JP2681742B2 - Lead-free solder alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to lead-free (non-Pb) solder.

[0002]

2. Description of the Related Art Conventionally, a solder alloy has tin = lead solder or tin = lead = bismuth solder as a base material,
Lead was essential in the alloy composition.

[0003]

However, lead is a toxic heavy metal for the human body, and there is a problem of pollution of the global environment due to lead collection and disposal of lead, or adverse effects on the human body and living organisms. However, as a current situation, a large amount of lead solder alloy is used for mounting electronic parts in electronic devices.
Therefore, if lead-free solder that does not use lead can be provided, lead damage can be effectively suppressed even in the industry as a whole.

By the way, in tin-lead solder, lead has a function of lowering the melting point of tin, 232 ° C.,
Solder in which 37 wt% of lead is alloyed is widely used as a eutectic solder having a melting point of 183 ° C. That is, since the electronic components are weak to heat, it is necessary to perform the heating temperature at the time of solder joining at a low temperature, and the eutectic solder meets these requirements. However, even if the melting point of the solder is too low, if it is affected by the heat generated by the electronic component or the solar heat, it will deviate from the original purpose of solder joining. Therefore, when forming a lead-free solder, it is necessary to develop a joining alloy that is easy to solder and that is not affected by other hot atmospheres. As a condition of the alloy that can substitute for the eutectic solder, the melting point must be at least in the range of 130 to 200 ° C. Also, when soldering electrical components, it is preferable to secure heat cycle resistance in a portion where the usage environment is severe, such as in-vehicle components.

The present invention focuses on the avoidance of lead damage, and an object of the present invention is to provide a lead-free solder alloy which can sufficiently substitute the action of lead in conventional tin-lead solder when forming a lead-free solder alloy. It is a thing.

[0006]

In the present invention, in order to achieve the above-mentioned objects, an alloy is composed of a plurality of kinds of metals using tin as a base material. That is, using Sn as a base material, Bi (bismuth), Sb (antimony), and Ga (gallium) are 20 to 57% by weight, 0.2 to 5% by weight, and 0.01%, respectively.
The alloy was formulated with a distribution of ~ 1% by weight.

Further, Cu (copper) is added to the above composition in an amount of 0.
It was added in a proportion of 3% by weight or less.

Furthermore, as a more preferable ratio of each alloy composition, Bi is in the range of 20 to 35% by weight, Sb is in the range of 1 to 5% by weight, or Ga is in the range of 0.
The range was 1 to 0.5% by weight.

[0009]

Action Sn itself has no toxicity and acts to obtain wetting with respect to the joining base material, and is an essential metal as a solder base material. Bi has a function of significantly lowering the original melting point of Sn, 232 ° C., by forming an alloy with Sn. When the maximum distribution of Bi is 57% by weight, the melting point of the alloy is 139 ° C.
Go down. On the other hand, when the content is 20% by weight, the liquidus temperature of the alloy becomes about 200 ° C. Sb is dispersed in Sn to prevent the β → α transformation of Sn. Also, B
Since i itself is a brittle material, the Sn = Bi alloy also becomes brittle, but the addition of Sb also has the effect of improving the brittleness of the Sn = Bi alloy.

Ga has a melting point of 30 ° C. and reacts with oxygen in the air on the surface of the molten solder alloy. As a result, an oxide film having a spinel structure is formed, and the progress of oxidation of the alloy is stopped. Further, since the atomic radius is slightly smaller than that of Cu, which is often used as a solder joining base material, the diffusion wetting at the time of joining becomes faster and the joining strength is improved. Ga is also
Since it belongs to the group III, it has an action of forming an intermetallic compound having a high melting point with Bi and Sb belonging to the group V, hindering the crystal coarsening in the solidified structure and slowing down the modification of the structure. ing.

When the joining base material is a copper wire or a copper plate,
The base material composition dissolves quickly in tin, and copper nicks tend to occur. Further, when a Cu = Sn compound layer is formed in the vicinity of the joint in the solidified structure, the joint becomes brittle. Therefore, copper is added to the solder alloy in advance in order to suppress copper nicking of the base material. . When the joining base material is not copper, addition of copper is not essential.

[0012]

The preferred embodiments for realizing the object of the present invention will be described below. (Example 1) Bi 20 wt%, Sb 5 wt%, Ga0.
5 wt%, Cu 0.15 wt%, balance Sn (Example 2) Bi 35 wt%, Sb 1 wt%, Ga0.
1 wt%, Cu 0.15 wt%, balance Sn

The physical properties of the alloy of Example 1 have a melting point of 13
2 to 197 degrees C, strength 8.0 kgf / mm ² , elongation rate 1.7
%, Young's modulus was 9.8 × 10 ⁴ kg / cm ² . Both the wetting property and the joining fluidity on the copper plate were good. In addition, when joining, use RMA flux
It was carried out in a temperature atmosphere of 40 ° C. The physical properties of the alloy of Example 2 are as follows: melting point 133-177 degrees C, strength 8.2 kgf / m.
m ² , elongation 4.1%, Young's modulus 9.1 × 10 ⁴ kg / cm ²
Met. Both the wetting property and the joining fluidity on the copper plate were good. In addition, RMA flux was used at the time of joining, and it performed in the temperature atmosphere of 240 degreeC. Here, 0.15% by weight of Cu is added for the purpose of suppressing the copper crack of the copper plate which is the joining base material, and the joining base material is a metal other than copper. In some cases, the addition of copper may be omitted from the alloy composition.

As is apparent from the above-mentioned two examples, the lead-free solder alloy of the present invention has a melting point range which is satisfactory as a low temperature solder used for mounting electronic parts and the like, and also has good numerical values in other physical characteristics. Is shown. Example 1
It is presumed that the physical properties also show good values that do not deviate from the above ranges even at the intermediate values of the respective compositions of Example 2 and Example 2.

[0015]

As described above, the present invention is completely different from the conventional leaded solder alloy and does not use lead at all. Therefore, the problem of lead damage can be completely avoided, and Since the soldering work can be performed in the same manner as eutectic solder or at a lower temperature than that, it is possible to improve workability even when joining electronic components that are weak to heat. Moreover, since the physical properties of the solder alloy are maintained in good condition, it can be adopted as an alternative alloy having the same performance as the eutectic solder, and has a very wide range of uses.

Moreover, in the solder alloy containing Cu, it is possible to suppress copper crevices when the joining base material is copper, and it is possible to perform firm joining.

Claims (5)

(57) [Claims] 1. A lead-free solder alloy comprising Bi 20 to 57% by weight, Sb 0.2 to 5% by weight, Ga 0.01 to 1% by weight, and the balance Sn. 2. The lead-free solder alloy according to claim 1, further comprising Cu
Lead-free solder alloy with 0.3 wt% or less added. 3. The lead-free solder alloy according to claim 1, wherein Bi is in the range of 20 to 35% by weight. 4. Sb in the range of 1 to 5% by weight.
Or the lead-free solder alloy according to 2. 5. The lead-free solder alloy according to claim 1, wherein Ga is in the range of 0.1 to 0.5% by weight.