JP2011012297A - Copper foil for printed circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide copper foil for a printed circuit board which is excellent in both of adhesive properties with an insulating substrate and etching properties, and which is suitable for fine pitching, and has suppressed magnetism and suppressed load on the environment.SOLUTION: The copper foil for a printed circuit board includes: a copper foil base material; and a covering layer covering at least a part of the surface of the copper base material. The covering layer comprises a Cu-Zn alloy layer or a Zn layer and a Cr layer laminated in order from the surface of the copper foil base material, and a Cu layer, and in the covering layer, Zn is present in the covering amount of 15 to 750 μg/dmand Cr in the covering amount of 18 to 180 μg/dm.

Description

  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 over the last half century and are now used in almost all electronic devices. In recent years, with the increasing needs for miniaturization and higher performance of electronic devices, higher density mounting of components and higher frequency of signals have progressed, and conductor patterns have become finer (fine pitch) and higher frequency than printed circuit boards. Response is required.

  In general, a printed wiring board is manufactured through a process of forming a copper-clad laminate by bonding an insulating substrate to a copper foil and then forming a conductor pattern on the surface of the copper foil by etching. Therefore, the copper foil for printed wiring boards is required to have adhesiveness and etching properties with an insulating substrate.

  As a technique for improving the adhesion to an insulating substrate, a surface treatment for forming irregularities on a copper foil surface called a roughening treatment is generally performed. For example, by using a copper sulfate acidic plating bath on the M surface (rough surface) of the electrolytic copper foil, a large number of coppers are electrodeposited in a dendritic or small spherical shape to form fine irregularities, and the adhesion is improved by the anchoring effect. There is. After the roughening treatment, a chromate treatment, a treatment with a silane coupling agent, or the like is generally performed in order to further improve the adhesive properties.

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

  However, the method of improving adhesiveness by roughening treatment is disadvantageous for fine line formation. That is, when the conductor interval is narrowed by fine pitch, the roughened portion may remain on the insulating substrate after the circuit is formed by etching, which may cause insulation deterioration. In order to prevent this, if an attempt is made to etch the entire roughened surface, a long etching time is required, and a predetermined wiring width cannot be maintained.

  When polyimide is laminated on a smooth copper foil surface that is not subjected to roughening treatment, the adhesion between the copper foil and the polyimide is low. This is because Cu atoms diffuse into the polyimide, and the polyimide layer near the interface becomes brittle and becomes a starting point of peeling.

  In the method of providing, for example, a Ni layer or a Ni—Cr alloy layer on a smooth copper foil surface, there is much room for improvement in the basic characteristic of adhesion to an insulating substrate. In addition, for example, by providing a Cr layer on the copper foil surface, relatively high adhesion can be obtained at room temperature. However, when this laminate is subjected to a thermal history, if the layer thickness is thin, Cu atoms derived from the copper foil become Cr atoms. It passes through the layer and diffuses to the polyimide layer, resulting in poor adhesion. Moreover, when the Cr layer is thick enough to prevent diffusion of Cu atoms, the etching property of the surface treatment layer is poor. This causes a problem that “etching residue”, in which Cr remains on the surface of the insulating substrate, is likely to occur after the etching process for forming the conductor pattern.

  Therefore, in recent years, a first metal layer that prevents diffusion of Cu atoms is formed on the surface of the copper foil that has not been roughened, and an insulating substrate and a second metal layer are formed on the first metal layer. Research and development have been conducted on a technique for simultaneously obtaining good adhesion to an insulating substrate and good etching properties by forming a Cr layer having good adhesion properties to such an extent that etching properties are good.

As such a technique, for example, in Patent Document 1, in a surface-treated copper foil for a polyimide-based flexible copper-clad laminate, a Ni layer containing Ni in an amount of 0.03 to 3.0 mg / dm ² or / and Ni By providing a Cr layer or / and a Cr alloy layer containing 0.03 to 1.0 mg / dm ^{2 as} a Cr treatment on the alloy layer as a surface treatment layer, a high peel strength can be obtained between the polyimide resin layer and the alloy layer. It is described that a copper foil for a polyimide-based flexible copper-clad laminate having excellent insulation reliability, etching characteristics when forming a wiring pattern, and bending characteristics can be obtained.

  Patent Document 2 describes that a surface-treated copper foil having excellent resin adhesion can be obtained even when a chromate layer is formed after a Zn layer is formed on a copper foil.

JP 2006-222185 A JP 2005-042139 A

  However, as described in Patent Document 1, when a large amount of Ni is present in the coating layer on the surface of the copper foil, there is a problem that the magnetism of Ni may adversely affect the electronic device. Moreover, the surface treatment layer of several nm to several tens nm is formed by electroplating. At this time, the copper foil itself acts as an electrode for electrochemical reaction. Since the surface of the copper foil has irregularities such as oil pits, and there are inclusions of several hundred nm in the vicinity of the surface, the flow of electrons is inhibited in this part. For this reason, it is difficult to form an ultra-thin surface treatment layer with a uniform thickness and achieve both adhesiveness with polyimide and etching properties.

  In addition, when a Zn layer is formed by electroplating as described in Patent Document 2, there is a chromate treatment process in an electronic circuit board application, and since there is a plating process and an etching process after the resin film is attached, the Zn layer is thick. And marked acid erosion occurs. For this reason, there exists a problem that resin adhesiveness will fall. At this time, even if it is attempted to reduce the thickness of the Zn layer, it is difficult to ensure the uniformity of the thickness for electroplating because of the above-described reason, and thus the resin adhesion cannot be stably ensured. For these reasons, generally, a Zn layer formed by electroplating is formed thick after a copper foil is roughened.

  Furthermore, although alloy plating for eutecting Cu and Zn is widely performed, it is difficult to eutect them from a simple salt bath because the standard electrode potential of Cu is much noble than that of Zn. . Therefore, various complex baths using Cu (II) ions and complexing agents such as cyanide, borofluoride, pyrophosphoric acid, tripolyphosphoric acid and tartaric acid having a large stability number are used. Although some cyanides have been put into practical use, there is a problem from the viewpoint of working in a safe environment. In addition, for environmental measures, even when changing from cyanide to non-cyanide, when these baths are used, it is difficult to remove copper and tin ions contained in washing wastewater etc. by neutralization precipitation treatment. There's a problem.

  Therefore, the present invention provides a copper foil for a printed wiring board that is excellent in both adhesion to an insulating substrate and etching property, is suitable for fine pitch, has reduced magnetism, and has reduced environmental load. This is the issue.

  Conventionally, it is understood that by providing a Ni layer and a Cr layer with an extremely thin thickness in order on the surface of a copper foil base material, it is possible to obtain good etching properties at the same time while obtaining good adhesion with an insulating substrate. was there. However, there is a problem that the magnetism of Ni in the coating layer may adversely affect the electronic device. Further, when the Zn layer is formed by electroplating, the resin adhesion cannot be stably secured by acid erosion. In addition, because there are inclusions of about 1 μm near the surface of the copper foil and surface irregularities, the copper foil itself is a film on the order of nanometers in wet plating (electroplating) that is involved in the electrochemical reaction. It is difficult to form the film uniformly. In order to ensure uniformity, the thickness of the film must be increased, but the etching property is impaired. As a result of diligent research, the present inventors, as a result of intensive studies, in the order of Zn atoms using a copper zinc alloy or a zinc simple substance that weakens polyimide in the vicinity of the adhesion interface with the metal as a sputtering target on the surface of the copper foil substrate. When Cu-Zn layer or Zn layer is formed by implanting on the surface of the copper foil, and when the Cr layer is uniformly provided with an ultrathin thickness on the order of nanometers, excellent adhesion to the insulating substrate and excellent It has been found that a copper foil coating layer can be obtained while at the same time obtaining a good etching property while suppressing magnetism and further reducing the burden on the environment. According to such a configuration of the copper foil, Cu atoms diffuse to the polyimide side even after being subjected to heat treatment, even though Cu atoms are present in the coating immediately below the surface layer, which causes a decrease in adhesion. It has a unique property that it never does.

The present invention completed on the basis of the above knowledge is, in one aspect, a copper foil for a printed wiring board provided with a copper foil substrate and a coating layer covering at least a part of the surface of the copper foil substrate, The coating layer is composed of a Cu—Zn alloy layer or a Zn layer laminated in order from the surface of the copper foil substrate, and a Cr layer. The coating layer has a Zn content of 15 to 750 μg / dm ² and a Cr content of 18 to 180 μg. Present at a coverage of / dm ² .

In one embodiment of the copper foil for printed wiring boards according to the present invention, the Zn coating amount is 35 to 80 μg / dm ² , and the Cr coating amount is 30 to 145 μg / dm ² .

In another embodiment of the copper foil for printed wiring boards according to the present invention, the Cr coating amount is 36 to 75 μg / dm ² .

  In still another embodiment of the copper foil for printed wiring board according to the present invention, the maximum thickness is 0.7 to 12 nm and the minimum thickness is the maximum thickness when the cross section of the coating layer is observed with a transmission electron microscope. 80% or more.

  In yet another embodiment of the copper foil for printed wiring board according to the present invention, the atomic concentration (%) of chromium in the depth direction (x: unit nm) obtained from the depth direction analysis from the surface by XPS. F (x), zinc atomic concentration (%) as g (x), copper atomic concentration (%) as h (x), oxygen atomic concentration (%) as i (x), carbon In the interval [0, 1.0], 原子 h (x) dx / (∫f (x) dx + ∫g (x) dx + ∫h (x ) dx + ∫i (x) dx + ∫j (x) dx) is 10% or less.

In yet another embodiment of the copper foil for printed wiring board according to the present invention, the depth of metallic chromium and oxide chromium (chromium in chromium oxide) obtained from the depth direction analysis from the surface by XPS. When the atomic concentration (%) in the direction (x: unit nm) is f ₁ (x) and f ₂ (x), respectively, 0 ≦ ∫f ₁ (x) dx / ∫ in the interval [0, 1.0] f ₂ (x) dx ≦ 1.0 is satisfied, and 0.1 ≦ ∫f ₁ (x) dx / ∫f ₂ (x) dx ≦ 1.2 is satisfied in the interval [1.0, 2.5]. .

In still another embodiment of the copper foil for printed wiring boards according to the present invention, the depth direction (x: unit nm) of metallic chromium, zinc, and copper obtained from the depth direction analysis from the surface by XPS. If the atomic concentration (%) is f ₁ (x), g (x), and h (x), respectively, and the depth at which h (x) and f ₁ (x) are the same is X, the interval [X− 0.5, X + 0.5], 0.1 ≦ ∫h (x) dx / ∫g (x) dx ≦ 1.2 is satisfied.

  In yet another embodiment of the copper foil for printed wiring board according to the present invention, the atomic concentration in the depth direction (x: unit nm) of chromium and zinc obtained from the depth direction analysis from the surface by XPS ( %) Are respectively f (x) and g (x), 0 ≦ ∫g (x) dx / ∫f (x) dx ≦ 0.5 is satisfied in the interval [0, 1].

  In yet another embodiment of the copper foil for printed wiring board according to the present invention, the depth of zinc and chromium obtained from the depth direction analysis from the surface by XPS when heat treatment equivalent to polyimide curing is performed. If the atomic concentration (%) in the direction (x: unit nm) is h (x) and f (x), respectively, 0.1 ≦ ∫h (x) dx / ∫f ( x) dx ≦ 0.5 is satisfied.

  In still another embodiment of the copper foil for printed wiring board according to the present invention, the copper foil satisfies the above-mentioned rule when subjected to a heat treatment equivalent to polyimide curing.

  In another embodiment of the copper foil for printed wiring boards according to the present invention, the copper foil is subjected to a heat treatment equivalent to polyimide curing.

In yet another embodiment of the copper foil for printed wiring board according to the present invention, the copper foil for printed wiring board in which the coating layer is bonded to the insulating substrate, the coating layer after peeling the insulating substrate from the coating layer. When the surface was analyzed, the atomic concentration (%) of chromium obtained from XPS depth direction analysis was defined as f (x), the atomic concentration (%) of zinc as g (x), and copper atoms The concentration (%) is h (x), the oxygen atomic concentration (%) is i (x), the carbon atomic concentration (%) is j (x), and the metallic chromium atomic concentration (%) is f _1. (x), where the atomic concentration (%) of chromium oxide is f ₂ (x), and the distance from the surface layer where the concentration of metallic chromium is maximum is F, in the interval [0, F], ∫h ( x) dx / (∫f (x) dx + ∫g (x) dx + ∫h (x) dx + ∫i (x) dx + ∫j (x) dx) is 10% or less, 0.1 ≦ ∫f ₁ (x) dx / ∫f ₂ (x) dx ≦ 1.0.

  In yet another embodiment of the copper foil for printed wiring board according to the present invention, the copper foil base material is a rolled copper foil.

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

  In another aspect, the present invention is a copper clad laminate comprising the copper foil according to the present invention.

  In one embodiment of the copper clad laminate according to the present invention, the copper foil has a structure bonded to polyimide.

  In yet another aspect, the present invention is a printed wiring board made of the copper clad laminate according to the present invention.

  According to the present invention, it is possible to obtain a copper foil for a printed wiring board that is excellent in both adhesion to an insulating substrate and etching property, suitable for fine pitch, suppressed in magnetism, and suppressed in environmental load. .

It is a TEM photograph (cross section) of the copper foil of Example 4 (immediately after film formation). It is a depth profile by XPS of the copper foil of Example 4 (immediately after film-forming). It is a depth profile by XPS of the copper foil of Example 4 (after heat treatment equivalent to polyimide varnish curing). It is a depth profile by XPS of the copper foil of Example 7 (after heat treatment equivalent to polyimide varnish curing).

(Copper foil base material)
Although there is no restriction | limiting in particular in the form of the copper foil base material which can be used for this invention, Typically, it can use with the form of rolled copper foil or electrolytic copper foil. In general, the electrolytic copper foil is produced by electrolytic deposition of copper from a copper sulfate plating bath onto a drum of titanium or stainless steel, and the rolled copper foil is produced by repeating plastic working and heat treatment with a rolling roll. Rolled copper foil is often used for applications that require flexibility.
In addition to high-purity copper such as tough pitch copper and oxygen-free copper, which are usually used as conductor patterns for printed wiring boards, for example, Sn-containing copper, Ag-containing copper, Cr, Zr or Mg are added as the copper foil base material It is also possible to use a copper alloy such as a copper alloy, a Corson copper alloy to which Ni, Si and the like are added. In addition, when the term “copper foil” is used alone in this specification, a copper alloy foil is also included.

  There is no restriction | limiting in particular also about the thickness of the copper foil base material which can be used for this invention, What is necessary is just to adjust to the thickness suitable for printed wiring boards suitably. For example, it can be set to about 5 to 100 μm. However, for the purpose of forming a fine pattern, it is 30 μm or less, preferably 20 μm or less, and typically about 5 to 20 μm.

  The copper foil substrate used in the present invention is preferably not roughened. Conventionally, the surface roughening treatment is performed by applying irregularities of the order of μm on the surface by special plating, and the adhesion to the resin is given by the physical anchor effect. On the other hand, fine pitch and high frequency electrical characteristics are considered to be smooth foils, and roughened foils work in a disadvantageous direction. Further, since the roughening process is omitted, there is an effect of improving economy and productivity. Therefore, the foil used in the present invention is a foil that is not specially roughened.

(Coating layer)
At least a part of the surface of the copper foil base material is sequentially coated with a Cu—Zn alloy layer or a Zn layer and a Cr layer. The Cu—Zn alloy layer or the Zn layer and the Cr layer constitute a coating layer. Although there is no restriction | limiting in particular in the location to coat | cover, It is common to set it as the location where adhesion | attachment with an insulated substrate is planned. Adhesion with the insulating substrate is improved by the presence of the coating layer. In general, the adhesive force between a copper foil and an insulating substrate tends to decrease when placed in a high temperature environment, which is considered to be caused by thermal diffusion of copper to the surface and reaction with the insulating substrate. In this invention, the thermal diffusion of copper can be prevented by previously providing the Cu-Zn alloy layer or Zn layer excellent in copper diffusion prevention on the copper foil base material. Here, the Cu-Zn alloy layer provided for preventing the diffusion of copper contains copper that is not desired to be diffused to the surface, but since copper is alloyed, there is no diffusion to the surface, which is good. It has adhesiveness and does not adversely affect the etching property.
Further, the adhesion to the insulating substrate can be further improved by providing the Cu layer on the Cu-Zn alloy layer or the Zn layer with a Cr layer having better adhesion to the insulating substrate than the Cu-Zn alloy layer or the Zn layer. it can. Since the thickness of the Cr layer can be reduced thanks to the presence of the Cu—Zn alloy layer or the Zn layer, adverse effects on the etching property can be reduced. In addition, the adhesiveness as used in the field of this invention also refers to adhesiveness (heat resistance) after being placed under high temperature and adhesiveness (humidity resistance) after being placed under high humidity, in addition to normal adhesiveness. .

  In the copper foil for printed wiring boards according to the present invention, the coating layer is extremely thin and has a uniform thickness. The reason why the adhesiveness with the insulating substrate has been improved by such a configuration is not clear, but Cr is extremely excellent in adhesiveness with the resin as the outermost surface on the Cu-Zn alloy layer or Zn layer. It is presumed that the formation of the single-layer coating retains the single-layer coating structure having high adhesion even after the high-temperature heat treatment during imidization (at about 350 ° C. for about 30 minutes to several hours). Further, it is considered that the etching property is improved by making the coating layer extremely thin and reducing the amount of Cr used as a two-layer structure of a Cu—Zn alloy layer or a Zn layer and a Cr layer.

  Specifically, the coating layer according to the present invention has the following configuration.

(1) Identification of Cr layer, Cu—Zn alloy layer or Zn layer In the present invention, at least a part of the surface of the copper foil material is coated in the order of the Cu—Zn alloy layer or the Zn layer and the Cr layer. . These coating layers are identified by sputtering with argon from the surface layer using a surface analyzer such as XPS or AES, and chemical analysis in the depth direction is performed. Depending on the presence of each detection peak, a Cu-Zn alloy layer or Zn layer, and Cr Layers can be identified. Moreover, the order of covering from the position of each detection peak can be confirmed.

(2) Amount of deposition On the other hand, since these Cu—Zn alloy layers or Zn layers and Cr layers are very thin, it is difficult to evaluate the thickness accurately with XPS and AES. Therefore, in this invention, it decided to evaluate the thickness of a Cu-Zn alloy layer or Zn layer, and Cr layer by the weight of the coating metal per unit area. In the coating layer according to the present invention, Zn is present in a coating amount of 15 to 750 μg / dm ² and Cr is 18 to 180 μg / dm ² . When Cr is less than 18 μg / dm ² , sufficient peel strength cannot be obtained, and when Cr exceeds 180 μg / dm ² , the etching property tends to be significantly reduced. When Zn is less than 15 μg / dm ² , sufficient peel strength cannot be obtained, and when Zn exceeds 750 μg / dm ² , the etching property tends to be significantly reduced. The coating amount of Cr is preferably 30 to 145 μg / dm ² , more preferably 36 to 75 μg / dm ² , and the coating amount of Zn is preferably 35 to 80 μg / dm ² .

  When sputtering the Ni layer, Ni is used as a target. This Ni target is strong in magnetism, and when sputtering is performed by magnetron sputtering or the like, the use efficiency per one target is lowered, which is disadvantageous in terms of cost. In contrast, the Cu—Zn alloy layer or the Zn layer according to the present invention does not contain Ni, can suppress the magnetism of the target, and can perform sputtering efficiently.

(3) Observation with a transmission electron microscope (TEM) When the cross section of the coating layer according to the present invention is observed with a transmission electron microscope, the maximum thickness is 0.7 nm to 12 nm, preferably 0.8 to 11 nm. The coating layer has a minimum thickness of 80% or more, preferably 85% or more of the maximum thickness, and very little variation. This is because when the coating layer thickness is less than 0.7 nm, the peel strength is greatly deteriorated in the heat resistance test and the moisture resistance test, and when the thickness exceeds 12 nm, the etching property decreases. When the minimum value of the thickness is 80% or more of the maximum value, the thickness of the coating layer is very stable and hardly changes after the heat test. Observation by TEM makes it difficult to find a clear boundary between the Cu—Zn alloy layer or the Zn layer and the Cr layer in the coating layer, and it looks like a single layer (see FIG. 1). According to the study results of the present inventors, the coating layer found by TEM observation is considered to be a layer mainly composed of Cr, and the Cu—Zn alloy layer or the Zn layer is considered to exist on the copper foil substrate side. Therefore, in the present invention, the thickness of the coating layer when observed by TEM is defined as the thickness of the coating layer that looks like a single layer. However, although there may be a part where the boundary of the coating layer is unclear depending on the observation part, such a part is excluded from the thickness measurement part.

  Since the structure of the present invention suppresses the diffusion of Cu, it is considered to have a stable thickness. The copper foil of the present invention adheres to the polyimide film, and even after the resin is peeled off after undergoing a heat resistance test (standing at 168 hours in a high temperature environment at 150 ° C. in an air atmosphere), the thickness of the coating layer is almost the same. Without change, the maximum thickness is 0.7-12 nm, and it is possible to maintain 80% of the maximum thickness even at the minimum thickness.

(4) Oxidation state of coating layer surface First, in order to increase the adhesive strength, it is desirable that the inner copper is not diffused on the outermost surface of the coating layer (in the range of 0 to 1.0 nm from the surface). Therefore, in the copper foil for printed wiring boards according to the present invention, the atomic concentration (%) of chromium in the depth direction (x: unit nm) obtained from the depth direction analysis from the surface by XPS is defined as f (x). The atomic concentration (%) of zinc is g (x), the atomic concentration (%) of copper is h (x), the atomic concentration (%) of oxygen is i (x), and the atomic concentration of carbon (%) Is j (x), in the interval [0, 1.0], ∫h (x) dx / (∫f (x) dx + ∫g (x) dx + ∫h (x) dx + ∫i ( x) dx + ∫j (x) dx) is preferably 10% or less.

  Also, when analyzing the surface of the coating layer after peeling the insulating substrate from the coating layer for the copper foil for a printed wiring board with the coating layer bonded to the insulating substrate, it is obtained from the depth direction analysis from the surface by XPS. The atomic concentration (%) of chromium is f (x), the atomic concentration (%) of zinc is g (x), the atomic concentration (%) of copper is h (x), and the atomic concentration of oxygen (%) Is i (x), the atomic concentration (%) of carbon is j (x), and the distance from the surface layer where the concentration of metallic chromium is maximum is F, in the interval [0, F], ∫h (x ) dx / (∫f (x) dx + ∫g (x) dx + ∫h (x) dx + ∫i (x) dx + ∫j (x) dx) is preferably 10% or less.

In addition, on the outermost surface of the coating layer, both chromium and chromium oxide are present. However, although chromium is preferable in terms of preventing the diffusion of copper inside and ensuring adhesion, it is better. In order to obtain a good etching property, chromium oxide is preferable. Therefore, in order to achieve both the etching property and the adhesive strength, the atomic concentration (%) in the depth direction (x: unit nm) of metal chromium and oxide chromium obtained from the depth direction analysis from the surface by XPS is used. Assuming that f ₁ (x) and f ₂ (x), respectively, 0 ≦ ∫f ₁ (x) dx / ∫f ₂ (x) dx ≦ 1.0 is satisfied in the interval [0, 1.0]. In [1.0, 2.5], it is preferable to satisfy 0.1 ≦ ∫f ₁ (x) dx / ∫f ₂ (x) dx ≦ 1.2.

Also, when analyzing the surface of the coating layer after peeling the insulating substrate from the coating layer for the copper foil for a printed wiring board with the coating layer bonded to the insulating substrate, it is obtained from the depth direction analysis from the surface by XPS. The atomic concentration (%) of chromium is f (x), the atomic concentration (%) of metallic chromium is f ₁ (x), and the atomic concentration (%) of chromium oxide is f ₂ (x). In the interval [0, F], 0.1 ≦ f ₁ (x) dx / ∫f ₂ (x) dx ≦ 1.0 in the interval [0, F]. preferable.

Moreover, just below the outermost surface of the coating layer, copper and metal chromium and zinc coexist, thereby suppressing the diffusion of copper atoms from the copper foil base material and the lower layer. At this time, if the amount of zinc is too large, zinc diffuses to the outermost layer, the concentration of chromium oxide is relatively lowered, and the peel strength is lowered. Moreover, when there is too little quantity of zinc, the effect of copper diffusion suppression is not enough. Therefore, in the coating layer, the atomic concentrations (%) in the depth direction (x: unit nm) of metallic chromium, zinc, and copper obtained from the depth direction analysis from the surface by XPS are respectively expressed as f ₁ (x), g (x), h (x), where X is a depth at which h (x) and f ₁ (x) are the same, 0.1 ≦ ≤ in section [X−0.5, X + 0.5] It is preferable that ∫h (x) dx / ∫g (x) dx ≦ 1.2 is satisfied.

  Moreover, it is preferable to satisfy | fill the prescription | regulation of the oxidation state of the above-mentioned coating layer surface, when copper foil performs the heat processing equivalent to polyimide hardening.

  Further, from the viewpoint of peel strength, it is desirable that the outermost layer is covered with chromium oxide. Furthermore, if there is zinc, the peel strength can be further improved. However, if zinc is excessively present in the outermost layer, the concentration of chromium oxide is relatively lowered, so that the peel strength is lowered. Therefore, if the atomic concentration (%) in the depth direction (x: unit nm) of chromium and zinc obtained from the depth direction analysis by XPS is f (x) and g (x) respectively, the interval [ 0, 1] preferably satisfies 0 ≦ を 満 た す g (x) dx / ∫f (x) dx ≦ 0.5.

  In addition, when heat treatment equivalent to polyimide curing was performed, the atomic concentration (%) in the depth direction (x: unit nm) of zinc and chromium obtained from the depth direction analysis from the surface by XPS was set to h (x ), F (x), it is preferable that 0.1 ≦ ∫h (x) dx / ∫f (x) dx ≦ 0.5 is satisfied in the interval [0, 1.0].

The chromium concentration and the oxygen concentration are calculated from the peak intensities of the Cr2p orbit and O1s orbit obtained from the depth direction analysis from the surface by XPS, respectively. 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 a total value of the oxide chromium concentration and the metal chromium concentration, and can be analyzed separately by the oxide chromium concentration and the metal chromium concentration.

(Method for producing copper foil according to the present invention)
The copper foil for printed wiring boards according to the present invention can be formed by a sputtering method. That is, a Cu-Zn alloy layer or Zn layer having a thickness of 0.2 to 11 nm, preferably 0.5 to 1.2 nm, and a thickness of 0.2 to at least part of the surface of the copper foil substrate by sputtering. It can be produced by sequentially coating with a Cr layer of ˜2.5 nm, preferably 0.4 to 2.0 nm, more preferably 0.5 to 1.2 nm. When such an extremely thin film is laminated by electroplating, the thickness varies, and the peel strength tends to decrease after the heat and humidity resistance test.
The thickness here is not the thickness determined by the XPS or TEM described above, but the thickness derived from the film formation rate of sputtering. The deposition rate under a certain sputtering condition can be measured from the relationship between the sputtering time and the sputtering thickness by performing sputtering of 0.1 μm (100 nm) or more. Once the deposition rate under the sputtering conditions can be measured, the sputtering time is set according to the desired thickness. Sputtering may be performed continuously or batchwise, and the coating layer can be uniformly laminated with a thickness as defined in the present invention. Examples of the sputtering method include a direct current magnetron sputtering method.

(Manufacture of printed wiring boards)
A printed wiring board (PWB) can be manufactured according to a conventional method using the copper foil according to the present invention. Below, the example of manufacture of a printed wiring board is shown.

  First, a copper-clad laminate is manufactured 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 applicable to a printed wiring board. For example, paper base phenolic resin, paper base epoxy resin, synthetic fiber for rigid PWB Use cloth base epoxy resin, glass cloth / paper composite base epoxy resin, glass cloth / glass non-woven composite base epoxy resin, glass cloth base epoxy resin, etc., use polyester film, polyimide film, etc. for FPC I can do things.

  In the case of the rigid PWB, a prepreg is prepared by impregnating a base material such as a glass cloth with a resin and curing the resin to a semi-cured state. It can be carried out by superposing and heating and pressing the surfaces having the prepreg and the copper foil coating layer.

  In the case of a flexible printed wiring board (FPC), a surface having a polyimide film or polyester film and a copper foil coating layer can be bonded using an epoxy or acrylic adhesive (three-layer structure). In addition, as a method without using an adhesive (two-layer structure), a polyimide varnish (polyamic acid varnish), which is a polyimide precursor, is applied to a surface having a copper foil coating layer, and imidized by heating. And a lamination method in which a thermoplastic polyimide is applied on a polyimide film, a surface having a copper foil coating layer is superimposed thereon, and heated and pressed. In the casting method, it is also effective to apply an anchor coating material such as thermoplastic polyimide in advance before applying the polyimide varnish.

  The effect of the copper foil according to the present invention is prominent when an FPC is produced by adopting a casting method. That is, when the copper foil and the resin are to be bonded without using an adhesive, the copper foil is particularly required to adhere to the resin, but the copper foil according to the present invention is bonded to the resin, particularly to the polyimide. It can be said that it is suitable for the production of a copper clad laminate by a casting method.

  The copper-clad laminate according to 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, single-sided PWB, double-sided PWB, multilayer It can be applied to PWB (3 layers or more), and can be applied to rigid PWB, flexible PWB (FPC), and rigid flex PWB from the viewpoint of the type of insulating substrate material.

  The process for producing a printed wiring board from a copper clad laminate may be performed by a method well known to those skilled in the art. By spraying on the copper foil surface, the unnecessary copper foil can be removed to form a conductor pattern, and then the etching resist can be peeled and removed to expose the conductor pattern.

  EXAMPLES Examples of the present invention will be described below, but these are provided for better understanding of the present invention and are not intended to limit the present invention.

(Example 1: Examples 1 to 10)
A rolled copper foil (Nikko Metal C1100) having a thickness of 18 μm was prepared as a copper foil base material. The surface roughness (Rz) of the rolled copper foil was 0.7 μm.

  A Cu—Ni alloy used for sputtering was prepared by the following procedure. First, elements of various compositions were added to electrolytic copper, ingots were cast in a high frequency melting furnace, and hot rolled at 900 ° C. Furthermore, after homogenizing annealing at 850 ° C. for 3 hours, the surface oxide layer was removed and used as a sputtering target. Table 1 shows the composition (mass%) of the sputtering target used at this time. In Table 1, Zn (III) having a purity of 3N was used.

On one side of this copper foil, a thin oxide film previously attached to the surface of the copper foil base material is removed by reverse sputtering under the following conditions, and a Cu-Zn alloy or Ni target is sputtered to obtain a Cu-Zn alloy. A layer or a Zn layer and a Cr layer were sequentially formed. The thickness of the coating layer was changed by adjusting the film formation time.
-Equipment: Batch type sputtering equipment (ULVAC, Model MNS-6000)
・ Achieving vacuum: 1.0 × 10 ⁻⁵ Pa
・ Sputtering pressure: 0.2 Pa
・ Reverse sputtering power: 100W
·target:
Cu-Zn layer = (I), (II)
Zn layer = (III)
Cr layer = Cr (purity 3N)
・ Sputtering power: 50W
Film formation rate: About 0.2 μm of film was formed for each target for a fixed time, the thickness was measured with a three-dimensional measuring device, and the sputtering rate per unit time was calculated.

A polyimide film was bonded to the copper foil provided with the coating layer by the following procedure.
(1) Using an applicator on a copper foil of 7 cm × 7 cm, Ube Industries-made U varnish-A (polyimide varnish) was applied to a dry body to a thickness of 25 μm.
(2) The resin-coated copper foil obtained in (1) is dried at 130 ° C. for 30 minutes in an air dryer.
(3) Imidization at 350 ° C. for 30 minutes in a high-temperature heating furnace with a nitrogen flow rate set to 10 L / min.

  In addition to the polyimide film adhesion test, as a “heat resistance test”, the polyimide film was not bonded to the copper foil provided with the coating layer, and was heated as it was at 350 ° C. for 2 hours in a nitrogen atmosphere.

<Measurement of adhesion amount>
A film on the surface of a copper foil of 50 mm × 50 mm is dissolved in a mixed solution of HNO ₃ (2% by weight) and HCl (5% by weight), and the metal concentration in the solution is measured by an ICP emission spectrometer (SII Nanotechnology). The amount of metal per unit area (μg / dm ² ) was calculated by quantitative determination using SFC-3100). In addition, the analysis value at the time of forming into a film on Ti foil on the same conditions was used for the adhesion amount of Cu and Zn at the time of making the Cu-Zn alloy of this invention a target.

<Measurement by XPS>
The operating conditions of XPS when creating the depth profile of the coating layer are shown below.
・ Device: XPS measuring device (ULVAC-PHI, Model 5600MC)
・ Achieving vacuum: 3.8 × 10 ⁻⁷ Pa
X-ray: Monochromatic AlKα or non-monochromatic MgKα, X-ray output 300 W, detection area 800 μmφ, angle between sample and detector 45 °
Ion beam: ion species Ar ⁺ , acceleration voltage 3 kV, sweep area 3 mm × 3 mm, sputtering rate 2.0 nm / min (SiO ₂ conversion)
In the XPS measurement results, separation of oxide chromium and metal chromium was performed using analysis software Multi Pak V7.3.1 manufactured by ULVAC.
・ Measurement is after film formation by sputtering, heat treatment (350 ° C. × 120 minutes) severer than polyimide curing conditions (350 ° C. × 30 minutes) at the time of adhesive strength measurement, and film after peeling of insulating substrate Was analyzed.

<Measurement by TEM>
The measurement conditions of TEM when the coating layer is observed by TEM are shown below. The thicknesses shown in the table below are the thicknesses of the entire coating layer reflected in the observation visual field, and the maximum and minimum values of the thickness between 50 nm are measured for one visual field. The value and the minimum value were determined, and the maximum value and the ratio of the minimum value to the maximum value were determined as percentages. Also, the TEM observation result of “After heat resistance test” in the table is that after a polyimide film is adhered on the coating layer of the test piece by the above procedure, the test piece is placed in the following high temperature environment, and the obtained test piece is obtained. Is a TEM image after the polyimide film is peeled according to the 90 ° peeling method (JIS C 6471 8.1). In FIG. 1, the observation photograph immediately after film-forming by TEM of Example 4 is shown as an example. The Cu—Zn alloy layer obtained by sputtering the Cu—Zn alloy cannot be confirmed from FIG. This is because the corresponding part is a copper alloy layer and cannot be distinguished from the copper foil of the base material. In FIG. 1, the Cr layer is confirmed. The layer obtained by sputtering zinc alone had a clear boundary with the base material. In the present invention, the thickness of only the layer whose boundary with the base material is clear is measured.
-Equipment: TEM (Hitachi, Ltd., model H9000NAR)
・ Acceleration voltage: 300 kV
-Magnification: 300,000 times-Observation field: 60 nm x 60 nm

<Adhesion evaluation>
For the copper foil laminated with polyimide as described above, the peel strength was immediately after lamination (normal state), after being left in a high-temperature environment in an air atmosphere at a temperature of 150 ° C. (heat resistance), and a relative temperature of 40 ° C. The measurement was performed under three conditions: after being left in a high humidity environment with a humidity of 95% air for 96 hours (humidity resistance). The peel strength was measured according to the 90 ° peeling method (JIS C 6471 8.1).

<Etching evaluation>
A white tape was applied to the coating layer of the copper foil produced as described above, and immersed for 7 minutes in an etching solution (copper chloride dihydrate, ammonium chloride, ammonia water, solution temperature 50 ° C.). Then, the metal component of the etching residue adhering to the tape was quantified with an ICP emission spectroscopic analyzer and evaluated according to the following criteria.
×: Etching residue is 140 μg / dm ² or more Δ: Etching residue is 70 μg / dm ² or more and less than 140 μg / dm ² ○: Etching residue is less than 70 μg / dm ²

  The measurement results are shown in Tables 2 and 3.

Examples 1-7 and 10 all showed good peel strength and etching properties. In Examples 8 and 9, although the etching properties were slightly inferior to those of other examples, the peel strength was good. In FIG. 2, each depth profile by XPS of each element from the film surface layer immediately after forming into a film by sputtering of the copper foil of Example 4 is shown. In the Cr layer, there is a Cr layer that forms an oxide on the surface layer, and a metal Cr layer is present immediately below the Cr layer, which are separated into two layers. Further, there is a Zn layer immediately below it, which is separated from the Cr layer. Furthermore, since Cu also coexists in this Zn layer, it can be said that it becomes a copper alloy layer immediately after sputtering.
In FIG. 3, each depth profile by XPS of each element from the film | membrane surface layer after the heat processing equivalent to polyimide varnish hardening of the copper foil of Example 4 is shown. In FIG. 4, each depth profile by XPS of each element from the film surface layer of the copper foil of Example 7 after the heat processing equivalent to polyimide varnish hardening is shown. When FIG. 2 obtained by sputtering a Cu—Zn alloy target was compared with FIG. 3, oxidation in the Cr layer proceeded before and after the heat treatment, but diffusion of Cu to the surface did not proceed. In FIG. 4 obtained by sputtering Zn alone, the diffusion of Cu to the surface did not proceed. 3 and 4, it was recognized that the Cu atom concentration rapidly decreased in the region within 1 to 3 nm from the coating surface layer. This is presumably because Cu, Cr, and Zn coexist in this region, thereby suppressing Cu diffusion.

(Example 2: Comparative Examples 1 to 5)
Sputtering time was changed on one side of the rolled copper foil base material used in Example 1 to form a film having a thickness shown in Table 4 to be described later. A polyimide film was bonded to the copper foil provided with the coating layer by the same procedure as in Example 1.

(Example 3: Comparative Example 6)
According to JP-A-2005-42139, after applying a Zn layer to one side of the rolled copper foil base used in Example 1 by electroplating, chromate treatment was performed. A polyimide film was bonded to the copper foil provided with the coating layer by the same procedure as in Example 1. The electroplating / chromate treatment conditions are shown below.
[Zn plating treatment]
・ Zinc chloride 40g / l
・ Potassium chloride 210g / l
・ Boric acid 30g / l
・ Liquid temperature 30 ℃
・ Current density 0.5A / dm ²
・ Plating thickness 3nm
[Chromate treatment]
・ Chromium sulfate (as trivalent chromium ion) 1.4mg / l
・ Sodium hydrogen fluoride (as fluoride ion) 0.8mg / l
・ Nitric acid 2.5mg / l
・ Liquid temperature 25 ℃
・ Plating time 5 seconds

  The measurement results of Examples 2 and 3 are shown in Tables 4 and 5.

In Comparative Example 1, Zn in the coating layer was less than 15 μg / dm ² , and the heat resistance and moisture peel strength were poor.
In Comparative Example 2, Cr in the coating layer was over 180 μg / dm ² and the etching property was poor.
In Comparative Example 3, Cr in the coating layer was less than 18 μg / dm ² and the peel strength was poor.
In Comparative Example 4, Zn in the coating layer was more than 750 μg / dm ² , and the moisture peel strength was poor.
In Comparative Example 5, the first layer was not formed, and the heat resistance and moisture peel strength were poor. This is presumably because Cu has diffused to the bonding interface. This also shows that if there is a region where Cu, Zn and Cr coexist, diffusion of Cu is suppressed.
In Comparative Example 6, the thicknesses of the Zn layer and the chromate layer were not uniform and the peel strength was poor as compared with the Examples.

Claims (17)

A copper foil for a printed wiring board comprising a copper foil substrate and a coating layer covering at least a part of the surface of the copper foil substrate, wherein the coating layer is laminated in order from the surface of the copper foil substrate. A copper foil for a printed wiring board comprising a Zn alloy layer or a Zn layer and a Cr layer, wherein the coating layer has a coating amount of 15 to 750 μg / dm ² of Zn and 18 to 180 μg / dm ² of Cr . The copper foil for printed wiring boards according to claim 1, wherein the coating amount of Zn is 35 to 80 µg / dm ² , and the coating amount of Cr is 30 to 145 µg / dm ² . The copper foil for printed wiring boards according to claim ² , wherein the coating amount of Cr is 36 to 75 µg / dm ² .   The printed wiring according to any one of claims 1 to 3, wherein when the cross section of the coating layer is observed with a transmission electron microscope, the maximum thickness is 0.7 to 12 nm and the minimum thickness is 80% or more of the maximum thickness. Copper foil for plates.   The atomic concentration (%) of chromium in the depth direction (x: unit nm) obtained from the depth direction analysis by XPS is f (x), and the atomic concentration (%) of zinc is g (x). When the atomic concentration (%) of copper is h (x), the atomic concentration (%) of oxygen is i (x), and the atomic concentration (%) of carbon is j (x), the interval [0, 1.. 0], ∫h (x) dx / (∫f (x) dx + ∫g (x) dx + ∫h (x) dx + ∫i (x) dx + ∫j (x) dx) is 10% It is the following, The copper foil for printed wiring boards in any one of Claims 1-4. When the atomic concentration (%) in the depth direction (x: nm) of metallic chromium and oxide chromium obtained from the depth direction analysis by XPS is f ₁ (x) and f ₂ (x), respectively. In the interval [0, 1.0], 0 ≦ ∫f ₁ (x) dx / ∫f ₂ (x) dx ≦ 1.0 is satisfied, and in the interval [1.0, 2.5], 0.1 The copper foil for printed wiring boards according to claim 1, wherein ≦ を 満 た す f ₁ (x) dx / ∫f ₂ (x) dx ≦ 1.2 is satisfied. The atomic concentrations (%) in the depth direction (x: nm) of metallic chromium, zinc, and copper obtained from the depth direction analysis from the surface by XPS are respectively f ₁ (x), g (x), h ( x), where X is the depth at which h (x) and f ₁ (x) are the same, 0.1 ≦ ∫h (x) dx in the interval [X−0.5, X + 0.5] The copper foil for printed wiring boards according to claim 1, satisfying /∫g(x)dx≦1.2.   When the atomic concentration (%) in the depth direction (x: nm) of chromium and zinc obtained from the depth direction analysis by XPS is f (x) and g (x), respectively, the interval [0, 1] The copper foil for printed wiring boards according to claim 1, wherein 0 ≦ ∫g (x) dx / ∫f (x) dx ≦ 0.5 is satisfied.   The copper foil for printed wiring boards in any one of Claims 5-8 which satisfy | fill the said regulations when the said copper foil performs the heat processing equivalent to polyimide hardening.   Assuming that the atomic concentrations (%) in the depth direction (x: unit nm) of zinc and chromium obtained from XPS depth direction analysis are h (x) and f (x), respectively, the interval [0, 1.0], the copper foil for printed wiring boards according to claim 9, wherein 0.1 ≦ (h (x) dx / ∫f (x) dx ≦ 0.5 is satisfied.   The copper foil for printed wiring boards according to any one of claims 5 to 10, wherein the copper foil has been subjected to a heat treatment equivalent to polyimide curing. Chromium obtained from analysis of depth direction from the surface by XPS when analyzing the surface of the coating layer after peeling the insulating substrate from the coating layer for the copper foil for printed wiring board with the coating layer bonded to the insulating substrate F (x) is the atomic concentration (%) of zinc, g (x) is the atomic concentration (%) of zinc, h (x) is the atomic concentration (%) of copper, and i is the atomic concentration (%) of oxygen. (x), the atomic concentration (%) of carbon is j (x), the atomic concentration (%) of chromium metal is f ₁ (x), and the atomic concentration (%) of chromium oxide is f ₂ (x). And the distance from the surface layer where the concentration of chromium metal is maximum is F, in the interval [0, F], ∫h (x) dx / (∫f (x) dx + ∫g (x) dx + ∫ h (x) dx + ∫i (x) dx + ∫j (x) dx) is 10% or less, and 0.1 ≦ ∫f ₁ (x) dx / ∫f ₂ (x) dx ≦ 1.0 The copper foil for printed wiring boards according to any one of claims 1 to 11.   A copper foil base material is a rolled copper foil, The copper foil for printed wiring boards in any one of Claims 1-12.   The printed wiring board is a flexible printed wiring board. Copper foil for printed wiring boards according to claim 1-13.   The copper clad laminated board provided with the copper foil in any one of Claims 1-14.   The copper clad laminate according to claim 15, wherein the copper foil has a structure bonded to polyimide.   A printed wiring board made of the copper-clad laminate according to claim 15 or 16.