Ohmic contact modified thick-film copper paste adaptive to spinel ceramics and preparation method of ohmic contact modified thick-film copper paste

Abstract

The invention discloses ohmic contact modified thick-film copper paste adaptive to spinel ceramics and a preparation method of the ohmic contact modified thick-film copper paste. The ohmic contact modified thick-film copper paste comprises 80-85 wt% of high-purity copper powder, 0.5-1 wt% of an interface modifier, 4-7 wt% of a bonding aid, 0.3-0.8 wt% of a grain refiner, 0.2-0.5 wt% of an antioxidant aid and 12-15 wt% of a carrier. The preparation method comprises the following steps: drying in a high-temperature vacuum environment; weighing all the materials except the carrier, adding 4wt% of terpilenol, and stirring and mixing to obtain mixed powder; adding the terpilenol and the ethyl cellulose in the remaining proportion into the mixed powder, stirring and dispersing, and grinding for three times; after grinding is completed, terpilenol is added, and the viscosity of the copper paste is adjusted; the copper slurry is filtered, and large-particle impurities and aggregates are removed; and defoaming the copper paste to obtain the modified thick-film copper paste. The method has the advantages that the interface modifier provides excellent ohmic contact performance; the sintered copper paste is high in density, low in porosity, stable in sheet resistance and large in through-flow density, and is obviously superior to the traditional copper paste; the grain refiner avoids structural failure, and the long-term working reliability is improved; sn powder and copper form an alloy, so that the service life is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of copper paste manufacturing technology, and relates to the formulation and preparation method of copper paste for NTC thermistors. Specifically, it relates to an ohmic contact modified thick film copper paste adapted to spinel ceramics and its preparation method. Background Technology

[0002] Thick-film copper paste is the core material for reducing the cost of power-type NTC thermistors by replacing silver paste (cost is only 1 / 5 to 1 / 10 of silver paste). However, its interface compatibility with NTC spinel ceramics is a technical bottleneck: when traditional copper paste comes into direct contact with ceramics, an interface reaction easily occurs to generate a high-resistivity CuO-MO transition layer, leading to ohmic contact failure (contact resistance > 40mΩ); at the same time, traditional copper paste has low density (porosity > 12%) after sintering, resulting in poor current flow capacity, which cannot meet the high current flow requirements of power-type NTCs; in addition, the wetting and bonding force between traditional copper paste and Ti-Ta composite barrier layer and silver seed layer is weak, and the layers are easily peeled off. Furthermore, copper grains tend to grow during sintering, affecting structural stability.

[0003] Therefore, developing a modified thick-film copper paste that is compatible with spinel ceramics and can synergistically improve ohmic contact and increase density through a barrier layer / seed layer has become the core material support for copper electrodes to replace silver electrodes. Summary of the Invention

[0004] To address the aforementioned problems, the main objective of this invention is to design a modified thick-film copper paste that is compatible with spinel ceramics and can synergistically improve ohmic contact and increase density through a barrier layer / seed layer.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: An ohmic contact modified thick film copper paste adapted to spinel ceramics comprises 80-85 wt% high-purity copper powder, 0.5-1 wt% interface modifier, 4-7 wt% binder, 0.3-0.8 wt% grain refiner, 0.2-0.5 wt% antioxidant, and 12-15 wt% carrier.

[0006] As a further description of the present invention, the high-purity copper powder is spherical copper powder with a purity ≥99.9% and a particle size of 1-3μm.

[0007] As a further description of the present invention, the interface modifier is Ti powder with a particle size of 50-100 nm; the binder is low-melting-point borosilicate glass powder; the grain refiner is Zr powder with a particle size of 1-2 μm; the antioxidant is Sn powder with a particle size of 1-2 μm; and the carrier includes 2-3 wt% ethyl cellulose and 10-12 wt% terpineol.

[0008] The preparation method of the ohmic contact modified thick film copper paste adapted to spinel ceramics includes the following steps: Step 1: Raw material pretreatment. High-purity copper powder, interface modifier, binder, grain refiner, and antioxidant are dried in a high-temperature vacuum environment. Step 2: Material premixing. Weigh all materials except the carrier according to the above copper paste material ratio, and add 4wt% terpineol. Stir and mix at medium-low speed to obtain a mixed powder. Step 3: Dispersion and grinding. Add the remaining proportion of terpineol and ethyl cellulose to the mixed powder, stir and disperse at high speed. After stirring, grind three times with a three-roll mill with grinding gaps of 10μm, 5μm and 3μm. Step 4: Viscosity adjustment. After grinding, add terpineol to adjust the viscosity of the copper paste to 30 Pa·s (25℃) and thixotropic index 1.8. Step 5: Filtration and impurity removal: Filter the copper paste through a filter screen to remove large particles and agglomerates; Step 6: Vacuum degassing: Degas the filtered copper paste under a vacuum of 0.09 MPa for 20 minutes to obtain modified thick film copper paste.

[0009] As a further description of the present invention, in step one, the high temperature of the vacuum environment is 120°C and the drying time is 2 hours.

[0010] As a further description of the present invention, in both steps two and three, a planetary mixer is used for mixing. The low-speed mixing speed is 500 r / min and the time is 30 min; the high-speed mixing speed is 3000 r / min and the time is 60 min.

[0011] As a further description of the present invention, in step three, the particle size of the mixed powder agglomerates after grinding is <2μm.

[0012] As a further description of the present invention, in step five, the filter mesh pore size is 20 μm.

[0013] Compared with the prior art, the technical advantages of the present invention are as follows: This invention provides an ohmic contact modified thick-film copper paste adapted to spinel ceramics and its preparation method, which has the following advantages compared with traditional copper pastes. 1. This application uses Ti powder as an interface modifier, which can synergize with the Ti-Ta composite barrier layer of the NTC thermistor and form stable chemical bonds with spinel ceramics, providing excellent ohmic contact performance; 2. After sintering, it has high density, low porosity, stable sheet resistance, and high flow density, which is significantly better than traditional copper paste; 3. Glass powder significantly improves the wetting and bonding force between copper paste and other functional layers; 4. Zr powder grain refiner prevents structural failure caused by grain growth, thus improving long-term reliability; 5. Sn powder forms an alloy with copper, preventing copper oxidation and extending service life; 6. The cost is only 1 / 5 to 1 / 10 of that of silver paste. Its viscosity and thixotropy are suitable for thick film printing processes, and it can be used directly on existing production lines without the need for equipment modification. Detailed Implementation

[0014] The present invention will now be described in detail: This application provides an ohmic contact modified thick film copper paste adapted to spinel ceramics, which is mainly composed of the following components: 80-85wt% high-purity copper powder, 0.5-1wt% interface modifier, 4-7wt% binder, 0.3-0.8wt% grain refiner, 0.2-0.5wt% antioxidant, and 12-15wt% carrier.

[0015] The high-purity copper powder is spherical copper powder with a purity ≥99.9% and a particle size of 1-3μm; the interface modifier is Ti powder with a particle size of 50-100nm; the binder is low-melting-point borosilicate glass powder; the grain refiner is Zr powder with a particle size of 1-2μm; the antioxidant is Sn powder with a particle size of 1-2μm; and the carrier includes 2-3wt% ethyl cellulose and 10-12wt% terpineol.

[0016] The preparation method of the ohmic contact modified thick film copper paste adapted to spinel ceramics based on the above formulation includes the following steps: Step 1: Raw material pretreatment. High-purity copper powder, interface modifier, binder, grain refiner, and antioxidant are dried in a high-temperature vacuum environment. Step 2: Material premixing. Weigh all materials except the carrier according to the above copper paste material ratio, and add 4wt% terpineol. Stir and mix at medium-low speed to obtain a mixed powder. Step 3: Dispersion and grinding. Add the remaining proportion of terpineol and ethyl cellulose to the mixed powder, stir and disperse at high speed. After stirring, grind three times with a three-roll mill with grinding gaps of 10μm, 5μm and 3μm. Step 4: Viscosity adjustment. After grinding, add terpineol to adjust the viscosity of the copper paste to 30 Pa·s (25℃) and thixotropic index 1.8. Step 5: Filtration and impurity removal: Filter the copper paste through a filter screen to remove large particles and agglomerates; Step 6: Vacuum degassing: Degas the filtered copper paste under a vacuum of 0.09 MPa for 20 minutes to obtain modified thick film copper paste.

[0017] In step one, the vacuum environment temperature is 120℃ and the drying time is 2 hours.

[0018] In both steps two and three, a planetary mixer is used for mixing. The low-speed mixing speed is 500 r / min for 30 min, and the high-speed mixing speed is 3000 r / min for 60 min.

[0019] In step three, the particle size of the mixed powder agglomerates after grinding is <2μm.

[0020] In step five, the filter mesh pore size is 20 μm. Example

[0021] Three different proportions of ohmic contact modified thick film copper paste composition for spinel ceramics were selected, and the specific formulations are as follows: Ingredient ratio 1: High-purity copper powder: 81wt%, spherical, purity 99.95%, D50=2μm; Interface modifier: 0.6 wt%, Ti powder, particle size 80 nm; Binder: 5wt%, borosilicate glass powder, softening temperature 550-580℃; Grain refiner: 0.4 wt%, Zr powder, particle size 1.5 μm; Antioxidant: 0.3wt%, Sn powder, particle size 1.5μm; Carrier: 12.7 wt%, of which ethyl cellulose 2.5 wt% and terpineol 10.2 wt%.

[0022] Ingredient ratio 2: High-purity copper powder: 82wt%, spherical, purity 99.95%, D50=2μm; Interface modifier: 0.9wt%, Ti powder, particle size 80nm; Binder: 6wt%, borosilicate glass powder, softening temperature 550-580℃; Grain refiner: 0.7wt%, Zr powder, particle size 1.5μm; Antioxidant: 0.4 wt%, Sn powder, particle size 1.5 μm; Carrier: 10 wt%, of which ethyl cellulose 2.1 wt% and terpineol 7.9 wt%.

[0023] Ingredient ratio 3: High-purity copper powder: 80.5 wt%, spherical, purity 99.95%, D50=2μm; Interface modifier: 0.6 wt%, Ti powder, particle size 80 nm; Binder: 5wt%, borosilicate glass powder, softening temperature 550-580℃; Grain refiner: 0.4 wt%, Zr powder, particle size 1.5 μm; Antioxidant: 0.3wt%, Sn powder, particle size 1.5μm; Carrier: 13.2 wt%, of which ethyl cellulose 2.5 wt% and terpineol 10.7 wt%.

[0024] Choose any of the above component ratios to prepare an ohmic contact modified thick film copper paste adapted to spinel ceramics. The specific steps are as follows: Step 1: Raw material pretreatment. Copper powder, Ti powder, glass powder, Zr powder, and Sn powder are placed in a vacuum environment at 120℃ and dried for 2 hours. Step 2: Material premixing. Weigh out copper powder, Ti powder, glass powder, Zr powder, and Sn powder according to any of the above copper paste material composition ratios, and add 4wt% terpineol. Mix the powder using a planetary mixer at a medium-low speed of 500r / min for 30min to obtain a mixed powder. Step 3: Dispersion and grinding. Add the remaining proportion of terpineol and ethyl cellulose to the mixed powder, and disperse it by high-speed stirring at 3000 r / min for 60 min using a planetary mixer. After stirring, grind it three times with a three-roll mill with grinding gaps of 10 μm, 5 μm and 3 μm. The particle size of the agglomerates after grinding is <2 μm. Step 4: Viscosity adjustment. After grinding, add terpineol to adjust the viscosity of the copper paste to 30 Pa·s (25℃) and thixotropic index 1.8. Step 5: Filtration and impurity removal: Filter the copper paste through a 20μm filter to remove large particles and agglomerates; Step 6: Vacuum degassing: Degas the filtered copper paste under a vacuum of 0.09 MPa for 20 minutes to obtain modified thick film copper paste.

[0025] The modified thick-film copper paste obtained by using the above component ratio 1, 2, 3 is printed on a spinel ceramic substrate with a Ti-Ta composite barrier layer + silver seed layer to prepare an 8-10μm thick copper electrode, which is then reduced and sintered to form a power-type NTC thermistor.

[0026] The test results are shown in the table below: Contact resistance Density Porosity Fang Zu Flux density interlayer peel strength Copper grain size Resistance increase after 1000 hours of air aging at 150℃ Ingredient ratio 1 3.8mΩ 97.8% 2.5% 0.08Ω / □ 7.8A / mm² 3.0 N / mm 1.8μm 2.3% Ingredient ratio 2 4.2mΩ 98.2% 2.2% 0.06Ω / □ 7.6A / mm² 3.2N / mm 1.9μm 2.1% Ingredient ratio 3 4.3mΩ 97.5% 2.3% 0.09Ω / □ 7.4A / mm² 3.3 N / mm 1.7μm 2.2% As shown in the table above, the modified thick-film copper paste of this application, as the core material of the copper electrode for NTC thermistors, exhibits a contact resistance of less than 4.3 mΩ, demonstrating excellent ohmic contact performance. After sintering, the copper electrode has a density greater than 97.5% and a flux density greater than 7.4 A / mm², showcasing outstanding density and flux capacity. The interlayer peel strength is greater than 3.0 N / mm, indicating strong interlayer bonding. The copper grain size is controlled below 1.9 μm, resulting in high structural stability. After aging in air at 150℃ for 1000 hours, the resistance increase is less than 2.3%, demonstrating excellent oxidation resistance. In summary, the modified thick-film copper paste of this application is fully compatible with the copper electrode of NTC thermistors.

[0027] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the direction and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. An ohmic contact modified thick film copper paste suitable for adapting spinel ceramics, characterized in that: The high purity copper powder is 80-85wt%, the interface modifier is 0.5-1wt%, the binding aid is 4-7wt%, the grain refining agent is 0.3-0.8wt%, the antioxidant aid is 0.2-0.5wt%, and the carrier is 12-15wt%.

2. The adapted spinel ceramic ohmic contact modified thick film copper paste of claim 1, characterized in that: The high purity copper powder is spherical copper powder with purity ≥99.9% and particle size 1-3μm.

3. The adapted spinel ceramic ohmic contact modified thick film copper paste of claim 1, wherein: The interface modifier is Ti powder with particle size 50-100nm; the binding aid is low melting point borosilicate glass powder; the grain refining agent is Zr powder with particle size 1-2μm; the antioxidant aid is Sn powder with particle size 1-2μm; and the carrier includes ethyl cellulose 2-3wt% and terpineol 10-12wt%.

4. The method of making an adapted spinel ceramic ohmic contact modified thick film copper paste according to claim 1, characterized in that: The method comprises the following steps, Step one: raw material pretreatment, the high purity copper powder, the interface modifier, the binding aid, the grain refining agent and the antioxidant aid are respectively placed in a high temperature vacuum environment for drying; Step two: material pre-mixing, all the materials except the carrier are weighed according to the above copper paste material ratio, 4wt% terpineol is added, and mixing is carried out by low-speed stirring to obtain a mixed powder; Step three: dispersion and grinding, the remaining proportion of terpineol and ethyl cellulose is added to the mixed powder, high-speed stirring and dispersion are carried out, and three-roll grinding machine is used for grinding three times after stirring is completed, with grinding gaps of 10μm, 5μm and 3μm; Step four: viscosity adjustment, after grinding is completed, terpineol is added to adjust the viscosity of the copper paste to 30Pa·s (25℃) and the thixotropy index to 1.8; Step five: impurity removal by filtration, the copper paste is filtered through a filter screen to remove large particle impurities and agglomerates; Step six: vacuum degassing, the filtered copper paste is degassed under a vacuum degree of 0.09MPa for 20min to obtain a modified thick film copper paste.

5. The method of making an adapted spinel ceramic ohmic contact modified thick film copper paste according to claim 4, characterized in that: In step one, the high temperature in the vacuum environment is 120℃, and the drying time is 2h.

6. The method for preparing ohmic contact modified thick film copper paste adapted to spinel ceramics according to claim 4, characterized in that: In steps two and three, a planetary stirrer is used for stirring, the low-speed stirring speed is 500r / min, and the time is 30min; the high-speed stirring speed is 3000r / min, and the time is 60min.

7. The method of claim 4, wherein the thick film copper paste is prepared by mixing the spinel ceramic with the organic vehicle, the organic vehicle including a solvent, a dispersant, a binder, and a rheology modifier. In step three, the agglomerate particle size of the ground mixed powder is <2μm.

8. The method for preparing ohmic contact modified thick film copper paste adapted to spinel ceramics according to claim 4, characterized in that: In step five, the filter screen aperture is 20μm.