Thick film slurry and preparation method thereof

Abstract

The invention relates to the technical field of electronic materials, in particular to thick film paste and a preparation method thereof, ZBS glass powder which is highly compatible with AIN ceramic and has specific components and particle sizes is adopted as a binding phase, an organic carrier formula is optimized, the thick film paste solves the problems of interface bubbles and layering caused by mismatching of traditional paste and an AIN substrate, and the thickness of the thick film paste is increased. The sufficient wetting of the glass relative to the substrate and the silver powder is realized, and a key foundation is laid for forming a compact and firmly combined metallized layer; according to the thick film paste, micron silver powder, nano silver powder and flake silver powder are compounded according to a specific proportion, the synergistic filling and overlapping effect of the silver powder with different morphologies is fully utilized, a more continuous and compact three-dimensional conductive network is constructed after sintering, and therefore the surface sheet resistance of a metallization layer is remarkably reduced, and the thickness of the metallization layer is improved. And excellent conductivity is obtained.

Description

Technical Field

[0001] This invention relates to the field of electronic materials technology, specifically to a thick film slurry and its preparation method. Background Technology

[0002] Thick film paste is a key material used in the manufacture of electronic components. It consists of a functional phase, a glass phase, an organic carrier, and additives. Its printing performance and electrical properties are directly affected by the ratio of the functional phase, glass phase, organic carrier, and additives. Due to its high thermal conductivity, thermal expansion coefficient matching that of silicon, and good electrical insulation, aluminum nitride ceramic has become an ideal packaging substrate material for high-power electronic devices and integrated circuits. However, the surface of AlN ceramic has high chemical inertness and poor wettability, and achieving reliable surface metallization is the key to its application in the packaging field. Thick film metallization is widely used due to its advantages such as simple process, low cost and suitability for high-density wiring. The core of this method is conductive paste, which is usually composed of conductive functional phase (such as silver powder), glass binder phase and organic carrier. Currently, most of the thick film pastes used in the market are designed for alumina (Al2O3) ceramics. If they are used directly for AlN ceramics, a large number of bubbles will be generated during the sintering process due to the poor compatibility between the glass binder phase and AlN, resulting in low density, poor adhesion and poor electrical performance of the metallization layer.

[0003] Therefore, developing a specialized thick-film conductive paste that is highly compatible with AlN ceramics and can simultaneously achieve high conductivity, high adhesion strength, and excellent printability has become a pressing technical problem to be solved in this field. Summary of the Invention

[0004] The purpose of this application is to provide a thick film slurry and a method for preparing the same.

[0005] Firstly, the thick film slurry provided in this application adopts the following technical solution: the thick film slurry, by mass percentage, is composed of the following components: Conductive functional phase: 65%-85%; Glass binder phase: 1%-10%; Organic carrier: 10%-30%; Functional additives: 0%-5%; The glass binder phase is a ZnO-B2O3-SiO2 system glass powder, and its composition by molar percentage is: ZnO 25%-35%, B2O3 55%-65%, and SiO2 5%-15%.

[0006] By adopting the above technical solution and selecting ZBS system glass powder with a specific composition range as a binder, this glass system has a low softening temperature and can form good wetting and chemical compatibility with the AIN ceramic substrate. This is the key to achieving high-performance AIN metallization and avoids problems such as bubbles and delamination caused by the mismatch between the glass phase and the substrate.

[0007] Preferably, the molar percentage composition of the glass binder phase is 30ZnO-60B2O3-10SiO2.

[0008] By adopting the above technical solution, the ZBS glass with this specific ratio has been proven in experiments to have the best comprehensive performance. It has a moderate softening point, the smallest wetting angle with AlN, a good matching coefficient of thermal expansion, and is dense and defect-free after sintering. It can most effectively promote the formation of a dense silver network and provide a strong interfacial bond.

[0009] Preferably, the median particle size D50 of the glass binder phase is 2.0 μm-4.0 μm.

[0010] By adopting the above technical solution, controlling the glass powder particle size within this range helps it to be evenly dispersed in the slurry, avoiding the formation of excessively large glass phase particles after sintering due to excessively large particle size, which would hinder the conductive path, or the easy agglomeration due to excessively fine particle size, which would affect the stability of the slurry and printing performance, thereby ensuring the formation of a uniform and dense glass adhesive layer.

[0011] Preferably, the conductive functional phase includes at least two of micron-sized silver powder, nano-sized silver powder, and flake-shaped silver powder.

[0012] By adopting the above technical solution and utilizing the synergistic effect of silver powders with different morphologies, the packing density and contact mode of silver powder in the slurry can be optimized. Micron-sized silver powder serves as a conductive framework, nano-sized silver powder fills the fine gaps and lowers the sintering temperature, while flake-shaped silver powder increases the conductive cross-section through surface contact, all working together to achieve [the desired effect]. Construct a conductive network with lower resistance.

[0013] Preferably, the conductive functional phase is composed of micron-sized silver powder, nano-sized silver powder, and flake-shaped silver powder; the nano-sized silver powder accounts for 5%-15% of the total mass of the conductive functional phase, the flake-shaped silver powder accounts for 30%-60% of the total mass of the conductive functional phase, and the remainder is micron-sized silver powder.

[0014] By adopting the above technical solution, the optimized compounding ratio can maximize the synergistic advantages of the three silver powders while ensuring good printability of the paste. The content of nano silver powder in this range can effectively fill the gaps without causing serious agglomeration; the content of flake silver powder in this range can form an effective surface contact conductive path, while avoiding the deterioration of the paste rheology due to excessive amount, thereby significantly reducing the sheet resistance of the sintered film.

[0015] Preferably, the functional additive is nano-copper oxide, and its addition amount is 1%-3% of the total mass of the slurry.

[0016] By adopting the above technical solution, the introduction of nano-copper oxide can react with the surface of the AlN substrate during sintering to form a CuAl2O4 spinel phase. Through strong chemical bonding, the adhesion strength between the metallization layer and the substrate is greatly improved. At the same time, its nanoscale characteristics help to form gas escape channels in the early stage of sintering, and because it forms a stable interface with Ag, it has minimal impact on electrical performance.

[0017] Preferably, the organic carrier comprises the following components by mass percentage: terpineol 55%-65%; Diethylene glycol butyl ether acetate 20%-25%; Dibutyl phthalate 4%-6%; Ethyl cellulose 4%-6%; Castor oil 3%-5%; Surfactants 1%-3%.

[0018] By adopting the above technical solution, this organic carrier formulation combines the hierarchical volatility characteristics of solvents with different boiling points, suitable thickening effect, good thixotropy and dispersibility, and can effectively encapsulate and support solid particles, enabling the slurry to obtain excellent screen printing performance and stable storage properties, and to achieve smooth operation during sintering. It decomposes and eliminates waste stably and thoroughly.

[0019] On the other hand, the thick film slurry preparation method provided in this application adopts the following technical solution: including the following steps: Step S1: Preparation of glass binder phase: Weigh ZnO, B2O3 or H3BO3, and SiO2 raw materials according to the ratio, mix them, melt and hold at 1300℃-1400℃ for 1-3 hours, and quench them with water to obtain glass slag; ball mill, sieve and dry the glass slag to obtain ZBS glass powder with the required particle size; Step S2: Preparation of organic carrier: Mix terpineol, diethylene glycol butyl ether acetate and dibutyl phthalate according to the ratio, add ethyl cellulose, heat and stir until dissolved, then add castor oil and surfactant, continue to stir and mix evenly, and cool for later use; Step S3: Preparation of slurry: Weigh the conductive functional phase, the glass binder phase obtained in step S1 and the functional additives according to the ratio, and premix them; then stir and mix them with the organic carrier obtained in step S2; finally, roll and disperse them through a three-roll mill to obtain a uniform conductive thick film slurry. Step S4: Application of conductive thick film paste: The conductive thick film paste is screen printed onto the surface of the AIN ceramic substrate. After drying, it is sintered in air at 830℃-870℃ for 10-20 minutes to form a metallization layer.

[0020] By adopting the above technical solution, the preparation method has a clear process flow and well-defined key process parameters. By first preparing stable glass powder and organic carrier, and then effectively premixing solid phase, mixing liquid phase, and rolling dispersion with high shear force, the high uniformity and good dispersion stability of each component in the slurry are ensured. Combined with the optimized sintering process, a dense, conductive and firmly bonded metallization layer can finally be formed on the AIN substrate.

[0021] Preferably, the peak temperature of the sintering is 850°C and the holding time is 15 minutes.

[0022] By adopting the above technical solution, the sintering process has been systematically optimized with key parameters. At this temperature and time, ZBS glass powder can be fully softened and melted, achieving optimal wetting of silver powder and optimal spreading and bonding to the AIN substrate. At the same time, the organic carrier is completely decomposed and discharged, and the silver particles form a dense and continuous conductive network, thereby enabling the metallization layer to achieve both the lowest sheet resistance and the highest bonding strength.

[0023] In summary, this application includes at least one of the following beneficial technical effects of thick film slurry and its preparation method: 1. By using ZBS glass powder with specific components and particle size that are highly compatible with AIN ceramics as the binder phase and optimizing the organic carrier formulation, the thick film slurry of this application solves the problems of interface bubbles and delamination caused by the mismatch between traditional slurries and AIN substrates, and achieves full wetting of the glass phase with the substrate and silver powder, laying a key foundation for the formation of a dense and firmly bonded metallization layer. 2. By using micron-sized silver powder, nano-sized silver powder and flake-shaped silver powder in a specific ratio, the thick film slurry of this application makes full use of the synergistic filling and overlapping effect of silver powder with different morphologies, and constructs a more continuous and dense three-dimensional conductive network after sintering, thereby significantly reducing the surface sheet resistance of the metallization layer and obtaining excellent conductivity. 3. By introducing a small amount of nano-copper oxide as a functional additive, the thick film slurry of this application can generate a CuAl2O4 spinel transition layer at the film-substrate interface through a chemical reaction during the sintering process, thereby greatly enhancing the bonding force between the metallization layer and the AlN ceramic substrate, increasing the shear strength by more than double, while having no adverse effect on the electrical properties of the slurry, achieving a perfect combination of high conductivity and high adhesion strength. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the preparation method of the present invention. Detailed Implementation

[0025] The following is in conjunction with the appendix Figure 1 This application will be described in further detail below.

[0026] Example 1: Preparation of ZBS glass powder Weigh out zinc oxide, boric acid and silicon dioxide raw materials with a molar ratio of 30:60:10, and mix them evenly in a mixer; put the mixture into an alumina crucible and place it in a lifting furnace; heat it to 1350℃ at a rate of 5℃ / min, and keep it at this temperature for 2 hours to fully homogenize and clarify the glass melt; Subsequently, the high-temperature molten glass was quickly poured into deionized water for water quenching, resulting in colorless, transparent or translucent brittle glass shards. After water quenching, the glass slag was dried in an oven at 120°C, then initially crushed using an alumina mortar and passed through a 200-mesh sieve to obtain coarse glass powder. Subsequently, the coarse glass powder, zirconia grinding balls, and deionized water were placed in a planetary ball mill jar at a mass ratio of ball:material:water = 2:1:1 and ball-milled at 300 rpm for 24 hours. After ball milling, the slurry was passed through a 325-mesh sieve, the undersize was collected, and dried at 120°C to obtain ZBS glass powder with a median particle size D50 of approximately 2.69 μm. The D90 of the powder was measured to be 5.16 μm using a Malvern MS2000 laser particle size analyzer.

[0027] Example 2: Preparation of organic carrier In a beaker equipped with a mechanical stirrer, add 62 g of terpineol, 22 g of diethylene glycol butyl ether acetate and 5 g of dibutyl phthalate in sequence, and stir at low speed until homogeneous. Then add 5 grams of ethyl cellulose to the mixed solvent, seal the beaker and place it in a water bath at 90°C using a heat-collecting constant-temperature magnetic stirrer; continue stirring for about 2.5 hours until the ethyl cellulose is completely dissolved and the system becomes a transparent, homogeneous, viscous liquid. Subsequently, 4 grams of castor oil as a thixotropic agent and 2 grams of triethanolamine as a surfactant were added to the system in sequence, and the mixture was stirred at 90°C for 1 hour to ensure that all components were fully and evenly mixed. Heating was stopped, the obtained organic carrier was removed, cooled to room temperature, and sealed for later use. The resulting organic carrier was a transparent, homogeneous, viscous liquid without visible particles or bubbles.

[0028] Example 3: Preparation of Thick Film Slurry Weigh each component according to the following mass percentages: Conductive functional phase: 70%; Micron-sized spherical silver powder, D50=1.01μm, tap density 5.09g / cm³, accounting for 40% of the conductive functional phase; Flaky silver powder, with a particle size range of 4-8 μm, accounts for 50% of the conductive functional phase; Nano-silver powder, D50≈100nm: accounts for 10% of the conductive functional phase; Glass binder phase: ZBS glass powder prepared in Example 1, 3%; Functional additives: Nano copper oxide, CuO, particle size <100nm, 3%; Organic carrier: The organic carrier prepared in Example 2, 24%; The preparation process is as follows: Place all the above-mentioned micron-sized silver powder, flake silver powder, nano silver powder, ZBS glass powder and nano CuO into a plastic container, add an appropriate amount of zirconia balls, and ball mill them at a low speed of 50 rpm for 2 hours on a drum ball mill to make all the solid powders initially mixed evenly. Transfer the premixed solid powder to a mixing tank and add the weighed organic carrier. Use a planetary mixer to stir at a low speed of 500 rpm for 10 minutes to allow the powder to be initially wetted by the organic carrier. Then switch to a high speed of 1500 rpm and stir at a vacuum of -0.095 MPa for 10 minutes to remove most of the air bubbles and obtain a pre-dispersed paste. The initially mixed slurry was rolled and dispersed using a three-roll mill; the gap between the rollers was gradually adjusted from large to small, and the slurry was rolled four times in total; finally, a paste-like conductive slurry with fine texture, uniform color, and good gloss was obtained; its fineness was measured to be 7.5 μm using a scraper fineness meter.

[0029] Example 4: Preparation and Properties of Metallized AlN Ceramic Substrates Substrate pretreatment: Commercial AlN ceramic substrate: 50mm×50mm×0.635mm was ultrasonically cleaned in anhydrous ethanol and deionized water for 15 minutes each, and then thoroughly dried in an oven at 120℃. Screen printing: The conductive silver paste prepared in Example 3 was printed onto a clean AlN substrate using a 400-mesh stainless steel screen; the printed pattern included 2mm×2mm squares and lines of a specific length; the printing parameters were set as follows: squeegee angle 60°, squeegee pressure 0.4MPa, and screen distance 1.5mm. Drying and leveling: After printing, the substrate is left to level at room temperature for 10 minutes, and then placed in a forced-air drying oven and kept at 150°C for 15 minutes to completely remove volatile solvents from the paste. Sintering: The dried substrate is placed in a muffle furnace and sintered in an air atmosphere. The sintering temperature profile used is as follows: the temperature is increased from room temperature to 350°C at a rate of 5°C / min and held for 30 minutes to ensure that the organic carrier is fully decomposed and discharged; then the temperature is increased to the peak temperature of 850°C at a rate of 5°C / min and held at 850°C for 15 minutes; finally, the substrate is allowed to cool naturally to room temperature in the furnace. Performance testing: Surface sheet resistance: Five different locations were randomly selected on the sintered silver layer using an SZT-2A four-probe tester, and the average value was taken; the measured surface sheet resistance was 6.2 milliohms. Shear strength: Tested using a STR-1000 micro solder joint strength tester; SnAgCu solder paste was coated on a 2mm×2mm silver layer, and copper foil was connected using a soft soldering process, and its shear strength was tested; the average value was 15.8MPa; Microstructure: The surface and cross-section of the silver layer were observed using a Zeiss Sigma 300 scanning electron microscope. The results showed that the silver layer was very dense with few pores and the silver particles were well connected to form a continuous conductive network. The silver layer was tightly bonded to the AlN substrate interface, with no visible delamination, cracks or large pores.

[0030] Comparative Example This comparative example uses the exact same formulation and preparation process as Example 3, but without adding 3% nano-CuO, to prepare a control slurry. A metallized AlN substrate is then prepared using the exact same process as in Example 4.

[0031] The performance test results are as follows: Surface sheet resistance: 7.6 milliohms; Shear strength: 7.6 MPa.

[0032] Effect Comparison and Analysis Comparing the test results of Example 4 with those of the comparative example, it is clear that: Regarding electrical performance, the sample of Example 4 with 3% nano-CuO added had a surface sheet resistance of 6.2 mMΩ, which was lower than the 7.6 mMΩ of the comparative example without addition. This indicates that under the preferred ratio, the introduction of nano-CuO in this invention not only did not impair conductivity, but may have a slight improvement effect on electrical performance by promoting sintering densification. In terms of mechanical properties, the effect is extremely significant. The shear strength of the sample in Example 4 was 15.8 MPa, more than double that of the comparative example (7.6 MPa). This fully demonstrates that nano-CuO, as a functional additive, plays a decisive role in enhancing the film-substrate adhesion by reacting with the AlN substrate to form the CuAl2O4 spinel phase.

[0033] In summary, this invention, through the synergistic effect of a ZBS glass binder with specific components, an optimized multimorphic silver powder gradation, and the key functional additive nano-CuO, combined with a refined preparation and sintering process, successfully prepared a thick-film conductive paste for AlN ceramic substrates with excellent comprehensive performance, particularly exhibiting both low sheet resistance and high adhesion.

[0034] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Identical components are represented by the same reference numerals. Therefore, all equivalent changes made to the structure, shape, and principle of this application should be covered within the scope of protection of this application.

Claims

1. A thick film slurry, characterized in that, The thick film slurry, by mass percentage, consists of the following components: Conductive functional phase: 65%-85%; Glass binder phase: 1%-10%; Organic carrier: 10%-30%; Functional additives: 0%-5%; The glass binder phase is a ZnO-B2O3-SiO2 system glass powder, and its composition by molar percentage is: ZnO 25%-35%, B2O3 55%-65%, and SiO2 5%-15%.

2. The thick film slurry according to claim 1, characterized in that: The molar percentage composition of the glass binder phase is 30ZnO-60B2O3-10SiO2.

3. The thick film slurry according to claim 1, characterized in that: The median particle size D50 of the glass binder phase is 2.0 μm-4.0 μm.

4. The thick film slurry according to claim 1, characterized in that: The conductive functional phase includes at least two of micron-sized silver powder, nano-sized silver powder, and flake-shaped silver powder.

5. The thick film slurry according to claim 4, characterized in that: The conductive functional phase is composed of micron-sized silver powder, nano-sized silver powder and flake-shaped silver powder; the nano-sized silver powder accounts for 5%-15% of the total mass of the conductive functional phase, the flake-shaped silver powder accounts for 30%-60% of the total mass of the conductive functional phase, and the remainder is micron-sized silver powder.

6. The thick film slurry according to claim 1, characterized in that: The functional additive is nano-copper oxide, and its addition amount is 1%-3% of the total mass of the slurry.

7. The thick film slurry according to claim 1, characterized in that: The organic carrier is composed of the following components by mass percentage: terpineol 55%-65%; Diethylene glycol butyl ether acetate 20%-25%; Dibutyl phthalate 4%-6%; Ethyl cellulose 4%-6%; Castor oil 3%-5%; Surfactants 1%-3%.

8. A method for preparing a thick film slurry as described in any one of claims 1-7, characterized in that, Includes the following steps: Step S1: Preparation of glass binder phase: Weigh ZnO, B2O3 or H3BO3, and SiO2 raw materials according to the ratio, mix them, melt and hold at 1300℃-1400℃ for 1-3 hours, and obtain glass slag after water quenching; ball mill, sieve and dry the glass slag to obtain ZBS glass powder with the required particle size; Step S2: Preparation of organic carrier: Mix terpineol, diethylene glycol butyl ether acetate and dibutyl phthalate according to the ratio, add ethyl cellulose, heat and stir until dissolved, then add castor oil and surfactant, continue to stir and mix evenly, and cool for later use; Step S3: Preparation of slurry: Weigh the conductive functional phase, the glass binder phase obtained in step S1 and the functional additives according to the ratio, and premix them; then stir and mix them with the organic carrier obtained in step S2; finally, roll and disperse them through a three-roll mill to obtain a uniform conductive thick film slurry. Step S4: Application of conductive thick film paste: The conductive thick film paste is screen printed onto the surface of the AIN ceramic substrate. After drying, it is sintered in air at 830℃-870℃ for 10-20 minutes to form a metallization layer.

9. The method for preparing a thick film slurry according to claim 8, characterized in that: the peak temperature of sintering is 850°C and the holding time is 15 minutes.

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