TW201837194A - 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 soft solder joint   

The present invention relates to a Sn-Ag-Cu based lead-free solder alloy that can be used for soldering to a substrate containing Al at least in its surface layer.

Compared with other metals, Al has high thermal conductivity and less thermal stress, and is often used as a heat sink for electronic equipment. In addition, in recent years, attention has been paid to a small specific gravity or strength as an Al characteristic, and studies have been made on materials that are lightweight for motors and the like.

However, as described above, when Al is used for a heat radiating member or a coil of a motor, although bonding using solder is quite common, there are problems in that sufficient bonding strength and reliability cannot be obtained.

As a solder for Al, Patent Literature 1 discloses a solder alloy composed of Sn- (3 ~ 40%) Zn- (1 ~ 10%) Ag- (0.5 ~ 4%) Cu, and Patent Literature 2 discloses Sn- ( 0.5 ~ 7%) solder alloy consisting of Mg- (1.5 ~ 20%) Zn- (0.5 ~ 15%) Ag.

In addition, Patent Literature 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 to 0.01%) B solder alloy, Patent Literature 4 discloses a solder alloy for direct bonding of Al members composed of Sn- (10% or less) Ag- (15% or less) Al.

Then, Patent Document 5 discloses a joining method for joining Al materials to each other or Al materials and heterogeneous materials, using a metal element selected from the group consisting of Cu, Ag, In, Bi, Co, and Ti and the remaining portion of Sn. Sn-based solder joints.

    [Prior technical literature]         [Patent Literature]    

Patent Document 1: Japanese Patent Application Laid-Open No. 50-50250.

Patent Document 2: Japanese Patent Application Laid-Open No. 50-56347.

Patent Document 3: Japanese Patent Application Laid-Open No. 2006-167800.

Patent Document 4: Japanese Patent Application Laid-Open No. 2008-142729.

Patent Document 5: Japanese Patent Application Laid-Open No. 2011-167714.

On the other hand, it is known that a Sn-Ag-Cu based solder alloy widely used as a lead-free solder alloy is not suitable for joining Al members. In detail, it is known that when an Sn member is used to bond Al members to each other, or when an Al member is bonded to a dissimilar metal member, an oxide film formed on the surface of the Al member or electrolytic corrosion is used ( Galvanic corrosion and other problems occur, and sufficient joint strength cannot be obtained.

Furthermore, when the related soft soldering is used in an environment such as salt water such as seawater, the above-mentioned electrolytic corrosion proceeds rapidly, and there is a problem that the Sn-Ag-Cu-based solder alloy and the Al member are separated in a short time.

However, Patent Documents 1 to 5 do not disclose Sn-Ag-Cu based solder alloys. In addition, soft soldering of Al members using Sn-Ag-Cu based solder alloys has not contributed to the improvement of corrosion resistance and joint reliability in salt water environments.

The present invention was made in view of the related facts, and as its object, it is to provide a Sn-Ag-Cu based lead-free solder capable of maintaining good corrosion resistance and high bonding reliability for bonding to an Al member even in a salt water environment. Alloy and soft welding.

The Sn-Ag-Cu-based lead-free solder alloy which can be used for soldering to a joined member containing Al at least in its surface layer according to the present invention is characterized in that it includes: Ni and a standard electrode potential with Al The difference is 0.7V or less.

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

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

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

The Sn-Ag-Cu lead-free solder alloy to which Ni is added in the soft soldering system according to the present invention is soft-welded to a member to be joined containing Al at least in its surface layer, wherein the lead-free solder alloy includes Al and Al Auxiliaries with a standard electrode potential difference of 0.7 V or less, which are distributed at the joints.

According to the present invention, there is provided a Sn-Ag-Cu-based lead-free solder alloy and a solder joint capable of maintaining good corrosion resistance and high joint reliability for joining to an Al member even in a salt water environment.

1,1a, 1b ‧‧‧test piece

2‧‧‧solder alloy foil

100‧‧‧soft welding

FIG. 1 is a side view showing a test piece used in a test sample for solder welding according to this embodiment.

FIG. 2 is a schematic diagram showing an example of a test sample for soft soldering according to this embodiment.

FIG. 3 is a bar graph showing the results of the corrosion test in Table 2.

FIG. 4 is a bar graph showing the measurement results of the maximum stress in Table 6.

FIG. 5 is a bar graph showing the ratio of the maximum stress in Table 7. FIG.

FIG. 6 is a graph showing the maximum stress of Comparative Example 1, and the difference between the maximum stress of the test samples of Examples 2 to 5 and Comparative Examples 2 to 5, plotted against the standard electrode potential difference (V) from Al. Chart.

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 with reference to the drawings.

The Sn-Ag-Cu-based lead-free solder alloy system according to this embodiment can be used when soldering to a member to be joined containing Al. Herein, the bonded member containing Al includes, for example, a member made of pure aluminum or a surface having an Al coating layer, or a member containing Al at least in the surface layer.

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

Table 1 is a table showing the composition of a Sn-Ag-Cu based solder alloy (Example 1) according to this embodiment. In addition, Table 1 shows Comparative Example 1 and Comparative Example 2 together.

As shown in Table 1, the Sn-Ag-Cu-based solder alloy (hereinafter, referred to as Example 1) related to this embodiment contains Cu, Ag, and Ni at 5 wt%, 3 wt%, and 0.05 wt%, respectively. It further contained 0.003% by weight of Mn, and the remainder was Sn. The soldering temperature in Example 1 was 320 ° C.

In addition, Comparative Example 1 contains Cu, Ag, and Ni at 5 wt%, 3 wt%, and 0.05 wt%, respectively, and the remainder is Sn. Comparative Example 2 contains Cu and Ag at 0.5% by weight and 3% by weight, respectively, and the remainder is Sn. In Comparative Examples 1 and 2, the soldering temperatures were 320 ° C and 245 ° C, respectively.

The above-mentioned Example 1, Comparative Example 1 and Comparative Example 2 were used to prepare test samples for soldering. The test samples were prepared by joining Al test pieces to each other using Example 1, Comparative Example 1, and Comparative Example 2. The details are described below.

FIG. 1 is a side view showing a test piece used in a test sample for soldering, and FIG. 2 is a schematic diagram showing an example of a test sample for soldering. The test piece 1 has a short strip shape of 25 × 5 × 1 mm.

First, as shown in FIG. 1, about 0.01 g of a flux was applied to the end of the test piece 1. The above-mentioned flux is No. 1261 made by Nihon superior. Next, at the end of the test piece 1, a welding range of approximately square with a width of 6 mm (shown by hatching in the first figure) was performed in Example 1, Comparative Example 1, or Comparative Example 2 to form these alloys. Plating. Prepare a pair of such test pieces.

The test pieces of Al prepared as described above were welded to each other to prepare a solder joint 100 of a test sample. That is, in any of Example 1, Comparative Examples 1, and 2, the solder joint 100 of the test sample is made of one test piece 1a and the other test piece 1b is made of an Al test piece. .

In the production of the soft solder joint 100 of the test specimen, as shown in FIG. 2, the above-mentioned welding ranges of the Al test pieces 1 a and 1 b were opposed to each other, and 6 × 5 × 0.4 mm was sandwiched between them. The solder alloy foil 2 is heated, the solder alloy foil 2 and its surroundings are heated, and the test pieces 1a and 1b are joined. At this time, the welding temperature is as described in Table 1, and the test pieces 1a and 1b are parallel to each other. Then, the prepared solder joint 100 was cooled to room temperature, and the solder joint 100 of the test sample shown in FIG. 2 was obtained.

Among the test samples of Example 1, the test pieces 1a and 1b were joined by Example 1. Among the test samples of Comparative Example 1, the test pieces 1a and 1b were joined by Comparative Example 1. In the test sample, the test pieces 1a and 1b were joined by Comparative Example 2.

Accordingly, the corrosion test was performed using the solder joint 100 of the test samples of Example 1 and Comparative Examples 1 and 2. The relevant corrosion test is that each test sample is completely immersed in a 3% NaCl aqueous solution and left at room temperature. At this time, the test specimens were left to stand without contacting each other. 24 hours after the start of immersion, the test sample was taken out, and it was confirmed whether it joined normally.

The relevant confirmation is that the position of P1, which is about 5 mm from one end of the soft solder joint 100 of the test sample, is squeezed and fixed by the tip of the resin welding tongs, and the position of P2, which is about 5 mm from the other end, is the front of the resin welding tongs. Press 3 times. At this time, the strength of the solder joint 100 that pressed the test sample was a strength in which the test sample was deformed and no forced peeling occurred. The normally joined test specimens were immersed again in the NaCl aqueous solution and failed to join normally, that is, the peeled specimens were taken out of the container.

The relevant corrosion test results are shown in Table 2. The results of the corrosion test in Table 2 show that peeling occurred at the joints of the test piece 1b. FIG. 3 is a bar graph showing the results of the corrosion test in Table 2. That is, when the test pieces 1a and 1b in Table 2 and FIG. 3 are Al test pieces, the results of the corrosion test on the test piece 1b are shown.

The relevant corrosion tests were performed three times in each of Example 1, Comparative Examples 1, and 2. Table 2 shows the number of days from the start of immersion until the occurrence of peeling (hereinafter referred to as the number of bonding days). In addition, the corrosion test results are shown in ascending order.

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

From the above, in Example 1, when the test piece 1b is Al, that is, when it is a member to be joined containing Al, the corrosion resistance and joint reliability are better than those of Comparative Examples 1 and 2.

As described above, Example 1 can maintain excellent corrosion resistance and high joint reliability even when it is placed in a use environment of salt water. This result is presumed to be the effect of Mn added as an auxiliary. The details are described below.

The larger the difference between the standard electrode potentials of the electrolytic corrosion system, the easier it becomes. That is, in the case of a member to be joined containing Al, the larger the difference between the standard electrode potential of Al and Al, the more severe the electrolytic corrosion of the solder alloy at the joint, and the faster the rate of electrolytic corrosion in salt water.

On the other hand, the standard electrode potential of Mn added in Example 1 was -1.18 V, and the standard electrode potential of Al was -1.68. The difference in standard electrode potential between Mn and Al (hereinafter referred to as the potential difference of Mn) is 0.5 V, which is relatively small. In Example 1, it is estimated that such Mn is distributed near the joint interface (joint portion) of the solder joint 100. It is estimated that, for example, Mn is contained in a Cu-Al-based or Cu-Ag-based metalloid compound formed at a joint. Therefore, in Example 1, the difference in the standard electrode potential between the member to be joined containing Al and the solder alloy was reduced at the joining portion. It is presumed that corrosion at the joints is thereby suppressed.

As mentioned above, although the case where Mn was added as an auxiliary agent which suppresses electrolytic corrosion is demonstrated as an example, this invention is not limited to these. It is sufficient if the difference between the standard electrode potential of Al and the potential difference (0.5 V) of Mn or less is sufficient. For example, since the standard electrode potentials of Ti and Zr are -1.63V and -1.55, respectively, and the standard electrode potentials of Al are 0.05V and 0.13V, respectively, the potential difference of Mn is smaller than 0.5V. Therefore, Ti or Zr can also be used as an auxiliary agent.

The present invention is not limited to those described above. As the auxiliary agent other than Mn, a difference between the standard electrode potential of Al and 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 difference between the standard electrode potential and Al is 0.68V, and the potential difference between Mn and 0.5V is about the same. Therefore, Mg can also be used as an adjuvant.

Based on the above, as the auxiliary agent for suppressing electrolytic corrosion, it is sufficient to use a difference between the standard electrode potential of Al and 0.7 V or less. That is, as a related auxiliary agent, any of Mn, Mg, Ti, and Zr may be used. In addition, it is not limited to this, and two or more of Mn, Mg, Ti, and Zr may be used.

As described above, the case where the Sn-Ag-Cu-based solder alloy according to this embodiment contains 0.003% by weight of Mn is described as an example, but the present invention is not limited to these. The Mn is in the range of 0 to 0.01% by weight, and the Sn-Ag-Cu-based solder alloy according to this embodiment achieves the above-mentioned effects.

As described above, it is necessary to confirm whether the effect of suppressing electrolytic corrosion can be achieved when using any of Mn, Mg, Ti, and Zr as an auxiliary agent and when 0 to 0.01% by weight of Mn is added as an auxiliary agent. When Zr is used as an adjuvant, and when 0 to 0.01% by weight Mn is added as an adjuvant, tests are also performed.

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

Table 3 is a table | surface which shows the composition of the solder joint 100 (Sn-Ag-Cu-type solder alloy) of the test sample used for the said tensile strength measurement. The comparative examples 1 and 2 described in Table 3 are the same as those described above. In addition, Comparative Examples 3 to 5 are added to Table 3 for comparison.

As shown in Table 3, the soft solder joints 100 (Examples 2 to 5 in Table 3) related to the present embodiment each contain Mn, Mg, Ti, and Zr as auxiliary agents. On the other hand, the new comparative examples 3 to 5 each contain Zn, Na, and Fe as auxiliary agents.

Among the solder joints 100 according to this embodiment, Example 2 contains 3% by weight, 5% by weight, 0.05% by weight of Ni, 0.05% by weight of Ti, 0.009% by weight of Ti, and the remaining portion is Sn. Example 3 contains the same amounts of Ag, Cu, and Ni as in Example 2, and further contains 0.008% by weight of Zr, and the remaining portion is Sn. Example 4 contains the same amounts of Ag, Cu, and Ni as in Example 2, and further contains 0.010% by weight of Mn, and the remaining portion is Sn. Example 5 contains Ag, Cu, and Ni in the same amount as in Example 2, and further contains 0.004% by weight of Mg, and the remaining portion is Sn. In Examples 2 to 5, the welding temperature was 320 ° C.

In addition, Comparative Example 3 was the same amount of Ag, Cu, and Ni as in Example 2, and further contained 0.012% by weight of Zn, and the remainder was Sn. Comparative Example 4 is the same amount of Ag, Cu, and Ni as in Example 2, and further contains 0.008% by weight of Na, and the remainder is Sn. Comparative Example 5 is the same amount of Ag, Cu, and Ni as in Example 2, and further contains 0.010% by weight of Fe, and the remainder is Sn.

In Comparative Examples 3 to 5, the soldering temperature was 320 ° C. Since Comparative Examples 1 to 2 have been described previously, descriptions thereof are omitted.

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

[Table 4]

When Mn, Mg, Ti, Zr, Zn, Na, and Fe are added as additives (Examples 2 to 5, Comparative Examples 3 to 4), the amounts of these components (elements) are fixed so that each element The amount of emitted electrons becomes equal. These are due to the phenomenon of electrolytic corrosion caused by the electron transfer between different metal elements (auxiliaries). Regarding the corrosion inhibition effect, in order to compare and evaluate the addition effect of each element, it is necessary to calibrate the electrons related to the transfer of the reaction the amount.

Specifically, based on the case where the amount of Mn added is 0.010% by weight, the amount of electrons emitted by each element at the time of ionization is made equal, and the ionization valence and atomic weight of each element are based on the following formula Figure it out. Table 5 shows the ionization valence, atomic weight, and calculated addition amount of each element (in Table 5, the addition amount is calculated).

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

The solder alloys of Examples 2 to 5 and Comparative Examples 1 to 5 described in Table 3 were used to prepare test samples for soldering. The test sample has the same shape as that shown in FIG. 2. In addition, the production of the test sample shown in FIG. 2 has already been described previously, so detailed description is omitted.

Before the test specimens of Examples 2 to 5 and Comparative Examples 1 to 5 thus prepared were measured for tensile strength, these test specimens were immersed in saline for a predetermined time. Specifically, the test samples related to Examples 2 to 5 and Comparative Examples 1 to 5 were completely immersed in brine (3% aqueous NaCl solution) and left at room temperature. At this time, the test specimens were left to stand without contacting 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 saline is changed every week.

The tensile strength was measured using a tester AG-IS10kN manufactured by Shimadzu Corporation. Specifically, the test samples of Examples 2 to 5 and Comparative Examples 1 to 5 after being immersed in salt water were stretched to break at a temperature of 10 mm / min at room temperature (20 ° C to 25 ° C). Until then, the tensile strength of the test specimen was measured. The measurement of tensile strength was performed 5 times for each test sample.

Table 6 shows the measurement results of the tensile strength (maximum stress). In Table 6, "0 hours" means before the salt water immersion treatment. In addition, the value of "0" in Table 6 indicates that peeling occurred between the solder alloy (solder alloy foil 2) and the test pieces 1a and 1b during the soft soldering of the test sample. FIG. 4 is a bar 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 based on the pre-dip treatment (0 hours) as a reference. That is, in Table 7, the maximum stress after the immersion treatment in each of Examples 2 to 5 and Comparative Examples 1 to 5 at a predetermined time is expressed as a ratio (percentage) to the maximum stress at 0 hours. FIG. 5 is a bar 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 Fig. 4 to Fig. 5 and Tables 6 to 7, the immersion treatment time of any of the test samples of Examples 2 to 5 and Comparative Examples 1 to 5 increased with 72 hours, 168 hours, and 336 hours. The longer the maximum stress decreases. That is, it is judged that as the time of the dipping treatment becomes longer, the corrosion becomes more serious, and the maximum stress decreases.

However, after the immersion treatment at 72 hours, 168 hours, and 336 hours, the maximum stress of the solder joint 100 of the test samples related to Examples 2 to 5 was higher than the maximum stress of the test samples related to Comparative Examples 1 to 5. Value.

In Examples 2 to 5, the maximum stress after the 72-hour immersion treatment was 299 N or more, the maximum stress after the 168-hour immersion treatment was 158 N or more, and the maximum stress after the 336-hour immersion treatment was 54 N or more.

In this way, it is known that after the dipping treatment, the maximum stress of the solder joint 100 of the test specimens related to Examples 2 to 5 is higher than the maximum stress of the test specimens related to Comparative Examples 1 to 5. Compared with the test samples related to Comparative Examples 1 to 5, the solder joint 100 of the test sample related to 5 has better corrosion resistance.

FIG. 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 standard electrode potential difference (V) from Al. chart. In FIG. 6, the vertical axis represents the maximum stress difference from Comparative Example 1, and the horizontal axis represents the difference (V) from the standard electrode potential of Al.

As can be seen from Fig. 6, the maximum stress is distinguished when the difference (V) from the standard electrode potential of Al is 0.70. The standard electrode potential difference (V) from Al is lower than 0.70, the maximum stress difference from Comparative Example 1 is greater than 0, and the standard electrode potential difference (V) from Al is larger than 0.70, compared to The maximum stress difference is less than 0. The standard electrode potential difference (V) lower than 0.70 corresponds to the solder joint 100 of the test samples related to Examples 2 to 5, and the standard electrode potential difference (V) to Al is larger than 0.70. This corresponds to Comparative Examples 2 to 5.

That is, in the soft-welded joint 100 of the test samples related to Examples 2 to 5, the maximum stress (tensile strength) after the dipping treatment was higher than that of Comparative Example 1, and the test samples related to Comparative Examples 2 to 5 However, the maximum stress (tensile strength) after the immersion treatment was lower than that of Comparative Example 1. In other words, any one of the solder joints 100 of the test samples related to Examples 2 to 5 showed a higher maximum stress (tensile strength) than that of Comparative Examples 1 to 5 after the dipping treatment.

From the above, it was confirmed that the use of Mn, Mg, Ti, and Zr having a difference between the standard electrode potential of Al and 0.7 V or less as an auxiliary suppresses electrolytic corrosion in the solder joint 100 (solder alloy).

In detail, by using a lead-free solder alloy containing more than 0 to 0.010% by weight of Mn as an auxiliary agent, the effect of suppressing electrolytic corrosion is achieved in the solder joint 100 of this embodiment.

In addition, Mn is an element having a property of being easily oxidized, and when an oxide, that is, a so-called slag, is formed on the surface of a solder (alloy), it causes a decrease in solderability or workability. In addition, when Mn is added to Sn, there is also a problem that the melting point of a so-called solder alloy rises. Such addition of Mn also has the viewpoint of lowering the performance of the solder alloy itself or soldering workability, and it is not desirable to add more than 0.010% by weight of Mn.

In addition, as described above, by using a lead-free solder alloy containing more than 0 to 0.009% by weight of Ti as an auxiliary agent, the solder joint 100 of this embodiment also achieves the effect of suppressing electrolytic corrosion.

Furthermore, by using a lead-free solder alloy containing more than 0 to 0.004% by weight of Mg as an auxiliary agent, the solder joint 100 of this embodiment also achieves the effect of suppressing electrolytic corrosion. Then, by using a lead-free solder alloy containing more than 0 to 0.008% by weight of Zr as an auxiliary agent, the solder joint 100 of this embodiment also achieves the effect of suppressing electrolytic corrosion.

Claims (5)

    A lead-free solder alloy used in a Sn-Ag-Cu-based lead-free solder alloy to be soldered to a joined member containing Al at least in its surface layer, comprising: Ni and a standard electrode potential difference from Al of 0.7 Auxiliaries below V.         The lead-free solder alloy according to item 1 of the scope of the patent application, wherein the auxiliary agent is at least one selected from the group consisting of Mn, Ti, Mg, and Zr. 0.009% by weight, the amount of Mg added exceeds 0 to 0.004% by weight, and the amount of Zr added exceeds 0 to 0.008% by weight.         The lead-free solder alloy according to item 1 or 2 of the patent application scope, which comprises: 3.00% by weight of Ag, 5.00% by weight of Cu, and 0.05% by weight of Ni.         The invention relates to a soft soldering joint, which is a Sn-Ag-Cu lead-free solder alloy added with Ni, and is soft-welded to a joined member containing Al at least in a surface layer, wherein the lead-free solder alloy includes: and Al Auxiliaries having a standard electrode potential difference of 0.7 V or less, the above-mentioned adjuvants are distributed at the joints.         A soft soldering joint, which is a Sn-Ag-Cu lead-free solder alloy with Ni added, and a soft soldering joint with a member to be joined containing Al at least in its surface layer, and is characterized by: In the lead-free solder alloy of item 3, the above additives are distributed at the joints.