CA1256459A - Electric insulating polycrystalline silicon carbide and process for the preparation thereof by isostatic hot pressing - Google Patents
Electric insulating polycrystalline silicon carbide and process for the preparation thereof by isostatic hot pressingInfo
- Publication number
- CA1256459A CA1256459A CA000539761A CA539761A CA1256459A CA 1256459 A CA1256459 A CA 1256459A CA 000539761 A CA000539761 A CA 000539761A CA 539761 A CA539761 A CA 539761A CA 1256459 A CA1256459 A CA 1256459A
- Authority
- CA
- Canada
- Prior art keywords
- weight
- silicon carbide
- sic
- pressure
- oxide
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L23/00—Details of semiconductor or other solid state devices
- H01L23/12—Mountings, e.g. non-detachable insulating substrates
- H01L23/14—Mountings, e.g. non-detachable insulating substrates characterised by the material or its electrical properties
- H01L23/15—Ceramic or glass substrates
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
- C04B35/56—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides
- C04B35/565—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides based on silicon carbide
- C04B35/575—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides based on silicon carbide obtained by pressure sintering
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
- H01L2924/0001—Technical content checked by a classifier
- H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
- H01L2924/095—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00 with a principal constituent of the material being a combination of two or more materials provided in the groups H01L2924/013 - H01L2924/0715
- H01L2924/097—Glass-ceramics, e.g. devitrified glass
- H01L2924/09701—Low temperature co-fired ceramic [LTCC]
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Ceramic Engineering (AREA)
- Organic Chemistry (AREA)
- Materials Engineering (AREA)
- Structural Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Computer Hardware Design (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Power Engineering (AREA)
- Ceramic Products (AREA)
- Compositions Of Oxide Ceramics (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The invention is an electrically insulating sintered polycrystalline silicon carbide and a sintering aid consisting essentially of at least 95.0% by weight silicon carbide, 0.25 to 3.5%
by weight aluminum oxide and/or magnesium oxide, up to 0.3% by weight free carbon and up to 0.03% by weight impurities due to elements of groups 3a and 5a of the Periodic System (predominantly A1 + B + N) in total, wherein the SiC has an essentially homogeneous isotropic microstructure with grain sizes of at most 5 µm, aluminum oxide and/or magnesium oxide are present predominantly at the grain boundaries of the SiC and are detectable as separate phase(s) having the following properties; thermal conductivity of at least 170 W/mk, specific electric resistance of at least 109 Ohm.cm, thermal expansion coefficient of up to 3.5 x 10-6/K and dielectric strength of 20 KV/mm.
Said substrate materials are formed from a homogeneous powder mixtures of SiC with a purity of at least 99.97% by weight based on impurities due predominantly to A1 + B + N and 0.25 to 3.5%
by weight aluminum oxide and/or magnesium oxide by isostatic hot pressing in a hermetically sealed casing at from 1700° to 2200°C and from 100 to 400 MPa using an inert gas as a pressure-transmitting medium.
The invention is an electrically insulating sintered polycrystalline silicon carbide and a sintering aid consisting essentially of at least 95.0% by weight silicon carbide, 0.25 to 3.5%
by weight aluminum oxide and/or magnesium oxide, up to 0.3% by weight free carbon and up to 0.03% by weight impurities due to elements of groups 3a and 5a of the Periodic System (predominantly A1 + B + N) in total, wherein the SiC has an essentially homogeneous isotropic microstructure with grain sizes of at most 5 µm, aluminum oxide and/or magnesium oxide are present predominantly at the grain boundaries of the SiC and are detectable as separate phase(s) having the following properties; thermal conductivity of at least 170 W/mk, specific electric resistance of at least 109 Ohm.cm, thermal expansion coefficient of up to 3.5 x 10-6/K and dielectric strength of 20 KV/mm.
Said substrate materials are formed from a homogeneous powder mixtures of SiC with a purity of at least 99.97% by weight based on impurities due predominantly to A1 + B + N and 0.25 to 3.5%
by weight aluminum oxide and/or magnesium oxide by isostatic hot pressing in a hermetically sealed casing at from 1700° to 2200°C and from 100 to 400 MPa using an inert gas as a pressure-transmitting medium.
Description
rJ-wp-36~3 - ~lacker Chemie ELECTRIC INS~LATING POLYCRYST~LLIN~ SILIC~l CA~ID~
AND PROCESS FOR TIIE P~EP~RATION TMEREOF ~Y ISOSTATIC
HOT P~F~SSING
Polycrystalline silicon carbide has been known or a long time~ It has a combination of valuable properties such as high strength, resistance to oxidation, resistance to thermal shock, lo~
thermal expansion and high heat conductivity and is useful in many technological fields.
BACKGROUND OF THE INVENTION
Pure silicon carbide, because of its predominantly covalent bonding, is difficult to sinter. Dense bodies of polycrystalline silicon carbide can only be produced by known processes such as hot pressing and pressureless sintering using sintering aids. One of the oldest sintering aids for silicon carbide is alumina, which, during the sintering, combines with the impurities in the silicon carbide to Eorm a ~luid phase which promotes compaction and which is detectable as a separate phase in the finished sintered body.
In pressureless sintering, aluminum oxide promotes compaction of the SiC by combining with impurities in the SiC. Additional adjuvants such as aluminum, silicon and/or carbon compounds are known to be formed by interaction with the surrounding atmosphere during the sintering.
Silicon carbide can be densiEied by isostatic hot pressing to densities oE almost 100% of the theoretical density (hereinaEter abbreviated as % TD), without the use of sinterlng aids when a very pure SiC powder with a total content oE metallic impurities oE at most 0.1~ by weight is used. Compared to the usual hot pressed or pressureless sintered materials, the polycrystalline SiC sintered bodies have, as a result of their high purity, an improved heat ~1 ~25~
conductivity of 220 W/mK at room temperature. ~lowever, pure SiC has semiconductor properties, and dense sintered articles otained by isostatic hot pressing pure silicon carbide have a specific electric resistance of only about 100 Ohm. cm.
To be useful as a substrate material ~or microcircuitry and structural parts of power electronics, the specific electric resistance must be at least 107 Ohm. cm.
Tests have been conducted to increase the specific electric resistance of SiC by addition of adjuvants. Beryllium oxide has proved especially reuseful since it increases the electric resistance and acts as a sintering adjuvant in hot pressing or in pressureless sintering. Electrically insulating substrate materials o~ SiC
containing beryllium oxide and additionally containing up to 0.1% by weight aluminum, up to 0.1~ by weight boron and up to 0.4% by weight free carbon, with a heat conductivity of at least 167 W/m.K, are known. It has been demonstrated, by comparison tests, that using aluminum oxide instead of beryllium oxide, under otherwise equivalent conditions (HP at 2000C and 30 MPa), there was produced sintered bodies having 99% TD and high mechanical strength but a considerablY
lower thermal conductivity (75 W/m.K) and a specific electric resistance of only 10 Ohm.cm Poor results were also obtained by using aluminum carbide, aluminum nitride and aluminum phosphate instead of beryllium oxide.
Instead of beryllium oxide per se, it is also possible to use beryllium compounds or boron compounds such as boron nitride and other adjuvants to improve the sinterability oE SiC. It has been demonstrated, by comparison examples ~HP at 2000C and 27 MPa) that, when using aluminum oxide and beryllium oxide (1% by weight A12O3 +
1% by weight BeO) to sinter silicon carbide, a sintered body with a thermal conductivity of only 8~ W/mk was produced when using MgO
alone (2% by weight), the sintered body was not dense (55% 't'D).
~56~5~
By lowering the nitrogen content to not more than 500 ppm in the powder mixture of SiC + berylliwn cotnpounds beiny sintered, no decrease in the ~esired properties appeared even in large bodies.
Since beryllium compounds are toxic, attempts were made to use aluminum nitride alone (equal to or ~ 10~ by weight) or mixtures of aluminum nitride and boron nitride (5 - 15% by weight). Although sintered SiC bodies with adequate insulating properties were obtained, the thermal conductivity values were less than 100W/m~.
Sintered bodies of SiC and AlN with additions of calcium, barium or strontium oxide (0.1 to 3~ by weight) had only a slightly improved thermal conductivity.
The course of development of electronics in the last year has led to a reduction in size of the structural parts that is, the development of megabit chips. The requirements of substrate materials have thus increased. The substrate materials must have not only a high specific electric resistance but also a high thermal eonductivity whieh, in the case of SiC, had been obtained only by use of beryllium eompounds as sintering aids. Compare~ to other insulating materials such as aluminum oxide considered for this purpose, silicon carbide has the advantage of a high mechanical strength (bending strength of at least 500 N/mm2 at room temperature) and a thermal expansion coefficient similar to that of silicon (approximately 3.3 x 10 6/oC).
The problem is to develop a process to produce electrical insulating substrate materials of dense polycrystalline silicon carbide which meet these requirements without use of highly toxic compounds.
BRIEF SUMM~RY OF THE INVENTION
_ Aecording to the invention, electrical insulating substrate materials of polycrystalline silicon carbide having a density o~ at least 99.8% TD calculated on the theoretically possible density oE
pure SiC, are provided which consist essentially o~
at least 95.0~ by weight sil:icon carbide 0.25 - 3.5% by weight aluminuM oxide and/or magnesium oxide, up to 0.3% by weight free carbon and up to 0.03% by weight impurities oF elements o~ groups 3a and 5a oE the Periodic System (predominantly Al + B ~ N) in total, in which the silicon carbide is essentially in the form of a homogeneous isotropic microstructure with grain sizes of 5 um maximum, aluminum oxide and/or magnesium oxide are present predominantly in the grain boundary of the silicon carbide and are detectable as separate phase(s). The silicon carbide substrate materials o~ the present invention have the following properties:
thermal conductivity at 300 K of at least 170 W/mK
specific electric resistance at 300 K of at least 10 Ohm.cm a coefficient of thermal expansion up to 3.5 x l~ S/K in the range of from 20C to 300C and a dielectric strength of more than 20 kV~mmO
DETAILED DESCRIPTION OF THE INVENTION
The substrate materials according to the invention are prepared by sintering homogeneous powder mixtures of silicon carbide having a purity of at least 99.97% by weight based on total impurities of elements of groups 3a and 5a of the Periodic System (predominantly Al + ~ + N) and 0.25 to 3.5~ hy weight aluminum oxide and/or magnesium oxide in a hermetically sealed casing by isostatic hot pressing at a temperature of 1700 to 2200C and a pressure of 100 to ~00 MPa in a high pressure autoclave using an inert gas as a pressure-transmitting medium.
Since the sintering is accomplished in a hermetically sealed casing, nothing can escape during the isostatic hot pres.sing opera-~25~6~5~1 tion, the substrate materials of the invention have a density of atleast 99.g~ TD, preferably 100% TD, and the same chemical composition as the starting powder mixt~lre. It i,s critical that pure sta~ting powders be used so that the fin;,shed substrate material does not contain more than the critical amounts of up to 0.?% by weight free carbon and up to 0.03~ by weight of the total of elements oE groups 3a and 5a of the Periodic System which are understood to be predom-inantly Al -~ B + N.
The substrate materials of the invention consist predomin-antly of polycrystalline silicon carbide which has an isotropic microstructure in which the SiC grain having a maximum grain size oE
5 ~m are homogeneously distributed independently o~ direction while aluminum oxide and/or magnesium oxide are predominantly present at the grain boudaries of the SiC and can be detected as a separate phase or phases by X-ray diffraction analysis or ceramographically.
The substrate materials according to the invention are preferably prepared from fine powders of alpha- or beta-SiC or mixtures of alpha- and beta-SiC with a particle size not larger than 5Jum corresponding to a specific surface of 4 to ~0 m /g, preferably of 5 - 10 m /g (measured according to the BET method), and a purity of at least 99.97% by weight based on the total amount of impurities due to elements of groups 3a and 5a of the Periodic System. These impurities are to be particularly understood to re~er to the elements Al, B and N, which altogether must not exceed 0.03% by weight of the SiC starting powder. The content of Al + B -~ N in the SiC powders preferably is less than 0.025% by weight. The best results are obtained with a content of Al + B + N of less than 0.0095% by weight.
It has been demonstrated that when a sintered body is Eormed from a SiC powder having a content of Al + B -~ N of about 0.0O% by weight, the specific electric resistance of the finished substrate material is lowered to 105 Ohm.cm. Adherent carbon which can be ~5~
present in the SiC powders is preEerably not yreater than 0.3% by weight and most preEerably not yreater than 0.2~ by weight. ~lowever, the small amount of oxygen present in the 5iC powder, which is generally predominantly in the form of adherent Si~2 is eormed as a result of oxidation of the SiC during the comrninuting operation, does not substantially degrade the electric resistance and thermal conductivity of the sintered body and therefore can be tolerated to a maximum of 0.6% by weight, but the oxygen content should preferably be less than 0.5~ by weight.
The sintering aids useful in the practice of the present invention are oxygen-containing aluminwn or magnesium compounds or mixtures thereof wich are either in the forrn o~ the oxide or mixed oxides such as ~12O3, MgO and spinel or can form oxides in situ like compounds such as MgCO3. The sintering aids must also be very pure and should have substantially the same particle size as tHe SiC
poweders used. These sintering aids are mixed homogeneously with the SiC powders in the defined amounts of 0.25 to 3.5 preferably 1 to 3 by weight, calculated as oxide or oxides. The homogeneous powder mixture are then compacted by molding to form preformed green bodies.
To facilitate forming the green bodies, the starting powder mixture can be mixed together with a temporary binder or be dispersed in a solution of the temporary binder in an organic solvent. Sinterable organic solvents are non~reactive relatively low boiling materials such as acetone or lower aliphatic alcohols having 1 to about 6 C
torns. Examples of suitable temporary binders are polyvinyl alcohol, stearic acid, polyethylene glycol, and camphor which can be used in amounts oE up to about 5% by weight, preferably up to about 3% hy weight, based on the total weight of the powder mixture. Use o-E a ~em~orary binder is not required.
The green bodies can be ~ormed by known molding processes, OJ': example, by forging press, isostatic press, injection molding, extrusion, slip casting or sheet casting at room temperature or at elevated temperature. After molding, the green bodies must have a theoretical density of at least 50%, preEerably at least 60% T~. The green bodies are porous structures with open porosity. Open porosity is understood to mean that the green bodies have pores or canals open at the surface. The green bodies are then preferably subjected to a thermal treatment by heating to 300 to 1200C before being provided with a gastight casing to ensure that during the hot isostatic compression no decomposition products Erom the binders or sintering aids hinder the densification operation or damage the casing.
The substrate materials according to the invention are prepared by isostatic hot pressing of the preEormed green bodies, oE
the homogeneous startincJ powder mixture, in a hermetically sealed casing, at a temperature of from 1700 to 2200C and a pressure of from 100 to 400 M Pa in a high-pressure autoclave using an inert gas as the pressure-transmitting medium. For carrying out this process, the preformed green bodies must be provided with a gas tight casing prior to being exposed to the high-pressure in the autoclave in order to prevent the gas used as pressure-transmitting medium from pene-trating into the green bodies and thereby hindering the compression.
The materials for said casings, which are hermetically sealed, must neither melt nor react with the green bodies at the pressing temperature (1700-2200C). They must be inert with respect to said green bodies. The casing must be suEEiciently plastic at the pressing temperature used, to adapt to the shape oE the body without tearing , and ensure that the gas pressure is uniEormly transmitted through the casing to the bodies. Examples oE useful casing materials that meet said requirements, are high-melting glasses such as pure quartz glass or high-melting ceramic materials. These ~naterials can be used in the form oE preEabricated casings or capsules in which the green bodies are introduced. The casings ~56~
together with the contents are then evacuated and herrnetically sealed. The casings can also be produced on the green bodies directly by coating, ~or instance, by applyiny a glass or cerarnic-like composition which is then melted or sintered under vacuum to form a gas tight casing. The expression "hermetically sealed casing"
is to be understood to refer to a cas;ng that i5 impervious to the pressure gas acting from outside an~ that does not contain in the casing, any substantial amount of residual gases that hinder the compression operation.
The green bodies provided with hermetically sealed casing are preferably placed in graphite containers and are then introduced into the high-pressure autoclaves and heated to the required compression temperature of at least 1700C. It is preferable to separately regulate pressure and temperature, that is, to raise the gas pressure only when the casing material reaches a temperature at which it can be deformed plastically. Preferably, argon or nitrogen is used as the inert gas for the transmission of pressure. The gas pressure applied to the casing is preferably in the range of from 150 to 250 MPa, which is reached by a slow increase of pressure at the ~inal temperature which is preferably in the range of 1800~ to 1950C. The optimum temperature used in each case depends on the fineness and purity of the SiC starting powder and should not be exceeded, since the danger exists that the substrate materials formed are practically pore free but have a "secondary re-crystallized microstructure" which is no longer homogeneous since some grains have become thicker than the rest. The "presence of a secondary recrystallized microstruc-ture" adversely affects the thermal conductivity.
After the pressure and temperature are lowered, the cooled substrate materials are removed from the high-pressure autoclave and removed from the casings, for instance, by sandblasting the glass or ceramic casings.
~2~ 9 The substrate materlals produce~ are practically free o~
pores and have a density of at least ~9.~%; and are also practicall~
texture-free as result oE the all-round application of pressure. ~rhe substrate materials have an isotropic microstructure so that their properties are not dependent on direction but are substantially the same in all directions.
Since the isostatic hot pressing takes p]ace at a relatively low temperature that i5, at a temperature which is generally about 100C lower than the temperature used in a conventional hot pressing process, only a slight grain growth occurs and the aluminum oxide or magnesium oxide sintering aids remain predominantly at the grain boundaries of the SiC. The fine-grain microstructure in the finished substrate material corresponds substantially to the grain distribu-tion in the starting powder mixture. ~ue to the high purity of the starting powder, the inclusion in the SiC grain of impurity atoms that increase the electric conductivity (Al, B and N) is accordingly low, the substrate materials of the invention have excellent electric insulating properties tha~ expressed as speciEic electric resistance at 300 K reach values of up to 1013 Ohm.cm and thermal conductivity values at 300 K of up to 260 W/mK.
As a result of the high density and the fine-grain isotropic microstructure, the substrate materials of the invention have a high mechanical strength which, expressed as bending strength measured according to the ~-point method, at room temperature, reaches values of at least 500 N/mm and thermal expansion coefficients of from 3.
to 3.4 x 10 6K in the range of from room temperature to 300C.
That the combination of properties namely, high density, high electric insulating capacity and high thermal conductivity, which characterize the substrate material of the invention, can be obtained by adding aluminum oxide and/or magnesiurn oxide to high-purity SiC
starting powders and forming the substrate by isostatic hot pressing, 5~5~
must be regarded as ~nexpected in view of the prior art. The prior art teaches that less pure SiC starting powders could be densiEied by conventional hot pressing by addition of alurninurn oxide alone but the materials produced had a relatively hiyh electrical conductivity and a low thermal conductivity; addition of magnesium oxide alone did not provide a powder which could be densified.
In the examples that follow the object of the invention is illustrated in detail.
Examples 1 to 9 (according to the invention):
The starting material was an alpha-SiC powder having a ,specific surface area (measured according to sET) of 12.5 m2/g and the following analysis:
~ we~
Ctotal 29.97 Cfree 0.18 O 0.3 Al 0 0O~O
B 0.0017 N 0.0035 Fe Ca 0.0020 ifree not determinable This SiC powder was homogeneously mixed with Einely dispersed aluminum oxide powder and/or magnesium carbonate powder in the indicated amounts by stirring in acetone. Shortly before terminating the mixing operation, 2.0% by weight camphor was incorporated as a temporary binder. The solvent was removed and the powder mixture pressed into cylindrical green bodies. The green bodies were ~2~5~
introduced into preformed quartz glass casings. The casings together with the green bodies were then heated under vacuum to remove the temporary binder and the casings were hermetically sealed by melting.
The encased samples were isostatica]ly hot pressed in a high-pressure autoclave under an argon pressure of 200 MPa at 1950C for 30 minutes. After decompression and cooling of the sintere~ bodies to room temperature, the sintered bodies were rernoved from the HIP
equipment and the glass casings removed by dismantling and sand-blasting The sintered bodies produced had a density of more than 99.8% TD. Test bodies were produced Erom the sintered bodies and surface grained to determine the heat conductivity, the specific electric resistance and the bending strength.
The thermal conductivity was determined according to the comparison bar method up to 927C using Armco Iron as reference material. The specific electric resistance was determined at room temperature (25C) with direct current according to the 3-point measuring method. The bending strength was measured according to the 4-point method with abutment spaces of 15 mm (top) and 30 mm (bottom) at room temperature. The thermal expansion coefficent was determined.
The following Table 1 sets forth the kind and amount o-E the sinterings aids, respectively calculated as oxide, and the meaSurement of the properties of the sintered bodies.
- ~ 2S6~5~
,, ., _ T~BL--L' 1 Example ~dit.ives in ~ by wt. ~ b ~ ~
~o. A123 MgO Ln ~/mn2 in W/mK in Ol~.an in 10-~/K
1 0,3 _ 6~0 190 1ol2 3 3 ~ 0.5 ~ 600 ~0 1013 3.3 3 1.0 - 530 2~0 1013 3.3 3.0 _ S00 205 loll 3 ~
- 0.5 ~00 180 lolO 3 3 6 _ 1.0 500 170 1ol2 3,~
7 - 3.0 ~70 170 109 3.~
8 0.3 0.3 550 190 1013 3.3 9 1.0 0.5 500 170 loll b = bending strength = thermal conduc~iYity ~ = specific electric resistiv.ity - -o~ - coefficien~ O:e thermal exp~nsion ~5~
Comparison E
The starting materials were an alpha-SiC powder having a high content of impurities (Al ~ B -~ N) and a specific sur~ace area of 12 - 13m2/g together with 0O5% by weight aluminum oxide. Sintered bodles were produced from the powder mixtures by a) isostatic hot pressing (HIP) under the same conditions as given in example 1 (temperature 1950C; pressure 200 M Pa; holding time 30 minutes) and b) conventional hot pressing (HP) in graphite molds (temperature 2000C; pressure 30 m Pa; holding time 60 minutes).
The thermal conductivity and the specific electric resistance of samples from the sintered bodies were determined. Table 2 contains a compilation of the contents of impurities (Al ~ B ~ N) in the alpha-SiC starting powder and the measurements of the sintered bodies produced therefrom according to a) and b).
_ _ Example No.
1~ 11 12 1 alpha-siC powder by wt. Al 0.0110 0.0420 0.0830 0.00~8 B 0.0035 0.0065 0.0095 0.0350 " N 0.0250 0.0175 0.0235 0.0065 " Sa:
Al + B + N 0.0395 0 0660 0.1160 ~.0463 Molded bodies prod. a) IHP
~ in W/mK 155 165 145 98 el. resist. - - 107 10-5 5 x_l_6 1o6_ Molded bodies prod. b) IMP
~ in W/mK 105 95 90 85 el. resist.
in Ohm.cm 103 103 103 105 _ _ . . _ The measurements in Table 2 clearly show the eEfect o~ the content of impurities (Al + s ~ N) in the SiC starting powder on the heat conductivity and the specific electric resistance oE the sintered bodies produced therefrom, which are degraded as the content oE said impurities increases. The measurements also show the e~Eect of the preparation process, since the sintered bodies produced Erom SiC powder with the same content oE impurities by convention hot pressing (HP) had lower heat conductivity and speci~ic electric resistance than the sintered bodies produced by isostatic hot pressing (HIP).
AND PROCESS FOR TIIE P~EP~RATION TMEREOF ~Y ISOSTATIC
HOT P~F~SSING
Polycrystalline silicon carbide has been known or a long time~ It has a combination of valuable properties such as high strength, resistance to oxidation, resistance to thermal shock, lo~
thermal expansion and high heat conductivity and is useful in many technological fields.
BACKGROUND OF THE INVENTION
Pure silicon carbide, because of its predominantly covalent bonding, is difficult to sinter. Dense bodies of polycrystalline silicon carbide can only be produced by known processes such as hot pressing and pressureless sintering using sintering aids. One of the oldest sintering aids for silicon carbide is alumina, which, during the sintering, combines with the impurities in the silicon carbide to Eorm a ~luid phase which promotes compaction and which is detectable as a separate phase in the finished sintered body.
In pressureless sintering, aluminum oxide promotes compaction of the SiC by combining with impurities in the SiC. Additional adjuvants such as aluminum, silicon and/or carbon compounds are known to be formed by interaction with the surrounding atmosphere during the sintering.
Silicon carbide can be densiEied by isostatic hot pressing to densities oE almost 100% of the theoretical density (hereinaEter abbreviated as % TD), without the use of sinterlng aids when a very pure SiC powder with a total content oE metallic impurities oE at most 0.1~ by weight is used. Compared to the usual hot pressed or pressureless sintered materials, the polycrystalline SiC sintered bodies have, as a result of their high purity, an improved heat ~1 ~25~
conductivity of 220 W/mK at room temperature. ~lowever, pure SiC has semiconductor properties, and dense sintered articles otained by isostatic hot pressing pure silicon carbide have a specific electric resistance of only about 100 Ohm. cm.
To be useful as a substrate material ~or microcircuitry and structural parts of power electronics, the specific electric resistance must be at least 107 Ohm. cm.
Tests have been conducted to increase the specific electric resistance of SiC by addition of adjuvants. Beryllium oxide has proved especially reuseful since it increases the electric resistance and acts as a sintering adjuvant in hot pressing or in pressureless sintering. Electrically insulating substrate materials o~ SiC
containing beryllium oxide and additionally containing up to 0.1% by weight aluminum, up to 0.1~ by weight boron and up to 0.4% by weight free carbon, with a heat conductivity of at least 167 W/m.K, are known. It has been demonstrated, by comparison tests, that using aluminum oxide instead of beryllium oxide, under otherwise equivalent conditions (HP at 2000C and 30 MPa), there was produced sintered bodies having 99% TD and high mechanical strength but a considerablY
lower thermal conductivity (75 W/m.K) and a specific electric resistance of only 10 Ohm.cm Poor results were also obtained by using aluminum carbide, aluminum nitride and aluminum phosphate instead of beryllium oxide.
Instead of beryllium oxide per se, it is also possible to use beryllium compounds or boron compounds such as boron nitride and other adjuvants to improve the sinterability oE SiC. It has been demonstrated, by comparison examples ~HP at 2000C and 27 MPa) that, when using aluminum oxide and beryllium oxide (1% by weight A12O3 +
1% by weight BeO) to sinter silicon carbide, a sintered body with a thermal conductivity of only 8~ W/mk was produced when using MgO
alone (2% by weight), the sintered body was not dense (55% 't'D).
~56~5~
By lowering the nitrogen content to not more than 500 ppm in the powder mixture of SiC + berylliwn cotnpounds beiny sintered, no decrease in the ~esired properties appeared even in large bodies.
Since beryllium compounds are toxic, attempts were made to use aluminum nitride alone (equal to or ~ 10~ by weight) or mixtures of aluminum nitride and boron nitride (5 - 15% by weight). Although sintered SiC bodies with adequate insulating properties were obtained, the thermal conductivity values were less than 100W/m~.
Sintered bodies of SiC and AlN with additions of calcium, barium or strontium oxide (0.1 to 3~ by weight) had only a slightly improved thermal conductivity.
The course of development of electronics in the last year has led to a reduction in size of the structural parts that is, the development of megabit chips. The requirements of substrate materials have thus increased. The substrate materials must have not only a high specific electric resistance but also a high thermal eonductivity whieh, in the case of SiC, had been obtained only by use of beryllium eompounds as sintering aids. Compare~ to other insulating materials such as aluminum oxide considered for this purpose, silicon carbide has the advantage of a high mechanical strength (bending strength of at least 500 N/mm2 at room temperature) and a thermal expansion coefficient similar to that of silicon (approximately 3.3 x 10 6/oC).
The problem is to develop a process to produce electrical insulating substrate materials of dense polycrystalline silicon carbide which meet these requirements without use of highly toxic compounds.
BRIEF SUMM~RY OF THE INVENTION
_ Aecording to the invention, electrical insulating substrate materials of polycrystalline silicon carbide having a density o~ at least 99.8% TD calculated on the theoretically possible density oE
pure SiC, are provided which consist essentially o~
at least 95.0~ by weight sil:icon carbide 0.25 - 3.5% by weight aluminuM oxide and/or magnesium oxide, up to 0.3% by weight free carbon and up to 0.03% by weight impurities oF elements o~ groups 3a and 5a oE the Periodic System (predominantly Al + B ~ N) in total, in which the silicon carbide is essentially in the form of a homogeneous isotropic microstructure with grain sizes of 5 um maximum, aluminum oxide and/or magnesium oxide are present predominantly in the grain boundary of the silicon carbide and are detectable as separate phase(s). The silicon carbide substrate materials o~ the present invention have the following properties:
thermal conductivity at 300 K of at least 170 W/mK
specific electric resistance at 300 K of at least 10 Ohm.cm a coefficient of thermal expansion up to 3.5 x l~ S/K in the range of from 20C to 300C and a dielectric strength of more than 20 kV~mmO
DETAILED DESCRIPTION OF THE INVENTION
The substrate materials according to the invention are prepared by sintering homogeneous powder mixtures of silicon carbide having a purity of at least 99.97% by weight based on total impurities of elements of groups 3a and 5a of the Periodic System (predominantly Al + ~ + N) and 0.25 to 3.5~ hy weight aluminum oxide and/or magnesium oxide in a hermetically sealed casing by isostatic hot pressing at a temperature of 1700 to 2200C and a pressure of 100 to ~00 MPa in a high pressure autoclave using an inert gas as a pressure-transmitting medium.
Since the sintering is accomplished in a hermetically sealed casing, nothing can escape during the isostatic hot pres.sing opera-~25~6~5~1 tion, the substrate materials of the invention have a density of atleast 99.g~ TD, preferably 100% TD, and the same chemical composition as the starting powder mixt~lre. It i,s critical that pure sta~ting powders be used so that the fin;,shed substrate material does not contain more than the critical amounts of up to 0.?% by weight free carbon and up to 0.03~ by weight of the total of elements oE groups 3a and 5a of the Periodic System which are understood to be predom-inantly Al -~ B + N.
The substrate materials of the invention consist predomin-antly of polycrystalline silicon carbide which has an isotropic microstructure in which the SiC grain having a maximum grain size oE
5 ~m are homogeneously distributed independently o~ direction while aluminum oxide and/or magnesium oxide are predominantly present at the grain boudaries of the SiC and can be detected as a separate phase or phases by X-ray diffraction analysis or ceramographically.
The substrate materials according to the invention are preferably prepared from fine powders of alpha- or beta-SiC or mixtures of alpha- and beta-SiC with a particle size not larger than 5Jum corresponding to a specific surface of 4 to ~0 m /g, preferably of 5 - 10 m /g (measured according to the BET method), and a purity of at least 99.97% by weight based on the total amount of impurities due to elements of groups 3a and 5a of the Periodic System. These impurities are to be particularly understood to re~er to the elements Al, B and N, which altogether must not exceed 0.03% by weight of the SiC starting powder. The content of Al + B -~ N in the SiC powders preferably is less than 0.025% by weight. The best results are obtained with a content of Al + B + N of less than 0.0095% by weight.
It has been demonstrated that when a sintered body is Eormed from a SiC powder having a content of Al + B -~ N of about 0.0O% by weight, the specific electric resistance of the finished substrate material is lowered to 105 Ohm.cm. Adherent carbon which can be ~5~
present in the SiC powders is preEerably not yreater than 0.3% by weight and most preEerably not yreater than 0.2~ by weight. ~lowever, the small amount of oxygen present in the 5iC powder, which is generally predominantly in the form of adherent Si~2 is eormed as a result of oxidation of the SiC during the comrninuting operation, does not substantially degrade the electric resistance and thermal conductivity of the sintered body and therefore can be tolerated to a maximum of 0.6% by weight, but the oxygen content should preferably be less than 0.5~ by weight.
The sintering aids useful in the practice of the present invention are oxygen-containing aluminwn or magnesium compounds or mixtures thereof wich are either in the forrn o~ the oxide or mixed oxides such as ~12O3, MgO and spinel or can form oxides in situ like compounds such as MgCO3. The sintering aids must also be very pure and should have substantially the same particle size as tHe SiC
poweders used. These sintering aids are mixed homogeneously with the SiC powders in the defined amounts of 0.25 to 3.5 preferably 1 to 3 by weight, calculated as oxide or oxides. The homogeneous powder mixture are then compacted by molding to form preformed green bodies.
To facilitate forming the green bodies, the starting powder mixture can be mixed together with a temporary binder or be dispersed in a solution of the temporary binder in an organic solvent. Sinterable organic solvents are non~reactive relatively low boiling materials such as acetone or lower aliphatic alcohols having 1 to about 6 C
torns. Examples of suitable temporary binders are polyvinyl alcohol, stearic acid, polyethylene glycol, and camphor which can be used in amounts oE up to about 5% by weight, preferably up to about 3% hy weight, based on the total weight of the powder mixture. Use o-E a ~em~orary binder is not required.
The green bodies can be ~ormed by known molding processes, OJ': example, by forging press, isostatic press, injection molding, extrusion, slip casting or sheet casting at room temperature or at elevated temperature. After molding, the green bodies must have a theoretical density of at least 50%, preEerably at least 60% T~. The green bodies are porous structures with open porosity. Open porosity is understood to mean that the green bodies have pores or canals open at the surface. The green bodies are then preferably subjected to a thermal treatment by heating to 300 to 1200C before being provided with a gastight casing to ensure that during the hot isostatic compression no decomposition products Erom the binders or sintering aids hinder the densification operation or damage the casing.
The substrate materials according to the invention are prepared by isostatic hot pressing of the preEormed green bodies, oE
the homogeneous startincJ powder mixture, in a hermetically sealed casing, at a temperature of from 1700 to 2200C and a pressure of from 100 to 400 M Pa in a high-pressure autoclave using an inert gas as the pressure-transmitting medium. For carrying out this process, the preformed green bodies must be provided with a gas tight casing prior to being exposed to the high-pressure in the autoclave in order to prevent the gas used as pressure-transmitting medium from pene-trating into the green bodies and thereby hindering the compression.
The materials for said casings, which are hermetically sealed, must neither melt nor react with the green bodies at the pressing temperature (1700-2200C). They must be inert with respect to said green bodies. The casing must be suEEiciently plastic at the pressing temperature used, to adapt to the shape oE the body without tearing , and ensure that the gas pressure is uniEormly transmitted through the casing to the bodies. Examples oE useful casing materials that meet said requirements, are high-melting glasses such as pure quartz glass or high-melting ceramic materials. These ~naterials can be used in the form oE preEabricated casings or capsules in which the green bodies are introduced. The casings ~56~
together with the contents are then evacuated and herrnetically sealed. The casings can also be produced on the green bodies directly by coating, ~or instance, by applyiny a glass or cerarnic-like composition which is then melted or sintered under vacuum to form a gas tight casing. The expression "hermetically sealed casing"
is to be understood to refer to a cas;ng that i5 impervious to the pressure gas acting from outside an~ that does not contain in the casing, any substantial amount of residual gases that hinder the compression operation.
The green bodies provided with hermetically sealed casing are preferably placed in graphite containers and are then introduced into the high-pressure autoclaves and heated to the required compression temperature of at least 1700C. It is preferable to separately regulate pressure and temperature, that is, to raise the gas pressure only when the casing material reaches a temperature at which it can be deformed plastically. Preferably, argon or nitrogen is used as the inert gas for the transmission of pressure. The gas pressure applied to the casing is preferably in the range of from 150 to 250 MPa, which is reached by a slow increase of pressure at the ~inal temperature which is preferably in the range of 1800~ to 1950C. The optimum temperature used in each case depends on the fineness and purity of the SiC starting powder and should not be exceeded, since the danger exists that the substrate materials formed are practically pore free but have a "secondary re-crystallized microstructure" which is no longer homogeneous since some grains have become thicker than the rest. The "presence of a secondary recrystallized microstruc-ture" adversely affects the thermal conductivity.
After the pressure and temperature are lowered, the cooled substrate materials are removed from the high-pressure autoclave and removed from the casings, for instance, by sandblasting the glass or ceramic casings.
~2~ 9 The substrate materlals produce~ are practically free o~
pores and have a density of at least ~9.~%; and are also practicall~
texture-free as result oE the all-round application of pressure. ~rhe substrate materials have an isotropic microstructure so that their properties are not dependent on direction but are substantially the same in all directions.
Since the isostatic hot pressing takes p]ace at a relatively low temperature that i5, at a temperature which is generally about 100C lower than the temperature used in a conventional hot pressing process, only a slight grain growth occurs and the aluminum oxide or magnesium oxide sintering aids remain predominantly at the grain boundaries of the SiC. The fine-grain microstructure in the finished substrate material corresponds substantially to the grain distribu-tion in the starting powder mixture. ~ue to the high purity of the starting powder, the inclusion in the SiC grain of impurity atoms that increase the electric conductivity (Al, B and N) is accordingly low, the substrate materials of the invention have excellent electric insulating properties tha~ expressed as speciEic electric resistance at 300 K reach values of up to 1013 Ohm.cm and thermal conductivity values at 300 K of up to 260 W/mK.
As a result of the high density and the fine-grain isotropic microstructure, the substrate materials of the invention have a high mechanical strength which, expressed as bending strength measured according to the ~-point method, at room temperature, reaches values of at least 500 N/mm and thermal expansion coefficients of from 3.
to 3.4 x 10 6K in the range of from room temperature to 300C.
That the combination of properties namely, high density, high electric insulating capacity and high thermal conductivity, which characterize the substrate material of the invention, can be obtained by adding aluminum oxide and/or magnesiurn oxide to high-purity SiC
starting powders and forming the substrate by isostatic hot pressing, 5~5~
must be regarded as ~nexpected in view of the prior art. The prior art teaches that less pure SiC starting powders could be densiEied by conventional hot pressing by addition of alurninurn oxide alone but the materials produced had a relatively hiyh electrical conductivity and a low thermal conductivity; addition of magnesium oxide alone did not provide a powder which could be densified.
In the examples that follow the object of the invention is illustrated in detail.
Examples 1 to 9 (according to the invention):
The starting material was an alpha-SiC powder having a ,specific surface area (measured according to sET) of 12.5 m2/g and the following analysis:
~ we~
Ctotal 29.97 Cfree 0.18 O 0.3 Al 0 0O~O
B 0.0017 N 0.0035 Fe Ca 0.0020 ifree not determinable This SiC powder was homogeneously mixed with Einely dispersed aluminum oxide powder and/or magnesium carbonate powder in the indicated amounts by stirring in acetone. Shortly before terminating the mixing operation, 2.0% by weight camphor was incorporated as a temporary binder. The solvent was removed and the powder mixture pressed into cylindrical green bodies. The green bodies were ~2~5~
introduced into preformed quartz glass casings. The casings together with the green bodies were then heated under vacuum to remove the temporary binder and the casings were hermetically sealed by melting.
The encased samples were isostatica]ly hot pressed in a high-pressure autoclave under an argon pressure of 200 MPa at 1950C for 30 minutes. After decompression and cooling of the sintere~ bodies to room temperature, the sintered bodies were rernoved from the HIP
equipment and the glass casings removed by dismantling and sand-blasting The sintered bodies produced had a density of more than 99.8% TD. Test bodies were produced Erom the sintered bodies and surface grained to determine the heat conductivity, the specific electric resistance and the bending strength.
The thermal conductivity was determined according to the comparison bar method up to 927C using Armco Iron as reference material. The specific electric resistance was determined at room temperature (25C) with direct current according to the 3-point measuring method. The bending strength was measured according to the 4-point method with abutment spaces of 15 mm (top) and 30 mm (bottom) at room temperature. The thermal expansion coefficent was determined.
The following Table 1 sets forth the kind and amount o-E the sinterings aids, respectively calculated as oxide, and the meaSurement of the properties of the sintered bodies.
- ~ 2S6~5~
,, ., _ T~BL--L' 1 Example ~dit.ives in ~ by wt. ~ b ~ ~
~o. A123 MgO Ln ~/mn2 in W/mK in Ol~.an in 10-~/K
1 0,3 _ 6~0 190 1ol2 3 3 ~ 0.5 ~ 600 ~0 1013 3.3 3 1.0 - 530 2~0 1013 3.3 3.0 _ S00 205 loll 3 ~
- 0.5 ~00 180 lolO 3 3 6 _ 1.0 500 170 1ol2 3,~
7 - 3.0 ~70 170 109 3.~
8 0.3 0.3 550 190 1013 3.3 9 1.0 0.5 500 170 loll b = bending strength = thermal conduc~iYity ~ = specific electric resistiv.ity - -o~ - coefficien~ O:e thermal exp~nsion ~5~
Comparison E
The starting materials were an alpha-SiC powder having a high content of impurities (Al ~ B -~ N) and a specific sur~ace area of 12 - 13m2/g together with 0O5% by weight aluminum oxide. Sintered bodles were produced from the powder mixtures by a) isostatic hot pressing (HIP) under the same conditions as given in example 1 (temperature 1950C; pressure 200 M Pa; holding time 30 minutes) and b) conventional hot pressing (HP) in graphite molds (temperature 2000C; pressure 30 m Pa; holding time 60 minutes).
The thermal conductivity and the specific electric resistance of samples from the sintered bodies were determined. Table 2 contains a compilation of the contents of impurities (Al ~ B ~ N) in the alpha-SiC starting powder and the measurements of the sintered bodies produced therefrom according to a) and b).
_ _ Example No.
1~ 11 12 1 alpha-siC powder by wt. Al 0.0110 0.0420 0.0830 0.00~8 B 0.0035 0.0065 0.0095 0.0350 " N 0.0250 0.0175 0.0235 0.0065 " Sa:
Al + B + N 0.0395 0 0660 0.1160 ~.0463 Molded bodies prod. a) IHP
~ in W/mK 155 165 145 98 el. resist. - - 107 10-5 5 x_l_6 1o6_ Molded bodies prod. b) IMP
~ in W/mK 105 95 90 85 el. resist.
in Ohm.cm 103 103 103 105 _ _ . . _ The measurements in Table 2 clearly show the eEfect o~ the content of impurities (Al + s ~ N) in the SiC starting powder on the heat conductivity and the specific electric resistance oE the sintered bodies produced therefrom, which are degraded as the content oE said impurities increases. The measurements also show the e~Eect of the preparation process, since the sintered bodies produced Erom SiC powder with the same content oE impurities by convention hot pressing (HP) had lower heat conductivity and speci~ic electric resistance than the sintered bodies produced by isostatic hot pressing (HIP).
Claims (3)
1. A sintered body of polycrystalline silicon carbide having a density of at least 99.8% TD, based on the theoretically possible density of pure SiC, consisting essentially of at least 95.0% by weight silicon carbide, 0.25 to 3.5% by weight aluminum oxide and/or magnesium oxide, up to 0.3% by weight free carbon and up to 0.03 by weight impurities of elements of groups 3a and 5a of the Periodic System (predominantly Al + B + N) in total, wherein the silicon carbide has a substantially homogeneous, isotropic microstructure with grain sizes not larger than 5µm aluminum oxide and/or magnesium oxide are detectable as separate phase or phases predominantly present at the grain boundaries of the silicon carbide said sintered body having a thermal conductivity at 300 K of at least 170W/mK, a specific electric resistance at 300 K of at least 109 Ohm.cm, a coefficient of thermal expansion of up to 3.5 x 10-6/K in the range of from 20° to 300°C and a dielectric strength greater than 20 kV/mm.
2. A sintered body of claim 1, produced by forming a homogeneous powder mixture of silicon carbide with a purity of at least 99.97% by weight based on impurities due to elements from groups 3a and 5a of the Periodic System (predominantly A1 + B + N) in total, and from 0.25 to 3.5% by weight aluminum oxide and/or magnes-ium oxide; forming a green body by compacting the powder mixture;
encasing the green body in a hermetically sealed evacuated casing;
and isostatic hot pressing said encased green body at a temperature of from 1700° to 2200°C and a pressure of from 100 to 400 MPa in a high-pressure autoclave using an inert gas as pressure-transmitting medium.
encasing the green body in a hermetically sealed evacuated casing;
and isostatic hot pressing said encased green body at a temperature of from 1700° to 2200°C and a pressure of from 100 to 400 MPa in a high-pressure autoclave using an inert gas as pressure-transmitting medium.
3. A process for preparing a sintered body of claim 1 which comprises preparing a homogeneous powder mixture of silicon carbide powder having a particle size not greater than 5 µm and a purity of at least 99.97% by weight based on impurities due to elements from groups 3a and 5a of the Periodic System (predominantly Al + B + N) in total, with 0.25 to 3.5% by weight of an oxygen-containing aluminum or magnesium compound or mixtures thereof calculated as oxide or oxides; compacting the homogeneous powder mixture to form a green body having a density of at least 50% TD, encasing the preformed green body in a casing of high-melting glass or ceramic; hermetically sealing the casing under vacuum to form an encased green body; isostatically hot pressing the encased green body at a temperature of from 1700°C to 2200°C while slowly raising the pressure to from 100 to 400 MPa by a gas used as pressure-transmit-ting medium to form a substantially pore-free sintered body having density of at least 99.8% by weight TD and the same chemical composition as the starting powder mixture; and cooling and reducing the pressure to recover the sintered body.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP3621450.7 | 1986-06-26 | ||
| DE19863621450 DE3621450A1 (en) | 1986-06-26 | 1986-06-26 | ELECTRICALLY INSULATING SUBSTRATE MATERIALS MADE OF POLYCRYSTALLINE SILICON CARBIDE AND METHOD FOR THEIR PRODUCTION THROUGH ISOSTATIC HOT PRESSING |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1256459A true CA1256459A (en) | 1989-06-27 |
Family
ID=6303776
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000539761A Expired CA1256459A (en) | 1986-06-26 | 1987-06-16 | Electric insulating polycrystalline silicon carbide and process for the preparation thereof by isostatic hot pressing |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0251218A3 (en) |
| JP (1) | JPS638261A (en) |
| CA (1) | CA1256459A (en) |
| DE (1) | DE3621450A1 (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1991006515A1 (en) * | 1989-10-26 | 1991-05-16 | Western Mining Corporation Limited | DENSE SiC CERAMIC PRODUCTS |
| WO1993012051A1 (en) * | 1991-12-13 | 1993-06-24 | Commonwealth Scientific And Industrial Research Organisation | Dense ceramic product |
| US6531423B1 (en) | 1999-07-15 | 2003-03-11 | Wacker-Chemie Gmbh | Liquid-phase-sintered SiC shaped bodies with improved fracture toughness and a high electric resistance |
| US7989380B2 (en) | 2008-11-26 | 2011-08-02 | Ceradyne, Inc. | High resistivity SiC material with B, N and O as the only additions |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5995645A (en) * | 1982-11-24 | 1984-06-01 | Toshiba Corp | Information arranging device |
| JP2551563Y2 (en) * | 1993-04-06 | 1997-10-22 | 横浜特殊船舶株式会社 | Lifting device for motorcycle |
| JPH07304510A (en) * | 1994-05-11 | 1995-11-21 | Yokohama Tokushu Senpaku Kk | Step lifting device for motorcycle |
| JPH11508868A (en) * | 1995-07-13 | 1999-08-03 | ネガバット、ゲゼルシャフト、ミット、ベシュレンクテル、ハフツング | Manufacturing method of electrically insulating silicon carbide |
| EP0940239B1 (en) * | 1998-03-06 | 2004-01-28 | Matsushita Electric Industrial Co., Ltd. | Recycling of cured phenolic resin |
| US7727919B2 (en) * | 2007-10-29 | 2010-06-01 | Saint-Gobain Ceramics & Plastics, Inc. | High resistivity silicon carbide |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5537414A (en) * | 1978-09-04 | 1980-03-15 | Hitachi Ltd | Manufacture of silicon carbide sintered body |
| DE2923728A1 (en) * | 1979-06-12 | 1980-12-18 | Kempten Elektroschmelz Gmbh | DENSITY MOLDED BODIES MADE OF POLYCRYSTALLINE ALPHA-SILICON CARBIDE AND METHOD FOR THEIR PRODUCTION BY HOT PRESSING |
| DE3064598D1 (en) * | 1979-11-05 | 1983-09-22 | Hitachi Ltd | Electrically insulating substrate and a method of making such a substrate |
| DE3129633A1 (en) * | 1981-07-28 | 1983-02-17 | Elektroschmelzwerk Kempten GmbH, 8000 München | "PRACTICAL, PORE-FREE SHAPED BODIES MADE OF POLYCRISTALLINE SILICON CARBIDE, MADE BY ISOSTATIC HOT PRESSING" |
| JPS5899172A (en) * | 1981-12-07 | 1983-06-13 | 株式会社日立製作所 | Electric insulating silicon carbide sintered body |
-
1986
- 1986-06-26 DE DE19863621450 patent/DE3621450A1/en not_active Withdrawn
-
1987
- 1987-06-16 CA CA000539761A patent/CA1256459A/en not_active Expired
- 1987-06-25 EP EP87109163A patent/EP0251218A3/en active Pending
- 1987-06-26 JP JP62157971A patent/JPS638261A/en active Pending
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1991006515A1 (en) * | 1989-10-26 | 1991-05-16 | Western Mining Corporation Limited | DENSE SiC CERAMIC PRODUCTS |
| AU637424B2 (en) * | 1989-10-26 | 1993-05-27 | Advanced Materials Enterprise Pty Ltd | Dense sic ceramic products |
| WO1993012051A1 (en) * | 1991-12-13 | 1993-06-24 | Commonwealth Scientific And Industrial Research Organisation | Dense ceramic product |
| US5855842A (en) * | 1991-12-13 | 1999-01-05 | Commonwealth Scientific And Industrial Research Organisation | Process for producing a dense ceramic product |
| US6531423B1 (en) | 1999-07-15 | 2003-03-11 | Wacker-Chemie Gmbh | Liquid-phase-sintered SiC shaped bodies with improved fracture toughness and a high electric resistance |
| US7989380B2 (en) | 2008-11-26 | 2011-08-02 | Ceradyne, Inc. | High resistivity SiC material with B, N and O as the only additions |
Also Published As
| Publication number | Publication date |
|---|---|
| DE3621450A1 (en) | 1988-01-14 |
| EP0251218A3 (en) | 1988-03-23 |
| EP0251218A2 (en) | 1988-01-07 |
| JPS638261A (en) | 1988-01-14 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA1261887A (en) | Dense molded bodies of polycrystalline aluminum nitride and process for preparation without use of sintering aids | |
| CA1194041A (en) | Dense shaped articles consisting of polycrystalline hexagonal boron nitride and process for their manufacture by isostatic hot-pressing | |
| CA1201730A (en) | SUBSTANTIALLY PORE FREE SINTERED POLYCRYSTALLINE ARTICLES OF .alpha.- SILICON CARBIDE, BORON CARBIDE AND FREE CARBON AND PROCESS OF MANUFACTURE | |
| US3853566A (en) | Hot pressed silicon carbide | |
| US4560668A (en) | Substantially pore-free shaped articles of polycrystalline silicon carbide, and a process for their manufacture by isostatic hot-pressing | |
| CA1230217A (en) | Refractory, electrically conductive, mixed materials containing boron nitride and process for their manufacture | |
| CA1272581A (en) | Nitriding silicon powder articles using high temperature and pressure dwells | |
| EP0626358A2 (en) | Electrically conductive high strength dense ceramic | |
| CA1256459A (en) | Electric insulating polycrystalline silicon carbide and process for the preparation thereof by isostatic hot pressing | |
| EP0166073B1 (en) | Aluminum nitride sintered body | |
| US5744411A (en) | Aluminum nitride sintered body with high thermal conductivity and its preparation | |
| US4564601A (en) | Shaped polycrystalline silicon carbide articles and isostatic hot-pressing process | |
| US4467043A (en) | Dense shaped articles of polycrystalline α-silicon carbide and process for the manufacture thereof by hot-pressing | |
| CA1079308A (en) | Hot pressed silicon carbide containing beryllium carbide | |
| Hirano et al. | Sintering and characterization of fully dense aluminium nitride ceramics | |
| EP0520211B1 (en) | Silicon nitride ceramics containing a dispersed pentamolybdenum trisilicide phase | |
| US5063184A (en) | Pressureless sintered body of boron nitride | |
| EP0540671B1 (en) | Preparing silicon nitride with densification aid, and results | |
| JP3472585B2 (en) | Aluminum nitride sintered body | |
| Wei et al. | Pressureless sintering of AlN-SiC composites | |
| CA1192389A (en) | Polycrystalline sintered compacts based on europium hexaboride and process for their manufacture | |
| WO1990002717A1 (en) | Increasing aluminum nitride thermal conductivity via pre-densification treatment | |
| US5746969A (en) | Process for the production of dense silicon nitride materials | |
| Cheng et al. | Boron nitride–aluminum nitride ceramic composites fabricated by transient plastic phase processing | |
| JPS6146431B2 (en) |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |