Nano-silver film for electrical contact processing as well as preparation method and application of nano-silver film

Abstract

The invention discloses a nano-silver film for electrical contact processing and a preparation method and application, and relates to the field of electrical contact processing, the preparation method of the nano-silver film comprises the following steps: (1) material preparation: preparing a nano-silver wire solution, the wire length of a nano-silver wire is 1-100 [mu] m, and the wire diameter is 10-250 nm; (2) suction filtration: transferring the silver nanowire solution into a suction filtration device, and performing suction filtration under the air pressure of 0.4-0.8 MPa to obtain a silver film; (3) shaping is conducted, specifically, the silver film is placed in a reciprocating roller press to be rolled, and the thickness of the silver film ranges from 0.02 mm to 0.5 mm; and (4) demolding is conducted, specifically, the silver film is placed at the temperature of 40-80 DEG C for 30 min, surface moisture is removed, the silver film is scraped off through a blade, the silver film is transferred to a dry and flat carrier, the carrier is placed at the temperature of 40-80 DEG C to be dried for 24 h, and the nano-silver film is obtained. The yield of the nano-silver film prepared through the method reaches up to 90% or above, the silver consumption and efficiency are effectively reduced, and the production cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of electric contact processing, and in particular to a nano silver film for electric contact processing and a preparation method and application thereof. Background Art

[0002] At present, electrical contacts are the "heart" of electrical switches, instruments, etc., and are responsible for switching current. The quality of their performance directly affects the performance of switch electrical appliances. Electrical contacts must have good electrical and thermal conductivity, arc burn resistance, welding resistance, wear resistance, etc. AgSnO2, AgZnO, AgW, AgWC, AgWCC, AgC and other materials are widely used in contact materials.

[0003] However, when the above contact materials are directly brazed with the contact bridge, the Ag on the contact material will diffuse with the elements in the contact bridge, and other materials will be enriched at the weld interface, resulting in many brazing holes and low brazing strength. In addition, materials such as SnO2, ZnO, and C are not conductive, and W begins to oxidize at 650°C. AgW, AgWC, and AgWCC are prone to form Ag2WO4 or WO during the welding process. X , which will increase the contact resistance, reduce the conductivity during actual working conditions, cause heating failures, and sharply reduce the overall life of the contact assembly.

[0004] Therefore, in order to obtain a solder joint with high reliability and good quality, a Ag layer must be compounded on the bottom of the substrate in advance. Existing contact materials with Ag layers are usually made by hot pressing, infiltration, electrolysis, electroplating and other methods.

[0005] For contact materials such as AgSnO2 and AgZnO, repeated hot pressing and other composite processes are generally required to complete the composite with the silver layer. The mold requirements are high, and a large number of high-power equipment are required during the repeated composite process. The operation is complicated and cumbersome, resulting in high production costs and low production efficiency. The thickness of the silver layer produced by the composite method is generally 0.55-0.65mm, the cost of the raw materials is high, and the amount used is large, resulting in high product costs. In addition, the composite materials produced by the existing method have weak bonding strength between the Ag layer and the contact material, resulting in frequent delamination of the Ag layer and the contact material layer, such as Figure 1-2 shown.

[0006] For example, AgW and AgWC 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 no silver layer at all.

[0007] However, no matter which method is 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 of the production line and high processing costs.

[0008] Therefore, there is an urgent need to develop an electrical contact and a preparation method thereof with high bonding strength, small silver usage and low production cost. Summary of the invention

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

[0010] The second object of the present invention is to provide a nanosilver film made by the above-mentioned method for preparing the nanosilver film for electrical contact processing.

[0011] The third object of the present invention is to provide an application of a nano silver film in the processing of an electrical contact, specifically a method for preparing an electrical contact with high composite strength, small silver dosage and low production cost.

[0012] A fourth object of the present invention is to provide an application of a nano-silver film in the processing of electric contacts, specifically an electric contact prepared by the above-mentioned method for preparing an electric contact, which has high composite strength, small silver dosage and low production cost.

[0013] One of the purposes of the present invention is achieved by the following technical solution: A method for preparing a nano silver film for electrical contact processing comprises the following steps:

[0014] (1) preparing materials: preparing a silver nanowire solution, wherein the silver nanowire has a length of 1-100 μm and a diameter of 10-250 nm;

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

[0016] (3) Shaping: The silver film is placed on a reciprocating roller press to a thickness of 0.02-0.5 mm;

[0017] (4) Demolding: Place the silver film at 40-80°C 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°C for 24 hours to obtain a nanosilver film.

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

[0019] Optionally, in step (2), a perforated mesh plate is provided in the filtration device, the perforated mesh plate has through-hole shapes that are compatible with the shapes and sizes of electrical contacts required for different purposes, and 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 provided with a thickness gauge for determining whether the thickness of the silver film reaches the thickness required for electrical contact processing.

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

[0022] The second object of the present invention is achieved by adopting the following technical solution: a nano silver film for processing electric contacts is made by the preparation method of the nano silver film for processing electric contacts as described above.

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

[0024] (a) applying solder paste on the surface of the contact bridge, and placing a nano-silver film and a contact material layer in sequence on the surface of the contact bridge on which the solder paste has been applied; 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) Using induction welding or resistance welding, the contact material layer is welded with the nanosilver film, and the nanosilver film is welded with the contact bridge in one step, so as 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 induction welding condition is 0.8-1.2KA, 3s; the resistance welding condition is 8.4-9.0KA, 1s.

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

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) In view of the existing processing methods of composite Ag layers, the present application adopts nano silver wire to prepare silver film. The shape and size of the Ag layer can be pre-designed by filtration, so that it can adapt to silver contact products of different sizes and shapes. The yield rate of the nano silver film prepared by this method is as high as over 90%.

[0031] (2) In the preparation process of the electrical contact with high composite strength of the present invention, by changing the molding method of the Ag layer, a uniform, thin, continuous and controllable silver layer is obtained, the quality stability of the silver layer is improved, and the bonding strength between the Ag layer and the contact material is improved. At the same time, the amount of precious metal silver is reduced, and the production raw material cost and production energy cost are greatly reduced, with significant economic benefits. Specifically, the Ag layer is made in advance by suction filtration, and then the composite process of the Ag layer is transferred to the contact bridge on which the solder paste has been applied. Induction welding or resistance welding is used to weld in one time to achieve the bonding of the contact material layer with the Ag layer and the Ag layer with the contact bridge, simplifying the composite process of each layer, and only one welding is required. In addition, the use of solder paste (a simple mixture of binder + flux + powdered solder) to replace the existing sheet solder can reduce production costs.

[0032] Specifically, taking AgSnO2 contact materials as an example, the melting point of silver blocks such as silver strips and silver sheets is 962°C. The nanosilver film of this technology can drive the diffusion and migration of silver atoms at a temperature far below the melting point of the silver block, thereby achieving metallurgical connection and structural densification between micron or nano silver particles. The present invention realizes the sintering and densification of the silver film at the welding temperature, and can be firmly combined with the contact material layer and the contact bridge to avoid the enrichment of non-silver contact materials in the brazing layer. The silver film sintered body of the present invention has physical properties similar to those of silver blocks, such as high thermal conductivity, high electrical conductivity, high mechanical strength, excellent cold and hot shock resistance, and high creep temperature. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0034] Figure 2 This is an electron microscope image of the separation of the AgSnO2 layer and the silver layer in the existing AgSnO2 type electrical contact;

[0035] Figure 3 It is a schematic diagram of the structure of the filtration device and the mesh plate with holes in the embodiment of the present invention;

[0036] Figure 4 This is an electron microscope photograph of the silver nanowire of the preferred embodiment 1 of the present invention;

[0037] Figure 5 This is an electron microscope photograph of a rectangular electric contact according to a preferred embodiment 1 of the present invention;

[0038] Figure 6 This is an electron microscope photograph of the silver nanowire of the preferred embodiment 2 of the present invention;

[0039] Figure 7 This is an electron microscope photograph of the square-shaped electric contact of the preferred embodiment 2 of the present invention;

[0040] Figure 8 This is an electron microscope photograph of the silver nanowire of the preferred embodiment 3 of the present invention;

[0041] Fig. 9 This is an electron microscope photograph of the circular electric contact of the preferred embodiment 3 of the present invention;

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

[0043] Fig.11 This is a resistance welding ultrasonic image of the electric contact of Example 4;

[0044] Fig.12 This is an ultrasonic image of induction welding of the electric contact of Example 4;

[0045] Fig.13 This is a resistance welding ultrasonic image of the electric contact of Example 5;

[0046] Fig.14 This is an ultrasonic image of induction welding of the electric contact of Example 5;

[0047] Fig.15 This is a resistance welding ultrasonic image of the electric contact of Example 6;

[0048] Fig.16 This is an ultrasonic image of induction welding of the electric contact of Example 6;

[0049] Fig.17 This is an ultrasonic image of induction welding of the electric contact of Comparative Example 3;

[0050] Fig.18 This is an ultrasonic image of induction welding of the electric contact of Comparative Example 3;

[0051] Fig.19 This is an ultrasonic image of induction welding of the electric contact of Comparative Example 4;

[0052] Fig. 20 This is an ultrasonic picture of induction welding of the electric contact of Comparative Example 4. DETAILED DESCRIPTION

[0053] The present invention is further described below in conjunction with the accompanying drawings and specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form a new embodiment.

[0054] In the present invention, unless otherwise specified, all parts and percentages are by weight, and the equipment and raw materials used can be purchased from the market or are commonly used in the art. The methods in the following embodiments are all conventional methods in the art unless otherwise specified.

[0055] The present invention provides a method for preparing a nano silver film for electric contact processing, comprising the following steps:

[0056] (1) preparing materials: preparing a silver nanowire solution, wherein the silver nanowire has a length of 1-100 μm and a diameter of 10-250 nm;

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

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

[0059] (4) Demolding: Place the silver film at 40-80°C 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°C for 24 hours to obtain a nanosilver film. In this step, if the temperature is too high, the silver wire is easy to melt, and if the temperature is too low, the drying efficiency of the silver film is too low.

[0060] As a further embodiment, in step (1), the length of the nano silver wire is 3-55 μm, and the diameter is 10-160 nm. The concentration of the nano silver wire solution is 1 mM / L-1 M / L. The nano silver wire solution refers to a solution in which the nano silver wire is dissolved in ultrapure water or a conventional reagent in the art as a solvent medium to prepare a nano silver wire solution with a concentration of 1 mM / L-1 M / L.

[0061] As a further embodiment, in step (2), a mesh plate with holes is provided in the filtration device, and the mesh plate with holes is provided with through-hole shapes that are compatible with the shapes and sizes of the electrical contacts required for different requirements, such as Figure 3 As shown, including but not limited to round, square, rectangular, cross, etc. The material of the perforated mesh plate is one of stainless steel, glass, PP film, and PET film.

[0062] With respect to the existing whole-piece Ag layer processing method, the present application can pre-design the shape and size of the Ag layer through filtration, so that it can adapt to silver contact products of different sizes and shapes. The resulting silver film yield is as high as over 90%, reducing production costs. In addition, the independent silver film welding method can improve the subsequent welding fixation wrapping and bonding strength, thereby improving the performance of the electrical contact product.

[0063] As a further embodiment, in step (3), the rolling pressure of the reciprocating roller press is 10-15 kg, and the reciprocating roller press is provided with a plurality of thickness gauges for determining whether the thickness of the silver film reaches the thickness required for electrical contact processing.

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

[0065] The present invention also provides a nano silver film for electric contact processing, which is made by the above-mentioned preparation method of the nano silver film for electric contact processing.

[0066] The present invention also provides a method for preparing an electrical contact with high composite strength, comprising the following steps:

[0067] (a) applying solder paste on the surface of the contact bridge, and placing a nano-silver film and a contact material layer in sequence on the surface of the contact bridge on which the solder paste has been applied; 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) Using induction welding or resistance welding, the contact material layer is welded with the nanosilver film, and the nanosilver film is welded with the contact bridge in one step, so as 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 embodiment, in step (b), the induction welding condition is 0.8-1.2KA, 3s; the resistance welding condition is 8.4-9.0KA, 1s.

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

[0072] The present application changes the forming method of the Ag layer, specifically, pre-fabricates the Ag layer by suction filtration, and then transfers the composite process of the Ag layer to the contact bridge on which the solder paste has been applied, and uses induction welding or resistance welding to weld once to achieve the combination of the contact material layer and the Ag layer and the Ag layer and the contact bridge, thereby simplifying the composite process of each layer, requiring only one welding, and having a high degree of automation. In addition, the use of solder paste (a simple mixture of binder + flux + powdered solder) to replace the existing sheet solder can reduce production costs.

[0073] Specifically, the melting point of silver blocks such as silver ribbons and silver sheets is 962°C. The nanosilver film of this technology can drive the diffusion and migration of silver atoms at a temperature far below the melting point of the silver block, thereby achieving metallurgical connection and structural densification between micron or nano silver particles. The present invention achieves sintering densification of the silver film at a welding temperature of 650-700°C, and can be firmly combined with the contact material layer and the contact bridge to avoid the enrichment of non-silver contact materials in the brazing layer. The silver film sintered body of the present invention has physical properties similar to those of silver blocks, such as high thermal conductivity, high electrical conductivity, high mechanical strength, excellent cold and hot shock resistance, and high creep temperature.

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

[0075] Example 1

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

[0077] (1) Preparation: Prepare a nano silver wire solution, wherein the nano silver wire has a wire length of 5-15 μm and a wire diameter of 15-70 nm. Specifically, propylene glycol is used as a solvent and a reducing agent, and a dispersant and a directing agent PVP (PVP molecular weight K55, 6.2 g, dissolved in 0.38 L propylene glycol) are added, and a silver source silver nitrate (3.16 g) is added, and stirred to dissolve. A nucleating agent sodium chloride (0.117 g, dissolved in 0.02 L propylene glycol) is added, and the mixture is stirred evenly and then transferred to a hydrothermal reactor, and the reaction is carried out at 170°C. After 10 hours, the mixture is cooled, and centrifuged and washed to obtain nano silver wires with a wire length of 5-15 μm and a wire diameter of 15-70 nm. The electron microscope photograph thereof is shown below. Figure 4 In this example, the nanosilver wire solution uses ultrapure water as a medium to dissolve the nanosilver wires to prepare a nanosilver wire solution with a concentration of 5 mM / L.

[0078] (2) Filtration: The silver nanowire solution is transferred to a filtration device and filtered under a pressure of 0.4 MPa to obtain a silver film; wherein the mesh plate with holes provided in the filtration device has rectangular through holes and the mesh plate with holes is a PP film.

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

[0080] (4) Demolding: Place the silver film at 40-80°C for 30 minutes to remove surface moisture, scrape off the silver film with a blade, transfer it to a dry and flat PET film carrier, and dry it at 40-80°C for 24 hours to obtain a rectangular nanosilver film. Figure 5 shown.

[0081] Example 2

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

[0083] (1) Preparation: Prepare a nano silver wire solution, wherein the nano silver wire has a length of 10-15 μm and a diameter of 60-150 nm. Specifically, ethylene glycol is used as a solvent, and a dispersant, a directing agent PVP (PVP molecular weight K50, 66.6 g, dissolved in 2 L ethylene glycol), and a nucleating agent sodium chloride (22 mg, dissolved in 2 L ethylene glycol) are added, and stirred evenly at room temperature for use; then, a silver source silver nitrate (34 g, dissolved in 2 L ethylene glycol) is added, stirred evenly, and then heated to 160°C for reaction for 3 hours, cooled, and centrifuged to obtain nano silver wires with a length of 10-15 μm and a diameter of 60-150 nm. The electron microscope photo thereof is shown in the following figure. Figure 6 In this example, the nanosilver wire solution uses ultrapure water as a medium to dissolve the nanosilver wires to prepare a nanosilver wire solution with a concentration of 0.05M / L.

[0084] (2) Filtration: The silver nanowire solution is transferred to a filtration device and filtered under a pressure of 0.6 MPa to obtain a silver film; wherein the mesh plate with holes provided in the filtration device has square holes and the mesh plate with holes is a PET film.

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

[0086] (4) Demolding: Place the silver film at 40-80°C for 30 min to remove surface moisture, scrape off the silver film with a blade, transfer it to a dry and flat PI film carrier, and dry it at 40-80°C for 24 h to obtain a square nanosilver film. Figure 7 shown.

[0087] Example 3

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

[0089] (1) Material preparation: Prepare a nano silver wire solution, wherein the nano silver wire has a length of 30-45 μm and a diameter of 50-100 nm. Specifically, ethylene glycol is used as a solvent, and a dispersant and a directing agent PVP (PVP molecular weight K40, 34 g, dissolved in 1 L ethylene glycol) are added, and a nucleating agent silver chloride (2.5 g, dissolved in 1 L ethylene glycol) is added, and the mixture is stirred evenly at room temperature for later use. Finally, silver nitrate (11 g, dissolved in 1 L ethylene glycol) is added, and the mixture is stirred evenly and heated to 160°C for reaction for 3 h, cooled, and centrifuged to obtain nano silver wires with a length of 30-45 μm and a diameter of 50-100 nm. The electron microscope photograph thereof is shown below. Figure 8In this example, the nanosilver wire solution uses ultrapure water as a medium to dissolve the nanosilver wires to prepare a nanosilver wire solution with a concentration of 0.2M / L.

[0090] (2) Filtration: The silver nanowire solution is transferred to a filtration device and filtered under a pressure of 0.8 MPa to obtain a silver film; wherein the mesh plate with holes provided in the filtration device has circular holes and is a glass plate.

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

[0092] (4) Demolding: Place the silver film at 40-80°C for 30 min to remove surface moisture, scrape off the silver film with a blade, transfer it to a dry and flat stainless steel plate carrier, and dry it at 40-80°C for 24 h to obtain a circular nanosilver film. Fig. 9 shown.

[0093] Example 4

[0094] An electrical contact with high composite strength is prepared by the following method:

[0095] (a) Solder paste is applied to the surface of the contact bridge, and the nanosilver film and the contact material layer are placed in sequence on the surface of the contact bridge with solder paste applied; the nanosilver film is the nanosilver film prepared in Example 2; the contact material layer is selected from AgSnO2 (6.3*6.3*1.7mm). The solder paste is Ag 65 CuZn solder paste is used for soldering.

[0096] (b) Using induction welding or resistance welding, the contact material layer is welded with the nanosilver film, and the nanosilver film is welded with the contact bridge in one step, so as to obtain an electrical contact with high composite strength. The induction welding condition is 1.1KA, 3s, and the resistance welding condition is 8.8KA, 1s.

[0097] Example 5

[0098] An electrical contact with high composite strength is prepared by the following method:

[0099] (a) Solder paste is applied to the surface of the contact bridge, and the nanosilver film and the contact material layer are placed in sequence on the surface of the contact bridge with the solder paste applied; the nanosilver film is the nanosilver film prepared in Example 1; the contact material layer is selected from AgZnO (6*5*2.0mm). The solder paste is Ag 45 CuZnSn solder paste is used for soldering.

[0100] (b) Using induction welding or resistance welding, the contact material layer is welded with the nanosilver film, and the nanosilver film is welded with the contact bridge in one step, so as to obtain an electrical contact with high composite strength. The induction welding condition is 1KA, 3s, and the resistance welding condition is 8.6KA, 1s.

[0101] Example 6

[0102] An electrical contact with high composite strength is prepared by the following method:

[0103] (a) Solder paste is applied to the contact bridge surface, and a nano-silver film and a contact material layer are sequentially placed on the contact bridge surface on which the solder paste has been applied; 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 is Ag 18 CuP solder paste for soldering.

[0104] (b) Using induction welding or resistance welding, the contact material layer is welded with the nanosilver film, and the nanosilver film is welded with the contact bridge in one step, so as to obtain an electrical contact with high composite strength. The induction welding condition is 0.95KA, 3s, and the resistance welding condition is 8.4KA, 1s.

[0105] Comparative Example 1

[0106] A nanosilver film, the difference between the nanosilver film in comparative example 1 and the nanosilver film in example 2 is that the length and diameter of the silver nanowires used are not within the scope of the present invention, such as short silver rods with a length of less than 1 μm and a diameter greater than 250 nm or spherical or quasi-spherical micron silver powder with a particle size of micrometer or nanometer level, and the other conditions of the nanosilver film are the same as those in example 2.

[0107] Comparative Example 2

[0108] A nano silver film is prepared by scraping film forming. The specific method is as follows: the silver nanowires (the conditions of Example 2) are centrifuged and concentrated to a solid content of 70-90%, and then scraped, the thickness of the silver film is controlled by controlling the coating height, after scraping, demoulding, obtaining the entire nano silver film, cutting to obtain the desired shape of the nano silver film, and the other conditions refer to Example 2.

[0109] Comparative Example 3

[0110] An AgSnO2 / Ag type electrical contact, the manufacturing method of which is as follows:

[0111] (1) Ag is pre-compounded on the AgSnO2 contact material: the silver tin oxide AgSnO2 contact material is compounded with the silver ribbon by hot pressing and extrusion. The current hot pressing and extrusion temperature is 700-1300°C, the extrusion speed is 0.1-2m / min, and the extrusion is repeated 2-5 times after cooling to form the AgSnO2 contact material with the Ag layer. The thickness of the Ag layer is about 0.55-0.65mm.

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

[0113] (3) Making AgSnO2 / Ag / solder composite layer: First, apply flux on the Ag layer of the contact sheet in step (2), then press the solder sheet onto the flux, and pass it through a 650-750°C tunnel furnace to form an AgSnO2 / Ag / solder composite layer.

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

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

[0116] Comparative Example 4

[0117] An AgW / Ag type electrical contact, the manufacturing method of which is as follows:

[0118] (1) The AgW contact skeleton and the Ag sheet are separately prepared, and the AgW contact skeleton and the Ag sheet are placed on a graphite plate and placed in a sintering furnace for infiltration. The infiltration temperature is 1000-1300°C, and the silver sheet melts and infiltrates into the skeleton to form an AgW contact material with an Ag layer. The thickness of the Ag layer is about 0.55-0.65 mm.

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

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

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

[0122] (5) Soldering process: The silver layer and the contact bridge are connected by solder, and the solder is a sheet solder (welding sheet). Specifically, the AgW / Ag / solder composite layer obtained in step (3) is welded with the contact bridge obtained in step (4), so that the solder layer of the composite layer and the soldering flux of the contact bridge are combined with each other to obtain an AgW / Ag type electrical contact. The induction welding conditions are 1KA, 3s, and the resistance welding conditions are 8.6KA, 1s. The thickness of the sheet solder is 0.1-0.3mm.

[0123] Effect evaluation and performance testing

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

[0125] The silver film yield rate refers to the ratio of the weight of the qualified silver film to the weight of the nano silver wire input.

[0126] The brazing rate in the industry is tested using Hiwave S100 ultrasonic non-destructive testing equipment from Hewu Intelligent Manufacturing, and the results are recorded in %.

[0127] Resistance welding ultrasonic pictures and induction welding ultrasonic pictures refer to the test result photos of each example during the welding process.

[0128] Table 1 The yield of nano silver film in Example 2 and Comparative Example 1-2

[0129]

[0130]

[0131] The nano silver film prepared by the suction filtration method has a silver film yield rate of more than 90%, a high yield rate and high efficiency.

[0132] Table 2 Soldering rate of electric contacts of Examples 4-6 and Comparative Examples 3-4

[0133]

[0134] Among them, in Table 2, the higher the ultrasonic soldering rate, the stronger the bonding ability between the contact material layer and the nanosilver film and the bonding ability between the nanosilver film and the contact bridge. The electric contact prepared by the preparation method of the present invention has high composite strength and can be promoted and applied in the processing of various different electric contact products.

[0135] In summary, compared with the existing processing methods, the method for preparing the electric contact of the present invention eliminates the process of pre-making the Ag layer, and can realize the combination of the contact material layer and the Ag layer and the Ag layer and the contact bridge by one welding, thereby simplifying the composite process of each layer, having a high degree of automation, avoiding the use of a large number of high-power equipment, reducing production costs, improving the composite strength of the nanosilver film, the contact material, and the contact bridge, and improving product quality.

[0136] The above-mentioned embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and substitutions made by technicians in this field on the basis of the present invention shall fall within the scope of protection required by the present invention.

Claims

1. A method for preparing a nano silver film for electrical contact processing, characterized in that: The steps include: (1) preparing materials: preparing a silver nanowire solution, wherein the silver nanowire has a length of 1-100 μm and a diameter of 10-250 nm; (2) Filtration: The silver nanowire solution is transferred to a filtration device and filtered at a pressure of 0.4-0.8 MPa to obtain a silver film; (3) Shaping: The silver film is placed on a reciprocating roller press to a thickness of 0.02-0.5 mm; (4) Demolding: Place the silver film at 40-80°C 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°C for 24 hours to obtain a nanosilver film.

2. The method for preparing a nano silver film for electric contact processing according to claim 1, characterized in that: In step (1), the concentration of the nano silver wire solution is 1 mM / L-1 M / L.

3. The method for preparing a nano silver film for electric contact processing according to claim 1, characterized in that: In step (2), a perforated mesh plate is provided in the filtration device, the perforated mesh plate is provided with through-hole shapes that are compatible with the shapes and sizes of electrical contacts required for different purposes, and the material of the perforated mesh plate is one of stainless steel, glass, PP film, and PET film.

4. The method for preparing a nano silver film for electric contact processing according to claim 1, characterized in that: In step (3), the rolling pressure of the reciprocating roller press is 10-15 kg, and the reciprocating roller press is provided with a thickness gauge for determining whether the thickness of the silver film reaches the thickness required for electrical contact processing.

5. The method for preparing a nano silver film for electric contact processing according to claim 1, characterized in that: In step (4), the carrier is one of PET film, PI film and stainless steel plate.

6. A nano silver film for electrical contact processing, characterized in that: The nano silver film is made by the preparation method of the nano silver film for electric contact processing as described in any one of claims 1-5.

7. A method for preparing an electrical contact with high composite strength, characterized in that: The steps include: (a) applying solder paste on the surface of the contact bridge, and placing the nanosilver film and the contact material layer in sequence on the surface of the contact bridge on which the solder paste has been applied; the nanosilver film is selected from the nanosilver film prepared by the preparation method according to any one of claims 1 to 5 or the nanosilver film according to claim 6; (b) Using induction welding or resistance welding, the contact material layer is welded with the nanosilver film, and the nanosilver film is welded with the contact bridge in one step, so as to obtain an electrical contact with high composite strength.

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

9. The method for preparing an electrical contact with high composite strength as claimed in claim 7, characterized in that: In step (b), the induction welding condition is 0.8-1.2KA, 3s; the resistance welding condition is 8.4-9.0KA, 1s.

10. An electrical contact, characterized in that: The invention is prepared by the method for preparing an electric contact as described in any one of claims 7 to 9.

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