CN115703683A - High-strength high-heat-conductivity large-size silicon nitride ceramic and preparation method thereof - Google Patents
High-strength high-heat-conductivity large-size silicon nitride ceramic and preparation method thereof Download PDFInfo
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Abstract
The invention provides a high-strength high-heat-conductivity large-size silicon nitride ceramic and a preparation method thereof, wherein submicron-grade low-oxygen silicon nitride powder is used as a raw material, non-oxygen-containing nitride and fluoride are added as composite sintering aids, and silicon nitride ceramic block blanks are prepared by mixing powder, cold isostatic pressing or vibration pressing molding, hot-pressing sintering and cooling annealing, wherein the bending strength is more than 800MPa, the oxygen content is low, the crystal boundary glass phase is less, the heat conductivity is more than 80W/m.K, and each silicon nitride ceramic block blank is 10-50 mm thick, 190-385 mm long and 230-350 mm wide; the silicon nitride ceramic substrate for packaging high-power semiconductor IGBT and the like which have urgent industrial requirements is prepared by cutting, slicing, grinding and polishing through a diamond wire multi-wire cutting technology. Compared with the wet tape casting-degreasing-high pressure atmosphere sintering process in the prior substrate manufacturing technology, the method can prepare the high-performance large-size silicon nitride ceramic substrate with low cost, high efficiency, no pollution, short flow and high performance.
Description
Technical Field
The invention belongs to the technical field of semiconductor packaging substrate materials, and particularly relates to a high-strength high-heat-conductivity large-size silicon nitride ceramic and a preparation method thereof, which are particularly suitable for preparing a silicon nitride ceramic substrate.
Background
The silicon nitride ceramic has excellent characteristics of high strength and high heat conduction, and the copper-clad ceramic substrate prepared by combining an active metal welding process (AMB) does not lose efficacy after 5000 times of thermal cycles, has extremely high environmental reliability, and becomes a key material with development prospect in module packaging of a high-voltage high-power Insulated Gate Bipolar Transistor (IGBT). Compared with common aluminum oxide ceramic substrate materials and aluminum nitride ceramic substrate materials, the silicon nitride ceramic substrate materials are honored as third-generation ceramic substrate materials due to excellent comprehensive performance, are the first choice materials for bearing third-generation semiconductor high-temperature modules represented by SiC wafers in the future, and have strong competitiveness.
Silicon nitride ceramic substrate materials are successfully used in the fields of electric automobiles, rail traffic, photovoltaic, wind power, smart power grids and other new energy sources at present, the consumption is rapidly increased, and the market is huge. In addition, the method has very wide application requirements in the fields of high-concentration solar cell modules, semiconductor refrigerators, high-power resistors, aerospace AC-DC (alternating Current-direct Current), DC-DC (direct Current-direct Current) conversion modules, aerospace novel chip-inverted power electronic integrated modules (PEBB) and the like. Therefore, there is a great need to develop Si 3 N 4 And other packaging substrate materials with good heat conduction and high-temperature reliability greatly reduce the thermal resistance of the power module and improve the performance.
Currently, commercially applied silicon nitride ceramic substrates are produced by a traditional process method of wet tape casting, degreasing and high-pressure nitrogen sintering, and the prior art has many defects. First, the technical threshold is high. The related technology of silicon nitride casting is mainly mastered in a few companies such as Japan, america and the like, the domestic start is late, no mature industrial production line exists at present, and the key formula, process and equipment are difficult to break through in a short time. Secondly, the pollution is serious. The solvent of the tape casting slurry is toxic and harmful organic matters such as benzene, ketone and the like, the environment pollution is serious, the harm to human bodies is large, the water-based tape casting technology is also created in recent years, but the water molecules have strong polarity and large surface tension, the blank deformation and cracking are difficult to control, the qualification rate is low, and the examples of batch production are few. Thirdly, the process flow is long. The preparation and tape casting of complex system slurry need to be carried out for a long time, organic matters need to be sintered for a long time in a 500-600 ℃ degreasing furnace to be removed, and finally sintering densification needs to be carried out in a high-pressure nitrogen atmosphere sintering furnace at 1850-2000 ℃, which means that two-step independent sintering is needed, the time consumption is long, besides a calendar can continuously form a raw blank tape, continuous operations such as degreasing, sintering and the like cannot be carried out. Fourthly, the matching cost is high. Silicon nitride powder produced by a silicon imine decomposition method for a tape casting method high-thermal-conductivity substrate can be produced in batches only by Japan, the price is very high, a high-pressure nitrogen sintering furnace controlled by a high-precision temperature field mainly depends on import, key consumable materials such as a high-quality boron nitride burning bearing plate and crucible kiln furniture basically depend on the Japan import, the price is very high, and the matching cost of the kiln furniture only exceeds the investment of the sintering furnace. Fifthly, the thermal conductivity is low. The thermal conductivity of the current casting method is 65-90W/m.K, and needs to be further improved. Sixthly, the product density is slightly low, the sintering percent of pass is low, a large amount of organic matters are required to be added in the casting process, the sintering shrinkage is large, the casting green body is a green body sheet which is directly formed into a size of 0.3-0.6 mm, the sheet is very easy to warp and deform in the sintering process, and the strength and the mechanical property are influenced.
Therefore, the silicon nitride ceramic substrate is single in industrial manufacturing technology system at present, has more defects, and needs to develop a new process technology system.
Disclosure of Invention
The invention aims to provide a high-strength high-heat-conductivity large-size silicon nitride ceramic and a preparation method thereof, overcomes the defects of preparing a silicon nitride ceramic substrate by a traditional tape casting process, and realizes substitution and progress.
In order to achieve the purpose of the invention, the technical scheme adopted by the invention comprises the following steps:
a preparation method of high-strength high-heat-conductivity large-size silicon nitride ceramics comprises the following steps:
a step of material mixing, which is to adopt submicron-order low-oxygen silicon nitride powder as a raw material, add non-oxygen nitride and fluoride as composite sintering aids, mix materials, and then uniformly mix to obtain formula powder;
a pre-pressing step, namely filling the formula powder into a mold, and after vacuumizing treatment, performing cold isostatic pressing or vibration pressure forming treatment to obtain a formed blank;
hot pressing and sintering, namely after finishing the formed blank, stacking at least one layer of the formed blank into a mold, and using graphite paper or a high-strength graphite plate as an interlayer between the stacked layers; then carrying out hot-pressing sintering treatment;
and a temperature reduction annealing step, namely after the high-temperature heat preservation process of the hot-pressing sintering treatment is finished, carrying out temperature reduction annealing treatment and then naturally cooling to obtain the high-strength high-heat-conductivity large-size silicon nitride ceramic.
In the above method for preparing a large-size silicon nitride ceramic with high strength and high thermal conductivity, as a preferred embodiment, after the step of annealing at a reduced temperature, the method further includes: and a post-processing step, namely, cutting, slicing and polishing by adopting an electroplating diamond wire slicer to obtain the silicon nitride ceramic substrate with the required size.
In the preparation method of the high-strength high-heat-conductivity large-size silicon nitride ceramic, as a preferred embodiment, in the step of mixing the ingredients and the powder, the oxygen content of the submicron low-oxygen silicon nitride powder is less than or equal to 1.2%; more preferably, the submicron low-oxygen silicon nitride powder is at least one of first silicon nitride powder prepared by adopting a high-temperature self-propagating combustion synthesis process and second silicon nitride powder prepared by adopting a silicon imine decomposition method process; more preferably, in the submicron low-oxygen silicon nitride powder, the first silicon nitride powder accounts for 30 to 100wt.%, the second silicon nitride powder accounts for 0 to 70wt.%, and further, the first silicon nitride powder accounts for 55 to 90wt.%, and the second silicon nitride powder accounts for 10 to 45wt.%.
In the above method for preparing a large-size silicon nitride ceramic with high strength and high thermal conductivity, as a preferred embodiment, in the step of mixing ingredients and powders, the nitride refers to SiMgN 2 、Mg 3 N 2 One or two of (1), the fluoride refers to MgF 2 、YF 3 、YbF 3 、LaF 3 One or more of them.
More preferably, the adding proportion of the composite sintering aid, namely the total amount of the nitride and the fluoride is less than or equal to 8% (mass fraction, such as 7%, 6%, 5%, 4% and the like); in other words, the amount of the composite sintering aid added is 8% or less of the total mass of the silicon nitride powder and the composite sintering aid.
In the above preparation method of the high-strength high-thermal-conductivity large-size silicon nitride ceramic, as a preferred embodiment, in the step of blending and mixing the powder, the uniformly mixing process includes ball milling, drying, granulating/sieving processes in sequence.
More preferably, the ball milling treatment is carried out in an alcohol medium, and the grinding balls are silicon nitride ceramic balls.
More preferably, the drying treatment is spray drying under the protection of inert gas such as nitrogen or argon; or drying in an oven at 60-110 deg.C (such as 65 deg.C, 70 deg.C, 80 deg.C, 90 deg.C, 100 deg.C, 105 deg.C).
More preferably, the granulation/sieving treatment, selected for example by a spray drying process, can be directly performed in a drying process with spray granulation in one step, selected for example by a drying process in an oven at 60-110 ℃ (e.g. 65 ℃, 70 ℃, 80 ℃, 90 ℃, 100 ℃, 105 ℃, etc.), and then sieved after crushing, preferably by a 40-60 mesh sieve (i.e. taking undersize, the mesh number can be selected between 40-60 meshes).
In the above method for preparing a large-size silicon nitride ceramic with high strength and high thermal conductivity, as a preferred embodiment, in the pre-pressing step, the cold isostatic pressing pressure is 150 to 300MPa (for example, 160MPa, 180MPa, 200MPa, 220MPa, 250MPa, 270MPa, 290MPa, etc.).
In the method for preparing the high-strength high-thermal-conductivity large-size silicon nitride ceramic, as a preferred embodiment, in the pre-pressing step, the vibration frequency of the vibration pressure forming treatment is 1000 to 3000 times/min (e.g., 1200 times/min, 1500 times/min, 1800 times/min, 2000 times/min, 2300 times/min, 2500 times/min, 2800 times/min, etc.), and the exciting force is 20 to 60KN (e.g., 25KN, 30KN, 40KN, 50KN, 55KN, etc.).
In the above preparation method of the large-size silicon nitride ceramic with high strength and high thermal conductivity, as a preferred embodiment, in the hot-pressing sintering step, the thickness of a green body after trimming the formed body is 15-80 mm, the length is 190-385 mm, and the width is 230-350 mm.
In the preparation method of the high-strength high-thermal-conductivity large-size silicon nitride ceramic, as a preferred embodiment, in the hot-pressing sintering step, the mold is a high-strength carbon fiber reinforced carbon-carbon composite mold, and the volume density of the mold is more than or equal to 1.7g/cm 3 And the annular tensile strength is more than or equal to 100MPa. The traditional graphite mold can also be adopted, but the effect is not better than that of the carbon-carbon composite material mold reinforced by the high-strength carbon fiber.
In the above method for preparing a large-size silicon nitride ceramic with high strength and high thermal conductivity, as a preferred embodiment, in the step of hot-pressing and sintering, the number of stacked thickness layers of the green body in the mold-filling stacking step is 1 to 5 (for example, 2, 3, and 4).
In the above method for preparing a large-sized silicon nitride ceramic with high strength and high thermal conductivity, as a preferred embodiment, in the hot-press sintering step, the hot-press sintering treatment is performed by performing heat preservation for 2 to 10 hours (e.g., 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, etc.) under a pressure condition of 30 to 60MPa (e.g., 35MPa, 40MPa, 45MPa, 50MPa, 55MPa, etc.) under a nitrogen protective atmosphere at 1600 to 1900 ℃ (e.g., 1620 ℃, 1650 ℃, 1700 ℃, 1750 ℃, 1800 ℃, 1850 ℃, 1880 ℃, etc.).
In the above method for preparing a large-size silicon nitride ceramic with high strength and high thermal conductivity, as a preferred embodiment, in the step of temperature reduction annealing, after the hot-pressing sintering high-temperature heat preservation process is finished, the temperature reduction annealing treatment is to reduce the temperature to 1200 to 1500 ℃ (for example, 1220 ℃, 1250 ℃, 1300 ℃, 1350 ℃, 1400 ℃, 1450 ℃, 1480 ℃ and the like) in the same furnace, and preserve the temperature for 2 to 6 hours (for example, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours and the like).
The large-size silicon nitride ceramic with high strength and high heat conductivity is prepared by the method.
Preferably, the high-strength high-heat-conductivity large-size silicon nitride ceramic has a density of over 99.3%, a bending strength of 800-1180 MPa and a thermal conductivity of 80-136W/m.K.
Preferably, the thickness of the high-strength high-heat conduction large-size silicon nitride ceramic is 10-50 mm, the length is 190-385 mm, and the width is 230-350 mm.
Compared with the prior art, the invention has the beneficial effects that:
1. the preparation method provided by the invention can be used for preparing the silicon nitride ceramic substrate with excellent performance, the density is more than 99.3%, the bending strength is 800-1180 MPa, the thermal conductivity is 80-136W/m.K, and the mechanical property and the thermal conductivity are excellent.
2. The preparation method provided by the invention can prepare 1-5 layers of large-size high-strength high-heat-conductivity silicon nitride ceramic blocks with the thickness of 10-50 mm, the length of 190-385 mm and the width of 230-350 mm at one time.
3. According to the large-size high-strength high-heat-conductivity silicon nitride ceramic block obtained in the invention, by combining a diamond wire multi-wire cutting technology, after cutting, slicing and polishing, a large-size silicon nitride ceramic substrate which is not limited to the conventional commercial large-size silicon nitride ceramic substrate with adjustable thickness of 114 × 114mm, 138 × 190mm and the like and 0.2-0.6 mm can be obtained through flexible adjustment according to the requirement, the roughness is less than or equal to 0.5 μm, and the silicon nitride ceramic substrate meets the requirements of high-power semiconductor IGBT and other packaging silicon nitride ceramic substrates.
4. Compared with the existing wet tape casting-degreasing-high pressure atmosphere sintering process of the substrate manufacturing technology, the method for preparing the high-strength high-thermal conductivity large-size ceramic substrate by the hot pressing sintering method develops a new process technology system, can solve the defects of the prior art, can prepare the high-strength high-thermal conductivity silicon nitride substrate material with low cost, high efficiency, no pollution, short flow and high performance, and can realize substitution and progress.
Drawings
FIG. 1 is a flow chart of a process for preparing a large-sized silicon nitride ceramic block with high strength and high thermal conductivity by hot-pressing sintering and further preparing a silicon nitride ceramic substrate according to an embodiment of the present invention;
fig. 2 is a flow chart of a process for preparing a large-sized silicon nitride ceramic substrate with high strength and high thermal conductivity by hot-pressing sintering according to a preferred embodiment of the present invention.
Detailed Description
In a specific preferred embodiment of the present invention, the method for preparing a large-size silicon nitride ceramic substrate with high strength and high thermal conductivity, as shown in the flowchart of fig. 1, comprises the following steps: proportioning, ball-milling, drying, granulating/screening, cold isostatic pressing, green body processing, single-layer or multi-layer die filling, hot-pressing sintering, cooling annealing, cutting, slicing and polishing. Referring to fig. 2, the preparation method specifically comprises the following steps:
100, adopting low-oxygen silicon nitride powder as a raw material, adding non-oxygen nitride and fluoride as a composite sintering aid, and batching;
102, filling the formula powder obtained in the step 101 into a mold, vacuumizing, and performing cold isostatic pressing to obtain a molded blank;
103, machining and trimming the formed blank obtained in the step 102 to obtain a green blank;
104, stacking the processed green bodies obtained in the step 103 into a high-strength carbon fiber reinforced carbon-carbon composite material mold, and using graphite paper or a high-strength graphite plate as an interlayer between the stacked layers;
105, performing hot-pressing sintering treatment under the condition of bidirectional pressure application in a nitrogen atmosphere;
and 107, cutting, slicing and polishing the high-strength, high-heat-conductivity and large-size silicon nitride block blank obtained in the step 106 by using an electroplating diamond wire slicing machine to obtain the silicon nitride ceramic substrate with the required size.
Preferably, the submicron low oxygen silicon nitride powder described in step 100 is an oxygen content of ≦ 1.2wt.%; the composite powder formed by the silicon nitride powder prepared by the low-cost high-temperature self-propagating combustion synthesis process and the high-purity silicon nitride powder prepared by the silicon imine decomposition process is mainly prepared by the silicon nitride powder prepared by the high-temperature self-propagating combustion synthesis process, for example, the silicon nitride powder prepared by the high-temperature self-propagating combustion synthesis process accounts for 55-90 wt.%, and the high-purity silicon nitride powder prepared by the silicon imine decomposition process accounts for 10-45 wt.%.
Preferably, the composite sintering aid is the one described in step 100, wherein the nitride is SiMgN 2 、Mg 3 N 2 One or two of (A) and (B), fluorideRefers to MgF 2 、YF 3 、YbF 3 、LaF 3 One or more of them.
Preferably, the composite sintering aid in step 100 includes a total addition ratio of nitride to fluoride of less than or equal to 8wt.% (such as 7wt.%, 6wt.%, 5wt.%, 4 wt.%), in other words, the addition amount of the composite sintering aid is 8% or less of the total mass of the silicon nitride powder and the composite sintering aid.
Preferably, the ball milling process in step 101 is performed in an ethanol medium, and the milling balls are silicon nitride ceramic balls.
Preferably, the drying process in step 101 is a spray drying process under the protection of inert gas such as nitrogen or argon, or a drying process in an oven at 60-110 ℃ (such as 65 ℃, 70 ℃, 80 ℃, 90 ℃, 100 ℃, 105 ℃ and the like), or one of them.
Preferably, the granulating/sieving process in step 101, such as selecting a spray drying process, can be directly completed in one step of spray granulation at the same time in the drying process, such as selecting a drying process in an oven at 60-110 deg.C (such as 65 deg.C, 70 deg.C, 80 deg.C, 90 deg.C, 100 deg.C, 105 deg.C, etc.), and sieving after crushing, wherein the mesh number can be 40-60 mesh.
Preferably, the cold isostatic preforming pressure in step 102 is 150 to 300MPa (e.g., 160MPa, 180MPa, 200MPa, 220MPa, 250MPa, 270MPa, 290MPa, etc.).
Preferably, in step 103, the formed blank obtained by the cold isostatic pressing preforming is machined and trimmed to obtain a green body, and the green body has the thickness of 15-80 mm, the length of 190-385 mm and the width of 230-350 mm.
Preferably, the high strength carbon fiber reinforced carbon-carbon composite mold of step 104 has a bulk density of 1.7g/cm or more 3 And the annular tensile strength is more than or equal to 100MPa.
Preferably, the number of layers of the green body die-filling stack thickness in step 104 is 1-5 (e.g., 2, 3, 4). If only 1 layer of green body is provided, it is obviously not necessary to use graphite paper or high-strength graphite plates for the barrier layer.
Preferably, the hot press sintering in step 105 is performed by performing a bidirectional 30-60 MPa (e.g., 35MPa, 40MPa, 45MPa, 50MPa, 55MPa, etc.) pressure application in a nitrogen atmosphere at 1600-1900 deg.C (e.g., 1620 deg.C, 1650 deg.C, 1700 deg.C, 1750 deg.C, 1800 deg.C, 1850 deg.C, 1880 deg.C, etc.) for 2-10 h (e.g., 3h, 4h, 5h, 6h, 7h, 8h, 9h, etc.).
Preferably, the temperature reduction annealing treatment in the step 106 is that after the hot-pressing sintering high-temperature heat preservation process is finished, the temperature is reduced to 1200-1500 ℃ (such as 1220 ℃, 1250 ℃, 1300 ℃, 1350 ℃, 1400 ℃, 1450 ℃, 1480 ℃ and the like) in the same furnace, the annealing is carried out for 2-6 h (such as 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h and the like), and then the annealing is carried out naturally. The same furnace is cooled and annealed, which not only can reduce the cost, but also is beneficial to reducing the thermal stress of the ceramic product, and is convenient for further cutting and thinning to prepare the finished product of the silicon nitride ceramic substrate.
The high-strength high-heat-conductivity large-size silicon nitride ceramic prepared by the method has the density of over 99.3 percent, the bending strength of 800-1180 MPa, the heat conductivity of 80-136W/m.K, and the size specification can reach the thickness of 10-50 mm, the length of 190-385 mm and the width of 230-350 mm.
The core idea of the invention is as follows:
1) The hot pressing process which is short in flow and more suitable for densification and sintering of products with simple shapes such as silicon nitride ceramic substrates and the like is adopted. The Si-N bond in the silicon nitride belongs to a strong bonding effect, the diffusion coefficient is very low, the densification driving force generated by the silicon nitride is low, and the hot-pressing sintering is used for preparing dense Si 3 N 4 An effective method of (1). In the sintering process, mechanical pressure acts on the material to increase the sintering driving force, so that Si can be enabled 3 N 4 The crystal grains of the ceramic are in more sufficient contact in the sintering process, the atomic diffusion of the ceramic is promoted, the generation of plastic deformation of silicon nitride in the densification process can be promoted, the rapid densification is facilitated, and good mechanical properties are obtained. Moreover, the substrate has simple shape, and the hot-pressing sintering is easier to transmit sintering power and is beneficial to industrial realization. In addition, the hot pressing has the more beneficial effects of reducing the using amount of sintering aids, reducing the content of grain boundary phases, improving the purity of main phases and being beneficial to improving the thermal conductivity.
2) In order to further break through the degree of hot-pressing densification, the traditional method that powder is directly filled into a die in hot pressing is improved, and a cold isostatic pressing preforming process is added before hot pressing. The cold isostatic pressing preforming can lead the blank to obtain density of more than 70 percent in advance, the compression amount is smaller in the later hot pressing process, the compression stroke of a pressure head is shorter, and the one-time furnace charging amount is larger.
3) A plurality of blocks can be sintered simultaneously by adopting one furnace of multi-layer die filling, and the length and the width can be according to the multiple sizes of the commercial substrate, thereby realizing large output and reducing the cost. To achieve this, high strength molds made of carbon fiber reinforced carbon-carbon composites are used. The large-size and multi-layer simultaneous pressurization needs to increase the pressure of hot pressing to realize densification, and a high-strength hot pressing mold is the key. In addition, the adopted pressurizing mode is bidirectional axial pressurizing with an upper pressure head and a lower pressure head for pressurizing simultaneously so as to ensure the uniformity of the density among different layers. Moreover, the problems of warping, deformation and the like in the casting process are not easy to occur by adopting thick sheet sintering.
4) To achieve high thermal conductivity, the oxygen content in silicon nitride ceramics needs to be reduced to reduce phonon scattering. The adverse effect of oxygen can be reduced by using a silicon nitride raw material with low oxygen and by using a nitride and fluoride sintering aid which do not contain oxygen. The compound non-oxide sintering aid is adopted, the content of an M-Si-O-N glass phase at a crystal boundary can be reduced, and research shows that the thermal conductivity of the glass phase is only about 1W/m.K and is far lower than that of crystal grains. Meanwhile, the oxygen content can be systematically reduced by adopting a vacuumizing method and hot-pressing sintering under the protection of nitrogen atmosphere during cold static pressure forming, which is beneficial to the improvement of heat conductivity.
5) In order to reduce the cost of raw materials, the silicon nitride powder synthesized by self-propagating combustion which is well developed in recent years is taken as the main material. The hot-pressing sintering process is beneficial to densification, the requirement on the sintering activity of the raw material is lower than that of the casting method, and the production cost can be greatly reduced by reducing the dependence on silicon nitride powder prepared by a silicon imine decomposition method.
6) And cutting, slicing and polishing the obtained high-strength high-heat-conductivity large-size hot-pressed sintered block by adopting diamond wire multi-line cutting to obtain the high-performance silicon nitride ceramic substrate with the quality meeting the requirement. The diamond wire multi-wire processing technology is successfully applied to high-hardness ceramic materials such as fields of polycrystalline silicon wafer processing, sapphire processing, silicon carbide wafer processing and the like after years of development and iteration, the processing efficiency is increased in multiples, the processing loss is gradually reduced, the material cost of equipment and electroplated diamond wires is reduced to a low point, multi-wire slicing can be realized, and the cutting efficiency is high. The hot-pressing sintering technology is fused with the mature diamond wire multi-wire cutting technology in recent years, which is the historical intersection of the material technology progress and the processing technology progress and can promote a new ceramic material preparation technology different from the traditional ceramic material preparation technology.
7) In order to ensure that the processing qualification rate of the large-size hot-pressed sintered block is high and the cracks are few, an annealing process is added at a low-temperature section when the temperature is reduced after the high-temperature heat preservation of the hot-pressed sintering is finished so as to reduce the internal stress of the sintered block and avoid the crack expansion caused by the internal stress in the process of cutting the sintered block into thin pieces after cooling.
The present invention will be further described in detail by the following examples, which include but are not limited to the following examples. The specific experimental procedures or conditions not indicated in the examples can be performed according to the procedures or conditions of the conventional procedures described in the literature in the field. The various reagents and starting materials used in the examples are all commercially available products. Examples high strength carbon fiber reinforced carbon-carbon composite molds for hot pressed sintering were produced by new materials for electronics, semken (suzhou), a carbon-carbon composite material reinforced with carbon fibers and their fabric, and having a low density (c: (a) (r))<2.0g/cm 3 ) High strength, high specific modulus, high thermal conductivity, low expansion coefficient, good friction performance, good thermal shock resistance, high dimensional stability and the like.
Example 1
The embodiment provides a large-size silicon nitride ceramic substrate with high strength and high thermal conductivity, and the preparation method sequentially comprises the following steps:
1) Taking a certain amount of silicon nitride powder and sintering aid, mixing, wherein the silicon nitride powder is synthesized by self-propagating combustion with d50=0.7 μm and oxygen content of 1wt.% according to mass percentage, and the nitrogen is decomposed by imine decomposition method by d50=0.8 μm36.8 percent of silicon powder and SiMgN as sintering aid 2 4％、Mg 3 N 2 1％、YF 3 1％、YbF 3 2％；
2) Selecting silicon nitride balls, ball-milling the silicon nitride balls in an alcohol medium for 6 hours, drying and spray-granulating slurry in a nitrogen protective atmosphere to obtain uniformly-mixed formula powder;
3) Putting the powder into a rubber mold, vacuumizing, performing cold isostatic pressing at 200MPa, machining a green blank, putting 1 layer of the green blank into a carbon fiber reinforced carbon-carbon composite mold, performing heat preservation for 4 hours under the condition of bidirectional 35MPa pressure in a nitrogen protective atmosphere at 1800 ℃, performing hot-pressing sintering, cooling to 1400 ℃ in the same furnace after high-temperature heat preservation is finished, performing heat preservation for 4 hours, annealing treatment, naturally cooling, and discharging to obtain 1 ceramic block with the thickness of 40mm, the length of 385mm and the width of 280 mm;
4) The silicon nitride ceramic substrate with 138 x 190mm and 0.4 μm roughness can be obtained by cutting, dicing and polishing with a diamond wire saw, and the bending strength of the material is 1180MPa and the thermal conductivity is 136W/m.K when the block is sampled.
Example 2
The embodiment provides a large-size silicon nitride ceramic substrate with high strength and high heat conductivity, and the preparation method sequentially comprises the following steps:
1) Taking a certain amount of silicon nitride powder and sintering aid, mixing, wherein 55.2% of self-propagating combustion synthetic powder silicon nitride powder with d50=0.7 μm and oxygen content of 1wt.%, 36.8% of silicon nitride powder with d50=0.8 μm by silicon imine decomposition method, and sintering aid SiMgN 2 4％、YF 3 4%, burdening;
2) Selecting silicon nitride balls and ball-milling the silicon nitride balls in an alcohol medium for 6 hours, drying and spray-granulating slurry in a nitrogen protective atmosphere to obtain uniformly-mixed formula powder;
3) Putting the powder into a rubber mold, vacuumizing, performing cold isostatic pressing at 200MPa, stacking 2 layers of green compacts after machining, putting the green compacts into a carbon fiber reinforced carbon-carbon composite material mold, separating the stacked layers by using a high-strength graphite plate, performing heat preservation for 4 hours under the condition of bidirectional applying 35MPa pressure in a nitrogen protective atmosphere at 1820 ℃, performing hot-pressing sintering, after the high-temperature heat preservation is finished, cooling to 1400 ℃ in the same furnace, performing heat preservation for 4 hours, performing annealing treatment, naturally cooling, and discharging to obtain 2 ceramic blocks with the thickness of 30mm, the length of 190mm and the width of 280 mm;
the silicon nitride ceramic substrate with 138 x 190mm and 0.4 μm roughness can be obtained by cutting, dicing and polishing with a diamond wire saw, and the bending strength of the material is 970MPa and the thermal conductivity is 118W/m.K when the block is sampled.
Example 3
The embodiment provides a large-size silicon nitride ceramic substrate with high strength and high heat conductivity, and the preparation method sequentially comprises the following steps:
1) Taking a certain amount of silicon nitride powder and sintering aid, mixing, wherein the silicon nitride powder is 55.2% of self-propagating combustion synthetic powder with d50=0.7 μm and oxygen content of 1%, the silicon nitride powder is 36.8% of silicon imine decomposition method with d50=0.8 μm, and the sintering aid is SiMgN 2 4％、YbF 3 4%, burdening;
2) Selecting silicon nitride balls and ball-milling the silicon nitride balls in an alcohol medium for 6 hours, and drying and spray-granulating the material paste in a nitrogen protective atmosphere to obtain uniformly mixed formula powder;
3) Loading the powder into a rubber mold, carrying out cold isostatic pressing at 250MPa after vacuumizing, stacking 3 layers after machining green bodies, loading the carbon fiber reinforced carbon-carbon composite material mold, separating the stacked layers by using a high-strength graphite plate, carrying out heat preservation for 5 hours under the condition of bidirectionally applying 40MPa pressure in a nitrogen protective atmosphere at 1850 ℃, carrying out hot-pressing sintering, after the high-temperature heat preservation is finished, cooling the green bodies to 1400 ℃ in the same furnace, carrying out heat preservation for 5 hours, carrying out annealing treatment, then naturally cooling and discharging the green bodies to obtain 3 ceramic blocks with the thickness of 25mm, the length of 240mm and the width of 240 mm;
4) The silicon nitride ceramic substrate with the roughness of 0.4 mu m and the thickness of 114 x 114mm can be obtained by cutting, dicing and polishing with a diamond wire saw, and the bending strength of the material is 870MPa and the thermal conductivity is 93W/m.K by block sampling.
Example 4
The embodiment provides a large-size silicon nitride ceramic substrate with high strength and high thermal conductivity, and the preparation method sequentially comprises the following steps:
1) Taking a certain amount of silicon nitride powder and sintering aid, addingThe raw materials are mixed according to the mass percentage, wherein, the self-propagating combustion synthetic powder silicon nitride powder with d50=0.7 μm and oxygen content of 1wt.% is 50.6 percent, the silicon nitride powder with d50=0.8 μm by the silicon imine decomposition method is 41.4 percent, and the sintering aid SiMgN 2 4％、Mg 3 N 2 1％、YbF 3 2％、LaF 3 1%, burdening;
2) Selecting silicon nitride balls and ball-milling the silicon nitride balls in an alcohol medium for 6 hours, and drying and spray-granulating the material paste in a nitrogen protective atmosphere to obtain uniformly mixed formula powder;
3) Filling the powder into a rubber mold, vacuumizing, performing cold isostatic pressing at 250MPa, stacking 5 layers of the green body after machining, filling the 5 layers of the green body into a carbon fiber reinforced carbon-carbon composite material mold, separating the stacked layers by graphite paper, performing heat preservation for 7 hours under the condition of bidirectionally applying 45MPa pressure in a nitrogen protective atmosphere at 1880 ℃, performing hot-pressing sintering, cooling to 1400 ℃ in the same furnace after the high-temperature heat preservation is finished, performing heat preservation for 5 hours, performing annealing treatment, naturally cooling, and discharging to obtain 5 ceramic blocks with the thickness of 20mm, the length of 240mm and the width of 240 mm;
4) The silicon nitride ceramic substrate with the roughness of 114 x 114mm and the roughness of 0.4 mu m can be obtained by cutting, dicing and polishing by a diamond wire saw, and the bending strength and the thermal conductivity of the material are 830MPa and 89W/m.K by block sampling.
According to the embodiment, the invention discloses a preparation method for preparing a high-strength high-heat-conductivity large-size silicon nitride ceramic substrate material by hot-pressing sintering, which is characterized in that low-oxygen silicon nitride powder is used as a raw material, non-oxygen-containing nitride and fluoride are added as composite sintering aids, and the large-size silicon nitride ceramic block blank with high mechanical property and high heat conductivity is prepared by batching, ball milling, drying, granulating/sieving, cold isostatic pressing preforming, green body machining and multilayer die filling, hot-pressing sintering and annealing, and has the advantages of high density, bending strength of over 800MPa, low oxygen content, less crystal boundary glass phase, thermal conductivity of over 80W/m.K, thickness of 10-50 mm, length of 190-385 mm and width of 230-350 mm; and then the silicon nitride ceramic substrate for packaging such as a high-power semiconductor IGBT and the like which has urgent industrial requirements can be prepared by cutting, slicing, grinding and polishing through a diamond wire multi-wire cutting technology. Compared with the existing wet tape casting-degreasing-high-pressure atmosphere sintering process of the substrate manufacturing technology, the hot-pressing sintering method provided by the invention is combined with a new process method of diamond wire multi-wire cutting which is started in recent years, and the high-strength high-heat-conductivity silicon nitride substrate material can be prepared with low cost, high efficiency, no pollution, short flow and high performance.
Finally, it should be further noted that, if any, relational terms such as left and right, first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrases "comprising a," "8230," "8230," or "comprising" does not exclude the presence of additional like elements in a process, method, article, or apparatus that comprises the element.
While the disclosure has been disclosed above by the description of specific embodiments thereof, it should be understood that various modifications, improvements or equivalents of the disclosure may be devised by those skilled in the art within the spirit and scope of the appended claims. Such modifications, improvements and equivalents are intended to be included within the scope of the present disclosure as claimed.
Claims (10)
1. A preparation method of large-size silicon nitride ceramics with high strength and high heat conductivity is characterized by comprising the following steps:
a step of material mixing, which is to adopt submicron-level low-oxygen silicon nitride powder as a raw material, add non-oxygen nitride and fluoride as a composite sintering aid, carry out material mixing, and then carry out uniform mixing treatment to obtain formula powder;
a pre-pressing step, namely filling the formula powder into a mold, and performing cold isostatic pressing or vibration pressure forming treatment after vacuum pumping treatment to obtain a formed blank;
hot pressing and sintering, namely after finishing the formed blank, stacking at least one layer of the formed blank into a mold, and using graphite paper or a high-strength graphite plate as an interlayer between the stacked layers; then carrying out hot pressing sintering treatment;
and a temperature reduction annealing step, namely, after the high-temperature heat preservation of the hot-pressing sintering treatment is finished, carrying out temperature reduction annealing treatment and then naturally cooling to obtain the high-strength high-heat-conductivity large-size silicon nitride ceramic.
2. The method of claim 1, further comprising, after the step of annealing at a reduced temperature: and a post-processing step, namely, cutting, slicing and polishing by adopting an electroplating diamond wire slicer to obtain the silicon nitride ceramic substrate with the required size.
3. The method according to claim 1 or 2, wherein in the step of compounding and mixing, the submicron low-oxygen silicon nitride powder has an oxygen content of 1.2wt.% or less;
preferably, the submicron low-oxygen silicon nitride powder is at least one of first silicon nitride powder prepared by adopting a high-temperature self-propagating combustion synthesis process and second silicon nitride powder prepared by adopting a silicon imine decomposition method process;
more preferably, in the submicron low-oxygen silicon nitride powder, the first silicon nitride powder accounts for 30-100 wt.%, and the second silicon nitride powder accounts for 0-70 wt.%; more preferably, the first silicon nitride powder accounts for 90 to 55wt.%, and the second silicon nitride powder accounts for 10 to 45wt.%.
4. The method according to claim 1 or 2, wherein in the step of mixing ingredients and powders, the nitride is SiMgN 2 、Mg 3 N 2 One or two of (1), the fluoride refers to MgF 2 、YF 3 、YbF 3 、LaF 3 One or more of the above; the addition amount of the composite sintering aid is the silicon nitride powder and the composite sinteringLess than 8 percent of the total mass of the auxiliary agent.
5. The preparation method according to claim 1 or 2, wherein in the step of compounding and mixing the powder, the uniform mixing treatment comprises ball milling, drying, granulating/sieving treatment in sequence;
preferably, the ball milling treatment is carried out in an alcohol medium, and the grinding balls are silicon nitride ceramic balls;
preferably, the drying treatment is spray drying under the protection of inert gas such as nitrogen or argon; or drying in an oven at 60-110 ℃;
preferably, the granulation/sieving treatment, such as spray drying process, can be directly completed in one step of spray granulation at the same time of drying process, such as drying process in an oven at 60-110 ℃, and sieving with a 40-60 mesh sieve after crushing.
6. The production method according to claim 1 or 2, wherein in the preliminary pressing step, the pressure of the cold isostatic pressing is 150 to 300MPa; or the vibration frequency of the vibration pressure forming treatment is 1000-3000 times/min, and the exciting force is 20-60KN;
preferably, the thickness of the green body after the shaping blank is trimmed is 15-80 mm, the length is 190-385 mm, and the width is 230-350 mm.
7. The method according to claim 1 or 2, wherein in the hot press sintering step, the mold is a high-strength carbon fiber reinforced carbon-carbon composite mold having a bulk density of 1.7g/cm or more 3 The annular tensile strength is more than or equal to 100MPa;
preferably, the number of the stacked thickness layers of the green body die filling is 1-5.
8. The method according to claim 1 or 2, wherein in the hot-pressing sintering step, the hot-pressing sintering treatment is carried out under the condition of bidirectional 30-60 MPa pressure in a nitrogen protective atmosphere at 1600-1900 ℃ for 2-10 h.
9. The preparation method according to claim 1 or 2, wherein in the cooling annealing step, the cooling annealing treatment is cooling to 1200-1500 ℃ in the same furnace and keeping the temperature for 2-6 h after the hot-pressing sintering high-temperature heat preservation is finished.
10. A high-strength high-thermal-conductivity large-size silicon nitride ceramic prepared by the method according to any one of claims 1 to 9;
preferably, the density of the high-strength high-heat-conductivity large-size silicon nitride ceramic is more than 99.3 percent, the bending strength is 800-1180 MPa, and the heat conductivity is 80-136W/m.K;
preferably, the thickness of the high-strength high-heat-conductivity large-size silicon nitride ceramic is 10-50 mm, the length is 190-385 mm, and the width is 230-350 mm.
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