JP6344914B2 - Flexible copper clad laminate and flexible circuit board - Google Patents

Description

  The present invention relates to a flexible copper clad laminate used for a flexible circuit board (FPC) and a flexible circuit board using the flexible copper clad laminate as a material.

  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, also in the flexible copper clad laminated board which is a material of a flexible circuit board, the improvement of the bending resistance from the material surface is calculated | required. Hereinafter, in this specification, folding the FPC so that the upper surface side of the FPC is inverted by approximately 180 ° C. to become the lower surface side may be referred to as “shell folding”.

  As intended for application to such applications, Patent Document 1 reduces the total stiffness of flexible circuit boards by controlling the elastic modulus of the polyimide base film and cover film used in flexible copper clad laminates. Thus, a technique for improving the bending resistance has been proposed. 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.

  Moreover, in patent document 2, from the viewpoint of high density in an electronic device, as an approach from the copper foil side, focusing on the crystal grain size of the copper foil, the copper foil for heat treatment with suppressed springback resistance Has been proposed. This proposal uses a rolled copper foil with various appropriate additives in the copper foil to increase the crystal grain size by adding 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 represented by smartphones, and it is difficult to meet the demand only with the conventional technology.

  As a means of obtaining a flexible circuit board with high-density wiring, it is generally known that thinning of the metal layer of a flexible metal-clad laminate used as a material is effective, and sputtering or electrolytic plating on a polyimide film For example, a technique for forming a thin metal layer has been proposed (see, for example, Patent Document 3). However, the approach of reducing the metal layer alone has its limitations due to design limitations.

JP 2007-208087 A JP 2010-280191 A JP-A-11-268183

  The present invention has been made in view of the above-mentioned problems, and its purpose is not only to have a copper foil layer suitable for forming a high-density wiring, but also to withstand intermittent repeated sliding, It is an object to provide a flexible copper-clad laminate and a flexible circuit board having excellent bending resistance that can prevent disconnection and cracking of a wiring circuit even in a narrow housing.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have focused on the characteristics of elastic-plastic deformation during the helix folding process of the flexible copper-clad laminate in which the copper foil and the polyimide film are laminated. It discovered that the flexible copper clad laminated board which can solve the said subject could be provided, and completed this invention.

The flexible copper clad laminate of the present invention comprises a polyimide insulating layer (A), a first copper foil layer (B1) provided on one surface of the polyimide insulating layer (A), and the polyimide insulating layer (A ) On the other surface of the second copper foil layer (B2). The flexible copper clad laminate of the present invention has the following configurations a and b:
a) The first copper foil layer (B1) has a thickness (T1) in the range of 5 to 20 μm. The thickness (T1) and the average crystal grain size (D1) in the cross section in the thickness direction In the relationship, (T1) × (D1) ≦ 100 μm ² of copper foil;
b) The second copper foil layer (B2) has a thickness in the range of 5 to 20 μm, a tensile elastic modulus in the range of 10 to 25 GPa, and an average crystal grain size in a cross section in the thickness direction of 40. The ratio of the diffraction intensity (I) of the (200) plane determined by X-ray diffraction to the diffraction intensity (I ₀ ) of the (220) plane determined by X-ray diffraction of fine powder copper (in the range of ˜70 μm) I / I ₀ ) comprising a copper foil in the range of 12-30;
It comprises.

The flexible copper-clad laminate of the present invention further has a configuration of c;
c) The polyimide insulating layer (A) has a thickness in the range of 7 to 17 μm and a tensile elastic modulus at 25 ° C. in the range of 2 to 9 GPa;
May be provided.

The flexible copper-clad laminate of the present invention further has a configuration of d;
d) The ratio of the thickness of the polyimide insulating layer (A) to the second copper foil layer (B2) [the thickness of the second copper foil layer (B2) / the thickness of the polyimide insulating layer (A)] is 0. Within the range of .48 to 2.4;
May be provided.

  The flexible circuit board of the present invention uses the second copper foil layer (B2) of the flexible copper clad laminate described in any of the above, and uses at least a part of the wiring circuit for the bent portion.

  In the flexible circuit board of the present invention, at least the first copper foil layer (B1) at a position corresponding to the bent portion may be removed.

  Since the flexible copper-clad laminate of the present invention can express the high bending resistance required for a wiring board, it provides a flexible circuit board material that is excellent in connection reliability in a state of being bent in an electronic device. be able to. Therefore, the flexible copper-clad laminate of the present invention is suitably used for electronic parts that require bending resistance such as a bent portion around a small liquid crystal such as a smartphone. Moreover, since the flexible copper clad laminate of the present invention has a copper foil layer that is advantageous for forming a high-density wiring and the performance that can withstand intermittent repeated sliding required for a wiring board, It is also suitably used as a flexible circuit board material for read / write cables in hard disk drives.

It is a section explanatory view (part) of a flexible circuit board obtained by partially removing the first copper foil layer of the flexible copper clad laminate. 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).

Embodiments of the present invention will be described below.
<Flexible copper-clad laminate>
The flexible copper-clad laminate of this embodiment includes a polyimide insulating layer (A), a first copper foil layer (B1) provided on one surface of the polyimide insulating layer (A), and the polyimide insulating layer. It is comprised from the 2nd copper foil layer (B2) provided in the other surface of (A). This flexible copper clad laminate is used as a flexible circuit board by forming a wiring circuit by processing a wiring circuit by etching the first copper foil layer (B1) and the second copper foil layer (B2). The in this case,
It is advantageous to form the first copper foil layer (B1) as a copper wiring of a high-density wiring and form the second copper foil layer (B2) as a copper wiring corresponding to the bent portion.

<Copper foil>
In the flexible copper clad laminate of the present embodiment, the thickness (T1) of the first copper foil layer (B1) is in the range of 5 to 20 μm, and preferably in the range of 6 to 19 μm. When the thickness (T1) of the first copper foil layer (B1) is less than 5 μm, for example, a polyimide insulating layer (A) is formed on the first copper foil layer (B1) during the production of the flexible copper-clad laminate. In the process of forming, the rigidity of the first copper foil layer (B1) itself is lowered, and as a result, there arises a problem that wrinkles and the like are generated on the flexible copper-clad laminate. In addition, if the thickness (T1) of the first copper foil layer (B1) exceeds 20 μm, the bottoming amount of the copper wiring formed by etching with the etching solution increases, resulting in poor insulation between adjacent wirings. As a result, miniaturization of the wiring circuit tends to be difficult.

Further, in the relationship between the thickness (T1) of the first copper foil layer (B1) and the average crystal grain size (D1) in the cross section in the thickness direction, (T1) × (D1) is 100 μm ² or less, preferably Is 80 μm ² or less, more preferably 70 μm ² or less. By setting it as such a range, it becomes possible to refine | miniaturize the copper wiring formed by the etching by etching liquid, for example. The lower limit of (T1) × (D1) is not particularly limited, but the etching rate with respect to the copper foil thickness direction at the time of forming the copper wiring with the etching solution increases by making (T1) × (D1) smaller. For this reason, since undercuts are likely to occur in the copper wiring, the thickness is preferably 5 μm ² or more, more preferably 10 μm ² or more. In addition, the average crystal grain diameter in the cross section of the thickness direction of the copper foil layer prescribed | regulated by this invention can be calculated | required with the measuring method described in the postscript Example.

  In the flexible copper-clad laminate of the present embodiment, the surface of the first copper foil layer (B1) may be roughened, and preferably the first copper foil in contact with the polyimide insulating layer (A). The surface roughness (Rz) of the surface of the layer (B1) is in the range of 0.7 to 2.5 μm, preferably 0.7 to 2.2 μm, more preferably 0.8 to 1.6 μm. . If the value of the surface roughness (Rz) is less than the above lower limit value, it becomes difficult to ensure adhesion reliability with the polyimide insulating layer (A). If the value exceeds the upper limit value, copper wiring formed by etching with an etching solution The linearity is impaired, and the formation of the fine wiring circuit is likely to be hindered. The surface roughness Rz is a value measured according to JIS B0601.

  In the flexible copper clad laminate of the present embodiment, the thickness of the second copper foil layer (B2) is in the range of 5 to 20 μm, and preferably in the range of 8 to 19 μm. If the thickness of the second copper foil layer (B2) is less than 5 μm, for example, a polyimide insulating layer (A) is formed on the second copper foil layer (B2) during the production of the flexible copper-clad laminate. In the process, the rigidity of the second copper foil layer (B2) itself is lowered, and as a result, there arises a problem that wrinkles and the like are generated on the flexible copper clad laminate. 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 layer (or copper wiring) when the flexible copper-clad laminate (or FPC) is bent.

  Moreover, the tensile elasticity modulus of a 2nd copper foil layer (B2) is in the range of 10-25 GPa, Preferably it is in the range of 10-20 GPa. When the tensile elastic modulus of the second copper foil layer (B2) is less than 10 GPa, a polyimide insulating layer (A) is formed on the second copper foil layer (B2), for example, when the flexible copper clad laminate is manufactured. In the step of performing, the rigidity of the second copper foil layer (B2) itself is lowered, and as a result, there arises a problem that wrinkles and the like are generated on the flexible copper-clad laminate. Moreover, when the tensile elastic modulus of the second copper foil layer (B2) exceeds 25 GPa, bending stress applied to the copper foil layer (or copper wiring) when the flexible copper clad laminate (or FPC) is bent increases. As a result, the bending resistance is lowered.

  In the flexible copper clad laminate of the present embodiment, the average crystal grain size in the cross section in the thickness direction of the second copper foil layer (B2) is in the range of 40 to 70 μm. By setting it as such a range, the expansion of the crack of the copper foil layer (or copper wiring) generated when the flexible copper clad laminate (or FPC) is bent can be suppressed, and as a result, the bending resistance can be improved. Can do.

The second copper foil layer (B2) has (200) plane diffraction intensity (I) determined by X-ray diffraction in the thickness direction and (220) plane diffraction determined by fine powder copper X-ray diffraction. The ratio (I / I ₀ ) to the intensity (I ₀ ) is in the range of 12-30. By setting it as such a range, the bending resistance of a flexible copper clad laminated board (or FPC) can be improved. Here, the I value and the I ₀ value can be measured by the X-ray diffraction method. The X-ray diffraction in the thickness direction of the copper foil layer is the surface of the copper foil layer (when the copper foil layer is made of a rolled copper foil). Indicates the orientation on the (rolled surface), and the diffraction intensity (I) of the (200) plane indicates the integrated intensity of the (200) plane determined by X-ray diffraction. The diffraction intensity (I ₀ ) represents the integrated intensity value of the (220) plane of fine powder copper (copper powder reagent class I, 325 mesh, purity 99.99% or more manufactured by Kanto Chemical Co., Inc.).

  In the flexible copper-clad laminate of the present embodiment, the surface of the second copper foil layer (B2) may be roughened, taking into account the relationship with the rigidity of the second copper foil layer (B2). Then, preferably, the surface roughness (ten-point average roughness; Rz) of the surface of the second copper foil layer (B2) in contact with the polyimide insulating layer (A) is in the range of 0.1 to 1.5 μm. There should be. When the value of the surface roughness (Rz) is less than the above lower limit value, it becomes difficult to ensure the adhesion reliability with the polyimide insulating layer (A), and when the value exceeds the above upper limit value, the flexible copper clad laminate (or FPC) is removed. When it is repeatedly bent, the unevenness of the roughened surface tends to be a starting point of crack generation, and as a result, the bending resistance of the flexible copper-clad laminate (or FPC) is lowered. The surface roughness Rz is a value measured according to JIS B0601.

<Polyimide insulation layer>
In the flexible copper clad laminate of the present embodiment, the thickness of the polyimide insulating layer (A) is set within a predetermined range depending on the thickness and rigidity of the second copper foil layer (B). Although it can set, it is preferable that it exists in the range of 7-17 micrometers, for example, and it is more preferable that it exists in the range of 8-13 micrometers. When the thickness of the polyimide insulating layer (A) is less than the lower limit, problems such as inability to ensure electrical insulation and difficulty in handling in the manufacturing process due to a decrease in handling properties tend to occur. On the other hand, when the thickness of the polyimide insulating layer (A) exceeds the above upper limit, bending stress applied to the copper foil layer (or copper wiring) when the flexible copper clad laminate (or FPC) is bent becomes larger. The bending resistance tends to be remarkably lowered.

  Further, the tensile elastic modulus at 23 ° C. of the polyimide insulating layer (A) is preferably in the range of 2 to 9 GPa, more preferably in the range of 4 to 9 GPa. When the tensile elastic modulus of the polyimide insulating layer (A) is less than 2 GPa, the rigidity of the polyimide itself is reduced, which causes handling problems such as wrinkles when processing a flexible copper-clad laminate on a circuit board. Sometimes. On the other hand, when the tensile modulus of the polyimide insulating layer (A) exceeds 9 GPa, the bending resistance of the flexible copper-clad laminate (or FPC) increases. As a result, when the flexible copper-clad laminate (or FPC) is folded. The bending stress applied to the copper wiring increases, and the bending resistance decreases.

<Ratio of the thickness of the polyimide insulating layer (A) and the second copper foil layer (B2)>
Further, in the present embodiment, as the configuration d, the thickness ratio between the polyimide insulating layer (A) and the second copper foil layer (B2) [the thickness of the second copper foil layer (B2) / polyimide insulation] The thickness of the layer (A)] is preferably in the range of 0.48 to 2.4. If this thickness ratio is less than 0.48 or greater than 2.4, the maximum tensile strain when the plastically deformed portion is stretched at the time of bending increases, resulting in a decrease in bending resistance.

<Total thickness of polyimide insulating layer (A) and second copper foil layer (B2)>
The flexible copper-clad laminate of the present embodiment has a thickness [that is, a total thickness of the polyimide insulating layer (A) and the second copper foil layer (B2)] within a range of 12 to 37 μm, preferably 16 The range of ~ 32 μm is preferable. If the thickness of the flexible copper clad laminate is less than 12 μm, the rigidity of the flexible printed wiring board obtained by processing the copper foil of the flexible copper clad laminate is reduced, and elasto-plastic deformation due to bending tends to occur. . On the other hand, when the thickness of the flexible copper-clad laminate exceeds 37 μm, a large bending stress is applied to the copper wiring when the FPC is bent, and the bending resistance is significantly reduced.

<Manufacture of flexible copper-clad laminates>
The flexible copper clad laminate of the present embodiment is one in which the first copper foil layer (B1), the polyimide insulating layer (A), and the second copper foil layer (B2) are laminated in this order. In this case, the first copper foil layer (B1) is preferably formed as a copper wiring of a high-density wiring, and the second copper foil layer (B2) is preferably formed as a copper wiring corresponding to the bent portion. From such a viewpoint, the flexible copper-clad laminate of the present embodiment has a polyimide precursor resin solution (on the surface of a copper foil (hereinafter referred to as the first copper foil) to be the first copper foil layer (B1) ( And then dried and cured to produce a single-sided copper-clad laminate, and then a second copper layer on the polyimide insulating layer (A) side of the single-sided copper-clad laminate. A method of thermocompression bonding a copper foil (hereinafter referred to as a second copper foil) to be the foil layer (B2) is preferable. The polyimide insulating layer obtained by applying a polyamic acid solution directly on the first copper foil to be the circuit wiring, the so-called casting method, can suppress the difference in the linear thermal expansion coefficient between the longitudinal direction and the lateral direction. Since stability can be improved, it is advantageous for forming a high-density wiring by processing the first copper foil layer (B1) on the wiring circuit. The heat treatment condition of the polyamic acid in the formation of the polyimide insulating layer (A) is, for example, by drying the coated polyamic acid solution by raising the temperature stepwise within a temperature range of less than 160 ° C. There is a method of curing by raising the temperature stepwise to 400 ° C.

  The polyimide insulating layer (A) may be formed of only a single layer, but the adhesion between the polyimide insulating layer (A), the first copper foil layer (B1), and the second copper foil layer (B2). In consideration of the above, a layer composed of a plurality of layers is preferable. When the polyimide insulating 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 the polyimide insulating layer (A) is composed of a plurality of layers, the polyimide precursor resin having the same configuration may be used twice or more.

The polyimide insulating layer (A) will be described in more detail. As described above, the polyimide insulating layer (A) is preferably a plurality of layers. As a specific example, the polyimide insulating layer (A) has a low thermal expansion coefficient of less than 30 × 10 ⁻⁶ / K. A laminated structure including the polyimide layer (i) and a high thermal expansion polyimide layer (ii) having a thermal expansion coefficient of 30 × 10 ⁻⁶ / K or more is preferable. More preferably, the polyimide insulating layer (A) has a laminated structure having a high thermal expansion polyimide layer (ii) on at least one of the low thermal expansion polyimide layers (i), preferably both sides thereof, and has a high thermal expansion. The polyimide layer (ii) is preferably in direct contact with the copper foil. Here, the “low thermal expansion polyimide layer (i)” is a thermal expansion coefficient of less than 30 × 10 ⁻⁶ / K, preferably in the range of 1 × 10 ^{−6 to} 25 × 10 ⁻⁶ / K, particularly preferably. Means a polyimide layer in the range of 3 × 10 ^{−6 to} 20 × 10 ⁻⁶ / K. The “high thermal expansion polyimide layer (ii)” refers to a polyimide layer having a thermal expansion coefficient of 30 × 10 ⁻⁶ / K or more, preferably in the range of 30 × 10 ⁻⁶ to 80 × 10 ⁻⁶ / K. Of these, a polyimide layer in the range of 30 × 10 ⁻⁶ to 70 × 10 ⁻⁶ / K is particularly preferable. 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 provides the polyimide insulating layer (A) can be produced by polymerizing a known diamine and an acid anhydride in the presence of a solvent. At this time, the viscosity of the resin to be polymerized is preferably in the range of 500 cps to 35,000 cps, for example.

  Examples of the diamine used as a raw material for polyimide include 4,6-dimethyl-m-phenylenediamine, 2,5-dimethyl-p-phenylenediamine, 2,4-diaminomesitylene, and 4,4′-methylenedi-o-. Toluidine, 4,4'-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'-diame Diphenyl 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- Silylenediamine, p-xylylenediamine, 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.

  Examples of the acid anhydride used as a raw material for polyimide include pyromellitic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride, 2,2 ′, 3,3 ′. -Benzophenone tetracarboxylic dianhydride, 2,3,3 ', 4'-benzophenone tetracarboxylic dianhydride, naphthalene-1,2,5,6-tetracarboxylic dianhydride, naphthalene-1,2, 4,5-tetracarboxylic 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-tetrachloro Phthalene-1,4,5,8-tetracarboxylic dianhydride, 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-terphenyltetracarboxylic dianhydride, 2,2``, 3,3 ''-p-terphenyltetracarboxylic dianhydride, 2,3,3 ' ', 4' '-p-terphenyltetracarboxylic dianhydride, 2,2-bis (2,3-dicarboxyphenyl) -propane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) ) -Propane dianhydride, bis (2,3-dicarboxyphenyl) ether dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3.4-dicarboxyphenyl) methane dianhydride, Bis (2,3-dicarboxyphenyl) sulfone dianhydride, bis (3,4-dicarboxyl) Phenyl) sulfone dianhydride, 1,1-bis (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, cyclopentane-1,2,3,4-tetracarboxylic dianhydride, pyrazine-2,3,5,6-tetracarboxylic dianhydride, pyrrolidine -2,3,4,5-tetracarboxylic dianhydride, thiophene-, 3,4,5-tetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, 2,3,6,7 -Naphthalene tetracarboxylic dianhydride, etc. And the like.

  Each of the 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 this embodiment, in order to obtain a low thermal expansion polyimide layer (i) having a thermal expansion coefficient of less than 30 × 10 ⁻⁶ / K, pyromellitic dianhydride, 3,3 ′ , 4,4'-biphenyltetracarboxylic dianhydride and 2,2'-dimethyl-4,4'-diaminobiphenyl, 2-methoxy-4,4'-diaminobenzanilide as the diamine component Particularly preferred are those containing pyromellitic dianhydride and 2,2′-dimethyl-4,4′-diaminobiphenyl as the main components of the respective raw materials.

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. In addition, the preferable glass transition temperature of the highly heat-expandable polyimide layer (ii) thus obtained is 260 ° C. or higher, and preferably in the range of 280 to 320 ° C. By setting the glass transition temperature in such a range, the adhesive strength and dimensional stability between the copper foil layer and the polyimide insulating layer (A) required when processing a flexible copper-clad laminate into FPC, parts, The solder heat resistance required for solder bonding during mounting is excellent.

  When the polyimide insulating layer (A) has a laminated structure of 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 are used. The ratio of the thickness of the expandable polyimide layer (ii) (low thermal expansion polyimide layer (i) / high thermal expansion polyimide layer (ii)) is preferably in the range of 2 to 12. When the ratio value is less than 2, the low thermal expansion polyimide layer (i) with respect to the entire polyimide insulating layer (A) becomes thin, so that it becomes difficult to control the dimensional characteristics of the polyimide film, and the copper foil is etched. When the ratio of dimensional change increases and exceeds 12, the high thermal expansion polyimide layer (ii) becomes thin, so that the adhesion reliability between the polyimide insulating layer (A) and the copper foil is lowered.

  As the first copper foil used for manufacturing the flexible copper-clad laminate of the present embodiment, an electrolytic copper foil is preferably used. Compared with rolled copper foil, electrolytic copper foil is advantageous because it is easy to suppress a decrease in rigidity in the process of forming a polyimide layer on the copper foil, for example, during the production of a flexible copper-clad laminate.

  Moreover, the 1st copper foil used for manufacture of the flexible copper clad laminated board of this Embodiment is the influence of the heat history (for example, heating for 10 to 60 minutes at 300-400 degreeC) at the time of manufacture of a flexible copper clad laminated board. It is preferable to use an electrolytic copper foil whose average crystal grain size (D1) is preferably in the range of 1 to 10 μm, more preferably in the range of 1 to 5 μm. As such electrolytic copper foil, commercially available products can be used. Specific examples thereof include WS foil manufactured by Furukawa Electric Co., Ltd., HL foil manufactured by Nihon Electrolytic Co., Ltd., and HTE foil manufactured by Mitsui Metal Mining Co., Ltd. Can be mentioned. Moreover, even if it is a case where other than that is used including these commercial items, the 1st copper foil layer (B1) in the flexible copper clad laminated board of this Embodiment becomes in a predetermined range. Thus, for example, after forming the polyimide insulating layer (A), the copper foil layer can be thinned by chemical polishing such as etching. In this case, the surface roughness (Rz) on the surface side (side not in contact with the polyimide insulating layer (A)) in the first copper foil layer (B1) after etching should be 1.7 μm or less. Is preferred. By setting the surface roughness to such a value, variations in the wiring interval can be suppressed when forming the copper wiring by processing the first copper foil layer (B1) on the wiring circuit.

  It is preferable to use a rolled copper foil as the second copper foil used for manufacturing the flexible copper-clad laminate of the present embodiment. As a rolled copper foil, a copper alloy foil in which Ag or Sn is added as an additive element so that the (200) plane crystal orientation proceeds during annealing of the polyimide layer on the copper foil, the thermocompression bonding process, and the post-process, etc. Is mentioned. Known examples include HA foil manufactured by JX Nippon Mining & Metals Co., Ltd. and HPF foil manufactured by SH Copper Products Co., Ltd.

Next, the thermocompression bonding conditions between the second copper foil and the single-sided copper clad laminate in the embodiment of the present invention will be described. As the laminating temperature t ₁ , that is, the temperature of the hot press roll in the thermocompression bonding step, the glass transition of the polyimide of the high thermal expansion polyimide layer (ii) from the viewpoint of adhesion to the polyimide of the adhesive layer to the second copper foil. It is necessary to set the temperature or higher, and it is preferable that the temperature is within a range of 300 to 400 ° C. In addition, it is desirable to heat-press the linear pressure between the heated rolls under the conditions of 50 to 500 Kg / cm and the roll passing time of 2 to 5 seconds. The atmosphere of the laminate includes an air atmosphere and an inert atmosphere. From the viewpoint of preventing copper foil oxidation and discoloration, an inert atmosphere is desirable. Here, the inert atmosphere is synonymous with an inert atmosphere and refers to a state in which the inert atmosphere is substantially substituted with an inert gas such as nitrogen or argon.

  Here, the crystal orientation of the (200) plane by the heat treatment of the second copper foil will be described in detail. In general, the copper foil described above is softened by heat treatment, the elastic modulus is lowered and softened, and the (200) plane preferential orientation proceeds to develop a cubic structure. The crystal orientation of the (200) plane proceeds by processing for a predetermined time at a temperature equal to or higher than the semi-softening temperature, but requires at least 10 seconds to 60 seconds at a temperature of 300 ° C. or higher. In the method of thermocompression bonding with a pair of hot press rolls as in the embodiment of the present invention, since the crimping with the roll is performed within 10 seconds from the viewpoint of ensuring the productivity, after the thermocompression bonding step It is necessary to combine the annealing process of the reheating process.

Reheating step (annealing) is required to be heat-treated at a lamination temperature t ₁ or higher. If it is lamination temperature t ₁ following the temperature once, it is impossible to partially crystalline growth recrystallized copper foil crystal structure again in thermocompression bonding step, cubic tissue due to crystal orientation of (200) plane Can't progress enough. That is, sufficiently proceed advanced partially recrystallized laminates thermocompression bonding step, a heat treatment temperature t ₂ of the reheating step to be set to a laminating temperature t ₁ or more is important. In this case, when the temperature of the subsequent reheating step is 300 ° C. or higher, a processing time of about 10 seconds to 60 seconds is sufficient. On the other hand, when the temperature is set to exceed 400 ° C., problems such as heat-resistant degradation of polyimide and warpage due to heating occur. Therefore, the temperature is preferably set to 400 ° C. or lower.

Through such a reheating step, the diffraction intensity (I) of (200) plane obtained by X-ray diffraction in the thickness direction of the second copper foil after the thermocompression bonding step and the X-ray diffraction of fine powder copper The ratio (I / I ₀ ) with the diffraction intensity (I ₀ ) of the (220) plane obtained by the above is in the range of 12-30. Moreover, by passing through a reheating process, the average crystal grain diameter in the cross section of the thickness direction of a 2nd copper foil layer (B2) can be controlled in the range of 40-70 micrometers.

  Although the means for annealing in the reheating process is not limited, considering that the second copper foil and the single-sided copper clad laminate that are continuously conveyed are placed in a uniform temperature environment, a section of the process is a furnace booth. It is preferable to heat with hot air. Moreover, it is preferable to use heated nitrogen for the hot air in order to prevent the influence of alteration or the like on the surface of the copper foil. Since heating with nitrogen has a limit in raising the temperature condition, other heating means can be added. A preferable heating means includes providing a heater near the conveyance path. In addition, it is also possible to install a plurality of heaters, and the types thereof may be the same or different.

<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 manufactured by processing the metal foil of the flexible copper-clad laminate of this embodiment into a pattern by a conventional method to form a wiring layer.

  The FPC according to the present embodiment is a wiring circuit component used for a bent or bent portion, and may be used as an FPC in which the wiring circuit used for the bent or bent portion is provided substantially only on one side. it can. Preferably, a wiring circuit is formed using the second copper foil layer (B2) of the flexible copper-clad laminate of the present embodiment, and at least a part of the wiring circuit is used as a bent portion. In other words, in the embodiment of the present invention, by providing the wiring circuit used for the bent or bent portion substantially on only one side, it is possible to obtain an FPC having excellent folding resistance such as repeated bending and helix folding. .

  FIG. 1 is a schematic view showing an FPC for removing a part of the first copper foil layer (B1) to form a bent portion. The first copper foil layer (B1) to be removed varies depending on the type and application of the FPC, but the main part (that is, 80% or more) of the first copper foil layer (B1) is removed, as shown in FIG. In addition, it is preferable that the first copper foil layer (B1) remains only in the portion not related to the planned bending portion 10 without leaving a portion that functions as a wiring circuit.

  In the FPC as described above, the wiring circuit formed by the second copper foil layer (B2) may be located outside or inside when bent. In addition, the bent portion formed in the FPC is not only formed by folding in two or the like, but also a bent portion with any repeated operation selected from, for example, sliding bending, bending bending, hinge bending, or sliding bending. Even so, excellent bending resistance can be exhibited.

  As described above, since the flexible copper-clad laminate of the present embodiment can exhibit the high bending resistance required for a wiring board, the FPC has excellent connection reliability in a state of being bent in an electronic device. Materials can be provided. Therefore, the flexible copper clad laminate of the present embodiment is particularly suitably used for electronic components that require bending resistance such as a bent portion around a small liquid crystal such as a smartphone. Further, the flexible copper clad laminate of the present embodiment has a performance capable of withstanding intermittent repeated sliding required for a wiring board and a copper foil layer that is advantageous for forming a high-density wiring. Therefore, it is also suitably used as an FPC material for a read / write cable in a hard disk drive.

  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]
In measuring the tensile elastic modulus, a copper foil subjected to a heat treatment equivalent to the treatment process of the flexible copper-clad laminate using a vacuum oven was used. Moreover, regarding the polyimide layer, the polyimide film which etched the flexible copper clad laminated board and removed copper foil completely was used. The material obtained in this manner was measured for tensile modulus in an environment of a temperature of 23 ° C. and a relative humidity of 50% using a strograph R-1 manufactured by Toyo Seiki Seisakusho.

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

[Measurement of glass transition temperature]
A polyamic acid resin solution was applied onto a copper foil and heat-treated to obtain a laminate. A polyimide film (10 mm × 22.6 mm) obtained by etching away the copper foil of this laminate was heated from 20 ° C. to 500 ° C. at 5 ° C./min with a dynamic viscoelasticity measuring device (DMA). The dynamic viscoelasticity was measured and the glass transition temperature Tg (tan δ maximum value) was determined.

[Measurement of average grain size of copper foil in thickness direction]
A sample was prepared, and a cross section of the copper foil was formed along the longitudinal direction (MD direction) of the copper foil by the IP (ion polish) method (cross section cut in the thickness direction), and OIM (software Ver5.2 manufactured by TSL) ) Was used to analyze the crystal grain size and orientation state of the copper foil cross section by EBSD (Backscattered Electron Diffraction Pattern Method). 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 crystal orientation I / Io by XRD]
Regarding the (200) plane crystal orientation of the copper foil, the (200) plane diffraction intensity of the sample with respect to the (220) plane diffraction intensity (Io) obtained by X-ray diffraction of fine powder copper by the XRD method using a Mo counter-cathode. (I) was calculated and defined as the I / Io value.

[Measurement of surface roughness (Rz)]
Using a contact-type surface roughness measuring machine (SE1700, manufactured by Kosaka Laboratory Ltd.), the surface roughness on the contact surface side between the copper foil and the polyimide insulating layer was measured.

[Measurement of etching factor]
A resist pattern (60 μm pitch circuit) of L / S = 50 μm / 10 μm is formed on the copper foil surface with a film resist, etched with ferric chloride (liquid temperature 50 ° C., 0.2 MPa), and the circuit bottom width is 30 μm. Before and after, the etching factor (EF) was calculated for 10 circuits, and the average value was obtained. The etching factor is the amount of sagging from the intersection of the vertical line from the edge in the width direction of the top surface of the circuit and the resin substrate when the circuit is etched vertically (when sagging occurs). When the distance of the length is D, the ratio of D to the thickness H of the copper foil: H / D is shown. The larger the value, the larger the inclination angle, and no etching residue remains. Since the sagging is reduced, it means that the workability of the fine wiring circuit is excellent. The case where the value of this etching factor was 2.5 or more was evaluated as “good”, and the case where it was less than 2.5 was evaluated as “bad”.

[Measurement of seam fold (bending test)]
A test piece (test circuit board piece) 40 in which a copper foil of a copper-clad laminate was etched and 10 rows of copper wirings 51 having a line width of 100 μm and a space width of 100 μm and a length of 40 mm were formed along the longitudinal direction. (Fig. 2). As shown in FIG. 2 showing only the copper wiring 51 in the test piece 40, the 10 rows of copper wirings 51 in the test piece 40 are all continuously connected via the U-shaped portion 52, and are connected to both ends thereof. Is provided with an electrode portion (not shown) for measuring the resistance value.

  The test piece 40 was fixed on the sample stages 20 and 21 that can be folded in half, and resistance value measurement wiring was connected to start monitoring of the resistance value (FIG. 3). The bending test was performed with respect to ten rows of copper wirings 51 by bending the copper wirings 51 so that they face each other at the center in the longitudinal direction. At this time, using the roller 22 made of urethane, the roller 22 is moved in parallel with the bent line while controlling the gap H of the bent portion 40C to be 0.3 mm, and all the 10 rows of copper wirings 51 are moved. After bending (FIGS. 4 and 5), the bent portion is opened to return the test piece 40 to a flat state (FIG. 6), and the creased portion is moved again while being suppressed by the roller 22 (FIG. 7). In this series of steps, the number of times of folding is counted as one. While the bending test is repeated in such a procedure, the resistance value of the copper wiring 51 is constantly monitored, and when the predetermined resistance (3000 Ω) is reached, it is determined that the copper wiring 51 is broken, and the bending is repeated until that time. The number of times was taken as the measured value of the folded fold. This case was evaluated as “good” when the measured value of the folding angle was 100 times or more and “bad” when it was less than 100 times.

  In the bending test, when using the test piece 40 that has been bent from the beginning, the state once unfolded to cancel the bending is regarded as zero folding, and the number of folding is counted according to the above procedure.

  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. ) Was added and dissolved in the container with stirring. Next, pyromellitic dianhydride (PMDA) was added so that the total amount of monomers added 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, and the glass transition temperature was 312 ° C.

(Synthesis Example 2)
A reaction vessel equipped with a thermocouple and a stirrer and capable of introducing nitrogen is charged with N, N-dimethylacetamide, and 2,2′-dimethyl-4,4′-diaminobiphenyl (m-TB) is added to the reaction vessel. Was dissolved while stirring in a container. Next, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) and pyromellitic dianhydride (PMDA) were added in a total monomer amount of 15 wt%, and the molar ratio of each acid anhydride ( (BPDA: PMDA) was charged to 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 25 μm-thick polyimide film formed from the polyamic acid b had a coefficient of thermal expansion (CTE) of 7 × 10 ⁻⁶ / K and a glass transition temperature of 385 ° C.

(Synthesis Example 3)
A reaction vessel equipped with a thermocouple and a stirrer and capable of introducing nitrogen is charged with N, N-dimethylacetamide, and 2,2′-dimethyl-4,4′-diaminobiphenyl (m-TB) is added to the reaction vessel. Then, 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 added 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 a 25 μm thick polyimide film formed from the polyamic acid c was 10 × 10 ⁻⁶ / K, and the glass transition temperature was 409 ° C.

Example 1
As the first copper foil, the polyamic acid a resin solution prepared in Synthesis Example 1 was continuously applied and dried on a long electrolytic copper foil having a thickness of 12 μm (manufactured by Nippon Electrolytic Co., Ltd.), and further The resin solution of polyamic acid b prepared in Synthesis Example 2 and the resin solution a were sequentially applied thereon and dried at 120 ° C. for about 3 minutes. Thereafter, a heat treatment was finally performed at 300 ° C. or higher for about 2 minutes to obtain a long single-sided flexible copper-clad laminate having a total polyimide layer thickness of 12 μm and a tensile modulus of 7 GPa. Next, a long rolled copper foil having a thickness of 12 μm (HA foil manufactured by JX Nippon Mining & Metals) is heated as the second copper foil to the surface of the polyimide layer of the single-sided flexible copper-clad laminate. Crimped. As a laminating apparatus, a long base material to be laminated is conveyed from an unwinding shaft through a guide roll, and a pair of opposing metal rolls (surface roughness Ra = 0.15 μm) in a furnace under an inert atmosphere. The method of thermocompression bonding was applied. The thermocompression bonding conditions were a temperature of 360 ° C., a pressure of 130 kg / cm, and a passage time of 2 to 5 seconds (laminate: thermocompression bonding process). Thereafter, heat treatment was performed for 60 seconds in a heated hot stove at 380 ° C. (reheating step) to obtain a double-sided flexible copper-clad laminate. The ratio of the thickness of the polyimide layer and the second copper foil layer at this time was 1.0.

In the double-sided flexible copper-clad laminate obtained above, the average crystal grain size of the cross section in the thickness direction calculated from the EBSD analysis is 3 for the copper foil coated with the polyamic acid resin solution (referred to as “cast copper face”). 0.5 μm, (T1) × (D1) = 42 μm ² , and the etching factor was 3.0, indicating good fine wiring processability. Moreover, about the copper foil laminated | stacked by the thermocompression bonding process (it is called "lamination surface copper foil"), the tensile elasticity modulus is 14 GPa, the average crystal grain diameter of the thickness direction cross section computed from the EBSD analysis is 56.7 micrometers, and thickness direction The ratio I / Io between the (200) plane diffraction intensity (I) determined by X-ray diffraction and the (220) plane diffraction intensity (Io) determined by X-ray diffraction of fine powder copper was 18.5. The cast surface copper foil was removed by etching and the laminate surface copper foil was etched to form a FPC with a fold measurement value of 148 times, indicating good bending resistance. The results are shown in Tables 1-3.

(Example 2)
As the second copper foil, the same process as in Example 1 was performed except that a long rolled copper foil (HA foil manufactured by JX Nippon Mining & Metals Co., Ltd.) having a thickness of 18 μm was used. A long double-sided flexible copper-clad laminate having a thickness of 12 μm, a tensile modulus of 7 GPa, and a thickness ratio of the polyimide layer to the second copper foil layer of 1.5 was obtained. Tables 1 to 3 show the average crystal grain size, (T1) × (D1), and etching factor of the cross section in the thickness direction of the first copper foil layer. Moreover, the tensile modulus of elasticity of the second copper foil layer, the average crystal grain size in the cross section in the thickness direction, I / Io, and the FPC fold measurement value of the FPC formed by wiring the laminated surface copper foil are also shown. Yes.

(Example 3)
As the second copper foil, except that a long rolled copper foil having a thickness of 12 μm (HA-V2 foil manufactured by JX Nippon Mining & Metals Co., Ltd.) was used, the same procedure as in Example 1 was performed, and the entire polyimide layer film A long double-sided flexible copper-clad laminate having a thickness of 12 μm, a tensile modulus of 7 GPa, and a thickness ratio of the polyimide layer to the second copper foil layer of 1.0 was obtained. Tables 1 to 3 show the average crystal grain size, (T1) × (D1), and etching factor of the cross section in the thickness direction of the first copper foil layer. Moreover, the tensile modulus of elasticity of the second copper foil layer, the average crystal grain size in the cross section in the thickness direction, I / Io, and the FPC fold measurement value of the FPC formed by wiring the laminated surface copper foil are also shown. Yes.

Example 4
As the first copper foil, the same procedure as in Example 2 was performed except that a long electrolytic copper foil (F2-WS foil manufactured by Furukawa Electric Co., Ltd.) having a thickness of 18 μm was used. A long double-sided flexible copper-clad laminate having a thickness of 12 μm, a tensile modulus of 7 GPa, and a thickness ratio of the polyimide layer to the second copper foil layer of 1.5 was obtained. Tables 1 to 3 show the average crystal grain size, (T1) × (D1), and etching factor of the cross section in the thickness direction of the first copper foil layer. Moreover, the tensile modulus of elasticity of the second copper foil layer, the average crystal grain size in the cross section in the thickness direction, I / Io, and the FPC fold measurement value of the FPC formed by wiring the laminated surface copper foil are also shown. Yes.

(Example 5)
As the first copper foil, except that an elongate electrolytic copper foil (SEED-S foil made by Nippon Electrolytic Co., Ltd.) having a thickness of 6 μm was used, the same procedure as in Example 1 was performed, and the total thickness of the polyimide layer was 12 μm. A long double-sided flexible copper-clad laminate having a tensile modulus of 7 GPa and a ratio of the thickness of the polyimide layer to the second copper foil layer of 1.0 was obtained. Tables 1 to 3 show the average crystal grain size, (T1) × (D1), and etching factor of the cross section in the thickness direction of the first copper foil layer. Moreover, the tensile modulus of elasticity of the second copper foil layer, the average crystal grain size in the cross section in the thickness direction, I / Io, and the FPC fold measurement value of the FPC formed by wiring the laminated surface copper foil are also shown. Yes.

(Example 6)
On the first copper foil, the polyamic acid a resin solution prepared in Synthesis Example 1 is continuously applied and dried, and then the polyamic acid c resin solution prepared in Synthesis Example 3 and the polyamic acid a resin solution are further prepared. Are applied in the same manner as in Example 1 except that a polyimide layer having a total film thickness of 16 μm and a tensile modulus of 5 GPa is formed, and the ratio of the thickness of the polyimide layer to the second copper foil layer is 0. .75 long double-sided flexible copper-clad laminate was obtained. Tables 1 to 3 show the average crystal grain size, (T1) × (D1), and etching factor of the cross section in the thickness direction of the first copper foil layer. Moreover, the tensile modulus of elasticity of the second copper foil layer, the average crystal grain size in the cross section in the thickness direction, I / Io, and the FPC fold measurement value of the FPC formed by wiring the laminated surface copper foil are also shown. Yes.

(Comparative Example 1)
Resin solution a / resin solution b in the same manner as in Example 1 on a long rolled copper foil (BHY-22B-T foil manufactured by JX Nippon Mining & Metals) having a thickness of 18 μm as the first copper foil / Resin solution a is applied and dried one after another, and finally a heat treatment is performed at 300 ° C. or higher for about 2 minutes, so that the total thickness of the polyimide layer is 12 μm and the long single-sided flexible copper-clad laminate with a tensile modulus of 7 GPa A plate is obtained, and a 6 μm-thick electrolytic copper foil (SEED-S foil manufactured by Nihon Electrolytic Co., Ltd.) is used as the second copper foil, on the polyimide layer surface of the single-sided flexible copper-clad laminate. It heat-pressed similarly to Example 1, Then, it heat-processed for 60 second with a 380 degreeC heating hot air oven, and obtained the double-sided flexible copper clad laminated board. The thickness ratio of the polyimide layer and the second copper foil layer at this time was 0.5.

The average crystal grain size of the cross section in the thickness direction of the cast-surface copper foil in the double-sided flexible copper-clad laminate obtained above was 10.0 μm and (T1) × (D1) = 180 μm ² . The etching factor was 2.1, indicating that the fine wiring processability was insufficient in practice. Moreover, the tensile modulus of the laminated surface copper foil was 55 GPa, the average crystal grain size of the cross section in the thickness direction calculated by EBSD analysis was 1.8 μm, and the diffraction strength of the (200) plane determined by X-ray diffraction in the thickness direction ( The ratio I / Io between I) and the (220) plane diffraction intensity (Io) determined by X-ray diffraction of fine powdered copper was 0.34. The cast surface copper foil was removed by etching and the laminate surface copper foil was etched to form an FPC with a folded fold measurement value of 66 times, which showed insufficient bending resistance in practical use. The results are shown in Tables 1-3.

(Comparative Example 2)
As the first copper foil, a long rolled copper foil having a thickness of 12 μm (BHY-22B-T foil manufactured by JX Nippon Mining & Metals Co., Ltd.) is used as the second copper foil, and the length of the electrolytic film is 12 μm. Except for using copper foil (HLB foil manufactured by Nihon Electrolytic Co., Ltd.), the same procedure as in Example 1 was performed. The total thickness of the polyimide layer was 12 μm, the tensile modulus was 7 GPa, and the thickness of the polyimide layer and the second copper foil layer. A long double-sided flexible copper-clad laminate with a ratio of 1.0 was obtained. Tables 1 to 3 show the average crystal grain size, (T1) × (D1), and etching factor of the cross section in the thickness direction of the first copper foil layer. Moreover, the tensile modulus of elasticity of the second copper foil layer, the average crystal grain size in the cross section in the thickness direction, I / Io, and the FPC fold measurement value of the FPC formed by wiring the laminated surface copper foil are also shown. Yes.

(Comparative Example 3)
A double-sided flexible copper-clad laminate was obtained in the same manner as in Example 3 except that the heat treatment in the heating hot stove after thermocompression bonding of the surface of the polyimide layer of the single-sided flexible copper-clad laminate and the second copper foil was removed. . Tables 1 to 3 show the average crystal grain size, (T1) × (D1), and etching factor of the cross section in the thickness direction of the first copper foil layer. Moreover, the tensile modulus of elasticity of the second copper foil layer, the average crystal grain size in the cross section in the thickness direction, I / Io, and the FPC fold measurement value of the FPC formed by wiring the laminated surface copper foil are also shown. Yes.

(Comparative Example 4)
A double-sided flexible copper-clad laminate was obtained in the same manner as in Example 2 except that the heat treatment in the heating hot stove after thermocompression bonding of the surface of the polyimide layer of the single-sided flexible copper-clad laminate and the second copper foil was removed. . Tables 1 to 3 show the average crystal grain size, (T1) × (D1), and etching factor of the cross section in the thickness direction of the first copper foil layer. Moreover, the tensile modulus of elasticity of the second copper foil layer, the average crystal grain size in the cross section in the thickness direction, I / Io, and the FPC fold measurement value of the FPC formed by wiring the laminated surface copper foil are also shown. Yes.

  As mentioned above, although embodiment of this invention was described in detail for the purpose of illustration, this invention is not restrict | limited to the said embodiment.

10: Bending portion 20, 21: Sample stage 22: Roller 40: Test piece 40C: Bending part 51 of test piece: Copper wiring 52: U-shaped portion of copper wiring

Claims (6)

The polyimide insulating layer (A), the first copper foil layer (B1) provided on one surface of the polyimide insulating layer (A), and the other surface of the polyimide insulating layer (A) A flexible copper-clad laminate comprising a second copper foil layer (B2), comprising the following a and b:
a) The first copper foil layer (B1) has a surface roughness (Rz) of a surface in contact with the polyimide insulating layer (A) in the range of 0.7 to 2.5 μm and a thickness (T1). In the relationship between the thickness (T1) and the average crystal grain size (D1) in the cross section in the thickness direction after thermocompression bonding, (T1) × (D1) is 10.8. Consisting of a copper foil in the range of ~ 59 μm ² ;
b) The second copper foil layer (B2) has a surface roughness (Rz) in a range of 0.1 to 1.5 μm and a thickness of 5 to 20 μm in contact with the polyimide insulating layer (A). X-ray diffraction after the thermocompression bonding, the tensile elastic modulus is in the range of 10-25 GPa, the average crystal grain size in the cross section in the thickness direction after thermocompression bonding is in the range of 40-70 μm. The ratio (I / I ₀ ) between the diffraction intensity (I) of the (200) plane determined by (1) and the diffraction intensity (I ₀ ) of the (220) plane determined by X-ray diffraction of fine powder copper is 15.4 to 18 Consisting of copper foil within the range of .5 ;
A flexible copper clad laminate comprising: And the configuration of c;
c) The polyimide insulating layer (A) has a thickness in the range of 7 to 17 μm and a tensile elastic modulus at 25 ° C. in the range of 2 to 9 GPa;
The flexible copper clad laminate according to claim 1, comprising: And the configuration of d;
d) The ratio of the thickness of the polyimide insulating layer (A) to the second copper foil layer (B2) [the thickness of the second copper foil layer (B2) / the thickness of the polyimide insulating layer (A)] is 0. Within the range of .48 to 2.4;
The flexible copper clad laminate according to claim 1 or 2, comprising:   A flexible circuit board according to any one of claims 1 to 3, which is used in a flexible circuit board that is folded and stored by folding into a casing of an electronic device so that the upper surface is turned 180 degrees and turned to the lower surface. Copper-clad laminate.   The flexible circuit board which uses at least one part of a wiring circuit for a bending part using the 2nd copper foil layer (B2) of the flexible copper clad laminated board of any one of Claims 1-4. The flexible circuit board according to claim 5, wherein at least the first copper foil layer (B1) at a position corresponding to the bent portion is removed.

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