Solder Alloy, Solder Paste, Solder Ball, Solder Preform, and Solder Joint

Abstract

Provided are a solder alloy, a solder paste, a solder ball, a solder preform, and a solder joint, which have a melting temperature within a predetermined range, and high tensile strength and shear strength, suppress generation of voids, and have excellent mountability due to their thin oxide films. The solder alloy has an alloy composition consisting of, by mass %, Ag: 2.5 to 3.7%, Cu: 0.25 to 0.95%, Bi: 3.0 to 3.9%, and In: 0.5 to 2.3%, with the balance being Sn, and the alloy composition satisfies the following relations (1) and (2): 8.1≤Ag+2Cu+Bi+In ≤11.5 (1), and 1.00≤(Bi+In)/Ag≤1.66 (2). Ag, Cu, Bi and In in the relations (1) and (2) each represent the contents (mass %) in the alloy composition.

Claims

1. A solder alloy having an alloy composition consisting of, by mass %: Ag: 2.5 to 3.7%, Cu: 0.25 to 0.95%, Bi: 3.0 to 3.9%, and In: 0.5 to 2.3%, with the balance being Sn, wherein the alloy composition satisfies the following relations (1) and (2):
8.1≤Ag+2Cu+Bi+In ≤11.5  Relation (1)
1.00≥(Bi+In)/Ag≤1.66  Relation (2) wherein Ag, Cu, Bi, and In in the relations (1) and (2) each represent the contents (mass %) thereof in the alloy composition.

2. The solder alloy according to claim 1, wherein the alloy composition further satisfies the following relation (3):
4.48≤Ag×Cu×Bi×In ≤7.7  Relation (3) wherein Ag, Cu, Bi, and In in the relation (3) each represent the contents (mass %) thereof in the alloy composition.

3. A solder paste comprising solder powders comprising the solder alloy according to claim 1.

4. A solder ball comprising the solder alloy according to claim 1.

5. A solder preform comprising the solder alloy according to claim 1.

6. A solder joint comprising the solder alloy according to claim 1.

Description

DETAILED DESCRIPTION

[0034] The present invention is described in more detail below. In the present specification, “%” used for indicating a solder alloy composition is “mass %” unless otherwise specified.

[0035] 1. Solder Alloy

[0036] (1) Ag: 2.5 to 3.7%

[0037] Ag can avoid an increase in melting temperature if its content is close to a SnAgCu eutectic composition. It also enables precipitation strengthening of a solder alloy because Ag.sub.3Sn is precipitated in granular form. If the Ag content is less than 2.5%, the melting temperature of the solder alloy increases due to hypoeutectic SnAgCu. In addition, strength is not improved since the amount of the compounds precipitated is small. In terms of the lower limit, the Ag content is 2.5% or more, preferably 2.8% or more, and more preferably 2.9% or more.

[0038] On the other hand, if the Ag content exceeds 3.7%, the melting temperature of the solder alloy increases due to hypereutectic SnAgCu. In addition, coarse Ag.sub.3Sn precipitates in a plate-like form, resulting in deteriorated strength. In terms of the upper limit, the Ag content is 3.7% or less, preferably 3.2% or less, and more preferably 3.1% or less.

[0039] (2) Cu: 0.25 to 0.95%

[0040] The closer both Cu and Ag contents are to the SnAgCu eutectic composition, the lower the melting temperature of the solder alloy. If the Cu content is less than 0.25%, the melting temperature of the solder alloy increases due to hypoeutectic SnAgCu. In terms of the lower limit, the Cu content is 0.25% or more, preferably 0.45% or more, and more preferably 0.55% or more.

[0041] On the other hand, if the Cu content exceeds 0.95%, tensile strength and shear strength are reduced due to a large amount of Sn and Cu compounds precipitated. As the Cu content further increases, the melting temperature of the solder alloy increases due to hypereutectic SnAgCu in addition to the deterioration of strength. In terms of the upper limit, the Cu content is 0.95% or less, preferably 0.80% or less, and more preferably 0.70% or less.

[0042] (3) Bi: 3.0 to 3.9%

[0043] Bi can avoid the increase in melting temperature and also improves the strength of the solder alloy by solid solution strengthening of Sn. If the Bi content is less than 3.0%, the strength is not sufficiently improved since the solid solution amount of Bi is small. In addition, the melting temperature of the solder alloy is not lowered. In terms of the lower limit, the Bi content is 3.0% or more, preferably 3.1% or more, and more preferably 3.2% or more.

[0044] On the other hand, if the Bi content exceeds 3.9%, the solidus temperature lowers due to eutectic SnBi precipitated. Furthermore, Bi may segregate to grain boundaries, resulting in deterioration of strength of the solder alloy. In terms of the upper limit, the Bi content is 3.9% or less, preferably 3.8% or less, more preferably 3.7% or less, and further preferably 3.4% or less.

[0045] (4) In: 0.5 to 2.3%

[0046] In can avoid the increase in melting temperature and also improves the strength of the solder alloy by solid solution strengthening of Sn. If the In content is less than 0.5%, the strength is not sufficiently improved since the solid solution amount of In is small. In addition, the melting temperature of the solder alloy is not lowered. In terms of the lower limit, the In content is 0.5% or more, preferably 0.7% or more, more preferably 0.9% or more, and even more preferably 1.0% or more.

[0047] On the other hand, if the In content exceeds 2.3%, molten solder is easily oxidized, and thus generation of voids cannot be suppressed. In addition, an oxide film thereof becomes thicker, resulting in poor mountability. Furthermore, the melting temperature becomes too low. In terms of the upper limit, the In content is 2.3% or less, preferably 1.5% or less, and more preferably 1.3% or less.

[0048] (5) Relations (1) and (2)

8.1≤Ag+2Cu+Bi+In ≤11.5  Relation (1)

1.00≤(Bi+In)/Ag≤1.66  Relation (2)

[0049] Ag, Cu, Bi, and In in the relations (1) and (2) each represent the contents (mass %) thereof in the alloy composition.

[0050] The solder alloy according to the present invention contains appropriate amounts of additive elements by satisfying the relation (1), and thus the melting temperature is in a proper range. These additive elements constituting the solder alloy according to the present invention affect tensile strength and shear strength since all of them contribute to Sn. In contributes to the solid solution strengthening of Sn, although addition of large amounts of In may cause voids and an increase in the thickness of an oxide film. For this reason, the relation (1) needs to be satisfied indirectly to suppress the generation of voids and reduce the thickness of the oxide film. Therefore, the relation (1) is a relational expression that must be satisfied in order to exhibit the effect of the present invention. Note that the coefficient of Cu in the relation (1) is doubled. In the solder alloy according to the present invention, this tends to significantly affect various properties of the solder alloy if the Cu content changes even slightly. For example, focusing on the melting temperature, when the amount of increase or decrease in the Cu content is the same as the amount of increase or decrease in the content of any other element, Cu is estimated to change the melting temperature at least twice larger than the other element.

[0051] The solder alloy according to the present invention can also exhibit higher strength by satisfying the relation (2). Ag is a precipitation strengthening element, while Bi and In are solution strengthening elements. If the content of a solution strengthening element is too large, the element may exist in excess because the element content exceeds the solid solution limit, and may cause segregation of Bi or deformation of the solder alloy. On the other hand, if the content of the precipitation strengthening element is too large, the strength rather decreases due to a large amount of the compound precipitated. The solder alloy according to the present invention can therefore strengthen Sn in a well-balanced manner by satisfying relation (2), although each element has an optimum content range as described above.

[0052] These relations are obtained by the interdependence of the constituent elements. This is because an alloy is an integrated object formed by combination of all constituent elements, and the constituent elements influence each other. Thus, the solder alloy according to the present invention, which is adjusted to the optimum content of each constituent element and further satisfies the relations (1) and (2), is set to a range where the interdependence of the constituent elements is fully considered. Accordingly, in the second soldering of step soldering, the solder alloy according to the present invention can simultaneously satisfy optimum melting temperature, high tensile and shear strength, suppression of void generation, and thin oxide films.

[0053] In terms of the lower limit, the relation (1) is 8.1 or more, preferably 8.2 or more, more preferably 8.3 or more, further preferably 8.4 or more, particularly preferably 8.5 or more, and most preferably 8.6 or more. In terms of the upper limit, the relation (1) is preferably 11.5 or less, more preferably 9.3 or less, further preferably 9.1 or less, even further preferably 8.9 or less, particularly preferably 8.8 or less, and most preferably 8.7 or less.

[0054] In terms of the lower limit, the relation (2) is 1.00 or more, preferably 1.14 or more, more preferably 1.23 or more, even further preferably 1.28 or more, particularly preferably 1.30 or more, and most preferably 1.31 or more, and may be 1.33 or more and 1.35 or more. In terms of the upper limit, the relation (2) is 1.66 or less, preferably 1.64 or less, more preferably 1.63 or less, further preferably 1.62 or less, even further preferably 1.57 or less, particularly preferably 1.50 or less, and most preferably 1.45 or less, and may be 1.42 or less and 1.40 or less.

[0055] (6) Balance: Sn The balance of the solder alloy according to the present invention is Sn. The solder alloy may contain unavoidable impurities besides the elements described above. Even when the solder alloy contains unavoidable impurities, this inclusion does not affect the effects described above. The solder alloy according to the present invention preferably does not contain Co and Ni because they increase the melting temperature.

[0056] (7) Relation (3)

4.48≤Ag×Cu×Bi×In ≤7.7  Relation (3)

[0057] Ag, Cu, Bi, and In in the relation (3) each represent the contents (mass %) thereof in the alloy composition.

[0058] The relation (3) is a relational consideration for the balance among additive elements, and the embodiment satisfying the relation (3) is preferable. The relation (3) is highly interdependent on each element because it is multiplied by the content of each element, and the overall balance of the solder alloy is maintained at a high level when the relation (3) is satisfied. Accordingly, it is preferred in terms of the further optimum of melting temperature, further improvement tensile and shear strength, further suppression of void generation, and further thinning of oxide films. In terms of the lower limit, the relation (3) is preferably 4.48 or more, more preferably 4.70 or more, further preferably 4.75 or more, particularly preferably 4.82 or more, most preferably 5.28 or more, and may be 5.76 or more, 6.27 or more, 6.50 or more, and 6.51 or more. In terms of the upper limit, the relation (3) is preferably 7.7 or less, more preferably 7.17 or less, further preferably 7.14 or less, even further preferably 6.94 or less, and most preferably 6.72 or less.

[0059] (8) Melting Temperature of Solder Alloy

[0060] The solder alloy according to the present invention are preferably used for the second soldering when soldering is performed twice, for example, by step soldering. In such a use, the melting temperature of the solder alloy used for the second time is preferably lower than the solidus temperature of the solder alloy used for the first time. For example, in the case of using a Sn-10Sb solder alloy that melts at a melting temperature of 245° C. in the first soldering, a sufficient temperature margin is considered for the use of components with large heat capacity. The melting temperature of the solder alloy according to the present invention is preferably 211 to 220° C. and particularly preferably 211 to 214° C.

[0061] The solidus temperature of the solder alloy according to the present invention should be in a temperature range where a temperature difference between the melting temperature and the solidus temperature is not too large, and the mountability of the component does not deteriorate, due to leaching, misalignment, reoxidation, generation of voids or the like. The solidus temperature of the solder alloy according to the present invention is preferably 198° C. or more, more preferably 200° C. or more, further preferably 203° C. or more, and particularly preferably 204° C. or more. The upper limit of the solidus temperature of the solder alloy according to the present invention is not particularly limited, but may be 211° C. or less.

[0062] 2. Solder Paste

[0063] The solder paste according to the present invention is a mixture of a solder powder containing the solder alloy having the alloy composition described above and a flux. The flux used in the present invention is not particularly limited as long as it is suitable for soldering by a conventional method. Accordingly, a commonly used rosin, an organic acid, an activator, and a solvent may be blended as appropriate for use. In the present invention, a blending ratio of a metal powder component to a flux component is not particularly limited, but preferably the metal powder component is 80 to 90 mass % while the flux component is 10 to 20 mass %.

[0064] 3. Solder Ball

[0065] The solder alloy according to the present invention can be used as a solder ball. The solder ball according to the present invention is used for forming bumps on electrodes and substrates of semiconductor packages such as BGA (ball grid array). The diameter of the solder ball according to the present invention is preferably in the range of 1 to 1000 μm. The solder ball can be manufactured by a general solder ball manufacturing method.

[0066] 4. Solder Preform

[0067] The shape of the solder preform according to the present invention is not limited and it can be used in the form of a plate, a ring, a cylinder, a ribbon, a square, a disc, a washer, a chip, a wire, or the like. The solder preform may internally contain high-melting metal grains (e.g., Ni or Cu grains and alloy powder mainly composed of Ni or Cu) whose melting point is higher than that of the solder alloy and which are easily wetted by the molten solder.

[0068] 5. Solder Joint

[0069] The solder joint according to the present invention is suitably used for joining at least two or more members to be joined. The members to be joined are, for example, a circuit element, a substrate, an electronic component, a printed circuit board, an insulating substrate, a heat sink, a lead frame, a semiconductor using electrode terminals, etc., as well as a power module and an inverter product, and are not particularly limited as long as they are electrically connected using the solder alloy according to the present invention.

[0070] 6. Other

[0071] The solder alloy according to the present invention enables a low α-ray alloy to be produced by using a low α-ray material as a raw material therefor. When such a low α-ray-alloy is used for forming solder bumps in the periphery of a memory, soft errors can be suppressed.

EXAMPLES

[0072] The present invention will be described by the following Examples, but the present invention is not limited to the following Examples. In order to demonstrate the effects of the present invention, melting temperature, tensile strength, shear strength, void area ratio, and thickness of an oxide film were measured using the solder alloy listed in Table 1.

[0073] (1) Melting Temperature

[0074] For solder alloys having alloy compositions each listed in Table 1, each temperature was determined from a DSC curve. The DSC curve was obtained by DSC (model: EXSTAR 6000) manufactured by Hitachi High-Tech Science Corporation by increasing the temperature at 5° C./min in the atmosphere. The liquidus temperature was determined from the obtained DSC curve and used as the melting temperature. The solidus temperature was also evaluated from the DSC curve.

[0075] When the melting temperature is 211 to 214° C., the temperature margin was sufficient for the second soldering in step soldering and thus was evaluated as “Excellent”. When the melting temperature is 215 to 220° C., it was evaluated as “Good” since there was no problem in practical use. When the temperature was less than 211° C. and exceeds 220° C., it was evaluated as “Poor”. When the solidus temperature was 204 to 211° C., it was evaluated as “Excellent”. When the solidus temperature was 198 to 203° C., it was evaluated as “Good”. When the temperature was less than 204° C. and exceeds 211° C., it was evaluated as “Poor”.

[0076] (2) Tensile Strength

[0077] The tensile strength was measured in accordance with JIS Z 3198-2. Each of the solder alloys listed in Table 1 was cast into a mold to produce a specimen with a gauge length of 30 mm and a diameter of 8 mm. The produced specimen was pulled by Type 5966 manufactured by Instron Corporation at room temperature at a stroke of 6 mm/min to measure the strength upon fracture of the specimen. In the present invention, when the tensile strength was 67 MPa or more, it was evaluated as “Excellent” because of its sufficient strength. When the tensile strength was less than 67 MPa and 63 MPa or more, it was evaluated as “Good” since there was no problem in practical use. When the tensile strength was less than 63 MPa, it was evaluated as “Poor”.

[0078] (3) Shear Strength

[0079] Solder alloy powders having the solder alloy compositions listed in Table 1 with an average particle size of 20 μm were produced, and the produced solder alloy powders were mixed with a known rosin flux in a ratio of 89 mass % to 11 mass % to produce a solder paste of each solder alloy. The solder paste was printed on a Cu-electrode in a printed circuit board (material: FR-4) having a thickness of 0.8 mm with a metal mask having a thickness of 120 μm, and a chip resistor component was mounted with a mounter, and reflow soldering was performed at a maximum temperature of 235° C. and a holding time of 60 seconds to produce a test substrate.

[0080] The shear strength (N) of this test substrate was measured by a shear strength measuring device (STR-1000 manufactured by RHESCA Corporation) under a condition of 6 mm/min. When the shear strength was 67 N or more, it was judged to be at a level of sufficient shear strength and evaluated as “Excellent”. When the shear strength was more than 63 N and 66 N or less, it was judged to be at a level capable of being used practically without any problem and evaluated as “Good”. When the shear strength was less than 62 N, it was evaluated as “Poor”.

[0081] (4) Void Area Ratio

[0082] As to the test substrate produced in “Shear Strength”, the X-ray plane image with 30-fold magnification was displayed on a monitor using a TOSMICRON-6090FP manufactured by Toshiba FA System Engineering Co., Ltd., and voids were detected from the displayed image to determine an area ratio thereof. The image analysis software used for the detection was Scandium, manufactured by Soft imaging system. Because the contrast between the voids and the other parts on the image is different, they can be identified using image analysis, and the measurement was performed by detecting only the voids. When the measured void area ratio was 3.2% or less of the silicon chip area, the void was evaluated as “Excellent”; when the void area ratio was more than 3.2% and 4.1% or less, the void was evaluated as “Good”: and when the void area ratio was more than 4.1%, the void was evaluated as “Poor”.

[0083] (5) Thickness of Oxide Film

[0084] The solder alloys listed in Table 1 were processed into ribbon-shaped preforms having a thickness of 0.1 mm, cut into 10 mm square preforms, and subjected to heat treatment in a thermostatic bath at 150° C. for 120 minutes. The oxide film thickness of the obtained preforms was measured by FE-AES (Field Emission Auger Electron Spectroscopy) to measure the thickness of the oxide film. The film thickness of the oxide film was measured with the following device under the following conditions. Note that a measured value of the thickness of the oxide film was obtained in terms of SiO.sub.2. When the thickness of the oxide film was 1.8 nm or less, it was evaluated as “Excellent” since formation of the oxide film was sufficiently suppressed. When the thickness of the oxide film was more than 1.8 nm and 2.8 nm or less, it was evaluated as “Good” since the film could be mounted without any problem. When the thickness of the oxide film was more than 2.8 nm, it was evaluated as “Poor”.

[0085] Measuring device: scanning FE-Auger Electron Spectroscopic Analyzer manufactured by ULVAC-PHI, INC.

Measuring conditions: 10 kV of Beam Voltage; 10 nA of Sample Current (The measuring method of sputtered depth by using an Ar ion gun is based on ISO/TR 15969)

[0086] Evaluation results are shown in Tables 1 and 2.

TABLE-US-00001 TABLE 1 Solder Composition (mass %) Melting Relation Relation Relation temperature Sn Ag Cu Bi In Other (1) (2) (3) (° C.) Ex. 1 Bal. 2.5 0.80 3.2 0.90 — 8.20 1.64 5.76 Excellent Ex. 2 Bal. 2.8 0.70 3.2 1.00 — 8.40 1.50 6.27 Excellent Ex. 3 Bal. 2.9 0.70 3.2 1.00 — 8.50 1.45 6.50 Excellent Ex. 4 Bal. 3.0 0.70 3.2 1.00 — 8.60 1.40 6.72 Excellent Ex. 5 Bal. 3.1 0.70 3.2 1.00 — 8.70 1.35 6.94 Excellent Ex. 6 Bal. 3.2 0.70 3.2 1.00 — 8.80 1.31 7.17 Excellent Ex. 7 Bal. 3.7 0.70 3.2 1.00 — 9.30 1.14 8.29 Good Ex. 8 Bal. 3.0 0.25 3.2 1.50 — 8.20 1.57 3.60 Good Ex. 9 Bal. 3.0 0.45 3.2 1.10 — 8.20 1.43 4.75 Excellent Ex. 10 Bal. 3.0 0.55 3.2 1.00 — 8.30 1.40 5.28 Excellent Ex. 11 Bal. 3.0 0.95 3.2 1.00 — 9.10 1.40 9.12 Good Ex. 12 Bal. 3.0 0.70 3.0 1.00 — 8.40 1.33 6.30 Excellent Ex. 13 Bal. 3.0 0.70 3.1 1.00 — 8.50 1.37 6.51 Excellent Ex. 14 Bal. 3.0 0.70 3.4 1.00 — 8.80 1.47 7.14 Excellent Ex. 15 Bal. 3.0 0.70 3.9 1.00 — 9.30 1.63 8.19 Excellent Ex. 16 Bal. 3.0 0.75 3.2 0.50 — 8.20 1.23 3.60 Good Ex. 17 Bal. 3.0 0.70 3.2 0.70 — 8.30 1.30 4.70 Excellent Ex. 18 Bal. 3.0 0.70 3.2 1.30 — 8.90 1.50 8.74 Good Ex. 19 Bal. 3.2 0.70 3.0 2.30 — 9.90 1.66 15.46 Excellent Ex. 20 Bal. 3.7 0.90 3.8 2.20 — 11.50 1.62 27.84 Good Ex. 21 Bal. 3.0 0.45 3.2 1.00 — 8.10 1.40 4.32 Good Ex. 22 Bal. 3.7 0.65 3.1 0.60 — 8.70 1.00 4.47 Excellent Solidus Tensile Shear Thickness of temperature strength strength oxide film Total (° C.) (MPa) (Mpa) Void (nm) evaluation Ex. 1 Excellent Excellent Excellent Excellent Excellent Excellent Ex. 2 Excellent Excellent Excellent Excellent Excellent Excellent Ex. 3 Excellent Excellent Excellent Excellent Excellent Excellent Ex. 4 Excellent Excellent Excellent Excellent Excellent Excellent Ex. 5 Excellent Excellent Excellent Excellent Excellent Excellent Ex. 6 Excellent Excellent Excellent Excellent Excellent Excellent Ex. 7 Good Excellent Excellent Good Good Good Ex. 8 Excellent Excellent Excellent Good Good Good Ex. 9 Excellent Excellent Excellent Excellent Excellent Excellent Ex. 10 Excellent Excellent Excellent Excellent Excellent Excellent Ex. 11 Excellent Excellent Excellent Good Good Good Ex. 12 Excellent Excellent Excellent Excellent Excellent Excellent Ex. 13 Excellent Excellent Excellent Excellent Excellent Excellent Ex. 14 Excellent Excellent Excellent Excellent Excellent Excellent Ex. 15 Good Excellent Excellent Good Good Good Ex. 16 Excellent Good Good Excellent Excellent Good Ex. 17 Excellent Excellent Excellent Excellent Excellent Excellent Ex. 18 Good Excellent Excellent Good Good Good Ex. 19 Good Excellent Excellent Good Good Good Ex. 20 Good Excellent Excellent Good Good Good Ex. 21 Excellent Excellent Excellent Excellent Excellent Good Ex. 22 Excellent Good Good Excellent Excellent Good Ex = Example

TABLE-US-00002 TABLE 2 Solder Composition (mass %) Melting Relation Relation Relation temperature Sn Ag Cu Bi In Other (1) (2) (3) (° C.) Comp. Bal. 2.4 0.95 3.1 0.70 — 8.10 1.58 4.95 Poor Ex. 1 Comp. Bal. 3.9 0.70 3.2 1.10 — 9.60 1.10 9.61 Poor Ex. 2 Comp. Bal. 3.0 0.20 3.2 1.50 — 8.10 1.57 2.88 Poor Ex. 3 Comp. Bal. 3.0 1.0  3.0 1.0  — 9.00 1.33 9.00 Good Ex. 4 Comp. Bal. 3.0 1.0  3.0 0.8  — 8.80 1.27 7.20 Good Ex. 5 Comp. Bal. 3.0 2.0  3.2 1.0  11.20  1.40 19.20 Poor Ex. 6 Comp. Bal. 3.5 0.80 0.5 6.00 — 11.60  1.86 8.40 Poor Ex. 7 Comp. Bal. 3.0 0.70 2.5 2.00 — 8.90 1.50 10.50 Poor Ex. 8 Comp. Bal. 3.1 0.50 4.1 1.00 — 9.20 1.65 6.36 Poor Ex. 9 Comp. Bal. 3.0 0.50 3.0 0.25 — 7.25 1.08 1.13 Poor Ex. 10 Comp. Bal. 3.0 0.80 3.2 0.30 — 8.10 1.17 2.30 Poor Ex. 11 Comp. Bal. 3.0 0.70 3.0 3.00 — 10.40  2.00 18.90 Poor Ex. 12 Comp. Bal. 3.0 0.50 3.0 1.00 — 8.00 1.33 4.50 Poor Ex. 13 Comp. Bal. 3.7 0.95 3.9 2.20 — 11.70  1.65 30.16 Poor Ex. 14 Comp. Bal. 3.7 0.70 3.0 0.50 — 8.60 0.95 3.89 Good Ex. 15 Comp. Bal. 2.5 0.70 3.2 2.00 — 9.10 2.08 11.20 Good Ex. 16 Comp. Bal. 3.0 0.70 3.0 1.00 Ni: 0.1 8.40 1.33 6.30 Poor Ex. 17 Comp. Bal. 3.0 0.70 3.0 1.00 Co: 0.1 8.40 1.33 6.30 Poor Ex. 18 Solidus Tensile Shear Thickness of temperature strength strength oxide film Total (° C.) (MPa) (Mpa) Void (nm) evaluation Comp. Poor Poor Poor Excellent Excellent Poor Ex. 1 Comp. Poor Poor Poor Good Good Poor Ex. 2 Comp. Poor Good Good Good Good Poor Ex. 3 Comp. Good Poor Poor Good Good Poor Ex. 4 Comp. Good Poor Poor Excellent Excellent Poor Ex. 5 Comp. Poor Poor Poor Good Good Poor Ex. 6 Comp. Poor Poor Poor Poor Poor Poor Ex. 7 Comp. Poor Poor Poor Good Good Poor Ex. 8 Comp. Poor Poor Poor Good Good Poor Ex. 9 Comp. Poor Poor Poor Good Good Poor Ex. 10 Comp. Poor Poor Poor Good Good Poor Ex. 11 Comp. Poor Poor Poor Poor Poor Poor Ex. 12 Comp. Poor Good Good Good Good Poor Ex. 13 Comp. Poor Poor Poor Poor Poor Poor Ex. 14 Comp. Good Poor Poor Excellent Excellent Poor Ex. 15 Comp. Good Poor Poor Good Poor Poor Ex. 16 Comp. Excellent Good Good Poor Good Poor Ex. 17 Comp. Excellent Good Good Poor Good Poor Ex. 18 Comp. Ex. = Comparative Example The underline indicates that it does not fall within the scope of the present invention.

[0087] As is clear from Table 1, Examples 1 to 22 each have Ag, Cu, Bi, and In contents within the scope of the present invention and also satisfy the relations (1) and (2). For this reason, it was clear that the melting temperature was low enough to allow soldering by step soldering, the tensile strength and shear strength were high, the void area ratio was low, and the thickness of the oxide film was thin. Particularly, it was clear that Examples 1 to 6, 9, 10, 12 to 14, and 17, which satisfy the relation (3), had even higher tensile strength and shear strength, suppressed the void generation, and had thinner oxide films.

[0088] On the other hand, Comparative Examples 1 and 2 were inferior in strength due to inappropriate Ag contents, which caused the melting temperatures to fall outside the desired ranges. In Comparative Example 3, the Cu content was low, resulting in an increase in melting temperature. In Comparative Examples 4 and 5, the Cu contents were high, resulting in inferior strength. In Comparative Example 6, the Cu content was too high, resulting in inferior strength and high melting temperature. Comparative Example 7 were inferior in all results due to low Bi content, high In content, and furthermore, not satisfying the relations (1) and (2). In Comparative Example 8, the Bi content was low, resulting in inferior strength and high melting temperature. In Comparative Example 9, the Bi content was high, resulting in inferior strength and low melting temperature.

[0089] Comparative Example 10 had a low In content and did not satisfy the relation (1), resulting in an increase in melting temperature and inferior strength. In Comparative Example 11, the In content was low, resulting in a further increase in melting temperature and inferior strength. Comparative Example 12 was inferior in all results due to high In content and not satisfying the relation (2).

[0090] Comparative Examples 13 and 14 did not satisfy the relation (1), resulting in inappropriate melting temperatures. Particularly, Comparative Example 14 exceeded the upper limit of the relation (1), resulting in an inappropriate melting temperature, as well as the other results were all inferior. Comparative Examples 15 and 16 did not satisfy the relation (2), resulting in inferior strength. Particularly, Comparative Example 16 exceeded the upper limit of the relation (2), resulting in thicker oxide film in addition to inferior strength. Comparative Examples 17 and 18 contained Ni or Co, resulting in high melting temperatures and increased void area ratios.