CN112958941B

CN112958941B - Sn-Bi-In-Zn-Ga low-melting-point high-entropy alloy lead-free solder and preparation method and application thereof

Info

Publication number: CN112958941B
Application number: CN202110297066.1A
Authority: CN
Inventors: 徐先东; 张天宇; 陈江华
Original assignee: Hunan University
Current assignee: Hunan University
Priority date: 2021-03-19
Filing date: 2021-03-19
Publication date: 2022-03-29
Anticipated expiration: 2041-03-19
Also published as: CN112958941A

Abstract

The invention discloses a Sn-Bi-In-Zn-Ga low-melting-point high-entropy alloy lead-free solder and a preparation method and application thereof, wherein the Sn-Bi-In-Zn-Ga low-melting-point high-entropy alloy lead-free solder comprises the following components In mole percentage: 20.0% of Sn, 20.0% of Bi, 20.0% of In, 20.0% of Zn and 20.0% of Ga. The preparation is that after smelting, alloy cast ingots are obtained by direct pouring, the preparation is simple, the energy consumption in the preparation process is low, and the preparation process is pollution-free and easy to control. The invention adopts five low-melting-point elements of Sn, Bi, In, Zn and Ga, designs the lead-free solder according to the formula (Sn: Bi: In: Zn: Ga 1:1:1:1) with equal atomic ratio, and finally obtains the novel low-temperature lead-free solder with the melting point lower than 80 ℃ by virtue of the special slow diffusion effect and the cocktail effect of the high-entropy alloy, and the lead-free solder has good wetting property at 100 ℃, good conductivity and good soldering property, and is suitable for the requirement of a 3D IC soldering and welding process.

Description

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

Technical Field

The invention relates to a solder In the technical field of welding materials, In particular to Sn-Bi-In-Zn-Ga low-melting-point high-entropy alloy lead-free solder and a preparation method and application thereof.

Background

With the rapid development of 5g technology, remote office work and online lectures become possible. The higher demands for the intelligent mobile devices around, such as more functions, faster response speed, smaller space and cheaper price, make the electronic package manufacturing industry face serious challenges. The warping problem of the silicon wafer at high temperature and the reliability problem of the welding spot are urgently needed to be solved, so that the development of a novel welding flux with low melting point, good mechanical property and slow IMC (intermetallic compound) growth speed is very important.

In addition, Moore's Law is approaching the limit in miniaturization, because the complexity and fault tolerance rate increase exponentially with the increase of the line density on the silicon wafer, which is equivalent to the size of only a few molecules once the width of the line on the chip reaches the order of nanometers, in which case the physical and chemical properties of the material change substantially, resulting in the failure of the semiconductor device to work properly, and the Moore's Law also reaches the end.

Currently, the most promising approach to break through the bottleneck encountered in the electronic packaging industry and promote moore's law is to develop from two-dimensional (2D) integrated circuits to three-dimensional (3D) integrated circuits. Through silicon via (tsv) technology used in 3D ICs can vertically stack multiple layers of silicon chips through micro Bumps (μ -Bumps), thereby reducing interconnection length, reducing signal delay, reducing capacitance/inductance, and achieving low power consumption, high speed, and miniaturization.

Currently, two prominent phenomena in 3D ICs are of concern: (1) the warping problem of the silicon chip. The problem of warpage due to mismatch in thermal expansion coefficients becomes particularly pronounced as the thickness of silicon wafers in 3D ICs is reduced from 200 μm to 50 μm due to size limitations. Therefore, the reduction of the temperature during welding is particularly important for reducing the warping and the displaying of the silicon wafer; (2) reliability of solder joints. The high diffusivity and fast response of lead-free solder and the shrinking chip size provided by 3DIC in solder microbumps has led to the widespread formation of intermetallic compounds (IMCs) in solder microbumps. In 3D IC fabrication, the interferometric compound (IMC) volume fraction in a pad is related to the size of the pad. There is therefore a need to develop a new solder with a low melting point, a low IMC growth rate and good wettability.

However, in the prior art, only Sn-Bi solder which has been applied has the melting point of 139 ℃, has the advantages of good wettability and lower welding temperature, but the problems of Bi segregation and welding spot brittleness generated in the welding process of the solder are not solved. In addition, no lead-free solder is available at 100 ℃ or lower.

The high-entropy alloy breaks through the traditional design concept and is alloyed according to equal atomic ratio or near equal atomic ratio, generally contains 5-13 elements, and cannot distinguish solvent components and solute components in the solid solution to form disordered multi-component super solid solution. The high-entropy alloy as a novel solid solution alloy has the characteristics different from those of the traditional alloy, and is mainly embodied in the following four aspects: 1. high entropy effect; 2. severe lattice distortion; 3. a slow diffusion effect; 4. cocktail effect. The high entropy effect effectively inhibits the precipitation of intermetallic compounds, reduces alloy brittleness caused by multi-component alloy, and forms a phase structure taking solid solution as a main component. It has been found that the unique solid solution structure of the high entropy alloy can cause the high entropy alloy to have excellent performance which can not be compared with the traditional alloy. Such as high strength, high hardness, high wear resistance, and corrosion resistance. However, no solder formulated with the concept of high entropy alloys is currently available among the solders used.

Disclosure of Invention

Aiming at the defects In the prior art, the invention aims to provide Sn-Bi-In-Zn-Ga low-melting-point high-entropy alloy lead-free solder and a preparation method thereof.

The invention relates to Sn-Bi-In-Zn-Ga low-melting-point high-entropy alloy lead-free solder which comprises the following components In percentage by mol: 20.0% of Sn, 20.0% of Bi, 20.0% of In, 20.0% of Zn and 20.0% of Ga.

The invention adopts the idea of high-entropy alloy, and unexpectedly discovers that the lead-free solder is designed by adopting five low-melting-point elements of Sn, Bi, In, Zn and Ga according to a formula (Sn: Bi: In: Zn: Ga: 1:1:1) with equal atomic ratio, and the novel low-temperature lead-free solder with the melting point lower than 80 ℃ is finally obtained by benefiting from the special slow diffusion effect and the cocktail effect of the high-entropy alloy, and has good wettability, good conductivity and good soldering performance at 100 ℃, thereby being suitable for the requirements of a 3D IC soldering and welding process.

In the actual operation process, when Sn, Bi, In, Zn and Ga are prepared, the mixture ratio error of each component needs to be controlled within the range of +/-0.2 percent. If the error is too large, the ideal high entropy effect cannot be obtained.

In the preferred scheme, the purities of Sn, Bi, In, Zn and Ga are all more than or equal to 99.99%.

The raw materials were collected as high-purity metal particles and weighed with an analytical balance.

The inventors have made a great deal of realization and found that the combination of Sn, Bi, In, Zn and Ga can obtain an excellent high-entropy effect, and finally lead-free solder has good wettability, good conductivity and good soldering performance, and if any element In the lead-free solder is adjusted, no ideal performance effect can be obtained.

In the preferable scheme, the melting point of the Sn-Bi-In-Zn-Ga low-melting-point high-entropy alloy lead-free solder is less than or equal to 80 ℃, and is preferably 72-76 ℃.

The invention relates to a preparation method of Sn-Bi-In-Zn-Ga low-melting-point high-entropy alloy lead-free solder, which comprises the following steps: preparing Sn, Bi, In, Zn and Ga according to a designed proportion; pouring the mixture into a crucible, then smelting to obtain a melt, and forming to obtain the Sn-Bi-In-Zn-Ga lead-free solder.

Preferably, Zn, Bi, Sn, In and Ga are poured into the crucible In sequence from bottom to top. The crucible used in the present invention is preferably a corundum crucible.

The inventors have found that by pouring the raw materials in the above order, the final melting is fastest and the final resulting melt composition is most uniform.

In a preferable scheme, the smelting is carried out in an argon atmosphere, and the pressure of the argon atmosphere is 0.03-0.04 MP.

In the preferred scheme, Sn, Bi, In, Zn and Ga are poured into a crucible, then the crucible is vacuumized, gas replacement is carried out for 3 times, and finally, a vacuum pump is closed, and high-purity argon with the purity of 99.99% is filled into the crucible, wherein the pressure of the atmosphere is 0.03-0.04 MP. .

The inventor finds that by adopting positive pressure smelting in the invention, Zn can be prevented from volatilizing in the smelting process, so that the uniformity of the final solder is higher.

Preferably, the smelting process comprises the steps of firstly controlling the smelting current at 170-180A, preheating for 2-3min, and then adjusting the smelting current to 195-205A, and heating for 4-5 min.

Preferably, the molding mode is from casting to copper mold molding or natural cooling molding, and preferably from casting to copper mold molding.

Further preferably, when the casting to copper mold forming is adopted, the copper mold is cooled by water cooling.

The invention discloses an application of Sn-Bi-In-Zn-Ga low-melting-point high-entropy alloy lead-free solder, which is applied to 3D IC welding.

Drawings

FIG. 1 DSC curve of Sn-Bi-In-Zn-Ga copper mold after water cooling In example 1,

FIG. 2 DSC curve of Sn-Bi-In-Zn-Ga In example 1 after furnace cooling.

Detailed Description

Example 1

The Sn-Bi-In-Zn-Ga low-melting-point high-entropy alloy lead-free solder of the embodiment comprises the following components In atomic mole percent: 20.0% of Sn, 20.0% of Bi, 20.0% of In, 20.0% of Zn and 20.0% of Ga, and the preparation steps are as follows: 100g of raw materials Sn, Bi, In, Zn and Ga with the purity of more than 99.99 percent are prepared according to the equal atomic mole percentage. The prepared raw materials are sequentially put into a corundum crucible from the top to the bottom according to the sequence of melting points, and the element with the lowest melting point is on the uppermost layer. And (3) putting the corundum crucible filled with the alloy material into a spiral induction coil in a high vacuum induction melting casting furnace, vacuumizing for 20min by using a mechanical pump, closing the vacuum pump, and filling high-purity argon with the purity of 99.99% to normal atmospheric pressure to finish a gas washing process. The gas washing process is repeated for three times, and the high-purity argon is filled to the positive pressure of 0.04MPa after the last gas washing. And (3) after preheating for 2min by adjusting the current to 180A, increasing the current to 200A, heating for 4min, closing induction current heating when the alloy is completely in a golden yellow liquid state, and pouring the alloy into a copper mold for cooling. This example provides a low melting point high entropy alloy lead-free solder with a melting point of 75.6 ℃.

Example 2

The Sn-Bi-In-Zn-Ga low-melting-point high-entropy alloy lead-free solder of the embodiment comprises the following components In atomic mole percent: 20.0% of Sn, 20.0% of Bi, 20.0% of In, 20.0% of Zn and 20.0% of Ga, and the preparation steps are as follows: 100g of raw materials Sn, Bi, In, Zn and Ga with the purity of more than 99.99 percent are prepared according to the equal atomic mole percentage. The prepared raw materials are sequentially put into a corundum crucible from the top to the bottom according to the sequence of melting points, and the element with the lowest melting point is on the uppermost layer. And (3) putting the corundum crucible filled with the alloy material into a spiral induction coil in a high vacuum induction melting casting furnace, vacuumizing for 20min by using a mechanical pump, closing the vacuum pump, and filling high-purity argon with the purity of 99.99% to normal atmospheric pressure to finish a gas washing process. The gas washing process is repeated for three times, and the high-purity argon is filled to the positive pressure of 0.04MPa after the last gas washing. Adjusting the current to 180A, preheating for 2min, increasing the current to 200A, heating for 4min, stopping induction current heating when the alloy is completely golden yellow liquid, and naturally cooling and molding in a furnace. The present example provides a low melting point high entropy alloy lead-free solder with a melting point of 73.3 ℃.

Comparative example 1

The other conditions are the same as the example 1, only the component proportion is different, and the ratio of Sn: bi: in: the Zn is mixed In the ratio of 1:1:1:1 (atomic percent), the melting point of the obtained solder is about 80 ℃ and higher than that of the solder, and the content of the rare metal In used by the solder of the invention In the same quality of the solder is less than the content, so the cost is reduced.

Comparative example 2

The other conditions were the same as in example 1 except that the melting was carried out under an argon atmosphere at normal pressure. As a result, a large amount of metal gas is volatilized during the melting process to deposit on the wall of the melting furnace, resulting in contamination of the equipment and deviation of the alloy composition from the designed composition.

Claims

1. The Sn-Bi-In-Zn-Ga low-melting-point high-entropy alloy lead-free solder is characterized In that: the composition comprises the following components in percentage by mole: 20.0% of Sn, 20.0% of Bi, 20.0% of In, 20.0% of Zn and 20.0% of Ga;

the melting point of the Sn-Bi-In-Zn-Ga low-melting-point high-entropy alloy lead-free solder is less than or equal to 80 ℃.

2. The Sn-Bi-In-Zn-Ga low-melting-point high-entropy alloy lead-free solder according to claim 1, characterized In that: the purities of the Sn, the Bi, the In, the Zn and the Ga are all more than or equal to 99.99 percent.

3. The method for preparing Sn-Bi-In-Zn-Ga low-melting-point high-entropy alloy lead-free solder according to any one of claims 1 to 2, characterized In that: the method comprises the following steps: preparing Sn, Bi, In, Zn and Ga according to a designed proportion; pouring the mixture into a crucible, then smelting to obtain a melt, and forming to obtain the Sn-Bi-In-Zn-Ga lead-free solder.

4. The method for preparing Sn-Bi-In-Zn-Ga low-melting-point high-entropy alloy lead-free solder according to claim 3, characterized In that: sequentially pouring Zn, Bi, Sn, In and Ga into the crucible from bottom to top.

5. The method for preparing Sn-Bi-In-Zn-Ga low-melting-point high-entropy alloy lead-free solder according to claim 3, characterized In that: the smelting is carried out in an argon atmosphere, and the pressure of the argon atmosphere is 0.03-0.04 MP.

6. The method for preparing Sn-Bi-In-Zn-Ga low-melting-point high-entropy alloy lead-free solder according to claim 3, characterized In that: the smelting process comprises the steps of firstly controlling the smelting current at 170-180A, preheating for 2-3min, and then adjusting the smelting current to 195-205A, and heating for 4-5 min.

7. The method for preparing Sn-Bi-In-Zn-Ga low-melting-point high-entropy alloy lead-free solder according to claim 3, characterized In that: the forming mode is casting to copper mould forming or natural cooling forming.

8. Use of a Sn-Bi-In-Zn-Ga low melting point high entropy alloy lead-free solder according to any one of claims 1-2, characterized In that: the Sn-Bi-In-Zn-Ga low-melting-point high-entropy alloy lead-free solder is applied to 3D IC welding.