JP3346848B2 - 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 a lead-free (non-Pb) solder.

[0002]

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

[0003]

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

By the way, in tin-lead solder, lead has the effect of lowering the melting point of tin, 232 ° C.,
Solder in which lead is alloyed at 37% by weight is widely used as a eutectic solder having a melting point of 183 ° C. That is, since electronic components are vulnerable to heat, it is necessary to perform heating at a low temperature at the time of soldering, and eutectic solder meets these requirements. However, even if the melting point of the solder is too low, it is affected by the heat generated by the electronic components and the solar heat, which deviates from the original purpose of the solder joint. Therefore, when forming a lead-free solder, it is necessary to develop a joining alloy that is easily solderable and is not affected by an external heat atmosphere. The condition of the alloy which can be substituted for the eutectic solder is that the melting point is at least 130 to 200 ° C.
Must be in the range. More preferably, a temperature close to 183 ° C., which is the melting point of the conventional eutectic solder, can be used as it is without having to modify the current soldering line. Also, when soldering electrical components, it is preferable to ensure heat cycle resistance in a severe use environment such as in-vehicle components.

An object of the present invention is to provide a lead-free solder alloy which can sufficiently substitute for the action of lead in conventional tin-lead solder when forming a lead-free solder alloy, focusing on avoiding lead damage. Things.

[0006]

In the present invention, in order to achieve the above-mentioned object, 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), Zn (zinc), Ag
(Silver) was distributed at 10 to 20% by weight, 0.1 to 5% by weight, 4 to 6% by weight, and 0.1 to 3% by weight, respectively, to form alloys.

[0007]

[Action] Sn itself has no toxicity and has a function of obtaining wetting of the joining base material, and is an essential metal as a solder base material. Bi has a function of drastically lowering 232 ° C., which is the original melting point of Sn, by forming an alloy with Sn. 20% by weight of Bi
, The liquidus temperature of the alloy drops to about 200 ° C. The addition of Zn acts to achieve a solidus temperature approaching that of conventional Sn-Pb eutectic solders. If the liquid phase temperature is lowered by adding only Bi, the solid phase temperature drops below a predetermined temperature. The addition of Zn prevents the solid phase temperature from dropping below a predetermined temperature due to Bi, and maintains the solid phase temperature. In the case of the Sn-Zn alloy having a 91: 9 distribution, a eutectic having a melting point of 199 ° C. is obtained.
Since the content of i is large, the reaction of Bi-Zn and Bi-Sn is also considered. Therefore, the content of Zn is determined in consideration of these three types of reactions.

Sb is dispersed in Sn to form Sb.
Prevent β → α transformation of n. Further, since Bi itself is a brittle material, the Sn = Bi alloy also becomes brittle. However, by adding Sb and dispersing it in Sn, the toughness is increased, and
It also has the effect of improving the brittleness of the n = Bi alloy. Since Sb is completely mixed with Bi, no adverse effect is caused by the addition of Sb. Ag has the smallest atomic radius among the components, and accelerates the diffusion speed to the joining base material during the melting of the solder. This improves wettability and increases the bonding strength between the solder alloy and the base material. Ag is dispersed in the alloy and increases the impact strength. These effects gradually appear from 0.1% by weight and gradually increase, but if it exceeds 3% by weight, the melting point of the alloy becomes higher than the expected upper limit.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments for realizing the object of the present invention will be described below. (Example 1) A solder alloy of 14 wt% Bi, 2 wt% Sb, 5 wt% Zn, 0.3 wt% Ag, and the balance Sn was prepared. (Example 2) A solder alloy of 14 wt% Bi, 2 wt% Sb, 5 wt% Zn, 2 wt% Ag, and the balance Sn was prepared.

The physical properties of the alloy of Example 1 are as follows:
5-189 ° C., tensile strength 7.3 kgf / mm ² , elongation 1.
It was 6% and the Young's modulus was 9.3 × 10 ⁴ kg / cm ² . Both the joining wetting property and the joining fluidity on the copper plate were good. In addition, RMA flux is used for joining,
The test was performed in a temperature atmosphere of 40 ° C. Physical properties of the alloy of Example 2 were as follows: melting point: 182 to 183 ° C .; tensile strength: 6.7 kg.
f / mm ² , elongation 1.1%, Young's modulus 9.4 × 10 ⁴ kg / c
It was m ^2. Both the joining wetting property and the joining fluidity on the copper plate were good. The joining was performed in an atmosphere of 240 ° C. using an RMA flux.

As is apparent from the results, the melting points of the two alloys are very close to 183 ° C., which is the melting point of the eutectic solder.
It can be understood that there is no problem even if the currently used soldering line is diverted as it is. The liquidus temperature of the Sn alloy when only 14% by weight of Bi is added is about 210 ° C., and the solid phase temperature is lower than 180 ° C.
The addition of 5% by weight of Zn acted synergistically, and was able to suppress the drop in solidus temperature while lowering the liquidus temperature.

As is apparent from the above two embodiments, the lead-free solder alloy of the present invention achieves a working temperature almost equal to that of a conventional Sn-Pb eutectic solder as a low-temperature solder used for mounting electronic parts and the like. Is possible,
Other physical properties also show good values. Even in a range other than those of Example 1 and Example 2, the melting point is 200.
If the distribution of Bi and Zn is adjusted so as not to exceed the temperature C and not to lower the solid phase temperature, it is presumed that the physical properties show good values which do not greatly deviate from the above range.

[0013]

As described above, the present invention is completely different from the conventional leaded solder alloy and uses no lead, so that the problem of lead damage can be completely avoided. In addition, since the soldering operation can be performed at the same temperature as that of the conventional Sn-Pb eutectic solder, it is possible to join electronic components that are vulnerable to heat without changing the current working line environment. In addition, since the physical properties of the solder alloy have also maintained a good state, it can be adopted as an alternative alloy having the same performance as the conventional eutectic solder,
Very wide use.

Claims (1)

(57) [Claims] 1. A lead-free solder alloy comprising 10 to 20% by weight of Bi, 0.1 to 5% by weight of Sb, 4 to 6% by weight of Zn, 0.1 to 3% by weight of Ag, and the balance Sn.