KR100756072B1 - Lead-free solder alloy - Google Patents

Abstract

A lead-free solder alloy which can obtain far improved mechanical properties and soldering strength as well as a dross reduction effect as compared with a conventional solder alloy even without using lead, and can minimize the influence on the human body due to gas and the like generated during soldering is provided. A lead-free solder alloy comprises 0.2 to 2.5 wt.% of silver(Ag), 0.1 to 2.0 wt.% of copper(Cu), 0.001 to 0.1 wt.% of nickel(Ni), 0.001 to 0.5 wt.% of phosphorous(P), 0.01 to 0.08 wt.% of bismuth(Bi), and the balance of tin(Sn).

Description

Lead-free solder alloy

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead-free alloy for soldering, and relates to a lead-free alloy designed to prevent damage caused by poisoning of lead by soldering by an alloy containing no lead.

In general, soldering melts solder to bond metals, and therefore, metals having a lower melting temperature than metals to be joined are used, such as solders that are melted at a temperature lower than the melting temperature of lead (327 ° C) and light solders having a melting temperature of generally 450 ° C or higher. Is roughly divided into. The lead components are lead and tin, and the tensile strength and shear strength are different depending on the content. On the other hand, braze is formed in the form of powder, band, wire, and the like, and copper (Cu), zinc (Zn), and lead (Pb) include brass lead and silver (Ag), which are added to improve flowability.

In general, when an electronic device is disposed of due to a malfunction, it is not incinerated, but is cut and embedded in the ground as a stable industrial waste. Recently, however, the landfilled electronic air has become a problem. In other words, a large amount of fossil fuel is used to generate a large amount of sulfur oxides and nitrogen oxides in the air, and acid rain is generated by non-passing the air in an acidic state. Such acid rain penetrates into the ground, elutes harmful metals such as lead from buried electronics, and contaminates groundwater, and drinking this groundwater for a long time may lead to lead poisoning. If there is a problem that accumulates in the human body through the respiratory system has a deadly effect on the human body called lead poisoning.

Lead-free solders developed to date include tin (Sn) as a main component, copper (Cu), silver (Ag), bismuth (Bi), zinc (Zn), nickel (Ni), phosphorus (P), etc. The metal of is added. Representative compositions of lead-free solders include Sn-0.7 wt% Cu, Sn-3.5 wt% Ag, Sn-58 wt% Bi, Sn-3.0 wt% Ag-0.5 wt% Cu alloys. It is used in combination.

However, these lead-free solders have problems with each alloy. For example, Sn-Zn-based solders such as Sn-9% by weight Zn tend to form a thick oxide film because zinc (Zn) is a very easy metal to oxidize, and poor wettability in air soldering. In addition, Sn-Bi-based solders such as Sn-58 wt% Bi have a weak mechanical strength due to the properties of bismuth (Bi), and there is a concern that the reliability of the solder joint is reduced.

Currently, lead-free solder is most practically considered to include copper (Cu) in Sn-Ag-based and Sn-Ag-based solders such as Sn-Cu-based, such as Sn-0.7% by weight Cu, and Sn-3.5% by weight-Ag. Sn-Ag-Cu-based solder was added.

However, Sn-Cu system such as Sn-0.7 wt% Cu is inexpensive in terms of cost but lacks wettability in soldering. On the other hand, the Sn-Ag-Cu system in which a small amount of copper (Cu) is added to Sn-Ag-based and Sn-Ag-based solders such as Sn-3.5 wt% Ag has good wettability but contains expensive silver (Ag). When the cost is high and the silver content is reduced for cost reduction, the wettability and the alloy strength of the solder are reduced. In addition, since the melting point is about 50 ~ 100 ℃ higher than the conventional solder of the Sn-37Pb alloy, it is inevitable to change the bonding facilities and processes, it is necessary to review the heat resistance limit when using the existing PCB.

The present invention has been invented to solve such a conventional problem, it is to be soldered without including lead in the components of the solder, it is characterized in that the damage to the human body by the lead can be prevented. Lead-free alloys tend to vary greatly in their inherent properties depending on the trace elements added and their content.

Therefore, the present invention is based on the tin (Sn) and to improve the workability and hardness to increase the mechanical properties and to minimize the amount of dross in the production of lead-free solder silver (Ag), copper (Cu) ), Phosphorus (P), nickel (Ni) is added, and bismuth (Bi) is added to improve wettability.

The present invention is 0.2 to 2.5% by weight of silver (Ag), 0.1 to 2.0% by weight of copper (Cu), 0.001 to 0.1% by weight of nickel (Ni), 0.001 to 0.5% by weight of phosphorus (P), bismuth ( A lead-free alloy for soldering, wherein Bi) is 0.01 to 0.08% by weight and the remainder is made of tin (Sn).

Tin (Sn) is an essential metal of a solder substrate which is not self toxic and serves to provide wettability to the bonded base material.

Silver (Ag) has a wettability-improving effect, improves mechanical performance, and plays a role in transformation. However, as the silver (Ag) content increases, the structure becomes finer, the strength increases, and at the same time, the coarse primary Ag ₃ Sn is generated, which is likely to become a defect. Investigation of the effect of Ag (Ag) content on the Ag ₃ Sn primary formation revealed that it occurs in the range of about 3.2 wt% or more. The mechanical strength increases in proportion to the amount added up to 3.5 wt%, and if it is higher than that, there is little change in the amount of silver (Ag) in the practical range. In the present invention, silver (Ag) is contained in 0.2 to 2.5% by weight. If the content exceeds 2.5% by weight, the effect of improving the wettability and the mechanical performance is insignificant. If the content is less than 0.2% by weight, there is little effect on the improvement of the solder properties.

Copper (Cu) is characterized by not being mostly dissolved in tin (Sn), and is converted to Cu ₆ Sn ₅ microdispersion. The microstructure of the alloy can be refined to improve bonding strength and increase viscosity, and to suppress erosion of electronic components and printed circuit boards. Copper (Cu) is contained in the present invention at 0.1 to 2.0% by weight. If the copper (Cu) content exceeds 2.0% by weight, the melting point may rise sharply, causing defects in the alloy composition, and less than 0.1% by weight has no effect on improving solder properties.

Nickel (Ni) helps to dissolve intermediates such as Cu ₆ Sn ₅ at trace addition. It also creates a smooth surface structure. This reduces the incidence of coagulation cracks and has little effect on wettability. In the present invention is contained 0.001 ~ 0.1% by weight. If the nickel (Ni) content is less than 0.001% by weight does not help the dissolution of the intermediate product, when contained more than 0.1% by weight, the solder melting point is improved.

Bismuth (Bi) has an excellent effect on the melting point of the solder alloy composition when added. Therefore, from early on, research has been actively conducted on low melting lead-free solder materials. However, if the structure is a process composition, it becomes a simple Bi / Sn process structure, but there is a feature not found in other alloy systems in which a large amount of bismuth (Bi) is dissolved in the tin (Sn) matrix. In addition, because of its brittle nature, which is inherently brittle, there is a concern that the soldering reliability of the solder may be reduced when a large amount is added. Addition of a large amount of bismuth (Bi) can be inferred that bismuth (Bi) is crystallized to a coarse shape of 10 µm or more, which adversely affects the structure of the solder. In addition, a small amount of bismuth (Bi) has been reported to improve the wettability of the solder.

Therefore, in the present invention, in order to obtain the effect of improving the wettability according to the addition of a small amount of bismuth (Bi), 0.01 to 0.08% by weight of bismuth (Bi) is contained. When it contains more than 0.08% by weight, the effect of improving wettability decreases and brittleness gradually increases. Therefore, when a large amount is contained, the mechanical properties and spreadability of the joint cannot be properly obtained, and in the case of 0.01 wt% or less, the wettability enhancing effect due to the addition of bismuth (Bi) cannot be effectively obtained.

The addition of phosphorus (P) is effective in preventing the oxidation of the solder. In the production of lead-free solder, phosphorus rises to the upper layer in the molten state so that a film is formed in contact with oxygen in the air, thereby minimizing the amount of dross. In the present invention, 0.001 to 0.5% by weight is contained. If the amount of phosphorus (P) is less than 0.001% by weight, it is not effective in preventing oxidation and improving wettability. If the amount of phosphorus (P) is more than 0.5% by weight, the viscosity of the solder is increased to cause defects such as bridges during soldering.

Hereinafter, preferred embodiments of the present invention will be described.

(Example 1)

A lead-free alloy was prepared in which 0.3 wt% silver, 0.7 wt% copper, and 0.01 wt% phosphorus were tin.

(Example 2)

A lead-free alloy was prepared in which 0.3 wt% silver, 0.7 wt% copper, 0.05 wt% nickel, and 0.01 wt% phosphorus were tin.

(Example 3)

A lead-free alloy was prepared in which 0.3 wt% silver, 0.7 wt% copper, 0.05 wt% nickel, 0.005% bismuth, and 0.01 wt% phosphorus were tin.

(Example 4)

A lead-free alloy was prepared in which 0.3 wt% silver, 0.7 wt% copper, 0.05 wt% nickel, 0.03% bismuth, and 0.01 wt% phosphorus were tin.

(Example 5)

A lead-free alloy was prepared in which 0.3 wt% silver, 0.7 wt% copper, 0.05 wt% nickel, 0.05 wt% bismuth, and 0.01 wt% phosphorus were tin.

(Example 6)

A lead-free alloy was prepared in which 0.3 wt% silver, 0.7 wt% copper, 0.05 wt% nickel, 0.08% bismuth, and 0.01 wt% phosphorus were tin.

(Example 7)

A lead-free alloy was prepared in which 0.3 wt% silver, 0.7 wt% copper, 0.05 wt% nickel, 0.1 wt% bismuth, and 0.01 wt% phosphorus were tin.

division Chemical composition (% by weight) Solid State Temperature (℃) Liquid Temperature (℃) Wetting Force Fmax (mN) Wetting time T1 (sec) Remark silver Copper sign nickel Bismus Example 1 Remainder 0.3 0.7 0.01 - - 222-225 227-228 1.98 3.95 Example 2 Remainder 0.3 0.7 0.01 0.05 - 222-225 228-230 2.11 3.81 Example 3 Remainder 0.3 0.7 0.01 0.05 0.005 222-225 228-230 2.13 3.80 Example 4 Remainder 0.3 0.7 0.01 0.05 0.03 222-225 228-230 2.226 3.39 Example 5 Remainder 0.3 0.7 0.01 0.05 0.05 222-225 228-230 2.204 3.66 Example 6 Remainder 0.3 0.7 0.01 0.05 0.08 222-225 228-230 2.180 3.70 Example 7 Remainder 0.3 0.7 0.01 0.05 0.1 222-225 227-229 2.12 3.79

As shown in the table above, the lead-free alloy of the present invention has a solid phase temperature of 222 to 225 ° C and a liquidus temperature of 228 to 230 ° C. Due to the addition of a small amount of nickel, the wetting force is improved and the wetting time is shortened.

The lead-free alloy thus manufactured has a melting point that can be used for wiring of general electronic components, and is narrowly solidified so that it is very advantageous for stepwise automatic soldering. Compared with the conventional Sn-Ag-Cu system has almost similar wetting characteristics, it is possible to obtain the effect of reducing the production cost due to the addition of less silver (Ag).

In addition, the wettability improvement effect can be seen by adding 0.01-0.08 weight% of bismuth (Bi).

As described above, the lead-free alloy of the present invention does not contain lead as compared to the conventional Sn-Pb-based solder, thereby improving the working environment and preventing environmental pollution.

By adding phosphorus, a film is formed on the upper layer in contact with oxygen when molten, thereby suppressing the oxidation of the added element, thereby minimizing the amount of dross generated during soldering, and by adding silver, the bonding strength between the lead-free alloy and the base alloy To increase the wetting effect can be obtained. It is also expected to improve the wettability by adding bismuth. In addition, by adding copper, it is possible to refine the alloy structure to improve the bonding strength and to suppress the erosion of the electronic component and the printed circuit board. In addition, even if a small amount of silver-based addition of the existing Sn-Ag-Cu system shows a similar wettability characteristics, manufacturing cost reduction effect is large.

Claims (1)

Silver (Ag) is 0.2-2.5 wt%, Copper (Cu) is 0.1-2.0 wt%, Nickel (Ni) is 0.001-0.1 wt%, Phosphorus (P) is 0.001-0.5 wt%, Bismuth (Bi) Is 0.01 to 0.08% by weight, the remainder is made of tin (Sn) lead-free alloy for soldering.