JP7216419B2 - Lead-free solder alloys and solder joints - Google Patents

Description

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

Al has high thermal conductivity and generates less thermal stress than other metals, so it is often used for heat dissipation members of electronic devices and the like. Moreover, in recent years, attention has been paid to the low specific gravity and strength, which are the characteristics of Al, and it is being studied as a material that contributes to the weight reduction of motors and the like.

However, as described above, when Al is used for heat radiation members, motor coils, etc., it is common to use solder for bonding, but there is the problem that sufficient bonding strength and reliability cannot be obtained. exists.

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

Further, in Patent Document 3, Sn- (10-15%) Zn- (0.1-1.5%) Cu- (0.0001-0.1%) Al- (0.0001-0.03%) ) Si- (0.0001 to 0.02%) Ti- (0.0001 to 0.01%) B solder alloy is described in Patent Document 4, Sn- (10% or less) Ag- (15% or less ) Al composition solder alloys for direct bonding of Al members are respectively disclosed.
Further, in Patent Document 5, as a bonding method for bonding between Al materials or between an Al material and a dissimilar material, Sn consisting of a metal element selected from the group of Cu, Ag, In, Bi, Co, and Ti and the balance Sn Joints using system solders are disclosed.

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

On the other hand, Sn--Ag--Cu solder alloys, which are widely used as lead-free solder alloys, are known to be unsuitable for joining Al members. Specifically, when joining Al members together or joining Al members and dissimilar metal members using a Sn—Ag—Cu solder alloy, the 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 progresses quickly, and the Sn--Ag--Cu solder alloy and the Al member are separated in a short time. was there.

However, Patent Documents 1 to 5 do not disclose a Sn--Ag--Cu solder alloy. In addition, no improvement in corrosion resistance and joint reliability in a salt water environment for solder joints in which Al members are joined using Sn--Ag--Cu solder alloys has been made.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a Sn-Ag-Cu adhesive that can maintain excellent corrosion resistance and high bonding reliability for bonding with Al members even in a salt water environment. It is another object of the present invention 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 to a member to be joined that contains Al in at least the surface layer, and the standard electrode potential with Ni and Al difference is 0.7 V or less.

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.

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

A solder joint according to the present invention is 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 Al in at least a surface layer, wherein the lead-free solder alloy contains Al. The auxiliary agent having a standard electrode potential difference of 0.7 V or less is included, and the auxiliary agent is distributed in the junction.

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 joint reliability for joining with an Al member even in a salt water environment.

FIG. 4 is a perspective view showing a test piece used as a test sample of the solder joint according to the present embodiment; FIG. 4 is a schematic diagram schematically showing an example of a test sample of the solder joint according to the present embodiment; 4 is a graph showing corrosion test results in Table 2. FIG. 7 is a graph showing measurement results of maximum stress in Table 6. FIG. 8 is a graph representing the percentage of maximum stress in Table 7. FIG. 1 is a graph plotting the difference between the maximum stress of Comparative Example 1 and the maximum stress of test samples of Examples 2-5 and Comparative Examples 2-5 against the difference (V) from the standard electrode potential of Al.

A Sn-Ag-Cu-based lead-free solder alloy and a solder joint according to embodiments of the present invention will be described in detail below with reference to the drawings.

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

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

Table 1 shows the composition of the Sn--Ag--Cu solder alloy (Example 1) according to the present embodiment. Table 1 also shows Comparative Examples 1 and 2.

As shown in Table 1, the Sn--Ag--Cu solder alloy according to the present embodiment (hereinafter referred to as Example 1) contains 5% by weight of Cu, 3% by weight of Ag, and 3% by weight of Ni, respectively. 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.

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

Solder joint test specimens were prepared using Example 1, Comparative Example 1 and Comparative Example 2 described above. Test specimens were prepared using Example 1, Comparative Example 1 and Comparative Example 2 by bonding Al specimens together. A detailed description will be given below.

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

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

A solder joint 100 as a test sample is produced by soldering Al test pieces prepared as described above. That is, in both Example 1 and Comparative Examples 1 and 2, the solder joints 100 of the test samples were made from Al test pieces, one test piece 1a and the other test piece 1b.

In manufacturing the solder joint 100 of the test sample, as shown in FIG. , the solder alloy foil 2 and its surroundings were heated to join the test pieces 1a and 1b. At this time, the soldering temperature is as shown in Table 1, and the test pieces 1a and 1b are parallel to each other. After that, the prepared solder joint 100 was cooled to room temperature, and the test sample solder joint 100 shown in FIG. 2 was obtained.

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

Corrosion tests were conducted using the solder joints 100 of the test samples of Example 1 and Comparative Examples 1 and 2. In such corrosion tests, each test specimen 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 come into contact with each other. A test sample was taken out every 24 hours from the start of immersion, and it was confirmed whether it was joined normally.

For such confirmation, position P1 about 5 mm from one end of the solder joint 100 of the test sample is pressed and fixed with the tip of resin tweezers, and position P2 about 5 mm from the other end is pressed three times with the tip of the resin tweezers. It was done by At this time, the strength with which the test sample is pressed against the solder joint 100 is such a strength that the test sample does not deform or forcibly peel off. The test samples that were normally bonded were immersed in the NaCl aqueous solution again, and the samples that were not properly bonded, that is, peeled off, were removed 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 portion of the test piece 1b. 3 is a graph showing the corrosion test results of Table 2. FIG. That is, Table 2 and FIG. 3 show the corrosion test results for 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. Table 2 shows the number of days from the start of immersion to the confirmation of the occurrence of peeling (hereinafter referred to as bonding days). Corrosion test results are shown in ascending order.

As can be seen from Table 2 and FIG. 3, the average number of bonding days in Comparative Example 2 is 12 days, the average number of bonding days in Comparative Example 1 is 36 days, and the average number of bonding days in Example 1 is 108 days. That is, when comparing the bonding days, Comparative Example 2, Comparative Example 1, and Example 1 are longer in this order. The bonding days of Comparative Example 1 are three times longer than the bonding days of Comparative Example 2, and the bonding days of Example 1 are three times longer than the bonding 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 joined containing Al, corrosion resistance and joining 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 a salt water environment. Such results are thought to be influenced by Mn added as an auxiliary agent. A detailed description will be given below.

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

On the other hand, the standard electrode potential of Mn added in 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 potential difference of Mn) is 0.5 V, which is relatively small. In Example 1, such Mn is presumed to be distributed near the joint interface (joint portion) of the solder joint 100 . For example, it is conceivable that a Cu—Al or Cu—Ag intermetallic compound formed at the junction contains Mn. Therefore, in Example 1, the difference in standard electrode potential between the member to be joined containing Al and the solder alloy is reduced at the joint. It is believed that this suppresses 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 to this. Any auxiliary agent having a standard electrode potential difference from Al equal to or less than the potential difference (0.5 V) of Mn may be used. For example, the standard electrode potentials of Ti and Zr are -1.63 V and -1.55, respectively, and the differences between the standard electrode potentials of Al are 0.05 V and 0.13 V, respectively. small. Therefore, Ti or Zr may be used as an auxiliary agent.

Moreover, the present invention is not limited to the above description. As an auxiliary agent other than Mn, an auxiliary agent having a standard electrode potential difference from Al that is approximately the same as 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, and the standard electrode potential difference with Al is 0.68V, which is about the same as the potential difference of Mn, 0.5V. Therefore, Mg may be used as an auxiliary agent.

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

In the above description, the Sn--Ag--Cu solder alloy according to the present embodiment contains 0.003% by weight of Mn as an example, but the present invention is not limited to this. When the Mn is in the range of 0 to 0.01% by weight, the Sn--Ag--Cu solder alloy according to the present embodiment exhibits the above 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 whether or not this is the case, tests were also conducted in cases where Mg, Ti, and Zr were used as auxiliary agents, and in cases where 0 to 0.01% by weight of Mn was added as an auxiliary agent.

Tests were conducted using test sample solder joints 100 with additive Mg, Ti, Zr, or 0-0.01 weight percent Mn as coagents. Specifically, after the solder joint 100 of the test sample was immersed in salt water for a predetermined period of time, the tensile strength of the solder joint 100 was measured to observe the change in joint strength with the immersion time in salt water.

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. Also, Comparative Examples 1 and 2 described in Table 3 are the same as those described above. Furthermore, Comparative Examples 3 to 5 are added to Table 3 for comparison.

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

Among the solder joints 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. It further contains Ti and the balance is Sn. Example 3 has the same amounts of Ag, Cu, and Ni as Example 2, and further contains 0.008% by weight of Zr and the balance is Sn. Example 4 has the same amounts of Ag, Cu, and Ni as Example 2, and further contains 0.010% by weight of Mn and the balance is Sn. Example 5 has the same amounts of Ag, Cu, and Ni as Example 2, and further contains 0.004% by weight of Mg and the balance is Sn. The soldering temperature in Examples 2-5 is 320°C.

Comparative Example 3 contains the same amounts of Ag, Cu, and Ni as in Example 2, further contains 0.012% by weight of Zn, and the balance is Sn. Comparative Example 4 contains the same amounts of Ag, Cu, and Ni as in Example 2, further contains 0.008% by weight of Na, and the balance is Sn. Comparative Example 5 contains the same amounts of Ag, Cu, and Ni as in Example 2, further contains 0.010% by weight of Fe, and the balance is Sn.
The soldering temperature in Comparative Examples 3-5 is 320°C. Note that Comparative Examples 1 and 2 have already been described, and the description will be omitted.

Table 4 shows the standard electrode potential (V) of the auxiliary agents 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 the value obtained by subtracting the standard electrode potential of the aid 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 assumed that Sn was added as an auxiliary agent, and the standard electrode potential (V) of the auxiliary agent and the difference (V) from the standard electrode potential of Al were described.

When Mn, Mg, Ti, Zr, Zn, Na, and Fe are added as auxiliary agents (Examples 2 to 5, Comparative Examples 3 to 4), the amount of each component (element) added is were determined to emit the same amount of electrons. Since galvanic corrosion is a reaction phenomenon caused by the transfer of electrons between dissimilar metal elements (auxiliaries), in order to comparatively evaluate the effect of addition of each element on the corrosion inhibition effect, electrons involved in the transfer of reaction This is because it was determined that it was necessary to match the amounts.

Specifically, based on the case where the amount of Mn added is 0.010% by weight, based on the ionization valence and atomic weight of each element, the amount of electrons emitted when each element is ionized is the same. 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 = Addition amount of Mn x (valence of Mn/valence of element) x (atomic weight of element/atomic weight of Mn)

The solder alloys of Examples 2-5 and Comparative Examples 1-5 listed in Table 3 were used to prepare test specimens of solder joints. The test sample has the same shape as that shown in FIG. Further, since the preparation of the test sample shown in FIG. 2 has already been described, detailed description thereof will be omitted.

Prior to measuring the tensile strength of the thus prepared test specimens of Examples 2-5 and Comparative Examples 1-5, the test specimens were immersed in salt water for a predetermined period of time. Specifically, the test samples according to Examples 2-5 and Comparative Examples 1-5 were completely immersed in salt water (3% NaCl aqueous solution) and left at room temperature. At this time, the test samples were allowed to stand so as not to come into contact with each other. The test samples were taken out at 72 hours, 168 hours and 336 hours after the start of immersion, and the tensile strength was measured. The saline was changed weekly.

The tensile strength was measured using a testing machine 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 treated 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 measurements were made five times for each test sample.

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

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

As can be seen from FIGS. 4 to 5 and Tables 6 to 7, the immersion treatment time was increased to 72 hours, 168 hours, and 336 hours in all of the test samples of Examples 2 to 5 and Comparative Examples 1 to 5. The maximum stress decreases as the That is, as the immersion treatment time increases, the corrosion becomes severer and the maximum stress decreases.

However, after the immersion treatment for 72 hours, 168 hours, and 336 hours, the maximum stress of the solder joints 100 of the test samples according to Examples 2-5 exceeded the maximum stress of the test samples according to Comparative Examples 1-5. showing.

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

Thus, after the immersion treatment, the maximum stress of the solder joints 100 of the test samples according to Examples 2-5 is higher than the maximum stress of the test samples according to Comparative Examples 1-5. It can be seen that the solder joint 100 of the test sample is superior in corrosion resistance to the test samples according to Comparative Examples 1-5.

FIG. 6 plots the difference between the maximum stress of Comparative Example 1 and the maximum stress of the test samples of Examples 2-5 and Comparative Examples 2-5 against the difference (V) from the standard electrode potential of Al. 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 divided on the boundary of the case where the difference (V) from the standard electrode potential of Al is 0.70. If the difference (V) from the standard electrode potential of Al is lower than 0.70, the maximum stress difference from Comparative Example 1 is greater than 0, and the difference (V) from the standard electrode potential of Al is greater than 0.70. In the other, the maximum stress difference from Comparative Example 1 is smaller than zero. Those where the difference (V) from the standard electrode potential of Al is lower than 0.70 correspond to the solder joints 100 of the test samples according to Examples 2 to 5, and the difference (V) from the standard electrode potential of Al is 0.70. Those above 70 correspond to Comparative Examples 2-5.

That is, in the solder joints 100 of the test samples according to Examples 2 to 5, the maximum stress (tensile strength) after immersion treatment is higher than that in Comparative Example 1, and in the test samples according to Comparative Examples 2 to 5, after immersion treatment The maximum stress (tensile strength) of is lower than that of Comparative Example 1. In other words, all of the test sample solder joints 100 according to Examples 2-5 exhibit a higher maximum stress (tensile strength) than Comparative Examples 1-5 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, and Zr whose standard electrode potential difference with Al is 0.7 V or less as an auxiliary agent. did it.

Specifically, by using a lead-free solder alloy containing 0.010% by weight of Mn as an auxiliary agent, the solder joint 100 of this embodiment has the effect of suppressing galvanic corrosion.
Note that Mn is an element that is easily oxidized, and if it forms an oxide, so-called dross, on the solder (alloy) surface, it causes deterioration 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 such, the addition of Mn has a side effect of deteriorating the performance of the solder alloy itself and the soldering workability, and the addition of Mn exceeding 0.010% by weight is not desirable.

Moreover, as described above, by using a lead-free solder alloy containing 0.009% by weight of Ti as an auxiliary agent, the solder joint 100 of this embodiment also has the effect of suppressing galvanic corrosion.
Furthermore, by using a lead-free solder alloy containing 0.004% by weight of Mg as an auxiliary agent, the solder joint 100 of this embodiment also has the effect of suppressing galvanic corrosion. By using a lead-free solder alloy containing 0.008% by weight of Zr in excess of 0 as an auxiliary agent, the solder joint 100 of this embodiment also has the effect of suppressing galvanic corrosion.

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

Claims (2)

In a Sn-Ag-Cu-based lead-free solder alloy used for soldering with a member to be joined containing Al in at least the surface layer,
3.00 wt% Ag, 5.00 wt% Cu and 0.05 wt% Ni,
further comprising at least one auxiliary agent selected from Mn, Ti, Mg, and Zr;
The amount of Mn added is 0.003 to 0.010% by weight, the amount of Ti added is 0.009% by weight, the amount of Mg added is 0.004% by weight, and the amount of Zr added is 0.008% by weight . ,
A lead-free solder alloy, wherein the balance is Sn . 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 Al in at least the surface layer,
A lead-free solder alloy according to claim 1,
A solder joint, characterized in that said aid is distributed in the joint.

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