CN113416094B - Thick film metallization slurry of aluminum nitride ceramic substrate and metallization method - Google Patents

Abstract

The invention discloses thick-film metallization slurry of an aluminum nitride ceramic substrate, which mainly comprises conductive phase powder, bonding phase glass powder and an organic carrier, wherein the sintering temperature of the bonding phase glass powder is 730-860 ℃; the thick-film metallization slurry of the aluminum nitride ceramic substrate also comprises tungsten boride. The thick-film metalized slurry of the aluminum nitride ceramic substrate comprises tungsten boride, nitrogen generated at the interface of the metalized slurry and aluminum nitride at the sintering temperature and oxygen in the slurry react with the tungsten boride, and the reaction product can also reduce the viscosity of a bonding phase in the thick-film metalized slurry at the sintering temperature and accelerate the discharge of bubbles; the factors are all helpful to reduce the bubble residue in the metal film layer and improve the compactness of the metal film layer and the bonding strength with the substrate. The invention also discloses a metallization method of the aluminum nitride ceramic substrate.

Description

Thick-film metallization paste and metallization method for aluminum nitride ceramic substrate

technical field

The invention relates to the technical field of copper clad laminates, in particular to a thick-film metallization slurry for an aluminum nitride ceramic substrate and a metallization method for the aluminum nitride ceramic substrate.

Background technique

With the increasing demand for high voltage and high power and the rapid innovation of process technology, the technical requirements of power semiconductor devices include: lower on-state voltage drop, reducing device loss and volume; High frequency, low power consumption and high pressure resistance; good heat dissipation capacity. Compared with organic materials and metal materials as packaging substrates, aluminum nitride ceramic materials have excellent temperature resistance, moisture resistance, insulation, thermal conductivity and mechanical strength, and are ideal packaging materials for new-generation power semiconductor device substrates.

Thick film metallization, also known as screen printing metallization, is to coat metal layers, electrodes, wires, etc. on the surface of aluminum nitride by screen printing, and then form the required circuit or conductive layer by drying and high temperature heat treatment. The main components of the thick film paste are metal powder, binder and organic carrier. The glass adhesive phase is sintered at high temperature, and the glass phase component penetrates into the crystal boundary of aluminum nitride, forming a layer on the surface of the substrate connecting the metal film layer and the ceramic layer. The glass phase of the substrate, which determines the adhesion of the metal film layer to the aluminum nitride. The technical defect is that the glass bonding phase will react with aluminum nitride to generate nitrogen gas at high temperature, and a large number of bubble defects will be generated at the interface between the thick film and the substrate, thereby reducing the compactness of the metal film layer and the bonding strength with the ceramic substrate.

SUMMARY OF THE INVENTION

One of the objectives of the present invention is to overcome the defects existing in the prior art and provide a thick film metallization slurry for aluminum nitride ceramic substrates, which reduces the bubbles at the interface between the thick film and the substrate, and improves the compactness and density of the metal film layer. Bonding strength to ceramic substrate.

In order to achieve the above purpose, the technical solution of the present invention is as follows: a thick film metallization slurry for aluminum nitride ceramic substrate, the main components are conductive phase powder, bonding phase glass powder and organic carrier, the bonding The sintering temperature of the phase glass powder is 730-860 DEG C; the thick-film metallization paste of the aluminum nitride ceramic substrate also contains a tungsten boride. A tungsten boride reacts with the nitrogen gas generated at the interface between the aluminum nitride ceramic substrate and the metallization slurry coating under the sintering temperature. The reaction product can reduce the viscosity of the adhesive phase, further improve the fluidity of the slurry, the bubbles are more likely to escape, the number of pores at the interface is reduced, the interface connection between the metal film layer and the ceramic pole piece is improved, and the thick film after sintering is reduced. cracks in the film and increase the density of the film. Compared with other tungsten boride compounds, tungsten monoboride has a lower metal resistivity, which helps to reduce the square resistance of the film.

A preferred technical solution is that, in parts by mass, the thick film metallization slurry for the aluminum nitride ceramic substrate mainly consists of: 80-95 parts of conductive phase powder and 2-8 parts of adhesive phase glass powder , 3 to 12 parts of organic carrier, and 0.03 to 0.45 parts of tungsten monoboride. The content of tungsten boride is too large, which affects the continuity of the bonding layer, which is not conducive to maintaining the predetermined adhesion strength between the metal film layer and the ceramic substrate. Defects increase.

A preferred technical solution is that, taking the mass of the conductive phase powder as 100%, the main composition of the conductive phase powder is: silver 60%-75%, copper 15%-30%, titanium 1.5%-12% %; based on the mass of the adhesive phase glass powder as 100%, the main composition of the adhesive phase glass powder is 17-27% of zinc oxide, 60-72% of diboron trioxide, and 10-20% of silicon dioxide. %. The melting point of the conductive phase powder is about 840°C, which is higher than the temperature at which tungsten boride reacts with oxygen and nitrogen. During the sintering and heating process, the adhesive phase glass powder first melts into a liquid state and penetrates into the ceramic substrate on the surface of the aluminum nitride. Between the grains, the surface of the aluminum nitride ceramic is wetted, and there is an exhaust gap between the unmelted conductive phase powder at this time, which reduces the porosity in the metal film layer (thick film) and improves the density.

A preferred technical solution is that the thick-film metallization paste of the aluminum nitride ceramic substrate further comprises a negative thermal expansion material with isotropic negative thermal expansion performance at 730-800°C. In the process of sintering and heating, the volume of the isotropic negative thermal expansion material is reduced, so that the internal stress distribution of the glass bonding layer is uniform, and the thermal expansion coefficient of the metal film layer and the aluminum nitride layer is matched. The negative thermal expansion material with reduced volume can also increase the open porosity, further accelerate the discharge of air bubbles on the surface of the ceramic substrate, and the volume of the negative thermal expansion material increases during the cooling process after sintering, compensating for the thermal expansion of glass frit and metal. The orientation of the negative thermal expansion material in the glass frit is uncertain, and the anisotropic negative thermal expansion material will also increase the unevenness of the internal stress distribution of the bonding layer and increase the probability of crack defects.

A preferred technical solution is that the negative thermal expansion material is zirconium tungstate, and the thick film metallization slurry of the aluminum nitride ceramic substrate is mainly composed of: 80-95 parts of conductive phase powder, 2-95 parts of adhesive phase glass powder 8 parts, 3-12 parts of organic carrier, 0.03-0.5 part of tungsten monoboride, and 0.05-0.3 part of zirconium tungstate. Further, 83-91 parts of conductive phase powder, 3-6 parts of adhesive phase glass powder, 5-12 parts of organic carrier, 0.1-0.35 parts of tungsten monoboride, and 0.08-0.22 parts of zirconium tungstate. The basic composition of the organic carrier is a solvent and a thickener, which include modifiers such as rheology agent, surfactant, defoaming agent, etc., to control the viscosity of the slurry. The optional solvent is terpineol, diethylene glycol butyl ether acetate, and dibutyl phthalate, and the optional thickener is ethyl cellulose and polyvinyl acetal.

A preferred technical solution is that the average particle size of the conductive phase powder is 1-2.5 μm, the average particle size of the adhesive phase glass powder is 2.5-3.5 μm, and the average particle size of the tungsten monoboride It is 200～600nm. The particle size combination of the above components is more favorable for tungsten boride to migrate to the metallization interface of the ceramic substrate.

A preferred technical solution is that the bonding phase glass powder and tungsten boride are composite powders. Under the sintering condition, the flow of the adhesive phase glass liquid can drive more tungsten boride to migrate to the aluminum nitride interface, and improve the probability of tungsten boride participating in the reaction of nitrogen and oxygen; further, the composite powder is a hybrid composite powder body. The preparation method of the mixed composite powder is as follows: mixing the adhesive phase glass powder with tungsten monoboride, adding it to the dispersion, ball milling, and sieving to obtain the mixed composite powder with a predetermined particle size.

A preferred technical solution is that the average particle size of the zirconium tungstate is 200-600 nm; the adhesive phase glass powder, tungsten monoboride and zirconium tungstate are composite powders.

The second purpose of the present invention is to provide a metallization method for an aluminum nitride ceramic substrate, which includes the following steps: screen printing the thick film metallization paste of the aluminum nitride ceramic substrate described above on the aluminum nitride substrate, inert Sintered in a gas atmosphere.

A preferred technical solution is that the sintering is staged sintering, the temperature of the first sintering stage is 730-780°C, and the sintering temperature of the second stage is 780-860°C. A tungsten boride fully reacts with oxygen and nitrogen and reacts with the interface gas, so that the gas is fully discharged under the temperature condition of the first sintering section. Further, the composition of the conductive phase powder and the adhesive phase glass powder satisfying the above sintering temperature is: the main composition of the conductive phase powder is: silver 60%-75%, copper 15%-30%, titanium 1.5%- 12%; based on the mass of the adhesive phase glass powder as 100%, the main composition of the adhesive phase glass powder is 17% to 27% of zinc oxide, 60% to 72% of boron trioxide, and 10% to 20% of silicon dioxide. . Further, the sintering holding time of the first sintering section is 3-8 minutes, and the sintering holding time of the second sintering section is 12-20 minutes. Further, the sintering temperature of the first stage is 750-780°C.

The advantages and beneficial effects of the present invention are:

The thick film metallization slurry of the aluminum nitride ceramic substrate of the present invention contains a tungsten boride, and the nitrogen gas generated at the interface between the metallization slurry and the aluminum nitride and the oxygen in the slurry react with the tungsten boride at the sintering temperature , the reaction product can also reduce the viscosity of the adhesive phase in the thick film metallization slurry at the sintering temperature, and accelerate the discharge of air bubbles; the above factors all help to reduce the residual air bubbles in the metal film layer of the metallized aluminum nitride ceramic substrate, Improve the compactness of the metal film layer and the bonding strength with the substrate.

Detailed ways

The specific embodiments of the present invention will be further described below with reference to the examples. The following examples are only used to illustrate the technical solutions of the present invention more clearly, and cannot be used to limit the protection scope of the present invention.

Embodiment (abbreviated as S, the same below)

Example 1 The composition of the thick film metallization paste of the aluminum nitride ceramic substrate is: 85 parts of conductive phase powder, 8 parts of adhesive phase glass powder, 11 parts of organic carrier, and 0.3 part of tungsten boride. Based on the mass of the conductive phase powder as 100%, the composition of the conductive phase powder is: silver 68.8%, copper 26.7%, titanium 4.5%; based on the mass of the adhesive phase glass powder as 100%, the adhesive phase glass The composition of the powder is 25% zinc oxide, 65% diboron trioxide, 10% silicon dioxide; based on the mass of the organic carrier as 100%, the composition of the organic carrier is 80% terpineol, 80% dibutyl phthalate Ester 14%, ethyl cellulose 6%. The average particle size of the conductive phase powder is 2.3 μm, the average particle size of the adhesive phase glass powder is 3 μm, and the average particle size of the tungsten monoboride is 400-500 nm.

The preparation method of the thick-film metallization slurry: mixing and sintering zinc oxide, diboron trioxide and silicon dioxide in proportion, grinding, and sieving to obtain a glass powder of bonding phase; fully mixing terpineol and phthalic acid Dibutyl ester and ethyl cellulose are used to prepare an organic carrier; silver-copper-titanium alloy powder, bonding phase glass powder and tungsten boride are added to the organic carrier, stirred and mixed evenly to obtain a thick aluminum nitride ceramic substrate. Film metallization paste.

Example 2

Example 2 is based on Example 1, except that the thick film metallization paste of the aluminum nitride ceramic substrate of Example 1 has the following composition: 85 parts of conductive phase powder, 8 parts of adhesive phase glass powder, and 11 parts of organic carrier parts, 0.3 parts of tungsten monoboride, and 0.15 parts of zirconium tungstate. The average particle size of the zirconium tungstate is 400 to 500 nm.

The difference between the preparation method of the thick-film metallization slurry is that zirconium tungstate and silver-copper-titanium alloy powder, bonding phase glass powder and tungsten boride are added to the organic carrier, and stirred and mixed evenly to obtain aluminum nitride ceramics. Thick film metallization paste for substrates.

Example 3

Example 3 is based on Example 1, the difference is: in the preparation process of the thick film metal frame slurry, the prepared adhesive phase glass powder and tungsten boride are placed in absolute ethanol to obtain a fluid mixture. The mixed system is added to the ball milling equipment for ball milling, and the mixed system after ball milling is dried to obtain the bonding phase glass powder/tungsten boride composite powder; silver-copper titanium alloy powder, bonding phase glass powder/monoboride The tungsten composite powder is added to the organic carrier, stirred and mixed evenly to obtain a thick-film metallization slurry of an aluminum nitride ceramic substrate.

Example 4

Example 4 The composition of the thick film metallization paste for the aluminum nitride ceramic substrate is based on Example 2; in the preparation process of the thick film metal frame paste, the prepared adhesive phase glass powder-tungsten boride and tungsten acid are mixed The zirconium is placed in anhydrous ethanol to obtain a mixed system with fluidity. The mixed system is added to the ball milling equipment for ball milling, and the mixed system after ball milling is dried to obtain the bonding phase glass powder/tungsten monoboride/zirconium tungstate composite powder ; Add silver-copper-titanium alloy powder, bonding phase glass powder/tungsten monoboride/zirconium tungstate composite powder into the organic carrier, stir and mix evenly to obtain a thick-film metallization slurry of aluminum nitride ceramic substrate.

Example 5

Example 5 The composition of the thick film metallization paste for the aluminum nitride ceramic substrate is based on Example 1; the difference is the composition of the adhesive phase glass powder: based on the mass of the adhesive phase glass powder as 100% The composition of the glass powder was 30% of zinc oxide, 60% of diboron trioxide, and 10% of silicon dioxide.

Comparative example (abbreviated as D, the same below)

Comparative Example 1 The thick film metallization paste of the aluminum nitride ceramic substrate is composed of 85 parts of conductive phase powder, 8 parts of adhesive phase glass powder, 11 parts of organic carrier, and does not contain tungsten boride.

Comparative Example 1 The composition of the conductive phase powder, the composition of the adhesive phase glass powder, the composition of the organic carrier, the particle size of each component and the preparation method are the same as those of Example 1.

The thick film metallization slurries of the above examples and comparative examples were tested for the metallization performance of the ceramic substrates as follows: the aluminum nitride ceramic substrate and the oxygen-free copper plate were cleaned with acetone respectively, and the aluminum nitride ceramic substrate was cleaned by a screen printing process. A printing area is formed on the substrate, the printing thickness is 160 μm, sintered, and the metallized aluminum nitride ceramic substrate is cleaned, and the oxygen-free copper plate is welded to the metallized surface of the aluminum nitride ceramic substrate by a vacuum brazing furnace. The sintering temperature of the ceramic substrate with the screen printing paste layer under argon protection is controlled as follows:

Group A: heat up from room temperature to 250°C at a heating rate of 5°C/min, then heat up from 250°C to a peak temperature of 850°C at a heating rate of 10°C/min, keep the temperature for 15 minutes, and cool slowly. The samples of the examples are respectively counted as S1A, S2A, S3A, S4A, S5A, the comparative samples are counted as DA;

Group B: The temperature was raised from room temperature to 250°C at a heating rate of 5°C/min, then from 750°C at a heating rate of 10°C/min, and kept for 5 minutes; the temperature was raised to a peak temperature of 860°C at a heating rate of 10°C/min, and the temperature was kept warm. 15min, slow cooling, the samples of the examples are respectively counted as S1B, S2B, S3B, S4B, and S5B, and the samples of the comparative examples are counted as DB;

Performance testing of metallized aluminum nitride ceramic substrates and copper clad laminates:

1. Quantitative detection of the porosity of the sintered metal film layer based on Image J software, porosity refers to the proportion of the area occupied by pores in the material to the total area. The porosity in the metal film layer is an important indicator of the reaction density;

2. Use the peel test to test the film adhesion between the copper layer and the ceramic substrate.

The porosity of Examples 1-5 and Comparative Example 1 is shown in Table 1 below:

Table 1

sample S1A S2A S3A S4A S5A DA Porosity/% 6.17 5.55 4.91 4.46 6.08 11.48 sample S1B S2B S3B S4B S5B DB Porosity/% 5.70 5.07 4.59 4.05 5.56 10.15

It can be seen from the above table that the porosity of Examples 1-5 of Group A and Group B are better than those of the comparative example, and the porosity of Group B is improved to varying degrees on the basis of Group A; composite powder and negative Both thermally expandable materials help to further reduce the porosity; the degree of improvement is more pronounced in the Examples compared to the Comparative Examples.

The copper layer of the embodiment 1-5 and the ceramic substrate film layer adhesion improvement (with DA as a reference) percentage is shown in the following table 2:

Table 2

sample S1A S2A S3A S4A S5A DA Film adhesion improvement/% 13 19 twenty four 30 15 —— sample S1B S2B S3B S4B S5B DB Film adhesion improvement/% 18 twenty four 30 36 20 3

The film adhesion of the examples in groups A and B is better than that of the comparative example, and the change trend of the film adhesion is the same as that of the porosity.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the technical principles of the present invention, several improvements and modifications can be made. These improvements and modifications It should also be regarded as the protection scope of the present invention.

Claims (9)

1. The thick-film metallization slurry of the aluminum nitride ceramic substrate is characterized by mainly comprising conductive phase powder, bonding phase glass powder and an organic carrier, wherein the sintering temperature of the bonding phase glass powder is 730-860 ℃; the thick film metallization slurry of the aluminum nitride ceramic substrate also comprises tungsten boride;

the thick film metallization slurry of the aluminum nitride ceramic substrate mainly comprises the following components in parts by weight: 80-95 parts of conductive phase powder, 2-8 parts of bonding phase glass powder, 3-12 parts of organic carrier and 0.03-0.45 part of tungsten boride.

2. The thick-film metallization paste for aluminum nitride ceramic substrates according to claim 1, wherein the conductive phase powder comprises, based on 100% by mass of the conductive phase powder: 60 to 75 percent of silver, 15 to 30 percent of copper and 1.5 to 12 percent of titanium; the adhesive phase glass powder mainly comprises, by mass, 100% of the adhesive phase glass powder, 17-27% of zinc oxide, 60-72% of boron trioxide and 10-20% of silicon dioxide.

3. The thick-film metallization paste of the aluminum nitride ceramic substrate as claimed in claim 1, further comprising a negative thermal expansion material having isotropic negative thermal expansion properties within 730-800 ℃.

4. The thick film metallization paste of aluminum nitride ceramic substrates of claim 3, wherein the negative thermal expansion material is zirconium tungstate, and the thick film metallization paste of aluminum nitride ceramic substrates consists essentially of: 80-95 parts of conductive phase powder, 2-8 parts of bonding phase glass powder, 3-12 parts of organic carrier, 0.03-0.5 part of tungsten boride and 0.05-0.3 part of zirconium tungstate.

5. The thick-film metallization paste for aluminum nitride ceramic substrates as claimed in claim 4, wherein the conductive phase powder has an average particle size of 1 to 2.5 μm, the binder phase glass powder has an average particle size of 2.5 to 3.5 μm, and the tungsten boride has an average particle size of 200 to 600 nm.

6. The thick-film metallization paste of an aluminum nitride ceramic substrate according to claim 1, wherein the binder phase glass powder and the tungsten boride are composite powders.

7. The thick-film metallization paste for aluminum nitride ceramic substrates as claimed in claim 5, wherein the average particle size of the zirconium tungstate is 200 to 600 nm; the bonding phase glass powder, the tungsten boride and the zirconium tungstate are composite powder.

8. A metallization method of an aluminum nitride ceramic substrate is characterized by comprising the following steps: screen printing a thick film metallisation paste of an aluminium nitride ceramic substrate as claimed in any one of claims 1 to 7 onto an aluminium nitride substrate and sintering under an inert gas atmosphere.

9. The method for metalizing the aluminum nitride ceramic substrate according to claim 8, wherein the sintering is a step sintering, and the temperature of the first sintering step is 730-780 ℃; the second-stage sintering temperature is 780-860 ℃.