CN115650759B - Porous alumina ceramic sheet applied to gas sensor packaging and preparation method thereof - Google Patents
Porous alumina ceramic sheet applied to gas sensor packaging and preparation method thereof Download PDFInfo
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Abstract
The application discloses a porous alumina ceramic sheet applied to gas sensor encapsulation and a preparation method thereof. The application combines the material formulation, the casting sheet tabletting and the sintering process, realizes the preparation of the large-area porous ceramic sheet with the thickness of micron level, and provides an effective method for the preparation of the ceramic sheet suitable for the encapsulation of the gas sensor. The porous alumina ceramic substrate provided by the application has the thermal conductivity of 6-8W/m.K (2-3W/m.K of general compact alumina), the mouth porosity of 5-8.5%, the water absorption of 2-5%, the pore diameter of 2-5 mu m, the tensile strength of 5.5-6.5MPa and the warpage of different batches of 7.5-9 mu m. The lower heat conductivity can be used on the sensor to store heat well, heat dissipation and energy consumption are reduced, and higher corresponding speed and sensitivity are ensured.
Description
Technical Field
The application belongs to the field of sensors, and relates to a porous alumina ceramic sheet applied to gas sensor packaging and a preparation method thereof.
Background
A gas sensor is a transducer that converts a certain gas volume fraction into a corresponding electrical signal. The probe conditions the gas sample with the gas sensor, typically including filtering out impurities and interfering gases, drying or refrigeration process meter display.
At present, the main technical research direction of the domestic sensor is MEMS (micro-mechanical electronic system), and a microprocessor and the sensor are integrated into a whole, so that the sensor becomes intelligent data terminal equipment with the functions of environment sensing, data processing, intelligent control and data communication. Gas sensor (e.g. CO, CO 2 ，H 2 ，NH 3 Gasoline, etc.) in order to ensure higher sensitivity and faster response speed, the sensor needs to operate at higher temperatures. At present, the domestic sensor chip material is mainly made of FR-4 substrate and compact ceramic. FR-4 substrates cannot withstand high temperatures; on one hand, the compact ceramic is generally alumina ceramic, and on the other hand, the problems of fast heat dissipation and unstable operation of the sensor exist; in addition, the bonding strength of the dense alumina ceramic and the metal layer is poor, so that the reliability is reduced, the work is unstable and the like.
Disclosure of Invention
The application aims to provide a porous alumina ceramic sheet applied to gas sensor packaging and a preparation method thereof.
The method for preparing the porous alumina ceramic flake provided by the application comprises the following steps:
1) Mixing alumina powder, a sintering aid, a solvent and a dispersing agent to obtain ceramic powder slurry, adding the complex phase ceramic powder and a ball milling medium provided by the application for performing first-stage ball milling, and adding a binder and a plasticizer for performing second-stage ball milling to obtain slurry;
2) Defoaming the slurry to obtain defoamed slurry;
3) Casting the defoamed slurry to obtain a casting film;
4) Removing the adhesive from the casting film to obtain a biscuit after the adhesive is removed;
5) And sintering the biscuit after the glue discharge while pressing to obtain the porous alumina ceramic sheet.
In the step 1) of the method, the sintering aid is a Ca-Mg-Si composite aid, wherein the molar ratio of Si to Mg to Ca is as follows: (5-20): (2-10): (1:5); specifically 11:3:1 or 15:2:5; when the proportion of the components is more than the range, the liquid phase sintering viscosity is rapidly reduced, the sintering condition is difficult to control, and the deformation is serious; when the ratio is smaller than the range, the liquid phase sintering viscosity is high, the sintering temperature needs to be greatly improved, and the porosity is difficult to control;
in the sintering aid, calcium is introduced in any one of calcium oxide, calcium carbonate and calcium hydroxide; magnesium is introduced in any one of magnesium oxide, magnesium hydroxide and magnesium silicate; silicon is introduced as any one of silicon dioxide and magnesium silicate;
the solvent is selected from any two of alcohol, butanone, isopropanol, toluene, xylene and acetic acid ethanol; in particular to an alcohol/toluene azeotropic solvent or an alcohol/butanone azeotropic solvent;
the dispersing agent is at least one of castor oil, phosphate, oleic acid, herring oil and BYK;
the binder is PVB;
the plastic agent is at least one selected from BBP, DOP and PEG;
the alumina powder accounts for 40-52% of the ceramic powder slurry by mass; specifically 45-50%;
the sintering aid accounts for 5-10% of the ceramic powder slurry by mass; specifically 8-9.8% or 9.3-9.7%;
the solvent accounts for 25-38% of the ceramic powder slurry by mass; specifically 29-33.8% or 31%;
the dispersant accounts for 0.1-2.0% of the ceramic powder slurry by mass; specifically 0.7%;
the composite ceramic powder accounts for 1-4% of the ceramic powder slurry by mass; specifically 1.5-2.6%;
the binder accounts for 3-10% of the ceramic powder slurry by mass; specifically 5-7.5% or 6.5%;
the plastic agent accounts for 1-5% of the ceramic powder slurry by mass; specifically, 2-3% or 2.1-2.7%;
the ceramic slurry is specifically any one of the following ceramic slurries a-e;
the ceramic slurry a comprises the following components in parts by mass:
alumina powder: 45-52%; sintering aid: 9.3-10%; dispersing agent: 0.7-1.5%; and (2) a binder: 6.5-7.5%; and (3) a plastic agent: 2.1-3.0%; solvent: 29-33.8%;
the ceramic slurry b comprises the following components in parts by mass:
alumina powder: 50-52%; sintering aid: 9.3-10%; dispersing agent: 0.7-1.5%; and (2) a binder: 6.5-7.5%; and (3) a plastic agent: 2.7-3.0%; solvent: 30-33.8%;
the ceramic slurry c comprises the following components in parts by mass:
alumina powder: 52%; sintering aid: 9.7%; dispersing agent: 0.7%; and (2) a binder: 6.5%; and (3) a plastic agent: 2.1%; solvent: 29%;
the ceramic slurry d comprises the following components in parts by mass:
alumina powder: 45%; sintering aid: 10%; dispersing agent: 0.7%; and (2) a binder: 7.5%; and (3) a plastic agent: 3.0%; solvent: 33.8%;
the ceramic slurry e comprises the following components in parts by mass:
alumina powder: 50%; sintering aid: 9.3%; dispersing agent: 1.5%; and (2) a binder: 6.5%; and (3) a plastic agent: 2.7%; solvent: 30%;
in the ball milling steps of the first stage and the second stage, the ball milling medium is alumina balls; the ball-material ratio is 1:2.5;
in the first-stage ball milling, the ball milling time is 20-48 hours;
in the second-stage ball milling, the ball milling time is 12-24 hours.
In the step, the composite ceramic powder particles are hydrolyzed in the slurry, the outer layer aluminum nitride is hydrolyzed into aluminum hydroxide, and the aluminum hydroxide can be dehydrated to form aluminum oxide in the subsequent sintering process, wherein the aluminum oxide is of a flaky structure. The reason may be that when aluminum hydroxide is converted into aluminum oxide, the aluminum oxide takes a certain area of the simple substance aluminum of the inner core as a nucleation core, and then is preferentially attached to new aluminum oxide to continue nucleation and growth.
The complex phase ceramic powder is used as a disperse phase, can slow down the growth of crystal grains in the sintering process, and avoids deformation or cracking of products caused by the overquick growth of the crystal grains. ( The dispersed phase is pinned at the grain boundary to prevent the grain boundary from moving too fast, so that the grains grow smoothly; the average size of the crystal grains is determined by the size and volume fraction of the dispersed phase, and when the volume fraction of the dispersed phase is fixed, the smaller the dispersed phase size is, the smaller the average size of the crystal grains is )
The complex phase ceramic powder is flaky in shape, has excellent spreadability and adhesion performance, can be well attached to a composite material, and is beneficial to improving the surface flatness of the composite material; when the composite material is stressed, the lamellar structure can also increase crack deflection and bridging action, so that the brittleness of the composite material is effectively reduced, namely the strength of the material is improved; and the thermal conductivity of the composite material can be improved, and the composite material can exhibit higher glossiness.
In the step 2) of defoaming, the vacuum degree is higher than-0.92 MPa, and the defoaming time is more than or equal to 1h, specifically 3-5h; defoaming until no bubbles are seen, wherein the viscosity is 15-25pa.s; specifically 18pa.s.
In the step 3), the thickness of the casting film is 0.1-1.2mm; specifically 0.3-0.5mm or 0.25mm;
in the isostatic pressing step, the temperature is 65-75 ℃; the pressure is 45-55MPa; the time is 60-90S;
when the tape casting method is adopted for preparing the green body, under the action of a scraper, flaky disperse phase ceramic powder is basically distributed in a laminated way, alumina powder is arranged between layers at intervals, and the alumina powder is generally of a spheroidal shape, so that the flaky disperse phase ceramic powder and the alumina spherical particles are communicated to form a heat conduction path, and the heat conductivity is improved.
In the step 4) of discharging the glue, the glue discharging curve is as follows:
the temperature is increased by 1-2 ℃/min at the room temperature of-200 ℃;
heating at 200-400 deg.c and rate of 0.2-1 deg.c/min;
heating at 400-650 deg.c at 1-3 deg.c/min;
preserving heat for 0.5-2h at 650 ℃;
in the step 5) of sintering, the sintering curve is as follows:
the temperature is increased by 5 to 10 ℃ per minute at the room temperature of between 600 ℃ and the room temperature;
600 ℃ to 130-1500 ℃, the heating rate is 3-5 ℃/min, and then the temperature is kept for 1-3h;
in the step of pressure sintering, the cooling rate from the highest temperature to 1000 ℃ is 1-2 ℃/min; the cooling rate from 1000 ℃ to 600 ℃ is 0.5-1 ℃/min; naturally cooling from 600 ℃ to room temperature;
the cover is not pressed or the porous ceramic pressing plate is used for providing pressure;
the porosity of the porous ceramic pressing plate is 20-25%;
the thickness of the porous ceramic pressing plate is 5-10 times of the thickness of the sintered biscuit;
the porous ceramic pressing plate protrudes by 1-10cm.
Ceramic flakes are susceptible to curling or warping during sintering, especially for areas greater than 100cm prepared without sintering pressure 2 And a ceramic platelet thickness of less than 500 microns. To solve the warpage problem, it is necessary to ensure that the material is uniformly transferred at every step in the preparation process, or that the sintering shrinkage variation is less than 1%. This is a requirement under the traditional formulation and conventional process, and there is no limitation on the new formulation and improved process, and 1% is difficult to achieve, so the raw materials and processes need to be improved, so that the process window of the preparation method is enlarged, and the industrial production is facilitated. The compact ceramic sheet has relatively high strength, so that the regulation and control range of a material formula and a process window is relatively large; the porous ceramic has extremely low strength and small window, and any change in preparation (such as deformation or cracking of a product caused by the proportion of a certain component in a formula or the tiny adjustment of a certain parameter in a process parameter) can cause the shape and or performance of the sintered product to be quite different, so that the preparation difficulty is far higher than that of dense ceramic. Thus, the preparation of porous ceramic sheets requires a unique combination of control strategies between the raw material formulation and the process parameters.
In addition, the porous alumina ceramic flake prepared by the method and the application of the porous alumina ceramic flake in sensor packaging also belong to the protection scope of the application.
Specifically, the sensor is a gas sensor.
The complex phase ceramic powder provided by the application consists of an inner core and an outer layer wrapping the inner core;
the material constituting the inner core is simple substance aluminum;
the material constituting the outer layer is aluminum nitride.
The method for preparing the complex phase ceramic powder provided by the application comprises the following steps: and carrying out high-temperature treatment on the aluminum powder in an inert atmosphere.
In the method, the average particle size of the aluminum powder is 4-8 mu m;
the inert atmosphere is nitrogen atmosphere;
in the high-temperature treatment step, the temperature is 800-1000 ℃ or 900 ℃;
the time is 20-60min or 40min.
The application combines the material formulation, the casting sheet tabletting and the sintering process, realizes the preparation of the large-area porous ceramic sheet with the thickness of micron level, and provides an effective method for the preparation of the ceramic sheet suitable for the encapsulation of the gas sensor.
The porous alumina ceramic substrate provided by the application has the thermal conductivity of 6-8W/m.K (2-3W/m.K of general compact alumina), the mouth porosity of 5-8.5%, the water absorption of 2-5%, the pore diameter of 2-5 mu m, the tensile strength of 5.5-6.5MPa and the warpage of different batches of 7.5-9 mu m. The lower heat conductivity can be used on the sensor to store heat well, heat dissipation and energy consumption are reduced, and higher corresponding speed and sensitivity are ensured. The perforated structure on the substrate can increase the bonding strength of the ceramic and metal layers and provide the reliability of the sensor as a whole. The alumina ceramic substrate prepared by the application effectively solves the problems of low bonding strength between the metal layer and the ceramic substrate and too fast heat dissipation.
Drawings
FIG. 1 is an SEM image of a porous alumina ceramic wafer prepared in example 3.
Detailed Description
The application will be further illustrated with reference to the following specific examples, but the application is not limited to the following examples. The methods are conventional methods unless otherwise specified. The starting materials are available from published commercial sources unless otherwise specified.
Example 1
1) The method comprises the following steps: aluminum powder with the average grain diameter of 4 mu m is treated for 20min at the high temperature of 1000 ℃ in nitrogen atmosphere to obtain complex phase ceramic powder with simple substance aluminum as an inner core and aluminum nitride as an outer layer;
the preparation of the ceramic slurry comprises the following specific components in percentage by mass:
alumina powder: 52%; sintering aid: 9.7%; dispersant castor oil: 0.7%; binder PVB:6.5%; plasticizer DOP:2.1%; solvent alcohol/toluene azeotropic solvent: 29%;
the sintering aid is Ca-Mg-Si composite aid, wherein the molar ratio of Si to Mg to Ca is 11:3:1; in the sintering aid, calcium is derived from calcium carbonate; magnesium is derived from magnesium oxide; silicon is from silicon dioxide;
preparing and weighing CaCO according to mass percent and mole ratio 3 、MgO、SiO 2 Placing alumina powder, a dispersing agent and a solvent into a ball milling tank, adding 26g of complex phase ceramic powder (accounting for 2.6 percent of the mass of the ceramic powder slurry), performing first-stage ball milling, wherein the ball milling medium is alumina balls, and the ball ratio is 1:2.5, ball milling time is 24 hours, continuously adding the binder and the plastic agent according to mass percent, and performing second-stage ball milling for 12 hours. And ball milling is carried out in two steps to obtain uniform slurry.
2) Defoaming device
And (3) stirring and defoaming the slurry obtained in the step (1) in vacuum, wherein the vacuum degree is higher than-0.92 MPa, the defoaming time is 3h (the defoaming time is until no bubbles are seen), and the viscosity is controlled at 18pa.
3) Casting process
And (3) casting the slurry obtained in the step (2) through a casting machine to obtain a casting film, wherein the thickness of the casting film is 0.3mm.
And (3) correcting uniformity of the green body: and (3) applying pressure in a specific direction to eliminate green stress (the peripheral shape of the casting film needs to be trimmed by a cutter before the glue discharge treatment (the cut peripheral area accounts for 1-2cm of the whole area of the casting film and is dependent on the area of the casting film), so that the peripheral of the film has larger stress than the middle area of the film, and the edge stress is eliminated by isostatic pressing, so that the film is uniformly stressed and the phenomenon of uneven sintering shrinkage rate is avoided). The isostatic pressing is adopted to treat the green body mainly for eliminating flaws such as cracks or holes of the ceramic casting sheet, thereby achieving the purpose of densification of the green body.
Isostatic pressure parameters: the temperature is 65 ℃, the pressure is 50MPa, and the isostatic treatment time is 90S;
4) Adhesive discharging device
And (3) applying the casting film obtained in the step (3) to a glue discharging and discharging curve: RT-200 ℃, and heating rate is 2 ℃/min; heating up at 200-400 deg.C at a rate of 0.2 deg.C/min; 400-650 ℃, and heating rate is 2 ℃/min; and (5) preserving heat for 2 hours at 650 ℃ to obtain the gelatin discharging biscuit.
5) Sintering
Sintering the glue discharging biscuit of the step 4) in a sintering furnace while pressing, wherein the porosity of the porous ceramic pressing plate is 20%, the thickness of the pressing plate is 7 times that of a green sheet, the pressing plate protrudes out of the peripheral edge 8CM of the ceramic sheet, the surface of the porous ceramic pressing plate facing the sample is set to be concave-convex (+ -0.18 mu m), and the sintering curve is that: RT-600 ℃, and heating rate of 10 ℃/min;600 ℃ to the highest temperature (T) max :1400 ℃, and the heating rate is 3 ℃/min; t (T) max And (1400 ℃) for 2 hours to obtain the porous alumina ceramic substrate provided by the application.
Example 2
1) The method comprises the following steps: aluminum powder with the average grain diameter of 8 mu m is treated for 40min at 900 ℃ under nitrogen atmosphere to obtain complex phase ceramic powder with simple substance aluminum as an inner core and aluminum nitride as an outer layer;
the preparation of the ceramic slurry comprises the following specific components in percentage by mass:
alumina powder: 45%; sintering aid: 10%; dispersant phosphate: 0.7%; binder PVB:7.5%; plasticizer BBP:3.0%; solvent alcohol/butanone azeotropic solvent: 33.8%;
the sintering aid is Ca-Mg-Si composite aid, wherein the molar ratio of Si to Mg to Ca is 15:2:5; in the sintering aid, calcium is derived from calcium oxide; magnesium is derived from magnesium oxide; silicon is from silicon dioxide;
preparation of weighing CaO, mgO, siO in mass percent and molar ratio 2 Placing alumina powder, a dispersing agent and a solvent into a ball milling tank, adding 26g of complex phase ceramic powder (accounting for 2.6 percent of the mass of the ceramic powder slurry), performing first-stage ball milling, wherein the ball milling medium is alumina balls, and the ball ratio is 1:2.5, ball milling time is 24 hours, continuously adding the binder and the plastic agent according to mass percent, and performing second-stage ball milling for 12 hours. And ball milling is carried out in two steps to obtain uniform slurry.
2) Defoaming device
And (3) stirring and defoaming the slurry obtained in the step (1) in vacuum, wherein the vacuum degree is higher than-0.92 MPa, the defoaming time is 5h (the defoaming time is until no bubbles are seen), and the viscosity is controlled at 25pa.
3) Casting process
And (3) casting the slurry obtained in the step (2) through a casting machine to obtain a casting film, wherein the thickness of the casting film is 0.5mm.
Isostatic pressure parameters: the temperature is 75 ℃, the pressure is 45MPa, and the isostatic treatment time is 75S;
4) Adhesive discharging device
And (3) applying the casting film obtained in the step (3) to a glue discharging and discharging curve: RT-200 ℃, and heating rate is 2 ℃/min; heating up at 200-400 deg.C at a rate of 0.2 deg.C/min; 400-650 ℃, and heating rate is 2 ℃/min; and (5) preserving heat for 2 hours at 650 ℃ to obtain the gelatin discharging biscuit.
5) Sintering
Sintering the gelatin discharging biscuit in the step 4) in a sintering furnace while pressing by adopting a cover without pressing (specifically, using micro pressure formed by gas flowing through or filling a pore between a cover plate and a sample at high temperature to prevent sheet warpage), wherein the porosity of a pressing plate of a porous ceramic pressing plate is 20%, the thickness of the pressing plate is 7 times that of a green sheet, and the pressing plate protrudes out of the peripheral edge 8CM of the ceramic sheet), and the sintering curve is as follows: RT-600 ℃,heating rate is 10 ℃/min;600 ℃ to the highest temperature (T) max :1350 ℃, heating rate is 3 ℃/min; t (T) max And (1350 ℃) for 1h to obtain the porous alumina ceramic substrate.
Example 3
1) The method comprises the following steps: aluminum powder with the average grain diameter of 8 mu m is treated for 60min at the high temperature of 800 ℃ in nitrogen atmosphere to obtain complex phase ceramic powder with simple substance aluminum as an inner core and aluminum nitride as an outer layer;
the preparation of the ceramic slurry comprises the following specific components in percentage by mass:
alumina powder: 50%; sintering aid: 9.3%; dispersant phosphate: 1.5%; binder PVB:6.5%; plasticizer DOP:2.7%; solvent alcohol/butanone azeotropic solvent: 30%;
the sintering aid is Ca-Mg-Si composite aid, wherein the molar ratio of Si to Mg to Ca is 11:3:1; in the sintering aid, calcium is derived from calcium carbonate; magnesium is derived from magnesium oxide; silicon is from silicon dioxide;
preparation of weighing CaO, mgO, siO in mass percent and molar ratio 2 Placing alumina powder, a dispersing agent and a solvent into a ball milling tank, adding 40g of complex phase ceramic powder (accounting for 4% of the mass of the ceramic powder slurry), performing first-stage ball milling, wherein the ball milling medium is alumina balls, and the ball ratio is 1:2.5, ball milling time is 24 hours, continuously adding the binder and the plastic agent according to mass percent, and performing second-stage ball milling for 12 hours. And ball milling is carried out in two steps to obtain uniform slurry.
2) Defoaming device
And (3) stirring and defoaming the slurry obtained in the step (1) in vacuum, wherein the vacuum degree is higher than-0.92 MPa, the defoaming time is 3h (the defoaming time is until no bubbles are seen), and the viscosity is controlled at 18pa.
3) Casting process
And (3) casting the slurry obtained in the step (2) through a casting machine to obtain a casting film, wherein the thickness of the casting film is 0.25mm.
Isostatic pressure parameters: the temperature is 70 ℃, the pressure is 55MPa, and the isostatic treatment time is 90S;
4) Adhesive discharging device
And (3) applying the casting film obtained in the step (3) to a glue discharging and discharging curve: RT-200 ℃, and heating rate is 2 ℃/min; heating up at 200-400 deg.C at a rate of 0.2 deg.C/min; 400-650 ℃, and heating rate is 2 ℃/min; and (5) preserving heat for 2 hours at 650 ℃ to obtain the gelatin discharging biscuit.
5) Sintering
Sintering the glue discharging biscuit of the step 4) in a sintering furnace while pressing, wherein the porosity of the porous ceramic pressing plate is 25%, the thickness of the pressing plate is 10 times of that of a green sheet, the pressing plate protrudes out of the peripheral edge of the ceramic sheet by 10CM, the surface of the porous ceramic pressing plate facing the sample is set to be concave-convex (+ -0.18 mu m), and the sintering curve is that: RT-600 ℃, and heating rate of 10 ℃/min;600 ℃ to the highest temperature (T) max :1450 ℃, the temperature rising rate is 3 ℃/min; t (T) max And (1450 ℃) for 2 hours to obtain the porous alumina ceramic substrate provided by the application.
Comparative example 1
According to the procedure of example 3, only the ceramic disperse phase was not added.
FIG. 1 is an SEM image of a porous alumina ceramic wafer obtained in example 3. The graph shows that the pore size distribution is uniform, the pore size range is 2-5 mu m, the grain size (grain diagonal line) is smaller than the pore size, and is between 1-4 mu m, and the grains develop into an approximate lamellar structure, so that the formation of through holes is facilitated, and the subsequent metallization of the ceramic substrate is decisive.
Table 1, examples 1-3 Performance List of porous alumina ceramic flakes prepared
In table 1, the detection method of each performance is as follows:
(1) the open porosity was measured using archimedes drainage as shown in formula (1):
Pa＝(R3－R1)×100/(R3－R2) (1)
wherein: r1 is dry sample empty weight, R2 is saturated sample water weight, R3 is saturated sample empty weight, each group of samples is measured for 10 times, and average value is obtained;
(2) water absorption rate: in the porous ceramic, the ratio of the weight of all liquid capable of penetrating into the open gaps of the material to the dry weight of the material is that the water absorption rate is = (R3-R1) multiplied by 100/R1;
(3) pore size is measured by mercury intrusion method, and AutoPoreV9500 is set;
(4) thermal conductivity: the sample size is 10 multiplied by 10, the thickness is 0.5-1.0mm, and the temperature is 25 ℃ by adopting a laser flash method (LFA 467) test;
(5) warp degree: the ceramic plate is placed on the marble plane, plug gauges with different thicknesses are used for detection, the warping OK is indicated when the two sides of the ceramic plate cannot be plugged in, and the thickness at the moment, namely the warping degree, is recorded.
(6) Sintering linear shrinkage rate: in the plane direction, the lengths L1 and L2, the widths W1 and W2 of the green body before sintering and the ceramic block after sintering are respectively measured, the linear shrinkage rate in the length direction is (L1-L2) multiplied by 100/L1, and the linear shrinkage rate in the width direction is (W1-W2) multiplied by 100/W1;
(7) tensile strength: according to GB 9622.7-88, a universal material testing machine is adopted for testing, and the calculation formula is as follows: σ=f/S, where: f- -the larger force that the sample bears when breaking, N; s- -original cross-sectional area of sample, mm 2 。
As is clear from Table 1, the porous alumina ceramic flakes obtained in examples 1 to 3 of the present application had an open porosity of 4 to 8%, a water absorption of 2 to 5%, a pore size of 2 to 5. Mu.m, and a thermal conductivity of 6.2 to 7.5w/m.K. By adopting the synergistic effect of the formula and the process, the warping degree of the porous ceramic sheet is greatly improved from the original 50 μm or more (see comparative example 1) to 9 μm or less, and the use requirement is well met.
Claims (10)
1. A method of making a porous alumina ceramic wafer comprising:
1) Mixing alumina powder, a sintering aid, a solvent and a dispersing agent to obtain ceramic powder slurry, adding complex-phase ceramic powder and a ball milling medium to perform first-stage ball milling, and adding a binder and a plastic agent to perform second-stage ball milling to obtain slurry; the sintering aid is Ca-Mg-Si composite aid, wherein the molar ratio of Si to Mg to Ca is as follows: (5-20): (2-10): (1:5);
the complex phase ceramic powder consists of an inner core and an outer layer wrapping the inner core;
the material constituting the inner core is simple substance aluminum;
the material constituting the outer layer is aluminum nitride;
the method for preparing the complex phase ceramic powder comprises the following steps: carrying out high-temperature treatment on aluminum powder in an inert atmosphere to obtain the aluminum powder;
the average particle diameter of the aluminum powder is 4-8 mu m;
the inert atmosphere is nitrogen atmosphere;
in the high-temperature treatment step, the temperature is 900 ℃;
the time is 40min;
the alumina powder accounts for 40-52% of the ceramic powder slurry by mass;
the sintering aid accounts for 5-10% of the ceramic powder slurry by mass;
the solvent accounts for 25-38% of the ceramic powder slurry by mass;
the dispersant accounts for 0.1-2.0% of the ceramic powder slurry by mass;
the composite ceramic powder accounts for 1-4% of the ceramic powder slurry by mass;
the binder accounts for 3-10% of the ceramic powder slurry by mass;
the plastic agent accounts for 1-5% of the ceramic powder slurry by mass;
2) Defoaming the slurry to obtain defoamed slurry;
3) Casting the defoamed slurry to obtain a casting film;
the step of casting includes: casting the defoamed slurry through a casting machine to obtain a casting film, and then carrying out green body uniformity correction; the green body uniformity correction includes applying pressure in a specific direction, and relieving edge stress by isostatic pressing; in the isostatic pressing, the temperature is 65 or 75 ℃; the pressure is 45 or 50 or 55MPa; the time is 75 or 90s;
4) Removing the adhesive from the casting film to obtain a biscuit after the adhesive is removed;
5) Sintering the biscuit after glue discharge while pressing to obtain the porous alumina ceramic sheet;
sintering the pressed ceramic plate to form a cover without pressing or providing pressure by using a porous ceramic pressing plate; the cover is not pressed to prevent warping of the sheet during sintering by micro-pressure formed at high temperature with gas flowing through or filling the pores between the cover plate and the sample.
2. The method according to claim 1, characterized in that: in the step 1), the molar ratio of Si to Mg to Ca is 11:3:1 or 15:2:5;
in the sintering aid, calcium is introduced in the form of any one of calcium oxide, calcium carbonate and calcium hydroxide; magnesium is introduced in the form of any one of magnesium oxide, magnesium hydroxide and magnesium silicate; silicon is introduced in the form of any one of silicon dioxide and magnesium silicate;
the solvent is selected from any two of alcohol, butanone, isopropanol, toluene, xylene and acetic acid ethanol;
the dispersing agent is at least one of castor oil, phosphate, oleic acid, herring oil and BYK;
the binder is PVB;
the plastic agent is at least one selected from BBP, DOP and PEG;
the alumina powder accounts for 45-50% of the ceramic powder slurry by mass;
the sintering aid accounts for 8-9.8% of the ceramic powder slurry by mass;
the solvent accounts for 29 to 33.8 percent of the ceramic powder slurry in percentage by mass;
the dispersant accounts for 0.7 percent of the ceramic powder slurry in mass percent;
the composite ceramic powder accounts for 1.5-2.6% of the ceramic powder slurry by mass;
the binder accounts for 5-7.5% of the ceramic powder slurry by mass;
the plastic agent accounts for 2-3% of the ceramic powder slurry by mass;
in the ball milling steps of the first stage and the second stage, the ball milling medium is alumina balls; the ball-material ratio is 1:2.5;
in the first-stage ball milling, the ball milling time is 20-48 hours;
in the second-stage ball milling, the ball milling time is 12-24 hours.
3. The method according to claim 1, characterized in that: the solvent is an alcohol/toluene azeotropic solvent or an alcohol/butanone azeotropic solvent;
the ceramic slurry is any one of the following ceramic slurries a-e;
the ceramic slurry a consists of the following components in parts by mass:
alumina powder: 45-52%; sintering aid: 9.3-10%; dispersing agent: 0.7-1.5%; and (2) a binder: 6.5-7.5%; and (3) a plastic agent: 2.1-3.0%; solvent: 29-33.8%;
the ceramic slurry b consists of the following components in parts by mass:
alumina powder: 50-52%; sintering aid: 9.3-10%; dispersing agent: 0.7-1.5%; and (2) a binder: 6.5-7.5%; and (3) a plastic agent: 2.7-3.0%; solvent: 30-33.8%;
the ceramic slurry c consists of the following components in parts by mass:
alumina powder: 52%; sintering aid: 9.7%; dispersing agent: 0.7%; and (2) a binder: 6.5%; and (3) a plastic agent: 2.1%; solvent: 29%;
the ceramic slurry d consists of the following components in parts by mass:
alumina powder: 45%; sintering aid: 10%; dispersing agent: 0.7%; and (2) a binder: 7.5%; and (3) a plastic agent: 3.0%; solvent: 33.8%;
the ceramic slurry e consists of the following components in parts by mass:
alumina powder: 50%; sintering aid: 9.3%; dispersing agent: 1.5%; and (2) a binder: 6.5%; and (3) a plastic agent: 2.7%; solvent: 30%.
4. The method according to claim 1, characterized in that: in the defoaming in the step 2), the vacuum degree is higher than-0.92 MPa, and the defoaming time is more than or equal to 1h; the foam was removed until no bubbles were visible, and the viscosity was 15 to 25Pa.s.
5. The method according to claim 4, wherein: in the defoaming in the step 2), the defoaming time is 3-5h; the viscosity was 18Pa.s.
6. The method according to any one of claims 1-5, wherein: in the casting of the step 3), the thickness of the casting film is 0.1-1.2mm;
in the step 4), the glue discharging curve is as follows:
the temperature is increased by 1-2 ℃/min at the room temperature of-200 ℃;
heating at 200-400 deg.c and rate of 0.2-1 deg.c/min;
heating at 400-650 deg.c at 1-3 deg.c/min;
preserving heat for 0.5-2h at 650 ℃;
in the sintering of the step 5), the sintering curve is as follows:
the temperature is increased by 5 to 10 ℃ per minute at the room temperature of between 600 ℃ and the room temperature;
600 ℃ to 1300-1500 ℃, the heating rate is 3-5 ℃/min, and then the temperature is kept for 1-3h;
in the sintering process while pressing, the cooling rate from the highest temperature to 1000 ℃ is 1-2 ℃/min; the cooling rate from 1000 ℃ to 600 ℃ is 0.5-1 ℃/min; naturally cooling from 600 ℃ to room temperature;
the porosity of the porous ceramic pressing plate is 20-25%;
the thickness of the porous ceramic pressing plate is 5-10 times of the thickness of the sintered biscuit;
the porous ceramic pressing plate protrudes by 1-10cm.
7. The method according to claim 6, wherein: in the casting of the step 3), the thickness of the casting film is 0.3-0.5mm.
8. A porous alumina ceramic wafer prepared by the method of any one of claims 1-7.
9. Use of the porous alumina ceramic wafer of claim 8 in a sensor package.
10. The use according to claim 9, characterized in that: the sensor is a gas sensor.
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| CN110330358A (en) * | 2019-07-04 | 2019-10-15 | 南充三环电子有限公司 | A kind of porous alumina ceramic plate and preparation method thereof |
| CN114702321A (en) * | 2022-04-18 | 2022-07-05 | 无锡市惠丰电子有限公司 | Sintering process of tape-casting alumina sheet |
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| US4256792A (en) * | 1980-01-25 | 1981-03-17 | Honeywell Inc. | Composite electronic substrate of alumina uniformly needled through with aluminum nitride |
| CN1422827A (en) * | 2002-12-24 | 2003-06-11 | 山东大学 | Nitride/alumina based composite ceramic material and process of preparing the same |
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