JPH08181402A - Method for manufacturing two-layer flexible substrate - Google Patents

Abstract

(57) [Abstract] [Purpose] An object of the present invention is to provide a method for manufacturing a two-layer flexible substrate in which pinholes are not formed even when a copper coating having an extremely thin thickness of about 5 μm is formed. . [Structure] A nickel layer is directly formed as a base metal layer on one or both sides of an insulating film without an adhesive.
A method for producing a printed wiring board by a subtractive method or a semi-additive method after further forming a copper conductor layer on the nickel layer or the copper layer of a substrate on which a thin copper layer is formed on the underlying metal layer After treating the substrate after forming the underlying metal layer and the thin copper layer with an inorganic alkaline solution and / or an organic alkaline solution, an electroless copper plating film is formed on the surface of the substrate to a thickness of 0.01 μm or more. A method for producing a two-layer flexible substrate, which comprises forming and further forming a copper conductor layer on the electroless copper plating film.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for manufacturing a two-layer flexible substrate.

[0002]

2. Description of the Related Art A substrate for a flexible wiring board is a three-layer flexible substrate for forming a desired wiring pattern by a subtractive method by laminating an insulating film with a copper foil by using an adhesive, and the insulating film. It is roughly classified into a two-layer flexible substrate in which a conductor metal layer is directly formed on a substrate on which a base metal layer is provided and then a desired wiring pattern is formed by a subtractive method or an additive method.

At the present time, a three-layer flexible wiring board which has a simple manufacturing process and can be manufactured at low cost is generally used. However, in recent years, with the increase in density of electronic devices, a flexible wiring board is required to have a narrow pitch wiring width.

However, in the case of a three-layer flexible wiring board, side etching occurs when the wiring portion is formed by etching, so that the shape of the wiring cross section becomes a trapezoid with a widened hem, so that electrical insulation between wirings is secured. If the etching is performed until then, the wiring pitch becomes too wide, and therefore there is a limit to narrowing the wiring width.

The thicker the copper is, the wider the hem spread by side etching becomes. Therefore, in order to reduce the spread and narrow the wiring width, a 35 μm-thick film which is generally used conventionally is used. It was necessary to use a copper foil having a thickness of 18 μm or less as thin as possible instead of the copper foil. However, thin-walled copper foil, especially ultra-thin copper foil with a thickness of about several μm, has low rigidity itself, and therefore has poor handling properties such as transportation.
There is a problem in that the rigidity needs to be increased by bonding aluminum carriers together. There is also a drawback that film defects such as variations in film thickness and pinholes and cracks are likely to occur. Therefore, the thinner the copper foil is, the more difficult it is to manufacture the wiring board, and the higher the manufacturing cost is. Therefore, the advantage of the three-layer flexible wiring board is lost.

[0006]

However, recently, there has been an increasing demand for a flexible wiring board having a narrow pitch wiring width that cannot be manufactured unless the thickness of the copper conductor layer is 10 μm or less, or about several μm. . Therefore, recently, a two-layer flexible wiring board has attracted attention. What is important is that the two-layer flexible wiring board directly forms the copper coating layer on the insulating film without applying an adhesive, so that the substrate can be made thin and the copper coating layer formed on the substrate can also be formed to an arbitrary thickness. This is because it is possible to reduce the cost.

This two-layer flexible substrate forms an extremely thin copper film on an insulating film by dry or wet plating, but most of those on the market are those plated with dry plating. .

In the two-layer flexible substrate which is dry-plated, the adhesion between the insulator film and the copper coating is poor, so that a metal other than copper, such as chromium, chromium oxide, or nickel, is generally deposited on the insulator film. The adhesion between the copper and the insulator film is increased by depositing a metal oxide as a base layer to a thickness of about 50 to 200 Å and then forming a thin copper film.

The thickness of the copper coating formed on the underlying metal layer is usually about 0.2 to 0.5 μm,
A large number of pinholes are likely to be formed in the thin copper film thus formed, and the underlying metal layer and the insulating film are often exposed in some cases. Further, since the underlying metal layer has a thickness of 50 to 200 angstroms as described above, it is dissolved when the substrate is electroplated with copper and is immersed in a strongly acidic electroplating solution such as copper sulfate and is energized, There was also a problem that the insulating film was exposed. Conventionally, the thickness of the conductive layer coating made of copper necessary for forming the wiring portion is 15 to 35 μm, and when a copper coating having such a considerable thickness is obtained by the electrolytic copper plating method, the copper coating is Since the film grows not only in the vertical direction but also in the horizontal direction with respect to the substrate, the pinhole is filled with the film,
Although the defect of the wiring portion does not occur due to the presence of the pinhole, the thickness of the copper coating for forming the wiring portion is 10 μm when the wiring having a narrow pitch as intended for the present invention is to be obtained.
In the following, for example, around 5 μm, which must be considerably thinner than the above-mentioned thickness, when the coating is formed by the electrolytic copper plating method, the growth of the coating in the horizontal direction is insufficient and the pinhole cannot be filled. There is a problem that problems such as defects in the wiring portion are likely to occur.

For example, in order to form a wiring by the subtractive method, (1) a copper conductor coating having a desired thickness is formed on an insulating substrate, and (2) only a wiring portion is masked on the copper coating. A resist layer having a desired wiring pattern is provided so that the copper coating on the other portions is exposed, (3) the exposed copper coating is removed by etching, and (4) the resist layer is finally removed. Done by. Therefore, as described above, in the case of a thin copper film, if the pinhole is in the wiring portion, the wiring portion will be chipped at the position of the pinhole, which not only causes a wiring defect but also causes poor wiring adhesion. It is easy to become.

The present invention has been made in view of the above problems and is a two-layer flexible substrate in which defects due to pinholes do not occur even when a copper conductor coating having an extremely thin thickness of about 5 μm is formed. It is an object of the present invention to provide a manufacturing method of.

[0012]

The present inventor has found that a copper film formed on the insulating film by a dry plating method or the like is formed by forming a nickel coating of a base metal layer and a thin copper coating of a surface metal layer on the substrate. The present invention was completed by finding that it is possible to reduce the number of pinholes in which the insulating film or the base metal is exposed by performing electroless plating and further forming a copper conductor layer on it by electrolytic copper plating. .

That is, according to the present invention for solving the above problems, a nickel layer is directly formed as a base metal layer on one side or both sides of an insulating film without an adhesive, and a thin film is further formed on the base metal layer. After further forming a copper conductor layer on the nickel layer or the copper layer of the substrate on which the copper layer is formed,
In a method of manufacturing a printed wiring board by a subtractive method or a semi-additive method, the substrate after forming the underlying metal layer and the thin copper layer is treated with an inorganic alkaline solution and / or an organic alkaline solution, and then the substrate is treated. The method for producing a two-layer flexible substrate is characterized in that an electroless copper plating film is formed on the surface to a thickness of 0.01 μm or more, and a copper conductor layer is further formed on the electroless copper plating film.

The method of the present invention will be described more specifically. The surface of the insulating film exposed in the pinhole portion is treated with an organic alkaline solution such as a mixed solution of hydrazine and ethylenediamine or with potassium hydroxide or sodium hydroxide. The surface of the insulating film and the pinholes are hydrophilized by treating the surface of the substrate with an inorganic alkaline solution or a mixed solution thereof to make them hydrophilic, and then applying a known catalyst for electroless plating to the entire substrate. Applying a catalyst on the nickel coating exposed on the
Then, a copper coating is formed by electroless plating to increase the thickness of the conductor layer. By doing so, a thin electrolytic copper plating film of about 5 μm can be easily obtained without dissolving the copper film even when electricity is applied under a strong acid plating solution in the next step of electrolytic copper plating.

The catalyst-applying solution used is an acidic palladium-tin colloidal solution or an alkaline palladium complex solution. Or, a general one such as an acidic palladium solution containing no tin may be used. Further, the catalyst application method may be a general method, but a sensitizing activation method and a catalyst accelerator method, which are usually performed as a pretreatment of the electroless plating method, are simple and preferable methods.

The pretreatment for applying the catalyst is not particularly limited, but it is preferable to perform a degreasing treatment or the like in order to improve the adhesion between the dry plating film and the wet plating film. However, it is important to avoid the condition that the nickel film and the copper film are dissolved by the pretreatment.

In the present invention, the treatment conditions such as the concentration of the alkali solution and the treatment temperature when the substrate is made hydrophilic are different depending on the kind of the alkali solution used. It is necessary to determine it experimentally according to the above.

[0018]

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

An ultra-thin nickel film of about 100 angstrom is formed on an insulating film such as a polyimide film by a dry plating method, and a thin copper film of about 0.3 μm is also formed on the nickel film by a dry plating method. The surface of the substrate formed by an organic alkali solution such as a mixed solution of hydrazine and ethyldiamine, an inorganic alkali solution such as potassium hydroxide or sodium hydroxide, or an organic alkali such as a mixed solution of hydrazine and potassium hydroxide. By treating with the mixed solution of inorganic alkali, the surface of the insulating film exposed at the pinhole portion is made hydrophilic. Next, when a catalyst is applied by electroless plating, the catalyst is applied on the hydrophilized insulator film, the nickel film exposed in the pinhole portion, and the outermost copper film. . Then, by immersing the substrate thus provided with a catalyst under a predetermined condition, for example, in an electroless copper plating solution, a portion where the catalyst is increased, that is, a hydrophilized insulator film surface, a nickel film, and a copper film An electroless copper-plated film is newly formed on and.

That is, a copper coating is newly formed on the surface of the hydrophilized insulating film and the nickel coating to enhance the conductivity of both surfaces, and the thickness of the metal layer is increased to form a copper sulfate plating solution. Even when the electrolytic copper plating used is performed, the exposed portion of the insulator film and the nickel coating portion are not dissolved. Therefore, the pinhole can be filled. After forming a copper conductor layer having a thickness of about 5 μm to 10 μm by an electrolytic copper plating method, a resist layer having a desired wiring pattern is formed on the copper conductor layer by a conventional method, and an exposed portion of the copper conductor layer is etched. And then the resist layer is peeled off to obtain a conductor thickness 5 which is free from defects such as wiring defects and disconnections.
A two-layer flexible wiring board of about μm can be obtained. The catalytically active metal used in the catalyst application method of the present invention may be any one that is more noble in potential than the complexed metal ion species added in the electroless plating solution. For example, gold, platinum, silver, palladium or the like can be used. However, from the viewpoint of simplicity, it is preferable to use a widely available palladium-based catalyst-providing liquid.

As the type of the electroless plating solution used in the present invention, since the catalytically active metal species is used as a catalyst, the type of metal ion contained in the plating solution is gold,
Hydrazine, which has autocatalytic properties such as silver, platinum, palladium, copper, nickel, cobalt, and chromium.
A reduction-precipitation type in which a metal is precipitated by being reduced with a reducing agent such as sodium phosphinate or formalin is suitable. However, the main purpose of the present invention is to repair the insulating film exposed at the pinhole portion to be conductive, and to prevent the thin underlying nickel layer from being dissolved during electroplating. It can be said that the electroless copper plating solution that is good and has relatively good workability is most suitable.
The thickness of this electroless copper plating film may be such that it is not dissolved by the plating solution when performing electrolytic copper plating, for example, 0.01 μm or more.

[0022]

Next, an embodiment of the present invention will be described. Example 1 A polyimide film having a thickness of 50 μm (“Kapton 200V” manufactured by Toray-Dupont Co., Ltd.) was cut into a size of 12 cm × 12 cm, and nickel was deposited on one side thereof by a vacuum deposition method to a thickness of 100 angstrom, Furthermore, a substrate was formed by depositing copper to a thickness of 0.25 μm thereon by vacuum deposition.

Next, the substrate is treated with a weakly alkaline degreasing agent.
After soaking for 1 minute to degrease, the surface was cleaned by washing with water for 2 minutes. Then 2.5 mol / l hydrazine and 1.
The exposed surface of the insulating film is made hydrophilic by immersing it in a mixed organic alkali solution of 0 mol / liter of ethylenediamine, washed with water and then immersed in a dilute hydrochloric acid solution to neutralize the surface of the substrate, and further characterization liquid and accelerating liquid. (Both made by Okuno Seiyaku Co., Ltd.) to apply a catalyst for electroless plating on the surface of the substrate. Subsequently, the substrate was immersed in an electroless copper plating solution having the composition shown in Table 1 for 3 minutes to form an electroless copper plating film on the surface. At this time, the plating conditions were such that the temperature of the plating solution was 60 ° C. and the pH was 12.5, and the treatment was performed by stirring with air.

[0024]

[Table 1] Electroless plating solution composition ───────── ──────────────────────── Copper sulfate: 10 g / l EDTA: 30 g / l HCHO (36% sol.): 5 ml / l PEG # 1000: 0.5 g / l dipyridyl: 10 ml / l ────────────────────── After the electroless plating treatment, an electrolytic copper plating solution having the composition shown in Table 2 was subsequently used to perform an electroplating treatment to form a copper coating having a thickness of 5 μm. The plating conditions at this time were: the temperature of the plating solution was room temperature, the stirring was mechanical stirring, and the current density during energization was 3
A / dm ² , and the energization time was 9 minutes.

[0025]

[Table 2] Composition of electrolytic copper plating solution ───────── ──────────────────── Copper sulfate: 80 g / l Sulfuric acid: 200 g / l Gloss Agent: Appropriate amount Chloride ion: 50 mg / l ──────────────────── When the presence of pinholes was confirmed by shining light from the copper coating side of the obtained substrate , 12 cm × 12 cm, no light transmission was observed, and it was found that there was no pinhole. Using this substrate, a flexible wiring board having a wiring width of 40 μm and a wiring pitch of 80 μm was prepared based on a subtractive method according to a conventional method. As a result, it was found that the wiring portion had defects such as a defect portion and a disconnection portion caused by pinholes. I got something not. The present example shows an example in which a single-sided flexible wiring board having a wiring pattern on one surface of an insulating film is prepared by a subtractive method, but a double-sided flexible wiring having wiring portions on both surfaces of the insulating film. It has been confirmed that the same excellent results can be obtained for a board or a single-sided or double-sided flexible wiring board prepared by the semi-additive method. Example 2 A single-sided flexible wiring board was prepared by the same procedure as in Example 1 except that the hydrophilizing treatment of the insulating film surface after the degreasing treatment was carried out by using a 2 mol / liter potassium hydroxide solution. The obtained wiring board was free from defects in the wiring part due to the presence of pinholes. Example 3 After the degreasing treatment, the surface of the insulator film was made hydrophilic by 2.5.
Example 1 except that a mixed alkaline solution of mol / l hydrazine and 2 mol / l potassium hydroxide was used.
When a single-sided flexible wiring board was prepared by the same procedure as in (1), the obtained wiring board was free from defects in the wiring part due to the presence of pinholes. Comparative Example 1 A polyimide film having a thickness of 50 μm (manufactured by Toray DuPont, “Kapton 200V”) was cut into a size of 12 cm × 12 cm, and nickel was deposited on one side of the film to a thickness of 100 angstrom by a vacuum deposition method. Furthermore, a substrate was formed by depositing copper to a thickness of 0.25 μm thereon by vacuum deposition.

Next, the substrate is treated with a weakly alkaline degreasing agent.
After soaking for 1 minute to degrease, the surface was cleaned by washing with water for 2 minutes. Then, the exposed surface of the insulating film was made hydrophilic by immersing it in a mixed organic alkaline solution of 0.01 mol / liter hydrazine and 0.01 mol / liter ethylenediamine. Then, a 5 μm copper coating was immediately formed by the electrolytic copper plating method in the same procedure as in Example 1 without passing through a step for subjecting the substrate to electroless copper plating.

When the presence or absence of pinholes was confirmed by shining light from the copper coating side of the obtained substrate, it was 12 cm × 12 cm.
There was light transmission in the region of, and the size of the pinholes was several μm to hundreds of tens of μm, and the number was almost the same as the number of pinholes after vacuum deposition.

Using this substrate, a flexible wiring board having a wiring width of 40 μm and a wiring pitch of 80 μm was prepared based on the subtractive method according to the usual method. As a result, a defective portion or a disconnection portion caused by a pinhole in the wiring portion was produced. Many defects were confirmed, and it was found that this substrate was not suitable for a fine pitch fine wiring substrate. Comparative Example 2 A substrate prepared in the same manner as in Comparative Example 1 was immersed in a weak alkaline degreasing agent for 1 minute to degrease it, and then washed with water for 2 minutes to clean the surface. Next, the exposed surface of the insulating film was made hydrophilic by immersing it in a mixed solution of 5 mol / liter of hydrazine and 3 mol / liter of ethylenediamine.
Thereafter, a 5 μm copper coating was immediately formed by the electrolytic copper plating method in the same procedure as in Example 1 without passing through the step of subjecting the substrate to electroless plating.

When the presence or absence of pinholes was confirmed by shining light from the copper coating side of the obtained substrate, it was 12 cm × 12 cm.
There was light transmission in the region (2), the size of the pinhole was from several μm to hundreds of tens of μm, and in addition, streak-like cracks were present. The number of pinholes was larger than that after vacuum evaporation.

When a flexible wiring board was prepared using this substrate in the same manner as in Comparative Example 1, the same defects as in Comparative Example 1 were confirmed, and it was found that it was not suitable for a fine pitch fine wiring board. Comparative Example 3 A substrate prepared in the same manner as in Comparative Example 1 was immersed in a weak alkaline degreasing agent for 1 minute to degrease it, and then washed with water for 2 minutes to clean the surface. Then, it was immersed in a mixed solution of 0.1 mol / liter hydrazine and 0.01 mol / liter potassium hydroxide to make the exposed surface of the insulating film hydrophilic. Thereafter, a 5 μm copper coating was immediately formed by the electrolytic copper plating method in the same procedure as in Example 1 without passing through the step of subjecting the substrate to electroless plating.

When a flexible wiring board was prepared using this substrate in the same manner as in Comparative Example 1, the same defects as in Comparative Example 1 were confirmed, and it was found that it was not suitable for a fine pitch fine wiring board. Comparative Example 4 A substrate prepared in the same manner as in Comparative Example 1 was immersed in a weak alkaline degreasing agent for 1 minute to degrease it, and then washed with water for 2 minutes to clean the surface. Then, the surface of the exposed insulating film was hydrophilized by immersing it in a mixed solution of 6 mol / liter hydrazine and 5 mol / liter potassium hydroxide. Thereafter, a 5 μm copper coating was immediately formed by the electrolytic copper plating method in the same procedure as in Example 1 without passing through the step of subjecting the substrate to electroless plating.

When the presence or absence of pinholes was confirmed by shining light from the copper coating side of the obtained substrate, it was 12 cm × 12 cm.
There was light transmission in the region of, and the size of the pinhole was several μm to several hundred and several tens μm, and in addition, there were streak-like cracks.
The number of pinholes was increased compared to the number of pinholes after vacuum evaporation.

When a flexible wiring board was prepared using this substrate in the same manner as in Comparative Example 1, the same defects as in Comparative Example 1 were confirmed, and it was found that it was not suitable for a fine pitch fine wiring board. Comparative Example 5 A substrate prepared in the same manner as in Comparative Example 1 was immersed in a weak alkaline degreasing agent for 1 minute to degrease it, and then washed with water for 2 minutes to clean the surface. Then, it was immersed in a 0.01 mol / liter potassium hydroxide solution to make the exposed surface of the insulating film hydrophilic. Thereafter, a 5 μm copper coating was immediately formed by the electrolytic copper plating method in the same procedure as in Example 1 without passing through the step of subjecting the substrate to electroless plating.

When the presence or absence of pinholes was confirmed by shining light from the copper coating side of the obtained substrate, it was 12 cm × 12 cm.
There was light transmission in the region of, and the size of the pinholes was from several μm to hundreds of tens of μm, and the number was almost the same as the number of pinholes after vacuum deposition.

When a flexible wiring board was prepared using this substrate in the same manner as in Comparative Example 1, the same defects as in Comparative Example 1 were confirmed, and it was found that it was not suitable for a fine pitch fine wiring board. Comparative Example 6 A substrate prepared in the same manner as in Comparative Example 1 was immersed in a weak alkaline degreasing agent for 1 minute to degrease it, and then washed with water for 2 minutes to clean the surface. Then, it was immersed in a 5 mol / liter potassium hydroxide solution to make the exposed surface of the insulating film hydrophilic.

Then, a 5 μm copper coating was immediately formed by the electrolytic copper plating method in the same procedure as in Example 1 without passing through the step of subjecting the substrate to electroless plating.

When the presence or absence of pinholes was confirmed by shining light from the copper coating side of the obtained substrate, it was 12 cm × 12 cm.
There was light transmission in the region of, and the size of the pinhole was several μm to several hundred and several tens μm, and in addition, there were streak-like cracks.
The number of pinholes was increased compared to the number of pinholes after vacuum deposition.

When a flexible wiring board was prepared using this substrate in the same manner as in Comparative Example 1, the same defects as in Comparative Example 1 were confirmed, and it was found that it was not suitable for a fine pitch fine wiring board.

[0039]

As described above, according to the present invention,
By forming an electroless plating film on a substrate having a dry plating film that easily causes many pinholes, the underlying metal layer exposed in the pinholes is prevented from being dissolved during electroplating, and the thickness is about 5 μm. A substrate without pinhole defects can be obtained even when an electroplating film is formed. Therefore, even when a wiring board having an extremely narrow pitch is formed by a subtractive method, etc., reliability without a defect in the wiring portion. It can be said that the invention is an industrially excellent invention because it is possible to obtain an excellent flexible wiring board.

Claims (3)

[Claims] 1. A nickel layer in a substrate in which a nickel layer is directly formed as a base metal layer on at least one surface of an insulating film without an adhesive, and a thin copper layer is further formed on the base metal layer. Alternatively, in the method for producing a flexible wiring board by further forming a copper conductor layer on the copper layer and then forming a wiring portion by the subtractive method or the semi-additive method, the metal underlayer and the thin copper layer are formed. The treated substrate is treated with at least one of an inorganic alkaline solution and an organic alkaline solution, and then an electroless plated copper film is formed on the surface of the substrate by 0.0
A method for producing a two-layer flexible substrate, which is characterized in that it is formed to a thickness of 1 μm or more, and a conductor layer of copper is further formed on the electroless copper plating film. 2. The method for producing a two-layer flexible substrate according to claim 1, wherein the thickness of the copper conductor layer formed on the electroless copper plating film is 5 μm to 10 μm. 3. The nickel of the underlying metal layer formed directly on one side or both sides of the insulating film and the thin copper layer formed on the underlying metal layer are formed by dry plating. -Layer flexible substrate manufacturing method.