A copper paste for internal electrodes in low-temperature co-fired ceramics and its preparation method

Abstract

This invention relates to an internal electrode copper paste for low-temperature co-fired ceramics and its preparation method, belonging to the technical field of internal electrode copper paste. The invention creatively involves first acid-washing copper powder, then surface-coating the acid-washed copper powder with calcium / silver co-doped silica using a sol-gel method to obtain a pretreated copper powder. Next, using silica, boron trioxide, barium oxide, aluminum oxide, titanium oxide, and lanthanum oxide as raw materials, an inorganic binder is prepared using a melt-water quenching method. This binder, along with a conventional organic carrier, is then simply physically blended to obtain an internal electrode copper paste, which is highly suitable for application in low-temperature co-fired ceramics. This effectively reduces copper powder oxidation, improves co-firing compatibility with the substrate, and enhances conductivity.

Description

Technical Field

[0001] This invention belongs to the field of internal electrode copper paste technology, specifically relating to an internal electrode copper paste for low-temperature co-fired ceramics and its preparation method. Background Technology

[0002] Low-temperature co-fired ceramics is a technology that co-fires multilayer ceramic green sheets at relatively low temperatures to form multilayer ceramic substrates. Due to its advantages such as high integration and strong compatibility, it is widely used in the fields of communication and electronics. Currently, most of the copper pastes used for internal electrodes in low-temperature co-fired ceramics are prepared using copper powder, inorganic binders, and organic carriers as raw materials. Although copper powder has better high-frequency characteristics and conductivity than gold and smaller migration defects than silver, the small particle size and large specific surface area of ​​copper powder make it very easy to oxidize. This leads to poor co-firing compatibility between the final internal electrode copper paste and the substrate, and a decrease in conductivity. Summary of the Invention

[0003] To address the problems existing in the prior art, the present invention aims to provide an internal electrode copper paste for low-temperature co-fired ceramics and its preparation method. The invention creatively involves first acid-washing copper powder, then surface-coating the acid-washed copper powder with calcium / silver co-doped silica using a sol-gel method to obtain a pretreated copper powder. Next, using silica, boron trioxide, barium oxide, aluminum oxide, titanium oxide, and lanthanum oxide as raw materials, an inorganic binder is prepared using a melt-water quenching method. This binder, along with a conventional organic carrier, is then simply physically blended to obtain an internal electrode copper paste, which is highly suitable for application in low-temperature co-fired ceramics. This effectively reduces copper powder oxidation, improves co-firing compatibility with the substrate, and enhances conductivity.

[0004] The objective of this invention can be achieved through the following technical solutions:

[0005] An internal electrode copper paste for low-temperature co-fired ceramics, wherein the internal electrode copper paste is prepared from pretreated copper powder, inorganic binder and organic carrier; the mass ratio of the pretreated copper powder, the inorganic binder and the organic carrier is 70-80:5-7:20.

[0006] As a preferred embodiment of the present invention, the pretreated copper powder is prepared through the following steps:

[0007] (1) Add 10-15 parts by weight of copper powder to 100 parts by weight of dilute hydrochloric acid solution, then stir at room temperature for 15-20 min to mix, filter, take the filter residue, add 80-100 parts by weight of acetone, then stir at 50-60℃ for 15-30 min to mix, filter, remove the filtrate, and finally vacuum dry at 60-70℃ until constant weight to obtain component A;

[0008] (2) Add 0.1-0.3 parts by weight of deionized water, 0.8-1 parts by weight of tetraethyl orthosilicate and 1 part by weight of ammonia to 70-80 parts by weight of anhydrous ethanol, then stir at 30-40℃ for 45-60 min to mix, keep warm, then add 0.05 parts by weight of calcium nitrate and 0.05-0.08 parts by weight of silver nitrate, and continue stirring for 20-30 min to mix to obtain component B;

[0009] (3) Add 15-20 parts by weight of anhydrous ethanol and 3 parts by weight of component A to component B, then stir at 60-65℃ for 6-8 hours to mix, dry, and calcine to complete the preparation.

[0010] Furthermore, the mass fraction of the dilute hydrochloric acid solution in step (1) is 5-7%.

[0011] Furthermore, the mass fraction of the ammonia solution in step (2) is 25%.

[0012] Furthermore, the drying in step (3) refers to vacuum drying at 80-90℃ for 2 hours.

[0013] Further, the calcination in step (3) refers to heating to 380°C at a heating rate of 8-10°C / min under a nitrogen atmosphere and then calcining for 1-2 hours.

[0014] As a preferred embodiment of the present invention, the inorganic binder is prepared by the following steps:

[0015] Silicon dioxide, boron trioxide, barium oxide, aluminum oxide, titanium oxide, and lanthanum oxide are mixed in a mass ratio of 25-30:15-20:10:15-20:3-4:2. The mixture is then heated to 1500-1600℃ at a heating rate of 10-15℃ / min and held at that temperature for 20-30 min. After water quenching, the mixture is vacuum dried at 30-40℃ until constant weight is achieved. Finally, the mixture is ground to complete the preparation.

[0016] Furthermore, the grinding refers to grinding to a particle size of 1.5-1.8 μm.

[0017] As a preferred embodiment of the present invention, the organic carrier is prepared by the following steps:

[0018] Add 2 parts by weight of thickener to 25-30 parts by weight of solvent, then stir at 90-95℃ until completely dissolved, let it cool naturally to room temperature, then add 1 part by weight of surfactant and 1.5-2 parts by weight of dispersant, continue stirring for 8-10 hours to mix, and finally let it stand naturally for 20-24 hours to complete the preparation.

[0019] Furthermore, the solvent is at least one of terpineol and butylcarbidol.

[0020] Furthermore, the thickener is ethyl cellulose.

[0021] Furthermore, the surfactant is polyethylene glycol 400.

[0022] Further, the dispersant is dibutyl phthalate and castor oil; the mass ratio of dibutyl phthalate to castor oil is 2:1-1.5.

[0023] A method for preparing internal electrode copper paste for low-temperature co-fired ceramics, the method comprising the following steps:

[0024] The pretreated copper powder, inorganic binder, and organic carrier are mixed by stirring at 300-500 rpm for 5-10 minutes at room temperature, and the preparation is complete.

[0025] The beneficial effects of this invention are:

[0026] (1) This invention creatively pickles copper powder first, and then coats the pickled copper powder with calcium / silver co-doped silicon dioxide based on the sol-gel method to obtain a pretreated copper powder. Then, using silicon dioxide, boron trioxide, barium oxide, aluminum oxide, titanium oxide and lanthanum oxide as raw materials, an inorganic binder is prepared based on the melt-water quenching method. After simple physical mixing of the two with conventional organic carriers, an internal electrode copper paste is obtained, which is very suitable for application in low-temperature co-fired ceramics. It effectively reduces the oxidation of copper powder, improves the co-firing compatibility with the substrate, and enhances the conductivity.

[0027] (2) In view of the problem of easy oxidation of copper powder, the present invention creatively uses the sol-gel method to coat the surface of the acid-washed copper powder with calcium / silver co-doped silica. On the one hand, silica can play a good role as a protective layer, thereby reducing the oxidation of copper powder, improving the co-firing compatibility between the subsequently prepared internal electrode copper paste and the substrate, and enhancing the conductivity. On the other hand, after calcium / silver co-doping, the generated silica has fewer micropores, further reducing the contact probability between copper powder and oxygen, and better playing the role of the protective layer. In addition, since the main function of inorganic binder is to provide adhesion and make the internal electrode copper paste and the substrate firmly bonded, the present invention also creatively designs the formulation of inorganic binder by synergistically compounding six different metal oxides, namely silica, boron trioxide, barium oxide, aluminum oxide, titanium oxide and lanthanum oxide, to further obtain a better co-firing effect and promote conductivity. Detailed Implementation

[0028] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with embodiments, is provided below.

[0029] In all embodiments and comparative examples of this invention, the copper powder was purchased from Zhejiang Manli Nanotechnology Co., Ltd., model number ML-Cu-W02; and the ethyl cellulose was purchased from Chengdu Kelong Chemical Co., Ltd., grade AR, in powder form.

[0030] Example 1

[0031] An internal electrode copper paste for low-temperature co-fired ceramics, wherein the internal electrode copper paste is prepared from pretreated copper powder, inorganic binder and organic carrier; the mass ratio of the pretreated copper powder, the inorganic binder and the organic carrier is 70:5:20.

[0032] The pretreated copper powder is prepared through the following steps:

[0033] (1) Add 10 parts by weight of copper powder to 100 parts by weight of dilute hydrochloric acid solution, then stir and mix at room temperature for 15 minutes, filter, take the filter residue, add 80 parts by weight of acetone, then stir and mix at 50°C for 15 minutes, filter, remove the filtrate, and finally vacuum dry at 60°C until constant weight to obtain component A.

[0034] (2) Add 0.1 parts by weight of deionized water, 0.8 parts by weight of tetraethyl orthosilicate and 1 part by weight of ammonia to 70 parts by weight of anhydrous ethanol, then stir at 30°C for 45 min to mix, keep warm, then add 0.05 parts by weight of calcium nitrate and 0.05 parts by weight of silver nitrate, and continue stirring for 20 min to mix to obtain component B.

[0035] (3) Add 15 parts by weight of anhydrous ethanol and 3 parts by weight of component A to component B, then stir at 60°C for 6 hours to mix, dry, and calcine to complete the preparation.

[0036] The mass fraction of the dilute hydrochloric acid solution in step (1) is 5%.

[0037] The ammonia solution in step (2) has a mass fraction of 25%.

[0038] The drying in step (3) refers to vacuum drying at 80°C for 2 hours.

[0039] The calcination in step (3) refers to heating to 380°C at a heating rate of 8°C / min under a nitrogen atmosphere and then calcining for 1 hour.

[0040] The inorganic binder is prepared by the following steps:

[0041] Silicon dioxide, boron trioxide, barium oxide, aluminum oxide, titanium oxide, and lanthanum oxide were mixed in a mass ratio of 25:15:10:15:3:2. The mixture was then heated to 1500℃ at a heating rate of 10℃ / min and held at that temperature for 20 min. After water quenching, the mixture was vacuum dried at 30℃ until constant weight was achieved. Finally, the mixture was ground to complete the preparation.

[0042] The grinding refers to grinding to a particle size of 1.5 μm.

[0043] The organic carrier is prepared through the following steps:

[0044] Add 2 parts by weight of thickener to 25 parts by weight of solvent, then stir at 90°C until completely dissolved, and allow to cool naturally to room temperature. Next, add 1 part by weight of surfactant and 1.5 parts by weight of dispersant, continue stirring for 8 hours to mix, and finally let stand naturally for 20 hours to complete the preparation.

[0045] The solvent is terpineol.

[0046] The thickener is ethyl cellulose.

[0047] The surfactant is polyethylene glycol 400.

[0048] The dispersant is dibutyl phthalate and castor oil; the mass ratio of dibutyl phthalate to castor oil is 2:1.

[0049] A method for preparing internal electrode copper paste for low-temperature co-fired ceramics, the method comprising the following steps:

[0050] The pretreated copper powder, inorganic binder, and organic carrier are mixed by stirring at 300 rpm for 5 minutes at room temperature, thus completing the preparation.

[0051] Example 2

[0052] An internal electrode copper paste for low-temperature co-fired ceramics, wherein the internal electrode copper paste is prepared from pretreated copper powder, inorganic binder and organic carrier; the mass ratio of the pretreated copper powder, the inorganic binder and the organic carrier is 80:7:20.

[0053] The pretreated copper powder is prepared through the following steps:

[0054] (1) Add 15 parts by weight of copper powder to 100 parts by weight of dilute hydrochloric acid solution, then stir and mix at room temperature for 20 minutes, filter, take the filter residue, add 100 parts by weight of acetone, then stir and mix at 60°C for 30 minutes, filter, remove the filtrate, and finally vacuum dry at 70°C until constant weight to obtain component A.

[0055] (2) Add 0.3 parts by weight of deionized water, 1 part by weight of tetraethyl orthosilicate and 1 part by weight of ammonia to 80 parts by weight of anhydrous ethanol, then stir at 40°C for 60 min to mix, keep warm, then add 0.05 parts by weight of calcium nitrate and 0.08 parts by weight of silver nitrate, and continue stirring for 30 min to mix to obtain component B.

[0056] (3) Add 20 parts by weight of anhydrous ethanol and 3 parts by weight of component A to component B, then stir at 65°C for 8 hours to mix, dry and calcine to complete the preparation.

[0057] The mass fraction of the dilute hydrochloric acid solution in step (1) is 7%.

[0058] The ammonia solution in step (2) has a mass fraction of 25%.

[0059] The drying in step (3) refers to vacuum drying at 90°C for 2 hours.

[0060] The calcination in step (3) refers to heating to 380°C at a heating rate of 10°C / min under a nitrogen atmosphere and then calcining for 2 hours.

[0061] The inorganic binder is prepared by the following steps:

[0062] Silicon dioxide, boron trioxide, barium oxide, aluminum oxide, titanium oxide, and lanthanum oxide were mixed in a mass ratio of 30:20:10:20:4:2. The mixture was then heated to 1600℃ at a heating rate of 15℃ / min and held at that temperature for 30 min. After water quenching, the mixture was vacuum dried at 40℃ until constant weight was achieved. Finally, the mixture was ground to complete the preparation.

[0063] The grinding refers to grinding to a particle size of 1.8 μm.

[0064] The organic carrier is prepared through the following steps:

[0065] Add 2 parts by weight of thickener to 30 parts by weight of solvent, then stir at 95°C until completely dissolved, let cool naturally to room temperature, then add 1 part by weight of surfactant and 2 parts by weight of dispersant, continue stirring for 10 hours to mix, and finally let stand naturally for 24 hours to complete the preparation.

[0066] The solvent is terpineol.

[0067] The thickener is ethyl cellulose.

[0068] The surfactant is polyethylene glycol 400.

[0069] The dispersant is dibutyl phthalate and castor oil; the mass ratio of dibutyl phthalate to castor oil is 2:1.5.

[0070] A method for preparing internal electrode copper paste for low-temperature co-fired ceramics, the method comprising the following steps:

[0071] The pretreated copper powder, inorganic binder, and organic carrier are mixed by stirring at 500 rpm for 10 minutes at room temperature, and the preparation is complete.

[0072] Example 3

[0073] An internal electrode copper paste for low-temperature co-fired ceramics, wherein the internal electrode copper paste is prepared from pretreated copper powder, inorganic binder and organic carrier; the mass ratio of the pretreated copper powder, the inorganic binder and the organic carrier is 75:6:20.

[0074] The pretreated copper powder is prepared through the following steps:

[0075] (1) Add 13 parts by weight of copper powder to 100 parts by weight of dilute hydrochloric acid solution, then stir and mix at room temperature for 18 minutes, filter, take the residue, add 90 parts by weight of acetone, then stir and mix at 55°C for 20 minutes, filter, remove the filtrate, and finally vacuum dry at 65°C until constant weight to obtain component A.

[0076] (2) Add 0.2 parts by weight of deionized water, 0.9 parts by weight of tetraethyl orthosilicate and 1 part by weight of ammonia to 75 parts by weight of anhydrous ethanol, then stir at 35°C for 50 min to mix, keep warm, then add 0.05 parts by weight of calcium nitrate and 0.07 parts by weight of silver nitrate, and continue stirring for 25 min to mix to obtain component B.

[0077] (3) Add 18 parts by weight of anhydrous ethanol and 3 parts by weight of component A to component B, then stir at 63°C for 7 hours to mix, dry and calcine to complete the preparation.

[0078] The mass fraction of the dilute hydrochloric acid solution in step (1) is 6%.

[0079] The ammonia solution in step (2) has a mass fraction of 25%.

[0080] The drying in step (3) refers to vacuum drying at 85°C for 2 hours.

[0081] The calcination in step (3) refers to heating to 380°C at a heating rate of 9°C / min under a nitrogen atmosphere and then calcining for 1.5 hours.

[0082] The inorganic binder is prepared by the following steps:

[0083] Silicon dioxide, boron trioxide, barium oxide, aluminum oxide, titanium oxide, and lanthanum oxide were mixed in a mass ratio of 28:17:10:18:3.5:2. The mixture was then heated to 1550°C at a heating rate of 13°C / min and held at that temperature for 25 min. After water quenching, the mixture was vacuum dried at 35°C until constant weight was achieved. Finally, the mixture was ground to complete the preparation.

[0084] The grinding refers to grinding to a particle size of 1.7 μm.

[0085] The organic carrier is prepared through the following steps:

[0086] Add 2 parts by weight of thickener to 28 parts by weight of solvent, then stir at 93°C until completely dissolved, and allow to cool naturally to room temperature. Next, add 1 part by weight of surfactant and 1.7 parts by weight of dispersant, continue stirring for 9 hours to mix, and finally allow to stand naturally for 23 hours to complete the preparation.

[0087] The solvent is terpineol.

[0088] The thickener is ethyl cellulose.

[0089] The surfactant is polyethylene glycol 400.

[0090] The dispersant is dibutyl phthalate and castor oil; the mass ratio of dibutyl phthalate to castor oil is 2:1.3.

[0091] A method for preparing internal electrode copper paste for low-temperature co-fired ceramics, the method comprising the following steps:

[0092] The pretreated copper powder, inorganic binder, and organic carrier are mixed by stirring at 400 rpm for 8 minutes at room temperature, thus completing the preparation.

[0093] Comparative Example 1

[0094] Based on Example 3, calcium nitrate was replaced with an equal weight of silver nitrate, while all other aspects remained unchanged.

[0095] Comparative Example 2

[0096] Based on Example 3, silver nitrate was replaced with an equal weight of calcium nitrate, while all other aspects remained unchanged.

[0097] Comparative Example 3

[0098] Based on Example 3, silver nitrate and calcium nitrate were replaced with an equal weight of anhydrous ethanol, while the rest remained unchanged.

[0099] Comparative Example 4

[0100] Based on Example 3, steps (2) and (3) are omitted, and the rest remain unchanged.

[0101] Comparative Example 5

[0102] Based on Example 3, titanium oxide was not added during the preparation of the inorganic binder, while all other aspects remained unchanged.

[0103] Comparative Example 6

[0104] Based on Example 3, lanthanum oxide was not added during the preparation of the inorganic binder, while all other processes remained unchanged.

[0105] Test Example 1

[0106] Conductivity test:

[0107] The internal electrode copper pastes prepared in Example 3 and Comparative Examples 1-6 were screen-printed onto LTCC substrates (purchased from the 43rd Research Institute of China Electronics Technology Group Corporation) to form copper films of 10mm*10mm in size. They were then dried at 90°C for 45 minutes, then heated to 400°C at a rate of 10°C / min in air and held for 1 hour. Finally, they were heated to 900°C at a rate of 10°C / min in nitrogen and held for 1 hour. After natural cooling to room temperature, sintered copper films with a thickness of 8μm were obtained. The sheet resistance of the sintered copper films was measured using a four-probe sheet resistance meter and rounded to one decimal place.

[0108] Table 1. Conductivity test results

[0109] Shear resistance / mΩ / □ Example 3 3.1 Comparative Example 1 3.6 Comparative Example 2 3.7 Comparative Example 3 4.0 Comparative Example 4 4.4 Comparative Example 5 3.6 Comparative Example 6 3.9

[0110] As can be seen from the comparison of Test Example 1, Example 3 and Comparative Examples 1-6, the internal electrode copper paste prepared by the present invention is very suitable for application in low-temperature co-fired ceramics, effectively reducing the oxidation of copper powder, improving the co-firing compatibility with the substrate, and enhancing the conductivity.

[0111] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A copper paste for internal electrodes in low-temperature co-fired ceramics, characterized in that: The internal electrode copper paste is prepared from pretreated copper powder, inorganic binder and organic carrier; the mass ratio of the pretreated copper powder, the inorganic binder and the organic carrier is 70-80:5-7:

20. The pretreated copper powder is prepared through the following steps: (1) Add 10-15 parts by weight of copper powder to 100 parts by weight of dilute hydrochloric acid solution, then stir at room temperature for 15-20 min to mix, filter, take the filter residue, add 80-100 parts by weight of acetone, then stir at 50-60℃ for 15-30 min to mix, filter, remove the filtrate, and finally vacuum dry at 60-70℃ until constant weight to obtain component A; (2) Add 0.1-0.3 parts by weight of deionized water, 0.8-1 parts by weight of tetraethyl orthosilicate and 1 part by weight of ammonia to 70-80 parts by weight of anhydrous ethanol, then stir at 30-40℃ for 45-60 min to mix, keep warm, then add 0.05 parts by weight of calcium nitrate and 0.05-0.08 parts by weight of silver nitrate, and continue stirring for 20-30 min to mix to obtain component B; (3) Add 15-20 parts by weight of anhydrous ethanol and 3 parts by weight of component A to component B, then stir at 60-65℃ for 6-8 hours to mix, dry, and calcine to complete the preparation. The inorganic binder is prepared by the following steps: Silicon dioxide, boron trioxide, barium oxide, aluminum oxide, titanium oxide, and lanthanum oxide are mixed in a mass ratio of 25-30:15-20:10:15-20:3-4:

2. The mixture is then heated to 1500-1600℃ at a heating rate of 10-15℃ / min and held at that temperature for 20-30 min. After water quenching, the mixture is vacuum dried at 30-40℃ until constant weight is achieved. Finally, the mixture is ground to complete the preparation.

2. The internal electrode copper paste for low-temperature co-fired ceramics according to claim 1, characterized in that: The mass fraction of the dilute hydrochloric acid solution in step (1) is 5-7%.

3. The internal electrode copper paste for low-temperature co-fired ceramics according to claim 1, characterized in that: The ammonia solution in step (2) has a mass fraction of 25%.

4. The internal electrode copper paste for low-temperature co-fired ceramics according to claim 1, characterized in that: The drying in step (3) refers to vacuum drying at 80-90℃ for 2 hours.

5. The internal electrode copper paste for low-temperature co-fired ceramics according to claim 1, characterized in that: The calcination in step (3) refers to heating to 380°C at a heating rate of 8-10°C / min under a nitrogen atmosphere and then calcining for 1-2 hours.

6. The internal electrode copper paste for low-temperature co-fired ceramics according to claim 1, characterized in that: The grinding refers to grinding to a particle size of 1.5-1.8 μm.

7. The internal electrode copper paste for low-temperature co-fired ceramics according to claim 1, characterized in that: The organic carrier is prepared through the following steps: Add 2 parts by weight of thickener to 25-30 parts by weight of solvent, then stir at 90-95℃ until completely dissolved, let it cool naturally to room temperature, then add 1 part by weight of surfactant and 1.5-2 parts by weight of dispersant, continue stirring for 8-10 hours to mix, and finally let it stand naturally for 20-24 hours to complete the preparation.

8. A method for preparing internal electrode copper paste for low-temperature co-fired ceramics as described in any one of claims 1-7, characterized in that: The preparation method includes the following steps: The pretreated copper powder, inorganic binder, and organic carrier are mixed by stirring at 300-500 rpm for 5-10 minutes at room temperature, and the preparation is complete.