CN113560562B - Nano silver particles, preparation method thereof, nano silver paste and welding joint - Google Patents
Nano silver particles, preparation method thereof, nano silver paste and welding joint Download PDFInfo
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- CN113560562B CN113560562B CN202110672819.2A CN202110672819A CN113560562B CN 113560562 B CN113560562 B CN 113560562B CN 202110672819 A CN202110672819 A CN 202110672819A CN 113560562 B CN113560562 B CN 113560562B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/10—Sintering only
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/16—Making metallic powder or suspensions thereof using chemical processes
- B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
- B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y40/00—Manufacture or treatment of nanostructures
Abstract
The invention relates to the technical field of new materials, in particular to a nano silver particle and a preparation method thereof, nano silver paste and a welding joint. According to the invention, micromolecular organic amine and organic acid are introduced in the process of preparing the nano silver particles, and the mass ratio of the micromolecular organic amine to the organic acid is set to be 1: (0.2-5), the reaction speed of the two can be controlled, so that the regulation and control of the size of the finally prepared nano silver particles are realized; in addition, the amide generated by the reaction of amine and acid can also be used as a dispersing agent, so that the agglomeration of nano silver particles is avoided, and organic polymer dispersing agents such as PVP and the like do not need to be additionally introduced into the system. The micromolecule amide can be rapidly decomposed at about 230 ℃ to generate volatile acid and amine, so that the porosity of a sintered body can be effectively reduced and higher connection strength can be realized when the nano silver particles prepared by the method are sintered after being prepared into nano silver paste.
Description
Technical Field
The invention relates to the technical field of new materials, in particular to a nano silver particle and a preparation method thereof, nano silver paste and a welding joint.
Background
With the large-scale application of high-power semiconductor materials such as GaN, SiC and the like, the working temperature of chips is higher and higher, and the traditional soft solder such as Sn base and the like has low reliability at high temperature and even generates remelting. Electronic slurry such as nano silver paste can realize low-temperature sintering connection, has no remelting phenomenon in service at high temperature, has the advantages of high heat conductivity, high electric conductivity and high reliability, and has a great amount of applications in the field of microelectronic interconnection.
The preparation method of the nano silver paste generally comprises two main steps: 1) reducing silver ions into nano silver simple substance particles by adding a reducing agent; 2) and mixing the prepared nano silver simple substance particles with a solvent, a thickening agent and the like to prepare the nano silver paste. In the prior art, the size of the nano-silver particles is difficult to regulate and control in the preparation process, the particle size distribution of the obtained nano-silver particles is wide, and the particle size of the nano-silver particles cannot be flexibly regulated according to actual production needs. In addition, in the conventional preparation method, in order to prevent the aggregation of the nano silver particles obtained by reduction, an organic high molecular polymer dispersant such as PVP (polyvinylpyrrolidone) is generally added to the system; the decomposition temperature of the high-molecular polymer dispersing agent is higher, so that the nano silver paste needs to be sintered at a higher temperature for a long time to obtain a high-strength welding joint, but the chip, the substrate and other components are damaged; if the sintering temperature is too low, the organic polymer dispersing agent with high content in the nano silver paste is not decomposed sufficiently, and the prepared welding joint has low connection strength.
Disclosure of Invention
Based on this, it is necessary to provide a nano silver particle, a preparation method thereof, a nano silver paste and a welding joint, the particle size of the silver particle can be controlled in the preparation process, and the high-strength welding joint can be prepared by sintering the nano silver paste at a low temperature, so that the problems in the prior art are effectively solved.
In one aspect of the present invention, there is provided a method for preparing nano silver particles, comprising the steps of:
a) mixing silver salt, organic amine and a first solvent to obtain a first solution, wherein the number of carbon atoms of a main chain of the organic amine is less than or equal to 6;
b) mixing an organic acid, a reducing agent and a second solvent to obtain a second solution, wherein the number of carbon atoms of a main chain of the organic acid is less than or equal to 6;
c) mixing the first solution and the second solution, and controlling the amount ratio of the organic amine to the organic acid to be 1: (0.2-5), and carrying out solid-liquid separation after the reaction is completed.
In the present invention, steps a) and b) are not in sequence.
According to the invention, micromolecular organic amine and organic acid are introduced in the process of preparing the nano silver particles, and the mass ratio of the micromolecular organic amine to the organic acid is set to be 1: (0.2-5), the reaction speed of the two can be controlled, so that the regulation and control of the size of the finally prepared nano silver particles are realized; in addition, the amide generated by the reaction of amine and acid can also be used as a dispersing agent, so that the agglomeration of nano silver particles is avoided, and organic polymer dispersing agents such as PVP and the like do not need to be additionally introduced into the system. The micromolecule amide can be rapidly decomposed at about 230 ℃ to generate volatile acid and amine, so that the porosity of a sintered body can be effectively reduced and higher connection strength can be realized when the nano silver particles prepared by the method are sintered after being prepared into nano silver paste. In addition, the volatile acids and amines can also remove oxides from the surface of the silver particles, further promoting atomic diffusion and the formation of sintering necks.
In some embodiments, the organic amine is one or more of isopropanolamine, diethanolamine, dipropylamine, tert-butylamine, acetamide.
In some embodiments, the concentration of the organic amine in the first solution is between 3mol/L and 15 mol/L.
In some embodiments, the organic acid is one or more of butyric acid, glycolic acid, α -hydroxypropionic acid, succinic acid, glutaric acid.
In some embodiments, the concentration of the organic acid in the second solution is between 0.6mol/L and 10 mol/L.
In some embodiments, the silver salt is one or more of silver nitrate, silver sulfate, silver tetrafluoroborate, silver triflate, silver trifluoroacetate.
In some embodiments, the concentration of the silver salt in the first solution is between 0.01mol/L and 0.5 mol/L.
In some embodiments, the first solvent and the second solvent are each independently selected from one or more of methanol, ethanol, ethylene glycol, glycerol, butanol, n-pentanol, benzene, toluene, xylene, acetone, n-hexane, cyclohexane.
In some embodiments, the reducing agent is one or more of sodium borohydride, formaldehyde, sodium citrate, hydrazine hydrate.
In some embodiments, the concentration of the reducing agent in the second solution is between 0.001mol/L and 0.1 mol/L.
In another aspect of the present invention, there is provided a nano silver particle prepared by the foregoing preparation method.
The invention also provides a nano silver paste which comprises the nano silver particles.
In some embodiments, the mass fraction of the nano silver particles in the nano silver paste is 30% to 80%.
The invention also provides a welding joint which is formed by sintering the nano silver paste.
Drawings
FIG. 1 is a scanning electron microscope image of the nano-silver particles prepared in example 1;
FIG. 2 is a scanning electron microscope image of the nano-silver particles prepared in example 2;
fig. 3 is a scanning electron microscope image of the nano silver particles prepared in example 3.
Detailed Description
To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the invention, "a plurality" means at least two, e.g., two, three, etc., unless explicitly specified otherwise. In the description of the present invention, "a plurality" means at least one, e.g., one, two, etc., unless specifically limited otherwise.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
In one aspect of the present invention, a method for preparing nano silver particles is provided, which comprises the following steps:
a) mixing silver salt, organic amine and a first solvent to obtain a first solution, wherein the number of carbon atoms of a main chain of the organic amine is less than or equal to 6;
b) mixing an organic acid, a reducing agent and a second solvent to obtain a second solution, wherein the number of carbon atoms of a main chain of the organic acid is less than or equal to 6;
c) mixing the first solution and the second solution, and controlling the amount ratio of the organic amine to the organic acid to be 1: (0.2-5), and carrying out solid-liquid separation after the reaction is completed.
In the present invention, steps a) and b) are not in sequence.
In some embodiments, the silver salt is dissolved in the first solvent, and the organic amine is added after the silver salt is completely dissolved; ways to make the silver salt dissolve better include, but are not limited to, temperature-rising dispersion, ultrasonic dispersion, and the like.
In some embodiments, the organic acid is dissolved in the second solvent, mixed well and then added to the reducing agent.
In the first solution, part of the organic amine is coordinated with the silver salt to form a silver-amine complex, and when mixed into the second solution containing the organic acid, the amino group reacts with the carboxyl group to form an amide to form a silver-amide complex. Due to the introduction of the organic acid molecular chain, the steric hindrance of the ligand is increased, the collision probability of the reducing agent and the central silver ion in the reaction system is reduced, and in addition, the existence of the carbonyl group also strengthens the coordination of the ligand and the central metal to a certain extent, so the speed of the reduction reaction is slowed down. Therefore, under the condition of a certain dosage of the reducing agent, the regulation of the reduction reaction speed of the silver ions can be realized by regulating the dosages of the organic acid and the organic amine. When the reduction reaction speed is high, the particles can not grow in time, so that the particle size of the generated silver simple substance is small, when the reduction reaction speed is low, the particles gradually grow, and the particle size of the finally obtained silver simple substance is large.
Specifically, when nano silver particles having a small particle size, such as nano silver particles having a particle size distribution in the range of 10nm to 30nm, are required, the reduction reaction rate needs to be fast, and thus, the amount of amide should be small. In this case, the ratio of the organic amine to the organic acid is maintained at 1 (0.2-0.5), preferably 1 (0.35-0.5), so that the reduction reaction is fast and the smooth morphology of the nano silver particles is maintained.
When nano silver particles having a large particle size, such as nano silver particles having a particle size distribution in the range of 160nm to 330nm, are required, the reduction reaction rate is required to be slow, and therefore, the amount of amide should be large. In this case, the ratio of the amounts of the organic amine and the organic acid is maintained at 1 (2-5), preferably 1 (2-3), so that the reduction reaction proceeds at an appropriate rate, and space is provided for the silver particles to grow to a desired particle size range.
It is understood that when the ratio of the amounts of the organic amine and the organic acid is maintained in the intermediate range, i.e., 1: (0.6 to 1.9), the nano silver particles having particle diameters mainly distributed in the range of 30 to 160nm can be obtained, but since the neutralization reaction of the acid and the amine in this ratio range is equivalent to the reduction reaction of silver ions and lacks selectivity, many nano silver particles having excessively large or excessively small particle diameters are included, and the particle diameter distribution is relatively broad. Although the particle size distribution cannot be accurately controlled to be a concentrated unimodal type within the proportion range, the gaps between large-particle nano silver can be filled to a certain degree by the small-particle nano silver due to the simultaneous existence of the large-particle nano silver and the small-particle nano silver, and therefore when the prepared silver paste is directly sintered, a welding joint with relatively high sintering strength can be obtained by a relatively simple process. Certainly, due to the low controllability of the reaction in this range, the proportion of the large and small particles cannot be accurately controlled, and therefore, compared with the silver paste sintered welding joint obtained by accurately compounding silver particles with different particle sizes according to needs, the strength of the welding joint is still slightly insufficient.
According to the invention, micromolecular organic amine and organic acid are introduced in the process of preparing the nano silver particles, and the mass ratio of the micromolecular organic amine to the organic acid is set to be 1: (0.2-5), the reaction speed of the two can be controlled, so that the regulation and control of the size of the finally prepared nano silver particles are realized; in addition, the amide generated by the reaction of amine and acid can also be used as a dispersing agent, so that the agglomeration of nano silver particles is avoided, and organic polymer dispersing agents such as PVP and the like do not need to be additionally introduced into the system. The micromolecule amide can be rapidly decomposed at about 230 ℃ to generate volatile acid and amine, so that the porosity of a sintered body can be effectively reduced and higher connection strength can be realized when the nano silver particles prepared by the method are sintered after being prepared into nano silver paste. In addition, the volatile acids and amines can also remove oxides from the surface of the silver particles, further promoting atomic diffusion and the formation of sintering necks.
In some embodiments, the solid-liquid separation comprises: centrifuge and remove supernatant.
In some embodiments, the solid-liquid separation further comprises washing the silver particles, wherein the washing agent is one or more of ethanol, acetone, benzene and homologues of benzene.
In some embodiments, the organic amine is one or more of isopropanolamine, diethanolamine, dipropylamine, tert-butylamine, acetamide.
In some embodiments, the concentration of the organic amine in the first solution is between 3mol/L and 15 mol/L.
Preferably, the concentration of the organic amine in the first solution is 6mol/L to 8 mol/L. The concentration of the organic amine is maintained in a certain range, so that the coordination of silver ions and amino groups is more suitable, and the subsequent reaction is further controlled.
In some embodiments, the organic acid is one or more of butyric acid, glycolic acid, α -hydroxypropionic acid, succinic acid, glutaric acid.
In some embodiments, the concentration of the organic acid in the second solution is between 0.6mol/L and 10 mol/L.
Preferably, the concentration of the organic acid in the second solution is 3mol/L to 5 mol/L. Although the final reaction of the organic amine and the organic acid is mainly determined by the quantity ratio of the organic amine to the organic acid, the concentration of the reactant in the reaction system is controlled, so that the local concentration difference can be avoided when the two solutions are mixed, the reaction can be controlled, the silver particles with narrow particle size distribution can be prepared, and the silver particles are ensured to be smoother and more uniform in appearance.
In some embodiments, the silver salt is one or more of silver nitrate, silver sulfate, silver tetrafluoroborate, silver triflate, silver trifluoroacetate.
In some embodiments, the concentration of the silver salt in the first solution is between 0.01mol/L and 0.5 mol/L.
Preferably, the concentration of the silver salt in the first solution is 0.2mol/L to 0.35 mol/L. The concentration of the silver salt also relates to whether the reaction can be carried out as expected, the collision probability of the reducing agent and the silver ions is excessively reduced when the concentration is too low, so that the reaction is difficult to smoothly occur, and the reaction is uneven when the concentration is too high, so that the particle size difference of silver particles is large and the distribution is too wide.
In some embodiments, the first solvent and the second solvent are each independently selected from one or more of methanol, ethanol, ethylene glycol, glycerol, butanol, n-pentanol, benzene, toluene, xylene, acetone, n-hexane, cyclohexane.
In some embodiments, the reducing agent is one or more of sodium borohydride, formaldehyde, sodium citrate, hydrazine hydrate.
In some embodiments, the concentration of the reducing agent in the second solution is between 0.001mol/L and 0.1 mol/L.
Preferably, the concentration of the reducing agent in the second solution is 0.02mol/L to 0.06 mol/L.
In another aspect of the present invention, there is provided a nano silver particle prepared by the foregoing preparation method.
The invention also provides nano silver paste which comprises the nano silver particles.
In some embodiments, the mass fraction of the nano silver particles in the nano silver paste is 30% to 80%.
In some embodiments, the viscosity of the nano silver paste is greater than or equal to 10Pa · s.
In some embodiments, the nano silver paste further comprises a thickener and a solvent.
In some embodiments, the thickener is one or more of polyethylene glycol, polyvinyl alcohol, ethyl cellulose, hydroxyethyl cellulose.
In some embodiments, the amount of thickener is no more than 5% by mass of the nano silver paste.
In some embodiments, the solvent is one or more of ethylene glycol, glycerol, terpineol, tributyl phosphate.
The invention also provides a welding joint which is formed by sintering the nano silver paste.
In some embodiments, the sintering process parameters of the weld joint are: the sintering temperature is 200-280 ℃, and the temperature is kept for 20-50 min.
The nano silver paste provided by the invention can obtain the shearing strength as high as 78MPa and the resistivity as low as 4.2 multiplied by 10 within one hour after being sintered at the low temperature of below 300 DEG C-6Omega cm, high thermal conductivity up to 164.3 w/m.K.
The present invention will be described in further detail with reference to specific examples and comparative examples. It is understood that the following examples are more specific in terms of apparatus and materials, and in other specific embodiments, are not limited thereto, and may be dispersed, for example, by ultrasound.
1) Preparing nano silver particles:
example 1
Dissolving silver nitrate in ethylene glycol, and performing ultrasonic treatment at 40 deg.C for 10min to dissolve silver nitrate completely; subsequently adding isopropanolamine into the silver nitrate-ethylene glycol solution to obtain a first solution; wherein the concentration of silver nitrate is 0.2mol/L, and the concentration of isopropanolamine is 8 mol/L;
dissolving alpha-hydroxypropionic acid in ethylene glycol, and then adding sodium borohydride into the alpha-hydroxypropionic acid-ethylene glycol solution to obtain a second solution; wherein the concentration of the alpha-hydroxypropionic acid is 4mol/L, and the concentration of the sodium borohydride is 0.06 mol/L;
mixing the first solution and the second solution, keeping the mass ratio of the isopropanolamine to the alpha-hydroxypropionic acid to be 1:0.5, and continuously stirring until the reaction is complete;
and (3) putting the completely reacted system into a centrifugal tube for centrifugation, pouring out supernatant after the centrifugation is finished, and washing the supernatant with ethanol for three times to obtain the nano-silver particles.
Example 2
Dissolving silver nitrate in ethylene glycol, and performing ultrasonic treatment at 40 deg.C for 10min to dissolve silver nitrate completely; subsequently adding isopropanolamine into the silver nitrate-ethylene glycol solution to obtain a first solution; wherein the concentration of silver nitrate is 0.2mol/L, and the concentration of isopropanolamine is 8 mol/L;
dissolving alpha-hydroxypropionic acid in ethylene glycol, and then adding sodium borohydride into the alpha-hydroxypropionic acid-ethylene glycol solution to obtain a second solution; wherein the concentration of the alpha-hydroxypropionic acid is 4mol/L, and the concentration of the sodium borohydride is 0.02 mol/L;
mixing the first solution and the second solution, keeping the mass ratio of the isopropanolamine to the alpha-hydroxypropionic acid to be 1:2, and continuously stirring until the reaction is complete;
and (3) putting the completely reacted system into a centrifugal tube for centrifugation, pouring out supernatant after the centrifugation is finished, and washing the supernatant with ethanol for three times to obtain the nano-silver particles.
Example 3
Dissolving silver nitrate in ethylene glycol, and performing ultrasonic treatment at 40 deg.C for 10min to dissolve silver nitrate completely; subsequently adding isopropanolamine into the silver nitrate-ethylene glycol solution to obtain a first solution; wherein the concentration of silver nitrate is 0.2mol/L, and the concentration of isopropanolamine is 8 mol/L;
dissolving alpha-hydroxypropionic acid in ethylene glycol, and then adding sodium borohydride into the alpha-hydroxypropionic acid-ethylene glycol solution to obtain a second solution; wherein the concentration of the alpha-hydroxypropionic acid is 4mol/L, and the concentration of the sodium borohydride is 0.03 mol/L;
mixing the first solution and the second solution, and continuously stirring until the reaction is complete, wherein the mass ratio of isopropanolamine to alpha-hydroxypropionic acid is 1: 1;
and (3) placing the completely reacted system into a centrifuge tube for centrifugation, pouring out supernatant after the centrifugation is finished, and washing the supernatant with ethanol for three times to obtain the nano-silver particles.
Example 4
Dissolving silver nitrate in ethylene glycol, and performing ultrasonic treatment at 40 deg.C for 10min to dissolve silver nitrate completely; subsequently adding isopropanolamine into the silver nitrate-ethylene glycol solution to obtain a first solution; wherein the concentration of silver nitrate is 0.2mol/L, and the concentration of isopropanolamine is 4 mol/L;
dissolving alpha-hydroxypropionic acid in ethylene glycol, and then adding sodium borohydride into the alpha-hydroxypropionic acid-ethylene glycol solution to obtain a second solution; wherein the concentration of the alpha-hydroxypropionic acid is 4mol/L, and the concentration of the sodium borohydride is 0.1 mol/L;
mixing the first solution and the second solution, keeping the mass ratio of the isopropanolamine to the alpha-hydroxypropionic acid to be 1:0.5, and continuously stirring until the reaction is complete;
and (3) putting the completely reacted system into a centrifugal tube for centrifugation, pouring out supernatant after the centrifugation is finished, and washing the supernatant with ethanol for three times to obtain the nano-silver particles.
Example 5
Dissolving silver nitrate in ethylene glycol, and performing ultrasonic treatment at 40 deg.C for 10min to dissolve silver nitrate completely; subsequently adding isopropanolamine into the silver nitrate-ethylene glycol solution to obtain a first solution; wherein the concentration of silver nitrate is 0.2mol/L, and the concentration of isopropanolamine is 12 mol/L;
dissolving alpha-hydroxypropionic acid in ethylene glycol, and then adding sodium borohydride into the alpha-hydroxypropionic acid-ethylene glycol solution to obtain a second solution; wherein the concentration of the alpha-hydroxypropionic acid is 4mol/L, and the concentration of the sodium borohydride is 0.04 mol/L;
mixing the first solution and the second solution, keeping the mass ratio of the isopropanolamine to the alpha-hydroxypropionic acid to be 1:0.5, and continuously stirring until the reaction is complete;
and (3) putting the completely reacted system into a centrifugal tube for centrifugation, pouring out supernatant after the centrifugation is finished, and washing the supernatant with ethanol for three times to obtain the nano-silver particles.
Example 6
Dissolving silver nitrate in ethylene glycol, and performing ultrasonic treatment at 40 deg.C for 10min to dissolve silver nitrate completely; subsequently adding isopropanolamine into the silver nitrate-ethylene glycol solution to obtain a first solution; wherein the concentration of silver nitrate is 0.2mol/L, and the concentration of isopropanolamine is 8 mol/L;
dissolving alpha-hydroxypropionic acid in ethylene glycol, and then adding sodium borohydride into the alpha-hydroxypropionic acid-ethylene glycol solution to obtain a second solution; wherein the concentration of the alpha-hydroxypropionic acid is 8mol/L, and the concentration of the sodium borohydride is 0.1 mol/L;
mixing the first solution and the second solution, keeping the mass ratio of the isopropanolamine to the alpha-hydroxypropionic acid to be 1:0.5, and continuously stirring until the reaction is complete;
and (3) putting the completely reacted system into a centrifugal tube for centrifugation, pouring out supernatant after the centrifugation is finished, and washing the supernatant with ethanol for three times to obtain the nano-silver particles.
Example 7
Dissolving silver nitrate in ethylene glycol, and performing ultrasonic treatment at 40 deg.C for 10min to dissolve silver nitrate completely; subsequently adding isopropanolamine into the silver nitrate-ethylene glycol solution to obtain a first solution; wherein the concentration of silver nitrate is 0.2mol/L, and the concentration of isopropanolamine is 8 mol/L;
dissolving alpha-hydroxypropionic acid in ethylene glycol, and then adding sodium borohydride into the alpha-hydroxypropionic acid-ethylene glycol solution to obtain a second solution; wherein the concentration of the alpha-hydroxypropionic acid is 2mol/L, and the concentration of the sodium borohydride is 0.03 mol/L;
mixing the first solution and the second solution, keeping the mass ratio of the isopropanolamine to the alpha-hydroxypropionic acid to be 1:0.5, and continuously stirring until the reaction is complete;
and (3) putting the completely reacted system into a centrifugal tube for centrifugation, pouring out supernatant after the centrifugation is finished, and washing the supernatant with ethanol for three times to obtain the nano-silver particles.
Example 8
Dissolving silver trifluoroacetate in methanol, and performing ultrasonic treatment at 40 deg.C for 10min to dissolve silver trifluoroacetate; subsequently adding tert-butylamine to the silver trifluoroacetate-methanol solution to obtain a first solution; wherein the concentration of silver trifluoroacetate is 0.08mol/L, and the concentration of tert-butylamine is 10 mol/L;
dissolving glycolic acid in methanol, and adding sodium citrate to the glycolic acid-methanol solution to obtain a second solution; wherein the concentration of the glycollic acid is 4mol/L, and the concentration of the sodium citrate is 0.1 mol/L;
mixing the first solution and the second solution, and continuously stirring until the reaction is complete, wherein the mass ratio of the tert-butylamine to the glycollic acid is 1: 0.4;
and (3) putting the completely reacted system into a centrifugal tube for centrifugation, pouring out supernatant after the centrifugation is finished, and washing the supernatant for three times by using methanol to obtain the nano-silver particles.
Example 9
Dissolving silver trifluoromethanesulfonate in acetone, and performing ultrasonic treatment at 40 deg.C for 10min to dissolve the silver trifluoromethanesulfonate; subsequently, adding dipropylamine into the silver trifluoromethanesulfonate-acetone solution to obtain a first solution; wherein the concentration of the silver trifluoromethanesulfonate is 0.4mol/L, and the concentration of the dipropylamine is 3 mol/L;
dissolving succinic acid in acetone, and then adding hydrazine hydrate into the succinic acid-acetone solution to obtain a second solution; wherein the concentration of the succinic acid is 1.2mol/L, and the concentration of the hydrazine hydrate is 0.03 mol/L;
mixing the first solution and the second solution, and continuously stirring until the reaction is complete, wherein the mass ratio of the dipropylamine to the succinic acid is 1: 4;
and (3) putting the completely reacted system into a centrifugal tube for centrifugation, pouring out supernatant after the centrifugation is finished, and cleaning the supernatant for three times by using acetone to obtain the nano-silver particles.
Comparative example 1
Dissolving silver nitrate in ethylene glycol, and performing ultrasonic treatment at 40 deg.C for 10min to dissolve silver nitrate completely; subsequently adding isopropanolamine into the silver nitrate-ethylene glycol solution to obtain a first solution; wherein the concentration of silver nitrate is 0.12mol/L, and the concentration of isopropanolamine is 8 mol/L;
dissolving alpha-hydroxypropionic acid in ethylene glycol, and then adding sodium borohydride into the alpha-hydroxypropionic acid-ethylene glycol solution to obtain a second solution; wherein the concentration of the alpha-hydroxypropionic acid is 4mol/L, and the concentration of the sodium borohydride is 0.1 mol/L;
mixing the first solution and the second solution, keeping the mass ratio of the isopropanolamine to the alpha-hydroxypropionic acid to be 1:0.15, and continuously stirring until the reaction is complete;
and (3) putting the completely reacted system into a centrifugal tube for centrifugation, pouring out supernatant after the centrifugation is finished, and washing the supernatant with ethanol for three times to obtain the nano-silver particles.
Comparative example 2
Dissolving silver nitrate in ethylene glycol, and performing ultrasonic treatment at 40 deg.C for 10min to dissolve silver nitrate completely; subsequently adding isopropanolamine into the silver nitrate-ethylene glycol solution to obtain a first solution; wherein the concentration of silver nitrate is 0.2mol/L, and the concentration of isopropanolamine is 8 mol/L;
dissolving alpha-hydroxypropionic acid in ethylene glycol, and then adding sodium borohydride into the alpha-hydroxypropionic acid-ethylene glycol solution to obtain a second solution; wherein the concentration of the alpha-hydroxypropionic acid is 4mol/L, and the concentration of the sodium borohydride is 0.004 mol/L;
mixing the first solution and the second solution, keeping the mass ratio of the isopropanolamine to the alpha-hydroxypropionic acid to be 1:7, and continuously stirring until the reaction is complete;
and (3) putting the completely reacted system into a centrifugal tube for centrifugation, pouring out supernatant after the centrifugation is finished, and washing the supernatant with ethanol for three times to obtain the nano-silver particles.
2) Preparing and sintering nano silver paste:
the nano silver particles prepared in the above examples and comparative examples are directly mixed with terpineol and ethyl cellulose, and the nano silver particles prepared in examples 1 and 2 are mixed according to the nano silver particle quantity of 1:1 to obtain nano silver paste with the viscosity of 100-150 pas and the nano silver content of 50%, and then the nano silver paste is sintered at 260 ℃ and is kept for 30min, and the shear strength, the resistivity and the thermal conductivity are tested, wherein the test results are shown in table 1:
and (3) testing the shear strength: the shearing strength is applied to a silicon carbide power chip and a copper plate, the size of the chip is 18.5 multiplied by 0.375mm, a Ti/Ni/Ag metal layer is deposited on the surface of the chip in sequence, the size of the copper plate is 15 multiplied by 1mm, and a Ni/Au metal layer is deposited on the surface of the copper plate. After sintering by the process, a shear testing machine is adopted to test the shear strength and the push-type broach distance Al2O3Distance between plates0.1mm, speed 0.1 mm/s.
And (3) resistivity testing: and coating a layer of nano silver paste with the thickness of 0.1mm on the ceramic substrate, and measuring the resistivity of the sintered silver film by using a four-probe tester after sintering by using the process.
And (3) testing thermal conductivity: and (3) manufacturing a mould according to the size requirement of the laser thermal conductivity instrument sample piece, pouring the nano silver paste into the mould, sintering by using the process, and measuring the thermal conductivity by using the laser thermal conductivity instrument.
TABLE 1
As can be seen from the attached drawings of the specification, in example 1, when the dosage ratio of the organic amine to the organic acid is 1:0.5, the reduction reaction speed is high, and the nano silver particles with the particle size mainly distributed between 10nm and 30nm and round particles can be prepared as shown in fig. 1; in example 2, when the dosage ratio of organic amine to organic acid is 1:2, the reduction reaction speed is slow, and the nano silver particles with the particle size mainly distributed between 160nm and 330nm and round particles can be prepared as shown in fig. 2; in example 3, when the amount ratio of the organic amine to the organic acid is 1:1, the reduction reaction rate is moderate, and the nano silver particles with the particle size mainly distributed between 30nm and 160nm as shown in fig. 2 can be prepared, but because the translation of the generated amide is equivalent to the reduction reaction rate of the silver ions and lacks of selectivity, silver particles with too large particle size or too small particle size are mixed, and the particle size distribution is wide.
As can be seen from table 1, in examples 1 and 2, the silver particles have uniform particle size, narrow distribution, smooth particle morphology, dense and ordered arrangement, so that the sintered silver particles have excellent shear strength, electrical conductivity and thermal conductivity; in the embodiment 3, because the silver particles with large particle size and small particle size exist at the same time, the small silver particles can fill gaps among large particles after sintering, so that the silver particles have better performance than the silver particles in the embodiments 1 and 2 with concentrated particle size distribution; however, due to the lack of selectivity in the reaction process, although the ratio of amine to acid is 1:1, large and small particles do not achieve a 1:1, and therefore, the performance of the silver paste is slightly inferior to that of the silver paste prepared in the mixed examples 1 and 2 by sintering the silver paste prepared by compounding the silver particles prepared in the examples 1 and 2 according to the calculated number ratio of the particles with the size of 1:1 strictly; in examples 4 to 7, the concentration of the organic amine or the organic acid is not in the preferred range, and compared with example 1 in the preferred range, the reaction process is not as stable as in example 1, so the particle size distribution of the prepared nano silver particles is not as narrow as in example 1, the shapes are mixed, the arrangement after sintering is not dense and ordered enough, and the performance of the sintered nano silver particles is reduced; in example 8, the ratio of organic amine to organic acid is slightly larger, so that the particles are too fine, the produced amide is not enough to disperse the particles thoroughly, and therefore, the performance after sintering is greatly reduced compared with the examples with the ratio in the preferred range, but the performance is still at a higher level on the whole, and the practical production requirement is met; in example 9, the ratio of organic amine to organic acid is slightly small, resulting in too slow reduction reaction, and a small amount of silver ions are not reduced, and therefore the properties after sintering are not as good as in the example where the ratio is in the preferred range. In comparative example 1, the ratio of organic amine to organic acid was too large, the agglomeration of silver particles was very severe, and the performance after sintering was severely reduced; in comparative example 2, the ratio of organic amine to organic acid was too small, which largely hampered the reduction reaction, and in the case of the same amount of silver particles, the number of silver particles obtained was small and the particle size distribution was not uniform, which resulted in a severe decrease in the performance after sintering.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that various changes and modifications can be made by those skilled in the art without departing from the spirit of the invention, and these changes and modifications are all within the scope of the invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims, and the description and the drawings can be used for explaining the contents of the claims.
Claims (14)
1. A preparation method of nano silver particles for preparing a welding joint is characterized by comprising the following steps:
a) mixing a silver salt, organic amine and a first solvent to obtain a first solution, wherein the number of carbon atoms of a main chain of the organic amine is less than or equal to 6;
b) mixing an organic acid, a reducing agent and a second solvent to obtain a second solution, wherein the number of carbon atoms of a main chain of the organic acid is less than or equal to 6;
c) mixing the first solution and the second solution, and controlling the amount ratio of the organic amine to the organic acid to be 1: (0.6-1.9), carrying out solid-liquid separation after the reaction is completed;
the particle size distribution of the nano-silver particles is within the range of 30 nm-160 nm, large-particle nano-silver and small-particle nano-silver exist at the same time, and the small-particle nano-silver can fill gaps among the large-particle nano-silver.
2. The method of claim 1, wherein the organic amine is one or more of isopropanolamine, diethanolamine, dipropylamine, tert-butylamine, and acetamide.
3. The method for preparing nano silver particles according to claim 2, wherein the concentration of the organic amine in the first solution is 3mol/L to 15 mol/L.
4. The method of claim 1, wherein the organic acid is one or more of butyric acid, glycolic acid, α -hydroxypropionic acid, succinic acid, and glutaric acid.
5. The method for preparing nano silver particles according to claim 4, wherein the concentration of the organic acid in the second solution is 0.6-10 mol/L.
6. The method for preparing nano silver particles according to claim 1, wherein the silver salt is one or more of silver nitrate, silver sulfate, silver tetrafluoroborate, silver triflate and silver trifluoroacetate.
7. The method of claim 6, wherein the concentration of the silver salt in the first solution is 0.01mol/L to 0.5 mol/L.
8. The method for preparing nano-silver particles according to claim 6, wherein the reducing agent is one or more of sodium borohydride, formaldehyde, sodium citrate and hydrazine hydrate.
9. The method of preparing nano silver particles according to claim 8, wherein the concentration of the reducing agent in the second solution is 0.001 to 0.1 mol/L.
10. The method for preparing nano-silver particles according to any one of claims 1 to 9, wherein the first solvent and the second solvent are each independently selected from one or more of methanol, ethanol, ethylene glycol, glycerol, butanol, n-pentanol, benzene, toluene, xylene, acetone, n-hexane, and cyclohexane.
11. A nano silver particle produced by the production method according to any one of claims 1 to 10.
12. A nano silver paste, comprising the nano silver particles of claim 11.
13. The nano silver paste of claim 12, wherein the nano silver paste comprises 30-80% by mass of the nano silver particles.
14. A solder joint formed by sintering the nano silver paste of claim 12 or 13.
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