Lead-free composite brazing filler metal and method for low-temperature connection of large-size ceramic and metal

Abstract

The invention relates to the technical field of dissimilar material connection, in particular to a lead-free composite brazing filler metal and method for low-temperature connection of large-size ceramic and metal, the composite brazing filler metal is obtained by mixing copper powder and tin-bismuth welding powder according to the mass ratio of 1: 75-100, tabletting and standing; wherein the tin content in the tin-bismuth welding powder is 42%, and the bismuth content in the tin-bismuth welding powder is 58%. According to the Cu-SnBi composite solder developed by the invention, the brittleness of the SnBi solder is effectively avoided, and the Cu-SnBi composite solder is particularly suitable for large-size (mainly aiming at electronic packaging welding spots at present and relatively small in size) brazing, can realize successful welding at the temperature of 200 DEG C or below without brittle cracking, and is excellent in comprehensive mechanical property.

Description

Technical Field

[0001] The invention relates to the technical field of connecting dissimilar materials, and in particular to a lead-free composite solder and a method for low-temperature connection of large-size ceramics and metals. Background Art

[0002] Nowadays, the connection between ceramics and metals is an important technology in the field of materials engineering. Ceramics are difficult to manufacture into large-sized or complex-shaped ceramic workpieces due to their inherent brittleness and low fracture toughness, which imposes certain restrictions on their application. Connecting ceramics to metals is an effective solution to expand their application range. For example, in the field of electronic packaging, ceramic substrates are connected to metal heat sinks. The ceramic substrate provides stable physical support and good insulation performance, and the metal heat sink uses its good thermal conductivity to quickly dissipate heat, thereby ensuring that the electronic components work at a suitable temperature. At present, the main methods for connecting ceramics to metals are brazing, solid-phase diffusion bonding, transient liquid phase (TLP) diffusion bonding, self-propagating high-temperature synthesis (SHS) bonding, etc. Brazing is the most widely used method for ceramic-metal bonding due to its simplicity and adaptability to joint structures. However, the brazing connection between ceramics and metals in industrial production is mostly based on high temperature, among which AgCuTi solder is the most commonly used high-melting point solder, which has a high connection temperature and large residual thermal stress. For many heat-sensitive applications in ceramic-metal packaging, excessively high connection temperatures can cause indelible damage to certain power devices, and for large-area ceramic-metal connections, thermal mismatches caused by high temperatures can easily lead to cracking of ceramic components. Therefore, it is particularly important to develop low-temperature solders and achieve low-temperature reliable connections between ceramics and metals. Summary of the invention

[0003] In view of this, the purpose of the present invention is to propose a lead-free composite solder and method for low-temperature connection of large-size ceramics and metals, to develop a low-melting point composite solder, to achieve low-temperature connection of large-area ceramics and metals, and to solve the brittleness problem of traditional SnBi solder.

[0004] Based on the above purpose, the present invention provides a lead-free composite solder for low-temperature connection of large-size ceramics and metals. The composite solder is obtained by mixing copper powder and tin-bismuth solder powder in a mass ratio of 1:75-100, pressing into tablets, and standing; wherein the tin content in the tin-bismuth solder powder is 42% and the bismuth content is 58%.

[0005] The copper powder is spherical nano Cu powder particles with a particle size of 500-1000nm.

[0006] The particle size of the tin-bismuth solder powder is 450-550 meshes.

[0007] The tableting and standing method is to put the mixed powder into a mold, and let it stand for 1-3 minutes under a pressure of 2-5N by a tablet press to form a 0.2-0.5mm welding sheet.

[0008] The present invention also provides a method for low-temperature connection of ceramic and metal, using the composite brazing material for vacuum brazing, the method comprising the following steps:

[0009] S1. Remove impurities from silicon carbide ceramics and copper plates;

[0010] S2. Use magnetron sputtering technology to perform surface metallization treatment on the silicon carbide ceramic after impurity removal. The specific method refers to the patent (CN202410273802.3);

[0011] S3, assembling the metallized silicon carbide ceramic, the composite brazing material and the copper plate into a sandwich structure and then performing vacuum brazing.

[0012] The method for removing impurities from silicon carbide ceramics and copper plates in S1 is to remove the oxide layer and impurities on the surface of SiC and Cu plates by mechanical grinding, and then remove surface stains by ultrasonic cleaning.

[0013] The process parameters of the vacuum brazing are as follows: welding temperature: 180-190°C, heating speed: 5-10°C / min, holding time: 5-20min, vacuum degree: 3.5-5×10 -3 Pa.

[0014] Beneficial effects of the present invention:

[0015] 1. The prior art uses SnAg, SnCu, SnAgCu and other methods, and the welding temperature is generally above 250°C, and the residual stress in the process of connecting large-sized dissimilar materials is large. Compared with the prior art, the present invention replaces SnPb to achieve lead-free solder for large-sized ceramic-metal connections. The developed Cu-SnBi composite solder effectively avoids the brittleness of SnBi solder, especially for large-sized (currently mainly for electronic packaging solder joints, which are smaller in size) brazing, and can achieve successful welding below 200°C without brittle cracking, and the solder has excellent comprehensive mechanical properties. 2. The present invention has developed a large-area connection method for ceramics and metals below 200°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 The SEM morphology of the composite solder and copper powder; wherein, (a) SEM morphology of Cu powder particles, (b) SEM morphology of Cu-Sn58Bi (1:100) composite solder in Example 1, (c) SEM morphology of Cu-Sn58Bi (1:75) composite solder in Example 2, (d) SEM morphology of Cu-Sn58Bi (1:50) composite solder in Comparative Example 1, (e) SEM morphology of pure Sn58Bi solder in Comparative Example 2;

[0018] Figure 2 The figures are morphologies of brazed joints of the embodiments and comparative examples; wherein, (a) SEM morphology of the ceramic-metal brazed joint in embodiment 1, (b) SEM morphology of the ceramic-metal brazed joint in embodiment 2, (c) SEM morphology of the ceramic-metal brazed joint in comparative example 1, (d) SEM morphology of the ceramic-metal brazed joint in comparative example 2;

[0019] Figure 3 The micro-area XRD patterns of ceramic-metal joints brazed with Cu-Sn58Bi composite brazing materials of different proportions;

[0020] Figure 4 Shear strength of the implementation case and the comparison case. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0022] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present invention should have the common meanings understood by persons having ordinary skills in the field to which the present invention belongs.

[0023] Example 1

[0024] After Cu powder (average particle size 500nm) and Sn58Bi solder powder (500 mesh) were fully mixed at a mass ratio of 1:100, 1.5g was weighed and allowed to stand for 1min under a pressure of 3N, and then pressed into a solder sheet with a thickness of about 0.1mm. Its microscopic morphology is as follows: Figure 1 (b) As shown. The SiC after impurity removal is metallized by magnetron sputtering technology. First, a Cr film is sputtered on its surface, and then a Cu film is sputtered as a metallization layer. For the specific method, refer to the existing patent (CN202410273802.3). The Cu-SnBi (1:100) composite brazing material, the SiC ceramic after metallization treatment and the Cu plate are assembled and placed in a brazing furnace for vacuum brazing. The welding temperature is 190°C, the heating rate is 10°C / min, and the heat preservation is 10 minutes. The microstructure of the brazed joint is shown as follows: Figure 3As shown in (a), the interface of the brazed joint is well bonded without obvious defects, achieving an effective low-temperature connection between SiC and Cu, with an average shear strength of 17 MPa.

[0025] Example 2

[0026] After Cu powder (average particle size 500nm) and Sn58Bi solder powder (500 mesh) were fully mixed at a mass ratio of 1:75, 2g was weighed and allowed to stand for 1min under a pressure of 5N, and then pressed into a solder sheet with a thickness of about 0.2mm. Its microscopic morphology is as follows: Figure 1 (c) As shown. The SiC after impurity removal is metallized by magnetron sputtering technology. First, a Cr film is sputtered on its surface, and then a Cu film is sputtered as a metallization layer. For the specific method, refer to the existing patent (CN202410273802.3). The Cu-SnBi (1:75) composite brazing material, the SiC ceramic after metallization treatment and the Cu plate are assembled and placed in a brazing furnace for vacuum brazing. The welding temperature is 180°C, the heating rate is 5°C / min, and the heat preservation is 20 minutes. The microstructure of the brazed joint is shown as follows: Figure 3 As shown in (b), the brazed joint interface is well bonded without obvious defects, the weld structure is refined, and the average shear strength is 20MPa.

[0027] Comparative Example 1

[0028] After Cu powder (average particle size 600nm) and Sn58Bi solder powder (500 mesh) were fully mixed at a mass ratio of 1:50, 2g was weighed and allowed to stand for 2min under a pressure of 5N, and then pressed into a solder sheet with a thickness of about 0.2mm. Its microscopic morphology is as follows: Figure 1 (d) As shown. The Cu-SnBi (1:50) composite brazing material, SiC ceramic and Cu plate were assembled and placed in a brazing furnace for vacuum brazing. The welding temperature was 190°C, the heating rate was 10°C / min, and the temperature was kept for 20 minutes. The microstructure of the brazed joint is shown in Figure 3 As shown in (c), the interface of the brazed joint is well bonded without obvious defects, but the weld structure is destroyed and the average shear strength is 12MPa.

[0029] Comparative Example 2

[0030] Weigh 1.5 g of pure Sn58Bi solder powder (500 mesh) and place it in a mold. Let it stand for 2 min under a pressure of 2N and press it into a solder sheet with a thickness of about 0.1 mm. Its microscopic morphology is as follows: Figure 1 (e) As shown. After assembling the pure Sn58Bi solder, SiC ceramic and Cu plate, they were placed in a brazing furnace for vacuum brazing. The welding temperature was 180°C, the heating rate was 5°C / min, and the temperature was kept for 5 minutes. The microstructure of the brazed joint is shown in Figure 3As shown in (d), micro cracks appeared in the joint weld and the average shear strength was 9.7MPa.

[0031] It can be seen from the above examples that the Cu-SnBi composite solder effectively avoids the brittleness of the SnBi solder and has excellent comprehensive mechanical properties.

[0032] Those skilled in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the present invention is limited to these examples; under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes in different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity. Any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A lead-free composite solder for low-temperature connection of large-sized ceramics and metals, characterized in that: The composite solder is obtained by mixing copper powder and tin-bismuth solder powder in a mass ratio of 1:75-100, pressing into tablets and standing still; wherein the tin content of the tin-bismuth solder powder is 42% and the bismuth content is 58%.

2. The lead-free composite solder for low-temperature connection of large-size ceramics and metals according to claim 1, characterized in that: The copper powder is spherical nano Cu powder particles with a particle size of 500-1000nm.

3. The lead-free composite solder for low-temperature connection of large-size ceramics and metals according to claim 1, characterized in that: The particle size of the tin-bismuth solder powder is 450-550 meshes.

4. The lead-free composite solder for low-temperature connection of large-size ceramics and metals according to claim 1, characterized in that: The tableting and standing method is to put the mixed powder into a mold, and let it stand for 1-3 minutes under a pressure of 2-5N by a tablet press to form a 0.2-0.5mm welding sheet.

5. A method for low temperature connection of ceramic and metal, characterized in that: The composite brazing material according to any one of claims 1 to 4 is used for vacuum brazing, and the method comprises the following steps: S1. Remove impurities from silicon carbide ceramics and copper plates; S2. Using magnetron sputtering technology to perform surface metallization treatment on the silicon carbide ceramic after impurities are removed; S3, assembling the metallized silicon carbide ceramic, the composite brazing material and the copper plate into a sandwich structure and then performing vacuum brazing.

6. The method for low temperature connection of ceramic and metal according to claim 5, characterized in that: The method for removing impurities from silicon carbide ceramics and copper plates in S1 is to remove the oxide layer and impurities on the surface of SiC and Cu plates by mechanical grinding, and then remove surface stains by ultrasonic cleaning.

7. The method for low temperature connection of ceramic and metal according to claim 5, characterized in that: The process parameters of the vacuum brazing are as follows: welding temperature: 180-190°C, heating speed: 5-10°C / min, holding time: 5-20min, vacuum degree: 3.5-5×10 -3 Pa.

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