Preparation method of anti-oxidation nano copper powder and low-temperature sintered copper slurry

Abstract

The present invention discloses a method for preparing an antioxidant nano-copper powder and a low-temperature sintered copper slurry. The preparation of the antioxidant nano-copper powder comprises the following steps: adding a reducing agent, L-ascorbic acid, and a surface modifier to pure water to dissolve and disperse the resulting solution; adding a copper-based nanopowder to the solution, placing the solution in an ultrasonic dispersion device for ultrasonic dispersion, and obtaining a dispersion liquid; the copper-based nanopowder comprises at least one of nano-scale copper oxide, nano-scale cuprous oxide, and nano-scale pure copper; heating the dispersion liquid to 40-60°C under stirring conditions and keeping the temperature for 10-30 minutes; centrifuging the dispersion liquid, washing with ethanol, and vacuum drying the resulting antioxidant nano-copper powder. The present invention can produce antioxidant copper powder through a simple liquid-solid reaction, has low-temperature sintering properties, can be used for sintering copper, has a simple process, can be mass-produced, and saves resources.

Description

Technical Field

[0001] The present invention relates to the field of preparation of nano copper powder, and in particular to a preparation method of anti-oxidation nano copper powder and a low-temperature sintered copper slurry. Background Art

[0002] The integration and miniaturization of the electronic packaging industry are driving demand for high thermal conductivity and reliability in Cu-Cu interconnects, a key process for 3D integrated circuits, chip stacking, and through-silicon via (TVS) vertical interconnects. These interconnects require low-temperature bonding and high-temperature operation. Sintered silver is currently a popular alternative to soldering. Copper is cheaper than silver and has excellent resistance to ion migration. Current literature reports and experimental evidence confirm that sintered copper surpasses sintered silver in both connection strength and environmental reliability.

[0003] However, copper nanoparticles are prone to spontaneous oxidation in air. Currently available commercially available nanocopper oxidizes very easily upon contact with air, forming copper oxide on the surface. Smaller particles (under 50nm) have a higher proportion of surface atoms, and virtually all of them convert to copper oxide upon contact with air. The formation of copper oxide increases the sintering temperature of copper-based nanopowders, reduces bonding performance, and degrades the mechanical, electrical, thermal, and reliability properties of the sintered product, limiting the application of nanocopper.

[0004] The physical vapor phase method is a relatively mature method for preparing nanopowders. Using steam condensation in an inert atmosphere, it can stably produce large quantities of nano-copper powders with a particle size distribution below 200 nm and high activity. However, the resulting nano-copper powder is partially oxidized to cupric oxide and cuprous oxide, losing its low-temperature sintering activity and electrical conductivity. This patent provides a simple treatment method for oxidized copper-based nanopowders, resulting in surface-modified, oxidation-resistant nano-copper powders. These nano-copper powders exhibit low-temperature sintering properties and can be used in sintering interconnect copper pastes. Summary of the Invention

[0005] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the object of the present invention is to provide a method for preparing antioxidant nano-copper powder. The method uses copper-based nano-powder (comprising at least one of nano-scale copper oxide, nano-scale cuprous oxide, and nano-scale pure copper) as a raw material, and can produce antioxidant copper powder through a simple liquid-solid reaction. The process is simple and can be produced in large quantities. The oxidized copper powder can be reduced to nano-copper powder for reuse, thereby saving resources.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] The present invention provides a method for preparing an oxidation-resistant nano-copper powder, comprising the following steps:

[0008] Adding a reducing agent, L-ascorbic acid, and a surface modifier into pure water to dissolve and disperse to form a solution;

[0009] Adding copper-based nanopowder to the solution and placing it in an ultrasonic dispersion device for ultrasonic dispersion to obtain a dispersion; the copper-based nanopowder comprises at least one of nano-scale copper oxide, nano-scale cuprous oxide, and nano-scale pure copper;

[0010] While stirring, heat the dispersion to 40-60°C and keep warm for 10-30 minutes; more preferably, the heating temperature is 50-60°C and the heating time is 15 minutes.

[0011] The dispersion liquid is centrifuged, washed with ethanol, and vacuum-dried to obtain antioxidant nano-copper powder.

[0012] Preferably, the surface modifier includes organic small molecules containing N functional groups and alkyd small molecules; the N functional groups are amino groups or nitrogen-containing heterocycles.

[0013] Preferably, the amount of the surface modifier is 4%-10% of the mass of the copper-based nanopowder.

[0014] Preferably, the organic small molecule containing an N functional group is one of fatty amine, alanine, proline, and N-methylpyrrolidone; and the alkyd small molecule is one of lactic acid, malic acid, and citric acid.

[0015] Preferably, the molar ratio of the reducing agent L-ascorbic acid to the copper-based nanopowder is (0.1-2):1.

[0016] Preferably, the particle size of the copper-based nanopowder is 20-200 nm; the particle size of the antioxidant nano-copper powder is 50-300 nm.

[0017] Preferably, the ultrasonic dispersion time is 10-60 min; more preferably, the ultrasonic dispersion time is 15-30 min, and it is best if the powder is dispersed into a paste in the solution without agglomerated particles.

[0018] Preferably, the stirring is specifically: stirring at a rate of 200-600 rpm; more preferably, the stirring rate is 300-400 rpm.

[0019] Preferably, the concentration of the reducing agent L-ascorbic acid used is a saturated aqueous solution.

[0020] Preferably, the vacuum drying temperature is set below 45°C.

[0021] The present invention also provides a low-temperature sintered copper paste, comprising the antioxidant nano-copper powder prepared by the preparation method of the antioxidant nano-copper powder.

[0022] Preferably, the low-temperature sintered copper paste comprises the nano copper powder, micron copper powder and a solvent; the weight ratio of the nano copper powder to the micron copper powder is 1:(0.8-1.2); and the sintering temperature of the low-temperature sintered copper paste in an air atmosphere is 200-250°C.

[0023] Preferably, the low-temperature sintered copper paste is used for Cu-Cu interconnection on a Cu substrate, the sintering temperature in air atmosphere is 200-250° C., the insulation time is 8-12 minutes, the sintering pressure is 15-25 MPa, and the interconnection strength can reach above 30 MPa.

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0025] (1) The method for preparing the antioxidant nano-copper powder of the present invention uses copper-based nano-powder (including one or more of nano-copper oxide, nano-cuprous oxide, and nano-copper) as raw materials, uses pure water as a reaction medium, and uses a saturated aqueous solution of L-ascorbic acid as a reducing agent to increase the concentration of the reaction system to prepare nano-copper powder in large quantities; the antioxidant copper powder can be obtained through a simple liquid-solid reaction, the process is simple, and it can be produced in large quantities.

[0026] (2) The method for preparing the antioxidant nano-copper powder of the present invention utilizes N-containing functional groups, -COOH functional groups and Cu to form coordination bonds or chemical bonds to coat the surface of nano-copper. -OH effectively blocks the action of oxygen, making the nano-copper powder antioxidant.

[0027] (3) The preparation method of the antioxidant nano-copper powder of the present invention uses a modifier with a decomposition temperature or boiling point lower than 250°C, which is close to the sintering temperature, so that the nano-copper powder does not oxidize under pre-baking conditions, but can decompose or volatilize at the sintering temperature. There is little or no organic matter remaining in the sintered body, thereby improving the interconnection strength of the sintered body.

[0028] (4) The method for preparing the antioxidant nano-copper powder of the present invention is not limited to copper-based nano-powders prepared by physical vapor phase method. Nano-copper powder purchased from the market is oxidized during storage. This method can be used to reduce the nano-copper powder and reuse it, thus saving resources.

[0029] (5) The method for preparing the antioxidant nano-copper powder of the present invention can ensure that the particle size distribution of the nano-powder remains substantially unchanged by controlling the concentration of the modifier, the ultrasonic dispersion time, and the heating temperature, and can produce antioxidant nano-copper powder in large quantities at high concentrations. If the ultrasonic dispersion time is too long or the heating and stirring temperature exceeds 70°C, the particle size of the resulting nano-copper powder will be larger. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is an SEM image of copper-based nanopowder prepared by the steam condensation method according to an embodiment of the present invention.

[0031] Figure 2 This is the XRD pattern of the copper-based nanopowder prepared by the steam condensation method according to an embodiment of the present invention.

[0032] Figure 3 This is a SEM image of nano-copper powder prepared in an embodiment of the present invention.

[0033] Figure 4 This is the XRD pattern of the nano copper powder prepared in the embodiment of the present invention.

[0034] Figure 5 XRD comparison diagrams of the nano copper powder prepared in the embodiment of the present invention stored at room temperature for different time periods.

[0035] Figure 6 SEM image of the fracture surface of the nano-copper paste sintered body in the embodiment of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below with reference to the examples, but the embodiments of the present invention are not limited thereto. Example

[0037] The method for preparing the antioxidant nano-copper powder according to the embodiment of the present invention comprises the following steps:

[0038] Adding a reducing agent, L-ascorbic acid, and a surface modifier into pure water to dissolve and disperse to form a solution;

[0039] Adding copper-based nanopowder to the solution and placing it in an ultrasonic dispersion device for ultrasonic dispersion to obtain a dispersion; the copper-based nanopowder comprises at least one of nano-scale copper oxide, nano-scale cuprous oxide, and nano-scale pure copper;

[0040] Under stirring conditions, heat the dispersion to 40-60°C and keep warm for 10-30 minutes;

[0041] The dispersion liquid is centrifuged, washed with ethanol, and vacuum-dried to obtain antioxidant nano-copper powder.

[0042] In some embodiments of the present invention, the surface modifier includes organic small molecules containing N functional groups and alkyd small molecules; the N functional groups are amino groups or nitrogen-containing heterocycles.

[0043] In some embodiments of the present invention, the amount of the surface modifier is 4%-10% of the mass of the copper-based nanopowder.

[0044] In some embodiments of the present invention, the organic small molecule containing an N functional group is one of fatty amine, alanine, proline, and N-methylpyrrolidone; and the alkyd small molecule is one of lactic acid, malic acid, and citric acid.

[0045] In some embodiments of the present invention, the molar ratio of the reducing agent L-ascorbic acid to the copper-based nanopowder is (0.1-2):1.

[0046] In a specific embodiment, the preparation process of antioxidant nano copper powder is as follows: weigh 80g of L-ascorbic acid, 7g of proline, and 3g of lactic acid, add them to 300mL of pure water to dissolve and disperse them to form solution A; then weigh copper-based nanopowder (containing copper oxide and copper nanopowder) prepared by steam condensation method with a diameter of less than 200nm, SEM morphology as shown Figure 1 , XRD as Figure 2 ) was added to solution A and ultrasonically dispersed for 30 minutes. The dispersion changed from dark green to wine red. The wine red dispersion was placed on a heating device and heated and stirred at 60°C for 15 minutes. It was then centrifuged, washed with ethanol, and vacuum dried at 30°C for 1 hour. Purple-red nano-copper powder was obtained. The SEM morphology is shown in Figure 3. The particle size is below 200nm. The XRD pattern is shown in Figure 4. Figure 4 The prepared nano copper powder was stored at room temperature for 1 to 7 weeks. The XRD patterns of the nano copper powders at different storage times are shown in Figure 2. Figure 5 The results showed that no characteristic peaks of copper oxide were detected in samples stored for 1 and 3 weeks, while trace amounts of copper oxide were detected in samples stored for 5 and 7 weeks, indicating that the nano-copper powder prepared in this example has excellent antioxidant properties.

[0047] The nano-copper powder prepared in the above embodiment is configured with a press-sintered nano-micro composite copper slurry: 50 g of the prepared nano-copper powder, 50 g of purchased micron powder (particle size 1 μm~3 μm), and 30 g of a mixed solvent (ethylene glycol: butoxycarbonyl alcohol: terpineol: ethyl cellulose = 8:10:5:0.6) are weighed, stirred, mixed by a three-roll mill, and degassed to prepare a nano-micro composite copper slurry.

[0048] Coat a 100-micron thick copper paste on a clean copper substrate, pre-bake at 80°C for 20 minutes, then place another clean copper substrate on the workbench of the hot press bonding equipment, apply a pressure of 20 MPa, keep warm at 220°C for 10 minutes, and then take it out and cool it naturally. Use a push-pull tester to test the bonding strength, and the bonding strength is 36.04 MPa. Push open the cross section and use SEM to analyze the microstructure, such as Figure 6 Nano-copper and micro-copper form a sintered interconnected network, and the cross section shows obvious plastic fracture when pushed open.

[0049] The present invention utilizes the small size and large specific surface area of ​​nanopowders, allowing the oxidized portion to be reduced in situ in the presence of a modifier. By controlling the modifier concentration, ultrasonic dispersion time, and heating temperature, the particle size distribution of the nanopowder can be kept substantially constant, enabling the production of high-concentration, large-scale, antioxidant nano-copper powders. However, if the ultrasonication time is too long or the heating and stirring temperature exceeds 70°C, the resulting nano-copper powder will have a larger particle size than the raw nano-powder.

[0050] The nano-micro composite sintered copper paste prepared by the present invention is used for Cu-Cu interconnection on a Cu substrate. The air atmosphere is 220° C., the sintering pressure is 20 MPa, and the heat preservation is 10 minutes. The interconnection strength can reach above 30 MPa.

[0051] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing an antioxidant nano copper powder, characterized in that: The following steps are involved: Adding a reducing agent, L-ascorbic acid, and a surface modifier into pure water to dissolve and disperse to form a solution; the surface modifier comprises an organic small molecule containing an N functional group and an alkyd small molecule; the N functional group is an amino group or a nitrogen-containing heterocycle; the organic small molecule containing an N functional group is one of a fatty amine, alanine, proline, and N-methylpyrrolidone; and the alkyd small molecule is one of lactic acid, malic acid, and citric acid; Adding copper-based nanopowder to a solution and placing it in an ultrasonic dispersing device for ultrasonic dispersion to obtain a dispersion; the copper-based nanopowder comprises at least one of nano-scale copper oxide and nano-scale cuprous oxide; the molar ratio of the reducing agent L-ascorbic acid to the copper-based nanopowder is (0.1-2):1; the amount of the surface modifier is 4%-10% of the mass of the copper-based nanopowder; Under stirring conditions, heat the dispersion to 40-60°C and keep warm for 10-30 minutes; The dispersion liquid is centrifuged, washed with ethanol, and vacuum-dried to obtain antioxidant nano-copper powder.

2. The method for preparing the antioxidant nano copper powder according to claim 1, wherein The particle size of the copper-based nanopowder is 20-200 nm; the particle size of the antioxidant nano-copper powder is 50-300 nm.

3. The method for preparing the antioxidant nano copper powder according to claim 1, wherein The ultrasonic dispersion time is 10-60 min.

4. The method for preparing the antioxidant nano copper powder according to claim 1, wherein The stirring is specifically: stirring at a speed of 200-600 revolutions per minute.

5. A low-temperature sintered copper paste comprising the antioxidant nano-copper powder prepared by the method for preparing the antioxidant nano-copper powder according to any one of claims 1 to 4.

6. The low-temperature sintered copper paste according to claim 5, characterized in that: The invention comprises micron copper powder, a solvent and the anti-oxidation nano copper powder; the weight ratio of the anti-oxidation nano copper powder to the micron copper powder is 1:(0.8-1.2); the sintering temperature of the low-temperature sintered copper paste in an air atmosphere is 200-250°C.

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