Method for synchronously realizing preparation and observation of small-size tin nanoparticles based on transmission electron microscope and application of method

Abstract

The invention discloses a method for synchronously realizing preparation and observation of small-size tin nanoparticles based on a transmission electron microscope and application of the method. The invention belongs to the field of solder particles and preparation thereof. The invention aims to provide a method for synchronously realizing preparation and observation of small-size tin nanoparticles based on a transmission electron microscope and application of the method. The method comprises the steps that absolute ethyl alcohol turbid liquid of large-size tin nanoparticles is dripped to an in-situ heating chip of a transmission electron microscope, after absolute ethyl alcohol is evaporated, the chip is placed in the high-vacuum environment of the transmission electron microscope, and temperature rise and heat preservation are conducted till liquid tin molten drops are obtained; and the electron beams are converged at the edge of the molten drop, the molten drop explodes and splashes, and the small-size tin nanoparticles are obtained. According to the method, on the premise that the quality of the tin nanoparticles is guaranteed, the preparation process is simplified, the operation difficulty is reduced, and observation of nano-scale liquid-solid phase change is achieved while preparation is conducted. And tin nanoparticles with various sizes can be obtained at the same time. In addition, the number of times of repeated use of a single in-situ heating chip is increased.

Description

Technical Field

[0001] The invention belongs to the field of solder particles and preparation thereof, and particularly relates to a method for synchronously realizing preparation and observation of small-sized tin nanoparticles based on a transmission electron microscope and application thereof. Background Art

[0002] Solder is an important interconnect material that forms electrical and mechanical connections during the assembly of electronic products. Over the past few decades, the use of tin-based lead-free solder has been technically stabilized. As electronic components are moving towards miniaturization and density, there is a growing demand for solder paste that can be used for finer pitch interconnections. In order to improve the fine pitch capability of solder paste, adding nano-scale solder particles, such as tin nanoparticles, to solder paste is an effective way. Due to the size effect, the phase transition temperature and surface activity of tin nanoparticles are very different from those of macroscopic bulk tin. Therefore, in order to develop a green new generation of solder paste with finer pitch interconnection capabilities as soon as possible, clarifying the intermediate process of the phase transition and alloying reaction of tin nanoparticles has become a highly anticipated scientific issue.

[0003] At present, the most effective means to study the intermediate process of phase transition of tin nanoparticles is to use in-situ transmission electron microscopy. Compared with the lag of traditional off-site research results, the high time resolution in-situ transmission electron microscopy can capture the intermediate process of phase transition in real time. At the same time, the size dependence of the phase transition temperature of tin nanoparticles can be explored by using an in-situ heating chip with precise temperature control function. By introducing tin nanoparticles and other metals on the in-situ heating chip at the same time, the actual welding environment can be simulated and the intermediate process of the alloying reaction can be studied in situ. At present, the preparation methods of small-sized tin nanoparticles used for transmission electron microscopy research mainly include chemical synthesis and physical vapor deposition, but the above methods all require the prepared small-sized tin nanoparticles to be loaded onto the in-situ heating chip outside the transmission electron microscope in advance, and then transferred to the inside of the transmission electron microscope. This requires the pre-configuration of an inert gas environment to prevent the surface oxidation of tin nanoparticles during the synthesis and transfer process, which has high requirements for equipment and operation. At the same time, the prepared small-sized tin nanoparticles are easily mixed with impurities and have a relatively single size distribution. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a method for synchronously realizing the preparation and observation of small-sized tin nanoparticles based on a transmission electron microscope and its application.

[0005] One of the purposes of the present invention is to provide a method for simultaneously preparing and observing small-sized tin nanoparticles based on a transmission electron microscope, wherein the method is carried out according to the following steps:

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

[0007] S2: Dropping the suspension onto the in-situ heating chip of the transmission electron microscope, evaporating the anhydrous ethanol, and obtaining the in-situ heating chip loaded with large-sized tin nanoparticles, placing the chip in a high vacuum environment of the transmission electron microscope, heating and maintaining the temperature until liquid tin droplets are obtained;

[0008] S3: The electron beam converges on the edge of the molten droplet, and the molten droplet explodes and splashes. After cooling to room temperature, small-sized tin nanoparticles are obtained at the far end from the explosion center.

[0009] S4: Select a prepared tin nanoparticle, raise the temperature from room temperature until the solid tin nanoparticle melts, and use a transmission electron microscope to in situ observe the liquid-solid phase transition process.

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

[0011] It is further defined that the in-situ heating chip in S2 is cleaned with plasma before use.

[0012] It is further defined that in S2, the anhydrous ethanol is evaporated by baking with an infrared baking lamp.

[0013] It is further defined that the temperature in S2 is raised to 400-600°C, kept at this temperature for 5-15 minutes, and the heating rate is 150-250°C / min.

[0014] It is further defined that the electron dosing rate of the electron beam in S3 is greater than 2700e / A 2 s, and the electron beam irradiation time is 4-6s.

[0015] It is further defined that the cooling rate in S3 is 150-250°C / min.

[0016] It is further defined that the diameter of the tin nanoparticles selected in S4 is less than 50 nm.

[0017] It is further defined that the heating rate in S4 is 150-250°C / min, and the temperature is raised to 240-250°C.

[0018] The second object of the present invention is to provide tin nanoparticles obtained according to the above method, wherein the diameter of the tin nanoparticles is less than 50 nm.

[0019] A third object of the present invention is to provide a solder paste comprising the tin nanoparticles obtained according to the above method.

[0020] A fourth object of the present invention is to provide an application of the above solder paste in forming electrical and mechanical interconnections during the assembly process of electronic products.

[0021] A fifth object of the present invention is to provide an application of the above method in realizing in-situ preparation and in-situ observation of other solder metal nanoparticles besides metallic tin.

[0022] Compared with the prior art, the present invention has the following significant effects:

[0023] (1) The method of the present invention simultaneously realizes the preparation of small-sized tin nanoparticles and the observation of phase change and alloying processes. There is no need to configure an inert gas protection environment outside the transmission electron microscope to consider the oxidation problem of raw material particles during the synthesis and transfer process. The high vacuum transmission electron microscope environment provides an oxygen-free environment to avoid oxidation during the preparation of small-sized tin nanoparticles. Under the premise of 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 change at the nanoscale is realized.

[0024] (2) The sizes of the tin nanoparticles prepared by the method of the present invention are distributed in a range from near to far of the edge of the explosion droplet from large to small, and tin nanoparticles of various sizes can be obtained at the same time.

[0025] (3) Although the nanoparticles prepared after one experiment will be oxidized, the same in-situ heating chip can be used multiple times to prepare small-sized tin nanoparticles without an oxide film on the surface using other large-sized particles on the chip, which greatly increases the number of times a single in-situ heating chip can be reused. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a physical picture of the anhydrous ethanol suspension of tin nanoparticles in Example 1;

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

[0028] Figure 3 This is a physical picture of assembling the in-situ heating chip onto the sample rod of a transmission electron microscope in Example 1;

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

[0030] Figure 5 is a schematic diagram of using electron beam irradiation to detonate large-sized tin nanoparticle droplets in Example 1;

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

[0032] Figure 7is a high-magnification transmission electron microscopy image 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 studied using the prepared tin nanoparticles in Example 1;

[0034] In the figure: 1 is anhydrous ethanol, 2 is anhydrous ethanol suspension of raw material tin nanoparticles, 3 is an in-situ heating chip, 4 is an electron beam transparent window, 5 is a temperature-controlled resistance wire, 6 is a transmission electron microscope sample rod, 7 is silicon nitride, 8 is an electron beam, 9 is a large-sized tin nanodroplet, and 10 is a surface oxide film. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0036] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art unless otherwise specified, and can be obtained through commercial channels by those skilled in the art.

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

[0038] When equivalent, concentration or other value or parameter is represented by the range limited by range, preferred range or a series of upper preferred value and lower preferred value, this should be understood as specifically disclosing all ranges formed by any pairing of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether the scope is disclosed separately. For example, when disclosing range "1 to 5", described range should be interpreted as including range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc. When numerical range is described in this article, unless otherwise stated, the scope is intended to include its end value and all integers and fractions within the scope. In the present application specification and claims, range limitation can be combined and / or interchanged, if these ranges are not otherwise stated, include all sub-ranges contained therein.

[0039] The indefinite articles "a" and "an" before the elements or components of the present invention have no limitation on the quantity requirements (i.e. the number of occurrences) of the elements or components. Therefore, "a" or "an" should be interpreted as including one or at least one, and the elements or components in the singular form also include the plural form, unless the quantity obviously refers to the singular form only.

[0040] The "one embodiment" or "embodiment" of the present invention refers to a specific feature, structure or characteristic that can be included in at least one implementation of the present invention. The "in one embodiment" that appears in different places in this specification does not refer to the same embodiment, nor is it a separate or selective embodiment that is mutually exclusive with other embodiments.

[0041] The endpoints and any values ​​of the ranges disclosed in the 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this article.

[0042] Embodiment 1:

[0043] The method for synchronously preparing and observing small-sized tin nanoparticles based on a transmission electron microscope in this embodiment comprises the following steps:

[0044] (1) Weigh large-sized tin nanoparticles with a diameter of 100-300nm and place them in a centrifuge tube. Fill the centrifuge tube with anhydrous ethanol and seal the centrifuge tube. Place the centrifuge tube in an ultrasonic cleaner filled with water and ultrasonically disperse it at a constant power of 120W for 30 minutes. The agglomerated raw tin nanoparticles are evenly dispersed under the action of ultrasonic cavitation. Then immediately place the centrifuge tube in a centrifuge and centrifuge it at a speed of 6000rpm for 30 minutes. Take the upper layer of liquid after centrifugation and place it in a new centrifuge tube, and add anhydrous ethanol to dilute it until the suspension is translucent. The actual photo of the resulting suspension is shown in the figure. Figure 1 shown.

[0045] (2) The in-situ heating chip of the transmission electron microscope is plasma cleaned for 5 seconds to improve the hydrophilicity of the silicon nitride film on the in-situ heating chip so that the droplets can be easily spread when the sample is dripped. Then, the in-situ heating chip is placed on a dry and clean filter paper, and a 0.1μL pipette is used to absorb the prepared suspension and drip a drop into the electron beam transparent window of the in-situ heating chip. After the droplet is spread, the in-situ heating chip is transferred to an infrared baking lamp and baked for 60 minutes to evaporate the anhydrous ethanol. Finally, an in-situ heating chip loaded with large-sized tin nanoparticles is obtained, and its actual photo is shown in the figure. Figure 2 shown.

[0046] (3) Assemble the above-mentioned in-situ heating chip onto the transmission electron microscope sample holder, such as Figure 3 Then, insert the sample rod into the transmission electron microscope and wait for 10 minutes to allow the sample chamber in the transmission electron microscope to reach high vacuum conditions with a vacuum degree of 10 -7 Pa. Low magnification transmission electron microscope image of the electron beam transparent window of the in-situ heating chip Figure 4 The temperature of the in-situ heating chip was calibrated, and then the temperature was raised to 500°C at a rate of 200°C / min and kept at this temperature for 10 minutes, so that the tin nanoparticles were completely melted into droplets. The volume expansion caused by melting put the surface oxide film in a tight state.

[0047] (4) Adjust the magnification to 400k times, focus the electron beam on the edge of the droplet, and give priority to the sharpest edge, such as Figure 5 As shown. After 5s, the molten droplet exploded, and then the electron beam was immediately dispersed until the light covered the screen to prevent the silicon nitride film from breaking. The temperature was reduced to 23°C at a rate of 200°C / min, and fresh small-sized tin nanoparticles without oxide film were obtained. The low-magnification transmission electron microscope image is shown in Figure 6 As shown, as the distance from the explosion center increases, the size of the tin nanoparticles gradually decreases, with 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 50nm. It can be seen that these tin nanoparticles are single crystals with good crystallinity and no oxide film on the 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 At room temperature of 23°C, the tin nanoparticles are stable in the form of solid tetragonal tin single crystals. At this time, 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 found that the solid tin nanoparticles undergo a liquid-solid phase transition and are transformed into completely disordered tin nanodroplets, confirming the occurrence of the melting process.

[0049] The above are only preferred specific embodiments of the present invention, which are all different implementations based on the overall concept of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for synchronously preparing and observing small-sized tin nanoparticles based on transmission electron microscopy, characterized in that: The method: S1: dispersing large-sized tin nanoparticles with a diameter of 100-300 nm into anhydrous ethanol to form a suspension; S2: Dropping the suspension onto the in-situ heating chip of the transmission electron microscope, evaporating the anhydrous ethanol, and obtaining the in-situ heating chip loaded with large-sized tin nanoparticles, placing the chip in a high vacuum environment of the transmission electron microscope, heating and maintaining the temperature until liquid tin droplets are obtained; S3: The electron beam converges on the edge of the molten droplet, and the molten droplet explodes and splashes. After cooling to room temperature, small-sized tin nanoparticles are obtained at the far end from the explosion center. S4: Select a prepared tin nanoparticle, raise the temperature from room temperature until the solid tin nanoparticle melts, and use a transmission electron microscope to in situ observe the liquid-solid phase transition process.

2. The method according to claim 1, characterized in that The preparation process of the suspension in S1 is as follows: the tin nanoparticles and anhydrous ethanol are mixed, ultrasonically treated, and then centrifuged. After centrifugation, the upper layer of liquid is taken and redispersed in anhydrous ethanol to obtain a suspension.

3. The method according to claim 1, characterized in that The in-situ heating chip in S2 is cleaned with plasma before use, and the anhydrous ethanol is evaporated by baking with an infrared baking lamp, and the temperature is raised to 400-600°C, kept warm for 5-15 minutes, and the heating rate is 150-250°C / min.

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

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

6. The method according to claim 1, characterized in that The diameter of the tin nanoparticles selected in S4 is less than 50 nm, the heating rate is 150-250°C / min, and the temperature is raised to 240-250°C.

7. Tin nanoparticles obtained by the method according to any one of claims 1 to 6, characterized in that: Diameter <50nm.

8. A solder paste, characterized in that: The solder paste contains the tin nanoparticles according to claim 7.

9. Use of the solder paste of claim 8 in forming electrical and mechanical interconnections during the assembly of electronic products.

10. Use of the method according to any one of claims 1 to 6 in realizing in-situ preparation and in-situ observation of solder metal nanoparticles other than metallic tin.

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