AlN has outstanding advantages such as high thermal conductivity, good insulation, low dielectric loss, stable chemical properties, proximity to the thermal expansion coefficient of Si and other conventional substrate materials AkO3, and is an ideal heat dissipation for large-scale integrated circuits and semiconductor module circuits. Materials and packaging materials. However, AlN ceramics have high hardness and brittleness, and even if carbide cutting tools are used, it is difficult to achieve precision machining. However, the injection molding method is used to produce complex shapes of AlN ceramic parts, which can form complex shape products on the basis of low cost and low consumption. High dimensional accuracy, no or only a small amount of mechanical processing, easy to implement the characteristics of mechanical automation, and become the receiving date in precision ceramic forming technology: 2001 - Fund Project: National "863" Program (715 - a new star. Usually pure AlN The ceramics are difficult to sinter and dense, and it is necessary to add a certain amount of sintering aids in AlN. This is mainly due to Y23, CaO, Si2. When sintering at about 1600°C, Y2O3 reacts with AlN on the surface of AlN to form AI2Y4O9, AI5Y3O12, A1YO3. Studies have shown that the oxygen content and microstructure defects are the main influencing factors in the thermal conductivity of AlN ceramics.When oxygen enters the AlN lattice in the form of oxygen ions, structural defects such as aluminum vacancies will be formed. Decreasing the mean free path of the phonons leads to a decrease in thermal conductivity, and it is therefore necessary to prevent the diffusion of oxygen ions into the AlN lattice. In general, the main measures to prevent oxygen ions from entering the AlN grains include: use of low-oxygen AlN powder, control of the amount of Y2O3 added and proper sintering temperature, and injection molding methods to prepare A1N ceramics in the country. Related reports, the effect of sintering additives on the type, distribution and material properties of the second phase in AlN under injection molding conditions remains to be further studied. This work adopts injection molding process to prepare AlN ceramic precision heat conduction ring, and study the influence of different content of Y2O3 sintering aids on the microstructure and properties of A1N ceramics. 1 Experimental experiment AlN powder was prepared by high temperature self-propagating method. The main properties of the powder are shown in Table 1. The sintering aid is Y2O3, and its purity is more than 99.9%. The mass fraction of Y2O3 is between 1% and 7% (hereinafter referred to as xY-A1N, where x is the mass fraction of Y2O3). The wax-based thermoplastic system is selected with adhesives. The main components include paraffin wax (PW), ethylene vinyl acetate (EVA), high density polyethylene (HDPE) and stearic acid (SA). See Table 1 AlN powder properties Table 2 Properties of the binder components Table ~ 7% of Y2O3 with anhydrous ethanol as a medium, placed in a plastic ball mill tube, ball milled with AI2O3 ball 3h, and then dried and sieved to obtain AIN +Y2O3 composite powder. The powder and the designed binder system were mixed in a XSS-300 mixer for 2 h at 60.8% (volume fraction) loading and the feed was extruded. After granulation, an A1N heat-conductive ring sample was injected on an S-28 injection machine. The degreasing of the ingot is performed in a silicon key degreasing furnace, and the flowing N2 is used as a protective atmosphere. The specific degreasing process can be seen. After the degreasing is completed, the debindered blank is placed in a carbon tube furnace and is sintered at a high temperature under a flowing N2 atmosphere to form a product. The density of the sample was measured by a drainage method. The phase analysis was performed on a Japanese Type 3014-Z2 X-ray automatic diffractometer. The microstructure was observed on a scanning electron microscope and the grain boundaries and crystal grains were subjected to energy spectrum analysis using heat. The pulse method was used to measure the thermal conductivity of A1N using an R-2 laser thermal conductivity meter. 2 Results and discussion 2.1 The relationship between the thermal conductivity and the sintering temperature and the amount of Y2O3 added in the injection-molded AlN ceramics is very obvious between 1 850°C. In the 5Y-A1N grain growth is not yet complete, the base body covered with holes (see a) When the sintering temperature reaches 1 800 °C, 5Y-AlN grains have grown, the grain is about 6 ~ 7 Mm The grain boundary is also gradually clear, but the sintered body is not yet dense, and there are still a small number of holes in the matrix (see b) to 1 pair of density has reached 99.5% (theoretical density takes 3.3g/cm3) thermal conductivity is 167.5WWmD The matrix is ​​dense, without defects, and the grains are about 8 to 9 m (see c). As the sintering temperature continues to increase to 1870, the relative density and thermal conductivity of 5Y-A1N are almost unchanged. It can be seen that under the conditions of this study, when AlY2°k and the number of rS bowls are 3%, the content of 2.2Y2O3 in the injection-forming AlN ceramic phase composition affects the phase composition of the 2h phase. See Table 3. The results show that the main crystal phase of AlN in each component is AlN, but the type of the second phase of the grain boundary produces a large change. When the content of Y2O3 is small, the second phase in the injection-molded AlN is mainly lanthanum aluminate, which is basically the same as the second phase of the grain boundary in AlN prepared by other conventional forming methods, namely Y2O3 and Al2O3. The reaction produces a lanthanum aluminate liquid phase to promote the densification process of the sintered body and deposit on the grain boundary to form a second phase of the grain boundary. However, with the increase of Y2O3 content, the grain boundary second phase in the injection-molded AlN undergoes a significant change. The yttrium aluminate disappears, and YN and Y2O3 appear. In the middle, when Y2O3 is added to 12%, AlN Y2O3 appears in the middle, and there is also the presence of lanthanum aluminates. It can be seen that the composition of the second phase in the grain boundary of the AlN ceramic with Y23 injection molding is different from that of the second phase of the AlN grain boundary prepared by the conventional forming method. Table 3 Phase Composition and Sintering Density of AlN Ceramics with Different Y2O3 Additives at 1850 °C for 2 h Addition of about 40% (volume fraction) of binder in the injection molding process, the binder is removed in AlN after removal After a certain amount of residual C, the mass fraction of carbon in the AlN degreasing blank of each component is between 0.34% and 0.52%, while the mass fraction of carbon in the original powder is only 0.072%. During the sintering process, this Part C will have a significant effect on the formation of the second phase in AlN. Watari study found that in the sintering process of AlN, the following reaction can take place in the C atmosphere: adding appropriate C in AlN, can also react in the grain boundary (3), generate YN to effectively remove the grain boundary Oxygen, improve thermal conductivity. From the thermodynamics point of view, Y2O3 is more stable than Al2O3. When sintering, the C in the injection-molded AlN will first react with Al2O3 on the surface of the AlN powder (1), so that the content of Al2O3 that reacts with Y2O3 to form lanthanum aluminate decreases. At the same time, sintering aid Y2O3 reacts with residual Al23 to form yttrium aluminate, but due to the reduction of Al2O3 content, yttrium aluminate is not easily formed in injection-forming AlN. With the increase of Y2O3 content, excess Y2O3 occurs. Deposited on the grain boundary to form a new second phase Y2O3, and a small amount of yttrium aluminate YN generated by the reaction formula (3), a small amount of Y2O3 by (2) can also produce a small amount of YN. Therefore, in the injection molding Y23 grain boundary phase; and when Y23 mass fraction is greater than 5%, lanthanum aluminate has been difficult to exist. 2.3 The microstructure and properties of injection-molded AlN-Y2O3 ceramics are the thermal conductivity curves of sintered AlN ceramics with different content of Y2O3 sintered at 1850 °C. The thermal conductivity of AlN produced by injection molding is basically the same as that of AlN ceramics prepared by conventional forming methods. With the increase of the content of sintering additive Y2O3, the thermal conductivity of AlN also increases, reaching the maximum at 5Y-AlN, which is 165.2 Wm. -1If1, then the thermal conductivity of AlN decreases sharply. When the mass fraction of Y2O3 is 7%, the bulk thermal conductivity of AlN drops to 120W. 1.1. Among the various factors affecting AlN thermal conductivity, whether AlN is densified is a prerequisite. Since AlN is a strong covalent bond compound, pure AlN is difficult to sinter and dense, and sintering aids must be added. The amount of Y2O3 added in 1Y-AlN and 2Y-AlN is less, sintering is not completely dense at 1850°C, so thermal conduction The rate is lower. With the increase of Y2O3 content, AlN has been able to complete the densification process, and its thermal conductivity has gradually increased. This is consistent with the variation of thermal conductivity of AlN prepared by the traditional method. That is, the addition of Y2O3 can react with Al2O3 to form various kinds of yttrium. The aluminates, thereby reducing the oxygen content dissolved in the AlN grains, increase the thermal conductivity of the polycrystalline AlN 16 and reach its maximum at 5Y-AlN. As a typical 5Y-AlN high-power fracture morphology, dense sintered AlN grains grow completely, showing a typical hexagonal system with a grain size of 7-8 Mm. There is a small amount of grain boundary second phases on the grain boundary. . When the mass fraction of Y2O3 exceeds 5%, the thermal conductivity of AlN begins to decrease. The typical fracture morphology of 5Y-AlN ceramics is also dense in 7Y-AlN AlN sintered body, and the crystal grains can also be well penetrated, but its thermal conductivity is significantly lower than that of 5Y-AlN. It can be seen that there are other factors. Affects the thermal conductivity of AlN. XRD diffraction results have shown that due to the influence of the amount of residual carbon by injection molding, excess Y2O3 has formed grain boundary phases in 5Y-AlN, remaining among AlN grains, and 7Y-AlN is more. Excess Y2O3 causes an increase in oxygen content in AlN. The results show that oxygen easily diffuses into the AlN grains at high temperatures, resulting in defects such as lattice distortion and oxygen ion vacancy, which seriously affect the thermal conductivity of the AlN matrix. The energy spectrum of the 5Y-AlN and 7Y-AlN grains shows that oxygen has diffused into the A1N grains in 7Y-A1N, but much less in 5Y-A1N. It can also be found that there is a small amount of carbon in the grains of A1N, which also weakens the thermal properties of the A1N grains. It can be seen that in injection molding A1N, it is practically significant to effectively control the content and distribution of C. 3 Conclusions The A1N ceramic heat-conducting ring with thermal conductivity -K-1 has been successfully prepared by an injection molding process. Under the experimental conditions, the A1N ceramics can be densified with the sintering temperature up to 1850°Q. The relative density is more than 99% and the thermal conductivity increases with the sintering temperature. Artisan, the composition of the grain boundary second phase and the traditional molding process are quite different, which is mainly related to the amount of carbon residue introduced in the injection molding process. When the mass fraction of Y2O3 is more than 5%, the lanthanum aluminate phase is hardly present in A1N, but a large number of yttrium aluminates and the remaining Y23 are present. With the increase of the content of sintering additive Y23, the thermal conductivity of A1N also increases, and 5Y-A1N reaches its maximum value. In the process of injection molding A1N ceramics, whether the diffusion of oxygen ions into the crystal lattice and the amount of residual carbon after the binder removal has a certain influence on the thermal conductivity of the injection-molded A1N ceramics. 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