JPH0951163A - Flexible circuit board - Google Patents

Abstract

(57) [Summary] [Structure] At least one surface of a polyimide film is subjected to plasma treatment with plasma containing oxygen, and then a flexible circuit board on which a metal thin film is formed is formed. A flexible circuit board whose surface roughness of polyimide film is from 5nm to 100nm. [Effect] A flexible circuit board having excellent adhesion between a metal thin film and a polyimide film is provided, as well as a flexible circuit board excellent in fine processing of a metal thin film of several 10 μm or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible circuit board which has excellent adhesion between a metal thin film and a polyimide base material and is suitable for fine processing in the electrical, electronic and semiconductor industries.

[0002]

2. Description of the Related Art Conventionally, a flexible circuit board in which a metal thin film is formed on an insulating polymer film has a film thickness of about 10 μm.
There is one in which the above metal film and polymer film are joined with an adhesive, but because the thermal properties of the adhesive are inferior to the performance of the polymer film and the thickness of the metal film to be joined is thicker than 10 μm, Due to the difficulty of fine processing of several tens of μm, there were problems such as not being able to support high-density wiring in the semiconductor industry, poor dimensional stability, and warpage of products.

In order to solve this, a technique of forming a metal film without an adhesive has been studied. This is, after forming a metal thin film by a physical thin film forming method such as vacuum deposition, sputtering, ion plating, ion cluster beam, etc., after increasing the metal film thickness by plating etc., if necessary, The circuit pattern is formed. With this material, the thickness of the metal thin film is 10 μm
Since it is as thin as below, microfabrication with a width of several tens of μm is easy. That is, it is a technique for forming a finely processed conductor by further depositing and growing a metal by electrolytic plating or the like based on the circuit pattern formed as described above.

Conventionally, there has been a problem that when a metal thin film typified by copper is formed on polyimide, the adhesive strength between copper and polyimide is low and it cannot be put to practical use. As a conventional method for solving this, Japanese Patent Laid-Open No. 52-136 is known.
No. 284 or JP-A-55-34415, a method of inserting an adhesive metal such as titanium or nickel between a copper conductor and a polyimide, JP-A-52-2417.
No. 2 or No. 52-137674, a method of forming a metal thin film by electroless plating after chemical treatment of a polyimide film, as described in JP-A-56-22331. There has been a method of forming a metal layer by a vacuum film forming means later, a method of forming a modified layer by chemical treatment of a polyimide film, and then diffusing a metal in the modified layer by a vacuum film forming means. However, in the method using the adhesive metal, the electric resistance value is increased, and the adhesive metal is difficult to be etched by the commonly used etching solution at the time of etching, so that two kinds of etching processes must be performed. Further, the method using electroless plating has a problem of low adhesiveness. Especially in adhesiveness,
Adhesive strength that can withstand practical use in a 90-degree peel test
It is difficult to obtain a peel strength of 1.0 kg / cm or more. Furthermore, when forming a metal thin film by a vacuum film forming means,
When the polyimide film is modified by chemical treatment, it cannot be introduced into the vacuum film forming apparatus unless it undergoes washing and drying steps, which is not always preferable in industrial processes.

Further, as disclosed in Japanese Patent Publication No. 2-279331, there is disclosed a method for obtaining a flexible circuit board free from adhesion and curl by defining surface roughness, contact angle of water and coefficient of thermal expansion. In the case of a polyimide film corresponding to the value defined by this publication, when the surface is roughened by argon plasma treatment, the adhesion strength is 1 kg / cm, which is practically durable.
Can't get In fact, it is easily presumed that the strength measurement of the adhesive force is a peel test using an adhesive tape and does not assume a peel strength of 1 kg / cm or more.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the circumstances of the prior art described above, and has a peel strength of 1 kg / cm or more, which has been difficult to manufacture in the past, and has an electric property. , It is to provide a flexible circuit board corresponding to fine processing in the electronic and semiconductor industries.

[0007]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that in a flexible circuit board on which a metal thin film is formed after plasma treatment on at least one surface of a polyimide film, It has been found that a peel strength of 1 kg / cm or more can be easily obtained when the surface roughness of the polyimide film containing oxygen and subjected to plasma treatment is 5 nm to 100 nm. Polyimide film at 150 ℃
To 500 ° C from 150 ° C to 500 ° C in a non-oxidizing atmosphere after the metal thin film is formed.
It was found that the peeling strength was further improved by carrying out the heat treatment at the above temperature, and the present invention was completed.

That is, the present invention is a flexible circuit board in which a metal thin film is formed after plasma treatment is performed on at least one surface of a polyimide film, wherein the plasma contains oxygen and the polyimide after the plasma treatment is performed. A flexible circuit board with a film surface roughness of 5 nm to 100 nm, and a flexible circuit board in which a polyimide film is heated to a temperature of 150 ° C to 500 ° C when a metal thin film is formed. The flexible circuit board is characterized in that a polyimide film is heat-treated at a temperature of 150 ° C to 500 ° C in a non-oxidizing atmosphere.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
In the present invention, the plasma treatment is a step of exposing the polyimide film substrate to glow discharge. It is possible to generate plasma by applying a DC or AC voltage to the plasma generating electrode, and it is possible to use an AC frequency of 20 Hz to 100 MHz. In particular, commercial power frequencies of 50 Hz and 60 Hz and 13.56 MHz which is approved for use under the Radio Law are preferred frequencies for use. However, the value of the frequency for plasma generation including this direct current does not hinder the implementation of the present invention.

[0010] power for generating plasma, the power density terms used 1mWcm ^-2 ~100Wcm ^-2. A parallel plate type electrode or the like can be used as the plasma generating electrode, but it is easily understood by those skilled in the art that the substrate can be used in the DC sputtering device, the RF sputtering device, the DC magnetron sputtering device, and the RF magnetron sputtering device. Plasma treatment can also be easily performed by using the opposite electrode side of the sputter target to be installed, that is, the substrate holder side as the cathode or the anode. Therefore, in order to generate a plasma containing oxygen, it is possible to select oxygen, a mixed gas of oxygen and another gas, or a gas containing oxygen in the molecule as the gas used to generate the plasma. is there. Examples of the gas used for mixing with oxygen include etching gases such as nitrogen trifluoride and carbon tetrafluoride. The mixing ratio of these gases with oxygen is not particularly limited, and the ratio of oxygen in the mixed gas is 1 to 99%, but preferably,
It is a ratio of 50 to 99%. Further, examples of the gas containing oxygen include nitrous oxide, carbon monoxide, carbon dioxide, and the like.

The pressure during the plasma treatment is not particularly limited, but specifically, it is in the range of atmospheric pressure to 10 ^-5 Torr. The plasma treatment time varies depending on the power density during plasma treatment, the pressure, the shape and function of the apparatus that performs plasma treatment, and is therefore determined by appropriately considering the surface roughness to be 5 to 100 nm. For example, in a roll-to-roll type sputtering apparatus used in industrial production equipment, the film feed rate, the film thickness of the metal thin film to be performed in the step after the plasma treatment, the film deposition rate, etc. are considered as appropriate. select. If the surface roughness of the polyimide film after plasma treatment is less than 5 nm, a sufficient peel strength value cannot be obtained, and if the surface roughness is greater than 100 nm, unevenness of the base material forms a circuit. Becomes an obstacle to time. When the surface roughness is 10 nm to 70 nm, it is more effective and a high peel strength value is obtained.

The surface roughness in the present invention is the root mean square roughness. In the present invention, the surface roughness is measured, for example, by an atomic force microscope (AFM) SFA manufactured by Seiko Instruments Inc.
Scan range of 20μm □, 256 lines, 256
It is assumed that the measurement is performed at the pixel resolution.

For forming the metal thin film, a general film forming method can be adopted as will be described later, and a dry forming method such as a vacuum vapor deposition method, a sputtering method, a CVD method, an ion plating method or an ion cluster beam method is preferable. The heating of the polyimide film at the time of its formation is carried out by heating the polyimide film from the substrate surface side with an infrared lamp heater and incorporating it into the substrate holder.
This can be performed by a method that those skilled in the art can easily understand, such as heating from the back surface side of the substrate with an ic heater or the like.

The substrate temperature during the metal thin film formation and the heat treatment after the metal thin film formation can be controlled by a method easily understood by those skilled in the art, such as a heater for heating the substrate and a thermocouple attached to the substrate holder. Since this temperature often does not accurately indicate the substrate temperature, it is preferable to calibrate the temperature in advance. As a calibration method, a method is generally used in which a paint that changes color with temperature is applied to a substrate, inserted into a film forming chamber, and the difference from the temperature displayed by a thermocouple is measured.

In the present invention, the metal thin film is formed at the time of film formation.
Heat the polyimide film to a temperature of 0 ° C to 500 ° C, or 150 ° C in a non-oxidizing atmosphere after forming the metal thin film.
It is preferable to heat treat the polyimide film at a temperature of up to 500 ° C. The effect of heating the polyimide film during the formation of the metal thin film and the heat treatment of the polyimide film after forming the metal thin film is not clear, but the thermal effect promotes the copper-carbon or copper-oxygen bond on the polyimide film surface. It is thought to be to do. The heating temperature of the polyimide film when forming the copper thin film is preferably in the range of 150 ° C to 500 ° C. At temperatures lower than 150 ° C, sufficiently high peel strength cannot be obtained, and at temperatures higher than 500 ° C, decomposition and embrittlement of the polyimide film substrate become a problem.

The heat treatment after the formation of the metal thin film can be easily performed under the same conditions and methods as the heating during the metal thin film formation. In that case, the heat treatment is carried out in a non-oxidizing atmosphere, and the non-oxidizing atmosphere for carrying out the heat treatment in the present invention means an inert gas atmosphere such as nitrogen, hydrogen or helium, neon, argon, xenon or the like. It is in a mixed atmosphere of two or more gases or in a vacuum. The pressure of the inert gas atmosphere or the mixed atmosphere of two or more kinds of these gases is not particularly limited, but specifically, 10 ^-3 torr to 100 atm, when considering the practicality of the industrial process. , 10 ⁻³ torr to 10 atm is a preferable value. Further, the term "in vacuum" refers to a reduced pressure state in which it is considered that metal oxidation does not easily proceed, and specifically, 10 ^-3 to 10 ^-10 torr, and more preferably 10
^-6 to 10 ^-10 torr. A pressure of less than 10 ^-10 torr is not preferable due to cost problems in view of technical difficulty and industrial process. The time for heat treatment depends on the heat treatment temperature, but 10 minutes to 1 hour at most is sufficient. Further, it is easy for those skilled in the art to use a vacuum dryer having a gas introduction system and a gas exhaust system in the range of 1 torr to atmospheric pressure, and to use an autoclave or the like at atmospheric pressure to 100 atmospheric pressure. It is understandable.

The metal thin film in the present invention is not particularly limited as long as it is a metal that is conductive and can be used in a circuit, but is preferably a copper thin film. Other than copper, nickel, titanium, cobalt, molybdenum, aluminum, tungsten, copper-silicon, alloys and the like can be preferably used. This is a typical circuit forming material. The copper thin film will be described in more detail below.
% Copper is used. Although the copper thin film is formed to a film thickness of 100 nm or more, the present invention is a flexible circuit board,
A circuit is formed through a plating process and a soldering process rather than being used as it is. Taking these post-processes into consideration, the film thickness is preferably 200 nm or more in order to facilitate circuit processing.

For forming the metal thin film, a dry forming method such as a vacuum deposition method, a sputtering method, a CVD method, an ion plating method or an ion cluster beam method can be preferably used. The sputtering method, which is excellent in the adhesiveness of the thin film and the controllability of the thin film, is a particularly preferable method. There is no particular limitation on the sputtering method. It is understood by those skilled in the art that a target is appropriately selected and used according to the thin film to be formed. The sputtering method is also not limited, and DC sputtering method, DC magnetron sputtering method, RF sputtering method, RF magnetron sputtering method, ion beam sputtering method and the like are effectively used.

The thickness of the polyimide film is not particularly limited, but normally a polyimide film having a thickness of about 10 μm to 125 μm is appropriately selected and used according to the application. As a concrete example of the polyimide film,
A polyimide film that is commercially available under the trade name of Kapton, Upilex, Apical, etc. can be effectively used. Furthermore, acid anhydrides such as pyromellitic acid anhydride, biphthalic acid anhydride, benzophenone tetracarboxylic acid anhydride, oxydiphthalic acid anhydride and hydrofurandiphthalic acid anhydride, and methoxydiaminobenzene, 4,
4'-oxydianiline, 3,4'-oxydianiline, 3,3'-oxydianiline, bisdianilinomethane, 3,3'-diaminozenzophenone, p, p-aminophenoxybenzene, p, m-aminophenoxybenzene, m, p-aminophenoxybenzene, m, m-amiophenoxybenzene, chloro-m-aminophenoxybenzene, p-pyridineaminophenoxybenzene,
m-pyridineaminophenoxybenzene, p-aminophenoxybiphenyl, m-aminophenoxybiphenyl, p-bisaminophenoxybenzisulfone, m-bisaminophenoxybenzisulphone p-bisaminophenoxybenzylketone, m-bisaminophenoxybenzylketone, p-bisaminophenoxybenzyl hexafluoropropane, m-bisaminophenoxybenzyl hexafluoropropane, m-bisaminophenoxybenzyl hexafluoropropane, p-bisaminophenoxybenzylpropane, o-bisaminophenoxybenzylpropane, m-bisamino Phenoxybenzyl propane, p-diaminophenoxybenzyl thioether, m-diaminophenoxybenzyl thioether, indandiamine, spin Bijiamin, reacting an amine such as diketone diamines, polyimide formed by imidizing can also be effectively used in the present invention. Hereinafter, an example of an embodiment of the present invention will be described with reference to examples.

[0020]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples. Example 1 Kapton V having a thickness of 50 μm as a polyimide film
(Toray DuPont) was used to form a copper film on one surface.
Plasma processing and copper film formation were performed using a batch-type RF sputtering device.

The polyimide film was placed on a substrate holder in a sputtering apparatus and evacuated to a pressure of 10 ^-5 torr. Oxygen using mass flow controller
Introduced into the chamber at 10sccm, pressure 1.5 × 10 ^-2 tor
Plasma treatment was performed for 10 minutes at r and RF power density of 1.3 Wcm ^{-2 using} the substrate holder as the cathode. The surface roughness of the polyimide film, which had been subjected to plasma treatment in advance, was measured and found to be 43 nm. After the plasma treatment, the introduction of oxygen into the chamber was stopped, and the chamber was evacuated to a pressure of 10 ^-5 torr. Argon gas was introduced into the chamber at 10 sccm, the pressure was 5 × 10 ^-3 torr, the RF power density was 2.5 Wcm ^-2 , the copper target electrode was the cathode, the copper film was formed for 10 minutes, and the plasma treatment was performed. A 250 nm-thick copper thin film was formed on the polyimide film. next,
The thickness of the circuit copper film was set to 35 μm by electrolytically plating copper on the copper thin film. When the 90-degree peel strength of the thus-prepared flexible circuit board was measured, it showed a value of 1.2 kg / cm, indicating high adhesion of copper to polyimide.

Example 2 A sample was prepared and tested under the same conditions as in Example 1 except that the plasma treatment time was 15 minutes. When the plasma treatment time was 15 minutes, the surface roughness of the polyimide film was 52 nm. When the 90 degree peel strength of the produced flexible circuit board was measured, it showed a value of 1.3 kg / cm, indicating high adhesion of copper to polyimide.

Example 3 A sample was prepared and tested under the same conditions as in Example 1 except that the plasma treatment time was 5 minutes. When the plasma treatment time was 5 minutes, the surface roughness of the polyimide film was 13 nm. When the 90 degree peel strength of the produced flexible circuit board was measured, it showed a value of 1.0 kg / cm, indicating high adhesion of copper to polyimide.

Example 4 Kapton V having a film thickness of 50 μm as a polyimide film
(Toray DuPont) was used to form a copper film on one surface.
Plasma processing and copper film formation were performed using a batch-type RF sputtering device.

The polyimide film was placed on a substrate holder in a sputtering apparatus, and vacuum exhausted to a pressure of 10 ^-5 torr. Oxygen using mass flow controller
Introduced into the chamber at 10sccm, pressure 1.5 × 10 ^-2 tor
Plasma treatment was performed for 10 minutes at r and RF power density of 1.3 Wcm ^{-2 using} the substrate holder as the cathode. The surface roughness of the polyimide film, which had been subjected to plasma treatment in advance, was measured and found to be 43 nm. After the plasma treatment, the introduction of oxygen into the chamber was stopped, and the chamber was evacuated to a pressure of 10 ^-5 torr. Argon gas was introduced into the chamber at 10 sccm, the pressure was 5 × 10 ^-3 torr, the RF power density was 2.5 Wcm ^-2 , the copper target electrode was the cathode, the copper film was formed for 10 minutes, and the plasma treatment was performed. A 250 nm-thick copper thin film was formed on the polyimide film.

After the application of RF power was stopped, the polyimide film was heated by a heater and heat-treated at 200 ° C. in an argon gas atmosphere at 5 × 10 ⁻³ torr for 1 hour.
Next, electrolytic plating of copper was performed on the copper thin film to make the thickness of the copper film for the circuit 35 μm. When the 90 degree peel strength of the thus-prepared flexible circuit board was measured, it showed a value of 1.6 kg / cm, and then the base film was broken, showing high adhesion of copper to polyimide.

Example 5 A sample was prepared and tested under the same conditions as in Example 4 except that the temperature during the heat treatment was 250 ° C. When the 90 degree peel strength of the thus-prepared flexible circuit board was measured, it showed a value of 1.6 kg / cm, and then the base film was broken, showing high adhesion of copper to polyimide.

Example 6 A sample was prepared and tested under the same conditions as in Example 4 except that the temperature during the heat treatment was 150 ° C. When the 90 degree peel strength of the thus-prepared flexible circuit board was measured, it showed a value of 1.4 kg / cm, indicating high adhesion of copper to polyimide.

Example 7 A sample was prepared and tested under the same conditions as in Example 4 except that the pressure of argon during the heat treatment was 1 torr. When the 90 degree peel strength of the thus-prepared flexible circuit board was measured, it showed a value of 1.6 kg / cm, and then the base film was broken, showing high adhesion of copper to polyimide.

Example 8 Kapton V having a thickness of 50 μm as a polyimide film
(Toray DuPont) was used to form a copper film on one surface.
Plasma processing and copper film formation were performed using a batch-type RF sputtering device.

The polyimide film was placed on a substrate holder in a sputtering device and evacuated to a pressure of 10 ^-5 torr. CF ₄ and oxygen were introduced into the chamber at a flow rate of 10 sccm using a mass flow controller, plasma treatment was performed for 30 minutes at a pressure of 0.1 torr and an RF power density of 1.3 Wcm ^-2 with the substrate holder serving as an anode.

The surface roughness of the polyimide film, which had been subjected to plasma treatment under these conditions, was measured and found to be 56 nm. CF ₄ after plasma treatment
Then, the introduction of oxygen into the chamber was stopped, and the chamber was evacuated to a pressure of 10 ^-5 torr. Argon gas was introduced into the chamber at 10 sccm, the pressure was set to 5 × 10 ⁻³ torr, RF power density was 2.5 W / cm ² , and a copper target electrode was used as a cathode to form a copper film for 10 minutes to perform plasma treatment. A 250 nm-thick copper thin film was formed on the polyimide film. Next, the thickness of the circuit copper film was set to 35 μm by electrolytically plating copper on the copper thin film. When the 90-degree peel strength of the thus-prepared flexible circuit board was measured, it showed a value of 1.3 kg / cm, indicating high adhesion of copper to polyimide.

Example 9 A sample was prepared and tested under the same conditions as in Example 8 except that NF ₃ and oxygen were used as the gas for the plasma treatment. The surface roughness of the polyimide film after the plasma treatment was 62 nm. When the 90 degree peel strength of the flexible circuit board manufactured in this way was measured, 1.
A value of 2 kg / cm was shown, indicating high adhesion of copper to polyimide.

Example 10 A flexible circuit board was prepared under the same conditions as in Example 1 except that the temperature of the polyimide film was set to 220 ° C. by using an infrared lamp heater when forming a copper thin film by sputtering. When the 90 degree peel strength of the thus-prepared flexible circuit board was measured, it showed a value of 1.6 kg / cm, and then the base film was broken, showing high adhesion of copper to polyimide.

Example 11 Except that nitrous oxide was used as a gas for plasma treatment,
A sample was prepared and tested under the same conditions as in Example 1. The surface roughness of the polyimide film after the plasma treatment was 48 nm. When the 90 degree peel strength of the produced flexible circuit board was measured, it showed a value of 1.3 kg / cm, indicating high adhesion of copper to polyimide.

Example 12 A sample was prepared and tested under the same conditions as in Example 1 except that the plasma treatment time was 1 minute. When the plasma treatment time was 1 minute, the surface roughness of the polyimide film was 8 nm. When the 90 degree peel strength of the produced flexible circuit board was measured, it showed a value of 1.0 kg / cm, indicating high adhesion of copper to polyimide.

Example 13 A sample was prepared and tested under the same conditions as in Example 4 except that the temperature for heating the polyimide film after forming the copper thin film was 300 ° C. When the 90 degree peel strength of the thus-prepared flexible circuit board was measured, it showed a value of 1.5 kg / cm, and then the base film broke, showing high adhesion of copper to polyimide.

Example 14 A sample was prepared and tested under the same conditions as in Example 4 except that the temperature for heating the polyimide film after forming the copper thin film was 400 ° C. When the 90 degree peel strength of the thus-prepared flexible circuit board was measured, it showed a value of 1.4 kg / cm and then the base material film broke, showing high adhesion of copper to polyimide.

Example 15 The heating temperature of the polyimide film during the copper thin film formation was 400 ° C.
A sample was prepared and tested under the same conditions as in Example 10 except that The 90 degree peel strength of the flexible circuit board manufactured in this way was measured to be 1.4k.
After showing the value of g / cm, the base film was torn and showed high adhesion of copper to polyimide.

Example 16 Titanium was used as the metal for sputtering film formation, titanium was used as the sputtering target, and the titanium layer was formed with a film formation time of 18 minutes.
A sample was prepared and tested under the same conditions as in Example 1 except that a 100 nm film was formed. When the 90-degree peel strength of the thus-prepared flexible circuit board was measured, it showed a value of 1.3 kg / cm, indicating high adhesion of copper to polyimide.

Example 17 A sample was prepared under the same conditions as in Example 1 except that nickel was used as a metal for sputtering film formation, nickel was used as a sputtering target, and a nickel layer was formed to 300 nm with a film formation time of 20 minutes. Fabrication and testing were performed. When the 90-degree peel strength of the thus-prepared flexible circuit board was measured, it showed a value of 1.3 kg / cm, indicating high adhesion of copper to polyimide.

Example 18 A sample was prepared under the same conditions as in Example 1 except that molybdenum was used as the metal for sputtering film formation, molybdenum was used as the sputter target, and a molybdenum layer was formed to a thickness of 200 nm with a film formation time of 20 minutes. Fabrication and testing were performed. When the 90-degree peel strength of the thus-prepared flexible circuit board was measured, it showed a value of 1.3 kg / cm, indicating high adhesion of copper to polyimide.

Example 19 A sample was prepared under the same conditions as in Example 1 except that cobalt was used as a metal for sputtering film formation, cobalt was used as a sputter target, and a cobalt layer was formed to 300 nm with a film formation time of 21 minutes. Fabrication and testing were performed. When the 90-degree peel strength of the thus-prepared flexible circuit board was measured, it showed a value of 1.4 kg / cm and showed high adhesion of copper to polyimide.

Example 20 A metal for forming a sputter film is a copper-silicon alloy (silicon).
1 wt%), a copper-silicon alloy (silicon 1 wt%) was used as a sputter target, and a copper-silicon alloy (silicon 1 wt%) was deposited to a thickness of 250 nm with a deposition time of 10 minutes. The sample was prepared and tested under the conditions. The flexible circuit board manufactured in this way
When the 90-degree peel strength was measured, copper having a value of 1.2 kg / cm showed high adhesion to polyimide.

Example 21 Preparation and test of a sample under the same conditions as in Example 1 except that after forming a copper thin film by sputtering, heat treatment was performed in an autoclave at 5 atmospheres of dry nitrogen and 350 ° C. for 1 hour. I went. When the 90 degree peel strength of the flexible circuit board manufactured in this way was measured, it was 1.7 kg /
After showing the value of cm, the base film was torn and showed high adhesion of copper to polyimide.

Comparative Example 1 A flexible circuit board was prepared and tested under the same conditions as in Example 1 except that the gas used for the plasma treatment was argon gas and the plasma treatment time was 60 minutes. The surface roughness of the polyimide film after the plasma treatment time is 19
was nm. When the 90 degree peel strength of the produced flexible circuit board was measured, it showed a value of 0.2 kg / cm, and did not show high adhesion of copper to polyimide.

Comparative Example 2 Kapton V having a thickness of 50 μm as a polyimide film
(Toray DuPont) was used to form a copper film on one surface.
Plasma processing and copper film formation were performed using a batch-type RF sputtering device.

The polyimide film was placed on a substrate holder in a sputtering device and evacuated to a pressure of 10 ^-5 torr. Oxygen was introduced into the chamber at 10 sccm using a mass flow controller, and the pressure was 1.5 × 10 ^-2 to
rr, RF power density was 1.3 Wcm ^-2 , and plasma treatment was performed for 10 minutes with the substrate holder as the cathode. The surface roughness of the polyimide film, which had been subjected to plasma treatment in advance, was measured and found to be 43 nm.

After the plasma treatment, oxygen was introduced into the chamber.
Installation stopped 10^-FiveIt was evacuated to a pressure of torr. A
Lgon gas was introduced into the chamber at 10 sccm and the pressure was adjusted to 5
× 10 ^-3RF power density of 2.5W / cm as torr²With copper target
Copper is formed for 10 minutes using the electrode as a cathode, and plasma
A film with a thickness of 250 nm is formed on the treated polyimide film.
A copper thin film was formed.

The film was taken out from the RF sputtering apparatus and heat-treated in a vacuum dryer at 1 torr and 150 ° C. for 1 hour. For the depressurization operation, the pressure was reduced from atmospheric pressure to 1 torr using a rotary pump. Next, the thickness of the circuit copper film was set to 35 μm by electrolytically plating copper on the copper thin film. After forming the copper thin film in this way, the 90 degree peel strength of the flexible circuit board prepared by heat treatment in air, which is not in a non-oxidizing atmosphere, was measured and showed a value of 0.8 kg / cm. No high adhesion to the polyimide was shown.

Comparative Example 3 A flexible circuit board was prepared and tested under the same conditions as in Example 7 except that oxygen was used during the heat treatment. When the 90 degree peel strength of the thus-prepared flexible circuit board was measured, it showed a value of 0.7 kg / cm, and did not show high adhesion of copper to polyimide.

Comparative Example 4 Except that a copper thin film was formed without plasma treatment,
A flexible circuit board was manufactured under the same conditions as in Example 1. When the plasma treatment was not performed, the surface roughness of the polyimide film was 2 nm. When the 90 degree peel strength of the thus-prepared flexible circuit board was measured, it showed a value of 0.1 kg / cm, and did not show high adhesion of copper to polyimide.

Comparative Example 5 Except that a copper thin film was formed without plasma treatment,
A flexible circuit board was manufactured under the same conditions as in Example 10. When the plasma treatment was not performed, the surface roughness of the polyimide film was 2 nm. When the 90 degree peel strength of the flexible circuit board thus produced was measured, it showed a value of 0.4 kg / cm, and did not show high adhesion of copper to polyimide. The above examples and comparative examples are summarized in Table 1.

[0054]

[Table 1]

[0055]

As is apparent from the above Examples and Comparative Examples, the flexible circuit board manufactured according to the present invention has excellent adhesion between the metal thin film and the polyimide base material, and has been difficult to manufacture in the past. It was found that it is possible to easily obtain a value of strength 1.0 kg / cm or more. That is,
The present invention provides a flexible circuit board having excellent adhesion between a metal thin film and a polyimide film, and also provides a flexible circuit board excellent in microfabrication of a metal thin film of several 10 μm or less, in the electrical, electronic and semiconductor industries. It is an extremely useful invention that provides a technology that enables fine processing.

Continuation of front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location // C08L 79:00 (72) Inventor Nobuhiro Fukuda 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Toatsu Chemical Co., Ltd. Within

Claims (3)

[Claims] 1. A flexible circuit board in which a metal thin film is formed on at least one surface of a polyimide film after plasma treatment with plasma containing oxygen.
A flexible circuit board in which the surface roughness of the polyimide film after the plasma treatment is 5 nm to 100 nm. 2. The flexible circuit board according to claim 1, wherein the polyimide film is heated to a temperature of 150 ° C. to 500 ° C. when the metal thin film is formed. 3. The flexible circuit board according to claim 1, wherein the polyimide film is heat-treated at a temperature of 150 ° C. to 500 ° C. in a non-oxidizing atmosphere after the metal thin film is formed.