WO2018181690A1 - Lead-free solder alloy and solder joint - Google Patents

Abstract

The lead-free solder alloy according to the present invention is a Sn-Ag-Cu-based lead-free solder alloy that is used for soldering a member to be joined that contains Al at least in the surface layer thereof, the lead-free solder alloy comprising Ni and an auxiliary agent, the difference in standard electrode potential between the auxiliary agent and Al being 0.7 V or lower. The solder joint of the present invention is such that, by using said lead-free solder alloy, the auxiliary agent is distributed in a joint portion with the member to be joined that contains Al at least in the surface layer thereof, and the difference in standard electrode potential between the member to be joined and the solder alloy is reduced.

Description

Lead-free solder alloy and solder joint

The present invention relates to a Sn-Ag-Cu-based lead-free solder alloy used for soldering with a substrate containing at least a surface layer of Al.

Al has a high thermal conductivity compared to other metals and generates less thermal stress. Therefore, Al is often used for heat dissipation members such as electronic devices. In recent years, attention has been paid to the small specific gravity or strength, which is a characteristic of Al, and it has been studied as a material contributing to weight reduction of motors and the like.

However, as described above, when Al is used for a heat radiating member, a motor coil or the like, it is common to use solder to join, but there is a problem that sufficient joint strength and reliability cannot be obtained. Is present.

As a solder for Al, Patent Document 1 discloses a Sn- (3-40%) Zn- (1-10%) Ag- (0.5-4%) Cu composition solder alloy, and Patent Document 2 discloses Sn- (3-40%). Solder alloys having a composition of (0.5-7%) Mg- (1.5-20%) Zn- (0.5-15%) Ag are disclosed.

Patent Document 3 discloses Sn- (10-15%) Zn- (0.1-1.5%) Cu- (0.0001-0.1%) Al- (0.0001-0.03%). ) Si- (0.0001-0.02%) Ti- (0.0001-0.01%) B solder alloy is disclosed in Patent Document 4 as Sn- (10% or less) Ag- (15% or less). ) Solder alloys for direct joining of Al members having an Al composition are disclosed.
In Patent Document 5, as a joining method for joining Al materials or between Al materials and different materials, Sn composed of a metal element selected from the group of Cu, Ag, In, Bi, Co, and Ti and the remaining Sn is used. Bonding using a system solder is disclosed.

Japanese Patent Laid-Open No. 50-50250 JP 50-56347 A JP 2006-167800 A JP 2008-142729 A JP 2011-167714 A

On the other hand, it is known that Sn—Ag—Cu-based solder alloys widely used as lead-free solder alloys are not suitable for joining Al members. Specifically, when joining Al members using an Sn—Ag—Cu based solder alloy, or when joining an Al member and a dissimilar metal member, an oxide film formed on the surface of the Al member, It is known that sufficient bonding strength cannot be obtained due to problems such as electrolytic corrosion (galvanic corrosion).

Furthermore, when such a solder joint is used in an environment such as salt water such as seawater, the electrolytic corrosion proceeds rapidly, and the Sn—Ag—Cu solder alloy and the Al member are peeled off in a short time. was there.

However, Patent Documents 1 to 5 do not disclose Sn—Ag—Cu based solder alloys. Further, no improvement has been devised for improving the corrosion resistance and joining reliability in a salt water environment with respect to a solder joint in which an Al member is joined using a Sn—Ag—Cu based solder alloy.

The present invention has been made in view of such circumstances, and an object thereof is Sn-Ag-Cu which can maintain excellent corrosion resistance and high bonding reliability with respect to bonding with an Al member even in a salt water environment. It is to provide a lead-free solder alloy and solder joint of the system.

The lead-free solder alloy according to the present invention is a Sn-Ag-Cu-based lead-free solder alloy used for soldering with a member to be joined containing at least a surface layer, and is a standard electrode potential with Ni and Al. The auxiliary | assistant whose difference of 0.7V or less is included is characterized by the above-mentioned.

The lead-free solder alloy according to the present invention is characterized in that the auxiliary agent is at least one of Mn, Ti, Mg, and Zr.

The lead-free solder alloy according to the present invention is characterized in that the amount of Mn added is more than 0 and 0.01% by weight.

The lead-free solder alloy according to the present invention is characterized by containing 3.00% by weight of Ag, 5.00% by weight of Cu, and 0.05% by weight of Ni.

The solder joint according to the present invention is a solder joint of a Sn-Ag-Cu-based lead-free solder alloy to which Ni is added and a member to be joined containing at least Al in the surface layer. The auxiliary electrode has a difference in standard electrode potential of 0.7 V or less, and the auxiliary agent is distributed in the joint.

According to the present invention, it is possible to provide a Sn-Ag-Cu-based lead-free solder alloy and a solder joint that can maintain excellent corrosion resistance and high bonding reliability with respect to bonding with an Al member even in a salt water environment.

It is a perspective view which shows the test piece used for the test sample of the solder joint which concerns on this Embodiment. It is a schematic diagram which shows typically an example of the test sample of the solder joint which concerns on this Embodiment. It is a graph showing the corrosion test result of Table 2. It is a graph showing the measurement result of the maximum stress of Table 6. FIG. It is a graph showing the ratio of the maximum stress of Table 7. 6 is a graph in which the difference between the maximum stress of Comparative Example 1 and the maximum stress of the test samples of Examples 2 to 5 and Comparative Examples 2 to 5 is plotted against the difference (V) from the standard electrode potential of Al.

Hereinafter, the Sn—Ag—Cu-based lead-free solder alloy and the solder joint according to the embodiment of the present invention will be described in detail based on the drawings.

The Sn-Ag-Cu-based lead-free solder alloy according to the present embodiment is used for soldering with a member to be joined containing Al. Here, the to-be-joined member containing Al includes, for example, a pure aluminum member, a member having an Al-coated surface, or a member containing Al at least in the surface layer.

Hereinafter, a case where Sn—Ag—Cu based lead-free solder alloy is soldered to at least one pure aluminum (Al) plate will be described as an example. The Sn—Ag—Cu-based lead-free solder alloy according to the present embodiment further includes Ni and an auxiliary agent in addition to Sn, Ag, and Cu. In the following, a case where Mn is added as an auxiliary agent will be described as an example.

Table 1 is a table showing the composition of the Sn—Ag—Cu solder alloy (Example 1) according to the present embodiment. Table 1 also shows Comparative Example 1 and Comparative Example 2.

As shown in Table 1, the Sn—Ag—Cu-based solder alloy according to the present embodiment (hereinafter referred to as Example 1) includes Cu, Ag, and Ni, 5 wt%, 3 wt%, It contains 0.05% by weight, further contains 0.003% by weight of Mn, and the balance is Sn. The soldering temperature in Example 1 is 320 ° C.

Further, Comparative Example 1 contains 5% by weight, 3% by weight, and 0.05% by weight of Cu, Ag, and Ni, respectively, with the balance being Sn. Comparative Example 2 contains 0.5% by weight and 3% by weight of Cu and Ag, respectively, with the balance being Sn. The soldering temperatures in Comparative Examples 1 and 2 are 320 ° C. and 245 ° C., respectively.

Test samples for solder joints were prepared using Example 1, Comparative Example 1 and Comparative Example 2 described above. The test sample was prepared by joining Al test pieces using Example 1, Comparative Example 1, and Comparative Example 2. This will be described in detail below.

FIG. 1 is a perspective view showing a test piece used for a test sample of a solder joint, and FIG. 2 is a schematic diagram schematically showing an example of the test sample of the solder joint. The test piece 1 has a strip shape of 25 × 5 × 1 mm.

First, as shown in FIG. 1, about 0.01 g of flux is applied to the end of the test piece 1. The flux is No. 1 manufactured by Nippon Superior Co., Ltd. 1261. Next, the soldering of Example 1, Comparative Example 1 or Comparative Example 2 was performed in the soldering range of about 6 mm in width (indicated by hatching in FIG. 1) at the end of the test piece 1, and these alloys The plating layer was formed. A pair of such test pieces is prepared.

The solder joint 100 of the test sample is prepared by soldering the Al test pieces prepared as described above. That is, in both Example 1 and Comparative Examples 1 and 2, the solder joint 100 of the test sample was manufactured from an Al test piece for both the one test piece 1a and the other test piece 1b.

In the production of the solder joint 100 of the test sample, as shown in FIG. 2, the soldering ranges of the Al test pieces 1a and 1b are faced to each other, and a 6 × 5 × 0.4 mm solder alloy foil 2 is sandwiched therebetween. The test pieces 1a and 1b were joined by heating the solder alloy foil 2 and the periphery thereof. At this time, the soldering temperature is as shown in Table 1, and the test pieces 1a and 1b are parallel to each other. Then, the created solder joint 100 was cooled to room temperature, and the solder joint 100 of the test sample shown in FIG. 2 was obtained.

In the test sample of Example 1, the test pieces 1a and 1b are joined by Example 1, and in the test sample of Comparative Example 1, the test pieces 1a and 1b are joined by Comparative Example 1, and the test sample of Comparative Example 2 is used. , The test pieces 1a and 1b are joined by the comparative example 2.

Such a corrosion test was performed using the solder joint 100 of the test sample of Example 1 and Comparative Examples 1 and 2. In such a corrosion test, each test sample was completely immersed in a 3% NaCl aqueous solution and left at room temperature. At this time, the test samples were allowed to stand so as not to contact each other. A test sample was taken out every 24 hours from the start of immersion, and it was confirmed whether it was normally joined.

Such confirmation is made by pressing and fixing a position P1 of approximately 5 mm from one end of the solder joint 100 of the test sample with the tip of the resin tweezers and pressing a position P2 of approximately 5 mm from the other end with the tip of the resin tweezers three times. Was done. At this time, the strength of pressing the solder joint 100 of the test sample is such a strength that the test sample is not deformed and forced peeling does not occur. The test sample that was normally bonded was immersed again in the NaCl aqueous solution, and the sample that was not normally bonded, that is, the sample where peeling occurred was taken out from the container.

The corrosion test results are shown in Table 2. The corrosion test results in Table 2 show the occurrence of peeling at the joint of the test piece 1b. FIG. 3 is a graph showing the corrosion test results in Table 2. That is, Table 2 and FIG. 3 show the corrosion test results on the test piece 1b when both the test pieces 1a and 1b are Al test pieces.

Such a corrosion test was performed three times each in Example 1 and Comparative Examples 1 and 2. In Table 2, the number of days from the start of immersion to the confirmation of occurrence of peeling (hereinafter referred to as “joining days”) is shown. The corrosion test results are shown in ascending order.

As can be seen from Table 2 and FIG. 3, the average joining days of Comparative Example 2 is 12 days, the average joining days of Comparative Example 1 is 36 days, and the average joining days of Example 1 is 108 days. That is, when comparing the number of days of joining, the length becomes longer in the order of Comparative Example 2, Comparative Example 1, and Example 1. The joining days of Comparative Example 1 are three times longer than the joining days of Comparative Example 2, and the joining days of Example 1 are three times longer than the joining days of Comparative Example 1.

From the above, in Example 1, when the test piece 1b is Al, that is, in the case of a member to be bonded containing Al, the corrosion resistance and bonding reliability are superior to those of Comparative Examples 1 and 2. .

As described above, Example 1 can maintain excellent corrosion resistance and high bonding reliability even when placed in an environment where salt water is used. Such a result is considered to be influenced by Mn added as an auxiliary agent. This will be described in detail below.

Electrolytic corrosion proceeds as the difference in standard electrode potential increases. That is, in the case of a member to be joined containing Al, the electrolytic alloy at the joint becomes more severe as the solder alloy having a larger difference in standard electrode potential from Al, and the rate of electrolytic corrosion is further increased in salt water.

On the other hand, the standard electrode potential of Mn added to Example 1 is -1.18 V, and the standard electrode potential of Al is -1.68. The difference in standard electrode potential between Mn and Al (hereinafter referred to as the Mn potential difference) is 0.5 V, which is relatively small. In Example 1, it is inferred that such Mn is distributed in the vicinity of the joint interface (joint portion) of the solder joint 100. For example, it is conceivable that Mn is contained in a Cu—Al-based or Cu—Ag-based intermetallic compound formed in the joint. Therefore, in Example 1, the difference in the standard electrode potential between the member to be joined containing Al and the solder alloy is reduced at the joint. This is considered to suppress the corrosion at the joint.

In the above description, the case where Mn is added as an auxiliary agent for suppressing electrolytic corrosion has been described as an example, but the present invention is not limited thereto. Any auxiliary may be used as long as the difference in standard electrode potential from Al is not more than the potential difference (0.5 V) of Mn. For example, the standard electrode potential of Ti and Zr is −1.63 V and −1.55, respectively, and the difference in standard electrode potential from Al is 0.05 V and 0.13 V, respectively. small. Therefore, Ti or Zr may be used as an auxiliary agent.

Further, the present invention is not limited to the above description. As an auxiliary agent other than Mn, a material having a difference in standard electrode potential from Al that is similar to the potential difference (0.5 V) of Mn may be used. For example, in the case of Mg, the standard electrode potential is −2.36, the standard electrode potential difference from Al is 0.68 V, which is about the same as the Mn potential difference of 0.5 V. Therefore, Mg may be used as an auxiliary agent.

From the above, as an auxiliary for suppressing electrolytic corrosion, a material having a standard electrode potential difference from Al of 0.7 V or less may be used. That is, such an auxiliary agent may be any one of Mn, Mg, Ti, and Zr. Moreover, it is not restricted to this, You may use two or more among Mn, Mg, Ti, and Zr.

In the above, the case where the Sn—Ag—Cu solder alloy according to the present embodiment contains 0.003% by weight of Mn has been described as an example, but the present invention is not limited thereto. When Mn is in the range of 0 to 0.01% by weight, the Sn—Ag—Cu based solder alloy according to the present embodiment has the above-described effects.

As described above, when any one of Mn, Mg, Ti, and Zr is used as an auxiliary agent, and when 0 to 0.01% by weight of Mn is added as an auxiliary agent, the effect of suppressing electrolytic corrosion is exhibited. In order to confirm this, a test was also conducted when Mg, Ti, Zr was used as an auxiliary agent, and when 0 to 0.01% by weight of Mn was added as an auxiliary agent.

A test was conducted using a solder joint 100 as a test sample to which Mg, Ti, Zr, or 0 to 0.01 wt% of Mn was added as an auxiliary agent. Specifically, after the solder joint 100 of the test sample was immersed in salt water for a predetermined time, the tensile strength of the solder joint 100 was measured, and the change in bonding strength with the immersion time in salt water was observed.

Table 3 is a table showing the composition of the solder joint 100 (Sn—Ag—Cu solder alloy) of the test sample used for the measurement of the tensile strength. Moreover, Comparative Example 1 and Comparative Example 2 described in Table 3 are the same as those described above. In Table 3, Comparative Examples 3 to 5 were added for comparison.

As shown in Table 3, the solder joint 100 according to the present embodiment (Examples 2 to 5 in Table 3) includes Mn, Mg, Ti, and Zr as auxiliary agents. On the other hand, new Comparative Examples 3 to 5 each contain Zn, Na, and Fe as auxiliaries.

Of the solder joint 100 according to the present embodiment, Example 2 contains 3% by weight, 5% by weight, and 0.05% by weight of Ag, Cu, and Ni, respectively, and 0.009% by weight. Ti is further contained and the balance is Sn. In Example 3, Ag, Cu, and Ni are the same amount as in Example 2, and further contain 0.008% by weight of Zr, with the balance being Sn. In Example 4, Ag, Cu, and Ni are the same amount as in Example 2, and further contain 0.010% by weight of Mn, with the balance being Sn. In Example 5, Ag, Cu, and Ni are the same amount as in Example 2, and further contain 0.004% by weight of Mg, with the balance being Sn. The soldering temperatures in Examples 2 to 5 are all 320 ° C.

Further, in Comparative Example 3, Ag, Cu, and Ni are the same amount as in Example 2, and further contain 0.012% by weight of Zn, with the balance being Sn. In Comparative Example 4, Ag, Cu, and Ni are the same amount as in Example 2, 0.008 wt% Na is further included, and the balance is Sn. In Comparative Example 5, Ag, Cu, and Ni are the same amount as in Example 2, further containing 0.010 wt% Fe, and the balance being Sn.
The soldering temperatures in Comparative Examples 3 to 5 are all 320 ° C. Note that Comparative Examples 1 and 2 have already been described, and a description thereof will be omitted.

Table 4 shows the standard electrode potential (V) of the auxiliary agent added to Examples 2 to 5 and Comparative Examples 2 to 5, and the difference between the standard electrode potential (V) of the auxiliary agent and the standard electrode potential of Al ( V). That is, the difference (V) from the standard electrode potential of Al is a value obtained by subtracting the standard electrode potential of the auxiliary agent from the standard electrode potential of Al. In Table 4, the difference (V) from the standard electrode potential of Al is shown as an absolute value. In Comparative Example 2, it was considered that Sn was added as an auxiliary agent, and the difference (V) between the standard electrode potential (V) of the auxiliary agent and the standard electrode potential of Al was described.

In the case where Mn, Mg, Ti, Zr, Zn, Na, and Fe are added as auxiliary agents (Examples 2 to 5 and Comparative Examples 3 to 4), the amount of each of these components (elements) added is the amount of each element. Was determined to have the same amount of electrons. This is a reaction phenomenon that occurs due to the exchange of electrons between dissimilar metal elements (auxiliaries). Therefore, in order to compare and evaluate the effect of adding each element on the corrosion inhibition effect, the electrons involved in the exchange of reactions. It was because it was judged that it was necessary to match the amount.

Specifically, based on the case where the amount of Mn added is 0.010% by weight, from the ionization valence and atomic weight of each element so that the amount of emitted electrons when each element ionizes becomes the same amount, It was calculated based on the following formula. Table 5 shows the ionization valence, atomic weight, and calculated addition amount (calculated addition amount in Table 5) of each element.

Addition amount = Mn addition amount × (Mn valence / element valence) × (element atomic weight / Mn atomic weight)

Test samples for solder joints were prepared using the solder alloys of Examples 2 to 5 and Comparative Examples 1 to 5 shown in Table 3. The test sample has the same shape as that shown in FIG. The production of the test sample shown in FIG. 2 has already been described, and detailed description thereof will be omitted.

Before measuring the tensile strength of the test samples of Examples 2 to 5 and Comparative Examples 1 to 5 prepared as described above, these test samples were immersed in salt water for a predetermined time. Specifically, the test samples according to Examples 2 to 5 and Comparative Examples 1 to 5 were completely immersed in brine (3% NaCl aqueous solution) and left at room temperature. At this time, the test samples were allowed to stand so as not to contact each other. When the elapsed time from the start of immersion was 72 hours, 168 hours, and 336 hours, the test sample was taken out and the tensile strength was measured. The salt water was changed every week.

Tensile strength was measured using a Shimadzu tester AG-IS 10 kN. Specifically, the test samples of Examples 2 to 5 and Comparative Examples 1 to 5 after being immersed in salt water were cut at room temperature (20 ° C. to 25 ° C.) and 10 mm / min until each test sample was cut. Pull and measure the tensile strength of the test sample. Tensile strength was measured five times for each test sample.

Table 6 shows the measurement results of tensile strength (maximum stress). In Table 6, “0 hour” indicates before immersion in salt water. In Table 6, a value of “0” indicates that peeling occurred between the solder alloy (solder alloy foil 2) and the test pieces 1a and 1b in the solder joint of the test sample. FIG. 4 is a graph showing the measurement results of the maximum stress in Table 6. In FIG. 4, the vertical axis represents the maximum stress value, and the horizontal axis represents Examples 2 to 5 and Comparative Examples 1 to 5.

Table 7 shows the measurement results of the maximum stress of the test samples of Examples 2 to 5 and Comparative Examples 1 to 5 on the basis of the immersion treatment (0 hour). That is, in Table 7, the maximum stress after the immersion treatment for a predetermined time in each of Examples 2 to 5 and Comparative Examples 1 to 5 is shown as a ratio (percentage) to the maximum stress at 0 hour. FIG. 5 is a graph showing the ratio of the maximum stress in Table 7. In FIG. 5, the vertical axis represents the ratio to the stress value before the immersion treatment, and the horizontal axis represents Examples 2 to 5 and Comparative Examples 1 to 5.

As can be seen from FIGS. 4 to 5 and Tables 6 to 7, in any of the test samples of Examples 2 to 5 and Comparative Examples 1 to 5, the immersion treatment time was as long as 72 hours, 168 hours, and 336 hours. As it becomes, the maximum stress decreases. That is, it is judged that the corrosion becomes severe and the maximum stress is reduced as the time of the immersion treatment becomes longer.

However, after 72 hours, 168 hours, and 336 hours of immersion treatment, the maximum stress of the solder joint 100 of the test samples according to Examples 2 to 5 exceeds the maximum stress of the test sample according to Comparative Examples 1 to 5. Show.

In Examples 2 to 5, the maximum stress after 72 hours of immersion treatment was all 299 N or more, the maximum stress after 168 hours of immersion treatment was 158 N or more, and the maximum stress after 336 hours of immersion treatment It can be seen that the stress is 54 N or more.

As described above, after the immersion treatment, the maximum stress of the solder joint 100 of the test samples according to Examples 2 to 5 is higher than the maximum stress of the test sample according to Comparative Examples 1 to 5. It can be seen that the solder joint 100 of the test sample is superior in corrosion resistance as compared with the test samples according to Comparative Examples 1 to 5.

FIG. 6 plots the difference between the maximum stress of Comparative Example 1 and the maximum stress of the test samples of Examples 2 to 5 and Comparative Examples 2 to 5 against the difference (V) from the standard electrode potential of Al. It is a graph. In FIG. 6, the vertical axis indicates the maximum stress difference from Comparative Example 1, and the horizontal axis indicates the difference (V) from the standard electrode potential of Al.

As can be seen from FIG. 6, the maximum stress is separated when the difference (V) from the standard electrode potential of Al is 0.70. When the difference (V) from the standard electrode potential of Al is lower than 0.70, the maximum stress difference from Comparative Example 1 is larger than 0, and the difference (V) from the standard electrode potential of Al is larger than 0.70. On the other hand, the maximum stress difference from Comparative Example 1 is smaller than zero. The one where the difference (V) from the standard electrode potential of Al is lower than 0.70 corresponds to the solder joint 100 of the test samples according to Examples 2 to 5, and the difference (V) from the standard electrode potential of Al is 0.00. A value larger than 70 corresponds to Comparative Examples 2 to 5.

That is, in the solder joints 100 of the test samples according to Examples 2 to 5, the maximum stress (tensile strength) after the immersion treatment is higher than that of Comparative Example 1, and in the test samples according to Comparative Examples 2 to 5, after the immersion treatment The maximum stress (tensile strength) is lower than that of Comparative Example 1. In other words, each of the solder joints 100 of the test samples according to Examples 2 to 5 shows a maximum stress (tensile strength) higher than that of Comparative Examples 1 to 5 after the immersion treatment.

From the above, it is confirmed that electrolytic corrosion in the solder joint 100 (solder alloy) can be suppressed by using Mn, Mg, Ti, Zr whose difference in standard electrode potential from Al is 0.7 V or less as an auxiliary agent. did it.

Specifically, by using a lead-free solder alloy containing Mn in excess of 0 as 0.010% by weight as an auxiliary agent, the solder joint 100 of this embodiment has an effect of suppressing electrolytic corrosion.
Note that Mn is an element that easily oxidizes. When an oxide, so-called dross, is formed on the surface of the solder (alloy), it causes a decrease in solderability and workability. There is also a problem that the melting point of the solder alloy increases when Mn is added to Sn. As described above, the addition of Mn also has a side effect of lowering the performance of the solder alloy itself and the soldering workability, and the addition of Mn exceeding 0.010% by weight is not desirable.

Further, as described above, the use of the lead-free solder alloy containing 0% over 0.009% by weight of Ti as an auxiliary agent also has the effect of suppressing electrolytic corrosion in the solder joint 100 of the present embodiment.
Further, by using a lead-free solder alloy containing Mg in excess of 0.004% by weight as an auxiliary agent, the solder joint 100 of the present embodiment also has an effect of suppressing electrolytic corrosion. And by using the lead-free solder alloy containing 0 to 0.008% by weight of Zr as an auxiliary agent, the solder joint 100 of this embodiment also has an effect of suppressing electrolytic corrosion.

1, 1a, 1b Test piece 2 Solder alloy foil 100 Solder joint

Claims (5)

1. In a lead-free solder alloy based on Sn-Ag-Cu used for soldering with a member to be joined containing at least a surface layer,
   A lead-free solder alloy comprising an auxiliary agent having a difference in standard electrode potential between Ni and Al of 0.7 V or less.
2. The auxiliary agent is at least one of Mn, Ti, Mg, and Zr, the added amount of Mn is over 0, 0.010% by weight, the added amount of Ti is over 0, 0.009% by weight, the added amount of Mg 2. The lead-free solder alloy according to claim 1, wherein 0 exceeds 0.004 wt%, and the amount of Zr added exceeds 0 and 0.008 wt%.
3. The lead-free solder alloy according to claim 1 or 2, comprising 3.00 wt% Ag, 5.00 wt% Cu, and 0.05 wt% Ni.
4. In a solder joint between a Sn-Ag-Cu-based lead-free solder alloy to which Ni is added and a member to be joined containing at least Al in the surface layer,
   The lead-free solder alloy contains an auxiliary agent whose difference in standard electrode potential from Al is 0.7 V or less,
   A solder joint, wherein the auxiliary agent is distributed in the joint.
5. In a solder joint between a Sn-Ag-Cu-based lead-free solder alloy to which Ni is added and a member to be joined containing at least Al in the surface layer,
   The lead-free solder alloy according to claim 2 or claim 3,
   A solder joint, wherein the auxiliary agent is distributed in the joint.

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