Silver alloy wire and conductive wire using the same, wire for joint, wire for semiconductor, and wire for structure

Abstract

To provide a silver alloy wire that can maintain high strength at high temperature as an industrial wire because of high strength to tension and high grain boundary degradation resistance.SOLUTION: A silver alloy wire contains 99.8 mass% or more of silver, a ratio of special particle boundary length of crystal grain on a cross section perpendicular to a longitudinal direction of the silver alloy wire is 30% or more, and a ratio of crystal orientation <111> in which an angle difference to a longitudinal direction of the silver alloy wire is 15 degrees or less out of crystal orientation <hkl> in a longitudinal direction measured on the cross section is 10% or more and 60% or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a silver alloy wire, and particularly to a silver alloy wire suitably used for a wide range of industrial applications (for example, conductive wires, bonding wires, semiconductor wires, structural wires, etc.).

Background Art

[0002] Since silver has a high light reflectance, it has a beautiful metallic luster and is inexpensive among precious metals, so it has been used as a jewelry since ancient times. However, pure silver is soft and easily sulfidated. For example, silver sulfide is formed on the surface by sulfur compounds such as automobile exhaust gas and hydrogen sulfide in hot spring areas, causing discoloration. Since silver with a higher purity is more likely to discolor, when silver is used as jewelry, it is common to mix other metals with pure silver to lower the purity. For jewelry, silver with purities of 92.5%, 83.5%, and 80% is used, and in the purities (grades) of jewelry metal alloys of ISO 9202 (International Organization for Standardization) and JIS H6309 (Japanese Industrial Standards), which are precious metal grade certification standards, they are defined as 925, 835, and 800, respectively.

[0003] Such silver alloys for jewelry have high electrical resistance and high hardness and are difficult to process due to their low purity. Therefore, silver alloy wires are not suitable for industrial materials and have not yet been widely applied industrially.

[0004] Conventionally, copper has been widely used as an industrial metal wire. However, with the rapid progress of advanced industrial technologies, materials with unprecedented new properties have been demanded. For example, in recent years, technologies have been developed to apply industrial fine metal wires to components and products through processes such as twisting, braiding, weaving, knotting, connecting, and joining. Also, even after being applied to components and products, depending on their use, long-term tensile forces are applied to the industrial fine metal wires, or the metal wires are heated by energization or the like. For example, in high-performance and multifunctional products, the directions and magnitudes of the above-described processes and applied tensile forces tend to become complex, and heating by large currents also tends to increase. Thus, in metal materials used as industrial wires, for example, materials are required that can support high-performance and multifunctional products, do not lead to failures, and have excellent strength that can withstand miniaturization of components and products and complex secondary processing.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention has been made to solve the above-described problems, and an object thereof is to provide a silver alloy wire that has high strength against tension and high intergranular corrosion resistance, and can maintain high strength even at high temperatures as an industrial wire. In addition, the present invention aims to provide a conductive wire, a bonding wire, a semiconductor wire, and a structural wire using a silver alloy wire that has high strength against tension and high grain boundary deterioration resistance, and can maintain high strength even at high temperatures as an industrial wire.

Means for Solving the Problems

[0007] Silver has the highest electrical conductivity and thermal conductivity among metals. The higher the purity, the higher the electrical conductivity and thermal conductivity, but it becomes soft (i.e., the stress is small) and is prone to break when pulled. Therefore, in conventional silver alloy wires, mainly, alloying by adding other metal elements, grain refinement by drawing, and strength improvement by introducing strain have been attempted. For example, in drawing, by adopting severe working (such as increasing the reduction ratio per die or increasing the working ratio), large strain can be introduced into the material, and the grain size can be refined to improve the strength. In conventional silver alloy wires in which strength improvement is achieved by alloying and grain refinement, the lower the silver purity, the more the number of crystals, and the smaller the crystal grain size, the higher the hardness and strength.

[0008] A silver alloy is a polycrystal composed of a plurality of crystal grains. Each crystal grain in the polycrystal has a different crystal orientation, and the relationship between the drawing direction of the silver alloy wire and the crystal orientation is different for each crystal grain. In drawing, the strength can be improved by aligning a plurality of crystal grains in a specific crystal orientation.

[0009] However, the inventors have found that in conventional silver alloy wires whose strength is increased by grain refinement, grain boundary deterioration occurs. In particular, although the strength of the silver alloy wire can be improved by aligning the crystal grains in a specific crystal orientation, grain boundary deterioration is likely to occur. It has also been found that although a significant decrease in strength is not observed during the progress of grain boundary deterioration, it may occasionally lead to fracture. Such unpredictable accidental fractures can lead to failures of parts and equipment manufactured by advanced industrial technologies, and there is a risk of serious accidents.

[0010] Furthermore, through investigations, the inventors of the present invention have found that by simultaneously controlling special grain boundaries and crystal orientations, it is possible to achieve both grain boundary deterioration resistance and high strength in silver alloy wires with a specific ratio of special grain boundary lengths and a crystal structure that does not concentrate in specific crystal orientations.

[0011] Generally, a metal material is a polycrystal composed of multiple single crystals. The boundary between crystal grains having different crystal arrangements (crystal orientations) in a polycrystal is called a crystal grain boundary (simply referred to as a "grain boundary"). In most of the crystal grain interior, atoms are regularly and densely arranged. At the grain boundary, which is the boundary between crystal grains, the atomic arrangement is irregularly disrupted and has a large number of gaps. Grain boundary deterioration is a phenomenon in which the strength and corrosion resistance of the grain boundary decrease due to the influence of high temperature, stress, etc. In the process of grain boundary deterioration, although there are no significant visible changes in the appearance of the material, starting from the grain boundary, it leads to small cracks, large cracks, and finally fracture. Therefore, the grain boundary deterioration resistance has a great impact on the lifespan and reliability of the material.

[0012] Generally, there are few reported cases of grain boundary deterioration in iron-based materials, and many cases are caused by corrosion or precipitation of alloying elements. On the other hand, the high-purity silver handled in this embodiment is a stable metal in which silver is difficult to oxidize and is of high purity, so there are no reported cases of grain boundary deterioration. Therefore, due to the lack of reference cases, it was very difficult to capture the phenomenon of grain boundary deterioration in high-purity silver alloy wires due to the influence of high-temperature usage environments, stress, etc. Under such circumstances, as a result of intensive research, the inventors of the present invention have discovered that it is effective to confirm the grain boundary deterioration of high-purity silver alloy wires by the phenomenon of grain boundary fracture in a creep test.

[0013] Furthermore, as a result of intensive research, the inventors of the present invention have discovered that grain boundary deterioration (grain boundary fracture) by a creep test is related to the crystal structure (special grain boundaries, crystal orientations, crystal grain sizes) of high-purity silver alloy wires.

[0014] Specifically, the inventors prepared silver alloy wires with various compositions and conducted tensile tests and creep tests. In the tensile tests, the silver alloy wires were continuously pulled at a constant speed until they broke at room temperature and high temperature (about 200°C, which is the recrystallization temperature of silver). In the high-temperature creep test, the wires were continuously pulled at a constant load at high temperature (about 200°C) until they broke. Then, the crystal structures of the silver alloy wires before and after each test were analyzed.

[0015] (Experimental Example) An experimental example, which is an example of the above test, will be described. Using the silver alloy wires prepared in the examples and comparative examples described below, the relationship between the ratio of the special grain boundary length (%) in the cross-section of the silver alloy wire, the <111> orientation ratio (%), the state of the fracture surface after the tensile test or high-temperature creep test at room temperature, the elongation at break (%) and the fracture time (hrs) (time until fracture) was investigated in advance. Among them, the results of the silver alloy wires of Example 5 and Comparative Example 1 are shown in Table 1 and Figures 9 to 10. Note that both Example 5 and Comparative Example 1 have a wire diameter of 400 μm.

[0016]

Table 1

[0017] Figure 9 is a photograph of the fracture surface of the silver alloy round wire of Example 5 after the tensile test. Figure 10 is a photograph of the fracture surface of the silver alloy round wire of Comparative Example 1 after the high-temperature creep test. All the photographs in Figures 9 to 10 were taken by a field emission scanning electron microscope (FE-SEM). Note that the high-temperature creep test was carried out at a heating temperature of 200°C and a load of 9.7 N. The load was set lower than the 0.2% proof stress of each silver alloy wire.

[0018] As shown in Figure 9, the fracture surface of the silver alloy wire in Example 5 after the tensile test is smooth and no grain boundary cracking is observed. From this, it can be seen that the fracture of the silver alloy wire by the tensile test is all intragranular fracture (similar to Figure 9).

[0019] In contrast, as shown in Fig. 10, many fine grain boundary cracks (voids) were confirmed on the fracture surface of the silver alloy round wire of Comparative Example 1 after the creep test. From this, it was determined that the fracture of the silver alloy wire by the high-temperature creep test was intergranular fracture (Fig. 10 is an example). From these results, the present inventors considered that the phenomenon of intergranular fracture starting from the grain boundary can be confirmed by the high-temperature creep test of the silver alloy wire. Also, from the results of the examples shown in Table 1, it can be seen that the silver alloy wire of Example 5 has a longer time until fracture and a slower rate of grain boundary deterioration than the silver alloy wire of Comparative Example 1.

[0020] Furthermore, it was found that the grain boundary deterioration and strength of the silver alloy wire strongly depend on the grain boundary structure of the crystal grains of the silver alloy wire and are affected by the crystal orientation. By controlling the crystal structure of the silver alloy wire by controlling the composition and manufacturing method of the silver alloy wire, that is, by controlling the ratio of the special grain boundary length and the specific crystal orientation ratio of the silver alloy wire, or by containing a specific alloy element to control the ratio of the special grain boundary length, it was discovered that both grain boundary deterioration resistance and high strength can be achieved.

[0021] Although the mechanism of grain boundary deterioration of the silver alloy wire is not clear, it is speculated as follows. The higher the ratio of the special grain boundary length, the more dominant the grain boundaries with high bonding strength become. Therefore, the recrystallization of the crystal grains of the silver alloy wire at high temperature becomes slower, and the strength reduction of the silver alloy wire is less likely to progress. Furthermore, the higher the ratio of the special grain boundary length, the stronger the bonding strength of the grain boundaries even after recrystallization, so it is considered that fracture due to grain boundary deterioration is less likely to occur. On the other hand, the lower the ratio of the special grain boundary length, the more dominant the grain boundaries with low bonding strength become. Therefore, at high temperature, the silver alloy wire is likely to reduce its strength before recrystallization, and fracture due to grain boundary deterioration is likely to occur. The lower the ratio of the special grain boundary length, the weaker the bonding strength of the grain boundaries even after recrystallization, so fracture due to grain boundary deterioration is likely to occur, and as a result, it is considered that fracture from the grain boundary occurs early. Thus, using the ratio of the special grain boundary length of the silver alloy wire as an index, the occurrence of grain boundary deterioration can be predicted at the initial stage of manufacturing the silver alloy wire, so that failures and major accidents of parts using the silver alloy wire can be avoided.

[0022] Also, from the above test results, although no specific correlation was found between the ratio of the special grain boundary length and the elongation at break in the tensile test, a correlation was found between the ratio of the elongation at break in the high-temperature creep and the elongation at break in the room-temperature tensile test (i.e., the deterioration rate described later = elongation at break in high-temperature creep / elongation at break in room-temperature tensile test) and the ratio of the special grain boundary length. It was found that the larger the ratio of the special grain boundary length, the lower the deterioration rate. From these results, in this embodiment, the grain boundary deterioration resistance of the silver alloy wire is evaluated based on the deterioration rate.

[0023] Note that unless otherwise specified, the ratio of the crystal orientation <111> (<111> orientation ratio) is the crystal orientation in the wire longitudinal direction. <hkl>It means the ratio of those including an angular difference within 15 degrees with respect to the wire longitudinal direction.

[0024] That is, the silver alloy wire, conductive wire, bonding wire, semiconductor wire, and structural wire of the embodiments of the present invention are as follows. [1] A silver alloy wire containing 99.8 mass% or more of silver, the ratio of the special grain boundary length defined by the following formula (1) of crystal grains in a cross-section perpendicular to the longitudinal direction of the silver alloy wire is 30% or more, and the crystal orientation in the longitudinal direction of the silver alloy wire measured in the cross-section <hkl>Among them, the silver alloy wire is characterized in that the ratio of the crystal orientation <111> with an angular difference of 15 degrees or less with respect to the longitudinal direction of the silver alloy wire is 10% or more and 60% or less. Ratio of special grain boundary length = Σ3 to Σ29 grain boundary length / total grain boundary length (1) [2] The silver alloy wire according to [1], wherein the average crystal grain diameter of the cross section of the silver alloy wire is 2 μm or more and 15 μm or less. [3] The silver alloy wire according to [1] or [2], which contains at least one element selected from the group consisting of Pt, Ti, Zn, Au, Cu, Mg, Ni, Al, Sn, Pd, Cd, In, W, Nd, and Bi, and the concentration of the element with respect to the total amount of the silver alloy wire is 0.003% by mass or more and 0.1% by mass or less in total. [4] A silver alloy wire containing 99.8% by mass or more of silver, The ratio of the special grain boundary length defined by the following formula (1) of the crystal grains in the cross section perpendicular to the longitudinal direction of the silver alloy wire is 30% or more, The silver alloy wire contains at least one element selected from the group consisting of Pt, Ti, Zn, Au, Cu, Mg, Ni, Al, Sn, Pd, Cd, In, W, Nd, and Bi, and the concentration of the element with respect to the total amount of the silver alloy wire is 0.003% by mass or more and 0.1% by mass or less in total. Ratio of special grain boundary length = Σ3 to Σ29 grain boundary length / total grain boundary length (1) [5] The crystal orientation in the longitudinal direction of the silver alloy wire measured in the cross section <hkl>Among them, the silver alloy wire according to [4], wherein the ratio of the crystal orientation <111> with an angular difference of 15 degrees or less with respect to the longitudinal direction of the silver alloy wire is 10% or more and 60% or less. [6] The silver alloy wire according to [4] or [5], wherein the average crystal grain size of the cross section of the silver alloy wire is 2 μm or more and 15 μm or less. [7] A conductive wire using the silver alloy wire according to any one of [1] to [6]. [8] A wire for bonding using the silver alloy wire according to any one of [1] to [6]. [9] A wire for semiconductor use using the silver alloy wire according to any one of [1] to [6].

[10] A wire for structural use using the silver alloy wire according to any one of [1] to [6]. Note that the symbol "~" indicates a numerical range including the numerical values before and after it.

Advantages of the Invention

[0025] According to the silver alloy wire of the embodiment, it has high strength and high grain boundary deterioration resistance, so that high strength can be maintained even at high temperatures as an industrial wire. Also, according to the conductive wire, bonding wire, semiconductor wire, and structural wire of the embodiment, they have high strength and high grain boundary deterioration resistance, so that high strength can be maintained even at high temperatures as industrial wires.

Brief Description of the Drawings

[0026]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Mode for Carrying Out the Invention

[0027] Hereinafter, the silver alloy wire of the embodiment of the present invention will be described in detail. In the silver alloy wire of this embodiment, the "ratio of special grain boundary length" defined by the following formula (1) of crystal grains in a cross section perpendicular to the longitudinal direction of the silver alloy wire is 30% or more, and the crystal orientation in the longitudinal direction of the silver alloy wire measured in the cross section of the silver alloy wire <hkl>Among them, the ratio of the crystal orientation <111> with an angular difference of 15 degrees or less with respect to the longitudinal direction of the silver alloy wire is 10% or more and 60% or less. Note that the crystal orientation in the longitudinal direction of the silver alloy wire <hkl>Among them, the ratio of the crystal orientation <111> with an angular difference of 15 degrees or less with respect to the longitudinal direction of the silver alloy wire is hereinafter referred to as the "<111> orientation ratio", and the other crystal orientations <hkl>The same shall apply thereto.

[0028] Ratio of special grain boundary length = Grain boundary length of Σ3 to Σ29 / Total grain boundary length (1)

[0029] Also, in the silver alloy wire of another embodiment of the present invention, in the cross-section perpendicular to the longitudinal direction of the silver alloy wire, the "ratio of special grain boundary length" defined by the above formula (1) of the crystal grains is 30% or more, and at least one element selected from the group consisting of Pt, Ti, Zn, Au, Cu, Mg, Ni, Al, Sn, Pd, Cd, In, W, Nd, and Bi is contained, and the concentration of the element with respect to the total amount of the silver alloy wire is 0.003% by mass or more and 0.1% by mass or less in total.

[0030] In the silver alloy wire of this embodiment, the "longitudinal direction" refers to the progress direction of the drawing process (wire drawing, rolling) when the silver alloy wire is obtained by drawing. For example, when the silver alloy wire is a round wire, the wire drawing direction of the round wire corresponds to the longitudinal direction of the round wire (the direction perpendicular to the wire diameter). Also, when the silver alloy wire is a plate material, the rolling direction immediately after the rolling process corresponds to the longitudinal direction. In the case of a plate material, it may be cut into small pieces by being cut into a predetermined size after the rolling process. In this case, the longer distance in the small piece may not coincide with the progress direction of the rolling process, and the shorter distance may coincide with the progress direction of the rolling process. Since the rolling direction of the plate material obtained by such fragmentation can be confirmed from the processing state of the plate material surface, this rolling direction is defined as the longitudinal direction.

[0031] In the silver alloy wire of this embodiment, the "cross-section" is a cross-section perpendicular to the "longitudinal direction". Examples of the shape of the cross-section of the silver alloy wire of this embodiment include a circular shape and a substantially rectangular shape. Here, the term "substantially rectangular" is because the corners of the cross-section of the silver alloy wire (the above-mentioned plate material) obtained by the rolling process do not have 90° vertices and have a rounded shape. Also, in this embodiment, a wire with a circular cross-section is also referred to as a round wire.

[0032] Here, FIG. 1 schematically shows the "cross-section" of the round wire among the silver alloy wires of this embodiment. Fig. 2 schematically shows the "cross section" of the sheet material among the silver alloy wires of the present embodiment. In Figs. 1 and 2, the axis of symmetry L of the line symmetry of the cross section is represented by a dotted line, the intersection (center) O of the axes of symmetry of the multiple line symmetries of the cross section is represented by a black circle, and the shortest distance from the outer periphery to the center of the cross section is represented by t. In the silver alloy wire of the embodiment, when 2t is defined as the thickness, the thickness is the shortest length in the direction perpendicular to the drawing direction of the wire drawing process or the rolling direction in the rolling process. In the case of the round wire in Fig. 1, the cross section of the silver alloy wire is a circle, and the thickness 2t is equal to the diameter of the circle. In the cross section of the round wire shown in Fig. 1, the observation of the crystal structure can be performed in a rectangular range (observation region R) with a height (tens of μm to 800 μm) × width (tens of μm to 800 μm), preferably a substantially square range, centered on the center O of the cross section. In the cross section of the sheet material shown in Fig. 2, it can be performed in a rectangular range (observation region R) with a height (tens to 800 μm) × width (tens to 800 μm), preferably a substantially square range, centered on the center O of the cross section and with the four sides parallel to the four sides of the cross section respectively.

[0033] As described later, the observation of the crystal structure of the cross-section can be carried out by the electron backscattered diffraction (EBSD) method. Since the resolution of the EBSD method depends on the observation magnification, it is preferable that the observation magnification is 100 times or more in order to clearly observe the crystal structure. However, the higher the magnification, the narrower the observation area. In the case of a silver alloy wire with a large cross-sectional area, if the observation magnification is increased to a value sufficient for observing the crystal structure, the entire cross-section may not be observable. In this case, a part of the cross-section may be set as the observation region R in consideration of symmetry. When the cross-sectional area is large and the entire cross-section cannot be observed in a single observation, for example, in the case of the circular line in FIG. 1, a region including a quadrant is set as the observation region (observation region R1 indicated by the dashed line). In the cross-section of the plate material shown in FIG. 2 having only two symmetry axes, as shown in FIG. 2, observations are made at two locations, near the center and near the ends of the rectangle (observation region R1 indicated by the dashed line). In addition, in the case of a cross-section having a shape with a large number of symmetry axes, it is preferable to set two observation regions in consideration of symmetry. In this way, it is desirable to optimize the observation magnification, observation region, and observation location so that the crystal structure can be clearly observed in consideration of the observation time, the cross-sectional shape (such as symmetry) of the sample, the cross-sectional size, etc. Further, when the cross-sectional shape is a figure having one or fewer line symmetry axes or when it is difficult to determine the observation region by the above-described method, it is desirable to optimize the observation region so that the crystal structure can be clearly observed near the center of gravity of the cross-sectional figure and near the outer periphery.

[0034] Next, the ratio of the special grain boundary length will be described. The grain boundaries observed in the crystal structure are roughly divided into two types: low-angle grain boundaries and high-angle grain boundaries. The high-angle grain boundaries are further divided into two types: random grain boundaries and coherent grain boundaries. The coherent grain boundaries are low-energy grain boundaries and mainly exist from Σ1 to Σ49 in the face-centered cubic crystal. The inventors have found that in the silver alloy wire used as an industrial wire, among the coherent grain boundaries, the grain boundaries of Σ3 to Σ29 have a high correlation with the grain boundary deterioration of the silver alloy wire. Furthermore, the ratio of the grain boundary length of Σ3 to Σ29 to the total grain boundary length (hereinafter referred to as "the ratio of the special grain boundary length") affects the grain boundary deterioration of the silver alloy wire. That is, it has been found that the higher the ratio (the ratio of the special grain boundary length) of the total grain boundary length occupied by the total grain boundary length of Σ3 to Σ29, the better the grain boundary deterioration resistance (the less likely grain boundary deterioration occurs).

[0035] In the deformed microstructure and recrystallized microstructure of face-centered cubic metals, as the deformation rate increases and as recrystallization progresses, the orientations to the crystal orientations <111> and <100> tend to increase. As the deformation rate increases, the ratio of the crystal orientation <111> increases to nearly 100%. The inventors have found that the strength of the silver alloy wire having a microstructure with a <111> orientation ratio close to 100% is high, but grain boundary deterioration is likely to occur. To achieve both high grain boundary deterioration resistance and high strength, it is effective to suppress the <111> orientation ratio within a predetermined range. In the silver alloy wire of the present embodiment, by controlling both the ratio of the special grain boundary length and the <111> orientation ratio, it is possible to achieve both high grain boundary deterioration resistance and high strength.

[0036] The ratio of the special grain boundary length of the silver alloy wire of the present embodiment is 30% or more. When the ratio of the special grain boundary length of the silver alloy wire is less than 30%, grain boundaries with weak bonding strength become dominant, and grain boundary deterioration is likely to occur. Therefore, when a certain load (for example, tensile force, bending force, compressive force, etc.) is continuously applied at high temperature as an industrial wire for a long period of time, there is a risk of fracture. The upper limit of the ratio of the special grain boundary length of the silver alloy wire is not particularly limited, and it is the value excluding the case where special grain boundaries other than Σ3 to Σ29 remain. Incidentally, the ratio of the special grain boundary length of the silver alloy wire is preferably 85% or less, and more preferably 80% or less. Thereby, while improving the grain boundary deterioration resistance, it is possible to reduce the ductility and hardness reduction of the material, so that secondary processing such as winding, knitting, twisting, and bending becomes easier.

[0037] In the silver alloy wire of the present embodiment, in terms of achieving both improved grain boundary deterioration resistance and high strength, the <111> orientation ratio of the cross-section of the silver alloy wire is preferably 10% or more and 60% or less. When the <111> orientation ratio of the cross-section of the silver alloy wire is 10% or more, the strength becomes high, so it is suitable as an industrial wire. When the <111> orientation ratio of the cross-section of the silver alloy wire is 60% or less, while achieving high strength, the brittleness does not become too high, so secondary processing such as winding, knitting, twisting, and bending becomes easier.

[0038] From the above, the silver alloy wire of the present embodiment preferably has a ratio of the special grain boundary length of 30% or more and a <111> orientation ratio of 10% or more and 60% or less. By having such a metal structure, the silver alloy wire of the present embodiment can achieve both grain boundary deterioration resistance and high strength.

[0039] In the silver alloy wire of the present embodiment, in terms of achieving both improved grain boundary deterioration resistance and high strength, the ratio of the special grain boundary length is preferably 30% or more, more preferably 50% or more, and even more preferably 70% or more. The <111> orientation ratio is preferably 10% or more, more preferably 30% or more, and even more preferably 40% or more.

[0040] In the silver alloy wire of the present embodiment, the average crystal grain size in the cross section perpendicular to the longitudinal direction is preferably 2 μm or more and 15 μm or less. When the average crystal grain size is 15 μm or less, it becomes easier to improve the strength of the silver alloy wire. Further, when the average crystal grain size is 2 μm or more, it becomes easier to obtain sufficient strength while maintaining the grain boundary deterioration resistance. Note that the average crystal grain size, the ratio of the special grain boundary length, and the <111> orientation ratio can be adjusted according to the wire drawing conditions and heat treatment conditions in the manufacturing process of the silver alloy wire.

[0041] (Measurement of crystal structure) For measuring the crystal structure of the crystal plane of the cross section of the silver alloy wire of the present embodiment, the electron backscattered diffraction (EBSD: Electron Backscattered Diffraction, hereinafter referred to as "EBSD") method can be used. By measuring the crystal structure by the EBSD method, the special grain boundary length, crystal orientation, average crystal grain size, etc. can be measured with high accuracy and sufficient reproducibility. In the present invention, a grain boundary is defined as having an orientation difference of 15 degrees or more between adjacent crystal grains, and a crystal grain having an orientation difference of 15 degrees or less and 5 or more pixels is recognized as one crystal grain.

[0042] In the EBSD method, usually, when the unevenness and curvature of the sample are large, it becomes difficult to measure the grain boundary, crystal orientation, crystal grain size, etc. with high accuracy. Therefore, in order to observe the cross section of the silver alloy wire of the present embodiment by EBSD, it is useful to smoothly process the surface of the cross section after cutting the silver alloy wire. As a method for smoothly processing the surface of the cross section, there are mechanical polishing, chemical polishing, FIB processing method, etc. According to these methods, the residual strain on the surface of the cross section can be removed and a smooth surface can be obtained.

[0043] As described above, if the pretreatment of the sample is optimized, it is possible to measure and analyze the grain boundary, crystal orientation, crystal grain size, etc. of the cross section of the silver alloy wire with high accuracy by the EBSD method. Further, by measuring at three or more different locations, it becomes possible to obtain average information considering the variation.

[0044] In the EBSD method, standard data (standard pattern files) of a material having the same composition as the structure to be measured is usually used. However, in the silver alloy wire of the present embodiment, since the concentration of alloying elements other than silver in the entire silver alloy wire is as extremely low as 0.2 mass (wt)% or less, data of pure silver may be used as the standard data when measuring the crystal structure by the EBSD method. When measuring the crystal structure by the EBSD method, measurement data is acquired under the conditions of an acceleration voltage of 15 kV and a measurement interval of 0.5 to 1.5 μm.

[0045] (Calculation method of ratio of special grain boundary length) Using the measurement data obtained by the EBSD method, Σ data of CSL grain boundaries (Coincidence Site Lattice) is acquired, and the total length of grain boundary lengths of Σ3 to 29 is defined as the special grain boundary length. The total grain boundary length adopts the "Total Length" of the CSL grain boundary data, and the ratio of the special grain boundary length is obtained. The same measurement is performed at a total of three randomly selected cross-sections of the same sample, and the average value of the ratio of the special grain boundary length is obtained.

[0046] (Measurement method of crystal grain size) Using the measurement data obtained by the EBSD method, the average crystal grain size of the cross-section of the sample is calculated, and the crystal grain size can be calculated by the circle approximation method (diameter).

[0047] (Alloying elements) The silver alloy wire of the present embodiment is made of a silver alloy having a silver purity (the amount of silver relative to the total amount of the silver alloy) of 99.8 mass% or more. That is, the silver alloy wire of the present embodiment contains 99.8 mass% or more of silver relative to the total amount of the silver alloy wire. Further, the silver content in the silver alloy wire of the present embodiment is preferably 99.99 mass% or less relative to the total amount of the silver alloy wire in terms of maintaining the strength as an industrial wire for a long period. The silver alloy wire of the present embodiment is likely to achieve both grain boundary deterioration resistance and high strength by containing specific elements (alloying elements described later). In particular, by containing specific elements, it becomes easier to achieve both grain boundary deterioration resistance and high strength without controlling the <111> orientation ratio.

[0048] Silver can contain a variety of alloying metals. Depending on the amount of alloying metal contained in silver, the crystal structure of the silver alloy varies. The lower the content of the alloying metal, the more the alloying metal dissolves while maintaining the crystal structure of pure silver, resulting in a stable crystal structure, but the strength of the silver alloy tends to be low. On the contrary, when the content of the alloying metal increases, it becomes easier to precipitate exceeding the solid solubility limit of the silver alloy, and precipitates with a different crystal structure are formed within the crystal structure of pure silver. Although the silver alloy can be strengthened by the precipitates, the presence of the precipitates makes the overall crystal structure more unstable than that of pure silver, so intergranular deterioration tends to occur. The inventors have found that in a silver alloy of 99.8 mass% or more, precipitates are less likely to occur, improving the intergranular corrosion resistance of the silver alloy wire. Therefore, the silver alloy wire of this embodiment contains 99.8 mass% or more of silver and 0.2 mass% or less of elements and inevitable impurities with respect to the total amount of the silver alloy wire. Hereinafter, elements other than silver and inevitable impurities contained in the silver alloy wire are also referred to as "alloying elements".

[0049] The alloying elements other than silver contained in the silver alloy wire of this embodiment are at least one or more elements selected from the group consisting of platinum (Pt), titanium (Ti), zinc (Zn), gold (Au), copper (Cu), magnesium (Mg), nickel (Ni), aluminum (Al), tin (Sn), palladium (Pd), cadmium (Cd), indium (In), tungsten (W), neodymium (Nd), and bismuth (Bi). The content of these alloying elements is 0.2 mass% or less, preferably 0.1 mass% or less, with respect to the total amount of the silver alloy.

[0050] The content of the alloying element is preferably 0.003% by mass or more, more preferably 0.01% by mass or more, in terms of achieving both grain boundary deterioration resistance and high strength. Among them, the silver alloy wire preferably contains one of nickel (Ni) and copper (Cu). In that case, the content of nickel (Ni) is preferably 0.01% by mass or more and 0.1% by mass or less with respect to the total amount of the silver alloy, and the content of copper (Cu) is preferably 0.01% by mass or more and 0.1% by mass or less with respect to the total amount of the silver alloy. Note that the higher the purity of silver (the content ratio of silver with respect to the total amount of the silver alloy), the more the alloying element content can be reduced while achieving both grain boundary deterioration resistance and high strength. Also, the amount of the alloying element is preferably equal to or less than the amount of inevitable impurities in the silver alloy.

[0051] The silver alloy wire of the present embodiment may contain inevitable impurities in addition to silver and the above-described alloying elements. Examples of the inevitable impurities include Ca, Gd, La, P, Ge, Fe, Pb, Sc, Si, Rh, Ir, etc., and their content is usually 160 mass ppm or less, preferably 150 mass ppm or less, and more preferably 100 mass ppm or less. Note that these inevitable impurities have extremely little influence on the strength and grain boundary deterioration resistance of the silver alloy wire.

[0052] The content ratio of the elements contained in the silver alloy wire of the present embodiment is generally measured by chemical analysis such as inductively coupled plasma (ICP) emission spectrometry, but is not limited thereto. For example, it can also be measured by secondary ion mass spectrometry (SIMS analysis), glow discharge mass spectrometry (GDMS), or analysis by energy dispersive X-ray spectrometry (EDX analysis).

[0053] The wire diameter of the silver alloy wire of this embodiment is, for example, 15 μm or more and 2000 μm or less, and may be 50 μm or more, 75 μm or more, or 100 μm or more, and may also be 1500 μm or less. When the cross-sectional shape of the silver alloy wire is a perfect circle, the wire diameter is the diameter, and when it is other shapes (such as elliptical, oval, polygonal, or polygonal-like shapes shown below), the wire diameter is the length of the major axis. However, when the cross-section is polygonal or polygonal-like, the length may be measured as the width or thickness. Fig. 3 schematically shows an example of the cross-sectional shape of the silver alloy wire. As shown in Fig. 3, the cross-sectional shape of the silver alloy wire may be, in addition to the circular shape (a in Fig. 3), an elliptical shape (for example, b in Fig. 3), an oval shape (for example, c in Fig. 3), a square shape (for example, e in Fig. 3), a triangular shape (for example, d in Fig. 3), or a polygonal-like shape (for example, f and g in Fig. 3). Further, for example, when the cross-section of a plate material obtained by rolling a silver alloy wire with a circular, elliptical, or oval cross-section is slit-processed, or when a plate material is obtained by cutting from a large plate-shaped silver alloy, the shapes shown in Figs. 3h and 3i may also be used.

[0054] (Manufacturing method of silver alloy wire) Next, the manufacturing method of the silver alloy wire of this embodiment will be described. The manufacturing method of the silver alloy wire of this embodiment can be mainly divided into the following four steps, although it also depends on the cross-sectional shape of the silver alloy wire. (1) Casting process (2) Drawing process (3) Rolling process (in the case of silver alloy wire plate materials, etc.) (4) Heat treatment process

[0055] (1) Regarding the casting process An Ag alloy material is obtained by melting Ag or an Ag alloy of a predetermined purity together with an alloy element in an amount such that the target composition is achieved. For melting, a heating furnace such as an arc heating furnace, a high-frequency heating furnace, a resistance heating furnace, or a continuous casting furnace can be used. The melted Ag alloy material is drawn down in a die while being solidified to a predetermined wire diameter from the heating furnace to obtain a rod-shaped ingot (continuous casting method), or the melted silver alloy material can be cast into a mold to obtain an ingot (pouring method). Among them, from the viewpoints of yield and productivity, the continuous casting method is preferred.

[0056] In the manufacturing method of this embodiment, the melting of the Ag alloy material is preferably carried out while maintaining the upper part of the molten silver in the heating furnace in a vacuum or an inert gas atmosphere such as argon or nitrogen for the purpose of preventing the mixing of oxygen from the atmosphere. More preferably, it is vacuum melting that maintains the upper part of the molten silver in the heating furnace in an inert gas atmosphere. When molten silver comes into contact with oxygen at 973°C and 1 atmosphere, it absorbs oxygen approximately 20 times its own volume. In contrast, the gas (including oxygen) solubility of solid silver is about 0.6%. Therefore, during the solidification process of molten silver, the absorbed oxygen is released. However, if a part of the oxygen in the molten silver is not released to the outside during the solidification process and remains inside the solid silver, it will also remain inside the silver alloy wire without being released to the outside during the wire drawing process and the heat treatment process described later. The oxygen remaining inside the silver alloy wire mainly exists at the grain boundaries, and the research by the present inventors has revealed that the oxygen existing at these grain boundaries can become internal defects or react with elements that are easily oxidized in the silver alloy, contributing to grain boundary deterioration.

[0057] In order to improve the grain boundary deterioration resistance, it is preferable to suppress the generation of processing strain in the silver alloy during each manufacturing process. Therefore, in continuous casting, it is preferable to draw the silver in a semi-molten or semi-solidified state. It is preferable to control both the drawing temperature and the drawing speed simultaneously. Specifically, the drawing temperature is 1000 to 1200°C, and the drawing speed is 200 to 500 mm / s for drawing, and then rapid cooling with cooling water is preferably performed. When the drawing speed in continuous casting is 200 mm / s or more, it is difficult for the silver to solidify during the drawing process, and the frictional resistance between the inner surface of the die and the silver during drawing tends to be low. Thereby, it is possible to suppress tensile strain inside the ingot, cracks on the ingot surface, or voids inside the ingot, which are factors contributing to grain boundary deterioration. By setting the drawing speed to 500 mm / s or less, the molten state of the silver during the drawing process can be appropriately maintained. Thereby, it is possible to suppress the generation of unevenness on the ingot surface and the occurrence of molten metal leakage while maintaining a low drawing resistance.

[0058] In addition, in order to improve the intergranular deterioration resistance, it is also effective to reduce the total processing ratio up to the final wire diameter in the following wire drawing process. Therefore, it is preferable that the diameter of the ingot is small. On the other hand, if the ingot is too thin, the casting time will be long, so the productivity tends to deteriorate. Therefore, the diameter of the ingot is preferably 5 mm to 20 mm, and more preferably 8 mm to 10 mm.

[0059] (2) Regarding the wire drawing process In the wire drawing process, (1) the ingot obtained in the casting process is wire drawn. In order to suppress the <111> orientation ratio to 60% or less, the reduction area ratio in the wire drawing process is effective. Also, processing with a weak reduction area ratio is effective for controlling the grain boundaries of the crystal grains of the silver alloy wire. In the wire drawing process, it is preferable to gradually reduce the wire diameter using a plurality of diamond dies. In this case, the reduction area ratio (processing ratio) per diamond die is preferably 5% or more and 25% or less. For intermediate thick wire processing, a die with a reduction area ratio of 12 to 25% is used, and for processing close to the final wire diameter, using a die with a reduction area ratio of 5 to 15% is effective for controlling the ratio of the special grain boundary length and the crystal orientation. Note that a silver alloy wire with a non-circular cross-sectional shape can be obtained by wire drawing using 1 to 3 shaped dies close to the final cross-sectional shape at the stage close to the final wire diameter.

[0060] (3) Regarding the rolling process When producing a plate-like silver alloy wire, (2) a rolling process is performed after the wire drawing process. In the rolling process, it is preferable to gradually roll the silver alloy wire using a pair of rotating rolls. When producing a silver alloy wire with a circular cross-section, the rolling process is not performed. In the rolling process, wire drawing is performed using a non-circular die whose processed shape is the same as the cross-sectional shape of the silver alloy wire in the final die of the (2) wire drawing process, or a silver alloy wire with a circular cross-section is obtained by the (2) wire drawing process, and this silver alloy wire can be pressed from the surface in the thickness direction to obtain a silver alloy wire plate material with the final shape. When the rolling process is performed, a low reduction rate is effective due to high strength and high intergranular deterioration resistance, and the reduction rate is preferably 20% or more and 85% or less. However, the lower the reduction rate, the more the number of steps to obtain the final shape increases, and the production cost becomes higher. The reduction rate is the reduction rate of the thickness (in the rolling direction) before and after each rolling from the cross-sectional diameter of the round wire with a circular cross-section.

[0061] (4) Heat treatment process It is preferable to perform heat treatment on the silver alloy wire with the final wire diameter obtained through the processes of (1) to (3) or the silver alloy wire plate material rolled into the final shape (heat treatment process). In the heat treatment process, it is effective to perform heat treatment once or multiple times. When performing multiple heat treatments, it is effective to reduce the processing rate of the (2) wire drawing process and the rolling processing rate of the (3) rolling process. The processing rate of the (2) wire drawing process is defined as the change rate of the cross-sectional area from the wire diameter in the heat treatment immediately before the final wire diameter (the wire diameter of the last intermediate heat treatment) to the final wire diameter.

[0062] As heat treatment methods in the heat treatment process, there are a running wire heating heat treatment method in which a silver alloy wire is heated while being continuously run, a running wire energization heat treatment method in which a voltage is applied while the silver alloy wire is continuously run for heat treatment, a batch treatment method in which the silver alloy wire is accommodated in a constant temperature heating furnace and heated, and the like. For controlling the ratio of the special grain boundary length and the orientation ratio of the silver alloy wire of the present embodiment, heat treatment at a low temperature for a long time is effective. As heat treatment conditions in the case of the running wire heating heat treatment method, it is preferably 300°C to 900°C and the running speed is 10 to 200 m / min. As heat treatment conditions in the case of the running wire energization heat treatment method, it is preferably a voltage of 5V to 20V and the running speed is 10 to 200 m / min. Further, it is preferable to perform heat treatment in an electric furnace under a gas atmosphere in which nitrogen (N2) gas or a gas atmosphere in which a small amount of hydrogen (H2) gas is mixed with nitrogen (N2) gas.

[0063] (Tensile test) The maximum stress (MPa) is obtained by dividing the maximum breaking strength (N) at the time of breaking by pulling both ends of the evaluation sample with a tensile test apparatus by the cross-sectional area of the evaluation sample. This maximum stress is automatically calculated by converting the pulling force into an electrical signal in the tensile test apparatus. The elongation rate is obtained by dividing the elongation at the time of breaking by the length of the sample before the test. Further, the 0.2% proof stress (MPa) is obtained by dividing the 0.2% proof strength (N) obtained from the tensile test by the cross-sectional area of the evaluation sample. The tensile test can be performed according to JIS Z2241. Further, the tensile test is performed on 5 evaluation samples, and the maximum stress and elongation rate can be the average values of 5 measurement values. Further, the stress (MPa) uses a value based on the conversion formula of 1 kgf / mm 2 = 9.8 MPa. The cross-sectional area of the plate material is calculated by width × thickness.

[0064] (Uses of silver alloy wire) The silver alloy wire of the present invention can be used for the same uses as all industrial wires for which copper-based materials and aluminum-based materials have been conventionally used. Specifically, it can be suitably used as a wire for conduction, a wire for bonding, a wire for semiconductors, a wire for structures, and the like. Since the cost of silver ingots is high, the silver alloy wire of the present embodiment is particularly suitable for applications that place importance on high functionality, high reliability, and high added value rather than cost.

[0065] Examples of the conductive wire include electric wires and cables. Examples of the bonding wire include the wire for connecting the electrode of the lithium-ion battery and the bus bar in the lithium-ion battery module mounted on an electric vehicle. Examples of the semiconductor wire include bonding wires that join members forming an electric circuit within a semiconductor module, such as between semiconductor chips, between a semiconductor chip and an external electrode, between circuit patterns on a semiconductor substrate, between a circuit pattern and a semiconductor chip, and between a circuit pattern and an external electrode. Examples of the structural wire include meshes and nets for current collectors used in batteries, etc., and coils (windings) of small generators and motors used in medical devices and other equipment. Further, the silver alloy wire of the embodiment can be preferably used as the stranded wire material for the above conductive, bonding, and structural uses.

[0066] More specifically, the conductive wire (conductive line) includes power electric wires such as overhead transmission lines, optical fiber composite overhead ground wires (OPGW), underground electric wires, and submarine cables, communication electric wires such as telephone cables and coaxial cables, cables for wired drones, cab tire cables, EV / HEV charging cables, twisted cables for offshore wind power generation, elevator cables, umbilical cables, robot cables, equipment electric wires such as trolley wires for electric trains, automotive wire harnesses, ship electric wires, aircraft electric wires, etc., bus bars, lead frames, flexible flat cables, lightning rods, antennas, connectors, terminals, and braiding of cables.

[0067] (For semiconductor wire) Next, as an example of using the silver alloy wire of the above-described embodiment for a semiconductor wire, a power semiconductor device will be described.

[0068] (For power semiconductor device) FIG. 4 is a diagram schematically showing a semiconductor device 103 using the silver alloy wire of the embodiment. The configuration of the semiconductor device 103 using the silver alloy wire of the embodiment will be described with reference to FIG. 4.

[0069] As shown in FIG. 4, the semiconductor device 103 includes a semiconductor element 1, a metal film 2, a wire 3, a circuit pattern 41, a metal pattern 42, an insulating member 43, a heat dissipation member 5, a bonding material 6, a case 7, a terminal 8, and a sealing material 9.

[0070] The semiconductor element 1 is, for example, a power semiconductor used for power supply. Examples of the semiconductor element 1 include a metal oxide semiconductor field effect transistor (MOSFET), an insulated gate bipolar transistor (IGBT), and the like.

[0071] The semiconductor element 1 is formed by laminating an electrode 11, a substrate portion 13, and a back surface electrode 12 in this order. The electrode 11 is, for example, an aluminum (Al)-silicon (Si) electrode, and the substrate portion 13 is, for example, a silicon (Si) substrate, a silicon carbide (SiC) substrate, a gallium nitride (GaN) substrate, or the like.

[0072] The metal film 2 is provided so as to cover the surface of the electrode 11 on the surface opposite to the substrate portion 13 of the electrode 11. The metal film 2 is a nickel (Ni) film, a copper (Cu) film, a titanium (Ti) film, a tungsten (W) film, or the like, and is a film formed by electroplating, electroless plating, vapor deposition, sputtering, or the like.

[0073] The wire 3 is made of the silver alloy wire of the above-described embodiment, and its configuration and characteristics are also as described above. The wire 3 is joined to the surface of the metal film 2.

[0074] In the semiconductor device 103, a semiconductor circuit is formed by the semiconductor element 1, the wire 3, the terminal 8, the circuit pattern 41, and the metal pattern 42. In the semiconductor device 103, the wire 3 is bent, and using this bent portion, the wire 3 is joined to the semiconductor element 1, the terminal 8, the circuit pattern 41, etc., respectively.

[0075] In the semiconductor device 103, a bonding material 6, a metal pattern 42, an insulating member 43, a circuit pattern 41, a bonding material 6, and a semiconductor element 1 are laminated in this order on the surface of the heat radiating member 5. The bonding material 6 bonds the heat radiating member 5 to the metal pattern 42, and the circuit pattern 41 to the back surface electrode 12 of the semiconductor element 1, respectively. The insulating member 43 is an insulating substrate or the like.

[0076] The case 7 is formed of an annular housing having a space inside, and is provided so as to surround the outer periphery of the heat radiating member 5. The semiconductor element 1, the metal film 2, the wire 3, the circuit pattern 41, the metal pattern 42, the insulating member 43, the bonding material 6, and the sealing material 9 described above are accommodated in the internal space of the case 7.

[0077] The terminal 8 functions as a connection terminal to an external device. The terminal 8 is provided on the upper surface of the case 7, and one end thereof protrudes from the case 7 into the internal space of the case 7, and the other end protrudes from the case 7 into the outer region of the case 7. The sealing material 9 fills the internal space of the case 7, encapsulating the semiconductor element 1, the metal film 2, the wire 3, the circuit pattern 41, the metal pattern 42, the insulating member 43, and the bonding material 6. The sealing material 9 is a cured product of a gel-like sealing resin or a molding resin.

[0078] The semiconductor device 103 shown in FIG. 4 may have a plurality of semiconductor elements 1, electrodes 11 on the plurality of semiconductor elements 1, a plurality of circuit patterns 41, and a plurality of terminals 8. The semiconductor device 103 preferably has an electrode-circuit pattern bonding structure including one electrode 11 out of the electrodes 11 on the plurality of semiconductor elements 1, one circuit pattern 41 out of the plurality of circuit patterns 41, and a wire 3 connecting the electrode 11 and the circuit pattern 41. Further, the semiconductor device 100 preferably has an electrode-terminal connection structure including one terminal 8 out of the plurality of terminals 8, one electrode 11 out of the plurality of electrodes 11, and a wire 3 connecting the terminal 8 and the electrode 11. Furthermore, the semiconductor device 100 preferably has a circuit pattern-terminal connection structure including one terminal 8 out of the plurality of terminals 8, one circuit pattern 41 out of the plurality of circuit patterns 41, and a wire 3 connecting the terminal 8 and the circuit pattern 41. The semiconductor device 100 preferably includes one or more, and more preferably two or more, of the electrode-circuit pattern bonding structure, the electrode-terminal connection structure, and the circuit pattern-terminal connection structure. That is, the silver alloy wire of the embodiment can be used for connecting the electrode 11 and the circuit pattern 41, connecting the terminal 8 and the electrode 11, or connecting the terminal 8 and the circuit pattern 41.

[0079] The semiconductor device 103 may have a plurality of circuit patterns 41, and preferably includes a circuit pattern bonding structure including a wire 3 connecting two adjacent circuit patterns out of the plurality of circuit patterns 41. The semiconductor device 103 preferably includes one or more, and more preferably two or more, of the circuit pattern bonding structures. That is, the silver alloy wire of the embodiment can be used for connecting the circuit pattern 41 and the circuit pattern 41.

[0080] The semiconductor device 103 may further have a substrate (substrate on the semiconductor element) on the semiconductor element 1. In this case, the semiconductor device 103 preferably has a bonding structure including the substrate on the semiconductor element and a wire 3 connecting the circuit pattern 41.

[0081] In the field of semiconductors, heretofore, the development of silver alloy wires for ball bonding has been progressing. As silver alloy wires for ball bonding, for example, Patent Document 1 discloses a composite silver wire aimed at avoiding the problem of copper oxidation, having good mass productivity, and keeping the manufacturing cost low. The composite silver wire contains gold in an amount of 4% by mass or more and 8% by mass or less, and contains palladium in an amount of 2 to 4% by mass. Patent Document 2 discloses an alloyed silver wire having an average diameter in the range of 8 to 80 μm, containing palladium in an amount in the range of 3 to 6 wt%, gold in an amount in the range of 0.2 to 2 wt%, and other metals. Patent Document 3 discloses a method for manufacturing a silver palladium alloy wire. Patent Document 4 discloses a silver alloy wire containing a silver component of 94.1 to 98.5% by weight and a palladium component of 1.5 to 5.9% by weight.

[0082] The silver alloy wire for ball bonding is joined to the electrode of a semiconductor element by a method called ball bonding. Ball bonding is performed as follows. With the tip of the silver alloy wire in the vertical direction, an arc discharge is formed between the wire and a discharge torch by an electron frame off (EFO) method, and heat is applied to the tip of the wire by the discharge current. Due to this applied heat, the tip of the wire is heated and melted. The molten metal rises along the wire due to its surface tension, and a true spherical molten ball is formed at the tip of the wire, and a free air ball (FAB) is formed by solidification. Then, while heating the electrode of the semiconductor element to about 140 to 300 °C, a free air ball is pressure-bonded onto the electrode while applying ultrasonic waves, whereby one end of the wire is joined onto the aluminum electrode. The joined electrode is generally sealed with a thermosetting epoxy resin for protection from external environments such as heat, dust, moisture, and light.

[0083] In the resin-sealed state, an intermetallic compound is formed between the ball of the silver alloy wire and the aluminum electrode (referred to as the bonding interface). Since the properties of this metal compound are unstable, it easily reacts with moisture, sulfur, etc. contained in the resin, and is likely to cause a decrease in bonding strength and an increase in electrical resistance with use in a high-temperature and high-humidity environment. When the bonding reliability decreases due to the decrease in bonding strength and the increase in electrical resistance, in the above prior art, in order to improve the bonding reliability of the bonding interface of the wire, a silver alloy wire with a silver purity of 99% by mass or less has been proposed.

[0084] In the conventional silver alloy wire, improvement in the reliability of the bonding interface has been confirmed by the effects of a highly accelerated stress test (HAST) based on JESD22-A110 and a thermal humidity bias life test (THB) based on JESD-A101. However, these conventional silver alloy wires have improved the reliability of the bonding interface, but the performance improvement of the silver alloy wire itself has not been achieved, so they are not suitable for processing. Also, since the purity of the silver alloy is low, the excellent electrical conductivity and excellent thermal conductivity of silver itself are impaired.

[0085] On the other hand, according to the silver alloy wire of the above-described embodiment, since the purity of silver is higher than that of the conventional silver alloy wire, it has excellent electrical conductivity and thermal conductivity. Also, it is possible to achieve both excellent electrical conductivity and thermal conductivity and good strength. Furthermore, since grain boundary deterioration hardly occurs, it is difficult to break even when a predetermined load continues to be applied, and the strength is also easily maintained even at high temperatures in industrial wires. From these facts, the silver alloy wire of the embodiment is extremely suitable for high-performance and multifunctional products using advanced industrial technologies.

[0086] When the silver alloy wire of the above-described embodiment is used as a wire for a semiconductor, the cross-section of the silver alloy wire is preferably circular, and its diameter (wire diameter) is preferably 15 μm or more and 700 μm or less, and more preferably 80 μm or more and 600 μm or less. When the cross-section of the silver alloy wire is elliptical or oval, the length of the major axis is preferably 0.3 mm or more and 4 mm or less, and the length of the minor axis is preferably 0.05 mm or more and 0.5 mm or less. When the cross-section of the silver alloy wire is square, the length of the long side is preferably 0.3 mm or more and 4 mm or less, and the length of a single side is preferably 0.05 mm or more and 0.5 mm or less. In particular, when the silver alloy wire of the above-described embodiment is used as a wire for a power semiconductor, its diameter (wire diameter) is preferably 80 μm or more and 600 μm or less, and more preferably 100 μm or more and 500 μm or less. When the cross-section of the silver alloy wire is square, the length of the long side is preferably 0.5 mm or more and 2 mm or less, and the length of the short side is preferably 0.1 mm or more and 0.3 mm or less.

[0087] (Wire for bonding) Next, a case where the silver alloy wire of the embodiment is applied to the connection between the bus bar of a lithium-ion battery module of an electric vehicle and the electrode of a lithium-ion battery as a wire for bonding will be described.

[0088] FIG. 5 is a diagram schematically showing a part of a lithium-ion battery module. The lithium-ion battery module shown in FIG. 5 includes a lithium-ion battery 51, a cathode-side bus bar 52, an anode-side bus bar 53, and a silver alloy wire 50 that electrically connects the lithium-ion battery 51 and the cathode-side bus bar 52. Further, the lithium-ion battery module shown in FIG. 5 further includes another silver alloy wire 50 that electrically connects the lithium-ion battery 51 and the anode-side bus bar 53. The silver alloy wire 50 used is the silver alloy wire of the above-described embodiment. In the lithium-ion battery module shown in FIG. 5, the anode and the cathode are respectively arranged on the upper surface and the lower surface of the columnar lithium-ion battery, and are usually mounted on the vehicle with the anode on the top and the cathode on the bottom.

[0089] FIG. 6 is a diagram schematically showing a part of another form of a lithium ion battery module. The lithium ion battery module shown in FIG. 6 includes a lithium ion battery 51, a cathode side bus bar 52, an anode side bus bar 53, and a silver alloy wire 50 that electrically connects the lithium ion battery 51 and the cathode side bus bar 52. Further, the lithium ion battery module shown in FIG. 14 further includes another silver alloy wire 50 that electrically connects the lithium ion battery 51 and the anode side bus bar 53. As the silver alloy wire 50, the silver alloy wire of the above-described embodiment is used. In the lithium ion battery module shown in FIG. 6, both the anode and the cathode are respectively disposed at the center and the outer edge of the upper surface of the columnar lithium ion battery, and are usually mounted with the anode facing up.

[0090] In the joining of the bus bar and the silver alloy wire and the joining of the electrode of the lithium ion battery and the silver alloy wire (wire bonding) in this lithium ion battery module, the silver alloy wire of the above-described embodiment is suitable. The silver alloy wire of the above embodiment can achieve both excellent conductivity and thermal conductivity and good strength. Further, since grain boundary deterioration hardly occurs, it is difficult to break even when a predetermined load is continuously applied, and the strength is easily maintained even at high temperatures in industrial wires. For these reasons, by applying the silver alloy wire of the embodiment to the lithium ion battery module, it is possible to contribute to the high performance and multi-functionality of the lithium ion battery module. Also, since it is difficult to break even when a predetermined load is continuously applied, and the strength is easily maintained even at high temperatures in industrial wires, it has high safety and low electrical resistance (high electrical conductivity), so it hardly generates heat and has a high temperature (for example, 80 ° C or higher). The safety of lithium ion batteries at risk of explosion can be further enhanced.

[0091] When using the silver alloy wire of the above-described embodiment as a bonding wire, the cross-section of the silver alloy wire is preferably a rectangular plate material (also referred to as a ribbon material), and its wire diameter (major axis) is preferably 80 μm or more and 600 μm or less, and more preferably 100 μm or more and 500 μm or less. When the cross-section of the silver alloy wire is square, the length of the long side is preferably 0.5 mm or more and 2 mm or less, and the length of the short side is preferably 0.1 mm or more and 0.3 mm or less.

[0092] As described above, the embodiments of the present invention have been described. However, the present invention is not limited to the above embodiments, and includes all aspects included in the concept and claims of the present invention, and can be variously modified within the scope of the present invention.

Examples

[0093] Next, examples will be described. The present invention is not limited to the following examples.

[0094] <Silver alloy wire (round wire)> The silver alloy wire of the example was produced as follows. High-purity silver ingots with a purity of 99.99 mass% or more were prepared. Alloying elements were added to this silver ingot, and after vacuum melting in an inert atmosphere, continuous casting was performed to obtain a silver wire rod (an ingot with a diameter of 8 mm). The ingot was subjected to wire drawing in two stages, from the intermediate wire diameter to 0.9 mm and from the intermediate wire diameter to the final wire diameter. In the wire drawing process, the area reduction rate (processing rate) per die from the initial diameter to the intermediate wire diameter was 12% or more and 25% or less, and the area reduction rate (processing rate) per die from the intermediate wire diameter to the final wire diameter was 5% or more and 15% or less. The final wire diameter of the silver alloy wire of the example is shown in Tables 2 to 4. The silver alloy wire processed to the final wire diameter was subjected to a final heat treatment in an electric heating furnace. As the conditions for electric heating, the voltage value was 5 V or more and 20 V or less, the distance between the electrode terminals was 800 mm or more and 1300 mm or less, and the wire running speed was 50 m / min or more and 200 m / min or less. The silver alloy wire after the final heat treatment was rewound onto a spool by a rewinding machine in lengths of about 100 m each. Thereby, a silver alloy wire (round wire) having a circular cross-section was obtained.

[0095] The silver alloy wires of the comparative examples were produced as follows. Similar to the examples, silver ingots with a purity of 99.99 mass% or more were prepared, and alloying elements were added to these silver ingots to obtain silver base wires. Subsequently, wire drawing was performed on the silver base wires. In the wire drawing process, the manufacturing conditions such as the heat treatment temperature and time at the intermediate wire diameter and the final wire diameter, the processing ratio from each wire diameter to the next wire diameter, the cooling rate after the intermediate heat treatment, and the area reduction ratio of each die were changed outside the range of the manufacturing conditions of the above examples to produce the silver alloy wires of each comparative example.

[0096] For example, in the silver alloy wire of Comparative Example 2, the area reduction ratio per die up to the intermediate wire diameter was less than 12%, the area reduction ratio per diamond die from the intermediate wire diameter to the final wire diameter was more than 15%, and the final heat treatment was performed with a running speed larger than the range adopted in the examples. In the silver alloy wire of Comparative Example 1, the area reduction ratio per die up to the intermediate wire diameter was less than 12%, the area reduction ratio per die from the intermediate wire diameter to the final wire diameter was less than 5%, and the final heat treatment was performed with a voltage value smaller than the range adopted in the examples. In the silver alloy wire of Comparative Example 5, the area reduction ratio per die up to the intermediate wire diameter was less than 12%, the area reduction ratio per die from the intermediate wire diameter to the final wire diameter was less than 5%, and the final heat treatment was performed with a running speed smaller than the range adopted in the examples. In the silver alloy wire of Comparative Example 6, the area reduction ratio per die up to the intermediate wire diameter was more than 25%, the area reduction ratio per die from the intermediate wire diameter to the final wire diameter was more than 15%, and the final heat treatment was performed with a voltage value larger than the range adopted in the examples. In the silver alloy wire of Comparative Example 12, the area reduction ratio per die up to the intermediate wire diameter was more than 25%, the area reduction ratio per diamond die up to the final wire diameter was less than 5%, and the final heat treatment was performed with a running speed smaller than the range adopted in the examples.

[0097] (Measurement of the ratio of the special grain boundary length, crystal orientation, and average crystal grain size of the cross-section of the silver alloy wire) The ratio of the special grain boundary length and the crystal orientation of the cross section of the silver alloy wires in the examples and comparative examples were measured as follows. The silver alloy wires were cut into several centimeters in length, and multiple evaluation samples were prepared. While taking care that the evaluation samples did not stretch or sag, they were attached straight and flat onto a metal plate (Ag plating frame was used, but it is not limited to this as long as it is a metal plate capable of fixing the evaluation sample). Then, the evaluation samples together with the metal plate were placed into a cylindrical mold such that the metal plate became the bottom surface of the cylinder, and then embedding resin was poured into the mold. Subsequently, a curing agent was added to cure the resin. Subsequently, the cylindrical resin containing the cured evaluation sample was roughly polished with a polishing machine so that the cross section of the silver alloy wire was exposed. Then, the cut surface was finished by final polishing. Subsequently, ion milling was performed to remove the residual strain on the polished surface to obtain a smooth surface. The ion milling apparatus was finely adjusted so that the cut surface of the silver alloy wire was perpendicular to the longitudinal direction of the silver alloy wire.

[0098] The cross section of the silver alloy wire of the evaluation sample (i.e., the polished surface of the evaluation sample) was attached to the sample stage of a field emission scanning electron microscope (FE-SEM, JSM-7800F manufactured by JEOL) so as to be parallel to the sample stage. Using FE-SEM, an observation magnification of 200 times, an acceleration voltage of 15 keV, a measurement area of approximately 420×420 μm, a measurement interval (Step Size) of 0.7 μm, and a standard phase (Phase) of silver were set, and information on the crystal structure such as the crystal orientation and crystal grain size of the cross section was obtained. The EBSD measurement data thus obtained were analyzed using dedicated analysis software (OIM analysis manufactured by TSL). In this example and the comparative examples, it was set such that when the angular difference was 15 degrees or less and five or more pixels were connected, they were recognized as one crystal grain.

[0099] In the analysis of EBSD measurement data, there may be regions where orientation data cannot be measured due to the roughness of the measurement surface, residual strain due to polishing, contamination, the presence of an oxide film, etc. Therefore, the cleaning function provided in the analysis software was used to replace the orientation data of points that could not be measured properly with the data of pixels where normal measurements were made in the surrounding area, thus complementing the incomplete parts of the measurement. This method is effective for removing points that could not be measured properly when they are sparse. However, if the cleaning process becomes excessive, the noise in the projected image increases. For example, regarding the recognition of crystal grains, it was assumed that five or more pixels with an orientation difference of 15 degrees or less were connected, and the Grain Dilation method was performed once, and further, the Grain CI Standardization method was performed once. Also, even if orientation data can be measured, the reliability of the measured data may be low. A reliability was set, and based on this reliability, analysis data was obtained. That is, parts where orientation data could not be measured or parts with low reliability even if measured were excluded to obtain analysis data. Here, the reliability may have parameters prepared in the analysis software. For example, several parameters such as Confidential Index (CI value) and Image Quality (IQ value) can be used to select the judgment criteria according to the sample state, analysis purpose, etc.

[0100] (Measurement of the ratio of special grain boundary length) From the data analyzed above, Σ data of CSL grain boundaries (Coincidence Site Lattice) was obtained, and the total grain boundary length of Σ3 to 29 was defined as the special grain boundary length. The total grain boundary length was adopted as the "Total Length" of the CSL grain boundary data, and the ratio of the special grain boundary length was calculated. The same measurement was performed on a total of three randomly selected cross-sections of the same sample, and the average value of the ratio of the special grain boundary length was obtained.

[0101] (Measurement of the <111> orientation ratio) The <111> orientation ratio was calculated from the data analyzed above.

[0102] (Method for measuring crystal grain size) From the analyzed data above, the average crystal grain size of the cross-section of the sample was calculated by the circle approximation method (diameter).

[0103] The ratio of the special grain boundary length, the <111> orientation ratio with an angular difference of 15 degrees or less with respect to the longitudinal direction, and the average crystal grain size in the cross-section (transverse cross-section) perpendicular to the longitudinal direction of each silver alloy wire of the examples and comparative examples obtained as described above are shown in Tables 2 to 4 below.

[0104] (Measurement of alloy element concentration) The concentrations of alloy elements (excluding inevitable impurities) in each silver alloy wire of the examples and comparative examples were measured as follows. Approximately 1 to 3 g of the prepared silver alloy wire was placed in dilute nitric acid, dissolved, and then the dissolved solution was collected. Hydrochloric acid was added to this dissolved solution, and the volume was fixed with ultrapure water. When the silver alloy wire contained Au, when making the fixed volume solution, the residue left after filtration was dissolved in aqua regia diluted, and the volume was fixed with ultrapure water. The concentrations of each element in these fixed volume solutions were determined by high-frequency inductively coupled plasma optical emission spectrometry (manufactured by Shimadzu Corporation, ICPE-9000). The alloy elements measured here are Pt, Ti, Zn, Au, Cu, Mg, Ni, Al, Sn, Pd, Cd, In, W, Nd, Bi, and are shown as the concentration (mass%) with respect to the total amount of the silver alloy wire. The results are shown in the table below. Also, the compositions of the obtained silver alloy wires of the examples and comparative examples are shown in Tables 2 to 4.

[0105] Using the silver alloy wires of the examples and comparative examples, characteristic evaluations were performed under the conditions and methods shown below. The results are shown in Tables 2 to 4.

[0106] (Tensile test) Each silver alloy wire of the examples and comparative examples was cut out to be slightly longer than 100 mm in length to obtain an evaluation sample. For the evaluation sample at room temperature of 15 to 28°C, the tensile strength, that is, the maximum endurance (N), was measured by a tensile test. The maximum endurance was calculated as the maximum value when the evaluation sample was pulled at a speed of 20 mm / min, with a load cell rating of 100 N and a measurement length of 100 mm using a tensile test apparatus (universal testing machine: AGS-X manufactured by SHIMADZU), until breakage occurred. The maximum endurance is the force applied to the evaluation sample pulled at the above speed, and usually, the tensile force is converted into an electrical signal by a load cell and automatically calculated. Considering the variation in the measurement results, the average value of three samples was obtained for the maximum endurance. The maximum stress (MPa) was obtained by dividing the maximum endurance by the cross-sectional area of the evaluation sample. Also, from the results of this tensile test, the elongation rate (elongation at break, %) and the 0.2% proof stress when the sample broke were obtained. Note that the elongation at break obtained in the above tensile test is denoted as "elongation rate A".

[0107] Regarding the tensile strength of the silver alloy wire, the evaluation was carried out as follows. Those with a maximum stress exceeding 180 MPa and less than or equal to 250 MPa were evaluated as having excellent strength as an industrial wire and indicated by the symbol "A". Those with a maximum stress exceeding 160 MPa and less than or equal to 180 MPa were evaluated as having good strength as an industrial wire and indicated by the symbol "B". Those with a maximum stress exceeding 140 MPa and less than or equal to 160 MPa were evaluated as being at a level without practical problems and indicated by the symbol "C". Those with a maximum stress less than or equal to 140 MPa were evaluated as having a potential for practical problems and indicated by the symbol "D". Note that those with a maximum stress exceeding 250 MPa were evaluated as having extremely high strength but, therefore, high brittleness and not being suitable for secondary processing, and indicated by the symbol "(A)". In the case of a silver alloy wire evaluated as "(A)", chip damage is likely to occur when used as a wire for semiconductor bonding.

[0108] (High-temperature creep test) Each silver alloy wire of the examples and comparative examples was cut out to be slightly longer than 100 mm in length to obtain an evaluation sample. For the high-temperature creep test, using a tensile testing apparatus (universal testing machine: AGS-X manufactured by SHIMADZU), with a measurement length of 100 m, a temperature of 200 °C, and a load of approximately 0.9 times the 0.2% proof stress of each example and comparative example (i.e., load ≒ 0.2% proof stress × 0.9), the evaluation sample was continuously pulled at a constant load, and the time until fracture (fracture time) and the elongation rate at the time of fracture (fracture elongation rate, %) were measured. Note that the fracture elongation rate obtained in the above high-temperature creep test is denoted as "elongation rate B".

[0109] (Calculation of deterioration rate) Using the elongation rate A obtained in the above tensile test and the elongation rate B obtained in the above high-temperature creep test, the deterioration rate was calculated by the following formula (2). The larger the deterioration rate, the more likely the grain boundary deterioration progresses due to high temperature. Those with a deterioration rate of 0.3 or less were evaluated as having excellent grain boundary deterioration resistance and indicated by the symbol "A". Those with a deterioration rate exceeding 0.3 and less than or equal to 0.7 were evaluated as having good grain boundary deterioration resistance and indicated by the symbol "B". Those with a deterioration rate exceeding 0.7 and less than or equal to 1 were evaluated as having slightly inferior grain boundary deterioration resistance but at a level where there are no practical problems and indicated by the symbol "C". Those with a deterioration rate exceeding 1 were evaluated as having poor grain boundary deterioration resistance and indicated by the symbol "D". Deterioration rate = "Elongation rate B" / "Elongation rate A" (2)

[0110] (Comprehensive evaluation) Based on the evaluations of the strength and grain boundary deterioration resistance obtained above, a comprehensive evaluation was performed as follows. When both of the two evaluations of strength and grain boundary deterioration resistance are A, it was indicated as "S" as being extremely excellent. When one of the two evaluations is A and the other is B, it was regarded as excellent and denoted as "A". When one of the two evaluations is A and the other is C and when both are B, it was regarded as good and indicated by "B". When one of the two evaluations is B and the other is C and when both are C, it was regarded as passing and indicated by "C". When one of the two evaluations is D, it was regarded as failing and indicated by "D". Summarizing the above, regardless of the order of the evaluations in the parentheses, it is as follows. Comprehensive evaluation S: The two evaluations are (A, A) Comprehensive Evaluation A: The two evaluations are (A, B) Comprehensive Evaluation B: The two evaluations are (A, C) or (B, B) Comprehensive Evaluation C: The two evaluations are (B, C) or (C, C) Comprehensive Evaluation D: The two evaluations are (D, D), (C, D), (B, D), (A, D)

[0111]

Table 2

[0112]

Table 3

[0113]

Table 4

[0114] <Evaluation of Rolled Silver Alloy Sheet Silver alloy wires with the same composition and the same final wire diameter as those of the examples and comparative examples of the Ag alloy wires shown in Tables 2 to 4, and with the same processing conditions, were rolled into a plate shape in one pass with the aim of the final thickness of the plates shown in Tables 5 to 7, to obtain silver alloy sheets of Examples 101 to 138 and Comparative Examples 101 to 112. After rolling, final heat treatment was performed under the following conditions. The conditions for the electric heating of the final heat treatment in the examples are a voltage value of 5 V or more and 20 V or less, a distance between electrode terminals of 800 mm or more and 1300 mm or less, and a wire running speed of 50 m / min or more and 200 m / min or less. The conditions for the electric current of the final heat treatment of Comparative Examples 101 to 104 and 107 to 111 are a voltage value of 5 V and a running speed of 210 m / min. The conditions for the electric current of the final heat treatment of Comparative Examples 106 and 112 are a voltage value of 20 V and a running speed of 40 m / min. The conditions for the electric current of the final heat treatment of Comparative Example 105 are a voltage value of 21 V and a running speed of 50 m / min. Using the obtained ribbon-shaped silver alloy wires (plates), the crystal structure was observed and evaluated in the same manner as in the examples. The results are shown in Tables 5 to 7. In Tables 5 to 7, w represents the width of the plate and t represents the thickness.

[0115]

Table 5

[0116]

Table 6

[0117]

Table 7

[0118] (Examples of wire for bonding and wire for semiconductor) Using the silver alloy wires of the examples and comparative examples with a wire diameter of 400 μm in Tables 2 to 4 and the silver alloy plates of the examples and comparative examples with w1×t 0.1 mm in Tables 5 to 7, a bonder BJ935 manufactured by HESSE was used to continuously bond them to an aluminum plate with a length of 50 mm, a width of 50 mm, and a thickness of 1 mm, and the bonding shape and bonding strength after bonding were evaluated. The bonding conditions were set at two conditions of Duration 50 ms, Power 40 V, and loads of 1500 gf and 2500 gf. For each sample, with the combination of the first bond and the second bond as n = 1 (1 set), continuous bonding was performed in 20 sets (n = 20), and evaluation samples for the bonding shape and bonding strength were prepared respectively. In this example, although the aluminum plate was used as the bonding target for evaluation, the bonding target is not limited to this, and for example, a copper plate or a nickel plate may be used instead.

[0119] (Evaluation method of bonding shape) The number of non-bonded joints and the number of shape defects of the evaluation samples prepared above were observed with an optical microscope. When both the number of non-bonded joints and the number of defects were 0, it was evaluated as "S", meaning it was very excellent. When either the number of non-bonded joints or the number of defects was 1, it was evaluated as "A", meaning it was good. When the total number of non-bonded joints and the number of defects was 2 or more and 3 or less, although there were points to be improved, since it was less likely to cause problems in terms of practical use due to the optimization of bonding conditions, it was designated as "B". When the total number of non-bonded joints and the number of defects was 4 or more, it was regarded as unqualified and designated as "C". The results are shown in Table 8. Note that the determination of the bonding shape was based on Figure 7. The photograph in Figure 7 is a photograph of the joint part of the silver alloy wire observed from above the bonding surface, and the silver alloy wires are arranged horizontally on the paper. The same applies to Figure 8. In the photograph of Figure 7, the burrs (the part surrounded by the dotted line) of the silver alloy wire around the joint can be seen. In the determination of bonding defects, when the burrs of the silver alloy wire around the joint were equal to or more than the area ratio (ratio to the entire joint part) in Figure 7, it was determined as a bonding shape defect, and when the burrs were smaller than those in Figure 7, it was determined as a qualified bonding shape. Figure 8 is a photograph of an example where the bonding shape is qualified. Note that when there are burrs around the joint, when it is mounted on a semiconductor device or the like, the possibility of damage to the chip or substrate is very high.

[0120] (Bonding Strength Evaluation Method) A pull test was conducted at the center of the loop of the evaluation samples prepared above, and the number of occurrences of joint lift-off in the pull test was evaluated. In the pull test with n = 20, when the number of occurrences of lift-off was 3 or more, it was regarded as unqualified and designated as "C". When the number of occurrences of lift-off was 2, although there were points to be improved, since it was less likely to cause problems in terms of practical use, it was designated as "B". When the number of occurrences of lift-off was 1, it was designated as "A", meaning it was good. Also, when the number of occurrences of lift-off was 0, it was designated as "S", meaning it was very excellent. The results are shown in Table 3. Note that lift-off refers to the peeling at the bonding interface between the silver alloy wire and the substrate during the pull test.

[0121]

Table 8

[0122] Next, the relationship between creep rupture and grain boundary deterioration will be described. As described above, the inventors used the silver alloy wires produced in the examples and comparative examples, and investigated in advance the relationship between the ratio (%) of the special grain boundary length, the state of the fracture surface after the tensile test and the creep test, the creep fracture elongation rate (%) and the fracture time (hrs). Among these, the results of Example 5 and Comparative Example 1 will be mainly described.

[0123] As shown in FIG. 9, the fracture surface of the tensile test of the silver alloy wire of Example 5 is smooth, and no grain boundary cracks are observed. It can be seen that the silver alloy wire of the example takes a longer time to reach fracture than the silver alloy wire of the comparative example, and the rate of grain boundary deterioration is slower. When the same observation was made for some of the other examples, in all cases, the silver alloy wire of the example had relatively large crystal grains on the high-temperature creep fracture surface, few grain boundary crack locations, and when compared with the same wire diameter, it generally took a longer time to reach fracture than the silver alloy wire of the comparative example, and it was found that the rate of grain boundary deterioration was slower.

[0124] On the other hand, on the fracture surface of the creep test of the silver alloy wire of Comparative Example 1 in FIG. 10, the crystal grains were small, and fine and many grain boundary cracks (voids) could be confirmed.

[0125] From these results, the inventors considered that the higher the ratio of the special grain boundary length, the more dominant the special grain boundary with higher bonding strength becomes in an environment where a predetermined load is continuously applied at high temperature, the slower the deformation rate of the silver alloy wire due to the load, and the less likely it is to deteriorate at the grain boundary. On the other hand, the lower the ratio of the special grain boundary length, the more dominant the grain boundary with lower bonding strength becomes, and grain boundary deterioration occurs before the silver alloy wire recrystallizes, leading to grain boundary fracture earlier. Also, by using the ratio of the special grain boundary length of the silver alloy wire as an index, it is possible to predict the occurrence of grain boundary deterioration at the initial stage of manufacturing the silver alloy wire, so that failures and major accidents of parts using the silver alloy wire can be avoided in advance.

[0126] Next, the silver alloy wire sheet material will be described. The inventors used the silver alloy sheets fabricated in Example 113 and Comparative Example 103, and investigated in advance the relationships between the ratio (%) of the special grain boundary length of the cross-section of the silver alloy sheet, the <111> orientation ratio (%), the state of the fracture surface after a tensile test or a creep test, the elongation at break (%) and the fracture time (hrs). Note that both Example 113 and Comparative Example 103 have a cross-sectional size of w2mm × t0.2mm. The results are shown in Table 9.

[0127]

Table 9

[0128] In the silver alloy sheets of Example 113 and Comparative Example 103, grain boundary cracks (voids) were confirmed in the fracture surfaces of both. However, in the case of the same cross-sectional shape, the silver alloy sheet of the example took a longer time to reach fracture than the silver alloy sheet of the comparative example. From this, it can be seen that the silver alloy sheet of the example has a slower grain boundary deterioration rate than the silver alloy sheet of the comparative example. Also, near the fracture surface of the high-temperature creep test of the silver alloy sheet of the comparative example, since the crystal grains are small, many fine grain boundary cracks are observed, whereas near the fracture surface of the high-temperature creep test of the silver alloy sheet of the example, the crystal grains are large and the number of grain boundary crack locations is small. From these results, it was confirmed that the relationship between the ratio of the special grain boundary length and grain boundary deterioration in the silver alloy sheet is the same as that in the silver alloy round wire.

Explanation of Symbols

[0129] 103… semiconductor device, 1… semiconductor element, 2… metal film, 3… wire, 41… circuit pattern, 42… metal pattern, 43… insulating member, 5… heat dissipation member, 6… bonding material, 7… case, 8… terminal, 9… encapsulant, 50… silver alloy wire, 51… lithium ion battery, 52… cathode side bus bar, 53… anode side bus bar, 54… gel-like substance< / hkl> < / hkl> < / hkl> < / hkl> < / hkl> < / hkl>

Claims

1. A silver alloy wire containing 99.8 mass% or more of silver, wherein the ratio of the special grain boundary length defined by the following formula (1) of the crystal grains in the cross-section perpendicular to the longitudinal direction of the silver alloy wire is 30% or more, and the ratio of the crystal orientation <111> with an angular difference of 15 degrees or less with respect to the longitudinal direction of the silver alloy wire among the crystal orientations <hkl> in the longitudinal direction of the silver alloy wire measured in the cross-section is 10% or more and 60% or less. A silver alloy wire characterized by the above. Ratio of special grain boundary length = Grain boundary length from Σ3 to Σ29 / Total grain boundary length (1)

2. The silver alloy wire according to claim 1, wherein the average crystal grain diameter of the cross-section of the silver alloy wire is 2 μm or more and 15 μm or less.

3. The silver alloy wire according to claim 1 or 2, containing at least one or more elements selected from the group consisting of Pt, Ti, Zn, Au, Cu, Mg, Ni, Al, Sn, Pd, Cd, In, W, Nd, and Bi, and the concentration of the element with respect to the total amount of the silver alloy wire is 0.003 mass% or more and 0.1 mass% or less in total.

4. A silver alloy wire containing 99.8 mass% or more of silver, wherein the ratio of the special grain boundary length defined by the following formula (1) of the crystal grains in the cross-section perpendicular to the longitudinal direction of the silver alloy wire is 30% or more, containing at least one or more elements selected from the group consisting of Pt, Ti, Zn, Au, Cu, Mg, Ni, Al, Sn, Pd, Cd, In, W, Nd, and Bi, and the concentration of the element with respect to the total amount of the silver alloy wire is 0.003 mass% or more and 0.1 mass% or less in total. A silver alloy wire. Ratio of special grain boundary length = Grain boundary length from Σ3 to Σ29 / Total grain boundary length (1)

5. The silver alloy wire according to claim 4, wherein the ratio of the crystal orientation <111> with an angular difference of 15 degrees or less with respect to the longitudinal direction of the silver alloy wire among the crystal orientations <hkl> in the longitudinal direction of the silver alloy wire measured in the cross-section is 10% or more and 60% or less.

6. The silver alloy wire according to claim 4 or 5, wherein the average crystal grain diameter of the cross-section of the silver alloy wire is 2 μm or more and 15 μm or less.

7. A conductive wire using the silver alloy wire according to claim 1 or 4.

8. A wire for bonding using the silver alloy wire according to claim 1 or 4.

9. A wire for semiconductors using the silver alloy wire according to claim 1 or 4.

10. A wire for structures using the silver alloy wire according to claim 1 or 4.

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