Solder alloy, solder ball, chip solder, solder paste and solder joint

Abstract

A solder alloy that contains 0.005 mass % or more and 0.1 mass % or less of Mn, 0.001 mass % or more and 0.1 mass % or less of Ge, and a balance of Sn. A plurality of Ge oxides is distributed on an outermost surface side of an oxide film including Sn oxide, Mn oxide and Ge oxide by adding 0.005 mass % or more and 0.1 mass % or less of Mn, 0.001 mass % or more and 0.1 mass % or less of Ge to the solder alloy having a principal ingredient of Sn, so that it is possible to obtain the discolor-inhibiting effect even under the high-temperature and high-humidity environment.

Claims

1. A solder alloy, consisting of: 0.005 mass % or more and 0.1 mass % or less of Mn; 0.05 mass % or more and 0.1 mass % or less of Ge; optionally one or more of: 0 mass % or more and 1 mass % or less of Cu; 0 mass % or more and 4 mass % or less of Ag; 0.002 mass % or more and 0.1 mass % or less of Ga; 0.02 mass % or more and 0.3 mass % or less of Ni; at least one species selected from a group of Co and Fe, wherein a total amount of Ni, Co, and Fe is 0.02 mass % or more and 0.3 mass % or less; and a total amount of 0.1 mass % or more and 10 mass % or less of at least one species selected from a group of Bi and In; and a balance of Sn, wherein the amount of Mn is smaller than or identical to the amount of Ge.

2. The solder alloy according to claim 1, wherein the solder alloy includes: 0 mass % or more and 4 mass % or less of Ag; and more than 0 mass % and 1 mass % or less of Cu.

3. The solder alloy according to claim 1, wherein the solder alloy includes: more than 0 mass % and 4 mass % or less of Ag; and more than 0 mass % and 1 mass % or less of Cu.

4. The solder alloy according to claim 1, wherein the solder alloy includes 0.003 mass % or more and 0.01 mass % or less of Ga.

5. The solder alloy according to claim 1, wherein the solder alloy includes a total amount of 0.5 mass % or more and 5.0 mass % or less of at least one species selected from a group of Bi and In.

6. The solder alloy according to claim 3, wherein the solder alloy includes 0.003 mass % or more and 0.01 mass % or less of Ga.

7. The solder alloy according to claim 3, wherein the solder alloy includes a total amount of 0.5 mass % or more and 5.0 mass % or less of at least one species selected from a group of Bi and In.

Description

BRIEF EXPLANATION OF DRAWINGS

(1) FIG. 1 is a graph showing a distribution of oxides in Sn—Ag—Cu based solder alloy including Mn and Ge.

(2) FIG. 2 is a diagram showing an application example of the solder alloy according to this invention.

(3) FIG. 3 is a diagram showing another application example of the solder alloy according to this invention.

DESCRIPTION OF THE INVENTION

(4) In the solder alloy having the principal ingredient of Sn, Sn oxide (SnO.sub.x) is generated on an outermost surface of the solder alloy, which causes its discoloration. This also causes its fusion property to be degraded.

(5) On the other hand, in the solder alloy having the principal ingredient of Sn, to which Ge is added, it is possible to inhibit the discoloration under the high temperature environment by the discolor-inhibiting effect of Ge oxide (GeO.sub.z) but it is impossible to inhibit its discoloration under the high temperature and high humidity environment, which also degrades the fusion property thereof.

(6) By the way, it is known that Mn oxide is easier generated than Sn oxide according to a value of standard free energy of formation of its oxide. Therefore, in the solder alloy having the principal ingredient of Sn, to which Mn is added, a generation of Sn oxides is inhibited. The addition of Mn, however, does not obtain the discolor-inhibiting effect, so that it is impossible to inhibit the discoloration under the high temperature environment or the high temperature and high humidity environment.

(7) On the other hand, it has been found that, in the solder alloy having the principal ingredient of Sn, to which predetermined amounts of Mn and Ge are added, the addition of Mn allows Ge oxides to be unevenly distributed to an outermost surface side of the oxide film. This allows Ge oxides (GeO.sub.z), which has the discolor-inhibiting effect even under the high temperature and high humidity environment, to remain on the outermost surface side of the oxide film. In addition, the generation of Mn oxide (Mn.sub.aO.sub.y) also inhibits generation of Sn oxide. Therefore, it is possible to inhibit the discoloration thereof even under the high temperature and high humidity environment and inhibit the generation of Sn oxide, thereby improving the fusion property thereof.

(8) As an amount of Mn for being capable of inhibiting the generation and growth of Sn oxide by reacting Mn with O.sub.2 to preventing reacting Sn with O.sub.2, 0.005 mass % or more and 0.1 mass % or less thereof is added. As an amount of Ge for being capable of allowing Ge oxides to remain on the outermost surface side of the oxide film, 0.001 mass % or more and 0.1 mass % or less thereof is added.

(9) Accordingly, as described above, in the solder alloy according to this invention having the principal ingredient of Sn, to which the predetermined amounts of Mn and Ge are added, the Mn oxide (Mn.sub.aO.sub.y) inhibits the growth of Sn oxide to allow the Ge oxides, which have the discolor-inhibiting effect, to remain on the outermost surface side. This enables the discoloration to be inhibited even under the high temperature and high humidity environment, and the growth of oxide to be prevented, thereby improving the fusion property. This effect is obtained when predetermined amounts of Mn and Ge are added but even when other element(s) is (are) added, this effect is not lost. It, however, is preferable that as the elements other than Mn and Ge in the solder alloy, Sn is added to the solder alloy and the remainder may be configured to be only Sn.

(10) Depending on intended uses, an additive element(s) is (are) optionally selectable. For example, when the solder alloy or the object to be jointed includes Cu, more than 0 mass % and 1 mass % or less of Cu may be added in order to suppresses the so-called copper leaching in which Cu is leached into the solder alloy. Further, in order to improve temperature cycle property thereof, more than 0 mass % and 4 mass % or less of Ag may be added. Ag precipitates network-like intermetallic compounds of Ag.sub.3Sn in a solder matrix and thus, has an effect to further improve its temperature cycle to form an alloy of precipitation strengthening type. It is to be noted that Ag may be omitted in a case of adding more than 0 mass % and 1 mass % or less of Cu. More than 0 mass % and 4 mass % or less of Ag may be also added in a case of adding more than 0 mass % and 1 mass % or less of Cu.

(11) Additionally, as other elements, the following elements may be contained as optional components.

(12) (a) A Total Amount of 0.002% Through 0.1% of at Least One Species Selected from a Group of P and Ga:

(13) These elements have effects to improve wettability. A total amount of these elements thus contained is more preferably 0.003% through 0.01%. Although content of each element thus contained is not specifically limited, the content of P is preferably 0.002% through 0.005% and the content of Ga is preferably 0.002% through 0.02%.

(14) (b) A Total Amount of 0.005% Through 0.3% of at Least One Species Selected from a Group of Ni, Co and Fe:

(15) These elements suppress diffusing components of a plating layer applied to the semiconductor element or an external board into the solder alloy when soldering them. Accordingly, these elements have effects to maintain an organization of the solder alloy constituting the solder joint and to thin the film thickness of an intermetallic compound layer which is formed in a bonded interface. Therefore, these elements allow bond strength of the solder joint to be enhanced. A total amount of these elements thus contained is more preferably 0.01% through 0.05%. Although content of each element thus contained is not specifically limited, the content of Ni is preferably 0.02% through 0.07%, the content of Co is preferably 0.02% through 0.04% and the content of Fe is preferably 0.005% through 0.02%. Specifically, Ni among these elements is a preferable element as an element that demonstrates the effect as described above.

(16) (c) A Total Amount of 0.1% Through 10% of at Least One Species Selected from a Group of Bi and in:

(17) The addition of these elements allows the solder strength to be improved, which is expected to keep the reliability of the jointed portions. A total amount of these elements thus contained is more preferably 0.5% through 5.0%, especially particularly 0.8% through 4.5%. Although content of each element thus contained is not specifically limited, the content of Bi is preferably 0.5% through 5.0%, and the content of In is preferably 0.2% through 5.0%.

(18) The following will describe a process of generating an oxide as follows, according to a study estimated at present. A Sn—Ag—Cu based solder alloy will be described as an example of the solder alloy having the principal ingredient of Sn.

(1) As for the Sn—Ag—Cu Based Solder Alloy Including Mn and Ge (Executed Examples)

(19) In the Sn—Ag—Cu based solder alloy including Mn and Ge, at an initial state of the oxide generation, Sn, Mn and Ge in the solder alloy react with O.sub.2 in the air to produce an oxide film composed of Sn oxide (SnO.sub.x), Mn oxide (Mn.sub.aO.sub.y) and Ge oxide (GeO.sub.z) on a surface of the solder alloy Sn.

(20) When setting the solder alloy on which the oxide film has been thus formed at the initial state under a high temperature and high humidity environment in which a predetermined amount or more of H.sub.2O and O.sub.2 exists, it is conceivable that a part of the oxide film composed of Sn oxide, Mn oxide and Ge oxide, which has formed on the outmost surface side of the solder alloy, is destroyed by H.sub.2O having high energy.

(21) When the part of the oxide film is destroyed, based on a relationship between the values of the standard free energy of formation of Sn oxide and Mn oxide, the generation of Sn oxide is inhibited and Mn oxide is generated so that Mn oxides are almost evenly distributed along a thickness direction of the oxide film.

(22) In addition, in the solder alloy having the principal ingredient of Sn, to which predetermined amounts of Mn and Ge are added, Sn oxides on the outermost surface side of the oxide film are decreased and Ge oxides are unevenly distributed to the outermost surface side of the oxide film.

(23) From this, in the Sn—Ag—Cu based Solder Alloy including Mn and Ge, the generation of Sn oxide is inhibited and Ge oxides are unevenly distributed to the outermost surface side of the oxide film, thereby allowing the discoloration to be inhibited by the discolor-inhibiting effect of Ge oxides.

(2) Sn—Ag—Cu Based Solder Alloy Neither Including Mn Nor Ge (Comparison Examples)

(24) In the Sn—Ag—Cu based solder alloy neither including Mn nor Ge, Sn in the solder alloy reacts with O.sub.2 in the air at an initial state of the oxide generation to produce an oxide film composed of Sn oxide (SnO.sub.x) on a surface of the solder alloy.

(25) When exposing the solder alloy on which the oxide film is thus formed at the initial state under a high temperature environment or a high temperature and high humidity environment, it is conceivable that a part of the oxide film which has been formed on the surface thereof is destroyed, so that Sn in the solder alloy reacts with O.sub.2 to further produce Sn oxide.

(26) From this, in the Sn—Ag—Cu based Solder Alloy neither including Mn nor Ge, the Sn oxide causes the discoloration thereof.

(3) Sn—Ag—Cu Based Solder Alloy Including Mn but not Including Ge (Comparison Examples)

(27) In the Sn—Ag—Cu based solder alloy including Mn but not including Ge, Sn and Mn in the solder alloy react with O.sub.2 in the air at an initial state of the oxide generation to produce an oxide film composed of Sn oxide (SnO.sub.x) and Mn oxide (Mn.sub.aO.sub.y) on a surface of the solder alloy.

(28) When exposing the solder alloy on which the oxide film has been thus formed at the initial state under a high temperature environment or a high temperature and high humidity environment, it is conceivable that a part of the oxide film, which has been formed on the surface thereof is destroyed.

(29) Based on the magnitudes of the standard free energy of formation of Sn oxide and Mn oxide, the generation of Sn oxide is inhibited and Mn oxide is generated.

(30) Mn oxide, however, does not have any discolor-inhibiting effect and in the Sn—Ag—Cu based solder alloy including Mn but not including Ge, Mn oxide discolors similar to the Sn oxide, so that its discoloration cannot be inhibited.

(4) Sn—Ag—Cu Based Solder Alloy Including Ge but not Including Mn (Comparison Examples)

(31) In the Sn—Ag—Cu based solder alloy including Ge but not including Mn, Sn and Ge in the solder alloy react with O.sub.2 in the air at an initial state of the oxide generation to produce an oxide film composed of Sn oxide (SnO.sub.x) and Ge oxide (GeO.sub.z) on a surface of the solder alloy.

(32) When exposing the solder alloy on which the oxide film has been thus formed at the initial state under a high temperature environment or a high temperature and high humidity environment, it is conceivable that a part of the oxide film, which has been formed on the surface thereof, is destroyed.

(33) From this, in the Sn—Ag—Cu based Solder Alloy including Ge but not including Mn, the discoloration of the oxide film by the growth of Sn oxide cannot be inhibited.

Executed Examples

(34) <Evaluation of Discolor-Inhibiting Effect>

(35) The solder alloys of the executed examples and comparison examples having compositions shown in following Tables 1 and 2 were prepared and their discolor-inhibiting effects were evaluated. It is to be noted that a percent of each composition shown in Tables 1 and 2 is mass %.

(36) The evaluation of discolor-inhibiting effect was performed according to the following procedure.

(37) (1) Manufacture of Specimens

(38) The prepared solder alloys were casted and rolled to make them plate materials. These plate members were punched out to be small pieces (each piece has a dimension of 2 mm (length), 2 mm (width) and 0.1 mm (thickness)) and they were manufactured as the specimens.

(39) (2) Verification Method

(40) Each specimen of the executed examples and comparison examples, thus manufactured above, was stored under a high temperature environment and a high temperature and high humidity environment and it was confirmed whether there is any discoloration. A storage condition was such that the specimen stayed in the high temperature and high humidity environment of temperature of 125 degrees C. and humidity RH of 100% for 24 hours. Under the high temperature leaving environment of temperature of 150 degrees C., the specimen was left for 7 days. The discoloration thereof was confirmed by using a DIGITAL MICROSCOPE VHX-500F made by KEYENCE. As a result of the confirmation, the one not showing any discoloration at all was evaluated as a double circle mark; the one confirming that a small amount of the gloss variation was evaluated as a circle mark; the one showing a little of the discoloration was evaluated as a triangle mark; and the one showing a discoloration was evaluated as a X-mark.

(41) TABLE-US-00001 TABLE 1 Sn Ag Cu Ge Mn P Ga Ni C○ Fe Bi In EXECUTED Bal. 0 0 0.001 0.005 EXAMPLE 1 EXECUTED Bal. 0 0 0.001 0.04 EXAMPLE 2 EXECUTED Bal. 0 0 0.001 0.1 EXAMPLE 3 EXECUTED Bal. 0 0 0.05 0.005 EXAMPLE 4 EXECUTED Bal. 0 0 0.05 0.05 EXAMPLE 5 EXECUTED Bal. 0 0 0.05 0.1 EXAMPLE 6 EXECUTED Bal. 0 0 0.1 0.005 EXAMPLE 7 EXECUTED Bal. 0 0 0.1 0.05 EXAMPLE 8 EXECUTED Bal. 0 0 0.1 0.1 EXAMPLE 9 EXECUTED Bal. 0 0.5 0.001 0.005 EXAMPLE 10 EXECUTED Bal. 0 0.5 0.05 0.05 EXAMPLE 11 EXECUTED Bal. 0 0.5 0.1 0.1 EXAMPLE 12 EXECUTED Bal. 0 1 0.05 0.05 EXAMPLE 13 EXECUTED Bal. 2 0.5 0.001 0.005 EXAMPLE 14 EXECUTED Bal. 2 0.5 0.05 0.05 EXAMPLE 15 EXECUTED Bal. 2 0.5 0.1 0.1 EXAMPLE 16 EXECUTED Bal. 4 1 0.05 0.05 EXAMPLE 17 EXECUTED Bal. 0 0 0.05 0.05 0.05 EXAMPLE 18 EXECUTED Bal. 0 0 0.05 0.05 0.05 EXAMPLE 19 EXECUTED Bal. 0 0 0.05 0.05 0.13 EXAMPLE 20 EXECUTED Bal. 0 0 0.05 0.05 0.11 EXAMPLE 21 EXECUTED Bal. 0 0 0.05 0.05 0.13 EXAMPLE 22 EXECUTED Bal. 0 0 0.05 0.05 3.1 EXAMPLE 23 EXECUTED Bal. 0 0 0.05 0.05 3.2 EXAMPLE 24 EXECUTED Bal. 0 0.5 0.05 0.05 0.04 EXAMPLE 25 EXECUTED Bal. 0 0.5 0.05 0.05 0.11 EXAMPLE 26 EXECUTED Bal. 0 1 0.05 0.05 0.10 EXAMPLE 27 EXECUTED Bal. 0 0.7 0.05 0.05 3.0 EXAMPLE 28 EXECUTED Bal. 0 0.7 0.05 0.05 3.1 EXAMPLE 29 EXECUTED Bal. 0 0 0.05 0.05 0.05 0.05 0.12 0.09 0.11 3.3 3.1 EXAMPLE 30 EXECUTED Bal. 0 0.5 0.05 0.05 0.04 0.05 0.11 0.1 0.11 3.1 3.2 EXAMPLE 31 INCIDENCE HIGH OF TEMPERATURE/ HIGH WETTABILITY DEFECT INITIAL HIGH TEMPERATURE [mm2] FUSION STATE HUMIDITY LEAVING Cu-OSP Ni/Au [%] EXECUTED ⊚ ○ ○ 5.9 12.1 0 EXAMPLE 1 EXECUTED ⊚ ○ ○ 5.7 11.9 0 EXAMPLE 2 EXECUTED ⊚ ○ ○ 5.5 11.6 0 EXAMPLE 3 EXECUTED ⊚ ⊚ ⊚ 5.8 11.9 0 EXAMPLE 4 EXECUTED ⊚ ⊚ ⊚ 5.4 12.0 0 EXAMPLE 5 EXECUTED ⊚ ○ ○ 5.5 11.4 0 EXAMPLE 6 EXECUTED ⊚ ⊚ ⊚ 5.4 11.8 0 EXAMPLE 7 EXECUTED ⊚ ⊚ ⊚ 5.5 12.0 0 EXAMPLE 8 EXECUTED ⊚ ⊚ ⊚ 5.2 12.1 0 EXAMPLE 9 EXECUTED ⊚ ○ ○ 5.3 12.3 0 EXAMPLE 10 EXECUTED ⊚ ⊚ ⊚ 5.2 12.0 0 EXAMPLE 11 EXECUTED ⊚ ⊚ ⊚ 5.2 12.1 0 EXAMPLE 12 EXECUTED ⊚ ⊚ ⊚ 5.1 11.9 0 EXAMPLE 13 EXECUTED ⊚ ○ ○ 5.8 12.6 0 EXAMPLE 14 EXECUTED ⊚ ⊚ ⊚ 5.7 12.2 0 EXAMPLE 15 EXECUTED ⊚ ⊚ ⊚ 5.4 12.3 0 EXAMPLE 16 EXECUTED ⊚ ⊚ ⊚ 5.1 12.0 0 EXAMPLE 17 EXECUTED ⊚ ⊚ ⊚ 5.4 11.8 0 EXAMPLE 18 EXECUTED ⊚ ⊚ ⊚ 5.2 11.9 0 EXAMPLE 19 EXECUTED ⊚ ⊚ ⊚ 5.1 12.2 0 EXAMPLE 20 EXECUTED ⊚ ⊚ ⊚ 5.2 12.0 0 EXAMPLE 21 EXECUTED ⊚ ⊚ ⊚ 5.1 11.7 0 EXAMPLE 22 EXECUTED ⊚ ⊚ ⊚ 5.9 12.8 0 EXAMPLE 23 EXECUTED ⊚ ⊚ ⊚ 5.2 12.3 0 EXAMPLE 24 EXECUTED ⊚ ⊚ ⊚ 5.3 11.9 0 EXAMPLE 25 EXECUTED ⊚ ⊚ ⊚ 5.1 12.1 0 EXAMPLE 26 EXECUTED ⊚ ⊚ ⊚ 5.2 11.7 0 EXAMPLE 27 EXECUTED ⊚ ⊚ ⊚ 5.8 12.5 0 EXAMPLE 28 EXECUTED ⊚ ⊚ ⊚ 5.3 12.2 0 EXAMPLE 29 EXECUTED ⊚ ⊚ ⊚ 5.3 12.8 0 EXAMPLE 30 EXECUTED ⊚ ⊚ ⊚ 5.2 12.5 0 EXAMPLE 31

(42) TABLE-US-00002 TABLE 2 Sn Ag Cu Ge Mn P Ga Ni Co COMPARISON EXAMPLE 1 100 0 0 0 0 COMPARISON EXAMPLE 2 Bal. 1.0 0.7 0 0 COMPARISON EXAMPLE 3 Bal. 0 0 0 0.005 COMPARISON EXAMPLE 4 Bal. 0 0 0 0.06 COMPARISON EXAMPLE 5 Bal. 0 0 0 0.1 COMPARISON EXAMPLE 6 Bal. 0 0 0 0.14 COMPARISON EXAMPLE 7 Bal. 0 0 0 0.19 COMPARISON EXAMPLE 8 Bal. 0 0 0.001 0 COMPARISON EXAMPLE 9 Bal. 0 0 0.001 0.14 COMPARISON EXAMPLE 10 Bal. 0 0 0.05 0 COMPARISON EXAMPLE 11 Bal. 0 0 0.05 0.15 COMPARISON EXAMPLE 12 Bal. 0 0 0.1 0 COMPARISON EXAMPLE 13 Bal. 0 0 0.1 0.15 COMPARISON EXAMPLE 14 Bal. 0 0 0.15 0.005 COMPARISON EXAMPLE 15 Bal. 0 0 0.15 0.05 COMPARISON EXAMPLE 16 Bal. 0 0 0.15 0.1 COMPARISON EXAMPLE 17 Bal. 0 0 0.15 0.15 COMPARISON EXAMPLE 18 Bal. 2 0.5 0.15 0.15 HIGH HIGH WETTABILITY INCIDENCE OF INITIAL TEMPERATURE/ TEMPERATURE [mm2] DEFECT Fe Bi In STATE HIGH HUMIDITY LEAVING Cu-OSP Ni/Au FUSION[%] COMPARISON EXAMPLE 1 ⊚ X X 3.9 10.1 24.4 COMPARISON EXAMPLE 2 ⊚ X X 4.2 10.8 15.6 COMPARISON EXAMPLE 3 ⊚ X X 4.6 10.5 20.0 COMPARISON EXAMPLE 4 ⊚ X X 4.5 10.5 11.1 COMPARISON EXAMPLE 5 ⊚ X X 4.4 10.3 13.3 COMPARISON EXAMPLE 6 ⊚ X X 4.1 10 26.7 COMPARISON EXAMPLE 7 ⊚ X X 4.1 10.3 31.1 COMPARISON EXAMPLE 8 ⊚ X Δ 4.3 10.4 17.8 COMPARISON EXAMPLE 9 ⊚ ◯ ◯ 4.7 10.2 6.67 COMPARISON EXAMPLE 10 ⊚ X ⊚ 4.4 10.8 26.7 COMPARISON EXAMPLE 11 ⊚ ⊚ ⊚ 4.6 11.1 11.1 COMPARISON EXAMPLE 12 ⊚ X ⊚ 4.5 10.9 15.6 COMPARISON EXAMPLE 13 ⊚ ⊚ ⊚ 4.2 10.7 6.67 COMPARISON EXAMPLE 14 ⊚ ⊚ ⊚ 4.2 10.8 6.67 COMPARISON EXAMPLE 15 ⊚ ⊚ ⊚ 4.3 10.8 11.1 COMPARISON EXAMPLE 16 ⊚ ⊚ ⊚ 4.3 10.3 13.3 COMPARISON EXAMPLE 17 ⊚ ⊚ ⊚ 4.0 10.1 17.8 COMPARISON EXAMPLE 18 ⊚ ⊚ ⊚ 4.4 10.6 20.0

(43) As shown in Tables 1 and 2, in the initial state, neither the executed examples nor the comparison examples showed any discoloration. In the executed examples 4, 7 and 8 in which Mn and Ge were added and a ratio of an added amount of Mn was smaller than that of Ge, any discoloration was not shown at all under the high temperature leaving environment and the high temperature and high humidity environment. In the executed examples 5, 9, 11-13, and 15-17 in which a ratio of an added amount of Mn was similar to that of Ge, any discoloration similarly was not shown at all under the high temperature leaving environment and the high temperature and high humidity environment. In the executed examples 1, 2, 3, 6, 10 and 14 in which a ratio of an added amount of Ge was smaller than that of Mn, it was confirmed under the high temperature leaving environment and the high temperature and high humidity environment that a small amount of the gloss thereof altered.

(44) In the executed examples 10 through 17 in which Mn and Ge were added and only Cu or both of Ag and Cu were added, any discoloration was not shown under the high temperature leaving environment and the high temperature and high humidity environment.

(45) In the executed examples 18 through 31 in which Mn and Ge were added, a ratio of an added amount of Mn was similar to that of Ge and any or all of P, Ga, Ni, Co, Fe, Bi and In were added, any discoloration was not shown at all under the high temperature leaving environment and the high temperature and high humidity environment.

(46) On the other hand, in the comparison examples 1 and 2 in which Mn and Ge were not added, a discoloration was shown under the high temperature leaving environment and the high temperature and high humidity environment. In the comparison examples 3 through 7 in which Mn was added but Ge was not added, a discoloration was similarly shown under the high temperature leaving environment and the high temperature and high humidity environment. In the comparison examples 8, 10 and 12 in which Ge was added but Mn was not added, a discolor-inhibiting effect was obtained under the high temperature leaving environment by increasing the added amount of Ge but a discoloration was shown under the high temperature and high humidity environment. In the comparison examples 9, 11 and 13 through 18 in which Mn and Ge were added, it was confirmed that a small amount of the gloss variation in the comparison example 9 but any discoloration was not shown at all under the high temperature leaving environment and the high temperature and high humidity environment in the comparison examples 11 and 13 through 18, even when any or both of Mn and Ge were excessively added beyond a scope of this invention.

(47) From the above results, it is understood that the discolor-inhibiting effect is obtained under the high temperature leaving environment and the high temperature and high humidity environment by adding Mn and Ge into a solder alloy containing the principal ingredient of Sn. When the ratio of an added amount of Mn was smaller than or similar to that of Ge, it is also understood that the better discolor-inhibiting effect is obtained.

(48) <Distribution of Oxides>

(49) Next, a distribution of Sn oxides, Mn oxides and Ge oxides in an oxide film about the solder alloys of the executed examples, the discolor-inhibiting effect of which had been verified under the high temperature leaving environment and the high temperature and high humidity environment as shown in Table 1 described above, was verified.

(50) FIG. 1 shows the distribution of major elements in a case of containing a principal ingredient of Sn and including Mn and Ge. In a graph of FIG. 1, a vertical axis indicates their contents and a horizontal axis indicates a depth from an outermost surface in which the elements are distributed. Any other contained elements such as oxygen and carbon are not shown therein.

(51) It is understood that in the executed example 1 containing a principal ingredient of Sn and including Mn and Ge, many of Ge oxides are distributed in a range of about 10 nm from the outermost surface of the oxide film and many of Ge oxides are also distributed at an outermost surface side of the oxide film. Further, it is understood that Mn is almost even distributed from the outermost surface thereof. On the other hand, it is understood that Sn is decreased in the outermost surface thereof. In even cases of the executed examples 2 through 31 in which the added amounts of Mn and Ge alter, an identical distribution is shown.

(52) From the distribution of elements shown in FIG. 1, it is understood that in the solder alloys each containing a principal ingredient of Sn and to which predetermined amounts of Mn and Ge are added, Ge oxides are distributed while they are unevenly distributed to the outermost surface side of the oxide film and Sn oxides are inhibited from being formed at the outermost surface thereof.

(53) Thus, the distribution of many of Ge oxides having the discolor-inhibiting effect at the outermost surface side allows inhibiting the discoloration. Further, the almost even distribution of Mn oxides along a thickness direction of the oxide film allows inhibiting the generation of Sn oxides.

(54) <Evaluation of Fusion Property>

(55) Fusion properties about the solder alloys of the executed examples and the comparison examples, the discolor-inhibiting effect of which had been verified under the high temperature leaving environment and the high temperature and high humidity environment as shown in Tables 1 and 2 described above, were verified. A method for verifying them was such that the prepared solder alloys having compositions of the executed examples and the comparison examples were casted and rolled and they were punched out to be made small pieces (each piece has a dimension of 2 mm (length), 2 mm (width) and 0.1 mm (thickness)). These small pieces were formed as plate materials having a predetermined dimension. They were put on a Cu plate on which organic solderability preservative (OSP) processing (water-soluble preflux processing) was performed and flux was applied and reflowed, and then the surface thereof was washed and they stayed under an environment of temperature of 125 degrees C. and humidity RH of 100% for 24 hours. Further, the solder balls (in a case of this embodiment, a diameter thereof is 300 μm) which were manufactured by using the solder alloy in which 3.0 mass % of Ag, 0.5 mass % of Cu and the balance of Sn (Sn-3.0Ag-0.5Cu) were contained stayed under an environment of temperature of 125 degrees C. and humidity RH of 100% for 24 hours, which was similar to the small pieces. Next, flux was applied to the specimens made of the solder alloys of the executed examples or the comparison examples and a predetermined number of solder balls was put thereon. In the examples, the number of solder balls was set to be nine pieces and respective 5 plate materials were prepared. Then, after reflowing was performed, a number of defectively fused solder balls was calculated and incidence of defect fusion was calculated. The term, “defect fusion” is referred to as a condition in which the Cu plate and the solder balls are not jointed to each other.

(56) In the executed examples 1 through 31 containing a principal ingredient of Sn and including Mn and Ge, the incidence of defect fusion of zero was shown.

(57) In all of the comparison examples 1 and 2 containing a principal ingredient of Sn and excluding Mn and Ge, the comparison examples 3 through 7 containing a principal ingredient of Sn, including Mn and excluding Ge, and the comparison examples 8, 10 and 12 containing a principal ingredient of Sn, including Ge and excluding Mn, the defect fusion occurred. Further, in the comparison examples 9, 11 and 13 to which an amount of Mn exceeding the range of this invention was excessively added, among the comparison examples 9, 11 and 13 through 18 to which Mn and Ge were added, the defect fusion occurred. In the comparison examples 14 through 18 to which an amount of Ge or both of Ge and Mn was excessively added within the range of this invention, the defect fusion occurred.

(58) <Evaluation of Wettability>

(59) Wettability about each of the solder alloys of the executed examples and the comparison examples, the discolor-inhibiting effect of which had been verified under the high temperature leaving environment and the high temperature and high humidity environment as shown in Tables 1 and 2 described above, was verified. A method for verifying it was such that the prepared solder alloys having compositions of the executed examples and the comparison examples were casted and rolled and they were punched out to be made small pieces (each piece has a dimension of 2 mm (length), 2 mm (width) and 0.1 mm (thickness)). These small pieces stayed under an environment of temperature of 125 degrees C. and humidity RH of 100% for 24 hours. Next, the flux was applied to each of the OSP processed Cu plates and Ni/Au plating plates in which Ni was plated on the Cu plate and Au was plated on the Ni plated plate. The small pieces, on which the high temperature and high humidity process had been performed, were put thereon and reflowed. An area in which the solder alloy was spread was measured and the OSP processed Cu plate in which 5.0 mm.sup.2 thereof was spread was fixed to be passed or the Ni/Au plating plate in which 11.0 mm.sup.2 thereof was spread was fixed to be passed.

(60) In the executed examples 1 through 31 containing a principal ingredient of Sn and including Mn and Ge, any deterioration was not seen in the wettability to the OSP processed Cu plates, nor in the wettability to the Ni/Au plating plate.

(61) In the comparison examples 3 through 7 in which Mn was contained but Ge was not contained, both of the wettability to the OSP processed Cu plates and the wettability to the Ni/Au plating plate were deteriorated when an added amount of Mn was increased. In any of the comparison examples 9, 11 and 13 to which an amount of Mn exceeding the range of this invention was excessively added, or the comparison examples 14 through 18 to which an amount of Ge or both of Mn and Ge exceeding the range of this invention was excessively added, among the comparison examples 9, 11 and 13 through 18 to which Mn and Ge were added, both of the wettability to the OSP processed Cu plates and the wettability to the Ni/Au plating plate were deteriorated. When an amount of Ge or Mn exceeding the range of this invention is excessively added, it is understood that the wettability is deteriorated.

(62) From the above results, it is understood that, in the solder alloy containing a principal ingredient of Sn, to which 0.005 mass % or more and 0.1 mass % or less of Mn and 0.001 mass % or more and 0.1 mass % or less of Ge are added, Mn and O.sub.2 are reacted to prevent Sn from reacting with O.sub.2, which inhibits the distribution of Sn oxides to the outermost surface of the oxide film by aging variation, so that since the oxide film containing Ge oxides having the discolor-inhibiting effect remains in the outermost surface side thereof, the discolor-inhibiting effect can be obtained even under the high temperature and high humidity environment. It is understood that when the ratio of the added amount of Mn and Ge is preferably set so that the added amount of Mn is smaller and identical to that of Ge, the more excellent discolor-inhibiting effect can be obtained even under the high temperature and high humidity environment and the high temperature leaving environment.

(63) It is understood that, in the solder alloy containing a principal ingredient of Sn, to which the above predetermined amounts of Mn and Ge are added, Mn and O.sub.2 are reacted to prevent Sn from reacting with O.sub.2, which inhibits the growth of Sn oxides, so that an increase in the thickness of the oxide film can be prevented. The prevention of an increase in the thickness of the oxide film allows the oxide to be satisfactorily removed by the flux in the soldering, thereby improving the fusion property thereof.

(64) <Application Examples of Solder Alloy>

(65) FIG. 2 is a diagram showing an application example of the solder alloy according to this invention. The solder alloy containing a principal ingredient of Sn, to which 0.005 mass % or more and 0.1 mass % or less of Mn and 0.001 mass % or more and 0.1 mass % or less of Ge are added, may be formed as a solder ball 10. It is preferable that a diameter of the solder ball 10 is 1 through 1000 μm. Within this range, the solder ball can be stably manufactured so that a short-circuit in the connection can be inhibited in a case where the terminals have a narrow pitch between them. Here, when each of the solder balls has the diameter of about 1 through 50 μm, these solder balls may be referred to as “solder powder”.

(66) FIG. 3 is a diagram showing another application example of the solder alloy according to this invention. The solder alloy containing a principal ingredient of Sn, to which 0.005 mass % or more and 0.1 mass % or less of Mn and 0.001 mass % or more and 0.1 mass % or less of Ge are added, may be applied as a chip solder 11. The chip solder 11 is formed so as to have a rectangular parallelepiped shape, for example.

(67) As other application example thereof, a solder paste may be exemplified in which the powdered solder alloy having a predetermined dimension and containing a principal ingredient of Sn, to which 0.005 mass % or more and 0.1 mass % or less of Mn and 0.001 mass % or more and 0.1 mass % or less of Ge are added, is mixed with the flux.

(68) The solder alloy, the solder ball, the chip solder and the solder paste according to the invention are formed as a solder joint which is used for joining a semiconductor chip with them or joining the printed circuit board with electronic components.

(69) α dose of the present invention may be 0.0200 cph/cm.sub.2 or less. When α dose is 0.0200 cph/cm.sub.2 or less, any software error in electronic device can be inhibited.