WO2006059825A1

WO2006059825A1 - Method of surface modification of polyimide film, manufacturing method of flexible copper clap laminate and its product thereby

Info

Publication number: WO2006059825A1
Application number: PCT/KR2005/001498
Authority: WO
Inventors: Young Taik Hong; Hwi Won Kang; Yong-Seok Kim; Jae Heung Lee
Original assignee: Korea Research Institute Of Chemical Technology; Atec Engineering Co., Ltd.
Priority date: 2004-11-30
Filing date: 2005-05-23
Publication date: 2006-06-08
Also published as: KR100656246B1; KR20060060082A

Abstract

Disclosed herein is a surface modification method of a polyimide film by dipping a polyimide film into a solution containing a diamine compound, a method of manufacturing a flexible copper clad laminate having a two-layered structure, using the above method, and a flexible copper clad laminate manufactured thereby. The surface modification method of a polyimide film includes dipping a polyimide film into a solution containing a specific diamine compound, and therefore, may simplify conventional surface modification method of a polyimide film. In addition, since the flexible copper clad laminate of the invention has a two-layered structure formed through copper sputtering and electroplating on the surface modified polyimide film, it has excellent adhesive strength between the copper foil and the polyimide film, it may be usefully applied to electronic parts, such as flexible printed circuit boards, TCPs (Tape Carrier Packages), COFs (Chips On Film) , etc.

Description

[DESCRIPTION]

[invention Title]

METHOD OF SURFACE MODIFICATION OF POLYIMIDE FILM, MANUFACTURING METHOD OF FLEXIBLE COPPER CLAD LAMINATE AND ITS PRODUCT THEREBY

[Technical Field]

The present invention relates to a flexible copper clad laminate and a method of manufacturing the same. More particularly, the present invention relates to a method of manufacturing a polyimide copper clad laminate having a two- layered structure, comprising dipping a polyimide film into a solution containing a diamine compound to modify surface of the polyimide film, and then sequentially performing sputtering and electroplating under optimal conditions, and to a polyimide copper clad laminate having increased adhesive strength, manufactured thereby.

[Background Art] A polyimide film has been variously applied to flexible printed circuit boards, tape automated bonding (TAB) , COFs (Chips On Film) as an insulating substrate material for electronic parts, since the polyimide film has heat resistance, electrical properties, chemical resistance and bending resistance that are superior to other polymer materials. A conventional copper clad laminate used in flexible printed circuit boards is exemplified by a copper clad laminate having a three-layered structure adhered with an epoxy adhesive. However, the copper clad laminate is improper for fine patterning because heat resistance of the adhesive is poor, thus deteriorating dimensional stability. Recently, it has been accelerated to replace a conventional copper clad laminate having a three-layered structure with a copper clad laminate having a two-layered structure. The two-layered structure is formed by directly die-casting a polyimide film to a copper foil or bonding a polyimide film to a copper foil at a high temperature, without an adhesive layer, and thus, provides advantages such as easy formation of fine patterns, and high flexibility. Moreover, due to the above-mentioned advantages, a copper clad laminate having a two-layered structure may be more widely marketable for use in display products, such as folding mobile phones, LCDs, PDP modules, etc. In particular, since Korea mainly imports substrate materials for use in electronic parts, domestic product of a flexible copper clad laminate (FCCL) having a two-layered structure using a novel process is urgently required. It has been reported on method of manufacturing a two-layered FCCL that was manufactured by laminating a polyimide film and a copper foil, rather than using an adhesive. In addition, sputtering-electroplating methods have been also proposed, in which a thin metal seed layer (nickel, chromium, etc.) is formed through sputtering, and then a copper layer is formed to a desired thickness through electroplating thereon. However, the above method has problems that the surface modification of the polyimide film should be previously preceded using plasma or ion beams, during which a specific seed layer is required.

Particularly, when both-sided copper clad laminate is manufactured, specific equipment is needed, thus the manufacturing cost becomes increased. Further, the adhesive strength of the copper clad laminate becomes unstable under conditions of high temperature and high humidity, resulting in decreased reliability. Furthermore, a drilling process for post-treatment of the prepared PCB (Printed Circuit Board) may cause environmental contamination. Leading to the present invention, intensive and thorough efforts to obtain two-layered FCCLs, carried out by the present inventors, aiming to avoid the problems encountered in the related art, resulted in a method of manufacturing a two-layered FCCL being provided, which comprises dipping a polyimide film into a solution containing a predetermined diamine compound, to obtain a surface modified polyimide film, which then undergoes copper sputtering and copper electroplating under optimal conditions, whereby an FCCL having a two-layered structure, and particularly, a double- sided FCCL, having high adhesive strength, may be easily manufactured.

[Disclosure] [Technical Problem]

Therefore, it is an object of the present invention to provide surface modification method of a polyimide film.

It is another object of the present invention to provide a method of manufacturing an FCCL having a two-layered structure, in which the method of surface modifying a polyimide film is used, and then copper sputtering and copper electroplating are sequentially performed under optimal conditions.

And, it is a further object of the present invention to provide a single-sided or both-sided FCCL, manufactured using the above method.

[Technical Solution] In order to achieve the above objects, the present invention provides a surface modification method of a polyimide film, comprising dipping one or both surfaces of a polyimide film into a solution containing a diamine compound represented by structural formula 1 below: [structural formula l] H₂N R NH₂

(wherein R is

, , or ,

Ri and R₂ are H or NH₂, Ri=R₂ or Ri≠R₂, x=l~5, y=l~5, 2≤x+y≤6, n=l~2, ItI=I, and X=

Specifically, the diamine compound is any one selected from the group consisting of ethylenediamine, triethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, 1,3-phenylenediamine, 1,4- phenylenediamine, 4,4'-diaminodiphenyl methane, 4,4'- diaminodiphenylether, 3,3-diaminobenzophenone, 4,4- diaminobenzophenone, 1,3-bis(aminophenoxy)benzene, 1,4- bis (aminophenoxy)benzene, bis (3-aminophenyl) sulfone, bis(4- aminophenylsulfone) , 3,3-diaminobenzidine, 4,4- (hexafluoroisopropylidine)dianiline, and 3,3- (hexafluoroisopropylidine) dianiline.

Usable in the present invention is a solution containing a diamine composition, prepared by dissolving the above- exemplified diamine compound to a concentration of 0.5-20 M in a solvent selected from the group consisting of water, acetone, methyl alcohol, ethyl alcohol, isopropyl alcohol, and combinations thereof. In addition, the present invention provides a method of manufacturing a copper clad laminate, using the surface modification method of a polyimide film. Specifically, the manufacturing method of the present invention comprises a first step of dipping one or both surfaces of a polyimide film into a solution containing a diamine compound represented by structural formula 1 to surface modify the polyimide film; a second step of washing and drying the surface modified polyimide film; a third step of copper sputtering the dried polyimide film at 0.5~30 mA and 50-500 W for 1-10 hr, to form a copper sputtered layer; and a fourth step of copper electroplating the copper sputtered layer, to form a copper electroplated layer.

In the first step, the dipping for surface modifying the polyimide film may be preferably performed at 40~100^°C for a time ranging from 30 sec to 2 hr. The copper sputtered layer prepared in the third step is 500-5,000 A thick, and the copper electroplated layer prepared in the fourth step is 1-50 μm thick. Therefore, the copper clad laminate of the present invention has a two- layered structure comprising the copper sputtered layer formed on the polyimide film, and the copper electroplated layer formed on the copper sputtered layer.

In addition, the present invention provides a polyimide copper clad laminate, which comprises a 500~5,000 A thick copper sputtered layer formed on one or both surfaces of the polyimide film surface treated by being dipped into the solution containing a diamine compound; and a 1-50 μm thick copper electroplated layer formed on the copper sputtered layer by electroplating the copper sputtered layer.

[Advantageous Effects]

First, a surface modification method of the present invention comprising of dipping the polyimide film into a solution containing a diamine compound, is advantageous because it may substitute for a conventional surface treatment process using ion beams, and also, does not require a specific seed layer, therefore decreasing the cost and reducing environmental contamination due to the use of heavy metals. Further, a post-treatment process becomes simplified, generating economic benefits.

Second, the method of surface modifying the polyimide film is used, and optimal conditions are provided upon performing copper sputtering and electroplating.

Third, a polyimide copper clad laminate having a two-layered structure is provided, and, in particular, a single-sided or both-sided polyimide copper clad laminate may be provided by surface modifying one or both surfaces of the polyimide film.

[Description of Drawings]

FIG. 1 is an SEM photograph of the surface of the polyimide film prepared in Example 1 of the present invention; FIG. 2 is an AFM photograph of the surface of the polyimide film prepared in Example 1 of the present invention;

FIG. 3 is an SEM photograph of the surface of the polyimide film prepared in Example 6 of the present invention; FIG. 4 is an AFM photograph of the surface of the polyimide film prepared in Example 6 of the present invention; FIG. 5 is an FT-IR spectrum of the polyimide film, which is surface modified according to the present invention; FIG. 6 is a spectrum showing the peel strength of a copper clad laminate manufactured according to the method of the present invention; and FIG. 7 is a schematic view showing a pulse DC sputtering device used in the present invention.

<Description of the Reference Numerals in the Drawings> 10: pulse DC sputtering device 1: argon gas inlet 2: vacuum chamber 3: cooling water inlet

4: height controlling device 5: cooling water outlet 6: cooling plate 7: polyimide film

8: vacuum measuring gauge 9: copper target

[Best Mode]

Hereinafter, a detailed description will be given of the present invention.

The present invention provides a surface modification method of a polyimide film, which comprises dipping one or both surfaces of a polyimide film into a solution containing a diamine compound represented by structural formula 1.

In the surface modification method of a polyimide film of the present invention, an acid component on the surface of polyimide film reacts with the diamine compound, and thus, an amide amine group is introduced to the polyimide film, thereby modifying the surface of the film.

The diamine compound of the present invention is represented by structural formula 1 below: [structural formula l] H₂N R NH₂

(wherein R is

,

Ri and R₂ are H or NH₂, Ri=R₂ or Ri≠R₂, x=l~5, y=l~5,

2 <χ+y<6, n=l~2, ITi=I, and X= o

-O- -CH₂- _c , -C(CF₃J₂- -O-^^τ-0-

Specifically, the diamine compound of the present invention is any one selected from the group consisting of ethylenediamine, triethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, 1,3- phenylenediamine, 1,4-phenylenediamine, 4,4'-diaminodiphenyl methane, 4,4'-diaminodiphenylether, 3,3-diaminobenzophenone, 4,4-diaminobenzophenone, 1,3-bis (aminophenoxy)benzene, 1,4- bis (aminophenoxy)benzene, bis (3-aminophenyl) sulfone, bis(4- aminophenylsulfone) , 3,3-diaminobenzidine, 4,4- (hexafluoroisopropylidine)dianiline, and 3,3- (hexafluoroisopropylidine) dianiline.

The diamine compound is dissolved in a solvent selected from the group consisting of water, acetone, methyl alcohol, ethyl alcohol, isopropyl alcohol, and combinations thereof, and thus, are prepared into a 0.5~20 M diamine solution. The polyimide film usable in the present invention is not particularly limited, and includes synthetic or commercially available ones, as long as it may have a thickness ranging from 10 to 100 μm- Preferably, the polyimide film includes Kapton H or Kapton E, available from Dupont Co. Ltd., USA, Upilex-S, available from Ube Co. Ltd., Japan, or Apical film, available from Kaneka Co. Ltd., Japan.

FIGS. 1 and 2 are photographs showing the surface of the polyimide film prepared in Example 1 of the present invention, observed using an SEM and an AFM, respectively. FIGS. 3 and 4 are photographs showing the surface of the polyimide film prepared in Example 6 of the present invention, observed using an SEM and an AFM, respectively. As shown in these drawings, the surface roughness of the polyimide film is increased by dipping the polyimide film into the solution containing a diamine compound according to the present invention. From the photograph observed using an SEM, the surface of the polyimide film of Example 1 is confirmed to have been modified due to the presence of fine protrusions. In addition, from the photograph observed using an AFM, it can be confirmed that the polyimide film is surface modified by increasing the surface roughness. FIG. 5 shows the FT-IR spectrum of the polyimide film according to the surface modification method of the present invention. In the present invention, an amide amine group is shown at 2700~2250 cm^"1, by dipping the polyimide film into the solution containing a diamine compound. On the other hand, in Comparative Examples for surface modifying the film using potassium hydroxide, a hydroxide group is shown at 3600-2700 cm^"1.

In addition, the present invention provides a method of manufacturing a copper clad laminate, using the surface modification method of a polyimide film. Specifically, the manufacturing method of the present invention comprises the first step of dipping one or both surfaces of a polyimide film into a solution containing a diamine compound represented by structural formula 1, to obtain a surface modified polyimide film; the second step of washing and drying the surface modified polyimide film; the third step of copper sputtering the dried polyimide film at 0.5~30 mA and 50-500 W for 1-10 hr, to form a copper sputtered layer; and the fourth step of electroplating the copper sputtered layer, to form a copper electroplated layer. In the first step, the dipping for surface modifying the polyimide film is preferably performed at a temperature ranging from room temperature to the boiling point of the selected solvent, and more preferably, at 40-100^°C. Although the dipping time may vary depending on the above temperature, it preferably ranges from 30 sec to 2 hr. If the treatment time is too short, the surface modification rate is low and thus the surface is only slightly modified. Meanwhile, if the treatment time is too long, the surface may be smoothly modified, however the physical properties may become undesirable.

In the second step, the polyimide film, surface-modified in the previous step, is washed with distilled water and then an alcoholic solvent, to remove unreacted diamine solution, after which the surface is sufficiently dried using a hot air dryer and is thus optimized for the following copper sputtering process.

In the third step, the sputtering process is performed, through which the washed and dried polyimide film having a modified surface collides with copper, to form a film. The sputtering process is conducted using a pulse DC sputtering device 10 shown in FIG. 7. In the drawing, a surface modified polyimide film 7 is placed onto a cooling plate 6 of the device, and argon gas is introduced through an inlet 1 into a vacuum chamber 2 maintained at lxl0^~3~lxl0^~5 torr in an amount of 5~30 seem to form a sputtering atmosphere. While a 0.5-30 mA current is maintained using 50-500 W of electrical power, a copper sputtering process is performed for 1-10 hr to obtain a film having a thickness of 500-5,000 A. If the thickness of the copper sputtered layer is less than 500 A, pinholes may be formed, current does not flow upon electroplating, or the plated layer may peel due to its low adhesive strength. On the other hand, if the thickness exceeds 5,000 A, energy loss is high and the resultant film is too thick and is thus unsuitable for use in a substrate material.

In the fourth step, the copper sputtered layer is electroplated with copper to form a copper electroplated layer. The copper foil the thickness of which is controlled in the sputtering process undergoes copper electroplating so that copper is directly deposited to a predetermined thickness. As such, the resultant copper foil preferably has a thickness of l~50 μxa. If the thickness of the copper electroplated layer exceeds 50 μm, the accuracy of line width in high density wires is lowered, and also, part mounting ability is reduced in terms of light weight and miniaturization. FIG. 6 shows the peel strength of the copper clad laminate manufactured according to the method of the present invention. The copper clad laminate of the present invention has peel strength 2~3 times higher than copper clad laminates conventionally obtained by dipping a polyimide film into an alkaline solution used for surface treatment. Hence, the present invention provides flexible cooper clad laminate having increased adhesive strength between the copper foil and the polyimide film, which is manufactured by dipping one or both surfaces of the polyimide film into the solution containing a diamine compound, thus obtaining a surface modified polyimide film. Thereafter, the surface modified polyimide film undergoes copper sputtering and then copper electroplating so that copper is directly layered to a predetermined thickness. The copper clad laminate having a two-layered structure of the present invention may be applied to methods of forming a patterned mask and selectively etching an exposed copper foil using a copper etching agent to remove it, to form a copper circuit pattern, and is thus useful as a substrate material for electronic parts, such as flexible printed boards, TCP (Tape Carrier Package), COF (Chip On Film), etc.

[Mode for Invention]

Hereinafter, the present invention is specifically explained using the following examples which are set forth to illustrate, but are not to be construed to limit the present invention.

<Example 1> A polyimide film was dipped into an aqueous solution of 10 M ethylenediamine at 80^°C for 3 min, and then washed with distilled water and isopropyl alcohol 5 times each for 10 min. Thereafter, the washed film was sufficiently dried using a hot air dryer, and then set in a copper sputtering device to be sputtered at 20 mA for 1 hr, so that the thickness of copper was uniformly realized at 2,000 A. Subsequently, the resultant film was immersed in a copper sulfate plating bath to be electroplated at room temperature for 1 hr, thus manufacturing a 10 jam thick polyimide copper clad laminate. <Example 2>

A polyimide copper clad laminate was manufactured in the same manner as in Example 1, with the exception that a polyimide film was dipped into an aqueous solution of 10 M ethylenediamine at 80^°C for 10 min. <Example 3>

A polyimide copper clad laminate was manufactured in the same manner as in Example 1, with the exception that a polyimide film was dipped into an aqueous solution of 10 M ethylenediamine at room temperature for 10 min. <Example 4>

A polyimide copper clad laminate was manufactured in the same manner as in Example 1, with the exception that a polyimide film was dipped into an aqueous solution of 10 M ethylenediamine at 100^°C for 3 min. <Example 5>

A polyimide film was dipped into an aqueous solution of 3 M triethylenetetramine at 80^°C for 3 min, and then washed with distilled water and isopropyl alcohol 5 times each for 10 min. Thereafter, the washed film was sufficiently dried using a hot air dryer, and then set in a copper sputtering device to be sputtered at 30 mA for 1 hr, so that the thickness of copper was uniformly realized at 2,000 A. Subsequently, the resultant film was immersed in a copper sulfate plating bath to be electroplated at room temperature for 1 hr, thus manufacturing a 20 μm thick polyimide copper clad laminate. <Example 6>

A polyimide copper clad laminate was manufactured in the same manner as in Example 5, with the exception that the polyimide film was dipped into an aqueous solution of 3 M triethylenetetramine at 25^°C for 10 min. <Example 7>

A polyimide copper clad laminate was manufactured in the same manner as in Example 5, with the exception that the polyimide film was dipped into an aqueous solution of 3 M triethylenetetramine at 60^°C for 1 min. <Example 8>

A 3 M 1, 4-phenylenediamine solution was prepared using a solvent mixture comprising acetone, ethanol and distilled water mixed at a volume ratio of 1:1:0.5. Subsequently, a polyimide film was dipped into the aqueous solution of 3 M 1, 4-phenylenediamine at 40^°C for 30 min, and then sputtered and electroplated in the same manner as in Example 5, thus manufacturing a polyimide copper clad laminate. <Comparative Example 1> In known techniques for increasing the adhesive strength of a polyimide film surface treated with an alkali [Journal KOSTEC, volume 34, No. 3, 178-185p] , a polyimide film was dipped into an aqueous solution of 3 M potassium hydroxide (KOH) at 85^°C for 3 min, and then sputtered and electroplated in the same manner as in Example 1, thus manufacturing a polyimide copper clad laminate. <Comparative Example 2>

A polyimide film was dipped into an aqueous solution of 3 M potassium hydroxide (KOH) at 25^°C for 10 min, and then sputtered and electroplated in the same manner as in Example 1, thus manufacturing a polyimide copper clad laminate. Comparative Example 3>

A polyimide film was dipped into an aqueous solution of 3 M potassium hydroxide (KOH) at 60^°C for 20 min, and then sputtered and electroplated in the same manner as in Example 1, thus manufacturing a polyimide copper clad laminate. <Comparative Example 4>

A polyimide film was dipped into an aqueous solution of 3 M potassium hydroxide (KOH) at 60^°C for 10 min, and then sputtered and electroplated in the same manner as in Example 1, thus manufacturing a polyimide copper clad laminate. Experimental Example 1>

The adhesive strength of the polyimide copper clad laminates manufactured in Examples 1 to 8 and Comparative Examples 1 to 4 was measured as follows. That is, the surface of each of the copper clad laminates prepared by electroplating in Examples 1 to 8 and Comparative Examples 1 to 4 was patterned using acid resistant paint or acid resistant tape, and then etched using an etching agent comprising sulfuric acid or copper sulfate, and then the 90°peel strength thereof was measured. The results are given in Table 1, below.

[Table l]

As is apparent from Table 1, the copper clad laminates manufactured by dipping the polyimide film into the diamine solution in Examples 1 to 8 had adhesive strength between the surface modified polyimide film and copper of 0.8 kg/cm or more, which was 2-3 times higher than that of copper clad laminates manufactured in Comparative Examples 1 to 4. Therefore, the copper clad laminate having increased adhesive strength may be obtained, thus providing a polyimide copper clad laminate having a two-layered structure without an additional adhesive layer. Thereby, the copper clad laminate of the present invention may be usefully applied to flexible printed circuit boards, due to fine wiring and excellent adhesive strength. [industrial Applicability]

As described hereinbefore, the present invention, which provides a surface modification method of a polyimide film, a method of manufacturing an FCCL, and an FCCL manufactured using the same, provides the following advantages. That is, first, a polyimide film is surface modified by dipping the polyimide film into a solution containing a diamine compound. Thus, the above process is advantageous because it may substitute for a conventional surface treatment process using ion beams, and also, does not require a specific seed layer, therefore decreasing the cost and reducing environmental contamination due to the use of heavy metals. Further, a post-treatment process becomes simplified, generating economic benefits.

Second, the surface modification method of a polyimide film of the present invention is used, and optimal conditions are provided upon performing copper sputtering and electroplating. Third, a polyimide copper clad laminate having a two-layered structure is provided, and, in particular, a single-sided or both-sided polyimide copper clad laminate may be provided by surface modifying one or both surfaces of the polyimide film. Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

[CLAIMS]

[Claim l]

A method of surface modification of a polyimide film, comprising dipping one or both surfaces of a polyimide film into a solution containing a diamine compound represented by structural formula 1 below:

[structural formula l]

H₂N R NH₂

(wherexn R xs

, , or ,

Ri and R₂ are H or NH₂, Ri=R₂ or Ri≠R₂, x=l~5, y=l~5,

2≤x+y≤6, n=l~2, m=l, and X= o

—O— -CH₂- —c _, —C(CF₃J₂- —O-rj^V-O—

) .

[Claim 2] The method according to claim 1, wherein the diamine compound is any one selected from the group consisting of ethylenediamine, triethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, 1_/3- phenylenediamine, 1,4-phenylenediamine, 4,4'-diaminodiphenyl methane, 4,4'-diaminodiphenylether, 3,3-diaminobenzophenone, 4,4-diaminobenzophenone, 1,3-bis (aminophenoxy)benzene, 1,4- bis (aminophenoxy)benzene, bis(3-aminophenyl)sulfone, bis (4-aminophenylsulfone) , 3,

3-diaminobenzidine, 4,

4- (hexafluoroisopropylidine)dianiline, and 3,3-

(hexafluoroisopropylidine) dianiline. [Claim 3] The method according to claim 1, wherein the solution containing a diamine compound is prepared by dissolving the diamine compound in a solvent selected from the group consisting of water, acetone, methyl alcohol, ethyl alcohol, isopropyl alcohol, and combinations thereof. [Claim 4]

The method according to claim 1, wherein the solution containing a diamine compound has a concentration of 0.5~20 M. [Claim 5] A method of manufacturing a flexible copper clad laminate having a two-layered structure, comprising: a first step of dipping one or both surfaces of a polyimide film into a solution containing a diamine compound represented by structural formula 1, to obtain a surface modified polyimide film, according to the method of claim 1; a second step of washing and drying the surface modified polyimide film; a third step of copper sputtering the dried polyimide film at 0.

5-30 mA and 50-500 W for 1-10 hr, to form a copper sputtered layer; and a fourth step of electroplating the copper sputtered layer, to form a copper electroplated layer.

[Claim 6]

The method according to claim 5, wherein the step of dipping one or both surfaces of the polyimide film into the solution containing a diamine compound in the first step is performed at 40-100^°C for a time ranging from 30 sec to 2 hr.

[Claim 7]

The method according to claim 5, wherein the copper sputtered layer is 500-5,000 A thick.

[Claim 8] The method according to claim 5, wherein the copper electroplated layer is 1-50 μm thick.

[Claim 9]

A polyimide copper clad laminate, manufactured according to the method of claim 5, which comprises a 500-5,000 A thick copper sputtered layer formed on one or both surfaces of the polyimide film surface treated by being dipped into the solution containing a diamine compound according to the first step of the method of claim 5; and a 1-50 μm thick copper electroplated layer formed on the copper sputtered layer by electroplating the copper sputtered layer.