A method for brazing aluminum nitride ceramics and Kovar alloy

Abstract

This invention relates to a method for brazing aluminum nitride ceramics and Kovar alloy, comprising the following steps: S1, pretreating the aluminum nitride ceramics and the Kovar alloy; S2, preparing a Ti layer with a thickness of 5μm-10μm on the surface of the aluminum nitride ceramic to be brazed; S3, preparing a Ni layer with a thickness of 20μm-30μm on the Ti layer on the surface of the aluminum nitride ceramic to be brazed; S4, preparing a Ni layer with a thickness of 20μm-30μm on the surface of the Kovar alloy to be brazed; S5, vacuum brazing the aluminum nitride ceramics and the Kovar alloy, adding AgCu28 powder brazing filler metal to the brazing gap, brazing at a temperature of 850℃-900℃, holding for 5 minutes, and cooling to room temperature in the brazing furnace after brazing. The method of this invention uses commercially available brazing filler metal, and the filler metal exhibits good fluidity and interfacial wettability within the brazing gap, resulting in a large, dense brazing gap without any defects.

Description

Technical Field

[0001] This invention relates to the field of brazing technology, and more particularly to a method for brazing aluminum nitride ceramics and Kovar alloys. Background Technology

[0002] With the rapid development of the electronics industry, electronic power devices are moving towards modularization and intelligence. As integration levels increase and device sizes shrink, there is a growing demand for ceramic materials with high thermal conductivity to replace beryllium oxide and alumina to address heat dissipation issues. Aluminum nitride ceramics possess exceptionally high thermal conductivity, second only to beryllium oxide and silicon carbide among ceramic materials. They also exhibit high mechanical strength, corrosion resistance, a thermal expansion coefficient matching that of silicon, and non-toxicity, making them one of the most promising ceramic substrate materials. However, for aluminum nitride ceramics to function as a heat dissipation substrate, effective bonding with other materials (metals, alloys, etc.) is crucial. Welding is a common method for achieving this bonding. Previous research on ceramic-metal welding has focused on the welding of alumina ceramics with Kovar alloy (Fe-Ni-Co), primarily because their thermal expansion coefficients are similar, resulting in lower residual stress during welding. For brazing alumina ceramics and Kovar alloys, Ag-Cu-Ti and Ag-Cu solders are generally used. When using Ag-Cu-Ti solder, due to the presence of active Ti elements, it has good wettability with ceramics. However, during the brazing process, Ti elements in the solder diffuse towards the Kovar alloy side. At the same time, Ti elements react with Fe and Ni in the Kovar alloy to form brittle Fe2Ni and Ni3Ti compounds, which reduces the wettability of Ag-Cu-Ti solder with ceramics. When using Ag-Cu solder, it has been found that Cu in Ag-Cu solder preferentially spreads along the grain boundaries of Kovar alloy, and forms island-shaped Cu-based solid solution regions at the spreading front. However, Ag-Cu solder has better wettability with Kovar alloys but worse wettability with ceramics than Ag-Cu-Ti solder.

[0003] Therefore, there is an urgent need for a method to braze aluminum nitride ceramics and Kovar alloys. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for brazing aluminum nitride ceramics and Kovar alloys.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for brazing aluminum nitride ceramic and Kovar alloy is provided, comprising the steps of:

[0007] S1. Pre-treat the aluminum nitride ceramic and the Kovar alloy;

[0008] S2. Prepare a Ti layer with a thickness of 5μm-10μm on the surface of the aluminum nitride ceramic to be brazed;

[0009] S3. Prepare a Ni layer with a thickness of 20μm-30μm on the Ti layer of the aluminum nitride ceramic surface to be brazed;

[0010] S4. Prepare a Ni layer with a thickness of 20μm-30μm on the surface of the Kovar alloy to be brazed;

[0011] S5. Vacuum brazing is performed on the aluminum nitride ceramic and the Kovar alloy. AgCu28 powder brazing filler metal is added to the brazing gap. The brazing temperature is 850℃-900℃ and the holding time is 5min. After brazing, the material is cooled to room temperature in the brazing furnace.

[0012] Preferably, the pretreatment includes: grinding, cleaning, and drying both the aluminum nitride ceramic and the Kovar alloy in sequence.

[0013] Preferably, the smoothing process includes: smoothing with metallographic sandpaper until 2000# sandpaper is used.

[0014] Preferably, the cleaning includes cleaning with acetone in an ultrasonic cleaner for 10 minutes.

[0015] Preferably, the method for preparing the Ti layer is magnetron sputtering.

[0016] Preferably, step S3 further includes: before preparing the Ni layer, cleaning the aluminum nitride ceramic in an ultrasonic cleaner with acetone to remove surface impurities.

[0017] Preferably, the method for preparing the Ni layer is electroplating.

[0018] The present invention adopts the above technical solution and has the following technical effects compared with the prior art:

[0019] The method of this invention can use commercially available brazing filler metal for welding, and the filler metal exhibits good fluidity and interfacial wettability within the weld seam, resulting in a large weld seam area, high density, and no defects. This is because existing technologies add titanium and nickel to the filler metal, which leads to the agglomeration of these two substances at the weld seam during high-temperature brazing, thereby reducing the wettability between the ceramic and Kovar alloy and resulting in poor weld seam density. In contrast, the method of this invention pre-prepares titanium and nickel layers on the aluminum nitride ceramic surface to be brazed. The nickel layer, to a certain extent, hinders the diffusion of titanium into the filler metal, thus ensuring the interfacial wettability on the aluminum nitride ceramic side. The nickel layer pre-prepared on the Kovar alloy surface ensures that both interfaces are nickel-based during brazing, resulting in good fluidity of the filler metal within the weld seam, leading to a large wetted area, dense interface, and no defects. Furthermore, by controlling the thickness of the titanium and nickel layers, this invention avoids defects such as titanium and nickel detaching from the aluminum nitride ceramic or Kovar alloy during high-temperature brazing, which could lead to an unstable interfacial layer or the formation of voids. Attached Figure Description

[0020] Figure 1 This is the interface morphology after brazing in Embodiment 1 of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0024] Example 1

[0025] This embodiment provides a method for brazing aluminum nitride ceramic and Kovar alloy, the steps of which include:

[0026] S1-1. Grind the aluminum nitride ceramic with dimensions of 50mm×50mm×2mm using metallographic sandpaper until it reaches 2000# sandpaper; after grinding, clean it with acetone in an ultrasonic cleaner for 10 minutes; dry it after cleaning.

[0027] S1-2. Grind the Kovar alloy with dimensions of 50mm×50mm×2mm using metallographic sandpaper until it reaches 2000# sandpaper; after grinding, clean it in an ultrasonic cleaner with acetone for 10 minutes; air dry after cleaning.

[0028] S2. A Ti layer with a thickness of 5μm-10μm is prepared on the surface of the aluminum nitride ceramic to be brazed using magnetron sputtering. If the thickness of the Ti layer is less than 5μm, the Ti on the interface will diffuse into the brazing seam, which will reduce the amount of Ti remaining on the interface layer and easily form void defects on the interface. If the thickness of the Ti layer is greater than 10μm, there will be residual stress at the interface, which will make the interface layer prone to cracking.

[0029] S3. The aluminum nitride ceramic is cleaned with acetone in an ultrasonic cleaner to remove surface impurities. After cleaning, an electroplating method is used to prepare a Ni layer with a thickness of about 20 μm on the Ti layer of the aluminum nitride ceramic surface to be brazed. If the Ni layer is too thin, the Ni on the interface will diffuse with the brazing filler metal at high temperature, resulting in poor interface density. This is because Ni has good fluidity. If the Ni layer is too thick, the residual stress at the interface will be large, which will lead to cracking.

[0030] S4. An electroplating method is used to prepare a Ni layer with a thickness of about 20 μm on the surface of the Kovar alloy to be brazed. If the Ni layer is too thin, the Ni on the interface will diffuse with the brazing filler metal at high temperature, resulting in poor interface density. This is because Ni has good fluidity. If the Ni layer is too thick, the residual stress at the interface will be large, which will lead to cracking.

[0031] S5. Vacuum brazing is performed on the aluminum nitride ceramic and the Kovar alloy. AgCu28 powder brazing filler metal is added to the brazing gap. The brazing temperature is 900℃ and the holding time is 5min. After brazing, the material is cooled to room temperature in the brazing furnace.

[0032] After brazing, the interface morphology was observed as follows: Figure 1 As shown, the brazing strength was measured to be 120 MPa, the brazing interface was well-dense with no defects, and it can be used as a sealing welding method for aluminum nitride ceramics and Kovar alloys.

[0033] The method of this invention can use commercially available brazing filler metal for welding, and the filler metal exhibits good fluidity and interfacial wettability within the weld seam, resulting in a large weld seam area, high density, and no defects. This is because existing technologies add titanium and nickel to the filler metal, which leads to the segregation of these two substances at the weld seam during high-temperature brazing, thereby reducing the wettability between the ceramic and Kovar alloy, and resulting in poor weld seam density. In contrast, the method of this invention pre-prepares titanium and nickel layers on the aluminum nitride ceramic surface to be brazed. The nickel layer, to a certain extent, hinders the diffusion of titanium into the filler metal, thus ensuring the interfacial wettability on the aluminum nitride ceramic side. The nickel layer pre-prepared on the Kovar alloy surface ensures that both interfaces are nickel-based during brazing, resulting in good fluidity of the filler metal within the weld seam, leading to a large wetted area, dense interface, and no defects. Furthermore, by controlling the thickness of the titanium and nickel layers, this invention avoids defects such as titanium and nickel detaching from the aluminum nitride ceramic or Kovar alloy during high-temperature brazing, which could lead to an unstable interfacial layer or the formation of voids.

[0034] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for brazing aluminum nitride ceramics and Kovar alloy, characterized in that the steps include... include: S1. Pre-treat the aluminum nitride ceramic and the Kovar alloy; S2. Prepare a Ti layer with a thickness of 5μm-10μm on the surface of the aluminum nitride ceramic to be brazed; S3. Prepare a Ni layer with a thickness of 20μm-30μm on the Ti layer of the aluminum nitride ceramic surface to be brazed; S4. Prepare a Ni layer with a thickness of 20μm-30μm on the surface of the Kovar alloy to be brazed; S5. Vacuum brazing is performed on the aluminum nitride ceramic and the Kovar alloy. AgCu28 powder brazing filler metal is added to the brazing gap. The brazing temperature is 850℃-900℃ and the holding time is 5min. After brazing, the material is cooled to room temperature in the brazing furnace. By controlling the thickness of the titanium and nickel layers, the separation of titanium and nickel from aluminum nitride ceramic or Kovar alloy during high-temperature brazing is avoided, which would result in an undense interface layer or the formation of pores. The method for preparing the Ti layer is magnetron sputtering. The method for preparing the Ni layer is electroplating.

2. The method according to claim 1, characterized in that, The pretreatment includes: grinding, cleaning, and drying both the aluminum nitride ceramic and the Kovar alloy in sequence.

3. The method according to claim 2, characterized in that, The smoothing process includes: smoothing with metallographic sandpaper until 2000# sandpaper is used.

4. The method according to claim 2, characterized in that, The cleaning process includes cleaning with acetone in an ultrasonic cleaner for 10 minutes.

5. The method according to claim 1, characterized in that, Step S3 further includes: before preparing the Ni layer, cleaning the aluminum nitride ceramic in an ultrasonic cleaner with acetone to remove surface impurities.

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