Microsphere surface chemical nickel plating method based on double-reduction system

Abstract

The invention discloses a microsphere surface chemical nickel plating method based on a double reduction system, which comprises the following steps of: compounding strong reducing agents such as hydroboron, dimethylamine borate, borane or hydrazine and weak reducing agents such as hypophosphite and hypophosphite according to a certain proportion for nickel plating; by using the strong reducing agent, the problem that the induction time of chemical nickel plating is long is avoided while the compactness of the plating is improved, and the plating uniformity and dispersity of the nickel-plated microspheres can be effectively improved by adjusting the proportion of the strong reducing agent and the weak reducing agent in the double reducing agents.

Description

Technical Field

[0001] The invention relates to the technical field of microsphere nickel plating, and in particular to a microsphere surface chemical nickel plating method based on a double reduction system. Background Art

[0002] The rapid development of the information and communication industry has promoted the electronic circuit boards to move towards refinement and integration, and also put forward higher requirements for the assembly of integrated circuits and circuit boards. As a result, the traditional tin-lead soldering technology is limited, and the anisotropic conductive film (ACF) with simple process and high reliability has developed rapidly.

[0003] ACF is mainly composed of insulating resin binder and conductive particles dispersed therein. In addition to its moisture-proof, bonding, heat-resistant and insulating functions, the resin binder mainly fixes the relative position of the interconnecting electrodes and provides a certain pressure to maintain the contact area between the electrodes and the conductive particles. Conductive particles are the core part of ACF and are used to achieve electrical conduction between interconnecting bumps. Therefore, the performance of conductive particles directly determines the conductivity and durability of ACF.

[0004] Composite microspheres with monodisperse microspheres as cores and conductive metal as shells have the advantages of uniform particle size, good elasticity, light weight and good conductivity of metals, and are therefore used as conductive particles in ACF. Among them, nickel-plated microspheres are highly favored in ACF applications due to their good conductivity, low price and high stability.

[0005] The existing chemical nickel plating method is to obtain activated microspheres by roughening, sensitizing and activating microspheres, and then mix nickel salt, complexing agent, reducing agent, stabilizer and surfactant to form a nickel plating solution, and then mix the nickel plating solution with the activated microspheres to perform chemical nickel plating. However, this chemical nickel plating method requires a long induction time before the nickel plating reaction, which is not conducive to industrial production, and the initial reaction is violent, and the nickel layer on the surface of the nickel ball is uneven and poorly dispersed. For example, invention patent applications CN1186820A, CN103276376A, and CN118459643A use functionalized microspheres to perform coordination reactions to complete the sensitization process, avoid the complex and cumbersome and dangerous roughening process in the traditional nickel plating microsphere synthesis process, and simplify the original nickel plating microsphere synthesis process, but the nickel plating solution is mixed with the activated microspheres during the chemical nickel plating process, and the nickel layer of the obtained nickel ball is uneven. For another example, invention patent application CN114807912 A divides the nickel plating solution into an oxidizing solution (nickel salt, complexing agent) and a reducing solution (reducing agent) based on functionalized microspheres. Adding the two solutions simultaneously can start the nickel plating reaction instantly, thus avoiding a long induction time. However, the simultaneous addition of the two solutions makes the nickel plating system unstable, resulting in poor surface cleanliness of the nickel spheres. Summary of the invention

[0006] In view of the technical defects of the existing microsphere chemical nickel plating method, the present invention aims to provide an improved chemical nickel plating method, which has the characteristics of short development induction time, stable system, uniform coating, high cleanliness and good dispersibility.

[0007] The present invention protects a method for chemical nickel plating on the surface of microspheres based on a double reduction system, wherein the microspheres are subjected to coarsening, sensitization and activation treatments in sequence to obtain activated microspheres. The microspheres may be polymer microspheres or silicon microspheres.

[0008] Polymer microspheres are tiny spherical particles made of polymer materials (such as polyolefins such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyisobutylene and polybutadiene, polyacrylic resins such as polymethyl methacrylate and polymethyl acrylate), usually with diameters ranging from nanometers to micrometers. Nickel plating on the surface of polymer microspheres is usually used to enhance their mechanical properties, chemical stability, or for electromagnetic shielding, conductive applications, etc.

[0009] Silicon microspheres are tiny particles made of silicon dioxide (SiO2) material with high chemical stability, mechanical strength and surface functionalization capabilities. Nickel plating on the surface of silicon microspheres can enhance their conductivity, which is important in applications such as sensors, electronic components, and micro batteries. The nickel plating layer can also provide additional chemical stability and protect the silicon microspheres from environmental corrosion, especially in complex chemical reaction environments.

[0010] The activated microspheres are dispersed in pure water, and nickel salt and a complexing agent are added to form a pre-reaction liquid; the pre-reaction liquid is then heated to 35-60°C, continuously stirred and dispersed, and a composite reducing agent is added thereto, wherein the composite reducing agent is obtained by mixing reducing agent I and reducing agent II, reducing agent I is a strong reducing agent used for nickel plating, and reducing agent II is a phosphorus-containing reducing agent; during the reaction, the pH is controlled at 7-10, and the reaction temperature is controlled at 35-60°C.

[0011] Preferably, reducing agent I is one or more of borohydride, dimethylamine borate, borane or hydrazine; reducing agent II is one or more of hypophosphite and hypophosphite.

[0012] Preferably, the nickel salt is a mixture of one or more of nickel acetate tetrahydrate, nickel benzenesulfonate hexahydrate, nickel chloride hexahydrate, nickel hypophosphite hexahydrate, and nickel sulfate hexahydrate; the complexing agent is a mixture of one or more of sodium citrate, ethylenediaminetetraacetic acid tetrasodium salt, ethylenediaminetetraacetic acid disodium salt, etc.

[0013] Preferably, the preparation process of activated microspheres is as follows: weigh 1-5g of microspheres into a beaker, add 10-50mL of concentrated sulfuric acid, ultrasonically stir, and centrifuge to obtain roughened microspheres; add the roughened microspheres to 40-100mL of stannous chloride sensitizing solution with a concentration of 10-40g / L, ultrasonically stir, and centrifuge to obtain sensitized microspheres; add the sensitized microspheres to 40-100mL of palladium chloride activation solution with a concentration of 1-4g / L, ultrasonically stir, and centrifuge to obtain activated microspheres.

[0014] Preferably, the amount of pure water used to disperse the activated microspheres is 20-100 mL; the nickel salt concentration is 20-60 g / L, and the amount used is 40-100 mL; the complexing agent concentration is 20-60 g / L, and the amount used is 40-100 mL.

[0015] Preferably, the concentration of reducing agent I is 20-60g / L, and the ratio of microspheres to reducing agent I is 1g:20-60mL; the concentration of reducing agent II is 20-60g / L, and the ratio of microspheres to reducing agent II is 1g:40-300mL; the ratio of reducing agent I to reducing agent II is 1:2-5.

[0016] Preferably, the ultrasonic stirring speed is controlled at 300-500 r / min, and the stirring time is 1-2 h.

[0017] Preferably, during the reaction, a pH adjuster is used to control the pH value, wherein the pH adjuster is one or a mixture of sodium hydroxide solution, potassium hydroxide solution, ammonia water, etc.

[0018] The invention also protects a nickel-plated microsphere, which is prepared by the microsphere surface chemical nickel plating method based on the double reduction system.

[0019] The present invention proposes a dual reducing agent system, in which strong reducing agents such as borohydride, dimethylamine borate, borane or hydrazine and weaker reducing agents such as hypophosphite and hypophosphite are compounded in a certain proportion for nickel plating. The use of the strong reducing agent improves the density of the coating while avoiding the problem of a long induction time for chemical nickel plating. By adjusting the ratio of the strong and weak reducing agents in the dual reducing agent, the coating uniformity and dispersibility of the nickel-plated microspheres can be effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a SEM photo of nickel-plated microspheres obtained in Example 1;

[0021] Figure 2 This is a SEM photo of nickel-plated microspheres obtained in Example 2;

[0022] Figure 3 This is a SEM photo of nickel-plated microspheres obtained in Example 3;

[0023] Figure 4This is a SEM photo of nickel-plated microspheres obtained in Example 4;

[0024] Figure 5 This is a SEM photo of nickel-plated microspheres obtained in Example 5;

[0025] Figure 6 This is a SEM photo of nickel-plated microspheres obtained in Comparative Example 1;

[0026] Figure 7 This is the SEM photo of nickel-plated microspheres prepared in Comparative Example 2. DETAILED DESCRIPTION

[0027] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively below in conjunction with the accompanying drawings and specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The technical scheme of the present invention is described more clearly and completely below in conjunction with specific embodiments and comparative examples.

[0029] Example 1

[0030] 1. Weigh 1g of polymer microspheres in a beaker, add 20mL of concentrated sulfuric acid, ultrasonically stir at 300r / min for 1h, and centrifuge to obtain roughened microspheres. Add the roughened microspheres to 40mL of stannous chloride sensitizing solution (SnCl220g / L, HCl20ml / L), ultrasonically stir at 300r / min for 1h, and centrifuge to obtain sensitized microspheres. Add the sensitized microspheres to 40mL of palladium chloride activation solution (PdCl21g / L, HCl 20ml / L), ultrasonically stir at 300r / min for 1h, and centrifuge to obtain activated microspheres.

[0031] 2. Disperse the activated microspheres in 20 mL of water, add 40 mL of 40 g / L nickel acetate tetrahydrate solution and 40 mL of 40 g / L sodium citrate solution, and stir at 400 r / min for 10 min to form a pre-reaction solution.

[0032] 3. Mix 20 mL of 30 g / L sodium borohydride solution (reducing agent I) and 70 mL of 30 g / L sodium hypophosphite (reducing agent II) to obtain a composite reducing agent solution.

[0033] 4. Heat the pre-reaction liquid to 40°C, stir and disperse at 400r / min, add the above-mentioned composite reducing agent solution to the pre-reaction liquid, maintain the reaction temperature at 40°C, and after hydrogen bubbling stops, wash with water to obtain nickel-plated microspheres. During the reaction, the pH is controlled at 8.5. The SEM photo of the obtained nickel-plated microspheres is shown in Figure 1 .

[0034] Example 2

[0035] Different from Example 1, in this example, 20 mL of 30 g / L sodium borohydride solution (reducing agent I) and 40 mL of 30 g / L sodium hypophosphite (reducing agent II) were mixed to obtain a composite reducing agent solution. The SEM photo of the obtained nickel-plated microspheres is shown in Figure 2 .

[0036] Example 3

[0037] Different from Example 1, in this example, 20 mL of 30 g / L sodium borohydride solution (reducing agent I) and 100 mL of 30 g / L sodium hypophosphite (reducing agent II) were mixed to obtain a composite reducing agent solution. The SEM photo of the obtained nickel-plated microspheres is shown in Figure 3 .

[0038] Example 4

[0039] Different from Example 1, in this example, 30 mL of 30 g / L sodium borohydride solution (reducing agent I) and 105 mL of 30 g / L sodium hypophosphite (reducing agent II) were mixed to obtain a composite reducing agent solution. The SEM photo of the obtained nickel-plated microspheres is shown in Figure 4 .

[0040] Example 5

[0041] Different from Example 1, in this example, 20 mL of 20 g / L sodium borohydride solution (reducing agent I) and 70 mL of 20 g / L sodium hypophosphite (reducing agent II) were mixed to obtain a composite reducing agent solution. The SEM photo of the obtained nickel-plated microspheres is shown in Figure 5 .

[0042] Comparative Example 1

[0043] Different from Example 1, only 90 mL of 30 g / L sodium borohydride solution (reducing agent I) was used in this example. The SEM photos of the obtained nickel-plated microspheres are shown in Figure 6 .

[0044] Comparative Example 2

[0045] Different from Example 1, only 90 mL of 30 g / L sodium hypophosphite (reducing agent II) was used in this example. The SEM photo of the obtained nickel-plated microspheres is shown in Figure 7 .

[0046] The performance of the nickel-plated microspheres prepared in Examples 1-5 and Comparative Examples 1-2 was tested, and the results are shown in Table 1.

[0047] Nickel layer thickness determination method: Use a laser particle size analyzer to measure the nickel ball D50 value and subtract the microsphere diameter.

[0048] Table 1

[0049]

[0050] From the data in Table 1, it can be seen that the present invention proposes a dual reducing agent system, in which strong reducing agents such as borohydride, dimethylamine borate, borane or hydrazine and weaker reducing agents such as hypophosphite and hypophosphite are compounded in a certain proportion for nickel plating. The use of a strong reducing agent improves the density of the coating while avoiding the problem of a long induction time for chemical nickel plating. By adjusting the ratio of the strong and weak reducing agents in the dual reducing agent, the coating uniformity and dispersibility of the nickel-plated microspheres can be effectively improved.

[0051] Combination Figure 1-5 It can be seen that the present invention can prepare microspheres with uniform and dense nickel layer, good dispersion, strong bonding force and good conductivity by adjusting the ratio and concentration of strong and weak reducing agents in the dual reducing agent system. Figure 6 It can be seen that the nickel-plated microspheres prepared by using reducing agent I alone for nickel plating have poor dispersibility; Figure 7 It can be seen that the nickel-plated microspheres obtained by using reducing agent II alone for nickel plating have poor uniformity and poor conductivity of the nickel layer.

[0052] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0053] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for chemical nickel plating on the surface of microspheres based on a double reduction system, wherein the microspheres are subjected to roughening, sensitization, and activation treatments in sequence to obtain activated microspheres, characterized in that: The activated microspheres are dispersed in pure water, and nickel salt and a complexing agent are added to form a pre-reaction liquid; the pre-reaction liquid is then heated to 35-60°C, continuously stirred and dispersed, and a composite reducing agent is added thereto, wherein the composite reducing agent is obtained by mixing reducing agent I and reducing agent II, reducing agent I is a strong reducing agent used for nickel plating, and reducing agent II is a phosphorus-containing reducing agent; during the reaction, the pH is controlled at 7-10, and the reaction temperature is controlled at 35-60°C.

2. The method for chemical nickel plating on microsphere surface based on double reduction system according to claim 1, characterized in that: The reducing agent I is one or more of borohydride, dimethylamine borate, borane or hydrazine; the reducing agent II is one or more of hypophosphite and hypophosphite.

3. The method for chemical nickel plating on microsphere surface based on double reduction system according to claim 1 or 2, characterized in that: The microspheres are one or more of polymer microspheres and silicon microspheres.

4. The method for chemical nickel plating on microsphere surface based on double reduction system according to claim 1, characterized in that: The nickel salt is one or a mixture of nickel acetate tetrahydrate, nickel benzenesulfonate hexahydrate, nickel chloride hexahydrate, nickel hypophosphite hexahydrate and nickel sulfate hexahydrate.

5. The method for chemical nickel plating on microsphere surface based on double reduction system according to claim 1, characterized in that: The complexing agent is one or a mixture of sodium citrate, tetrasodium ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetic acid, etc.

6. The method for chemical nickel plating on microsphere surface based on double reduction system according to claim 1, characterized in that: The preparation process of activated microspheres is as follows: weigh 1-5g of microspheres into a beaker, add 10-50mL of concentrated sulfuric acid, ultrasonically stir, and centrifuge to obtain coarsened microspheres; add the coarsened microspheres into 40-100mL of stannous chloride sensitizing solution with a concentration of 10-40g / L, ultrasonically stir, and centrifuge to obtain sensitized microspheres; add the sensitized microspheres into 40-100mL of palladium chloride activation solution with a concentration of 1-4g / L, ultrasonically stir, and centrifuge to obtain activated microspheres.

7. The method for chemical nickel plating on microsphere surface based on double reduction system according to claim 6, characterized in that: The amount of pure water used to disperse and activate the microspheres is 20-100 mL; the nickel salt concentration is 20-60 g / L, and the amount is 40-100 mL; the complexing agent concentration is 20-60 g / L, and the amount is 40-100 mL.

8. The method for chemical nickel plating on microsphere surface based on double reduction system according to claim 6, characterized in that: The concentration of reducing agent I is 20-60g / L, and the ratio of microspheres to reducing agent I is 1g:20-60mL; the concentration of reducing agent II is 20-60g / L, and the ratio of microspheres to reducing agent II is 1g:40-300mL; the ratio of reducing agent I to reducing agent II is 1:2-5.

9. The method for chemical nickel plating on microsphere surface based on double reduction system according to claim 1, characterized in that: During the reaction, the pH value is controlled by a pH adjuster, wherein the pH adjuster is one or a mixture of sodium hydroxide solution, potassium hydroxide solution, ammonia water, etc.

10. A nickel-plated microsphere, characterized in that: The microspheres are prepared by the chemical nickel plating method on the surface of the microspheres based on a double reduction system as described in any one of items 1-9.

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