Preparation method of tin or tin alloy coated copper powder and low-temperature conductive paste

Abstract

The present invention provides a method for preparing tin or tin alloy-coated copper powder and a low-temperature conductive paste, wherein the method comprises the following steps: S10, pretreating the surface of the copper powder to remove oxides and impurities on the copper powder surface; S20, placing the pretreated copper powder in an electroplating solution containing an organic phosphine compound additive; electroplating the copper powder using tin metal or tin alloy as an anode and copper powder as a cathode, wherein the copper powder is dispersed during the electroplating process; S30, after the electroplating is completed, filtering, washing, and drying to obtain the tin or tin alloy-coated copper powder. The addition of the organic phosphine compound in the present invention greatly improves the compactness of the tin or tin alloy coating formed on the surface of the copper powder, thereby making the prepared tin-coated copper powder or tin alloy-coated copper powder have the advantage of better oxidation resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of metal powders, and in particular to a method for preparing copper powder coated with tin or a tin alloy, and a low-temperature conductive paste prepared by using the copper powder obtained by the method as a raw material component. Background Art

[0002] Due to process limitations in heterojunction crystalline silicon photovoltaic cells, the metallization of heterojunction cells is performed using a low-temperature curing conductive paste. The thin-line capability and conductivity of the low-temperature conductive paste directly impact the power generation efficiency of the heterojunction cell. Compared to the direct conductivity mechanism of high-temperature sintering conductive pastes, which fuse the conductive particles together after sintering, low-temperature curing conductive pastes achieve this through tunneling or direct contact between the conductive particles. Furthermore, the polymer resin remaining in the cured low-temperature curing paste reduces its conductivity. Therefore, the conductivity of a low-temperature curing paste using the same conductive material is generally lower than that of a high-temperature sintering paste. This requires the use of more low-temperature conductive paste to achieve comparable conductivity to a high-temperature sintering paste, increasing the cost of the heterojunction cell. The high cost of silver-based metallization solutions is currently one of the factors hindering the development of heterojunction photovoltaic cells.

[0003] Nano-silver powder can be sintered at low temperatures. Therefore, under appropriate processes, adding nano-silver powder to low-temperature conductive silver paste can improve its conductivity, but the use of nano-silver powder greatly increases the cost. The existing technology uses copper powder as a low-temperature conductive material to replace silver powder, which is also one of the ways to reduce costs. However, copper is easily oxidized in the air. In this case, the art has developed related technical solutions to improve the oxidation resistance of copper powder by silver coating, and currently silver-coated copper low-temperature conductive paste has begun to be used in heterojunction batteries. Although this solution reduces costs, those skilled in the art are still looking for low-temperature curing conductive pastes that can further reduce costs while ensuring conductivity.

[0004] Tin and tin-based alloys have low melting points and can "melt" together at low-temperature curing temperatures. Therefore, those skilled in the art have proposed replacing silver powder or silver-coated copper powder with copper powder coated with tin or tin-based alloys, thereby achieving the dual effects of improving the conductivity of low-temperature curing conductive pastes and reducing costs. Tin has properties such as oxidation resistance, corrosion resistance, and easy soldering, and is widely used in electronic circuits. For example, electroplating tin is usually the last step (tin in-finish) in electronic components. Electroplating tin has also been widely studied. Walsh and Low's review article summarizes the latest progress in electroplating tin (A review of developments in the electrodeposition of tin, FC Walsh and CTJ Low, Surface and Coatings Technology, Volume 288, pages 79-94, 2016). Ilgar's patent discloses a process for tin plating on steel substrates (US 5814202, Electrolyt ic tin plating process with reduced sludge production, 1998).

[0005] In the tin electroplating process, the choice of plating solution, particularly its additives, plays a crucial role in the quality of the plated layer and the performance of the resulting coated copper powder. However, existing plating solutions often struggle to form a dense plating layer on the copper powder surface, making it difficult for the resulting coated copper powder to meet oxidation resistance requirements. This significantly limits the application of tin and tin-based alloy-coated copper powder in low-temperature conductive pastes. Summary of the Invention

[0006] In response to the defects in the prior art, the purpose of the present invention is to provide a method for preparing tin or tin alloy-coated copper powder, and a low-temperature conductive paste prepared using the copper powder obtained by the method as a raw material component. The tin-coated copper powder or tin alloy-coated copper powder prepared by the present invention has good oxidation resistance, and the low-temperature conductive paste prepared with the copper powder has high conductivity while greatly reducing the cost.

[0007] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solution:

[0008] A method for preparing tin or tin alloy coated copper powder comprises the following steps:

[0009] S10, pre-treating the surface of the copper powder to remove oxides and impurities on the surface of the copper powder;

[0010] S20, placing the pretreated copper powder in an electroplating solution containing an organic phosphine compound additive; electroplating the copper powder using tin metal or tin alloy as an anode and the copper powder as a cathode, wherein the copper powder is kept in a dispersed state during the electroplating process;

[0011] S30, after the electroplating is completed, the copper powder coated with tin or tin alloy is obtained by filtering, washing and drying.

[0012] Preferably, the organic phosphine compound is any one or more of diphosphonic acid, triphosphonic acid, methylenephosphonic acid and carboxylic acid phosphonic acid.

[0013] Preferably, the organic phosphine compound is any one or more of aminotrimethylphosphonic acid (ATMP), ethylenediaminetrimethylphosphonic acid (EDTMP), hydroxyethyldiphosphonic acid (HEDP), diethylenetriaminepentamethylphosphonic acid (DTPMP), and phosphonobutanetricarboxylic acid (PBTCA).

[0014] Preferably, in step S10, the pretreatment is to use a dilute sulfuric acid aqueous solution to wash and remove oxides and impurities on the surface of the copper powder.

[0015] Preferably, in step S10, the copper powder is micron copper powder.

[0016] Preferably, the metal that forms the tin alloy coating layer with tin is any one or more of Pb, In, Bi, Zn, and Ag. Preferably, in step S20, the electroplating solution is a sulfuric acid solution of the anode metal.

[0017] Preferably, in step S20, when the copper powder is electroplated, the electroplating working chamber is in a rotating state so that the copper powder is in a dispersed state.

[0018] A method for preparing tin or tin alloy coated copper powder comprises the following steps:

[0019] S10, pre-treating the surface of the copper powder to remove oxides and impurities on the surface of the copper powder;

[0020] S20, placing the pretreated copper powder in a chemical plating solution containing metal ions corresponding to tin or a tin alloy, wherein the chemical plating solution further contains a reducing agent and an organic phosphine compound additive, so that the copper powder is in a dispersed state during the chemical plating process;

[0021] S30: After the chemical plating is completed, the copper powder coated with tin or tin alloy is obtained by filtering, washing and drying.

[0022] A low-temperature conductive paste uses tin or tin alloy coated copper powder prepared by any of the above methods as a raw material component.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention provides a method for preparing tin- or tin-alloy-coated copper powder. An organic phosphine compound additive in an electroplating solution or chemical plating solution influences and controls the nucleation and growth of tin and tin alloy particles by adsorbing the tin and tin alloy particles formed on the copper powder and the copper powder surface, thereby influencing and controlling the properties of the coating. The addition of the organic phosphine compound significantly improves the compactness of the tin or tin alloy coating formed on the copper powder surface, thereby imparting to the prepared tin-coated copper powder or tin alloy-coated copper powder improved oxidation resistance.

[0025] 2. The low-temperature conductive paste provided by the present invention is prepared using the copper powder obtained by the above method as a raw material component, and copper powder coated with tin or tin-based alloy is used to replace the traditional silver powder or silver-coated copper powder, thereby achieving the goal of improving the conductivity of the low-temperature curing conductive paste while greatly reducing the cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0027] Figure 1 The graph shows how the weight of the tin-lead coated copper powder prepared in Example 2 and Comparative Example 2 changes with heat treatment time. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments.

[0029] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in the present application without making any creative efforts shall fall within the scope of protection of the present application.

[0030] Unless otherwise specified, the materials, reagents, etc. used in the following examples can be obtained from commercial channels; the implementation methods used in the following examples are all conventional methods unless otherwise specified.

[0031] According to a first aspect of the present invention, there is provided a method for preparing tin or tin alloy coated copper powder, comprising the following steps:

[0032] S10, pre-treating the surface of the copper powder to remove oxides and impurities on the surface of the copper powder;

[0033] S20, placing the pretreated copper powder in an electroplating solution containing an organic phosphine compound additive; electroplating the copper powder using tin metal or tin alloy as an anode and the copper powder as a cathode, wherein the copper powder is kept in a dispersed state during the electroplating process;

[0034] S30, after the electroplating is completed, the copper powder coated with tin or tin alloy is obtained by filtering, washing and drying.

[0035] In the present invention, the copper powder used as the starting material is not limited. Conductive powder suitable for low-temperature conductive pastes is generally micron-sized, such as 0.1 to 50 microns, preferably 0.5 to 10 microns. For example, the copper powder product (product code 6B, hereinafter referred to as "copper powder 6B") manufactured by Japan Dowa Holdings Co., Ltd. can be used. Copper powder 6B has an average particle size of 3.7 microns and a typical oxygen content of 0.39%.

[0036] The copper powder used as the base material can be produced by chemical methods (such as liquid phase reduction) or physical methods (such as high-temperature atomization). It can be spherical, flake, or irregular in shape. Copper powder is easily oxidized in air to form oxides on the surface. The oxides and other impurities on the surface can generally be removed by washing with a 2% dilute sulfuric acid solution.

[0037] The electroplating equipment used for tin or tin alloy electroplating can be purchased from conventional commercial sources or customized, such as plating tanks or tanks manufactured by Technic in the United States. During electroplating, tin metal or its alloy serves as the anode, and copper powder serves as the cathode. When electroplating tin, the plating solution is acidic tin sulfate. When electroplating tin alloys, such as tin-lead alloys, the plating solution is acidic tin sulfate and lead sulfate. During electroplating, the working chamber of the plating equipment can be rotated to prevent adhesion between copper powder particles. Alternatively, other methods can be used to keep the plating solution and copper powder in a dynamic state to prevent adhesion between copper powder particles.

[0038] The selection of the electroplating solution, especially the selection of additives in the electroplating solution, plays a vital role in the quality of the electroplated layer and the performance of the prepared coated copper powder. The surface coating layer of the tin or tin alloy coated copper powder prepared by the electroplating process is formed by nucleation and diffusion growth of tin or tin alloy on the surface of the copper powder. The additives in the electroplating solution affect and control the nucleation and growth of tin and tin alloy by adsorption of tin and tin alloy particles generated on the copper powder and the copper powder surface, thereby affecting and controlling the performance of the coating layer. The applicant has found through a large number of experiments that organic phosphine compound additives can generate a denser electroplated layer on the surface of the copper powder, and the tin-coated copper powder or tin alloy-coated copper powder prepared thereby has the advantage of better antioxidant properties. The organic phosphine compound can be any one or more of diphosphonic acid, triphosphonic acid, methylene phosphonic acid and carboxylic acid phosphonic acid, and further, can be any one or more of aminotrimethylphosphonic acid (ATMP), ethylenediaminetrimethylphosphonic acid (EDTMP), hydroxyethyldiphosphonic acid (HEDP), diethylenetriaminepentamethylphosphonic acid (DTPMP), phosphonic acid butane tricarboxylic acid (PBTCA).

[0039] The metal that forms the tin alloy coating layer with tin may be any one or more of Pb, In, Bi, Zn, and Ag.

[0040] In addition to providing a method for forming a tin or tin alloy coating on the surface of copper powder by electroplating, the present invention also provides a method for forming a tin or tin alloy coating on the surface of copper powder by chemical plating. Specifically, according to a second aspect of the present invention, a method for preparing copper powder coated with tin or tin alloy is provided, comprising the following steps:

[0041] S10, pre-treating the surface of the copper powder to remove oxides and impurities on the surface of the copper powder;

[0042] S20, placing the pretreated copper powder in a chemical plating solution containing metal ions corresponding to tin or a tin alloy, wherein the chemical plating solution further contains a reducing agent and an organic phosphine compound additive, so that the copper powder is in a dispersed state during the chemical plating process;

[0043] S30: After the chemical plating is completed, the copper powder coated with tin or tin alloy is obtained by filtering, washing and drying.

[0044] Reducing agents that can be used in electroless plating include any one or more of glucose, ascorbic acid, potassium borohydride, potassium sodium tartrate, hydrazine hydrate, formaldehyde, primary or secondary alcohols containing 3 to 8 carbon atoms, and diols containing 2 to 6 carbon atoms. The selection of copper powder and organophosphine compound for electroless plating can be consistent with those described in the electroplating method and will not be repeated here.

[0045] According to a third aspect of the present invention, a low-temperature conductive paste is provided, wherein the tin or tin alloy-coated copper powder prepared by any of the above methods is used as a raw material component.

[0046] The following is a description of the beneficial effects of the embodiments of the present invention compared to the prior art using specific experimental data. In the following embodiments, the copper powder used is the copper powder 6B mentioned above.

[0047] Example 1

[0048] The copper powder 6B is placed in a 2% dilute sulfuric acid aqueous solution and stirred to remove oxides and other impurities on the surface of the copper powder 6B. The copper powder 6B is then dried in a vacuum to reduce the typical oxygen content to below 0.1%.

[0049] Take 200g of the copper powder 6B treated as described above and add it to an electroplating tank. Add an electroplating solution to the tank. Refer to Table 1 for its composition: 20g of tin sulfate, 45ml of sulfuric acid, 350ml of deionized water, and 0.5g of aminotrimethylphosphonic acid. Heat to 50°C and electroplate at 5V for 4 hours. During the electroplating process, rotate the electroplating tank to prevent adhesion between copper powder particles. After electroplating, filter the tin-clad copper powder P1 obtained by electroplating and wash it four times with deionized water to a neutral pH. Then wash it once with alcohol, dry it at 65°C, and sieve it through a 200-mesh screen.

[0050] Comparative Example 1

[0051] The copper powder 6B is placed in a 2% dilute sulfuric acid aqueous solution and stirred to remove oxides and other impurities on the surface of the copper powder 6B. The copper powder 6B is then dried in a vacuum to reduce the typical oxygen content to below 0.1%.

[0052] Take 200g of the treated copper powder 6B and add it to an electroplating tank. Add prepared deionized water (refer to Table 1): 400ml of deionized water and 0.5g of aminotrimethylphosphonic acid. Heat to 50°C and stir for 0.2 hours. Then, filter the resulting copper powder D1, wash it with deionized water, rinse it once with alcohol, dry it at 65°C, and sieve it through a 200-mesh screen.

[0053] Table 1

[0054] Example 1 Comparative Example 1 Tin sulfate (g) 20 0 Sulfuric acid (ml) 45 0 Deionized water (ml) 350 400 Aminotrimethylphosphonic acid (g) 0.5 0.5 Temperature (℃) 50 50 Time (hours) 4 0.2

[0055] Performance Testing

[0056] Referring to Table 2, weigh 6.5g of epoxy resin, 2.8g of curing agent, 4.0g of butyl carbitol, 0.2g of dispersant, and 87g of conductive metal powder (in Example 1, the conductive metal powder was tin-coated copper powder P1; in Comparative Example 1, the conductive metal powder was copper powder D1). These ingredients were mixed at high speed and then rolled using a three-roll mill to a fineness of less than 18 to produce low-temperature conductive pastes.

[0057] The low-temperature conductive pastes prepared in Example 1 and Comparative Example 1 were then printed onto an alumina substrate in a serpentine pattern. The patterns were then dried at 100°C for 1 hour and then cured at 250°C for 20 minutes. The serpentine resistance was then measured, and the results are shown in Table 2. As can be seen, the low-temperature conductive paste prepared with tin-coated copper powder P1 had a lower resistance (1.2Ω) than the low-temperature conductive paste prepared with copper powder without metal coating D1 (1.6Ω).

[0058] Table 2

[0059]

[0060]

[0061] Example 2

[0062] The copper powder 6B is placed in a 2% dilute sulfuric acid aqueous solution and stirred to remove oxides and other impurities on the surface of the copper powder 6B. The copper powder 6B is then dried in a vacuum to reduce the typical oxygen content to below 0.1%.

[0063] Take 200g of the copper powder 6B treated as described above and add it to a 1-liter electroplating tank. Add an electroplating solution to the tank. The composition of the electroplating solution, as shown in Table 3, contains 20g of tin sulfate, 2g of lead sulfate, 45ml of sulfuric acid, 400ml of deionized water, and 0.5g of aminotrimethylphosphonic acid. Heat to 50°C and electroplate at 5V for 4 hours. During the electroplating process, rotate the electroplating tank to prevent adhesion between copper powder particles. After electroplating, filter the tin-lead-coated copper powder P2 obtained by electroplating and wash it four times with deionized water until the pH is neutral. Then wash it once with alcohol, dry it at 65°C, and sieve it through 200 mesh.

[0064] Comparative Example 2

[0065] The formula and process of Comparative Example 2 are substantially the same as those of Example 2, with the only difference being that gelatin is used as the organic additive in the electroplating solution of Comparative Example 2, while aminotrimethylphosphonic acid is used as the organic additive in the electroplating solution of Example 2. Specifically:

[0066] The copper powder 6B is placed in a 2% dilute sulfuric acid aqueous solution and stirred to remove oxides and other impurities on the surface of the copper powder 6B. The copper powder 6B is then dried in a vacuum to reduce the typical oxygen content to below 0.1%.

[0067] Take 200g of the treated copper powder 6B and add it to a 1-liter electroplating tank. Add the electroplating solution to the tank. Refer to Table 3 for its composition: 20g of tin sulfate, 2g of lead sulfate, 45ml of sulfuric acid, 400ml of deionized water, and 0.5g of gelatin. Heat to 50°C and electroplate at 5V for 4 hours. During the electroplating process, rotate the electroplating tank to prevent adhesion between copper powder particles. After electroplating, filter the tin-lead-coated copper powder D2 obtained by electroplating and wash it four times with deionized water to a neutral pH. Then, wash it once with alcohol, dry it at 65°C, and sieve it through a 200-mesh screen.

[0068] Table 3

[0069]

[0070]

[0071] Performance Testing

[0072] 20 mg of the tin-lead coated copper powder P2 prepared in Example 2 and the tin-lead coated copper powder D2 prepared in Comparative Example 2 were respectively taken and heat-treated in an oven at 200° C. The weight of the powders was measured after cooling.

[0073] Figure 1 The weight changes of the tin-lead coated copper powder P2 and the tin-lead coated copper powder D2 with heat treatment time are shown, and it can be seen that the oxidation weight gain of Comparative Example 2 is higher than that of Example 2. This result shows that the organic phosphonic acid additive can further improve the oxidation resistance of the tin-based alloy coated copper powder.

[0074] The above describes the specific embodiments of the present invention. Based on the above description, relevant personnel can make various changes and modifications without departing from the scope of the technical concept of this invention.

Claims

1. A method for preparing tin or tin alloy coated copper powder, characterized in that: The steps include: S10, pre-treating the surface of the copper powder to remove oxides and impurities on the surface of the copper powder; S20, placing the pretreated copper powder in an electroplating solution containing an organic phosphine compound additive; The copper powder is electroplated with tin metal or tin alloy as the anode and copper powder as the cathode. During the electroplating process, the copper powder is kept in a dispersed state. S30, after the electroplating is completed, filtering, washing, and drying to obtain tin or tin alloy coated copper powder; In step S20, the electroplating solution is a sulfuric acid solution of the anode metal.

2. The method for preparing tin or tin alloy coated copper powder according to claim 1, characterized in that: The organic phosphine compound is any one or more of diphosphonic acid, triphosphonic acid, methylenephosphonic acid and carboxylic acid phosphonic acid.

3. The method for preparing tin or tin alloy coated copper powder according to claim 1, characterized in that: The organic phosphine compound is any one or more of aminotrimethylphosphonic acid, ethylenediaminetrimethylphosphonic acid, hydroxyethyldiphosphonic acid, diethylenetriaminepentamethylphosphonic acid, and phosphonic acid butanetricarboxylic acid.

4. The method for preparing tin or tin alloy coated copper powder according to claim 1, characterized in that: In step S10, the pretreatment is to use a dilute sulfuric acid aqueous solution to wash and remove oxides and impurities on the surface of the copper powder.

5. The method for preparing tin or tin alloy coated copper powder according to claim 1, characterized in that: In step S10, the copper powder is micron copper powder.

6. The method for preparing tin or tin alloy coated copper powder according to claim 1, characterized in that: The metal that forms the tin alloy coating layer with tin is any one or more of Pb, In, Bi, Zn, and Ag.

7. The method for preparing tin or tin alloy coated copper powder according to claim 1, characterized in that: In step S20, when the copper powder is electroplated, the electroplating working chamber is in a rotating state to keep the copper powder in a dispersed state.

8. A low-temperature conductive paste, characterized in that: The tin or tin alloy coated copper powder prepared by the method according to any one of claims 1 to 7 is used as a raw material component.

Images