Preparation method of low-temperature sintered high-thermal-conductivity 99 ceramic alumina ceramic substrate

Abstract

The invention relates to the technical field of ceramic materials, in particular to a preparation method of a low-temperature sintered high-thermal-conductivity 99 ceramic aluminum oxide ceramic substrate, which comprises the following steps of: 1, preparing slurry; step 2, tape casting; step 3, stamping and forming; 4, performing warm isostatic pressing treatment; step 5, performing main firing to obtain porcelain; and 6, inspecting a finished product. By regulating the particle size of the alumina powder, adopting the specific sintering aid of the solid solution and the liquid phase forming agent, introducing trace La2O3 into the system and combining low-temperature co-firing, the problem that the 99 ceramic alumina ceramic substrate is easy to crack in the processing process is improved while the sintering temperature of the 99 ceramic alumina ceramic substrate is remarkably reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ceramic materials, and particularly relates to a preparation method of a low-temperature sintering high-thermal-conductivity 99 porcelain alumina ceramic substrate. BACKGROUND

[0002] PCB circuit board is an important basic component in electronic equipment, which is used for supporting electronic components and realizing electrical connection. The core components of the PCB circuit board include a substrate, a conductive layer and an insulating layer. The substrate as the basic carrier of the PCB circuit board not only needs to withstand the mechanical stress and temperature deformation in the component mounting, welding process and long-term use to ensure the integrity of the physical structure of the PCB circuit board, but also needs to have excellent insulation performance to isolate the electrical interference between the conductive layers and ensure the stability and safety of signal transmission. Meanwhile, the substrate should also have good thermal conductivity to ensure the heat dissipation efficiency of high-power components and avoid performance degradation and failure risk caused by local overheating.

[0003] The substrate of the PCB circuit board can be divided into high-molecular substrate, metal substrate and ceramic substrate according to the material. In recent years, with the continuous development of electronic technology towards high power and high frequency, the high-molecular substrate gradually exposes problems such as poor heat dissipation performance and unstable insulation performance. The metal substrate has high thermal conductivity and moderate cost, but has problems such as heavy weight, limited temperature resistance of the insulating layer and poor electromagnetic shielding performance. The ceramic substrate has characteristics of high strength, light weight, high temperature resistance and radiation resistance, and has become a key material in high-end electronic packaging. The 99 porcelain alumina ceramic substrate has become a core candidate material for high-power LED substrate, IGBT module packaging and aerospace high-temperature components due to its high thermal conductivity, thermal expansion coefficient close to that of silicon chip, extremely low dielectric loss and good mechanical strength. However, the traditional preparation method of the 99 porcelain alumina ceramic substrate often relies on expensive high-purity raw materials, high-temperature long-time sintering or complex post-processing process. In addition, due to the high purity of the raw materials, stress is easy to occur during the sintering process, and cracking is easy to occur during the processing process. SUMMARY

[0004] In view of the technical problems of high sintering temperature, long sintering time and easy cracking of the existing preparation method of the 99 porcelain alumina ceramic substrate, the present application provides a preparation method of a low-temperature sintering high-thermal-conductivity 99 porcelain alumina ceramic substrate. By adjusting the particle size of the alumina powder, using a specific sintering aid of solid solution + liquid phase forming agent and introducing a small amount of La2O3 and low-temperature co-sintering into the system, the sintering temperature of the 99 porcelain alumina ceramic substrate is significantly reduced, and the problem of easy cracking of the 99 porcelain alumina ceramic substrate during the processing process is improved.

[0005] The technical scheme of the present application is as follows: A method for preparing a low-temperature sintered high-thermal-conductivity 99 ceramic alumina ceramic substrate, comprising the following steps: Step one: slurry preparation, first put the alumina powder with a particle size of 0.20±0.05 μm, lanthanum oxide powder (La2O3) and dispersant into a ball mill for ball milling to obtain a powder, then dissolve the powder, a binder, a plasticizer and a sintering aid in a solvent and put them into the ball mill for secondary ball milling, followed by vacuum degassing aging to obtain a slurry, the sintering aid includes Y2O3, ZrO2 and MgO, the mass of the sintering aid accounts for 0.04%-0.2% of the mass of the powder; Step two: tape casting, uniformly coat the slurry obtained in step one on a PET film and control the thickness of the slurry, and after the solvent in the slurry evaporates, a green body is obtained; Step three: die forming, the left lower corner of the green body is prepared with an identification angle of C=1.50, and the other three corners are prepared with a chamfer of C=0.75; Step four: warm isostatic pressing, the temperature of the warm isostatic pressing is 25℃, the pressure of the warm isostatic pressing is 150-200 MPa, and the time of the warm isostatic pressing is 2-5 min; Step five: main sintering, the green body obtained in step four is sequentially subjected to gradient temperature rising degassing and sintering to obtain a ceramic substrate, the sintering temperature is 1468-1510℃, and the sintering time is 2-4 h, preferably 2.5 h.

[0006] Further, in step one, the purity of the alumina powder is >99%, the dispersant is one or more of polyacrylate, phosphate, polyethyleneimine and glyceride, preferably glyceride, the mass of the dispersant accounts for 0.5%-1.5% of the mass of the alumina powder, preferably 1%, the dispersant can prevent the particles of the alumina powder from agglomerating, increase the dispersibility of the particles, and is conducive to improving the uniformity of the alumina ceramic substrate. The mass of the lanthanum oxide powder accounts for 0.03% of the mass of the alumina powder.

[0007] Further, in step one, the binder is one or more of polyvinyl butyl (PVB), polyacrylate and polyvinyl alcohol (PVA), preferably polyvinyl butyl; the plasticizer is one or more of dibutyl phthalate (DBP), polyethylene glycol (PEG), diethyl phthalate (DEP) and dioctyl phthalate (DOP), preferably dibutyl phthalate, the plasticizer can reduce the viscosity of the slurry and improve the spreadability and uniformity of the slurry in the subsequent tape casting process; the solvent is a mixture of toluene and isopropyl alcohol, and the mass ratio of toluene to isopropyl alcohol in the solvent is 5:10.5.

[0008] Further, the total mass of the binder and the plasticizer accounts for 6%-10% of the mass of the alumina powder, and the mass of the plasticizer accounts for 30%-40% of the mass of the binder, so that the strength and flexibility of the green body can be increased, and the powder aggregation can be avoided by adjusting the mass ratio of the plasticizer and the binder.

[0009] Further, in the solvent, the mass ratio of toluene and isopropyl alcohol is 5:10.5.

[0010] Further, in the step one, the mass ratio of Y2O3, ZrO2 and MgO in the sintering aid is 2-5:2-5:2-5, and the mass ratio of Y2O3, ZrO2 and MgO is preferably 5:3:2, 5:2:3, 2:5:3 or 3:2:5.

[0011] Further, in the step two, the slurry obtained in the step one is uniformly coated on the PET film by using a hopper, and the thickness of the slurry flowing out is adjusted by adjusting the height of the scraper.

[0012] Further, in the step five, the temperature rising speed of the gradient temperature rising glue removal is 1.2-1.8 ℃ / min, preferably 1.5 ℃ / min, the glue removal temperature of the gradient temperature rising glue removal is 580-620 ℃, preferably 600 ℃, and the holding time of the gradient temperature rising glue removal is 3-5 h, preferably 4 h.

[0013] Further, the step six is further included: product inspection, the ceramic substrate is subjected to a warping test, the ceramic substrate unqualified in the warping test is corrected, and the ceramic substrate qualified in the warping test is the finished product.

[0014] Further, in the step six, the ceramic substrate unqualified in the warping test is heated and softened at 1400 ℃, and the warping correction is performed by stacking and burning under the action of gravity. After the main burning of the ceramic, if the ceramic substrate passes through a certain gap of a marble flat plate at an inclination angle of 45° under the action of gravity, it indicates that the ceramic substrate is qualified in the warping test, and if the ceramic substrate does not pass through the certain gap of the marble flat plate at the inclination angle of 45° under the action of gravity, it indicates that the ceramic substrate is unqualified in the warping test. In the step six, the warping degree of the surface of the finished product is ≤2‰, the roughness of the surface of the finished product is 0.05-0.2 μm, the mass percentage of the alumina in the finished product is ≥99%, and the ceramic particle size of the alumina is 0.08-0.59 μm.

[0015] The beneficial effects of the present application are as follows: The application provides a preparation method of a low-temperature sintering high-thermal-conductivity 99 porcelain alumina ceramic substrate, which comprises the following steps: in the slurry configuration process, the particle size of the alumina powder is regulated, and a sintering aid including a solid solution+liquid phase forming agent of Y2O3, ZrO2 and MgO is used, so that the crystal boundary energy can be reduced, liquid phase diffusion can be promoted, and abnormal grain growth can be avoided; a small amount of La2O3 is introduced into the system, the La2O3 and the Y2O3 / ZrO2 / MgO form a low-melting-point liquid phase, the material diffusion and void filling are accelerated through liquid phase sintering, the product densification is promoted, and the sintering temperature is reduced; meanwhile, the La2O3 promotes the phase transformation toughening of ZrO2, the second phase formed by the La2O3 can induce crack deflection and branching, and the mechanical properties of the product are improved; in the warm isostatic pressing process, the interlayer voids are eliminated, and the green body is more dense. The application also adopts the gradient temperature rising degassing process to completely remove the organic matter in the green body, ensures the stability of the sintering process, significantly reduces the sintering temperature of the 99 porcelain alumina ceramic substrate, and improves the problem that the 99 porcelain alumina ceramic substrate is prone to cracking in the processing process. DETAILED DESCRIPTION

[0016] In order for those skilled in the art to better understand the technical solutions in the application, the technical solutions in the embodiments of the application will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work should belong to the protection scope of the application.

[0017] Embodiment 1 A preparation method of a low-temperature sintering high-thermal-conductivity 99 porcelain alumina ceramic substrate comprises the following steps: Step one: slurry configuration, first, the alumina powder with a purity of >99% and a particle size of 0.20±0.05 microns, lanthanum oxide powder and glyceride are put into a planetary ball mill for ball milling, the ball milling time is 16 hours, and after the ball milling is completed, the powder is filtered and dried to obtain a powder, the mass of the lanthanum oxide powder accounts for 0.03% of the mass of the alumina powder, and the mass of the glyceride accounts for 1% of the mass of the alumina powder. Then, the powder, PVB, DBP and a sintering aid are dissolved in a solvent and put into a ball mill for secondary ball milling, the secondary ball milling time is 4 hours, and then vacuum degassing aging is performed to obtain a slurry, the total mass of PVB and DBP accounts for 6.2% of the mass of the alumina powder, the mass of DBP accounts for 32% of the mass of PVB, the mass of the solvent accounts for 50% of the mass of the alumina powder, the solvent is a mixture of toluene and isopropyl alcohol, and the mass ratio of toluene to isopropyl alcohol in the solvent is 5:10.5; the sintering aid includes Y2O3, ZrO2 and MgO, the mass ratio of Y2O3, ZrO2 and MgO is 5:3:2, and the mass of the sintering aid accounts for 0.05% of the mass of the powder.

[0018] Step two: cast molding, using a hopper to evenly coat the slurry obtained in step one on the PET film to fully spread, and by adjusting the height of the doctor blade to control the thickness of the slurry flow, and then heating, drying to make the solvent in the slurry volatilize, to obtain a green body with a thickness of 0.1-3mm. During the heating and drying process: the temperature of the first temperature zone is 35-55℃, the temperature of the second temperature zone is 50-70℃, and the temperature of the third temperature zone is 68-90℃.

[0019] Step three: die forming, placing the green body under the punch, using the blade structure mold on the punch to punch the green body, so that the left lower part of the green body is prepared with an identification angle of C=1.50, and the other three angles are prepared with a chamfer of C=0.75.

[0020] Step four: warm isostatic pressing treatment, the temperature of the warm isostatic pressing treatment is 25℃, the pressure of the warm isostatic pressing treatment is 150-200MPa, and the time of the warm isostatic pressing treatment is 3min, which eliminates the interlayer voids and makes the body more dense.

[0021] Step five: main sintering, using fine sintering process to separate the degassing process and the sintering process, ensure that the degassing environment and the sintering environment do not interfere with each other, and ensure the stability of the sintering process. First, the green body obtained in step four is degassed by slow stepwise heating, and the temperature is raised to 600℃ at a rate of 1.5℃ / min and then kept for 4h to completely remove the organic matter. Then sintering at 1485℃ for 2.5h, during which migration densification and recrystallization occur, causing the alumina particles to bond and produce a certain strength. Using appropriate sintering temperature and sintering time can make the sintering more sufficient, promoting the densification of the body while avoiding excessive grain growth. After sintering, use a high-pressure sandblasting machine to sandblast and dry the surface of the ceramic substrate to obtain the ceramic substrate.

[0022] Step six: product inspection, after main sintering, place the ceramic substrate in a leveling furnace and heat it at 1400℃ to soften it, and then correct the warping by using its own gravity through the lamination method; then test the warping of the ceramic substrate, if the ceramic substrate passes through a certain gap of a marble flat plate at an angle of 45° under its own weight, it means that the ceramic substrate passes the warping test, and the ceramic substrate that passes the warping test is the finished product, the warping degree of the finished product surface is ≤2‰; if the ceramic substrate does not pass through a certain gap of a marble flat plate at an angle of 45° under its own weight, it means that the ceramic substrate fails the warping test.

[0023] After the warping test, place the finished product under the light, the front of the finished product is transparent, and the identification angle is upward, and the appearance defects are removed piece by piece; rotate the finished product by 180°, the front is transparent, and the identification angle is downward, and the appearance defects are removed piece by piece.

[0024] The roughness of the surface of the finished product obtained in this example is 0.05-0.2 μm; the mass percentage of aluminum oxide in the finished product is ≥99%.

[0025] Example 2 Example 2 differs from Example 1 only in that the mass of DBP is 35% of the mass of PVB.

[0026] Example 3 Example 3 differs from Example 1 only in that the mass of DBP is 39% of the mass of PVB.

[0027] Example 4 Example 4 differs from Example 1 only in that the mass of DBP is 37% of the mass of PVB.

[0028] Example 5 Example 5 differs from Example 1 only in that the mass of DBP is 36% of the mass of PVB.

[0029] Example 6 Example 6 differs from Example 1 only in that the mass of DBP is 36% of the mass of PVB; the sintering aid comprises Y2O3, ZrO2 and MgO, the mass ratio of Y2O3, ZrO2 and MgO is 5:2:3, the mass of the sintering aid is 0.06% of the mass of the powder; the sintering temperature is 1475°C.

[0030] Example 7 Example 7 differs from Example 1 only in that the mass of DBP is 36% of the mass of PVB; the sintering aid comprises Y2O3, ZrO2 and MgO, the mass ratio of Y2O3, ZrO2 and MgO is 5:3:2, the mass of the sintering aid is 0.04% of the mass of the powder; the sintering temperature is 1493°C.

[0031] Example 8 Example 8 differs from Example 1 only in that the mass of DBP is 36% of the mass of PVB; the sintering aid comprises Y2O3, ZrO2 and MgO, the mass ratio of Y2O3, ZrO2 and MgO is 2:5:3, the mass of the sintering aid is 0.04% of the mass of the powder; the sintering temperature is 1468°C.

[0032] Example 9 Example 9 differs from Example 1 only in that the mass of DBP is 36% of the mass of PVB; the sintering aid comprises Y2O3, ZrO2 and MgO, the mass ratio of Y2O3, ZrO2 and MgO is 3:2:5, the mass of the sintering aid is 0.06% of the mass of the powder; the sintering temperature is 1510°C.

[0033] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the mass of DBP accounts for 36% of the mass of PVB; the sintering aid includes Y2O3, ZrO2 and MgO, the mass ratio of Y2O3, ZrO2 and MgO is 2:5:3, the mass of the sintering aid accounts for 0.04% of the mass of the powder, La2O3 is not added in the system, and the sintering temperature is 1541℃.

[0034] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the mass of DBP accounts for 36% of the mass of PVB; the sintering aid includes MgO, SiO2 and CaO, the mass ratio of MgO, SiO2 and CaO is 2:1:1, the mass of the sintering aid accounts for 0.04% of the mass of the powder; and the sintering temperature is 1562℃.

[0035] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the mass of DBP accounts for 36% of the mass of PVB; the sintering aid includes MgO, SiO2 and CaO, the mass ratio of MgO, SiO2 and CaO is 1:2:1, the mass of the sintering aid accounts for 0.06% of the mass of the powder; and the sintering temperature is 1552℃.

[0036] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the mass of DBP accounts for 36% of the mass of PVB; the sintering aid includes MgO, SiO2 and CaO, the mass ratio of MgO, SiO2 and CaO is 1:1:2, the mass of the sintering aid accounts for 0.04% of the mass of the powder; and the sintering temperature is 1555℃.

[0037] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that the green body is directly sintered into porcelain after being stamped, without warm isostatic pressing treatment; and the glue is removed by rapid stepwise heating, with a heating rate of 5℃ / min to 600℃; and the sintering temperature is 1573℃.

[0038] The green body cracking and glue removal cracking of Examples 1-9 and Comparative Examples 1-5 are tested, and the testing method is described as follows: I. Green body cracking test After die forming, the green body is wound at a fixed time, and the surface crack of the green body winding is observed visually.

[0039] II. Glue removal cracking test The surface of the ceramic substrate after sintering is drawn red, and then the product cracking is observed on the non-red side of the ceramic substrate.

[0040] Table 1 Cracking of Examples 1-9 and Comparative Examples 1-5

[0041] The performance of the ceramic substrates of Example 1-Example 9, Comparative Example 1-Comparative Example 5 was tested, and the test methods are described as follows: I. Surface roughness test The surface roughness of the finished ceramic substrate was tested by using a stylus method, the test stylus was gently drawn on the surface of the ceramic substrate to obtain the Ra value of the surface roughness of the ceramic substrate, at least three samples were selected for each example / comparative example, and three points were selected for testing at different positions of the samples, and the average value of the test results was taken.

[0042] II. Density test The density of the finished ceramic substrate was tested by using a drainage method, at least five samples were selected for testing for each example / comparative example, and the average value of the test results was taken.

[0043] III. Bending strength test The bending strength of the finished ceramic substrate was tested by using a universal testing machine, at least three samples were selected for testing for each example / comparative example, the average value of the test results was taken, the size of the test sample was 30x20mm, the test span was 25mm, and the drop speed was 0.5mm / min.

[0044] The ceramic particle size, density, bending strength and thermal conductivity of the finished products of Example 1-Example 9, Comparative Example 1-Comparative Example 5 were tested, and the test results are shown in Table 2.

[0045] Table 2 Test results of the finished products of Example 1-Example 9, Comparative Example 1-Comparative Example 5

[0046] As can be seen from Table 1 and Table 2, the specific sintering aid (Y2O3-ZrO2-MgO) of the solid solution + liquid phase forming agent is used in Example 1-Example 9, and a small amount of La is introduced into the system and combined with slow stepwise temperature rising and degassing, which not only greatly reduces the sintering temperature, but also ensures the density of the surface of the finished ceramic substrate by inhibiting abnormal grain growth; in addition, by optimizing the ratio of plasticizer and binder, the degassing cracking is improved under the premise of ensuring the strength and toughness of the green body, and the low-cost production of high-performance ceramic substrate is realized.

[0047] Although the present application has been described in detail by preferred embodiments, the present application is not limited thereto. Any modification or replacement of the embodiments of the present application made by those skilled in the art without departing from the spirit and essence of the present application shall fall within the scope of the present application. Any modification or replacement within the technical scope disclosed by the present application can be easily thought of by those skilled in the art, and shall be covered within the protection scope of the present application.

Claims

1. A method for preparing a low-temperature sintered high thermal conductivity 99% alumina ceramic substrate, characterized in that: The steps include: Step 1: Preparation of slurry: First, alumina powder, lanthanum oxide powder and dispersant with a particle size of 0.20±0.05μm are put into a ball mill for ball milling to obtain a powder; then the powder, binder, plasticizer and sintering aid are dissolved in a solvent and put into a ball mill for secondary ball milling, followed by vacuum degassing and aging to obtain a slurry. The sintering aid includes Y2O3, ZrO2 and MgO, and the mass of the sintering aid accounts for 0.04%-0.2% of the mass of the powder; Step 2: tape casting, the slurry obtained in step 1 is evenly coated on a PET film, and the thickness of the slurry is adjusted. After the solvent in the slurry evaporates, a green body is obtained; Step 3: Die forming, so that the lower left corner of the green body is prepared with a recognition angle of C=1.50, and the other three corners are prepared with chamfers of C=0.75; Step 4: warm isostatic pressing treatment, the temperature of warm isostatic pressing treatment is 25°C, the pressure of warm isostatic pressing treatment is 150-200MPa, and the time of warm isostatic pressing treatment is 2-5min; Step 5: Main firing of porcelain. The green body obtained in step 4 is subjected to gradient temperature increase, debinding, and sintering in sequence to obtain a ceramic substrate. The sintering temperature is 1468-1510°C and the sintering time is 2-4 hours.

2. The method for preparing a low-temperature sintered high thermal conductivity 99% alumina ceramic substrate according to claim 1, characterized in that: In step 1, the purity of the alumina powder is greater than 99%, the dispersant is one or more of polyacrylate, phosphate, polyethyleneimine, and glyceride, and the mass of the dispersant accounts for 0.5%-1.5% of the mass of the alumina powder; the mass of the lanthanum oxide powder accounts for 0.03% of the mass of the alumina powder.

3. The method for preparing a low-temperature sintered high thermal conductivity 99% alumina ceramic substrate according to claim 1, characterized in that: In step 1, the binder is one or more of polyvinyl butyral, polyacrylate, and polyvinyl alcohol; the plasticizer is one or more of dibutyl phthalate, polyethylene glycol, diethyl phthalate, and dioctyl phthalate; and the solvent is a mixture of toluene and isopropyl alcohol.

4. The method for preparing a low-temperature sintered high thermal conductivity 99% alumina ceramic substrate according to claim 3, characterized in that: The total mass of the binder and the plasticizer accounts for 6%-10% of the mass of the alumina powder, the mass of the plasticizer accounts for 30%-40% of the mass of the binder; and the mass of the solvent accounts for 30%-50% of the mass of the alumina powder.

5. The method for preparing a low-temperature sintered high thermal conductivity 99% alumina ceramic substrate according to claim 3, characterized in that: In the solvent, the mass ratio of toluene to isopropanol is 5:10.

5.

6. The method for preparing a low-temperature sintered high thermal conductivity 99% alumina ceramic substrate according to claim 1, characterized in that: In step 1, the mass ratio of Y2O3, ZrO2 and MgO in the sintering aid is 2-5:2-5:2-5.

7. The method for preparing a low temperature sintered high thermal conductivity 99% alumina ceramic substrate according to claim 1, characterized in that: In step 2, the slurry obtained in step 1 is evenly coated on the PET film using a hopper, and the thickness of the slurry outflow is controlled by adjusting the height of the scraper.

8. The method for preparing a low-temperature sintered high thermal conductivity 99% alumina ceramic substrate according to claim 1, characterized in that: In step 5, the heating rate of the gradient temperature increase debinding is 1.2-1.8°C / min, the debinding temperature of the gradient temperature increase debinding is 580-620°C, and the holding time of the gradient temperature increase debinding is 3-5h.

9. The method for preparing a low-temperature sintered high thermal conductivity 99% alumina ceramic substrate according to claim 1, characterized in that: The method also includes step six: finished product inspection, performing a warpage test on the ceramic substrate, correcting the ceramic substrate that fails the warpage test, and the ceramic substrate that passes the warpage test is the finished product.

10. The method for preparing a low-temperature sintered high thermal conductivity 99% alumina ceramic substrate according to claim 9, characterized in that: In step 6, the ceramic substrate that failed the warpage test is heated and softened at 1400°C and then stacked and fired to correct the warpage under its own gravity. In step 6, the warpage of the finished product is ≤2‰, and the surface roughness of the finished product is 0.05-0.2μm. In the finished product, the mass percentage of aluminum oxide is ≥99%, and the ceramic particle size of aluminum oxide is 0.08-0.59μm.

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