JP2015070237A - Flexible copper clad laminate and flexible circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flexible copper-clad laminate and a flexible circuit board, capable of preventing the disconnection or crack of a wiring circuit even in a narrow housing and excellent in bending resistance.SOLUTION: The flexible copper clad laminate includes a polyimide insulation layer (A) and copper foil (B). a) the flexible copper clad laminate has a thickness of 15-38 μm, b) the polyimide insulation layer (A) has a thickness of 5-30 μm and a tensile elasticity of 4-10 GPa, c) the copper foil (B) has a thickness of 5-20 μm and a tensile elasticity of 10-35 GPa and d) a ratio [(B)/(A)] of the thickness of the polyimide insulation layer (A) to that of the copper foil (B) is 0.48-1.5. When a bending test at a gap 0.3 mm is provided with a flexible circuit board obtained by processing the copper foil (B) into a wiring circuit, a variation (θ1-θ5) between a bending angle θ1 caused by the first bending and a bending angle θ5 caused by the fifth bending is less than 8°.

Description

The present invention relates to a flexible copper-clad laminate, and more particularly to a flexible copper-clad laminate used for a flexible circuit board (FPC) that is folded and stored 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 a narrower housing 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 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-mentioned problems, and an object of the present invention is to provide a flexible copper-clad laminate and a flexible circuit having excellent bending resistance that can prevent disconnection and cracking of a wiring circuit even in a narrow housing. It is to provide a substrate.

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

That is, the flexible copper-clad laminate of the present invention includes a polyimide insulating layer (A) and a copper foil (B) provided on at least one surface of the polyimide insulating layer (A). This flexible copper-clad laminate has the following configurations a to d:
a) The thickness of the flexible copper-clad laminate is in the range of 15 to 38 μm;
b) The polyimide insulating layer (A) has a thickness in the range of 5 to 30 μm and a tensile modulus of elasticity in the range of 4 to 10 GPa;
c) The copper foil (B) has a thickness in the range of 5 to 20 μm and a tensile modulus of elasticity in the range of 10 to 35 GPa;
d) The ratio of the thickness of the polyimide insulating layer (A) to the copper foil (B) [the thickness of the copper foil (B) / the thickness of the polyimide insulating layer (A)] is in the range of 0.48 to 1.5. Be within;
It comprises. And the flexible copper clad laminated board of this invention is a flexible circuit board created by forming a copper wiring by processing the copper foil (B) of the flexible copper clad laminated board with a gap of 0.3 mm. When subjected to a bending test, the amount of change (θ1−θ5) between the bending angle (θ1) generated by the first bending and the bending angle (θ5) generated by the fifth bending is less than 8 °. It is characterized by.

  The flexible copper-clad laminate of the present invention further comprises a flexible circuit board produced by processing a copper circuit (B) of the flexible copper-clad laminate to form a copper wiring with a gap of 0.3 mm. In the case of the bending test, the amount of change (θ3-θ5) between the bending angle (θ3) generated by the third bending and the bending angle (θ5) generated by the fifth bending is 1 ° or less. Also good.

  A flexible circuit board according to the present invention is obtained by processing a copper foil of any one of the flexible copper-clad laminates as a wiring circuit.

  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.

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 drawing used for description of the bending angle produced by a bending test.

Embodiments of the present invention will be described below.
<Flexible copper-clad laminate>
The flexible copper clad laminate of the present embodiment is composed of a polyimide insulating layer (A) and a copper foil (B). The copper foil (B) is provided on one side or both sides of the polyimide insulating layer (A). This flexible copper-clad laminate is processed as a wiring circuit by etching the copper foil (B) to form a copper wiring and used as a flexible circuit board. In the flexible copper-clad laminate of the present embodiment, when copper foil is provided on both sides of the polyimide insulating layer, the wiring circuit is processed to form a copper wiring, and the copper wiring corresponds to the bent portion. Copper foil is defined as copper foil (B). Therefore, even when the copper foil is provided on both surfaces of the polyimide insulating layer, the wiring circuit is processed to form a copper wiring, and the copper foil in which the copper wiring does not correspond to the bent portion is a copper foil (B). Not.

  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 copper foil (B)] in the range of 15 to 38 μm, preferably in the range of 15 to 35 μm. Inside is good. If the thickness of the flexible copper clad laminate is less than 15 μm, the rigidity of the flexible printed wiring board formed 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 38 μm, bending stress is applied by the copper wiring when the FPC is bent, and the bending resistance is significantly reduced.

<Polyimide insulation layer>
In the flexible copper-clad laminate of the present embodiment, the polyimide insulating layer (A) needs to have a thickness in the range of 5 to 30 μm, depending on the thickness and rigidity of the copper foil (B). The thickness can be set within the range. For example, when the copper foil (B) is a rolled copper foil, the thickness of the polyimide insulating layer (A) is preferably in the range of 10 to 25 μm, more preferably in the range of 10 to 20 μm. It is particularly preferable that it is in the range of ˜15 μm. For example, when the copper foil (B) is an electrolytic copper foil, the thickness of the polyimide insulating layer (A) is preferably in the range of 5 to 30 μm, and more preferably in the range of 8 to 15 μm. , Particularly preferably in the range of 9-12 μm. If the thickness of the polyimide insulating layer (A) is less than the above lower limit, problems such as inability to secure electrical insulation and difficulty in handling in the manufacturing process due to a decrease in handling properties occur. When the thickness of the insulating layer (A) exceeds the above upper limit value, bending stress is applied by the copper wiring when the FPC is bent, and the bending resistance is remarkably lowered.

  Moreover, the tensile elasticity modulus of a polyimide insulating layer (A) needs to be in the range of 4-10 GPa, Preferably it is in the range of 6-10 GPa. If the tensile modulus of the polyimide insulating layer (A) is less than 4 GPa, the strength of the polyimide itself is reduced, which causes handling problems such as film tearing when the flexible copper clad laminate is processed into a circuit board. Sometimes. On the contrary, if the tensile modulus of the polyimide insulating layer (A) exceeds 10 GPa, the bending resistance of the flexible copper clad laminate increases, resulting in an increase in bending stress applied to the copper wiring when the flexible copper clad laminate is folded. And bending resistance will fall.

  The polyimide insulating layer (A) can be a commercially available polyimide film as it is, but from the ease of controlling the thickness and physical properties of the insulating layer, after applying the polyamic acid solution directly on the copper foil, A so-called cast (coating) method in which drying and curing are performed by heat treatment is preferable. Moreover, although a polyimide insulating layer (A) may be formed only from a single layer, when the adhesiveness etc. of a polyimide insulating layer (A) and copper foil (B) are considered, what consists of multiple 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. It is preferable that the polyimide layer (ii) is in direct contact with the copper foil (B). 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 high thermal expansion polyimide layer (ii) obtained in this way is in the range of 300-400 degreeC.

  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 15. If the value of this ratio is less than 2, the low thermal expansion polyimide layer (i) with respect to the entire polyimide insulating layer (A) becomes thin, so it becomes difficult to control the dimensional characteristics of the polyimide film, and the copper foil (B) When the dimensional change rate at the time of etching becomes large and exceeds 15, the polyimide layer (ii) having high thermal expansion becomes thin, so that the adhesion reliability between the polyimide insulating layer (A) and the copper foil (B) is lowered.

<Copper foil>
In the flexible copper clad laminate of the present embodiment, the thickness of the copper foil (B) is in the range of 5 to 20 μm, and preferably in the range of 8 to 15 μm. When the thickness of the copper foil (B) is less than 5 μm, the copper foil (B) itself is formed in the process of forming the polyimide insulating layer (A) on the copper foil (B), for example, during the production of the flexible copper-clad laminate. The rigidity is lowered, and as a result, there arises a problem that wrinkles or 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 (or copper wiring) when the flexible copper-clad laminate (or FPC) is bent. Depending on the type of the copper foil, it tends to be annealed by a predetermined heat treatment to improve the flexibility of the copper foil. Examples of such copper foil include rolled copper foil. From such a viewpoint, when the copper foil (B) is a rolled copper foil, the thickness of the copper foil (B) is preferably within a range of 8 to 20 μm, and within a range of 10 to 15 μm. Is more preferable.

  Moreover, although the tensile elasticity modulus of copper foil (B) exists in the range of 10-35 GPa, for example, when copper foil (B) is a rolled copper foil, it may exist in the range of 10-20 GPa. Preferably, when the copper foil (B) is an electrolytic copper foil, the range of 25 to 35 GPa is more preferable. If the tensile modulus of the copper foil (B) is less than the lower limit, during the production of the flexible copper-clad laminate, for example, in the step of forming the polyimide insulating layer (A) on the copper foil (B), by heating The rigidity of copper foil (B) itself will fall. As a result, the problem that wrinkles etc. generate | occur | produce on a flexible copper clad laminated board arises. On the other hand, when the tensile modulus exceeds the above upper limit value, a large bending stress is applied to the copper wiring when the FPC is bent, and the bending resistance is remarkably lowered.

  The surface of the copper foil (B) may be roughened, and considering the relationship with the rigidity of the copper foil (B), when the copper foil (B) is a rolled copper foil, preferably a polyimide The surface roughness (ten-point average roughness; Rz) of the surface of the copper foil (B) in contact with the insulating layer (A) is preferably in the range of 0.5 to 1.5 μm. When the copper foil (B) is an electrolytic copper foil, preferably, the surface roughness (Rz) of the surface of the copper foil (B) in contact with the polyimide insulating layer (A) is in the range of 0.7 to 2.2 μm, More preferably, it is in the range of 0.8 to 1.6 μm. 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.

  The copper foil (B) used for the flexible copper clad laminate of the present embodiment is not particularly limited as long as it satisfies the above characteristics, and a commercially available copper foil can be used. Specific examples thereof 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 thereof include HL foil and HTE foil manufactured by Mitsui Metal Mining Co., Ltd. Moreover, even if it is a case where other than that including these commercial items is used, the heat processing conditions and polyimide insulation layer at the time of forming the polyimide insulation layer (A) on the copper foil (B) mentioned above Since the tensile elastic modulus of the copper foil (B) can be changed by annealing the copper foil (B) after forming the (A), in the present invention, the flexible copper-clad laminate obtained as a result is the predetermined one. If it becomes the range of.

<Ratio of thickness of polyimide insulating layer (A) and copper foil (B)>
In the present embodiment, the ratio of the thickness of the polyimide insulating layer (A) to the copper foil (B) [the thickness of the copper foil (B) / the thickness of the polyimide insulating layer (A)] is 0.48 to 1.5. It is preferable to be within the range. When the thickness ratio is less than 0.48 or greater than 1.5, the maximum tensile strain when the plastically deformed portion is extended at the time of bending is increased, so that the bending resistance is lowered.

<Change in bending angle>
The flexible copper-clad laminate of the present embodiment was subjected to a bending test with a gap of 0.3 mm using a flexible circuit board formed by forming a copper wiring by processing a copper foil (B) on a wiring circuit. In this case, the amount of change (θ1−θ5) between the bending angle (θ1) generated by the first bending and the bending angle (θ5) generated by the fifth bending is less than 8 °. Here, the amount of change (θ1−θ5) may be a negative value. This amount of change (θ1-θ5) is an index indicating the degree of elasto-plastic deformation of the FPC, and is controlled by the configurations a to d.

  When the flexible circuit board created by forming the copper wiring by processing the copper foil (B) of the flexible copper-clad laminate of the present embodiment to form a copper wiring is subjected to a bending test with a gap of 0.3 mm In this case, the amount of change (θ3-θ5) between the bending angle (θ3) generated by the third bending and the bending angle (θ5) generated by the fifth bending is preferably 1 ° or less. Here, the amount of change (θ3−θ5) may be a negative value. This amount of change (θ3−θ5) is also an index indicating the degree of elasto-plastic deformation of the FPC, and is controlled by the configurations a to d.

  The “bending test with a gap of 0.3 mm” for measuring the bending angles (θ1, θ3, θ5) is performed by the method and conditions described later.

<Action>
In the present embodiment, assuming that the above configurations a to c are satisfied, the ratio of the thickness of the polyimide insulating layer (A) and the copper foil (B) of the configuration d [the thickness of the copper foil (B) / the polyimide insulating layer] The thickness of (A)] is controlled within the range of 0.48 to 1.5, and the amount of change (θ1-θ5) in the bending angle of the flexible circuit board produced from the flexible copper-clad laminate is less than 8 ° Preferably, the amount of change in the bending angle (θ3−θ5) is also set to 1 ° or less. The amount of change in bending angle is calculated from the average bending mean strain in the copper wiring, the distance from the bending center to the neutral plane of the copper wiring, the gap spacing, and the neutral plane position of the copper wiring. It can be determined by the radius of curvature. By controlling within such a range, it is possible to easily disperse the strain at the time of bending in two or more locations without concentrating the strain at the time of bending. As a result, the bending resistance of the flexible circuit board can be improved, and the reliability of the flexible circuit board can be improved by reducing the breakage of the copper wiring or the poor conduction. The reason why such an excellent effect can be obtained can be rationally explained as follows. That is, by satisfying the above configurations a to d, it becomes possible to relatively increase the amount of plastic deformation (expressed as the bending angle θ1) when the flexible circuit board is bent for the first time. You can create a state with a moderately heel. In such a state having an appropriate crease, since the stress applied to the bent portion is greatly relieved when bent from the second time onward, an increase in strain at the bent portion is suppressed, and the flexible circuit board is bent. It is estimated that the performance is greatly improved.

<Manufacture of flexible copper-clad laminates>
The flexible copper clad laminate of the present embodiment is subjected to a heat treatment step in which, for example, a polyimide precursor resin solution (also referred to as a polyamic acid solution) is applied to the surface of the copper foil (B), and then dried and cured. Can be manufactured. The heat treatment in the heat treatment step is to remove the solvent in the polyamic acid by drying and removing the coated polyamic acid solution at a temperature of less than 160 ° C., and then gradually increase the temperature in a temperature range of 150 ° C. to 400 ° C. to cure. It is done by letting. 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 (B) prepared separately from this are 300 to 400 ° C. And a method of thermocompression bonding.

<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.

  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 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 of the copper foil with the polyimide insulating layer was measured.

[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. Was produced (FIG. 1). As shown in FIG. 1 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 a resistance value measurement wiring was connected to start monitoring of the resistance value (FIG. 2). 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 G of the bent portion 40C to be 0.3 mm, and all the 10 rows of copper wirings 51 are moved. After bending (FIGS. 3 and 4), the bent portion is opened to return the test piece 40 to a flat state (FIG. 5), and the creased portion is moved again while being suppressed by the roller 22 (FIG. 6). 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 50 times or more, and “bad” when it was less than 50 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.

[Measure bending angle]
In the above bending test, the test piece 40 is removed from the sample stages 20 and 21 after the number of times of folding, and the angle formed by the folds of the test piece 40 in an unfixed state is measured as shown in FIG. This was defined as the bending angle θ1. The test piece was placed on the sample stage 20 and 21 again, and the bending test was repeated. The bending angle after the total number of times of folding was three times was measured in the same manner, and this was set as the bending angle θ3. Further, the same operation was repeated and the bending angle θ5 after 5 times of folding was measured. Each of the bending angles θ1, θ3, and θ5 is an angle formed by the copper wiring 51 and the copper wiring with the bent portion interposed therebetween.

  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 polyimide film having a thickness of 25 μm formed from the polyamic acid a was 55 × 10 ⁻⁶ / K.

(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 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 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 the polyimide film having a thickness of 25 μm formed from the polyamic acid c was 22 × 10 ⁻⁶ / K.

Example 1
Uniform so that the thickness after curing the resin solution of polyamic acid a prepared in Synthesis Example 1 on one side (surface roughness Rz = 0.8 μm) of a long rolled copper foil having a thickness of 12 μm is 2.2 μm. After coating, the solvent was removed by heating at 130 ° C. Next, the resin solution of polyamic acid b 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, apply the same polyamic acid a resin solution as that applied in the first layer on the coated surface side so that the thickness after curing is 2.2 μm, and heat dry at 130 ° C. to remove the solvent. did. This continuous laminate was heat-treated in a continuous curing furnace set so that the temperature gradually increased from 300 ° C. to 300 ° C. over a period of about 6 minutes. A 12 μm single-sided flexible copper-clad laminate was obtained.

  Table 1 shows the evaluation results of physical properties such as the tensile elastic modulus of the copper foil constituting the obtained flexible copper-clad laminate, the tensile elastic modulus of the polyimide layer, the bending angle and the bending resistance of the flexible copper-clad laminate. . In addition, evaluation of the polyimide layer used what removed the copper foil by etching from the manufactured copper clad laminated board.

(Example 2)
Single-sided flexible copper was used in the same manner as in Example 1 except that a commercially available electrolytic 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. A tension laminate was obtained. Table 1 shows the evaluation results of bending angle and bending resistance of the obtained single-sided flexible copper-clad laminate.

(Example 3)
Example having the characteristics shown in Table 1 and using an electrolytic copper foil having a thickness of 12 μm (surface roughness Rz = 1.1 μm of the coated surface) and changing the thickness configuration 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 structure of the polyimide layer is such that the thickness after curing the polyamic acid a resin solution prepared in Synthesis Example 1 on a copper foil is 2.0 μm, and the polyamic acid b resin prepared in Synthesis Example 2 thereon. The thickness after curing of the solution was 5.0 μm, and the thickness after curing of the resin solution of polyamic acid a prepared in Synthesis Example 1 was 2.0 μm. Table 1 shows the evaluation results of bending angle and bending resistance of the obtained single-sided flexible copper-clad laminate.

Example 4
A single-sided flexible copper was used in the same manner as in Example 3 except that a commercially available electrolytic copper foil having a characteristic shown in Table 1 and a thickness of 9 μm was used as the copper foil (surface roughness Rz = 1.1 μm on the coated surface). A tension laminate was obtained. Table 1 shows the evaluation results of bending angle and bending resistance of the obtained single-sided flexible copper-clad laminate.

(Example 5)
One-sided flexible copper was used 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 = 0.8 μm on the coated surface) was used. A tension laminate was obtained. Table 1 shows the evaluation results of bending angle and bending resistance of the obtained single-sided flexible copper-clad laminate.

(Example 6)
Resin of polyamic acid a prepared in Synthesis Example 1 on a commercially available electrolytic copper foil having a characteristic shown in Table 1 and having a thickness of 12 μm (long surface roughness Rz = 1.1 μm) The solution was uniformly applied 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. Furthermore, the same polyamic acid a resin solution as that applied in the first layer is applied on the coated surface side uniformly so that the thickness after curing is 2.5 μm, and the solvent is removed by heating at 130 ° C. did. 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 period of about 6 minutes, and the polyimide resin layer thickness was 25 μm. A single-sided flexible copper-clad laminate was obtained. Table 1 shows the evaluation results of bending angle and bending resistance of the obtained single-sided flexible copper-clad laminate.

(Comparative Example 1)
Example having the characteristics shown in Table 1 and using an electrolytic copper foil having a thickness of 12 μm (surface roughness Rz = 1.1 μm of the coated surface) and changing the thickness configuration 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 structure of the polyimide layer is such that the thickness after curing the polyamic acid a resin solution prepared in Synthesis Example 1 on a copper foil is 2.0 μm, and the polyamic acid b resin prepared in Synthesis Example 2 thereon. The thickness after curing of the solution was 16.0 μm, and the thickness after curing of the resin solution of polyamic acid a prepared in Synthesis Example 1 was 2.0 μm. Table 1 shows the evaluation results of bending angle and bending resistance of the obtained single-sided flexible copper-clad laminate.

(Comparative Example 2)
Resin of polyamic acid a prepared in Synthesis Example 1 on a commercially available electrolytic copper foil having a characteristic shown in Table 1 and having a thickness of 12 μm (long surface roughness Rz = 1.1 μm) The solution was uniformly applied so that the thickness after curing was 4.0 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 42.0 μm, and the solvent was removed by heating and drying at 120 ° C. Furthermore, the same polyamic acid a resin solution as that applied in the first layer is applied uniformly to the coated surface so that the thickness after curing is 4.0 μm, and the solvent is removed by heating at 130 ° C. did. 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 period of about 10 minutes, and the polyimide resin layer thickness was 50 μm. A single-sided flexible copper-clad laminate was obtained. Table 1 shows the evaluation results of bending angle and bending resistance of the obtained single-sided flexible copper-clad laminate.

(Comparative Example 3)
Single-sided flexible copper as in Comparative Example 2 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 on the coated surface) was used as the copper foil. A tension laminate was obtained. Table 1 shows the evaluation results of bending angle and bending resistance of the obtained single-sided flexible copper-clad laminate.

  The above results are summarized in Table 1.

  From Table 1, the flexible copper clad laminates of Examples 1 to 6 all have the above-described configurations a to d, so that the amount of change in the bending angle (θ1-θ5) is less than 8 °. The measured value of the hull fold was as good as 50 times or more, and the bending resistance was satisfactory. On the other hand, in Comparative Examples 2 and 3 in which the thickness of the polyimide layer exceeded 30 μm, the number of helix folding was small, and the bending resistance was poor. In Comparative Example 1, the configurations a to d described above were provided, but since the amount of change in the bending angle (θ1-θ5) was 10 °, the number of helix folding was small and the bending resistance was poor.

  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.

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

Claims (3)

A flexible copper-clad laminate comprising a polyimide insulating layer (A) and a copper foil (B) provided on at least one surface of the polyimide insulating layer (A), the following configurations a to d:
a) The thickness of the flexible copper-clad laminate is in the range of 15 to 38 μm;
b) The polyimide insulating layer (A) has a thickness in the range of 5 to 30 μm and a tensile modulus of elasticity in the range of 4 to 10 GPa;
c) The copper foil (B) has a thickness in the range of 5 to 20 μm and a tensile modulus of elasticity in the range of 10 to 35 GPa;
d) The ratio of the thickness of the polyimide insulating layer (A) to the copper foil (B) [the thickness of the copper foil (B) / the thickness of the polyimide insulating layer (A)] is in the range of 0.48 to 1.5. Be within;
Comprising
When a flexible circuit board prepared by forming a copper wiring by processing a copper foil (B) of the flexible copper-clad laminate is subjected to a bending test with a gap of 0.3 mm, the first bending is performed. The flexible copper-clad laminate is characterized in that the amount of change (θ1−θ5) between the bending angle (θ1) generated by the bending and the bending angle (θ5) generated by the fifth bending is less than 8 °.   Furthermore, in the case where the flexible circuit board prepared by forming the copper wiring by processing the copper foil (B) of the flexible copper-clad laminate to form a copper wiring is subjected to a bending test with a gap of 0.3 mm, the third time The flexible copper-clad laminate according to claim 1, wherein a change amount (θ3−θ5) between a bending angle (θ3) caused by bending of the wire and a bending angle (θ5) caused by the fifth bending is 1 ° or less. .   The flexible circuit board formed by wiring circuit processing the copper foil of the flexible copper clad laminated board of Claim 1 or 2.

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