JP5443157B2 - High frequency copper foil, copper clad laminate using the same, and method for producing the same - Google Patents

Description

  The present invention relates to a high-frequency copper foil with low transmission loss at high frequencies, a copper-clad laminate using the same, and a method for manufacturing the same.

  Along with the increase in capacity and diversification of communication information, communication base station printed boards, server printed boards, router printed boards and the like are increasing in communication speed. Higher communication speeds lead to higher signal frequencies. These high-frequency substrates are required to reduce transmission loss in order to ensure the quality of output signals.

  Transmission loss mainly consists of dielectric loss due to resin and conductor loss due to conductor. The dielectric loss decreases as the dielectric constant and dielectric loss tangent of the resin decrease. The conductor loss is derived from the fact that as the frequency increases, the cross-sectional area through which current flows due to the skin effect decreases and the resistance value increases.

  The increase in resistance value is caused by factors other than the reduction in cross-sectional area due to the skin effect. Copper foil used for printed circuit boards is roughened and rust-prevented to improve the adhesion to the resin base material on at least one side of the copper foil (base copper foil) that is the base obtained by rolling or electrolytic methods. It has been processed.

  The resistance value is also influenced by the resistance of the base copper foil itself, the resistance of the roughened layer, and the resistance generated at the interface between them. In particular, when the frequency is 1 GHz or more, the skin depth through which the signal current flows is 2.1 μm or less, so that the influence of the interface between the base copper foil and the roughened layer and the resistance of the roughened layer becomes large.

  As a means for reducing the interface between the base copper foil and the roughened layer and the resistance of the roughened layer, a method of bonding to the resin base material only by chemical treatment without forming the roughened layer is disclosed. However, with chemical treatment alone, it is difficult to obtain the same characteristics as the roughened copper foil in terms of deterioration of adhesive strength with a resin base material due to thermal history and chemical resistance. On the other hand, a method for roughening the surface of the base copper foil by an etching method is disclosed (for example, see Patent Document 1). However, in the case of the etching method, the shape after the roughening changes depending on the crystal state of the base, so that it is difficult to control the etching conditions in accordance with the base crystal state.

JP 2006-351777 A

  An object of the present invention is to provide a copper foil for a high-frequency circuit that has a small electrical resistance near the surface and can reduce transmission loss when used as a conductor for a high-frequency circuit.

The present invention is a high-frequency copper foil in which at least one surface of an electrolytic copper foil is roughened, and the high-frequency copper foil and a resin base material are laminated so that the roughened surface is in contact with the resin base material. When the copper foil for high frequency is made into a copper layer having a thickness of 3 μm in terms of weight by half-etching, the resistivity of the copper layer is 2.2 × 10 ⁻⁸ Ωm or less, preferably The present invention provides a high-frequency copper foil characterized by being 2.0 × 10 ⁻⁸ Ωm or less.

  Further, in the present invention, the roughening treatment of the electrolytic copper foil is performed by electrolytically treating the electrolytic copper foil as a cathode, using a plating bath containing copper ions at a current density equal to or higher than a limiting current density of the plating bath, and then plating. Provided is the above high-frequency copper foil that is a roughening treatment by forming bump-shaped copper particles on at least one surface of the electrolytic copper foil by electrolytic treatment at a current density lower than the limiting current density of the bath It is.

  Moreover, this invention provides the copper clad laminated board characterized by using said copper foil for high frequencies.

  Further, the present invention provides a copper-clad characterized in that the high-frequency copper foil and the resin base material are laminated and heated and pressed so that the roughened surface of the high-frequency copper foil is in contact with the resin base material. The manufacturing method of a laminated board is provided.

  The copper-clad laminate using the high-frequency copper foil of the present invention has the advantage of low transmission loss when a high-frequency circuit is formed.

It is an electron micrograph which shows the copper clad laminated board preparation in a comparative example, and the cross section of the copper foil after half etching. It is an electron micrograph which shows the cross section of the copper foil after copper clad laminated board preparation and a half etching in an Example.

  In copper-clad laminates used for circuit board fabrication, electrolytic copper foil is generally used as a circuit-forming conductor, and the present invention also relates to a high-frequency copper foil using electrolytic copper foil. Because copper-clad laminates require strong adhesion between the resin substrate and the copper foil, the copper foil is a process that forms fine irregularities, generally called roughening treatment, on at least one side that contacts the resin substrate. Is done. The high-frequency copper foil of the present invention is also obtained by roughening at least one surface of the electrolytic copper foil (hereinafter, this roughened electrolytic copper foil may be simply referred to as a copper foil).

  Electrolytic copper foil usually deposits copper on the cathode by applying a direct current in a copper electrolytic bath containing copper ions, using titanium, stainless steel or the like as a cathode, and peels the copper deposited on the cathode. It is manufactured by this. Normally, the surface in contact with the cathode is a glossy glossy surface, and the surface on the electrolytic bath side is rough. However, the surface of both surfaces of the electrolytic copper foil can be adjusted by adjusting the cathode surface shape and the composition of the electrolytic bath. The roughness may be adjusted. In the present invention, the side of the electrolytic copper foil in contact with the cathode is referred to as a glossy surface, and the surface on the electrolytic bath side is referred to as a rough surface.

  The thickness of the electrolytic copper foil used in the present invention is not particularly limited, but is preferably 9 to 105 μm, and more preferably 12 to 35 μm. The electrolytic copper foil used in the present invention is subjected to a roughening treatment on at least one surface thereof, and the surface subjected to the roughening treatment may be any of a glossy surface, a rough surface, or both surfaces. The surface roughness Rz (measured according to JIS B 0601) on the side of the electrolytic copper foil subjected to the roughening treatment (before the roughening treatment) is preferably 3 μm or less, and preferably 0.5 to 2.5 μm. Is more preferable. When the surface roughness Rz on the side subjected to the roughening treatment is less than 0.5 μm, when the roughening treatment is performed by forming bumpy copper particles on the surface of the copper foil, the bumpy copper particles tend to be difficult to be formed. If it exceeds 1, the copper foil after the roughening treatment tends to have a high resistivity at a thickness of 3 μm.

  The surface roughness Rz (measured according to JIS B 0601) of the copper foil treated surface after the roughening treatment of the electrolytic copper foil is preferably 1.0 to 4.5 μm or less, and 1.5 to 4.0 μm. It is more preferable that the thickness is 2.5 to 3.5 μm. If the surface roughness Rz of the copper foil treated surface after the roughening treatment is less than 1.5 μm, the adhesive strength with the resin substrate tends to be low, and the low dielectric constant resin used in the printed wiring board for high frequency is particularly polar. However, it is difficult to form a chemical bond, so that there is a risk that the copper foil is peeled off during the manufacturing process. Moreover, when the surface roughness of the copper foil treated surface after the roughening treatment exceeds 4.5 μm, the resistivity at the thickness of 3 μm of the copper foil after the roughening treatment increases, or due to the etching residue at the time of microcircuit formation When the remaining copper or the roughening treatment is performed by forming bumpy copper particles, there is a tendency that powder falling off the bumpy copper particles due to friction during the manufacturing process of the copper clad laminate tends to occur.

The roughening treatment method of the electrolytic copper foil is not particularly limited as long as the resistivity of the copper foil after the roughening treatment measured by the test method specified in the present invention is 2.2 × 10 ⁻⁸ Ωm or less. . Usually, it is preferable to form a roughened layer made of copper on the surface of the electrolytic copper foil. As a suitable method for forming a roughened layer made of copper, an electrolytic copper foil is used as a cathode, a plating bath containing copper ions is used, and an electrolytic treatment is performed at a current density equal to or higher than the limiting current density of the plating bath, and then the plating bath. There is a roughening treatment method by forming bump-shaped copper particles on at least one surface of an electrolytic copper foil by electrolytic treatment at a current density lower than the limit current density. In this method, a dendritic copper electrodeposition layer by so-called kogashi plating is formed on the surface of the electrolytic copper foil by electrolytic treatment at a current density equal to or higher than the limit current density, and the dendritic copper electrodeposition layer has a density less than the limit current density. By electrolytic treatment with current density, a smooth copper electrodeposition layer (Kabse plating) is formed on the dendritic copper electrodeposition layer, and as a result, the dendritic copper changes to so-called bumpy copper. By forming this bumpy copper, the surface area of the copper foil is increased as compared with that before the electrolytic treatment, and the anchor effect by the bumpy copper is exhibited to improve the adhesive strength between the resin substrate and the copper foil.

  The roughening treatment by the above-described kogashi plating and kabuse plating is preferably performed using a sulfuric acid copper sulfate bath (aqueous solution) using copper sulfate as a copper ion source, but if it is a method of forming similar bumpy copper particles, The copper ion source is not limited. The preferred composition of the sulfuric acid copper sulfate bath is as follows.

Copper sulfate pentahydrate (CuSO ₄ .5H ₂ O): 20 to 300 g / l (copper metal conversion: 5 to 75 g / l, more preferably 50 to 200 g / l (copper metal conversion: 10 to 50 g / l) Particularly preferably 80 to 160 g / l (in terms of copper metal: 20 to 40 g / l) When the concentration of copper sulfate pentahydrate is less than 20 g / l (in terms of copper metal: less than 5 g / l) The limit current density is less than 3 A / dm ^2, and the Kabuse plating time for obtaining a predetermined plating thickness becomes too long to be practical from the viewpoint of productivity. 300 g / l (copper metal conversion: 75 g / l) If it exceeds 1, the limit current density at the time of kogashi plating becomes 100 A / dm ² or more, and it is necessary to use a large current, which is not practical.

  Sulfuric acid: 40 to 200 g / l, more preferably 80 to 160 g / l, particularly preferably 90 to 120 g / l. If the concentration of sulfuric acid is less than 40 g / l, the liquid resistance at the time of plating increases and power consumption increases, which is not practical. If it exceeds 200 g / l, the liquid resistance increases due to an increase in viscosity. Not right.

  Bath temperature: 20-60 ° C, preferably 25-50 ° C, particularly preferably 30-40 ° C. If the bath temperature is less than 20 ° C, the limit current density at the time of Kabuse plating tends to decrease and the Kabuse plating time tends to be longer. If the bath temperature exceeds 60 ° C, the amount of water vapor generated in the plating tank increases, resulting in condensed water drops. Unevenness in appearance occurs.

  In the plating bath, a compound containing a metal other than copper may be added in order to further improve the uniform precipitation of copper plating, but when added, the concentration is preferably 5 g / l or less, More preferably, it is 2 g / l or less. If the concentration of the compound containing a metal other than copper exceeds 5 g / l, the amount of eutectoid of metal other than copper on the interface between the unroughened electrolytic copper foil surface and the roughened layer increases, and the surface of the copper foil The layer resistivity is insufficiently reduced.

The preferable electrolytic treatment conditions for Kogashi plating and Kabuse plating are as follows.
Current density:
Kogashi plating (more than limit current density): [limit current density + 0 A / dm ² ] to [limit current density + 40 A / dm ² ], more preferably [limit current density + 5 A / dm ^2] to [limit current density + 30 A / dm ² ] Particularly preferably, limiting current density + 10 A / dm ^2] to [limiting current density + 20 A / dm ² . When the current density is less than the limit current density, no dendritic copper precipitates are obtained. When the value exceeds [limit current density + 40 A / dm ² ], circular unevenness tends to occur due to the influence of hydrogen gas generated by plating. .

Kabuse plating (less than the limit current density): [limit current density −2 A / dm ² ] to [limit current density −20 A / dm ² ], more preferably [limit current density −5 A / dm ² ] to [limit current density −10 A / Dm ² ]. If it is less than [the limiting current density -20A / dm ^2], tend to Kabusemekki time is prolonged, it exceeds the critical current density -2A / dm ^2], when the variation in the current density distribution occurs, partial Can cause residual copper and powder falling.

Electrolytic treatment time:
Kogashi plating: 0.2 to 10 seconds, more preferably 0.5 to 8 seconds, and particularly preferably 1 to 5 seconds. Kogashi plating may be performed once for a specified time or divided into a plurality of times such as pulse plating. When the total time of the kogashi plating is less than 0.2 seconds, the dendritic copper deposited by the kogashi plating does not grow sufficiently, and there is a tendency that the adhesive strength with the resin base material cannot be sufficiently obtained. Even if the copper-like copper grows too long and the adhesive force is obtained, there is a tendency that residual copper and powder fall off occur.
Kabuse plating: The Kabuse plating time is not particularly limited as long as sufficient adhesive strength with the resin base material is obtained and no residual copper or powder falling off occurs, but a range of 10 to 200 seconds is usually preferable.

  In the roughened copper foil of the present invention, after the roughening treatment, if necessary, a rust preventive treatment layer composed of a chromate layer usually provided on a copper foil for a copper clad laminate, or a coupling agent treatment layer An adhesive resin layer such as a phenol resin, an epoxy resin, or a polyimide resin may be provided.

  The method of forming the chromate layer is not particularly limited, and is not particularly limited as long as the chromate film necessary for rust prevention is formed. Formation of a coupling treatment layer that improves wettability with a resin substrate and forms a chemical bond is usually performed by applying and drying each treatment agent, or dipping and drying in a treatment agent.

  In the present invention, when preparing a sample used for measuring the resistivity of a copper foil, first, the copper foil and the resin base material are laminated and formed such that the roughened surface of the copper foil is in contact with the resin base material. A copper clad laminate is produced. Next, the copper foil of the copper-clad laminate is etched from the exposed surface to a thickness of 3 μm by half etching, and then pattern-etched into a circuit pattern suitable for resistivity measurement. Although there is no restriction | limiting in particular as a resin base material, It is preferable that it has a suitable rigidity after lamination molding, for example, a glass cloth base material epoxy resin prepreg and a polyimide resin film are suitable. The same applies to the resin base material used in the method for producing a copper-clad laminate of the present invention. In the preparation of the sample used for measuring the resistivity of the copper foil, it is preferable to select a thin prepreg or film because the measurement error tends to increase if the weight of the prepreg is large. 0.1 to 1.0 mm, and in the case of a film, it is preferably 25 to 50 μm. In the manufacturing method of the copper clad laminated board of this invention, those thickness can be suitably selected according to a use. Lamination molding is usually performed by heat and pressure, and it is preferable to heat and press at 150 to 230 ° C. and a pressure of 3.0 to 5.0 MPa for 60 to 120 minutes. In sample preparation, the thickness of the copper foil after half-etching is obtained by measuring the weight of the copper foil. In practice, since it is difficult to etch precisely to 3 μm, several samples, for example, 3 to 10 samples etched to a thickness of about 3 μm are prepared, and the measured value is obtained by interpolation. The resistance value is measured by the 4-terminal method. For the half etching and pattern etching, a copper chloride etching solution, an iron chloride etching solution, and various known half etching solutions can be used. In the case of half etching, in order to make the thickness of the copper foil after etching uniform, it is important to spray the etching solution uniformly.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[Example 1]
1. Manufacture of copper foil (1) An electrolytic copper foil having a thickness of 18 μm (manufactured by Nihon Denki Co., Ltd., HL foil, roughness Rz 1.5 μm, measured in accordance with JIS B 0601) with a 10 wt% sulfuric acid solution for 20 seconds Pickled.
(2) This electrolytic copper foil was washed with water, and a plating bath (limit current density: 15 A / dm ²⁾ adjusted to a copper sulfate pentahydrate 150 g / l, sulfuric acid 100 g / l, and bath temperature 30 ° C. using the electrolytic copper foil as a cathode. ) (1) Electrolytic treatment at a current density of 30 A / dm ² for 3 seconds, (2) Electrolytic treatment at a current density of 5 A / dm ² for 80 seconds to roughen a roughened layer made of bumpy copper particles. Formed on the surface side. The surface roughness after roughening was Rz 3.0 μm.
(3) Next, this roughened copper foil was washed with water, and using an aqueous solution adjusted to sodium dichromate dihydrate 3.5 g / l, pH 4.0, bath temperature 28 ° C., current density 0.5 A Electrolytic treatment was carried out at / dm ² for 2.5 seconds to form a chromate layer on the roughened layer.
(4) This copper foil is washed with water, immersed in a 0.1 wt% 3-glycidoxypropyltrimethoxysilane aqueous solution for 10 seconds, and then immediately dried at 80 ° C. to form a silane coupling agent-treated layer on the chromate layer. Formed.
2. Measurement of resistivity (1) FR-4 prepreg with a thickness of 0.25 mm (manufactured by Hitachi Chemical Co., Ltd., trade name: GEA-67N, thickness: 0.25 mm) The above 18 μm copper foil on one side Are laminated so that the roughened surface is in contact with the prepreg, and is heated and pressure-molded at a temperature of 168 ° C. and a pressure of 3.8 MPa for 90 minutes to form a copper-clad laminate, cut into a size of 200 mm × 40 mm, and then a copper-clad laminate The weight of the plate was measured to the nearest 0.1 mg. In addition, it dried at 100 degreeC for 10 minutes before the measurement, and stood to cool in a desiccator.
(2) Next, the copper foil of the copper clad laminate was half-etched from the exposed surface side using a copper chloride etchant in a shower type etching machine, and the weight was measured to the unit of 0.1 mg (in Table 1) Five copper-clad laminates having a weight before and after each measured thickness were produced.
(3) Each copper-clad laminate after weight measurement is spray-etched with a ferric chloride etchant to produce a test pattern with a width of 10 mm and a length of 200 mm, and a digital multimeter manufactured by Advantest (model number) : R6561), the direct current resistance value between 100 mm was measured by the 4-terminal method.
(4) Furthermore, the weight after etching the test pattern of each copper clad laminate after etching using a copper chloride etchant in a shower type etching machine was measured to the unit of 0.1 mg, and the weight difference before and after etching From this, the copper foil thickness was calculated. However, the copper foil thickness was calculated with the specific gravity of copper being 8.92 g / cm ³ .
(5) The resistivity was calculated using the resistance value and the copper foil thickness.
3. Interface observation of base foil (untreated electrolytic copper foil) -roughened layer (1) A copper foil was embedded in an epoxy resin, and a cross-section was observed. No interface between the base foil and the roughened layer was observed. The cross-section was mirror polished and then immersed in sulfuric acid-hydrogen peroxide chemical etchant (Mitsubishi Gas Chemical Co., CPB-60) at 30 ° C. for 10 seconds, washed and dried with an electron microscope. Observed.

[Example 2]
Instead of FR-4 prepreg, a polyimide resin (manufactured by Ube Industries, product number: U-Varnish-A) was applied to the treated copper foil to a thickness of 210 μm, dried at 350 ° C. for 30 minutes and dried. A copper clad laminate was produced in the same manner as in Example 1 except that a copper clad laminate was produced with a polyimide thickness of 25 μm, and the characteristics were evaluated. The results are shown in Table 1.

[Example 3]
As a roughening treatment, using a plating bath adjusted to copper sulfate pentahydrate 150 g / l, sulfuric acid 100 g / l, and bath temperature 30 ° C., (1) Electrolytic treatment at a current density of 30 A / dm ² for 0.5 seconds. (2) Electrolytic treatment was performed at a current density of 5 A / dm ² for 80 seconds to form a roughened layer made of bump-shaped copper particles. The results are shown in Table 1.

[Example 4]
Using an electrolytic copper foil having a rough surface roughness of Rz 2.0 μm (manufactured by Nippon Denki Co., Ltd., SLP foil, thickness 18 μm), as a roughening treatment, copper sulfate pentahydrate 100 g / l, sulfuric acid 100 g / l, bath Using a plating bath adjusted to a temperature of 30 ° C. (limit current density: 10 A / dm ² ), (1) electrolytic treatment at a current density of 40 A / dm ² for 2 seconds, and (2) current density of 5 A / dm ² for 80 seconds. The same procedure as in Example 1 was performed except that a roughened layer made of bump-shaped copper particles was formed on the rough surface side by electrolytic treatment. The results are shown in Table 1.

[Example 5]
The same procedure as in Example 1 was performed except that an electrolytic copper foil having a glossy surface roughness Rz of 1.0 μm (manufactured by Nihon Denki Co., Ltd., HL foil, thickness 18 μm) was used, and the glossy surface side was roughened. . The results are shown in Table 1.

[Comparative Example 1]
An electrolytic copper foil having a rough surface roughness Rz of 1.5 μm (manufactured by Nippon Electrolytic Co., Ltd., HL foil, thickness 18 μm) was used as a roughening treatment, and copper sulfate pentahydrate 100 g / l, sulfuric acid 100 g / l, Using a plating bath (limit current density: 10 A / dm ² ) adjusted to 10 g / l potassium arsenate and a bath temperature of 30 ° C., (1) electrolytic treatment was performed at a current density of 30 A / dm ² for 3 seconds, (2 ) The same operation as in Example 1 was conducted except that an electrolytic treatment was performed at a current density of 5 A / dm ² for 80 seconds to form a roughened layer made of bump-shaped copper particles on the rough surface side. The results are shown in Table 1.

[Comparative Example 2]
Using an electrolytic copper foil having a rough surface roughness of Rz 2.0 μm (manufactured by Nippon Denki Co., Ltd., SLP foil, thickness 18 μm), as a roughening treatment, copper sulfate pentahydrate 100 g / l, sulfuric acid 100 g / l, molybdenum Using a plating bath (limit current density: 10 A / dm ² ) adjusted to 15 g / l of sodium acid dihydrate and a bath temperature of 30 ° C., (1) Electrolytic treatment was performed at a current density of 40 A / dm ² for 2 seconds. (2) The same operation as in Example 1 was conducted except that an electrolytic treatment was performed for 80 seconds at a current density of 5 A / dm ² to form a roughened layer made of bump-shaped copper particles on the rough surface side. The results are shown in Table 1.

[Comparative Example 3]
The same procedure as in Example 1 was performed except that an electrolytic copper foil having a rough surface roughness Rz of 5.0 μm (manufactured by Nippon Electrolytic Co., Ltd., Y foil) was used. The results are shown in Table 1.

[Comparative Example 4]
The same procedure as in Comparative Example 1 was performed, except that an electrolytic copper foil having a glossy surface roughness Rz of 1.0 μm (manufactured by Nippon Denki Co., Ltd., HL foil, thickness 18 μm) was used, and the glossy surface was roughened. . The results are shown in Table 1.

表１中、界面有りとは、図１の電子顕微鏡写真に示されるように（比較例１）、ベース銅箔の表面形状に沿って粗化層との間に界面が観察されたことを意味する。界面無しとは、図１の電子顕微鏡写真に示されるように（実施例１）、ベース銅箔と粗化層との間に界面が観察されないことを意味する。

In Table 1, the presence of an interface means that the interface was observed between the roughened layer and the surface shape of the base copper foil, as shown in the electron micrograph of FIG. 1 (Comparative Example 1). To do. “No interface” means that no interface is observed between the base copper foil and the roughened layer as shown in the electron micrograph of FIG. 1 (Example 1).

  The high frequency circuit using the high frequency copper foil of the present invention has low resistance loss and excellent transmission characteristics.

Claims (5)

A copper foil for high frequency in which at least one surface of an electrolytic copper foil is roughened , and the electrolytic copper foil roughening treatment uses the electrolytic copper foil as a cathode, the concentration of the compound containing copper ions and containing a metal other than copper is By using a plating bath of 0 to 5 g / l, electrolytic treatment at a current density equal to or higher than the limiting current density of the plating bath, and then electrolytic treatment at a current density lower than the limiting current density of the plating bath, the electrolytic copper foil A roughening treatment in which a roughening layer formed of bump-shaped copper particles is formed on at least one side of the surface, and the surface roughness Rz of the roughening treatment surface after the roughening treatment is 1.5 to 4.5 μm. When the cross section of the high-frequency copper foil is observed with an electron microscope, no interface is observed between the electrolytic copper foil and the roughened layer, and the high-frequency copper foil and the resin base Laminated to form a copper-clad laminate in contact with the resin substrate, and herb etching High frequency copper foil, wherein the resistivity of the copper layer when 3μm thick copper layer at a high frequency copper foil in terms of weight thickness is 2.2 × 10 ^-8 Ωm or less. The high-frequency copper foil according to claim 1, wherein the roughened surface has a surface roughness Rz of 2.5 to 4.5 μm. The high-frequency copper foil according to claim 1 or 2, wherein the concentration of the compound containing a metal other than copper in the plating bath used for the roughening treatment is 0 to 2 g / l. A copper-clad laminate comprising the high-frequency copper foil according to any one of claims 1 to 3 . The high frequency copper foil according to any one of claims 1 to 3 and a resin base material are laminated and heated and pressed so that the roughened surface of the high frequency copper foil is in contact with the resin base material. A method for producing a copper clad laminate.

Images