In the field of microelectronic packaging, aluminum nitride ceramics are gradually becoming the preferred material for high-performance chip cooling substrates due to their excellent thermal conductivity, mechanical strength and electrical properties. However, its high hardness and high brittleness can easily cause surface micro-cracks and sub-surface damage during processing, which directly affect the final properties and application effects of the material. Therefore, how to optimize the chemical mechanical polishing (CMP) process of aluminum nitride ceramics to effectively reduce or eliminate these processing defects has become a hot and difficult point in current research.

 

Aluminum nitride ceramics, as a high-performance advanced material, with its excellent thermal conductivity efficiency (thermal conductivity up to about 200-300 W/m·K, far exceeding traditional ceramic materials), excellent mechanical properties (high hardness, high strength), excellent corrosion resistance, as well as good electrical insulation and weldability characteristics, It has shown great potential in the field of microelectronics, especially in the cooling substrate and packaging materials of large-scale integrated circuits (ics). AlN substrate’s lightweight design not only effectively reduces the volume and weight of electronic devices, but also significantly reduces thermal resistance through its ultra-smooth surface (ideal surface roughness Ra ≤ 8 nm, and even requires surface accuracy RMS < 2 nm after polishing), optimizing the heat dissipation efficiency of the chip, which is crucial to improving the overall performance and reliability of integrated circuits.

 

However, the high hardness (Mohs hardness of about 9), high brittleness and relatively low fracture toughness of aluminum nitride ceramics pose great challenges for precision machining, especially surface flattening. In the process of processing, it is easy to produce surface scratches, micro-cracks and other defects as well as difficult to detect sub-surface damage, which will directly affect the performance and service life of the material. Therefore, how to achieve efficient and high-quality aluminum nitride ceramic surface flattening processing and reduce processing defects has become a key problem to be solved in the field of materials science and engineering.

 

The core of the chemical mechanical polishing process of aluminum nitride ceramics is to realize the fine processing and flat treatment of the material surface through the dual action of chemical corrosion and mechanical friction. This process can not only significantly improve the surface roughness of the material, but also adjust the surface stress state of the material to a certain extent, so as to improve the overall performance. However, the traditional CMP process is often difficult to balance the processing efficiency and surface quality when processing aluminum nitride ceramics, especially in the prevention of micro-cracks and sub-surface damage.

 

It is worth noting that compared with more mature semiconductor materials such as silicon carbide, there are still some research gaps in the selection of abrasives, the types of polishing pads and the optimization process of aluminum nitride ceramics in CMP process. In the future, with the in-depth understanding of the characteristics of aluminum nitride ceramic materials and the continuous innovation of CMP technology, it is expected to develop a more efficient, environmentally friendly and suitable for aluminum nitride ceramics CMP process system, and further promote its wide application in the field of high-performance electronic packaging.

 

 

To solve the problem that the surface of aluminum nitride after processing is prone to micro-cracks and sub-surface damage, it is necessary to start from many aspects:

 

1. Optimize the formulation of polishing fluid: Develop polishing fluid with higher selectivity, which can more effectively remove the surface of the material without damaging its internal structure. At the same time, the pH value, concentration and additive types of the polishing liquid are adjusted to reduce the chemical erosion of aluminum nitride ceramics and reduce the risk of micro-cracks.

 

2. Improve the selection of polishing pads and abrasives: select polishing pads with moderate hardness and good wear resistance, as well as abrasive particles with uniform particle size distribution and regular shape to reduce mechanical stress concentration during processing and avoid sub-surface damage.

 

3. Precise control of polishing parameters: including polishing pressure, rotation speed, polishing time, etc. The reasonable setting of these parameters can directly affect the polishing effect and processing quality. By fine-tuning these parameters, it is possible to minimize surface defects while ensuring processing efficiency.

 

4. Adopt advanced detection and feedback technology: the online monitoring and feedback system is introduced in the CMP process to detect the quality of the machined surface in real time, and adjust the polishing parameters in time according to the feedback results to realize the intelligent and fine control of the processing process.

 

In summary, the optimization and improvement of chemical mechanical polishing process of aluminum nitride ceramics is the key to solve the micro-cracks and sub-surface damage of aluminum nitride surface after processing. Through the comprehensive application of the above strategies, the processing quality and application performance of aluminum nitride ceramics can be significantly improved, and the wide application and development of aluminum nitride ceramics in the field of microelectronics packaging can be promoted.

As a new inorganic nonmetallic material with high performance and multiple functions, transparent ceramics show great application potential in optics, electronics, aerospace and other fields because of its excellent light transmission, high strength, high hardness and good thermal and chemical stability. Among the many methods to prepare transparent ceramics, hot pressing sintering has become one of the key technologies to achieve high performance transparent ceramic materials because of its unique technological characteristics. The purpose of this paper is to discuss the application principle and technological advantages of hot pressing sintering technology in the preparation of transparent ceramics and its promoting effect on the development of materials science in the future.

 

 

The basic principle and process of hot pressing sintering

Hot press sintering technology through the powder or preliminary forming ceramic body placed in a high melting point metal or graphite mold, in a high temperature environment to apply a certain pressure to promote the close contact and diffusion of powder particles, so as to complete the sintering process in a short time. This process can not only improve the density of ceramics, but also effectively inhibit the abnormal growth of grains, and obtain transparent ceramic materials with fine grains and uniform structure.

 

Advantages of direct sintering of ceramic blanks

Hot pressing sintering technology can directly sintering the ceramic blank without complicated pretreatment, simplifying the production process, reducing energy consumption and cost. At the same time, because the pressure applied in the sintering process helps to eliminate the pores, improve the light transmission and mechanical strength of the ceramics, so that the prepared transparent ceramics have significant advantages in optical components, window materials and other applications.

 

Innovation of molding and sintering integration process

One of the highlights of this technology is the ability to combine the molding process with the sintering process, that is, to complete the sintering while applying pressure, which not only improves the production efficiency, but also reduces the defects that may be introduced due to multiple processing, ensuring the overall performance and consistency of the ceramic material. This integrated process is particularly important for the preparation of transparent ceramic parts with complex shapes and provides the possibility for precision manufacturing.

 

In summary, hot press sintering technology plays a crucial role in the development and production of transparent ceramic materials with its efficient and high-quality preparation characteristics. It not only optimizes the traditional sintering process, promotes the improvement of transparent ceramics performance and the reduction of cost, but also broadens the application field of transparent ceramics and lays a solid foundation. With the continuous deepening of material science research and continuous progress of technology, hot press sintering technology is expected to show its unique value in the preparation of more high-performance and multi-functional ceramic materials, and inject new vitality into the development of new materials industry. In the future, the exploration of more environmentally friendly and energy-saving hot press sintering new processes, as well as the development of new transparent ceramic materials with specific functions, will be the focus of research in this field.

With the rapid development of microelectronics technology, the requirements for electronic packaging materials are increasingly stringent. Aluminum nitride ceramics, with its excellent thermal conductivity, excellent mechanical properties, corrosion resistance and excellent electrical properties, become the leader of large-scale integrated circuit cooling substrate and packaging materials. However, the high hardness, high brittleness and low fracture toughness of aluminum nitride ceramics are like an insurmountable gap, which greatly challenges its application in the field of ultra-precision machining. Especially in the pursuit of ultra-smooth surface with surface roughness Ra ≤ 8 nm or even RMS < 2 nm, how to effectively reduce surface defects and sub-surface damage during machining has become a key problem restricting the wide application of aluminum nitride ceramics. In this context, ELID (Electrolytic in-process Dressing) grinding process offers innovative solutions to the processing challenges of AlN substrates with its unique advantages.

 

ELID grinding technology is a composite mirror processing technology that integrates traditional grinding, grinding and polishing. The core of ELID grinding technology is to realize dynamic self-sharpening during grinding through electrolytic in-situ dressing of grinding wheels, thus significantly improving grinding efficiency and processing quality. ELID grinding technology shows exceptional applicability for high-hardness brittle materials such as aluminum nitride ceramics.

Firstly, ELID grinding uses a weak electrolyte solution as the grinding fluid, which not only avoids the potential corrosion of the traditional grinding fluid on the machine tool and the workpiece, but also simplifies the processing environment and reduces the production cost. More importantly, this technology can effectively control the temperature during grinding, reducing workpiece burns, residual stresses and cracks caused by high temperatures, which is essential to protect the microstructure and properties of aluminum nitride ceramics.

Secondly, ELID grinding forms a uniform and dense oxide film on the surface of the grinding wheel through electrolysis, which not only improves the cutting ability of the grinding wheel, but also enhances the wear resistance of the grinding wheel, ensuring the stability and continuity of the grinding process. At the same time, by precisely controlling the correction current, the fine adjustment of the oxide layer thickness can be achieved, and then the grinding effect can be optimized, the surface roughness and sub-surface damage can be reduced, and the harsh requirements of aluminum nitride ceramics for ultra-smooth surfaces can be met.

In addition, ELID grinding technology also has the characteristics of simple process and flexible operation, which is easy to promote and apply in industrial production. Through continuous optimization of grinding parameters and process conditions, the processing efficiency and processing quality of aluminum nitride ceramics can be further improved to meet the growing demand for high-performance materials in the field of microelectronics packaging.

 

In summary, ELID grinding process, with its unique advantages, has shown great potential in solving the processing problems caused by high hardness, high brittleness and low fracture toughness of aluminum nitride ceramics. Through this technology, not only can effectively reduce the surface defects and sub-surface damage in the processing process, but also significantly improve the processing efficiency and processing quality, which lays a solid foundation for the wide application of aluminum nitride ceramics in the field of electronic packaging. In the future, with the continuous development and improvement of ELID grinding technology, it is believed that its application prospects in the field of ultra-precision machining will be broader, and contribute to the continuous progress of microelectronics technology.

In today's rapidly changing electronics industry, ceramic substrate materials as a key basis for supporting high-performance electronic devices, its performance and characteristics directly affect the overall performance and reliability of electronic products. From the early alumina ceramics to the later aluminum nitride, silicon nitride and other new materials, the development of ceramic substrate materials has witnessed the continuous progress and innovation of science and technology. This article will take you to explore the unique advantages and application prospects of these ceramic substrate materials, especially how aluminum nitride and silicon nitride ceramics stand out in the solution of high-power device heat dissipation and high-intensity heat dissipation environment with their excellent performance, and become an indispensable important material in the modern electronics industry.

 

Alumina substrate, as the pioneer of ceramic substrate, has been successfully developed by Siemens in Germany since 1929 and entered industrial production in 1933, with its low price, excellent stability, good insulation and mechanical properties, has long occupied a dominant position in a wide range of applications. However, its relatively low thermal conductivity and thermal expansion coefficient that do not match Si limit its further development in high-power electronic products, and it is mainly used in the field of low-voltage and low-integration circuit packaging.

 

Subsequently, although BeO substrates stood out for its high thermal conductivity, the toxicity problem became an insurmountable obstacle, which was not only banned in Japan, but also severely restricted in Europe, greatly hindering its wide application.

 

In contrast, although the SiC single crystal has an amazing thermal conductivity, the thermal conductivity of polycrystalline SiC ceramics decreases significantly due to the difference in grain orientation, coupled with poor insulation performance and high dielectric loss, which makes the research progress in the field of circuit board materials slow.

 

Under this background, aluminum nitride and silicon nitride ceramics are gradually emerging with their unique performance advantages. Aluminum nitride substrate with its excellent high thermal conductivity (theoretical value up to 320W/ (m·K), commercial product thermal conductivity is also between 180W/ (m·K) ~260W/ (m·K)) has become a key material to solve the heat dissipation problem of high-power devices, and since the 1980s, under the promotion of developed countries, especially Japan, It has rapidly developed into a new generation of advanced ceramic packaging materials. Its high mechanical strength and chemical stability ensure stable operation in harsh environments.

 

 

Silicon nitride substrates, after experiencing the early stage of underestimated thermal conductivity, through scientific research and process optimization, its thermal conductivity has been significantly improved, breaking through 177W/ (m·K), while maintaining a very low coefficient of thermal expansion (3.2×10−6/℃), becoming one of the most excellent ceramic substrate materials with comprehensive performance. Its excellent bending strength and wear resistance show extraordinary competitiveness in high intensity heat dissipation environment.

 

 

In summary, aluminum nitride ceramics are the best choice for heat dissipation of high-power devices due to their high thermal conductivity and thermal expansion coefficient matching semiconductor materials. Silicon nitride ceramics, with their comprehensive performance advantages, lead the way in demanding thermal environments. Together, the two lead the ceramic substrate materials to higher performance and a wider range of applications.

With the rapid development of electronic technology, the integration and performance requirements of large-scale integrated circuits are increasing day by day. As a key supporting material, aluminum nitride ceramics have become an ideal cooling substrate and packaging material because of their excellent thermal conductivity, mechanical strength, corrosion resistance and excellent electrical properties. However, the high hardness, high brittleness and low fracture toughness of aluminum nitride ceramics pose a great challenge in the process of pursuing ultra-smooth surface quality. In particular, in the field of electronic packaging, surface roughness needs to be controlled at the nanoscale to minimize volume, reduce internal resistance and optimize heat dissipation performance. Therefore, how to use laser processing technology to achieve high quality flat processing surface of aln substrate has become a key problem to be solved in the field of material science and precision manufacturing.

 

Application and challenge of laser processing technology in aluminum nitride ceramics

Laser processing technology, with its advantages of no contact, no tool wear, high precision and flexibility, has shown great potential in the processing of brittle and hard ceramic materials. In this technology, the high energy density laser beam directly acts on the surface of the material, so that the local area quickly heats up and decomposes or melts, so as to achieve the removal or modification of the material. However, for the laser processing of aluminum nitride ceramics, how to accurately control the energy distribution in the processing process, reduce the heat affected zone, avoid cracks and sub-surface damage, and ensure the high smoothness of the machined surface has become the difficulty of technical breakthrough.

 

 

Strategies for achieving high quality flatness of machined surfaces

Optimize laser parameters: By adjusting laser power, pulse width, scanning speed and spot size and other parameters, accurately control the thermal effect of laser and material interaction, reduce thermal stress concentration and avoid cracks. The research shows that the use of ultra-short pulse laser (such as femtosecond laser) can effectively reduce the heat affected zone and improve the machining accuracy.

Introduction of auxiliary gas: Inert gas (such as argon) is introduced as a protective gas during laser processing to reduce the surface oxidation of the material, while the impact effect of the gas is used to help remove melt and debris, and improve the surface finish.

Composite processing technology: Combining laser processing with other precision processing technologies (such as chemical mechanical polishing), laser roughing is performed first to remove most of the material, and then chemical mechanical polishing is used to further refine the surface to achieve the processing goal of nanoscale roughness.

Real-time monitoring and feedback control: The advanced online monitoring system is used to detect the temperature distribution, surface topography and stress state during the processing in real time, and dynamically adjust the processing parameters through the feedback control mechanism to ensure the stability of the processing quality.

 

conclusion

As a high performance electronic packaging material, aluminum nitride ceramics are very important to improve the overall performance of integrated circuits by obtaining high quality flat machined surfaces. With its unique advantages, laser processing technology has shown broad application prospects in the precision machining of aluminum nitride ceramics. However, in order to achieve the machining goals of nanoscale surface roughness and low damage, further research and innovation are needed in laser parameter optimization, auxiliary process introduction, composite machining strategy and machining process control. In the future, with the continuous progress and improvement of laser processing technology, we believe that we can provide more reliable and efficient solutions for the application of aluminum nitride ceramics in the field of high-end electronic packaging.

In cutting-edge technologies such as high-performance electronic packaging, aerospace and energy conversion, silicon nitride (Si3N4) substrate materials are highly regarded for their excellent mechanical properties, chemical stability and high temperature resistance. However, the thermal conductivity of silicon nitride, as one of the key factors affecting its wide application, has always been the focus and difficulty of materials science research. This paper aims to deeply explore the main heat transfer mechanisms of silicon nitride substrate, namely lattice vibration and phonon conduction, and systematically analyze the influence of the selection and optimization strategy of sintering additives on the thermal conductivity of silicon nitride substrate, in order to provide theoretical basis and practical guidance for improving the thermal management efficiency of silicon nitride substrate.

 

 

A deeper understanding of heat transfer mechanisms

The main heat transfer mechanism of silicon nitride, namely lattice vibration and phonon conduction, is a complex and fine process. The nonlinear propagation and collision of phonons in the lattice are not only limited by the interlattice coupling, but also deeply affected by the internal microstructure characteristics of materials. In particular, many defects (such as vacancies, dislocations), impurity atoms and grain interfaces exist in Si3N4 crystals, which, as the center of phonon scattering, significantly reduce the mean free path of phonons, and thus become the main bottleneck limiting the improvement of silicon nitride thermal conductivity. Lattice oxygen, as one of the most important defect types, not only increases the probability of phonon scattering, but also causes lattice distortion, which further weakens the heat conduction efficiency.

 

 

Optimization strategy of sintering additives

In view of the strong covalent bond of silicon nitride and the difficulty of compact sintering through solid phase diffusion, the selection and application of sintering additives are particularly important. Traditionally, oxides such as MgO, Al2O3, CaO and rare earth oxides are widely used as sintering additives, which promote liquid phase sintering by forming low melting point eutectic melts, thereby increasing the density of silicon nitride. However, these oxide sintering additives bring densification at the same time, but also introduce a new problem: their own low thermal conductivity and may cause grain boundary phase changes (such as the formation of SiAlON solid solution), have an adverse effect on the overall thermal conductivity of silicon nitride ceramics.

In order to overcome this problem, scientists began to explore the application of non-oxide sintering additives. Non-oxides, such as MgSiN2 and rare earth fluoride, show unique advantages. They can not only reduce the secondary phase and lattice oxygen content of silicon nitride, but also promote the reduction of grain boundary phase and the reduction of SiO2 through specific chemical reactions (such as rare earth fluoride reacting with SiO2 to produce volatile SiF4), so as to effectively reduce the lattice oxygen content and improve the thermal conductivity. However, the commercial application of non-oxide sintering additives still faces challenges, and their high cost and supply constraints limit their application in large-scale production.

 

Comprehensive strategy: oxide + non-oxide sintering additives

In view of the above analysis, a possible solution is to adopt an "oxide + non-oxide" composite sintering auxiliary system. This strategy aims to combine the advantages of two types of sintering additives: oxide additives provide the necessary liquid phase sintering environment to ensure the densification of the material; The non-oxide additives further reduce the lattice oxygen content and increase the thermal conductivity through their unique chemical properties. Through a carefully designed formulation system, it is possible to achieve fine control of the sintering process and the performance of the final product, so as to maximize the thermal conductivity of the silicon nitride substrate while ensuring the production efficiency.

 

In summary, the optimization of thermal conductivity of silicon nitride substrate material is a complex process involving multiple factors and layers. By deeply understanding the microscopic mechanism of lattice vibration and phonon conduction, as well as precisely regulating the selection and formulation system of sintering additives, we can effectively overcome the bottleneck faced by silicon nitride materials in improving thermal conductivity. In the future, with the continuous deepening of material science research and continuous progress of technology, we have reason to believe that silicon nitride substrate materials will show its unique charm and broad application prospects in more fields. At the same time, this will also promote technological innovation and industrial upgrading in related fields, and contribute to the sustainable development of human society.

As a kind of high performance material, transparent ceramics show great application potential in optics, electronics, aerospace and other fields because of its unique light transmission, high strength and good thermal stability. However, the preparation process of transparent ceramics is complicated, especially the sintering process, which is directly related to the final properties of the material. Among many sintering methods, hot isostatic pressing has become one of the key technologies for preparing high quality transparent ceramics with its unique advantages. In this article, the principle, characteristics and application of hot isostatic pressing sintering technology in the preparation of transparent ceramics will be discussed in depth, in order to provide reference for the research and development of related fields.

 

 

Overview of hot isostatic pressing sintering technology

Hot isostatic sintering combines the advantages of normal temperature isostatic pressure and high temperature sintering, and realizes uniform and efficient sintering of ceramic billet by applying isostatic pressure to the protective gas in the high pressure vessel.

 

Advantages of isostatic pressure uniformity

Compared with the traditional sintering method, hot isostatic pressing applies the same pressure in all directions through high pressure protection gas, which effectively avoids the defects caused by uneven pressure inside the body, such as cracks, deformation, etc., thus improving the yield and optical properties of transparent ceramics.

 

The role of protective gases

The selection of appropriate protective gases (such as argon, nitrogen, etc.) can not only prevent the ceramics from being oxidized during the high-temperature sintering process, but also reduce the loss of the mold, ensure the purity and stability of the sintering environment, and provide a strong guarantee for the preparation of high-quality transparent ceramics.

 

Applicability of hot isostatic pressing sintering

The technology is suitable for many types of transparent ceramic materials, including but not limited to alumina, aluminum nitride, yttrium oxide, etc., showing a wide range of material adaptability and process flexibility.

 

In summary, hot isostatic pressing sintering technology has opened up a new path for the preparation of transparent ceramics with its unique pressure application method and good sintering environment control. It not only solves the common problems of uneven pressure and oxidation pollution in traditional sintering methods, but also significantly improves the light transmission, mechanical properties and thermal stability of transparent ceramics. With the continuous progress of material science and technology, hot isostatic pressing sintering technology is expected to achieve application expansion in more fields, and promote the development of transparent ceramic materials to higher performance and wider application direction. In the future, further optimization of sintering parameters and exploration of new ceramic material systems will be an important direction of hot isostatic pressing sintering technology research, in order to continuously meet the new challenges of scientific and technological development and market demand.

As a kind of high-efficiency material, transparent ceramics show great application potential in optics, electronics, aerospace and other fields because of its unique optical transmittance, high strength and good thermal stability. However, the traditional methods of preparing transparent ceramics often face challenges such as abnormal grain growth, high sintering temperature and complicated process. In recent years, the use of ultrahigh pressure technology to prepare transparent ceramics has become a research hotspot, especially for the preparation of nanostructured transparent ceramics, this method not only simplifies the process, but also significantly improves the performance of the material. In this paper, the methods, advantages and potential applications of ultrahigh pressure preparation of nanostructured transparent ceramics are discussed.

 

 

The basic principle of ultrahigh pressure preparation of transparent ceramics

The core of ultrahigh pressure preparation of transparent ceramics is to directly sintering high-purity powder raw materials into bulk ceramics under ultra-high pressure environment of more than 1GPa. In this process, the ultra-high pressure environment exerts great pressure on the powder particles , effectively inhibits the growth of the grains, and reduces the sintering temperature. When the initial material is nano-powder, the ultrahigh pressure sintering can preserve the nano-structure of the powder, so as to obtain nano-structured transparent ceramics.

 

Advantages of ultrahigh pressure preparation of transparent ceramics

1. Short sintering time: Ultra-high pressure environment accelerates the diffusion and bonding between powder particles, significantly shortening the sintering time.

2. Low sintering temperature: Ultra-high pressure reduces the activation energy required for sintering, so that densification can be achieved at a lower temperature.

Grain size control: By adjusting the parameters of ultra-high pressure sintering, the size of the grain can be precisely controlled, so as to obtain the ideal microstructure.

3. High density of the sample: the sample obtained by ultra-high pressure sintering has high density, reducing pores and defects, and improving the overall performance of the material.

4. Excellent light transmission performance: nanostructured transparent ceramics have higher light transmittance and lower light scattering, showing excellent optical properties.

 

Application potential of ultrahigh pressure transparent ceramics

Nanostructured transparent ceramics have wide application potential in many fields because of their unique properties. For example, in the field of optics, it can be used as a substrate for high-performance lenses, window materials and optoelectronic devices; In the field of electronics, it can be used to make high-reliability encapsulation materials for capacitors, sensors and integrated circuits; In the aerospace field, it can be used as a transparent window and protective material under high temperature and high pressure environment. In addition, With the continuous progress of materials science, the application of nanostructured transparent ceramics in biomedicine, energy storage and conversion will continue to expand.

 

In summary, the preparation of nanostructured transparent ceramics by ultrahigh pressure is a method with significant advantages and wide application potential. This method not only simplifies the process, reduces the production cost, but also significantly improves the performance and quality of the material. In the In the future, with the continuous development and improvement of ultra-high pressure technology, the application field of nanostructured transparent ceramics will be further expanded, providing strong support for scientific and technological progress and social development. Therefore, in-depth research and development of ultrahigh pressure preparation of nanostructured transparent ceramics technology and methods, to promote the development of materials science is of great significance.

As a kind of high performance material, transparent ceramics show great application potential in the fields of optical window, laser medium and high temperature wave transmittance materials because of its unique optical transparency and excellent mechanical properties. Among the many methods of preparing transparent ceramics, vacuum sintering technology has become one of the most widely researched and applied methods with its unique advantages. In this paper, the principle, characteristics and application of vacuum sintering technology in the preparation of transparent ceramics are discussed in order to provide theoretical reference and practical guidance for the research and development of transparent ceramic materials.

 

 

Basic principle and mechanism of vacuum sintering

Vacuum sintering refers to the method of heating the ceramic body in a complete or partial vacuum environment to reach the sintering temperature and complete the densification process. The vacuum environment creates the internal and external pressure difference, promotes the effective discharge of pores, significantly reduces the porosity of ceramics, and promotes the growth of grains, forming a high density microstructure. In addition, the vacuum condition effectively inhibits the decomposition and element volatilization of ceramic materials at high temperatures, ensuring the chemical stability of the materials.

 

Advantages of vacuum sintering technology

Compared with other sintering methods, vacuum sintering has remarkable operation simplicity, cost effectiveness and production efficiency. No need for complex pressure control system, reducing equipment cost and maintenance difficulty; At the same time, because the vacuum environment accelerates the process of pore elimination and grain growth, the sintering cycle is shortened, and the production efficiency is improved. These advantages make vacuum sintering the preferred technology for large-scale industrial production of transparent ceramics.

 

Application of vacuum sintering in the preparation of transparent ceramics

Many kinds of oxide based ceramics, especially rare earth activated Yttrium aluminum garnet (YAG), Yttrium oxide (Y₂O₃) and alumina (Al₂O₃), have been successfully prepared by vacuum sintering technology of high quality transparent ceramics. These materials not only have excellent light transmission properties, but also show good thermal stability and mechanical strength, and are widely used in solid state lasers, optical lenses, high temperature sensors and other fields, promoting the rapid development of related technologies.

 

In summary, vacuum sintering technology plays an important role in the preparation of transparent ceramics due to its unique sintering mechanism, significant cost effectiveness and wide application prospects. With the continuous progress of material science and the continuous optimization of preparation technology, vacuum sintering technology is expected to show greater potential in the preparation of more types of transparent ceramic materials, further broaden the application field of transparent ceramics, and inject new vitality into the development of high-tech industry. In the future, in-depth study of the microscopic mechanism in the vacuum sintering process and exploration of more efficient sintering process parameters will be the key direction to promote the performance of transparent ceramic materials and expand its application range.

With the rapid development of power electronic technology, especially the wide application of power semiconductor devices such as high voltage, high current and high frequency IGBT modules, more stringent requirements are put forward for ceramic copper-covered substrates. As a kind of ceramic material with high thermal conductivity, low dielectric constant and good mechanical properties, aluminum nitride (AlN) is an ideal choice for preparing high performance ceramic copper-coated substrates. However, the surface properties of aluminum nitride substrate  make it difficult for copper and copper oxides to wet and spread on it, limiting its direct application to DBC (direct bonded copper) processes. Therefore, to explore the efficient preparation process of aluminum nitride ceramic copper clad plate and optimize its performance has become the focus of current research.

 

 

Challenges and solutions for the Aluminum nitride DBC preparation process: The surface properties of aluminum nitride make direct bonding with copper difficult. The wettability of copper and copper oxides on the surface of aluminum nitride can be significantly improved by forming a dense and uniform aluminum composite layer on the surface of aluminum nitride. The DBC process uses the eutectic bonding of copper and alumina, and realizes the firm bonding of ceramic and copper foil through chain furnace sintering.

 

Introduction and advantages of the AMB process: As an improvement of the DBC process, the AMB (Active metal brazing) process uses the active element in the filler metal (such as Ti) to react with the ceramic to generate a reaction layer (such as TiN) that can be wetted by the liquid filler metal, thus enhancing the binding force of the ceramic and copper foil. The AMB process requires vacuum sintering to prevent oxidation of the active metal, and although the process complexity increases, the binding force is stronger and the reliability is higher.

 

Comparison of DBC and AMB process: The DBC process uses one step copper etching, while the AMB process consists of one step copper etching and one step TiN etching, the latter process is more difficult. However, the binding force of AMB-AlN is superior to that of DBC-AlN, showing higher reliability and performance.

 

Performance optimization direction of aluminum nitride ceramic copper-covered plate: With the development of power semiconductor devices, the performance requirements of ceramic copper-covered substrate are constantly improving. Improving the strength of aluminum nitride ceramics and further optimizing the preparation process to achieve higher reliability , temperature resistance and current carrying capacity are important directions of subsequent research.

 

To sum up, the preparation process of aluminum nitride ceramic copper clad plate has experienced the evolution from DBC to AMB, through the introduction of active metal brazing and vacuum sintering technology, effectively solve the problem of aluminum nitride surface wettability, significantly improve the bonding force and overall reliability of ceramics and copper foil. However, with the continuous progress of power semiconductor device technology, the performance requirements of ceramic copper-covered substrates are also increasing. Therefore, future research should focus on further optimizing the preparation process and improving the strength of aluminum nitride ceramics to meet the packaging needs of high-performance power semiconductor devices such as high voltage, high current and high frequency IGBT modules, and promote the sustainable development of power electronics technology.