JP2012136719A - Metallic material having highly conductive structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silver material having a highly conductive structure which is superior in mass productivity and has a crystal structure with an attribute of allowing the performance of electronic parts or equipment to be exhibited to its maximum.SOLUTION: A recrystallized structure having a highly conductive structure is formed by subjecting a silver material to the final plastic working, followed by heat treatment performed in at least any of a vacuum environment, an inert gas environment, and a reducing gas environment. The recrystallized structure is crystallized into a single crystal, wherein the size of the crystal grains is coarsened to a size larger than in a 4N silver material having an electrical conductivity of 106 (%) or less, and the grain boundary density per unit volume is lower than that of the 4N silver material.

Description

  The present invention relates to a silver material having a highly conductive structure used for power transmission cables, wiring materials between audio equipment and electronic equipment or between its components, bonding wires, and the like.

  Examples of wiring materials for connecting electronic components constituting audio equipment and video equipment include oxygen-free copper (OFC), oxygen-free copper containing silver, oxygen-free copper containing zirconium, and the like. These wiring materials are known to have a relatively high conductivity efficiency than ordinary copper wires, etc., but because of their fine crystal structure, the number of crystal grain boundaries existing in the direction in which electrons are conducted It is known that impurities such as orientation, sulfides and intermetallic compounds have an adverse effect on the conduction efficiency. This may increase the electrical resistance due to grain boundaries and impurities accumulated there. It is thought to work as a capacitor with a very small capacity and to bring in capacitance. This increases the electrical resistance to some extent, and the electrostatic capacity is accumulated in the wiring material in the form of static electricity, which has a considerable adverse effect on the operation of the electronic component.

In order to improve this point, in the technique disclosed in Patent Document 1, after the OFC crystal grains are coarsened by heat treatment, wire drawing is performed to orient the crystal grains in the longitudinal direction. However, this technology reduces the number of crystal grain boundaries by enlarging the crystal grains, but breaks the formed crystal grains with external stress during the manufacturing process of the metal material by plastic working called wire drawing. Then, the crystal structure is disturbed, and lattice defects such as atomic vacancies and dislocations are generated. As in the case of impurities, there remains a problem that it acts to cause an increase in electrical resistance and formation of capacitance.
In the first place, generally, a metal deformed by processing such as rolling causes processing strain, and lattice distortion and defects occur in the crystal. The technique disclosed in Patent Document 2 focused on improving the manufacturing process of the metal material is to solve this problem.

  Patent Document 2 discloses a wire rod-shaped ingot having a single crystal structure of OFC or a unidirectionally solidified structure in the longitudinal direction or a plastic processing such as slight wire drawing to obtain a copper wire for signal transmission, and its conductivity is By making IACS (International Anneld Cupper Standard) 100 [%] or more or having a tensile strength of 20 [kg / mm 2] or less, the manufactured metal material has a very excellent signal transmission characteristic.

  This technique has improved this point because the above-described lattice defects that have conventionally occurred during processing have caused the signal transmission characteristics to deteriorate. The electrical conductivity of the copper wire is set to IACS 100 [%] or more, or the tensile strength is set to 20 [kg / mm 2] or less. The signal transmission characteristic when the OFC copper wire is used as a conductor as it is is that the conductivity value is IACS 100 [% ], Because the tensile strength value changes markedly with 20 [kg / mm 2] as a boundary. This is because the unidirectional solidification structure has few grain boundaries that prevent the movement of electrons, and oxygen, hydrogen gas, and other impurities are discharged from the solidification interface into the molten metal during casting, and defects due to this hardly occur.

JP 60-003808 A JP 63-174217 A

From a microscopic viewpoint, a metal material having a polycrystalline structure inevitably has a loss during conduction due to the presence of many crystal grain boundaries. The technique of Patent Document 2 improves signal transmission characteristics by using the above-described signal transmission copper wire. As a means for solving this grain boundary problem, in the technique of Patent Document 2, a signal is obtained by adding a plastic processing such as a wire rod ingot having a single crystal structure or a unidirectionally solidified structure in the longitudinal direction or a slight wire drawing to the ingot. Although a copper wire for transmission is used, in order to obtain a bar-shaped ingot having a single crystal structure and a solidified structure, a very complicated metal solidification control management process such as a heating mold continuous casting method or a chocolate lasky method is required. Since time (200 mm / min in the reference) is required, a huge amount of cost is consumed and mass production within a predetermined time is very difficult. For this reason, there is a fatal problem that the material is expensive and only a small amount can be obtained, which has hindered industrial use. In addition, according to this method, the formation of the large-diameter wire takes more time, and the production of the plate-like material and the belt-like material has to be extremely difficult. In addition, it is not considered that the performance of electronic devices and the like changes due to the presence of static electricity. Therefore, it is still not enough to fulfill the original function of a metal material as a medium for transmitting electrons.

  That is, even if a high-performance electronic device or electronic component is prepared, the wiring material connecting the electronic component, between the electronic devices, or these and the ground portion is highly conductive (the numerical value disclosed in Patent Document 2 can be obtained). Therefore, it is not possible to maximize the original performance of each electronic component, etc. due to signal attenuation or signal distortion caused by noise components caused by resistance or static electricity. It was. For example, an audio device cannot provide sufficient sound quality, a display cannot provide sufficient display capability, and an unnecessary electromagnetic wave is generated in a power transmission cable or a transmission distance is limited.

  If only the conduction efficiency is considered, it is conceivable to use silver having the highest conduction efficiency among metals, particularly “4N silver”, which is said to be high purity, instead of copper as the starting material. However, even though it is “4N silver”, the above-mentioned problem occurs due to the fineness of the crystal grains in addition to the occurrence of distortion and transition in the structure due to the drawing process when obtaining the wire. Impurities such as oxides and sulfides are mixed, which causes rust and static electricity accumulation. Further, the inventors tried to manufacture a “4N silver” wire by the heating mold continuous casting method in accordance with Reference 2, but since only a length of about 1 [cm] can be secured in one minute, the material itself Is not only expensive, but also cannot be mass-produced, so that it is too expensive to use it as a power transmission cable, wiring material, bonding wire or the like. Furthermore, since it is more so with plate materials and strips, it is difficult to manufacture lead frames and metal foils for circuit boards.

  An object of the present invention is to provide a metal material, particularly a silver material, having a crystal structure that is excellent in mass productivity and maximizes the performance of an electronic component or an electronic device.

  In the silver material of the present invention, a recrystallized structure having a highly conductive structure is formed by a heat treatment performed in an atmosphere of at least one of a vacuum, an inert gas, and a reducing gas after undergoing final plastic processing on the silver material. It is characterized by being.

More specifically, the recrystallized structure of the silver material is a single crystallized structure. Single crystallization means that crystal grains having a polycrystalline structure are enlarged. For example, the recrystallized structure is coarser than the 4N silver material having a conductivity of 106 [%] or less derived from the following formula, and the crystal grain size per unit volume is larger than that of the 4N silver material. The grain boundary density is low.
Conductivity γ = X × 100 / [(R ・ m / I ²・ G) + Y (20-t)]

However, R = electric resistance [Ω], m = mass of measurement length material [g], I = measurement length [m], t = measurement temperature (Celsius), G = density of material [g / cm ³ ] ( = 10.5), X = material with 100% conductivity, length 1m, cross-sectional area 1mm ² resistance value at 20 degrees (Celsius), Y = length 1m, cross-sectional area 1mm ² sample temperature 20 degrees When the temperature changes by 1 degree (Celsius) near (Celsius), the amount α by which the resistance changes is the low mass temperature coefficient near 20 degrees (Celsius) of the sample.

The silver material has the following attributes.
(1) The conductivity γ exceeds 106 [%].
(2) The elongation obtained by the metal material tensile test under the following conditions exceeds 5%.
JISZ2201 (1998) JIS9 tensile test piece, using JISZ2241 (1998) metal material tensile test method, test chamber temperature 22 [° C], sample average wire diameter 1.54 [mm], gauge distance 50 [mm], The sample was fixed at both ends, and the initial load was 2 [N], the average load was 199 [N] at 1.0 [mm] displacement, the maximum load was 353 [N], and the test speed was 5 [mm / min].
(3) The maximum load by the three-point bending compression test under the following conditions is less than 30 [N].
Implemented with jib span 20 [mm], inner radius R2 of the metal fittings, and initial load 0.1 [N].

  Such a silver material is, for example, a molding step of molding a silver material having a polycrystalline structure into a predetermined shape and size at room temperature, and the entire formed material exceeds the recrystallization temperature of the material, and A heating step of heating the material substantially uniformly in a vacuum or an inert gas atmosphere while maintaining a temperature below the melting point of the material, and the heated material over a period of time equal to or longer than the time at which the temperature is maintained, or An annealing process in which annealing is performed in an inert gas atmosphere, whereby the crystal structure of the material is deformed into a highly conductive structure in which the conduction speed of conducting electrons is higher than that before heating. it can.

  In other words, the crystal structure of the material manufactured through the heating / annealing process is important to make the entire structure homogeneous when it is completed through the final process of plastic working in order to obtain a highly conductive structure. The processing after heating or after annealing is distorted somewhere, and a highly conductive structure cannot be obtained. This will be described based on the physical properties inherent in the material.

  Silver material conducts electricity well because there are electrons that move freely in the crystal. When electrons are conducted through a crystal having periodicity without defects, they do not receive resistance in any direction except for the influence of thermal vibration (highly conductive state). However, in the process of manufacturing the material, processing such as extending and stretching is generally performed. Also in the manufacturing method of the present invention, the material is formed into a predetermined shape and size at room temperature. At that time, many processing strains (lattice defects) are generated in the crystal. This phenomenon cannot be avoided. When these processing distortions are intertwined in a complicated manner, it becomes an obstacle to smooth movement of electrons.

  However, when a material having a processing strain is heated at a temperature exceeding the recrystallization temperature to give a certain amount of thermal energy, the material uses this thermal energy to try to eliminate the processing strain. That is, a new crystal grain grows from the original crystal grain, covers the whole, and exhibits periodicity again. After the periodicity is restored in this way, no processing is performed thereafter, and annealing is performed over time, so that the crystal structure of the material has periodicity and is sufficiently flexible. Determined after obtaining bending strength, corrosion resistance, and wear resistance. This state is exactly the state in which the crystal structure of the material is transformed into a highly conductive structure.

  From the viewpoint of performing the heating process more stably, the heating process heats the material by mixing a reducing gas composed of hydrogen gas or a hydrogen-containing gas into the vacuum or an inert gas atmosphere. Thereby, the chemical reaction of the starting material in a heating process can be prevented. More preferably, the drawing of at least one of the reducing gas and the inert gas and the supply of these gases are repeated.

The silver material of the present invention has a highly conductive structure in which the crystal grains are substantially isotropic in the longitudinal direction and the density is substantially uniform at the central portion and the peripheral portion in the cross section. High and the conduction efficiency per unit time is improved.
Therefore, the performance of electronic devices and electronic parts can be maximized by using the wiring. Loss is also significantly reduced, so improvement in energy conversion efficiency and transmission efficiency is also expected.
Further, the silver material of the present invention has an elongation rate obtained by a metal material tensile test of more than 5 [%] and a maximum load obtained by a three-point bending compression test of less than 30 [N]. Therefore, the wiring of the electronic component or the electronic device becomes extremely easy, and the reliability of the operation after the wiring can be increased.

The block diagram of the vacuum furnace suitable for implementation of the manufacturing method of this invention, and its control mechanism. Process explanatory drawing of the manufacturing method of this invention. FIG. 5 is a schematic explanatory diagram of a control operation according to the present embodiment. The chart which showed the example of a measurement result of the performance when changing the heating condition using the silver wire manufactured with the manufacturing method of the present invention as a sample. Micrograph showing the crystal structure of the vertical section of Sample A Micrograph showing the crystal structure of the cross section of sample A Micrograph showing the crystal structure of the vertical section of Sample B Micrograph showing the crystal structure of the cross section of Sample B Photomicrograph showing crystal structure of sample C in longitudinal section Micrograph showing the crystal structure of the cross section of Sample C

The best embodiment of the present invention will be described below.
In this embodiment, an example in the case of producing silver (silver material) as a high conductive wire is given. Silver has a polycrystalline FCC structure and is the metal material with the highest electron conductivity at a popular level. Soft and easy to handle and difficult to oxidize. The number of intrinsic electrons is larger than that of iron, aluminum, etc., the conduction speed of electrons is faster than copper, and the extensibility is excellent. This is a major reason for using a silver material in this embodiment. The purity of silver is preferably about “4N”. However, according to the manufacturing method to be described, impurities are removed by a special heating step, so that the purity may be actually “4N” or less.

First, the furnace and its control mechanism used in this embodiment will be described.
In order to heat in the state which does not raise | generate a chemical reaction, and the state which has a reduction | restoration effect | action, in this embodiment, the vacuum furnace of the structure shown in FIG. 1 is used. This vacuum furnace is provided with a heating element 105 on the side wall of the electric furnace 103 in the container 101, and has a structure in which a starting material can be accommodated in a heating space surrounded by the heating element 105 through an opening / closing door (not shown). In the illustrated example, the starting material is a silver wire 203 wound around a quartz tube 201 that can withstand high temperatures.

  A gas supply valve 107 and a gas vent valve 109 are attached to the heating space via a pipe line connected to the outside of the space. From the gas supply valve 107, an inert gas and a hydrogen-containing gas are mixed from the gas supply device 133 through the valve drive mechanism 131. A gas suction mechanism (not shown) is connected to the gas vent valve 109, and gas and moisture in the heating space are sucked through the valve drive mechanism 131 by this gas suction mechanism. A state where all the gas and the like are sucked is a vacuum state.

  The current atmospheric pressure in the heating space is measured by the pressure gauge 123, and the current temperature in the heating space is measured by the thermometer 125. The measurement results of the pressure gauge 123 and the thermometer 125 are output to the control device 121, where the state of the heating space is monitored. The control device 121 is a kind of computer having a memory and a processor. The processor inputs various setting conditions and parameters stored in the memory from the pressure gauge 123 and the thermometer 125 according to a computer program prepared in advance. Based on the measured data, a control operation for manufacturing a highly conductive metal material is executed. Specifically, this control operation is ON / OFF switching of the heating element 105 performed based on the measurement results of the pressure gauge 123 and the thermometer 125. The control device 121 also controls valve opening / closing in the valve drive mechanism 131. In other words, at a timing according to the set conditions, the gas supply valve 107 is opened to supply gas into the heating space, or it is stopped, or the gas vent valve 109 is opened to degas or drain water, or Or stop.

  The manufacturing method of the highly conductive wire using this vacuum furnace and control mechanism is implemented by each process shown in FIG. Hereinafter, the content of each process is demonstrated concretely.

[Preparation step S1]
Prepare a silver block of sufficient size to obtain the required amount of silver wire 203, shape, size, and heating conditions (heating time, atmospheric pressure, temperature, type of gas used, amount of gas mixed) Etc.), annealing conditions (time, degassing timing, etc.) and finishing conditions (removal timing, etc.). Since the heating conditions, annealing conditions, and finishing conditions differ depending on the thickness and length of the silver wire 203, these are preset in the memory of the control device 121.

[Molding step S2]
The silver block is processed at room temperature to form a silver wire 203, which is used as a starting material. The silver wire 203 is formed by, for example, a drawing process using a diamond die, that is, a process of passing a silver lump through a die having a hole and drawing it to a predetermined size. However, the processing method is not limited to this, and may be arbitrary, for example, wire drawing or other modes. At this time, it is not necessary to consider crystal distortion due to processing, mixing of impurities, and the like. Moreover, since normal temperature processing is sufficient, the necessary amount can be obtained in a relatively short time. For example, a silver wire 203 of 10 m or more can be obtained in a few minutes. Thereafter, the silver wire 203 is wound around the quartz tube 201 to prepare for heating.

[Heating step S3]
The silver wire 203 wound around the quartz tube 201 is set in the heating space of the vacuum furnace, and the control device 121 starts control for heating and annealing.
An overview of the control operation by the control device 121 is shown in FIG. Referring to FIG. 3, the control device 121 gradually raises the heat generation temperature of the heating element 105 from the start time t1 to the time t2 when the temperature of the heating space first reaches the predetermined temperature TH0 from the normal temperature. This temperature TH0 is a temperature that exceeds the recrystallization temperature of the silver wire 203 (around 300 degrees Celsius) and less than the melting point of the silver wire 203 (961 degrees Celsius). The time between the time points t1 and t2 is set to about the time required for vacuum annealing described later. By gradually heating in this way, the temperature of the entire silver wire 203 rises almost uniformly. When reaching the time point t2, the controller 121 heats the entire silver wire 203 in the heating space substantially uniformly while maintaining the temperature TH0.

  At that time, the control device 121 supplies an inert gas, a reducing gas, or a gas mixed thereof to the heating space, and removes impurities in the crystal of the silver wire 203, particularly impurities remaining in the crystal grain boundary. At the same time, crystal grain growth is stabilized. The inert gas is, for example, helium gas or argon gas. The reducing gas is, for example, hydrogen or a hydrogen-containing gas. Since the pressure and temperature of the heating space are increased by mixing these supplied gases, the extraction of moisture generated by the reduction action and the supply of these gases (including circulation in the heating space) are repeated. The temperature and pressure in the heating space are kept almost constant. This is performed based on the measurement results of the pressure gauge 123 and the thermometer 125.

[Annealing Step S4]
When reaching the end t3 of the heating time, the control device 121 performs control for degassing and dehumidifying to make the heating space in a vacuum state and adjust the amount of heat generated by the heating element 105, so that the inside of the heating space The temperature is gradually lowered until reaching a time point t4 when the temperature reaches room temperature. The time between t3 and t4 is approximately twice the time between t2 and t3.

[Finish step S5]
When the time point t4 is reached, the crystal structure of the silver wire 203 is almost completely stabilized. Therefore, the quartz tube 201 is taken out of the vacuum furnace, and the silver wire 203 is removed to obtain a product as it is. The crystal structure is not changed by re-processing as before. Thereby, a crystal structure having periodicity is determined without any defects. Under this crystal structure, even when rust is generated on the contact surface with air, the rust is easily separated from the outer surface. Therefore, the electron conduction speed is faster than before heating, and sufficient flexibility, bending strength, corrosion resistance, and wear resistance can be obtained. The above rust can be easily removed with a soft material such as an eraser.

[Performance measurement 1]
FIG. 4 shows an example of performance measurement results when the silver wire 203 manufactured by the above manufacturing method is used as a sample and the heating conditions are changed. The measurement was performed according to the test of JIS-H0505 (volume resistivity and conductivity measuring method of non-ferrous metal material). The length of the sample is 1 [m], and the cross-sectional area of the sample is slightly different in thickness at the time of processing. Therefore, the sample density is 10.5 and the average cross-sectional area at 1 [m] is obtained by the gravimetric method. Calculated. The resistance measurement method was a double bridge method, and was performed in an environment where the resistance measurement current was 1 [A], the test temperature was 23 degrees Celsius (23 [° C.]), and the humidity was 50 [%].

  In FIG. 4, “500” of the material symbol “Ag500-1H” indicates that the temperature TH0 that is maintained substantially constant for the time t2-t3 in the above heating process is 500 degrees Celsius, and “−1H” is t2-t3. This means that the time of 1 is 1 hour. “−2H” is obtained by setting the time of t2−t3 to 2 hours. The same explanation holds for other temperatures.

  Recrystallization is a function of temperature and time. The thermal energy for recrystallization needs to be a certain amount or more. Although the recrystallization temperature is 500 degrees Celsius, as can be seen from FIG. 4, in about 1 hour, the volume resistivity is around 1.630 × 10 −6 [Ω · cm], and from “4N silver” In comparison with the wire, the improvement was not so much, but even in the same hour, a great improvement was seen from around 650 degrees Celsius.

  That is, the cross sectional area was less than 1.62 × 10 −6 [Ω · cm] in terms of 1.98 [mm 2]. Incidentally, the volume resistivity of aluminum (Al) having the same average cross-sectional area is 2.655 × 10 −6 [Ω · cm], and the volume resistivity of gold (Au) is 2.19 × 10 −6 [Ω · cm]. The volume resistivity of pure copper (Cu) is 1.673 × 10 −6 [Ω · cm]. Since the electron conduction speed is about 1.5 times faster than copper than copper, as described above, the conduction efficiency of the silver wire 203 obtained by the production method of the present invention is 1.98 [mm 2 in cross section. In terms of conversion, it is currently superior to any metal material. Excellent electrical conductivity means that the same resistance value is fine, and it is less susceptible to the influence of an electric field. Therefore, it is advantageous because it is less susceptible to noise and vibration, and the contact area with air is also good. It means that it is small and rust is not easily generated.

[Performance measurement 2]
When the silver wire 203 manufactured by the manufacturing method of the present invention was used as an audio line, the frequency bandwidth was wide and the dynamic range was increased, and the sound quality was significantly improved as compared with the conventional product. Specifically, only a speaker cable of a certain audio device (commercially available LCOFC. PCOCC) was replaced with a silver wire 203, and a sound quality confirmation test was conducted by 50 subjects, and the following reports were received from all the subjects. .
-Sound balance, no particularly noticeable resonance from bass to treble.
・ Lower volume increases volume but improves separation. There is no sound.
・ Transparency and resolution are improved in spite of no harsh sound in high sounds.
・ Raises and falls quickly, and a three-dimensional feeling, a sense of distance, and space are expressed.

  By additionally wiring the silver wire 203 to the ground line of the power supply circuit of the television receiver, the image quality was significantly improved. Specifically, color balance, changes in human face color, and camera differences were clearly improved. In addition, a high-definition image with little blur throughout the details gives a good sense of depth, so the image looked three-dimensional. The flickering on the screen has been reduced, and the processing signal has also become faster. Overall, the tone of the colors has improved, and the expression of natural colors has been improved rather than the colors that have been created. In addition, although it experimented with the copper wire (conventional product) of the same diameter, there was almost no change. This is also an objective report from the above 50 subjects.

By using the silver wire 203 as a wiring material for an existing solar cell module, the conversion efficiency was significantly improved. Specifically, a commercially available 15 [w] power generation module is exposed to direct sunlight and measured with a hollow enamel resistor so that the wiring material of normal copper wire is 10 [w] at 5 [m]. While adjusting. The module output voltage was measured with a DC voltmeter and found to be 10.8 [v].
Thereafter, in this state, the wiring material was replaced with the silver wire 203, and the voltage was measured. The result was 12.8 [v]. That is, the conversion efficiency was improved by about 20%.

[Examination in public institutions]
Since the high-conductivity silver material of the present invention was expected to have an attribute different from that of a normal silver material, in a public institution, three types of samples (specimen) structure test, image observation, conductivity and A load test (tensile / compression test) was performed. The three types of samples are manufactured under the following conditions.
○ Sample A (comparative object): Pure silver wire itself formed by cold working. The conventional product itself which does not depend on the manufacturing method of the present invention.
Sample B (Example 1): A pure silver wire formed by cold working (processed under the same conditions as Sample A) was heated at 750 ° C. for 2 hours in an inert gas atmosphere and then cooled for 2 hours. thing.
Sample C (Example 2): Pure silver wire formed by cold working (processed under the same conditions as Sample A) while visually observing the melting temperature, for example, 900 degrees Celsius for 6 hours, inert gas atmosphere Heated for 6 hours and then cooled for 6 hours.

I Observation of structure and image (1) Test method A sample was embedded in a resin, and a sample having a longitudinal section parallel to the longitudinal direction of the wire and a cross section perpendicular to the longitudinal direction of the wire was prepared. Each sample was polished, subjected to electric field etching, and photographed with an optical microscope. Polishing was performed up to approximately 0.25 [μm] diamond paste. The etching solution used was a citric acid aqueous solution 100 [ml] added with a few drops of nitric acid, and electric field etching was performed at a voltage of 5 [v]. The photo magnification is 50 times in the longitudinal section and 100 times in the transverse section.
(2) Test organization: Tokyo Metropolitan Industrial Technology Research Center (3) Test results: as shown in FIGS.

Sample A: FIG. 5A is a photomicrograph of the vertical cross section of sample A, and FIG. 5B is a photomicrograph of the same cross section. Referring to these photographs, it is confirmed that the structure is oriented in the longitudinal direction by drawing, but many strains and defects are observed. Crystal grains are oriented in the longitudinal direction of the wire, and the cross section has different densities at the central portion and the peripheral portion.
<What to understand>
-It is presumed that the plasticity is remarkably lowered and work hardening occurs due to the distortion and defect caused by the drawing process. Elongation and bending properties are significantly deteriorated before processing.
・ Because the crystal is broken, the periodicity of atoms is broken, and defects are generated, so the structure prevents the flow of electrons.
-A potential difference occurs on the metal surface due to strain and defects, and a local battery is formed and corrosion is easily promoted.
-When an external stress such as pulling or bending is applied, the structure tends to cause stress concentration in the internal stress accumulation part and defect part due to strain, that is, the structure having low fracture strength, tensile strength, crack strength, etc.

Sample B: FIG. 6A is a photomicrograph of the vertical cross section of sample B, and FIG. 6B is a photomicrograph of the same cross section. From these photographs, it is observed that the distortion and defects are eliminated, and the entire structure is homogeneous and dense. It is observed that crystal grains (structure with regularity, face-centered cubic in the case of silver) are larger than Sample A and are oriented in the longitudinal direction of the wire. In the cross section, the density is substantially uniform at the central portion and the peripheral portion.
<What to understand>
-A recrystallized structure having a highly conductive structure is formed.
・ Plasticity (ductility, malleability) is increased because strain and defects are eliminated.
・ Although it cannot be clearly confirmed in the structure, it is presumed that the atoms of the broken crystal are recovered and reordered to form ordered grains, and strain and defects are eliminated, and the density and periodicity are eliminated. It has a homogeneous structure with the structure, and is oriented in the long direction, so that it has a structure in which electrons easily flow.
-Since it has a homogeneous structure, a potential difference is unlikely to occur on the metal surface, local batteries are suppressed, and it is difficult to corrode.
・ Since it has a homogeneous structure, even when external stress such as pulling or bending is applied, stress concentration is unlikely to occur, and the structure has high fracture strength, tensile strength, crack strength, and the like.

Sample C: FIG. 7A is a photomicrograph of the vertical cross section of sample C, and FIG. 7B is a photomicrograph of the same cross section. The crystal grains grow larger than Sample B and have the same size, and periodicity and homogeneity can be confirmed. In addition, the number of crystal grain boundaries per unit volume and the total area are greatly reduced. In addition, it is presumed that the content of impurities such as metal oxides / intermetallic compounds, oxygen and inevitable elements precipitated at the grain boundaries is also greatly reduced.
<What to understand>
-A recrystallized structure having a highly conductive structure is formed.
・ Strains and defects are almost completely eliminated, and crystal grains grow large, so that the structure can exhibit the plasticity (ductility, malleability) of the metal crystal itself.
-Since crystal grains are growing large, there are many "high-purity regions (high-purity single crystal regions) in which silver atoms are aligned with regularity" per unit volume. Furthermore, the number of crystal boundaries and the total area of the grain boundaries are greatly reduced, and the factors that scatter and suppress the flow of electrons are greatly reduced.
・ As the number and area of grain boundaries decrease, the content of impurities such as metal oxides and intermetallic compounds, oxygen, and inevitable elements existing in the grain boundaries has greatly decreased. The factor that scatters and suppresses the flow of water is greatly reduced.
・ Grain boundaries, metal oxides and intermetallic compounds, oxygen and inevitable elements such as oxygen and unavoidable elements present at the grain boundaries have a potential difference from the crystal grains themselves. Although it becomes a cause of attraction, since this impurity is reduced, it has a structure in which corrosion is greatly suppressed.
-Since the insulator at the grain boundary is removed, it is expected that the capacitance is lost.

In addition, according to an experiment by a private institution other than the above-described test institution, according to atomic absorption analysis, the content of oxygen and inevitable impurities in sample B is greatly reduced with respect to sample A, and the purity of silver is improved. Further, it was confirmed that the content of oxygen and inevitable impurities in C was greatly reduced, and the purity of silver was greatly improved.
<What to understand>
・ Purity is greatly improved by vacuum annealing and deoxidation / reduction during recrystallization.
-By deoxidizing and reducing during the process of high-temperature heating and recrystallization, the reducing gas will react with oxygen, metal oxides, metal tube compounds, and inevitable impurities in a highly reactive radical state. Removal of these impurities is promoted, and the purity is remarkably improved.

II Conductivity (1) Test method
JIS C 3002-1992-C16 (3) (6. Electrical conductivity of "Testing methods for electrical copper and aluminum wires")
Conductivity γ = X × 100 / [(R ・ m / I2 ・ G) + Y (20-t)]%
However,
R = electric resistance [Ω], m = mass of material of measurement length [g], I = measurement length [m], t = measurement temperature (Celsius), G = density of material [g / cm3] (= 10.5) , X = 100% conductivity material with a length of 1m and cross-sectional area of 1mm2, resistance value at 20 degrees (Celsius), Y = length of 1m and cross-sectional area of 1mm2 sample temperature around 20 degrees (Celsius) If the change is 1 degree (degrees Celsius), the amount of change in resistance α is the low mass temperature coefficient near 20 degrees (degrees Celsius) of the sample. (2) Test organization: Yokohama Institute of Electrical Safety and Environment Laboratory (3) )Test results:

○ Sample A
X = 0.017241, R = 8.414 × 10 −3 [Ω], m = 21.0316 [g], I = 1 [m],
t = 20 [° C.], G = 10.5, conductivity γ = 102.3 [%].
○ Sample B
X = 0.017241, R = 8.387 × 10 −3 [Ω], m = 20.1950 [g], I = 1 [m],
t = 20 [° C.], G = 10.5, conductivity γ = 106.7 [%].
○ Sample C
X = 0.017241, R = 8.096 × 10 −3 [Ω], m = 20.7394 [g], I = 1 [m],
t = 20 [° C.], G = 10.5, conductivity γ = 107.8 [%].

<What to understand>
The conductivity γ of pure silver has been set to 106 [%] at the maximum. The conductivity γ of the sample A was 102.3 [%]. This is because, as described above, the structure of the sample A hinders the flow of electrons. Even with the same starting material as Sample A, Sample B increased to 106.7%. The reason for this is thought to be that the distortion and defects caused by the processing are eliminated, the structure becomes a homogeneous structure having a denseness and periodicity, and a highly conductive structure in which electrons easily flow.
In Sample C, the value was 107.8 [%], which exceeded the published value so far, and the conductivity was higher than any other kind of metal. In other words, it turned out that it has evolved into a metal material that can be called a new material. As can be seen from “Observation of structure / image”, in the case of Sample C, the crystal grains are large and the number of high-purity single crystal regions per unit volume increases, and the number of crystal boundaries and the total area of the grain boundaries are greatly reduced. Therefore, it is considered that the conductivity is remarkably improved because the factors that scatter and suppress the flow of electrons are greatly reduced. In addition, as the number and area of grain boundaries decreased, the content of impurities such as metal oxides and intermetallic compounds, oxygen, and inevitable elements existing at the grain boundaries also decreased significantly. It is thought that one of the reasons is that there is no longer any factor that scatters or suppresses.

III Load test (1) Test method
JISZ2201 (1998) JIS No. 9 tensile test piece was used, and JISZ2241 (1998) metal material tensile test method was used. Three test pieces were used for each of Samples A, B, and C (the wire diameters varied somewhat).
The tensile test was performed at a test chamber temperature of 22 [° C.], with both ends of the specimen (sample) fixed, an initial load of 2 [N], and a test speed of 5 [mm / min].
The compression test was a three-point bending compression test with a jib span of 20 [mm], a pusher inner radius R2, and an initial load of 0.1 [N].
(2) Testing organization: Tokyo Metropolitan Industrial Technology Research Center (3) Test results:

○ Sample A
[Table 1]
・ Tensile test symbol Wire diameter Scoring distance Load Maximum load Elongation (sample) [mm] [mm] (1.0mm displacement) [N] [%]
1 1.54 50 555 701 1
2 1.53 50 551 686 1
3 1.53 50 657 707 4
Average 1.53 50 587 698 2
・ 3-point bending compression test symbol Wire diameter Load (0.5mm displacement) Maximum load (sample) [mm] [N] [N]
1 1.52 34.5 49.3
2 1.53 37.2 49.4
3 1.52 38.2 49.5
Average 1.52 36.6 49.4

○ Sample B
[Table 2]
・ Tensile test symbol Wire diameter Scoring distance Load Maximum load Elongation (sample) [mm] [mm] (1.0mm displacement) [N] [%]
1 1.52 50 313 380 33
2 1.53 50 313 379 35
3 1.53 50 306 379 30
Average 1.53 50 310 379 33
・ 3-point bending compression test symbol Wire diameter Load (0.5mm displacement) Maximum load (sample) [mm] [N] [N]
1 1.54 22.0 29.0
2 1.53 23.3 29.6
3 1.53 22.4 28.7
Average 1.53 22.6 29.1

○ Sample C
[Table 3]
・ Tensile test symbol Wire diameter Scoring distance Load Maximum load Elongation (sample) [mm] [mm] (1.0mm displacement) [N] [%]
1 1.54 50 208 354 30
2 1.53 50 198 355 31
3 1.54 50 192 351 29
Average 1.54 50 199 353 30
・ 3-point bending compression test symbol Wire diameter Load (0.5mm displacement) Maximum load (sample) [mm] [N] [N]
1 1.54 16.4 22.6
2 1.53 16.2 23.4
3 1.54 15.8 22.7
Average 1.54 16.1 22.9

<What to understand>
The plasticity (ductility and malleability) has been greatly recovered, and even when external stress such as tension and bending is applied, stress concentration hardly occurs, and the fracture strength, tensile strength, crack strength, etc. are remarkably improved. For example, as is clear from the above-mentioned “observation of structure / image”, samples B and C have a highly conductive structure in which the distortion and defects due to sample A are eliminated and the structure is homogeneous. JISZ2201 (1998) JIS9 No. tensile test piece, using JISZ2241 (1998) metal material tensile test method, test room temperature 22 [° C], sample average wire diameter 1.54 [mm], gauge distance 50 [mm], both ends of the sample Obtained by a metal material tensile test with fixed initial load of 2 [N], average load of 1.0 [mm] displacement 199 [N], maximum load of 353 [N] and test speed of 5 [mm / min]. It has been found that the obtained elongation rate exceeds 5 [%], which is the test result for sample A at least.
It was also found that the maximum load obtained by a three-point bending compression test conducted with a jib span of 20 [mm], a pressing metal inner radius R2, and an initial load of 0.1 [N] was less than 30 [N].

[Mass productivity]
According to the manufacturing method of the present invention, the silver wire 203 of several [m] to several tens [m] or more is applied once compared to the conventional silver wire that can secure only a length of about 1 [cm] per minute. Could be secured in the manufacturing process. The production cost was confirmed to be 1/10 to 1/20 or less of the conventional cost including the operation cost of the vacuum furnace. If the capacity and performance of the furnace used for heating and annealing are good, the cost reduction becomes even more remarkable. Therefore, mass production becomes possible and the selling price decreases, so that the silver wire 203 can be expected to spread rapidly.

[Expected utility]
Since the silver wire 203 is used as a wiring material for an electronic component or connected to a ground part, the conduction efficiency is increased, so that no burden is imposed on the operation of the electronic component. Therefore, the probability of occurrence of failure is also reduced.

  In addition, by using the softness and high bending strength of the silver wire 203 for the bonding wire of the semiconductor chip, the original processing capability of the semiconductor chip can be exhibited. It can also contribute to the improvement of processing capacity.

  Further, by using the silver wire 203 as a power transmission cable, loss and emission of unnecessary electromagnetic waves are remarkably reduced, which can contribute to environmental problems in various fields including energy problems.

  Further, a silver coil 203 and a dynamo using the same can be manufactured by covering the silver wire 203. When producing a silver coil, it is necessary to coat | cover the surface of a linear silver material with an enamel, vinyl, etc., However, these silver coating could not be performed. The reason for this is that the surface of general silver materials reacts with enamel to produce sulfides, which lowers the electrical conductivity and physical strength. The same applies to the case of vinyl, and sulfur gas or the like comes out and reacts with the surface. The silver wire 203 produced by the production method of the present invention is resistant to corrosion, that is, it is strong against chemical substances, so that the characteristics do not deteriorate even if it is coated with enamel or vinyl. Therefore, a silver coil can be manufactured. With these realizations, energy can be extracted with extremely high efficiency, and as a result, an energy source excellent in the environment can be secured.

  The silver wire 203 can also be used as a high-performance electrical contact. In general electrical contacts, migration (a phenomenon in which atoms move little by little due to collision of electrons flowing through metal atoms in the wiring, etc.) causes contact failure. On the other hand, since the silver wire 203 manufactured by the manufacturing method of the present invention has high corrosion resistance and migration hardly occurs, a high-performance electrical contact can be realized.

[Modification]
In FIG. 1, an example in which a silver wire 203 wound around a quartz tube 201 is used as a starting material in a heating space of a vacuum furnace is shown, but an auxiliary component such as the quartz tube 201 is not necessarily used, and silver The material may be placed directly in the heating space. Moreover, it can replace with a wire, and can also use the printed circuit board which drawn the wiring pattern with silver, a lead frame, a plate-shaped or sheet-shaped silver plate as a starting material.
The heat treatment may be performed not only in an inert gas or reducing gas atmosphere but also in an atmosphere of at least one of vacuum, inert gas, and reducing gas.

In addition, the crystal grain size and orientation can be adjusted by controlling the heat treatment temperature so as to form a temperature gradient in a predetermined direction of the silver material during cooling.
In addition, FIG. 1 shows an example of a vacuum furnace having a simple structure that simply heats the starting material, but a mechanism for applying a strong electric field is added to the back side of the heating element 105 of the furnace, and the above heating process is performed. When applying, an electric field having different polarities is applied to one end and the other end of the silver material having both ends, so that the crystal orientation of the silver material can be forcibly aligned. . In this case, since the long side direction of each of the plurality of crystal grain boundaries of the silver material is oriented to the conduction direction of electrons, the conduction speed of electrons becomes faster, and further improvement of the conduction efficiency can be expected.

  Moreover, although the example at the time of using silver as a starting material was shown in this embodiment, the manufacturing method of this invention is applicable to copper and other metals similarly. As a result, as long as at least the same metal material is used, a metal material with higher conductivity efficiency can be manufactured at a lower cost than in the case of using another manufacturing method.

  The highly conductive metal material of the present invention includes an antistatic unit, a printed board, a capacitor, an antenna for a communication device, a bonding wire for a semiconductor chip, a lead frame, an automotive power system wiring material, a solar power generation lead wire, a lightning rod, and a medical device wiring. It can be used in a wide range of fields such as materials, other sensing materials that sense electrons, electrical contacts, connectors, etc.

  DESCRIPTION OF SYMBOLS 101 ... Vacuum furnace container, 103 ... Electric furnace, 105 ... Heating element, 107 ... Gas supply valve, 109 ... Degassing valve, 121 ... Control device, 123 ... Pressure gauge, 125 ... thermometer, 131 ... valve drive mechanism, 133 ... gas supply device, 201 ... quartz tube, 203 ... silver wire.

Claims (7)

  A silver material in which a recrystallized structure having a highly conductive structure is formed by a heat treatment performed in an atmosphere of at least one of a vacuum, an inert gas, and a reducing gas after a final plastic working on the silver material.   The silver material according to claim 1, wherein the recrystallized structure is a single crystallized structure. The recrystallized structure is coarser than the 4N silver material having a conductivity of 106 [%] or less, the size of the crystal grains derived from the following formula, and is larger per unit volume than the 4N silver material. The silver material according to claim 1 or 2, having a low crystal grain boundary density.
Conductivity γ = X × 100 / [(R ・ m / I ²・ G) + Y (20-t)]
However, R = electric resistance [Ω], m = mass of measurement length material [g], I = measurement length [m], t = measurement temperature (Celsius), G = density of material [g / cm ³ ] ( = 10.5), X = 100% conductivity material with a length of 1 m and a cross-sectional area of 1 mm ² , resistance value at 20 degrees (Celsius), Y = temperature of a sample with a length of 1 m and a cross-sectional area of 1 mm ² is 20 degrees A low mass temperature coefficient in the vicinity of 20 degrees (Celsius) of the sample when the amount of change α is changed by 1 degree (Celsius) near (Celsius).   The silver material according to claim 3, wherein the conductivity exceeds 106%.   The silver material according to claim 3, wherein the early crystal grains of the recrystallized structure are oriented in a predetermined direction. The silver material according to claim 3, wherein an elongation obtained by a metal material tensile test performed under the following conditions exceeds 5%.
JISZ2201 (1998) JIS9 tensile test piece, using JISZ2241 (1998) metal material tensile test method, test chamber temperature 22 [° C], sample average wire diameter 1.54 [mm], gauge distance 50 [mm], The sample was fixed at both ends, and the initial load was 2 [N], the average load was 199 [N] at 1.0 [mm] displacement, the maximum load was 353 [N], and the test speed was 5 [mm / min]. The silver material according to claim 3, wherein the maximum load by a three-point bending compression test carried out under the following conditions is less than 30 [N].
Implemented with jib span 20 [mm], inner radius R2 of the metal fittings, and initial load 0.1 [N].