JP2011009453A - 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 superior in both of adhesion with an insulating substrate and an etching property, and is suitable for a fine pitch.SOLUTION: The copper foil for the printed wiring board includes a copper foil substrate and a coating layer coating at least part of the surface of the copper foil substrate. The coating layer includes a Ti layer and a Cr layer laminated in this order from the surface of the copper foil substrate. The coating layer contains Ti with a coating amount of 15-140 μg/dmand Cr with a coating amount of 30-150 μg/dm, wherein the ratio Ti/Cr of the coating amounts of Ti and Cr is ≤1.2.

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.

  In the method of providing, for example, a Ni layer or a Ni—Cr alloy layer on the surface of the copper foil, there is much room for improvement in the basic characteristic of adhesion to the insulating substrate. For example, a method of providing a Cr layer on a copper foil surface provides relatively high adhesiveness, but is poor in etching property, and after etching for forming a conductor pattern, Cr remains on the insulating substrate surface. "Is likely to occur.

  Therefore, in recent years, a first metal layer is formed on the surface of the copper foil, and a Cr layer having good adhesiveness with an insulating substrate is formed on the first metal layer as the second metal layer with good etching properties. Research and development have been conducted on a technique for simultaneously obtaining good adhesion to an insulating substrate and good etching property by forming the thin film to such a degree.

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.

JP 2006-222185 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.

  Then, this invention makes it a subject to provide the copper foil for printed wiring boards which was excellent in both the adhesiveness with an insulated substrate and etching property, was suitable for fine pitch formation, and the magnetism was suppressed. Moreover, this invention makes it another subject to provide the manufacturing method of such copper foil for printed wiring boards.

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. As a result of intensive studies, the present inventors, as a result of intensive studies, are excellent when a Ti layer and a Cr layer are sequentially provided on the surface of the copper foil substrate with an extremely thin thickness of nanometer order. It has been found that a coating layer of copper foil with suppressed magnetism can be obtained while at the same time obtaining adhesion with an insulating substrate and excellent etching properties.
In addition, as a copper foil base material surface treatment technique using Ti, there is one that suppresses precipitation of copper protrusions using Ti ions (Japanese Patent Laid-Open No. 2001-355092), but the Ti ions form a Ti layer. It is not used to do.

The present invention completed on the basis of the above knowledge, in one aspect,
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 a Ti layer laminated in order from the copper foil substrate surface And the coating layer has a coating amount of Ti of 15 to 140 μg / dm ² , Cr of 30 to 150 μg / dm ² , and a ratio Ti / Cr of the coating amount of Ti and Cr is 1. It is a copper foil for printed wiring boards existing at 2 or less.

In one embodiment of the copper foil for printed wiring boards according to the present invention, the coating amount of Ti is coverage of 30~90μg / dm ^2, Cr is 50-100 [mu] g / dm ^2.

  In yet another embodiment of the copper foil for printed wiring board according to the present invention, when the cross section of the coating layer is observed with a transmission electron microscope, the maximum thickness is 0.5 to 6.0 nm, and the minimum thickness is 80% or more of the maximum thickness.

  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 still another embodiment of the copper foil for printed wiring board according to the present invention, a polyamic acid solution, which is a polyimide precursor, is applied on the coating layer so as to have a dry body of 25 μm, and is 130 ° C. with an air dryer. A polyimide is formed on the coating layer through a step of drying in 30 minutes and a step of imidization at 350 ° C. for 30 minutes in a high-temperature heating furnace in which the nitrogen flow rate is set to 10 L / min, and then at a temperature of 150 ° C. When the cross-section of the coating layer is peeled off from the coating layer according to the 180 ° peeling method (JIS C 6471 8.1) after being left in a high-temperature environment under an air atmosphere for 168 hours, the maximum is observed. The thickness is 0.5 to 6 nm, and the minimum thickness is 80% or more of the maximum thickness.

  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 all chromium and titanium obtained from the depth direction analysis from the surface by XPS. Assuming that (%) is f (x) and g (x), 区間 g (x) dx / ∫f (x) dx ≦ 0.3 is satisfied in the interval [0, 1.0].

  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), oxygen atomic concentration (%) as i (x), copper atomic concentration (%) as h (x), titanium atomic concentration (%) as g (x), carbon If j (x) is the atomic concentration (%), h (x) dx / (∫f (x) dx + ∫g (x) dx + ∫h (x) in the interval [0, 1.0] dx + ∫i (x) dx + ∫j (x) dx) is 1.0% or less.

  In another aspect of the present invention, at least a part of a copper foil base material surface is sequentially coated with a Ti layer having a thickness of 0.3 to 3 nm and a Cr layer having a thickness of 0.5 to 2.5 nm by a sputtering method. It is a manufacturing method of the copper foil for printed wiring boards containing.

  In still another aspect, the present invention is a copper clad laminate including 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, is suitable for fine pitch formation, and has reduced magnetism.

4 is a TEM photograph (cross section) of a copper foil (sputtered up) in Example 3. FIG. It is a TEM photograph (cross section) of the copper foil of Example 3 (after heat treatment equivalent to polyimide varnish curing). It is a depth profile by XPS of the copper foil (sputter rising) of Example 3. It is a depth profile by XPS of the copper foil of Example 3 (after heat treatment equivalent to polyimide varnish curing). It is a depth profile by XPS of the copper foil of Comparative Example 6 (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 7 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 Ti layer and a Cr layer. The Ti 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 Ti layer excellent in copper diffusion prevention on the copper foil base material. In addition, the adhesion with the insulating substrate can be further improved by providing on the Ti layer a Cr layer having better adhesion with the insulating substrate than with the Ti layer. Since the thickness of the Cr layer can be reduced by virtue of the presence of the Ti layer, the adverse effect on the etching property can be reduced. In addition, the adhesiveness as used in the present invention refers to adhesiveness after being placed under high temperature (heat resistance) and adhesiveness after being placed under high humidity (humidity resistance) in addition to normal adhesiveness. Also refers to.
The inventor has confirmed through the present invention that if the Ti layer is too thick, Ti atoms diffuse into the Cr layer and reach the adhesion interface. Thereby, even though Cu atoms are not present at the metal / insulating substrate interface, Ti atoms that are inferior in adhesion to the insulating substrate as compared to Cr atoms are present at the interface, resulting in poor adhesion. Therefore, in order to prevent the diffusion of Cu and ensure good adhesion to the insulating substrate, it is necessary to define the ratio of the Ti layer to the Cr layer. In the present invention, the ratio of the amount of adhesion between the two is specified.

  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 is improved by such a configuration is not clear, but a Cr single layer coating having excellent adhesiveness with the resin as the outermost surface was formed on the Ti coating. Thus, it is presumed that the single-layer coating structure having high adhesiveness is maintained even after high temperature thermal history during imidization (about 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 Ti and Cr.

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

(1) Identification of Ti and Cr coating layer In this invention, at least one part of the surface of a copper foil raw material is coat | covered in order of Ti layer and Cr layer. These coating layers can be 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 Ti layer and Cr layer by the presence of each detection peak. 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 Ti layer and Cr layer are very thin, it is difficult to evaluate the thickness accurately with XPS and AES. For this reason, in the present invention, the thicknesses of the Ti layer and the Cr layer are evaluated by the weight of the coated metal per unit area. In the coating layer according to the present invention, Ti is present in a coating amount of 15 to 140 μg / dm ² and Cr is 30 to 150 μg / dm ² . When Ti is less than 15 μg / dm ² , sufficient peel strength cannot be obtained, and when Ti exceeds 140 μg / dm ² , the etching property tends to be significantly reduced. When Cr is less than 30 μg / dm ² , sufficient peel strength cannot be obtained, and when Cr exceeds 150 μg / dm ² , the etching property tends to be significantly reduced. The coating amount of Ti is preferably 30 to 90 μg / dm ² , and the coating amount of Cr is preferably 50 to 100 μg / dm ² . Moreover, the ratio Ti / Cr of the coating amount of Ti and Cr is 1.2 or less.

(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 6 nm, preferably 2.5 to 4.0 nm. In other words, the coating layer has a minimum thickness of 80% or more, preferably 90% 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 6 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 Ti layer and the Cr layer in the coating layer, and it looks like a single layer (see FIGS. 1 and 2). 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 Ti layer is considered to exist on the copper foil base material 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 to 6 nm, and even at the minimum thickness, it is possible to maintain 80% or more of the maximum thickness.

(4) Atomic concentration ratio between each element in the vicinity of the surface of the coating layer First, the fact that internal copper is not diffused on the outermost surface of the coating layer (in the range of 0 to 1.0 nm from the surface) increases the adhesive strength. Then it is desirable. 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 oxygen is i (x), the atomic concentration (%) of copper is h (x), the atomic concentration (%) of titanium is g (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 1.0% or less.

  On the coating layer surface, if the coating amount of titanium is a certain amount or more with respect to the coating amount of chromium, there is a possibility that titanium reaches the adhesion interface and lowers the peel strength. For this reason, assuming that the atomic concentration (%) in the depth direction (x: unit nm) of all chromium and titanium obtained from the depth direction analysis from the surface by XPS is f (x) and g (x), respectively. In the interval [0, 1.0], it is preferable to satisfy ∫g (x) dx / ∫f (x) dx ≦ 0.3.

(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, at least a part of the surface of the copper foil base material is formed by sputtering to a thickness of 0.3 to 3 nm, preferably 0.5 to 2 nm, and a thickness of 0.5 to 2.5 nm, preferably 0.5. It can be manufactured by sequentially coating with a Cr layer of ˜1.5 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. In addition, a uniform and thin film can be formed without being affected by electrochemical defects of the substrate as in wet plating. Note that the Ti layer of the present invention cannot be formed by wet plating. This is because the standard potential of Ti is extremely lower than that of hydrogen, so that hydrogen is generated and Ti is not plated.
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: Cover layer formed by sputtering of Ti layer and Cr layer)
As the copper foil base material, a rolled copper foil (C1100 made by Nikko Metal) having a thickness of 18 μm and a non-roughened foil of electrolytic copper foil were prepared. The surface roughness (Rz) of the rolled copper foil and the electrolytic copper foil was 0.7 μm and 1.5 μm, respectively.

On one side of the copper foil, a thin oxide film previously adhered to the surface of the copper foil base material was removed by reverse sputtering under the following conditions, and a Ti 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:
For Ti layer = Ti (purity 3N)
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. (Ti: 2.73 nm / min, Cr: 2.82 nm / min)

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.

<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).
<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, 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 2.3 nm / min (SiO ₂ conversion)
In the XPS measurement results, separation of chromium oxide and metallic chromium was performed using analysis software Multi Pak V7.3.1 manufactured by ULVAC.
<Measurement by TEM>
The measurement conditions of TEM when the coating layer is observed by TEM are shown below. The thicknesses shown in Table 1 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. In Table 1, the TEM observation result “after the heat resistance test” was obtained by adhering a polyimide film on the coating layer of the test piece according to the above procedure, and then placing the test piece in the following high-temperature environment. It is a TEM image after peeling a polyimide film from a test piece according to 180 degree peeling method (JIS C 6471 8.1). FIGS. 1 and 2 exemplarily show respective observation photographs immediately after sputtering by TEM and after heat treatment equivalent to polyimide varnish curing.
-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 150 ° C. in an air atmosphere (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 180 ° peeling method (JIS C 6471 8.1).

<Etching evaluation>
For the copper foil laminated with polyimide as described above, a circuit pattern of line and space 20 μm / 20 μm is formed using a predetermined resist, and then etched using an etching solution (ferric chloride, temperature 43 ° C.). Processed. The resin surface between the treated circuits was measured with EPMA, the remaining Cr and Ti were analyzed, and evaluated according to the following criteria.
×: Cr or Ti was observed on the entire surface between circuits Δ: Cr or Ti was partially observed between circuits ○: Cr or Ti was not observed between circuits

  The measurement results are shown in Table 1. In Table 1, SP / SP indicates that both Ti and Cr are coated by sputtering.

  As shown in Table 1, Examples 1 to 5 all have good peel strength and etching properties. For reference, FIGS. 3 and 4 show depth profiles obtained by XPS after the spattering of the copper foil of Example 3 and heat treatment equivalent to polyimide varnish curing.

On the other hand, in Comparative Example 1, the adhesion amount of titanium was less than 15 μg / dm ² , Cu diffusion could not be prevented, and the peel strength was poor.
In Comparative Example 2, the chromium adhesion amount was less than 30 μg / dm ² , and the peel strength was poor.
In Comparative Example 3, the adhesion amount of titanium was more than 140 μg / dm ² and the etching property was poor.
In Comparative Example 4, the adhesion amount of chromium was more than 150 μg / dm ² and the etching property was poor.
In Comparative Examples 5 and 6, although the adhesion amounts of titanium and chromium were within the specified range, the peel strength was poor. This is because the amount of titanium attached is larger than the amount of chromium attached, so that titanium diffuses in the chromium layer and reaches the adhesion interface with the polyimide. FIG. 6 is a XPS depth profile of the copper foil of Comparative Example 6 (after heat treatment equivalent to polyimide varnish curing). The ratio of the total titanium amount to the total chromium amount within 1 nm of the surface layer exceeded 0.3.
From Comparative Examples 5 and 6 and Example 5, it can be seen that the adhesion amount of titanium and chromium is within the specified range, and the ratio Ti / Cr of the adhesion amount needs to be 1.2 or less. . Moreover, it turns out from the density | concentration profile of the film | membrane after these polyimide hardening | curing that the ratio of the total titanium amount in the surface layer vicinity 1nm and the total chromium amount needs to be 0.3 or less.

(Example 2: Conventional coating layer)
Each copper foil sample was manufactured on the same conditions as Example 1 except having provided the coating layer on the following conditions.

<Comparative example 7: Ni-Cr alloy layer>
A coating layer was formed using a Ni—Cr alloy of Ni: 80 mass% and Cr 20 mass% as a sputtering target.

<Comparative Example 8: Coating layer in which Ni layer and Cr layer are formed by electroplating>
Ni electroplating and Cr electroplating were performed in order under the following conditions. This comparative example is for comparison with a coating layer formed by the method described in JP-A-2006-222185.
(1) Ni plating / plating bath: nickel sulfamate (110 g / L as Ni ²⁺ ), H ₃ BO ₃ (40 g / L)
・ Current density: 1.0 A / dm ²
・ Bath temperature: 55 ℃
(2) Cr plating / plating bath: CrO ₃ (1 g / L), Zn (powder 0.4 g), Na ₃ SO ₄ (10 g / L)
Current density: 2.0 A / dm ²
・ Bath temperature: 55 ℃

<Comparative Examples 9 and 10: Coating layer in which only Cr layer is formed by electroplating>
Only the Cr electroplating treatment was performed under the following conditions.
-Plating bath: CrO ₃ (1 g / L), Zn (powder 0.4 g), Na ₃ SO ₄ (10 g / L)
Current density: 2.0 A / dm ²
・ Bath temperature: 55 ℃

  The measurement results are shown in Table 2.

In Comparative Example 7, the Ti layer of the coating layer of the present invention was a Ni layer, and the peel strength was poor.
In Comparative Example 8, a Ni layer and a Cr layer are formed by electroplating. Thus, although the Ni layer was formed by electroplating as a Cu diffusion preventing layer, the thickness of the film became uneven and the peel strength was poor.
In Comparative Example 9, only the Cr layer was formed by electroplating, and the peel strength was poor because the thickness of the coating became uneven and there was no Cu diffusion prevention layer.
In Comparative Example 10, as in Comparative Example 9, only the Cr layer was formed by electroplating. However, since the Cr coating amount was sufficient, the film thickness was uniform, and the Cu diffusion prevention function was also provided. Was. However, the etching property was poor.
From the results of Comparative Examples 9 and 10, it was confirmed that it was difficult to achieve both etching properties and film uniformity by electroplating.

1, 2 Coating layer thickness

Claims (12)

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 a Ti layer laminated in order from the copper foil substrate surface And the coating layer has a coating amount of Ti of 15 to 140 μg / dm ² , Cr of 30 to 150 μg / dm ² , and a ratio Ti / Cr of the coating amount of Ti and Cr is 1. Copper foil for printed wiring boards existing at 2 or less. Ti copper foil for printed wiring boards according to claim 1, wherein the amount of coating coverage of 30~90μg / dm ^2, Cr is 50-100 [mu] g / dm ² of.   The printed wiring board according to claim 1 or 2, wherein when the cross section of the coating layer is observed with a transmission electron microscope, the maximum thickness is 0.5 to 6.0 nm, and the minimum thickness is 80% or more of the maximum thickness. Copper foil.   The copper foil for a printed wiring board according to any one of claims 1 to 3, wherein the copper foil base material is a rolled copper foil.   A printed wiring board is a flexible printed wiring board, Copper foil for printed wiring boards as described in any one of Claims 1-4.   A polyamic acid solution, which is a polyimide precursor, is applied on the coating layer to a dry body of 25 μm, dried at 130 ° C. for 30 minutes in an air dryer, and further heated at a high temperature with a nitrogen flow rate set to 10 L / min. The polyimide film is formed on the coating layer through a process of imidization at 350 ° C. for 30 minutes in a furnace, and then left at a temperature of 150 ° C. in a high temperature environment under an air atmosphere for 168 hours, and then the polyimide film is peeled by 180 ° When the cross section of the coating layer after peeling from the coating layer according to the method (JIS C 6471 8.1) is observed with a transmission electron microscope, the maximum thickness is 0.5 to 6 nm, and the minimum thickness is 80, which is the maximum thickness. The copper foil for printed wiring boards according to any one of claims 1 to 5, wherein the copper foil for printed wiring boards is at least%.   If the atomic concentrations (%) in the depth direction (x: unit nm) of all chromium and titanium obtained from the depth direction analysis by XPS are f (x) and g (x), respectively, the interval [0 , 1.0], the copper foil for printed wiring boards according to any one of claims 1 to 6, which satisfies ∫g (x) dx / ∫f (x) dx ≦ 0.3.   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 oxygen is i (x). When the atomic concentration (%) of copper is h (x), the atomic concentration (%) of titanium is g (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 1.0. The copper foil for printed wiring boards according to any one of claims 1 to 7.   A copper foil for a printed wiring board comprising sequentially coating at least a part of a copper foil substrate surface with a Ti layer having a thickness of 0.3 to 3 nm and a Cr layer having a thickness of 0.5 to 2.5 nm by a sputtering method. Production method.   The copper clad laminated board provided with the copper foil as described in any one of Claims 1-8.   The copper clad laminate according to claim 10, wherein the copper foil has a structure bonded to polyimide.   The printed wiring board which used the copper clad laminated board of Claim 10 or 11 as a material.