Method for preparing silver-coated copper adhesive by using silver methanesulfonate as silver source

Abstract

The invention discloses a method for preparing silver-coated copper glue by using silver methanesulfonate as a silver source. The method comprises the following steps: firstly, carrying out hydrothermal pretreatment on copper powder to remove surface oxides and improve the crystallinity; meanwhile, preparing a silver methanesulfonate solution as a main salt for chemical plating; then, a chemical plating method is adopted, the surface of the pretreated copper powder is coated with a uniform silver layer, and high-quality silver-coated copper powder is obtained; and finally, mixing the prepared silver-coated copper powder serving as a conductive filler with epoxy resin and a curing agent according to a preset proportion to obtain the silver-coated copper conductive adhesive. The silver methanesulfonate is used for replacing traditional silver nitrate, oxidation corrosion of nitrate to a copper matrix is effectively avoided, the oxidation resistance of the filler and the coating quality are remarkably improved by combining the hydrothermal treatment of the copper powder, and the finally prepared conductive adhesive has excellent conductivity and long-term stability and is suitable for the fields of electronic packaging and the like.

Description

Technical Field

[0001] This invention relates to technologies related to conductive adhesives and conductive adhesive metal fillers used in fields such as packaging and connection of electronic components, electromagnetic interference shielding, manufacturing of flexible electronic devices and touch screens, and the photovoltaic industry. Specifically, it includes a method for preparing silver-coated copper adhesive using silver methanesulfonate as the silver source. Background Technology

[0002] As electronic devices evolve towards higher performance and miniaturization, higher demands are placed on the connection and packaging technologies of internal circuits. Conductive adhesives, as a key electronic interconnect material, are widely used in the packaging and connection of electronic components, electromagnetic shielding, and flexible electronic devices due to their advantages such as simple processing, low curing temperature, and adaptability to fine circuits.

[0003] Among various conductive adhesives, silver-coated copper adhesive is a high-performance composite material that has attracted much attention. It typically consists of conductive filler (silver-coated copper powder) and an organic carrier (such as epoxy resin and a curing agent). During curing, the silver-coated copper powder dispersed in the resin matrix comes into contact with each other, forming a stable three-dimensional conductive network, thus endowing the adhesive with excellent conductivity. The final conductivity, stability, and reliability of the silver-coated copper adhesive fundamentally depend on the quality of the silver-coated copper powder used as the conductive filler. An ideal conductive filler should possess high conductivity, excellent oxidation resistance, good dispersibility, and a reasonable cost.

[0004] The industry has long explored the selection of conductive fillers. While pure silver powder possesses excellent conductivity and oxidation resistance, its high price and the risk of silver migration leading to short circuits under high electric fields limit its large-scale application. Pure copper powder, with its low cost, is considered an ideal alternative, but its surface is highly susceptible to oxidation in air, forming a poorly conductive oxide layer that severely degrades the performance of conductive adhesives. Therefore, coating copper powder with a chemically stable and highly conductive silver layer to create silver-coated copper powder is widely recognized as an effective way to achieve the best balance between cost and performance. This structure not only effectively prevents the oxidation of the core copper powder but also inhibits silver migration, while significantly reducing material costs.

[0005] However, the preparation process is crucial for producing silver-coated copper powder that meets the requirements of high-performance conductive adhesives. Currently, chemical plating has become the mainstream technology due to its simplicity, low cost, and good coating effect. However, several problems still exist in existing chemical plating processes, which directly affect the performance of the final silver-coated copper adhesive:

[0006] Existing technologies (such as patents CN 115156529 A and CN 118832162 A) mostly use silver nitrate or silver ammonia solution as the silver source. This not only limits the choice of process optimization, but more importantly, when using silver nitrate as the silver source, its inherent oxidizing property (NO3⁻) will corrode the copper powder matrix, affecting the uniformity and density of the coating, resulting in defects in the internal conductive pathways of the conductive adhesive, thus affecting its conductivity and long-term working stability. At the same time, commercially available copper powder often has oxides and impurities on its surface. If not effectively treated, these will directly affect the adhesion of the subsequent silver layer, causing the coating to peel off during mixing with resin, scraping, or curing, ultimately leading to increased resistivity or even failure of the conductive adhesive.

[0007] In summary, while existing technologies have explored the preparation of silver-coated copper powder, they often treat it as a standalone material, lacking a systematic and holistic solution that integrates powder optimization with improved colloidal properties. In particular, the limited selection of silver sources and their potential side effects have become key bottlenecks hindering further performance enhancements in silver-coated copper adhesives. Therefore, developing a complete method for innovating powder preparation processes from the source, obtaining high-quality fillers, and using this as a basis to prepare high-performance silver-coated copper conductive adhesives is a pressing technical problem that needs to be solved in this field. Summary of the Invention

[0008] This invention discloses a method for preparing silver-coated copper adhesive using silver methanesulfonate as the silver source, aiming to solve the problems of silver powder migration, easy oxidation of copper powder, and limited selection of silver source in the prior art, thereby obtaining a conductive adhesive with simple process, controllable cost and excellent performance.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing silver-coated copper adhesive using silver methanesulfonate as the silver source includes the following steps:

[0011] Step 1: Place copper powder in formaldehyde solution, adjust the pH value to 11-12 with alkaline solution, and then carry out hydrothermal reaction at 180-200℃ for 2-4 hours. After the reaction is completed, wash and dry the product to obtain pretreated copper powder.

[0012] Step 2: Soluble silver salt reacts with carbonate to form silver carbonate precipitate. After washing and purification, the solid silver carbonate is reacted with methanesulfonic acid to obtain silver methanesulfonate solution.

[0013] Step 3: Divide the electroless plating solution into solution A and solution B. Solution A contains the pretreated copper powder and dispersant obtained in step 1; solution B contains the silver methanesulfonate solution and complexing agent prepared in step 2. Under stirring, solution B is added dropwise to solution A to carry out a displacement reaction; after the displacement reaction is completed, glucose is added to the mixture as a reducing agent to carry out a reduction reaction, obtaining silver-coated copper powder.

[0014] Step 4: Use the silver-coated copper powder obtained in Step 3 as a conductive filler, and mix it with epoxy resin and curing agent. The conductive filler content is 65%-85%, the epoxy resin content is 7.5%-17.5%, and the curing agent content is 7.5%-17.5% by mass percentage. After mixing evenly, silver-coated copper adhesive is obtained.

[0015] Preferably, in step 1, the hydrothermal reaction temperature is 180°C and the reaction time is 4 h.

[0016] Preferably, in step 2, a silver carbonate precipitate is generated by adding sodium carbonate solution to silver nitrate solution, and the precipitate is washed and purified before being reacted with methanesulfonic acid to finally obtain a silver methanesulfonate solution with a concentration of 60 g / L.

[0017] Preferably, in step 3, the dispersant in solution A is polyvinylpyrrolidone (PVP); and the complexing agent in solution B is disodium ethylenediaminetetraacetate (EDTA-2Na).

[0018] Preferably, in step 3, the time for adding liquid B to liquid A is 10-15 minutes; after the addition is complete, the displacement reaction continues for 5-10 minutes.

[0019] Preferably, the silver content in the silver-coated copper powder obtained in step 3 is controlled between 15 wt% and 20 wt%.

[0020] Furthermore, the epoxy resin in step 4 is one or more of the following: bisphenol A type epoxy resin, bisphenol F type epoxy resin, heterocyclic resin, mixed resin, aliphatic glycidyl ether resin, glycidyl amine type resin, or modified resin.

[0021] Furthermore, in step 4, the curing agent is one or more of aliphatic polyamines, alicyclic polyamines, aromatic polyamines, low molecular weight polyamides, dicyandiamides, or amino resins.

[0022] The beneficial effects of this invention are:

[0023] This invention provides a complete preparation method from raw material processing to the final product. It innovatively uses silver methanesulfonate as the silver source, avoiding the corrosion and oxidation of copper powder by nitrate ions, thus broadening the selection of silver sources for electroless silver plating. The initial hydrothermal treatment effectively improves the oxidation resistance and crystallinity of the copper powder; the subsequent two-step electroless plating process ensures the integrity and density of the silver plating layer, resulting in a conductive adhesive with excellent conductivity and stability. The electroless plating process used in this invention is mature, simple to operate, and easy to implement for large-scale production. By using copper instead of silver as the core material and optimizing the utilization efficiency of silver, the cost of raw materials is significantly reduced. Attached Figure Description

[0024] Figure 1 This is a schematic flowchart of the preparation method of the present invention;

[0025] Figure 2 SEM images of copper powder before and after hydrothermal treatment (a is before hydrothermal treatment, b is after hydrothermal treatment).

[0026] Figure 3 SEM images of the silver-plated copper adhesive (a is a planar view, b is a cross-section).

[0027] Figure 4 This is the XRD pattern of silver-coated copper powder. Detailed Implementation

[0028] The following examples and accompanying drawings will allow those skilled in the art to easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0029] In this invention, the copper powder used is commercial copper powder with a particle size of 10 μm.

[0030] Weigh 10 g of copper powder and add it to 20 mL of formaldehyde solution. While stirring, alternately add formaldehyde solution and 4 mol / L sodium hydroxide solution to adjust the pH of the system to 11-12. Transfer the mixture to a reaction vessel and carry out a hydrothermal reaction at 180-200℃ for 2-4 h. After the reaction is complete, centrifuge and wash the product until neutral, then dry it for later use.

[0031] A sodium carbonate solution of a certain concentration was added dropwise to a silver nitrate solution, and the reaction proceeded to form a silver carbonate precipitate. The precipitate was washed three times with water at 8000 r / min using a high-speed centrifuge to obtain pure silver carbonate solid. The solid was then ultrasonically dispersed in deionized water, and methanesulfonic acid was added stoichiometrically to carry out the reaction. After the reaction was complete, the volume was adjusted to obtain a silver methanesulfonate solution with a concentration of 60 g / L.

[0032] In a constant temperature water bath at 20-60℃, solution A is mechanically stirred at a speed of 300-500 r / min, while solution B is slowly added dropwise over 10-15 min. After reacting for another 5-10 min, a glucose solution with a final concentration of 0-20 g / L is added to the system, and the reaction is continued for another 5-10 min. After the reaction is complete, the product is washed and dried to obtain silver-coated copper powder. (Formula for solution A: Disperse 1 g of hydrothermally treated copper powder in an aqueous solution containing 5-15 g / L PVP; Formula for solution B: Mix 4-7 mL of 60 g / L methyl silver nitrate solution with 5-25 g / L EDTA-2Na until homogeneous.)

[0033] The silver-coated copper powder (conductive filler) prepared by the above method, epoxy resin and curing agent are thoroughly mixed in a predetermined ratio to obtain silver-coated copper conductive adhesive.

[0034] The conductive adhesive was applied to the ceramic substrate and cured under a nitrogen atmosphere according to the following procedure: 40℃ for 30 min, 90℃ for 30 min, and 100℃ for 60 min.

[0035] The sheet resistance (R) of the cured samples was measured using a four-probe tester (Four-Probe Technology Co., Ltd.), and the sample thickness (L) was also measured. Five measurements were taken for each sample, and the average value was calculated. The volume resistivity (ρ) was calculated using the formula ρ = R * L.

[0036] Example 1

[0037] Copper powder pretreatment: Take 10 g of commercial copper powder and carry out a hydrothermal reaction at 180℃ for 4 h.

[0038] Electroless plating: carried out at 30℃. Solution A contains 1 g of hydrothermal copper powder and 7.5 g / L PVP; Solution B contains 4 mL of 60 g / L silver methanesulfonate solution and 10 g / L EDTA-2Na. Solution B is added dropwise over 12 min, and the reaction continues for 10 min. Then, glucose is added to bring the final solution concentration to 5 g / L, and the reaction continues for another 5 min.

[0039] Preparation of conductive adhesive: Take the above-mentioned silver-coated copper powder as conductive filler, and mix it with 80% conductive filler, 10% bisphenol A type epoxy resin and 10% triethanolamine curing agent by mass ratio.

[0040] Performance testing: The volume resistivity after curing was measured to be 1.17 × 10⁻ 4 Ω·cm.

[0041] Example 2

[0042] The preparation method of this embodiment is basically the same as that of Example 1, except that the amount of silver methanesulfonate solution used in the chemical plating step is changed to 3 mL.

[0043] The measured volume resistivity was 2.12 × 10⁻⁻⁻⁶. 4 Ω·cm

[0044] Example 3

[0045] The preparation method of this embodiment is basically the same as that of Example 1, except that the amount of silver methanesulfonate solution used in the chemical plating step is changed to 5 mL.

[0046] The measured volume resistivity was 8.03 × 10⁻ 5 Ω·cm.

[0047] Example 4

[0048] The preparation method of this embodiment is basically the same as that of Example 1, except that the amount of silver methanesulfonate solution used in the chemical plating step is changed to 6 mL.

[0049] The measured volume resistivity was 3.46 × 10⁻ 4 Ω·cm.

[0050] Example 5

[0051] The preparation method of this embodiment is basically the same as that of Example 1, except that the amount of silver methanesulfonate solution used in the chemical plating step is changed to 7 mL.

[0052] The measured volume resistivity was 4.44 × 10⁻ 4 Ω·cm.

[0053] Comparing Examples 1-5, it is evident that the amount of silver methanesulfonate solution used has a significant impact on conductivity. Too low a amount (e.g., 3 mL) results in a thin silver layer and incomplete coating; too high a amount (e.g., 6-7 mL) leads to a rapid deposition rate, a rough coating, and the potential formation of elemental silver particles. Under the experimental conditions, 5 mL (corresponding to a silver content of approximately 18 wt%) yielded the best results and the lowest volume resistivity.

[0054] Example 6

[0055] The preparation method in this embodiment is basically the same as that in Example 1, except that the reaction temperature of the electroless plating is changed to 20°C.

[0056] The measured volume resistivity was 1.58 × 10⁻ 4 Ω·cm.

[0057] Example 7

[0058] The preparation method in this embodiment is basically the same as that in Example 1, except that the reaction temperature of the electroless plating is changed to 40°C.

[0059] The measured volume resistivity was 1.19 × 10⁻ 4 Ω·cm.

[0060] Example 8

[0061] The preparation method in this embodiment is basically the same as that in Example 1, except that the reaction temperature of the electroless plating is changed to 50°C.

[0062] The measured volume resistivity was 1.59 × 10⁻ 4 Ω·cm.

[0063] Example 9

[0064] The preparation method in this embodiment is basically the same as that in Example 1, except that the reaction temperature of the electroless plating is changed to 60°C.

[0065] The measured volume resistivity was 2.44 × 10⁻ 4 Ω·cm.

[0066] A comparison of Examples 1 and 6-9 shows that reaction temperature is a key factor affecting coating quality. Too low a temperature results in a slow reaction rate; too high a temperature increases side reactions and makes copper more susceptible to oxidation. Under the conditions of this experiment, 30℃ is the optimal reaction temperature.

[0067] Example 10

[0068] The preparation method in this embodiment is basically the same as that in Example 1, except that glucose solution is not added in the chemical plating step.

[0069] The measured volume resistivity was 1.66 × 10⁻ 4 Ω·cm.

[0070] Example 11

[0071] The preparation method in this embodiment is basically the same as that in Example 1, except that the final concentration of the glucose solution added in the chemical plating step is 10 g / L.

[0072] The measured volume resistivity was 9.93 × 10⁻⁻⁻⁶. 5 Ω·cm.

[0073] Example 12

[0074] The preparation method in this embodiment is basically the same as that in Example 1, except that the final concentration of the added glucose solution in the chemical plating step is 15 g / L.

[0075] The measured volume resistivity was 1.24 × 10⁻ 4 Ω·cm.

[0076] Example 13

[0077] The preparation method in this embodiment is basically the same as that in Example 1, except that the final concentration of the added glucose solution in the chemical plating step is 20 g / L.

[0078] The measured volume resistivity was 2.46 × 10⁻ 4 Ω·cm.

[0079] Comparing Examples 1 and 10-13, it is evident that the addition of glucose as a reducing agent is crucial for improving the integrity of the coating. Without the reducing agent (Example 10), the displacement is incomplete, resulting in poor conductivity. Excessive reducing agent (15-20 g / L) causes silver ions to be rapidly reduced to elemental silver in the solution, rather than deposited on the copper surface, leading to a loose coating. Under the experimental conditions, a glucose concentration of 10 g / L yielded the best results.

[0080] In summary, this invention provides a novel and complete method for preparing silver-coated copper adhesive using silver methanesulfonate as the silver source. Those skilled in the art should understand that any modifications or refinements to this invention made through equivalent substitutions or transformations should be covered within the scope of the claims.

Claims

1. A method for preparing silver-coated copper adhesive using silver methanesulfonate as the silver source, characterized in that: Includes the following steps: Step 1: Place copper powder in formaldehyde solution, adjust the pH value to 11-12 with alkaline solution, and then carry out hydrothermal reaction at 180-200℃ for 2-4 hours to obtain pretreated copper powder. Step 2: React soluble silver salt with carbonate to form silver carbonate precipitate. After washing and purification, react the silver carbonate solid with methanesulfonic acid to obtain silver methanesulfonate solution. Step 3: Prepare solution A and solution B: Solution A contains the pretreated copper powder and dispersant obtained in step 1; solution B contains the silver methanesulfonate solution and complexing agent prepared in step 2; under stirring, solution B is added dropwise to solution A to carry out the displacement reaction; after the displacement reaction is completed, glucose is added to the mixture as a reducing agent to carry out the reduction reaction, and silver-coated copper powder is obtained. Step 4: Use the silver-coated copper powder obtained in Step 3 as a conductive filler, and mix it with epoxy resin and curing agent. The conductive filler content is 65%-85%, the epoxy resin content is 7.5%-17.5%, and the curing agent content is 7.5%-17.5% by mass percentage. After mixing evenly, silver-coated copper adhesive is obtained.

2. The method for preparing silver-coated copper adhesive using silver methanesulfonate as the silver source according to claim 1, characterized in that: The hydrothermal reaction temperature in step 1 is 180°C, and the reaction time is 4 hours.

3. The method for preparing silver-coated copper adhesive using silver methanesulfonate as the silver source according to claim 1, characterized in that: In step 2, sodium carbonate solution is added dropwise to silver nitrate solution to generate silver carbonate precipitate; after washing and purifying the precipitate, it is reacted with methanesulfonic acid, and after adjusting the volume, a silver methanesulfonate solution with a concentration of 60 g / L is obtained.

4. The method for preparing silver-coated copper adhesive using silver methanesulfonate as the silver source according to claim 1, characterized in that: In step 3, the dispersant in solution A is polyvinylpyrrolidone (PVP); the complexing agent in solution B is disodium ethylenediaminetetraacetate (EDTA-2Na).

5. The method for preparing silver-coated copper adhesive using silver methanesulfonate as the silver source according to claim 1, characterized in that: In step 3, the time for adding solution B to solution A is 10-15 minutes; after the addition is complete, the displacement reaction continues for 5-10 minutes.

6. The method for preparing silver-coated copper adhesive using silver methanesulfonate as the silver source according to claim 1, characterized in that: In the silver-coated copper powder obtained in step 3, the silver content is controlled between 15 wt% and 20 wt%.

7. The method for preparing silver-coated copper adhesive using silver methanesulfonate as the silver source according to claim 1, characterized in that: The epoxy resin in step 4 is one or more of the following: bisphenol A type epoxy resin, bisphenol F type epoxy resin, heterocyclic resin, mixed resin, aliphatic glycidyl ether resin, glycidyl amine type resin, or modified resin.

8. The method for preparing silver-coated copper adhesive using silver methanesulfonate as the silver source according to claim 1, characterized in that: The curing agent in step 4 is one or a mixture of aliphatic polyamines, alicyclic polyamines, aromatic polyamines, low molecular weight polyamides, dicyandiamides, or amino resins.

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