Nanosilver film for electrical contact processing and its preparation method and application

Abstract

This invention discloses a nano-silver film for electrical contact processing, its preparation method, and its application. The preparation method of the nano-silver film includes the following steps: (1) Material preparation: Prepare a nano-silver wire solution, wherein the length of the nano-silver wire is 1-100 μm and the diameter is 10-250 nm; (2) Filtration: Transfer the nano-silver wire solution to a filtration device and perform filtration under a pressure of 0.4-0.8 MPa to obtain a silver film; (3) Shaping: Place the silver film in a reciprocating roller press and roll it, with a thickness of 0.02-0.5 mm; (4) Demolding: Place the silver film at 40-80℃ for 30 min to remove surface moisture, scrape off the silver film with a blade, transfer it to a dry and flat carrier, and dry it at 40-80℃ for 24 h to obtain the nano-silver film. The nano-silver film prepared by this method has a yield of over 90%, effectively reducing silver usage and efficiency, and lowering production costs.

Description

Technical Field

[0001] This invention relates to the field of electrical contact processing technology, and in particular to a nano-silver film for electrical contact processing, its preparation method, and its application. Background Technology

[0002] Currently, electrical contacts are the "heart" of electrical switches and instruments, responsible for switching current on and off. Their performance directly affects the performance of the switching devices. Electrical contacts must possess good electrical and thermal conductivity, resistance to arc burn-off, resistance to welding, and wear resistance. Materials such as AgSnO2, AgZnO, AgW, AgWC, AgWCC, and AgC are widely used in contact materials.

[0003] However, directly brazing the aforementioned contact materials to the contact bridge results in Ag in the contact material interdiffusion with elements in the contact bridge, and other materials accumulating at the weld interface, leading to numerous braze voids and low braze strength. Furthermore, materials such as SnO2, ZnO, and C are non-conductive, W begins to oxidize at 650℃, and AgW, AgWC, and AgWCC easily form Ag2WO4 or WO during the welding process. X All of these will increase contact resistance, reduce conductivity during actual operation, cause overheating failure, and drastically reduce the overall lifespan of the contact assembly.

[0004] Therefore, to obtain a reliable and high-quality brazed joint, an Ag layer needs to be laminated onto the bottom of the substrate beforehand. Existing contact materials with Ag layers are typically manufactured using methods such as hot pressing, melt infiltration, electrolysis, and electroplating.

[0005] For contact materials such as AgSnO2 and AgZnO, repeated hot pressing and other composite processes are generally required to complete the bonding with the silver layer. This places high demands on the molds, and the repeated bonding process requires a large amount of high-power equipment, making the operation complex and cumbersome, resulting in high production costs and low production efficiency. The silver layer produced by this composite method is typically 0.55-0.65mm thick, and the high cost and large quantity of raw materials contribute to the high product cost. Furthermore, the bonding strength between the Ag layer and the contact material in composite materials produced by existing methods is not strong, leading to frequent delamination of the Ag layer and contact material layers. Figure 1-2 As shown.

[0006] For example, AgW and AgWC type contact materials generally use the melt infiltration method to prepare the silver layer, but after melt infiltration, it is difficult to form a continuous silver layer on the surface of the silver-tungsten electrical contact, or even there is no silver layer at all.

[0007] However, regardless of the method used to prepare the silver layer, since the melting point of bulk silver is 962°C, high-temperature treatment is required, resulting in high energy consumption and high processing costs in the production line.

[0008] Therefore, there is an urgent need to develop an electrical contact with high bonding strength, low silver consumption, and low production cost, as well as its preparation method. Summary of the Invention

[0009] In order to overcome the shortcomings of the prior art, one of the objectives of the present invention is to provide a method for preparing a nano-silver film for electrical contact processing.

[0010] The second objective of this invention is to provide a method for preparing a nano-silver film for electrical contact processing as described above.

[0011] The third objective of this invention is to provide an application of nano-silver film in the processing of electrical contacts, specifically a method for preparing electrical contacts with high composite strength, low silver consumption, and low production cost.

[0012] The fourth objective of this invention is to provide an application of a nano-silver film in the processing of electrical contacts, specifically an electrical contact with high composite strength, low silver content, and low production cost prepared by the method described above.

[0013] One of the objectives of this invention is achieved by the following technical solution: a method for preparing a nano-silver film for electrical contact processing, comprising the following steps:

[0014] (1) Material preparation: Prepare a solution of silver nanowires, wherein the length of the silver nanowires is 1-100μm and the diameter is 10-250nm;

[0015] (2) Vacuum filtration: The solution of silver nanowires is transferred to a vacuum filtration device and vacuum filtered at a pressure of 0.4-0.8 MPa to obtain a silver film;

[0016] (3) Shaping: The silver film is rolled in a reciprocating roller press, and the thickness of the silver film is 0.02-0.5mm;

[0017] (4) Demolding: Place the silver film at 40-80℃ for 30 minutes to remove surface moisture, scrape off the silver film with a blade, transfer it to a dry and flat carrier, and dry it at 40-80℃ for 24 hours to obtain the nano silver film.

[0018] Optionally, in step (1), the concentration of the silver nanowire solution is 1 mM / L-1 M / L.

[0019] Optionally, in step (2), the filtration device is provided with a perforated mesh plate, which has through holes that are adapted to the shape and size of electrical contacts with different requirements. The material of the perforated mesh plate is one of stainless steel, glass, PP film, and PET film.

[0020] Optionally, in step (3), the rolling pressure of the reciprocating roller press is 10-15 kg, and the reciprocating roller press is equipped with a thickness gauge to determine whether the thickness of the silver film reaches the thickness required for the processing of the electrical contacts.

[0021] Optionally, in step (4), the carrier is one of PET film, PI film, and stainless steel plate.

[0022] The second objective of this invention is achieved by the following technical solution: a nano-silver film for electrical contact processing, which is prepared by the method described above for preparing a nano-silver film for electrical contact processing.

[0023] The third objective of this invention is achieved by the following technical solution: a method for preparing an electrical contact with high composite strength, comprising the following steps:

[0024] (a) Apply solder paste to the surface of the contact bridge, and place the nano-silver film and the contact material layer on the surface of the contact bridge with solder paste applied in sequence; the nano-silver film is selected from the nano-silver film prepared by the preparation method described above or the nano-silver film described above.

[0025] (b) By using induction welding or resistance welding, the contact material layer and the nano-silver film are bonded together in one welding process, and the nano-silver film is bonded together with the contact bridge, to obtain an electrical contact with high composite strength.

[0026] Optionally, in step (a), the contact material layer is selected from one of AgSnO2, AgZnO, AgW, AgWC, AgWCC, and AgC.

[0027] Optionally, in step (b), the conditions for induction welding are 0.8-1.2 kA for 3 seconds; and the conditions for resistance welding are 8.4-9.0 kA for 1 second.

[0028] The fourth objective of this invention is achieved by the following technical solution: an electrical contact, prepared by the method described above for preparing an electrical contact.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] (1) In view of the existing processing methods of composite Ag layer, this application uses silver nanowires to prepare silver film. The shape and size of Ag layer can be pre-designed by filtration so that it can be adapted to silver contact products with different sizes and shapes. The yield of silver nanofilm prepared by this method is as high as 90% or more.

[0031] (2) In the high composite strength electrical contact preparation process of this invention, by changing the forming method of the Ag layer, a uniform, thin, and continuously controllable silver layer is obtained, which improves the quality stability of the silver layer, increases the bonding strength between the Ag layer and the contact material, and reduces the amount of precious metal silver used, greatly reducing the production raw material cost and production energy cost, resulting in significant economic benefits. Specifically, the Ag layer is pre-prepared by filtration, and then the Ag layer composite process is transferred to the contact bridge with solder paste already applied. Using induction welding or resistance welding, the bonding between the contact material layer and the Ag layer and the Ag layer and the contact bridge is achieved in one welding operation, simplifying the composite process of each layer, which only requires one welding operation. In addition, the use of solder paste (a simple mixture of binder, flux, and powdered solder) to replace the existing sheet solder can reduce production costs.

[0032] Specifically, taking AgSnO2-based contact materials as an example, the melting point of silver blocks such as silver strips and sheets is 962℃. This technology uses a nano-silver film that can drive the diffusion and migration of silver atoms at temperatures far below the melting point of the silver block, achieving metallurgical bonding and densification between micron or nano-silver particles. This invention achieves sintering and densification of the silver film at welding temperatures, and it can firmly bond with the contact material layer and contact bridge, preventing the accumulation of non-silver contact materials in the brazing layer. The sintered silver film of this invention possesses physical properties similar to those of silver blocks, such as high thermal conductivity, high electrical conductivity, high mechanical strength, excellent resistance to thermal shock, and high creep temperature. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the structure of AgSnO2-type electrical contacts in the prior art;

[0034] Figure 2 Electron micrograph of the separation of AgSnO2 layer and silver layer in existing AgSnO2-based electrical contacts;

[0035] Figure 3 This is a schematic diagram of the structure of the filtration device and the perforated mesh plate in an embodiment of the present invention;

[0036] Figure 4 Electron micrograph of silver nanowires in preferred embodiment 1 of the present invention;

[0037] Figure 5 An electron microscope image of the rectangular electrical contact of the preferred embodiment 1 of the present invention;

[0038] Figure 6 Electron micrograph of silver nanowires in preferred embodiment 2 of the present invention;

[0039] Figure 7 An electron microscope image of the square-shaped electrical contact of the preferred embodiment 2 of the present invention;

[0040] Figure 8 Electron micrograph of silver nanowires in preferred embodiment 3 of the present invention;

[0041] Figure 9 An electron microscope image of the circular electrical contact of the preferred embodiment 3 of the present invention;

[0042] Figure 10 This is a schematic diagram of the structure of the AgSnO2 type electrical contact in Embodiment 4 of the present invention;

[0043] Figure 11 Ultrasonic images of resistance welding of the electrical contacts in Example 4;

[0044] Figure 12 Ultrasonic images of induction welding of the electrical contacts in Example 4;

[0045] Figure 13 Ultrasonic images of resistance welding of the electrical contacts in Example 5;

[0046] Figure 14 Ultrasonic images of induction welding of the electrical contacts in Example 5;

[0047] Figure 15 Ultrasonic images of resistance welding of the electrical contacts in Example 6;

[0048] Figure 16 Ultrasonic images of induction welding of the electrical contacts in Example 6;

[0049] Figure 17 Ultrasonic images of induction welding for comparative example 3 electrical contacts;

[0050] Figure 18 Ultrasonic images of induction welding for comparative example 3 electrical contacts;

[0051] Figure 19 Ultrasonic images of induction welding of electrical contacts for Comparative Example 4;

[0052] Figure 20 The image shows an ultrasonic image of induction welding of the electrical contacts in Comparative Example 4. Detailed Implementation

[0053] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0054] In this invention, unless otherwise specified, all parts and percentages are by weight, and the equipment and raw materials used are commercially available or commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0055] This invention provides a method for preparing a nano-silver film for electrical contact processing, comprising the following steps:

[0056] (1) Material preparation: Prepare a solution of silver nanowires, wherein the length of the silver nanowires is 1-100μm and the diameter is 10-250nm;

[0057] (2) Vacuum filtration: The solution of silver nanowires is transferred to a vacuum filtration device and vacuum filtered at a pressure of 0.4-0.8 MPa to obtain a silver film;

[0058] (3) Shaping: The silver film is placed in a reciprocating roller press for rolling. The rolling pressure of the reciprocating roller press is 10-15 kg. If the pressure is too high, it will be difficult to demold later. If the pressure is too low, the silver film will not be dense. The thickness of the silver film is 0.02-0.5 mm. If the thickness is too thin, the silver film is easy to melt and flow away during the welding process, losing the function of the silver layer. If the silver film is too thick, the cost is high.

[0059] (4) Demolding: Place the silver film at 40-80℃ for 30 minutes to remove surface moisture, scrape off the silver film with a blade, transfer it to a dry and flat carrier, and dry it at 40-80℃ for 24 hours to obtain the nano silver film. In this step, if the temperature is too high, the silver wires are prone to melting; if the temperature is too low, the drying efficiency of the silver film will be too low.

[0060] As a further embodiment, in step (1), the length of the silver nanowire is 3-55 μm and the diameter is 10-160 nm. The concentration of the silver nanowire solution is 1 mM / L-1 M / L. The silver nanowire solution refers to a solution with a concentration of 1 mM / L-1 M / L prepared by dissolving silver nanowires in ultrapure water or conventional reagents in the art as solvent media.

[0061] As a further implementation, in step (2), the filtration device is provided with a perforated mesh plate, the perforated mesh plate having through holes adapted to the shape and size of electrical contacts with different requirements, such as... Figure 3 As shown, the shapes include, but are not limited to, circles, squares, rectangles, and crosses. The perforated mesh is made of one of the following materials: stainless steel, glass, PP film, or PET film.

[0062] In contrast to existing methods for processing a single piece of Ag layer, this application utilizes a filtration method to pre-design the shape and size of the Ag layer, enabling it to adapt to silver contact products of different sizes and shapes. The resulting silver film yield is over 90%, reducing production costs. Furthermore, the independent silver film welding method improves the encapsulation and bonding strength of subsequent welding fixation, thereby enhancing the performance of the electrical contact products.

[0063] As a further implementation, in step (3), the rolling pressure of the reciprocating roller press is 10-15 kg, and the reciprocating roller press is equipped with multiple thickness gauges to determine whether the thickness of the silver film reaches the thickness required for the processing of the electrical contacts.

[0064] As a further embodiment, in step (4), the carrier is one of PET film, PI film, and stainless steel plate.

[0065] The present invention also provides a nano-silver film for electrical contact processing, which is prepared by the method described above for preparing a nano-silver film for electrical contact processing.

[0066] This invention also provides a method for preparing a high-strength composite electrical contact, comprising the following steps:

[0067] (a) Apply solder paste to the surface of the contact bridge, and place the nano-silver film and the contact material layer on the surface of the contact bridge with solder paste applied in sequence; the nano-silver film is selected from the nano-silver film prepared by the preparation method described above or the nano-silver film described above.

[0068] (b) By using induction welding or resistance welding, the contact material layer and the nano-silver film are bonded together in one welding process, and the nano-silver film is bonded together with the contact bridge, to obtain an electrical contact with high composite strength.

[0069] As a further embodiment, in step (a), the contact material layer is selected from one of AgSnO2, AgZnO, AgW, AgWC, AgWCC, and AgC.

[0070] As a further implementation, in step (b), the conditions for induction welding are 0.8-1.2 kA for 3 seconds; and the conditions for resistance welding are 8.4-9.0 kA for 1 second.

[0071] The present invention also provides an electrical contact, which is prepared by the method for preparing an electrical contact as described above.

[0072] This application modifies the Ag layer forming method, specifically by pre-fabricating the Ag layer using a vacuum filtration process. The Ag layer lamination process is then transferred to the contact bridge with pre-applied solder paste, where induction welding or resistance welding is used to achieve bonding between the contact material layer and the Ag layer, as well as between the Ag layer and the contact bridge, in a single welding operation. This simplifies the lamination process, requiring only one welding operation, resulting in a high degree of automation. Furthermore, using solder paste (a simple mixture of binder, flux, and powdered solder) instead of existing sheet solder reduces production costs.

[0073] Specifically, the melting point of silver blocks such as silver strips and sheets is 962℃. This technology uses a nano-silver film that can drive the diffusion and migration of silver atoms at temperatures far below the melting point of silver blocks, achieving metallurgical bonding and densification between micron or nano-silver particles. This invention achieves sintering and densification of the silver film at a welding temperature of 650-700℃, and it can firmly bond with the contact material layer and contact bridge, preventing the accumulation of non-silver contact materials in the brazing layer. The sintered silver film of this invention possesses physical properties similar to those of silver blocks, such as high thermal conductivity, high electrical conductivity, high mechanical strength, excellent resistance to thermal shock, and high creep temperature.

[0074] The following are specific embodiments of the present invention. Unless otherwise specified, the raw materials, equipment and other materials used in the following embodiments can be obtained by purchasing.

[0075] Example 1

[0076] A nano-silver film for electrical contact processing is prepared by the following method:

[0077] (1) Material Preparation: Prepare a solution of silver nanowires with a length of 5-15 μm and a diameter of 15-70 nm. Specifically, using glycerol as the solvent and reducing agent, add dispersant and directing agent PVP (PVP molecular weight K55, 6.2 g, dissolved in 0.38 L of glycerol), add silver source silver nitrate (3.16 g), and stir to dissolve. Add nucleating agent sodium chloride (0.117 g, dissolved in 0.02 L of glycerol), stir evenly, transfer to a hydrothermal reactor, react at 170 °C for 10 h, cool, centrifuge and wash to obtain silver nanowires with a length of 5-15 μm and a diameter of 15-70 nm. Electron micrographs are shown below. Figure 4 As shown. In this example, the silver nanowire solution is prepared by dissolving the silver nanowires in ultrapure water to a concentration of 5 mM / L.

[0078] (2) Filtration: The nano-silver wire solution is transferred to a filtration device and filtered under a pressure of 0.4 MPa to obtain a silver film; wherein, the perforated mesh plate inside the filtration device has a rectangular through hole shape and is a PP film.

[0079] (3) Shaping: The silver film is placed in a reciprocating roller press for rolling. The thickness of the silver film is 0.02mm. The rolling pressure of the reciprocating roller press is 10Kg. The reciprocating roller press is equipped with 4 thickness gauges to determine whether the thickness of the silver film reaches the thickness required for the processing of the electrical contacts.

[0080] (4) Demolding: Place the silver film at 40-80℃ for 30 minutes to remove surface moisture. Scrape off the silver film with a blade and transfer it to a dry and flat PET film carrier. Dry at 40-80℃ for 24 hours to obtain a rectangular nano-silver film, such as... Figure 5 As shown.

[0081] Example 2

[0082] A nano-silver film for electrical contact processing is prepared by the following method:

[0083] (1) Material Preparation: Prepare a solution of silver nanowires with a length of 10-15 μm and a diameter of 60-150 nm. Specifically, using ethylene glycol as a solvent, add a dispersant, a directing agent PVP (PVP molecular weight K50, 66.6 g, dissolved in 2 L of ethylene glycol), and a nucleating agent sodium chloride (22 mg, dissolved in 2 L of ethylene glycol). Stir well at room temperature and set aside. Then add silver source silver nitrate (34 g, dissolved in 2 L of ethylene glycol), stir well, and heat to 160 °C for 3 h. After cooling, centrifuge and wash, obtain silver nanowires with a length of 10-15 μm and a diameter of 60-150 nm. The electron microscope image is shown below. Figure 6 As shown. In this example, the silver nanowire solution is prepared by dissolving the silver nanowires in ultrapure water to a concentration of 0.05 M / L.

[0084] (2) Filtration: The nano-silver wire solution is transferred to a filtration device and filtered under a pressure of 0.6 MPa to obtain a silver film; wherein, the perforated mesh plate inside the filtration device has a square hole shape and is a PET film.

[0085] (3) Shaping: The silver film is placed in a reciprocating roller press for rolling, and the thickness of the silver film is 0.25mm. In step (3), the rolling pressure of the reciprocating roller press is 12.5kg. The reciprocating roller press is equipped with 4 thickness gauges to determine whether the thickness of the silver film reaches the thickness required for the processing of the electrical contacts.

[0086] (4) Demolding: Place the silver film at 40-80℃ for 30 minutes to remove surface moisture. Scrape off the silver film with a blade and transfer it to a dry and flat PI film carrier. Dry at 40-80℃ for 24 hours to obtain a square silver nanofilm. Figure 7 As shown.

[0087] Example 3

[0088] A nano-silver film for electrical contact processing is prepared by the following method:

[0089] (1) Material Preparation: Prepare a solution of silver nanowires with a length of 30-45 μm and a diameter of 50-100 nm. Specifically, using ethylene glycol as the solvent, add dispersant and directing agent PVP (PVP molecular weight K40, 34 g, dissolved in 1 L of ethylene glycol), and nucleating agent silver chloride (2.5 g, dissolved in 1 L of ethylene glycol). Stir evenly at room temperature and set aside. Finally, add silver source silver nitrate (11 g, dissolved in 1 L of ethylene glycol), stir evenly, heat to 160℃ and react for 3 h, cool down, centrifuge and wash to obtain silver nanowires with a length of 30-45 μm and a diameter of 50-100 nm. Electron micrographs are shown below. Figure 8As shown. In this example, the silver nanowire solution is prepared by dissolving the silver nanowires in ultrapure water to a concentration of 0.2 M / L.

[0090] (2) Filtration: The nano-silver wire solution is transferred to a filtration device and filtered under a pressure of 0.8 MPa to obtain a silver film; wherein, the perforated mesh plate inside the filtration device has circular holes and is made of glass.

[0091] (3) Shaping: The silver film is placed in a reciprocating roller press for rolling, and the thickness of the silver film is 0.5mm. In step (3), the rolling pressure of the reciprocating roller press is 15kg. The reciprocating roller press is equipped with 4 thickness gauges to determine whether the thickness of the silver film reaches the thickness required for the processing of the electrical contact.

[0092] (4) Demolding: Place the silver film at 40-80℃ for 30 minutes to remove surface moisture. Scrape off the silver film with a blade and transfer it to a dry and flat stainless steel plate carrier. Dry it at 40-80℃ for 24 hours to obtain a circular nano-silver film. Figure 9 As shown.

[0093] Example 4

[0094] A high-strength composite electrical contact is prepared by the following method:

[0095] (a) Apply solder paste to the surface of the contact bridge, and then sequentially place the nano-silver film and the contact material layer on the surface of the contact bridge with the applied solder paste; the nano-silver film is the nano-silver film prepared in Example 2; the contact material layer is selected from AgSnO2 (6.3*6.3*1.7mm). The solder paste uses Ag... 65 CuZn solder paste is used for soldering.

[0096] (b) Using induction welding or resistance welding, a single welding process is used to bond the contact material layer to the nano-silver film, and the nano-silver film to the contact bridge, resulting in an electrical contact with high composite strength. The induction welding conditions are 1.1 kA for 3 seconds, and the resistance welding conditions are 8.8 kA for 1 second.

[0097] Example 5

[0098] A high-strength composite electrical contact is prepared by the following method:

[0099] (a) Apply solder paste to the surface of the contact bridge, and then sequentially place the nano-silver film and the contact material layer on the surface of the contact bridge with the applied solder paste; the nano-silver film is the nano-silver film prepared in Example 1; the contact material layer is selected from AgZnO (6*5*2.0mm). The solder paste uses Ag... 45 CuZnSn solder paste is used for soldering.

[0100] (b) Using induction welding or resistance welding, a single welding process is used to bond the contact material layer to the nano-silver film, and to bond the nano-silver film to the contact bridge, resulting in an electrical contact with high composite strength. The induction welding conditions are 1 kA for 3 seconds, and the resistance welding conditions are 8.6 kA for 1 second.

[0101] Example 6

[0102] A high-strength composite electrical contact is prepared by the following method:

[0103] (a) Apply solder paste to the surface of the contact bridge, and then sequentially place the nano-silver film and the contact material layer on the surface of the contact bridge with the applied solder paste; the nano-silver film is the nano-silver film prepared in Example 3; the contact material layer is selected from AgSnO2 (Φ7.4*2.0mm). The solder paste uses Ag... 18 Soldering is performed using CuP solder paste.

[0104] (b) Using induction welding or resistance welding, a single welding process is used to bond the contact material layer to the nano-silver film, and the nano-silver film to the contact bridge, resulting in an electrical contact with high composite strength. The induction welding conditions are 0.95 kA for 3 seconds, and the resistance welding conditions are 8.4 kA for 1 second.

[0105] Comparative Example 1

[0106] A nanosilver film, the difference between the nanosilver film of Comparative Example 1 and the nanosilver film of Example 2 is that the length and diameter of the silver nanowires used are not within the scope of this invention. For example, short rod silver with a length of less than 1 μm and a diameter of more than 250 nm or spherical or near-spherical micron silver powder with a particle size of micron or nanon can be used. The other conditions of the nanosilver film are the same as those of Example 2.

[0107] Comparative Example 2

[0108] A nano-silver film is prepared by a blade coating method. The specific method is as follows: silver nanowires (under the same conditions as in Example 2) are centrifuged and concentrated to a solid content of 70-90%, and then blade coated. The thickness of the silver film is controlled by controlling the coating height. After the coating is completed, the film is demolded to obtain a whole nano-silver film, which is then cut to the desired shape. Other conditions are the same as in Example 2.

[0109] Comparative Example 3

[0110] An AgSnO2 / Ag-based electrical contact is manufactured as follows:

[0111] (1) Ag is pre-composite on AgSnO2 contact material: Silver tin oxide AgSnO2 contact material is hot-pressed and extruded with silver strip. The current hot-pressing temperature is 700-1300℃, and the extrusion speed is 0.1-2m / min. After cooling, the extrusion is repeated 2-5 times to form AgSnO2 contact material with an Ag layer. The thickness of the Ag layer is about 0.55-0.65mm.

[0112] (2) Cut the AgSnO2 contact material with Ag layer from step (1) into contact pieces with a shape of 6.3*6.3mm.

[0113] (3) Fabrication of AgSnO2 / Ag / solder composite layer: First, apply flux to the Ag layer of the contact piece in step (2), then press the solder piece onto the flux, and pass it through a tunnel furnace at 650-750℃ to form AgSnO2 / Ag / solder composite layer.

[0114] (4) Apply flux to the contact bridge to form a contact bridge with flux.

[0115] (5) Brazing process: The silver layer and the contact bridge are connected by using a solder sheet (solder sheet). Specifically, the AgSnO2 / Ag / solder composite layer obtained in step (3) is welded to the contact bridge obtained in step (4), so that the solder layer of the composite layer and the flux of the contact bridge are combined to obtain an AgSnO2 / Ag type electrical contact. The conditions for induction welding are 1.1KA, 3s, and the conditions for resistance welding are 8.8KA, 1s. The thickness of the solder sheet is 0.1-0.3mm.

[0116] Comparative Example 4

[0117] An AgW / Ag type electrical contact is manufactured as follows:

[0118] (1) Prepare AgW contact skeleton and Ag sheet separately. Place AgW contact skeleton and Ag sheet on graphite plate and put them into sintering furnace for melting and infiltration. The melting and infiltration temperature is 1000-1300℃. The silver sheet melts and infiltrates into the skeleton to form AgW contact material with Ag layer. The thickness of Ag layer is about 0.55-0.65mm.

[0119] (2) Cut the AgW contact material with Ag layer in step (1) into a contact material with a shape of Φ7.8*2.0mm.

[0120] (3) Making AgW / Ag / Solder metal composite layer: First, apply flux to the Ag layer of the contact piece in step (2), then press the solder piece onto the flux, and pass it through a tunnel furnace at 650-750℃ to form AgW / Ag / Solder metal composite layer.

[0121] (4) Apply flux to the contact bridge to form a contact bridge with flux.

[0122] (5) Brazing process: The silver layer and the contact bridge are connected by using a brazing filler metal, which is a sheet-shaped brazing filler metal (solder sheet). Specifically, the AgW / Ag / brazing filler metal composite layer obtained in step (3) is welded to the contact bridge obtained in step (4), so that the brazing filler metal layer of the composite layer and the flux of the contact bridge are combined to obtain AgW / Ag type electrical contacts. The conditions for induction welding are 1KA, 3s, and the conditions for resistance welding are 8.6KA, 1s. The thickness of the sheet-shaped brazing filler metal is 0.1-0.3mm.

[0123] Effect evaluation and performance testing

[0124] 1. The performance of the nano-silver film or electrical contact in each example and comparative example was tested. The test items and results are shown in Table 1-2.

[0125] Silver film yield refers to the ratio of the weight of qualified silver film to the weight of silver nanowires used.

[0126] The bonding rate within the industry is tested using the Hiwave S100 ultrasonic non-destructive testing equipment from Hewu Intelligent Manufacturing, and the results are recorded as a percentage.

[0127] Ultrasonic images of resistance welding and induction welding refer to photographs of the test results during the welding process in various examples.

[0128] Table 1. Yield of nano-silver films in Example 2 and Comparative Examples 1-2

[0129]

[0130]

[0131] The nano-silver membrane prepared by the present invention using the vacuum filtration method has a silver membrane yield of over 90%, which is both high and efficient.

[0132] Table 2 shows the bonding rates of the electrical contacts in Examples 4-6 and Comparative Examples 3-4.

[0133]

[0134] In Table 2, the higher the ultrasonic bonding rate, the stronger the bonding ability between the contact material layer and the nano-silver film, as well as the bonding ability between the nano-silver film and the contact bridge. The electrical contact prepared by the method of the present invention has high composite strength and can be widely used in the processing of various electrical contact products.

[0135] In summary, compared with existing processing methods, the electrical contact preparation method of the present invention eliminates the step of pre-fabricating the Ag layer, and the bonding of the contact material layer with the Ag layer and the Ag layer with the contact bridge can be achieved in one welding process. This simplifies the composite process of each layer, has a high degree of automation, avoids the use of a large number of high-power equipment, reduces production costs, improves the composite strength of the nano-silver film with the contact material and the contact bridge, and improves product quality.

[0136] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a nano-silver film for electrical contact processing, characterized in that, Includes the following steps: (1) Preparation of materials: Prepare a solution of silver nanowires, wherein the length of the silver nanowires is 1-100 μm and the diameter is 10-250 nm; (2) Filtration: The nano silver wire solution is transferred to a filtration device, which is equipped with a perforated mesh plate. The perforated mesh plate has through holes that are adapted to the shape and size of the electrical contacts for different needs. Filtration is carried out under a gas pressure of 0.4-0.8MPa to obtain a silver film that is adapted to the shape and size of the electrical contacts. (3) Shaping: The silver film is placed in a reciprocating roller press for rolling. The thickness of the silver film is 0.02-0.5mm. The rolling pressure of the reciprocating roller press is 10-15kg. The reciprocating roller press is equipped with a thickness gauge to determine whether the thickness of the silver film reaches the thickness required for the processing of the electrical contact. (4) Demolding: Place the silver film at 40-80℃ for 30 minutes to remove surface moisture, scrape off the silver film with a blade, transfer it to a dry and flat carrier, and dry it at 40-80℃ for 24 hours to obtain the nano silver film.

2. The method for preparing a nano-silver film for electrical contact processing as described in claim 1, characterized in that, In step (1), the concentration of the silver nanowire solution is 1 mM / L-1 M / L.

3. The method for preparing a nano-silver film for electrical contact processing as described in claim 1, characterized in that, In step (2), the perforated mesh plate is made of one of stainless steel, glass, PP film, or PET film.

4. The method for preparing a nano-silver film for electrical contact processing as described in claim 1, characterized in that, In step (4), the carrier is one of PET film, PI film, and stainless steel plate.

5. A nano-silver film for processing electrical contacts, characterized in that, It is prepared by the method for preparing a nano-silver film for electrical contact processing as described in any one of claims 1-4.

6. A method for preparing a high-strength composite electrical contact, characterized in that, Includes the following steps: (a) Apply solder paste to the surface of the contact bridge, and place the nano-silver film and the contact material layer on the surface of the contact bridge with solder paste applied in sequence; the nano-silver film is selected from the nano-silver film prepared by the preparation method described in any one of claims 1-4 or the nano-silver film described in claim 5; (b) By using induction welding or resistance welding, the contact material layer and the nano silver film are bonded together in one welding process, and the nano silver film is bonded together with the contact bridge, to obtain an electrical contact with high composite strength.

7. The method for preparing a high-strength composite electrical contact as described in claim 6, characterized in that, In step (a), the contact material layer is selected from one of AgSnO2, AgZnO, AgW, AgWC, AgWCC, and AgC.

8. The method for preparing a high-strength composite electrical contact as described in claim 6, characterized in that, In step (b), the conditions for induction welding are 0.8-1.2 kA for 3 seconds; the conditions for resistance welding are 8.4-9.0 kA for 1 second.

9. An electrical contact, characterized in that, It is prepared by the method of preparing electrical contacts as described in any one of claims 6-8.

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