JPH08330695A - High adhesive 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 molybdenum 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 alloy 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 molybdenum intermediate layer 2 an the principal surface of the polyimide film 1, a copper thin film layer 3 on it, and a copper film 4 for circuit on it, are formed in this order. Here, the molybdenum 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 palyimide layer to within 5% even when the molybdenum layer is heated at 150 deg.C for 24 hours. That is, after surface treatment is performed on the polyimide film 1 by plasma, the molybdenum layer acting as the metal intermediate layer 2 is formed into the thickness 10-500nm in the sputtering manner, and then on it, the copper or copper alloy layer 3 is formed.

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 copper layer is formed after a molybdenum layer is formed on a polyimide film, and particularly, the adhesiveness between the metal layer and the polyimide film is excellent in high temperature durability. Flexible circuit board.

[0002]

2. Description of the Related Art A flexible circuit board in which a metal film is formed on an insulating polymer film has a film thickness of about 10 μm.
There are those in which a metal film of m or more and a polymer film are joined with an adhesive, but the thermal characteristics 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 thicker than m, it is difficult to perform fine processing of several tens of μm and the like, so that there are problems that it cannot be applied to 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 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 present inventors have diligently investigated the cause of the decrease in adhesiveness and found that reactive gases such as air and oxygen that permeate through the polyimide film affect the adhesiveness. I found it. Then, when a titanium 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.

We have used titanium for the intermediate layer and
When the peeling interface before and after the heat treatment was analyzed by Auger electron spectroscopy (AES) in the case where aluminum was used as the intermediate layer, in the case of the aluminum intermediate layer,
In the state 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 titanium layer even after the heat treatment. That is, it was found that the titanium intermediate layer had an effect of suppressing diffusion of copper into the polyimide. However, in the case of the titanium intermediate layer, a new problem is encountered in that the etching process of the flexible circuit board, that is, the etching with the ferric chloride solution is difficult.

[0007]

Means for Solving the Problems The inventors of the present invention have earnestly studied an intermediate layer having a diffusion suppressing effect in which copper diffuses into polyimide other than a titanium intermediate layer, and found that a molybdenum intermediate layer is also effective. I found it. Japanese Patent Publication 57-
In Japanese Patent No. 33718, it is stated that cobalt or the like is used as an intermediate layer and the adhesive strength is hardly reduced even after the heat treatment, but the temperature of the heat treatment is 130 ° C., which is 20 ° C. from the heat resistance aimed by the present inventors. Is also low. That is, the inventors of the present invention can provide a flexible circuit board having high heat resistance by setting the heating temperature to 150 ° C., and the present circuit board can be used in a wider range of applications. The layer thickness is preferably 1 to 1000 nm, but when molybdenum is used as the intermediate layer, it is 10 nm.
It has been found that the heat treatment at 150 ° C. does not have the effect of preventing diffusion suppression in the range below.

In the example of Japanese Patent Publication No. 57-33718, the intermediate layer of nickel, palladium, zirconium, and cobalt is vapor-deposited by the ion plating method. Found that the formation of the intermediate layer by the sputtering method rather than the ion plating method can prevent the lowering of the adhesive strength. The reason is not clear, but it seems that one of the reasons is that sputtering can give a higher ion energy more stably. Also,
In the case of a refractory metal such as molybdenum, it is difficult to deposit by an ion plating method, and a sputtering method can form a thin film even with a refractory metal such as molybdenum.

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 if heated at 150 ° C. for 24 hours, A high-adhesion flexible circuit board, characterized in that a molybdenum layer is formed as the metal intermediate layer by a sputtering method to a thickness such that a decrease in adhesive strength is suppressed within 5%, and (2) Polyimide The high adhesion property according to claim 1, wherein after the film is subjected to a surface treatment with plasma, a molybdenum layer which is a metal intermediate layer is formed with a thickness of 10 to 500 nm by a sputtering method, and a copper or copper alloy layer is formed thereon. The present invention relates to a 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 molybdenum 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).
METHODS MANUAL No. 2.4.9S
UBJECT Peel Strength, Flex
Ible Printed Wiring Mater
even after heating at 150 ° C. for 24 hours, the decrease in the adhesive strength can be suppressed within 5%. As described above, the heat-resistant flexible circuit board formed by 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 molybdenum, and the ratio of copper to molybdenum is not particularly limited, but in reality, 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 molybdenum intermediate layers, 3 and 3 '. Is a copper thin film, 4 and 4'is a circuit copper film,
Is shown.

The present invention will be described in detail below with reference to these drawings. According to the present invention, as shown in FIG. 1, a polyimide film 1, a metal molybdenum intermediate layer 2 on the main surface of the polyimide film, a copper thin film layer 3 thereon, and a circuit copper film 4 are further formed thereon. It is a heat-resistant flexible circuit board that is formed.

As shown in FIG. 2, the heat-resistant flexible circuit board according to the present invention has the molybdenum intermediate layer 2 on one surface of the polyimide film 1, the copper thin film layer 3 on the one surface, and the circuit film on the molybdenum intermediate layer 2 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', molybdenum intermediate layer 2 ', polyimide film 1, molybdenum 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.
Further, as shown in FIG. 3, the circuit copper films 4 and 4'may not be formed by sufficiently controlling the thickness of the copper thin film layers 3 and 3 '.

With respect to the polyimide film used in the present invention, the film thickness of the polyimide film is not particularly limited, but normally a polyimide film having a film thickness of 25 μm to 125 μm is appropriately 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, benzophenonetetracarboxylic 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, it is preferable to pretreat the surface of the polyimide film in order to improve the adhesion to the metal. As the method, corona discharge treatment, plasma treatment, and ultraviolet irradiation treatment are preferable, and among them, plasma treatment is often preferable because it can be performed in the same apparatus as the sputtering used for forming the alloy layer.

For forming the molybdenum intermediate layer, a sputtering method which is excellent in the adhesiveness of the thin film and the controllability of the thin film is a particularly preferable method. 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, but a molybdenum target for sputtering of 99.9% or more is preferably used.

The thickness of such a molybdenum intermediate layer is at least required to be such that 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. , 10 to 500 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 time to form the molybdenum intermediate layer, which is not preferable in terms of production efficiency.

The copper thin film formed on the molybdenum 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 at the time of sputtering or plating, and then removing the mask and measuring the step difference between the masked part and the unmasked 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.

[0021]

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 molybdenum as a target. A 40 nm thick molybdenum thin film layer was formed by the 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.

After that, a masking tape having a width of 2 mm was applied on the substrate, the unnecessary metal layer was removed with a ferric chloride solution, and then the masking tape was removed, and the adhesive strength between the metal layer and the polyimide layer was measured. Method (IPC No.
When measured according to 2.4.9), the normal strength was 1.2 kg / cm on average. This was placed in an oven at 150 ° C. and kept for 24 hours, and then the adhesive strength was measured in the same manner. The average was 1.2 kg / cm, and no decrease in adhesive strength was observed. Furthermore, in an oven at 150 ° C, 10
After maintaining for a day, the adhesive strength was measured in the same manner and found to be 1.2 kg / cm on average, 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, and then placed in an oven at 150 ° C. and held 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 the surface of the polyimide film was treated by glow discharge of oxygen on one surface of the polyimide film, and then molybdenum was used as a target and argon gas was used. 10 nm thick by DC magnetron sputtering method
Was formed into a molybdenum thin film layer. 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 peel strength was measured by the same method as in Example 1. The average strength was 1.2 kg / cm.
Met. This was placed in an oven at 150 ° C. and kept for 24 hours, and then the adhesive strength was measured in the same manner. The average was 1.2 kg / cm, and no decrease in adhesive strength was observed. Furthermore, after holding in an oven at 150 ° C. for 10 days, the adhesive strength was measured in the same manner.
cm, and the decrease in adhesive strength was 8.3%.

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 8.3%,
I confirmed that there was no problem.

(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. A molybdenum thin film layer having a thickness of 5 nm was formed by the DC 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 peel strength was measured in the same manner as in Example 1. The average strength was 1.4 kg / cm.
Met. This was put in an oven at 150 ° C. and kept for 24 hours, and then the adhesive strength was measured in the same manner. The average was 1.2 kg / cm, and the decrease in adhesive strength was 14%. Furthermore, after holding in an oven at 150 ° C for 10 days,
Similarly, when the adhesive force was measured, the average was 1.0 kg / cm.
The decrease in adhesive strength was 29%.

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, 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 29%, and there was a problem in practical performance.

[0030]

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'Molybdenum intermediate layer 3, 3'Copper thin film 4, 4'Copper film for circuit

[Procedure amendment]

[Submission date] June 16, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction content]

That is, the present invention provides (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. A high-adhesion flexible circuit board, characterized in that a molybdenum layer is formed as the metal intermediate layer by a sputtering method to a thickness such that a decrease in adhesive strength is suppressed within 5%, and (2) Polyimide After subjecting the film to a surface treatment with plasma, a molybdenum layer which is a metal intermediate layer is formed by a sputtering method to a thickness of 10 to 500 nm, and a copper or copper alloy layer is formed thereon (1) . The present invention relates to a 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 comprising 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 adhesion strength between the metal layer and the polyimide layer decreases. %, And a molybdenum layer is formed as the metal intermediate layer by a sputtering method to a thickness that can be suppressed within 10%. 2. A molybdenum layer, which is a metal intermediate layer, is formed on a polyimide film after the surface treatment with plasma.
The highly adhesive flexible circuit board according to claim 1, wherein the flexible circuit board is formed to a thickness of 0 to 500 nm by a sputtering method, and a copper or copper alloy layer is formed thereon.