REFINED COPPER, METHOD OF PRODUCING REFINED COPPER, ELECTRIC WIRE AND METHOD OF MANUFACTURING ELECTRIC WIRE
20170327961 · 2017-11-16
Inventors
Cpc classification
Y02P10/20
GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
International classification
Abstract
A method of producing a refined copper includes depositing the refined copper on a cathode by an electroplating process or an electroless plating process in an alkaline plating bath including a solution of a copper compound that includes none of sulfur, chlorine and oxygen elements and produces copper ions having a valence of +1 in the solution.
Claims
1. A method of producing a refined copper, comprising depositing the refined copper on a cathode by an electroplating process or an electroless plating process in an alkaline plating bath comprising a solution of a copper compound that includes none of sulfur, chlorine and oxygen elements and produces copper ions having a valence of +1 in the solution.
2. The method according to claim 1, wherein the copper compound comprises a copper cyanide.
3. The method according to claim 1, wherein only the copper compound composes a copper compound in the plating bath.
4. The method according to claim 1, wherein a sulfur concentration in the refined copper from an outermost surface to a depth of 80 nm is not more than 620 mass ppm.
5. The method according to claim 1, wherein a chlorine concentration in the refined copper from an outermost surface to a depth of 60 nm is not more than 700 mass ppm.
6. The method according to claim 1, wherein a sulfur concentration in the refined copper from an outermost surface to a depth of 2.5 μm is not more than 300 mass ppm.
7. The method according to claim 1, wherein a chlorine concentration in the refined copper from an outermost surface to a depth of 2.5 μm is not more than 61 mass ppm.
8. The method according to claim 1, wherein a sulfur concentration in an entirety of the refined copper is not more than 3.1 mass ppm.
9. The method according to claim 1, wherein a chlorine concentration in an entirety of the refined copper is not more than 1.1 mass ppm.
10. The method according to claim 1, wherein a particle size on a surface of the refined copper is not less than 0.5 μm and not more than 5 μm.
11. The method according to claim 1, wherein a starting sheet comprising copper is used as the cathode and is included in the refined copper, and wherein a sulfur concentration in an entirety of the refined copper including the starting sheet is not more than 3.1 mass ppm.
12. The method according to claim 1, wherein a starting sheet comprising copper is used as the cathode and is included in the refined copper, and wherein a chlorine concentration in an entirety of the refined copper including the starting sheet is not more than 1.1 mass ppm.
13. The method according to claim 1, wherein a conductive metal plate comprising an alloy including at least one or more of stainless steel, transition metals or transition metal elements is used as the cathode, and wherein the refined copper is obtained by stripping from the conductive metal plate.
14. The method according to claim 1, wherein a conductive plate comprising a composite material comprising a metal in the form of mesh or plate and a carbon nanotube is used as the cathode, and wherein the refined copper is obtained by stripping from the conductive plate.
15. A refined copper, wherein a sulfur concentration from an outermost surface to a depth of 80 nm is not more than 620 mass ppm.
16. A refined copper, wherein a chlorine concentration from an outermost surface to a depth of 60 nm is not more than 700 mass ppm.
17. A refined copper, wherein a sulfur concentration from an outermost surface to a depth of 2.5 μm is not more than 300 mass ppm.
18. A refined copper, wherein a chlorine concentration from an outermost surface to a depth of 2.5 μm is not more than 61 mass ppm.
19. A refined copper, wherein a sulfur concentration in an entirety of the refined copper is not more than 3.1 mass ppm.
20. A refined copper, wherein a chlorine concentration in an entirety of the refined copper is not more than 1.1 mass ppm.
21. A refined copper, wherein a sulfur concentration from an outermost surface to a depth of 80 nm is not more than 620 mass ppm, wherein a chlorine concentration from the outermost surface to a depth of 60 nm is not more than 700 mass ppm, wherein a sulfur concentration from the outermost surface to a depth of 2.5 μm is not more than 300 mass ppm, wherein a chlorine concentration from the outermost surface to a depth of 2.5 μm is not more than 61 mass ppm, wherein a sulfur concentration in an entirety of the refined copper is not more than 3.1 mass ppm, and wherein a chlorine concentration in the entirety of the refined copper is not more than 1.1 mass ppm.
22. A refined copper, wherein a particle size on a surface of the refined copper is not less than 0.5 μm and not more than 5 μm.
23. A method of manufacturing an electric wire, comprising making a wire conductor using the refined copper produced by the method according to claim 1.
24. The method according to claim 23, wherein the wire conductor has a sulfur concentration of not more than 3.1 mass ppm, a conductivity of not less than 102.5% IACS and a half-softening temperature of not less than 125° C. and not more than 133° C.
25. An electric wire, comprising a conductor that does not titanium as an additive element, and that has a sulfur concentration of not more than 3.1 mass ppm, a chlorine concentration of not more than 1.1 mass ppm, a conductivity of not less than 102.5% IACS and a half-softening temperature of not less than 125° C. and not more than 133° C.
26. A method of manufacturing an electric wire, comprising making a wire conductor using the refined copper according to claim 15.
27. A method of manufacturing an electric wire, comprising making a wire conductor using the refined copper according to claim 16.
28. A method of manufacturing an electric wire, comprising making a wire conductor using the refined copper according to claim 17.
29. A method of manufacturing an electric wire, comprising making a wire conductor using the refined copper according to claim 18.
30. A method of manufacturing an electric wire, comprising making a wire conductor using the refined copper according to claim 19.
31. A method of manufacturing an electric wire, comprising making a wire conductor using the refined copper according to claim 20.
32. A method of manufacturing an electric wire, comprising making a wire conductor using the refined copper according to claim 21.
33. A method of manufacturing an electric wire, comprising making a wire conductor using the refined copper according to claim 22.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0047] Next, the present invention will be explained in more detail in conjunction with appended drawings, wherein:
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0069] Method of Producing Refined Copper
[0070] A method of producing refined copper in the embodiment of the invention include a step of depositing refined copper on a cathode by an electroplating process or an electroless plating process in an alkaline plating bath formed using a solution of a copper compound that does not contain any of sulfur, chlorine and oxygen elements. The refined copper in the invention means copper or copper alloy (including a starting sheet therein when not stripped from the starting sheet) which is used at least as a raw material to manufacture conductors (copper wires) of electric wires and is obtained by electrorefining or non-electrolytic refining. Therefore, copper foil (with a thickness of, e.g., not more than 100 μm) to not be used as a raw material to manufacture conductors (copper wires) of electric wires is not regarded as the refined copper of the invention. The size and shape of the refined copper manufactured according to the invention are not specifically limited, and the refined copper is, e.g., a copper plate of not less than 0.5 m in length, not less than 0.5 m in width and not less than 3 mm in thickness. The refined copper, when used as a raw material to manufacture conductors (copper wires) of electric wires, is preferably a copper plate of not less than 0.7 m and not more than 1.5 m in length, not less than 0.7 m and not more than 1.5 m in width and not less than 4 mm and not more than 10 mm in thickness. The embodiment of the invention will be described in detail below.
[0071] In the method of producing refined copper in the embodiment of the invention, either an electroplating process or an electroless plating process may be used but the electroplating process is preferably used. Next, the method using the electroplating process will be described as an example.
[0072] A plating solution contained in a plating bath is a solution of a copper compound which does not contain any of sulfur, chlorine and oxygen elements. Therefore, copper sulfate containing sulfur and oxygen elements and copper pyrophosphate containing oxygen element do not fall under the category of this copper compound.
[0073] The copper compound not containing any of sulfur, chlorine and oxygen elements is preferably a copper compound producing copper ions having a valence of +1 when dissolved in the solution. For example, copper cyanide is suitable as the copper compound producing copper ions having a valence of +1 when dissolved in the solution.
[0074] Preferably, the above-described copper compound not containing any of sulfur, chlorine and oxygen elements is the only copper compound used for the plating solution contained in the plating bath.
[0075] Example of How to Form Plating Bath
[0076] An example of how to form a plating bath used in the embodiment of the invention will be described below.
[0077] A copper cyanide plating bath used in the embodiment of the invention is made of the materials showing Table 1 below. Purified water after removing impurity components such as sulfur and chlorine is poured into an auxiliary tank in an amount of about 60% of the total amount of the plating bath. Next, sodium cyanide or potassium cyanide is added to and dissolved in the purified water. Then, pasty cuprous cyanide is added to and dissolved in this pre-made alkaline cyanide solution while stirring further using purified water. In addition, sodium hydroxide or potassium hydroxide is added to adjust pH (e.g., pH=9 to 13) and conductivity of the plating bath so that decomposition of cyanide is inhibited. After adding activated carbon, etc., and sufficiently stirring while heating to 40 to 70° C. which is close to practical plating bath solution temperature, the mixture is left to stand so that the activated carbon absorbs impurities and settles out. After that, the activated carbon, etc., trapping impurities is removed through a filtration equipment, the solution is transferred to a plating tank and the amount of the solution is adjusted by adding purified water, thereby obtaining a plating bath. This plating bath is analyzed. Then, additive materials are added, as needed, to improve and stabilize plating performance In detail, an appropriate amount of sodium carbonate or potassium carbonate as a pH buffering agent (pH adjuster) is added. Then, potassium sodium tartrate (Rochelle salt) is added, as needed, to facilitate dissolution of copper used as an anode and thereby to efficiently supply copper ions. Lastly, a stainless steel plate is suspended as a cathode and a rolled copper sheet as an anode, and weak electrolysis is performed at a low current density (0.2 to 0.5 A/dm.sup.2).
TABLE-US-00001 TABLE 1 Composition of copper cyanide plating bath Composition of Concentration plating bath Chemical formula (g/L) Cuprous cyanide CuCN 15 to 120 Sodium cyanide NaCN 25 to 135 (or potassium cyanide) (KCN) Potassium sodium tartrate KNaC.sub.4H.sub.4O.sub.6•4H.sub.2O 15 to 60 Sodium carbonate Na.sub.2CO.sub.3 10 to 30 (or potassium carbonate) (K.sub.2CO.sub.3) Sodium hydroxide NaOH 10 to 30 (or potassium hydroxide) (KOH)
[0078] Example of How to Produce Refined Copper (Electrolytic Copper)
[0079] Next, an example of how to produce refined copper in the embodiment of the invention will be described.
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[0081] Anodes 111 formed by rolling/casting molten copper (blister copper with a purity of 99%) made of copper melt are prepared as a copper ion source for electroplating. Alternatively, a stainless steel plate or a titanium plate may be used as a cathode while using blister copper as an anode and, in this case, copper is deposited on a surface of the cathode by electrolysis, the formed pure copper sheet is stripped, and a resulting stripped copper sheet (electrolytic copper) with improved purity is used as the anode 111. Meanwhile, a thin copper sheet called starting sheet is used as a cathode 112. The cathodes 112, together with the anodes 111, are arranged in a plating tank 116 filled with a copper cyanide plating bath 115 and electricity is passed therethrough using a DC power supply 117. During when electricity is passed, copper is deposited on the surfaces of the cathodes 112 by electrolysis. The cathodes 112 are moved upward when copper plating growth layers 114 reach a desired weight, and refined copper (electrolytic copper) including the starting sheet is then obtained. The starting sheet used in the embodiment of the invention is preferably a copper sheet having a copper purity of not less than 99.9%, a sulfur concentration of not more than 3.4 mass ppm and a chlorine concentration of not more than 1.6 mass ppm.
[0082] Alternatively, stainless steel plates may be used as the cathodes 112 without using copper starting sheets and, in this case, the copper plating growth layers 114 electrodeposited on the cathodes 112 are stripped and obtained as refined copper (electrolytic copper). In the electroplating equipment shown in
[0083] Alternatively, instead of the stainless steel plate, a conductive metal plate formed of an alloy containing at least one or more of transition metals or transition metal elements, or a conductive plate formed of a composite material composed of a metal in the form of mesh or plate and a carbon nanotube, may be used as the cathode 112. The refined copper (electrolytic copper) is obtained by stripping from the conductive metal plate or the conductive plate.
[0084] Table 2 shows an example of the electroplating conditions in the method of producing refined copper in the embodiment of the invention.
TABLE-US-00002 TABLE 2 Electroplating conditions for copper cyanide plating Items Control value Temperature of plating bath (° C.) 30 to 80 Cathode current density (A/dm.sup.2) 0.2 to 10 Anode current density (A/dm.sup.2) 0.1 to 5.sup. pH of plating bath 10 to 13
[0085] In production of electrolytic copper using stainless steel plates as cathodes, it is possible to maintain a uniform current density across the entire surface of the cathode since the parallel distance between two electrodes is better than when using copper starting sheets and the surface is flat. Therefore, it is possible to increase current efficiency and to reduce the incidence of short-circuit and the frequency of correction work associated with the short-circuit faults. In addition, since a distance between the electrodes can be reduced, it is possible to increase the number of cathodes to be placed in the plating tank and thus possible to increase production capacity without additional equipment investments. Furthermore, since it is also possible to reduce effective voltage, reduction in power consumption is expected. Also when the conductive metal plate formed of an alloy containing at least one or more of transition metals or transition metal elements is used as the cathode 112 in place of the stainless steel plate, the same advantages are obtained. In addition, when the conductive plate formed of a composite material composed of a metal in the form of mesh or plate and a carbon nanotube is used as the cathode 112, it is possible to realize 100-fold current capacity of more than two digits while maintaining the same performance of electrical conductivity as that of the copper starting sheet and this allows the current limit value during electrolytic copper production to be improved. Therefore, it is possible to increase the growth rate of electrolytic plating as compared to the conventional technique and it is advantageous in that electrolytic copper can be produced highly efficiently. The key feature of each cathode is shown in
TABLE-US-00003 TABLE 3 Types, key features and advantages of cathodes used for production of refined copper Cathode Key feature Advantage Stainless steel plate Equal distance Improvement in between surfaces due current efficiency by to flat plate preventing short circuit Copper plate No need of stripping Possible to shorten the from starting sheet process of electrolytic copper production Composite material of Increase in current Improvement in carbon nanotube and capacity productivity by metal increase in film formation rate
[0086] Refined Copper
[0087] The refined copper in the embodiment of the invention can be obtained by the above-described method of producing refined copper in the embodiment of the invention, and has one or more of the following characteristics. That is, the refined copper in the present embodiment is refined copper with controlled sulfur and/or chlorine concentrations within appropriate ranges (e.g., pure copper having a copper concentration of not less than 99.9%).
[0088] The sulfur concentration from the outermost surface to a depth of 80 nm in the refined copper is not more than 620 mass ppm and, in a preferred embodiment, not more than 613 mass ppm.
[0089] The chlorine concentration from the outermost surface to a depth of 60 nm in the refined copper is not more than 700 mass ppm and, in a preferred embodiment, not more than 653 mass ppm.
[0090] The sulfur concentration from the outermost surface to a depth of 2.5 μm in the refined copper is not more than 300 mass ppm and, in a preferred embodiment, not more than 296 mass ppm.
[0091] The chlorine concentration from the outermost surface to a depth of 2.5 μm in the refined copper is not more than 61 mass ppm and, in a preferred embodiment, not more than 60 mass ppm.
[0092] The sulfur concentration in the entire refined copper is not more than 3.1 mass ppm and, in a preferred embodiment, not more than 3.0 mass ppm. When a copper starting sheet is used as a cathode, the refined copper includes the starting sheet and the sulfur concentration in the entire refined copper including the starting sheet is not more than 3.1 mass ppm and, in a preferred embodiment, not more than 3.0 mass ppm.
[0093] The chlorine concentration in the entire refined copper is not more than 1.1 mass ppm and, in a preferred embodiment, not more than 1.0 mass ppm. When a copper starting sheet is used as a cathode, the refined copper includes the starting sheet and the chlorine concentration in the entire refined copper including the starting sheet is not more than 1.1 mass ppm and, in a preferred embodiment, not more than 1.0 mass ppm.
[0094] In the refined copper in the embodiment of the invention, a particle size on the surface of the refined copper is not less than 0.5 μm and not more than 5 μm and, in a preferred embodiment, not less than 1.1 μm and not more than 1.3 μm.
[0095] Impurity Concentration Analysis Methods
[0096] Detailed analysis of concentrations of trace amounts of impurities contained in three regions of the refined copper (electrolytic copper); a region near the surface, a region from the surface to a predetermined depth and the entire region, which has conventionally not been done, was conducted in the embodiment of the invention. That is, to precisely optimize the impurity concentrations, the following three analytical techniques were fully used to know the exact impurity concentrations. The present inventors particularly focused on the concentrations of sulfur and chlorine as impurities closely related to a decrease in basic performance (a decrease in conductivity and an increase in softening temperature) of copper wire conductor. Any of the following analysis methods can be used to measure the sulfur and chlorine concentrations in the three regions of the refined copper (electrolytic copper); a region near the surface, a region from the surface to a predetermined depth and the entire region, or to measure the sulfur and chlorine concentrations in a wire conductor.
[0097] (1) Secondary Ion Mass Spectrometry
[0098] This analysis method is also called SIMS analysis (an abbreviation of Secondary Ion Mass Spectrometry). The principle of this analysis is as follows: a surface of a solid material is exposed to C.sub.S.sup.+ or O.sub.2.sup.+ ions having an energy of several hundred eV to several tens of KeV, individual ions emitted from the material surface through sputter etching are mass-separated by an electric field or a magnetic field, and mass spectrometry is conducted by a detector such as Faraday cup or electron multiplier to identify elements present on the material surface and to measure concentrations thereof. This analysis method uses a measurement technique which is in principle capable of analyzing an ultra-trace amount of element with a detection limit of several hundred ppb to 0.1 ppm in analysis of regions near the surface and in a depth direction. Therefore, in Example described later, the concentrations of impurities (sulfur (S) and chlorine (Cl), etc.) contained in the adhered state, the segregated state, the dissolved state or at least two or more of these states were measured in a region near the surface (from the surface to a depth of about 60 to 80 nm) of the electrolytic copper. In Example, the detection limit is 1×10.sup.16 atoms/cm.sup.3 for S and 8×10.sup.15 atoms/cm.sup.3 for Cl, and the detection limit in terms of mass concentration is 0.06 mass ppm for S and 0.05 mass ppm for Cl. The measurement conditions in Example are shown in Table 4 below. After sputter etching followed by the concentration measurement, the depth was actually measured by a stylus-based profilometer, e.g., Tencor P10, Tencor P20 or Alpha Step 500, etc.
TABLE-US-00004 TABLE 4 Measurement conditions for secondary ion mass spectrometry Items Conditions Element (ion) measured S, Cl Irradiation ion beam Cs.sup.+ Irradiation ion energy 14.5 keV Polarity of measured secondary ion Negative
[0099] (2) X-Ray Fluorescence Analysis
[0100] This analysis is also called XRF analysis (an abbreviation of X-ray fluorescence analysis). This method is a non-destructive analysis and is excellent particularly for quality control on production line. The principle of this analysis is as follows: a surface of a material is exposed to X-rays to eject inner shell electrons from individual atoms contained in the material, and energy and intensity of X-ray fluorescence resulting from transition of adjacent electrons from higher energy level to lower energy levels after ejection of electrons are measured by a detector. Since the X-ray fluorescence energy (wavelength) of each element is known, it is possible to specify the elements present in the material and to measure the concentrations of the contained elements. A wavelength-dispersive X-ray fluorescence spectrometer (model: ZSX Primus II, manufactured by Rigaku Corporation) was used in Example described later. Since the elements to be analyzed here are sulfur and chlorine which have adjacent atomic numbers and thus emit X-ray fluorescence of similar energy, the analysis was conducted using a wavelength-dispersive spectrometer which is less affected by overlap of x-ray fluorescence peaks and has high X-ray energy resolution. The measurement conditions in Examples are shown in Table 5 below.
TABLE-US-00005 TABLE 5 Measurement conditions for wavelength- dispersive X-ray fluorescence analysis Items Conditions Radiation source Rh tube (Kα.sub.1 = 20.2161 keV) Output 50 kV, 50 mA Detector SC (scintillation counter) PC (proportional counter) Spectrometer LiF crystal (heavy element) Ge, PET crystal (light element) Diameter analyzed φ10 mm Degree of vacuum in 1 to 10 Pa measurement chamber Element measured S (Kα.sub.1 = 2.3078 keV) Cl (Kα.sub.1 = 2.6224 keV)
[0101] (3) High-Frequency Combustion-Infrared Absorption Analysis
[0102] This analysis method is a destructive analysis but is advantageous in that the concentrations of impurity elements contained in the entire refined copper (electrolytic copper) can be precisely measured down to several ppm. CSLS600 manufactured by LECO Corporation was used in Example described later. The detailed procedure was as follows: Firstly, a sample was cut. 2 g of analytical sample taken therefrom and 1 g of copper combustion improver were put in a ceramic crucible for combustion. At this time, the measurement sample was combusted in an oxygen stream by means of high-frequency heating to cause reaction of S (sulfur) in copper with oxygen, and SO.sub.2 as a volatile substance produced as a result of the reaction was measured by an infrared detector. Measurement reproducibility was checked by performing measurement at least twice or more and it was confirmed that measurement was precise. Based on the confirmation, the average values were defined as the analytical values.
[0103] Cost Reduction in Electrolytic Copper Production
[0104] When a copper cyanide (CuCN) solution is used as a plating bath for electroplating, reaction to produce Cu metal from Cu ions is expressed by the following equation (1). This shows that a Cu.sup.+ ion having a valence of 1 accepts one electron and thereby turns into a Cu atom (metal).
Cu.sup.++e.sup.−.fwdarw.Cu (1)
[0105] In the equation (1), one electron is required for one Cu ion and the quantity of electric charge required to produce 1 mol of Cu is about 96,485 (C) (equivalent to Faraday constant) derived by multiplying the elementary charge by Avogadro constant. Therefore, taking into account that the atomic weight of copper is 63.54, the quantity of electric charge required to produce 1 g of copper is about 1,518 (C/g).
[0106] In practice, producing electrolytic copper of, e.g., 1.2 m in length, 1.0 m in width and 5 mm in thickness means to produce 53,640 g of electrolytic copper since the specific gravity of copper is 8.94. Therefore, in this case, the required quantity of electric charge is about 81,452,207 (C). Then, when the current density during electroplating is 5 A/dm.sup.2 and electric current flowing through a surface of the cathode is 600A, a relation of current i, quantity of electric charge Q and time t is expressed by the formula (2). Therefore, the production (plating) time is estimated to be about 135,754 seconds (about 37.7 hours).
i=dQ/dt (2)
[0107] Meanwhile, when a conventional cupric sulfate (CuSO.sub.4) solution is used as a plating bath for electroplating, reaction to produce a Cu atom (metal) from Cu ions is expressed by the following equation (3). This shows that a Cu.sup.+ ion having a valence of 2 accepts two electrons and thereby turns into a Cu atom (metal).
Cu.sup.2++2e.sup.−.fwdarw.Cu (3)
[0108] In the equation (3), two electrons are required for one Cu ion and the quantity of electric charge required to produce 1 mol of Cu is about 192,971 (C) which is double the value derived by multiplying the elementary charge by Avogadro constant, and the quantity of electric charge required to produce 1 g of copper is about 3,037 (C/g). Therefore, when producing electrolytic copper of the same size as described above, the required quantity of electric charge is about 162,904,415 (C). When the current density is the same as described above and is 5 A/dm.sup.2, the required production time is considered to be about 271,507 seconds (about 75.4 hours) based on the formula (2).
[0109] In other words, electrolytic copper formed in the plating bath of the copper cyanide (CuCN) solution containing copper ions having a low valence (a valence of +1) can be, in principle, produced in half the time it takes when using the plating bath of the sulfuric acid-cupric sulfate (CuSO.sub.4) solution. Therefore, if voltage and current used for electroplating are the same, power consumption directly linked to an increase or decrease in plating time is considered to be halved and it is thus possible to reduce the energy cost. In addition, since factory operating time to produce electrolytic copper is halved, labor cost per production volume is expected to be reduced. Putting it the other way around, use of copper cyanide plating allows a double amount of electrolytic copper to be produced within the time required when using cupric sulfate plating, which improves production throughput of electrolytic copper and of high-quality electric wires using the electrolytic copper as a raw material.
[0110] Method of Manufacturing Electric Wire
[0111] The method of manufacturing an electric wire in the embodiment of the invention includes a step of making a wire conductor using refined copper produced by the above-described method of producing refined copper in the embodiment of the invention or using the above-described refined copper in the embodiment of the invention.
[0112] The electric wire can be manufactured by a known electric wire manufacturing method, except that the above-described refined copper is used as a material of the wire conductor.
[0113] The wire conductor has a sulfur concentration of not more than 3.1 mass ppm, a conductivity of not less than 102.5% IACS and a half-softening temperature of not less than 125° C. and not more than 133° C. In a preferred embodiment, the sulfur concentration is not more than 2.5 mass ppm, the conductivity is not less than 102.6% IACS and the half-softening temperature is not less than 125° C. and not more than 131° C.
[0114] Electric Wire
[0115] The electric wire in the embodiment of the invention can be obtained by the above-described method of manufacturing an electric wire in the embodiment of the invention.
[0116] The electric wire in the embodiment of the invention is provided with a conductor not containing titanium as an additive element and having a sulfur concentration of not more than 3.1 mass ppm, a chlorine concentration of not more than 1.1 mass ppm, a conductivity of not less than 102.5% IACS and a half-softening temperature of not less than 125° C. and not more than 133° C. In a preferred embodiment, the conductor does not contain titanium as an additive element, and has a sulfur concentration of not more than 2.5 mass ppm, a chlorine concentration of not more than 1.1 mass ppm, a conductivity of not less than 102.6% IACS and a half-softening temperature of not less than 125° C. and not more than 131° C.
[0117] The configuration of the electric wire is not specifically limited and the electric wire may have various configurations. For example, the conductor may be formed of a single strand or plural strands, and the number of conductors is not limited to one and may be two or more.
[0118] Effects of the Embodiment of the Invention
[0119] The plating bath using the copper cyanide (CuCN) solution in the embodiment of the invention does not contain inevitable impurities such as sulfur and chlorine which are contained in the conventionally often used cupric sulfate (CuSO.sub.4) solution. Therefore, except for contamination with trace amounts of sulfur and chlorine, etc., due to external environment such as a distance from seashores or volcanic belts to factory sites or water source to be used, refined copper (electrolytic copper) does not contain sulfur and chlorine, etc., derived from the raw materials. Therefore, when using such refined copper as a raw material to form copper wires, a decrease in quality (a decrease in conductivity and an increase in softening temperature) due to containing sulfur and chlorine, etc., is prevented. In other words, it is possible to realize a copper electric wire in which the concentrations of sulfur and chlorine, etc., are reduced as much as possible, and high-performance copper wires with high conductivity and low softening temperature can be manufactured in high yield.
[0120] In addition, the plating bath using the copper cyanide (CuCN) solution has better throwing power than the conventional plating bath of the cupric sulfate (CuSO.sub.4) solution and is thus suitable for producing electrolytic copper on a large area.
[0121] Meanwhile, when electrolytic copper refining is performed by an electroplating process while using a steel plate of stainless steel, etc., as a cathode to grow a copper plating layer, use of the plating bath of the cupric sulfate (CuSO.sub.4) solution causes displacement deposition in which ions of Cr, Fe or Ni, etc., having a higher ionization tendency than Cu are eluted and copper is precipitated, and the stainless steel plate deteriorates in a short period of time. In the plating bath of the copper cyanide (CuCN) solution in the embodiment of the invention which can solve such a problem, a reduction potential is lower than the plating bath of the cupric sulfate (CuSO.sub.4) solution since copper ions have a valence of +1 and form cyano complexes ([Cu(CN).sub.4].sup.3−), resulting in that displacement deposition substantially does not occur and metal ions are substantially not eluted from the stainless steel plate which thus shows less deterioration. Therefore, it is advantageous in that recyclability of the stainless steel plate is excellent and it is possible to reduce the cost of purchasing new stainless steel plates.
[0122] Furthermore, since an interfacial reaction layer associated with the displacement deposition is hardly formed and a deposited copper plating sheet is less adhesive, the copper plating sheet can be stripped from a starting sheet with a lower tensile stress than when using the conventional copper sulfate plating and it is thereby possible to prevent the copper plating sheet from being partially stripped or cracking. As a result, workload for a stripping process can be reduced as compared to the conventional electrolytic copper production, and productivity and yield are improved.
[0123] As previously described, the valence of copper ion in the plating bath of the copper cyanide (CuCN) solution used in the embodiment of the invention is one-half of the valence of those in the conventional plating bath of the cupric sulfate (CuSO.sub.4) solution. Therefore, when the thickness of a plating layer (electrolytic copper) to be produced is the same, the current density (power consumption) required for electroplating is half of that in the conventional technique and it is therefore possible to advantageously halve the energy cost. In addition, in case of production with the same current density as when using the conventional plating bath of the cupric sulfate (CuSO.sub.4) solution, electrolytic copper having a desired thickness (weight) can be produced in half the time (operating time of refining plant is advantageously halved), which allows an electrolytic copper production process with improved throughput to be established and thus the total production cost including working hours, etc., to be reduced. In other words, with the same power consumption and the same production time, it is possible to produce twice as much electrolytic copper as the conventional technique and it is possible to manufacture twice as many high-performance electric wires with the same energy cost.
[0124] In addition, while the conventional plating bath of the cupric sulfate (CuSO.sub.4) solution is highly acidic and use thereof requires a measure for preventing equipment and components inside buildings from rusting, the plating bath of the copper cyanide (CuCN) solution in the invention is alkaline and has a low impact on aged deterioration of the components due to oxidation. Therefore, use of the copper cyanide (CuCN) solution is advantageous in that production facilities can have a longer life and also it is possible to prevent contamination with impurities such as corroded rust from such facilities during plating production.
[0125] In addition, the conventional copper sulfate solution is unstable as a plating bath since hydrolysis of copper occurs, sediments are likely to be formed and the copper ion concentration largely varies. On the other hand, the copper plating solution containing cyanide used in the invention is excellent in long-term storage stability since the function as a complexing agent prevents formation of hydroxide sediments in an alkaline solution and maintains the constant concentration, and the plating solution shows less deterioration since cyanogen and copper ions form stable complexes.
[0126] In addition, in the embodiment of the invention, since the refined copper in the embodiment of the invention is used as a raw material of the wire conductor, it is possible to obtain a wire conductor with less inevitable impurities (sulfur (S) and chlorine (Cl)) than those contained in refined copper conventionally used as a raw material and formed using the plating bath of the cupric sulfate (CuSO.sub.4) solution. Therefore, in manufacturing of wire conductors, it is possible to omit a process of eliminating sulfur and chlorine mixed in conductors or to control the impurity concentrations to a desired level by removing only small amounts of impurities, and it is thus possible to stably mass produce high-quality conductors.
[0127] In addition, by using the wire conductors formed using the refined copper in the embodiment of the invention, high-quality audio cables and wiring materials for audio equipment capable of efficiently transmitting electrical signals across a wide frequency range can be mass-produced at lower cost in a shorter period of time than copper electric wires manufactured by the conventional method. In addition, the refined copper in the embodiment of the invention can be used as a material of extra-fine connection conductors used in semiconductor devices or MEMS devices, etc., to connect between microscopic devices at narrow pitches, and stable supply of such a material is realized at low cost.
EXAMPLES
[0128] Next, the invention will be described in more detail based on Examples. However, the invention is not limited thereto.
[0129] Production of Refined Copper (Electrolytic Copper) in Example and Comparative Example
[0130] In Example and Comparative Example, a starting sheet (rolled copper sheet) was used as a cathode to form copper plating. The compositions of the plating baths used are as shown in Table 6 below, and the electroplating conditions are as shown in Table 7 below. Configuration comparison and concentration analysis described later were conducted on the produced refined coppers.
TABLE-US-00006 TABLE 6 Composition of plating bath Composition of Concentration plating bath Chemical formula (g/L) Example Cuprous cyanide CuCN 100 Sodium cyanide NaCN 125 Sodium carbonate Na.sub.2CO.sub.3 15 Sodium hydroxide NaOH 30 Comparative Copper sulfate CuSO.sub.4•5H.sub.2O 220 Example Sulfuric acid (98%) H.sub.2SO.sub.4 55 Sodium chloride NaCl 0.1
TABLE-US-00007 TABLE 7 Electroplating conditions Items Control value Example Temperature of Plating bath (° C.) 78 Cathode current density (A/dm.sup.2) 2 Anode current density (A/dm.sup.2) 1 Comparative Temperature of Plating bath (° C.) 25 Example Cathode current density (A/dm.sup.2) 2 Anode current density (A/dm.sup.2) 1
[0131] Comparison in Refined Copper (Electrolytic Copper) Configuration Between Example and Comparative Example
[0132]
[0133]
[0134] As understood from
[0135] In addition, size distribution of grown particles on the surface of the refined copper in Example was uniform as compared to the refined copper in Comparative Example. This shows that the copper cyanide (CuCN) plating has excellent throwing power and is suitable for producing refined copper having uniform particle size.
[0136]
[0137] In
[0138] In
[0139] Concentrations of Sulfur and Chlorine Contained in Refined Copper (Electrolytic Copper)
[0140]
[0141]
[0142]
[0143]
[0144] The sulfur concentration was measured by the previously described X-ray fluorescence analysis method (XRF analysis) and was estimated based on S—Kα X-ray fluorescence intensity shown in
[0145] It is understood from
TABLE-US-00008 TABLE 8 XRF measurement results of sulfur concentration in refined copper (electrolytic copper) S concentration Samples (mass ppm) Starting sheet (rolled copper sheet) 371 Electrolytic copper in Comparative Example 396 Electrolytic copper in Example 297 Electrolytic copper of company A 396 Electrolytic copper of company B 414 Electrolytic copper of company C 388
[0146] The sulfur concentration from the surface to a depth of 2.5 μm in the electrolytic copper of Comparative Example was 396 mass ppm which is about 7% higher than 371 mass ppm in the starting sheet (rolled copper sheet). On the other hand, it was found that the sulfur concentration from the surface to a depth of 2.5 μm in the electrolytic copper of Example was 297 mass ppm which is about 20% lower than the starting sheet and about 25% lower than the electrolytic copper of Comparative Example. This shows that the electrolytic copper produced using the copper cyanide solution can have a low sulfur concentration even when a region near the surface is contaminated with sulfur during electrolytic copper production due to an external source such as the air. For reference, the average of the sulfur concentrations in refined coppers produced using a conventional electroplating technique and sold by other companies (A, B and C) was about 400 mass ppm.
[0147]
[0148] The sulfur concentration was measured by the previously described high-frequency combustion-infrared absorption analysis. Table 9 shows the measurement results of the actual sulfur concentration.
TABLE-US-00009 TABLE 9 Sulfur concentration in the entire refined copper (electrolytic copper) S concentration Samples (mass ppb) Starting sheet (rolled copper sheet) 3350 Electrolytic copper in Comparative Example 3250 Electrolytic copper in Example 3060 Electrolytic copper of company A 3440 Electrolytic copper of company B 3490 Electrolytic copper of company C 3430
[0149] It is understood from Table 9 that the sulfur concentration in the entire electrolytic copper is within a range of 3000 to 3500 mass ppb in any of the samples and a difference therebetween is several hundred mass ppb. The sulfur concentration in the entire electrolytic copper of Example is 3060 mass ppb and is about 400 mass ppb less than the electrolytic coppers produced by the other companies.
[0150] When manufacturing highly conductive wires requiring to control the sulfur concentration to the order of sub-ppm or when there is a possibility that sulfur concentrated near the surface may affect the production yield of high-quality electric wires, electrolytic copper (raw material) with as reduced sulfur as possible is essential.
[0151] Meanwhile,
[0152] The chlorine concentration was measured by the previously described X-ray fluorescence analysis method (XRF analysis) and was estimated based on Cl—Kα X-ray fluorescence intensity shown in
[0153] It is understood from
TABLE-US-00010 TABLE 10 XRF measurement results of chlorine concentration in refined copper (electrolytic copper) Cl concentration Samples (mass ppm) Starting sheet (rolled copper sheet) 156 Electrolytic copper in Comparative Example 171 Electrolytic copper in Example 61 Electrolytic copper of company A 140 Electrolytic copper of company B 265 Electrolytic copper of company C 312
[0154] The chlorine concentration from the surface to a depth of 2.5 μm in the electrolytic copper of Comparative Example was 171 mass ppm which is about 10% higher than 156 mass ppm in the starting sheet (rolled copper sheet). On the other hand, it was found that the chlorine concentration from the surface to a depth of 2.5 μm in the electrolytic copper of Example was 61 mass ppm which is about 60% lower than the starting sheet and about 64% lower than the electrolytic copper of Comparative Example. This shows that the electrolytic copper produced using the copper cyanide solution can have a low chlorine concentration even when a region near the surface is contaminated with chlorine during electrolytic copper production due to an external source such as the air. For reference, the average of the chlorine concentrations in refined coppers produced using a conventional electroplating technique and sold by other companies (A, B and C) was about 240 mass ppm.
[0155]
TABLE-US-00011 TABLE 11 Chlorine concentration in the entire refined copper (electrolytic copper) Cl concentration Samples (mass ppb) Starting sheet (rolled copper sheet) 1527 Electrolytic copper in Comparative Example 1425 Electrolytic copper in Example 1144 Electrolytic copper of company A 1473 Electrolytic copper of company B 1871 Electrolytic copper of company C 1871
[0156] It is understood from Table 11 that the chlorine concentration in the entire electrolytic copper is within a range of about 1100 to 1900 mass ppb in any of the samples. The chlorine concentration in the entire electrolytic copper of Example is 1144 mass ppb and is up to about 730 mass ppb less than the electrolytic coppers produced by the other companies.
[0157] When manufacturing highly conductive wires requiring to control the chlorine concentration to the order of sub-ppm or when there is a possibility that chlorine concentrated near the surface may affect the production yield of high-quality electric wires, electrolytic copper (raw material) with as reduced chlorine as possible is essential, in the same manner as sulfur.
[0158] According to the invention, it is possible to reduce the sulfur concentration and the chlorine concentration in the electrolytic copper (it is possible to control the sulfur concentration and the chlorine concentration within appropriate ranges). Therefore, when the electrolytic copper of the invention is used as a raw material to manufacture electric wires, it is possible to prevent a decrease in conductivity due to contamination with impurity elements and thus possible to stably produce high-quality copper electric wires.
[0159] Manufacturing and Evaluation of Wire Conductor
[0160] Next, wire conductors manufactured using the refined copper (electrolytic copper) of the invention as a raw material were subjected to measurement of the sulfur concentration and quality evaluation (conductivity and half-softening temperature). The details are as follows.
Examples 1 to 3
[0161] In Examples 1 to 3, electrolytic copper obtained through the same process as the above-described Example was melted, casted and then hot-rolled, thereby making drawing stocks. In Examples 1 to 3, however, the amount of sulfur or sulfuric acid ions in purified water used to control the concentration of the copper cyanide plating bath was adjusted by an ion-exchange resin and the sulfur concentration was changed. The drawing stocks were reduced in diameter to a desired outer diameter by cold rolling and were then annealed, thereby making wire conductors.
Comparative Examples 1 to 4
[0162] In Comparative Examples 1 to 4, electrolytic copper obtained through the same process as the above-described Comparative Example was melted, casted and then hot-rolled, thereby making drawing stocks. In Comparative Examples 1 to 4, however, the concentrations of copper sulfate and sulfuric acid in the plating bath were adjusted and the sulfur concentration was changed. The drawing stocks were reduced in diameter to a desired outer diameter by cold rolling and were then annealed, thereby making wire conductors.
[0163] Evaluation
[0164] The wire conductors obtained in Examples 1 to 3 and Comparative Examples 1 to 4 were evaluated for the relation between sulfur concentration, conductivity and half-softening temperature. The results are shown in Table 12 below and
[0165] Definition of Conductivity
[0166] Conductivity here is expressed as IACS (International Annealed Copper Standard) which is 100% at a resistivity of 1.7241×10.sup.−8 Ωm.
[0167] Definition of Half-Softening Temperature
[0168] Half-softening temperature is a temperature corresponding to an average value of tensile strength before heating and tensile strength one hour after heating on a thermal softening curve representing the relationship between heating temperature (holding time of 1 hour) and tensile strength of copper conductor, and is a temperature at which tensile strength of the copper conductor is reduced to about half due to heating.
TABLE-US-00012 TABLE 12 S concentration in copper conductor and quality evaluation results (conductivity and half-softening temperature) Half-softening S concentration Conductivity temperature Samples (mass ppm) (% IACS) (° C.) Example 1 1 102.8 127 Example 2 1 102.8 130 Example 3 3.1 102.5 132 Comparative Example 1 5 102.4 134 Comparative Example 2 10 102.3 135 Comparative Example 3 12 102.2 136 Comparative Example 4 18 101.5 162
[0169] It is understood from Table 12 and
[0170] The invention is not limited to the embodiment and Examples and various modifications can be implemented.