JPH11226776A - Lead free solder excellent in oxidation resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the oxidation resistance of Sn solder and to obtain the high ductility by mixing/adding Ag, Cu, Ge, Te respectively in a specified ratio to the Sn solder. SOLUTION: This lead free solder is prepared by adding and mixing 0.5-3.0 wt.% Ag, 0.1-0.8 wt.% Cu (preferably 0.1-0.5 wt.%), respectively 0.01-0.1 wt.% Ge, Te, as necessary, 6-20 wt.% Bi to Sn solder (solder of single Sn). By adding Ag, the strength of Sn is increased as well as the prevention effect of silver consuming is exhibited and, by adding Cu, the structure is refined to increase the ductility as well as to prevent Cu consuming. By adding Ge, Te, the oxide generation of a solder bath is halved to keep the oxidation resistance for a long time. By adding Bi, the high strength solder having >=90 Nmm<2> at a temp. and >=50 Nmm<2> at 125 deg.C is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead-free solder used for soldering of electronic equipment, and more particularly to a lead-free solder having excellent oxidation resistance for suppressing generation of oxides and having high ductility or high strength. This is related to soldering.

[0002]

2. Description of the Related Art In the electronics industry, until now, Sn-Pb
A lot of system solders are used, and in most cases, they are in a molten state. Thus, the molten solder at this time reacts with oxygen contained in the air or the molten solder to generate a large amount of oxide.

[0003] Particularly, in a jet-type solder bath used for soldering a printed circuit board when assembling electronic equipment,
This tendency is remarkable because the agitation comes into contact with a large amount of air. When a powdery solder is used as a paste, a solder ball may be generated due to an oxide, which may render the paste unusable.

In order to solve such a problem, Sn-P
It has been proposed to add various elements to the b-based solder for the purpose of preventing oxidation.

On the other hand, in the electronics industry, the use of lead-free solder has become mandatory in the near future as an environmental measure due to the toxicity of lead. However, there has been no attempt to improve the oxidation resistance of lead-free solders.

In the soldering of electronic equipment,
In order to increase the reliability of soldering, high ductility or high strength solder is required.

[0007]

Heretofore, no lead-free solder having excellent oxidation resistance and high ductility or high strength has been known at all.

The present invention has been made in view of such a point, and has as its object to provide a lead-free solder having excellent oxidation resistance and high ductility or high strength.

[0009]

In order to achieve the above-mentioned object, the present invention provides a method for forming a solder on an Sn solder (solder of Sn alone).
g 0.5-3.0% by weight, Cu 0.1-0.8% by weight
(Preferably 0.1 to 0.5% by weight) and 0.01 to 0.1% by weight of Ge and Te are added and mixed.

When 6 to 20% by weight of Bi is further added to and mixed with the above composition, 90 Nmm ² or more at room temperature and 5 N at 125 ° C.
A lead-free solder having a high strength of 0 Nmm ² or more and excellent in oxidation resistance can be obtained.

In short, the present invention significantly improves oxidation resistance by adding Ge and Te,
High ductility by the composition according to claim 1,
Further, the gist of the present invention is to increase the strength by adding Bi thereto.

In the case of high ductility, when a force is applied from the outside, the stress is effectively absorbed, so that the solder is hardly peeled off as in the case of high strength.

[0013]

Next, an embodiment of the present invention will be described. First, the reason why the composition of the lead-free solder of the present invention is limited as described above will be described.

When Ag is 0.5% by weight or more, Ag enhances the strength of Sn and exerts an effect of preventing silver from being broken. Ag is
If more than 3.0% by weight is added, the structure is coarsened,
On the contrary, it hinders ductility and is expensive, so 0.5%
To 3.0% by weight.

Cu, when added in a small amount of 0.1% by weight or more, makes the structure finer, increases the ductility, and exerts an effect of preventing copper from cracking in the solder. Adding Cu in an amount of more than 0.8% by weight is not very effective, but rather impairs ductility and increases the amount of oxide (or dross) generated in the solder bath.

Further, by adding 6 to 20% by weight of Bi to the above composition, the strength at room temperature and high temperature is remarkably increased,
In addition, it lowers the melting point and improves solderability. Specifically, a high-strength solder of 90 Nmm ² or more at room temperature and 50 Nmm ² or more at 125 ° C. can be obtained.

The above Sn-Ag-Cu or Sn-Ag-C
Ge and Te are further added to the u-Bi alloy by 0.01
By adding 0.1 wt% to the composite, the amount of oxide (or dross) generated in the solder bath can be halved,
Moreover, the effect of maintaining the oxidation resistance for a long time can be obtained.

The dross is a sticky viscous substance having a metallic luster and containing 90% or more of the metal added to the solder, and impairs the solderability. On the other hand, the oxide is a free-flowing gray granular or powdery substance generated by oxidizing the solder, and does not impair the solderability in a small amount.

[0019]

Next, the present invention will be further described with reference to examples and comparative examples, but the present invention is not limited to these examples. Example 1 Test samples 1 to 3 listed in the following Table 1 and comparative samples 1 and 2
Oxidation tests were performed on the solder of the present invention and the solder of the comparative example in which 0.5% by weight of Ge and Te were each added to the solder. For comparison, an oxidation test was also performed on the same solder except that Ge and Te were not added.

[0020]

Table 1 Alloy composition of test sample

In the oxidation test, the operation of melting the solder at a solder bath temperature of 250 ° C., stirring continuously at a stirring speed of 60 rpm, scooping out the amount of oxide generated every 30 minutes, and weighing three times (1. .5 hours).
The measurement was performed by adding 05% Ge and 0.05% Te, and weighing three times every 30 minutes (1.5 hours). The results are shown in the following Table 2 together with the average oxide weight (M _A, M _B ). In addition, pure Sn equivalent to the weight of the oxide was additionally added for each weighing. In Table 2, M _A is the total average oxide weight (g / 30 minutes) when Ge and Te are not added,
M _B is the average oxide weight of the total in the case of adding Ge and Te (g / 30 min).

[0022]

Table 2 Oxidation test results (amount of oxide (g))

As is clear from the results in Table 2 above, Ge
By adding Ti and Te in combination, the oxidation resistance is remarkably increased to twice or more.

In the composition shown in Table 1 above, 0.05% Ge and 0.
Tensile tests were performed on test samples 1 ', 2', 3 'and comparative samples 1', 2 'to which 05% Te was added.

The tensile test was performed according to a JIS test method using a JIS No. 4 test piece. The results are shown in Table 3 below.

[0026]

[Table 3]

From Table 3 above, the solder of the present invention without Bi added (test sample 1 ') has high ductility, as is clear from the results of the elongation (%) at room temperature and 125 ° C. Also, Bi-added solder (test samples 2 'and 3')
The tensile strength at room temperature and at 125 ° C. is significantly increased.

Example 2 An oxidation test was conducted in the same manner as in Example 1 for the solder of Test Sample 1 shown in Table 1 and a solder to which one or both of Ge and Te were added. The results are shown in Table 4 below.

[0029]

As is clear from the results in Table 4 above, Te
When used alone, the effect of addition is almost the same as in the case where no additive is added, but when Te is combined with Ge, the duration of oxidation prevention is significantly improved as compared with Ge alone. As a result of investigating the cause, it was confirmed from the result of elemental analysis that Te had an effect of suppressing the decrease in the concentration of Ge.

[0031]

As described above, the lead-free solder of the present invention is excellent in oxidation resistance and has a long duration of antioxidation. Generation can be effectively prevented, and occurrence of soldering failure can be effectively avoided.

Further, since the solder of the present invention has high ductility or high strength, it does not easily peel off even when subjected to an impact or the like, so that the fatigue fracture life is extended and the reliability for soldering is enhanced.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Tatsuo Akuzawa 487 Motomachi, Sekijuku-cho, Higashi-Katsushika-gun, Chiba Pref.

Claims (6)

[Claims] 1. A method in which 0.5 to 3.0% by weight of Ag, 0.1 to 0.8% by weight of Cu, and 0.01 to 0.1% by weight of Ge and Te are added to Sn solder and mixed. Lead-free solder with excellent oxidation resistance. 2. The solder according to claim 1, wherein said Cu is added and mixed in an amount of 0.1 to 0.5% by weight. 3. The solder according to claim 1, wherein the lead-free solder has excellent oxidation resistance and high ductility. 4. The solder according to claim 3, wherein said lead-free solder exhibits an elongation of at least 40% at room temperature. 5. The solder according to claim 1, further comprising 6 to 20% by weight of Bi and having high strength and excellent oxidation resistance. 6. The solder according to claim 5, wherein the lead-free solder has a strength of 90 Nmm ² or more at room temperature and 50 Nmm ² or more at 125 ° C.