Copper conductive paste and glass-coated copper powder for end electrode of multilayer ceramic capacitor and preparation method of copper conductive paste and glass-coated copper powder

Abstract

The invention provides copper conductive paste and glass-coated copper powder for a multi-layer ceramic capacitor terminal electrode and a preparation method of the copper conductive paste and the glass-coated copper powder. Through the design of the glass components, the sintering temperature of the glass is matched with the sintering temperature of the copper powder, and the sintering compactness and conductivity are improved. According to the glass-coated copper powder prepared by adopting a sol-gel method, the specific surface area of the glass is increased, so that the sintering activity of a glass phase is improved, molten glass is formed at a relatively low temperature, the sintering activity can be improved, a liquid phase is formed at a relatively low temperature, and the molten glass wets and permeates along a copper grain boundary due to a large contact area with the copper powder, so that the copper powder can be effectively sintered. Along with the progress of the infiltration, the original relatively thick copper powder particles are split into a plurality of smaller particles, so that the specific surface energy of the copper powder is increased, the sintering activity of the copper powder is improved, the sintering temperature is reduced, and the sintering density is improved.

Description

Technical Field

[0001] This invention belongs to the field of electronic materials, specifically relating to a method for preparing glass-coated copper powder and copper conductive paste for use as terminal electrodes of multilayer ceramic capacitors by sol-gel method. Background Technology

[0002] Existing copper conductive pastes are mainly made by mixing copper powder, glass powder, solvent, resin, thixotropic agent and other additives evenly, and then grinding them with three rollers to obtain conductive copper paste.

[0003] In the prior art, patent publication number CN116000287A discloses a method for preparing zinc borosilicate glass-coated copper powder using the sol-gel method, and also discloses a method for mixing glass-coated copper powder with organic polymers and organic solvents to form copper paste. This method uses a relatively simple glass composition and does not consider the influence of the glass's softening point on the sintering temperature, sintering density, and capacitance of multilayer ceramic capacitors. It also fails to consider the difficulty of dispersing glass-coated copper powder in organic polymers and organic solvents.

[0004] In addition, patent publication number CN 118832159A discloses a method for preparing low-temperature sintering, oxidation-resistant zinc-borosilicate-aluminum-sodium glass-coated copper powder using the sol-gel method. It also discloses a method for mixing the glass-coated copper powder with organic polymers and organic solvents to prepare copper paste. In this method, aluminum and sodium are added to the glass composition in addition to borosilicate-zinc, and a dispersant is added to the copper paste. However, this method still uses a single glass composition and does not consider the effects of glass composition on surface tension, wettability, and acid resistance. Although the sintering temperature is reduced to 720℃, the overall sintering time is long.

[0005] In summary, existing technologies for using glass-coated copper powder in electronic pastes have the following technical problems: (1) The dispersion is difficult, especially the submicron grade glass powder, which is very easy to agglomerate and has a large preparation process. Since glass powder is usually irregular flakes or particles, while copper powder can be spherical copper powder or spherical copper powder that has been flake-processed, the difference in morphology and particle size between the two leads to the difference in fluidity. During the sintering process of copper paste to form a film, the different fluidity will lead to uneven distribution of glass and copper powder, resulting in various film surface defects. (2) High sintering temperature. The melting temperature of copper is around 1080℃, and the sintering temperature generally needs to be above 750℃. (3) The sintering temperatures of glass powder and copper powder are not matched, which will result in poor density or poor conductivity after sintering. (4) An inappropriate glass composition ratio can lead to crystallization after sintering. Summary of the Invention

[0006] To solve the problems existing in the above-mentioned technologies, the solution provided by the present invention aims to: (1) solve the problem of uneven distribution of glass powder and copper powder; (2) solve the problem of excessively high sintering temperature; (3) solve the problem of low sintering density or poor conductivity; (4) improper glass component ratio will lead to crystallization after sintering.

[0007] This invention provides a glass-coated copper powder, wherein the core is copper powder and the coating layer is a glass coating layer; the mass of the glass coating layer accounts for 1% to 10% of the mass of the copper powder; the glass coating layer is formed by preparing a solution based on an oxide precursor to form a glass sol, the glass sol is aged and dried to form a glass gel, and the glass gel is heat-treated to finally form the glass coating layer.

[0008] Preferably, the glass cladding layer comprises the following components: SiO2, B2O3, ZnO2, Al2O3, Na2O, BaO, CaO, CuO, K2O, Li2O, CoO, and Fe2O3. The mass percentages of each component are as follows: SiO2 2%-16%, B2O3 15%-45%, ZnO2 10%-60%, Al2O3 0%-10%, Na2O 0%-10%, BaO 0%-50%, CaO 0%-10%, CuO 0%-10%, K2O 0%-10%, Li2O 0%-5%, CoO 0%-5%, and Fe2O3 0%-5%.

[0009] The method for preparing glass-coated copper powder of the present invention involves first pretreating the copper powder, then preparing a glass sol, coating the copper powder surface with the glass sol, aging it for several hours, drying it to obtain glass gel-coated copper powder, and finally heat-treating the glass gel-coated copper powder to obtain glass-coated copper powder with a uniform surface coating.

[0010] Preferably, the method for treating glass-coated copper powder includes the following steps: Step 1: Copper powder pretreatment: Prepare a dilute sulfuric acid or citric acid solution, add the copper powder to the prepared acid solution, heat and stir under a nitrogen atmosphere, wash with anhydrous ethanol or acetone, and then vacuum dry. Step 2: Glass sol preparation: Calculate the corresponding precursor mass ratio based on the mass of the oxides, weigh the appropriate precursor raw materials, dissolve the silica precursor in ethanol, then add deionized water, and hydrolyze it under electromagnetic stirring at room temperature to obtain a clear silica precursor pre-hydrolyzed solution A; add the boron oxide precursor to ethanol, and mix to obtain a clear solution B; add the other oxide precursors (excluding silica and boron oxide) to deionized water, and mix to obtain solution C; mix solution B and solution C, adjust to a clear and transparent solution with deionized water, and then pour into solution A; add citric acid or ascorbic acid for stabilization, adjust the pH to 2-7, and stir at room temperature to obtain a clear glass sol; the mass concentration fraction of citric acid or ascorbic acid after addition is 1%-20%; Step 3: Copper powder coated with glass gel: Weigh an appropriate amount of pretreated copper powder according to the final glass layer mass being 1% to 10% of the copper powder mass, add ethanol to obtain copper powder ethanol suspension, mix the glass sol and the pretreated copper powder ethanol suspension, heat and stir, mix evenly, seal and age at room temperature for 4h to 36h, then dry under vacuum or in a nitrogen atmosphere until the solvent is completely evaporated to obtain dry glass gel coated copper powder; Step 4: Heat treatment: The glass gel-coated copper powder is calcined in a N2 atmosphere in stages. After reaching the first stage temperature, it is held at that temperature for a certain period of time, and then the temperature is raised to the second stage temperature and held at that temperature for a certain period of time to obtain glass-coated copper powder.

[0011] Preferably, the glass-coating copper powder step is as follows: (1) Copper powder pretreatment: Prepare dilute sulfuric acid or citric acid solution, add 100g of copper powder to the prepared acid solution, heat and stir under nitrogen atmosphere, wash with anhydrous ethanol or acetone, and then vacuum dry. (2) Preparation of glass sol: Calculate the precursor mass ratio according to the oxide mass ratio in Table 1 (001), weigh the corresponding raw materials, and prepare the following solutions: Solution A: Weigh 0.21 TEOS and dissolve it in 0.54 ml of ethanol, then add deionized water. The molar ratio of silicon to deionized water is nsilicon:ndeionized water = 1:(2~5). Stir at room temperature to obtain a clear and transparent silicon precursor pre-hydrolyzed solution. Solution B: Weigh the prescribed amount of boron precursor and add it to ethanol to obtain an ethanol solution. The molar ratio of boron to ethanol is nboron:nethanol = 1:(10~30). Solution C: Weigh the other precursors in the formula and add them to deionized water. The mass ratio of the other precursors to the volume of deionized water is 1 g : (8-15) ml. After mixing solutions B and C, adjust the solution to a clear and transparent state with deionized water, then pour the mixture into solution A. Add citric acid or ascorbic acid for stabilization; the added citric acid or ascorbic acid should have a mass concentration of 1%-20%. Adjust the pH to 2-7 and stir at room temperature to obtain a clear glass sol. (3) Copper powder coated with glass gel: Weigh an appropriate amount of pretreated copper powder according to the final glass layer mass being 1% to 3% of the copper powder mass, add ethanol to obtain copper powder ethanol suspension, the ratio of copper powder mass to ethanol volume is (10 to 20) g: 100 ml, mix the glass sol and the pretreated copper powder ethanol suspension, heat to 30℃ to 70℃ and stir for 1 to 3 hours, seal and age at room temperature for 4 to 36 hours, and then dry under vacuum or in a nitrogen atmosphere at 40℃ to 80℃ until the solvent is completely evaporated to obtain dry glass gel coated copper powder; (4) Heat treatment: Glass gel coated copper powder is heated at 200℃~400℃ in N2 atmosphere for 0.5h~4h, and then calcined at 500℃~700℃ for 1h~4h to obtain glass coated copper powder.

[0012] Preferably, in step 1: the mass concentration of the dilute sulfuric acid is 0.1%–0.5%; the mass concentration of the citric acid solution is 1%–10%; the copper powder is spherical copper or sheet copper with a particle size of 0.5μm–10μm; the mass of the copper powder and the volume of the dilute sulfuric acid or citric acid solution are (10–50) g: 100 ml; the heating and stirring under a nitrogen atmosphere is carried out at a temperature of 40℃–80℃ for 10 min–60 min; the drying temperature is 30℃–60℃ for 1 h–4 h. In step 2: Precursors for silicon oxide include alkoxysilane Si(OR)4; precursors for boron oxide include any or a combination of the following substances: boric acid, alkoxyboron B(OR)3, alkylborane R3B, organoboroxane -B(R)-OB(R)-O-; precursors for zinc oxide include any or a combination of the following substances: alkoxyzinc Zn(OR)2, zinc acetate, zinc acetate dihydrate, zinc nitrate, zinc nitrate hexahydrate, and zinc-based MOF; precursors for aluminum oxide include any or a combination of the following substances: alkoxyaluminum Al(OR)3, aluminum nitrate, and nonaluminophosphates. Aluminum nitrate hydrate, aluminum sulfate, aluminum sulfate octahydrate; precursors of barium oxide include any or a combination of the following substances: barium alkoxy (Ba(OR)2), barium citrate, barium acetate; precursors of calcium oxide include any or a combination of the following substances: calcium alkoxy (Ca(OR)2), calcium alginate, calcium oxalate, calcium acetate, calcium acetate monohydrate, calcium isopropoxide; precursors of sodium oxide include any or a combination of the following substances: sodium alkoxy (Na(OR)), sodium acetate, sodium acetate trihydrate, sodium oxalate, sodium citrate, sodium stearate, etc.; precursors of potassium oxide. Precursors to lithium oxide include any or a combination of the following substances: potassium alkoxykine (K(OR)), potassium acetate, potassium oxalate, potassium citrate, potassium stearate; lithium oxide precursors include any or a combination of the following substances: lithium alkoxykine (Li(OR)), lithium acetate, lithium oxalate, lithium citrate; copper oxide precursors include any or a combination of the following substances: copper alkoxykine (Cu(OR)2), copper citrate, copper carboxylate; copper carboxylate precursors include any or a combination of the following substances: copper oxalate, copper acetate, copper stearate; iron oxide precursors include any or a combination of the following substances: iron alkoxykine (F) e(OR)3, ferric nitrate, iron-based MOF; the precursors of cobalt oxide include any or a combination of the following substances: alkoxycobalt Co(OR)2, cobalt acetate, cobalt acetate tetrahydrate, cobalt nitrate, cobalt nitrate hexahydrate, cobalt-based MOF; R refers to alkyl or aromatic group, alkyl is preferably methyl (-CH3), ethyl (-CH2CH3), isopropyl (-CH2(CH3)2), OR refers to alkoxy, preferably methoxy (-OCH3), ethoxy (-OCH2CH3), propoxy (-OCH2CH2CH3); In step 2: the molar ratio of silica precursor to ethanol in solution A is 1:(5-20); the molar ratio of silica precursor to deionized water in solution A is 1:(2-10); the molar ratio of boron oxide precursor to ethanol in solution B is 1:(10-30); and the total mass of other precursors in solution C is 1g:(8-15)ml of deionized water. In step 3: the mass ratio of copper powder to ethanol is (10-20) g: 100 ml; the heating temperature is 30℃-70℃, and the stirring time is 1h-3h; the vacuum or nitrogen atmosphere drying temperature is 40℃-80℃. In step 4: the temperature of the first stage is 200℃~400℃, and the holding time is 0.5h~4h; the temperature of the second stage is 500℃~700℃, and the holding time is 1h~4h.

[0013] The present invention provides a copper conductive paste for the terminal electrodes of a multilayer ceramic capacitor, comprising 70-80% glass-coated copper powder, 2-10% glass powder, 15-25% organic carrier, and 0-10% sintering aid; the glass-coated copper powder is the glass-coated copper powder described above.

[0014] The present invention relates to a copper conductive paste for the terminal electrodes of a multilayer ceramic capacitor. The preparation method of the organic carrier includes: weighing and mixing the corresponding raw materials in proportion, and stirring at 40-60°C for 4-6 hours; the components and their mass percentages include: 60-80% organic solvent, 4-30% resin, and 5-20% dispersant; specifically, in several embodiments: 60% organic solvent, 20% resin, and 20% dispersant; or 80% organic solvent, 10% resin, and 10% dispersant; or 70% organic solvent, 20% resin, and 10% dispersant.

[0015] The organic solvent is one or a mixture of the following reagents: diethylene glycol butyl ether, terpineol, hydrogenated terpineol, dodecyl alcohol ester, and diethylene glycol butyl ether acetate. The resin is an acrylic resin with a number-average molecular weight of 200,000 to 600,000; the dispersant is one or a mixture of the following reagents: phosphate esters (such as BYK111 from BYK Corporation, soybean lecithin), polyether phosphate esters (such as HIPLAAD ED152 from Kusunoki Chemical Co., Ltd.), polyether acids (such as HIPLAAD ED420 from Kusunoki Chemical Co., Ltd.), polyether ester acid amine salts (such as HIPLAAD ED360), preferably phosphate esters, and more preferably BYK111; The sintering aid is spherical copper with a diameter of 50 nm to 500 nm. During the sintering process, it preferentially diffuses into the liquid glass melt at 500 °C to 600 °C to form a solid solution with the glass. In the solid-liquid sintering process, it adjusts and controls the surface tension of the liquid phase and the wettability of the copper powder, thereby increasing the diffusion rate of the copper powder particles in the glass melt. The glass-coated copper powder has a large specific surface area, which can improve sintering activity. It forms a liquid phase at a lower temperature. Due to the large contact area with the copper powder, it will wet and penetrate along the copper particle boundaries. As this penetration progresses, the originally relatively large copper powder particles break down into several smaller particles, thereby increasing the specific surface energy of the copper powder, improving the sintering activity of the copper powder, and reducing the sintering temperature.

[0016] The glass powder used is a commercially available ordinary glass powder, or it can be prepared in the following manner: The preparation method of the glass powder includes: selecting appropriate chemical raw materials, calculating and weighing the ingredients, mixing the raw materials evenly, keeping them at 1200℃~1400℃ for 0.5h~2h, naturally cooling and crushing or water quenching the molten glass, ball milling, and drying to obtain powder with a particle size of 0.5μm~10μm.

[0017] The method for preparing copper conductive paste for the terminal electrodes of multilayer ceramic capacitors according to the present invention includes the following steps: Copper-coated glass powder, glass powder, sintering aid, and organic phase are mixed in proportion using a planetary mixer and then dispersed using a three-roll mill; or dispersed using a high-pressure homogenizer; to prepare a copper conductive paste.

[0018] The present invention discloses a method for preparing a copper electrode on the end face of an MLCC, wherein the chamfered end face of the MLCC is immersed in a copper conductive paste prepared by the above method and dried; the dried sample is placed in an N2 atmosphere furnace and heated to the heat treatment temperature and held at that temperature; then the temperature is further increased to the sintering temperature and held at that temperature; and the sample is allowed to cool naturally after sintering.

[0019] Preferably, the drying temperature is 80℃~120℃ and the drying time is 30min~120min; The heat treatment temperature is 400℃~500℃, the holding time is 20min~60min, and the heating rate is 10℃ / min~30℃ / min; The sintering temperature is 600℃~780℃, the holding time is 20min~60min, and the heating rate is 10℃ / min~30℃ / min; The copper electrode prepared according to the above scheme has a sheet resistance of less than 4 mΩ / □ (10 μm), or as low as 2.75 mΩ / □ (10 μm).

[0020] The beneficial effects of this invention are as follows: (1) By designing the glass composition, the sintering temperature of the glass is matched with that of copper powder, thereby improving the sintering density and conductivity. Copper-coated glass prepared by the sol-gel method increases the specific surface area of ​​the glass, thereby improving the sintering activity of the glass phase. The formation of a molten glass at a relatively low temperature enhances sintering activity. The large contact area between the molten glass phase and the copper powder allows it to wet and penetrate along the copper particle boundaries. As this penetration progresses, the initially coarser copper powder particles break down into several smaller particles, increasing the specific surface energy of the copper powder, improving its sintering activity, lowering the sintering temperature, and increasing the sintering density.

[0021] (2) The glass phase in the copper conductive paste comes from two parts: one part is the glass coating layer of glass-coated copper powder prepared by the sol-gel method, and the other part is the added glass powder. The two glass phases can have the same composition or different composition. The material properties (working range) of the glass are improved by designing the difference in softening point.

[0022] (3) Add sintering aids and add copper powder with small particle size (50nm~500nm). Due to the large curvature and high specific surface energy of the sintering aids, the sintering activity is high. It preferentially forms a solid solution with the glass powder, which improves the wettability of the glass liquid relative to the copper powder. Under the capillary pressure of the liquid phase, it accelerates the mass transfer rate of copper powder in solid-liquid sintering and reduces the sintering temperature. Attached Figure Description

[0023] Figure 1 This is a SEM image of glass-coated copper powder prepared according to Example 1 of the present invention; Figure 2 This is an end face view of the copper paste prepared in Example 1 of the present invention after sintering at 680°C on an MLCC. Figure 3 This is a partial SEM image of the copper paste prepared in Example 1 of the present invention after sintering at 680°C on an MLCC end cap. Figure 4 This is an end face diagram of copper paste after sintering at 680℃ in MLCC end capping according to existing technology. Figure 5 This is a local SEM image of copper paste after sintering at 680℃ in MLCC end caps, according to existing technology. Detailed Implementation

[0024] Example 1: (1) Preparation of glass-coated copper powder: Copper powder pretreatment: Weigh 100g of copper powder with D50 of 2.5μm and add it to 200mL of 0.1wt% dilute sulfuric acid solution. Under nitrogen atmosphere, heat to 50℃ and stir for 30min. Wash with ethanol 3 times and vacuum dry at 40℃ for 2h to obtain pretreated copper powder.

[0025] Preparation of glass sol: Based on the final glass layer mass being 2% of the copper powder mass, the following raw materials were weighed according to the mass percentage content of glass phase 001 in Table 1: 0.21g tetraethyl orthosilicate (TEOS), 0.54g boric acid, 1.59g barium citrate, 0.83g zinc acetate dihydrate, 0.31g aluminum nitrate nonahydrate, 0.11g sodium acetate trihydrate, 0.17g calcium acetate monohydrate, 0.07g copper citrate, and 0.15g cobalt acetate tetrahydrate. TEOS was dissolved in 0.48g ethanol, and then 0.04g deionized water was added. The mixture was magnetically stirred at room temperature to obtain a clear and transparent TEOS pre-hydrolyzed solution A. Boric acid was added to 8.49g ethanol to obtain solution B. Barium citrate, zinc acetate dihydrate, sodium acetate trihydrate, aluminum nitrate nonahydrate, calcium acetate monohydrate, copper citrate, and cobalt acetate tetrahydrate were dissolved in 62.97g deionized water to obtain solution C. Mix solution B with solution C, then pour the mixture into solution A. Add 2.0 g of ascorbic acid for stabilization, adjust the pH to 3.0, and stir at room temperature to obtain a clear glass sol.

[0026] Preparation of glass gel-coated copper powder: The pretreated copper powder was dissolved in 500 mL of ethanol to obtain a copper powder ethanol suspension. The glass sol and the pretreated copper powder ethanol suspension were mixed and heated to 60°C and stirred for 3 hours. After sealing, the mixture was aged at room temperature for 12 hours. Then, it was dried at 60°C in a nitrogen atmosphere until the solvent was completely evaporated to obtain dry glass gel-coated copper powder.

[0027] Heat treatment: Glass gel-coated copper powder is heated at 250°C for 1 hour in N2 atmosphere, and then calcined at 600°C for 2 hours to obtain glass-coated copper powder.

[0028] (2) Preparation of copper conductive paste: Preparation of glass powder: According to the corresponding chemical raw materials in organic phase formula 001 in Table 1, the following ingredients were calculated and weighed: silicon dioxide 3.10g, boric acid 53.64g, zinc oxide 15.40g, aluminum oxide 5.8g, barium carbonate 47.23g, calcium carbonate 4.82g, copper oxide 1.40g, sodium carbonate 4.10g, and cobalt oxide 2.30g. The raw materials were mixed evenly and kept at 1300℃ for 0.5h. The molten glass was then water-quenched, ball-milled, and dried to obtain glass powder with a particle size D50 of 1.5μm.

[0029] Organic carrier preparation: Weigh 65g of terpineol, 25g of acrylic resin, and 10g of dispersant BYK111, mix them, stir and heat to 60℃, and keep warm for 4h.

[0030] Preparation of copper conductive paste: Weigh 71g of the above-mentioned glass-coated copper powder, 4g of glass powder, 5g of sintering aid, and 20g of organic carrier, mix them evenly, and then disperse them 8 times in a three-roll mill. The fineness reaches 6μm. Filter through a 300-mesh filter to prepare copper paste. After sintering at 680℃ for MLCC end capping, the density of the ends is tested using a scanning electron microscope (test results are shown in the figure). Figure 3 (As shown).

[0031] Examples 2-6 The oxide composition and glass powder composition of the final glass component in the glass-coated copper powder glass coating layer were replaced with glass phase formulations 002-006 in Table 1. In the glass sol, potassium acetate was used as the potassium oxide precursor, lithium acetate as the lithium oxide precursor, and ethoxyferric as the iron oxide precursor; lithium acetate was used as the lithium oxide in the glass powder raw material. Everything else remained the same as in Example 1.

[0032] Examples 7-11 The oxide composition of the final glass component in the glass coating layer of the copper conductive slurry coated with copper powder was replaced with glass phase formulations 002-006 in Table 1, wherein the potassium oxide precursor in the glass sol was potassium acetate, the lithium oxide precursor was lithium acetate, and the iron oxide precursor was ethoxyferric. Everything else was the same as in Example 1.

[0033] The beneficial effects of this invention are as follows: (1) By designing the glass composition, the sintering temperature of the glass is matched with that of copper powder, thereby improving the sintering density and conductivity.

[0034] Copper-coated glass prepared by the sol-gel method increases the specific surface area of ​​the glass, thereby improving the sintering activity of the glass phase. The formation of a glass melt at a relatively low temperature enhances sintering activity. The large contact area between the glass melt and the copper powder allows it to wet and penetrate along the copper particle boundaries. As this penetration progresses, the initially coarse copper powder particles break down into several smaller particles, increasing the specific surface energy of the copper powder, improving its sintering activity, lowering the sintering temperature, and increasing the sintering density.

[0035] Specifically, through Figure 2 and Figure 4 As can be seen from the comparison, the MLCC end-cap particles obtained through this application are uniform and dense; in comparison, Figure 4 In existing MLCC technologies, the end-cap particles are coarse and lack sufficient dispersibility. Similarly, in Figure 3 In the SEM images of this application, the particles appear to be relatively uniformly dispersed in a liquid state, while... Figure 5 In this process, the particles do not form a distribution similar to that of a solution, resulting in a larger particle size on the surface and a rough surface structure.

[0036] Overall, as illustrated by the images, the MLCC end electrode fabricated according to this invention exhibits significantly improved densification during low-temperature sintering, which is attributed to the technological improvement in the use of glass-coated copper powder.

[0037] (2) The glass phase in the copper conductive paste comes from two parts: one part is the glass coating layer of glass-coated copper powder prepared by the sol-gel method, and the other part is the added glass powder. The two glass phases can have the same composition or different composition. The material properties (working range) of the glass are improved by designing the difference in softening point.

[0038] (3) Add sintering aids and add copper powder with small particle size (50nm~500nm). Due to the large curvature and high specific surface energy of the sintering aids, the sintering activity is high. It preferentially forms a solid solution with the glass powder, which improves the wettability of the glass liquid relative to the copper powder. Under the capillary pressure of the liquid phase, it accelerates the mass transfer rate of copper powder in solid-liquid sintering and reduces the sintering temperature.

[0039] This technology can be applied to the preparation of high-temperature sintering conductive silver paste and conductive nickel paste. In addition to MLCC, it can also be used for LTCC.

[0040] The present invention is characterized by the application of multi-component glass-coated copper powder in copper conductive paste. Small-particle-size copper powder is added as a sintering aid. The glass phase of the copper conductive paste consists of a glass coating layer of glass-coated copper powder and the added glass powder.

[0041] Table 1. Composition of the glass phase (based on oxides) Glass phase number <![CDATA[SiO2]]> <![CDATA[B2O3]]> <![CDATA[ZnO2]]> <![CDATA[Al2O3]]> BaO CaO CuO <![CDATA[Na2O]]> <![CDATA[K2O]]> <![CDATA[Li2O]]> <![CDATA[Fe2O3]]> CoO 001 3.1 30.2 15.4 5.8 36.7 2.7 1.4 2.4 0.0 0.0 0.0 2.3 002 10.4 40.7 40.7 0.6 0.0 0.0 0.0 2.6 5.0 0.0 0.0 0.0 003 6.4 25.7 20.1 0.5 40.5 0.0 0.0 5.5 0.8 0.5 0.0 0.0 004 7.8 35.2 40.7 0.8 0.0 3.6 0.0 3.4 8.5 0.0 0.0 0.0 005 8.2 37.2 32.0 0.8 0.0 3.8 5.4 3.6 9.0 0.0 0.0 0.0 006 8.2 37.1 21.9 0.8 10.0 3.8 5.4 3.6 9.0 0.0 0.2 0.0

Claims

1. A glass-coated copper powder, characterized in that, The core is copper powder, and the coating layer is a glass coating layer; the mass of the glass coating layer accounts for 1% to 10% of the mass of the copper powder; the glass coating layer is formed by preparing a solution based on an oxide precursor to form a glass sol, and the glass sol is aged and dried to form a glass gel, and the glass gel is heat-treated to finally form the glass coating layer.

2. The glass-coated copper powder according to claim 1, characterized in that, The glass cladding layer comprises the following components: SiO2, B2O3, ZnO2, Al2O3, Na2O, BaO, CaO, CuO, K2O, Li2O, CoO, and Fe2O3. The mass percentages of each component are as follows: SiO2 2%-16%, B2O3 15%-45%, ZnO2 10%-60%, Al2O3 0%-10%, Na2O 0%-10%, BaO 0%-50%, CaO 0%-10%, CuO 0%-10%, K2O 0%-10%, Li2O 0%-5%, CoO 0%-5%, and Fe2O3 0%-5%.

3. The method for preparing glass-coated copper powder according to claim 1 or 2, characterized in that, First, copper powder is pretreated, then glass sol is prepared, and then the glass sol is coated on the surface of copper powder for aging and drying to obtain glass gel coated copper powder. Finally, the glass gel coated copper powder is heat-treated to obtain glass coated copper powder with uniform surface coating.

4. The method for processing glass-coated copper powder according to claim 3, characterized in that, Includes the following steps: Step 1: Copper powder pretreatment: Prepare a dilute sulfuric acid or citric acid solution, add the copper powder to the prepared acid solution, heat and stir under a nitrogen atmosphere, wash with anhydrous ethanol or acetone, and then vacuum dry. Step 2: Glass sol preparation: Calculate the corresponding precursor mass ratio according to the mass of the oxides, weigh the corresponding precursor raw materials, dissolve the silica precursor in ethanol, then add deionized water, and hydrolyze it with electromagnetic stirring at room temperature to obtain a clear silica precursor pre-hydrolyzed solution A; add the boron oxide precursor to ethanol, and then mix to obtain a clear solution B; add the other oxide precursors (excluding silica and boron oxide) to deionized water, and mix to obtain solution C; mix solution B and solution C, adjust to a clear and transparent solution with deionized water, and then pour it into solution A; add citric acid or ascorbic acid for stability, adjust the pH to 2-7, and stir at room temperature to obtain a clear glass sol; Step 3: Coating copper powder with glass gel: Weigh an appropriate amount of pretreated copper powder according to the final glass layer mass being 1% to 10% of the copper powder mass, add ethanol to obtain copper powder ethanol suspension, mix the glass sol and the pretreated copper powder ethanol suspension, heat and stir until uniform, seal and age at room temperature for several hours, then dry in a vacuum or nitrogen atmosphere until the solvent is completely evaporated to obtain dry glass gel coated copper powder; Step 4: Heat treatment: The glass gel-coated copper powder is calcined in a N2 atmosphere in stages. After reaching the first stage temperature, it is held at that temperature for a certain period of time, and then the temperature is raised to the second stage temperature and held at that temperature for a certain period of time to obtain glass-coated copper powder.

5. The method for processing glass-coated copper powder according to claim 4, characterized in that, In step 1: the mass concentration of the dilute sulfuric acid is 0.1%–0.5%; the mass concentration of the citric acid solution is 1%–10%; the copper powder is spherical copper or sheet copper with a particle size of 0.5μm–10μm; the mass of the copper powder and the volume of the dilute sulfuric acid or citric acid solution are (10–50)g:100ml; the heating and stirring are carried out under a nitrogen atmosphere at a temperature of 40℃–80℃ for 10min–60min; the drying temperature is 30℃–60℃ for 1h–4h. In step 2: the precursor of silicon oxide includes any or a combination of the following substances: alkoxysilane Si(OR)4; the precursor of boron oxide includes any or a combination of the following substances: boric acid, alkoxyboron B(OR)3, alkylborane R3B, organoboroxane -B(R)-OB(R)-O-; the precursor of zinc oxide includes any or a combination of the following substances: alkoxyzinc Zn(OR)2, zinc acetate, zinc acetate dihydrate, zinc nitrate, zinc nitrate hexahydrate, and zinc-based MOF; the precursor of aluminum oxide includes any or a combination of the following substances: alkoxyaluminum. Al(OR)3, aluminum nitrate, aluminum nitrate nonahydrate, aluminum sulfate, aluminum sulfate octadecahydrate; Barium oxide precursors include any or a combination of the following substances: barium alkoxyba(OR)2, barium citrate, barium acetate; Calcium oxide precursors include any or a combination of the following substances: calcium alkoxyca(OR)2, calcium alginate, calcium oxalate, calcium acetate, calcium acetate monohydrate, calcium isopropoxide; Sodium oxide precursors include any or a combination of the following substances: sodium alkoxyna(OR), sodium acetate, sodium acetate trihydrate, sodium oxalate, sodium citrate, sodium stearate. Precursors for potassium oxide include any or a combination of the following substances: potassium alkoxykine (K(OR)), potassium acetate, potassium oxalate, potassium citrate, potassium stearate; precursors for lithium oxide include any or a combination of the following substances: lithium alkoxykine (Li(OR)), lithium acetate, lithium oxalate, lithium citrate; precursors for copper oxide include any or a combination of the following substances: copper alkoxykine (Cu(OR)2), copper citrate, copper carboxylate; copper carboxylate includes any or a combination of the following substances: copper oxalate, copper acetate, copper stearate; precursors for iron oxide include any or a combination of the following substances: Alkoxy iron Fe(OR)3, iron nitrate, iron-based MOF; precursors of cobalt oxide include any or a combination of the following substances: alkoxy cobalt Co(OR)2, cobalt acetate, cobalt acetate tetrahydrate, cobalt nitrate, cobalt nitrate hexahydrate, cobalt-based MOF; R refers to alkyl or aromatic group, alkyl is preferably methyl (-CH3), ethyl (-CH2CH3), isopropyl (-CH2(CH3)2), OR refers to alkoxy, preferably methoxy (-OCH3), ethoxy (-OCH2CH3), propoxy (-OCH2CH2CH3); In step 2: the molar ratio of silica precursor to ethanol in solution A is 1:5-20; the molar ratio of silica precursor to deionized water in solution A is 1:2-10; the molar ratio of boron oxide precursor to ethanol in solution B is 1:10-30; and the total mass of other precursors in solution C is 1g:(8-15)ml of deionized water. In step 3: the mass ratio of copper powder to ethanol is (10-20) g: 100 ml; the heating temperature is 30℃-70℃, and the stirring time is 1h-3h; the vacuum or nitrogen atmosphere drying temperature is 40℃-80℃; and the aging time is 4h-36h. In step 4: the temperature of the first stage is 200℃~400℃, and the holding time is 0.5h~4h; the temperature of the second stage is 500℃~700℃, and the holding time is 1h~4h.

6. A copper conductive paste for the terminal electrodes of a multilayer ceramic capacitor, characterized in that, It comprises 70-80% glass-coated copper powder, 2-10% glass powder, 15-25% organic carrier, and 0-20% sintering aid; the glass-coated copper powder is the glass-coated copper powder as described in claim 1 or 2.

7. The copper conductive paste for the terminal electrodes of a multilayer ceramic capacitor according to claim 6, characterized in that, The preparation method of the organic carrier includes: weighing and mixing the corresponding raw materials in proportion, and stirring at 40℃~60℃ for 4h~6h; the components and their mass percentages include: organic solvent 60~80%, resin 4~30%, and dispersant 5~20%; The organic solvent is one or a mixture of the following reagents: diethylene glycol butyl ether, terpineol, hydrogenated terpineol, dodecyl alcohol ester, and diethylene glycol butyl ether acetate. The resin is an acrylic resin with a number average molecular weight of 200,000 to 600,000; for example, the MR200IBM acrylic resin manufactured by Zongyan Chemical. The dispersant is one or a mixture of the following reagents: phosphate ester, polyether phosphate ester, polyether acid, polyether ester acid amine salt, preferably phosphate ester, and more preferably BYK111; The sintering aid is spherical copper with a diameter of 50 nm to 500 nm. During the sintering process, it preferentially diffuses into the liquid glass at 500°C to 600°C to form a solid solution with the glass. In the solid-liquid sintering process, it adjusts and controls the surface tension of the liquid phase and the wettability of the copper powder, improves the diffusion rate of copper powder particles in the glass melt, and adjusts the sintering density. The glass-coated copper powder has a large specific surface area, which can improve sintering activity. It forms a liquid phase at a lower temperature. Due to the large contact area with the copper powder, it will wet and penetrate along the copper particle boundaries. As this penetration progresses, the originally relatively large copper powder particles break down into several smaller particles, thereby increasing the specific surface energy of the copper powder, improving the sintering activity of the copper powder, and reducing the sintering temperature. The preparation method of the glass powder includes: selecting appropriate chemical raw materials, calculating and weighing the ingredients, mixing the raw materials evenly, keeping them at 1200℃~1400℃ for 0.5h~2h, naturally cooling and crushing or water quenching the molten glass, ball milling, and drying to obtain powder with a particle size of 0.5μm~10μm.

8. The method for preparing copper conductive paste for the terminal electrodes of a multilayer ceramic capacitor according to claim 7, characterized in that, Includes the following steps: Copper-coated glass powder, glass powder, sintering aid, and organic phase are mixed in proportion using a planetary mixer and then dispersed using a three-roll mill; or dispersed using a high-pressure homogenizer; to prepare a copper conductive paste.

9. A method for fabricating a copper electrode on the end face of an MLCC, characterized in that, Immerse the beveled end face of the MLCC in the copper conductive paste prepared by any one of the methods in 6 to 8 above, and dry it; put the dried sample into an N2 atmosphere furnace and heat it to the heat treatment temperature, and hold it at that temperature; then continue to heat it to the sintering temperature and hold it at that temperature; after sintering, let it cool down naturally.

10. The method for preparing the copper electrode at the end face of an MLCC according to claim 9, characterized in that, The drying temperature is 80℃~120℃, and the time is 30~120min; The heat treatment temperature is 400℃~500℃, the holding time is 20min~60min, and the heating rate is 10℃ / min~30℃ / min; The sintering temperature is 600℃~780℃, the holding time is 20min~60min, and the heating rate is 10℃ / min~30℃ / min; The copper electrode prepared according to the above scheme has a sheet resistance of less than 4 mΩ / □ (10 μm), or as low as 2.75 mΩ / □ (10 μm).

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