CN115011820B

CN115011820B - Preparation method of high-elongation SnBi alloy

Info

Publication number: CN115011820B
Application number: CN202111606668.7A
Authority: CN
Inventors: 李才巨; 周广吉; 肖坤璇; 高鹏; 易健宏
Original assignee: Kunming University of Science and Technology
Current assignee: Kunming University of Science and Technology
Priority date: 2021-12-26
Filing date: 2021-12-26
Publication date: 2023-08-22
Anticipated expiration: 2041-12-26
Also published as: CN115011820A

Abstract

The invention discloses a preparation method of a high-elongation SnBi alloy, belonging to the technical field of electronic packaging materials. Vacuum smelting is carried out on SnBi alloy, the smelting condition is 500-800 ℃, the heat preservation is carried out for 1h, and then the SnBi alloy is put into water for cooling when the temperature is reduced to 300-400 ℃; the cooled sample is subjected to room temperature compression treatment, and the compression rate is 50-80%; finally, annealing the compressed sample, and preserving heat for 1h at 120 ℃ to prepare a high-elongation sample; the preparation method can refine the structure of the SnBi alloy matrix, thereby greatly improving the elongation of the alloy and improving the brittleness of the SnBi alloy matrix.

Description

Preparation method of high-elongation SnBi alloy

Technical Field

The invention relates to a preparation method of a high-elongation SnBi alloy, belonging to the technical field of electronic packaging materials.

Background

With the continuous development of miniaturization and microminiaturization of electronic products, the performance requirements on the required welding materials are also higher and higher. Sn—pb solder has long been the most predominant solder in the electronics industry with its proper use temperature, excellent soldering performance, high reliability, and lower price, and has been widely used in the field of electronic packaging. However, lead is toxic, and can pollute the environment after long-term use and seriously harm the health of human bodies. With the increasing awareness of environmental protection, countries have been restricted to the use of lead-containing products by legislation. In order to develop a lead-free solder that can replace Sn-Pb solder, many studies have been made by various nations around the world, and the main lead-free solder alloy systems are Sn-Ag, sn-Zn, sn-Bi, and the like. The Sn-Bi solder has the advantages of low melting point, good wettability, higher fatigue resistance, mechanical property, low price and the like, and becomes one of the low-temperature solder alloys with the most research significance and use value. Particularly low melting point, and is particularly suitable for products requiring low temperature welding.

However, the Bi element is a brittle element, so that the lattice structure is a rhombohedral structure and the denaturation capability is poor. Meanwhile, in order to reduce the melting point of the alloy, the content of Bi element in the matrix is relatively high, and the content of eutectic point is about 58wt%, so that the alloy is easy to be biased and exists in the matrix in a sheet or net form, and the matrix has relatively high brittleness; thus, new methods of preparation are needed to improve the brittleness problem of the SnBi alloy.

Disclosure of Invention

The invention aims at solving the brittleness problem of a SnBi alloy matrix, and provides a preparation method of a high-elongation SnBi alloy, which comprises the following steps:

(1) Smelting the proportioned SnBi alloy raw materials in a vacuum environment, cooling to 300-400 ℃ after smelting, taking out, and cooling in water.

(2) And compressing the smelted sample at room temperature.

(3) And (3) annealing the compressed sample to finally prepare the SnBi alloy with high elongation.

Preferably, the compression rate in step (2) of the present invention is 1X 10 ^-4 -1×10 ^-3 s ^-1 The compression ratio is 50-80%.

Preferably, the smelting temperature in the step (1) is 500-800 ℃, and the temperature is kept for 1h.

Preferably, the vacuum degree in the step (1) of the present invention is 10 ^-3 -10 ⁵ Pa, avoiding oxidation of the sample during smelting.

Preferably, the annealing condition in the step (3) is that the annealing is performed for 1 hour at 120 ℃, and the annealing treatment can be performed in a resistance heating furnace.

The invention has the beneficial effects that:

compared with the method for preparing the SnBi alloy by adopting a casting method, the elongation percentage of the alloy prepared by the method can be greatly improved; the reason is that the Bi content in the SnBi alloy is high, and the alloy is a brittle element and has poor denaturation capability; bi forms eutectic structures with Sn in the alloy matrix, and is distributed in a lamellar manner, which ensures a certain strength of the alloy but deteriorates the elongation. In the alloy deformation process, dislocation is easy to gather near the laminar Bi phase, a serious stress concentration effect is generated, the Bi phase is broken, a crack source is formed, and finally the material is cracked. After cold pressing treatment, a large amount of lamellar Bi is broken, so that the lamellar Bi is finer, and the stress concentration effect is greatly reduced; therefore, the elongation is greatly improved, but the strength is reduced; after annealing treatment, bi dissolved in Sn in a solid solution manner is precipitated in a fine dot form to play a role of dispersion strengthening, and broken Bi is grown in a compression process, so that the alloy strength is improved, but the elongation is reduced.

Drawings

FIG. 1 is a diagram of the morphology of a sample tissue without cold press deformation and annealing;

FIG. 2 is a graph of tissue morphology of a sample subjected to 50% room temperature compression deformation without annealing;

FIG. 3 is a graph of the morphology of a sample after 50% room temperature compression set and annealing;

fig. 4 shows stress-strain curves for uncompressed samples and samples treated at different compression ratios.

Detailed Description

The invention will be further described with reference to specific embodiments in which the Sn50Bi alloy is used as an example, but the scope of the invention is not limited to this.

Example 1

A preparation method of high-elongation SnBi alloy comprises the following specific steps:

(1) 50g of Sn and Bi particles are arranged according to the weight ratio of 1:1 and are put into a quartz tube for sealing, and the internal vacuum degree is pumped to 10 ^-3 Pa, smelting in a resistance furnace, preserving heat at 500 ℃ for 1h, periodically shaking the quartz tube to ensure uniform components, cooling to 300 ℃, taking out, cooling in water, and knocking the quartz tube to take out a sample.

(2) Cutting the cooled sample into cylinders with the length of 10mm, and putting the cylinders under a universal mechanical testing machine for compression treatment, wherein the compression rate is 10 ^-3 s ^-1 The method comprises the steps of carrying out a first treatment on the surface of the The compression ratio is 50%, the mixture is put into a resistance heating furnace for annealing treatment after being pressed, the annealing temperature is 120 ℃, the time is 1h, and the sample preparation is completed; compared with the SnBi alloy which is not subjected to compression treatment, the strength is slightly reduced, but the elongation exceeds 140%, and the elongation is obviously improved.

Example 2

(1) 50g of Sn and Bi particles are arranged according to the weight ratio of 1:1 and are put into a quartz tube for sealing, and the internal vacuum degree is pumped to 10 ^-3 Pa, then placing into a resistance furnace for smelting, preserving heat for 1h at 500 ℃, periodically shaking the quartz tube during the period to ensure uniform components, then cooling to 300 ℃, taking out, placing into water for cooling, and knocking out the quartz tube to take out a sample.

(2) Cutting the cooled sample into cylinders with the length of 10mm, and placing the cylinders under a universal mechanical testing machine for cold pressing treatment, wherein the compression rate is 10 ^-3 s ^-1 The method comprises the steps of carrying out a first treatment on the surface of the The compression ratio is 65%, the sample is put into a resistance heating furnace for annealing treatment after being pressed, the annealing temperature is 120 ℃, the time is 1h, and the sample preparation is completed; compared with the SnBi alloy which is not subjected to compression treatment, the ultimate tensile strength of the SnBi alloy is continuously reduced along with the increase of the compression amount, the elongation is continuously increased by more than 200%, and the ultimate tensile strength is remarkably improved.

Example 3

(2) Cutting the cooled sample into cylinders with the length of 10mm, and placing the cylinders under a universal mechanical testing machine for room temperature compression treatment, wherein the compression rate is 10 ^-3 s ^-1 The method comprises the steps of carrying out a first treatment on the surface of the The compression ratio is 75%, the mixture is put into a resistance heating furnace for annealing treatment after being pressed, the annealing temperature is 120 ℃, the time is 1h, and the sample preparation is completed. The ultimate tensile strength of the sample was reduced by about 10MPa and the elongation was over 210% compared to the SnBi alloy without compression and annealing and the alloy with different compression ratios, although the increase was continued but the increase was insignificant.

Comparative example 1

The present example method is the same as example 1, except that no compression and annealing steps are performed.

Comparative example 2

The method of this example is the same as example 1, except that: only compression was performed and no annealing step was performed.

Table 1 test data for ultimate tensile strength and elongation for different compression ratio examples

It can be seen from table 1 that as the deformation amount increases, the elongation of the alloy gradually increases and the strength gradually decreases. Compared with the structure diagram of fig. 1 and 2, after compression treatment, the coarse lamellar Bi phase distributed in the matrix is broken and becomes finer and denser, and the distribution state greatly improves the elongation of the alloy, and simultaneously reduces the blocking effect on dislocation movement, so that the strength of the alloy is reduced. As the deformation amount increases, the degree of fracture of the Bi phase increases, the elongation also gradually increases, and the strength gradually decreases. It can be seen from fig. 3 that the Bi phase broken before the annealing treatment of the alloy is recovered to grow up, so that the strength of the strength alloy is improved but the elongation is reduced.

Claims

1. The preparation method of the SnBi alloy with high elongation is characterized by comprising the following steps:

(1) Smelting SnBi alloy in a vacuum state; after smelting, taking out the sample at 300-400 ℃, and putting the sample into water for cooling;

(2) Compressing the smelted sample at room temperature;

(3) Annealing the compressed sample to finally prepare the SnBi alloy with high elongation;

the compression rate in step (2) is 1×10 ^-4 -1×10 ^-3 s ^-1 The compression ratio is 50-80%;

the annealing conditions in the step (3) are as follows: the temperature was kept at 120℃for 1h.

2. The method for producing a high-elongation SnBi-based alloy according to claim 1, wherein: the smelting temperature in the step (1) is 500-800 ℃, and the temperature is kept for 1h.

3. The method for producing a high-elongation SnBi-based alloy according to claim 1, wherein: the vacuum degree of the sample smelting in the step (1) is 10 ^-3 -10 ^-5 Pa。