A silver powder for medium-temperature curing conductive adhesive and its preparation method

Abstract

This invention discloses a silver powder for medium-temperature curing conductive adhesives and its preparation method, belonging to the technical field of conductive adhesive silver powder filler. The preparation method includes: preparing a 0.65–1.5 M sulfate solution and a 1.70–2.70 M silver nitrate solution; adding 30–37% by volume of the sulfate solution and an organic acid to a reaction vessel, stirring, and controlling the temperature at 15–85°C; while stirring, simultaneously adding the silver nitrate solution and the remaining 63–70% by volume of the sulfate solution dropwise into the reaction vessel, continuing stirring for 7–20 minutes, followed by separation, washing, surface modification, and drying to obtain the silver powder for medium-temperature curing conductive adhesives. The silver powder for medium-temperature curing conductive adhesives prepared by this invention has good dispersibility, high ball-sheet matching rate, and does not require ball milling; it can be directly formulated into a slurry for medium-temperature conductive adhesives.

Description

Technical Field

[0001] This invention belongs to the technical field of conductive adhesive silver powder filler, and particularly relates to a silver powder for medium-temperature curing conductive adhesive and its preparation method. Background Technology

[0002] Silver powder is a key material for conductive adhesives, and its morphology, particle size, and tap density all affect the adhesive's performance. Currently, silver powder fillers for conductive adhesives are mainly prepared by ball milling. Compared to the direct liquid-phase reduction method, ball milling is not only a longer process and more energy-intensive, but also has a relatively lower silver powder recovery rate. Furthermore, the work hardening that inevitably occurs during ball milling limits the applicability of silver powder. To ensure the filling properties of silver powder, nano-silver powder or spherical silver powder is often added during use, which increases the cost of the conductive adhesive to some extent.

[0003] Existing technology uses hydrazine hydrate as a reducing agent, and employs a reverse feeding method to dropwise add hydrazine hydrate to a silver nitrate solution whose pH has been adjusted with alkali. The resulting ultrafine silver powder for low-temperature conductive adhesives has a suitable particle size distribution, but it has a large surface energy and is prone to hard agglomeration. The silver powder is difficult to break up in post-processing, and direct preparation into a paste for printing is prone to grid breakage. At the same time, hydrazine hydrate has a very strong reducing property and is a potentially explosive reagent. Improper handling of excessive hydrazine hydrate poses a significant safety hazard to production. Furthermore, using excessive amounts of hydrazine hydrate with an irritating odor as a reducing agent in an open system is not conducive to industrial production. Summary of the Invention

[0004] One of the objectives of this invention is to provide a method for preparing silver powder for medium-temperature curing conductive adhesives. The silver powder prepared by this method has good dispersibility, high ball-sheet matching rate, and can be directly formulated into a slurry for medium-temperature conductive adhesives without the need for ball milling.

[0005] The second objective of this invention is to provide a silver powder for medium-temperature curing conductive adhesive.

[0006] To achieve one of the above objectives, the present invention employs the following technical solution:

[0007] A method for preparing silver powder for medium-temperature curing conductive adhesive, the method comprising the following steps:

[0008] Step S1: Prepare a 0.65–1.5 M sulfate solution and a 1.70–2.70 M silver nitrate solution;

[0009] The volume ratio of the sulfate solution to the silver nitrate solution is 1.5 to 3:1;

[0010] Step S2: Add 30-37% by volume of sulfate solution and organic acid to the reaction vessel, stir and control the temperature at 15-85℃;

[0011] The mass ratio of silver nitrate to organic acid in the silver nitrate solution is 100:1-5;

[0012] Step S3: While stirring, add silver nitrate solution and the remaining 63-70% by volume of sulfate solution dropwise into the reaction vessel, continue stirring for 7-20 minutes, then separate, wash, surface modify and dry to obtain silver powder for medium-temperature curing conductive adhesive.

[0013] This invention utilizes SO4 in sulfate solution 2- The strong bonding ability of the silver crystal nucleus [1,1,0] crystal facet is utilized by organic acids to make the grains grow along the two-dimensional plane, thereby obtaining hexagonal plate-shaped silver powder. In the later stage of reduction, the reduction motive force is insufficient, and the newly generated silver particles cannot be deposited on the plate-shaped silver powder. Instead, they preferentially grow through collision and aggregation to produce nano- and submicron spherical silver powder.

[0014] Furthermore, in step S1, the volume ratio of the sulfate solution to the silver nitrate solution is 2 to 2.5:1.

[0015] Furthermore, in step S1, the organic acid is one or a mixture of two or more of succinic acid, tartaric acid, citric acid and adipic acid.

[0016] The sulfate solution is one or a mixture of two or more of the following: ferrous ammonium sulfate solution, ferrous sulfate solution, and hydroxylamine sulfate solution.

[0017] Furthermore, in step S2, the temperature is 30–60°C.

[0018] Furthermore, in step S3, the dropping rate of the silver nitrate solution is 60–100 ml / min;

[0019] The sulfate solution is added at a rate of 50–70 ml / min.

[0020] Furthermore, in step S3, the silver nitrate solution is added by inserting a conduit along the wall of the reaction vessel below the liquid level.

[0021] The sulfate solution is added dropwise by maintaining the liquid level above the level by a conduit along the wall of the reactor.

[0022] Furthermore, in step S3, hexadecanoic acid is used for surface modification;

[0023] The mass ratio of silver nitrate to hexadecanoic acid in the silver nitrate solution is 100:0.2-0.3.

[0024] To achieve the second objective mentioned above, the present invention employs the following technical solution:

[0025] A silver powder for medium-temperature curing conductive adhesive, wherein the silver powder for medium-temperature curing conductive adhesive is prepared by the preparation method described above.

[0026] Furthermore, the silver powder used in the medium-temperature curing conductive adhesive is a spherical composite silver powder;

[0027] The spherical composite silver powder includes micron-sized flake silver powder, nano-sized spherical silver powder, and submicron-sized spherical silver powder.

[0028] Furthermore, the silver powder used in the medium-temperature curing conductive adhesive has an average particle size of 1.22–3.52 μm and a tap density of 2.4–2.8 g / cm³. 3 .

[0029] In summary, the technical solution of the present invention has the following beneficial effects:

[0030] This invention uses an odorless, mildly reducing sulfate solution as a reducing agent and a silver nitrate solution as an oxidizing agent. Under the dispersion effect of organic acids, a composite silver powder consisting of micron-sized flake silver powder, nano-sized spherical silver powder, and submicron-sized spherical silver powder can be prepared simultaneously. It exhibits good dispersibility, high spherical-to-flake ratio, and eliminates the need for ball milling, allowing direct preparation into a medium-temperature conductive adhesive slurry. This invention is simple to operate, uses readily available raw materials, saves energy, and has low production costs. The byproducts of this invention are water-soluble ferric sulfate and ferric nitrate, reducing wastewater treatment difficulty and making it suitable for industrial production. The composite silver powder can be directly washed using cake filtration, preventing the micro- and nano-sized silver powder from "passing through the filter," thus minimizing equipment requirements. The composite silver powder is suitable for medium-temperature curing conductive adhesives, exhibiting high conductivity, good thixotropy, and high shear strength. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1:

[0033] S1. Prepare a 0.90M ferrous ammonium sulfate solution and a 2.00M silver nitrate solution, respectively. The volume ratio of the ferrous ammonium sulfate solution to the silver nitrate solution is 2:1.

[0034] S2. Add 33% (30-37%) volume of ferrous ammonium sulfate solution and succinic acid as the base solution to the reaction vessel, start stirring and maintain the temperature of the base solution at 45°C. The mass ratio of silver nitrate to succinic acid in the silver nitrate solution is 100:1.5.

[0035] S3. Under stirring, silver nitrate solution and the remaining 67% volume of ferrous ammonium sulfate solution are simultaneously dripped into the reaction vessel using a peristaltic pump. Stirring is continued for 7 minutes. After separation and washing, the surface is modified with hexadecanoic acid and then dried to obtain silver powder for medium-temperature curing conductive adhesive.

[0036] The silver nitrate solution was added by inserting a conduit along the wall of the reaction vessel below the liquid level, while the ferrous ammonium sulfate solution was added by maintaining the conduit above the liquid level along the wall of the reaction vessel. The dropping rate of the silver nitrate solution was 80 ml / min, and the dropping rate of the ferrous ammonium sulfate solution was 70 ml / min. The mass ratio of hexadecanoic acid to silver nitrate in the silver nitrate solution was 0.2:100.

[0037] The silver powder used in the medium-temperature curing conductive adhesive of this embodiment has an average particle size of 1.72 μm and a tap density of 2.8 g / cm³. 3 .

[0038] Example 2:

[0039] S1. Prepare 1.5M ferrous sulfate solution and 1.75M silver nitrate solution respectively. The volume ratio of ferrous sulfate solution to silver nitrate solution is 2.5:1.

[0040] S2. Add 30% by volume of ferrous sulfate solution and tartaric acid as the base solution to the reaction vessel, start stirring and maintain the temperature of the base solution at 15°C. The mass ratio of silver nitrate to tartaric acid in the silver nitrate solution is 100:3.

[0041] S3. Under stirring, silver nitrate solution and the remaining 70% volume of ferrous sulfate solution are simultaneously dripped into the reaction vessel using a peristaltic pump. Stirring is continued for 20 minutes. After separation and washing, the surface is modified with hexadecanoic acid and then dried to obtain silver powder for medium-temperature curing conductive adhesive.

[0042] The silver nitrate solution was added by inserting a conduit along the wall of the reaction vessel below the liquid level, while the ferrous sulfate solution was added by keeping the conduit above the liquid level along the wall of the reaction vessel. The dropping rate of the silver nitrate solution was 100 ml / min, and the dropping rate of the ferrous sulfate solution was 50 ml / min. The mass ratio of hexadecanoic acid to silver nitrate in the silver nitrate solution was 0.3:100.

[0043] The silver powder used in the medium-temperature curing conductive adhesive of this embodiment has an average particle size of 3.52 μm and a tap density of 2.5 g / cm³.3 .

[0044] Example 3:

[0045] S1. Prepare 1.2M hydroxylamine sulfate solution and 1.70M silver nitrate solution respectively. The volume ratio of hydroxylamine sulfate solution to silver nitrate solution is 3:1.

[0046] S2. Add a 37% volume solution of hydroxylamine sulfate and citric acid as the base solution to the reaction vessel, start stirring and maintain the temperature of the base solution at 85°C. The mass ratio of silver nitrate to citric acid in the silver nitrate solution is 100:5.

[0047] S3. Under stirring, silver nitrate solution and the remaining 63% volume of hydroxylamine sulfate solution are simultaneously dripped into the reaction vessel using a peristaltic pump. Stirring is continued for 10 minutes. After separation and washing, the surface is modified with hexadecanoic acid and then dried to obtain silver powder for medium-temperature curing conductive adhesive.

[0048] The silver nitrate solution was added by inserting a conduit along the wall of the reaction vessel below the liquid level, while the hydroxylamine sulfate solution was added by maintaining the conduit above the liquid level along the wall of the reaction vessel. The dropping rate of both the silver nitrate and hydroxylamine sulfate solutions was 60 ml / min. The mass ratio of hexadecanoic acid to silver nitrate in the silver nitrate solution was 0.25:100.

[0049] The silver powder used in the medium-temperature curing conductive adhesive of this embodiment has an average particle size of 1.22 μm and a tap density of 2.4 g / cm³. 3 .

[0050] Example 4:

[0051] S1. Prepare 0.65M hydroxylamine sulfate solution and 2.70M silver nitrate solution respectively. The volume ratio of hydroxylamine sulfate solution to silver nitrate solution is 1.5:1.

[0052] S2. Add a 35% volume of hydroxylamine sulfate solution and citric acid as the base solution to the reaction vessel, start stirring and maintain the temperature of the base solution at 60°C. The mass ratio of silver nitrate to citric acid in the silver nitrate solution is 100:1.

[0053] S3. Under stirring, silver nitrate solution and the remaining 65% volume of hydroxylamine sulfate solution are simultaneously dripped into the reaction vessel using a peristaltic pump. Stirring is continued for 15 minutes. After separation and washing, the surface is modified with hexadecanoic acid and then dried to obtain silver powder for medium-temperature curing conductive adhesive.

[0054] The silver nitrate solution was added by inserting a conduit along the wall of the reaction vessel below the liquid level, while the hydroxylamine sulfate solution was added by keeping the conduit above the liquid level along the wall of the reaction vessel. The dropping rate of the silver nitrate solution was 85 ml / min, and the dropping rate of the hydroxylamine sulfate solution was 65 ml / min. The mass ratio of hexadecanoic acid to silver nitrate in the silver nitrate solution was 0.3:100.

[0055] The silver powder used in the medium-temperature curing conductive adhesive of this embodiment has an average particle size of 2.15 μm and a tap density of 2.6 g / cm³. 3 .

[0056] The silver powder from Examples 1-4 was used in conductive adhesive, comprising the following components by weight percentage: 70% silver powder, 10% DBE, 10% silicone resin, and 10% epoxy resin. After screen printing on a substrate using a 300-mesh screen and curing at 135°C for 45 minutes, performance tests were performed, and the results are shown in Table 1.

[0057] Table 1: Performance test data of conductive adhesive

[0058]

[0059] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing silver powder for medium-temperature curing conductive adhesive, characterized in that, The preparation method includes the following steps: Step S1: Prepare a 0.65–1.5 M sulfate solution and a 1.70–2.70 M silver nitrate solution; The volume ratio of the sulfate solution to the silver nitrate solution is 1.5 to 3:1; The sulfate solution is one or a mixture of two or more of ferrous ammonium sulfate solution, ferrous sulfate solution and hydroxylamine sulfate solution; Step S2: Add 30-37% by volume of sulfate solution and organic acid to the reaction vessel, stir and control the temperature at 15-85℃; The mass ratio of silver nitrate to organic acid in the silver nitrate solution is 100:1-5; In step S2, the organic acid is one or a mixture of two or more of succinic acid, tartaric acid, citric acid and adipic acid; Step S3: While stirring, add silver nitrate solution and the remaining 63-70% volume of sulfate solution dropwise into the reaction vessel, continue stirring for 7-20 minutes, then separate, wash, surface modify and dry to obtain silver powder for medium-temperature curing conductive adhesive. In step S3, the dropping rate of the silver nitrate solution is 60–100 ml / min; The sulfate solution is added at a rate of 50–70 ml / min. In step S3, the silver nitrate solution is added by inserting a conduit along the wall of the reaction vessel below the liquid level. The sulfate solution is added dropwise by maintaining the liquid level above the liquid level along the wall of the reaction vessel using a conduit.

2. The preparation method according to claim 1, characterized in that, In step S1, the volume ratio of the sulfate solution to the silver nitrate solution is 2 to 2.5:

1.

3. The preparation method according to claim 2, characterized in that, In step S2, the temperature is 30~60℃.

4. The preparation method according to claim 3, characterized in that, In step S3, hexadecanoic acid is used for surface modification; The mass ratio of silver nitrate to hexadecanoic acid in the silver nitrate solution is 100:0.2~0.

3.

5. A silver powder for medium-temperature curing conductive adhesive, characterized in that, The silver powder used in the medium-temperature curing conductive adhesive is prepared using the preparation method described in any one of claims 1 to 4.

6. The silver powder for medium-temperature curing conductive adhesive according to claim 5, characterized in that, The silver powder used in the medium-temperature curing conductive adhesive is a spherical composite silver powder. The spherical composite silver powder includes micron-sized flake silver powder, nano-sized spherical silver powder, and submicron-sized spherical silver powder.

7. The silver powder for medium-temperature curing conductive adhesive according to claim 6, characterized in that, The silver powder used in the medium-temperature curing conductive adhesive has an average particle size of 1.22~3.52μm and a tap density of 2.4~2.8g / cm³. 3 .

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