阅读说明：本技术 一种氮化铝陶瓷基板的厚膜金属化浆料及金属化方法 (Thick film metallization slurry of aluminum nitride ceramic substrate and metallization method ) 是由 谢斌 刘亮 于 2021-08-03 设计创作，主要内容包括：本发明公开了一种氮化铝陶瓷基板的厚膜金属化浆料,主要组分为导电相粉体,粘接相玻璃粉体和有机载体,粘接相玻璃粉体的烧结温度为730～860℃；氮化铝陶瓷基板的厚膜金属化浆料还包含一硼化钨。本发明氮化铝陶瓷基板的厚膜金属化浆料中包含一硼化钨,烧结温度下金属化浆料与氮化铝的界面处产生的氮气以及浆料中的氧气与一硼化钨反应,反应产物还能降低烧结温度下厚膜金属化浆料中的粘接相粘度,加速气泡的排出；上述因素均有助于减少金属膜层中的气泡残留,提高金属膜层的致密性和与基板的结合强度。本发明还公开了一种氮化铝陶瓷基板的的金属化方法。(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.)

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.

2. The thick film metallization paste of the aluminum nitride ceramic substrate according to claim 1, wherein the thick film metallization paste of the aluminum nitride ceramic substrate mainly comprises, in parts by mass: 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.

3. 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.

4. 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 ℃.

5. The thick film metallization paste of aluminum nitride ceramic substrates of claim 4, 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.

6. The thick-film metallization paste for aluminum nitride ceramic substrates as claimed in claim 5, 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.

7. 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.

8. The thick-film metallization paste for aluminum nitride ceramic substrates according to claim 6, 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.

9. 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 8 onto an aluminium nitride substrate and sintering under an inert gas atmosphere.

10. The method for metalizing the aluminum nitride ceramic substrate according to claim 9, 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 ℃.

Technical Field

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

Background

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: the on-state voltage drop is low, and the loss and the volume of the device are reduced; the current control capability is strong, and the running speed of the equipment is improved; ultrahigh frequency, low power consumption and high pressure resistance; good heat dissipation capability. Compared with organic materials and metal materials as packaging substrates, the aluminum nitride ceramic material has excellent temperature resistance, humidity resistance, insulation, heat conduction performance and mechanical strength, and is an ideal packaging material for a new generation of power semiconductor device substrates.

Thick film metallization, also known as screen printing metallization, is to coat a metal layer, an electrode, a wire, etc. on the surface of aluminum nitride by screen printing, and then to form a desired circuit or conductive layer by drying and high temperature heat treatment. The thick film paste mainly comprises metal powder, an adhesive and an organic carrier, wherein a glass bonding phase is sintered at high temperature, components of a glass box conveniently permeate into aluminum nitride for crystallization, a glass phase for connecting a metal film layer and a ceramic substrate is formed on the surface of the substrate, and the glass phase determines the adhesive force of the metal film layer and the aluminum nitride. The technical defects are as follows: the glass bonding phase can react with aluminum nitride at high temperature to generate nitrogen, and a large amount of bubble defects are generated at the interface of the thick film and the substrate, so that the compactness of the metal film layer and the bonding strength of the metal film layer and the ceramic substrate are reduced.

Disclosure of Invention

One of the objectives of the present invention is to overcome the defects in the prior art, and to provide a thick film metallization paste for an aluminum nitride ceramic substrate, so as to reduce bubbles at the interface between the thick film and the substrate, and improve the compactness of the metal film layer and the bonding strength with the ceramic substrate.

In order to achieve the purpose, the technical scheme of the invention is as follows: the thick-film metallization slurry of the aluminum nitride ceramic substrate 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. Tungsten boride is mixed with nitrogen generated at the interface of an aluminum nitride ceramic substrate and a metalized slurry coating under the condition of sintering temperature, the nitrogen is mixed with oxygen on the surface of the ceramic substrate and shallow layers, the tungsten boride reacts with mixed gas, the viscosity of a bonding phase can be reduced by a reaction product, the fluidity of the slurry is further improved, bubbles can escape more easily, the number of air holes at the interface is reduced, the interface connection condition of a metal film layer and a ceramic pole piece is improved, cracks in a sintered thick film are reduced, and the density of the film layer is improved. Compared with other tungsten boride compounds, tungsten boride has lower metal resistivity, and is helpful for reducing sheet resistance of the film.

The preferable technical scheme is that 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. The content of tungsten boride is too large, so that the continuity of the bonding layer is affected, the preset adhesive strength between the metal film layer and the ceramic substrate is not favorably maintained, the internal stress distribution of the bonding layer is not uniform due to glass crystallization, and the crack defect is increased.

The preferred technical scheme is that the conductive phase powder mainly comprises the following components by mass percent of 100 percent: 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. The melting point of the conductive phase powder is about 840 ℃ and higher than the temperature of the reaction of tungsten boride with oxygen and nitrogen, during the sintering and temperature rising process, the bonding phase glass powder is firstly melted into liquid state to permeate into crystal grains of the ceramic substrate on the surface of aluminum nitride and wet the surface of the aluminum nitride ceramic, and at the moment, an exhaust gap exists between the unmelted conductive phase powder, so that the porosity in the metal film layer (thick film) is reduced, and the compactness is improved.

The preferable technical scheme is that the thick-film metallization slurry of the aluminum nitride ceramic substrate further comprises a negative thermal expansion material with isotropic negative thermal expansion performance within 730-800 ℃. The volume of the isotropic negative thermal expansion material is reduced in the sintering and temperature rising process, so that the internal stress of the glass bonding layer is uniformly distributed, and the thermal expansion coefficients of the metal film layer and the aluminum nitride are matched. The negative thermal expansion material with the reduced volume can also improve the open porosity, further accelerate the discharge of bubbles on the surface of the ceramic substrate, increase the volume of the negative thermal expansion material in the cooling process after sintering, and compensate the thermal expansion of the 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 can also cause the uneven degree of the internal stress distribution of the bonding layer to be intensified, so that the probability of crack defects is increased.

The preferred technical scheme is that the negative thermal expansion material is zirconium tungstate, and thick film metallization slurry of the aluminum nitride ceramic substrate mainly comprises the following components: 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. Further, 83-91 parts of conductive phase powder, 3-6 parts of bonding phase glass powder, 5-12 parts of organic carrier, 0.1-0.35 part of tungsten boride and 0.08-0.22 part of zirconium tungstate. The organic carrier is composed of solvent and thickener, including rheology agent, surfactant, defoaming agent and other modifier, to control the viscosity of the slurry. The solvent can be selected from terpineol, diethylene glycol butyl ether acetate and dibutyl phthalate, and the thickening agent can be selected from ethyl cellulose and polyvinyl acetal.

The preferable technical scheme is that the average particle size of the conductive phase powder is 1-2.5 mu m, the average particle size of the bonding phase glass powder is 2.5-3.5 mu m, and the average particle size of the tungsten boride is 200-600 nm. The combination of the particle sizes of the above components further facilitates migration of tungsten boride to the metallization interface of the ceramic substrate.

The preferred technical scheme is that the bonding phase glass powder and the tungsten boride are composite powder. The flowing of the bonding phase glass liquid under the sintering condition can drive more tungsten boride to migrate to an aluminum nitride interface, so that the probability of the tungsten boride participating in the reaction of nitrogen and oxygen is improved; furthermore, the composite powder is mixed type composite powder. The preparation method of the mixed composite powder comprises the following steps: and mixing the bonding phase glass powder with tungsten boride, adding the mixture into the dispersion liquid, performing ball milling, and sieving to obtain mixed composite powder with a preset particle size.

The preferred technical scheme is that the average particle size of the zirconium tungstate is 200-600 nm; the bonding phase glass powder, the tungsten boride and the zirconium tungstate are composite powder.

The second purpose of the present invention is to provide a metallization method of an aluminum nitride ceramic substrate, comprising the following steps: and screen printing the thick film metallization paste of the aluminum nitride ceramic substrate on an aluminum nitride substrate, and sintering in an inert gas atmosphere.

The preferable technical scheme is that the sintering is segmented sintering, and the temperature of a first sintering segment is 730-780 ℃; the second-stage sintering temperature is 780-860 ℃. The tungsten boride fully reacts with oxygen and nitrogen and interface gas, so that the gas is fully discharged under the temperature condition of the first sintering section. Further, the conductive phase powder and the bonding phase glass powder which meet the sintering temperature comprise the following components: the conductive phase powder mainly comprises the following components: 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. Further, the sintering heat preservation time of the first sintering section is 3-8 min, and the sintering heat preservation time of the second sintering section is 12-20 min. Furthermore, the sintering temperature of the first section is 750-780 ℃.

The invention has the advantages and beneficial effects that:

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 in the metallized aluminum nitride ceramic substrate and improve the compactness of the metal film layer and the bonding strength with the substrate.

Detailed Description

The following further describes embodiments of the present invention with reference to examples. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.

EXAMPLE (abbreviation S, the same applies hereinafter)

Example 1 the thick film metallization paste for an aluminum nitride ceramic substrate had the composition: 85 parts of conductive phase powder, 8 parts of bonding phase glass powder, 11 parts of organic carrier and 0.3 part of tungsten boride. The conductive phase powder comprises the following components by mass percent of 100 percent: 68.8% of silver, 26.7% of copper and 4.5% of titanium; the composition of the bonding phase glass powder is 25 percent of zinc oxide, 65 percent of boron trioxide and 10 percent of silicon dioxide by taking the mass of the bonding phase glass powder as 100 percent; the organic carrier comprises 80% of terpineol, 14% of dibutyl phthalate and 6% of ethyl cellulose by taking the mass of the organic carrier as 100%. 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 boride is 400-500 nm.

The preparation method of the thick film metallization paste comprises the following steps: mixing and sintering zinc oxide, boron trioxide and silicon dioxide according to a proportion, grinding and screening to obtain bonding phase glass powder; fully mixing terpineol, dibutyl phthalate and ethyl cellulose to prepare an organic carrier; adding silver-copper-titanium alloy powder, bonding phase glass powder and tungsten boride into an organic carrier, and uniformly stirring and mixing to obtain thick-film metalized slurry of the aluminum nitride ceramic substrate.

Example 2

Example 2 is based on example 1 with the difference that: the thick film metallization paste of the aluminum nitride ceramic substrate of example 1 had the composition: 85 parts of conductive phase powder, 8 parts of bonding phase glass powder, 11 parts of organic carrier, 0.3 part of tungsten boride and 0.15 part of zirconium tungstate. The average grain diameter of the zirconium tungstate is 400-500 nm.

The difference of the preparation method of the thick-film metallization paste is that zirconium tungstate, silver-copper-titanium alloy powder, bonding phase glass powder and tungsten boride are added into an organic carrier and are stirred and mixed uniformly to obtain the thick-film metallization paste of the aluminum nitride ceramic substrate.

Example 3

Example 3 is based on example 1 with the difference that: in the preparation process of thick film metal frame slurry, placing the prepared bonding phase glass powder and tungsten boride in absolute ethyl alcohol to obtain a mixed system with fluidity, adding the mixed system into ball milling equipment for ball milling, and drying the mixed system after ball milling to obtain bonding phase glass powder/tungsten boride composite powder; adding the silver-copper-titanium alloy powder and the bonding phase glass powder/tungsten boride composite powder into an organic carrier, and uniformly stirring and mixing to obtain the thick-film metalized slurry of the aluminum nitride ceramic substrate.

Example 4

Example 4 the composition of the thick film metallization paste for aluminum nitride ceramic substrates is based on example 2; in the preparation process of thick film metal frame slurry, placing prepared bonding phase glass powder-tungsten boride and zirconium tungstate into absolute ethyl alcohol to obtain a mixed system with fluidity, adding the mixed system into ball milling equipment for ball milling, and drying the mixed system after ball milling to obtain bonding phase glass powder/tungsten boride/zirconium tungstate composite powder; adding silver-copper-titanium alloy powder and bonding phase glass powder/tungsten boride/zirconium tungstate composite powder into an organic carrier, and uniformly stirring and mixing to obtain thick-film metallization slurry of the aluminum nitride ceramic substrate.

Example 5

Example 5 the composition of a thick film metallization paste for an aluminum nitride ceramic substrate is based on example 1; the difference is the composition of the bonding phase glass powder: the composition of the bonding phase glass powder is 30 percent of zinc oxide, 60 percent of boron trioxide and 10 percent of silicon dioxide by taking the mass of the bonding phase glass powder as 100 percent.

Comparative example (abbreviation D, same below)

Comparative example 1 the thick film metallization paste for an aluminum nitride ceramic substrate had the composition: 85 parts of conductive phase powder, 8 parts of bonding phase glass powder and 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 binder phase glass powder, the composition of the organic vehicle, the particle size of each component, and the preparation method were the same as in example 1.

The thick film metallization pastes of the above examples and comparative examples were subjected to the following ceramic substrate metallization performance test: respectively scrubbing the aluminum nitride ceramic substrate and the oxygen-free copper plate by using acetone, forming a printing area on the aluminum nitride ceramic substrate by adopting a screen printing process, wherein the printing thickness is 160 mu m, sintering, cleaning the metalized aluminum nitride ceramic substrate, and welding the oxygen-free copper plate to the metalized surface of the aluminum nitride ceramic substrate by using a vacuum brazing furnace. The sintering temperature of the ceramic substrate with the screen printing slurry layer under the argon protection condition is respectively controlled as follows:

group A: raising the temperature from room temperature to 250 ℃ at a temperature raising rate of 5 ℃/min, then raising the temperature from 250 ℃ to a peak temperature of 850 ℃ at a temperature raising rate of 10 ℃/min, preserving the temperature for 15min, and slowly cooling, wherein the samples in the examples are respectively counted as S1A, S2A, S3A, S4A and S5A, and the samples in the comparative examples are counted as DA;

group B: heating from room temperature to 250 deg.C at a heating rate of 5 deg.C/min, and maintaining at 750 deg.C at a heating rate of 10 deg.C/min for 5 min; raising the temperature to the peak temperature of 860 ℃ at the temperature raising rate of 10 ℃/min, preserving the temperature for 15min, and slowly cooling, wherein samples in examples are respectively counted as S1B, S2B, S3B, S4B and S5B, and samples in comparative examples are counted as DB;

carrying out performance test on the metallized aluminum nitride ceramic substrate and the copper-clad plate:

1. and (3) quantitatively detecting the porosity of the metal film layer obtained by sintering based on Image J software, wherein the porosity refers to the proportion of the area occupied by the pores in the material in the total area. The porosity in the metal film layer is an important index of reaction density;

2. and testing the film adhesion of the copper layer and the ceramic substrate by adopting a glass test.

The porosities of examples 1-5 and comparative example 1 are shown in table 1 below:

TABLE 1

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

As can be seen from the above table, the porosities of the examples 1 to 5 of the groups A and B are superior to those of the comparative example, and the porosity of the group B is improved to different degrees on the basis of the group A; the introduction of the composite powder and the negative thermal expansion material into the slurry is helpful for further reducing the porosity; the degree of improvement is more evident in the examples than in the comparative examples.

The percentage adhesion enhancement (by DA) of the cu layers of examples 1-5 to the ceramic substrate film layer is shown in table 2 below:

TABLE 2

Test specimen	S1A	S2A	S3A	S4A	S5A	DA
							Increase/decrease of film adhesion	13	19	24	30	15	——
Test specimen	S1B	S2B	S3B	S4B	S5B	DB
							Increase/decrease of film adhesion	18	24	30	36	20	3

The adhesion of the film layers of the examples of group A and group B is superior to the comparative examples, and the variation trend of the adhesion of the film layers is the same as the porosity.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the technical principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.