CN115536402A - A kind of preparation method of silicon nitride/tungsten high temperature co-fired ceramic substrate - Google Patents

Abstract

The invention relates to a preparation method of a silicon nitride/tungsten high-temperature co-fired ceramic substrate, which comprises the following steps: (1) Taking silicon powder/silicon nitride powder as raw material powder, taking rare earth oxide and alkaline earth metal oxide as composite sintering aids, carrying out primary ball milling mixing with a solvent, adding a plasticizer and a binder for secondary ball milling, and finally carrying out vacuum deaeration to obtain mixed slurry; (2) Adopting tape casting equipment to tape-cast the mixed slurry to prepare a raw material tape; (3) Drawing a conductive pattern on the casting film by using metal W slurry as printing conductive slurry through a screen printing machine, and drying to obtain a raw material belt printed with the conductive pattern; (4) And cutting and laminating the raw material belt printed with the conductive pattern to obtain a silicon nitride membrane with required thickness, and then performing vacuum de-bonding and air pressure sintering to obtain the silicon nitride/tungsten high-temperature co-fired ceramic.

Description

A kind of preparation method of silicon nitride/tungsten high temperature co-fired ceramic substrate

technical field

The invention relates to a method for preparing a silicon nitride/tungsten high temperature co-fired ceramic substrate, belonging to the technical field of power device packaging.

Background technique

With the increasing development of electronic technology, power electronic devices are gradually developing in the direction of high integration, high power, and high energy consumption. As the digital-to-electrical conversion center and signal transmission path in electronic equipment, power electronic devices are used in various fields such as energy, transportation, and basic industries. The characteristics of high power, high frequency and integration make its power reach GW level. Due to the high energy density, serious heating is caused, and the problem that seriously affects the working stability and life of the device is also becoming more and more prominent. Therefore, obtaining a ceramic substrate with higher heat dissipation performance becomes a very reasonable choice. Alumina and aluminum nitride are currently commonly used ceramic substrate materials. However, the thermal conductivity of alumina is relatively low, which cannot meet the increasing heat dissipation requirements; while aluminum nitride ceramics have relatively high thermal conductivity, but their mechanical properties are poor, and they cannot bear the mechanical impact on the substrate due to thermal shock, collision and other application environments. Performance challenges. Silicon nitride ceramics have the advantage of high reliability, and as the research on silicon nitride ceramics with high thermal conductivity becomes more and more mature, the problem of thermal conductivity has gradually been solved. Therefore, silicon nitride ceramics are currently very advantageous candidate materials. However, there are few reports on metallization based on silicon nitride ceramics, which directly limits the application of silicon nitride ceramics in power electronic devices. Therefore, the present invention proposes a method for metallizing a silicon nitride ceramic substrate, providing reference for its application in the field of power electronic devices.

Contents of the invention

The object of the present invention is to provide a method for metallizing a silicon nitride ceramic substrate to solve the problems of heating and working stability caused by high power density electronic devices to the substrate material.

On the one hand, the present invention provides a kind of preparation method of silicon nitride/tungsten high temperature co-fired ceramics, comprising:

(1) Using silicon powder/silicon nitride powder as the raw material powder, rare earth oxides and alkaline earth metal oxides as composite sintering aids, and performing ball milling and mixing with solvents, and then adding plasticizers and binders for secondary ball milling, Finally, the mixed slurry is obtained through vacuum defoaming;

(2) Tape-casting the mixed slurry by tape-casting equipment to prepare a raw tape;

(3) Use the metal W paste as the printing conductive paste, draw conductive patterns on the casting film by a screen printing machine, and after drying, obtain a raw material tape printed with conductive patterns;

(4) Cutting and laminating the obtained raw tape printed with conductive patterns to obtain a silicon nitride diaphragm of required thickness, and then vacuum debonding and air pressure sintering to obtain silicon nitride/tungsten high temperature co-fired ceramics.

In the early research process, the inventors found through research (as shown in FIG. 3 ) that compared with tungsten and molybdenum, the thermodynamic reaction tendency of molybdenum and silicon nitride at high temperature is greater. However, the inventors also found that the bonding strength between the metal layer and the substrate should not be provided by the metal functional phase, and excessive interfacial reactions will have a negative impact on the conductivity of the metal layer. Therefore, the inventors chose metal tungsten. Further, the present invention also has the following technical difficulties: (1) Use raw materials containing silicon powder to prepare silicon nitride with high thermal conductivity, mainly by optimizing the ratio of sintering aids, controlling reaction sintering and post-sintering technology to improve the thermal conductivity of silicon nitride. (2) Realize a good interfacial bonding between the tungsten metal layer and the silicon nitride substrate to achieve sintering matching and the conductivity of the metal layer. Mainly pre-treat the powder by ball milling to obtain finer powder raw materials; by optimizing the solid content of the slurry, reduce the porosity of the matrix and the metal layer after debonding; A suitable tungsten metallized film is obtained by screen printing technology; finally, a smaller sintering shrinkage rate is achieved, and the shrinkage rate matching of the two is achieved. In order to achieve sintering matching and metal layer conduction. The invention realizes the conduction of the metal layer and provides test data.

Preferably, the solvent is ethanol, ethyl acetate, 2-butanone or a mixture of ethanol/butanone, ethyl acetate/butanone.

Preferably, the rare earth oxide is at least one of erbium oxide and samarium oxide; the alkaline earth metal oxide is at least one of MgO and CaO; wherein the alkaline earth metal oxide and the rare earth oxide mass ratio content (20 ~40): (60~80).

Preferably, the raw material is at least one of silicon powder and silicon nitride powder. When the silicon powder content is > 0%, the quality of the silicon powder is calculated as the quality after complete nitriding, and the mass content of the sintering aid is based on this The total powder mass obtained after the calculation method is obtained.

Preferably, when silicon powder and silicon nitride are used together as raw materials, the mass content of the sintering aid is 5%-13%. Preferably, the content of the silicon powder is ≥0wt% (more preferably 20-100wt%), and the total mass of the silicon powder and silicon nitride powder is recorded as 100wt%.

Preferably, the silicon powder has a particle size in the range of 0.5-20 μm, and the oxygen content is 0.42 wt %; the silicon nitride powder has a particle size in the range of 0.3-2 μm.

Preferably, the binder is one of polyvinyl butyral, polymethyl methacrylate, and polypropylene carbonate.

Preferably, the dispersant is one of triolein, castor oil phosphate and terpineol.

Preferably, the plasticizer is at least one of butyl benzyl phthalate, dioctyl phthalate and polyethylene glycol 400, such as butyl benzyl phthalate-polyethylene glycol 400 Or dioctyl phthalate-polyethylene glycol 400.

Preferably, the vacuum degree of the vacuum degassing is 15-400 Pa, and the degassing time is 15-40 minutes.

Preferably, the parameters of tape casting include: the height of the scraper is 100 μm-1.00 mm; the thickness of each raw material belt is 50 μm-0.50 mm.

Preferably, the setting parameters of the screen printing machine include: the rubber squeegee is 30-50°, the plate distance is 1-10 mm, the lifting stroke is 100-200 mm, and the printing speed and ink return speed are 10% and 30% respectively.

Preferably, the size of the cut raw material tape printed with conductive patterns is 50mm×50mm;

The number of laminated layers is at least 10, the pressure is 2-30 MPa, and the time is 15-40 minutes.

Preferably, the debonding temperature is 400-700° C. under vacuum condition, and the time is 1-6 hours; preferably, the heating rate of the vacuum debonding is 1-5° C./min.

Preferably, the temperature of the air pressure sintering is 1800-1950°C, the pressure of nitrogen is 200-900KPa, and the holding time is 2-24 hours; preferably, the heating rate of the air pressure sintering is 1-5°C/min.

Preferably, when the raw material contains silicon powder, the debonded silicon nitride diaphragm is then subjected to nitriding treatment before pressure sintering; the temperature of the nitriding treatment is 1350-1550° C., and the holding time is 2 ~24 hours; preferably, the heating rate of the nitriding treatment is 1-5° C./min.

In another aspect, the present invention provides a silicon nitride/tungsten high temperature co-fired ceramic prepared according to the above preparation method.

Beneficial effect:

The invention provides a method for preparing a silicon nitride ceramic substrate by tape casting: using the mixed solvent, silicon powder, and the sintering aid, binder and plasticizer as raw materials to prepare a uniformly mixed silicon tape casting slurry , to obtain a curlable green body with suitable strength and plasticity by tape casting;

The present invention uses commercial AlN tungsten metallization paste as ink, and coats a clear metallization circuit with uniform thickness on the surface of the green body through a screen printing process. The silicon/tungsten multi-layer green body is obtained through laser cutting and lamination hot pressing. After the joint debonding, nitriding, and sintering processes, the W metal layer is smooth without warping, the interface is stable, and the silicon nitride substrate has stable performance. Silicon nitride/tungsten high-temperature co-fired ceramics;

The invention provides a silicon nitride ceramic substrate with reliable quality, on which the metallization of the silicon nitride ceramic substrate is successfully realized. This provides an experimental basis for the application of silicon nitride ceramic substrates in multilayer co-fired components, which is conducive to expanding the application of silicon nitride ceramics in the electronics industry.

Description of drawings

Figure 1 is a surface diagram of a W-containing multilayer sintered sample;

Figure 2 is a side view of a W-containing multilayer sintered sample;

Figure 3 shows the change in Gibbs energy of the reaction between W/Mo and Si ₃ N ₄ substrate at 0-1850°C;

Fig. 4 is the XRD pattern of the cross-section of the sintered body of the silicon nitride multilayer assembly in the embodiment.

detailed description

The present invention will be further described below through the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, not to limit the present invention.

The invention uses silicon nitride/silicon powder as a raw material to obtain a silicon nitride biscuit through tape casting, and after debonding, carries out nitriding and sintering to prepare a silicon nitride ceramic substrate. Silicon nitride/silicon powder is used as the raw material for reaction sintering. The use of silicon powder can avoid the high cost of high-purity silicon nitride raw materials and the limitation of deliquescence, realize the low-cost preparation of silicon nitride ceramics, and promote silicon nitride ceramics mass production. In addition, silicon powder has the advantage of low oxygen content, and it is easy to obtain a silicon nitride substrate with higher thermal conductivity.

The present invention uses tape casting technology to prepare silicon nitride biscuit, uses silicon nitride/silicon powder as raw material powder, and rare earth oxide Re ₂ O ₃ and metal oxide MgO/CaO as composite sintering aids to obtain mixed powder. After being mixed with the dispersant and the solvent by ball milling once, the binder and dispersant are added, the slurry is obtained by ball milling and degassing for the second time, and the biscuit is obtained by tape casting. After debonding, nitriding and sintering, a silicon nitride ceramic substrate is obtained.

The silicon nitride ceramic substrate metallization technology proposed by the present invention uses the biscuit obtained by the tape casting technology as the substrate, and uses the commercial tungsten metallization slurry as the ink to prepare silicon nitride/tungsten co-fired by screen printing Blank.

Tape casting: Silicon nitride/silicon powder is used as raw material, rare earth oxide RE ₂ O ₃ and alkali metal oxide (MgO/CaO) are used as composite sintering aids. Using ethanol, ethyl acetate, 2-butanone or a mixture of ethanol/butanone, ethyl acetate/butanone as a solvent, one of triolein, castor oil phosphate and terpineol as a dispersant, One of polyvinyl butyral, polymethyl methacrylate, and polypropylene carbonate is used as a binder, and one of butyl benzyl phthalate and dioctyl phthalate is used as a plasticizer Ⅰ, polyethylene glycol 400 as plasticizer Ⅱ. First ball mill the solvent, dispersant, silicon nitride/silicon powder, and sintering aids once, then add the binder and plasticizer for the second ball mill after 24-36 hours, and obtain a uniformly mixed slurry after 48-72 hours, after defoaming , using a casting machine for casting.

Silicon nitride ceramic green body obtained by tape casting process, tungsten metallization slurry.

Use screen printing equipment to print tungsten paste with uniform thickness on the above-mentioned silicon nitride ceramic green body. The blanks dried at room temperature are cut into squares of the same size for multi-layer equal-pressure lamination to obtain multi-layer green blanks with required thickness. Preferably, a laser cutting method is used to obtain squares with a size of 50mm×50mm, and laminated.

As an example of screen printing, it includes: after setting the parameters of the screen printing machine, screen printing is performed on the blank by the screen printing machine. Set the parameters of the screen printing machine as follows, the rubber scraper is 30-50°, the plate distance is 1-10mm, the lifting stroke is 100-200mm, the printing speed and ink return speed are 10% and 30% respectively. Then laser cutting to obtain square pieces of the same size of 50mm×50mm, 10-20 pieces each time, laminated under a pressure of 2-30MPa for 15-40min to obtain squares with uniform thickness, and then debonding, nitriding and sintering.

Debonding, nitriding and sintering. Firstly, the debonding process is carried out, the debonding temperature is usually at 400-700°C, vacuum condition, heat preservation for 1-6 hours, and the heating rate is 1-5°C/min. If the raw material of the book contains silicon powder, nitriding treatment is carried out after debonding. The nitriding temperature is 1350-1550°C, the heating rate is 1-5°C/min, and the holding time is 2-24 hours. The mouth circumference is sintered by air pressure sintering process, the atmosphere is nitrogen atmosphere, the temperature is 1800-1950°C, the air pressure is 200-900KPa, the time is 2-24 hours, and the heating rate of the sintering is 1-5°C/min.

In the present invention, the silicon nitride ceramic substrate is prepared by tape casting method, and the tungsten paste is printed on the silicon nitride ceramic green blank by using the screen printing process, and then common debonding, nitriding and sintering. In addition to the performance of traditional silicon nitride substrates, it also has the advantages of low cost, higher thermal conductivity, and high production efficiency. It is a preparation solution with advantages in mass production.

The invention uses the Archimedes drainage method to measure the relative density of the silicon nitride ceramic substrate material to be 90-97%. The thermal conductivity of the silicon nitride ceramic substrate material is measured to be 65-70 W/m·K by means of a laser thermal conductivity meter. The flexural strength of the silicon nitride ceramic substrate material measured by a three-point bending method is 700-900 MPa. After measurement, with 100wt% silicon powder as raw material, the sintering shrinkage rate is 8%-12%. With 100wt% silicon nitride as the raw material, the sintering shrinkage rate is 15%-20%. When the silicon powder content changes, the sintering shrinkage rate ranges from 8% to 20%. After measurement, the thickness of the metallization layer after co-firing is 7-10 μm. X-ray diffraction analysis shows that W ₅ Si ₃ phase is formed at the silicon nitride/W interface after co-firing. The square resistance of the metal layer measured by the square resistance method is 0.8-1.0Ω/sq.

Examples are given below to describe the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention, and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art according to the above contents of the present invention all belong to the present invention scope of protection. The specific process parameters and the like in the following examples are only examples of suitable ranges, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific values exemplified below.

Example 1

Silicon powder is used as raw material (107.67g), an azeotropic mixture of 78wt% ethyl acetate and _22wt % ₂ -butanone is used as solvent, MgO and Er2O3 are used as sintering aids, MgO content is 3wt%, _{Er2O 3} content is 9 wt%. Glyceryl trioleate is a dispersant. The above solvent, dispersant and powder were ball milled once for 24 hours. Polypropylene carbonate was used as binder, butyl benzyl phthalate and polyethylene glycol 400 were used as plasticizers, and after adding, ball milling was performed twice for 48 hours to obtain a uniformly mixed slurry, which was degassed for 25 After -30 min, casting was carried out using a tape casting machine with a blade height of 0.4 mm and a casting speed of 120 mm/min. After the cast film dries, the reel is removed. Use a screen printing machine to print tungsten paste, set the rubber scraper to 45, the plate distance to 2mm, the lifting stroke to 150mm, and the printing speed and ink return speed to be 10% and 30% respectively. Print the tungsten paste on the obtained silicon nitride blank, and dry it at room temperature. Cut the cast film into a rectangle with a size of 50mm×50mm, take 10 pieces at a time, hold the pressure under the manual hydraulic press for 1 minute, put it in a 60°C oven for 30 minutes, and continue to apply the same pressure to the mold after taking it out. Remove the sample from the mold. Insulate in a vacuum debonding furnace at 600°C for 1h. After debonding, keep it warm at 1450°C for 2 hours under a nitrogen atmosphere. After nitriding, further raise the temperature of the product to 1830°C and keep it for 2 hours to complete sintering. After cooling with the furnace, a silicon nitride/tungsten high temperature co-fired ceramic with smooth W metal layer, stable interface bonding, and stable performance of the silicon nitride substrate is prepared.

Example 2

In this embodiment 2, the preparation process of silicon nitride/tungsten high-temperature co-fired ceramics refers to embodiment 1, the only difference is that Si powder and Si ₃ N ₄ powder are selected as raw materials (total 107.67g), wherein the content of Si powder is 80 %. A silicon nitride/tungsten high temperature co-fired ceramic with smooth W metal layer, stable interfacial bonding, and stable performance of the silicon nitride substrate was prepared.

Example 3

In this embodiment 3, the preparation process of silicon nitride/tungsten high-temperature co-fired ceramics refers to embodiment 1, the only difference is that Si powder and Si ₃ N ₄ powder are selected as raw materials (total 107.67g), wherein the content of Si powder is 60 %. A silicon nitride/tungsten high temperature co-fired ceramic with smooth W metal layer, stable interfacial bonding, and stable performance of the silicon nitride substrate was prepared.

Example 4

In this embodiment 4, the preparation process of silicon nitride/tungsten high-temperature co-fired ceramics refers to embodiment 1, the only difference is that Si powder and Si ₃ N ₄ powder are selected as raw materials (total 107.67g), wherein the content of Si powder is 40 %. A silicon nitride/tungsten high temperature co-fired ceramic with smooth W metal layer, stable interfacial bonding, and stable performance of the silicon nitride substrate was prepared.

Example 5

In this embodiment 5, the preparation process of silicon nitride/tungsten high temperature co-fired ceramics refers to embodiment 1, the only difference is that Si powder and Si ₃ N ₄ powder are selected as raw materials (total 107.67g), wherein the content of Si powder is 0 %; In order to ensure dense sintering, an azeotropic mixture of 78wt% ethyl acetate and 22wt% 2-butanone is used as a solvent, MgO and Er ₂ O ₃ are used as sintering aids, the content of MgO is 3wt%, and the content of Er ₂ O ₃ 9wt%. Co-fired ceramics with smooth W metal layer and no warpage were prepared, but the shrinkage of the metal layer pattern was inconsistent.

After experimental exploration, changing the ratio of Si/Si ₃ N ₄ in the powder during the silicon nitride tape casting process, the results of the square resistance of the metal layer are as follows. Si powder and Si3N4 powder are selected as raw materials (107.67g in total), and when the content of Si powder is 100%, the square resistance of the metal layer is 0.89Ω/sq. When the content of Si powder is 80%, the square resistance of the metal layer is 1.22Ω/sq. When the content of Si powder is 60%, the square resistance of the metal layer is 1.09Ω/sq. When the content of Si powder is 40%, the square resistance of the metal layer is 1.14Ω/sq. When the Si powder content is 20%, the square resistance of the metal layer is 1.47Ω/sq. When the Si powder content is 0%, the square resistance of the metal layer is 1.21Ω/sq. In addition, there is a lack of precise testing methods for the bonding strength of the metal-ceramic interface. Macroscopically, it shows a sintering matching result without defects such as warping, delamination, and peeling.

Claims (12)

1. A preparation method of silicon nitride/tungsten high-temperature co-fired ceramic is characterized by comprising the following steps:

(1) Taking silicon powder/silicon nitride powder as raw material powder, taking rare earth oxide and alkaline earth metal oxide as composite sintering aids, carrying out primary ball milling mixing with a solvent, adding a plasticizer and a binder for secondary ball milling, and finally carrying out vacuum defoaming to obtain mixed slurry;

(2) Adopting tape casting equipment to tape-cast the mixed slurry to prepare a raw material tape;

(3) Drawing a conductive pattern on the casting film by using metal W slurry as printing conductive slurry through a screen printing machine, and drying to obtain a raw material tape printed with the conductive pattern;

(4) And cutting and laminating the obtained raw material belt printed with the conductive pattern to obtain a silicon nitride membrane with required thickness, and then performing vacuum de-bonding and gas pressure sintering to obtain the silicon nitride/tungsten high-temperature co-fired ceramic.

2. The method according to claim 1, wherein the solvent is ethanol, ethyl acetate, 2-butanone or a mixture of ethanol/butanone, ethyl acetate/butanone;

the rare earth oxide is at least one of erbium oxide and samarium oxide; the alkaline earth metal oxide is at least one of MgO and CaO; wherein the mass ratio content of the alkaline earth metal oxide to the rare earth oxide is (20-40): (60-80).

3. The preparation method according to claim 1 or 2, characterized in that the raw material is at least one of silicon powder and silicon nitride powder, when the content of the silicon powder is more than 0%, the mass of the silicon powder is calculated as the mass after complete nitridation, and the mass content of the sintering aid is calculated based on the total powder mass obtained after the calculation;

when silicon powder and silicon nitride are used as raw materials, the mass content of the sintering aid is 5-13%; the content of the silicon powder is more than or equal to 0wt%, and the total mass of the silicon powder and the silicon nitride powder is recorded as 100wt%.

4. The method according to any one of claims 1 to 3, wherein the silicon powder has a particle size in the range of 0.5 to 20 μm and an oxygen content of 0.42wt%; the grain diameter of the silicon nitride powder is 0.3-2 mu m.

5. The production method according to any one of claims 1 to 4, characterized in that the binder is one of polyvinyl butyral, polymethyl methacrylate, polypropylene carbonate;

the dispersant is one of triolein, castor oil phosphate and terpineol;

the plasticizer is at least one of butyl benzyl phthalate, dioctyl phthalate and polyethylene glycol 400.

6. The preparation method of any one of claims 1-5, wherein the vacuum degree of the vacuum defoaming is 15-400 mbar, and the defoaming time is 15-40 min.

7. A production method according to any one of claims 1 to 6, wherein the parameters of the tape casting include: the height of the scraper is 100 mu m-1.00 mm; the thickness of each raw material belt is 50 mu m-0.50 mm.

8. The preparation method of any one of claims 1 to 7, wherein the setting parameters of the screen printing machine comprise: the rubber scraper is 30-50 degrees, the plate pitch is 1-10mm, the lifting stroke is 100-200mm, and the printing speed and the ink returning speed are 10% and 30% respectively.

9. The method for preparing a printed material tape according to any one of claims 1 to 8, wherein the cut raw material tape printed with the conductive pattern has a size of 50mm x 50mm;

the number of the laminated layers is at least 10, the pressure is 2-30MPa, and the time is 15-40 min.

10. The method according to any one of claims 1 to 9, wherein the temperature of the de-binding is 400 to 700 ℃, and the time is 1 to 6 hours under vacuum; preferably, the heating rate of the vacuum debonding is 1-5 ℃/min;

the temperature of the air pressure sintering is 1800-1950 ℃, the nitrogen pressure is 200-900KPa, and the heat preservation time is 2-24 hours; preferably, the heating rate of the air pressure sintering is 1-5 ℃/min.

11. The preparation method according to any one of claims 1 to 10, characterized in that when the raw material contains silicon powder, before the air pressure sintering, the silicon nitride membrane after the debonding is subjected to nitriding treatment; the temperature of the nitriding treatment is 1350-1550 ℃, and the heat preservation time is 2-24 hours; preferably, the temperature increase rate of the nitriding treatment is 1 to 5 ℃/min.

12. A silicon nitride/tungsten high temperature co-fired ceramic prepared according to the preparation method described in any one of claims 1 to 11.

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