Method for brazing aluminum nitride ceramic to oxygen-free copper and composite filler

Abstract

The embodiment of the present disclosure provides a brazing method and composite filler of aluminum nitride ceramic and oxygen-free copper, and relates to the technical field of electronic packaging. The method comprises the following steps: putting silver-copper-titanium filler and niobium powder into a ball mill tank and performing ball milling with alcohol as a dispersion medium to obtain a filler suspension; drying the filler suspension to obtain a composite filler; adding ethyl cellulose into a mixed solvent formed by pine oil and diethylene glycol butyl ether acetate to obtain a mixed solution by heating and dissolving; adding hydrogenated castor oil and fatty alcohol polyoxyethylene ether into the mixed solution in sequence, and heating to dissolve to obtain a uniform adhesive for solder paste; stirring the composite filler and the adhesive for solder paste to obtain a composite filler solder paste; coating the composite filler solder paste on a bonding area of the aluminum nitride ceramic; and performing brazing on the aluminum nitride ceramic coated with the composite filler solder paste and stacked with an oxygen-free copper foil. The present disclosure can improve the peeling strength of the aluminum nitride ceramic and the oxygen-free copper connection and improve the welding quality.

Description

Technical Field

[0001] This disclosure relates to the field of electronic packaging technology, and more specifically, to a brazing method for aluminum nitride ceramic and oxygen-free copper, and a composite solder. Background Technology

[0002] As power devices continue to evolve, their operating voltage and current are constantly increasing, placing more stringent demands on their heat dissipation capabilities. Aluminum nitride ceramics have higher thermal conductivity than alumina ceramics and lower dielectric constant than silicon carbide ceramics, and their coefficient of thermal expansion is similar to that of semiconductor chips, thus possessing a very broad application and development prospect. The fabrication processes for aluminum nitride ceramic copper-clad laminates include direct copper plating, direct copper bonding, active metal brazing (AMB), and laser-activated metallization. Among these, active metal brazing offers advantages such as simple process, wide applicability, high interfacial bonding strength, and strong current carrying capacity.

[0003] Silver-copper-titanium brazing filler metal is the most commonly used active brazing filler metal system for ceramic-metal bonding, and it has been used to achieve active brazing of various ceramic / metal systems. However, active metal brazing still suffers from drawbacks. Due to the large mismatch in the coefficients of thermal expansion (CTE) between ceramics and metals, the shrinkage and deformation of each material during cooling leads to significant residual thermal stress at the joint interface, reducing the interfacial bonding strength. Summary of the Invention

[0004] The purpose of this disclosure is to provide a brazing method and composite brazing filler metal for aluminum nitride ceramics and oxygen-free copper, thereby overcoming, to at least some extent, the problem of low interfacial bonding strength caused by the limitations and defects of related technologies.

[0005] According to one aspect of this disclosure, a method for brazing aluminum nitride ceramics to oxygen-free copper is provided, comprising: loading silver-copper-titanium brazing filler metal and niobium powder into a ball mill jar and ball milling them with alcohol as a dispersion medium to obtain a brazing filler metal suspension; drying the brazing filler metal suspension to obtain a composite brazing filler metal; adding ethyl cellulose to a mixed solvent formed by terpineol and diethylene glycol butyl ether acetate and heating to dissolve to obtain a mixed solution; sequentially adding hydrogenated castor oil and fatty alcohol polyoxyethylene ether to the mixed solution and heating until dissolved to obtain a solder paste binder with uniform composition; stirring the composite brazing filler metal and the solder paste binder to obtain a composite brazing filler metal paste; coating the bonding area of ​​the aluminum nitride ceramic with the composite brazing filler metal paste; and stacking oxygen-free copper foil on the aluminum nitride ceramic coated with the composite brazing filler metal paste for brazing.

[0006] In one exemplary embodiment of this disclosure, the composite brazing filler metal includes silver-copper-titanium brazing filler metal and niobium powder. The silver-copper-titanium brazing filler metal contains 68.0~70.5wt% silver, 4.0~5.0wt% titanium and copper, and the mass of the niobium powder is 0~10wt% of the total mass of the composite brazing filler metal.

[0007] In one exemplary embodiment of this disclosure, drying the brazing filler metal suspension to obtain a composite brazing filler metal includes: placing the brazing filler metal suspension in a vacuum drying oven and drying it at a target temperature to obtain a dried composite brazing filler metal; the target temperature is less than or equal to 80°C.

[0008] In one exemplary embodiment of this disclosure, the silver-copper-titanium powder has a particle size of less than or equal to 45 μm, and the niobium powder has a particle size of less than or equal to 80 nm.

[0009] In one exemplary embodiment of this disclosure, the solder paste binder comprises: 5-15 wt% ethyl cellulose, 15-25 wt% diethylene glycol butyl ether acetate, 1-5 wt% hydrogenated castor oil, 0.1-3 wt% fatty alcohol polyoxyethylene ether, and terpineol.

[0010] In one exemplary embodiment of this disclosure, the mass ratio of composite solder to solder paste binder is 9:1 to 8:2.

[0011] In one exemplary embodiment of this disclosure, brazing an oxygen-free copper foil stacked on an aluminum nitride ceramic coated with a composite brazing filler metal includes: placing the oxygen-free copper foil stacked on the aluminum nitride ceramic coated with the composite brazing filler metal into a furnace, heating it to a first temperature at a target vacuum level and holding it at that temperature for a first time, and then heating it to a second temperature and holding it at that temperature for a second time, so as to braze the aluminum nitride ceramic and the oxygen-free copper foil.

[0012] In one exemplary embodiment of this disclosure, the target vacuum level is higher than 3 × 10⁻⁶. ‒3 Pa.

[0013] In one exemplary embodiment of this disclosure, the heating rate is 3℃ / min to 10℃ / min, the first temperature is 450℃, the first time is 10min to 30min, the second temperature is 840℃ to 920℃, and the second time is 5min to 20min.

[0014] According to one aspect of this disclosure, a composite brazing filler metal is provided for brazing aluminum nitride ceramics and oxygen-free copper in any of the above-mentioned methods; wherein the composite brazing filler metal comprises silver-copper-titanium brazing filler metal and niobium powder, the silver-copper-titanium brazing filler metal comprises 68.0~70.5wt% silver, 4.0~5.0wt% titanium and copper, and the mass of niobium powder is 0~10wt% of the total mass of the composite brazing filler metal.

[0015] In the technical solutions provided in this disclosure, on the one hand, niobium powder is added to silver-copper-titanium brazing filler metal to prepare a composite brazing filler metal. Niobium particles enhance the strength of the connection between the silver-copper-titanium composite brazing filler metal and aluminum nitride ceramic and oxygen-free copper. By adding niobium particles to the silver-copper-titanium brazing filler metal, the thermal expansion coefficient of niobium is much lower than that of the silver-copper-titanium brazing filler metal, thus reducing the thermal expansion coefficient mismatch between the aluminum nitride ceramic and oxygen-free copper. This alleviates the residual stress at the joint between the aluminum nitride ceramic and oxygen-free copper in related technologies, improves the joint strength between the aluminum nitride ceramic and oxygen-free copper foil, and increases the peel strength. On the other hand, niobium has good ductility. During load-bearing, niobium particles can undergo a certain degree of plastic deformation to absorb some energy, alleviating the stress concentration phenomenon within the silver-copper-titanium composite brazing filler metal layer, and improving the reliability and quality of the aluminum nitride copper-clad laminate.

[0016] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0018] Figure 1 The flowchart illustrates a brazing method for aluminum nitride ceramics and oxygen-free copper according to an embodiment of the present disclosure.

[0019] Figure 2 The microstructure of the aluminum nitride ceramic copper-clad laminate joint prepared according to Example 1 is illustrated schematically. Detailed Implementation

[0020] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided to make this disclosure more comprehensive and complete, and to fully convey the concept of the example embodiments to those skilled in the art. The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced with one or more of the specific details omitted, or other methods, components, apparatus, steps, etc., can be employed. In other instances, well-known technical solutions are not shown or described in detail to avoid obscuring various aspects of this disclosure.

[0021] The terms “a,” “an,” “the,” and “the” are used in this specification to indicate the presence of one or more elements / components, etc.; the terms “including” and “having” are used to indicate an open-ended inclusion and to mean that there may be other elements / components, etc., in addition to those listed; the terms “first” and “second” are used only as markings and are not a limitation on the number of objects.

[0022] Silver-copper-titanium brazing filler metal is the most commonly used active brazing filler metal system for ceramic-metal bonding, and it has been used to achieve active brazing of various ceramic / metal systems. However, active metal brazing still suffers from the problem of large residual thermal stress at the joint interface due to the large mismatch in the coefficients of thermal expansion (CTE) between ceramics and metals. This residual stress, caused by the shrinkage and deformation of the materials during cooling, reduces the interfacial bonding strength. Therefore, alleviating the residual stress at the weld joint is crucial for the fabrication of high-reliability aluminum nitride copper-clad laminates.

[0023] To address the aforementioned problems, this disclosure provides a brazing method for aluminum nitride ceramics and oxygen-free copper, as well as a composite brazing filler metal for brazing aluminum nitride ceramics and oxygen-free copper. This composite brazing filler metal is produced by adding niobium powder to a traditional silver-copper-titanium brazing filler metal. The addition of niobium particles reduces the coefficient of thermal expansion of the brazing filler alloy, and during load-bearing, the niobium particles can undergo a certain degree of plastic deformation to absorb some energy, thus solving the problems of high residual stress and low joint strength at the aluminum nitride ceramics and oxygen-free copper joint.

[0024] refer to Figure 1 As shown, the brazing method between the aluminum nitride ceramic and oxygen-free copper mainly includes the following steps:

[0025] In step S110, silver-copper-titanium brazing filler metal and niobium powder are loaded into a ball mill jar and ball milled with alcohol as the dispersion medium to obtain a brazing filler metal suspension.

[0026] In step S120, the brazing filler metal suspension is dried to obtain a composite brazing filler metal;

[0027] In step S130, ethyl cellulose is added to a mixed solvent formed by terpineol and diethylene glycol butyl ether acetate and heated to dissolve to obtain a mixed solution. Hydrogenated castor oil and fatty alcohol polyoxyethylene ether are added to the mixed solution in sequence and heated until dissolved to obtain a solder paste adhesive with uniform composition.

[0028] In step S140, the composite brazing filler metal and solder paste are mixed with a binder to obtain the composite brazing filler metal and solder paste.

[0029] In step S150, a composite solder paste is applied to the bonding area of ​​the aluminum nitride ceramic, and oxygen-free copper foil is stacked on the aluminum nitride ceramic coated with the composite solder paste for brazing.

[0030] Next, the brazing method of aluminum nitride ceramic and oxygen-free copper in the embodiments of this disclosure will be described in detail.

[0031] In step S110, silver-copper-titanium brazing filler metal and niobium powder are loaded into a ball mill jar and ball milled with alcohol as the dispersion medium to obtain a brazing filler metal suspension.

[0032] In this embodiment, the silver-copper-titanium brazing filler metal is an active brazing filler metal system used to join ceramics and metals. The silver-copper-titanium brazing filler metal contains 68.0~70.5 wt% silver, 4.0~5.0 wt% titanium, and copper. Specifically, the mass of silver accounts for 68.0%~70.5% of the total mass of the silver-copper-titanium brazing filler metal. The mass of titanium accounts for 4.0%~5.0% of the total mass of the silver-copper-titanium brazing filler metal, and the remaining component is copper. The mass of niobium powder is 0~10% of the total mass of the composite brazing filler metal. The particle size of the silver-copper-titanium powder is less than or equal to 45 μm, and the particle size of the niobium powder is less than or equal to 80 nm.

[0033] The silver-copper-titanium brazing filler metal and niobium powder can be weighed according to the above ratio, loaded into a ball mill jar and ball milled with alcohol as the dispersion medium to obtain a brazing filler metal suspension.

[0034] In step S120, the brazing filler metal suspension is dried to obtain a composite brazing filler metal.

[0035] In this embodiment, the brazing filler metal suspension can be placed in a vacuum drying oven and dried at a target temperature to obtain a dried composite brazing filler metal. The target temperature is less than or equal to 80°C, and can be, for example, 40°C, 50°C, 60°C, 80°C, or other suitable temperatures. The drying time is not limited, as long as the composite brazing filler metal is obtained.

[0036] In step S130, ethyl cellulose is added to a mixed solvent formed by terpineol and diethylene glycol butyl ether acetate and heated to dissolve to obtain a mixed solution. Hydrogenated castor oil and fatty alcohol polyoxyethylene ether are added to the mixed solution in sequence and heated until dissolved to obtain a solder paste adhesive with uniform composition.

[0037] In this embodiment, terpineol and diethylene glycol butyl ether acetate are mixed to form a mixed solvent, and ethyl cellulose is added to the mixed solvent. The mixed solvent with ethyl cellulose is heated and stirred until the ethyl cellulose is completely dissolved to obtain a mixed solution. Terpineol is the main solvent, providing good volatility and wetting properties. Diethylene glycol butyl ether acetate is an auxiliary solvent, adjusting the evaporation rate and improving stability. Ethyl cellulose is a thickener, adjusting viscosity and enhancing adhesion. The mass percentage of ethyl cellulose is 5-15 wt%, and the mass percentage of diethylene glycol butyl ether acetate is 15-25 wt%. The mixed solvent with ethyl cellulose can be heated to a first preset temperature, which can be 60-70°C. Heating the mixed solution can be done via a water bath or a non-water bath, depending on the actual requirements.

[0038] Further, hydrogenated castor oil and fatty alcohol polyoxyethylene ether are added sequentially to the mixed solution and heated until dissolved to obtain a solder paste binder with uniform composition. Hydrogenated castor oil is a thixotropic agent used for thickening and improving wettability, thereby enhancing stability. Fatty alcohol polyoxyethylene ether is a surfactant used to improve wettability and reduce surface tension.

[0039] The hydrogenated castor oil comprises 1-5 wt% by mass, and the fatty alcohol polyoxyethylene ether comprises 0.1-3 wt% by mass. The mixed solution containing hydrogenated castor oil and fatty alcohol polyoxyethylene ether can be heated to a second preset temperature, which can be higher than the first preset temperature, for example, 85-95°C. Heating the mixed solution can be done via a water bath or a non-water bath, depending on the specific requirements. When the hydrogenated castor oil and fatty alcohol polyoxyethylene ether added to the mixed solution are completely dissolved, a solder paste binder with uniform composition can be obtained. It should be noted that the composition of this solder paste binder can be determined based on the composition of the added substances and the mixed solvent. For example, the solder paste binder includes 5-15 wt% ethyl cellulose, 15-25 wt% diethylene glycol butyl ether acetate, 1-5 wt% hydrogenated castor oil, 0.1-3 wt% fatty alcohol polyoxyethylene ether, and terpineol.

[0040] In step S140, the composite brazing filler metal and solder paste are mixed with a binder to obtain the composite brazing filler metal and solder paste.

[0041] In this embodiment of the present disclosure, after preparing the composite solder paste, the composite solder and the solder paste binder are stirred and mixed according to a mass ratio to obtain the composite solder paste. The mass ratio of the composite solder to the solder paste binder is 9:1 to 8:2.

[0042] In step S150, a composite solder paste is applied to the bonding area of ​​the aluminum nitride ceramic, and oxygen-free copper foil is stacked on the aluminum nitride ceramic coated with the composite solder paste and then brazed.

[0043] In this embodiment, the bonding region refers to the interface region where aluminum nitride ceramics are joined to other materials such as metals through a specific process, and the localized area near this region affected by the bonding process. For example, it can be the physical or chemical interface between aluminum nitride ceramics and other materials. The size of the bonding region can be determined according to actual needs.

[0044] For aluminum nitride ceramics, the composite solder paste prepared in step S140 can be coated onto the bonding area of ​​the aluminum nitride ceramic, and the coating thickness can be determined according to actual needs. Further, oxygen-free copper foil can be stacked on the aluminum nitride ceramic coated with the composite solder paste and then brazed. For example, oxygen-free copper foil can be stacked on the surface of the aluminum nitride ceramic coated with the composite solder paste, and the oxygen-free copper foil is fixed to the surface of the aluminum nitride ceramic coated with the composite solder paste in a stacking and bonding manner.

[0045] Based on this, aluminum nitride ceramics stacked with oxygen-free copper foil are placed in a furnace for brazing. The brazing process parameters are as follows: under a target vacuum level, the temperature is increased to a first temperature and held for a first time at a rising rate, then increased to a second temperature and held for a second time to braze the aluminum nitride ceramics and oxygen-free copper foil. The target vacuum level can be higher than 3 × 10⁻⁶. ‒ 3 Pa. The heating rate is 3℃ / min~10℃ / min, the first temperature is 450℃, the first time is 10min~30min, the second temperature is 840℃~920℃, and the second time is 5min~20min. Exemplarily, it can be higher than 3×10... ‒3 Under vacuum conditions, the temperature is first raised to 450℃ at a heating rate of 3℃ / min to 10℃ / min and held for 10min to 30min to volatilize the organic matter in the composite brazing paste. Then the temperature is raised to 840℃ to 920℃ and held for 5min to 30min to achieve the brazing process.

[0046] In this embodiment, niobium powder is added to prepare a composite brazing filler metal. Niobium particles are used to reinforce the silver-copper-titanium composite brazing filler metal to connect aluminum nitride ceramic and oxygen-free copper. By adding niobium particles to the silver-copper-titanium brazing filler metal, the thermal expansion coefficient of niobium is significantly lower than that of the silver-copper-titanium filler metal, thus reducing the thermal expansion coefficient mismatch between the aluminum nitride ceramic and oxygen-free copper, alleviating joint stress, and improving joint strength. Simultaneously, niobium has good ductility; during load-bearing, niobium particles can undergo a certain degree of plastic deformation to absorb some energy, alleviating stress concentration within the brazing filler layer.

[0047] Next, the brazing method of aluminum nitride ceramic and oxygen-free copper of this disclosure will be described with reference to the embodiments.

[0048] Comparative Example 1

[0049] Step 1: Soak the copper substrate in dilute hydrochloric acid for several minutes, then ultrasonically clean it in anhydrous ethanol, and finally rinse it with distilled water and dry it to remove impurities from the surface of the copper substrate.

[0050] Step 2: The dried copper substrate is electroplated to form an oxygen-containing copper layer on the bonding surface. The electroplating solution consists of copper sulfate, lactic acid, and water. The concentration of copper sulfate in the electroplating solution is 0.5 mol / L, and the concentration of lactic acid is 2.5 mol / L. During electroplating, the pH of the electroplating solution is adjusted to 11 using a 5 mol / L sodium hydroxide solution. The electroplating current is a constant 3 mA, and the electroplating time is 20 minutes.

[0051] Step 3: The aluminum nitride substrate is sequentially cleaned with acetone, water, and then ultrasonically cleaned with ethanol, each ultrasonic cleaning lasting 10 minutes. After ultrasonic cleaning, it is dried in an oven at 80℃.

[0052] Step 4: Heat the dried aluminum nitride substrate in air to form an aluminum oxide layer on the bonding surface of the aluminum nitride substrate.

[0053] Step 5: Stack the copper substrate and aluminum nitride substrate so that the oxygen-containing copper layer and the aluminum oxide layer are in direct contact to prepare the pre-finished product.

[0054] Step Six: Place the pre-finished product smoothly into the sintering furnace, purge it three times, and then evacuate it. Then maintain the temperature. After maintaining the temperature, allow it to cool naturally in the furnace. After cooling, you will obtain aluminum nitride copper-clad ceramic.

[0055] The peel strength of the aluminum nitride copper-clad ceramic prepared according to the comparative example is 11 N / mm.

[0056] Example 1

[0057] In this embodiment, the raw materials and proportions of the composite brazing filler metal used for brazing aluminum nitride ceramic and oxygen-free copper are as follows: the silver-copper-titanium brazing filler metal contains 68wt% silver, 28wt% copper, and 4wt% titanium, and the mass of niobium powder is 2wt% of the total mass of the composite brazing filler metal. The particle size of the silver-copper-titanium powder is less than or equal to 45μm, and the particle size of the niobium powder is less than or equal to 80nm.

[0058] The brazing method for brazing composite filler metals of aluminum nitride ceramics and oxygen-free copper specifically includes the following steps:

[0059] Step 1: Weigh out the silver, copper, and titanium brazing filler metal and niobium powder according to the ratio, put them into a ball mill jar, and use alcohol as the dispersion medium. After ball milling, a uniformly mixed brazing filler metal suspension is obtained.

[0060] Step 2: Place the brazing filler metal suspension in a vacuum drying oven and dry it at 50°C to obtain the dried composite brazing filler metal.

[0061] Step 3: Add ethyl cellulose to a mixed solvent formed by terpineol and diethylene glycol butyl ether acetate, heat to 60°C and stir until the ethyl cellulose is completely dissolved to obtain a mixed solution; add hydrogenated castor oil and fatty alcohol polyoxyethylene ether to the obtained mixed solution in sequence, heat to 90°C and stir until completely dissolved to obtain a solder paste adhesive with uniform composition.

[0062] The solder paste binder includes: 10 wt% ethyl cellulose, 19 wt% diethylene glycol butyl ether acetate, 3 wt% hydrogenated castor oil, 1 wt% fatty alcohol polyoxyethylene ether, and 67 wt% terpineol.

[0063] Step 4: Weigh the composite brazing filler metal and the solder paste binder at a mass ratio of 9:1 and mix them thoroughly to obtain the composite brazing filler metal solder paste.

[0064] Step 5: Apply composite solder paste to the bonding area of ​​the aluminum nitride ceramic, and then stack the surface of the aluminum nitride ceramic coated with composite solder paste together with oxygen-free copper foil before placing it in the furnace at a temperature higher than 3×10⁻⁶. ‒3 Brazing is performed under a vacuum of Pa. The brazing process includes: first heating to 450℃ at a heating rate of 10℃ / min and holding for 30min to volatilize the organic matter in the composite brazing paste, and then heating to 880℃ and holding for 10min.

[0065] As shown in Table 1, the peel strength of the aluminum nitride copper-clad laminate prepared according to Example 1 is 26.1 N / mm. Figure 2 The microstructure morphology of the aluminum nitride ceramic copper-clad laminate connector is shown. Figure 2 It can be seen that the aluminum nitride ceramic and oxygen-free copper interface are well bonded, and no microcracks were found.

[0066] Example 2

[0067] Compared to Example 1, the mass of niobium powder was adjusted in Example 2. Exemplarily, the mass of niobium powder was 0 wt% of the total mass of the composite solder, meaning no niobium powder was added in Example 2. Specific steps included:

[0068] Step 1: Weigh out silver, copper, and titanium brazing filler metals and load them into a ball mill jar. Use alcohol as the dispersion medium and ball mill to obtain a brazing filler metal suspension.

[0069] Step 2: Place the brazing filler metal suspension in a vacuum drying oven and dry it at 50°C to obtain the dried composite brazing filler metal.

[0070] Step 3: Add ethyl cellulose to a mixed solvent formed by terpineol and diethylene glycol butyl ether acetate, heat to 60°C and stir until the ethyl cellulose is completely dissolved to obtain a mixed solution; add hydrogenated castor oil and fatty alcohol polyoxyethylene ether to the obtained mixed solution in sequence, heat to 90°C and stir until completely dissolved to obtain a solder paste adhesive with uniform composition.

[0071] The solder paste binder includes: 10 wt% ethyl cellulose, 19 wt% diethylene glycol butyl ether acetate, 3 wt% hydrogenated castor oil, 1 wt% fatty alcohol polyoxyethylene ether, and 67 wt% terpineol.

[0072] Step 4: Weigh the composite brazing filler metal and the solder paste binder at a mass ratio of 9:1 and mix them thoroughly to obtain the composite brazing filler metal solder paste.

[0073] Step 5: Apply composite solder paste to the bonding area of ​​the aluminum nitride ceramic, and then stack the surface of the aluminum nitride ceramic coated with composite solder paste together with oxygen-free copper foil before placing it in the furnace at a temperature higher than 3×10⁻⁶. ‒3 Brazing is performed under a vacuum of Pa. The brazing process includes: first heating to 450℃ at a heating rate of 10℃ / min and holding for 30min to volatilize the organic matter in the composite brazing paste, and then heating to 880℃ and holding for 10min.

[0074] As shown in Table 1, the peel strength of the aluminum nitride copper-clad laminate prepared according to Example 2 is 15.7 N / mm.

[0075] Example 3

[0076] Compared to Example 1, the mass of niobium powder was adjusted in Example 3. For example, the mass of niobium powder was 4 wt% of the total mass of the composite solder, meaning that Example 3 increased the amount of niobium powder added. Specifically, the steps included were:

[0077] Step 1: Weigh out the silver, copper, and titanium brazing filler metal and niobium powder according to the ratio, put them into a ball mill jar, and use alcohol as the dispersion medium. After ball milling, a uniformly mixed brazing filler metal suspension is obtained.

[0078] Step 2: Place the brazing filler metal suspension in a vacuum drying oven and dry it at 50°C to obtain the dried composite brazing filler metal.

[0079] Step 3: Add ethyl cellulose to a mixed solvent formed by terpineol and diethylene glycol butyl ether acetate, heat to 60°C and stir until the ethyl cellulose is completely dissolved to obtain a mixed solution; add hydrogenated castor oil and fatty alcohol polyoxyethylene ether to the obtained mixed solution in sequence, heat to 90°C and stir until completely dissolved to obtain a solder paste adhesive with uniform composition.

[0080] The solder paste binder includes: 10 wt% ethyl cellulose, 19 wt% diethylene glycol butyl ether acetate, 3 wt% hydrogenated castor oil, 1 wt% fatty alcohol polyoxyethylene ether, and 67 wt% terpineol.

[0081] Step 4: Weigh the composite brazing filler metal and the solder paste binder at a mass ratio of 9:1 and mix them thoroughly to obtain the composite brazing filler metal solder paste.

[0082] Step 5: Apply composite solder paste to the bonding area of ​​the aluminum nitride ceramic, and then stack the surface of the aluminum nitride ceramic coated with composite solder paste together with oxygen-free copper foil before placing it in the furnace at a temperature higher than 3×10⁻⁶. ‒3 Brazing is performed under a vacuum of Pa. The brazing process includes: first heating to 450℃ at a heating rate of 10℃ / min and holding for 30min to volatilize the organic matter in the composite brazing paste, and then heating to 880℃ and holding for 10min.

[0083] Referring to Table 1, the peel strength of the aluminum nitride copper-clad laminate obtained according to Example 3 is 25.1 N / mm.

[0084] Example 4

[0085] Compared with Example 1, Example 4 adjusted the brazing process parameters, specifically the heating rate, the first time, and the second temperature.

[0086] The brazing method for brazing composite filler metals of aluminum nitride ceramics and oxygen-free copper specifically includes the following steps:

[0087] Step 1: Weigh out the silver, copper, and titanium brazing filler metal and niobium powder according to the ratio, put them into a ball mill jar, and use alcohol as the dispersion medium. After ball milling, a uniformly mixed brazing filler metal suspension is obtained.

[0088] Step 2: Place the brazing filler metal suspension in a vacuum drying oven and dry it at 50°C to obtain the dried composite brazing filler metal.

[0089] Step 3: Add ethyl cellulose to a mixed solvent formed by terpineol and diethylene glycol butyl ether acetate, heat to 60°C and stir until the ethyl cellulose is completely dissolved to obtain a mixed solution; add hydrogenated castor oil and fatty alcohol polyoxyethylene ether to the obtained mixed solution in sequence, heat to 90°C and stir until completely dissolved to obtain a solder paste adhesive with uniform composition.

[0090] The solder paste binder includes: 10 wt% ethyl cellulose, 19 wt% diethylene glycol butyl ether acetate, 3 wt% hydrogenated castor oil, 1 wt% fatty alcohol polyoxyethylene ether, and 67 wt% terpineol.

[0091] Step 4: Weigh the composite brazing filler metal and the solder paste binder at a mass ratio of 9:1 and mix them thoroughly to obtain the composite brazing filler metal solder paste.

[0092] Step 5: Apply composite solder paste to the bonding area of ​​the aluminum nitride ceramic, and then stack the surface of the aluminum nitride ceramic coated with composite solder paste together with oxygen-free copper foil before placing it in the furnace at a temperature higher than 3×10⁻⁶. ‒3 Brazing is performed under a vacuum of Pa. The brazing process includes: first heating to 450℃ at a heating rate of 3℃ / min and holding for 10min to volatilize the organic matter in the composite brazing paste, and then heating to 840℃ and holding for 10min.

[0093] Referring to Table 1, the peel strength of the aluminum nitride copper-clad laminate obtained according to Example 4 is 18.9 N / mm.

[0094] Example 5

[0095] Compared to Example 1, Example 5 adjusted the brazing process parameters, specifically the second temperature. The specific steps include:

[0096] Step 1: Weigh out the silver, copper, and titanium brazing filler metal and niobium powder according to the ratio, put them into a ball mill jar, and use alcohol as the dispersion medium. After ball milling, a uniformly mixed brazing filler metal suspension is obtained.

[0097] Step 2: Place the brazing filler metal suspension in a vacuum drying oven and dry it at 50°C to obtain the dried composite brazing filler metal.

[0098] Step 3: Add ethyl cellulose to a mixed solvent formed by terpineol and diethylene glycol butyl ether acetate, heat to 60°C and stir until the ethyl cellulose is completely dissolved to obtain a mixed solution; add hydrogenated castor oil and fatty alcohol polyoxyethylene ether to the obtained mixed solution in sequence, heat to 90°C and stir until completely dissolved to obtain a solder paste adhesive with uniform composition.

[0099] The solder paste binder includes: 10 wt% ethyl cellulose, 19 wt% diethylene glycol butyl ether acetate, 3 wt% hydrogenated castor oil, 1 wt% fatty alcohol polyoxyethylene ether, and 67 wt% terpineol.

[0100] Step 4: Weigh the composite brazing filler metal and the solder paste binder at a mass ratio of 9:1 and mix them thoroughly to obtain the composite brazing filler metal solder paste.

[0101] Step 5: Apply composite solder paste to the bonding area of ​​the aluminum nitride ceramic, and then stack the surface of the aluminum nitride ceramic coated with composite solder paste together with oxygen-free copper foil before placing it in the furnace at a temperature higher than 3×10⁻⁶. ‒3 Brazing was performed under a vacuum of Pa.

[0102] The brazing process in step five includes: first heating to 450℃ at a heating rate of 10℃ / min and holding for 30 minutes to allow the organic matter in the composite brazing paste to volatilize, and then heating to 920℃ and holding for 10 minutes.

[0103] Referring to Table 1, the peel strength of the aluminum nitride copper-clad laminate obtained according to Example 5 is 16.5 N / mm.

[0104] Example 6

[0105] Compared to Example 1, Example 6 adjusted the brazing process parameters, specifically the second time, which was reduced. The specific steps include:

[0106] Step 1: Weigh out the silver, copper, and titanium brazing filler metal and niobium powder according to the ratio, put them into a ball mill jar, and use alcohol as the dispersion medium. After ball milling, a uniformly mixed brazing filler metal suspension is obtained.

[0107] Step 2: Place the brazing filler metal suspension in a vacuum drying oven and dry it at 50°C to obtain the dried composite brazing filler metal.

[0108] Step 3: Add ethyl cellulose to a mixed solvent formed by terpineol and diethylene glycol butyl ether acetate, heat to 60°C and stir until the ethyl cellulose is completely dissolved to obtain a mixed solution; add hydrogenated castor oil and fatty alcohol polyoxyethylene ether to the obtained mixed solution in sequence, heat to 90°C and stir until completely dissolved to obtain a solder paste adhesive with uniform composition.

[0109] The solder paste binder includes: 10 wt% ethyl cellulose, 19 wt% diethylene glycol butyl ether acetate, 3 wt% hydrogenated castor oil, 1 wt% fatty alcohol polyoxyethylene ether, and 67 wt% terpineol.

[0110] Step 4: Weigh the composite brazing filler metal and the solder paste binder at a mass ratio of 9:1 and mix them thoroughly to obtain the composite brazing filler metal solder paste.

[0111] Step 5: Apply composite solder paste to the bonding area of ​​the aluminum nitride ceramic, and then stack the surface of the aluminum nitride ceramic coated with composite solder paste together with oxygen-free copper foil before placing it in the furnace at a temperature higher than 3×10⁻⁶. ‒3 Brazing was performed under a vacuum of Pa.

[0112] For example, the brazing process in step five includes: the brazing heat treatment regime is: first heat to 450°C at a heating rate of 10°C / min and hold for 30 minutes to volatilize the organic matter in the composite brazing paste, and then heat to 880°C and hold for 5 minutes.

[0113] Referring to Table 1, the peel strength of the aluminum nitride copper-clad laminate obtained according to Example 6 is 23.6 N / mm.

[0114] Example 7

[0115] Compared to Example 1, Example 7 adjusted the brazing process parameters, specifically increasing the second time. The specific steps include:

[0116] Step 1: Weigh out the silver, copper, and titanium brazing filler metal and niobium powder according to the ratio, put them into a ball mill jar, and use alcohol as the dispersion medium. After ball milling, a uniformly mixed brazing filler metal suspension is obtained.

[0117] Step 2: Place the brazing filler metal suspension in a vacuum drying oven and dry it at 50°C to obtain the dried composite brazing filler metal.

[0118] Step 3: Add ethyl cellulose to a mixed solvent formed by terpineol and diethylene glycol butyl ether acetate, heat to 60°C and stir until the ethyl cellulose is completely dissolved to obtain a mixed solution; add hydrogenated castor oil and fatty alcohol polyoxyethylene ether to the obtained mixed solution in sequence, heat to 90°C and stir until completely dissolved to obtain a solder paste adhesive with uniform composition.

[0119] The solder paste binder includes: 10 wt% ethyl cellulose, 19 wt% diethylene glycol butyl ether acetate, 3 wt% hydrogenated castor oil, 1 wt% fatty alcohol polyoxyethylene ether, and 67 wt% terpineol.

[0120] Step 4: Weigh the composite brazing filler metal and the solder paste binder at a mass ratio of 9:1 and mix them thoroughly to obtain the composite brazing filler metal solder paste.

[0121] Step 5: Apply composite solder paste to the bonding area of ​​the aluminum nitride ceramic, and then stack the surface of the aluminum nitride ceramic coated with composite solder paste together with oxygen-free copper foil before placing it in the furnace at a temperature higher than 3×10⁻⁶. ‒3 Brazing was performed under a vacuum of Pa.

[0122] For example, the brazing process in step five includes: the brazing heat treatment regime is: first heat to 450°C at a heating rate of 10°C / min and hold for 30 minutes to volatilize the organic matter in the composite brazing paste, and then heat to 880°C and hold for 30 minutes.

[0123] Referring to Table 1, the peel strength of the aluminum nitride copper-clad laminate obtained according to Example 7 is 20.4 N / mm.

[0124] Table 1

[0125]

[0126] In summary, under the conditions of 2wt% niobium powder addition, a first brazing temperature of 880℃, and a first holding time of 10 min, the peel strength at the aluminum nitride and oxygen-free copper joint is the highest, reaching 26.1 N / mm. This peel strength is 1.7 times that of the brazed joint without niobium powder. The peel strength of the aluminum nitride ceramic-oxygen-free copper joint obtained in this embodiment is significantly higher than that in related technologies.

[0127] In this embodiment, the addition of niobium particles reduces the thermal expansion coefficient of the brazing alloy, and the niobium particles can undergo a certain degree of plastic deformation to absorb some energy during the load-bearing process. This solves the problem of high residual stress and low joint strength in the joint between aluminum nitride ceramic and oxygen-free copper in related technologies, and realizes high-quality welding between aluminum nitride ceramic and oxygen-free copper.

[0128] In addition, this disclosure also provides a composite brazing filler metal for performing a brazing method of aluminum nitride ceramics and oxygen-free copper. The composite brazing filler metal comprises a silver-copper-titanium brazing filler metal and niobium powder. The silver-copper-titanium brazing filler metal comprises 68.0~70.5wt% silver, 4.0~5.0wt% titanium, and copper, and the niobium powder accounts for 0~10wt% of the total mass of the composite brazing filler metal.

[0129] Aluminum nitride ceramic and oxygen-free copper are joined using a niobium-reinforced silver-copper-titanium composite brazing filler metal. By adding niobium particles to the silver-copper-titanium filler metal, the thermal expansion coefficient of niobium, which is much lower than that of the filler metal, is reduced. This lowers the thermal expansion coefficient mismatch between the aluminum nitride ceramic and oxygen-free copper, alleviating joint stress, increasing joint strength, and achieving high-quality welding between the aluminum nitride ceramic and oxygen-free copper. Simultaneously, niobium's good ductility allows the niobium particles to undergo a certain degree of plastic deformation during load-bearing, absorbing some energy and alleviating stress concentration within the filler metal layer, thus improving the welding effect.

[0130] Furthermore, the above figures are merely illustrative of the processes included in the method according to exemplary embodiments of this disclosure and are not intended to be limiting. It is readily understood that the processes shown in the above figures do not indicate or limit the temporal order of these processes. Additionally, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0131] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the appended claims.

[0132] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.

Claims

1. A brazing method for aluminum nitride ceramic and oxygen-free copper, characterized in that, include: Weigh out silver-copper-titanium brazing filler metal and niobium powder according to the specified ratio, load them into a ball mill jar, and ball mill them using alcohol as the dispersion medium to obtain a brazing filler metal suspension; the silver-copper-titanium brazing filler metal contains 68 wt.% silver, 28 wt.% copper, and 4 wt.% titanium; the niobium powder particle size is... 80nm; Particle size of silver-copper-titanium powder 45μm; The brazing filler metal suspension was dried in a vacuum drying oven at 50°C to obtain a dried composite brazing filler metal; the composite brazing filler metal comprises silver-copper-titanium brazing filler metal and niobium powder, wherein the mass of the niobium powder is 2 wt.% of the total mass of the composite brazing filler metal. Ethyl cellulose was added to a mixed solvent of terpineol and diethylene glycol butyl ether acetate and heated to 60°C with stirring until the ethyl cellulose was completely dissolved, resulting in a mixed solution. Hydrogenated castor oil and fatty alcohol polyoxyethylene ether were added sequentially to the mixed solution, and the mixture was heated to 90°C with stirring until dissolved, thus obtaining a solder paste binder with uniform composition. The solder paste binder comprises: 10 wt.% ethyl cellulose, 19 wt.% diethylene glycol butyl ether acetate, 3 wt.% hydrogenated castor oil, 1 wt.% fatty alcohol polyoxyethylene ether, and 67 wt.% terpineol. Weigh the composite brazing filler metal and solder paste binder at a mass ratio of 9:1 and stir them to obtain the composite brazing filler metal solder paste. Composite solder paste is coated onto the bonding region of aluminum nitride ceramics. The surface of the aluminum nitride ceramics coated with composite solder paste is then stacked with oxygen-free copper foil and placed in a furnace at a temperature higher than 3 × 10⁻⁶. -3 Brazing was performed under a vacuum of Pa. The brazing process includes: First, heat the material to 450℃ at a heating rate of 10℃ / min and hold for 30 minutes to allow the organic matter in the composite solder paste to volatilize. Then, heat the material to 880℃ and hold for 10 minutes.

2. A composite brazing filler metal, characterized in that, The composite brazing filler metal is used to perform the brazing method of aluminum nitride ceramic and oxygen-free copper as described in claim 1; The composite brazing filler metal comprises silver-copper-titanium brazing filler metal and niobium powder. The silver-copper-titanium brazing filler metal contains 68 wt.% silver, 28 wt.% copper, and 4 wt.% titanium. The niobium powder accounts for 2 wt.% of the total mass of the composite brazing filler metal. The niobium powder particle size is... 80nm; Particle size of silver-copper-titanium powder 45μm.

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