JPH1065061A - Method for manufacturing double-layer flexible board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a double-layer flexible substrate inexpensively without causing the defect of a wiring due to a pin hole even when a dry-type plating covering provided on an insulation film is used as one layer and an extremely thin copper conductor covering that is approximately 5-18μm is formed on it. SOLUTION: A ground metal layer that is 50-200Å in thickness is formed by a dry-type plating method using at least one type of nickel, chrome, and chrome oxide without using an adhesive on one or both sides of an insulator film, a ground metal layer is formed, electroless copper plating is formed for at least 0.01μm, and further a conductor layer of copper that is 5-18μm in thickness is formed on the electroless copper plating covering.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a two-layer flexible substrate.

[0002]

2. Description of the Related Art As a substrate for a flexible wiring board, a three-layer flexible substrate in which an insulating film is bonded with a copper foil having a thickness of about 35 μm using an adhesive, and a base metal layer directly on the insulating film. It is roughly divided into the provided two-layer flexible substrate.

When a three-layer flexible substrate is used, a desired wiring pattern is formed by a subtractive method to manufacture a three-layer flexible wiring board. When a two-layer flexible substrate is used, a subtractive method or an additive method is used. A two-layer flexible wiring board is manufactured by forming a desired wiring pattern. Generally, a three-layer flexible wiring board, which has a simple manufacturing process and can be manufactured at low cost, is mainly used.

[0004] With the recent increase in the density of electronic equipment, flexible wiring boards having a narrower wiring width have been required. However, in the case of a three-layer flexible wiring board, when a wiring portion is formed by etching, a cross-sectional shape becomes a trapezoid with a widened skirt because side etching occurs. Therefore, if etching is performed until electrical insulation between the wirings is ensured, the wiring pitch must be widened, and there is a limit to narrowing the pitch as long as a copper foil having a thickness of 35 μm is used.

For this reason, attempts have been made to use a copper foil as thin as possible, having a thickness of 18 μm or less, to reduce the spread of the skirt due to side etching to narrow the pitch. However, the copper foil having a thickness of several μm has low rigidity itself and thus has poor handling properties such as conveyance. Therefore, the rigidity must be increased by bonding the copper foil to an aluminum carrier. In addition, after laminating the copper foil and the insulating film, there is a problem that the aluminum carrier must be removed. Further, such a thin copper foil has a problem that film defects such as variations in film thickness and pinholes and cracks increase.

Further, as the thickness of the copper foil becomes thinner, the production of the copper foil itself becomes more difficult and the price becomes higher. Therefore, a three-layer flexible wiring board using the thin copper foil is inevitably expensive. As a result, the low price, which is an advantage of the three-layer flexible wiring board, is lost.

Further, recently, there has been an increasing demand for a flexible substrate having a narrow pitch wiring width which cannot be manufactured unless the copper thickness is less than 10 μm or less and about several μm. It is becoming difficult to achieve

Therefore, two-layer flexible wiring boards have begun to receive more attention. The two-layer flexible substrate used to obtain the two-layer flexible printed wiring board has a copper film directly formed on an insulator film without applying an adhesive, so that the entire substrate can be thinned and formed on the substrate. This is because the thickness of the copper film to be formed can also be arbitrarily adjusted.

This two-layer flexible substrate is to form an extremely thin copper film on an insulating film by a dry or wet plating method, but most of those on the market mostly have a copper film formed by a dry plating method. It is a thing that has been given.

Generally, when a copper coating is applied directly to the surface of an insulating film, the adhesion between the insulating film and the copper coating is poor. Therefore, generally, a metal other than copper, such as chromium, chromium oxide, and nickel, is deposited on the insulating film to a thickness of about 50 to 200 angstroms as a base metal layer. Forming a coating is performed. As a result, the adhesion between the metal coating layer and the insulating film is enhanced.

The underlying metal layer provided by the dry plating method has a thickness of 50 to 200 angstroms, and the copper film thereon has a thickness of usually about 0.2 to 0.5 μm. With these thicknesses, the coating film to be provided has a large number of pinholes having diameters of several tens to several hundreds, and some of these portions have exposed insulating films.

In order to avoid this problem, if an attempt is made to directly deposit an electrolytic copper plating on the underlying metal layer, the underlying metal layer is only 50 to 200 angstroms thick as described above. There is also a problem that the base metal layer is dissolved when a current is applied by immersion in a plating solution, the insulating film is exposed, and electroplating becomes impossible.

Conventionally, the thickness of a conductive film made of copper required for forming wiring is 15 to 35 μm. When a copper film having such a large thickness is obtained by an electrolytic copper plating method, a copper film is required. Grows not only in the vertical direction but also in the horizontal direction with respect to the substrate, so that the pinholes of the metal film layer are filled with the copper electroplating film, and the presence of the pinholes does not cause a defect in the wiring portion.

However, in order to obtain a wiring having a narrow pitch as the object of the present invention, the thickness of the copper film for forming the wiring portion is 10 μm or less, for example, about 5 μm, which is considerably smaller than the above thickness. There is a need to. Therefore, when the copper film is formed by the electrolytic copper plating method, the film is insufficiently grown in the horizontal direction, so that the pinhole cannot be filled, so that there is a problem that a problem such as a defect in the wiring portion is easily caused.

For example, when wiring is formed by a subtractive method, (1) a copper film having a desired thickness is formed on an insulating film, and (2) only a wiring portion is masked on the copper film. Providing a resist layer having a desired wiring pattern so that the copper film in other portions is exposed,
(3) The exposed copper film is removed by etching, and (4) Finally, the resist layer is removed.

Therefore, when the copper film is thin as described above, if the pinhole is formed on the wiring portion, the wiring portion is chipped at the position of the pinhole, which causes not only a wiring defect but also a poor adhesion of the wiring. Is easy to cause.

Therefore, there has been proposed a method in which a base metal layer and a thin copper film are formed on an insulating film by a dry plating method and further subjected to electroless copper plating to eliminate pinholes.
According to this method, a substrate excellent in function as a two-layer flexible substrate can be manufactured, but the cost is high because dry plating is repeated twice.

The wiring width of the narrow pitch wiring which is required at present is about 40 μm, and a width of １ ／ of the width is used as a guideline of the tolerance of chipping. Therefore, even a pinhole of about several μm poses a practical problem in some applications.

[0019]

SUMMARY OF THE INVENTION According to the present invention, a dry plating film provided on an insulating film is used as a base metal layer,
It is an object of the present invention to provide a method for manufacturing a two-layer flexible substrate which does not cause wiring defects due to pinholes even when an extremely thin copper conductor film having a thickness of about 5 to 18 μm is formed thereon.

[0020]

That is, according to the method of the present invention for solving the above-mentioned problems, a base metal layer is formed on one or both sides of an insulating film without using an adhesive, and the base metal layer is formed on the base metal layer. Forming a copper conductor layer as an intermediate layer by electroless plating, and then providing a copper layer so as to have a desired thickness, a method of manufacturing a two-layer flexible substrate, wherein the underlying metal layer is at least nickel, chromium, chromium oxide One type is formed by a dry plating method, and then an electroless copper plating is formed to a thickness of 0.01 μm or more on the surface of the insulating film, and 5 to 18 μm is formed on the electroless copper plating film.
This is to form a copper layer having a thickness of m.

The method of the present invention will be described more specifically. The thickness of the underlying metal layer may be 50 to 200 angstroms, and examples of the dry plating method that can be used include a vapor deposition method and a sputtering method.

Next, after providing the base metal layer, a catalyst is applied to the entire surface of the insulator film and the base metal surface by applying a catalyst for electroless plating. The thickness of the metal layer is increased by forming an electroless copper film on the insulating film surface and the underlying metal layer surface by a copper plating method. In this way, a sound electroplated copper film having a thickness of about 5 to 18 μm can be easily obtained without dissolving the metal layer even when current is applied under the electrocopper plating solution in the next step.

The catalyst-providing solution used may be a commonly used solution such as an acidic palladium-tin colloid solution, an alkaline palladium complex solution, or an tin-free acidic palladium solution. The method of applying the catalyst is not particularly limited, but a general sensitizing activation method or a catalyst accelerator method or the like as a pretreatment of the electroless plating method is simple, and is appropriately determined depending on the situation. You can choose.

The pretreatment for applying the catalyst is not particularly limited, but it is preferable to appropriately incorporate a pretreatment such as degreasing in order to obtain adhesion between the dry plating film and the electroless copper plating film. However, it is advisable to avoid conditions under which the pretreatment dissolves the underlying metal layer.

As a method of providing a copper layer on an electroless copper plating film in the present invention, it is preferable to use an electrolytic copper plating method in order to obtain a dense conductor layer. A general method can be applied as an electrolytic copper plating method for this purpose.

[0026]

Next, the details of the present invention and its operation will be specifically described.

A coating of, for example, about 100 Å of nickel, chromium, chromium oxide, or the like is formed on an insulating film such as polyimide by a dry plating method as a base metal layer.

Next, if a catalyst is applied by an electroless plating method, the catalyst is applied to the surface of the insulating film which has been hydrophilized and to the surface of the underlying metal layer. Then, when the catalyst-coated product is immersed in, for example, electroless copper plating under predetermined conditions, an electroless copper plating film is formed on the entire surface including the pinhole portion.

By newly forming a copper coating on the surface of the insulating film and the surface of nickel which have been rendered hydrophilic as described above, pinholes can be eliminated and the thickness of the metal layer can be increased. As a result, even when electrolytic copper plating using copper sulfate plating is performed thereafter, the electrolytic copper plating layer can be provided on the entire surface without dissolving the underlying metal layer.

After a copper conductor layer having a thickness of about 5 to 18 μm is formed by an electrolytic copper plating method, a resist layer having a desired wiring pattern is formed on the copper conductor layer according to a conventional method. The exposed part is removed by etching,
Thereafter, the resist layer is peeled off to obtain a two-layer flexible wiring board having a conductor thickness of about 5 to 18 μm without defects such as chipping or disconnection of wiring.

The catalytically active metal species used in the catalyst application method of the present invention may be any potential that is higher in potential than the complexed metal ion species contained in the electroless plating solution. For example, gold,
Platinum, silver, palladium and the like can be used. However, in consideration of simplicity, it is desirable to use a widely available palladium-based catalyst-imparting liquid.

The type of electroless plating solution used in the present invention uses a catalytically active metal species as a catalyst.
The types of metal ions contained in the plating solution are gold, silver, platinum,
Suitable are those having autocatalytic properties, such as palladium, copper, nickel, cobalt, and chromium, and being reduced by a reducing agent such as hydrazine, sodium phosphinate, formalin, and the like, to deposit metals, and thus to be of a reduced deposition type.

However, the present invention covers the surface of the insulating film exposed at the pinhole portion with a conductive material,
Since the main purpose is to prevent the nickel layer, which is a thin underlying metal layer, from being dissolved during electroplating, it can be said that an electroless copper plating solution having good conductivity and being relatively easy to work with is most suitable. The thickness of the electroless plating film may be a thickness that is not dissolved by the plating solution when performing the electrolytic copper plating, and a thickness of 0.01 μm or more.

[0034]

Next, the present invention will be further described with reference to examples.

Example 1 A polyimide film having a thickness of 50 μm (product name “Kapton 200” manufactured by Du Pont-Toray Co., Ltd.)
V ") was cut into a size of 12 cm x 12 cm, and nickel was applied to one surface thereof by a vacuum deposition method to a thickness of 100 angstroms to produce a substrate.

Next, the substrate was immersed in a weak alkaline degreasing agent for 1 minute and then washed with water for 2 minutes to wash the surface. Next, the catalyst was applied to the surface of the substrate by dipping in a catalizing liquid and an accelerating liquid (both manufactured by Okuno Pharmaceutical Co., Ltd.). Subsequently, the substrate was placed in an electroless copper plating solution having the composition shown in Table 1 for 3 hours.
After immersion for a minute, an electroless copper plating film was formed on the surface. The plating solution was treated at 60 ° C., pH = 12.5, and stirred with air.

Table 1 Composition of electroless copper plating solution 銅 Copper sulfate: 10 g / l EDTA: 30 g / l HCHO (36% sol.): 5 ml / l PEG1000: 0.5 g / l Dipyridyl: 10 mg / l (4) After electroless copper plating, an electrolytic copper plating solution having the composition shown in Table 2 To form a copper film having a thickness of 5 μm. The plating conditions at this time were as follows: the temperature of the plating solution was room temperature, the stirring was air stirring, and the current density during energization was 3 A
/ Dm ² and the plating time was 9 minutes.

Table 2 Composition of electrolytic copper plating solution {copper sulfate: 80 g / l sulfuric acid: 200 g / l Brightener: appropriate amount chloride ion: 50 mg / l}光 Light was applied from the copper coating side of the obtained substrate to confirm the presence or absence of pinholes. Light transmission was recognized within the area of 12 cm x 12 cm. No pinholes were found to exist.

A flexible wiring board having a wiring width of 40 .mu.m and a wiring pitch of 80 .mu.m using this substrate and having no defect such as a defect or disconnection caused by a pinhole in a wiring portion manufactured based on a subtractive method according to a conventional method. was gotten.

This embodiment shows an example in which a single-sided flexible substrate having a single-sided wiring pattern of an insulating film is manufactured by a subtractive method, but a double-sided flexible wiring board having wiring portions on both sides of the insulating film. It has been confirmed that excellent results can also be obtained with a single-sided or double-sided flexible substrate by the semi-additive method.

Example 2 A polyimide film having a thickness of 50 μm (product name “Kapton 200” manufactured by Du Pont-Toray Co., Ltd.)
V ") was cut into a size of 12 cm x 12 cm, and chromium oxide was applied to one surface thereof by a vacuum evaporation method to a thickness of 100 angstroms to produce a substrate.

Next, a single-sided flexible wiring board was manufactured in the same procedure as in Example 1.

When light was applied from the copper coating side of the obtained substrate to confirm the presence or absence of pinholes, no light transmission was observed in the area of 12 cm × 12 cm, indicating that no pinholes existed.

A flexible wiring board having a wiring width of 40 μm and a wiring pitch of 80 μm using this substrate and having no defects such as defects or disconnections caused by pinholes in a wiring portion manufactured by a subtractive method using a conventional method. was gotten.

In this embodiment, an example is shown in which a single-sided flexible board having a single-sided wiring pattern of an insulating film is manufactured by a subtractive method. It has been confirmed that excellent results can also be obtained with a single-sided or double-sided flexible substrate by the semi-additive method.

Example 3 A polyimide film having a thickness of 50 μm (product name “Kapton 200” manufactured by Du Pont-Toray Co., Ltd.)
V ") was cut into a size of 12 cm x 12 cm, and chromium was applied to one surface thereof by vacuum evaporation to a thickness of 100 angstroms to produce a substrate.

Next, a single-sided flexible wiring board was manufactured in the same procedure as in Example 1.

When light was applied to the obtained substrate from the copper coating side to check for the presence or absence of pinholes, no light transmission was observed in the area of 12 cm × 12 cm, indicating that there was no pinhole.

A flexible wiring board having a wiring width of 40 .mu.m and a wiring pitch of 80 .mu.m using this substrate and having no defect such as a defect or disconnection caused by a pinhole in a wiring portion manufactured by a subtractive method according to a conventional method. was gotten.

In this embodiment, an example is shown in which a single-sided flexible substrate having a single-sided wiring pattern of an insulating film is manufactured by a subtractive method. It has been confirmed that excellent results can also be obtained with a single-sided or double-sided flexible substrate by the semi-additive method.

Comparative Example 1 A polyimide film having a thickness of 50 μm (product name “Kapton 200” manufactured by Du Pont-Toray Co., Ltd.)
V ") was cut into a size of 12 cm x 12 cm, and nickel was applied to one surface thereof by a vacuum deposition method to a thickness of 100 angstroms to produce a substrate.

Next, it was immersed in a weak alkaline degreasing agent for 1 minute, and then washed with water for 2 minutes to wash the surface. Next, the same treatment as in the example was performed using an electrolytic copper plating solution having the composition shown in Table 2, and a 5 μm copper film was obtained by an electrolytic copper plating method.

When light was applied from the copper coating side of the obtained substrate to confirm the presence or absence of pinholes, light transmission was observed in a region of 12 cm × 12 cm, and the size of the pinhole was several tens μm to a hundred At 10 μm, the number was almost equal to the number of pinholes after vacuum evaporation.

Using this substrate, a flexible wiring board having a wiring width of 40 μm and a wiring pitch of 80 μm was manufactured based on a subtractive method according to a conventional method, and defects such as chipping or disconnection caused by pinholes were found in the wiring portion. Were confirmed, indicating that this substrate was not suitable for a fine wiring board having a narrow pitch.

Comparative Example 2 A polyimide film having a thickness of 50 μm (product name “Kapton 200” manufactured by Du Pont-Toray Co., Ltd.)
V ") was cut into a size of 12 cm x 12 cm, and chromium oxide was applied to one surface thereof by a vacuum evaporation method to a thickness of 100 angstroms to produce a substrate.

Next, the surface was washed by immersing it in a weak alkaline degreasing agent for 1 minute, followed by washing with water for 2 minutes. Next, the same treatment as in the example was performed using an electrolytic copper plating solution having the composition shown in Table 2, and a 5 μm copper film was obtained by an electrolytic copper plating method.

The presence or absence of pinholes was confirmed by irradiating light from the copper coating side of the obtained substrate. Light transmission was observed in a region of 12 cm × 12 cm, and the size of the pinhole was several tens μm to a hundred At 10 μm, the number was almost equal to the number of pinholes after vacuum evaporation.

Using this substrate, a flexible wiring board having a wiring width of 40 μm and a wiring pitch of 80 μm was manufactured based on a subtractive method according to a conventional method. Were confirmed, indicating that this substrate was not suitable for a fine wiring board having a narrow pitch.

Comparative Example 3 A polyimide film having a thickness of 50 μm (product name “Kapton 200” manufactured by Du Pont-Toray Co., Ltd.)
V ") was cut into a size of 12 cm x 12 cm, and chromium was applied to one surface thereof by vacuum evaporation to a thickness of 100 angstroms to produce a substrate.

Next, it was immersed in a weakly alkaline degreasing agent for 1 minute, and then washed with water for 2 minutes to wash the surface. Next, the same treatment as in the example was performed using an electrolytic copper plating solution having the composition shown in Table 2, and a 5 μm copper film was obtained by an electrolytic copper plating method.

When light was applied from the copper coating side of the obtained substrate to confirm the presence or absence of pinholes, light transmission was observed within a 12 cm × 12 cm area, and the size of the pinholes was several tens μm to a hundred At 10 μm, the number was almost equal to the number of pinholes after vacuum evaporation.

Using this substrate, a flexible wiring board having a wiring width of 40 μm and a wiring pitch of 80 μm was manufactured based on a subtractive method according to a conventional method, and defects such as chipping or disconnection caused by pinholes were found in the wiring portion. Were confirmed, indicating that this substrate was not suitable for a fine wiring board having a narrow pitch.

[0063]

As described above, according to the method of the present invention, the pinhole is formed by forming an electroless plating film on a substrate provided with a dry plating film as a base metal layer, which is likely to cause many pinholes. An electroless copper plating layer is also provided in the portion, and the dissolution of the underlying metal layer during the subsequent electrolytic copper plating can be prevented. As a result, a substrate free of pinhole defects can be obtained even when a thin electrolytic copper plating film of about 5 to 18 μm is formed. By using the substrate obtained in this way, even when a wiring board having an extremely fine wiring pattern is manufactured, a flexible wiring board having excellent reliability without a defect in a wiring portion can be obtained.

Claims (4)

[Claims] An underlayer metal layer is formed on one or both sides of an insulating film without an adhesive, and a copper conductor layer is formed as an intermediate layer on the underlayer metal layer by electroless plating.
Next, in a method for manufacturing a two-layer flexible substrate in which a copper layer is provided on the intermediate layer so as to have a desired thickness, (1) dry plating the underlying metal layer using at least one of nickel, chromium, and chromium oxide; (2) electroless copper plating as an intermediate layer on the substrate surface after the treatment
μm or more, and (3) 5 μm on the intermediate layer.
A method for manufacturing a two-layer flexible substrate, comprising forming a copper conductor layer having a thickness of １８18 μm. 2. The production method according to claim 1, wherein any one of an acidic palladium-tin colloid solution, an alkaline palladium complex solution, and an tin-free acidic palladium solution is used as the catalyst-providing solution. 3. The method according to claim 1, wherein the thickness of the base metal layer is 50 to 200 Å. 4. The method according to claim 1, wherein the dry plating method is one of a vapor deposition method and a sputtering method.