Si3N4 powder is the main raw material for the preparation of silicon nitride balls. Selecting the appropriate treatment method to obtain the powder with regular shape and uniform particle size distribution is the basis for the stable implementation of Si3N4 ceramic ball forming, sintering, processing and other processes.

According to the different atomization methods, the spray granulation methods of Si3N4 powder mainly include centrifugal spray granulation, pressure spray granulation and two-fluid spray granulation. Pressure spray granulation The slurry with uniform Si3N4 powder is sprayed into the granulation tower under high pressure for atomization, and the droplets are quickly dried into spherical powder by hot air flow, which can prevent the agglomeration and sedimentation of various components in the slurry. By controlling the volatilization rate of the solvent on the surface of the particles, the regular particle morphology can be obtained, and the spray granulation powder with uniform particle size distribution, good fluidity and suitable loose density can be packed. Thus, the performance of the powder filling mold is improved, and the density and uniformity of the blank are increased. Therefore, the pressure spray granulation method was selected to study the effect of the loose density of spray granulation powder on the properties of Si3N4 ceramic balls.

 

Test Material

Si3N4 powder (when the cumulative volume fraction in the particle size distribution is 50%, the corresponding particle size D50=1.5μm, α-Si3N4 content is 93%, the purity is 99.9%), Y2O3 powder (D50=1.8μm, the purity is 99.9%), Al2O3 powder (D50=2.2μm, the purity is 99.95%), etc.

 

Sample preparation

According to Si3N4∶Y2O3∶Al2O3= 92%∶4%∶4%(mass ratio), the mixture was added to the ball mill, anhydrous ethanol was used as the solvent, Si3N4 ball was used as the grinding medium for mixing and dispersing, mixing time was 24h, the mass ratio of Si3N4 ball and mixed powder was 3:1. After uniform mixing, the mass fraction of solid phase of the slurry is 55%, and the viscosity is 4000MPa·s. By controlling the inlet temperature of the spray drying tower and the diameter of the spray plate, the granulated powder with different loose density was obtained. The Si3N4 spray granulation powder was pressed into a ceramic pellet with a diameter of 8.731mm by a dry press, and then the atmosphere pressure sintering was carried out at 1850℃, the heating rate was 3℃ /min, the holding time was 1.5h, and the nitrogen pressure was 9MPa. The properties were tested after preparation.

 

Result

The screening fraction data and loose density of the granulated powder prepared by different spray granulation processes with the same batch slurry are shown in Table 1. The density of ceramic pellet blank, sintering density, bending strength, crushing load, fracture toughness and Vickers hardness of the ceramic pellet pressed by spray granulation powder with different loose density are shown in Table 2.

 

The mechanical properties of Si3N4 ceramic ball pressed by 5# granulated powder are the best. Too high or too low loose density will affect the pressing performance of the powder and the density of Si3N4 ceramic ball blanks, thus affecting the mechanical properties of Si3N4 ceramic balls. The mechanism is that the loose density directly affects the porosity of the spray granulation powder after pressing, and the gas is difficult to discharge, resulting in the long migration distance of particles and substances during the sintering process, which is not conducive to sintering densification.

The particle morphology of the 5# Si3N4 spray granulation powder is solid and spherical (Figure 1).

The microstructure of Si3N4 ceramic ball GPS by 1# ~ 9# spray granulation powder is shown in Figure 2. With the increase of loose density of granulation powder, the number of pores inside Si3N4 ceramic ball after GPS first increases and then decreases, and the density of Si3N4 ceramic ball first increases and then decreases.

SEM was used to observe the microstructure and grain fracture morphology of the crushed samples of Si3N4 ceramic balls with the best mechanical properties and poor mechanical properties. As shown in Figure 3, the density of Si3N4 ceramic balls first increased and then decreased with the increase of loose density of granulated powder. Too high or too low loose density would lead to uneven grain growth and internal pores.

 

Conclusion

With Si3N4 powder as raw material and Y2O3 and Al2O3 as sintering additives, the influence of loose density of spray granulation powder on densification and mechanical properties of ceramic ball sintering was analyzed. The following conclusions were drawn:

1) The density of Si3N4 ceramic ball blank increases first and then decreases with the increase of the bulk density of granulated powder. When the loose packing density is 0.89g /cm3, the Si3N4 ceramic ball has the highest densification degree and the best mechanical properties.

2) When the bulk density of spray granulation powder is 0.89g /cm3, the formed Si3N4 ceramic ball has the smallest pores, uniform grain size, and mainly adopts the mode of transgranular fracture.

With the continuous progress of microelectronics packaging technology, the power and integration of electronic components have significantly increased, which has led to a significant increase in the heat generation per unit volume, which has put forward more stringent requirements for the heat dissipation efficiency (that is, its heat conduction performance) of the new generation of circuit boards. At present, researchers are working to develop a variety of ceramic substrate materials with high thermal conductivity, including aluminum nitride (AlN), silicon carbide (SiC) and beryllium oxide (BeO). However, BeO is environmentally limited due to its toxicity; SiC is not suitable for use as substrate material because of its high dielectric constant properties. In contrast, AlN is the preferred substrate material choice due to its similar thermal expansion coefficient and moderate dielectric constant to silicon (Si) materials.

 

Traditionally, thick film slurps are mainly designed for alumina (Al2O3) substrates, but the composition of these slurps is prone to chemical reactions when in contact with AlN substrates, producing gases, which poses a serious threat to the stability and performance of thick film circuits. In addition, since the coefficient of thermal expansion of the AlN substrate is lower than that of the Al2O3 substrate, directly applying the slurry and sintering process suitable for the Al2O3 substrate to the AlN substrate will lead to the problem of thermal expansion mismatch, which will affect the performance of the circuit. Therefore, it is not advisable to simply copy the material system and production process of the Al2O3 substrate to the AlN substrate. This paper describes in detail the fabrication process of the resistance designed for AlN substrate, and studies and analyzes the performance of the resistance.

 

resistance temperature coefficient measurement

The resistance temperature coefficient (TCR) represents the relative change of the DC resistance value of the resistor at the test temperature to the DC resistance value at the reference temperature, that is, the relative change of the resistance value ΔTCR for every 1 ° C temperature between the test temperature and the reference temperature:

 

Where: R1 is the resistance value at the reference temperature; R2 is the resistance value at the test temperature. T1 is the reference temperature; T2 is the test temperature.

 

The thick film resistance on the AlN substrate was measured by TCR. The high temperature temperature coefficient (HTCR) test data were shown in Table 1, and the low temperature temperature coefficient (CTCR) test data were shown in Table 2. From the test data, it can be seen that the design size has a certain effect on the temperature coefficient of the resistance. All the resistance models have a positive temperature coefficient on this AlN substrate, and the TCR of FK9931M is less than 150×10-6/℃, and the remaining models are less than 100×10-6/℃.

 

resistance stability assessment

Resistance can be regarded as a three-dimensional network structure composed of many conductive chains. When the resistance layer is subjected to tension, the more fragile conductive chain will break or locally elongate, so that the overall conductive capacity will be reduced and the resistance value will be increased. Conversely, when the coefficient of thermal expansion of the resistance layer is obviously smaller than that of the substrate, the stress inside the resistance layer is pressure. When the resistance layer is subjected to pressure, the contact between the particles will be tighter, and even a new conductive chain will be added, thus enhancing the conductive ability of the entire thick film resistor, and the resistance value will be reduced on the macro level. Because the thick film resistor is firmly bound to the substrate and the stress release is slow, the resistance value will change when the thick film resistor is stored at a certain temperature. The greater the difference between the thermal expansion coefficient of the thick film resistance and the substrate, the greater the stress inside the thick film resistance, and the greater the change rate of the thick film resistance when stored at high temperature.

 

According to different design sizes, four kinds of square resistance resistors were printed on the AlN substrate, and the resistors were adjusted by laser. After temperature storage at 150℃ and 1000h, the change of resistance values before and after temperature storage was compared. The resistance of each square resistance measures the resistance value of five resistors. As can be seen from Table 4 to Table 6, the resistance value change rate is less than 1.5% after being stored at high temperature.

 

In summary, with the rapid development of microelectronics packaging technology, the power and integration of electronic components have achieved a qualitative leap, but also put forward unprecedented challenges to the heat dissipation efficiency of the circuit board. Researchers have actively responded to this challenge by exploring and developing a series of ceramic substrate materials with high thermal conductivity, among which aluminum nitride (AlN) stands out among many candidate materials with its superior thermal expansion matching and moderate dielectric constant, and has become the focus of current research.

 

In this paper, the limitations of the traditional thick film slurry in the application of AlN substrate are analyzed in depth, and the resistance manufacturing process designed for the characteristics of AlN substrate is described in detail. The experimental results show that the thick film resistance on AlN substrate has stable performance, its temperature coefficient is within the acceptable range, and the resistance change rate is very small after high temperature storage, which verifies the feasibility and effectiveness of the production process.

 

In the future, with the further research and optimization of the AlN substrate and its supporting production process, we have reason to believe that the AlN substrate will play a more important role in the packaging of high-power density electronic components, and promote the development of the microelectronics industry to higher performance and higher integration.

Although the processing of silicon carbide substrate is difficult, in order to make the application of single crystal silicon carbide in electronic components become the future direction of development, so that silicon carbide devices are large-scale application and promotion, it is necessary to find a way to solve the problem of difficult silicon carbide processing.

 

 

At present, the SiC material processing technology mainly has the following processes: directional cutting, chip rough grinding, fine grinding, mechanical polishing and chemical mechanical polishing (fine polishing). Among them, chemical-mechanical polishing is the final process, and its process method selection, process route arrangement and process parameter optimization directly affect the polishing efficiency and processing cost.

 

However, due to the high hardness and chemical stability of SiC materials, the material removal rate in the traditional CMP polishing process is low. Therefore, the industry began to study the auxiliary efficiency technology supporting the flattening ultra-precision machining technology, including plasma assisted, catalyst assisted, ultraviolet assisted and electric field assisted, as follows:

 

01 Plasma assisted technology

YAMAMURA Kazuy et al. first proposed the plasma-assisted polishing (PAP) process, which is an auxiliary chemical-mechanical polishing that oxidizes surface materials to a softer oxide layer through plasma, while still removing materials by abrasive friction and wear.

 

The basic principle is: through the RF generator reaction gas (such as water vapor, O, etc.) to produce a plasma containing free groups (such as OH free groups, O free radicals), with strong oxidation capacity of free groups on the surface of the SiC material oxidation modification. A soft oxide layer is obtained, and then the oxide layer is removed by polishing with soft abrasives (such as CeO2, Al2O3, etc.), so that the surface of SiC material reaches the atomic level smooth surface. However, due to the high price of PAP process test equipment and processing costs, the promotion of PAP process processing SiC chips is also limited.

 

02 Catalyst assisted process

In the industrial field, in order to explore the high-efficiency ultra-precision machining technology of SiC crystal materials, researchers use reagents for catalytic assisted chemical-mechanical polishing. The basic mechanism of material removal is that the soft oxide layer is formed on the SiC surface under the catalysis of reagents, and the oxide layer is removed by the mechanical removal of abrasive. For a high quality surface. In the literature, Fe3O4 catalyst and H2O2 oxidizer were used to assist the enhancement of chemical mechanical polishing technology with diamond W0.5 as abrasive. After optimization, the surface roughness Ra=2.0 ~ 2.5 nm was obtained at the polishing rate of 12.0 mg/h.

 

03 UV-assisted technology

In order to improve the SiC surface flattening processing technology. Some researchers have used ultraviolet radiation to assist catalysis in chemical-mechanical polishing process. Uv photocatalytic reaction is one of the strong oxidation reactions. Its basic principle is to produce active free radicals (·OH) by photocatalytic reaction between photocatalyst and electron catcher under the action of UV light.

 

Due to the strong oxidation of OH free groups. The oxidation reaction occurs on the SiC surface layer to generate a softer SiO2 oxide layer (MOE hardness is 7), and the softened SiO2 oxide layer is easier to be removed by abrasive polishing; On the other hand, the bonding strength between the oxide layer and the surface of the wafer is lower than the internal bonding strength of the SiC wafer, which reduces the cutting force of the abrasive in the polishing process, reduces the scratch depth left on the surface of the wafer, and improves the surface processing quality.

 

04 Electric field assisted technology

In order to improve the removal rate of SiC materials, some researchers have proposed electrochemical mechanical polishing (ECMP) technology. The basic principle is: by applying direct current electric field to the polishing liquid in the traditional chemical mechanical polishing treatment, the oxidation layer is formed on the SiC polishing surface under electrochemical oxidation, and the hardness of the oxide layer is significantly reduced. Abrasive is used to remove the softened oxide layer to achieve efficient ultra-precision machining. However, it should be noted that if the anode current is weak, the machining surface quality is better, but the material removal rate does not change much; If the anode current is strong, the material removal rate is significantly increased. However, too strong anode current will lead to lower surface accuracy and porosity.

 

In short, chemical-mechanical polishing is still the most potential flattening ultra-precision machining method for SiC materials, but in order to obtain high-quality SiC wafers more efficiently, the above mentioned auxiliary processes are potential options. However, due to the lack of relevant studies, the impact on SiC materials is still lack of predictability. Therefore, if we can deeply study the influence of related auxiliary processes on chemical-mechanical polishing technology, and further reveal the processing mechanism of chemical-mechanical polishing auxiliary efficiency enhancement technology by quantitative and qualitative research means, it will be of great significance for realizing the industrialization application and promotion of SiC materials.

With the rapid development of modern microwave communication technology, the design of microwave circuit components with high performance and high precision has become increasingly important. In microwave radio frequency (RF) modules, thin-film circuit technology has become a key design method with its unique advantages. In this paper, several thin film circuit components based on alumina substrate are introduced in detail, including thin film microstrip circuit, thin film filter, thin film load, thin film equalizer and thin film power divider. These components play an irreplaceable role in microwave circuits, and their design accuracy and performance directly affect the performance of the whole microwave system.

 

 

Applications of alumina substrate in circuit

 

1 Thin film microstrip circuit

Aluminum oxide ceramic substrate is used to design thin film microstrip circuit, the thickness of the gold layer can be up to 3.5um, and the metal wire bonding can be used to connect with the external circuit. The common plate thickness is 0.127mm, 0.254mm, 0.381mm, 0.508mm, and the transmission frequency can reach more than 40GHz. It meets the frequency band requirements of most microwave RF module modules, and the thin film circuit line accuracy of the thin film process is ±5um. The microwave RF field often uses ceramic substrates for microstrip transmission lines or circuit design with high precision.

 

2 Thin film filter

The frequency of the thin film filter made of alumina ceramic substrate can be as high as 40GHz, which is often used as a functional unit of frequency selection in various microwave module modules and systems. Thin film filter is processed by thin film technology, through sputtering, lithography, wet or dry etching, cleaning, slicing to obtain thin film filter substrate, common interfinger type, hairpin type, comb type, parallel coupling type, C-type and other structural filters can be designed based on alumina ceramic substrate processing, can be designed low pass high pass band pass band resistance and other different types of filters. Because the dielectric constant of the alumina ceramic sheet is greater than that of the general PCB substrate, the volume of the film filter made by the alumina ceramic sheet is smaller than that of the general microstrip filter, and the electrical parameters of the film filter made by the alumina ceramic sheet are good. It is usually fixed with conductive adhesive or gold tin eutectic.

 

3 Film load

The aluminum oxide ceramic substrate is used to design the thin film load, which is often used to match the terminal of the module assembly of the microwave circuit to absorb the excess reflected power. For the load, the machining accuracy of the resistance value is very important, and the greater the deviation, the worse the final load performance. Due to the controllable square resistance of the tantalum nitride film layer in the film process, the film load with high precision can be produced, and the film load volume is very small, which is a good choice for the miniaturization of component modules. It is usually fixed to the end of the circuit using conductive adhesive or gold tin eutectic.

 

4 Film equalizer

The thin-film equalizer is designed with alumina ceramic substrate, which is often used to adjust the broadband power flatness of microwave circuits. The output waveform of the device is adjusted by changing the square resistance of the integrated tantalum nitride film layer and the different resistance values of the graphic design, so as to balance the power signal at the front end to achieve the power flatness adjustment effect.

 

5 Film power divider

The thin-film power divider designed with alumina ceramic substrate is often used in the multi-channel communication network system. It has the function of power distribution according to a certain proportion, with one input and multiple output. Since the isolation resistor can be integrated into the thin film circuit using the tantalum nitride film layer to design a suitable resistance value, this can avoid the deterioration of the circuit performance due to the welding of the patch resistance of the microstrip power divider and the instability of the resistance value of the patch resistor, and the thin film power divider is easier to achieve the multi-stage ultra-wideband design, and the designed object is small in size, easy to integrate and good in performance.

 

In summary, alumina ceramic substrate plays a crucial role in the design of thin-film circuit components. From thin film microstrip circuit to thin film power distributor, these components not only meet the requirements of high precision and high frequency of microwave RF modules, but also realize the miniaturization and high performance of the components. Through the precise control of thin film technology, we can obtain thin film circuit components with excellent electrical parameters, which further improves the overall performance of microwave systems. In the future, with the continuous progress of microwave communication technology, thin film circuit components based on alumina ceramic substrates will continue to play a greater role in the microwave field, contributing to the development of wireless communication, radar detection and other fields.

In exploring silicon nitride (Si3N4) substrate materials as core to a high-performance thermal management solution, our understanding of their heat transfer mechanisms is critical. The main heat transfer mechanism of silicon nitride is known to rely on lattice vibration, a process that transfers heat through quantized hot charge carriers called phonons.

 

The propagation of phonons in the lattice is not a simple linear motion, but is affected by the complex coupling between the lattice, resulting in frequent collisions between phonons, which significantly reduces the mean free path of phonons, that is, the mean distance that phonons can travel freely between two collisions. This mechanism directly affects the thermal conductivity of silicon nitride materials.

 

Furthermore, various defects, impurities and grain interfaces in Si3N4 crystals become the main sources of phonon scattering. These scattering events also lead to a decrease in the mean free path of phonons, which in turn reduces the overall thermal conductivity of the material. In particular, lattice oxygen, as one of the main defects affecting the thermal conductivity of silicon nitride ceramics, significantly hinders the smooth propagation of phonons and reduces the thermal conductivity efficiency of the material.

 

To overcome this challenge and improve the thermal conductivity of the silicon nitride substrate, we started at the source and focused on reducing the oxygen content in the lattice. Specific strategies include:

 

 

Optimize raw material powder

Choosing Si powder with low oxygen content as starting material is the key. The oxygen impurity content in the initial raw material is reduced through a rigorous raw material screening and pretreatment process. Subsequently, a two-step nitrided sintering process is used, in which Si powder is first heated in a nitrogen atmosphere to close to its melting point (1414℃), so that it reacts with nitrogen to form porous Si3N4 sintered body. This process ensures adequate nitriding of Si while controlling the oxygen content in the newly generated silicon nitride. Then, porous Si3N4 was further sintered at high temperature to promote grain growth and pore closure, and finally the Si3N4 ceramic substrate with high density, low oxygen content and high thermal conductivity was formed.

 

 

Direct sintering of high purity α-Si3N4 powder

Another way is to use high purity α-Si3N4 powder with very low oxygen content for sintering. This method avoids the conversion process from Si to Si3N4 and directly uses α-Si3N4 powders with high purity and specific crystal structure for sintering, reducing the possibility of oxygen impurity introduction. By precisely controlling sintering parameters such as temperature, atmosphere and pressure, silicon nitride substrates with high density, few defects and excellent thermal conductivity can be obtained.

 

 

Sintering application of β-Si3N4

Although β-Si3N4 may differ from α-Si3N4 in some physical properties, its low oxygen content and high purity are also suitable for the preparation of high-performance silicon nitride substrates. The use of β-Si3N4 powder for sintering can also prepare high thermal conductivity silicon nitride materials, especially in specific application scenarios, some characteristics of β-Si3N4 may be more advantageous.

 

In summary, the Silicon nitride (Si3N4) substrate material is a key component of a high-performance thermal management solution, and the optimization of its thermal conductivity is crucial to improve the overall thermal management efficiency. By deeply understanding the heat transfer mechanism of silicon nitride, namely lattice vibration and phonon conduction process, we realize that phonon scattering is one of the key factors affecting the thermal conductivity. In particular, oxygen defects in the lattice, acting as the main scattering source, significantly reduce the mean free path of phonons, thereby hindering the effective conduction of heat.

To overcome this challenge, we propose a variety of strategies to reduce the oxygen content in the silicon nitride substrate, thereby improving its thermal conductivity. From the optimal selection of raw material powder, to the direct sintering of high-purity α-Si3N4 powder, to the sintering application of β-Si3N4, each method aims to reduce the introduction of oxygen impurities at the source and achieve high density and low defect status of the material through fine process control.

Future research will further focus on exploring more efficient silicon nitride preparation processes and further understanding the mechanism by which different crystal structures and microstructure affect the thermal conductivity of silicon nitride. Through these efforts, we are expected to develop silicon nitride substrate materials with higher thermal conductivity and lower thermal resistance, providing strong support for high-performance thermal management in electronic packaging, aerospace, energy conversion and other fields.

In practical applications, in addition to high thermal conductivity and high electrical insulation properties, aluminum nitride substrates are also required to have high bending strength in many fields. At present, the three-point bending strength of aluminum nitride in circulation on the market is usually 400~500MPa, which seriously limits the promotion and application of aluminum nitride ceramic substrates, especially in the field of IGBT power devices with high reliability requirements. Due to the complex production process and high production cost of AlN materials, most of the domestic AlN materials are still unable to meet the application requirements of high thermal conductivity and high strength.

 

In the preparation of aluminum nitride ceramic substrate, the selection of sintering methods and sintering additives is often twice the result with half the effort, and the introduction of sintering additives is a common method for sintering aluminum nitride ceramics at present. On the one hand, the formation of low temperature eutectic phase, the realization of liquid phase sintering, promote the compact body; On the other hand, the oxygen impurity in aluminum nitride is removed, the lattice is improved, and the thermal conductivity is increased. At present, the sintering additives used in sintering AlN ceramics mainly include Y2O3, CaO, Yb2O3, Sm2O3, Li2O3, B2O3, CaF2, YF3, CaC2, etc., or their mixtures.

  

In the sintered aluminum nitride ceramic formula system, when Y2O3 is higher than 3.5wt%, the content of Y-Al-O increases significantly and aggregates in the sintering process. Due to the low thermal conductivity of Y3Al5O12 (about 9 W/ (m·K)), the thermal conductivity of aluminum nitride ceramic products after sintering is seriously affected. When the content of CaF2 and Li2O is higher than 1.33wt%, due to the volatilization of fluoride and Li-containing compounds, the porosity of the sintered aluminum nitride ceramic body is increased during the sintering process, and the density of the ceramic is reduced, resulting in a sharp decline in the bending strength of aluminum nitride ceramic products after sintering. When each additive is less than the minimum value, the effect of enhancing mechanical properties cannot be played or the effect is very small.

 

In summary, aluminum nitride ceramic substrate in practical applications face the comprehensive requirements of high thermal conductivity, high electrical insulation properties and high bending strength, but the flexural strength of the products in circulation on the market is generally low, limiting its wide application in the field of high reliability such as IGBT power devices. At the same time, the domestic AlN material is difficult to meet the application needs of high thermal conductivity and high strength due to the complex production process and high production cost. Therefore, in the preparation of aluminum nitride ceramic substrate, it is very important to select the appropriate sintering method and sintering additives, not only to form a low temperature eutectic phase to promote the compact body, but also to remove oxygen impurities to improve the thermal conductivity. However, the selection and dosage of sintering additives need to be strictly controlled to avoid negative effects on thermal conductivity and bending strength. In the future, in order to improve the performance of aluminum nitride ceramic substrates, it is still necessary to further optimize the sintering process and formulation system to meet the needs of higher levels of application.

In the field of high-tech materials, aluminum nitride (AlN) ceramics, with its excellent thermal conductivity, excellent electrical insulation properties and excellent mechanical strength, have become the core material in key fields such as electronic packaging, power electronics and microwave communication equipment. However, the preparation of aluminum nitride substrate is a complex process, in which the sintering process and the selection of sintering additives have important effects on the properties of the final product. In this paper, starting from the preparation process of aln ceramic substrate, the selection of sintering additives and their influence on the performance of the substrate will be discussed in detail, and combined with frontier research, how to improve the comprehensive performance of aluminum nitride substrate by optimizing the sintering additives and sintering process will be analyzed.

 

Preparation Technology of Aluminum Nitride Substrate

The preparation of aluminum nitride substrate mainly includes raw material preparation, mixing, molding, sintering and other key steps.

 

1. Raw material preparation

Raw material preparation is the first step in the preparation of aluminum nitride ceramic substrate, which mainly includes the selection and ratio of aluminum nitride powder, alumina powder and additives. As the main material, aluminum nitride powder is required to have the characteristics of high purity, small particle size, large specific surface area, low carbon content and low oxygen content. Alumina powder is usually used as part of the sintering aid to form a low melting point composite oxide during the sintering process to promote the densification of aluminum nitride ceramics. Additives are used to regulate the molding properties, sintering properties and mechanical properties of the material.

 

2. Mix and form

In the mixing process, it is necessary to mix aluminum nitride powder, alumina powder and additives according to a certain ratio to ensure the uniformity and stability of subsequent molding. Mixing can be done by dry or wet method. Molding is usually by pressing molding, injection molding or die molding, etc., the mixed raw materials are made into billets with a certain shape and size.

 

3. Sintering

Sintering is the last process and the most critical step in the preparation of aluminum nitride ceramic substrate. Under the condition of high temperature, the particles in the billet are combined by sintering to form a dense ceramic substrate. In the sintering process, temperature, atmosphere and time need to be controlled to ensure the forming quality and performance of the ceramic substrate. The commonly used sintering processes include hot pressing sintering, non-pressing sintering, microwave sintering, discharge plasma sintering and self-propagating sintering.

 

The Selection of Sintering Additives and Its Influence on The Properties of Substrate

Sintering additives play an important role in the preparation of aluminum nitride ceramic substrates. They react with the alumina composition on the surface of the aluminum nitride particle to form a composite oxide with a low melting point, resulting in a liquid phase in the sintered body. These liquid phases surround the aluminum nitride particles, and the particle rearrangement and internal pore discharge occur under the action of capillary force, and finally the compact sintering of aluminum nitride ceramics is realized.

 

1. Commonly used sintering additives

The commonly used sintering auxiliaries for aluminum nitride ceramic substrates include CaO, Li2O, B2O3, Y2O3, CaF2, CaC2 and CeO2. These materials play a dual role in the sintering process: first, they combine with aluminum oxide on the surface of aluminum nitride particles to form liquid aluminate, accelerating mass transfer and promoting sintering; Secondly, they can react with oxygen to reduce the lattice oxygen content and increase the thermal conductivity of aluminum nitride ceramics.

 

2. Principle of selection of sintering additives

When selecting sintering additives, it is necessary to consider their influence on the properties of aluminum nitride ceramic substrate. On the one hand, the sintering additives should promote the densification of aluminum nitride ceramics, improve the thermal conductivity and mechanical strength; On the other hand, sintering additives should avoid the introduction of excessive impurities, so as not to affect the electrical insulation properties and chemical stability of aluminum nitride ceramics. Therefore, when selecting sintering additives, a lot of experiments and optimization are needed to determine the best sintering additives formula.

 

3. Influence of sintering additives on substrate performance

The selection and content of sintering additives have significant influence on the performance of aluminum nitride ceramic substrate. For example, Y2O3, as one of the commonly used sintering additives, can significantly improve the thermal conductivity and bending strength of aluminum nitride ceramics when the content is moderate. However, when the content of Y2O3 is too high, Y-Al-O phase will be formed, resulting in a significant decrease in thermal conductivity. Therefore, when preparing aluminum nitride ceramic substrate, it is necessary to precisely control the content of sintering additives to obtain the best performance.

 

Improved Performance of AlN Substrate

In order to meet the high requirements for the performance of aluminum nitride ceramic substrates in different application fields, researchers are constantly exploring new sintering additives, optimizing sintering processes and developing new preparation technologies.

 

1. Development of new sintering additives

In order to further improve the performance of aluminum nitride ceramic substrates, researchers are actively developing new sintering additives. For example, by introducing rare earth elements or transition metal elements, the lattice structure of aluminum nitride ceramics can be optimized to improve thermal conductivity and mechanical properties. In addition, a variety of properties can be achieved through the use of composite sintering additives.

 

2. Optimization of sintering process

The optimization of sintering process is the key to improve the performance of aluminum nitride ceramic substrate. By adjusting sintering temperature, holding time and atmosphere, the microstructure of aluminum nitride ceramics can be accurately controlled. For example, rapid sintering methods such as microwave sintering or discharge plasma sintering can significantly shorten the sintering time and improve the production efficiency. At the same time, the microstructure and properties of Al nitride ceramics can be further optimized by precisely controlling the oxygen content and temperature gradient in the sintering atmosphere.

 

3. Innovation of preparation technology

With the continuous development of preparation technology, researchers are constantly exploring new preparation methods to improve the performance of aluminum nitride ceramic substrates. For example, the precise preparation of aluminum nitride ceramic substrate can be achieved by using advanced molding technologies such as casting molding and injection molding. In addition, the welding performance, stability and corrosion resistance of aluminum nitride ceramic substrate can be further improved by electroless copper plating, ceramic substrate encapsulation and other post-treatment processes.

 

Conclusion

In summary, the preparation of aluminum nitride ceramic substrate and the selection of sintering additives have important effects on its properties. The comprehensive properties of aluminum nitride ceramic substrate can be significantly improved by optimizing the sintering auxiliary formula, improving the sintering process and developing new preparation technology. In the future, with the continuous development of material science and preparation technology, the application field of aluminum nitride ceramic substrate will be further expanded, providing strong support for the development of electronic packaging, power electronic devices and microwave communication equipment. At the same time, we also need to pay close attention to the development trend of new technologies and new materials, constantly expand the research horizon, and promote the continuous progress and innovation of aluminum nitride ceramic substrate technology.

In the field of semiconductor materials, silicon carbide (SiC) with its excellent thermal conductivity, wide band gap characteristics, high breakdown electric field strength and high electron mobility, is gradually becoming a research and development hotspot, leading the innovation of a new generation of electronic devices. As a substrate material for key components, the broad application prospects of silicon carbide are self-evident, from high-efficiency power electronics to high-frequency communication chips, its figure is everywhere. However, the extremely high hardness of silicon carbide materials (Mohs hardness of about 9.5) is like a double-edged sword, both giving it excellent physical properties, but also set up numerous obstacles for its processing.

 

 

Faced with the difficult problem of polishing and grinding silicon carbide substrate, traditional processing methods are often inadequate, inefficient and costly. It is in this context that the metal friction induced reaction grinding technology came into being, and opened up a new path for the efficient processing of silicon carbide. This technology cleverly uses the chemical reaction produced by metal and silicon carbide friction at high temperature, through the continuous formation and removal of the reaction metamorphic layer, to achieve high speed and low damage removal of silicon carbide materials. This innovation not only overcomes the processing problems caused by the high hardness of silicon carbide, but also significantly improves the processing efficiency and surface quality.

 

It is worth noting that the metal friction-induced reaction grinding technology needs to be applied under precisely controlled conditions to avoid the decomposition of silicon carbide at high temperatures and the formation of unstable compounds with the metal, thus exacerbating tool wear. The experimental data show that the selection of suitable metals (such as iron, pure nickel) as friction media can achieve differentiated and efficient removal of different surfaces of silicon carbide substrate (carbon and silicon). Due to its structural stability, the surface quality of carbon surface is almost free of damage. Although there are crystal defects in the silicon surface, the material removal rate can reach 534µm/h under the friction of pure nickel, showing the great potential of this technology under certain conditions.

 

Looking forward to the future, metal friction induced reaction grinding technology is expected to achieve a wider application in the field of silicon carbide substrate processing. With the deepening of the research and the maturity of the technology, the technology is expected to expand to the processing of large-size silicon carbide wafers, and further improve the manufacturing efficiency and yield of silicon carbide devices. At the same time, combined with other advanced processing technologies, such as ultra-precision polishing and laser-assisted processing, it is expected to achieve comprehensive optimization of silicon carbide material processing and promote the silicon carbide semiconductor industry to a new height.

 

In short, silicon carbide substrate processing challenges and opportunities coexist, and the emergence of metal friction induced reaction grinding technology provides an innovative solution to this problem. With the continuous progress of technology and the continuous expansion of application fields, silicon carbide semiconductor materials will certainly play a more important role in the future development of electronic science and technology.

Silicon nitride (Si3N4) balls show great potential in the field of high-speed, high-precision, long-life bearings due to their excellent properties, such as lightweight, self-lubricating, high insulation, non-magnetic, high elastic modulus and excellent corrosion resistance. This paper aims to discuss the optimization of the spray granulation process of Si3N4 powder, especially the pressure spray granulation method, in order to improve the density, mechanical properties and microstructure of Si3N4 balls, so as to meet the urgent demand for high-performance bearing materials in aerospace, automotive and wind power generation fields.

 

With the rapid development of industrial technology, the requirements for material properties are increasingly stringent. As a new type of high performance bearing material, Si3N4 ceramic ball has become a research hotspot to further improve its performance. Among them, the blank density, as a key factor affecting the final performance of ceramic balls, is directly related to the number of micro-pores and fatigue life of ceramic balls after sintering. Therefore, optimizing the spray granulation process of Si3N4 powder to achieve regular powder morphology, uniform particle size distribution and increased bulk density is an effective way to improve the performance of ceramic balls.

 

Performance Advantages and Application Fields of Si3N4 Balls

With its unique physical and chemical properties, Si3N4 ceramic balls show significant advantages in many fields: low mass reduces the overall load of the bearing system and improves the operating efficiency; Self-lubricating features reduce lubrication requirements and reduce maintenance costs; High insulation and non-magnetic suitable for special environments; High elastic modulus and corrosion resistance ensure long-term stable operation under extreme conditions. These advantages make Si3N4 ceramic balls widely used in high-speed, high-precision and long-life bearing systems such as machine tool spindles, electric spindles, automotive engines, aerospace engines and wind turbines.

 

Effect of Spray Granulation Process on Properties of Si3N4 Ball

 

The Importance of Blank Density

The density of blank is a key parameter in the preparation of ceramic ball, which directly affects the density and properties of ceramic ball after sintering. Increasing the density of the blank is helpful to reduce the formation of pores in the sintering process, so as to improve the mechanical properties and fatigue life of ceramic balls.

 

The Relationship Between the Morphology of Spray-pelleted Powder and the Bulk Density

Spray granulation is one of the important processes for preparing high quality ceramic powders. Through pressure spray granulation, Si3N4 slurry is sprayed into the granulation tower under high pressure, and the droplets are quickly dried into spherical powder in the hot air flow. In this process, controlling the evaporation rate of the solvent on the particle surface is the key to obtain the powder with regular morphology and uniform particle size distribution. The regular spherical powder is beneficial to increase the loose density of the powder, and then improve the density and uniformity of the blank.

 

Optimization Strategy

1. Optimize the slurry formula: adjust the proportion of each component in the slurry and the use of dispersant to reduce agglomeration and settling stratification and improve the uniformity and stability of the slurry.

 

2. Precise control of spray parameters, such as spray pressure, nozzle design, hot air flow temperature, etc., to optimize the particle size distribution and drying rate of droplets, to ensure the regularity of powder morphology and the improvement of loose density.

Post-treatment optimization: The powder after spray granulation is screened and graded, and unqualified particles are removed to further improve the overall quality of the powder.

 

3. Experiment and result analysis

Through a series of experiments, we found that the raw density of Si3N4 ceramic balls prepared by optimized pressure spray granulation technology was significantly increased, and the sintered ceramic balls showed lower microporosity, higher hardness and better fatigue resistance. The microstructure analysis shows that the grain structure of the ceramic ball is more dense and the interface bonding strength is enhanced.

 

 

Conclusion and Prospect

In this paper, through the optimization of Si3N4 spray granulation process, especially the in-depth study of pressure spray granulation method, the density, mechanical properties and microstructure of Si3N4 ceramic balls have been successfully improved, which provides theoretical basis and technical support for the preparation of high-performance ceramic balls. In the future, with the continuous progress of material science and preparation technology, Si3N4 ceramic balls will show their unique advantages in more high-end fields and promote the sustainable development of related industries. At the same time, further exploration of new spray granulation technology and process parameter optimization will be an important direction to improve the performance of ceramic balls. Optimizing the Si3N4 spray granulation process to improve the performance of ceramic balls: Performance advantages, application areas and process exploration

 

With the rapid development of high-tech industry, the requirements for fineness, purity and consistency of powder materials are increasing. As a key component in the powder preparation process, the performance of grinding medium directly determines the quality of the final product. Traditionally, zirconia ceramic balls are widely used in the field of ultra-fine grinding because of their high bending strength, wear resistance and certain high toughness. However, its timeliness failure and performance instability at high temperatures limit its application in high-end powder manufacturing. This paper aims to explore the unique advantages of silicon nitride balls as a new generation of grinding media, and explain how they can replace zirconia balls and significantly improve the quality of high-tech powder products.

 

Powder industry as an important branch of materials science, the performance of its products is directly related to the development of semiconductor, biomedicine, aerospace and other high-tech fields. As the core tool of powder preparation, the selection of grinding medium directly affects the grinding efficiency, particle size distribution and impurity content. Silicon nitride (Si₃N₄) ceramics, a high performance engineering ceramic material, have shown great potential in materials science and engineering in recent years, especially as an alternative to traditional grinding media.

 

Performance Advantages of Silicon Nitride Balls

Excellent high-temperature stability

Silicon nitride ceramics have extremely high thermal stability and thermal conductivity, and can maintain structural stability and physical properties at high temperatures, and will not lose metastable phase at high temperatures like zirconia, resulting in performance degradation. This feature enables the silicon nitride ceramic ball to work stably in the high temperature grinding process, meeting the needs of high-tech powder materials for high temperature treatment.

Excellent wear resistance and durability

Silicon nitride ceramics have extremely high hardness and good wear resistance, far exceeding zirconia ceramics. In the long, high-intensity grinding process, the silicon nitride ceramic ball can effectively resist wear and maintain the geometry and dimensional accuracy of the ball, thus ensuring the grinding efficiency and the uniformity of the product particle size.

Excellent chemical stability

Silicon nitride ceramics show good chemical inertia to most acids, bases and organic solvents, which means that it is not easy to chemically react with the material during the grinding process, thus avoiding the introduction of impurities and product pollution, which is particularly important for the preparation of high-purity powders.

No timeliness problem

Compared with zirconia ceramic balls, silicon nitride ceramic balls do not have the performance degradation problem caused by long placement time. Its stable physical and chemical properties ensure the long-term stability and reliability of the grinding medium, which provides the possibility for large-scale and long-term continuous production.

 

Application Prospect of Si3N4 Ball in the Preparation of High-tech Powder Products

Based on the above performance advantages, silicon nitride ceramic ball as a grinding medium in the preparation of high-tech powder products shows broad application prospects. Especially in the fields of semiconductor materials, precision ceramic powders, high-performance metal powders and biomedical materials, silicon nitride ceramic balls can effectively improve the purity, particle size distribution uniformity and processing efficiency of the powder, so as to meet the strict requirements of the high-end market for product quality.

 

 

Conclusion

In summary, silicon nitride ceramic balls with its excellent high temperature stability, wear resistance, chemical stability and timeless advantages, successfully make up for the shortcomings of zirconia ceramic beads in the application of grinding media, become an important choice to improve the quality of high-tech powder products. With the continuous progress of material science and the continuous optimization of manufacturing processes, silicon nitride ceramic balls are expected to replace traditional grinding media in a wider range of fields, and promote the development of the powder industry to a higher level. In the future, further optimized design and cost control for silicon nitride ceramic balls will be the key to promote their wide application.