KR20140086899A - Flexible copper-clad laminate - Google Patents

Abstract

The present invention provides a flexible copper-clad laminate capable of providing a flexible circuit board having excellent bending resistance to prevent the disconnection or crack of a wiring circuit even when it is used in the thin or narrow luminous body of an electronic device. The flexible copper-clad laminate used in the flexible circuit board, which is stored in the luminous body of the electronic device while being folded, comprises a polyimide layer (A) having the thickness of 5-30 μm and the tensile modulus of 4-10 GPa, and a copper clad (B) laminated on at least one surface of the polyimide layer (A) while having the thickness of 6-20 μm and the tensile modulus of 25-35 GPa. In the flexible copper-clad laminate, the ten point average roughness (Rz) of one surface of the copper clad (B) being in contact with the polyimide layer (A) is within 0.7-2.2 μm. A folding coefficient [PF] calculated by an equation (I) in a bending test when the gap of an arbitrary flexible circuit board having a copper wire formed of the copper clad (B) is 0.3 mm. (In the equation (I), ¦ε¦ is the absolute value of the average distortion cost of a curved copper wire and εC is the distortion cost of tensile limit).

Description

[0001] FLEXIBLE COPPER-CLAD LAMINATE [0002]

The present invention relates to a flexible copper-clad laminate, and more particularly, to a flexible copper-clad laminate used for a flexible circuit board (FPC) which is folded and housed in a housing of an electronic apparatus and used.

In recent years, with the miniaturization and high functionality of electronic devices, FPC, which is one of the electronic components constituting these electronic devices, is required to have higher performance such as electrical characteristics, mechanical characteristics, and heat resistance. Most of FPCs are manufactured by forming a circuit in a copper foil of a flexible copper-clad laminate in which a polyimide as an insulating layer is laminated on a copper foil as a metal layer. The copper clad laminate having such a polyimide as an insulating layer comprises a copper clad laminate (also referred to as " 3-layer CCL ") in which polyimide and copper foil are laminated through a thermosetting adhesive layer such as an epoxy resin between polyimide and copper foil, Layer laminate (also referred to as " two-layer CCL ") in which a polyimide and a copper foil are directly laminated without passing through the copper foil.

Since the three-layer CCL uses an epoxy resin or the like as an adhesive layer, there is a problem in heat resistance. Concretely, a problem is likely to occur in a step requiring high-temperature processing, such as a step of bonding an electrode on a wiring of an FPC to a monitor panel substrate, a rigid substrate, or a semiconductor chip using solder or a heat tool. In addition, the three-layer CCL has a problem that the thickness of the adhesive layer is greater than that of the two-layer CCL, the dimension control is difficult due to the difference in thermal expansion coefficient between dissimilar materials, and further, have. Therefore, in applications where heat resistance and reliability are highly demanded, a two-layer CCL that does not use a thermosetting adhesive such as an epoxy resin has been released.

Therefore, according to the recent diversification of the model of the portable terminal device, the usage pattern of the FPC used here is also changed. Unlike a usage mode in which a certain amount of bending radius such as a hinge bend portion or a slide bending portion, which is found in a conventional cellular phone, is secured, a more stringent bendability is required to be folded in order to accommodate the folding wire in a thin light body. Hereinafter, in the present specification, the case where the upper surface of the FPC is inverted by about 180 DEG C so as to be the lower surface side is sometimes called " folding ".

As a purpose of application to such a use, Patent Document 1 proposes a high flexing flexible circuit board which exhibits high flexibility and excellent dimensional stability. However, the invention of Patent Document 1 is that a metal wiring pattern is formed on a polyimide base film through an adhesive layer, and polyimide having a relatively low elastic modulus range is used as a base substrate. In addition, since the adhesive layer is required, the characteristics such as the heat resistance of the two-layer CCL by polyimide alone can not be fully utilized.

Patent Document 2 proposes a polyimide metal laminate suitable for a circuit board used in a bent state in an electronic apparatus. However, the polyimide metal laminate disclosed here focuses on the elastic modulus of the non-thermoplastic polyimide film constituting the polyimide layer, but does not pay attention to the modulus of elasticity of the copper foil used together, and shows only about one folding resistance It was practically insufficient.

Further, in the design of the FPC, the wiring can be made thick if the thickness of the polyimide layer which is the insulating layer of the flexible copper clad laminate is thick, from the viewpoint of impedance matching with the bonding line substrate. That is, the wiring is easy to process, whereas when it is intended to store in a thin or narrow body, the repulsive force of the substrate affects the folding of the substrate. On the other hand, if the thickness of the polyimide layer is thin, it is also necessary to make the wiring thinner from the viewpoint of impedance matching. That is, the degree of difficulty of wiring workability is high, but because it is low rebound, it is relatively easy to store into a thin or narrow body, and handling property of FPC is good.

Japanese Patent Application Laid-Open No. 2007-208087 Japanese Patent Laid-Open Publication No. 62-0000

An object of the present invention is to provide a flexible copper-clad laminate to which an FPC having excellent bending resistance capable of preventing disconnection and cracking of a wiring circuit, even when used in a thin or narrow electronic device body, is provided.

The present inventors have intensively studied and, as a result, have provided a flexible copper clad laminate capable of solving the above problems by paying attention to the characteristics of a wiring circuit board obtained by optimizing the characteristics of a copper foil and a polyimide film and fabricating a flexible copper clad laminate The present invention has been completed.

That is, the flexible copper-plated laminated board of the present invention is a flexible copper-clad laminate used in a flexible circuit board folded and housed in a housing of an electronic apparatus,

A polyimide layer (A) having a thickness in the range of 5 to 30 mu m and a tensile modulus within a range of 4 to 10 GPa,

And a copper foil (B) laminated on at least one surface of the polyimide layer (A) and having a tensile elastic modulus within a range of from 25 to 35 GPa in a thickness of 6 to 20 mu m,

Wherein the copper foil on the side contacting the polyimide layer (A) has a ten-point average roughness (Rz) in the range of 0.7 to 2.2 占 퐉 and the copper foil (B) (PF) calculated by the following formula (I) in a bending test at a gap of 0.3 mm of the flexible circuit board of the present invention is in the range of 0.96 + 0.025.

Is the absolute value of the bending average distortion value of the copper wiring, and? _C is the tensile elastic limit distortion of the copper wiring)

A flexible copper clad laminate of the present invention, the polyimide layer (A) has a thermal expansion coefficient 30 × 10 ^-6 / K is less than the low thermal expansion of the polyimide layer (i) and the thermal expansion coefficient 30 × 10 ^-6 / K or more high thermal expansion properties of the polyimide It is preferable that the high temperature expandable polyimide layer (ii) including the intermediate layer (ii) directly contacts the copper foil (B).

In the flexible copper clad laminate of the present invention, it is preferable that the thickness of the polyimide layer (A) is in the range of 8 to 15 mu m and the tensile elastic modulus is in the range of 6 to 10 GPa.

The flexible copper clad laminate of the present invention preferably has a thickness ratio of the polyimide layer (A) and the copper foil (polyimide layer (A) / copper foil (B)) within the range of 0.9 to 1.1.

In the flexible copper clad laminate of the present invention, it is preferable that the copper foil (B) is an electrolytic copper foil.

INDUSTRIAL APPLICABILITY The flexible copper clad laminate of the present invention can exhibit a high bending resistance required for a wiring board and can provide a material for a flexible circuit board which is excellent in connection reliability in a bent state in an electronic apparatus. Therefore, the flexible copper-plated laminated board of the present invention is preferably used for electronic parts which require a bending part such as a bent part around a small liquid crystal, such as a smart phone.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a perspective view showing an important part of a flexible circuit board obtained by processing a copper foil of a flexible copper clad laminate according to the present invention by a wiring circuit; FIG.
2 is a plan explanatory view showing a state of the copper wiring of the test circuit board used in the embodiment.
3 is a side view illustrating a sample stage and a test circuit board in a bending test (a state in which a test circuit board piece is fixed on a sample stage).
Fig. 4 is a side view illustrating a sample stage and a test circuit board in a bending test (a state immediately before pressing a bending portion of the test circuit board with a roller). Fig.
5 is a side view illustrating a sample stage and a test circuit board in a bending test (a state in which a bending portion of the test circuit board is pressed by a roller).
6 is a side view illustrating a sample stage and a test circuit board in a folding test (a state in which a test piece is returned to a flat state by unfolding a bent portion);
7 is a lateral explanatory view showing a sample stage and a test circuit board member in a bending test (a state in which a folding line portion of a bending portion is evenly pressed by a roller).
8 is a cross-sectional explanatory view (partial view) of a flexible circuit board.

Hereinafter, an embodiment of the present invention will be described. The flexible copper clad laminate of the present embodiment is composed of a polyimide layer (A) and a copper foil (B). The copper foil (B) is provided on one side or both sides of the polyimide layer (A), and is preferably an electrolytic copper foil. This flexible copper-clad laminate is used for an FPC that is folded and housed in a housing of an electronic apparatus by forming a copper wiring by etching or the like of a copper foil and processing the wiring circuit.

<Polyimide layer>

In the flexible copper clad laminate of this embodiment, the thickness of the polyimide layer (A) is in the range of 5 to 30 mu m, preferably in the range of 8 to 15 mu m, and more preferably in the range of 9 to 12 mu m desirable. When the thickness of the polyimide layer (A) exceeds 30 占 퐉, a large bending stress is applied by the copper wiring when the FPC is bent, and the bending resistance of the FPC is significantly lowered.

Further, the tensile modulus of the polyimide layer (A) may be in the range of 4 to 10 GPa, preferably in the range of 6 to 10 GPa. If the tensile modulus of elasticity of the polyimide layer (A) is less than 4 GPa, the strength of the polyimide itself is lowered, which may cause handling problems such as tearing of the film when the flexible copper clad laminate is processed into a circuit board. On the other hand, when the tensile modulus of elasticity of the polyimide layer (A) exceeds 10 GPa, the flexural rigidity of the flexible copper clad laminate increases, resulting in an increase in the bending stress applied to the copper wiring when the FPC is bent, do.

As the polyimide layer (A), a commercially available polyimide film can be used as it is. However, since the thickness and physical properties of the insulating layer can be easily controlled, the polyamic acid solution is directly applied onto the copper foil, Drying, and curing, by a so-called casting (coating) method. The polyimide layer (A) may be formed of only a single layer, but it is preferable that the polyimide layer (A) is composed of a plurality of layers in consideration of adhesion between the polyimide layer (A) and the copper foil (B). When the polyimide layer (A) is composed of a plurality of layers, another polyamic acid solution may be sequentially applied on the polyamic acid solution containing different constituent components. When the polyimide layer (A) is composed of a plurality of layers, the polyimide precursor resin having the same constitution may be used more than once.

The polyimide layer (A) will be described in more detail. As described above, the polyimide layer (A) is preferably a plurality of layers, but its concrete example polyimide layer (A) the thermal expansion coefficient of 30 × 10 ^-6 / K is less than low thermal expansion polyimide layer (i) of the And a polyimide layer (ii) having a thermal expansion coefficient of 30 x 10 &lt; ^-6 &gt; / K or more and a high thermal expansion coefficient. More preferably, the polyimide layer (A) has a laminated structure having at least one of the low-heat-expandable polyimide layers (i), preferably a polyimide layer (ii) of high thermal expansion on both sides thereof, It is preferable that the polyimide layer (ii) is in direct contact with the copper foil (B). Here, the &quot; low heat expandable polyimide layer (i) &quot; means a layer having a thermal expansion coefficient of less than 30 10 ^-6 / K, preferably in the range of 1 10 ^-6 to 25 10 ^-6 / K, Refers to a polyimide layer within a range of 3 x 10 ^-6 to 20 x 10 ^-6 / K. The term "high heat expandable polyimide layer (ii)" refers to a polyimide layer having a thermal expansion coefficient of 30 × 10 ^-6 / K or more, preferably 30 × 10 ^-6 to 80 × 10 ^-6 / K , Particularly preferably in the range of 30 x 10 ^-6 to 70 x 10 ^-6 / K. Such a polyimide layer can be a polyimide layer having a desired thermal expansion coefficient by suitably changing the combination of materials to be used, the thickness, and the drying and curing conditions.

The polyamic acid solution providing the polyimide layer (A) can be prepared by polymerizing known diamines and acid anhydrides in the presence of a solvent. In this case, the viscosity of the resin to be polymerized is preferably within a range of 500 cps to 35,000 cps, for example.

Examples of the diamine used as the raw material of the polyimide include 4,6-dimethyl-m-phenylenediamine, 2,5-dimethyl-p-phenylenediamine, 2,4-diaminomeshtylane, -Methylene di-o-toluidine, 4,4'-methylene di-2,6-xylidine, 4,4'-methylene-2,6-diethylaniline, 2,4-toluene diamine, Diamine, p-phenylenediamine, 4,4'-diaminodiphenylpropane, 3,3'-diaminodiphenylpropane, 4,4'-diaminodiphenylethane, 3,3'-diaminodiphenyl Ethane, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, Diphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl ether, Bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, Benzene, benzidine, 3,3'-diaminobiphenyl, 3 , 3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethoxybenzidine, 4,4'-diamino-p-terphenyl, 3,3'-diamino- Bis (p-aminocyclohexyl) methane, bis (p-β-amino-t-butylphenyl) ether, bis (Aminopentyl) benzene, p-bis (1,1-dimethyl-5-aminopentyl) benzene, 1,5- diaminonaphthalene, 2,6-diaminonaphthalene, 2,4- -Butyl) toluene, 2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine, m-xylylenediamine, Diaminopyridine, 2,5-diaminopyridine, 2,5-diamino-1,3,4-oxadiazole, piperazine, 2,2'-dimethyl-4,4'-diaminobiphenyl, 1,3-diaminodibenzofuran, 1,5-diaminofluorene, dibenzo-p-dioxin-2,7-diamine, and 4,4'-diaminobenzyl.

Examples of the acid anhydrides used as raw materials for the polyimide include pyromellitic dianhydride, 3,3 ', 4,4'-benzophenonetetracarboxylic acid dianhydride, 2,2', 3,3 ' -Benzophenone tetracarboxylic acid dianhydride, 2,3,3 ', 4'-benzophenonetetracarboxylic dianhydride, naphthalene-1,2,5,6-tetracarboxylic acid dianhydride, naphthalene-1, 2,4,5-tetracarboxylic acid dianhydride, naphthalene-1,4,5,8-tetracarboxylic acid dianhydride, naphthalene-1,2,6,7-tetracarboxylic acid dianhydride, 4,8 -Dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylic acid dianhydride, 4,8-dimethyl-1,2,3,5,6- Hexahydronaphthalene-2,3,6,7-tetracarboxylic acid dianhydride, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, 2,7-dichloronaphthalene- 1,4,5,8-tetracarboxylic acid dianhydride, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, 1,4,5,8- rim 3,3 ', 4,4'-biphenyltetracarboxylic acid dianhydride, 2,2', 3,3'-biphenyl, 3,3'-biphenyltetracarboxylic dianhydride, Tetracarboxylic dianhydride, 2,3,3 ', 4'-biphenyltetracarboxylic dianhydride, 3,3 ", 4,4" -p-terphenyl tetracarboxylic acid dianhydride, 2,2 ", 3,3" -p-terphenyltetracarboxylic dianhydride, 2,3,3 ", 4" -p-terphenyltetracarboxylic dianhydride, 2,2- Carboxyphenyl) -propane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) -propane dianhydride, bis (2,3-dicarboxyphenyl) ether dianhydride, bis ) Dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride, perylene-2,3,8,9-tetracarboxylic acid dianhydride , 4,4,9,10-tetracarboxylic acid dianhydride, perylene-4,5,10,11-tetracarboxylic acid dianhydride, perylene-5,6,11,12-tetracarboxylic acid Dianhydride, phenanthrene-1,2,7,8-tetracarboxylic acid dianhydride, phenanthrene-1,2,6,7-tetracarboxylic acid dianhydride, phenanthrene-1,2,9,10- Tetracarboxylic acid dianhydride, cyclopentane-1,2,3,4-tetracarboxylic acid dianhydride, pyrazine-2,3,5,6-tetracarboxylic acid dianhydride, pyrrolidine- 4,5-tetracarboxylic acid dianhydride, thiophene-2,3,4,5-tetracarboxylic acid dianhydride, 4,4'-oxydiphthalic dianhydride, 2,3,6,7-naphthalene tetra Carboxylic acid dianhydride and the like.

The diamine and the acid anhydride may be used alone or in combination of two or more. The solvent used for the polymerization is exemplified by dimethylacetamide, N-methylpyrrolidinone, 2-butanone, diglyme, xylene and the like, and they may be used alone or in combination of two or more.

In the present embodiment, in order to obtain a polyimide layer (i) having a low thermal expansion coefficient of less than 30 x 10 &lt; ^-6 &gt; / K, pyromellitic acid dianhydride, 3,3 ' -Biphenyltetracarboxylic dianhydride, and as the diamine component, 2,2'-dimethyl-4,4'-diaminobiphenyl and 2-methoxy-4,4'-diaminobenzanilide are preferably used , Particularly preferably pyromellitic dianhydride and 2,2'-dimethyl-4,4'-diaminobiphenyl as main components of the raw material components.

In order to obtain a polyimide layer (ii) having a thermal expansion coefficient of 30 x 10 &lt; ^-6 &gt; / K or more and having a high thermal expansion coefficient, pyromellitic acid dianhydride, 3,3 ', 4,4'-biphenyltetra 3,3 ', 4,4'-benzophenonetetracarboxylic acid dianhydride, 3,3', 4,4'-diphenylsulfone tetracarboxylic dianhydride as the diamine component and 2 , 2'-bis [4- (4-aminophenoxy) phenyl] propane, 4,4'-diaminodiphenyl ether and 1,3-bis (4-aminophenoxy) Preferably, pyromellitic dianhydride and 2,2'-bis [4- (4-aminophenoxy) phenyl] propane are used as the main components of the raw material components. The glass transition temperature of the polyimide layer (ii) of high heat expansion obtained in this way is preferably in the range of 300 to 400 占 폚.

When the polyimide layer (A) has a laminated structure of the polyimide layer (i) having a low thermal expansion property and the polyimide layer (ii) having a high heat expansion property, the polyimide layer (i) Of the polyimide layer (ii) of the low thermal expansion property (the heat expansion polyimide layer (i) / the high heat expansion polyimide layer (ii)) is within the range of 2 to 15. If the ratio does not satisfy 2, the low thermal expansion polyimide layer is thinned over the entire polyimide layer, so that it becomes difficult to control the dimensional characteristics of the polyimide film, and the dimensional change ratio when the copper foil is etched becomes large, , The adhesion of the polyimide film to the copper foil is deteriorated because the high-heat-expandable polyimide layer is thinned. Further, even when the polyimide layer (A) is composed of a plurality of layers, the thickness and the elastic modulus of the entire polyimide layer (A) can be used in calculating the folding modulus [PF].

<Copper>

In the flexible copper clad laminate of the present embodiment, the thickness of the copper foil B is in the range of 6 to 20 mu m and preferably in the range of 8 to 15 mu m. If the thickness of the copper foil B is less than 6 占 퐉, the rigidity of the copper foil itself is lowered in the process of forming the polyimide layer on the copper foil, for example, on the flexible copper clad laminate, Wrinkles and the like occur. If the thickness of the copper foil B exceeds 20 占 퐉, the bending stress applied to the copper wiring when the FPC is bent increases, and the bending resistance is lowered.

In the present embodiment, it is preferable that the thickness ratio of the polyimide layer (A) and the copper foil (polyimide layer (A) / copper foil (B)) is in the range of 0.9 to 1.1. If the thickness ratio is less than 0.9 or larger than 1.1, the maximum tensile strain at the time of plastic deformation at the time of bending is increased, and the bending resistance is lowered.

The tensile modulus of the copper foil (B) is in the range of 25 to 35 GPa. If the tensile modulus of elasticity of the copper foil B is less than 25 GPa, the heating conditions and the like of the copper foil itself are affected during the production of the flexible copper clad laminate, for example, in the step of forming the polyimide layer on the copper foil, . As a result, there is a problem that wrinkles or the like are generated on the flexible copper-clad laminate. On the other hand, when the tensile modulus exceeds 35 GPa, a large bending stress is applied by the copper wiring when the FPC is bent, and the bending resistance of the FPC remarkably lowers.

The surface of the copper foil B may be roughened and the surface roughness (ten-point average roughness Rz) of the surface of the copper foil in contact with the polyimide layer A is in the range of 0.7 to 2.2 mu m and in the range of 0.8 to 1.6 mu m I am preferable. If the value of the surface roughness Rz of the copper foil B does not satisfy 0.7 mu m, it becomes difficult to assure the reliability of adhesion with the polyimide film. If the surface roughness Rz exceeds 2.2 mu m, when the FPC is repeatedly bent, It is likely to become a starting point of occurrence. As a result, the bending resistance of the FPC is lowered. The surface roughness Rz is a value measured in accordance with JIS B0601.

The copper foil used in the flexible copper clad laminate of the present embodiment is not particularly limited as long as it satisfies the above characteristics and may be either an electrolytic copper foil or a rolled copper foil. However, in view of ease of manufacture and cost in the case of using a thin copper foil, Is preferably used. As the electrolytic copper foil, a commercially available product can be used. Specific examples thereof include WS foil manufactured by Furukawa Denki Kogyo K.K., HL foil manufactured by Nippon Densa Kogyo K.K. and HTE foil manufactured by Mitsui Kinzoku Kogyo K.K. In addition, even when other products including these commercially available products are used, the tensile elastic modulus of the copper foil B can be changed in accordance with the heat treatment conditions at the time of forming the polyimide layer (A) on the above-mentioned copper foil, In the present embodiment, it is preferable that the resultant flexible copper-clad laminate has these predetermined ranges.

The flexible copper clad laminate of the present embodiment can be produced by, for example, applying a polyimide precursor resin solution (also referred to as a polyamic acid solution) to the surface of a copper foil, followed by a heat treatment step of drying and curing. The heat treatment conditions in the heat treatment process are as follows: the coated polyamic acid solution is dried at a temperature lower than 160 deg. C to remove the solvent in the polyamic acid solution, then heated stepwise within a temperature range of 130 deg. C to 400 deg. C, . In order to obtain the thus obtained single-sided flexible copper-clad laminate as a double-sided copper-clad laminate, the single-sided flexible copper-clad laminate and the copper foil separately prepared therefrom are thermocompression bonded at a temperature within a range of 300 to 400 ° C.

<FPC>

The flexible copper clad laminate of the present embodiment is mainly useful as an FPC material. That is, the FPC which is one embodiment of the present invention can be produced by processing the copper foil of the flexible copper clad laminate of this embodiment into a pattern by a conventional method to form a wiring layer.

The flexible copper-clad laminate according to the present invention is constituted by the polyimide layer (A) and the copper foil (B). The copper foil (B) of the flexible copper clad laminate is subjected to wiring circuit processing to form an arbitrary flexible circuit board The folding modulus [PF] calculated by the following formula (I) in the bending test (gap 0.3 mm) needs to be in the range of 0.96 + 0.025, preferably in the range of 0.96 + 0.02, 0.015. &Lt; / RTI &gt; This folding modulus [PF] is a value determined by the stress-strain curve obtained from the uniaxial tensile test of the copper foil used. If the folding coefficient [PF] deviates from the above range, the stress is locally concentrated at one point or two points, and the bending resistance is lowered. On the other hand, when the folding modulus [PF] is in the above range, the stress is appropriately dispersed to improve the bending resistance such as folding. For example, in the case of using an electrolytic copper foil in the present invention, the folding modulus [PF] defined in the present invention is set in the above range in the stress-strain curve obtained from the uniaxial tensile test of the electrolytic copper foil used, And a stress of 175 MPa or less at a strain of 5% is used as the stress of the portion where the curvature becomes maximum.

In the formula (I), |? Is the absolute value of the bending average distortion value of the copper wiring, and? C is the tensile elastic limit distortion of the copper wiring.

As described above, the folding modulus [PF] is represented by the absolute value |? | Of the bending average distortion value? Of the copper wiring and the tensile elastic limit strain? C of the copper wiring, and the bending average distortion value? Lt; / RTI &gt; A copper wiring 12 obtained by wiring-circuiting one layer of copper foil on one side of the polyimide layer 11 including one polyimide layer shown in Fig. 8 with respect to the folding modulus [PF] A description will be given of a case where the circuit board is bent so that the reference plane SP, which is the lower surface of the polyimide layer 11 as the first layer, becomes a convex shape (outer surface of the bent portion). In addition, the circuit board shown in Fig. 8 shows a portion where a copper wiring is present in a cross section perpendicular to the longitudinal direction of the circuit board (that is, a cross section).

Here, with respect to the equation (2), the bending average distortion? Is the bending average distortion in the longitudinal direction generated in the copper wiring by the simple bending when the longitudinal direction of the circuit board is folded in two, and yc in the formula is the polyimide layer 11 The distance from the reference plane SP to the center plane of the copper wiring 12. In addition, reference numeral NP denotes a neutral plane of the circuit board. Here, the distance between the neutral plane NP and the reference plane SP is set to the neutral plane position [NP], and this neutral plane position [NP] is calculated by the space portion formed between the copper wiring and the copper wiring formed by the wiring circuit processing of the copper foil, do. The neutral plane position [NP] is calculated by the following equation (3).

Here, E _i is the tensile strength of the material constituting the i-th layer (in the example shown in Fig. 8, the first layer is the polyimide layer 11 and the second layer is the copper wiring 12) in the circuit board, Lt; / RTI &gt; This elastic modulus E _i corresponds to &quot; the relationship between stress and distortion in each layer &quot; in the present embodiment. B _i is the width of the i-th layer and corresponds to the width B shown in Fig. 8 (parallel to the lower surface of the first layer and dimension in the direction perpendicular to the longitudinal direction of the circuit board).

은, i가 1부터 n까지의 총 합계를 나타낸다. 또한, 구리 배선에서의 중립면 위치에 대해서는 [NP]_Line으로 표기한다.When the neutral plane position [NP] of the copper wiring is obtained, the line width LW value of the copper wiring is used as B _i , and when the neutral plane position [NP] of the space portion is obtained, the line width SW value of the copper wiring is set as B _i . h _i is the distance between the center plane of the i-th layer and the reference plane SP. The center plane of the i-th layer is a virtual plane located at the center in the thickness direction of the i-th layer. t _i is the thickness of the i-th layer. In addition,

Represents the total sum from 1 to n. The position of the neutral plane in the copper wiring is indicated by [NP] _Line .

In the formula (2), R represents the effective radius of curvature, and the effective radius of curvature R is the distance from the bending center at the bent portion when the circuit board is bent in the bending test to the neutral plane NP of the copper wiring. That is, the effective radius of curvature R is calculated from the gap distance G and the neutral plane position [NP] _Line of the copper wiring by the following equation (4).

As described above, the folding modulus [PF] indicating the degree of foldability of the entire circuit board is calculated by obtaining the neutral plane position, the effective curvature radius, and the bent average distortion. As described above, the folding coefficient [PF] is determined by the thickness of each layer constituting the circuit board, the modulus of elasticity of each layer constituting the circuit board, the gap distance G in the bending test, , The line width LW in the line width LW, and the like.

In the above (FIG. 8), a model in which the circuit board has two layers has been described for convenience, but the above description is also suitable when the circuit board is formed of two or more layers. In other words, when the number of layers of the circuit board 1 is n, n is an integer of 2 or more, and from the reference plane SP among the layers constituting the circuit board, i (i = 1, 2, ) Layer is referred to as an i-th layer.

1, the copper foil is patterned by wiring circuit processing, and there are a portion where the copper wiring 12 exists and a portion where the copper wiring 12 does not exist. Here, when the portion where the copper wiring 12 is present is referred to as a wiring portion and the portion where the copper wiring 12 does not exist is referred to as a space portion, the configuration of the wiring portion and the space portion are different. For example, in the case of the circuit board 1 shown in Fig. 1, the wiring portion on the polyimide layer 11 is composed of the copper wiring 12 in 10 rows (only four rows in Fig. 1) And a gap between the copper wirings 12 mainly. From the above, the folding coefficient [PF] can be calculated by dividing the wiring portion and the space portion.

[Example]

Hereinafter, the present invention will be described in more detail based on examples. Each characteristic evaluation in the following examples was carried out by the following methods.

[Measurement of tensile modulus of elasticity]

The tensile modulus of elasticity was measured using Strograph R-1 manufactured by Toyo Seiki Seisakusho Co., Ltd. under an environment of a temperature of 23 캜 and a relative humidity of 50%.

[Measurement of CTE]

The sample was heated to 250 DEG C using a thermomechanical analyzer manufactured by Seiko Instruments Inc., held at this temperature for 10 minutes, cooled at a rate of 5 DEG C / min, and an average thermal expansion coefficient (linear thermal expansion coefficient) Respectively.

[Measurement of surface roughness (Rz)] [

The surface roughness of the contact surface side of the copper foil with the polyimide layer was measured using a contact type surface roughness tester (SE1700 manufactured by Kosaka Kagaku Co., Ltd.).

[Measurement of folding (bending test)]

The copper foil of the flexible copper-plated laminated board was etched to prepare a test piece (test circuit board piece) in which 10 rows of copper wirings having a line width of 100 mu m and a space width of 100 mu m and a length of 40 mm were formed along the longitudinal direction thereof ). As shown in Fig. 2 showing only the copper wiring in the test piece, the ten copper wiring lines 51 in the test piece 40 are continuously connected to each other through the U-shaped portion 52, (Not shown) is provided on the surface of the substrate. The test piece 40 was fixed on the sample stages 20 and 21 capable of being folded in two, and the resistance value was monitored by connecting wires for measuring the resistance value (FIG. 3). The bending test was carried out in parallel with 10 lines of the copper wiring 51 while controlling the gap G of the bending portion 40C to be 0.3 mm by using the urethane roller 22 at the central portion in the longitudinal direction (FIG. 4 and FIG. 5), the bent portion is opened to return the test piece to a flat state (FIG. 6), and the portion having the fold line is again rolled (FIG. 7), and the number of times of folding is counted by one in this series of steps. The bending test was repeated while monitoring the resistance value of the wiring at all times. The breaking point of the wiring was judged to be the point of time when the predetermined resistance value (3000?) Was reached. The case where the folding measurement value was 50 or more times was evaluated as &quot; good &quot;, and the case of less than 50 times was evaluated as &quot; defective &quot;.

Next, the manufacturing method of the flexible copper clad laminate described in Examples and Comparative Examples will be described.

[Synthesis of polyamic acid solution]

(Synthesis Example 1)

Synthesis of Bottom Resin:

Bis [4- (4-aminophenoxy) phenyl] propane (BAPP) was added to a reaction vessel equipped with a stirrer, a thermocouple, and a stirrer in which N, N-dimethylacetamide was placed, And dissolved in the container while stirring. Then, pyromellitic dianhydride (PMDA) was added so that the total amount of the monomers was 12 mass%. Thereafter, stirring was continued for 3 hours to carry out a polymerization reaction to obtain a resin solution of polyamic acid a. The polyimide film having a thickness of 25 占 퐉 formed from polyamic acid a had a coefficient of thermal expansion (CTE) of 55 占^10-6 / K.

(Synthesis Example 2)

Dimethyl-4,4'-diaminobiphenyl (m-TB) was added to a reaction vessel equipped with a stirrer, a thermocouple, and a stirrer in which N, N-dimethylacetamide was placed, And 4,4'-diaminodiphenyl ether (DAPE) were added so that the molar ratio (m-TB: DAPE) of each diamine was 60:40, and dissolved in the vessel while stirring. Then, pyromellitic dianhydride (PMDA) was added so that the total amount of the monomers was 16 mass%. Thereafter, stirring was continued for 3 hours to carry out a polymerization reaction to obtain a resin solution of polyamic acid b. The polyimide film having a thickness of 25 占 퐉 formed from the polyamic acid b had a coefficient of thermal expansion (CTE) of 22 占^10-6 / K.

(Synthesis Example 3)

Dimethyl-4,4'-diaminobiphenyl (m-TB) was added to a reaction vessel equipped with a stirrer, a thermocouple, and a stirrer in which N, N-dimethylacetamide was placed, And dissolved in the container while stirring. Then, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride (BPDA) and pyromellitic dianhydride (PMDA) were added in an amount of 15% by mass of the total amount of monomers, and the molar ratio of each acid anhydride (BPDA : PMDA) was 20:80. Thereafter, stirring was continued for 3 hours to carry out a polymerization reaction to obtain a resin solution of polyamic acid c. The polyimide film having a thickness of 25 占 퐉 formed from the polyamic acid c had a coefficient of thermal expansion (CTE) of 22 占^10-6 / K.

(Example 1)

A resin solution of polyamic acid a prepared in Synthesis Example 1 was uniformly applied to a surface of a commercially available electrolytic copper foil having a thickness of 12 占 퐉 and having a thickness of 2.5 占 퐉 after curing on one surface (surface roughness Rz = 1.2 占 퐉) After that, it was dried by heating at 130 DEG C to remove the solvent. Subsequently, the resin solution of the polyamic acid b prepared in Synthesis Example 2 was uniformly applied to the coated side so that the thickness after curing became 20.0 占 퐉, and the resultant was dried by heating at 120 占 폚 to remove the solvent. The same resin solution of polyamic acid a as applied on the first layer was coated uniformly on the coated surface side so that the thickness after curing became 2.5 占 퐉 and dried by heating at 130 占 폚 to remove the solvent. The elongated laminate was subjected to heat treatment for a total time of about 6 minutes in a continuous curing furnace in which the temperature of the laminate was set so that the temperature was gradually increased from 130 ° C to 300 ° C step by step to obtain a single- To obtain a copper clad laminate. The evaluation results of physical properties such as tensile modulus of elasticity and the like of the polyimide layer and the copper foil constituting the flexible copper-clad laminate, the thickness, the thickness ratio of the polyimide layer and the copper foil, the folding coefficient and the bending resistance (folding number) of the flexible copper clad laminate are shown in Table 1 (The same applies to the second and subsequent embodiments). The evaluation of the polyimide layer was performed by removing the copper foil from the produced flexible copper-clad laminate.

Here, specific calculation procedures will be described with respect to the calculation of the folding coefficient [PF] of the flexible copper clad laminate produced in the embodiment, taking Example 1 as an example.

With respect to the wiring portion in which the copper wiring 12 is present, a two-layer structure as shown in Fig. 8 is considered, and the materials constituting the first and second layers are made of polyimide and copper, respectively. As shown in Table 1 (Example 1), the elastic modulus of each layer is E ₁ = 4 GPa, E ₂ = 29 GPa, thickness t ₁ = 25 μm, and t ₂ = 12 μm. Moreover, each distance h ₁ = 12.5 ㎛ of thickness direction center plane and the reference plane SP in the each layer, h is ₂ = 31 ㎛. With respect to the width B, the width B ₂ of the copper wiring 12 and the width B _{2 '} of the space portion were both 100 μm, and the width B ₁ of the polyimide immediately below the copper wiring 12 was also 100 μm (The width B _{1 '} of the polyimide immediately below the space portion is also 100 μm).

Substituting these values into the equation (3), the position of the neutral plane in the wiring portion where the copper wiring 12 exists first is calculated as [NP] _Line = 26.9 mu m. Then, substituting this neutral plane position [NP] _Line and the gap gap G = 0.3 mm into equation (4), the effective bending radius R is calculated to be 0.123 mm. In addition, the reference surface because the distance yc is yc = h is ₂ = 31 ㎛ to the center plane of the SP and the copper wiring 12, the winding average strain ε is calculated previously and the yc [NP] _Line, equation (2) the value of R And is calculated as? = -0.0333. Here, the minus sign indicates compression distortion. From the stress-strain curve obtained from the tensile test of the copper foil of the copper wiring in Example 1, the tensile elastic limit strain? C of the copper wiring was determined to be? C = 0.00058. Substituting this and the obtained bending average distortion ε into equation (I), the folding modulus [PF] is calculated as [PF] = 0.983. In the present embodiment, the operation of obtaining [NP] is not necessary because the space portion is composed only of the polyimide layer, and the folding coefficient [PF] of the other examples and comparative examples in Table 1 to be.

(Example 2)

The resin solution of polyamic acid a prepared in Synthesis Example 1 was uniformly applied to a surface of a commercially available electrolytic copper foil having a thickness of 12 占 퐉 and having a thickness of 2.0 占 퐉 after being cured (surface roughness Rz = 1.2 占 퐉) After that, it was dried by heating at 130 DEG C to remove the solvent. Subsequently, the resin solution of polyamic acid c prepared in Synthesis Example 3 was coated uniformly on the coated surface side so as to have a thickness of 16 탆 after curing, and then dried by heating at 130 캜 to remove the solvent. The same resin solution of polyamic acid a as applied on the first layer was coated uniformly on the coated side so that the thickness after curing became 2.0 占 퐉, and the resultant was dried by heating at 130 占 폚 to remove the solvent. The laminate of this elongated shape was subjected to heat treatment for a total of about 6 minutes in a continuous curing furnace in which the temperature was raised stepwise from 300 ° C to 130 ° C for a total of six minutes to obtain a one-sided flexible To obtain a copper clad laminate. Table 1 shows the evaluation results of the bendability of the obtained single-sided flexible copper-clad laminate.

(Example 3)

A resin solution of polyamic acid a prepared in Synthesis Example 1 was uniformly applied to a surface of a commercially available electrolytic copper foil having a thickness of 12 占 퐉 and having a thickness of 2.2 占 퐉 after curing on one surface (surface roughness Rz = 1.2 占 퐉) After that, it was dried by heating at 130 DEG C to remove the solvent. Subsequently, the resin solution of polyamic acid c prepared in Synthesis Example 3 was uniformly applied to the coated side so that the thickness after curing was 7.6 占 퐉, and the solvent was removed by heating at 130 占 폚. The same polyamic acid a resin solution as applied on the first layer was coated uniformly on the coated surface side so that the thickness after curing became 2.2 占 퐉, and then dried by heating at 130 占 폚 to remove the solvent. The laminate of this elongated shape was subjected to a heat treatment for a total of about 6 minutes in a continuous curing furnace in which the temperature was set to be gradually increased from 130 캜 to 300 캜 in a stepwise manner to obtain a single- To obtain a copper clad laminate. Table 1 shows the evaluation results of the bendability of the obtained single-sided flexible copper-clad laminate.

(Example 4)

The resin solution of polyamic acid a prepared in Synthesis Example 1 was uniformly applied to a surface of a commercially available electrolytic copper foil having a thickness of 12 占 퐉 and having a thickness of 2.0 占 퐉 after being cured on one surface (surface roughness Rz = 1.20 占 퐉) After that, it was dried by heating at 130 DEG C to remove the solvent. Subsequently, the resin solution of polyamic acid c prepared in Synthesis Example 3 was uniformly applied to the coated side so that the thickness after curing became 5.0 占 퐉, and the resultant was dried by heating at 130 占 폚 to remove the solvent. The same resin solution of polyamic acid a as applied on the first layer was coated uniformly on the coated side so that the thickness after curing became 2.0 占 퐉, and the resultant was dried by heating at 130 占 폚 to remove the solvent. The laminate of this elongated shape was subjected to heat treatment for a total of about 6 minutes in a continuous curing furnace in which the temperature was raised stepwise from 300 DEG C to 130 DEG C for a total of 6 minutes to obtain a one-sided flexible To obtain a copper clad laminate. Table 1 shows the evaluation results of the bendability of the obtained single-sided flexible copper-clad laminate.

(Example 5)

A flexible copper clad laminate was obtained in the same manner as in Example 4 except that one surface (surface roughness Rz = 1.2 占 퐉) of a commercially available electrolytic copper foil having a thickness of 9 占 퐉 and a long shape was used. Table 1 shows the evaluation results of flexural resistance of the obtained flexible copper clad laminate.

(Example 6)

A flexible copper clad laminate was obtained in the same manner as in Example 3 except that one side (surface roughness Rz = 1.9 mu m) of a commercially available electrolytic copper foil having a thickness of 12 mu m and a long shape was used. Table 1 shows the evaluation results of the endurance sag of the obtained flexible copper clad laminate.

(Example 7)

A flexible copper clad laminate was obtained in the same manner as in Example 3 except that one surface (surface roughness Rz = 1.2 占 퐉) of a commercially available electrolytic copper foil having a thickness of 9 占 퐉 and a long shape was used. Table 1 shows the evaluation results of flexural resistance of the obtained flexible copper clad laminate.

(Example 8)

A flexible copper clad laminate was obtained in the same manner as in Example 3 except that one surface (surface roughness Rz = 2.2 占 퐉) of a commercially available electrolytic copper foil having a thickness of 12 占 퐉 and a long shape was used. Table 1 shows the evaluation results of flexural resistance of the obtained flexible copper clad laminate.

(Comparative Example 1)

Except that one surface (surface roughness Rz = 1.2 占 퐉) of a commercially available electrolytic copper foil having a thickness of 12 占 퐉 and a characteristic shown in Table 1 was used and the thickness of the polyimide layer was changed as follows. A flexible copper-clad laminate was obtained in the same manner as in Example 1. Here, the thickness of the polyimide layer was measured by the same method as in Example 1 except that the resin solution of polyamic acid a prepared in Synthesis Example 1 had a thickness of 4.0 mu m after curing and a resin solution of polyamic acid b prepared in Synthesis Example 2 thereon The thickness after curing was 42.0 占 퐉, and the resin solution of polyamic acid a prepared in Synthesis Example 1 had a thickness of 4.0 占 퐉 after curing. Table 1 shows the evaluation results of the bendability of the obtained flexible copper clad laminate.

(Comparative Example 2)

Except that one surface (surface roughness Rz = 2.0 占 퐉) of a commercially available electrolytic copper foil having a thickness of 12 占 퐉 and a thickness of 12 占 퐉 and a characteristic shown in Table 1 was used and the thickness of the polyimide layer was changed as follows. A flexible copper-clad laminate was obtained in the same manner as in Example 2. Here, the thickness of the polyimide layer was measured by the same method as in Example 1, except that the resin solution of polyamic acid a prepared in Synthesis Example 1 had a thickness of 3.0 mu m after curing and a resin solution of polyamic acid c prepared in Synthesis Example 3 thereon The thickness after curing was 32.0 占 퐉, and further, the resin solution of polyamic acid a prepared in Synthesis Example 1 had a thickness after curing of 3.0 占 퐉.

(Comparative Example 3)

Except that one surface (surface roughness Rz = 1.8 占 퐉) of a commercially available electrolytic copper foil having the characteristics shown in Table 1 and having a thickness of 12 占 퐉 and a long shape was used and the thickness composition of the polyimide layer was changed as follows, A flexible copper-clad laminate was obtained in the same manner as in Example 2. Here, the thickness of the polyimide layer was measured by the same method as in Example 1 except that the resin solution of polyamic acid a prepared in Synthesis Example 1 was applied on the copper foil to a thickness of 2.5 mu m after curing, The thickness after curing was 20.0 占 퐉, and further, the resin solution of polyamic acid a prepared in Synthesis Example 1 had a thickness after curing of 2.5 占 퐉.

Table 1 shows that the thickness of the polyimide layer is 5 to 30 占 퐉, the tensile elastic modulus is 4 to 10 GPa, the thickness of the copper foil is 6 to 20 占 퐉, the tensile elastic modulus is 25 to 35 GPa, The flexible copper clad laminate of Examples 1 to 8, in which the ten point average roughness Rz of the copper foil on the surface in contact with the copper foil in the range of 0.7 to 2.2 탆 and the folding modulus [PF] within the range of 0.96 ± 0.025, It was a result. On the other hand, in Comparative Examples 1 and 2 in which the thickness of the polyimide layer exceeded 30 占 퐉 and in Comparative Example 3 in which the tensile modulus of the copper foil exceeded 35 GPa, the number of times of folding was small and the bending resistance was poor.

While the embodiments of the present invention have been described in detail for the purpose of illustration, the present invention is not limited to the above embodiments.

1: circuit board
11: polyimide layer
12, 51: Copper wiring
20, 21: sample stage
22: Rollers
40: Specimen
40C: Bending point of specimen
52: U-shaped portion of copper wiring

Claims (5)

A flexible copper-clad laminate used in a flexible circuit board folded and housed in a housing of an electronic device,
A polyimide layer (A) having a thickness in the range of 5 to 30 mu m and a tensile modulus within a range of 4 to 10 GPa,
And a copper foil (B) laminated on at least one surface of the polyimide layer (A) and having a tensile elastic modulus within a range of from 25 to 35 GPa in a thickness of 6 to 20 mu m,
Wherein the copper foil on the side contacting the polyimide layer (A) has a ten-point average roughness (Rz) in the range of 0.7 to 2.2 占 퐉 and the copper foil (B) Wherein a folding modulus [PF] calculated by the following formula (I) in a folding test at a gap of 0.3 mm of the flexible circuit board of the flexible copper clad laminate is within a range of 0.96 + 0.025.

Is the absolute value of the bending average distortion value of the copper wiring, and? _C is the tensile elastic limit distortion of the copper wiring) The method of claim 1 wherein the polyimide layer (A) has a thermal expansion coefficient 30 × 10 ^-6 / K is less than the low thermal expansion of the polyimide layer (i) and a thermal expansion coefficient 30 × 10 ^-6 / K or more high thermal expansion properties of the polyimide Layer (ii), wherein the polyimide layer (ii) having a high thermal expansion is directly in contact with the copper foil (B). The flexible copper clad laminate according to Claim 1 or 2, wherein the thickness of the polyimide layer (A) is in the range of 8 to 15 탆 and the tensile elastic modulus is in the range of 6 to 10 GPa. The multilayer printed wiring board according to any one of claims 1 to 3, wherein the polyimide layer (A) and the copper foil (B) have a thickness ratio (polyimide layer (A) / copper foil (B) Laminates. The flexible copper-clad laminate according to any one of claims 1 to 4, wherein the copper foil (B) is an electrolytic copper foil.

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