JPH08139422A - Flexible circuit board having metallic oxide layer - Google Patents

Abstract

PURPOSE: To perfectly restrain the peeling of metal from a polyimide film and improve high temperature durability, by sandwiching a layer of metallic oxide wherein metal is previously oxidized between a polyimide layer and metal. CONSTITUTION: A flexible circuit board material is constituted of a multilayered thin film wherein a polyimide film 1 is a base, a metallic oxide layer 2 is formed on the main surface of the polyimide film, and a thin film 3 of metal is formed on the metallic oxide layer 2. The thin film 2 of metallic oxide formed on the surface of the polyimide film l is a copper oxide film, and the thin film 3 of metal formed on the thin film 2 is a copper film. The thin films 2 and 3 of metallic oxide are formed by sputtering.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material for a flexible circuit board composed of a polyimide film and a metal thin film, and more particularly to a material for a flexible board which has excellent adhesiveness between the metal thin film and the polyimide film at high temperature.

[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 metal film has a thickness of 10 μm.
Since it is thicker than m, it is difficult to perform fine processing of several tens of μm. Therefore, there are problems such as not being able to support high-density wiring in the semiconductor industry, poor dimensional stability, and warping of products. It was To solve these,
Techniques for forming metal films without adhesive have been investigated. This is to form a circuit pattern after forming a metal thin film on an insulating polymer film by a thin film forming method such as vacuum deposition and sputtering. With this material, the metal thin film is as thin as 1 μm or less, so that 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. A technique such as forming a metal layer of palladium, etc. by an ion plating method, and forming a nickel or nickel-containing alloy layer by an inoplating method has been already disclosed in Japanese Patent Publication No. 57-18356. .

However, although these known techniques have been partially successful, they are still unsatisfactory as a material for enabling high-density wiring in the semiconductor industry, and are a hindrance to practical use. Was becoming. That is, in a circuit pattern forming step using a lithographic technique, an electrolytic plating step of laminating a metal layer on a forming pattern for lowering electrical resistance or improving mechanical strength,
The problem arises that the metal layer peels off the polyimide film. Although this problem was partially solved, 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, at a temperature of about 150 ° C in air, 2
There was a problem that the adhesiveness between the metal layer and the polyimide film was remarkably lowered only by holding for 4 hours.

[0005]

Therefore, the inventors of the present invention have made a diligent investigation into the cause of the decrease in adhesiveness and found that the reactive gas that permeates through the polyimide film greatly affects the adhesiveness. Furthermore, it has been found that a decrease in adhesiveness can be prevented by providing a gas barrier layer for blocking passing gas (Japanese Patent Application No. 04-183700). As a result, the flexible circuit board material composed of the metal layer / polyimide film can be put to practical use in the semiconductor industry having the harsh process as described above. As a specific example, as a gas barrier layer, a substantially silicon oxide layer is formed on one surface of a polyimide film by plasma chemical vapor deposition (P-CVD) using tetramethyldisiloxane and oxygen as raw materials. A method of forming a ~ 300 nm thickness has been disclosed.
It has been found that such a method can dramatically improve the gas barrier property of the film and thus suppress the deterioration of high temperature strength. However, we have encountered a problem in that some of the samples obtained by subjecting such a film to secondary processing such as bending and cutting still show a decrease in adhesion when subjected to a heating test.

[0006]

According to the knowledge of the present inventors, it is considered that the reactive gas that permeates through the polyimide film reacts with the metal layer in contact with the polyimide surface to partially generate a metal oxide. To be It was presumed that this metal oxide was the main cause of exfoliation, but surprisingly, by sandwiching a layer of metal oxide in which a metal was previously oxidized between the polyimide layer and the metal layer, it was possible to remove from the metal polyimide film. It has been found that the peeling off of is completely suppressed.

That is, according to the present invention, (1) a polyimide film, a thin film of a metal oxide is formed on at least one surface of the polyimide film, and a multilayer film is formed by forming a metal thin film on the thin film. Flexible circuit board material, (2) The thin film of metal oxide formed on the surface of the polyimide film is cupric oxide, (3) Flexible circuit board material according to (3) On the surface of the polyimide film. The thin film of metal oxide formed on is copper (II) oxide, and the thin metal film formed on it is copper (1).
To the flexible circuit board material according to any one of (2),
(4) A thin film of metal oxide formed on the surface of the polyimide film is formed by the sputtering method (1) to
The flexible circuit board material according to any one of (3),
(5) The flexible circuit board material according to any one of (1) to (4), wherein the metal thin film formed on the metal oxide thin film formed on the surface of the polyimide film is formed by a sputtering method. It is a thing.

First, the drawings will be described with reference to FIGS.
Shows an embodiment of the material for a flexible circuit board of the present invention, wherein 1 is a polyimide film, 2 and 2'are metal oxide layers, 3 and 3'are metal thin films, and 4 is a circuit forming metal film. , A circuit forming copper film layer, for example.

The present invention will be described below with reference to these drawings. That is, the present invention relates to the polyimide film 1
And a metal oxide layer 2 on the main surface of the polyimide film.
And a multi-layer thin film formed by forming a metal thin film 3 on the flexible circuit board material. The flexible circuit board material in the present invention is not limited to the one in which the metal oxide layer 2 and the metal thin film 3 are laminated in this order on one surface of the polyimide film 1 as described above, but also the metal thin film 3 ′ and the metal oxide layer 2 ′. Needless to say, a multi-layer thin film laminated on both surfaces such as the polyimide film 1, the metal oxide layer 2, and the metal thin film 3 is also included. It goes without saying that different metals may be used for the metal oxide layers 2 and 2'and the metal thin films 3 and 3 ', respectively.

Examples of metal oxides include, but are not limited to, oxides of aluminum, chromium, nickel, titanium, molybdenum, tungsten, zinc, iron, copper, silver and the like.

The thickness of such a metal oxide layer should be such that adhesion to the metal thin film layer and the polyimide layer can be maintained.
0 to 3000 nm is preferable, and more preferably 60 to 2
00 nm. If the film thickness is too thin, a portion where the metal oxide is laminated and a portion where the metal oxide is not laminated may occur, that is, there is a problem in the uniformity of the metal oxide film,
On the other hand, if it is too thick, the adhesion with the polyimide film tends to decrease.

As a method for forming the metal oxide layer, there is a physical vapor deposition method. Specific examples of the physical vapor deposition method include a vacuum vapor deposition method and a sputtering method. In the vacuum deposition method, a metal oxide film is formed on a substrate by evaporating a metal oxide as a raw material in a vacuum. It is also possible to introduce oxygen gas at the time of evaporation or discharge the introduced oxygen gas. In the sputtering method, a metal oxide or metal is used as a target, and argon and oxygen are used as a discharge gas to form a metal oxide film.

Examples of the metal forming the metal thin film include metals such as aluminum, chromium, nickel, titanium, molybdenum, tungsten, zinc, iron, copper and silver.
It is not limited to this.

The combination of the metal thin film and the metal oxide does not necessarily have to correspond as a metal. For example, in addition to copper and copper oxide, a combination of copper and aluminum oxide may be used.

The case of using cupric oxide for the metal oxide layer will be described in more detail below. The oxide of copper is formed on the substrate made of a glass plate by the DC magnetron sputtering method using argon gas and oxygen gas. . At this time, by changing the ratio of the flow rates of the introduced argon gas and oxygen gas, the state of the metal oxide formed on the glass plate changes (the oxidation number of copper changes), so the film thickness changes. . By analyzing the color of the thin film at this time and the X-ray crystal structure of the thin film formed on the glass plate, the state of copper oxide (oxidation number) can be known.

In this way, copper is oxidized into cuprous oxide and cupric oxide. Based on the data of the flow rate ratio of Ar / O ₂ , the cuprous oxide and cupric oxide are deposited on the polyimide film. Formed. There was a difference in adhesiveness between the case where the copper thin film was formed after forming the cuprous oxide on the polyimide film and the case where the copper thin film was formed after forming the cupric oxide.

That is, the adhesion between the polyimide layer and the metal layer was better when the cupric oxide was used as the metal oxide layer than when the cupric oxide was used. Therefore, when copper oxide is used as the metal oxide layer, it is more preferable to use a copper oxide layer that has been oxidized to cupric oxide.

The copper thin film is a material for forming a circuit, which can be easily understood by those skilled in the art. More specifically, the copper thin film is preferably made of copper having a purity of 99.99% or more. Although the copper thin film is usually formed to have 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. In consideration of these subsequent steps, the film thickness is preferably 200 nm or more in order to facilitate circuit processing. Although the upper limit of the thickness is not particularly specified, it is usually about 1000 μm. Further, in the present invention, as shown in FIGS. 2 and 3, a metal thin film for forming a circuit, usually a copper thin film, may be further formed on the metal thin film.

For forming the metal thin film, not only a dry forming method such as a vacuum deposition method, an ion plating method, a sputtering method and a CVD method but also a wet thin film forming method such as an immersion method and a printing method can be 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 methods such as DC magnetron sputtering, high frequency magnetron sputtering, and ion beam sputtering are effectively used.

The thickness of the polyimide film is not particularly limited, but normally a polyimide film having a 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. Furthermore, pyromellitic anhydride,
Biphthalic anhydride, benzophenone tetracarboxylic acid anhydride, oxydiphthalic anhydride, hydrofurandiphthalic anhydride and other acid anhydrides, 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, an amine such as diketone diamines, polyimide formed by imidizing can also be used effectively in the present invention.

[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) As a polyimide film, the film thickness is 50.
A surface of a polyimide film was treated on this one side with 8 μm Kapton-V (manufactured by DuPont) by glow discharge of oxygen, and then a thickness of 180 nm was obtained by a DC magnetron sputtering method using argon and oxygen gas with copper as a target. After forming the cupric oxide thin film layer as a thin film of the underlying metal oxide, the target copper is kept without breaking the vacuum state and the DC cupron thin film is continuously formed by the DC magnetron sputtering. In contact with each other, a copper thin film having an average film thickness of about 250 nm was laminated. Next, the thickness of the circuit copper film was set to 20 μm by electrolytically plating copper on the copper thin film. When the adhesive strength of the circuit copper film obtained by such a method to the polyimide film was measured, the average strength in normal state was 1.5 kg / cm on average. This was placed in an oven at 150 ° C. and kept for 10 days, and the adhesive strength was measured in the same manner.
It was g / cm, and although the adhesive force was reduced to 93.3%, it was confirmed that the high adhesive force exceeding 1.0 kg / cm was still maintained.

On the other hand, 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 kept for 10 days, and the adhesive strength was measured in the same manner. It was confirmed that the adhesive strength was lowered to 93.3% in this case as well, but the high adhesive strength exceeding 1.0 kg / cm was still maintained.

Example 2 As a polyimide film,
Using Kapton-V (manufactured by DuPont) having a film thickness of 50.8 μm, the surface of the polyimide film was treated by glow discharge of oxygen on this one surface, and then DC magnetron sputtering was performed with argon and oxygen gas using aluminum as a target. After forming an aluminum oxide thin film layer having a thickness of 100 nm by a method to form a thin film of a base metal oxide, the aluminum oxide thin film is continuously formed by DC magnetron sputtering with aluminum as a target without breaking a vacuum state. And an aluminum thin film having an average film thickness of about 200 nm was laminated.
Next, the thickness of the aluminum film was set to 1.0 μm on the aluminum thin film by a vacuum vapor deposition device. The adhesive strength of the copper film for a circuit obtained by such a method to the polyimide film was measured and found to be 1.3 kg / cm on average in normal strength. This was placed in an oven at 150 ° C. and kept for 10 days, and the adhesive strength was measured in the same manner.
It was 1 kg / cm, and although it was found that the adhesive force decreased to 84.6%, it was confirmed that the high adhesive force still exceeding 1.0 kg / cm was maintained. On the other hand, 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 1
When the adhesive strength was measured in the same manner after being placed in an oven at 50 ° C. for 10 days, the average adhesive strength was 1.0 kg / cm, and in this case as well, although the adhesive strength decreased to 76.9%, 1. It was confirmed that the adhesive strength was as high as 0 kg / cm.

Example 3 As a polyimide film,
Upilex-S (made by Ube Industries) instead of Kapton
Using, on one side, after treating the surface of the polyimide film with glow discharge of oxygen, targeting copper,
A 180 nm-thick cupric oxide thin film layer was formed by a DC magnetron sputtering method using argon and oxygen gas, and was formed as a thin film of a base metal oxide, and then continuously targeting silver without breaking the vacuum state. Then, by DC magnetron sputtering, a silver thin film with an average film thickness of about 250 nm was laminated in contact with the cupric oxide thin film. Next, the thickness of the circuit copper film was set to 20 μm by electrolytically plating copper on the silver thin film. The adhesion strength of the copper film for a circuit obtained by such a method to a polyimide film was measured, and the average strength in normal state was 1.4 kg.
Was / cm. Put this in an oven at 150 ° C,
After holding for 10 days, the adhesive strength was measured in the same manner.
It was 1.2 kg / cm on average, and although it was found that the adhesive force was reduced to 85.7%, it was confirmed that the high adhesive force still exceeding 1.0 kg / cm was maintained. On the other hand, before putting it in an oven at 150 ° C, the film was wrapped around a stainless steel rod having a diameter of 10 mm, 5 times each on the front and back sides, a total of 10 times, then put in an oven at 150 ° C, kept for 10 days, and then similarly bonded. When the force was measured, the average was 1.1 kg /
cm, and even in this case, the adhesive force is 78.6%
However, it was confirmed that the high adhesive strength exceeding 1.0 kg / cm was still maintained.

(Comparative Example 1) In Example 1, the second oxidation
When the adhesive strength of the copper circuit board to the polyimide film was measured by preparing one having no copper layer, the average strength in normal state was 1.5 kg / cm. This was put in an oven at 150 ° C. and kept for 10 days, and then the adhesive strength was measured in the same manner. As a result, the decrease was remarkable, and it was 0.01 kg / cm or less.

(Comparative Example 2) In Example 2, one having no aluminum oxide layer was prepared, and the adhesive strength of the circuit board to the polyimide film was measured. The average strength in normal state was 1.3 kg / cm. . This is 150
After placing it in an oven at ℃ for 10 days and then measuring the adhesive strength in the same way, a remarkable decrease was found to be 0.01 kg / c.
It has become less than m.

(Comparative Example 3) In Example 3, the second oxidation
An adhesive having no copper layer was prepared, and the adhesive strength of the copper circuit board to the polyimide film was measured. The average strength was 1.4 kg / cm on average. This was put in an oven at 150 ° C. and kept for 10 days, and then the adhesive strength was measured in the same manner. As a result, the decrease was remarkable, and it was 0.01 kg / cm or less.

[0028]

As is apparent from the above examples and comparative examples, the present invention not only fully satisfies the heat resistance for realizing high integration of semiconductor IC chips, The present invention provides a technique for a material for a flexible circuit board that exhibits excellent properties in terms of flexibility that makes the most of the 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 Metal oxide layer 2'Metal oxide layer 3 Metal thin film 3'Metal thin film 4 Copper film for circuit formation

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

Claims (5)

[Claims] 1. A flexible circuit board material comprising a polyimide film and a multilayer film formed by forming a metal oxide thin film on at least one surface of the polyimide film and forming a metal thin film on the thin film. 2. The flexible circuit board material according to claim 1, wherein the metal oxide thin film formed on the surface of the polyimide film is cupric oxide. 3. The metal oxide thin film formed on the surface of the polyimide film is cupric oxide, and the metal thin film formed thereon is copper. Flexible circuit board material. 4. The flexible circuit board material according to claim 1, wherein the metal oxide thin film formed on the surface of the polyimide film is formed by a sputtering method. 5. The flexible circuit board material according to claim 1, wherein the metal thin film formed on the metal oxide thin film formed on the surface of the polyimide film is formed by a sputtering method.