Aluminum oxide ceramic substrate, preparation method thereof and application of aluminum oxide ceramic substrate in thin film integrated circuit

Abstract

The invention belongs to the technical field of ceramic circuit substrates, and particularly relates to an aluminum oxide ceramic substrate, a preparation method thereof and application of the aluminum oxide ceramic substrate in a thin film integrated circuit. The preparation method comprises the following steps: mixing a ceramic material, an adhesive and an organic solvent to obtain slurry; the slurry is subjected to film forming, drying and forming in sequence, and a green sheet is obtained; glue discharging is conducted on the green body sheet in the oxygen atmosphere, and the green body sheet subjected to glue discharging is obtained; sintering the green body sheet subjected to glue removal in a protective gas atmosphere to obtain a sintered substrate; and carrying out annealing treatment on the sintered substrate to obtain the aluminum oxide ceramic substrate. The aluminum oxide ceramic substrate prepared by the invention has relatively high purity and compactness and low dielectric loss, and can be widely applied to high-end electronic components.

Description

Technical Field

[0001] This invention belongs to the field of ceramic circuit substrate technology, specifically relating to an alumina ceramic substrate, its preparation method, and its application in thin-film integrated circuits. Background Technology

[0002] Alumina ceramic substrates are the most widely used ceramic substrate material in the electronics industry. Currently, the mainstream products on the market are alumina ceramic substrates with a purity of 96% and 99%, and a thickness of 0.2 mm or more. The higher the purity of the ceramic substrate, the higher its dielectric constant, the lower its dielectric loss, and the better its surface finish. The current conventional preparation method is as follows: alumina powder, sintering aids (such as SiO2, MgO, CaO, etc.), and organic binders (such as polyvinyl butyral (PVB)) are mixed by ball milling, and then the mixture is dry-pressed or cast into a green body, which is then sintered in an air atmosphere at 1550~1650℃.

[0003] A related technology discloses an alumina ceramic substrate, its preparation method, and its applications. This method uses components comprising the following mass percentages: 99-99.5% alumina, 0.1-0.6% MgO-CaO-SiO2, 0.3-0.5% variable-valence oxides, and 0.1-0.5% rare-earth oxides. By employing a composite of alumina, MgO-CaO-SiO2, rare-earth oxides, and variable-valence oxides, it achieves high purity (99% alumina content), a relatively low sintering temperature, high density, high mechanical strength, and high breakdown strength, making it suitable for electronic products requiring low loss and high purity. However, to ensure effective low-temperature sintering, various additives are added in a total amount up to 1.6%, which limits further improvement in material purity. These additives, especially the MgO-CaO-SiO2 glass phase and variable valence metal ions, may accumulate at grain boundaries, increasing dielectric loss at high frequencies and making their dielectric loss tangent (tanδ) too high, which makes it difficult to meet the extreme requirements of ultra-high frequency (such as millimeter wave and terahertz) applications.

[0004] Another related technology discloses a high-purity, ultrathin, high-strength alumina ceramic substrate, its preparation method, and its applications. This method uses 99.9% pure α-phase alumina powder, without adding any sintering aids, to prepare the alumina ceramic substrate under atmospheric conditions. The resulting substrate has a thickness of 0.13~1.10 mm and a bulk density >3.88 g / cm³. 3 Bending strength > 550 MPa, dielectric loss tangent (tanδ) ≤ 5 × 10⁻⁶ -4The advantage of this approach is that it avoids the influence of sintering aids on purity and achieves high strength through fine grain strengthening. However, its disadvantages are: 1) To achieve sufficient density and strength, the sintering temperature window is narrow, and it is highly dependent on the powder particle size; 2) Without sintering aids to inhibit grain growth, abnormal grain growth is easily caused when pursuing higher densification, resulting in high ceramic porosity, easy product warping, and low yield; 3) When the thickness is reduced to 0.13mm, the densification kinetic energy of low-temperature sintering is insufficient, resulting in low volume density, which is not conducive to further improving structural strength and reducing dielectric loss.

[0005] The methods disclosed in the aforementioned related technologies either have low substrate material purity and contain a lot of sintering aids (such as CaO-SiO2 forming a glass phase), or the substrate material has high purity but is difficult to sinter, has low bulk density and many pores, resulting in a large dielectric loss tangent (tanδ) at high frequencies and severe signal transmission energy loss. Summary of the Invention

[0006] The purpose of this invention is to provide an alumina ceramic substrate, its preparation method, and its application in thin-film integrated circuits. The alumina ceramic substrate prepared by this invention has high purity and density, low dielectric loss, and can be widely used in high-end electronic components.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing an alumina ceramic substrate, comprising the following steps: A ceramic material, adhesive, and organic solvent are mixed to obtain a slurry. The ceramic material includes α-alumina powder and a sintering aid. The purity of the α-alumina powder is >99.99%. The sintering aid includes one or more of MgO, ZrO2, Y2O3, and La2O3. The sintering aid is of analytical grade, and the mass percentage of the sintering aid in the ceramic material is ≤0.5%. The slurry is sequentially formed into a film, dried, and shaped to obtain a green sheet; The green sheet is debonded in an oxygen atmosphere to obtain a debonded green sheet. The debinding green sheet is sintered in a protective gas atmosphere to obtain a sintered substrate. The sintering includes heating from a first temperature to a second temperature at a first heating rate, then heating from the second temperature to a third temperature at a second heating rate, and then holding at the third temperature. The first temperature is 1000~1200℃, the second temperature is 1200~1500℃, and the third temperature is 1500~1600℃. The first heating rate is ≤2℃ / min, the second heating rate is ≤1℃ / min, and the holding time is 2~6h. The sintered substrate is annealed to obtain the alumina ceramic substrate.

[0008] Preferably, the film formation method is casting, the thickness of the green sheet is ≤0.3mm, the heat preservation temperature for glue removal is 400~600℃, the heat preservation time is 6~8h, and the heating rate from room temperature to the heat preservation temperature for glue removal is ≤1℃ / min.

[0009] Preferably, the annealing treatment is carried out in an oxygen-containing atmosphere, the annealing temperature is 1100~1200℃, and the holding time of the annealing treatment is 3~4h; the surface roughness Ra of the alumina ceramic substrate is ≤0.1μm.

[0010] Preferably, the sintering atmosphere is hydrogen, the first temperature is 1150°C, the second temperature is 1500°C, the third temperature is 1600°C, the first heating rate is 2°C / min, and the second heating rate is 0.5~1°C / min.

[0011] Preferably, the average particle size of the α-alumina powder is 0.2~0.5μm; the sintering aid is MgO, ZrO2 and Y2O3, or MgO, ZrO2 and La2O3; and the mass percentage of the sintering aid in the ceramic material is 0.3~0.5%.

[0012] Preferably, the adhesive comprises polyvinyl butyral and di(2-ethylhexyl) phthalate, wherein the mass ratio of polyvinyl butyral to di(2-ethylhexyl) phthalate is (4~6):(2~3); and the mass ratio of ceramic material to polyvinyl butyral is (40~55):(2.8~4.5).

[0013] Preferably, the organic solvent includes xylene and ethanol, and the mass ratio of xylene to ethanol is (13.5~14.4):(12.0~13.3); the viscosity of the slurry is 6500~9500 mPa·s.

[0014] The present invention provides an alumina ceramic substrate prepared by the preparation method described in the above technical solution.

[0015] Preferably, the thickness of the alumina ceramic substrate is ≤0.3mm; and the purity of the alumina ceramic substrate is ≥99.6%.

[0016] This invention provides the application of the alumina ceramic substrate described above in high-frequency communication devices, semiconductor devices, advanced packaging, or MEMS sensors.

[0017] This invention provides a method for preparing an alumina ceramic substrate, comprising the following steps: mixing a ceramic material, an adhesive, and an organic solvent to obtain a slurry, wherein the ceramic material includes α-alumina powder and a sintering aid, the purity of the α-alumina powder being >99.99%, and the sintering aid including one or more of MgO, ZrO2, Y2O3, and La2O3, wherein the sintering aid is analytically pure, and the mass percentage of the sintering aid in the ceramic material is ≤0.5%; sequentially forming, drying, and shaping the slurry to obtain a green sheet; subjecting the green sheet to binder removal in an oxygen atmosphere to obtain a binder-removed green sheet; and then subjecting the binder-removed green sheet to a heat treatment process. Sintering is performed in a protective gas atmosphere to obtain a sintered substrate. The sintering process includes heating from a first temperature to a second temperature at a first heating rate, then heating from the second temperature to a third temperature at a second heating rate, and then holding at the third temperature. The first temperature is 1000~1200℃, the second temperature is 1200~1500℃, and the third temperature is 1500~1600℃. The first heating rate is ≤2℃ / min, the second heating rate is ≤1℃ / min, and the holding time is 2~6h. The sintered substrate is then annealed to obtain the alumina ceramic substrate. This invention uses α-alumina powder with a purity >99.99% as raw material, adds trace amounts of sintering aids, and precisely controls the sintering curve in stages. By controlling the first and second heating rates, this invention allows the sintering aids to form a solid solution with the α-Al2O3 grains, or to generate a small amount of liquid phase. This causes rearrangement between particles and grain boundary movement, thus eliminating pores. During the high-temperature holding stage at the third temperature, the holding time is 2-6 hours. This holding promotes further grain growth, improves intercrystalline bonding, and allows gases to escape through grain boundaries. Controlling the first and second heating rates effectively prevents excessively rapid grain boundary movement, which could lead to grain encapsulation of pores or incomplete pore removal, thus reducing defects such as pores or microcracks in the microstructure. By employing an appropriate holding time at the third temperature, this invention allows for optimal crystal development, enabling the crystal grains to grow to a certain size (2-4 μm), reducing the number of grain boundaries and residual pores, thereby improving the density and structural strength of the alumina ceramic substrate. Furthermore, because this invention achieves sufficient densification of the alumina ceramic substrate by controlling the third sintering temperature to 1500-1600℃, it significantly reduces impurity ions and the glassy phase, resulting in extremely low dielectric loss (≤1.0 × 10⁻⁶). -4This invention solves the problem of insufficient dielectric properties in existing alumina ceramic substrates, making them perfectly suitable for high-frequency applications. Furthermore, because this invention involves high-temperature sintering and controlled holding time, a fine and uniform grain structure (2~4μm) is obtained, which also imparts high mechanical strength (≥470MPa) to the alumina ceramic substrate material, making it more reliable in subsequent processing and use. Finally, the annealing treatment of this invention can better release sintering thermal stress, improving the mechanical and dielectric properties of the alumina ceramic substrate. In summary, the alumina ceramic substrate prepared by this invention has high purity and density, low dielectric loss, and can be widely used in high-end electronic components.

[0018] Furthermore, the existing technology produces alumina ceramic substrates with a relatively large thickness (≥0.20 mm), resulting in high thermal resistance. This hinders the timely dissipation of heat generated by high-power devices (such as GaN power amplifiers and laser diodes), affecting device performance and reliability. In this invention, the film formation method is casting, the thickness of the green sheet is 0.02~0.1 mm, the holding temperature for debinding is 400~600℃, the holding time is 6~8 h, and the heating rate from room temperature to the holding temperature for debinding is ≤1℃ / min. This invention employs a casting process to achieve a green sheet thickness of ≤0.1mm. By controlling the heating rate and holding temperature during binder removal, this invention can thoroughly and slowly remove organic components while effectively suppressing deformation and cracking of the green sheet and ceramic body during binder removal. This successfully achieves a high yield of ultra-thin ceramic sheets, solving the problem of difficulty in achieving ultra-thinness in existing technologies. This invention can successfully control the thickness of the final alumina ceramic substrate product to 0.1mm while maintaining high thermal conductivity, thus significantly reducing the thermal resistance of the substrate and greatly improving its heat dissipation capacity. This solves the problem of limited thermal management performance of alumina ceramic substrates and is suitable for high power density devices.

[0019] Furthermore, the annealing treatment is carried out in an oxygen-containing atmosphere at a temperature of 1100~1200℃ for 3~4 hours. This invention, by annealing in an oxygen-containing atmosphere, can oxidize the small amount of impurities remaining on the material surface generated during sintering, achieving a surface purification effect. This further improves the surface smoothness and flatness of the alumina ceramic substrate, resulting in an alumina ceramic substrate with a precise final thickness of 0.1mm and an ultra-smooth surface (Ra≤0.1μm).

[0020] This invention provides an alumina ceramic substrate prepared by the method described above. The alumina ceramic substrate prepared by this invention can simultaneously meet the requirements of ultra-high purity (≥99.6%) and high bulk density (≥3.92 g / cm³). 3It meets requirements for both high density and extremely thin thickness (0.1mm), and possesses high mechanical strength (flexural strength ≥470MPa) and excellent high-frequency dielectric properties (dielectric loss ≤1×10⁻⁶). -4 This overcomes the technical bottlenecks of existing ordinary alumina ceramic substrates in high-frequency, high-power, and miniaturized electronic applications, such as high dielectric loss, high thermal resistance, and bulky size. Attached Figure Description

[0021] Figure 1 Physical images of the product provided for embodiments of the present invention; Figure 2 SEM images of the products provided in this embodiment of the invention; Figure 3 The preparation process flowchart is provided for an embodiment of the present invention. Detailed Implementation

[0022] This invention provides a method for preparing an alumina ceramic substrate, comprising the following steps: A ceramic material, adhesive, and organic solvent are mixed to obtain a slurry. The ceramic material includes α-alumina powder and a sintering aid. The purity of the α-alumina powder is >99.99%. The sintering aid includes one or more of MgO, ZrO2, Y2O3, and La2O3. The sintering aid is of analytical grade, and the mass percentage of the sintering aid in the ceramic material is ≤0.5%. The slurry is sequentially formed into a film, dried, and shaped to obtain a green sheet; The green sheet is debonded in an oxygen atmosphere to obtain a debonded green sheet. The debinding green sheet is sintered in a protective gas atmosphere to obtain a sintered substrate. The sintering includes heating from a first temperature to a second temperature at a first heating rate, then heating from the second temperature to a third temperature at a second heating rate, and then holding at the third temperature. The first temperature is 1000~1200℃, the second temperature is 1200~1500℃, and the third temperature is 1500~1600℃. The first heating rate is ≤2℃ / min, the second heating rate is ≤1℃ / min, and the holding time is 2~6h. The sintered substrate is annealed to obtain the alumina ceramic substrate.

[0023] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0024] This invention mixes ceramic material, adhesive, and organic solvent to obtain a slurry. The ceramic material includes α-alumina powder and sintering aid. The purity of the α-alumina powder is >99.99%. The sintering aid includes one or more of MgO, ZrO2, Y2O3, and La2O3. The sintering aid is analytically pure, and the mass percentage of the sintering aid in the ceramic material is ≤0.5%.

[0025] In this invention, the average particle size (D) of the α-alumina powder is... 50 The preferred particle size is 0.2~0.5 μm. The sintering aid is nanoscale. The preferred sintering aid is MgO, ZrO2, and Y2O3. Alternatively, the preferred sintering aid is MgO, ZrO2, and La2O3. The mass percentage of the sintering aid in the ceramic material is preferably 0.3~0.5%, more preferably 0.3~0.4%. When the preferred sintering aid is MgO, ZrO2, and Y2O3, the mass percentage of MgO in the ceramic material is preferably 0.05~0.1%, the mass percentage of ZrO2 is preferably 0.05~0.1%, the mass percentage of Y2O3 is preferably 0.1~0.2%, and the balance is α-alumina powder. When the sintering aid is preferably MgO, ZrO2 and La2O3, the mass percentage of MgO in the ceramic material is preferably 0.1~0.2%, the mass percentage of ZrO2 is preferably 0.05~0.1%, the mass percentage of Y2O3 is preferably 0.05~0.1%, and the balance is α-alumina powder.

[0026] In this invention, the adhesive preferably comprises polyvinyl butyral and di(2-ethylhexyl) phthalate. The mass ratio of polyvinyl butyral to di(2-ethylhexyl) phthalate is preferably (4~6):(2~3), and in the examples it can be 2:1. The mass ratio of the ceramic material to the polyvinyl butyral is preferably (40~55):(2.8~4.5).

[0027] In this invention, the organic solvent preferably includes xylene and ethanol. The mass ratio of xylene to ethanol is preferably (13.5~14.4):(12.0~13.3). The viscosity of the slurry is preferably 6500~9500 mPa·s.

[0028] In this invention, the mixing is preferably ball milling. After the ball milling is completed, the resulting material is sequentially filtered and degassed to obtain a slurry. This invention uses ball milling to fully mix and disperse the components, forming a uniform, stable, and bubble-free slurry.

[0029] After obtaining the slurry, the present invention sequentially forms a film, dries and shapes the slurry to obtain a green sheet.

[0030] In this invention, the film formation method is casting. Preferably, in a clean, temperature-controlled environment, the slurry is cast onto a PET carrier film using a precision casting machine to form a green film strip. Preferably, the green film strip is then dried and shaped sequentially. The shaping process preferably includes one or more of cutting and laser cutting. This invention obtains a green sheet of the desired shape through this shaping process.

[0031] The present invention preferably obtains a defect-free green sheet with a thickness ≤0.3mm by precisely controlling the doctor blade gap, casting speed, and drying temperature during the casting process. In the present invention, the thickness of the green sheet is preferably ≤0.3mm, more preferably 0.02~0.1mm.

[0032] After obtaining the green sheet, the present invention removes the glue from the green sheet in an oxygen atmosphere to obtain a de-glue green sheet.

[0033] In this invention, the green sheets are preferably stacked or individually packed in a bowl and placed in an oxygen atmosphere furnace for debinding. In this invention, when multiple green sheets are stacked together before debinding, the stacking process further includes isostatic pressing before debinding. This invention does not have specific requirements for the isostatic pressing method. After packing, the stacked green sheets can be PTC cut. The preferred holding temperature for debinding is 400~600℃, the preferred holding time is 6~8h, and the heating rate from room temperature to the holding temperature for debinding is preferably ≤1℃ / min, more preferably 0.5~1.0℃ / min. By controlling the debinding conditions, this invention can thoroughly and slowly remove organic components from the green sheets while avoiding internal cracking.

[0034] After obtaining the debinding green sheet, the present invention sintersects the debinding green sheet in a protective gas atmosphere to obtain a sintered substrate. The sintering includes heating from a first temperature to a second temperature at a first heating rate, then heating from the second temperature to a third temperature at a second heating rate, and then holding the substrate at the third temperature. The first temperature is 1000~1200℃, the second temperature is 1200~1500℃, and the third temperature is 1500~1600℃. The first heating rate is ≤2℃ / min, the second heating rate is ≤1℃ / min, and the holding time is 2~6h.

[0035] This invention reveals that sintering methods and sintering aid systems under air atmosphere are insufficient to guarantee the strength and densification of ceramic bodies sintered in extremely thin (e.g., 0.1 mm) conditions. The substrate material is prone to developing 1-3% residual porosity. This porosity is primarily due to the pores being enclosed within the alumina ceramic during the later stages of sintering. Further shrinkage of these pores requires diffusion to the surface via grain boundaries, leading to warping, cracking, and deformation during sintering, resulting in extremely low yield. Furthermore, improper sintering regime control leads to insufficient grain growth control, resulting in uneven grain growth and abnormally large grains, causing structural deformation and warping, thus limiting the substrate's bending strength.

[0036] In this invention, the sintering atmosphere is hydrogen or a rare gas, and the rare gas can be argon. The sintering atmosphere is preferably hydrogen. The first temperature is preferably 1150℃, the second temperature is preferably 1500℃, and the third temperature is preferably 1600℃. The first heating rate is preferably 2℃ / min, and the second heating rate is preferably 0.5~1℃ / min. In this invention, the green sheet after debinding is preferably sintered in a hydrogen reducing atmosphere furnace. The heating rate is controlled at 2℃ / min within the 1150~1500℃ temperature range, and maintained at 0.5~1℃ / min in the high-temperature range of 1500~1600℃. This promotes the formation of a solid solution between the sintering aid and the α-Al2O3 grains, or generates a small amount of liquid phase, causing rearrangement between particles and grain boundary movement to eliminate pores. During the high-temperature holding stage at 1600℃ for 2~6 hours, the grains grow further, the intercrystalline bonding becomes more complete, and gases are eliminated through the grain boundaries. Controlling the heating rate during sintering is crucial to prevent excessively rapid grain boundary movement, which could lead to grains encasing pores or incomplete pore removal, thus reducing defects such as pores or microcracks in the microstructure. This invention employs an appropriate holding time to allow for optimal crystal development, enabling the crystal grains to grow to a certain size, reducing the number of grain boundaries and residual pores, thereby improving the density and structural strength of the alumina ceramic substrate.

[0037] After obtaining the sintered substrate, the present invention performs annealing treatment on the sintered substrate to obtain the alumina ceramic substrate.

[0038] In this invention, the annealing treatment is preferably carried out in an oxygen-containing atmosphere. The annealing atmosphere is preferably a mixture of oxygen and argon. The volume content of oxygen in the annealing treatment can be 3-5%. Preferably, the sintered substrate is stacked or packaged as a single sheet in an annealing furnace for annealing. The annealing temperature is preferably 1100-1200℃, and the holding time is preferably 3-4 hours. The surface roughness of the alumina ceramic substrate is preferably Ra≤0.1μm. By controlling the annealing conditions, this invention oxidizes the small amount of impurities remaining on the material surface generated during sintering, achieving a surface purification effect. This further improves the surface smoothness and flatness of the alumina ceramic substrate, resulting in an alumina ceramic substrate with a precise final thickness of 0.1mm and an ultra-smooth surface (Ra≤0.1μm).

[0039] In this invention, after the annealing process, the resulting alumina ceramic substrate is cut and inspected sequentially, and finally stored in the warehouse.

[0040] The present invention provides an alumina ceramic substrate prepared by the preparation method described in the above technical solution.

[0041] In this invention, the thickness of the alumina ceramic substrate is preferably ≤0.3mm; the purity of the alumina ceramic substrate is ≥99.6%.

[0042] In this invention, the alumina ceramic substrate preferably has the following characteristic parameters: Purity: ≥99.6 wt%; Thickness: 0.1 mm ± 0.01 mm; Relative density: ≥3.92 g / cm³ 3 Three-point bending strength: ≥ 470 MPa; Thermal conductivity (25℃): ≥ 26.9 W / (m·K); Dielectric constant (1MHz): 9.9±0.1; Dielectric loss (1MHz): ≤1.0×10 -4 Dielectric breakdown strength: ≥ 12kV / mm; Microstructure: Uniform grain size, with an average grain size of 2~4μm.

[0043] This invention has found that a larger substrate thickness (≥0.20 mm) results in higher thermal resistance, which is detrimental to the timely dissipation of heat generated by high-power devices (such as GaN power amplifiers and laser diodes), affecting device performance and reliability. The alumina ceramic substrate provided by this invention preferably has a thickness of 0.1 mm ± 0.01 mm, which is beneficial for its application in high-power devices.

[0044] This invention provides the application of the alumina ceramic substrate described above in high-frequency communication devices, semiconductor devices, advanced packaging, or MEMS sensors.

[0045] In this invention, the application may include: Case 1: Carrier Substrate for High-Frequency / Microwave Modules 1. Application scenarios: Thin-film circuits are a technology that uses processes such as vacuum evaporation and sputtering to deposit micron-sized metal (such as gold and copper) wires and resistors on insulating substrates. The substrates are required to have extremely high surface flatness, high thermal conductivity and excellent high-frequency performance.

[0046] In the transmit / receive (T / R) components of 5 / 6G communication base stations and radar systems, core microwave chips (such as GaN power amplifiers and low-noise amplifiers) need to be mounted on a substrate that needs to transmit high-frequency signals and dissipate the large amount of heat generated by the chips in a timely manner.

[0047] 2. Problems and Solutions: Traditionally, relatively thick alumina or aluminum nitride substrates (0.38mm or 0.25mm) are used. While performance is acceptable, the thickness limits further thinning of the module, and there is room for optimization of thermal resistance. This invention utilizes a 0.1mm thick, 99.6% pure alumina ceramic substrate as the carrier. The chip is directly die-attached to this ultra-thin ceramic substrate.

[0048] 3. Advantages: 1) Improved Thermal Performance: The ultra-thin structure significantly reduces the thermal resistance from the chip to the module casing, resulting in a substantial decrease in the junction temperature of the GaN power amplifier chip. Experimental data shows that, under the same conditions, using a 0.1mm substrate can reduce the chip junction temperature by 10-15% compared to a 0.25mm substrate. This directly improves the stability of output power and device lifespan. 2) Excellent High-Frequency Performance: The high purity of 99.6% ensures extremely low dielectric loss tangent (tanδ), reducing microwave signal transmission loss and improving the efficiency and signal quality of the entire T / R module. 3) Miniaturization and Lightweight Design: The 0.1mm thickness enables 3D stacking and compact design of the entire microwave module, aligning with the development trend of modern communication equipment.

[0049] Case Study 2: Interposer in Advanced Semiconductor Packaging 1. Application Scenarios: In 2.5D / 3D advanced packaging, the interposer is used to connect the high-speed chips above (such as CPU, GPU, HBM high-speed memory) and the organic packaging substrate below, undertaking the tasks of high-density interconnection and signal relay.

[0050] 2. Problems and Solutions: Traditionally, silicon interposers (TSV technology) or organic interposers are used. Silicon interposers are extremely expensive and conductive; organic interposers have poor thermal conductivity and are difficult to handle the heat generated by multi-chip integration. This invention uses a 0.1mm thick high-purity alumina ceramic sheet as the interposer substrate. High-density redistribution layers (RDLs) are fabricated on its upper and lower surfaces using thin-film processes (sputtering, photolithography, electroplating) to achieve interconnection between chips.

[0051] 3. Advantages: 1) Excellent thermal management: The alumina interposer acts as a highly efficient heat conduction channel within the package, rapidly diffusing and conducting the heat generated by stacked chips laterally to the outside of the package—a capability unmatched by organic interposers. 2) Good electrical performance: Provides stable insulation and a reliable signal transmission environment; its dielectric constant and loss factor are suitable for high-speed signal transmission. 3) Strength and flatness: Compared to extremely thin silicon wafers or organic materials, alumina ceramics maintain high mechanical strength and flatness even at a thickness of 0.1mm, facilitating large-area packaging manufacturing and processing.

[0052] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0053] Example 1 This example provides a method for preparing an alumina ceramic substrate, the preparation process of which is as follows: Figure 3 As shown, the detailed steps are as follows: (1) Preparation of Al2O3 raw materials: Select average particle size (D 50 High-purity α-alumina powder with a particle size of 0.2~0.5μm (purity >99.99%).

[0054] (2) Sintering aids: MgO, ZrO2, Y2O3, analytical grade.

[0055] (3) Ingredients: The ceramic material is composed of α-alumina powder, MgO, ZrO2 and Y2O3, with 0.1wt% MgO, 0.1wt% ZrO2 and 0.2wt% Y2O3, and the balance is α-alumina powder.

[0056] (4) The above-mentioned ceramic material is mixed with an adhesive and an organic solvent. The adhesive is polyvinyl butyral and di(2-ethylhexyl) phthalate, with a mass ratio of 2:1. The organic solvent is xylene and anhydrous ethanol, with a mass ratio of 13.5:12.0. The mass ratio of ceramic powder to polyvinyl butyral is 40.0:2.8. The above mixture is placed in a ball mill jar and the components are fully mixed and dispersed by ball milling. Then, it is filtered and degassed to form a uniform, stable, bubble-free slurry with a viscosity controlled at 6500~9500 mPa·s.

[0057] (5) In a clean and constant temperature environment, the slurry is cast onto a PET carrier film using a precision casting machine to form a green film strip. By precisely controlling the doctor blade gap, casting speed, and drying temperature, a defect-free green strip with a thickness of 0.02~0.1mm is obtained. The green strip is then cut into green sheets according to the actual required dimensions. Alternatively, the green strip can be laser-cut according to the design dimensions to obtain green sheets of a specific shape.

[0058] (6) Stack the green sheets or pack them into a pot as single sheets and put them into an oxygen atmosphere furnace. Remove the glue at 600°C, control the heating rate at 1.0°C / min, and keep them at 600°C for 8 hours to thoroughly and slowly remove the organic components and avoid internal cracking, so as to obtain the green sheets after glue removal.

[0059] (7) After the sintering process, the green sheet is sintered in a hydrogen reducing atmosphere furnace. The heating rate is controlled at 2℃ / min in the 1150~1500℃ temperature range and 1℃ / min in the high-temperature range of 1500~1600℃. This allows the sintering aid to form a solid solution with the α-Al2O3 grains or to generate a small amount of liquid phase. The particles rearrange themselves, and the grain boundaries move, allowing the pores to be eliminated. During the high-temperature holding stage at 1600℃, the temperature is maintained for 6 hours. This holding allows the grains to grow further and the inter-crystal bonding to be more complete. Gases can be eliminated through the grain boundaries. Controlling the heating rate during sintering is mainly to prevent the grain boundaries from moving too quickly, which could lead to problems such as grains encasing pores or incomplete elimination of pores. This reduces defects such as pores or microcracks in the microstructure. By using an appropriate holding time, the crystals can be developed as completely as possible, allowing the crystal grains to grow to a certain size, reducing the number of grain boundaries and residual pores, thereby improving the density and structural strength of the alumina ceramic substrate.

[0060] (8) To better release the sintering thermal stress and improve the surface smoothness and flatness of the alumina ceramic substrate, the sintered substrate product obtained in step (7) is subjected to annealing treatment. The sintered substrate products are stacked or packed in a single piece and placed in an annealing furnace. The annealing temperature is 1200℃, the protective atmosphere for annealing is Ar+O2 (where the volume content of argon is 95% and the volume content of oxygen is 5%), and the high-temperature treatment time is 4h. Through the action of annealing, the small amount of impurities remaining on the surface of the material generated during the sintering process are oxidized to achieve the effect of surface purification, further improving the surface smoothness and flatness of the alumina ceramic substrate, so as to achieve an alumina ceramic substrate with a precise final thickness of 0.1mm and an ultra-smooth surface (Ra ≤ 0.1μm).

[0061] Figure 1 This is a photograph of the alumina ceramic substrate product prepared in Example 1. Figure 2 The image shows a SEM image of the alumina ceramic substrate product prepared in Example 1. The alumina ceramic substrate prepared in this example has the following characteristic parameters: purity: ≥99.6wt%; thickness: 0.1 mm ± 0.01 mm; relative density: ≥3.92 g / cm³. 3 Three-point bending strength: ≥ 470 MPa; Thermal conductivity (25℃): ≥ 26.9 W / (m·K); Dielectric constant (1MHz): 9.9±0.1; Dielectric loss (1MHz): ≤ 1.0 × 10⁻⁶ -4 Dielectric breakdown strength: ≥ 12kV / mm; Microstructure: Uniform grain size, with an average grain size of 2~4μm.

[0062] Example 2 The preparation method is basically the same as that provided in Example 1, except that: sintering aids: MgO, ZrO2 and La2O3, analytical grade. Ingredients: the ceramic material composed of α-alumina powder, MgO, ZrO2 and La2O3, with MgO 0.2wt%, ZrO2 0.1wt%, La2O3 0.1wt%, and the balance being α-alumina powder.

[0063] As can be seen from the above examples: (1) The present invention uses raw materials with a purity >99.99% and trace amounts of nano-sintering aids, and fully densifies them through high-temperature sintering (1600℃), thus greatly reducing impurity ions and glass phase, thereby obtaining extremely low dielectric loss (≤1.0×10). -4(1) This invention solves the problem of insufficient dielectric properties in the prior art and is perfectly suitable for high-frequency applications. (2) Since the thickness of the final product is successfully controlled at 0.1 mm and high thermal conductivity is maintained, the thermal resistance of the substrate is significantly reduced, thereby greatly improving its heat dissipation capacity and solving the problem of limited thermal management performance in the prior art, making it suitable for high power density devices. (3) Since the present invention adopts an optimized casting slurry formula and a staged precise control of the sintering curve (especially slow glue removal, reducing atmosphere sintering and annealing treatment), the deformation and cracking of the green body and ceramic body during the production process are effectively suppressed, thereby successfully achieving high yield of ultra-thin ceramic sheets and solving the problem of difficulty in ultra-thinning in the prior art. (4) Since the present invention sintersulates at high temperature and controls the holding time, a fine and uniform (2~4 μm) microstructure is obtained, thereby giving the material high mechanical strength (≥470 MPa), making it more reliable in subsequent processing and use.

[0064] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing an alumina ceramic substrate, characterized in that, Includes the following steps: A ceramic material, adhesive, and organic solvent are mixed to obtain a slurry. The ceramic material includes α-alumina powder and a sintering aid. The purity of the α-alumina powder is >99.99%. The sintering aid includes one or more of MgO, ZrO2, Y2O3, and La2O3. The sintering aid is of analytical grade, and the mass percentage of the sintering aid in the ceramic material is ≤0.5%. The slurry is sequentially formed into a film, dried, and shaped to obtain a green sheet; The green sheet is debonded in an oxygen atmosphere to obtain a debonded green sheet. The debinding green sheet is sintered in a protective gas atmosphere to obtain a sintered substrate. The sintering includes heating from a first temperature to a second temperature at a first heating rate, then heating from the second temperature to a third temperature at a second heating rate, and then holding at the third temperature. The first temperature is 1000~1200℃, the second temperature is 1200~1500℃, and the third temperature is 1500~1600℃. The first heating rate is ≤2℃ / min, the second heating rate is ≤1℃ / min, and the holding time is 2~6h. The sintered substrate is annealed to obtain the alumina ceramic substrate.

2. The preparation method according to claim 1, characterized in that, The film formation method is casting, the thickness of the green sheet is ≤0.3mm; the heat preservation temperature for glue removal is 400~600℃, the heat preservation time is 6~8h, and the heating rate from room temperature to the heat preservation temperature for glue removal is ≤1℃ / min.

3. The preparation method according to claim 1, characterized in that, The annealing process is carried out in an oxygen-containing atmosphere, the annealing temperature is 1100~1200℃, and the holding time is 3~4h; the surface roughness Ra of the alumina ceramic substrate is ≤0.1μm.

4. The preparation method according to claim 1, characterized in that, The sintering atmosphere is hydrogen, the first temperature is 1150℃, the second temperature is 1500℃, the third temperature is 1600℃, the first heating rate is 2℃ / min, and the second heating rate is 0.5~1℃ / min.

5. The preparation method according to claim 1, characterized in that, The average particle size of the α-alumina powder is 0.2~0.5μm; the sintering aid is MgO, ZrO2 and Y2O3, or MgO, ZrO2 and La2O3; the mass percentage of the sintering aid in the ceramic material is 0.3~0.5%.

6. The preparation method according to claim 1, characterized in that, The adhesive comprises polyvinyl butyral and di(2-ethylhexyl) phthalate, wherein the mass ratio of polyvinyl butyral to di(2-ethylhexyl) phthalate is (4~6):(2~3); and the mass ratio of ceramic material to polyvinyl butyral is (40~55):(2.8~4.5).

7. The preparation method according to claim 1, characterized in that, The organic solvent includes xylene and ethanol, and the mass ratio of xylene to ethanol is (13.5~14.4):(12.0~13.3); the viscosity of the slurry is 6500~9500 mPa·s.

8. The alumina ceramic substrate prepared by the preparation method according to any one of claims 1 to 7.

9. The alumina ceramic substrate according to claim 8, characterized in that, The thickness of the alumina ceramic substrate is ≤0.3mm; the purity of the alumina ceramic substrate is ≥99.6%.

10. The application of the alumina ceramic substrate according to claim 8 or 9 in high-frequency communication devices, semiconductor devices, advanced packaging or MEMS sensors.

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