JPH03225995A - Wiring board - Google Patents

Abstract

PURPOSE:To enhance a corrosion-resistant property and the contact tight property of a wiring pattern with an insulating board by a method wherein the insulating board is formed of a polyimide-based film, and a nickel layer at the lower part of the wiring pattern is formed by a vacuum film formation method. CONSTITUTION:A nickel layer 3 having through holes 2 is vapor-deposited by an electron beam by using a vacuum vapor deposition apparatus. A dry film photoresist is laminated on both faces of the nickel layer. The photoresist is exposed to light; it is developed by trichloroethane; resist patterns 4 are obtained; after that, patterns 5 are plated by an electroless copper plating operation. An electroless nickel plating operation is executed; the surface (excluding the lower part of a wiring part) of the wiring patterns 6 is covered with nickel 6.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a wiring board with excellent electrolytic corrosion resistance.

(Prior Art) Conventionally, in order to improve the electrolytic corrosion resistance of wiring boards, heavy metal removers or rust preventives such as benzotriazole,
There are some in which organic compounds such as vinyl triazine and triazine trithiol are dispersed in polymeric insulation for wiring boards.

In some cases, after forming a wiring pattern, the wiring pattern is immersed in a solution containing the above-mentioned organic compound and dried to form a film of an organic compound on the surface of the wiring pattern.

In addition, a wiring structure in which a nickel film is formed on the surface of the wiring pattern (including the sidewalls and lower part of the wiring pattern) by electroless plating has also been proposed.

(Problems to be Solved by the Invention) Although the electrolytic corrosion resistance is improved in the method using an organic compound, the heat resistance of the insulating layer is reduced due to the low heat resistance of the organic compound itself, or in particular, In the latter case, there was a problem that a uniform film could not be formed if the solution had poor wettability with respect to the wiring pattern (copper wiring inside the shell).

On the other hand, the method of forming a nickel film on the wiring surface can improve electrolytic corrosion resistance without sacrificing heat resistance due to the high stability of nickel or nickel oxide formed on the nickel surface. However, in order to ensure the adhesion between the wiring and the board, there is a process of physically roughening the board surface (for example, a process of etching away the copper foil of a copper-clad laminate and transferring the roughened shape of the copper foil). ), the resolution of the resist pattern for wiring formation on the roughened surface is lowered, and the resist remains undeveloped.

The present invention provides a wiring board having excellent electrical corrosion resistance and adhesion of a wiring pattern to a substrate.

(Means for solving the problem) In order to solve the above problem, it is effective to lower the profile of the board surface while ensuring the adhesive strength between the nickel layer and the board at the bottom of the wiring pattern. It is.

The present invention aims to achieve a nickel-coated wiring structure with excellent electrolytic corrosion resistance. A thin nickel layer is formed on a polyimide film having a smooth surface by a vacuum film-forming method such as sputtering. After a wiring pattern of copper or the like is formed using a nickel method, the top and sidewall surfaces of the wiring pattern are coated with nickel using an electroless plating method.

A chemically stable oxide film is formed as a material for the thin metal layer formed on polyimide film using the vacuum deposition method.
Nickel is preferred because it has a greater ionization tendency than copper, which is a wiring metal, and has good adhesion to the substrate. Nickel is not limited to a single metal, and can also be used in combination with chromium, as well as metal compounds thereof, alumina, etc. It is also possible to use ceramics and the like.

As a film forming method, a normal vacuum film forming method such as a vapor deposition method, a sputtering method, an ion blating method, or a cluster ion PIM method can be used.

Note that the wiring lower material in the present invention is not limited to a single metal, and metal compounds thereof and ceramics such as alumina can also be used. Furthermore, if necessary, after forming a nickel or metal compound layer on the lower wiring layer,
It is also possible to apply a multilayer thin film in which thin metal layers such as copper are successively formed.

Nickel exhibits good adhesion to polyimide films, but in order to obtain higher adhesion, low-temperature plasma treatment or reactive ion etching may be applied to the surface of the polyimide film.

In addition, the adhesion between polyimide film and nickel is also affected by the amount of nickel diffused into the polyimide.
It is preferable that 0A or more nickel is diffused into the polyimide ferm. Diffusion can be carried out, for example, by heating.

In the present invention, the nickel formed on the polyimide film does not need to be completely layered, and may be in the form of an island structure.

The wiring pattern can be formed using a semi-additive method that uses a combination of electroless plating and electroplating, or if the required wiring thickness is several microns, after forming a wiring metal layer using a vacuum evaporation method, The wiring may be formed by a subtract method.

As a method of forming a nickel film on the upper part of the wiring pattern and the side wall part (not including the lower part of the wiring pattern), electroplating or electroless plating can be used.

An embodiment of the present invention will be described with reference to the drawings.

FIGS. 1(a) to 1(C) are cross-sectional views showing one embodiment of the present invention.

Polyimide film UPILEX 5-Ty with a thickness of 50 μm having through holes 2 with a diameter of 0 and 4 mm at predetermined positions
Thickness 5000A on pe (Ube Industries Co., Ltd. dehiscence product name) 1
A nickel layer 3 of
)reference). The vapor deposition conditions are shown below.

Accelerating voltage: 10 kV EB lightning current: 8 A Pressure: I x 10 Torr Film forming temperature: 270°C Film forming rate: 10 A/min Next, dry film photoresist (5R-3000 manufactured by Hitachi Chemical Co., Ltd.) was laminated on both sides of the nickel layer. . The lamination conditions were roll temperature, feed speed, and roll pressure of 120°C, 0.8 m/min, and 30 ps, respectively.
It is i.

Next, using a specified photomask, exposure was performed using an ultraviolet exposure machine with a mask alignment mechanism (Model M-3L manufactured by Mikasa Co., Ltd.) at an exposure amount of 120 mJ/cm'L, and a desired resist pattern 4 was obtained by developing with trichloroethane. After that, electroless copper plating was performed under the conditions shown below to a thickness of 18 μm.
Pattern plating 5 was performed (see (b)).

Copper sulfate 10g/I EDTA ・4Na 40g/lpn
12.4 37% formalin 3ml/1 Additive Small amount Plating solution temperature 70°C After removing the resist pattern 4 with methylene chloride, remove the desired part of the nickel layer by etching, and electroless nickel plating under the conditions shown below. and wiring pattern 5
The surface (excluding the lower part of the wiring) was coated with nickel 6 with a thickness of 3.0 μm (see (C)).

Nickel chloride 30g/l Sodium acetate 10g/l Sodium dihydrogen phosphate 10g/1 pH 5 Plating solution temperature 80°C Next, a solder resist pattern for gold plating was formed by screen printing on areas other than the areas that would become wire bonding pads. , gold plating was applied to a thickness of 1.5 μm.

In the above embodiments, the present invention is applied to a chip-on-board flexible wiring board compatible with wire bonding, but it may also be applied to the production of general multilayer wiring boards and inner layer boards for multilayer boards.

(Effect of the invention) The effects of the present invention are as shown below.

(1) The surface roughness of polyimide film is less than 2.0 μm even when surface treatment such as reactive ion etching is applied to improve adhesion. With almost no influence of diffused reflection, it has become possible to stably form fine wiring with a line width and space of about 20 μm.

(2) Because low dielectric constant materials such as polyimide can be used, signal transmission speeds are faster than flexible wiring boards manufactured using conventional rubber adhesives or wiring boards manufactured using only glass cloth prepreg. Electrical properties were significantly improved.

(3) The film formation on the insulating film in the present invention can be made continuous, and the process of copper foil roughening treatment - copper foil lamination → copper foil etching, etc. in the conventional roughened shape transfer method is possible. It was possible to omit a process and improve productivity.

[Brief explanation of drawings]

FIGS. 1(a) to 1(c) are cross-sectional views showing a method of manufacturing a wiring board according to the present invention. Explanation of symbols 1, polyimide film 2, through hole 3, nickel layer 4, resist pattern 5, pattern plating 6, electroless nickel layer・'

Claims (2)

[Claims] 1. In a wiring board having a wiring structure in which the upper part, side wall part, and lower part of a wiring pattern formed on an insulating substrate are coated with a nickel layer, the insulating substrate is a polyimide film, and the nickel layer under the wiring pattern is formed by vacuum deposition. A wiring board characterized in that it is formed by a film method. 2. 2. The wiring board according to claim 1, wherein the nickel layer is diffused in the polyimide film by 30A or more.