JPH0919792A - Lead-free solder of which mechanical property is excellent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a lead free solder having a melting point and solidification temp. range usable for electronic equipment wiring as well as an increased mechanical strength by specifying a composition of lead free solder. SOLUTION: A lead free solder has a composition consisting of, by weight, 4-9% Zn, 2-5% indium, 1-24% bismuth and the balance Sn. By welting in vacuum atmosphere or inert gas atmosphere when producing a solder, a melting method to minimize generation of dross with suppressing oxidation of materials of Bi, Zn, etc., is desirable. By this method, the solder can be produced to various forms (ingot, rectangular shape, round shape, etc.), further to a spherical shaped powder of various sizes as well.

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 wiring electronic equipment such as printed circuit boards and hybrid boards, and more specifically, tin-zinc-indium having excellent mechanical properties. -It relates to bismuth-based lead-free solder.

[0002]

2. Description of the Related Art Sn-Pb alloys, which have been used most often among solders, are excellent in various mechanical and physical properties and are mainly used for structures such as pipes and heat exchangers. Widely used for general electronics industry. However, S
In the case of solder containing lead such as n-Pb alloy,
Lead itself is a metal that does not decompose, and once it is ingested, it is not released and accumulates in the body. As an example, Center for Disease in the United States
The toxicity of lead specified in the case control is fatal at a blood concentration of 10 μg / dl or more, and particularly, it induces a decrease in intelligence in infants. Not only that, but also lead waste pollutes the soil.

Particularly, 50Sn-50Pb and 70Sn-3
Traditional piping solders such as 0Pb can be used in a wide temperature range and form strong mechanical joints, which is very useful for copper pipe welding, but lead dissolves in water and after a long time Has been found to cause fatal damage to health, and the use of lead has begun to be regulated in solders for pipes such as pipes that carry drinking water.

[0004] With the advent of such lead control measures, the development of lead-free solder has recently started.
By way of example, Sn-Ag (0.005) is presented in US Pat. No. 1,778,733.
-3%)-Cu (0.7-6%) lead-free solder has been proposed. Further, U.S. Pat. No. 4,929,423 discloses Sn-Bi (0.08-20%). -Ag (0.
01-1.5%)-Cu (0.02-1.5%)-P
(0.01%)-A lead-free solder having a composition of a rare earth mixture has been proposed. However, the lead-free solder or the like is used for piping and has a high melting temperature and a wide melting temperature range, so that it is difficult to apply it to electronic parts. Lead-free solders used for electronic parts have unique characteristics so that they are suitable for the operating temperature. However, in the case of lead-free solders for electronic parts, its melting temperature and solidification temperature range are particularly important. Is.

That is, the lead-free solder for an electronic component selected according to a specific application should not only have a low melting temperature so as not to damage adjacent components, particularly temperature-sensitive components, but also after soldering. Must have a high melting temperature range so that the bonding state is thermally stable during use.

Furthermore, since most lead-free solders are composed of component systems in which a eutectic reaction occurs, when they have a specific composition other than the eutectic composition, they pass through the liquidus line where solidification starts from the molten state after soldering. As a result, the liquid phase and the solid phase coexist, and then there is a solidification temperature range that reaches the solidus line at which solidification is completely completed, but the solidification temperature range of lead-free solder for electronic parts is large by any chance. In this case, since the solidification time after soldering may be prolonged and a shrinkage phenomenon may occur, a lead-free solder having a solidification temperature range that is as small as possible is more advantageous for stepwise soldering during continuous automatic soldering. Because there is a point.

On the other hand, there is a Sn-Zn-In lead-free solder recently developed as a lead-free solder suitable for electronic parts and the like.
A typical example thereof is US Pat. No. 5,242,6.
The lead-free solder presented in the specification of No. 58 can be mentioned.
The lead-free solder presented in US Pat. No. 5,242,658 is Sn: 72.8-89.4%, Zn: 6.7-1.
The composition is 9.2% and In: 2.7 to 19.4%. However, in the case of the lead-free solder, In is added to the conventional Sn-Zn alloy.
To reduce the melting temperature, solve the problems of ln oxidation, corrosion, and scale formation, and have a narrow melting temperature range with a low melting temperature. However, since the lead-free solder has a fine structure in which dendrites having an irregular needle-like pattern are formed while In is added, the mechanical strength value is relatively reduced and the final conforming strength deteriorates. There is a disadvantage

[0008]

Therefore, the present invention has been proposed to solve the above problems of the conventional lead-free solder, and is suitable for the conventional Sn-Zn-In lead-free solder of the present invention. By adding a sufficient amount of Bi so as to suppress the formation of needle-like dendrites and have another fine structure, not only has a melting point and a solidification temperature range usable for electronic device wiring, In particular, it is an object to provide a lead-free solder with increased mechanical strength.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above object, and the present invention provides
Then, Zn: 4 to 9%, In: 2 to 5%, Bi: 1 to 24
% And the balance Sn, and lead-free solder having excellent mechanical properties.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

First, it is preferable that the composition ratio of zinc contained in the lead-free solder according to the present invention be maintained near the eutectic composition (Sn-9Zn). If the zinc content is too small or too large, the melting temperature range of the solder is widened. Therefore, the zinc content in the lead-free solder of the present invention is 4 to 9% by weight (hereinafter, simply referred to as%). ) Should be restricted to.

Further, the indium component lowers the melting temperature of the lead-free solder while improving the wettability, but the indium content should be limited to 2 to 5%.
If the content of indium is less than 2%, the effect is small, and if it exceeds 5%, the γ-Sn phase is precipitated at room temperature and the γ-Sn phase (Hcxagonal) becomes α-S.
A phase change occurs in the n-phase (face centered cubic), and eventually the thermal fatigue property of the joint is deteriorated.

Further, in the case of bismuth which is added in combination with the above indium, it plays a role of lowering the melting temperature of the solder, but more importantly, it suppresses the formation of needle-like dendrites due to the addition of indium to improve the mechanical strength. Play a role in increasing. At this time, in the case of bismuth, needle-like dendrites can be suppressed even if added in a small amount, but if the addition amount is too large, the melting temperature is greatly lowered, and in order to widen the melting temperature range, such a point is taken into consideration. Considering this, the content of bismuth should be set to 1 to 24%.

The solder having the above composition can be manufactured by a usual casting method in which a metal raw material is weighed and melted in the air while heating and stirring with a pot or a crucible. At this time, when dissolved in the atmosphere, impurities or non-metallic inclusions in the metal raw material and the molten alloy react with the atmosphere, and dissolved gases such as dissolved nitrogen and dissolved oxygen remain in the solder alloy. May impair the wettability on the surface of the solder base material and reduce the solderability,
Since the pores are generated in the solder joint, the heat conduction also has a problem that the thermal fatigue characteristics and the product reliability are problematic.
Therefore, impurities or non-metallic inclusions generated during alloy production in the atmosphere and dissolved gas in the alloy are minimized,
In order to improve the solderability and improve the thermal fatigue property and the reliability of the product, the solder of the present invention is melted in a vacuum state or an inert atmosphere to suppress the oxidation of raw materials such as Bi and Zn. More desirable is a dissolution method that minimizes the formation of scale.

The lead-free solder of the present invention manufactured by such a method can be manufactured in various forms (ingot, rectangle, circle, etc.), and also in spherical powders of various sizes. You can Furthermore, in the case of solder in powder form, it is possible to prepare a paste by mixing with a suitable flux.

The lead-free solder of the present invention thus manufactured is
Not only does it have a melting point that can be used for wiring electronic devices of general electronic parts, but it is also very advantageous for stepwise automatic soldering because it has a narrow solidification range.
It has a feature that mechanical strength is increased as compared with Zn-In based solder. In particular, the lead-free solder of the present invention has a composition of Zn: 5.
-9%, In: 2-5%, Bi: 1-10%, and the balance Sn is even more desirable.

[0017]

EXAMPLES The present invention will be described below with reference to examples, but these are representative examples and the present invention is not limited to these examples.

(Examples 1 to 11) (Comparative Examples 1 and 2) Sn, Zn, In having the composition shown in Table 1 below.
The Bi metal raw material was weighed, melted in the atmosphere using a high frequency induction furnace, and then cast.

Further, for comparison, conventional Sn, Zn, I
An n-containing solder was cast.

For each of the cast alloys, the liquidus temperature and the solidus temperature during solidification were measured, and the results are shown in Table 1.
It was shown to.

[0021]

[Table 1] As shown in Table 1 above, Examples 1 to 11 according to the present invention
In the case of, it can be seen that compared with the conventional Sn-Zn-In lead-free solder, the solidification temperature range of almost the same level can be provided, and the melting point can be further lowered. This means that the Sn-Zn-In-Bi lead-free solder of the present invention has soldering characteristics that can be used for electronic parts and the like, like the conventional lead-free solder.

Mechanical Properties In order to consider the mechanical properties of the lead-free solder of the present invention and the conventional solder, Sn-40Pb, Sn-8Zn-5I.
Mechanical properties of n solder and Examples 1 and 5 were measured, and the results are shown in FIG.

As shown in FIG. 1, it was found that the tensile strength of Examples 1 and 5 was extremely superior to that of the conventional solder.

Further, conventional Sn-9Zn, Sn-8Zn
The stress-deformation relationship was measured for -5In solder and Examples 1 and 5, and the results are shown in FIG.

As shown in FIG. 2, in the case of Examples 1 and 5, Sn-9Zn and Sn-8Zn-5 of the conventional solder were used.
It has been found that a large stress is required for deformation as compared with In lead-free solder.

In consideration of the above mechanical characteristics, the lead-free solder of the present invention is excellent in final joint strength as compared with the conventional Sn-Pb, Sn-Zn or Sn-Zn-In solder. You can know.

In order to consider such a fact through the microstructure, the above Sn-8Zn-5In alloy and Example 1 were used.
On the other hand, the microstructure was observed and the result is shown in FIG.

As shown in FIG. 3, in the case of Sn-8Zn-5In alloy, which is a conventional lead-free solder, dendrites in the form of needles are observed, while in the case of the lead-free solder of Example 1, Bi
It can be seen that the addition of is suppressed by irregular needle-like dendrites. After all, it has been confirmed that the lead-free solder of the present invention exhibits excellent mechanical properties as compared with the conventional lead-free solder due to such structural difference.

[0029]

As described above, the lead-free solder of the present invention not only has almost the same soldering characteristics as the conventional Sn-An-In lead-free solder but also has excellent mechanical properties, There is an effect that the final joint strength is excellent when used for wiring parts.

[Brief description of the drawings]

FIG. 1 is a graph showing mechanical characteristics of a conventional solder and a lead-free solder of the present invention.

FIG. 2 is a graph showing a stress-deformation relationship between a conventional solder and a lead-free solder of the present invention.

FIG. 3 is a microstructure photograph of a conventional lead-free solder and the lead-free solder of the present invention.

 ─────────────────────────────────────────────────── ───Continued from the front page (72) Inventor Yongdeok Dragon South Korea Seoul Gangnam-Kuchun Dam-Don 63 Hyosun Villa 33-203 (72) Inventor Lee Hook Im Korea Daejon Yousung-Queun-Don 99 Humbit Apartment 101-1203

Claims (5)

[Claims] 1. Zn: 4-9%, In: 2- by weight%
Lead-free solder with excellent mechanical properties, characterized in that the composition is 5%, Bi: 1 to 24%, and the balance Sn. 2. Zn: 5-9%, In: 2 by weight%
The lead-free solder according to claim 1, which has a composition of 5%, Bi: 1 to 10%, and the balance Sn. 3. Zn: 7-9% and In: 2 by weight%
The lead-free solder according to claim 1, which has a composition of 3%, Bi: 4 to 9%, and the balance Sn. 4. Zn: 8-9%, In: 4-
The lead-free solder according to claim 1, which has a composition of 5%, Bi: 6 to 10%, and the balance Sn. 5. A solidus temperature of 140 to 193 ° C., a liquidus temperature of 167 to 196 ° C., and excellent mechanical properties characterized by including Zn, In, Bi and Sn. Lead-free solder.