JP2007305704A - Flexible circuit substrate with enhanced flexibility - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flexible circuit substrate with enhanced flexibility without comparatively limiting a material to be used. <P>SOLUTION: The flexible circuit substrate 10 is obtained by forming a circuit 13 with copper foil on a first base film 14, and allowing an adhesive layer 12 to adhere onto a coverlay film including a second base film 11 so as to protect the circuit. The flexibility of an FPC is enhanced by using a film with the MIT flaw coefficient of not less than 30 concerning the first base film 14 and/or the second base film 11. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a highly flexible flexible circuit board.

  A flexible circuit board (also referred to as a flexible printed wiring board or a flexible printed wiring board) (hereinafter abbreviated as FPC) has a conductor patterned between a polyimide film and a polyethylene terephthalate film sandwiched with an epoxy or acrylic adhesive. Since it has a structure and can be bent, it is used as a cable replacement or circuit board that requires bending.

  In recent years, the electronics field has been remarkably developed, and in particular, electronic devices for communication and consumer use have been reduced in size, weight and density, and the demand for these performances has become increasingly sophisticated. In response to such demands, flexible circuit boards (FPCs) are flexible and can withstand repeated bending, so that they can be mounted in three-dimensional high density in a narrow space. Wiring to electronic devices, cables, or Its application is expanding as a composite part with a connector function. In recent years, the FPC has been increasingly used to connect a machine body such as a printer, a floppy (registered trademark) disk drive, and a hard disk drive to movable parts, and accordingly, the demand for flexibility has become particularly strong. ing. Therefore, as a method for improving the flexibility of the FPC, Patent Document 1 defines the composition of the copper foil, Patent Document 2 defines the complex shear elastic modulus of the adhesive used for the FPC, Patent Document 3 proposes to define the elastic modulus of the base film and the cover film.

However, these proposals often limit the materials used.
JP 2000-212661 A JP 2000-1531030 A JP-A-6-164085

  The present invention has been accomplished as a result of studying the solution of the above-described problems in the prior art as an object, and an object thereof is to provide a flexible circuit board having high flexibility without relatively limiting the materials to be used. Is.

  The present invention provides a flexible circuit board having a structure in which a copper foil on a first base film is formed as a circuit, and a coverlay film including an adhesive layer and a second base film is bonded to protect the circuit. The base film and / or the second base film is a flexible circuit board having a MIT scratch coefficient of 30 or more. Further, the first base film and / or the second base film may be a polyimide film.

  According to the present invention, a flexible circuit board having a sufficient bending life can be provided.

  Hereinafter, the flexible circuit board of the present invention will be described.

  The flexible circuit board of the present invention is produced as follows. First, a copper foil is formed on a first base film to form a flexible metal-clad laminate, and a circuit is formed. A coverlay film including an adhesive layer and a second base film is laminated thereon to protect the circuit, thereby forming a flexible circuit board. Each process will be described in detail below.

<Flexible metal-clad laminate>
First, the flexible metal-clad laminate used in the present invention will be described.

  The first base film used in the flexible metal-clad laminate of the present invention is not particularly limited, but is preferably a polyimide film in view of the usage environment of the flexible circuit board.

  Moreover, the 1st base film and the 2nd base film used for the coverlay film mentioned later may be the same, and may differ. Therefore, the polyimide film described below can be used as the first base film, and can also be used as the second base film.

  Below, the method to obtain a typical polyimide film as a 1st base film is demonstrated.

  First, the polyamic acid organic solvent solution which is a precursor for obtaining a polyimide film will be described.

  As a method for producing the polyamic acid, a known method can be used. Usually, at least one aromatic dianhydride and at least one diamine are dissolved in a substantially equimolar amount in an organic solvent, The resulting organic solvent solution is produced by stirring under controlled temperature conditions until polymerization of the acid dianhydride and diamine is completed.

  Any known method can be used as the polymerization method.

  Here, the material used for the polyamic-acid organic solvent solution concerning this invention is demonstrated. The material is not particularly limited. From the point that it is possible to control film properties, linear expansion coefficient, elastic modulus, chemical resistance, water absorption, hygroscopic expansion coefficient, etc. necessary for using the obtained polyimide film laminate for FPC, TAB, and COF applications. Suitable acid dianhydrides that can be used in the above are pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic acid Examples thereof include dianhydrides, 4,4′-oxyphthalic dianhydride, p-phenylenebis (trimellitic acid monoester acid anhydride), and the like. It is preferable to use at least one selected from these exemplified acid dianhydrides.

  As a suitable diamine that can be used in the polyamic acid according to the present invention, a diamine having a rigid structure and a diamine having a flexible structure can be used in combination. In order to control the value of the linear expansion coefficient of the obtained film, the linear expansion coefficient can be reduced when the use ratio of the rigid diamine is increased, and the linear expansion coefficient is increased when the use ratio of the diamine having a flexible structure is increased. can do.

  Examples of the diamine having a flexible structure include 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 2,2-bis {4- (4-aminophenoxy) phenyl} propane, and the like.

  Examples of the diamine having a rigid structure include paraphenylenediamine.

  As the preferred solvent for synthesizing the polyamic acid, any solvent can be used as long as it dissolves the polyamic acid. However, amide solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl are preferred. -2-pyrrolidone and the like can be mentioned, and these are preferably used alone or in combination.

  Next, a method for obtaining a polyimide film from a polyamic acid organic solvent solution will be described. A polyimide gel film is obtained by chemically cyclizing the polyamic acid organic solvent solution using a cyclization catalyst and a dehydrating agent or by thermal cyclization.

  When the resulting polyamic acid is cyclized into a polyimide film, either a chemical ring closure method using a dehydrating agent and an imidization catalyst to dehydrate, or a thermal ring closure method using thermal dehydration, Productivity tends to be better with the chemical ring closure method. In addition, what is necessary is just to implement the film formation method by a chemical ring closure method and a thermal ring closure method suitably referring a well-known public method.

  The dehydrating agent and imidation catalyst used in the chemical ring closure method will be described. Examples of the dehydrating agent include aliphatic acid anhydrides such as acetic anhydride and aromatic acid anhydrides such as benzoic anhydride. Examples of the imidization catalyst include aliphatic tertiary amines such as triethylamine, aromatic tertiary amines such as dimethylaniline, and heterocyclic tertiary amines such as pyridine, picoline, isoquinoline, and dimethylpyridine. Can be mentioned.

  A thin film of the solution is formed by continuously casting the mixed solution of the polyamic acid organic solvent solution, the dehydrating agent and the imidization catalyst on the surface of a metal support having a smooth surface. Next, the thin film is dried, and the heating conditions at that time are preferably 60 to 160 ° C. and about 2 to 20 minutes. Thereafter, the self-supporting film (gel film) is peeled off from the metal support, and the gel film is gripped at both ends by a film gripping device attached to a chain driven along the rail. A polyimide film is obtained by inserting into a continuous heating furnace and heating.

  Next, a method for obtaining a flexible metal-clad laminate will be described. Generally, there are five types of methods for obtaining a flexible metal-clad laminate, and the first method is to laminate an adhesive typified by epoxy, acrylic, phenol, etc. on at least one side on a polyimide film, It is obtained by bonding copper foil used as a conductor layer after that. The second method can be obtained by laminating a polyimide-based adhesive, particularly preferably a thermoplastic polyimide resin, on at least one surface of a polyimide film, and then bonding a copper foil serving as a conductor layer. In the third method, a polyimide resin is laminated on a copper foil serving as a conductor layer to obtain a flexible metal-clad laminate. In the fourth method, a polyamic acid resin is laminated on a copper foil serving as a conductor layer, and then heated and dried to obtain a flexible metal-clad laminate using the polyamic acid resin as a polyimide resin. Here, in the third and fourth methods, a polyimide resin layer having a multilayer structure of two or more layers is used for the purpose of reducing warpage of the flexible metal-clad laminate produced by solvent evaporation or the like, or inorganic to the polyimide resin layer. You may take means, such as adding a filler. The fifth method is obtained by laminating a conductor layer on a polyimide film by a dry plating method and / or a wet plating method. The conductor layer used at this time is preferably made of a metal such as copper, chromium, or nickel.

  Of the methods described above, as an example, a method using an adhesive will be described below.

  The flexible metal-clad laminate according to the present invention can be obtained by bonding a metal foil to the polyimide film via an adhesive. The metal foil to be used is not particularly limited, but when the flexible metal-clad laminate of the present invention is used for electronic equipment / electric equipment, for example, copper or copper alloy, stainless steel or its alloy, nickel Alternatively, a foil made of a nickel alloy (including 42 alloy), aluminum, or an aluminum alloy can be used. In general flexible metal-clad laminates, copper foil such as rolled copper foil and electrolytic copper foil is frequently used, but it can also be preferably used in the present invention. In addition, you may implement the coupling agent process etc. in order to improve the antirust layer, a heat-resistant layer, or adhesiveness on the surface of these metal foils. In the present invention, the thickness of the metal foil is not particularly limited, and may be any thickness as long as a sufficient function can be exhibited depending on the application.

<Flexible circuit board>
Next, the flexible circuit board will be described.

  A general basic structure of a flexible circuit board obtained by laminating conductor layers using an adhesive is shown in FIG. 1 (cross-sectional view). There are flexible circuit boards in which the conductor layer (copper layer) is disposed only on one side of the first base film (single-sided FPC) and those in which both sides of the first base film are disposed (double-sided FPC). However, a single-sided FPC will be described as an example.

  The flexible circuit board 10 first forms a circuit 13 by etching a copper foil of a material (flexible metal-clad laminate) in which a copper foil is laminated on one side of a polyimide film 14 as a first base film into a predetermined pattern. To do.

  The flexible metal-clad laminate may be either a polyimide film directly formed with a copper foil or a laminate with an adhesive.

  In this example, the first base film and the copper foil are bonded together via the adhesive layer 15.

  As the adhesive to be used, various resins such as acrylic, epoxy, and polyimide are appropriately selected in consideration of the use and the thickness of the FPC layer.

  Next, a flexible circuit board is obtained by laminating a coverlay film on the circuit side of the laminate on which the circuit is formed.

  In this example, the coverlay film is illustrated as a laminate of the polyimide film 11 that is the second base film and the adhesive layer 12. A publicly known and publicly used method is applied to the method for producing the coverlay film and the method for laminating the laminate formed with the circuit.

  Here, the flexibility of the flexible circuit board can be improved by using a film that satisfies the following conditions as the characteristics of the second base film used for the first base film and / or the coverlay film.

  The above conditions are as follows.

  The base film was cut to 15mm x 130mm, and the tester was stopped when it was refracted 1000 times with a load of 500g, a refraction angle of 135 °, a refraction cycle of 175cpm, and a refractive part locality radius of 0.38mm. Then, the base film sample was removed, and the surface of the base film was observed with a microscope to observe scratches generated on the film surface. As the observation location, the bending location of the testing machine is observed within a range of width 0.5 mm × length 0.5 mm, and the number of scratches occurring at a length of 30 to 100 μm in the film longitudinal direction is counted. In the present application, this number of scratches is defined as an MIT scratch coefficient. It has been found that by using a base film having an MIT scratch coefficient of 30 or more, preferably 40 or more, for the first base film and / or the second base film, the number of flexures of the flexible circuit board (FPC) is greatly improved. More preferably, a base film having an MIT scratch coefficient of 40 or more is preferably used. As the base film, a polyimide film is preferable from the viewpoint of bending resistance.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited only to these Examples.

Example 1
(Manufacturing method of base film)
In the DMAc solution, 4,4′-diaminodiphenyl ether (1 equivalent) was dissolved, and after dissolution, pyromellitic dianhydride (0.96 equivalent) was added and dissolved. Thereafter, a solution of pyromellitic dianhydride dissolved in DMAc (solid content concentration 6%) was gradually added, and the addition and stirring were terminated when the viscosity reached 3000 poise at 23 ° C.
This polymerization solution is cooled to about 0 ° C., a mixed solution of acetic anhydride, isoquinoline and DMAc is added and stirred sufficiently, and then extruded from a die maintained at about 0 ° C. and cast onto an endless belt. Dry until self-supporting on the belt, then peel off from the endless belt, fix both ends of the film to the pin sheet that is continuously conveyed to the sheet, 1st heating furnace, 2nd heating furnace, 3rd heating furnace When the film was transported to the fourth heating furnace and the slow cooling furnace and unloaded from the slow cooling furnace, the film was peeled off from the pin sheet and wound up to obtain a 12.5 um polyimide film having a width of about 1.1 m.

(FPC production)
An epoxy adhesive is applied to one side of the polyimide film obtained above so as to have a thickness after curing of 13 um, heated and semi-cured, and a rolled copper foil (thickness of 12 um) is thermocompression bonded, After-curing, a flexible metal-clad laminate was obtained. The circuit shown in FIG. 2 is formed from the obtained flexible metal-clad laminate, and the polyimide film obtained above has a semi-cured epoxy adhesive (the thickness of the cured adhesive is 13 μm). Was heat-pressed, the circuit was protected, and after-curing was performed to obtain a flexible circuit board (FPC).

(MIT flex test)
Using an MIT bending tester manufactured by Toyo Seiki Co., Ltd., the number of times until the energized state was cut off due to circuit breakage was measured by an energization test under the conditions of a load of 500 g, a refraction angle of 135 °, a refraction cycle of 175 cpm, and a refractive part locality radius of 0.38 mm. The number of MIT flexing was 11137. The results are shown in Table 1.

(Measurement of MIT scratch coefficient of polyimide film)
The polyimide film was cut into 15mm x 130mm, and the tester was stopped when it was refracted 1000 times with a load of 500g, a refraction angle of 135 °, a refraction cycle of 175cpm, and a refractive part locality radius of 0.38mm with a Toyo Seiki MIT tester. Then, the polyimide film sample was removed, the surface of the polyimide film was observed with a microscope, and scratches generated on the film surface were observed. As the observation location, the bending location of the tester was observed within a range of width 0.5 mm × length 0.5 mm, and the number of scratches occurring at a length of 30 to 100 μm in the film longitudinal direction was counted. The MIT scratch coefficient was 54. The results are shown in Table 1.

（実施例２）
ポリイミドフィルムの製造方法を下記のように変更した以外は実施例１と同様に実施した。得られたポリイミドフィルムを用いて実施例１と同様にしてＦＰＣを作製しＭＩＴ屈曲試験を実施した。ＭＩＴキズ係数は４５であり、ＭＩＴ屈曲回数は８２１１回であった。結果を表１に示す。

(Example 2)
It implemented like Example 1 except having changed the manufacturing method of a polyimide film as follows. Using the obtained polyimide film, an FPC was produced in the same manner as in Example 1, and an MIT flex test was performed. The MIT scratch coefficient was 45, and the MIT flex number was 8211. The results are shown in Table 1.

(Production method of polyimide film)
In a DMF solution, 4,4′-diaminodiphenyl ether (0.75 equivalent) was dissolved, and after dissolution, pyromellitic dianhydride (1 equivalent) was added and dissolved. Thereafter, a solution in which paraphenylenediamine was dissolved in DMF (solid content concentration 20%) was gradually added, and when the viscosity reached 3000 poise at 23 degrees, the addition and stirring were terminated.

  This polymerization solution is cooled to about 0 ° C., a mixed solution of acetic anhydride, isoquinoline and DMAc is added and stirred sufficiently, and then extruded from a die maintained at about 0 ° C. and cast onto an endless belt. Dry until self-supporting on the belt, then peel off from the endless belt, fix both ends of the film to the pin sheet that is continuously conveyed to the sheet, 1st heating furnace, 2nd heating furnace, 3rd heating furnace When the film was transported to the fourth heating furnace and the slow cooling furnace and unloaded from the slow cooling furnace, the film was peeled off from the pin sheet and wound up to obtain a 12.5 um polyimide film having a width of about 1.1 m.

(Example 3)
It implemented like Example 1 except having changed the manufacturing method of a polyimide film as follows. Using the obtained polyimide film, an FPC was produced in the same manner as in Example 1, and an MIT flex test was performed. The MIT scratch coefficient was 31, and the MIT flex number was 5325. The results are shown in Table 1.

(Production method of polyimide film)
In the DMAc solution, 2,2- (bis- (4-aminophenoxy) phenyl) propane (0.6 equivalent) is dissolved, and after dissolution, pyromellitic dianhydride (1 equivalent) is charged and dissolved. It was. Thereafter, a solution in which paraphenylenediamine was dissolved in DMF (solid content concentration 20%) was gradually added, and when the viscosity reached 3000 poise at 23 degrees, the addition and stirring were terminated.
This polymerization solution is cooled to about 0 ° C., a mixed solution of acetic anhydride, isoquinoline and DMAc is added and stirred sufficiently, and then extruded from a die maintained at about 0 ° C. and cast onto an endless belt. Dry until self-supporting on the belt, then peel off from the endless belt, fix both ends of the film to the pin sheet that is continuously conveyed to the sheet, 1st heating furnace, 2nd heating furnace, 3rd heating furnace When the film was transported to the fourth heating furnace and the slow cooling furnace and unloaded from the slow cooling furnace, the film was peeled off from the pin sheet and wound up to obtain a 12.5 um polyimide film having a width of about 1.1 m.

(Comparative Example 1)
It implemented like Example 1 except having changed the manufacturing method of a polyimide film as follows. Using the obtained polyimide film, an FPC was produced in the same manner as in Example 1, and an MIT flex test was performed. The MIT scratch coefficient was 9, and the MIT flex number was 1480. The results are shown in Table 1.

(Production method of polyimide film)
In the DMAc solution, 2,2- (bis- (4-aminophenoxy) phenyl) propane (0.3 equivalent) is dissolved, and after dissolution, 3,4'-diaminodiphenyl ether (0.2 equivalent) is dissolved. It was. Then, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (0.3 equivalent) was dissolved, and after dissolution, pyromellitic dianhydride (0.15 equivalent) was charged and dissolved. . Thereafter, paraphenylenediamine (0.5 equivalent) was dissolved. Thereafter, pyromellitic dianhydride (0.53 equivalent) was added and dissolved. Thereafter, a solution (solid content concentration 6%) of pyromellitic dianhydride dissolved in DMAc was gradually added, and the addition and stirring were terminated when the viscosity reached 3000 poise at 23 degrees.

  This polymerization solution is cooled to about 0 ° C., a mixed solution of acetic anhydride, isoquinoline and DMAc is added and stirred sufficiently, and then extruded from a die maintained at about 0 ° C. and cast onto an endless belt. Dry until self-supporting on the belt, then peel off from the endless belt, fix both ends of the film to the pin sheet that is continuously conveyed to the sheet, 1st heating furnace, 2nd heating furnace, 3rd heating furnace When the film was transported to the fourth heating furnace and the slow cooling furnace and unloaded from the slow cooling furnace, the film was peeled off from the pin sheet and wound up to obtain a 12.5 um polyimide film having a width of about 1.1 m.

  The data of Table 1 obtained above is shown in FIG.

FPC cross section FPC circuit pattern Relationship between MIT scratch coefficient and MIT flex number

Explanation of symbols

11 Second Base Film 12 Adhesive Layer 13 Circuit 14 First Base Film 15 Adhesive Layer

Claims (2)

  A flexible circuit board having a structure in which a copper foil on a first base film is formed, and a coverlay film including an adhesive layer and a second base film is bonded to protect the circuit, wherein the first base film and The flexible circuit board is characterized in that the second base film is a film having an MIT scratch coefficient of 30 or more.   The flexible circuit board according to claim 1, wherein the first base film and / or the second base film is a polyimide film.

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