Low temperature sinterable silver powder and method for making same

Abstract

The application provides a low-temperature sinterable silver powder and a preparation method thereof, and belongs to the technical field of metal powder preparation. The preparation method comprises the following steps: adding a pH regulator solution into a silver nitrate solution, adjusting the pH of the solution to 9-12, then adding an ammonia water solution, then adding a dispersant, finally quickly pouring a reducing agent solution, and after the reaction is completed, washing with deionized water and ethanol, and drying to obtain a nano silver powder. Through the above method, the silver powder with a particle size of 100-500nm can be prepared in a simple process, the surface morphology of the silver powder is smooth, the powder size is uniform, the dispersibility is good, the tap density can reach 4.8-5.3g / cm 3 , and the dispersibility in an organic system is good, the powder is not aggregated, and low-temperature sintering can be realized at 140 DEG C. The prepared silver powder is suitable for the fields of solar photovoltaic positive electrode silver paste and electronic paste.

Description

Technical Field

[0001] This application relates to the field of metal powder preparation technology, specifically to a low-temperature sinterable silver powder and its preparation method. Background Technology

[0002] In the field of electronic packaging, nano-silver paste stands out with its unique "low-temperature sintering, high-temperature service" characteristics, becoming the preferred material for the packaging and interconnection of high-power electronic devices. By nano-sizing silver particles, the surface energy surges, allowing sintering temperatures as low as 130°C, while the resulting dense structure can withstand temperatures approaching 1000°C. This property perfectly solves the temperature gradient problem in multi-level assembly, clearing obstacles for cutting-edge technologies such as 3D chip stacking.

[0003] Patent application CN 113399678 A discloses a low-cost, highly dispersed ultrafine silver powder preparation method, but its production process is complex and time-consuming, making it unsuitable for industrial production. Furthermore, this preparation method requires grinding and dispersing the silver powder using a ball mill, resulting in a wide particle size distribution, with individual particle sizes ranging from 100-500 nm and an average particle size of 0.3-1.0 μm, and poor low-temperature sintering performance.

[0004] In view of this, it is necessary to design a low-temperature sinterable silver powder and its preparation method to solve the above problems. Summary of the Invention

[0005] In view of the technical problems existing in the background art, this application provides a low-temperature sinterable silver powder and its preparation method. The preparation method can control the particle size by adjusting the concentration of pH adjuster and ammonia water, so as to achieve the preparation of low-temperature sinterable silver powder with a particle size of 100-500nm. In addition, the preparation method adopts a rapid mixing method, the process preparation time is short, and continuous production can be realized. The raw materials used in this application are non-toxic and non-polluting, and environmentally friendly. The process has high stability and can realize the large-scale production of silver powder.

[0006] In a first aspect, embodiments of this application provide a method for preparing silver powder that can be sintered at low temperatures, the specific steps of which are as follows:

[0007] S1, under stirring conditions, add the pH adjuster solution to the silver nitrate solution to adjust the pH of the solution to 9-12, then add the ammonia solution, then add the dispersant, and finally quickly pour in the reducing agent solution. The reaction temperature throughout the process is 45-55℃.

[0008] S2, after all the reducing agent solution is added, stir the reaction for 1-10 minutes, stop stirring, let it stand and settle, then remove the supernatant, collect the settled silver powder, wash, dry, and polish the silver powder to obtain silver powder that can be sintered at low temperature, the particle size of the silver powder being between 100-500 nm.

[0009] In some embodiments, in step S1, the concentration of the ammonia solution is 8-11 mol / L, and the mass ratio of ammonia to silver nitrate is (1.35-2.25):1.

[0010] In some embodiments, in step S1, the concentration of the silver nitrate solution is 0.05-0.10 mol / L.

[0011] In some embodiments, the pH adjuster is one of sodium hydroxide, sodium bicarbonate, and sodium carbonate.

[0012] In some embodiments, the pH adjuster is sodium carbonate, and the molar ratio of sodium carbonate to silver nitrate is (10-20):1.

[0013] In some embodiments, the reducing agent is hydrazine hydrate, hydrazine carbonate, hydrazine sulfate, hydrazine monohydrochloride, or hydrazine dihydrochloride; the molar ratio of the reducing agent to silver nitrate is (2-5):1.

[0014] In some embodiments, the dispersant is one or more of methylcellulose, ethylcellulose, polyvinylpyrrolidone, dodecylamine, hexadecylamine, octadecylamine, oleylamine, stearic acid, 12-hydroxystearic acid, lauric acid, ricinoleic acid, and shellac acid.

[0015] In some embodiments, the mass of the dispersant is 0.3-1.0 wt% of the silver content in the silver nitrate solution.

[0016] In some embodiments, in step S1, the stirring speed is 500-700 rpm / min.

[0017] Secondly, embodiments of this application provide a low-temperature sinterable silver powder, which is prepared according to any of the foregoing technical solutions. The sintering temperature of the low-temperature sinterable silver powder is 140℃, and the tap density is 4.8-5.3 g / cm³. 3 .

[0018] The beneficial effects of this application are:

[0019] This application provides a method for preparing low-temperature sinterable silver powder. This method controls the size of silver powder particles by adjusting the pH using a pH adjuster and simultaneously controlling the ammonia concentration. It eliminates the need for pre-preparing a seed solution and uses silver nitrate solution directly as the reaction substrate. It also eliminates the need for secondary surface coating treatment, reducing time and raw material costs. Furthermore, this method employs a rapid pouring method, resulting in fast reaction speed, short process preparation time, and the ability to achieve continuous production. The raw materials used in this invention are non-toxic and non-polluting, making it environmentally friendly. The process exhibits high stability and enables large-scale production of this type of silver powder.

[0020] The low-temperature sinterable silver powder prepared in this application has a particle size in the range of 100-500 nm, a smooth surface morphology, uniform powder size, narrow particle size distribution, good dispersibility, and a high tap density of 4.8~5.3 g / cm³. 3 It exhibits good dispersibility in organic systems, does not agglomerate, and can be sintered at a low temperature of 140℃.

[0021] The micro / nano silver powder prepared in this application is suitable for use in solar photovoltaic cathode silver paste and electronic paste fields.

[0022] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0024] Figure 1 SEM image of the low-temperature sinterable silver powder prepared in Example 1.

[0025] Figure 2 SEM image of the low-temperature sinterable silver powder prepared in Example 2.

[0026] Figure 3 SEM image of the low-temperature sinterable silver powder prepared in Example 3.

[0027] Figure 4 The image shows the SEM image of the silver powder prepared in Example 3 after sintering at 140°C.

[0028] Figure 5 The image shows a SEM image of the silver powder prepared in Comparative Example 1.

[0029] Figure 6 The image shows the SEM image of the silver powder prepared in Comparative Example 2.

[0030] Figure 7 The image shows the SEM image of the silver powder prepared in Comparative Example 3.

[0031] Figure 8 The image shows the SEM image of the silver powder prepared in Comparative Example 4.

[0032] Figure 9 The image shows a SEM image of the silver powder prepared in Comparative Example 5.

[0033] Figure 10 The image shows a SEM image of the silver powder prepared in Comparative Example 6.

[0034] Figure 11 The image shows the SEM image of the silver powder prepared in Comparative Example 7.

[0035] Figure 12 This is a SEM image of the silver powder prepared in Comparative Example 7 after one day of storage.

[0036] Figure 13 SEM image of the low-temperature sinterable silver powder prepared in Example 6.

[0037] Figure 14 The image shows the SEM image of the silver powder prepared in Comparative Example 8.

[0038] Figure 15 The image shows the SEM image of the silver powder prepared in Comparative Example 9. Detailed Implementation

[0039] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0040] Unless otherwise defined, 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 application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0041] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0042] In the description of the embodiments of this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0043] In a first aspect, embodiments of this application provide a method for preparing silver powder that can be sintered at low temperatures, the specific steps of which are as follows:

[0044] S1, under stirring conditions, add the pH adjuster solution to the silver nitrate solution to adjust the pH of the solution to 9-12, then add the ammonia solution, then add the dispersant, and finally pour the reducing agent solution directly and quickly. The reaction temperature throughout the process is 45-55℃; direct and quick pouring means that the reducing agent solution is completely added within 5 seconds.

[0045] The concentration of the silver nitrate solution is 0.05-0.10 mol / L.

[0046] The pH adjuster is one of sodium hydroxide, sodium bicarbonate, or sodium carbonate. Sodium carbonate is preferred, and the molar ratio of sodium carbonate to silver nitrate is (10-20):1.

[0047] The concentration of the ammonia solution is 8-11 mol / L, and the mass ratio of ammonia to silver nitrate is (1.35-2.25):1.

[0048] The reducing agent is hydrazine hydrate, hydrazine carbonate, hydrazine sulfate, hydrazine monohydrochloride, or hydrazine dihydrochloride; the molar ratio of the reducing agent to silver nitrate is (2-5):1.

[0049] The dispersant is one or more of the following: methylcellulose, ethylcellulose, polyvinylpyrrolidone, dodecylamine, hexadecylamine, octadecylamine, oleylamine, stearic acid, 12-hydroxystearic acid, lauric acid, ricinoleic acid, and shellac acid.

[0050] The mass of the dispersant is 0.3-1.0 wt% of the silver content in the silver nitrate solution.

[0051] The stirring speed is 500-700 rpm / min.

[0052] S2, after all the reducing agent solution is added, stir the reaction for 1-10 minutes, stop stirring, let it stand and settle, then remove the supernatant, collect the settled silver powder, wash, dry, and polish the silver powder to obtain silver powder that can be sintered at low temperature. The particle size of the silver powder is between 100-500 nm.

[0053] Secondly, this application also provides a low-temperature sinterable silver powder, which is prepared by the preparation method described in any of the foregoing technical solutions. The sintering temperature of the low-temperature sinterable silver powder is 140℃, and the tap density is 4.8-5.3 g / cm³. 3 .

[0054] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0055] Example 1

[0056] Example 1 provides a method for preparing low-temperature sinterable silver powder, comprising the following steps:

[0057] S1, prepare pH adjustment solution, silver nitrate solution, ammonia solution, dispersant solution and reducing agent solution respectively;

[0058] Prepare pH adjustment solution: Prepare 50 ml of 1.5 mol / L sodium carbonate solution;

[0059] Preparation of silver nitrate solution: Prepare 2.5 L of 0.085 mol / L silver nitrate solution;

[0060] Prepare an ammonia solution: Prepare 70 ml of an 8.6 mol / L ammonia solution;

[0061] Preparation of reducing agent solution: Prepare 250 ml of 0.315 mol / L hydrazine carbonate solution;

[0062] Preparation of dispersant solution: Prepare 10 ml of 0.238 mol / L stearic acid solution.

[0063] Under stirring conditions, 15 ml of pH adjuster solution was added to 2.5 L of silver nitrate solution to adjust the pH to 9.02. Then, 70 ml of ammonia solution was added, followed by 10 ml of dispersant. Finally, 250 ml of reducing agent was poured in directly and quickly. The reaction temperature was 48℃ throughout the process, and the stirring speed was 600 rpm / min. That is, the mass ratio of ammonia solution to silver nitrate was 1.5:1.

[0064] S2, after all the reducing agent solution is added, stir for 2 minutes, stop stirring, let stand and settle, then remove the supernatant, collect the settled silver powder, wash the silver powder with deionized water and ethanol, dry, and polish to obtain silver powder that can be sintered at low temperature.

[0065] SEM image of the low-temperature sinterable silver powder prepared in Example 1 is shown below. Figure 1 As shown, the particle size range of silver powder is approximately 300-400 nm.

[0066] The particle size and tap density data of the silver powder prepared in Example 1 are shown in Table 2.

[0067] Example 2

[0068] The difference between Example 2 and Example 1 is that 70 ml of 8.6 mol / L ammonia solution is replaced with 75 ml of 10 mol / L ammonia solution; that is, the mass ratio of ammonia to silver nitrate is 1.875:1; other contents are roughly the same as in Example 1, and will not be repeated here.

[0069] SEM image of the low-temperature sinterable silver powder prepared in Example 2 is shown below. Figure 2 As shown, the particle size range of silver powder is approximately 200-300 nm.

[0070] The particle size and tap density data of the silver powder prepared in Example 2 are shown in Table 2.

[0071] Example 3

[0072] Example 3 provides a method for preparing low-temperature sinterable silver powder, which is a scaled-up experiment based on Example 1, and includes the following steps:

[0073] S1, prepare pH adjustment solution, silver nitrate solution, ammonia solution, dispersant solution and reducing agent solution respectively;

[0074] Prepare pH adjustment solution: Prepare 560 ml of 1.5 mol / L sodium carbonate solution;

[0075] Preparation of silver nitrate solution: Prepare 104 L of 0.085 mol / L silver nitrate solution;

[0076] Preparation of ammonia solution: Prepare 3.1 L of 8.6 mol / L ammonia solution;

[0077] Preparation of reducing agent solution: Prepare 10.4 L of 0.315 mol / L hydrazine carbonate solution;

[0078] Preparation of dispersant solution: Prepare 420 ml of 0.238 mol / L stearic acid solution.

[0079] Under stirring conditions, 560 ml of pH adjuster solution was added to 104 L of silver nitrate solution to adjust the pH to 9.1. Then, 3.1 L of ammonia solution was added, followed by 420 ml of dispersant. Finally, 10.4 L of reducing agent was rapidly poured in. The entire reaction was carried out at a temperature of 48°C and a stirring speed of 600 rpm / min. That is, the mass ratio of ammonia solution to silver nitrate was 1.6:1.

[0080] After adding all of the reducing agent solution (S2), stir for 5 minutes, stop stirring, let stand and settle, then remove the supernatant, collect the settled silver powder, wash the silver powder with deionized water and ethanol, dry, and polish to obtain silver powder that can be sintered at low temperature.

[0081] SEM image of the low-temperature sinterable silver powder prepared in Example 3 is shown below. Figure 3 As shown, the particle size range of silver powder is approximately 300-400 nm.

[0082] The particle size and tap density data of the silver powder prepared in Example 3 are shown in Table 2.

[0083] SEM image of the silver powder prepared in Example 3 after sintering at 140℃ is shown below. Figure 4 As shown, silver powder can be sintered at a low temperature of 140℃.

[0084] Comparative Example 1

[0085] The difference between Comparative Example 1 and Example 1 is that the reducing agent was added by a peristaltic pump instead of by rapid pouring, with a dripping rate of 50 ml / min. Other aspects are largely the same as in Example 1 and will not be repeated here.

[0086] SEM image of the silver powder prepared in Comparative Example 1 is shown below. Figure 5 As shown.

[0087] As can be seen, the prepared silver powder particles are uneven in size and have poor morphology. The reason is that the reaction between silver nitrate and hydrazine carbonate is an instantaneous reaction. When it is first added dropwise, the solution is alkaline, and the grown particles are small. During the dropwise addition and reaction process, nitric acid is gradually generated, and the pH of the solution decreases, so large particles are formed. Therefore, in this reaction process, the reducing agent solution needs to be quickly added to the silver nitrate solution to ensure that the reaction takes place in a homogeneous system and improve the uniformity of particle size.

[0088] Examples 4-5

[0089] The difference between Examples 4-5 and Example 1 is that the mass ratio of ammonia to silver nitrate, the concentration of silver nitrate solution, and the amount of hydrazine carbonate were changed. In Example 4, the amount of hydrazine carbonate was 147 ml, and in Example 5, the amount of hydrazine carbonate was 295 ml, as shown in Table 1. Other contents are roughly the same as in Example 1, and will not be repeated here.

[0090] Comparative Examples 2-3

[0091] The difference between Comparative Examples 2-3 and Example 1 is that the mass ratio of ammonia to silver nitrate and the concentration of silver nitrate solution were changed, as shown in Table 1; the other contents are roughly the same as those in Example 1, and will not be repeated here.

[0092] Comparative Example 4

[0093] The difference between Comparative Example 4 and Example 1 is that 2.5 L of 0.085 mol / L silver nitrate solution was replaced with 708 ml of 0.30 mol / L silver nitrate solution. The other contents are roughly the same as those in Example 1, and will not be repeated here.

[0094] Table 1 Summary of process parameters for Examples 1-2, Examples 4-5 and Comparative Examples 2-4

[0095]

[0096] SEM image of the silver powder prepared in Comparative Example 2 is shown below. Figure 6 As shown, the silver powder has low sphericity, insufficient particle dispersion, and irregular morphology.

[0097] SEM image of the silver powder prepared in Comparative Example 3 is shown below. Figure 7 As shown, the silver powder particle size is uneven; in addition, the high concentration of ammonia affects the reducing power of hydrazine carbonate, resulting in incomplete reduction of silver nitrate during the reaction process, which seriously affects the yield of silver powder.

[0098] It is evident that the mass ratio of ammonia water to silver nitrate, as a complexing agent, is crucial to the morphological reducing properties of silver powder.

[0099] SEM image of the silver powder prepared in Comparative Example 4 is shown below. Figure 8 As shown.

[0100] As can be seen, the silver powder prepared in Comparative Example 4 has low sphericity, large particle size, and severe agglomeration. This is because the silver nitrate concentration is too high, increasing the number of nuclei and causing the growth rate to exceed the nucleation rate, leading to particle aggregation and growth.

[0101] Table 2. Properties of the silver powders prepared in Examples 1-5

[0102]

[0103] Comparative Example 5

[0104] The difference between Comparative Example 5 and Example 1 is that no pH adjuster was used. Otherwise, the contents are largely the same as those in Example 1 and will not be repeated here.

[0105] SEM image of the silver powder prepared in Comparative Example 5 is shown below. Figure 9 As shown, the particle size is uneven and the powder dispersion is poor.

[0106] Comparative Example 6

[0107] The difference between Comparative Example 6 and Example 1 is that ammonia solution was not used. Other contents are roughly the same as Example 1, and will not be repeated here.

[0108] SEM image of the silver powder prepared in Comparative Example 6 is shown below. Figure 10 As shown, the silver powder particles are small in size and exhibit significant agglomeration.

[0109] Comparative Example 7

[0110] The difference between Comparative Example 7 and Example 1 is that no dispersant was added. The other contents are roughly the same as those in Example 1, and will not be repeated here.

[0111] The SEM image of the silver powder prepared in Comparative Example 7 is shown below. Figure 11 As shown in Figure 12, the SEM image of the silver powder after one day of storage is shown in Figure 12.

[0112] As can be seen, the freshly prepared silver powder has good morphology, dispersibility, and particle size uniformity. After being left for one day, the morphology of the silver powder changes, such as... Figure 12 As shown. This is mainly because no dispersant was added during the preparation process to coat the silver particles, which may cause irregular secondary growth of the particles, thus resulting in a significant change in morphology.

[0113] Example 6 and Comparative Examples 8-9

[0114] The difference between Examples 6 and Comparative Examples 8-9 and Example 1 is that the type of reducing agent was changed. The other contents are roughly the same as Example 1, and will not be repeated here.

[0115] Table 3

[0116]

[0117] Experiments show that silver powder with the same high tap density as in Example 1 can also be prepared using hydrazine hydrate. Figure 13 As shown; silver powder prepared using ascorbic acid as a reducing agent exhibits poor particle size uniformity and insufficient dispersion, such as Figure 14 As shown, the poor particle size uniformity may be due to the weak reducing power and slow reduction rate of ascorbic acid, which cannot be reduced instantaneously. Silver powder prepared using sodium borohydride as a reducing agent has a smaller particle size, such as... Figure 15 As shown, this may be because sodium borohydride has a stronger reducing power than hydrazine, resulting in a faster reduction rate and explosive nucleation followed by growth, leading to excessively small powder particle size and poor dispersibility.

[0118] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for producing a low temperature sinterable silver powder, characterized by, The method comprises the following steps: S1, under stirring, a pH regulator solution is added to a silver nitrate solution, the pH of the solution is adjusted to 9-12, then an ammonia solution is added, then a dispersant is added, and finally a reducing agent solution is quickly poured in, the whole reaction temperature being 45-55℃; wherein the mass ratio of ammonia to silver nitrate is (1.35-2.25):1; the reducing agent is hydrazine hydrate, carbonic acid, hydrazine sulfate, monohydrochloric acid hydrazine or dihydrochloric acid hydrazine; the pH regulator is sodium carbonate, the molar ratio of sodium carbonate to silver nitrate being (10-20):1; S2, after the reducing agent solution is added completely, stirring the reaction for 1-10 minutes, stopping the stirring, standing and settling, then removing the supernatant, collecting the settled silver powder, washing, drying and polishing the silver powder, so that the low-temperature sinterable silver powder is obtained, the particle size of the silver powder is between 100-500 nm, the sintering temperature is 140℃, and the tap density is 4.8-5.3 g / cm 3 .

2. The process for the production of a low temperature sinterable silver powder according to claim 1, characterized in that In step S1, the concentration of the ammonia solution is 8-11 mol / L.

3. The method of producing a low temperature sinterable silver powder according to claim 1, characterized by, In step S1, the concentration of the silver nitrate solution is 0.05-0.10 mol / L.

4. The method of producing a low temperature sinterable silver powder according to claim 1, characterized by, The molar ratio of the reducing agent to silver nitrate is (2-5):

1.

5. The method of producing a low temperature sinterable silver powder according to claim 1, characterized by, The dispersant is one or a mixture of more than one of methyl cellulose, ethyl cellulose, polyvinyl pyrrolidone, dodecylamine, hexadecylamine, octadecylamine, oleylamine, stearic acid, 12-hydroxystearic acid, lauric acid, ricinoleic acid and aleuritic acid.

6. The method of producing a low temperature sinterable silver powder according to claim 1, characterized by, The mass of the dispersant is 0.3-1.0 wt% of the silver content in the silver nitrate solution.

7. The method of producing a low temperature sinterable silver powder according to claim 1, characterized by, In step S1, the stirring speed is 500-700 rpm / min.

8. A low temperature sinterable silver powder, characterized in that The low-temperature sinterable silver powder is prepared according to the method for preparing the low-temperature sinterable silver powder of any one of claims 1-7.

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