JPH08330694A - Heat resistant flexible circuit board - Google Patents

Abstract

PURPOSE: To prevent drop of adhesive strength of a flexible circuit board having high heat resistance by forming a titanium layer into a specified thickness in a sputtering manner, as a metal intermediate layer of a copper polyimide film which consists of a copper or copper allay layer, the metal intermediate layer, and a polyimide film, in this order. CONSTITUTION: Relating to a heat resistant flexible circuit substrate, a polyimide film 1, a metal titanium intermediate layer 2 on the principal surface of the palyimide film 1, a copper thin film layer 3 on it, and a copper film 4 for circuit an it, are formed in this order. Here, the titanium layer acting as the metal intermediate layer 2 is formed, in sputtering manner, into such a thickness as to suppress drop of adhesive strength between the metal layer and polyimide layer to within 5% even when the titanium layer is heated at 150 deg.C for 24 hours. That is, after the polyimide film 1 is surface-treated by plasma, the titanium layer acting as the metal intermediate layer 2 is formed into the thickness 5-50nm in the spattering manner, and then on it, the copper or copper alloy layer 3 is forced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant flexible circuit board in which a titanium layer is formed on a polyimide film and then a copper layer is formed, and particularly, the adhesiveness between the metal layer and the polyimide film is excellent in high temperature durability. A flexible circuit board.

[0002]

2. Description of the Related Art A flexible circuit board having a metal film formed on an insulating polymer film has a film thickness of about 10 μm.
Some of the above metal films and polymer films are bonded with an adhesive, but the thermal properties of the adhesive are inferior to the performance of the polymer film and the thickness of the metal film is 10 μm.
Since it is thick as described above, there are problems that it cannot be applied to high-density wiring in the semiconductor industry, that dimensional stability is poor, and that the product has a warp, because it is difficult to perform fine processing of several tens of μm. In order to solve this, a technique of forming a metal film without an adhesive has been studied. This is a method of forming a circuit pattern after forming a metal thin film by a thin film forming method such as vacuum deposition and sputtering. In this material, since the metal thin film is as thin as 1 μm or less, fine processing with a width of several tens of μm is easy.

That is, this 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. Note that the latter technique is a technique that enables high-density wiring in the semiconductor industry, but there has been a problem of a decrease in adhesive force in a post process such as a circuit forming process and an electrolytic plating process. In JP-A-02-98994, a chromium layer having a thickness of 0.01 to 5 μm is formed by sputtering, and in JP-A-62-181488, it is 5-1000.
nm nickel layer or nickel-chromium layer by vapor deposition, JP-A-62-62551 discloses a chromium layer by vapor deposition, and JP-B-57-18357 discloses nickel, cobalt and zirconium. JP-A-57-18356 discloses a technique for forming a metal layer of palladium, etc. by an ion plating method, and a technique for forming a nickel, nickel-containing alloy layer by an inoplating method. .

However, although these known techniques have been partially successful, they are still unsatisfactory in performance as materials for enabling high-density wiring in the semiconductor industry, which is a hindrance to practical use. Was there. That is,
The problem of the metal layer peeling from the polyimide film was partially solved in the circuit pattern formation process using lithography technology and the electrolytic plating process of laminating the metal layer on the formation pattern for lowering the conduction resistance and improving the mechanical strength. However, sufficient performance could not be achieved in the heat resistance, which is the original characteristic of the flexible circuit board composed of the metal layer / polyimide film. For example, 15 in the air
There has been a problem that the adhesiveness between the metal layer and the polyimide film is remarkably lowered only by keeping the temperature at about 0 ° C. for 24 hours.

[0005]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention The inventors of the present invention have made extensive studies as to the cause of the decrease in adhesiveness and found that the reactive gas that permeates through the polyimide film affects the adhesiveness. Therefore, when a chromium layer was formed as an intermediate layer between the copper and the polyimide film, no decrease in the adhesive strength between the metal layer and the polyimide layer was observed even in the heat treatment at 150 ° C. for 24 hours in an oxygen atmosphere. On the other hand, when aluminum was used as the intermediate layer, it was not effective in preventing the decrease of the adhesive strength in the heat treatment at 150 ° C. for 24 hours in the oxygen atmosphere.

When the peeling interface before and after the heat treatment was analyzed by Auger electron spectroscopy (AES) when chromium was used for the intermediate layer and when aluminum was used for the intermediate layer, it was found that In some cases, after the heat treatment, copper had penetrated into the polyimide beyond the aluminum layer. On the other hand, in the case of the titanium intermediate layer, copper did not penetrate into the polyimide beyond the chromium layer even after the heat treatment. That is, it was found that in the case of the chromium intermediate layer, copper has a diffusion suppressing effect of diffusing into the polyimide. However, in the case of the chromium intermediate layer, not only the etching process of the flexible circuit board, that is, the etching with the ferric chloride solution is difficult, but also the waste liquid generated in the etching process contains chromium, which is a harmful substance, and the environmental aspect. But new problems arise.

[0007]

Means for Solving the Problems The inventors of the present invention have made earnest studies on an intermediate layer having a diffusion suppressing effect in which copper diffuses into polyimide other than the chromium intermediate layer, and found that a titanium intermediate layer is also effective. I found it. When titanium is used for the intermediate layer, the peeling interface before and after the heat treatment is similarly analyzed by Auger electron spectroscopy (AES).
It was found that the copper did not penetrate into the polyimide even after the heat treatment, exceeding the titanium layer, and it had a diffusion suppressing effect.

In the case of the titanium intermediate layer, the thickness of the intermediate layer is 5n.
If it is less than m, the above diffusion suppressing effect is small. Also in the case of the titanium intermediate layer, the etching step of the flexible circuit board, that is, the etching with the ferric chloride solution is relatively difficult, and the etching becomes particularly difficult when the thickness exceeds 50 nm.

Further, in the example of Japanese Patent Publication No. 57-33718, an intermediate layer of nickel, palladium, zirconium, and cobalt is vapor-deposited by the ion plating method. It was found that the formation of the intermediate layer by the sputtering method can prevent the decrease in the adhesive strength rather than the ion plating method. I'm not sure why,
It is also considered that one reason is that sputtering can give higher ion energy more stably.

That is, according to the present invention, (1) in a copper-polyimide film composed of a copper or copper alloy layer, a metal intermediate layer, and a polyimide film in this order, even when heated at 150 ° C. for 24 hours, the metal layer and the polyimide layer are separated from each other. Is a heat-resistant flexible circuit board, characterized in that a titanium layer is formed as a metal intermediate layer by a sputtering method to a thickness such that the decrease in the adhesive strength is suppressed within 5%.
(2) After subjecting a polyimide film to a surface treatment with plasma, a titanium layer which is a metal intermediate layer is formed by a sputtering method to a thickness of 5 to 50 nm, and a copper or copper alloy layer is formed thereon. The present invention relates to a heat-resistant flexible circuit board.

In the present invention, the metal layer is a generic term for a layer formed of a metal composed of a copper or copper alloy layer and a titanium layer formed thereon as a metal intermediate layer. In the present invention, the adhesive strength between the metal layer and the polyimide layer is measured by a peel strength measuring method (IPC TEST M).
ETHODS MANUAL No. 2.4.9 SU
BJECT Peel Strength, Flexi
ble Printed Wiring Material
The decrease in the adhesive strength is suppressed within 5% even after heating at 150 ° C. for 24 hours. As described above, the heat-resistant flexible circuit board formed according to the present invention is a flexible circuit board in which not only the characteristics during the high temperature test but also the performance deterioration during the secondary processing are remarkably alleviated.

The copper alloy layer in the present invention refers to an alloy of copper and titanium, and the ratio of copper to titanium is not particularly limited, but in practice, it is preferably about 20 at% or more of copper. First, referring to the drawings, FIGS. 1 to 3 show an embodiment of a material for a flexible circuit board of the present invention, in which 1 is a polyimide film, 2 and 2'are titanium intermediate layers, 3 and 3 '. Indicates a copper thin film, and 4 and 4'indicate a circuit copper film.

The present invention will be described in detail below with reference to these drawings. That is, according to the present invention, as shown in FIG. 1, a polyimide film 1, a titanium intermediate layer 2 of metal on the main surface of the polyimide film, and a copper thin film layer 3 thereon.
Further, it is a heat resistant flexible circuit board having a circuit copper film 4 formed thereon.

As shown in FIG. 2, the heat-resistant flexible circuit board according to the present invention has a titanium intermediate layer 2 on one surface of a polyimide film 1, a copper thin film layer 3 thereon, and a circuit film on it, as described above. Not only those in which the copper film 4 is formed and laminated, but also the circuit copper film 4 ', copper thin film layer 3', titanium intermediate layer 2 ', polyimide film 1, titanium intermediate layer 2, copper thin film layer 3, circuit It goes without saying that a multi-layered thin film laminated on both surfaces such as the copper film 4 is also included. Furthermore, as shown in FIG. 3, the circuit copper films 4, 4 ′ may not be formed by controlling the thickness of the copper thin film layers 3, 3 ′.

With respect to the polyimide film used in the present invention, the film thickness of the polyimide film is not particularly limited, but a polyimide film having a film thickness of 25 μm to 125 μm is usually selected and used according to the application. If a concrete example is given as the polyimide film, it is possible to effectively use a polyimide film available on the market as a trade name of Kapton, Upilex, Apical, and the like.

Further, 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′-diaminobenzophenone, p, p-aminophenoxybenzene, p, m-aminophenoxybenzene, m, p-aminophenoxybenzene, m, m-aminophenoxybenzene, chloro-m-aminophenoxybenzene, p- Pyridineaminophenoxybenzene, m
-Pyridineaminophenoxybenzene, p-aminophenoxybiphenyl, m-aminophenoxybiphenyl,
p-bisaminophenoxybenzyl sulfone, m-bisaminophenoxybenzyl sulfone, p-bisaminophenoxybenzyl ketone, m-bisaminophenoxybenzyl ketone, p-bisaminophenoxybenzyl hexafluoropropane, m-bisaminophenoxybenzyl hexafluoro Propane, p-bisaminophenoxybenzylpropane, o-bisaminophenoxybenzylpropane, m-bisaminophenoxybenzylpropane, p-diaminophenoxybenzylthioether, m
A polyimide formed by reacting with an amine such as diaminophenoxybenzyl thioether, indanediamine, spirobidiamine, diketonediamine and imidizing can be effectively used in the present invention.

In the method of manufacturing a flexible circuit board according to the present invention, first, the surface of the polyimide film is pretreated in order to improve the adhesion to the metal. The method is preferably corona discharge treatment, plasma treatment, ultraviolet irradiation treatment,
Of these, the plasma treatment is often performed in the same apparatus as the sputtering used for forming the alloy layer, and is particularly preferable.

The titanium intermediate layer is preferably formed by a sputtering method which is excellent in the adhesiveness of the thin film and the controllability of the thin film. The sputtering method is not particularly limited, and methods such as DC magnetron sputtering, high frequency magnetron sputtering, and ion beam sputtering are effectively used. 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, preferably,
A titanium target for sputtering of 99.99% or more is used.

The thickness of such a titanium intermediate layer is at least required to be such that the copper particles do not substantially penetrate into the polyimide layer (diffusion suppressing effect) by heat treatment at 150 ° C. for 24 hours in the air. , 5 to 50 nm is preferable. If the film thickness is too thin, the copper particles will penetrate into the polyimide layer under such conditions and will not be effective as a diffusion suppressing layer. Further, if it is too thick, it takes a long time to form the titanium intermediate layer, which is not preferable in terms of production efficiency and also causes a problem in terms of etching a flexible circuit board as a product with a ferric chloride solution.

The copper thin film formed on the titanium intermediate layer is a material for forming a circuit, which can be easily understood by those skilled in the art. In the present invention, there are no further particular requirements. Copper having a purity of 99.99% or more is preferably used. Although the copper thin film is formed to have a film thickness of 100 nm or more, the present invention is a flexible circuit board, and a circuit is formed through a plating process and a soldering process rather than being used as it is. In consideration of these subsequent steps, the film thickness is preferably 200 nm or more in order to facilitate circuit processing.

The thickness of these metal thin films is determined by providing a mask on a part of the sample during sputtering or plating, and then removing the mask and measuring the step difference between the masked part and a non-masked part using a step measuring machine. I asked.
When the length of the step portion exceeds the measurement limit of the device, the sputtering or plating time was adjusted so as to be within the measurement limit.

[0022]

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 A polyimide film (Kapton V) having a film thickness of 50.0 μm was used, and the surface of the polyimide film was treated by glow discharge of oxygen on one surface of the polyimide film, and then DC magnetron sputtering was performed with argon gas using titanium as a target. By the method, a titanium thin film layer having a thickness of 15 nm was formed. Immediately thereafter, a copper thin film layer having a thickness of 250 nm was formed by a DC magnetron sputtering method using argon gas with copper as a target. Next, the thickness of the circuit copper film was set to 20 μm by electrolytically plating copper on the copper thin film.

Thereafter, the above-mentioned film is dried, and IC
After forming a pattern with a tape [masking tape manufactured by IZUMIYA I.CINC], an attempt was made to etch with a ferric chloride solution. As a result, both the copper and titanium layers were etched except where they were masked with an IC tape.

The adhesive strength of the circuit copper film obtained by the above method to the polyimide film was measured (peel strength measuring method: IPC No. 2.4.9), and the normal strength was 1.3 kg / cm on average. . This was put in an oven at 150 ° C. and kept for 24 hours, and then the adhesive strength was measured. The average was 1.3 kg / cm, and no decrease in adhesive strength was observed. Further, after holding in an oven at 150 ° C. for 10 days, the adhesive strength was measured in the same manner.
It was kg / cm, and no decrease in adhesive strength was observed.

Also, before placing in an oven at 150 ° C,
The film was wound around a stainless steel rod having a diameter of 10 mm, 5 times on each side, 10 times in total, then put in an oven at 150 ° C. and kept for 10 days, and the adhesive strength was measured in the same manner. In this case, no decrease in adhesive strength was observed, and it was confirmed that there was no problem in practical performance.

Example 2 A polyimide film (Kapton V) having a film thickness of 50.0 μm was used, and one surface of the polyimide film was treated by glow discharge of oxygen, and then titanium was used as a target with argon gas. DC
A titanium thin film layer having a thickness of 5 nm was formed by the magnetron sputtering method. Immediately thereafter, a copper thin film layer having a thickness of 250 nm was formed by a DC magnetron sputtering method using argon gas with copper as a target. Next, the thickness of the circuit copper film was set to 20 μm by electrolytically plating copper on the copper thin film.

Then, the above-mentioned film is dried, and IC
After forming a pattern with a tape [masking tape manufactured by IZUMIYA I.CINC], an attempt was made to etch with a ferric chloride solution. As a result, both the copper and titanium layers were etched except where they were masked with an IC tape.

The adhesive strength of the circuit copper film obtained by the above method to the polyimide film was measured by the same method as in Example 1. The average strength was 1.2 kg / cm. This was placed in an oven at 150 ° C. and kept for 24 hours, after which the adhesive strength was measured and found to be 1.2 kg / c on average.
m, and no decrease in adhesive strength was observed. Furthermore, 1
After holding in an oven at 50 ° C. for 10 days, the adhesive strength was measured in the same manner. The average adhesive strength was 1.0 kg / cm, and the decrease in adhesive strength was 16.7%.

Also, before placing in an oven at 150 ° C,
The film was wound around a stainless steel rod having a diameter of 10 mm, 5 times on each side, 10 times in total, placed in an oven at 150 ° C. and held for 10 days, and the adhesive strength was measured in the same manner. cm, and even in this case, the decrease in adhesive strength was 16.7%, confirming that there is no problem in practical performance.

(Comparative Example 1) A polyimide film (Kapton V) having a film thickness of 50.0 μm was used, and the surface of the polyimide film was treated by glow discharge of oxygen on one surface of the polyimide film, and then titanium was used as a target with argon gas. DC
A titanium thin film layer having a thickness of 3 nm was formed by the magnetron sputtering method. Immediately thereafter, a copper thin film layer having a thickness of 250 nm was formed by a DC magnetron sputtering method using argon gas with copper as a target. Next, the thickness of the circuit copper film was set to 20 μm by electrolytically plating copper on the copper thin film.

Thereafter, the above-mentioned film is dried, and IC
After forming a pattern with a tape [masking tape manufactured by IZUMIYA I.CINC], an attempt was made to etch with a ferric chloride solution. As a result, both the copper and titanium layers were etched except where they were masked with an IC tape.

When the adhesive strength of the copper film for a circuit obtained by the above method to the polyimide film was measured by the same method as in Example 1, the average strength in normal state was 1.3 kg / cm. This was placed in an oven at 150 ° C. and kept for 24 hours, after which the adhesive strength was measured and found to be 1.1 kg / c on average.
m, and the decrease in adhesive strength was 15.4%. Furthermore,
After holding in an oven at 150 ° C. for 10 days, the adhesive strength was measured in the same manner. The average adhesive strength was 1.0 kg / cm, and the decrease in adhesive strength was 23%.

Before putting it in an oven at 150 ° C.,
The film was wound around a stainless steel rod having a diameter of 10 mm, 5 times on each side, 10 times in total, and then placed in an oven at 150 ° C. and held for 10 days, and the adhesive strength was measured in the same manner. cm, and even in this case, the decrease in adhesive strength was 23%, and there was a problem in practical performance.

(Comparative Example 2) A polyimide film (Kapton V) having a film thickness of 50.0 μm was used, and the surface of the polyimide film was treated by glow discharge of oxygen on one surface of the polyimide film, and then titanium was used as a target with argon gas. DC
A titanium thin film layer having a thickness of 80 nm was formed by the magnetron sputtering method. Immediately thereafter, a copper thin film layer having a thickness of 250 nm was formed by a DC magnetron sputtering method using argon gas with copper as a target. Next, the thickness of the circuit copper film was set to 20 μm by electrolytically plating copper on the copper thin film.

Then, the above-mentioned film is dried, and IC
After forming a pattern with a tape [masking tape made by IZUMIYA CINC], an attempt was made to etch with ferric chloride solution. As a result, the copper layer was etched except where it was masked with the IC tape, but titanium was used. The layer remained unetched completely.

[0036]

As is clear from the above examples and comparative examples, the present invention shows that the adhesive strength between the metal layer and the polyimide layer is not significantly lowered even when heated at 150 ° C. for 24 hours, and high temperature durability is achieved. It provides a flexible substrate having excellent properties and is an extremely useful invention for the semiconductor industry.

[Brief description of drawings]

FIG. 1 is a layer structure of an embodiment of a material for a flexible circuit board of the present invention.

FIG. 2 is a layer structure of an embodiment of the material for a flexible circuit board of the present invention.

FIG. 3 is a layer structure of one embodiment of the material for a flexible circuit board of the present invention.

[Explanation of symbols]

 1 Polyimide film 2, 2'titanium intermediate layer 3, 3'copper thin film 4, 4'circuit copper film

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[Procedure amendment]

[Submission date] June 16, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

That is, the present invention relates to (1) a copper-polyimide film composed of a copper or copper alloy layer, a metal intermediate layer, and a polyimide film in this order, even if heated at 150 ° C. for 24 hours, between the metal layer and the polyimide layer. Is a heat-resistant flexible circuit board, characterized in that a titanium layer is formed as a metal intermediate layer by a sputtering method to a thickness such that the decrease in the adhesive strength is suppressed within 5%.
(2) After subjecting the polyimide film to a surface treatment with plasma, a titanium layer that is a metal intermediate layer is formed with a thickness of 5 to 50 nm by a sputtering method, and a copper or copper alloy layer is formed thereon (1). The present invention relates to a heat-resistant flexible circuit board.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shin Fukuda 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Toatsu Chemical Co., Ltd. (72) Nobuhiro Fukuda 1190 Kasama-cho, Sakae-ku, Yokohama, Kanagawa Mitsui Toatsu Chem Within the corporation

Claims (2)

[Claims] 1. A copper-polyimide film composed of a copper or copper alloy layer, a metal intermediate layer, and a polyimide film in that order, even if heated at 150 ° C. for 24 hours, the adhesive strength between the metal layer and the polyimide layer decreases by 5%. A heat-resistant flexible circuit board, characterized in that a titanium layer is formed as a metal intermediate layer by a sputtering method to a thickness that can be suppressed within 10%. 2. The surface of the polyimide film is treated with plasma, and then a titanium layer, which is a metal intermediate layer, is added in an amount of 5 to 5.
The heat resistant flexible circuit board according to claim 1, wherein the heat resistant flexible circuit board is formed to have a thickness of 0 nm by a sputtering method, and a copper or copper alloy layer is formed thereon.