Preparation method of core-shell type nickel-coated copper powder and application of core-shell type nickel-coated copper powder in electronic paste

Abstract

The application discloses a preparation method of core-shell type nickel-coated copper powder and application of the core-shell type nickel-coated copper powder in electronic paste, relates to the technical fields of electronic functional materials, metal materials and powder materials, and comprises the following steps: S1, copper powder pretreatment: copper powder is placed in an acid solution and an activation solution respectively, and stirring and soaking are carried out for 10 min; the copper powder is filtered, separated and cleaned; S2, primary chemical nickel plating: the pretreated copper powder is put into chemical plating liquid A or chemical plating liquid B, chemical plating is carried out under ultrasonic stirring process at a certain temperature, a reducing agent solution is added dropwise, and primary chemical nickel-coated copper powder is obtained through filtering, separating and cleaning; and S3, secondary chemical nickel plating: the primary chemical nickel-coated copper powder is put into chemical plating liquid A, chemical plating is carried out under ultrasonic stirring process at a certain temperature, and secondary chemical nickel-coated copper powder is obtained through filtering, separating and cleaning. The application guarantees the conductivity of the copper powder and improves the oxidation resistance of the copper powder, and effectively solves the agglomeration problem in the chemical plating process.

Description

Technical Field

[0001] This invention relates to the fields of electronic functional materials, metallic materials, and powder materials, and particularly to a method for preparing core-shell nickel-coated copper powder and its application in electronic pastes. Background Technology

[0002] With the rapid development of the electronics industry, high integration, miniaturization, and green technology have become the mainstream development directions for electronic products. To further enhance intelligence, the requirements for flexibility, lightweight design, and multifunctionality in next-generation electronic products are increasing. The development of new integrated circuit materials has become a crucial aspect, among which electronic paste, as one of the fundamental materials for manufacturing integrated circuits and consumer electronics, has become a research hotspot. Electronic paste can be used to manufacture packaged integrated circuits, solar cells, thick-film resistors, capacitors, and other electronic components, and has been widely applied in consumer electronics, aerospace, and many other fields.

[0003] Conductive fillers in electronic pastes mainly include metals such as gold, silver, and copper, with silver-based electronic pastes dominating the market due to their excellent conductivity and oxidation resistance. In recent years, with the continuous rise in precious metal prices and the potential for electromigration in silver-based conductive pastes leading to short circuits in electronic devices, the development of base metal-based electronic pastes has become a hot topic. Traditional copper powder is inexpensive and has good conductivity, but it is prone to oxidation, leading to a decrease in the conductivity and stability of copper-based electronic pastes, severely limiting their application. Coating the copper surface with an antioxidant metal or organic material to prevent copper oxidation is considered an effective method.

[0004] The journal *npj Flexible Electronics* (2022, Vol. 6, pp. 1-9) reported a method for modifying copper powder with formate ions and dodecyl mercaptan to prepare conductive pastes. However, due to the organic coating layer, the stability under conditions such as high temperature, high humidity, strong acid, and strong alkali is poor, failing to meet the requirements for long-term use. Therefore, developing a simple and efficient method for preparing core-shell nickel-coated copper powder with a nickel shell can significantly improve the oxidation resistance of micro / nano copper powder while maintaining excellent conductivity. Applying this method to electronic pastes is expected to achieve a synergistic improvement in conductivity and oxidation resistance, which is of great significance for enhancing the performance and reliability of electronic components. Summary of the Invention

[0005] One object of the present invention is to provide a method for preparing core-shell nickel-coated copper powder.

[0006] Another objective of this invention is to provide an application of core-shell nickel-coated copper powder as a conductive filler in the preparation of conductive adhesives.

[0007] The technical problem to be solved by this invention is to overcome the disadvantage of copper powder being easily oxidized, and to achieve a synergistic improvement in conductivity and oxidation resistance.

[0008] To solve the above-mentioned technical problems, the present invention provides a core-shell type nickel-coated copper powder, wherein the core of the nickel-coated copper powder is copper powder and its outer shell is a nickel-plated layer.

[0009] This invention also provides a method for preparing core-shell nickel-coated copper powder, comprising the following steps:

[0010] S1. Copper powder pretreatment: Place copper powder in acidic solution and activation solution respectively, stir and soak for 10 minutes, filter to separate and wash;

[0011] S2. One-time electroless nickel plating: The pretreated copper powder is put into electroless plating solution A or electroless plating solution B, and electroless plating is carried out under ultrasonic stirring at a certain temperature. A reducing agent solution is added, and the powder is filtered, separated and cleaned to obtain one-time electroless nickel-coated copper powder.

[0012] S3. Secondary electroless nickel plating: The primary electroless nickel-coated copper powder is added to electroless plating solution A and electroless plating is carried out under ultrasonic stirring at a certain temperature. After filtration, separation and cleaning, secondary electroless nickel-coated copper powder is obtained.

[0013] Preferably, the acidic solution is a mixture of one or more of the aqueous solutions of sulfuric acid, nitric acid, hydrochloric acid, formic acid, acetic acid, and propionic acid, with a pH value of 0.1 to 4.

[0014] The activation solution is an acidic aqueous solution of palladium chloride, with a concentration of palladium chloride of 0.004–2 g / L and a pH value of 0.1–4.

[0015] The electroless plating solution A is a mixture obtained by dissolving nickel salt, reducing agent, dispersant, buffer system, and complexing agent in water;

[0016] The chemical plating solution B refers to the filtrate remaining after chemical plating solution A has undergone one electroless nickel plating process, and after filtration to remove the copper powder from the electroless nickel plating process.

[0017] Preferably, the nickel salt is one or more of nickel nitrate, nickel sulfate, nickel fluoride, nickel chloride, nickel bromide, nickel iodide, and nickel carbonate, and the nickel ion concentration is 0.02–0.2 mol / L;

[0018] The reducing agent is one of hydrazine hydrate, sodium borohydride, potassium borohydride, sodium hypophosphite, and potassium hypophosphite. The concentration of the reducing agent in the plating solution is 0.1 to 1 mol / L. The reducing agent solution is an aqueous solution of the reducing agent with a concentration of 1 to 10 mol / L. The amount of reducing agent used in the plating solution is 0.1 to 1 times the amount of the reducing agent solution.

[0019] The dispersant is selected from one or more of polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, polyvinyl butyral, polyethylene glycol, polyurethane, polyoxyethylene 20 oil ether, and sodium dodecyl sulfonate; and its concentration is 0.1–10 g / L.

[0020] The buffer system is selected from one of the following: citric acid and disodium hydrogen phosphate, acetic acid and sodium acetate, borax and potassium dihydrogen phosphate, and potassium hydrogen phthalate and sodium hydroxide. The pH of the buffer system is controlled between 4 and 8.

[0021] The complexing agent is one or more of lactic acid, glycolic acid, citrate, tetraborate, sodium succinate, and glycine, with a concentration of 0.05–0.5 mol / L.

[0022] Preferably, the ultrasonic stirring process in S2 and S3 refers to simultaneous ultrasonication and stirring or intermittent alternation of ultrasonication and stirring, wherein when intermittent alternation is performed, the duration of a single ultrasonic session is 0-10 minutes.

[0023] The ratio of single ultrasonic duration to single stirring duration is 3:1, 2:1, 1:1, 1:2, 1:3, and the total ultrasonic stirring process time is 1 to 6 hours.

[0024] Preferably, the electroless plating temperature in S2 and S3 is 30–90°C.

[0025] Preferably, the copper powder used in S1 has an average particle size of 1 to 30 micrometers and a morphology of one or both of the following: flake-shaped and spherical.

[0026] This invention also provides a core-shell nickel-coated copper powder as a conductive filler for preparing electronic pastes, which are used in the fields of electronic component packaging, flexible circuit board printing, flexible hybrid electronic device packaging, semiconductor packaging, flexible photovoltaics, flexible displays, and flexible sensors. The nickel-coated copper powder is mixed with organic resin in a certain proportion and homogenized to form a paste. After coating and curing, a core-shell nickel-coated copper powder conductive adhesive with excellent conductivity and oxidation resistance is obtained. The nickel-coated copper conductive powder and organic resin are mixed evenly at a mass fraction of 70-85% and 30-15%, respectively, to obtain the conductive adhesive.

[0027] Compared with related technologies, the present invention has the following beneficial effects:

[0028] 1. In this invention, the conductivity of copper powder is guaranteed while the oxidation resistance of copper powder is improved; the preparation of nickel-coated copper powder by secondary chemical plating saves plating solution while ensuring a denser nickel coating and improving the oxidation resistance of nickel-coated copper powder; the ultrasonic stirring process effectively solves the agglomeration problem in the chemical plating process, and prepares nickel-coated copper powder with excellent morphology and no agglomeration. The prepared nickel-coated copper powder is used as a filler to prepare conductive adhesive, and the relevant parameters are controlled in multiple dimensions to obtain nickel-coated copper powder conductive adhesive with high conductivity and strong oxidation resistance.

[0029] 2. In this invention, the chemical plating solution is recycled, saving the chemical plating solution and making it environmentally friendly. Furthermore, the conductive adhesive performance is optimized by precisely adjusting the ratio of conductive filler to resin and optimizing the preparation process parameters. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the process for preparing nickel-coated copper powder according to the present invention.

[0031] Figure 2 The images show SEM images of copper powder and nickel-coated copper powder prepared in Example 1 of this invention.

[0032] Figure 3 The images show SEM images of copper powder and nickel-coated copper powder prepared in Example 2 of this invention.

[0033] Figure 4 The TGA curve of the nickel-coated copper powder prepared in Example 1 of this invention is shown.

[0034] Figure 5 This is the EDS elemental analysis diagram of the nickel-coated copper powder prepared in Example 1 of the present invention.

[0035] Figure 6 This is an EDS elemental distribution diagram of the nickel-coated copper powder prepared in Example 1 of the present invention. Detailed Implementation

[0036] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0037] Example 1

[0038] S1. Copper powder pretreatment: Place 1-5 micron flake copper powder in a dilute sulfuric acid solution with a pH of 0.1 and an activation solution (palladium chloride concentration of 1 g / L, pH of 0.1) and stir and soak for 10 min respectively, then filter, separate and wash.

[0039] S2. Single-stage electroless nickel plating: Prepare an aqueous solution of nickel sulfate (0.15 mol / L), sodium hypophosphite (0.2 mol / L), polyvinylpyrrolidone (1 g / L), polyoxyethylene 20 oil ether (2 g / L), sodium citrate (0.1 mol / L), and an acetic acid and sodium acetate buffer system (pH = 4.5) as electroless plating solution A. Prepare a 2 mol / L sodium hypophosphite aqueous solution as a reducing agent solution; the amount of reducing agent in the plating solution is 0.5 times the amount of reducing agent solution.

[0040] The pretreated copper powder was added to chemical plating solution A, and a reducing agent solution was added dropwise under ultrasonic stirring. Chemical plating was carried out at 70°C. The powder was filtered, separated, and washed to obtain nickel-coated copper powder after one-time chemical plating. The duration of each ultrasonic session was 1 minute, and the ratio of the duration of each ultrasonic session to the duration of each stirring session was 1:1. The total duration of the ultrasonic stirring process was 3 hours.

[0041] S3. Secondary electroless nickel plating: The primary electroless nickel-coated copper powder is added to electroless plating solution A and electroless plating is carried out under ultrasonic stirring. After filtration, separation and cleaning, secondary electroless nickel-coated copper powder and electroless plating solution B are obtained.

[0042] Its appearance is like Figure 2 As shown, Figure 2 SEM images of the copper powder from Example 1 and the prepared nickel-coated copper powder are shown. EDS elemental analysis confirms their structure and composition.

[0043] Its thermogravimetric curve is as follows Figure 4 As shown, Figure 4 This is a schematic diagram of the thermogravimetric curve of the nickel-coated copper powder prepared in Example 1. The prepared nickel-coated copper powder is not oxidized at temperatures below 400°C and has excellent antioxidant capacity.

[0044] Example 2

[0045] S1. Copper powder pretreatment: Place 5-25 micron flake copper powder in a dilute sulfuric acid solution with a pH of 0.1 and an activation solution (palladium chloride concentration of 0.5).

[0046] (g / L, pH value 0.1) Stir and soak for 10 min, filter and separate, and wash.

[0047] S2. Single-stage electroless nickel plating: Prepare an aqueous solution of nickel sulfate (0.15 mol / L), sodium hypophosphite (0.1 mol / L), polyvinylpyrrolidone (1 g / L), polyoxyethylene 20 oil ether (2 g / L), sodium citrate (0.1 mol / L), and a system of citric acid and disodium hydrogen phosphate (pH = 6.5) as electroless plating solution A. Prepare a 1.5 mol / L sodium hypophosphite aqueous solution as a reducing agent solution; the amount of reducing agent in the plating solution is 0.5 times the amount of reducing agent solution.

[0048] Pretreated copper powder was added to electroless plating solution B, and a reducing agent solution was added dropwise under ultrasonic stirring. Electroless plating was carried out at 70°C. After filtration, separation, and washing, nickel-coated copper powder was obtained through a single electroless plating process. The duration of each ultrasonic cycle was 0.5 seconds during the intermittent alternating process.

[0049] The ratio of single ultrasonic duration to single stirring duration is 1:2, and the total ultrasonic stirring process time is 6 hours.

[0050] S3. Secondary electroless nickel plating: The primary electroless nickel-coated copper powder is added to electroless plating solution A and electroless plating is carried out under ultrasonic stirring. After filtration, separation and cleaning, secondary electroless nickel-coated copper powder and electroless plating solution B are obtained.

[0051] Its appearance is like Figure 3 As shown, Figure 3 The images show SEM images of the copper powder from Example 2 and the prepared nickel-coated copper powder. EDS elemental analysis confirms their structure and composition.

[0052] Example 3

[0053] S1. Copper powder pretreatment: Mix 5-15 micrometer flake copper powder and 1-3 micrometer spherical copper powder in a dilute sulfuric acid solution with a pH of 0.1 and an activation solution (palladium chloride concentration of 1 g / L, pH of 0.1), stir and soak for 10 min respectively, filter to separate and wash.

[0054] S2. Single-stage electroless nickel plating: Prepare an aqueous solution of nickel sulfate (0.15 mol / L), sodium hypophosphite (0.2 mol / L), polyvinylpyrrolidone (1 g / L), sodium dodecyl sulfonate (2 g / L), sodium citrate (0.1 mol / L), and an acetic acid and sodium acetate buffer system (pH = 4.5) as electroless plating solution A. Prepare a 2 mol / L sodium hypophosphite aqueous solution as a reducing agent solution; the amount of reducing agent in the plating solution is 1 times the amount of the reducing agent solution.

[0055] The pretreated copper powder was added to chemical plating solution B, and a reducing agent solution was added dropwise under ultrasonic stirring. Chemical plating was carried out at 70°C. The powder was filtered, separated, and washed to obtain nickel-coated copper powder after one-time chemical plating. The duration of each ultrasonic session was 1 minute, and the ratio of the duration of each ultrasonic session to the duration of each stirring session was 1:1. The total duration of the ultrasonic stirring process was 3 hours.

[0056] S3. Secondary electroless nickel plating: The primary electroless nickel-coated copper powder is added to electroless plating solution A and electroless plating is carried out under ultrasonic stirring. After filtration, separation and cleaning, secondary electroless nickel-coated copper powder and electroless plating solution B are obtained.

[0057] Comparative Example 1

[0058] An application of copper powder as a conductive filler in the preparation of conductive adhesives includes the following steps:

[0059] The copper powder described in Example 1 and the organic resin phase were mixed in a homogenization process at mass fractions of 70-85% and 30-15% respectively to form an electronic paste, which was then coated and cured.

[0060] Its initial resistivity and its resistivity after 72 hours at 85°C and 85%RH were measured.

[0061] The properties of copper powder conductive adhesive are as follows:

[0062]

[0063]

[0064] Application Example 1

[0065] The application of a core-shell nickel-coated copper powder as a conductive filler in the preparation of conductive adhesives includes the following steps:

[0066] The nickel-coated copper powder prepared in Example 1 was mixed with an organic resin phase at mass fractions of 70-85% and 30-15% respectively through a homogenization process to form an electronic paste, which was then coated and cured.

[0067] Its initial resistivity and its resistivity after 72 hours at 85°C and 85%RH were measured.

[0068] The properties of the antioxidant nickel-coated copper powder conductive adhesive are as follows:

[0069]

[0070] Application Example 2

[0071] The nickel-coated copper powder prepared in Example 2 was mixed with an organic resin phase at mass fractions of 70-85% and 30-15% respectively through a homogenization process to form an electronic paste, which was then coated and cured.

[0072] Its initial resistivity and its resistivity after 72 hours at 85°C and 85%RH were measured.

[0073] The properties of the antioxidant nickel-coated copper powder conductive adhesive are as follows:

[0074]

[0075] Application Example 3

[0076] The nickel-coated copper powder prepared in Example 3 was mixed with an organic resin phase at mass fractions of 70-85% and 30-15% respectively through a homogenization process to form an electronic paste, which was then coated and cured.

[0077] Its initial resistivity and resistivity after 72 hours at 85°C and 85%RH were measured.

[0078] The properties of the antioxidant nickel-coated copper powder conductive adhesive are as follows:

[0079]

[0080] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0081] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing core-shell nickel-coated copper powder, characterized in that, The core of the nickel-coated copper powder is copper powder, and its outer shell is a nickel-plated layer, comprising the following steps: S1. Copper powder pretreatment: Place copper powder in acidic solution and activation solution respectively, stir and soak for 10 min, filter to separate and wash; S2. One-time electroless nickel plating: The pretreated copper powder is put into electroless plating solution B, and electroless plating is carried out under ultrasonic stirring at a certain temperature. A reducing agent solution is added, and the powder is filtered, separated and cleaned to obtain one-time electroless nickel-coated copper powder. S3. Secondary electroless nickel plating: The primary electroless nickel-coated copper powder is added to electroless plating solution A, and electroless plating is carried out under ultrasonic stirring at a certain temperature. After filtration, separation and cleaning, secondary electroless nickel-coated copper powder is obtained. The acidic solution is a mixture of one or more of the following: sulfuric acid, nitric acid, hydrochloric acid, formic acid, acetic acid, and propionic acid, with a pH value of 0.1 to 4. The activation solution is an acidic aqueous solution of palladium chloride, with a concentration of palladium chloride of 0.004~2 g / L and a pH value of 0.1~4; The electroless plating solution A is a mixture obtained by dissolving nickel salt, reducing agent, dispersant, buffer system, and complexing agent in water; The chemical plating solution B refers to the filtrate remaining after chemical plating solution A has undergone one chemical nickel plating process, and after filtering to remove the copper powder coating from the first chemical nickel plating process. The ultrasonic stirring process in S2 and S3 refers to the alternating operation of ultrasonic and stirring intermittently. When the process is intermittently alternating, the duration of a single ultrasonic session is 0.5 to 1 minute, and the ratio of the duration of a single ultrasonic session to the duration of a single stirring session is 3:1, 2:1, 1:1, 1:2 or 1:

3. The total duration of the ultrasonic stirring process is 1 to 6 hours. The electroless plating temperature in S2 and S3 is 30~90℃.

2. The method for preparing a core-shell nickel-coated copper powder according to claim 1, characterized in that, The nickel salt is one or more of nickel nitrate, nickel sulfate, nickel fluoride, nickel chloride, nickel bromide, nickel iodide, and nickel carbonate, and the nickel ion concentration is 0.02~0.2 mol / L; The reducing agent is one of hydrazine hydrate, sodium borohydride, potassium borohydride, sodium hypophosphite, and potassium hypophosphite. The concentration of the reducing agent in the plating solution is 0.1~1 mol / L, and the reducing agent solution is an aqueous solution of the reducing agent with a concentration of 1~10 mol / L. The amount of reducing agent used in the plating solution is 0.1~1 times the amount of the reducing agent solution. The dispersant is selected from one or more of polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, polyvinyl butyral, polyethylene glycol, polyurethane, polyoxyethylene 20 oil ether, and sodium dodecyl sulfonate; and its concentration is 0.1~10 g / L. The buffer system is selected from one of the following: citric acid and disodium hydrogen phosphate, acetic acid and sodium acetate, borax and potassium dihydrogen phosphate, and potassium hydrogen phthalate and sodium hydroxide. The pH of the buffer system is controlled between 4 and 8. The complexing agent is one or more of lactic acid, glycolic acid, citrate, tetraborate, sodium succinate, and glycine, with a concentration of 0.05~0.5 mol / L.

3. The method for preparing a core-shell nickel-coated copper powder according to claim 1, characterized in that, The copper powder used in S1 has an average particle size of 1 to 30 micrometers and a morphology of one or both of the following: flake-shaped and spherical.

4. Using the core-shell nickel-coated copper powder obtained by the preparation method according to any one of claims 1-3 as a conductive filler to prepare electronic paste, and its application in the fields of flexible circuit board printing, semiconductor packaging, flexible photovoltaics, flexible displays or flexible sensors.

Images