Aluminum connection material

Abstract

The present invention provides an Al connecting material that satisfies excellent temperature cycle reliability and good first bonding strength. The Al connecting material contains 3.0 mass % to 12.0 mass % of Si, and when the crystal orientation of the Al phase in the L cross section of the Al connecting material is measured, the difference in angle with respect to the central axis is 15° or less. <111> Crystal orientation and <110> The total orientation ratio of the crystal orientation is 20% or more and 70% or less, and when the total orientation ratio is 25% or less, the angle difference with respect to the central axis direction is 15° or less. <110> The orientation ratio of the crystal orientation is 5% or more, and when the crystal orientation of the Si phase in the L cross section of the Al connecting material is measured, the angular difference with respect to the central axis direction is 15° or less. <111> Crystal orientation and <110> An Al connector having a crystal orientation ratio of 20% or more and 70% or less.

Description

[Technical field]

[0001] The present invention relates to an Al connecting material. [Background technology]

[0002] In semiconductor devices, electrodes formed on a semiconductor chip are connected to electrodes on a lead frame or a substrate by bonding wires (wire material) or bonding ribbons (strip material). In power semiconductor devices, bonding wires and bonding ribbons made of aluminum (Al) are mainly used. The wire diameter of Al bonding wires is mainly in the range of 100 μm to 600 μm, and the width of Al bonding ribbons is mainly in the range of 100 μm to 3000 μm, and the thickness is mainly in the range of 50 μm to 600 μm. Here, Al bonding wires and Al bonding ribbons are collectively called Al connection materials.

[0003] In power semiconductor devices, silicon (Si) is often used as the material for the semiconductor chip, and Al-Si alloys or Al-Cu alloys are often used as the material for the electrodes formed on the semiconductor chip. Power semiconductor devices using Al connecting materials are often used as high-power devices such as air conditioners and solar power generation systems, and as semiconductor devices for vehicles.

[0004] There are two methods for joining Al connecting materials: the first joining with electrodes on a semiconductor chip, and the second joining with electrodes on a lead frame or substrate, both of which use wedge joining. Wedge joining is a method in which ultrasonic vibration and load are applied to the Al connecting material via a metal tool, destroying the surface oxide film on the Al connecting material and the electrode material, exposing the new surface, and performing solid-state diffusion bonding. This joining method is characterized by the fact that it connects the connecting material in a solid state without melting it, and is a joining technology that differs from welding technology, which melts the connecting material.

[0005] Next-generation power semiconductor devices are required to operate stably for a long period of time compared to general-purpose power semiconductor devices. Power semiconductor devices operate by repeatedly turning current on and off. When current is supplied to a Si semiconductor chip through an Al connecting material, the temperature of the first junction rises. On the other hand, when the current supply is stopped, the temperature of the first junction drops. In this way, the first junction repeatedly rises and falls in temperature during operation of the power semiconductor. As a result, thermal stress caused by the difference in thermal expansion between the Al connecting material and the semiconductor chip is repeatedly applied to the first junction. When a connecting material made only of high-purity Al is used, the Al connecting material breaks down in a relatively short time due to thermal stress, making it difficult to satisfy the performance required for next-generation power semiconductor devices. Therefore, next-generation power semiconductors are required to improve the junction life (hereinafter also referred to as "temperature cycle reliability") associated with the rise and fall of temperature of the first junction.

[0006] In response to the demand for temperature cycle reliability, Al bonding wires that focus on improving mechanical strength have been proposed. As a method for improving the mechanical properties of Al bonding wires, a method of adding specific elements to Al has been proposed.

[0007] Patent Document 1 discloses a bonding wire made of an Al alloy containing at least magnesium (Mg) and silicon (Si) and having a total content of Mg and Si of 0.03% by mass to 0.3% by mass. This patent document discloses that the decrease in the bonding strength of the first bonding part in a cold-temperature cycle test in the temperature range from 70°C to 120°C is delayed due to the effect of increasing the strength by solid solution strengthening of Mg and Si and the effect of suppressing crack growth by precipitated magnesium silicide (Mg2Si).

[0008] Patent Document 2 discloses a bonding wire made of an alloy containing 0.01-0.2 mass% iron (Fe), 1-20 mass ppm silicon (Si), and the remainder being Al with a purity of 99.997 mass% or more, in which the amount of Fe in solid solution is 0.01-0.06%, the amount of Fe precipitated is 7 times or less the amount of Fe in solid solution, and the wire has a fine structure with an average crystal grain size of 6-12 μm. This patent document discloses that the mechanical strength of the matrix is ​​improved by uniformly dispersing intermetallic compound particles of Fe and Al in Al, and the recrystallized grains are further refined, thereby suppressing a decrease in the bonding strength of the 1st bonding portion in a thermal shock test in a temperature range of -50°C to 200°C.

[0009] Patent Document 3 discloses a bonding wire obtained by melting an Al-Si alloy containing 0.1 to 5 mass% silicon (Si) with the remainder being Al and impurities, and then extruding and quenching the melted Al-Si alloy to form it into a thin wire. This patent document discloses that mechanical strength is improved by quenching the molten Al-Si alloy to finely and uniformly disperse Si. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2014-131010 A [Patent Document 2] JP 2014-129578 A [Patent Document 3] Japanese Patent Application Publication No. 59-57440 Summary of the Invention [Problem to be solved by the invention]

[0011] As described above, the next-generation power semiconductor device is required to be able to withstand longer use than the general-purpose power semiconductor device. During the operation of the power semiconductor device, the temperature of the first joint repeatedly rises and falls. As a result, since the Al connecting material has a larger linear expansion coefficient than the semiconductor chip, thermal stress occurs in the first joint due to the difference in linear expansion coefficient between the two, and the Al connecting material may eventually be fatigued. A temperature cycle test is one of the tests for accelerating evaluation of the life (temperature cycle reliability) of the joint associated with the rise and fall in temperature of the first joint. The Al connecting material used in the next-generation power semiconductor is required to exhibit excellent temperature cycle reliability in a temperature cycle test. However, when an Al connecting material with high strength due to the addition of Si or the like as disclosed in Patent Documents 1 to 3 is used, in a temperature cycle test assuming use in the next-generation power semiconductor device, it has been confirmed that there is a problem that cracks progress at a relatively high speed in the Al alloy electrode, which has a lower strength than the Al connecting material, and it is difficult to stably obtain good temperature cycle reliability.

[0012] In addition, if a bonding failure occurs during bonding, such as the peeling off of the Al connecting material from the electrode, this leads to product defects and a decrease in manufacturing yield, so it is required to obtain good bonding strength at each bonding part. In this regard, if ultrasonic vibration or load is applied strongly to the 1st bonding part in order to obtain good bonding strength, the semiconductor chip may be damaged. In particular, when an Al connecting material strengthened by adding Si or the like is used, the semiconductor chip is easily damaged during the 1st bonding due to its hardness, and when the ultrasonic vibration or load is adjusted to reduce such damage, the bonding area cannot be stably secured due to its high deformation resistance and instability of the deformation direction, so that sufficient bonding strength of the 1st bonding part (hereinafter, also simply referred to as "1st bonding strength") cannot be obtained in some cases. These problems at the initial bonding of the 1st bonding part eventually cause a decrease in temperature cycle reliability and instability, which is an obstacle to practical use of the Al connecting material strengthened by adding Si or the like.

[0013] An object of the present invention is to provide an Al connecting material that satisfies excellent temperature cycle reliability and good first bonding strength. [Means for solving the problem]

[0014] As a result of intensive research into the above-mentioned problem, the inventors have found that in an Al connecting material containing 3.0 mass % or more and 12.0 mass % or less of Si, the Al phase in the L cross section (cross section in the central axis direction including the central axis) of the Al connecting material is <111> Crystal orientation and <110> The total orientation ratio of the crystal orientation and the Si phase in the L section <110> The inventors found that an Al connecting material having a crystal orientation ratio within a specific range can solve the above problems, and further studies were carried out based on this finding, leading to the completion of the present invention.

[0015] That is, the present invention includes the following. <1> An Al connecting material containing 3.0 mass% or more and 12.0 mass% or less of Si, When the crystal orientation of the Al phase in the L cross section (cross section in the direction of the central axis including the central axis) of the Al connecting material is measured, the angular difference with respect to the central axis is 15° or less. <111> Crystal orientation and <110> The total orientation ratio of the crystal orientation is 20% or more and 70% or less, and when the total orientation ratio is 25% or less, the angle difference with respect to the central axis direction is 15° or less. <110> The orientation ratio of the crystal orientation is 5% or more, When the crystal orientation of the Si phase in the L cross section of the Al connecting material is measured, the angular difference with respect to the central axis direction is 15° or less. <111> Crystal orientation and <110> An Al connector having a total crystal orientation ratio of 20% or more and 70% or less. <2> The crystal orientation of the Al phase in the L cross section has an angle difference of 15° or less with respect to the central axis direction. <110> The orientation ratio of the crystal orientation is 5% or more and 40% or less. <1> The Al connecting material described in <3> The average diameter of the Al phase in the L cross section is 5 μm or more and 40 μm or less. <1> or <2> The Al connecting material described in <4> The average ratio (e / f) of the short side length e to the long side length f of the Si phase in the L cross section is 0.2 to 0.70. <1> ~ <3> The Al connecting material according to any one of the preceding claims. <5> Furthermore, it contains one or more of Sr, Ca, Eu, and Sb in a total amount of 10 mass ppm or more and 800 mass ppm or less. <1> ~ <4> The Al connecting material according to any one of the preceding claims. <6> Further, it contains one or more of Ni, Mg, Fe, and In in a total amount of 10 mass ppm or more and 500 mass ppm or less. <1> ~ <5> The Al connecting material according to any one of the preceding claims. <7> The total concentration of other elements in the Al connecting material is 0.5 mass% or less. <1> ~ <6> The Al connecting material according to any one of the preceding claims. Effect of the Invention

[0016] According to the present invention, it is possible to provide an Al connecting material that satisfies excellent temperature cycle reliability and good first bonding strength. [Brief description of the drawings]

[0017] [Figure 1] 1 is a schematic diagram for explaining a measurement surface (inspection surface) when measuring the crystal orientation, average diameter, and shape of the Al phase and the Si phase of an Al connecting material. The measurement surface is a cross section (L cross section) in the central axis direction including the central axis of the Al connecting material. [Diagram 2] FIG. 2 is a schematic diagram for explaining the short side length (e) and long side length (f) of the Si phase in the L cross section. [Diagram 3] FIG. 3 is a schematic diagram for explaining the hollow defect of the first bonded portion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The present invention will be described in detail below based on preferred embodiments. Although the drawings may be referred to in the description, 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 may be modified and implemented as desired within the scope of the claims of the present invention and their equivalents.

[0019] [Al connection material] The Al connecting material of the present invention is an Al connecting material containing 3.0 mass% or more and 12.0 mass% or less of Si, When the crystal orientation of the Al phase in the L cross section (cross section in the direction of the central axis including the central axis) of the Al connecting material is measured, the angular difference with respect to the central axis is 15° or less. <111> Crystal orientation and <110> The total orientation ratio of the crystal orientation is 20% or more and 70% or less, and when the total orientation ratio is 25% or less, the angle difference with respect to the central axis direction is 15° or less. <110> The orientation ratio of the crystal orientation is 5% or more, When the crystal orientation of the Si phase in the L cross section of the Al connecting material is measured, the angular difference with respect to the central axis direction is 15° or less. <111> Crystal orientation and <110> The total orientation ratio of the crystal orientations is 20% or more and 70% or less.

[0020] As mentioned above, in the temperature cycle test, when a connecting material made of only high-purity Al was used, cracks propagated relatively quickly inside the connecting material, making it difficult to obtain good temperature cycle reliability. On the other hand, when an Al connecting material strengthened by adding Si or the like was used, cracks propagated inside the Al alloy electrode, which has a relatively low strength, so it was confirmed that it was difficult to obtain the temperature cycle reliability required for next-generation power semiconductor devices. Furthermore, when an Al connecting material strengthened by adding Si or the like was used, the semiconductor chip was easily damaged during the first bonding, and when the ultrasonic vibration or load was adjusted to reduce such damage, sufficient first bonding strength was not obtained in some cases.

[0021] As a result of intensive research to solve the above problems, the present inventors have discovered that an Al connecting material containing 3.0 mass % or more and 12.0 mass % or less of Si has an Al phase in its L cross section. <111> Crystal orientation and <110> The total orientation ratio of the crystal orientation and the Si phase in the L section <111> Crystal orientation and <110> It was found that the Al connecting material having a specific range of the total orientation ratio of the crystal orientations can improve the temperature cycle reliability and the 1st bond strength. The Al connecting material of the present invention significantly contributes to realizing the temperature cycle reliability required for next-generation power semiconductor devices and good 1st bond strength.

[0022] The Al connecting material of the present invention contains 3.0 mass% to 12.0 mass% of Si, and is composed of an Al phase in which Si is dissolved in Al, and a Si phase formed by crystallization or precipitation of Si. Here, the Al phase may contain other additive elements in addition to Si. The Si phase is a general term for Si crystallized particles and Si precipitates. The Si crystallized particles are formed from the melt during solidification and are coarse with a size of about 1 to 20 μm, while the Si precipitates are formed from the solid state and are small with a size of about 0.1 to several μm.

[0023] In the present invention, the L cross section of the Al connection material, i.e., the cross section in the central axis direction including the central axis of the Al connection material, is as will be explained later in the section "(Method of measuring the orientation ratio of the crystal orientations of the Al phase and the Si phase)" with reference to Figure 1.

[0024] The reason why the Al connecting material of the present invention can provide excellent temperature cycle reliability and good first bonding strength is presumed to be as follows.

[0025] First, regarding the temperature cycle reliability, the Si phase has a smaller linear expansion coefficient than Al, which contributes to reducing the difference in linear expansion coefficient between the Al connecting material and the semiconductor chip, and thus reduces the thermal stress that occurs. It is also believed that the particulate Si phase can suppress the growth of cracks that occur at the bonding interface into the Al connecting material. <111> Crystal orientation and <110> The total ratio of crystal orientations is in the range of 20% to 70% (however, when the total ratio of the orientations is 25% or less, the angle difference with respect to the central axis direction is 15° or less). <110> When the crystal orientation ratio is 5% or more, the effect of increasing the yield strength in the central axis direction during the temperature cycle test and reducing slip deformation is obtained. Furthermore, the Si phase <111> Crystal orientation and <110> It is believed that when the total orientation ratio of the crystal orientations is within the range of 20% to 70%, the effect of reducing the stress concentration around the Si phase can be obtained.

[0026] In addition, with regard to the first bonding strength, it is believed that by setting the orientation ratio of the crystal orientations of the Al phase and the Si phase within the range of the present invention, the deformation of the Al phase and the rotation of the crystal lattice near the bonding interface when ultrasonic vibration and load are applied are controlled, thereby improving the bonding strength. <111> Crystal orientation and <110> The total ratio of crystal orientations is in the range of 20% to 70% (however, when the total ratio of the orientations is 25% or less, the angle difference with respect to the central axis direction is 15° or less). <110> When the crystal orientation ratio is 5% or more, the deformation of the Al connecting material in the direction perpendicular to the central axis is promoted, which has the effect of improving the adhesion of the bonding interface, and the Si phase <111> Crystal orientation and <110> It is believed that when the total orientation ratio of the crystal orientations is in the range of 20% to 70%, the effect of controlling the deformation of the Al connector in the central axis direction can be obtained. It is believed that by simultaneously controlling the crystal orientations of the Al phase and the Si phase, the deformation of the Al connector in both the direction perpendicular to the central axis and the direction of the central axis can be promoted, and the effect of destroying the oxide film at the bonding interface and promoting metal bonding can be enhanced.

[0027] As described above, it is presumed that the Al connecting material of the present invention can provide excellent temperature cycle reliability and good 1st bond strength as a result of appropriately controlling the factors that contribute to improving temperature cycle reliability and 1st bond strength, as described above.

[0028] -Si concentration- The Si concentration in the range of 3.0 mass% or more and 12.0 mass% or less reduces the thermal distortion of the joint and helps to improve the temperature cycle characteristics. If it is less than 3.0 mass%, the improvement effect is small, and if it exceeds 12.0 mass%, problems such as a decrease in initial joint strength due to hardening and damage to the semiconductor chip occur. From the viewpoint of obtaining good temperature cycle reliability, the concentration of Si in the Al connecting material of the present invention is 3.0 mass% or more, preferably 4.0 mass% or more, more preferably 4.2 mass% or more, 4.4 mass% or more, 4.5 mass% or more, 4.6 mass% or more, 4.8 mass% or more, or 5.0 mass% or more. On the other hand, if the hardness of the Al connecting material is excessive, damage to the semiconductor chip is likely to occur during 1st joining under the joining conditions of ultrasonic vibration and load that are generally used. From the viewpoint of obtaining good bonding strength when performing 1st bonding under general bonding conditions, the Si concentration in the Al connecting material of the present invention is 12.0 mass% or less, preferably 11.5 mass% or less or 11.0 mass% or less, and more preferably 10.8 mass% or less, 10.6 mass% or less, 10.5 mass% or less, 10.4 mass% or less, 10.2 mass% or less, or 10.0 mass% or less.

[0029] For example, an ICP (Inductively Coupled Plasma) emission spectrometer or an ICP mass spectrometer can be used to analyze the concentration of elements contained in the Al connecting material of the present invention. If elements derived from atmospheric contaminants such as oxygen and carbon are adsorbed on the surface of the Al connecting material, it is effective to wash the surface with an acid or alkali according to the adsorbed substance before analysis.

[0030] -Crystal orientation of Al phase in L section- From the viewpoint of obtaining excellent temperature cycle reliability and good 1st joint strength, when the crystal orientation of the Al phase in the L cross section of the Al joint material is measured, the angular difference with respect to the central axis is 15° or less. <111> Crystal orientation and <110> The total orientation ratio of the crystal orientation (hereinafter, "Al phase <111> + <110> The ratio of the Al phase to the total of the Al phase is 20% or more, preferably 22% or more, 24% or more, 25% or more, or more than 25%, more preferably 26% or more or 28% or more, even more preferably 30% or more, and even more preferably 35% or more, 40% or more, 42% or more, 44% or more, or 45% or more. <111> + <110> When the total ratio is low, it has been confirmed that the effect of improving the temperature cycle reliability and the first bonding strength can be obtained even when the total ratio is in the range of 20% or more and less than 30%. <111> + <110> When the total ratio is 25% or less, the angle difference with respect to the central axis direction is 15° or less. <110> It has been confirmed that it is important that the orientation ratio of the crystal orientation is 5% or more. <111> + <110> The upper limit of the total ratio is 70% or less, preferably 65% ​​or less, more preferably 60% or less, and even more preferably 58% or less, 56% or less, or 55% or less, from the viewpoint of obtaining excellent temperature cycle reliability and good first bonding strength.

[0031] From the viewpoint of obtaining better 1st joint strength and suppressing hollowing of the 1st joint (phenomenon in which a part where the metal joint is insufficient is formed in the joint area between the Al joint material and the electrode), when the crystal orientation of the Al phase in the L cross section of the Al joint material is measured, the angular difference with respect to the central axis direction is 15° or less. <110> The orientation ratio of the crystal orientation (hereinafter, “Al phase <110> The ratio of the Al phase to the Al phase is preferably in the range of 5% to 40%. <111> + <110> The total ratio is in the range of 20% to 70%. After satisfying the above condition, the Al phase <110> By setting the ratio to 5% or more and 40% or less, it is possible to obtain a high effect of suppressing the hollowing out of the first joint and improving the strength of the first joint. <110> The reason why the above effect is obtained when the ratio is in this range is presumed to be as follows. <110> When the ratio is in this range, it is believed that the deformation of the Al connecting material in the ultrasonic vibration direction can be promoted, and the 1st joint strength can be further improved. In addition, since hollow holes often occur in the ultrasonic vibration direction, it is believed that hollow holes can also be suppressed by promoting the deformation of the Al connecting material in the ultrasonic vibration direction as described above. <110> The ratio is more preferably 10% or more, further preferably 12% or more, 14% or more, or 15% or more, from the viewpoint of obtaining a better first joint strength and suppressing hollowing out of the first joint portion. <110> The upper limit of the ratio is more preferably 38% or less, 36% or less, or 35% or less.

[0032] To measure the orientation ratio of the crystal orientation of the Al phase in the L-section of the Al joint material, a method can be used that combines the information on the Al concentration and Si concentration obtained by SEM-EDS with the information on the crystal orientation obtained by electron backscatter diffraction (EBSD). In detail, in the measurement area where the L-section of the Al joint material is used as the inspection surface, the concentration measurement of Al and Si using EDS and the crystal orientation analysis using EBSD are performed simultaneously. Next, the Al phase and the Si phase are separated and extracted from the EDS measurement results using the analysis software attached to the device. Specifically, it is preferable to use the Chi Scan function, which is a function of the analysis software OIM Data Collection or OIM Anaysis (both made by TSL Solutions) attached to the FE-SEM device. Then, for the area identified as the Al phase, the analysis software attached to the device is used to determine the presence or absence of the Al phase. <111> Crystal orientation and <110> The orientation ratio of the crystal orientations and their total can be calculated. In calculating the orientation ratio, a partial ratio is used, which is calculated as a population of the area of ​​only the crystal orientations that could be identified with a certain degree of reliability within the measurement area. <111> Crystal orientation and <110> The area ratio of each crystal orientation is <111> Orientation ratio of crystal orientation, <110> Therefore, in one embodiment, the orientation ratio of the crystal orientation of the Al phase in the L cross section of the Al connecting material of the present invention is calculated by the following procedures (1) to (3). (1) In the measurement area where the L-section of the Al joint material is used as the inspection surface, the Al and Si concentrations are measured using EDS and the crystal orientation is measured using EBSD simultaneously. (2) Use the Chi Scan function to separate and extract Al and Si. Specifically, by setting a Tolerance equivalent to the Si threshold from the Si EDS measurement results, Al and Si can be separated and identified. The crystal orientation can be analyzed using the Al and Si crystal information from the material file. (3) The crystal orientation of the region identified as the Al phase was analyzed, and the Al phase <111> The orientation ratio of the crystal orientation and <110> The orientation ratio of the crystal orientation is calculated.

[0033] In the above step (2), the Tolerance (%) setting can be selected in the range of 20 to 40%, and in a standard analysis of the L cross section of an Al joint material, it is preferable to compare at about 30%. Here is a supplementary explanation of the procedure for adjusting this Tolerance. It is preferable to select or confirm the Tolerance value so that the shape and size of the Si phase extracted and identified by the Chi Scan function are equivalent to those of the Si phase identified from the EDS map that displays the Si element concentration in EDS analysis in two dimensions.

[0034] In the present invention, the Al phase in the L cross section <111> The orientation ratio of the crystal orientation and <110> The orientation ratio of the crystal orientation was determined as the average value of the orientation ratios obtained by measuring three or more locations. In selecting the measurement area, it is preferable to obtain measurement samples from the Al connection material to be measured at intervals of 50 cm or more in the central axis direction of the Al connection material from the viewpoint of ensuring the objectivity of the measurement data, and provide them for measurement. In the present invention, the measurement area of ​​the crystal orientation by the EBSD method is preferably such that the length in the central axis direction of the Al connection material is 300 μm or more and less than 800 μm, and the entire Al connection material is included in the direction perpendicular to the central axis of the Al connection material, but if the size is large and it is difficult to measure the entire Al connection material, it can be adjusted to a range of less than 600 μm.

[0035] -Crystal orientation of the Si phase in the L cross section- From the viewpoint of obtaining excellent temperature cycle reliability and good 1st joint strength, when the crystal orientation of the Si phase in the L cross section of the Al connecting material is measured, the angular difference with respect to the central axis is 15° or less. <111> Crystal orientation and <110> The total orientation ratio of the crystal orientation (hereinafter, "Si phase <111> + <110> The total ratio of the Si phase is 20% or more, preferably 25% or more, more preferably 26% or more, 28% or more, or 30% or more. <111> + <110> From the viewpoint of obtaining excellent temperature cycle reliability and good 1st bonding strength, the total ratio is 70% or less, preferably 65% ​​or less, more preferably 60% or less, and even more preferably 58% or less, 56% or less, 55% or less, 54% or less, 52% or less, or 50% or less.

[0036] To measure the orientation ratio of the crystal orientation of the Si phase in the L cross section of the Al joint material, a method can be used that combines the information on the Al concentration and Si concentration obtained by SEM-EDS with the information on the crystal orientation obtained by EBSD, just like in the measurement of the orientation ratio of the crystal orientation of the Al phase. The detailed procedure can be the same as that described above in relation to the measurement of the orientation ratio of the crystal orientation of the Al phase. In other words, for the area identified as the Si phase, the analysis software attached to the device can be used to determine the orientation ratio of the Si phase. <111> Crystal orientation and <110> The orientation ratio of the crystal orientations and their total can be calculated. In calculating the orientation ratio, a partial ratio is used, which is calculated as a population of the area of ​​only the crystal orientations that can be identified based on a certain reliability within the measurement area. Therefore, in one embodiment, the orientation ratio of the crystal orientations of the Si phase in the L cross section of the Al connecting material of the present invention is calculated by the following steps (1) to (3). (1) In the measurement area where the L-section of the Al joint material is used as the inspection surface, the Al and Si concentrations are measured using EDS and the crystal orientation is measured using EBSD simultaneously. (2) Use the Chi Scan function to separate and extract Al and Si. Specifically, by setting a Tolerance equivalent to the Si threshold from the Si EDS measurement results, Al and Si can be separated and identified. The crystal orientation can be analyzed using the Al and Si crystal information from the material file. (3) The crystal orientation of the region identified as the Si phase was analyzed, and the Si phase <111> The orientation ratio of the crystal orientation and <110> The orientation ratio of the crystal orientation is calculated.

[0037] In the present invention, the Si phase in the L cross section <111> The orientation ratio of the crystal orientation and <110> The orientation ratio of the crystal orientation was the average value of the orientation ratios obtained by measuring at three or more locations. The setting range of Tolerance in the above procedure (2), the method of obtaining the sample for measurement, and the measurement area of ​​the crystal orientation by the EBSD method are as described above for the measurement of the orientation ratio of the crystal orientation of the Al phase.

[0038] -Average diameter of Al phase in L section- In the Al connecting material of the present invention, the average diameter of the Al phase in the L cross section is preferably 5 μm or more and 40 μm or less.

[0039] In many cases, the target of the 2nd bonding is a material harder than Al, such as a Cu substrate, and the ultrasonic vibration and load conditions during the 2nd bonding are set higher than those during the 1st bonding, which tends to make the deformation of the Al connecting material, which has been strengthened by adding Si, unstable during the 2nd bonding. In this regard, the present inventors have found that the variation in bonding strength during the 2nd bonding can be reduced by setting the average diameter of the Al phase in the L cross section to a range of 5 μm to 40 μm. The reason for this is considered to be that the effect of promoting the deformation of the Al connecting material by ultrasonic vibration by containing Si at a predetermined concentration and controlling the orientation ratio of the crystal orientations of the Al phase and the Si phase within a predetermined range, and the effect of making the deformation of the Al connecting material uniform in both directions parallel and perpendicular to the central axis of the Al connecting material by setting the average diameter of the Al phase to 5 μm to 40 μm work synergistically.

[0040] From the viewpoint of further reducing the variation in the bonding strength in the 2nd bonding and realizing a better stability of the bonding strength, the average diameter of the Al phase in the L cross section of the Al connecting material of the present invention is more preferably 10 μm or more, more preferably 12 μm or more, 14 μm or more, or 15 μm or more. Also, the upper limit of the average diameter of the Al phase in the L cross section is more preferably 35 μm or less, more preferably 30 μm or less, and even more preferably 28 μm or less, 26 μm or less, or 25 μm or less.

[0041] A method for measuring the average diameter of the Al phase in the L cross section of the Al connecting material will be described. For measuring the average diameter of the Al phase in the L cross section, a method of combining information on the Al concentration and Si concentration obtained by SEM-EDS and information on the crystal orientation obtained by EBSD can be used, as in the measurement of the orientation ratio of the crystal orientation described above. The detailed procedure may be the same as that described above in relation to the measurement of the orientation ratio of the crystal orientation, that is, the crystal orientation of the region specified as the Al phase can be analyzed by using the analysis software attached to the device. If the orientation difference between the measurement points is 15° or more, it is determined to be a grain boundary and the circle equivalent diameter is calculated. The average value of the circle equivalent diameter of each Al phase is defined as the average diameter of the Al phase. In the process of calculating the average diameter of the Al phase, the parts where the crystal orientation cannot be measured or the parts where the crystal orientation can be measured but the reliability of the orientation analysis is low were excluded from the calculation. Therefore, in one embodiment, the average diameter of the Al phase in the L cross section of the Al connecting material of the present invention is calculated by the following procedures (1) to (3). (1) The L-section of the Al joint material is used as the inspection surface, and the Al and Si concentrations are measured using EDS and the crystal orientation is measured using EBSD simultaneously. (2) Use the Chi Scan function to separate and extract Al and Si. Specifically, by setting a Tolerance equivalent to the Si threshold from the Si EDS measurement results, Al and Si can be separated and identified. The crystal orientation can be analyzed using the Al and Si crystal information from the material file. (3) For the region identified as Al phase, the crystal orientation is analyzed, and if the orientation difference between the measurement points is 15° or more, it is determined to be a grain boundary and the circle equivalent diameter of each crystal grain is calculated. The circle equivalent diameters of each crystal grain are then averaged to calculate the average diameter of the Al phase. Here, for the average calculation, the average value obtained by area averaging, which can be selected in the software provided with the device, is used. By using the average value obtained by area averaging, it is possible to accurately measure and judge whether the conditions related to the average diameter of the Al phase, which are suitable for improving the stability of the bonding strength in the second bonding, are met. In the calculation of the area average, the ratio of each particle area to the total particle area is multiplied by each particle area value to calculate the average, and the software automatically calculates it.

[0042] In the present invention, when calculating the average diameter of the Al phase in the L cross section, only Al phases having a diameter (equivalent circle diameter) of 0.5 μm or more are considered. This makes it possible to accurately determine whether the requirement related to the average diameter of the Al phase in the L cross section, which is suitable for improving the stability of the bonding strength in the 2nd bonding, is met.

[0043] When measuring the average diameter of the Al phase in the L cross section, the setting range of Tolerance in the above procedure (2), the method of obtaining the measurement sample, and the measurement area of ​​the crystal orientation by the EBSD method are the same as those described above for the measurement of the orientation ratio of the crystal orientation of the Al phase.

[0044] -Shape of the Si phase in the L cross section- When the bond strength of multiple wires was evaluated in a temperature cycle test, it was confirmed that multiple bonds do not deteriorate simultaneously, but that there is variation in the failure time (lifetime) when the bond strength decreases. In order to achieve the temperature cycle reliability required for next-generation power semiconductor devices, it is necessary to not only manage the life based on the average bond strength in the temperature cycle test, but also to control the variation in bond strength.

[0045] The inventors have found that the Si content is 3.0 mass% or more and 12.0 mass% or less, and that the Al phase in the L cross section <111> + <110> The total ratio and the Si phase in the L section <111> + <110> In the process of investigating an Al connecting material in which the ratio of the short side length e to the long side length f of the Si phase in the L cross section is within a specific range, it was found that the shape of the Si phase in the L cross section affects the variation in the bonding strength in the temperature cycle test. In detail, it was found that the average value of the ratio (e / f) of the short side length e to the long side length f of the Si phase in the L cross section is in the range of 0.2 to 0.70, and in addition to the effect of suppressing the deterioration of the bonding strength after the temperature cycle test, the variation in the bonding strength is reduced. The value of this ratio (e / f) is an index indicating the flatness. Further explanation will be given with reference to FIG. 2. FIG. 2 is a schematic diagram showing the Si phase in the L cross section of an Al connecting material, and the central axis direction of the Al connecting material is shown to correspond to the horizontal direction (left-right direction) of FIG. 2, and the direction perpendicular to the central axis is shown to correspond to the vertical direction (up-down direction) of FIG. 2. For the Si phase in the L cross section, the above-mentioned "short side length e" corresponds to the dimension indicated by the symbol e in FIG. 2. Also, for the Si phase in the L cross section, the above-mentioned "long side length f" corresponds to the dimension indicated by the symbol f in FIG. 2. Hereinafter, the ratio (e / f) of the short side length e to the long side length f of the Si phase in the L cross section is also referred to as the "Si phase shape ratio (e / f)." The value of the Si phase shape ratio (e / f) can be obtained by the Grain Shape Aspect Ratio in the analysis software provided with the device.

[0046] In the Al connecting material of the present invention, the reason why the variation in the bonding strength in the temperature cycle test can be reduced by controlling the average value of the shape ratio (e / f) of the Si phase is presumed to be as follows. The reason why the bonding strength decreases in the temperature cycle test is that cracks propagate along the central axis of the Al connecting material or a direction close to it inside the Al connecting material or at the bonding interface. Here, the Si phase tends to be arranged so that the direction of the long side length f is the central axis of the Al connecting material or a direction close to it due to plastic processing by wire drawing. When the average value of the shape ratio (e / f) of the Si phase is in the range of 0.2 to 0.70, the Si phase has a shape such as an ellipse or a column, and exhibits the effect of relaxing the thermal stress in the central axis direction of the Al connecting material, which is considered to be able to suppress the propagation of cracks along the central axis direction of the Al connecting material or a direction close to it. In order to reduce the variation in the bonding strength in the temperature cycle test, it is sufficient that the average value of the shape ratio (e / f) of the Si phase in the L cross section is within the above-mentioned preferred range, and it is not necessary that the shape ratio (e / f) of all the Si phases is in the range of 0.2 to 0.70. For example, the Si phase may have a shape ratio (e / f) of less than 0.2, or may have a shape ratio (e / f) of more than 0.70.

[0047] From the viewpoint of reducing the variation in bonding strength in a temperature cycle test and achieving better temperature cycle reliability required for next-generation power semiconductor devices, the average value of the shape ratio (e / f) of the Si phase in the L cross section of the Al connecting material of the present invention is more preferably 0.25 or more. From the viewpoint of achieving better temperature cycle reliability, the upper limit of the average value of the shape ratio (e / f) of the Si phase is more preferably 0.6 or less.

[0048] A method for measuring the shape ratio (e / f) of the Si phase in the L-section of the Al connecting material will be described. First, as in the above-mentioned measurement of the crystal orientation and the measurement of the average diameter of the Al phase, a method can be used in which the information on the Al concentration and Si concentration obtained by SEM-EDS is combined with the information on the crystal orientation obtained by EBSD. The detailed procedure may be the same as that described above in relation to the measurement of the orientation ratio of the crystal orientation, that is, the crystal orientation can be analyzed by using the analysis software attached to the device for the area specified as the Si phase. If the orientation difference between the measurement points is 15° or more, it is determined to be a grain boundary and the shape ratio (e / f) is calculated. The average value of the shape ratio (e / f) of each Si phase is defined as the average value of the shape ratio (e / f) of the Si phase. In the process of calculating the shape ratio (e / f) of the Si phase, the parts where the crystal orientation cannot be measured or the parts where the crystal orientation can be measured but the reliability of the orientation analysis is low are excluded from the calculation. Therefore, in one embodiment, the average value of the shape ratio (e / f) of the Si phase in the L-section of the Al connecting material of the present invention is calculated by the following procedures (1) to (3). (1) The L-section of the Al joint material is used as the inspection surface, and the Al and Si concentrations are measured using EDS and the crystal orientation is measured using EBSD simultaneously. (2) Use the Chi Scan function to separate and extract Al and Si. Specifically, by setting a Tolerance equivalent to the Si threshold from the Si EDS measurement results, Al and Si can be separated and identified. The crystal orientation can be analyzed using the Al and Si crystal information from the material file. (3) For the region identified as the Si phase, the crystal orientation is analyzed, and if the orientation difference between the measurement points is 15° or more, it is determined to be a grain boundary, and the shape ratio (e / f) of each grain is obtained. The shape ratios (e / f) of each grain are averaged to calculate the average value of the shape ratio (e / f) of the Si phase. Here, the average value of the shape ratio (e / f) of the Si phase is the value of the Grain Shape Aspect Ratio (hereinafter referred to as the "grain shape aspect ratio") of the analysis software. This value is obtained by averaging the grain shape aspect ratios of each grain. The grain shape aspect ratio is calculated by the ratio (e / f) of the short side length (e) (Grain Shape Minor Axis) and the long side length (f) (Grain Shape Major Axis) of one grain. In addition, for the average calculation, the average value obtained by the Area Average, which can be selected in the software attached to the device, is used. By adopting the average value obtained by area averaging, it is possible to reduce the variation in bonding strength in temperature cycle tests and to accurately measure and judge whether the conditions related to the average value of the shape ratio (e / f) of the Si phase are met, which is suitable for achieving the temperature cycle reliability required for next-generation power semiconductor devices even better.

[0049] When measuring the average value of the shape ratio (e / f) of the Si phase in the L cross section, the setting range of Tolerance in the procedure (2) above and the measurement area of ​​the crystal orientation by the EBSD method are as described above for the measurement of the orientation ratio of the crystal orientation of the Al phase.

[0050] In addition to the above, there are several other methods for measuring the average diameter of the Al phase and the shape ratio (e / f) of the Si phase, including binarization processing from the observed image of the L cross section. However, in the present invention, a method is used that combines the information on the Al concentration and Si concentration obtained by SEM-EDS with the information on the crystal orientation obtained by EBSD, as described above, for the following reasons: the present invention is equipped with many measurement functions and can obtain multiple characteristics such as the above-mentioned crystal orientation, the average diameter of the Al phase, and the shape ratio (e / f) of the Si phase in a single measurement; automatic analysis is possible; and the measurement is easy using widely used equipment and analysis techniques.

[0051] -Addition of Sr, Ca, Eu, and Sb- The Al connecting material of the present invention may further contain at least one of Sr, Ca, Eu and Sb (hereinafter also referred to as the "first element group") in a total amount of 10 ppm by mass or more and 800 ppm by mass or less.

[0052] Furthermore, by containing at least one of Sr, Ca, Eu, and Sb in a total amount of 10 mass ppm to 800 mass ppm, the frequency of wire breakage during wire drawing of the Al connecting material can be reduced. An Al alloy containing a high concentration of Si of 3.0 mass % to 12.0 mass % tends to have an increased frequency of wire breakage during the wire drawing process. One of the causes is thought to be that particles of the Si phase crystallized during solidification cause stress concentration during wire drawing, inducing wire breakage. It is presumed that the addition of the first element group can uniformly distribute the particulate Si phase and inhibit the Si phase from growing and becoming coarse, thereby alleviating stress concentration during wire drawing and reducing wire breakage. It is thought that the effect of alleviating stress concentration during wire drawing can be enhanced by controlling the orientation ratio of the crystal orientations of the Al phase and the Si phase in the L cross section and adding the first element group.

[0053] From the viewpoint of reducing the frequency of wire breakage during wire drawing, the total concentration of the first element group in the Al connecting material of the present invention is more preferably 20 ppm by mass or more, even more preferably 30 ppm by mass or more, 40 ppm by mass or more, or 50 ppm by mass or more, and the upper limit is preferably 750 ppm by mass or less, more preferably 740 ppm by mass or less, 720 ppm by mass or less, or 700 ppm by mass or less.

[0054] -Addition of Ni, Mg, Fe, and In- The Al connecting material of the present invention may further contain at least one of Ni, Mg, Fe and In (hereinafter also referred to as "second element group") in a total amount of 10 ppm by mass or more and 500 ppm by mass or less.

[0055] Furthermore, by containing at least one of Ni, Mg, Fe, and In in a total amount of 10 mass ppm to 500 mass ppm, the occurrence of scratches and chipping on the surface of the Al connecting material can be suppressed, and a smooth surface can be formed. In an Al alloy containing Si at a high concentration of 3.0 mass % to 12.0 mass %, the surface hardens, and the Si phase and Al oxide present on the surface fall off, and the surface may be scratched and chipped during wire drawing, resulting in an Al connecting material with large surface irregularities. It is presumed that the addition of the second element group stabilizes the Al oxide on the surface of the Al connecting material, refines the structure of the Al crystal grains, and hardens it, thereby reducing scratches and chipping during wire drawing. It is considered that the effect of suppressing scratches and chipping on the surface of the Al connecting material and forming a smooth surface can be enhanced by controlling the orientation ratio of the crystal orientations of the Al phase and the Si phase in the L cross section and adding the second element group.

[0056] From the viewpoint of forming an Al connecting material having a smooth surface while suppressing the occurrence of scratches and chipping on the surface, the total concentration of the second element group in the Al connecting material of the present invention is more preferably 20 ppm by mass or more, even more preferably 30 ppm by mass or more, 40 ppm by mass or more, or 50 ppm by mass or more, and the upper limit is preferably 450 ppm by mass or less, more preferably 440 ppm by mass or less, 420 ppm by mass or less, or 400 ppm by mass or less.

[0057] When manufacturing the Al connecting material of the present invention, it is preferable to use Al with a purity of 4N (Al: 99.99% by mass or more) as the aluminum raw material, and it is even more preferable to use Al with a purity of 5N (Al: 99.999% by mass or more) or more, which has a lower amount of impurities.

[0058] The Al connecting material of the present invention may further contain elements other than Al, Si, the first element group, and the second element group (hereinafter, also referred to as "other elements"). The total concentration of the other elements in the Al connecting material is not particularly limited as long as the effects of the present invention are not impaired. The total concentration of the other elements may be, for example, 0.5 mass% or less, 0.4 mass% or less, 0.3 mass% or less, 0.2 mass% or less, 0.15 mass% or less, 0.1 mass% or less, 0.08 mass% or less, 0.06 mass% or less, 0.05 mass% or less, 0.04 mass% or less, 0.03 mass% or less, 0.025 mass% or less, 0.02 mass% or less, 0.018 mass% or less, 0.016 mass% or less, 0.015 mass% or less, 0.014 mass% or less, 0.012 mass% or less, or 0.01 mass% or less. The lower limit of the total concentration of the other elements is not particularly limited, and may be 0 mass%. In one embodiment, the remainder of the Al connecting material of the present invention is composed of Al and other elements. Therefore, in a preferred embodiment, the Al connecting material of the present invention is composed of Al, Si, and other elements. In another preferred embodiment, the Al connecting material of the present invention is composed of Al, Si, one or more elements of the first element group, and other elements. In yet another preferred embodiment, the Al connecting material of the present invention is composed of Al, Si, one or more elements of the second element group, and other elements. In yet another preferred embodiment, the Al connecting material of the present invention is composed of Al, Si, one or more elements of the first element group, one or more elements of the second element group, and other elements.

[0059] In one embodiment, the balance of the Al connecting material of the present invention is composed of Al and inevitable impurities. Therefore, in a preferred embodiment, the Al connecting material of the present invention is composed of Al, Si, and inevitable impurities. In another preferred embodiment, the Al connecting material of the present invention is composed of Al, Si, one or more elements of the first element group, and inevitable impurities. In yet another preferred embodiment, the Al connecting material of the present invention is composed of Al, Si, one or more elements of the second element group, and inevitable impurities. In yet another preferred embodiment, the Al connecting material of the present invention is composed of Al, Si, one or more elements of the first element group, one or more elements of the second element group, and inevitable impurities.

[0060] In a preferred embodiment, the Al connecting material of the present invention does not have a coating mainly composed of a metal other than Al on the outer periphery of the Al connecting material. Here, the "coating mainly composed of a metal other than Al" refers to a coating in which the content of a metal other than Al is 50 mass % or more.

[0061] The Al connecting material of the present invention may be an Al bonding wire or an Al bonding ribbon. When the Al connecting material of the present invention is an Al bonding wire, its wire diameter is not particularly limited, and may be, for example, in the range of 100 to 600 μm. When the Al connecting material of the present invention is an Al bonding ribbon, its rectangular or approximately rectangular cross-sectional dimensions (W×T) are not particularly limited, and, for example, W may be 100 to 3000 μm, and T may be 50 to 600 μm.

[0062] The Al connecting material of the present invention can provide excellent temperature cycle reliability and good first bonding strength, and therefore can be suitably used as an Al connecting material for semiconductor devices, particularly as an Al connecting material for power semiconductor devices.

[0063] -Method of manufacturing Al connection material- An example of a method for producing an Al connecting material of the present invention will be described below. Hereinafter, an example will be described in conjunction with the production of an Al bonding wire having a wire diameter of 200 to 400 μm.

[0064] The Al and alloying elements used as raw materials are preferably of high purity. The purity of Al is preferably 99.99% by mass or more, with the remainder being composed of inevitable impurities. The purity of Si, the first element group, and the second element group used as alloying elements is preferably 99.9% by mass or more, with the remainder being composed of inevitable impurities. The Al alloy used for the bonding wire can be produced by loading the Al raw material and the raw material of the alloying elements into a graphite or alumina crucible processed to obtain a cylindrical ingot, and melting it using an electric furnace or a high-frequency heating furnace. The diameter of the cylindrical ingot is preferably Φ6 mm or more and less than 8 mm, taking into consideration the workability in the subsequent processing steps. The atmosphere in the furnace during melting is preferably an inert atmosphere or a reducing atmosphere to prevent excessive oxidation of Al and other elements constituting the wire. The maximum temperature of the molten metal during melting is preferably in the range of 800 ° C or more and less than 1050 ° C, taking into consideration the ease of controlling the shape and size of the Si phase during solidification while ensuring the fluidity of the molten metal. The cooling method after melting can be water cooling, furnace cooling, air cooling, or the like.

[0065] The cylindrical ingot obtained by melting is subjected to solution treatment by heating at high temperature, and then repeatedly subjected to wire drawing using a die to produce wire of the desired diameter. The wire after wire drawing can be used as Al alloy bonding wire by performing final heat treatment in an electric furnace.

[0066] In order to control the crystal orientation of the Si phase and the Al phase in the L cross section, it is effective to control the heat treatment conditions such as the solution treatment, homogenization treatment, and final heat treatment, as well as the wire drawing conditions, etc. During the wire drawing process, it is effective to use a lubricant to ensure lubrication at the contact interface between the wire and the die.

[0067] Al phase in L section <111> + <110> The total ratio is in the range of 20% to 70%, and the Si phase in the L cross section is <111> + <110> An example of the production conditions for controlling the total ratio to be within the range of 20% to 70% is shown below.

[0068] In order to adjust the crystal orientation of the Si phase, it is effective to perform two-stage heat treatment on the ingot and control the reduction in area during wire drawing.

[0069] It is effective to set the temperature range of the solution treatment to 400°C or higher and lower than 550°C, and the time range to 1 hour or higher and lower than 6 hours. It is effective to perform homogenization treatment after the solution treatment at 250°C or higher and lower than 350°C, and the time range to 2 hours or higher and lower than 6 hours. This promotes the division and growth of the Si phase that crystallizes during the solidification process, and improves the crystal orientation of the Si phase. <111> and <110> The orientation of the molecules can be promoted.

[0070] Regarding the wire drawing conditions, it is effective to set the wire area reduction rate per die used during wire drawing to be in the range of 10% to less than 20%. Here, if the wire area reduction rate per die is P1, P1 is expressed by the following formula.

[0071] P1 = {(R2 2 -R1 2 ) / R2 2}×100 In the formula, R2 represents the diameter (mm) of the wire before processing, and R1 represents the diameter (mm) of the wire after processing.

[0072] By adjusting the wire area reduction rate within the above range, the entire wire is significantly deformed during die processing, and processing strain increases even inside the wire, so that the Si phase is aligned in the direction of the wire's central axis, while at the same time, processing strain within the Si phase is adjusted. From this state of wire drawing, by carrying out subsequent heat treatment, a high atomic density is obtained. <111> Crystal orientation and <110> The orientation ratio of the crystal orientation can be increased, and the Si phase has a high elastic modulus. <111> Crystal orientation and <110> It is possible to increase the orientation ratio of the crystal orientation.

[0073] In order to adjust the crystal orientation of the Al phase, it is effective to combine control of the area reduction rate of the wire drawing process and the final heat treatment conditions.

[0074] Specifically, the die reduction rate is adjusted to a range of 10% or more and less than 20% to control the processing strain, which is formed as a processing texture. <111> Crystal orientation and <110> The ratio of crystal orientation can be promoted. For example, as the reduction in area increases, the processing strain increases and <111> Crystal orientation and <110> The proportion of crystal orientations tends to increase.

[0075] Regarding the final heat treatment conditions, it is effective to adjust the temperature range to 200°C or higher and lower than 360°C, and the time range to 2 hours or higher and lower than 24 hours. The final heat treatment advances the recovery and recrystallization of the Al phase, and at the same time, the amount of Si dissolved in the Al phase changes depending on the heat treatment temperature, which changes the recrystallization temperature. In addition to the formation of the above-mentioned processed texture, by adjusting the progress of recrystallization by the final heat treatment, it becomes easy to control the orientation of the crystal orientation. For example, by adjusting the temperature or time of the final heat treatment, it is possible to obtain a highly dense alloy. <111> Crystal orientation and <110> The orientation ratio of the crystal orientations tends to increase.

[0076] In order to control the average diameter of the Al phase in the L cross section to the range of 5 μm to 40 μm, it is effective to adjust the temperature and time of the heat treatment at the final wire diameter to control the growth of crystal grains due to recrystallization of the Al phase.

[0077] It is effective to control the temperature range of the final heat treatment to 250° C. or higher and lower than 340° C., and the time range to 5 hours or higher and lower than 24 hours. By performing homogenization treatment at a relatively low temperature and adjusting the amount of solid solution of Si contained in the Al phase, it becomes easy to adjust the recrystallization temperature of the Al phase in the final heat treatment, and the size of the Al phase can be controlled to the desired range.

[0078] In addition, if intermediate heat treatment is performed as necessary, it becomes easy to adjust the conditions of the final heat treatment. Intermediate heat treatment is a heat treatment performed in the middle of the process of processing from an ingot to the final wire diameter. The temperature range of intermediate heat treatment is 250°C or higher and lower than 400°C, and the time is 30 minutes or more and less than 3 hours. It is effective to perform intermediate heat treatment at a wire diameter that is 2.5 to 4.0 times the final wire diameter. By performing intermediate heat treatment, it is possible to reduce the processing strain of the Al phase and advance recrystallization, and by first adjusting the Al phase, it becomes easy to adjust the grain size of the Al phase in the subsequent final heat treatment. For example, if the intermediate heat treatment temperature is increased, the diameter of the Al phase tends to decrease.

[0079] In order to adjust the shape (shape ratio (e / f)) of the Si phase in the L cross section, it is effective to control the above-mentioned two-stage heat treatment and the final heat treatment.

[0080] The temperature range for the solution treatment of the ingot is 400°C or higher and lower than 550°C, and the time is 1 hour or higher and lower than 6 hours, and the subsequent homogenization treatment is preferably 250°C or higher and lower than 350°C, and the time is 2 hours or higher and lower than 6 hours. The solution treatment causes the division and growth of the Si phase that crystallized during the solidification process, and the homogenization treatment causes the solid solution and precipitation of Si at the interface of the Si phase, allowing the shape of the Si phase to be controlled. For example, when solution treatment is performed at high temperature, the shape ratio (e / f) of the Si phase tends to become smaller.

[0081] As mentioned above, the above is an example of the manufacture of Al bonding wire, which is a wire material, as a representative example of Al connecting material. The same procedure can be basically used to manufacture Al bonding ribbon, which is a strip material. The temperature and time of the heat treatment can be approximately the same as those described above. In addition, when manufacturing Al bonding ribbon by rolling processing, the reduction rate of the die can be replaced with the reduction rate to adjust it.

[0082] [Semiconductor Devices] A semiconductor device can be manufactured by connecting electrodes on a semiconductor chip to external electrodes on a lead frame or substrate using the Al connecting material of the present invention. As mentioned above, wedge bonding is used for both the first bonding with the electrodes on the semiconductor chip and the second bonding with the electrodes on the lead frame or substrate.

[0083] In one embodiment, the semiconductor device of the present invention includes a circuit board, a semiconductor chip, and an Al connecting material for electrically connecting the circuit board and the semiconductor chip, and is characterized in that the Al connecting material is the Al connecting material of the present invention.

[0084] In the semiconductor device of the present invention, the circuit board and the semiconductor chip are not particularly limited, and a known circuit board and a semiconductor chip 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, the semiconductor device may be configured to include a lead frame and a semiconductor chip mounted on the lead frame, as in the semiconductor device described in JP 2020-150116 A.

[0085] Examples of the semiconductor device include various semiconductor devices used in electrical products (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.), and among these, power semiconductor devices are preferred. EXAMPLES

[0086] The present invention will be specifically described below with reference to examples, although the present invention is not limited to the examples shown below.

[0087] (sample) The method of preparing the samples will be described. The raw material Al had a purity of 4N (99.99% by mass or more), with the remainder consisting of inevitable impurities. The alloying elements Si, the first element group (Sr, Ca, Eu, Sb), and the second element group (Ni, Mg, Fe, In) had a purity of 99.99% by mass or more, with the remainder consisting of inevitable impurities. The Al alloy used for the Al connecting material was produced by loading the Al raw material and the raw material of the alloying elements into an alumina crucible and melting them using a high-frequency heating furnace. The atmosphere in the furnace during melting was an Ar atmosphere, and the maximum temperature of the molten metal during melting was 800°C or more and less than 1050°C. The cooling method after melting was air cooling in the air or water cooling in water.

[0088] A cylindrical ingot with a diameter of 6 mm was obtained by melting, and the ingot was subjected to solution treatment and homogenization treatment, followed by wire drawing using a die and intermediate heat treatment to produce an Al connection material (Al bonding wire) with a diameter of 300 μm. The temperature range of the solution treatment was 500°C or higher and lower than 550°C, and the time was 2 hours or higher and lower than 4 hours. After the solution treatment, a homogenization treatment was performed continuously during cooling. The temperature range of the homogenization treatment was 250°C or higher and lower than 350°C, and the time was 2 hours or higher and lower than 5 hours. The cooling method after the homogenization treatment was air cooling in the atmosphere.

[0089] A commercially available lubricant was used during the wire drawing process, and the wire area reduction rate per die during the wire drawing process was set to 12.5% ​​or more and less than 16.0%. The temperature range of the final heat treatment was set to 250°C or more and less than 360°C, and the final heat treatment time was set to 2 hours or more and less than 24 hours.

[0090] In some examples, the wire was drawn using dies with a die angle of 14° or more and less than 18°.

[0091] (Method of measuring element content) The concentration of elements contained in the Al connecting material was measured using an ICP-OES ("PS3520UVDDII" manufactured by Hitachi High-Tech Science Corporation) or an ICP-MS ("Agilent 7700x ICP-MS" manufactured by Agilent Technologies, Inc.) as an analytical device.

[0092] (Method for measuring the orientation ratio of the crystal orientations of the Al phase and the Si phase) The L-section (cross section in the central axis direction including the central axis) of the Al connecting material was used as the inspection surface, and the crystal orientation of the Al phase and the Si phase was measured. In the present invention, the central axis of the Al connecting material and the cross section in the central axis direction including the central axis (L-section) are as shown in FIG. 1. FIG. 1 shows a case where the Al connecting material is an Al bonding wire having a circular cross-sectional shape, but when the Al connecting material is an Al bonding ribbon having a rectangular or approximately rectangular cross-sectional shape with a width W and a thickness T, the central axis refers to the axis passing through the center of the width W and the center of the thickness T, and the L-section refers to a cross section in the central axis direction including the central axis and in the direction of the thickness T. When processing the cross section to expose the L-section of the Al connecting material, it may deviate from the central axis of the Al connecting material. In this case, if the length in the direction perpendicular to the central axis of the L-section is 90% or more of the wire diameter of the Al connecting material (thickness T in the case of a ribbon), it can be considered as a cross section including the central axis.

[0093] In addition, FE-SEM (SU-70 manufactured by Hitachi High-Technologies Corporation) was used for the measurement, and analysis software APEX (for data collection), OIM Data Collection (for chiscan), and OIM Anaysis (for data analysis) manufactured by TSL Solutions were used for the analysis. Three measurement areas were randomly selected at intervals of 50 cm or more in the central axis direction of the Al connecting material, and measurements were performed on the three areas. The measurement area was determined so that the Al connecting material was included in its entirety in the direction perpendicular to the central axis, and 300 μm or more in the central axis direction of the Al connecting material. In addition, the main conditions of the EDS and EBSD measurements were set as follows: acceleration voltage was 15 kV, measurement magnification was 350 times, scan speed was 30 to 120 points / sec, and measurement interval was in the range of 0.1 to 0.3 μm. Here, if the scan speed is fast, the measurement time can be shortened, but there is a concern that the measurement accuracy of the EDS will decrease. It is desirable to select an appropriate scan speed within the above range.

[0094] -Crystal orientation of Al phase- The orientation ratio of the Al phase crystal orientation in the L cross section of the Al joint material was measured by combining the information on the Al concentration and Si concentration obtained by SEM-EDS with the information on the crystal orientation obtained by EBSD. In detail, the measurement was carried out according to the following steps (1) to (3). (1) In the measurement area where the L-section of the Al joint was used as the inspection surface, the Al and Si concentrations were measured using EDS and the crystal orientation was measured using EBSD simultaneously. (2) The Chi Scan function of the EBSD analysis software was used to separate and extract Al and Si. Specifically, Al and Si were separated and identified by setting a tolerance equivalent to the Si threshold from the Si EDS measurement results. The crystal orientation was analyzed using the crystal information of Al and Si from the material file. Here, the tolerance condition was mainly set to 30%, and was adjusted as necessary. (3) The crystal orientation of the region identified as the Al phase was analyzed, and the Al phase <111> The orientation ratio of the crystal orientation and <110> The orientation ratio of the crystal orientation was calculated. The crystal orientation to be investigated is the typical crystal orientation of Al metal. <111> , <110> , <100> At least three of the above were selected, and the crystal orientation with the highest ratio was selected as necessary. Here, the partial ratio was used for the orientation ratio of the crystal orientations.

[0095] Al phase <111> The orientation ratio of the crystal orientation and <110> The orientation ratio of the crystal orientation was determined as the average value of the values ​​obtained for the three measurement regions by the above steps (1) to (3).

[0096] -Crystal orientation of the Si phase- The orientation ratio of the crystal orientation of the Si phase in the L cross section of the Al joint material was measured using a method that combines the information on the Al concentration and Si concentration obtained by SEM-EDS with the information on the crystal orientation obtained by EBSD, in the same way as in the measurement of the orientation ratio of the crystal orientation of the Al phase. In detail, after carrying out the above steps (1) and (2), the measurement was carried out according to the following step (3). (3) The crystal orientation of the region identified as the Si phase was analyzed, and the Si phase <110> The orientation ratio of the crystal orientation and <110> The orientation ratio of the crystal orientation was calculated. The partial ratio was used for the orientation ratio of the crystal orientation.

[0097] Si phase <111> The orientation ratio of the crystal orientation and <110> The orientation ratio of the crystal orientation was determined as the average value of the values ​​obtained for the three measurement regions by the above steps (1) to (3).

[0098] (Method for measuring the average diameter of the Al phase) The average diameter of the Al phase in the L cross section of the Al joint material was measured using a method that combines the information on the Al concentration and Si concentration obtained by SEM-EDS with the information on the crystal orientation obtained by EBSD, in the same way as the measurement of the orientation ratio of the crystal orientation of the Al phase. In detail, after carrying out the above steps (1) and (2), the measurement was carried out according to the following step (3). (3) The crystal orientation of the region identified as Al phase was analyzed, and if the orientation difference between the measurement points was 15° or more, it was determined to be a grain boundary, and the circle equivalent diameter of each crystal grain was calculated. The circle equivalent diameters of each crystal grain were then averaged to calculate the average diameter of the Al phase. Here, for the average calculation, the average value obtained by the Area Average, which can be selected in the software attached to the device, was used. In addition, when calculating the average diameter of the Al phase in the L cross section, only Al phases with a diameter (circle equivalent diameter) of 0.5 μm or more were considered.

[0099] The average diameter of the Al phase was determined as the average value of the values ​​obtained for the three measurement regions by the above steps (1) to (3).

[0100] (Method for measuring the shape of the Si phase) The shape (shape ratio (e / f)) of the Si phase in the L cross section of the Al joint material was measured using a method that combines the information on the Al and Si concentrations obtained by SEM-EDS with the information on the crystal orientation obtained by EBSD, in the same way as in the measurement of the orientation ratio of the crystal orientation of the Al phase. In detail, after carrying out the above steps (1) and (2), the measurement was carried out according to the following step (3). (3) The crystal orientation of the region identified as the Si phase was analyzed, and if the orientation difference between the measurement points was 15° or more, it was determined to be a grain boundary, and the shape ratio (e / f) of each grain was calculated. The shape ratio (e / f) of each grain was then averaged to calculate the average value of the shape ratio (e / f) of the Si phase. Here, the average value of the shape ratio (e / f) of the Si phase was calculated using the value of the Grain Shape Aspect Ratio ("Grain Shape Aspect Ratio") of the analysis software. The grain shape aspect ratio was calculated by automatically calculating the ratio (e / f) of the short side length (e) (Grain Shape Minor Axis) and the long side length (f) (Grain Shape Major Axis) of one grain. Here, the average value calculated by the area average was used for the average calculation.

[0101] (Evaluation method for Al connecting materials) The evaluation method of the Al connecting material will be explained. The wire diameter of the Al connecting material (Al bonding wire) used for the evaluation was Φ300μm. The semiconductor chip used was made of Si, and the electrodes on the semiconductor chip were made of an alloy with a composition of Al-0.5%Cu, which was deposited to a thickness of 4μm. The substrate used was an Al alloy with a Ni film deposited to a thickness of 5μm. A commercially available wire bonder (manufactured by Ultrasonic Industries Co., Ltd.) was used to bond the Al connecting material, and both the 1st and 2nd bondings were wedge bonded.

[0102] (Method of evaluating temperature cycle reliability) A commercially available thermal shock tester was used to evaluate the temperature cycle test. In the temperature cycle test, the sample chamber was moved between a low-temperature chamber and a high-temperature chamber to repeatedly raise and lower the temperature. The temperature of the low-temperature chamber was -40°C, and that of the high-temperature chamber was 175°C. The test started with the sample chamber in the high-temperature chamber, and the test was started when the sample chamber moved to the low-temperature chamber and returned to the high-temperature chamber, which was defined as one cycle. The time the sample chamber stayed in the low-temperature chamber and the high-temperature chamber was 20 minutes each. The sample to be subjected to the temperature cycle test had a structure in which a semiconductor chip was mounted on a substrate, and the electrodes on the semiconductor chip and the electrodes on the substrate were connected with an Al connecting material. After the start of the test, the sample was taken out every 250 cycles, and a shear test was performed on the first joint. The average value of the shear strength of the first joints at five randomly selected locations was used as the value of the shear strength of the first joints to evaluate the temperature cycle reliability. The number of cycles at which the shear strength dropped to 70% or less of the value before the temperature cycle test was taken as the joint life. If the joint life was less than 500 cycles, it was judged to have practical problems and was rated "0", if it was between 500 and 750 cycles it was judged to have no practical problems and was rated "1", if it was between 750 and 1000 cycles it was judged to be excellent and was rated "2", and if it was 1000 cycles or more it was judged to be particularly excellent and was rated "3". "0" is a failure, while "1", "2", and "3" are passes. The evaluation results are shown in the "Temperature cycle reliability" column in the table.

[0103] (Method of evaluating the variation in bonding strength in temperature cycle testing) In the above-mentioned temperature cycle test, the shear strength of 20 1st joints was measured after 1400 cycles. When evaluating the variation in joint strength in the temperature cycle test, the population standard deviation (σ) of the shear strength was calculated. If σ was less than 30gf, the variation in joint strength was judged to be particularly small and the stability was excellent, and it was evaluated as "3". If σ was 30gf or more but less than 50gf, the variation in joint strength was judged to be small and the stability was excellent, and it was evaluated as "2". If σ was 50gf or more but less than 70gf, the variation in joint strength was judged to be within the acceptable range and the stability was good, and it was evaluated as "1". If σ was 70gf or more, the variation in joint strength was judged to be large and there was a problem in practical use, and it was recorded as "0". In addition, from a different perspective from the population standard deviation, if the average value of the shear strength decreased to 70% or less of the value before the temperature cycle test, it was judged to have exceeded its lifespan, and it was recorded as "0". "0" is a failure, and "1", "2", and "3" are passes. The evaluation results are shown in the column "Temperature cycle reliability - Variation in bonding strength (1,400 cycles)" in the table.

[0104] (1st bonding strength evaluation method) The evaluation method of the 1st joint strength is explained below. The 1st joint strength was evaluated by a shear strength test. The 1st joint was performed at 10 places under general joining conditions, and the shear strength of the 1st joint was measured. A commercially available micro shear strength tester (Nordson 4000-PLUS) was used to measure the shear strength. The shear speed was 200 μm / sec, and the height of the shear tool was 10 μm from the electrode surface. The shear strength was measured by fixing the substrate to which the Al connection material was joined with a jig. If the average value of the shear strength of the 10 1st joints was 1400gf or more, it was judged to be excellent and rated as "3", if it was 1200gf or more but less than 1400gf, it was judged to be practically acceptable and rated as "2", if it was 1000gf or more but less than 1200gf, it was judged to need improvement and rated as "1", and if it was less than 1000gf, it was judged to have practical problems and rated as "0". The evaluation results are shown in the "1st bonding strength" column in the table.

[0105] (Evaluation method for 1st joint hollow) The method for evaluating the hollow defect of the 1st joint is explained below. After the shear strength test of the 1st joint described above, the indentation on the fracture surface on the electrode side was observed with an optical microscope or SEM, and the area where no metal bonding was obtained in the fractured area was judged to be hollow. The area where hollow occurred is an area where the electrode is not bonded even if it is deformed, and can be distinguished from the area where the joint is metallically bonded. The shear strength test was performed under the above conditions, and the fracture surface of 10 1st joints was observed. Then, the ratio of the total length of the hollow area in the joint width direction (K) to the joint length (J) in the direction perpendicular to the central axis of the Al connecting material (joint width direction) was calculated as the hollow ratio (K / J) (Fig. 3). The hollow ratio was confirmed on the fracture surfaces of 10 places, and the maximum value was defined as the "hollow defect rate." If the defect rate of hollow parts was less than 5%, it was judged to be good and rated as "3", if it was between 5% and 15%, it was judged to be no problem for practical use and rated as "2", if it was between 15% and 25%, it was judged to require improvement and rated as "1", and if it was over 25%, it was judged to be an obstacle to mass production and rated as "0". The evaluation results are shown in the "Hollow parts of 1st joint" column in the table.

[0106] (Method for evaluating the stability of the bond strength of the 2nd bond) Shear strength tests were conducted on 30 randomly selected 2nd joints, and the joint strength was obtained and the population standard deviation (σ) was calculated. If σ was 70gf or more, it was judged to be problematic in practical use and rated "0", if σ was between 50gf and 70gf, it was judged to be good and rated "1", if σ was between 30gf and 50gf, it was judged to be excellent and rated "2", and if σ was less than 30gf, it was judged to be particularly excellent and rated "3". "0" is a failure, and "1", "2", and "3" are passes. The evaluation results are shown in the "Stability of joint strength of 2nd joint" column in the table.

[0107] (Method of evaluating wire breakage during processing) The method for evaluating wire breakage during processing is explained below. Wire drawing was performed from a wire diameter of 6 mmφ to a wire diameter of 0.3 mmφ, and the number of wire breakages was confirmed. The wire drawing conditions, such as the feed rate and area reduction rate, were selected from the conditions described above, and the manufacturing conditions were adjusted and changed appropriately for each wire. The length of the drawn Al connector was in the range of 100 to 200 m, and the number of wire breakages was calculated by converting it to per 100 m. If the number of wire breakages was 0, it was judged to be good and rated "3." If it was 1, it was judged that it could be dealt with by improving the manufacturing conditions and rated "2." If it was 2 to 4, it was considered that there was a problem with reduced productivity and rated "1." If it was 5 or more, it was judged that it was difficult to put into practical use and rated "0." The evaluation results are shown in the "Wire breakage during processing" column in the table.

[0108] (Evaluation method for surface scratches and scrapes) The surface quality of the Al connector was evaluated with attention to scratches and chipping. The wire diameter of the Al connector was 0.3 mmφ. Three measurement areas were randomly selected at intervals of 1 m or more along the central axis of the Al connector, and three pieces of approximately 2 cm were taken from each of the three locations, for a total of nine samples. The surface was observed at a magnification range of 50 to 500 times with an SEM. Scratches longer than 50 μm and chipping longer than 30 μm were judged to be defective. The number of scratches and chips was counted, and if there were zero, it was judged to be good and passed, and was rated as "3," if there were two or less, it was judged to be no problem in practical use, and was rated as "2," if there were three to seven, it was judged to have poor surface quality, and was rated as "1," and if there were eight or more, it was judged to be difficult to use, and was rated as "0." The evaluation results are shown in the "Surface Quality" column in the table.

[0109] The evaluation results of the examples and comparative examples are shown in Tables 1 to 3.

[0110] [Table 1]

[0111] [Table 2]

[0112] [Table 3]

[0113] All of the Al connecting materials of Examples 1 to 58 contain 3.0 mass% or more and 12.0 mass% or less of Si, and the Al phase in the L cross section <111> + <110> The total ratio is 20% or more and 70% or less (however, when the total of the orientation ratios is 25% or less, the angle difference with respect to the central axis direction is 15° or less. <110> The crystal orientation ratio is 5% or more, and the Si phase in the L section <111> + <110> It was confirmed that the total ratio was between 20% and 70%, and that the material exhibited excellent temperature cycle reliability and good 1st bonding strength. In addition, the Al phase in the L section <110> It was confirmed that the Al connecting materials of Examples 1 to 4, 6 to 13, 15, 16, 18 to 23, 25 to 32, 34 to 39, 41 to 49, 51, 52, and 54 to 58, which have a ratio of 5% or more and 40% or less, exhibit better results in terms of first joint strength and can suppress hollowing out of the first joint. It was also confirmed that the Al connecting materials of Examples 1, 3 to 23, 25 to 27, 29 to 47, 49, 50, and 52 to 58, in which the average diameter of the Al phase in the L cross section is 5 μm or more and 40 μm or less, tend to result in better results in terms of joint strength stability of the 2nd joint. It was confirmed that the Al connecting materials of Examples 1, 2, 4 to 9, 11 to 21, 23 to 28, 30 to 35, and 37 to 58, in which the average value of the shape ratio (e / f) of the Si phase in the L cross section is 0.2 or more and 0.7 or less, tend to reduce the variation in bonding strength in a temperature cycle test. Furthermore, it was confirmed that the Al connecting materials of Examples 32 to 43 and 53 to 58, which contain at least one element from the first element group (Sr, Ca, Eu, Sb) in a total amount of 10 mass ppm or more and 800 mass ppm or less, can reduce the frequency of wire breakage during processing. It was confirmed that the Al connecting materials of Examples 45 to 50 and 52 to 58, which contain a total of 10 mass ppm or more and 500 mass ppm or less of one or more of the second element group (Ni, Mg, Fe, In), have a smooth surface with reduced surface scratches and chipping. On the other hand, the Al connectors of Comparative Examples Nos. 1 to 10 have Si concentrations and Al phases in the L cross section. <111> + <110> Total ratio (Al phase when the total ratio is 20% or more and 25% or less) <110> ratio), Si phase at L cross section <111> + <110> Total ratio (if the total ratio is 25% or less, the Al phase <110> It was confirmed that either the temperature cycle reliability or the first bonding strength was not sufficient, and that either the temperature cycle reliability or the first bonding strength was not sufficient.

Claims

1. An Al connecting material containing 3.0 mass% or more and 12.0 mass% or less of Si, When the crystal orientation of the Al phase in an L cross section (a cross section in the central axis direction including the central axis) of the Al connecting material is measured, the total orientation ratio of the <111> crystal orientation and the <110> crystal orientation, which have an angular difference of 15° or less with respect to the central axis direction, is 20% or more and 70% or less, and when the total orientation ratio is 25% or less, the orientation ratio of the <110> crystal orientation, which has an angular difference of 15° or less with respect to the central axis direction, is 5% or more, An Al connection material, wherein when the crystal orientation of the Si phase in the L cross section of the Al connection material is measured, the total orientation ratio of the <111> crystal orientation and the <110> crystal orientation, which have an angular difference of 15° or less with respect to the central axis direction, is 20% or more and 70% or less.

2. 2. The Al connecting material according to claim 1, wherein the ratio of the <110> crystal orientation, which has an angle difference of 15° or less with respect to the central axis direction, in the crystal orientation of the Al phase in the L cross section is 5% or more and 40% or less.

3. 2. The Al connecting material according to claim 1, wherein the average diameter of the Al phase in the L cross section is 5 μm or more and 40 μm or less.

4. 2. The Al connecting material according to claim 1, wherein the average value of the ratio (e / f) of the short side length e to the long side length f of the Si phase in the L cross section is 0.2 or more and 0.7 or less.

5. The Al connecting material according to claim 1, further containing at least one of Sr, Ca, Eu, and Sb in a total amount of 10 ppm by mass or more and 800 ppm by mass or less.

6. The Al connecting material according to claim 1, further containing at least one of Ni, Mg, Fe, and In in a total amount of 10 ppm by mass or more and 500 ppm by mass or less.

7. The Al connecting material according to claim 5, further containing at least one of Ni, Mg, Fe, and In in a total amount of 10 ppm by mass or more and 500 ppm by mass or less.

8. The Al connecting material according to any one of claims 1 to 7, wherein the total concentration of other elements in the Al connecting material is 0.5 mass% or less.

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