JP3125838B2 - Method for manufacturing two-layer flexible substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. 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 composed of a three-layer flexible substrate in which a desired wiring pattern is formed by a subtractive method by bonding a copper foil to an insulating film by using an adhesive, and a substrate on the insulating film. After a conductor metal layer is formed on a substrate directly provided with a base metal layer, it is roughly classified into a two-layer flexible substrate in which a desired wiring pattern is formed by a subtractive method or an additive method.

[0003] At present, 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 the density of electronic devices, a narrow wiring width is also required for a flexible wiring board.

However, in the case of a three-layer flexible wiring board, side insulation is generated when a wiring portion is formed by etching, so that the cross section of the wiring has a trapezoidal shape with a wide skirt, so that electrical insulation between the wirings is ensured. If the etching is performed until the wiring width becomes too large, the wiring pitch becomes too wide, so that there is a limit to the narrowing of the wiring width.

Since the skirt spread due to side etching increases as the thickness of copper increases, the spread is reduced and the wiring width is reduced to a narrower pitch. It was necessary to use a copper foil as thin as 18 μm or less in place of the copper foil. However, thin copper foil, especially ultra-thin copper foil of about several μm, is poor in handling properties such as transport because of its low rigidity.
There was a problem that the rigidity had to be increased by bonding an aluminum carrier. There is also a disadvantage that film defects such as variations in film thickness and pinholes and cracks are likely to occur. Therefore, as the thickness of the copper foil becomes thinner, the production of the wiring board becomes more difficult and the production cost becomes higher, so that the advantage of cost, which is an 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 less than 10 μm and about several μm. . Therefore, recently, a two-layer flexible wiring board has attracted attention. What is necessary is that this two-layer flexible wiring board forms a copper coating layer directly on an insulator film without applying an adhesive, so that the substrate can be made thinner and the copper coating layer formed on the substrate can also be formed to an arbitrary thickness This is because the cost can be reduced.

This two-layer flexible substrate has an extremely thin copper film formed on an insulating film by dry or wet plating, but most of those on the market are those subjected to dry plating. .

In the dry-plated two-layer flexible substrate, since the adhesion between the insulator film and the copper film is poor, a metal other than copper, such as chromium, chromium oxide, nickel or the like, is generally formed on the insulator film. It has been practiced to increase the adhesion between copper and an insulator film by forming a thin copper film after applying a metal oxide as a base layer to a thickness of about 50 to 200 angstroms.

Usually, the thickness of the copper film formed on the base 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 formed in this way, and the underlying metal layer and the insulating film are often exposed. In addition, since the base metal layer has a thickness of only 50 to 200 angstroms as described above, when the substrate is subjected to electrolytic copper plating, it is dissolved when immersed in a strongly acidic electroplating solution such as copper sulfate and energized, There is also a problem that the insulating film is exposed. Conventionally, the thickness of the conductive layer film made of copper necessary for forming the wiring portion is 15 to 35 μm. When such a considerably thick copper film is obtained by the electrolytic copper plating method, the copper film is Since the pinhole grows not only in the vertical direction but also in the horizontal direction with respect to the substrate, the pinhole is filled with the coating,
No defect in the wiring portion is caused by the presence of the pinhole. 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.
In the following, for example, the thickness must be about 5 μm, which is considerably thinner than the above-mentioned thickness. Therefore, when the film is formed by the electrolytic copper plating method, the growth of the film in the horizontal direction is insufficient and the pinhole cannot be filled. There is a problem that a problem such as a defect in the wiring portion is likely to occur.

For example, to form a wiring by a subtractive method, (1) a copper conductor film having a desired thickness is formed on an insulating substrate, 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) removing the exposed copper film by etching, and (4) finally removing the resist layer This is done by: Therefore, as described above, in the case of a thin copper film, if a pinhole is formed on a 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. It is easy to be.

The present invention has been made in view of the above problems, and has been made in consideration of the above-mentioned problems, and is intended to provide a two-layer flexible substrate which does not cause defects due to pinholes even when a copper conductor film having a very small thickness of about 5 μm is formed. It is an object of the present invention to provide a production method of

[0012]

Means for Solving the Problems The present inventor has proposed a method in which a nickel film of a base metal layer and a copper film of a thin film as a surface metal layer are formed on the insulating film by a dry plating method or the like. The present invention was completed by finding that it is possible to reduce the number of pinholes exposing the insulating film or the underlying metal by performing electroless plating and further forming a copper conductor layer thereon by an electrolytic copper plating method. .

That is, the present invention for solving the above-mentioned problems is to form a nickel layer as a base metal layer directly on one or both sides of an insulating film without using an adhesive, and to further form a thin film on the base metal layer. After further forming a copper conductor layer on the nickel layer or copper layer of the substrate on which the copper layer is formed,
In a method for manufacturing a printed wiring board by a subtractive method or a semi-additive method, the substrate after forming the base metal layer and the copper layer of the thin film is treated with an inorganic alkali solution and / or an organic alkali solution. A method for manufacturing a two-layer flexible substrate, comprising: forming an electroless copper plating film on a surface to a thickness of 0.01 μm or more, and further forming a copper conductor layer on the electroless copper plating film.

The method of the present invention will be described in more detail. The surface of the insulator film exposed at the pinhole portion is treated with an organic alkali solution such as a mixture of hydrazine and ethylenediamine or a potassium hydroxide or sodium hydroxide solution. By treating with an inorganic alkali solution or a mixed solution thereof to make it hydrophilic, and then applying a known catalyst for electroless plating to the entire substrate, the surface of the insulator film that has been made hydrophilic and the pinhole portion Applying a catalyst on the nickel coating exposed to the
Next, a copper film is formed by an electroless plating method to increase the thickness of the conductor layer. This makes it possible to easily obtain a sound copper plating film having a thickness of about 5 μm without dissolving the copper film even when current is applied under a strongly acidic plating solution in the subsequent copper plating treatment in the next step.

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

The pretreatment at the time of applying the catalyst is not particularly limited. However, it is preferable to perform a treatment such as degreasing in order to ensure the adhesion between the dry plating film and the wet plating film. However, it is important to avoid conditions where the nickel film and the copper film are dissolved by the pretreatment.

In the present invention, the processing conditions such as the concentration of the alkaline solution and the processing temperature for performing the hydrophilic treatment of the substrate differ depending on the kind of the alkaline solution to be used. It is necessary to determine experimentally according to the above.

[0018]

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

An extremely thin nickel film of, for example, about 100 angstroms is formed on an insulating film such as a polyimide film by dry plating, and a thin copper film of, for example, about 0.3 μm is further formed thereon by dry plating. The surface of the substrate formed by an organic alkali solution such as hydrazine and ethyldiamine mixed solution, or an inorganic alkali solution such as potassium hydroxide and sodium hydroxide, or an organic alkali such as a mixed solution of hydrazine and potassium hydroxide. By performing the treatment with the mixed solution of the inorganic alkali, the surface of the insulating film exposed at the pinhole portion is hydrophilized. Next, if the catalyst application performed by the electroless plating method is performed, the catalyst is applied on the insulating film that has been hydrophilized, on the nickel film exposed in the pinhole portion, and on the uppermost copper film. . Then, when the substrate provided with the catalyst is immersed in, for example, an electroless copper plating solution under predetermined conditions, the portion where the catalyst is increased, that is, the surface of the insulator film, the surface of the nickel film, and the surface of the copper film which are hydrophilized At this time, a new electroless copper plating film is formed.

That is, by newly forming a copper film on the surface of the insulator film and the nickel film which have been made hydrophilic, the conductivity of both surfaces is increased, and by increasing the thickness of the metal layer, the copper sulfate plating solution is formed. Even when the used electrolytic copper plating is performed, the exposed portion of the insulator film and the nickel coating portion do not dissolve. 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 remove the conductor thickness 5 without defect such as a defective portion of the wiring or disconnection.
A two-layer flexible wiring board of about μm is obtained. The catalytically active metal used in the catalyst application method of the present invention may be any metal that is more noble in potential than the complexed metal ion species added in the electroless plating solution. For example, gold, platinum, silver, palladium and the like can be used. However, considering simplicity, it is preferable to use a widely available palladium-based catalyst-imparting liquid.

As the type of electroless plating solution used in the present invention, since a catalytically active metal species is used as a catalyst, the type of metal ions contained in the plating solution is gold,
Silver, platinum, palladium, copper, nickel, cobalt, chromium, etc. with autocatalytic properties, and hydrazine,
A reduction-precipitation type in which metal is deposited by being reduced by a reducing agent such as sodium phosphinate or formalin is suitable. However, the present invention mainly aims 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 an electroless copper plating solution having good and relatively good workability is most suitable.
The thickness of the electroless copper plating film may be a thickness that is not dissolved by the plating solution when performing the electrolytic copper plating, for example, a thickness of 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 (manufactured by Du Pont-Toray Co., Ltd., “Kapton 200V”) was cut into a size of 12 cm × 12 cm, and nickel was applied on one surface thereof by vacuum evaporation to a thickness of 100 Å. Further, a substrate on which copper was applied to a thickness of 0.25 μm by vacuum evaporation was formed thereon.

Next, the substrate was treated with a weak alkaline degreasing agent for 1 hour.
The surface was cleaned by immersion for 2 minutes and degreased, and then washed with water for 2 minutes. Then 2.5 mol / l of hydrazine and 1.
The exposed insulator film surface is hydrophilized by immersion in a mixed organic alkali solution of 0 mol / liter ethylenediamine, and after washing with water, immersed in a dilute hydrochloric acid solution to neutralize the substrate surface. (Both manufactured by Okuno Pharmaceutical Co., Ltd.) to give a catalyst for electroless plating on the substrate surface. 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. The plating conditions at this time were a plating solution temperature of 60 ° C. and a pH of 12.5, and the treatment was carried out by air stirring.

[0024]

[Table 1] Composition of electroless plating solution ───────── 銅 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 (4) After the electroless plating, an electroplating treatment was performed using 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 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 ───────── 銅 Copper sulfate: 80 g / l Sulfuric acid: 200 g / l Gloss Agent: Appropriate amount Chloride ion: 50 mg / l と こ ろ Light was applied from the copper coating side of the obtained substrate to confirm the presence or absence of pinholes , 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. Not what you got. The present embodiment shows an example in which a single-sided flexible wiring board having a wiring pattern on one side of an insulating film is formed by a subtractive method. It has been confirmed that excellent results can be similarly obtained with a board or a single-sided or double-sided flexible wiring board by a semi-additive method. Example 2 A single-sided flexible wiring board was prepared in the same procedure as in Example 1, except that the surface of the insulator film after the degreasing treatment was hydrophilized using a 2 mol / L potassium hydroxide solution. The obtained wiring board had no wiring part defect based on the presence of the pinhole. Example 3 The surface of the insulator film after the degreasing treatment was hydrophilized by 2.5.
Example 1 except that a mixed alkali solution of hydrazine (mol / l) and potassium hydroxide (2 mol / l) was used.
When a single-sided flexible wiring board was prepared in the same procedure as described above, the obtained wiring board was free from defects in the wiring portion due to the presence of pinholes. Comparative Example 1 A 50 μm thick polyimide film (manufactured by Du Pont-Toray Co., Ltd., “Kapton 200V”) was cut into a size of 12 cm × 12 cm, and nickel was applied to one surface thereof by vacuum evaporation to a thickness of 100 Å. Further, a substrate was formed on which copper was applied to a thickness of 0.25 μm by a vacuum evaporation method.

Next, the substrate was treated with a weak alkaline degreasing agent for 1 hour.
The surface was cleaned by immersion for 2 minutes and degreased, and then washed with water for 2 minutes. Next, the exposed insulator film surface was hydrophilized by immersion in a mixed organic alkali solution of 0.01 mol / l hydrazine and 0.01 mol / l ethylenediamine. Thereafter, a 5 μm-thick copper film was formed by an electrolytic copper plating method immediately following the same procedure as in Example 1 without going through a step of performing electroless copper plating on the substrate.

The substrate was irradiated with light from the copper coating side to check for pinholes.
In the region of No. 3, light was transmitted, and the size of the pinholes was several μm to one hundred and several tens 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 a subtractive method according to a conventional method. Many defects were confirmed, and it was found that this substrate was not suitable for a fine wiring substrate having a narrow pitch. Comparative Example 2 The 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 5 mol / l hydrazine and 3 mol / l ethylenediamine to hydrophilize the exposed surface of the insulator film.
Thereafter, a 5 μm copper film was formed immediately by an electrolytic copper plating method in the same procedure as in Example 1 without passing through a step of performing electroless plating on the substrate.

When light was applied to the obtained substrate from the copper coating side to check for the presence or absence of pinholes, a 12 cm × 12 cm
In the region, light was transmitted, and the size of the pinhole was several μm to one hundred and several tens μm, and in addition, a streak-like crack was also present. The number of pinholes 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, defects similar to those in Comparative Example 1 were confirmed, and it was found that the substrate was not suitable for a fine wiring board having a narrow pitch. Comparative Example 3 The substrate prepared in the same manner as in Comparative Example 1 was immersed in a weakly alkaline degreasing agent for 1 minute to degrease it, and then washed with water for 2 minutes to clean the surface. Then, the exposed insulator film surface was hydrophilized by immersion in a mixed solution of 0.1 mol / l hydrazine and 0.01 mol / l potassium hydroxide. Thereafter, a 5 μm copper film was formed immediately by an electrolytic copper plating method in the same procedure as in Example 1 without passing through a step of performing electroless plating on the substrate.

When a flexible wiring board was prepared using this substrate in the same manner as in Comparative Example 1, the same defects as those in Comparative Example 1 were confirmed, and it was found that the flexible wiring board was not suitable for a fine wiring board having a narrow pitch. Comparative Example 4 The substrate prepared in the same manner as in Comparative Example 1 was immersed in a weakly 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 6 mol / l hydrazine and 5 mol / l potassium hydroxide to hydrophilize the exposed surface of the insulator film. Thereafter, a 5 μm copper film was formed immediately by an electrolytic copper plating method in the same procedure as in Example 1 without passing through a step of performing electroless plating on the substrate.

The substrate was irradiated with light from the copper coating side to check for the presence of pinholes.
In the region, light was transmitted, and the size of the pinhole was from several μm to one hundred and several tens μm, and there was also a streak-like crack.
The number of pinholes 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 those in Comparative Example 1 were confirmed, and it was found that the substrate was not suitable for a fine wiring board having a narrow pitch. Comparative Example 5 The substrate prepared in the same manner as in Comparative Example 1 was immersed in a weakly alkaline degreasing agent for 1 minute to degrease it, and then washed with water for 2 minutes to clean the surface. Then, the exposed insulator film surface was hydrophilized by immersion in a 0.01 mol / liter potassium hydroxide solution. Thereafter, a 5 μm copper film was formed immediately by an electrolytic copper plating method in the same procedure as in Example 1 without passing through a step of performing electroless plating on the substrate.

When light was applied from the copper coating side of the obtained substrate to confirm the presence or absence of pinholes, it was 12 cm × 12 cm.
In the region, the light was transmitted, and the size of the pinholes was several μm to one hundred and several tens 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 the flexible wiring board was not suitable for a fine wiring board having a narrow pitch. Comparative Example 6 A substrate prepared in the same manner as in Comparative Example 1 was immersed in a weakly 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 / l potassium hydroxide solution to hydrophilize the exposed surface of the insulator film.

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

When light was applied from the copper coating side of the obtained substrate to confirm the presence or absence of pinholes, it was found that the size was 12 cm × 12 cm.
In the region, light was transmitted, and the size of the pinhole was from several μm to one hundred and several tens μm, and there was also a streak-like crack.
The number of pinholes 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, defects similar to those in Comparative Example 1 were confirmed, and it was found that the flexible wiring board was not suitable for a fine wiring board having a narrow pitch.

[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 a large number of pinholes, dissolution of the underlying metal layer exposed in the pinhole portion during electroplating is prevented, and the thickness is reduced to about 5 μm. Even when an electroplated film is formed, a substrate free of pinhole defects can be obtained. Therefore, even when a wiring board having an extremely narrow pitch is formed by a subtractive method or the like, the reliability of the wiring portion is free from defects. Therefore, it can be said that the present invention is an industrially excellent invention because a flexible wiring board excellent in the above can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H05K 1/03 670 C23C 14/14 C23C 18/18 C25D 5/10 H05K 3/38

Claims (3)

(57) [Claims] 1. A nickel layer on a substrate, wherein a nickel layer is directly formed as a base metal layer on at least one side of an insulator film without using an adhesive, and a thin copper layer is formed on the base metal layer. Or after further forming a copper conductor layer on the copper layer, in a method of manufacturing a flexible wiring board by forming a wiring portion by a subtractive method or a semi-additive method, forming the copper layer of the metal base layer and the thin film After treating the substrate with at least one of an inorganic alkaline solution and an organic alkaline solution, the surface of the substrate is coated with an electroless plated copper film by 0.0
A method for manufacturing a two-layer flexible substrate, comprising: forming a layer having a thickness of 1 μm or more; and further forming a copper conductor layer on the electroless copper plating film. 2. The method according to claim 1, wherein a thickness of the copper conductor layer formed on the electroless copper plating film is 5 μm to 10 μm. Wherein the insulator layer of copper thin film formed of nickel and the lower ground metal layer on the base metal layer to one surface or formed directly on both surfaces of the film claims characterized in that it is formed by dry plating method Item 3. The method for producing a two-layer flexible substrate according to item 1 or 2 .