Electricity: conductors and insulators – Conduits – cables or conductors – Conductor structure
Reexamination Certificate
2000-11-17
2003-02-11
Nguyen, Chau N. (Department: 2831)
Electricity: conductors and insulators
Conduits, cables or conductors
Conductor structure
Reexamination Certificate
active
06518505
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an ultrafine copper alloy wire and a process for producing the same, and more particularly to an ultrafine copper alloy wire having a diameter of not more than 0.08 mm for use, for example, in electronic equipment, IC testers, and medical ultrasound system, and a process for producing the same.
BACKGROUND OF THE INVENTION
A reduction in size of electronic equipment, IC testers, medical ultrasound system and the like has led to a demand for a reduction in diameter of electric wires for these types of equipment. In particular, in the case of electric wires for medical ultrasound system, there is a demand for electric wires (cables) which have an increased number of wire cores (micro coaxial cables) while maintaining the outer diameter of conventional electric wires.
An example of a material for conductors of electric wires for medical ultrasound system currently in use in practical applications is a dilute copper alloy comprising an oxygen-free copper (OFC) as a base metal and a very small amount of a metallic element, such as tin, added to the base metal. The dilute copper alloy is melted and cast into a wire rod which is then drawn through a die to a diameter of 0.03 mm&phgr; to prepare an ultrafine copper alloy wire. This ultrafine copper alloy wire is mainly used as conductors in electric wires for medical ultrasound system.
When an ultrafine copper alloy wire having a smaller diameter (for example, not more than 0.025 mm&phgr;) is formed as a conductor for electric wires from the viewpoint of further reducing the diameter of wire cores for medical ultrasound system, however, excessively low breaking strength of the conductors using the conventional copper alloy causes frequent breaking of wires at the time of wire drawing or standing of the conductors. For this reason, the formation of ultrafine copper alloy wires having a diameter of not more than 0.025 mm&phgr; using conventional alloys was very difficult.
Thus, ultrafine copper alloy wires having higher tensile strength have been desired. Merely increasing the tensile strength, however, results in lowered electrical conductivity. This had led to a demand for copper alloys having both high tensile strength and high electrical conductivity.
Further, excellent drawability is required for the formation of ultrafine copper alloy wires having a diameter of not more than 0.025 mm&phgr;. When a wire rod is drawn by dicing, the presence of foreign materials having a size of about one-third of the wire diameter in the wire rod poses a problem of wire breaks. Therefore, the amount of foreign materials contained in the wire rod should be reduced to improve the wire drawability.
Detailed analysis of the foreign materials contained in a sample of a broken wire has revealed that the cause of the inclusion of foreign materials in the wire rod is classified roughly into two routes. One of them is inclusions contained in the copper alloy as a base material and the metallic elements as the additive, and peeled pieces produced by the separation of refractories such as SiC, SiO
2
, and ZrO
2
, which are components of ceramics and cement used in crucibles employed in melting and/or molds used in casting. The other route is foreign materials externally included during wire drawing. Among these foreign materials, the inclusion of the latter type of foreign materials can be reduced by performing the step of wire drawing in a clean environment.
On the other hand, improving the quality of the base material (improving the purity of substances constituting the base material) is necessary for reducing the amount of the former type of foreign materials (inclusions and peeled pieces). Therefore, when ultrafine wires are formed by wire drawing, very careful attention should be paid so as to avoid the inclusion of foreign materials in steps from melting to wire drawing, and the factor in the inclusion of the foreign material should be minimized.
SUMMARY OF THE INVENTION
The invention has been made with a view to solving the above problems of the prior art, and it is an object of the invention to provide an ultrafine copper alloy, wire having excellent tensile strength, electrical conductivity, and drawability, and a process for producing the same.
According to the first feature of the invention, there is provided an ultrafine copper alloy wire drawn to a diameter of not more than 0.08 mm, said ultrafine copper alloy wire being formed of an alloy comprising a copper matrix of high purity copper with a total unavoidable impurity content of not more than 10 mass ppm and, contained in the matrix, 0.05 to 0.9 mass % of at least one metallic element selected from the group consisting of tin, indium, silver, antimony, magnesium, aluminum, and boron.
According to the second feature of the invention, there is provided an ultrafine copper alloy wire comprising: a core wire formed of an alloy and drawn to a diameter of not more than 0.08 mm, said alloy comprising a copper matrix of high purity copper with a total unavoidable impurity content of not more than 10 mass ppm and, contained in the matrix, 0.05 to 0.9 mass % of at least one metallic element selected from the group consisting of tin, indium, silver, antimony, magnesium, aluminum, and boron; and, provided on the periphery of the core wire, a tin plating, a silver plating, a nickel plating, a tin-lead solder plating, a tin-copper-bismuth-base plating, or a tin-silver-copper-base lead-free solder plating.
The above constitutions can realize ultrafine copper alloy wires having high tensile strength and high electrical conductivity.
According to the third feature of the invention, there is provided a process for producing an ultrafine copper alloy wire to be drawn to a diameter of not more than 0.08 mm, comprising the steps of: melting an alloy in a carbon crucible, said alloy comprising a copper matrix of high purity copper with a total unavoidable impurity content of not more than 10 mass ppm and, contained in the matrix, 0.05 to 0.9 mass % of at least one metallic element selected from the group consisting of tin, indium, silver, antimony, magnesium, aluminum, and boron; and casting the molten alloy by means of a carbon mold.
In this production process, preferably, the casting is carried out by continuous casting to form a wire rod which is subjected to primary wire drawing, annealing, and then secondary wire drawing.
The production process according to the third feature of the invention can provide ultrafine copper alloy wires having high tensile strength and high electrical conductivity and, in addition, good drawability.
According to the fourth feature of the invention, there is provided an electric wire comprising a plurality of ultrafine copper alloy wires stranded together, said ultrafine copper alloy wires each having been drawn to a diameter of not more than 0.08 mm and being formed of an alloy comprising a copper matrix of high purity copper with a total unavoidable impurity content of not more than 10 mass ppm and, contained in the matrix, 0.05 to 0.9 mass % of at least one metallic element selected from the group consisting of tin, indium, silver, antimony, magnesium, aluminum, and boron.
According to the fifth feature of the invention, there is provided an electric wire comprising a plurality of ultrafine copper alloy wires stranded together, said ultrafine copper alloy wire comprising: a core wire formed of an alloy and drawn to a diameter of not more than 0.08 mm, said alloy comprising a copper matrix of high purity copper with a total unavoidable impurity content of not more than 10 mass ppm and, contained in the matrix, 0.05 to 0.9 mass % of at least one metallic element selected from the group consisting of tin, indium, silver, antimony, magnesium, aluminum, and boron; and, provided on the periphery of the core wire, a tin plating, a silver plating, a nickel plating, a tin-lead solder plating, a tin-copper-bismuth-base plating, or a tin-silver-copper-base lead-free solder plating.
The fourth and fifth features of the invention having the above
Aoyama Seigi
Ichikawa Takaaki
Matsui Hakaru
Okada Ryohei
Seya Osamu
Hitachi Cable Ltd.
Nguyen Chau N.
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