CN111618314B

CN111618314B - Preparation method of nano silver-coated copper solder based on sonochemistry

Info

Publication number: CN111618314B
Application number: CN202010412418.9A
Authority: CN
Inventors: 计红军; 张文武; 修子进; 马秋晨; 曹依琛; 潘浩; 张琳; 李明雨
Original assignee: Shenzhen Graduate School Harbin Institute of Technology
Current assignee: Shenzhen Graduate School Harbin Institute of Technology
Priority date: 2020-05-15
Filing date: 2020-05-15
Publication date: 2023-01-03
Anticipated expiration: 2040-05-15
Also published as: CN111618314A

Abstract

The invention provides a preparation method of a sonochemistry-based nano silver-coated copper solder, which comprises the following steps: mixing organic solvent solution of copper salt and organic solvent solution of sodium phosphite and protective agent, applying horn-type pulse ultrasonic wave directly downwards to the solution, heating and reacting to obtain copper nanoparticle dispersion liquid, cooling, centrifuging and washing to obtain Cu nanoparticles; adding Cu nanoparticles and a reducing agent into deionized water, uniformly mixing, adding a silver salt solution at 30-50 ℃ for reaction to obtain a silver-coated copper nanoparticle dispersion liquid, and centrifuging and washing the silver-coated copper nanoparticle dispersion liquid to obtain silver-coated copper nanoparticles; and uniformly mixing the silver-coated copper nanoparticles with the soldering paste by using an organic solvent to obtain the silver-coated copper nanoparticle soldering paste. The silver-coated copper nanoparticle solder prepared by the technical scheme of the invention has the characteristics of high reliability, low-temperature connection and high-temperature service, does not need protective gas in the preparation process, and is simple in process, green and environment-friendly.

Description

Preparation method of nano silver-coated copper solder based on sonochemistry

Technical Field

The invention belongs to the technical field of nano material preparation, and particularly relates to a preparation method of a sonochemistry-based nano silver-coated copper solder.

Background

Since the new century, the trend of light weight and miniaturization of electronic products is more and more obvious, and the nanometer conductive particles are very important components as interconnection materials in microelectronic products. After the nano conductive particles are made into the conductive slurry in a dispersion mode, the requirements of processes such as micro-nano connection and the like in a high-power device on bonding materials are well met. Meanwhile, with the continuous development of the semiconductor industry and the introduction of the post-Mole era, concepts such as the combination of silicon-based technology and non-silicon-based technology are provided, higher requirements are provided for packaging materials, the sintering of nano particles becomes the packaging trend of high-power devices, and whether efficient preparation can be realized becomes an important factor in the development process.

Metals commonly used as conductive fillers are: gold, platinum, silver, copper, nickel, tin, and the like, and mixtures of two or more thereof. Gold and platinum solder pastes are commonly used in the military electronic field, and silver solder pastes are commonly used in high-end commercial electronic products, but the prices of the gold and platinum solder pastes are too high, so that the industrial popularization of the gold and platinum solder pastes is greatly limited. Under the precondition of ensuring the main performance of the product, the material cost is reduced as much as possible, and the copper material is most likely to replace silver to become the common soldering paste in industry. However, the nano-scale copper particles are very easy to oxidize, so a layer of silver is required to cover the surface of the copper particles after the copper particles are prepared, so that the raw material has the characteristic of ensuring cost economy and also has good oxidation resistance and electrical conductivity. The key points for preparing the silver-coated copper soldering paste are the particle size and the dispersity of the nano particles and the efficient and simple preparation flow. At present, the preparation of nano silver-coated copper particles mainly comprises a microwave-assisted method, a weak reducing agent liquid phase method, a multi-step metal replacement method, a pulse line evaporation method and the like. The silver-coated copper nanoparticles prepared by the microwave-assisted method and the pulse line evaporation method have the characteristics of high efficiency and excellent oxidation resistance, but the equipment cost is too high, the particle dispersibility is poor, and the difference of the performance is large due to the instability of materials in the practical process; the weak reducing agent liquid phase method and the multi-step metal replacement method are developed based on a chemical reduction method, and have the advantages that the prepared nanoparticles have good dispersibility and low cost, but have the greatest defects of extremely low efficiency and unsuitability for large-scale production. Therefore, the development of a preparation method of the silver-coated copper nanoparticles which is low in cost, stable in process, excellent in performance and capable of being efficiently prepared is extremely important, and the preparation method brings a very potential application prospect to the nano soldering paste for packaging high-power devices.

Disclosure of Invention

Aiming at the technical problems, the invention discloses a preparation method of a sonochemistry-based nano silver-coated copper solder, which utilizes the special action effect of ultrasonic waves in a liquid phase to greatly shorten the reaction time while ensuring the stable performance and achieve simple and efficient preparation process, thereby obtaining a nano silver-coated copper solder paste with the characteristics of low-temperature connection and high-temperature service, and solving the problems of high cost, serious electromigration, unstable nano copper paste and the like of the nano silver paste in industrial application and poor reliability.

In contrast, the technical scheme adopted by the invention is as follows:

a preparation method of a nano silver-clad copper solder based on sonochemistry comprises the following steps:

s1, preparing an organic solvent solution of copper salt and an organic solvent solution of sodium phosphite and a protective agent; mixing an organic solvent solution of copper salt and an organic solvent solution of sodium phosphite and a protective agent, applying direct downward pulse ultrasonic waves to the solution, heating to 60-90 ℃, and reacting to obtain a copper nanoparticle dispersion liquid; cooling, centrifuging and washing the copper nanoparticle dispersion liquid to obtain Cu nanoparticles;

step S2, adding the Cu nanoparticles obtained in the step S1 and a reducing agent into deionized water, uniformly mixing, adding a silver salt solution at the temperature of 30-50 ℃ for reaction to obtain a silver-coated copper nanoparticle dispersion liquid, and centrifuging and washing the silver-coated copper nanoparticle dispersion liquid to obtain silver-coated copper nanoparticles;

and S3, uniformly mixing the prepared silver-coated copper nanoparticles with an organic solvent for soldering paste, and further uniformly mixing by adopting ultrasonic oscillation to obtain the silver-coated copper nanoparticle soldering paste.

Ultrasonic waves as a carrier of energy have the characteristics of high strength, good directivity, large vibration frequency and the like, and the ultrasonic waves can provide a special chemical environment which cannot be compared with other systems when being used for chemical synthesis. According to the technical scheme, by applying direct downward pulse ultrasonic waves, ultrasonic pulse waves are mutually interfered and superposed in a liquid phase environment, so that a uniform sound field with high energy and high chemical activity is generated, along with continuous generation and growth of cavitation bubbles in a liquid phase until implosion disappears, a local area is continuously subjected to rapid heating and cooling in the process, a high-temperature and high-pressure (micro-flame) environment is generated around the local area, and the activity and energy of reactants are greatly improved; on the other hand, the implosion of the cavitation bubbles can generate high-speed shock waves in a liquid phase environment and extremely high-speed jet flow on the surface of a solid, so that strong stripping and stirring effects are caused, the metal particles have good dispersibility, and in addition, the effects can also remove inactive coatings on the surface of the solid particles, so that great help is brought to sintering and particle size control; finally, the ultrasonic can increase the reactivity of the metal, improve the energy of metal bonds and accelerate the reaction process, and the ultrasonic effect is very suitable for a synthesis system of metal nano-particles.

Further, weighing a proper amount of copper salt, adding the copper salt into the organic solvent, uniformly mixing, continuously stirring, heating to 40-60 ℃, and obtaining an organic solvent solution of the copper salt after the copper salt is completely dissolved.

Further, weighing a proper amount of sodium hypophosphite, adding the sodium hypophosphite and polyvinylpyrrolidone serving as a protective agent into the organic solvent, uniformly mixing, continuously stirring, heating to 40-60 ℃, and completely dissolving to obtain an organic solvent solution of the sodium hypophosphite and the protective agent.

And further reacting for 10 to 30 min in the step S1 to obtain the copper nanoparticle dispersion liquid.

Further, in step S1, the copper nanoparticle dispersion liquid is cooled to room temperature and then subjected to centrifugal separation, and then washed and centrifuged for a plurality of times by using one or more of absolute ethyl alcohol, acetone, and ionized water thereof.

Further, in step S1, the copper salt is a compound in which a cation capable of being dissolved in water is a copper ion, and is preferably one or a mixture of two or more of copper chloride, copper sulfate and copper nitrate.

As a further improvement of the present invention, in step S1, the pulse ultrasonic wave in the radial direction is horn pulse ultrasonic wave in the radial direction.

As a further improvement of the invention, the power of the ultrasonic wave is 200W to 1000W, and the ultrasonic frequency is 20-60kHz. Furthermore, the power of the ultrasonic wave is 200 to 700W.

As a further improvement of the invention, the pulse ultrasonic wave is a symmetrical pulse, and the pulse period is 2 to 8s.

As a further improvement of the present invention, in step S1, the protective agent is one or a mixture of two or more of polyvinylpyrrolidone, sodium dodecyl sulfate, polyacrylamide, polyethylene glycol (PEG), and span.

As a further improvement of the invention, the polyvinylpyrrolidone is one or a mixture of more than two of K-15, K-30 and K-60 in molecular weight.

As a further improvement of the invention, in step S1, the molar ratio of the copper salt to the sodium hypophosphite is 1: 2 to 4; the mass ratio of the copper salt to the polyvinylpyrrolidone is 0.1 to 0.25; the organic solvent is one or a mixture of more than two of isopropanol, ethylene glycol and diethylene glycol.

As a further improvement of the method, the Cu nanoparticles obtained in the step S1 and a reducing agent are added into deionized water, and the mixture is uniformly mixed by ultrasound for 3 to 5 min.

As a further improvement of the present invention, in step S2, the silver salt solution is prepared by the following steps: weighing a certain amount of silver salt, adding the silver salt into deionized water, continuously stirring, and completely dissolving to obtain the silver salt.

As a further improvement of the invention, in step S2, slowly adding a silver salt solution at a reaction temperature of 30 to 50 ℃, and reacting for 30 min to 2 h to obtain a silver-coated copper nanoparticle dispersion liquid.

As a further improvement of the present invention, in step S2, the silver-coated copper nanoparticle dispersion liquid is cooled to room temperature and then centrifuged, and then washed and centrifuged several times with one or more mixed washing solutions of absolute ethyl alcohol, acetone, and ionized water thereof, to obtain silver-coated copper nanoparticles.

In a further improvement of the invention, in step S2, the molar ratio of the silver salt to the copper is 0.05 to 0.2.

As a further improvement of the invention, in step S2, the reducing agent is one or a mixture of two of ascorbic acid (VC) and sodium citrate;

as a further improvement of the invention, the silver salt is one or a mixture of two of silver nitrate and silver sulfate.

As a further improvement of the invention, in step S3, the mass ratio of the silver-coated copper nanoparticles to the organic solvent for the solder paste is 7 to 10; the organic solvent for the soldering paste is one or a mixture of at least two of ethanol, glycol, glycerol, terpineol and ethyl cellulose.

As a further improvement of the invention, in the soldering paste, the particle size of the silver-coated copper nanoparticles is less than 100 nm, and the average particle size is about 55 to 60 nm.

As a further improvement of the invention, in the step S3, the time of ultrasonic oscillation is 5-10 min, and in the process of ultrasonic oscillation mixing, a paste mixing machine is continuously used for stirring, and the rotating speed of the paste mixing machine is 100-1000 r/min. More preferably, the paste mixing times are 4-6 times.

Preferably, in the solder, the mass fraction of the silver-coated copper nanoparticles is 40-80%, and the mass fraction of the organic solvent for the solder paste is 20-60%.

Compared with the prior art, the invention has the following beneficial effects:

firstly, the silver-coated copper nanoparticle solder prepared by the technical scheme integrates the advantages of silver paste and copper paste, has higher reliability, and the obtained nano-grade silver-coated copper solder paste has the characteristics of low-temperature connection and high-temperature service, does not need protective gas in the preparation process, is easy to obtain raw materials, has a simple process, and is green and environment-friendly.

Secondly, the technical scheme of the invention leads the system to better perform solid-phase synthesis reaction in a liquid phase environment by introducing vertical downward ultrasonic waves, greatly improves the activity and energy of reactants, and the implosion of cavitation bubbles can generate high-speed shock waves in the liquid phase environment and high-speed jet flow on the surface of a solid, so that metal particles have good dispersibility, and inactive coating on the surface of the solid particles can be removed, thereby being greatly helpful for sintering and particle size control; finally, the ultrasonic wave can increase the reactivity of the metal, improve the energy of metal bonds, accelerate the synthesis of copper nanoparticles, further obtain silver-coated copper nanoparticles with the particle size of less than 100 nm and better dispersibility, have lower sintering temperature and higher service temperature, and meet the urgent requirements of low-temperature connection and high-temperature service of third-generation semiconductor devices.

Thirdly, aiming at the problems of poor tissue compactness, poor reliability, unstable performance and the like after the sintering of common nano particles, the preparation process of the soldering paste in the technical scheme of the invention adopts a unique formula and fine process steps, and particularly adds a special organic solvent to remove surface coating substances of the nano particles, thereby greatly reducing the sintering temperature, further increasing the weldability of the soldering paste, obtaining a compact joint with silver and copper interwoven, and realizing that the joint has excellent performances of electromigration resistance, high electric conduction and heat conduction, high reliability and the like at low temperature.

Drawings

FIG. 1 is a schematic representation of the ultrasonic sonochemical reaction of the present invention.

Fig. 2 is an XRD pattern of the nano silver-coated copper particles obtained in example 1 of the present invention.

Fig. 3 is a TEM image of the nano silver-coated copper particles obtained in example 1 of the present invention, wherein (a) is a TEM image, and (b) is a line scan image corresponding to Cu and Ag elements.

Fig. 4 is SEM images of silver-coated copper nanoparticles obtained in example 1 of the present invention and comparative example 1, wherein (a) is in horn ultrasonic mode of example 1, and (b) is in bath ultrasonic mode of comparative example 1.

FIG. 5 is a SEM cross-sectional view of a joint using nano silver-clad copper solder paste obtained in examples 1 to 3 of the present invention and comparative example 2 as a solder, wherein (a) is a SEM image of example 1 (ultrasonic power of 200W); (b) is the SEM image of example 2 (ultrasonic power of 400W); (c) is the SEM image of example 3 (ultrasonic power of 600W); (d) is an SEM image of example 4 at an ultrasonic power of 800W; wherein (a 1), (b 1), (c 1) and (d 1) are partial enlarged views of (a), (b), (c) and (d).

FIG. 6 is a comparative UV chart during the process of nano silver-coated copper particles of example 1 and comparative example 2 of the present invention, wherein (a) is that of comparative example 2; (b) is of example 1.

Fig. 7 is a SEM cross-sectional view of a joint of a nanosilver-copper-clad solder paste as a solder obtained under ultrasonic conditions of example 1 and comparative example 3 at different pulse ratios, wherein (a) is a pulse ratio of 1 for example 1, (b) is a pulse ratio of 5 for comparative example 3.

Detailed Description

In view of the incompleteness of the prior art, the specific technical route of the invention is as follows: copper nanoparticles with good particle size, morphology and dispersibility are efficiently prepared under the assistance of pulse ultrasonic waves and are used as precursors, then nano silver-coated copper particles are prepared by adopting a composite method of displacement and chemical reduction, and finally the nano silver-coated copper particles and soldering flux are prepared into soldering paste according to a certain mass ratio. Wherein, the copper nano-particles are introduced with ultrasonic action, the pulse sound wave can be equivalent to the combination of a plurality of resonant waves with different frequencies, and the interaction and the superposition are carried out in a liquid phase environment, so that the whole reaction container is filled with a uniform, high-activity and high-energy ultrasonic field; cavitation bubbles produced by cavitation are generated in a very short time and grow until implosion disappears, and the process can provide local instantaneous extreme high temperature and high pressure (micro flame) under the condition of not changing the ambient temperature and pressure; the cavitation bubbles interact with the solid phase to generate high-speed jet flow and shock wave on the surface of the solid phase, so that the prepared nano particles are dispersed more strongly under the action of stirring and stripping. The special effects brought by the ultrasound are beneficial to the chemical synthesis of the nano particles to a certain extent, and are also the key points of the invention.

A silver-coated copper nanoparticle soldering paste for high-power device packaging is prepared by the following steps:

(1) Weighing a proper amount of copper salt, adding the copper salt into an organic solvent, uniformly mixing, continuously stirring, heating to 40-60 ℃, and obtaining a solution A after complete dissolution. And weighing a proper amount of sodium hypophosphite, adding the sodium hypophosphite and polyvinylpyrrolidone serving as a protective agent into the organic solvent, uniformly mixing, continuously stirring, heating to 40-60 ℃, and completely dissolving to obtain a solution B.

(2) Adding the freshly prepared solution A into the freshly prepared solution B, applying horn pulse ultrasonic waves acting downwards directly, heating to 60-90 ℃, and reacting for 10-30 min to obtain a copper nanoparticle dispersion liquid; the reaction device is shown in figure 1 and comprises a double-layer beaker 1, an ultrasonic generator 2, an ultrasonic transducer 3 and a titanium alloy amplitude transformer 4, wherein constant-temperature circulating water is introduced into the double-layer beaker 1 for heating, the ultrasonic generator 2 is connected with the titanium alloy amplitude transformer 4 through the ultrasonic transducer 3, and the titanium alloy amplitude transformer 4 extends into a reaction solution 5 containing reactants 6 in the double-layer beaker 1 to generate a pulse sound field 7, so that a large amount of cavitation bubbles 8 are generated to promote and accelerate the reaction.

(3) And (3) cooling the copper nanoparticle dispersion liquid obtained in the step (2) to room temperature, performing centrifugal separation, and performing multiple washing and centrifugation by using a washing liquid mixed by one or more of absolute ethyl alcohol, acetone and ionized water thereof.

(4) Weighing a certain amount of the Cu nanoparticles obtained in the step (3) and a proper amount of reducing agent, adding into deionized water, and carrying out ultrasonic treatment for 3-5 min to uniformly mix to obtain a solution C. And weighing a certain amount of silver salt, adding the silver salt into deionized water, continuously stirring, and obtaining a solution D after the silver salt is completely dissolved.

(5) And slowly dripping the solution D into the solution C at the reaction temperature of 30 to 50 ℃ to react for 30 min to 2 h to obtain the silver-coated copper nanoparticle dispersion liquid.

(6) And (4) cooling the silver-coated copper nanoparticle dispersion liquid obtained in the step (5) to room temperature, then carrying out centrifugal separation, and washing and centrifuging for multiple times by using one or more than two mixed washing liquids of absolute ethyl alcohol, acetone and ionized water thereof to obtain the silver-coated copper nanoparticles.

(7) Uniformly mixing the silver-coated copper nanoparticles and soldering flux such as ethylene glycol, terpineol, ethyl cellulose and the like by ultrasonic oscillation according to a certain mass ratio, and continuously stirring by using a paste mixer in the process to finally obtain the silver-coated copper nanoparticle soldering paste.

The technical solution of the present invention is further described below with reference to several examples.

Example 1

(1) 10 g of copper sulfate pentahydrate powder is weighed and added into 100 ml of ethylene glycol, heated to 70 ℃, stirred for 15 min and completely dissolved to obtain solution A. In addition, 8g of sodium hypophosphite powder and 5g of polyvinylpyrrolidone are weighed and added into 200 ml of ethylene glycol, heated to 70 ℃, stirred for 20 min and completely dissolved to obtain a solution B.

(2) Adding the freshly prepared solution A into the freshly prepared solution B, applying horn type (horn) pulse ultrasonic waves (with the power of 200W and the pulse ratio of 2 s-2 s) acting directly downwards, heating to 70 ℃, and reacting for 15 min to obtain the copper nanoparticle dispersion liquid.

(3) The copper nanoparticle dispersion obtained in step (2) was cooled to room temperature and then centrifuged (5000 rmp,15 min), and anhydrous ethanol was used: deionized water according to the weight ratio of 3: the mixed solution at a volume ratio of 1 was washed 3 times.

(4) And (4) weighing 2g of the Cu nanoparticles obtained in the step (3) and 2g of sodium citrate, adding the Cu nanoparticles and the sodium citrate into 100 ml of deionized water, and performing ultrasonic treatment for 5 min to uniformly mix the Cu nanoparticles and the sodium citrate to obtain a solution C. In addition, 0.5 g of silver sulfate powder is weighed and added into 200 ml of deionized water, and the solution D is obtained after stirring for 15 min and full dissolution.

(5) And slowly dropwise adding the solution D into the solution C at the reaction temperature of 40 ℃ to react for 1.5 h to obtain the silver-coated copper nanoparticle dispersion liquid.

(6) Cooling the silver-coated copper nanoparticle dispersion obtained in step (5) to room temperature, centrifuging (5000 rmp,15 min), and using absolute ethanol: deionized water according to the weight ratio of 3: and washing the mixed solution with the volume ratio of 1 for 3 times to obtain the silver-coated copper nanoparticles.

The XRD pattern of the nano silver-coated copper particles obtained in example 1 of the present invention is shown in fig. 2, and the TEM pattern is shown in fig. 3, which shows that the copper surface is coated with a thin layer of silver.

Example 2

(2) Adding the freshly prepared solution A into the freshly prepared solution B, applying horn type (horn) pulse ultrasonic waves (400W, the pulse ratio is 2 s-2 s) which act directly downwards, heating to 70 ℃, and reacting for 15 min to obtain the copper nanoparticle dispersion liquid.

(6) Cooling the silver-coated copper nanoparticle dispersion obtained in step (5) to room temperature, centrifuging (5000 rmp,15 min), and using absolute ethanol: deionized water according to the weight ratio of 3: the mixed solution was washed 3 times at a volume ratio of 1.

Example 3

(1) 10 g of copper sulfate pentahydrate powder is weighed and added into 100 ml of glycol, heated to 70 ℃, stirred for 15 min and completely dissolved to obtain a solution A. In addition, 8g of sodium hypophosphite powder and 5g of polyvinylpyrrolidone are weighed and added into 200 ml of ethylene glycol, heated to 70 ℃, stirred for 20 min and completely dissolved to obtain a solution B.

(2) Adding the freshly prepared solution A into the freshly prepared solution B, applying horn type (horn) pulse ultrasonic waves (600W, the pulse ratio is 4 s-2 s) which act directly downwards, heating to 70 ℃, and reacting for 15 min to obtain the copper nanoparticle dispersion liquid.

(4) Weighing 2g of the Cu nanoparticles obtained in the step (3) and 2g of sodium citrate, adding into 100 ml of deionized water, and carrying out ultrasonic treatment for 5 min to uniformly mix to obtain a solution C. In addition, 0.5 g of silver sulfate powder is weighed and added into 200 ml of deionized water, and the solution D is obtained after stirring for 15 min and full dissolution.

(5) And slowly dripping the solution D into the solution C at the reaction temperature of 40 ℃ to react for 1.5 hours to obtain the silver-coated copper nanoparticle dispersion liquid.

(6) Cooling the silver-coated copper nanoparticle dispersion obtained in step (5) to room temperature, centrifuging (5000 rmp,15 min), and using absolute ethanol: deionized water according to the weight ratio of 3: the mixed solution at a volume ratio of 1 was washed 3 times.

(7) Uniformly mixing the silver-coated copper nanoparticles and soldering flux such as ethylene glycol, terpineol, ethyl cellulose and the like according to a certain mass ratio by adopting ultrasonic oscillation, and continuously stirring by using a paste mixing machine in the process to finally obtain the silver-coated copper nanoparticle soldering paste.

Example 4

On the basis of example 1, in the step (2) of this example, horn-type (horn) pulsed ultrasonic waves (800W, pulse ratio of 2 s-2 s) acting directly downward were applied, heated to 70 ℃, and reacted for 15 min to obtain a copper nanoparticle dispersion. The other steps are the same as in example 1.

The welding experiments are respectively carried out on the solders of the examples 1 to 4, the structure morphology diagram of the joint is analyzed, the comparison diagram is shown in fig. 5, and as can be seen from fig. 5, the joint particles with the ultrasonic powers of 200W, 400W and 600W are fused together, the specific power is better than 800W, and the effect of the power of 600W is best.

Comparative example 1

(2) Adding the freshly prepared solution A into the freshly prepared solution B, applying bath type (bath) pulse ultrasonic waves (800W, with the pulse ratio of 2 s-2 s) acting directly downwards, heating to 70 ℃, and reacting for 15 min to obtain the copper nanoparticle dispersion liquid.

(3) The copper nanoparticle dispersion liquid obtained in step (2) was cooled to room temperature and then centrifuged (5000 rmp,15 min), and the mixture was extracted with absolute ethanol: deionized water according to the weight ratio of 3: the mixed solution was washed 3 times at a volume ratio of 1.

The morphology of the silver-coated copper nanoparticles obtained in the two ultrasonic modes of the embodiment 3 and the comparative example 1 is analyzed, and as shown in fig. 4, it can be seen that the morphology of the silver-coated copper nanoparticles obtained in the horn (horn) pulse ultrasonic mode in the embodiment 3 is approximately spherical and has better dispersibility, while the morphology of the silver-coated copper nanoparticles obtained in the bath pulse ultrasonic mode in the comparative example 1 is thorn-shaped, and the silver-coated copper nanoparticles prepared in the horn (horn) pulse ultrasonic mode in the embodiment 3 have large specific surface area and higher surface energy, and are easier to sinter at low temperature, so that the morphologies are easier to fuse with each other in joint connection to form a whole, and the goal of low-temperature connection and high-temperature service is realized.

Comparative example 2

In the comparative example, UV comparative analysis is performed on the copper-clad silver nanoparticles obtained by a conventional alcohol reduction method in the process of cladding the copper nanoparticles with the silver-clad nanoparticles of example 1, and the result is shown in FIG. 6.

Comparative example 3

The comparative example differs from example 1 in the pulse ratio, which is 10s to 2s, i.e., 5:1. the solders of example 1 and comparative example 3 were respectively subjected to a soldering experiment, and the texture and morphology of the joint were analyzed, and as shown in fig. 7, as can be seen from fig. 7, the joint morphology of the solder having the pulse ratio of 1 in example 1: the solder joint of 1 had voids, and the joint strength was inferior to that of example 1.

The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, numerous simple deductions or substitutions may be made without departing from the spirit of the invention, which shall be deemed to belong to the scope of the invention.

Claims

1. A preparation method of a sonochemistry-based nano silver-coated copper solder is characterized by comprising the following steps:

s1, preparing an organic solvent solution of copper salt and an organic solvent solution of sodium hypophosphite and a protective agent; mixing an organic solvent solution of copper salt and an organic solvent solution of sodium hypophosphite and a protective agent, applying direct downward horn type pulse ultrasonic waves to the solutions, heating to 60-90 ℃, and reacting to obtain a copper nanoparticle dispersion liquid; cooling, centrifuging and washing the copper nanoparticle dispersion liquid to obtain Cu nanoparticles;

s3, uniformly mixing the prepared silver-coated copper nanoparticles with an organic solvent for soldering paste, and further uniformly mixing by adopting ultrasonic oscillation to obtain silver-coated copper nanoparticle soldering paste;

in the step S1, the power of the ultrasonic wave is 200W to 700W, and the ultrasonic frequency is 20-60kHz;

the pulse ultrasonic wave is a symmetrical pulse, and the pulse period is 2 to 8s.

2. The method for preparing the sonochemistry-based nano-silver-clad brazing filler metal according to claim 1, wherein the sonochemistry-based nano-silver-clad brazing filler metal comprises the following steps: in the step S1, the protective agent is one or a mixture of more than two of polyvinylpyrrolidone, sodium dodecyl sulfate, polyacrylamide, polyethylene glycol or span.

3. The method for preparing the sonochemistry-based nano-silver-clad brazing filler metal according to claim 2, wherein the sonochemistry-based nano-silver-clad brazing filler metal comprises the following steps: the polyvinylpyrrolidone is one or a mixture of more than two of K-15, K-30 and K-60 in molecular weight.

4. The method for preparing the sonochemistry-based nano silver-coated copper solder according to any one of claims 1 to 2, which is characterized in that: in the step S1, the molar ratio of the copper salt to the sodium hypophosphite is 1: 2 to 4; the mass ratio of the copper salt to the polyvinylpyrrolidone is 0.1 to 0.25;

the organic solvent is one or a mixture of more than two of isopropanol, glycol and diethylene glycol;

the copper salt is one or a mixture of more than two of copper chloride, copper sulfate and copper nitrate.

5. The method for preparing the sonochemistry-based nano-silver-clad brazing filler metal according to claim 4, wherein the sonochemistry-based nano-silver-clad brazing filler metal comprises the following steps: in the step S2, the molar ratio of the silver salt to the copper is 0.05 to 0.2.

6. The method for preparing the sonochemistry-based nano-silver-clad brazing filler metal according to claim 5, wherein the method comprises the following steps: in the step S2, the reducing agent is one or a mixture of two of ascorbic acid and sodium citrate;

the silver salt is one or a mixture of two of silver nitrate and silver sulfate.

7. The method for preparing the sonochemistry-based nano silver-coated copper solder according to any one of claims 1 to 2, which is characterized in that: in the step S3, the mass ratio of the silver-coated copper nanoparticles to the organic solvent for the soldering paste is 7 to 10, and the particle size of the nanoparticles in the solder is less than 100 nm; the organic solvent for the soldering paste is one or a mixture of at least two of ethanol, glycol, glycerol, terpineol and ethyl cellulose.

8. The method for preparing the sonochemistry-based nano-silver-clad brazing filler metal according to claim 7, wherein the method comprises the following steps: in the step S3, the ultrasonic oscillation time is 5-10 min, and in the ultrasonic oscillation mixing process, the paste mixing machine is continuously used for stirring, and the rotating speed of the paste mixing machine is 100-1000 r/min.