US20130042949A1

US20130042949A1 - Method of manufacturing soft-dilute-copper-alloy-material

Info

Publication number: US20130042949A1
Application number: US13/571,781
Authority: US
Inventors: Hideyuki Sagawa; Seigi Aoyama; Hiromitsu Kuroda; Toru Sumi; Keisuke Fujito; Ryohei Okada; Shinichi Masui
Original assignee: Hitachi Cable Ltd
Current assignee: Proterial Ltd
Priority date: 2011-08-17
Filing date: 2012-08-10
Publication date: 2013-02-21
Also published as: JP2013057121A; CN102953022A

Abstract

A method of manufacturing a soft-dilute-copper-alloy material includes a plastic working of a soft-dilute-copper-alloy including an additional element selected from the group consisting of Ti, Mg, Zr, Nb, Ca, V, Ni, Mn and Cr, and a balance consisting of copper and inevitable impurity, and a subsequent annealing treatment of the soft-dilute-copper-alloy. A working ratio in the plastic working before the annealing treatment is not less than 50%.

Description

The present application is based on Japanese patent application No. 2011-178349 filed on Aug. 17, 2011, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to a method of manufacturing a high conductive soft-dilute-copper-alloy material having high tensile strength and high elongation percentage even though it is a soft material.
2. Description of the Related Art
In recent science and technology, electricity is used for everything such as electric power as a power source or electric signals, etc., and conductors such as cables or lead wires, or in the electronic component field, bonding wires, etc., are used for transmission thereof. Metals having relatively high conductivity such as copper, silver or gold are used as a material of such conductors, and particularly, copper wires are often used in view of the cost.
Although it is generically called “copper”, it is broadly classified into hard copper and soft copper depending on a molecular arrangement thereof. In addition, copper of the type having desired properties is used depending on the intended use.
A hard copper wire is often used for a lead wire for electronic component. However, a rigid hard copper wire is unsuitable as a cable used in, e.g., electronic devices, etc., such as medical equipment, industrial robot or notebook computer since it is used in an environment in which a combined external force of extreme bending, torsion and tension, etc., is repeatedly applied, and thus, a soft copper wire is used instead.
A conductor used for such an application is required to have conflicting characteristics, which are good conductivity (high conductivity), good tensile strength, elongation percentage, bending characteristics and small hardness, and accordingly, a copper material maintaining conductivity, tensile strength and an elongation percentage has been developed to date.
For example, the invention according to JP-A-2002-363668 relates to a flexible cable conductor having good tensile strength, elongation percentage and conductivity, and particularly, a flexible cable conductor is described in which a wire rod is formed of a copper alloy made of oxygen-free copper with a purity of not less than 99.99 mass containing indium with a purity of not less than 99.99 mass % at a concentration range of 0.05 to 0.70 mass % and P with a purity of not less than 99.9 mass % at a concentration range of 0.0001 to 0.003 mass %.
Meanwhile, in the invention according to JP-A-9-256084, a flexible copper alloy wire containing 0.1 to 1.0 mass % of indium, 0.01 to 0.1 mass % of boron and a balance consisting of copper is described.
JP-A-61-224443 proposes a conductor which is used for a wire bonding and has small hardness as a raw material in addition to good tensile strength and elongation percentage, wherein the conductor achieves all of high tensile strength, high elongation percentage and softness by adjusting the amount of impurity in high purity copper of not less than 99.999 mass %.

SUMMARY OF THE INVENTION

The invention of JP-A-2002-363668 only relates to a hard copper wire containing a large amount of In as an additional element, and a soft copper wire excellent in tensile strength and elongation percentage is not examined. In addition, conductivity is low due to the large amount of In as an additional element.
Meanwhile, in JP-A-9-256084 which is the invention related to a soft copper wire, conductivity is low due to the large amount of additional elements in the same manner as the invention according to JP-A-2002-363668.
On the other hand, high conductivity could be ensured by selecting a highly conductive copper material such as oxygen-free copper (OFC), etc., as a raw copper material. In this regard, when oxygen-free copper (OFC) is used as a raw material without adding any other elements in order to maintain conductivity, it is considered that a crystalline structure in the oxygen-free copper wire is made finer by drawing a copper wire rod at an increased working ratio to achieve high tensile strength and elongation percentage and the oxygen-free copper work-hardened due to the wire drawing process is suitable for application as a hard wire rod, however, there is a problem that it cannot be used for a soft wire rod.
In the invention according to JP-A-61-224443, high conductivity is expected since copper with high purity of not less than 99.999 mass % is used as a base, however, high purification of copper requires a special process such as zone melting method or vacuum beam melting method, which inevitably results in the complicated manufacturing process and the expensive material.
It is an object of the invention to provide a method of manufacturing a high conductive soft-dilute-copper-alloy material that has high tensile strength and high elongation percentage even though it is a soft copper material, wherein the manufacturing steps are simple and low-cost.
According to one embodiment of the invention, a method of manufacturing a soft-dilute-copper-alloy material comprises:
a plastic working of a soft-dilute-copper-alloy comprising an additional element selected from the group consisting of Ti, Mg, Zr, Nb, Ca, V, Ni, Mn and Cr, and a balance consisting of copper and inevitable impurity; and

- a subsequent annealing treatment of the soft-dilute-copper-alloy,
- wherein a working ratio in the plastic working before the annealing treatment is not less than 50%.

Preferably, in the method of manufacturing a soft-dilute-copper-alloy material of the invention, annealing treatment is continuously performed by passing a material through a tubular furnace at a temperature of 250° C. to 800° C. for 0.6 seconds to 10.0 seconds, or is performed by an electric annealer at an applied voltage of 21V to 35V and at a velocity of 100 m/min to 600 m/min or is performed by batch processing at a temperature of 150° C. to 700° C. for not more than 3 hours, and the soft-dilute-copper-alloy contains 2 to 12 mass ppm of sulfur, more than 2 mass ppm and not more than 30 mass ppm of oxygen and 4 to 55 mass ppm of Ti as the additional element.
Preferably, the soft-dilute-copper-alloy material of the invention is formed of a soft copper material which satisfies a conductivity of 98% LACS (International Annealed Copper Standard, conductivity is defined as 100% when resistivity is 1.7241×10⁻⁸Ωm), 100% IACS, or further, 102% IACS. Additionally, the soft-dilute-copper-alloy material is preferably formed of a material having a softening temperature of not more than 148° C. when a working ratio of a wire rod is 90% (e.g., processing from an 8 mm diameter wire into a 2.6 mm diameter wire) by using a SCR continuous casting and rolling machine which allows stable production in a wide range of manufacturing with less generation of surface flaws.
In order to obtain a copper wire rod which satisfies softening temperature and conductivity after the cold wire drawing process, it is preferable to crystallize and precipitate sulfur in copper by following (a) and (b).
(a) It is preferable that the oxygen concentration in the material be increased to more than 2 mass ppm, followed by the addition of Ti. It is considered that, as a result, TIS, titanium oxide (TiO₂) or Ti—O—S particles are initially formed in molten copper.
(b) Next, it is preferable that the hot rolling temperature be set to 880 to 550° C. which is lower than 950 to 600° C. of the typical manufacturing conditions of copper so that dislocation is introduced into copper for easy precipitation of S. As a result, S is precipitated on the dislocation or is precipitated using titanium oxide (TiO₂) as a nucleus, and for example, particles of Ti—O—S, etc., are formed in the same manner as in the molten copper.

(1) Additional Element

The reason why element(s) selected from the group consisting of Ti, Mg, Zr, Nb, Ca, V, Ni, Mn, and Cr is chosen as an additional element is that these elements are active elements being prone to bind to other elements, especially to sulfur (S), and thus can trap S, which allows a copper base material (matrix) to be highly purified and hardness of the material to be reduced. In addition, an effect of realizing higher conductivity is obtained by trapping S. One or two or more additional elements are contained. In addition, other elements and impurities which do not adversely affect the properties of an alloy may be contained in the alloy.
The total content of one or two or more of Ti, Ca, V, Ni, Mn, and Cr as an additional element is 4 to 55 mass ppm, more preferably 10 to 20 mass ppm. The content of Mg is 2 to 30 mass ppm, more preferably 5 to 10 mass ppm, and the content of Nb is 8 to 100 mass ppm, more preferably 20 to 40 mass ppm.
Meanwhile, in the below-described preferred embodiment, the favorable oxygen content is more than 2 mass ppm and not more than 30 mass ppm, more preferably 5 to 15 mass ppm, and more than 2 up to 400 mass ppm of oxygen can be contained within a range providing the properties of the alloy, depending on the added amount of the additional element and the sulfur content.
The sulfur content is 3 to 12 mass ppm, and more preferably, 3 to 8 mass ppm.
In order to obtain a soft copper alloy material having a conductivity of not less than 98% IACS, a soft-dilute-copper-alloy material in which pure copper with inevitable impurities (a base material) contains 3 to 12 mass ppm of sulfur, more than 2 mass ppm and not more than 30 mass ppm of oxygen and 4 to 55 mass ppm of Ti is used to manufacture a wire rod (a roughly drawn wire). So-called low-oxygen copper (LOC) is used in the present embodiment since more than 2 mass ppm and not more than 30 mass ppm of oxygen is contained.
Here, in order to obtain a soft copper alloy material having a conductivity of not less than 100% IACS, a wire rod is formed of a soft-dilute-copper-alloy material containing pure copper with inevitable impurities, 2 to 12 mass ppm of sulfur, more than 2 mass ppm and not more than 30 mass ppm of oxygen and 4 to 37 mass ppm of Ti.
In addition, in order to obtain a soft copper alloy material having a conductivity of not less than 102% IACS, a wire rod is formed of a soft-dilute-copper-alloy material containing pure copper with inevitable impurities, 3 to 12 mass ppm of sulfur, more than 2 mass ppm and not more than 30 mass ppm of oxygen and 4 to 25 mass ppm of Ti.
Sulfur is generally introduced into copper at the time of manufacturing electrolytic copper in the industrial production of pure copper and it is thus difficult to adjust sulfur to be not more than 3 mass ppm. The upper limit of the sulfur concentration in general-purpose electrolytic copper is 12 mass ppm.
Oxygen is preferably controlled to be more than 2 mass ppm since the softening temperature is less likely to decrease when the amount of oxygen is low, as described above. On the other hand, since surface flaws are likely to be generated during the hot process when the amount of oxygen is too large, it is preferably adjusted to not more than 30 mass ppm.

(2) Dispersed Substance

Desirably, dispersed particles are small in size and a large number of dispersed particles are distributed. It is because the dispersed particle functions as a precipitation site of sulfur and it is thus required to be small in size and large in number.
In general, sulfur and titanium form a compound or an aggregate in the form of TiO, TiO₂, TiS or Ti—O—S, and the remainders of S and Ti are present in the form of solid solution. In the soft-dilute-copper-alloy material to be formed, TiO with a size of not more than 200 nm, TiO₂with a size of not more than 1000 nm, TiS with a size of not more than 200 nm or Ti—O—S with a size of not more than 300 nm is distributed in the crystal grain. The “crystal grain” means a crystalline structure of copper.
Note that, since the size of particle to be formed varies depending on holding time or a cooling status of the molten copper during the casting, it is also necessary to correspondingly determine casting conditions.

(3) Conditions of Continuous Casting and Rolling

A wire rod is manufactured by the SCR (Southwire Continuous Rod System) continuous casting and rolling method where a working ratio for processing an ingot rod is 90% (30 mm in diameter) to 99.8% (5 mm in diameter). As an example, a method of manufacturing an 8 mm diameter wire rod at a working ratio of 99.3% is employed.
(a) It is desirable that the molten copper temperature in a melting furnace be not less than 1100° C. and not more than 1320° C. The molten copper temperature is determined to be not more than 1320° C. since there is a tendency that a blow hole is increased, a flaw is generated and a particle size is enlarged when the temperature of the copper is high. Although the molten copper temperature is determined to be not less than 1100° C. since otherwise copper is likely to solidify and the manufacturing is not stable, the casting temperature is desirably as low as possible.
(b) The hot rolling temperature is desirably not more than 880° C. at the initial roll and not less than 550° C. at the final roll.
Unlike the typical manufacturing conditions of pure copper, the subject of the invention is to crystallize sulfur in the molten copper and to precipitate the sulfur during the hot rolling, and accordingly, the molten copper temperature and the hot rolling temperature should be as described in (a) and (b) in order to further decrease a solid solubility limit as an activation energy thereof.
The typical hot rolling temperature is not more than 950° C. at the initial roll and not less than 600° C. at the final roll, however, in order to further decrease the solid solubility limit, it is desirable to set to not more than 880° C. at the initial roll and not less than 550° C. at the final roll.
Under such conditions, it is possible to obtain a soft-dilute-copper-alloy wire or sheet material such that a wire rod with a diameter of 8 mm has a conductivity of not less than 98% IACS, not less than 100% IACS, or more preferably not less than 102% IACS and that a wire rod after the cold wire drawing process (e.g., 2.6 mm in diameter) has a softening temperature from 130° C. to 148° C.
For the industrial use, not less than 98% IACS is required when it is in the form of soft copper wire which is formed of electrolyte copper and has industrially usable purity, and the softening temperature is not more than 148° C. in light of the industrial value thereof. The softening temperature in case of not adding Ti is 160 to 165° C. Since the softening temperature of high purity copper (6N) is 127 to 130° C., the threshold limit value is determined to be 130° C. based on the obtained data. This slight difference is caused by inevitable impurities which are not present in high purity copper (6N).
The conductivity of oxygen-free copper is about 101.7% IACS and that of high purity copper (6N) is 102.8% IACS, and therefore, it is desirable to have a conductivity as close to high purity copper (6N) as possible.
Since melting of copper as a base material in a shaft furnace causes contamination of cuprate or enlargement of particle size and decreases quality, the method should be such that, after melting the copper, casting is carried out in a ladle controlled to be a reduced-state, i.e., under reductive gas (CO) atmosphere while controlling concentrations of sulfur, Ti and oxygen, which are constituent elements of a dilute alloy, to stably manufacture a wire rod to be rolled.
As described above, the soft-dilute-copper-alloy material manufactured by the manufacturing method of the invention allows a practical soft-dilute-copper-alloy material excellent in conductivity, softening temperature and surface quality to be obtained and can be used as a molten solder plating material (wire, plate, foil), an enameled wire, soft pure copper, high conductivity copper and a soft copper wire and it is possible to reduce energy at the time of annealing, and high productivity is thereby obtained.
In addition, in the case of the soft-dilute-copper-alloy material manufactured by the manufacturing method of the invention, a plating layer may be formed on a surface thereof. A plating layer consisting mainly of, e.g., tin, nickel, silver, zinc or palladium is applicable, or, so-called Pb-free plating may be used therefor.
In addition, it is possible to form a soft-dilute-copper-alloy stranded wire by twisting plural wires formed of the soft-dilute-copper-alloy material manufactured by the manufacturing method of the invention.
Furthermore, it is possible to form a cable in which an insulation layer is provided around a wire or a stranded wire formed of the soft-dilute-copper-alloy material manufactured by the manufacturing method of the invention.
Also, it is possible to form a coaxial cable in which plural wires formed of the soft-dilute-copper-alloy material manufactured by the manufacturing method of the invention are twisted to form a central conductor, an insulation cover is formed on an outer periphery of the central conductor, an outer conductor formed of copper or copper alloy is arranged on an outer periphery of the insulation cover and a jacket layer is provided on an outer periphery of the outer conductor. In addition, it is possible to form a composite cable in which plural coaxial cables are arranged in a shield layer and a sheath is provided on an outer periphery of the shield layer.
In addition, the soft-dilute-copper-alloy material manufactured by the manufacturing method of the invention is suitable for a wide range of applications such as a copper sheet used for a heatsink, a gauge copper strip used for a lead frame and copper foil used for a circuit board, etc.
The intended use of the soft-dilute-copper-alloy material of the invention includes use as, e.g., a wiring material for consumer solar cell, a motor enameled wire, a soft copper material for high-temperature application used at 200° C. to 700° C., a power cable conductor, a signal line conductor, a molten solder plating material which does not require annealing, a conductor for FPC wiring, a copper material excellent in thermal conductivity and a substitute material for high purity copper, and meets such a wide range of needs. In addition, the shape is not specifically limited, and a conductor having a circular cross section, a rod-shaped conductor or a rectangular conductor may be used.
Meanwhile, although an example in which a wire rod is made by the SCR continuous casting and rolling method and a soft material is made by the hot rolling has been described as the method of manufacturing a soft-dilute-copper-alloy material of the invention, a twin-roll continuous casting and rolling method or a Properzi continuous casting and rolling method may be used for the manufacturing.

(4) Working Ratio and Annealing Method of Soft-Dilute-Copper-Alloy Material

In the method of manufacturing a soft-dilute-copper-alloy material of the invention, a working ratio during plastic working before heat treatment for annealing is not less than 50% in order to obtain a desired crystalline structure. The working ratio here is defined as follows.
Working ratio (%)=[Cross sectional area before wire drawing (soft material)−Cross sectional area after wire drawing]×100/[Cross sectional area before wire drawing (soft material)]
This is because, when a material having a working ratio of less than 50% is annealed, strain energy for generating multiple crystal nuclei in the process of recrystallization is not sufficient and only few crystal nuclei are present, and accordingly, crystal are likely to coarsen at the time of growth thereof. The more preferred working ratio is 80 to 99.8%.
In the method of manufacturing a soft-dilute-copper-alloy material of the invention, a soft-dilute-copper-alloy is cold-drawn in multiple steps at a working ratio of not less than 50% for each time, and annealing treatment is performed after each step.
Preferably, the soft-dilute-copper-alloy material obtained by the manufacturing method of the invention has a crystalline structure in which the average crystal grain size from the surface toward the inner side up to a depth of 20% of a wire diameter or a sheet thickness is not more than 20 μM.
As an annealing method using a plastic-worked material to obtain a desired crystalline structure, continuous annealing by passing a material through a tubular furnace at a temperature of 250° C. to 550° C. for 0.6 seconds to 5.0 seconds is applicable to a line-shaped material having a diameter of less than 1 mm. The reason therefor is that, when the temperature is lower than 250° C. or the annealing time is shorter than 0.6 seconds, the worked structure is still present in the material and the value of the elongation percentage is small. On the other hand, when the temperature is more than 550° C. or the annealing time is longer than 5.0 seconds, a desired crystalline structure or elongation percentage may not be obtained due to coarsened crystal grains or an excessively softened conductor may be deformed by tension at the time of winding up. In addition, continuous annealing by passing a material through a tubular furnace at a temperature of 300° C. to 800° C. for 1.0 second to 10.0 seconds is applicable to a line-shaped material having a diameter of not less than 1 mm.
As another annealing method, batch annealing at a temperature of 150° C. to 550° C. for not more than 3 hours is applicable to a line-shaped material having a diameter of less than 1 mm. The batch annealing is characterized in that use of a large capacity annealing furnace allows a large amount of material to be annealed for each annealing process and it is effective to anneal a thin conductor of which volume per unit length is small. The reason for selecting such annealing conditions is that, when the temperature is lower than 150° C., softening is not enough and the value of the elongation percentage is low in the same manner as described above. On the other hand, when the temperature is more than 550° C. or the annealing time is longer than 3 hours, a desired crystalline structure may not be obtained due to coarsened crystal grains, or elongation percentage may be small or defects such as adhesion between wires may be likely to occur.
In addition, batch annealing at a temperature of 170° C. to 700° C. for not more than 3 hours is applicable to a line-shaped material having a diameter of not less than 1 mm.
The lower limit of the annealing time is desirably not less than 0.5 hours in order to obtain a desired crystalline structure and to soften the material.
As another annealing method, continuous treatment using an electric annealer at an applied voltage of 21V to 33V and at a velocity of 300 m/min to 600 m/min is applicable to a line-shaped material having a diameter of less than 1 mm. Annealing using an electric annealer allows softening at a high processing speed and it is thus possible to contribute to high efficiency production, i.e., cost reduction. The reason for selecting such annealing conditions is that, when the applied voltage is less than 20V or the velocity is greater than 600 m/min, softening is not enough and the value of the elongation percentage is low. On the other hand, when the applied voltage is more than 30V or the velocity is less than 300 m/min, a desired crystalline structure may not be obtained due to coarsened crystal grains, or elongation percentage may be small or the conductor may be deformed or broken due to excessive thermal energy.
In addition, continuous treatment using an electric annealer at an applied voltage of 25V to 35V and at a velocity of 100 m/min to 500 m/min is applicable to a line-shaped material having a diameter of not less than 1 mm.
Meanwhile, it is desirable that these annealings be performed in an inert gas such as nitrogen gas or argon gas in order to prevent oxidation of the copper alloy material.

(5) Crystalline Structure of Soft-Dilute-Copper-Alloy Material

The soft-dilute-copper-alloy material in the invention has a crystalline structure in which the average size of crystal grains included in a surface layer is not more than 20 μm at least from the surface of a wire or a sheet toward the inner side of the copper conductor up to a depth of 20% of a wire diameter or a sheet thickness and the average crystal grain size of the inner side is larger than that in the surface layer.
This is because improvement in tensile strength or elongation percentage of the material can be expected due to fine crystals especially due to presence of fine crystals in the surface layer. The reason therefor is considered that the local strain introduced near a grain boundary due to tensile deformation becomes smaller as the crystal grain size becomes finer, this contributes to relieve stress concentration at grain boundary, and accordingly, the stress concentration at grain boundary is reduced and grain boundary fracture is suppressed.

Effects of the Invention

One embodiment of the invention can offer a method of manufacturing a high conductive soft-dilute-copper-alloy material that has high tensile strength and high elongation percentage even though it is a soft copper material, wherein the manufacturing steps are simple and low-cost.

BRIEF DESCRIPTION OF THE DRAWINGS

Next, the present invention will be explained in more detail in conjunction with appended drawings, wherein:

FIG. 1 is graph showing a relation between an annealing temperature and elongation percentage of Example Material 1 and Comparative Material 1;

FIG. 2 is a photograph showing a radial cross section structure of Example Material 1 at an annealing temperature of 500° C.;

FIG. 3 is a photograph showing a radial cross section structure of Example Material 1 at an annealing temperature of 700° C.;

FIG. 4 is a photograph showing a radial cross section structure of Comparative Material 1;

FIG. 5 is a schematic view showing a bending fatigue test;

FIG. 6 is a graph as a result of measuring a bending life, showing a relation between surface bending strain and the number of bending cycle of Example Material 2 and Comparative Material 2;

FIG. 7 is a photograph showing a cross section structure across-the-width of Example Material 2;

FIG. 8 is a photograph showing a cross section structure across-the-width of a sample Comparative Material 2;

FIG. 9 is a graph as a result of measuring a bending life, showing a relation between surface bending strain and the number of bending cycle of Example Material 3 and Comparative Material 3;

FIG. 10 is a photograph showing a cross section structure across-the-width of Example Material 3;

FIG. 11 is a photograph showing a cross section structure across-the-width of Comparative Material 3;

FIG. 12 is a schematic view showing a method of measuring an average crystal grain size in a surface layer of a sample;

FIG. 13 is a graph showing a relation between tensile strength and an elongation percentage of Example Material 4 and Comparative Material 4;

FIG. 14 is a graph showing a relation between an elongation percentage and hardness of Example Material 4 and Comparative Material 4;

FIG. 15 is a graph showing a relation between tensile strength and hardness of Example Material 4 and Comparative Material 4;

FIGS. 16A and 16B are photographs showing a cross section structure across-the-width of Example Material 4;

FIG. 17 is a photograph showing a cross section structure across-the-width of Comparative Material 4; and

FIG. 18 is a schematic view showing a method of measuring an average crystal grain size in a surface layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Although the embodiments of the invention will be described below, the invention according to claims is not to be limited to the embodiments below. Further, it should be noted that all combinations of the features described in the embodiment are not always necessary to solve the problem of the invention.

Experimental Examples

Manufacturing of Soft-Dilute-Copper-Alloy Material of the Invention
8 mm diameter copper wires (wire rods, a working ratio of 99.3%) containing low-oxygen copper (oxygen concentration of 7 mass ppm to 8 mass ppm and sulfur concentration of 5 mass ppm) and 13 mass ppm of Ti were made as experimental materials. The 8 mm diameter copper wires have been hot rolled by SCR continuous casting and rolling. Copper molten metal which was melted in a shaft furnace was poured into a ladle under a reductive gas atmosphere, the molten copper poured into the ladle was introduced into a casting pot under the same reductive gas atmosphere, and Ti was added in the casting pot, and subsequently, an ingot rod was made in a casting mold formed between a casting wheel and an endless belt by sending the resulting molten copper through a nozzle. The 8 mm diameter copper wire was made by hot rolling the ingot rod. Then, each experimental material was cold-drawn. A 2.6 mm diameter copper wire (copper bonding wire, a working ratio of 89.4%) was thereby made.
Firstly, characteristics of the material used for a copper bonding wire was examined using the 2.6 mm diameter copper wire.
Softening Characteristics of Soft-Dilute-Copper-Alloy Material
Comparative Material 1 using an oxygen-free copper wire and Example Material 1 using a soft-dilute-copper-alloy wire containing low-oxygen copper and 13 mass ppm of Ti were used as samples and were annealed at different annealing temperatures for 1 hour, and the results of examining Vickers hardness (Hv) thereof are shown in Table 1.

	TABLE 1

	Sample	20° C.	400° C.	600° C.

	Example Material
1	120	52	48
	Comparative Material 1	124	53	56

	(Unit: Hv)

Table 1 shows that Vickers hardness (Hv) of Comparative Material 1 is at the equivalent level to that of Example Material 1 at the annealing temperature of 400° C., as well as at the annealing temperature of 600° C. This shows that the soft-dilute-copper-alloy wire of the invention has sufficient softening characteristics and is especially excellent in softening characteristics at the annealing temperature of more than 400° C. even in comparison to an oxygen-free copper wire.
Proof Stress and Bending Life of Soft-Dilute-Copper-Alloy Wire
Comparative Material 1 using an oxygen-free copper wire and Example Material 1 using a soft-dilute-copper-alloy wire containing low-oxygen copper and 13 mass ppm of Ti were annealed at different annealing temperatures for 1 hour, and the result of examining variation in a 0.2% proof stress value thereof are shown in Table 2. The samples having a diameter of 2.6 mm were used.

TABLE 2

Sample	20° C.	250° C.	400° C.	600° C.	700° C.

Example Material
1	421	80	58	35	25
Comparative Material 1	412	73	53	32	24

(Unit: MPa)

Table 2 shows that the 0.2% proof stress value of Comparative Material 1 and that of Example Material 1 are at the equivalent level at the annealing temperature of 400° C., and are nearly the same at the annealing temperature of 600° C.
Relation Between Elongation Characteristics and Crystalline Structure of Soft-Dilute-Copper-Alloy Wire
FIG. 1 is a graph showing variation in elongation (%) of Comparative Material 1 using a 2.6 mm diameter oxygen-free copper wire and Example Material 1 using a 2.6 mm diameter soft-dilute-copper-alloy wire containing low-oxygen copper and 13 mass ppm of Ti which were annealed at different annealing temperatures for 1 hour. In FIG. 1, a circle point indicates Example Material 1 and a square point indicates Comparative Material 1.
FIG. 1 shows that Example Material 1 exhibits better elongation characteristics than Comparative Material 1 at an annealing temperature of more than 100° C. in a wide range of around 130° C. to 900° C.
FIG. 2 is a photograph showing a cross section of a copper wire of Example Material 1 at an annealing temperature of 500° C. As shown in FIG. 2, a fine crystalline structure is formed on the entire cross section of the copper alloy wire and it appears that the fine crystalline structure contributes to the elongation characteristics. On the other hand, secondary recrystallization has proceeded in the cross section structure of Comparative Material 1 at the annealing temperature of 500° C., and crystal grains in the cross section structure were coarsened as compared to the crystalline structure of FIG. 2. It is considered that this decreases the elongation characteristics.
FIG. 3 is a photograph showing a cross section of the copper wire of Example Material 1 at an annealing temperature of 700° C. It is found that the crystal aain size in the surface layer on the cross section of the copper alloy wire is extremely smaller than the crystal grain size of the inner side. Although secondary recrystallization has proceeded in the crystalline structure of the inner side, a fine crystal grain layer remains as the outer layer. It is considered that the high elongation characteristics are maintained since the fine crystal layer remains as the surface layer even though the crystalline structure of the inner side grows to be large.
FIG. 4 is a photograph showing across section structure in Comparative Material 1. In Comparative Material 1, it is considered that the elongation characteristics in a high temperature range of not less than 600° C. are lower than those of Example Material 1 since crystal grains having a substantially equal size all around are uniformly aligned from the surface to the middle portion and secondary recrystallization has proceeded in the entire cross section structure.
As described above, since Example Material 1 exhibits better elongation characteristics than Comparative Material 1, handling properties are excellent at the time of manufacturing a stranded wire using this conductor, bending resistance characteristics are excellent and it is advantageous in that it is easy to lay a cable due to flexibility.
A long bending life is required for the soft-dilute-copper-alloy material of the invention. Accordingly, the bending life was measured on Comparative Material 2 using an oxygen-free copper wire and on Example Material 2 using a soft-dilute-copper-alloy wire containing low-oxygen copper and 13 mass ppm of Ti. The samples used here are a 0.26 mm diameter wire rod annealed at the annealing temperature of 400° C. for 1 hour. Comparative Material 2 has the same element composition as that of Comparative Material and also Example Material 2 has the same element composition as that of Example Material 1.
FIG. 5 shows a method of measuring the bending life, and a bending fatigue test was conducted by this method. The bending fatigue test is a test in which a load is applied to a sample to impart tension and compression strain to the surface thereof by cyclic bending. The sample is placed between bending jigs (which are referred to as “ring” in the drawing) as shown in (A) and is bent by a 90° rotation of the jigs as shown in (B) while the load is still applied. By this operation, a compressive strain is applied to a surface of the wire rod in contact with the bending jig and a tensile strain is applied to an opposite surface. After that, it returns to a state (A) again. Then, the sample is bent by a 90° rotation in a direction opposite to the direction shown in (B). Also in this case, a compressive strain is applied to the surface of the wire rod in contact with the bending jig and a tensile strain is applied to the opposite surface, and it becomes a state (C). Then, it returns to the initial state (A) from (C). One bending fatigue cycle consisting of (A)-(B)-(A)-(C)-(A) requires 4 seconds. The surface bending strain can be derived by the following formula.
Surface bending strain (%)=r/(R+r)×100(%)
{R: bending radius of wire (30 mm), r: radius of wire}
FIG. 6 is a graph showing a relation between surface bending strain and the number of bending cycle when the bending life is measured on Comparative Material 2 using an oxygen-free copper wire and Example Material 2 using a soft-dilute-copper-alloy wire containing low-oxygen copper and 13 mass ppm of Ti which were annealed at 400° C. for 1 hour. As shown in FIG. 6, the number of bending cycles at the surface bending strain of 0.45% was slightly more than 4000 cycles in Example Material 2 of the invention while that of Comparative Material 2 is slightly less than 2000 cycles, which shows that the bending life of Example Material 2 is twice longer than Comparative Material 2.
FIG. 7 is a photograph of a cross section structure showing a crystalline structure across-the-width of Example Material 2 and FIG. 8 is a photograph of a cross section structure showing a crystalline structure across-the-width of Comparative Material 2. Example Material 2 is a 0.26 mm diameter wire rod which has the same element composition as that of Comparative Material 1 and the highest soft material conductivity and is made through annealing treatment at an annealing temperature of 400° C. for 1 hour. Meanwhile, Comparative Material 2 is a 0.26 mm diameter wire rod formed of oxygen-free copper (OFC) and is made through annealing treatment at an annealing temperature of 400° C. for 1 hour.
The conductivity of Example Material 2 and Comparative Material 2 is shown in Table 3.

	TABLE 3

	Conductivity of soft material (% IACS)

Example Material 2	102.4
Comparative Material 2	101.8

As shown in Table 3, when passing an electric current through Example Material 2, electron flow is less disturbed as compared to Comparative Material 2, hence, electrical resistance decreases. Therefore, the conductivity (% IACS) of Example Material 2 is greater than that of Comparative Material 2.
As shown in FIG. 8, it is understood that crystal grains having an equal size all around are uniformly aligned from the surface to the middle portion in the crystalline structure of Comparative Material 2. In contrast, as shown in FIG. 7, the crystalline structure of Example Material 2 has a difference in the size of crystal grain between the surface layer and the inner side and a crystal grain size of the inner side is extremely larger than that in the surface layer.
In Example Material 2, S in copper of a conductor which is processed to have a diameter of, e.g., 2.6 mm or 0.26 mm is trapped in the form of Ti—S or Ti—O—S. In addition, oxygen (O) included in copper is present in the form of Ti₃O_y, e.g., TiO₂, and is precipitated in a crystal grain or at crystal grain boundary.
Therefore, in Example Material 2, recrystallization is likely to proceed when copper is annealed to recrystallize the crystalline structure, and thus, the crystal grains of the inner side grow to be large. Accordingly, when passing an electric current through Example Material 2, electron flow is less disturbed as compared to Comparative Material 2, hence, electrical resistance decreases. Therefore, the conductivity (%IACS) of Example Material 2 is greater than that of Comparative Material 2.
As a result, a product using Example Material 2 is soft and can have an improved conductivity and improved bending characteristics. A conventional conductor requires high temperature annealing treatment in order to recrystallize the crystalline structure to have a size equivalent to that in Example Material 2. However, S is re-dissolved when the annealing temperature is too high. In addition, there is a problem that the conventional conductor is softened when recrystallized and the bending characteristics decreases. In Example Material 2, while crystal grains of the inner side become large and the material becomes soft since it can be recrystallized without twining at the time of annealing, the bending characteristics do not decrease since fine crystals remain in the surface layer.
FIG. 9 is a graph showing a relation between surface bending strain and the number of bending cycle, indicating the results of the bending life measured on Comparative Material 3 using an oxygen-free copper wire and Example Material 3 using a soft-dilute-copper-alloy wire containing low-oxygen copper and Ti which were annealed at 600° C. for 1 hour. The samples used here are a 0.26 mm diameter wire rod annealed at the annealing temperature of 600° C. for 1 hour. Comparative Material 3 has the same element composition as that of Comparative Material 1 and also Example Material 3 has the same element composition as that of Example Material 1. The bending life was measured under the same conditions as the measuring method shown in FIG. 5.
As shown in FIG. 9, also in this case, the number of bending cycles at the surface bending strain of 0.45% was slightly less than 2000 cycles in Example Material 3 of the invention while that of Comparative Material 3 is 1000 cycles, which shows that the bending life of Example Material 3 is twice longer than Comparative Material 3. It is understood that this is resulted from that the Example Materials 2 and 3 exhibit a greater 0.2% proof stress value than Comparative Materials 2 and 3 under any annealing conditions.
FIG. 10 is a photograph of a cross section structure showing a crystalline structure across-the-width of Example Material 3 and FIG. 11 is a photograph of a cross section structure showing a crystalline structure across-the-width of Comparative Material 3. As shown in FIGS. 10 and 11, it is found that crystal grains having an equal size all around are uniformly aligned from the surface to the middle portion in the crystalline structure of Comparative Material 3. In contrast, the size of crystal grain in the crystalline structure of Example Material 3 is uneven as a whole, and it is notable here that a crystal grain size in a thin layer formed on the sample near a surface thereof in a cross-sectional direction is extremely smaller than that of inner side.
The inventors consider that a fine crystal grain layer appeared as a surface layer of Example Material 3, which is not formed in Comparative Material 3, contributes to improve bending characteristics of Example Material 3.
In general, it is understood that uniformly coarsened crystal grains are formed by recrystallization as is in Comparative Material 3 if annealing treatment is carried out at an annealing temperature of 600° C. for 1 hour. However, a fine crystal grain layer remains as a surface layer in the invention even after the annealing treatment at the annealing temperature of 600° C. for 1 hour, hence, a soft-dilute-copper-alloy material with satisfactory bending characteristics is obtained even though it is a soft copper material.
Average crystal grain sizes in the surface layers of the samples of Example Material 3 and Comparative Material 3 were measured based on the cross-sectional images of the crystalline structures shown in FIGS. 10 and 11.
FIG. 12 shows a method of measuring an average crystal grain size in the surface layer. A crystal grain size was measured within 1 mm in length from a surface of a widthwise cross section of a 0.26 mm diameter wire rod up to a depth of 50 μm at intervals of 10 μm in a depth direction as shown in FIG. 12, and an average of the actual measured values was defined as an average crystal grain size in the surface layer.
As a result of the measurement, the average crystal grain size in the surface layer of Comparative Material 3 was 50 μm, and is largely different from that of Example Material 3 which was 10 μm. It is believed that a fine average crystal grain size in the surface layer suppresses development of cracks caused by the bending fatigue test, which extends the bending fatigue life. That is, cracks are developed along a crystal grain boundary when the crystal grain size is large. However, the development of cracks is suppressed when the crystal grain size is small since a developing direction of cracks is changed, and it is considered that this is the reason why a large difference in the bending characteristics is caused between Comparative Material 3 and Example Material 3 as described above.
Meanwhile, as average crystal grain sizes in the surface layers of Example Material 1 and Comparative Material 1 each having a diameter of 2.6 mm, the crystal grain size was measured within 10 mm in length from the surface of a widthwise cross section of a 2.6 mm diameter wire rod up to a depth of 50 μm in a depth direction. As a result of the measurement, the average crystal grain size in the surface layer of Comparative Material 1 was 100 μm and that of Example Material 1 was 20 μm. In order to achieve the effects of the invention, the upper limit of the average crystal grain size in the surface layer is preferably not more than 20 μm, and considering a limit value for production, the average crystal grain size is supposed to be not less than 5 μm.

Example 1

Manufacturing of Soft-Dilute-Copper-Alloy Material

The procedure to make a 2.6 mm diameter copper wire is the same as that in Example Material 1 of the soft-dilute-copper-alloy material. Then, the copper wire was drawn to have a diameter of 0.9 mm, was once annealed by an electric annealer and was drawn again to have a diameter of 0.05 mm. A working ratio for processing from 2.6 mm to 0.9 mm in diameter is 88.0%.
The 0.05 mm diameter material was continuously annealed by an electric annealer at an applied voltage of 21V to 33V and at a take-up speed of 500 m/min, thereby preparing a material as Example Material 4. For the purpose of comparison, oxygen-free copper (OFC with a purity of not less than 99.99%) having a diameter of 0.05 mm which was made under the same thermomechanical treatment conditions was prepared as a material as Comparative Material 4. In this case, the wire drawing working ratio for processing from 0.9 mm to 0.05 mm diameter is 99.7%.
As an another annealing method, the soft-dilute-copper-alloy material drawn from 0.9 mm to 0.05 mm in diameter in the same manner as described above was annealed by running in a tubular furnace at 400° C. to 600° C. for 0.8 to 4.8 seconds, thereby preparing a material as Example Material 4. For the purpose of comparison, oxygen-free copper (OFC with a purity of not less than 99.99%) having a diameter of 0.05 mm which was made under the same thermomechanical treatment conditions was prepared as a material as Comparative Material 4.
Mechanical characteristics (tensile strength, elongation percentage), hardness and crystal grain size of the materials were measured. To derive the average crystal grain size in the surface layer, the crystal grain size within 0.25 mm in length from a surface of a widthwise cross section of a 0.05 mm diameter material up to a depth of 10 μm in a depth direction was measured.
Softening Characteristics, Elongation Percentage and Tensile Strength
FIG. 13 shows a relation between tensile strength and elongation percentage of Example Material 4 and Comparative Material 4 which are measured after a wire rod of Comparative Material 1 using an oxygen-free copper wire and a wire rod of Example Material 1 using a soft-dilute-copper-alloy wire containing low-oxygen copper and 13 mass ppm of Ti are drawn from 0.9 mm (annealed material) to 0.05 mm in diameter and are annealed by an electric annealer (voltage: 21 to 33V, take-up speed: 500 m/min).
As shown in FIG. 13, it is understood that the tensile strength of Example Material 4 is 15 MPa or more greater than that of Comparative Material 4 when compared at substantially the same elongation percentage. Since it is possible to increase tensile strength without decreasing elongation percentage even in comparison to oxygen-free copper, occurrence of wire breakage due to application of stress can be more reduced in, e.g., the soft-dilute-copper-alloy wire of Example Material 4 than in a conductor using oxygen-free copper.
FIG. 14 shows a relation between cross-sectional hardness (Hv) and a mechanical characteristic (elongation percentage) which are measured on a wire rod of Comparative Material 4 using an oxygen-free copper wire and a wire rod of Example Material 4 using a soft-dilute-copper-alloy wire containing low-oxygen copper and 13 mass ppm of Ti after drawing from 0.9 mm (annealed material) to 0.05 mm in diameter and annealing by running in a tubular furnace (temperature: 300° C. to 600° C., annealing time: 0.8 to 4.8 seconds).
For evaluating the cross-sectional hardness, a horizontal section of the 0.05 mm diameter wire embedded in a resin was polished and Vickers hardness at the center portion of the wire was measured. The number of measurements (n) is 5 (n=5) and the average value thereof is defined as the cross-sectional hardness.
Tensile strength and an elongation percentage were measured and evaluated by conducting a tensile test on the 0.05 mm diameter wire under the conditions of a gage length of 100 mm and a tension rate of 20 mm/min. The maximum tensile stress at which the material is fractured is defined as tensile strength, and the maximum deformation volume (strain) at which the material is fractured is defined as an elongation percentage.
As shown in FIG. 14, it is understood that the hardness of Example Material 4 is about 10 Hv smaller than that of Comparative Material 4 when compared at substantially the same elongation percentage. Since it is possible to reduce the hardness without decreasing the elongation percentage even in comparison to oxygen-free copper, damage to a pad at the time of bonding can be more reduced in, e.g., the soft-dilute-copper-alloy wire of Example Material 4 than in a bonding wire using oxygen-free copper.
The data under the conditions in which the hardness of Example Material 4 is substantially equal to that of Comparative Material 4 is extracted from the evaluation results shown in FIG. 13, and comparison of the results is shown in Table 4. The data of Example Material 4 is mechanical characteristics and hardness when the wire rod of Example Material 1 was drawn from 0.9 mm (annealed material) to 0.05 mm in diameter and was annealed by running in a tubular furnace at 400° C. for 1.2 seconds. Likewise, the data of Comparative Material 4 is mechanical characteristics and hardness when the wire rod of Comparative Material 1 was drawn from 0.9 mm (annealed material) to 0.05 mm in diameter and was annealed by running in a tubular furnace at 600° C. for 2.4 seconds.

TABLE 4

	Tensile	Elongation	Vickers
	strength	Percentage	hardness
Sample	(MPa)	(%)	(Hv)

Example Material 4	279	20	61
Comparative Material 4	211	13	61

As shown in Table 4, the elongation percentage of Example Material 4 is 7% or more higher than Comparative Material 4 even though Example Material 4 and Comparative Material 4 are materials having the same hardness. Therefore, when Example Material 4 is used as, e.g., a bonding wire, it is possible to greatly contribute to improvement in connection reliability and handling properties at the time of wire bonding. In addition, since the tensile strength is higher than that of the bonding wire using oxygen-free copper even though the hardness is the same, it is possible to greatly contribute to strength reliability of a connecting portion (a ball neck portion).
The connection reliability of the wire bonding portion here is resistance to stress generated by a difference in thermal expansion between a copper wire and a resin material after performing wire bonding and then resin molding.
Meanwhile, the handling properties are resistance to stress at the time of feeding a wire from a wire spool to the bonding portion, and also being not susceptible to permanent set of winding.
FIG. 15 is a graph showing a relation between hardness (Hv) and tensile strength. As shown in FIG. 15, it is understood that the hardness of Example Material 4 is about 10 Hv smaller than that of Comparative Material 4 when compared at substantially the same tensile strength. Since it is possible to reduce the hardness without decreasing the tensile strength, damage to a pad at the time of bonding can be reduced when the soft-dilute-copper-alloy material of Example Material 4 is used for, e.g., a bonding wire.
The data under the conditions in which the tensile strength of Example Material 4 is substantially equal to that of Comparative Material 4 is extracted and comparison of the results is shown in Table 5. The data of Example Material 4 is mechanical characteristics and hardness when the wire rod of Example Material 1 was drawn from 0.9 mm (annealed material) to 0.05 mm in diameter and was annealed by running in a tubular furnace at 500° C. for 4.8 seconds. Likewise, the data of Comparative Material 4 is mechanical characteristics and hardness the wire rod of Comparative Material 1 was drawn from 0.9 mm (annealed material) to 0.05 mm in diameter and was annealed by running in a tubular furnace at 600° C. for 2.4 seconds.

TABLE 5

	Tensile	Elongation	Vickers
	strength	Percentage	hardness
Sample	(MPa)	(%)	(Hv)

Example Material 4	213	18	53
Comparative Material 4	211	13	61

As shown in Table 5, the elongation percentage of Example Material 4 is 5% higher than Comparative Material 4 even though Example Material 4 and Comparative Material 4 are materials having the same tensile strength. Therefore, when Example Material 4 is used as, e.g., a bonding wire, it is possible to greatly contribute to improvement in connection reliability and handling properties at the time of wire bonding. In addition, since the hardness of Example Material 4 is sufficiently smaller than that of Comparative Material 4 even though the tensile strength is the same, damage to a pad at the time of bonding can be reduced.
The connection reliability and the handling properties of the wire bonding portion here are the same as described above.
The required technical specification of the balance among tensile strength, elongation percentage and hardness is somewhat different depending on products, and as an example, the invention can provide a conductor having a tensile strength of not less than 270 MPa and elongation of not less than 7% when considering that the tensile strength is important, and can provide a conductor having a tensile strength of not less than 210 MPa up to 270 MPa, an elongation percentage of not less than 15% and a hardness of not more than 65 Hv when considering that small hardness is additionally important.
Crystalline Structure of Soft-Dilute-Copper-Alloy Wire
FIGS. 16A and 16B are photographs showing a cross section structure across-the-width of Example Material 4 and FIG. 17 is a photograph showing a cross section structure across-the-width of Comparative Material 14. The photographs of FIGS. 16A and 16B are taken at different positions.
As shown in FIG. 17, it is found that crystal grains having an equal size all around are uniformly aligned from the surface to the middle portion in the crystalline structure of Comparative Material 4. In contrast, the size of crystal grain in the crystalline structure of Example Material 4 is uneven as a whole, and a crystal grain size in a thin layer formed on the sample near a surface thereof in a cross-sectional direction is extremely smaller than that of inner side.
The inventors consider that a fine crystal grain layer appeared as a surface layer of Example Material 4, which is not formed in Comparative Material 4, contributes to having softening characteristics of Example Material 4 and achieving both of tensile strength and elongation characteristics.
In general, it is understood that uniformly coarsened crystal grains are formed by recrystallization as is in Comparative Material 4 if heat treatment is carried out for the purpose of softening. However, a fine crystal grain layer remains as a surface layer in the present example even after the annealing treatment for forming the coarsened crystal grains in the inner side. It is therefore considered that a soft-dilute-copper-alloy material excellent in tensile strength and elongation percentage is obtained in the present example even though it is a soft copper material.
Average crystal grain sizes in the surface layers of the samples of Example Material 4 and Comparative Material 4 were measured based on the cross-sectional images of the crystalline structures shown in FIGS. 16A to 17.
FIG. 18 is a schematic view showing a method of measuring an average crystal grain size in the surface layer. A crystal grain size was measured within 0.25 mm in length from a surface of a widthwise cross section of a 0.05 mm diameter wire up to a depth of 10 μm at intervals of 5 μm in a depth direction as shown in FIG. 18. Then, an average of the measured values (actual measured values) was derived and was defined as an average crystal grain size.
As a result of the measurement, the average crystal grain size in the surface layer of Comparative Material 4 was 22 μm, and is different from that of Example Material 4 which was 7 μm in FIG. 16A and 15 μm in FIG. 16B. One of the reasons why high tensile strength and elongation percentage were obtained is believed that the average crystal grain size in the surface layer is fine. Note that, cracks are developed along a crystal grain boundary when the crystal grain size is large. However, the development of cracks is suppressed when the crystal grain size is small since a developing direction of cracks is changed. It is considered that this is the reason why fatigue characteristics of Example Material 4 are better than those of Comparative Material 4. The fatigue characteristics mean the number of stress application cycles or time until the material is fractured when receiving stress repeatedly.
In order to achieve the effects of the present example, the average crystal grain size in the surface layer is preferably not more than 15 μm.

Example 2

Tubular Furnace, Electric Annealer and Batch Processing for 0.05 mm Diameter Soft-Dilute-Copper-Alloy Material
Tables 6 to 8 show working ratios and heat treatment conditions of the 0.05 mm diameter soft-dilute-copper-alloy material, presence of fine crystals in the surface layer which contributes to improvement in tensile strength, an elongation percentage and bending characteristics as described above, and evaluation results of elongation percentage or hardness. The procedure to make a 0.9 mm diameter copper wire is the same as that in Example Material 1 of the soft-dilute-copper-alloy material.
The wire with a final diameter was annealed by running in a tubular furnace, and Table 6 shows the evaluations of the average crystal grain size in the surface layer and the elongation percentage with respect to the temperature and the annealing time.
The wire with a final diameter was annealed by an electric annealer, and Table 7 shows the evaluations of the average crystal grain size in the surface layer and the cross sectional hardness of the conductor with respect to the applied voltage and the velocity.

TABLE 6

		Average
	Heat treatment	crystal	Elonga-
	conditions	grain size	tion

Working	Temperature	Time	in surface	percent-
ratio (%)	(° C.)	(sec)	layer	age

Examples	1	50	400	1.2	◯	◯
	2	65			◯	◯
	3	80			◯	◯
	4	90	250		◯	◯
	5		300		◯	◯
	6		400	0.6	◯	◯
	7			1.2	◯	◯
	8			3.8	◯	◯
	9			5.0	◯	◯
	10		500	1.2	◯	◯
	11		550		◯	◯
	12	99.8	400		◯	◯
Comparative	1	30	400	1.2	X	Δ
Examples	2	48			X	Δ
	3	90	230		X	X
	4		820		X	Δ
	5		400	0.5	X	X
	6		500	0.2	X	Δ
	7			11	X	Δ

TABLE 7

	Average

	Heat treatment	crystal
	conditions	grain size

Working	Voltage	Velocity	in surface	Hard-
ratio (%)	(V)	(m/min)	layer	ness

Examples	1	50	25	450	◯	◯
	2	78			◯	◯
	3	90	21		◯	◯
	4		23		◯	◯
	5		25	100	◯	◯
	6			300	◯	◯
	7			450	◯	◯
	8			500	◯	◯
	9		33	450	◯	◯
Comparative	1	45	25	450	X	X
Examples	2	90	18		X	X
	3		36		X	◯
	4		25	80	X	◯
	5			700	X	X

The working ratios of the samples used for evaluations in Tables 6 and 7 were adjusted by annealing the wire still having a non-final diameter for several times during the processing of an annealed material from a 0.9 mm diameter to 0.05 mm as a final diameter of each sample.
The elongation percentage was evaluated by conducting a tensile test, and then, not less than 15% of elongation percentage was regarded as “passed the test (◯)”, 10 to less than 15% was regarded as “insufficient (Δ)” and below 10% was regarded as “unsuitable (X)”. For evaluating the hardness, Vickers hardness test was conducted on the horizontal section of the material embedded in a resin, and then, not more than 80 Hv was regarded as “passed the test (◯)” and more than 80 Hv was regarded as “unsuitable (X)”.
For the average crystal grain size in the surface layer, measurement was conducted by the method shown in FIG. 18 and an average of the measured values (actual measured values) was derived. Not more than 15 μm was regarded as “passed the test (◯)” and more than 15 μm was regarded as “unsuitable (X)”.
The wire with a final diameter was batch-annealed, and Table 8 shows the evaluations of the average crystal grain size in the surface layer and the elongation with respect to the temperature and the annealing time.

TABLE 8

		Average
	Heat treatment	crystal	Elonga-
	conditions	grain size	tion

Working	Temperature	Time	in surface	percent-
ratio (%)	(° C.)	(hr.)	layer	age

Examples	1	50	400	1	◯	◯
	2	90	150		◯	◯
	3		250		◯	◯
	4		400	0.5	◯	◯
	5			1	◯	◯
	6			2	◯	◯
	7			3	◯	◯
	8		550	1	◯	◯
	9	99.8	400		◯	◯
Comparative	1	47	400	1	X	X
Examples	2	90	120		X	X
	3		750		X	Δ
	4		400	5	X	Δ
	5		550	3.5	X	Δ

The working ratios of the samples used for evaluations in Tables 8 were adjusted by annealing the wire still having a non-final diameter for several times during the processing of an annealed material from a 0.9 mm diameter to 0.25 mm as a final diameter of each sample.
The average crystal grain size in the surface layer was measured by the same method as in Tables 6 and 7. The value of the elongation percentage was evaluated by conducting a tensile test, and then, not less than 18% of elongation percentage was regarded as “passed the test (◯)”, 13 to less than 18% was regarded as “insufficient (Δ)” and below 13% was regarded as “unsuitable (X)”.
Annealing by Running in Tubular Furnace
From the results of annealing by running in a tubular furnace in Table 6, it is understood that difference in the working ratio affects the crystal grain size in the surface layer even though the heat treatment conditions are the same. At the working ratio of not less than 50%, fine crystals for improving tensile strength, an elongation percentage and bending characteristics can be formed and elongation characteristics are also provided as shown in Examples 1 to 12 in Table 6. On the other hand, the average crystal grain in the surface layer cannot be fine when the working ratio is less than 50% as shown in Comparative Examples 1 to 7. In addition, partially in association with this, it is not possible to obtain a high elongation percentage. The reason therefor is that strain energy for forming multiple crystal nuclei for recrystallization is not sufficient when the working ratio is less than 50%, which results in that few coarsened crystal grains grow.
Under the heat treatment conditions of a temperature of not less than 250° C. and not more than 550° C. for not less than 0.6 seconds and not more than 5.0 seconds, a crystal grain size is fine and an elongation percentage is excellent in the same manner.
On the other hand, when the heat treatment temperature is less than 250° C. or more than 550° C. or when the heat treatment time is not more than 0.5 seconds or more than 5.0 seconds, it is not possible to obtain a fine crystal grain size and a high elongation percentage. This is because a worked structure is still present due to insufficient recrystallization in the case of the temperature of less than 250° C. or the treatment time of not more than 0.5 seconds, and on the other hand, crystals are coarsened due to excessive heat and also an elongation percentage decreases in the case of the temperature of more than 550° C. or the treatment time of more than 5.0 seconds.
Annealing by Electric Annealer
From the results of annealing by an electric annealer in Table 7, it is understood that it is possible to manufacture a conductor which has a surface layer with a fine crystal grain size and is also soft when the voltage of the heat treatment conditions is in a range of 21V to 33V. On the other hand, it was found that these characteristics are not obtained when the voltage is smaller than 21V or more than 33V. The reason therefor is considered that thermal energy for sufficiently releasing strain caused by a working effect is not sufficient when the voltage is smaller than 21V. On the other hand, when heat-treating at a voltage of more than 33V, the material was melted due to excessive resistance heat.
It was found that it is also possible to manufacture a conductor which has a surface layer with a fine crystal grain size and is also soft when the velocity is 300 to 600 m/min. On the other hand, it was found that it is not possible to obtain these characteristics when the velocity is smaller than 300 m/min or more than 600 m/min. The reason therefor is considered that crystals were coarsened due to excessive thermal energy at the velocity of less than 300 m/min and the thermal energy for softening was not sufficiently provided at more than 600 m/min.
Batch Annealing
According to the results of batch annealing in Table 8, a small crystal grain size in the surface layer and excellent elongation were obtained when the heat treatment temperature was not less than 150° C. and not more than 550° C. On the other hand, it was not possible to obtain the above-mentioned characteristics when the temperature was not more than 120° C. or not less than 560° C. This is because a worked structure is still present due to insufficient recrystallization in the case of the temperature of not more than 120° C., and crystals are coarsened due to excessive heat in the case of the temperature of not less than 560° C.
When the heat treatment time was within 3 hours, a small crystal grain size in the surface layer and an excellent elongation percentage were obtained. On the other hand, it was not possible to obtain the above-mentioned characteristics when more than 3 hours. This is because crystals are coarsened due to excessive thermal energy. In the case of the hatch type, it is difficult to treat in short time and the appropriate lower limit of the heat treatment time is thus 0.5 hours.
Considering the above results, in the method of manufacturing a soft-dilute-copper-alloy material of the invention, it is desirable that continuous annealing be performed by passing a material through a tubular furnace under the annealing conditions of a temperature of 250° C. to 550° C. for 0.6 seconds to 5.0 seconds when the working ratio is not less than 50% and the wire diameter is less than 1.0 mm.
In addition, as another aspect, it is desirable to continuously anneal by an electric annealer under the annealing treatment conditions of an applied voltage of 21V to 33V and a velocity of 300 m/min to 600 m/min.
In addition, as another aspect, it is desirable to perform batch annealing under the annealing treatment conditions of a temperature of 150° C. to 550° C. for not more than 3 hours.
Tubular Furnace, Electric Annealer and Batch Processing for 0.05 mm Diameter Soft-Dilute-Copper-Alloy Material
In order to confirm how the wire diameter affects, Tables 9 to 11 show working ratios and heat treatment conditions of the material, presence of fine crystals in the surface layer which contributes to improvement in tensile strength, an elongation percentage and bending characteristics and evaluation results of elongation percentage or hardness. The procedure to make a 2.6 mm diameter copper wire is the same as that in Experimental Example of the soft-dilute-copper-alloy material.
The working ratios of the samples used for evaluations in Tables 9 and 10 were adjusted by annealing the wire still having a non-final diameter for several times during the processing of an ingot rod from an 8.0 mm diameter to 2.6 mm as a final diameter of each sample.
The wire with a final diameter was annealed by running in an tubular furnace, and Table 9 shows the evaluations of the average crystal grain size in the surface layer and the elongation percentage with respect to the temperature and the annealing time.
The wire with a final diameter was annealed by an electric annealer, and Table 10 shows the evaluations of the average crystal grain size in the surface layer and the cross sectional hardness of the conductor with respect to the applied voltage and the velocity.
The wire with a final diameter was batch-annealed, and Table 11 shows the evaluations of the average crystal grain size in the surface layer and the cross sectional hardness of the conductor with respect to the temperature and heat holding time.

TABLE 9

	Average

	Heat treatment	crystal	Elonga-
	conditions	grain size	tion

Working	Temperature	Time	in surface	percent-
ratio (%)	(° C.)	(sec)	layer	age

Examples	1	50	500	3.5	◯	◯
	2	70			◯	◯
	4	90	300		◯	◯
	5		450		◯	◯
	6		500	1.0	◯	◯
	7			3.5	◯	◯
	8			5.0	◯	◯
	9			10.0	◯	◯
	10		700	3.5	◯	◯
	11		800		◯	◯
	12	99.8	500		◯	◯
Comparative	1	30	500	3.5	X	Δ
Examples	2	48			X	Δ
	3	90	230		X	X
	4		820		X	Δ
	5		500	0.5	X	Δ
	6		600	0.2	X	X
	7			11	X	Δ

TABLE 10

	Average

	Heat treatment	crystal
	conditions	grain size

Working	Voltage	Velocity	in surface	Hard-
ratio (%)	(V)	(m/min)	layer	ness

Examples	1	50	25	450	◯	◯
	2	78			◯	◯
	3	90	21		◯	◯
	4		23		◯	◯
	5		25	300	◯	◯
	6			450	◯	◯
	7			550	◯	◯
	8			600	◯	◯
	9		33	450	◯	◯
Comparative	1	45	25	450	X	X
Examples	2	90	18		X	X
	3		36		—	—
					(Frac-	(Frac-
					tured)	tured)
	4		25	80	X	◯
	5			700	X	X

TABLE 11

		Average
	Heat treatment	crystal	Elonga-
	conditions	grain size	tion

Working	Temperature	Time	in surface	percent-
ratio (%)	(° C.)	(hr.)	layer	age

Examples	1	50	400	1	◯	◯
	2	90	170		◯	◯
	3		250		◯	◯
	4		400	0.5	◯	◯
	5			1	◯	◯
	6			2	◯	◯
	7			3	◯	◯
	8		700	1	◯	◯
	9	99.8	400		◯	◯
Comparative	1	47	400	1	X	X
Examples	2	90	120		X	X
	3		750		X	Δ
	4		400	5	X	Δ
	5		550	3.5	X	Δ

For the average crystal grain size in the surface layer, measurement was conducted by the method shown in FIG. 12 and an average of the measured values (actual measured values) was derived. Not more than 20 μm of the average crystal grain size was regarded as “passed the test (◯)” and more than 20 μm was regarded as “unsuitable (X)”.
The elongation percentage was evaluated by conducting a tensile test, and then, not less than 18% of elongation percentage was regarded as “passed the test (◯)”, 13 to less than 18% was regarded as “insufficient (Δ)” and below 13% was regarded as “unsuitable (X)”. For evaluating the hardness, Vickers hardness test was conducted on the horizontal section of the material embedded in a resin, and then, not more than 80 Hv was regarded as “passed the test (◯)” and more than 80 Hv was regarded as “unsuitable (X)”.
As shown in Tables 9 to 11, it is understood that difference in the working ratio affects the crystal grain size in the surface layer even though the heat treatment conditions are the same. At the working ratio of not less than 50%, fine crystals for improving tensile strength, an elongation percentage and bending characteristics can be formed and elongation characteristics are also provided as shown in Examples. On the other hand, the average crystal grain in the surface layer cannot be fine when the working ratio is less than 50% as shown in Comparative Examples. In addition, partially in association with this, it is not possible to obtain a high elongation percentage.
Annealing by Tubular Furnace
In the annealing by a tubular furnace shown in Table 9, under the heat treatment conditions of a temperature of not less than 300° C. and not more than 800° C. for not less than 1.0 second and not more than 10.0 seconds, a crystal grain size is fine and an elongation percentage is excellent in the same manner.
On the other hand, when the heat treatment temperature is less than 300° C. or more than 820° C. or when the heat treatment time is not more than 0.5 seconds or more than 10.0 seconds, it is not possible to obtain a fine crystal grain size and a high elongation percentage. This is because a worked structure is still present due to insufficient recrystallization in the case of the temperature of less than 300° C. or the treatment time of not more than 0.5 seconds, and on the other hand, crystals are coarsened due to excessive heat and also an elongation percentage decreases in the case of the temperature of more than 820° C. or the treatment time of more than 10.0 seconds.
Annealing by Electric Annealer
In the annealing by an electric annealer in Table 10, it is understood that it is possible to manufacture a conductor which has a surface layer with a fine crystal grain size and is also soft when the voltage of the heat treatment conditions is in a range of 25V to 35V. On the other hand, it was found that these characteristics are not obtained when the voltage is smaller than 21V or more than 35V. The reason therefor is considered that thermal energy for sufficiently releasing strain caused by a working effect is not sufficient when the voltage is smaller than 21V. On the other hand, when heat-treating at a voltage of more than 35V, crystals were coarsened due to excessive resistance heat.
It was found that it is also possible to manufacture a conductor which has a surface layer with a fine crystal grain size and is also soft when the velocity is 100 to 500 in/min. On the other hand, it was found that it is not possible to obtain these characteristics when the velocity is smaller than 80 m/min or more than 700 m/min. The reason therefor is considered that crystals were coarsened due to excessive thermal energy at the velocity of less than 300 m/min and the thermal energy for softening was not sufficiently provided at more than 700 m/min. Production efficiency is poor at the velocity of less than 80 m/min, which increases the cost.
Batch Annealing
In the batch annealing in Table 11, a small crystal grain size in the surface layer and excellent elongation were obtained when the heat treatment temperature was not less than 170° C. and not more than 700° C. On the other hand, it was not possible to obtain the above-mentioned characteristics when the temperature was not more than 120° C. or not less than 750° C. This is because a worked structure is still present due to insufficient recrystallization in the case of the temperature of not more than 120° C., and crystals are coarsened due to excessive heat in the case of the temperature of not less than 750° C.
When the heat treatment time was within 3 hours, a small crystal grain size in the surface layer and excellent elongation were obtained. On the other hand, it was not possible to obtain the above-mentioned characteristics when more than 5 hours. This is because crystals are coarsened due to excessive thermal energy when more than 5 hours. In the case of the batch type, it is difficult to treat in short time in view of speed of temperature rise and cooling down, and the appropriate lower limit of the heat treatment time is thus 0.5 hours.
Considering the above results, in the method of manufacturing a soft-dilute-copper-alloy material of the invention, it is desirable that the working ratio be not less than 50% and the annealing be performed by a tubular furnace under the annealing treatment conditions of a temperature of 250° C. to 800° C. for 0.6 seconds to 10.0 seconds after the compression.
In addition, as another aspect, it is desirable to anneal by an electric annealer under the annealing treatment conditions of an applied voltage of 21V to 35V and a velocity of 100 m/min to 600 m/min.
In addition, as another aspect, it is desirable to perform batch annealing under the annealing treatment conditions of a temperature of 150° C. to 700° C. for not more than 3 hours.
In more detail, when a material to be annealed after the compression has a wire diameter of less than 1.0 mm, annealing by a tubular furnace under the annealing treatment conditions of a temperature of 250° C. to 550° C. for 0.6 seconds to 5.0 seconds is more desirable, and in addition, annealing by an electric annealer under the annealing treatment conditions of an applied voltage of 21V to 33V and a velocity of 300 m/min to 600 m/min is more desirable as an another aspect, and also, batch annealing under the annealing treatment conditions of a temperature of 150° C. to 550° C. for not more than 3 hours is more desirable as a still another aspect.
Meanwhile, when a material to be annealed after the compression has a wire diameter of not less than 1.0 mm, annealing by a tubular furnace under the annealing treatment conditions of a temperature of 300° C. to 800° C. for 1.0 second to 10.0 seconds is more desirable, and in addition, annealing by an electric annealer under the annealing treatment conditions of an applied voltage of 25V to 35V and a velocity of 100 m/min to 500 m/min is more desirable as an another aspect, and also, batch annealing under the annealing treatment conditions of a temperature of 170° C. to 700° C. for not more than 3 hours is more desirable as a still another aspect.
In the method of manufacturing a soft-dilute-copper-alloy material of the present embodiment, since a crystalline structure in which an average crystal grain size at least from the surface up to a depth of 20% of a wire diameter is not more than 15 μm can be obtained by plastic working of a soft-dilute-copper-alloy containing Ti, etc., and a balance consisting of copper and inevitable impurity and then by adjusting the working ratio prior to the annealing treatment to be not less than 50%, high conductivity is provided and also it is possible to achieve both of high tensile strength and elongation percentage even though it is a soft material, hence, it is possible to improve connection reliability of the product.
In addition, in the method of manufacturing a soft-dilute-copper-alloy material of the present embodiment, since an additional element selected from the group consisting of Mg, Zr, Nb, Cu, V, Ni, Mn and Cr also traps sulfur (S) as an impurity in the same manner as Ti does, copper matrix is highly purified and softening characteristics of the material are improved. It is confirmed that, as a result, it is possible to obtain an effect of suppressing damage to a fragile aluminum pad on a silicon chip at the time of bonding by using the soft-dilute-copper-alloy material as a copper bonding wire.
In addition, since the soft-dilute-copper-alloy material obtained by the manufacturing method of the present embodiment does not require high purification of copper (not less than 99.999 mass %) and can realize high conductivity by a cheap SCR continuous casting and rolling method, productivity is high and it is possible to reduce the cost.
Furthermore, a copper bonding wire formed of the soft-dilute-copper-alloy material obtained by the manufacturing method of the present embodiment is applicable as a substitute for an Al bonding wire having a diameter of about 0.3 mm for vehicle power module. Therefore, even though current density is increased by downsizing of the module in accordance with reduction of wire diameter due to high thermal conductivity of a material or an increase in heat dissipation due to improvement in thermal conductivity, a decrease in connection reliability caused thereby can be avoided.

Claims

1. A method of manufacturing a soft-dilute-copper-alloy material, comprising:

a plastic working of a soft-dilute-copper-alloy comprising an additional element selected from the group consisting of Ti, Mg, Zr, Nb, Cu, V, Ni, Mn and Cr, and a balance consisting of copper and inevitable impurity; and

a subsequent annealing treatment of the soft-dilute-copper-alloy,

wherein a working ratio in the plastic working before the annealing treatment is not less than 50%.

2. The method according to claim 1, wherein the soft-dilute-copper-alloy material has a linear shape having a diameter of less than 1.0 mm, and

wherein the annealing treatment is continuously performed by passing the material through a tubular furnace at a temperature of 250° C. to 550° C. for 0.6 seconds to 5.0 seconds.

3. The method according to claim 1, wherein the soft-dilute-copper-alloy material has a linear shape having a diameter of less than 1.0 mm, and

wherein the annealing treatment is continuously performed by an electric annealer at an applied voltage of 21V to 33V and a velocity of 300 m/min to 600 m/min.

4. The method according to claim 1, wherein the soft-dilute-copper-alloy material has a linear shape having a diameter of less than 1.0 mm, and

wherein the annealing treatment is performed by a batch processing at a temperature of 150° C. to 550° C. for not more than 3 hours.

15. The method according to claim 1, wherein the soft-dilute-copper-alloy material has a linear shape having a diameter of not less than 1.0 mm, and

wherein the annealing treatment is continuously performed by passing the material through a tubular furnace at a temperature of 300° C. to 800° C. for 1.0 second to 10.0 seconds.

6. The method according to claim 1, wherein the soft-dilute-copper-alloy material has a linear shape having a diameter of not less than 1.0 mm, and

wherein the annealing treatment is continuously performed by an electric annealer at an applied voltage of 25V to 35V and at a velocity of 100 m/min to 500 m/min.

7. The method according to claim 1, wherein the soft-dilute-copper-alloy material has a linear shape having a diameter of not less than 1.0 mm, and

wherein the annealing treatment is performed by a batch processing at a temperature of 170° C. to 700° C. for not more than 3 hours.

8. The method according to claim 1, wherein the soft-dilute-copper-alloy comprises 2 to 12 mass ppm of sulfur, more than 2 mass ppm and not more than 30 mass ppm of oxygen and 4 to 55 mass ppm of titanium as the additional element.