Semiconductor graphite material with strong electric conductivity and heat conductivity and preparation method thereof

Abstract

The invention relates to the technical field of carbon material preparation, and discloses a semiconductor graphite material with strong electrical and thermal conductivity and a preparation method thereof, and the semiconductor graphite material is prepared from 68%-73% of carbonaceous aggregate and 27%-32% of modified medium-temperature coal pitch binder. The preparation method comprises the following steps: preparing the raw materials into primary superfine powder, mixing and kneading, and performing secondary crushing and shaping to obtain secondary granulation powder with specific grain size distribution; preparing a green body by adopting a gradient pressure process from low-pressure prepressing to standing relaxation and then to high-pressure main forming; in the subsequent dipping roasting link, the heating rate of the volatilization temperature zone is dynamically adjusted according to the dipping weight gain rate feedback; and finally, carrying out high-temperature graphitization treatment. According to the method, a compact framework is constructed through secondary granulation, internal stress is eliminated through gradient forming, the problem of gas expansion cracking is solved through dynamic temperature control, and the comprehensive performance and the finished product yield of the semiconductor-grade graphite material are improved.

Description

Technical Field

[0001] This invention relates to the field of carbon material preparation technology, specifically to a highly conductive and thermally conductive semiconductor graphite material and its preparation method. Background Technology

[0002] The semiconductor industry is the cornerstone of modern electronic information technology. The growth of single-crystal silicon primarily employs the Czochralski method, a process that requires high temperature, high cleanliness, and a precise thermal environment. High-strength, high-purity, high-density, and highly conductive and thermally conductive isostatic graphite, due to its excellent high-temperature mechanical properties and chemical stability, has become an indispensable key material for manufacturing single-crystal furnace thermal systems (such as heaters, crucibles, and flow guides). As semiconductor wafer sizes evolve from 8 inches to 12 inches and even larger, more stringent requirements are placed on the size and performance indicators of thermal components, necessitating that graphite materials possess higher volumetric density, lower resistivity, and excellent structural uniformity.

[0003] However, the current process for preparing high-performance semiconductor-grade graphite materials faces several irreconcilable technical contradictions. To achieve high density and strength, existing processes typically involve grinding raw materials into extremely fine powders, utilizing the high specific surface energy of ultrafine particles to enhance sintering activity and filling density. However, this sole pursuit of fine powder leads to a decrease in the bulk density of the raw material and extremely narrow venting channels between powder particles. During cold isostatic pressing, the gas trapped within the powder cannot escape smoothly, limiting further increases in green density and easily causing pores or delamination defects within the material, resulting in impaired electrical and thermal conductivity of the final product.

[0004] Furthermore, as semiconductor thermal field components become larger in size, internal stress control during the molding process has become a bottleneck restricting the yield of finished products. In traditional isostatic pressing (OSP) processes, the pressure is often increased directly to the maximum working pressure in one step and then released directly after holding the pressure. Due to the viscoelastic properties of asphalt binders and the accumulation of enormous elastic potential energy by carbonaceous particles under high pressure, this molding method, lacking a stress release mechanism, results in a large residual stress gradient inside the green body. When the mold is depressurized or subsequent firing heat treatment is performed, once these residual stresses are released, they can easily induce macroscopic cracks or microscopic damage that is difficult to detect with the naked eye, severely reducing the yield of large-size products.

[0005] On the other hand, in order to achieve semiconductor-grade high density (such as a volume density greater than 1.85 g / cm³), 3Typically, calcined materials require multiple impregnation and re-calcination processes to fill the matrix pores. Current industrial production often employs fixed heating curves in the calcination process, failing to consider the differences in permeability at different densification stages. Especially after multiple impregnations, the material's internal pores are largely filled, increasing its airtightness. If a conventional rapid heating procedure is still used at this point, the volatile gases generated by the pyrolysis of the impregnating agent cannot diffuse out through the increasingly dense matrix in time, leading to a sharp increase in internal pressure exceeding the matrix strength. This results in material expansion, peeling, or cracking, making it difficult to balance production efficiency and structural integrity when preparing ultra-dense graphite materials. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a highly conductive and thermally conductive semiconductor graphite material and its preparation method. This solves the problems in the preparation of existing large-size, high-density semiconductor graphite materials, such as difficulty in venting ultrafine powder, residual internal stress during molding, and the gas expansion effect during the densification process, which lead to easy cracking, low yield, and difficulty in simultaneously achieving high density and excellent electrical and thermal conductivity.

[0007] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a highly conductive and thermally conductive semiconductor graphite material, employing the following technical solution: A highly conductive and thermally conductive semiconductor graphite material is made from raw materials comprising the following weight percentages: carbonaceous aggregate: 68%-73%; binder pitch: 27%-32%; wherein the carbonaceous aggregate is petroleum coke or pitch coke, and the binder pitch is modified medium-temperature coal tar pitch; the bulk density of the graphite material is ≥1.85 g / cm³. 3 Resistivity ≤12.0μΩm.

[0008] By adopting the above technical solution, this invention strictly limits the mixing ratio range of carbonaceous aggregate and binder bitumen. Under this ratio, the dominant carbonaceous aggregate constructs a high-density conductive and thermally conductive framework, while the 27%-32% binder bitumen ensures sufficient wetting and coating of the aggregate particles during mixing, and avoids the problems of excessive binder causing shrinkage and deformation during calcination or insufficient binder causing a loose structure. This mixing system is compatible with subsequent secondary granulation and gradient molding processes, enabling the final graphite material to achieve a macroscopic bulk density ≥1.85 g / cm³. 3 The high density of the material forms a continuous and complete conductive network at the microscopic level, thereby controlling the resistivity below 12.0 μΩm, which meets the stringent requirements of the semiconductor manufacturing industry for high strength, high conductivity, and high purity of tooling and fixture materials.

[0009] Preferably, the carbonaceous aggregate meets one of the following characteristics: the carbonaceous aggregate is low-sulfur sponge petroleum coke, with a volatile matter content of 0.5%-1.5%, an ash content of ≤0.05%, and a true density of 2.08-2.12 g / cm³. 3 The carbonaceous aggregate is coal-based pitch coke, with a volatile matter content of 0.5%-1.0%, an ash content of ≤0.03%, and a true density of 2.05-2.10 g / cm³. 3 .

[0010] By adopting the above technical solution, low-sulfur sponge petroleum coke is selected as aggregate. Its easily graphitized needle-like or sponge-like microcrystalline structure enhances the material's electrical and thermal conductivity. Coal-based pitch coke is selected, utilizing its high density and mechanical strength to enhance the material's wear resistance. Strict control of ash content at extremely low levels (≤0.05% or ≤0.03%) avoids impurities contaminating the wafer during high-temperature semiconductor processes and reduces the catalytic or hindering effect of metallic impurities on the graphitization process, ensuring uniform lattice development.

[0011] Preferably, the binder bitumen has a softening point of 105℃-115℃, a coking value of 56%-62%, a quinoline insoluble content of 8%-12%, and a toluene insoluble content of 26%-32%.

[0012] By adopting the above technical solution, the selected modified medium-temperature coal tar pitch has a moderate softening point, which ensures the rheological properties at the kneading temperature, allowing it to penetrate into the micropores of ultrafine aggregates; the high coking value (56%-62%) and the appropriate amount of quinoline insolubles (QI, 8%-12%) serve as primary crystal nuclei, ensuring the formation of a high-strength bonded coke network during the roasting process, improving the roasting residual carbon rate, and thus enhancing the final density and mechanical strength of the product.

[0013] Secondly, the present invention provides a method for preparing a highly conductive and thermally conductive semiconductor graphite material, employing the following technical solution: A method for preparing a highly conductive and thermally conductive semiconductor graphite material, applied to the aforementioned highly conductive and thermally conductive semiconductor graphite material, includes the following steps: S1. Raw material pretreatment and primary grinding: Carbonaceous aggregates are crushed and ground to obtain primary ultrafine powder; S2. Mixing and secondary granulation: The primary ultrafine powder and the binder asphalt are mixed and kneaded under heating, and after cooling, they are subjected to secondary crushing and shaping to obtain secondary granulated powder with a specific particle size distribution. S3, Gradient pressure molding: The secondary granulated powder is loaded into a mold and subjected to low-pressure pre-pressing micro-forming, static relaxation, and cold isostatic pressing main forming in sequence to obtain a green body. S4. Firing and densification: The green body is fired once, followed by at least one impregnation and re-firing cycle; in the re-firing step, the heating rate of the volatilization zone is dynamically adjusted according to the weight gain feedback data of the impregnation process. S5. Graphitization and processing: The calcined product is subjected to high-temperature graphitization treatment, and after cooling and processing, the highly conductive and thermally conductive semiconductor graphite material is obtained.

[0014] By adopting the above technical solution, this invention solves the technical contradiction between the difficulty in degassing ultrafine powder and the ease with cracking in high density graphite preparation through process innovation in three core dimensions: secondary granulation, gradient pressure molding, and dynamic calcination feedback. First, a secondary crushing and shaping process, or secondary granulation, is introduced in step S2 after kneading. This step pre-binds the originally loose ultrafine powder (primary powder) into dense secondary particles. During subsequent pressing, these secondary particles form a high-density core framework, while micron-level venting channels are retained between the particles. This mesoscopic structure of dense core and venting channels achieves high packing density of ultrafine powder while effectively avoiding molding defects such as trapped air and delamination caused by excessively fine powder.

[0015] Second, a gradient forming mechanism from pre-compression to relaxation and then to main compression is constructed in step S3. Utilizing the viscoelastic properties of the asphalt binder, low-pressure pre-compression first rearranges the particles and preliminarily shapes them; the subsequent static relaxation stage allows the elastic potential energy accumulated inside the material due to forced compression to dissipate through the creep slip of polymer chain segments; finally, high-pressure main forming is applied. This process completely eliminates the internal stress gradient inside the green body, preventing the generation of springback cracks after pressure relief.

[0016] Third, a dynamic temperature control model based on the weight gain rate was established in step S4. To address the issues of increased material air tightness and difficulty in volatile matter removal after multiple impregnations, the internal filling degree was quantified by detecting the impregnation weight gain rate, and the heating rate of the volatile matter zone was adjusted accordingly. When the weight gain rate was high, the heating rate was actively reduced to balance the volatile matter generation rate with the gas diffusion rate in the dense matrix, thereby eliminating gas expansion cracks and improving the yield of high-density products.

[0017] Preferably, in step S2, the particle size distribution control logic of the secondary granulation powder is as follows: the particle size of the primary ultrafine powder is controlled to have a sieve passing rate of 90%-95% for 400-600 mesh; after mixing and secondary crushing and shaping, the particle size of the secondary granulation powder is controlled to have a sieve passing rate of 65%-75% for 150-250 mesh.

[0018] By adopting the above technical solution, the 400-600 mesh ultrafine primary powder ensures a very large specific surface area for the aggregate and binder to contact, which is conducive to the formation of a dense microstructure. Controlling the powder after secondary granulation to 150-250 mesh with a passing rate of 65%-75% is key to constructing an ideal packing structure. This gradation retains approximately 25%-35% of coarse particles (oversize) as a supporting skeleton, preventing excessive filling of fine powder and clogging of the venting channels, thus ensuring the optimal balance between green density and permeability.

[0019] Preferably, in step S3, the specific process parameters of the gradient pressure forming are as follows: the pressure P1 of the low-pressure pre-compression micro-forming is 25MPa-35MPa, and the holding time is 5-10 minutes; the static relaxation environment is a state without external load, and the relaxation time is 12-24 hours; the pressure P2 of the cold isostatic pressing main forming is 140MPa-160MPa, and the holding time is 110-130 minutes; and the pressure P1 and pressure P2 satisfy the relationship: P1 is 15%-25% of P2.

[0020] By adopting the above technical solution, the pre-compression pressure P1 is controlled at 15%-25% of the main pressure P2, which effectively overcomes the friction between powder particles to achieve initial densification, while avoiding excessive pressure that prematurely closes the venting channels. The 12-24 hour relaxation time perfectly matches the stress relaxation characteristic time of the asphalt binder at room temperature, allowing the elastic deformation generated by pre-compression to transform into plastic deformation. Finally, the main pressure of 140MPa-160MPa ensures that the green body reaches 1.85g / cm³. 3 The above is the theoretical volume density.

[0021] Preferably, in step S4, the dynamic adjustment of the heating rate of the volatile temperature zone specifically includes: calculating the impregnation weight gain rate after the impregnation step is completed; setting a baseline weight gain rate threshold of 13%-15%; when the impregnation weight gain rate is greater than or equal to the baseline weight gain rate threshold, setting the heating rate of the 300℃-500℃ temperature zone in the subsequent re-calcination step to 1.0℃ / h-1.5℃ / h; when the impregnation weight gain rate is less than the baseline weight gain rate threshold, setting the heating rate of the 300℃-500℃ temperature zone in the subsequent re-calcination step to 2.0℃ / h-3.0℃ / h.

[0022] By employing the above technical solution, graded control is implemented for the severe pyrolysis of the binder and volatilization of light components within the temperature range of 300℃-500℃. When the impregnation weight gain exceeds a threshold (e.g., 14%), it means that the internal pores of the material are largely filled, resulting in extremely low air permeability. At this point, if a conventional heating rate is used, high-pressure air pockets can easily form inside the material, leading to defective products. This invention forcibly reduces the heating rate to 1.0℃ / h-1.5℃ / h, extending the diffusion time window of volatile components and ensuring that gases can safely escape through the micropores; while for cases with lower weight gain, a faster rate is used to balance production efficiency.

[0023] Preferably, in step S2, the specific process of mixing is as follows: first, the primary ultrafine powder and solid binder asphalt are dry-mixed at 130℃-140℃ for 20-30 minutes; then, the temperature is raised to 165℃-175℃ and wet-mixed for 50-70 minutes, with the discharge temperature controlled at 155℃-165℃; the temperature of the secondary crushing and shaping is controlled at 15℃-30℃.

[0024] By adopting the above technical solution, a stepped mixing process from low-temperature dry mixing to high-temperature wet mixing is used. In the low-temperature dry mixing stage, the shearing action between solid particles achieves macroscopically uniform dispersion of the components. In the high-temperature wet mixing stage, the temperature is more than 50°C above the asphalt softening point, significantly reducing the asphalt viscosity. This allows the asphalt to penetrate the microcracks and pores of the primary ultrafine powder under capillary force, forming a paste with extremely strong binding force. Low-temperature control during the secondary crushing and shaping process ensures that the asphalt remains in a brittle state during granulation, facilitating the crushing into angular particles and preventing agglomeration.

[0025] Preferably, in step S4, the specific process conditions for impregnation are as follows: preheat the calcined product and evacuate it to a vacuum degree ≤ -0.095MPa; inject impregnating bitumen with a softening point of 85℃-95℃ and a quinoline insoluble content of less than 0.5%; pressurize to 1.8MPa-2.5MPa and maintain the pressure for 2-3 hours.

[0026] By adopting the above technical solution, the high vacuum eliminates the residual gas in the pores, creating negative pressure conditions for the impregnating agent to enter; the special impregnating bitumen with extremely low quinoline insoluble matter (<0.5%) is selected to avoid solid particles clogging the micropores, and with high pressure (1.8-2.5MPa) driving, deep filling of micron- and nano-sized pores is achieved, maximizing the bulk density of the material.

[0027] Preferably, in step S5, the highest temperature of the graphitization treatment is 2800℃-3000℃, and the total duration of high temperature and heat preservation is 48-120 hours; the highest temperature of the first calcination is 1050℃-1150℃, and the total cycle is 55-65 days.

[0028] By employing the above technical solution, the ultra-high temperature graphitization process at 2800℃-3000℃ provides sufficient activation energy, prompting disordered carbon atoms to rearrange into a three-dimensional ordered graphite lattice, significantly reducing electron scattering and thus achieving extremely low resistivity and extremely high thermal conductivity. Simultaneously, this high-temperature process effectively volatilizes impurities such as ash, ensuring semiconductor-grade high purity. The long-cycle calcination process guarantees the structural integrity of thick-walled, large-size products during carbonization.

[0029] This invention provides a highly conductive and thermally conductive semiconductor graphite material and its preparation method. It has the following beneficial effects: 1. This invention utilizes easily graphitized low-sulfur, spongy petroleum coke or high-density coal-based pitch coke as aggregate, and employs a secondary granulation process involving fine grinding, kneading, and coarse crushing. This process constructs a skeletal structure at the microscopic level, composed of dense secondary particle packing. This structure ensures effective filling of ultrafine powders while reserving micron-level venting channels, resolving the contradiction in traditional processes where increasing density leads to trapped air. This results in a final product with a bulk density of 1.85 g / cm³. 3 The resistivity is reduced to below 12.0 μΩm, which can meet the stringent requirements of high strength and high conductivity of materials in the semiconductor single crystal growth thermal field.

[0030] 2. This invention introduces a gradient pressure molding and static relaxation mechanism, utilizing the viscoelastic properties of the binder asphalt. A long-term unloaded relaxation stage is established between low-pressure pre-forming and high-pressure main molding, allowing the elastic potential energy accumulated within the powder to be fully dissipated through the creep slip of the polymer chain segments. This process effectively eliminates the internal stress gradient within the green body, preventing the generation of pressure relief rebound cracks, and improving the stability of yield in the industrial production of large-format semiconductor graphite products.

[0031] 3. This invention employs a dynamic calcination temperature control strategy based on impregnation weight gain feedback, establishing a balance model between material airtightness and volatile matter emission rate. For intermediates with high weight gain (high density), the heating rate in the 300℃-500℃ volatilization temperature range is actively reduced, thereby preventing excessive internal pressure and microscopic delamination caused by the rapid vaporization of the impregnating agent and its inability to be discharged in time. This strategy enables the material to maintain the mechanical stability of the matrix while undergoing deep densification, achieving a balance between high performance and high quality. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments and comparative examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] Preparation Examples 1-4: Preparation Example 1: This preparation example provides a secondary granulation powder (powder A) for preparing DS series high electrical and thermal conductivity graphite materials.

[0034] Low-sulfur spongy petroleum coke was crushed to particles smaller than 5 mm using a jaw crusher, and then fed into a vibrating mill for ultrafine grinding. The grinding frequency and classifier speed were adjusted to ensure that 92% of the ground powder passed through a 500-mesh sieve (25 μm aperture). 70 kg of the above 500-mesh ultrafine petroleum coke powder and 30 kg of crushed modified medium-temperature coal tar pitch binder were added to a twin-shaft heated mixing pot. The mixture was first dry-mixed at 135°C for 25 minutes, then wet-mixed at 165°C for 60 minutes to ensure the binder fully impregnates and coats the ultrafine coke powder. The discharge temperature was controlled at 160°C. The kneaded paste was allowed to cool naturally to room temperature to harden, and then fed into a mechanical mill for secondary crushing and shaping. By adjusting the mill gap and screening system, the powder after secondary grinding was controlled to pass through a 200-mesh sieve (74 μm aperture) with a 70% pass rate and 30% oversize, thus obtaining secondary granulated powder A.

[0035] Preparation Example 2: This preparation example provides a secondary granulation powder (powder B) for preparing DL series high-strength wear-resistant graphite materials.

[0036] Coal-based pitch coke is crushed to particles smaller than 5mm using a jaw crusher and then fed into a vibrating mill for ultrafine grinding. The passing rate of the ground powder through a 500-mesh sieve is controlled at 95%. 72kg of the above-mentioned 500-mesh pitch coke ultrafine powder and 28kg of modified medium-temperature coal tar pitch binder are added to a twin-shaft heated mixing pot. First, dry mixing is performed at 140℃ for 30 minutes, followed by wet mixing at 175℃ for 50 minutes. The discharge temperature is controlled at 165℃. After the kneaded paste is cooled and hardened, it is fed into a mechanical mill for secondary crushing and shaping. The passing rate of the powder after secondary grinding through a 200-mesh sieve is controlled at 68%, with 32% of the material remaining on the sieve, thus obtaining secondary granulated powder B.

[0037] Preparation Example 3: This preparation example provides a secondary granulated powder (powder C) with a relatively fine particle size distribution.

[0038] Low-sulfur spongy petroleum coke was subjected to a first ultrafine grinding process, with the passing rate of the ground powder through a 500-mesh sieve controlled at 90%. 68 kg of the above 500-mesh ultrafine petroleum coke powder and 32 kg of modified medium-temperature coal tar pitch binder were added to a twin-shaft heated mixing pot; wet mixing was carried out at 165℃ for 70 minutes. After the paste cooled, it underwent a second crushing and shaping process, with the passing rate of the powder after the second grinding controlled at 75% through a 200-mesh sieve, and the oversize content at 25%, thus obtaining the secondary granulated powder C.

[0039] Preparation Example 4 This preparation example provides a secondary granulated powder (powder D) with a relatively coarse particle size distribution.

[0040] Low-sulfur spongy petroleum coke was subjected to a first ultrafine grinding process, with the passing rate of the ground powder through a 500-mesh sieve controlled at 95%. 73 kg of the above 500-mesh ultrafine petroleum coke powder and 27 kg of modified medium-temperature coal tar pitch binder were added to a twin-shaft heated mixing pot; the mixture was wet-mixed at 165°C for 50 minutes. After the paste cooled, it underwent a second crushing and shaping process, with the passing rate of the powder after the second grinding controlled at 65% through a 200-mesh sieve, and the oversize content at 35%, thus obtaining the secondary granulated powder D.

[0041] Examples 1-4: Example 1: This example provides a highly conductive and thermally conductive semiconductor graphite material (DS series) and its preparation method, including the following steps: The secondary granulated powder A obtained in Preparation Example 1 was used as the molding raw material and loaded into a rubber elastic mold. The loading was vibrated on a vibrating table for 4 minutes to eliminate accumulation gaps. The mold after loading was placed on a hydraulic press for pre-compression micro-forming. The pre-compression pressure was set to 30 MPa and the holding time was 8 minutes. After demolding, a micro-formed soft blank with a certain strength was obtained.

[0042] The micro-formed green blank was placed in a constant temperature chamber at 25°C and allowed to relax for 18 hours without external load to release the elastic internal stress generated by pre-compression. The relaxed green blank was then loaded into a cold isostatic press for main forming, with the pressure increased to 150 MPa at a rate of 3 MPa / min and held for 120 minutes. Subsequently, the pressure was slowly released to atmospheric pressure at a rate of 1 MPa / min to obtain a high-density green blank.

[0043] The green blanks were loaded into a ring-shaped roasting furnace, filled with coke protective material, and roasted once according to a long-cycle curve with a maximum temperature of 1100℃ for a total cycle of 60 days, yielding the first-roasted product. After preheating and vacuuming, the first-roasted product was injected with special low-QI impregnating asphalt and impregnated for 2.5 hours at a pressure of 2.0 MPa. After cooling and cleaning, its weight gain was measured to be 15.2% (greater than the benchmark value of 14%). Based on this weight gain data, the heating rate in the 300℃-500℃ temperature zone of the second roasting process was set at 1.2℃ / h, while the remaining temperature zones were processed according to conventional methods, with a maximum temperature of 1000℃, yielding the second-roasted product.

[0044] The second-calcined product was subjected to a second impregnation under the same process conditions, and its second weight gain was measured to be 8.5%. Based on this data, the heating rate in the 300℃-500℃ temperature range of the tertiary calcination process was set at 2.5℃ / h, with a maximum temperature of 1000℃, to obtain the tertiary calcined product. Finally, the tertiary calcined product was placed in an Atchison graphitization furnace and subjected to high-temperature graphitization treatment at 3000℃. After cooling, it was machined to obtain the finished product.

[0045] Example 2: This example provides a high-strength, wear-resistant semiconductor graphite material (DL series) and its preparation method, including the following steps: The secondary granulated powder B obtained in Preparation Example 2 was used as the molding raw material, loaded into the mold, and vibrated to compact it. A pre-compression pressure of 35 MPa was applied to the mold for micro-forming, and the pressure was held for 10 minutes. The micro-formed blank was then demolded.

[0046] The blank was allowed to relax at a constant temperature of 22℃ for 24 hours. Then, it was subjected to cold isostatic pressing, with the main pressure set at 160MPa and held for 120 minutes to obtain the green blank.

[0047] The green blanks are fired once at a maximum temperature of 1100℃ for 60 days. The fired blanks are then subjected to high-pressure impregnation, and the weight gain is measured to be 13.5% (less than the benchmark value of 14%). Based on this weight gain, the heating rate in the 300℃-500℃ range of the secondary firing process is set at 2.0℃ / h to improve production efficiency, with a maximum temperature of 1000℃.

[0048] The product is subjected to a second impregnation and a third firing, and finally graphitized at 3000℃. After cooling, it is processed to obtain the finished product.

[0049] Example 3: This example provides a method for preparing a semiconductor graphite material, including the following steps: The fine-sized secondary granulated powder C obtained in Preparation Example 3 was used as the molding raw material. The powder was micro-shaped under a pre-compression pressure of 25 MPa for 5 minutes. The micro-shaped preform was then allowed to relax for 12 hours. Subsequently, isostatic pressing was performed under a main pressure of 140 MPa for 110 minutes to obtain the green body. After a first calcination, impregnation was performed, and the weight gain was measured to be 14.8%. Based on this, the heating rate in the volatile matter removal range during the second calcination was set to 1.4 °C / h. Subsequent secondary impregnation, a third calcination, and graphitization at 3000 °C yielded the finished product.

[0050] Example 4: This example provides a method for preparing a semiconductor graphite material, including the following steps: The coarser-sized secondary granulated powder D obtained in Preparation Example 4 was used as the molding raw material. The powder was micro-shaped under a pre-compression pressure of 35 MPa for 10 minutes. The micro-shaped green body was then allowed to relax for 20 hours. Subsequently, it was isostatically pressed under a main pressure of 160 MPa for 130 minutes to obtain the green body. After a first firing, it underwent impregnation treatment, and the weight gain was measured to be 15.5%. Based on this, the heating rate in the volatile matter removal zone during the second firing was set to 1.0 °C / h to prevent cracking due to high bitumen content. The final product was obtained after a second impregnation, a third firing, and graphitization treatment at 3000 °C.

[0051] Comparative Examples 1-5: Comparative Example 1: Compared with Example 1, the difference is that the secondary granulation and gradation process of first ultrafine grinding to kneading and then secondary grinding is eliminated.

[0052] The specific operation is as follows: the petroleum coke aggregate is directly ground to a 200-mesh sieve with a passing rate of 70%, and then mixed with the binder at the same temperature. After cooling, it is simply crushed and used as the molding powder for subsequent molding and calcination. The remaining steps and parameters are the same.

[0053] This comparative example aims to verify the necessity of the secondary granulation process for constructing a dense skeletal structure and resolving the exhaust contradiction.

[0054] Comparative Example 2: Compared with Example 1, the difference lies in the particle size control parameters of the secondary grinding. In this comparative example, the mixed paste was over-ground to control the passing rate of the powder after secondary grinding to 95% through a 200-mesh sieve (far higher than 70% in Example 1). The remaining steps and parameters were the same.

[0055] This comparative example aims to verify the necessity of retaining a certain proportion of coarse particles (secondary agglomerates) in the secondary granulation powder for the formation of exhaust channels.

[0056] Comparative Example 3: Compared with Example 1, the difference is that the static relaxation step in the molding process was eliminated.

[0057] The specific operation is as follows: after completing the pre-compression micro-forming at 30MPa, instead of allowing it to stand for 18 hours, the micro-formed blank is immediately loaded into a cold isostatic press for the main forming at 150MPa. The remaining steps and parameters are the same.

[0058] This comparative example aims to verify the necessity of stress relaxation mechanisms for eliminating forming internal stress and preventing the formation of microcracks.

[0059] Comparative Example 4: Compared with Example 1, the difference is that the pre-compression microforming step in the molding process was eliminated.

[0060] The specific operation is as follows: After the secondary granulated powder is loaded into the mold, it is directly molded in the isostatic press from atmospheric pressure to 150MPa without low-pressure pre-compression. The remaining steps and parameters are the same.

[0061] This comparative study aims to verify the necessity of setting a pressure gradient for improving the uniformity of green body density and yield.

[0062] Comparative Example 5: The difference from Example 1 is that a dynamic roasting strategy based on weight gain feedback was not used.

[0063] The specific operation is as follows: when the weight gain rate measured in the first impregnation is 15.2% (high weight gain), the second calcination still adopts the conventional heating rate of 3.0℃ / h in the volatilization temperature range of 300℃-500℃ (not reduced to 1.2℃ / h), and the other steps and parameters are the same.

[0064] This comparative example aims to verify the necessity of a dynamic temperature control strategy for preventing gas expansion cracking in high-density products during the densification process. Test Example 1-3: Test Example 1: Comprehensive Evaluation of the Physicochemical Properties of the Product in the Embodiment of the Invention Experimental description: The graphite materials prepared in Examples 1 to 4 were selected as test samples and precision-machined into standard test blocks that meet the requirements of each testing standard. Quantitative characterization of bulk density, resistivity, compressive strength, thermal conductivity, and ash content was performed to meet the core requirements of semiconductor applications. Specific testing methods and standards are as follows: Bulk density determination: The determination of bulk density of carbon materials was performed using a geometric method, in accordance with GB / T24528-2009 "Method for Determination of Bulk Density". The sample was processed into a regular cylinder, its dimensions were measured using a digital caliper with an accuracy of 0.01 mm, and its mass was weighed using an electronic balance with an accuracy of 0.1 mg. The bulk density was then calculated.

[0065] Resistivity determination: Following YS / T63.2-2006 "Test Methods for Carbon Materials for Aluminum - Part 2: Determination of Resistivity", the DC four-probe method was used. Voltage drop was measured under constant current supply to eliminate the influence of contact resistance, and the material resistivity was calculated.

[0066] Compressive strength test: According to GB / T1431-2019 "Method for Determination of Compressive Strength of Carbon Materials", an electronic universal testing machine was used to apply axial pressure to the sample at a loading rate of 0.5 mm / min until failure, the maximum failure load was recorded and the strength was calculated.

[0067] Thermal conductivity determination: Laser flare method (LFA) was used. The sample was processed into a thin sheet with a diameter of 12.7 mm and a thickness of 2 mm. The thermal diffusivity was measured at room temperature (25℃), and the thermal conductivity was calculated by combining the specific heat capacity and density.

[0068] Ash content determination: According to GB / T1429-2009 "Determination of Ash Content in Carbon Materials", the sample is completely burned in a high-temperature furnace, the mass of the residue is weighed, and the ash content (in PPM) is calculated.

[0069] Test results: Table 1. Summary of Physicochemical Property Test Data of Samples from Examples

[0070] Results analysis: Based on the test data in Table 1, and in conjunction with the technical solution proposed in this invention, the following analysis is conducted: The bulk density of all samples in the examples remained stable at 1.87 g / cm³. 3 The above examples show that Example 2 even achieved a concentration of 1.903 g / cm³. 3 This result confirms that the secondary granulation gradation logic of fine grinding to kneading and then coarse crushing effectively solves the venting problem during the molding of ultrafine powders. By constructing a secondary particle structure with a highly dense core and appropriate venting channels, and combining it with a multiple impregnation-dynamic calcination process, the effective filling and closure of the internal pores of the material are achieved, thereby obtaining a high-density matrix.

[0071] In terms of electrical and thermal properties, Example 1 (petroleum coke-based) exhibits advantages, with a resistivity as low as 9.54 μΩ·m and a thermal conductivity as high as 132.5 W / (K·m). This is mainly attributed to the selection of easily graphitizable petroleum coke in the raw material and the high-temperature graphitization treatment at 3000℃, which results in a highly ordered arrangement of carbon atoms in the lattice, reducing electron and phonon transport and scattering. Meanwhile, the data from Examples 3 and 4 show that within the range of process parameters (such as fine-tuning of grinding particle size distribution), the product performance fluctuations are small, and both can meet the stringent requirements of semiconductor-grade graphite materials (resistivity ≤12 μΩ·m, ash content ≤500 PPM), proving that this process window has good robustness.

[0072] In terms of mechanical properties, the compressive strength of Example 2 (asphalt coke base) reached 93.4 MPa, which was higher than that of Example 1. This verifies the dense structure and high mechanical strength of the asphalt coke raw material itself. After eliminating internal stress defects through gradient pressure molding, it can maintain excellent mechanical integrity in large-size products, making it suitable for semiconductor tooling components with high requirements for wear resistance and load-bearing capacity.

[0073] In summary, the graphite material prepared by this invention successfully achieves a synergistic effect of high density, high strength, and excellent electrical and thermal conductivity while ensuring high purity, and the process parameters possess stability for industrial implementation. Test Example 2: Comparative Analysis of Key Performance Indicators Experimental description: To verify the specific impact of each process step of the present invention on the performance of the final product, samples prepared in Example 1 (complete process) and Comparative Examples 1 to 5 (single variable missing or parameter deviation from process) were selected for comparative testing. All comparative example samples were taken from parts of the material without obvious macroscopic cracks during the preparation process to ensure that the test data reflects the structural performance differences of the material itself, rather than measurement failures caused by macroscopic defects.

[0074] The tests focus on indicators reflecting the density and mechanical integrity of the microstructure, specifically including bulk density, apparent porosity, and compressive strength. Apparent porosity was determined according to GB / T24528-2009 standard using the Archimedes' displacement method; this indicator directly reflects the distribution of open-cell structures within the material. The testing methods for the other indicators are the same as in Test Example 1.

[0075] Test results: Table 2. Comparative data on the impact of process variables on key material properties

[0076] Results analysis: Based on the data in Table 2, a comparative analysis of the impact mechanism of each process step on material properties is conducted: Regarding the effect of the secondary granulation gradation process: The bulk density of Example 1 is higher than that of Comparative Example 1 (1.884 g / cm³). 3 vs1.762g / cm 3 Furthermore, the apparent porosity was significantly reduced. Comparative Example 1 used a traditional one-step grinding process, resulting in a lack of dense aggregate structure between the powder particles. During pressing, the particles simply piled up, making it difficult to eliminate tiny voids. Example 1, through secondary granulation, pre-constructed high-density secondary particles, which not only improved the packing efficiency but also effectively discharged gas through the channels between coarse particles. Although Comparative Example 2 underwent secondary grinding, the excessively fine particle size (95% passing rate at 200 mesh) disrupted the skeletal effect of the coarse-fine gradation, leading to blockage of the exhaust channels. Some gas was trapped inside the green body, resulting in lower density and strength than Example 1. This confirms that a specific particle size distribution logic is a prerequisite for achieving high density.

[0077] Regarding the influence of gradient pressure and relaxation mechanism: Comparing Example 1 with Comparative Examples 3 and 4, although the volumetric density of Comparative Example 3, which lacks a static relaxation step, decreased only slightly, its compressive strength plummeted from 86.2 MPa to 74.5 MPa. This is because the powder accumulates elastic potential energy after mechanical pre-compression. If high-pressure main molding is carried out directly without relaxation, the internal stress cannot be released, leading to shear damage or microcracks at the microscopic level, severely weakening the material's mechanical properties. Comparative Example 4, without a pre-compression step, suffers from uneven initial bulk density, resulting in a dispersed density distribution in the final product and a decline in overall performance indicators. The data show that the gradient combination of pre-compression, relaxation, and main compression is crucial to ensuring the homogeneity and integrity of the material's internal structure.

[0078] Regarding the impact of dynamic calcination temperature control strategy: Comparative Example 5 did not adjust the heating rate under the condition of high weight gain (15.2%) in a single impregnation, resulting in a decrease in bulk density to 1.793 g / cm³. 3The apparent porosity increased to 12.8%. This is because the asphalt that penetrated the pores volatilized violently during the rapid heating process, and the resulting internal pressure exceeded the strength of the matrix, causing the microstructure to expand and break (crack). In Example 1, the heating rate of the volatilization zone was reduced based on the weight gain feedback, which effectively balanced the discharge of volatiles with the matrix's bearing capacity, ensuring the maximization of the densification effect.

[0079] In summary, this invention effectively eliminates the causes of structural defects in traditional processes through the synergistic control of various process parameters, resulting in materials with advantages in density, strength, and microstructural integrity. Test Example 3: Statistics on Process Stability and Finished Product Yield Experimental description: To evaluate the stability of the process of this invention in large-scale production and its ability to control product defects, a pilot-scale yield statistical test was conducted. Following the process parameters set in Examples 1, 3, 4, and Comparative Examples 1 to 5, 50 cylindrical blanks with dimensions of Φ200mm × 300mm were prepared for each group.

[0080] All blanks undergo a complete process (forming, multiple firing and impregnation, graphitization) followed by precision machining using CNC machine tools to remove the surface oxide layer and skin (5mm removal per side). After machining, the finished products undergo visual inspection and ultrasonic non-destructive testing.

[0081] The defect judgment criteria are as follows: Macroscopic cracks: Through-cracks or non-through-cracks that are visible to the naked eye.

[0082] Delamination / Peeling: The surface shows flaking or ultrasonic testing reveals the presence of layered discontinuous interfaces inside.

[0083] Processing chipping: Edge breakage caused by loose internal structure or stress concentration during processing.

[0084] Product qualification: Products with no defects on the surface and no defects in internal testing are considered qualified products.

[0085] Formula for calculating yield rate: Yield rate = (Number of qualified products / Total number of materials used) × 100% Test results: Table 3. Statistics on Product Defects and Yield Rate During Large-Scale Production

[0086] Results analysis: Table 3 shows the statistical data on the final yield of the finished product, which is combined with the failure mode analysis as follows: The decisive role of stress relaxation mechanism in crack control: Example 1 achieved a yield rate as high as 96.0%, while Comparative Example 3, which omitted the static relaxation step, had a yield rate of only 62.0%, with the main defects concentrated in macroscopic cracks (14 pieces). After mechanical pre-compression microforming, elastic potential energy (elastic aftereffect) accumulates between the powder particles. If a static time window is not set to allow it to be released slowly, and high pressure is applied directly for main molding, the residual internal stress will superimpose the molding stress, inducing crack propagation during decompression or subsequent firing thermal cycles. The data from Example 1 demonstrates that introducing a stress relaxation mechanism is key to eliminating internal stress cracks and improving the yield of large-size products.

[0087] The effect of dynamic calcination strategy on suppressing gas expansion defects: Comparative Example 5 did not adjust the heating rate according to the high weight gain rate, resulting in a significant increase in delamination / peeling defects (12 pieces). This indicates that during the densification process, the excessively rapid heating rate causes the liquid asphalt that has penetrated the pores to vaporize rapidly, and the resulting internal gas pressure exceeds the tensile strength of the matrix, causing delamination at the microstructural level. Example 1 effectively avoided this type of gas expansion damage by reducing the heating rate in the volatile zone through dynamic feedback, ensuring structural integrity.

[0088] The role of secondary granulation gradation in constructing exhaust channels: In Comparative Example 2, due to excessively fine secondary grinding particles, 9 pieces exhibited delamination / peeling defects. The excessively fine powder blocked the gas escape channels inside the green body, leading to air entrainment during molding or the inability of volatiles to escape smoothly during firing, resulting in delamination. Example 1, by controlling a reasonable fine powder particle size distribution, ensured density while reserving exhaust paths, thus maintaining a yield rate of over 90% within the process fluctuation range of Examples 3 and 4.

[0089] In summary, the present invention solves the common problems of cracking and gas expansion in the production of high-density graphite materials through systematic optimization of process parameters, and has excellent industrial stability.

Claims

1. A highly conductive and thermally conductive semiconductor graphite material, characterized in that, The graphite material is made from raw materials comprising the following weight percentages: Carbonaceous aggregate: 68%-73%; Binder bitumen: 27%-32%; The carbonaceous aggregate is petroleum coke or pitch coke, and the binder pitch is modified medium-temperature coal tar pitch.

2. The highly conductive and thermally conductive semiconductor graphite material according to claim 1, characterized in that, The carbonaceous aggregate satisfies one of the following characteristics: The carbonaceous aggregate is low-sulfur spongy petroleum coke with a volatile matter content of 0.5%-1.5%, an ash content of ≤0.05%, and a true density of 2.08-2.12 g / cm³. 3 ; The carbonaceous aggregate is coal-based pitch coke, with a volatile matter content of 0.5%-1.0%, an ash content of ≤0.03%, and a true density of 2.05-2.10 g / cm³. 3 .

3. The highly conductive and thermally conductive semiconductor graphite material according to claim 1, characterized in that, The binder bitumen has a softening point of 105℃-115℃, a coking value of 56%-62%, a quinoline insoluble content of 8%-12%, and a toluene insoluble content of 26%-32%.

4. A method for preparing a highly conductive and thermally conductive semiconductor graphite material, characterized in that, The application of a highly conductive and thermally conductive semiconductor graphite material according to any one of claims 1-3 includes the following steps: S1. Raw material pretreatment and primary grinding: Carbonaceous aggregates are crushed and ground to obtain primary ultrafine powder; S2. Mixing and secondary granulation: The primary ultrafine powder and the binder asphalt are mixed and kneaded under heating, and after cooling, they are subjected to secondary crushing and shaping to obtain secondary granulated powder with a specific particle size distribution. S3, Gradient pressure molding: The secondary granulated powder is loaded into a mold and subjected to low-pressure pre-pressing micro-forming, static relaxation, and cold isostatic pressing main forming in sequence to obtain a green body. S4. Firing and densification: The green body is fired once, followed by at least one impregnation and re-firing cycle; in the re-firing step, the heating rate of the volatilization zone is dynamically adjusted according to the weight gain feedback data of the impregnation process. S5. Graphitization and processing: The calcined product is subjected to high-temperature graphitization treatment, and after cooling and processing, the highly conductive and thermally conductive semiconductor graphite material is obtained.

5. The method for preparing a highly conductive and thermally conductive semiconductor graphite material according to claim 4, characterized in that, In step S2, the particle size distribution control logic of the secondary granulation powder is as follows: The particle size of the primary ultrafine powder is controlled to have a sieve passing rate of 90%-95% (400-600 mesh). After mixing and secondary crushing and shaping, the particle size of the secondary granulated powder is controlled to have a sieve passing rate of 65%-75% for 150-250 mesh.

6. The method for preparing a highly conductive and thermally conductive semiconductor graphite material according to claim 4, characterized in that, In step S3, the specific process parameters for gradient pressure forming are as follows: The pressure P1 for low-pressure pre-compression microforming is 25MPa-35MPa, and the holding time is 5-10 minutes; The environment for relaxation is one without external load, and the relaxation time is 12-24 hours; The pressure P2 for cold isostatic pressing is 140MPa-160MPa, and the holding time is 110-130 minutes. Furthermore, the pressures P1 and P2 satisfy the following relationship: P1 is 15%-25% of P2.

7. The method for preparing a highly conductive and thermally conductive semiconductor graphite material according to claim 4, characterized in that, In step S4, the dynamic adjustment of the heating rate of the evaporation temperature zone specifically includes: After the impregnation step is completed, the impregnation weight gain rate is calculated; The baseline weight gain rate threshold is set at 13%-15%; When the impregnation weight gain rate is greater than or equal to the benchmark weight gain rate threshold, the heating rate in the 300℃-500℃ temperature zone in the subsequent re-calcination step is set to 1.0℃ / h-1.5℃ / h. When the impregnation weight gain rate is less than the benchmark weight gain rate threshold, the heating rate in the 300℃-500℃ temperature zone in the subsequent re-calcination step is set to 2.0℃ / h-3.0℃ / h.

8. The method for preparing a highly conductive and thermally conductive semiconductor graphite material according to claim 4, characterized in that, In step S2, the specific process of kneading is as follows: First, dry mix the ultrafine powder with the solid binder asphalt at 130℃-140℃ for 20-30 minutes; Then, heat the mixture to 165℃-175℃ and wet mix for 50-70 minutes, with the discharge temperature controlled at 155℃-165℃. The temperature for the secondary crushing and shaping is controlled between 15℃ and 30℃.

9. The method for preparing a highly conductive and thermally conductive semiconductor graphite material according to claim 4, characterized in that, In step S4, the specific process conditions for impregnation are as follows: Preheat the roasted product and evacuate it to a vacuum level of ≤-0.095MPa; Inject impregnated bitumen with a softening point of 85℃-95℃ and a quinoline insoluble content of less than 0.5%; Pressurize to 1.8MPa-2.5MPa and maintain the pressure for 2-3 hours.

10. The method for preparing a highly conductive and thermally conductive semiconductor graphite material according to claim 4, characterized in that, In step S5, the highest temperature of the graphitization treatment is 2800℃-3000℃, and the total duration of high temperature treatment and heat preservation is 48-120 hours. The highest temperature for a single roasting is 1050℃-1150℃, and the total cycle is 55-65 days.

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