Method for pressureless sintering and welding of aluminum nitride ceramics

Abstract

The invention relates to a pressureless sintering welding method for aluminum nitride ceramics, which comprises the following steps of: ball-milling mixed welding flux to obtain welding flux slurry, coating the welding flux slurry on an aluminum nitride substrate in a silk-screen printing manner to form a welding flux coating, drying, and carrying out pressureless sintering on the aluminum nitride substrate coated with the welding flux coating, the solder slurry comprises solder and a solvent; the welding flux comprises aluminum nitride, a sintering aid, a slow drying agent and an oiling agent. The slow drying agent and the oil boiling agent are additionally added into the solder used in the method, meanwhile, the aluminum nitride ceramic substrate is coated with the solder slurry in a silk-screen printing mode, and the slow drying agent and the oil boiling agent are beneficial to the coating uniformity of the solder slurry; the welding flux slurry is distributed on the aluminum nitride ceramic in a latticed mode, uniform distribution of the slurry in the follow-up pressureless sintering process is facilitated, a pressureless sintering mode is adopted, pressureless sintering furnace equipment which is the same as that of aluminum nitride sintering is used in the welding process, and high welding strength is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of ceramic welding, and in particular to a method for pressureless sintering welding of aluminum nitride ceramics. Background Art

[0002] With the rapid development of the semiconductor industry, the demand for the types and quantities of ceramic parts is increasing, and the requirements for their quality are also getting higher and higher. Most ceramic parts have complex structures and are difficult to form in one go. Some methods are needed to connect the ceramic parts. Aluminum nitride ceramics have excellent thermal and mechanical properties and are the preferred material for ceramic parts. At present, there is little research on aluminum nitride ceramic welding methods in China.

[0003] High-quality ceramic connection and sealing have been applied to ceramic packaging devices such as micro-electromechanical systems, microwave devices, and imaging devices. Due to some inherent characteristics of ceramics, such as high chemical inertness, low diffusion rate, and high melting point, it is difficult to process large or complex-shaped parts, making ceramic connection a difficult technology, which has greatly restricted the development of ceramics. In addition, it is very important to ensure good wettability between the bonding layer and the ceramic and a low thermal expansion coefficient mismatch rate during the ceramic connection process.

[0004] The current ceramic connection technologies mainly include diffusion bonding, active brazing, liquid phase bonding and glass solder bonding. Diffusion welding has high requirements on the surface finish and roughness of the base material to be welded, and is not suitable for the connection of parts with complex shapes. Active brazing uses metal as the connection material, and the use temperature and oxidation resistance of the joint are significantly lower than those of the ceramic base material. The glass or microcrystalline glass connection method has the problem of softening of the glass phase, and the high temperature resistance of the joint is insufficient.

[0005] The existing technology generally uses laser, EB, electromagnetic wave and other equipment to heat the solder to achieve the purpose of welding. The requirements for equipment are higher, the preparation process is more complicated and the required conditions are more stringent. Therefore, it has become an urgent problem to provide a welding method that is simple and easy to operate, suitable for firing welding of objects of different shapes and sizes, has low equipment requirements and can achieve high welding strength. Summary of the invention

[0006] In order to solve the above technical problems, the purpose of the present invention is to provide a method for pressureless sintering welding of aluminum nitride ceramics. The method described in the present invention solves the problems of regulating the solder formula of aluminum nitride ceramic welding and uniformity of solder coating, adopts a pressureless sintering process, and realizes low-temperature welding of aluminum nitride ceramics.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for pressureless sintering welding of aluminum nitride ceramics, the method comprising the following steps:

[0009] The mixed solder is ball-milled to obtain solder paste, the solder paste is coated on the aluminum nitride substrate by screen printing to form a solder coating, and after drying, the aluminum nitride substrate coated with the solder coating is pressurelessly sintered to obtain a welded aluminum nitride ceramic;

[0010] The solder paste includes solder and solvent;

[0011] The solder comprises aluminum nitride, a sintering aid, a slow-drying agent and an oil-opening agent.

[0012] The solder used in the present invention includes not only conventional aluminum nitride, sintering aids and solvents, but also additionally slow-drying agents and oil-opening agents. The slow-drying agents and oil-opening agents are beneficial to the uniformity of solder paste coating, thereby improving the welding effect and increasing the welding strength. At the same time, the present invention adopts screen printing to coat the solder paste on the aluminum nitride ceramic substrate. The grid-like distribution of the solder paste on the aluminum nitride ceramic is beneficial to the uniform distribution of the paste during the subsequent pressureless sintering process. In addition, the present invention adopts a pressureless sintering method. During the welding process, the same pressureless sintering furnace equipment as that of aluminum nitride sintering can be used. There is no need for separate laser, EB, electromagnetic wave and other equipment to heat the solder. The solder and the substrate are fully combined through sintering, and the low-melting-point sintering aid in the solder diffuses into the substrate to achieve higher welding strength.

[0013] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0014] The present invention does not impose any special restrictions on the types of the slow-drying agent and the oil-opening agent, and the slow-drying agent and the oil-opening agent materials commonly used in the market can be selected.

[0015] Preferably, the main component of the slow-drying agent includes triethoxyethyl acrylate.

[0016] Preferably, the main components of the oil-opening agent include organic substances such as ethyl acetate, butyl acetate, benzene, and toluene.

[0017] The slow-drying agent used in the present invention can delay the time for the solder paste to dry out, so that the solder has sufficient time to be evenly distributed during the subsequent pressureless sintering. The oil-opening agent can adjust the viscosity of the solder paste and improve the printing applicability. The two work together to reduce the solvent volatilization rate, reduce the drying speed, and ensure that the paste is evenly coated. The solder that dries too quickly cannot be repeatedly coated. In the subsequent stage, a certain welding strength can be achieved without pressure sintering, which greatly simplifies the difficulty of process operation.

[0018] Preferably, based on the total weight of the solder as 100%, the mass fraction of the aluminum nitride is 50%-80%, for example, it can be 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78% or 80%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0019] Preferably, based on the total weight of the solder as 100%, the mass fraction of the sintering aid is 20%-50%, for example, it can be 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48% or 50%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] Preferably, based on the total weight of the solder as 100%, the mass fraction of the retarder is 2%-5%, for example, it can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] Preferably, based on the total weight of the solder as 100%, the mass fraction of the degreasing agent is 2%-5%, for example, it can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] The present invention achieves good welding strength by further regulating the mass fractions of the slow-drying agent and the oil-opening agent. If the mass fraction of the slow-drying agent is too high, the slurry viscosity is too low and cannot be coated; if the mass fraction of the slow-drying agent is too low, it will not have the effect of reducing the drying speed.

[0023] Preferably, the solid content of the solder paste is 30%-40%, for example, it can be 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39% or 40%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] Preferably, the sintering aid includes a compound of any one or at least two of Si, Y, Ga, Na or Mg, wherein typical but non-limiting combinations include a combination of Si compounds and Y compounds, a combination of Y compounds and Ga compounds, a combination of Ga compounds and Na compounds, a combination of Y compounds, Ga compounds and Na compounds, a combination of Ga compounds, Na compounds and Mg compounds, a combination of Si compounds, Y compounds and Ga compounds, and a combination of Y compounds, Ga compounds, Na compounds and Mg compounds.

[0025] Preferably, the compound comprises an oxide and / or a fluoride.

[0026] Preferably, the solvent comprises any one of anhydrous ethanol, isopropanol or n-butanol, or a combination of at least two thereof, wherein typical but non-limiting combinations include a combination of anhydrous ethanol and isopropanol, a combination of isopropanol and n-butanol, a combination of anhydrous ethanol and n-butanol, and a combination of anhydrous ethanol, isopropanol and n-butanol.

[0027] Preferably, the median particle size of the aluminum nitride is 0.5 μm-3 μm, for example, it can be 0.5 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm or 3 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] Preferably, the ball-to-material ratio of the ball mill is (5-10):1, for example, it can be 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] Preferably, the rotation speed of the ball mill is 200rpm-800rpm, for example, it can be 200rpm, 300rpm, 400rpm, 500rpm, 600rpm, 700rpm or 800rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0030] Preferably, the ball milling time is 12h-48h, for example, it can be 12h, 14h, 16h, 20h, 24h, 28h, 32h, 34h, 36h, 40h, 42h, 44h, 46h or 48h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] Preferably, the aluminum nitride substrate needs to be polished on the welding surface before coating the solder slurry to make its roughness reach 0.1μm-0.4μm, for example, it can be 0.1μm, 0.2μm, 0.3μm or 0.4μm, but it is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, and ultrasonic cleaning is performed after polishing.

[0032] In the present invention, the welding surface of the aluminum nitride substrate is polished and then ultrasonically cleaned to remove surface dirt, so that the solder and the substrate can achieve better wetting and diffusion, thereby achieving higher welding strength.

[0033] Preferably, the drying temperature is 70°C-110°C, for example, it can be 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C or 110°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] Preferably, the drying time is 2 h-5 h, for example, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h or 5 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] After the screen printing coating is completed, the present invention performs a drying treatment to evaporate part of the solvent to prevent the solder paste from overflowing during high-temperature welding and bubbles from appearing at the weld, which is not conducive to improving the welding strength. The dried ceramic substrate is fixed with a fixture, pressurized with bolts and a torque wrench, and the assembled sample is placed in a pressureless sintering furnace for sintering.

[0036] Preferably, the pressureless sintering includes a high-temperature sintering stage and a low-temperature insulation stage.

[0037] In this application, pressureless sintering is used for welding, and no other equipment is required, which reduces the equipment cost and difficulty of sintering.

[0038] Preferably, the temperature of the high temperature sintering stage is 1600°C-1800°C, for example, it can be 1600°C, 1650°C, 1700°C, 1750°C or 1800°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] Preferably, the high temperature sintering stage lasts for 2 hours to 5 hours, for example, 2 hours, 3 hours, 4 hours or 5 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0040] Preferably, the temperature of the low-temperature insulation stage is 300°C-600°C, for example, it can be 300°C, 350°C, 400°C, 450°C, 500°C, 550°C or 600°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] The present invention controls the temperature of the low temperature insulation stage to be 300°C-600°C. The low temperature insulation stage is to volatilize and decompose the slow drying agent, oil opening agent and binder added to the slurry and then discharge them, otherwise it will affect the performance and appearance after sintering.

[0042] Preferably, the duration of the low-temperature insulation stage is 5h-10h, for example, it can be 5h, 6h, 7h, 8h, 9h or 10h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0043] As a preferred technical solution of the preparation method of the present invention, the preparation method comprises the following steps:

[0044] The mixed solder and the solvent are ball-milled at a rotation speed of 200 rpm-800 rpm to obtain a solder slurry with a solid content of 30%-40%, the solvent includes any one of anhydrous ethanol, isopropanol or n-butanol or a combination of at least two thereof, and based on the total weight of the solder being 100%, the solder includes 50%-80% by mass of aluminum nitride, 20%-50% by mass of a sintering aid, 2%-5% by mass of a slow-drying agent, and 2%-5% by mass of an oil-opening agent.

[0045] The solder slurry is coated on the polished aluminum nitride substrate by screen printing to form a solder coating on the aluminum nitride substrate, which is dried at 70°C-110°C for 2h-5h, and the aluminum nitride substrate is fixed by a fixture, and the aluminum nitride substrate is pressurized by bolts and torque wrenches. The assembled aluminum nitride substrate is placed in a pressureless sintering furnace, and the aluminum nitride substrate coated with the solder coating is pressurelessly sintered, sintered at a high temperature of 1600°C-1800°C for 2h-5h, and then kept at a low temperature of 300°C-600°C for 5h-10h to obtain a welded aluminum nitride ceramic.

[0046] In a second aspect, the present invention provides an aluminum nitride ceramic prepared by the preparation method described in the first aspect.

[0047] The aluminum nitride ceramic provided by the present invention has the characteristics of high welding strength. The welded aluminum nitride solder is evenly coated without gaps, can meet the use of scenes with requirements for sealing, and is not prone to failure after repeated use.

[0048] In a third aspect, the present invention provides a use of the aluminum nitride ceramic as described in the second aspect, wherein the aluminum nitride ceramic is applied in the semiconductor field.

[0049] The aluminum nitride ceramic provided by the invention is used in the semiconductor field, and significantly reduces the welding difficulty while maintaining the welding strength.

[0050] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0051] Compared with the prior art, the present invention has at least the following beneficial effects:

[0052] (1) The present invention improves the problem of solder coating uniformity by regulating the aluminum nitride ceramic solder formula, and realizes low-temperature welding of aluminum nitride ceramics by using screen printing and pressureless sintering processes.

[0053] (2) In addition to conventional aluminum nitride, sintering aids and solvents, the solder used in the present invention also contains a slow-drying agent and an oil-opening agent. The slow-drying agent and the oil-opening agent are beneficial to the uniformity of solder paste coating, thereby improving the welding effect and increasing the welding strength. At the same time, the solder paste is coated on the aluminum nitride ceramic substrate by screen printing. The grid-like distribution of the solder paste on the aluminum nitride ceramic is beneficial to the uniform distribution of the paste during the subsequent pressureless sintering process.

[0054] (3) The present invention adopts a pressureless sintering method. During the welding process, the same pressureless sintering furnace equipment as that for aluminum nitride sintering can be used. No separate laser, EB, electromagnetic wave or other equipment is required to heat the solder. The solder and the substrate can be fully combined through sintering. This method is suitable for the sintering and welding of objects of different shapes and sizes. It has low equipment requirements and can achieve high welding strength. This method simplifies the process flow and reduces manufacturing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 This is a schematic diagram of the screen printing device of Example 1 of the present invention, wherein 1 is a scraper, 2 is a screen, 3 is a solder, and 4 is a polished aluminum nitride substrate. DETAILED DESCRIPTION

[0056] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and through specific implementation methods. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0057] In the following examples, unless otherwise specified, all reagents and consumables were purchased from conventional reagent manufacturers in the field; unless otherwise specified, the experimental methods and technical means used were conventional methods and means in the field.

[0058] Example 1

[0059] This embodiment provides a method for pressureless sintering welding of aluminum nitride ceramics, the method comprising the following steps:

[0060] (1) The mixed solder was ball-milled at 500 rpm for 12 h at a ball-to-solder ratio of 7:1 to obtain a solder paste, wherein the solvent was anhydrous ethanol, the solid content of the solder paste was 35%, and the total weight of the solder was 100%, including 70% by mass of aluminum nitride, 25% by mass of SiO 2 , 2.5% by mass of slow-drying agent and 2.5% by mass of oil-opening agent;

[0061] (2) The solder paste is applied by screen printing. The schematic diagram of the screen printing device is shown in FIG. Figure 1As shown, the solder 3 is placed on the screen 2, and the solder 3 is coated on the polished aluminum nitride substrate 4 using a scraper 1, and dried at 90°C for 3h;

[0062] (3) The aluminum nitride substrate is fixed with a fixture, and the aluminum nitride substrate is pressurized by bolts and a torque wrench. The assembled aluminum nitride substrate is placed in a pressureless sintering furnace for pressureless sintering. It is first sintered at 1700°C for 4 hours, and then kept at 450°C for 7 hours to obtain a welded aluminum nitride ceramic.

[0063] Example 2

[0064] This embodiment provides a method for pressureless sintering welding of aluminum nitride ceramics, the method comprising the following steps:

[0065] (1) ball milling the mixed solder at a ball-to-solder ratio of 10:1 for 48 hours at 300 rpm to obtain a solder slurry, wherein the solvent is isopropanol, the solid content of the solder slurry is 30%, and the total weight of the solder is 100%, including 60% by mass of aluminum nitride, 30% by mass of MgO, 5% by mass of a slow drying agent, and 5% by mass of an oil-opening agent;

[0066] (2) applying the solder paste onto the polished aluminum nitride substrate by screen printing and drying at 80° C. for 2 h;

[0067] (3) The aluminum nitride substrate is fixed with a fixture, and the aluminum nitride substrate is pressurized by bolts and a torque wrench. The assembled aluminum nitride substrate is placed in a pressureless sintering furnace for pressureless sintering. It is first sintered at 1600°C for 5 hours, and then kept at 300°C for 10 hours to obtain a welded aluminum nitride ceramic.

[0068] Example 3

[0069] This embodiment provides a method for pressureless sintering welding of aluminum nitride ceramics, the method comprising the following steps:

[0070] (1) The solder paste is obtained by ball milling the mixed solder at a ball-to-solder ratio of 6:1 for 12 h at 750 rpm, wherein the solvent is anhydrous ethanol, the solid content of the solder paste is 40%, and the total weight of the solder is 100%, including 75% by mass of aluminum nitride, 20% by mass of SiO 2 , 1% by mass of slow-drying agent and 4% by mass of oil-opening agent;

[0071] (2) applying the solder paste onto the polished aluminum nitride substrate by screen printing and drying at 100° C. for 5 h;

[0072] (3) The aluminum nitride substrate is fixed with a fixture, and the aluminum nitride substrate is pressurized by bolts and a torque wrench. The assembled aluminum nitride substrate is placed in a pressureless sintering furnace for pressureless sintering. It is first sintered at 1800°C for 2 hours, and then kept at 550°C for 5 hours to obtain a welded aluminum nitride ceramic.

[0073] Example 4

[0074] This embodiment provides a method for pressureless sintering welding of aluminum nitride ceramics, which is different from Embodiment 1 only in that the amount of the slow-drying agent added is 2.5%, and the reduced mass is distributed to the remaining components in proportion.

[0075] Example 5

[0076] This embodiment provides a method for pressureless sintering welding of aluminum nitride ceramics, which is different from Embodiment 1 only in that the amount of the slow-drying agent added is 15%, and the increased mass comes from less of the other components in proportion.

[0077] Example 6

[0078] This embodiment provides a method for pressureless sintering welding of aluminum nitride ceramics, which is different from Embodiment 1 only in that the amount of oil-opening agent added is 2.5%, and the reduced mass is distributed to the remaining components in proportion.

[0079] Example 7

[0080] This embodiment provides a method for pressureless sintering welding of aluminum nitride ceramics, which is different from Embodiment 1 only in that the amount of oil-opening agent added is 15%, and the increased mass comes from less of the other components in proportion.

[0081] Comparative Example 1

[0082] This comparative example provides a method for pressureless sintering welding of aluminum nitride ceramics, which is different from Example 1 only in that no slow-drying agent is added during the preparation of the solder paste, and the reduced mass is distributed to the remaining components in proportion.

[0083] Comparative Example 2

[0084] This comparative example provides a method for pressureless sintering welding of aluminum nitride ceramics, which is different from Example 1 only in that no oil-opening agent is added during the preparation of the solder paste, and the reduced mass is distributed to the remaining components in proportion.

[0085] Comparative Example 3

[0086] This comparative example provides a method for pressureless sintering welding of aluminum nitride ceramics, which is different from Example 1 only in that no slow-drying agent and oil-opening agent are added during the preparation of the solder paste.

[0087] Comparative Example 4

[0088] This comparative example provides a method for pressureless sintering welding of aluminum nitride ceramics, which is different from Example 1 only in that the screen printing method is replaced by a direct brush coating method for coating.

[0089] Testing method: The present invention reflects the welding strength by comparing it with the matrix strength during the stretching process, that is, by observing whether the aluminum nitride ceramic breaks first at the matrix or at the welding point to judge whether the welding strength meets the use requirements; if the matrix breaks during the stretching process and the welding point is not broken, it means that the improved welding strength is higher than the aluminum nitride matrix strength and meets the use requirements; otherwise, the welding strength is lower and will break at the welding interface, which does not meet the use requirements.

[0090] Table 1

[0091]

[0092]

[0093] The test results show that:

[0094] (1) It can be seen from Examples 1-3 that the present invention adds a slow-drying agent and an oil-opening agent to the solder of conventional composition, and the slow-drying agent and the oil-opening agent are beneficial to the uniformity of the solder slurry coating, thereby improving the welding effect and increasing the welding strength; at the same time, the present invention adopts a screen printing method to coat the solder slurry on the aluminum nitride ceramic substrate, which improves the uniformity of the welding, and subsequently adopts a pressureless sintering method to achieve a higher welding strength, which greatly simplifies the preparation process and reduces the manufacturing cost.

[0095] (2) By comparing Example 1 with Examples 4-7, it can be seen that the present invention achieves good welding strength by further adjusting the mass fractions of the slow-drying agent and the oil-opening agent. If the mass fraction of the slow-drying agent is too high, the slurry viscosity is too low and coating cannot be performed; if the mass fraction of the slow-drying agent is too low, it will not have the effect of reducing the drying speed.

[0096] (3) It can be seen from Example 1 and Comparative Examples 1-3 that the slow-drying agent used in the present invention can delay the time for the solder paste to dry out, so that the solder has sufficient time to achieve uniform distribution during the subsequent pressureless sintering. The oil-opening agent can adjust the viscosity of the solder paste and improve the printing applicability. The two work together to reduce the solvent volatilization rate, reduce the drying speed, and ensure uniform slurry coating. Solder that dries too quickly cannot be repeatedly coated. In the subsequent stage, a certain welding strength can be achieved without pressure sintering, which greatly simplifies the difficulty of process operation.

[0097] (4) It can be seen from Example 1 and Comparative Example 4 that the present invention uses screen printing to coat the solder slurry on the aluminum nitride ceramic substrate. The grid-like distribution of the solder slurry on the aluminum nitride ceramic is beneficial to the uniform distribution of the slurry during the subsequent pressureless sintering process. At the same time, it lays a good foundation for the subsequent pressureless sintering. If a direct brushing coating method is used, the distribution of the welding slurry is not very uniform, and there are incomplete welding parts, which greatly reduces the welding strength.

[0098] In summary, the present invention adds additional slow-drying agent and oil-opening agent to the solder of conventional composition. The slow-drying agent and oil-opening agent are beneficial to the uniformity of solder slurry coating, thereby improving the welding effect and increasing the welding strength. At the same time, the solder slurry is coated on the aluminum nitride ceramic substrate by screen printing, which improves the uniformity of welding. Subsequently, pressureless sintering is adopted to achieve higher welding strength, which greatly simplifies the process flow and reduces manufacturing costs.

[0099] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for pressureless sintering welding of aluminum nitride ceramics, characterized in that: The method comprises the following steps: The mixed solder is ball-milled to obtain solder paste, the solder paste is coated on the aluminum nitride substrate by screen printing to form a solder coating, and after drying, the aluminum nitride substrate coated with the solder coating is pressurelessly sintered to obtain a welded aluminum nitride ceramic; The solder paste includes solder and solvent; The solder comprises aluminum nitride, a sintering aid, a slow-drying agent and an oil-opening agent.

2. The method according to claim 1, characterized in that Based on the total weight of the solder being 100%, the mass fraction of the aluminum nitride is 50%-80%, the mass fraction of the sintering aid is 20%-50%, the mass fraction of the slow-drying agent is 2%-5%, and the mass fraction of the oil-opening agent is 2%-5%.

3. The method according to claim 1 or 2, characterized in that: The solid content of the solder paste is 30%-40%.

4. The method according to any one of claims 1 to 3, characterized in that: The sintering aid includes any one or a compound of at least two of Si, Y, Ga, Na or Mg; Preferably, the compound comprises an oxide and / or a fluoride; Preferably, the solvent comprises any one of anhydrous ethanol, isopropanol or n-butanol, or a combination of at least two thereof; Preferably, the median particle size of the aluminum nitride is 0.5 μm-3 μm.

5. The method according to any one of claims 1 to 4, characterized in that: The ball-to-material ratio of the ball mill is (5-10):1; Preferably, the rotation speed of the ball mill is 200rpm-800rpm; Preferably, the ball milling time is 12h-48h; Preferably, the drying temperature is 70°C-110°C; Preferably, the drying time is 2h-5h.

6. The method according to any one of claims 1 to 5, characterized in that: The aluminum nitride substrate needs to be polished on the welding surface before coating the solder paste to make its roughness reach 0.1 μm-0.4 μm, and then ultrasonically cleaned after polishing.

7. The method according to any one of claims 1 to 6, characterized in that: The pressureless sintering includes a high-temperature sintering stage and a low-temperature insulation stage; Preferably, the temperature of the high temperature sintering stage is 1600°C-1800°C; Preferably, the high temperature sintering stage lasts for 2h-5h; Preferably, the temperature of the low temperature insulation stage is 300°C-600°C; Preferably, the low-temperature insulation stage lasts for 5 hours to 10 hours.

8. The method according to any one of claims 1 to 7, characterized in that: The mixed solder and the solvent are ball-milled at a rotation speed of 200 rpm-800 rpm to obtain a solder slurry with a solid content of 30%-40%, wherein the solvent comprises any one of anhydrous ethanol, isopropanol or n-butanol or a combination of at least two thereof, and the solder comprises 50%-80% by mass of aluminum nitride, 20%-50% by mass of a sintering aid, 2%-5% by mass of a slow-drying agent, and 2%-5% by mass of an oil-opening agent based on the total weight of the solder as 100%; The solder slurry is coated on the polished aluminum nitride substrate by screen printing to form a solder coating on the aluminum nitride substrate, which is dried at 70°C-110°C for 2h-5h, and the aluminum nitride substrate is fixed by a fixture, and the aluminum nitride substrate is pressurized by bolts and torque wrenches. The assembled aluminum nitride substrate is placed in a pressureless sintering furnace, and the aluminum nitride substrate coated with the solder coating is pressurelessly sintered, sintered at a high temperature of 1600°C-1800°C for 2h-5h, and then kept at a low temperature of 300°C-600°C for 5h-10h to obtain a welded aluminum nitride ceramic.

9. An aluminum nitride ceramic, characterized in that: The aluminum nitride ceramic is prepared according to the preparation method according to any one of claims 1-8.

10. The use of the aluminum nitride ceramic according to claim 9, characterized in that: The aluminum nitride ceramic is used in the semiconductor field.

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