Method of manufacturing flexible wiring board Number:7,098,132 from the United States Patent and Trademark Office (PTO) owispatent In the present invention, a reference conductive layer and a first surface conductive layer are respectively provided on a surface and a back face of a first base film. The first base film includes a first via hole penetrating the first surface conductive layer. After a first electroless plating layer and a first conductive material are sequentially grown on a surface of the first base film, a first coating conductive layer composed of the first electroless plating layer, the first conductive material and the first surface conductive layer, is etched to have a reduced thickness. Then, the first coating conductive layer is patterned to form a first wiring layer. In this manner, a desired pattern width can be obtained even in the case where the first coating conductive layer is patterned by isotropic etching such as wet etching.<H manufacturing, flexible, Method, of, manuf, 7098132.html, Patent, pto, 7098132

Title: Method of manufacturing flexible wiring board

Abstract: In the present invention, a reference conductive layer and a first surface conductive layer are respectively provided on a surface and a back face of a first base film. The first base film includes a first via hole penetrating the first surface conductive layer. After a first electroless plating layer and a first conductive material are sequentially grown on a surface of the first base film, a first coating conductive layer composed of the first electroless plating layer, the first conductive material and the first surface conductive layer, is etched to have a reduced thickness. Then, the first coating conductive layer is patterned to form a first wiring layer. In this manner, a desired pattern width can be obtained even in the case where the first coating conductive layer is patterned by isotropic etching such as wet etching.

Patent Number: 7,098,132 Issued on 08/29/2006 to Naitoh, et al.

Inventors: Naitoh; Keiichi (Kanuma, JP), Shinohara; Toshihiro (Kanuma, JP), Watanabe; Masahiro (Kanuma, JP)
Assignee: Sony Chemicals Corp. (Tokyo, JP)
Sony Corporation (Tokyo, JP)

Appl. No.: 11/087,211

Filed: March 23, 2005

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
10646623	Aug., 2003	6912779
PCT/JP02/01349	Feb., 2002

Foreign Application Priority Data


Feb 23, 2001 [JP]			2001-048878

Current U.S. Class: 438/678 ; 29/846; 29/852; 427/97.9

Current International Class: H01L 21/44 (20060101)

Field of Search: 438/618-680 29/846-860 427/97.1-97.9

References Cited [Referenced By]

U.S. Patent Documents


6197425	March 2001	Sekimoto et al.

Primary Examiner: Tsai; H. Jey
Attorney, Agent or Firm: Osha Liang LLP

Parent Case Text

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application of U.S. patent application Ser. No. 10/646,623, filed on Aug. 22, 2003 now U.S. Pat. No. 6,912,779. The '623 Application is a Continuation of PCT/JP02/01349, filed on Feb. 18, 2002. The present application claims benefit under 35 U.S.C. .sctn. 120 of these applications and incorporates these prior applications by reference in their entireties.

Claims

What is claimed is:

1. A method of manufacturing a flexible wiring board, with a substrate, wherein the wiring board comprises a reference conductive layer; a first base film provided on said reference conductive layer; and a first surface conductive layer provided on said first base film, the method comprising: forming a first hole penetrating said first surface conductive layer and said first base film so that said reference conductive layer is exposed on its bottom and said first base film is exposed on an inner peripheral side face; depositing, by electroless plating, a first electroless plating layer on at least a surface of said first base film exposed on the inner peripheral side face of said first hole; growing, by electrolytic plating, a first electrolytic plating layer on a surface of said first electroless plating layer so as to fill said first hole with said first electrolytic plating layer and then providing said electroless plating layer and said electrolytic plating layer on said first surface conductive layer to form a first surface coating layer; etching said first electrolytic plating layer so as to reduce a thickness of said first surface coating layer on said first base film; and forming a patterned resist film on a surface of said first surface coating layer having a reduced thickness and then removing said first surface coating layer situated on a bottom of an opening of said resist film so as to pattern said first surface coating layer.

2. The method of manufacturing a flexible wiring board according to claim 1, wherein said first surface conductive layer is a metal foil and is adhered to said first base film.

3. The method of manufacturing a flexible wiring board according to claim 1, wherein said reference conductive layer is brought into contact with an electrode when said electrolytic plating is conducted.

4. The method of manufacturing a flexible wiring board according to claim 1, further comprising the step of depositing an auxiliary electrolytic plating layer by electrolytic plating on a surface of said reference conductive layer, exposed on the bottom of said first hole, prior to said step of depositing the first electroless plating layer.

5. The method of manufacturing a flexible wiring board according to claim 4, wherein growth of said auxiliary electrolytic plating layer is terminated before said auxiliary electrolytic plating layer reaches said first surface conductive layer.

6. The method of manufacturing a flexible wiring board according to claim 1, further comprising the steps of: providing a second base film and a second surface conductive layer on said patterned first surface coating layer; forming a second hole penetrating said second surface conductive layer and said second base film so that said first surface coating layer is exposed on its bottom and said second base film is exposed on its inner peripheral side face; depositing, by electroless plating, a second electroless plating layer on at least a surface of said second base film exposed on inner peripheral side face of said second hole; and growing, by electrolytic plating, a second electrolytic plating layer on a surface of said second electroless plating layer so as to fill said second hole with said second electrolytic plating layer.

7. The method of manufacturing a flexible wiring board according to claim 6, wherein said second surface conductive layer is a metal foil and adhered to said second base film.

8. The method of manufacturing a flexible wiring board according to claim 6, further comprising the step of patterning said second surface conductive layer.

9. The method of manufacturing a flexible wiring board according to claim 6, further comprising the steps of: providing a third base film and a third surface conductive layer on the surface of said reference conductive layer opposite to the side where said first base film is provided; forming a third hole penetrating said third surface conductive layer and said third base film so that said reference conductive layer is exposed on its bottom and said third base film is exposed on an inner peripheral side face; depositing, by electroless plating, a third electroless plating layer on at least a surface of said third base film exposed on the inner peripheral side face of said third hole; growing, by electrolytic plating, a third electrolytic plating layer on a surface of said third electroless plating layer so as to fill said third hole with said third electrolytic plating layer; and removing said third electrolytic plating layer and said third electroless plating layer provided on said third surface conductive layer so as to expose said third surface conductive layer.

10. The method of manufacturing a flexible wiring board according to claim 9, further comprising the step of patterning said third surface conductive layer.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing a flexible wiring board, and in particular, to an improvement of a wiring layer included in a flexible wiring board frequently used for a multi-layered wiring board.

2. Description of the Related Art

Conventionally, a flexible wiring board having such a structure that a desired circuit pattern is formed on a surface of an insulating film is frequently used for various devices.

Since even a build-up of a plurality of such flexible wiring boards does not have a large thickness, the flexible wiring board is frequently used particularly for constituting a multi-layered wiring board by building up a plurality of wiring boards, each having a circuit pattern formed thereon.

A method of manufacturing such a multi-layered wiring board will be described below. FIGS. 66 to 75 are cross sectional views showing the steps of the manufacturing method.

First, a polyimide precursor is applied onto a surface of a metal foil such as a copper foil. The polyimide precursor is semi-cured to form a first base film made of polyimide. The first base film and the metal foil are bonded to each other in this state. Next, after a second metal foil is placed on the surface of the first base film, the second metal foil is heated while being pressed against the surface of the first base film to bond the first base film and the second metal film to each other. As a result, the first base film is sandwiched between two metal foils. Thereafter, a carrier film made of polyethylene terephthalate (PET) is provided onto the surface of one of the metal foils. This state is shown in FIG. 66. Reference numeral 111 in FIG. 66 denotes the first base film, and reference numerals 112 and 113 denote the metal foils, respectively. Reference numeral 114 denotes the carrier film.

Subsequently, the surface of the metal foil 113 is irradiated with laser light at a predetermined position for a plurality of times, wherein on the surface the carrier film 114 is not provided (hereinafter, referred to as a first surface-side conductive layer). As a result, the first surface-side conductive layer 113 and the first base film 111 are removed at the laser irradiated position so that a first via hole 115 is formed so as to penetrate the first surface-side conductive layer 113 and the first base film 111 to reach the metal foil 112 (hereinafter, referred to as a back-side conductive layer) on the side where the carrier film 114 is formed. This state is shown in FIG. 67.

Next, the first base film 111 including the first via hole 115 formed therethrough is immersed into an electroless plating solution (not shown) to grow an electroless plating layer 118 made of copper from the surface of the back-side conductive layer 112 over the surfaces of the first base film 111 which is exposed on the inner side face of the first via hole 115 and the first surface-side conductive layer 113. This state is shown in FIG. 68.

Subsequently, after the first base film 111 is immersed into an electrolytic plating solution containing copper (not shown), a DC voltage is applied between the electrolytic plating solution and the back-side conductive layer 112. As a result, a conductive material made of copper is grown on a surface of the electroless plating layer 118. Since the electroless plating layer 118 is provided over the entire surface of the first base film 111, the grown conductive material fills the first via hole 115 while covering the entire surface of the first base film 111. When the first via hole 115 is completely filled with the conductive material so that the surface of the conductive material becomes flat, the growth of the conductive material is terminated. Subsequently, a resist is applied onto the surface of the conductive material and is then patterned to form a resist film 190. This state is shown in FIG. 69, where reference numerals 116 and 190 denote the conductive material and the resist film, respectively.

Next, the conductive material 116, the electroless plating layer 118, and the first surface-side conductive layer 113 are etched by isotropic etching such as wet etching using the resist film 190 as a mask so as to pattern these layers into a desired pattern. As a result, a first surface wiring layer composed of the conductive material 116, the electroless plating layer 118 and the first surface-side conductive layer 113 is formed. This state is shown in FIG. 70, where reference numeral 120 denotes the first surface wiring layer.

At this moment, the conductive material 116 is grown to such a degree that the conductive material 116 fills the first via hole 115 to provide a flat surface thereof. Therefore, the conductive material 116 has a considerably large thickness. When the conductive material 116 having such a considerably large thickness is etched by isotropic etching such as wet etching to form the first surface wiring layer, there arises a problem in that a pattern width .DELTA.w.sub.1 of the actually formed first surface wiring layer 120 becomes smaller than a pattern width .DELTA.w.sub.0 of the resist film 190, that is, a desired pattern width, as shown in FIG. 70.

Next, after the resist film 190 is stripped off, a polyimide precursor solution is applied onto the surfaces of the first surface wiring layer 120 and the first surface-side conductive layer 113. Then, the polyimide precursor solution is semi-cured to form a second base film made of polyimide. This state is shown in FIG. 71, where reference numeral 151 denotes the second base film. The second base film 151, and the first surface wiring layer 120 and the first surface-side conductive layer 113 are bonded to each other in this state.

Next, after a third metal foil is placed on a surface of the second base film 151, the third metal foil is heated while being pressed against the surface of the second base film 151 to bond the second base film 151 and the third metal foil (hereinafter, referred to as a second surface-side conductive layer) to each other. Thereafter, the surface of the second surface-side conductive layer is irradiated with laser light for a plurality of times. As a result, a second via hole is formed at the laser irradiated position so as to penetrate the second surface-side conductive layer and the second base film 151 to reach the first surface-side wiring layer 120. This state is shown in FIG. 72, where reference numerals 153 and 155 denote the second surface-side conductive layer and the second via hole, respectively.

Subsequently, the first base film 111 is immersed into an electroless plating solution (not shown). Then, an electroless plating layer 158 made of copper is grown from the surface of the second surface-side conductive layer 153 over the surfaces of the second base film 151 which is exposed on the inner side face of the second via hole 155, and the first surface wiring layer 120. The state after the growth of the electroless plating layer 158 is shown in FIG. 73.

Thereafter, as shown in FIG. 74, a conductive material 156 made of copper is grown on the entire surface of the electroless plating layer 158 by electrolytic plating. After the conductive material 156 is grown to such a degree that the conductive material 156 fills the second via hole 155 to provide a flat surface. Then, a second surface-side wiring layer 170 composed of the conductive material 156, the electroless plating layer 158, and the second surface conductive layer 153 is formed by patterning as shown in FIG. 75. Thereafter, the metal foil 112 on the back side is patterned to form a wiring layer 121 on the back side, thereby completing a double-layered flexible wiring board 101.

As described above, however, the conductive materials 116, 156 and the like, each having a considerably large thickness, are patterned by isotropic etching such as wet etching to form the first and second surface wiring layers 120 and 170. As a result, there arises a problem that a pattern width of each of the surface wiring layers 120 and 170 becomes smaller than a desired pattern width.

Moreover, an increased thickness of each of the surface wiring layers 120 and 170 also disadvantageously increases a thickness and weight of the flexible wiring board 101. Since these problems appear in a more notable manner with increase in the number of layers constituted by the flexible wiring board, such problems present major obstacles to increase in the number of layers.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, in a method of manufacturing a flexible wiring board including, a substrate including a reference conductive layer, a first base film provided on said reference conductive layer, and a first surface conductive layer provided on said first base film, the method comprising the steps of forming a first hole penetrating said first surface conductive layer and said first base film so that said reference conductive layer is exposed on its bottom and said first base film is exposed on its inner peripheral side face, depositing a first electroless plating layer by electroless plating at least on a surface of said first base film exposed on inner peripheral side face of said first hole, growing a first electrolytic plating layer by electrolytic plating on a surface of said first electroless plating layer so as to fill said first hole with said first electrolytic plating layer and removing said first electrolytic plating layer and said first electroless plating layer provided on said first surface conductive layer so as to expose said first surface conductive layer.

In one aspect of a method of manufacturing a flexible wiring board according to the present invention, the method includes said first surface conductive layer is a metal foil and adhered to said first base film.

In one aspect of a method of manufacturing a flexible wiring board according to the present invention, the method includes said reference conductive layer is brought into contact with an electrode when said electrolytic plating is conducted.

Furthermore, in one aspect of a method of manufacturing a flexible wiring board according to the present invention, the method further includes the steps of depositing an auxiliary electrolytic plating layer by electrolytic plating on a surface of said reference conductive layer, exposed on the bottom of said first hole, prior to said step of depositing said first electroless plating layer.

In one aspect of a method of manufacturing a flexible wiring board according to the present invention, the method includes growth of said auxiliary electrolytic plating layer is terminated before the auxiliary electrolytic plating layer reaches said first surface conductive layer.

Furthermore, in one aspect of a method of manufacturing a flexible wiring board according to the present invention, the method further includes the steps of patterning said first surface conductive layer after said step of exposing the first surface conductive layer.

Furthermore, in one aspect of a method of manufacturing a flexible wiring board according to the present invention, the method further includes the steps of providing a second base film and a second surface conductive layer on said patterned first surface conductive layer, forming a second hole penetrating said second surface conductive layer and said second base film so that said first surface conductive layer is exposed on its bottom and said second base film is exposed on its inner peripheral side face, depositing a second electroless plating layer by electroless plating at least on a surface of said second base film exposed on inner peripheral side face of said second hole and growing a second electrolytic plating layer by electrolytic plating on a surface of said second electroless plating layer so as to fill said second hole with said second electrolytic plating layer.

In one aspect of a method of manufacturing a flexible wiring board according to the present invention, the method includes said second surface conductive layer is a metal foil and adhered onto said second base film.

Furthermore, in one aspect of a method of manufacturing a flexible wiring board according to the present invention, the method further includes the steps of patterning said second surface conductive layer.

Furthermore, in one aspect of a method of manufacturing a flexible wiring board according to the present invention, the method further includes the steps of providing a third base film and a third surface conductive layer on the surface of said reference conductive layer, opposite to the side where said first base film is provided, forming a third hole penetrating said third surface conductive layer and said third base film so that said reference conductive layer is exposed on its bottom and said third base film is exposed on its inner peripheral side face, depositing a third electroless plating layer by electroless plating at least on a surface of said third base film, exposed on inner peripheral side face of said third hole, growing a third electrolytic plating layer by electrolytic plating on a surface of said third electroless plating layer so as to fill said third hole with said third electrolytic plating layer and removing said third electrolytic plating layer and said third electroless plating layer provided on said third surface conductive layer so as to expose said third surface conductive layer.

Furthermore, in one aspect of a method of manufacturing a flexible wiring board according to the present invention, the method further includes the steps of patterning said third surface conductive layer.

According to one aspect of the present invention, in a method of manufacturing a flexible wiring board including, a substrate including a reference conductive layer, a first base film provided on said reference conductive layer and a first surface conductive layer provided on said first base film, the method comprising the steps of forming a first hole penetrating said first surface conductive layer and said first base film so that said reference conductive layer is exposed on its bottom and said first base film is exposed on its inner peripheral side face, depositing a first electroless plating layer by electroless plating at least on a surface of said first base film exposed on inner peripheral side face of said first hole, growing a first electrolytic plating layer by electrolytic plating on a surface of said first electroless plating layer so as to fill said first hole with said first electrolytic plating layer and then providing said electroless plating layer and said electrolytic plating layer on said first surface conductive layer to form a first surface coating layer, etching said first electrolytic plating layer to reduce a thickness thereof so as to reduce a thickness of said first surface coating layer on said first base film and forming a patterned resist film on a surface of said first surface coating layer having a reduced thickness and then removing said first surface coating layer situated on a bottom of an opening of said resist film so as to pattern said first surface coating layer.

In one aspect of a method of manufacturing a flexible wiring board according to the present invention, said first surface conductive layer is a metal foil and is adhered to said first base film.

In one aspect of a method of manufacturing a flexible wiring board according to the present invention, said reference conductive layer is brought into contact with an electrode when said electrolytic plating is conducted.

In one aspect of a method of manufacturing a flexible wiring board according to the present invention, the method further includes the step of depositing an auxiliary electrolytic plating layer by electrolytic plating on a surface of said reference conductive layer, exposed on the bottom of said first hole, prior to said step of depositing the first electroless plating layer.

In one aspect of a method of manufacturing a flexible wiring board according to the present invention, growth of said auxiliary electrolytic plating layer is terminated before said auxiliary electrolytic plating layer reaches said first surface conductive layer.

In one aspect of a method of manufacturing a flexible wiring board according to the present invention, the method further includes the step of providing a second base film and a second surface conductive layer on said patterned first surface coating layer, forming a second hole penetrating said second surface conductive layer and said second base film so that said first surface coating layer is exposed on its bottom and said second base film is exposed on its inner peripheral side face, depositing a second electroless plating layer by electroless plating at least on a surface of said second base film exposed on inner peripheral side face of said second hole and growing a second electrolytic plating layer by electrolytic plating on a surface of said second electroless plating layer so as to fill said second hole with said second electrolytic plating layer.

In one aspect of a method of manufacturing a flexible wiring board according to the present invention, said second surface conductive layer is a metal foil and adhered to said second base film.

In one aspect of a method of manufacturing a flexible wiring board according to the present invention, the method further includes the step of patterning said second surface conductive layer.

In one aspect of a method of manufacturing a flexible wiring board according to the present invention, the method further includes the step of providing a third base film and a third surface conductive layer on the surface of said reference conductive layer opposite to the side where said first base film is provided, forming a third hole penetrating said third surface conductive layer and said third base film so that said reference conductive layer is exposed on its bottom and said third base film is exposed on its inner peripheral side face, depositing a third electroless plating layer by electroless plating at least on a surface of said third base film exposed on inner peripheral side face of said third hole, growing a third electrolytic plating layer by electrolytic plating on a surface of said third electroless plating layer so as to fill said third hole with said third electrolytic plating layer, and removing said third electrolytic plating layer and said third electroless plating layer provided on said third surface conductive layer so as to expose said third surface conductive layer.

Furthermore, in one aspect of a method of manufacturing a flexible wiring board according to the present invention, the method further includes the steps of patterning said third surface conductive layer.

According to one aspect of a method of manufacturing a flexible wiring board according to the present invention, after the conductive material is grown in the first hole and on the surface of the first base film to form the first coating conductive layer, a thickness of the first coating conductive layer is reduced to form the first conductive layer.

As described above, when the first conductive layer is formed by reducing a thickness of the first coating conductive layer in this manner, a pattern width of the patterned first conductive layer is not reduced even in the case where, for example, the first conductive layer is patterned by using isotropic etching such as wet etching in the following step, contrary to a conventional case where a considerably thick coating conductive layer is patterned by etching. Therefore, a desired pattern width can be obtained. Moreover, even in the case where a multi-layered flexible wiring board is formed, a thickness of the first conductive layer is reduced to also reduce a total thickness of a wiring board itself, which in turn reduces weight of the wiring board itself.

In embodiments of the present invention, the following structure may be employed. A second base film is formed on the first conductive layer and a second surface conductive layer is provided on the surface of the second base film. A second hole having an aperture penetrating the second base film opposite to the side where the first conductive layer is formed. Then, a conductive material is grown in the second hole and on the surface of the second surface conductive layer, thereby forming a second coating conductive layer. Thereafter, a thickness of the second coating conductive layer is reduced to form the second conductive layer.

In such a structure, a single-layered flexible wiring board can be built up onto a surface of another flexible wiring board on the surface of substrate where the first conductive layer is provided. By successively repeating the build-up of the surface where the first conductive layer is provided, a multi-layered flexible wiring board composed of two or more layers can be built up on the flexible wiring board on the side where the first conductive layer is formed. In this case, since a thickness of the second conductive layer is reduced, a pattern width of the patterned second conductive layer is not reduced as in the case of the first conductive layer, even in the case where the second conductive layer is patterned. Furthermore, the first and second conductive layers are thinned to reduce the thickness of the wiring board.

In embodiments of the present invention, the following structure may alternatively be employed. The third base film is formed on a surface of the reference conductive layer, opposite to the side where the first base film is provided and a third surface conductive layer is provided on the surface of the third conductive layer. The third hole having an aperture penetrating the third surface conductive layer and the third base film is formed. Then, a conductive material is grown on the surface of the third base film at the inner side of the third hole, and on the surface of the third surface conductive layer to form the third coating conductive layer. Thereafter, a thickness of the third coating conductive layer is reduced to form a third conductive layer.

In such a structure, a single-layered flexible wiring board can be built up on the first base film, opposite to the side where the first conductive layer is formed. By successively repeating the build-up of flexible wiring boards on the surface opposite to the side where the first conductive layer is formed, a multi-layered flexible wiring board can be built up on the surface opposite to the side where the first conductive layer is formed. Moreover, even in the case where the third conductive layer is patterned, a pattern width of the patterned third conductive layer is not reduced, as in the first and second conductive layers. Furthermore, the second and third conductive layers are thinned to reduce a thickness of the wiring board.

In certain embodiments of the present invention, in the step of reducing a thickness of at least any one of the first to the third coating conductive layers, the reducing may be subjected to wet etching. Moreover, a surface of at least one of the first to the third coating conductive layers may be physically polished to have a reduced thickness.

In embodiments the present invention, the following structure may be employed. A thin film made of the first conductive material is grown on the surface of the first base film by electroless plating. Thereafter, a voltage is applied to the grown thin film so as to further deposit the first conductive material on a surface of the grown thin film by electrolytic plating.

In such a structure, even on the surface of the first base film on which a thin film cannot be directly formed by electrolytic plating because it is made of an insulating material, the thin film made of the first conductive material can be grown by electroless plating. Thereafter, the first conductive material is deposited on a surface of the thin film made of the first conductive material by electrolytic plating. Since a deposition rate can be controlled by the amount of a current in electrolytic plating, the amount of a current is increased to increase a deposition rate, whereby a thick film made of the first conductive material can be grown in a short period of time. Similarly, after thin films made of the second and third conductive materials are first grown on the surfaces of the second and third base films by electroless plating, the second and third conductive materials are deposited by electrolytic plating on the surfaces of the respective thin films. As a result, the thick films of the second and third conductive materials can be grown on the surfaces of the second and third base films in a short period of time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a first cross section illustrating a method of manufacturing a single-layered flexible wiring board according to one embodiment of the present invention;

FIG. 2 is a second cross section illustrating the method of manufacturing the single-layered flexible wiring board according to one embodiment of the present invention;

FIG. 3 is a third cross section illustrating the method of manufacturing the single-layered flexible wiring board according to one embodiment of the present invention;

FIG. 4 is a fourth cross section illustrating the method of manufacturing the single-layered flexible wiring board according to one embodiment of the present invention;

FIG. 5 is a fifth cross section illustrating the method of manufacturing the single-layered flexible wiring board according to one embodiment of the present invention;

FIG. 6 is a sixth cross section illustrating the method of manufacturing the single-layered flexible wiring board according to one embodiment of the present invention;

FIG. 7 is a seventh cross section illustrating the method of manufacturing the single-layered flexible wiring board according to one embodiment of the present invention;

FIG. 8 is an eighth cross section illustrating the method of manufacturing the single-layered flexible wiring board according to one embodiment of the present invention;

FIG. 9 is a ninth cross section illustrating the method of manufacturing the single-layered flexible wiring board according to one embodiment of the present invention;

FIG. 10 is a tenth cross section illustrating the method of manufacturing the single-layered flexible wiring board according to one embodiment of the present invention;

FIG. 11 is an eleventh cross section illustrating the method of manufacturing the single-layered flexible wiring board according to one embodiment of the present invention;

FIG. 12 is a twelfth cross section illustrating the method of manufacturing the single-layered flexible wiring board according to one embodiment of the present invention;

FIG. 13 is a thirteenth cross section illustrating the method of manufacturing the single-layered flexible wiring board according to one embodiment of the present invention;

FIG. 14 is a fourteenth cross section illustrating the method of manufacturing the single-layered flexible wiring board according to one embodiment of the present invention;

FIG. 15 is a fifteenth cross section illustrating the method of manufacturing the single-layered flexible wiring board according to one embodiment of the present invention;

FIG. 16A is a cross section for illustrating a structure including a first electroless plating layer on a surface of a first surface conductive layer in the single-layered flexible wiring board according to one embodiment of the present invention, and

FIG. 16B is a cross section for illustrating a structure including the first electroless plating layer and a first conductive material sequentially deposited on the surface of the first surface conductive layer in the single-layered flexible wiring board according to one embodiment of the present invention;

FIG. 17 is a first cross section for illustrating a method of manufacturing a double-layered flexible wiring board according to one embodiment of the present invention;

FIG. 18 is a second cross section for illustrating the method of manufacturing the double-layered flexible wiring board according to one embodiment of the present invention;

FIG. 19 is a third cross section for illustrating the method of manufacturing the double-layered flexible wiring board according to one embodiment of the present invention;

FIG. 20 is a fourth cross section for illustrating the method of manufacturing the double-layered flexible wiring board according to one embodiment of the present invention;

FIG. 21 is a fifth cross section for illustrating the method of manufacturing the double-layered flexible wiring board according to one embodiment of the present invention;

FIG. 22 is a sixth cross section for illustrating the method of manufacturing the double-layered flexible wiring board according to one embodiment of the present invention;

FIG. 23 is a seventh cross section for illustrating the method of manufacturing the double-layered flexible wiring board according to one embodiment of the present invention;

FIG. 24 is an eighth cross section for illustrating the method of manufacturing the double-layered flexible wiring board according to one embodiment of the present invention;

FIG. 25 is a ninth cross section for illustrating the method of manufacturing the double-layered flexible wiring board according to one embodiment of the present invention;

FIG. 26A is a tenth cross section for illustrating the method of manufacturing the double-layered flexible wiring board according to one embodiment of the present invention, and

FIG. 26B an eleventh cross section for illustrating the method of manufacturing the double-layered flexible wiring board according to one embodiment of the present invention;

FIG. 27 is a twelfth cross section for illustrating the method of manufacturing the double-layered flexible wiring board according to one embodiment of the present invention;

FIG. 28 is a thirteenth cross section for illustrating the method of manufacturing the double-layered flexible wiring board according to one embodiment of the present invention;

FIG. 29 is a first cross section for illustrating a method of manufacturing a multi-layered flexible wiring board according to another embodiment of the present invention;

FIG. 30 is a second cross section for illustrating the method of manufacturing the multi-layered flexible wiring board according to another embodiment of the present invention;

FIG. 31 is a third cross section for illustrating the method of manufacturing the multi-layered flexible wiring board according to another embodiment of the present invention;

FIG. 32 is a fourth cross section for illustrating the method of manufacturing the multi-layered flexible wiring board according to another embodiment of the present invention;

FIG. 33 is a fifth cross section for illustrating the method of manufacturing the multi-layered flexible wiring board according to another embodiment of the present invention;

FIG. 34 is a cross section for illustrating a method of manufacturing a multi-layered flexible wiring board according to a further embodiment of the present invention;

FIG. 35 is a first cross section for illustrating a method of manufacturing a flexible wiring board according to a further embodiment of the present invention;

FIG. 36 is a second cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 37 is a third cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 38 is a fourth cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 39 is a fifth cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 40 is a sixth cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 41 is a seventh cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 42 is an eighth cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 43 is a ninth cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 44 is a tenth cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 45 is an eleventh cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 46 is a twelfth cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 47 is a thirteenth cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 48 is a fourteenth cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 49 is a fifteenth cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 50A is a sixteenth cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention, and FIG. 50B is a seventeenth cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 51 is an eighteenth cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 52 is a nineteenth cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 53 is a twentieth cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 54 is a twenty-first cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 55 is a twenty-second cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 56 is a twenty-third cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 57 is a twenty-fourth cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 58 is a twenty-fifth cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 59 is a twenty-sixth cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 60 is a twenty-seventh cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 61 is a twenty-eighth cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 62 is a twenty-ninth cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 63 is a thirtieth cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 64A is a thirty-first cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention, and FIG.

64B is a thirty-second cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 65 is a thirty-third cross section for illustrating the method of manufacturing the flexible wiring board according to the further embodiment of the present invention;

FIG. 66 is a first view for illustrating a conventional method of manufacturing a flexible wiring board;

FIG. 67 is a second view for illustrating the conventional method of manufacturing the flexible wiring board;

FIG. 68 is a third view for illustrating the conventional method of manufacturing the flexible wiring board;

FIG. 69 is a fourth view for illustrating the conventional method of manufacturing the flexible wiring board;

FIG. 70 is a fifth view for illustrating the conventional method of manufacturing the flexible wiring board;

FIG. 71 is a sixth view for illustrating the conventional method of manufacturing the flexible wiring board;

FIG. 72 is a seventh view for illustrating the conventional method of manufacturing the flexible wiring board;

FIG. 73 is an eighth view for illustrating the conventional method of manufacturing the flexible wiring board;

FIG. 74 is a ninth view for illustrating the conventional method of manufacturing the flexible wiring board; and

FIG. 75 is a tenth view for illustrating the conventional method of manufacturing the flexible wiring board.

BRIEF DESCRIPTION OF REFEREBCE NUMERAL

In each of the accompanying drawings, the following components are commonly denoted by the reference numerals as follows: Reference numerals 1, 2 denote flexible wiring boards; 11 denotes a first base film; 12 denotes a reference conductive layer; 13 denotes a first surface conductive layer; 15 denotes a first via hole; 16 denotes a first conductive material; 18 denotes a first electroless plating layer; 74 denotes a first surface-side conductive material; 20 denotes a first wiring layer; 21 denotes a reference wiring layer; 51 denotes a second base film; 53 denotes a second surface conductive layer; 55 denotes a second via hole; 76 denotes a second bottom-side conductive material; 70 denotes a second wiring layer; 91 denotes a first coating conductive layer; 92 denotes a first conductive layer; 93 denotes a second coating conductive layer; and 94 denotes a second conductive layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIGS. 1 to 26 are views for illustrating the manufacturing steps of a flexible wiring board according to one embodiment of the present invention.

With reference to the below embodiments, suitable polyimide polymers are decribed in Japanese laid open Application No. 2000-151046 and Japanese laid open Application No. 2000-186143, and may be produced from the combinations of pyromellitic dianhydride/diaminodiphenyl ether, diphenyltetra carboxylic dianhydride/p-phenylenediamine and the like. Examples of suitable electrolytic plating solutions include acid copper sulfate plating solution, copper pyrophosophate plating solution, and the like. Examples of electroless plating solutions include a solution comprising a copper salt (such as copper sulfate), a reducing agent (such as formaldehyde, or hydrazine), a pH adjusting agent (such as NaOH, or KOH), a chelating agent (such as EDTA, or Rochelle salt), and an addition agent (such as polyethylene glycol, or dipyridyl). Those having ordinary skill in the art will recognize that the above solutions and agents are simply representative and that other solutions may be used. Suitable concentrations and amounts used are also known to those having ordinary skill in the art.

First, after a polyimide precursor solution is applied onto a surface of a metal foil made of copper, the polyimide precursor solution is semi-cured to form a first base film made of polyimide. This state is shown in FIG. 1, where reference numerals 12 denotes the metal foil (hereinafter, referred to as a reference conductive layer) and 11 denotes the first base film. In this state, the first base film 11 and the reference conductive layer 12 are in close contact with each other.

Next, as shown in FIG. 2, a second metal foil (hereinafter, referred to as a first surface conductive layer) 13 is placed on a surface of the first base film 11. The first surface conductive layer 13 is heated while being pressed against the first base film 11 so as to adhere the first surface conductive layer 13 and the first base film 11 to each other. In this state, the first base film 11 is sandwiched between the reference conductive layer 12 and the first surface conductive layer 13. In this case, each of the reference conductive layer 12 and the first surface conductive layer 13 has a thickness of 30 .mu.m, and the first base film 11 has a thickness of 35 .mu.m.

Subsequently, as shown in FIG. 3, a carrier film 14 made of polyethylene terephthalate (PET) is provided onto a surface of the reference conductive layer 12. In this state, the surface of the reference conductive layer 12 is completely covered with the carrier film 14.

Next, the surface of the first surface conductive layer 13 is irradiated with laser light at a predetermined position for a plurality of times. As a result, the first surface conductive layer 13 and the first base film 11 are removed at the laser irradiated position to form a first via hole penetrating the first surface conductive layer 13 and the first base film 11 to reach the reference conductive layer 12 at the bottom of the via hole. This state is shown in FIG. 4. A reference numeral 15 denotes first via hole. The first via hole 15, which is an example of a first hole of the present invention, has an opening diameter of about 50 .mu.m and a depth of about 35 .mu.m.

Subsequently, as shown in FIG. 5, the above-described first base film 11 is immersed into an electroless plating solution 37 in a container 36.

As a result, a first electroless plating layer made of copper is grown over the surface of the first surface conductive layer 13 to a surface of the first base film 11 which is exposed on the inner side face of the first via hole 15 and a surface of the reference conductive layer 12 which is exposed on the bottom face of the first via hole 15. When a thickness of the first electroless plating layer substantially reaches a predetermined thickness (5 .mu.m in this embodiment), the first base film 11 is taken out of the electroless plating solution 37 to terminate the growth. Then, the carrier film 14 is stripped off. This state is shown in FIG. 6, where the thus formed first electroless plating layer is denoted by reference numeral 18, which is electrically connected to the reference conductive layer 12.

Next, as shown in FIG. 7, after another carrier film 41 is provided onto the surface of the reference conductive layer 12, a part of the carrier film 41 is etched away to form an opening 41a.

Next, as shown in FIG. 8, a DC power source 30, an electrode 33 for electrolysis, a container 31, and an electrolytic plating solution 32 containing copper in the container 31 are prepared. A negative pole and a positive pole of the DC power source 30 are connected to the reference conductive layer 12 exposed through the opening 41a and to the electrode 33, respectively. In this state, the first base film 11 and the electrode 33 are immersed into the electrolytic plating solution 32.

Next, as shown in FIG. 9, when the DC power source 30 is activated to apply a DC voltage between the electrolytic plating solution 32 and the reference conductive layer 12, the electrolytic plating solution 32 is electrolyzed. As a result, a first conductive material 16 made of copper starts growing on the surface of the first electroless plating layer 18 that is connected to the negative pole through the reference conductive layer 12. The first electroless plating layer 18 is provided on the entire surface so as to cover the inner surface of the first via hole 15 and the surface of the first surface conductive layer 13. Therefore, the grown first conductive material 16 completely fills the first via hole 15 while covering the entire surface of the first base film 11. When the first conductive material 16 is sufficiently grown to completely fill the first via hole 15 so as to provide a flat surface for the first conductive material 16 as shown in FIG. 10, the application of the DC voltage is stopped to terminate the growth. Herein, when the first conductive material 16 is grown to a thickness of 60 .mu.m from the surface of the reference conductive layer 12 that is exposed on the bottom of the first via hole 15, the growth is terminated. An upper part composed of the thus grown first conductive material 16, the first electroless plating layer 18, and the first surface conductive layer 13, which is situated above the surface of the first base film 11, comprises a first coating conductive layer of the present invention. The first coating conductive layer is denoted by reference numeral 91 in FIG. 10.

Next, as shown in FIG. 11, an etchant such as a mixed solution of a hydrogen peroxide solution and sulfuric acid (sold under the name: CP 750 distributed by Mitsubishi Gas Chemical Company, Inc.) is sprayed from a shower nozzle (not shown) onto a surface of the first coating conductive layer 91. As a result, the first coating conductive layer 91 is etched to have a reduced thickness.

The amount of required time from the beginning of etching, to completely remove the first conductive material 16 and the first electroless plating layer 18, which are formed on the surface of the first surface conductive layer 13, is obtained in advance by an experiment or the like. When the first coating conductive layer 91 is etched for this required amount of time, the first conductive material 16 and the first electroless plating layer 18 are completely removed at termination of etching, resulting in the entirely exposed surface of the first surface conductive layer 13. This state is shown in FIG. 12.

As a result of such etching, the first conductive material 16 and the first electroless plating layer 18 remain in the first via hole 15, whereas the first surface conductive layer 13 remains on the surface of the first base film 11 where the first via hole 15 is not formed. A part of the remaining first conductive material 16 and a part of the remaining first electroless plating layer 18 provided at the vicinity of the surface of the substrate comprising the first base film 11, the reference conductive layer 12 and the first surface conductive layer 13, are respectively labeled a first electroless plating layer 18b and a first conductive material 16b. The first electroless plating layer 18b, the first conductive material 16b, and the first surface conductive layer 13 comprise a first conductive layer according to the present invention. The first conductive layer 92 in FIG. 12 is connected to the reference conducive layer 12 through the first conductive material 16c and the first electroless plating layer 18c which are provided on the bottom of the first via hole 15.

Next, as shown in FIG. 13, after a resist is applied onto a surface of the first conductive layer 92, the resist is patterned into a desired pattern to form a resist film 7.

Next, as shown in FIG. 14, the first conductive layer 92 is etched by isotropic etching such as wet etching, using the resist film 7 as a mask. Since only the first surface conductive layer 13 of the first surface conductive layer 92 is exposed on the bottom of an opening of the resist film 7 before etching, the etching of the first conductive layer 92 allows only the first surface conductive layer 13 to be etched, and the first base film is exposed.

Since the first surface conductive layer 13 is thin, a pattern width of the patterned first surface conductive layer 13 is not reduced different from conventionally happens in the case where a thick conductive layer is etched.

The patterned first surface conductive layer 13, the first electroless plating layer 18b, and the first conductive material 16b, which are placed above the surface of the first base film 11, are collectively referred to as a first wiring layer 20 hereinafter. A pattern of the first wiring layer 20 is the same as that of the resist film 7.

Thereafter, as shown in FIG. 15, after the resist film 7 is stripped off, followed by stripping of the carrier film 43, the reference conductive layer 12 is patterned into a desired pattern to form a reference wiring layer 21. As a result, the single-layered flexible wiring board 1 as shown in FIG. 15 is completed.

In this embodiment, as described above, after formation of the first coating conductive layer 91, the first coating conductive layer 91 is etched to have a reduced thickness as described with reference to FIG. 12. The first conductive layer 92 having a reduced thickness is patterned by etching to form the first wiring layer 20. Therefore, contrary to a conventional case where a considerably thick conductive material is patterned to reduce a pattern width to be smaller than a desired pattern width, a pattern of the first wiring layer 20 is substantially identical with the pattern of the resist film 7 serving as a mask, thereby obtaining a desired pattern.

It seems that it is not necessary to reduce a thickness of the first coating conductive layer 91 having a large thickness after formation of the first coating conductive layer 91 as in this embodiment because, if the thin first conductive material 16 is formed to have a small thickness at the beginning of manufacture when the first conductive material 16 is to be formed, the first conductive material 16 having a small thickness may be obtained without etching.

However, if the first conductive material 16 is formed thin, the first via hole 15 is not completely filled with the first conductive material 16. Therefore, a dent is generated at the position where the first via hole 15 is formed. Accordingly, when a multi-layered wiring board is formed, in particular, connection failure adversely occurs between a plurality of layers.

Therefore, in this embodiment, after the thick first conductive material 16 is formed to completely fill the first via hole 15, a thickness of the thick first conductive material 16 is reduced by etching. With such a structure, the first via hole 15 is completely filled with the first conductive material 16 without fail.

In the above-described embodiment, when the first coating conductive layer 91 is etched to have a reduced thickness, the first conductive material 16 and the first electroless plating layer 18 which are placed on the first surface conductive layer 13, are entirely removed. However, the present invention is not limited thereto. For example, the following structure may alternatively be employed. When the first coating conductive layer 91 is thinned by etching, only the first conductive material 16 that is situated on the first surface conductive layer 13 may be completely removed while the first electroless plating layer 18 provided on the first surface conductive layer 13 is left. In this manner, the first wiring layer 20 including the first electroless plating layer 18 placed on the first surface conductive layer 13 is formed as shown in FIG. 16A.

Alternatively, another structure as follows may also be employed. When the first coating conductive layer 91 is thinned by etching, the first electroless plating layer 18 and the first conductive material 16 are left on the first surface conductive layer 13 without completely removing, and in the result, the first conductive material 16 provided on the first surface conductive layer 13. In this manner, the first wiring layer 20 including the first electroless plating layer 18 and the thinned first conductive material 16 provided on the first surface conductive layer 13 is formed as shown in FIG. 16B.

Although the method of manufacturing the single-layered flexible wiring board has been described so far, the present invention is not limited thereto. The present invention is also applicable to the manufacture of a multi-layered flexible wiring board.

Hereinafter, a method of manufacturing a multi-layered flexible wiring board will be described. FIGS. 17 to 28 are cross sectional views for illustrating a method of manufacturing a double-layered flexible wiring board which is an example of a multi-layered flexible wiring board.

Through the steps illustrated in FIGS. 1 to 12, a state shown in FIG. 13, that is, the first base film 11, on which the first wiring layer 20 is formed, is obtained. Thereafter, the resist film 7 is stripped off. After a polyimide precursor solution is applied onto the surface of the first base film 11 and the surface of the first wiring layer 20, the polyimide precursor solution is semi-cured to form a second base film. Thereafter, a metal foil is placed on a surface of the second base film. Then, the metal foil is heated while being pressed against the second base film so as to adhere the metal foil (hereinafter, referred to as a second surface conductive layer) and the second base film to each other. Th