Solder alloy and solder joint

Abstract

Provided are a solder alloy and a solder joint, which have a narrow ?T to suppress solder bridges and solder icicles, and a small amount of dross generated in a solder tank, suppress Cu leaching, and have higher strength. The solder alloy has an alloy composition of, by mass %, Cu: more than 2.0% and less than 3.0%; Ni: 0.010% or more and less than 0.30%; and Ge: 0.0010 to 0.20% with the balance being Sn. Preferably, by mass %, Cu is more than 2.5% and less than 3.0%, and the alloy composition satisfies the following relations (1) and (2): 2.400?Cu+Ni+Ge?3.190 (1), and 0.33?Ge/Ni?1.04 (2). Cu, Ni, and Ge 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 %: Cu: more than 2.0% and less than 3.0%, Ni: 0.10% or more and less than 0.30%, and Ge: 0.0010 to 0.20%, with the balance being Sn, wherein the alloy composition satisfies the following relations (1) and (2):
2.700%?Cu+Ni+Ge?3.190%relation (1)
0.33?Ge/Ni?1.04relation (2) wherein Cu, Ni, and Ge in the relations (1) and (2) each represent the contents (mass %) thereof in the alloy composition, and wherein the solder alloy comprises the following properties: a ?T that is obtained by subtracting a solidus temperature from a liquidus temperature is less than 110? C., no solder bridges or solder icicles are observed after flow soldering at a temperature of 255? C., a tensile strength measured in accordance with JIS Z 3198-2 (2003) is 38 MPa or more, a dross weight is 25 g or less, and a dimension of copper wiring on a test sample is not reduced by half after immersion of seven times or more in jetting molten solder.

2. The solder alloy according to claim 1, wherein, by mass %, Cu: more than 2.5% and less than 3.0%.

3. A solder joint, comprising a solder alloy, wherein the solder alloy is the solder alloy according to claim 1.

4. A solder joint, comprising a solder alloy, wherein the solder alloy is the solder alloy according to claim 2.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 is a schematic view of a dross occurrence apparatus.

DETAILED DESCRIPTION

(2) Embodiments of the present invention will be described in more detail below. In the present specification, % used for indicating a solder alloy composition is mass % unless otherwise specified.

1. Solder Alloy

(3) (1) Cu: more than 2.0% and less than 3.0%

(4) Cu can improve strength of a solder alloy and also suppress Cu leaching. If the Cu content is 2.0% or less, Cu leaching may occur, and the strength may be reduced. In terms of the lower limit, the Cu content is more than 2.0%, preferably 2.1% or more, more preferably 2.3% or more, and further preferably 2.5% or more. On the other hand, if the Cu content is 3.0% or more, the liquidus temperature increases, resulting in a large ?T. Solder bridges and solder icicles also increase. Furthermore, coarse intermetallic compounds are generated, and the strength is reduced. In addition to this, solderability deteriorates. In terms of the upper limit, the Cu content is less than 3.0%, preferably 2.9% or less, more preferably 2.8% or less, further preferably 2.7% or less, and particularly preferably 2.6% or less.

(5) (2) Ni: 0.010% or more and less than 0.30%

(6) Ni can improve the strength of the solder alloy and also suppress Cu leaching since it forms an all-proportional solid solution with Cu. If the Ni content is less than 0.010%, Cu leaching may occur, and the strength may be reduced. In terms of the lower limit, the Ni content is 0.010% or more, preferably 0.050% or more, more preferably 0.10% or more, and even more preferably 0.15% or more. On the other hand, if the Ni content is 0.30% or more, the liquidus temperature increases, resulting in a large ?T. Solder bridges and solder icicles also increase. Furthermore, coarse intermetallic compounds are generated, and the strength is reduced. In addition to this, solderability deteriorates. In terms of the upper limit, the Ni content is less than 0.30%, preferably 0.29% or less, more preferably 0.24% or less, further preferably 0.22% or less, particularly preferably 0.20% or less, and most preferably 0.16% or less.

(7) (3) Ge: 0.0010 to 0.20%

(8) Ge can suppress oxidation of the molten solder and generation of solder bridges and solder icicles. If the Ge content is less than 0.0010%, the oxidation suppressing effect is reduced. Thus, dross is generated, and solder bridges and solder icicles increase. In terms of the lower limit, the Ge content is 0.0010% or more, preferably 0.0050% or more, and more preferably 0.0100% or more. It is further preferably 0.0600% or more. On the other hand, if the Ge content is more than 0.20%, the viscosity of the molten solder increases and solderability deteriorates. The liquidus temperature also increases, resulting in a large ?T. In addition, solder bridges and solder icicles increase. In terms of the upper limit, the Ge content is 0.2000% or less, preferably 0.1400% or less, and more preferably 0.1000% or less.

(9) (4) Balance: Sn

(10) 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.

(11) (5) P, Ga, and Co

(12) It is preferable that the solder alloy according to the present invention do not contain P, Ga, or Co. It is difficult to control P and Ga since they rapidly disappear into the atmosphere or as dross in a molten state in a solder tank. In addition, Ga promotes the generation of solder bridges and solder icicles due to increased viscosity, which increases the amount of dross. P causes an increase in the liquidus temperature, thus increasing ?T and promoting the generation of solder bridges and solder icicles due to increased viscosity. Although Co is not a problem when added in very small amounts, the melting point increases as the content increases, resulting in a large ?T. It also causes the generation of solder bridges and solder icicles.

(13) (6) Relations (1) and (2)
2.400%?Cu+Ni+Ge?3.190%(1)
0.33?Ge/Ni?1.04(2)

(14) Cu, Ni, and Ge in the relations (1) and (2) each represent the contents (mass %) in the alloy composition.

(15) The solder alloy according to the present invention preferably satisfies the relations (1) and (2). The solder alloy satisfying all relations exhibits particularly excellent effects.

(16) The relation (1) indicates a range of the total amount of additive elements constituting the solder alloy according to the present invention. Since the solder alloy according to the present invention can simultaneously exhibit diverse properties due to the additive elements Cu, Ni, and Ge, it is preferable that the total amount of these elements be precisely regulated. If the total amount of these additive elements is within the above range, the critical significance of each constituent element near the upper limit is mutually complemented, and they can work in tandem with each other to simultaneously exhibit various properties. More specifically, since Cu and Ni contribute to the formation of compounds during solidification, they contribute to solder bridges and solder icicles, amount of dross, improvement of the strength, and reduction of Cu leaching. Ge also contributes to the amount of dross since it forms oxides with oxygen in the atmosphere. Hence, the effects of the present invention are exhibited at a higher level when the total amount of these elements is regulated so as to satisfy the relation (1).

(17) In terms of the lower limit, the value of Cu+Ni+Ge in the relation (1) is preferably 2.400% or more, more preferably 2.610% or more, further preferably 2.701% or more, particularly preferably 2.710% or more, and most preferably 2.760% or more. In terms of the upper limit, the value of Cu+Ni+Ge in the relation (1) is preferably 3.190% or less, more preferably 3.100% or less, even more preferably 2.900% or less, further preferably 2.890% or less, particularly preferably 2.840% or less, and most preferably 2.800% or less.

(18) The relation (2) indicates a ratio of Ge content to Ni content. In the solder alloy according to the present invention, Ni and Ge contribute to the suppression of solder bridges and solder icicles. Cu also contributes to this, but its content is an order of magnitude higher than that of Ni and Ge. In the solder alloy according to the present invention, however, even Ni and Ge of which content are less than 1% significantly contribute to the properties. For this reason, the content ratio of Ge to Ni is important for obtaining even better effects. A high Ni content promotes the generation of solder bridges and solder icicles, while a low Ge content promotes the generation of solder bridges and solder icicles. In view of this, it is important to regulate the content ratio of Ge to Ni.

(19) In terms of the lower limit, the value of Ge/Ni in the relation (2) is preferably 0.33 or more, more preferably 0.34 or more, and even more preferably 0.42 or more. In terms of the upper limit, the value of Ge/Ni in the relation (2) is preferably 1.04 or less, more preferably 1.00 or less, even more preferably 0.70 or less, particularly preferably 0.63 or less, and most preferably 0.50 or less.

2. Solder Joint

(20) The solder joints according to the present invention are used in connecting electronic components to their boards, or in joining and connecting packaged components to a printed circuit board. In other words, the solder joint according to the present invention refers to a connecting part of an electrode and can be formed using general soldering conditions.

3. Method for Manufacturing Solder Alloy

(21) A method for manufacturing the solder alloy preferably includes the following steps so that each constituent element of the solder alloy according to the present invention will exhibit an excellent effect within the above-described range. Here, the mother alloy means raw material of the present alloy having the desired alloy composition.

(22) (1) Step of Forming Mother Alloy

(23) Since Cu, Ni, and Ge each have a high melting point, it takes a very long time to melt them if a predetermined amount of each element is weighed from the ingot and attempted to be molten at once as in a conventional method. Especially, Ge is considered to preferentially react with oxygen in the atmosphere during melting since it has an oxidation suppressing effect. For this reason, when adding a predetermined amount of Ge, it has conventionally been necessary to weigh the amount considering the melting temperature, melting time, and the amount of Ge that disappears as an oxide. Therefore, in the manufacture of the solder alloy according to the present invention, Cu, Ni, and Ge are manufactured as SnCu, SnNi, and SnGe mother alloys, respectively, and the present alloy is produced from these mother alloys. Alternatively, SnNi and SnGe mother alloys may be manufactured and then mixed with Cu alone to produce the present alloy. Consequently, the total time for manufacturing the present alloy is reduced, thus allowing it to be manufactured in a shorter time and reducing the loss of Ge.

(24) However, if a large number of coarse intermetallic compounds having high melting points (Cu.sub.6Sn.sub.5 and Ni.sub.3Sn.sub.4) are formed in the mother alloy, the time required to heat the alloy to a temperature at which the intermetallic compounds are sufficiently melted during the production of the present alloy will be extended, resulting in longer manufacturing time than that for alloys with relatively less formation of intermetallic compounds.

(25) Therefore, it is necessary to regulate the cooling rate during solidification to prevent the formation of the coarse intermetallic compounds having high melting points when producing the mother alloy. In a temperature range between the liquidus temperature and the solidus temperature, the cooling rate is specifically set to 50? C./sec or more between 200? C. and 400? C., which is within the temperature range between the liquidus temperature and solidus temperature for SnCuNi-based intermetallic compounds.

(26) (2) Step of Forming the Present Alloy

(27) Thereafter, the Present alloy is produced in the temperature range of the liquidus temperature of the present alloy+30? C. to the liquidus temperature of the present alloy+50? C. using the mother alloy produced through this step. For example, the mother alloy is melted in the temperature range of approximately 430 to 450? C. to manufacture the present alloy.

(28) If the mother alloy is sufficiently melted and then cooled by air cooling as in a conventional method, coarse intermetallic compounds having high melting points will be generated. Therefore, it should be cooled under the same conditions as when the mother alloy is produced. The present alloy produced under these conditions has various advantages: 1. avoidance of generation of coarse intermetallic compounds; 2. uniform alloy composition; and 3. reduction of environmental impact by reducing the amount of oxides (amount of dross) after production.

(29) Particularly, the production of the present alloy under these conditions is effective in the range where the Cu content of the solder alloy according to the present invention is more than 2% and less than 3%. If the Cu content is 2% or less, Cu leaching suppressing effect is reduced. In addition, if the Cu content is 3% or more, it is not practical because the liquidus temperature increases, causing deterioration of solderability and generation of solder bridges and solder icicles.

4. Method for Forming Solder Joint

(30) A jointing method with the solder alloy according to the present invention may be performed according to an ordinary method using, for example, a flow method. The heating temperature may be appropriately adjusted depending on the heat resistance of the electronic components or the liquidus temperature of the solder alloy. When the joining is performed with the solder alloy according to the present invention, the structure can be further refined by considering a cooling rate during solidification. For example, the solder joint is cooled at a cooling rate of 2 to 3? C./s or more. It may be cooled under the same conditions as when the the present alloy is produced. Other joining conditions can be appropriately adjusted depending on the alloy composition of the solder alloy.

Examples

(31) Solder alloys consisting of alloy compositions shown in Table 1 were prepared as follows.

(32) First, SnCu, SnNi, and SnGe were each manufactured as mother alloys from ingots of each constituent element. In manufacturing each of the mother alloys, the cooling rate was regulated to be 50? C./sec between 200 and 400? C. by circulating cooling water using a chiller or the like. From the mother alloys manufactured in this manner, the mother alloys were weighed to reach the contents listed in Table 1, and then the cooling rate was regulated to be 50? C./sec between 200 and 400? C. by circulating cooling water using a chiller or the like to produce the present alloy in the same manner as the mother alloys. Regarding P and Co used in Comparative Examples, the mother alloys were produced as well in the same manner as described above (that is, SnP, and SnCo), and the present alloy was obtained from the mother alloys to reach the contents shown in Table 1. Ga was added alone to obtain the present alloy.

(33) The present alloy (solder alloy) obtained through this preparation was evaluated for ?T, obtained from the liquidus temperature and solidus temperature, solder bridges and solder icicles, tensile strength, amount of dross, and Cu leaching. Evaluation methods and evaluation criteria for each item are as follows.

(34) ?T

(35) To determine ?T, liquidus and solidus temperatures were measured by DSC in accordance with JIS Z 3198-1 (2014). When the ?T, obtained by subtracting the solidus temperature from the liquidus temperature, was less than 110? C., it was evaluated as Excellent; when the ?T was 110 to 120? C., it was evaluated as Good; when the ?T was more than 120? C. and 130? C. or less, it was evaluated as Acceptable; and when the ?T was more than 130? C., it was evaluated as Poor. When evaluations of the ?T were Good and Excellent, there was no problem in practical use.

(36) Solder Bridges and Solder Icicles

(37) Twelve 4-terminal Sn plated resistances with a terminal width of 0.5 mm and a terminal interval of 0.8 mm were first prepared, the terminals were then inserted in through-holes of a glass epoxy printed circuit board (CEM-3), and the present alloy manufactured as described above was introduced into a solder tank to perform flow soldering. The flow soldering was performed under the following test conditions using Flow Simulator FS-1 manufactured by Malcom Co., Ltd.

Test Conditions

(38) Solder tank: Flow Simulator FS-1 manufactured by Malcom Co., Ltd.

(39) Amount of solder: 15 kg

(40) Flux: Flux (trade name: ES-1061SP2) manufactured by Senju Metal Industry Co., Ltd.

(41) Solder temperature in solder tank: 255? C.

(42) Whether or not solder bridges were generated was visually evaluated. Whether or not solder icicles were generated in a fillet was also visually observed. When no solder bridges or solder icicles could be observed, it was evaluated as Excellent; when the number of resistances with solder bridges or solder icicles generated was 1 to 2, it was evaluated as Good; when the number of resistances with solder bridges or solder icicles generated was 3 to 4, it was evaluated as Acceptable; and when the number of resistances with solder bridges or solder icicles generated was 5 or more, it was evaluated as Poor. When evaluations of the solder bridges or solder icicles were Good and Excellent, there was no problem in practical use.

(43) Tensile Strength

(44) The tensile strength was measured in accordance with JIS Z 3198-2 (2003). The present alloy, each of the solder alloys produced as described above and 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. When the tensile strength was 38 MPa or more, it was evaluated as Excellent; when the tensile strength was 33 MPa or more and less than 38 MPa, it was evaluated as Good: and when the tensile strength was less than 33 MPa, it was evaluated as Poor. When evaluations of the tensile strength were Good and Excellent, there was no problem in practical use.

(45) Dross Weight

(46) FIG. 1 is a schematic view of a dross occurrence apparatus 1 for measuring dross weight. Into a solder tank 12 with a volume of 150 cc, which was capable of being heated by a heater 11, 1000 g of the present alloy, the solder alloy produced as described above and shown in Table 1, was introduced. The solder alloy introduced into the solder tank 12 was heated and molten to be a solder bath 13 so that the temperature of the solder alloy was 400? C. measured by a temperature sensor 14. The air was then blown into the solder bath 13 for 10 minutes through a gas pipe 15 at a condition of 150 cc/min. After finishing the blow, dross formed on the surface of the solder bath 13 was gathered, and its dross weight was measured. A dross weight of 25 g or less was evaluated as Excellent; a dross weight of more than 25 g and 30 g or less was evaluated as Good; a dross weight of more than 30 g and 35 g or less was evaluated as Acceptable; and a dross weight of more than 35 g was evaluated as Poor. When evaluations of the dross weight were Good and Excellent, there was no problem in practical use.

(47) Cu Leaching

(48) The present alloy, each of the solder alloys produced as described above and listed in Table 1, was put into a small jet soldering tank with a capacity of 15 kg and brought into a molten state at 260? C. The jet height from the nozzle of the jet soldering tank was then adjusted to be 5 mm. The test sample used in this Example was obtained by cutting an FR-4 glass epoxy substrate having copper wiring with a thickness of 35 ?m into an appropriate size.

(49) The test method included applying a pre-flux to the surface of the copper wiring of the test sample and preheating it for about 60 seconds to bring the temperature of the substrate to about 120? C. Thereafter, the test sample was placed 2 mm above the nozzle of the jet soldering tank and immersed in jetting molten solder for 3 seconds. This step was performed repeatedly, and the number of times of immersion until the dimension of the copper wiring on the test sample was reduced by half was measured. Those which did not decrease in dimension by half after immersion seven times or more were evaluated as Excellent; those which did not decrease in dimension by half in five to six immersions were evaluated as Good; those which did not decrease by half in dimension in three to four immersions were evaluated as Acceptable; and those which decreased in dimension by half in two or fewer immersions were evaluated as Poor. When evaluations of the number of times of immersion was carried out were Good and Excellent, there was no problem in practical use.

(50) Evaluation results are shown in Table 1.

(51) TABLE-US-00001 TABLE 1 Relation Relation Alloy composition (mass %) (1) (Cu + (2) Sn Cu Ni Ge Ga P Co Ni + Ge) Ge/Ni EX. 1 bal. 2.1 0.20 0.1000 2.400 0.50 EX. 2 bal. 2.5 0.20 0.1000 2.800 0.50 EX. 3 bal. 2.6 0.20 0.1000 2.900 0.50 EX. 4 bal. 2.7 0.20 0.1000 3.000 0.50 EX. 5 bal. 2.8 0.20 0.1000 3.100 0.50 EX. 6 bal. 2.9 0.20 0.1000 3.200 0.50 Ref. EX. 7 bal. 2.5 0.01 0.1000 2.610 10.00 EX. 8 bal. 2.5 0.10 0.1000 2.700 1.00 EX. 9 bal. 2.5 0.16 0.1000 2.760 0.63 EX. 10 bal. 2.5 0.24 0.1000 2.840 0.42 EX. 11 bal. 2.5 0.29 0.1000 2.890 0.34 Ref. EX. 12 bal. 2.5 0.20 0.0010 2.701 0.01 Ref. EX. 13 bal. 2.5 0.20 0.0100 2.710 0.05 Ref. EX. 14 bal. 2.5 0.20 0.0600 2.760 0.30 EX. 15 bal. 2.5 0.20 0.1400 2.840 0.70 EX. 16 bal. 2.5 0.20 0.2000 2.900 1.00 Comp. Ex. 1 bal. 0.693 0.02 0.0050 0.713 0.00 Comp. Ex. 2 bal. 0.7 0.05 0.0100 0.0030 0.760 0.20 Comp. Ex. 3 bal. 1 0.040 0.0100 1.050 0.25 Comp. Ex. 4 bal. 2.0 0.20 0.0500 2.250 0.25 Comp. Ex. 5 bal. 3 0.20 0.1000 3.300 0.50 Comp. Ex. 6 bal. 2.5 0.005 0.1000 2.605 20.00 Comp. Ex. 7 bal. 2.5 0.31 0.1000 2.910 0.32 Comp. Ex. 8 bal. 2.5 0.20 0.0005 2.701 0.00 Comp. Ex. 9 bal. 2.5 0.20 0.2100 2.910 1.05 Comp. Ex. 10 bal. 2.5 0.30 0.5000 3.300 1.67 Comp. Ex. 11 bal. 2.5 0.20 0.0100 0.0100 2.710 0.05 Comp. Ex. 12 bal. 2.5 0.20 0.2000 2.700 0.00 Comp. Ex. 13 bal. 2.5 0.20 0.1000 0.2000 2.800 0.50 Comp. Ex. 14 bal. 3.0 0.03 0.0050 0.0030 3.035 0.17 Comp. Ex. 15 bal. 2.5 0.20 0.1000 0.2000 2.800 0.50 Comp. Ex. 16 bal. 2.5 0.20 0.1000 0.1000 0.1000 2.800 0.50 Solder bridge and Strength Amount Cu Total ?T solder icicle (MPa) of dross leaching 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 Good Excellent Excellent Excellent Excellent Good Ref. EX. 7 Excellent Excellent Good Excellent Good Good EX. 8 Excellent Excellent Excellent Excellent Excellent Excellent EX. 9 Excellent Excellent Excellent Excellent Excellent Excellent EX. 10 Excellent Excellent Excellent Excellent Excellent Excellent EX. 11 Excellent Excellent Excellent Excellent Excellent Excellent Ref. EX. 12 Excellent Excellent Excellent Good Excellent Good Ref. EX. 13 Excellent Excellent Excellent Good Excellent Good Ref. EX. 14 Excellent Excellent Excellent Good Excellent Good EX. 15 Excellent Excellent Excellent Excellent Excellent Excellent EX. 16 Excellent Excellent Excellent Excellent Excellent Excellent Comp. Ex. 1 Excellent Excellent Poor Acceptable Poor Poor Comp. Ex. 2 Excellent Excellent Poor Good Poor Poor Comp. Ex. 3 Excellent Excellent Poor Good Poor Poor Comp. Ex. 4 Good Good Good Good Acceptable Poor Comp. Ex. 5 Poor Poor Good Good Good Poor Comp. Ex. 6 Good Good Good Good Acceptable Poor Comp. Ex. 7 Poor Poor Good Good Good Poor Comp. Ex. 8 Good Poor Good Poor Good Poor Comp. Ex. 9 Acceptable Acceptable Good Good Good Poor Comp. Ex. 10 Poor Poor Good Good Good Poor Comp. Ex. 11 Good Acceptable Good Acceptable Good Poor Comp. Ex. 12 Acceptable Acceptable Good Good Good Poor Comp. Ex. 13 Acceptable Acceptable Good Good Good Poor Comp. Ex. 14 Poor Poor Good Good Good Poor Comp. Ex. 15 Acceptable Acceptable Good Good Good Poor Comp. Ex. 16 Acceptable Acceptable Good Good Good Poor *Each underline indicates that it is outside the scope of the present invention.

(52) As is clear from Table 1, the content of each constituent element in Examples 1 to 16 is appropriate, resulting in appropriate ?T, almost no generation of solder bridges and solder icicles, high strength of the solder alloys, and reduced dross and Cu leaching. Particularly, it was confirmed that Examples 1 to 5, 8 to 11, 15, and 16, which satisfy relations (1) and (2), exhibited remarkably excellent results in all evaluation items.

(53) On the other hand, in Comparative Example 1, the content of Cu was too low, resulting in low tensile strength, a large amount of dross, and the occurrence of Cu leaching. In Comparative Examples 2 and 3, the content of Cu was quite low, resulting in low tensile strength and the occurrence of Cu leaching. In Comparative Example 4, the content of Cu was low, resulting in the occurrence of Cu leaching.

(54) In Comparative Examples 5 and 14, the Cu content was high, resulting in large ?T and the generation of solder bridges and solder icicles.

(55) In Comparative Example 6, the content of Ni was low, resulting in the occurrence of Cu leaching. In Comparative Examples 7 and 10, the content of Ni was high, resulting in large ?T and the generation of solder bridges and solder icicles.

(56) In Comparative Example 8, the content of Ge was low, resulting in the generation of solder bridges and solder icicles and a large amount of dross. In Comparative Example 9, the content of Ge was high, resulting in large ?T and the generation of solder bridges and solder icicles.

(57) In Comparative Example 11, Ga was contained, resulting in the generation of solder bridges and solder icicles and a large amount of dross.

(58) In Comparative Examples 12 and 13, P was contained, resulting in large ?T and generation of solder bridges and solder icicles.

(59) In Comparative Examples 15 and 16, Co was contained, resulting in large ?T and generation of solder bridges and solder icicles.

REFERENCE SIGN LIST

(60) 1 Dross Occurrence Apparatus