JP5373453B2 - Copper foil for printed wiring boards - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide copper foil for a printed wiring board with improved adhesion with an insulating substrate. <P>SOLUTION: The copper foil for a printed wiring board includes a copper foil substrate and a coating layer covering at least a part of the surface of the copper foil substrate. The copper foil substrate satisfies the following relationships: E(l)/E(d)&ge;2.0 and E(d)&le;1.5 &mu;m where, when observed from a cross section parallel to the rolling direction, E(d) is the average value of an oil pit depth d and E(l) is the average value of an oil pit width l. The coating layer comprises a Ni layer and a Cr layer that are sequentially stacked from the surface of the copper foil substrate. The coating layer has a Cr content of 15-210 &mu;g/dm<SP>2</SP>and a Ni content of 15-440 &mu;g/dm<SP>2</SP>. Observations of the cross section of the coating layer through a transmission electron microscope prove that the maximum thickness of the coating layer is 0.5-5 nm and the minimum thickness of the coating layer is at least 80% of the maximum thickness. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

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.

  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.

  Generally, a printed wiring board is manufactured through a process in which an insulating substrate is bonded to a copper foil to form a copper-clad laminate, and then a conductor pattern is formed on the copper foil surface by etching. Therefore, the copper foil for printed wiring boards is required to have adhesiveness and etching properties with an insulating substrate.

  In order to improve the adhesion to the insulating substrate, it has been generally performed surface treatment to form unevenness on the copper foil surface called roughening treatment, but recently, tin, chromium, copper, A method of forming a metal layer or an alloy layer of iron, cobalt, zinc, nickel or the like has come to be used.

  Japanese Patent Application Laid-Open No. 2000-340911 describes that the adhesion strength between the base material and the copper foil is improved by forming a metal chromium layer on the surface of the copper foil for printed wiring board by vapor deposition.

  In JP 2007-207812 A, a Ni-Cr alloy layer is formed on the surface of a copper foil, and an oxide layer having a predetermined thickness is formed on the surface of the alloy layer, thereby making the surface of the copper layer smooth and anchoring effect. It is described that the adhesiveness with the resin base material is greatly improved even in a state where the amount of the resin is small. Then, a Ni—Cr alloy layer having a thickness of 1 to 100 nm is formed by vapor deposition 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.

In JP-A-2006-222185, in a surface-treated copper foil for a polyimide-based flexible copper-clad laminate, (1) Ni layer or / and Ni alloy containing 0.03-3.0 mg / dm ² in terms of Ni amount. (2) Chromate layer containing 0.03 to 1.0 mg / dm ^{2 in} terms of Cr, (3) Cr layer or / Cr alloy layer containing 0.03 to 1.0 mg / dm ^{2 in} terms of Cr (4) A chromate layer containing 0.03 to 1.0 mg / dm ^{2 of} Cr on the Ni layer and / or Ni alloy layer containing 0.03 to 3.0 mg / dm ^{2 of} Ni , (5) Cr layer in the Cr content on the Ni layer and / or Ni alloy layer in the Ni amount 0.03~3.0mg / dm ² contain containing 0.03~1.0mg / dm ² or / And by providing a Cr alloy layer as a surface treatment layer, a polyimide resin layer It is described that a copper foil for a polyimide-based flexible copper-clad laminate having a high peel strength and excellent insulation reliability, etching characteristics when forming a wiring pattern, and bending characteristics can be obtained. When the thickness of the surface treatment layer is estimated from the above-mentioned Ni amount and Cr amount, it is on the order of μm. In the examples, it is described that a surface treatment layer is provided using electroplating.

JP 2000-340911 A JP 2007-207812 A JP 2006-222185 A

  In the method of providing 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 an insulating substrate. Japanese Patent Laid-Open No. 2003-228561 has a description that the Ni—Cr alloy layer is provided so that the adhesiveness to the resin base material can be improved even if the surface of the copper foil is smoothed, but there is still room for improvement.

  In the method of providing a Cr layer on the copper foil surface, relatively high adhesion can be obtained. However, the Cr layer has room for improvement in etchability. That is, the Cr layer has higher adhesiveness than the Ni layer, but Cr is inferior in etching property, so that after the etching process for forming the conductor pattern, the “etching residue”, in which Cr remains on the insulating substrate surface, is likely to occur. . In addition, the heat resistance is not sufficient, and there is a problem that the adhesion to the insulating substrate is significantly lowered after being placed in a high temperature environment. For this reason, it is hard to say that it is a promising technique under the circumstances where fine pitch of printed wiring boards is progressing. On the other hand, the chromate layer has room for improvement in adhesion.

Described in Patent Document 3, in the amount of Cr 0.03~1.0mg / dm ² contained over the 0.03~3.0mg / dm ² Ni layer containing and / or Ni alloy layer in the Ni amount Although the method of providing a Cr layer or / and a Cr alloy layer as a surface treatment layer can provide relatively high adhesion and etching properties, there is still room for improvement in characteristics.

Under such a background, the applicant has excellent adhesion to an insulating substrate when a Ni layer and a Cr layer are uniformly provided on the surface of a copper foil base material with an extremely thin thickness of nanometer order. PCT / JP2008 / 073256 (unpublished at the time of this application) was filed earlier. Specifically, the invention according to claim 1 is a copper foil for a printed wiring board comprising a copper foil base material and a coating layer covering at least a part of the surface of the copper foil base material, 1) The coating layer is composed of a Ni layer and a Cr layer laminated in order from the surface of the copper foil substrate. (2) The coating layer has Cr of 15 to 210 μg / dm ² and Ni of 15 to 440 μg / dm ² . (3) Copper for printed wiring boards having a maximum thickness of 0.5 to 5 nm and a minimum thickness of 80% or more of the maximum thickness when the cross section of the coating layer is observed with a transmission electron microscope It is a foil. According to this invention, the copper foil for printed wiring boards excellent in both the adhesiveness with the insulating substrate and the etching property can be obtained.

  However, it has been found that even if a thin coating layer such as the Ni layer and the Cr layer as described above is provided on the copper foil base material, sufficient adhesive strength may not be obtained depending on the copper foil base material. Accordingly, the present invention aims to provide an improved invention of the above prior invention, more specifically, to provide a copper foil for a printed wiring board with improved adhesion to an insulating substrate and a method for producing the same. Is an issue.

  As a result of intensive studies in order to solve the above problems, the present inventor has found that the surface state of the copper foil before providing the coating layer has a significant effect on the adhesion to the insulating substrate. That is, it has been found that oil pits generated on the surface of the copper foil impair the uniformity of the thickness of the coating layer and cause a decrease in adhesion to the insulating substrate. The oil pit is a fine dent having a depth of several μm to several tens of μm that is formed when the rolling oil supplied between the rolling roll and the metal plate is pushed into the metal plate by a force acting during rolling.

  Since etching occurs not only in the plate thickness direction but also in the circuit width direction, the thicker the copper foil, the longer the trapezoidal skirt of the circuit cross section formed by etching. Therefore, to make fine wiring, it is necessary to reduce the thickness of the copper foil, but oil pits are likely to occur as the copper foil becomes thinner. The plastic deformation of the copper foil is slip deformation or shear band deformation, but as the copper foil becomes thinner, the shear band deformation becomes dominant, and as a result, deep oil pits are easily formed in the copper foil.

  The present inventor continued further investigation based on the above findings, and it is practically difficult to completely eliminate the oil pit. However, the oil pit is small overall, and the width of the oil pit relative to the depth of the oil pit. It has been found that if the thickness is large, the uniformity of the coating layer laminated on the copper foil can be easily obtained. Specifically, when the average value of the oil pit depth d when the copper foil is observed from a cross section parallel to the rolling direction is E (d) and the average value of the oil pit width l is E (l), E It was found that when (d) ≦ 1.5 μm and E (l) / E (d) ≧ 2.0 were satisfied, a coating layer having a uniform thickness was easily obtained.

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,
When the copper foil base material is observed from a cross section parallel to the rolling direction, the average value of the oil pit depth d is E (d) and the average value of the oil pit width l is E (l). (L) / E (d) ≧ 2.0, E (d) ≦ 1.5 μm,
The coating layer is composed of a Ni layer and a Cr layer laminated in order from the copper foil base material surface,
In the coating layer, Cr is present in a coverage of 15 to 210 μg / dm ² , Ni is 15 to 440 μg / dm ² ,
When the cross section of the coating layer is observed with a transmission electron microscope, the maximum thickness is 0.5 to 5 nm, and the minimum thickness is 80% or more of the maximum thickness.
It is a copper foil for printed wiring boards.

  In one embodiment of the copper foil for printed wiring board according to the present invention, E (l) / E (d) ≧ 5.0.

  In another embodiment of the copper foil for printed wiring boards according to the present invention, E (l) / E (d) ≧ 10.0.

  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 yet another embodiment of the copper foil for printed wiring board according to the present invention, a polyimide varnish is applied on the coating layer so as to have a dry body of 25 μm, and imidized in an air dryer at 130 ° C. for 30 minutes. The polyimide film is adhered onto the coating layer through the steps and the step of imidizing at 350 ° C. for 30 minutes in a high-temperature heating furnace set at a nitrogen flow rate of 10 L / min, and then at a temperature of 150 ° C. under an air atmosphere When the cross section of the coating layer after detaching from the coating layer according to the 180 ° peeling method (JIS C 6471 8.1) after standing in the environment for 168 hours is observed with a transmission electron microscope, the maximum thickness is 0.5. The minimum thickness is 70% or more of the maximum thickness.

  In another aspect of the present invention, at least a part of the surface of the copper foil substrate is sequentially coated with a Ni layer having a thickness of 0.2 to 5.0 nm and a Cr layer having a thickness of 0.2 to 3.0 nm by sputtering. The copper foil base material has an oil pit depth average value E (d) and an oil pit width average value E (l) when observed from a cross section parallel to the rolling direction. , E (l) / E (d) ≧ 2.0 and E (d) ≦ 1.5 μm.

  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.

  ADVANTAGE OF THE INVENTION According to this invention, the copper foil for printed wiring boards with improved adhesiveness with an insulated substrate can be provided.

It is an example of the depth profile by XPS when a Ni layer and a Cr layer are each sputtered to a copper foil base material with a thickness of 1 nm. It is a TEM photograph of the section of the coating layer which consists of a Ni layer and a Cr layer. It is an example of the photograph by the three-dimensional roughness analyzer (3D-SEM) of the copper foil surface (1000 times). It is an example of the roughness profile of the copper foil surface by 3D-SEM.

1. Copper foil base material copper foil base material used in the present invention is a rolled copper foil. This is because the oil pit is a problem peculiar to rolled copper foil. Generally, a rolled copper foil is manufactured 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 10 to 20 μm. However, oil pits are likely to be a problem when the thickness of the copper foil is 30 μm or less, more typically 20 μm or less, and in the present invention, copper having a thickness of 20 μm or less, more typically 12 μm. Of particular interest are foil substrates.

  The copper foil base material used in the present invention is controlled to have a small oil pit. Specifically, when the average value of the oil pit depth d is E (d) and the average value of the oil pit width l is E (l) when observed from a cross section parallel to the rolling direction, E (l ) / E (d) ≧ 2.0 and E (d) ≦ 1.5 μm. If the copper foil base material has a surface shape with controlled oil pits, smoothness is easily obtained when the coating layer is formed on the surface, and excellent adhesion to the resin substrate can be obtained. .

  If the oil pits become deeper, the thickness of the copper foil becomes non-uniform and it becomes difficult to obtain a coating layer with a uniform thickness, and the adhesiveness with the insulating substrate is reduced where the film is thin, resulting in reduced circuit reliability. Become. In addition, if there is a deep oil pit, the strength of the circuit itself is low at that portion, and this causes the circuit to be easily peeled from the substrate when stress is applied to the circuit from the outside. Specifically, if the average value E (d) of the oil pit depth exceeds 1.5 μm, these tendencies become strong. Accordingly, the average value of the oil pit depth E (d) is 1.5 μm or less, preferably 1.0 μm or less, more preferably 0.5 μm or less, and typically 0.2 to 1.m. 5 μm.

  However, even if the depth of the oil pit satisfies the above condition, the ratio of the average value of the oil pit width to the average value of the oil pit depth E (l) / E (d) (hereinafter referred to as “aspect ratio”) When the.) Is small, the inside of the oil pit is difficult to be coated, and the coating layer is likely to be adversely affected. In other words, even if the oil pits are somewhat deep, if the width of the oil pits is large, there will be no major disadvantage in the uniformity of the coating layer. Specifically, E (l) / E (d) ≧ 2.0, preferably E (l) / E (d) ≧ 5.0, and E (l) / E ( d) ≧ 10.0 is more preferred, E (l) / E (d) ≧ 20.0 is even more preferred, typically 1.0 ≦ E (l) / E (d ) ≦ 50.0.

  In a typical embodiment of the present invention, the average value of oil pit width E (l) is 1.0 to 10.0 μm. As the average value E (l) of the oil pit width is decreased, the aspect ratio tends to decrease. Therefore, E (l) is more typically 5.0 to 10.0 μm.

  In the present invention, the average value E (d) of the oil pit depth d and the average value E (l) of the oil pit width l are obtained as follows. Using a three-dimensional roughness analyzer (3D-SEM), a 1000 times SEM image is taken. A sample SEM image at this time is shown in FIG. Select one line in the rolling direction (90 μm) arbitrarily, and add the two adjacent line segments (90 μm) away from each other by 20 μm. calculate. FIG. 4 is an example of a roughness profile for one of the line segments obtained by 3D-SEM. l is the length of the line segment that connects both ends of the V-shape representing the oil pit, and d is the length from the vertex of the V-shape to the intersection with the line segment that connects both ends of the V-shape with respect to the straight line. That's it. This is repeated 5 times (1000 times), and the arithmetic averages E (d) and E (l) of d and l are calculated. Thereby, the aspect ratio is also obtained.

  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.

2. At least a part of the surface of the coating layer copper foil base material is sequentially coated with a Ni layer and a Cr layer. The Ni layer and the Cr layer constitute a coating layer. Although there is no restriction | limiting in particular in the location to coat | cover, Generally it is set 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 Ni layer excellent in copper diffusion prevention on the copper foil base material. Further, by providing a Cr layer on the Ni layer that has better adhesion to the insulating substrate than the Ni layer, the adhesion to the insulating substrate can be further improved. Since the thickness of the Cr layer can be reduced by virtue of the presence of the Ni 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.

  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 a Cr single layer film having excellent adhesiveness with the resin as the outermost surface was formed on the Ni coating. Thus, it is presumed that the single-layer coating structure having high adhesiveness is maintained even after the 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 Ni and Cr.

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

(1) Identification of Cr, Ni 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 Ni layer and the 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 Ni layer and the Cr layer by the presence of each detection peak. Moreover, the order of covering from the position of each detection peak can be confirmed. FIG. 1 is an example of a depth profile by XPS when a Ni layer and a Cr layer are each sputtered to a copper foil base with a thickness of 1 nm.

(2) Adhering amount On the other hand, since these Ni layer and Cr layer are very thin, it is difficult to evaluate the thickness accurately with XPS and AES. Therefore, in the present invention, the thicknesses of the Ni layer and the Cr layer are evaluated by the weight of the coated metal per unit area as in Patent Document 3. In the coating layer according to the present invention, Cr is present in a coating amount of 15 to 210 μg / dm ² and Ni is 15 to 440 μg / dm ² . When Cr is less than 15 μg / dm ² , sufficient peel strength cannot be obtained, and when Cr exceeds 210 μg / dm ² , the etching property tends to be significantly lowered. 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 18 to 150 μg / dm ² , more preferably 30 to 100 μg / dm ² , and the coverage of Ni is preferably 20 to 195 μg / dm ² , more preferably 40 to 180 μg / dm ² , Typically 40 to 100 μg / dm ² .

(3) Observation by transmission electron microscope (TEM) When the cross section of the coating layer according to the present invention is observed by a transmission electron microscope, the maximum thickness is 0.5 nm to 5 nm, preferably 1 to 4 nm, and the minimum thickness. The coating layer has a thickness of 80% or more of the maximum thickness, preferably 85% or more, and very little variation. 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 5 nm, the etching property tends to be lowered. 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 Ni layer and the Cr layer in the coating layer, and it looks like a single layer (see FIG. 2). According to the examination result of the present inventors, the coating layer found by TEM observation is considered to be a layer mainly composed of Cr, and the Ni 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. Although the boundary of the coating layer may be unclear depending on the observation location, such a location is excluded from the thickness measurement location. 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 5.0 nm, and even at the minimum thickness, 70% or more, preferably 80% of the maximum thickness can be maintained.

3. Manufacturing method of copper foil which concerns on this invention The copper foil for printed wiring boards which concerns on this invention can be formed by sputtering method. That is, at least a part of the surface of the copper foil base material is formed by sputtering, with a thickness of 0.2 to 5.0 nm, preferably 0.25 to 2.5 nm, more preferably 0.5 to 2.0 nm. It can be produced by sequentially coating with a Cr layer having a thickness of 0.2 to 3.0 nm, preferably 0.25 to 2.0 nm, more preferably 0.5 to 1.5 nm. 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 1 μm (1000 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.

  As described above, the plastic deformation of the rolled material is mainly the slip deformation in which the crystal grain boundary slides in the region where the thickness is large, but the shear band deformation becomes dominant as the thickness decreases. In copper foil, when shear band deformation occurs near the surface, it appears in the form of oil pits. The occurrence of oil pits can be suppressed by any one or a combination of lowering the viscosity of the rolling oil, lowering the sheet passing speed, and increasing the total rolling reduction of cold rolling. For example, the rolling oil viscosity is 8.0 cSt or less, preferably 7.0 cSt or less, the sheet passing speed is 800 m / min or less, preferably 600 m / min or less, and the total rolling reduction of cold rolling is 85% or more, preferably 90 % Or more.

Furthermore, in forming the surface defined by the present invention, it is important to increase the tension applied to the rolled material. As a result, even in a processing region where shear band deformation is dominant in normal cases, slip deformation can be induced to control the generation of oil pits, and the oil pits become shallow. That is, the aspect ratio of the oil pit is increased. Specifically, either the front or rear tension of the final two passes is 100 N / mm ² or more, preferably 120 N / mm ² or more. In order to control the shape of the copper foil, either the front or rear tension may be less than 100 N / mm ² .

4). Production of Printed Wiring Board A printed wiring board (PWB) can be produced 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 coating layer of copper foil, 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. For example, an etching resist is applied only to a necessary portion as a conductor pattern on the copper foil surface of the copper clad laminate, and an etching solution 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 (Ni layer: 2.0 nm, Cr layer: 2.0 nm sputtering)
A tough pitch copper ingot was cast, homogenized and annealed at 850 ° C., and then hot-rolled. Further, it was face-cut and cold-rolled to prepare each copper foil sample. Each manufacturing condition is shown in Table 1. The rolled work roll had a roughness Ra of 0.1 μm and a diameter of 125 mm. Measurement of E (l) and E (d) was performed using a 3D roughness analyzer ERA-8000 manufactured by Elionix Corporation. In Table 1, “forward tension during sheeting” and “backward tension during sheeting” are average values of the final two passes of cold rolling.

On one side of these copper foils, the thin oxide film adhering to the copper foil substrate surface in advance under the following conditions was removed by reverse sputtering, and the Ni layer (2.0 nm) and Cr layer (2.0 nm) were removed. Films were formed in order. 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 Ni layer = Ni (purity 3N)
For Cr layer = Cr (purity 3N)
・ Sputtering power: 50W
Film formation rate: About 2 μm of film was formed for each target for a certain time, the thickness was measured with a three-dimensional measuring device, and the sputtering rate per unit time was calculated. (Ni: 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) was imidized at 130 ° C. for 30 minutes with 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 TEM>
The measurement conditions of TEM when the coating layer is observed by TEM are shown below. The thickness shown in the table is the thickness 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 ratio of the minimum value to the maximum value were determined as percentages. Also, in the table, the TEM observation result after “heat resistance test” means that after the polyimide film is adhered on the coating layer of the test piece by the above procedure, the test piece is placed in the following high-temperature environment and obtained. It is the result of having observed the TEM image after peeling a polyimide film from the piece according to the 180 degree peeling method (JIS C6471 8.1).
-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 humidity. The measurement was performed under three conditions after being left in a high humidity environment of 95% air atmosphere for 96 hours (moisture 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 an etching solution (ammonia water, cupric chloride dihydrate, temperature (40 ° C.). The resin surface between the treated circuits was measured with EPMA, the remaining Cr and Ni were analyzed, and evaluated according to the following criteria.
×: Cr or Ni was observed on the entire surface between the circuits Δ: Cr or Ni was partially observed between the circuits ○: Cr or Ni was not observed between the circuits

The measurement results are shown in Table 2.

Example 2 (Effect of changing Ni layer and Cr layer)
Each copper foil sample was manufactured under the same conditions as in Example 9 except that the thicknesses of the Ni layer and the Cr layer were changed as shown in Table 3. Table 3 shows the measurement results.

Example 3 (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 14: Ni-Cr alloy layer>
A Ni—Cr alloy of Ni: 80 mass% and Cr 20 mass% was used as a sputtering target, and a coating layer having a thickness of 4.0 nm was formed.

<Comparative Example 15: Electroplating of Ni layer 2.0 nm and Cr layer 2.0 nm>
Ni electroplating and Cr electroplating were performed in order under the following conditions. This comparative example is for comparison with the method taught in Japanese Patent Application Laid-Open No. 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 ℃

Table 4 shows the measurement results.

1 Coating layer thickness

Claims (9)

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,
When the copper foil base material is observed from a cross section parallel to the rolling direction, the average value of the oil pit depth d is E (d) and the average value of the oil pit width l is E (l). (L) / E (d) ≧ 2.0, E (d) ≦ 1.5 μm,
The coating layer is composed of a Ni layer and a Cr layer laminated in order from the copper foil base material surface,
In the coating layer, Cr is present in a coverage of 15 to 210 μg / dm ² , Ni is 15 to 440 μg / dm ² ,
When the cross section of the coating layer is observed with a transmission electron microscope, the maximum thickness is 0.5 to 5 nm, and the minimum thickness is 80% or more of the maximum thickness.
Copper foil for printed wiring boards.   The copper foil for printed wiring boards according to claim 1, wherein E (l) / E (d) ≥5.0.   The copper foil for printed wiring boards according to claim 1, wherein E (l) / E (d) ≥10.0.   A printed wiring board is a flexible printed wiring board, The copper foil for printed wiring boards as described in any one of Claims 1-3.   A polyimide varnish is applied on the coating layer to a dry thickness of 25 μm, imidized at 130 ° C. for 30 minutes with an air dryer, and further at 350 ° C. 30 in a high-temperature heating furnace with a nitrogen flow rate set to 10 L / min. The polyimide film is bonded onto the coating layer through the step of imidizing in minutes, and then left for 168 hours in a high-temperature environment at 150 ° C. in an air atmosphere, and then the polyimide film is peeled off by 180 ° (JIS C 6471). The maximum thickness is 0.5 to 5 nm and the minimum thickness is 70% or more of the maximum thickness when the cross-section of the coating layer after peeling from the coating layer according to 8.1) is observed with a transmission electron microscope. 4. The copper foil for printed wiring boards according to any one of 4 above.   Covering at least a part of the surface of the copper foil base material with a Ni layer having a thickness of 0.2 to 5.0 nm and a Cr layer having a thickness of 0.2 to 3.0 nm by a sputtering method, When the average value of oil pit depth d when observed from a cross section parallel to the rolling direction is E (d) and the average value of oil pit width l is E (l), the material is E (l) / E. The manufacturing method of the copper foil for printed wiring boards which is (d)> = 2.0 and E (d) <= 1.5micrometer.   The copper clad laminated board provided with the copper foil as described in any one of Claims 1-5.   The copper clad laminate according to claim 7, wherein the copper foil has a structure bonded to polyimide.   A printed wiring board made of the copper-clad laminate according to claim 7 or 8.