Copper electrode slurry for annular strontium titanate varistor, and use thereof

Abstract

The present invention relates to the technical field of electronic materials. Particularly disclosed are a copper electrode slurry for an annular strontium titanate varistor, and the use thereof. The copper electrode slurry for an annular strontium titanate varistor is prepared from the following components in percentages by mass: 82-88% of a copper conductive powder, 0.3-0.5% of an inorganic glass binder, 11-18% of an organic carrier, and 0-0.3% of a dispersing agent. The copper electrode slurry for an annular strontium titanate varistor provided in the present invention can be stacked and sintered in nitrogen at 800-900°C, the sintered copper electrode slurry has a good appearance and good welding performance, the adhesive force between a copper layer and strontium titanate varistor ceramic is high, the ohmic contact is good, and the electrostatic capacity is high.

Description

A copper electrode paste for a toroidal strontium titanate varistor and its application Technical Field

[0001] This invention relates to the field of electronic materials technology, and in particular to a copper electrode paste for a cyclic strontium titanate varistor and its application. Background Technology

[0002] The toroidal strontium titanate (SrTiO3) varistor is an electronic component based on strontium titanate material. It has unique nonlinear current-voltage characteristics, capacitance characteristics, and a toroidal structure, and is widely used in overvoltage protection, surge absorption, and other applications.

[0003] Toroidal strontium titanate varistors require a specific metal electrode layer to be attached to their surface before tinning, and then soldered into the circuit to achieve their electrical performance. Currently, the vast majority of toroidal strontium titanate varistor chips on the market use silver electrode layers. Silver is a precious metal, and its price has remained high in recent years, highlighting the cost issue of toroidal strontium titanate varistors. Furthermore, the silver electrode process involves printing a bottom layer of ohmic silver paste and a top layer of pure silver paste, followed by sintering to form the resistor. This two-step printing process is relatively complex and technically challenging.

[0004] Compared to silver electrodes, copper electrodes have higher sintering requirements, but are cheaper, have better ohmic contact performance with resistor ceramic bodies, are more resistant to soldering, and have superior performance. Therefore, mass production of copper electrodes will be the general trend.

[0005] In the patent application number 202110357141, a layer of copper electrode is printed and fired on the surface of the annular strontium titanate varistor ceramic body, and then tin plating is performed. The tin plating process is relatively friendly to the copper firing process and welding performance, but tin plating is an additional process, which is complex and technically difficult.

[0006] The mass production of copper electrodes for toroidal strontium titanate varistors is mainly constrained by the following factors: 1. Low-temperature sintering (<800℃) makes it difficult to achieve a dense copper layer, and the adhesion between the copper layer and the strontium titanate varistor substrate is difficult to meet requirements; 2. High-temperature sintering (>900℃) makes it difficult to meet the long-term stability requirements of commercially available nitrogen sintering furnaces; 3. Sintering at 800℃-900℃ requires the addition of a certain proportion of glass powder to meet adhesion requirements. As the amount of glass powder added increases, chemical reactions or penetration phenomena easily occur at the interface between the copper layer and the substrate, and the ohmic contact deteriorates rapidly. Summary of the Invention

[0007] Based on this, the purpose of the present invention is to provide a copper electrode paste for a ring-shaped strontium titanate varistor and its application. The copper paste can be stacked and sintered in nitrogen at 800℃-900℃. After sintering, it has a good appearance, excellent welding performance, strong adhesion between the copper layer and the strontium titanate varistor ceramic, good ohmic contact, and high electrostatic capacitance.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] The present invention first provides a copper electrode paste for a toroidal strontium titanate varistor, which is prepared from the following components by mass percentage: 82%-88% copper conductive powder, 0.3%-0.5% inorganic glass binder, 11%-18% organic carrier, and 0-0.3% dispersant.

[0010] As a further improvement to the above-mentioned solution of the present invention, the inorganic glass binder adopts a combination of several of B2O3, Bi2O3, SiO2, ZnO, CaO, CuO, and Al2O3, and the particle size of each component is 500-1200 mesh.

[0011] As a further improvement to the above-mentioned solution of the present invention, the mass percentage of each component in the inorganic glass adhesive is as follows: B2O3 25%-35%, Bi2O3 30%-40%, SiO2 2%-5%, ZnO 15%-25%, CaO 1%-10%, CuO 16%-18%, Al2O3 4%-5%.

[0012] As a further improvement to the above-mentioned solution of the present invention, the softening point of the inorganic glass adhesive is 600-650℃.

[0013] As a further improvement of the above-mentioned solution of the present invention, the organic carrier includes an organic solvent and a polymeric thickener, wherein the organic solvent is at least one of terpineol and terpineol, and the polymeric thickener is ethyl cellulose; the dispersant is at least one of dispersant ED116 and dispersant ED120.

[0014] As a further improvement to the above-mentioned solution of the present invention, the particle size of the copper conductive powder is 1-2 μm.

[0015] The present invention also provides a method for preparing the copper electrode paste for the toroidal strontium titanate varistor as described above, which includes the following steps: mixing copper conductive powder, inorganic glass binder, organic carrier and dispersant in proportion to obtain a mixture, and grinding the mixture until a toroidal strontium titanate varistor with a particle size ≤10µm and uniform dispersion is obtained.

[0016] The present invention also provides the application of the copper electrode paste for the annular strontium titanate varistor as described above in the preparation of the metallization layer of the annular strontium titanate varistor.

[0017] As a further improvement to the above-mentioned solution of the present invention, it includes the following steps: printing the annular strontium titanate varistor onto the annular strontium titanate varistor ceramic substrate using copper electrode paste through screen printing, drying it, and then sintering it in a mesh belt furnace under a nitrogen atmosphere.

[0018] As a further improvement to the above-mentioned scheme of the present invention, the oxygen content in the mesh belt furnace is 0-30ppm; the sintering curve is to heat to 400-500℃ at a heating rate of 15-20℃ / min for 5min to remove the binder, and then heat to 800-900℃ at a heating rate of 10-15℃ / min and hold for 10min.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The copper electrode paste for toroidal strontium titanate varistors provided by this invention can significantly reduce the cost of metallization of toroidal strontium titanate varistors. The copper electrode has a wide firing range, good firing appearance, excellent welding performance and adhesion, good ohmic contact, and high electrostatic capacitance.

[0021] In the copper electrode paste for the annular strontium titanate varistor provided by the present invention, the softening point of the inorganic glass binder is 600-650℃, and the sintering range of the copper electrode is 800-900℃. At 800-900℃, the inorganic glass binder has been fully softened and has a high viscosity, making it difficult to penetrate the matrix and allowing it to be well distributed between the copper electrode layer and the matrix. Attached Figure Description

[0022] Figure 1 shows the high-temperature melting state of inorganic glass binders with different formulations;

[0023] Figure 2 shows the effect of copper layer solder lead pull-out;

[0024] Figure 3 shows the microstructure of copper layers at different sintering temperatures. Embodiments of the present invention

[0025] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0027] Example 1

[0028] This embodiment proposes a copper electrode paste for a toroidal strontium titanate varistor, comprising the following components by weight percentage: 82% copper conductive powder, 0.3% inorganic glass binder, 12.3% terpineol, 4.4% dodecyl alcohol ester, and 1% ethyl cellulose. The inorganic glass binder is prepared according to Formula 1, which comprises the following components by weight percentage: 29% B₂O₃, 30% Bi₂O₃, 4% SiO₂, 15% ZnO, 2% CaO, 16% CuO, and 4% Al₂O₃.

[0029] The method for preparing the copper electrode paste for the toroidal strontium titanate varistor in this embodiment includes the following steps:

[0030] S1. Preparation of inorganic glass binder: Weigh each component according to the proportion and mix them mechanically. Place them in a muffle furnace and heat them to melt at 1100-1300℃. Hold the temperature for 10 minutes, pour them into cold water to quench, and then ball mill them in water medium until the powder particle size is ≤10μm. After drying at 120℃, the inorganic glass binder is obtained. The softening point is tested to be 600-650℃.

[0031] S2. Preparation of organic carrier: Terpineol, dodecyl alcohol ester and ethyl cellulose are mixed in proportion, and then the mixture is heated to 80-100℃ and stirred thoroughly to dissolve all the ethyl cellulose, thus obtaining the organic carrier;

[0032] S3. Preparation of slurry: Copper conductive powder, inorganic glass binder and organic carrier are mixed in proportion to obtain a mixture. The mixture is then ground on a three-roll mill until a uniformly dispersed annular strontium titanate varistor copper electrode slurry with a particle size ≤10µm is obtained.

[0033] The appearance of the copper electrode slurry for the annular strontium titanate varistor prepared in this embodiment is: paste-like, bright red, uniform and fine, with a particle size ≤10µm, viscosity: 100-250Pa·s (25℃, 5rpm), and firing temperature of 800-900℃.

[0034] Example 2

[0035] The difference between this embodiment and Embodiment 1 is that the copper electrode paste for the toroidal strontium titanate varistor in this embodiment includes the following components by mass percentage: 85% copper conductive powder, 0.4% inorganic glass binder, 10% terpineol, 3.7% twelfthyl alcohol ester, 0.8% ethyl cellulose, and 0.1% dispersant ED116.

[0036] The appearance of the copper electrode slurry for the annular strontium titanate varistor prepared in this embodiment is: paste-like, bright red, uniform and fine, with a particle size ≤10µm, viscosity: 100-250Pa·s (25℃, 5rpm), and firing temperature of 800-900℃.

[0037] Example 3

[0038] The difference between this embodiment and Embodiment 1 is that the copper electrode paste for the toroidal strontium titanate varistor in this embodiment includes the following components by mass percentage: 88% copper conductive powder, 0.5% inorganic glass binder, 4% terpineol, 6.6% twelfthyl alcohol ester, 0.6% ethyl cellulose, and 0.3% dispersant ED120.

[0039] The appearance of the copper electrode slurry for the annular strontium titanate varistor prepared in this embodiment is: paste-like, bright red, uniform and fine, with a particle size ≤10µm, viscosity: 100-250Pa·s (25℃, 5rpm), and firing temperature of 800-900℃.

[0040] Example 4

[0041] The difference between this embodiment and Embodiment 1 is that the copper electrode paste for the toroidal strontium titanate varistor in this embodiment includes the following components by mass percentage: 85% copper conductive powder, 0.4% inorganic glass binder, 10% terpineol, 3.7% dodecyl alcohol ester, 0.8% ethyl cellulose, and 0.1% dispersant ED120. The inorganic glass binder is prepared according to Formula 2, which includes the following components by mass percentage: 28% B2O3, 33% Bi2O3, 2% SiO2, 10% ZnO, 4% CaO, 18% CuO, and 5% Al2O3. The softening point of the inorganic glass binder is 600-650℃.

[0042] The appearance of the copper electrode slurry for the annular strontium titanate varistor prepared in this embodiment is: paste-like, bright red, uniform and fine, with a particle size ≤10µm, viscosity: 100-250Pa·s (25℃, 5rpm), and firing temperature of 800-900℃.

[0043] Comparative Example 1

[0044] The difference between this comparative example and Example 1 is that the copper electrode paste for the toroidal strontium titanate varistor in this comparative example includes the following components by mass percentage: 85% copper conductive powder, 0.2% inorganic glass binder, 10% terpineol, 3.9% twelfthyl alcohol ester, 0.8% ethyl cellulose, and 0.1% dispersant ED116.

[0045] Comparative Example 2

[0046] The difference between this comparative example and Example 1 is that the copper electrode paste for the toroidal strontium titanate varistor in this comparative example includes the following components by mass percentage: 85% copper conductive powder, 0.6% inorganic glass binder, 10% terpineol, 3.5% twelfthyl alcohol ester, 0.8% ethyl cellulose, and 0.1% dispersant ED116.

[0047] Comparative Example 3

[0048] The difference between this comparative example and Example 1 is that the copper electrode paste for the toroidal strontium titanate varistor in this comparative example includes the following components by mass percentage: 85% copper conductive powder, 0.5% inorganic glass binder, 10% terpineol, 3.6% dodecyl alcohol ester, 0.8% ethyl cellulose, and 0.1% dispersant ED116; wherein, the inorganic glass binder is prepared according to Formula 3, which includes the following components by mass percentage: 28% B2O3, 35% Bi2O3, 2% SiO2, 10% ZnO, 4% CaO, 18% CuO, and 3% Al2O3.

[0049] Comparative Example 4

[0050] The difference between this comparative example and Example 1 is that the copper electrode paste for the toroidal strontium titanate varistor in this comparative example includes the following components by mass percentage: 85% copper conductive powder, 1% inorganic glass binder, 10% terpineol, 3.1% dodecyl alcohol ester, 0.8% ethyl cellulose, and 0.1% dispersant ED120; wherein, the inorganic glass binder is prepared according to Formula 3, which includes the following components by mass percentage: 28% B2O3, 35% Bi2O3, 2% SiO2, 10% ZnO, 4% CaO, 18% CuO, and 3% Al2O3.

[0051] Comparative Example 5

[0052] The difference between this comparative example and Example 1 is that the copper electrode paste for the toroidal strontium titanate varistor in this comparative example includes the following components by mass percentage: 85% copper conductive powder, 2% inorganic glass binder, 9% terpineol, 3.2% dodecyl alcohol ester, 0.7% ethyl cellulose, and 0.1% dispersant ED120; wherein, the inorganic glass binder is prepared according to Formula 3, which includes the following components by mass percentage: 28% B2O3, 35% Bi2O3, 2% SiO2, 10% ZnO, 4% CaO, 18% CuO, and 3% Al2O3.

[0053] Comparative Example 6

[0054] The difference between this comparative example and Example 1 is that the copper electrode paste for the toroidal strontium titanate varistor in this comparative example includes the following components by mass percentage: 85% copper conductive powder, 0.5% inorganic glass binder, 10% terpineol, 3.6% dodecyl alcohol ester, 0.8% ethyl cellulose, and 0.1% dispersant ED120. The inorganic glass binder is prepared according to Formula 4, which includes the following components by mass percentage: 31% B2O3, 30% Bi2O3, 2% SiO2, 10% ZnO, 4% CaO, 15% CuO, and 5% Al2O3.

[0055] Comparative Example 7

[0056] The difference between this comparative example and Example 1 is that the copper electrode paste for the toroidal strontium titanate varistor in this comparative example includes the following components by mass percentage: 85% copper conductive powder, 1% inorganic glass binder, 10% terpineol, 3.1% twelfthyl alcohol ester, 0.8% ethyl cellulose, and 0.1% dispersant ED120; wherein, the inorganic glass binder is prepared according to Formula 4, which includes the following components by mass percentage: 31% B2O3, 30% Bi2O3, 2% SiO2, 10% ZnO, 4% CaO, 15% CuO, and 5% Al2O3.

[0057] Comparative Example 8

[0058] The difference between this comparative example and Example 1 is that the copper electrode paste for the toroidal strontium titanate varistor in this comparative example includes the following components by mass percentage: 85% copper conductive powder, 0.5% inorganic glass binder, 10% terpineol, 3.6% dodecyl alcohol ester, 0.8% ethyl cellulose, and 0.1% dispersant ED116; wherein, the inorganic glass binder is prepared according to Formula 5, which includes the following components by mass percentage: 26% B2O3, 30% Bi2O3, 4% SiO2, 15% ZnO, 2% CaO, 19% CuO, and 4% Al2O3.

[0059] Comparative Example 9

[0060] The difference between this comparative example and Example 1 is that the copper electrode paste for the toroidal strontium titanate varistor in this comparative example includes the following components by mass percentage: 85% copper conductive powder, 0.5% inorganic glass binder, 10% terpineol, 3.6% dodecyl alcohol ester, 0.8% ethyl cellulose, and 0.1% dispersant ED116; wherein, the inorganic glass binder is prepared according to Formula 6, which includes the following components by mass percentage: 29% B2O3, 28% Bi2O3, 4% SiO2, 15% ZnO, 2% CaO, 16% CuO, and 6% Al2O3.

[0061] The formulations of the inorganic glass adhesives in the above embodiments and comparative examples are shown in Table 1.

[0062] Table 1 Formulation of Inorganic Glass Adhesives (by weight)

[0063]

[0064] Different formulations of inorganic glass binders were melted at high temperatures, resulting in the high-temperature melting state diagrams shown in Figure 1. Figure 1 shows that at 750℃, the inorganic glass binders corresponding to formulations one through four exhibited good melting states, while the inorganic glass binders corresponding to formulations five and six did not soften. At 850℃, the inorganic glass binders corresponding to formulations one and two had higher melt viscosity, while the inorganic glass binders corresponding to formulations three and four had lower melt viscosity and exhibited severe flow in the softened state. The inorganic glass binders corresponding to formulations five and six did not soften sufficiently.

[0065] The composition of the copper electrode paste for the toroidal strontium titanate varistors in the above embodiments and comparative examples is shown in Table 2.

[0066] Table 2. Composition ratio (mass percentage) of copper electrode slurry in the examples and comparative examples.

[0067]

[0068] Application examples

[0069] (1) The copper electrode pastes of Examples 1-4 and Comparative Examples 1-9 were used to prepare the metallized layer of the annular strontium titanate varistor: The prepared copper paste was screen printed on the annular strontium titanate varistor substrate, dried at 150°C and then placed in a mesh belt furnace for sintering. The oxygen content in the furnace was controlled at 0-30 ppm. The sintering process was as follows: nitrogen atmosphere, heating to 500°C at a heating rate of 15°C / min and holding at 500°C for 5 min in the glue removal zone, heating to 850°C at a heating rate of 15°C / min and holding at 850°C for 10 min to obtain the copper metallized sample of the annular strontium titanate varistor.

[0070] The prepared samples were subjected to copper layer solder lead pull-out test. The copper layer solder lead pull-out effect is shown in Figure 2. As can be seen from Figure 2, the copper layer of Comparative Example 1 and Comparative Example 9 was pulled off by the lead, and the bonding force was poor. A small amount of ceramic substrate was pulled off in the samples of Comparative Example 3 and Comparative Example 7, and the bonding force was average. A large amount of ceramic substrate in Example 1 and Example 4 was directly pulled off by the lead, and the film layer bonding force was reliable.

[0071] The obtained samples were tested for adhesion (N / mm). 2 The test results are shown in Table 3; the electrostatic capacitance (nF) of the prepared samples was tested, and the test results are shown in Table 4.

[0072] Table 3 Sample adhesion (N / mm) 2 Test results

[0073]

[0074] Table 4. Test results of capacitance values ​​(nF)

[0075]

[0076] As can be seen from the results in Table 3, the copper paste samples of Examples 1-4, Comparative Examples 2, 4, and 5 have an adhesion of ≥ 8 N / mm. 2 The requirements were met. Comparative Example 1 had a low amount of inorganic glass binder, resulting in low sample adhesion. Comparative Examples 3, 6, and 7 had low proportions of copper or aluminum in their inorganic glass binders, leading to low melting viscosity of the glass at 800-900℃, severe penetration into the ceramic matrix, and inappropriate addition amounts, resulting in low sample adhesion. Comparative Examples 8 and 9 had high proportions of copper and aluminum in their inorganic glass binders, resulting in a high softening point of the glass powder, failure of the glass to melt at 800-900℃, and poor adhesion of the copper paste samples.

[0077] As can be seen from Table 4, the electrostatic capacity of the copper electrode paste in Examples 1-4 is ≥105 nF, which meets the requirements. The samples in Comparative Examples 1, 3, and 6-9 have lower electrostatic capacities due to poor bonding. Although the bonding of Comparative Examples 2, 4, and 5 is better, the amount of inorganic glass binder added is too large. During sintering at 800-900℃, the chemical reaction at the interface between the glass and the substrate is too full, resulting in poor ohmic contact of the samples.

[0078] According to the results in Tables 3 and 4, compared with Example 1: In Comparative Example 1, due to the lower amount of inorganic glass adhesive added, the pull-off force was small, and the electrostatic capacity shifted slightly; In Comparative Example 2, the amount of inorganic glass adhesive added was higher, resulting in better sample adhesion, but the electrostatic capacity decreased significantly; In Comparative Example 3, the inorganic glass adhesive contained less aluminum, resulting in slightly poorer sample adhesion and a slight decrease in electrostatic capacity; In Comparative Example 4, the inorganic glass adhesive contained less aluminum, and the amount of inorganic glass adhesive added was higher, resulting in normal sample adhesion, but a decrease in electrostatic capacity; In Comparative Example 5, the inorganic glass adhesive contained less aluminum... In Comparative Example 6, the inorganic glass adhesive contained less copper, resulting in weaker adhesion and a slight decrease in electrostatic capacity. In Comparative Example 7, the inorganic glass adhesive contained less copper and a higher amount of it, resulting in weaker adhesion and a smaller electrostatic capacity. In Comparative Example 8, the inorganic glass adhesive contained more copper, resulting in poorer adhesion and a smaller electrostatic capacity. In Comparative Example 9, the inorganic glass adhesive contained more aluminum, resulting in poorer adhesion and a significant decrease in electrostatic capacity.

[0079] It is evident that the amount of inorganic glass binder added to the copper electrode paste of this invention has a significant impact on the adhesion and electrostatic capacity of the sample. The introduction of copper and aluminum elements in the inorganic glass binder formulation promotes the ohmic contact characteristics of the product, but the proportion must be appropriate.

[0080] (2) The copper electrode paste from Example 2 was sintered at different temperatures to prepare annular strontium titanate varistor metallization layers. The obtained samples were then subjected to adhesion testing (N / mm). 2 The test results are shown in Table 5.

[0081] Table 5 Adhesion after sintering at different temperatures (N / mm) 2 Test results

[0082]

[0083] As shown in Table 5, when the copper electrode paste of Example 2 was sintered at 800-900℃, the adhesion of the paste sample was ≥ 8 N / mm. 2 All samples met the required specifications. However, the copper electrode paste in Example 2, when sintered at 750℃, exhibited poor copper layer density, low glass content, and low sample adhesion. Figure 3 shows the microstructure of the copper layer after sintering the copper electrode paste at 750℃ and 850℃. Figure 3 shows that at 750℃, the copper layer is relatively porous; while at 850℃, the copper grains grow significantly, resulting in high copper layer density. Therefore, the sintering temperature of the samples in this embodiment should not be lower than 800℃. At 750℃, the adhesion is low, and the electrostatic capacity decreases significantly. If the sintering temperature is too low, the copper layer will be poorly dense, and adhesion will be difficult to guarantee.

[0084] In summary, the copper electrode paste for the annular strontium titanate varistor prepared by this invention has the following characteristics: paste-like, bright red, uniform and fine texture, particle size ≤10µm; viscosity: 100-250 Pa·s (25℃, 5 rpm); firing temperature: 800-900℃; film thickness: 5-15µm; adhesion: ≥8N / mm. 2 Ohmic contact: good, capacitance ≥ 105 nF.

[0085] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0086] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A copper electrode paste for a toroidal strontium titanate varistor, characterized in that, It is prepared from the following components by mass percentage: 82%-88% copper conductive powder, 0.3%-0.5% inorganic glass binder, 11%-18% organic carrier, and 0-0.3% dispersant.

2. The copper electrode paste for a toroidal strontium titanate varistor according to claim 1, characterized in that, The inorganic glass binder is a combination of several of B2O3, Bi2O3, SiO2, ZnO, CaO, CuO, and Al2O3, and the particle size of each component is 500-1200 mesh.

3. The copper electrode paste for a toroidal strontium titanate varistor according to claim 2, characterized in that, The inorganic glass binder contains the following components by mass percentage: B2O3 25%-35%, Bi2O3 30%-40%, SiO2 2%-5%, ZnO 15%-25%, CaO 1%-10%, CuO 16%-18%, and Al2O3 4%-5%.

4. The copper electrode paste for a toroidal strontium titanate varistor according to claim 1, characterized in that, The inorganic glass adhesive has a softening point of 600-650℃.

5. The copper electrode paste for a toroidal strontium titanate varistor according to claim 1, characterized in that, The copper conductive powder has a particle size of 1-2 μm.

6. The copper electrode paste for a toroidal strontium titanate varistor according to claim 1, characterized in that, The organic carrier includes an organic solvent and a polymeric thickener, wherein the organic solvent is at least one of terpineol and terpineol, and the polymeric thickener is ethyl cellulose; and / or, the dispersant is at least one of dispersant ED116 and dispersant ED120.

7. The use of a copper electrode paste for a ring-shaped strontium titanate varistor as described in any one of claims 1-6 in the preparation of a metallization layer for a ring-shaped strontium titanate varistor.

8. The application according to claim 7, characterized in that, It includes the following steps: The toroidal strontium titanate varistor is printed onto the toroidal strontium titanate varistor ceramic substrate using copper electrode paste via screen printing. After drying, it is placed in a mesh belt furnace for sintering under a nitrogen atmosphere.

9. The application according to claim 8, characterized in that, The oxygen content in the mesh belt furnace is 0-30 ppm; the sintering curve is to heat to 400-500℃ at a heating rate of 15-20℃ / min for 5 min to remove the binder, and then heat to 800-900℃ at a heating rate of 10-15℃ / min and hold for 10 min.

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