JP4385298B2 - Two-layer flexible substrate and manufacturing method thereof - Google Patents

Description

  The present invention relates to a two-layer flexible substrate and a manufacturing method thereof, more specifically, a nickel-titanium-chromium base metal layer (seed layer) is formed on an insulator film by a dry plating method, and then the base metal The present invention relates to a two-layer flexible substrate in which a copper coating layer is formed on the layer, has a high adhesion, has corrosion resistance, and has a high insulation reliability, and a method for manufacturing the same.

  In general, a substrate used for producing a flexible wiring board is a three-layer flexible substrate (for example, see Patent Document 1) in which a copper foil serving as a conductor layer is bonded onto an insulator film using an adhesive, It is roughly classified into a two-layer flexible substrate in which a copper coating layer that is a conductor layer is directly formed on an insulating film by a dry plating method or a wet plating method without using an adhesive.

  Here, when using a three-layer flexible substrate, a three-layer flexible wiring board can be manufactured by forming a desired wiring pattern on the substrate by a subtractive method, and when using a two-layer flexible substrate In the conventional method, a two-layer flexible wiring board can be manufactured by forming a desired wiring pattern on a substrate by a subtractive method or an additive method. However, conventionally, the manufacturing method is simple and manufactured at low cost. The use of three-layer flexible substrates that can be used has been dominant.

By the way, with the recent increase in the density of electronic devices, a wiring board with a narrower wiring width has been demanded.
However, in manufacturing a three-layer flexible substrate, when a wiring board is formed by etching a copper coating layer formed on an insulating film as a substrate according to a desired wiring pattern to form a wiring board, Since so-called side etching in which the side surface is etched occurs, the cross-sectional shape of the wiring portion is likely to be a trapezoid with a widened bottom.
Therefore, if etching is performed until the electrical insulation between the wiring portions is ensured, the wiring pitch width becomes too wide. Therefore, a copper foil having a thickness of 35 μm that has been generally used in the past is used as an insulator with an adhesive. As long as a three-layer flexible substrate bonded to a film is used, there is a limit to narrowing the wiring portion of the wiring board.
For this reason, instead of the conventional 35 μm thick copper foil laminated substrate, a thin copper foil laminated substrate having a thickness of 18 μm or less is used, and the width of the skirt spread by side etching is reduced to narrow the pitch of the wiring portion in the wiring board. It has been carried out.
However, since such a thin copper foil has low rigidity and poor handling properties, a reinforcing material such as an aluminum carrier is once bonded to the copper foil to increase the rigidity, and then the copper foil and the insulator film are bonded together. However, this method had a problem that workability and productivity were poor because it took too much time and time.
In addition, with such thin copper foils, there are problems in manufacturing technology such as film thickness variations, pinholes, cracks, etc. resulting in increased coating defects, and as the copper foil gets thinner, the copper foil itself As a result, the manufacturing cost becomes high and the cost merit of the three-layer flexible wiring board is lost.

  In particular, recently, there is an increasing demand for a wiring board having a narrow width and a narrow pitch wiring portion that cannot be manufactured without using a copper foil having a thickness of less than 10 μm or about several μm. The wiring board using a three-layer flexible substrate has a problem in terms of manufacturing cost as well as the above technical problems.

Then, the 2 layer flexible wiring board using the 2 layer flexible substrate which can form a copper coating layer directly on an insulator film, without giving an adhesive agent came to attract attention.
Such a two-layer flexible substrate forms a copper conductor layer directly on an insulator film without an adhesive, so that the thickness of the substrate itself can be reduced and the thickness of the copper conductor film to be deposited is also reduced. It has the advantage that it can be adjusted to any thickness.
And when manufacturing such a two-layer flexible substrate, as a means for forming a copper conductor layer having a uniform thickness on an insulator film, an electrolytic copper plating method is usually employed. In general, a thin base metal layer is formed on an insulator film on which an electrolytic copper plating film is applied to impart conductivity to the entire surface, and then an electrolytic copper plating process is performed thereon (for example, Patent Document 2).

By the way, in order to obtain a thin base metal layer on an insulator film, it is common to use a dry plating method such as a vacuum deposition method or an ion plating method. In the coating layer to be formed, a large number of pinholes having a size of several tens of μm to several hundreds of μm are usually generated. Therefore, an insulating film exposed portion due to pinholes is often generated in the base metal layer.
Conventionally, in this type of flexible wiring board, the thickness of the conductive film of copper necessary for wiring is generally considered to be more than 35 μm and up to 50 μm, but the width of the formed wiring is also several hundred μm. Therefore, the defect of the wiring part due to the presence of several tens of μm pinholes was rare.
However, when it is intended to obtain a flexible wiring board having a narrow width and narrow pitch wiring portion oriented in the present invention, as described above, the thickness of the copper coating for forming the wiring portion is 18 μm or less. The thickness is preferably 8 μm or less, ideally about 5 μm, and the thickness of the wiring portion is likely to be increased.

Taking this situation as an example, a flexible wiring board is manufactured by a subtractive method, for example, using a two-layer flexible substrate in which a copper coating layer having a desired thickness is formed on an insulator film on which a base metal layer is formed. If it demonstrates, formation of a wiring part pattern will be performed at the following process.
(1) A resist layer having a desired wiring portion pattern is provided on the copper conductor layer so that only the wiring portion is masked and the copper conductor layer of the non-wiring portion is exposed. (2) The exposed copper conductor layer (3) Finally, the resist layer is peeled and removed.
Therefore, when a wiring board having a narrow wiring width and a narrow wiring pitch such as a wiring width of 15 μm and a wiring pitch of 30 μm is manufactured using a substrate in which the thickness of the copper coating layer is extremely thin, for example, 5 μm. In particular, among the pinholes generated in the base metal layer of the substrate by the dry plating process, the coarse ones reach the order of several tens to several hundreds of micrometers, so that the electrolytic copper having a thickness of about 5 μm is used. When the plating film is formed, the exposed portion of the insulator film due to the pinhole can hardly be filled, so this exposed portion, that is, the missing portion of the conductor layer is applied to the wiring portion, and the wiring portion is missing at the position of the pinhole. As a result, a wiring defect is caused, or even if this is not the case, it causes a poor adhesion of the wiring part.

As a method for solving the above-mentioned problems, a base metal layer is formed on an insulator film by a dry plating method, and a copper coating layer by electroless plating is further applied as an intermediate metal layer to expose the insulator film by a pinhole. A method of covering the part has been proposed (see, for example, Patent Document 3).
However, when this method is used, the exposed part of the insulator film due to pinholes can be eliminated to some extent, but on the other hand, the plating solution used for the electroless copper plating treatment or its pretreatment solution is already formed. Penetration between the insulator film and the underlying metal layer from various pinhole parts, which is the cause of this, impedes the adhesion of the underlying metal layer and the conductor layer due to the subsequent electro copper plating Has been found to be a possible solution and has not been a sufficient solution.

  Further, for example, Patent Document 4 discloses a polymer film having a plasma-treated surface, a nickel tie coat layer containing nickel or a nickel alloy attached to the plasma-treated surface, and copper attached to the nickel layer. A non-adhesive flexible laminate including a coating layer and another copper layer attached to the copper coating layer has been proposed, and metals for nickel alloys are Cu, Cr, Fe, V, Ti, Al, Si, A nickel tie coat layer selected from the group consisting of Pd, Ta, W, Zn, In, Sn, Mn, Co and mixtures of two or more thereof is described. Specifically, useful Ni alloys include Monel (about 67% Ni, 30% Cu), Inconel (about 76% Ni, 16% Cr, 8% Fe) and the like. Although the obtained laminate film is shown to be excellent in initial peel strength, peel strength after solder float, and peel strength after thermal cycling, there is no description about the good characteristics of the composite metal film.

  Furthermore, for example, in Patent Document 5, the heat resistance adhesion at the polyimide / metal interface on the polyimide side of a copper-clad polyimide film obtained by applying and curing a polyimide varnish on a copper foil is improved. In order to improve the durability and reliability of the electrical product, a vacuum is applied to the first thin layer made of at least one metal selected from the group consisting of nickel, chromium, molybdenum, tungsten, vanadium, titanium and manganese on the polyimide side. A second thin layer having a predetermined thickness made of copper is formed thereon by a vacuum film forming method, and a third thin layer made of copper having a predetermined thickness is formed on the second thin layer. However, in the examples, only chromium is shown as the first thin layer, and there is no description about the good characteristics of the composite metal film. The Not.

  Similarly, for example, Patent Document 6 also aims to obtain a flexible printed wiring board that is excellent in adhesion between layers, heat resistance, chemical resistance, bending resistance, and electrical characteristics, and is highly reliable and inexpensive. In addition, a nickel, cobalt, chromium, palladium, titanium, zirconium, molybdenum, or tungsten vapor deposition layer on one or both surfaces of the plastic film and a deposited particle size laminated on the vapor deposition layer is in the range of 0.007 to 0.850 μm. It is described that a flexible printed wiring board is formed by laminating a laminated body formed of an electron beam heat-deposited copper layer made of an assembly of the above and forming a desired circuit and a mask layer made of an insulating organic material that does not form a circuit. However, only the chromium deposition layer is described in the examples, and the description of the good characteristics of the composite metal film is described. There.

In addition, for example, in Patent Document 7, titanium, cobalt, molybdenum, and nickel are formed on one side or both sides of a plastic film for the purpose of improving high-temperature durability and alleviating performance deterioration during secondary workability. Among them, a metal polymer film has been proposed in which an alloy layer containing at least two kinds is formed, and a copper layer is formed on the alloy layer. In the examples, only a region with a high amount of molybdenum was shown, and the heat-resistant peel strength was not sufficient in this region.
JP-A-6-132628 Japanese Patent Laid-Open No. 8-139448 JP-A-10-195668 Special Table 2000-508265 JP 7-197239 A JP-A-5-283848 JP-A-8-332697

  The present invention solves the above problems in the production of a flexible wiring board using a dry plating method and an electroplating method, and is caused by a pinhole generated when a base metal layer is formed on an insulator film by a dry plating process. An object of the present invention is to provide a two-layer flexible substrate having a copper coating layer formed with a copper coating layer having no copper coating portion, excellent adhesion and corrosion resistance between the insulator film and the base metal layer, and having high insulation reliability. It is what.

  The inventors have formed a base metal layer directly on at least one surface of the insulator film without using an adhesive, and a copper conductor layer having a desired thickness is formed on the base metal layer. Nickel-titanium-chromium formed on the insulator film by a dry plating method with a thickness of 3 to 50 nm, with a titanium ratio of 3 to 22% by weight, a chromium ratio of 5 to 22% by weight and the balance being nickel. Using a base metal layer mainly containing an alloy and a two-layer flexible substrate characterized by forming a copper film layer on the base metal layer, the above problems are solved, adhesion is high, and corrosion resistance is obtained. In addition, the present inventors have found that a two-layer flexible substrate on which a copper conductor layer with high insulation reliability is formed can be obtained and can be applied to a flexible wiring board having a narrow-width and narrow-pitch wiring portion.

That is, the first invention of the present invention is a two-layer flexible substrate in which a base metal layer is formed directly on at least one surface of an insulator film without using an adhesive, and then a copper coating layer is formed on the base metal layer. The base metal layer mainly contains a nickel-titanium-chromium alloy formed by a dry plating method with a titanium ratio of 3 to 22% by weight, a chromium ratio of 5 to 22% by weight and the balance being nickel. The present invention provides a two-layer flexible substrate comprising a base metal layer having a thickness of 3 to 50 nm.
According to a second aspect of the present invention, there is provided the two-layer flexible substrate according to the first aspect, wherein the copper coating layer formed on the base metal layer has a thickness of 10 nm to 35 μm. It is to provide.
Further, according to a third aspect of the present invention, the insulator film includes a polyimide film, a polyamide film, a polyester film, a polytetrafluoroethylene film, a polyphenylene sulfide film, a polyethylene naphthalate film, and a liquid crystal polymer film. The present invention provides a two-layer flexible substrate according to the first invention, which is a resin film selected from films.

According to a fourth aspect of the present invention, there is provided a two-layer flexible substrate in which a base metal layer is directly formed on at least one surface of an insulator film without using an adhesive, and then a copper coating layer is formed on the base metal layer. In the method, a base metal layer of a nickel-titanium-chromium alloy having a titanium ratio of 3 to 22% by weight, a chromium ratio of 5 to 22% by weight and the balance of nickel is formed on the insulator film by a dry plating method. The present invention provides a method for producing a two-layer flexible substrate, wherein a thickness of 3 to 50 nm is formed, and then a copper coating layer is formed on the underlying metal layer.
The fifth invention of the present invention is characterized in that after the copper coating layer is formed by a dry plating method, a copper coating layer is further formed on the copper coating layer by a wet plating method. A method for producing a two-layer flexible substrate according to the invention is provided.
Further, according to a sixth invention of the present invention, the dry plating method is any one of a vacuum deposition method, a sputtering method, and an ion plating method. A method for manufacturing a substrate is provided.

According to the method for producing a two-layer flexible substrate of the present invention, a base metal layer is directly formed on at least one surface of an insulator film without using an adhesive, and a copper conductor layer having a desired thickness is formed on the base metal layer. In the two-layer flexible substrate for forming a film, a thickness of 3 to 50 nm is formed on the insulator film by a dry plating method, the proportion of titanium is 3 to 22% by weight, and the proportion of chromium is 5 to 22% by weight. A two-layer flexible substrate characterized in that a base metal layer mainly containing a nickel-titanium-chromium alloy of nickel and a copper coating layer having a thickness of 10 nm to 35 μm formed on the base metal layer it can.
And, according to the two-layer flexible substrate of the present invention, since the base metal layer contains titanium and chromium, it is possible to prevent the heat-resistant peel strength from decreasing, and the total amount of titanium and chromium can be reduced. In the same way, even if the proportion of chromium is decreased, the decrease in heat-resistant peel strength is slight. As a result, the amount of chromium can be reduced and the etching property can be improved, and the two-layer flexible substrate should be used. Therefore, it is possible to efficiently obtain a flexible wiring board having a highly reliable narrow width and narrow pitch wiring portion having a high adhesion and corrosion resistance and a defect-free wiring portion, and the effect is extremely great.

1) Two-layer flexible substrate In the two-layer flexible substrate of the present invention, a base metal layer is directly formed on at least one surface of an insulator film without using an adhesive, and a copper conductor having a desired thickness is formed on the base metal layer. A two-layer flexible substrate for forming a layer, wherein the ratio of titanium formed by dry plating on the insulator film is 3 to 22% by weight, and the ratio of chromium is 5 to 22% by weight. And the remainder is nickel, and the base metal layer mainly contains a nickel-titanium-chromium alloy, and the copper coating layer is formed on the base metal layer.
By adopting the above configuration, it is possible to obtain a two-layer flexible substrate on which a copper conductor layer having high adhesion, corrosion resistance and high insulation reliability is formed.
Here, the film thickness of the base metal layer mainly containing the nickel-titanium-chromium alloy obtained by the dry plating method is preferably in the range of 3 to 50 nm. If the film thickness is less than 3 nm, it is not preferable because an etching solution infiltrate when the wiring process is performed and the wiring part is floated, which causes a problem that the wiring peel strength is significantly reduced. Moreover, since it will become difficult to perform etching when this film thickness becomes thicker than 50 nm, it is not preferable.
Further, the composition of the base metal layer needs to be 3 to 22% by weight of titanium, 5 to 22% by weight of chromium, and the balance being nickel.
First, it is necessary for the ratio of titanium to be 3 to 22% by weight to prevent the heat-resistant peel strength from being significantly lowered due to thermal degradation. If the ratio of titanium is less than 3% by weight, it is not preferable because the heat-resistant peel strength cannot be prevented from significantly decreasing due to thermal deterioration. Further, if the proportion of titanium is more than 22% by weight, etching becomes difficult, which is not preferable.
For this reason, in the case of titanium, 5 to 15% by weight is more preferable, and 6 to 12% by weight is particularly preferable.
In the case of nickel-titanium-chromium, when an alloy target containing titanium is manufactured by melt casting and rolling, the alloy target can be produced up to about 9% by weight. However, if a binary simultaneous sputtering method of a pure titanium target and a nickel-chromium alloy is used, a film formation of 9% by weight or more is possible. However, there is a slight decrease in productivity.
Next, it is necessary for the ratio of chromium to be 5 to 22% by weight in order to prevent the heat-resistant peel strength from being significantly lowered due to thermal deterioration. When the chromium ratio is lower than 5% by weight, it is not preferable because the heat-resistant peel strength cannot be prevented from significantly decreasing due to thermal deterioration. On the other hand, if the chromium content exceeds 22% by weight, etching becomes difficult, which is not preferable.
However, when titanium and chromium are added at the same time, they can be added within the appropriate ranges of the above titanium and chromium, for example, exceeding the upper limit of the addition amount of chromium alone. It can be carried out.
Further, in the case of a nickel-based alloy target, if the nickel ratio is greater than 93%, the sputtering target itself becomes a ferromagnetic material, and the film forming speed decreases when the film is formed by magnetron sputtering. Therefore, it is not preferable. In the target composition of this configuration, since the nickel amount is 92% or less, a good film formation rate can be obtained even when the film is formed using the magnetron sputtering method.
By the way, a transition metal element can be appropriately added to the nickel-titanium-chromium alloy in accordance with the target characteristics for the purpose of improving heat resistance and corrosion resistance.
In addition to the nickel-titanium-chromium alloy, the base metal layer may contain 1% by weight or less of unavoidable impurities contained by being taken in during target production.
For this reason, in Table 1 to be described later, the balance (= bal. (Balance)) is expressed as the nickel amount including inevitable impurities of 1 wt% or less.
In the two-layer flexible substrate of the present invention, a copper coating layer formed on the underlying metal layer by a dry plating method and a copper coating layer formed on the copper coating layer by a wet plating method are provided. The film thickness of the combined copper coating layer is preferably 10 nm to 35 μm. When the thickness is less than 10 nm, the copper coating layer formed by the dry plating method becomes thin, so that it is difficult to supply power in the subsequent wet plating process, which is not preferable. Moreover, when it becomes thicker than 35 micrometers, since productivity falls, it is unpreferable.
In the two-layer flexible substrate of the present invention, as the insulator film, a polyimide film, a polyamide film, a polyester film, a polytetrafluoroethylene film, a polyphenylene sulfide film, a polyethylene naphthalate film, or a liquid crystal polymer film is used. Although the resin film chosen is mentioned, a polyimide-type film is preferable at the point which can be applied also to the use which requires high temperature connections, such as solder reflow.
Further, the film having a film thickness of 8 to 75 μm can be suitably used. An inorganic material such as glass fiber can be added as appropriate.
Furthermore, as the dry plating method, any one of a vacuum vapor deposition method, a sputtering method, and an ion plating method can be used.
On the other hand, it is suitable to form a relatively thick film by forming a copper layer by the wet plating method after forming the copper layer by the dry plating method.

2) Manufacturing method of 2 layer flexible board | substrate Hereafter, the manufacturing method of the two layer flexible board | substrate of this invention is explained in full detail.
In the present invention, as described above, it is a resin film selected from a polyimide film, a polyamide film, a polyester film, a polytetrafluoroethylene film, a polyphenylene sulfide film, a polyethylene naphthalate film, and a liquid crystal polymer film. A base metal layer is directly formed on at least one surface of the insulator film without using an adhesive, and a copper conductor layer having a desired thickness is formed on the base metal layer.
a) Dehydration treatment The film usually contains moisture, and before the base metal layer mainly containing nickel-titanium-chromium alloy is formed by dry plating, air drying and / or vacuum drying are performed in the film. It is necessary to remove the existing moisture. If this is insufficient, the adhesion with the underlying metal layer will be deteriorated.
b) Formation of base metal layer When a base metal layer mainly containing a nickel-titanium-chromium alloy is formed by dry plating, for example, when the base metal layer is formed using a winding type sputtering apparatus, the base metal layer is formed. An alloy target having a layer composition is mounted on the sputtering cathode.
The nickel-titanium-chromium alloy target has a marked reduction in rolling workability when the titanium content exceeds 9% by weight. When forming a base metal layer with a content exceeding 9% by weight, a nickel-chromium alloy target and a pure titanium target are attached to two cathodes, and simultaneous sputtering is performed, and the input power of each cathode is controlled. A base metal layer having a desired film composition can be obtained.
Specifically, after evacuating the inside of the sputtering apparatus in which the film is set, Ar gas is introduced, the inside of the apparatus is held at about 1.3 Pa, and an insulator film mounted on a winding / unwinding roll in the apparatus is attached. While transporting at a speed of about 3 m / min, power is supplied from a DC power source for sputtering connected to the cathode to start sputtering discharge, and a metal layer mainly containing nickel-titanium-chromium alloy is continuously formed on the film. To do. By this film formation, a base metal layer mainly containing a nickel-titanium-chromium alloy having a desired film thickness is formed on the film.
c) Formation of copper coating layer Similarly, a copper coating layer can be formed by dry plating using a sputtering apparatus in which a copper target is mounted on a sputtering cathode. At this time, the base metal layer and the copper coating layer are preferably formed continuously in the same vacuum chamber.
In addition, when a copper coating layer is further formed on the copper coating layer by a wet plating method, the electroplating treatment is performed as the primary plating, the electroless copper plating treatment as the primary plating, and the electrolytic copper plating as the secondary plating. In some cases, wet plating methods such as treatment are combined.
Here, the electroless copper plating treatment is performed as the primary plating because, when dry plating is performed by vapor deposition, coarse pinholes may be formed, and the resin film may be exposed on the surface. This is because an electroless copper plating film layer is formed on the entire surface of the substrate so as to cover the film exposed surface and make the entire surface of the substrate a good conductor so that it is not affected by pinholes.
The electroless plating solution used in electroless plating is a reduction deposition type in which the contained metal ions have autocatalytic properties and are reduced by a reducing agent such as hydrazine, sodium phosphinate, formalin, etc. However, in view of the gist of the present invention, the purpose is to improve the conductivity of the exposed portion of the insulator film exposed by the pinhole generated in the underlying metal layer. An electroless copper plating solution that is good and has relatively good workability is optimal.
Moreover, the thickness of the copper plating film layer by the electroless copper plating treatment as the primary plating is capable of repairing defects by pinholes on the substrate surface, and when performing the electrolytic copper plating treatment as the secondary plating described later. The thickness may be such that it is not dissolved by the electrolytic copper plating solution, and is preferably in the range of 0.01 to 1.0 μm.
Next, the electrolytic copper plating process is performed as the secondary plating on the electroless copper plating film layer in order to form a copper conductor layer having a desired thickness.
According to the copper coating layer formed on the base metal layer in this way, a two-layer flexible substrate having a high degree of adhesion of the conductor layer, which is not affected by the large and small pinholes generated when the base metal layer is formed, can be obtained. Can be obtained.
In addition, the wet copper plating process performed in this invention should just employ | adopt the conditions in the wet copper plating method by a conventional method for both primary and secondary.
Further, the total thickness of the copper coating layer formed by the dry / wet plating method formed on the base metal layer in this way needs to be 35 μm or less at the maximum.

3) Formation of wiring pattern Using the two-layer flexible substrate according to the present invention as described above, a wiring pattern is individually formed on at least one surface of the two-layer flexible substrate. In addition, via holes for interlayer connection can be formed at predetermined positions and used for various purposes.
More specifically, (a) high-density wiring patterns are individually formed on at least one surface of the flexible sheet. (B) A via hole penetrating the wiring layer and the flexible sheet is formed in the flexible sheet on which the wiring layer is formed. (C) In some cases, the via hole is filled with a conductive substance to make the inside of the hole conductive.
As the method for forming the wiring pattern, a conventionally known method such as photoetching can be used. For example, a two-layer flexible substrate having a copper coating layer formed on at least one surface is prepared, and screen printing or dry film is formed on the copper. Are laminated to form a photosensitive resist film, which is then exposed and developed for patterning. Next, the metal foil is selectively removed by etching with an etchant such as a ferric chloride solution, and then the resist is removed to form a predetermined wiring pattern.
In order to further increase the density of the wiring, it is preferable to prepare a two-layer flexible substrate having a copper coating layer formed on both surfaces, and pattern the both surfaces to form a wiring pattern on both surfaces of the substrate. Whether or not the entire wiring pattern is divided into the number of wiring areas depends on the distribution of wiring density of the wiring pattern. For example, the wiring pattern has a wiring width and a wiring interval of 50 μm or less, respectively, and other wiring areas. In consideration of the difference in thermal expansion from the printed circuit board and convenience in handling, the size of the wiring board to be divided may be set to about 10 to 65 mm and divided appropriately.
As a method for forming the via hole, a conventionally known method can be used. For example, a via hole penetrating the wiring pattern and the flexible sheet is formed at a predetermined position of the wiring pattern by laser processing, photoetching, or the like. . The diameter of the via hole is preferably reduced within a range that does not hinder the conductivity in the hole, and is usually 100 μm or less, preferably 50 μm or less.
The via hole is filled with a conductive metal such as copper by plating, vapor deposition, sputtering, etc., or a conductive paste is press-fitted and dried using a mask having a predetermined opening pattern to make the inside of the hole conductive. To make electrical connection between layers. Examples of the conductive metal include copper, gold, and nickel.
[Example]

Next, examples of the present invention will be described together with comparative examples.
The peel strength was measured by a method based on IPC-TM-650 and NUMBER 2.4.9. However, the lead width was 1 mm and the peel angle was 90 °. Leads were formed by the subtractive method or the semi-additive method. In addition, as an index of heat resistance, a film substrate on which a 1 mm lead is formed is left in an oven at 150 ° C. for 168 hours, taken out to room temperature, and then evaluated for 90 ° peel strength. went.
First, using the obtained two-layer flexible substrate, a 30 μm pitch (line / space = 15/15 μm) comb-teeth test piece was formed by ferric chloride etching by the subtractive method or by the semi-additive method A piece was made.
The etching property was basically confirmed by microscopic observation of the test piece. Further, the insulation resistance value of the HHBT test piece was also measured, and when the resistance value was 10 ⁻⁶ Ω or less, it was determined that there was an etching residue between the leads, and it was determined that the etching property was not good.
The measurement of the HHBT (High Temperature High Humidity Bias Test) test, which is an environmental resistance test, was performed using the above test piece in accordance with JPCA-ET04, applying DC 40 V between terminals under an environment of 85 ° C. and 85% RH, and 1000 hr. Observe resistance. When the resistance became 10 ⁶ Ω or less, it was judged as a short circuit defect, and after 1000 hours, it was judged as acceptable if it was 10 ⁶ Ω or more.
As an index of corrosion, discoloration of the back surface can be mentioned. This was performed by observation of the back surface of the sample after the HHBT test. When significant discoloration was seen, it was judged as bad, and when discoloration was slight, it was judged as acceptable.

A polyimide film having a thickness of 50 μm (product name “Kapton 150EN” manufactured by Toray Diupon Co., Ltd.) is cut into a size of 12 cm × 12 cm, and 20 wt% Ti-5 wt% Cr as the first layer of the base metal layer on one side. A 20 wt% Ti-22 wt% Cr—Ni alloy base metal layer was formed by DC sputtering using a —Ni alloy target (manufactured by Sumitomo Metal Mining). A part of the film formed separately under the same conditions was measured using a transmission electron microscope (TEM: manufactured by Hitachi, Ltd.) to find a film thickness of 20 nm. Using the Cu target (manufactured by Sumitomo Metal Mining) as a second layer on the NiTiCr film, a copper coating layer is formed to a thickness of 200 nm by sputtering and electroplating. A film having a thickness of 8 μm was used as a raw material substrate for evaluation. From this base material, a 1 mm lead for peel strength evaluation and a 30 μm pitch comb-teeth test piece for HHBT test were formed by the subtract method.
The obtained two-layer flexible substrate had an initial peel strength of 580 N / m. The heat-resistant peel strength after leaving in an oven at 150 ° C. for 168 hours was good with no significant change of 556 N / m.
An insulation reliability test was performed on three samples, but no deterioration was observed in any of the samples. Moreover, there was no etching residue and the etching property was good. Furthermore, no change was observed in the corrosion resistance test (discoloration of the back surface of the film after being left in a constant temperature bath at 85 ° C. and 85% RH for 1000 hours).

A 20 wt% Ti-22 wt% Cr—Ni alloy target (manufactured by Sumitomo Metal Mining) was used as the first layer of the base metal layer, and a 20 wt% Ti-22 wt% Cr—Ni alloy base metal layer was formed by DC sputtering. A raw material substrate for evaluation was obtained in the same manner as in Example 1 except that was formed into a film.
A part of the film formed separately under the same conditions was measured using a transmission electron microscope (TEM: manufactured by Hitachi, Ltd.) to find a film thickness of 20 nm. From this base material, a 1 mm lead for peel strength evaluation and a 30 μm pitch comb-teeth test piece for HHBT test were formed by the subtract method.
The initial peel strength of the obtained two-layer flexible substrate was 650 N / m. The heat-resistant peel strength after leaving in an oven at 150 ° C. for 168 hours was as good as 633 N / m with no significant change.
An insulation reliability test was performed on three samples, but no deterioration was observed in any of the samples. Moreover, there was no etching residue and the etching property was good. Furthermore, no change was observed in the corrosion resistance test (discoloration of the back surface of the film after being left in a constant temperature bath at 85 ° C. and 85% RH for 1000 hours).

A 3 wt% Ti-5 wt% Cr—Ni alloy target (manufactured by Sumitomo Metal Mining) was used as the first layer of the base metal layer, and a 3 wt% Ti-5 wt% Cr—Ni alloy base metal layer was formed by DC sputtering. A raw material substrate for evaluation was obtained in the same manner as in Example 1 except that was formed into a film.
A part of the film formed separately under the same conditions was measured using a transmission electron microscope (TEM: manufactured by Hitachi, Ltd.) to find a film thickness of 20 nm. From this base material, a 1 mm lead for peel strength evaluation and a 30 μm pitch comb-teeth test piece for HHBT test were formed by the subtract method.
The initial peel strength of the obtained two-layer flexible substrate was 601 N / m. The heat-resistant peel strength after leaving in an oven at 150 ° C. for 168 hours was good with no significant change of 543 N / m.
An insulation reliability test was performed on three samples, but no deterioration was observed in any of the samples. Moreover, there was no etching residue and the etching property was good. Furthermore, no change was observed in the corrosion resistance test (discoloration of the back surface of the film after being left in a constant temperature bath at 85 ° C. and 85% RH for 1000 hours).

Using a 22 wt% Ti-5 wt% Cr—Ni alloy target (manufactured by Sumitomo Metal Mining) as the first layer of the under metal layer, a 22 wt% Ti-5 wt% Cr—Ni alloy under metal layer is formed by DC sputtering. A raw material substrate for evaluation was obtained in the same manner as in Example 1 except that was formed into a film.
A part of the film formed separately under the same conditions was measured using a transmission electron microscope (TEM: manufactured by Hitachi, Ltd.) to find a film thickness of 20 nm. From this base material, a 1 mm lead for peel strength evaluation and a 30 μm pitch comb-teeth test piece for HHBT test were formed by the subtract method.
The initial peel strength of the obtained two-layer flexible substrate was 620 N / m. The heat-resistant peel strength after leaving in an oven at 150 ° C. for 168 hours was good with no significant change of 576 N / m.
An insulation reliability test was performed on three samples, but no deterioration was observed in any of the samples. Moreover, there was no etching residue and the etching property was good. Furthermore, no change was observed in the corrosion resistance test (discoloration of the back surface of the film after being left in a constant temperature bath at 85 ° C. and 85% RH for 1000 hours).

A 20 wt% Ti-7 wt% Cr—Ni alloy target (manufactured by Sumitomo Metal Mining) was used as the first layer of the under metal layer, and a 20 wt% Ti-7 wt% Cr—Ni alloy under metal layer was formed by DC sputtering. A raw material substrate for evaluation was obtained in the same manner as in Example 1 except that was formed into a film.
A part of the film formed separately under the same conditions was measured using a transmission electron microscope (TEM: manufactured by Hitachi, Ltd.) to find a film thickness of 20 nm. From this base material, a 1 mm lead for peel strength evaluation and a 30 μm pitch comb-teeth test piece for HHBT test were formed by the subtract method.
The initial peel strength of the obtained two-layer flexible substrate was 650 N / m. The heat-resistant peel strength after leaving in an oven at 150 ° C. for 168 hours was good with no significant change of 624 N / m.
An insulation reliability test was performed on three samples, but no deterioration was observed in any of the samples. Moreover, there was no etching residue and the etching property was good. Furthermore, no change was observed in the corrosion resistance test (discoloration of the back surface of the film after being left in a constant temperature bath at 85 ° C. and 85% RH for 1000 hours).

A 20 wt% Ti-15 wt% Cr—Ni alloy target (manufactured by Sumitomo Metal Mining) was used as the first layer of the base metal layer, and a 20 wt% Ti-15 wt% Cr—Ni alloy base metal layer was formed by DC sputtering. A raw material substrate for evaluation was obtained in the same manner as in Example 1 except that the film thickness was changed by changing the sputtering time.
A part of the film formed separately under the same conditions was measured with a transmission electron microscope (TEM: manufactured by Hitachi, Ltd.), and the film thickness was 30 nm. From this base material, a 1 mm lead for peel strength evaluation and a 30 μm pitch comb-teeth test piece for HHBT test were formed by the subtract method.
The initial peel strength of the obtained two-layer flexible substrate was 667 N / m. The heat-resistant peel strength after standing in an oven at 150 ° C. for 168 hours was as good as 641 N / m without any significant change.
An insulation reliability test was performed on three samples, but no deterioration was observed in any of the samples. Moreover, there was no etching residue and the etching property was good. Furthermore, no change was observed in the corrosion resistance test (discoloration of the back surface of the film after being left in a constant temperature bath at 85 ° C. and 85% RH for 1000 hours).

A 5 wt% Ti-10 wt% Cr—Ni alloy target (manufactured by Sumitomo Metal Mining) was used as the first layer of the under metal layer, and a 5 wt% Ti-10 wt% Cr—Ni alloy under metal layer was formed by DC sputtering. A raw material substrate for evaluation was obtained in the same manner as in Example 1 except that the film thickness was changed by changing the sputtering time.
A part of the film formed separately under the same conditions was measured with a transmission electron microscope (TEM: manufactured by Hitachi, Ltd.) to find a film thickness of 25 nm. From this base material, a 1 mm lead for peel strength evaluation and a 30 μm pitch comb-teeth test piece for HHBT test were formed by the subtract method.
The initial peel strength of the obtained two-layer flexible substrate was 642 N / m. The heat-resistant peel strength after leaving in an oven at 150 ° C. for 168 hours was 627 N / m, showing no significant change and good.
An insulation reliability test was performed on three samples, but no deterioration was observed in any of the samples. Moreover, there was no etching residue and the etching property was good. Furthermore, no change was observed in the corrosion resistance test (discoloration of the back surface of the film after being left in a constant temperature bath at 85 ° C. and 85% RH for 1000 hours).

A 13 wt% Ti-10 wt% Cr—Ni alloy target (manufactured by Sumitomo Metal Mining) was used as the first layer of the base metal layer, and a 13 wt% Ti-10 wt% Cr—Ni alloy base metal layer was formed by DC sputtering. A raw material substrate for evaluation was obtained in the same manner as in Example 1 except that the film thickness was changed by changing the sputtering time to a shorter one.
A part of the film formed separately under the same conditions was measured using a transmission electron microscope (TEM: manufactured by Hitachi, Ltd.) to find a film thickness of 20 nm. From this base material, a 1 mm lead for peel strength evaluation and a 30 μm pitch comb-teeth test piece for HHBT test were formed by the subtract method.
The initial peel strength of the obtained two-layer flexible substrate was 635 N / m. The heat-resistant peel strength after leaving in an oven at 150 ° C. for 168 hours was 617 N / m, which was good with no significant change.
An insulation reliability test was performed on three samples, but no deterioration was observed in any of the samples. Moreover, there was no etching residue and the etching property was good. Furthermore, no change was observed in the corrosion resistance test (discoloration of the back surface of the film after being left in a constant temperature bath at 85 ° C. and 85% RH for 1000 hours).

A 10 wt% Ti-10 wt% Cr—Ni alloy target (manufactured by Sumitomo Metal Mining) was used as the first layer of the base metal layer, and a 10 wt% Ti-10 wt% Cr—Ni alloy base metal layer was formed by DC sputtering. A raw material substrate for evaluation was obtained in the same manner as in Example 1, except that the film thickness was changed by increasing the sputtering time.
A part of the film formed separately under the same conditions was measured with a transmission electron microscope (TEM: manufactured by Hitachi, Ltd.) and found to have a thickness of 3 nm. From this base material, a 1 mm lead for peel strength evaluation and a 30 μm pitch comb-teeth test piece for HHBT test were formed by the subtract method.
The initial peel strength of the obtained two-layer flexible substrate was 613 N / m. The heat-resistant peel strength after leaving in an oven at 150 ° C. for 168 hours was good with no significant change of 498 N / m.
An insulation reliability test was performed on three samples, but no deterioration was observed in any of the samples. Moreover, there was no etching residue and the etching property was good. Furthermore, no change was observed in the corrosion resistance test (discoloration of the back surface of the film after being left in a constant temperature bath at 85 ° C. and 85% RH for 1000 hours).

A 10 wt% Ti-10 wt% Cr—Ni alloy target (manufactured by Sumitomo Metal Mining) was used as the first layer of the base metal layer, and a 10 wt% Ti-10 wt% Cr—Ni alloy base metal layer was formed by DC sputtering. A raw material substrate for evaluation was obtained in the same manner as in Example 1, except that the film thickness was changed by increasing the sputtering time.
A part of the film formed separately under the same conditions was measured with a transmission electron microscope (TEM: manufactured by Hitachi, Ltd.) to find a film thickness of 50 nm. From this base material, a 1 mm lead for peel strength evaluation and a 30 μm pitch comb-teeth test piece for HHBT test were formed by the subtract method.
The initial peel strength of the obtained two-layer flexible substrate was 656 N / m. The heat-resistant peel strength after leaving in an oven at 150 ° C. for 168 hours was good with no significant change of 645 N / m.
An insulation reliability test was performed on three samples, but no deterioration was observed in any of the samples. Moreover, there was no etching residue and the etching property was good. Furthermore, no change was observed in the corrosion resistance test (discoloration of the back surface of the film after being left in a constant temperature bath at 85 ° C. and 85% RH for 1000 hours).

In the same manner as in Example 1, a 20 nm thick NiTiCr film was formed. Furthermore, as a second layer, a Cu target (made by Sumitomo Metal Mining) is used to form a copper film layer with a thickness of 1 μm by sputtering, and a film thickness of 8 μm is formed by electroplating. A material was used. From this base material, a 1 mm lead for peel strength evaluation and a 30 μm pitch comb-teeth test piece for HHBT test were formed by the subtract method.
The initial peel strength of the obtained two-layer flexible substrate was 615 N / m. The heat-resistant peel strength after leaving in an oven at 150 ° C. for 168 hours was good with no significant change of 570 N / m.
An insulation reliability test was performed on three samples, but no deterioration was observed in any of the samples. Moreover, the etching property was also good. Furthermore, no change was observed in the corrosion resistance test (discoloration of the back surface of the film after being left in a constant temperature bath at 85 ° C. and 85% RH for 1000 hours).

In the same manner as in Example 1, a 20 nm thick NiTiCr film was formed. Further, as a second layer, a Cu target (made by Sumitomo Metal Mining) was used to form a copper coating layer up to 8 μm by sputtering, and a 1 mm lead for peel strength evaluation by subtracting from this substrate. A 30 μm pitch comb test piece for HHBT test was formed.
The obtained two-layer flexible substrate had an initial peel strength of 630 N / m. The heat-resistant peel strength after leaving in an oven at 150 ° C. for 168 hours was good with no significant change of 545 N / m.
An insulation reliability test was performed on three samples, but no deterioration was observed in any of the samples. Moreover, the etching property was also good. Furthermore, no change was observed in the corrosion resistance test (discoloration of the back surface of the film after being left in a constant temperature bath at 85 ° C. and 85% RH for 1000 hours).

In the same manner as in Example 1, a 20 nm thick NiTiCr film was formed. Furthermore, as a second layer, a Cu target layer (made by Sumitomo Metal Mining) was used to form a copper film layer up to 500 nm by sputtering, and a 1 mm lead for peel strength evaluation from this substrate, and HHBT A 30 μm pitch comb test piece for testing was formed by thickening to 8 μm by a semi-additive method.
The initial peel strength of the obtained two-layer flexible substrate was 610 N / m. The heat-resistant peel strength after leaving in an oven at 150 ° C. for 168 hours was as good as 510 N / m with no significant change.
An insulation reliability test was performed on three samples, but no deterioration was observed in any of the samples. Moreover, the etching property was also good. Furthermore, no change was observed in the corrosion resistance test (discoloration of the back surface of the film after being left in a constant temperature bath at 85 ° C. and 85% RH for 1000 hours).
(Comparative Example 1)

A 20 wt% Ti-4 wt% Cr—Ni alloy target (manufactured by Sumitomo Metal Mining) was used as the first layer of the under metal layer, and a 20 wt% Ti-4 wt% Cr—Ni alloy under metal layer was formed by DC sputtering. A raw material substrate for evaluation was obtained in the same manner as in Example 1 except that was formed into a film.
A part of the film formed separately under the same conditions was measured using a transmission electron microscope (TEM: manufactured by Hitachi, Ltd.) to find a film thickness of 20 nm. From this base material, a 1 mm lead for peel strength evaluation and a 30 μm pitch comb-teeth test piece for HHBT test were formed by the subtract method.
The initial peel strength of the obtained two-layer flexible substrate was 640 N / m. The heat-resistant peel strength after standing in an oven at 150 ° C. for 168 hours was greatly reduced to 380 N / m.
An insulation reliability test was performed on three samples, but no deterioration was observed in any of the samples. Moreover, there was no etching residue and the etching property was good. Furthermore, no change was observed in the corrosion resistance test (discoloration of the back surface of the film after being left in a constant temperature bath at 85 ° C. and 85% RH for 1000 hours).
(Comparative Example 2)

A 20 wt% Ti-24 wt% Cr-Ni alloy target (manufactured by Sumitomo Metal Mining Co., Ltd.) is used as the first layer of the base metal layer, and a 20 wt% Ti-24 wt% Cr-Ni alloy base metal layer is formed by DC sputtering. A raw material substrate for evaluation was obtained in the same manner as in Example 1 except that was formed into a film.
A part of the film formed separately under the same conditions was measured using a transmission electron microscope (TEM: manufactured by Hitachi, Ltd.) to find a film thickness of 20 nm. From this base material, a 1 mm lead for peel strength evaluation and a 30 μm pitch comb-teeth test piece for HHBT test were formed by the subtract method.
The initial peel strength of the obtained two-layer flexible substrate was 655 N / m. The heat-resistant peel strength after leaving in an oven at 150 ° C. for 168 hours was as good as 623 N / m with no significant change.
However, although an insulation reliability test was performed on three samples, the base metal layer could not be etched by salt iron etching in two samples, and leads with a pitch of 30 μm could not be formed. Further, in the corrosion resistance test (discoloration of the back side of the film after being left in a constant temperature bath at 85 ° C. and 85% RH) for 1000 hours, no change was observed on the back side of the film.
(Comparative Example 3)

Using a 1 wt% Ti-10 wt% Cr-Ni alloy target (manufactured by Sumitomo Metal Mining) as the first layer of the underlayer metal layer, a 1 wt% Ti-10 wt% Cr-Ni alloy underlayer metal layer is formed by DC sputtering. A raw material substrate for evaluation was obtained in the same manner as in Example 1 except that was formed into a film.
A part of the film formed separately under the same conditions was measured using a transmission electron microscope (TEM: manufactured by Hitachi, Ltd.) to find a film thickness of 20 nm. From this base material, a 1 mm lead for peel strength evaluation and a 30 μm pitch comb-teeth test piece for HHBT test were formed by the subtract method.
The initial peel strength of the obtained two-layer flexible substrate was 608 N / m. The heat-resistant peel strength after being left in an oven at 150 ° C. for 168 hours was good with no significant change of 432 N / m.
However, the insulation reliability test was performed on 3 samples. However, in 2 samples, the resistance became 10 ⁶ Ω or less, resulting in a short circuit failure. On the other hand, the etching property was good. Further, in the corrosion resistance test (discoloration of the back side of the film after being left in a constant temperature bath at 85 ° C. and 85% RH) for 1000 hours, discoloration was observed in many parts on the back side of the film.
(Comparative Example 4)

A 24 wt% Ti-10 wt% Cr-Ni alloy target (manufactured by Sumitomo Metal Mining Co., Ltd.) was used as the first layer of the base metal layer, and a 24 wt% Ti-10 wt% Cr-Ni alloy base metal layer was formed by DC sputtering. A raw material substrate for evaluation was obtained in the same manner as in Example 1, except that the film thickness was changed by changing the sputtering time to be shorter than that in Example 9.
A part of the film formed separately under the same conditions was measured with a transmission electron microscope (TEM: manufactured by Hitachi, Ltd.) and found to have a thickness of 2 nm. From this base material, a 1 mm lead for peel strength evaluation and a 30 μm pitch comb-teeth test piece for HHBT test were formed by the subtract method.
The initial peel strength of the obtained flexible substrate was 645 N / m. The heat-resistant peel strength after leaving in an oven at 150 ° C. for 168 hours was good with no significant change of 625 N / m.
However, an insulation reliability test was performed on three samples, and in all cases, the resistance became 10 ⁶ Ω or less, resulting in a short circuit failure. On the other hand, the etching property was good.
Further, in the corrosion resistance test (discoloration of the back side of the film after being left in a constant temperature bath at 85 ° C. and 85% RH) for 1000 hours, discoloration was observed in many portions on the back side of the film.
(Comparative Example 5)

A 20 wt% Ti-10 wt% Cr—Ni alloy target (manufactured by Sumitomo Metal Mining) was used as the first layer of the under metal layer, and a 20 wt% Ti-10 wt% Cr—Ni alloy under metal layer was formed by DC sputtering. A raw material substrate for evaluation was obtained in the same manner as in Example 1 except that the film thickness was changed by making the sputtering time longer than that in Example 10.
A part of the film formed under the same conditions was measured with a transmission electron microscope (TEM: manufactured by Hitachi, Ltd.), and the film thickness was 53 nm. From this base material, a 1 mm lead for peel strength evaluation and a 30 μm pitch comb-teeth test piece for HHBT test were formed by the subtract method.
The initial peel strength of the obtained two-layer flexible substrate was 650 N / m. The heat-resistant peel strength after being left in an oven at 150 ° C. for 168 hours was as good as 618 N / m with no significant change.
In the etching test, in 2 of the 3 samples, the base metal layer could not be etched by salt iron etching, and leads with a pitch of 30 μm could not be formed.
Furthermore, although the insulation reliability test was done about 3 samples, deterioration was not recognized by all.
Further, no change was observed in the corrosion resistance test (discoloration of the film back surface after being left in a constant temperature bath at 85 ° C. and 85% RH for 1000 hours).
The results of the above examples and comparative examples are summarized in Table 1.

As described above, according to the method for producing a two-layer flexible substrate of the present invention, a base metal layer is formed directly on at least one surface of the insulator film without using an adhesive, and a desired thickness is formed on the base metal layer. In the two-layer flexible substrate for forming the copper conductor layer, the titanium film is formed on the insulator film by a thickness of 3 to 50 nm by a dry plating method, the titanium ratio is 3 to 22% by weight, and the chromium ratio is 5 to 5%. A base metal layer mainly containing a nickel-titanium-chromium alloy having a nickel content of 22% by weight, and a copper film layer having a thickness of 10 nm to 35 μm can be formed on the base metal layer. According to the two-layer flexible substrate, since the base metal layer contains titanium, it is possible to prevent a decrease in heat-resistant peel strength, and at the same time, because chromium is contained, Since the corrosion resistance and the insulation reliability can be improved, by using the two-layer flexible substrate, a highly reliable narrow width and narrow pitch wiring portion having a wiring portion having high adhesion and corrosion resistance and no defects. Since the flexible wiring board with it can be obtained efficiently, the effect is very large.

Claims (6)

In a two-layer flexible substrate in which a base metal layer is directly formed on at least one surface of an insulator film without using an adhesive, and then a copper coating layer is formed on the base metal layer.
The base metal layer is formed by a dry plating method and mainly contains a nickel-titanium-chromium alloy having a titanium ratio of 3 to 22% by weight, a chromium ratio of 5 to 22% by weight and the balance being nickel. A two-layer flexible substrate comprising a base metal layer of 3 to 50 nm.   2. The two-layer flexible substrate according to claim 1, wherein the copper coating layer formed on the base metal layer has a thickness of 10 nm to 35 μm.   The insulator film is a resin film selected from a polyimide film, a polyamide film, a polyester film, a polytetrafluoroethylene film, a polyphenylene sulfide film, a polyethylene naphthalate film, and a liquid crystal polymer film. The two-layer flexible substrate according to claim 1 or 2, characterized in that:   In a method for manufacturing a two-layer flexible substrate, in which a base metal layer is directly formed on at least one surface of an insulator film without using an adhesive, and then a copper coating layer is formed on the base metal layer, A base metal layer of nickel-titanium-chromium alloy having a titanium ratio of 3 to 22 wt%, a chromium ratio of 5 to 22 wt% and the balance being nickel is formed by dry plating, A method for producing a two-layer flexible substrate, comprising forming a copper coating layer on a base metal layer.   5. The method for producing a two-layer flexible substrate according to claim 4, wherein after the copper coating layer is formed by a dry plating method, a copper coating layer is further formed on the copper coating layer by a wet plating method. 6. The method for manufacturing a two-layer flexible substrate according to claim 4, wherein the dry plating method is any one of a vacuum deposition method, a sputtering method, and an ion plating method.