JP2008091596A - Copper-coated polyimide substrate with smooth surface, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a copper-coated polyimide substrate with a smooth surface rarely involving plating unevenness due to a dense aggregation of pits, which are 5 μm or above in size and 0.5 μm or above in depth, or projections 0.5 μm or above in height, and to provide an efficient method of manufacturing the same. <P>SOLUTION: The manufacturing method of a copper-plated polyimide substrate comprises processes of forming metal seed layers 2 and 3 directly on, at least, either surface of a polyimide film 1 without interposing an adhesive agent and laminating a copper layer 4 thereon through a plating method. Before the copper layer 4 is laminated, the surface of the metal seed layer 3 is subjected to modification treatment so as to have a wet tensile strength of 50 to 73 mN/m specified by a JIS K6768 plastic-film and sheet wet tensile strength test method. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a copper-coated polyimide substrate having surface smoothness and a method for producing the same, and more specifically, the surface of a copper layer is smooth, for example, pits or high pits having a size of 5 μm or more and a depth of 0.5 μm or more. The present invention relates to a copper-coated polyimide substrate excellent in surface smoothness with little plating unevenness due to denseness of protrusions having a thickness of 0.5 μm or more, and a method for producing the same.

  In recent years, a copper-coated polyimide substrate has been widely used as a semiconductor mounting substrate for mounting a driving semiconductor for displaying an image on a liquid crystal screen. The polyimide film has excellent heat resistance and is not inferior to other plastic materials in mechanical, electrical and chemical characteristics. For example, a printed wiring board (PWB), a flexible printed wiring board ( It is widely used as an insulating substrate material for electronic components such as FPC), tape automatic bonding tape (TAB), and chip on film (COF). Such PWB, FPC, TAB, and COF are obtained by processing a polyimide-coated polyimide substrate in which copper is mainly coated as a metal conductor layer on at least one surface of a polyimide film.

  In general, as a copper-coated polyimide substrate, a three-layer copper-coated polyimide substrate (hereinafter sometimes referred to as a three-layer substrate) in which a polyimide film and a copper foil are bonded via an adhesive, and the polyimide film directly. A copper-coated polyimide substrate (hereinafter sometimes referred to as a two-layer substrate) composed of two layers formed with a metal layer is used. Furthermore, as a two-layer substrate, a metal seed layer is formed by a direct sputtering method on a casting substrate obtained by forming a polyimide film on a commercially available copper foil and a commercially available polyimide film, and a sputtering method and / or plating is formed thereon. There is a substrate composed of two layers manufactured by laminating a copper layer as a conductor layer by a method (hereinafter sometimes referred to as a two-layer plated substrate).

  By the way, TAB and COF have recently been demanded to have high density due to miniaturization, thinning, etc., especially with the miniaturization and thinning of portable electronic devices, and therefore their wiring pitch (wiring width / space width). Is getting narrower. In order to cope with such a situation, since the adhesive layer is not provided as a copper-coated polyimide substrate, the high temperature stability inherent in the polyimide film can be exhibited without being affected by the characteristics of the adhesive layer. At the same time, attention has been focused on a two-layer plated substrate in which the copper conductor layer can be made thin and freely prepared.

  As such a two-layer plating substrate, for example, a copper-coated polyimide substrate comprising at least a polyimide film, a metal seed layer directly formed on the polyimide film, and a copper layer formed on the metal seed layer ( For example, see Patent Document 1.).

  However, in such a polyimide substrate, the high temperature stability inherent in the polyimide film can be exhibited without being affected by the properties of the adhesive layer, and at the same time, the thickness of the copper layer can be made thin and free. Although it can be prepared, in order to cope with higher precision and adapt to ultrafine wiring pitch, strict surface smoothness of the copper-coated polyimide substrate itself is required. There is a need for a copper-coated polyimide substrate with less plating unevenness due to dense pits having a depth of 5 μm or more and a depth of 0.5 μm or more or protrusions having a height of 0.5 μm or more.

JP 2003-334890 A (first page, second page)

  The object of the present invention is to provide a smooth surface of the copper layer in view of the above-mentioned problems of the prior art. An object of the present invention is to provide a copper-coated polyimide substrate excellent in surface smoothness with less plating unevenness due to dense projections and an efficient manufacturing method thereof.

  In order to achieve the above object, the present inventor conducted extensive research on the surface smoothness of the two-layer plating substrate. As a result, the surface of the metal seed layer was modified under specific conditions, and then plated on the surface. When a copper layer is laminated by the method, the surface smoothness of the copper layer is improved, and plating is performed by densely gathering pits having a target size of 5 μm or more and a depth of 0.5 μm or more or protrusions having a height of 0.5 μm or more. The present inventors have found that a copper-coated polyimide substrate with little unevenness and excellent surface smoothness can be obtained.

In other words, according to the first aspect of the present invention, a copper-coated polyimide in which a metal seed layer is directly formed on at least one surface of a polyimide film without using an adhesive, and a copper layer is laminated thereon by a plating method. In the method for manufacturing a substrate,
Prior to laminating the copper layer, the surface of the metal seed layer is subjected to a modification treatment so that the wetting tension determined by the JIS K6768 plastic-film and sheet-wetting tension test method is 50 to 73 mN / m. A method for producing a copper-coated polyimide substrate is provided.

  According to a second aspect of the present invention, there is provided the method for producing a copper-coated polyimide substrate according to the first aspect, wherein the modification process is an etching process.

  According to a third aspect of the present invention, in the second aspect, the etching solution used for the etching treatment contains 1 to 10% by weight of hydrogen peroxide with respect to the total amount, and the pH is 3 to 6 with sulfuric acid. There is provided a method for producing a copper-coated polyimide substrate, which is obtained by adjusting to the above.

  According to a fourth aspect of the present invention, there is provided the method for producing a copper-coated polyimide substrate according to the second or third aspect, wherein the etching treatment is performed at room temperature.

  According to a fifth invention of the present invention, in any one of the first to fourth inventions, the metal seed layer is a nickel layer, a chromium layer, a copper layer, or nickel formed by a sputtering method or a vapor deposition method. There is provided a method for producing a copper-coated polyimide substrate, comprising at least one selected from an alloy layer containing at least two of chromium and copper.

  Moreover, according to the sixth invention of the present invention, there is provided a copper-coated polyimide substrate obtained by the production method of any one of the first to fifth inventions.

  The copper-coated polyimide substrate having surface smoothness and the manufacturing method thereof according to the present invention are such that the wetting tension determined by the JIS K6768 plastic-film and sheet-wetting tension test method is 50 to 73 mN / m on the surface of the metal seed layer. After the modification treatment, the copper layer is laminated so that the surface of the copper layer is smooth, pits having a size of 5 μm or more and a depth of 0.5 μm or more or protrusions having a height of 0.5 μm or more The copper-coated polyimide substrate having excellent surface smoothness with less plating unevenness due to the denseness of the metal and its efficient manufacturing method, and its industrial value is extremely large.

The copper-coated polyimide substrate having surface smoothness according to the present invention and the production method thereof will be described in detail.
1. Method for Producing Copper-Coated Polyimide Substrate According to the method for producing a copper-coated polyimide substrate having surface smoothness of the present invention, a metal seed layer is directly formed on at least one surface of a polyimide film without using an adhesive, and further thereon. In the method of manufacturing a copper-coated polyimide substrate in which a copper layer is laminated by a plating method, the wet tension specified in the JIS K6768 plastic-film and sheet-wet tension test method is applied to the surface of the metal seed layer before the copper layer is laminated. The modification treatment is performed so as to be 50 to 73 mN / m.

  In the present invention, prior to laminating the copper layer, the surface of the metal seed layer is subjected to a modification treatment so that the wetting tension determined by the JIS K6768 plastic-film and sheet-wetting tension test method is 50 to 73 mN / m. It is important to do. Although the mechanism of this action has not been clearly clarified, the surface tension on the surface of the metal seed layer before thickening the copper layer greatly affects the occurrence of abnormalities called plating unevenness such as pits and protrusions on the surface. Inferred. That is, when the wettability of the metal seed layer surface is increased, the wettability of the plating solution on the metal seed layer surface becomes uniform, and uniform plating is performed, so the laminated copper layer surface becomes smooth, Generation of uneven plating such as pits and protrusions can be suppressed.

  That is, when the wetting tension on the surface of the metal seed layer is less than 50 mN / m, the wetting of the plating solution on the surface of the metal seed layer becomes non-uniform, and unevenness due to dense pits or protrusions occurs in the portion where the wetting is insufficient during copper plating. Is considered to occur. On the other hand, the maximum surface tension of water is 73 mN / m, which is the upper limit. The wetting tension is a scale indicating the ability of a substance to hold a liquid. The higher the wetting tension, the better the wetting of the plating solution on the surface of the metal layer, and the uniform and less uneven plating can be performed. The wetting tension is evaluated according to the JIS K6768 plastic-film and sheet-wetting tension test method.

  As the manufacturing method, a metal seed layer is directly formed on at least one surface of a predetermined polyimide film, and a copper layer is laminated thereon by a plating method to manufacture a copper-coated polyimide substrate, for example, First, a step (A1) of forming a primary metal seed layer with a predetermined thickness on the surface of a predetermined polyimide film by sputtering or vapor deposition. When the primary metal seed layer is a nickel layer, a chromium layer or a nickel chromium layer Is a step (A2) of laminating a copper layer as a conductor layer to a predetermined thickness as a secondary metal seed layer by sputtering or vapor deposition, if necessary, and then JIS K6768 on its surface. The step of performing the modification treatment so that the wetting tension specified in the plastic-film and sheet-wetting tension test method is 50 to 73 mN / m (B) Further, it is performed by the step (C) of forming the copper conductor layer by thickening the copper layer to a predetermined thickness by an electroplating method or an electroless plating method, or a method using both in combination.

  Industrially, the process (A1) is performed while the polyimide film is conveyed at several tens of centimeters to several tens of meters / minute, and the process (A2) is performed as necessary, and then the processes (B) and (C). It can be performed continuously by moving in a cell having the above function.

  The primary metal seed layer in the step (A1) is not particularly limited, and the role of ensuring the adhesion strength between the polyimide film and the metal layer, the heat resistance of the substrate, and the stability in a humidity resistant environment. Among these, a nickel layer, a chromium layer, a copper layer, or an alloy layer containing any two or more of nickel, chromium, and copper formed by a sputtering method or a vapor deposition method is used. At least one selected is preferable, in particular, a nickel layer, a chromium layer, or a nickel chromium alloy layer is more preferable, and a nickel chromium alloy layer is more preferable. For example, the alloy composition and thickness of the nickel chromium alloy layer are not particularly limited, but the chromium quality in the alloy layer is preferably 5 to 30% by weight and the thickness is preferably 5 to 500 angstroms.

  The copper layer (secondary metal seed layer) as the conductor layer in the above step (A2) is continuously sputtered after the metal seed layer is formed by sputtering or vapor deposition to ensure conductivity before electroplating. The copper layer is formed by a method or a vapor deposition method, and the thickness of the copper layer is not particularly limited, but in order to impart conductivity in order to uniformly and smoothly deposit by electroplating, 50-5000 Angstroms are preferred.

  The apparatus used for the sputtering method is not particularly limited, and a magnetron sputtering apparatus or the like is used. Moreover, it does not specifically limit as an apparatus used for a vapor deposition method, A vacuum vapor deposition apparatus etc. are used.

  The step (B) is a step of modifying the surface of the metal seed layer so that the wetting tension determined by the JIS K6768 plastic-film and sheet-wetting tension test method is 50 to 73 mN / m.

  The reforming treatment is not particularly limited, and various methods for adjusting the surface tension so as to obtain a predetermined wetting tension can be used. Among them, the method can be efficiently performed with particularly simple equipment. Etching is preferred. For example, as an etching process, after forming a metal seed layer on the surface of a commercially available polyimide film by a sputtering method, it is immersed in an etching solution at room temperature, or an etching solution is supplied onto a polyimide substrate on which a metal seed layer is formed. Thus, the wet tension of the surface of the metal seed layer can be adjusted to a predetermined value by a method of contacting with the etching solution for several tens of seconds.

  The etching solution is not particularly limited, and a commercially available one is used. For example, hydrogen peroxide is contained in an amount of 1 to 10% by weight, and the pH is adjusted to 3 to 6 with sulfuric acid. What was obtained is mentioned.

  The method of thickening the copper by the plating method in the step (C) is not particularly limited, and an electrolytic copper plating method, an electroless copper plating method, or a method using both of them is used. Here, electroless plating can be performed prior to electroplating or alternately with electroplating as a countermeasure against pinholes in the sputtered layer. The thickness of the copper layer by the plating method is preferably 1 to 500 μm, more preferably 2 to 20 μm. The formation of the copper film by electroplating is performed by using an acidic plating solution mainly composed of sulfuric acid and copper sulfate. Usually, the thickness of the copper layer is from several μm to several hundred μm.

2. Copper-coated polyimide substrate The copper-coated polyimide substrate having surface smoothness according to the present invention is obtained by the above-described manufacturing method, and the surface of the copper layer is smooth, having a size of 5 μm or more and a depth of 0.5 μm or more. This is a copper-coated polyimide substrate having excellent surface smoothness with little plating unevenness due to dense pits or projections having a height of 0.5 μm or more. As a result, it is possible to have sufficient characteristics as a material for a flexible substrate or the like that can cope with higher precision of electronic components and adapt to ultrafine wiring pitches.

  The structure of the copper-coated polyimide substrate will be described with reference to the drawings. FIG. 1 shows an example of a schematic cross-sectional view of a copper-coated polyimide substrate of the present invention. In FIG. 1, the cross section of the copper-coated polyimide substrate includes a primary metal seed layer 2 and a secondary metal seed layer 3 formed by sputtering or vapor deposition on the surface of the polyimide film 1, and a copper layer 4 by plating. It has a structure that is sequentially stacked. Here, a copper conductor layer is formed by the secondary metal seed layer 3 formed by sputtering or vapor deposition and the copper layer 4 by plating. In addition, when copper is used for the primary metal seed layer 2, the secondary metal seed layer 3 may not be provided.

Hereinafter, the present invention will be described in more detail by way of examples and comparative examples of the present invention, but the present invention is not limited to these examples. In addition, it was as follows as a measurement of the wet tension of the metal seed layer surface used by the Example and the comparative example, and the external appearance evaluation method of the copper layer of a copper covering polyimide substrate.
(1) Measurement of the wetting tension on the surface of the metal seed layer: JIS K6768 Plastic-film and sheet-wetting tension test method.
(2) Appearance evaluation of copper layer of copper-coated polyimide substrate: The inside of a 300 mm square of the surface was microscopically examined to check the state of pits or protrusions.

(Example 1)
On the surface of a commercially available polyimide film, a nickel chromium alloy layer as a metal seed layer was formed to a thickness of 0.1 μm by sputtering.
Next, while maintaining a mixed solution containing 3% by weight of hydrogen peroxide and adding sulfuric acid so as to have a pH of 5 at 25 ° C., a polyimide substrate on which a metal seed layer was formed was placed for 20 seconds. Modification treatment was performed by dipping. Here, the wetting tension of the surface of the metal seed layer after the treatment was measured. The wetting tension at this time was 67 mN / m.
Thereafter, electroplating was performed on the surface of the metal seed layer to obtain a copper-coated polyimide substrate, and the appearance was evaluated. As a result, the surface of the copper layer is smooth, the number of pits having a size of 5 μm or more, a depth of 0.5 μm or more, and the number of protrusions having a height of 0.5 μm or more is only three, and the appearance is good. It was found that a copper-coated polyimide substrate was obtained.

(Comparative Example 1)
A copper-coated polyimide substrate was produced in the same manner as in Example 1 except that the modification treatment was not performed after the metal seed layer was formed, and then the appearance was evaluated.
As a result, the wetting tension on the surface of the metal seed layer was 47 mN / m. Further, on the surface of the copper layer, a total of 98 pits having a size of 5 μm or more and a depth of 0.5 μm or more and protrusions having a height of 0.5 μm or more were detected, and more than 1 μm or more of dents or protrusions were detected. Unevenness due to crowding was observed, and it was found that a substrate with poor appearance was obtained.

  As described above, in Example 1, the modification was performed by the etching method, and the wetting tension of the surface of the metal seed layer was adjusted to 50 mN / m or more according to the method of the present invention. A copper-coated polyimide substrate having a small appearance can be obtained. On the other hand, in Comparative Example 1, the metal seed layer is not modified, and the wetting tension on the surface of the metal seed layer does not meet the above conditions, so that a substrate with a poor appearance can be obtained.

  As is clear from the above, the copper-coated polyimide substrate having surface smoothness of the present invention is excellent in surface smoothness, which corresponds to higher precision of electronic parts and adapts to extremely fine wiring pitch. Since it has sufficient characteristics as a material such as a flexible substrate, it is useful as a substrate corresponding to miniaturization and thinning of TAB and COF for portable electronic devices.

It is a figure showing an example of the schematic sectional view of the copper covering polyimide substrate of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polyimide film 2 Primary metal seed layer 3 Secondary metal seed layer 4 Copper layer by plating method

Claims (6)

In the method for producing a copper-coated polyimide substrate, a metal seed layer is directly formed on at least one surface of a polyimide film without using an adhesive, and a copper layer is further laminated thereon by a plating method.
Prior to laminating the copper layer, the surface of the metal seed layer is subjected to a modification treatment so that the wetting tension determined by the JIS K6768 plastic-film and sheet-wetting tension test method is 50 to 73 mN / m. A method for producing a copper-coated polyimide substrate.   The method for producing a copper-coated polyimide substrate according to claim 1, wherein the modification process is an etching process.   The etching solution used for the etching treatment contains 1 to 10% by weight of hydrogen peroxide with respect to the total amount, and is obtained by adjusting the pH to 3 to 6 with sulfuric acid. The manufacturing method of the copper covering polyimide board of description.   The said etching process is performed at normal temperature, The manufacturing method of the copper covering polyimide substrate of Claim 2 or 3 characterized by the above-mentioned.   The metal seed layer is made of at least one selected from a nickel layer, a chromium layer, a copper layer, or an alloy layer containing any two or more of nickel, chromium, and copper formed by a sputtering method or a vapor deposition method. The manufacturing method of the copper covering polyimide substrate in any one of Claims 1-4 characterized by the above-mentioned.   A copper-coated polyimide substrate obtained by the production method according to claim 1.

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