Sn-Bi-In-Zn-Al low-melting-point high-entropy alloy lead-free solder and preparation method thereof

Abstract

The invention discloses a preparation method of Sn-Bi-In-Zn-Al low-melting-point high-entropy alloy lead-free brazing filler metal, and belongs to the technical field of lead-free brazing filler metal for welding, and the Sn-Bi-In-Zn-Al low-melting-point high-entropy alloy lead-free brazing filler metal comprises the following components in percentage by mole: 21.0% of Sn, 29.0% of Bi, 16.7% of In, 16.7% of Zn and 16.7% of Al. On the basis of a high-entropy alloy design concept, the high-entropy alloy lead-free solder Sn-Bi-In-Zn-Al with the entropy value of 1.58 R is designed according to a formula of (Sn-58Bi) 0.5 (InZnAl) 0.5 by adopting five elements with lower melting points, namely Sn, Bi, In, Zn and Al, and due to the special hysteresis diffusion effect and cocktail effect of the high-entropy alloy, the novel lead-free solder with the melting point lower than 83 DEG C is finally obtained. The wetting angle of the high-entropy alloy lead-free brazing filler metal is 28 degrees, which shows that the brazing filler metal can effectively reduce the wetting angle and improve the wettability, the melting point of the high-entropy alloy lead-free brazing filler metal is 82.03 DEG C, the high-entropy alloy lead-free brazing filler metal can meet the requirement of low-temperature welding, and the welding temperature can be controlled to be about 120 DEG C.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lead-free solder for welding, in particular to a Sn-Bi-In-Zn-Al low-melting-point high-entropy alloy lead-free solder and a preparation method thereof. BACKGROUND

[0002] In the field of electronic packaging, low-temperature solder has a unique application in the fields of automobiles, aviation, electrical instruments, light industry, etc. due to its low welding temperature, cost saving, etc. For a long time, Sn-Pb solder has served as the main connecting material in the assembly and interconnection of silicon modules (or chips) due to its low melting point, good wettability and reliable welding, etc. With the enhancement of people's environmental awareness and the promulgation and implementation of the WEEE directive (Waste Electrical and Electronic Equipment) and the RoHS directive (Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment) by the European Union, the traditional Sn-Pb solder is strictly limited and gradually eliminated in the market. Therefore, the development of low-temperature lead-free solder that can be practically applied has become the focus of attention in the field of electronic packaging.

[0003] Generally, solder with a melting point lower than 180℃ is considered as low-temperature solder. In the lead-free solder alloy system, such solder mainly includes Sn-In, In-Bi (Ag) and Sn-Bi. Among them, Sn-In solder has a low melting point of 117℃ when the mass ratio is 48:52, but In is a scarce and expensive metal, so it is difficult to be commercially applied. In-Bi (Ag) solder is also limited in application due to its low tensile strength. In the prior art, only Sn-Bi solder has been applied, which has a eutectic temperature of 139℃, low melting point, low cost and mechanical properties close to traditional Sn-Pb solder, and is therefore considered as an ideal substitute for traditional Sn-Pb solder. However, the problems of Bi segregation, solder wettability and solder reliability during the welding process of the solder have not been solved. In addition, with the miniaturization and lightness of electronic products, the high welding temperature leads to the risk of cracking, bridging and ball socket caused by warping and deformation of materials due to different thermal expansion coefficients. Therefore, it is necessary to reduce the soldering temperature of Sn-Bi solder.

[0004] In the related reports of reducing the melting point of Sn-Bi solder, adding trace elements is a common method, but the effect is not ideal. In recent years, the concept of high-entropy alloy breaks through the design limitations of traditional alloys, selects five or more elements to form an alloy, the atomic fraction of each metal element is between 5% and 35%, if there is a secondary element, the content of the secondary element is less than 5%, and the mixing entropy of the alloy is greater than 1.5R. As a new type of alloy material, high-entropy alloy has high mixing entropy, can effectively inhibit the precipitation of intermetallic compounds, and can effectively reduce the brittleness caused by the mixing of multiple components. In addition, related studies have shown that by using the concept of high-entropy alloy, designing appropriate components and their corresponding ratios, the melting point of the prepared alloy material can be greatly reduced, and the wettability of the solder can be effectively improved. However, in the field of welding, low-melting point lead-free solders designed and prepared by using the concept of high-entropy alloy are currently relatively rare. SUMMARY

[0005] The purpose of the present application is to provide a Sn-Bi-In-Zn-Al low-melting-point high-entropy alloy lead-free solder and a preparation method thereof.

[0006] The purpose of the present application can be achieved by the following technical solutions: A Sn-Bi-In-Zn-Al low-melting-point high-entropy alloy lead-free solder, in terms of mole percentage, its components are as follows: Sn is 21.0%, Bi is 29.0%, In is 16.7%, Zn is 16.7%, and Al is 16.7%.

[0007] The present application is based on the design concept of high-entropy alloy, and five elements with low melting point, Sn, Bi, In, Zn and Al, are used to design the high-entropy alloy lead-free solder Sn-Bi-In-Zn-Al with an entropy value of 1.58R according to the formula (Sn-58Bi) 0.5 (InZnAl) 0.5 The final new lead-free solder with a melting point lower than 83℃ is obtained due to the special sluggish diffusion effect and the cocktail effect of high-entropy alloy.

[0008] In the actual operation process, when Sn, Bi, In, Zn and Al are prepared, the error of the ratio of each component should be controlled within ±0.2%. If the error is too large, it will be difficult to obtain the ideal high-entropy component.

[0009] Preferably, the purity of Sn, Bi, In and Zn is ≥99.99%, and the purity of Al is ≥99.95%.

[0010] Each raw material is a high-purity metal particle, and an analytical balance is used for weighing.

[0011] The application discloses a preparation method of Sn-Bi-In-Zn-Al low-melting-point high-entropy alloy lead-free solder.

[0012] Preferably, the Sn, Bi, In, Zn and Al are poured into the mortar and then grinded, and the grinding time is 30-45 min.

[0013] The inventors find that, in the application, the metal particles can be mixed more uniformly by adding 2-3 mL of anhydrous ethanol twice in the grinding process.

[0014] Preferably, the pressure applied by the tablet press in the tabletting process is 8-10 MPa.

[0015] Preferably, the high-temperature heating is carried out in a nitrogen atmosphere, and the pressure of the nitrogen atmosphere is 0.015-0.020 MPa.

[0016] Preferably, the high-temperature heating process starts from 20 DEG C, the temperature is raised at a rate of 10 DEG C / min, the temperature is kept at 400 DEG C for 4 h, and then the temperature is naturally cooled to room temperature.

[0017] Preferably, the forming mode is natural cooling forming.

[0018] The application has the following beneficial effects: The wetting angle of the high-entropy alloy lead-free solder is 28 DEG, which indicates that the solder provided in the embodiment can effectively reduce the wetting angle and improve the wettability. BRIEF DESCRIPTION OF DRAWINGS

[0019] The application will be further described below in combination with the drawings.

[0020] Figure 1 The DSC curve of Sn-Bi-In-Zn-Al after natural cooling in the embodiment.

[0021] Figure 2 The DSC curve of Sn-Bi-In-Zn-Al after natural cooling in the comparative example 1.

[0022] Figure 3DSC curve of Sn-Bi-In-Zn-Al after natural cooling in Comparative Example 2.

[0023] Figure 4 Wetting angle of Sn-Bi-In-Zn-Al in Comparative Example 1.

[0024] Figure 5 Wetting angle of Sn-Bi-In-Zn-Al in Comparative Example 2.

[0025] Figure 6 Wetting angle of Sn-Bi-In-Zn-Al in Comparative Example 2. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0027] EMBODIMENT The Sn-Bi-In-Zn-Al low-melting-point high-entropy alloy lead-free solder in the embodiment has the components and atomic mole percentages of Sn 21.0%, Bi 29.0%, In 16.7%, Zn 16.7%, and Al 16.7%, and the calculated entropy value is 1.58R; The specific preparation operation steps are as follows: The raw materials Sn, Bi, In, and Zn with a purity of more than 99.99% and the raw material Al with a purity of more than 99.95% are prepared according to (Sn-58Bi) 0.5 (InZnAl) 0.5 4.5g is prepared; The prepared raw materials are poured into an agate mortar, and 2-3 mL of anhydrous ethanol is added dropwise twice during continuous grinding for 30-40 min; The ground alloy powder is tabletted by a tablet machine, and the applied pressure is controlled to be 10 MPa. Subsequently, the tablet-shaped alloy material is placed in a graphite crucible, and the graphite crucible is placed in a tube furnace for high-temperature heating. The heating rate is 10℃ / min, the temperature is kept at 400℃ for 4h after the temperature is raised to 400℃, and then the temperature is naturally cooled to room temperature for forming. The entire high-temperature heating process is carried out in a nitrogen atmosphere, and the pressure of the nitrogen is 0.015-0.020 MPa.

[0028] COMPARATIVE EXAMPLE 1 The other conditions are the same as in the embodiment, and only the component proportioning is different, according to (Sn-58Bi)0.75 (InZnAl) 0.25 The ingredients and their atomic mole percentages are as follows: Sn is 31.50%, Bi is 43.50%, In is 8.33%, Zn is 8.33%, and Al is 8.33%, and the calculated entropy value is 1.35R.

[0029] Comparative Example 2 The other conditions are the same as in the example, and only the component proportions are different, according to (Sn-58Bi) 0.95 (InZnAl) 0.05 The ingredients and their atomic mole percentages are as follows: Sn is 39.90%, Bi is 55.10%, In is 1.67%, Zn is 1.67%, and Al is 1.67%, and the calculated entropy value is 0.90R.

[0030] Melting temperature test: A STA449F5 simultaneous thermal analyzer was used to measure the melting points of the prepared lead-free solders in the example, comparative example 1 and comparative example 2. About 10 mg of solder was taken, nitrogen gas was used as the protective gas, and the heating rate was set to 5°C / min in the range of 40°C to 350°C.

[0031] The test results are shown in Figure 1 , Figure 2 and Figure 3 The melting point of the high-entropy alloy lead-free solder in the example is 82.03°C, the melting point of the entropy alloy lead-free solder in comparative example 1 is 137.08°C, and the melting point of the low-entropy alloy lead-free solder in comparative example 2 is 139.03°C. It can be seen that the melting temperature of the application example is significantly lower than that of comparative examples 1 and 2, which shows that the high-entropy alloy lead-free solder provided by the application example can meet the requirements of low-temperature welding, and the welding temperature can be controlled around 120°C.

[0032] Wettability test: A copper sheet with a size of 25mm x 25mm x 0.2mm was used as the substrate, and after polishing to 1500 mesh with SiC sandpaper, it was first acid washed with 0.1 mol / L hydrochloric acid to remove surface impurities; The surface residual hydrochloric acid was washed clean with deionized water; then it was washed with anhydrous ethanol and dried for standby; Then about 0.02g of solder was taken from the solder provided in the example, comparative example 1 and comparative example 2, mixed with a small amount of flux (Xilifex rosin flux), and placed in a graphite crucible, heated on a 130°C constant temperature heating table, and agglomerated into a spherical shape under the action of tension. After solidification, the wetting angle was measured.

[0033] The test results are shown in Figure 4、 Figure 5 and Figure 6 As shown in the figure, the wetting angle of the high-entropy alloy lead-free solder of the embodiment is 28°, the wetting angle of the medium-entropy alloy lead-free solder in the comparative example 1 is 43°, and the wetting angle of the low-entropy alloy lead-free solder in the comparative example 2 is 65°, which indicates that the solder provided in the embodiment can effectively reduce the wetting angle and improve the wettability.

[0034] The above-described embodiments, the comparative example 1 and the comparative example 2 are only used to illustrate the technical solutions of the present application, but not to limit them; although the above-described embodiments, the comparative example 1 and the comparative example 2 are referred to, those skilled in the art should understand that the technical solutions recorded in the above-described embodiments can be modified, or the technical features therein can be replaced by equivalents; and the modifications and replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments and the comparative example 1 and the comparative example 2 of the present application.

[0035] The above content is only an example and description of the present application, and those skilled in the art can make various modifications or supplements or use similar ways to replace the described specific embodiments, as long as they do not deviate from the application or exceed the scope defined by the present claims, which should belong to the protection scope of the present application.

Claims

1. A Sn-Bi-In-Zn-Al low-melting-point high-entropy alloy lead-free solder, characterized in that: Based on molar percentages, its composition is as follows: Sn 21.0%, Bi 29.0%, In 16.7%, Zn 16.7%, Al 16.7%, and its compound expression is (Sn-58Bi). 0.5 (InZnAl) 0.5 .

2. The Sn-Bi-In-Zn-Al low-melting-point high-entropy alloy lead-free solder according to claim 1, characterized in that: The purity of Sn, Bi, In, and Zn is ≥99.99%, and the purity of Al is ≥99.95%.

3. The method for preparing lead-free solder according to any one of claims 1 to 2, characterized in that, Includes the following steps: Take Sn, Bi, In, Zn and Al according to the design ratio, pour them into a mortar and grind them together; The ground metal particles are compressed into tablets using a tablet press. The sheet is heated at high temperature in a nitrogen atmosphere to obtain a melt, which is then cooled and shaped to obtain Sn-Bi-In-Zn-Al lead-free solder.

4. The preparation method according to claim 3, characterized in that: The mixing and grinding time is 30 to 45 minutes.

5. The preparation method according to claim 4, characterized in that: During the mixing and grinding process, anhydrous ethanol is added dropwise multiple times, with the ratio of metal particles to anhydrous ethanol being 9g:4mL-6mL.

6. The preparation method according to claim 4, characterized in that: During the mixing and grinding process, the tableting process is carried out by applying a pressure of 8~10MPa by the tablet press.

7. The preparation method according to claim 3, characterized in that: The nitrogen pressure in the nitrogen atmosphere is 0.015~0.020 MPa.

8. According to the preparation method of claim 3, the high-temperature heating process is as follows: the heating rate is 10℃ / min, the temperature is raised to 400℃ and then kept constant for 4 hours, and then cooled to room temperature.

9. The preparation method according to claim 8, wherein the cooling and molding method is natural cooling and molding.

Images