Probe pins, thermocouples, and electron tube heaters

Abstract

To provide a W wire for a wire-drawing process that can prevent cutting during wire-drawing and improve surface unevenness.SOLUTION: A tungsten wire according to an embodiment is formed of a W alloy containing Re, which has a mixture in at least a portion of a surface thereof. The mixture includes W, C and O as constituent elements. When a cross-sectional thickness in a radial direction of the mixture is defined as A mm and a diameter of the tungsten wire is defined as B mm, the average of the ratio A / B of A to B is 0.3% or more and 0.8% or less.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The embodiments described below relate to a tungsten wire, a tungsten wire processing method using the same, and an electrolytic wire. [Background technology]

[0002] Various types of tungsten (W) wire have traditionally been used as cathode heaters in TV electron guns, filaments for automotive and home appliance lighting, high-temperature structural components, contact materials, and discharge electrodes. Among these, tungsten alloy (ReW) wire containing a certain amount of rhenium (Re) has excellent high-temperature strength and ductility after recrystallization, making it widely used as heaters for electron tubes and filaments for vibration-resistant light bulbs. It also has excellent electrical resistance and abrasion resistance, making it suitable for use in high-temperature thermocouples and, in particular, probe pins for probe cards used in electrical property testing of semiconductor integrated circuit (LSI) wafers. This testing method involves directly applying a probe pin, whose tip has been chemically or mechanically shaped for optimal contact, to the terminal of the device under test.

[0003] As semiconductor integration increases and miniaturization technology advances, there is a continuing demand for probe cards with finer pin pitches and smaller diameters, and currently ReW pins with a wire diameter of 0.02mm to 0.04mm are also being used. As the probe pin wire diameter decreases, the number of pins per unit area can be increased, which is advantageous for testing highly integrated LSIs.

[0004] In the case of such small-diameter W wire (thin wire), the sintered body is first subjected to primary processing, such as rolling and wire drawing (wire drawing), to produce a wire of a certain diameter range (0.3 mm to 1.5 mm). Then, the appropriate amount of wire is subjected to additional necessary processes, such as wire drawing and heat treatment, to produce the desired tungsten wire (diameter). This thinning process is prone to breaks during the wire drawing process and the formation of fine linear irregularities (die marks, as specified in JIS H0201 718) that appear on the material surface in the drawing direction. Breaks during wire drawing of thin wire, especially in multi-stage wire drawing machines that process with multiple dies, significantly reduce yield. Furthermore, repairs and restarting the machine after breakage increase labor hours. If die marks cannot be removed by subsequent surface polishing and probe pin processing, they become defects that increase yield and processing costs.

[0005] Conventional countermeasures against wire breakage include controlling the number of recrystallizations by heat treatment during the process to improve workability. For example, when the cross-sectional area reduction rate (area reduction rate) of the molded product from the sintered compact exceeds 75% and reaches 90% or less, a final recrystallization treatment is carried out to reduce the number of recrystallized grains in the center and surface layer of the molded product to 500 grains / mm. 2 ~800 pieces / mm 2 There is a ReW wire that adjusts the thickness to 100 nm (see Patent Document 1). There are also wires that have improved workability by controlling the Re segregated phase (σ phase) in the W matrix. For example, if the σ phase is unevenly distributed, wire breaks are likely to occur starting from the σ phase during wire drawing, so there is a ReW wire in which the maximum grain size of the σ phase is set to 10 μm or less (see Patent Document 2). Furthermore, in secondary processing such as coil processing, if a lubricant containing graphite (C) remains in the recesses on the material surface, this C component may contaminate the W at high temperatures during processing, causing embrittlement. For this reason, some wires prevent embrittlement by controlling the surface roughness. For example, there is a ReW wire in which the average spacing and maximum height of the recesses on the material surface are adjusted to a predetermined range by electrolysis after drawing to a wire diameter of 0.175 mm (see Patent Document 3).

[0006] Regarding die marks, a common method is to remove them by chemical polishing (electrolysis) after wire drawing to a specified size. For example, there is a method for manufacturing W electrodes in which the center line average roughness and ten-point average roughness are specified and electrolytic processing is performed to those values ​​(see Patent Document 4). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent No. 2637255 [Patent Document 2] Japanese Patent No. 4256126 [Patent Document 3] Japanese Patent No. 3803675 [Patent Document 4] Japanese Patent Publication No. 2000-100377 Summary of the Invention [Problem to be solved by the invention]

[0008] The method described in Patent Document 1 for controlling the number of crystals by heat treatment during the intermediate process requires a certain reduction in area between the sintered body and the recrystallization process. This effect is also relevant to processing the material to the above-mentioned size, which is a finished diameter of 1.0 mm. When considering application to thin wires, the cross-sectional area of ​​the sintered body must be made very small, which significantly reduces productivity. Furthermore, the reduced size of the recrystallization process is likely to result in a decrease in strength at the finished size. For example, probe pins are difficult to use because they must be strong enough to not deform when they come into contact with the terminals of the device under test. The method described in Patent Document 2 is very effective in preventing fractures initiated by the σ phase. However, the method only controls the occurrence of σ phase segregation in the process leading up to the production of a sintered body, and subsequent processes are conventional. Therefore, it does not prevent wire breaks due to other factors such as die marks. Patent Document 3 describes a method for preventing embrittlement due to a reaction between W and C by improving the surface quality of the thin wire so that residual C on the surface can be easily evaporated by high-temperature heating during secondary processing such as coiling. In the thin wire processing described in Patent Document 3, a C-based lubricant with excellent heat resistance is generally used. The measure of evaporating C deteriorates lubricity and poses the risk of seizure between the wire and the die.

[0009] Patent Document 4 describes a method for removing and managing die marks that have occurred, but does not mention how to suppress die marks.

[0010] The problem to be solved by the present invention is to provide a W wire for wire drawing that is improved in terms of breakage during drawing and surface irregularities. [Means for solving the problem]

[0011] In order to solve the above problems, the tungsten (W) wire according to the embodiment is a W wire made of a W alloy containing rhenium (Re), and has a mixture on at least a part of the surface, the mixture containing W, C, and O as constituent elements, and when the radial cross-sectional thickness of the mixture is A mm and the diameter of the W wire is B mm, the average value of the ratio A / B of A to B in the same cross section is 0.3% or more and 0.8% or less. Also provided are probe pins, thermocouples, and electron tube heaters that use the tungsten wire. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing an example of a tungsten wire for wire drawing according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram of a radial cross section of a tungsten wire (cross section XX in FIG. 1). [Figure 3] FIG. 3 is a schematic diagram of the mixture at an arbitrary point A in a radial cross section. [Figure 4-1] FIG. 4-1 is a graph showing the change in oxygen content of the mixture in a radial cross section in Comparative Example 3 (EPMA line analysis). [Figure 4-2] FIG. 4-2 is a graph showing the change in oxygen content of the mixture in a radial cross section in Example 2 (EPMA line analysis). [Figure 5] Figure 5 shows a cross-sectional schematic diagram of a wire deformation model during wire drawing and the stresses at the center and surface. [Figure 6-1] FIG. 6-1 is a schematic diagram of Comparative Example 3 illustrating the difference in the shape of the mixture layer between Comparative Example 3 and Example 2 in radial cross section. [Figure 6-2] FIG. 6-2 is a schematic diagram of Example 2 showing the difference in the shape of the mixture layer between Comparative Example 3 and Example 2 in radial cross section. [Figure 7-1] FIG. 7-1 is a cross-sectional view showing the radial cross-sectional shape (overall view) of the wire body before electrolytic polishing. [Figure 7-2] FIG. 7-2 is a cross-sectional view showing the radial cross-sectional shape (overall view) of the wire body after electrolytic polishing. Embodiment

[0013] Hereinafter, a tungsten wire for wire drawing according to an embodiment will be described with reference to the drawings. Hereinafter, the tungsten wire for wire drawing will also be referred to as a W wire for wire drawing. Note that the drawings are schematic, and for example, the dimensional ratios of each part are not limited to those shown in the drawings.

[0014] Figure 1 shows an example of a W wire sample taken from a W wire for wire drawing. The sample length should be long enough (100mm to 150mm) to allow for multiple cross-sectional observations after embedding in resin. The sampling position can be arbitrary, but to ensure good product yield in subsequent processes, it is best to sample from a position excluding the front and rear ends. The front and rear ends have unstable conditions due to the start and stop of the wire drawing equipment, so these areas are not included in the sampling. The length of the unstable area varies depending on the layout and size of the equipment. The diameter of the sample taken is measured in the X and Y directions using a micrometer. Measurements are taken at three locations, and the average of the six data points obtained is taken as the diameter B (mm) of each sample.

[0015] Figure 2 shows the XX cross section (cross section perpendicular to the wire drawing direction: radial cross section) of Figure 1. As shown in the figure, lines are drawn through the center to divide the area into eight equal parts, and the intersections with the periphery are designated A1 to A8. The mixture is observed at any eight equally spaced points on the periphery. Figure 3 shows a schematic diagram of the mixture at any one of the points. For example, the sample can be embedded in resin and polished to obtain a clearer image, but the mixture may peel off during this process. Such parts are excluded from the measurement points. Using an SEM image observed at 10,000x magnification, the thickest part of the mixture (A) in a 30 μm x 30 μm area is measured. max ) and the thinnest part (A min ) and take the average value as the thickness of the mixture. In the same way, find the thickness of each of the eight points (A1 to A8) on the same cross section. Let the thickness at any one point be A (mm). Using the diameter B of the observed sample, find the ratio A / B (%) of A to B. For the same cross section, the number of A / B data points is 8. Due to the number of observed samples (n), the number of A / B data points is "8 x n".

[0016] The average value of A / B of the tungsten wire in this embodiment is 0.3% or more and 0.8% or less (0.003 or more and 0.008 or less). More preferably, it is 0.3% or more and 0.6% or less (0.003 or more and 0.006 or less). If the average value of A / B is less than 0.3%, breakage occurs during wiredrawing, and if the A / B ratio is greater than 0.8%, the rate at which die marks occur increases. If the average value of A / B is within the range of 0.3% or more and 0.8% or less, breakage and die marks can be suppressed during wiredrawing.

[0017] Figure 4 (Figures 4-1 and 4-2) shows, as an example, the results of an analysis of the O (oxygen) content in the mixture in a radial cross section with a diameter of 0.80 mm. Figure 4-1 shows the results of measurements of a portion of Comparative Example 3, and Figure 4-2 shows the results of measurements of a portion of Example 2. The analysis was performed using an EPMA (electron probe microanalyzer: JXA-8100 manufactured by JEOL Ltd.), with an accelerating voltage of 15 kV and a sample current of 5.0 x 10 -8The conditions were as follows: beam diameter: Spot (up to Φ1 μm), analysis time: 500 ms / point, scan mode: stage scan, analysis distance: 29.7 μm (151 points). The vertical axis represents the count number, and the horizontal axis represents the observation direction distance. Hereinafter, Comparative Example 3 may also be referred to as the conventional W line. The A / B ratio of the observed area is 1.4% (0.014) for the conventional W wire and 0.7% (0.007) for Example 2. The O content in the mixture of the conventional W wire fluctuates in the cross-sectional direction (length L of the mixture), whereas that of Example 2 is stable. The O content in the mixture exists as a compound (oxide) with W. The oxide composition of W includes WO3, W 20 O 58 , W 18 O 49 , WO2, and W3O, and their physical properties (strength and adhesion) differ. In conventional W wire, the O content varies within the cross section of the mixture, indicating that oxides of different compositions exist within the cross section. This causes inhomogeneity in deformation during wire drawing, which can lead to cracks and peeling of the oxide film. The peeled-off parts are likely to become die marks.

[0018] Figure 5 shows a deformation model of the wire during wire drawing, and the stresses at the center and surface. Shear forces are generated in the surface layer of the wire due to contact with the die during wire drawing. The outer periphery 1 also undergoes plastic deformation due to shear forces. As a result, the material does not stretch uniformly across the radial cross section, but rather advances more towards the center 2. When the surface mixture is thick, the amount of shear deformation in the mixture layer is greater than when it is thin. For this reason, the shear force acting between the W and the mixture is greater the thicker the layer. This causes partial shearing of the mixture. The presence of oxides with different compositions within the mixture, as mentioned above, further increases the likelihood of shearing.

[0019] If the average value of A / B is less than 0.3% (0.003), W and C react directly, increasing the risk of embrittlement. Also, there is a possibility that sufficient lubrication cannot be ensured.

[0020] Next, for A / B of the same cross section (8 data points), the average value (Ave), standard deviation (Sd), and coefficient of variation (CV) calculated by Sd / Ave are calculated. CV indicates the ratio of the magnitude of data variation to the average, and can be used to compare variations regardless of layer thickness.

[0021] The CV of the same cross section of the tungsten wire in this embodiment is preferably 0.30 or less. More preferably, it is 0.20 or less. If the CV is greater than 0.30, there is a high possibility of breakage or die marks occurring during wire drawing. If the thickness of the mixture varies greatly, there is a possibility that the A / B ratio may be large or small in some areas. Such areas may be at risk of defects such as the aforementioned detachment or cracking of the mixture and C-embrittlement of the W wire.

[0022] Figure 6 (Figure 6-1 and Figure 6-2) shows a schematic diagram of the difference in the shape of the mixture in a radial cross section with a diameter of 0.8 mm. When an actual sample was observed using an SEM at a magnification of 5000 times for a cross section with a peripheral length of 60 μm, the difference in thickness (A ma x‐A min ) was 6 μm, while that of Example 2 was 1 μm, a large difference. Furthermore, the CV of this cross section was found to be 0.5 for the conventional wire and 0.1 for Example 2. When the CV is large, it is highly likely that not only are there large differences (variations) in thickness depending on the position on the periphery, but there are also large differences (variations) in thickness at the same location. A mixture layer with this type of shape does not have a uniform processing force during wire drawing, making it prone to cracking and falling off.

[0023] The cross section from which the A / B data was obtained was subjected to energy dispersive X-ray analysis (EDS: accelerating voltage 15 kV, magnification 10,000x, measurement range 30 μm × 30 μm) using a Phenom ProX desktop scanning electron microscope. max and A minThe central part of the mixture in the thickness direction is measured and the average value is calculated. Measurements are taken at any five of the eight locations (A1 to A8) on the cross section, and the ratio of each location (Owt% / Wwt%) is calculated from the obtained W (wt%) and O (wt%) data values. W (wt%) is the mass % of tungsten, and O (wt%) is the mass % of oxygen.

[0024] In the W wire of the embodiment, the average ratio of O (wt%) to W (wt%) (O wt% / W wt%) at the center of the mixture in the thickness direction is preferably 0.10 or less. If it exceeds 0.10, the production of WO3, which is a W oxide, may progress. WO3 is very brittle, making the mixture prone to falling off. While the lower limit is not particularly limited, a value of 0.05 or more is preferred. If it is below 0.05, the production of W oxide is insufficient, and the reaction between C in the C layer and W is likely to occur.

[0025] The Re content of the W wire of the embodiment is preferably 1 wt% to 30 wt%, and more preferably 2 wt% to 28 wt%. If the Re content is less than 1 wt%, the strength decreases. For example, when used in a probe pin, the amount of deformation increases with frequency of use, resulting in poor contact and reduced semiconductor inspection accuracy. If the Re content exceeds approximately 28 wt%, the solid solubility limit with W is exceeded, making it more likely that the σ phase will be unevenly distributed. This phase may become the origin of fracture during wire drawing, significantly reducing the processing yield. By setting the Re content to 1 wt% to 30 wt%, or 2 wt% to 28 wt%, for example, electrolytic wire for probe pins made from the material of this embodiment can be produced with high yield while maintaining mechanical properties (strength and wear resistance).

[0026] The W wire of the embodiment may contain 30 wtppm to 90 wtppm of K as a dopant. By containing K, the doping effect improves tensile strength and creep strength at high temperatures. If the K content is less than 30 wtppm, the doping effect will be insufficient. If it exceeds 90 wtppm, workability may decrease, resulting in a significant decrease in yield. By containing 30 wtppm to 90 wtppm of K as a dopant, for example, thin wires for thermocouples and electron tube heaters made from the material of this embodiment can be produced with high yield while maintaining high-temperature properties (preventing breakage and deformation when used at high temperatures).

[0027] According to this embodiment, a tungsten wire for wire drawing can be realized that suppresses breakage and surface irregularities during thin wire processing, greatly contributing to improved yield, and can be used as an electrolytic wire for probe pins. It can also be used as a high-temperature thermocouple.

[0028] Next, a method for manufacturing a W wire for wire drawing according to this embodiment will be described. The manufacturing method is not particularly limited, but the following method can be mentioned, for example.

[0029] W powder and Re powder are mixed so that the Re content is 1 wt% or more, for example, 3 wt% or more and 30 wt% or less. While the mixing method is not particularly limited, a method in which the powders are mixed in a slurry form using water or an alcohol-based solution is particularly preferred because it produces a powder with good dispersibility. The Re powder to be mixed preferably has a maximum particle size of less than 100 μm. It also preferably has an average particle size of less than 20 μm. The W powder is either pure W powder excluding unavoidable impurities, or doped W powder containing a K content that takes into account the yield of wire rod. The W powder preferably has an average particle size of less than 30 μm. If the maximum or average particle size of the Re powder is greater than the above range, coarse σ phases are likely to be formed. Furthermore, if the average particle size of the W powder is greater than the above range, formability during the subsequent press molding process is reduced, and breakage, chipping, cracks, etc. are likely to occur in the molded body.

[0030] For example, when producing a W-Re mixed powder with an Re content of more than 18 wt%, a ReW alloy with an Re content of 18 wt% or less is first produced by powder metallurgy, melting, or other methods, and then finely pulverized using conventional methods. Another method is to add the necessary amount of Re to achieve the desired composition. Hereafter, tungsten wire containing Re may be referred to as a ReW wire.

[0031] Next, the mixed powder is placed in a predetermined mold and press-molded. The pressing pressure is preferably 100 MPa or higher. To facilitate handling, the molded body may be pre-sintered at 1200-1400°C in a hydrogen furnace. The resulting molded body is sintered in a hydrogen atmosphere, an inert gas atmosphere such as argon, or a vacuum. The sintering temperature is preferably 2125°C or higher. At temperatures below 2125°C, sintering does not result in sufficient densification. The upper limit of the sintering temperature is 3400°C (below the melting point of W, 3422°C). The relative density after sintering (relative density (%) to true density = [sintered body density / true density] × 100%) is preferably 90% or higher. By achieving a relative density of 90% or higher, it is possible to reduce cracks, chips, breaks, etc. during the subsequent rolling (SW) process.

[0032] Molding and sintering may be performed simultaneously by hot pressing in a hydrogen atmosphere, an inert gas atmosphere such as argon, or in a vacuum. The pressing pressure is preferably 100 MPa or more, and the heating temperature is preferably 1700°C to 2825°C. This hot pressing method can produce a dense sintered body even at a relatively low temperature.

[0033] The sintered body obtained in this sintering step is subjected to a first rolling and punching process. The first rolling and punching process is preferably carried out at a heating temperature of 1300°C to 1600°C. The reduction rate of the cross-sectional area (area reduction rate) in one heat treatment (one heat) is preferably 5% to 15%.

[0034] Rolling may be performed instead of the first rolling. The rolling is preferably performed at a heating temperature of 1200°C to 1600°C. The area reduction rate per heat is preferably 40% to 75%. As the rolling mill, a two-way roller rolling mill, a four-way roller rolling mill, a die roll rolling mill, or the like can be used. Rolling can significantly improve manufacturing efficiency. The first rolling and rolling may be combined.

[0035] The sintered body (ReW bar) that has undergone the first rolling process, rolling process, or a combination thereof is subjected to the second rolling process. The second rolling process is preferably performed at a heating temperature of 1200°C to 1500°C. The area reduction rate per heat is preferably about 5% to 20%.

[0036] The ReW bar that has undergone the second rolling step is then subjected to a recrystallization treatment, which can be carried out, for example, using a high-frequency heating device in a hydrogen atmosphere, an inert gas atmosphere such as argon, or a vacuum at a treatment temperature in the range of 1800°C to 2600°C.

[0037] The ReW bar material that has completed the recrystallization treatment is subjected to the third rolling and striking process. The third rolling and striking process is preferably carried out at a heating temperature of 1200°C to 1500°C. The area reduction rate per heat is preferably about 10% to 30%. The third rolling and striking process is carried out until the ReW bar has a diameter that can be drawn (preferably a diameter of 2mm to 4mm).

[0038] After the third rolling process, the ReW rod material is subjected to the first wiredrawing process, which involves repeatedly applying a lubricant to the surface to enable smooth wiredrawing, drying the lubricant, heating to a workable temperature, and drawing using a drawing die. This process is repeated until the diameter reaches 0.7 mm to 1.2 mm. A C-based lubricant with excellent heat resistance is preferable. The processing temperature is preferably 800°C to 1100°C. The workable temperature varies depending on the diameter, and is higher for larger diameters. If the temperature is lower than the workable temperature, cracks and breakage frequently occur. If the temperature is higher than the workable temperature, seizure between the wire and the die and the wire's deformation resistance decrease, causing diameter fluctuations (thinning) after wiredrawing due to the drawing force. The area reduction ratio is preferably 15% to 35%. If it is less than 15%, internal and external differences in the structure and residual stress will occur during processing, leading to cracks. If it is greater than 35%, the drawing force will be excessive, causing large diameter fluctuations after wiredrawing and resulting in breakage. The wire drawing speed is determined by the balance between the capacity of the heating device, the distance from the device to the die, and the area reduction rate.

[0039] The composition of the mixture formed on the surface, particularly the W oxide, varies depending on the processing conditions (heating temperature, atmosphere, etc.). Repeated heating makes the processing conditions more likely to fluctuate. The optimum processing temperature also changes with changes in diameter. In particular, when the diameter is large, a higher heating temperature is required, making the conditions more likely to fluctuate. For this reason, there is a high possibility that W oxides with different compositions will be generated as the thickness increases. Therefore, wire drawn to a diameter of 0.7 mm to 1.2 mm is polished to remove the mixture formed on the surface during previous processing and any irregularities on the wire surface.

[0040] Polishing can be achieved by electrochemical polishing (electrolytic polishing), for example, in a 7-15 wt% sodium hydroxide aqueous solution. The area reduction ratio during polishing is preferably 10-25%. If it is less than 10%, it may be impossible to remove the unevenness on the material surface caused by the rolling and first wiredrawing processes, as well as the adhering mixture. If it exceeds 25%, the material yield will decrease. For electrolytic polishing, a processing speed of 0.5-2.0 m / min is preferred. A speed slower than 0.5 m / min significantly increases the processing time. If it exceeds 2.0 m / min, the amount of electrolysis per unit time increases, resulting in rapid electrolysis, which may result in insufficient correction of the wire cross-sectional shape. Alternatively, the equipment must be significantly larger. Figure 7 (Figures 7-1 and 7-2) shows the results of observing the radial cross-sectional shape of the ReW wire body before and after electrolytic polishing. The electrolytic polishing process eliminates the unevenness on the wire surface.

[0041] After polishing, the wire is heated in an atmospheric furnace to form a dense, uniform oxide layer on the surface. The heating temperature is preferably 700°C to 1100°C. If the temperature is lower than 700°C, oxide formation is difficult. If the temperature is higher than 1100°C, variations in the oxide composition occur. The processing speed is preferably 5m / min to 20m / min. If it is less than 5m / min, the processing time increases significantly. If it is more than 20m / min, a large amount of heat is required to raise the temperature, which makes the oxide layer more likely to become non-uniform. Alternatively, the equipment must be very large.

[0042] To form and adhere the C layer on the oxide layer, the following processes are performed: applying a lubricant to the surface, drying the lubricant, heating to a workable temperature, and wire drawing using a drawing die. By adhering the C layer, changes and peeling of the oxide layer in subsequent processes are prevented. The area reduction rate is preferably 10% to 30%, and more preferably 15% to 25%. If it is less than 10%, there is a risk that the oxide layer and C layer will not adhere sufficiently. If it is more than 30%, the drawing force will be too large, which may cause peeling of the layers on the die entry side.

[0043] After this, a second wiredrawing process is carried out. The heating temperature is preferably 1000°C or less. If the temperature exceeds 1000°C, the C in the adhesive C layer will react with O in the air to become CO2 and be released, which may cause the C layer to become sparse and the composition of the oxide layer underneath to change. The area reduction rate in the second wiredrawing process is preferably 15% to 35%, as in the first wiredrawing process. The second wiredrawing process produces a W wire for wiredrawing with a diameter of 0.3 mm to 1.0 mm.

[0044] After this, the appropriate amount of W wire for wire drawing is subjected to additional necessary processes such as wire drawing and heat treatment to produce a W wire with the required characteristics (strength, hardness, etc.) at the specified wire diameter. This is then electrolytically polished to produce electrolytic wire. (Example)

[0045] By the above-mentioned powder mixing, molding, and sintering methods, sintered bodies were manufactured with the compositions shown in Table 1. In Examples 1 to 6, the first rolling and punching process, rolling process, second rolling and punching process, recrystallization treatment, third rolling and punching process, first wiredrawing process, electrolytic polishing, heat treatment to form an oxide layer, wiredrawing process to adhere the C layer, and second wiredrawing process were carried out to obtain the diameters shown in Table 1.

[0046] In Example 7, the area reduction rate was reduced to 8% in the electrolytic polishing process after the first wiredrawing. In Comparative Example 1, the heating temperature for forming an oxide layer after electrolytic polishing was reduced to 680°C to 700°C, resulting in a thin mixture layer. In Comparative Example 2, the heating temperature for the second wiredrawing was increased to 1150°C, resulting in a thick mixture layer. In Comparative Examples 3 to 5, a conventional processing step was performed in which the second wiredrawing was performed directly after the first wiredrawing. Each wire was processed to the diameter shown in Table 1. Analysis of Re and K was performed using inductively coupled plasma-optical emission spectrometry (ICP-OES), which is suitable for evaluating constituent elements, rather than inductively coupled plasma-mass spectrometry (ICP-MS), which is suitable for evaluating trace impurities. The lower detection limit for K is 5 wtppm, and if the analytical value is below 5 wtppm without addition, it is recorded as "-".

[0047] [Table 1]

[0048] Sampling was performed from the obtained wire, and the A / B, CV, and Owt% / Wwt% were evaluated using the methods described above. The mixture contained W, C, and O as constituent elements. 1 kg of each wire was used and drawn to a diameter of 0.08 mm. The rate of break failure during drawing and the rate of appearance failure after completion were investigated. The breakage defect rate was calculated by counting the weight of the wire after breakage as defective if the wire broke during drawing and the weight of the wire was 0.05 kg or less, and dividing the total defective weight by the input weight (1 kg). To determine the appearance defect rate, 100m of wire was cut into 50mm lengths at both ends after drawing, and boiled in caustic soda to remove any impurities. The wire was then observed under a microscope at 30x magnification, and if any discernible scratches or irregularities were found on the surface, 50mm was counted as a die mark defect. The length of the defect was calculated as the defective length divided by the evaluation length (200m). The results are shown in Table 2.

[0049] [Table 2]

[0050] As can be seen from the table, the W wire for wire drawing according to the embodiment had a reduced rate of wire drawing breakage and a reduced rate of appearance defect, whereas the comparative example had a high rate of wire drawing breakage and a low rate of appearance defect.

[0051] Although several embodiments of the present invention have been described above, these embodiments are presented by way of example only and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. Modifications of these embodiments are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other. The inventions described in the original claims of this application are set forth below. [1] A tungsten wire made of a tungsten alloy containing rhenium, having a mixture on at least a portion of its surface, the mixture containing W, C, and O as constituent elements, and wherein, when the radial cross-sectional thickness of the mixture is A mm and the diameter of the tungsten wire is B mm, the average value of the ratio A / B of A to B is 0.3% or more and 0.8% or less. [2] The tungsten wire according to [1], wherein the coefficient of variation of A / B in the same cross section is 0.30 or less. [3] The tungsten wire according to any one of [1] and [2], wherein the average ratio of O (wt%) to W (wt%) (Owt% / Wwt%) at the center of the thickness direction of the radial cross section in the mixture is 0.05 or more and 0.10 or less. [4] The tungsten wire according to any one of [1] to [3], wherein the rhenium content is 1 wt% or more and 30 wt% or less. [5] The tungsten wire according to any one of [1] to [3], wherein the rhenium content is 2 wt% or more and 28 wt% or less. [6] The tungsten wire according to any one of [1] to [5], wherein the tungsten alloy has a potassium (K) content of 30 wtppm or more and 90 wtppm or less. [7] The tungsten wire according to any one of [1] to [6], wherein the diameter of the tungsten wire is 0.3 mm or more and 1.0 mm or less. [8] A tungsten wire processing method, comprising drawing the tungsten wire according to any one of [1] to [7]. [9] An electrolytic wire using a tungsten wire that has been drawn using the tungsten wire processing method described in [8].

[10] A tungsten wire according to any one of [1] to [7], which is for wire drawing. [Explanation of symbols]

[0052] XX: Cut surface perpendicular to the wire drawing axis (radial direction) Y...Mixture Z...ReW wire body A1 to A8: Diameter-direction cross section, dividing the circumference into eight equal parts A max …Maximum thickness of the mixture within the observation field A min …Minimum thickness of the mixture within the observation field 1...Outer periphery 2…Center

Claims

1. A probe pin using a tungsten wire, A probe pin, wherein the tungsten wire is made of a tungsten alloy containing rhenium and has a mixture on at least a portion of its surface, the mixture containing W, C, and O as constituent elements, and when the radial cross-sectional thickness of the mixture is A mm and the diameter of the tungsten wire is B mm, the average value of the ratio A / B of A to B in the same cross section is 0.3% or more and 0.8% or less.

2. 2. The probe pin according to claim 1, wherein the coefficient of variation of A / B in the same cross section is 0.30 or less.

3. 3. The probe pin according to claim 1, wherein in the mixture, the average value of the ratio of O (wt%) to W (wt%) (O wt% / W wt%) at the center of the thickness direction of the radial cross section is 0.05 or more and 0.10 or less.

4. 3. The probe pin according to claim 1, wherein the content of said rhenium is 1 wt % or more and 30 wt % or less.

5. 3. The probe pin according to claim 1, wherein the content of said rhenium is 2 wt % or more and 28 wt % or less.

6. 3. The probe pin according to claim 1, wherein the diameter of the tungsten wire is 0.3 mm or more and 1.0 mm or less.

7. A thermocouple using a tungsten wire, The thermocouple is characterized in that the tungsten wire is made of a tungsten alloy containing rhenium and has a mixture on at least a portion of its surface, the mixture containing W, C, and O as constituent elements, and when the radial cross-sectional thickness of the mixture is A mm and the diameter of the tungsten wire is B mm, the average value of the ratio A / B of A to B in the same cross section is 0.3% or more and 0.8% or less.

8. 8. The thermocouple according to claim 7, wherein the coefficient of variation of A / B in the same cross section is 0.30 or less.

9. 9. The thermocouple according to claim 7, wherein in the mixture, an average value of a ratio of O (wt%) to W (wt%) (O wt% / W wt%) at a central part in the thickness direction of a radial cross section is 0.05 or more and 0.10 or less.

10. 9. The thermocouple according to claim 7, wherein the tungsten alloy has a potassium (K) content of 30 wtppm or more and 90 wtppm or less.

11. 9. The thermocouple according to claim 7, wherein the diameter of the tungsten wire is 0.3 mm or more and 1.0 mm or less.

12. An electron tube heater using a tungsten wire, An electron tube heater, wherein the tungsten wire is made of a tungsten alloy containing rhenium and has a mixture on at least a portion of its surface, the mixture containing W, C, and O as constituent elements, and when the radial cross-sectional thickness of the mixture is A mm and the diameter of the tungsten wire is B mm, the average value of the ratio A / B of A to B in the same cross section is 0.3% or more and 0.8% or less.

13. 13. The electron tube heater according to claim 12, wherein the coefficient of variation of A / B in the same cross section is 0.30 or less.

14. An electron tube heater as described in any one of claims 12 to 13, wherein in the mixture, the average value of the ratio of O (wt%) to W (wt%) (O wt% / W wt%) at the thickness-wise center of the radial cross section is 0.05 or more and 0.10 or less.

15. 14. The electron tube heater according to claim 12, wherein the tungsten alloy has a potassium (K) content of 30 wtppm or more and 90 wtppm or less.

16. 14. The electron tube heater according to claim 12, wherein the diameter of the tungsten wire is 0.3 mm or more and 1.0 mm or less.

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