Production method of novel tin-coated copper powder for electronic paste

Abstract

The invention relates to the technical field of metal powder composite materials, in particular to a production method of novel tin-coated copper powder for electronic paste. Comprising the following steps that copper powder is subjected to acid pickling and drying pretreatment; preparing a tin salt solution containing soluble stannous salt, a complexing agent and a dispersing agent, and a reducing agent solution; under the protection of inert atmosphere, the pretreated copper powder is dispersed in water to form suspension liquid, and the suspension liquid is heated to 40-70 DEG C; simultaneously dropwise adding the tin salt solution and the reducing agent solution into the suspension liquid by adopting a double-liquid injection method, carrying out chemical plating reaction, and controlling the pH value of a reaction system to be 3-6; after the reaction is completed, separating, washing and vacuum-drying a product to obtain tin-coated copper composite powder; in this way, the purposes of being good in coating layer effect, simple in technological process, environmentally friendly and suitable for industrial production are achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal powder composite materials, and particularly relates to a production method of a novel tin-coated copper powder for electronic paste. BACKGROUND

[0002] Electronic paste is a key material for manufacturing thick film integrated circuits, solar cell electrodes, chip components, conductive glue and other electronic components, and its performance directly affects the conductivity, reliability and cost of electronic components. Copper powder becomes an ideal material for replacing silver powder due to its excellent conductivity and much lower cost than silver. However, copper powder is chemically active and is easily oxidized to form a non-conductive copper oxide layer in the air, which leads to a sharp increase in paste resistivity and performance degradation.

[0003] In order to prevent copper powder from being oxidized, the prior art usually adopts a layer of inert or more stable metal, such as silver, tin and the like, on the surface of copper powder. Among them, tin-coated copper powder is concerned due to its low cost and good solderability. At present, the methods for preparing tin-coated copper powder mainly include chemical displacement method, electrodeposition method and mechanical ball milling method, etc. However, these methods have the following defects: the chemical displacement method: the produced coating layer is loose and porous, has poor compactness, and produces a large amount of wastewater, which causes serious environmental pollution; the electrodeposition method: the process flow is complex, the energy consumption is high, and it is difficult to form a uniform coating on the surface of powder with a complex shape; the mechanical ball milling method: impurities are easily introduced, the morphology of the powder is difficult to control, and cold welding and oxidation are prone to occur.

[0004] In view of the above, it is necessary to provide a production method of a novel tin-coated copper powder for electronic paste, which has good coating effect, simple process flow, is environmentally friendly and suitable for industrial production. SUMMARY

[0005] The present application aims to provide a production method of a novel tin-coated copper powder for electronic paste, which has good coating effect, simple process flow, is environmentally friendly and suitable for industrial production.

[0006] To achieve the above-mentioned purpose, the present application adopts a production method of a novel tin-coated copper powder for electronic paste, which comprises the following steps:

[0007] The copper powder is pretreated by pickling and drying;

[0008] A tin salt solution containing soluble stannous salt, complexing agent and dispersant, and a reducing agent solution are prepared;

[0009] The pretreated copper powder is dispersed in water to form a suspension under the protection of inert atmosphere, and heated to 40-70 DEG C;

[0010] The tin salt solution and the reducing agent solution are simultaneously added to the suspension by double injection method, and a chemical plating reaction is carried out, and the pH value of the reaction system is controlled to be 3-6.

[0011] After the reaction is completed, the product is separated, washed and vacuum dried to obtain the tin-coated copper composite powder.

[0012] In the step of pretreating the copper powder by acid washing and drying:

[0013] The average particle size of the copper powder is 0.5-5 μm, the morphology of the copper powder is one of flake and sphere, and the acid used in the acid washing is one of 1-5 wt% citric acid and oxalic acid solution.

[0014] In the step of preparing a tin salt solution containing a soluble stannous salt, a complexing agent and a dispersing agent, and a reducing agent solution:

[0015] The soluble stannous salt is one of stannous chloride and stannous sulfate; the complexing agent is one of sodium citrate and potassium sodium tartrate, and the addition amount is 5-15% of the mass of the tin salt; the dispersing agent is one of polyvinylpyrrolidone and polyethylene glycol, and the addition amount is 0.5-2% of the mass of the copper powder.

[0016] In the step of preparing a tin salt solution containing a soluble stannous salt, a complexing agent and a dispersing agent, and a reducing agent solution:

[0017] The reducing agent is one of sodium hypophosphite and sodium borohydride, and the solution concentration is 0.2-1.0 mol / L.

[0018] In the step of dispersing the pretreated copper powder in water to form a suspension under the protection of an inert atmosphere, and heating to 40-70℃:

[0019] The solid content of the copper powder in the suspension is 5-15 wt%.

[0020] In the step of simultaneously adding the tin salt solution and the reducing agent solution to the suspension by a double injection method, performing a chemical plating reaction, and controlling the pH value of the reaction system to be 3-6:

[0021] The dropwise adding time of the double injection method is 1-3 h, and the molar feed ratio of the tin salt solution to the reducing agent solution is 1:1.2-2.0.

[0022] In the step of separating, washing and vacuum drying the product after the reaction is completed to obtain the tin-coated copper composite powder:

[0023] The temperature of the vacuum drying is 60-80℃, and the time is 4-8 h.

[0024] The application discloses a production method of a novel tin-coated copper powder for electronic paste, and adopts the following steps: acid pickling and drying pretreatment of copper powder; preparation of a tin salt solution containing soluble stannous salt, complexing agent and dispersant, and a reducing agent solution; under the protection of inert atmosphere, the pretreated copper powder is dispersed in water to form a suspension, and heating is performed at 40-70 DEG C; the tin salt solution and the reducing agent solution are simultaneously added dropwise into the suspension by using a double-liquid injection method, a chemical plating reaction is performed, and the pH value of the reaction system is controlled to be 3-6; after the reaction is completed, the product is separated, washed and vacuum dried to obtain the tin-coated copper composite powder; by the above method, the purposes of good coating effect, simple process flow, environmental protection and suitability for industrial production are achieved.

[0025] The basic principle of the application is that, by using a double-liquid injection method of chemical plating technology, a controllable redox reaction of a reducing agent and tin ions is caused on the surface of copper powder in a mild aqueous environment, so that uniform and dense chemical deposition of tin is realized. The complexing agent is used for stabilizing stannous ions and preventing oxidation and hydrolysis of the stannous ions; and the dispersant ensures that the copper powder does not agglomerate in the suspension, and creates conditions for uniform coating. By accurately controlling the pH value, temperature, dropping speed and proportion of reactants, spontaneous nucleation and particle growth of tin can be effectively inhibited, and the tin layer is ensured to preferentially and firmly coat the surface of the copper core.

[0026] Compared with the prior art, the application has the following advantages: (1) high coating quality: the tin layer formed by chemical plating is dense and continuous, is firmly combined with the copper matrix, can effectively isolate oxygen and moisture, and has significantly better oxidation resistance than products prepared by physical mixing or replacement (see comparison data in the examples); (2) simple and environmentally-friendly process: the whole process is performed in an aqueous phase, so that the use of organic solvents is avoided; the pretreatment is performed by using weak acids such as citric acid and oxalic acid, and biodegradable complexing agents (such as sodium citrate) are used, so that the process is environmentally friendly, and the pressure for wastewater treatment is small; (3) easy industrialization: the reaction conditions are mild (40-70 DEG C), the equipment requirement is low, and the double-liquid injection process is easy to realize automatic control, so that the application is suitable for large-scale continuous production; and (4) controllable powder morphology: by adjusting the reaction parameters, uniform coating can be realized on the surface of copper powder with different morphologies (spherical and flaky), and the thickness of the coating layer can be controlled by adjusting the tin salt dosage. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only show some embodiments of the application, and for those skilled in the art, other drawings can also be obtained from these drawings without any creative effort.

[0028] Figure 1is a flow chart of the steps of the production method of the novel tin-coated copper powder for electronic paste of the present invention.

[0029] Figure 2 is a metallographic chart of the powder obtained by the production method of the novel tin-coated copper powder for electronic paste of the present invention.

[0030] Figure 3 is a SEM chart of the powder obtained by the production method of the novel tin-coated copper powder for electronic paste of the present invention.

[0031] Figure 4 is a point scanning result chart of the powder obtained by the production method of the novel tin-coated copper powder for electronic paste of the present invention.

[0032] Figure 5 is a face scanning result chart of the powder obtained by the production method of the novel tin-coated copper powder for electronic paste of the present invention. DETAILED DESCRIPTION

[0033] The exemplary embodiments will be described in detail herein with reference to the attached drawings. The description of the exemplary embodiments is merely representative of all possible embodiments consistent with the present application. The following description is not to be taken in a limiting sense as the scope of the present application is defined by the appended claims.

[0034] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0035] It should be understood that although the terms first, second, third, etc. can be used herein to describe various information, but these information should not be limited to these terms. These terms are only used to distinguish information of the same type from each other. For example, without departing from the scope of the present application, the first information can also be referred to as the second information, and similarly, the second information can also be referred to as the first information. Depending on the context, the word "if" as used herein can be interpreted as "when" or "upon" or "in response to determining".

[0036] Referring to Figures 1-5 The present application provides a production method of a novel tin-coated copper powder for electronic paste, comprising the following steps:

[0037] S100: acid washing and drying pretreatment of copper powder;

[0038] S200: Prepare a tin salt solution containing soluble stannous salt, complexing agent and dispersant, as well as a reducing agent solution;

[0039] S300: Under an inert atmosphere, the pretreated copper powder is dispersed in water to form a suspension and heated to 40~70℃;

[0040] S400: The tin salt solution and reducing agent solution are simultaneously added to the suspension using a dual-injection method to carry out a chemical plating reaction, and the pH value of the reaction system is controlled to be 3~6.

[0041] S500: After the reaction is complete, the product is separated, washed and vacuum dried to obtain tin-coated copper composite powder.

[0042] In this embodiment, the copper powder is first pretreated by acid washing and drying. The average particle size of the copper powder is 0.5~5μm, and the morphology of the copper powder is either flake-shaped or spherical. The acid used for acid washing is either citric acid or oxalic acid solution at 1~5wt%. Then, a tin salt solution is prepared, containing a soluble stannous salt (either stannous chloride or stannous sulfate), a complexing agent (either sodium citrate or potassium sodium tartrate, added at 5%~15% of the tin salt mass), and a dispersant (either polyvinylpyrrolidone or polyethylene glycol, added at 0.5%~2% of the copper powder mass), as well as a reducing agent solution (either sodium hypophosphite or sodium borohydride, with a solution concentration of 0.2~1.0 mol / L). Under an inert atmosphere, the pretreated copper powder is dispersed in water to form a suspension and heated to 40~70℃, wherein the solid content of the copper powder in the suspension is 5~15%. The tin salt solution and reducing agent solution are then added dropwise to the suspension simultaneously using a double-injection method to carry out a chemical plating reaction. The pH value of the reaction system is controlled at 3-6, and the dropwise addition time of the double-injection method is 1-3 hours. The molar ratio of tin salt solution to reducing agent solution is 1:1.2-2.0. After the reaction is completed, the product is separated, washed, and vacuum dried to obtain tin-coated copper composite powder. The vacuum drying temperature is 60-80℃ and the time is 4-8 hours. Through the above method, the purpose of good coating effect, simple process flow, environmental protection and suitability for industrial production is achieved.

[0043] In addition, in the step of adding the tin salt solution and the reducing agent solution into the suspension simultaneously by using the double-injection method to perform the electroless plating reaction, and controlling the pH value of the reaction system to be 3-6: controlling the pH value of the reaction system to be 3-6 is crucial, and a too low pH value (<3) can accelerate the instability of stannous ions, leading to a too fast reduction reaction, a rough and porous tin layer, and even a large number of independent tin particles; a too high pH value (>6) can make the stannous ions easily hydrolyzed to form Sn(OH)2precipitate, affecting the effective deposition on the surface of the copper powder, leading to uneven coating, and on-line adjustment of the pH value by using a dilute NaOH or dilute acid solution is a key to keeping the reaction stable.

[0044] Referring to Figure 2 and Figure 3 The tin-coated copper powder produced by the method is subjected to metallographic and SEM detection, and the results show that the tin element is uniformly distributed on the surface of the powder and the sphericity is complete.

[0045] Referring to Figure 4 and Figure 5 The tin-coated copper powder produced by the method is subjected to energy spectrum point scanning and area scanning detection, the point scanning result shows that the proportion of Sn element is more than 60%, and the area scanning result shows that the Sn element is uniformly distributed on the surface of the copper powder, further verifying the feasibility of the method.

[0046] Example 1:

[0047] Take 10 g of spherical copper powder with an average particle size of 1 μm, ultrasonically clean it in a 3 wt% citric acid solution for 10 min, then wash it with deionized water and anhydrous ethanol for 3 times respectively, and dry it in a 70°C vacuum drying oven for 3 h;

[0048] Weigh 4.5 g of stannous chloride (SnCl2·2H2O), dissolve it in 200 mL of deionized water, add 0.45 g of sodium citrate and 0.1 g of PVP, stir until completely dissolved, and obtain a tin salt solution;

[0049] Weigh 8 g of sodium hypophosphite (NaH2PO2·H2O), dissolve it in 100 mL of deionized water, and obtain a reducing agent solution;

[0050] Disperse the pretreated copper powder in 500 mL of deionized water, and protect it by passing nitrogen gas. Heat it to 50°C in a water bath and keep it at constant temperature. Under mechanical stirring, slowly add the tin salt solution and the reducing agent solution simultaneously through two constant-pressure funnels, control the dropping time to be about 2 h, and maintain the pH value of the system at about 4.5 by using a dilute NaOH solution during the process;

[0051] After the dropping is completed, continue to keep the temperature and stir for 1 h. After the reaction is completed, cool, filter, wash, and dry at 70°C in a vacuum drying oven for 6 h to obtain the final product. The tin coating amount is about 20 wt%.

[0052] Comparative Example 1

[0053] 10 g of copper powder of the same specification and 2 g of tin powder (similar particle size) were mixed by mechanical ball milling for 2 h to obtain a physically mixed Cu-Sn powder.

[0054] The powders obtained in Example 1 and Comparative Example 1 were subjected to an accelerated oxidation test in a constant temperature and humidity chamber at 85°C / 85% relative humidity. After 168 h, the weight gain rate of the tin-coated copper powder of Example 1 was <0.5%, while the weight gain rate of the physically mixed powder of Comparative Example 1 was >3.0%. The results show that the tin-coated copper powder prepared has extremely excellent oxidation resistance.

[0055] Comparative Example 2

[0056] 10 g of copper powder of the same specification as in Example 1 was directly added to an acidic aqueous solution containing 4.5 g of stannous chloride, and stirred at 50°C for 2 h. During the reaction, a large amount of gas bubbles were observed (hydrogen evolution due to displacement reaction), and the solution quickly became turbid. The post-reaction treatment was the same as in Example 1.

[0057] Characterization of the product showed that the tin layer of the powder obtained by displacement was loose, with obvious pores, and the powder was severely agglomerated. The same accelerated oxidation test was performed on the product together with the product of Example 1, and the weight gain rate was about 1.8%, which was much lower than that of the product obtained by the method of the present application (<0.5%). This demonstrates the significant superiority of the double injection method of controllable electroless plating in obtaining a dense coating layer.

[0058] Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. It is intended that the application be limited only by the scope of the claims, including all variations and adaptations thereof that are evident upon consideration of this disclosure or are otherwise known in the art.

[0059] It should be understood that the application is not limited to the precise construction that has been described above and illustrated in the accompanying drawings, and that various modifications and changes can be made by those skilled in the art without departing from the scope of the application.

Claims

1. A method for producing a novel tin-coated copper powder for electronic pastes, characterized in that, Includes the following steps: Copper powder undergoes acid washing and drying pretreatment; Prepare a tin salt solution containing a soluble stannous salt, a complexing agent, and a dispersant, as well as a reducing agent solution; Under an inert atmosphere, the pretreated copper powder is dispersed in water to form a suspension and heated to 40~70℃; The tin salt solution and reducing agent solution are simultaneously added dropwise to the suspension using a dual-injection method to carry out a chemical plating reaction, with the pH value of the reaction system controlled at 3~6; After the reaction is complete, the product is separated, washed and vacuum dried to obtain tin-coated copper composite powder.

2. The production method of the novel tin-coated copper powder for electronic paste as described in claim 1, characterized in that, In the steps of acid washing and drying pretreatment of copper powder: The average particle size of the copper powder is 0.5~5μm, and the copper powder is in the form of either flakes or spheres; the acid used for pickling is either citric acid or oxalic acid solution at a concentration of 1~5wt%.

3. The production method of the novel tin-coated copper powder for electronic paste as described in claim 1, characterized in that, In the steps of preparing a tin salt solution containing a soluble stannous salt, a complexing agent, and a dispersant, as well as a reducing agent solution: The soluble stannous salt is one of stannous chloride and stannous sulfate; the complexing agent is one of sodium citrate and sodium potassium tartrate, wherein the amount added is 5% to 15% of the mass of the stannous salt; the dispersant is one of polyvinylpyrrolidone and polyethylene glycol, wherein the amount added is 0.5% to 2% of the mass of the copper powder.

4. The method for producing novel tin-coated copper powder for electronic pastes as described in claim 3, characterized in that, In the steps of preparing a tin salt solution containing a soluble stannous salt, a complexing agent, and a dispersant, as well as a reducing agent solution: The reducing agent is either sodium hypophosphite or sodium borohydride, with a solution concentration of 0.2–1.0 mol / L.

5. The method for producing novel tin-coated copper powder for electronic pastes as described in claim 1, characterized in that, In the step of dispersing pretreated copper powder in water to form a suspension under an inert atmosphere and heating it to 40~70℃: The solid content of copper powder in the suspension is 5~15 wt%.

6. The method for producing novel tin-coated copper powder for electronic pastes as described in claim 1, characterized in that, In the step of simultaneously adding the tin salt solution and the reducing agent solution to the suspension using a dual-injection method to carry out a chemical plating reaction, and controlling the pH value of the reaction system to be 3-6: The dripping time for the double-injection method is 1-3 hours, and the molar ratio of tin salt solution to reducing agent solution is 1:1.2-2.

0.

7. The method for producing novel tin-coated copper powder for electronic pastes as described in claim 1, characterized in that, In the step of separating, washing, and vacuum drying the product after the reaction is complete to obtain tin-coated copper composite powder: The vacuum drying temperature is 60~80℃, and the time is 4~8h.

Images