JP6284325B2 - Flexible copper clad laminate - Google Patents

Description

  The present invention relates to a flexible copper clad laminate used for a flexible circuit board that is folded and accommodated in a casing of an electronic device.

  In recent years, electronic devices represented by mobile phones, notebook computers, digital cameras, game machines, and the like have been rapidly reduced in size, thickness, and weight. High-density, high-performance materials that can accommodate components are desired. Also in flexible circuit boards, with the spread of high-performance small electronic devices such as smartphones, the density of parts storage has increased, so it has become necessary to store flexible circuit boards in smaller enclosures than ever before. Yes. Therefore, the flexible copper-clad laminate, which is a material for the flexible circuit board, has been demanded to improve the bending resistance from the material surface.

  Technology to improve the bending resistance by reducing the total stiffness of the flexible circuit board by controlling the elastic modulus of the polyimide base film and cover film used in the flexible copper-clad laminate, Is known (see Patent Document 1). However, controlling the properties of polyimide and cover film alone is not sufficient for the strict bending mode of folding and storing in electronic equipment, and it can be used for flexible circuit boards with excellent folding resistance. A copper clad laminate cannot be provided.

  In addition, from the viewpoint of increasing the density in electronic equipment, as an approach from the copper foil side, focusing on the crystal grain size of the copper foil, a copper foil for heat treatment with reduced springback resistance has been reported. (See Patent Document 2). This technology uses a rolled copper foil with various appropriate additives in the copper foil to increase the crystal grain size by applying a sufficient amount of heat to enlarge the crystal grains. As a result, the copper foil It is a technology that tries to improve the spring back resistance.

  However, further miniaturization is demanded for small electronic devices typified by smartphones. For this reason, it is difficult to meet the demand for higher density with the conventional technology alone.

JP 2007-208087 A JP 2010-280191 A

  The present invention has been made in view of the above problems. The object is to provide a flexible copper-clad laminate having excellent bending resistance that can prevent disconnection and cracking of a wiring circuit even in a narrow housing.

  As a result of the study by the present inventors to solve the above-mentioned problems, the characteristics of the copper foil and the polyimide film are optimized, and attention is paid to the characteristics of the wiring circuit board obtained by processing the copper-clad laminate. The present inventors have found that a copper-clad laminate that can solve the above-mentioned problems can be provided.

（式（Ｉ）において、|ε|は銅配線の屈曲平均ひずみ値の絶対値であり、e _Cは銅配線の引張弾性限界ひずみである。） That is, the present invention has a thickness of 10 to 25 μm, a thickness of 8 to 20 μm, a tensile modulus of 10 to 20 GPa on at least one surface of the polyimide layer (A) having a tensile modulus of 4 to 10 GPa, and A flexible copper-clad laminate used for a flexible circuit board having a copper foil (B) having an average crystal grain size of 10 μm or more in a cross section in the thickness direction and being folded and housed in a casing of an electronic device, Folding coefficient [PF] calculated by the following formula (I) in a bending test at a gap of 0.3 mm of an arbitrary flexible circuit board in which copper wiring of a flexible copper-clad laminate is processed by wiring circuit processing Is a flexible copper-clad laminate characterized by having a range of 0.96 ± 0.02.

(In formula (I), | ε | is the absolute value of the bending average strain value of the copper wiring, and e _C is the tensile elastic limit strain of the copper wiring.)

The flexible copper-clad laminate, a polyimide layer (A), the thermal expansion coefficient of 30 × 10 ^-6 / K less than the low thermal expansion polyimide layer (i) and the thermal expansion coefficient of 30 × 10 ^-6 / K or more high heat It is preferably composed of an expandable polyimide layer (ii), and the high thermal expansion polyimide layer (ii) is in direct contact with the copper foil (B). In addition, preferably, the surface roughness (Rz) of the copper foil (B) at the contact surface between the high thermal expansion polyimide layer (ii) and the copper foil (B) is in the range of 0.5 to 1.5 μm. It is good.

  The polyimide layer (A) preferably has a tensile modulus in the range of 6 to 10 GPa and a thickness in the range of 10 to 15 μm, and further, in the thickness direction of the copper foil (B). The average crystal grain size in the cross section is preferably in the range of 10 to 60 μm.

  Since the flexible copper-clad laminate of the present invention can express the high bending resistance required for wiring boards, it is particularly suitable for electronic components that require bending resistance such as bent portions around small liquid crystals such as smartphones. Preferably used.

FIG. 1 is a perspective explanatory view showing a flexible circuit board obtained by processing a copper foil of the flexible copper-clad laminate of the present invention on a wiring circuit. It is plane explanatory drawing which shows the mode of the copper wiring of the test circuit board piece used in the Example. It is side surface explanatory drawing which shows the mode of the sample stage and test circuit board piece in a bending test (state figure which fixed the test circuit board piece on the sample stage). It is side surface explanatory drawing which shows the mode of the sample stage and test circuit board piece in a bending test (state figure before pressing the bending location of a test circuit board piece with a roller). It is side surface explanatory drawing which shows the mode of the sample stage and test circuit board piece in a bending test (state figure which pressed the bending location of the test circuit board piece with the roller). It is side surface explanatory drawing which shows the mode of the sample stage and test circuit board piece in a bending test (the state figure which opened the bending location and returned the test piece to the flat state). It is side surface explanatory drawing which shows the mode of the sample stage and test circuit board piece in a bending test (state figure which presses and equalizes the crease | fold part of a bending location with a roller). It is a section explanatory view (part) of a flexible circuit board.

Hereinafter, the present invention will be described in detail.
The flexible copper clad laminate of the present invention is composed of a copper foil (B) and a polyimide layer (A). The copper foil (B) is provided on one side or both sides of the polyimide layer (A). This flexible copper clad laminate is used for a flexible printed circuit board by forming a copper wiring by etching a copper foil to form a wiring circuit.

  In the flexible copper clad laminate of the present invention, the polyimide layer (A) needs to have a thickness of 10 to 25 μm, preferably in the range of 10 to 20 μm, and in the range of 10 to 15 μm. Particularly preferred. If the thickness of the polyimide layer (A) is less than 10 μm, problems such as inability to secure electrical insulation and difficulty in handling in the manufacturing process due to a decrease in handling properties occur, while the polyimide layer (A ) Exceeds 25 μm, bending stress is applied by the copper wiring when the flexible circuit board is bent, and the bending resistance is remarkably lowered.

  The tensile modulus of the polyimide layer (A) needs to be 4 to 10 GPa, preferably 6 to 10 GPa. If the tensile modulus of the polyimide layer (A) is less than 4 GPa, the strength of the polyimide itself will decrease, causing problems such as film tearing when handling flexible copper clad laminates. If it exceeds 10 GPa, the bending resistance of the copper-clad laminate is increased. As a result, the bending stress applied to the copper wiring when the copper-clad laminate is bent is increased, and the bending resistance is reduced.

  Moreover, the thickness of copper foil (B) needs to be 8-20 micrometers, and the range of 10-15 micrometers is preferable. If the thickness of the copper foil (B) is less than 8 μm, the rigidity of the copper foil itself is lowered in the process of forming the polyimide layer on the copper foil during the production of the copper clad laminate, and as a result, on the copper clad laminate There arises a problem that wrinkles and the like occur. On the other hand, when the thickness exceeds 20 μm, the bending resistance is reduced due to an increase in bending stress applied to the copper foil when the copper clad laminate is bent.

  Moreover, about the tensile elasticity modulus of copper foil (B), it is required to be the range of 10-20 GPa. If the tensile modulus of the copper foil (B) is less than 10 GPa, the rigidity of the copper foil itself is lowered in the process of forming the polyimide layer on the copper foil during the production of the copper clad laminate, and as a result, the copper clad laminate The problem that wrinkles etc. generate | occur | produce on a board arises. On the other hand, when the tensile elastic modulus exceeds 20 GPa, a large bending stress is applied to the copper wiring when the flexible circuit board is bent, and the bending resistance is remarkably lowered.

  Furthermore, in this invention, it is required that the average crystal grain diameter in the cross section of the thickness direction of copper foil is 10 micrometers or more, and it is preferable that it is 10-60 micrometers. When this average crystal grain size is smaller than 10 μm, the ratio of the crystal grain boundaries of the copper foil is increased, and the extension of cracks generated when the copper-clad laminate is folded is further promoted. Will lead to a decline in sex. In addition, the average crystal grain diameter in the copper foil cross section prescribed | regulated by this invention can be calculated | required with the measuring method described in the postscript Example.

  The surface of the copper foil (B) may be roughened, and preferably the surface roughness (Rz) of the copper foil surface in contact with the polyimide layer (A) is 0.5 to 1.5 μm. Good. If the value of the surface roughness (Rz) is less than 0.5 μm, it will be difficult to ensure the reliability of adhesion to the polyimide film, and if it exceeds 1.5 μm, the copper-clad laminate will be roughened when it is repeatedly bent. The unevenness of the particles tends to be a starting point of crack generation, and as a result, the bending resistance of the copper clad laminate is lowered. The surface roughness Rz is a value measured according to JIS B0601.

The flexible copper-clad laminate of the present invention is composed of the polyimide layer (A) and the copper foil (B). The copper foil of this flexible copper-clad laminate is processed by a wiring circuit to form a copper wiring. The bending coefficient [PF] calculated by (I) below in the flexible circuit board bending test (gap 0.3 mm) must be in the range of 0.96 ± 0.02, and in the range of 0.96 ± 0.01. It is more preferable. If this crease coefficient [PF] is out of the above range, the bending resistance decreases.
[PF] = (| ε | −εc) / | ε | (I)
In equation (I), | ε | is the absolute value of the bending average strain value of the copper wiring, and εc is the tensile elastic limit strain of the copper wiring.

As described above, the bending coefficient [PF] is expressed by the absolute value | ε | of the bending average strain value ε of the copper wiring and the tensile elastic limit strain εc of the copper wiring. Calculated by (2). Hereinafter, a polyimide substrate, which is a first layer, is modeled on a circuit board provided with a copper wiring 12 in which a single layer of copper foil is processed into a wiring circuit on one side of a polyimide layer 11 made of one layer of polyimide shown in FIG. The case where the circuit board is bent so that the reference surface SP, which is the lower surface of No. 11, is convex downward (outer surface of the bent portion) will be described. The circuit board shown in FIG. 8 shows a portion where copper wiring exists in a cross section (that is, a transverse cross section) cut perpendicular to the longitudinal direction of the circuit board.
ε = (yc− [NP] _Line ) / R (2)

Here, with respect to Equation (2), the bending average strain ε is the bending average strain in the longitudinal direction generated in the copper wiring by pure bending when the longitudinal direction of the circuit board is folded in half, and yc in the equation is the polyimide layer 11 is a distance from the reference plane SP, which is the lower surface of 11, to the center plane of the copper wiring 12. The symbol NP represents the neutral plane of the circuit board. Here, the distance between the neutral plane NP and the reference plane SP is defined as a neutral plane position [NP]. With respect to the neutral plane position [NP], a copper wiring and a copper wiring formed by wiring circuit processing of copper foil It calculates separately with the space part formed between. The neutral plane position [NP] is calculated by the following equation (3).

Here, E _i is the tensile modulus 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. It is. This elastic modulus E _i corresponds to “relation between stress and strain in each layer” in the present embodiment. B _i is the width of the i-th layer and corresponds to the width B shown in FIG. 8 (dimension in the direction parallel to the lower surface of the first layer and perpendicular to the longitudinal direction of the circuit board).

In case of obtaining the neutral plane position of the copper wiring [NP], when a B _i using the values of the line width LW of the copper wiring, obtaining the neutral plane position of the space portion [NP], the copper as B _i The value of the line width SW of the wiring is used. h _i is the distance between the center plane of the i-th layer and the reference plane SP. The central surface of the i-th layer is a virtual surface located at the center in the thickness direction of the i-th layer. t _i is the thickness of the i-th layer. Further, the symbol “Σ _{i = 1} ⁿ ” represents the sum of i from 1 to n. The neutral plane position in the copper wiring is denoted as [NP] _Line .

Further, R in the expression (2) represents an effective radius of curvature, and the effective radius of curvature R is a distance from the bending center of the bent portion to the neutral plane NP of the copper wiring when the circuit board is bent in the bending test. is there. That is, the effective curvature radius R is calculated by the following equation (4) from the gap interval G and the neutral plane position [NP] _{Line of the} copper wiring.
R = G / 2- [NP] _Line (4)

  As described above, the crease coefficient [PF] representing the degree of crease of the entire circuit board is calculated by obtaining the neutral plane position, effective radius of curvature, and bending average strain. Further, as described above, the folding coefficient [PF] is the thickness of each layer constituting the circuit board, the elastic modulus of each layer constituting the circuit board, the gap interval G in the bending test, and the copper wiring 12. It can be calculated using each information such as the line width LW.

  In the above description (FIG. 8), for the sake of convenience, the model in which the circuit board has two layers has been described. However, the above description also applies to the case where the circuit board is formed of two or more layers. That is, when the number of layers of the circuit board 1 is n, n is an integer equal to or greater than 2, and the i-th (i = 1, 2,... The layer n) is called the i-th layer.

  Further, as shown in FIG. 1, the circuit board has a copper foil patterned by wiring circuit processing, and has a portion where the copper wiring 12 is present and a portion where the copper wiring 12 is not present. Here, if a portion where the copper wiring 12 exists is called a wiring portion and a portion where the copper wiring 12 does not exist is called a space portion, the wiring portion and the space portion have different configurations. For example, in the case of the circuit board 1 shown in FIG. 1, the wiring part is constituted by 10 rows of copper wirings, and the space part is constituted by a gap between the copper wirings except for the wiring part. As described above, the folding coefficient can be calculated separately for the wiring portion and the space portion.

  The flexible copper-clad laminate of the present invention can be produced, for example, by applying a polyimide precursor resin solution (also referred to as a polyamic acid solution) to the surface of the copper foil, followed by drying and curing. The heat treatment condition in the heat treatment step is that after the solvent in the polyamic acid is dried and removed from the coated polyamic acid solution at a temperature of less than 160 ° C., the temperature is raised stepwise in a temperature range of 150 ° C. to 400 ° C., This is done by curing. In order to make the single-sided flexible copper-clad laminate obtained in this way into a double-sided copper-clad laminate, the single-sided flexible copper-clad laminate and a copper foil prepared separately were heated at 300 to 400 ° C. The method of crimping is mentioned.

  The copper foil used for the flexible copper clad laminate of the present invention is not particularly limited as long as it satisfies the above characteristics, and a commercially available copper foil can be used. Specific examples include HA foil and TP foil manufactured by JX Nippon Mining & Metals Co., Ltd. as rolled copper foil, and WS foil manufactured by Furukawa Electric Co., Ltd. and Nippon Electrolytic Co., Ltd. as electrolytic copper foil. Examples include HL foil and HTE foil manufactured by Mitsui Mining & Smelting Co., Ltd. Moreover, even if it is a case where other than that including these commercial items is used, according to the heat processing conditions at the time of forming the polyimide layer (A) on copper foil mentioned above, copper foil (B) Since the tensile modulus of elasticity and the average crystal grain size can vary, the resulting flexible copper-clad laminate need only be in these predetermined ranges in the present invention.

  As the polyimide layer (A), a commercially available polyimide film can be used as it is. However, in order to easily control the thickness and physical properties of the insulating layer, the polyamic acid solution is directly applied on the copper foil, followed by heat treatment. It is preferable to use a so-called casting method that dries and hardens. Moreover, although a polyimide layer (A) may be formed only from a single layer, when the adhesiveness etc. of a polyimide layer (A) and copper foil (B) are considered, what consists of multiple layers is preferable. When the polyimide layer (A) has a plurality of layers, it can be formed by sequentially applying another polyamic acid solution on a polyamic acid solution composed of different components. When a polyimide layer (A) consists of multiple layers, you may use the polyimide precursor resin of the same structure twice or more.

The polyimide layer (A) will be described in more detail. As described above, the polyimide layer (A) is preferably a plurality of layers. Specifically, the polyimide layer (A) has a thermal expansion coefficient of 30 × 10 ^−6. It is preferably composed of a low thermal expansion polyimide layer (i) less than / K and a high thermal expansion polyimide layer (ii) having a thermal expansion coefficient of 30 × 10 ⁻⁶ / K or more. More preferably, the polyimide layer (A) has a high thermal expansion polyimide layer (ii) having at least one of the low thermal expansion polyimide layers (i), preferably the high thermal expansion polyimide layers (ii) on both sides thereof. ) May be in direct contact with the copper foil (B). Here, the low thermal expansion polyimide layer (i) referred to in the present invention refers to a polyimide layer having a thermal expansion coefficient of less than 30 × 10 ⁻⁶ / K, preferably 1 × 10 ^{−6 to} 25 × 10 ⁻⁶ / K, particularly preferably a polyimide layer of 3 × 10 ^{−6 to} 20 × 10 ⁻⁶ / K. The high thermal expansion polyimide layer (ii) in the present invention 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, it refers to a polyimide layer of 30 × 10 ⁻⁶ to 70 × 10 ⁻⁶ / K. Such a polyimide layer can be made into a polyimide layer having a desired thermal expansion coefficient by appropriately changing the combination of raw materials used, thickness, and drying / curing conditions.

  The polyamic acid solution that gives the polyimide layer can be produced by polymerizing a known diamine and acid anhydride in the presence of a solvent, and the viscosity of the polymerized resin ranges from 500 cps to 35,000 cps. It is preferable that

  Examples of the diamine used include 4,6-dimethyl-m-phenylenediamine, 2,5-dimethyl-p-phenylenediamine, 2,4-diaminomesitylene, 4,4′-methylenedi-o-toluidine, 4'-methylenedi-2,6-xylidine, 4,4'-methylene-2,6-diethylaniline, 2,4-toluenediamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylpropane 3,3'-diaminodiphenylpropane, 4,4'-diaminodiphenylethane, 3,3'-diaminodiphenylethane, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 2,2-bis [ 4- (4-aminophenoxy) phenyl] propane, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4, 4'-diaminodiphenyl ether, 3, 3-diaminodiphenyl ether, 1,3-bis (3-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, benzidine, 3,3 ' -Diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethoxybenzidine, 4,4'-diamino-p-terphenyl, 3,3'-diamino-p-terphenyl Bis (p-aminocyclohexyl) methane, bis (p-β-amino-t-butylphenyl) ether, bis (p-β-methyl-δ-aminopentyl) benzene, p-bis (2-methyl-4- Aminopentyl) benzene, p-bis (1,1-dimethyl-5-aminopentyl) benzene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,4-bis (β-amino-t-butyl) Toluene, 2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine, m-xylylenediamine, p-chi Silylenediamine, 2,6-diaminopyridine, 2,5-diaminopyridine, 2,5-diamino-1,3,4-oxadiazole, piperazine, 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,7-diaminodibenzofuran, 1,5-diaminofluorene, dibenzo-p-dioxin-2,7-diamine, 4,4′-diaminobenzyl and the like can be mentioned.

  Examples of the acid anhydride include pyromellitic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride, and 2,2 ′, 3,3′-benzophenone tetracarboxylic acid dianhydride. Anhydride, 2,3,3 ', 4'-benzophenonetetracarboxylic dianhydride, naphthalene-1,2,5,6-tetracarboxylic dianhydride, naphthalene-1,2,4,5-tetracarboxylic Acid dianhydride, naphthalene-1,4,5,8-tetracarboxylic dianhydride, naphthalene-1,2,6,7-tetracarboxylic dianhydride, 4,8-dimethyl-1,2,3 , 5,6,7-Hexahydronaphthalene-1,2,5,6-tetracarboxylic dianhydride, 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-2, 3,6,7-tetracarboxylic dianhydride, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,7-dichloronaphthalene-1,4,5,8- Tetracarboxylic dianhydride, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic acid Anhydride, 1,4,5,8-tetrachloronaphthalene-2,3,6,7-tetracarboxylic dianhydride, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride, 2, 2 ', 3,3'-biphenyltetracarboxylic dianhydride, 2,3,3', 4'-biphenyltetracarboxylic dianhydride, 3,3``, 4,4 ''-p-terphenyl Tetracarboxylic dianhydride, 2,2``, 3,3 ''-p-terphenyltetracarboxylic dianhydride, 2,3,3 '', 4 ''-p-terphenyltetracarboxylic dianhydride Anhydride, 2,2-bis (2,3-dicarboxyphenyl) -propane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) -propane dianhydride, bis (2,3-di Carboxyphenyl) ether dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3.4-dicarboxyphenyl) methane dianhydride, bis (2,3-dicarboxyphenyl) sulfone dianhydride Bis (3,4-dicarboxyphenyl) sulfone dianhydride, 1,1- (2,3-dicarboxyphenyl) ethane dianhydride, 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride, perylene-2,3,8,9-tetracarboxylic dianhydride Perylene-3,4,9,10-tetracarboxylic dianhydride, perylene-4,5,10,11-tetracarboxylic dianhydride, perylene-5,6,11,12-tetracarboxylic dianhydride Phenanthrene-1,2,7,8-tetracarboxylic dianhydride, phenanthrene-1,2,6,7-tetracarboxylic dianhydride, phenanthrene-1,2,9,10-tetracarboxylic dianhydride Anhydride, cyclopentane-1,2,3,4-tetracarboxylic dianhydride, pyrazine-2,3,5,6-tetracarboxylic dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic Acid dianhydride, thiophene-3,4,5-tetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride It is done.

  Each diamine and acid anhydride may be used alone or in combination of two or more. Examples of the solvent used for the polymerization include dimethylacetamide, N-methylpyrrolidinone, 2-butanone, diglyme, xylene and the like, and they can be used alone or in combination of two or more.

In the present invention, in order to obtain a low thermal expansion polyimide layer (i), pyromellitic dianhydride and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride are used as the raw acid anhydride component. As the diamine component, 2,2′-dimethyl-4,4′-diaminobiphenyl, 2-methoxy-4,4′-diaminobenzanilide is preferably used, and particularly preferably pyromellitic dianhydride and It is preferable that 2,2′-dimethyl-4,4′-diaminobiphenyl is a main component of each component. Further, in order to obtain a high thermal expansion polyimide layer (ii) having a thermal expansion coefficient of 30 × 10 ⁻⁶ / K or more, pyromellitic dianhydride, 3,3 ′, 4,4 is used as the raw acid anhydride component. '-Biphenyltetracarboxylic dianhydride, 3,3', 4,4'-benzophenonetetracarboxylic dianhydride, 3,3 ', 4,4'-diphenylsulfone tetracarboxylic dianhydride, diamine component 2,2′-bis [4- (4-aminophenoxy) phenyl] propane, 4,4′-diaminodiphenyl ether, and 1,3-bis (4-aminophenoxy) benzene are particularly preferable. It is preferable that pyromellitic dianhydride and 2,2′-bis [4- (4-aminophenoxy) phenyl] propane are the main components of the raw materials.

  When the polyimide layer (A) is a low thermal expansion polyimide layer (i) and a high thermal expansion polyimide layer (ii), preferably, the low thermal expansion polyimide layer (i) and the high thermal expansion polyimide layer are used. The thickness ratio (low thermal expansion polyimide layer (i) / high thermal expansion polyimide layer (ii)) to (ii) is preferably in the range of 2 to 15. If the value of this ratio is less than 2, the low thermal expansion polyimide layer with respect to the entire polyimide layer becomes thin, so it becomes difficult to control the dimensional characteristics of the polyimide film, and the dimensional change rate when the copper foil is etched increases. If it exceeds 15, the high thermal expansion polyimide layer becomes thin, so that the reliability of adhesion between the polyimide film and the copper foil is lowered. Even when the polyimide layer (A) is composed of a plurality of layers, the thickness and elastic modulus of the entire polyimide layer (A) can be used for calculating the folding coefficient [PF].

  Hereinafter, based on an Example, this invention is demonstrated in detail. In addition, each characteristic evaluation in the following Example was performed with the following method.

[Measurement of tensile modulus]
The value of tensile elastic modulus was measured in an environment of a temperature of 23 ° C. and a relative humidity of 50% using Toyo Seiki Co., Ltd. Strograph R-1.

[Measurement of thermal expansion coefficient (CTE)]
Using a thermomechanical analyzer manufactured by Seiko Instruments Inc., heated up to 250 ° C, held at that temperature for 10 minutes, cooled at a rate of 5 ° C / min, and an average coefficient of thermal expansion from 240 ° C to 100 ° C ( (Linear thermal expansion coefficient) was determined.

[Measurement of surface roughness (Rz)]
The surface roughness of the contact surface side with the polyimide layer of copper foil was measured using the contact-type surface roughness measuring machine (SE1700 by Kosaka Laboratory).

[Measurement of average crystal grain size of copper foil]
For the flexible copper-clad laminate produced in each example, by the IP (ion polish) method, the copper foil cross-section is formed along the longitudinal direction (MD direction) of the copper foil (cross-section cut in the thickness direction), The crystal grain size and orientation state of the copper foil cross section were analyzed by EBSD (backscattered electron diffraction pattern method) using OSL (software Ver5.2) manufactured by TSL. The analysis was performed under the conditions of an acceleration voltage of 20 kV and a sample inclination angle of 70 °, and the analysis range was analyzed with a width of 500 μm along the longitudinal direction of the copper foil. From the reverse pole figure orientation map obtained in the analysis, grain size distribution analysis is performed under the condition that Σ3CSL (twin grain boundary) is the grain boundary and 2-5 ° grain boundary is not the grain boundary. The crystal grain size was calculated by a weighted average based on the ratio.

[Measurement of seam fold (bending test)]
Etching the copper foil of the copper-clad laminate to produce test pieces (test circuit board pieces) in which 10 rows of copper wiring with a line width of 100 μm and a space width of 100 μm and a length of 40 mm are formed along the longitudinal direction. (FIG. 2). As shown in FIG. 2 showing only the copper wiring in the test piece, ten rows of copper wirings 51 in the test piece 40 are all continuously connected via the U-shaped portion 52, and resistances are connected to both ends thereof. An electrode portion (not shown) for value measurement is provided. The test piece 40 was fixed on the sample stages 20 and 21 which can be folded in half, and a resistance value measurement wiring was connected to start monitoring of the resistance value (FIG. 3). In the bending test, 10 rows of copper wirings 51 were bent using a urethane roller 22 at a central portion in the longitudinal direction while controlling the gap G of the folding portion 40C to be 0.3 mm. After moving the roller parallel to the line and bending all 10 rows of copper wiring 51 (FIGS. 4 and 5), the bent portion is opened to return the test piece to a flat state (FIG. 6), and the creased portion Was moved again while being held down by the roller (FIG. 7), and the number of times of folding was counted by this series of steps. While constantly monitoring the resistance value of the wiring, the bending test was repeated, and when the predetermined resistance (3000 Ω) was reached, it was judged that the wiring was broken, and the number of repeated bendings up to that time was taken as the measured value of the folded fold.

  The method for producing the flexible copper-clad laminate described in Examples and Comparative Examples will be described below.

[Synthesis of polyamic acid solution]
(Synthesis Example 1)
A reaction vessel equipped with a thermocouple and a stirrer and capable of introducing nitrogen is charged with N, N-dimethylacetamide, and 2,2-bis [4- (4-aminophenoxy) phenyl] propane (BAPP) is added to the reaction vessel. The solution was added and dissolved in the container with stirring. Next, pyromellitic dianhydride (PMDA) was added so that the total amount of monomers was 12 wt%. Thereafter, stirring was continued for 3 hours to carry out a polymerization reaction to obtain a resin solution of polyamic acid a.
The thermal expansion coefficient (CTE) of the 25 μm thick polyimide film formed from the polyamic acid a was 55 × 10 ⁻⁶ / K.

(Synthesis Example 2)
N, N-dimethylacetamide is placed in a reaction vessel equipped with a thermocouple and a stirrer and into which nitrogen can be introduced, and 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB) is charged into this reaction vessel. And dissolved in the container with stirring. Next, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride (BPDA) and pyromellitic dianhydride (PMDA) were added at a total monomer charge of 15 wt% and the molar ratio of each acid anhydride ( (BPDA: PMDA) was added so as to be 20:80. Thereafter, stirring was continued for 3 hours to carry out a polymerization reaction to obtain a resin solution of polyamic acid b.
The thermal expansion coefficient (CTE) of the 25 μm thick polyimide film formed from the polyamic acid b was 22 × 10 ⁻⁶ / K.

(Synthesis Example 3)
A reaction vessel equipped with a thermocouple and a stirrer and capable of introducing nitrogen was charged with N, N-dimethylacetamide, and 2,2′-dimethyl-4,4′-diaminobiphenyl (m-TB) and 4 , 4'-diaminodiphenyl ether (DAPE) was added so that the molar ratio of each diamine (m-TB: DAPE) was 60:40 and dissolved in the container with stirring. Next, pyromellitic dianhydride (PMDA) was added so that the total amount of monomers was 16 wt%. Thereafter, stirring was continued for 3 hours to carry out a polymerization reaction to obtain a resin solution of polyamic acid c.
The thermal expansion coefficient (CTE) of the 25 μm thick polyimide film formed from the polyamic acid c was 22 × 10 ⁻⁶ / K.

Example 1
The resin solution of polyamic acid a prepared in Synthesis Example 1 was uniformly applied to one side of a long copper foil having a thickness of 12 μm (surface roughness Rz = 0.8 μm) so that the thickness after curing was 2.2 μm. Then, the solvent was removed by heating and drying at 130 ° C. Next, the polyamic acid b resin solution prepared in Synthesis Example 2 was uniformly applied to the coated surface side so that the thickness after curing was 7.6 μm, and the solvent was removed by heating and drying at 135 ° C. Further, the same polyamic acid a resin solution as that applied in the first layer was applied on the coated surface side uniformly so that the thickness after curing was 2.2 μm, and the solvent was removed by heating at 130 ° C. . This continuous laminate was heat-treated over a period of about 6 minutes in a continuous curing furnace set so that the temperature gradually increased from 300 ° C to 300 ° C. A 12 μm single-sided flexible copper-clad laminate was obtained.
Properties of physical properties such as tensile elastic modulus of copper foil constituting the obtained flexible copper-clad laminate, average crystal grain size of copper foil cross-section, tensile elastic modulus of polyimide layer, folding coefficient, bending resistance of flexible copper-clad laminate Table 1 shows the evaluation results of the sex. In addition, evaluation of the polyimide layer used what removed the copper foil by etching from the manufactured copper clad laminated board.

Here, a specific calculation procedure for the calculation of the folding coefficient [PF] of the copper-clad laminate manufactured in the example will be described using Example 1 as an example.
Considering a two-layer structure as shown in FIG. 8 for the wiring portion where the copper wiring 12 exists, the materials constituting the first layer and the second layer are polyimide and copper, respectively. As shown in Table 1 (Example 1), the elastic modulus of each layer is E ₁ = 7.2 GPa, E ₂ = 14 GPa, and the thickness is t ₁ = t ₂ = 12 μm. Further, the distance between the center plane and the reference plane SP in the thickness direction in each layer is h ₁ = 6 μm and h ₂ = 18 μm, respectively. Further, regarding the width B, the width B ₂ of the copper wiring 12 and the width B _{2 ′} of the space portion are both 100 μm, and the width B ₁ of the polyimide immediately below the copper wiring 12 is also 100 μm (space portion) The width B _{1 ′} of the polyimide immediately below is also 100 μm).

When these values are substituted into the expression (3), first, the neutral plane position in the wiring portion where the copper wiring 12 exists is calculated as [NP] = 13.9 μm. Next, the effective bending radius R = 0.136 mm is calculated by substituting the neutral surface position [NP] and the gap interval G = 0.3 mm into the equation (4). Further, since the distance yc from the reference plane SP to the center plane of the copper wiring 12 is yc = h ₁ = 18 μm, the bending average strain ε is the value of [NP] and R obtained in the above equation (2) ) And calculated as ε = −0.02995. Here, a minus sign indicates a compressive strain. From the stress-strain curve obtained from the tensile test of the copper foil that is the copper wiring in Example 1, the tensile elastic limit strain εc of the copper wiring was determined to be εc = 0.0012. By substituting this and the value of the bending average strain ε obtained previously into equation (I), the folding coefficient [PF] is calculated as [PF] = 0.960. In this example, since the space part is composed only of the polyimide layer, the operation for obtaining [NP] is not required, and the folding coefficient of other examples and comparative examples in Table 1 is also the above. The value calculated in the procedure.

(Example 2)
As the copper foil, a single-sided flexible copper-clad was applied in the same manner as in Example 1 except that a commercially available rolled copper foil having a characteristic shown in Table 1 and having a thickness of 12 μm (surface roughness Rz = 1.0 μm on the coated surface) was used. A laminate was obtained. Table 1 shows the evaluation results of the bending resistance of the obtained single-sided flexible copper-clad laminate.

(Example 3)
As a copper foil, a single-sided flexible copper-clad is carried out in the same manner as in Example 1 except that a commercially available rolled copper foil having a characteristic shown in Table 1 and having a thickness of 18 μm (surface roughness Rz = 1.1 μm of coated surface) is used. A laminate was obtained. Table 1 shows the evaluation results of the bending resistance of the obtained single-sided flexible copper-clad laminate.

Example 4
Resin solution of polyamic acid a prepared in Synthesis Example 1 on a commercially available rolled copper foil having a characteristic shown in Table 1 and having a thickness of 12 μm and a long surface (coating surface roughness Rz = 1.0 μm) Was applied uniformly so that the thickness after curing was 2.5 μm, and then dried by heating at 130 ° C. to remove the solvent. Next, the polyamic acid c resin solution prepared in Synthesis Example 3 was uniformly applied to the coated surface side so that the thickness after curing was 20.0 μm, and the solvent was removed by heating and drying at 120 ° C. Further, the same polyamic acid a resin solution as that applied in the first layer was applied uniformly on the coated surface so that the thickness after curing was 2.5 μm, and the solvent was removed by heating at 130 ° C. . This long laminate was heat-treated in a continuous curing furnace set so that the temperature gradually increased from 300 ° C to 300 ° C over a total time of about 6 minutes, and the polyimide resin layer thickness was 25 µm. A single-sided flexible copper-clad laminate was obtained.
Evaluation results of physical properties such as tensile elastic modulus of copper foil constituting the obtained flexible copper-clad laminate, average crystal grain size of copper foil cross section, tensile elastic modulus of polyimide layer, and bending resistance of flexible copper-clad laminate Is shown in Table 1.

(Example 5)
A single-sided flexible copper-clad laminate is obtained in the same manner as in Example 1 except that a rolled copper foil having a characteristic shown in Table 1 and having a thickness of 12 μm (coating surface roughness Rz = 1.1 μm) is used. It was. Table 1 shows the evaluation results of the bending resistance of the obtained single-sided flexible copper-clad laminate.

(Example 6)
A single-sided flexible copper-clad laminate is obtained in the same manner as in Example 1 except that a rolled copper foil having a characteristic shown in Table 1 and a thickness of 11 μm (coating surface roughness Rz = 0.8 μm) is used. It was. Table 1 shows the evaluation results of the bending resistance of the obtained single-sided flexible copper-clad laminate.

(Comparative Example 1)
Example 4 except that a rolled copper foil having a characteristic shown in Table 1 and having a thickness of 12 μm (surface roughness Rz = 1.1 μm on the coated surface) was used, and the thickness of the polyimide layer was changed as follows. In the same manner, a single-sided flexible copper-clad laminate was obtained.
Here, the thickness structure of the polyimide layer is 4.0 μm after curing the polyamic acid a resin solution prepared in Synthesis Example 1 on a copper foil, and the polyamic acid c resin solution prepared in Synthesis Example 3 thereon. The thickness after curing was set to 42.0 μm, and the thickness after curing of the resin solution of polyamic acid a prepared in Synthesis Example 1 was set to 4.0 μm. Table 1 shows the evaluation results of the bending resistance of the obtained single-sided flexible copper-clad laminate.

(Comparative Example 2)
Except for using the characteristics shown in Table 1 and using a commercially available rolled copper foil with a thickness of 18 μm (surface roughness Rz = 1.0 μm on the coated surface) and changing the thickness of the polyimide layer as follows: In the same manner as in Example 1, a single-sided flexible copper-clad laminate was obtained.
Here, the thickness of the polyimide layer is 2.5 μm after curing the polyamic acid a resin solution prepared in Synthesis Example 1 on a copper foil, and the polyamic acid c resin solution prepared in Synthesis Example 3 thereon. The thickness after curing was 20.0 μm, and the thickness after curing of the polyamic acid a resin solution prepared in Synthesis Example 1 was 2.5 μm.

(Comparative Example 3)
Example 1 except that the electrolytic copper foil having the characteristics shown in Table 1 and having a thickness of 12 μm (surface roughness Rz = 1.3 μm of the coated surface) was used and the thickness of the polyimide layer was changed as follows. In the same manner, a single-sided flexible copper-clad laminate was obtained.
Here, the polyimide layer has a thickness of 2.0 μm after curing the polyamic acid a resin solution prepared in Synthesis Example 1 on a copper foil, and the polyamic acid b resin solution prepared in Synthesis Example 2 thereon. The thickness after curing was 8.0 μm, and the thickness after curing of the polyamic acid a resin solution prepared in Synthesis Example 1 was 2.0 μm.

(Comparative Example 4)
Example 1 except that the electrolytic copper foil having the characteristics shown in Table 1 and having a thickness of 12 μm (surface roughness Rz = 2.1 μm of the coated surface) was used and the thickness of the polyimide layer was changed as follows. In the same manner, a single-sided flexible copper-clad laminate was obtained.
Here, the thickness of the polyimide layer is 2.5 μm after curing the polyamic acid a resin solution prepared in Synthesis Example 1 on a copper foil, and the polyamic acid b resin solution prepared in Synthesis Example 2 thereon. The thickness after curing was 20.0 μm, and the thickness after curing of the polyamic acid a resin solution prepared in Synthesis Example 1 was 2.5 μm.

(Comparative Example 5)
Other than having the characteristics shown in Table 1 and using a long electrolytic copper foil with a thickness of 12 μm (surface roughness Rz = 1.4 μm on the coated surface) and changing the thickness of the polyimide layer as follows: Obtained a single-sided flexible copper-clad laminate in the same manner as in Example 4.
Here, the thickness of the polyimide layer is such that the thickness after curing the resin solution of polyamic acid a prepared in Synthesis Example 1 on a copper foil is 4.0 μm, and the resin solution of polyamic acid c prepared in Synthesis Example 3 thereon. The thickness after curing was set to 42.0 μm, and the thickness after curing of the resin solution of polyamic acid a prepared in Synthesis Example 1 was set to 4.0 μm.

1: Circuit board
11: Polyimide layer
12, 51: Copper wiring
20, 21: Sample stage
22: Roller
40: Test piece
40C: Bending part of the test piece
52: U-shaped part of copper wiring

Claims (6)

The thickness of the polyimide layer (A) having a thickness of 10 to 25 μm and a tensile elastic modulus of 4 to 10 GPa is 8 to 20 μm thick, has a tensile elastic modulus of 10 to 20 GPa, and is an average in a cross section in the thickness direction. grain size becomes only 10μm or more copper (B), a flexible copper clad laminate used in the flexible circuit board accommodated folded in a casing of an electronic device, the copper of the flexible copper-clad laminate Folding coefficient [PF] calculated by the following formula (I) in a bending test with a gap of 0.3 mm of an arbitrary flexible circuit board in which copper wiring is formed by processing a foil with a wiring of 0.96 ± 0 A flexible copper clad laminate characterized by being in the range of .02.

(In the formula (I), | ε | is the absolute value of the bending average strain value of the copper wiring, and ε _C is the tensile elastic limit strain of the copper wiring.) The polyimide layer (A) is a low thermal expansion polyimide layer (i) having a thermal expansion coefficient of less than 30 × 10 ⁻⁶ / K and a high thermal expansion polyimide layer (ii) having a thermal expansion coefficient of 30 × 10 ⁻⁶ / K or more. The flexible copper-clad laminate according to claim 1, wherein the high thermal expansion polyimide layer (ii) is in direct contact with the copper foil (B).   3. The surface roughness (Rz) of the copper foil (B) at the contact surface between the high thermal expansion polyimide layer (ii) and the copper foil (B) is in the range of 0.5 to 1.5 [mu] m. The flexible copper clad laminate as described.   The flexible copper-clad laminate according to any one of claims 1 to 3, wherein the polyimide layer (A) has a tensile modulus of 6 to 10 GPa.   The flexible copper-clad laminate according to any one of claims 1 to 4, wherein the polyimide layer (A) has a thickness in the range of 10 to 15 µm.   The flexible copper-clad laminate according to any one of claims 1 to 5, wherein the average crystal grain size in the cross section in the thickness direction of the copper foil (B) is in the range of 10 to 60 µm.

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