Gold paste for high-temperature NTC (Negative Temperature Coefficient) thermistor as well as preparation method and application thereof

Abstract

The invention relates to gold paste for a high-temperature NTC (Negative Temperature Coefficient) thermistor as well as a preparation method and application of the gold paste. The gold paste for the high-temperature NTC thermistor is prepared from the following components in percentage by mass: 60-69% of gold conductive powder, 3-8% of an inorganic binder, 22-30% of an organic carrier and 1-3% of a dispersing agent, the gold conductive powder comprises superfine spherical gold powder with the granularity of 150-350 nm and coarse spherical gold powder with the granularity of 1-2 microns. According to the gold paste provided by the invention, the superfine spherical gold powder and the coarse spherical gold powder are matched for use, so that the growth rate of gold crystals can be controlled within a proper range, an inorganic binder can permeate between a metallization layer and a substrate after being softened, enough adhesive force and excellent conductivity are formed, the resistance value of the substrate is truly reflected, and the service life of the metallization layer is prolonged. Therefore, the NTC thermistor prepared by using the gold paste has higher accuracy and reliability, so that the dosage of the gold conductive powder can be reduced, and a gold paste metallization product can be ensured to have higher accuracy and higher reliability.

Description

Technical Field

[0001] The invention relates to the technical field of electronic materials, and in particular to a gold paste for a high-temperature NTC thermistor, and a preparation method and application thereof. Background Art

[0002] NTC high temperature thermistor is a temperature sensing element with the characteristics of significantly decreasing resistance value as temperature increases and stable resistance characteristics. Its excellent sensitivity enables it to detect very small temperature changes and is widely used in temperature measurement, control, temperature compensation and other occasions.

[0003] At present, the electrode layer of NTC thermistor chips in the market is mostly silver electrode layer, which has the characteristics of fast heat transfer and excellent electrical performance. Metallic silver has a natural silver ion migration phenomenon, which will cause performance problems of the base component. In the field of high precision and miniaturization, it is difficult to meet the requirements of resistance accuracy and aging change rate.

[0004] Compared with silver electrodes, gold electrodes are not easy to oxidize, and have better reliability and stability. Gold electrodes are widely used in automotive electronics, large energy storage equipment and other fields. However, the selection of gold paste materials, how to ensure the ohmic contact and adhesion between the gold electrode and the ceramic substrate, the control of the preparation process, and how to verify the rationality and effectiveness of the electrode preparation process still need further research.

[0005] The patent with publication number CN202210198112 discloses a gold electrode NTC thermistor chip, preparation method and temperature sensor. By printing and burning a layer of gold paste on a ceramic substrate, the mass ratio of gold powder, inorganic binder and organic carrier in the gold paste is 70-80:5-15:15-25, and the prepared gold electrode NTC thermistor chip has high resistance accuracy and high reliability. For example, the patent with publication number CN117342797A discloses a gold electrode glass powder, preparation method, gold electrode slurry and NTC thermistor. The gold electrode slurry is composed of the following components: 70-80% gold powder, 2-10% glass powder, 1-3% glass carbon and 15-20% organic carrier. In summary, the gold paste of the gold electrode NTC thermistor currently has a gold powder mass content of 70-80%, and the gold paste cost is relatively high. Summary of the invention

[0006] Based on this, the purpose of the present invention is to provide a gold paste for high-temperature NTC thermistors and a preparation method and application thereof, which can reduce the amount of gold conductive powder used and ensure that the gold paste metallization products have higher accuracy and higher reliability.

[0007] To achieve the above object, the present invention adopts the following technical solutions: The present invention first provides a gold paste for a high-temperature NTC thermistor, which is prepared from the following components in percentage by mass: 60%-69% of gold conductive powder, 3%-8% of an inorganic binder, 22%-30% of an organic carrier, and 1%-3% of a dispersant; the gold conductive powder includes ultrafine spherical gold powder with a particle size of 150-350nm and coarse spherical gold powder with a particle size of 1-2μm.

[0008] The gold paste proposed in the present invention uses ultrafine spherical gold powder and coarse spherical gold powder in combination, which can control the growth rate of gold crystals within a suitable range, so that the inorganic binder can penetrate between the metallization layer and the substrate after softening, forming sufficient adhesion and excellent conductivity, and truly reacting to the resistance value of the substrate, so that the NTC thermistor prepared using the gold paste has higher accuracy and reliability. Therefore, the present invention can reduce the amount of gold conductive powder used, and can also ensure that the gold paste metallization product has higher accuracy and higher reliability.

[0009] As a further improvement of the above solution of the present invention, the mass percentage of each component in the gold conductive powder is: ultrafine spherical gold powder 80%-90% and coarse spherical gold powder 20%-10%; And / or, the specific surface area of ​​the ultrafine spherical gold powder is 6-9m 2 / g, the specific surface area of ​​the coarse spherical gold powder is 1-3.5m 2 / g.

[0010] As a further improvement of the above solution of the present invention, the inorganic binder includes the following components in percentage by mass: B 2 O 3 15%-25%, Bi 2 O 3 40%-60%, SiO 2 1%-3%, ZnO 0.5%-13%, MnO 3%-10%, NiO 0.5%-15%.

[0011] As a further improvement of the above-mentioned solution of the present invention, the preparation method of the inorganic binder comprises: mixing B 2 O 3 、Bi 2 O 3 、SiO 2 After mixing, ZnO, MnO and NiO are placed in a muffle furnace and heated at 1150-1300°C until melted, kept warm for 10-15 minutes, poured into cold water for quenching, ball-milled in an aqueous medium for 48 hours until the powder particle size is ≤10μm, and then dried.

[0012] As a further improvement of the above solution of the present invention, the particle size of the inorganic binder is 500-1200 mesh and the softening point is 760-860°C.

[0013] As a further improvement of the above scheme of the present invention, the organic carrier includes an organic solvent and a polymer thickener, the organic solvent is at least one of terpineol, a film-forming aid, and hydrogenated terpineol, and the polymer thickener is at least one of ethyl cellulose and acrylic resin; And / or, the dispersant is at least one of RE610, Dg655, and BYK333.

[0014] The present invention also provides a method for preparing the gold paste for high temperature NTC thermistor as described above, characterized in that it comprises the following steps: S1. dissolving and dispersing the polymer thickener in an organic solvent to obtain an organic carrier; S2. Mix the gold conductive powder, the inorganic binder and the organic carrier obtained in step S1 in proportion to obtain a mixed raw material; S3. Grind the mixed raw material obtained in step S2 to obtain a slurry with a particle size of ≤10 μm, add a dispersant to the slurry in proportion, and mix them evenly to obtain a gold slurry for a high-temperature NTC thermistor.

[0015] As a further improvement of the above scheme of the present invention, in step S1, dissolving and dispersing the polymer thickener in the organic solvent includes: mixing the polymer thickener and the organic solvent, heating to 90-120° C., and fully stirring at a stirring speed of 60-120 rpm and a stirring time of 240-300 min.

[0016] The present invention also provides an application of the aforementioned gold paste for high-temperature NTC thermistors in preparing a surface metallization layer of high-temperature NTC thermistors.

[0017] As a further improvement of the above scheme of the present invention, it includes the following steps: printing the high-temperature NTC thermistor with gold paste on both sides of the NTC thermistor ceramic substrate by screen printing, drying at 150°C for 5 minutes, and sintering. Preferably, the sintering is to increase the temperature to 200-500°C at a heating rate of 30°C / min, then increase the temperature to 500-850°C at a heating rate of 15°C / min, and keep the temperature at 850°C for 10 minutes, and the temperature difference in each temperature zone is ≤3°C.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. The gold paste proposed in the present invention uses ultrafine spherical gold powder and coarse spherical gold powder in combination, which can control the growth rate of gold crystals within an appropriate range, avoid crystal growth that is too fast or too slow, and allow the inorganic binder to penetrate between the metallization layer and the substrate after softening, forming sufficient adhesion and excellent conductivity, and truly reacting to the resistance value of the substrate, so that the NTC thermistor prepared using the gold paste has higher accuracy and reliability. Therefore, the present invention can reduce the amount of gold conductive powder used, and can also ensure that the gold paste metallization product has higher accuracy and higher reliability, and the lower gold content can effectively reduce the cost of the product.

[0019] 2. The gold paste proposed in the present invention is sintered at 750°C-880°C in air. After sintering, the film layer is dense and flat, has strong adhesion to NTC ceramics, has good ohmic contact, and the resistance of the product is consistent and stable, with a resistance fluctuation rate of ≤0.4%. The product has a high B value and is sensitive to temperature changes. After aging for 1000h at 350°C, the resistance change rate is about ±0.3%, and the stability after long-term aging is excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a microscope image of the surface morphology of the high-temperature NTC thermistor of Example 1 after sintering with gold paste; Figure 2 This is a microscope image of the surface morphology of the high temperature NTC thermistor of Comparative Example 3 after sintering with gold paste; Figure 3 This is a 2000x SEM crystal growth image of the high temperature NTC thermistor of Example 1; Figure 4 This is a 2000x SEM crystal growth image of the high temperature NTC thermistor of Comparative Example 3; Figure 5 This is a microscopic picture of the surface metallization layer and the ceramic body peeling of the high temperature NTC thermistor of comparative example 1. DETAILED DESCRIPTION

[0021] For ease of understanding of the present invention, the present invention will be described more fully below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0023] Example 1 This embodiment provides a gold paste for a high-temperature NTC thermistor, which includes the following raw materials by mass percentage: 62.5% of ultrafine spherical gold powder, 6.5% of coarse spherical gold powder, 8% of inorganic binder, 8% of pine alcohol, 4.5% of film-forming aid, 4.5% of hydrogenated pine alcohol, 3% of ethyl cellulose, 2% of acrylic resin, 0.5% of dispersant RE610, and 0.5% of dispersant BYK333; wherein the inorganic binder includes the following raw materials by mass percentage: 21% of B 2 O 3 , 60% Bi 2 O 3 , 2% SiO 2 , 2% ZnO, 10% MnO, 5% NiO. The preparation method of the gold paste for high temperature NTC thermistor of this embodiment comprises the following steps: A. Preparation of organic carrier Mix terpineol, film-forming aid, hydrogenated terpineol, ethyl cellulose and acrylic resin in proportion, then heat the mixed system to 90-120°C and stir thoroughly at a stirring speed of 60-120 rpm for 240-300 minutes to completely dissolve the ethyl cellulose and acrylic resin, and stir evenly to obtain an organic carrier; B. Preparation of inorganic binder Proportionally 2 O 3 、Bi 2 O 3 、SiO 2 , ZnO, MnO and NiO are mechanically mixed, placed in a muffle furnace and heated at 1150-1300°C until melted, kept warm for 10 minutes, poured into cold water for quenching, ball-milled in an aqueous medium for 48 hours until the powder particle size is ≤10um, dried at 120°C, and the softening point is tested to be 760-860°C, to obtain an inorganic binder; C. Preparation of slurry Mix and stir the ultrafine spherical gold powder, the coarse spherical gold powder, the inorganic binder obtained in step B, and the organic carrier obtained in step A in proportion to obtain a mixed raw material; D. Manufacturing of slurry The mixed raw material obtained in step C is ground on a three-roll mill. After a certain grinding process, a uniformly dispersed slurry is obtained, and the slurry particle size is ≤10µm. Then, dispersant RE610 and dispersant BYK333 are added in proportion and mixed evenly to obtain gold slurry for high-temperature NTC thermistors. The appearance of the gold slurry for high-temperature NTC thermistors prepared in this embodiment is: paste-like, golden yellow, uniform and fine, with a particle size of ≤10µm, a viscosity of 100-250 Pa·s (25°C, 5rpm), and a sintering temperature of 750-850°C.

[0024] Example 2 This embodiment adopts the same implementation as that of the embodiment 1, and the difference from the embodiment 1 is that the gold paste for high temperature NTC thermistor of this embodiment comprises the following raw materials by mass percentage: 56% of ultrafine spherical gold powder, 13% of coarse spherical gold powder, 8% of inorganic binder, 9% of pine alcohol, 4.5% of film-forming aid, 4.5% of hydrogenated pine alcohol, 3% of ethyl cellulose, 1% of acrylic resin, 0.5% of dispersant RE610, and 0.5% of dispersant Digo 655; wherein the inorganic binder comprises the following raw materials by mass percentage: 21% of B 2 O 3 , 60% Bi 2 O 3 , 2% SiO 2 , 2% ZnO, 10% MnO, 5% NiO. The appearance of the gold paste for high-temperature NTC thermistor prepared in this embodiment is: paste-like, golden yellow, uniform and fine, with a particle size of ≤10µm, a viscosity of 100-250 Pa·s (25°C, 5rpm), and a sintering temperature of 750-850°C.

[0025] Example 3 This embodiment adopts the same implementation as that of the embodiment 1, and the difference from the embodiment 1 is that the gold paste for high temperature NTC thermistor of this embodiment comprises the following raw materials by mass percentage: 62.5% of ultrafine spherical gold powder, 6.5% of coarse spherical gold powder, 5% of inorganic binder, 9% of pine alcohol, 6% of film-forming aid, 5% of hydrogenated pine alcohol, 2% of ethyl cellulose, 2% of acrylic resin, 1% of dispersant RE610, and 1% of dispersant Digo 655; wherein the inorganic binder comprises the following raw materials by mass percentage: 21% of B 2 O 3 , 60% Bi 2 O 3 , 2% SiO 2 , 2% ZnO, 10% MnO, 5% NiO. The appearance of the gold paste for high-temperature NTC thermistor prepared in this embodiment is: paste-like, golden yellow, uniform and fine, with a particle size of ≤10µm, a viscosity of 100-250 Pa·s (25°C, 5rpm), and a sintering temperature of 750-850°C.

[0026] Comparative Example 1 This comparative example adopts the same implementation as Example 1, and the difference from Example 1 is that the gold paste for high-temperature NTC thermistor in this comparative example includes the following raw materials by mass percentage: 62.5% of ultrafine spherical gold powder, 6.5% of coarse spherical gold powder, 2% of inorganic binder, 9% of pine alcohol, 5% of film-forming aid, 5% of hydrogenated pine alcohol, 4% of ethyl cellulose, 4% of acrylic resin, 1% of dispersant RE610, and 1% of dispersant Digo 655; wherein the inorganic binder includes the following raw materials by mass percentage: 21% of B 2 O 3 , 60% Bi 2 O 3 , 2% SiO 2 , 2% ZnO, 10% MnO, 5% NiO.

[0027] Comparative Example 2 This comparative example adopts the same implementation as Example 1, and the difference from Example 1 is that the gold paste for high-temperature NTC thermistor in this comparative example includes the following component raw materials in percentage by mass: 56% of ultrafine spherical gold powder, 13% of coarse spherical gold powder, 8% of inorganic binder, 9% of pine alcohol, 4.5% of film-forming aid, 4.5% of hydrogenated pine alcohol, 3% of ethyl cellulose, 1% of dispersant RE610, and 1% of dispersant Digo 655; wherein the inorganic binder includes the following component raw materials in percentage by mass: 21% of B 2 O 3 , 60% Bi 2 O 3 , 2% SiO 2 , 2% ZnO, 10% MnO 2 , 5% NiO.

[0028] Comparative Example 3 This comparative example adopts the same implementation as Example 1, and the difference from Example 1 is that the gold paste for high-temperature NTC thermistor in this comparative example includes the following component raw materials in mass percentage: 70% ultrafine spherical gold powder, 10% coarse spherical gold powder, 8% inorganic binder, 4.5% film-forming aid, 3.5% hydrogenated terpineol, 2% ethyl cellulose, 1% dispersant RE610, and 1% dispersant Digo 655; wherein the inorganic binder includes the following component raw materials in mass percentage: 21% B 2 O 3 , 60% Bi 2 O 3 , 2% SiO 2 , 2% ZnO, 10% MnO, 5% NiO.

[0029] Comparative Example 4 This comparative example adopts the same implementation as Example 1, and the difference from Example 1 is that the gold paste for high-temperature NTC thermistor in this comparative example includes the following raw materials by mass percentage: 62.5% of ultrafine spherical gold powder, 6.5% of coarse spherical gold powder, 10% of inorganic binder, 8% of pine alcohol, 4.5% of film-forming aid, 4.5% of hydrogenated pine alcohol, 1.5% of ethyl cellulose, 0.5% of acrylic resin, 1% of dispersant RE610, and 1% of dispersant Digo 655; wherein the inorganic binder includes the following raw materials by mass percentage: 21% of B 2 O 3 , 60% Bi 2 O 3 , 2% SiO 2 , 2% ZnO, 10% MnO, 5% NiO.

[0030] The proportions of the above embodiments and comparative examples are shown in Table 1.

[0031] Table 1 Proportions of Examples and Comparative Examples (mass percentage)

[0032] Test Case High-temperature NTC thermistor samples were prepared using the gold paste prepared in the above Examples 1-3 and Comparative Examples 1-4, and 6 samples were prepared respectively. The high-temperature NTC thermistor sample preparation process is as follows: the high-temperature NTC thermistor is printed on both sides of the NTC thermistor ceramic substrate with gold paste by screen printing, dried at 150°C for 5 minutes, and sintered. The sintering is to increase the temperature to 200-500°C at a heating rate of 30°C / min, and then increase the temperature to 500-850°C at a heating rate of 15°C / min, and keep the temperature at 850°C for 10 minutes, and the temperature difference in each temperature zone is ≤3°C. The resistance value of the prepared high-temperature NTC thermistor and the resistance value after aging are tested, and the test results are shown in Tables 2 and 3, respectively, wherein the aging is to place the high-temperature NTC thermistor in a hot air circulation oven at a constant temperature of 350°C for 1000h.

[0033] Table 2 Sample resistance

[0034] In Table 2, resistance fluctuation rate = (resistance with the largest difference from the average resistance - average resistance) / average resistance * 100% Table 3 Resistance of samples after aging

[0035] In Table 3, the initial resistance change rate = (sample resistance - resistance after aging test) / sample resistance * 100%, taking the maximum value, comparative examples 3 and 4 are unqualified because the resistance fluctuation rate is greater than 2%, so there is no need to conduct aging test.

[0036] According to the data in Table 2 and Table 3, it can be seen that the resistance value and resistance fluctuation rate of the high-temperature NTC thermistor prepared by the gold paste provided by the present invention are smaller than those of the comparative example, which can explain that the gold paste in the present invention has better ohmic contact with the substrate and can better reflect the true resistance value of the substrate. This is because the inorganic binder has a larger density and a smaller viscosity after softening, and is easier to deposit on the interface between the metallization layer and the porcelain body, and the Mn in the inorganic binder 2+ and Bi 3+ It is easier to penetrate into the porcelain body and then occupy the octahedral center, realizing the process of converting valence electrons into free electrons and then into valence electrons, while manganese in other valence states does not have this function. This is also the reason why the gold paste provided by the present invention has good ohmic contact and low resistance.

[0037] from Figure 2 It can be seen that the surface of Comparative Example 3 has a blackening phenomenon. This is because the gold content increases, the crystals grow too fast, and part of the inorganic binder does not have time to melt. It exists on the surface of the metallization layer and floats up significantly, resulting in an increase in the surface inorganic binder and uneven distribution. This not only affects the appearance of the product, but also has an adverse effect on the consistency of the resistance of the product area. This is consistent with the result of the resistance increase in Table 1. Therefore, the amount of gold added in the present invention cannot be increased, otherwise it will have an adverse effect on the performance and appearance of the product. Similarly, Comparative Example 4 of the present invention also has a similar situation. When the inorganic binder content is higher than 8%, the surface of the product will also turn black, and the electrical properties will also be poor. Therefore, the amount of inorganic binder in the present invention cannot be added to exceed 8%. When the amount of inorganic binder is less than 3%, the situation in Comparative Example 1 will occur. Although the electrical properties are normal, the metallization layer and the substrate will peel off (see Figure 5 ), which is caused by too little inorganic binder and insufficient adhesion.

[0038] Figure 3 is an electron microscope image of Example 1, Figure 4 This is the electron microscope image of Example 3. By comparing the two pictures, it can be seen that the gold crystals in Example 1 are larger and denser. It can also be seen that there is an inorganic binder on the surface of Example 3, which indicates that the gold in Example 1 has better conductivity, which is consistent with the resistance test results.

[0039] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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.

[0040] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A gold paste for high temperature NTC thermistor, characterized in that: It is prepared from the following components in percentage by mass: 60%-69% gold conductive powder, 3%-8% inorganic binder, 22%-30% organic carrier, and 1%-3% dispersant; the gold conductive powder includes ultrafine spherical gold powder with a particle size of 150-350nm and coarse spherical gold powder with a particle size of 1-2μm.

2. The gold paste for high temperature NTC thermistor according to claim 1, characterized in that: The mass percentage of each component in the gold conductive powder is: 80%-90% of ultrafine spherical gold powder and 20%-10% of coarse spherical gold powder; And / or, the specific surface area of ​​the ultrafine spherical gold powder is 6-9m 2 / g, the specific surface area of ​​the coarse spherical gold powder is 1-3.5m 2 / g.

3. The gold paste for high temperature NTC thermistor according to claim 1, characterized in that: The inorganic binder includes the following components in percentage by mass: B2O3 15%-25%, Bi2O3 40%-60%, SiO2 1%-3%, ZnO 0.5%-13%, MnO3%-10%, and NiO 0.5%-15%.

4. The gold paste for high temperature NTC thermistor according to claim 3, characterized in that: The preparation method of the inorganic binder comprises: mixing B2O3, Bi2O3, SiO2, ZnO, MnO and NiO in proportion, heating the mixture in a muffle furnace at 1150-1300°C until it is melted, keeping the mixture warm for 10-15 minutes, pouring the mixture into cold water for quenching, ball milling the mixture in an aqueous medium for 48 hours until the powder particle size is ≤10μm, and drying the mixture.

5. The gold paste for high temperature NTC thermistor according to claim 1, characterized in that: The inorganic binder has a particle size of 500-1200 meshes and a softening point of 760-860°C.

6. The gold paste for high temperature NTC thermistor according to claim 1, characterized in that: The organic carrier comprises an organic solvent and a polymer thickener, wherein the organic solvent is at least one of terpineol, a film-forming aid, and hydrogenated terpineol, and the polymer thickener is at least one of ethyl cellulose and acrylic resin; And / or, the dispersant is at least one of RE610, Dg655, and BYK333.

7. A method for preparing a gold paste for a high temperature NTC thermistor as claimed in any one of claims 1 to 6, characterized in that: It includes the following steps: S1. dissolving and dispersing the polymer thickener in an organic solvent to obtain an organic carrier; S2. Mix the gold conductive powder, the inorganic binder and the organic carrier obtained in step S1 in proportion to obtain a mixed raw material; S3. Grind the mixed raw material obtained in step S2 to obtain a slurry with a particle size of ≤10 μm, add a dispersant to the slurry in proportion, and mix well to obtain a gold slurry for a high-temperature NTC thermistor.

8. The method for preparing gold paste for high temperature NTC thermistor according to claim 7, characterized in that: In step S1, dissolving and dispersing the polymer thickener in the organic solvent comprises: mixing the polymer thickener and the organic solvent, heating to 90-120° C., and fully stirring at a stirring speed of 60-120 rpm for 240-300 min.

9. Use of the gold paste for high-temperature NTC thermistor according to any one of claims 1 to 6 in preparing a surface metallization layer of a high-temperature NTC thermistor.

10. The use according to claim 9, characterized in that: It includes the following steps: The high-temperature NTC thermistor is printed on both sides of the NTC thermistor ceramic substrate with gold paste by screen printing, dried, and sintered.

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