Sn-Zn lead-free solder containing Ag, Bi and Ge and preparation method thereof

Abstract

The present invention discloses a Sn-Zn lead-free solder containing Ag, Bi, and Ge and a preparation method thereof, belonging to the field of soldering materials of electronic materials. The present invention regulates the microstructure morphology, phase composition, and melting properties of the solder alloy by controlling the content of Ag, Bi, and Ge elements in the solder, and provides a preparation method of the Sn-Zn lead-free solder containing Ag, Bi, and Ge. The solder is prepared by a three-master alloy mixing method. Compared with the traditional melting and casting method, the solder alloy has a uniform structure, accurate composition, simple process, and cost savings, and the solder alloy has improved wettability, antioxidant properties, and corrosion resistance. The solder can be used for brazing microelectronic chip circuit boards of electrical equipment serving in high-temperature and high-humidity environments.

Description

Technical Field

[0001] The invention relates to a Sn-Zn lead-free solder containing Ag, Bi and Ge and a preparation method thereof, and belongs to the field of soldering materials of electronic materials. Background Art

[0002] As a primary method of connecting materials, soldering provides a crucial technical foundation for electronic chip packaging and circuit board connections. Solder is a crucial carrier for the assembly and interconnection of electronic components during soldering, and its durability and reliability are crucial to the functionality and lifespan of electronic products. However, due to the health and ecological hazards of lead, many countries have legal restrictions on the use of traditional Sn-Pb solder. Meanwhile, the rapid development of modern electronic packaging technology has placed higher demands on the comprehensive performance of lead-free solders. Therefore, there is an urgent need to develop an economical, non-toxic, environmentally friendly, and high-performance lead-free solder alternative.

[0003] SnZn-based lead-free solders offer advantages such as cost-effectiveness, environmental friendliness, excellent mechanical properties, and a moderate melting point. They can be widely used in the soldering process of electronic devices without changing existing soldering equipment in the electronics industry, making them the most promising lead-free solder alloy to replace Sn-Pb. However, the Sn-Zn-based solders commonly used on the market are mostly binary Sn-9Zn eutectic solders, which suffer from disadvantages such as poor wettability, oxidation resistance, and corrosion resistance, severely restricting their large-scale commercial application. Furthermore, the volatilization and oxidation of the Zn element during the smelting process in Sn-Zn-based solders leads to inflexible production processes, severely limiting their production, storage, and commercial application. Summary of the Invention

[0004] The purpose of the present invention is to improve the defects of the commonly used Sn-9Zn eutectic solder and provide an economical and environmentally friendly Sn-Zn five-element lead-free solder with a moderate melting point and excellent wettability, oxidation resistance and corrosion resistance by optimizing the alloy composition and ratio.

[0005] In view of this, the present invention provides a Sn-Zn lead-free solder containing Ag, Bi and Ge, which is prepared using the following raw materials calculated by mass percentage: Zn: 9%, Ag: 0.2-0.6%, Bi: 0.25-0.75%, Ge: 0.2-0.6%, and the balance is Sn.

[0006] Another object of the present invention is to provide a method for preparing a Sn-Zn lead-free solder containing Ag, Bi, and Ge, which specifically comprises the following steps:

[0007] (1) Refining the alloy intermediate SnAg: Weigh the metal raw materials Sn and Ag, and smelt them under vacuum conditions. After the smelting is completed, the sample is cooled in the furnace to obtain the alloy intermediate SnAg.

[0008] (2) Refining the alloy intermediate SnGe: Weigh the metal raw material Sn and the powdered semi-metal raw material Ge, and smelt them under vacuum conditions. After the smelting is completed, the sample is cooled in the furnace to obtain the alloy intermediate SnGe.

[0009] (3) Refining the alloy intermediate SnBi: Weigh the metal raw materials Sn and Bi, and smelt them under vacuum conditions. After the smelting is completed, the sample is cooled in the furnace to obtain the alloy intermediate SnBi.

[0010] (4) Alloy Refining: Weigh the alloy intermediate SnAg obtained in step (1), weigh the alloy intermediate SnGe obtained in step (2), weigh the alloy intermediate SnBi obtained in step (3), and the metal raw material Zn, and smelt them under vacuum conditions. After smelting, the sample is first cooled in the furnace, then removed and water quenched to finally obtain a Sn-Zn-Ag-Bi-Ge alloy sample.

[0011] Preferably, the smelting conditions in step (1) of the present invention are: vacuum conditions of 1×10 -4 Pa, the temperature rises to 800-1000℃, and is kept warm for 60-90min. The melting furnace body automatically swings up and down at a rate of 15-20r / min and a swing angle of ±15°.

[0012] Preferably, the smelting conditions in step (2) of the present invention are: vacuum conditions of 1×10 -4 Pa, the temperature rises to 900-1000℃, keeps warm for 60-90min, the melting furnace body automatically swings up and down at a rate of 15-20r / min, and the swing angle is ±15°

[0013] Preferably, the smelting conditions in step (3) of the present invention are: vacuum conditions of 1×10 -4 Pa, the temperature rises to 300-500℃, and is kept warm for 30-60min. The melting furnace body automatically swings up and down at a rate of 15-20r / min and a swing angle of ±15°.

[0014] Preferably, the smelting conditions in step (4) of the present invention are: vacuum conditions of 1×10 -4 Pa, the temperature rises to 400-500℃, and is kept warm for 30-60min. The melting furnace body automatically swings up and down at a rate of 15-20r / min and a swing angle of ±15°.

[0015] Preferably, the furnace temperature decrease rate during furnace cooling in step (4) of the present invention is 8°C / min, and when cooled to 300°C, the sample is taken out and water quenched.

[0016] Preferably, the metal raw material of the present invention has a purity of 99.99%.

[0017] Beneficial effects of the present invention:

[0018] (1) The Sn-Zn lead-free solder containing Ag, Bi, and Ge described in the present invention is prepared by adding trace elements Ag, Bi, and Ge to the eutectic Sn-9Zn solder commonly used in the traditional electronic solder market and optimizing their content. The prepared Sn-Zn-Ag-Bi-Ge alloy has uniform composition, a moderate melting point, and excellent wettability, oxidation resistance, and corrosion resistance, significantly improving the brazing and service performance of the Sn-Zn solder alloy.

[0019] (2) The method for preparing a Sn-Zn lead-free solder containing Ag, Bi, and Ge, described in the present invention, takes into account the high melting points of metallic Ag and semi-metallic Ge, as well as the volatility of metallic Zn, based on conventional lead-free solder alloy preparation methods. A step-by-step smelting process is employed, first preparing SnAg and SnGe alloy intermediates at high temperature, and then preparing SnBi intermediates and the solder alloy at low temperature. This significantly improves the uniform distribution of Ag, Bi, and Ge in the solder, reduces the loss of Zn during alloy preparation, and promotes the accuracy of the alloy's composition and uniformity of its structure.

[0020] (3) In Sn-Zn alloys, the solder structure is significantly refined by the composite addition of Ag, Bi, and Ge alloying elements. The Ag element in the alloy mainly plays a role in improving corrosion resistance, the Bi element mainly plays a role in improving wettability, and the Ge element mainly plays a role in improving oxidation resistance. The combined addition of Ag, Bi, and Ge will produce a synergistic enhancement effect in the alloy, jointly improving the overall solder properties of the solder alloy, such as wettability, oxidation resistance, and corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Microstructure diagram of the lead-free solder alloy according to an embodiment of the present invention;

[0022] Figure 2 Graph showing the oxidation resistance of the lead-free solder alloys described in Examples 1 to 5 of the present invention;

[0023] Figure 3 Corrosion resistance of the lead-free solder alloys described in Examples 1 to 5 of the present invention. DETAILED DESCRIPTION

[0024] To help those skilled in the art better understand the technical solutions of the present invention, the following will clearly describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments and accompanying drawings. The described embodiments are only part of the embodiments of the present invention, not all of them. Therefore, the scope of protection of the present invention is not limited to the contents described above.

[0025] Example 1

[0026] A Sn-Zn lead-free solder containing Ag, Bi, and Ge has the following chemical composition and mass percentages: Zn: 9.0%, Ag: 0.2%, Bi: 0.75%, Ge: 0.6%, and the balance is Sn. The specific preparation method is as follows:

[0027] (1) Preparation of alloy intermediate SnAg: Weigh metal raw materials Sn and Ag with a purity of 99.99% according to a certain weight percentage and put them into a quartz tube. Vacuum the quartz tube to 1×10 -4 The tube mouth was sealed under Pa conditions, and the quartz tube was placed in a 16-channel swing melting furnace. The temperature was raised to 900°C and kept warm for 90 minutes. During the melting process, the furnace body was always kept automatically swinging up and down at a rate of 15r / min and a swing angle of ±15°. After the melting was completed and the furnace was cooled, the alloy intermediate SnAg was obtained.

[0028] (2) Refining alloy intermediate SnGe: Weigh a certain weight percentage of the metal raw material Sn with a purity of 99.99% and the powdered semi-metal raw material Ge into a quartz tube, and evacuate the quartz tube to 1×10 -4 The tube mouth was sealed under Pa conditions, and the quartz tube was placed in a 16-channel swing melting furnace. The temperature was raised to 950°C and kept warm for 90 minutes. During the melting process, the furnace body was always kept automatically swinging up and down at a rate of 15r / min and a swing angle of ±15°. After the melting was completed and the furnace was cooled, the alloy intermediate SnGe was obtained.

[0029] (3) Refining the alloy intermediate SnBi: Weigh the metal raw materials Sn and Bi with a purity of 99.99% according to a certain weight percentage and put them into a quartz tube. Vacuum the quartz tube to 1×10 -4 The tube mouth was sealed under Pa conditions, and the quartz tube was placed in a 16-channel swing melting furnace. The temperature was raised to 300°C and kept warm for 60 minutes. During the melting process, the furnace body was always kept automatically swinging up and down at a rate of 15 r / min and a swing angle of ±15°. After the melting was completed and the furnace was cooled, the alloy intermediate SnBi was obtained.

[0030] (4) Alloy refining: The alloy intermediate SnAg obtained in step (1), the intermediate SnGe obtained in step (2), the intermediate SnBi obtained in step (3) and the metal raw material Zn with a purity of 99.99% are combined and placed in a quartz tube. The quartz tube is vacuumed to 1×10 -4 The tube opening was sealed under Pa conditions. The quartz tube was then placed in a 16-channel rocking melting furnace and the temperature was raised to 500°C for 30 minutes. During the melting process, the furnace was automatically rocked up and down at a rate of 15 r / min and an angle of ±15°. After melting, the alloy was cooled at a rate of 8°C / min. When it cooled to 300°C, the sample was removed and water quenched to obtain the Sn-9Zn-0.2Ag-0.75Bi-0.6Ge alloy sample.

[0031] Example 2

[0032] A Sn-Zn lead-free solder containing Ag, Bi, and Ge has the following chemical composition and mass percentages: Zn: 9.0%, Ag: 0.4%, Bi: 0.25%, Ge: 0.4%, and the balance is Sn. The specific preparation method is as follows:

[0033] (1) Preparation of alloy intermediate SnAg: Weigh metal raw materials Sn and Ag with a purity of 99.99% according to a certain weight percentage and put them into a quartz tube. Vacuum the quartz tube to 1×10 -4 The tube mouth was sealed under Pa conditions, and the quartz tube was placed in a 16-channel swing melting furnace. The temperature was raised to 900°C and kept warm for 90 minutes. During the melting process, the furnace body was always kept automatically swinging up and down at a rate of 15r / min and a swing angle of ±15°. After the melting was completed and the furnace was cooled, the alloy intermediate SnAg was obtained.

[0034] (2) Refining alloy intermediate SnGe: Weigh a certain weight percentage of the metal raw material Sn with a purity of 99.99% and the powdered semi-metal raw material Ge into a quartz tube, and evacuate the quartz tube to 1×10 -4 The tube mouth was sealed under Pa conditions, and the quartz tube was placed in a 16-channel swing melting furnace. The temperature was raised to 950°C and kept warm for 90 minutes. During the melting process, the furnace body was always kept automatically swinging up and down at a rate of 15r / min and a swing angle of ±15°. After the melting was completed and the furnace was cooled, the alloy intermediate SnGe was obtained.

[0035] (3) Refining the alloy intermediate SnBi: Weigh the metal raw materials Sn and Bi with a purity of 99.99% according to a certain weight percentage and put them into a quartz tube. Vacuum the quartz tube to 1×10 -4The tube mouth was sealed under Pa conditions, and the quartz tube was placed in a 16-channel swing melting furnace. The temperature was raised to 300°C and kept warm for 60 minutes. During the melting process, the furnace body was always kept automatically swinging up and down at a rate of 15 r / min and a swing angle of ±15°. After the melting was completed and the furnace was cooled, the alloy intermediate SnBi was obtained.

[0036] (4) Preparation of solder alloy: The alloy intermediate SnAg obtained in step (1), the intermediate SnGe obtained in step (2), the intermediate SnBi obtained in step (3) and the metal raw material Zn with a purity of 99.99% are combined and placed in a quartz tube. The quartz tube is vacuumed to 1×10 -4 The tube opening was sealed under Pa conditions. The quartz tube was then placed in a 16-channel rocking melting furnace and the temperature was raised to 500°C for 30 minutes. During the melting process, the furnace was automatically rocked up and down at a rate of 15 r / min and an angle of ±15°. After melting, the alloy was cooled at a rate of 8°C / min. When it cooled to 300°C, the sample was removed and water quenched to obtain the Sn-9Zn-0.4Ag-0.25Bi-0.4Ge alloy sample.

[0037] Example 3

[0038] A Sn-Zn lead-free solder containing Ag, Bi, and Ge has the following chemical composition and mass percentages: Zn: 9.0%, Ag: 0.4%, Bi: 0.5%, Ge: 0.6%, and the balance is Sn. The specific preparation method is as follows:

[0039] (1) Preparation of alloy intermediate SnAg: Weigh metal raw materials Sn and Ag with a purity of 99.99% according to a certain weight percentage and put them into a quartz tube. Vacuum the quartz tube to 1×10 -4 The tube mouth was sealed under Pa conditions, and the quartz tube was placed in a 16-channel swing melting furnace. The temperature was raised to 900°C and kept warm for 90 minutes. During the melting process, the furnace body was always kept automatically swinging up and down at a rate of 15r / min and a swing angle of ±15°. After the melting was completed and the furnace was cooled, the alloy intermediate SnAg was obtained.

[0040] (2) Refining alloy intermediate SnGe: Weigh a certain weight percentage of the metal raw material Sn with a purity of 99.99% and the powdered semi-metal raw material Ge into a quartz tube, and evacuate the quartz tube to 1×10 -4 The tube mouth was sealed under Pa conditions, and the quartz tube was placed in a 16-channel swing melting furnace. The temperature was raised to 950°C and kept warm for 90 minutes. During the melting process, the furnace body was always kept automatically swinging up and down at a rate of 15r / min and a swing angle of ±15°. After the melting was completed and the furnace was cooled, the alloy intermediate SnGe was obtained.

[0041] (3) Refining the alloy intermediate SnBi: Weigh the metal raw materials Sn and Bi with a purity of 99.99% according to a certain weight percentage and put them into a quartz tube. Vacuum the quartz tube to 1×10 -4 The tube mouth was sealed under Pa conditions, and then the quartz tube was placed in a 16-channel swing melting furnace, and the temperature was raised to 500°C and kept warm for 30 minutes. During the melting process, the furnace body was always kept automatically swinging up and down at a rate of 15r / min and a swing angle of ±15°. After the melting was completed and the furnace was cooled, the alloy intermediate SnBi was obtained.

[0042] (4) Preparation of solder alloy: The alloy intermediate SnAg obtained in step (1), the intermediate SnGe obtained in step (2), the intermediate SnBi obtained in step (3) and the metal raw material Zn with a purity of 99.99% are combined and placed in a quartz tube. The quartz tube is vacuumed to 1×10 -4 The tube opening was sealed under Pa conditions. The quartz tube was then placed in a 16-channel rocking melting furnace and the temperature was raised to 400°C for 60 minutes. During the melting process, the furnace was automatically rocked up and down at a rate of 15 r / min and an angle of ±15°. After melting, the alloy was cooled at a rate of 8°C / min. When it cooled to 300°C, the sample was removed and water quenched to obtain the Sn-9Zn-0.4Ag-0.5Bi-0.6Ge alloy sample.

[0043] Example 4

[0044] A Sn-Zn lead-free solder containing Ag, Bi, and Ge has the following chemical composition and mass percentages: Zn: 9.0%, Ag: 0.6%, Bi: 0.5%, Ge: 0.2%, and the balance is Sn. The specific preparation method is as follows:

[0045] (1) Preparation of alloy intermediate SnAg: Weigh metal raw materials Sn and Ag with a purity of 99.99% according to a certain weight percentage and put them into a quartz tube. Vacuum the quartz tube to 1×10 -4 The tube mouth was sealed under Pa conditions, and the quartz tube was placed in a 16-channel swing melting furnace. The temperature was raised to 800°C and kept warm for 90 minutes. During the melting process, the furnace body was always kept automatically swinging up and down at a rate of 15r / min and a swing angle of ±15°. After the melting was completed and the furnace was cooled, the alloy intermediate SnAg was obtained.

[0046] (2) Refining alloy intermediate SnGe: Weigh a certain weight percentage of the metal raw material Sn with a purity of 99.99% and the powdered semi-metal raw material Ge into a quartz tube, and evacuate the quartz tube to 1×10 -4The tube mouth was sealed under Pa conditions, the quartz tube was placed in a 16-channel swing melting furnace, and the temperature was raised to 900℃ and kept warm for 90 minutes. During the melting process, the furnace body was always kept automatically swinging up and down at a rate of 15r / min and a swing angle of ±15°. After the melting was completed and the furnace was cooled, the alloy intermediate SnGe was obtained.

[0047] (3) Refining the alloy intermediate SnBi: Weigh the metal raw materials Sn and Bi with a purity of 99.99% according to a certain weight percentage and put them into a quartz tube. Vacuum the quartz tube to 1×10 -4 The tube mouth was sealed under Pa conditions, and the quartz tube was placed in a 16-channel swing melting furnace. The temperature was raised to 500°C and kept warm for 30 minutes. During the melting process, the furnace body was always kept automatically swinging up and down at a rate of 15r / min and a swing angle of ±15°. After the melting was completed and the furnace was cooled, the alloy intermediate SnBi was obtained.

[0048] (4) Preparation of solder alloy: Weigh the alloy intermediates SnAg, SnGe, SnBi and 99.99% pure metal raw material Zn according to certain weight percentages and put them into a quartz tube. Vacuum the quartz tube to 1×10 -4 The tube opening was sealed under Pa conditions. The quartz tube was then placed in a 16-channel rocking melting furnace and the temperature was raised to 400°C for 60 minutes. During the melting process, the furnace was automatically rocked up and down at a rate of 15 r / min and an angle of ±15°. After melting, the alloy was cooled at a rate of 8°C / min. When it cooled to 300°C, the sample was removed and water quenched to obtain the Sn-9Zn-0.6Ag-0.5Bi-0.2Ge alloy sample.

[0049] Example 5

[0050] A Sn-Zn lead-free solder containing Ag, Bi, and Ge has the following chemical composition and mass percentages: Zn: 9%, Ag: 0.6%, Bi: 0.75%, Ge: 0.4%, and the balance is Sn. The specific preparation method is as follows:

[0051] (1) Preparation of alloy intermediate SnAg: Weigh metal raw materials Sn and Ag with a purity of 99.99% according to a certain weight percentage and put them into a quartz tube. Vacuum the quartz tube to 1×10 -4 The tube mouth was sealed under Pa conditions, and the quartz tube was placed in a 16-channel swing melting furnace. The temperature was raised to 1000℃ and kept warm for 60 minutes. During the melting process, the furnace body was always kept automatically swinging up and down at a rate of 20r / min and a swing angle of ±15°. After the melting was completed and the furnace was cooled, the alloy intermediate SnAg was obtained.

[0052] (2) Refining alloy intermediate SnGe: Weigh a certain weight percentage of the metal raw material Sn with a purity of 99.99% and the powdered semi-metal raw material Ge into a quartz tube, and evacuate the quartz tube to 1×10 -4 The tube mouth was sealed under Pa conditions, the quartz tube was placed in a 16-channel swing melting furnace, and the temperature was raised to 1000℃ and kept warm for 60 minutes. During the melting process, the furnace body was always kept automatically swinging up and down at a rate of 20r / min and a swing angle of ±15°. After the melting was completed and the furnace was cooled, the alloy intermediate SnGe was obtained.

[0053] (3) Refining the alloy intermediate SnBi: Weigh the metal raw materials Sn and Bi with a purity of 99.99% according to a certain weight percentage and put them into a quartz tube. Vacuum the quartz tube to 1×10 -4 The tube mouth was sealed under Pa conditions, and the quartz tube was placed in a 16-channel swing melting furnace. The temperature was raised to 500°C and kept warm for 30 minutes. During the melting process, the furnace body was always kept automatically swinging up and down at a rate of 20r / min and a swing angle of ±15°. After the melting was completed and the furnace was cooled, the alloy intermediate SnBi was obtained.

[0054] (4) Preparation of solder alloy: Weigh the alloy intermediates SnAg, SnGe, SnBi and 99.99% pure metal raw material Zn according to certain weight percentages and put them into a quartz tube. Vacuum the quartz tube to 1×10 -4 The tube opening was sealed under Pa conditions. The quartz tube was then placed in a 16-channel rocking melting furnace and heated to 400°C for 60 minutes. The furnace was automatically rocked up and down at a rate of 20 r / min throughout the melting process. The rocking angle was ±15°. After melting, the alloy was cooled at a rate of 8°C / min. When it cooled to 300°C, the sample was removed and water quenched to obtain the Sn-9Zn-0.6Ag-0.75Bi-0.4Ge alloy sample.

[0055] Performance testing:

[0056] (1) Melting Performance Test: Differential Scanning Calorimetry (DSC) curves of the lead-free solder alloy were measured during the heating and cooling processes. A 5-10 mg sample of lead-free solder was used for DSC analysis. The test parameters were: rapid heating from room temperature to 100°C, holding for 30 seconds, then heating to 250°C at a rate of 5°C / min to test the melting process of the lead-free solder. Finally, the solidification process was tested by cooling from 250°C to room temperature at a rate of 5°C / min.

[0057] (2) Antioxidation performance test: The antioxidation performance of the solder alloy is characterized by thermogravimetric analysis test. The test is carried out in a thermogravimetric analyzer with a weighing sensitivity of <0.1μg, and the experimental atmosphere is oxygen. The test parameters are: weighing a sample of about 60mg, heating to 250℃ at a rate of 10℃ / min and keeping warm for 30min, and collecting alloy weight change data in real time throughout the experiment. In the molten state, the metal elements in the solder easily combine with oxygen to form metal oxides, resulting in an increase in the mass of the alloy. The more oxygen atoms adsorbed in this process, the greater the mass increase, which means that its antioxidation performance is worse.

[0058] (3) Electrochemical corrosion performance: Testing was performed using an electrochemical workstation in a 3.5 wt.% NaCl solution at room temperature (25±2°C) using a three-electrode system. Potentiodynamic polarization curves were obtained by step-scanning from -1.5 V to 0 V at a scan rate of 5 mV / s.

[0059] Table 1 shows the comparison of the composition ratio and melting performance of the solder of the embodiment of the present invention and the comparative solder.

[0060] As can be seen from Table 1, compared with the base Sn-9Zn, the melting points of Examples 1-5 are slightly lower and the freezing points are slightly higher. The experimental results show that when Ag, Bi, and Ge elements are added to Examples 1-5, the melting point of the alloy decreases, which is more conducive to the soldering process of the solder. This is mainly because after the Bi element is added, Bi solid dissolves in the Sn matrix and interacts with the matrix, reducing the overall melting point of the solder alloy. When selecting the soldering process, if a solder with a lower melting point is used, the soldering temperature can be reduced, which can ensure that the solder with a lower melting point is completely melted and spread out, while also protecting the circuit board (PCB board) from high temperature damage. As can be seen from the table, among the Sn-Zn solder alloys, Example 5 (Sn-9Zn-0.6Ag-0.75Bi-0.4Ge) has a relatively low melting point (196.26°C), which is more suitable for low-temperature soldering of consumer electronic product chip circuit boards.

[0061] pass Figure 1 It can be seen that the microstructure of the base Sn-9Zn solder ( Figure 1 a, b) are relatively rough, and a large number of long strips of Zn-rich phase are precipitated in the matrix. Due to the relatively active chemical properties of Zn itself, the wettability, oxidation resistance and corrosion resistance of the Sn-9Zn matrix solder alloy are poor. From Example 2 Sn-9Zn-0.4Ag-0.25Bi-0.4Ge ( Figure 1 c, d) and Example 3Sn-9Zn-0.4Ag-0.5Bi-0.6Ge ( Figure 1e, f) can be seen that the solder alloy structure is significantly refined. In Example 2, the addition of Ag element consumes Zn and generates massive AgZn3 phase, reducing the precipitation of long strip-shaped Zn-rich phase, so that the alloy structure is effectively refined. In Example 3, the comprehensive addition of Ag, Bi, and Ge elements significantly refines the alloy microstructure, and obvious grains appear in the alloy structure, and a small amount of Zn is precipitated around the grains. In summary, the refinement effect of the structure of the Sn-9Zn-0.4Ag-0.5Bi-0.6Ge alloy in Example 3 is the most obvious. Alloys with uniform composition and fine structure will have better mechanical properties than other alloys. This is mainly because the fine and uniform structure reduces the degree of stress concentration during the deformation process of the alloy, thereby reducing the probability of fracture and improving the mechanical properties. At the same time, during the corrosion process of the alloy, the alloy with uniform and fine structure is not easy to form a primary cell reaction between the matrix and the precipitated phase, thereby improving the corrosion resistance of the alloy.

[0062] pass Figure 2 Thermogravimetric measurements of the solder alloys' oxidation weight gain curves revealed that after heating to 250°C, the base Sn-9Zn solder alloy experienced the greatest weight gain, indicating significant surface oxygen adsorption and severe surface oxidation, resulting in the poorest oxidation resistance. After the addition of Ag, Bi, and Ge, the thermogravimetric curves of Examples 1-5 all decreased relative to the base Sn-9Zn alloy, demonstrating improved oxidation resistance for all examples. The thermogravimetric curve of Example 2 showed the greatest decrease, indicating that the Sn-9Zn-0.4Ag-0.25Bi-0.4Ge alloy exhibited relatively superior oxidation resistance. While metallic Zn is susceptible to oxidation, AgZn3 exhibits superior oxidation resistance. Therefore, the improved oxidation resistance of Example 2 is primarily due to the formation of an AgZn3 intermetallic compound by the added Ag in the alloy and the reduced Zn-rich phase content. Therefore, Sn-9Zn-0.4Ag-0.25Bi-0.4Ge with relatively high Ag content exhibited better antioxidant properties.

[0063] pass Figure 3 The potential polarization curves of the solder alloys in electrochemical corrosion show that, relative to the base Sn-9Zn, the self-corrosion potentials E corr The corrosion current density I corr This indicates that the corrosion resistance of the solder alloys of Examples 1-5 has been effectively improved. This is due to the higher self-corrosion potential E corr The alloy is less likely to lose electrons and be oxidized or corroded in a humid environment. It has a lower self-corrosion current density I corrSince the current density is proportional to the electron transfer rate per unit time, and the electron transfer rate represents the corrosion rate of the alloy, the lower the self-corrosion current density I corr This can indirectly indicate that the alloy has a relatively low corrosion rate. In Example 2, the passivation current density I pass The decrease is the most obvious, indicating that the electrochemical corrosion rate of the alloy is relatively low during the long-term corrosion process, and the corrosion resistance of the alloy is improved.

[0064] Solder alloy passivation current density I pass The main reason for the decline is that after adding Ag, Bi and Ge elements, the precipitation of large Zn-rich phases in the alloy is reduced and the alloy microstructure is refined. This will reduce the probability of forming a galvanic reaction between the large Zn-rich phase and the matrix Sn, and at the same time reduce the probability of pitting corrosion of the alloy, thereby significantly improving the corrosion resistance of the solder. When uniform surface corrosion occurs on the alloy surface, a relatively dense passivation film will be generated on the alloy surface to protect the substrate from continuous corrosion. The above comprehensive analysis shows that the Sn-9Zn-0.4Ag-0.25Bi-0.4Ge alloy of Example 2 has a relatively high corrosion resistance potential E corr , lower self-corrosion current density I corr and the passivation current density I pass , indicating that it has relatively the best corrosion resistance.

[0065] Table 1 Melting performance data of lead-free solders and base Sn-9Zn alloy of Examples 1-5

[0066]

Claims

1. A Sn-Zn lead-free solder containing Ag, Bi and Ge, characterized in that: The lead-free solder comprises the following components by weight percentage: Zn: 9%, Ag: 0.2-0.6%, Bi: 0.25-0.75%, Ge: 0.2-0.6%, and the balance is Sn.

2. The Sn-Zn lead-free solder containing Ag, Bi and Ge according to claim 1, characterized in that: The lead-free solder is a bulk master alloy, solder wire, solder ball or solder powder.

3. The method for preparing the Sn-Zn lead-free solder containing Ag, Bi and Ge according to claim 1, characterized in that: The steps include: (1) Refining the alloy intermediate SnAg: Weigh the metal raw materials Sn and Ag, melt them under vacuum conditions, and cool the sample with the furnace after refining to obtain the alloy intermediate SnAg; (2) Refining alloy intermediate SnGe: Weigh the metal raw material Sn and the powdered semi-metal raw material Ge, smelt them under vacuum conditions, and cool the sample with the furnace after smelting to obtain the alloy intermediate SnGe; (3) Refining the alloy intermediate SnBi: Weigh the metal raw materials Sn and Bi, melt them under vacuum conditions, and cool the sample in the furnace after refining to obtain the alloy intermediate SnBi; (4) Alloy refining: weigh the alloy intermediate SnAg obtained in step (1), weigh the alloy intermediate SnGe obtained in step (2), weigh the alloy intermediate SnBi obtained in step (3), and the metal raw material Zn, and smelt them under vacuum conditions. After smelting, the sample is first cooled in the furnace, and then the sample is taken out and water quenched to finally obtain a Sn-Zn-Ag-Bi-Ge alloy sample.

4. The method for preparing the Sn-Zn lead-free solder containing Ag, Bi and Ge according to claim 3, characterized in that: The melting conditions in step (1) are: vacuum condition is 1×10 -4 Pa, the temperature rises to 800~1000℃, and is kept warm for 60~90min. The melting furnace body automatically swings up and down at a rate of 15~20r / min and a swing angle of ±15°.

5. The method for preparing the Sn-Zn lead-free solder containing Ag, Bi and Ge according to claim 3, wherein: The melting conditions in step (2) are: vacuum condition is 1×10 -4 Pa, the temperature rises to 900~1000℃, and is kept warm for 60~90min. The melting furnace body automatically swings up and down at a rate of 15~20r / min and a swing angle of ±15°.

6. The method for preparing the Sn-Zn lead-free solder containing Ag, Bi and Ge according to claim 3, wherein: The melting conditions in step (3) are: vacuum condition is 1×10 -4 Pa, the temperature rises to 300~500℃, and is kept warm for 30~60min. The melting furnace body automatically swings up and down at a rate of 15~20r / min and a swing angle of ±15°.

7. The method for preparing the Sn-Zn lead-free solder containing Ag, Bi and Ge according to claim 3, characterized in that: The melting conditions in step (4) are: vacuum condition is 1×10 -4 Pa, the temperature rises to 400~500℃, and is kept warm for 30~60min. The melting furnace body automatically swings up and down at a rate of 15~20r / min and a swing angle of ±15°.

8. The method for preparing the Sn-Zn lead-free solder containing Ag, Bi and Ge according to claim 3, characterized in that: The temperature of the furnace is decreased at a rate of 8°C / min during the furnace cooling in step (4); when the sample is cooled to 300°C, it is taken out and then water quenched.

9. The method for preparing the Sn-Zn lead-free solder containing Ag, Bi and Ge according to claim 3, wherein: The purity of the metal raw materials used is 99.99%.

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