JPH08231716A - Flexible circuit substrate - Google Patents

Abstract

PURPOSE: To obtain a flexible circuit substrate, excellent in heat resistance, flexibility, etc., and useful as semiconductor chips, etc., by polymerizing a specific acid anhydride with a diamine, carrying out the dehydrating condensation of the resultant polyamic acid and using a film of the prepared polyimide. CONSTITUTION: This flexible circuit substrate comprises a polyimide film formed from a polyimide of formula I or II and a thin film of at least copper (having preferably >=200μm film thickness) formed on the principal plane of the film. Furthermore, the polyimide of formula I is obtained by polymerizing (A) 3,3'- diaminodiphenyl ether with (B) 3,3',4,4'-diphenyl ether-tetracarboxylic dianhydride, carrying out the dehydrating condensation of the resultant polyamic acid and then carrying out the imidation. The polyimide of formula II is prepared by polymerizing (C) 3,4'-diaminobenzophenone with (D) 3,3',4,4'- benzophenonetetracarboxylic dianhydride, carrying out the dehydrating condensation of the resultant polyamic acid and then conducting the imidation.

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 material composed of a polyimide film and a copper thin film,
In particular, the present invention relates to a material for a flexible substrate, which has good adhesiveness between a copper thin film and a polyimide film at high temperature durability.

[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 is a case where a metal film having a length of m or more and a polymer film are joined with an adhesive, but the thermal property of the adhesive is inferior to the performance of the polymer film. Further, since the metal thin film has a large thickness of 10 μm or more, it is difficult to perform fine processing of several tens of μm, and there is a problem that it cannot be applied to high-density wiring in the semiconductor industry. 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, the thickness of the metal thin film is as thin as 1 μm or less, and a copper layer having a thickness of several μm to 10 μm can be formed on the metal thin film by a plating method. Therefore, fine processing with a width of several tens μm is easy.

That is, as described above, it is a technique of forming a finely processed conductor based on a designed circuit pattern by further depositing and growing a metal by electrolytic plating or the like. 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 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]

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 passing through the polyimide film affects the adhesiveness. , It was found that the deterioration of the adhesiveness can be prevented by providing a gas barrier layer for blocking the passing gas. As a result, it has been possible to obtain a flexible circuit board material composed of a metal layer / polyimide film that can be put to practical use in the semiconductor industry having the harsh process as described above. As a specific example, a plasma chemical vapor deposition method (P-CVD) using tetramethyldisiloxane and oxygen as raw materials is formed on one surface of a polyimide film as a gas barrier layer.
Method) to substantially form a silicon oxide layer with a thickness of 30 to 300 nm. It has been found that such a method dramatically improves the gas barrier property of the film and thus suppresses deterioration of high temperature strength. However, the film has a problem that the gas barrier layer is an obstacle to wiring on both sides.

[0006]

Then, as a result of intensive research to solve these problems, it was obtained by polymerizing a specific acid anhydride and a diamine instead of a commercially available polyimide which has been conventionally used. The inventors have found that the above problems can be solved by using a film, and have reached the present invention. That is, the present invention is a polyimide film obtained by further dehydrating and condensing a specific polyimide film of a flexible circuit board material composed of a metal / polyimide film, which is obtained by polymerizing an acid anhydride and a diamine. By using, to provide a flexible circuit board substantially excellent in high temperature durability, that is, the present invention,
A flexible circuit board comprising a polyimide film and at least a copper thin film formed on a main surface of the polyimide film, wherein the polyimide is represented by the formula (1), [Chemical formula 3] or the formula (2), [Chemical formula 3] 4] is a flexible circuit board made of polyimide as shown in

[0007]

Embedded image

[0008]

[Chemical 4] The polyimide represented by the formula (1) includes 3,3′-diaminodiphenyl ether (3,3′-ODA) and 3,3 ′, 4.
A flexible circuit board, which is a polyimide obtained by dehydration condensation of polyamic acid polymerized with 4′-diphenyl ether tetracarboxilic dianhydride (ODPA) and imidization, and the polyimide represented by the formula (2) is 4'-diaminobenzophenone (3,
4'-DABP) and 3,3 ', 4,4'-benzophenone tetracarboxylic dianhydride (BDT)
A flexible circuit board which is a polyimide obtained by dehydration condensation of polyamic acid polymerized with A) and imidization.

It is not clear why the use of the polyimide of the present invention does not reduce the adhesive force between the polyimide and copper even when it is held at a high temperature, but copper is often used as a polyimide in an oxidizing atmosphere. It is conceivable that the reactivity of polyimide with oxygen or polyimide with water vapor in the presence of copper may be significantly different depending on the structure of the polyimide itself or the structure or composition of the monomer.

First, the drawings will be described with reference to FIG.
Shows an embodiment of the material for a flexible circuit board of the present invention, wherein 10 is a polyimide film and 15 is a copper thin film. Further, FIG. 2 shows an example of a cross section of a flexible circuit board in which a copper layer 20 is further laminated on the above board by a plating method. Hereinafter, the present invention will be described with reference to these drawings.

The copper thin film formed on the polyimide film is a material for forming a circuit, as will be easily recognized by those skilled in the art. Needless to say, materials having low electric resistance such as gold, silver, and aluminum can be used in addition to copper. In the present invention, there are no further particular requirements. Copper having a purity of 99.99% or more is preferably used. 1 copper thin film
Although formed to a film thickness of 00 nm or more, the present invention is a flexible circuit board, and a circuit is formed through a plating step and a soldering step 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 copper thin film can be formed not only by a dry forming method such as a vacuum vapor deposition method, an ion plating method, a sputtering method and a CVD method but also by a wet thin film forming method such as an immersion method and a printing method. . 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 is usually 25 μm to 250
A polyimide film having a thickness of about μm is appropriately selected and used according to the application within the range of design conditions.

As the polyimide used in the present invention,
3,3'-diaminodiphenyl ether (3,3'-O
DA) and 3,3 ', 4,4'-diphenyl ether tetracarboxylic dianhydride (ODPA)
Polyimide obtained by dehydration polymerization of polyimide acid obtained by polymerization of and, or 3,4′-diaminobenzophenone (3,4′-DABP) and 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride ( (BDTA) is a polyimide obtained by dehydration polymerization of polyamic acid polymerized with BDTA). This polyimide film can be obtained by a casting method and has a thickness of 12 to
A 100 μm layer is generally used, but is not necessarily limited to this range.

Regarding specific reagents, ODPA can be purchased from Occidental Chemical Co., Ltd., and BDTA can be purchased from Daicel Chemical Co., Ltd., for example. Three
A method for synthesizing 3'-ODA and 3,4'-DABP is described in JP-A-61-1197546 and JP-A-61-22115.
As described in No. 9, for example, a method in which metaaminophenol and parachlorobenzene are reacted to reduce or a method in which metadinitrobenzene and metanitrophenol are reacted in the presence of potassium carbonate and then reduced is synthesized. be able to. The method of synthesizing polyimide from these monomers is a general method of synthesizing polyimide from acid anhydride and diamine, but one example is as follows. ODPA, 3,3′-ODA, phthalic anhydride, picoline and m-cresol are mixed and stirred at 150 ° C. for 4 hours. After cooling, the reaction solution was mixed with methyl ethyl ketone (ME
When it is poured into K), a polymer is deposited, so that the desired polyimide can be obtained by filtering the deposit, then washing the deposit with MEK and drying in an oven at 230 ° C.

[0015]

EXAMPLES The present invention will be described in more detail below with reference to examples. (Example 1) Polyimide film shown in Chemical formula 1 (thickness 25
After the main surface of (μm) was treated by glow discharge of oxygen, copper (purity 99.999%) was used as a target and DC magnetron sputtering was performed to obtain an average film thickness of 2500 n.
m copper thin film was laminated. Next, as shown in FIG. 2, electrolytic plating of copper was performed on the copper thin film to make the thickness of the copper film for the circuit 20 μm. When the adhesive strength of the copper film for a circuit obtained by such a method to the polyimide film was measured, it was 1.1 kg / cm on average in normal strength. After placing this in an oven at 150 ° C for 10 days,
Similarly, when the adhesive strength was measured, the average was 1.2 kg / cm.
It was confirmed that the high adhesive strength still exceeding 1.0 kg / cm was maintained.

(Example 2) After the main surface of the polyimide film (thickness: 25 μm) shown in Chemical formula 2 was treated by glow discharge of oxygen, copper (purity 99.999%) was targeted, and DC magnetron sputtering was performed. Thus, a copper thin film having an average film thickness of 2500 nm was laminated. Next, as shown in FIG. 2, electrolytic plating of copper was performed on the copper thin film to make the thickness of the copper film for the circuit 20 μm. When the adhesive strength of the copper film for a circuit obtained by such a method to the polyimide film was measured, the average strength in normal state was 1.0 kg / cm on average. This was put 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 still higher than 1.0 kg / cm and that the adhesive strength was still higher than 1.0 kg / cm.

COMPARATIVE EXAMPLE 1 In Example 1, a commercially available polyimide, Kapton V (Toray-DuPont, thickness: 25 μm) was used in place of the polyimide shown in Chemical formula 1, and the adhesive force of the copper thin film to the polyimide film was measured. When measured, the normal strength was 1.2 kg / cm on average. After placing this in an oven at 150 ° C for 10 days,
Similarly, when the adhesive strength was measured, the decrease was remarkable, and
It has become less than kg / cm.

[0018]

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 diagram showing a layer structure of an embodiment of a material for a flexible circuit board of the present invention.

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

[Explanation of symbols]

 10 Polyimide 15 Copper thin film 20 Plated copper layer

 ─────────────────────────────────────────────────── (72) Inventor Yoshinori Ashida 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 Kagaku (72) Inventor Shoji Tamai, 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Toatsu Chemical Co., Ltd. (72) Wataru Yamashita 1190, Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Toatsu Chem., Ltd. ( 72) Inventor Akihiro Yamaguchi 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Toatsu Chemical Co., Ltd.

Claims (3)

[Claims] 1. A flexible circuit board comprising a polyimide film and at least a copper thin film formed on a main surface of the polyimide film, wherein the polyimide is represented by the formula (1), [formula 1] or formula (1) 2) A flexible circuit board made of polyimide shown in [Chemical Formula 2]. Embedded image Embedded image 2. The polyimide represented by the formula (1) is 3,3 ′.
A polyimide obtained by dehydration condensation of polyamic acid obtained by polymerizing diaminodiphenyl ether (3,3′-ODA) and 3,3 ′, 4,4′-diphenyl ether tetracarboxylic dianhydride (ODPA) and imidization. The flexible circuit board according to claim 1. 3. The polyimide represented by the formula (2) is 3,4 ′.
A polyimide obtained by dehydration condensation of polyamic acid obtained by polymerization of diaminobenzophenone (3,4′-DABP) and 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride (BDTA), and imidization. The flexible circuit board according to claim 1.