KR0177681B1 - Lead-free soldering flux - Google Patents

Abstract

An object of the present invention is to provide a lead-free solder which is excellent in spreadability and particularly suitable for wiring of electronic devices of general electronic components.

The technical gist of the present invention relates to a lead-free solder having excellent spreadability composed of Ag: 3-5%, Bi: 5-10%, Cu: 0.1-2%, and the balance Sn.

Description

Lead free solder with excellent spreadability

1 is a graph comparing the spread of the conventional solder with the lead-free solder of the present invention.

[TECHNICAL FIELD OF THE INVENTION]

The present invention relates to a lead-free solder used for electronic device wiring of electronic components, and more particularly to a tin-silver-bismuth-copper lead-free solder having excellent spreadability during soldering.

[Private Technology]

Solders used for soldering have inherent characteristics so that their use is suitable. In ordinary soldering, the melting temperature and the solidification temperature range are important. That is, the solder selected for a particular application not only has a low melting temperature that will not damage adjacent components, especially temperature sensitive components, but also has a high melting temperature range after soldering so that the bonding state is thermally stable during use. need. In addition, since most of the solder is composed of a component system in which a process reaction occurs, when a specific composition other than the process composition is obtained, the solder passes through a liquid line where solidification starts in the molten state after soldering, so that the liquid phase and the solid phase coexist, and then the solidification ends completely. It has a solidification temperature range up to a solid state line. If the solidification temperature range of the solder is large, it is necessary to have a solidification temperature range as small as possible since the solidification time after soldering may increase and shrinkage may occur. Solders having a low solidification temperature range are more advantageous for stepwise soldering in continuous automatic soldering.

As a conventional solder having the above characteristics, for example, a Sn-Pb-based alloy may be mentioned.

This Sn-Pb-based alloy is also excellent in various mechanical and physical properties, and is mainly used for structural and general electronic industries such as piping and heat exchangers. However, lead is a non-degradable metal that, once ingested, does not release and accumulates in the body. For example, the toxicity of lead as defined by the US Center for Discease Control is fatal at blood levels above 10 µg / dl, especially in children. Not only can lead to a loss of intelligence, but also lead waste contaminates the soil. In particular, traditional piping solders, such as 50Sn-50Pb or 70Sn-30Pb, can be used over a wide temperature range, form strong mechanical connections, and are very useful for copper pipe welding, but after a long time It has been found to be fatal to health and the use of lead has also been regulated in plumbing solder, such as pipes that carry drinking water. For example, in the United States, the US Environmental Protection Agency (EPA) has regulated the Toxic Substance Control Act (TSCA) since the use of lead has been fully regulated in the field of consumer paint in 1978. Under the law, manufacturers of lead-containing intermediates are obliged to dispose of and recover the final product, and the US House of Representatives proposes a 100-200% tax to finance the Pb-Cleanup fund. HR 2479), and the US Senate issued the Lead Exposure Act (S-729), which proposed full regulation of industrial lead. In addition, the Occupational Safety and Health Association (OSHA) has established lead standards that regulate the concentrations of lead allowed in the atmosphere and in the workplace, and require that employees be exposed to lead in the event of high levels of lead release. . As such, the United States law prohibits plumbers, especially 50 Sn-50Pb, prohibits the use of lead-containing solder in all parts related to beverages, and regulates the use of lead-containing solder other than piping. Is almost the same in Korea.

On the other hand, lead-free solders began to be developed in response to the regulation of lead, and lead-free solders composed of Sn-Ag (0.05-3%)-Cu (0.7-6%) were disclosed in US Patent No. 4,778,733. Solder is proposed and US Pat. No. 4,929,423 also discloses a composition consisting of Sn-Bi (0.08-20%)-Ag (0.01-1.5%)-Cu (0.02-1.5%)-P (0.01%)-rare earth mixture. Lead-free solder is proposed.

In addition, European Patent EP 0,499,452A1 suggests a lead-free solder composed of Sn 87-97%, Ag 0.1-3%, Bi 3-7%, and also Japanese Unexamined Patent Application Publication No. 5-228685 No. suggests a lead-free solder containing Sn 92-95.8%, Ag 3-5%, Bi 1.2-3%. However, since the lead-free solders are high temperature lead-free solders with high melting temperature, they are suitable for special purposes and are difficult to use for soldering general electronic components. Accordingly, the present inventors have proposed a Sn-Ag-Bi-based lead-free solder in order to compensate for the drawbacks of the conventional lead-free solder (Korean Patent Application No. 95-19012; Application Date 1995.10.30).

[Purpose of invention]

Accordingly, the present invention is an improvement of the above-described Korean Patent Application No. 95-19012, and unlike the conventional lead-free solder, the present invention is more suitable than the conventional Sn-40 Pb solder by appropriately controlling the composition of the Sn-Ag-Bi-Cu-based lead-free solder. The purpose of the present invention is to provide a Sn-Ag-Bi-Cu-based lead-free solder suitable for wiring of electronic devices having excellent spreadability.

[Configuration and Function of Invention]

The present invention for achieving the above object relates to a lead-free solder having excellent spreadability composed of Ag: 3-5%, Bi: 5-10%, Cu: 0.1-2% and the balance Sn.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

First, Ag contained in the general purpose Sn-Ag-Bi-based solder according to the present invention preferably maintains a process composition near 3% in consideration of the low melting temperature of the solder, but if it contains too much amount, the melting temperature of the solder rises rapidly. Preferably limited to 5% or less.

The Bi serves to lower the melting temperature and improve the wettability when added to a Sn-Ag alloy system, for example, a Sn-3% Ag alloy system (melting temperature of 221 ° C.). However, when Bi is contained in an amount of 5% or less, the effect is less. When 10% or more is contained, the melting temperature is low and the wettability is further improved. However, when Bi is contained, the solder itself becomes weak and the melting temperature is widened. .

The Cu plays a role of improving the spreadability because the mutual reaction is good when soldering the substrate, and the content is insufficient when the content is less than about 0.1%. However, when the Cu content is added 2% or more, the melting temperature of the lead-free solder is increased, which is not preferable as the solder.

Solder having the above composition can be cast and manufactured by a conventional method of measuring a metal raw material and dissolving it under heating or stirring using a pot or crucible in the atmosphere. At this time, when dissolved in the atmosphere, impurities in the metal raw materials or non-metallic inclusions and alloy molten metal react with the atmosphere, causing dissolved gases such as dissolved nitrogen and dissolved oxygen to remain in the solder alloy, thereby preventing wettability on the surface of the solder base material. Since solderability is degraded or voids are generated in the solder joint, problems may occur in thermal conductivity, thermal fatigue characteristics, and product reliability. Therefore, in order to minimize the impurities or non-metallic inclusions and dissolved gases in the alloy generated in the air to improve the solderability, and to improve the thermal fatigue characteristics and product reliability in the manufacture of the solder of the present invention by melting in a vacuum or inert atmosphere Among the raw materials, a dissolution method that minimizes the occurrence of dross by inhibiting oxidation of Bi and the like is more preferable. The general purpose lead-free solder of the present invention produced by this method may be produced in various forms (ingot, rectangular, circular, etc.), and may also be made of spherical powders of various sizes. In addition, in the case of powder solder, it can be manufactured as a paste by mixing with a suitable flux.

The lead-free solder according to the present invention has not only a melting point that can be used for electronic device wiring of general electronic components, but also a narrow solidification range, which is very advantageous for step-by-step automatic soldering, and has a feature of increasing spreadability than conventional Sn-Pb systems. have.

Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited to these exemplary embodiments.

Example 1

Invention Example 1

After measuring the Sn, Ag, Bi, Cu metal raw materials to have a composition as shown in Table 1, and melted in a vacuum state of 10 ^-3 torr or more using a high frequency induction furnace and then cast. The solid state temperature and the liquidus temperature at the time of solidification of the prepared alloy were measured and the results are shown in Table 1 below.

As shown in Table 1, the lead-free solder of the invention material (1) was found that the liquidus temperature is 217 ℃, the solidus temperature is 193 ℃, the solidification section is 24 ℃ suitable for general purpose lead-free solder.

Invention Example 2

After dissolving the metal raw materials using a high frequency induction furnace in the air to have a composition as shown in Table 2 and casting it, the solidification temperature and the liquidus solidification temperature of the cast alloy was measured and the results are shown in Table 2 below.

As shown in Table 2, the lead-free solder of the invention material (2) has a liquidus temperature of 213 ℃, solidus temperature of 190 ℃, solidification temperature range of 23 ℃, it can be seen that it is suitable as a general purpose lead-free solder .

Invention Example 3

The lead-free solder having a composition as shown in Table 3 below was dissolved in a high frequency induction furnace, but was cast after maintaining and dissolving inert gas (N) at 250-300 mbar. The solidus and liquidus temperatures of the cast alloys were measured and the results are shown in Table 3 below.

As shown in Table 3, the lead-free solder of the invention material (3) has a liquidus temperature of 218 ℃, solidus temperature of 198 ℃, solidification temperature range of 20 ℃, it can be seen that it is very suitable as a general purpose lead-free solder have.

Invention Example 4

A lead-free solder having a composition as shown in Table 4 was prepared in the same manner as inventive material (3), and the results of solidification temperature measurement of the prepared lead-free solder are shown in Table 4 below.

As shown in Table 4, the lead-free solder of the inventive material 4 has a liquidus temperature of 203 ° C, a solidus temperature of 185 ° C, and a solidification temperature section of 18 ° C, which is particularly suitable for low temperature. .

Invention Example 5

A lead-free solder having a composition as shown in Table 5 was prepared in the same manner as inventive material (3), and the results of measurement of solidification temperature of the prepared lead-free solder are shown in Table 5 below.

As shown in Table 5, the lead-free solder of the invention material 5 has a liquidus temperature of 230 ° C, a solidus temperature of 200 ° C, a solidification temperature section of 30 ° C, it can be seen that it is applicable to lead-free solder.

Example 2

Using a high frequency induction furnace, the invention material (3) composed of Sn-3.5% Ag-10% Bi-0.5% Cu and the conventional material composed of Sn-40Pb are melted and cast in each atmosphere, After measuring the wettability, the result is shown in FIG.

As shown in FIG. 1, it was found that the invention material 3 had better wettability and superior solderability than the conventional material.

[Effects of the Invention]

As can be seen from the above embodiment, the lead-free solder according to the present invention does not contain lead as compared to the conventional Sn-Pb-based solder not only can improve the working environment, etc., but also has a low melting temperature, narrow solidification section, particularly spreadability Because of this very excellent, there is an effect that can be applied to a variety of applications, such as wiring for general electronic components compared to the conventional Sn-Ag-Bi lead-free solder.

Claims (1)

A lead-free solder having excellent spreadability, which is composed of Ag: 3-5%, Bi: 5-10%, Cu: 0.1-2%, and the balance Sn.