JP7745446B2 - Polyimide film, metal-clad laminate, its manufacturing method, and circuit board - Google Patents

Description

The present invention relates to electronic materials, such as polyimide films and metal-clad laminates used to form circuit boards, and circuit boards made from these.

Metal-clad laminates, in which a metal layer such as copper foil is laminated on one or both sides of a polyimide insulating layer, are widely used in the manufacture of circuit boards such as flexible printed circuit boards (FPCs). Such polyimide insulating layers are generally required to exhibit relatively low dielectric constants and dielectric loss tangents in order to improve the high-frequency transmission characteristics of the circuits.

The polyimide insulating layer of a metal-clad laminate is formed using a "casting method," in which a polyamic acid solution is applied to the metal layer, dried, and then subjected to an imidization heat treatment. However, during the imidization heat treatment, the volumetric expansion of the remaining solvent and the imidization water produced can sometimes cause so-called "blistering" or "peeling" (hereinafter sometimes referred to as "foaming") between the metal layer and the polyimide insulating layer.

For this reason, a metal-clad laminate that suppresses foaming without degrading dielectric properties has been proposed. This metal-clad laminate contains 40 or more moles of tetracarboxylic dianhydride residues that have a ketone group, a relatively highly polar group, in the molecule per 100 moles of acid anhydride residues that make up the polyimide insulating layer, so that the storage modulus of the polyimide insulating layer in contact with the metal layer is a predetermined value or greater (Patent Document 1).

As mentioned above, double-sided metal-clad laminates, in which metal layers are provided on both sides of a polyimide insulating layer, are also widely used as metal-clad laminates. However, double-sided metal-clad laminates are generally manufactured by placing the polyimide insulating layers of two single-sided metal-clad laminates facing each other and bonding the polyimide insulating layers together with a double-sided adhesive sheet (hereinafter referred to as bonding sheet (BS)) made by forming a polyimide adhesive into a sheet. The metal-clad laminate of Patent Document 1 can also be manufactured in a similar manner when used as a double-sided metal-clad laminate.

Japanese Patent Application Laid-Open No. 2020-104340

However, in the case of the metal-clad laminate in Patent Document 1, the focus is on ensuring adhesion at the interface between the metal layer and the adjacent polyimide insulating layer, and sufficient consideration is not given to adhesion at the interface between the extremely flat surface of the polyimide insulating layer opposite the metal layer and the bonding sheet. Furthermore, because the acid anhydride residues that make up the polyimide contain 40 or more moles of tetracarboxylic dianhydride residues that have a ketone group, a relatively highly polar group, in the molecule, there is a problem in that not only the relative dielectric constant but also the dielectric loss tangent tend to increase. For this reason, Patent Document 1 fails to identify a specific configuration for the polyimide insulating layer of a metal-clad laminate that not only suppresses foaming without degrading its dielectric properties, but also achieves good adhesion at the interface with the bonding sheet.

The object of the present invention is to provide a specific configuration for a polyimide film or metal-clad laminate that can achieve good adhesion at the interface between the polyimide film or polyimide insulating layer and the bonding sheet without degrading the dielectric properties.

The present inventors have investigated a huge number of specific factors regarding polyimide films or polyimide insulating layers of metal-clad laminates, and have found that the object of the present invention can be achieved by controlling only a limited number of specific factors shown in (a) to (c) below, thereby completing the present invention.
(a) The polyimide film or polyimide insulating layer is made of a plurality of polyimide layers, and a specific polyimide layer is disposed on the exposed surface side;
(b) The "oxygen permeability coefficient,""thermal expansion coefficient,""dielectric loss tangent," and "layer thickness" of the entire polyimide film or polyimide insulating layer are set within predetermined ranges, respectively; and (c) the polyimide constituting the polyimide layer on the exposed surface of the polyimide film or polyimide insulating layer contains, as diamine residues, diamine residues derived from 1,3-bis(aminophenoxy)benzene in a content equal to or greater than a predetermined level.

That is, a first aspect of the present invention is a polyimide film having a plurality of polyimide layers, which satisfies the following conditions (i) to (iv):
(i) an oxygen permeability coefficient of 2.0 × 10 ⁻¹⁸ mol·m/m ² ·s·Pa or less;
(ii) a thermal expansion coefficient in the range of 10 to 30 ppm/K;
(iii) a dielectric loss tangent (Tan δ) at 10 GHz of 0.004 or less; and (iv) a thickness within the range of 10 μm to 100 μm;
Fulfilling
the polyimide film has a polyimide layer (P) on at least one exposed surface side,
The polyimide film is characterized in that the polyimide (p) constituting the polyimide layer (P) contains an acid anhydride residue derived from a tetracarboxylic dianhydride component and a diamine residue derived from a diamine component, and the diamine residues contain diamine residues derived from a diamine compound represented by the following general formula (1) in an amount of at least 30 mol % based on the total diamine residues:

A second aspect of the present invention is a metal-clad laminate having a metal layer and a polyimide insulating layer having a plurality of polyimide layers,
(a) the polyimide insulating layer has a polyimide layer (P) on an exposed surface side opposite to the metal layer,
(b) The polyimide insulating layer as a whole meets the following conditions (i) to (iv):
(i) an oxygen permeability coefficient of 2.0×10 ⁻¹⁸ mol·m/m ² ·s·Pa or less;
(ii) a thermal expansion coefficient in the range of 10 to 30 ppm/K;
(iii) a dielectric loss tangent (Tan δ) at 10 GHz of 0.004 or less; and (iv) a layer thickness within the range of 10 μm to 100 μm;
and
(c) A metal-clad laminate is provided, characterized in that the polyimide (p) constituting the polyimide layer (P) contains an acid anhydride residue derived from a tetracarboxylic dianhydride component and a diamine residue derived from a diamine component, and the diamine residue contains diamine residues derived from a diamine compound represented by the following general formula (1) in an amount of at least 30 mol % relative to the total diamine residues:

A third aspect of the present invention is a method for manufacturing a metal-clad laminate, which manufactures the above-mentioned metal-clad laminate,
a step of applying a solution of polyamic acid onto the metal layer and drying it to form a first polyamic acid layer of one or more layers;
a step of applying a solution of polyamic acid, which is a precursor of the polyimide (p), onto the first polyamic acid layer and drying the solution to form a second polyamic acid layer;
The present invention provides a manufacturing method including a step of forming the polyimide insulating layer by imidizing the polyamic acid contained in the first polyamic acid layer and the polyamic acid contained in the second polyamic acid layer.

Furthermore, a fourth aspect of the present invention provides a circuit board in which the metal layer of the aforementioned metal-clad laminate is processed into wiring.

The polyimide film and metal-clad laminate of the present invention have a polyimide film or polyimide insulating layer composed of multiple polyimide layers, and the "oxygen permeability coefficient," "thermal expansion coefficient," "dielectric loss tangent," and "layer thickness" of the entire polyimide film or polyimide insulating layer are each set within a predetermined range, thereby achieving excellent dimensional stability and reduced transmission loss. Furthermore, by disposing a specific polyimide layer on the exposed surface of the polyimide film and metal-clad laminate of the present invention, good adhesion can be achieved at the interface with resin materials such as bonding sheets without degrading the dielectric properties of the entire polyimide film or polyimide insulating layer. Therefore, the metal-clad laminate of the present invention can be processed into a double-sided metal-clad laminate without compromising the excellent properties of a single-sided metal-clad laminate. Furthermore, circuit boards formed from the metal-clad laminate of the present invention have excellent dimensional stability and heat resistance, and can also achieve good high-frequency transmission characteristics.

1 is a schematic cross-sectional view showing a configuration of a metal-clad laminate according to an embodiment of the present invention.

The polyimide film and metal-clad laminate of the present invention will be described below with reference to the drawings.

[Polyimide film of the present invention and metal-clad laminate of the present invention]
The polyimide film of the present invention has multiple polyimide layers. The metal-clad laminate of the present invention has a metal layer and a polyimide insulating layer having multiple polyimide layers. The polyimide film of the present invention differs from the metal-clad laminate of the present invention in that it does not necessarily include a metal layer. In other words, the polyimide film of the present invention has substantially the same configuration as the "polyimide insulating layer" in the metal-clad laminate of the present invention.
In the following, to avoid repetition, the configuration of the polyimide film of the present invention will be clarified in the detailed description of the metal-clad laminate of the present invention. In the following description, unless otherwise noted, the "polyimide insulating layer" in the metal-clad laminate can be read as the "polyimide film."

1 is a schematic cross-sectional view showing the basic structure of one embodiment of a metal-clad laminate 30 of the present invention. This metal-clad laminate 30 has a structure in which a polyimide insulating layer 20 is provided on one side of a metal layer 10, and has the following components (a), (b), (i) to (vi), and (c). Each component will be described in detail below.
As described above, the polyimide film of the present invention has the same structure as the polyimide insulating layer 20 of the metal-clad laminate 30 .

<Configuration (a)>
(Polyimide insulating layer 20)
In the present invention, the polyimide insulating layer 20 has a polyimide layer 21 composed of a single layer or multiple polyimide layers, and a polyimide layer (P) 23 containing a specific polyimide (p) described below, and the polyimide layer (P) 23 is provided as a part of the surface side of the polyimide insulating layer 20 opposite to the metal layer 10. In Fig. 1, the polyimide layer (P) 23 is exposed.
In the case of the polyimide film of the present invention, it is sufficient that the polyimide layer (P) is provided on at least one exposed surface side.

The polyimide layer 21 is composed of a single layer or multiple polyimide layers. The primary polyimide layer is preferably a non-thermoplastic polyimide layer composed of a non-thermoplastic polyimide to ensure high heat resistance and dimensional stability. However, a thermoplastic polyimide layer composed of a thermoplastic polyimide may also be included as long as the effects of the invention are not impaired. The total thickness of the primary polyimide layers is preferably 50% or more of the thickness of the polyimide layer 21. Furthermore, to improve the adhesiveness of the polyimide surface of the polyimide insulating layer 20, a polyimide layer (P) 23 is laminated on the exposed surface of the polyimide layer 21. The polyimide constituting the polyimide layer (P) 23 is not limited to thermoplastic or non-thermoplastic polyimide, and may be any polyimide that can improve adhesiveness with other materials.

Both non-thermoplastic polyimides and thermoplastic polyimides are produced by the imidization reaction of a tetracarboxylic dianhydride component and a diamine component, and contain, as monomer residues, a tetravalent acid anhydride residue derived from the tetracarboxylic dianhydride component and a divalent diamine residue derived from the diamine component. These tetracarboxylic dianhydride components and diamine components will be described later in connection with thermoplastic polyimides and non-thermoplastic polyimides.

In the present invention, the term "non-thermoplastic" in "non-thermoplastic polyimide" means that the storage modulus at 30°C measured using a dynamic viscoelasticity measuring apparatus (DMA) is 1.0 x ¹⁰⁹ Pa or more and the storage modulus in a temperature range within 30°C above the glass transition temperature is 1.0 x ¹⁰⁸ Pa or more. Furthermore, the term "thermoplastic" in "thermoplastic polyimide" means that the storage modulus at 30°C measured using a dynamic viscoelasticity measuring apparatus (DMA) is 1.0 x ¹⁰⁹ Pa or more and the storage modulus in a temperature range within 30°C above the glass transition temperature is less than 1.0 x ¹⁰⁸ Pa.

The non-thermoplastic polyimide layer constitutes a low-thermal expansion polyimide layer, and the thermoplastic polyimide layer constitutes a high-thermal expansion polyimide layer. Here, "low thermal expansion" for a low-thermal expansion polyimide layer means that the coefficient of thermal expansion (CTE) is preferably in the range of 1 ppm/K to 25 ppm/K, more preferably 3 ppm/K to 25 ppm/K. On the other hand, "high thermal expansion" for a high-thermal expansion polyimide layer means that the CTE is preferably in the range of 35 ppm/K to 80 ppm/K, more preferably 35 ppm/K to 70 ppm/K. The thermal expansion of the polyimide layer can be adjusted by appropriately changing the polyimide monomer composition, the thickness of the polyimide insulating layer, the polyimide layer formation conditions (coating, drying, curing), etc.

<Configuration (b)>
In the metal-clad laminate 30 of this embodiment, the polyimide insulating layer 20 as a whole satisfies the following conditions (i) to (iv).

(i) The oxygen permeability coefficient is 2.0×10 ⁻¹⁸ mol·m/m ² ·s·Pa or less.
In the present invention, the oxygen permeability coefficient of the polyimide insulating layer 20 is adjusted to 2.0×10 ⁻¹⁸ mol m/m ² s Pa or less. The oxygen permeability coefficient can be measured in accordance with the differential pressure method of JIS K-7126-1. By adjusting the oxygen permeability coefficient to 2.0×10 ⁻¹⁸ mol m/m ² s Pa or less, the dielectric loss tangent can be reduced by suppressing the molecular motion of the polyimide constituting the polyimide insulating layer 20. Furthermore, when the metal layer 10 of the metal-clad laminate 30 is processed into a circuit and the polyimide insulating layer 20 is used as an insulating resin layer of a circuit board, adhesion to the wiring layer is maintained for a long period of time, even in an environment where the polyimide insulating layer 20 is repeatedly exposed to high temperatures, and excellent long-term heat-resistant adhesion can be obtained. If the oxygen permeability coefficient of the polyimide insulating layer 20 exceeds 2.0×10 ⁻¹⁸ mol m/m ² s Pa, there is a concern that oxygen that has permeated the polyimide insulating layer 20 will accelerate oxidation of the wiring layer, resulting in a decrease in adhesion between the wiring layer and the polyimide insulating layer 20. The oxygen permeability coefficient of the polyimide insulating layer 20 can be adjusted mainly by the thickness and thickness ratio of the polyimide layer 21, as well as the ratio of biphenyl skeleton-containing residues in the polyimide constituting the polyimide layer 21, preferably in the non-thermoplastic polyimide, the presence or absence of aliphatic skeleton residues, and the types of substituents of the diamine residues and acid anhydride residues.

(ii) The coefficient of thermal expansion (CTE) is in the range of 10 to 30 ppm/K.
In the present invention, the coefficient of thermal expansion (CTE) of the entire polyimide insulating layer 20 is adjusted to 10 ppm/K or more and 30 ppm/K or less, preferably 10 ppm/K or more and 25 ppm/K or less, and more preferably 15 ppm/K or more and 25 ppm/K or less. This prevents warpage and a decrease in dimensional stability in the metal-clad laminate 30. If the CTE of the entire polyimide insulating layer 20 is outside the range of 10 to 30 ppm/K, warpage and a decrease in dimensional stability are likely to occur. The coefficient of thermal expansion (CTE) of the polyimide insulating layer 20 can be adjusted by, for example, using a non-thermoplastic polyimide layer as the main polyimide layer, the thickness ratio of the non-thermoplastic polyimide layer contained in the polyimide layer 21, the ratio of rigid monomer residues such as phenyl skeleton-containing residues, naphthalene skeleton-containing residues, and biphenyl skeleton-containing residues in the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer, and the heat treatment conditions in the imidization step.

(iii) The dielectric loss tangent (Tan δ) at 10 GHz is 0.004 or less.
In the present invention, the dielectric loss tangent (Tan δ) of the entire polyimide insulating layer 20 at 10 GHz is adjusted to 0.004 or less. This allows the polyimide insulating layer 20 of the metal-clad laminate 30 to be used, for example, as an insulating resin layer in a circuit board, thereby reducing dielectric loss during high-frequency signal transmission. The dielectric loss tangent can be measured using a split post dielectric resonator (SPDR). Therefore, when the polyimide insulating layer 20 is used, for example, as an insulating resin layer in a high-frequency circuit board, transmission loss can be efficiently reduced. Note that if the dielectric loss tangent at 10 GHz exceeds 0.004, there is a concern that problems such as increased electrical signal loss may occur in the high-frequency signal transmission path when the polyimide insulating layer 20 is used as an insulating resin layer in a circuit board. The lower limit of the dielectric loss tangent at 10 GHz is not particularly limited, but can be determined depending on the required characteristics when the polyimide insulating layer 20 is used as an insulating resin layer in a circuit board. The dielectric loss tangent (Tan δ) of the polyimide insulating layer 20 can be adjusted mainly by the thickness ratio of the polyimide layer 21, as well as the ratio of biphenyl skeleton-containing residues and imide group ratio in the polyimide constituting the polyimide layer 21.

On the other hand, when the polyimide insulating layer 20 is used, for example, as an insulating resin layer for a circuit board, it is preferable that the polyimide insulating layer 20 as a whole have a dielectric constant of 4.0 or less at 10 GHz, as measured using a split post dielectric resonator (SPDR), in order to ensure impedance matching. If the dielectric constant at 10 GHz exceeds 4.0, there is a concern that when the polyimide insulating layer 20 is used as an insulating resin layer for a circuit board, this will lead to increased dielectric loss, potentially resulting in problems such as increased electrical signal loss in the high-frequency signal transmission path. Furthermore, for a given thickness of the polyimide insulating layer 20, a higher dielectric constant will narrow the circuit wiring width when impedance matching is achieved, which could potentially lead to increased conductor loss.

(iv) The layer thickness is in the range of 10 μm to 100 μm.
In the present invention, the overall thickness of the polyimide insulating layer 20 is set within the range of 10 μm to 100 μm. This is because if the layer thickness is too thin, the polyimide insulating layer 20 is prone to tearing, while if the layer thickness is too thick, there is a concern that cracks will occur in the metal layer 10 when the metal-clad laminate 30 is bent. The overall thickness of the polyimide insulating layer 20 can be set to an appropriate thickness within this range of 10 μm to 100 μm depending on the intended use of the metal-clad laminate 30. For example, when the metal-clad laminate 30 is used in a circuit board, the thickness can be set preferably within the range of 30 to 60 μm, more preferably within the range of 35 to 50 μm.

<Configuration (c)>
(Polyimide layer (P) 23)
In the present invention, the polyimide layer (P) 23 is exposed on the surface of the metal-clad laminate 30, forming an exposed surface to which, for example, a bonding sheet is directly attached. The polyimide (p) constituting the polyimide layer (P) 23 contains an acid anhydride residue derived from a tetracarboxylic dianhydride component and a diamine residue derived from a diamine component, and the diamine residue contains diamine residues derived from a diamine compound (1,3-bis(aminophenoxy)benzene) represented by the following general formula (1) in an amount of at least 30 mol %, preferably at least 50 mol %, based on the total diamine residues.

The diamine compound represented by general formula (1) has two aminophenoxy groups at the meta position of the central benzene ring. This suppresses rotational motion due to the meta bond, and because it has a relatively larger molecular weight than common diamine compounds such as di(aminophenyl)ether, it is possible to suppress an increase in the imide group concentration, thereby achieving a low dielectric constant and low dielectric loss tangent in the polyimide insulating layer 20. Furthermore, even when reacted with highly polar tetracarboxylic dianhydrides, which tend to degrade dielectric properties, it is possible to ensure adhesion to the bonding sheet without degrading the dielectric properties.

Examples of diamine compounds represented by general formula (1) include 1,3-bis(3-aminophenoxy)benzene (APB) and 1,3-bis(4-aminophenoxy)benzene (TPE-R). 1,3-bis(4-aminophenoxy)benzene (TPE-R) is particularly preferred because of the expected favorable rotational motion suppression effect of the meta bond.

The diamine residues of polyimide (p) contain diamine residues derived from the diamine compound represented by general formula (1) in an amount of at least 30 mol %, preferably at least 50 mol %, and more preferably at least 70 mol % based on the total diamine residues. If the content of diamine residues derived from the diamine compound represented by general formula (1) is too small, there is a concern that the polyimide insulating layer 20 may not achieve a low dielectric constant and low dielectric loss tangent.

The diamine residues of the polyimide (p) constituting the polyimide layer (P) 23 may contain diamine residues derived from known diamine compounds, as long as the effects of the present invention are not impaired. Examples of such known diamine compounds include 1,4-diaminobenzene (p-PDA; paraphenylenediamine), 4-aminophenyl-4'-aminobenzoate (APAB), 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, and 3,4'-diaminodiphenylpropane. benzophenone, 3,4'-diaminodiphenyl sulfide, 3,3'-diaminobenzophenone, (3,3'-bisamino)diphenylamine, 1,4-bis(3-aminophenoxy)benzene, 3-[4-(4-aminophenoxy)phenoxy]benzenamine, 3-[3-(4-aminophenoxy)phenoxy]benzenamine, 4,4'-[2-methyl-(1,3-phenylene)bisoxy]bisaniline, 4,4'-[4-methyl-(1,3-phenylene)bisoxy]bisaniline, 4,4'-[5-methyl-(1,3- 4,4'-[4-(4-aminophenoxy)phenyl] bisaniline, bis[4,4'-(3-aminophenoxy)]benzanilide, 4-[3-[4-(4-aminophenoxy)phenoxy]phenoxy]aniline, 4,4'-[oxybis(3,1-phenyleneoxy)]bisaniline, bis[4-(4-aminophenoxy)phenyl]ether (BAPE), bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS), bis[4-(4-aminophenoxy)phenyl]ketone (BAPK), 2,2-bis-[4-(3-aminophenoxy)]benzanilide, 4-[3-[4-(4-aminophenoxy)phenoxy]phenoxy]aniline, 4,4'-[oxybis(3,1-phenyleneoxy)]bisaniline, bis[4-(4-aminophenoxy)phenyl]ether (BAPE), bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS), bis[4-(4-aminophenoxy)phenyl]ketone (BAPK), bis[4-(3-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)]benzophenone, 9,9-bis[4-(3-aminophenoxy)phenyl]fluorene, 2,2-bis-[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis- [4-(3-aminophenoxy)phenyl]hexafluoropropane, 3,3'-dimethyl-4,4'-diaminobiphenyl, 4,4'-methylenedi-o-toluidine, 4,4'-methylenedi-2,6-xylidine, 4,4'-methylene-2,6-diethylaniline, 3,3'-diaminodiphenylethane, 3,3'-diaminobiphenyl, 3,3'-dimethoxybenzidine, 3,3''-diamino-p-terphenyl, 4,4'-[1,4-phenylenebis(1-methylethylidene)]bisaniline, 4,4'-[1, 3-phenylenebis(1-methylethylidene)]bisaniline, bis(p-aminocyclohexyl)methane, bis(p-β-amino-t-butylphenyl)ether, bis(p-β-methyl-δ-aminopentyl)benzene, p-bis(2-methyl-4-aminopentyl)benzene, p-bis(1,1-dimethyl-5-aminopentyl)benzene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,4-bis(β-amino-t-butyl)toluene, 2,4-diaminotoluene, m-xylene-2,5-diamino benzene, p-xylene-2,5-diamine, m-xylylenediamine, p-xylylenediamine, 2,6-diaminopyridine, 2,5-diaminopyridine, 2,5-diamino-1,3,4-oxadiazole, piperazine, 2'-methoxy-4,4'-diaminobenzanilide, 4,4'-diaminobenzanilide, 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene, 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene, 1,4-bis(4-aminophenoxy)-2,5-di-tert-butyl ether Examples include aromatic diamine compounds such as t-butylbenzene, 6-amino-2-(4-aminophenoxy)benzoxazole, 2,6-diamino-3,5-diethyltoluene, 2,4-diamino-3,5-diethyltoluene, 2,4-diamino-3,3'-diethyl-5,5'-dimethyldiphenylmethane, and bis(4-amino-3-ethyl-5-methylphenyl)methane, and aliphatic diamine compounds such as dimer acid diamines in which the two terminal carboxylic acid groups of a dimer acid are substituted with primary aminomethyl groups or amino groups.

The acid anhydride residues derived from the tetracarboxylic dianhydride component of polyimide (p) can be selected from a variety of acid anhydride residues that can achieve a good balance between the low dielectric properties of the polyimide insulating layer 20 and high adhesion to the bonding sheet. In particular, the acid anhydride residues preferably contain at least 60 mol%, more preferably at least 90 mol%, of the total acid anhydride residues, including acid anhydride residues derived from 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), which has a highly polar carbonyl group, and acid anhydride residues derived from pyromellitic dianhydride (PMDA), which has a relatively low molecular weight and therefore a relatively high imide group concentration. Either BTDA alone or PMDA alone may be used. However, when both are contained, the preferred ranges are 50-80 mol% BTDA and 20-50 mol% PMDA, based on the total acid anhydride residues.

The acid anhydride residues of the polyimide (p) may contain acid anhydride residues derived from known tetracarboxylic dianhydrides, as long as the effects of the present invention are not impaired. Examples of such known acid dianhydrides include 1,4-phenylenebis(trimellitic acid monoester)dianhydride (TAHQ), 2,3,6,7-naphthalenetetracarboxylic dianhydride (NTCDA), 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 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 acid dianhydride, 2,2-bis(2,3- or 3,4-dicarboxyphenyl)-propane dianhydride, bis(2,3- or 3,4-dicarboxyphenyl)methane dianhydride, bis(2,3- or 3,4-dicarboxyphenyl)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-phenanthrenetetracarboxylic acid dianhydride, 2,3,6,7-anthraquinone dianhydride, 1,2,5,6-naphthalenetetracarboxylic 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-)tetrachloronaphthalene Examples of aromatic tetracarboxylic dianhydrides include 1,4,5,8-(or 2,3,6,7-) perylene tetracarboxylic dianhydride, 2,3,8,9-, 3,4,9,10-, 4,5,10,11-, or 5,6,11,12-perylene tetracarboxylic dianhydride, cyclopentane 1,2,3,4-tetracarboxylic dianhydride, pyrazine 2,3,5,6-tetracarboxylic dianhydride, pyrrolidine 2,3,4,5-tetracarboxylic dianhydride, thiophene 2,3,4,5-tetracarboxylic dianhydride, 4,4'-bis(2,3-dicarboxyphenoxy)diphenylmethane dianhydride, and ethylene glycol bisanhydrotrimellitate.

In polyimide (p), the thermal expansion coefficient, tensile modulus, glass transition temperature, and other properties can be controlled by selecting the types of acid anhydride residues and diamine residues, or by selecting the respective molar ratios when two or more types of acid anhydride residues or diamine residues are used. Furthermore, when polyimide (p) contains multiple polyimide structural units, they may exist as blocks or randomly, but random existence is preferred. Furthermore, polyimide (p) preferably contains aromatic tetracarboxylic acid anhydride residues derived from aromatic tetracarboxylic acid dianhydrides and aromatic diamine residues derived from aromatic diamines. By making both the acid anhydride residues and diamine residues contained in polyimide (p) aromatic groups, degradation of the polyimide in the high-temperature environment of the polyimide insulating layer 20 can be suppressed.

The imide group concentration of the polyimide (p) is preferably 30% by weight or less. Here, "imide group concentration" means the value obtained by dividing the molecular weight of the imide group (-(CO) ₂ -N-) in the polyimide by the molecular weight of the entire polyimide structure. If the imide group concentration exceeds 30% by weight, it becomes difficult to reduce the elastic modulus at temperatures equal to or higher than the glass transition temperature, and the increase in polar groups also deteriorates the low moisture absorption property.

The weight-average molecular weight of polyimide (p) 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 film tends to have reduced strength and 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.

In addition, in the polyimide insulating layer 20 of the present invention, by further laminating a metal layer (not shown) on the polyimide layer (P) 23, the polyimide layer (P) 23 can function as an adhesive layer.

(Polyimide layer 21)
In the present invention, the polyimide layer 21 constituting the polyimide insulating layer 20 of the metal-clad laminate 30 is composed of a single layer or multiple polyimide layers, and it is preferable that the main polyimide layer contains a non-thermoplastic polyimide layer, and that the non-thermoplastic polyimide layer satisfies the following conditions (A) to (C). Each condition will be explained below.

(A) The non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer contains 50 mol % or more of monomer residues having a biphenyl skeleton among all monomer residues derived from all monomer components;
(b) the thickness is within the range of 7 μm to 70 μm; and (c) the ratio of the thickness of the non-thermoplastic polyimide layer to the thickness of the entire polyimide insulating layer 20 is 70% or more.

(Condition (a))
In the polyimide insulating layer 20, the non-thermoplastic polyimide layer is contained as the main layer of the polyimide layer 21. This is to facilitate control of the oxygen permeability coefficient, CTE, and dielectric properties of the polyimide insulating layer 20. Here, "main layer" refers to a layer that accounts for more than 50%, preferably 60 to 100%, of the overall thickness of the polyimide layer 21. Furthermore, the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer preferably contains 50 mol% or more, more preferably 70 mol% or more, of monomer residues having a biphenyl skeleton (hereinafter sometimes referred to as "biphenyl skeleton-containing residues") among all monomer residues derived from all monomer components constituting the non-thermoplastic polyimide. This increases the content of biphenyl skeleton-containing residues in the entire polyimide constituting the polyimide insulating layer 20, thereby reducing the oxygen permeability coefficient and achieving a low dielectric loss tangent. Meanwhile, to maintain the physical properties required for the polyimide insulating layer 20 of the metal-clad laminate 30 used as a circuit board material, the proportion of biphenyl skeleton-containing residues relative to all monomer residues is preferably 80 mol% or less. Here, the biphenyl skeleton is a skeleton formed by two single-bonded phenyl groups. Therefore, examples of biphenyl skeleton-containing residues include biphenyldiyl residues and biphenyltetrayl residues. The aromatic rings contained in these residues may have any substituent. Representative examples of biphenyldiyl groups include biphenyl-3,3'-diyl residues and biphenyl-4,4'-diyl residues. Representative examples of biphenyltetrayl residues include biphenyl-3,4,3',4'-tetrayl residues.

Furthermore, the proportion of biphenyl skeleton-containing residues in the non-thermoplastic polyimide layer is preferably 20 mol % or more, more preferably 30 mol % or more, and even more preferably 40 mol % or more, based on each of all diamine residues and all acid anhydride residues. By containing 20 mol % or more biphenyl skeleton-containing residues based on each of all diamine residues and all acid anhydride residues, the formation of an ordered structure throughout the polymer is more promoted than when the biphenyl skeleton-containing residues are biased toward either diamine residues or acid anhydride residues, and the effect of reducing the oxygen permeability coefficient and dielectric loss tangent is enhanced.

The biphenyl skeleton-containing residue has a structure derived from the raw material monomer, and may be derived from a tetracarboxylic dianhydride or a diamine compound.

Representative examples of acid anhydride residues having a biphenyl skeleton include residues derived from acid dianhydrides such as 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,3',3,4'-biphenyltetracarboxylic dianhydride, and 4,4'-biphenol-bis(trimellitate anhydride). Among these, acid anhydride residues derived from BPDA (hereinafter also referred to as "BPDA residues") are particularly preferred because they facilitate the formation of an ordered polymer structure and can reduce dielectric tangent and moisture absorption by suppressing molecular motion. Furthermore, BPDA residues can impart self-supporting properties to the gel film of the polyimide precursor polyamic acid.

The acid anhydride residues of the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer may contain acid anhydride residues derived from known tetracarboxylic dianhydrides in addition to acid anhydride residues having a biphenyl skeleton, as long as the effects of the present invention are not impaired. Examples of such known acid dianhydrides include pyromellitic dianhydride (PMDA), 1,4-phenylenebis(trimellitic acid monoester) dianhydride (TAHQ), 2,3,6,7-naphthalenetetracarboxylic dianhydride (NTCDA), 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 2,2',3,3'-, 2,3,3',4'-, or 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,3',3,4'-diphenylethertetracarboxylic dianhydride, bis(2,3-dicarboxylate) dianhydride, and bis(2,3-dicarboxylate) dianhydride. phenyl) ether dianhydride, 3,3",4,4",-, 2,3,3",4", or 2,2",3,3"-p-terphenyltetracarboxylic acid dianhydride, 2,2-bis(2,3- or 3,4-dicarboxyphenyl)-propane dianhydride, bis(2,3- or 3,4-dicarboxyphenyl)methane dianhydride, bis(2,3- or 3,4-dicarboxyphenyl)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-phenanthrenetetracarboxylic acid dianhydride Anhydride, 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-)tetracarboxylic dianhydride Examples include aromatic tetracarboxylic dianhydrides such as tetrachloronaphthalene-1,4,5,8- (or 2,3,6,7-) tetracarboxylic dianhydride, 2,3,8,9-, 3,4,9,10-, 4,5,10,11-, or 5,6,11,12-perylene tetracarboxylic dianhydride, cyclopentane-1,2,3,4-tetracarboxylic dianhydride, pyrazine-2,3,5,6-tetracarboxylic dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic dianhydride, thiophene-2,3,4,5-tetracarboxylic dianhydride, 4,4'-bis(2,3-dicarboxyphenoxy)diphenylmethane dianhydride, and ethylene glycol bisanhydrotrimellitate.

On the other hand, representative examples of diamine compounds having a biphenyl skeleton include diamine compounds having only two aromatic rings, such as 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB), 2,2'-diethyl-4,4'-diaminobiphenyl (m-EB), 2,2'-diethoxy-4,4'-diaminobiphenyl (m-EOB), 2,2'-dipropoxy-4,4'-diaminobiphenyl (m-POB), 2,2'-di-n-propyl-4,4'-diaminobiphenyl (m-NPB), 2,2'-divinyl-4,4'-diaminobiphenyl (VAB), 4,4'-diaminobiphenyl, and 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl (TFMB). Residues derived from these diamine compounds have a rigid structure and therefore have the effect of imparting an ordered structure to the entire polymer. By including residues derived from these diamine compounds, polyimides with low oxygen permeability and low moisture absorption can be obtained, and moisture content within the molecular chain can be reduced, resulting in a lower dielectric tangent. Of these, m-TB is preferred.

The diamine residues of the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer may contain diamine residues derived from known diamine compounds in addition to the above-mentioned diamine compounds having a biphenyl skeleton, as long as the effects of the present invention are not impaired. Examples of such known diamine compounds include 1,4-diaminobenzene (p-PDA; paraphenylenediamine), 4-aminophenyl-4'-aminobenzoate (APAB), 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, (3,3'-bisamino)diphenylamine, 1,4-bis(3-aminophenoxy)benzene, 3-[4-(4-aminophenoxy)phenoxy]benzenamine, 3-[3-(4-aminophenoxy)phenoxy]benzenamine, 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 bis[4,4'-(3-aminophenoxy)]benzanilide, 4-[3-[4-(4-aminophenoxy)phenoxy]phenoxy]aniline, 4,4'-[oxybis(3,1-phenyleneoxy)]bisaniline, bis[4-(4-aminophenoxy)phenyl]ether (BAPE), bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS), bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS), 2,2-bis-[4-(3-aminophenoxy)phenyl]ketone (BAPK), 2,2-bis-[4-(3-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)]benzophenone, 9,9-bis[4-(3-aminophenoxy)phenyl]fluorene, 2,2-bis-[4-(4-aminophenoxy)phenyl] 4,4'-methylene-2,6-diethylaniline, 4,4'-methylenedi-o-toluidine, 4,4'-methylenedi-2,6-diethylaniline, 3,3'-diaminodiphenylethane, 3,3'-diaminobiphenyl, 3,3'-dimethoxybenzidine, 3,3''-diamino-p-terphenyl, 4,4'-[1,4-phenylenebis(1-methylphenyl)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-methylphenyl)phenyl]hexafluoropropane 4,4'-[1,3-phenylenebis(1-methylethylidene)]bisaniline, 4,4'-[1,3-phenylenebis(1-methylethylidene)]bisaniline, bis(p-aminocyclohexyl)methane, bis(p-β-amino-t-butylphenyl)ether, bis(p-β-methyl-δ-aminopentyl)benzene, p-bis(2-methyl-4-aminopentyl)benzene, p-bis(1,1-dimethyl-5-aminopentyl)benzene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,4-bis(β-amino-t-butyl)toluene, 2,4-diaminotoluene , m-xylene-2,5-diamine, p-xylene-2,5-diamine, m-xylylenediamine, p-xylylenediamine, 2,6-diaminopyridine, 2,5-diaminopyridine, 2,5-diamino-1,3,4-oxadiazole, piperazine, 2'-methoxy-4,4'-diaminobenzanilide, 4,4'-diaminobenzanilide, 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene, 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene, 1,4-bis(4-aminophenoxy)-2, Examples include aromatic diamine compounds such as 5-di-tert-butylbenzene, 6-amino-2-(4-aminophenoxy)benzoxazole, 2,6-diamino-3,5-diethyltoluene, 2,4-diamino-3,5-diethyltoluene, 2,4-diamino-3,3'-diethyl-5,5'-dimethyldiphenylmethane, and bis(4-amino-3-ethyl-5-methylphenyl)methane, and aliphatic diamine compounds such as dimer acid diamines in which the two terminal carboxylic acid groups of a dimer acid are substituted with primary aminomethyl groups or amino groups.

(Condition (b))
In the present invention, the thickness of the non-thermoplastic polyimide layer is preferably within the range of 7 μm to 70 μm. The thickness of the non-thermoplastic polyimide layer can be appropriately set within the range of 7 μm to 70 μm depending on the purpose of use, but is more preferably within the range of 25 μm to 49 μm, and even more preferably within the range of 30 μm to 49 μm. When the thickness of the non-thermoplastic polyimide layer is within the above range, it is expected to have an effect of improving the dielectric properties of the polyimide insulating layer 20, and furthermore, it is possible to suppress an increase in the oxygen permeability coefficient and to suppress a decrease in adhesion between the wiring layer and the insulating resin layer when repeatedly exposed to high temperatures.

(Condition (C))
In the present invention, the ratio of the thickness of the non-thermoplastic polyimide layer to the total thickness of the polyimide insulating layer 20 is preferably 70% or more. This prevents the oxygen permeability coefficient of the polyimide insulating layer 20 from increasing excessively, facilitates CTE control, and increases the freedom of selection of the polyimide layer (P) 23 that can be used when considering a decrease in dielectric loss tangent. This makes it easier to control the dimensional change rate and adapt to high-speed transmission when used in, for example, a circuit board. Note that the larger this ratio, the easier it tends to be to control the oxygen permeability coefficient and dimensional change rate and reduce the dielectric loss tangent.

In non-thermoplastic polyimides, the oxygen permeability coefficient, dielectric properties, thermal expansion coefficient, storage modulus, tensile modulus, etc. can be controlled by selecting the types of acid anhydride residues and diamine residues, or by selecting the respective molar ratios when two or more types of acid anhydride residues or diamine residues are used. Furthermore, when non-thermoplastic polyimides contain multiple polyimide structural units, they may exist as blocks or randomly, but random existence is preferred. Preferably, non-thermoplastic polyimides are composed of aromatic tetracarboxylic acid anhydride residues derived from aromatic tetracarboxylic acid dianhydrides and aromatic diamine residues derived from aromatic diamines. By making both the acid anhydride residues and diamine residues contained in the non-thermoplastic polyimide aromatic groups, the dimensional accuracy of the polyimide insulating layer 20 in high-temperature environments can be improved.

The imide group concentration of the non-thermoplastic polyimide is preferably 33% by weight or less. Here, "imide group concentration" refers to 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% by weight, the moisture absorption increases due to the increase in polar groups. Note that by selecting the combination of the acid dianhydride and diamine compound, the molecular orientation in the non-thermoplastic polyimide can be controlled, thereby suppressing the increase in CTE that accompanies a decrease in the imide group concentration and ensuring low moisture absorption.

The weight-average molecular weight of the non-thermoplastic polyimide is preferably 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 film tends to have reduced strength and become brittle. On the other hand, if the weight-average molecular weight exceeds 400,000, the viscosity increases excessively, making the film more susceptible to defects such as uneven thickness and streaks during coating.

The polyimide insulating layer 20 of this embodiment may contain inorganic fillers or organic fillers in the polyimide layer 21 or the polyimide layer (P) 23, as needed. Specific examples include inorganic fillers such as silicon dioxide, aluminum oxide, magnesium oxide, beryllium oxide, boron nitride, aluminum nitride, silicon nitride, aluminum fluoride, and calcium fluoride, and organic fillers such as fluorine-based polymer particles and liquid crystal polymer particles. These can be used alone or in combination of two or more.

In the present invention, the polyimide layer 21 of the polyimide insulating layer 20 may be a single non-thermoplastic polyimide layer that is laminated directly on the metal layer 10.

<Metal layer>
The material of the metal layer 10 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 copper alloys are particularly preferred. The material of the wiring layer in the circuit board, which will be described later, is also the same as that of the metal layer 10.

The thickness of the metal layer 10 is not particularly limited, but when using a metal foil such as copper foil, the upper limit of the thickness is preferably 35 μm or less, and more preferably in the range of 5 to 25 μm. From the viewpoint of production stability and ease of handling, the lower limit of the thickness is preferably 5 μm. The copper foil used as the metal layer 10 may be rolled copper foil or electrolytic copper foil. Commercially available copper foil can also be used.

The ten-point average roughness (Rzjis) of the surface of the metal layer 10 that contacts the polyimide layer 21 is preferably 1.2 μm or less, and more preferably 1.0 μm or less. When the metal layer 10 is made from metal foil, achieving a surface roughness Rzjis of 1.2 μm or less enables fine wiring processing that supports high-density packaging and reduces conductor loss during high-frequency signal transmission, making it applicable to circuit boards for high-frequency signal transmission. If the surface roughness Rzjis exceeds 1.2 μm, the wiring shape during fine wiring processing deteriorates, making processing difficult, and conductor loss increases, making the material unsuitable for high-frequency signal transmission.

The metal layer 10 may also be surface-treated with, for example, siding, aluminum alcoholate, aluminum chelate, or a silane coupling agent, for the purposes of rust prevention or improving adhesion.

[Metal-clad laminate manufacturing method]
The metal-clad laminate 30 of the present invention can be produced by a production method including the following steps (A), (B), and (C).

<Process (A)>
A solution of polyamic acid, which is a polyimide precursor, is applied to a metal foil that will become the metal layer 10, and then dried to form a single or multiple first polyamic acid layers. The method for applying the polyamic acid solution to the metal layer 10 is not particularly limited, and application can be performed using a coater such as a comma coater, a die coater, a knife coater, or a lip coater. When the first polyamic acid layer is to be multiple layers, for example, a method in which the polyamic acid solution is repeatedly applied to the metal foil and dried, or a method in which multiple layers of polyamic acid are simultaneously applied to the metal foil by multilayer extrusion and then dried, can be used.

A polyamic acid solution can be obtained by dissolving approximately equimolar amounts of the acid dianhydride component and the diamine component in an organic solvent such as N,N-dimethylformamide (DMF), and then stirring at a temperature between 0 and 100°C for 30 minutes to 24 hours to cause a polymerization reaction. Typically, the amount used is adjusted so that the polyamic acid concentration of the polyamic acid solution is approximately 5 to 30% by weight, and the viscosity is preferably 500 cps to 100,000 cps.

<Process (B)>
Next, a solution of polyamic acid, which is a precursor of polyimide (p), is applied to the first polyamic acid layer in the same manner as in step (A), and dried to form a second polyamic acid layer. Note that the first polyamic acid layer and the second polyamic acid layer may be simultaneously formed by multilayer extrusion in the same manner as above.

<Step (C)>
Next, the polyamic acid contained in the first polyamic acid layer and the polyamic acid contained in the second polyamic acid layer are imidized to form polyimide layer 21 and polyimide layer (P) 23, thereby forming polyimide insulating layer 20. The method for imidizing polyamic acid is not particularly limited, and a suitable method is, for example, heat treatment in which the polyamic acid is heated at a temperature in the range of 80 to 400°C for 1 to 24 hours. This results in metal-clad laminate 30 shown in FIG. 1.

The polyimide film of the present invention can be produced by the above-mentioned method for producing a metal-clad laminate 30, by removing the metal layer 10 by etching or other means after producing the metal-clad laminate 30, or by using a peelable substrate (including peelable metal foil) instead of metal foil, and peeling the metal layer 10 from the polyimide insulating layer 20 after producing the metal-clad laminate 30.

[Circuit board]
The metal-clad laminate 30 of the present invention is useful as a circuit board material for FPCs and the like, and a circuit board produced by processing the metal-clad laminate 30 of the present invention is also an aspect of the present invention. This circuit board is obtained by processing the metal layer 10 of the metal-clad laminate 30 of the present invention into wiring using a conventional method, and its structural features inherit the structural features of the metal-clad laminate 30 of the present invention. Therefore, this circuit board can achieve stable and good high-frequency transmission characteristics.

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

[Viscosity measurement]
The viscosity of the polyamic acid solutions of Synthesis Examples 1 to 16 and A to C was measured at 25°C using an E-type viscometer (manufactured by Brookfield, trade 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 glass transition temperature and storage modulus]
The polyimide film was cut into a size of 5 mm x 70 mm, and the glass transition temperature and storage modulus were measured using a dynamic viscoelasticity measuring device (DMA: manufactured by TA Instruments, product name: RSA G2) at a heating rate of 4°C/min from 30°C to 400°C and a frequency of 10 Hz. The temperature at which the change in modulus (tan δ) was maximum was taken as the glass transition temperature. From these measurement results, the polyimide film was judged to be "non-thermoplastic." A polyimide film was judged to be "non-thermoplastic" when its storage modulus at 30°C was 1.0 x ¹⁰⁹ Pa or more and its storage modulus in a temperature range within the glass transition temperature + 30°C was 1.0 x ¹⁰⁸ Pa or more.

[Measurement of coefficient of thermal expansion (CTE)]
The polyimide films obtained by removing the copper foil from the single-sided copper-clad laminates of Examples 1 to 30 and Comparative Examples 1 to 4 were cut into pieces measuring 3 mm x 20 mm. Using a thermomechanical analyzer (trade name: TMA/SS6100, manufactured by Hitachi High-Tech Science Corporation (formerly Seiko Instruments Inc.)), the films were heated from 30°C to 260°C at a constant rate while applying a load of 5.0 g, and then held at that temperature for 10 minutes. After cooling at a rate of 5°C/min, the average thermal expansion coefficient (thermal expansion coefficient) from 250°C to 100°C was determined. In practice, it is desirable that the thermal expansion coefficient be within the range of 10 to 30 ppm/K.

[Peel Strength Measurement]
Two polyimide films obtained by removing the copper foil from the single-sided copper-clad laminates of Examples 1 to 30 and Comparative Examples 1 to 4 were laminated with a bonding sheet (polyimide-based, manufactured by Nippon Steel Chemical & Material Co., Ltd., product name: NB25A-M, thickness: 25 μm) so that the side of the polyimide film opposite to the side in contact with the copper foil was in contact with the bonding sheet, and the laminate was heated and pressed for 60 minutes at a temperature of 160 ° C and a surface pressure of 3.5 MPa using a vacuum press. The resulting laminated sheet was cut to a width of 5 mm, and one of the polyimide films was pulled in a 180 ° direction at a rate of 50 mm / min using a Tensilon tester (product name: Strograph VE-1D, manufactured by Toyo Seiki Seisakusho, Ltd.). The peel strength was determined from the median strength when peeled 20 mm. In practice, the peel strength is desired to be 0.7 kN / m or more.

[Measurement of relative permittivity and dielectric loss tangent]
The polyimide films obtained by removing the copper foil from the single-sided copper-clad laminates of Examples 1 to 30 and Comparative Examples 1 to 4 were measured for their dielectric constant and dielectric dissipation factor at a frequency of 10 GHz using a vector network analyzer (manufactured by Agilent, product name: E8363C) and a split post dielectric resonator (SPDR resonator). The materials used for the measurements were left for 24 hours under conditions of a temperature of 24 to 26°C and a humidity of 45 to 55%. For practical purposes, it is desirable for the dielectric constant to be 3.5 or less and the dielectric dissipation factor to be 0.004 or less.

[Measurement of oxygen permeability coefficient]
The polyimide films obtained by removing the copper foil from the single-sided copper-clad laminates of Examples 1 to 30 and Comparative Examples 1 to 4 were measured for their oxygen permeability coefficients in accordance with the differential pressure method of JIS K7126-1 under conditions of a temperature of 23°C ± 2°C and a humidity of 65% RH ± 5% RH. The vapor permeability measuring devices used were a GTR-30XAD2 manufactured by GTR Tech Co., Ltd. and a G2700T F manufactured by Yanaco Technical Science Co., Ltd. For practical purposes, the oxygen permeability coefficient is desirably 2.0 × 10 ^-18 mol m/m ² s Pa or less.

The abbreviations used in the following synthesis examples, examples, and comparative examples represent the following compounds.
PMDA: pyromellitic dianhydride BTDA: 3,3',4,4'-benzophenonetetracarboxylic dianhydride BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride m-TB: 2,2'-dimethyl-4,4'-diaminobiphenyl TPE-R: 1,3-bis(4-aminophenoxy)benzene TPE-Q: 1,4-bis(4-aminophenoxy)benzene APB: 1,3-bis(3-aminophenoxy)benzene BAPP: 2,2-bis[4-(4-aminophenoxy)phenyl]propane BAPB: 4,4'-bis(4-aminophenoxy)biphenyl 4,4'-DAPE: 4,4'-diaminodiphenyl ether Bisaniline-P: 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene (manufactured by Mitsui Chemicals Fine Co., Ltd., trade name: Bisaniline-P)
DMAc: N,N-dimethylacetamide

(Synthesis Example 1)
Under a nitrogen stream, 20.670 g of TPE-R (0.0707 mol) and an amount of DMAc such that the solids concentration after polymerization would be 12 wt % were added to a 500 ml separable flask and dissolved by stirring at room temperature. Next, 15.330 g of PMDA (0.0703 mol) was added, and the mixture was allowed to polymerize with stirring at room temperature for 3 hours, yielding polyamic acid solution 1 having the composition shown in Table 1. The solution viscosity of polyamic acid solution 1 was 4,600 cps.

(Synthesis Example 2)
Under a nitrogen stream, 19.862 g of TPE-R (0.0680 mol) and an amount of DMAc such that the solids concentration after polymerization would be 12 wt% were added to a 500 ml separable flask and stirred at room temperature to dissolve. Next, 11.785 g of PMDA (0.0540 mol) and 4.353 g of BTDA (0.0135 mol) were added, and the polymerization reaction was continued with stirring at room temperature for 3 hours to obtain polyamic acid solution 2. The solution viscosity of polyamic acid solution 2, having the composition shown in Table 1, was 4,300 cps.

(Synthesis Example 3)
Under a nitrogen stream, 19.482 g of TPE-R (0.0666 mol) and an amount of DMAc such that the solids concentration after polymerization would be 12 wt% were added to a 500 ml separable flask and stirred at room temperature to dissolve. Next, 10.114 g of PMDA (0.0464 mol) and 6.404 g of BTDA (0.0199 mol) were added, and the polymerization reaction was continued with stirring at room temperature for 3 hours to obtain Polyamic Acid Solution 3. The solution viscosity of Polyamic Acid Solution 3, having the composition shown in Table 1, was 4,000 cps.

(Synthesis Example 4)
Under a nitrogen stream, 19.116 g of TPE-R (0.0654 mol) and an amount of DMAc such that the solids concentration after polymerization would be 12 wt% were added to a 500 ml separable flask and stirred at room temperature to dissolve. Next, 8.506 g of PMDA (0.0390 mol) and 8.378 g of BTDA (0.0260 mol) were added, and the polymerization reaction was continued with stirring at room temperature for 3 hours to obtain Polyamic Acid Solution 4. The solution viscosity of Polyamic Acid Solution 4, having the composition shown in Table 1, was 4,300 cps.

(Synthesis Example 5)
Under a nitrogen stream, 18.763 g of TPE-R (0.0642 mol) and an amount of DMAc such that the solids concentration after polymerization would be 12 wt% were added to a 500 ml separable flask and stirred at room temperature to dissolve. Next, 6.958 g of PMDA (0.0319 mol) and 10.279 g of BTDA (0.0319 mol) were added, and the polymerization reaction was continued with stirring at room temperature for 3 hours to obtain Polyamic Acid Solution 5. The solution viscosity of Polyamic Acid Solution 5, having the composition shown in Table 1, was 4,400 cps.

(Synthesis Example 6)
Under a nitrogen stream, 18.095 g of TPE-R (0.0619 mol) and an amount of DMAc such that the solids concentration after polymerization would be 12 wt% were added to a 500 ml separable flask and stirred at room temperature to dissolve. Next, 4.026 g of PMDA (0.0185 mol) and 13.879 g of BTDA (0.0431 mol) were added, and the polymerization reaction was continued with stirring at room temperature for 3 hours to obtain Polyamic Acid Solution 6. The solution viscosity of Polyamic Acid Solution 6, having the composition shown in Table 1, was 3,700 cps.

(Synthesis Example 7)
Under a nitrogen stream, 17.779 g of TPE-R (0.0608 mol) and an amount of DMAc such that the solids concentration after polymerization would be 12 wt% were added to a 500 ml separable flask and stirred at room temperature to dissolve. Next, 2.637 g of PMDA (0.0121 mol) and 15.584 g of BTDA (0.0484 mol) were added, and the polymerization reaction was continued with stirring at room temperature for 3 hours to obtain Polyamic Acid Solution 7. The solution viscosity of Polyamic Acid Solution 7, having the composition shown in Table 1, was 3,400 cps.

(Synthesis Example 8)
Under a nitrogen stream, 17.178 g of TPE-R (0.0588 mol) and an amount of DMAc such that the solids concentration after polymerization would be 12 wt % were added to a 500 ml separable flask and dissolved by stirring at room temperature. Next, 18.822 g of BTDA (0.0584 mol) was added, and the mixture was allowed to polymerize with stirring at room temperature for 3 hours, yielding polyamic acid solution 8 having the composition shown in Table 1. The solution viscosity of polyamic acid solution 8 was 3,800 cps.

(Synthesis Example 9)
Under a nitrogen stream, 18.182 g of TPE-R (0.0622 mol) and an amount of DMAc such that the solids concentration after polymerization would be 12 wt% were added to a 500 ml separable flask and stirred at room temperature to dissolve. Next, 4.046 g of PMDA (0.0185 mol), 11.953 g of BTDA (0.0371 mol), and 1.819 g of BPDA (0.0062 mol) were added, and the polymerization reaction was continued with stirring at room temperature for 3 hours to obtain polyamic acid solution 9 having the composition shown in Table 1. The solution viscosity of polyamic acid solution 9 was 4,100 cps.

(Synthesis Example 10)
Under a nitrogen stream, 18.270 g of TPE-R (0.0625 mol) and an amount of DMAc such that the solids concentration after polymerization would be 12 wt% were added to a 500 ml separable flask and stirred at room temperature to dissolve. Next, 4.065 g of PMDA (0.0186 mol), 10.009 g of BTDA (0.0311 mol), and 3.656 g of BPDA (0.0124 mol) were added, and the polymerization reaction was continued with stirring at room temperature for 3 hours to obtain polyamic acid solution 10 having the composition shown in Table 1. The solution viscosity of polyamic acid solution 10 was 3,800 cps.

(Synthesis Example 11)
Under a nitrogen stream, 18.359 g of TPE-R (0.0628 mol) and an amount of DMAc such that the solids concentration after polymerization would be 12 wt% were added to a 500 ml separable flask and stirred at room temperature to dissolve. Next, 4.085 g of PMDA (0.0187 mol), 8.046 g of BTDA (0.0250 mol), and 5.510 g of BPDA (0.0187 mol) were added, and the polymerization reaction was continued with stirring at room temperature for 3 hours to obtain polyamic acid solution 11 having the composition shown in Table 1. The solution viscosity of polyamic acid solution 11 was 4,300 cps.

(Synthesis Example 12)
Under a nitrogen stream, 14.476 g of TPE-R (0.0495 mol), 3.619 g of APB (0.0124 mol), and an amount of DMAc such that the solids concentration after polymerization would be 12 wt% were added to a 500 ml separable flask and stirred at room temperature to dissolve. Next, 4.026 g of PMDA (0.0185 mol) and 13.879 g of BTDA (0.0431 mol) were added, and the polymerization reaction was continued with stirring at room temperature for 3 hours to obtain polyamic acid solution 12 having the composition shown in Table 1. The solution viscosity of polyamic acid solution 12 was 3,100 cps.

(Synthesis Example 13)
Under a nitrogen stream, 8.348 g of TPE-R (0.0286 mol), 11.723 g of BAPP (0.0286 mol), and an amount of DMAc such that the solids concentration after polymerization would be 12 wt% were added to a 500 ml separable flask and stirred at room temperature to dissolve. Next, 4.953 g of PMDA (0.0227 mol) and 10.976 g of BTDA (0.0341 mol) were added, and the polymerization reaction was continued with stirring at room temperature for 3 hours to obtain polyamic acid solution 13 having the composition shown in Table 1. The solution viscosity of polyamic acid solution 13 was 4,200 cps.

(Synthesis Example 14)
Under a nitrogen stream, 6.940 g of TPE-R (0.0237 mol), 13.120 g of BAPB (0.0356 mol), and an amount of DMAc such that the solids concentration after polymerization would be 12 wt% were added to a 500 ml separable flask and stirred at room temperature to dissolve. Next, 6.434 g of PMDA (0.0295 mol) and 9.505 g of BTDA (0.0295 mol) were added, and the polymerization reaction was continued with stirring at room temperature for 3 hours to obtain polyamic acid solution 14 having the composition shown in Table 1. The solution viscosity of polyamic acid solution 14 was 3,700 cps.

(Synthesis Example 15)
Under a nitrogen stream, 15.417 g of TPE-R (0.0527 mol), 2.799 g of m-TB (0.0132 mol), and an amount of DMAc such that the solids concentration after polymerization would be 12 wt% were added to a 500 ml separable flask and stirred at room temperature to dissolve. Next, 4.288 g of PMDA (0.0197 mol) and 13.496 g of BPDA (0.0459 mol) were added, and the polymerization reaction was continued with stirring at room temperature for 3 hours to obtain polyamic acid solution 15 having the composition shown in Table 1. The solution viscosity of polyamic acid solution 15 was 3,500 cps.

(Synthesis Example 16)
Under a nitrogen stream, 13.848 g of 4,4'-DAPE (0.0692 mol) and an amount of DMAc such that the solids concentration after polymerization would be 12 wt% were placed in a 500 ml separable flask and stirred at room temperature to dissolve. Next, 22.152 g of BTDA (0.0687 mol) was added, and the mixture was stirred at room temperature for 3 hours to carry out a polymerization reaction, yielding polyamic acid solution 16 having the composition shown in Table 1. The solution viscosity of polyamic acid solution 16 was 3,300 cps.

(Synthesis example A)
Under a nitrogen stream, 120.612 g of m-TB (0.5681 mol), 9.227 g of TPE-Q (0.0316 mol), 10.873 g of bisaniline-P (0.0316 mol), and an amount of DMAc such that the solids concentration after polymerization would be 15 wt% were added to a 3000 ml separable flask and stirred at room temperature to dissolve. Next, 67.814 g of PMDA (0.3109 mol) and 91.474 g of BPDA (0.3109 mol) were added, and the polymerization reaction was continued with stirring at room temperature for 3 hours to obtain polyamic acid solution A with the composition shown in Table 1. The solution viscosity of polyamic acid solution A was 28,300 cps.

Polyamic acid solution A was uniformly applied to the substrate so that the thickness after curing was approximately 25 μm, and then the solution was dried by heating at 120°C to remove the solvent. Further, stepwise heat treatment from 120°C to 360°C was carried out within 10 minutes, completing the imidization, and the resulting polyimide film was non-thermoplastic.

(Synthesis example B)
Under a nitrogen stream, 127.501 g of m-TB (0.6006 mol), 12.976 g of BAPP (0.0316 mol), and an amount of DMAc such that the solids concentration after polymerization would be 15 wt% were added to a 3000 ml separable flask and stirred at room temperature to dissolve. Next, 67.914 g of PMDA (0.3114 mol) and 91.609 g of BPDA (0.3114 mol) were added, and the polymerization reaction was continued with stirring at room temperature for 3 hours to obtain polyamic acid solution B having the composition shown in Table 1. The solution viscosity of polyamic acid solution B was 25,600 cps.

Polyamic acid solution B was uniformly applied to the substrate to a thickness of approximately 25 μm after curing, and then heated and dried at 120°C to remove the solvent. Further, stepwise heat treatment from 120°C to 360°C was performed within 10 minutes to complete the imidization, resulting in a non-thermoplastic polyimide film.

(Synthesis example C)
Under a nitrogen stream, 114.972 g of m-TB (0.5416 mol), 39.580 g of TPE-R (0.1354 mol), and an amount of DMAc such that the solids concentration after polymerization would be 15 wt% were added to a 3000 ml separable flask and stirred at room temperature to dissolve. Next, 145.447 g of PMDA (0.6668 mol) was added, and the polymerization reaction was carried out by continuing to stir at room temperature for 3 hours, yielding polyamic acid solution C having the composition shown in Table 1. The solution viscosity of polyamic acid solution C was 27,200 cps.

Polyamic acid solution C was uniformly applied to the substrate to a thickness of approximately 25 μm after curing, and then heated and dried at 120°C to remove the solvent. Further, stepwise heat treatment from 120°C to 360°C was performed within 10 minutes to complete the imidization, resulting in a non-thermoplastic polyimide film.

[Example 1]
Polyamic acid solution A was uniformly applied to the copper foil as the first layer, which would contact the copper foil, to a thickness of 23 μm after curing, and then heated and dried at 120°C for 2 minutes to remove the solvent. Polyamic acid solution 1, which would form the second layer, was uniformly applied to the first layer to a thickness of 2 μm after curing, and then heated and dried at 130°C for 30 seconds to remove the solvent. Subsequently, imidization was completed by stepwise heat treatment from 140°C to 360°C, producing a copper-clad laminate. The copper foil was then etched away using an aqueous ferric chloride solution to obtain a polyimide film. The physical properties of the resulting polyimide film are shown in Table 2.

[Examples 2] to [Example 15] and [Comparative Examples 1] to [Comparative Examples 2]
Polyimide films were obtained in the same manner as in Example 1, except that the polyamic acid solutions for the first and second layers were changed as shown in Table 2.

[Example 16]
Polyamic acid solution A was uniformly applied to the copper foil as the first layer, which would be in contact with the copper foil, to a thickness of 47 μm after curing, and then heated and dried at 120°C for 4 minutes to remove the solvent. Polyamic acid solution 1, which would be the second layer, was uniformly applied to the first layer to a thickness of 3 μm after curing, and then heated and dried at 130°C for 1 minute to remove the solvent. Subsequently, imidization was completed by stepwise heat treatment from 140°C to 360°C, producing a copper-clad laminate. The copper foil was then etched away using an aqueous ferric chloride solution to obtain a polyimide film. The physical properties of the resulting polyimide film are shown in Table 3.

[Examples 17] to [Examples 30] and [Comparative Examples 3] to [Comparative Examples 4]
Polyimide films were obtained in the same manner as in Example 16, except that the polyamic acid solutions for the first and second layers were changed as shown in Table 3.

In the polyimide films prepared from the copper-clad laminates of Examples 1 to 30, 30 mol % or more of the diamine residues in the second polyimide layer are 1,3-bis(aminophenoxy)benzene residues. Furthermore, the polyimide insulating layer formed by laminating the first and second layers has an oxygen permeability coefficient of (i) 2.0 x ^10-18 mol m/ ^m2 s Pa or less, (ii) a thermal expansion coefficient within the range of 10 to 30 ppm/K, (iii) a dielectric loss tangent (Tan δ) at 10 GHz of 0.004 or less, and a layer thickness within the range of 10 μm to 100 μm. Therefore, the dielectric properties are not deteriorated and the peel strength is 0.7 kN/m or more. Therefore, the films can be processed into double-sided copper-clad laminates without impairing the excellent properties of single-sided copper-clad laminates. Furthermore, circuit boards formed from the copper-clad laminates of the present invention can achieve stable and excellent high-frequency transmission characteristics.

On the other hand, the results of Comparative Examples 1 and 3 show that even if the first layer has low dielectric properties, if the second layer does not contain 1,3-bis(aminophenoxy)benzene residues, the inherent low dielectric properties will be impaired.

In addition, the polyimide films produced from the copper-clad laminates of Comparative Examples 2 and 4 had satisfactory peel strength because the diamine residues in the polyimide film second layer consisted only of 1,3-bis(aminophenoxy)benzene residues, but due to the influence of the first layer, the oxygen permeability coefficient exceeded 2.0 × 10 ^-18 mol m/m ² s Pa and the dielectric loss tangent exceeded 0.004. Note that in the case of Comparative Example 4, the thickness was twice that of the polyimide film in Comparative Example 2, but no improvement in the dielectric loss tangent was observed.

These results show that by adopting the configuration of the example, it is possible to obtain a copper-clad laminate that has excellent adhesion to the bonding sheet while maintaining low dielectric properties.

The above describes in detail an embodiment of the present invention for illustrative purposes, but it goes without saying that the present invention is not limited to the above embodiment and various modifications are possible.

10...metal layer, 20...polyimide insulating layer, 21...polyimide layer, 23...polyimide layer (P), 30...metal-clad laminate

Claims (8)

A polyimide film having a plurality of polyimide layers, which meets the following conditions (i) to (iv):
(i) an oxygen permeability coefficient of 2.0 × 10 ⁻¹⁸ mol·m/m ² ·s·Pa or less;
(ii) a thermal expansion coefficient in the range of 10 to 30 ppm/K;
(iii) a dielectric loss tangent (Tan δ) at 10 GHz of 0.004 or less; and (iv) a thickness within the range of 10 μm to 100 μm;
Fulfilling
the polyimide film has a polyimide layer (P) on at least one exposed surface side,
the polyimide (p) constituting the polyimide layer (P) contains an acid anhydride residue derived from a tetracarboxylic dianhydride component and a diamine residue derived from a diamine component, and the diamine residue contains a diamine residue derived from a diamine compound represented by the following general formula (1) in an amount of at least 30 mol % based on the total diamine residues,
The plurality of polyimide layers include a non-thermoplastic polyimide layer, and the non-thermoplastic polyimide layer satisfies the following conditions (A) to (C):
(A) the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer contains 50 mol % or more of monomer residues having a biphenyl skeleton among all monomer residues derived from all monomer components;
(b) the thickness is in the range of 7 μm to 70 μm; and
(c) the ratio of the thickness of the polyimide film to the total thickness of the polyimide film is 70% or more;
A polyimide film characterized by satisfying the above .
The polyimide film according to claim 1, wherein the diamine compound represented by general formula (1) is 1,3-bis(4-aminophenoxy)benzene. The polyimide film according to claim 2, wherein the polyimide (p) contains at least 60 mol% in total of acid anhydride residues derived from pyromellitic dianhydride and acid anhydride residues derived from 3,3',4,4'-benzophenonetetracarboxylic dianhydride. 2. The polyimide film according to claim 1, wherein in the non-thermoplastic polyimide layer, diamine residues derived from the diamine component constituting the non-thermoplastic polyimide contain diamine residues having a biphenyl skeleton in an amount of 20 mol % or more relative to all diamine residues, and acid anhydride residues derived from the tetracarboxylic dianhydride component contain acid anhydride residues having a biphenyl skeleton in an amount of 20 mol % or more relative to all acid anhydride residues. 5. The polyimide film according to claim 1 , wherein the monomer residue having a biphenyl skeleton is a diamino residue derived from 2,2'-dimethyl-4,4'-diaminobiphenyl and an acid anhydride residue derived from 3,3'-4,4'-biphenyltetracarboxylic dianhydride. A metal-clad laminate having a metal layer and a polyimide insulating layer, wherein the polyimide insulating layer is made of the polyimide film according to any one of claims 1 to 5 . A method for producing the metal-clad laminate according to claim 6 , comprising:
a step of applying a solution of polyamic acid onto the metal layer and drying it to form a first polyamic acid layer of one or more layers;
a step of applying a solution of polyamic acid, which is a precursor of the polyimide (p), onto the first polyamic acid layer and drying the solution to form a second polyamic acid layer;
A method for producing a metal-clad laminate, comprising the step of forming the polyimide insulating layer by imidizing the polyamic acid contained in the first polyamic acid layer and the polyamic acid contained in the second polyamic acid layer. A circuit board in which the metal layer of the metal-clad laminate according to claim 6 is processed into wiring.