TWI386136B - Copper foil for printed wiring board - Google Patents

Description

Copper foil for printed wiring board

The present invention relates to a copper foil for a printed wiring board, and more particularly to a copper foil for a flexible printed wiring board.

Printed wiring boards have made great progress in this half century, and now even progress to almost all electronic machines use printed wiring boards. With the increase in the demand for miniaturization and high performance of electronic devices in recent years, the high-density encapsulation of mounted components or the high-frequency of signals have progressed. Therefore, the printed wiring board is required to be finer (decrease) in the conductor pattern. Pitching, fine pitch or high frequency correspondence.

In general, a printed wiring board is manufactured by a process in which a copper-clad laminate is formed on a copper foil surface after an insulating substrate is formed as a copper-clad laminate. Therefore, the copper foil for a printed wiring board is required to have adhesion to an insulating substrate or etching property.

In order to improve the adhesion to the insulating substrate, in general, a surface treatment called roughening treatment for forming irregularities on the surface of the copper foil is performed. For example, in the M surface (rough surface) of the electrolytic copper foil, a copper sulfate acid plating bath is used, and copper is electrodeposited in a dendritic or small spherical shape to form fine irregularities by an anchoring effect. A method to improve adhesion. In general, after the roughening treatment, in order to further enhance the subsequent characteristics, chromate treatment or treatment with a decane coupling agent is performed.

A method of forming a metal or alloy layer of tin, chromium, copper, iron, cobalt, zinc, nickel or the like on the surface of the copper foil is also known.

In the Japanese Patent Publication No. 2000-340911, it is described that a metal chromium layer is formed on the surface of a copper foil for a printed wiring board by vapor deposition to improve the adhesion strength between the substrate and the copper foil.

Japanese Patent Publication No. 2007-207812 discloses that a nickel-chromium alloy layer is formed on the surface of a copper foil, and an oxide layer having a predetermined thickness is formed on the surface of the alloy layer, even if the surface of the copper layer is smooth. Under the condition that the anchoring effect is weak, the adhesion to the resin substrate can be greatly improved. Then, a copper foil for a printed wiring board is formed by vapor-depositing a nickel-chromium alloy layer having a thickness of 1 to 100 nm, and a chromium oxide layer having a thickness of 0.5 to 6 nm is formed on the surface of the alloy layer. The average surface roughness Rz of the outermost surface is 2.0 μm or less in accordance with JIS.

In JP-A-2006-222185, it is described that, in the surface-treated copper foil for a polyimide-based flexible copper-clad laminate, it is provided by:

(1) a nickel layer or/and a nickel alloy layer containing a nickel content of 0.03 to 3.0 mg/dm ² ;

(2) a chromate layer containing a chromium content of 0.03 to 1.0 mg/dm ² ;

(3) a chromium layer or/and a chromium alloy layer containing a chromium content of 0.03 to 1.0 mg/dm ² ;

(4) containing an amount of nickel and / or nickel alloy layer and above 0.03 ~ 3.0mg / dm ² of nickel layer, chromium containing an amount of 0.03 ~ 1.0mg / dm ² of a chromate layer;

(5) containing an amount of nickel and / or nickel alloy layer and above 0.03 ~ 3.0mg / dm ² of nickel layer, chromium containing an amount of 0.03 ~ 1.0mg / dm ² of a chromium layer or / and the nichrome layer;

As a surface treatment layer, it is possible to obtain a polyimide-based flexible copper-clad having high peel strength with respect to a polyimide-based resin layer, excellent insulation reliability, etching characteristics at the time of pattern formation, and bending characteristics. Copper foil for laminates. If the thickness of the surface treatment layer is estimated from the above-described amount of nickel or chromium, it is a μm level. Moreover, in the examples, the case where the surface treatment layer was provided by electroplating was described.

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2000-340911

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2007-207812

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2006-222185

The method of improving the adhesion by the roughening process is not advantageous for the formation of a fine line. In other words, if the conductor spacing is narrowed by the fine pitch, there is a fear that the roughening treatment portion remains on the insulating substrate after the circuit is formed by etching, and the insulation is deteriorated. If all the roughened surfaces are to be etched in order to prevent such a situation, a considerable etching time is required and a predetermined line width cannot be maintained.

In the method of providing a nickel layer or a nickel-chromium alloy layer on the surface of a copper foil, there is still a large room for improvement in the substrate characteristics of the adhesion to the insulating substrate. In Patent Document 2, it is described that by providing a nickel-chromium alloy layer, even if the surface of the copper foil is smooth, the adhesion to the resin substrate can be improved, but there is still room for improvement.

A higher adhesion can be obtained by the method of providing a chromium layer on the surface of the copper foil. However, there is room for improvement in the etchability of the chrome layer. That is, although the chrome layer has a higher adhesion to the nickel layer, the etching property of the chrome is inferior, and after the etching treatment for forming the conductor pattern, the "etching residue" in which the chrome remains on the surface of the insulating substrate is likely to occur. Further, there is also a problem that the heat resistance is insufficient, and the adhesion between the insulating substrate and the insulating substrate is remarkably lowered after being placed in a high temperature environment. Therefore, in the case where the fine pitch of the printed wiring board continues to progress, it is difficult to call it a feasible method. On the other hand, the chromate layer still has room for improvement in adhesion.

In the provision described in Patent Document 3, a chromium layer or/and a chromium alloy having a chromium content of 0.03 to 1.0 mg/dm ² is contained on a nickel layer or/and a nickel alloy layer containing a nickel content of 0.03 to 3.0 mg/dm ² . Although the layer is used as a surface treatment layer, although a relatively high adhesion and etching property can be obtained, there is still room for improvement in characteristics.

In view of the above, an object of the present invention is to provide a copper foil for a printed wiring board which is excellent in adhesion to an insulating substrate and etching property, and is suitable for fine pitch. Moreover, another object of the present invention is to provide a method for producing such a copper foil for a printed wiring board.

In the past, in general understanding, if the coating layer was made thinner, the strength would be lowered. However, the inventors of the present invention have focused on the results of the review and found that when the nickel layer and the chromium layer are uniformly disposed on the surface of the copper foil substrate in a very thin thickness of the nanometer layer, an excellent insulating substrate can be obtained. The closeness. By making the thickness extremely thin, the amount of chromium having a low etching property is reduced, and the coating layer is uniform, which is advantageous for etching property.

In one aspect of the invention, which is based on the above findings, the copper foil for a printed wiring board comprises a copper foil substrate and a coating layer covering at least a portion of the surface of the copper foil substrate, wherein:

(1) The coating layer is composed of a nickel layer and a chromium layer which are sequentially laminated from the surface of the copper foil substrate;

(2) in the coating layer, chromium is present in an amount of 15 to 210 μg/dm ² and nickel is present in an amount of 15 to 440 μg/dm ² ;

(3) When the cross section of the fracture layer is observed using a transmission electron microscope, the maximum thickness is 0.5 to 5 nm, and the minimum thickness is 80% or more of the maximum thickness.

In one embodiment of the copper foil for a printed wiring board of the present invention, the coating amount of chromium is 18 to 150 μg/dm ² , and the coating amount of nickel is 20 to 195 μg/dm ² .

In another embodiment of the copper foil for a printed wiring board of the present invention, the amount of chromium coating is 30 to 100 μg/dm ² , and the amount of nickel coating is 40 to 180 μg/dm ² .

In still another embodiment of the copper foil for a printed wiring board of the present invention, the copper foil substrate is a rolled copper foil.

In still another embodiment of the copper foil for a printed wiring board of the present invention, the printed wiring board is a flexible printed wiring board.

In still another embodiment of the copper foil for a printed wiring board of the present invention, the polyaminic acid solution of the polyimide precursor is applied to the coating layer so that the dried body is 25 μm, and is subjected to air. The polyimine was prepared by a drier imidization process at 350 ° C for 30 minutes in a high-temperature heating furnace with a nitrogen flow rate of 10 L/min using a dryer at 130 ° C for 30 minutes. The film was placed on the coating layer, and then placed in a high-temperature environment at a temperature of 150 ° C in an air atmosphere for 168 hours, and then the polyimide film was peeled off from the coating layer according to the 180° peeling method (JIS C 6471 8.1). When the cross section of the coating layer is observed through a transmission electron microscope, the maximum thickness is 0.5 to 5 nm, and the minimum thickness is 70% or more of the maximum thickness.

In still another embodiment of the copper foil for a printed wiring board of the present invention, atomic concentration (%) of total chromium and oxygen in the depth direction (x: unit nm) obtained by analyzing XPS from the surface in the depth direction When f(x) and g(x) are respectively set, 0.6 ≦∫f(x)dx/∫g(x)dx≦2.2 is satisfied in the interval [1.0; 2.5].

In still another embodiment of the copper foil for a printed wiring board according to the present invention, the atomic concentration of the metal chromium and the chromium oxide obtained in the depth direction (x: unit nm) obtained by analyzing the XPS from the surface in the depth direction is used ( When %) is set to f ₁ (x) and f ₂ (x), respectively, in the interval [0; 1.0], 0.1≦∫f ₁ (x)dx/∫f ₂ (x)dx≦1.0, interval [1.0] is satisfied. ; 2.5], satisfying 0.8≦∫f ₁ (x)dx/∫f ₂ (x)dx≦2.0.

In still another embodiment of the copper foil for a printed wiring board of the present invention, the atomic concentration (%) of chromium in the depth direction (x: unit nm) obtained by analyzing XPS from the surface in the depth direction is f. (x), the atomic concentration (%) of oxygen is set to g(x), the atomic concentration (%) of copper is h(x), and the atomic concentration (%) of nickel is set to i(x), the atomic concentration of carbon When (%) is set to j(x), 区间h(x)dx/(∫f(x)dx+∫g(x)dx+∫h(x)dx+∫i(x) in the interval [0;1.0] Dx+∫j(x)dx) is 1.0% or less.

According to still another aspect of the present invention, a method for producing a copper foil for a printed wiring board, comprising: coating at least a portion of a surface of a copper foil substrate with a nickel layer having a thickness of 0.2 to 5.0 nm by sputtering; And a step of a chromium layer having a thickness of 0.2 to 3.0 nm.

A still further aspect of the present invention is a copper clad laminate comprising the copper foil of the present invention.

In one embodiment of the copper clad laminate according to the present invention, the copper foil is bonded to the polyimine.

A still further aspect of the present invention is a printed wiring board comprising the copper clad laminate of the present invention as a material.

According to the present invention, it is possible to obtain a copper foil for a printed wiring board which is excellent in both adhesiveness and etching property with an insulating substrate.

Copper foil substrate

The form of the copper foil base material which can be used in the present invention is not particularly limited, but a form of a rolled copper foil or an electrolytic copper foil can be typically used. In general, an electrolytic copper foil is produced by electroplating copper on a titanium or stainless steel drum from a copper sulfate plating bath, and the rolled copper foil is produced by repeating plastic working and heat treatment using a calender roll. The use of bendability is mostly suitable for rolling copper foil.

As a material of the copper foil substrate, in terms of the conductor pattern of the printed wiring board, in addition to the so-called high-purity copper of so-called perfect copper (TPC) or oxygen-free copper (OFC) In addition, for example, a copper alloy to which tin-coated copper, silver-coated copper, chromium, zirconium or magnesium is added may be used, and a copper alloy such as nickel or tantalum such as Corson Alloy may be added. In addition, the term "copper foil" as used in this specification also covers copper alloy foil when used alone.

The thickness of the copper foil substrate which can be used in the present invention is not particularly limited as long as it is appropriately adjusted to a thickness suitable for a printed wiring board. For example, the thickness of the copper foil base material can be set to about 5 to 100 μm. However, when it is intended to form a fine pattern, it is 30 μm or less, preferably 20 μm or less, and typically about 10 to 20 μm.

The copper foil substrate used in the present invention is preferably not subjected to roughening treatment. In the past, it has been conventionally applied to the surface to leave irregularities of μm level on the surface, to perform surface roughening treatment, and to have adhesion to the resin by a physical anchoring effect. On the other hand, however, a smooth metal foil is considered to be preferable in terms of fine pitch or high-frequency electrical characteristics because the condition of the roughened metal foil acts in an unfavorable direction. Moreover, since the roughening process is omitted, there is also an effect of improving economy and productivity. Therefore, the metal foil used in the present invention is a metal foil which has not been subjected to special roughening treatment.

2. Cover layer

At least a portion of the surface of the copper foil substrate is sequentially coated with a nickel layer and a chromium layer. The nickel layer and the chromium layer constitute a coating film. The covering portion is not particularly limited, but generally, it is a portion to be placed next to the insulating substrate as a covering portion. The adhesion between the insulating substrate and the insulating substrate is improved by the presence of the coating layer. In general, when placed in a high-temperature environment, the adhesion between the copper foil and the insulating substrate tends to decrease, which is considered to be caused by a phenomenon in which copper is thermally diffused on the surface and reacts with the insulating substrate. In the present invention, by disposing a nickel layer having excellent copper diffusion preventing effect on the copper foil base material in advance, heat diffusion of copper can be prevented. Moreover, by providing a chromium layer which is more excellent in adhesion to the insulating layer between the nickel layer and the insulating layer, the adhesion to the insulating substrate can be further improved. Since the thickness of the chromium layer can be made thin by the presence of the nickel layer, it is possible to alleviate the adverse effect on the etching property. Further, the term "adhesiveness" as used in the present invention means, in addition to the adhesion in the normal state, the adhesion (heat resistance) after being placed at a high temperature and the adhesion (moisture resistance) after being placed under a high humidity. .

In the copper foil for a printed wiring board of the present invention, the coating layer is extremely thin and uniform in thickness. With such a configuration, the reason why the adhesion to the insulating substrate is improved is not clear, but it is presumed that the adhesion between the resin and the resin is excellent as the outermost surface of the nickel coating layer. Since the chromium single-layer coating film is used, even after high-temperature heat during the imidization (about 350 ° C for several hours), a single-layer coating film structure having high adhesion is maintained. Further, it is generally considered that the coating layer is made extremely thin, and the use amount of chromium is reduced by the two-layer structure of nickel and chromium, thereby improving the etching property.

Specifically, the coating layer of the present invention has the following constitution.

(1) Identification of chromium and nickel coatings

In the present invention, at least a portion of the surface of the copper foil material is sequentially coated with a nickel layer and a chromium layer. For the identification of such coating layers, a surface analysis device such as XPS or AES can be used to perform argon sputtering from the surface layer, perform chemical analysis in the depth direction, and identify the nickel layer and the chromium layer by the presence of respective detection peaks. Further, the order of the coatings can be confirmed from the positions of the respective detection peaks.

(2) Adhesion amount

On the other hand, since these nickel layers and chromium layers are very thin, it is difficult to make accurate thickness evaluation by XPS and AES. Therefore, in the invention of the present application, the thickness of the nickel layer and the chromium layer is evaluated in the same manner as in Patent Document 3 by the weight of the coated metal per unit area. In the coating layer of the present invention, chromium is present in an amount of 15 to 210 μg/dm ² and nickel is present in an amount of 15 to 440 μg/dm ² . When chromium is less than 15μg / ² when dm, sufficient peel strength can not be obtained when Cr exceeds 210μg / dm ^2, then the etching resistance may tend to exhibit significant reduction of. When the nickel is less than 15 μg/dm ² , sufficient peel strength cannot be obtained, and when the nickel exceeds 440 μg/dm ² , the etching property tends to be remarkably lowered. The coating amount of chromium is preferably from 18 to 150 μg/dm ² , more preferably from 30 to 100 μg/dm ² , and the coating amount of nickel is preferably from 20 to 195 μg/dm ² , more preferably from 40 to 180 μg/dm ² , typically 40 to 100 μg/dm ² .

(3) Observation using a transmission electron microscope (TEM)

When the cross section of the coating layer of the present invention is observed by a transmission electron microscope, the maximum thickness is 0.5 nm to 5 nm, preferably 1 to 4 nm, and the minimum thickness is 80% or more of the maximum thickness, preferably 85% or more. A coating with very few deviations. This is because when the thickness of the coating layer is less than 0.5 nm, the peel strength is deteriorated in the heat resistance test and the moisture resistance test, and when the thickness exceeds 5 nm, the etching property is lowered. When the minimum value of the thickness is 80% or more of the maximum value, the thickness of the coating layer is extremely stable, and there is almost no change after the heat resistance test. In the observation by TEM, it is difficult to find a clear boundary between the nickel layer and the chromium layer in the coating layer, and it looks like a single layer (refer to FIG. 3). According to the findings of the present inventors, it is considered that the coating layer found by TEM observation is a layer mainly composed of chromium, and it is also considered that a nickel layer exists on the side of the copper foil substrate. Therefore, in the present invention, the thickness of the coating layer at the time of TEM observation is defined as the thickness of the coating film which looks like a single layer. Among them, although there may be places where the boundary of the coating layer is not obvious depending on the observation, such observation is excluded from the measurement of the thickness. With the constitution of the present invention, since the diffusion of copper is suppressed, it is considered to have a stable thickness. The copper foil of the present invention, followed by the polyimide film, even after undergoing a heat resistance test (placement at a high temperature of 150 ° C under a high temperature atmosphere for 168 hours) and after the resin is peeled off, the coating layer The thickness is hardly changed, and the following criteria can be achieved: the maximum thickness is 0.5 to 5.0 nm, and even the minimum thickness is 70% or more of the maximum thickness, preferably 80%.

(4) Oxidation state of the surface of the coating layer

First, if it is desired to increase the adhesion strength, it is preferable that the internal copper is not diffused in the outermost surface of the coating layer (the range from 0 to 1.0 nm in the surface). Therefore, in the copper foil for a printed wiring board of the present invention, the atomic concentration (%) of chromium in the depth direction (x: unit nm) from the surface obtained by XPS is f(x), and the atomic concentration of oxygen is used. (%) is g(x), the atomic concentration (%) of copper is h(x), the atomic concentration (%) of nickel is i(x), and the atomic concentration (%) of carbon is set to In the case of j(x), in the interval [0; 1.0], it is preferable that ∫h(x)dx/(∫f(x)dx+∫g(x)dx+∫h(x)dx+∫i(x) Dx+∫j(x)dx) is set to 1.0% or less.

Further, in the outermost surface of the coating layer, chromium is present in the form of metal chromium and chromium oxide. However, from the viewpoint of preventing the diffusion of copper inside and securing the adhesion, the chromium is preferably in the form of metal chromium. If good etching properties are desired, it is preferably chromium oxide. Therefore, in order to achieve the coexistence of the etching property and the adhesion force, the atomic concentration (%) of the metal chromium and chromium oxide in the depth direction (x: unit nm) obtained by analyzing the XPS from the surface in the depth direction is set to When f ₁ (x) and f ₂ (x), in the interval [0; 1.0], it is preferable to satisfy 0.1 ≦∫ f ₁ (x) dx / ∫ f ₂ (x) dx ≦ 1.0.

On the other hand, among the depths of 1.0 to 2.5 nm directly below the outermost surface of the coating layer, it is preferred that the oxygen concentration is small and the chromium exists in a metallic state. This is because when chromium is present in a metal state as compared with the oxidized state, its ability to prevent internal copper diffusion is high, and heat resistance can be improved. However, from the viewpoint of strictly controlling the cost associated with oxygen, or having a certain degree of oxygen on the outermost surface and etching property when chromium is oxidized, it is not practical to completely eliminate oxygen in the lower layer. Therefore, in the copper foil for a printed wiring board of the present invention, the atomic concentration (%) of the total chromium and oxygen in the depth direction (x: unit nm) obtained by analyzing the XPS from the surface in the depth direction is respectively set to f ( In the case of x) and g(x), in the interval [1.0; 2.5], it is preferable to satisfy 0.6≦∫f(x)dx/∫g(x)dx≦2.2, and more preferably to satisfy 0.8≦∫f(x). ) dx / ∫ g (x) dx ≦ 1.8, typically satisfying 1.0 ≦∫ f (x) dx / ∫ g (x) dx ≦ 1.5. Further, in the interval [1.0; 2.5], 0.8 ≦∫ f ₁ (x) dx / ∫ f ₂ (x) dx ≦ 2.0 is preferable.

The chromium concentration and the oxygen concentration were calculated from the highest peak intensities of the Cr2p orbitals and the O1s orbitals obtained by analyzing the XPS from the surface to the depth direction. Further, the distance in the depth direction (x: unit nm) is a distance calculated from the sputtering rate in terms of SiO ₂ . The chromium concentration is the sum of the chromium oxide concentration and the metal chromium concentration, and can be separated into a chromium oxide concentration and a metal chromium concentration and then analyzed.

3. The method for preparing copper foil of the present invention

The copper foil for a printed wiring board of the present invention can be formed by a sputtering method. That is, the sputtering method may be used to sequentially coat at least a portion of the surface of the copper foil substrate with a thickness of 0.2 to 5.0 nm, preferably 0.25 to 2.5 nm, more preferably 0.5 to 2.0 nm. The layer and the chromium layer having a thickness of 0.2 to 3.0 nm, preferably 0.25 to 2.0 nm, more preferably 0.5 to 1.5 nm, are produced. When such an extremely thin coating film is laminated by electroplating, the thickness may be inconsistent, and after the heat resistance and moisture resistance test, the peel strength may be easily lowered.

The thickness referred to herein is not the thickness determined by the XPS or TEM described above, but the thickness derived from the film formation speed of the sputtering. The film formation rate under specific sputtering conditions is 1 μm (1000 nm) or more, which can be measured from the relationship between the sputtering time and the sputtering thickness. If the film formation speed under the sputtering conditions can be measured, the sputtering time can be set according to the required thickness. Further, the sputtering may be carried out in any of continuous or batch, and the coating layer may be laminated on the thickness specified in the present invention. As the sputtering method, a DC magnetron sputtering method can be cited.

4. Manufacturing of printed wiring boards

A printed wiring board (PWB) can be manufactured in accordance with a conventional method using the copper foil of the present invention. A manufacturing example of a printed wiring board is shown below.

First, a copper clad laminate is produced by bonding a copper foil and an insulating substrate. The insulating substrate on which the copper foil is laminated is not particularly limited as long as it has characteristics suitable for the printed wiring board. For example, for a rigid printed wiring board, a paper substrate phenol resin or a paper substrate epoxy resin can be used. , synthetic fiber cloth substrate epoxy resin, glass cloth ‧ paper composite substrate epoxy resin, glass cloth ‧ glass non-woven composite substrate epoxy resin and glass cloth substrate epoxy resin; in flexible printed wiring board ( For FPC), a polyester film or a polyimide film can be used.

In the case of a rigid printed wiring board, the resin is impregnated into a substrate such as a glass cloth to prepare a prepreg in which the resin is hardened to a semi-hardened state. This can be carried out by heating and pressurizing the prepreg and the surface of the coating layer having the copper foil.

In the case of a flexible printed wiring board (FPC), an epoxy-based or propylene-based adhesive may be used to bond the surface of the coating layer (three-layer structure) of the polyimide film to the polyimide film and the polyester film. Moreover, as a method (two-layer structure) which does not use an adhesive agent, the polyimine varnish (poly amide varnish) which is a precursor of a polyimide polyimide film is apply|coated to the coating layer which has a copper foil. a method of casting a yttrium imidization by heating, or coating a thermoplastic polyimide on a polyimide film, and laminating a coating layer having a copper foil on the polyimide film. The surface is then subjected to a laminate method of heating and pressurization. Among the casting methods, a method of previously coating an anchor coating material such as thermoplastic polyimine before applying a polyimide varnish is also effective.

The effect of the copper foil of the present invention is remarkably exhibited when the FPC is produced by a casting method. That is, when the copper foil and the resin are bonded without using an adhesive, the adhesion of the copper foil to the resin may be particularly required, however, because the copper foil of the present invention is bonded to the resin, particularly to the polyimide. It is excellent in properties and is therefore suitable for the manufacture of copper-clad laminates using the casting method.

The copper clad laminate of the present invention can be used for various printed wiring boards (PWB), and is not particularly limited. For example, from the viewpoint of the number of layers of the conductor pattern, it can be applied to single-sided PWB, double-sided PWB, and multi-layer PWB ( Three or more layers can be applied to rigid PWB, flexible PWB (FPC), and rigid flexible PWB from the viewpoint of the type of insulating substrate material.

The process for producing a printed wiring board from a copper clad laminate can be carried out by a method known to those skilled in the art. For example, it can be applied as a necessary part of the conductor pattern on the copper foil surface of the copper clad laminate. The etching resist is formed by spraying an etching solution on the copper foil surface to remove an unnecessary copper foil to form a conductor pattern, and then peeling off and removing the etching stopper to expose the conductor pattern.

[Examples]

The embodiments of the present invention are shown in the following, which are intended to provide a better understanding of the present invention and are not intended to limit the invention.

example 1

As the copper foil base material, a rolled copper foil (C1100 made of Nippon Minerals Co., Ltd.) having a thickness of 18 μm and a non-roughened foil of an electrolytic copper foil were prepared. The surface roughness (Rz) of the rolled copper foil and the electrolytic copper foil was 0.7 μm and 1.5 μm, respectively.

On one side of the copper foil, a thin oxide film adhering to the surface of the copper foil substrate was removed in advance by reverse sputtering in accordance with the following conditions, and a nickel layer and a chromium layer were sequentially formed. The thickness of the coating layer can be changed by adjusting the film formation time. Also, in several cases, a nickel-chromium alloy layer was formed.

‧ Device: Batch type sputtering device (manufactured by ULVAC, Inc., type MNS-6000)

‧ Reaching vacuum: 1.0×10 ^-5 Pa

‧ Sputtering pressure: 0.2Pa

‧ Reverse sputtering power: 100W

‧ Target:

Nickel layer = nickel (purity 3N)

Chromium layer = chromium (purity 3N)

Nickel-chromium alloy layer = nickel: 80% by mass, chromium 20% by mass of nickel

One chromium alloy (Comparative Example No. 9)

‧ Sputtering power: 50W

‧ Film formation rate: The thickness of each target was about 2 μm for a certain period of time, and the thickness was measured with a 3-dimensional measuring device to calculate the sputtering rate per unit time. (nickel: 2.73 nm/min, chromium: 2.82 nm/min)

The polyimide film was attached to the copper foil provided with the coating layer in accordance with the following procedure.

(1) U-lacquer A (polyimine varnish) manufactured by Ube Industries Co., Ltd. was applied to a copper foil of 7 cm × 7 cm, and the dried body was applied to a thickness of 25 μm.

(2) The copper foil with a resin obtained in (1) was imidized by immersion in air at 130 ° C for 30 minutes using a dryer.

(3) The hydrazine was imidized at 350 ° C for 30 minutes in a high-temperature heating furnace in which the nitrogen flow rate was set to 10 L/min.

<Measurement of adhesion amount>

A film of a surface of a copper foil of 50 mm × 50 mm was dissolved in a solution in which HNO ₃ (2% by weight) and HCl (5% by weight) were mixed, and quantified using an ICP emission spectrometer (SFC-3100, manufactured by SII NanoTechnology Inc.). The amount of metal per unit area (μg/dm ² ) was calculated.

<Measurement using XPS>

The operating conditions of the XPS when the depth profile of the coating layer is created are shown below.

‧ Device: XPS measuring device (manufactured by ULVAC-PHI, Inc., type 5600MC)

‧ Reaching vacuum: 3.8×10 ^-7 Pa

‧ X-ray: monochromatic AlKα, X-ray output 300W, detection area 800μmΦ, sample and detector angle 45°

‧ Ion line: ion source Ar ⁺ , accelerating voltage 3kV, scanning area 3mm × 3mm, sputtering rate 2.3nm / min (converted by cerium oxide)

‧ In the measurement results of XPS, the separation of chromium oxide and metallic chromium was carried out using the analysis software Multi Pak V7.3.1 manufactured by ULVAC, Inc.

<Measurement by TEM>

The measurement conditions of the TEM when the coating layer is observed by TEM are shown below. The thickness shown in the table is the maximum value and the minimum value of the thickness between 50 nm of the thickness of the entire coating layer reflected in the observation field in one field of view, and the maximum and minimum values of the arbitrarily selected three fields of view are obtained. And find the percentage of the maximum and the ratio to the minimum of the maximum. Further, in the table, the TEM observation result of "after heat resistance test" was carried out by placing the test piece on the coating layer of the test piece in accordance with the above procedure, and then placing the test piece in the high temperature environment described below, in accordance with 180. The TEM image after the polyimine film was peeled off from the obtained test piece by the peeling method (JIS C 6471 8.1). In Fig. 3, the copper foil of No. 2 is exemplarily shown as an observation photograph after completion of sputtering by TEM observation.

‧ Device: TEM (Hitachi Manufacturing Co., Ltd., type H9000NAR)

‧ Accelerating voltage: 300kV

‧ Magnification: 300,000 times

‧ Observation field of view: 60nm × 60nm

<Continuity evaluation>

The peeling strength of the copper foil in which the polyimine was laminated in the above manner was measured under the following three conditions.

(1) just after layering (normal);

(2) After 168 hours (heat resistance) in a high temperature environment at a temperature of 150 ° C in an air atmosphere;

(3) After standing for 96 hours in a high-humidity environment at a temperature of 40 ° C and a relative humidity of 95% in an air atmosphere (moisture resistance);

The peel strength was measured in accordance with the 180° peeling method (JIS C 6471 8.1).

<etchability evaluation>

For the copper foil in which the polyimine is laminated in the above manner, a predetermined resist is used to form a line-and-space circuit pattern of 20 μm/20 μm, followed by an etching solution (ammonia water, copper chloride (II)). The dihydrate, temperature 40 ° C) was subjected to an etching treatment. The surface of the resin between the circuits after the treatment was measured by EPMA, and the residual chromium and nickel were analyzed and evaluated based on the following criteria.

×: Chromium or nickel was observed comprehensively between circuits

△: Chromium or nickel was partially observed between circuits

○: No chrome or nickel was observed between the circuits

Table 1 shows the measurement conditions and measurement results. In No. 1 to 8, each of the coating films was coated on a rolled copper foil, and No. E was coated on each of the coating films in an electrolytic copper foil. The SP/SP system is coated with either nickel or chromium. The plating/SP of No. 8 is an example of nickel plating, but since the layer is thicker, a certain degree of peel strength can be secured. Good results were also obtained with the electrolytic copper foil of No. E.

For reference, FIG. 1 shows a depth profile of the copper foil of No. 2 of Example 1 using XPS.

Example 2 (comparative)

The sputtering time was changed on one side of the rolled copper foil substrate used in Example 1, and the coating film of the thickness of Table 2 was formed. Further, in No. 14, 15 (plating/chromate), nickel plating and chromate treatment were sequentially performed in accordance with the following conditions. This comparative example is for comparison with the method taught in Japanese Laid-Open Patent Publication No. 2006-222185.

(1) Nickel plating

‧ plating bath: nickel sulfonate (Ni ²⁺ 110g / L), H ₃ BO ₃ (40g / L)

‧ Current density: 1.0A/dm ²

‧Bath temperature: 55 ° C

‧ Nickel amount: 95μg / dm ² (thickness about 1.1nm) (2) chromate treatment

‧ plating bath: CrO ₃ (1g / L), zinc (powder 0.4g), Na ₃ SO ₄ (10g / L)

‧ Current density: 2.0A/dm ²

‧Bath temperature: 55 ° C

‧Chromium content: 37μg/dm ² (thickness about 0.5nm)

The copper foil provided with the coating layer was subjected to the same procedure as in Example 1 followed by a polyimide film. The evaluation results are shown in Table 2. In Comparative Example No. 16, similarly to No. 8 being an example of nickel plating, since the nickel layer was thin and the thickness distribution was uneven, sufficient peel strength could not be obtained. In No. 17, an alloy target of 80% nickel and 20% chromium was used, and at the same time, nickel and chromium were coated with 2.5 nm, but the peel strength was low and the etching property was not good.

For reference, FIG. 2 shows a depth profile using XPS for a copper foil having a thickness of 2 nm. Regarding No. 14 and 15, a phenomenon in which the thickness was uneven was observed.

1. . . Thickness of the coating layer during TEM observation

Fig. 1 is a longitudinal distribution diagram of the copper foil of No. 2 of Example 1 using XPS.

Figure 2 is a plot of the depth profile of a copper foil sputtered with 2 nm of chromium using XPS.

Fig. 3 is a TEM photograph of the copper foil of No. 2 of Example 1.

Fig. 4 is a longitudinal distribution diagram using XPS when the copper foil of No. 2 of Example 1 separates chromium into metallic chromium and chromium oxide.

Claims (14)

A copper foil for a printed wiring board comprising a copper foil substrate and a coating layer covering at least a portion of a surface of the copper foil substrate, wherein: (1) the coating layer is sequentially surfaced from the surface of the copper foil substrate (2) in the coating layer, chromium is present in the range of 15 to 210 μg/dm ² and nickel is present in the coating amount of 15 to 440 μg/dm ² ; (3) using a transmission electron microscope When the cross section of the coating layer is observed, the maximum thickness is 0.5 to 5 nm, and the minimum thickness is 80% or more of the maximum thickness. The copper foil for a printed wiring board according to the first aspect of the invention, wherein the coating amount of chromium is 18 to 150 μg/dm ² and the coating amount of nickel is 20 to 195 μg/dm ² . The copper foil for a printed wiring board according to the first aspect of the invention, wherein the coating amount of chromium is 30 to 100 μg/dm ² and the coating amount of nickel is 40 to 180 μg/dm ² . The copper foil for a printed wiring board according to any one of claims 1 to 3, wherein the copper foil base material is a rolled copper foil. The copper foil for a printed wiring board according to any one of claims 1 to 3, wherein the printed wiring board is a flexible printed wiring board. The copper foil for a printed wiring board according to any one of the first to third aspects of the present invention, wherein the polyamimidic acid solution of the polyimide precursor is applied to the coating layer so that the dried body is 25 μm. The mixture was subjected to a hydrazine imidization process at 130 ° C for 30 minutes using a dryer under air, and a bismuth imidization process at 350 ° C for 30 minutes in a high-temperature heating furnace in which the nitrogen flow rate was further set to 10 L/min. The quinone imine was formed on the coating layer, and then placed in a high-temperature environment at a temperature of 150 ° C in an air atmosphere for 168 hours and then in accordance with 180. In the peeling method (JIS C6471 8.1), after the polyimine film is peeled off from the coating layer, the cross section of the coating layer is observed by a transmission electron microscope, and the maximum thickness is 0.5 to 5 nm, and the minimum thickness is 70% or more of the maximum thickness. The copper foil for a printed wiring board according to any one of the first to third aspects of the present invention, wherein the total chromium and oxygen obtained by the XPS analysis from the surface in the depth direction are in the depth direction (x: unit nm). When the atomic concentration (%) is f(x) or g(x), respectively, 0.6 ≦∫f(x)dx/∫g(x)dx≦2.2 is satisfied in the interval [1.0; 2.5]. The copper foil for a printed wiring board according to any one of the first to third aspects of the invention, wherein the metal chromium and the chromium oxide obtained by the XPS analysis from the surface in the depth direction are in the depth direction (x: unit nm) When the atomic concentration (%) is set to f ₁ (x) and f ₂ (x), respectively, in the interval [0; 1.0], 0.1≦∫f ₁ (x)dx/∫f ₂ (x)dx≦ is satisfied. 1.0, in the interval [1.0; 2.5], satisfies 0.8≦∫f ₁ (x)dx/∫f ₂ (x)dx≦2.0. The copper foil for a printed wiring board according to any one of the first to third aspects of the present invention, wherein the atomic concentration of chromium in the depth direction (x: unit nm) obtained by analyzing XPS from the surface in the depth direction is used ( %) is f(x), the atomic concentration (%) of oxygen is g(x), the atomic concentration (%) of copper is h(x), and the atomic concentration (%) of nickel is i(x) When the atomic concentration (%) of carbon is set to j(x), 区间h(x)dx/(∫f(x)dx+∫g(x)dx+∫h(x)dx+ in the interval [0;1.0] ∫i(x)dx+∫j(x)dx) is 1.0% or less. The copper foil for a printed wiring board according to the fourth aspect of the patent application, wherein the atomic concentration (x: unit nm) of the metal chromium and chromium oxide obtained by analyzing the XPS from the surface to the depth direction is used. When respectively set to f ₁ (x), f ₂ (x), in the interval [0; 1.0], 0.1≦∫f ₁ (x)dx/∫f ₂ (x)dx≦1.0, interval [1.0; In 2.5], 0.8≦∫f ₁ (x)dx/∫f ₂ (x)dx≦2.0 is satisfied. A method for producing a copper foil for a printed wiring board, comprising: coating at least a portion of a surface of a copper foil substrate with a thickness of 0.2 to 5.0 nm and a chromium layer having a thickness of 0.2 to 3.0 nm by sputtering; The steps. A copper-clad laminate having the copper foil of any one of claims 1 to 10. A copper clad laminate according to claim 12, wherein the copper foil is followed by a polyimine. A printed wiring board is made of a copper clad laminate of claim 12 or 13.