A method for synchronously preparing and observing small tin nanoparticles based on transmission electron microscopy and application thereof

Abstract

The application discloses a method for synchronously preparing and observing small-size tin nanoparticles based on a transmission electron microscope and application thereof, and belongs to the field of solder particles and preparation thereof. The application aims to provide a method for synchronously preparing and observing small-size tin nanoparticles based on a transmission electron microscope and application thereof. The method comprises the following steps: dropping anhydrous ethanol suspension liquid of large-size tin nanoparticles on an in-situ heating chip of a transmission electron microscope; placing the transmission electron microscope in a high-vacuum environment after the anhydrous ethanol is evaporated; and raising and maintaining the temperature to obtain a liquid tin droplet; and converging an electron beam on the edge of the tin droplet, so that the tin droplet explodes and splashes to obtain small-size tin nanoparticles. The method can simplify the preparation process, reduce the operation difficulty, realize the observation of nanoscale liquid-solid phase transition while preparing the tin nanoparticles, and can obtain tin nanoparticles with various sizes. In addition, the reusability of a single in-situ heating chip is improved.

Description

Technical Field

[0001] This invention belongs to the field of solder particles and their preparation, specifically relating to a method for the simultaneous preparation and observation of small-sized tin nanoparticles based on transmission electron microscopy and its application. Background Technology

[0002] Solder is a crucial interconnecting material for forming electrical and mechanical connections during the assembly of electronic products. Over the past few decades, the use of tin-based lead-free solder has become technologically stable. As electronic components continue to evolve towards miniaturization and densification, the demand for solder paste capable of finer-pitch interconnects is increasing. Adding nanoscale solder particles, such as tin nanoparticles, to solder paste is an effective way to improve its fine-pitch capabilities. Due to size effects, the phase transition temperature and surface activity of tin nanoparticles differ significantly from those of macroscopic bulk tin. Therefore, clarifying the intermediate processes of phase transition and alloying reactions of tin nanoparticles has become a highly anticipated scientific issue in order to develop a new generation of green solder paste with finer-pitch interconnect capabilities as soon as possible.

[0003] Currently, the most effective method for studying the intermediate phase transition processes of tin nanoparticles is in-situ transmission electron microscopy (TEM). Compared to the lag in traditional ex-situ studies, high temporal resolution in-situ TEM can capture the intermediate phase transition processes in real time. Furthermore, by using an in-situ heating chip with precise temperature control, the size dependence of the phase transition temperature of tin nanoparticles can be investigated. By simultaneously introducing tin nanoparticles and other metals onto the in-situ heating chip, the actual welding environment can be simulated, and the intermediate processes of the alloying reaction can be studied in situ. Currently, the main methods for preparing small-sized tin nanoparticles for TEM research include chemical synthesis and physical vapor deposition (PVD). However, both methods require loading the prepared small-sized tin nanoparticles onto the in-situ heating chip outside the TEM before transferring them inside. This necessitates the pre-configuration of an inert gas environment to prevent surface oxidation of the tin nanoparticles during synthesis and transfer, placing high demands on equipment and operation. Additionally, the prepared small-sized tin nanoparticles are prone to impurities and exhibit a relatively uniform size distribution. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a method for simultaneously preparing and observing small-sized tin nanoparticles using transmission electron microscopy, and its application.

[0005] One objective of this invention is to provide a method for simultaneously preparing and observing small-sized tin nanoparticles using transmission electron microscopy, the method comprising the following steps:

[0006] S1: Disperse large-sized tin nanoparticles with a diameter of 100-300 nm into anhydrous ethanol to form a suspension;

[0007] S2: Drop the suspension onto the in-situ heating chip of the transmission electron microscope. After evaporating anhydrous ethanol, the in-situ heating chip loaded with large-sized tin nanoparticles is obtained. The chip is placed in the high vacuum environment of the transmission electron microscope and heated and kept at that temperature to obtain liquid tin droplets.

[0008] S3: The electron beam is focused at the edge of the molten droplet, the droplet explodes and splashes, and after cooling to room temperature, small tin nanoparticles are obtained at the far end from the explosion center;

[0009] S4: Select one of the prepared tin nanoparticles, heat it from room temperature until the solid tin nanoparticle melts, and observe the liquid-solid phase transition process in situ using transmission electron microscopy.

[0010] Further specifying the preparation process of the suspension in S1: tin nanoparticles and anhydrous ethanol are mixed and ultrasonically treated, then centrifuged. After centrifugation, the upper liquid is taken and redispersed in anhydrous ethanol to obtain the suspension.

[0011] Further specifying, the in-situ heating chip in S2 is cleaned with plasma before use.

[0012] Further specifying, in S2, anhydrous ethanol is evaporated by baking with an infrared lamp.

[0013] Further specified, in S2, the temperature is raised to 400-600℃, held for 5-15 minutes, and the heating rate is 150-250℃ / min.

[0014] Further specified, the electron stoichiometry of the electron beam in S3 is >2700e / A. 2 The electron beam irradiation time is 4-6 seconds.

[0015] Further specified, the cooling rate in S3 is 150-250℃ / min.

[0016] Further, the diameter of the tin nanoparticles selected in S4 is <50nm.

[0017] Further specified, the heating rate in S4 is 150-250℃ / min, and the temperature is raised to 240-250℃.

[0018] A second objective of this invention is to provide tin nanoparticles obtained by the above method, wherein the diameter of the tin nanoparticles is <50 nm.

[0019] A third objective of this invention is to provide a solder paste comprising tin nanoparticles obtained by the method described above.

[0020] The fourth objective of this invention is to provide an application of the above-mentioned solder paste in forming electrical and mechanical interconnections during the assembly of electronic products.

[0021] The fifth objective of this invention is to provide an application of the above-mentioned method in achieving in-situ preparation and in-situ observation of solder metal nanoparticles other than metallic tin.

[0022] The significant advantages of this invention compared to existing technologies are:

[0023] (1) The method of the present invention simultaneously realizes the preparation of small-sized tin nanoparticles and the observation of phase transformation and alloying processes. There is no need to configure an inert gas protective environment outside the transmission electron microscope to consider the oxidation problem of raw material particles during synthesis and transfer. The high vacuum transmission electron microscope environment provides an oxygen-free environment, avoiding oxidation during the preparation of small-sized tin nanoparticles. While ensuring the quality of tin nanoparticles, the preparation process is simplified and the operation difficulty is reduced. At the same time, the observation of liquid-solid phase transformation at the nanoscale is realized.

[0024] (2) The tin nanoparticles prepared by the method of the present invention are distributed in descending order of size within a range from near to far at the edge of the explosive droplet, and multiple sizes of tin nanoparticles can be obtained at the same time.

[0025] (3) Although the nanoparticles prepared by the method of the present invention will be oxidized after one experiment, the same in-situ heating chip can still be used multiple times to re-prepare small-sized tin nanoparticles without oxide film on the surface using other large-sized particles, which greatly increases the number of times a single in-situ heating chip can be reused. Attached Figure Description

[0026] Figure 1 This is a photograph of the anhydrous ethanol suspension of tin nanoparticles from Example 1.

[0027] Figure 2 This is a physical image of the in-situ heating chip loaded with large-sized tin nanoparticles in Example 1;

[0028] Figure 3 This is a photograph of the in-situ heating chip assembled onto the transmission electron microscope sample holder in Example 1.

[0029] Figure 4 These are low-magnification transmission electron microscope images of the in-situ heated chip in Example 1 at different magnifications; (a) -160x, (b) -8000x;

[0030] Figure 5 This is a schematic diagram of the large-size tin nanoparticle droplet ignition using electron beam irradiation in Example 1;

[0031] Figure 6 This is a low-magnification transmission electron microscope image of small-sized tin nanoparticles with a certain size distribution obtained in Example 1;

[0032] Figure 7These are high-magnification transmission electron microscope images of small-sized tin nanoparticles of different sizes obtained in Example 1;

[0033] Figure 8 This is a high-magnification transmission electron microscope image of the liquid-solid phase transition process of the same nanoparticles using the tin nanoparticles prepared in Example 1;

[0034] In the figure: 1 is anhydrous ethanol, 2 is anhydrous ethanol suspension of raw material tin nanoparticles, 3 is in-situ heating chip, 4 is electron beam transparent window, 5 is temperature control resistance wire, 6 is transmission electron microscope sample rod, 7 is silicon nitride, 8 is electron beam, 9 is large-size tin nanoparticle droplet, and 10 is surface oxide film. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0036] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0037] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used in the following embodiments, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such a composition, step, method, article, or apparatus.

[0038] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1 to 5” is disclosed, the described range should be interpreted as including ranges “1 to 4”, “1 to 3”, “1 to 2”, “1 to 2 and 4 to 5”, “1 to 3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range. In this specification and claims, range definitions may be combined and / or interchanged, unless otherwise stated, these ranges include all subranges contained therein.

[0039] The indefinite articles “a” and “an” preceding an element or component of this invention do not impose any limitation on the quantity (i.e., number of times) of the element or component. Therefore, “an” or “a” should be interpreted as including one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity clearly refers only to the singular form.

[0040] In this invention, "an embodiment" or "embodiment" refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that excludes other embodiments.

[0041] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0042] Example 1:

[0043] This embodiment describes a method for simultaneously preparing and observing small-sized tin nanoparticles using transmission electron microscopy, which includes the following steps:

[0044] (1) Weigh large-sized tin nanoparticles with a diameter of 100-300 nm and place them in a centrifuge tube. Fill the centrifuge tube with anhydrous ethanol and seal it. Place the centrifuge tube in an ultrasonic cleaner filled with water and ultrasonically disperse it at a constant power of 120 W for 30 min. The agglomerated raw material tin nanoparticles are uniformly dispersed under ultrasonic cavitation. Then, immediately place the centrifuge tube in a centrifuge and centrifuge it at 6000 rpm for 30 min. Take the supernatant after centrifugation and place it in a new centrifuge tube. Add anhydrous ethanol to dilute it until the suspension is transparent. The actual photo of the obtained suspension is shown below. Figure 1 As shown.

[0045] (2) The in-situ heated chip for transmission electron microscopy (TEM) was subjected to continuous plasma cleaning for 5 seconds to improve the hydrophilicity of the silicon nitride film on the chip, making the droplets easier to spread during sample preparation. The chip was then placed on dry and clean filter paper, and a 0.1 μL pipette was used to draw up a prepared suspension and drop it into the electron beam transparent window of the chip. After the droplet spread, the chip was transferred to an infrared lamp and baked for 60 minutes to evaporate the anhydrous ethanol. The final in-situ heated chip loaded with large-sized tin nanoparticles was obtained, as shown in the photograph below. Figure 2 As shown.

[0046] (3) Assemble the above-mentioned in-situ heating chip onto the transmission electron microscope sample holder, such as... Figure 3 As shown. The sample holder was then inserted into the transmission electron microscope (TEM), and 10 minutes were allowed to reach a high vacuum condition in the sample chamber of the TEM, with a vacuum level of 10. -7 Pa. Low-magnification transmission electron microscope image of the electron beam transparent window of the in-situ heated chip, as shown in Figure 1. Figure 4 As shown, the temperature of the in-situ heated chip was calibrated, and then the temperature was increased to 500℃ at a rate of 200℃ / min and held for 10 min, allowing the tin nanoparticles to completely melt into droplets. The volume expansion caused by melting resulted in a taut surface oxide film.

[0047] (4) Adjust the magnification to 400kx, focus the electron beam on the edge of the molten droplet, prioritizing the sharpest edge, such as... Figure 5 As shown. The molten droplet explodes after 5 seconds, immediately dispersing the electron beam to cover the screen, preventing the silicon nitride film from rupturing. By reducing the temperature to 23℃ at a rate of 200℃ / min, fresh, oxide-free small-sized tin nanoparticles can be obtained, as shown in the low-magnification transmission electron microscope image. Figure 6 As shown, the size of the tin nanoparticles gradually decreases with increasing distance from the explosion center, exhibiting a certain size distribution. Figure 7 This is a high-resolution transmission electron microscope image of the prepared small-sized tin nanoparticles with a diameter of less than 50 nm. As can be seen, these tin nanoparticles are well-crystallized single crystals with no oxide film on their surface.

[0048] (5) A solid tin single crystal with a diameter of 12 nm was selected as the research object, and its liquid-solid phase transition process was characterized in situ, such as... Figure 8 As shown, at room temperature (23°C), the tin nanoparticles exist stably as solid tetragonal tin single crystals. When the temperature is increased from 23°C to 245°C at a rate of 200°C / min using an in-situ heating chip, it is observed that the solid tin nanoparticles undergo a liquid-solid phase transition and transform into completely disordered tin nanodroplets, confirming the occurrence of the melting process.

[0049] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for simultaneously preparing and observing small-sized tin nanoparticles using transmission electron microscopy, characterized in that, The method described: S1: Disperse large-sized tin nanoparticles with a diameter of 100-300 nm into anhydrous ethanol to form a suspension; S2: Drop the suspension onto the in-situ heating chip of the transmission electron microscope. After evaporating anhydrous ethanol, the in-situ heating chip loaded with large-sized tin nanoparticles is obtained. The chip is placed in the high vacuum environment of the transmission electron microscope and heated and kept at that temperature to obtain liquid tin droplets. S3: The electron beam is focused at the edge of the molten droplet, the droplet explodes and splashes, and after cooling to room temperature, small tin nanoparticles are obtained at the far end from the explosion center; S4: Select one of the prepared tin nanoparticles and heat it from room temperature to melt the solid tin nanoparticles. At the same time, observe the liquid-solid phase transition process in situ using transmission electron microscopy. The preparation process of the suspension in S1 is as follows: Tin nanoparticles and anhydrous ethanol are mixed and ultrasonically treated, then centrifuged. After centrifugation, the upper liquid is taken and redispersed in anhydrous ethanol to obtain the suspension.

2. The method according to claim 1, characterized in that, Before use, the in-situ heating chip in S2 is cleaned with plasma, baked with an infrared lamp to evaporate anhydrous ethanol, heated to 400-600℃, and held for 5-15 minutes at a heating rate of 150-250℃ / min.

3. The method according to claim 1, characterized in that, The electron stoichiometry of the electron beam in S3 is >2700e / A 2 The electron beam irradiation time is 4-6 seconds.

4. The method according to claim 1, characterized in that, The cooling rate in S3 is 150-250℃ / min.

5. The method according to claim 1, characterized in that, The tin nanoparticles selected in S4 have a diameter of <50nm, and the heating rate is 150-250℃ / min, with the temperature increased to 240-250℃.

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