JP2000151079A - Fine pattern and method of forming via hole - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve adhesion between polyimide and a conductive layer without chemical modification to a surface layer by enhancing deposition accuracy of a conductive layer to a via hole and performingalkaline solution processing such as hydrazine or glow discharge without electroless copper plating, in a method of forming a multilayer printed wiring board using a two-layer printed wiring board. SOLUTION: A metal thin-film layer 3 is formed on a rough surface of a metal foil 2, this metal thin-film layer 3 surface is laminated on a polyimide layer 1 formed on a substrate, this metal foil 2 is removed, this metal thin-film layer 3 is patterned, the polyimide layer 1 is drilled to form a hole 4, a conductive layer 6 is formed on the drilled portion of the polyimide layer 1 and a patterning region by direct plating, and a pattern and via holes are formed by electro-plating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the formation of wiring and via holes in a flexible printed wiring board, and more particularly to the fine wiring of a multilayer flexible printed wiring board using a two-layer flexible printed wiring board without using an adhesive. And a method of forming a via hole.

[0002]

2. Description of the Related Art Conventionally, as a wiring board material used for a flexible printed wiring board, a three-layer wiring board using an epoxy-based adhesive such as copper / adhesive layer / polyimide layer has been generally used. . However, with the recent increase in density, speed, and multi-functionality of electronic devices, an adhesive layer that can meet these demands and has excellent heat resistance, flexibility, migration resistance, and bonding properties has been developed. Attention has been focused on a two-layer wiring board with a copper / polyimide layer not containing HD
D, FDD, TAB, etc.

A two-layer wiring board can be roughly classified into two types according to a manufacturing method. One uses copper foil for the base material,
Casting method to apply and imidize polyamic acid, which is a precursor of polyimide on copper foil, is a polyimide adhesive method using thermoplastic polyimide as an adhesive, another is using a polyimide film as a base material, This is a metallizing method in which a metal thin film serving as a conductive layer is directly formed on a polyimide film by sputtering, vapor deposition, electroless plating, or the like, and the metal layer is thickened by electroplating. in recent years,
Multilayer flexible printed wiring boards in which flexible printed wiring boards are stacked in multiple layers by a method using such a two-layer wiring board have been developed.

[0004] In a multilayer flexible printed wiring board using a two-layer wiring board by a casting method or a polyimide adhesive method, a via hole which plays a role of wiring and electrical connection between layers is formed after forming a hole in the polyimide layer. A conductive layer was formed by electroless plating on the wiring and via hole portions of the polyimide, and the resultant was plated by electroplating. Further, there is a case where the plating is performed by a direct plating method instead of the electroless plating method today. However, in this method, thick plating for interlayer connection is also formed on the copper foil as the base material, and the wiring layer becomes thick, so that it has been difficult to form fine wiring.

In the case of a multilayer flexible printed wiring board using a two-layer wiring board by a metallizing method, the above-mentioned problems caused by the casting method and the polyimide adhesive method can be avoided. Is difficult to form, and is generally formed by an electroless plating method. Then, after forming a metal thin film to be a conductive layer by electroless plating, electroplating is performed, and wiring is formed by etching, or a resist for wiring formation is patterned, and then electroplating is performed to form wiring. I was

[0006]

However, when an electroless plating method is used to form a metal thin film on a via hole portion, hydrogen gas is generated in the electroless plating process and gas is accumulated in the via hole, so that a conductive layer is deposited. The reliability becomes worse. This becomes more remarkable as the via hole diameter becomes smaller, and is disadvantageous for small diameter via holes. The electroless copper plating generally used as the electroless plating method contains formaldehyde, and there are many problems in the working environment due to plating bath instability, waste liquid of aging plating solution, wastewater treatment, etc., and cost increases. Get out. In addition, since it is difficult to roughen a polyimide layer such as a polyimide film and to improve the adhesion between the polyimide layer and the conductor layer due to an anchor effect, it is necessary to form a conductive layer having excellent adhesion on the polyimide layer. It is necessary to chemically modify the surface layer by performing glow discharge treatment or treatment with an alkali solution such as hydrazine, so that the cost is high. It was difficult to obtain the same adhesion as a wiring board.

[0007] The present invention has solved the above problems,
Since the electroless plating method is not used, the reliability of deposition of the conductive layer in the via hole can be increased, and the work environment can be improved because the burden of waste liquid treatment is greatly reduced. In addition, since the adhesion between the conductive layer and the polyimide layer is good even if the polyimide surface layer is not chemically modified by performing a glow discharge treatment or an alkali solution treatment such as hydrazine, a highly reliable fine wiring In addition, a via hole can be formed, and the cost can be reduced.

[0008]

In a method for forming fine wiring and via holes, a metal thin film layer is formed on a roughened surface of a metal foil, and the metal thin film layer surface is formed on a polyimide layer formed on a substrate. After laminating and removing the metal foil by etching, a part of the metal thin film layer is removed by etching, and a hole is formed in the polyimide layer using the metal thin film layer. Except for the contact part for the terminal, remove by etching, form a conductive layer using the direct plating method on the drilled part of the polyimide layer and the wiring formation area, and then perform thick plating by electroplating on it Thus, a wiring and an interlayer connection in a perforated portion of the polyimide layer are formed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for forming a fine wiring and a via hole will be described below with reference to FIG. The wiring board material shown in FIG. 1 uses a copper substrate as a substrate and a polyimide layer 1 as an insulating layer of wiring on the substrate. A metal thin film layer 3 is formed on a roughened surface of a roughened metal foil 2. Is formed, and the surface of the metal thin film layer 3 is laminated on the polyimide layer 1 (FIG. 1).
(A)). First, after the metal foil corresponding to the processed portion for forming the wiring and the via hole is removed by etching (FIG. 1B), the metal thin film layer 3 is partially removed by etching to be used as a mask for forming the via hole 4. (FIG. 1 (c)), the via hole 4 is formed in the polyimide layer 1 by etching using the metal thin film layer 3 as a mask.
Was formed (FIG. 1D). Thereafter, the metal thin film layer 3 of the wiring board material is removed by etching except for a portion to be left as an electrode terminal contact 5 when performing direct plating, which will be described later (FIG. 1E). further,
After performing a pretreatment on the exposed polyimide layer 1, the electrode terminal contact 5, and the via hole 4, using a copper sulfate plating solution,
Copper plating 6 was formed on the entire surface by direct plating (FIG. 1 (f)). Next, a plating resist 7 was applied and plate-formed on a copper plating 6 formed by direct plating as a mask for forming copper plating by an electroplating method (FIG. 1 (g)). Then, after forming a copper-plated wiring so as to have a thickness of 10 μm by an electroplating method and performing copper plating thickening of the via hole at the same time (FIG. 1H), the plating resist 7 for the mask is peeled off ( FIG. 1 (i)) The copper plating 6 exposed thereby.
Was removed by soft etching (FIG. 1 (j)).

[0010]

Next, an embodiment will be described with reference to FIG.
The wiring board material of the embodiment is composed of a metal foil, a metal thin film layer, and a polyimide layer.
Using a copper foil of 20 OZ (18 μm), the metal thin film layer 3 is formed on the roughened surface of the metal foil 2 by electroplating to a thickness of 0.5 μm.
Ni was formed to a thickness of m and the metal thin film layer 3 was laminated on the polyimide layer 1 (FIG. 1A). Next, the metal foil 2 laminated on the processed portion for forming the wiring and the via hole (including at least the wiring forming region and the via hole portion) is removed using an ammonia-based alkali etching solution (A process manufactured by Meltec) (FIG. 1). (B)). Thereafter, a dry film resist (Sunfort AQ manufactured by Asahi Kasei Corporation) is laminated on the metal thin film layer 3,
The dry film resist was patterned. Using this patterned dry film resist, the metal thin film layer 3 on the via hole portion is etched with a hydrogen peroxide-sulfuric acid type etching solution (trips RS-II manufactured by Okuno Pharmaceutical).
(FIG. 1 (c)). Using the metal thin film layer 3 as a mask, a via hole 4 is formed in the polyimide layer 1 by using an etching solution (TPE-3000 manufactured by Toray Engineering Co., Ltd.) mainly containing a mixture of potassium hydroxide and an aliphatic amine. Opening was performed (FIG. 1D). Further, using a patterned dry film resist, using a hydrogen peroxide-sulfuric acid type etching solution (trips RS-II manufactured by Okuno Pharmaceutical Co., Ltd.), the metal thin film layer 3 is processed, and the electrode terminal contact 5 is formed. It was formed (FIG. 1 (e)). After this, the exposed polyimide layer 1,
A pretreatment for direct plating was performed on the electrode terminal contact 5 and the via hole 4 using a Neopact process manufactured by Atotech Japan. Table 1 shows the outline and conditions of the neopact process. After the neopact process, a copper sulfate plating solution is used, and a copper plating 6 is formed on the entire surface by direct plating using the electrode terminal contacts 5, but in order to form the copper plating 6 as thin as possible, This was performed under the condition of low current density (FIG. 1 (f)). Table 2 shows the composition of the copper sulfate plating solution and the plating conditions at this time.
In addition, Captoside HL manufactured by Atotech Japan was used as an additive. Thereafter, a plating resist 7 (PMER P-LA900 PM manufactured by Tokyo Ohka Kogyo Co., Ltd.) was used as a mask for forming copper wiring by electroplating on the copper plating 6 formed by direct plating.
It was applied to a thickness of μm and made into a plate (Fig. 1
(G)). Then, when the copper plating wiring is 10
The copper wiring was thickened by electroplating so as to have a thickness of μm, and at the same time, the copper plating was also thickened on the copper plating 6 in the via hole portion by electroplating (FIG. 1 (h)). Table 3 shows the conditions for thickening the copper plating by the electroplating method at this time. However, the through cup AC-90M is an additive manufactured by Uemura Kogyo. Then, after forming the copper plating wiring, the plating resist 7 for the mask is peeled off (FIG. 1).
(I)) The exposed copper plating 6 was removed by soft etching (FIG. 1 (j)).

In the embodiment, the roughened copper foil is used as the metal foil. However, the metal foil is not limited thereto.
Any material can be used as long as the roughened metal foil can be removed by etching. In addition, although the wet etching method was used for the via hole processing of the polyimide layer, the present invention is not limited to this method, and any method capable of processing the polyimide layer such as laser processing, plasma processing, blast processing, or the like may be used.

[0012]

[Table 1]

[0013]

[Table 2]

[0014]

[Table 3]

[0015]

According to the present invention, in a method of forming a wiring board, a roughened surface of a metal thin film layer is laminated on a polyimide layer, and a pattern for using the metal thin film layer as a mask for forming a via hole is formed. To form a hole in the polyimide layer, remove the metal thin film layer leaving only the electrode terminal portions, and form a conductive layer by a direct plating method in the hole-formed portion and the wiring formation region of the polyimide layer. By forming thick plating for wiring and interlayer connection by an electroplating method, a conductive layer can be formed in a via hole without using electroless plating. As a result, the reliability of deposition in the small-diameter via hole is increased, the burden of waste liquid treatment can be greatly reduced, and the working environment is improved. In addition, the roughened metal thin film layer can improve the adhesion between the polyimide layer and the conductive layer without chemically modifying the surface layer by glow discharge treatment or treatment with an alkali solution such as hydrazine. High reliability because it can be
The cost can be reduced. In addition, when leaving the metal thin film layer only in the electrode terminal portion and removing the metal thin film layer other than the portion corresponding to the electrode terminal portion, when directly plating the via hole portion and the wiring formation region,
Contact burning of the electrode terminals does not occur, good direct plating is possible, and the process is stabilized. In addition, since the metal thin film layer also serves as a contact for the electrode terminal, production efficiency can be promoted.

[Brief description of the drawings]

FIG. 1 is a diagram showing a method for forming a fine wiring and a via hole.

[Explanation of symbols]

 1 ··· Polyimide layer 2 ··· Metal foil 3 ··· Metal thin film layer 4 ··· Via hole 5 ··· Contact for electrode terminal 6 ··· Copper plating 7 ··· Plating Resist

Claims (1)

[Claims] In a method of forming fine wiring and via holes, a metal thin film layer is formed on a roughened surface of a metal foil, and the metal thin film layer surface is laminated on a polyimide layer formed on a substrate. After the metal foil is removed by etching, a part of the metal thin film layer is removed by etching, and a hole is formed in the polyimide layer using the metal thin film layer. Removed by etching, forming a conductive layer using a direct plating method in the hole forming portion of the polyimide layer and the wiring forming area, and performing thick plating by electroplating on the conductive layer, Forming a via and a via hole in a portion of the polyimide layer where a hole is formed by punching.