaction, thereby preparing a polyamic acid solution 2 (viscosity: 26,500 cps).

(Synthesis Example 3)
<Preparation of polyamic acid solution for insulating resin layer>
A polyamic acid solution 3 (viscosity; 2,650 cps) was prepared in the same manner as in Synthesis Example 2, except that the raw material composition was changed to 69.59 g of m-TB (0.328 mol), 542.75 g of TPE-R (1.857 mol), DMAc in an amount such that the solid content concentration after polymerization was 12% by weight, 194.39 g of PMDA (0.891 mol), and 393.31 g of BPDA (1.337 mol).

(Preparation Example 1)
Preparation of Adhesive Film
Polyimide varnish 1 was prepared by mixing 1.8 g of N-12 (0.0036 mol) and 12.5 g of OP935 with 169.49 g of polyimide solution 1 (50 g as solid content), and diluting the mixture with 6.485 g of NMP and 19.345 g of xylene.

Polyimide varnish 1 was applied to the silicone-treated surface of a release substrate (length x width x thickness = 320 mm x 240 mm x 25 μm) so that the thickness after drying was 25 μm, and then the coating was dried by heating at 80 ° C for 15 minutes and peeled off from the release substrate to prepare an adhesive film 1. The Tg of the adhesive film 1 was 78 ° C, and the relative dielectric constant (hereinafter sometimes referred to as Dk) and dielectric loss tangent (hereinafter sometimes referred to as Df) at 10 GHz were 2.68 and 0.0028, respectively. The maximum values of the storage modulus at 50 ° C and the storage modulus in the steep gradient temperature range of 180 ° C to 260 ° C after curing of the adhesive film 1 were 5.0 × 10 ² MPa and 3.0 MPa, respectively.

(Preparation Example 2)
<Preparation of single-sided metal-clad laminate>
On the copper foil 1 (electrolytic copper foil, thickness: 12 μm, surface roughness Rz on the resin layer side: 0.6 μm), polyamic acid solution 3 was uniformly applied so that the thickness after curing was about 2 to 3 μm, and then heated and dried at 120 ° C. to remove the solvent. Next, polyamic acid solution 2 was uniformly applied thereon so that the thickness after curing was about 21 μm, and then heated and dried at 120 ° C. to remove the solvent. Furthermore, polyamic acid solution 3 was uniformly applied thereon so that the thickness after curing was about 2 to 3 μm, and then heated and dried at 120 ° C. to remove the solvent. Furthermore, a stepwise heat treatment was performed from 120 ° C. to 360 ° C. to complete the imidization, and a single-sided metal-clad laminate 1 was prepared. The dimensional change rate of the single-sided metal-clad laminate 1 is as follows. The maximum storage modulus at 50° C. and the maximum storage modulus in the steep temperature range of 180° C. to 260° C. after curing of the polyamic acid solution 3 used in the single-sided metal-clad laminate 1 were 3.35 MPa and 2.71 MPa, respectively.
Dimensional change rate after etching in MD (longitudinal) direction: 0.01%
Dimensional change rate after etching in TD direction (width direction): -0.04%
Dimensional change rate after heating in MD (longitudinal) direction: -0.03%
Dimensional change rate after heating in TD direction (width direction): -0.01%

<Preparation of Polyimide Film>
The copper foil layer of the single-sided metal-clad laminate 1 was etched away using an aqueous ferric chloride solution to prepare a polyimide film 1 (thickness: 25 μm, CTE: 20 ppm/K, Dk: 3.40, Df: 0.0029).

(Preparation Example 3)
<Preparation of single-sided metal-clad laminate>
A polyamic acid solution 3 was uniformly applied onto a copper foil 1 (electrolytic copper foil, thickness: 12 μm, surface roughness Rz on the resin layer side: 0.6 μm) so that the thickness after curing would be about 2 to 3 μm, and then the solvent was removed by heating and drying at 120° C. Next, a single-sided metal-clad laminate 2 was prepared in the same manner as in Preparation Example 2, except that a polyamic acid solution 2 was uniformly applied onto the copper foil 1 so that the thickness after curing would be about 46 μm.

(Preparation Example 4)
<Preparation of single-sided metal-clad laminate>
A polyamic acid solution 3 was uniformly applied onto a copper foil 1 (electrolytic copper foil, thickness: 12 μm, surface roughness Rz on the resin layer side: 0.6 μm) so that the thickness after curing would be about 2 to 3 μm, and then the solvent was removed by heating and drying at 120° C. Next, a single-sided metal-clad laminate 3 was prepared in the same manner as in Preparation Example 2, except that a polyamic acid solution 2 was uniformly applied onto the copper foil 1 so that the thickness after curing would be about 8 μm.

[Example 1]
A surface-treated PTFE film (length x width x thickness = 200 mm x 100 mm x 50 μm, Dk; 2.1, Df; 0.00029) was prepared, and two adhesive films 1 were laminated on both sides of the film to prepare a resin film 1. The Dk and Df of the resin film 1 were 2.5 and 0.0013, respectively. Next, the insulating resin layer side of the single-sided metal-clad laminate 1 was laminated on both sides of the resin film 1 through the resin film 1, and the laminate was pressed at 160 ° C. for 1 hour under a pressure of 3.5 MPa to prepare a metal-clad laminate 1. The evaluation results of the metal-clad laminate 1 are as follows.
Dimensional change rate after etching in MD direction: -0.08%
Dimensional change rate after etching in the TD direction: -0.09%
Dimensional change rate after heating in MD direction: 0.00%
Dimensional change rate after heating in TD direction: -0.01%
There was no warpage in the metal-clad laminate 1, and there were no problems with dimensional change or peel strength. In addition, Dk and Df of the resin laminate 1 (thickness: 150 μm) prepared by etching and removing the copper foil layer in the metal-clad laminate 1 were 2.70 and 0.0031, respectively. These evaluation results are shown in Table 1.

[Examples 2 and 3]
Metal-clad laminates 2 and 3 were prepared in the same manner as in Example 1, except that single-sided metal-clad laminate 2 and single-sided metal-clad laminate 3 were used. The evaluation results of metal-clad laminates 2 and 3 and resin laminates 2 and 3 after removing the copper foil are shown in Table 1.

(Comparative Example 1)
Copper foil 1 was placed on both sides of the surface-treated PTFE film and pressure-bonded at 330° C. for 1 hour under a pressure of 3.5 MPa, but the foil peeled off.

(Comparative Example 2)
The single-sided metal-clad laminate 1 was placed on both sides of the surface-treated PTFE film and pressure-bonded at 330° C. for 1 hour under a pressure of 3.5 MPa, but peeling occurred.

The above results are summarized in Table 1.

It can be seen that Examples 1, 2, and 3 have low dimensional change rates after etching and heating, and high peel strength. In contrast, in Comparative Examples 1 and 2, lamination was performed by thermocompression bonding at 330°C, but sufficient adhesion could not be obtained, and lamination was not possible.

100...metal-clad laminate, 101...metal layer, 110...polyimide layer, 111...non-thermoplastic polyimide layer, 112...thermoplastic polyimide layer, 120...adhesive layer, 130...single-sided metal-clad laminate

Claims (9)

A polytetrafluoroethylene layer;
a first adhesive layer laminated to one side of the polytetrafluoroethylene layer;
a second adhesive layer laminated on the polytetrafluoroethylene layer on the opposite side to the first adhesive layer;
A resin film comprising:
the first adhesive layer and the second adhesive layer contain polyimide as a resin component,
the polyimide contains an acid anhydride residue derived from a tetracarboxylic acid anhydride component and a diamine residue derived from a diamine component, and contains 50 mol % or more of diamine residues derived from a diamine derived from a dimer acid in which two terminal carboxylic acid groups of a dimer acid are substituted with primary aminomethyl groups or amino groups, relative to the total diamine residues;
The first adhesive layer and the second adhesive layer each have a storage modulus of 1800 MPa or less at 50° C., and each have a maximum storage modulus of 800 MPa or less at 180 to 260° C. The resin film according to claim 1, in which the dielectric tangent of the entire resin film at 10 GHz is 0.0016 or less. The resin film according to claim 1, wherein the first adhesive layer and the second adhesive layer each have a glass transition temperature (Tg) of 180°C or less. The resin film according to claim 1 , wherein when the thickness of the polytetrafluoroethylene layer is T _FE , the thickness of the first adhesive layer is T _B1 , and the thickness of the second adhesive layer is T _B2 , the following relationship is satisfied: T FE =T B1 +T B2 +T B2 .
0.15≦(T _B1 +T _B2 )/(T _FE +T _B1 +T _B2 )≦0.70 a first single-sided metal-clad laminate having a first metal layer and a first insulating resin layer laminated on at least one surface of the first metal layer;
a second single-sided metal-clad laminate having a second metal layer and a second insulating resin layer laminated on at least one surface of the second metal layer;
An intermediate resin layer is arranged so as to abut against the first insulating resin layer and the second insulating resin layer, and is laminated between the first single-sided metal-clad laminate and the second single-sided metal-clad laminate,
A metal-clad laminate, wherein the intermediate resin layer is made of the resin film according to any one of claims 1 to 4. The metal-clad laminate according to claim 5, wherein the total thickness T1 of the first insulating resin layer, the intermediate resin layer, and the second insulating resin layer is within a range of 50 to 500 μm, and the ratio (T2/T1) of the thickness T2 of the intermediate resin layer to the total thickness T1 is within a range of 0.50 to 0.90. each of the first insulating resin layer and the second insulating resin layer has a multilayer structure in which a thermoplastic polyimide layer, a non-thermoplastic polyimide layer, and a thermoplastic polyimide layer are laminated in this order;
The metal-clad laminate according to claim 5 , wherein the intermediate resin layer is provided in contact with two of the thermoplastic polyimide layers. The metal-clad laminate according to claim 7, wherein the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer contains a tetracarboxylic acid residue and a diamine residue, and the content of the diamine residue derived from the diamine compound represented by the following general formula (A1) is 80 parts by mole or more per 100 parts by mole of the total diamine residues.

[In formula (A1), the linking group Z represents a single bond or -COO-, Y independently represents a monovalent hydrocarbon having 1 to 3 carbon atoms which may be substituted with a halogen atom or a phenyl group, an alkoxy group having 1 to 3 carbon atoms, a perfluoroalkyl group having 1 to 3 carbon atoms, or an alkenyl group, n represents an integer of 0 to 2, and p and q independently represent integers of 0 to 4.] a first circuit board having a first wiring layer and a first insulating resin layer laminated on at least one surface of the first wiring layer;
a second circuit board having a second wiring layer and a second insulating resin layer laminated on at least one surface of the second wiring layer;
an intermediate resin layer disposed so as to be in contact with the first insulating resin layer and the second insulating resin layer and laminated between the first circuit board and the second circuit board,
A circuit board, characterized in that the intermediate resin layer is made of the resin film according to any one of claims 1 to 4.

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