LEAD-FREE SOLDER ALLOY

Abstract

The purpose of the present invention is to provide a lead-free solder alloy that maintains high bond strength even at high temperatures after soldering. This lead-free solder alloy offers a high degree of reliability and versatility. In the present invention, the base composition is Sn-Cu-Ni. The lead-free alloy composition contains 0.1 to 2.0% by mass of Cu, 0.01 to 0.5% by mass of Ni, 0.1 to 5% by mass of Bi, and 76.0 to 99.5% by mass of Sn. As a result of this lead-free alloy composition, the solder bond strength does not decrease during soldering, even when the solder is exposed to high temperatures for extended periods, thus enabling highly reliable soldering.

Description

LEAD-FREE SOLDER ALLOY FIELD OF INVENTION The present invention concerns a lead-free solder alloy that has less deterioration over time and excellent long-term reliability, and a solder joint using the solder alloy. BACKGROUND OF THE INVENTION In order to reduce the global environmental burden, lead-free solder has been widely distributed as a joining material for electronic components, and a Sn-Ag-Cu system solder alloy or a Sn-Cu-Ni system solder alloy is a representative composition thereof. Recently, in addition to the Sn-Ag-Cu system solder alloy and the Sn-Cu-Ni system solder alloy, a lead-free solder alloy in which Bi, In or Sb, etc., are added, and a lead-free solder such as a Sn-Zn solder alloy, according to the purpose of soldering and solder characteristics, has been proposed. In particular, a lead-free solder alloy is described in which Bi, Sb or In is added for the purpose of increasing the mechanical strength of the soldered joints or lowering the solid-state temperature. naznnn / Lznz / E / YiAi For example, patent document 1 describes a lead-free solder alloy that allows the solder melting point to be easily controlled by adding 0.01 to 3 wt% of Bi to a Sn-Cu-Ni base composition. Furthermore, patent document 2 describes a lead-free solder alloy that has improved mechanical strength by adding Bi to a Sn-Cu-Sb base composition in a ratio of 1% by weight or less. Furthermore, patent document 3 describes a lead-free solder alloy that has the effects of increasing adhesive strength and decreasing solid-state temperature by adding 0.001 to 5 wt% of Cu, Ni, and Bi to Sn. In addition, the applicant describes, in Patent Document 4, a lead-free solder alloy that exhibits strong bond strength at soldering time by forming an intermetallic compound having a close-packed hexagonal structure at a soldered joint and its bonding interface, by adding a prescribed amount of Ni and Cu to a Sn-Bi eutectic composition. However, the techniques described in patent documents 1 to 4 also have problems to solve. For example, the solder alloy composition described in patent document 1 requires 2 to 5 wt% of the Cu mixture and a soldering temperature that exceeds 400°C, which is at least 150°C higher than that of the Sn-Ag-Cu solder alloy or the Sn-Cu-Ni solder alloy, which is a representative lead-free solder composition. Furthermore, in the solder alloy composition described in patent document 2, 10% by weight or more of Sb is mixed into the base composition thereof, such that the solid-state temperature is 230°C or higher, as described in the example and as in patent document 1, it is necessary to perform a soldering process at a higher temperature, compared to a conventional representative lead-free solder composition. Furthermore, the technique described in patent document 3 is not a welding alloy composition capable of being applied to various welding joints, but a welding alloy composition limited to superfine wire welding and thus has problems with regard to versatility. Furthermore, the technique described in patent document 4 is a technique for the purpose of providing strong bonding by forming an intermetallic compound having a NiAs-type crystal structure at a bonding interface, wherein the mixing ratio of Sn and Bi is Sn:Bi = 76 to 37% by weight and atomic weight: 23 to 63%, and the technique is directed to a composition in the vicinity of the eutectic point. Furthermore, the publication of patent document 5 discloses a technique concerning a solder alloy composition suitable for preventing tin pest at extremely low temperatures. This composition includes Sn-Cu-Ni-Bi, which has good wettability and impact resistance. For the purposes of the invention, the composition's numerical values ​​are limited to a range whereby the Cu content is 0.5 to 0.8% by mass, the Ni content is 0.02 to 0.04% by mass, and the Bi content is 0.1% by mass or more but less than 1% by mass. In general, when an electronic device is used, the soldered joint of the electronic device is in a conductive state and in some cases, the soldered part may be exposed to high temperature. Currently, in terms of the reliability of the weld joint, the bond strength when the welded part is exposed to high temperature becomes very important, as well as the bond strength at the time of welding. Furthermore, the techniques described in patent documents 1 to 5 do not teach any content concerning the bond strength when the welded joint is exposed to high temperature for a long time. Furthermore, there is a need for a lead-free NaZnnn / LZnz / E / YiAi solder alloy that allows for highly reliable soldering, is sufficient to withstand long-term use of the electronic device, and has versatility with respect to solder jointing. Related prior art documents Patent documents Patent Document 1: Japanese Open Patent Publication No. 2001-334.384. Patent Document 2: Japanese Open Patent Publication No. 2004-298931. Patent Document 3: Japanese Open Patent Publication No. 2006-255762. Patent Document 4: Japanese Open Patent Publication No. 2013-744. Patent Document 5: Publication WO 2009 / 131114. BRIEF DESCRIPTION OF THE INVENTION Problems to be solved by the invention An object of the present invention is to provide a lead-free solder alloy and soldered joint capable of maintaining a strong bond strength without reducing the adhesion strength even in a high temperature state after soldering and that has high reliability and versatility. Means to solve the problems The present inventors focused on a lead-free solder alloy composition and an intermetallic compound and have repeatedly conducted intensive studies for the aforementioned purpose. As a result, they found that by adding a specific amount of Bi to a lead-free solder alloy having Sn-Cu-Ni as its base composition, the decrease in adhesion strength is suppressed even when a soldered part is exposed to high temperatures, and thus the present invention has been realized based on the foregoing finding. That is, the present invention provides a lead-free solder alloy composition having Sn-Cu-Ni as its base composition, which includes 76.0 to 99.5% by mass of Sn, 0.1 to 2.0% by mass of Cu and 0.01 to 0.5% by mass of Ni and which also includes 0.1 to 5.0% by mass of Bi, thereby enabling highly reliable soldering that maintains the bond strength without diminishing the adhesion strength of a soldered joint even when exposed to high temperatures for a long time, as well as during the bonding time. Advantageous effects The lead-free solder alloy according to the present invention has versatility that is not limited by the method of use of a soldering product or its shape, and even when the soldered joint is exposed to a high-temperature state for a long time, the bond strength will not decrease. Therefore, the lead-free solder alloy can be widely applied to devices that have a soldered part through which high current flows, devices exposed to a high-temperature state, or similar applications, as well as for the junction of an electronic device. BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a graph illustrating an experimental result. Figure 2 is a graph summarizing tensile strength measurement results for each sample that has the composition in Table 2. Figure 3 is a graph summarizing the tensile strength measurement results for each sample that has the composition in Table 4. Figure 4 is a graph summarizing tensile strength measurement results of samples having different additional amounts of Cu. Figure 5 is a graph summarizing tensile strength measurement results of samples having different additional amounts of Ni. Figure 6 is a graph summarizing tensile strength measurement results of samples that naznnn / Lznz / E / YiAi have different additional amounts of Ge. Figure 7 is a graph summarizing tensile strength measurement results of samples having different additional amounts of In. Figure 8 is a graph summarizing measurement results of the elongation ratio of samples with changed In content. Figure 9 is a graph summarizing tensile strength measurement results of samples with an additional element added. DETAILED DESCRIPTION OF THE INVENTION The present invention will henceforth be described in detail. Conventionally, the bond strength at the time of soldering has become an important factor for soldering electronic or similar devices, and solder alloys capable of improving bond strength at the time of soldering have been developed and provided. However, soldered joints used in electronic devices or similar equipment can frequently be exposed to high temperatures or a state in which current flows, especially during the use of the electronic device, and in some cases the temperature increase of the soldered joints can be accelerated by the external environment. Therefore, in order to improve the reliability of soldered joints, it is necessary to suppress the deterioration over time of soldered joints that are exposed to a high-temperature state. As a method for evaluating welded joints, a test known as a thermal cycling test is generally used, in which a welded joint is repeatedly subjected to a high-temperature state followed by a low-temperature state for a prescribed time. However, it is also known that in this method, because the welded joints are subjected to a high-temperature state and then to a low-temperature state for a prescribed time, the condition of the welded joints after the test differs from that of an aging test in which the welded joints are only subjected to a high-temperature state for an extended period. The present invention concerns a solder alloy composition capable of suppressing the decrease in bond strength of a soldered joint due to continuous exposure of the soldered joints to a high-temperature state, i.e., an environment that is an example of a situation according to the current state of use of electronic devices. In particular, the present invention concerns a lead-free solder alloy that may include 76.0 to 99.5% by mass of Sn, 0.1 to 2.0% by mass of Cu, 0.01 to 2.0% of Sn, and 0.01 to 2.0% of Sn. 0.5% by mass of Ni and 0.1 to 5.0% by mass of Bi and a soldered joint using lead-free solder alloy. In addition, it is also possible to add one or two or more selected elements from 0.1 to 5.0% by mass of Sb, 0.1 to 10.0% by mass of In, 0.001 to 1.0% by mass of Ge and 0.001 to 1.0% by mass of Ga to a base composition that includes 6.0 to 99.5% by mass of Sn, 0.1 to 2.0% by mass of Cu, 0.01 to 0.5% by mass of Ni and 0.1 to 5.0% by mass of Bi. Furthermore, an element such as P, Co, Al, Ti, Ag, etc., can also be arbitrarily added to the lead-free solder alloy having Sn-Cu-Ni-Bi as the base composition thereof of the present invention, within a range in which the effects of the present invention are obtained. A synergistic effect is expected to increase the mechanical strength of the welded joints, while the effects of the present invention are obtained by adding Sb to the welding alloy having the same Sn-Cu-Ni-Bi base composition. Furthermore, when In is added, even if Cu or Sb is combined with the solder alloy in an amount exceeding 1% by mass, a solid-state temperature lowering effect can be obtained, while achieving the effects of the present invention and a load-reducing effect on the electronic components attached to electronic devices, soldering work, or the like can be expected. Furthermore, when Ge or Ga is added, it is possible to suppress oxidation of the welded joint and improve wettability, and a synergistic effect can also be expected to improve the long-term reliability and welding characteristics of the welded joint, while achieving the effects of the present invention. The effects of the present invention will now be described by illustrating an experimental example. An aging test to be described below was performed on the lead-free solder alloy of the present invention and its properties were evaluated. Aging Test Method 1) A welding alloy having the composition shown in Table 1 was prepared and melted and then poured into a dog bone-shaped mold having a cross-section of 10 mm x 10 mm, thereby preparing a sample for measurement. 2) The measurement sample was left at 150°C for 500 hours to carry out the aging process. 3) The samples in which the aging process was carried out and the samples in which the aging process was not carried out are cut using a testing machine, AG-IS (manufactured by Shimadzu Corp.) under a condition of 10 mm / minute at room temperature (20°C to 25°C), to measure by this the tensile strength of the samples. Result The measured results are illustrated in Figure 1. naznnn / Lznz / E / YiAi Table 1 Sample No. Compositions (% by weight) Element (% by weight) Sn Cu Ni Bi Ge Ag In Mn 1 Sn - 07 Cu-0.05 Ni- Ge Rest 0.7 0.05 - 0.007 - - - 2 Sn - 0.7 Cu - 0.05 Ni - 0.5 Bi-Ge Rest 0.7 0.05 0.5 0.007 - - - 3 Sn - 0.7 Cu - 0.05 Ni 1.0 Bi-Ge Rest 0.7 0.05 1.0 0.006 - - - 4 Sn - 0.7 Cu-0.05N¡- 1.5Bi-Ge Rest 0.7 0.05 1.5 0.006 - - - 5 Sn - 0.7 Cu-0.05N¡- 2.0BÍ-Ge Rest 0.7 0.05 2.0 0.006 - - - 6 Sn - 0.7 Cu - 0.3 Ag Rest 0.7 - - - 0.3 - - 7 Sn - 0.7 Cu - 0.3 Ag Rest 0.7 - - - 0.8 - - 8 Sn - 1.0 Cu - 0.5 Ag - 0.05 Mn Rest 1.0 - - - 0.5 - 0.008 9 Sn - 0.5 Cu - 3.0 Ag Rest 0.5 - - - 3.0 - - The graph illustrated in Figure 1 shows the measurement results of samples in which the aging process was not carried out on the left side and the measurement results of samples in which the aging process was carried out on the right side, respectively. The samples of the present invention correspond to No. 2-5 and it can be seen that the tensile strength of the sample in which the aging process was carried out does not decrease much, compared to that of the sample in which the aging process was not carried out. While sample No. 1 and samples No. 6-9, which are comparative samples, show a notable decrease in tensile strength of the sample in which the aging process was carried out, compared to the sample in which the aging process was not carried out. From the results, it could be clearly seen that although the lead-free solder alloy having SnCu-Ni-Bi as the base composition of the present invention was exposed to a high temperature of 150°C for 500 hours, the decrease in its tensile strength was suppressed, compared to other lead-free solder alloy compositions. From this point forward, with respect to the base composition of Sn-Cu-Ni-Bi, a change in tensile strength resulting from a change in the amount of Bi will be described in detail. More specifically, the tensile strength of samples in which 0% to 6% by mass of Bi is added to this composition will be described based on the measurement result of a change in naznnn / Lznz / E / YiAi. Table 2 is a compositional table showing the compositions of the samples used in the tensile strength measurement. As a comparative example (Sample i: the sample name is SN2), a Sn-Cu-Ni composition containing no Bi is included. Furthermore, the samples that include Bi are designated as sample ii: sample name: +0.1 Bi*, sample iii: sample name: +0.5 Bi*, sample iv: sample name: +1.0 Bi*, sample v: sample name: +1.5 Bi*, sample vi: sample name: +2.0 Bi*, sample vii: sample name: +3.0 Bi*, sample viii: sample name: +4.0 Bi*, sample ix: sample name: +5.0 Bi*, and sample x: sample name: +6.0 Bi*. In samples ii ax, Bi is included in an amount of 0.1% by mass, 0.5% by mass, 1.0% by mass, 1.5% by mass, 2.0% by mass, 3.0% by mass, 4.0% by mass, 5.0% by mass and 6.0% by mass, respectively. The iax samples having the compositions in Table 2 were prepared using the method described above in paragraph

[0016] . Subsequently, the aging process was carried out on the samples at 150°C for 0 hours and 500 hours and their tensile strength was measured. naznnn / Lznz / E / YiAi Table 2 naznnn / Lznz / E / YiAi No. Sample Name Element (% by weight) Sn Cu Ni Bi Sample i SN2 Remainder 0.7 0.05 0 Sample ii +0.1 Bi* Remainder 0.7 0.05 0.1 Sample iii +0.5 Bi* Remainder 0.7 0.05 0.5 Sample iv +1.0Bi* Remainder 0.7 0.05 1.0 Sample v +1.5Bi* Remainder 0.7 0.05 1.5 Sample vi +2.0Bi* Remainder 0.7 0.05 2.0 Sample vii +3.0Bi* Remainder 0.7 0.05 3.0 Sample viii +4.0Bi* Remainder 0.7 0.05 4.0 Sample ix +5.0Bi* Remainder 0.7 0.05 5.0 Sample x +6.0Bi* Remainder 0.7 0.05 6.0 TABLE 3 SAMPLE No F it VV vi VFf VÍí! FX 68.0 78.1 81.5 87 0 SAMPLE No i ii iii iv V vi vii viii ¡X Γ“........... 30.2 ....... 36.7 46.2 52.6 60.0 69.1 74.9 71.8 62.5 ........ PROPORTION •CHANGE OF «Rr SYSTEM: (CZA) 85.0¾ 91.5% 91.8¾ 98.3% 102.1% 101.9% WI.K 95 9% 88.1% 71.8% Table 3 shows the measurement results for samples ia x. Item A in Table 3 represents the tensile strength measurement result after 0 hours of aging, and Item C in Table 3 represents the tensile strength measurement result after 500 hours of aging. The ratio of strength change is the result obtained by measuring the change in tensile strength after 500 hours of aging, considering A (0 hours) as 100%. Figure 2 summarizes the tensile strength measurement results for samples ia x. With respect to the aging processing time of 0 hours and 500 hours, it can be seen that the samples ii ax in which Bi is added have a higher tensile strength than that of sample i in which Bi is not added. Furthermore, in the case of aging for 500 hours, samples ii to vii, in which the additional amount of Bi is 0.1% by mass or more, show a higher tensile strength than sample i, in which no Bi is added. Additionally, samples iv to vii, in which the additional amount of Bi is 1.0% to 3.0% by mass, show a strength change ratio of 98% or greater. It is evident that the tensile strength change ratio after aging for 500 hours is significantly low, and in particular, the tensile strength after aging for 500 hours of samples va to vii is more improved than in the case where no aging process is performed. naznnn / Lznz / E / YiAi Meanwhile, sample x in which the additional amount of Bi is 6% by mass shows a proportion of change in tensile strength of 71.8% which is lower than 85.2% of sample i in which no Bi is added, thus, it can be said that 6% by mass is not a preferable amount of mixture. Furthermore, with regard to the case of adding Ge to the basic composition of Sn-Cu-Ni-Bi, the change in tensile strength resulting from the addition of Bi will be described in detail. More specifically, the change in tensile strength of samples in which Bi is added to this composition in an amount of 0 to 6% by mass will be measured. Table 4 shows the compositions of the samples used in the tensile strength measurement. As illustrated in Figure 3, Bi is not included in sample 1 SAC305 and sample 2 SN1. In sample 3 +0.1 Bi, sample 4 +0.5 Bi, sample 5 +1.0 Bi, sample 6 +1.5 Bi, sample 7 +2.0 Bi, sample 8 +3.0 Bi, sample 9 +4.0 Bi, sample 10 +5.0 Bi, and sample 11 +6.0 Bi, Bi is included in amounts of 0.1% by mass, 0.5% by mass, 1% by mass, 1.5% by mass, 2% by mass, 3% by mass, 4% by mass, 5% by mass, and 6% by mass, respectively. Furthermore, in all samples except Sample 1 SAC305, 0.7% by mass of Cu, 0.05% by mass of Ni, and 0.006% by mass of Ge are included, and the remainder is Sn. Additionally, in Sample 1 SAC305, 3% by mass of Ag and 0.5% by mass of Cu are included, and the remainder is Sn. From here on in this document, for the sake of clarity, sample 1 SAC305, sample 2 SN1, sample 3 +0.1 Bi, sample 4 +0.5 Bi, sample 5 +1.0 Bi, sample 6 +1.5 Bi, sample 7 +2.0 Bi; sample 8 +3.0 Bi, sample 9 + 4.0 Bi, sample 10 + 5.0 Bi and sample 11 +6.0 Bi will be referred to as sample 1, sample 2, sample 3, sample 4, sample 5, sample 6, sample 7, sample 8, sample 9, sample 10 and sample 11, respectively. Table 4 naznnn / Lznz / E / YiAi No. Sample Name Element (% by weight) Sn Ag Cu Ni Ge Bi Sample 1 SNC305 Remainder 3 0.5 0 0 0 Sample 2 SN1 Remainder 0 0.7 0.05 0.006 0 Sample 3 +0.1 Bi Remainder 0 0.7 0.05 0.006 0.1 Sample 4 +0.5 Bi Remainder 0 0.7 0.05 0.006 0.5 Sample 5 +1.0 Bi Remainder 0 0.7 0.05 0.006 1 Sample 6 +1.5 Bi Remainder 0 0.7 0.05 0.006 1.5 Sample 7 +2.0 Bi Remainder 0 0.7 0.05 0.006 2 Sample 8 +3.0 Bi Remainder 0 0.7 0.05 0.006 3 Sample 9 +4.0 Bi Remainder 0 0.7 0.05 0.006 4 Sample 10 +5.0 Bi Remainder 0 0.7 0.05 0.006 5 Sample 11 +6.0 Bi Remainder 0 0.7 0.05 0.006 6 Samples 1 to 11, which have compositions as shown in Table 4, were prepared using the method described above. The aging process was carried out on samples 1 to 11 for 0 hours and 500 hours at 150°C and the tensile strength was measured using the method described above. naznnn / Lznz / E / YiAi TABLE 5 SAMPLE 1 2 3 4 5 6 7 8 9 10 11 A (CHORAS) NAME OF SNC305 SN1 +0.18i +0.5 B i +1.08 i +1.5Bi +2.08 i +3.0 B i +4.08I MEASUREMENT RESULT (MPa) 48.2 32.5 32.8 39.9 46.5 51.6 58.7 68.2 78.3 81.6 86.1 c (500 HOURS) SAMPLE SAMPLE NAME 1 2 3 4 5 6 í 01 í-........... co j í 5 r- 10 11 SNC305 SN1 +0.1 Bi +0.5BÍ + 1.08Í + 1.5YES +2.0Bi|+3.0Bíh4.0B¡ +5.QSiH.0Bi RESULT MEASUREMENT (MPa) 35 6 27.7 30 36.5 45.6 52.7 59.1 | 70.2 j 751 71.9 81 8 PROPORTION OF CANSIO DERESISTENC1A (C / AJ (%) 73.9¾ 85.2% 91.5% 91.6% 98.2% 102.2% 100.7^102.9% 95.9% 88.1%| 71.8% Table 5 shows the measurement results for samples 1 through 11. Item A in Table 5 represents the tensile strength measurement result after 0 hours of aging, and Item C in Table 5 represents the tensile strength measurement result after 500 hours of aging. The percentage change in strength is the result showing the change in tensile strength after 500 hours of aging, expressed as a percentage (%). Figure 3 summarizes the tensile strength measurement results for samples 1 through 11. With respect to the aging processing time of 0 hours and 500 hours, it can be seen that samples 3 to 11 in which Bi is added, have a higher tensile strength than sample 2 in which Bi is not added. Furthermore, in the case of the 500-hour aging process, samples 4 through 11, in which the additional amount of Bi is 0.5% by mass or more, show higher tensile strength than sample 1, in which no Bi is added and Ag is added. Additionally, samples 5 through 8, in which the additional amount of Bi is from 1.0% to 3.0% by mass, show a strength change ratio of 98% or higher, which is a significantly low tensile strength change ratio after 500 hours of aging. Thus, in the case of samples 4 to 11, because Ag is not used, it is possible to obtain a decrease in cost, while having the effect of improving tensile strength. Furthermore, it can be seen that in the case of samples 3 to 9, that is, as the additional amount of Bi is increased from 0.1% by mass to 4% by mass, the tensile strength was increased. Moreover, within this range of additional Bi content, there is no significant difference between the tensile strength of the case where no aging process was performed and the tensile strength of the case where aging was performed for 500 hours. Meanwhile, in the case of samples 10 and 11 in which the additional amount of Bi is 5% by mass or more, as the additional amount of Bi increases, the tensile strength of the case in which the aging process was not carried out increases, but the rate of change of strength tended to decrease, in particular, in the case of 6% by mass, the rate of change of tensile strength is 71.8%, which is lower than the 85.2% of the case in which no Bi is added (Sample 2) and thus it can be said that 6% by mass is not a preferable amount of mixture. As can be seen from the above measurement results, when the lead-free solder alloy consisting of Sn, Cu, Ni, Bi, and Ge is exposed to a harsh operating environment, i.e., a high temperature of 150°C for an extended period, it is preferable for the additional Bi content to be 0.5 to 4.0% by mass, and even more preferably, 1.0 to 3.0% by mass. Within this range of additional Bi content, as described above, even after aging for 500 hours, high tensile strength can be achieved. Furthermore, there is no significant difference in tensile strength between the case where aging is not performed and the case where aging is performed for 500 hours; that is, stable tensile strength can be obtained. Furthermore, in the case of sample 10, where the additional amount of Bi is 5% by mass, the tensile strength after the aging process was lower than the tensile strength of the sample where no aging process was performed, as described above. However, since the tensile strength of samples 1 and 2, where no Bi is added, is lower than that of sample 10 after the aging process, the additional amount of Bi can range from 0.1% to 5.0% by mass. Furthermore, from this point forward, with respect to the case of adding Ge to the base composition of Sn-Cu-Ni-Bi, a change in tensile strength resulting from a change in an additional amount of Cu will be described in detail. In this case, Ni, Bi, and Ge are included in amounts of 0.05% by mass, 1.5% by mass, and 0.006% by mass, respectively. Additionally, Cu is added in amounts of 0.05 to 2.2% by mass, and the remainder is Sn. From this point forward, for the sake of clarity, a sample in the naznnn / Lznz / E / YiAi to which 0.05% by mass of Cu is added, a sample to which 0.1% by mass of Cu is added, a sample to which 0.7% by mass of Cu is added, a sample to which 2% by mass of Cu is added, and a sample to which 2.2% by mass of Cu is added will be referred to as 0.05 Cu, 0.1 Cu, 0.7 Cu, 2 Cu, and 2.2 Cu, respectively. The samples were prepared using the method described above and the aging process was carried out on the prepared samples at 150°C for 0 hours and 500 hours and the tensile strength of the same was measured using the method described above. naznnn / Lznz / E / YiAi TABLE 6 SAMPLE NAME 0.1 Cu 0.7Cu 2 Cu 2.2Cu (©HOURS) MEASUREMENT RESULT (MPs) 46.4 46.5 51.6 612 60.2 or SAMPLE NAME O.ÜSCu 0.1 Gu 0.70u 2Cu 2.2Cu (50® HOURS) MEASUREMENT RESULT (MPs) 44.7 45.4 52.7 60.9 57.6 CHANGE RATE | RESISTANCE (C / A) (%) I 96% 97% 5 W2% | 100% 96% Table 6 shows the tensile strength measurement results for samples with varying amounts of added copper, as described above. Item A in Table 6 represents the tensile strength measurement result after 0 hours of aging, and item C in Table 6 represents the tensile strength measurement result after 500 hours of aging. Figure 4 summarizes the tensile strength measurement results for samples with varying amounts of added copper. All copper alloys from 0.05% to 2.2% exhibit a desirable strength change ratio greater than 90% before and after aging. However, because problems such as increased copper leaching can occur, an additional copper content of 0.05% by mass is not preferable. Similarly, because problems such as increased liquid-phase temperature, shrinkage cavity formation, or similar issues can arise, an additional copper content of 2.2% by mass is not preferable. From the above description, when Ge is added to the base composition of Sn-Cu-Ni-Bi, in the composition described above, it is preferable that the additional amount of Cu be 0.1 to 2.0% by mass. Furthermore, from here on in this document, in relation to the case in which Ge is added to the base composition of Sn-Cu-Ni-Bi, a change in tensile strength resulting from a change in an additional amount of Ni will be described in detail. In this case, Cu, Bi, and Ge are included in amounts of 0.7% by mass, 1.5% by mass, and 0.006% by mass, respectively. In addition, Ni is added in amounts of 0.005 to 0.55% by mass, and the remainder is Sn. From this point forward, for the sake of clarity, a sample in which 0.005% by mass of Ni is added, a sample in which 0.01% by mass of Ni is added, a sample in which 0.05% by mass of Ni is added, a sample in which 0.5% by mass of Ni is added, and a sample in which 0.55% by mass of Ni is added will be referred to as 0.005 Ni, 0.01 Ni, 0.05 Ni, 0.5 Ni, and 0.55 Ni, respectively. The samples were prepared using the method described above and the aging process was carried out on the prepared samples at 150°C for 0 hours and 500 hours and the tensile strength of the same was measured using the method described above. TABLE 7 SAMPLE NAME 0.005Ni 0.01Ni 0.5Ni 0.5Ni (©HOURS) RESULT BE | MEASUREMENT (MPa) 52.7 ...... 51.5 | 51.6 | 55.5 56.1 or HOURS) SAMPLE NAME MEASUREMENT RESULT (MPa) 0.005Ni 50.7 0.01Ni 50.7 0.05Ni 0.5Ni 52.7 | 56.5 0.55Ni 55.1 | PROPORTION CHANGE RESISTANCE (C / A) (%) 96% 98% 102% | 102% ______________ 98% ___________i Table 7 shows the tensile strength measurement results for samples with varying amounts of added Ni, as described above. Item A in Table 7 represents the tensile strength measurement result after 0 hours of aging, and item C in Table 7 represents the tensile strength measurement result after 500 hours of aging. Figure 5 summarizes the tensile strength measurement results for samples with varying amounts of added Ni. All alloys with 0.005 Ni to 0.55 Ni exhibit a desirable strength change ratio greater than 90% before and after aging. However, it is not preferable for the additional amount of Ni to be too small, as the effect of suppressing intermetallic compound thickening at the alloy layer interface may be lost, leading to cracking. Similarly, it is not preferable for the additional amount of Ni to exceed 0.5% by mass, as the liquid-phase temperature may rise, potentially causing shrinkage activity. From the above description, when Ge is added to the basic composition of Sn-Cu-Ni-Bi, in the composition described above, it is preferable that the additional amount of Ni naznnn / Lznz / E / YiAi be 0.01 to 0.5% by mass. Furthermore, from this point forward, in relation to the case in which Ge is added to the basic composition of Sn-Cu-Ni-Bi, a change in tensile strength resulting from a change in an additional amount of Ge will be described in detail. In this case, Cu, Ni, and Bi are included in amounts of 0.7% by mass, 0.05% by mass, and 1.5% by mass, respectively. Additionally, Ge is added in amounts of 0.0001 to 1% by mass, and the remainder is Sn. From this point forward, for the sake of clarity, a sample containing 0.0001% by mass of Ge, a sample containing 0.001% by mass of Ge, a sample containing 0.006% by mass of Ge, a sample containing 0.1% by mass of Ge, and a sample containing 1% by mass of Ge will be referred to as 0.0001 Ge, 0.001 Ge, 0.006 Ge, 0.1 Ge, and 1 Ge, respectively. The samples were prepared using the method described above and the aging process was carried out on the prepared samples at 150°C for 0 hours and 500 hours and the tensile strength of the same was measured using the method described above. naznnn / Lznz / E / YiAi TABLE 8 i A 1 (©HOURS) 0.001 Ge | aome 10.1 Ge) 1& AUO Ut MEASUREMENT (MPa) 52.4 52.7 ¡ 516 59.0 I 79.4 c (5&β HOURS) SAMPLE NAME AkϋΠΜΜ1 MEASUREMENT (MPa) 0.0001 Ge 0.001 Ge 0.006 Ge 0.1 Ge j 1Ge 50.7 51.5 52.7 | 52.9 | 55.3 RATE OF CHANGE RESISTANCE (€ / A) (%) -___ 97% | 98% 102% 90?« 7G% ηαζηηη / Lznz / E / YiA Table 8 shows the tensile strength measurement results for samples with varying amounts of added Ge, as described above. Item A in Table 8 represents the tensile strength measurement result after 0 hours of aging, and Item C in Table 8 represents the tensile strength measurement result after 500 hours of aging. Figure 6 summarizes the tensile strength measurement results for samples with varying amounts of added Ge. All components with an addition of Ge from 0.0001 to 0.1 Ge exhibit a desirable resistance change ratio greater than 90% before and after aging. However, an addition of Ge of 0.0001% by mass is not preferable, as this can suppress the oxidation-preventing effect. Meanwhile, when the addition of Ge reaches 1% by mass, the resistance change ratio before and after aging is significantly lower than 90%. From the above description, when Ge is added to the basic composition of Sn-Cu-Ni-Bi, in the composition described above, it is preferable that an additional amount of Ge be from 0.001 to 0.1% by mass. Furthermore, because the effect of preventing oxidation is expected to be enhanced as the additional amount of Ge is increased, the additional amount of Ge can also be from 0.001 to 1.0% by mass. Furthermore, from this point forward, with respect to the case in which In is added to the basic composition of Sn-Cu-Ni-Bi, a change in tensile strength resulting from a change in an additional amount of In will be described in detail. In this case, Cu, Ni, Bi, and Ge are included in amounts of 0.7% by mass, 0.05% by mass, 1.5% by mass, and 0.006% by mass, respectively. Additionally, In is added in amounts of 0 to 10% by mass, and the remainder is Sn. From here on, for the sake of clarity, a sample in which 0% by mass of In is added, a sample in which 0.1% by mass of In is added, a sample in which 3% by mass of In is added, a sample in which 4% by mass of In is added, a sample in which 5% by mass of In is added, a sample in which 6% by mass of In is added, a sample in which 7% by mass of In is added, and a sample in which 10% by mass of In is added, will be referred to as 0 In, 0.1 In, 3 In, 4 In, 5 In, 6 In, 7 In, and 10 In, respectively. The samples were prepared using the method described above and the aging process was carried out on the prepared samples at 150°C for 0 hours and 500 hours and the tensile strength of the same was measured using the method described above. naznnn / Lznz / E / YiAi TABLE 9 TO NAMES® SAMPLE Oín O.Un 51c Qín í p 0In (O HOURS) MEASUREMENT RESULT MFa 51.6 51.4 56.7 57 9 62Ό 66.11 67.5 67.3 C SAMPLE NAME Oln (Q.Un 3ín 4In 51n 7ϊπ {500 HOURSÍ) MEASUREMENT RESULT' MPa 52.7 ¡51.4 58.7 60.4 67 73.5 74.4 48.8 RATE OF CHANGE RESISTANCE (CIA) 104¾ 108^111^110% 73¾ Table 9 shows tensile strength measurement results for samples with varying amounts of added In (hereafter referred to simply as the Added In sample) as described above. Item A in Table 9 is the tensile strength measurement result after aging for 0 hours, and Item C in Table 9 is the tensile strength measurement result after aging for 500 hours. Figure 7 summarizes the tensile strength measurement results for the samples with varying amounts of added In. All samples with altered In content, except for 10 In, exhibit a desirable strength change ratio greater than 90% before and after aging. Therefore, an additional In content of 0.1 to 7% by mass can also be considered effective. Furthermore, Table 10 shows the elongation rate measurement results for samples with altered In content. Item A in Table 10 represents the elongation rate measurement result after 0 hours of aging, and Item C in Table 10 represents the elongation rate measurement result after 500 hours of aging. The elongation rate change is a result that shows the change in elongation rate after 500 hours of aging, expressed as a percentage (%). Additionally, Figure 8 summarizes the elongation rate measurement results for the samples with altered In content described above. naznnn / Lznz / E / YiAi TABLE 10 A NAME BE SAMPLE 01η 0 11'1 3ín 4ΪΠ 51n 6ln i. 7ih | 101η .............L..... <G HORAS) RESULT ADO BE MEDICIÓN aw. 33 39 38 32 27 2'2 22 14 | 1 G NOMBRE BE MUESTRA OJln 3!n 4!n 51n 7in 101η | HORAS) RESULTADO DE MEDICIÓN W 37 37 35 35 32 26 21 24 | [PROPORCION DE CAMBIO | DE RESISTENCIA (CIA) {%) 112% 95% — 109% 119% 118% 95% In this case, the elongation rate can be obtained using the following equation. In the equation, σ represents the elongation rate, Lo represents the length between calibration points before the tensile strength measurement, and L is the length between calibration points after the tensile strength measurement. σ (%) = (L-Lo) / Lo X 100 In addition, the elongation rate was calculated using the above equation by marking a prescribed length (50 mm, Lo) between calibration points on a test specimen, before tensile strength measurement and measuring the length (L) between calibration points at the time of matching fractured pieces of the test specimen after tensile strength measurement. As can be seen from Table 10 and Figure 8, in a range where the additional amount of In is from 4% by mass (4 In) to 6% by mass (6 In), all samples have a stable elongation change ratio greater than 100%. That is, in such a range, the elongation ratio is improved after aging. In other words, within this timeframe, the transformation can occur more readily after aging than before. When an external impact is applied, it will be absorbed through the transformation, and the overall strength will increase to some degree. Consequently, this improvement in the elongation rate can contribute to the overall strength improvement. However, when the additional amount of In is excessively large, the temperature at which the transformation begins can be lowered. From the above description, when In is added to the base composition of Sn-Cu-Ni-Bi, in the composition described above, it is preferable that an additional amount of In be from 0.1 to 6% by mass. Meanwhile, because the additional amount of In is expected to increase, the liquid-phase temperature is decreased and the resistance is increased, and therefore the additional amount of In can also be from 0.1 to 10% by mass. naznnn / Lznz / E / YiAi From here on, the resistance change of SAC305 which includes only Ag, Cu and Sn without Ni, Ge and Bi being added to it and samples with the basic composition of Sn-Cu-Ni-Bi in which Ge, Sb, In, Ga, P, Co, Al, Ti or Ag are added (hereinafter referred to as additional element), will be described below. TABLE 11 SAMPLE No. IV VI A NOMBRE DE MUESTRA SAC308 +1..5θί O.ÜOlGe 0.1 Ge 5Sb 0.1 fe result of MEDICIÓN GíPal AS. 2 SU 52.7 5S.C 5? 6 84.6 514 c NOMBRESE MUESTRA SAC3O5 +L5Ss 0.001 Ge ai G e 0 155 5Sk SJfe «Si» HOURS) MEASUREMENT RESULT (IMPA) 35.5 52.7 51.5 52.8 52.2 £4.4 51.-4 PROFORaON CAMBIOSE RESlSTEXCiA o 7« 102¾ 93% 90¾ s 99% 103% ....................... ................ w KXXI xa xsi Wín O.OOÍGs ¡Ga 0W5P aascs 0.31 Al δ.δοετί ¢7.3 596 62 5 SO 7 50.4 45.5 52.4 1 0.0Θ5Ρ COSO·· 001 AI 48.3 l SU 71 δ 535 540 51.8 54.2 ) 73% 115¾ ..... 05% 107% 104% 103S | Table 11 shows the tensile strength measurement results for the samples with the added element. Item A in Table 11 represents the tensile strength measurement result after 0 hours of aging, and item C in Table 11 represents the tensile strength measurement result after 500 hours of aging. Figure 9 summarizes the tensile strength measurement results for the samples with the added element. Furthermore, the composition of the samples in which the additional element is added is shown in Table 12. Here, since SAC305 has the same composition as that of SAC305 (produced by Nihon Superior Co., Ltd.) in Table 4 above and the composition of +1.5 Bi(I) has already been shown in Table 2, their compositions will not be represented in detail. naznnn / Lznz / E / YiAi Table 12 Ge Sb In Ga P Co Al Ti Ag 0.001 Ge (II) 0.001 0 0 0 0 0 0 0 0 0.1 Ge (III) 0.1 0 0 0 0 0 0 0 0 0.1 Sb (IV) 0.006 0.1 0 0 0 0 0 0 0 0 5 Sb (V) 0.006 5 0 0 0 0 0 0 0 0.1 In (VI) 0.006 0 0.1 0 0 0 0 0 0 10 In (Vil) 0.006 0 10 0 0 0 0 0 0 0.001 Ga (VIII) 0.006 0 0 0.001 0 0 0 0 0 1 Ga(IX) 0.006 0 0 1 0 0 0 0 0 0.005 P (X) 0.006 0 0 0 0.005 0 0 0 0 0.05 Co (XI) 0.006 0 0 0 0 0.05 0 0 0 0.01 Al (XII) 0.006 0 0 0 0 0 0.01 0 0 0.005 Ti (XIII) 0.006 0 0 0 0 0 0 0.005 0 1 Ag (XIV) 0.006 0 0 0 0 0 0 0 1 Unit: % by mass In all samples II to XIV illustrated in Tables 11 and 12, Cu, Ni, and Bi are included in amounts of 0.7% by mass, 0.05% by mass, and 1.5% by mass, respectively. Hereafter, for the sake of clarity, the Cu, Ni, and Bi content as described above will be referred to as a basis composition. Furthermore, in samples II and III, Ge is also included in an amount of 0.001% by mass or 0.1% by mass, respectively, in addition to the basic composition described above, and the remainder is Sn. In addition, samples IV to XIV contain 0.006% by mass of Ge, along with the basic composition described above, and also contain the additional elements. As can be seen from Figure 9 and Table 11, only SAC305 and 10 In (VII) have a strength change ratio of less than 90% before and after aging. That is, it is determined that, except for Sample VII, the additional element and the corresponding additional quantity for each sample maintain the effects of the present invention, that is, the effect of improving reliability after aging (improved tensile strength), while also producing unique effects due to the additional elements. For example, Ge and P have the unique effect of inhibiting the oxidation of Sn and welding ingredients due to the formation of NaZnnn / LZnz / E / YiAi oxide films. Ti and Ga have unique effects of self-oxidation and increased overall strength. In has the unique effect of lowering the liquid-phase temperature and increasing strength, and Ag has the unique effect of increasing strength before aging through dispersion and precipitation reinforcement. Co has the unique effect of thinning an intermetallic compound layer, and Al has the unique effects of refining the intermetallic compound, suppressing the decrease in strength after aging, and inhibiting self-oxidation. Table 13 compares the tensile strength of SAC305 with that of samples I through XIV before and after aging. Specifically, Table 13 shows the tensile strength ratios of samples I through XIV to SAC305, and the tensile strength ratios of SAC305 and samples II through XIV to sample I, expressed as percentages (%). In other words, Table 13 displays the relative tensile strength of samples I through XIV compared to SAC305 and sample I before and after aging. Table 13 Alloy BEFORE AGING AFTER AGING COMPARISON WITH SAC305 COMPARISON WITH SN1+1.5BI COMPARISON WITH SAC305 COMPARISON WITH SN1+1.5BI SAC305 100 93 100 67 1.5 Bi 107 100 148 100 0.001 Ge 109 102 145 98 0.1 Ge 123 115 149 100 0.1 Sb 109 102 147 99 5Sb 134 125 181 122 0.1 In 107 100 144 97 10 In 140 131 137 93 0.001 Ga 105 98 145 98 1 Ga 130 121 202 136 0.005 P 105 98 150 101 0.05 Co 105 98 152 102 0.01 Al 104 97 146 98 0.005 Ti 109 102 152 103 1 Ag 124 116 157 106 Unit: % by mass As can be seen from Table 13, all samples II through XIV have a relative tensile strength of 93% or more both before and after aging; in particular, samples V and IX have a relative tensile strength exceeding 120% both before and after aging. From the results described above, it was also determined that by adding the additional elements described above, the effects of the present invention can be maintained, and the unique effects of the additional elements can also be obtained, as described above. If it falls within the range in which the effects of the present invention are obtained, the form or use of the lead-free solder alloy of the present invention, having Sn-Cu-Ni-Bi as the base composition, is not limited, and the lead-free solder alloy may be used for flux soldering or reflow soldering. The lead-free solder alloy may be in the form of a solder paste, a resin-alkaline flux-cored solder, a powder, a preform, or a ball, according to its use, and also as a flux-cored soldering rod. Furthermore, the present invention also relates to the soldered joint that is soldered with the lead-free solder alloy of the present invention, which is processed to have various shapes. Industrial applicability The present invention consists of a lead-free solder alloy that is versatile enough not to be limited by the shape of the soldered product. Since the bond strength of the soldered joint decreases minimally even when exposed to high temperatures for extended periods, the long-term reliability of the soldered joint is maintained. Thus, the present invention can be widely applied to apparatus and devices with soldered joints where high currents flow, apparatus and devices exposed to high temperatures, or similar applications, including as a solder for electronic devices. It is noted that, with regard to this date, the best method known to the applicant, to put the aforementioned invention into practice, is the conventional one for the manufacture 5 of the objects to which it refers.

Claims

1. A silver-free and lead-free solder alloy characterized in that it comprises: 76.0 to 99.5% by mass of Sn; 0.1 to 2.0% by mass of Cu; 0.01 to 0.5% by mass of Ni; 0.1 to 5.0% by mass of Bi; 0.001 to 1.0% by mass of Ge; 0.1 to 5% by mass of Sb, and unavoidable impurities.

2. The silver-free and lead-free solder alloy according to claim 1, characterized in that it further comprises at least 0.001 to 1.0% by mass of Ga, 0.005% by mass of P, 0.05% by mass of Co, 0.005% by mass of Ti and 0.01% by mass of Al.

3. The silver-free and lead-free solder alloy according to claim 1, characterized in that Bi is included in more than 1.0 to 5.0% by mass and In is further included in 3 to 10% by mass.

4. The silver-free and lead-free solder alloy according to claim 3, characterized in that it further comprises at least one of 0.001 to 1.0% by mass of Ga, 0.005% by mass of P, 0.05% by mass of Co, 0.005% by mass of Ti and 0.01% by mass of Al.

5. A soldered joint using the silver-free and lead-free solder alloy characterized in that it conforms to claim 1 to 4.