A low-damage silicon carbide wafer thinning grinding wheel with directional porous structure regulation and a preparation method thereof

Abstract

This invention discloses a silicon carbide wafer low-damage thinning grinding wheel with directional porous structure control and its preparation method. The grinding wheel comprises Al ₂ O ₃ -Si ₃ N ₄ -ZrO ₂ The ternary composite ceramic binder matrix and ultrafine diamond abrasive contain a directional, uniform porous structure formed by gradient pressing and programmed sintering using a 5–20 μm pore-forming agent. Fine and coarse grinding wheels correspond to specific pore sizes and porosity ranges, respectively. The ceramic binder incorporates 5%–8% sintering aids, resulting in excellent mechanical properties and compatibility with diamond. The ultrafine diamond abrasive is uniformly dispersed without agglomeration. The preparation method includes raw material selection, abrasive dispersion, directional pore-forming mixing, gradient pressing, programmed temperature-controlled sintering, and precision grinding inspection. This invention solves the problems of disordered pores in existing grinding wheels, easy abrasive agglomeration, significant processing damage, and process instability, achieving low-damage, high-precision thinning of silicon carbide wafers with high batch yield and stable performance.

Description

Technical Field

[0001] This invention relates to the field of semiconductor grinding wheel technology, specifically to a silicon carbide wafer low-damage thinning grinding wheel with directional porous structure control and its preparation method. Background Technology

[0002] Silicon carbide, as a core material for third-generation semiconductors, possesses significant advantages such as a large bandgap, high breakdown electric field, excellent thermal conductivity, and high mechanical strength. It is a crucial substrate for fabricating high-end power devices, and the quality of its wafer thinning directly determines the performance and reliability of subsequent devices. However, silicon carbide wafers have a Mohs hardness exceeding 9.25, a stable molecular structure, high brittleness, and extremely strong chemical stability. During processing, they are prone to surface scratches, subsurface damage layers, and edge chipping, placing stringent demands on the performance of the thinning grinding wheel.

[0003] Currently, the development of silicon carbide-specific thinning grinding wheels still faces several technical bottlenecks: First, the disordered and unevenly distributed pore structure inside the grinding wheel easily leads to chip clogging during grinding, resulting in decreased wheel sharpness and processing efficiency. Simultaneously, severe localized grinding heat accumulation can cause thermal damage to the wafer surface. Second, the ceramic binder has poor compatibility with diamond abrasives. The binder's insufficient mechanical properties and significant difference in thermal expansion coefficients with diamond can easily cause diamond abrasives to detach, resulting in scratches on the wafer surface and affecting processing accuracy. Third, ultrafine diamond abrasives tend to agglomerate in the binder matrix, failing to fully exert their grinding effect and making it difficult to achieve nanoscale surface roughness. Fourth, the grinding wheel manufacturing process lacks stability, resulting in significant performance differences between batches, making it difficult to meet the demands of industrial mass production.

[0004] In existing technologies, some grinding wheels utilize pore-forming agents to create porous structures, but these often result in disordered pores, making precise control of pore size and porosity impossible, and balancing the porous structure with the matrix strength is difficult. Furthermore, the binder systems are mostly single or binary systems, whose mechanical properties and compatibility with abrasives are insufficient to meet the requirements for low-damage thinning of silicon carbide wafers. Therefore, developing a low-damage thinning grinding wheel for silicon carbide wafers with a uniformly oriented porous structure, a high-performance binder system, uniform abrasive dispersion, and a stable fabrication process is crucial to overcoming current technological bottlenecks. Summary of the Invention

[0005] In view of this, the purpose of this application is to provide a silicon carbide wafer low-damage thinning grinding wheel with directional porous structure control and its preparation method, so as to solve the problem that the existing technology cannot achieve precise control of pore size and porosity, and it is difficult to balance the porous structure and the strength of the matrix.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A low-damage thinning grinding wheel for silicon carbide wafers with directional porous structure control, comprising a ternary composite ceramic binder matrix and diamond abrasive. The grinding wheel has a uniformly oriented porous structure inside, which is formed by gradient pressing and programmed sintering of a pore-forming agent with a particle size of 5–20 μm. Fine grinding wheels have a pore size of 8–15 μm and a porosity of 50%–60%; coarse grinding wheels have a pore size of 10–20 μm and a porosity of 70%–80%. The ceramic binder is an Al2O3-Si3N4-ZrO2 system, with sintering aids added at a mass ratio of 5%–8%.

[0007] Furthermore, the diamond abrasive is ultrafine diamond powder with a particle size ≤1μm, exhibiting no agglomeration in the matrix and a distribution uniformity ≥93.5%. The selection of ultrafine diamond powder can significantly improve grinding accuracy and avoid surface scratches caused by coarse abrasive particles, while high dispersion uniformity can ensure the consistency of grinding wheel performance and fully utilize the grinding effect of each abrasive particle.

[0008] Furthermore, the ceramic binder has a hardness of HRC38–42, a fracture toughness ≥4.2 MPa·m¹ / ², and a thermal expansion coefficient difference with diamond ≤0.5×10⁻⁶. -6 / K. This mechanical property parameter ensures that the binder can firmly hold the diamond abrasive, preventing it from falling off, while also possessing sufficient toughness to prevent the grinding wheel from cracking during high-speed grinding; and the extremely small difference in the coefficient of thermal expansion reduces thermal stress during sintering and grinding, preventing interfacial cracks between the binder and the abrasive, and extending the service life of the grinding wheel.

[0009] Furthermore, the grinding wheel flatness is <2μm, the dynamic balance is <150mg, the surface roughness Ra of the processed silicon carbide wafer is ≤3nm, and the edge chipping rate is <0.005%. These performance parameters can meet the requirements of low damage and high precision thinning of silicon carbide wafers, effectively reduce wafer processing defects, and improve the yield of subsequent device fabrication.

[0010] Furthermore, the pore-forming agent is polymethyl methacrylate microspheres with a particle size of 5–20 μm, and the addition amount is precisely controlled according to the porosity target. Polymethyl methacrylate microspheres have the characteristics of uniform particle size, easy decomposition at high temperature, and no residue. By precisely controlling its addition amount and particle size, the pore size and porosity of the directional porous structure inside the grinding wheel can be precisely controlled, while avoiding the impact of pore-forming agent residue on the performance of the grinding wheel.

[0011] This invention also provides a method for preparing a low-damage thinning grinding wheel for silicon carbide wafers with the above-mentioned directional porous structure, comprising the following steps: S1 Raw Material Selection: Diamond abrasive, nano Al2O3, Si3N4, ZrO2 sintering aid, and pore-forming agent with a particle size of 5–20 μm are selected as raw materials. All raw materials are screened for purity to ensure that the impurity content is less than 0.1% to avoid impurities affecting the performance of the grinding wheel. S2 Abrasive Dispersion: A combination of ultrasonic-assisted, surface-modified, and sol-gel co-deposition methods is used to achieve uniform dispersion of ultrafine diamond powder. Ultrasonic assistance breaks up abrasive agglomerates, surface modification improves the compatibility between the abrasive and the binder, and sol-gel co-deposition further stabilizes the abrasive dispersion, ensuring that the abrasive is free of agglomerates in the matrix and has a distribution uniformity ≥93.5%. S3 Directional Pore Forming Mixture: According to the requirements of fine grinding or coarse grinding, add the corresponding particle size (8-15μm for fine grinding and 10-20μm for coarse grinding) and proportion of pore forming agent. Put the pore forming agent into a high-speed mixer along with the dispersed abrasive, binder raw materials and sintering aids. Mix at a speed of 2000-3000 r / min to ensure that the pore forming agent is evenly distributed in the mixture, laying the foundation for the subsequent formation of directional porous structures. S4 gradient pressing molding: The gradient pressure molding process is adopted, with the pressure gradually increasing from 5–10MPa to 20–30MPa and the holding time being 10–20min. Through gradient pressure control, the compactness of the green body can be guaranteed, and the pore-forming agent can be oriented in the green body, which provides a guarantee for the formation of a directional through-porous structure in subsequent sintering. S5 programmable temperature controlled sintering: The pressed green body is placed in a sintering furnace and sintered using a programmable temperature controlled method. The heating rate is controlled at 5–10℃ / min. The green body goes through low temperature debinding (200–400℃, holding for 2–3h), medium temperature pre-firing (600–800℃, holding for 1–2h), and high temperature sintering (1200–1400℃, holding for 3–4h). Finally, the green body is cooled to room temperature at a rate of 3–5℃ / min. Through programmable temperature controlled sintering, a high-strength and high-toughness Al2O3-Si3N4-ZrO2 ternary composite ceramic matrix is ​​formed, and the pore-forming agent is completely decomposed to form a directional and interconnected porous structure. S6 Precision Grinding and Inspection: CNC grinding equipment is used to grind the sintered grinding wheel at a speed of 3000 r / min and a feed rate of 5 mm / min to ensure the accuracy of the grinding wheel tooth profile. Subsequently, the grinding wheel is subjected to dynamic balancing and flatness inspection to ensure that the dynamic balance is <150mg and the flatness is <2μm. After passing the inspection, the finished grinding wheel is obtained.

[0012] Furthermore, the batch qualification rate of the produced grinding wheels is ≥98.5%, and the performance variation coefficient is ≤4%, which can stably realize industrialized production and meet the needs of large-scale semiconductor manufacturing.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention uses polymethyl methacrylate microspheres with a particle size of 5–20 μm as a pore-forming agent, combined with gradient pressing and programmed sintering processes, to construct a directional and uniform porous structure. The pore size and porosity can be precisely controlled according to the requirements of fine grinding and rough grinding. This can effectively remove grinding debris generated during grinding, avoid grinding wheel clogging, reduce grinding heat accumulation, and reduce thermal damage to silicon carbide wafers. At the same time, the directional porous structure can also improve the self-sharpening property of the grinding wheel and extend its service life.

[0014] 2. An Al2O3-Si3N4-ZrO2 ternary composite ceramic binder system is adopted, with the addition of 5%–8% sintering aids. Combined with precise sintering process control, the binder exhibits suitable hardness (HRC38–42) and excellent fracture toughness (≥4.2MPa·m¹ / ²), and the difference in thermal expansion coefficient with that of diamond abrasive is extremely small (≤0.5×10⁻⁶). -6 / K), effectively solving the problems of poor compatibility between traditional binders and abrasives and easy abrasive detachment, thus improving the structural stability of the grinding wheel and the reliability of grinding.

[0015] 3. By using a composite dispersion method of ultrasonic-assisted surface modification and sol-gel co-deposition, uniform dispersion of ultrafine diamond powder (particle size ≤1μm) in the binder matrix was achieved, with a distribution uniformity ≥93.5%. This method avoids abrasive agglomeration and fully leverages the high-precision grinding advantages of ultrafine abrasives. The resulting silicon carbide wafer has a surface roughness Ra≤3nm and an edge chipping rate <0.005%, meeting the requirements for low-damage processing.

[0016] 4. The preparation method of this invention has a clear process and controllable parameters. Through precise raw material selection, abrasive dispersion optimization, gradient pressing molding, programmed temperature-controlled sintering, and precision testing, the stability of the grinding wheel performance is ensured, with a batch qualification rate of ≥98.5% and a performance variation coefficient of ≤4%. It can stably achieve industrialized production, solving the problems of instability and difficulty in mass production in existing grinding wheel preparation processes, and has significant industrial application value. The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the preferred embodiments of this application are described in detail below with reference to the accompanying drawings.

[0017] The above and other objects, advantages and features of this application will become more apparent to those skilled in the art from the following detailed description of specific embodiments in conjunction with the accompanying drawings. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In all drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0019] Figure 1 This is a flowchart of the method of the present invention; Figure 2 Microscopic image of the porous structure in this invention; Figure 3 This is a micrograph of the abrasive dispersed in this invention; Figure 4 The figures show the comparison results of embodiments of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. In the following description, specific details such as specific configurations and components are provided merely to help fully understand the embodiments of this application. Therefore, those skilled in the art should understand that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this application. In addition, for clarity and brevity, descriptions of known functions and structures are omitted in the embodiments.

[0021] Furthermore, reference numerals and / or letters may be repeated in different examples within this application. Such repetition is for the purpose of simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or settings discussed.

[0022] In this article, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, B exists alone, and A and B exist simultaneously. The term " / and" in this article describes another type of relationship between related objects, indicating that two relationships can exist. For example, A / and B can mean: A exists alone, and A and B exist alone. In addition, the character " / " in this article generally indicates that the related objects before and after it are in an "or" relationship.

[0023] It should also be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion.

[0024] Please see Figure 1-4 This invention provides a technical solution for a silicon carbide wafer low-damage thinning grinding wheel with directional porous structure control and its preparation method: Example 1: Low-damage thinning grinding wheel for precision grinding of oriented porous silicon carbide wafers and its preparation A low-damage thinning grinding wheel for precision grinding of silicon carbide wafers with directional porous structure control comprises an Al2O3-Si3N4-ZrO2 ternary composite ceramic binder matrix and diamond abrasive. The grinding wheel has a directional and uniform porous structure with a pore size of 10 μm and a porosity of 55%. The diamond abrasive is ultrafine diamond powder with a particle size of 0.8 μm, exhibiting no agglomeration in the matrix and a distribution uniformity of 94.2%. The ceramic binder has a hardness of HRC40, a fracture toughness of 4.5 MPa·m¹ / ², and a thermal expansion coefficient difference of 0.4 × 10⁻⁶ between it and diamond. -6 / K; grinding wheel flatness 1.8μm, dynamic balance 140mg, surface roughness of processed silicon carbide wafer Ra2.8nm, edge chipping rate 0.004%; pore-forming agent is polymethyl methacrylate microspheres with a particle size of 10μm, and the addition amount is precisely controlled according to a porosity of 55%.

[0025] Its preparation method includes the following steps: S1 Raw Material Selection: Ultrafine diamond powder with a particle size of 0.8μm, nano-Al2O3, Si3N4, ZrO2, sintering aid (Y2O3-Al2O3 composite system) with a mass ratio of 6%, and polymethyl methacrylate microspheres with a particle size of 10μm were selected as raw materials. After screening, the impurity content of all materials was less than 0.1%. S2 abrasive dispersion: The uniform dispersion of ultrafine diamond powder is achieved by a combination of ultrasonic-assisted (500W power, ultrasonic time 30min) - surface modification (addition of silane coupling agent, modification temperature 80℃, modification time 2h) - sol-gel co-deposition (sol concentration 5%, deposition temperature 60℃). S3 Directional Pore Forming Mixture: Add polymethyl methacrylate microspheres with a particle size of 10μm (the amount added is adjusted according to a porosity of 55%), and put them together with the dispersed abrasive, binder raw materials and sintering aids into a high-speed mixer and mix them at a speed of 2500r / min for 30min. S4 gradient pressing: Gradient pressure is used to form a compact body with a pressure gradient from 8MPa to 25MPa and a holding time of 15min. S5 programmable temperature-controlled sintering: The green body is placed in a sintering furnace and heated at a rate of 8℃ / min. It is held at 200–400℃ for 2.5h for debinding, held at 600–800℃ for 1.5h for pre-firing, held at 1300℃ for 3.5h for high-temperature sintering, and then cooled to room temperature at a rate of 4℃ / min to form a ceramic matrix with a directional porous structure. 6) Precision Gear Grinding and Inspection: CNC gear grinding equipment is used to grind the gears at a speed of 3000 r / min and a feed rate of 5 mm / min. Then, the dynamic balance and flatness are inspected to ensure that the dynamic balance is 140 mg and the flatness is 1.8 μm. After passing the inspection, the finished grinding wheel for precision grinding is obtained.

[0026] The fine grinding wheel prepared in this embodiment has a batch qualification rate of 98.8%, a performance variation coefficient of 3.5%, and when processing silicon carbide wafers, the surface roughness Ra is stable at 2.5–2.8 nm, the edge chipping rate is ≤0.004%, and there are no obvious surface scratches or subsurface damage, which meets the requirements of fine grinding.

[0027] Example 2: Low-damage thinning grinding wheel for rough grinding of silicon carbide wafers and its preparation A low-damage thinning grinding wheel for coarse grinding of silicon carbide wafers with a directional porous structure is disclosed, comprising an Al2O3-Si3N4-ZrO2 ternary composite ceramic binder matrix and diamond abrasive. The grinding wheel has a directional, uniform porous structure with a pore size of 15 μm and a porosity of 75%. The diamond abrasive is ultrafine diamond powder with a particle size of 0.9 μm, exhibiting no agglomeration in the matrix and a distribution uniformity of 93.8%. The ceramic binder has a hardness of HRC39, a fracture toughness of 4.3 MPa·m¹ / ², and a thermal expansion coefficient difference of 0.45 × 10⁻⁶ between it and diamond. -6 / K; grinding wheel flatness 1.7μm, dynamic balance 135mg, surface roughness of processed silicon carbide wafer Ra2.9nm, edge chipping rate 0.0045%; pore-forming agent is polymethyl methacrylate microspheres with a particle size of 15μm, and the addition amount is precisely controlled according to a porosity of 75%.

[0028] Its preparation method includes the following steps: S1 Raw Material Selection: Ultrafine diamond powder with a particle size of 0.9μm, nano Al2O3, Si3N4, ZrO2, sintering aid (Y2O3-ZrO2 composite system) with a mass ratio of 7%, and polymethyl methacrylate microspheres with a particle size of 15μm were selected as raw materials. After screening, the impurity content of all materials was less than 0.1%. S2 abrasive dispersion: The uniform dispersion of ultrafine diamond powder is achieved by a combination of ultrasonic-assisted (600W power, ultrasonic time 25min) - surface modification (addition of titanate coupling agent, modification temperature 85℃, modification time 1.5h) - sol-gel co-deposition (sol concentration 6%, deposition temperature 65℃). S3 Directional Pore Forming Mixture: Add polymethyl methacrylate microspheres with a particle size of 15μm (the amount added is adjusted according to the porosity of 75%), and put them into a high-speed mixer together with the dispersed abrasive, binder raw materials and sintering aids. Mix them at a speed of 2800r / min for 25min. S4 gradient pressing: Gradient pressure is used to pressurize the green body. The pressure is gradually increased from 7MPa to 22MPa and the holding time is 12min to obtain a dense green body with oriented pore-forming agent. S5 programmable temperature-controlled sintering: The green body is placed in a sintering furnace and heated at a rate of 7℃ / min. It is held at 200–400℃ for 2 hours to remove the binder, held at 600–800℃ for 1 hour for pre-firing, held at 1250℃ for 3 hours for high-temperature sintering, and then cooled to room temperature at a rate of 3.5℃ / min to form a ceramic matrix with a directional porous structure. S6 Precision Grinding and Inspection: CNC gear grinding equipment is used to perform gear grinding at a speed of 3000 r / min and a feed rate of 5 mm / min. Then, the dynamic balance and flatness are inspected to ensure that the dynamic balance is 135 mg and the flatness is 1.7 μm. After passing the inspection, the finished grinding wheel for rough grinding is obtained.

[0029] The coarse grinding wheel prepared in this embodiment has a batch qualification rate of 99.0%, a performance variation coefficient of 3.2%, and smooth chip removal when processing silicon carbide wafers with no wheel clogging. The surface roughness Ra is stable at 2.7–2.9 nm, and the chipping rate is ≤0.0045%. It balances processing efficiency and low damage requirements and can be stably used for coarse grinding.

[0030] Example 3: Stability Verification of the Preparation Process Following the preparation method of Example 1, 10 batches of grinding wheels for precision grinding were continuously produced. Ten samples were randomly selected from each batch to test the flatness, dynamic balance, binder hardness, abrasive dispersion uniformity, and processing performance (surface roughness, chipping rate) of the grinding wheels. The batch pass rate and performance variation coefficient were statistically analyzed.

[0031] The test results showed that the batch pass rate of all 10 batches of grinding wheels was ≥98.5%, with an average batch pass rate of 98.9%; the performance coefficient of variation was ≤4%, of which the coefficient of variation for binder hardness was 3.1%, the coefficient of variation for abrasive dispersion uniformity was 2.8%, the coefficient of variation for surface roughness was 3.3%, the coefficient of variation for dynamic balance was 3.5%, and the coefficient of variation for flatness was 3.0%. This indicates that the preparation method of the present invention has excellent stability and can meet the requirements of industrial mass production.

[0032] The above description is merely a preferred embodiment of the present invention and does not limit the scope of protection of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any changes, modifications, substitutions, integrations, and parameter alterations to these embodiments within the spirit and principles of the present invention, achieved through conventional substitutions or by achieving the same function without departing from the principles and spirit of the present invention, fall within the scope of protection of the present invention.

Claims

1. A silicon carbide wafer low-damage thinning grinding wheel with directional porous structure control, characterized in that, It comprises a ternary composite ceramic binder matrix and diamond abrasive; the grinding wheel has a uniformly oriented porous structure, formed by gradient pressing and programmed sintering of a pore-forming agent with a particle size of 5–20 μm; the fine grinding wheel has a pore size of 8–15 μm and a porosity of 50%–60%; the coarse grinding wheel has a pore size of 10–20 μm and a porosity of 70%–80%. The ceramic binder is an Al2O3-Si3N4-ZrO2 system, with sintering aids added at a mass ratio of 5%–8%.

2. The thinning grinding wheel according to claim 1, characterized in that, The diamond abrasive is ultrafine diamond powder with a particle size ≤1μm, no agglomeration in the matrix, and a distribution uniformity ≥93.5%.

3. The thinning grinding wheel according to claim 1, characterized in that, The ceramic binder has a hardness of HRC38–42, a fracture toughness ≥4.2 MPa·m¹ / ², and a thermal expansion coefficient difference with diamond ≤0.5×10⁻⁶. -6 / K.

4. The thinning grinding wheel according to claim 1, characterized in that, The grinding wheel flatness is <2μm, the dynamic balance is <150mg, the surface roughness of the processed silicon carbide wafer Ra is ≤3nm, and the edge chipping rate is <0.005%.

5. The thinning grinding wheel according to claim 1, characterized in that, The pore-forming agent is polymethyl methacrylate microspheres with a particle size of 5–20 μm, and the amount added is precisely controlled according to the porosity target.

6. A method for preparing a low-damage thinning grinding wheel for silicon carbide wafers with directional porous structure controlled according to any one of claims 1-5, characterized in that, Including the following steps: S1 raw material selection: diamond abrasive, nano Al2O3, Si3N4, ZrO2, sintering aid, pore-forming agent with a particle size of 5–20 μm; S2 abrasive dispersion: Ultrasonic-assisted surface modification-sol-gel co-deposition achieves uniform dispersion of ultrafine diamond; S3 Directional Pore Forming Mixture: Add pore-forming agent of the corresponding particle size and proportion according to the fine / coarse grinding requirements, and mix well; S4 gradient pressing: Gradient pressure forming is used to ensure uniform hole distribution and compactness of the blank; S5 programmable temperature-controlled sintering: forming a high-strength, high-toughness ceramic matrix and a directional, interconnected porous structure; S6 Precision Grinding and Inspection: CNC grinding, dynamic balancing, and flatness inspection to obtain finished grinding wheels.

7. The preparation method according to claim 6, characterized in that, Step 6) Grinding speed 3000 r / min, feed rate 5 mm / min, dynamic balance <150 mg, flatness <2 μm. The preparation method according to claim 6 is characterized in that, The batch qualification rate of the produced grinding wheels is ≥98.5%, the coefficient of variation of performance is ≤4%, and it can be stably industrialized.

Images