Flexible metal-clad laminate and flexible circuit board

Abstract

To provide excellent crease resistance to an FPC formed from a flexible metal-clad laminate sheet, even when a polyimide insulation layer thickness is set to 50 μm or more in order to apply the flexible metal-clad laminate sheet on which a polyimide insulation layer as a dielectric is laminated on a metal layer to high frequency use.SOLUTION: A flexible metal-clad laminate sheet used for a flexible circuit board that is folded and housed in a housing of an electronic device by folding so that an upper surface side is turned by 180 degrees and is folded to be a lower surface side, has: an insulation resin layer having a thickness of 50 μm or more and 150 μm or less and a tensile elastic modulus (TM1) within a range of 1 GPa or more and 7 GPa or less; and a metal layer laminated on at least one surface of the insulating resin layer. A tensile elastic modulus (TM2) in a range of 5 μm in a thickness direction from an interface with the metal layer in the insulating resin layer is in a range of 2 GPa or more and 10 GPa or less, and the tensile elastic modulus (TM2) is larger than the tensile elastic modulus (TM1).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a flexible metal-clad laminate and a flexible circuit board. [Background technology]

[0002] In recent years, a technology has been proposed in which a flexible circuit board (FPC) obtained by processing a copper foil of a flexible metal-clad laminate having a polyimide insulating layer on a copper foil into a wiring circuit is folded by inverting the upper surface (circuit forming side) 180 degrees to bend it to the lower surface, and the folded FPC (i.e., FPC for seam folding) is housed in a thin housing of a light, thin, small electronic device (Patent Document 1). In this technology, in order to prevent breaks or cracks from occurring in the wiring circuit of the FPC due to the seam folding, it is proposed to configure the polyimide insulating layer of the FPC from a laminate of two types of polyimide layers with different thermal expansion coefficients, set the thickness and tensile modulus of the entire polyimide insulating layer to a specific range, set the surface roughness of the copper foil to a specific range, and further set a predetermined fold habit coefficient to a specific range.

[0003] Incidentally, when a flexible metal-clad laminate for FPC is applied to high frequency applications, it is common to thicken the polyimide insulating layer, which is a dielectric, to improve high frequency characteristics. For this reason, attempts have been made to thicken the polyimide insulating layer of the FPC for seam folding applications described in Patent Document 1 in order to apply it to high frequency applications. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6320031 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the FPCs for seam folding applications described in Patent Document 1, the thickness range of the polyimide insulation layer is limited to 5 to 30 μm, and there is no consideration at all of achieving good "seam folding resistance" for FPCs having polyimide insulation layers thickened to 50 μm or more. Rather, it is concluded that when an FPC with a polyimide insulation layer thickness exceeding 30 μm is folded, the folding resistance is significantly reduced (see paragraph 0020 of Patent Document 1).

[0006] The object of the present invention is to provide an FPC made from a flexible metal-clad laminate in which a polyimide insulation layer is laminated as a dielectric on a metal layer, with good resistance to bending when the polyimide insulation layer is made 50 μm thick or more in order to make the flexible metal-clad laminate suitable for high-frequency applications. [Means for solving the problem]

[0007] As a result of extensive research, the inventors have discovered that when the polyimide insulation layer of a flexible metal-clad laminate, which is a material for manufacturing an FPC, is thickened by stacking multiple polyimide layers in order to make the FPC suitable for high-frequency applications, not only the tensile modulus of the entire polyimide insulation layer but also the tensile modulus of the region of the polyimide insulation layer adjacent to the metal layer is closely related to the resistance to bending of the FPC, and have completed the present invention.

[0008] That is, the present invention relates to a flexible metal-clad laminate used for a flexible circuit board that is folded and stored in a housing of an electronic device by a seam fold in which the upper surface side is inverted 180 degrees to become the lower surface side, An insulating resin layer having a thickness in the range of 50 μm to 150 μm and a tensile modulus (TM1) in the range of 1 GPa to 7 GPa; a metal layer laminated on at least one surface of the insulating resin layer, The present invention provides a flexible metal-clad laminate, characterized in that the tensile modulus (TM2) of the insulating resin layer within a range of 5 μm in the thickness direction from the interface with the metal layer is in the range of 2 GPa or more and 10 GPa or less, and the tensile modulus (TM2) is greater than the tensile modulus (TM1).

[0009] In the flexible metal-clad laminate of the present invention, the equivalent bending stiffness (RF) [N / mm 2 ] divided by the cube of the total thickness (L) [mm] (RF / L 3 ) is 400N / mm 5 More than 1200N / mm 5 It is preferable that the content is within the following range:

[0010] In the flexible metal-clad laminate of the present invention, the thickness of the metal layer is preferably within the range of 6 μm or more and 15 μm or less.

[0011] Furthermore, in the flexible metal-clad laminate of the present invention, it is preferable that the insulating resin layer is formed by laminating a plurality of polyimide layers, has a polyimide layer (A) as a central layer of the plurality of polyimide layers, and the thickness of the polyimide layer (A) is in the range of 0.5 to 0.96 with respect to the total thickness of the insulating resin layer.

[0012] The tensile modulus of elasticity of such a polyimide layer (A) is preferably 1 GPa or more and 5 GPa or less.

[0013] The present invention provides a flexible circuit board obtained by wiring the metal layer of the flexible metal-clad laminate described above. This flexible circuit board is preferably bent so that the metal layer faces inward. Effect of the Invention

[0014] The flexible metal-clad laminate of the present invention has an insulating resin layer having a thickness in the range of 50 μm to 150 μm and a tensile modulus (TM1) in the range of 1 GPa to 7 GPa, and a metal layer laminated on at least one surface of the insulating resin layer. In this insulating resin layer, the tensile modulus (TM2) within a range of 5 μm in the thickness direction from the interface with the metal layer is in the range of 2 GPa to 10 GPa, and the tensile modulus (TM2) is greater than the tensile modulus (TM1). Therefore, the flexible metal-clad laminate of the present invention, in which an insulating resin layer is laminated on a metal layer, exhibits good resistance to bending and is useful as a material for manufacturing FPCs suitable for high frequency applications. [Brief description of the drawings]

[0015] [Figure 1] 1 is a schematic cross-sectional view showing the configuration of a flexible single-sided metal-clad laminate according to one embodiment of the present invention. [Diagram 2] 4 is a schematic cross-sectional view showing the configuration of a flexible double-sided metal-clad laminate according to another embodiment of the present invention. FIG. [Diagram 3] FIG. 2 is a schematic cross-sectional view showing the configuration of a preferred embodiment of the flexible single-sided metal-clad laminate of FIG. [Figure 4] FIG. 3 is a schematic cross-sectional view showing the configuration of a preferred embodiment of the flexible double-sided metal-clad laminate of FIG. 2. [Diagram 5] FIG. 2 is a cross-sectional view illustrating a multilayer polyimide layer for calculating an average tensile elastic modulus. [Figure 6] FIG. 2 is a plan view illustrating the copper wiring of a test circuit board piece used in the examples. [Figure 7] FIG. 13 is an explanatory side view showing the state of the sample stage and the test circuit board piece in a bending test (a diagram showing the state in which the test circuit board piece is fixed on the sample stage). [Figure 8] FIG. 13 is an explanatory side view showing the state of the sample stage and the test circuit board piece in a bending test (a view showing the state just before the bending portion of the test circuit board piece is pressed with a roller). [Figure 9]FIG. 13 is an explanatory side view showing the state of the sample stage and the test circuit board piece during a bending test (a diagram showing the state in which the bent portion of the test circuit board piece is pressed with a roller). [Figure 10] FIG. 13 is an explanatory side view showing the state of the sample stage and the test circuit board piece during the bending test (a diagram showing the state after the bent portion is opened and the test piece is returned to a flat state). [Figure 11] FIG. 13 is an explanatory side view showing the state of the sample stage and the test circuit board piece during a bending test (a state diagram showing the crease at the bending portion being pressed and smoothed with a roller). [Figure 12] FIG. 2 is a cross-sectional explanatory view (part) of a flexible circuit board. [Figure 13] FIG. 2 is a schematic cross-sectional view of a laminate used in calculating the equivalent bending rigidity of a flexible metal-clad laminate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the accompanying drawings.

[0017] [Flexible metal-clad laminates] 1 is a schematic cross-sectional view showing the configuration of a flexible single-sided metal-clad laminate according to one embodiment of the present invention. The flexible single-sided metal-clad laminate (CA) of this embodiment has a metal layer (MA) and an insulating resin layer (X) laminated on one side of the metal layer (MA). The insulating resin layer (X) has a structure in which a bottom insulating resin layer (PA) and an adhesive layer (BA) are laminated, and the bottom insulating resin layer (PA) is disposed on the metal layer (MA) side. It is preferable that the bottom insulating resin layer (PA) and the adhesive layer (BA) are each composed of a polyimide layer.

[0018] 2 is a schematic cross-sectional view showing the configuration of a flexible double-sided metal-clad laminate according to another embodiment of the present invention. This flexible double-sided metal-clad laminate (C) has a structure in which a pair of metal layers (M1, M2) sandwich an insulating resin layer (X), or in other words, a pair of flexible single-sided metal-clad laminates (CA) are bonded together with an adhesive layer (B). That is, the flexible double-sided metal-clad laminate (C) includes a first single-sided metal-clad laminate (C1), a second single-sided metal-clad laminate (C2), and an adhesive layer (B) laminated between the first single-sided metal-clad laminate (C1) and the second single-sided metal-clad laminate (C2). Here, the first single-sided metal-clad laminate (C1) has a first metal layer (M1) and a first insulating resin layer (P1) laminated on at least one side of the first metal layer (M1). The second single-sided metal-clad laminate (C2) has a second metal layer (M2) and a second insulating resin layer (P2) laminated on at least one side of the second metal layer (M2). The adhesive layer (B) is disposed so as to abut against the first insulating resin layer (P1) and the second insulating resin layer (P2). In other words, the flexible double-sided metal-clad laminate (C) has a structure in which the first metal layer (M1), the first insulating resin layer (P1), the adhesive layer (B), the second insulating resin layer (P2), and the second metal layer (M2) are laminated in this order. The first metal layer (M1) and the second metal layer (M2) are located on the outermost side, the first insulating resin layer (P1) and the second insulating resin layer (P2) are located on the inner side, and an adhesive layer (B) is interposed between the first insulating resin layer (P1) and the second insulating resin layer (P2). It is preferable that the first insulating resin layer (P1), the second insulating resin layer (P2), and the adhesive layer (B) are each composed of a polyimide layer.

[0019] (Thickness of insulating resin layer) The insulating resin layer (X) constituting the flexible metal-clad laminate of the present invention has a layer thickness of 50 μm to 150 μm, preferably 50 μm to 125 μm, in order to manufacture an FPC for high frequency applications from the flexible metal-clad laminate. If the layer thickness is below this range, the wiring width becomes narrower from the viewpoint of impedance control essential for high frequency FPC boards, making it difficult to control the variation in wiring width during wiring processing in a subtractive method, while if the layer thickness exceeds this range, the wiring width becomes wider, which tends to easily cause impedance mismatching at the joint with other components.

[0020] (tensile modulus of elasticity of the entire insulating resin layer) In addition, in the flexible metal-clad laminate of the present invention, the insulating resin layer (X) as a whole exhibits a tensile modulus (TM1) of 1 GPa or more and 7 GPa or less, preferably 2 GPa or more and 6 GPa or less. If the tensile modulus (TM1) is below this range, the rigidity of the substrate itself is low when it is bent severely at 180 degrees to be mounted on an electronic device, and the angle of the bent tip becomes sharper, leading to a decrease in bending resistance. If the tensile modulus (TM1) is above this range, the bending rigidity of the substrate itself becomes high, which tends to easily develop problems such as springback when mounted on an electronic device. Therefore, if the tensile modulus (TM1) is within this range, even a substrate using a thick insulator is unlikely to cause problems when mounted on an electronic device. The tensile modulus can be measured by etching away the metal layer and measuring the remaining insulating resin layer (X) at a temperature of 23°C and a relative humidity of 50% using a commercially available tensile elasticity tester (for example, Strograph R-1 by Toyo Seiki Seisakusho Co., Ltd.).

[0021] (Tensile modulus of elasticity of insulating resin layer near metal layer) In the flexible metal-clad laminate of the present invention, attention is paid not only to the overall tensile modulus (TM1) of the insulating resin layer (X) but also to the tensile modulus (TM2) of the insulating resin layer (X) within a range of 5 μm in the thickness direction from the interface with the metal layer. This is because, when the substrate is severely bent at 180 degrees as described above, if the rigidity of the insulating resin layer near the metal wiring is low, the bent tip of the wiring will be at an acute angle, which will cause significant damage to the copper wiring. Therefore, in the flexible metal-clad laminate of the present invention, the tensile modulus (TM2) is 2 GPa or more and 10 GPa or less, preferably 4 GPa or more and 7 GPa or less. If the tensile modulus (TM2) is below this range, the rigidity near the interface with the copper foil cannot be expressed, and if it exceeds this range, the rigidity becomes too high and tends to damage the copper foil side. Therefore, if the tensile modulus (TM2) is within this range, the wiring shape at the bent tip will not be at an acute angle and good bending resistance can be maintained.

[0022] The tensile modulus of elasticity (TM2) must be greater than the tensile modulus of elasticity (TM1), and preferably greater than 1 and equal to or less than 3 times the tensile modulus of elasticity (TM1). This is because, if the tensile modulus of elasticity (TM2) is equal to or less than the tensile modulus of elasticity (TM1), there is a concern that the rigidity of the entire insulating resin layer will become too high.

[0023] (Equivalent bending stiffness) In the flexible metal-clad laminate of the present invention, the equivalent bending stiffness (RF) [N / mm 2 If the equivalent bending stiffness value is small, there is a concern that the flexible metal-clad laminate will not be able to maintain the minimum rigidity required as a copper wiring board, and if the value is large, there is a concern that the rigidity of the flexible metal-clad laminate will become too large, leading to problems such as springback due to the high repulsive force when mounted on electronic equipment. For this reason, the equivalent bending stiffness (RF) [N / mm 2 ] is preferably 0.1N / mm 2 More than 3.0N / mm 2 Less than or equal to 0.5N / mm 2 More than 2.0N / mm 2The equivalent bending rigidity can be calculated in accordance with the contents of paragraphs 0030 to 0038 and 0055 to 0058 of JP2016-146419A.

[0024] Thus, the flexible metal-clad laminate of the present invention has an equivalent bending stiffness within a preferred range, but the equivalent bending stiffness increases as the total thickness increases. Therefore, as a parameter that is least affected by the total thickness, the equivalent bending stiffness is divided by the cube of the total thickness (L) [mm] of the flexible metal-clad laminate (RF / L 3 ) is used to evaluate the value. 3 ) is in [N / mm 5 ]

[0025] In the flexible metal-clad laminate of the present invention, such "RF / L 3 The numerical range of " is preferably 400N / mm 5 More than 1200N / mm 5 Less than or equal to 400N / mm 5 More than 900N / mm 5 The following is the RF / L 3 If the numerical range of " is below this range, the minimum rigidity required for a copper wiring board cannot be maintained, and if it exceeds this range, the repulsive force tends to become high.

[0026] (When the insulating resin layer is made up of multiple polyimide layers) In the flexible metal-clad laminate of the present invention, the insulating resin layer (X) may be a single polyimide layer, but is preferably composed of a laminate of multiple polyimide layers as shown in Figures 1 and 2. This makes it easier to increase the thickness of the insulating resin layer (X), lowering the hurdle when applying the FPC to high frequency applications. In the case of a single-sided metal layer type as shown in Figure 1, the insulating resin layer (X) is preferably composed of two polyimide layers laminated together, and in the case of a double-sided metal layer type as shown in Figure 2, the insulating resin layer (X) is preferably composed of three polyimide layers laminated together.

[0027] When the insulating resin layer (X) of the flexible metal-clad laminate of the present invention is composed of a laminate of multiple polyimide layers, the thickness of the polyimide layer (A) of the central layer of the insulating resin layer (X) is preferably 0.5 to 0.96 times the total thickness of the insulating resin layer (X). If the ratio of the thickness of the polyimide layer (A) to the total thickness of the insulating resin layer (X) is below this range, the dielectric tangent of the insulating resin layer (X) tends to be insufficient and sufficient dielectric properties cannot be obtained, and if it exceeds this range, problems such as a decrease in the dimensional stability of the insulating resin layer (X) tend to occur. Here, the central layer of the insulating resin layer (X) refers to the polyimide layer laminated in the middle when an odd number of polyimide layers of 3 or more are laminated, and refers to the thicker polyimide layer of the two adjacent polyimide layers in the middle when an even number of polyimide layers of 4 or more are laminated. In addition, when two polyimide layers are laminated, it means the polyimide layer directly laminated on the polyimide layer in contact with the metal layer. Therefore, in FIG. 1, the polyimide layer (A) corresponds to the adhesive layer (BA), and in FIG. 2, the polyimide layer (A) corresponds to the adhesive layer (B).

[0028] The tensile modulus of the polyimide layer (A) contained in the insulating resin layer (X) of the flexible metal-clad laminate of the present invention is preferably in the range of 0.1 GPa to 5 GPa, more preferably 0.2 GPa to 3 GPa. If the tensile modulus of the polyimide layer (A) is in this range, it is possible to reduce the occurrence of wrinkles, prevent air bubbles from being trapped during lamination, and improve handling properties. In addition, it is preferable to specify the storage modulus of the polyimide layer (A) in addition to the tensile modulus from the viewpoint of stress relaxation during thermocompression bonding. Specifically, the storage modulus of the polyimide layer (A) at 50°C is preferably 1800 MPa or less, and the maximum value of the storage modulus at 180 to 260°C is preferably 800 MPa or less, more preferably 500 MPa or less. By controlling the storage modulus within such a range, warping is unlikely to occur even after passing through a solder reflow process after circuit processing. The storage modulus can be measured using a commercially available viscoelasticity measuring device.

[0029] <Flexible single-sided metal-clad laminate> The configurations of the flexible single-sided metal-clad laminate (CA) and the pair of single-sided metal-clad laminates (C1, C2) are not particularly limited, and may be general FPC materials, such as commercially available copper-clad laminates, etc. The first single-sided metal-clad laminate (C1) and the second single-sided metal-clad laminate (C2) may have the same configuration or different configurations.

[0030] (metal layer) The materials of the metal layer (MA), the first metal layer (M1) and the second metal layer (M2) are not particularly limited, but examples thereof include copper, stainless steel, iron, nickel, beryllium, aluminum, zinc, indium, silver, gold, tin, zirconium, tantalum, titanium, lead, magnesium, manganese and alloys thereof. Among these, copper or a copper alloy is particularly preferable. The materials of the wiring layer in the circuit board of this embodiment described later are the same as those of the metal layer (MA), the first metal layer (M1) and the second metal layer (M2).

[0031] The thickness of the metal layer (MA), the first metal layer (M1) and the second metal layer (M2) is not particularly limited, and is preferably 5 μm or more and 35 μm or less, more preferably 25 μm or less, from the viewpoint of production stability and handling. Particularly preferably 6 μm or more and 15 μm or less. When a metal foil such as a copper foil is used as the metal layer, the thickness is preferably 35 μm or less, more preferably within the range of 5 to 25 μm. From the viewpoint of production stability and handling, the lower limit of the thickness of the metal foil is preferably 5 μm. When a copper foil is used, it may be a rolled copper foil or an electrolytic copper foil. In addition, a commercially available copper foil can be used as the copper foil.

[0032] The metal foil may be subjected to a surface treatment using, for example, siding, aluminum alcoholate, aluminum chelate, a silane coupling agent, or the like, for the purpose of, for example, rust prevention or improving adhesive strength.

[0033] (insulating resin layer) In FIG. 1, the insulating resin layer (X) has a structure in which a bottom insulating resin layer (PA) and an adhesive layer (BA) are laminated, and in FIG. 2, it has a structure in which a first insulating resin layer (P1) and a second insulating resin layer (P2) sandwich an adhesive layer (B).

[0034] (Bottom insulating resin layer, first insulating resin layer, second insulating resin layer) The bottom insulating resin layer (PA), the first insulating resin layer (P1) and the second insulating resin layer (P2) are not particularly limited as long as they are made of a resin having electrical insulation properties, and examples thereof include polyimide, epoxy resin, phenolic resin, polyethylene, polypropylene, polytetrafluoroethylene, silicone, ETFE, etc., but are preferably made of polyimide. In addition, the bottom insulating resin layer (PA), the first insulating resin layer (P1) and the second insulating resin layer (P2) are not limited to a single layer, and may be a laminate of multiple resin layers. In addition, when polyimide is used in the present invention, it means a resin made of a polymer having an imide group in the molecular structure, such as polyamideimide, polyetherimide, polyesterimide, polysiloxaneimide, polybenzimidazoleimide, etc.

[0035] (adhesive layer) The adhesive layer (BA) and adhesive layer (B) constituting the insulating resin layer (X) correspond to the polyimide layer (A) when the insulating resin layer (X) is composed of a laminate of multiple polyimide layers, and contain a thermoplastic polyimide containing a tetracarboxylic acid residue derived from a tetracarboxylic dianhydride and a diamine residue derived from a diamine compound (hereinafter, sometimes referred to as an "adhesive polyimide").

[0036] In the present invention, the term "tetracarboxylic acid residue" refers to a tetravalent group derived from a tetracarboxylic dianhydride, and the term "diamine residue" refers to a divalent group derived from a diamine compound. In addition, the term "thermoplastic polyimide" generally refers to a polyimide whose glass transition temperature (Tg) can be clearly confirmed, but in the present invention, the term "thermoplastic polyimide" refers to a polyimide whose storage modulus at 30°C measured using a dynamic viscoelasticity measuring apparatus (DMA) is 1.0×10 8 Pa or more, and the storage modulus at 300°C is 3.0×10 7 The term "non-thermoplastic polyimide" generally refers to a polyimide that does not soften or exhibit adhesiveness even when heated. In the present invention, however, the term "non-thermoplastic polyimide" refers to a polyimide that does not soften or exhibit adhesiveness even when heated, but in the present invention, the term "non-thermoplastic polyimide" refers to a polyimide that has a viscosity of less than 3 Pa measured using a dynamic viscoelasticity measuring device (DMA). Storage modulus at 0°C is 1.0×10 9 Pa or more, and the storage modulus at 300°C is 3.0×10 8 This refers to polyimides with a modulus of tensile strength (MPa) or higher.

[0037] (Tetracarboxylic acid residue) The adhesive polyimide may contain, without particular limitation, tetracarboxylic acid residues derived from tetracarboxylic dianhydrides generally used in thermoplastic polyimides, but preferably contains a total of 90 molar parts or more of tetracarboxylic acid residues derived from tetracarboxylic dianhydrides represented by the following general formula (1) (hereinafter, sometimes referred to as "tetracarboxylic acid residues (1)") relative to 100 molar parts of the tetracarboxylic acid residues. By containing a total of 90 molar parts or more of tetracarboxylic acid residues (1) relative to 100 molar parts of the tetracarboxylic acid residues, it is easy to achieve both flexibility and heat resistance of the adhesive polyimide, which is preferable. If the total amount of tetracarboxylic acid residues (1) is less than 90 molar parts, the solvent solubility of the adhesive polyimide tends to decrease.

[0038] [ka]

[0039] In general formula (1), X represents a single bond or a divalent group selected from the following formulae:

[0040] [ka]

[0041] In the above formula, Z is -C 6 H 4 -, -(CH 2 ) n -or-CH 2 -CH(-OC(=O)-CH 3 )-CH 2 -, where n is an integer from 1 to 20.

[0042] Examples of tetracarboxylic acid dianhydrides for deriving the tetracarboxylic acid residue (1) include 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA), 4,4'-oxydiphthalic dianhydride (ODPA), 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propanoic dianhydride (BPADA), p-phenylenebis(trimellitic acid monoester dianhydride) (TAHQ), and ethylene glycol bisanhydrotrimellitate (TMEG).

[0043] The adhesive polyimide may contain a tetracarboxylic acid residue derived from an acid anhydride other than the tetracarboxylic acid dianhydride represented by the above general formula (1) within a range that does not impair the effects of the invention. Such tetracarboxylic acid residues are not particularly limited, but examples thereof include pyromellitic dianhydride, 1,4-phenylene bis(trimellitic acid monoester) dianhydride, 2,3',3,4'-biphenyl tetracarboxylic acid dianhydride, 2,2',3,3'- or 2,3,3',4'-benzophenone tetracarboxylic acid dianhydride, 2,3',3,4'-diphenyl ether tetracarboxylic acid dianhydride, bis(2,3-dicarboxyphenyl) ether dianhydride, 3,3'',4,4''-, 2,3,3'',4''- or 2,2'',3,3''-p-terphenyl tetracarboxylic acid dianhydride, 2,2-bis(2,3- or 3,4-dicarboxyphenyl)-propane dianhydride, bis(2,3- or 3.4-dicarboxyphenyl)methane dianhydride, bis(2,3- or 3,4-dicarboxyphenyl)sulfone dianhydride, 1,1-bis(2,3- or 3,4-dicarboxyphenyl)ethane dianhydride, 1,2,7,8-, 1,2,6,7- or 1,2,9,10-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 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 Examples of the tetracarboxylic acid residue include those derived from aromatic tetracarboxylic dianhydrides such as bisanhydrotrimellitate.

[0044] (Diamine residue) The adhesive polyimide contains 20 molar parts or more, preferably 40 molar parts or more, more preferably 60 molar parts or more of dimer acid type diamine residues derived from dimer acid type diamines per 100 molar parts of diamine residues. By containing the dimer acid type diamine residues in the above amounts, the dielectric properties of the adhesive layers (BA) and (B) are improved, and the glass transition temperatures (Tg) of the adhesive layers (BA) and (B) are lowered to improve the thermocompression bonding properties, and the internal stress can be alleviated by lowering the elastic modulus of the adhesive layers (BA) and (B). If the dimer acid type diamine residue is less than 20 molar parts per 100 molar parts of the diamine residue, the adhesive layers (BA) and (B) interposed between the bottom insulating resin layer (PA), the first insulating resin layer (P1) and the second insulating resin layer (P2) may not have sufficient adhesion, and the elastic modulus of the adhesive layers (BA) and (B), which have high thermal expansion properties, may increase, which may deteriorate the post-etching dimensional change rate of the metal layer (MA), the first metal layer (M1) and the second metal layer (M2).

[0045] Here, the dimer acid type diamine is a diamine in which the two terminal carboxylic acid groups (-COOH) of the dimer acid are replaced by primary aminomethyl groups (-CH 2 -NH 2 ) or amino group (-NH 2 ) is substituted. Dimer acid is a known dibasic acid obtained by intermolecular polymerization of unsaturated fatty acids, and its industrial production process is almost standardized in the industry, and is obtained by dimerizing unsaturated fatty acids having 11 to 22 carbon atoms using a clay catalyst or the like. Industrially obtained dimer acid is mainly composed of a dibasic acid having 36 carbon atoms obtained by dimerizing unsaturated fatty acids having 18 carbon atoms, such as oleic acid and linoleic acid, but contains any amount of monomer acid (having 18 carbon atoms), trimer acid (having 54 carbon atoms), and other polymerized fatty acids having 20 to 54 carbon atoms depending on the degree of purification. In the present invention, it is preferable to use dimer acid whose dimer acid content has been increased to 90% by weight or more by molecular distillation. In addition, although double bonds remain after the dimerization reaction, in the present invention, dimer acids whose degree of unsaturation has been reduced by further hydrogenation reaction are also included in the dimer acid.

[0046] As a feature of the dimer acid type diamine, the polyimide can be endowed with the characteristics derived from the dimer acid skeleton. That is, since the dimer acid type diamine is an aliphatic macromolecule with a molecular weight of about 560 to 620, the molar volume of the molecule can be increased and the polar group of the polyimide can be relatively reduced. It is considered that such a feature of the dimer acid type diamine contributes to improving the dielectric properties by reducing the dielectric constant and the dielectric loss tangent while suppressing the deterioration of the heat resistance of the polyimide. In addition, since it has two freely moving hydrophobic chains with 7 to 9 carbon atoms and two chain-like aliphatic amino groups with a length close to 18 carbon atoms, not only can it give flexibility to the polyimide, but it can also make the polyimide have an asymmetric chemical structure or a non-planar chemical structure, so it is considered that it is possible to reduce the dielectric constant and the dielectric loss tangent of the polyimide.

[0047] Dimer acid diamines are commercially available, such as PRIAMINE 1073 (trade name), PRIAMINE 1074 (trade name), and PRIAMINE 1075 (trade name) manufactured by Croda Japan, and VERSAMINE 551 (trade name) and VERSAMINE 552 (trade name) manufactured by BASF Japan.

[0048] In addition, the adhesive polyimide preferably contains a diamine residue derived from at least one diamine compound selected from the diamine compounds represented by the following general formulas (B1) to (B7) in a total amount of 20 to 80 mol parts, more preferably 20 to 60 mol parts, relative to 100 mol parts of the total diamine components. Since the diamine compounds represented by the general formulas (B1) to (B7) have a molecular structure with flexibility, the flexibility of the polyimide molecular chain can be improved and thermoplasticity can be imparted by using at least one diamine compound selected from these in an amount within the above range. If the total amount of the diamine compounds represented by the general formulas (B1) to (B7) exceeds 80 mol parts relative to 100 mol parts of the total diamine components, the flexibility of the polyimide becomes insufficient and Tg increases, so that the residual stress due to thermocompression bonding increases and the dimensional change rate after etching tends to deteriorate.

[0049] [ka]

[0050] In formulas (B1) to (B7), R 1 each independently represents a monovalent hydrocarbon group or alkoxy group having 1 to 6 carbon atoms; the linking group A is independently -O-, -S-, -CO-, -SO-, -SO 2 -, -COO-, -CH 2 -, -C(CH 3 ) 2 represents a divalent group selected from -, -NH-, or -CONH-, and n1 independently represents an integer of 0 to 4, with the proviso that formula (B3) excludes those which overlap with formula (B2), and formula (B5) excludes those which overlap with formula (B4).

[0051] In addition, "independently" means that in one or more of the above formulae (B1) to (B7), multiple linking groups A, multiple R1s, or multiple n1s may be the same or different. In addition, in the formulae (B1) to (B7), the hydrogen atoms in the two terminal amino groups may be substituted, for example, -NR 2 R 3 (where R 2 ,R 3 may be independently any substituent such as an alkyl group.

[0052] The diamine represented by formula (B1) (hereinafter sometimes referred to as "diamine (B1)") is an aromatic diamine having two benzene rings. This diamine (B1) has an amino group directly bonded to at least one benzene ring and a divalent linking group A at the meta position, which increases the degree of freedom of the polyimide molecular chain and provides high flexibility, which is thought to contribute to improving the flexibility of the polyimide molecular chain. Therefore, the use of diamine (B1) enhances the thermoplasticity of the polyimide. Here, examples of the linking group A include -O-, -CH 2 -, -C(CH 3 ) 2 -, -CO-, -SO 2-, -S- and -COO- are preferred.

[0053] Examples of the diamine (B1) include 3,3'-diaminodiphenylmethane, 3,3'-diaminodiphenylpropane, 3,3'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,3-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylpropane, 3,4'-diaminodiphenyl sulfide, 3,3'-diaminobenzophenone, and (3,3'-bisamino)diphenylamine.

[0054] The diamine represented by formula (B2) (hereinafter sometimes referred to as "diamine (B2)") is an aromatic diamine having three benzene rings. In this diamine (B2), the amino group directly bonded to at least one benzene ring and the divalent linking group A are at the meta position, so that the degree of freedom of the polyimide molecular chain is increased and the polyimide molecular chain has high flexibility, which is thought to contribute to improving the flexibility of the polyimide molecular chain. Therefore, by using diamine (B2), the thermoplasticity of the polyimide is increased. Here, the linking group A is preferably -O-.

[0055] Examples of the diamine (B2) include 1,4-bis(3-aminophenoxy)benzene, 3-[4-(4-aminophenoxy)phenoxy]benzeneamine, and 3-[3-(4-aminophenoxy)phenoxy]benzeneamine.

[0056] The diamine represented by formula (B3) (hereinafter, sometimes referred to as "diamine (B3)") is an aromatic diamine having three benzene rings. In this diamine (B3), two divalent linking groups A directly bonded to one benzene ring are in meta positions with respect to each other, so that the degree of freedom of the polyimide molecular chain is increased and the polyimide molecular chain has high flexibility, which is considered to contribute to improving the flexibility of the polyimide molecular chain. Therefore, by using diamine (B3), the thermoplasticity of the polyimide is increased. Here, as the linking group A, -O- is preferable.

[0057] Examples of 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, and 4,4'-[5-methyl-(1,3-phenylene)bisoxy]bisaniline.

[0058] The diamine represented by formula (B4) (hereinafter sometimes referred to as "diamine (B4)") is an aromatic diamine having four benzene rings. This diamine (B4) has high flexibility due to the fact that at least one amino group directly bonded to the benzene ring and the divalent linking group A are at the meta position, and is considered to contribute to improving the flexibility of the polyimide molecular chain. Therefore, the use of diamine (B4) enhances the thermoplasticity of the polyimide. Here, examples of the linking group A include -O-, -CH 2 -, -C(CH 3 ) 2 -, -SO 2 -, -CO- and -CONH- are preferred.

[0059] Examples of the 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, and bis[4,4'-(3-aminophenoxy)]benzanilide.

[0060] The diamine represented by formula (B5) (hereinafter, sometimes referred to as "diamine (B5)") is an aromatic diamine having four benzene rings. This diamine (B5) is a polyamine having two divalent linking groups A directly bonded to at least one benzene ring at meta positions relative to each other. The degree of freedom of the imide molecular chain is increased, and it has high flexibility, which is thought to contribute to improving the flexibility of the polyimide molecular chain. Therefore, by using the diamine (B5), the thermoplasticity of the polyimide is increased. Here, the linking group A is preferably -O-.

[0061] Examples of the diamine (B5) include 4-[3-[4-(4-aminophenoxy)phenoxy]phenoxy]aniline, 4,4'-[oxybis(3,1-phenyleneoxy)]bisaniline, and the like.

[0062] The diamine represented by formula (B6) (hereinafter sometimes referred to as "diamine (B6)") is an aromatic diamine having four benzene rings. This diamine (B6) has high flexibility due to having at least two ether bonds, and is considered to contribute to improving the flexibility of the polyimide molecular chain. Therefore, the use of diamine (B6) enhances the thermoplasticity of the polyimide. Here, the linking group A is -C(CH 3 ) 2 -, -O-, -SO 2 - and -CO- are preferred.

[0063] Examples of diamines (B6) include 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), bis[4-(4-aminophenoxy)phenyl]ether (BAPE), bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS), and bis[4-(4-aminophenoxy)phenyl]ketone (BAPK).

[0064] 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, which is believed to contribute to improving the flexibility of the polyimide molecular chain. Therefore, the use of diamine (B7) enhances the thermoplasticity of the polyimide. Here, the linking group A is preferably -O-.

[0065] Examples of the diamine (B7) include bis[4-(3-aminophenoxy)]biphenyl, bis[4-(4-aminophenoxy)]biphenyl, and the like.

[0066] The adhesive polyimide may contain a diamine residue derived from a diamine compound other than the above dimer acid type diamine and diamines (B1) to (B7) within the scope of the invention. As the diamine residue derived from a diamine compound other than the above dimer acid type diamine and diamines (B1) to (B7), any diamine compound generally used in thermoplastic polyimides may be used without limitation.

[0067] In the adhesive polyimide, 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, and when two or more types of tetracarboxylic acid residues or diamine residues are used, respectively. When the adhesive polyimide has a plurality of polyimide structural units, they may be present as blocks or randomly, but are preferably present randomly.

[0068] The imide group concentration of the adhesive polyimide is preferably 20% by weight or less. Here, the "imide group concentration" refers to the ratio of the imide group (-(CO) 2 It means the value obtained by dividing the molecular weight of the imide group (-N-) by the molecular weight of the entire polyimide structure. When the imide group concentration exceeds 20% by weight, the molecular weight of the resin itself becomes small, and the low moisture absorption property deteriorates due to the increase in polar groups, and Tg and elastic modulus increase.

[0069] The weight-average molecular weight of the adhesive polyimide is, for example, preferably in the range of 10,000 to 400,000, more preferably in the range of 20,000 to 350,000. If the weight-average molecular weight is less than 10,000, the strength of the adhesive layers (BA) and (B) tends to decrease and become brittle. On the other hand, if the weight-average molecular weight exceeds 400,000, the viscosity increases excessively, and defects such as uneven thickness and streaks tend to occur in the adhesive layers (BA) and (B) during coating.

[0070] The adhesive polyimide is most preferably a completely imidized structure. However, a part of the polyimide may be an amic acid. The imidization rate can be determined by measuring the infrared absorption spectrum of the polyimide thin film by a single reflection ATR method using a Fourier transform infrared spectrophotometer (commercially available: FT / IR620 manufactured by JASCO Corporation) at 1015 cm -1 Based on the benzene ring absorber near 1780cm -1 It can be calculated from the absorbance of the C=O stretching originating from a nearby imide group.

[0071] (Crosslink formation) When the adhesive polyimide has a ketone group, the ketone group can be reacted with the amino group of an amino compound having at least two primary amino groups as functional groups to form a C=N bond, thereby forming a crosslinked structure. The heat resistance of the adhesive polyimide can be improved by forming a crosslinked structure. A preferred tetracarboxylic dianhydride for forming an adhesive polyimide having a ketone group is, for example, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), and a preferred diamine compound is, for example, an aromatic diamine such as 4,4'-bis(3-aminophenoxy)benzophenone (BABP) or 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene (BABB).

[0072] Examples of amino compounds that can be used to crosslink adhesive polyimides include dihydrazide compounds, aromatic diamines, and aliphatic amines. Among these, dihydrazide compounds are preferred. Aliphatic amines other than dihydrazide compounds are easy to form crosslinked structures even at room temperature, but there are concerns about the storage stability of the varnish, while aromatic diamines require high temperatures to form crosslinked structures. When a dihydrazide compound is used, it is possible to achieve both the storage stability of the varnish and a shortened curing time. Examples of dihydrazide compounds include oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, pimelic acid dihydrazide, suberic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, dodecanedioic acid dihydrazide, maleic acid dihydrazide, fumaric acid dihydrazide, diglyceryl ester dihydrazide, ... Preferred are dihydrazide compounds such as cholic acid dihydrazide, tartaric acid dihydrazide, malic acid dihydrazide, phthalic acid dihydrazide, isophthalic acid dihydrazide, terephthalic acid dihydrazide, 2,6-naphthoedioic acid dihydrazide, 4,4-bisbenzene dihydrazide, 1,4-naphthoic acid dihydrazide, 2,6-pyridine diacid dihydrazide, itaconic acid dihydrazide, etc. The above dihydrazide compounds may be used alone or in combination of two or more.

[0073] The adhesive polyimide can be produced by reacting the above-mentioned tetracarboxylic dianhydride with a diamine compound in a solvent, generating a polyamic acid, and then heating to close the ring. For example, the tetracarboxylic dianhydride and the diamine compound are dissolved in an organic solvent in approximately equal moles, and the mixture is stirred at a temperature in the range of 0 to 100°C for 30 minutes to 24 hours to cause a polymerization reaction, thereby obtaining a polyamic acid, which is a precursor of the polyimide. In the reaction, the reaction components are dissolved in the organic solvent so that the generated precursor is in the range of 5 to 50% by weight, preferably in the range of 10 to 40% by weight. Examples of organic solvents used in the polymerization reaction include N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2-butanone, dimethylsulfoxide (DMSO), hexamethylphosphoramide, N-methylcaprolactam, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diglyme, triglyme, and cresol. Two or more of these solvents can be used in combination, and aromatic hydrocarbons such as xylene and toluene can also be used in combination. The amount of such organic solvents is not particularly limited, but it is preferable to adjust the amount of the organic solvent to be used so that the concentration of the polyamic acid solution obtained by the polymerization reaction is about 5 to 50% by weight.

[0074] The synthesized polyamic acid is usually advantageously used as a reaction solvent solution, but can be concentrated, diluted, or replaced with another organic solvent if necessary. Polyamic acid is generally advantageously used because it 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, for example, defects such as uneven thickness and streaks are likely to occur in the film during coating work using a coater or the like.

[0075] The method for imidizing the polyamic acid to form the adhesive polyimide is not particularly limited, and for example, a heat treatment in which the polyamic acid is heated in the above-mentioned solvent at a temperature in the range of 80 to 400° C. for 1 to 24 hours is preferably used.

[0076] When the adhesive polyimide obtained as described above is crosslinked, the above amino compound is added to a resin solution containing an adhesive polyimide having a ketone group, and the ketone group in the adhesive polyimide and the primary amino group of the amino compound are condensed. This condensation reaction causes the resin solution to harden and become a hardened product. In this case, the amount of the amino compound added is such that the total amount of the primary amino group is 0.004 mol to 1.5 mol, preferably 0.005 mol to 1.2 mol, more preferably 0.03 mol to 0.9 mol, and most preferably 0.04 mol to 0.5 mol per mol of the ketone group. When the amount of amino compound added is such that the total number of primary amino groups per mole of ketone groups is less than 0.004 moles, the crosslinking of the adhesive polyimide by the amino compound is insufficient, and the heat resistance of the adhesive layers (BA) and (B) after curing tends to be difficult to exhibit. When the amount of amino compound added exceeds 1.5 moles, the unreacted amino compound acts as a thermoplasticizer, tending to reduce the heat resistance of the adhesive layers (BA) and (B).

[0077] The conditions of the condensation reaction for forming crosslinks are not particularly limited as long as the ketone group in the adhesive polyimide reacts with the primary amino group of the amino compound to form an imine bond (C=N bond). The temperature of the heat condensation is preferably within the range of, for example, 120 to 220°C, more preferably within the range of 140 to 200°C, for the purpose of releasing water produced by condensation out of the system, or for the purpose of simplifying the condensation step when the heat condensation reaction is carried out subsequently to the synthesis of the adhesive polyimide. The reaction time is preferably about 30 minutes to 24 hours, and the end point of the reaction is determined by measuring the infrared absorption spectrum using, for example, a Fourier transform infrared spectrophotometer (commercially available: FT / IR620 manufactured by JASCO Corporation) at 1670 cm. -1 The decrease or disappearance of the absorption peak due to the ketone group in the polyimide resin near 1635 cm -1 This can be confirmed by the appearance of an absorption peak derived from a nearby imine group.

[0078] The thermal condensation of the ketone group of the adhesive polyimide and the primary amino group of the amino compound can be carried out, for example, by (a) adding an amino compound and heating following the synthesis (imidization) of the adhesive polyimide, (b) charging an excess amount of an amino compound as a diamine component in advance, and heating the adhesive polyimide together with the remaining amino compound not involved in imidization or amidation following the synthesis (imidization) of the adhesive polyimide, or (c) processing the adhesive polyimide composition to which the amino compound has been added into a predetermined shape (for example, after applying it to any substrate or forming it into a film) and then heating it, or the like.

[0079] In the above description, the formation of imine bonds is used to form a crosslinked structure in order to impart heat resistance to the adhesive polyimide. However, the present invention is not limited to this method. For example, the adhesive polyimide can be cured by blending an epoxy resin, an epoxy resin curing agent, or the like.

[0080] By using the adhesive polyimide obtained as described above, the adhesive layers (BA) and (B), i.e., the polyimide layer (A), have excellent flexibility and dielectric properties (low dielectric constant and low dielectric tangent). As described later, the adhesive polyimide has a sufficiently low storage modulus in the temperature range of about 100° C., so that the bonding temperature can be significantly lowered compared to other adhesive resins such as fluorine-based resins.

[0081] <Thermal expansion coefficient of insulating resin layer> The bottom insulating resin layer (PA), the first insulating resin layer (P1) and the second insulating resin layer (P2) constituting the insulating resin layer (X) of the flexible metal-clad laminate of the present invention have a coefficient of thermal expansion (CTE) of 10 ppm / K or more, preferably in the range of 10 ppm / K to 30 ppm / K, more preferably in the range of 15 ppm / K to 25 ppm / K. If the CTE is less than 10 ppm / K or more than 30 ppm / K, warping occurs or dimensional stability decreases. A polyimide layer having a desired CTE can be obtained by appropriately changing the combination of raw materials used, the thickness, and the drying and curing conditions.

[0082] In addition, since the adhesive polyimide constituting the adhesive layers (BA) and (B) has high thermal expansion but low elasticity, it is possible to alleviate the internal stress generated during lamination even if the CTE exceeds 30 ppm / K.

[0083] In the flexible single-sided metal-clad laminate (CA) of Fig. 1, the overall coefficient of thermal expansion (CTE) of the insulating resin layer (X) consisting of the bottom insulating resin layer (PA) and the adhesive layer (BA) is preferably in the range of 10 ppm / K to 30 ppm / K, more preferably in the range of 15 ppm / K to 25 ppm / K. If the CTE is less than 10 ppm / K or more than 30 ppm / K, warping occurs or dimensional stability decreases.

[0084] In the flexible double-sided metal-clad laminate (C) of Fig. 2, the coefficient of thermal expansion (CTE) of the first insulating resin layer (P1), the adhesive layer (B) and the second insulating resin layer (P2) as a whole is preferably in the range of 10 ppm / K to 30 ppm / K, more preferably in the range of 15 ppm / K to 25 ppm / K. If the CTE is less than 10 ppm / K or more than 30 ppm / K, warping occurs or dimensional stability decreases.

[0085] <Glass transition temperature (Tg) of adhesive polyimide constituting adhesive layers (BA) and (B)> The adhesive polyimide preferably has a glass transition temperature (Tg) of 250°C or less, more preferably in the range of 40°C to 200°C. By making the Tg of the adhesive polyimide 250°C or less, thermocompression bonding at a low temperature is possible, which alleviates the internal stress generated during lamination and suppresses dimensional changes after circuit processing. If the Tg of the adhesive polyimide exceeds 250°C, the temperature when laminating the bottom insulating resin layer (PA) or when bonding between the first insulating resin layer (P1) and the second insulating resin layer (P2) becomes high, which may impair dimensional stability after circuit processing.

[0086] <Storage modulus of adhesive polyimide constituting adhesive layers (BA) and (B)> The adhesive polyimide is characterized by the presence of a temperature range in the range of 40 to 250°C where the storage modulus decreases sharply with increasing temperature. It is believed that such a characteristic of the adhesive polyimide is the factor that relieves the internal stress during thermocompression bonding and maintains dimensional stability after circuit processing. The adhesive polyimide has a storage modulus of 5×10 at the upper limit temperature of the above temperature range. 7 [Pa] or less is preferable, and 1×10 5 ~5×10 7 It is more preferable that the storage modulus is within the range of [Pa]. By setting the storage modulus in this range, even if the temperature is the upper limit of the above-mentioned range, thermocompression bonding is possible at 250°C or less, and the adhesion is ensured and dimensional change after circuit processing can be suppressed.

[0087] <Dielectric tangent of insulating resin layer (X)> In order to suppress deterioration of dielectric loss when the bottom insulating resin layer (PA), the first insulating resin layer (P1) and the second insulating resin layer (P2) are applied to, for example, a circuit board, the dielectric loss tangent (Tan δ) at 10 GHz is preferably 0.02 or less, more preferably in the range of 0.0005 to 0.01, and even more preferably in the range of 0.001 to 0.008. If the dielectric loss tangent at 10 GHz of the bottom insulating resin layer (PA), the first insulating resin layer (P1) and the second insulating resin layer (P2) exceeds 0.02, inconvenience such as loss of electric signals on the transmission path of high frequency signals is likely to occur when applied to a circuit board. On the other hand, the lower limit value of the dielectric loss tangent at 10 GHz of the bottom insulating resin layer (PA), the first insulating resin layer (P1) and the second insulating resin layer (P2) is not particularly limited, but the physical property control as an insulating resin layer of a circuit board is taken into consideration.

[0088] When the adhesive layers (BA) and (B) are applied to, for example, a circuit board, in order to suppress deterioration of dielectric loss, the dielectric loss tangent (Tan δ) at 10 GHz is preferably 0.004 or less, more preferably in the range of 0.0005 to 0.004, and even more preferably in the range of 0.001 to 0.0035. If the dielectric loss tangent at 10 GHz of the adhesive layers (BA) and (B) exceeds 0.004, when the adhesive layers are applied to a circuit board, problems such as loss of electrical signals on the transmission path of high-frequency signals are likely to occur. On the other hand, the lower limit of the dielectric loss tangent at 10 GHz of the adhesive layers (BA) and (B) is not particularly limited.

[0089] <Dielectric constant of insulating resin layer (X)> When the bottom insulating resin layer (PA), the first insulating resin layer (P1) and the second insulating resin layer (P2) are applied as insulating layers of a circuit board, for example, the insulating layers as a whole preferably have a relative dielectric constant of 4.0 or less at 10 GHz. If the relative dielectric constants of the bottom insulating resin layer (PA), the first insulating resin layer (P1) and the second insulating resin layer (P2) exceed 4.0 at 10 GHz, when applied to a circuit board, this leads to deterioration of the dielectric loss of the bottom insulating resin layer (PA), the first insulating resin layer (P1) and the second insulating resin layer (P2), and is likely to cause inconveniences such as loss of electrical signals on the transmission path of high-frequency signals.

[0090] In order to ensure impedance matching, the adhesive layers (BA) and (B) preferably have a dielectric constant of 4.0 or less at 10 GHz when applied to a circuit board, for example. If the dielectric constant of the adhesive layers (BA) and (B) exceeds 4.0 at 10 GHz, the adhesive layers (BA) and (B) may have a deteriorated dielectric loss when applied to a circuit board, which may easily cause inconveniences such as loss of electrical signals on the transmission path of high-frequency signals.

[0091] [Manufacturing flexible metal-clad laminates] The flexible metal-clad laminate of the present invention can be manufactured according to a conventional method. For example, an adhesive layer is prepared on a release film as a resin sheet. Separately, a single-sided metal-clad laminate consisting of a metal layer / polyimide layer is prepared by applying and drying a single or multiple polyamide solutions on a metal layer. Then, a resin sheet is attached to the polyimide layer of the single-sided metal-clad laminate, and the release film is removed to obtain the flexible single-sided metal-clad laminate of FIG. 1. Alternatively, the polyimide layers of a pair of single-sided metal-clad laminates are placed opposite each other, a resin sheet from which the release film has been removed is sandwiched between them, and the whole is bonded to obtain the flexible double-sided metal-clad laminate of FIG. 2. The flexible metal-clad laminate of the present invention can also be manufactured by methods other than those described above.

[0092] [Flexible circuit board] The flexible metal-clad laminate of this embodiment as shown in Figures 1 and 2 obtained as described above can be used to manufacture circuit boards such as single-sided FPCs or double-sided FPCs by wiring and circuit processing the metal layer (MA) or the first metal layer (M1) and / or the second metal layer (M2).

[0093] [Preferable configuration example 1 of flexible metal-clad laminate] Next, the flexible single-sided metal-clad laminate (CA) of FIG. 1 will be described in more detail with reference to FIG. 3, taking as an example a case in which the bottom insulating resin layer (PA) and the adhesive layer (BA) are both polyimide.

[0094] Fig. 3 is a schematic cross-sectional view showing the structure of a flexible single-sided metal-clad laminate 100A according to the present embodiment. As shown in Fig. 3, the flexible single-sided metal-clad laminate 100A includes a metal layer 101A as a metal layer (MA), a bottom polyimide layer 110A as a bottom insulating resin layer (PA), and an adhesive polyimide layer 120A as an adhesive layer (BA). Here, the bottom polyimide layer 110A and the adhesive polyimide layer 120A correspond to an insulating resin layer (X).

[0095] The bottom polyimide layer 110A may have a structure in which a plurality of polyimide layers are laminated. For example, in the embodiment shown in Fig. 3, the bottom polyimide layer 110A has a three-layer structure including a non-thermoplastic polyimide layer 111A made of a non-thermoplastic polyimide and a thermoplastic polyimide layer 112A made of a thermoplastic polyimide provided on both sides of the non-thermoplastic polyimide layer 111A as a base layer. However, the bottom polyimide layer 110A is not limited to a three-layer structure.

[0096] In the flexible single-sided metal-clad laminate 100A shown in Fig. 3, the adhesive polyimide layer 120A is an adhesive layer for bonding the flexible single-sided metal-clad laminate 100A to another member, and has the function of improving the dielectric properties of the flexible single-sided metal-clad laminate 100A while ensuring dimensional stability. The adhesive polyimide constituting the adhesive polyimide layer 120A is as described above for the adhesive layer (BA).

[0097] Next, the non-thermoplastic polyimide layer 111A and the thermoplastic polyimide layer 112A constituting the bottom polyimide layer 110A will be briefly described.

[0098] Non-thermoplastic polyimide layer: The polyimide used in the non-thermoplastic polyimide layer 111A is preferably a non-thermoplastic polyimide obtained by reacting an acid dianhydride component containing an aromatic tetracarboxylic dianhydride component with a diamine component containing an aliphatic diamine and / or an aromatic diamine. Since monomers generally used in the synthesis of non-thermoplastic polyimides can be used as the acid dianhydride and diamine, their description is omitted here. By selecting the types of acid anhydride and diamine, or the respective molar ratios when two or more types of acid anhydride or diamine are used, the thermal expansion, adhesiveness, glass transition temperature, etc. can be controlled.

[0099] The polyimide constituting the non-thermoplastic polyimide layer 111A preferably has an imide group concentration of 33% or less, more preferably 32% or less. If the imide group concentration exceeds 33%, the flame retardancy of the polyimide decreases, and the dielectric properties also deteriorate due to an increase in polar groups.

[0100] The thickness of the non-thermoplastic polyimide layer 111A is preferably in the range of 6 μm to 100 μm, more preferably in the range of 9 μm to 50 μm, from the viewpoint of ensuring the function as a base layer and transportability during production and thermoplastic polyimide coating. If the thickness of the non-thermoplastic polyimide layer 111A is less than the lower limit, the electrical insulation and handling properties become insufficient, and if it exceeds the upper limit, the productivity decreases.

[0101] From the viewpoint of heat resistance, the non-thermoplastic polyimide layer 111A preferably has a glass transition temperature (Tg) of 280° C. or higher, and more preferably 300° C. or higher.

[0102] In addition, from the viewpoint of suppressing warping, the thermal expansion coefficient of the non-thermoplastic polyimide layer 111A is in the range of 1 ppm / K or more and 30 ppm / K or less, preferably in the range of 1 ppm / K or more and 25 ppm / K or less, and more preferably in the range of 15 ppm / K or more and 25 ppm / K or less.

[0103] In addition, the non-thermoplastic polyimide used in the non-thermoplastic polyimide layer 111A may contain optional components such as plasticizers, other curable resin components such as epoxy resins, curing agents, curing accelerators, coupling agents, fillers, solvents, flame retardants, etc. However, some plasticizers contain many polar groups, which may promote the diffusion of copper from the copper wiring, so it is preferable to avoid using plasticizers as much as possible.

[0104] Thermoplastic polyimide layer: The polyimide used in the thermoplastic polyimide layer 112A is preferably a thermoplastic polyimide obtained by reacting an acid anhydride component containing an aromatic tetracarboxylic dianhydride component with a diamine component containing an aliphatic diamine component and / or an aromatic diamine component. As the acid anhydride and diamine, monomers generally used in the synthesis of thermoplastic polyimides can be used, so their description is omitted here. By selecting the types of acid anhydride and diamine, or the respective molar ratios when two or more types of acid anhydride or diamine are used, it is possible to control the thermal expansion, adhesiveness, glass transition temperature, and the like. In addition, from the viewpoint of improving the dielectric properties, it is preferable to use an adhesive polyimide for forming the adhesive polyimide layer 120A as the adhesive layer (BA) as the polyimide used in the thermoplastic polyimide layer 112A.

[0105] The polyimide constituting the thermoplastic polyimide layer 112A preferably has an imide group concentration of 33% or less, more preferably 32% or less. If the imide group concentration exceeds 33%, the flame retardancy of the polyimide decreases, and the dielectric properties also deteriorate due to an increase in polar groups.

[0106] From the viewpoint of ensuring adhesive function, the thickness of the thermoplastic polyimide layer 112A is preferably in the range of 1 μm to 10 μm, more preferably in the range of 1 μm to 5 μm. If the thickness of the thermoplastic polyimide layer 112A is less than the lower limit, the adhesiveness becomes insufficient, and if it exceeds the upper limit, the dimensional stability tends to deteriorate.

[0107] In order to suppress warping, the thermoplastic polyimide layer 112A has a thermal expansion coefficient of 30 ppm / K or more, preferably in the range of 30 ppm / K to 100 ppm / K, and more preferably in the range of 30 ppm / K to 80 ppm / K.

[0108] In addition to polyimide, the resin used for the thermoplastic polyimide layer 112A may contain optional components such as plasticizers, other hardening resin components such as epoxy resins, hardeners, hardening accelerators, inorganic fillers, coupling agents, bulking agents, solvents, flame retardants, etc. However, some plasticizers contain many polar groups, which may promote the diffusion of copper from the copper wiring, so it is preferable to avoid using plasticizers as much as possible.

[0109] In order to ensure dimensional stability after circuit processing in the flexible single-sided metal-clad laminate 100A, the overall thermal expansion coefficient of the bottom polyimide layer 110A and the adhesive polyimide layer 120A should be 10 ppm / K or more, preferably in the range of 10 ppm / K or more and 30 ppm / K or less, and more preferably in the range of 15 ppm / K or more and 25 ppm / K or less.

[0110] In the flexible single-sided metal-clad laminate 100A, the ratio of the thickness of the adhesive polyimide layer 120A to the total thickness of the bottom polyimide layer 110A and the adhesive polyimide layer 120A is as described with reference to FIG.

[0111] [Circuit board] The flexible single-sided metal-clad laminate 100A of the present embodiment is useful mainly as a circuit board material for FPCs, rigid-flex circuit boards, etc. That is, by processing the metal layer 101A of the flexible metal-clad laminate 100A of the present embodiment into a pattern by a conventional method to form a wiring layer, a circuit board such as an FPC, which is one embodiment of the present invention, can be manufactured.

[0112] [Preferable configuration example 2 of flexible metal-clad laminate] Next, the flexible double-sided metal-clad laminate (C) of Figure 2 will be described in more detail with reference to Figure 4, taking as an example a case in which the first insulating resin layer (P1), the second insulating resin layer (P2), and the adhesive layer (B) are all polyimide.

[0113] FIG. 4 is a schematic cross-sectional view showing the structure of the flexible double-sided metal-clad laminate 100 of the present embodiment. As shown in FIG. 4, the metal-clad laminate 100 includes metal layers 101, 101 as the first metal layer (M1) and the second metal layer (M2), polyimide layers 110, 110 as the first insulating resin layer (P1) and the second insulating resin layer (P2), and an adhesive polyimide layer 120 as the adhesive layer (B). Here, the metal layer 101 and the polyimide layer 110 form a single-sided metal-clad laminate 130 as the first single-sided metal-clad laminate (C1) or the second single-sided metal-clad laminate (C2). In this embodiment, the first single-sided metal-clad laminate (C1), the second single-sided metal-clad laminate (C2), and the single-sided metal-clad laminate 130 have the same configuration. Here, the polyimide layers 110, 110 and the adhesive polyimide layer 120 correspond to the insulating resin layer (X).

[0114] Each of the polyimide layers 110, 110 may have a structure in which a plurality of polyimide layers are laminated. For example, in the embodiment shown in Fig. 4, a three-layer structure is formed with non-thermoplastic polyimide layers 111, 111 made of non-thermoplastic polyimide as a base layer, and thermoplastic polyimide layers 112, 112 made of thermoplastic polyimide provided on both sides of the non-thermoplastic polyimide layers. However, each of the polyimide layers 110, 110 is not limited to a three-layer structure.

[0115] In the flexible double-sided metal-clad laminate 100 shown in Fig. 4, the inner thermoplastic polyimide layers 112, 112 of the two single-sided metal-clad laminates 130, 130 are each bonded to an adhesive polyimide layer 120 to form the flexible metal-clad laminate 100. The adhesive polyimide layer 120 is an adhesive layer for bonding the two single-sided metal-clad laminates 130, 130 in the metal-clad laminate 100, and has the function of improving the dielectric properties of the flexible metal-clad laminate 100 while ensuring dimensional stability. The adhesive polyimide constituting the adhesive polyimide layer 120 is as described above for the adhesive layer (B).

[0116] Next, the non-thermoplastic polyimide layer 111 and the thermoplastic polyimide layer 112 constituting the polyimide layers 110, 110 will be briefly described.

[0117] Non-thermoplastic polyimide layer: The polyimide used in the non-thermoplastic polyimide layer 111 is preferably a non-thermoplastic polyimide obtained by reacting an acid dianhydride component containing an aromatic tetracarboxylic dianhydride component with a diamine component containing an aliphatic diamine and / or an aromatic diamine. Since monomers generally used in the synthesis of non-thermoplastic polyimides can be used as the acid dianhydride and diamine, their description is omitted here. By selecting the types of acid anhydride and diamine, or the respective molar ratios when two or more types of acid dianhydrides or diamines are used, the thermal expansion, adhesiveness, glass transition temperature, and the like can be controlled.

[0118] The polyimide constituting the non-thermoplastic polyimide layer 111 preferably has an imide group concentration of 33% or less, more preferably 32% or less. If the imide group concentration exceeds 33%, the flame retardancy of the polyimide decreases, and the dielectric properties also deteriorate due to an increase in polar groups.

[0119] The thickness of the non-thermoplastic polyimide layer 111 is preferably in the range of 6 μm to 100 μm, more preferably in the range of 9 μm to 50 μm, from the viewpoint of ensuring the function as a base layer and transportability during production and thermoplastic polyimide coating. If the thickness of the non-thermoplastic polyimide layer 111 is less than the lower limit, electrical insulation and handling properties become insufficient, and if it exceeds the upper limit, productivity decreases.

[0120] From the viewpoint of heat resistance, the non-thermoplastic polyimide layer 111 preferably has a glass transition temperature (Tg) of 280° C. or higher, and more preferably 300° C. or higher.

[0121] In addition, from the viewpoint of suppressing warping, the thermal expansion coefficient of the non-thermoplastic polyimide layer 111 is in the range of 1 ppm / K or more and 30 ppm / K or less, preferably in the range of 1 ppm / K or more and 25 ppm / K or less, and more preferably in the range of 15 ppm / K or more and 25 ppm / K or less.

[0122] In addition, the non-thermoplastic polyimide used in the non-thermoplastic polyimide layer 111 may contain optional components such as plasticizers, other curable resin components such as epoxy resins, curing agents, curing accelerators, coupling agents, fillers, solvents, flame retardants, etc. However, some plasticizers contain many polar groups, which may promote the diffusion of copper from the copper wiring, so it is preferable to avoid using plasticizers as much as possible.

[0123] Thermoplastic polyimide layer: The polyimide used in the thermoplastic polyimide layer 112 is preferably a thermoplastic polyimide obtained by reacting an acid dianhydride component containing an aromatic tetracarboxylic dianhydride component with a diamine component containing an aliphatic diamine component and / or an aromatic diamine component. Since monomers generally used in the synthesis of thermoplastic polyimides can be used as the acid anhydride and diamine, their description will be omitted here. By selecting the types of acid anhydride and diamine, or the respective molar ratios when two or more types of acid anhydride or diamine are used, it is possible to control the thermal expansion, adhesiveness, glass transition temperature, and the like. In addition, from the viewpoint of improving the dielectric properties, it is preferable to use an adhesive polyimide for forming the adhesive polyimide layer 120 as the adhesive layer (B) as the polyimide used in the thermoplastic polyimide layer 112.

[0124] The polyimide constituting the thermoplastic polyimide layer 112 preferably has an imide group concentration of 33% or less, more preferably 32% or less. If the imide group concentration exceeds 33%, the flame retardancy of the polyimide decreases, and the dielectric properties also deteriorate due to an increase in polar groups.

[0125] From the viewpoint of ensuring adhesive function, the thickness of the thermoplastic polyimide layer 112 is preferably in the range of 1 μm to 10 μm, more preferably in the range of 1 μm to 5 μm. If the thickness of the thermoplastic polyimide layer 112 is less than the lower limit, the adhesiveness becomes insufficient, and if it exceeds the upper limit, the dimensional stability tends to deteriorate.

[0126] In order to suppress warping, the thermoplastic polyimide layer 112 has a thermal expansion coefficient of 30 ppm / K or more, preferably in the range of 30 ppm / K to 100 ppm / K, and more preferably in the range of 30 ppm / K to 80 ppm / K.

[0127] In addition to polyimide, the resin used for the thermoplastic polyimide layer 112 may contain optional components such as plasticizers, other hardening resin components such as epoxy resins, hardeners, hardening accelerators, inorganic fillers, coupling agents, bulking agents, solvents, flame retardants, etc. However, some plasticizers contain many polar groups, which may promote the diffusion of copper from the copper wiring, so it is preferable to avoid using plasticizers as much as possible.

[0128] In order to ensure dimensional stability after circuit processing in the flexible metal-clad laminate 100, the overall thermal expansion coefficient of the two polyimide layers 110 and the adhesive polyimide layer 120 should be 10 ppm / K or more, preferably in the range of 10 ppm / K or more and 30 ppm / K or less, and more preferably in the range of 15 ppm / K or more and 25 ppm / K or less.

[0129] In the flexible metal-clad laminate 100, the thickness ratio of the adhesive polyimide layer 120 to the total thickness of the two polyimide layers 110 and the adhesive polyimide layer 120 is as described with reference to FIG.

[0130] [Circuit board] The flexible metal-clad laminate 100 of the present embodiment is useful mainly as a circuit board material for FPCs, rigid-flex circuit boards, etc. That is, one or both of the two metal layers 101 of the flexible metal-clad laminate 100 of the present embodiment are processed into a pattern by a conventional method to form a wiring layer, thereby making it possible to manufacture a circuit board such as an FPC, which is one embodiment of the present invention. EXAMPLES

[0131] The features of the present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to the examples. In the following examples, various measurements and evaluations are as follows, unless otherwise specified.

[0132] [Measurement of tensile modulus] The tensile modulus was measured at a temperature of 23° C. and a relative humidity of 50% using a Strograph R-1 manufactured by Toyo Seiki Seisakusho Co., Ltd. The measurement sample had dimensions of MD; 250 mm × TD; 12.7 mm, and was measured under the following conditions: load cell; 500 N, tensile speed; 50 mm / min, and chuck distance; 50 mm.

[0133] [Measurement of average tensile modulus] The average tensile modulus is the tensile modulus of the insulating resin layer within a range of 5 μm in the thickness direction from the interface with the metal layer, and is calculated by the following formula (1).

[0134]

number

[0135] In formula (1), M i is the tensile modulus (unit: GPa) of the i-th polyimide layer from the metal layer interface, and T i is the thickness (unit: μm) of the i-th polyimide layer, and n is an integer of 1 or more.

[0136] [Measurement of storage modulus] The measurements were performed using a dynamic viscoelasticity analyzer (DMA: manufactured by UBM, product name: E4000F). The storage modulus at 30°C was 1.0×10 9 Pa or more, and the storage modulus at 280°C is 3.0×10 8 Polyimides with a storage modulus of 1.0×10 Pa or more at 30°C are considered to be "non-thermoplastic polyimides". 8 Pa or more, and the storage modulus at 280°C is 3.0×10 7 Polyimides with a compressive strength of less than 1 Pa were classified as "thermoplastic polyimides."

[0137] [Evaluation of dielectric properties] The polyimide film (cured polyimide film) was left for 24 hours under the conditions of temperature: 23°C and humidity: 50% RH, and then the relative dielectric constant (ε) and dielectric loss tangent (Tan δ) at a frequency of 10 GHz were measured using a vector network analyzer (manufactured by Agilent, product name: Vector Network Analyzer E8363C) and an SPDR resonator.

[0138] [Glass transition temperature (Tg)] The adhesive sheet was pressed under the conditions of temperature: 160°C, pressure: 3.5MPa, and time: 60 minutes, and then cut into test pieces measuring 5mm x 20mm. Measurements were performed using a dynamic viscoelasticity measuring device (DMA: manufactured by TA Instruments, product name: RSA-G2) at a heating rate of 4°C / min from 30°C to 200°C and a frequency of 11GHz. The temperature at which the change in elastic modulus (tan δ) was maximum was determined as the glass transition temperature.

[0139] [Measurement of seam folds (bending test)] As described in Japanese Patent No. 6320031, a test piece (test circuit board piece) was fabricated by etching the metal foil of a flexible metal-clad laminate and forming 10 rows of copper wiring with a line width of 100 μm and a space width of 100 μm along its length, with a length of 40 mm (FIG. 6). As shown in FIG. 6, which shows only the conductor wiring in the test piece, the 10 rows of copper wiring 51 in the test piece 40 are all continuously connected via a U-shaped portion 52, and electrodes (not shown) for measuring resistance are provided on both ends. The test piece 40 was fixed on the sample stages 20 and 21 that can be folded in half, and the wiring for measuring resistance was connected to start monitoring the resistance (FIG. 7). The bending test was performed by bending all ten rows of copper wiring 51 at the exact center of the longitudinal direction using a urethane roller 22, moving the roller parallel to the bent line while controlling the gap G at the bent portion 40C to be 0.5 to 1.5 mm (FIGS. 8 and 9), opening the bent portion to return the test piece to a flat state (FIG. 10), and moving the folded portion again while holding it down with the roller (FIG. 11), with this series of steps counting as one seam fold. The bending test was repeated while constantly monitoring the resistance of the wiring, and the point at which the resistance reached a predetermined value (3000Ω) was judged to be the breakage of the wiring, and the number of times the wiring had been bent up to that point was the measured seam fold value.

[0140] [Calculation of neutral plane position] As described in Japanese Patent No. 6320031, the lower surface of the first layer shown in Fig. 12 is taken as the reference plane SP. Below, we consider the case where the laminate is bent so that the reference plane SP has a downward convex shape in Fig. 12. In Fig. 12, the symbol NP represents the neutral plane of the laminate. The neutral plane position [NP] is calculated by the following formula (2). Here, E is the elastic modulus, B is the depth width (usually the unit width of all layers is taken as Bi = 1), h is the distance between the center plane of the layer and the reference plane, and t is the layer thickness.

[0141]

number

[0142] [Calculation of equivalent bending stiffness] As described in Japanese Patent No. 6320031, the equivalent bending rigidity [BR], which is the bending rigidity of the entire flexible circuit board, is calculated by the following formula (3).

[0143]

number

[0144] In formula (2), as shown in FIG. 12, ai is the distance between the top surface of the i-th layer and the neutral plane NP, bi is the distance between the bottom surface of the i-th layer and the neutral plane NP, E is the tensile modulus of elasticity, B is the depth width (usually the whole layer unit width is taken as Bi = 1), h is the distance between the center plane of the layer and the reference plane, and t is the layer thickness. Σ i=1 n E i (ai 3 -bi 3 ) / 3 is E i (ai 3 -bi 3 ) / 3, where i is from 1 to n. Note that, in relation to equation (2), for the i-th layer, Bi(a i 3 -b i 3 ) / 3 is a parameter that represents the geometric characteristics of a cross section, generally known as the second moment of area. The bending rigidity of the i-th layer is calculated by multiplying the second moment of area of ​​the i-th layer by the tensile modulus of elasticity of the i-th layer.

[0145] The abbreviations used in the Examples and Reference Examples represent the following compounds. BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride PMDA: Pyromellitic dianhydride m-TB: 2,2'-dimethyl-4,4'-diaminobiphenyl TPE-R: 1,3-bis(4-aminophenoxy)benzene Bisaniline-M: 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene NMP: N-methyl-2-pyrrolidone DMAc: N,N-dimethylacetamide BTDA: 3,3',4,4'-benzophenonetetracarboxylic dianhydride DDA: aliphatic diamine with 36 carbon atoms (manufactured by Croda Japan Co., Ltd., trade name: PRIA MINE1074, amine value: 205mgKOH / g, dimer with cyclic and chain structures Diamine mixture, dimer content: 95% by weight or more BAPP: 2,2-bis[4-(4-aminophenoxy)phenyl]propane N-12: Dodecanedioic acid dihydrazide OP935: organic phosphinic acid aluminum salt (manufactured by Clariant Japan, trade name: E xolit OP935)

[0146] [Synthesis Example 1] (Preparation of polyimide solution 1) In a 500mL four-neck flask equipped with a nitrogen inlet tube, a stirrer, a thermocouple, a Dean-Stark trap, and a cooling tube, 44.92g of BTDA (0.139 mol), 75.08g of DDA (0.141 mol), 168g of NMP, and 112g of xylene were charged and mixed at 40°C for 30 minutes to prepare a polyamic acid solution. This polyamic acid solution was heated to 190°C, heated and stirred for 4 hours, and the distilled water and xylene were removed from the system. Thereafter, it was cooled to 100°C, 112g of xylene was added and stirred, and further cooled to 30°C to prepare a polyimide solution 1 (solid content: 29.5% by weight, weight average molecular weight: 75,700) in which imidization was completed.

[0147] [Synthesis Example 2] (Preparation of polyamic acid solution 1) In a nitrogen stream, 64.20 g of m-TB (0.302 mol), 5.48 g of bisaniline-M (0.016 mol) and DMAc in an amount 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, 34.20 g of PMDA (0.157 mol) and 46.13 g of BPDA (0.157 mol) were added, and the mixture was stirred at room temperature for 3 hours to carry out the polymerization reaction, thereby preparing polyamic acid solution 1 (viscosity: 26,500 cps).

[0148] [Synthesis Example 3] (Preparation of polyamic acid solution 2) A polyamic acid solution 2 (viscosity: 2,650 cps) was prepared in the same manner as in Synthesis Example 2, except that the raw material composition was 69.56 g of m-TB (0.328 mol), 542.75 g of TPE-R (1.857 mol), DMAc in an amount such that the solid concentration after polymerization was 12 wt%, 194.39 g of PMDA (0.891 mol), and 393.31 g of BPDA (1.337 mol).

[0149] [Preparation Example 1] (Preparation of resin sheet 1 from polyimide varnish 1) Polyimide varnish 1 was prepared by mixing 1.8 g of N-12 (0.0036 mol) and 12.5 g of OP935 with 169.49 g of polyimide solution 1 (50 g as solid content) and diluting it with 6.485 g of NMP and 19.345 g of xylene.

[0150] Polyimide varnish 1 was applied to the silicone-treated surface of a release substrate (length x width x thickness = 320 mm x 240 mm x 25 μm) so that the thickness after drying was 50 μm, and then heated and dried at 80 ° C for 15 minutes, and peeled off from the release substrate to produce a resin sheet 1 (thickness: 50 μm). The Tg of the resin sheet 1 was 78 ° C, and the relative dielectric constant (Dk) and dielectric loss tangent (Df) were 2.68 and 0.0028, respectively. The storage modulus properties of the resin sheet 1 were as follows.

[0151] Storage modulus steepness temperature range: 40~74℃ Storage modulus (40°C): 5.0 x 10 8Pa Storage modulus (74°C): 1.1 x 10 7 Pa Storage modulus (250°C): 3.0 x 10 6 Pa

[0152] [Examples 2 to 5] (Preparation of resin sheets 2 to 5 from polyimide varnish 1) Resin sheet 2 (thickness: 75 μm), resin sheet 3 (thickness: 25 μm), resin sheet 4 (thickness: 19 μm) and resin sheet 5 (thickness: 38 μm) were prepared in the same manner as in Preparation Example 1, except that the thickness after drying was changed.

[0153] [Preparation Example 6] (Preparation of single-sided metal-clad laminate 1) On the copper foil 1 (electrolytic copper foil CF-T49A-DS-HD2 manufactured by Fukuda Metals, thickness: 12 μm, surface roughness Rz on the resin layer side: 0.6 μm, tensile modulus: 30 GPa), polyamic acid solution 2 was uniformly applied so that the thickness after curing was about 2 to 3 μm, and then heated and dried at 120 ° C to remove the solvent. Next, polyamic acid solution 1 was uniformly applied thereon so that the thickness after curing was about 21 μm, and then heated and dried at 120 ° C to remove the solvent. Furthermore, polyamic acid solution 3 was uniformly applied thereon so that the thickness after curing was about 2 to 3 μm, and then heated and dried at 120 ° C to remove the solvent. Furthermore, a stepwise heat treatment was performed from 120 ° C to 360 ° C to complete the imidization, and a flexible single-sided metal-clad laminate 1 (resin layer thickness: 25 μm) was produced.

[0154] [Preparation Example 7] (Preparation of single-sided metal-clad laminate 2) A single-sided metal-clad laminate 2 (resin layer thickness: 12 μm) was produced in the same manner as in Production Example 6, except that the polyamic acid solution was applied so that the thickness after curing would be about 8 μm.

[0155] [Preparation Example 8] (Preparation of single-sided metal-clad laminate 3) A single-sided metal-clad laminate 3 (resin layer thickness: 38 μm) was produced in the same manner as in Production Example 6, except that the polyamic acid solution was applied so that the thickness after curing would be about 34 μm.

[0156] [Example 1] (Preparation of flexible circuit board 1) Two single-sided metal-clad laminates 1 were prepared, and the resin layer sides of each were overlapped on both sides of resin sheet 1, and the sheets were pressed together at 180°C for 2 hours under a pressure of 3.5 MPa to produce flexible metal-clad laminate 1. Next, the metal layer on one side of flexible metal-clad laminate 1 was etched away using an aqueous ferric chloride solution to prepare a single-sided metal-clad laminate, and then the other metal layer was subjected to a predetermined wiring process to prepare flexible circuit board 1. The evaluation results of flexible circuit board 1 are shown in Table 1.

[0157] [Example 2] (Preparation of flexible circuit board 2) Two single-sided metal-clad laminates 2 were prepared, and the resin layer sides of each were laminated on both sides of a resin sheet 2 to produce a flexible metal-clad laminate 2 in the same manner as in Example 1, and further a flexible circuit board 2 was produced. The evaluation results of the flexible circuit board 2 are shown in Table 1.

[0158] [Example 3] (Preparation of flexible circuit board 3) Two single-sided metal-clad laminates 1 were prepared, and the resin layer sides of each were laminated on both sides of the resin sheet 1 to produce a flexible metal-clad laminate 3 in the same manner as in Example 1, and further a flexible circuit board 3 was produced. The evaluation results of the flexible circuit board 3 are shown in Table 1.

[0159] [Example 4] (Preparation of flexible circuit board 4) Two single-sided metal-clad laminates 3 were prepared, and the resin layer sides of each were laminated on both sides of a resin sheet 3 to produce a flexible metal-clad laminate 4 in the same manner as in Example 1, and further a flexible circuit board 4 was produced. The evaluation results of the flexible circuit board 4 are shown in Table 1.

[0160] [Example 5] (Preparation of flexible circuit board 5) Two single-sided metal-clad laminates 1 were prepared, and the resin layer sides of each were laminated on both sides of a resin sheet 2 to produce a flexible metal-clad laminate 5 in the same manner as in Example 1, and further a flexible circuit board 5 was produced. The evaluation results of the flexible circuit board 5 are shown in Table 1.

[0161] [Reference example 1] (Creating reference circuit board 1) Resin sheet 1 was placed on copper foil 1, and polyimide film 1 (manufactured by Toray DuPont, product name: Kapton EN-S, thickness: 25 μm) was placed on top of that, and in this state, vacuum lamination was performed under conditions of temperature 170°C, pressure 0.85 MPa, and time 1 minute, and then heated in an oven at temperature 160°C and time 1 hour to produce metal-clad laminate 1. The metal layer of the obtained metal-clad laminate 1 was subjected to a predetermined wiring processing to produce reference circuit board 1. The evaluation results of reference circuit board 1 are shown in Table 2.

[0162] [Reference example 2] (Creating reference circuit board 2) A metal-clad laminate 2 was produced in the same manner as in Reference Example 1, with a resin sheet 4, a polyimide film 1, a resin sheet 4 and a copper foil 1 stacked in this order on the copper foil 1. The metal layer on one side of the obtained metal-clad laminate 2 was etched away using an aqueous ferric chloride solution to prepare a single-sided metal-clad laminate, and then the other metal layer was subjected to a predetermined wiring process to produce a reference circuit board 2. The evaluation results of the reference circuit board 2 are shown in Table 2.

[0163] [Reference example 3] (Creating reference circuit board 3) A metal-clad laminate 3 was produced in the same manner as in Reference Example 1, with a resin sheet 3, a polyimide film 1, a resin sheet 3 and a copper foil 1 stacked in this order on a copper foil 1. The metal layer on one side of the obtained metal-clad laminate 3 was etched away using an aqueous ferric chloride solution to produce a single-sided metal-clad laminate, and then a predetermined wiring process was performed on the other metal layer to produce a reference circuit board 3. The evaluation results of the reference circuit board 3 are shown in Table 2.

[0164] [Reference example 4] (Creating reference circuit board 4) A metal-clad laminate 4 was produced in the same manner as in Reference Example 1, with a resin sheet 5, a polyimide film 1, a resin sheet 5 and a copper foil 1 stacked in this order on the copper foil 1. The metal layer on one side of the obtained metal-clad laminate 4 was etched away using an aqueous ferric chloride solution to produce a one-sided metal-clad laminate, and then the other metal layer was subjected to a predetermined wiring process to prepare a reference circuit board 4. The evaluation results of the reference circuit board 4 are shown in Table 2.

[0165] [Reference example 5] (Production of reference circuit board 5) A metal-clad laminate 5 was prepared in the same manner as in Reference Example 1, with a resin sheet 1, a polyimide film 1, a resin sheet 1, and a copper foil 1 stacked in this order on a copper foil 1. The metal layer on one side of the obtained metal-clad laminate 5 was etched away using an aqueous ferric chloride solution to produce a single-sided metal-clad laminate, and then a predetermined wiring process was performed on the other metal layer to prepare a reference circuit board 5. The evaluation results of the reference circuit board 5 are shown in Table 2.

[0166] <Preparation of a sample for measuring the tensile modulus of polyimide layer> A predetermined polyamic acid solution was uniformly applied to a predetermined thickness on copper foil 1, then heated and dried at 120°C to remove the solvent, and heat-treated stepwise from 120°C to 360°C to complete imidization, preparing a single-sided metal-clad laminate. A polyimide film was prepared by etching away the copper foil layer of the single-sided metal-clad laminate using an aqueous ferric chloride solution. The tensile modulus of this polyimide film was taken as the tensile modulus of a single polyimide layer.

[0167] <Calculation of equivalent bending stiffness> The calculation of the equivalent bending stiffness of a flexible metal-clad laminate will be explained using an example of a laminate as shown in Figure 13. Assuming the state of the sample in the above seam folding test, the calculation is performed using the above formula (3) for a layered structure in which copper foil is attached to one side of the insulating resin layer. All values ​​used in calculating the equivalent bending stiffness of the laminate were values ​​measured for a single-layer insulator. In the case of Example 1, the copper foil layer (tensile modulus M1: 30.0 GPa, thickness T1: 12 μm) is the first layer, and on top of that are the second insulator layer (tensile modulus M2: 3.4 GPa, thickness T2: 2 μm), the third insulator layer (tensile modulus M3: 8.0 GPa, thickness T3: 21 μm), the fourth insulator layer (tensile modulus M4: 3.4 GPa, thickness T4: 2 μm), and the fifth insulator layer (tensile modulus M5: 0.8 GPa, thickness T5: 12 μm), resulting in a layer structure with an equivalent bending rigidity of 0.15 N / mm 2 The value divided by the cube of the total thickness (87 μm) is 234 N / mm 2 It becomes.

[0168] The evaluation results of Examples 1 to 5 and Reference Examples 1 to 5 are shown in Tables 1 and 2.

[0169] [Table 1]

[0170] [Table 2]

[0171] <Summary> Comparing Example 1 with Reference Examples 1 and 3, Examples 2 to 4 with Reference Example 4, and Example 5 with Reference Example 5, it can be seen that the number of times of the seam folding test is greatly increased in the Examples even though the insulating resin layer has the same thickness. Note that the number of times of seam folding in Reference Example 2 is relatively high at 94 times, but if the flexible metal-clad laminate of the present invention has an insulating resin layer of the same thickness as Reference Example 2, it can be reliably seen that the number of times of seam folding is greatly increased compared to the result of Reference Example 2, based on the results of Examples 1 to 5 (the number of times of seam folding tends to increase as the insulating resin layer becomes thinner).

[0172] 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. [Explanation of symbols]

[0173] C, CA flexible metal-clad laminate C1 1st single-sided metal-clad laminate C2 Second single-sided metal-clad laminate MA, M1, M2 metal layer PA bottom insulating resin layer P1 First insulating resin layer P2 Second insulating resin layer B, BA adhesive layer X Insulating resin layer 100, 100A Flexible Metal-Clad Laminate 101, 101A metal layer 110, 110A Polyimide layer 111, 111A Non-thermoplastic polyimide layer 112, 112A Thermoplastic polyimide layer 120, 120A Adhesive polyimide layer 130, 130A single-sided metal clad laminate

Claims

1. A flexible metal-clad laminate used for a flexible circuit board that is folded and stored in a housing of an electronic device by a seam fold in which an upper surface side is inverted 180 degrees to become a lower surface side, an insulating resin layer having a thickness in the range of 50 μm or more and 150 μm or less and a tensile modulus (TM1) in the range of 1 GPa or more and 7 GPa or less; a metal layer laminated on at least one surface of the insulating resin layer, the insulating resin layer is formed by laminating a plurality of polyimide layers, has a polyimide layer (A) as a central layer of the plurality of polyimide layers, and a thickness of the polyimide layer (A) is in the range of 0.5 to 0.96 with respect to a total thickness of the insulating resin layer, A flexible metal-clad laminate, characterized in that the tensile modulus (TM2) of the insulating resin layer within a range of 5 μm in the thickness direction from the interface with the metal layer is in the range of 2 GPa or more and 10 GPa or less, and the tensile modulus (TM2) is greater than the tensile modulus (TM1).

2. 2. The flexible metal-clad laminate according to claim 1, wherein the thickness of the metal layer is in the range of 6 μm or more and 15 μm or less.

3. 2. The flexible metal-clad laminate according to claim 1, wherein the polyimide layer (A) has a storage modulus of 1800 MPa or less at 50° C. and a maximum storage modulus of 800 MPa or less at 180 to 260° C.

4. A flexible circuit board obtained by wiring the metal layer in the flexible metal-clad laminate according to any one of claims 1 to 3.

5. 5. The flexible circuit board according to claim 4, wherein the metal layer is folded inward.

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