Bonding wire for semiconductor device

Abstract

Provided is a novel Cu bonding wire that, even if a sealing resin material having a high sulfur content is used, suppresses galvanic corrosion in high temperature environments and provides good bonding reliability of secondary bonded sections. This bonding wire for semiconductor devices includes a core material comprising Cu or a Cu alloy and a covering layer that contains a non-Cu conductive metal formed on the surface of the core material. The covering layer contains Ni and Pd. The ratio CNi / CPd of the Ni concentration CNi (mass%) and the Pd concentration CPd (mass%) relative to the whole wire is 0.02–0.75. In a concentration profile in the thickness direction of the wire, obtained by auger electron spectroscopy (AES) measurement, the position of maximum Ni concentration is within the range of a depth of 0.5d from the wire surface when the thickness of the covering layer is d (μm). The maximum Ni concentration is at least 10 atom%. An Ni sulfide is generated on the wire surface side of the coating layer, in the thickness direction of the coating layer, when a sealed body is obtained by sealing the bonding wire using a sealing resin material that has a S concentration of at least 20 mass ppm and the sealed body is heated for 50 hours at 250°C.

Description

Bonding wire for semiconductor devices

[0001] The present invention relates to a bonding wire for a semiconductor device, and further to a semiconductor device including the bonding wire.

[0002] In semiconductor devices, electrodes formed on a semiconductor chip are connected to electrodes on a lead frame or substrate using bonding wires. The bonding wire is typically connected using ultrasonic thermocompression bonding, using a general-purpose bonding device or a capillary jig through which the bonding wire is passed for connection. The connection process is completed by first bonding to an electrode on the semiconductor chip, then forming a loop, and then second bonding the wire to an external electrode on the lead frame or substrate. The first bonding involves heating and melting the tip of the wire with arc heat input, forming a free air ball (FAB) due to surface tension, and then crimping the ball to an electrode on the semiconductor chip (hereinafter referred to as "ball bonding"). The second bonding involves crimping the wire to an external electrode by applying ultrasonic waves and a load (hereinafter referred to as "wedge bonding") without forming a ball. After the connection process, the bonded portion is sealed with a sealing resin material to obtain a semiconductor device.

[0003] Until now, gold (Au) has been the mainstream material for bonding wire, but copper (Cu) is increasingly being used instead, primarily for LSI applications (see, for example, Patent Documents 1 to 3). Furthermore, with the recent spread of electric and hybrid vehicles, it is expected that Cu, which has high thermal conductivity and fusing current, will be used in automotive devices and also in power devices (power semiconductor devices) for high-power equipment such as air conditioners and solar power generation systems. Cu is therefore expected to be a highly efficient and reliable alternative.

[0004] Cu has the disadvantage of being more easily oxidized than Au, and as a method of preventing the surface oxidation of Cu bonding wire, a structure in which the surface of the Cu core material is coated with a metal such as Pd or Ni has been proposed (Patent Document 4). In addition, a Pd-coated Cu bonding wire has also been proposed in which the surface of the Cu core material is coated with Pd and Pd or Pt is further added to the Cu core material, thereby improving the bonding reliability of the first bonded portion (Patent Document 5).

[0005] Japanese Patent Application Laid-Open No. 61-48543 Japanese Patent Application Laid-Open No. 2018-503743 International Publication No. 2017 / 221770 Japanese Patent Application Laid-Open No. 2005-167020 International Publication No. 2017 / 013796

[0006] Automotive devices and power devices tend to be exposed to higher temperatures during operation than general electronic devices, and the bonding wires used are required to exhibit good bonding reliability even in harsh high-temperature environments.

[0007] The present inventors conducted evaluations in high-temperature environments based on the characteristics required for automotive devices and power devices, and found that galvanic corrosion occurs in conventional Cu bonding wires having a Pd coating layer, and bonding reliability at the second joint may not be sufficient, as described below. That is, due to the wedge bonding process, the Pd coating layer is partially missing at the second joint, partially exposing the Cu core material. In this regard, in a high-temperature environment of 175 ° C or higher, water vapor, oxygen, and sulfur-based outgassing are significantly generated from the sealing resin, and a water film is formed on the surface of the second joint, into which oxygen and sulfur-based gases dissolve. As a result, a battery is formed with the large Pd surface as the cathode and the small Cu exposed area as the anode, accelerating the dissolution of Cu and causing local corrosion of Cu. At this time, the dissolved sulfur-based gas becomes sulfuric acid, which lowers the pH of the water film, further accelerating the local corrosion of Cu.

[0008] Furthermore, the sulfur content in encapsulating resin materials used in semiconductor devices has tended to increase in recent years. Conventionally, commercially available epoxy resins containing sulfur-containing silane coupling agents have been used as encapsulating resin materials. In contrast, in order to further improve the adhesion of encapsulating resin materials to lead frames and semiconductor chips, the sulfur content of recent encapsulating resin materials has been increased compared to conventional materials. As mentioned above, even when the sulfur content is at conventional levels, significant sulfur-based outgassing from the encapsulating resin occurs in high-temperature environments of 175°C or higher. However, in systems using encapsulating resin materials with such high sulfur content, the amount of sulfur-based gas generated in high-temperature environments further increases, further accelerating local corrosion of Cu. Therefore, it tends to become increasingly difficult to achieve sufficient bonding reliability at the second bonding portion.

[0009] The present invention provides a novel Cu bonding wire that suppresses galvanic corrosion in a high-temperature environment and provides good bonding reliability at the second bonded portion, even when a sealing resin material with a high sulfur content is used.

[0010] As a result of intensive research into the above-mentioned problems, the inventors have found that some Cu-based bonding wires with a coating layer containing Pd and Ni can suppress galvanic corrosion in high-temperature environments and provide good bonding reliability at the second bond, even when using a sealing resin material with a high sulfur content. After testing the bonding reliability of these wires in a high-temperature environment, SEM observation of their cross sections confirmed that, for wires that showed good bonding reliability at the second bond, a product was generated on the surface side of the coating layer in the thickness direction of the coating layer. The composition of the product was examined using a TEM electron diffraction pattern, and it was found to be Ni. ３ S ２ As a result of further investigation based on this finding, the inventors have found that the above-mentioned problems can be solved by providing the following constitution, and have thus completed the present invention.

[0011] That is, the present invention includes the following: [1] A bonding wire for a semiconductor device, comprising a core material made of Cu or a Cu alloy and a coating layer containing a conductive metal other than Cu formed on the surface of the core material, wherein the coating layer contains Ni and Pd, and the Ni concentration C of the entire wire is Ｎｉ (mass%) and Pd concentration C Ｐｄ Ratio C (mass%) Ｎｉ / C Ｐｄ

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[0098] [ [4] The bonding wire according to any one of [1] to [3], wherein, when the cross section of the wire in the sealing body after heat treatment is observed under SEM, the average value of the perimeter of Ni sulfides in the observation area is a (μm), and the average value a (μm) and the thickness d (μm) of the coating layer satisfy the relationship a ≧ 0.8d. [5] The bonding wire according to any one of [1] to [4], wherein, when the cross section of the wire in the sealing body after heat treatment is observed under SEM, the total value of the perimeter of Ni sulfides in the observation area is b (μm) and the wire perimeter L (μm), and the total value b (μm) and the wire perimeter L (μm) satisfy the relationship b ≧ 0.8L (μm). [6] The bonding wire according to [4] or [5], wherein the observation area is determined so that the observed wire perimeter is 3 μm or more during SEM observation. [7] The bonding wire according to any one of [1] to [6], wherein the coating layer has a region containing Pd as a main component on the core material side in the thickness direction of the coating layer, and a region containing Ni and Pd within a range of a depth of 0.5d from the wire surface, where d (μm) is the thickness of the coating layer. [8] The bonding wire according to any one of [1] to [7], wherein the coating layer has a thickness d of 0.01 μm or more and 0.13 μm or less.[9] The bonding wire according to any one of [1] to [8], wherein the concentration profile in the depth direction of the wire is obtained by measuring by AES under the following <Conditions> while digging from the surface of the wire in the depth direction by Ar sputtering. <Conditions> The center of the wire width is positioned to be the center of the width of the measurement surface, and the width of the measurement surface is 5% to 15% of the wire diameter, and the length of the measurement surface is 5 times the width of the measurement surface.

[10] The bonding wire according to any one of [1] to [9], wherein the wire surface contains Au.

[11] The bonding wire according to

[10] , wherein the concentration of Au on the wire surface is 10 atomic % to 90 atomic %.

[12] The bonding wire according to

[11] , wherein the concentration of Au on the wire surface is measured by AES under the following <Conditions>.

[14] The bonding wire according to any one of [1] to

[13] , wherein when a free air ball (FAB) is formed using the wire, the crystal orientation of a cross section perpendicular to the crimp bonding direction of the FAB is measured, and the proportion of <100> crystal orientations having an angle difference of 15 degrees or less with respect to the crimp bonding direction is 30% or more.

[15] The bonding wire according to any one of [1] to

[13] , wherein the bonding wire contains one or more elements selected from the group consisting of B, P, and Mg (hereinafter referred to as "first additional element"), and the total concentration of the first additional element in the entire wire is 1 ppm by mass or more and 100 ppm by mass or less.

[15] The bonding wire according to any one of [1] to

[14] , which contains one or more elements (hereinafter referred to as "second additional elements") selected from the group consisting of Se, Te, As, and Sb, and the total concentration of the second additional elements in the entire wire is 1 mass ppm to 100 mass ppm.

[16] The bonding wire according to any one of [1] to

[15] , which contains one or more elements (hereinafter referred to as "third additional elements") selected from the group consisting of Ga, Ge, and In, and the total concentration of the third additional elements in the entire wire is 0.011 mass% to 1.5 mass%.

[17] A semiconductor device including the bonding wire according to any one of [1] to

[16] .

[0012] According to the present invention, even when a sealing resin material with a high sulfur content is used, a novel Cu bonding wire can be provided that suppresses galvanic corrosion in a high-temperature environment and provides good bonding reliability of the second bonding portion.

[0013] Fig. 1 is a schematic diagram for explaining the position and dimensions of a measurement surface when performing composition analysis by AES, Fig. 2 is a schematic diagram for explaining the position and dimensions of an observation area when performing SEM observation, and Fig. 3 is a schematic diagram for explaining a cross section perpendicular to the compression bonding direction of FAB.

[0014] The present invention will be described in detail below with reference to preferred embodiments. While the description may refer to drawings, each drawing merely shows the shape, size, and arrangement of components to the extent that the invention can be understood. The present invention is not limited to the following embodiments and examples, and can be modified and implemented as desired within the scope of the claims and their equivalents.

[0015] [Bonding Wire for Semiconductor Device] The bonding wire for semiconductor device of the present invention (hereinafter also referred to simply as "wire of the present invention" or "wire") includes a core material made of Cu or a Cu alloy, and a coating layer containing a conductive metal other than Cu formed on the surface of the core material, wherein the coating layer contains Ni and Pd, and the concentration C of Ni relative to the entire wire is Ｎｉ (mass%) and Pd concentration C Ｐｄ Ratio C (mass%) Ｎｉ / C Ｐｄ is 0.02 or more and 0.75 or less, in a concentration profile in the depth direction of the wire obtained by measurement using Auger electron spectroscopy (AES), when the thickness of the coating layer is d (μm), the position showing the maximum Ni concentration is within a range of 0.5d depth from the wire surface and the maximum Ni concentration is 10 atomic % or more, and when the bonding wire is sealed with a sealing resin material having an S concentration of 20 ppm by mass or more to obtain a sealed body, and then the sealed body is heat-treated at 250°C for 50 hours, Ni sulfide is generated in the coating layer on the wire surface side in the thickness direction of the coating layer.

[0016] As mentioned above, bonding wires used in automotive devices and power devices are required to exhibit good bonding reliability in harsh high-temperature environments. The inventors conducted evaluations in high-temperature environments based on the characteristics required for automotive devices, etc., and found that with conventional Cu bonding wires having a Pd coating layer, galvanic corrosion occurs in high-temperature environments, and sufficient bonding reliability at the second bond may not be achieved. Furthermore, the sulfur content in encapsulating resin materials used in semiconductor devices has tended to increase in recent years, but in systems using encapsulating resin materials with such high sulfur content, galvanic corrosion is further accelerated in high-temperature environments, making it increasingly difficult to achieve sufficient bonding reliability at the second bond.

[0017] In the course of investigating the above-mentioned problems, the inventors discovered that some Cu-based bonding wires with a coating layer containing Pd and Ni can suppress galvanic corrosion in high-temperature environments and provide good bonding reliability at the second bond, even when using a sealing resin material with a high sulfur content. After testing the bonding reliability of these wires in a high-temperature environment, SEM observation of their cross sections confirmed that wires that showed good bonding reliability at the second bond had a product on the surface side of the coating layer in the thickness direction of the coating layer. The composition of the product was examined using a TEM electron diffraction pattern, and it was found to be Ni. ３ S ２ It has been found that the Ni sulfides are Ni sulfides such as Ni. As a result of further investigation based on this finding, it has been found that the wire of the present invention having the above-mentioned specific configuration suppresses galvanic corrosion in high-temperature environments and provides good bonding reliability of the second bond. The present invention significantly contributes to the practical application and promotion of Cu bonding wire in automotive devices and power devices.

[0018] <Core Material Made of Cu or Cu Alloy> The wire of the present invention includes a core material made of Cu or a Cu alloy (hereinafter, also simply referred to as "Cu core material").

[0019] The Cu core material is not particularly limited as long as it is made of Cu or a Cu alloy, and a known Cu core material that constitutes a conventional Pd-coated Cu wire known as a bonding wire for semiconductor devices may be used.

[0020] In the present invention, the concentration of Cu in the Cu core material can be, for example, 97 atomic % or more, 97.5 atomic % or more, 98 atomic % or more, 98.5 atomic % or more, 99 atomic % or more, 99.5 atomic % or more, 99.8 atomic % or more, 99.9 atomic % or more, or 99.99 atomic % or more at the center (axial core portion) of the Cu core material.

[0021] The Cu core material may contain, for example, one or more dopants selected from the first additional element, the second additional element, and the third additional element described below. The preferred contents of these dopants are as described below.

[0022] In one embodiment, the Cu core material is composed of Cu and inevitable impurities. In another embodiment, the Cu core material is composed of Cu, one or more elements selected from the first additional element, the second additional element, and the third additional element described below, and inevitable impurities. Note that the term "unavoidable impurities" used in reference to the Cu core material also includes elements constituting the coating layer containing a conductive metal other than Cu described below.

[0023] <Coating Layer Containing a Conductive Metal Other Than Cu> The wire of the present invention includes a coating layer (hereinafter also simply referred to as "coating layer") that contains a conductive metal other than Cu and is formed on the surface of a Cu core material.

[0024] Even when a sealing resin material with a high sulfur content is used, in order to suppress galvanic corrosion in a high-temperature environment and provide good bonding reliability at the second bonded portion, it is important that the coating layer of the wire of the present invention satisfy all of the following conditions (1) to (3): (1) Ni concentration C of the entire wire Ｎｉ (mass%) and Pd concentration C Ｐｄ Ratio C (mass%) Ｎｉ / C Ｐｄ(2) In a concentration profile in the depth direction of the wire obtained by AES measurement, when the thickness of the coating layer is d (μm), the position showing the maximum Ni concentration is within a range of 0.5d depth from the wire surface, and the maximum Ni concentration is 10 atomic % or more. (3) When the wire is sealed with a sealing resin material having an S concentration of 20 mass ppm or more to obtain a sealed body, and the sealed body is then heat-treated at 250°C for 50 hours, Ni sulfides are generated in the coating layer on the wire surface side in the thickness direction of the coating layer.

[0025] Condition (1) Condition (1) is the concentration C of Ni in the entire wire. Ｎｉ (mass%) and Pd concentration C Ｐｄ Ratio C (mass%) Ｎｉ / C Ｐｄ Regarding the range of.

[0026] By including a coating layer that satisfies condition (1) in combination with conditions (2) and (3), the wire of the present invention can significantly suppress galvanic corrosion in high-temperature environments, and can achieve good bonding reliability of the second joint even when using a sealing resin material with a high sulfur content.

[0027] Regarding condition (1), the ratio C Ｎｉ / C Ｐｄ From the viewpoint of realizing good bonding reliability of the second bonded portion in a high temperature environment, the ratio C is 0.02 or more, preferably 0.04 or more, more preferably 0.05 or more, 0.06 or more, 0.08 or more, or 0.1 or more. Ｎｉ / C Ｐｄ If the ratio C is less than 0.02, galvanic corrosion in a high-temperature environment cannot be suppressed, and sufficient high-temperature bonding reliability tends not to be obtained at the second bonding portion. Ｎｉ / C Ｐｄ The upper limit of is 0.75 or less from the viewpoint of suppressing deterioration of the FAB shape, and is more preferably 0.7 or less, even more preferably 0.65 or less, still more preferably 0.6 or less, 0.55 or less, 0.5 or less, 0.48 or less, 0.46 or less, 0.45 or less, 0.44 or less, 0.42 or less, or 0.4 or less from the viewpoint of realizing a good FAB shape.

[0028] Ratio C under condition (1) Ｎｉ / C Ｐｄ is the Ni concentration C of the entire wire measured by the method described in [Measurement of element content] below. Ｎｉ (mass%) was measured in the same manner as the Pd concentration C Ｐｄ It can be calculated by dividing by (mass %).

[0029] Condition (2) Condition (2) relates to the position and maximum concentration value of the maximum Ni concentration in the concentration profile in the depth direction of the wire obtained by AES measurement (hereinafter simply referred to as the "concentration profile in the depth direction of the wire").

[0030] By including a coating layer that satisfies condition (2) in combination with conditions (1) and (3), the wire of the present invention can significantly suppress galvanic corrosion in high-temperature environments, and can achieve good bonding reliability at the second joint even when using a sealing resin material with a high sulfur content.

[0031] In condition (2), from the viewpoint of realizing good bonding reliability of the second bond in a high-temperature environment, when the thickness of the coating layer is d (μm; the calculation method based on the concentration profile in the depth direction of the wire will be described later. The thickness d is based on the concentration profile in the depth direction of the wire before heat treatment), the position showing the maximum Ni concentration in the concentration profile in the depth direction of the wire is within a depth range of 0.5d from the wire surface, preferably within a depth range of 0.4d from the wire surface, and more preferably within a depth range of 0.3d from the wire surface.

[0032] Regarding condition (2), from the viewpoint of realizing good bonding reliability of the second bonded portion in a high-temperature environment, the maximum concentration of Ni in the concentration profile in the depth direction of the wire is 10 atomic % or more, preferably 15 atomic % or more, more preferably 20 atomic % or more, and even more preferably 25 atomic % or more or 30 atomic % or more. The upper limit of the maximum concentration of Ni is not particularly limited and may be 100 atomic %, but from the viewpoint of realizing good bonding properties at the second bonded portion, it is preferably 99 atomic % or less, 98 atomic % or less, 96 atomic % or less, 95 atomic % or less, 94 atomic % or less, 92 atomic % or less, or 90 atomic % or less.

[0033] The position and maximum concentration value of Ni under condition (2) can be confirmed and determined by performing composition analysis by AES while digging from the surface of the wire in the depth direction (toward the center of the wire) by Ar sputtering. In detail, by repeating 1) composition analysis of the wire surface, 2) sputtering with Ar, and 3) composition analysis of the surface after sputtering, the concentration change of each element in the depth direction (center) from the surface of the wire (so-called depth direction concentration profile) can be obtained, and the maximum concentration value and the position and maximum concentration value of Ni under condition (2) can be confirmed and determined based on the concentration profile. In the present invention, when obtaining the depth direction concentration profile, the unit of depth is SiO ２ It was converted.

[0034] When performing 1) compositional analysis of the wire surface or 3) compositional analysis of the surface after sputtering, the position and dimensions of the measurement surface are determined as follows. In the following, the width of the measurement surface refers to the dimension of the measurement surface in the direction perpendicular to the wire axis (wire thickness direction), and the length of the measurement surface refers to the dimension of the measurement surface in the wire axis direction (wire length direction). This will be further explained with reference to Figure 1. Figure 1 is a schematic plan view of a wire 1, in which the wire axis direction (wire length direction) corresponds to the vertical direction (up and down direction) in Figure 1, and the direction perpendicular to the wire axis (wire thickness direction) corresponds to the horizontal direction (left and right direction) in Figure 1. Figure 1 shows a measurement surface 2 in relation to the wire 1, and the width of the measurement surface 2 is the dimension w of the measurement surface in the direction perpendicular to the wire axis. ａand the length of the measuring surface 2 is the dimension l of the measuring surface in the direction of the wire axis. ａ is.

[0035] When measuring by AES, the wire is positioned so that the center of its width in the direction perpendicular to the wire axis is the center of the width of the measurement surface, and the measurement surface is determined so that the width of the measurement surface is 5% to 15% of the wire diameter. The length of the measurement surface is set to be 5 times the width of the measurement surface. In Figure 1, the width of the wire is indicated by the symbol W, and the center of the wire width is indicated by the dashed line X. Therefore, the measurement surface 2 is positioned so that the center of its width coincides with the dashed line X, which is the center of the wire width, and the width w of the measurement surface is set to be 5 times the width of the measurement surface. ａ is determined to be 5% to 15% of the wire diameter (same value as the wire width W), that is, 0.05W to 0.15W. ａ Is, l ａ =5w ａ By determining the position and dimensions of the measurement surface as described above, it is possible to accurately measure whether condition (2) is met, which is suitable for suppressing galvanic corrosion in a high-temperature environment and providing good bonding reliability for the second bonded portion, even when a sealing resin material with a high sulfur content is used.

[0036] The thickness d of the coating layer can be determined from the obtained concentration profile in the depth direction. First, the boundary between the Cu core material and the coating layer is determined based on the Cu concentration. The position where the Cu concentration is 50 atomic % is determined as the boundary, and the region where the Cu concentration is 50 atomic % or more is the Cu core material, and the region where the Cu concentration is less than 50 atomic % is the coating layer. In the present invention, the boundary between the Cu core material and the coating layer does not necessarily have to be a grain boundary. Then, the concentration profile is confirmed from the wire surface toward the wire center, and the thickness d can be determined as the distance from the wire surface position Z0 to the depth position Z1 where the concentration of the Cu core material first reaches 50 atomic %. In addition, it is preferable to obtain concentration profiles for multiple measurement surfaces (n≧3) spaced 1 mm or more apart in the wire axial direction and use the arithmetic average value.

[0037] The position or maximum concentration value of Ni under condition (2) can be determined from the position where the concentration is maximum by focusing on the increase or decrease in Ni concentration in the obtained concentration profile in the depth direction.

[0038] The position and maximum concentration value of the maximum Ni concentration under the above condition (2) are based on the results of measurements under the conditions described in the section "Analysis of coating layer thickness by Auger electron spectroscopy (AES)" below.

[0039] Condition (3) Condition (3) relates to the generation of Ni sulfides in the coating layer on the wire surface side in the thickness direction of the coating layer when a wire is sealed using a sealing resin material having a sulfur concentration equal to or higher than a certain value to obtain a sealed body and then the sealed body is heat-treated at 250° C. for 50 hours. In combination with conditions (1) and (2), by providing a coating layer that satisfies condition (3), galvanic corrosion in high-temperature environments can be significantly suppressed, and good bonding reliability of the second joint can be achieved in high-temperature environments even when a sealing resin material with a high sulfur content is used.

[0040] Even when using a sealing resin material with a high sulfur content, from the viewpoint of providing better bonding reliability at the second bond in a high-temperature environment, when the thickness of the coating layer is d (μm) (as described above, the thickness d is based on the concentration profile in the depth direction of the wire before heat treatment), it is preferable that Ni sulfide is generated within a range of 0.5d from the wire surface to a depth of 0.4d from the wire surface, and even more preferably within a range of 0.3d from the wire surface, a range of 0.2d from the wire surface, or a range of 0.1d from the wire surface. Here, "Ni sulfide is generated within a range of depth x from the wire surface" does not exclude the generation of Ni sulfide in a range greater than x from the wire surface, as long as Ni sulfide is generated within the range of depth x from the wire surface. The inventors have discovered that when a wire is sealed with a sealing resin material having an S concentration equal to or higher than a certain value to obtain a sealed body, and then the sealed body is heat-treated at 250°C for 50 hours, a wire having a coating layer in which Ni sulfides are generated closer to the wire surface side of the coating layer in the thickness direction of the coating layer can significantly suppress galvanic corrosion in a high-temperature environment, and even when a sealing resin material with a high sulfur content is used, it is possible to achieve even better joint reliability at the second joint.

[0041] Regarding condition (3), the presence of a product (Ni sulfide) in the coating layer of the wire in the heat-treated sealed body can be determined by observing the cross section of the wire in the heat-treated sealed body using an SEM and looking at the obtained SEM image. Furthermore, the amount of the product (Ni sulfide) can be quantified by analyzing the obtained SEM image using image analysis software. Examples of image analysis software include "Particle Analysis" manufactured by Nippon Steel Technology Co., Ltd.

[0042] When observing the cross section of the wire in the sealed body after heat treatment with an SEM, the SEM observation area is determined as follows. First, the SEM observation area is tentatively determined at a position where the interface between the wire and the sealing resin material falls within the observation area. Then, the observation magnification and observation position are adjusted so that the perimeter of the wire in the SEM observation area is 3 μm or more. Further explanation will be given with reference to FIG. 2 . FIG. 2 is a schematic diagram showing an SEM image obtained by SEM observation of the cross section of the wire in the sealed body after heat treatment. In SEM image 9 of FIG. 2 , the wire 1 is on the left and the sealing resin material 6 is on the right, and the interface between the wire and the sealing resin material falls within the observation area. In SEM image 9, the Cu core material 1a inside the wire and the coating layer 1b on its surface can be distinguished from the contrast due to differences in composition of the wire 1, and further, the sealing resin material 6 is confirmed around the wire 1. The above-mentioned "wire perimeter" refers to the length of the wire perimeter extending as the interface between the wire and the sealing resin material, and corresponds to the A-B arc length of the wire 1 in FIG. 2 . The observation magnification and observation position are adjusted so that the A-B arc length is 3 μm or more. Even when a sealing resin material with a high sulfur content is used, from the viewpoint of accurately determining whether condition (3) is met, which is important for suppressing galvanic corrosion in a high-temperature environment and providing good bonding reliability at the second bonded portion, it is preferable to adjust the observation magnification and observation position so that the wire periphery in the SEM observation area is 3 μm or more and 8 μm or less, and the magnification for SEM observation in this case is preferably in the range of 10,000x to 50,000x.

[0043] As described above, for wires that exhibit the desired effect, products (Ni sulfides) 5 are observed in the SEM image 9 on the wire surface side of the coating layer 1b in the thickness direction of the coating layer 1b (near the interface between the wire and the encapsulating resin material). Six products are illustrated in the SEM image 9 shown in FIG. 2 . In the present invention, for an SEM image obtained by determining the SEM observation area as described above, image analysis software is used to binarize the SEM image to extract particles derived from the products, and their number (when determining whether conditions (4) and (5) described below are met, the perimeter of the color area) is determined.

[0044] When confirming particles derived from the product within the SEM observation area, it is preferable to prepare multiple sealed bodies (n≧3), perform the above-mentioned SEM observation and image analysis on the observation surface of each sealed body, and use the arithmetic average value.

[0045] Even when a sealing resin material with a high sulfur content is used, from the viewpoint of significantly suppressing galvanic corrosion in a high-temperature environment and providing particularly good bonding reliability at the second bond, the wire of the present invention preferably satisfies one or more of the following conditions (4) and (5) in addition to condition (3) when the wire is sealed with a sealing resin material having an S concentration of 20 ppm by mass or more to obtain a sealed body, and then the sealed body is heat-treated at 250° C. for 50 hours, and it is particularly preferable that both of these conditions be satisfied. (4) When the cross section of the wire in the sealed body after heat treatment is observed with an SEM, if the average value of the perimeter length of Ni sulfides in the observed region is a (μm), the average value a (μm) and the thickness d (μm) of the coating layer satisfy the relationship a≧0.8d. (5) When the cross section of the wire in the sealing body after the heat treatment is observed by SEM, the total value of the perimeter lengths of Ni sulfides in the observed region is b (μm) and the wire perimeter L (μm) satisfies the relationship b≧0.8L (μm), where b (μm) is the total value of the perimeter lengths of Ni sulfides in the observed region and L (μm) is the wire perimeter.

[0046] Condition (4) Condition (4) relates to the relationship between the average value a (μm) of the perimeter of Ni sulfides in an observation region when the cross section of the wire in the sealing body after heat treatment is observed with an SEM and the thickness d (μm) of the coating layer, where the thickness d (μm) of the coating layer is based on the concentration profile in the depth direction of the wire before heat treatment.

[0047] Even when a sealing resin material with a high sulfur content is used, from the viewpoint of significantly suppressing galvanic corrosion in a high-temperature environment and providing particularly good bonding reliability at the second bonded portion, when the cross section of the wire in the sealing body after heat treatment is observed with an SEM, if the average value of the perimeter of Ni sulfides in the observed area is a (μm), then the average value a (μm) and the thickness d (μm) of the coating layer preferably satisfy the relationship a ≧ 0.8d, more preferably a ≧ 0.9d, and even more preferably a ≧ d.

[0048] Regarding condition (4), the average value a (μm) of the perimeter of Ni sulfides in the observation area can be determined by performing SEM observation and image analysis in the same manner as for condition (3).

[0049] That is, when observing the cross section of the wire in the sealed body after the heat treatment with an SEM, the SEM observation region is tentatively determined at a position where the interface between the wire and the sealing resin material falls within the observation region, and the observation magnification and observation position are adjusted so that the perimeter of the wire in the SEM observation region is 3 μm or more. The preferable upper limit of the perimeter of the wire in the SEM observation region and the preferable range of the magnification for SEM observation are as described for condition (3).

[0050] Next, the obtained SEM image is analyzed using image analysis software. By analyzing the obtained SEM image using image analysis software, the perimeter of each particle derived from the product (Ni sulfide) can be determined, and the perimeter of each obtained particle can be arithmetically averaged to calculate the average value a (μm) of the perimeter of Ni sulfide in the observation area. For example, as shown in FIG. 2, when six particles derived from the product (Ni sulfide) are confirmed in the observation area, and the perimeter (μm) of each particle is a1, a2, a3, a4, a5, and a6, the average value a (μm) of the perimeter of Ni sulfide in the observation area can be calculated as (a1 + a2 + a3 + a4 + a5 + a6) / 6.

[0051] Condition (5) Condition (5) relates to the relationship between the total value b (μm) of the perimeter of Ni sulfides in an observation region when the cross section of the wire in the sealing body after heat treatment is observed with an SEM and the wire perimeter L (μm).

[0052] Even when a sealing resin material with a high sulfur content is used, from the viewpoint of significantly suppressing galvanic corrosion in a high-temperature environment and providing particularly good bonding reliability at the second bonded portion, when the cross section of the wire in the sealing body after heat treatment is observed with an SEM, if the total value of the perimeter lengths of Ni sulfides in the observed region is b (μm) and the wire perimeter length is L (μm), the total value b (μm) and the wire perimeter length L (μm) preferably satisfy the relationship b ≧ 0.8L, more preferably satisfy the relationship b ≧ 0.9L, and even more preferably satisfy the relationship b ≧ L.

[0053] Regarding condition (5), the total value b (μm) of the perimeter of the Ni sulfides in the observation area can be determined by performing SEM observation and image analysis in the same manner as in condition (4) (and thus condition (3)). By analyzing the SEM image obtained by SEM observation using image analysis software, the perimeter of each particle derived from the product (Ni sulfide) can be determined, and the total value b (μm) of the perimeter of the Ni sulfides in the observation area can be calculated by summing the perimeters of each particle obtained. For example, as shown in FIG. 2, when six particles derived from the product (Ni sulfide) are confirmed in the observation area, when the perimeters (μm) of each particle are b1, b2, b3, b4, b5, and b6, the total value b (μm) of the perimeter of the Ni sulfides in the observation area can be calculated as (b1 + b2 + b3 + b4 + b5 + b6).

[0054] Regarding condition (5), the wire perimeter L (μm) in the observation area is as described for condition (3). For example, in the SEM image 9 shown in FIG. 2, the wire perimeter L corresponds to the A-B arc length of the wire 1.

[0055] In determining whether conditions (4) and (5) are met, it is preferable to prepare a plurality of sealing bodies (n≧3), perform the above-described SEM observation and image analysis on the observation surface of each sealing body, and use the arithmetic average values ​​of the average value a (μm) and total value b (μm) of the perimeter of Ni sulfides in the observation area and the wire perimeter L (μm).

[0056] The presence or absence of Ni sulfide generation under the above condition (3), and Ni under conditions (4) and (5) ３ S２ The average value a (nm) and total value b (μm) of the perimeters, and the wire perimeter L (μm) are based on the results of measurements made under the conditions described in the section "SEM observation and image analysis of the cross section of the wire in the sealed body after heat treatment" below.

[0057] Under the above conditions (3) to (5), the S concentration of the encapsulating resin material can be measured by combustion-ion chromatography. In combustion-ion chromatography, the encapsulating resin material is crushed and washed with pure water to prepare a sample. The prepared sample is then placed in a combustion decomposition unit and combusted in a combustion gas stream containing oxygen, and the generated gas is collected in an absorption liquid. Next, sulfate ions (SO ４ ２－ ) is separated by ion chromatography, and the total S concentration in the sample is quantified. In the present invention, the S concentration in the encapsulating resin material is based on the results of measurement under the conditions described in the section "Measurement of S concentration in encapsulating resin material (combustion-ion chromatography)" below.

[0058] In determining whether conditions (3) to (5) are met, the S concentration of the encapsulating resin material is 20 ppm by mass or more, and the upper limit of the S concentration may be 200 ppm by mass or less, 100 ppm by mass or less, etc. By using an encapsulating resin material having such an S concentration in the evaluation test, even when an encapsulating resin material with a high sulfur content is used, it is possible to accurately determine whether conditions (3), (4), and (5) are met, which are important and suitable for suppressing galvanic corrosion in a high-temperature environment and providing good bonding reliability of the second bond.

[0059] -Other preferable conditions for the coating layer- In the wire of the present invention, the coating layer satisfies all of the above conditions (1) to (3), and preferably also satisfies one or both of the above conditions (4) and (5). From the viewpoint of easily satisfying these conditions (1) to (5) and from the viewpoint of being able to enjoy the effects of the present invention more effectively, it is important that the coating layer in the wire of the present invention satisfies one or more of the following conditions (6) and (7): (6) In the thickness direction of the coating layer, there is a region containing Pd as a main component on the core material side, and there is a region containing Ni and Pd within a range of a depth of 0.5d from the wire surface, where the thickness of the coating layer is d (μm). (7) The thickness d of the coating layer is 0.01 μm or more and 0.13 μm or less.

[0060] Condition (6) Condition (6) relates to the coating layer having a region containing Pd as a main component on the core material side in the thickness direction of the coating layer, and also having a region containing Ni and Pd within a range of a depth of 0.5d from the wire surface, where d (μm) is the thickness of the coating layer.

[0061] By including a coating layer that satisfies the condition (6), conditions (2), (3) and conditions (4), (5) can be easily satisfied, galvanic corrosion in high-temperature environments can be significantly suppressed, and even when a sealing resin material with a high sulfur content is used, it is easy to achieve good bonding reliability of the second bonding portion, which is preferable.

[0062] In condition (6), the coating layer has a region containing Pd as a main component on the core material side in the thickness direction of the coating layer. In the present invention, the "region containing Pd as a main component" in the coating layer means a region in which the Pd concentration is 50 atomic % or more. The coating layer contains Ni in addition to Pd as a conductive metal other than Cu, and may further contain a conductive metal such as Au as described below. However, from the viewpoint of being able to further enjoy the effects of the present invention, the total concentration C of Pd, Ni, and Au in the entire wire is set to 50 atomic % or more. Ｍ (mass%) and Pd concentration C Ｐｄ Ratio C (mass%) Ｐｄ / C Ｍ It is preferable that the coating layer contains Pd so that the ratio C is preferably 0.5 or more, more preferably 0.6 or more, and even more preferably 0.7 or more or 0.8 or more. Ｐｄ / CＭ When the ratio C is in the above range, the bonding reliability of the first bonded portion in a high-temperature and high-humidity environment can be further improved, and the bondability of the second bonded portion can be further improved, which is preferable. Ｐｄ / C Ｍ The upper limit of is not particularly limited as long as conditions (1) to (3) are satisfied, and may be, for example, 0.98 or less, 0.96 or less, or 0.95 or less. In the wire of the present invention, the coating layer preferably has a region containing Ni and Pd within a range of a depth of 0.5d from the wire surface, where d is the thickness of the coating layer. However, from the viewpoint of suppressing galvanic corrosion in a high-temperature environment and providing good bonding reliability at the second bonded portion, the total concentration C of Pd, Ni, and Au in the entire wire is preferably 0.5d or less. Ｍ (mass%) and Ni concentration C Ｎｉ Ratio C (mass%) Ｎｉ / C Ｍ The coating layer preferably contains Ni so that the ratio C is preferably 0.01 or more, more preferably 0.02 or more, and even more preferably 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, or 0.08 or more. Ｎｉ / C Ｍ The upper limit of the ratio C is not particularly limited as long as it satisfies the conditions (1) to (3), and may be, for example, 0.4 or less, 0.35 or less, or 0.3 or less. Ｐｄ / C Ｍ Yahi C Ｎｉ / C Ｍ is the Pd concentration C of the entire wire measured by the method described in [Measurement of element content] below. Ｐｄ (mass%) and Ni concentration C Ｎｉ (mass%) was measured in the same manner as the total concentration C of Pd, Ni, and Au. Ｍ It can be calculated by dividing by (mass %).

[0063] Regarding condition (6), the coating layer has a region containing Pd as the main component on the core material side in the thickness direction of the coating layer, and when the thickness of the coating layer is d (μm; measurement and calculation methods are as described in relation to condition (2)), the coating layer has a region containing Ni and Pd within a range of 0.5d depth from the wire surface. This can be confirmed by performing composition analysis using Auger electron spectroscopy (AES) while digging from the wire surface in the depth direction (toward the wire center) using Ar sputtering, as described in relation to condition (2). In detail, after 1) performing composition analysis of the wire surface, 2) sputtering with Ar and 3) repeating composition analysis of the surface after sputtering obtain a concentration profile in the depth direction, and confirmation can be made from the concentration profile. The position and dimensions of the measurement surface when performing composition analysis by AES are also as described in relation to condition (2). By determining the position and dimensions of the measurement surface as described above, it is possible to accurately confirm the presence of regions in the coating layer that are primarily composed of Pd or that contain Ni and Pd, which is preferable from the viewpoint of easily satisfying conditions (2) and (3) and conditions (4) and (5).

[0064] In the present invention, the coating layer has a region containing Pd as a main component on the core material side in the thickness direction of the coating layer, and also has a region containing Ni and Pd within a range of 0.5d depth from the wire surface, based on the results of measurements performed under the conditions described in the section "Analysis of coating layer thickness by Auger electron spectroscopy (AES)" below.

[0065] The trend of the depth concentration profile obtained for a wire of the present invention according to a preferred embodiment is described below. A region containing Ni and Pd exists from the surface of the wire to a certain depth. In this region, the Ni concentration tends to decrease and the Pd concentration tends to increase from the surface of the wire toward the depth. Further in the depth direction, the Pd concentration reaches a maximum, then decreases and the Cu concentration tends to increase. The Pd concentration may exhibit a maximum concentration at a certain depth position (d1), or it may exhibit a maximum value over a certain depth range (d1 to d2). In such a concentration profile, by focusing on the increase or decrease in the Ni and Pd concentrations, it is possible to determine the presence and location of regions containing both Ni and Pd and regions containing Pd as the main component. Furthermore, by focusing on the increase or decrease in the Ni and Pd concentrations in such a concentration profile, the maximum Ni and Pd concentrations can be determined from the positions where their concentrations are maximum. As described below, when the coating layer contains Au on the wire surface side, there tends to be a region in the depth direction concentration profile where the Au concentration decreases and the Ni concentration increases from the wire surface to a very shallow position. Even in such cases, by focusing on the increase or decrease in the Ni and Pd concentrations in the coating layer, the presence of a region containing both Ni and Pd or a region mainly composed of Pd, the location of these regions, and the maximum concentrations of Ni and Pd can be determined. In the wire of the present invention, as long as there is a region containing Ni and Pd within a depth range of 0.5d from the wire surface, there may also be a region containing Ni and Pd at a depth greater than 0.5d from the wire surface. To determine the maximum concentrations of Ni and Pd in ​​the coating layer, it is preferable to obtain concentration profiles for multiple measurement surfaces (n≧3) spaced apart by 1 mm or more in the wire axial direction and use the arithmetic mean value. The preferred range for the maximum Pd concentration will be described later. A "region mainly composed of Pd" can be said to exist when the maximum Pd concentration is 50% by mass or more.

[0066] In a preferred embodiment, the position showing the maximum Ni concentration in the concentration profile in the depth direction of the wire is closer to the surface of the wire than the position showing the maximum Pd concentration.

[0067] From the viewpoint of further improving the bondability of the second bonded portion (initial bondability of the second bonded portion) and further improving the bond reliability of the first bonded portion in a high-temperature, high-humidity environment, the maximum concentration of Pd in ​​the concentration profile in the depth direction of the wire is preferably 80 atomic % or more, more preferably 85 atomic % or more, and even more preferably 90 atomic % or more, more than 90 atomic %, 92 atomic % or more, 94 atomic % or more, or 95 atomic % or more. The upper limit of the maximum Pd concentration in the coating layer is not particularly limited and may be, for example, 100 mass %.

[0068] Condition (7) Condition (7) relates to the thickness d of the coating layer. The method for measuring and calculating the thickness d of the coating layer is as explained in relation to condition (2).

[0069] In addition to the conditions (1) to (3), the inclusion of a coating layer satisfying the condition (7) can further improve the bondability at the second bonded portion and the bonding reliability at the first bonded portion. In addition, the inclusion of a coating layer satisfying the condition (7) is preferable because it can provide a wire that is excellent in the FAB shape and the crimped shape of the first bonded portion.

[0070] Regarding condition (7), from the viewpoint of being able to enjoy the effects of the present invention more effectively, the thickness d of the coating layer is preferably 0.005 μm or more, more preferably 0.006 μm or more, 0.008 μm or more, 0.01 μm or more, 0.012 μm or more, even more preferably 0.014 μm or more, still more preferably 0.015 μm or more or 0.016 μm or more, and particularly preferably 0.018 μm or more or 0.020 μm or more. Furthermore, from the viewpoint of being able to enjoy the effects of the present invention more effectively, the upper limit of the thickness d of the coating layer is preferably 0.18 μm or less, more preferably 0.16 μm or less, 0.15 μm or less, or 0.14 μm or less, and even more preferably 0.13 μm or less, 0.125 μm or less, 0.12 μm or less, 0.115 μm or less, 0.11 μm or less, 0.105 μm or less, 0.1 μm or less, 0.095 μm or less, or 0.09 μm or less. In a preferred embodiment, the thickness d of the coating layer is 0.01 μm or more and 0.13 μm or less.

[0071] The coating layer may contain, for example, one or more dopants selected from the first additional element, the second additional element, and the third additional element described below. The preferred contents of these dopants are as described below.

[0072] In the wire of the present invention, the coating layer may further contain Au on the wire surface side in the thickness direction of the coating layer. When the coating layer further contains Au, the bondability at the second bonded portion can be further improved.

[0073] From the viewpoint of further improving the bondability at the 2nd bonded portion, the Au concentration on the surface of the wire of the present invention is preferably 10 atomic % or more, more preferably 15 atomic % or more, even more preferably 20 atomic % or more, 22 atomic % or more, 24 atomic % or more, 25 atomic % or more, 26 atomic % or more, 28 atomic % or more, or 30 atomic % or more. From the viewpoint of realizing a good crimped shape of the 1st bonded portion, the upper limit of the Au concentration on the surface of the wire of the present invention is preferably 90 atomic % or less, more preferably 85 atomic % or less, even more preferably 80 atomic % or less, 78 atomic % or less, 76 atomic % or less, 75 atomic % or less, 74 atomic % or less, 72 atomic % or less, or 70 atomic % or less. Therefore, in a preferred embodiment, the Au concentration on the surface of the wire of the present invention is 10 atomic % or more and 90 atomic % or less.

[0074] In the present invention, the concentration of Au on the wire surface can be determined by performing composition analysis of the wire surface using Auger electron spectroscopy (AES) with the wire surface as the measurement surface, ignoring gas components such as carbon (C), sulfur (S), oxygen (O), and nitrogen (N), and nonmetallic elements.

[0075] The composition analysis of the wire surface can be performed under the same conditions as those of 1) the composition analysis of the wire surface, which was explained in relation to the method for obtaining a concentration profile in the depth direction. That is, when performing composition analysis of the wire surface by Auger electron spectroscopy (AES), the position and dimensions of the measurement surface are determined as follows.

[0076] The wire is positioned so that the center of the wire width in the direction perpendicular to the wire axis is the center of the width of the measurement surface, and the measurement surface is determined so that the width of the measurement surface is 5% to 15% of the wire diameter. The length of the measurement surface is set to be 5 times the width of the measurement surface. By determining the position and dimensions of the measurement surface as described above, the Au concentration on the wire surface can be measured with high accuracy, which is suitable for further improving the second bondability. In addition, it is preferable to perform measurements on multiple measurement surfaces (n≧3) spaced 1 mm or more apart from each other in the wire axis direction, and use the arithmetic average value.

[0077] The above-mentioned concentration of Au on the surface is based on the results of measurements performed under the conditions described in the section "Analysis of Wire Surface Composition by Auger Electron Spectroscopy (AES)" below.

[0078] When the coating layer contains Au on the surface side of the wire in the thickness direction of the coating layer, the position showing the maximum concentration of Au in the concentration profile in the depth direction of the wire is closer to the surface side of the wire than the position showing the maximum concentration of Ni or the position showing the maximum concentration of Pd.

[0079] In one embodiment, the coating layer is composed of Pd and Ni; and inevitable impurities. In another embodiment, the coating layer is composed of Pd and Ni; and one or more elements selected from Au, the first additional element, the second additional element, and the third additional element described below; and inevitable impurities. Note that the term "unavoidable impurities" used in reference to the coating layer also includes the elements that make up the Cu core material described above.

[0080] The wire of the present invention may further contain one or more elements ("first additional elements") selected from the group consisting of B, P, and Mg. When the wire of the present invention contains the first additional element, the total concentration of the first additional element relative to the entire wire is preferably 1 ppm by mass or more. This makes it possible to realize a bonding wire that provides a better crimped shape of the first bonded portion. The total concentration of the first additional element relative to the entire wire is more preferably 2 ppm by mass or more, and even more preferably 3 ppm by mass or more, 5 ppm by mass or more, 8 ppm by mass or more, 10 ppm by mass or more, 15 ppm by mass or more, or 20 ppm by mass or more. From the viewpoint of suppressing hardening of the wire and reducing chip damage during the first bonding, the total concentration of the first additional element is preferably 100 ppm by mass or less, and more preferably 90 ppm by mass or less, 80 ppm by mass or less, 70 ppm by mass or less, 60 ppm by mass or less, or 50 ppm by mass or less. Therefore, in one preferred embodiment, the wire of the present invention contains a first additional element, and the total concentration of the first additional element in the entire wire is 1 mass ppm or more and 100 mass ppm or less.

[0081] When the wire of the present invention contains the first additive element, the first additive element may be contained in either the Cu core material or the coating layer, or may be contained in both. From the viewpoint of realizing a bonding wire that provides a better crimped shape of the first bonded portion, it is preferable that the first additive element be contained in the Cu core material.

[0082] The wire of the present invention may further contain one or more elements ("second additional elements") selected from the group consisting of Se, Te, As, and Sb. When the wire of the present invention contains the second additional elements, the total concentration of the second additional elements relative to the entire wire is preferably 1 ppm by mass or more. This can improve the bonding reliability of the first bonded portion in a high-temperature, high-humidity environment. The total concentration of the second additional elements relative to the entire wire is more preferably 2 ppm by mass or more, and even more preferably 3 ppm by mass or more, 5 ppm by mass or more, 8 ppm by mass or more, 10 ppm by mass or more, 15 ppm by mass or more, or 20 ppm by mass or more. From the viewpoint of realizing a good crimp shape of the first bonded portion, the total concentration of the second additional elements is preferably 100 ppm by mass or less, and more preferably 90 ppm by mass or less, 80 ppm by mass or less, 70 ppm by mass or less, 60 ppm by mass or less, or 50 ppm by mass or less. Therefore, in a preferred embodiment, the wire of the present invention contains a second additional element, and the total concentration of the second additional element in the entire wire is 1 mass ppm or more and 100 mass ppm or less.

[0083] When the wire of the present invention contains a second additive element, the second additive element may be contained in either the Cu core material or the coating layer, or may be contained in both. From the viewpoint of further improving the bonding reliability of the first bonded portion in a high-temperature, high-humidity environment, it is preferable that the second additive element be contained in the coating layer. When the coating layer contains the second additive element, the second additive element may be contained in a region containing Ni and Pd, or may be contained in a region on the core material side that is mainly composed of Pd. Furthermore, when the coating layer contains Au on the wire surface side, the second additive element may be contained together with the Au.

[0084] The wire of the present invention may further contain one or more elements ("third additional element") selected from the group consisting of Ga, Ge, and In. When the wire of the present invention contains the third additional element, the total concentration of the third additional element relative to the entire wire is preferably 0.011 mass% or more. This can improve the bonding reliability of the first bonded portion in high-temperature environments. The total concentration of the third additional element relative to the entire wire is more preferably 0.015 mass% or more, and even more preferably 0.02 mass% or more, 0.025 mass% or more, 0.03 mass% or more, 0.031 mass% or more, 0.035 mass% or more, 0.04 mass% or more, 0.05 mass% or more, 0.07 mass% or more, 0.09 mass% or more, 0.1 mass% or more, 0.12 mass% or more, 0.14 mass% or more, 0.15 mass% or more, or 0.2 mass% or more. From the viewpoint of realizing a good crimped shape of the first bonded portion and good bondability at the second bonded portion, the total concentration of the third additional element is preferably 1.5 mass% or less, and more preferably 1.4 mass% or less, 1.3 mass% or less, or 1.2 mass% or less. Therefore, in a preferred embodiment, the wire of the present invention contains the third additional element, and the total concentration of the third additional element with respect to the entire wire is 0.011 mass% or more and 1.5 mass% or less.

[0085] When the wire of the present invention contains a third additive element, the third additive element may be contained in either the Cu core material or the coating layer, or in both. When the wire of the present invention contains Au on its surface, the third additive element may be contained together with the Au.

[0086] The contents of the first additional element, the second additional element, and the third additional element in the wire can be measured by the method described later in [Measurement of element contents].

[0087] In the wire of the present invention, the total concentration of Cu, Ni, Au, and Pd can be, for example, 98.5 mass % or more, 98.6 mass % or more, 98.7 mass % or more, or 98.8 mass % or more.

[0088] Other Preferred Conditions Further preferred conditions that the wire of the present invention should satisfy will be described below.

[0089] When a FAB is formed using the wire of the present invention, the crystal orientation of a cross section of the FAB perpendicular to the crimp bonding direction is measured, and the proportion of <100> crystal orientations with an angle difference of 15 degrees or less with respect to the crimp bonding direction is preferably 30% or more. This allows for the realization of an exceptionally good crimp shape at the first bonded portion.

[0090] As mentioned above, the bonding wire connection process is completed by first bonding to an electrode on a semiconductor chip, then forming a loop, and then second bonding the wire portion to an external electrode on a lead frame or substrate. The first bonding involves heating and melting the tip of the wire with arc heat input, forming a fabricated ball (FAB) by surface tension, and then crimping (ball-bonding) the FAB to an electrode on the semiconductor chip. The inventors have found that, based on measurements of the crystal orientation of a cross section perpendicular to the crimp bonding direction of the FAB, a wire with a proportion of <100> crystal orientations at an angle of 15 degrees or less relative to the crimp bonding direction (hereinafter simply referred to as the "proportion of <100> crystal orientations in the cross section of the FAB") of 30% or more can achieve a particularly good crimp shape at the first bond.

[0091] From the viewpoint of realizing a better crimped shape of the first bonded portion, a wire having a <100> crystal orientation ratio of 35% or more in the cross section of the FAB is more preferably 40% or more, even more preferably 45% or more, and particularly preferably 50% or more, 55% or more, or 60%. In particular, a wire having a <100> crystal orientation ratio of 50% or more in the cross section of the FAB can realize an exceptionally good crimped shape of the first bonded portion. Therefore, in a preferred embodiment, the <100> crystal orientation ratio in the cross section of the FAB is 30% or more, more preferably 50% or more. The upper limit of the <100> crystal orientation ratio in the cross section of the FAB is not particularly limited, and may be, for example, 100%, 99.5% or less, 99% or less, 98% or less, or the like.

[0092] Referring to FIG. 3, a cross section perpendicular to the crimping direction of the FAB will be described. FIG. 3 shows a schematic diagram of the process in which the tip of the wire 1 is heated and melted by arc heat input, forming the FAB 10 by surface tension. The formed FAB 10 is crimped to an electrode (not shown) on a semiconductor chip. In FIG. 3, the crimping direction of the FAB 10 is the direction indicated by arrow Z (the vertical direction (up and down) in FIG. 3). The cross section perpendicular to the crimping direction Z is the cross section exposed by cutting the FAB along dotted line A-A perpendicular to the Z direction. Here, the dotted line A-A, which serves as the reference for cross sectioning, is set at the position where the diameter of the exposed cross section is maximum, i.e., the position where the diameter of the exposed cross section is D when the diameter of the FAB is D. During the cross sectioning process, it is possible for the line A-A to deviate from the target and the diameter of the exposed cross section to be smaller than D. However, as long as the diameter of the exposed cross section is 0.9D or greater, the effect of this deviation on the crystal orientation ratio is negligibly small and is therefore acceptable.

[0093] The crystal orientation of a cross section perpendicular to the FAB compression bonding direction can be measured using electron backscattered diffraction (EBSD). The device used for the EBSD method is composed of a scanning electron microscope and a detector attached thereto. The EBSD method is a technique in which the diffraction pattern of reflected electrons generated when a sample is irradiated with an electron beam is projected onto a detector and the diffraction pattern is analyzed to determine the crystal orientation at each measurement point. Dedicated software (such as OIM analysis by TSL Solutions, Inc.) can be used to analyze data obtained by the EBSD method. The proportion of a specific crystal orientation can be calculated by using the analysis software provided with the device and using the cross section perpendicular to the FAB compression bonding direction as the inspection surface.

[0094] In this invention, the percentage of the <100> crystal orientation in the cross section of the FAB is defined as the area of ​​the <100> crystal orientation relative to the measured area, expressed as a percentage. In calculating this percentage, only crystal orientations within the measurement surface that could be identified based on a certain reliability were used, and areas where the crystal orientation could not be measured, or areas where the crystal orientation could be measured but the reliability of the orientation analysis was low, were excluded from the measurement area and the area of ​​the <100> crystal orientation. If the excluded data here exceeds, for example, 20% of the total, there is a high possibility that the measurement target was contaminated in some way, and the measurement should be repeated from the cross section. Furthermore, in this invention, the percentage of the <100> crystal orientation in the cross section of the FAB was defined as the arithmetic average of the percentages obtained by measuring three or more FABs.

[0095] The inventors speculate as follows about the reason why a wire having a ratio of <100> crystal orientation of 30% or more in the cross section of the FAB can achieve a particularly good crimped shape of the first joint.

[0096] It is known that metals deform by sliding along specific crystal planes and crystal directions (these planes and directions are also referred to as "slip planes" and "slip directions"). The FAB formed using the wire of the present invention is primarily composed of a core material, Cu or a Cu alloy, and has a face-centered cubic crystal structure. When such a crystal structure is adopted, if the crystal orientation of the cross section perpendicular to the crimping direction is <100>, metal slip occurs in a direction 45 degrees to the crimped surface, causing deformation. The FAB deforms in a direction 45 degrees to the crimped surface and radially expands relative to the plane parallel to the crimped surface. It is believed that this results in a more circular crimped shape.

[0097] In the present invention, the proportion of the <100> crystal orientation in the cross section of the FAB tends to fall within a desired range by adjusting the thickness of the coating layer, the Ni and Pd concentrations in the coating layer, and the Cu purity of the core material. For example, the inventors speculate as follows about the reason why the thickness of the coating layer affects the proportion of the <100> crystal orientation in the cross section of the FAB. Specifically, during the melting stage, the Ni and Pd in ​​the coating layer diffuse and mix appropriately toward the center of the FAB, and the Cu or Cu alloy containing the moderately diffused and mixed Ni and Pd in ​​solid solution has a <100> crystal orientation oriented in the compression bonding direction. It is speculated that when the thickness of the coating layer is within a predetermined range, the diffusion and mixing of Ni and Pd during melting is appropriate, making it easier for the <100> crystal orientation to be oriented in the compression bonding direction. On the other hand, if the coating layer is too thin, it is easier for a random crystal orientation to be formed, and if the coating layer is too thick, it is easier for a different crystal orientation to be dominant.

[0098] The diameter of the wire of the present invention is not particularly limited and may be determined appropriately depending on the specific purpose, but is preferably 15 μm or more, 18 μm or more, 20 μm or more, etc. The upper limit of the diameter is not particularly limited and may be, for example, 80 μm or less, 70 μm or less, or 50 μm or less.

[0099] <Method for Manufacturing Wire> An example of a method for manufacturing the bonding wire for semiconductor device of the present invention will be described.

[0100] First, raw copper of high purity (4N to 6N; 99.99 to 99.9999 mass % or more) is processed into a large diameter (diameter of about 3 to 6 mm) by continuous casting to obtain an ingot.

[0101] When dopants such as the first, second, and third additive elements are added, the addition method can be, for example, by incorporating them into the Cu core material, incorporating them into the coating layer, depositing them on the surface of the Cu core material, or depositing them on the surface of the coating layer. A combination of these methods may also be used. The effects of the present invention can be achieved regardless of the addition method. In the method of incorporating a dopant into the Cu core material, a copper alloy containing the dopant at the required concentration can be used as a raw material to produce the Cu core material. When adding a dopant to the raw material Cu to obtain such a copper alloy, a high-purity dopant component can be directly added to Cu, or a mother alloy containing about 1% of the dopant component can be used. In the method of incorporating a dopant into the coating layer, the dopant can be incorporated into a Pd or Ni plating bath (in the case of wet plating) or a target material (in the case of dry plating) used to form the coating layer. In the method of depositing on the surface of a Cu core material or on the surface of a coating layer, the surface of the Cu core material or the surface of the coating layer can be used as the deposition surface, and one or more deposition processes selected from (1) application of an aqueous solution ⇒ drying ⇒ heat treatment, (2) plating method (wet type), and (3) vapor deposition method (dry type) can be carried out.

[0102] A large diameter ingot is forged, rolled, and drawn to produce a wire (hereinafter also referred to as "intermediate wire") made of Cu or a Cu alloy and having a diameter of about 0.7 to 2.0 mm.

[0103] Although electrolytic plating, electroless plating, vapor deposition, and the like can be used as methods for forming a coating layer on the surface of a Cu core material, electrolytic plating, which can stably control the film thickness, is industrially preferred. For example, a coating layer may be formed on the surface of an intermediate wire. Alternatively, the coating layer may be formed on the surface of the Cu core material after the intermediate wire has been drawn and further thinned (e.g., after drawing to the final diameter of the Cu core material). The coating layer may be formed, for example, by providing a Pd layer on the surface of the Cu core material and then providing a Ni layer or a NiPd alloy layer containing Ni and Pd in ​​a predetermined ratio, or by providing a Ni layer or a NiPd alloy layer and then further providing a layer containing Pd. From the viewpoint of forming a coating layer with excellent adhesion to the Cu core material, a predetermined coating layer may be formed after strike plating of a conductive metal on the surface of the Cu core material.

[0104] When forming a coating layer having a region containing Au on the surface side of the wire, it can be formed by providing an Au layer on the surface side of the coating layer using the same method as described above.

[0105] The wiredrawing process can be performed using a continuous wiredrawing device that can accommodate multiple diamond-coated dies. If necessary, heat treatment can be performed during the wiredrawing process. The heat treatment can diffuse the constituent elements between the Ni layer or NiPd alloy layer on the wire surface and the underlying Pd layer, forming a region containing Ni and Pd within a depth of 0.5d from the wire surface. Furthermore, when forming a coating layer having an Au-containing region on the wire surface, the heat treatment can diffuse the constituent elements between the Au layer on the wire surface and the underlying Ni layer or NiPd alloy layer (or Pd-containing layer, if provided), forming an Au-containing region (e.g., an alloy region containing Au, Ni, and Pd) on the wire surface side of the coating layer so that the Au concentration on the wire surface falls within the above-mentioned preferred range. A preferred method for this is to continuously sweep the wire at a constant speed in an electric furnace at a constant furnace temperature to promote alloying, since this method allows the alloy composition, such as the maximum Ni concentration in the coating layer, to be controlled within the desired range. Instead of forming an Au layer on the surface of the coating layer and then forming a region containing Au by heat treatment, a method may be adopted in which an alloy region containing Au and one or more of Ni and Pd is deposited from the beginning.

[0106] The bonding wire of the present invention can suppress galvanic corrosion in a high-temperature environment and provide good bonding reliability of the second bond, even when using an encapsulating resin material with a high sulfur content. Therefore, the bonding wire of the present invention can be suitably used, particularly as a bonding wire for automotive devices and power devices.

[0107] [Method for Manufacturing a Semiconductor Device] A semiconductor device can be manufactured by connecting electrodes on a semiconductor chip to electrodes on a lead frame or a circuit board using the bonding wire for a semiconductor device of the present invention.

[0108] In one embodiment, the semiconductor device of the present invention includes a circuit board, a semiconductor chip, a bonding wire for electrically connecting the circuit board and the semiconductor chip, and an encapsulating resin material for encapsulating the semiconductor chip and the conductive portion, and is characterized in that the bonding wire is the wire of the present invention.

[0109] In the semiconductor device of the present invention, the circuit board and semiconductor chip are not particularly limited, and known circuit boards and semiconductor chips that can be used to configure a semiconductor device may be used. Alternatively, a lead frame may be used instead of the circuit board. For example, a semiconductor device may be configured including a lead frame and a semiconductor chip mounted on the lead frame, as in the semiconductor device described in JP 2020-150116 A.

[0110] Examples of the semiconductor device include various semiconductor devices used in electrical appliances (e.g., computers, mobile phones, digital cameras, televisions, air conditioners, solar power generation systems, etc.) and vehicles (e.g., motorcycles, automobiles, trains, ships, aircraft, etc.).

[0111] The present invention will be specifically described below with reference to examples, although the present invention is not limited to the examples shown below.

[0112] (Sample) First, a method for preparing the sample will be described. The Cu used as the raw material for the Cu core material had a purity of 99.99% by mass or more (4N), with the remainder consisting of inevitable impurities. When the first additional element, second additional element, and third additional element were added, the purity of these elements was 99% by mass or more, with the remainder consisting of inevitable impurities, or a master alloy in which these additional elements were blended in high concentrations with Cu was used.

[0113] The core Cu alloy was first prepared by loading raw materials into a graphite crucible and heating them in a high-frequency furnace. ２The copper alloy was heated to 1090-1500°C in an inert atmosphere of nitrogen or argon gas to melt it, and then continuously cast into ingots with diameters of approximately 3-6 mm. The resulting ingots were then drawn to produce intermediate wires with diameters of 0.7-2.0 mm. The wires were then continuously drawn using a die to reduce their diameter to the wire diameter to be coated. A commercially available lubricant was used for the wiredrawing process, and the wiredrawing speed was 20-150 m / min. The coating layer was formed by pickling with hydrochloric acid or sulfuric acid to remove the oxide film from the wire surface, followed by forming a Pd layer covering the entire surface of the Cu alloy core, and then forming a Ni layer on that surface. Furthermore, some wires (Examples Nos. 5-7, 22, and 25) had an Au layer on top of the Ni layer. The Pd, Ni, and Au layers were formed using electroplating. Commercially available plating solutions were prepared as Pd plating solution, Ni plating solution, and Au plating solution, and were prepared as appropriate.

[0114] Thereafter, further wire drawing and other processes were carried out to process the wire into a final diameter of 20 μm. If necessary, intermediate heat treatment was carried out once or twice during the wire drawing process at 300 to 700°C for 2 to 15 seconds. When intermediate heat treatment was carried out, the wire was continuously swept and heated in N ２ After processing to the final wire diameter, the wire was continuously swept and N ２ The thermal refining treatment was performed while flowing nitrogen or Ar gas. The thermal refining treatment temperature was 200 to 600°C, the wire feed speed was 20 to 200 m / min, and the thermal refining time was 0.2 to 1.0 seconds. When the coating layer was thin or the Ni concentration was low, the thermal refining temperature was lowered and the wire feed speed was set to a higher value, and in the opposite cases, the thermal refining temperature was increased and the wire feed speed was set to a lower value.

[0115] (Test and Evaluation Methods) Test and evaluation methods will be described below.

[0116] [SEM Observation and Image Analysis of Wire Cross Sections in Sealed Body After Heat Treatment] (1) Production of Sealed Body The bonding wire to be observed and analyzed was wedge-bonded to the lead portion of the lead frame using a commercially available wire bonder, and the resulting sample was sealed with a sealing resin material (S concentration 90 ppm by mass) to obtain a sealed body. Three sealed bodies were produced for each bonding wire.

[0117] (2) Heat Treatment of Sealed Body The resulting sealed body was subjected to heat treatment by exposing it to an environment at a temperature of 250° C. for 50 hours using a high-temperature thermostat.

[0118] (3) Preparation of SEM Observation Samples The sealed bodies after the heat treatment were cross-sectioned using a cross-section sample preparation device (IB-19510CP, cross-section polisher, manufactured by JEOL Ltd.) so that the wire cross section perpendicular to the wire axial direction was exposed, and SEM observation samples were prepared. Note that SEM observation samples were obtained for each of the three sealed bodies prepared.

[0119] (4) SEM Observation The obtained SEM observation sample was subjected to SEM observation using an SEM device (JSM-7800F manufactured by JEOL Ltd.). For the observation, the SEM observation area was provisionally determined at a position where the interface between the wire and the encapsulating resin material was included in the observation area. Then, the observation magnification and observation position were adjusted so that the periphery of the wire in the SEM observation area was 3 μm or more and 8 μm or less.

[0120] (5) Image Analysis The obtained SEM images were analyzed using image analysis software (Nippon Steel Technology Co., Ltd.'s "Particle Analysis," version 3.5). In the image analysis using the image analysis software, the SEM image was input, and then a binarized image (particles derived from the products generated in the coating layer were displayed as a red image) was created by automatic binarization. The product-derived particles were extracted, and their number and the perimeter of each color region were analyzed. The average value a (μm) of the perimeter of the products (Ni sulfides) in the observation region was calculated as the arithmetic mean value of the perimeter of each particle confirmed in the observation region. The total value (μm) of the perimeter of the products (Ni sulfides) in the observation region was calculated by adding up the perimeter of each particle confirmed in the observation region. The number of products (Ni sulfides) in the observation region, the average perimeter a, and the total value b were calculated by the arithmetic mean values ​​of the values ​​obtained for the three SEM observation samples. It was confirmed that, for the wires of the examples, Ni sulfides were formed on the surface side of the coating layer in the thickness direction of the coating layer, and more specifically, when the thickness of the coating layer is d (μm), Ni sulfides were formed within a range of 0.5d depth from the wire surface.

[0121] [Measurement of S concentration in encapsulating resin material (combustion-ion chromatography)] The S concentration in the encapsulating resin material was measured by combustion-ion chromatography. Specifically, the encapsulating resin material was crushed and washed with pure water to prepare a sample. The prepared sample was then placed in the combustion decomposition unit of a combustion-ion chromatography analyzer and combusted in a combustion gas stream containing oxygen, and the generated gas was collected in an absorption liquid. Next, sulfate ions (SO ４ ２－ The total sulfur concentration in the sample was quantified using an analytical device that combined a sample combustion unit manufactured by Mitsubishi Chemical Corporation with a detection unit manufactured by Thermo Fisher Scientific, and hydrogen peroxide was used as the absorption solution.

[0122] [Composition Analysis of Wire Surface by Auger Electron Spectroscopy (AES)] For wires provided with a coating layer containing Au on the wire surface side, the Au concentration on the wire surface was measured by Auger electron spectroscopy (AES) as follows, using the wire surface as the measurement surface. First, the bonding wire to be measured was fixed linearly to a sample holder. Next, the wire was positioned so that the center of the width of the wire in the direction perpendicular to the wire axis was the center of the width of the measurement surface, and the measurement surface was determined so that the width of the measurement surface was 5% to 15% of the wire diameter. The length of the measurement surface was 5 times the width of the measurement surface. Then, using an AES device (PHI-700 manufactured by ULVAC-PHI), composition analysis of the wire surface was performed at an acceleration voltage of 10 kV, and the surface Au concentration (atomic %) was determined. Note that the composition analysis by AES was performed on three measurement surfaces spaced 1 mm or more apart from each other in the wire axial direction, and the arithmetic average value was used. When determining the concentration of Au on the surface, gas components such as carbon (C), sulfur (S), oxygen (O), and nitrogen (N), non-metallic elements, etc. were not taken into consideration.

[0123] [Coating layer thickness analysis by Auger electron spectroscopy (AES)] Depth analysis by AES was used for the thickness analysis of the coating layer. Depth analysis by AES involves alternately performing composition analysis and sputtering to analyze changes in composition in the depth direction, and can obtain concentration changes of each element in the depth (center) direction from the wire surface (so-called depth direction concentration profile). Specifically, after 1) performing composition analysis of the wire surface by AES, 2) sputtering with Ar and 3) composition analysis of the surface after sputtering were repeated to obtain a concentration profile in the depth direction. The sputtering in 2) was performed with Ar. ＋ The analysis was performed using ions and an acceleration voltage of 2 kV. In the surface composition analysis of 1) and 3), the dimensions of the measurement surface and the conditions for the AES composition analysis were the same as those described in the above section [Auger electron spectroscopy (AES) composition analysis of wire surface]. The concentration profile in the depth direction was obtained for three measurement surfaces spaced 1 mm or more apart from each other in the wire axial direction.

[0124] - Thickness d of coating layer - In the obtained concentration profile in the depth direction, the concentration profile was confirmed from the wire surface toward the wire center, and the distance from the wire surface position Z0 to the depth position Z1 where the concentration of the core material Cu first reached 50 atomic % was obtained as the thickness of the measured coating layer. The thickness d of the coating layer was the arithmetic mean value of the values ​​obtained for the three measurement surfaces. The depth measured by AES analysis was obtained as the product of the sputtering rate and time. Generally, the sputtering rate is determined by the standard sample SiO ２ The depth analyzed by AES is measured using SiO ２ In other words, the unit of thickness of the coating layer is SiO ２ A conversion value was used.

[0125] - Maximum Pd and Ni Concentration in Coating Layer - In the obtained depth-direction concentration profile, the increase or decrease in the Pd and Ni concentrations was focused on, and the maximum Pd and Ni concentrations were determined from the positions where the concentrations were maximum. The arithmetic mean of the values ​​obtained for the three measurement surfaces was adopted as the maximum Pd and Ni concentrations. It was confirmed that the wire of the example had a region mainly composed of Pd on the core side, a region containing Ni and Pd within a depth range of 0.5d from the wire surface, the position showing the maximum Ni concentration was within a depth range of 0.5d from the wire surface, and the position showing the maximum Ni concentration was closer to the surface than the position showing the maximum Pd concentration. For the wire of the example provided with a coating layer containing Au on the wire surface side, it was confirmed that the position showing the maximum Au concentration was closer to the surface than the positions showing the maximum Ni concentration and the positions showing the maximum Pd concentration.

[0126] [Measurement of element content] The contents of Ni, Pd, Au, the first additional element, the second additional element, and the third additional element in the wire were detected by analyzing a solution obtained by dissolving the bonding wire in strong acid using an ICP optical emission spectrometer and an ICP mass spectrometer, and the contents were detected as the concentration of the elements contained in the entire wire. As the analyzer, an ICP-OES ("PS3520UVDDII" manufactured by Hitachi High-Tech Science Corporation) or an ICP-MS ("Agilent 7700x ICP-MS" manufactured by Agilent Technologies, Inc.) was used. The total concentration C of Pd, Ni, and Au was Ｍ The concentration (mass %) was calculated by adding up the concentrations of Pd, Ni, and Au.

[0127] [Bonding Reliability of Second Bonding Portion] The bonding reliability of the second bonding portion was evaluated by a high temperature storage life test (HTSL).

[0128] A sample was wedge-bonded to the lead portion of the lead frame using a commercially available wire bonder and sealed with a sealing resin material (S concentration 90 ppm by mass) to prepare a sample for testing the bonding reliability of the second bonding portion. The lead frame was an Fe-42 atomic % Ni alloy lead frame plated with 1 to 3 μm of Ag. The prepared sample for evaluating bonding reliability was exposed to an environment at a temperature of 175°C using a high-temperature incubator. The bonding life of the second bonding portion was determined by conducting a pull test on the wedge bonding portion every 500 hours, and the time until the pull strength value became half of the initial pull strength. The pull strength value was the arithmetic mean value of measurements taken at 50 randomly selected locations on the wedge bonding portion. The pull test after the high-temperature storage test was performed after removing the resin by acid treatment to expose the wedge bonding portion. Evaluation was then performed according to the following criteria.

[0129] Evaluation criteria: ◎: Bonding life is 2000 hours or more ○: Bonding life is 1000 hours or more but less than 2000 hours ×: Bonding life is less than 1000 hours

[0130]

[0111] The bondability of the second bond was evaluated by a second bond window test, in which the horizontal axis indicates the ultrasonic current during second bonding, with six levels ranging from 30 mA to 80 mA in 10 mA increments, and the vertical axis indicates the load during second bonding, with six levels ranging from 20 gf to 70 gf in 10 gf increments, to determine the number of conditions under which bonding was possible for a total of 36 second bonding conditions.

[0131]

[0132] In this test, 200 wires for each condition were bonded to the lead portion of a lead frame using a commercially available wire bonder for each of the examples and comparative examples. The lead frame was Ag-plated, and the stage temperature was 200°C, N ２ +5% H ２ Bonding was carried out under a gas flow of 0.5 L / min. The number of conditions under which continuous bonding was possible without problems such as non-adhesion or bonder stoppage was determined and evaluated according to the following criteria.

[0133] Evaluation criteria: ◎: 33 or more conditions ○: 30 to 32 conditions △: 26 to 29 conditions ×: 25 or less conditions

[0134] [Fab Shape] The fabrication bonder (FAB) was fabricated on a lead frame using a commercially available wire bonder and observed with a scanning electron microscope (SEM) (number of evaluations: N=100). The fabrication current was set to 30-75 mA, the EFO gap was set to 762 μm, and the tail length was set to 254 μm. ２ +5% H ２ The gas was flowed at a rate of 0.4 to 0.6 L / min, and the diameter was set to 1.5 to 1.9 times the wire diameter. The FAB shape was judged as good if it was perfectly spherical, and poor if it was eccentric, irregular, or had poor melting properties. Evaluation was based on the following criteria:

[0135] Evaluation criteria: ◎: 5 ​​or less defects ○: 6 to 10 defects (no practical problem) ×: 11 or more defects

[0136] [Measurement of Crystal Orientation in FAB Cross Section] A commercially available wire bonder was used to form a FAB under the conditions described in the [FAB Shape] section above, and the crystal orientation was measured using a cross section perpendicular to the FAB compression bonding direction as the measurement surface. In the present invention, the cross section perpendicular to the FAB compression bonding direction refers to the cross section exposed by cutting the FAB along the dotted line A-A shown in Figure 3, and the reference dotted line A-A was set at the position where the diameter of the exposed cross section was maximum. For the measurement, an EBSD method was used, and the proportion of the <100> crystal orientation was calculated using the analysis software provided with the device using the procedure described above. Three FABs were measured, and the arithmetic average of the obtained proportions was determined as the proportion of the <100> crystal orientation in the FAB cross section.

[0137] [Bonding Reliability of First Bonded Portion] The bonding reliability of the first bonded portion was evaluated by both a High Temperature Storage Life Test (HTSL) and a Highly Accelerated Temperature and Humidity Stress Test (HAST).

[0138] -HTSL- A sample for testing the bonding reliability of the first bonding portion was prepared by ball-bonding a sample to an electrode formed by depositing a 1.5 μm-thick film of an Al-1.0 mass % Si-0.5 mass % Cu alloy on a Si substrate on a typical metal frame using a commercially available wire bonder. The sample was then sealed with a commercially available thermosetting epoxy resin. The ball was formed under the conditions described in the [FAB Shape] section above. The prepared sample for evaluating bonding reliability was exposed to an environment at a temperature of 175°C using a high-temperature incubator. The bonding life of the first bonding portion was determined by conducting a shear test on the ball bonding portion every 500 hours, and the time until the shear strength value reached half of the initial shear strength was used. The shear strength value was the arithmetic mean value of measurements taken at 50 randomly selected locations on the ball bonding portion. The shear test after the high-temperature storage test was performed after removing the resin using acid treatment to expose the ball bonding portion. Evaluation was then performed according to the following criteria.

[0139] Evaluation criteria: ◎: Bonding life is 2000 hours or more ○: Bonding life is 1000 hours or more but less than 2000 hours ×: Bonding life is less than 1000 hours

[0140] -HAST- Samples for evaluating the bonding reliability of the first bonded portion, prepared using the same procedure as above, were exposed to a high-temperature, high-humidity environment at a temperature of 130°C and a relative humidity of 85% using an unsaturated pressure cooker tester, and a bias of 7 V was applied. The bonding life of the first bonded portion was determined by conducting a shear test on the ball bonded portion every 48 hours, and the time it took for the shear strength value to become half of the initial shear strength. The shear strength value was the arithmetic mean value of measurements taken at 50 randomly selected points on the ball bonded portion. The shear test was performed after removing the resin by acid treatment to expose the ball bonded portion. Evaluation was then performed according to the following criteria.

[0141] Evaluation criteria: ◎: Bonding life is 480 hours or more ○: Bonding life is 384 hours or more but less than 480 hours △: Bonding life is 288 hours or more but less than 384 hours ×: Bonding life is less than 288 hours

[0142] [Bonded Shape] The bonded shape of the first bonded portion (the crushed shape of the ball) was evaluated by forming a ball using a commercially available wire bonder under the conditions described in the [FAB Shape] section above, crimping it to an electrode formed by depositing a 1.5 μm thick film of an Al-1.0 mass % Si-0.5 mass % Cu alloy on a Si substrate, and observing it from directly above with an optical microscope (number of evaluations N = 100). The crushed shape of the ball was judged as good if it was close to a perfect circle, and as poor if it was oval or petal-like. Evaluation was then performed according to the following criteria.

[0143] Evaluation criteria: ◎: No defects ○: 1 to 3 defects △: 4 or 5 defects ×: 6 or more defects

[0144] [Chip Damage] Evaluation of chip damage was performed by forming a ball using a commercially available wire bonder under the conditions described in the above [FAB Shape] section, crimping the ball to an electrode prepared by depositing a 1.5 μm thick film of an Al-1.0 mass % Si-0.5 mass % Cu alloy on a Si substrate, dissolving the wire and electrode in a chemical solution to expose the Si substrate, and observing the Si substrate directly below the bonded portion with an optical microscope (number of evaluations N=50). Evaluation was then performed according to the following criteria.

[0145] Evaluation criteria: ○: No cracks or bonding traces; △: No cracks, but bonding traces were found in some places (3 places or less); ×: Other than that

[0146] The evaluation results of the Examples and Comparative Examples are shown in Tables 2 and 3.

[0147]

[0148]

[0149] It was confirmed that all of the wires of Example Nos. 1 to 27 had coating layers that satisfied all of the specific conditions (1) to (3) of the present invention, and provided good bonding reliability at the second bonded portion. It was also confirmed that the wires of Example Nos. 5 to 7, 23, and 26, which contained Au on the surface, exhibited exceptionally excellent initial bondability at the second bonded portion. The Ni concentration C Ｎｉ (mass%) and Pd concentration C Ｐｄ Ratio C (mass%) Ｎｉ / C ＰｄIt was confirmed that examples in which the σ is 0.7 or less had good FAB shapes and crimped shapes of the first bonded portion. Furthermore, it was confirmed that wires of Examples 8, 9, 14-16, 20, 21, and 25, which had a coating layer thickness d of 0.01 μm or more and contained a total of 1 ppm by mass or more of the first additional element, provided exceptionally good crimped shapes of the first bonded portion. It was confirmed that wires of Examples 10-16, 21, and 23, which contained a total of 1 ppm by mass or more of the second additional element, provided exceptionally good bonding reliability of the first bonded portion in a high-temperature, high-humidity environment. It was confirmed that wires of Examples 17-21 and 25, which contained a total of 0.011 mass% or more of the third additional element, provided exceptionally good bonding reliability of the first bonded portion in a high-temperature, high-humidity environment. On the other hand, it was confirmed that wires of Comparative Example Nos. It was confirmed that wires Nos. 1 to 4 had coating layers that did not satisfy at least one of the specific conditions (1) to (3) of the present invention, and the bonding reliability of the second bonded portion was poor.

[0150] When a FAB was formed using a wire, the crystal orientation of the cross section of the FAB perpendicular to the bonding direction was measured. It was confirmed that a good crimped shape of the first bonded portion could be achieved when the proportion of the <100> crystal orientation, which has an angle difference of 15 degrees or less with respect to the bonding direction, was 30% or more (Examples 28, 29, and 31). In particular, it was confirmed that an exceptionally good crimped shape of the first bonded portion could be achieved when the proportion of the <100> crystal orientation was 50% or more (Example 31).

[0151] 1 Bonding wire (wire) 2 Measurement surface 5 Product (Ni sulfide) 6 Sealing resin material 9 SEM image X Center of wire width W Wire width (wire diameter) w ａ Measurement surface width l ａ Length of measurement surface 10 FAB Z FAB crimping direction

Claims

1. A bonding wire for a semiconductor device, comprising a core material made of Cu or a Cu alloy and a coating layer containing a conductive metal other than Cu formed on a surface of the core material, The coating layer contains Ni and Pd, and the Ni concentration C Ｎｉ (mass%) and Pd concentration C Ｐｄ Ratio C (mass%) Ｎｉ / C Ｐｄ is equal to or greater than 0.02 and equal to or less than 0.75, In a concentration profile in the depth direction of the wire obtained by measurement using Auger electron spectroscopy (AES), when the thickness of the coating layer is d (μm), the position showing the maximum Ni concentration is within a range of a depth of 0.5d from the wire surface, and the maximum Ni concentration is 10 atomic % or more, The bonding wire is sealed with a sealing resin material having an S concentration of 20 ppm by mass or more to obtain a sealed body, and when the sealed body is then heat-treated at 250°C for 50 hours, Ni sulfides are generated on the wire surface side of the coating layer in the thickness direction of the coating layer.

2. The bonding wire according to claim 1, wherein the S concentration of the sealing resin material is measured by a combustion-ion chromatography method.

3. The bonding wire according to claim 1, wherein Ni sulfide is generated within a range of a depth of 0.5d from the wire surface, where the thickness of the coating layer is d (μm).

4. When the cross section of the wire in the sealing body after the heat treatment is observed with an SEM, the average value of the perimeter of the Ni sulfide in the observation area is a (μm), The bonding wire according to claim 1 , wherein the average value a (μm) and the thickness d (μm) of the coating layer satisfy the relationship a≧0.8d.

5. When the cross section of the wire in the sealing body after the heat treatment is observed with an SEM, the total value of the perimeter of the Ni sulfide in the observation area is b (μm) and the wire perimeter is L (μm), The bonding wire according to claim 1 , wherein the total value b (μm) and the wire outer periphery L (μm) satisfy the relationship b≧0.8L (μm).

6. The bonding wire according to claim 4 or 5, wherein an observation region is determined in SEM observation so that the peripheral length of the wire observed is 3 μm or more.

7. The bonding wire according to claim 1, wherein the coating layer has a region containing Pd as a main component on the core material side in the thickness direction of the coating layer, and has a region containing Ni and Pd within a range of a depth of 0.5d from the wire surface when the thickness of the coating layer is d (μm).

8. The bonding wire according to claim 1 , wherein the thickness d of the coating layer is 0.01 μm or more and 0.13 μm or less.

9. The bonding wire according to claim 1, wherein the concentration profile in the depth direction of the wire is obtained by measuring by AES under the following <conditions> while digging in the depth direction from the surface of the wire by Ar sputtering. <Conditions> The center of the wire width is positioned to be the center of the width of the measurement surface, and the width of the measurement surface is 5% to 15% of the wire diameter, and the length of the measurement surface is 5 times the width of the measurement surface.

10. The bonding wire according to claim 1 , wherein the surface of the wire contains Au.

11. The bonding wire according to claim 10, wherein the concentration of Au on the surface of the wire is 10 atomic % or more and 90 atomic % or less.

12. The bonding wire according to claim 11, wherein the concentration of Au on the surface of the wire is measured by AES under the following conditions: <Conditions> The center of the wire width is positioned to be the center of the width of the measurement surface, and the width of the measurement surface is 5% to 15% of the wire diameter, and the length of the measurement surface is 5 times the width of the measurement surface.

13. 2. The bonding wire according to claim 1, wherein when a free air ball (FAB) is formed using the wire, a crystal orientation of a cross section of the FAB perpendicular to the bonding direction is measured, and the proportion of <100> crystal orientations having an angle difference of 15 degrees or less with respect to the bonding direction is 30% or more.

14. The bonding wire according to claim 1, comprising one or more elements (hereinafter referred to as "first additive elements") selected from the group consisting of B, P, and Mg, and a total concentration of the first additive element in the entire wire is 1 ppm by mass or more and 100 ppm by mass or less.

15. The bonding wire according to claim 1, further comprising one or more elements (hereinafter referred to as “second additive elements”) selected from the group consisting of Se, Te, As, and Sb, and a total concentration of the second additive elements relative to the entire wire is 1 ppm by mass or more and 100 ppm by mass or less.

16. The bonding wire according to claim 1, further comprising one or more elements (hereinafter referred to as “third additive elements”) selected from the group consisting of Ga, Ge, and In, and a total concentration of the third additive element with respect to the entire wire is 0.011% by mass or more and 1.5% by mass or less.

17. A semiconductor device comprising the bonding wire according to any one of claims 1 to 5 and 7 to 16.

18. A semiconductor device comprising the bonding wire according to claim 6.