JPH08181433A - Manufacture of two-layer flexible substrate - Google Patents

Abstract

PURPOSE: To provide a manufacturing method of a two-layer flexible substrate which does not produce a pin hole even if an extremely thin copper film is formed. CONSTITUTION: A chromium or chromium oxide layer is directly formed as a foundation layer in one side or both sides of an insulator film without incorporating adhesive. A copper conductor layer is further formed on a chromium layer or a chromium oxide layer, or a copper layer of a substrate wherein a thin copper layer is formed on a foundation metallic layer. Thereafter, a wiring part is formed by a subtractive method or a semiadditive method and a flexible wiring board is manufactured. After a substrate wherein a foundation layer and a thin copper layer are formed is treated by inorganic alkaline solution and/or organic alkaline solution, an electroless copper plating film is formed at least 0.01μm thick in a substrate surface and a copper conductor layer is further formed on an 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 flexible wiring board is a three-layer flexible wiring board in which a desired wiring pattern is formed by a subtractive method by using a three-layer flexible board in which a copper foil is bonded to an insulating film with an adhesive. A two-layer structure in which a desired wiring pattern is formed by a subtractive method or an additive method using a two-layer flexible substrate having a copper conductor layer formed directly after providing an underlying layer made of a metal or metal oxide on an insulator film. Broadly divided into flexible wiring boards.

Conventionally, a three-layer flexible wiring board which has a simple manufacturing process and can be manufactured at low cost has been generally used. By the way, with the recent increase in the density of electronic equipment, a narrow wiring width is required for flexible wiring boards.

In the case of a three-layer flexible wiring board, since side etching occurs when forming a wiring portion by etching, the shape of the wiring cross section becomes a trapezoid with a widened hem, so that electrical insulation between wirings is ensured. If etching is performed up to this point, the wiring pitch becomes too wide, and therefore there is a limit to narrowing the wiring width.

Further, the skirt spread due to this side etching becomes larger as the thickness of the copper becomes thicker. Therefore, in order to reduce the spread and narrow the wiring width,
Replace with the copper foil of 35 μm thickness that is commonly used in the past
It was necessary to use a copper foil having a thickness as thin as 8 μm or less.
However, a thin copper foil, especially an extremely thin copper foil with a thickness of about several μm, has a low rigidity itself and therefore has poor handling properties such as transportation, and it is necessary to bond an aluminum carrier to increase the rigidity. There's a problem. Also,
There is also a problem 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 cost merit, which is an advantage of the three-layer flexible wiring board, is lost. There was also.

[0007]

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 which are dry plated. .

Since the dry-plated two-layer flexible substrate has poor adhesion between the insulator film and the copper coating, it is generally a metal or metal oxide other than copper, such as chromium, chromium oxide or nickel, on the insulator film. It has been practiced to increase the adhesion between copper and an insulating film by depositing an object as a base layer to a thickness of about 50 to 200 Å and then forming the copper coating.

And, usually, the thickness of the copper coating is usually 0.
Although the thickness is about 2 to 0.5 μm, a large number of pinholes are likely to be formed in the copper coating thus formed, and the underlayer or the insulating film is often exposed in some cases.
In addition, since the underlayer 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, Since the copper film grows not only in the vertical direction but also in the horizontal direction with respect to the substrate, the pinholes are filled with the film, and the defect of the wiring portion due to the presence of the pinholes does not occur, but it is an object of the present invention. In order to obtain a wiring with a narrow pitch, the thickness of the copper coating for forming the wiring portion should be 10 μm or less, for example, about 5 μm, which is considerably smaller than the above thickness. When the coating is formed by the method, the growth of the coating in the horizontal direction is insufficient and the pinholes cannot be filled, so that there is a problem that problems such as defects of the wiring portion are likely to occur.

For example, when wiring is formed by the subtractive method, (1) a copper film having a desired thickness is formed on an insulating substrate, and (2) only the wiring portion is masked on the copper film. , Providing a resist layer having a desired wiring pattern so that the copper coating on the other part is exposed,
(3) The exposed copper film is removed by etching,
(4) Finally, the resist layer is removed. 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-mentioned problems, and does not cause pinholes even when a copper coating having an extremely thin thickness of about 5 μm is formed.
An object of the present invention is to provide a method for manufacturing a layer flexible substrate.

[0014]

The present inventor has found that a thin film of a thin film is formed on a substrate on which a chromium or chromium oxide film as a base layer and a copper film as a surface metal layer are formed on the insulating film by a dry plating method. When an electroless plating film is formed and then a copper conductive film layer is formed by the electrolytic copper plating method, even if a thin conductor layer is formed, the number of pinholes exposed in the insulating film or the underlayer is reduced. I found that I can.

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

To explain the method of the present invention more specifically, the surface of the insulating film exposed at the pinhole portion is treated with an organic alkaline solution such as a mixed solution of hydrazine and ethylenediamine or with a potassium hydroxide or sodium hydroxide solution. It is treated with an inorganic alkaline solution or a mixed solution thereof to make it hydrophilic, and at the same time, removes the natural oxide film or chromium oxide on the chromium surface to expose the active metal chromium surface or the insulating film surface (as a matter of course, When the chromium oxide is removed, the surface of the insulating film is exposed, so that the surface is made hydrophilic).

Next, by applying a known catalyst for electroless plating to the entire substrate, the catalyst is applied on the surface of the hydrophilized insulating film and the nickel coating exposed on the pinhole portion. Then, the thickness of the conductor layer is increased by forming a copper film by an electroless plating method. By doing so, an electrolytic copper plating film can be obtained without dissolving the film even during energization under a strongly acidic electroplating solution in the case of performing electrolytic copper plating in the next step.

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 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.

[0020]

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

An extremely thin film of chromium or chromium oxide having a thickness of, for example, about 100 Å is formed on an insulating film such as a polyimide film by dry plating.
Further, on the surface of the substrate on which a thin copper film having a thickness of, for example, about 0.3 μm is formed by dry plating, an organic alkaline solution such as a mixed solution of hydrazine and ethyldiamine, or an inorganic solution such as potassium hydroxide or sodium hydroxide is used. By treating with an alkaline solution or a mixed solution of an organic alkali and an inorganic alkali such as a mixed solution of hydrazine and potassium hydroxide, the surface of the insulating film exposed in the pinhole portion is made hydrophilic. Then, by applying a catalyst by a known catalyst applying method that has been conventionally performed by electroless plating, the chrome coating exposed on the hydrophilized insulator film and the pinhole portion and the outermost surface A catalyst is applied on the copper coating. When the substrate thus provided with the catalyst is immersed in an electroless copper plating solution under predetermined electroless plating conditions, the portion provided with the catalyst, that is, the surface of the hydrophilized insulator film, the chromium film, and the copper film An electroless copper plating film is newly formed on the top.

That is, by newly forming a copper coating on the surface of the hydrophilized insulating film and the chromium coating, the conductivity of both surfaces is enhanced, and by increasing the thickness of the metal layer, the copper sulfate plating solution is added. Even when the electrolytic copper plating used is performed, the exposed portion of the insulator film and the chromium 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 electrolytic copper plating,
A resist layer having a desired wiring pattern is formed on the copper conductor layer by a conventional method, the exposed portion of the copper conductor layer is removed by etching, and then the resist layer is removed by peeling to remove a missing portion or a disconnection of the wiring. Defect-free conductor thickness 5 μm
A two-layer flexible wiring board of about 10 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-used paradigm-based catalyst-adding 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 types of metal ions contained in the plating solution are gold, silver, platinum, palladium, copper, nickel, cobalt. A reduction-precipitation type that has an autocatalytic property such as chromium and a metal that is reduced by a reducing agent such as hydrazine, sodium phosphinate, or formalin to cause metal precipitation is suitable.

However, the main purpose of the present invention is to make the insulating film exposed at the pinholes electrically conductive and to prevent the thin chromium underlayer from dissolving during electroplating. It can be said that the electroless copper plating solution having good conductivity and relatively good workability is most suitable. The thickness of this electroless plating film may be such that it is not dissolved by the plating solution when performing electrolytic copper plating.

Further, in the present invention, the treatment conditions such as the concentration of the alkali solution and the treatment temperature at the time of carrying out the hydrophilic treatment of the substrate are different depending on the kind of the alkali solution used and the like. It is necessary to determine it experimentally according to the above.

[0026]

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 chromium 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 was treated with a weak alkaline degreasing agent 1
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 a temperature of the plating solution of 60 ° C. and a pH of 12.5, and the treatment was performed by stirring with air.

[0028]

[Table 1] Composition of electroless plating solution ──────────────────────── 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, continue to Table 2 Electroplating treatment was performed using the electrolytic copper plating solution having the composition shown in (1) to form a copper coating having a thickness of 5 μm. The plating conditions at this time were that 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.

[0029]

[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 ─────────────────────── When the presence of pinholes was confirmed by shining light from the copper coating side of the obtained substrate, 12 cm × No light transmission was observed within the 12 cm region, indicating that there were no pinholes. Using this substrate, a flexible wiring board having a wiring width of 40 μm and a wiring pitch of 80 μm was prepared by a conventional method based on the subtractive method. As a result, it was found that the wiring portion had defects such as missing portions and disconnection portions 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 was prepared by a subtractive method, but a double-sided flexible wiring board having wiring portions on both surfaces of the insulating film. It has been confirmed that the same excellent results can be obtained for a single-sided or double-sided flexible wiring board 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 (“Kapton 200V” manufactured by Toray-Dupont Co., Ltd.) having a thickness of 50 μm was cut into a size of 12 cm × 12 cm, and chromium was deposited on one surface 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 was 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 substrate. 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.

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 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.

[0043]

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 substrate in which a chromium or chromium oxide layer is directly formed as an underlayer on at least one surface of an insulating film without an adhesive, and a thin copper layer is formed on the underlayer. In a method for producing a flexible wiring board by forming a wiring layer by a subtractive method or a semi-additive method after further forming a copper conductor layer on a chromium layer, a chromium oxide layer or a copper layer, the underlying layer and The substrate after forming a thin copper layer,
After treatment with at least one of an inorganic alkaline solution and 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, and copper is further deposited on the electroless copper plating film. A method for manufacturing a two-layer flexible substrate, which comprises forming a conductor layer. 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 chromium or chromium oxide of the underlayer directly formed on one side or both sides of the insulating film and the thin copper layer formed on the underlayer are formed by a dry plating method. And a method for manufacturing a two-layer flexible substrate.