A method for preparing a black alumina substrate
By using Fe2O3 and MnO2 composite colorants and nano-encapsulated SiO2 treatment, combined with Y2O3, La2O3 and MgO to regulate the grain boundary phase, and employing hydrogen sintering and air annealing, the problems of lattice distortion and defects in the blackening process of alumina substrates were solved, and a black alumina substrate with high thermal conductivity and excellent mechanical strength was prepared, which is suitable for high-precision optical devices and covert integrated devices.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- FUJIAN HUAQING ELECTRONICS MATERIAL TECH
- Filing Date
- 2026-02-06
- Publication Date
- 2026-05-26
AI Technical Summary
It is difficult to achieve stable and uniform blackening of existing alumina substrates during the preparation process, resulting in low thermal conductivity and low mechanical strength. Furthermore, foreign ions introduced by traditional doping colorants cause lattice distortion and defects.
A specific ratio of Fe2O3 and MnO2 is used as a composite colorant, and SiO2 is nano-encapsulated. Y2O3, La2O3 and MgO are combined to regulate the grain boundary phase. Hydrogen atmosphere sintering and air annealing are used to form a uniform black grain boundary network, reducing lattice distortion and point defects. At the same time, plasma cleaning is performed.
A black alumina substrate with high thermal conductivity and mechanical strength has been developed, with a smooth and uniform surface, making it suitable for high-precision optical devices and covert integrated equipment, while reducing the impact of stray light interference and lattice defects.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of electronic ceramic substrates, and more particularly to a method for preparing a black alumina substrate. Background Technology
[0002] In the fields of electronic packaging, semiconductor heat dissipation, and optoelectronic devices, alumina ceramic substrates have long been widely used as key basic materials due to their excellent insulation properties, high thermal conductivity, good mechanical strength, and chemical stability. However, most commercially available alumina substrates currently exhibit an inherent white appearance. This white characteristic leads to a series of inherent limitations in practical applications: in high-precision optical sensors or camera modules, light reflection from the substrate surface can create stray light interference, reducing the signal-to-noise ratio and image quality; in military or high-end consumer electronic devices requiring concealed integration, the conspicuous white substrate is not conducive to visual concealment and integration; furthermore, in some specific application scenarios based on light absorption or thermal radiation, a white surface is not the optimal choice.
[0003] Therefore, there is a clear and continuous technological demand in the market for black alumina substrates with high light absorption capabilities. However, achieving stable, uniform, and high-performance blackening of alumina substrates has long faced severe materials science challenges. The core difficulty lies in the fact that color change is not a simple surface coating treatment, but often involves bulk phase modification of the matrix material. If traditional transition metal ion (such as Fe, Co, Mn, Cr, etc.) doping coloring strategies are adopted, these foreign ions, while entering the alumina lattice to achieve dd transitions and broadband light absorption, will inevitably introduce lattice distortion, point defects, and heterogeneous phases, thereby severely impairing the thermal conductivity, mechanical strength, and other properties of alumina. Summary of the Invention
[0004] Therefore, in view of the above problems, the present invention provides a method for preparing a black alumina substrate, which solves the defects of existing black alumina substrates, such as low thermal conductivity and low mechanical strength due to defects in the preparation process.
[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing a black alumina substrate, comprising the following preparation steps:
[0006] (1) Preparation of raw materials: Select α-alumina powder with a purity ≥99.9% (97.0wt%-98.8wt%), Fe2O3 (0.1wt%-0.3wt%), MnO2 (0.1wt%-0.3wt%), Y2O3 (0.05wt%-0.15wt%), MgO (0.05wt%-0.15wt%), La2O3 (0.1wt%-0.3wt%), and dispersant (0.8wt%-1.5wt%).
[0007] (2) Preparation of slurry: Place all the raw materials in step (1) into a ball mill jar, use anhydrous ethanol as the medium, use zirconium oxide grinding balls, and ball mill for 24h-48h at a ball milling speed of 200rpm-300rpm to obtain slurry;
[0008] (3) Casting: Add 8wt%-12wt% of binder and 3wt%-5wt% of plasticizer based on the total solid content of the slurry to the slurry obtained in step (2), and after ball milling and mixing evenly again, cast the slurry on the carrier film through a casting machine to form a wet film with a thickness of 0.1mm-1.0mm. After drying and demolding, cut the film into blanks of the required shape.
[0009] (4) Degreasing: Increase the temperature to 600℃ at a rate of 1℃ / min-3℃ / min and keep it at that temperature for 2h-2.5h;
[0010] (5) Sintering: Place the debinding blank in a sintering furnace under a hydrogen atmosphere, raise the temperature to 1450℃-1550℃ at a heating rate of 3℃ / min-5℃ / min, and sinter at this temperature for 3h-5h.
[0011] (6) Annealing: Anneal in air at 1300℃-1400℃ for 1.5h-2h, then allow to cool naturally;
[0012] (7) Surface treatment: Double-sided polishing until the surface roughness Ra≤0.02μm.
[0013] Furthermore, the dispersant is a phosphate ester.
[0014] Furthermore: the particle size of the zirconia grinding balls is 1mm-10mm, and the weight ratio of the zirconia grinding balls to the raw materials is 2.5:1-3.5:1.
[0015] Furthermore: the adhesive is polyvinyl butyral, and the plasticizer is a mixture of dibutyl phthalate and polyethylene glycol in a weight ratio of 1:1 to 3:1.
[0016] Further: After step (7), the obtained substrate is subjected to plasma cleaning, which is carried out in a mixed atmosphere of argon and oxygen, with a power of 300w-500W and a time of 3min-10min.
[0017] Further: Before preparing the raw materials in step (1), the Fe2O3 and MnO2 are pretreated by nano-encapsulation: using the sol-gel method, with tetraethyl orthosilicate as the precursor, a layer of SiO2 amorphous layer with a thickness of 5nm-20nm is coated on the surface of the colorant particles to form a core-shell structured composite powder, which is then used for subsequent mixing.
[0018] Further: In step (2), the ball milling is carried out in two stages: in the first stage, the ball milling is carried out at a speed of 300 rpm-400 rpm for 4 h-6 h, using large balls with a particle size of Φ8 mm-10 mm for preliminary crushing and mixing; in the second stage, the ball milling is carried out at a speed of 150 rpm-200 rpm for 20 h-30 h, using small balls with a particle size of Φ1 mm-3 mm for fine dispersion and homogenization.
[0019] Further: In step (3), after adding the binder and plasticizer, the slurry is subjected to online circulating shear dispersion treatment. The treatment is carried out by a high shear disperser at a speed of 2000 rpm-5000 rpm, while the slurry is continuously circulated in a closed pipeline. The treatment time is 30 min-60 min, so that the viscosity of the slurry is 3000±500 mPa˙s.
[0020] By adopting the aforementioned technical solution, the beneficial effects of the present invention are as follows:
[0021] 1. The method for preparing the black alumina substrate of the present invention uses Fe2O3 and MnO2 as composite colorants, wherein Fe... 3+ Ions and Mn 3+ / 4+ At high temperatures, it can partially dissolve in the alumina lattice and absorb visible light through dd electron transitions. It also tends to form black Fe3O4 and MnO4 spinel phases at grain boundaries. By strictly limiting its total amount to an ultra-low range of 0.2-0.6 wt%, lattice distortion and point defects caused by deep solid solution of foreign ions can be minimized. Thus, while achieving bulk coloring, the negative impact of black coloring on the inherent high thermal conductivity and electrical insulation properties of the substrate can be minimized.
[0022] 2. The introduction of Y2O3 and La2O3 helps to form high-melting-point grain boundary phases, promoting densification without forming a low thermal conductivity glass phase. MgO inhibits abnormal grain growth. The three work together to achieve sintering while ensuring a fine-grained structure, resulting in a high thermal conductivity of the final product.
[0023] 3. This invention employs medium-temperature sintering under a hydrogen atmosphere, which ensures sufficient densification while inhibiting excessive diffusion of colorant ions into the alumina lattice, causing them to preferentially segregate at grain boundaries, achieving "grain boundary coloring." This lays the microstructural foundation for obtaining a uniform black color. Subsequent air annealing can adjust the valence state of colorant ions at the grain boundaries, stabilizing them in a dark valence state and eliminating oxygen vacancies that may be introduced by the reducing atmosphere, further stabilizing and homogenizing the blackness while releasing stress.
[0024] 4. Furthermore, adding a plasma cleaning step after polishing can remove residual organic contaminants and adsorbates from the substrate surface, resulting in a more uniform surface appearance. In addition, it can provide a better surface condition for subsequent processing and improve product reliability.
[0025] 5. Before batching, Fe2O3 and MnO2 colorants are pretreated with SiO2 nano-encapsulation using a sol-gel method to form a core-shell structure. The SiO2 shell layer can effectively block direct contact between colorant particles during powder storage and slurry preparation, preventing hard agglomeration from the source and ensuring that they remain in an ultra-fine dispersed state in subsequent processes. In addition, during sintering, the SiO2 layer softens at high temperature and becomes a "channel" and "slow-release reservoir" for the diffusion of colorant ions (Fe³⁺, Mn³⁺, etc.) to the alumina grain boundaries, guiding the colorant ions to diffuse preferentially and uniformly and enrich in the alumina grain boundaries, forming a continuous black grain boundary network, achieving efficient and uniform "grain boundary coloring", while minimizing point defect scattering caused by colorant ions entering the alumina lattice, effectively protecting the thermal conductivity of the substrate. Detailed Implementation
[0026] Example 1
[0027] A method for preparing a black alumina substrate includes the following preparation steps:
[0028] (1) Preparation of raw materials: 98.8 wt% α-alumina powder with a purity of 99.9%, 0.1 wt% Fe2O3, 0.1 wt% MnO2, 0.05 wt% Y2O3, 0.05 wt% MgO, 0.1 wt% La2O3, and 0.8 wt% phosphate ester dispersant;
[0029] (2) Preparation of slurry: Place all the raw materials in step (1) into a ball mill jar, use anhydrous ethanol as the medium, use zirconium oxide grinding balls, and ball mill for 24 hours at a ball mill speed of 200 rpm to obtain slurry;
[0030] The zirconium oxide grinding balls have a particle size of 1-10 mm, and the ratio of zirconium oxide grinding balls to raw materials is 2.5:1 by weight. Specifically, the ball milling is carried out in two stages: the first stage is ball milling at 300 rpm for 4 hours, using large balls with a particle size of Φ8 mm for preliminary crushing and mixing; the second stage is ball milling at 150 rpm for 20 hours, using small balls with a particle size of Φ1 mm for fine dispersion and homogenization.
[0031] (3) Casting: Add 8 wt% binder and 3 wt% plasticizer based on the total solid content of the slurry to the slurry obtained in step (2), and after ball milling and mixing evenly, cast the slurry on the carrier film through a casting machine to form a wet film with a thickness of 0.1 mm. After drying and demolding, cut the film into blanks of the required shape.
[0032] (4) Degreasing: Increase the temperature to 600℃ at 1℃ / min and keep it at that temperature for 2 hours;
[0033] (5) Sintering: The debinding blank is placed in a sintering furnace in a hydrogen atmosphere and heated to 1450°C at a heating rate of 3°C / min, and sintered at this temperature for 3 hours.
[0034] (6) Annealing: Anneal in air at 1300℃ for 1.5h, then allow to cool naturally;
[0035] (7) Surface treatment: Double-sided polishing to a surface roughness Ra=0.02μm.
[0036] In this embodiment, the adhesive is polyvinyl butyral, and the plasticizer is a mixture of dibutyl phthalate and polyethylene glycol in a weight ratio of 1:1.
[0037] Example 2
[0038] A method for preparing a black alumina substrate includes the following preparation steps:
[0039] (1) Preparation of raw materials: 98.1 wt% α-alumina powder with a purity of 99.95%, 0.2 wt% Fe2O3, 0.2 wt% MnO2, 0.1 wt% Y2O3, 0.1 wt% MgO, 0.2 wt% La2O3, and 1.1 wt% phosphate ester dispersant;
[0040] (2) Preparation of slurry: All raw materials in step (1) are placed in a ball mill jar, and anhydrous ethanol is used as the medium. Zirconia grinding balls are used to ball mill for 36 hours at a speed of 250 rpm to obtain slurry. The particle size of the zirconia grinding balls is 1-10 mm. The ratio of the amount of zirconia grinding balls to the raw materials is 3:1 by weight. The ball milling is carried out in two stages: the first stage is ball milling at a speed of 350 rpm for 5 hours, using large balls with a particle size of Φ9 mm for preliminary crushing and mixing; the second stage is ball milling at a speed of 180 rpm for 25 hours, using small balls with a particle size of Φ2 mm for fine dispersion and homogenization.
[0041] (3) Casting: Add 10 wt% binder and 4 wt% plasticizer based on the total solid content of the slurry to the slurry obtained in step (2), and after ball milling and mixing evenly again, cast the slurry on the carrier film through a casting machine to form a wet film with a thickness of 0.5 mm. After drying and demolding, cut the film into blanks of the required shape.
[0042] (4) Glue removal: Increase the temperature to 600℃ at 2℃ / min and keep it at that temperature for 2.3h;
[0043] (5) Sintering: The debinding blank is placed in a sintering furnace in a hydrogen atmosphere and heated to 1500℃ at a heating rate of 4℃ / min, and sintered at this temperature for 4h.
[0044] (6) Annealing: Anneal in air at 1350℃ for 1.8h, then allow to cool naturally;
[0045] (7) Surface treatment: Double-sided polishing to a surface roughness Ra=0.01μm.
[0046] (8) The obtained substrate is subjected to plasma cleaning in an atmosphere of argon and oxygen, with a power of 300W and a time of 3min.
[0047] The adhesive is polyvinyl butyral, and the plasticizer is a mixture of dibutyl phthalate and polyethylene glycol in a weight ratio of 2:1.
[0048] Example 3
[0049] A method for preparing a black alumina substrate includes the following preparation steps:
[0050] (1) Preparation of raw materials: 97.3 wt% α-alumina powder with a purity of 99.97%, 0.3 wt% Fe2O3, 0.3 wt% MnO2, 0.15 wt% Y2O3, 0.15 wt% MgO, 0.3 wt% La2O3, and 1.5 wt% phosphate ester dispersant;
[0051] The steps for nano-encapsulation pretreatment of Fe2O3 and MnO2 are as follows: using the sol-gel method, with tetraethyl orthosilicate as a precursor, a 10 nm thick SiO2 amorphous layer is coated on the surface of the colorant particles to form a core-shell structured composite powder, which is then used for subsequent mixing.
[0052] (2) Preparation of slurry: Place all the raw materials in step (1) in a ball mill jar, use anhydrous ethanol as the medium, and use zirconia grinding balls to ball mill for 24h-48h at a ball milling speed of 200rpm-300rpm to obtain slurry; the particle size of the zirconia grinding balls is 10mm, and the ratio of the amount of zirconia grinding balls to the raw materials is 3.5:1 by weight; the ball milling is carried out in two stages: the first stage is ball milling at 400rpm for 6h, using large balls with a particle size of Φ10mm for preliminary crushing and mixing; the second stage is ball milling at 200rpm for 30h, using small balls with a particle size of Φ3mm for fine dispersion and homogenization;
[0053] (3) Casting: Add 12 wt% binder and 5 wt% plasticizer based on the total solid content of the slurry to the slurry obtained in step (2), and after ball milling and mixing evenly again, cast the slurry on the carrier film through a casting machine to form a wet film with a thickness of 1.0 mm. After drying and demolding, cut the film into blanks of the required shape. After adding binder and plasticizer, the slurry is subjected to online circulating shear dispersion treatment. The treatment is carried out by a high shear disperser at a speed of 3800 rpm, while the slurry is continuously circulated in a closed pipeline. The treatment time is 45 min, so that the viscosity of the slurry is 3000 mPa·s.
[0054] (4) Degreasing: Increase the temperature to 600℃ at 3℃ / min and keep it at that temperature for 2.5h;
[0055] (5) Sintering: The debinding blank is placed in a sintering furnace in a hydrogen atmosphere and heated to 1550°C at a heating rate of 5°C / min, and sintered at this temperature for 5 hours.
[0056] (6) Annealing: Anneal in air at 1400℃ for 2 hours, then allow to cool naturally;
[0057] (7) Surface treatment: Double-sided polishing to a surface roughness Ra=0.01μm;
[0058] The adhesive is polyvinyl butyral, and the plasticizer is a mixture of dibutyl phthalate and polyethylene glycol in a weight ratio of 3:1.
[0059] The substrate is subjected to plasma cleaning in a mixed atmosphere of argon and oxygen, with a power of 500W and a time of 10 minutes.
[0060] The performance of the black alumina substrates obtained in Examples 1 to 3 of this application was tested, and the results are shown in the table below:
[0061]
[0062] The thermal conductivity was tested using the laser flare method, the bending strength was tested using the three-point bending method (JIS R1601), and the blackness was measured using the reflectance spectrophotometry method.
[0063] In this invention, the thickness of the SiO2 amorphous layer is 5nm-20nm. In step (3), after adding the binder and plasticizer, the slurry is subjected to online circulating shear dispersion treatment. The treatment is carried out by the high shear disperser at a speed of 2000 rpm-5000 rpm, while the slurry is continuously circulated in a closed pipeline for a treatment time of 30 min-60 min, so that the slurry viscosity is 3000±500 mPa˙s. The purpose of this invention can be achieved within the above parameter range.
[0064] Although the invention has been specifically shown and described in conjunction with preferred embodiments, those skilled in the art should understand that various changes in form and detail may be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims, all of which shall be within the scope of protection of the invention.
Claims
1. A method of producing a black alumina substrate, characterized by, The preparation steps include the following: (1) Preparation of raw materials: Select α-alumina powder with a purity ≥99.9% (97.3wt%-98.8wt%), Fe2O3 (0.1wt%-0.3wt%), MnO2 (0.1wt%-0.3wt%), Y2O3 (0.05wt%-0.15wt%), MgO (0.05wt%-0.15wt%), La2O3 (0.1wt%-0.3wt%), and dispersant (0.8wt%-1.5wt%). (2) Preparation of slurry: Place all the raw materials in step (1) into a ball mill jar, use anhydrous ethanol as the medium, use zirconium oxide grinding balls, and ball mill for 24h-48h at a ball milling speed of 200rpm-300rpm to obtain slurry; (3) Casting: Add 8wt%-12wt% of binder and 3wt%-5wt% of plasticizer based on the total solid content of the slurry to the slurry obtained in step (2), and after ball milling and mixing again, cast the slurry on the carrier film through a casting machine to form a wet film with a thickness of 0.1mm-1.0mm. After drying and demolding, cut the film into blanks of the required shape. (4) Degreasing: Increase the temperature to 600℃ at a rate of 1℃ / min-3℃ / min and keep it at that temperature for 2h-2.5h; (5) Sintering: Place the debinding blank in a sintering furnace under a hydrogen atmosphere, raise the temperature to 1450℃-1550℃ at a heating rate of 3℃ / min-5℃ / min, and sinter at this temperature for 3h-5h. (6) Annealing: Anneal in air at 1300℃-1400℃ for 1.5h-2h, then allow to cool naturally; (7) Surface treatment: Double-sided polishing until the surface roughness Ra≤0.02μm.
2. The method for preparing a black alumina substrate according to claim 1, characterized in that: The dispersant is a phosphate ester.
3. The method for preparing a black alumina substrate according to claim 1, characterized in that: The zirconium oxide grinding balls have a particle size of 1mm-10mm, and the ratio of the zirconium oxide grinding balls to the raw materials is 2.5:1-3.5:1 by weight.
4. The method for preparing a black alumina substrate according to claim 1, characterized in that: The adhesive is polyvinyl butyral, and the plasticizer is a mixture of dibutyl phthalate and polyethylene glycol in a weight ratio of 1:1 to 3:
1.
5. The method for preparing a black alumina substrate according to claim 1, characterized in that: After step (7), the obtained substrate is further subjected to plasma cleaning, which is carried out in a mixed atmosphere of argon and oxygen, with a power of 300w-500W and a time of 3min-10min.
6. The method for preparing a black alumina substrate according to claim 1, characterized in that: Before preparing the raw materials in step (1), the Fe2O3 and MnO2 are further subjected to a nano-encapsulation pretreatment step: using the sol-gel method, tetraethyl orthosilicate is used as a precursor to coat the surface of the colorant particles with a SiO2 amorphous layer with a thickness of 5nm-20nm to form a core-shell structured composite powder, which is then used for subsequent mixing.
7. The method for preparing a black alumina substrate according to claim 1, characterized in that: In step (2), the ball milling is carried out in two stages: the first stage is ball milling at a speed of 300 rpm-400 rpm for 4 h-6 h, using large balls with a particle size of Φ8 mm-10 mm for preliminary crushing and mixing; the second stage is ball milling at a speed of 150 rpm-200 rpm for 20 h-30 h, using small balls with a particle size of Φ1 mm-3 mm for fine dispersion and homogenization.
8. The method for preparing a black alumina substrate according to claim 1, characterized in that: In step (3), after adding the binder and plasticizer, the slurry is subjected to online circulating shear dispersion treatment. The treatment is carried out by a high shear disperser at a speed of 2000 rpm-5000 rpm, while the slurry is continuously circulated in a closed pipeline. The treatment time is 30 min-60 min, so that the viscosity of the slurry is 3000±500 mPa·s.