Nickel-plated conductive microspheres with roughened surface, and preparation method and application thereof

Abstract

The application belongs to the technical field of conductive microsphere preparation, and particularly relates to a kind of surface roughening nickel-plated conductive microspheres and its preparation method and application.The preparation process includes pretreatment to make the surface of polymer microspheres contain nickel ions, reduction of nickel ions into nickel nanoparticles, microsphere activation and chemical plating steps.The application adopts the way of reducing nickel nanoparticles on the surface of microspheres to increase the specific surface area of conductive microspheres, which will not produce a large number of impurities between microspheres, and can effectively prevent the adhesion between microspheres.The conductive microspheres prepared by the application have a firm combination between the plating layer and polystyrene microspheres, which reduces the risk of reduced conductivity caused by the surface shedding of the plating layer.The preparation method is safe, environmentally friendly and simple, and is suitable for industrial production needs.

Description

Technical Field

[0001] This invention belongs to the field of conductive microsphere preparation technology, specifically relating to a surface-roughened nickel-plated conductive microsphere, its preparation method, and its application. Background Technology

[0002] Anisotropic conductive film (ACF) is widely used for TAB connections between flexible circuit boards and glass display substrates. It is a thermosetting resin film containing micron-sized conductive particles, which are used to achieve electrical conduction of interconnect bumps. These conductive particles are generally polymer microspheres.

[0003] As a core component of ACF (Active Conductive Coating), existing methods for preparing conductive microspheres often focus on improving the density and uniformity of the surface nickel layer. Currently, most conductive microspheres used in ACF conductive films are smooth. However, the inventors discovered through long-term research that smooth conductive microspheres have a smaller surface area, leading to higher contact resistance and relatively lower conductivity in the prepared conductive film. Rough conductive microspheres, with their higher specific surface area, provide a larger contact area with the electrodes in ACF applications, resulting in superior conductivity.

[0004] Based on this, the applicant's previous patent CN117966137A disclosed a method for preparing conductive microspheres for anisotropic conductive films and their application, which involves controlling the Ni content in the chemical plating solution. 2+ / H2PO2 -1 The ratio controls the electroless plating rate, thereby preparing nickel-plated conductive microspheres with a rough surface. However, this patent only roughens the microspheres to increase their specific surface area, with limited effect. The adsorbed palladium is relatively low, leading to localized incomplete plating during electroless plating and resulting in voids in the coating. Another patent by the applicant, CN118852657A, discloses a method for preparing polymer composite conductive microspheres and its application, further improving the preparation method by adding nano-nickel particles to the surface of the microspheres to prepare a rough coating. However, it is difficult for all the added nano-nickel particles to be adsorbed onto the spheres, and the nano-nickel particles scattered outside the spheres will generate a large amount of impurities in subsequent electroless plating.

[0005] In addition, other studies have mentioned the preparation of rough conductive microspheres. For example, patent CN116855928 A discloses a conductive microsphere and its manufacturing method, which prepares a rough conductive microsphere by setting a polymer nanolayer of silane coupling agent and polyvinyl alcohol on the surface of the microsphere core. However, the conductivity of the prepared conductive microspheres varies greatly and the uniformity of the local microsphere coating is poor.

[0006] Therefore, further improving the preparation of nickel-plated conductive microspheres and providing a method for preparing conductive microspheres with rough surfaces and strong coating adhesion is a technical problem that needs to be solved. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention first provides a method for preparing surface-roughened nickel-plated conductive microspheres.

[0008] The technical solution adopted in this invention is as follows:

[0009] A method for preparing surface-roughened nickel-plated conductive microspheres includes the following steps:

[0010] S1. Pretreatment: The polymer microspheres are dispersed in a solvent, a nickel precursor solution is added, the reaction is stirred, filtered and washed to obtain pretreated microspheres with nickel ions on the surface;

[0011] S2. Reduction: Pretreated microspheres containing nickel ions on the surface are dispersed in deionized water, and a nano-nickel reducing agent solution is added dropwise under ice-water bath conditions. After ultrasonic stirring and reaction, the mixture is filtered and washed to obtain microspheres containing nickel nanoparticles on the surface.

[0012] S3. Activation: Microspheres with nickel nanoparticles on the surface are dispersed in deionized water, an activator is added for activation treatment, then filtered and washed. The resulting filter cake is further dispersed in deionized water, palladium sol is added, the mixture is stirred and reacted, then filtered, washed and dried to obtain activated microspheres.

[0013] S4. Chemical plating: Activated microspheres are dispersed in deionized water, and chemical plating solution is added dropwise under ultrasonic stirring. After the reaction is set for a set time, the microspheres are filtered, washed, and dried to obtain nickel-plated conductive microspheres with roughened surfaces.

[0014] Preferably, in step S1, the polymer microspheres are polystyrene microspheres with a particle size of 3-10 μm, and the solvent is a 20-40 wt% ethanol solution; the polystyrene microspheres are added to the solvent at a ratio of 1 g : (20-40) mL to disperse them, and the nickel precursor is any one or a combination of nickel sulfate, nickel chloride, and nickel nitrate, and the amount of nickel precursor solution used is 10 mL / 1 g polystyrene microspheres, with a concentration of 0.1-0.2 M.

[0015] Preferably, in step S2, the nano-nickel reducing agent is any one or a combination of several of borohydride, hydrazine hydrate, ascorbic acid, dimethylamine borate, and borane, and the amount of nano-nickel reducing agent solution used is 20 mL / 1 g of pretreated microspheres containing nickel ions on the surface, with a concentration of 0.15~0.3 M.

[0016] Preferably, in step S3, the activator is a pyridine-based ionic liquid, and the amount used is (5~20) g / 1 g of microspheres containing nickel nanoparticles on the surface.

[0017] Preferably, the activator is any one or a combination of several of 1-ethyl-3-methylpyridine ethanesulfonate, N-butylsulfonate pyridine hydrochloride, N-butylpyridine tetrafluoroborate, and N-ethylpyridine dinitrileamine salt.

[0018] Preferably, in step S3, the palladium sol is composed of 45~100 mg / L of nano-palladium, 3.5~12 g / L of divalent tin salt, and 200~270 mL / L of hydrochloric acid, and the amount used is (10~20) g / 1 g filter cake.

[0019] Preferably, in step S4, the electroless plating solution comprises 25-35 g / L of nickel salt, 6-18 g / L of complexing agent, 15-30 g / L of buffer, 25-36 g / L of reducing agent, and 0.01-0.02 g / L of stabilizer; the nickel salt is any one or a combination of nickel sulfate, nickel chloride, nickel hypophosphite, and nickel carbonate; the complexing agent is any one or a combination of EDTA, citric acid, citrate, ammonium chloride, succinic acid, succinate, triethanolamine, ethylenediamine, and lactic acid; the buffer is any one or a combination of sodium acetate and ammonia; the reducing agent is sodium hypophosphite; and the stabilizer is any one or a combination of bismuth salt, lead salt, cerium salt, lanthanum salt, and neodymium salt.

[0020] Preferably, in steps S2-S4, the dispersion ratio of pretreated microspheres containing nickel ions on the surface, microspheres containing nickel nanoparticles on the surface, filter cakes, or activated microspheres in deionized water is 1 g : (10~20) mL.

[0021] Preferably, all stirring is ultrasonic stirring, with an ultrasonic power of 240~360 W.

[0022] Preferably, the stirring time in steps S1-S3 is 10~40 min.

[0023] Preferably, the reaction time in step S4 is set to 40-60 min.

[0024] The present invention further provides a surface-roughened nickel-plated conductive microsphere, prepared by the method described above, wherein the nickel-plated conductive microsphere has a coating thickness of 0.1~0.2 μm and a specific surface area of ​​8~9 m². 2 / g.

[0025] Finally, the present invention provides a conductive adhesive film, wherein a nickel-plated conductive microsphere with a roughened surface is added as described above.

[0026] The beneficial effects of this invention are as follows:

[0027] 1) A surface-roughened conductive microsphere is provided. Compared to a smooth conductive microsphere, the surface-roughened conductive shell has a larger contact area with the electrode, resulting in lower and more stable contact resistance. Furthermore, the roughened coating ensures that the microsphere is firmly fixed between the upper and lower circuits after being flattened, preventing connection failure due to elastic recovery or stress relaxation.

[0028] 2) This invention improves the surface modification method of microspheres by using a method of reducing nickel nanoparticles on the surface of microspheres to grow nickel nanoparticles, thereby increasing the specific surface area of ​​the conductive microspheres and resulting in superior conductivity. Compared with traditional methods of physical adsorption of nickel nanoparticles by roughening or directly adding nickel nanoparticles, this invention does not generate a large number of impurities between microspheres, effectively preventing the adhesion between microspheres, and eliminates the traditional step of roughening with strong acid to increase the specific surface area of ​​microspheres, making the production process safer and more environmentally friendly.

[0029] 3) Using pyridine ionic liquids as activators, pyridine ionic liquids will adsorb on the surface of microspheres with nickel particles. Not only can they physically adsorb palladium ions, but their anions and cations can also interact with more palladium ions through ion exchange and coordination, increasing the activation sites on the surface of the microspheres and making the bonding force between the coating and the microspheres stronger.

[0030] 4) The conductive microspheres prepared by this invention have a strong bond between the coating and the polystyrene microspheres, reducing the risk of conductivity reduction due to coating surface peeling. The preparation method of this invention is simple, without cumbersome steps, and does not require the purchase of other auxiliary equipment for large-scale mass production, making it particularly suitable for industrial production needs. Attached Figure Description

[0031] Figure 1 The image shows a SEM image of the microspheres with nickel-containing nanoparticles on the surface obtained in step S2 of Example 1, where B is a magnified view of A.

[0032] Figure 2 This is an SEM image of the surface-roughened nickel-plated conductive microspheres prepared in Example 1.

[0033] Figure 3 This is an SEM image of the surface-roughened nickel-plated conductive microspheres prepared in Example 2.

[0034] Figure 4 SEM image of the nickel-plated conductive microspheres prepared in Comparative Example 1.

[0035] Figure 5 SEM image of the nickel-plated conductive microspheres prepared in Comparative Example 2.

[0036] Figure 6 SEM image of the nickel-plated conductive microspheres prepared in Comparative Example 3.

[0037] Figure 7 The image shows a SEM image of the nickel-plated conductive microspheres prepared in Comparative Example 4.

[0038] Figure 8 This is a breakage curve of the rough-surfaced nickel-plated conductive microspheres prepared in Example 1, Comparative Example 1, and Comparative Example 2. Detailed Implementation

[0039] To facilitate understanding, the technical solution of the present invention will be described in more detail below with reference to the embodiments.

[0040] Example 1

[0041] A method for preparing surface-roughened nickel-plated conductive microspheres includes the following steps:

[0042] S1. Preprocessing:

[0043] 1 g of polystyrene microspheres were dispersed in 20 mL of 20 wt% ethanol solution and ultrasonically stirred for 10 min. Then, 10 mL of 0.1 M nickel nitrate solution was added and ultrasonically stirred for 15 min. After filtration, the microspheres were washed with deionized water until neutral and dried to obtain pretreated microspheres with nickel ions on the surface.

[0044] S2. Nano-nickel reduction:

[0045] 1 g of pretreated microspheres containing nickel ions on their surface were dispersed in 20 mL of deionized water and ultrasonically stirred for 10 min. Then, 20 mL of 0.3 M nano-nickel reducing agent solution (sodium borohydride) was added dropwise under ice-water bath conditions. After 5 min of addition, the solution was filtered, washed with deionized water until neutral, and dried at 60 °C for 4 h to obtain microspheres with nickel nanoparticles on their surface.

[0046] S3. Activation treatment:

[0047] 1 g of nickel-containing nanoparticles on the surface of microspheres were dispersed in 20 mL of deionized water and ultrasonically stirred for 10 min. Then, 5 g of 1-ethyl-3-methylpyridine ethanesulfonate was added and ultrasonically stirred for another 10 min for activation treatment. After filtration and washing, the resulting filter cake was dispersed in 10 mL of deionized water and ultrasonically stirred for 10 min. Then, 5 g of palladium sol was added and ultrasonically stirred for another 15 min. After filtration, the filter cake was washed with deionized water until neutral and dried at 60 °C for 4 h to obtain activated microspheres.

[0048] The palladium sol was composed of 100 mg / L nano-palladium, 12 g / L tin chloride, and 250 mL / L hydrochloric acid.

[0049] S4. Chemical plating:

[0050] 1 g of activated microspheres were dispersed in 20 mL of deionized water and ultrasonically stirred for 10 min. Then, chemical plating solution was added dropwise. After 5 min of addition, the mixture was filtered, washed with deionized water until neutral, and dried at 60 ℃ for 4 h to obtain nickel-plated conductive microspheres with roughened surfaces.

[0051] The electroless plating solution consists of 30 g of nickel sulfate as the main salt, 15 g of sodium citrate as the complexing agent, 30 g of sodium acetate as the buffer, 30 g of sodium hypophosphite as the reducing agent, 0.02 g of lead sulfate as the stabilizer, and 1000 g of deionized water.

[0052] Example 2

[0053] A method for preparing surface-roughened nickel-plated conductive microspheres includes the following steps:

[0054] S1. Preprocessing:

[0055] 1 g of polystyrene microspheres were dispersed in 40 mL of 40 wt% ethanol solution and ultrasonically stirred for 10 min. Then, 10 mL of 0.1 M nickel nitrate solution was added and ultrasonically stirred for 15 min. The mixture was then filtered, washed with deionized water until neutral, and dried to obtain pretreated microspheres with nickel ions on the surface.

[0056] S2. Nano-nickel reduction:

[0057] 1 g of pretreated microspheres containing nickel ions on their surface were dispersed in 20 mL of deionized water and ultrasonically stirred for 10 min. Then, 20 mL of 0.15 M nano-nickel reducing agent solution (hydrazine hydrate) was added dropwise under ice-water bath conditions. After 5 min of addition, the solution was filtered, washed with deionized water until neutral, and dried at 60 °C for 4 h to obtain microspheres with nickel nanoparticles on their surface.

[0058] S3. Activation treatment:

[0059] 1 g of nickel-containing nanoparticles on the surface of microspheres were dispersed in 20 mL of deionized water and ultrasonically stirred for 10 min. Then, 10 g of N-butylsulfonate pyridine hydrochloride was added and ultrasonically stirred for another 10 min for activation treatment. After filtration and washing, the resulting filter cake was dispersed in 10 mL of deionized water and ultrasonically stirred for 10 min. Then, 5 g of palladium sol was added and ultrasonically stirred for another 15 min. After filtration, the filter cake was washed with deionized water until neutral and dried at 60 °C for 4 h to obtain activated microspheres.

[0060] The palladium sol was composed of 100 mg / L nano-palladium, 12 g / L stannous sulfate and 250 mL / L hydrochloric acid.

[0061] S4. Chemical plating:

[0062] 1 g of activated microspheres were dispersed in 20 mL of deionized water and ultrasonically stirred for 10 min. Then, chemical plating solution was added dropwise. After 5 min of addition, the mixture was filtered, washed with deionized water until neutral, and dried at 60 ℃ for 4 h to obtain nickel-plated conductive microspheres with roughened surfaces.

[0063] The electroless plating solution consists of 30 g of nickel sulfate as the main salt, 15 g of sodium citrate as the complexing agent, 30 g of sodium acetate as the buffer, 30 g of sodium hypophosphite as the reducing agent, 0.02 g of lead sulfate as the stabilizer, and 1000 g of deionized water.

[0064] Comparative Example 1

[0065] A method for preparing nickel-plated conductive microspheres, differing from Example 1 in that no pyridine-based ionic liquid is added before activation, includes the following steps:

[0066] S1. Preprocessing:

[0067] 1 g of polystyrene microspheres were dispersed in 20 mL of 20 wt% ethanol solution and ultrasonically stirred for 10 min. Then, 10 mL of 0.1 M nickel nitrate solution was added and ultrasonically stirred for 15 min. After filtration, the microspheres were washed with deionized water until neutral and dried to obtain pretreated microspheres with nickel ions on the surface.

[0068] S2. Nano-nickel reduction:

[0069] 1 g of pretreated microspheres containing nickel ions on their surface were dispersed in 20 mL of deionized water and ultrasonically stirred for 10 min. Then, 20 mL of 0.3 M nano-nickel reducing agent solution (sodium borohydride) was added dropwise under ice-water bath conditions. After 5 min of addition, the solution was filtered, washed with deionized water until neutral, and dried at 60 °C for 4 h to obtain microspheres with nickel nanoparticles on their surface.

[0070] S3. Activation treatment:

[0071] 1 g of nickel-containing nanoparticles on the surface of the microspheres were dispersed in 20 mL of deionized water and ultrasonically stirred for 10 min. 5 g of palladium sol was added and ultrasonically stirred for another 15 min. The mixture was then filtered, washed with deionized water until neutral, and dried at 60 °C for 4 h to obtain activated microspheres.

[0072] The palladium sol was composed of 100 mg / L nano-palladium, 12 g / L tin chloride, and 250 mL / L hydrochloric acid.

[0073] S4. Chemical plating:

[0074] 1 g of activated microspheres were dispersed in 20 mL of deionized water and ultrasonically stirred for 10 min. Then, chemical plating solution was added dropwise. After 5 min of addition, the mixture was filtered, washed with deionized water until neutral, and dried at 60 °C for 4 h to obtain nickel-plated conductive microspheres.

[0075] The electroless plating solution consists of 30 g of nickel sulfate as the main salt, 15 g of sodium citrate as the complexing agent, 30 g of sodium acetate as the buffer, 30 g of sodium hypophosphite as the reducing agent, 0.02 g of lead sulfate as the stabilizer, and 1000 g of deionized water.

[0076] Comparative Example 2

[0077] A method for preparing nickel-plated conductive microspheres, differing from Example 1 in that no pretreatment or nickel nanoparticle reduction is performed; the method includes the following steps:

[0078] S1. Activation treatment:

[0079] 1 g of polystyrene microspheres were dispersed in 20 mL of deionized water and ultrasonically stirred for 10 min. Then, 5 g of 1-ethyl-3-methylpyridine ethanesulfonate was added and ultrasonically stirred for another 10 min. The mixture was then filtered and washed. The resulting filter cake was dispersed in 10 mL of deionized water and ultrasonically stirred for another 10 min. Then, 5 g of palladium sol was added and ultrasonically stirred for another 15 min. The mixture was then filtered, washed with deionized water until neutral, and dried at 60 °C for 4 h to obtain activated microspheres.

[0080] The palladium sol was composed of 100 mg / L nano-palladium, 12 g / L tin chloride, and 250 mL / L hydrochloric acid.

[0081] S2. Chemical plating:

[0082] 1 g of activated microspheres were dispersed in 20 mL of deionized water and ultrasonically stirred for 10 min. Then, chemical plating solution was added dropwise. After 5 min of addition, the mixture was filtered, washed with deionized water until neutral, and dried at 60 °C for 4 h to obtain nickel-plated conductive microspheres.

[0083] The electroless plating solution consists of 30 g of nickel sulfate as the main salt, 15 g of sodium citrate as the complexing agent, 30 g of sodium acetate as the buffer, 30 g of sodium hypophosphite as the reducing agent, 0.02 g of lead sulfate as the stabilizer, and 1000 g of deionized water.

[0084] Comparative Example 3

[0085] A method for preparing nickel-plated conductive microspheres, the comparative example of which uses an acid roughening scheme, includes the following steps:

[0086] S1. Coarsening treatment:

[0087] 1 g of polystyrene microspheres were dispersed in 10 mL of 50 wt% sulfuric acid and stirred at 60 °C for 1 h. The mixture was then filtered, washed until neutral, and dried at 60 °C for 4 h to obtain coarsened microspheres.

[0088] S2. Sensitization treatment:

[0089] 1 g of coarsened microspheres were dispersed in 15 mL of deionized water, and 15 mL of 40 g / L stannous chloride solution was added. The mixture was stirred in a constant temperature water bath at 55 °C for 30 min, washed with deionized water until neutral, and dried at 60 °C for 4 h to obtain sensitized microspheres.

[0090] S3. Activation treatment:

[0091] 1 g of sensitized microspheres were dispersed in 15 mL of deionized water. 15 mL of 4 g / L palladium chloride solution was added to the dispersion. The mixture was stirred in a constant temperature water bath at 55 °C for a period of time. The microspheres were washed with deionized water until neutral and dried at 60 °C for 4 h to obtain activated microspheres.

[0092] S4. Chemical plating:

[0093] 1 g of activated microspheres were dispersed in 20 mL of deionized water and ultrasonically stirred for 10 min. Then, chemical plating solution was added dropwise. After 5 min of addition, the mixture was filtered, washed with deionized water until neutral, and dried at 60 °C for 4 h to obtain nickel-plated conductive microspheres.

[0094] The electroless plating solution consists of 30 g of nickel sulfate as the main salt, 15 g of sodium citrate as the complexing agent, 30 g of sodium acetate as the buffer, 30 g of sodium hypophosphite as the reducing agent, 0.02 g of lead sulfate as the stabilizer, and 1000 g of deionized water.

[0095] Comparative Example 4

[0096] A method for preparing nickel-plated conductive microspheres, in which nickel nanoparticles are directly added in this comparative example; includes the following steps:

[0097] S1. Preprocessing:

[0098] 1 g of polystyrene microspheres were dispersed in 20 mL of 20 wt% ethanol solution and ultrasonically stirred for 10 min. Then, 10 mL of nano-nickel slurry was added and ultrasonically stirred for 15 min. The mixture was then filtered, washed with deionized water until neutral, and dried to obtain microspheres with nickel nanoparticles on the surface.

[0099] S2. Activation treatment:

[0100] 1 g of nickel-containing nanoparticles on the surface of microspheres were dispersed in 20 mL of deionized water and ultrasonically stirred for 10 min. Then, 5 g of 1-ethyl-3-methylpyridine ethanesulfonate was added and ultrasonically stirred for another 10 min for activation treatment. After filtration and washing, the resulting filter cake was dispersed in 10 mL of deionized water and ultrasonically stirred for 10 min. Then, 5 g of palladium sol was added and ultrasonically stirred for another 15 min. After filtration, the filter cake was washed with deionized water until neutral and dried at 60 °C for 4 h to obtain activated microspheres.

[0101] The palladium sol was composed of 100 mg / L nano-palladium, 12 g / L tin chloride, and 250 mL / L hydrochloric acid.

[0102] S3. Chemical plating:

[0103] 1 g of activated microspheres were dispersed in 20 mL of deionized water and ultrasonically stirred for 10 min. Then, chemical plating solution was added dropwise. After 5 min of addition, the mixture was filtered, washed with deionized water until neutral, and dried at 60 °C for 4 h to obtain nickel-plated conductive microspheres.

[0104] The electroless plating solution consists of 30 g of nickel sulfate as the main salt, 15 g of sodium citrate as the complexing agent, 30 g of sodium acetate as the buffer, 30 g of sodium hypophosphite as the reducing agent, 0.02 g of lead sulfate as the stabilizer, and 1000 g of deionized water.

[0105] In the above Examples 1-2 and Comparative Examples 1-4, the ultrasonic power is uniformly in the range of 240~360 W.

[0106] verify

[0107] Figure 1 The image shows a SEM image of the microspheres with nickel particles on their surface obtained in step S2 of Example 1. It can be seen that the nickel particles are firmly adsorbed on the surface of the microspheres, the microspheres are in a monodisperse state, and there is no adhesion between the microspheres, which is beneficial to the subsequent chemical plating process. Figure 2 and Figure 3 The images show SEM images of the nickel-plated conductive microspheres prepared in Examples 1 and 2, respectively. As can be seen from the images, the surface of the conductive microsphere coating is rough, the protrusions are dense, and there are almost no foreign objects between the microspheres.

[0108] Figures 4-7 The images shown are SEM images of the nickel-plated conductive microspheres prepared in Comparative Examples 1-4, in order. Figure 4As can be seen, the prepared nickel-plated conductive microspheres exhibit a rough morphology with uneven protrusions, resulting in poor coating density. Pyridine-based ionic liquids can physically adsorb onto the microsphere surface, and their anions or cations can further adsorb palladium catalysts through ion exchange or coordination, forming more activation sites on the microsphere surface. The more activation sites, the stronger the coating adhesion and the higher the density. In contrast, Comparative Example 1, lacking the pyridine-based ionic liquid step, suffers from reduced coating adhesion and poor density. Figure 5 and Figure 6 As can be seen, the microspheres prepared in Comparative Examples 2 and 3 have no nickel nanoparticles on their surface, and the prepared conductive microspheres are smooth and without protrusions. From... Figure 7 It can be seen that the conductive microspheres prepared by adsorbing nano-nickel slurry onto microspheres have uneven coating protrusions and metallic nickel exists between the microspheres. This is because although the nano-nickel slurry can be adsorbed onto the microspheres, nickel nanoparticles also exist between the microspheres, which will act as catalytic active centers and generate impurities in the chemical plating solution.

[0109] The mechanical properties of the nickel-plated conductive microspheres prepared in Examples 1-2 and Comparative Examples 1-4 were tested using a micro compression tester. The results of the fracture resistance are shown in Table 1. Figure 8 The figures show the breakage curves of the nickel-plated conductive microspheres prepared in Examples 1, 1, and 2. It can be seen from the figures that the breakage curve of Example 1 is continuous, indicating that the coating is tightly bonded to the polystyrene microspheres. The breakage curves of 1 and 2 have multiple breakage points, indicating that the bonding force between the coating and the polystyrene microspheres is poor.

[0110] The specific surface area of ​​the nickel-plated conductive microspheres prepared in Examples 1-2 and Comparative Examples 1-4 was tested using a specific surface area and pore size analyzer. The test results are shown in Table 1.

[0111] Finally, the nickel-plated conductive microspheres prepared in Examples 1-2 and Comparative Examples 1-4 were fabricated into anisotropic conductive films to test their conductivity. Specifically, bisphenol A epoxy resin, fumed silica, curing agent (4,4'-dihydroxydiphenyl disulfide), nickel-plated conductive microspheres, and tetrahydrofuran were uniformly mixed in a mass ratio of 100:10:7:5:20 to form a tape. This tape was then placed on ITO (indium tin oxide). A digital camera on a hot press was used to align the polyimide film flexible circuit with the ITO circuit. Hot pressing was then performed: first, pre-pressing at 80 ℃ for 1 min; after pre-pressing, bonding was performed at 165 ℃, with a bonding pressure of 3 MPa and a bonding time of 5 s. After hot pressing, the sample was post-treated in a 100 ℃ oven for 1 h to form a device for resistance testing. The resistance was tested using a UNI-T UT620B DC low resistance tester, with 5 measurements taken for each group and the average value recorded. The test results are shown in Table 1.

[0112] Table 1. Properties of the nickel-plated conductive microspheres prepared in Examples 1-2 and Comparative Examples 1-4

[0113]

[0114] It can be seen that the nickel-plated conductive microspheres prepared in Examples 1-2 have high breakage resistance, large specific surface area, and low surface resistivity. Furthermore, when applied to anisotropic conductive films, they significantly reduce connection resistance, exhibiting high conductivity reliability and good stability. Their performance is superior to that of the nickel-plated conductive microspheres prepared in Comparative Examples 1-4. Although Comparative Examples 1 and 4 also have high specific surface areas, this is due to the presence of more scattered nickel elements on their surface coatings, resulting in a scattered and non-dense surface. These results demonstrate that the nickel-plated conductive microspheres prepared by the method of this invention possess excellent conductivity and have broad application prospects.

[0115] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing surface-roughened nickel-plated conductive microspheres, characterized in that, Includes the following steps: S1. Pretreatment: The polymer microspheres are dispersed in a solvent, a nickel precursor solution is added, the mixture is stirred and reacted, then filtered and washed to obtain pretreated microspheres with nickel ions on the surface; S2. Reduction: Pretreated microspheres containing nickel ions on the surface are dispersed in deionized water, and a nano-nickel reducing agent solution is added dropwise under ice-water bath conditions. After ultrasonic stirring and reaction, the mixture is filtered and washed to obtain microspheres containing nickel nanoparticles on the surface. S3. Activation: Microspheres with nickel nanoparticles on their surface are dispersed in deionized water, an activating agent is added for activation treatment, and then the mixture is filtered and washed. The resulting filter cake is further dispersed in deionized water, palladium sol is added, and the mixture is stirred and reacted. After filtration, washing, and drying, activated microspheres are obtained. The activating agent is a pyridine-based ionic liquid. S4. Chemical plating: Activated microspheres are dispersed in deionized water, and chemical plating solution is added dropwise under ultrasonic stirring. After the reaction is set for a time, the microspheres are filtered, washed, and dried to obtain nickel-plated conductive microspheres with roughened surfaces. In step S1, the polymer microspheres are polystyrene microspheres with a particle size of 3-10 μm, and the solvent is a 20-40 wt% ethanol solution. The polystyrene microspheres are added to the solvent at a ratio of 1 g : (20-40) mL to disperse them. The nickel precursor is any one or a combination of nickel sulfate, nickel chloride, and nickel nitrate. The amount of nickel precursor solution used is 10 mL / 1 g polystyrene microspheres, and the concentration is 0.1-0.2 M. In step S2, the nano-nickel reducing agent is any one or a combination of several of borohydride, hydrazine hydrate, ascorbic acid, dimethylamine borate, and borane. The amount of nano-nickel reducing agent solution used is 20 mL / 1 g of pretreated microspheres containing nickel ions on the surface, and the concentration is 0.15~0.3 M.

2. The method for preparing surface-roughened nickel-plated conductive microspheres as described in claim 1, characterized in that, In step S3, the amount of activator used is (5~20) g / 1 g of microspheres containing nickel nanoparticles on the surface.

3. The method for preparing surface-roughened nickel-plated conductive microspheres as described in claim 2, characterized in that, The activator is any one or a combination of several of 1-ethyl-3-methylpyridine ethanesulfonate, N-butylsulfonic acid pyridine hydrochloride, N-butylpyridine tetrafluoroborate, and N-ethylpyridine dinitrile amine salt.

4. The method for preparing surface-roughened nickel-plated conductive microspheres as described in claim 1, characterized in that, In step S3, the palladium sol is composed of 45~100 mg / L of nano-palladium, 3.5~12 g / L of divalent tin salt, and 200~270 mL / L of hydrochloric acid, and the amount used is (10~20) g / 1 g filter cake.

5. The method for preparing surface-roughened nickel-plated conductive microspheres as described in claim 1, characterized in that, In step S4, the electroless plating solution comprises 25-35 g / L of nickel salt, 6-18 g / L of complexing agent, 15-30 g / L of buffer, 25-36 g / L of reducing agent, and 0.01-0.02 g / L of stabilizer; the nickel salt is any one or a combination of nickel sulfate, nickel chloride, nickel hypophosphite, and nickel carbonate; the complexing agent is any one or a combination of EDTA, citric acid, citrate, ammonium chloride, succinic acid, succinate, triethanolamine, ethylenediamine, and lactic acid; the buffer is any one or a combination of sodium acetate and ammonia; the reducing agent is sodium hypophosphite; and the stabilizer is any one or a combination of bismuth salt, lead salt, cerium salt, lanthanum salt, and neodymium salt.

6. The method for preparing surface-roughened nickel-plated conductive microspheres as described in claim 1, characterized in that, In steps S2-S4, the dispersion ratio of pretreated microspheres containing nickel ions on the surface, microspheres containing nickel nanoparticles on the surface, filter cakes, or activated microspheres in deionized water is 1 g : (10~20) mL. All stirring is ultrasonic stirring with an ultrasonic power of 240~360 W. The stirring time in steps S1-S3 is 10~40 min. The reaction time in step S4 is 40~60 min.

7. A surface-roughened nickel-plated conductive microsphere, prepared by the preparation method according to any one of claims 1-6, wherein the coating thickness of the nickel-plated conductive microsphere is 0.1~0.2 μm and the specific surface area is 8~9 m². 2 / g.

8. A conductive adhesive film, characterized in that, The conductive film contains nickel-plated conductive microspheres with roughened surfaces as described in claim 7.

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