阅读说明：本技术 一种氮化铝陶瓷基板的丝网印刷浆料及金属化方法 (Screen printing slurry of aluminum nitride ceramic substrate and metallization method ) 是由 谢斌 刘亮 于 2021-09-08 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丝网印刷浆料,浆料的主要组成为导电相粉体、玻璃相粉体和有机载体,玻璃相粉体包含第一玻璃粉体和第二玻璃粉体,第一玻璃粉体的粒径小于第二玻璃粉体的粒径,第一玻璃粉体具有铝镀层；玻璃相粉体的烧结温度为770～825℃。本发明氮化铝陶瓷基板的丝网印刷浆料利用第一玻璃粉体和第二玻璃粉体在浆料涂覆过程中的分布以及烧结过程中的流动差异,促使第一玻璃粉体更多的渗入基板的氮化铝晶界之间,使得玻璃相与基板的界面处无明显的气泡缺陷,增加金属化层与基板的粘接强度。本发明还公开了一种基于氮化铝陶瓷基板丝网印刷浆料的金属化方法。(The invention discloses a screen printing slurry of an aluminum nitride ceramic substrate, which mainly comprises conductive phase powder, glass phase powder and an organic carrier, wherein the glass phase powder comprises first glass powder and second glass powder, the particle size of the first glass powder is smaller than that of the second glass powder, and the first glass powder is provided with an aluminum coating; the sintering temperature of the glass phase powder is 770-825 ℃. The screen printing slurry of the aluminum nitride ceramic substrate of the invention utilizes the distribution of the first glass powder and the second glass powder in the slurry coating process and the flow difference in the sintering process to promote the first glass powder to more permeate into the aluminum nitride crystal boundaries of the substrate, so that no obvious bubble defect exists at the interface of the glass phase and the substrate, and the bonding strength of a metallization layer and the substrate is increased. The invention also discloses a metallization method based on the aluminum nitride ceramic substrate silk-screen printing slurry.)

1. The screen printing paste for the aluminum nitride ceramic substrate is characterized by mainly comprising conductive phase powder, glass phase powder and an organic carrier, wherein the glass phase powder comprises first glass powder and second glass powder, the particle size of the first glass powder is smaller than that of the second glass powder, and the first glass powder is provided with an aluminum coating; the sintering temperature of the glass phase powder is 770-825 ℃.

2. The paste for screen printing of an aluminum nitride ceramic substrate according to claim 1, wherein the glass phase powder is formed by mixing a first glass powder and a second glass powder having the same glass phase composition, the first glass powder has a particle size of 0.3 to 0.7 μm, and the second glass powder has a particle size of 1.5 to 3.5 μm.

3. The aluminum nitride ceramic substrate screen printing paste according to claim 2, wherein the mass percentage of the first glass powder in the glass phase powder is 3% to 15%.

4. The aluminum nitride ceramic substrate screen printing paste according to claim 1, wherein the paste comprises 50 to 75 parts by mass of conductive phase powder, 10 to 20 parts by mass of glass phase powder, and 10 to 20 parts by mass of an organic vehicle.

5. A paste for screen printing of an aluminum nitride ceramic substrate according to claim 1, wherein the second glass frit comprises silver-coated glass frit, and the silver-coated glass frit is silver-coated glass frit.

6. The aluminum nitride ceramic substrate screen printing paste as claimed in claim 5, wherein the glass phase powder contains 12-35% by mass of silver-coated glass powder, and the silver-coated glass powder contains 15-37% by mass of silver.

7. The paste for screen printing of an aluminum nitride ceramic substrate according to claim 1, wherein the first glass powder has an aluminum content of 0.3 to 3%.

8. The aluminum nitride ceramic substrate screen printing paste according to claim 1, wherein the glass phase powder has the following glass phase composition in parts by mass: SiO 2₂37 to 40 parts by weight of B₂O₃22 to 24 parts of K₂O20-22 parts and Al₂O₃16-18 parts;

the organic carrier comprises terpineol and polyvinyl acetal, and the mass ratio of the terpineol to the polyvinyl acetal is (3.5-4): 1; the conductive phase powder is silver-copper-titanium alloy.

9. The paste for screen printing of an aluminum nitride ceramic substrate according to claim 1, wherein the first glass powder is prepared by a method comprising: putting the glass micro powder in a roller, rotating the roller, and carrying out magnetron sputtering on an aluminizer under a vacuum condition; crushing and screening to obtain glass powder with a preset particle size, and annealing in a hydrogen atmosphere to obtain first glass powder.

10. A metallization method of an aluminum nitride ceramic substrate is characterized by comprising the following steps: the method comprises the steps of screen printing the screen printing slurry of the aluminum nitride ceramic substrate according to any one of claims 1 to 9 on the aluminum nitride substrate, heating to 300-400 ℃ for pre-sintering under the condition of inert gas, and then heating to 770-825 ℃ for sintering for 10-30 min.

Technical Field

The invention relates to the technical field of aluminum nitride ceramic metallization, in particular to screen printing slurry and a metallization method for an aluminum nitride ceramic substrate.

Background

The aluminum nitride substrate has the characteristics of high insulation resistance, high insulation withstand voltage, low dielectric constant, high thermal conductivity, matching of thermal expansion coefficient and silicon and the like, and is suitable for packaging and high-density packaging of high-power semiconductor chips. For the purpose of sealing the package structure, mounting components, connecting input and output terminals, etc., the surface and inside of the aluminum nitride ceramic substrate should be metallized. It is desirable to have strong adhesion strength between the metallization layer and the substrate, good sealing properties and solder erosion resistance, as well as high thermal conductivity and low dielectric constant of the interface.

One of the metallization methods suitable for large-scale automated production is screen printing metallization, in which a metal layer, an electrode, a wire, etc. are coated on the surface of aluminum nitride by screen printing, and then dried and heat-treated at high temperature to form a desired circuit or conductive layer. The main components of the metallization paste are metal powder, adhesive and organic carrier, wherein oxide in the adhesive and glass adhesive are easy to generate oxidation-reduction reaction on the aluminum nitride substrate to generate nitrogen, so that bubbles are generated on the surface of the substrate, and the bonding strength of the metal layer is deteriorated.

Disclosure of Invention

One of the objectives of the present invention is to overcome the defects in the prior art, and to provide a screen printing paste for an aluminum nitride ceramic substrate, which can reduce the generation of bubbles on the interface surface between a glass phase and aluminum nitride, and improve the adhesion of a metallization layer.

In order to achieve the purpose, the technical scheme of the invention is as follows: the screen printing slurry for the aluminum nitride ceramic substrate mainly comprises conductive phase powder, glass phase powder and an organic carrier, wherein the glass phase powder comprises first glass powder and second glass powder, the grain diameter of the first glass powder is smaller than that of the second glass powder, and the first glass powder is provided with an aluminum coating; the sintering temperature of the glass phase powder is 770-825 ℃.

The first glass powder with smaller grain diameter is softened at the sintering temperature, the aluminum flows along with the glass phase, wets the substrate through the gap of the second glass powder and permeates into the substrate layer, the aluminum reacts with the slurry and the oxygen in the substrate to generate aluminum oxide, the contact between the oxygen and the surface of the aluminum nitride is blocked, the occurrence probability of the redox reaction of the aluminum nitride is reduced, the generation of bubbles on the interface surface of the glass phase and the aluminum nitride is reduced, and the adhesion between the glass phase and the aluminum nitride is enhanced. Because the aluminum coating layer flows along with the glass micro powder and permeates into the substrate, the internal stress between aluminum oxide generated by aluminum oxidation and aluminum nitride is lower, and the probability of the bonding strength deterioration caused by overlarge stress at the bonding part after sintering and cooling is reduced.

The preferable technical scheme is that the glass phase powder is formed by mixing first glass powder and second glass powder with the same glass phase composition, the particle size of the first glass powder is 0.3-0.7 mu m, and the particle size of the second glass powder is 1.5-3.5 mu m. The same glass phase composition of the first glass powder and the second glass powder contributes to the formation of a uniform metal inorganic material composite layer. The preferred particle sizes of the first glass powder and the second glass powder are effective to promote the first glass powder to permeate into the substrate layer.

The preferred technical scheme is that the mass percentage of the first glass powder in the glass phase powder is 3-15%.

The preferable technical scheme is that the slurry comprises, by mass, 50-75 parts of conductive phase powder, 10-20 parts of glass phase powder and 10-20 parts of organic carrier.

The preferable technical scheme is that the second glass powder comprises silver coating glass powder, and the silver coating glass powder is silver coating glass powder crushing material. The surface microstructure of the metallized sintered substrate comprises an aluminum nitride substrate layer which is stacked in sequence, the substrate layer in which an aluminum nitride crystal boundary is soaked by glass components, a metal-inorganic material composite binding layer and a sintered metal layer, a silver coating glass powder crushing material has a local glass phase surface, a gap between silver coatings contains glass phases which are heated to flow, the glass powder on the upper layer is filled between lower silver coatings in a flowing mode, the silver coatings are connected with the sintered metal layer on the upper layer, the silver coatings are embedded between the glass phases to form a net-shaped communicating structure in the composite sintered layer, the connection between the composite sintered layer and the sintered metal layer is more reliable, and the heat conductivity is high.

The preferable technical scheme is that the mass percent of the silver-coated glass powder in the glass phase powder is 12-35%, and the mass percent of the silver-coated glass powder is 15-37%. Further, the mass percent of the silver-coated glass powder in the glass phase powder is 17-25%, and the mass percent of the silver in the silver-coated glass powder is 20-28%. Based on the content and the silver mass percentage of the silver plating glass powder, the content and the silver mass percentage of the silver plating glass powder are too low to be beneficial to forming a continuous reticular communicating structure, and the numerical value is too high, so that the interface of silver and a glass phase is too large, the flowing infiltration of the glass phase is not beneficial, the compact structure of a glass phase bonding layer is influenced, a hollow hole in a bonding layer is increased, and the bonding strength is reduced.

The preferable technical scheme is that the aluminum content of the first glass powder is 0.3-3%. Further, the aluminum content of the first glass powder is 1-1.9%. Based on the above preferred aluminum content percentage of the first glass powder, the aluminum content percentage is too high, and the adhesion surface between unoxidized aluminum and the aluminum nitride substrate is too large, which adversely affects the adhesion strength between the metallization layer and the substrate.

The preferable technical scheme is that the glass phase components of the glass phase powder are as follows according to the mass portion: SiO 2₂37 to 40 parts by weight of B₂O₃22 to 24 parts of K₂O20-22 parts and Al₂O₃16-18 parts; the organic carrier comprises terpineol and polyvinyl acetal, and the mass ratio of the terpineol to the polyvinyl acetal is (3.5-4): 1; the conductive phase powder is silver-copper-titanium alloy. B is₂O₃Al formed by oxidation with aluminium coating₂O₃Reaction to Al₄B₂O₉Further improving the bonding strength inside the glass phase.

The preferable technical scheme is that the preparation method of the first glass powder comprises the following steps: putting the glass micro powder in a roller, rotating the roller, and carrying out magnetron sputtering on an aluminizer under a vacuum condition; crushing and screening to obtain glass powder with a preset particle size, and annealing in a hydrogen atmosphere to obtain first glass 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 screen printing slurry of the aluminum nitride ceramic substrate on the aluminum nitride substrate, heating to 300-400 ℃ for pre-sintering under the condition of inert gas, and then heating to 770-825 ℃ for sintering for 10-30 min under heat preservation.

The invention has the advantages and beneficial effects that:

the screen printing slurry of the aluminum nitride ceramic substrate comprises first glass powder with an aluminum coating, and the first glass powder and the second glass powder are distributed in the slurry coating process and flow difference in the sintering process, so that the first glass powder is more infiltrated into the aluminum nitride crystal boundary of the substrate, the interface between the glass phase and the substrate has no obvious bubble defect, and the bonding strength of a metallization layer and the substrate is increased;

the screen printing slurry is prepared by adopting the optimized glass powder, so that the bonding strength of the metalized layer and the aluminum nitride substrate is improved, and compared with substrate metallization methods such as a film metallization method and an active metal welding method, the method has the advantages of simple and rapid process, strong universality and suitability for mass production.

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.

Examples

Preparing glass phase powder:

1. according to SiO₂37 to 40 parts by weight of B₂O₃22 to 24 parts of K₂O20-22 parts and Al₂O₃Preparing oxide powder according to the mass ratio of 16-18 parts, grinding, uniformly mixing, melting glass powder at the temperature of 800-950 ℃, cooling and drying, crushing, ball-milling and screening the cooled glass powder to obtain glass powder with a preset particle size;

2. putting glass powder with the particle size of 20-70 microns into a magnetron sputtering coating system, and ensuring the flowability of the glass powder through the rotation and shaking of a roller; the sputtering target material is an aluminum target with the purity of 99.999 percent, and the sputtering parameters are as follows: background vacuum of 3 x 10^{- 3}Pa, the pressure of the sputtering argon gas is 0.35Pa, and the sputtering power density is 3W/cm²Crushing, screening and annealing the sputtered glass powder in a hydrogen atmosphere to obtain glass powder with a preset particle size and an aluminum coating;

3. chemically plating silver on glass powder with the particle size of 20-70 microns by adopting a silver ammonia solution to obtain glass powder with a silver coating, and drying, crushing, screening and annealing in a hydrogen atmosphere to obtain glass powder with a predetermined particle size and the silver coating;

4. mixing the non-coating glass powder with a preset grain diameter, the aluminum-coating glass powder and the silver-coating glass powder in proportion to obtain the glass phase powder used in the metallization slurry.

The screen printing slurry is prepared from the following components in parts by mass: silver-copper-titanium alloy AgCuTi34.5-1.560 parts, glass phase powder 15 parts, terpineol 6 parts and polyvinyl acetal 1.5 parts, and the components are uniformly mixed.

Printing and coating the silk-screen printing slurry on the surface of the substrate: and respectively scrubbing the aluminum nitride ceramic substrate and the oxygen-free copper plate by using acetone, and 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 process of the substrate with the screen printing paste printing pattern: raising the temperature from room temperature to 370-375 ℃ at a temperature raising rate of 5 ℃/min under the condition of inert gas, preserving heat, pre-sintering for 10min, then raising the temperature to 780-785 ℃ at a temperature raising rate of 10 ℃/min, preserving heat, and sintering for 20 min.

Compounding the oxygen-free copper plate and the substrate: cleaning the metallized aluminum nitride ceramic substrate, and welding the oxygen-free copper plate to the metallized surface of the aluminum nitride ceramic substrate by using a vacuum brazing furnace to obtain the copper-clad plate.

Example 1 glass phase powder: 10 parts of aluminum-coated glass powder with the thickness of 0.1-0.5 mu m (the aluminum content percentage is 2.27%) and 90 parts of glass powder with the thickness of 1.5-3.5 mu m without a coating;

example 2 glass phase powder: 10 parts of aluminum-coated glass powder with the thickness of 0.1-0.5 mu m (the aluminum content percentage is 5.04 percent) and 90 parts of glass powder with the thickness of 1.5-3.5 mu m without a coating;

example 3 glass phase powder: 17 parts of aluminum-coated glass powder with the thickness of 0.1-0.5 mu m (0.2 percent of aluminum content) and 83 parts of glass powder with the thickness of 1.5-3.5 mu m without a coating;

example 4 glass phase powder: 10 parts of aluminum-coated glass powder with the thickness of 0.1-0.5 mu m (the mass percentage of aluminum is 2.27%), 17 parts of silver-coated glass powder with the thickness of 1.5-3.5 mu m (the mass percentage of silver is 12%), and 73 parts of glass powder with the thickness of 1.5-3.5 mu m without a coating;

example 5 glass phase powder: 10 parts of aluminum-coated glass powder with the thickness of 0.1-0.5 mu m (the mass percentage of aluminum is 2.27%), 17 parts of silver-coated glass powder with the thickness of 1.5-3.5 mu m (the mass percentage of silver is 40%), and 73 parts of glass powder with the thickness of 1.5-3.5 mu m without a coating;

example 6 glass phase powder: 10 parts of aluminum-coated glass powder with the thickness of 0.1-0.5 mu m (the mass percentage of aluminum is 2.27%), 25 parts of silver-coated glass powder with the thickness of 1.5-3.5 mu m (the mass percentage of silver is 12%), and 50 parts of glass powder with the thickness of 1.5-3.5 mu m without a coating;

the comparative example glass phase powder is 1.5-3.5 mu m glass powder without a coating.

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

1. observing the compactness of the metallized layer in the SEM picture of the section of the substrate;

2. and testing the bonding strength of the copper layer and the metalized layer by adopting a peeling test.

The porosity and metallized layer bond strength for examples 1-6 and comparative examples are as follows:

1. the interface of the metallized film and the substrate after sintering of the comparative example has a large amount of bubbles, the amount of bubbles of examples 1, 2 and 4 is reduced, and no obvious bubble defect exists, the interface of the metallized film and the substrate of example 3 has a small amount of bubbles, and the metal-inorganic material composite bonding layers of examples 5 to 6 have a small amount of bubbles;

2. the metallized layer adhesion strength of examples 1-6 and the comparative example were, in order: 12.12MPa, 10.94 MPa, 10.15 MPa, 13.37 MPa, 12.03 MPa, 11.48 MPa and 8.91 MPa.

Example 1 the adhesive strength was improved based on comparative example 1; example 4 the adhesive strength is further improved by adding the glass powder containing the silver coating into the glass phase powder; in the embodiment 2, the aluminum content in the aluminum-coated glass powder is too high, the adhesion surface between unoxidized aluminum and the aluminum nitride substrate is too large, and the bonding strength is reduced compared with that in the embodiment 1; in example 3, the aluminum content in the aluminum-coated glass powder was too low, and the bubble content was more than that in example 1, and the adhesive strength was reduced as a whole; in example 5, the silver content in the silver-plated glass powder was too high, and in example 6, the mass fraction of the silver-plated glass powder in the glass phase powder was too large, so that the degree of densification of the glass phase bonding layer was reduced, and the bonding strength was reduced.

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.