Method of producing aluminium nitride-based heat-conducting ceramic. RU patent 2433108.

FIELD: chemistry.

SUBSTANCE: invention relates to production of aluminium nitride-based heat-conducting ceramic which can be used in electronics and electrical engineering, particularly as substrate material for powerful microwave and power semiconductor devices, as well as other devices where there is need for good dielectric properties, strength and heat conductivity of the material. Powder of aluminium nitride with particle size less than 1 mcm, containing not less than 10% cubic phase of aluminium nitride with particle size less than 100 nm, and a technical additive selected from Y₂O₃, CaO, MgO in amount of not more than 6 wt % is used to prepare a mixture, with addition of not more than 65 vol. % organic component containing a solvent (mixture of methylethyl ketone with ethanol in ratio of 1:2), a dispersant (phosphate ether), binder (polyvinyl butyral) and a plasticiser (mixture of polyethylene glycol with dibutyl phthalate), followed by stirring with simultaneous deaeration for not less than 30 minutes rarefaction of air of not less than 0.15 atm. A belt is formed from the obtained slip, dried and cooled to room temperature. A plate is formed from the belt. The organic component is removed at temperature 150-500°C. The obtained half-finished product is sintered at pressure 0.1-1.0 MPa in the atmosphere of a nitrogen-containing gas at temperature 1650-1820°C for 1-3 hours and then cooled under given conditions.

EFFECT: increase in heat-conductivity to 230 W/m·K, strength and output of the ceramic material.

4 cl, 4 ex, 2 tbl

The invention relates to the production of ceramic materials, in particular to the manufacturing of ceramics on the basis of nitride of aluminium with a high thermal conductivity, when combined method of slip casting and powder sintering under the pressure of nitrogen-containing gas.

Ceramics on the basis of aluminum nitride (AlN) high thermal conductivity is intended for use in electronics and electrical, primarily as a material substrate of high power microwave semiconductor devices (diodes, transistors, thyristors), chips, micro and multichip modules, thermal modules and substrates high-power LEDs, as well as other components and devices that require high dielectric characteristics, strength and thermal conductivity of the material.

Ceramics on the basis of aluminum nitride is intended to replace the ceramics of beryllium oxide EEO, because initial powders EEO are highly toxic and have a harmful effect both on the human body (a carcinogenic effect), and environment. Powders of beryllium oxide in Russia or produced. Currently all ceramics with high thermal conductivity as AlN, and EEO, supplied to Russia only by import. Therefore, the problem of obtaining ceramics on the base of aluminum nitride is topical and timely.

In Russia, attempts were made to the production of AlN ceramic method of hot pressing and casting under pressure, but they all ended in failure for the following reasons:

- low the quality of the initial powder AlN;

- low productivity of the method of hot pressing and high cost of the finished goods;

- the lack of demand for ceramics of AlN, first of all, due to the lack of norms of technical specifications for such ceramics, intended for use in electronics, and the absence at that time experience with its metallization.

Analogues on the characteristics described in the present invention of ceramics was not produced in Russia.

A method of obtaining dense heat-conductive ceramics on the base of aluminum nitride, including sintering of powder aluminum nitride, obtained by a carbothermic method, in the presence of 2 wt.% yttrium oxide or alkali earth metal oxide at a temperature 1850-1900 degC in the environment of nitrogen, followed by annealing of sintered ceramics at a temperature 1820-1880 OC for 4-12 hours in a stream of nitrogen and hydrogen (EN 2029752, 04 35/58, 1995).

This method economic and easy, but it allows to obtain ceramics with low thermal conductivity (not exceeding 150 W/m·K). A method of obtaining ceramic products, including on the basis of nitride of aluminium, which is that prepare an exothermic powder mixture containing at least one component from the group of metal III-VIII group of the periodic system of elements, boron, silicon, carbon, as well as at least one inorganic compound from the group of , iron silicide, nitride of transition metals IVB-VIB groups; carbide, nitride, oxide of silicon nitride, aluminum oxide; boron nitride, oxide of item II-IV group of the mixture is formed into the harvesting of products, which is subjected to heat treatment in combustion mode in the environment of nitrogen-containing gas under temperature control from 2000 to 3000 OC and pressure from 0.1 to 1000 MPa (SU 1720258 A1, 04 35/58, 04 35/65, 1995). The porosity of the obtained products - 1-10%, strength - 25-40 kg/mm 2 , microhardness up to 91 HRA. A well-known method were obtained not only products, but also the plate, however, thermal conductivity of such plates, as well as the products does not exceed 150 W/m·K.

There is a method of obtaining heat-conductive ceramics on the base of aluminum nitride with high thermal conductivity, which includes batch preparation of aluminum nitride powder in the form of microcrystals with the needle form of particles obtained in the mode of self-propagating high temperature synthesis, or a mixture of received by any known method aluminum nitride with not less than 5 wt.% aluminum nitride, obtained in the mode of self-propagating high temperature synthesis (in combustion mode) and containing particles in the form of a single crystal fibers, in the presence of not more than 6% of yttrium oxide, training charge by pelleting of the charge on a bunch of synthetic rubber in gasoline, pressing her into the steel to the mould at a pressure of 0.1 MPa, then compacts with the density of 2.2-2.4 g/cm 3 is placed in a graphite glass with filling of coarse powder aluminum nitride, produce subsequent sintering compacts at a temperature 1850-1900 OC for 1 hour in the environment of chemical nitrogen at a pressure of not less than 0.12 MPa with the annealing of sintered ceramics in the same gas environment at a temperature of 1750-1800 OC for 8-10 hours (EN 2144010 C1, C04B 35/581, 2000). Known technological and economical way to obtain heat-conductive ceramics on the basis of nitride of aluminium provides thermal conductivity 206-217 W/m·K when using powders with ordinary level of impurities. The disadvantages of this invention are the low strength of the material bending (not more than 150 MPa), high degree of shrinkage during preparation charge before sintering (over 30%) and a low output suitable to use the material (60%).

The closest analogue of the claimed invention for the totality essential sign is a method of obtaining heat-conductive ceramics from aluminum nitride, disclosed in the patent US 4814302, 04 35/58, 21.03.1989. The known method includes batch preparation of powders of aluminum nitride with particle size of less than 2 microns and specific surface of 10 m 2 /g and sintering additives, selected from a number of Y 2 O 3 , CaO, MgO, in the amount not more than 6 wt.% preparation of foundry slip of the powders - inorganic component and an organic component, solvent, dispersant, binder and plasticizer, forming the slip in the form of tape, drying, forming of a tape of semi finished products in the form of plates and sintering of a semifinished product at a temperature of more than 1700°under pressure in an atmosphere of nitrogen-containing gas.

The main disadvantages of this method are its low thermal conductivity and low strength of the target product bending due to the high content of impurities in the original aluminum nitride (more than 3%weight), the high degree of shrinkage (over 30%).

The technical result of the invention is to increase thermal conductivity, strength and output heat-conductive ceramics at lowering the degree of shrinkage.

The technical result is achieved when combined method of slip casting and high-temperature sintering of semi-products (semi-product) in nitrogen-containing atmosphere.

The technical result is achieved by the method of obtaining heat-conductive ceramics on the base of aluminum nitride, including the preparation of the charge of powders of aluminum nitride and sintering additives, selected from a number of Y 2 O 3 , CaO, MgO, in the amount not more than 6 wt.% preparation of foundry slip of the powders - inorganic component and an organic component, casting, drying and high-temperature sintering the resulting semi-finished product, according to the invention as aluminum nitride powder is used, containing not less than 10% of the cubic phase aluminum nitride with nanosized particles of less than 100 nm, cooking foundry slip includes consistently mixing the components of the charge, in which add not more than 65% the organic component, containing as a solvent mixture of methyl ethyl ketone with ethanol in the ratio 1:2, as phosphate ester, mainly BEYCOSTAT C213 as a binder polyvinyl butyral PVB and as a plasticizer mix polyethylene glycol with dibutyl phthalate, mainly in the ratio 1:1; mixing of the components with simultaneous for at least 30 minutes after diverging air not less than 0,015 MPa; submission received the slip in the injection-molding machine for the formation of a ribbon by thickness from 0.1 to 1.5 mm, with a density of 1,90-2.0 g/cm 3 , with the speed of the conveyor 10 mm/min, drying tape at a temperature of 30 to 40 degrees C for not more than 180 minutes; subsequent cooling of the tape to the room temperature at the exit from the installation cast in the natural way; the forged plates from a tape by stamping; the following heating plates at a temperature of 400 to 500 degrees, if which the removal of the organic components component, then the resulting intermediate product in the form of billets is sintered under the pressure of 0,1-1,0 MPa in an atmosphere of nitrogen-containing gas with a temperature of 1650-1820 OC for 1-3 hours, with the subsequent cooling of the obtained ceramics up to 1200C, at The rate of 100 C/hour, then at the rate of 300 Deg/hour to room temperature. Before the moulding, the plates in the ribbon perform perforation holes with a diameter of 0.2 mm and more. As a nitrogen-containing gas using nitrogen or a mixture of nitrogen with hydrogen or argon, in an amount not exceeding 10% the supplements injected into the charge separately or in mixture.

As a powder aluminum nitride powder is used with a specific surface of 10-12 m 2 /g, with an average size particles less than 1 mm and containing not less than 10% of the cubic phase aluminum nitride with nanosized particles of less than 100 nm, when the content of impurities Of not more than 0,7% by weight; (C - 130-270 ppm; Ca - 200-240V ppm; Si - 39-48 ppm; Fe - 10 to 14 ppm. The use of such powder aluminum nitride promotes the formation of crystallization centers and decreasing the density of the final material to 96-98% from theoretical one.

Adding technological additives Y 2 O 3 , CaO, MgO, in the amount not more than 6% of the composition of the charge provides for the formation of dense structure of aluminum nitride during hot pressing, the introduction of oxides of magnesium and calcium allows stage of sintering under more mild conditions (T=1650-1750 OC and R=0,1-0,2 MPa), compared with the regime of sintering composition nitride, aluminum yttrium oxide (T=1750-1820 OC and P=0,1-1,0 MPa). Yttrium oxide also forms the properties of the liquid phase, providing seal ceramics, and clears it from the oxygen.

The use of slip casting of inorganic material-aluminium nitride (+technological additives and organic constituents helps reduce shrinkage during sintering of semi-finished products and increase the density or reduce the porosity of the final material. Each component of the organic component of the slip as elements of the process of slip casting and sintering, play their indispensable role and contribute along with the entire set of features of the invention achieve a technical effect.

Binder, which is used as polyvinyl butyral PVB, provides flexibility ceramic tape after casting, the possibility of its storage and processing (cutting, punching, perforating holes etc). Plasticizer, which is used as a mixture of polyethylene glycol with dibutyl phthalate, mainly in the ratio 1:1, ensures the softening of the binding substances and increasing the flexibility of ceramic tape after casting.

In addition, binder and plasticizer exclude sticking slip into the pipeline during the casting process.

These components of the organic component does not limit your ability to use other known components in preparation charge. In this case, the experiments have been worked out on the known components presented in the formula.

The essence of the method is confirmed by examples.

Example 1.

Prepare a mixture mixing of powders of aluminum nitride (95%by weight), produced by IFOR, with a specific surface of 10 m 2 /g, with particle sizes less than 1 mkm and yttrium oxide (5 wt.%) particles with the size less than 1 mm, aluminum nitride ceramics, contains 10 wt.% the cubic phase particles with the size ≤60 nm. Next the specified mix will be identified as the inorganic portion of K 1 of the slip. Then prepare the foundry slip, for this purpose in inorganic component (35 wt.%), contains aluminum nitride and Y 2 O 3 , add organic component K 2 , containing: solvent 53 wt.% as azeotropic mixture with ethanol methyl ethyl ketone (MEK/EtOH), dispersant, which is used as a phosphate ester, mainly brand BEYCOSTAT 213 in the amount of 0.6 wt.% binder 5,4% which is used as polyvinyl butyral PVB, plasticizer, which is used as a mixture of polyethylene glycol 3 wt.% with dibutyl phthalate 3 wt.%, in 1:1 ratio.

Preparation of the slip spend in spherical to a mill with grinding bodies. Ball mill should simultaneously provide and deaeration (removal of air bubbles) of the mixture components.

Mixing produce over one hour, at the time of the de-aeration 30 minutes after diverging air 0,15 ATM (0,015 MPa). The mixture (slurry) is served in the injection-molding machine with speed of movement of the container 10 mm/min Drying tape is carried out at temperature of 40 C within 150 min, followed by cooling tape at the exit from the installation naturally. From the resulting tape thickness of 0.1 mm shaped plate with a density of 2.0 g/cm 3 . Plate perforate to obtain holes with a diameter of 0.20 mm and more. After that formed the perforated plate is heated at a temperature of 400 to 500 OC to complete removal of the organic components component. Next, the resulting cake mix (blank) is sintered under nitrogen pressure of 1.0 MPa (10 bar) at a temperature of 1820 OC for 1 hour, with the subsequent cooling of the obtained temperature ceramics to 1200C, at The rate of 100 C/hour, then at the rate of 300 Deg/hour to room temperature.

Received ceramic is a product in the form of plates of aluminium nitride density of 98% from theoretical one, Flexural strength of 450 MPa, thermal conductivity 215 W/m·K at an output of suitable material of 85% and shrinkage 10%.

Example 2.

Prepare a mixture mixing of powders of aluminum nitride 94% with specific surface area 12 m2 /g, a particle size less than 1 microns and a mixture of calcium oxide and magnesium in equal shares (3+3=6 wt.%) particles with the size less than 1 mm, aluminum nitride contains 15 wt.% the cubic phase particles with the size ≤100 nm. Then prepare the foundry slip, for this purpose in inorganic fractions To 1 (36,0%), contains aluminum nitride and CaO+MgO, add organic component To 2 , including: solvent 51,0% Mas. as azeotropic mixture with ethanol methyl ethyl ketone (MEK/EtOH), dispersant, which is used as a phosphate ester, mostly brand BEYCOSTAT C213 in the amount of 0.4 wt. %, binder 5,6% which is used as polyvinyl butyral PVB, plasticizer, which is used as a mixture of polyethylene glycol 3.5% with dibutyl phthalate 3.5%, in 1:1 ratio.

Preparation of the slip spend in spherical to a mill with grinding bodies. Ball mill should simultaneously provide and deaeration (removal of air bubbles) from charge.

Mixing produce over one hour, at the time of the de-aeration 45 minutes after diverging air 0.1 bar (0.01 MPa). Ready slip served in the injection-molding machine with speed of movement of the container 10 mm/min Drying tape spend at 30 OC for 180 minutes, then cooling tape made at the exit from the installation naturally. From the obtained a tape thickness of 1,0 mm are formed plate with density 1,90 g/cm 3 , after which carry out heat received plates at a temperature of 400 to 500 OC to complete removal of the organic components component To 2 .

Next, the resulting cake mix (blank) in the form of plates is sintered under the pressure of 1 MPa (10 ATM) a mixture of nitrogen and 10% hydrogen at a temperature of 1650 OC for 3 hours, with the subsequent cooling of the obtained temperature ceramics to 1200C, at The rate of 100 C/hour, then at the rate of 300 Deg/hour to room temperature.

Prepare a mixture mixing of powders of aluminum nitride 97% obtained by the method of SHS-particles with the size less than 1 microns and a specific surface of 11 m 2 /g and Y 2 O 3 (3 wt.%) particles with the size less than 1 mm, aluminum nitride contains 25 wt.% the cubic phase particles with the size ≤90 nm. Then prepare foundry slip, for this purpose in inorganic fractions To 1 (35,0%), contains aluminum nitride and Y 2 O 3 , add organic component To 2 , including: solvent-52,4% Mas. as azeotropic mixture with ethanol methyl ethyl ketone (MEK/EtOH), dispersant, which use phosphate ester, mainly brand BEYCOSTAT 213 in the amount of 0.5% binder 5,4% which is used as polyvinyl butyral PVB, plasticizer, which is used as a mixture of polyethylene glycol 3,35 wt.% with dibutyl phthalate 3,35% in a ratio of 1:1.

Batch preparation is produced in a ball mill with grinding bodies with simultaneous .

Mixing produce over one hour, at the time of the de-aeration 30 minutes and vacuum air 0,15 ATM (0,015 MPa). Ready slip served in the injection-molding machine with speed of movement of the container 10 mm/min Drying tape spend at 30 OC for 180 minutes, then cooling tape is carried out at the exit from the installation naturally. From the obtained a tape thickness of 1,0 mm are formed plate with a density of 2.0 g/cm 3 , after followed by heating of the plates at a temperature of 400 to 500 degree C for complete removal of the organic component.

Next, the resulting intermediate product in the form of a plate without perforation holes is sintered under the pressure of 1.0 MPa (10 ATM) a mixture of nitrogen and 10% argon at temperature 1750 OC for 2 hours, with the subsequent cooling of the obtained temperature ceramics to 1200C, at The rate of 100 C/hour, then at the rate of 300 Deg/hour to room.

Received ceramics is a plate with a density of 98% from theoretical one, shrinkage of 8.0%, Flexural strength of 300 MPa and thermal conductivity 230 W/m·K. Output suitable for plates is 90%.

Example 4.

All, as in example 2, only additive is a blend of: 2 wt.% Y 2 O 3 +4 wt.% CaO, and sintering of conduct under nitrogen pressure of 0.1 MPa.

Received ceramics is a plate with a density of 98% from theoretical one, Flexural strength of 450 MPa, thermal conductivity 215 W/m·K at an output of suitable material of 85% and shrinkage 16%.

After sintering of ceramics grind and, if necessary, Polish. These operations are performed on special plants that provide automatic control of the thickness and surface quality. As abrasive materials used materials based on artificial diamond, which provide for the highest performance installations. Then measure the performance characteristics of the known methods.

Additionally, you can specify that improve productivity and the quality of AlN tape injection unit is available in two capacity for the slip, which are filled alternately, and of which alternately delivery slip for the smooth operation cast installation. Its length of the conveyor can be from 12 to 18 m, depending on the width and thickness of the manufactured AlN tape.

Blade cast installation provides for the formation of AlN tape certain thickness from 0,1 to 1,5 mm Typically, these units provide the tape's width to 300 or 600 mm. With more than a narrow ribbon will differ best quality, namely uniformity in thickness. Received the ribbon leaves in a roll. Usually before winding it is cut longitudinally on strips in width of 100-200 mm, the coils are starting material for sintering AlN ceramic. They can be stored for several weeks prior to sintering.

Directly before sintering of tape through stamping mold plate. The plates can be made perforation holes with a diameter of 0.25 mm and more, to prevent the closure of their walls in the sintering process. The sizes of plates, as a rule, should be no more than 150 x 150 mm, This is due to the effect of expansion them during sintering, because the edges of the plates in the stack is warmed faster than the middle. To exclude expansion of the plate in the microwave loaded in trays, providing uniform warming up of a stack of plates on the sides and in the middle. The cell are the «boxes», made of boron nitride, in that load plate, placing them one on one, and many layers of boron nitride powder.

For illustration, the table below summarizes the key parameters of the method and the properties of the resulting ceramics of the proposed method.

As can be seen from tables 1 and 2, the proposed method of manufacturing the ceramics based on aluminum nitride method combination of slip casting and high-temperature sintering under the excessive pressure of nitrogen-containing gas allows to obtain ceramics with a maximum value of thermal conductivity 230 W/m·K, bending strength 450 MPa, at an output suitable for plates up to 90%.

Components of inorganic 1 organic constituents To 2

The components of The 1 +2 for the slip in the sample,%

95 wt.% AlN, sod. 10 wt.% kubiš. phase + 5 wt.% Y 2 O 3

94 wt.% AlN, sod. 15 wt.% kubiš. phase + 6 wt.% (3CaO+3MgO)

by weight 97% AlN, sod. 25 wt.% kubiš. phase + 3 wt.% Y 2 O 3

95 wt.% AlN, sod. 25 wt.% kubiš. phase + 2 wt.% Y 2 O 3 +4 CaO

Solvent, azeotropic mixture with ethanol methyl ethyl ketone, MEK/EtOH

Dispersant, phosphate ester, Beycostat C213

Binder, polyvinyl butyral (PVB)

Plasticizer, Polyethylene Glycol: Dibutyl = 1:1

3,35+3,35

Parameters of synthesis of ceramics in examples

Gas environment

nitrogen + 10% hydrogen

nitrogen + 10% argon

Properties of ceramics on examples

Number example

Thermal conductivity, W/m·K

Bending strength, MPa

Shrinkage, %

Dielectric strength, kV/mm

KTR, 1·10 -6 /°

Volume resistivity, Ohm·cm

& GE 1·10 13

& GE 1·10 13

& GE 1·10 13

0,9·10 13

Dielectric constant (at f=1 MHz)

The output of metal material, %

1. The method of obtaining heat-conductive ceramics on the base of aluminum nitride, includes batch preparation of powders of aluminum nitride and sintering additives, selected from a number of Y 2 Of 3 , CaO, MgO, not more than 6 wt.% preparation of foundry slip of the powders - inorganic component and of the organic components, casting, drying and high-temperature sintering received semi-finished product, wherein as aluminum nitride powder is used, containing not less than 10% of the cubic phase aluminum nitride with nanosized particles of less than 100 nm, cooking foundry slip includes consistently mixing the components of the charge, in which add no more than 65% the organic component, containing as a solvent mixture of methyl ethyl ketone with ethanol in the ratio 1:2; as - phosphoric-acid ester, mainly BEYCOSTAT C213; as a binder - polyvinyl butyral PVB and as a plasticizer - polyethylene glycol mixture with dibutyl phthalate, mainly in the ratio 1:1; mixing of the components with simultaneous for at least 30 min after diverging air not less than 0,015 MPa; submission received the slip in the injection-molding machine for the formation of tape thickness from 0,1 to 1,5 mm, with a density of 1,90-2.0 g/cm 3 , with the speed of the conveyor 10 mm/min, drying tape at a temperature of 30 to 40 degrees C for not more than 180 minutes; subsequent cooling of the tape to the room temperature at the exit from the installation cast in the natural way; the forged plates of tape by stamping with the following heating plates at a temperature of 400 to 500 degrees, if which the removal of the organic components component, then the resulting intermediate product in the form of billets is sintered under the pressure of 0,1-1,0 MPa in an atmosphere of nitrogen-containing gas with a temperature of 1650-1820 OC for 1-3 hours with the subsequent cooling of the obtained ceramics up to 1200C, at The rate of 100 C/h, then at the rate of 300 C/h at room temperature.

2. The method according to claim 1, characterized in that before the moulding, the plates in the ribbon perform perforation holes with a diameter of 0.2 mm and more.

3. The method according to claim 1, characterized in that in the capacity of nitrogen-containing gas using nitrogen or a mixture of nitrogen with hydrogen, or with argon in an amount not exceeding 10%.

4. The method according to claim 1, characterized in that the supplements injected into the charge separately or in mixture.