阅读说明：本技术 无铅焊料合金和焊料接合部 (Lead-free solder alloy and solder joint ) 是由 西村哲郎 于 2020-04-10 设计创作，主要内容包括：通过使用含有32质量％以上40质量％以下的Bi、0.1质量％以上1.0质量％以下的Sb、0.1质量％以上1.0质量％以下的Cu、0.001质量份以上0.1质量份以下的Ni、且剩余部分包括Sn和不可避免的杂质的无铅焊料合金或进一步以规定范围含有特定元素的无铅焊料合金,能够维持Sn－Bi系焊料合金的低熔点,并且形成具有比现有技术更好的物理特性且比现有技术可靠性更高的焊料接合部。(By using a lead-free solder alloy containing 32 mass% to 40 mass% of Bi, 0.1 mass% to 1.0 mass% of Sb, 0.1 mass% to 1.0 mass% of Cu, 0.001 mass% to 0.1 mass% of Ni, and the balance including Sn and inevitable impurities, or a lead-free solder alloy further containing a specific element in a predetermined range, a solder joint portion having better physical properties than those of the prior art and higher reliability than those of the prior art can be formed while maintaining the low melting point of the Sn — Bi solder alloy.)

1. A lead-free solder alloy characterized by:

contains 32 to 40 mass% of Bi, 0.1 to 1.0 mass% of Sb, 0.1 to 1.0 mass% of Cu, 0.001 to 0.1 part by mass of Ni, and the balance of Sn and unavoidable impurities.

2. The lead-free solder alloy of claim 1, wherein:

contains 36 to 38 mass% of Bi.

3. The lead-free solder alloy according to claim 1 or 2, wherein:

contains 0.3 mass% or less of Ag.

4. The lead-free solder alloy according to any one of claims 1 to 3, wherein:

contains at least 1 kind selected from Fe and Co, and the content of each is 0.001-0.1% by mass.

5. The lead-free solder alloy according to any one of claims 1 to 4, wherein:

contains at least 1 kind selected from Ga, Mn, V, P and Ge, and the content of each is 0.001-0.01 mass%.

6. A solder joint, characterized in that:

a solder joint formed by using the lead-free solder alloy according to any one of claims 1 to 5.

Technical Field

The invention relates to a lead-free solder alloy and a solder joint.

Background

In order to reduce the global environmental load, lead-free solders have been widely used as bonding materials for electronic components. As a typical composition of lead-free solder, Sn — Ag — Cu based solder alloy and Sn — Cu — Ni based solder alloy containing Sn as a main component are known. However, it is known that the melting point of Sn-Ag-Cu based solder alloy is 217 ℃ and that of Sn-Cu-Ni based solder alloy is 227 ℃ which is 183 ℃ higher than the melting point of Sn-Pb eutectic composition currently used. Therefore, for example, for substrates such as personal computers to which electronic components having low heat resistance are required to be bonded, Sn — Bi-based and Sn-In-based lead-free solder alloys having melting points lowered by containing predetermined amounts of Bi and In are used.

Further, when Bi is used and a large amount of Bi is added to the Sn-Bi solder alloy, the solder alloy becomes brittle and the mechanical strength is lowered. Further, since the electronic component and the substrate are repeatedly expanded and contracted by heat and stress is repeatedly generated in the solder joint portion, cracks are easily generated by thermal fatigue, and long-term reliability is low. In is expensive and disadvantageous In terms of cost.

Then, studies have been made to improve the properties of Sn — Bi solder alloys (patent documents 1 to 4).

Patent document 1 discloses a solder bonding material characterized by containing: a solder alloy represented by Sn-57 or 45 mass% Bi-x mass% M (wherein M is at least 1 metal selected from the group consisting of copper, silver, nickel, germanium, antimony, and indium, and x is 4.0 or less), and a thermosetting adhesive in an arbitrary content or 5 to 20 mass% with respect to the solder alloy. Further, it is considered that such a configuration can sufficiently lower the reflow temperature, and can obtain a lead-free solder alloy joint having sufficient characteristics as a substitute for Sn — Pb solder alloy.

Patent document 2 discloses a lead-free solder alloy, which is characterized by including: 20 to 57 wt% of Bi, 0.2 to 5 wt% of Sb, 0.01 to 1 wt% of Ga, and the balance Sn. Further, it is considered that, with this configuration, soldering can be performed at a low temperature equal to or lower than that of an Sn — Pb solder alloy (eutectic composition), and therefore, workability can be improved and good physical properties as a solder alloy can be secured even when an electronic component having poor heat resistance is bonded.

Patent document 3 discloses a lead-free solder alloy having an alloy composition containing, in mass%, Bi selected from the group consisting of: 31-59%, Sb: 0.15 to 0.75%, and Cu: 0.3-1.0% and P: 0.002-0.055%, 1 or 2 kinds, and the balance of Sn. Further, it is considered that such a configuration has a sufficiently low melting point necessary for suppressing thermal deformation of the substrate at the time of solder bonding, is excellent in ductility and high in tensile strength, suppresses generation of a P-rich layer at the bonding interface at the time of soldering an electrode treated by electroless Ni plating, and can improve the shear strength of the solder bonding portion, and that a solder joint obtained from the solder alloy can secure excellent connection reliability even when a substrate thinner than the conventional one is used.

Patent document 4 discloses a lead-free solder containing 20 to 60 mass% of Bi, 1 or more elements selected from Cu, Ni, and P, 0 to 3 mass% of the selected Cu, 0.005 to 0.5 mass% of the selected Ni, and 0.005 to 0.05 mass% of the selected P, with the remainder being composed of Sn and unavoidable impurities. Further, it is considered that with such a configuration, even if Ag, In, and Sb are not used, a lead-free solder having a lower melting point than a lead-containing solder and excellent fatigue resistance can be provided.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2007-90407

Patent document 2: japanese laid-open patent publication No. 7-40079

Patent document 3: japanese patent No. 5679094

Patent document 4: japanese patent laid-open publication No. 2014-140865

Disclosure of Invention

Technical problem to be solved by the invention

Although the physical properties can be improved to some extent while maintaining the low melting point of the Sn — Bi solder alloy by the conventional techniques as described above, there is still room for improvement. Accordingly, an object of the present invention is to provide a lead-free solder alloy which can form a joint portion having higher reliability than the conventional solder alloy, while maintaining the low melting point of the Sn — Bi solder alloy and having better physical properties than the conventional solder alloy.

Technical solution for solving technical problem

The present inventors have conducted extensive studies to solve the above-mentioned problems, and as a result, have found that the above-mentioned problems can be solved by containing a specific amount of a specific component in an Sn — Bi solder alloy.

A first aspect of the present invention relates to a lead-free solder alloy containing 32 mass% to 40 mass% of Bi, 0.1 mass% to 1.0 mass% of Sb, 0.1 mass% to 1.0 mass% of Cu, 0.001 mass% to 0.1 mass% of Ni, and the balance including Sn and unavoidable impurities.

In the embodiment of the present invention, Bi may be contained in an amount of 36 to 38 mass%.

In the embodiment of the present invention, (1) 0.3 mass% or less of Ag may be contained, (2) at least 1 kind selected from Fe and Co may be contained in an amount of 0.001 mass% or more and 0.1 mass% or less, respectively, and (3) at least 1 kind selected from Ga, Mn, V, P and Ge may be contained in an amount of 0.001 mass% or more and 0.01 mass% or less, respectively.

A second aspect of the present invention relates to a solder joint formed using the above lead-free solder alloy.

The inevitable impurities referred to herein are those present in the raw material of the solder or inevitably mixed in the manufacturing process.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a lead-free solder alloy can be provided which can maintain the low melting point of the Sn — Bi solder alloy, has better physical properties than the prior art, and can form a joint portion with higher reliability than the prior art.

Drawings

Fig. 1(a) shows an SEM image of a cross section of a solder joint between a lead-free solder alloy of example 1 and a copper foil substrate. (b) An enlarged view (1000 times) of the portion shown in (1) of fig. 1(a) is shown. (c) An enlarged view (3000 times) of the portion shown in (2) of fig. 1(a) is shown.

Fig. 2 shows an image (600 times) of an SEM photograph of a cross section of a joint interface portion of a solder joint portion between the lead-free solder alloy of example 1 and a copper foil substrate.

Fig. 3(a) shows an SEM image of a cross section of a solder joint between the lead-free solder alloy of example 1 and the copper foil substrate after aging. (b) An enlarged view of the portion shown in (3) of fig. 3(a) is shown. (c) An enlarged view of the portion shown in (4) of fig. 3(a) is shown.

Fig. 4 shows an image (600 times) of an SEM photograph of a cross section of a bonding interface portion of a solder bonding portion between the lead-free solder alloy of example 1 and a copper foil substrate after aging.

FIG. 5 is a graph showing the change rates (aged/initial X100) of the absorption energy and the bonding strength of a measurement sample (initial) that was not aged and a measurement sample (aged) that was aged in an impact shear test using the solder alloys of examples 1 to 36 and a shear rate of 10 mm/s.

FIG. 6 is a graph showing the change rates (aged/initial X100) of the absorption energy and the bonding strength of a measurement sample (initial) that was not aged and a measurement sample (aged) that was aged in an impact shear test using the solder alloys of examples 1 to 36 and a shear rate of 1000 mm/s.

FIG. 7 is a graph showing the change rates (aged/initial X100) of the absorption energy and the bonding strength of a measurement sample (initial) that was not aged and a measurement sample (aged) that was aged in an impact shear test that was performed using the solder alloys of comparative examples 1 to 14 and the shear rate was set to 10 mm/s.

FIG. 8 is a graph showing the change rates (aged/initial X100) of the absorption energy and the bonding strength of a measurement sample (initial) that was not aged and a measurement sample (aged) that was aged in an impact shear test using the solder alloys of comparative examples 1 to 14 and setting the shear rate at 1000 mm/s.

Fig. 9 (a) shows an SEM photograph (1000 times) of a cross section of a solder joint between the lead-free solder alloy of example 3 and the copper foil substrate. (b) An SEM photograph (1000 times) of a cross section of a solder joint between the lead-free solder alloy of example 3 and the copper foil substrate after the aging treatment is shown.

Fig. 10 (a) shows an SEM photograph (1000 times) of a cross section of a solder joint between the lead-free solder alloy of example 4 and the copper foil substrate. (b) An SEM photograph (1000 times) of a cross section of a solder joint between the lead-free solder alloy of example 4 and the copper foil substrate after the aging treatment is shown.

Fig. 11 (a) shows an SEM photograph (1000 times) of a cross section of a solder joint between the lead-free solder alloy and the copper foil substrate in comparative example 4. (b) An image of an SEM photograph (1000 times) of a cross section of a solder joint between the lead-free solder alloy of comparative example 4 and a copper foil substrate after the aging treatment is shown.

Fig. 12 (a) shows an SEM photograph (1000 times) of a cross section of a solder joint between the lead-free solder alloy and the copper foil substrate in comparative example 5. (b) An image of an SEM photograph (1000 times) of a cross section of a solder joint between the lead-free solder alloy of comparative example 5 and the copper foil substrate after the aging treatment is shown.

Fig. 13(a) is an explanatory view for explaining fig. 11 (b). (b) Is an explanatory diagram for explaining fig. 12 (b).

Detailed Description

Hereinafter, embodiments of the present invention will be described.

The lead-free solder alloy according to the embodiment of the present invention (hereinafter, may be simply referred to as "solder alloy") contains 32 mass% to 40 mass% of Bi, 0.1 mass% to 1.0 mass% of Sb, 0.1 mass% to 1.0 mass% of Cu, and 0.001 parts to 0.1 parts by mass of Ni, with the remainder including Sn and unavoidable impurities.

In this way, by using Sn as the matrix phase and containing Bi, Sb, Cu, and Ni in specific ranges, the melting point depressing effect of Bi can be maintained well, and the lowering of physical properties by Bi can be greatly suppressed. In particular, the composition can suppress deterioration in long-term use and has good thermal fatigue resistance. Therefore, a highly reliable solder joint can be formed. Further, since Sb, Cu, and Ni are elements having a lower volume resistivity than Bi, when Bi is contained in a composition close to a eutectic composition with Sn, the volume resistivity of the solder alloy can be made lower than that of conventional solders as the content thereof is low.

Further, by having a specific composition, it is possible to suppress Cu6Sn5 η - η' phase transformation occurring at 186 ℃. As a result, cracks can be prevented from occurring in the solder alloy, and interfacial separation between the solder alloy and the metal wiring can be prevented, thereby forming a highly reliable joint.

In addition, the occurrence of electromigration can be suppressed by having a specific composition. Although the mechanism of action is not clear, since the movement of metal atoms in the solder alloy, which may occur due to the application of electricity or a high-temperature environment, is suppressed, the defect of the solder alloy can be suppressed, and a highly reliable joint can be formed.

The Bi content is 32-40 mass%. When the amount is less than 32% by mass, the melting point depressing effect tends to be insufficient. If the amount is more than 40% by mass, the solder alloy tends to become brittle and fail to obtain desired physical properties. The content of Bi may be in such a range, and is preferably 36 mass% to 38 mass%.

The content of Sb is 0.1-1.0 mass%. Preferably 0.1 to 0.6 mass%. Sb is known to have an action of imparting ductility to an Sn — Bi solder alloy and suppressing a change in volume by suppressing a phase change from β -Sn to α -Sn. However, when Sb is contained in the above-described range, various effects as described above can be exhibited due to the relationship with other metal components.

The Cu content is 0.1-1.0 mass%. Preferably 0.3 to 0.7 mass%. Cu is known to have an effect of imparting ductility to Sn — Bi solder alloys. However, when Cu is contained in the above-described range, various effects as described above can be exhibited due to the relationship with other metal components.

The Ni content is 0.001-0.1 mass%. Preferably 0.005 mass% or more and 0.07 mass% or less, and more preferably 0.01 mass% or more and 0.05 mass% or less. Ni is known to have an effect of suppressing generation of intermetallic compounds of Cu and Sn, an effect of suppressing increase in melting point and decrease in fluidity, and an effect of improving strength and bondability of an alloy. However, when Ni is contained in the above-described range, the effect of suppressing the Cu6Sn5 η — η' transformation occurring at 186 ℃ can be exhibited due to the relationship with other metal components.

The solder alloy according to the embodiment may contain, as necessary, other elements than Bi, Sb, Cu, and Ni for Sn. Examples of such elements include Ag, Fe, Co, Ga, Mn, V, Ge, P, Si, Ca, and Ti. Among them, Ag, Fe, Co, Ga, Mn, V, Ge, and P are preferable, and Ge, Ag, Fe, Co, Ga, Mn, and V are more preferable.

Ag can improve the wettability of the solder alloy. From the viewpoint of improving the wettability, the content of Ag is preferably 0.3 mass% or less, and more preferably 0.1 mass% or less. In particular, when a high-temperature treatment such as an aging treatment is performed, particles of Ag3Sn as an intermetallic compound are generated and coarsened, and thus long-term reliability tends to be lowered. Also, Ag is generally expensive, and therefore the manufacturing cost of the solder alloy increases. Therefore, the smaller the Ag content, the better.

Fe and Co have a function of stabilizing the solder joint. Further, the iron-containing compound may be contained in a case where it is necessary to prevent the iron of the tip or nozzle of the iron from being corroded (iron-eating われ). The content of each of these is preferably 0.001 mass% or more and 0.1 mass% or less.

Ge. Ga, Mn, V, and P have an effect of preventing surface oxidation of the solder alloy. Among them, Ge, Ga, Mn, and V are preferable. If the surface of the solder alloy is oxidized to form an oxide film, water generated when the oxide film is reduced may cause voids (void) at the time of solder bonding. Therefore, it is considered that the thickness of the oxide film is reduced by suppressing the oxidation of the surface, and the bonding quality and reliability can be improved. The content of each of these is preferably 0.001 mass% or more and 0.01 mass% or less. In addition, Ge has an effect of further improving creep strength.

Si, Ca, and Ti also have an effect of preventing surface oxidation of the solder alloy. The content of each of these is preferably 0.001 mass% or more and 0.01 mass% or less.

The solder alloy according to the embodiment may contain inevitable impurities. However, the above-described effects can be exhibited even if unavoidable impurities are contained.

The form of the solder alloy is not particularly limited, and can be appropriately selected according to the application. For example, when the solder is joined by a dip soldering method, the shape can be a rod shape. When solder bonding is performed by reflow soldering, the solder may be in an amorphous paste shape or a spherical or prepreg (pre form) shape. When the solder bonding is performed by using a solder iron, a material made into a rosin-containing soft solder is molded into a linear shape.

The solder joint according to the embodiment of the present invention is formed using the above-described solder alloy. More specifically, in the solder joint portion, for example, an electrode terminal of an electronic component and an electrode terminal of a metal wiring or the like on a substrate are joined by the above-described solder alloy. Since the solder joint is formed using the solder alloy, the solder alloy is inhibited from deteriorating in long-term use, has good thermal fatigue resistance, and has high reliability.

Examples

Hereinafter, embodiments of the present invention will be described in more detail based on examples.

Examples 1 to 36 and comparative examples 1 to 14

The respective metals were mixed by a conventional method so as to have the compositions shown in tables 1 to 3, to prepare solder alloys. Using the obtained solder alloy, an evaluation test was performed by the method described below. Each solder alloy contains inevitable impurities derived from the raw materials because the metals as the raw materials are mixed so as to have the composition ratios shown in tables 1 to 3.

[ Table 1]

[ Table 2]

[ Table 3]

(evaluation)

< impact shear test >

1) Spherical solder balls having a diameter of 0.5mm and made of the solder alloys obtained in examples 1 to 36 and comparative examples 1 to 14 were prepared.

2) A copper foil substrate was prepared, and 0.01g of "FLUX RM-5" (manufactured by JEOL Ltd.) was applied to the mounting portion, and solder balls were mounted thereon.

3) The FLUX was heated under reflux at a temperature of 1.5 ℃/sec at the highest temperature of 200 ℃ or 250 ℃ for 50 seconds, and after joining, the FLUX was cooled and washed with IPA, and the FLUX-removed article was used as a sample for measurement.

4) A part of the measurement sample prepared in the above step was placed in an electric furnace maintained at 150 ℃ for 100 hours, and subjected to aging treatment.

5) The measurement sample (initial) which was not subjected to the aging treatment and the measurement sample (aged) which was subjected to the aging treatment were set in an impact shear tester (4000 HS manufactured by DAGE corporation).

6) With respect to the measurement conditions, the shear load stress (N) and the absorption energy (adsorbed E) (mJ) were measured by performing 3 kinds of shear rates of 10 mm/sec, 1000 mm/sec and 2000 mm/sec for example 1 and comparative example 1, and 2 kinds of shear rates of 10 mm/sec and 1000 mm/sec for examples 2 to 36 and comparative examples 2 to 14. In the shear load stress, the maximum value (Max force) was evaluated as the joint strength. Then, for the case where the shear rate was 10 mm/sec or 1000 mm/sec, the change rate of each measured value (after aging/initial x 100) was calculated for the initial and after aging, and the influence of aging was evaluated. The measurement results are shown in tables 4 to 8. Tables 5 and 7 show the results of examples 1 to 36 and comparative examples 1 to 14 in which the shear rate was 10 mm/sec and tables 6 and 8 show the shear rate was 1000 mm/sec. The results of the "change rates" shown in tables 5 to 8 are summarized in the form of bar graphs in FIGS. 5 to 8. In fig. 5 and 7, a broken line is provided as a reference at a position of 90% of the rate of change, and in fig. 6 and 8, at a position of 100% of the rate of change.

[ Table 4]

[ Table 5]

[ Table 6]

[ Table 7]

[ Table 8]

< solder joint section view >)

Using the solder alloys obtained in examples 1, 3, and 4 and comparative examples 4 and 5, samples for measurement were prepared in the same manner as in 1) to 3) of < impact shear test >. The cross section of the measurement sample was photographed by SEM. The images of the obtained SEM photographs are shown in FIGS. 1 to 4 and 9 to 12.

< evaluation of iron erosion >

FLUX (NS-65, manufactured by Spanish corporation, Japan) was applied to a sheet (made of pure iron, width 10 mm. times. length 50 mm. times. thickness 20 μm) corresponding to the nozzle, followed by tin plating. The tin-plated sheet was used as a test piece in the following test.

Solder alloys of examples 23 to 26 and comparative examples 1 and 2 were prepared, and about 1kg of each solder alloy was put into a solder bath and heated at 220 ℃ to prepare a molten solder alloy.

The test piece was fixed to the tip of a rod-shaped rotating body of a screw type stirring apparatus (BL 600, manufactured by HEIDON corporation) and immersed so that the immersion depth of the test piece became 40 mm. At this time, the rod-shaped rotating body was rotated at 50rpm with the longitudinal center axis thereof as the rotation axis. The central axis is inclined by 10 ° with respect to the liquid surface of the molten solder. After 120 minutes had elapsed, the iron reduction rate was calculated by taking the difference in area of the immersed portion of the test piece before and after immersion as the amount of iron melt loss, and the degree of corrosion (iron corrosion) was evaluated. The areas of the test piece before and after the dipping were measured by Digital Microscope VHX-7000, manufactured by Yoshiji corporation. The iron reduction rate was calculated as follows. The evaluation results are shown in table 9. The evaluation criteria were "good" when the iron reduction ratio was less than 5.0%, Δ "when it was 5.0% or more and less than 10.0%, and" poor "when it was 10.0% or more.

Iron reduction (%) (area before immersion-area after immersion)/area to be immersed x 100

[ Table 9]

	Area reduction (%)	The result of the judgment
			Example 23	3.2	○
Example 24	0.8	○
			Example 25	3.9	○
Example 26	1.4	○
			Comparative example 1	7.7	×
Comparative example 2	10.1	×

< evaluation of wettability >

The solder samples (diameter: 6.5 mm. phi., height: 1.24mm) prepared from the solder alloys of example 22 and comparative examples 7, 11 to 14 were evaluated by calculating the spreading ratio (%) in accordance with JIS Z3198-3. As evaluation criteria, the expansion ratio was 80.0% or more, Δ was 75.0% or more and less than 80.0%, and x was less than 75.0%. The evaluation results are shown in table 10.

[ Table 10]

	Expansion ratio (%)	The result of the judgment
			Example 22	83.1	○
Comparative example 7	72.6	×
			Comparative example 11	75.4	△
Comparative example 12	78.9	△
			Comparative example 13	71.4	×
Comparative example 14	75.5	△

< oxide film thickness test >

The molten solders of the solder alloys of examples 27 to 36 and comparative examples 8 to 10, 13 and 14 were poured into a mold to obtain test pieces (width 2 cm. times. length 10 c)m × thickness 1 cm). The Surface oxide film thicknesses (SnO and SnO) of the test pieces on the day of production were measured by an oxide film thickness measuring apparatus (Surface Scan SERA QC-100, manufactured by ECI Technology Co., Ltd.)₂Total of) is measured to obtain an initial film thickness D₀Thereafter, the test piece was exposed to an atmosphere at room temperature of 25 ℃ and a humidity of 65% for 168 hours to be naturally oxidized. Then, the oxide film thickness was measured again in the same manner, and the post-exposure film thickness D was obtained. Calculation with respect to the initial film thickness D₀Rate of change (D/D)₀X 100) and evaluated. As evaluation criteria, the rate of change in the oxide film thickness of the solder alloy surface before and after exposure was defined as "o" when the rate was less than 25%, as "Δ" when the rate was 25% or more and less than 50%, and as "x" when the rate was 50% or more. The evaluation results are shown in table 11.

[ Table 11]

	Rate of change (%)	The result of the judgment
			Example 27	8	○
Example 28	6	○
			Example 29	7	○
Example 30	6	○
			Example 31	8	○
Example 32	7	○
			Example 33	7	○
Example 34	6	○
			Example 35	7	○
Example 36	6	○
			Comparative example 8	35	△
Comparative example 9	31	△
			Comparative example 10	34	△
Comparative example 13	72	×
			Comparative example 14	58	×

As is apparent from tables 4 to 8 and FIGS. 5 to 8, by using Sn as the matrix phase and containing Bi, Sb, Cu and Ni in specific ranges, a good shear load stress is obtained, and a shear stress equal to or greater than the initial shear stress is obtained even after aging. Further, as shown in FIGS. 1 to 4, it is understood that the generation of voids at the initial stage and after aging is suppressed. In particular, focusing on the light gray intermetallic compound (IMC) layer of Cu6Sn5 in the explanatory diagram of fig. 13(a), a plurality of kirkendall voids were observed as black spots in the dark gray IMC layer of Cu3Sn on the surface of the black copper substrate after the aging treatment in comparative example 4. This is because the Sn amount of comparative example 4 is the largest in examples 3 and 4 and comparative examples 4 and 5, and the cu is diffused into the solder the most. It is known that the kirkendall voids can serve as starting points of stress concentration, and in fig. 13(a), cracks can be observed around the kirkendall voids. After the aging treatment in comparative example 5, as shown in fig. 13(b), although no kirkendall voids were observed, cracks were observed in the light gray IMC layer of Cu6Sn 5. This is presumably because the hard Bi becomes concentrated near the junction interface, and a stress load is likely to occur in the IMC layer. On the other hand, according to fig. 9 and 10, cracks and kirkendall voids were not observed in the IMC layer of Cu6Sn5 in light gray in the solder alloys of examples 3 and 4. As is clear from table 9, by containing Fe and Co in the predetermined ranges, iron corrosion can be suppressed. As is clear from table 10, the wettability can be improved by containing Ag in a predetermined range. As is clear from table 11, by containing Ga, Mn, V, P, and Ge in predetermined ranges, oxidation of the surface of the solder alloy can be suppressed. As described above, the solder alloy having the composition in the specific range has a low melting point based on the Bi content, and can have good thermal fatigue resistance by suppressing deterioration in long-term use. Therefore, a highly reliable solder joint can be formed. In addition to the essential components of Sn, Bi, Sb, Cu, and Ni, when a predetermined arbitrary element is contained in a predetermined range, the functions unique to the arbitrary elements can be exhibited in addition to the functions based on the essential components.