JP2011014651A - Copper foil for printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper foil for a printed wiring board which is excellent in both bondability with an insulated substrate and etching performance and suitable for fine pitch.SOLUTION: The copper foil for a printed wiring board includes a copper foil base material and a coating layer for coating at least a part of the surface of the copper foil base material. The coating layer consists of a Cu-Ni alloy layer and a Cr layer which are sequentially laminated from the surface of the copper alloy base material, wherein Ni and Cr are contained at 15-440 μg/dmand 18-180 μg/dmof coating amount in the coating layer, respectively.

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.

  Since polyimide is often used for the insulating substrate to be bonded to the copper foil, a method of coating the copper foil surface with chromium having high adhesive strength with polyimide is common.

  Also, when the copper foil is bonded to the insulating substrate formed of polyimide in this way, if the Cu atom or Cu oxide of the copper foil diffuses to the polyimide side, the polyimide layer near the bonding interface becomes brittle, The part becomes the starting point of peeling. For such a problem, on the smooth copper foil surface, a first metal layer that prevents diffusion of Cu atoms to the polyimide layer is formed, and a second metal layer is formed on the first metal layer, Research and development of technology to simultaneously obtain good adhesion to the insulating substrate and good etching properties by forming a Cr layer with good adhesion to the insulating substrate thin enough to have good etching properties. ing.

Examples of the method for coating the copper foil surface with the chromium layer include a wet processing method and a dry processing method. Among these, as a method of coating the chromium layer on the surface by wet processing, a method of forming a Zn layer or a Zn alloy layer on the surface of the copper foil and further forming a chromate layer on the layer, and a method of coating Zn on the surface of the copper foil There is a method in which a layer not containing is formed and a chromate layer is not formed on the layer. The former example is disclosed in Patent Document 1, and the latter example is disclosed in Patent Document 2. When a chromate layer is formed on a Zn layer or a Zn alloy layer, a substitution reaction occurs between Zn in the Zn layer or Zn alloy layer and Cr ⁶⁺ in the solution, and Cr hydroxide precipitates. In this method, Cr is precipitated in a hydroxide state. For this reason, the valence of the deposited Cr is not zero, but trivalent, which is considered excellent in adhesion to polyimide.

  A method using dry processing is disclosed in Patent Document 3. In Patent Document 3, by forming a Ni—Cr alloy layer on the surface of the copper foil and forming an oxide layer having a predetermined thickness on the surface of the alloy layer, the surface of the copper foil is smooth and the anchor effect is low. It is described that the adhesiveness with the resin base material is significantly increased even in the state. Then, a Ni—Cr alloy layer having a thickness of 1 to 100 nm is formed on the surface, a Cr oxide layer having a thickness of 0.5 to 6 nm is formed on the surface of the alloy layer, and the average surface roughness RzJIS of the outermost surface is A printed circuit board copper foil having a thickness of 2.0 μm or less is disclosed.

JP 2005-344174 A JP 2007-007937 A JP 2007-207812 A

  In the various prior arts described above, from the viewpoint of fine pitch circuit formation, a method for improving adhesiveness by roughening treatment is disadvantageous. 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.

  From the viewpoint of adhesive strength, the method of laminating polyimide on the smooth copper foil surface is disadvantageous compared to the method of laminating polyimide on the roughened surface. This is because the anchoring effect is obtained by the anchor effect on the roughened surface, but the anchor effect is not obtained when the roughening treatment is not performed, and further, the Cu atoms diffuse into the polyimide, and the vicinity of the interface. This is because the polyimide layer becomes brittle and the part becomes a starting point of peeling.

  Furthermore, the method of providing, for example, a Ni layer or a Ni—Cr alloy layer on the smooth copper foil surface has a large room for improvement in the basic characteristic of adhesion to an insulating substrate. Further, for example, a method of providing a Cr layer on the surface of the copper foil provides relatively high adhesion at room temperature. However, when this laminate is subjected to a thermal history, if the layer is thin, Cu atoms derived from Cu Passes through the Cr layer and diffuses to the polyimide layer, and the adhesive strength deteriorates. Furthermore, if 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 after etching for forming a circuit pattern is likely to occur.

  Moreover, the surface treatment layer described in Patent Documents 1 and 2 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 hundreds of nanometers in the vicinity of the surface, the flow of electrons is obstructed in this part, and an extremely thin surface treatment layer is made uniform. It is difficult to achieve a good balance between adhesiveness with polyimide and etching properties.

Furthermore, in order to adhere Cr effective for adhesion to polyimide to the surface of the copper foil, it is necessary to form a chromate layer on the Zn layer or the Zn alloy layer. The present inventors have found that when a chromate layer is formed on a -Zn alloy layer, the chromium oxide concentration in the vicinity of the adhesion interface becomes low and high adhesion strength cannot be obtained. Further, as described in Patent Document 2, when a chromate layer is not formed on a Zn layer or a Zn alloy layer, a substitution reaction between Zn and Cr ⁶⁺ cannot be used. There is a limit to the amount of adhesion.

  Then, this invention makes it a subject to provide the copper foil for printed wiring boards which is excellent in both the adhesiveness with an insulated substrate, and etching property, and is suitable for fine pitching.

  Conventionally, it was generally understood that the adhesive strength decreases when the coating layer is thinned. However, as a result of intensive studies, the present inventors have found that excellent insulation is achieved when a Cu—Ni alloy layer and a Cr layer are uniformly provided on the surface of a copper foil substrate in an ultrathin thickness on the order of nanometers. It was found that adhesion to the substrate can be obtained. By making the thickness of each layer extremely thin, the amount of Cr having low etching property is reduced, and the coating layer has a uniform thickness, which is advantageous for etching property. Moreover, since the Cu—Ni alloy layer is formed, the adhesiveness between the coating layer on the surface of the copper foil and the base material is improved, and thereby excellent adhesiveness between the copper foil and the insulating substrate is obtained. Furthermore, compared with wet plating, the concentration of chromium oxide in the vicinity of the adhesion interface can be increased, and excellent adhesion with an insulating substrate can be obtained.

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—Ni alloy layer and a Cr layer laminated in order from the surface of the copper foil base. The coating layer is a coating of Ni of 15 to 440 μg / dm ² and Cr of 18 to 180 μg / dm ² . Present in quantity.

In one embodiment of the copper foil for printed wiring boards according to the present invention, Cr is present in the coating layer in a coating amount of 30 to 145 μg / dm ² .

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

  In yet another embodiment of the copper foil for printed wiring board according to the present invention, the maximum thickness is 0.5 to 3 nm when the cross section of the coating layer is observed with a transmission electron microscope, and the minimum thickness is the maximum thickness. 80% or more.

In yet another embodiment of the copper foil for printed wiring board according to the present invention, the atomic concentration (%) of metallic chromium in the depth direction (x: unit nm) obtained from the depth direction analysis from the surface by XPS. ) Is f ₁ (x), the atomic concentration (%) of chromium oxide (chromium in chromium oxide) is f ₂ (x), and the atomic concentration (%) of all chromium is f (x) (f (x) = f ₁ (x) + f ₂ (x)), the atomic concentration (%) of nickel is g (x), the atomic concentration (%) of copper is h (x), and the atomic concentration of oxygen ( %) Is i (x) and the atomic concentration (%) of carbon is j (x), 区間 h (x) dx / (∫f (x) dx + ∫ in the interval [0, 1.0] g (x) dx + ∫h (x) dx + ∫i (x) dx + ∫j (x) dx) is 10% or less and ∫f ₂ (x) dx / (∫f (x) dx + ∫ g (x) dx + ∫h (x) dx + ∫i (x) dx + ∫j (x) dx) is 20% or more, and 0.1 ≦ ∫ in the interval [1.0, 2.5] _{f 1 (x) dx / ∫f} 2 (x) satisfies the dx ≦ 1.0, the interval [0, In], ∫g (x) dx / ∫h (x) dx satisfy <1.

In yet another embodiment of the copper foil for printed wiring boards according to the present invention, when heat treatment equivalent to polyimide curing is performed, the depth direction (x: unit) obtained from the depth direction analysis from the surface by XPS nm) atomic concentration (%) of chromium metal is f ₁ (x), atomic concentration (%) of chromium oxide is f ₂ (x), and atomic concentration (%) of all chromium is f (x). (F (x) = f ₁ (x) + f ₂ (x)), nickel atomic concentration (%) is g (x), copper atomic concentration (%) is h (x), oxygen atoms If the concentration (%) is i (x) and the atomic concentration (%) of carbon is j (x), 区間 h (x) dx / (∫f (x) dx in the interval [0, 1.0] + ∫g (x) dx + ∫h (x) dx + ∫i (x) dx + ∫j (x) dx) is 10% or less, ∫f ₂ (x) dx / (∫f (x) dx + ∫g (x) dx + ∫h (x) dx + ∫i (x) dx + ∫j (x) dx) is 20% or more and 0.1 [0.1, 2.5] in the interval [1.0, 2.5] meet _{≦ ∫f 1 (x) dx /} ∫f 2 (x) dx ≦ 1.0 , In the interval [0,5], it satisfies the ∫g (x) dx / ∫h (x) dx <1.

In yet another embodiment of the copper foil for printed wiring board according to the present invention, the copper foil for printed wiring board is subjected to a heat treatment equivalent to polyimide curing, and is obtained from a depth direction analysis from the surface by XPS. The atomic concentration (%) of metallic chromium in the depth direction (x: unit nm) is f ₁ (x), the atomic concentration (%) of chromium oxide is f ₂ (x), and the total chromium atomic concentration (%) Is f (x) (f (x) = f ₁ (x) + f ₂ (x)), nickel atomic concentration (%) is g (x), and copper atomic concentration (%) is When h (x) is assumed, the atomic concentration (%) of oxygen is i (x), and the atomic concentration (%) of carbon is j (x), に お い て h (x) in the interval [0, 1.0] dx / (∫f (x) dx + ∫g (x) dx + ∫h (x) dx + ∫i (x) dx + ∫j (x) dx) is 10% or less, and ∫f ₂ (x) dx / (∫f (x) dx + ∫g (x) dx + ∫h (x) dx + ∫i (x) dx + ∫j (x) dx) is 20% or more, and the interval [1.0, 2.5], 0.1 ≦ ∫f ₁ (x ) dx / ∫f ₂ (x) dx ≦ 1.0 is satisfied, and 区間 g (x) dx / ∫h (x) dx <1 is satisfied in the interval [0, 5].

In yet another embodiment of the copper foil for printed wiring board according to the present invention, the copper foil for printed wiring board on which the insulating substrate is formed via the coating layer, after the insulating substrate is peeled from the coating layer When the surface of the coating layer is analyzed, the atomic concentration (%) of metal chromium in the depth direction (x: unit nm) obtained from the depth direction analysis from the surface by XPS is f ₁ (x), and the oxide The atomic concentration (%) of chromium is f ₂ (x), the atomic concentration (%) of all chromium is f (x) (f (x) = f ₁ (x) + f ₂ (x)), and chromium metal Assuming that the distance from the surface layer where the concentration of is maximum is F, in the interval [0, F], 0.1 ≦ ∫f ₁ (x) dx / ∫f ₂ (x) dx ≦ 1.0 and ∫h (x) dx / (∫f (x) dx + ∫g (x) dx + ∫h (x) dx + ∫i (x) dx + ∫j (x) dx) satisfies 5% or less.

  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 which is excellent in both adhesion to an insulating substrate and etching property and suitable for fine pitch.

It is a TEM photograph (cross section) of the copper foil (after film formation) of Example 2. It is a depth profile by XPS of the copper foil of Example 2 (after heat treatment equivalent to polyimide varnish curing). It is a depth profile by XPS of the copper foil of Comparative Example 2 (after heat treatment equivalent to polyimide varnish curing). It is a depth profile by XPS of the copper foil (after electroplating) of the comparative example 7. It is a depth profile by XPS of the copper foil (after electroplating) of the comparative example 8.

(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—Ni alloy layer and a Cr layer. The Cu—Ni alloy 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 addition, the Cu—Ni alloy layer in the coating layer of the present invention has better adhesion to the copper foil surface than the Ni single 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 providing the Cu-Ni alloy layer excellent in copper diffusion prevention beforehand on the copper foil base material. Here, the Cu-Ni alloy layer provided for preventing the diffusion of copper contains copper that is not desired to be diffused to the surface. However, 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.
Moreover, the adhesiveness with an insulated substrate can further be improved by providing on the Cu-Ni alloy layer the Cr layer excellent in the adhesiveness with an insulated substrate rather than a Cu-Ni alloy layer. Since the thickness of the Cr layer can be reduced by virtue of the presence of the Cu—Ni alloy layer, the adverse effect 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 the Cr single layer coating that is extremely excellent in adhesiveness with the resin as the outermost surface on the Cu-Ni alloy coating This is presumed to be because the single-layer coating structure having high adhesiveness is maintained even after high-temperature heat treatment during imidization (about 30 minutes to several hours at about 350 ° C.). 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—Ni alloy and Cr.

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

(1) Identification of Cr, Cu—Ni alloy coating 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—Ni alloy layer and the Cr layer. These coating layers are identified by sputtering argon from the surface layer with a surface analyzer such as XPS or AES, performing chemical analysis in the depth direction, and identifying the Cu-Ni alloy layer and Cr layer by the presence of each detection peak. Can do. 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-Ni alloy 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-Ni alloy layer and Cr layer by the weight of the coating metal per unit area. In the coating layer according to the present invention, Ni is present in a coating amount of 15 to 440 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 Ni is less than 15 μg / dm ² , sufficient peel strength cannot be obtained, and when Ni exceeds 440 μg / dm ² , the etching property tends to be significantly reduced. The coverage of Cr is preferably 30 to 145 μg / dm ² , more preferably 36 to 75 μg / dm ² , and the coverage of Ni is preferably 40 to 360 μg / dm ² , more preferably 80 to 270 μg / dm ² . is there.

  When sputtering a pure Ni layer, pure Ni is used as a target. However, this pure Ni target has strong magnetism, and when sputtering is performed by magnetron sputtering or the like, the use efficiency per target becomes low, which is disadvantageous in terms of cost. It is. On the other hand, since the Cu—Ni alloy layer according to the present invention contains Cu, the magnetism of the target can be suppressed and sputtering can be efficiently performed as compared with a pure Ni target.

(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 0.5 nm to 3 nm, preferably 1.0 to 2.5 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 0.5 nm, the peel strength is greatly deteriorated in the heat resistance test and the moisture resistance test, and when the thickness exceeds 3 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—Ni alloy layer and the Cr layer in the coating layer, and it looks like a single layer (see FIG. 1). According to the examination 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—Ni alloy 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 0.5-3 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 metal chromium in the depth direction (x: unit nm) obtained from the depth direction analysis from the surface by XPS is expressed as f ₁ (x ), The atomic concentration (%) of chromium oxide is f ₂ (x), and the atomic concentration (%) of all chromium is f (x) (f (x) = f ₁ (x) + f ₂ (x )), The atomic concentration (%) of nickel 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 ( %) 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.

In addition, when analyzing the surface of the coating layer after peeling the insulating substrate from the coating layer on the copper foil for a printed wiring board on which the insulating substrate is formed via the coating layer, depth direction analysis from the surface by XPS The atomic concentration (%) of chromium metal in the depth direction (x: unit nm) obtained from the above is defined as f ₁ (x), the atomic concentration (%) of chromium oxide as f ₂ (x), If the atomic concentration (%) is f (x) (f (x) = f ₁ (x) + f ₂ (x)) and the distance from the surface layer where the concentration of metallic chromium is maximum is F, the interval [0 , F], ∫h (x) dx / (∫f (x) dx + ∫g (x) dx + ∫h (x) dx + ∫i (x) dx + ∫j (x) dx) is 5 % Or less is desirable.

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, in the interval [0, 1.0], ∫f ₂ (x) dx / (∫f (x) dx + ∫g (x) dx + ∫h (x) dx + ∫i (x) dx + ∫j (x) dx) is 20% or more, and 0.1 ≦ ０．１f ₁ (x) dx / ∫ in the interval [1.0, 2.5] It is preferable to satisfy f ₂ (x) dx ≦ 1.0.

In addition, when analyzing the surface of the coating layer after peeling the insulating substrate from the coating layer on the copper foil for a printed wiring board on which the insulating substrate is formed via the coating layer, depth direction analysis from the surface by XPS The atomic concentration (%) of chromium metal in the depth direction (x: unit nm) obtained from the above is defined as f ₁ (x), the atomic concentration (%) of chromium oxide as f ₂ (x), If the atomic concentration (%) is f (x) (f (x) = f ₁ (x) + f ₂ (x)) and the distance from the surface layer where the concentration of metallic chromium is maximum is F, the interval [0 , F], it is desirable that 0.1 ≦ ∫f ₁ (x) dx / ∫f ₂ (x) dx ≦ 1.0.

  As a constituent material of the Cu—Ni alloy layer of the coating layer, it is preferable from the viewpoint of sputtering efficiency that the magnetism of Ni is suppressed. Therefore, in the coating layer, the atomic concentration (%) of nickel in the depth direction (x: unit nm) obtained from the depth direction analysis from the surface by XPS is g (x), and the atomic concentration of copper (%) Is h (x), it is preferable that ∫g (x) dx / ∫h (x) dx <1 in the interval [0, 5].

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, Cu—Ni having a thickness of 0.25 to 5.0 nm, preferably 0.3 to 4.0 nm, more preferably 0.5 to 3.0 nm is formed on at least a part of the copper foil base material surface by sputtering. It can manufacture by coat | covering in order with an alloy layer and Cr layer of thickness 0.25-2.5 nm, Preferably 0.4-2.0 nm, More preferably, 0.5-1.0 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 1-8)
As a copper foil base material in Examples 1 to 7, a rolled copper foil (C1100 made by Nikko Metal) having a thickness of 18 μm was prepared. The surface roughness (Rz) of the rolled copper foil was 0.7 μm. In addition, as the copper foil base material of Example 8, a non-roughened electrolytic copper foil having a thickness of 18 μm was prepared. The surface roughness (Rz) of the electrolytic copper foil was 1.5 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, Ni (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-Ni alloy or Ni target is sputtered to form a Ni layer or Cu A Ni 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-Ni layer = (I), (II)
Ni layer = (III)
For 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 Ni when using the Cu-Ni alloy of this invention as 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 Table 2 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 maximum 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. Moreover, the TEM observation result of “After the heat resistance test” in Table 2 is that the polyimide film was adhered on the coating layer of the test piece according to the above procedure, and then the test piece was placed in the following high-temperature environment, and the test obtained It is a TEM image after peeling a polyimide film from a piece according to 90 degree peeling method (JIS C6471 8.1). In FIG. 1, the observation photograph after film-forming by TEM of Example 2 is shown illustratively. The Cu—Ni alloy layer obtained by sputtering the Cu—Ni 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. 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 at a temperature of 150 ° C. in an air atmosphere for 168 hours (heat resistance), and at a temperature of 40 ° C. relative The measurement was performed under three conditions: after being allowed to stand for 96 hours in a high humidity environment with a humidity of 95% air (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

(Example 2: Comparative Examples 1-6)
Sputtering time was changed on one side of the rolled copper foil substrate used in Example 1 to form a film having a thickness shown in Table 2 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 7)
One side of the rolled copper foil substrate used in Example 1 was subjected to Ni—Zn plating treatment, chromate treatment and silane coupling agent treatment taught in JP-A-2005-344174 under the following conditions.
[Ni-Zn plating treatment]
・ Nickel sulfate 1.5g / l (Ni conversion)
・ Zinc pyrophosphate 0.5g / l (Zn conversion)
-Potassium pyrophosphate 200g / l
・ PH 9
・ Bath temperature 40 ℃
・ Current density 5A / dm ²
[Chromate treatment]
・ CrO ₃ 1g / l
・ Bath temperature 35 ℃
・ Current density 8A / dm ²
[Silane coupling agent treatment]
・ Gamma-aminopropyltriethoxysilane 5g / l solution is applied

(Example 4: Comparative Example 8)
Ni plating treatment, chromate treatment, and silane coupling agent treatment taught in JP 2007-007937 A were performed on one side of the rolled copper foil base material used in Example 1 under the following conditions.
[Ni plating treatment]
・ NiSO ₄ / 7H ₂ O 300g / l (as Ni ²⁺ )
・ H ₃ BO ₃ 40g / l
・ Bath temperature 25 ℃
・ Current density 1.0A / dm ²
[Chromate treatment]
・ CrO ₃ 1g / l
・ Bath temperature 25 ℃
・ Current density 2.0A / dm ²
[Silane coupling agent treatment]
・ Applying 0.3% solution of 3-aminopropyltriethoxysilane

  The measurement results of Examples 1 to 4 are shown in Tables 2 and 3. 3 shows the depth profile by XPS of the copper foil of Comparative Example 2 (after heat treatment equivalent to polyimide varnish curing), FIG. 4 shows the depth profile by XPS of the copper foil of Comparative Example 7 (after electroplating), FIG. 5 shows the XPS depth profiles of the copper foil of Comparative Example 8 (after electroplating).

Examples 1-4 and 6-8 all have good peel strength and etching properties. Further, Example 5 had good peel strength, although the etching property was slightly inferior to those of other Examples.
Moreover, the depth profile by XPS after the heat processing equivalent to the polyimide varnish hardening of Example 2 is shown in FIG. In the Cr layer, an oxide Cr layer is present on the surface layer, and a metal Cr layer is present immediately below the oxide Cr layer. Since the distances from the surface layer where the concentrations of the oxide Cr and the metal Cr are maximum are different, it can be said that they are separated into two layers. Within the range of 1 nm from the surface layer, the atomic concentration ratio of the oxide Cr exceeded 20%, unlike that formed by electroplating. When a Cu—Ni alloy is targeted, the Ni concentration is always lower than the Cu concentration within the analysis range. Although the heat treatment conditions are severe as polyimide curing conditions, the Cu atoms that cause the deterioration of the adhesive strength with the polyimide hardly reach the surface layer, and the Cu atom concentration is about 1 nm from the surface layer. It has dropped rapidly. This is thought to be because Cu diffusion is suppressed by the coexistence of Cu, Cr and Ni in this region.

In Comparative Example 1, various peel strengths were low as compared with Example 4 in which the Ni adhesion amount was comparable.
In Comparative Example 2, various peel strengths were low as compared with Example 3 in which the Ni adhesion amount was comparable.
In Comparative Example 3, Ni in the Cu—Ni alloy layer was less than 15 μg / dm ² , and various peel strengths were insufficient.
In Comparative Example 4, Ni in the Cu—Ni alloy layer was over 440 μg / dm ² and the etching property was poor.
In Comparative Example 5, the Cr amount was less than 18 μg / dm ² and various peel strengths were insufficient.
In Comparative Example 6, the amount of Cr was over 180 μg / dm ² and the etching property was poor.
In Comparative Example 7, heat resistance and moisture peel strength were poor. According to the surface analysis by XPS, it is estimated that the amount of trivalent Cr in the range of 0 to 1 nm from the surface layer was small.
In Comparative Example 8, various peel strengths were poor. According to the surface analysis by XPS, it is estimated that the amount of trivalent Cr in the range of 0 to 1 nm from the surface layer was small.

Claims (13)

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 Ni alloy layer and a Cr layer, wherein Ni is present in a coating amount of 15 to 440 μg / dm ² and Cr is 18 to 180 μg / dm ² . The copper foil for printed wiring boards according to claim 1, wherein Cr is present in the coating layer in a coating amount of 30 to 145 µg / dm ² . The copper foil for printed wiring boards according to claim ² , wherein Cr is present in the coating layer in a coating amount of 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 0.5 to 3 nm and the minimum thickness is 80% or more of the maximum thickness. Copper foil for plates. The atomic concentration (%) of the chromium metal in the depth direction (x: unit nm) obtained from the analysis of the depth direction from the surface by XPS is f ₁ (x), and the atomic concentration (%) of the chromium oxide is f ₂ (x), the atomic concentration (%) of all chromium as f (x) (f (x) = f ₁ (x) + f ₂ (x)), and the atomic concentration (%) of nickel as 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), the interval [0, 1.0], ∫h (x) dx / (∫f (x) dx + ∫g (x) dx + ∫h (x) dx + ∫i (x) dx + ∫j (x) dx) is以下 f ₂ (x) dx / (∫f (x) dx + ∫g (x) dx + ∫h (x) dx + ∫i (x) dx + ∫j (x) dx) 20% or more, 0.1 ≦ 区間 f ₁ (x) dx / ∫f ₂ (x) dx ≦ 1.0 is satisfied in the interval [1.0, 2.5], and in the interval [0, 5] The copper foil for printed wiring boards according to any one of claims 1 to 4, wherein ∫g (x) dx / ∫h (x) dx <1 is satisfied. When a heat treatment equivalent to polyimide curing is performed, the atomic concentration (%) of the metallic chromium in the depth direction (x: unit nm) obtained from the depth direction analysis from the surface by XPS is f ₁ (x), and oxidation The atomic concentration (%) of chromium is f ₂ (x), the atomic concentration (%) of all chromium is f (x) (f (x) = f ₁ (x) + f ₂ (x)), nickel The atomic concentration (%) of carbon 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 If (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 10% or less, ∫f ₂ (x) dx / (∫f (x) dx + ∫g (x) dx + ∫h (x) dx + ∫i (x) dx + ∫j (x) dx) is 20% or more, and in the interval [1.0, 2.5], 0.1 ≦ ∫f ₁ (x) dx / ∫f ₂ (x) dx ≦ 1.0 And satisfying ∫g (x) dx / ∫h (x) dx <1 in the interval [0, 5]. The copper foil for printed wiring boards in any one of 5. Copper foil for printed wiring board that has been heat-treated equivalent to polyimide curing, and the atomic concentration (%) of metallic chromium in the depth direction (x: unit nm) obtained from the depth direction analysis from the surface by XPS Is f ₁ (x), the atomic concentration (%) of chromium oxide is f ₂ (x), and the atomic concentration (%) of all chromium is f (x) (f (x) = f ₁ (x) + f ₂ (x)), the atomic concentration (%) of nickel is g (x), the atomic concentration (%) of copper is h (x), the atomic concentration (%) of oxygen is i (x), If 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 10% or less, ∫f ₂ (x) dx / (∫f (x) dx + ∫g (x) dx + ∫h ( x) dx + ∫i (x) dx + ∫j (x) dx) is 20% or more, and in the interval [1.0, 2.5], 0.1 ≦ ∫f ₁ (x) dx / ∫f satisfy the ₂ (x) dx ≦ 1.0, in the interval [0,5], ∫g (x) dx / ∫ (X) dx <copper foil for printed wiring boards according to claim 1 satisfying 1. When analyzing the surface of the coating layer after peeling the insulating substrate from the coating layer on the copper foil for a printed wiring board on which the insulating substrate was formed via the coating layer, it was obtained from the depth direction analysis from the surface by XPS. The atomic concentration (%) of metallic chromium in the depth direction (x: unit nm) is f ₁ (x), the atomic concentration (%) of chromium oxide is f ₂ (x), and the total chromium atomic concentration (%) Is f (x) (f (x) = f ₁ (x) + f ₂ (x)), nickel atomic concentration (%) is g (x), and copper atomic concentration (%) is Assuming that h (x), oxygen atomic concentration (%) is i (x), and carbon atomic concentration (%) is j (x), the distance from the surface layer where the concentration of metallic chromium is maximum is F. Then, in the interval [0, F], 0.1 ≦ ∫f ₁ (x) dx / ∫f ₂ (x) dx ≦ 1.0 and ∫h (x) dx / (∫f (x) dx + 8 (g) (x) dx + (h) (x) dx + (i) (x) dx + (j) (x) dx) satisfies 5% or less. Copper foil for printed wiring boards.   A copper foil base material is a rolled copper foil, The copper foil for printed wiring boards in any one of Claims 1-8.   The printed wiring board is a flexible printed wiring board. The copper foil for a printed wiring board according to any one of claims 1 to 9.   The copper clad laminated board provided with the copper foil in any one of Claims 1-10.   The copper clad laminate according to claim 11, wherein the copper foil has a structure bonded to polyimide.   The printed wiring board which used the copper clad laminated board of Claim 11 or 12 as a material.