Copper-clad laminate, circuit board, electronic device and electronic equipment

Abstract

To provide a copper-clad laminate which is excellent in visibility and can enhance processing accuracy, and can reduce transmission loss of a high frequency signal after circuit processing.SOLUTION: A copper-clad laminate includes an insulation resin layer including a single or a plurality of layers of polyimide layers, and a copper layer laminated on at least one surface of the insulation resin layer, wherein a) the thickness of the insulation resin layer is within the range of 12 μm or more and 100 μm or less, b) total light transmittance of the insulation resin layer is 40% or more, c) HAZE of the insulation resin layer is 90% or less, d) when the surface of the copper layer contacting the insulation resin layer is measured through the insulation resin layer, a color difference Δa* (1) is -2 or less. The copper layer is preferably within the range of thickness of 10 μm or more and 20 μm or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a copper-clad laminate which is a material for electronic components, a circuit board using the same, an electronic device, and an electronic apparatus.

Background Art

[0002] In recent years, with the progress of miniaturization, weight reduction, and space saving of electronic devices, the demand for flexible printed wiring boards (FPCs) that are thin, lightweight, flexible, and have excellent durability even when repeatedly bent has been increasing. Since FPCs can achieve three-dimensional and high-density mounting even in limited space, their applications are expanding to various electronic devices and electronic apparatuses. FPCs are manufactured by etching the copper layer of a copper-clad laminate (CCL) used as a material for wiring processing. Currently, as the copper-clad laminate, a material using polyimide with high heat resistance in the insulating resin layer in contact with the copper layer is widely used. However, with the recent high-speed development of communication devices, the development of 5G communication and further 6G communication is underway. For circuit board materials as well, in order to meet high-speed communication standards, such as substrates for millimeter-wave radars and antenna substrates, it is required to further reduce the transmission loss of high-frequency signals.

[0003] The transmission loss of high-frequency signals in a circuit board is considered to be mainly caused by two factors: dielectric loss in the insulating resin layer and conductor loss in the conductor layer. Patent Document 1 proposes an invention of a copper foil in which the color difference Δa* from white when measuring the color difference of the roughened surface in the color difference system described in JIS Z8730 is 2.22 to 3.73, based on the finding that controlling the color difference on the surface of the roughened particle layer formed on the surface of the copper layer is effective in suppressing the transmission loss when used in a high-frequency circuit board.

[0004] Incidentally, in the photolithography process for copper-clad laminates and in the process of FPC mounting using copper-clad laminates, various processes such as bonding, cutting, exposure, and etching are performed based on the alignment marks provided on the copper-clad laminates. In order to maintain the processing accuracy in these processes, it is important to accurately recognize the alignment marks through the resin layer of the copper-clad laminate. When the light transmittance of the resin layer of the copper-clad laminate is small or when scattering, refraction, etc. are large, the visibility is significantly reduced. As a result, the alignment marks cannot be accurately recognized, which may lead to a decrease in processing accuracy. In Patent Document 2, in order to improve the visibility of copper-clad laminates, an invention of a copper-clad laminate has been proposed in which the HAZE value of the portion where no copper foil exists is 60% or less, and the color difference E*ab between the insulating resin layer where no copper foil exists and the remaining copper foil portion measured through the insulating resin layer is 60 or more.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] As described in the prior art, while there is a demand to suppress the transmission loss of high-frequency signals in a circuit board as much as possible, as a required characteristic of a copper-clad laminate, ensuring visibility for improving processing accuracy is also required. However, in Patent Document 1, in order to reduce the transmission loss of the circuit board, the color difference Δa* on the surface of the copper foil itself is the subject of study, and the influence of the insulating resin layer is not considered. In Patent Document 2, the color difference E*ab between the insulating resin layer and the remaining copper foil portion measured through the insulating resin layer is studied, but this is for the purpose of improving visibility, and the relationship between the color difference and the transmission loss is not considered.

[0007] An object of the present invention is to provide a copper-clad laminate that is excellent in visibility, can improve processing accuracy, and can reduce transmission loss of high-frequency signals after circuit processing.

Means for Solving the Problems

[0008] As a result of intensive research, the present inventors have found that, in a copper-clad laminate in which an insulating resin layer having a polyimide layer and a copper layer are laminated, by controlling the color difference Δa* of the copper layer surface measured through the insulating resin layer to a predetermined value, excellent visibility and suppression of transmission loss of high-frequency signals after circuit processing can be achieved at the same time, and the present invention has been completed.

[0009] That is, the copper-clad laminate of the present invention is a copper-clad laminate including an insulating resin layer containing a single layer or a plurality of polyimide layers and a copper layer laminated on at least one surface of the insulating resin layer. The copper-clad laminate of the present invention satisfies the following conditions a to d; a) The thickness of the insulating resin layer is in the range of 12 μm or more and 100 μm or less; b) The total light transmittance of the insulating resin layer is 40% or more; c) The HAZE of the insulating resin layer is 90% or less; d) When the surface of the copper layer in contact with the insulating resin layer is measured through the insulating resin layer, the color difference Δa*(1) is -2 or less; which satisfies the above conditions.

[0010] In the copper-clad laminate of the present invention, the copper layer may have a thickness in the range of 10 μm or more and 20 μm or less.

[0011] In the copper-clad laminate of the present invention, for the surface on the side where the insulating resin layer is laminated, the color difference Δa*(2) measured in a state where the insulating resin layer is not laminated is larger than the color difference Δa*(1), and the absolute value of the difference [Δa*(2) - Δa*(1)] between the color difference Δa*(2) and the color difference Δa*(1) may be 8 or more.

[0012] The circuit board of the present invention is a circuit board including an insulating resin layer containing a single-layer or multiple-layer polyimide layer and a copper wiring layer laminated on at least one surface of the insulating resin layer. The circuit board of the present invention satisfies the following conditions a to d; a) The thickness of the insulating resin layer is in the range of 12 μm or more and 100 μm or less; b) The total light transmittance of the insulating resin layer is 40% or more; c) The HAZE of the insulating resin layer is 90% or less; d) When the surface of the copper wiring layer in contact with the insulating resin layer is measured through the insulating resin layer, the color difference Δa*(1) is -2 or less; and meets the requirements.

[0013] The electronic device of the present invention is characterized by including the above circuit board.

[0014] The electronic apparatus of the present invention is characterized by including the above circuit board.

Effects of the Invention

[0015] By satisfying the conditions a to d, the copper-clad laminate of the present invention has excellent visibility and can greatly suppress the transmission loss of high-frequency signals after circuit processing. Therefore, by using the copper-clad laminate of the present invention as a circuit board material, it is possible to provide a circuit board with improved processing accuracy in the photolithography process and the mounting process, excellent reliability, and capable of suppressing the transmission loss of high-frequency signals.

Embodiments for Carrying Out the Invention

[0016] [Copper-Clad Laminate] The copper-clad laminate (hereinafter sometimes referred to as "CCL") according to an embodiment of the present invention includes an insulating resin layer containing a single-layer or multiple-layer polyimide layer and a copper layer laminated on at least one surface of the insulating resin layer. The CCL of the present invention may be a single-sided CCL having a copper layer on only one side of the insulating resin layer or a double-sided CCL having copper layers on both sides of the insulating resin layer.

[0017] The CCL of the present invention satisfies the following conditions a) to d); a) The thickness of the insulating resin layer is in the range of 12 μm or more and 100 μm or less; b) The total light transmittance of the insulating resin layer is 40% or more; c) The HAZE of the insulating resin layer is 90% or less; d) When the surface of the copper layer in contact with the insulating resin layer is measured through the insulating resin layer, the color difference Δa*(1) is -2 or less; and meets the requirements.

[0018] Condition a): The thickness of the insulating resin layer is in the range of 12 μm or more and 100 μm or less. By satisfying Condition a), it is possible to achieve both excellent visibility and suppression of transmission loss of high-frequency signals after circuit processing. If the thickness of the insulating resin layer does not meet the lower limit of the above range, the insulation property, dimensional stability, mechanical properties, etc., which are the original functions of the insulating resin layer, will deteriorate. From this perspective, the thickness of the insulating resin layer is preferably 12 μm or more, more preferably 25 μm or more, and even more preferably 50 μm or more. On the other hand, if the thickness of the insulating resin layer exceeds the upper limit of the above range, it may be difficult to ensure visibility. From this perspective, the thickness of the insulating resin layer is preferably 100 μm or less.

[0019] Condition b): The total light transmittance of the insulating resin layer is 40% or more. If the total light transmittance of the insulating resin layer is less than 40%, the visibility through the insulating resin layer will be reduced. Therefore, it becomes difficult to accurately measure the color difference Δa*(1) of Condition d), and in the photolithography process for the CCL of the present invention and the process of mounting an FPC (flexible printed circuit board) using the CCL, the visibility of the alignment marks provided on the CCL will be reduced, making it difficult to align with the alignment marks. From the perspective of ensuring such visibility, the total light transmittance of the insulating resin layer is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more. Note that the total light transmittance can be 100% as long as its high value improves visibility, and thus there is no particular limitation on the upper limit value from the perspective of visibility. However, from the perspective of achieving both improvement in dielectric properties due to the formation of the ordered structure of the polyimide molecular chain, the upper limit value of the total light transmittance is preferably 90% or less, more preferably 80% or less.

[0020] Condition c): The HAZE of the insulating resin layer is 90% or less. When the HAZE of the insulating resin layer exceeds 90%, the visibility through the insulating resin layer decreases. As a result, it becomes difficult to accurately measure the color difference Δa*(1) in condition d), and in the photolithography process for the CCL of the present invention and the process of mounting an FPC (flexible printed circuit board) using the CCL, the visibility of the alignment marks provided on the CCL decreases, making it difficult to align with the alignment marks. From the perspective of ensuring such visibility, the HAZE of the insulating resin layer is preferably 90% or less, more preferably 80% or less. Note that since the lower the value of HAZE, the better the visibility, there is no particular limitation on the lower limit value from the perspective of visibility. However, when HAZE is extremely low, there is a concern about deterioration of dielectric properties due to the lack of progress in the formation of the ordered structure of the polyimide molecular chain. Therefore, the lower limit value of HAZE is preferably 50% or more, more preferably 60% or more.

[0021] Condition d): When the surface of the copper layer in contact with the insulating resin layer is measured through the insulating resin layer, the color difference Δa*(1) is -2 or less. By satisfying condition d), it becomes possible to suppress the transmission loss of high-frequency signals in the range of, for example, 1 to 40 GHz after circuit processing, and at the same time, the visibility required in the photolithography process for the CCL of the present invention and the process of mounting an FPC (flexible printed circuit board) using the CCL is ensured. From such a perspective, the color difference Δa*(1) is preferably -2 or less, more preferably -3 or less. Note that "when measuring the surface of the copper layer through the insulating resin layer" means irradiating light at an angle orthogonal to the surface of the insulating resin layer and measuring the color difference Δa* of the surface of the copper layer laminated on the insulating resin layer.

[0022] Although it is not clear why the transmission loss of high-frequency signals is suppressed in the circuit board after circuit processing by satisfying condition d), it is presumed that the ordered structure of the polymer constituting the insulating resin layer is involved. That is, when the thickness of the insulating resin layer, the thickness and surface state of the copper layer, etc. are constant, the color difference Δa*(1) of the copper foil surface measured through the insulating resin layer changes under the influence of the ordered structure of the polymer constituting the insulating resin layer. As the ordered structure becomes higher and the polymer has a lower dielectric tangent, the color difference Δa*(1) changes to a lower value (negative side), and it has been experimentally confirmed that the transmission loss is suppressed. From this, it is presumed that the circuit board obtained from the CCL satisfying condition d) can suppress the transmission loss even if the type of polyimide constituting the insulating resin layer, its film-forming conditions, the surface state of the copper layer, etc. are unknown. Therefore, it is considered that the transmission loss of the circuit board manufactured from the CCL can be reduced by controlling the CCL to satisfy condition d). Note that the resin type (raw material monomer and its blending ratio) and its film-forming conditions with a particularly high correlation between the color difference Δa*(1) and the suppression of transmission loss will be described later.

[0023] [Insulating Resin Layer] The insulating resin layer includes a single layer or a plurality of polyimide layers, and preferably has a non-thermoplastic polyimide layer containing a non-thermoplastic polyimide and a thermoplastic polyimide layer containing a thermoplastic polyimide laminated on at least one surface of the non-thermoplastic polyimide layer. In order to enhance the adhesiveness between the insulating resin layer and the copper layer, the layer in contact with the copper layer in the insulating resin layer is preferably a thermoplastic polyimide layer. Here, "non-thermoplastic polyimide" means that the storage elastic modulus at 30°C measured using a dynamic viscoelasticity measuring device (DMA) is 1.0×10 9 Pa or more, and the storage elastic modulus in the temperature range within the glass transition temperature + 30°C is 1.0×108 It means those showing 1.0×10 9 Pa or more, and the storage elastic modulus at 30°C measured using a dynamic viscoelasticity measuring device (DMA) is 1.0×10 8 Pa or less, and it means those showing less than 1.0×10 Note that the insulating resin layer can include any resin layer other than the polyimide layer as long as it does not significantly affect conditions b) to d) and does not impair the effects of the invention. However, from the viewpoint of expressing the effects of the invention, it is preferably composed only of the polyimide layer.

[0024] When the insulating resin layer has a plurality of polyimide layers including a non-thermoplastic polyimide layer and a thermoplastic polyimide layer, the thickness of each layer is exemplified as follows. The thickness of the non-thermoplastic polyimide layer can be set within a predetermined range according to the purpose of use. For example, it is preferably in the range of 12 μm or more and 100 μm or less, more preferably in the range of 25 μm or more and 100 μm or less, and even more preferably in the range of 50 μm or more and 100 μm or less. If the thickness of the non-thermoplastic polyimide layer is less than the lower limit value of the above range, the insulation property, dimensional stability, mechanical properties, etc. may be impaired. If it exceeds the upper limit value of the above range, the visibility may decrease. The thickness of the thermoplastic polyimide layer can be set within a predetermined range according to the purpose of use. For example, it is preferably in the range of 1 μm or more and 4 μm or less, more preferably in the range of 1.5 μm or more and 4 μm or less. If the thickness of the thermoplastic polyimide layer is less than the lower limit value of the above range, the adhesion reliability between the insulating resin layer and the copper layer is likely to decrease. If it exceeds the upper limit value of the above range, the non-thermoplastic polyimide layer relative to the entire insulating resin layer becomes relatively thin, and thus the dimensional stability may be impaired.

[0025] Also, when the insulating resin layer has a three-layer structure with thermoplastic polyimide layers on both sides of the non-thermoplastic polyimide layer, in order to improve the visibility in the thickness direction of the insulating resin layer, it is preferable to provide a difference in thickness between one thermoplastic polyimide layer and the other thermoplastic polyimide layer. For example, when one thermoplastic polyimide layer is layer A and the other thermoplastic polyimide layer is layer B, the thickness ratio of layer A to layer B (A layer / B layer) is preferably in the range of 1 or more and 2 or less, and more preferably in the range of 1 or more and 1.5 or less. By having the thickness ratio (A layer / B layer) within the above range, the visibility in the thickness direction of the insulating resin layer can be improved. In particular, when the CCL of the present invention is a single-sided CCL, it is preferable that layer A is the thermoplastic polyimide layer in contact with the copper layer and layer B is the thermoplastic polyimide layer not in contact with the copper layer.

[0026] Also, in the insulating resin layer, when the thickness ratio of the non-thermoplastic polyimide layer to the thermoplastic polyimide layer (non-thermoplastic polyimide layer / thermoplastic polyimide layer) is within the range of, for example, 10 μm to 100 μm for the entire thickness of the insulating resin layer, it is preferably in the range of 1.0 or more and 50 or less, and more preferably in the range of 1.0 or more and 20 or less. If the value of this ratio is less than 1.0, the non-thermoplastic polyimide layer with respect to the entire insulating resin layer becomes thin, so there is a concern that the dimensional stability decreases and the transmission loss of high-frequency signals after circuit processing increases. On the other hand, when the thickness ratio (non-thermoplastic polyimide layer / thermoplastic polyimide layer) exceeds 50, the thermoplastic polyimide layer becomes thin, so the adhesion reliability between the insulating resin layer and the copper layer tends to decrease.

[0027] When the insulating resin layer is applied as the insulating layer of a circuit board, in order to prevent warpage and a decrease in dimensional stability, the overall coefficient of thermal expansion (CTE) is preferably 30 ppm / K or less, and more preferably in the range of 10 ppm / K or more and 25 ppm / K or less. When the CTE exceeds 30 ppm / K, warpage may occur or dimensional stability may decrease.

[0028] Next, for the non-thermoplastic polyimide layer and the thermoplastic polyimide layer that constitute the insulating resin layer, resin types with a particularly high correlation between the color difference Δa*(1) and transmission loss suppression will be exemplified and described.

[0029] <Non-thermoplastic polyimide layer> The non-thermoplastic polyimide that constitutes the non-thermoplastic polyimide layer contains a tetracarboxylic acid residue and a diamine residue. In the present invention, the tetracarboxylic acid residue represents a tetravalent group derived from a tetracarboxylic dianhydride, and the diamine residue represents a divalent group derived from a diamine compound. 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, and more preferably consists of an aromatic tetracarboxylic acid residue and an aromatic diamine residue.

[0030] (Tetracarboxylic acid residue) The tetracarboxylic acid residue contained in the non-thermoplastic polyimide that constitutes the non-thermoplastic polyimide layer preferably contains 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).

[0031] The tetracarboxylic acid residue derived from BPDA (hereinafter also referred to as "BPDA residue") and the tetracarboxylic acid residue derived from TAHQ (hereinafter also referred to as "TAHQ residue") are residues that enhance the correlation between the color difference Δa*(1) under condition d) and the suppression of transmission loss, are likely to form an ordered structure of the polymer, and can reduce the dielectric tangent and hygroscopicity by suppressing molecular motion. Therefore, the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer preferably contains the total of the BPDA residue and the TAHQ residue in the range of 30 to 60 mol parts, more preferably in the range of 40 to 50 mol parts, per 100 mol parts of the tetracarboxylic acid residue. If the total of the BPDA residue and the TAHQ residue is less than 30 mol parts, the formation of the ordered structure of the polymer becomes insufficient, making it difficult to achieve sufficient reduction of the dielectric tangent. If it exceeds 60 mol parts, there is a risk of an increase in CTE or a decrease in heat resistance.

[0032] Also, 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 enhance the correlation between the color difference Δa*(1) under condition d) and the suppression of transmission loss. Due to their rigidity, they enhance the in-plane orientation, suppress the CTE to a low level, and play a role in controlling the glass transition temperature. Therefore, the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer preferably contains the total of the PMDA residue and the NTCDA residue in the range of 40 to 70 mol parts, more preferably in the range of 50 to 60 mol parts, still more preferably in the range of 50 to 55 mol parts, per 100 mol parts of the tetracarboxylic acid residue. If the total of the PMDA residue and the NTCDA residue is less than 40 mol parts, there is a risk of an increase in CTE or a decrease in heat resistance. If it exceeds 70 mol parts, there is a risk of deterioration of dielectric properties such as an increase in the imide group concentration of the polymer, an increase in polar groups, an increase in hygroscopicity, and an increase in the dielectric tangent. Also, there is a risk that the film becomes brittle and the self-supporting property of the film decreases.

[0033] Also, from the viewpoint of sufficiently suppressing the dielectric loss in the insulating resin layer, the total of at least one of the BPDA residue and the TAHQ residue and at least one of the PMDA residue and the NTCDA residue is preferably contained in an amount of 80 mol parts or more, more preferably 90 mol parts or more, per 100 mol parts of the tetracarboxylic acid residue. Further, the molar ratio {(BPDA residue + TAHQ residue) / (PMDA residue + NTCDA residue)} of at least one of the BPDA residue and the TAHQ residue to at least one of the PMDA residue and the NTCDA residue is in the range of 0.6 or more and 1.3 or less, preferably in the range of 0.7 or more and 1.3 or less, more preferably in the range of 0.8 or more and 1.2 or less, so as to control the formation of the CTE and the polymer's ordered structure.

[0034] The non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer can contain, in addition to the above BPDA residue, TAHQ residue, PMDA residue, and NTCDA residue, tetracarboxylic acid residues derived from tetracarboxylic dianhydrides generally used as raw materials for polyimides, as long as the effects of the invention are not impaired. Examples of such tetracarboxylic acid residues include 3,3’,4,4’-diphenylsulfone tetracarboxylic dianhydride, 4,4’-oxydiphthalic anhydride, 2,3',3,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-, 2,3,3',4'- or 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 2,3',3,4'-diphenyl ether tetracarboxylic dianhydride, bis(2,3-dicarboxyphenyl) ether dianhydride, 3,3'',4,4''-, 2,3,3'',4''- or 2,2'',3,3''-p-terphenyltetracarboxylic dianhydride, 2,2-bis(2,3- or 3,4-dicarboxyphenyl)-propane dianhydride, bis(2,3- or 3.Tetracarboxylic acid residues derived from aromatic tetracarboxylic dianhydrides such as 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, 2,3,5,6-cyclohexane dianhydride, 1,2,5,6-naphthalene tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride, 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylic dianhydride, 2,6- or 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-(or 1,4,5,8-)tetrachloronaphthalene-1,4,5,8-(or 2,3,6,7-)tetracarboxylic dianhydride, 2,3,8,9-, 3,4,9,10-, 4,5,10,11- or 5,6,11,12-perylene-tetracarboxylic dianhydride, 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, ethylene glycol bisanhydrotrimellitate, etc. are included.

[0035] (Diamine residue) As the diamine residue contained in the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer, a diamine residue derived from a diamine compound represented by the general formula (A1) [hereinafter, may be referred to as "(A1) residue"] is preferable. The (A1) residue is a residue that enhances the correlation between the color difference Δa*(1) of condition d) and the suppression of transmission loss.

[0036] [Chemical formula]

[0037] In formula (A1), the linking group X independently represents a single bond or -COO-, Y independently represents a monovalent hydrocarbon group having 1 to 3 carbon atoms, or an alkoxy group, n represents an integer of 0 to 2, and p and q independently represent an integer of 0 to 4. Here, "independently" means that in the above formula (A1), a plurality of linking groups X, a plurality of substituents Y, and further the integers p and q may be the same or different. In the above formula (A1), the hydrogen atoms in the two terminal amino groups may be substituted, and for example, -NR2R3 (where R2 and R3 independently represent any substituent such as an alkyl group) may be used.

[0038] The diamine compound represented by the general formula (A1) (hereinafter sometimes referred to as "diamine (A1)") is an aromatic diamine having two benzene rings. Since diamine (A1) has a rigid structure, it has an effect of imparting an ordered structure to the whole polymer. Therefore, by containing the (A1) residue, a polyimide with low gas permeability and low hygroscopicity can be obtained, and since the moisture inside the molecular chain can be reduced, the dielectric tangent can be lowered. Here, as the linking group X, a single bond is preferable.

[0039] Examples of the diamine (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), 4-aminophenyl-4'-aminobenzoate (APAB), and the like.

[0040] The non-thermoplastic polyimide preferably contains the (A1) residue in an amount of preferably 80 mol parts or more, more preferably 85 mol parts or more, based on 100 mol parts of the diamine residue. By containing the (A1) residue in an amount within the above range, due to the rigid structure derived from the monomer, an ordered structure is likely to be formed in the whole polymer, and thus it is easy to achieve a low dielectric tangent.

[0041] The non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer can contain diamine residues derived from diamine compounds generally used as raw materials for polyimides, as long as the effects of the invention are not impaired. Examples of such diamine residues include 2,2-bis-[4-(3-aminophenoxy)phenyl]propane, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)biphenyl, bis[1-(3-aminophenoxy)]biphenyl, bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)]benzophenone, 9,9-bis[4-(3-aminophenoxy)phenyl]fluorene, 2,2-bis-[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis-[4-(3-aminophenoxy)phenyl]hexafluoropropane, 3,3'-dimethyl-4,4'-diaminobiphenyl, 4,4'-methylenedi-o-toluidine, 4,4'-methylenedi-2,6-xylidine, 4,4'-methylene-2,6-diethylaniline, 3,3'-diaminodiphenylethane, 3,3'-diaminobiphenyl, 3,3'-dimethoxybenzidine, 3,3''-diamino-p-terphenyl, 4,4'-[1,4-phenylenebis(1-methylethylidene)]bisaniline, 4,4'-[1,3-phenylenebis(1-methylethylidene)]bisaniline, bis(p-aminocyclohexyl)methane, bis(p-β-amino-t-butylphenyl)ether, bis(p-β-methyl-δ-aminopentyl)benzene, p-bis(2-methyl-4-aminopentyl)benzene, p-bis(1,1-dimethyl-5-aminopentyl)benzene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,4-bis(β-amino-t-butyl)toluene, 2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine, m-xylylenediamine, p-xylylenediamine, 2,6-diaminopyridine, 2,5-diaminopyridine, 2,5-diamino-1,3,4-oxadiazole, piperazine, 2'-methoxy-4,4'-diaminobenzanilide, 4,4'-diaminobenzanilide, 1,Diamine residues derived from aromatic diamine compounds such as 3-bis[2-(4-aminophenyl)-2-propyl]benzene, 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, bis(4-amino-3-ethyl-5-methylphenyl)methane, 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene, 1,4-bis(4-aminophenoxy)-2,5-di-tert-butylbenzene, and diamine residues derived from aliphatic diamine compounds such as dimer acid type diamine in which two terminal carboxylic acid groups of dimer acid are substituted with primary aminomethyl group or amino group.

[0042] In non-thermoplastic polyimide, by selecting the types of the above-mentioned tetracarboxylic acid residues and diamine residues and the respective molar ratios when applying two or more types of tetracarboxylic acid residues or diamine residues, dielectric properties, thermal expansion coefficient, storage elastic modulus, tensile elastic modulus, etc. can be controlled. Further, in non-thermoplastic polyimide, when having a plurality of structural units of polyimide, they may be present as blocks or randomly, but it is preferable that they are present randomly.

[0043] The weight average molecular weight of the non-thermoplastic polyimide is preferably in the range of, for example, 10,000 to 400,000, and more preferably in the range of 50,000 to 350,000. When 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, when the weight average molecular weight exceeds 400,000, the viscosity excessively increases and defects such as film thickness unevenness and streaks tend to occur during the coating operation.

[0044] The non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer preferably has a glass transition temperature of 280°C or higher, and more preferably in the range of 300°C or higher and 400°C or lower. When the glass transition temperature is within the above range, it becomes easy to control the imidization temperature in the formation of the insulating resin layer.

[0045] <Thermoplastic polyimide layer> The thermoplastic polyimide constituting the thermoplastic polyimide layer contains a tetracarboxylic acid residue and a diamine residue, preferably contains an aromatic tetracarboxylic acid residue derived from an aromatic tetracarboxylic dianhydride and an aromatic diamine residue derived from an aromatic diamine, and more preferably consists of an aromatic tetracarboxylic acid residue and an aromatic diamine residue.

[0046] (Tetracarboxylic acid residue) As the tetracarboxylic acid residue used for the thermoplastic polyimide constituting the thermoplastic polyimide layer, the same ones as those exemplified as the tetracarboxylic acid residue in the non-thermoplastic polyimide constituting the above non-thermoplastic polyimide layer can be used.

[0047] (Diamine residue) As the diamine residue contained in the thermoplastic polyimide constituting the thermoplastic polyimide layer, a diamine residue derived from a diamine compound represented by general formulas (B1) to (B7) is preferable.

[0048] [Chemical formula]

[0049] In formulas (B1) to (B7), R1 independently represents a monovalent hydrocarbon group or an alkoxy group having 1 to 6 carbon atoms, the linking group A independently represents a divalent group selected from -O-, -S-, -CO-, -SO-, -SO2-, -COO-, -CH2-, -C(CH3)2-, -NH- or -CONH-, and n1 independently represents an integer of 0 to 4. However, those overlapping with formula (B2) are excluded from formula (B3), and those overlapping with formula (B4) are excluded from formula (B5). Here, "independently" means that in one or more of the above formulas (B1) to (B7), a plurality of linking groups A, a plurality of R1s or a plurality of n1s 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, -NR2R3 (where R2 and R3 independently represent any substituent such as an alkyl group) may be used.

[0050] 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), the amino group directly bonded to at least one benzene ring and the divalent linking group A are in the meta position, so that the degree of freedom of the polyimide molecular chain increases and it has high flexibility, which is considered to contribute to the improvement of the flexibility of the polyimide molecular chain. Therefore, by using diamine (B1), the thermoplasticity of the polyimide is enhanced. Here, as the linking group A, -O-, -CH2-, -C(CH3)2-, -CO-, -SO2-, -S- are preferred. Examples of diamine (B1) include 3,3'-diaminodiphenylmethane, 3,3'-diaminodiphenylpropane, 3,3'-diaminodiphenylsulfide, 3,3'-diaminodiphenylsulfone, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylpropane, 3,4'-diaminodiphenylsulfide, 3,3'-diaminobenzophenone, (3,3'-bisamino)diphenylamine and the like.

[0051] 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), since the amino group directly bonded to at least one benzene ring and the divalent linking group A are in the meta position, the degree of freedom of the polyimide molecular chain increases and it has high flexibility, and it is considered to contribute to the improvement of the flexibility of the polyimide molecular chain. Therefore, by using diamine (B2), the thermoplasticity of the polyimide is enhanced. Here, as the linking group A, -O- is preferable. Examples of the diamine (B2) include 1,4-bis(3-aminophenoxy)benzene, 3-[4-(4-aminophenoxy)phenoxy]benzenamine, 3-[3-(4-aminophenoxy)phenoxy]benzenamine, and the like.

[0052] 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), since the two divalent linking groups A directly bonded to one benzene ring are in the meta position to each other, the degree of freedom of the polyimide molecular chain increases and it has high flexibility, and it is considered to contribute to the improvement of the flexibility of the polyimide molecular chain. Therefore, by using diamine (B3), the thermoplasticity of the polyimide is enhanced. Here, as the linking group A, -O- is preferable. Examples of the diamine (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, 4,4'-[5-methyl-(1,3-phenylene)bisoxy]bisaniline, and the like.

[0053] 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 amino group directly bonded to at least one benzene ring and the divalent linking group A being in the meta position, and is considered to contribute to the improvement of the flexibility of the polyimide molecular chain. Therefore, by using diamine (B4), the thermoplasticity of the polyimide is enhanced. Here, as the linking group A, -O-, -CH2-, -C(CH3)2-, -SO2-, -CO-, -CONH- are preferable. Examples of diamine (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, bis[4,4'-(3-aminophenoxy)]benz anilide, and the like.

[0054] The diamine represented by formula (B5) (hereinafter sometimes referred to as "diamine (B5)") is an aromatic diamine having four benzene rings. This diamine (B5) has increased degrees of freedom and high flexibility due to two divalent linking groups A directly bonded to at least one benzene ring being in the meta position to each other, and is considered to contribute to the improvement of the flexibility of the polyimide molecular chain. Therefore, by using diamine (B5), the thermoplasticity of the polyimide is enhanced. Here, as the linking group A, -O- is preferable. Examples of diamine (B5) include 4-[3-[4-(4-aminophenoxy)phenoxy]phenoxy]aniline, 4,4’-[oxybis(3,1-phenyleneoxy)]bis aniline, and the like.

[0055] 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 the improvement of the flexibility of the polyimide molecular chain. Therefore, by using diamine (B6), the thermoplasticity of the polyimide is enhanced. Here, as the linking group A, -C(CH3)2-, -O-, -SO2-, -CO- are preferable. Examples of diamine (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), bis[4-(4-aminophenoxy)phenyl]ketone (BAPK), and the like.

[0056] 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 considered to contribute to the improvement of the flexibility of the polyimide molecular chain. Therefore, by using diamine (B7), the thermoplasticity of the polyimide is enhanced. Here, as the linking group A, -O- is preferable. Examples of diamine (B7) include bis[4-(3-aminophenoxy)]biphenyl, bis[4-(4-aminophenoxy)]biphenyl, and the like.

[0057] The thermoplastic polyimide constituting the thermoplastic polyimide layer preferably contains, in the range of 70 mol parts or more, preferably in the range of 70 mol parts or more and 99 mol parts or less, more preferably in the range of 80 mol parts or more and 95 mol parts or less, of a diamine residue derived from at least one diamine compound selected from diamines (B1) to (B7) with respect to 100 mol parts of the diamine residue. Since diamines (B1) to (B7) have a molecular structure with flexibility, by using at least one diamine compound selected from these in the amount within the above range, the flexibility of the polyimide molecular chain can be improved and thermoplasticity can be imparted.

[0058] In addition, as the diamine residue contained in the thermoplastic polyimide constituting the thermoplastic polyimide layer, the (A1) residue is also preferable. The (A1) residue is as described in the explanation of the non-thermoplastic polyimide. Since the (A1) residue has a rigid structure and has the effect of imparting an ordered structure to the whole polymer, it can suppress molecular motion and reduce the dielectric tangent and hygroscopicity. Furthermore, by using it as a raw material of the thermoplastic polyimide, a polyimide having low gas permeability and excellent long-term heat-resistant adhesiveness can be obtained.

[0059] The thermoplastic polyimide constituting the thermoplastic polyimide layer may contain the (A1) residue, preferably in the range of 1 to 30 mol parts, more preferably in the range of 5 to 20 mol parts. By containing the (A1) residue in the amount within the above range, an ordered structure is formed in the whole polymer due to the rigid structure derived from the monomer, so that a polyimide having high heat resistance while being thermoplastic can be obtained.

[0060] The thermoplastic polyimide constituting the thermoplastic polyimide layer may contain, within a range not impairing the effects of the invention, diamine residues derived from diamine compounds generally used as raw materials for polyimides in addition to the diamines (A1), (B1) to (B7).

[0061] In the thermoplastic polyimide, by selecting the types of the above tetracarboxylic acid residues and diamine residues, and the respective molar ratios in the case of applying two or more types of tetracarboxylic acid residues or diamine residues, dielectric properties, thermal expansion coefficient, tensile elastic modulus, glass transition temperature, etc. can be controlled. Also, in the thermoplastic polyimide, when it has a plurality of structural units of polyimide, they may be present as blocks or randomly, but it is preferable that they are present randomly.

[0062] The weight average molecular weight of the thermoplastic polyimide is preferably in the range of, for example, 10,000 to 400,000, more preferably in the range of 50,000 to 350,000. When 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, when the weight average molecular weight exceeds 400,000, the viscosity increases excessively, and defects such as film thickness unevenness and streaks are likely to occur during the coating operation.

[0063] The thermoplastic polyimide constituting the thermoplastic polyimide layer can improve the adhesion to the copper foil. Such a thermoplastic polyimide preferably has a glass transition temperature in the range of 200°C or higher and 350°C or lower, more preferably in the range of 200°C or higher and 320°C or lower.

[0064] [Copper layer] As the material of the copper layer, copper or a copper alloy is preferred. When using a copper foil, either a rolled copper foil or an electrolytic copper foil may be used. Also, as the copper foil, commercially available copper foils can be used. Note that the material of the wiring layer in the circuit board described later is the same as that of the copper layer.

[0065] The thickness of the copper layer is not particularly limited, but is preferably 10 μm or more, more preferably 12 μm or more. From the viewpoints of production stability and handling properties, the lower limit of the thickness of the copper foil is preferably set to 10 μm. On the other hand, the upper limit of the thickness of the copper layer is not particularly limited, but is preferably 35 μm, more preferably 20 μm, from the viewpoint of improving circuit processability.

[0066] Also, the copper foil may be subjected to surface treatment, for example, rust prevention treatment or surface treatment with, for example, siding, aluminum alcoholate, aluminum chelate, silane coupling agent, etc. for the purpose of improving adhesion.

[0067] In the copper layer, the ten-point average roughness (Rzjis) of the surface on the side where the insulating resin layer is laminated is preferably 1.0 μm or less, more preferably 0.8 μm or less, from the viewpoint of reducing the transmission loss of high-frequency signals after circuit processing. From the viewpoint of ensuring adhesion to the insulating resin layer and reducing conductor loss, it is more preferably 0.8 μm or less.

[0068] Also, the copper layer preferably has a color difference Δa*(2) measured in a state where the insulating resin layer is not laminated of 30 or less, more preferably 10 or less. When the color difference Δa*(2) is 10 or less, the correlation between the color difference Δa*(1) and the transmission loss in the state where the insulating resin layer is laminated is enhanced. In this case, in order to achieve both improved visibility and reduced transmission loss, Δa*(2)>Δa*(1), and the absolute value of the difference [Δa*(2)-Δa*(1)] between the color difference Δa*(2) and the color difference Δa*(1) is preferably 8 or more, more preferably in the range of 8 to 25. Generally, the color difference Δa*(2) on the surface of the copper layer takes a positive value and tends to be strongly reddish, but in the present invention, the color difference Δa*(1) in the state where the insulating resin layer is laminated shifts to the negative side and becomes strongly greenish. The fact that the absolute value of the difference [Δa*(2)-Δa*(1)] is 8 or more means that the polymer constituting the insulating resin layer forms an ordered structure of a certain degree or more. Even if the surface state of the copper layer is the same, it is considered that laminating the insulating resin layer on the copper layer shows that the effect of suppressing the transmission loss of the entire CCL (or the entire circuit board) is increased. The color difference Δa*(2) measured in a state where the insulating resin layer is not laminated is the color difference measured by irradiating light at an angle perpendicular to the surface of the copper foil that becomes the copper layer.

[0069] [Manufacturing method of CCL] The CCL of the present invention may be prepared, for example, by preparing a resin film including an insulating resin layer, sputtering a metal thereon to form a seed layer, and then forming a copper layer by, for example, plating. In this case, after applying and drying a solution of polyamic acid on a support substrate, a gel film of polyamic acid can be peeled off from the support substrate and imidized to form a resin film as the insulating resin layer.

[0070] Alternatively, the CCL of the present invention may be prepared by preparing a resin film including an insulating resin layer and laminating a copper foil thereon by a method such as thermocompression bonding.

[0071] Furthermore, the CCL of the present invention may be prepared by casting a coating solution containing polyamic acid, which is a precursor of polyimide, on a copper foil, drying it to form a coating film, and then subjecting it to heat treatment to imidize and form an insulating resin layer (casting method).

[0072] As a preferred embodiment of the method for manufacturing the CCL of the present invention, for example, [1] a method of applying and drying a solution of polyamic acid on a copper foil and then imidizing it to produce an insulating resin layer, [2] a method of repeatedly applying and drying a solution of polyamic acid on a copper foil a plurality of times and then performing imidization, [3] a method of applying and drying while simultaneously laminating polyamic acid in multiple layers on a copper foil by multi-layer extrusion and then performing imidization (hereinafter, multi-layer extrusion method), etc. may be mentioned.

[0073] The method of [1] above may include, for example, the following steps 1a to 1b; (1a) A step of applying a solution of polyamic acid on a copper foil and drying it, and (1b) A step of forming a polyimide layer by heat-treating polyamic acid on the copper foil to imidize it. can be included.

[0074] The polyamic acid used in Process 1a can generally be synthesized by reacting a tetracarboxylic dianhydride and a diamine compound in a solvent. For example, a tetracarboxylic dianhydride and a diamine compound are dissolved in an organic solvent in approximately equimolar amounts and stirred at a temperature in the range of 0 to 100 °C for 30 minutes to 24 hours to carry out a polymerization reaction, whereby a polyamic acid, which is a precursor of polyimide, is obtained. In the reaction, the reaction components are dissolved so that the resulting precursor is in the range of 5 to 30% by weight, preferably 10 to 20% by weight, in the organic solvent. Examples of the organic solvent used in the polymerization reaction include N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2-butanone, dimethyl sulfoxide (DMSO), hexamethylphosphoramide, N-methylcaprolactam, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diglyme, triglyme, cresol, etc. Two or more of these solvents can be used in combination, and furthermore, an aromatic hydrocarbon such as xylene or toluene can also be used in combination. Also, the amount of such an organic solvent used is not particularly limited, but it is preferably adjusted to an amount such that the concentration of the polyamic acid solution obtained by the polymerization reaction is about 5 to 30% by weight. The synthesized polyamic acid is usually advantageously used as a reaction solvent solution, but can be concentrated, diluted, or substituted with another organic solvent if necessary. The viscosity of the polyamic acid solution is preferably in the range of 500 cps to 100,000 cps. If it is outside this range, defects such as film thickness unevenness and streaks are likely to occur during coating operations using, for example, a coater.

[0075] The method described in [2] above can be carried out in the same manner as the method described in [1] above, except that in the method described in [1] above, Process 1a is repeated a plurality of times to form a laminated coating film of polyamic acid on a copper foil.

[0076] The method described in [3] above can be carried out in the same manner as the method described in [1] above, except that in Process 1a of the method described in [1] above, a laminate of a coating film of polyamic acid is simultaneously coated and dried by multi-layer extrusion.

[0077] In Step 1b, by heat treatment, imidization is carried out to thermally cyclize the polyamic acid in the coating film to form a polyimide, and an insulating resin layer including a single-layer or multiple-layer polyimide layer is formed. The method for imidizing the polyamic acid is not particularly limited, and for example, heat treatment such as heating at a temperature condition within the range of 80 to 400°C for 1 to 24 hours is preferably employed. Therefore, the temperature of the heat treatment including the imidization step will be described in detail. Note that the "temperature" of the heat treatment means the temperature of the coating film.

[0078] In principle, the heat treatment time for imidization in Step 1b is the sum of the temperature increase time and the heating time at the maximum temperature Tmax. The drying step is not included in the heat treatment of Step 1b but is included in Step 1a. Also, in principle, the temperature decrease time is not included in the heat treatment of Step 1b. When thermal imidization is performed at a high temperature where the maximum temperature Tmax of the heat treatment is near the glass transition temperature (Tg) of the non-thermoplastic polyimide, since the imidization of the polyamic acid is substantially completed at the maximum temperature Tmax, the influence on the ordered structure of the polyimide layer can be almost ignored even if residual heat is applied during the subsequent temperature decrease time. However, when the maximum temperature Tmax of the heat treatment exceeds the Tg of the non-thermoplastic polyimide, exceptionally, the temperature decrease time in the temperature range exceeding Tg is also included in the heat treatment time. In the manufacture of CCL, it is preferable to proceed with imidization at as high a temperature as possible within the range where dimensional stability can be controlled. It is considered that by exposing to a high temperature in a state containing a large amount of the polyamic acid structure with higher molecular chain mobility and higher degree of freedom than that of the polyimide and imidizing, the formation of the ordered structure of the polyimide layer can be promoted. Thus, even when the maximum temperature Tmax of the heat treatment in Step 1b is set to a temperature exceeding the Tg of the non-thermoplastic polyimide, it is important that it is Tg + 80°C or lower, preferably Tg + 50°C or lower. When heat treatment is performed at a temperature exceeding Tg + 80°C, the molecular chain mobility may increase excessively, and there is a risk that the molecular chains may take a random orientation regardless of the heat treatment time, inhibiting the formation of the ordered structure or causing thermal decomposition.

[0079] When the maximum temperature Tmax of the heat treatment in Process 1b exceeds the Tg of the non-thermoplastic polyimide (that is, when the maximum temperature Tmax exceeds Tg and is within the range of Tg + 80°C or less), from the viewpoint of ensuring productivity and suppressing foaming due to rapid volatilization of the solvent, it is preferable that the overall heat treatment time is within the range of, for example, 5 minutes to 180 minutes, more preferably within the range of 7 minutes to 150 minutes. Among these, the heat treatment time at a temperature exceeding Tg is preferably within the range of, for example, 1 minute to 30 minutes.

[0080] In Process 1b, it is preferable to complete the imidization of the polyamic acid on the substrate. Since the coating film containing the polyamic acid is imidized in a state fixed to the substrate, it is possible to suppress the expansion and contraction changes of the polyimide layer during the imidization process and suppress the dimensional changes of the insulating resin layer.

[0081] [Circuit Board] The CCL of the above embodiment is mainly useful as a circuit board material such as an FPC. By processing the copper layer of the CCL into a pattern by a conventional method to form a wiring layer, a circuit board according to an embodiment of the present invention can be manufactured. That is, a circuit board according to an embodiment of the present invention is a circuit board including an insulating resin layer containing a single-layer or multiple-layer polyimide layer and a copper wiring layer laminated on at least one surface of the insulating resin layer. The circuit board of the present invention may have a copper wiring layer on only one side of the insulating resin layer or may have copper wiring layers on both sides of the insulating resin layer.

[0082] The circuit board of the present embodiment satisfies the following conditions a to d; a) The thickness of the insulating resin layer is within the range of 12 μm or more and 100 μm or less; b) The total light transmittance of the insulating resin layer is 40% or more; c) The HAZE of the insulating resin layer is 90% or less; d) When the surface of the copper wiring layer in contact with the insulating resin layer is measured through the insulating resin layer, the color difference Δa*(1) is -2 or less; is satisfied. In the circuit board of the present invention, conditions a) to d) correspond to conditions a) to d) of the CCL of the present invention described above. Also, since the configurations of the insulating resin layer of the circuit board and the insulating resin layer of the CCL are the same in the present invention, the description of the CCL is incorporated by reference and redundant descriptions are omitted.

[0083] [Electronic device and electronic equipment] The electronic device and electronic equipment according to the embodiment of the present invention include the above circuit board. Examples of the electronic device of the present embodiment include display devices such as liquid crystal displays, organic EL displays, and electronic papers, organic EL lighting, solar cells, touch panels, camera modules, inverters, converters, and their constituent members. Examples of the electronic equipment include HDDs, DVDs, mobile phones, smartphones, tablet terminals, electronic control units (ECUs) of automobiles, power control units (PCUs), and the like. The circuit board is preferably used as components such as wiring of movable parts, cables, and connectors in these electronic devices and electronic equipment.

Example

[0084] Examples are shown below to more specifically explain the features of the present invention. However, the scope of the present invention is not limited to the examples. In the following examples, unless otherwise specified, various measurements and evaluations are as follows.

[0085] [Measurement of viscosity] Using an E-type viscometer (manufactured by Brookfield, product name; DV-II+Pro), the viscosity at 25°C was measured. The rotation speed was set so that the torque was 10% to 90%, and after 2 minutes from the start of the measurement, the value when the viscosity became stable was read.

[0086] [Measurement of the thickness of the polyimide layer] Using a digital film thickness gauge manufactured by Heidenhain, five arbitrary points of the polyimide film obtained by etching and removing the copper foil in the metal-clad laminate were measured, and the average value was taken as the thickness of the polyimide layer.

[0087] [Measurement of the surface roughness of the copper foil] Using an AFM (manufactured by Bruker AXS, product name: Dimension Icon type SPM), a probe (manufactured by Bruker AXS, product name: TESPA (NCHV), tip radius of curvature: 10 nm, spring constant: 42 N / m), in tapping mode, the measurement was performed in a range of 80 μm × 80 μm on the copper foil surface, and the ten-point average roughness (Rzjis) was obtained.

[0088] [Measurement of the color difference Δa*] Δa* is the color difference from white a* when measuring a* with a color difference meter (manufactured by X-Rite, product name: Portable Simple Color Difference Meter RM200QC, measurement diameter: φ8 mm, CIE L*a*b*, light source: D65, 10° field of view). The measurement was performed at 3 points in a range of 350 mm × 250 mm, and the average value was obtained.

[0089] [Measurement of the glass transition temperature (Tg)] The glass transition temperature was measured using a dynamic viscoelasticity measuring device (DMA: manufactured by UBM, product name: E4000F) for a polyimide film with a size of 5 mm × 20 mm, at a heating rate of 4 °C / min from 30 °C to 400 °C and a frequency of 11 Hz. The temperature at which the change in elastic modulus (tanδ) is maximum was taken as the glass transition temperature. Note that the storage elastic modulus at 30 °C measured using the DMA is 1.0×10 9 Pa or more, and the storage elastic modulus in the temperature range within the glass transition temperature + 30 °C is 1.0×10 8 Pa or less is defined as "thermoplastic", and the storage elastic modulus at 30 °C is 1.0×10 9 Pa or more, and the storage elastic modulus in the temperature range within the glass transition temperature + 30 °C is 1.0×10 8 Pa or more is defined as "non-thermoplastic".

[0090] [Measurement of the coefficient of thermal expansion (CTE)] A polyimide film with a size of 3 mm × 20 mm was heated from 30°C to 265°C at a constant heating rate while applying a load of 5.0 g using a thermomechanical analyzer (manufactured by Bruker, product name: 4000SA), held at that temperature for 10 minutes, and then cooled at a rate of 5°C / min. The average coefficient of thermal expansion (coefficient of thermal expansion) from 250°C to 100°C was determined.

[0091] [Measurement of total light transmittance (T.T.) and HAZE (turbidity)] Using a haze measuring device (turbidimeter: manufactured by Nippon Denshoku Industries Co., Ltd., product name: NDH8000), measurements were carried out on a polyimide film with a size of 5 cm × 5 cm in accordance with JIS K 7361-1 and JIS K 7136.

[0092] [Measurement of relative permittivity and dielectric tangent] Using a vector network analyzer (manufactured by Agilent, product name: E8363C) and a split post dielectric resonator (SPDR resonator), the relative permittivity (Dk) and dielectric tangent (Df) of the polyimide film at a frequency of 10 GHz were measured. The polyimide film used for the measurement was left standing for 72 hours under the conditions of temperature; 22 - 24°C, humidity; 45 - 55%.

[0093] [Evaluation of transmission loss] A microstrip line (MSL) was formed by etching so that the characteristic impedance was 50 Ω. The transmission loss of the fabricated circuit board from 0 to 40 GHz was determined using a PNA Network Analyzer (manufactured by Keysight Technologies, product name: E8363C).

[0094] The abbreviations used in the examples and reference 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 TPE-Q: 1,4-bis(4-aminophenoxy)benzene BAPP: 2,2-bis[4-(4-aminophenoxy)phenyl]propane Bis-aniline-P: 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene (manufactured by Mitsui Chemicals Fine Inc., trade name; Bis-aniline-P) DMAc: N,N-dimethylacetamide Copper foil 1: Commercially available electrolytic copper foil, thickness; 12 μm, Rzjis on the side where the insulating resin layer is laminated; 0.6 μm, Δa* on the side where the insulating resin layer is laminated; 8.2 Copper foil 2: Commercially available electrolytic copper foil, thickness; 18 μm, Rzjis on the side where the insulating resin layer is laminated; 0.6 μm, Δa* on the side where the insulating resin layer is laminated; 8.2 Copper foil 3: Commercially available rolled copper foil, thickness; 12 μm, Rzjis on the side where the insulating resin layer is laminated; 1.0 μm, Δa*; 1.4

[0095] (Synthesis Example 1) Under a nitrogen stream, 241.2 parts by weight of m-TB (0.568 mol part), 9.3 parts by weight of TPE-Q (0.032 mol part), 15.9 parts by weight of Bis-aniline-P (0.032 mol part), and an amount of DMAc such that the solid content concentration after polymerization was 15% by weight were charged into a reaction vessel and stirred at room temperature to dissolve. Next, 67.8 parts by weight of PMDA (0.311 mol part) and 91.5 parts by weight of BPDA (0.311 mol part) were added, and then the polymerization reaction was continued by stirring at room temperature for 3 hours to obtain a polyamic acid solution a. The solution viscosity of the polyamic acid solution a was 29,800 cps. The polyimide film a obtained by curing the polyamic acid solution a was non-thermoplastic (Tg; 316°C).

[0096] (Synthesis Example 2) Under a nitrogen stream, 119.2 parts by weight of m-TB (0.562 mole part), 28.5 parts by weight of TPE-Q (0.099 mole part), and an amount of DMAc such that the solid content concentration after polymerization becomes 15% by weight were charged into a reaction vessel and stirred at room temperature to dissolve. Next, after adding 113.6 parts by weight of PMDA (0.521 mole part) and 38.3 parts by weight of BPDA (0.13 mole part), stirring was continued at room temperature for 3 hours to conduct a polymerization reaction, and a polyamic acid solution b was obtained. The solution viscosity of the polyamic acid solution b was 31,200 cps. The polyimide film b obtained by curing the polyamic acid solution b was non-thermoplastic (Tg; 375°C).

[0097] (Synthesis Example 3) Under a nitrogen stream, 155.9 parts by weight of BAPP (0.38 mole part) and an amount of DMAc such that the solid content concentration after polymerization becomes 12% by weight were charged into a reaction vessel and stirred at room temperature to dissolve. Next, after adding 84.1 parts by weight of PMDA (0.386 mole part), stirring was continued at room temperature for 3 hours to conduct a polymerization reaction, and a polyamic acid solution c was obtained. The solution viscosity of the polyamic acid solution c was 2,350 cps. The polyimide film c obtained by curing the polyamic acid solution c was thermoplastic (Tg; 320°C).

[0098] (Synthesis Example 4) Under a nitrogen stream, 18.5 parts by weight of m-TB (0.087 mole part), 101.7 parts by weight of TPE-R (0.348 mole part), and an amount of DMAc such that the solid content concentration after polymerization becomes 12% by weight were charged into a reaction vessel and stirred at room temperature to dissolve. Next, after adding 28.9 parts by weight of PMDA (0.132 mole part) and 90.9 parts by weight of BPDA (0.309 mole part), stirring was continued at room temperature for 3 hours to conduct a polymerization reaction, and a polyamic acid solution d was obtained. The solution viscosity of the polyamic acid solution d was 2,210 cps. The polyimide film d obtained by curing the polyamic acid solution d was thermoplastic (Tg; 226°C).

[0099] [Example 1] On the copper foil 1, after uniformly applying the polyamic acid solution d so that the cured thickness becomes 2.2 μm (the first layer), it was heated and dried at 140 °C to remove the solvent. On top of that, after uniformly applying the polyamic acid solution a so that the cured thickness becomes 19.6 μm (the second layer), it was heated and dried at 90 - 120 °C to remove the solvent. Further, on top of that, after uniformly applying the polyamic acid d so that the cured thickness becomes 3.2 μm (the third layer), it was heated and dried at 140 °C to remove the solvent. Thereafter, a heat treatment including a stepwise temperature increase from 140 °C to 360 °C and a part of the cooling process started immediately after reaching the maximum temperature was performed for a total of 120 minutes to complete imidization and prepare a single-sided metal-clad laminate 1a.

[0100] The polyimide layer side of the single-sided metal-clad laminate 1a and the separately prepared copper foil 1 were arranged to be in contact with each other, and thermocompression bonding was performed to prepare a double-sided metal-clad laminate 1.

[0101] Also, for the double-sided metal-clad laminate 1, the copper foil 1 on the pressure-bonded surface side was etched and removed using an aqueous ferric chloride solution to obtain a single-sided metal-clad laminate 1a'. The color difference Δa* measured through the polyimide layer on the copper foil 1 surface in the single-sided metal-clad laminate 1a' was -6.0, and the transmission losses at 10 GHz, 20 GHz, 30 GHz, and 40 GHz were -3.9 dB, -6.0 dB, -7.9 dB, and -9.7 dB, respectively. Also, the absolute value of the difference between the color difference Δa* of the copper foil 1 itself and the color difference Δa* measured through the polyimide layer was 14.2.

[0102] Also, for the double-sided metal-clad laminate 1, the copper foil 1 on the coating surface side was etched and removed using an aqueous ferric chloride solution to obtain a single-sided metal-clad laminate 1b'. The color difference Δa* measured through the polyimide layer on the copper foil 1 surface in the single-sided metal-clad laminate 1b' was -3.2, and the transmission losses at 10 GHz, 20 GHz, 30 GHz, and 40 GHz were -3.9 dB, -5.9 dB, -7.7 dB, and -9.5 dB, respectively. Also, the absolute value of the difference between the color difference Δa* of the copper foil 1 itself and the color difference Δa* measured through the polyimide layer was 11.4.

[0103] Also, for the double-sided metal-clad laminate 1, the copper foils 1 on both sides were etched away using an aqueous ferric chloride solution to obtain a polyimide film 1a (T.T.; 73%, HAZE; 82%, CTE; 24 ppm / K, Dk; 3.37, Df; 0.0032).

[0104] [Example 2] A single-sided metal-clad laminate 2a and a double-sided metal-clad laminate 2 were prepared in the same manner as in Example 1, except that a copper foil 2 was used instead of the copper foil 1, and the thickness after curing of the first layer was 2.2 μm, the thickness after curing of the second layer was 32.6 μm, and the thickness after curing of the third layer was 3.2 μm.

[0105] In the same manner as in Example 1, the copper foil 2 on the pressure-bonding surface side was etched away to obtain a single-sided metal-clad laminate 2a'. The color difference Δa* in the single-sided metal-clad laminate 2a' was -8.9, and the transmission losses at 10 GHz, 20 GHz, 30 GHz, and 40 GHz were -2.8 dB, -4.4 dB, -5.9 dB, and -7.4 dB, respectively. Also, the absolute value of the difference between the color difference Δa* of the copper foil 2 itself and the color difference Δa* measured through the polyimide layer was 17.1.

[0106] Also, in the same manner as in Example 1, the copper foil 2 on the coating surface side was etched away to obtain a single-sided metal-clad laminate 2b'. The color difference Δa* in the single-sided metal-clad laminate 2b' was -7.2, and the transmission losses at 10 GHz, 20 GHz, 30 GHz, and 40 GHz were -2.7 dB, -4.2 dB, -5.7 dB, and -7.1 dB, respectively. Also, the absolute value of the difference between the color difference Δa* of the copper foil 2 itself and the color difference Δa* measured through the polyimide layer was 15.4.

[0107] Also, in the same manner as in Example 1, a polyimide film 2a (T.T.; 57%, HAZE; 80%, CTE; 24 ppm / K, Dk; 3.33, Df; 0.0031) was obtained.

[0108] [Example 3] A single-sided metal-clad laminate 3a and a double-sided metal-clad laminate 3 were prepared in the same manner as in Example 1, except that the thickness after curing of the first layer was 2.2 μm, the thickness after curing of the second layer was 44.6 μm, and the thickness after curing of the third layer was 3.2 μm.

[0109] In the same manner as in Example 1, the copper foil 1 on the pressure-bonding surface side was removed by etching to obtain a single-sided metal-clad laminate 3a'. The color difference Δa* in the single-sided metal-clad laminate 3a' was -7.5, and the transmission losses at 10 GHz, 20 GHz, 30 GHz, and 40 GHz were -2.4 dB, -3.9 dB, -5.4 dB, and -6.8 dB, respectively. Also, the absolute value of the difference between the color difference Δa* of the copper foil 1 itself and the color difference Δa* measured through the polyimide layer was 15.7.

[0110] Also, in the same manner as in Example 1, the copper foil 1 on the coating surface side was removed by etching to obtain a single-sided metal-clad laminate 3b'. The color difference Δa* in the single-sided metal-clad laminate 3b' was -5.6, and the transmission losses at 10 GHz, 20 GHz, 30 GHz, and 40 GHz were -2.3 dB, -3.7 dB, -5.0 dB, and -6.4 dB, respectively. Also, the absolute value of the difference between the color difference Δa* of the copper foil 1 itself and the color difference Δa* measured through the polyimide layer was 13.8.

[0111] Also, in the same manner as in Example 1, a polyimide film 3a (T.T.; 60%, HAZE; 81%, CTE; 24 ppm / K, Dk; 3.32, Df; 0.0034) was obtained.

[0112] [Example 4] A single-sided metal-clad laminate 4a and a double-sided metal-clad laminate 4 were prepared in the same manner as in Example 3, except that copper foil 2 was used instead of copper foil 1.

[0113] In the same manner as in Example 1, the copper foil 2 on the crimping surface side was removed by etching to obtain a single-sided metal-clad laminate 4a', the color difference Δa* in the single-sided metal-clad laminate 4a' was -5.9, and the transmission losses at 10 GHz, 20 GHz, 30 GHz, and 40 GHz were -2.3 dB, -3.7 dB, -5.0 dB, and -6.3 dB, respectively. Also, the absolute value of the difference between the color difference Δa* of the copper foil 2 itself and the color difference Δa* measured through the polyimide layer was 14.1.

[0114] Also, in the same manner as in Example 1, the copper foil 2 on the coating surface side was removed by etching to obtain a single-sided metal-clad laminate 4b', the color difference Δa* in the single-sided metal-clad laminate 4b' was -5.2, and the transmission losses at 10 GHz, 20 GHz, 30 GHz, and 40 GHz were -2.2 dB, -3.6 dB, -4.9 dB, and -6.1 dB, respectively. Also, the absolute value of the difference between the color difference Δa* of the copper foil 2 itself and the color difference Δa* measured through the polyimide layer was 13.4.

[0115] Also, in the same manner as in Example 1, a polyimide film 4a (T.T.; 64%, HAZE; 84%, CTE; 24 ppm / K, Dk; 3.30, Df; 0.0036) was obtained.

[0116] [Example 5] A single-sided metal-clad laminate 5a and a double-sided metal-clad laminate 5 were prepared in the same manner as in Example 3, except that copper foil 3 was used instead of copper foil 1.

[0117] In the same manner as in Example 1, the copper foil 3 on the crimping surface side was removed by etching to obtain a single-sided metal-clad laminate 5a', the color difference Δa* in the single-sided metal-clad laminate 5a' was -8.4, and the transmission losses at 10 GHz, 20 GHz, 30 GHz, and 40 GHz were -2.8 dB, -4.0 dB, -5.2 dB, and -6.6 dB, respectively. Also, the absolute value of the difference between the color difference Δa* of the copper foil 3 itself and the color difference Δa* measured through the polyimide layer was 9.8.

[0118] Also, in the same manner as in Example 1, the copper foil 3 on the coating surface side was removed by etching to obtain a single-sided metal-clad laminate 5b'. The color difference Δa* in the single-sided metal-clad laminate 5b' was -7.6, and the transmission losses at 10 GHz, 20 GHz, 30 GHz, and 40 GHz were -2.7 dB, -3.9 dB, -5.1 dB, and -6.4 dB, respectively. Also, the absolute value of the difference between the color difference Δa* of the copper foil 3 itself and the color difference Δa* measured through the polyimide layer was 9.0.

[0119] Also, in the same manner as in Example 1, a polyimide film 5a (T.T.; 54%, HAZE; 79%, CTE; 24 ppm / K, Dk; 3.33, Df; 0.0036) was obtained.

[0120] [Example 6] On the pressure-bonding surface of the polyimide film 1a obtained in Example 1, a first metal layer serving as a seed layer with a thickness of 100 nm made of a Zn alloy was formed using a sputtering apparatus as dry plating, and then copper was sputtered thereon, followed by copper plating to form a second metal layer with a thickness of 10 μm. Thereafter, heat treatment was performed in the range of 140°C to 360°C to prepare a single-sided metal-clad laminate 6a'. The color difference Δa* measured through the polyimide layer on the surface of the conductor layer in the single-sided metal-clad laminate 6a' was -6.0, and the transmission losses at 10 GHz, 20 GHz, 30 GHz, and 40 GHz were -3.9 dB, -5.9 dB, -7.7 dB, and -9.5 dB, respectively.

[0121] [Example 7] Except that the thickness after curing of the first layer was 2.2 μm, the thickness after curing of the second layer was 69.6 μm, and the thickness after curing of the third layer was 3.2 μm, a single-sided metal-clad laminate 7a and a double-sided metal-clad laminate 7 were prepared in the same manner as in Example 3.

[0122] In the same manner as in Example 1, the copper foil 1 on the pressure-bonding surface side was removed by etching to obtain a single-sided metal-clad laminate 7a'. The color difference Δa* in the single-sided metal-clad laminate 7a' was -7.9, and the transmission losses at 10 GHz, 20 GHz, 30 GHz, and 40 GHz were -1.7 dB, -2.7 dB, -3.7 dB, and -4.6 dB, respectively. Also, the absolute value of the difference between the color difference Δa* of the copper foil 1 itself and the color difference Δa* measured through the polyimide layer was 16.1.

[0123] [Example 8] A single-sided metal-clad laminate 8a and a double-sided metal-clad laminate 8 were prepared in the same manner as in Example 3, except that the thickness after curing of the first layer was 2.2 μm, the thickness after curing of the second layer was 94.6 μm, and the thickness after curing of the third layer was 3.2 μm.

[0124] In the same manner as in Example 1, the copper foil 1 on the pressure-bonding surface side was removed by etching to obtain a single-sided metal-clad laminate 8a'. The color difference Δa* in the single-sided metal-clad laminate 8a' was -8.2, and the transmission losses at 10 GHz, 20 GHz, 30 GHz, and 40 GHz were -1.4 dB, -2.3 dB, -3.1 dB, and -3.9 dB, respectively. Also, the absolute value of the difference between the color difference Δa* of the copper foil 1 itself and the color difference Δa* measured through the polyimide layer was 16.4.

[0125] [Comparative Example 1] After uniformly applying polyamic acid solution c onto the copper foil 1 so that the thickness after curing would be 2.5 μm (the first layer), it was heated and dried at 120°C for 1 minute to remove the solvent. Then, polyamic acid solution b was uniformly applied thereon so that the thickness after curing would be 20.0 μm (the second layer), and it was heated and dried at 120°C for 3 minutes to remove the solvent. Further, polyamic acid c was uniformly applied thereon so that the thickness after curing would be 2.5 μm (the third layer), and it was heated and dried at 120°C for 1 minute to remove the solvent. Thereafter, a stepwise heat treatment was performed from 140°C to 360°C to complete imidization, thereby preparing a single-sided metal-clad laminate 9a.

[0126] The polyimide layer side of the single-sided metal-clad laminate 9a and the separately prepared copper foil 1 were arranged to be in contact with each other, and thermocompression bonding was performed to prepare a double-sided metal-clad laminate 9.

[0127] In the same manner as in Example 1, the copper foil 1 on the pressure-bonding surface side was etched away to obtain a single-sided metal-clad laminate 9a'. The color difference Δa* in the single-sided metal-clad laminate 9a' was 3.2, and the transmission losses at 10 GHz, 20 GHz, 30 GHz, and 40 GHz were -4.0 dB, -6.3 dB, -8.3 dB, and -10.3 dB, respectively. Also, the absolute value of the difference between the color difference Δa* of the copper foil 1 itself and the color difference Δa* measured through the polyimide layer was 5.0.

[0128] Also, in the same manner as in Example 1, the copper foil 1 on the coating surface side was etched away to obtain a single-sided metal-clad laminate 9b'. The color difference Δa* in the single-sided metal-clad laminate 9b' was 3.9, and the transmission losses at 10 GHz, 20 GHz, 30 GHz, and 40 GHz were -4.0 dB, -6.1 dB, -8.1 dB, and -10.0 dB, respectively. Also, the absolute value of the difference between the color difference Δa* of the copper foil 1 itself and the color difference Δa* measured through the polyimide layer was 4.3.

[0129] Also, in the same manner as in Example 1, a polyimide film 9a (T.T.; 84%, HAZE; 77%, CTE; 22 ppm / K, Dk; 3.3, Df; 0.0060) was obtained.

[0130] As described above, the embodiments of the present invention have been described in detail for illustrative purposes, but the present invention is not limited to the above embodiments, and various modifications are possible.

Claims

1. A copper-clad laminate comprising an insulating resin layer including a single-layer or multiple-layer polyimide layer, and a copper layer laminated on at least one surface of the insulating resin layer, satisfying the following conditions a to d; a) The thickness of the insulating resin layer is in the range of 12 μm or more and 100 μm or less; b) The total light transmittance of the insulating resin layer is 40% or more; c) The Haze of the insulating resin layer is 90% or less; d) When the surface of the copper layer in contact with the insulating resin layer is measured through the insulating resin layer, the color difference Δa*(1) is -2 or less; A copper-clad laminate characterized by satisfying the above.

2. The copper-clad laminate according to Claim 1, wherein the copper layer has a thickness in the range of 10 μm or more and 20 μm or less.

3. Regarding the surface on which the insulating resin layer is laminated, the color difference Δa*(2) measured in a state where the insulating resin layer is not laminated is larger than the color difference Δa*(1), and the absolute value of the difference [Δa*(2) - Δa*(1)] between the color difference Δa*(2) and the color difference Δa*(1) is 8 or more. The copper-clad laminate according to Claim 1.

4. A circuit board comprising an insulating resin layer including a single-layer or multiple-layer polyimide layer, and a copper wiring layer laminated on at least one surface of the insulating resin layer, satisfying the following conditions a to d; a) The thickness of the insulating resin layer is in the range of 12 μm or more and 100 μm or less; b) The total light transmittance of the insulating resin layer is 40% or more; c) The Haze of the insulating resin layer is 90% or less; d) When the surface of the copper wiring layer in contact with the insulating resin layer is measured through the insulating resin layer, the color difference Δa*(1) is -2 or less; A circuit board characterized by satisfying the above.

5. An electronic device characterized by comprising the circuit board according to Claim 4.

6. An electronic apparatus characterized by comprising the circuit board according to Claim 4.

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