Conductive microsphere and preparation method thereof

Abstract

The invention provides a conductive microsphere and a preparation method thereof, and the preparation method comprises the following steps: S1, dissolving 4, 4 '-dimercapto dithiophenol and an acid-binding agent in an organic solvent at a certain temperature to obtain a mixed solution; s2, adding phosphonitrilic chloride trimer into the mixed solution, continuously reacting in inert gas, and condensing and refluxing to obtain a first precipitation solution; s3, centrifugally separating, washing and drying the first precipitation solution to obtain sulfhydrylated polymer microspheres; s4, sieving and grading the sulfhydrylated polymer microspheres, dispersing the sulfhydrylated polymer microspheres in a silver-ammonia solution, adding a reducing agent, and reacting at normal temperature for 2-4 hours to obtain a second precipitation solution; and S5, filtering and drying the second precipitation solution to obtain the silver-plated conductive microspheres. The conductive microsphere is good in heat resistance and high in mechanical strength, the conductive microsphere and the surface of a device bump form sintered silver contact, the conductive microsphere has lower contact resistance compared with a traditional ACF conductive microsphere, and the electrical contact performance of the bump is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of electronic packaging materials technology, and in particular relates to a conductive microsphere and its preparation method. Background Technology

[0002] With the rapid development of electronic devices towards miniaturization, thinning, and flexibility, anisotropic conductive films (ACFs), due to their unique unidirectional conductivity along the Z-axis and insulation properties in the X and Y directions, have become a key interconnect material to replace traditional soldering processes. The core function of ACFs relies on their internal conductive microspheres. In existing technologies, conductive microspheres typically use a micron-sized monodisperse polymer as the core, with a conductive metal layer (gold, silver, copper, nickel, etc.) coated on the surface as the shell. Conductivity in the vertical direction (Z-axis) is achieved through a hot-pressing process, while insulation is maintained in the horizontal direction (X and Y axes).

[0003] However, existing conductive microspheres have significant defects in terms of temperature resistance, mechanical strength and electrical contact performance, specifically as follows: (1) During the ACF curing process, conductive microspheres need to withstand high temperatures to cooperate with the adhesive tape for curing. However, existing conductive microsphere materials are prone to thermal decomposition, deformation or glass transition at high temperatures, which leads to the collapse of the conductive microsphere structure and the peeling of the metal coating, ultimately affecting the reliability of interconnection and thus limiting its application in high-temperature processes; (2) During the ACF hot pressing process, conductive microspheres need to withstand certain mechanical pressure to achieve stable contact between electrodes. However, the conductive microspheres in the existing technology are prone to breakage after being pressed, which not only affects the reliability and stability of interconnection, but may also lead to short circuits; (3) The electrical contact performance between the surface coating of the conductive microsphere and the device bumps directly affects the conductivity of ACF. In the existing technology, the adhesion between the conductive metal layer and the conductive microsphere is weak, and interface peeling is prone to occur during hot pressing, resulting in unstable electrical contact performance. Especially under high-temperature curing conditions, the activity of the conductive metal layer is insufficient, making it difficult to form good contact with the device.

[0004] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a conductive microsphere and its preparation method, so as to solve the problems of insufficient temperature resistance, low mechanical strength and poor electrical contact performance with devices in the prior art.

[0006] To achieve the above and other related objectives, the present invention provides a method for preparing conductive microspheres, the method comprising the following steps:

[0007] S1. Dissolve 4,4'-dimercaptobis(thiophenol) and an acid-binding agent in an organic solvent at a certain temperature to obtain a mixture;

[0008] S2. Add hexachlorocyclotriphosphazene to the mixture, stir continuously under inert gas protection and reflux to obtain the first precipitate;

[0009] S3. The first precipitate is centrifuged and washed, and then dried under vacuum to obtain thiolized polymer microspheres;

[0010] S4. The thiolized polymer microspheres are sieved and classified, and the sieved and classified thiolized polymer microspheres are dispersed in silver ammonia solution. A reducing agent is added, and the reaction is carried out at room temperature for 2-4 hours to obtain a second precipitate.

[0011] S5. Filter and dry the second precipitate to obtain silver-plated conductive microspheres.

[0012] Preferably, the acid-binding agent in step S1 is one or a mixture of triethylamine, pyridine, or both.

[0013] Preferably, the organic solvent in step S1 includes one or a mixture of acetonitrile, acetone, or both.

[0014] Preferably, in step S1, the temperature at which the mixture is stirred until it dissolves is 20–80°C.

[0015] Preferably, the molar ratio of the acid-binding agent to the 4,4'-dimercaptobis(thiophenol) in step S1 is 2.5 to 3.5.

[0016] Preferably, the molar ratio of 4,4'-dimercaptobis(thiophenol) in step S1 to hexachlorocyclotriphosphazene in step S2 is 4 to 8.

[0017] Preferably, after adding hexachlorocyclotriphosphazene to the mixture in step S2, the concentration of hexachlorocyclotriphosphazene is 5-20 mmol / L.

[0018] Preferably, the inert gas in step S2 includes one or a combination of nitrogen and argon.

[0019] Preferably, the time for continuous stirring and condensation reflux under inert gas protection in step S2 is 2 to 8 hours.

[0020] Preferably, the particle size of the thiolized polymer microspheres after sieving and grading in step S4 is 3–10 μm.

[0021] Preferably, the reducing agent in step S4 is formaldehyde or ascorbic acid.

[0022] Preferably, the molar ratio of the reducing agent added in step S4 to the silver in the silver ammonia solution is 1.2 to 2.

[0023] The present invention also provides a conductive microsphere, which is prepared by the conductive microsphere preparation method described above.

[0024] As described above, the conductive microspheres and their preparation method of the present invention have the following beneficial effects:

[0025] The preparation method of conductive microspheres in this invention is simple and convenient. First, 4,4'-dithiobis(thiophenol) and an acid-binding agent are added to an organic solvent, and then reacted with hexachlorocyclotriphosphazene to obtain thiolated nitrogen-phosphorus heterocyclic polymer microspheres. The structure of these thiolated polymer microspheres contains benzene rings and thiol side groups, forming a highly cross-linked organic-inorganic hybrid structure with high mechanical strength, capable of withstanding certain mechanical pressure, reducing breakage during press-fit interconnection, and good heat resistance, able to withstand curing temperatures above 250°C. Due to the large number of thiol groups on the thiolated polymer microspheres, silver plating can be achieved on their surface in one step to form silver-plated conductive microspheres. Furthermore, due to the strong coupling effect of thiol groups, the nano-silver layer attached to the surface of the thiolated polymer microspheres has high activity. Combined with the high curing temperature, it forms a sintered silver contact with the device bump surface, resulting in a lower contact resistance than traditional ACF conductive microspheres, greatly improving the electrical contact performance of the bumps and meeting the needs of miniaturized, high-performance electronic component interconnection. Attached Figure Description

[0026] Figure 1 The diagram shown is a process flow chart for the preparation of conductive microspheres in a specific embodiment of the present invention.

[0027] Figure 2 The image shown is a low-magnification SEM image of the conductive microspheres prepared in Example 1 of this invention.

[0028] Figure 3 This shows a high-magnification SEM image of the conductive microspheres prepared in Example 1 of the present invention. Detailed Implementation

[0029] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0030] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the respective manufacturers.

[0031] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or equivalent to those described, apparatus, and materials in the embodiments of this invention may be used to implement the present invention.

[0032] This invention provides a method for preparing conductive microspheres, such as... Figure 1 As shown, the preparation method includes the following steps:

[0033] S1. Dissolve 4,4'-dimercaptobis(thiophenol) and an acid-binding agent in an organic solvent at a certain temperature to obtain a mixture;

[0034] S2. Add hexachlorocyclotriphosphazene to the mixture, stir continuously under inert gas protection and reflux to obtain the first precipitate;

[0035] S3. Centrifuge the first precipitate, wash and dry it to obtain thiolized polymer microspheres;

[0036] S4. The thiolized polymer microspheres are sieved and classified. The sieved and classified thiolized polymer microspheres are dispersed in silver ammonia solution, a reducing agent is added, and the reaction is carried out at room temperature for 2-4 hours (e.g., 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, etc.) to obtain the second precipitate.

[0037] S5. Filter and dry the second precipitate to obtain silver-plated conductive microspheres.

[0038] Specifically, the thiol group of 4,4'-dimercaptobis(thiophenol) undergoes a condensation reaction with the chlorine substituent of hexachlorocyclotriphosphazene to form a cross-linked network. The acid-binding agent neutralizes HCl and promotes the reaction, while the inert gas prevents oxygen inhibition during the heating process and protects the surface-active thiol groups. The resulting thiolized polymer microspheres are highly cross-linked nitrogen-phosphorus heterocycles and benzene-thiocyanate hybrid heat-resistant microspheres, and the surface thiol groups combine with silver ions to form an active nano-silver shell.

[0039] Preferably, the drying in step S5 includes vacuum drying or freeze drying. The temperature for vacuum drying and the conditions for freeze drying are not overly restricted, as long as drying can be achieved.

[0040] As an example, the acid-binding agent in step S1 is one or a mixture of triethylamine, pyridine, or both.

[0041] As an example, the organic solvent in step S1 includes one or a mixture of acetonitrile, acetone, or both.

[0042] As an example, in step S1, the temperature at which the mixture is stirred until it dissolves is between 20 and 80°C.

[0043] Specifically, the temperature for stirring and dissolving in step S1 can be any value within a range such as 20℃, 25℃, 40℃, 60℃, 70℃, or 80℃.

[0044] As an example, in step S1, the molar ratio of the acid-binding agent to 4,4'-dimercaptobis(thiophenol) is 2.5 to 3.5.

[0045] Specifically, in step S1, the acid-binding agent is an alkaline substance that can neutralize the hydrochloric acid generated by the combination of hydrogen and chlorine in the thiol group, promoting the cross-linking reaction. The molar ratio of the acid-binding agent to 4,4'-dimercaptobis(thiophenol) can be any value in any range, such as 2.5, 2.8, 3.0, 3.2, or 3.5.

[0046] As an example, the molar ratio of 4,4'-dimercaptobis(thiophenol) in step S1 to hexachlorocyclotriphosphazene in step S2 is 4 to 8.

[0047] Specifically, to ensure the complete progress of the reaction, 4,4'-dimercaptobis(thiophenol) needs to be in excess in step S1 to ensure that the chlorine atom in hexachlorocyclotriphosphazene can be completely replaced. An acid-binding agent is also added to the reaction to neutralize the acidic groups generated during the reaction and promote the cross-linking reaction. The molar ratio of 4,4'-dimercaptobis(thiophenol) in step S1 to hexachlorocyclotriphosphazene in step S2 can be any value in the range of 4, 5, 6, 7, 8, etc., and can be adjusted according to the actual situation.

[0048] As an example, after adding hexachlorocyclotriphosphazene to the mixture in step S2, the concentration of hexachlorocyclotriphosphazene is 5–20 mmol / L.

[0049] Specifically, after adding hexachlorocyclotriphosphazene to the mixture, the concentration of hexachlorocyclotriphosphazene in the total mixture can be any value within the range of 5 mmol / L, 10 mmol / L, 15 mmol / L, 20 mmol / L, etc.

[0050] As an example, the inert gas in step S2 includes one or a combination of nitrogen and argon.

[0051] Specifically, in industrial classification, nitrogen is generally considered an inert gas.

[0052] As an example, the time for continuous stirring and condensation reflux under inert gas protection in step S2 is 2 to 8 hours.

[0053] Specifically, reflux condensation can be achieved by using room temperature water for condensation during the reaction process, without much restriction. The reaction time under inert gas protection with continuous stirring can be any value within the range of 2h, 3h, 4h, 5h, 6h, 7h, 8h, etc.

[0054] As an example, the particle size of the thiolized polymer microspheres after sieving and grading in step S4 is 3–10 μm.

[0055] Specifically, the particle size of the thiolized polymer microspheres after sieving and classification can be any value within any range, such as 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, etc.

[0056] Preferably, a vibrating screen is used for sieving and grading.

[0057] As an example, the reducing agent in step S4 is formaldehyde or ascorbic acid.

[0058] As an example, the molar ratio of the reducing agent added in step S4 to the silver in the silver ammonia solution is 1.2 to 2.

[0059] Specifically, the molar ratio of the amount of reducing agent added to the silver ammonia solution can be any value within the range of 1.2, 1.4, 1.6, 1.8, 2.0, etc.; preferably, the molar concentration of silver in the silver ammonia solution is 0.08 mol / L to 0.1 mol / L (e.g., 0.08 mol / L, 0.09 mol / L, 0.1 mol / L, etc.).

[0060] The present invention also provides a conductive microsphere, which is prepared by the conductive microsphere preparation method described above.

[0061] Specifically, the conductive microspheres are composed of thiolized polymer microspheres as the core and a silver layer as the shell. The silver layer surrounds the thiolized polymer microspheres, and the particle size of the thiolized polymer microspheres ranges from 3 to 10 μm (e.g., μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc.). Since the conductive microspheres are composed of thiolized polymer microspheres as the core and a silver layer on the outside, the particle size of the conductive microspheres is slightly larger than that of the thiolized polymer microspheres.

[0062] To better understand the conductive microspheres and their preparation method in this invention, specific embodiments are described below. It should be noted that these embodiments are merely descriptive and do not limit the invention in any way.

[0063] Example 1

[0064] This embodiment provides a method for preparing conductive microspheres, which includes the following steps:

[0065] S1. Add 0.05 mol of 4,4'-dimercaptobis(thiophenol) and 0.15 mol of acid-binding agent (triethylamine) to 1 L of organic solvent (acetonitrile), and stir at 60 °C until dissolved to obtain a mixture.

[0066] S2. Add 10 mmol of hexachlorocyclotriphosphazene to the mixture, stir continuously under nitrogen protection and reflux for 6 hours to obtain the first precipitate.

[0067] S3. Centrifuge the first precipitate, wash and dry it to obtain thiolized polymer microspheres;

[0068] S4. The thiolized polymer microspheres were sieved and classified using a vibrating screen. The thiolized polymer microspheres with a particle size of 5.0 μm were dispersed in 1 L of silver ammonia solution with a molar concentration of 0.08 mol / L. 1 L of reducing agent (ascorbic acid) with a concentration of 0.11 mol / L was added, and the reaction was carried out at room temperature for 2.5 h to obtain the second precipitate.

[0069] S5. Filter the second precipitate and freeze-dry it to obtain silver-plated conductive microspheres.

[0070] This embodiment also provides conductive microspheres, which are prepared by the method described in this embodiment. The particle size and particle size distribution of the conductive microspheres were determined using a Beckman Counter particle size analyzer. The particle size of the conductive microspheres was 5.1 μm, and the coefficient of variation (CV) was 2.9%. See also... Figure 2 and Figure 3 The images show low-magnification and high-magnification SEM images of the conductive microspheres. As can be seen from the images, the conductive microspheres have uniform particle size and are covered with a dense nano-silver shell layer on their surface.

[0071] Example 2

[0072] This embodiment provides a method for preparing conductive microspheres, which includes the following steps:

[0073] S1. Add 0.08 mol of 4,4'-dimercaptobis(thiophenol) and 0.2 mol of acid-binding agent (triethylamine) to 1 L of organic solvent (acetonitrile), and stir at 60 °C until dissolved to obtain a mixture;

[0074] S2. Add 20 mmol of hexachlorocyclotriphosphazene to the mixture, stir continuously under nitrogen protection and reflux for 2 hours to obtain the first precipitate.

[0075] S3. Centrifuge the first precipitate, wash and dry it to obtain thiolized polymer microspheres;

[0076] S4. The thiolized polymer microspheres were sieved and classified using a vibrating screen. The thiolized polymer microspheres with a particle size of 3.8 μm were dispersed in 1 L of silver ammonia solution with a molar concentration of 0.1 mol / L. 1 L of reducing agent (ascorbic acid) with a concentration of 0.12 mol / L was added, and the reaction was carried out at room temperature for 1 h to obtain the second precipitate.

[0077] S5. Filter the second precipitate and freeze-dry it to obtain silver-plated conductive microspheres.

[0078] This embodiment also provides a conductive microsphere, which is prepared by the method of preparing conductive microsphere in this embodiment. The particle size and particle size distribution of the conductive microsphere are measured by Beckman Counter particle size analyzer. The particle size of the conductive microsphere is 3.9 μm, the coefficient of variation (CV) is 2.5%, and the particle size distribution is relatively uniform.

[0079] Example 3

[0080] This embodiment provides a method for preparing conductive microspheres, which includes the following steps:

[0081] S1. Add 0.04 mol of 4,4'-dimercaptobis(thiophenol) and 0.14 mol of acid-binding agent (pyridine) to 1 L of organic solvent (acetonitrile), and stir at 60 °C until dissolved to obtain a mixture;

[0082] S2. Add 5 mmol of hexachlorocyclotriphosphazene to the mixture, stir continuously under nitrogen protection and reflux for 8 hours to obtain the first precipitate.

[0083] S3. Centrifuge the first precipitate, wash and dry it to obtain thiolized polymer microspheres;

[0084] S4. The thiolized polymer microspheres were sieved and classified using a vibrating screen. The thiolized polymer microspheres with a particle size of 9.6 μm were dispersed in 1 L of silver ammonia solution with a molar concentration of 0.1 mol / L. 1 L of reducing agent (formaldehyde) with a concentration of 0.2 mol / L was added, and the reaction was carried out at room temperature for 2 h to obtain the second precipitate.

[0085] S5. Filter the second precipitate and vacuum dry it to obtain silver-plated conductive microspheres.

[0086] This embodiment also provides a conductive microsphere, which is prepared by the method of preparing conductive microsphere in this embodiment. The particle size and particle size distribution of the conductive microsphere are measured by Beckman Counter particle size analyzer. The particle size of the conductive microsphere is 9.6 μm, the coefficient of variation (CV) is 3.3%, and the particle size distribution is relatively uniform.

[0087] Comparative Example 1

[0088] This comparative example provides a conductive microsphere, which is a commercially available PS conductive microsphere with a particle size of 5 μm.

[0089] Performance testing:

[0090] The diameter and compressive strength of the conductive microspheres prepared in Examples 1-3 and the conductive microspheres in Comparative Example 1 were tested using a Shimadzu MCT micro compression tester. The test results are shown in Table 1.

[0091] The conductive microspheres prepared in Examples 1-3 and the conductive microspheres in Comparative Example 1 were dispersed and mixed with epoxy-based conductive adhesives, and coated to form anisotropic conductive films (ACF). The shapes remained unchanged under pre-compression temperature (80℃) and pre-compression pressure (1MPa). Deformation was then carried out at 200℃ and 4MPa; 200℃ and 6MPa; 260℃ and 4MPa; and 260℃ and 6MPa, respectively. The conduction resistance performance was tested in sequence, and the test results are shown in Table 1.

[0092] Table 1. Performance test results of conductive microspheres prepared in Examples 1-3 and conductive microspheres in Comparative Example 1

[0093]

[0094] Based on the diameter and compressive strength results of the conductive microspheres obtained by testing with the Shimadzu MCT micro compression tester in Examples 1-3 and Comparative Example 1, it can be seen that the compressive strength of the mercapto-nitrogen-phosphorus heterocyclic polymer microspheres formed in Example 1 is higher than that of the traditional PS conductive microspheres. Compared with Comparative Example 1, the conductive microspheres in Examples 1-3, after being made into ACF tape, show a significant reduction in Z-conductive resistance under high-temperature curing conditions. The higher curing temperature helps the nano-silver fusion welding of the contact device bumps on the surface of the conductive microspheres to reduce the contact resistance. In contrast, the ACF tape made from traditional PS conductive microspheres shows damage and increased resistance under high-temperature curing conditions, and a significant increase in planar leakage conduction under high pressure, resulting in anisotropic conduction failure.

[0095] In summary, the preparation method of conductive microspheres in this invention is simple and convenient. First, 4,4'-dithiobis(thiophenol) and an acid-binding agent are added to an organic solvent, and then reacted with hexachlorocyclotriphosphazene to obtain thiolized polymer microspheres. These thiolized polymer microspheres contain nitrogen-phosphorus heterocycles and benzene-sulfur structures, forming a highly cross-linked organic-inorganic hybrid structure with high mechanical strength, capable of withstanding certain mechanical pressure, reducing breakage during press-fit interconnection, and exhibiting good heat resistance, able to withstand curing temperatures above 250°C. Due to the large number of thiol groups on the thiolized polymer microspheres, silver plating can be achieved on their surface in one step, forming silver-plated conductive microspheres. Furthermore, due to the strong coupling effect of the thiol groups, the nano-silver layer attached to the surface of the thiolized polymer microspheres has high activity. Combined with the high curing temperature, it forms a sintered silver contact with the device bump surface, resulting in a lower contact resistance than traditional ACF conductive microspheres, significantly improving the electrical contact performance of the bumps and meeting the needs of miniaturized, high-performance electronic component interconnection. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and has high industrial application value. The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing conductive microspheres, characterized in that, The preparation method includes the following steps: S1. Dissolve 4,4'-dimercaptobis(thiophenol) and an acid-binding agent in an organic solvent at a certain temperature to obtain a mixture; S2. Add hexachlorocyclotriphosphazene to the mixture, stir continuously under inert gas protection and reflux to obtain the first precipitate; S3. Centrifuge the first precipitate, wash and dry it to obtain thiolized polymer microspheres; S4. The thiolized polymer microspheres are sieved and classified, and the sieved and classified thiolized polymer microspheres are dispersed in silver ammonia solution. A reducing agent is added, and the reaction is carried out at room temperature for 2-4 hours to obtain a second precipitate. S5. Filter and dry the second precipitate to obtain silver-plated conductive microspheres.

2. The method for preparing conductive microspheres according to claim 1, characterized in that: Step S1 includes one or a combination of the following conditions: The acid-binding agent is one of triethylamine and pyridine, or a mixture of both. The organic solvent includes one or a mixture of acetonitrile and acetone; The temperature at which the mixture is stirred until it dissolves is between 20 and 80°C.

3. The method for preparing conductive microspheres according to claim 1, characterized in that: The molar ratio of the acid-binding agent to the 4,4'-dimercaptobis(thiophenol) in step S1 is 2.5 to 3.

5.

4. The method for preparing conductive microspheres according to claim 1, characterized in that: The molar ratio of 4,4'-dimercaptobis(thiophenol) in step S1 to hexachlorocyclotriphosphazene in step S2 is 4 to 8.

5. The method for preparing conductive microspheres according to claim 1, characterized in that: In step S2, after adding hexachlorocyclotriphosphazene to the mixture, the concentration of hexachlorocyclotriphosphazene is 5-20 mmol / L.

6. The method for preparing conductive microspheres according to claim 1, characterized in that: Step S2 includes one or a combination of the following conditions: The inert gas includes one or a combination of nitrogen and argon; The stirring and reflux under inert gas protection lasted for 2 to 8 hours.

7. The method for preparing conductive microspheres according to claim 1, characterized in that: The particle size of the thiolized polymer microspheres after sieving and grading in step S4 is 3–10 μm.

8. The method for preparing conductive microspheres according to claim 1, characterized in that: The reducing agent mentioned in step S4 is formaldehyde or ascorbic acid.

9. The method for preparing conductive microspheres according to claim 1, characterized in that: In step S4, the molar ratio of the reducing agent added to the silver ammonia solution is 1.2 to 2.

10. A conductive microsphere, characterized in that: The conductive microspheres are prepared by the method described in any one of claims 1 to 9.

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