CN114654126B - Silver-coated copper soldering paste and preparation method thereof - Google Patents
Silver-coated copper soldering paste and preparation method thereof Download PDFInfo
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- CN114654126B CN114654126B CN202210466837.XA CN202210466837A CN114654126B CN 114654126 B CN114654126 B CN 114654126B CN 202210466837 A CN202210466837 A CN 202210466837A CN 114654126 B CN114654126 B CN 114654126B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
- B23K35/02—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
- B23K35/0222—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape for use in soldering, brazing
- B23K35/0244—Powders, particles or spheres; Preforms made therefrom
- B23K35/025—Pastes, creams, slurries
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
- B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
- B23K35/36—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest
- B23K35/362—Selection of compositions of fluxes
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Abstract
The invention discloses a silver-coated copper soldering paste and a preparation method thereof, wherein the silver-coated copper soldering paste comprises the following components: metal powder of silver-coated copper and flux; wherein the silver-coated copper metal powder is prepared by the following method: and (2) carrying out reduction reaction on copper powder and a copper ion source under the condition of a reducing agent, coating a copper layer on the surface of the copper powder, continuing carrying out reduction reaction on the copper powder and the silver ion source, and coating a silver layer on the surface of the copper layer to obtain the metal powder of the silver-coated copper. The invention provides a silver-coated copper soldering paste and a preparation method thereof.
Description
Technical Field
The invention belongs to the technical field of welding materials, and particularly relates to silver-coated copper soldering paste and a preparation method thereof.
Background
With the rapid development of electronic science and technology, electronic components are continuously developed to high power and miniaturization, and particularly in the field of packaging, the components need to be used under high temperature and high current, which also puts higher requirements on interconnection materials which are connected under low temperature environment and used under high temperature environment.
The micro-nano material can be sintered at a lower temperature due to the size effect, has higher reliability at a high temperature, and is expected to be. At present, nano silver paste is a more successful example of being used as a low-temperature interconnection and high-temperature service thermal interface material in the industrial field. However, silver is prone to electromigration and thermomigration during service, which causes great hidden danger to reliability of devices, and the price of silver is high, which is not beneficial to reducing the cost of devices. In this case, copper, which is a highly conductive and thermally conductive metal comparable to silver, is considered as a preferred material that can replace silver, and copper is not only low in cost but also has high migration resistance. However, copper is very susceptible to oxidation with oxygen in the air during storage and sintering. The nano Cu @ Ag prepared in the core-shell coating mode has the advantages of both the Cu @ Ag and the Ag @ Ag, and overcomes the defects that copper is easy to oxidize, silver ions migrate, silver is expensive and the like. Therefore, in recent years, there has been an increasing study on metal powder of silver-coated copper.
At present, two chemical methods are commonly used for preparing the metal powder of Cu @ Ag: one is a direct silver plating method and the other is an electroless plating method. The direct silver plating method is to directly use copper powder as a reducing agent to replace silver-ammonia coordination ions to obtain silver particles, and the silver particles are deposited on the surface of the copper powder. Although the process is simple and low in cost, a complete silver layer cannot be obtained on the surface of the copper core, and a large number of results show that the silver is coated on the surface of the copper powder in a dotted manner because Cu generated by reaction 2+ Is easy to form [ Cu (NH) by being matched with complexing agents such as ammonia and the like 3 ) 4 ] 2+ And copper to [ Cu (NH) 3 ) 4 ] 2+ Has strong adsorption effect, and prevents further replacement of copper. The most classical example of the electroless plating process is the silver mirror reaction, also known as the glucose bath process, by which a complete and uniform silver layer can be obtained, the thickness of the silver layer can be controlled, the preparation process is relatively simple, but the silver layer is not dense and has a large number of pores.
Disclosure of Invention
Based on the technical problem, the invention provides the silver-coated copper soldering paste and the preparation method thereof, the soldering paste comprises the metal powder of the silver-coated copper, and the metal powder of the silver-coated copper obtains a compact and complete coated silver layer on the surface of micron-sized copper powder, so that the copper powder is effectively prevented from being oxidized, and the aim of low-temperature connection and high-temperature service is fulfilled.
The invention provides a silver-coated copper soldering paste, which comprises: metal powder of silver-coated copper and flux;
wherein the silver-coated copper metal powder is prepared by the following method:
and (2) carrying out reduction reaction on copper powder and a copper ion source under the condition of a reducing agent, coating a copper layer on the surface of the copper powder, continuing carrying out reduction reaction on the copper powder and the silver ion source, and coating a silver layer on the surface of the copper layer to obtain the metal powder of the silver-coated copper.
The soldering paste comprises the silver-coated copper metal powder, a copper particle layer is firstly deposited on the surface of micron-sized copper powder by the silver-coated copper metal powder through two coating processes, and gaps exist in the copper particle layer, so that a large specific surface area can be increased for the growth of a subsequent silver particle layer, the copper particle layer is tightly combined with the subsequent silver particle layer, and the subsequent formation of a compact silver-coated layer is facilitated; compared with the prior art that the silver layer is only coated on the surface of the micron-sized copper powder, the copper particle layer is firstly deposited on the surface of the micron-sized copper powder, which is equivalent to forming a thin diffusion layer between the copper core and the silver particle layer, so that the bonding strength between the silver layer and the copper core is effectively improved, the oxidation resistance of the obtained metal powder is greatly improved, and the obtained soldering paste not only has good melting property and wettability, but also can effectively inhibit silver migration.
Preferably, the copper powder is acid-washed copper powder;
preferably, the particle size of the copper powder is 0.1-2 μm.
Preferably, the "performing a reduction reaction on copper powder and a copper ion source under the condition of a reducing agent" specifically comprises the following steps: dispersing copper powder, a copper ion source and a dispersing agent in a reaction solvent to obtain a copper dispersion liquid, dispersing a reducing agent in the reaction solvent to obtain a reducing agent solution, and mixing the copper dispersion liquid and the reducing agent solution for a reduction reaction to obtain a copper-clad layer solution;
preferably, the copper ion source is at least one of copper nitrate, copper sulfate or copper chloride, the dispersant is at least one of polyvinylpyrrolidone or gelatin, the reducing agent is at least one of sodium borohydride, ferrous sulfate or chromite chloride, and the reaction solvent is at least one of water, ethylene glycol, methanol or ethanol;
preferably, the molar ratio of the copper powder to the copper ion source is 10-100, and the mass ratio of the copper powder to the dispersing agent is 10-30.
In the invention, the molar ratio of the copper powder to the copper ion source is 10-100, and if the molar ratio of the copper powder to the copper ion source is more than 100, the deposition amount of a copper particle layer on the surface of the copper powder after the reduction reaction is too small, and the copper particle layer cannot be combined with a subsequent silver particle layer; if the molar ratio of the copper powder to the copper ion source is less than 10, the deposition amount of a copper particle layer on the surface of the copper powder after the reduction reaction is too large, which is not beneficial to improving a large specific surface area for the growth of a subsequent silver particle layer.
Preferably, the "continuing the reduction reaction with the silver ion source" specifically includes: dispersing a silver ion source and a dispersing agent in a reaction solvent to obtain a silver dispersion solution, and mixing the silver dispersion solution and the copper layer coating solution for reduction reaction to obtain metal powder of silver-coated copper;
preferably, the source of silver ions is at least one of silver nitrate or silver chloride;
preferably, the molar ratio of the copper powder to the silver ion source is 1-10.
Preferably, the thickness of the silver clad layer in the metal powder of silver clad copper is 0.05 to 0.5 μm.
Preferably, the solder paste comprises, in mass percent: 80-90% of metal powder of silver coated copper and 10-20% of soldering flux.
Preferably, the flux paste includes: active agents, film formers, thixotropic agents, surfactants, and solvents;
preferably, the flux paste comprises, by mass percent: 10-20% of active agent, 20-40% of film forming agent, 1-5% of thixotropic agent, 1-3% of surfactant and the balance of solvent.
Preferably, the active agent is at least one of butyric acid, lauric acid, stearic acid, phthalic acid or adipic acid;
the film-forming agent is at least one of gum rosin, hydrogenated rosin, polymerized rosin or esterified rosin;
the thixotropic agent is at least one of castor oil, fatty acid amide or polyethylene glycol;
the surfactant is at least one of octylphenol polyoxyethylene ether or polyvinylpyrrolidone;
the solvent is at least one of isopropanol, ethylene glycol butyl ether or ethylene glycol hexyl ether.
The invention provides a preparation method of silver-coated copper soldering paste, which comprises the following steps: and mixing the soldering flux with the metal powder of the silver-coated copper to obtain the soldering paste.
The invention also provides application of the silver-coated copper soldering paste in electronic packaging.
Compared with the prior art, the invention has the following beneficial effects:
(1) According to the invention, a copper particle layer is chemically deposited on the surface of the copper powder through a chemical plating method, and then a silver particle layer is deposited, and the copper particle layer and the silver particle layer are in good contact and combination, so that the metal powder with a Cu @ Ag core-shell structure is formed. The silver layer film which is composed of silver particles with uniform size and uniform distribution and has no holes on the surface and high compactness effectively improves the oxidation resistance of the copper powder.
(2) In the invention, the particle size of the metal powder is selected to be submicron scale, thereby not only ensuring good oxidation resistance and dispersibility, but also solving the problem of shrinkage cracks of the pure nano soldering paste in the sintering process. Meanwhile, the silver layer film on the surface of the metal powder is of a nano structure, so that sintering at a lower temperature is realized.
(3) The soldering paste has the advantages of high melting point, high welding strength and good heat dissipation after sintering, so that low-temperature sintering in the air can be realized, good electric conduction, heat dissipation and high temperature resistance can be realized, the soldering paste can be used for connecting and packaging high-power electronic devices, and the soldering paste is simple in experimental operation and low in cost.
Drawings
FIG. 1 is a TEM image of silver-coated copper as described in example 1.
Detailed Description
The present invention will be described in detail with reference to specific examples, but these examples should be explicitly mentioned for illustration, but should not be construed as limiting the scope of the present invention.
Example 1
The invention provides a silver-coated copper soldering paste which is prepared by the following method:
preparation of metal powder of silver-coated copper: adding copper powder with the particle size of 0.8 mu m into acetone, ultrasonically removing organic matters on the surface, cleaning with deionized water, adding into dilute sulfuric acid (5 wt%) for acid cleaning, removing copper oxide and cuprous oxide on the surface, centrifuging, washing, and drying to obtain pure copper powder;
adding 0.1mol of copper powder and 0.002mol of copper sulfate into 1000mL of deionized water, adding 0.5g of polyvinylpyrrolidone, performing ultrasonic dispersion uniformly to obtain a copper dispersion solution, adding 0.03mol of chromite (newly prepared) into 100mL of deionized water, adjusting the pH value to 1 by using hydrochloric acid to obtain a reducing agent solution, slowly dripping the reducing agent solution into the copper dispersion solution under stirring, and stirring until the reaction is complete to obtain a copper layer coating solution;
adding 0.02mol of silver nitrate into 1000mL of deionized water, adjusting the pH value to 1 by using hydrochloric acid, adding 0.2g of polyvinylpyrrolidone, uniformly stirring to obtain a silver dispersion solution, adding the silver dispersion solution into the copper layer coating solution under stirring, stirring until the reaction is complete, standing the obtained solution, filtering, washing with water, and drying to obtain the metal powder of the silver coated copper;
after the silver-coated copper metal powder is diluted, the morphology of the silver-coated copper particles is observed by using a TEM (transmission electron microscope), and the result is shown in figure 1;
preparing the soldering flux: mixing 7% of stearic acid, 8% of adipic acid, 30% of hydrogenated rosin, 3% of castor oil, 2% of polyvinylpyrrolidone, 20% of isopropanol and 30% of ethylene glycol monobutyl ether according to the mass percentage, and uniformly stirring to obtain the soldering flux;
preparing silver-coated copper soldering paste: and mixing 85% of the metal powder of the silver-coated copper and 15% of the soldering flux according to the mass percentage, and uniformly stirring to obtain the silver-coated copper soldering paste.
The silver-coated copper soldering paste is coated on the lapping surfaces of two copper metal sheets, the length and the width of each metal sheet are 50mm, the thickness of each metal sheet is 2mm, the length of each lapping surface is 10mm, the coating thickness of the soldering paste is 50 micrometers, and the connecting joint with good connectivity is obtained by hot-pressing and sintering the two copper metal sheets at 200 ℃ and under 5MPa for 30 min. The shear strength of the resulting joint was measured by a universal testing machine, and it was found that the shear strength of the resulting joint was 31.6MPa.
The detection result shows that when the silver-coated copper soldering paste is used for soldering a substrate, the connection between the soldering paste and the substrate is good, the whole soldering point has no defects such as any hole and the like, and when the silver-coated copper soldering paste is used for packaging a device, the mechanical strength and the reliability are good.
Example 2
The invention provides a silver-coated copper soldering paste which is prepared by the following method:
preparation of metal powder of silver-coated copper: adding copper powder with the particle size of 0.8 mu m into acetone, ultrasonically removing organic matters on the surface, cleaning with deionized water, adding into dilute sulfuric acid (5 wt%) for acid cleaning, removing copper oxide and cuprous oxide on the surface, centrifuging, washing, and drying to obtain pure copper powder;
adding 0.1mol of copper powder and 0.01mol of copper sulfate into 1000mL of deionized water, adding 0.5g of polyvinylpyrrolidone, performing ultrasonic dispersion uniformly to obtain a copper dispersion solution, adding 0.03mol of chromite (newly prepared) into 100mL of deionized water, adjusting the pH to 1 with hydrochloric acid to obtain a reducing agent solution, slowly dropwise adding the reducing agent solution into the copper dispersion solution under stirring, and stirring until the reaction is complete to obtain a copper layer coating solution;
adding 0.01mol of silver nitrate into 1000mL of deionized water, adjusting the pH value to 1 by using hydrochloric acid, adding 0.1g of polyvinylpyrrolidone, uniformly stirring to obtain a silver dispersion solution, adding the silver dispersion solution into the copper layer coating solution under stirring, stirring until the reaction is complete, standing the obtained solution, filtering, washing, and drying to obtain the metal powder of the silver coated copper;
preparing the soldering flux: mixing 7% of stearic acid, 8% of adipic acid, 30% of hydrogenated rosin, 3% of castor oil, 2% of polyvinylpyrrolidone, 20% of isopropanol and 30% of ethylene glycol monobutyl ether according to the mass percentage, and uniformly stirring to obtain the soldering flux;
preparing silver-coated copper soldering paste: and mixing 85% of the metal powder of the silver-coated copper and 15% of the soldering flux according to the mass percentage, and uniformly stirring to obtain the silver-coated copper soldering paste.
The silver-coated copper soldering paste is coated on the lapping surfaces of two copper metal sheets, the length and the width of each metal sheet are 50mm, the thickness of each metal sheet is 2mm, the length of each lapping surface is 10mm, the coating thickness of the soldering paste is 50 micrometers, and the connecting joint with good connectivity is obtained by hot-pressing and sintering the two copper metal sheets at 200 ℃ and under 5MPa for 30 min. The shear strength of the resulting joint was measured by a universal testing machine, and it was found that the shear strength of the resulting joint was 28.3MPa.
The detection result shows that when the silver-coated copper soldering paste is used for soldering a substrate, the connection between the soldering paste and the substrate is good, the whole soldering point has no defects such as any hole and the like, and when the silver-coated copper soldering paste is used for packaging a device, the mechanical strength and the reliability are good.
Example 3
The invention provides a silver-coated copper soldering paste which is prepared by the following method:
preparation of metal powder of silver-coated copper: adding copper powder with the particle size of 0.8 mu m into acetone, ultrasonically removing organic matters on the surface, cleaning with deionized water, adding into dilute sulfuric acid (5 wt%) for acid cleaning, removing copper oxide and cuprous oxide on the surface, centrifuging, washing, and drying to obtain pure copper powder;
adding 0.1mol of copper powder and 0.001mol of copper sulfate into 1000mL of deionized water, adding 0.5g of polyvinylpyrrolidone, performing ultrasonic dispersion uniformly to obtain a copper dispersion solution, adding 0.12mol of chromite (newly prepared) into 100mL of deionized water, adjusting the pH to 1 with hydrochloric acid to obtain a reducing agent solution, slowly dropwise adding the reducing agent solution into the copper dispersion solution under stirring, and stirring until the reaction is complete to obtain a copper layer coating solution;
adding 0.1mol of silver nitrate into 1000mL of deionized water, adjusting the pH value to 1 by using hydrochloric acid, adding 1g of polyvinylpyrrolidone, uniformly stirring to obtain a silver dispersion solution, adding the silver dispersion solution into the copper layer coating solution under stirring, stirring until the reaction is complete, standing the obtained solution, filtering, washing with water, and drying to obtain the metal powder of the silver coated copper;
preparing the soldering flux: mixing 7% of stearic acid, 8% of adipic acid, 30% of hydrogenated rosin, 3% of castor oil, 2% of polyvinylpyrrolidone, 20% of isopropanol and 30% of ethylene glycol monobutyl ether according to the mass percentage, and uniformly stirring to obtain the soldering flux;
preparing silver-coated copper soldering paste: and mixing 85% of the metal powder of the silver-coated copper and 15% of the soldering flux according to the mass percentage, and uniformly stirring to obtain the silver-coated copper soldering paste.
The silver-coated copper soldering paste is coated on the lapping surfaces of two copper metal sheets, the length and the width of each metal sheet are 50mm, the thickness of each metal sheet is 2mm, the length of each lapping surface is 10mm, the coating thickness of the soldering paste is 50 micrometers, and the connecting joint with good connectivity is obtained by hot-pressing and sintering the two copper metal sheets at 200 ℃ and under 5MPa for 30 min. The shear strength of the resulting joint was measured by a universal testing machine, and it was found that the shear strength of the resulting joint was 26.7MPa.
The detection result shows that when the silver-coated copper soldering paste is used for soldering a substrate, the connection between the soldering paste and the substrate is good, the whole soldering point has no defects such as any hole and the like, and when the silver-coated copper soldering paste is used for packaging a device, the mechanical strength and the reliability are good.
Example 4
The invention provides a silver-coated copper soldering paste which is prepared by the following method:
preparation of metal powder of silver-coated copper: adding copper powder with the particle size of 0.8 mu m into acetone, ultrasonically removing organic matters on the surface, cleaning with deionized water, adding into dilute sulfuric acid (5 wt%) for acid cleaning, removing copper oxide and cuprous oxide on the surface, centrifuging, washing, and drying to obtain pure copper powder;
adding 0.1mol of copper powder and 0.002mol of copper sulfate into 1000mL of deionized water, adding 0.5g of polyvinylpyrrolidone, performing ultrasonic dispersion uniformly to obtain a copper dispersion solution, adding 0.03mol of chromite (newly prepared) into 100mL of deionized water, adjusting the pH value to 1 by using hydrochloric acid to obtain a reducing agent solution, slowly dropwise adding the reducing agent solution into the copper dispersion solution under stirring, and stirring until the reaction is complete to obtain a copper layer coating solution;
adding 0.02mol of silver nitrate into 1000mL of deionized water, adjusting the pH value to 1 by using hydrochloric acid, adding 0.2g of polyvinylpyrrolidone, uniformly stirring to obtain a silver dispersion solution, adding the silver dispersion solution into the copper layer coating solution under stirring, stirring until the reaction is complete, standing the obtained solution, filtering, washing with water, and drying to obtain the metal powder of the silver coated copper;
preparing the soldering flux: mixing 5% of lauric acid, 10% of adipic acid, 30% of hydrogenated rosin, 3% of fatty acid amide, 2% of octyl phenol polyoxyethylene ether, 30% of isopropanol and 20% of glycol hexyl ether according to the mass percentage, and uniformly stirring to obtain the soldering flux;
preparing silver-coated copper soldering paste: and mixing 85% of the metal powder of the silver-coated copper and 15% of the soldering flux according to the mass percentage, and uniformly stirring to obtain the silver-coated copper soldering paste.
The silver-coated copper soldering paste is coated on the lapping surfaces of two copper metal sheets, the length and the width of each metal sheet are 50mm, the thickness of each metal sheet is 2mm, the length of each lapping surface is 10mm, the coating thickness of the soldering paste is 50 micrometers, and the connecting joint with good connectivity is obtained by hot-pressing and sintering the two copper metal sheets at 200 ℃ and under 5MPa for 30 min. The joint was subjected to a shear strength test using a universal tester, and it was found that the joint had a shear strength of 30.8MPa.
The detection result shows that when the silver-coated copper soldering paste is used for soldering a substrate, the connection between the soldering paste and the substrate is good, the whole soldering point has no defects such as any hole and the like, and when the silver-coated copper soldering paste is used for packaging a device, the mechanical strength and the reliability are good.
Comparative example 1
The invention provides a silver-coated copper soldering paste which is prepared by the following method:
preparation of metal powder of silver-coated copper: adding copper powder with the particle size of 0.8 mu m into acetone, ultrasonically removing organic matters on the surface, cleaning with deionized water, adding into dilute sulfuric acid (5 wt%) for acid cleaning, removing copper oxide and cuprous oxide on the surface, centrifuging, washing, and drying to obtain pure copper powder;
adding 0.1mol of copper powder into 1000mL of deionized water, adding 0.5g of polyvinylpyrrolidone, performing ultrasonic dispersion uniformly to obtain a copper dispersion solution, adding 0.03mol of chromite chloride (newly prepared) into 100mL of deionized water, adjusting the pH value to 1 by using hydrochloric acid to obtain a reducing agent solution, adding 0.022mol of silver nitrate into 1000mL of deionized water, adjusting the pH value to 1 by using hydrochloric acid, adding 0.2g of polyvinylpyrrolidone, and stirring uniformly to obtain a silver dispersion solution; slowly dripping a reducing agent solution into the copper dispersion liquid under stirring, then adding the silver dispersion liquid, stirring until the reaction is complete, standing the obtained solution, filtering, washing with water, and drying to obtain the metal powder of the silver-coated copper;
preparing the soldering flux: mixing 7% of stearic acid, 8% of adipic acid, 30% of hydrogenated rosin, 3% of castor oil, 2% of polyvinylpyrrolidone, 20% of isopropanol and 30% of ethylene glycol monobutyl ether according to the mass percentage, and uniformly stirring to obtain the soldering flux;
preparing silver-coated copper soldering paste: and mixing 85% of the metal powder of the silver-coated copper and 15% of the soldering flux according to the mass percentage, and uniformly stirring to obtain the silver-coated copper soldering paste.
Coating the silver-coated copper soldering paste on the lapping surfaces of two copper metal sheets, wherein the length and the width of the metal sheets are 50mm, the thickness of the metal sheets is 2mm, the length of the lapping surfaces is 10mm, the coating thickness of the soldering paste is 50 mu m, and hot-pressing sintering is carried out for 30min at 200 ℃ and 5MPa to obtain the connecting joint with good connectivity. The obtained joint was subjected to a shear strength test using a universal testing machine, and it was found that the shear strength of the obtained joint was 16.3MPa.
The above test results show that, when the silver-coated copper soldering paste of the present comparative example is used for soldering a substrate, the prepared soldering paste has poor oxidation resistance because the silver-coated layer of the metal powder of the silver-coated copper is not compact enough, and the joint obtained by sintering in air has low shear strength.
Comparative example 2
The invention provides a silver-coated copper soldering paste which is prepared by the following method:
preparation of metal powder of silver-coated copper: adding copper powder with the particle size of 0.8 mu m into acetone, ultrasonically removing organic matters on the surface, cleaning with deionized water, adding into dilute sulfuric acid (5 wt%) for acid cleaning, removing copper oxide and cuprous oxide on the surface, centrifuging, washing, and drying to obtain pure copper powder;
adding 0.1mol of copper powder and 0.02mol of copper sulfate into 1000mL of deionized water, adding 0.5g of polyvinylpyrrolidone, performing ultrasonic dispersion uniformly to obtain a copper dispersion solution, adding 0.05mol of chromite (newly prepared) into 100mL of deionized water, adjusting the pH to 1 by using hydrochloric acid to obtain a reducing agent solution, slowly dropwise adding the reducing agent solution into the copper dispersion solution under stirring, and stirring until the reaction is complete to obtain a copper layer coating solution;
adding 0.02mol of silver nitrate into 1000mL of deionized water, adjusting the pH value to 1 by using hydrochloric acid, adding 0.2g of polyvinylpyrrolidone, uniformly stirring to obtain a silver dispersion solution, adding the silver dispersion solution into the copper layer coating solution under stirring, stirring until the reaction is complete, standing the obtained solution, filtering, washing with water, and drying to obtain the metal powder of the silver coated copper;
preparing the soldering flux: mixing 7% of stearic acid, 8% of adipic acid, 30% of hydrogenated rosin, 3% of castor oil, 2% of polyvinylpyrrolidone, 20% of isopropanol and 30% of ethylene glycol monobutyl ether according to the mass percentage, and uniformly stirring to obtain the soldering flux;
preparing silver-coated copper soldering paste: and mixing 85% of the metal powder of the silver-coated copper and 15% of the soldering flux according to the mass percentage, and uniformly stirring to obtain the silver-coated copper soldering paste.
Coating the silver-coated copper soldering paste on the lapping surfaces of two copper metal sheets, wherein the length and the width of the metal sheets are 50mm, the thickness of the metal sheets is 2mm, the length of the lapping surfaces is 10mm, the coating thickness of the soldering paste is 50 mu m, and hot-pressing sintering is carried out for 30min at 200 ℃ and 5MPa to obtain the connecting joint with good connectivity. The obtained joint was subjected to a shear strength test using a universal testing machine, and it was found that the shear strength of the obtained joint was 20.9MPa.
The above test results show that, when the silver-coated copper soldering paste of the present comparative example is used for soldering a substrate, the silver-coated layer of the metal powder of the silver-coated copper is not compact enough, the prepared soldering paste has poor oxidation resistance, and the joint obtained by sintering in air has low shear strength.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.
Claims (10)
1. A silver-coated copper solder paste, comprising: metal powder of silver-coated copper and flux;
wherein the silver-coated copper metal powder is prepared by the following method:
carrying out reduction reaction on copper powder and a copper ion source under the condition of a reducing agent, coating a copper layer on the surface of the copper powder, continuing carrying out reduction reaction on the copper powder and the silver ion source, and coating a silver layer on the surface of the copper layer to obtain metal powder of the silver-coated copper;
specifically, copper powder, a copper ion source and a dispersing agent are dispersed in a reaction solvent to obtain a copper dispersion liquid, a reducing agent is dispersed in the reaction solvent to obtain a reducing agent solution, and the copper dispersion liquid and the reducing agent solution are mixed for reduction reaction to obtain a copper-clad layer solution; dispersing a silver ion source and a dispersing agent in a reaction solvent to obtain a silver dispersion solution, and mixing the silver dispersion solution and the copper layer coating solution for reduction reaction to obtain metal powder of silver-coated copper; wherein the molar ratio of the copper powder to the copper ion source is 10-100, the mass ratio of the copper powder to the dispersing agent is 10-30.
2. The silver-coated copper solder paste according to claim 1, wherein the copper powder is acid-washed copper powder, and the particle size of the copper powder is 0.1 to 2 μm.
3. The silver-coated copper solder paste according to claim 1 or 2, wherein the copper ion source is at least one of copper nitrate, copper sulfate or copper chloride, the dispersant is at least one of polyvinylpyrrolidone or gelatin, the reducing agent is at least one of sodium borohydride, ferrous sulfate or chromite chloride, and the reaction solvent is at least one of water, ethylene glycol, methanol or ethanol.
4. The silver-coated copper solder paste of claim 3, wherein the source of silver ions is at least one of silver nitrate or silver chloride.
5. The silver-coated copper solder paste according to claim 1 or 2, wherein the thickness of the silver-coated layer in the metal powder of the silver-coated copper is 0.05 to 0.5 μm.
6. The silver-coated copper solder paste according to claim 1 or 2, characterized in that the solder paste comprises, in mass percent: 80-90% of metal powder of silver coated copper and 10-20% of soldering flux.
7. The silver-coated copper solder paste of claim 6, wherein the flux comprises: active agents, film formers, thixotropic agents, surfactants, and solvents;
the soldering flux comprises the following components in percentage by mass: 10-20% of active agent, 20-40% of film forming agent, 1-5% of thixotropic agent, 1-3% of surfactant and the balance of solvent.
8. The silver-coated copper solder paste according to claim 7, wherein the active agent is at least one of butyric acid, lauric acid, stearic acid, phthalic acid, or adipic acid;
the film-forming agent is at least one of gum rosin, hydrogenated rosin, polymerized rosin or esterified rosin;
the thixotropic agent is at least one of castor oil, fatty acid amide or polyethylene glycol;
the surfactant is at least one of octylphenol polyoxyethylene ether or polyvinylpyrrolidone;
the solvent is at least one of isopropanol, ethylene glycol butyl ether or ethylene glycol hexyl ether.
9. A method of preparing a silver coated copper solder paste according to any one of claims 1 to 8, comprising: and mixing the soldering flux with the metal powder of the silver-coated copper to obtain the soldering paste.
10. Use of the silver-coated copper solder paste of any one of claims 1 to 8 in an electronic package.
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| CN101642858B (en) * | 2009-08-27 | 2011-11-09 | 中国科学院过程工程研究所 | Nuclear shell structure Pb-free solder ball for electronic packaging and preparation method thereof |
| CN102211186B (en) * | 2011-06-08 | 2013-10-16 | 北京工业大学 | Method for plating silver on surface of dendritic copper powder |
| JP6136690B2 (en) * | 2012-08-01 | 2017-05-31 | 三菱マテリアル株式会社 | Solder paste |
| CN103521945B (en) * | 2013-10-16 | 2015-08-19 | 哈尔滨工业大学 | A kind of Nano Silver coated copper powder low-temperature sintering soldering paste and preparation method thereof |
| JP6165399B1 (en) * | 2015-08-31 | 2017-07-19 | 三井金属鉱業株式会社 | Silver coated copper powder |
| CN112157371B (en) * | 2020-09-23 | 2022-05-10 | 哈尔滨工业大学（深圳） | Submicron Cu @ Ag solder paste and preparation method thereof |
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