CN109048115B - A Sn-Ag-Cu lead-free solder containing Ga and Nd - Google Patents

Abstract

The invention discloses a Sn-Ag-Cu lead-free solder containing Ga and Nd, belonging to the metal material class and the brazing material in the metallurgy field. The Sn-Ag-Cu lead-free solder comprises, by mass, 0.1-0.35% of Ag, 0.1-1.0% of Cu, 0.125-0.5% of Ga, 0.025-0.1% of Nd, 0.002-0.006% of Zr, 0.001-0.003% of Te and the balance of Sn, wherein the mass ratio of Ga to Nd is 5: 1, and the mass ratio of Zr to Te is Zr: Te ═ 2: 1. The solder has good wettability, can effectively inhibit the growth of tin whiskers of a soldered joint, greatly improves the reliability of the soldered joint, can be used for reflow soldering (reflow soldering) of components in the electronic industry and can also be used for wave soldering.

Description

A Sn-Ag-Cu lead-free solder containing Ga and Nd

technical field

The invention relates to a Sn-Ag-Cu lead-free solder containing Ga and Nd, which belongs to metal materials and brazing materials in the field of metallurgy.

Background technique

At present, the representative lead-free solders are Sn-Ag-Cu, Sn-Cu, Sn-Cu-Ni and other alloys, each with its own strengths, but compared with tin-lead solder, the cost of solder and solder There is still a certain gap in melting point. The melting point and raw material cost of Sn-Zn solder are lower than those of Sn-Ag-Cu, Sn-Cu, Sn-Cu-Ni solder, especially the melting point of Sn-Zn solder is very close to tin-lead solder. -Zn-based solder has poor wettability, so it is difficult to apply to industrial production at present.

In recent years, on the basis of Sn-Ag-Cu at home and abroad, "Sn-Ag-Cu lead-free solder containing Pr, Zr, Co" (Chinese patent application, CN101579789A), "Nd, Li, As, In "Sn-Ag-Cu lead-free solder" (Chinese patent application, CN101579790A), "Sn-Ag-Cu lead-free solder containing Pr, Ni, Ga" (Chinese patent application, CN101537546A) and "Nd, Ni , Co Sn-Ag-Cu lead-free solder" (Chinese patent application, CN101537547A) and other "multi-element alloy system" Sn-Ag-Cu solder, they are compared with ternary Sn-Ag-Cu alloy in Many properties have been improved, but they all have an obvious "weak point", that is, their silver content is between 0.5% and 4.5%, no matter compared with Sn-Cu, Sn-Cu-Ni and Sn-Zn solders , or compared with the traditional Sn-Pb solder, the raw material cost is much higher.

Since silver is a precious metal that is in global "scarce", in addition to its high price, its price fluctuates greatly. Therefore, low-silver and even ultra-low-silver Sn-Ag-Cu lead-free solders are studied to meet the requirements of low cost and high quality. The need for manufacturing is a "hot topic" in recent years. Although the "Nd and Ga-containing Sn-Ag-Cu lead-free solder" reduces the Ag content to 0.01-0.5%, the content of the rare element Ga is still high at 0.003-1.5%, and when the rare earth element Nd When the upper limit of 0.001 to 0.5% is 0.5%, the brazing joint is prone to a hidden danger that has a huge impact on electronic products - tin whisker. According to the article "Sn-Ag-Cu Lead-Free Solder Patent Technology Overview" published by Zhang Sumin, Hubei Center for Patent Examination Cooperation of the Patent Office of the State Intellectual Property Office in July 2017 in "Technology and Market", in recent years, China's Sn-Ag- There are relatively few studies on Cu lead-free solders. Therefore, it is urgent to develop Sn-Ag-Cu lead-free solders with high performance, low cost, no tin whiskers, and high reliability to meet the needs of the rapid development of the electronics industry.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a kind of method that helps to save rare and precious metal resources, has excellent wettability and mechanical properties of brazing, is suitable for reflow soldering (reflow soldering) in the electronics industry and can be used for wave soldering, High-performance, low-cost, whisker-free, high-reliability Sn-Ag-Cu lead-free solder containing Ga and Nd that meets the requirements of the RoHS directive.

The technical scheme that realizes the object of the present invention is as follows:

The Sn-Ag-Cu lead-free solder containing Ga and Nd, by mass percentage, includes: 0.1-0.35% Ag, 0.1-1.0% Cu, 0.125-0.5% Ga, 0.025-0.1% Nd, 0.002-0.006% of Zr, 0.001-0.003% of Te, and the remainder as Sn, wherein the mass ratio of Ga to Nd is 5:1, and the mass ratio of Zr to Te is 2:1.

The mass percentage content of silver in the solder of the present invention is only 0.01-0.35%, which is significantly reduced compared to the prior art, so that precious metal silver, which is a strategic resource, can be saved; since a reasonable addition amount is found between Ga and Nd. Therefore, it can not only reduce the silver content to an ultra-low level, but also improve the wettability of the solder, which can effectively suppress the growth of the thickness of the intermetallic compound at the interface of the brazing seam and the growth of tin whiskers in the brazing joint. Therefore, the "reliability" of the brazed joint can be greatly improved; a balance of reasonable additions between Zr and Te can be found, which can significantly improve the shear strength of the brazed joint. With commercially available water-soluble flux (ie medium active flux, RMA flux), the mechanical properties of the brazing seam can reach 85MPa ± 5MPa (shear strength), which can be applied to the electronic industry such as wave soldering, reflow soldering and Manual welding; Pb element is used as an "impurity element" in tin ingots, electrolytic copper and other raw materials, and the total amount is controlled within the range of Pb≤0.07wt.% to meet the national standard of the People's Republic of China GB/T 20422-2018 Soldering Materials (Pb≤0.07wt.% is specified in the standard).

Description of drawings

Figure 1 shows Example 3 with a commercially available no-clean flux (GW9810A-6A flux) and different contents of Nd to Sn-0.3Ag-0.7 under different test conditions when the mass ratio of Ga to Nd is 5 to 1 Schematic illustration of the effect of Cu lead-free solder wetting time.

Figure 2 shows that Example 3 mixes a commercially available water-soluble flux (FLUX 3355-11 water-soluble organic acid flux) and under different test conditions, when the mass ratio of Ga to Nd is 5 to 1, for Sn-0.3Ag- Schematic illustration of the effect of wetting time for 0.7Cu lead-free solder.

FIG. 3 is a microstructure diagram of Sn-0.3Ag-0.7Cu-0.5Ga-0.1Nd structure (magnified 300 times).

Figure 4 shows the microstructure of the Sn-0.3Ag-0.7Cu-0.5Ga-0.1Nd/Cu interface aged at 150°C for 6 months (1000 times magnification).

Figure 5 shows the microstructure of the Sn-0.3Ag-0.7Cu-0.5Ga-0.1Nd/Cu interface aged at 150°C for 6 months (2000 times magnification).

Detailed ways

The brazing filler metal of the present invention is prepared by conventional methods, that is, commercially available tin ingots, silver plates, cathode copper, metal gallium, metal neodymium, zirconium-copper alloy, and tellurium-copper alloy are used. The "covering agent" determined by optimized screening or smelting and casting with "inert gas" protection can obtain bars. By extrusion and drawing, the wire is obtained (the flux can also be added to make a "flux cored wire"). Lead (ie Pb) element is used as the "impurity element" in raw materials such as tin ingots and cathode copper, and the total amount (mass percentage) is controlled within the range of Pb≤0.07wt.% to meet the requirements of the National Standard of the People's Republic of China GB/T 20422 -2018 "Lead-free Solder" regulations (Pb≤0.07wt.% is specified in the standard).

Considering that the metal neodymium has a high melting point and is easily oxidized, the metal neodymium can also be smelted into an intermediate alloy in advance according to production needs, and added in the form of Sn-Nd to ensure the accuracy of the composition of neodymium in the solder; GB/T 5231 is selected. -Zirconium copper and TTe0.5 tellurium copper with the grades of TZr0.4 and TTe0.5 tellurium copper as raw materials in "Processing Copper and Copper Alloy Grades and Chemical Composition" in 2012, adding zirconium and tellurium.

Referring to Figure 1, the figure reveals that the commercial no-clean flux (GW9810A-6A flux) is used under different test temperature conditions, and the mass ratio of Zr to Te satisfies Zr:Te=2:1, Ga content and Nd Under the premise that the content of Ga:Nd=5:1, the influence of different content of Nd on the wetting time of Sn0.3Ag0.7Cu lead-free solder.

Referring to Figure 2, the figure shows that the mass ratio of Zr to Te satisfies Zr:Te=2:1, The effect of different content of Nd on the wetting time of Sn0.3Ag0.7Cu lead-free solder under the premise that Ga content and Nd content keep Ga:Nd=5:1.

Compared with previous research, the inventiveness of the present invention lies in:

1) It is found that the "reasonable addition" between Zr and Te can significantly improve the mechanical properties of the low-silver (in this specification, the silver content is less than or equal to 0.35wt.%) Sn-Ag-Cu lead-free solder, and the effect of the solder is There is no negative impact on the wetting performance. When Ga and Nd are added at the same time, the growth of the thickness of the intermetallic compound at the brazing interface can be effectively suppressed and the growth of tin whiskers in the brazed joint can be effectively suppressed, which can greatly improve the performance of the brazed joint. "Reliability", and is suitable for reflow soldering (reflow soldering) in the electronics industry, taking into account the new Sn-Ag-Cu lead-free solder used for soldering methods such as wave soldering.

When adding Ga and Nd elements at the same time, when the addition amount of Ga and Nd is in a "specified range", the low-silver Sn-Ag-Cu lead-free solder has the same value as the high-silver Sn2.5Ag0.7Cu lead-free solder. Wetting properties. After the silver content was reduced from 2.5% to 0.35%, the liquidus temperature increased from about 220 °C for Sn2.5Ag0.7Cu to about 225 °C for Sn0.35Ag0.7Cu. The addition of trace Ga and Nd elements can improve the wettability of Sn0.35Ag0.7Cu solder, and at the same time reduce the solidus temperature and liquidus temperature of the solder, which is beneficial to actual brazing production. Through experimental determination, the liquidus temperature of the solder determined in the embodiment of the present invention is 7°C lower than that of the Sn0.35Ag0.7Cu solder, and the liquidus temperature of the Sn0.35Ag0.7Cu-Ga-Nd-Zr-Te solder is lower than that of the Sn0.35Ag0.7Cu solder. The liquidus temperature is 218°C, which is equivalent to the liquidus temperature of Sn3.8Ag0.7Cu solder, which is 217°C.

In the test process of the present invention, it is found by studying the Sn-Te binary phase diagram that metal Te and Sn are completely insoluble in each other, but Te and Sn are easy to form high-melting intermetallic compounds, and the melting point temperature of the intermetallic compounds is 806° C. ; By studying the Sn-Zr binary phase diagram, it is found that the metal Sn has a large "solid solubility" in the Zr element, and can form a variety of high-melting intermetallic compounds. The melting point of the intermetallic compound is the highest reaching 1988 ℃. According to the theory of metallology and metallurgy, the formation of trace intermetallic compounds with high melting point can be used as the "nucleation particle" of liquid metal, which is beneficial to grain refinement and improves the mechanical properties of brazing joints. However, since the liquidus temperature of Sn0.35Ag0.7Cu solder is only 218°C, the temperature difference from liquid to solid is not very large. Therefore, even if the high melting point intermetallic compound can be used as the "nucleation particle" of liquid metal, it needs to be The amount is also very small. After theoretical calculation and experimental verification such as finite element simulation, the addition amount that can play a "positive role" must be controlled within the range of 0.002-0.006% for Zr element, 0.001-0.003% for Te element, and the mass ratio of Zr to Te The most effective control is in the range of Zr:Te=2:1.

2) The addition range and ratio of Ga and Nd elements were verified and optimized by experiments.

Through the "sequential experimental design" method, it was found that in the ultra-low silver Sn-Ag-Cu lead-free solder with Ag content less than or equal to 0.5% (mass percentage, the same below), when the Ag content is less than or equal to 0.35%, Sn- In order for Ag-Cu lead-free solder to obtain comparable wetting properties to Sn2.5Ag0.7Cu and Sn3.8Ag0.7Cu lead-free solder, it is necessary to find new element combinations and use many new trace amounts that have never been discovered. The special properties of the elements can only achieve the expected effect after the proportion adjustment and composition optimization.

The test results shown in Figure 1 and Figure 2 show that, compared with Sn0.3Ag0.7Cu lead-free solder, whether it is used with commercially available no-clean flux or commercially available water-soluble flux, the ratio of Ga:Nd to 5 to 1 is guaranteed. When the Nd content changes, the optimum addition range of Sn0.3Ag0.7Cu-Ga-Nd-Zr-Te lead-free solder Nd is 0.025-0.1%, and the optimum addition range of Ga is 0.125-0.5%. Within this composition range, the wetting time of the new solder can be guaranteed to be less than 1 second (according to the American electronics industry standard IPC/EIA J-STD-003B: 2004, the wetting of the solder that can be used for wave soldering on the substrate material The recommended value of wetting time is t ₀ ≤ 1s. It is generally accepted in the electronics industry that the smaller the wetting time (at least less than one second), the better the wetting performance of the solder). After the addition of Nd is greater than 0.1%, the wetting time is ≥ 1 second, indicating that its negative effect on the wettability of the solder begins to appear. In the microstructure, the possibility of the initiation and growth of "tin whiskers" increases.

The test results of the mechanical properties of the brazing seam show that the shear strength of the brazing seam (solder joint) of the brazing filler metal obtained in the examples of the present application reaches 85MPa±5MPa, which indicates that the examples of the present application have the same properties as Sn2.5Ag0.7Cu, Sn3.8Ag0.7Cu without While the lead solder has comparable wetting properties, the mechanical properties of the solder joint are much higher than that of the Sn3.8Ag0.7Cu0.05RE lead-free solder, which is 50 MPa±10MPa, which is mainly due to the strengthening of extremely small amounts of Zr and Te elements. .

The optimization results of various components show that the addition of Ga should be controlled in the range of 0.125-0.5%, the addition of Nd should be controlled in the range of 0.025-0.1%, the addition of Zr should be controlled in the range of 0.002-0.006%, and the addition of Te should be controlled in the range of 0.002-0.006%. It should be controlled within the range of 0.001-0.003%, the mass ratio of Ga to Nd should be controlled at Ga:Nd=5:1; the mass ratio of Zr to Te should be controlled at Zr:Te=2:1. Under the "synergistic effect" of the above four elements, the Sn-Ag-Cu lead-free solder containing Ga and Nd obtained by the new element combination has high mechanical properties of solder joints, excellent wetting and spreading properties and excellent Solder seam reliability.

According to the mass ratio of the "Sn-Ag-Cu lead-free solder containing Ga and Nd" of the present invention, the specific embodiments of the present invention are described as follows.

Example 1

Sn-Ag-Cu lead-free solder containing Ga and Nd, including by mass percentage: 0.1% Ag, 1.0% Cu, 0.125% Ga, 0.025% Nd, 0.006% Zr, 0.003% Te , the remainder is Sn.

The liquidus temperature of the "Sn-Ag-Cu lead-free solder containing Ga and Nd" obtained by the above composition ratio is about 218 ℃ (taking into account the experimental error), with the commercially available water-soluble flux (FLUX 3355-11 water-soluble flux) Organic acid flux) has excellent wetting performance on T2 copper plate, and the mechanical properties of brazing seam can reach 85MPa±5MPa (shear strength). After 6 months of aging at 150°C, the intermetallic compounds at the interface of the newly invented lead-free solder have no obvious change and no tin whiskers are formed, indicating that the reliability of the solder joint (brazing) has been significantly improved.

Example 2

Sn-Ag-Cu lead-free solder containing Ga and Nd, including by mass percentage: 0.35% Ag, 0.1% Cu, 0.5% Ga, 0.1% Nd, 0.002% Zr, 0.001% Te , the remainder is Sn.

The liquidus temperature of "a kind of Sn-Ag-Cu lead-free solder containing Ga and Nd" obtained by the above composition ratio is about 218 ℃ (taking into account the experimental error), with the commercially available water-soluble flux (FLUX 3355- 11 Water-soluble organic acid flux) has excellent wetting performance on T2 copper plate, and the mechanical properties of brazing seam can reach 85MPa±5MPa (shear strength). After 6 months of aging at 150°C, the intermetallic compounds at the interface of the newly invented lead-free solder have no obvious change and no tin whiskers are formed, indicating that the reliability of the solder joint (brazing) has been significantly improved.

Example 3

Sn-Ag-Cu lead-free solder containing Ga and Nd, including by mass percentage: 0.3% Ag, 0.7% Cu, 0.4% Ga, 0.08% Nd, 0.004% Zr, 0.002% Te , the remainder is Sn.

The liquidus temperature of the "Sn-Ag-Cu lead-free solder containing Ga and Nd" obtained by the above composition ratio is about 218 ℃ (taking into account the experimental error), with the commercially available water-soluble flux (FLUX 3355-11 water-soluble flux) Organic acid flux) has excellent wetting performance on T2 copper plate, and the mechanical properties of brazing seam can reach 85MPa±5MPa (shear strength). After 6 months of aging at 150°C, the intermetallic compounds at the interface of the newly invented lead-free solder have no obvious change and no tin whiskers are formed, indicating that the reliability of the solder joint (brazing) has been significantly improved.

Example 4

Sn-Ag-Cu lead-free solder containing Ga and Nd, including by mass percentage: 0.25% Ag, 0.65% Cu, 0.3% Ga, 0.06% Nd, 0.003% Zr, 0.0015% Te , the remainder is Sn.

The liquidus temperature of the "Sn-Ag-Cu lead-free solder containing Ga and Nd" obtained by the above composition ratio is about 218 ℃ (taking into account the experimental error), with the commercially available water-soluble flux (FLUX 3355-11 water-soluble flux) Organic acid flux) has excellent wetting performance on T2 copper plate, and the mechanical properties of brazing seam can reach 85MPa±5MPa (shear strength). After 6 months of aging at 150°C, the intermetallic compounds at the interface of the newly invented lead-free solder have no obvious change and no tin whiskers are formed, indicating that the reliability of the solder joint (brazing) has been significantly improved.

Example 5

Sn-Ag-Cu lead-free solder containing Ga and Nd, including by mass percentage: 0.15% Ag, 0.75% Cu, 0.2% Ga, 0.04% Nd, 0.005% Zr, 0.0025% Te , the remainder is Sn.

The liquidus temperature of the "Sn-Ag-Cu lead-free solder containing Ga and Nd" obtained by the above composition ratio is about 218 ℃ (taking into account the experimental error), with the commercially available water-soluble flux (FLUX 3355-11 water-soluble flux) Organic acid flux) has excellent wetting performance on T2 copper plate, and the mechanical properties of brazing seam can reach 85MPa±5MPa (shear strength). After 6 months of aging at 150°C, the intermetallic compounds at the interface of the newly invented lead-free solder have no obvious change and no tin whiskers are formed, indicating that the reliability of the solder joint (brazing) has been significantly improved.

Claims (1)

1. Sn-Ag-Cu lead-free solder containing Ga and Nd, characterized in that, in terms of mass percentages, it comprises: 0.1-0.35% Ag, 0.1-1.0% Cu, 0.125-0.5% Ga, 0.025- 0.1% of Nd, 0.002 to 0.006% of Zr, 0.001 to 0.003% of Te, and the balance is Sn, wherein the mass ratio of Ga to Nd is 5:1, and the mass ratio of Zr to Te is 2:1.

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