JPH036361A - Method for sticking metal on polyimide film - Google Patents

Abstract

PURPOSE:To directly stick a metal having high bonding strength on a polyimide film by forming a modified layer of a specified thickness on the surface of the polyimide film, forming a metal layer on the modified layer and then forming a metal diffusion layer of a specified thickness by heat treatment. CONSTITUTION:The surface of a polyimide film having relatively low chemical resistance is treated with an alkaline soln. of NaOH, etc., to form a modified layer of 100-1,500Angstrom thickness. A metal layer of about 1-10mum thickness such as a copper layer is formed on the modified layer by a vacuum film forming means such as vacuum deposition and the metal is diffused into the modified layer by heat treatment at about >=100 deg.C to form a metal diffusion layer of >=50Angstrom thickness within the thickness of the modified layer. A polyamide film used to produce a metal laminated polyimide film for a flexible wiring board is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for attaching metal to a polyimide film used in the production of metal-laminated polyimide films used in flexible wiring boards.

(Prior Art) Conventionally, when attempting to form a conductive metal layer, particularly a copper layer, on polyimide, there has been a problem that the adhesive strength between copper and polyimide is so low that it cannot be put into practical use. As a conventional method to solve this problem, as shown in (1) JP-A-52-136284 or JP-A-55-34415, bonding of titanium, nickel, etc. is used between the copper conductor and polyimide. Method of injecting sexual metal, (2) JP-A-52-1
Publication No. 24172 or JP-A-52-13.767
A method of forming a metal layer by electroless plating after treating a polyimide surface with a chemical solution as shown in Publication No. 4, (3)
As shown in Japanese Unexamined Patent Publication No. 5,622,331, there is a method in which a polyimide surface is treated with a chemical solution and then a metal layer is formed by vacuum film forming means.

(Problems to be solved by the invention) However, in method (1), the resistance value of the circuit increases, the electrical characteristics deteriorate due to the skin effect at high frequencies, and when removing unnecessary parts of metal, However, there was a problem in that it was difficult to remove two types of metals at once or in sequence without affecting each other.

Also, in method (2), the method disclosed in JP-A-52-124172 uses metals with good adhesive properties such as nickel and cobalt, but there is a problem that the resistance value of the circuit increases. Although the method disclosed in JP-A-52-137674 does not specify the electroless plating solution, there is a problem similar to the former when using nickel, and a problem of low adhesive strength when using copper plating solution.

Furthermore, even with the method (3), the adhesive strength between copper and polyimide is insufficient, and there is a problem in that, depending on the type of polyimide in particular, sufficient adhesive strength cannot be obtained.

As described above, when attempting to directly form a conductive metal layer, particularly a copper layer, on polyimide, conventional methods have had problems in that sufficient adhesion strength cannot be obtained or other properties are degraded.

The present invention provides a method for forming metals such as copper layers with high adhesion directly onto polyimide films.

(Means for Solving the Problems) The present invention involves treating the surface of a polyimide film with a chemical solution to form a modified layer with a thickness of 100 to 1,500 layers, and forming a metal layer on the modified layer by vacuum film formation. , the metal is diffused by heat from the metal layer formed on the modified layer so that the thickness of the metal diffusion layer is kept within the range of -50 Å or more and the total thickness of the modified layer.

As the polyimide film, commercially available polyimide films can be used, and those with relatively low chemical resistance are suitable.In particular, Kapton film (trade name of Azuma DuPont), Avical film (Kanebuchi) Chemistry (trade name) is good.

As the chemical solution for forming a modified layer on the surface of the polyimide film, alkali metal hydroxide salt aqueous solutions such as sodium hydroxide and potassium hydroxide aqueous solutions, alkaline solutions such as hydrazine hydrate and tetramethylammonium hydroxide can be used.

The modified layer must have chemical interaction with the metal, and for this purpose, the modification method must be changed depending on the metal to be deposited to generate suitable functional groups. In particular, in the case of copper, an alkaline aqueous solution is preferable.

The ease with which polyimide can be modified is closely related to its molecular structure. In particular, when modifying with an aqueous alkaline solution, the acid monomer forming the polyimide is preferably pyromellitic anhydride or naphthalenetetracarboxylic anhydride.

The thickness of the modified layer ranges from 100 to 1500, and 20
A range of 0 to 800 people is preferred.

If there are fewer than 100 people, it will be difficult to control the diffusion of metal, and the metal will easily diffuse into unmodified polyimide, making it impossible to increase the adhesive strength of the metal. 15
If the thickness exceeds 0.00, the thickness of the mechanically weak modified layer becomes too large, making it difficult to increase the adhesive strength of the metal. Compared to an unmodified layer, a polyimide modified layer contains more functional groups that chemically interact with metal, and thus contributes to improving adhesive strength. In addition, mechanically, the modulus of elasticity is different, and the layer in which copper is diffused into the modified layer has a further different material constant, which has the effect of controlling the progress of fracture when the metal layer is peeled off.

A metal layer is formed on the modified layer on the surface of the polyimide film by vacuum deposition means such as vacuum evaporation, magnetron sputtering, ion beam sputtering, ion cluster beam evaporation, ion blating, etc. The thickness is, for example, 0.1 μm ~
10 μm is preferred. Depending on the application of the metallized polyimide film, the thickness of the metal layer can be added by electroplating, electroless plating, vacuum deposition, etc. after a suitable subsequent step, such as a heating step for diffusion.

Metal is diffused into the modified layer by heat from the metal layer formed on the modified layer. In order to efficiently diffuse the metal into the modified layer, heating to 100° C. or higher is necessary. The upper limit of the heating temperature depends on the heat resistance of the polyimide film, but is suitably below the glass transition temperature. Furthermore, since the diffusion rate changes depending on the temperature, it is necessary to determine the optimum heating time to obtain the desired diffusion layer thickness.

In the present invention, the thickness of the metal diffusion layer is set to be 50 Å or more and within the range of the total thickness of the modified layer. In this way, the thickness of the metal diffusion layer is set to about 60 mm on the surface of the controbuton film.
0 modified layers were generated. Copper was sputtered onto this Kapton film at a substrate temperature of 200° C. and an applied voltage of 440 V to form a copper layer of about 0.5 μm. At this time, the thickness of the copper diffusion layer was approximately 550 mm. Furthermore, copper sulfate plating was applied on the sputtered copper layer so that the total thickness of the copper layer was approximately 18 μm. As a result of a 90° peel test of the copper-adhered Kapton film created in this way, the peel strength was 0.75 kgf/c.
It was m.

[Example 2] Copper was sputtered onto a Kapton film treated in the same manner as in Example 1 at a substrate temperature of 23° C. and an applied voltage of 440 V to form a copper layer of about 0.5 μm. Thereafter, this copper-attached Kapton film was heated in vacuum at 150° C. for 40 minutes. At this time, the thickness of the copper diffusion layer was approximately 500 mm. Furthermore, copper plating was performed on the sputtered copper layer in the same manner as in Example 1, and a 90° peel test was performed to increase the adhesive strength between the polyimide film and the metal layer formed directly on the film. It becomes possible to do so.

In the present invention, when the metal layer is peeled off, the damage occurs between the modified layer containing the diffused metal layer and the modified layer not containing the diffused metal (or the unmodified layer when the thickness of the modified layer not containing the diffused metal is small). It was observed that this phenomenon occurred near the interface with the high quality polyimide layer).

The metal is also diffused by heat treatment in various steps after the metal is deposited and thermally diffused. If this diffusion does not remain within the modified layer and reaches the unmodified polyimide layer, the position of the surface on which the fracture progresses as described above may change and the adhesive force (peel strength) may decrease. Therefore, it is necessary to control the manufacturing process of the wiring board so that the diffusion of metal is confined within the modified polyimide layer.

[Example 1 Cokapton film (trade name of Toshi DuPont ■) was
It was immersed in a 20 wt % aqueous sodium hydroxide solution at ℃ for 5 seconds. As a result of this treatment, the peel strength was 0.7 kgf and 7 cm.

[Comparative Example 1] A Kapton film was immersed in hydrazine hydrate at 50° C. for 5 seconds. This treatment produced a modified layer of about 8,000 layers on the surface of the Kapton film. Copper was sputtered onto this Kapton film in the same manner as in Example 1. At this time,
The thickness of the copper diffusion layer was approximately 550 mm. Further, on this sputtered copper layer, copper plating was performed in the same manner as in Example 1, and a 90' peel test was performed, and the peel strength was 0.04 kgf/cm.

[Comparative Example 2] A cokapton film was immersed in a 20 wt % aqueous sodium hydroxide solution at 30° C. for 1 minute. This treatment produced a modified layer of about 200 layers on the surface of the Kapton film. Copper was sputtered onto this Kapton film in the same manner as in Example 1.

At this time, the thickness of the copper diffusion layer was approximately 550 mm.

Further, on this sputtered copper layer, copper plating was performed in the same manner as in Example 1, and a 90' peel test was performed, and the peel strength was 0.4 kg f / cm
Met.

Claims (4)

[Claims] 1. The surface of the polyimide film is treated with a chemical solution to a thickness of 100 mm.
A modified layer with a thickness of ~1500 Å is formed, a metal layer is formed on the modified layer by vacuum film formation, and the thickness of this metal diffusion layer is determined by diffusing metal from the metal layer formed on the modified layer by heat. A method for attaching a metal to a polyimide film, the method comprising: keeping the thickness within the overall thickness of the modified layer at 50 Å or more. 2. Adhering metal to the polyimide film according to claim 1, wherein the heat for diffusing the metal is heating the polyimide film during vacuum film formation or heating the metal-attached polyimide film after film formation, and the heating temperature is 100 ° C. or higher. How to do it. 3. 3. The method of attaching a metal to a polyimide film according to claim 1 or 2, wherein the chemical treatment is a treatment with an alkaline aqueous solution and the metal to be attached is copper. 4. 4. A method for attaching metal to a polyimide film according to claims 1 to 3, wherein the acid monomer forming the polyimide is pyromellitic anhydride or naphthalenetetracarboxylic anhydride.