Nickel-plated conductive microspheres with protrusions and preparation method and application thereof

Abstract

The present application belongs to the technical field of preparation of conductive microspheres, and particularly relates to a kind of nickel-plated conductive microspheres with protrusions and a preparation method and application thereof. The preparation process includes the following steps: pretreatment to make the surface of polymer microspheres adhere to anionic polymer, amide reaction to make the surface of microspheres combine with aminated nickel nanoparticles, sensitization and activation, and chemical plating. The present application can directly impart carboxyl groups to the surface of microspheres, avoiding the synthesis of polymer microspheres with groups by a complex method and the traditional roughening method with strong acid, and the production process is more environmentally friendly and simple. Then, through amide reaction, the aminated nickel nanoparticles are covalently combined with the polymer microspheres, the combination is more firm and will not fall off, and impurities between the conductive microspheres are avoided. The conductive microspheres prepared by the present application have high specific surface area and firm plating layer, and are suitable for industrial application requirements.

Description

Technical Field

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

[0002] With the trend towards miniaturization of electronic devices, anisotropic conductive materials (such as anisotropic conductive films (ACF), conductive pastes (ACP), and conductive sheets) have become key materials for achieving high-density electrical interconnections between electrodes. These materials rely on conductive microspheres dispersed in insulating resin to achieve vertical conductivity and horizontal insulation. However, as electrode spacing continues to shrink, more stringent requirements are placed on the performance of conductive microspheres: they not only need to possess good conductivity and reliable mechanical strength, but also need to achieve more stable and efficient contact in high-density connections.

[0003] Most conductive microspheres currently on the market have smooth surface coatings. However, the inventors discovered through long-term research that while these microspheres meet basic conductivity requirements, their limited specific surface area results in a small actual contact area with the electrode during bonding, which to some extent limits further improvement in conductivity. In contrast, conductive microspheres with rough surfaces have a higher specific surface area, a larger contact area with the electrode, and superior conductivity.

[0004] Furthermore, the uniformity and fracture strength of the coating on conductive microspheres directly affect the overall performance of anisotropic conductive materials. If the coating is not firmly bonded to the substrate, it is prone to peeling or microsphere breakage due to mechanical or thermal stress during practical use, leading to conductive failure or short circuits. Therefore, preparing conductive microspheres with raised surfaces and firmly bonded coatings can not only optimize conductivity by increasing the contact area, but also improve the reliability and durability of the material in long-term use by enhancing coating adhesion and structural stability, thus meeting the development needs of high-precision and high-reliability electronic interconnects.

[0005] Based on this, the applicant applied for a patent for a method for preparing conductive microspheres with rough surfaces and has made continuous improvements. These technologies and improvements can be found in patents CN117966137A, CN118852657A, CN121046825A, etc. Among them, patent CN118852657A discloses a method for preparing polymer composite conductive microspheres and its application, proposing a method to directly adsorb nano-nickel particles on the surface of the microspheres to prepare a rough coating. However, in this method, it is difficult for all nano-nickel particles to be adsorbed on the spheres, and the scattered nano-nickel particles will generate a large number of impurities in the subsequent chemical plating. Patent CN121046825A discloses a surface-roughened nickel-plated conductive microsphere, its preparation method, and its application. This method aims to solve the adsorption problem of nano-nickel particles. Although it can solve the impurity problem, the ionic liquid used is expensive, difficult to degrade, and easy to leave residues, which may lead to coating defects. Palladium sol has poor stability and is prone to agglomeration and deactivation. Moreover, both ionic liquid and palladium sol are special raw materials, which have high requirements for procurement and storage control, and there are batch fluctuations, which may affect the repeatability of product batches.

[0006] Other technologies have also been used to study the preparation of rough microspheres. For example, CN121394050A discloses a protruding conductive microsphere and its pretreatment method. By adding a surfactant (polyvinylpyrrolidone), the dispersibility of Ni nanoparticles is improved. However, in this scheme, the binding of Ni nanoparticles and microspheres is mainly achieved through electrostatic adsorption and steric hindrance of polyvinylpyrrolidone. The binding force is weak, and it is difficult for all Ni nanoparticles to be adsorbed on the spheres. There is also a risk of impurities, and the process is relatively complicated.

[0007] It is essential to provide a novel method for preparing nickel-plated conductive microspheres, which can improve the bonding force between nickel nanoparticles and microspheres and simplify the preparation method. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention first provides a method for preparing nickel-plated conductive microspheres with protrusions.

[0009] The technical solution adopted in this invention is as follows: A method for preparing nickel-plated conductive microspheres with protrusions includes the following steps: S1. Pretreatment: The polymer microspheres are dispersed in an aqueous solution of anionic polyacrylic acid surface treatment agent, the pH value is adjusted to 5.0~7.0, and ultrasonic stirring is performed to obtain pretreated microspheres with anionic polymers attached to the surface; S2. Adsorption and binding: The pretreated microspheres are added to the dispersion of aminated nickel nanoparticles, and then an amide reactive agent is added to carry out the amide reaction. After the reaction is completed, the microspheres are filtered and washed to obtain microspheres with nickel nanoparticles bound to the surface. S3. Activation: Microspheres with nickel nanoparticles bound to their surface are added to a sensitizer for sensitization treatment to obtain sensitized microspheres. The sensitized microspheres are then added to a palladium ion solution for activation treatment to obtain activated microspheres. 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 protrusions on the surface.

[0010] Preferably, the anionic polyacrylic acid surface treatment agent is selected from any one or a combination of polyacrylic acid, sodium polyacrylate, polymethacrylic acid, and sodium polymethacrylate.

[0011] Preferably, the concentration of the aqueous solution of the anionic polyacrylic acid surface treatment agent is 0.5 wt% to 1.5 wt%, and the dosage is 40 to 100 mL / 1 g polymer microspheres.

[0012] Preferably, the reagent for adjusting the pH value is selected from any one or a combination of several of the following: dilute hydrochloric acid (5 wt%~10 wt%), dilute sulfuric acid (5 wt%~10 wt%), sodium hydroxide, and ammonia water. The ultrasonic stirring power is 240~360W, and the stirring time is 20~50 min.

[0013] Preferably, in step S2, the dispersion of the aminated nickel nanoparticles is prepared by uniformly mixing nickel nanoparticles, aminated reagent and deionized water in a mass ratio of (0.4~1.5): (0.6~2): (8~12), and the amount of nickel nanoparticle dispersion is 5~7 g / 1 g of pretreated microspheres.

[0014] Preferably, the nickel nanoparticles have a particle size of 20~400 nm.

[0015] Preferably, the amination reagent is selected from any one or a combination of several of mercaptoethylamine, cysteine, ethanolamine phosphate, and aminotrimethylene phosphate.

[0016] Preferably, the amide reactive agent is selected from any one or a combination of EDC and HOBt, EDCI and HOBt, and lipase, and the amount of amide reactive agent used is 0.05~0.10 g / 1 g of pretreated microspheres, and the amide reaction time is 1~2 h.

[0017] The Chinese names corresponding to the above abbreviations are: EDC: 1-ethyl-(3-dimethylaminopropyl)carbodiimide; HOBt: 1-hydroxybenzotriazole; EDCI: 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride.

[0018] Preferably, in the composition of EDC and HOBt, the mass ratio of EDC to HOBt is (1.2~1.5):1; and in the composition of EDCI and HOBt, the mass ratio of EDCI to HOBt is (1.4~1.8):1.

[0019] Preferably, the sensitizer is an aqueous solution containing 0.3 wt% to 2 wt% stannous ions, and the amount of sensitizer used is 10 to 20 g / 1 g of microspheres with nickel nanoparticles bound to the surface.

[0020] Preferably, the palladium ion solution is selected from any one of the following: a hydrochloric acid solution of palladium chloride, a sulfuric acid solution of palladium sulfate, and a nitric acid solution of palladium nitrate. The mass fraction of palladium ions in the palladium ion solution is 0.05 wt% to 0.1 wt%, and the amount of palladium ion solution used is 10 to 20 g / 1 g sensitized microspheres.

[0021] Preferably, the sensitization treatment is performed by stirring at room temperature for 15-30 minutes.

[0022] Preferably, the activation treatment is performed at a reaction temperature of 40-60 °C and a stirring time of 20-40 min.

[0023] Preferably, the electroless plating solution comprises 4 wt% to 8 wt% nickel salt, 0.6 wt% to 1.2 wt% complexing agent, 3 wt% to 5 wt% buffer, 2 wt% to 6 wt% reducing agent, and the balance being deionized water, based on a total mass fraction of 100 wt%.

[0024] Preferably, the nickel salt is selected from any one or a combination of nickel sulfate, nickel chloride, nickel hypophosphite, or nickel nitrate; the complexing agent is selected from any one or a combination of ethylenediaminetetraacetic acid (EDTA), sodium ethylenediaminetetraacetic acid, tartaric acid, citric acid, triethanolamine, and citric acid; the buffer is sodium acetate and / or ammonia; and the reducing agent is sodium hypophosphite.

[0025] Preferably, the amount of the chemical plating solution used is 140~170 mL / 1 g activated microspheres, and the reaction time is set to 40~60 min.

[0026] Preferably, the drying conditions are vacuum drying at 85 °C for 4 h.

[0027] The present invention further provides a nickel-plated conductive microsphere with protrusions, which is prepared by the preparation method described above. The coating thickness of the nickel-plated conductive microsphere is 75~200 nm, and the coating surface has uniform protrusions composed of nickel nanoparticles.

[0028] The present invention also provides the application of nickel-plated conductive microspheres with protrusions as described above in the preparation of anisotropic conductive adhesives, wherein the anisotropic conductive adhesives include, but are not limited to, film, liquid, and paste forms, such as anisotropic conductive films (ACF), anisotropic conductive pastes (ACP), etc.

[0029] The present invention also provides an anisotropic conductive adhesive, wherein the anisotropic conductive adhesive contains nickel-plated conductive microspheres with protrusions as described above.

[0030] The beneficial effects of this invention are as follows: This invention improves the preparation method of conductive microspheres. First, by mixing polyacrylic resin with polymer microspheres, a large number of carboxyl groups are directly imparted to the surface of the microspheres. This avoids the need for complex synthesis of polymer microspheres with groups and traditional strong acid roughening methods, making the production process more environmentally friendly and simpler.

[0031] Furthermore, the aminated nickel nanoparticles have positively charged amino groups, while the polymer microspheres have a large number of negatively charged carboxyl groups. Through the amide reaction, the two are covalently bonded. Under the repulsion of like charges, the microspheres are easier to disperse and do not agglomerate. The nickel nanoparticles can also be more uniformly dispersed on the surface of the microspheres, and the bond is stronger and will not fall off, thus avoiding the generation of impurities between the conductive microspheres.

[0032] The above steps result in a large number of carboxyl, amino, and amide group active sites on the surface of the microspheres and nickel nanoparticles. These sites can efficiently bind stannous ions in the sensitizer and palladium ions in the activator, significantly improving activation efficiency. At the same time, the amide groups can also strengthen the binding of nickel nanoparticles, ensuring that the nickel nanoparticles do not fall off. This gives the microspheres with bound nickel nanoparticles a larger overall specific surface area, resulting in more and more uniform Pd and Ni binding sites. The nickel plating layer is also more uniform and firm. Through the above synergistic effect, conductive microspheres with tight coating and stronger adhesion are finally obtained.

[0033] The conductive microspheres with protrusions prepared by this invention have a large specific surface area. During the pressing process, they can displace the insulating resin adhesive, forming a more thorough contact with the electrode. Under certain pressure, they can also pierce the oxide layer of the electrode or gold finger, thereby significantly improving conductivity and connection reliability. The prepared conductive microspheres have uniform protrusions, and the nickel nanoparticles and coating are firmly bonded to the microspheres, avoiding the risk of short circuits or reduced conductivity caused by the detachment of the coating or nickel nanoparticles.

[0034] The preparation method of the present invention is simple and efficient, without complicated steps, and does not require the purchase of other equipment for large-scale mass production, making it particularly suitable for industrial production needs. Attached Figure Description

[0035] Figure 1 This is a SEM image of the activated microspheres prepared in Example 1.

[0036] Figure 2 This is a SEM image of the nickel-plated conductive microspheres prepared in Example 1.

[0037] Figure 3 This is a SEM image of the nickel-plated conductive microspheres prepared in Example 2.

[0038] Figure 4 SEM image of the activated microspheres prepared for Comparative Example 1.

[0039] Figure 5 SEM image of the nickel-plated conductive microspheres prepared in Comparative Example 1.

[0040] Figure 6 SEM image of the nickel-plated conductive microspheres prepared in Comparative Example 2.

[0041] Figure 7 SEM image of the nickel-plated conductive microspheres prepared in Comparative Example 3.

[0042] Figure 8 The image shows a SEM image of the nickel-plated conductive microspheres prepared in Comparative Example 4.

[0043] Figure 9 This is a breakage curve of the nickel-plated conductive microspheres prepared in Example 1 and Comparative Examples 1-4. Detailed Implementation

[0044] To facilitate understanding, the technical solution of the present invention will be described in more detail below with reference to the embodiments.

[0045] Example 1 A method for preparing nickel-plated conductive microspheres with protrusions includes the following steps: S1. Preprocessing: 1 g of polystyrene microspheres with a particle size of 5 μm were added to 60 mL of 0.5 wt% polyacrylic acid (average molecular weight M). W The mixture was stirred in a 5000 ppm aqueous solution, and the pH was adjusted to 5.5 using a 10 wt% NaOH aqueous solution. The mixture was ultrasonically stirred at room temperature for 30 min, filtered, and the unattached polyacrylic acid was washed with 50 mL × 3 deionized water to obtain pretreated microspheres with negatively charged carboxyl groups attached to the surface of the microspheres.

[0046] S2. Adsorption and binding: 1 g of pretreated microspheres were added to a dispersion of 6 g of aminated nickel nanoparticles and mixed for 5 min. Then, 0.05 g of amide reactive agent (composed of 0.03 g EDCI and 0.02 g HOBt) was added and reacted at room temperature for 1 h. After filtration and washing, microspheres with nickel nanoparticles bound to the surface were obtained. The above-mentioned dispersion of aminated nickel nanoparticles was obtained by adding 0.26 g of nickel nanoparticles (particle size of 100~200 nm) and 0.52 g of ethanolamine phosphate to 5.22 g of deionized water, and then ultrasonically dispersing at room temperature for 30 min.

[0047] S3. Activation: 1 g of surface-bonded nickel nanoparticle microspheres were added to 15 g of stannous chloride solution containing 0.5 wt% stannous ions. The mixture was stirred at room temperature for 15 min to sensitize the microspheres. After filtration and washing until neutral, the sensitized microspheres were obtained. The sensitized microspheres were then added to 15 g of palladium chloride hydrochloric acid solution containing 0.07 wt% palladium ions. The mixture was stirred at 50 °C for 30 min to activate the microspheres. After filtration and washing until neutral, the microspheres were dried to obtain activated microspheres.

[0048] S4. Chemical plating: The electroless plating time was calculated from the start of adding the electroless plating solution until the end of the reaction time. 1 g of activated microspheres were ultrasonically dispersed in 5 mL of deionized water. 150 mL of electroless plating solution was added dropwise under ultrasonic stirring for 30 min. After the addition was complete, the reaction was continued for 10 min. The mixture was then filtered, washed until neutral, and vacuum dried at 85 ℃ for 4 h to obtain nickel-plated conductive microspheres with protrusions.

[0049] The above chemical plating solution consists of 9 g of nickel sulfate (nickel salt), 0.9 g of complexing agent EDTA, 4.5 g of buffer ammonia, 4.5 g of reducing agent sodium hypophosphite, and 130 g of deionized water.

[0050] SEM images of the activated microspheres prepared in Example 1 are shown below. Figure 1 SEM image of the nickel-plated conductive microspheres with protrusions can be found in [link to image]. Figure 2 .

[0051] Example 2 A method for preparing nickel-plated conductive microspheres with protrusions includes the following steps: S1. Preprocessing: 1 g of polystyrene microspheres with a particle size of 5 μm were added to 60 mL of 0.5 wt% polymethacrylic acid (molecular weight of 40,000~50,000) aqueous solution, stirred and mixed, and the pH value was adjusted to 5.5 with 10 wt% NaOH aqueous solution. The mixture was ultrasonically stirred at room temperature for 30 min, filtered, and the unattached polymethacrylic acid was washed with 50 mL × 3 deionized water to obtain pretreated microspheres with negatively charged carboxyl groups attached to the surface of the pretreated microspheres.

[0052] S2. Adsorption and binding: 1 g of pretreated microspheres were added to a dispersion of 6 g of aminated nickel nanoparticles and mixed for 7 min. Then, 0.05 g of amide reactive agent (composed of 0.03 g EDCI and 0.02 g HOBt) was added and reacted at room temperature for 1 h. After filtration and washing, microspheres with nickel nanoparticles bound to the surface were obtained. The above-mentioned dispersion of aminated nickel nanoparticles was obtained by adding 0.26 g of nickel nanoparticles (particle size of 100~200 nm) and 0.31 g of mercaptoethylamine to 5.43 g of deionized water, and then ultrasonically dispersing at room temperature for 30 min.

[0053] S3. Activation: 1 g of surface-bonded nickel nanoparticle microspheres were added to 15 g of stannous chloride solution containing 0.5 wt% stannous ions. The mixture was stirred at room temperature for 15 min to sensitize the microspheres. After filtration and washing until neutral, the sensitized microspheres were obtained. The sensitized microspheres were then added to 15 g of palladium chloride hydrochloric acid solution containing 0.07 wt% palladium ions. The mixture was stirred at 50 °C for 30 min to activate the microspheres. After filtration and washing until neutral, the microspheres were dried to obtain activated microspheres.

[0054] S4. Chemical plating: The electroless plating time was calculated from the start of adding the electroless plating solution until the end of the reaction time. 1 g of activated microspheres were ultrasonically dispersed in 5 mL of deionized water, and 150 mL of electroless plating solution was added dropwise under ultrasonic stirring for 40 min. After the addition was complete, the reaction was continued for 10 min, then filtered, washed until neutral, and vacuum dried at 85 ℃ for 4 h to obtain nickel-plated conductive microspheres with protrusions.

[0055] The above chemical plating solution consists of 9 g of nickel sulfate (nickel salt), 0.9 g of complexing agent EDTA, 4.5 g of buffer ammonia, 4.5 g of reducing agent sodium hypophosphite, and 130 g of deionized water.

[0056] SEM image of the nickel-plated conductive microspheres with protrusions prepared in Example 2 is shown below. Figure 3 .

[0057] Comparative Example 1 The preparation method of Comparative Example 1 is the same as that of Example 1, except that the polystyrene microspheres are treated with small molecule succinic acid in the pretreatment process of step S1, specifically: 1 g of polystyrene microspheres with a particle size of 5 μm were added to 60 mL of 0.5 wt% succinic acid aqueous solution, stirred and mixed, and the pH value was adjusted to 5.5 with 10 wt% NaOH aqueous solution. The mixture was ultrasonically stirred at room temperature for 30 min, filtered, and washed with 50 mL × 3 deionized water to remove any unadhered succinic acid, thus obtaining the pretreated microspheres.

[0058] SEM images of the activated microspheres prepared in Comparative Example 1 are shown below. Figure 4 SEM image of the nickel-plated conductive microspheres with protrusions can be found in [link to image]. Figure 5 .

[0059] Comparative Example 2 The preparation method of Comparative Example 2 is the same as that of Example 1, except that in the adsorption and binding process of step S2, nickel nanoparticles modified with 3-aminopropyltriethoxysilane are used, specifically: 1 g of pretreated microspheres were added to a dispersion of 6 g of aminated nickel nanoparticles and mixed for 5 min. Then, 0.05 g of amide reactive agent (composed of 0.03 g EDCI and 0.02 g HOBt) was added and reacted at room temperature for 1 h. After filtration and washing, microspheres with nickel nanoparticles bound to the surface were obtained. The above-mentioned nickel nanoparticle dispersion was prepared as follows: nickel nanoparticles (particle size of 100~200 nm) were dispersed in ethanol to obtain a suspension with a concentration of 3 mg / mL. 3-aminopropyltriethoxysilane was added to the suspension at an amount of 10% of the mass of the nickel nanoparticles. After stirring and reacting at 70 °C for 4 h, aminated nickel nanoparticles were obtained by centrifugation and washing with ethanol. Then, 0.8 g of aminated nickel nanoparticles were added to 5.2 g of deionized water and ultrasonically dispersed at room temperature for 30 min to obtain the final product.

[0060] SEM image of the nickel-plated conductive microspheres with protrusions prepared in Comparative Example 2 is shown below. Figure 6 .

[0061] Comparative Example 3 The preparation method of Comparative Example 3 is the same as that of Example 1, except that no amide reactive agent is added during the adsorption and binding process in step S2. Specifically: 1 g of pretreated microspheres were added to a dispersion of 6 g of aminated nickel nanoparticles, stirred at room temperature for 1 h, filtered, and washed to obtain microspheres with nickel nanoparticles bound to the surface. The above-mentioned dispersion of aminated nickel nanoparticles was obtained by adding 0.26 g of nickel nanoparticles (particle size of 100~200 nm) and 0.52 g of ethanolamine phosphate to 5.22 g of deionized water, and then ultrasonically dispersing at room temperature for 30 min.

[0062] SEM image of the nickel-plated conductive microspheres with protrusions prepared in Comparative Example 3 is shown below. Figure 7 .

[0063] Comparative Example 4 The preparation method of Comparative Example 4 is the same as that of Example 1, except that step S2 adsorption and binding is omitted, and the pretreated microspheres are directly used for step S3 activation treatment, specifically: S1. Preprocessing: 1 g of polystyrene microspheres with a particle size of 5 μm were added to 60 mL of 0.5 wt% polyacrylic acid (average molecular weight M). W The mixture was stirred in a 5000 ppm aqueous solution, and the pH was adjusted to 5.5 using a 10 wt% NaOH aqueous solution. The mixture was ultrasonically stirred at room temperature for 30 min, filtered, and the unattached polyacrylic acid was washed with 50 mL × 3 deionized water to obtain pretreated microspheres with negatively charged carboxyl groups attached to the surface of the microspheres.

[0064] S2. Activation: 1 g of pretreated microspheres were added to 15 g of stannous chloride solution containing 0.5 wt% stannous ions and stirred at room temperature for 15 min for sensitization. The mixture was then filtered and washed until neutral to obtain sensitized microspheres. The obtained sensitized microspheres were then added to 15 g of palladium chloride hydrochloric acid solution containing 0.07 wt% palladium ions and stirred at 50 °C for 30 min for activation. The mixture was then filtered, washed until neutral, and dried to obtain activated microspheres.

[0065] S3. Chemical plating: The electroless plating time was calculated from the start of adding the electroless plating solution until the end of the reaction time. 1 g of activated microspheres were ultrasonically dispersed in 5 mL of deionized water. 150 mL of electroless plating solution was added dropwise under ultrasonic stirring for 30 min. After the addition was complete, the reaction was continued for 10 min. The mixture was then filtered, washed until neutral, and vacuum dried at 85 ℃ for 4 h to obtain nickel-plated conductive microspheres with protrusions.

[0066] The above chemical plating solution consists of 9 g of nickel sulfate (nickel salt), 0.9 g of complexing agent EDTA, 4.5 g of buffer ammonia, 4.5 g of reducing agent sodium hypophosphite, and 130 g of deionized water.

[0067] SEM image of the nickel-plated conductive microspheres with protrusions prepared in Comparative Example 4 is shown below. Figure 8 .

[0068] analyze

[0069] Figures 2-3 The images show SEM images of the nickel-plated conductive microspheres prepared in Examples 1 and 2, respectively. It can be seen that the conductive microspheres have a dense coating with dense and uniform protrusions on the surface, and there are no foreign objects between the microspheres. Figures 5-7 The images show SEM images of the nickel-plated conductive microspheres prepared in Comparative Examples 1-3, respectively. Figure 5 , Figure 6 It is evident that a large number of metal particles and foreign matter are present between the microspheres and on the outer surface of the coating. Figure 7 The number of metal particles between the microspheres has decreased, but has not been completely eliminated.

[0070] Analysis of the causes revealed that Comparative Example 1 involved treating polystyrene microspheres with small-molecule succinic acid, which... Figure 5 As can be seen, nickel nanoparticles cannot be adsorbed onto the surface of polystyrene microspheres, and the coating is not dense enough. This is mainly because the surface contact area between succinic acid and polystyrene is small, making it difficult to adhere to the surface of polystyrene microspheres, and thus unable to provide activation sites for binding palladium ions. Although it can bind nickel nanoparticles containing amino groups, it cannot form a connection with the polystyrene microspheres. In contrast, Example 1 uses polyacrylic acid with a longer molecular chain, which has a similar polarity to the surface of polystyrene microspheres, and can better "coat" the polystyrene microspheres. Figure 1 The SEM image of the activated microspheres in Example 1 is shown. Figure 4 As shown in the SEM image of the activated microspheres in Comparative Example 1, the nickel nanoparticles in the activated microspheres obtained without polyacrylic acid treatment showed significantly poor bonding with the polymer microspheres, with obvious scattering.

[0071] The nickel nanoparticle dispersion of Comparative Example 2 contains 3-aminopropyltriethoxysilane-modified nickel nanoparticles, which are composed of... Figure 6 As can be seen, some nickel nanoparticles are still scattered. This may be because 3-aminopropyltriethoxysilane undergoes hydrolysis and condensation on the surface of the nickel nanoparticles, easily forming a slightly cross-linked siloxane layer, causing the nanoparticles to aggregate and making it difficult to uniformly adsorb on the surface of polystyrene microspheres. Moreover, although EDCI / HOBt is added to the system, the amino groups introduced by 3-aminopropyltriethoxysilane are not fully exposed due to aggregation, reducing the probability of effective contact with the carboxyl groups on the microsphere surface, resulting in a low actual covalent bonding amount. Ultimately, this makes it difficult for the nickel nanoparticles loaded on the microsphere surface to form continuous and effective activation sites. Therefore, the nickel nanoparticles are more likely to detach and scatter during subsequent stirring, washing, and filtration. In contrast, the amination reagent (ethanolamine phosphate) in Example 1 not only contains amino groups but also phosphate groups that can coordinate with nickel. The multiple chemical interactions promote the firm adsorption of nickel nanoparticles onto the surface of polystyrene microspheres.

[0072] Although Comparative Example 3 used a surface treatment agent and a nickel nanoparticle amination reagent, no covalent bonding occurred. The amination of nickel nanoparticles could only bind to carboxylated polystyrene microspheres via non-covalent electrostatic interactions. Figure 7 As can be seen, nickel nanoparticles are still detaching.

[0073] Comparative Example 4 directly used pre-treated microspheres without adding nickel nanoparticles to create the protruding structure. Figure 8As can be seen, due to the absence of nickel nanoparticles, the final conductive microspheres have a dense coating, a smooth surface, and no protrusions. However, since the same surface treatment agent was used to treat the raw material microspheres, the surface treatment agent adhered to the surface of the raw material microspheres and provided a large number of activation sites, resulting in a coating that is significantly denser than that of Comparative Example 1.

[0074] verify

[0075] 1. Test of resistance to breakage force

[0076] The fracture resistance of nickel-plated conductive microspheres prepared in Examples 1-2 and Comparative Examples 1-4 was tested using a nanoindenter (Step X00-NHT3). The test results are shown in [Figure number missing]. Figure 9 And Table 1. From Figure 9 As can be seen, the pressure resistance curves of Example 1 and Comparative Examples 2-4 are smooth and continuous before breakage, indicating that the coating and polystyrene microspheres are tightly and firmly bonded; the pressure resistance curve of Comparative Example 1 has multiple segments of breakage before breakage, indicating that the coating and polystyrene microspheres have poor bonding force.

[0077] 2. Conductivity test

[0078] The nickel-plated conductive microspheres prepared in Examples 1-2 and Comparative Examples 1-4 were used to fabricate anisotropic conductive films for conductivity testing. 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 and made into a tape. This tape was placed on indium tin oxide (ITO). A digital camera on a hot press was used to align the gold fingers of the FPC (flexible printed circuit board) with the ITO circuit. Then, hot pressing was performed at 165 °C and 3 MPa for 5 s to form a conductive connection. After hot pressing, the resistance was tested using a HIOKI RM3544-01 microresistance meter. Five measurements were taken for each group, and the average value was recorded. The test results are shown in Table 1.

[0079] Table 1 Performance test results of nickel-plated conductive microspheres prepared in Examples 1-2 and Comparative Examples 1-4

[0080] The fracture resistance of nickel-plated conductive microspheres is an important indicator, but actual tests have shown that it is mainly affected by the fracture resistance of the microsphere raw materials, and a higher value is not necessarily better. If the fracture resistance is too high, sufficient deformation cannot occur during bonding in ACF (acoustic fibroblast polymer) (particles do not open), resulting in a small contact area and high resistance. It is more important to test whether the nickel-plated conductive microspheres break in multiple stages during the fracture process. The more fracture stages, the weaker the bond between the coating and the polymer microspheres, leading to coating detachment, poor pressure resistance, and lower conductivity.

[0081] As shown in Table 1, the breakage resistance of the nickel-plated conductive microspheres prepared in Examples 1-2 can be controlled between 13 and 15 mN, with no multi-stage breakage and uniform protrusions on the surface, exhibiting good contact conductivity, significantly superior to Comparative Examples 1-4. Comparative Example 1, due to the lack of surface treatment agent on the polystyrene microspheres, exhibited multi-stage breakage. Examples 1-2 and Comparative Examples 2-3, due to the presence of nickel protrusions in the plating, showed a significant reduction in connection resistance in ACF compared to Comparative Example 4. Compared to Examples 1-2, Comparative Example 2-3 showed some nickel nanoparticle detachment, a lower density of nickel protrusions on the microsphere surface, and slightly poorer conductivity in ACF. Comparative Example 1, due to the weak bond between the plating and the polystyrene sphere core, suffered from plating detachment and significant breakage in ACF, resulting in the worst conductivity.

[0082] The results indicate that the nickel-plated conductive microspheres prepared by the method of the present invention have ideal morphology and mechanical properties as well as excellent conductivity, and have good application value and broad application prospects.

[0083] 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 nickel-plated conductive microspheres with protrusions, characterized in that, Includes the following steps: S1. Pretreatment: The polymer microspheres are dispersed in an aqueous solution of anionic polyacrylic acid surface treatment agent, the pH value is adjusted to 5.0~7.0, and ultrasonic stirring is performed to obtain pretreated microspheres with anionic polymers attached to the surface; S2. Adsorption and binding: The pretreated microspheres are added to the dispersion of aminated nickel nanoparticles, and then an amide reactive agent is added to carry out the amide reaction. After the reaction is completed, the microspheres are filtered and washed to obtain microspheres with nickel nanoparticles bound to the surface. S3. Activation: Microspheres with nickel nanoparticles bound to their surface are added to a sensitizer for sensitization treatment to obtain sensitized microspheres. The sensitized microspheres are then added to a palladium ion solution for activation treatment to obtain activated microspheres. 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 protrusions on the surface. The anionic polyacrylic acid surface treatment agent is selected from any one or a combination of polyacrylic acid, sodium polyacrylate, polymethacrylic acid, and sodium polymethacrylate; the concentration of the aqueous solution of the anionic polyacrylic acid surface treatment agent is 0.5 wt%~1.5 wt%, and the dosage is 40~100 mL / 1 g polymer microspheres; In step S2, the dispersion of the amination-treated nickel nanoparticles is prepared by uniformly mixing nickel nanoparticles, an amination reagent, and deionized water at a mass ratio of (0.4~1.5):(0.6~2):(8~12). The amount of nickel nanoparticle dispersion used is 5~7 g / 1 g of pretreated microspheres. The particle size of the nickel nanoparticles is 20~400 nm. The amination reagent is ethanolamine phosphate. The amide reactive agent is selected from a combination of 1-ethyl-(3-dimethylaminopropyl)carbodiimide and 1-hydroxybenzotriazole or a combination of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and 1-hydroxybenzotriazole. The amount of amide reactive agent used is 0.05~0.10 g / 1 g of pretreated microspheres, and the amide reaction time is 1~2 h.

2. The method for preparing nickel-plated conductive microspheres with protrusions as described in claim 1, characterized in that, The sensitizer is an aqueous solution containing 0.3 wt% to 2 wt% stannous ions, and the amount of sensitizer used is 10 to 20 g / 1 g of microspheres with nickel nanoparticles bound to the surface.

3. The method for preparing nickel-plated conductive microspheres with protrusions as described in claim 1, characterized in that, The palladium ion solution is selected from any one of the following: hydrochloric acid solution of palladium chloride, sulfuric acid solution of palladium sulfate, and nitric acid solution of palladium nitrate. The mass fraction of palladium ions in the palladium ion solution is 0.05 wt% to 0.1 wt%, and the amount of palladium ion solution used is 10 to 20 g / 1 g sensitized microspheres.

4. The method for preparing nickel-plated conductive microspheres with protrusions as described in claim 1, characterized in that, The sensitization treatment is performed by stirring at room temperature for 15-30 min, and the activation treatment is performed at a reaction temperature of 40-60 °C for 20-40 min.

5. The method for preparing nickel-plated conductive microspheres with protrusions as described in claim 1, characterized in that, Based on a total mass fraction of 100 wt%, the electroless plating solution comprises 4 wt%~8 wt% nickel salt, 0.6 wt%~1.2 wt% complexing agent, 3 wt%~5 wt% buffer, 2 wt%~6 wt% reducing agent, and the balance being deionized water; the nickel salt is selected from any one or a combination of nickel sulfate, nickel chloride, nickel hypophosphite, or nickel nitrate; the complexing agent is selected from any one or a combination of ethylenediaminetetraacetic acid, sodium ethylenediaminetetraacetic acid, tartaric acid, citric acid, triethanolamine, or citric acid; the buffer is sodium acetate and / or ammonia; and the reducing agent is sodium hypophosphite; the amount of the electroless plating solution used is 140~170 mL / 1 g activated microspheres, and the reaction time is set to 40~60 min.

6. A nickel-plated conductive microsphere with protrusions, prepared by the preparation method according to any one of claims 1-5, wherein the coating thickness of the nickel-plated conductive microsphere is 75~200 nm, and the coating surface has uniform protrusions composed of nickel nanoparticles.

7. An anisotropic conductive adhesive, characterized in that, The anisotropic conductive adhesive contains nickel-plated conductive microspheres with protrusions as described in claim 6.

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