JP7465060B2 - Metal-clad laminates and circuit boards - Google Patents

Description

The present invention relates to a metal-clad laminate and a circuit board.

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

FPCs are manufactured by etching the copper layer of a copper-clad laminate (CCL) and processing the wiring. For mobile phones and smartphones, rolled copper foil is often used as the material for the copper layer in FPCs that are continuously bent or bent 180 degrees. For example, Patent Document 1 proposes that the bending resistance of a copper-clad laminate made using rolled copper foil be determined by the number of times it can be folded. Patent Document 2 proposes a copper-clad laminate using rolled copper foil that is determined by the gloss level and number of times it can be folded.

In the photolithography process for copper-clad laminates and the process of mounting FPCs, various processes such as joining, cutting, exposure, and etching are performed based on the alignment marks provided on the copper-clad laminates. The processing accuracy in these processes is important for maintaining the reliability of electronic devices equipped with FPCs. However, since the copper-clad laminates have a structure in which copper layers and resin layers with different thermal expansion coefficients are laminated, stress occurs between the layers due to the difference in thermal expansion coefficients between the copper layer and the resin layer. When a part or all of this stress is released when the copper layer is etched and processed for wiring, it causes expansion and contraction, which causes changes in the dimensions of the wiring pattern. Therefore, dimensional changes ultimately occur at the FPC stage, which causes poor connections between the wiring or between the wiring and the terminals, reducing the reliability and yield of the circuit board. Therefore, dimensional stability is a very important characteristic of copper-clad laminates as circuit board materials. However, in the above-mentioned Patent Documents 1 and 2, no consideration is given to the dimensional stability of the copper-clad laminates.

In addition, in Patent Document 3, in order to reduce the thermal expansion coefficient of the insulating resin layer and increase dimensional stability, a thermoplastic polyimide layer is not provided, and instead a flexible metal-clad laminate consisting of copper foil and a non-thermoplastic polyimide layer is proposed to use a diamine compound consisting of p-phenylenediamine (p-PDA) or 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB) and a diamine compound such as 1,3-bis(4-aminophenoxy)benzene (TPE-R) as the diamine component of the non-thermoplastic polyimide layer. p-PDA is a monomer that reduces the thermal expansion coefficient and contributes to dimensional stability, but because of its small molecular weight, there is a problem that the imide group concentration increases and the hygroscopicity of the polyimide becomes high. If the hygroscopicity of the polyimide becomes high, there is a problem that dimensional changes and warping are likely to occur due to environmental changes such as heating during circuit processing.

On the other hand, Patent Document 4 discloses the use of a combination of m-TB and p-PDA as diamine compounds for the raw material of non-thermoplastic polyimide in a multilayer polyimide film in which the occurrence of cracks during circuit processing is suppressed. However, in the monomer composition of Patent Document 4, the molar ratio of p-PDA in the diamine compound is too large, so that, as above, the hygroscopicity of the polyimide is high, and dimensional changes and warping are likely to occur due to environmental changes during circuit processing. Patent Document 4 also discloses that when m-TB, p-PDA, and 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) are used in combination as diamine compounds, crack resistance is deteriorated. In this case, too, it is thought that the molar ratio of p-PDA in the diamine compound is too large, so that, as above, the hygroscopicity of the polyimide is high.

JP 2014-15674 A (Claims, etc.) JP 2014-11451 A (Claims, etc.) Patent No. 5162379 (Claims, etc.) WO2016/159104 (Synthesis Example 6, Synthesis Example 9, etc.)

The present invention aims to provide a metal-clad laminate that can reduce dimensional changes caused by changes in temperature, humidity, and pressure during processes such as circuit processing, board lamination, and component mounting, as well as changes in temperature and humidity environments between processes.

As a result of intensive research, the inventors discovered that the above problems could be solved by controlling the in-plane birefringence (Δn) and birefringence in the thickness direction of the insulating resin layer, and thus completed the present invention.

That is, the metal-clad laminate of the present invention is a metal-clad laminate comprising an insulating resin layer and a metal layer laminated on at least one side of the insulating resin layer, the insulating resin layer having a thermoplastic polyimide layer containing a thermoplastic polyimide on at least one side of the non-thermoplastic polyimide layer containing a non-thermoplastic polyimide. The metal-clad laminate of the present invention is characterized in that the insulating resin layer satisfies the following conditions (i) to (iv).
(i) The in-plane birefringence (Δn) is 2×10 ⁻³ or less.
(ii) The variation [Δ(Δn)] of the in-plane birefringence (Δn) in the width direction (TD) is 4×10 ⁻⁴ or less.
(iii) In the thickness direction of the non-thermoplastic polyimide layer, the difference (Δna-Δnb) between the birefringence (Δna) at a point 1.5 μm away from the center from one surface and the birefringence (Δnb) at a point 1.5 μm away from the center from the other surface is ±0.01 or less.
(iv) The difference between the sum (Δna+Δnb+Δnc) of the Δna and Δnb and the birefringence (Δnc) at the center in the thickness direction and the average value (Δnv) is ±0.01 or less for both Δna and Δnb.

In the metal-clad laminate of the present invention, the non-thermoplastic polyimide contains tetracarboxylic acid residues and diamine residues, and the diamine residues derived from the diamine compound represented by the following general formula (1) may be 20 or more molar parts per 100 molar parts of the total diamine residues.

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

In the metal-clad laminate of the present invention, the diamine residues derived from the diamine compound represented by the general formula (1) may be in the range of 70 to 95 molar parts relative to 100 molar parts of all diamine residues contained in the non-thermoplastic polyimide, and the total amount of diamine residues selected from the following general formulas (2) and (3) may be in the range of 5 to 30 molar parts.

In general formula (2) and general formula (3), R ₅ , R ₆ , R ₇ and R ₈ each independently represent a halogen atom, or an alkyl group or alkoxy group having 1 to 4 carbon atoms which may be substituted with a halogen atom, or an alkenyl group; X each independently represents a divalent group selected from -O-, -S-, -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -CO-, -COO-, -SO ₂ -, -NH- or -NHCO-; X ₁ and X ₂ each independently represent a divalent group selected from a single bond, -O-, _-S- , -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -CO-, -COO-, -SO ₂ -, -NH- or -NHCO-; Except for the case where both of _{m and n} are single bonds, m, n, o and p each independently represent an integer of 0 to 4.

In the metal-clad laminate of the present invention, the thermoplastic polyimide contains tetracarboxylic acid residues and diamine residues, and the total amount of diamine residues selected from the above general formulas (2) and (3) may be 50 molar parts or more per 100 molar parts of all diamine residues.

In the metal-clad laminate of the present invention, the diamine residue represented by the general formula (2) may be a diamine residue derived from 1,3-bis(4-aminophenoxy)benzene,
The diamine residue represented by the general formula (3) may be a diamine residue derived from 2,2-bis[4-(4-aminophenoxy)phenyl]propane.

In the metal-clad laminate of the present invention, the thickness ratio (A)/(B) of the thickness (A) of the non-thermoplastic polyimide layer to the thickness (B) of the thermoplastic polyimide layer may be within a range of 1 to 20.

The metal-clad laminate of the present invention may have a length in the width direction (TD direction) of 490 mm or more.

The circuit board of the present invention is formed by processing the metal layer of any of the metal-clad laminates described above into wiring.

The metal-clad laminate of the present invention satisfies conditions (i) to (iv), and therefore has excellent dimensional stability of the insulating resin layer even under high temperature and high pressure environments and environments of changing humidity, so that defects such as warping are unlikely to occur due to environmental changes (e.g., high temperature, high pressure, humidity changes, etc.) during the circuit processing process, the board lamination process, and the component mounting process. In particular, even in a wide metal-clad laminate, the dimensional change rate is low and the dimensions are stable over the entire width of the insulating resin layer, so that the FPC obtained from the metal-clad laminate can be made to be capable of high-density mounting. Therefore, by using the metal-clad laminate of the present invention as an FPC material, it is possible to improve the reliability and yield of circuit boards.

Next, we will explain the embodiment of the present invention.

<Metal-clad laminate>
The metal-clad laminate of the present embodiment includes an insulating resin layer and a metal layer laminated on at least one side of the insulating resin layer.

<Insulating resin layer>
In the metal-clad laminate of the present embodiment, the insulating resin layer has a thermoplastic polyimide layer on at least one side of the non-thermoplastic polyimide layer. That is, the thermoplastic polyimide layer is provided on one or both sides of the non-thermoplastic polyimide layer. For example, in the metal-clad laminate of the present embodiment, the metal layer is laminated on the surface of the thermoplastic polyimide layer.
Here, non-thermoplastic polyimide generally refers to polyimide that does not soften or exhibit adhesiveness even when heated, but in the present invention refers to polyimide having a storage modulus of 1.0×10 ⁹ Pa or more at 30° C. and a storage modulus of 1.0×10 ⁸ Pa or more at 360° C., as measured using a dynamic mechanical analyzer (DMA). Furthermore, thermoplastic polyimide generally refers to polyimide whose glass transition temperature (Tg) can be clearly confirmed, but in the present invention refers to polyimide having a storage modulus of 1.0×10 ⁹ Pa or more at 30° C. and a storage modulus of less than 1.0×10 ⁸ Pa at 360° C., as measured using a DMA.

In the metal-clad laminate of the present embodiment, the insulating resin layer satisfies the following conditions (i) to (iv).
(i) The in-plane birefringence (Δn) is 2×10 ⁻³ or less.
(ii) The variation [Δ(Δn)] of the in-plane birefringence (Δn) in the width direction (TD) is 4×10 ⁻⁴ or less.
(iii) In the thickness direction of the non-thermoplastic polyimide layer, the difference (Δna-Δnb) between the birefringence (Δna) at a point 1.5 μm away from the center from one surface and the birefringence (Δnb) at a point 1.5 μm away from the center from the other surface is ±0.01 or less.
(iv) The difference between the sum (Δna+Δnb+Δnc) of the Δna and Δnb and the birefringence (Δnc) at the center in the thickness direction and the average value (Δnv) is ±0.01 or less for both Δna and Δnb.

By satisfying the above conditions (i) to (iv), the orientation of the polyimide that constitutes the insulating resin layer is enhanced, improving dimensional stability and suppressing the occurrence of warping.

If the value of the in-plane birefringence (Δn) exceeds 2×10 ⁻³ , the anisotropy of the in-plane orientation increases, causing deterioration of dimensional stability. The lower limit of the value of Δn is not particularly limited, but it is preferable to set it to 2×10 ⁻⁴ or more from the viewpoint that the in-plane orientation is isotropic and the dimensional stability is improved, while the thermal expansion coefficient is excessively reduced, and warping due to mismatch with the thermal expansion coefficient of the metal foil is suppressed. From the above viewpoint, the value of the in-plane birefringence (Δn) of the insulating resin layer is preferably in the range of 2×10 ⁻⁴ or more and 8×10 ⁻⁴ or less, more preferably in the range of 2×10 ⁻⁴ or more and 6×10 ⁻⁴ or less.

Furthermore, when the variation in Δn in the TD direction [Δ(Δn)] exceeds 4×10 ⁻⁴ , the variation in the in-plane orientation increases, causing the in-plane variation in the dimensional change rate. The variation in Δn in the TD direction [Δ(Δn)] is preferably 2×10 ⁻⁴ or less, more preferably 1.2×10 ⁻⁴ or less. Within such a range, high dimensional accuracy can be maintained, for example, even when scaled up.

In addition, by having the difference in birefringence (Δna-Δnb) in the thickness direction of the non-thermoplastic polyimide layer be ±0.01 or less, and the differences (Δnv-Δna) and (Δnv-Δnb) between the Δna and Δnb and the average value (Δnv) being both ±0.01 or less, the uniformity of the polyimide orientation in the thickness direction is increased and the occurrence of warping can be suppressed. The differences (Δnv-Δna) and (Δnv-Δnb) are preferably ±0.008 or less, and more preferably ±0.006 or less.

By satisfying the above conditions (i) to (iv), dimensional changes and warping due to environmental changes (e.g., high temperature/high pressure environments, humidity changes, etc.) during the circuit processing, board lamination, and component mounting processes can be effectively suppressed. If any one of the above conditions (i) to (iv) is not met, the amount of dimensional change will increase due to high temperatures, high pressures, and humidity changes during the circuit processing, board lamination, and component mounting processes, resulting in reduced dimensional accuracy and warping.

When the metal-clad laminate of this embodiment is used as a circuit board material, for example, it is important that the coefficient of thermal expansion (CTE) of the insulating resin layer is in the range of 10 ppm/K to 30 ppm/K inclusive, and preferably in the range of 10 ppm/K to 25 ppm/K inclusive, in order to prevent warping and reduced dimensional stability. If the CTE is less than 10 ppm/K or more than 30 ppm/K, warping may occur or dimensional stability may decrease. In addition, in the metal-clad laminate of this embodiment, the CTE of the insulating resin layer is more preferably in the range of ±5 ppm/K or less, and most preferably in the range of ±2 ppm/K or less, relative to the CTE of the metal layer made of copper foil or the like.

In the insulating resin layer, the non-thermoplastic polyimide layer constitutes a polyimide layer with low thermal expansion, and the thermoplastic polyimide layer constitutes a polyimide layer with high thermal expansion. Here, the low thermal expansion polyimide layer refers to a polyimide layer having a coefficient of thermal expansion (CTE) preferably in the range of 1 ppm/K to 25 ppm/K, more preferably in the range of 3 ppm/K to 25 ppm/K. Also, the high thermal expansion polyimide layer refers to a polyimide layer having a CTE preferably in the range of 35 ppm/K or more, more preferably in the range of 35 ppm/K to 80 ppm/K, and even more preferably in the range of 35 ppm/K to 70 ppm/K. The polyimide layer can be made to have a desired CTE by appropriately changing the combination of raw materials used, the thickness, and the drying and curing conditions.

The thickness of the insulating resin layer can be set within a predetermined range depending on the purpose of use, but is preferably within the range of 4 to 50 μm, and more preferably within the range of 11 to 26 μm. If the thickness of the insulating resin layer is less than the above lower limit, problems such as the inability to ensure electrical insulation and difficulty in handling during the manufacturing process due to reduced handleability may occur. On the other hand, if the thickness of the insulating resin layer exceeds the above upper limit, the manufacturing conditions must be controlled with high precision in order to control the in-plane birefringence (Δn) and birefringence in the thickness direction (Δn), resulting in problems such as reduced productivity.

In addition, in the insulating resin layer, the thickness ratio ((A)/(B)) of the thickness (A) of the non-thermoplastic polyimide layer to the thickness (B) of the thermoplastic polyimide layer is preferably in the range of 1 to 20, more preferably in the range of 2 to 12. In addition, when the number of layers of the non-thermoplastic polyimide layer and/or the thermoplastic polyimide layer is plural, the thickness (A) and the thickness (B) mean the total thickness. If the value of this ratio is less than 1, the non-thermoplastic polyimide layer becomes thin relative to the entire insulating resin layer, so the variation in the in-plane birefringence (Δn) tends to increase, and if it exceeds 20, the thermoplastic polyimide layer becomes thin, so the adhesive reliability between the insulating resin layer and the metal layer tends to decrease. Here, the control of the in-plane birefringence (Δn) is correlated with the resin composition and the thickness of each polyimide layer constituting the insulating resin layer. The thermoplastic polyimide layer, which is a resin composition that has adhesiveness, i.e., high thermal expansion or softening, has a greater effect on the value of Δn of the insulating resin layer as its thickness increases. Therefore, it is preferable to increase the thickness ratio of the non-thermoplastic polyimide layer and decrease the thickness ratio of the thermoplastic polyimide layer to reduce the value of Δn of the insulating resin layer and its variation. As described later, in this embodiment, even if the thickness ratio of the thermoplastic polyimide layer is decreased, the adhesion between the metal layer and the insulating resin layer can be ensured by designing the thermoplastic polyimide layer to contain a predetermined amount of diamine residues selected from general formulas (2) and (3).

From the viewpoint of achieving a greater effect of improving the dimensional accuracy of the insulating resin layer, the metal-clad laminate of this embodiment has a width direction (TD direction) length (film width) of preferably 490 mm to 1200 mm, more preferably 520 mm to 1100 mm, and preferably a long length of 20 m or more. When the metal-clad laminate of this embodiment is continuously manufactured, the effect of the invention becomes particularly prominent as the width direction (TD direction) becomes wider. Note that this also includes a metal-clad laminate that is continuously manufactured, and then slit at a certain value in the longitudinal direction (MD direction) and TD direction of the long metal-clad laminate.

The insulating resin layer preferably has a tensile modulus of elasticity in the range of 3.0 to 10.0 GPa when made into a polyimide film, and more preferably in the range of 4.5 to 8.0 GPa. If the tensile modulus of elasticity in the polyimide film is less than 3.0 GPa, the strength of the polyimide itself will decrease, which may cause handling problems such as cracking of the insulating resin layer when the metal-clad laminate is processed into a circuit board. On the other hand, if the tensile modulus of elasticity in the polyimide film exceeds 10.0 GPa, the rigidity of the metal-clad laminate against bending will increase, and the bending stress applied to the metal wiring will increase when the metal-clad laminate is folded, resulting in a decrease in bending resistance. By making the tensile modulus of elasticity in the polyimide film within the above range, the strength and flexibility of the insulating resin layer can be ensured.

(Non-thermoplastic polyimide)
In the present embodiment, the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer contains a tetracarboxylic acid residue and a diamine residue, and both of these preferably contain an aromatic group. The tetracarboxylic acid residue and the diamine residue contained in the non-thermoplastic polyimide both contain an aromatic group, which makes it easier to form an ordered structure of the non-thermoplastic polyimide, reduces the amount of change in the in-plane birefringence (Δn) of the insulating resin layer under a high temperature environment, suppresses the variation in the in-plane birefringence (Δn), and suppresses the change in the birefringence in the thickness direction.

In the present invention, the tetracarboxylic acid residue refers to a tetravalent group derived from a tetracarboxylic dianhydride, and the diamine residue refers to a divalent group derived from a diamine compound. The "diamine compound" may have hydrogen atoms in the two terminal amino groups substituted, for example, -NR ₃ R ₄ (wherein R ₃ and R ₄ are independently any substituent such as an alkyl group).

The tetracarboxylic acid residue contained in the non-thermoplastic polyimide is not particularly limited, but for example, a tetracarboxylic acid residue derived from pyromellitic dianhydride (PMDA) (hereinafter also referred to as PMDA residue) and a tetracarboxylic acid residue derived from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) (hereinafter also referred to as BPDA residue) are preferred. These tetracarboxylic acid residues are easy to form an ordered structure, and can reduce the amount of change in in-plane birefringence (Δn) in a high-temperature environment and suppress the change in birefringence in the thickness direction. In addition, the PMDA residue is a residue that plays a role in controlling the thermal expansion coefficient and the glass transition temperature. Furthermore, since the BPDA residue has no polar group and a relatively large molecular weight among tetracarboxylic acid residues, it is expected to have the effect of lowering the imide group concentration of the non-thermoplastic polyimide and suppressing the moisture absorption of the insulating resin layer. From this viewpoint, the total amount of PMDA residues and/or BPDA residues is preferably 50 molar parts or more, more preferably in the range of 50 to 100 molar parts, and most preferably in the range of 70 to 100 molar parts, relative to 100 molar parts of all tetracarboxylic acid residues contained in the non-thermoplastic polyimide.

Other tetracarboxylic acid residues contained in the non-thermoplastic polyimide include, for example, 2,3',3,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 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-dicarboxyphenyl)ether dianhydride, 3,3'',4,4''-,2 ,3,3'',4''- or 2,2'',3,3''-p-terphenyltetracarboxylic dianhydride, 2,2-bis(2,3- or 3,4-dicarboxyphenyl)-propane dianhydride, bis(2,3- or 3,4-dicarboxyphenyl)methane dianhydride, bis(2,3- or 3,4-dicarboxyphenyl)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-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, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylic dianhydride, 2,6- or 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-(or 1,4,5,8-)tetrachloronaphthalene-1,4,5,8-(or tetracarboxylic acid residues derived from aromatic tetracarboxylic dianhydrides such as 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, and 4,4'-bis(2,3-dicarboxyphenoxy)diphenylmethane dianhydride.

Preferably, the diamine residue contained in the non-thermoplastic polyimide is a diamine residue derived from a diamine compound represented by general formula (1).

In general formula (1), the linking group Z represents a single bond or -COO-, Y represents a monovalent hydrocarbon having 1 to 3 carbon atoms, which may be independently substituted with a halogen or a phenyl group, an alkoxy group having 1 to 3 carbon atoms, a perfluoroalkyl group having 1 to 3 carbon atoms, or an alkenyl group, n represents an integer from 0 to 2, and p and q represent independently an integer from 0 to 4. Here, "independently" means that in the above formula (1), the multiple substituents Y and the integers p and q may be the same or different.

The diamine residue derived from the diamine compound represented by the general formula (1) (hereinafter, sometimes referred to as "diamine residue (1)") is likely to form an ordered structure, improves dimensional stability, and can effectively suppress the change in birefringence in the thickness direction as well as the change in in-plane birefringence (Δn) particularly under high temperature environments. From this perspective, it is preferable that the diamine residue (1) is contained in an amount of 20 molar parts or more, preferably in the range of 70 to 95 molar parts, and more preferably in the range of 80 to 90 molar parts, relative to 100 molar parts of all diamine residues contained in the non-thermoplastic polyimide.

Preferred specific examples of the diamine residue (1) include diamine residues derived from diamine compounds such as p-phenylenediamine (p-PDA), 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'-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). Among these, 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB) is particularly preferred because it easily forms an ordered structure, reduces the amount of change in in-plane birefringence (Δn) in a high-temperature environment, and suppresses the change in birefringence in the thickness direction.

In addition, in order to reduce the elastic modulus of the insulating resin layer and improve the elongation and bending resistance, etc., it is preferable that the non-thermoplastic polyimide contains at least one diamine residue selected from the group consisting of diamine residues represented by the following general formulas (2) and (3).

In the above formula (2) and formula (3), R ₅ , R ₆ , R ₇ and R ₈ each independently represent a halogen atom, or an alkyl group or alkoxy group having 1 to 4 carbon atoms which may be substituted with a halogen atom, or an alkenyl group; X independently represents a divalent group selected from -O-, -S-, -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -CO-, -COO-, -SO ₂ -, -NH- or -NHCO-; X ₁ and X ₂ each independently represent a divalent group selected from a _single bond, -O-, -S-, -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -CO-, -COO-, -SO ₂ -, -NH- or -NHCO-; Except for the case where both of _{m and n} are single bonds, m, n, o and p each independently represent an integer of 0 to 4.
In addition, "independently" means that in one or both of the above formulas (2) and (3), the multiple linking groups X, the linking groups _X1 and _X2 , the multiple substituents _R5 , _R6 , _R7 , and _R8 , and further the integers m, n, o, and p may be the same or different.

The diamine residues represented by the general formulas (2) and (3) have a flexible portion, and therefore can impart flexibility to the insulating resin layer. Here, since the diamine residue represented by the general formula (3) has four benzene rings, it is preferable that the terminal group bonded to the benzene ring is in the para position in order to suppress an increase in the coefficient of thermal expansion (CTE). In addition, from the viewpoint of suppressing an increase in the coefficient of thermal expansion (CTE) while imparting flexibility to the insulating resin layer, the diamine residues represented by the general formulas (2) and (3) are preferably contained in a range of 5 to 30 mol parts, more preferably 10 to 20 mol parts, relative to 100 mol parts of the total diamine residues contained in the non-thermoplastic polyimide. If the diamine residues represented by the general formulas (2) and (3) are less than 5 mol parts, the elastic modulus of the insulating resin layer increases and the elongation decreases, which may cause a decrease in bending resistance, etc., and if they exceed 30 mol parts, the molecular orientation decreases and it may be difficult to achieve a low CTE.

The diamine residue represented by formula (2) is preferably one in which at least one of m, n and o is 0, and preferred examples of groups R ₅ , R ₆ and R ₇ include an alkyl group having 1 to 4 carbon atoms which may be substituted with a halogen atom, an alkoxy group having 1 to 3 carbon atoms, or an alkenyl group having 2 to 3 carbon atoms. In formula (2), preferred examples of the linking group X include -O-, -S-, -CH ₂ -, -CH(CH ₃ )-, -SO ₂ - and -CO-. Preferred specific examples of the diamine residue represented by general formula (2) include diamine residues derived from diamine compounds such as 1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,4-bis(4-aminophenoxy)benzene (TPE-Q), bis(4-aminophenoxy)-2,5-di-tert-butylbenzene (DTBAB), 4,4-bis(4-aminophenoxy)benzophenone (BAPK), 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene, and 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene.

The diamine residue represented by formula (3) is preferably one in which at least one of m, n, o and p is 0, and preferred examples of groups R ₅ , R ₆ , R ₇ and R ₈ include an alkyl group having 1 to 4 carbon atoms which may be substituted with a halogen atom, an alkoxy group having 1 to 3 carbon atoms, or an alkenyl group having 2 to 3 carbon atoms. In formula (3), preferred examples of linking groups X ₁ and X ₂ include a single bond, -O-, -S-, -CH ₂ -, -CH(CH ₃ )-, -SO ₂ - or -CO-. However, from the viewpoint of imparting a bending portion, cases in which both linking groups X ₁ and X ₂ are single bonds are excluded. Preferred specific examples of the diamine residue represented by general formula (3) include diamine residues derived from diamine compounds such as 4,4'-bis(4-aminophenoxy)biphenyl (BAPB), 2,2'-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), 2,2'-bis[4-(4-aminophenoxy)phenyl]ether (BAPE), and bis[4-(4-aminophenoxy)phenyl]sulfone.

Among the diamine residues represented by general formula (2), the diamine residue derived from 1,3-bis(4-aminophenoxy)benzene (TPE-R) (sometimes referred to as "TPE-R residue") is particularly preferred, and among the diamine residues represented by general formula (3), the diamine residue derived from 2,2'-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) (sometimes referred to as "BAPP residue") is particularly preferred. TPE-R residues and BAPP residues have flexible sites, so they can reduce the elastic modulus of the insulating resin layer and impart flexibility. In addition, since the BAPP residue has a large molecular weight, it is expected to have the effect of reducing the imide group concentration of the non-thermoplastic polyimide and suppressing the moisture absorption of the insulating resin layer.

Other diamine residues contained in non-thermoplastic polyimides include, for example, m-phenylenediamine (m-PDA), 4,4'-diaminodiphenyl ether (4,4'-DAPE), 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl methane, 3,3'-diaminodiphenyl methane, 3,4'-diaminodiphenyl methane, 4,4'-diaminodiphenyl propane, 3,3'-diaminodiphenyl propane, 3,4'-diaminodiphenyl propane, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl methane, 4,4'-diaminodiphenyl methane, 4,4'-diaminodiphenyl propane, 3,4'-diaminodiphenyl propane, 4,4'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl methane, 4 ... methane, 4,4'-diaminodiphenyl methane, 4,4'-diaminodiphenyl methane, 4,4'-diaminodiphenyl methane, 4,4'-diaminodiphenyl methane, 4, ,3'-diaminodiphenyl sulfone, 4,4'-diaminobenzophenone, 3,4'-diaminobenzophenone, 3,3'-diaminobenzophenone, 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] nyl]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- Examples of diamine residues derived from aromatic diamine compounds such as 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, and piperazine.

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

The imide group concentration of the non-thermoplastic polyimide is preferably 35% by weight or less. Here, the "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 35% by weight, the molecular weight of the resin itself decreases, and the low moisture absorption property also deteriorates due to an increase in polar groups. By selecting the combination of the acid anhydride and the diamine compound, the molecular orientation in the non-thermoplastic polyimide is controlled, thereby suppressing the increase in CTE associated with a decrease in the imide group concentration and ensuring low moisture absorption.

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

(Thermoplastic polyimide)
In the present embodiment, the thermoplastic polyimide constituting the thermoplastic polyimide layer contains a tetracarboxylic acid residue and a diamine residue, and it is preferable that both of them contain an aromatic group. By containing both of the tetracarboxylic acid residue and the diamine residue contained in the thermoplastic polyimide and the aromatic group, it is possible to suppress the change in the in-plane birefringence (Δn) of the insulating resin layer under a high temperature environment and to suppress the change in the birefringence in the thickness direction.

The tetracarboxylic acid residue contained in the thermoplastic polyimide is not particularly limited, but for example, a tetracarboxylic acid residue derived from pyromellitic dianhydride (PMDA) (hereinafter also referred to as PMDA residue) and a tetracarboxylic acid residue derived from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) (hereinafter also referred to as BPDA residue) are preferred. These tetracarboxylic acid residues are easy to form an ordered structure, and can reduce the amount of change in in-plane birefringence (Δn) in a high-temperature environment and suppress the change in birefringence in the thickness direction. In addition, the PMDA residue is a residue that plays a role in controlling the thermal expansion coefficient and the glass transition temperature. Furthermore, since the BPDA residue has no polar group and a relatively large molecular weight among tetracarboxylic acid residues, it is expected to have the effect of lowering the imide group concentration of the thermoplastic polyimide and suppressing the moisture absorption of the insulating resin layer. From this viewpoint, the total amount of PMDA residues and/or BPDA residues is preferably 50 molar parts or more, more preferably in the range of 50 to 100 molar parts, and most preferably in the range of 70 to 100 molar parts, relative to 100 molar parts of all tetracarboxylic acid residues contained in the thermoplastic polyimide.

Other tetracarboxylic acid residues contained in the thermoplastic polyimide include tetracarboxylic acid residues derived from aromatic tetracarboxylic dianhydrides similar to those exemplified for the non-thermoplastic polyimides above.

In the present embodiment, the diamine residue contained in the thermoplastic polyimide is preferably at least one diamine residue selected from the above general formulas (2) and (3). The diamine residues selected from the general formulas (2) and (3) are preferably 50 molar parts or more in total, more preferably 50 to 100 molar parts, and most preferably in the range of 70 to 100 molar parts, relative to 100 molar parts of the total diamine residues. By including 50 molar parts or more of the diamine residues selected from the general formulas (2) and (3) in total, relative to 100 molar parts of the total diamine residues, flexibility and adhesiveness can be imparted to the thermoplastic polyimide layer, and it can function as an adhesive layer for the metal layer. Furthermore, among the diamine residues represented by the general formula (2), TPE-R residues are particularly preferred, and among the diamine residues represented by the general formula (3), BAPP residues are particularly preferred. Since the TPE-R residues and the BAPP residues have a flexible site, they can reduce the elastic modulus of the insulating resin layer and impart flexibility. In addition, because the BAPP residue has a large molecular weight, it is expected to reduce the imide group concentration of the thermoplastic polyimide and suppress moisture absorption in the insulating resin layer.

As described above, when the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer contains a diamine residue selected from the general formulas (2) and (3), the thermoplastic polyimide constituting the thermoplastic polyimide layer also preferably contains a diamine residue of a similar structure, preferably the same type of diamine residue selected from the general formulas (2) and (3). In this case, the content ratio of diamine residues differs between the thermoplastic polyimide and the non-thermoplastic polyimide, but by containing similar or the same type of diamine residues, it becomes easier to control the orientation of the thermoplastic polyimide layer and the non-thermoplastic polyimide layer, particularly when forming a polyimide film by a casting method, and it becomes easier to manage the dimensional accuracy. From this viewpoint, in this embodiment, it is preferable that both the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer and the thermoplastic polyimide constituting the thermoplastic polyimide layer contain at least one diamine residue selected from the general formulas (2) and (3), and it is most preferable that the diamine residue contains a TPE-R residue and/or a BAPP residue.

In the present embodiment, examples of diamine residues contained in the thermoplastic polyimide other than those of the general formulas (2) and (3) include 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'-n-propyl-4,4'-diaminobiphenyl (m-NPB), 2,2'-divinyl-4,4'-diaminobiphenyl (VAB), 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)-2,2'-diaminobiphenyl, and 2,2'-diamino-4,4'-diaminobiphenyl. (3-aminomethyl)biphenyl (TFMB), p-phenylenediamine (p-PDA), m-phenylenediamine (m-PDA), 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(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, bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(3-aminophenoxy)phenyl]propane, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)phenyl]ether, Examples of diamine residues include those derived from diamine compounds such as bis[4-(3-aminophenoxy)]sulfone, bis[4-(3-aminophenoxy)]benzophenone, 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]ketone (BAPK), bis[4-(3-aminophenoxy)]biphenyl, and bis[4-(4-aminophenoxy)]biphenyl.

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

The thermoplastic polyimide constituting the thermoplastic polyimide layer can improve adhesion with the metal layer. Such thermoplastic polyimides have a glass transition temperature in the range of 200°C or more and 350°C or less, preferably in the range of 200°C or more and 320°C or less.

The imide group concentration of the thermoplastic polyimide is preferably 35% 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 35% by weight, the molecular weight of the resin itself decreases, and the low moisture absorption property also deteriorates due to an increase in polar groups. By selecting the above combination of the acid anhydride and the diamine compound, the molecular orientation in the thermoplastic polyimide is controlled, thereby suppressing the increase in CTE associated with a decrease in the imide group concentration and ensuring low moisture absorption.

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

(Synthesis of Non-Thermoplastic and Thermoplastic Polyimides)
Generally, polyimide can be produced by reacting tetracarboxylic dianhydride with a diamine compound in a solvent to generate polyamic acid, which is then subjected to ring closure by heating. For example, tetracarboxylic dianhydride and diamine compound are dissolved in an organic solvent in approximately equal molar amounts, and the mixture is stirred at a temperature in the range of 0 to 100°C for 30 minutes to 24 hours to polymerize, thereby obtaining polyamic acid, which is a precursor of polyimide. In the reaction, the reaction components are dissolved so that the precursor generated is in the range of 5 to 30% by weight, preferably in the range of 10 to 20% by weight, in the organic solvent. Examples of organic solvents used in the polymerization reaction include N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2-butanone, dimethylsulfoxide (DMSO), hexamethylphosphoramide, N-methylcaprolactam, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diglyme, triglyme, cresol, and the like. Two or more of these solvents can be used in combination, and aromatic hydrocarbons such as xylene and toluene can also be used in combination. The amount of such an organic solvent to be used is not particularly limited, but it is preferable to adjust the amount to be used so 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 it can be concentrated, diluted, or replaced with another organic solvent if necessary. Polyamic acid is also advantageously used because it generally has excellent solvent solubility. The viscosity of the polyamic acid solution is preferably within the range of 500 cps to 100,000 cps. If it is outside this range, defects such as uneven thickness and streaks are likely to occur in the film during coating operations using a coater or the like. There are no particular restrictions on the method for imidizing polyamic acid, and a heat treatment such as heating in the above-mentioned solvent at a temperature condition within the range of 80 to 400°C for 1 to 24 hours is preferably used.

<Metal Layer>
Examples of the metal constituting the metal layer include metals selected from copper, aluminum, stainless steel, iron, silver, palladium, nickel, chromium, molybdenum, tungsten, zirconium, gold, cobalt, titanium, tantalum, zinc, lead, tin, silicon, bismuth, indium, and alloys thereof. The metal layer can be formed by methods such as sputtering, vapor deposition, and plating, but it is preferable to use a metal foil from the viewpoint of adhesion. Copper foil is particularly preferable from the viewpoint of conductivity. The copper foil may be either electrolytic copper foil or rolled copper foil. In addition, when the metal-clad laminate of this embodiment is continuously produced, a long metal foil having a predetermined thickness wound into a roll is used as the metal foil.

Below, we will explain a preferred embodiment of a metal-clad laminate, taking as an example a copper-clad laminate having a copper layer.

<Copper-clad laminate>
The copper clad laminate of this embodiment may include an insulating layer and a copper layer such as copper foil on at least one side of the insulating layer. In addition, in order to increase the adhesion between the insulating layer and the copper layer, the layer in contact with the copper layer in the insulating layer is a thermoplastic polyimide layer. The copper layer is provided on one or both sides of the insulating layer. That is, the copper clad laminate of this embodiment may be a single-sided copper clad laminate (single-sided CCL) or a double-sided copper clad laminate (double-sided CCL). In the case of a single-sided CCL, the copper layer laminated on one side of the insulating layer is the "first copper layer" in the present invention. In the case of a double-sided CCL, the copper layer laminated on one side of the insulating layer is the "first copper layer" in the present invention, and the copper layer laminated on the side of the insulating layer opposite to the side on which the first copper layer is laminated is the "second copper layer" in the present invention. The copper clad laminate of this embodiment is used as an FPC by forming copper wiring by etching the copper layer or the like through wiring circuit processing.

A copper-clad laminate may be prepared, for example, by preparing a resin film, sputtering a metal onto it to form a seed layer, and then forming a copper layer, for example, by copper plating.

Copper-clad laminates can also be prepared by preparing a resin film and laminating copper foil to it using a method such as thermocompression bonding.

Furthermore, a copper-clad laminate may be prepared by casting a coating solution containing polyamic acid, a precursor of polyimide, onto copper foil, drying to form a coating film, and then heat-treating it to imidize it and form a polyimide layer.

(First Copper Layer)
In the copper-clad laminate of this embodiment, the copper foil used for the first copper layer (hereinafter, sometimes referred to as the "first copper foil") is not particularly limited, and may be, for example, a rolled copper foil or an electrolytic copper foil.

The thickness of the first copper foil is preferably 13 μm or less, and more preferably in the range of 6 to 12 μm. If the thickness of the first copper foil exceeds 13 μm, the bending stress applied to the copper layer (or copper wiring) when the copper-clad laminate (or FPC) is bent increases, resulting in a decrease in bending resistance. In addition, from the viewpoints of production stability and handling, it is preferable that the lower limit of the thickness of the first copper foil is 6 μm.

The tensile modulus of the first copper foil is preferably, for example, within the range of 10 to 35 GPa, and more preferably within the range of 15 to 25 GPa. When a rolled copper foil is used as the first copper foil in this embodiment, the flexibility is easily increased when it is annealed by heat treatment. Therefore, if the tensile modulus of the copper foil is less than the above lower limit, the rigidity of the first copper foil itself is reduced by heating in the process of forming an insulating layer on the long first copper foil. On the other hand, if the tensile modulus of the copper foil exceeds the above upper limit, a large bending stress is applied to the copper wiring when the FPC is folded, and its bending resistance is reduced. The tensile modulus of the rolled copper foil tends to change depending on the heat treatment conditions when forming an insulating layer on the copper foil and the annealing treatment of the copper foil after forming the insulating layer. Therefore, in this embodiment, it is sufficient that the tensile modulus of the first copper foil is within the above range in the finally obtained copper-clad laminate.

The first copper foil is not particularly limited, and commercially available rolled copper foil can be used.

(Second Copper Layer)
The second copper layer is laminated on the surface of the insulating layer opposite to the first copper layer. The copper foil (second copper foil) used for the second copper layer is not particularly limited, and may be, for example, a rolled copper foil or an electrolytic copper foil. In addition, a commercially available copper foil may be used as the second copper foil. The second copper foil may be the same as the first copper foil.

<Circuit board>
The metal-clad laminate of the present embodiment is useful mainly as a material for circuit boards such as FPCs, etc. For example, the copper layer of the copper-clad laminate exemplified above is processed into a pattern by a conventional method to form a wiring layer, thereby manufacturing a circuit board such as an FPC, which is one embodiment of the present invention.

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

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

[Measurement of glass transition temperature (Tg)]
The glass transition temperature was measured by measuring a polyimide film having a size of 5 mm x 20 mm using a dynamic viscoelasticity measuring device (DMA: manufactured by U.B.M., product name: E4000F) from 30°C to 400°C at a heating rate of 4°C/min and a frequency of 11 Hz, and the temperature at which the change in elastic modulus (tan δ) was maximum was defined as the glass transition temperature. Note that, those showing a storage modulus of 1.0 x 10 ⁹ Pa or more at 30°C and less than 1.0 x 10 ⁸ Pa at 360°C measured using the DMA were defined as "thermoplastic", and those showing a storage modulus of 1.0 x 10 ⁹ Pa or more at 30°C and a storage modulus of 1.0 x 10 ⁸ Pa or more at 360°C were defined as "non-thermoplastic".

[Measurement of coefficient of thermal expansion (CTE)]
A polyimide film having a size of 3 mm x 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), and then held at that temperature for 10 minutes. The film was then cooled at a rate of 5°C/min to determine the average thermal expansion coefficient (thermal expansion coefficient) from 250°C to 100°C.

[Measurement of in-plane retardation (RO)]
The retardation in the in-plane direction of a given sample was measured using a birefringence meter (manufactured by Photonic Lattice, product name: Wide Range Birefringence Evaluation System WPA-100, measurement area: MD: 140 mm × TD: 100 mm). The incident angle was 0°, and the measurement wavelength was 543 nm.

[Preparation of samples for evaluation of in-plane retardation (RO)]
The metal layer of a long metal-clad laminate was etched to obtain a polyimide film, which was then cut into A4 size pieces (TD: 210 mm x MD: 297 mm) at each of the two left and right ends (Left and Right) and the center (Center) in the TD direction to prepare Sample L (Left), Sample R (Right), and Sample C (Center).

[Evaluation of in-plane birefringence (Δn)]
The in-plane retardation (RO) was measured for each of Sample L, Sample R, and Sample C. The maximum value of the measured value of each sample was divided by the thickness of the evaluation sample to obtain the "in-plane birefringence (Δn)", the difference between the maximum and minimum values of the measured in-plane retardation (RO) was obtained as the "variation (ΔRO) of in-plane retardation (RO) in the width direction (TD direction)", and the value obtained by dividing this ΔRO by the thickness of the evaluation sample was obtained as the "variation [Δ(Δn)] of in-plane birefringence (Δn) in the width direction (TD direction)".

[Measurement of retardation and birefringence in the thickness direction]
For the polyimide layer as the insulating resin layer, a thin film slice having a thickness of 0.5 μm was prepared by an ultramicrotome, and the retardation in the thickness direction was measured. At this time, a birefringence meter (manufactured by Photonic Lattice, Inc., product name: Birefringence distribution observation camera for mounting on a microscope PI-micro) was used. The measurement wavelength was 520 nm, and the incident angle was 0°.
ROa is the retardation value at a point 1.5 μm away from one surface of a non-thermoplastic polyimide layer in a polyimide layer (film) toward the center.
ROb is the retardation value at a point 1.5 μm away from the other surface of the non-thermoplastic polyimide layer in the polyimide layer (film) toward the center.
ROv is the average value of the sum (ROa+ROb+ROc) of ROa, ROb, and the retardation value (ROc) at the center in the thickness direction of the non-thermoplastic polyimide layer in the polyimide layer (film).
In addition, the value obtained by dividing the value of ROa by the thickness (0.5 μm) of the thin film slice was defined as "the birefringence (Δna) at a point 1.5 μm away from one surface toward the center in the thickness direction of the non-thermoplastic polyimide layer", the value obtained by dividing the value of ROb by the thickness (0.5 μm) of the thin film slice was defined as "the birefringence (Δnb) at a point 1.5 μm away from the other surface toward the center in the thickness direction of the non-thermoplastic polyimide layer", and the value obtained by dividing the value of ROc by the thickness (0.5 μm) of the thin film slice was defined as "the birefringence (Δnc) at the center in the thickness direction of the non-thermoplastic polyimide layer".
Δnv is the average value of the sum of Δna, Δnb, and Δnc (Δna+Δnb+Δnc).

[Warpage measurement]
A polyimide film having a size of 50 mm x 50 mm was placed on a flat table with the curled side facing up after being conditioned at 23°C and 50% RH for 24 hours. The curl amount was measured using a caliper. When the film curled toward the etched surface of the substrate, it was indicated as a plus sign, and when the film curled toward the opposite side, it was indicated as a minus sign, and the average of the measured values at the four corners of the film was taken as the curl amount.

[Peel strength measurement]
The copper foil of the single-sided copper-clad laminate (copper foil/resin layer) was processed into a circuit width of 1.0 mm, and then cut to a width of 8 cm and a length of 4 cm to prepare a measurement sample. Using a Tensilon tester (manufactured by Toyo Seiki Seisakusho, product name: Strograph VE-1D), the resin layer side of the measurement sample was fixed to an aluminum plate with double-sided tape, and the copper foil was peeled off 10 mm from the resin layer in a 90° direction at a rate of 50 mm/min to determine the central strength.

The abbreviations used in the examples and comparative 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 DAPE: 4,4'-diaminodiphenyl ether BAPP: 2,2-bis[4-(4-aminophenoxy)phenyl]propane p-PDA: p-phenylenediamine DMAc: N,N-dimethylacetamide

(Synthesis Example 1)
Under a nitrogen gas flow, 23.0 parts by weight of m-TB (0.108 mol parts), 3.5 parts by weight of TPE-R (0.012 mol parts), and DMAc in an amount such that the solid content concentration after polymerization is 15% by weight were charged into the reaction vessel, and the mixture was stirred at room temperature to dissolve. Next, 26.0 parts by weight of PMDA (0.119 mol parts) were added, and the mixture was stirred at room temperature for 3 hours to carry out a polymerization reaction, thereby obtaining a polyamic acid solution a. The solution viscosity of the polyamic acid solution a was 41,100 cps. The glass transition temperature of the polyimide obtained from this polyamic acid solution a was 421°C, non-thermoplastic, and had a thermal expansion coefficient of 10 (ppm/K).

(Synthesis Example 2)
Under a nitrogen stream, 17.3 parts by weight of m-TB (0.081 mol parts), 10.2 parts by weight of TPE-R (0.035 mol parts), and an amount of DMAc such that the solid content concentration after polymerization is 15% by weight were charged into the reaction vessel, and the mixture was stirred at room temperature to dissolve. Next, 25.1 parts by weight of PMDA (0.115 mol parts) were added, and the mixture was stirred at room temperature for 3 hours to carry out a polymerization reaction, thereby obtaining a polyamic acid solution b. The solution viscosity of the polyamic acid solution b was 38,200 cps. The glass transition temperature of the polyimide obtained from this polyamic acid solution b was 427°C, non-thermoplastic, and had a thermal expansion coefficient of 22 (ppm/K).

(Synthesis Example 3)
Under a nitrogen stream, 16.4 parts by weight of m-TB (0.077 mol parts), 9.7 parts by weight of TPE-R (0.033 mol parts), and an amount of DMAc such that the solid content concentration after polymerization is 15% by weight were charged into the reaction vessel, and stirred at room temperature to dissolve. Next, 16.7 parts by weight of PMDA (0.077 mol parts) and 9.7 parts by weight of BPDA (0.033 mol parts) were added, and the polymerization reaction was continued by stirring at room temperature for 3 hours to obtain a polyamic acid solution c. The solution viscosity of the polyamic acid solution c was 46,700 cps. The glass transition temperature of the polyimide obtained from this polyamic acid solution c was 366°C, non-thermoplastic, and the thermal expansion coefficient was 23 (ppm/K).

(Synthesis Example 4)
Under a nitrogen gas flow, 22.4 parts by weight of m-TB (0.105 mol parts), 4.8 parts by weight of BAPP (0.012 mol parts), and DMAc in an amount such that the solid content concentration after polymerization was 15% by weight were charged into the reaction vessel, and the mixture was stirred at room temperature to dissolve. Next, 25.3 parts by weight of PMDA (0.116 mol parts) were added, and the mixture was stirred at room temperature for 3 hours to carry out a polymerization reaction, thereby obtaining a polyamic acid solution d. The solution viscosity of the polyamic acid solution d was 36,800 cps. The glass transition temperature of the polyimide obtained from this polyamic acid solution d was 408°C, non-thermoplastic, and had a thermal expansion coefficient of 9 (ppm/K).

(Synthesis Example 5)
Under a nitrogen stream, 12.3 parts by weight of m-TB (0.058 mol), 10.1 parts by weight of TPE-R (0.035 mol), 2.5 parts by weight of p-PDA (0.023 mol), and an amount of DMAc such that the solid content concentration after polymerization becomes 15% by weight were charged into the reaction vessel, and the mixture was stirred at room temperature to dissolve. Next, 17.5 parts by weight of PMDA (0.080 mol) and 10.1 parts by weight of BPDA (0.034 mol) were added, and the mixture was stirred at room temperature for 3 hours to carry out a polymerization reaction, thereby obtaining a polyamic acid solution e. The solution viscosity of the polyamic acid solution e was 42,700 cps. The glass transition temperature of the polyimide obtained from this polyamic acid solution e was 360° C., non-thermoplastic, and had a thermal expansion coefficient of 18 (ppm/K).

(Synthesis Example 6)
Under a nitrogen gas flow, 2.2 parts by weight of m-TB (0.010 mol parts), 27.6 parts by weight of TPE-R (0.094 mol parts), and DMAc in an amount such that the solid content concentration after polymerization is 15% by weight were charged into the reaction vessel, and the mixture was stirred at room temperature to dissolve. Next, 22.7 parts by weight of PMDA (0.104 mol parts) were added, and the mixture was stirred at room temperature for 3 hours to carry out a polymerization reaction, thereby obtaining a polyamic acid solution f. The solution viscosity of the polyamic acid solution f was 33,900 cps. The glass transition temperature of the polyimide obtained from this polyamic acid solution f was 446°C, and the thermoplasticity and thermal expansion coefficient were 55 (ppm/K).

(Synthesis Example 7)
Under nitrogen flow, 30.2 parts by weight of BAPP (0.074 mol parts) and DMAc in an amount that would result in a solid content concentration of 15% by weight after polymerization were added to the reaction vessel, and the mixture was stirred at room temperature to dissolve. Next, 22.3 parts by weight of BPDA (0.076 mol parts) were added, and the mixture was stirred at room temperature for 3 hours to carry out a polymerization reaction, to obtain a polyamic acid solution g. The solution viscosity of the polyamic acid solution g was 9,800 cps. The glass transition temperature of the polyimide obtained from this polyamic acid solution g was 252°C, and the thermoplasticity and thermal expansion coefficient were 46 (ppm/K).

(Synthesis Example 8)
Under a nitrogen gas flow, 25.8 parts by weight of TPE-R (0.088 mol parts) and an amount of DMAc such that the solid content concentration after polymerization becomes 15% by weight were charged into the reaction vessel, and the mixture was stirred at room temperature to dissolve. Next, 26.7 parts by weight of BPDA (0.091 mol parts) were added, and the mixture was stirred at room temperature for 3 hours to carry out a polymerization reaction, thereby obtaining a polyamic acid solution h. The solution viscosity of the polyamic acid solution h was 8,800 cps. The glass transition temperature of the polyimide obtained from this polyamic acid solution h was 243°C, and the thermoplasticity and thermal expansion coefficient were 65 (ppm/K).

(Synthesis Example 9)
Under a nitrogen gas flow, 17.6 parts by weight of TPE-R (0.060 mol parts), 1.6 parts by weight of p-PDA (0.015 mol parts), and DMAc in an amount such that the solid content concentration after polymerization was 15% by weight were charged into the reaction vessel, and the mixture was stirred at room temperature to dissolve. Next, 22.8 parts by weight of BPDA (0.077 mol parts) were added, and the mixture was stirred at room temperature for 3 hours to carry out a polymerization reaction, thereby obtaining a polyamic acid solution i. The solution viscosity of the polyamic acid solution i was 7,800 cps. The glass transition temperature of the polyimide obtained from this polyamic acid solution i was 239°C, and the thermoplasticity and thermal expansion coefficient were 65 (ppm/K).

(Synthesis Example 10)
Under a nitrogen gas flow, 11.7 parts by weight of DAPE (0.058 mol parts), 11.4 parts by weight of TPE-R (0.039 mol parts), and an amount of DMAc such that the solid content concentration after polymerization becomes 15% by weight were charged into the reaction vessel, and stirred at room temperature to dissolve. Next, 29.5 parts by weight of BPDA (0.100 mol parts) were added, and the mixture was stirred at room temperature for 3 hours to carry out a polymerization reaction, thereby obtaining a polyamic acid solution j. The solution viscosity of the polyamic acid solution j was 11,200 cps. The glass transition temperature of the polyimide obtained from this polyamic acid solution j was 265°C, and the thermoplasticity and thermal expansion coefficient were 58 (ppm/K).

[Example 1]
The polyamic acid solution g prepared in Synthesis Example 7 was uniformly applied to one side of a long electrolytic copper foil having a thickness of 12 μm and a width of 1,080 mm so that the thickness after curing was 2.5 μm (first layer), and then heated and dried at 120 ° C to remove the solvent. The polyamic acid solution a prepared in Synthesis Example 1 was uniformly applied thereon so that the thickness after curing was 20 μm (second layer), and then heated and dried at 120 ° C to remove the solvent. Furthermore, the polyamic acid solution g prepared in Synthesis Example 7 was uniformly applied thereon so that the thickness after curing was 2.5 μm (third layer), and then heated and dried at 120 ° C to remove the solvent. Then, a stepwise heat treatment was performed from 130 ° C to 360 ° C to complete the imidization, and a single-sided copper-clad laminate was prepared.

[Examples 2 to 8 and Comparative Examples 1 to 3]
A polyamic acid resin solution was applied to one side of an electrolytic copper foil, followed by heat drying and stepwise heat treatment to prepare a single-sided copper-clad laminate. A single-sided copper-clad laminate was obtained in the same manner as in Example 1, except that the resins and thicknesses used in the first to third layers were changed to those shown in Table 1 below.

Table 1 shows the thickness ratio (non-thermoplastic polyimide layer (A)/thermoplastic polyimide layer (B)) of the non-thermoplastic polyimide layer (A) in the insulating resin layer of the single-sided copper-clad laminates obtained in Examples 1 to 8 and Comparative Examples 1 to 3, the in-plane retardation (RO), the variation (ΔRO) of the in-plane retardation (RO) in the width direction (TD direction), and the difference in retardation in the thickness direction of the non-thermoplastic polyimide layer (|ROa-ROb|, |ROv-ROa|, |ROv-ROb|), the amount of warping, and the peel strength. Table 2 also shows the in-plane birefringence (Δn) in the insulating resin layer of the single-sided copper-clad laminates obtained in Examples 1 to 8 and Comparative Examples 1 to 3, the variation in in-plane birefringence (Δn) in the width direction (TD direction) [Δ(Δn)], and the difference in birefringence in the thickness direction of the non-thermoplastic polyimide layer (|Δna-Δnb|, |Δnv-Δna|, |Δnv-Δnb|).

<IC chip mountability>
A dry film was laminated on the copper foil surface of the single-sided copper-clad laminate prepared in Examples 1 to 8 and Comparative Examples 1 to 3, and the dry film resist was patterned, and the copper foil was etched along the pattern to form a circuit, thereby preparing a circuit board. When an IC chip was mounted on the copper wiring side of the obtained circuit board by bonding treatment at 400°C for 0.5 seconds, there was no misalignment between the copper wiring and the IC chip in Examples 1 to 8, and no problems occurred. On the other hand, there was a misalignment between the copper wiring and the IC chip in Comparative Example 1, and there was a misalignment between the copper wiring and the IC chip and warping of the circuit board in Comparative Examples 2 and 3, resulting in problems with mounting.

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

Claims (8)

A metal-clad laminate comprising an insulating resin layer and a metal layer laminated on at least one surface of the insulating resin layer,
the insulating resin layer has a thermoplastic polyimide layer containing a thermoplastic polyimide on at least one surface of a non-thermoplastic polyimide layer containing a non-thermoplastic polyimide,
the non-thermoplastic polyimide and the thermoplastic polyimide contain a tetracarboxylic acid residue and a diamine residue, and both of these residues are composed of an aromatic group;
The insulating resin layer satisfies the following conditions (i) to (iv):
(i) the value of in-plane birefringence (Δn) is 2×10 ⁻³ or less;
(ii) the variation [Δ(Δn)] of the in-plane birefringence (Δn) in the width direction (TD) is 4×10 ⁻⁴ or less;
(iii) in the thickness direction of the non-thermoplastic polyimide layer, the difference (Δna-Δnb) between the birefringence (Δna) at a point 1.5 μm away from the center from one surface and the birefringence (Δnb) at a point 1.5 μm away from the center from the other surface is ±0.01 or less;
(iv) the difference between the sum (Δna+Δnb+Δnc) of the Δna and Δnb and the birefringence (Δnc) at the center in the thickness direction and the average value (Δnv) is ±0.01 or less for both Δna and Δnb;
A metal-clad laminate comprising: The metal-clad laminate according to claim 1, characterized in that the non-thermoplastic polyimide contains 20 or more molar parts of diamine residues derived from a diamine compound represented by the following general formula (1) per 100 molar parts of all diamine residues.

[In general formula (1), the linking group Z represents a single bond or -COO-, Y represents a monovalent hydrocarbon having 1 to 3 carbon atoms, which may be substituted with a halogen or a phenyl group, an alkoxy group having 1 to 3 carbon atoms, a perfluoroalkyl group having 1 to 3 carbon atoms, or an alkenyl group, n represents an integer of 0 to 2, and p and q independently represent integers of 0 to 4.] The metal-clad laminate according to claim 2, characterized in that, relative to 100 molar parts of all diamine residues contained in the non-thermoplastic polyimide, the diamine residues derived from the diamine compound represented by the general formula (1) are in the range of 70 molar parts to 95 molar parts, and the total amount of diamine residues selected from the diamine residues represented by the following general formulas (2) and (3) is in the range of 5 to 30 molar parts:

[In general formula (2) and general formula (3), R ₅ , R ₆ , R ₇ and R ₈ each independently represent a halogen atom, or an alkyl group or alkoxy group having 1 to 4 carbon atoms which may be substituted with a halogen atom, or an alkenyl group; X independently represents a divalent group selected from -O-, -S-, -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -CO-, -COO-, -SO ₂ -, -NH- or -NHCO-; X ₁ and X ₂ each independently represent a divalent group selected from a _single bond, -O-, -S-, -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -CO-, -COO-, -SO ₂ -, -NH- or -NHCO-; and m, n, o and p each independently represent an integer of 0 to 4, except for the case where both of m and _n are single bonds. The metal-clad laminate according to claim 2 or 3, characterized in that the thermoplastic polyimide has a total amount of diamine residues selected from the following general formulas (2) and (3) of 50 parts by mole or more per 100 parts by mole of all diamine residues.

[In general formula (2) and general formula (3), R ₅ , R ₆ , R ₇ and R ₈ each independently represent a halogen atom, or an alkyl group or alkoxy group having 1 to 4 carbon atoms which may be substituted with a halogen atom, or an alkenyl group; X independently represents a divalent group selected from -O-, -S-, -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -CO-, -COO-, -SO ₂ -, -NH- or -NHCO-; X ₁ and X ₂ each independently represent a divalent group selected from a _single bond, -O-, -S-, -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -CO-, -COO-, -SO ₂ -, -NH- or -NHCO-; and m, n, o and p each independently represent an integer of 0 to 4, except for the case where both of m and _n are single bonds. the diamine residue represented by the general formula (2) is a diamine residue derived from 1,3-bis(4-aminophenoxy)benzene,
The metal-clad laminate according to claim 3 or 4, characterized in that the diamine residue represented by the general formula (3) is a diamine residue derived from 2,2-bis[4-(4-aminophenoxy)phenyl]propane. The metal-clad laminate according to any one of claims 1 to 5, characterized in that the thickness ratio (A)/(B) of the thickness (A) of the non-thermoplastic polyimide layer to the thickness (B) of the thermoplastic polyimide layer is within the range of 1 to 20. The metal-clad laminate according to any one of claims 1 to 6, characterized in that the length in the width direction (TD direction) is 490 mm or more. A circuit board obtained by processing the metal layer of the metal-clad laminate described in any one of claims 1 to 7 into wiring.