KR100743240B1 - Low temperature lead-free solder alloy - Google Patents

Abstract

A lead-free solder is provided to prevent the human body from being injured by lead and be acted similarly to lead-containing solders without modifying additional facilities by performing soldering although lead is not contained in the solder, and be used as a specific solder for bonding glass materials such as an EEFL electrode by maintaining excellent viscosity and adhesion properties. A lead-free alloy for soldering comprises 10 to 30 wt.% of bismuth(Bi), 0.5 to 2.0 wt.% of indium(In), and the balance of tin(Sn). The lead-free alloy for soldering comprises 0.005 to 0.5 wt.% of germanium(Ge), 0.001 to 0.5 wt.% of phosphorous(P), 0.01 to 2.0 wt.% of copper(Cu), 0.001 to 0.5 wt.% of gallium(Ga), and 0.01 to 0.5 wt.% of aluminum(Al). The lead-free alloy for soldering comprises 0.01 to 2.0 wt.% of zinc(Zn) and 0.005 to 0.5 wt.% of germanium(Ge). The total content of the zinc(Zn), copper(Cu), aluminum(Al), germanium(Ge) and gallium(Ga) is 5.5 wt.% or less.

Description

Low temperature 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 the solder to bond metals, and therefore metals having a lower melting temperature than the metal to be connected are used.Both solders melted at a temperature lower than the melting temperature of lead (327 ° C) and light solder having a melting temperature of generally 450 ° C or higher are used. It is rough. 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 failure, 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 atmosphere, and acid rain is generated by rain passing through the acidic atmosphere. Such acid rain penetrates into the ground, elutes harmful metals such as lead from the buried electronics, and contaminates groundwater. If the groundwater is consumed for a long time, lead poisoning may occur, and workers may be exposed to gases generated by solder melting during soldering. 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 and metals such as Cu, Ag, Bi, Zn, Ni, and P. Representative compositions of lead-free solder 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 further.

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

At present, the most practically conceived lead-free solders include the addition of Cu to 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 solder.

However, Sn-Cu system such as Sn-0.7 wt% Cu is low in cost but lacks wettability in soldering. On the other hand, Sn-Ag-Cu based Sn-Ag and Sn-Ag-based solders, such as Sn-3.5 wt% Ag, have a high wettability but contain expensive Ag, resulting in high cost and cost reduction. In order to reduce the Ag content, the wettability and the alloy strength of the solder are reduced. In addition, the melting point is about 50 ~ 100 ℃ higher than the conventional solder of Sn-37Pb alloy, so it is inevitable to change the bonding facilities and processes, and 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, to prevent the damage caused by the human body by the solder to be made without including the lead in the solder components, similar to the flexible solder without a separate equipment change It is about a lead-free solder that can be applied.

In addition, the solder of the present invention has an excellent viscosity and adhesiveness, and its purpose is to be used as a specialized solder for glass material bonding, such as EEFL electrode bonding.

Therefore, the present invention is based on tin (Sn) and added Bi to the purpose of melting point drop, zinc (Zn), indium (In), copper ( Cu), aluminum (Al), germanium (Ge), phosphorus (P), gallium (Ga) is added and characterized in that the composition.

In the lead-free alloy according to the present invention, bismuth (Bi) is 10 to 30% by weight in tin (Sn), and indium (In), zinc (Zn), copper (Cu), aluminum (Al), and germanium (Ge) as additives. The present invention relates to a lead-free alloy characterized in that at least one of phosphorus (P) and gallium (Ga) is added.

In the present invention, tin (Sn) is an essential metal of a solder substrate which does not have self toxicity and serves to provide wettability to the bonded base material.

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 Bi is dissolved in the Sn matrix. In addition, since it has a brittle property, which is fragile, it is feared that the soldering reliability of the solder will be lowered at a large amount. Adding a large amount of Bi can assume that Bi is crystallized in a coarse shape of 10 µm or more, which adversely affects the structure of the solder. Therefore, in the present invention, while obtaining the maximum melting point effect, it contains 10 to 30% by weight to reduce the brittleness. If more than 30% by weight, the brittleness is too strong to obtain a good mechanical properties and spreadability when bonding, less than 10% by weight can not effectively obtain the melting point drop effect compared to the added amount.

Zinc (Zn) is to obtain a low melting point corresponding to the flexible solder, and to input for the purpose of enhancing the mechanical properties. However, Sn-Zn-based alloys are inferior in oxidation because Zn is active and exposed to the surface, and alloying elements are hardly dissolved and are separated into Sn and Zn phases. In addition, the increase in Zn tends to decrease the hardness. In order to increase the bonding strength, it is preferable to thin the reaction layer, and reducing the amount of Zn reduces the thickness of the reaction layer. Therefore, in this invention, it contains 0.01 to 2.0 weight%. When it is 2.0 wt% or more, the melting point of the solder alloy is increased, the dross amount is increased, and when it is less than 0.01 wt%, there is little effect on lowering the melting point and improving the mechanical properties.

Indium (In) can effectively lower the melting point of the solder alloy with the addition of Bi. A large amount of Bi may be hardened to cause ductility deterioration, but mechanical aging due to the addition of In is not as remarkable as Bi, and an improvement in creep properties can be seen. In addition, since In easily dissolves uniformly in Sn and segregation hardly occurs, thermal fatigue characteristics and the like are reduced. Therefore, the purpose of adding In is to design a low melting point solder alloy without significantly deteriorating the metal properties of the alloy. However, since In is classified as a precious metal, the burden of cost increase due to the massive addition is high. Therefore, the present invention contains 0.5 to 2.0% by weight. If it is less than 0.5% by weight, there is little effect on melting point drop and improvement of properties.

Copper (Cu) It is characteristic that most of it is not dissolved in Sn and is converted into Cu6Sn5 microdispersion. The structure of the alloy can be refined to improve the bonding strength and increase the viscosity, and to suppress the erosion of the electronic component or the printed circuit board. Sn-Bi-based solders were tested by adding Cu, which increased the strength to compensate for the brittleness of Bi, because a thin Bi-rich layer was formed at the interface to reduce the bonding strength. In the present invention, it is contained in 0.01 to 2.0% by weight. When the Cu content is more than 2.0% by weight, the melting point is sharply increased and the low temperature characteristic effect of the present invention cannot be expected, and when the Cu content is less than 0.01% by weight, there is little effect on improving solder properties.

Aluminum (Al) is often classified as an impurity in the solder alloy system, but when added in a small amount, it is possible to suppress the growth of the interfacial reaction layer. Therefore, the addition of trace elements may be used to control the formation and growth of the intermetallic compound and the microstructure control element according to the interfacial reaction between the solder and Cu rather than to improve the spreadability. In general, however, even with a small amount of addition, the fluidity of the solder is lowered and the gloss is lost, and in particular, the oxidizing property is strong. This is very similar to Zn. In the present invention, it is contained in 0.01 to 0.5% by weight, when added in excess of 0.5% by weight, the oxidizing property is increased and the utility as a microstructure control element disappears, when less than 0.01% by weight microstructure control utility is insignificant.

The addition of germanium (Ge) is effective in preventing the oxidation of the solder. In the present invention, it is contained at 0.005 to 0.5% by weight or less. If it is added more than 0.5% by weight, the antioxidant effect is lowered compared to the increase in raw material costs, and less than 0.005% by weight has no antioxidant effect.

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 is less than 0.001% by weight, it is not effective in preventing oxidation and improving wettability. If the amount of phosphorus is more than 0.5% by weight, the viscosity of the solder is increased to cause defects such as bridges during soldering.

The addition of gallium (Ga) lowers the melting point, thereby improving workability and improving wettability. The addition of gallium to the molten solder diffuses thinly on the surface of the molten solder, so that thin oxides of gallium cover the surface of the molten solder during soldering to block contact with the atmosphere, and have some effects on the prevention of oxidation of lead-free solder melted at high temperatures. There is. In the present invention, 0.001 to 0.5% by weight is contained. If the amount is less than 0.001% by weight, the addition amount is insignificant, so that the effect of lowering the melting point, the prevention of oxidation, and the improvement of the wettability is insignificant.

Hereinafter, embodiments of the present invention will be described.

Example 1

A lead-free alloy was prepared in which bismuth was 20% by weight, indium was 1.5% by weight, phosphorus was 0.01% by weight, and the balance was tin.

Example 2

A lead-free alloy was prepared in which bismuth was 25% by weight, copper was 1.0% by weight, phosphorus was 0.01% by weight, and the balance was tin.

Comparative Example 1

A flexible alloy having 63.0 wt% tin and 37 wt% lead was prepared.

Table 1 compares the solid-state temperature, liquid-phase temperature, soldering strength and creep life of the lead-free alloys prepared in Examples 1 and 2 and the solder according to Comparative Example 1.

division Chemical composition (% by weight) Solid State Temperature (℃) Liquid Temperature (℃) Soldering Strength (Kgf) Creep Life (hr) Remark Bismuth indium Copper sign Example 1 Remainder 20 1.5 - 0.01 153 ~ 159 178-185 108.1 11.9 Example 2 Remainder 25 - 1.0 0.01 171-179 201-208 98.0 11.8 Comparative Example 1 63.0 Lead 37.0 183 183 8.5 1.4

As shown in Table 1, the lead-free alloy of the present invention has a solid phase temperature of 153 to 159 ° C. and a liquid phase temperature of 178 to 185 ° C., which has a narrow solidification range and low melting point. It is possible. In addition, it can be seen that due to the addition of the additive element of the present invention, the soldering strength and the creep life are increased to improve the mechanical properties.

Example 3

A lead-free alloy was prepared in which bismuth was 20% by weight, indium was 1.5% by weight, phosphorus was 0.02% by weight, and the balance was tin.

Example 4

A lead-free alloy was prepared in which bismuth was 20% by weight, indium was 1.5% by weight, aluminum was 0.5% by weight, phosphorus was 0.02% by weight, and the balance was tin.

Example 5

A lead-free alloy was prepared in which bismuth was 20% by weight, zinc was 1.0% by weight, indium was 1.5% by weight, phosphorus was 0.02% by weight, and the balance was tin.

Example 6

A lead-free alloy was prepared in which bismuth was 20% by weight, zinc was 1.0% by weight, indium was 1.5% by weight, aluminum was 0.5% by weight, phosphorus was 0.02% by weight, and the balance was tin.

Example 7

A lead-free alloy was prepared in which bismuth was 20% by weight, zinc was 2.0% by weight, indium was 1.5% by weight, germanium was 0.01% by weight, phosphorus was 0.02% by weight, and the balance was tin.

Example 8

A lead-free alloy was prepared in which bismuth was 20% by weight, zinc was 2.0% by weight, indium was 1.5% by weight, phosphorus was 0.02% by weight, and the balance was tin.

Example 9

A lead-free alloy was prepared in which bismuth was 20% by weight, zinc was 2.0% by weight, indium was 2.0% by weight, aluminum was 0.5% by weight, phosphorus was 0.02% by weight, gallium 0.05% by weight, and the balance was tin.

Example 10

A lead-free alloy was prepared in which bismuth was 25 wt%, copper 1.5 wt%, aluminum 0.1 wt%, phosphorus 0.02 wt%, and the balance tin.

Example 11

A lead-free alloy was prepared in which bismuth was 25% by weight, copper was 1.5% by weight, phosphorus was 0.02% by weight, and the balance was tin.

Example 12

A lead-free alloy was prepared in which bismuth was 25 wt%, copper 0.5 wt%, aluminum 0.1 wt%, phosphorus 0.02 wt%, and the balance tin.

Example 13

A lead-free alloy was prepared in which bismuth was 25 wt%, indium 1.5 wt%, copper 0.5 wt%, phosphorus 0.02 wt%, and the balance tin.

Comparative Example 1

A lead alloy of 63 wt% tin and 37 wt% lead was prepared.

Table 2 shows the amount of dross generated for one hour when the lead-free alloys prepared in Examples 3 to 13 and the flexible alloys prepared in Comparative Example 1 were melted and stirred for 10 kg in a small solder fractionation tank. .

 division Chemical composition (% by weight) Dross generation amount (g) Remark Bismus zinc indium Copper aluminum Germanium sign gallium Example 3 Remainder 20 - 1.5 - - - 0.02 - 103 Example 4 Remainder 20 - 1.5 - 0.5 - 0.02 - 105 Example 5 Remainder 20 1.0 1.5 - - - 0.02 - 187 Example 6 Remainder 20 1.0 1.5 - 0.5 - 0.02 - 190 Example 7 Remainder 20 2.0 1.5 - - 0.01 0.02 - 297 Example 8 Remainder 20 2.0 1.5 - - - 0.02 - 309 Example 9 Remainder 20 2.0 2.0 - 0.5 - 0.02 0.05 202 Example 10 Remainder 25 - - 1.5 0.1 - 0.02 - 179 Example 11 Remainder 25 - - 1.5 - - 0.02 - 196 Example 12 Remainder 25 - - 0.5 0.1 - 0.02 - 144 Example 13 Remainder 25 - 1.5 0.5 - - 0.02 - 138 Comparative Example 1 Sn-37Pb 91

As shown in Table 2, the amount of dross generated is comparable to that of the conventional flexible alloy, and a lead-free alloy for low temperature soldering can be manufactured which can drastically reduce the amount of dross according to a combination of bismuth and other elements.

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

Compared with the conventional Sn-Pb process solder as in the above embodiment, it has an excellent effect of extending the melting point, the solder strength and the creep life.

In addition, it is possible to improve the reduction of the dross amount affecting the workability due to the comparable alloy combination compared to the conventional flexible solder.

Therefore, since the melting point is almost similar to that of the existing solder without using lead, the equipment using Sn-Pb-based solder can be used as it is, and the use of lead-free alloy is minimized by improving wettability and reducing dross generation. This is a very economical effect. In addition, it can be used as a characterization solder for glass material bonding, such as EEFL electrode bonding sensitive to low temperature properties and mechanical properties.

Claims (10)

Bismuth (Bi) is 10 to 30% by weight, indium (In) is 0.5 to 2.0% by weight, the remainder is made of tin (Sn) lead-free alloy for soldering. The method of claim 1, Lead-free alloy for soldering, characterized in that it contains 0.005 to 0.5% by weight of germanium (Ge). The method of claim 1, Lead-free alloy for soldering, characterized in that it contains 0.001 to 0.5% by weight of phosphorus (P). The method of claim 3, wherein Lead-free alloy for soldering, characterized in that it contains 0.01 to 2.0% by weight of copper (Cu). The method of claim 3, wherein Lead-free alloy for soldering, characterized in that it contains 0.005 to 0.5% by weight of germanium (Ge). The method of claim 3, wherein Lead-free alloy for soldering, characterized in that it contains 0.001 to 0.5% by weight of gallium (Ga). The method of claim 6, Lead-free alloy for soldering, characterized in that it contains 0.01 to 2.0% by weight of copper (Cu). The method of claim 6, Lead-free alloy for soldering, characterized in that it contains 0.01 to 0.5% by weight of aluminum (Al). The method of claim 6, Lead-free alloy for soldering, characterized in that it comprises 0.01 to 2.0% by weight of zinc (Zn) and 0.005 to 0.5% by weight of germanium (Ge). The method of claim 3, wherein A lead-free alloy for soldering comprising zinc (Zn), copper (Cu), aluminum (Al), germanium (Ge), and gallium (Ga) so that the sum of the components is not more than 5.5% by weight.