KR100293180B1 - Lead free solder paste - Google Patents

Abstract

PURPOSE: Provided is Sn-Ag-Si-Bi based lead free solder, which has superior mechanical strength at high temperatures. This lead free solder has melting point applicable for wiring of electronic components as well as is suitable to automatic welding due to its narrow solidification temperature ranges. CONSTITUTION: The lead free solder comprises Ag 3.0-4.5wt.%, Si 0.05-0.3wt.%, Bi 5-10wt.%, and a balance of Sn, wherein solidus curve is 195 to 205deg.C and liquidus temperature is 210 to 218deg.C.

Description

Lead-free Solder for High Temperature

1 is a graph showing the solderability of the lead-free solder according to the present invention

2 is a graph comparing the mechanical properties of the conventional solder and the lead-free solder of the present invention

3 shows a microstructure photograph of a lead-free solder according to the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to lead-free solder used for electronic device wiring of electronic components, and more particularly, to tin-silver-bismuth-silicon-based lead-free solder suitable for high temperature.

Solders used for soldering have inherent characteristics to suit their intended use. In conventional soldering, the melting temperature and the solidification temperature range are important.

That is, the solder chosen according to a particular application must not only have a low melting temperature to damage adjacent parts, particularly temperature sensitive parts, but also have a high melting temperature range after soldering to ensure thermally stable joint conditions. Do.

In addition, since most of the solder is composed of a component system in which a process reaction occurs, if 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 solidus 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 be long and shrinkage may occur. In the case of solders having a low solidification temperature range, there is an advantage in staged soldering during continuous automatic soldering.

Conventional solders having the above characteristics include, for example, Sn-Pb-based alloys. 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 pipe solders, such as 50Sn-50Pb or 70Sn-30Pb, can be used over a wide temperature range and form strong mechanical connections and are very useful for copper pipe welding, but after a long time the lead has dissolved in water The use of lead has also been regulated in plumbing solders, such as pipes that carry drinking water, when it has been found to be harmful to health.

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 intermediates containing lead are obligated to dispose of and recover the final product, and the US House of Representatives proposes a 100-200% tax for the Pb-Cleanup fund. 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 a lead standard that regulates the concentration of lead allowed in the atmosphere and in the workplace, and requires that employees' exposure to lead be minimized in situations where high levels of lead are released into the atmosphere. . As such, the US law prohibits plumbers, especially 50Sn-50Pb, prohibits the use of lead-containing solder in all areas related to beverages, and regulates the use of lead-containing solder other than piping. This trend is almost the same in Korea.

In the meantime, lead-free solders have begun to develop as regulations on lead have emerged. According to U.S. Patent No. 1,778,733, a lead-free solder composed of Sn-Ag (0.05-3%)-Cu (0.7-6%) is proposed, and U.S. Patent No. 4,929,423 discloses Sn-Bi (0.08-20 Lead-free solder composed of%)-Ag (0.01-1.5%)-Cu (0.02-1.5%)-P (0.01%)-rare earth mixture is proposed.

In addition, a lead-free solder composed of Sn 87-97%, Ag 0.1-3%, and Bi 3-7% is proposed according to US Pat. No. 499,452 Al, and Sn 70 according to US Pat. No. 5,256,370. Lead-free solder composed of -92%, Ag 1-6% and In 4-35% has been proposed. However, the lead-free solders described above are more used for general purpose lead-free solders and are not suitable for high temperature use.

As a representative example of the lead-free solder for Goyon, Japanese Unexamined Patent Application Publication No. 5-228685 proposes a lead-free solder containing Sn 92-95.8%, Ag 3-5%, and Bi 1.2-3%. However, the lead-free solder has a disadvantage of insufficient uniform strength after soldering.

Therefore, the present inventors have made a number of studies and experiments to solve the above-mentioned disadvantages of the conventional lead-free solder, and proposed the present invention based on the results. The present invention provides Si-Ag-Bi-based lead-free solder appropriately. The purpose of the present invention is to provide a high-temperature Sn-Ag-Bi-Si-based lead-free solder that maintains a uniform strength after soldering, in particular, compared to conventional Sn-40Pb solder.

The present invention for achieving the above object relates to a high-temperature lead-free solder composed of Ag: 3.0-4.5%, Bi: 5-10%, Si: 0.05-0.3% and the balance Sn.

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

First, Ag contained in the high-temperature Sn-Ag-Bi-Si-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 is added at least 3.0% to improve thermal fatigue characteristics. .

However, if it contains too much amount, it is preferable to limit the melting temperature of the solder to 4.5% or less.

The Bi serves to lower the melting temperature and improve the wettability when added to the Sn—Ag alloy system, for example, Sn-3% Ag alloy system (melting temperature of 221 ° C.). If the Bi content is less than 5%, the Bi content is less than 10%. The Bi content is less than 10% and the melting temperature is low and the wettability is further improved. However, the Bi content becomes more vulnerable and the melting temperature becomes wider.

The Si serves to maintain uniform strength even when only a small amount is added to the lead-free solder.

Solder having the above composition can be cast and produced by a conventional method of measuring a metal raw material and dissolving it by heating and stirring using a pot or crucible in the air. 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 solderability on the solder base surface. Because of poor performance or voids in the solder joint, there is a possibility of problems 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 produced in the air in order to improve the solderability and to improve the thermal fatigue characteristics and product reliability in the manufacture of the solder of the present invention dissolved in vacuum or inert atmosphere Therefore, a dissolution method for minimizing dross generation by inhibiting oxidation of Bi and the like, in particular, is more preferable.

The lead-free solder for high temperature of the present invention produced by this method can be produced in various forms (ingot, rectangular, circular, etc.), and can also be made of spherical powders of various sizes. In addition, in the case of powder solder, it is possible to prepare a solder paste by mixing with a suitable flux.

The lead-free solder of the present invention is not only has a melting point usable for electronic device wiring of general electronic components, but also has a narrow solidification range, which is very advantageous for stepwise automatic soldering, and is more uniform than conventional Sn-Pb-based or high temperature lead-free solders. Mechanical strength is increased.

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, Si metal raw materials to have a composition as shown in Table 1, using a high frequency induction furnace was melted in a vacuum state of 10 ^-3 torr or more and then cast.

For the prepared alloy, the solidus temperature and the liquidus temperature at the time of solidification were measured and the results are shown in Table 1 below.

TABLE 1

As shown in Table 1, the lead-free solder of Inventive Example (1) has a liquidus temperature of 218 ° C, a solidus temperature of 204 ° C, and a solidification section of 14 ° C, which is very suitable for high temperature 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.

TABLE 2

As shown in Table 2, the lead-free solder of Inventive Example 2 has a liquidus temperature of 215 ° C, a solidus temperature of 203 ° C, and a solidification temperature range of 12 ° C, which is very suitable for high temperature lead-free solder. Can be.

Invention Example 3

Lead-free solder having a composition as shown in Table 3 was dissolved in a high frequency induction furnace, but was cast after maintaining inert gas (Ar) at 250-300 mbar to melt. The solidus and liquidus temperatures for the cast alloy were measured and the results are shown in Table 3 below.

TABLE 3

As shown in Table 3, the lead-free solder of Inventive Example (3) has a liquidus temperature of 218 ° C, a solidus temperature of 195 ° C, and a solidification temperature range of 23 ° C, which can be used as a high-temperature 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 in Example 3, and the results of solidification temperature measurement of the prepared lead-free solder are shown in Table 4 below.

TABLE 4

As shown in Table 4, the lead-free solder of Inventive Example 4 has a liquidus temperature of 215 ° C, a solidus temperature of 200 ° C, and a solidification temperature section of 15 ° C, which is suitable for high temperature.

Example 2

The wettability was measured for Inventive Example 2 composed of Sn-3% Ag-6.9% Bi-0.1% Si in the air using a high frequency induction furnace, and the results are shown in FIG.

As shown in FIG. 1, in the invention example (2), the wettability in the short time was excellent and the solderability was excellent.

Example 3

In order to find out the mechanical properties of the lead-free solder and the conventional solder according to the present invention, the mechanical properties of the conventional material and Sn Example (2) of Sn-40Pb solder were measured, and the results are shown in FIG.

As shown in FIG. 2, in the case of the invention example (2), it can be seen that the tensile strength is extremely superior to the conventional material, which means that the final bonding strength after soldering is better when using the lead-free solder of the present invention. do.

In order to examine this fact through the microstructure, the microstructure of the Invention Example (2) was observed, and the results are shown in FIG. As shown in FIG. 3, in the case of the lead-free solder of Inventive Example (2), it was confirmed that the Si precipitates were uniformly distributed so that the lead-free solder according to the present invention exhibited superior mechanical properties as compared with the conventional lead-free solder.

As can be seen from the above embodiment, the lead-free solder according to the present invention has excellent mechanical properties as compared to the conventional Sn-Pb-based solder, so that the final bonding strength after soldering is not only superior to that of the conventional solder, but also does not contain lead. The working environment can be improved, and in particular, since the melting temperature is low and the solidification section is narrow, there is an effect that can be variously applied for wiring of general electronic components, compared to the conventional Sn-Ag-Bi lead-free solder for high temperature.

Claims (2)

High-strength lead-free solder characterized by weight percent Ag: 3.0-4.5%, Bi: 5-10%, Si: 0.05-0.3% and balance Sn High temperature lead-free solder, characterized in that the solidus temperature is 195-205 ℃, the liquidus temperature is 210-218 ℃, including Ag, Bi, Si and Sn