Silver migration resistant silver paste for chip resistor suitable for ultra-fine line width printing and preparation method thereof

Abstract

The application discloses a silver migration resistant silver paste for chip resistors suitable for ultra-fine line width printing and a preparation method thereof, and belongs to the technical field of electronic materials. The silver paste comprises thick flaky silver powder, nano zinc molybdate glass phase and vinyl bis-stearamide (EBS) modified by a silane coupling agent. The thick flaky silver powder constructs a three-dimensional conductive network and reduces the square resistance; the nano zinc molybdate forms a passivation layer by capturing silver ions and generating Zn2+ after sintering, thereby effectively inhibiting silver migration; the modified EBS solves the compatibility problem of traditional EBS and significantly improves the off-network performance and yield of ultra-narrow line width printing. The silver paste has low square resistance (≤7.5 mΩ / □), a silver migration time of ≥500 s, a printing yield of ≥65%, and a cost significantly lower than that of a traditional palladium-containing system, and is suitable for manufacturing chip resistors with high humidity and high density integration.

Description

Technical Field

[0001] This invention belongs to the field of electronic materials technology, specifically a silver paste for anti-silver migration used in chip resistors suitable for ultra-fine linewidth printing and its preparation method. Background Technology

[0002] As one of the most fundamental and widely used passive components in electronic circuits, the performance of surface-mount resistors directly determines the stability and lifespan of the entire electronic device. Conductive silver paste is a key material in the manufacture of surface-mount resistors, mainly composed of a conductive phase (silver powder), a binder phase (glass powder), and an organic carrier. With the miniaturization and high-density development of electronic devices, the size of surface-mount resistors is constantly shrinking (e.g., from 2512 to 01005 and smaller), which places more stringent requirements on the performance of conductive silver paste: it not only needs to have basic characteristics such as low sheet resistance and high adhesion, but also must meet the precision printing requirements of ultra-fine linewidths (e.g., 80μm and below) and ensure long-term reliability in high-humidity electric field environments.

[0003] Currently, the main technical problems with conductive silver paste for chip resistors are as follows: 1. Silver migration is a serious problem, and existing suppression methods have shortcomings.

[0004] Silver migration refers to the phenomenon where silver ions migrate from the anode to the cathode and form dendrites under the combined influence of a humid environment and a DC electric field, leading to a decrease in the insulation performance between electrodes and even short circuits. The mainstream traditional technique for suppressing silver migration is to add palladium to form a silver-palladium alloy, but palladium is about 35 times more expensive than silver, resulting in a significant increase in material costs. Furthermore, patent CN112992402B discloses a method for suppressing silver migration using two-dimensional layered MXene materials, but the transition metals used (such as Nb, Hf, and Ta) are expensive and pose safety risks. Patent CN114360762B passivates the silver layer surface by adding low-melting-point and high-melting-point rare-earth glass powders, but increasing the glass powder content significantly reduces conductivity (increasing sheet resistance by more than 15%). It is evident that existing technologies struggle to achieve a balance between cost, safety, and conductivity.

[0005] 2. Poor adaptability to ultra-narrow linewidth printing, resulting in low product yield.

[0006] For small-sized chip resistors such as 0201 and 01005, the linewidth of the front conductor (C1) has been reduced to 80μm or even smaller. When using a 500-mesh screen for extended printing, existing silver pastes, due to insufficient rheological and screen removal properties, are prone to printing defects such as broken lines, smearing, faded lines, and rough edges. Currently, printing defects account for over 70% of all defects, resulting in an overall product yield of only about 40%, severely restricting production efficiency and corporate economic benefits.

[0007] 3. It is difficult to balance the stability and printability of silver paste systems.

[0008] Vinyl bis-stearamide (EBS), as an excellent lubricant and release agent, can theoretically improve the screen release performance of silver paste. However, EBS is insoluble in most solvents at room temperature, has poor compatibility with silver paste systems, and is prone to precipitating during storage, leading to paste stratification and deterioration. Therefore, how to utilize the advantages of EBS while solving its compatibility problem has become a key technical challenge that urgently needs to be overcome in this field.

[0009] In summary, developing a conductive silver paste for chip resistors that combines excellent anti-silver migration properties, ultra-narrow linewidth and high-precision printing adaptability, good storage stability, and controllable cost is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0010] To solve the above problems, the technical solution provided by the present invention is as follows: The present invention provides an anti-silver migration silver paste for chip resistors suitable for ultra-fine linewidth printing, the silver paste comprising the following components: Thick flakes of silver powder; Nano zinc molybdate glass phase; and Vinyl bis-stearamide (EBS) modified with silane coupling agent.

[0011] Preferably, the thick sheet-like silver powder has a particle size D50 of 1.0-4.0 μm, an aspect ratio of (1-3):1, and a thickness of 0.5-2 μm.

[0012] Preferably, the particle size of the nano-zinc molybdate glass phase is 10-100 nm, and the amount added to the silver paste is 0.5-2 wt%.

[0013] Preferably, the vinyl bis-stearamide modified with a silane coupling agent is obtained by modifying vinyl bis-stearamide with an epoxy silane coupling agent.

[0014] Preferably, the silver paste comprises, by weight percentage: Thick flake silver powder 60%-70%; 1-5% glass powder; Metal oxides 1-5%; Nano-zinc molybdate glass phase 0.5-2%; Resin material 5-10%; 0.5-2% vinyl bis-stearamide modified with silane coupling agent; Solvent 10-25%; and additives 1-5%.

[0015] Preferably, the glass powder is a borosilicate bismuth system glass powder with a glass transition temperature Tg of 400-600℃ and a particle size D50 of 1.0-4.0 μm; and / or, the metal oxide is one or more of aluminum oxide, bismuth oxide, copper oxide, titanium oxide, and zinc oxide, with a purity >99.5% and a particle size D50 of 1.0-4.0 μm.

[0016] Preferably, the silane coupling agent-modified vinyl bis-stearamide is prepared by a method comprising the following steps: S11. Add the dried EBS to the reactor, introduce N2 gas at a flow rate of 0.5 L / min, and slowly heat to 125°C while stirring at 350 rpm, then keep the temperature and stir for 30 min until the EBS is completely melted. S12. Slowly add dibutyltin dilaurate to molten EBS and stir at a constant temperature for 30 minutes. S13. Increase the temperature of the reactor to 140℃, increase the stirring speed to 500rpm, and add KH-560 coupling agent dropwise at a uniform rate. After the addition is completed, stir at a constant temperature for 2 hours. S14. After the reaction is complete, stop heating, keep nitrogen gas flowing in and stirring, and reduce the stirring speed to 200 rpm. Allow it to cool naturally to below 60°C, turn off the nitrogen gas and stirring, open the reactor, take out the block-shaped modified EBS product, put the product into a high-speed pulverizer for pulverization, and pass it through a 325-mesh sieve to obtain a white powdery epoxy silane modified EBS product.

[0017] Preferably, in step S2, the ratio of dibutyltin dilaurate to EBS is 1:500, the ratio of KH-560 coupling agent to EBS is 1:25, and the dropping time is 30-40 minutes.

[0018] A process for preparing anti-silver migration silver paste for chip resistors suitable for ultra-fine linewidth printing includes the following steps: S21. Pour the required solvent into the mixing tank, and slowly heat it to 80°C at a stirring speed of 350 rpm. Stir at this constant temperature for 30 minutes. S22. Slowly add the resin material. After the addition is complete, increase the stirring speed to 500 rpm and stir at a constant temperature of 80°C for 4 hours until the final liquid is clear and transparent to obtain the intermediate product. S23. Place the intermediate product in a stirrer, and then add silver powder, glass powder, metal oxide, EBS-560, nano zinc molybdate glass phase, and dispersant in sequence, and stir at 10 rpm for 4 hours. S24. Grind 8-10 times, then pour into a mixer, add a certain proportion of diluent and stir for 4 hours to obtain the silver paste.

[0019] The above-mentioned silver paste is used in the fabrication of chip resistors. Beneficial effects

[0020] Compared with the prior art, the technical solution provided by this invention has the following advantages: This invention discloses an anti-silver migration silver paste for chip resistors suitable for ultra-fine linewidth printing and its preparation method. The silver paste comprises thick sheet silver powder, a nano-zinc molybdate glass phase, and vinyl bis-stearamide (EBS) modified with a silane coupling agent. The thick sheet silver powder constructs a three-dimensional conductive network, reducing sheet resistance; the nano-zinc molybdate forms Zn²⁺ after sintering to dynamically capture silver ions and generate a passivation layer, effectively inhibiting silver migration; the modified EBS solves the compatibility problem of traditional EBS, significantly improving screen removal performance and yield in ultra-narrow linewidth printing. This invention's silver paste maintains low sheet resistance (≤7.5 mΩ / □), achieves a silver migration time ≥500 s, increases printing yield to over 65%, and has a significantly lower cost than traditional palladium-containing systems, making it suitable for manufacturing chip resistors with high humidity and high-density integration. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the test results for the product of Example 4. Detailed Implementation

[0022] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0023] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this application described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0024] In this application, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing this application and its embodiments, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation.

[0025] Furthermore, in addition to indicating location or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in some cases to indicate a certain dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0026] Furthermore, the terms "installation," "setup," "equipped with," "connection," "linking," and "socketing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral structure; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium, or an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0027] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments. Example

[0028] The silver paste of this embodiment contains 68% thick flake silver powder DSP-403D, 5% glass powder DGF-0256, 3% oxide ALO, 7% resin EC-200, 1% additive nano zinc molybdate glass phase, and 16% diluent ethylene glycol monoethyl ether. Example

[0029] The silver paste of this embodiment contains 68% thick flake silver powder DSP-403D, 5% glass powder DGF-0256, 3% oxide ALO, 6% resin EC-200, 2% additive nano zinc molybdate glass phase, and 16% diluent ethylene glycol monoethyl ether. Example

[0030] The silver paste of this embodiment contains 68% thick flake silver powder DSP-403D, 5% glass powder DGF-0256, 3% oxide ALO, 6% resin EC-200, 3% additive nano zinc molybdate glass phase, and 15% diluent ethylene glycol monoethyl ether. Example

[0031] The silver paste of this embodiment comprises 68% thick flake silver powder DSP-403D, 5% glass powder DGF-0256, 3% oxide ALO, 6% resin EC-200, 2% additive nano zinc molybdate glass phase, 1.5% silane coupling agent modified vinyl bis-stearamide EBS-560, and 14.5% diluent ethylene glycol monoethyl ether. Example

[0032] The silver paste of this embodiment contains 68% thick flake silver powder DSP-403D, 5% glass powder DGF-0256, 3% oxide ALO, 6% resin EC-200, 2% additive nano zinc molybdate glass phase, 1.5% unmodified EBS, and 14.5% diluent ethylene glycol monoethyl ether. Example

[0033] The silver paste of this embodiment comprises 65% thick flake silver powder DSP-403D, 5% glass powder DGF-0256, 3% oxide ALO, 8% resin EC-200, 2% additive nano zinc molybdate glass phase, 1.5% silane coupling agent modified vinyl bis-stearamide EBS-560, and 15.5% diluent ethylene glycol monoethyl ether. Comparative Example 1 The silver paste of this embodiment contains 68% microcrystalline silver powder DSP-103D, 3% palladium powder Pd, 5% glass powder DGF-0256, 3% oxide ALO, 6% resin EC-200, and 15% diluent ethylene glycol monoethyl ether. Comparative Example 2 The silver paste of this embodiment contains 68% microcrystalline silver powder DSP-103D, 3% palladium powder Pd, 5% glass powder DGF-0256, 3% oxide ALO, 5% resin EC-200, 1.5% unmodified EBS, and 14.5% diluent ethylene glycol monoethyl ether. Comparative Example 3 The silver paste of this embodiment contains 68% microcrystalline silver powder DSP-103D, 3% palladium powder Pd, 5% glass powder DGF-0256, 3% oxide ALO, 5% resin EC-200, 1.5% silane coupling agent modified vinyl bis-stearamide EBS-560, and 14.5% diluent ethylene glycol monoethyl ether. Comparative Example 4 The silver paste of this embodiment contains 68% microcrystalline silver powder DSP-103D, 5% glass powder DGF-0256, 3% oxide ALO, 5% resin EC-200, 2% additive nano zinc molybdate glass phase, and 17% diluent ethylene glycol monoethyl ether. Comparative Example 5 The silver paste of this embodiment contains 68% microcrystalline silver powder DSP-103D, 5% glass powder DGF-0256, 3% oxide ALO, 5% resin EC-200, 2% additive nano zinc molybdate glass phase, 1.5% silane coupling agent modified vinyl bis-stearamide EBS-560, and 15.5% diluent ethylene glycol monoethyl ether. The preparation processes of Examples 1-6 and Comparative Examples 1-5 were all as follows: S21. Pour the required solvent into the mixing tank, and slowly heat it to 80°C at a stirring speed of 350 rpm. Stir at this constant temperature for 30 minutes. S22. Slowly add the resin material. After the addition is complete, increase the stirring speed to 500 rpm and stir at a constant temperature of 80°C for 4 hours until the final liquid is clear and transparent to obtain the intermediate product. S23. Place the intermediate product in a mixer, then add the remaining ingredients in sequence, and mix at 10 rpm for 4 hours; S24. Grind 8-10 times, then pour into a mixer, add a certain proportion of diluent and stir for 4 hours to obtain the silver paste.

[0034] The silver pastes prepared in Examples 1-6 and Comparative Examples 1-5 were subjected to performance tests, and the test results are as follows: Experimental data description: 1. Examples 2, 1, and 4 illustrate that adding nano zinc molybdate glass phase can replace Pd powder, effectively reducing silver migration, while the content can be reduced to 2% to meet existing requirements. 2. Examples 1-3 illustrate that the addition of nano-zinc molybdate glass phase improves the product's resistance to silver migration; 3. Examples 4-5 and Comparative Examples 2-3 all demonstrate that the compatibility of the modified EBS with the system is greatly improved, with no risk of precipitation, which can improve the printing yield of the product. 4. In Example 6, reducing the silver content on the surface improves the product's resistance to silver migration, but it also increases sheet resistance.

[0035] 5. General Explanation: Refer to Appendix Figure 1 Example 4 uses thick sheet silver powder, modified EBS-560, and nano zinc molybdate glass phase, which achieves the best level of silver migration resistance and electrical properties, and can greatly improve the printing yield of the product. Test method: 1. Viscosity: The viscosity value at 10 rpm at 25±0.5℃ was measured using a Brookfield HB DV-II+ viscometer, model spindle-14#. 2. Acid resistance: Print the silver paste to a thickness of 8-10μm, sinter at 850℃, soak in 5% concentrated hydrochloric acid for 2 hours, and then tear it with 3M 600 tape. If it comes off easily, it is OK; otherwise, it is NG. 3. Fineness: Use a scraper fineness gauge to test the location where the fourth continuous scratch of the slurry breaks or the color becomes lighter, and read the fineness.

[0036] 4. Sheet resistance: After printing the silver paste to a thickness of 8-10μm and sintering at 850℃, the sheet resistance is measured using a four-probe method. 5. Silver migration time: Print two silver lines with a thickness of 8-10 μm and a spacing of 400 μm on an alumina substrate, and sinter at 850℃. Place one drop of deionized water between the two silver lines (ensuring the water droplet covers both silver lines and the middle area), then apply a rated DC voltage of 1V to the two silver lines and record the time it takes for silver ions to migrate from the positive electrode to the negative electrode (visible to the naked eye). 6. Printing yield: At the customer's production site, 30,000 products are produced using the same process. The number of defective products caused by printing defects is recorded, and the yield is calculated. 7. Compatibility verification: Take 20g of silver paste, put it into a 100ml centrifuge tube, and centrifuge at 3500rpm for 30 seconds. Observe whether there is white substance on the surface. If there is, it means that EBS has precipitated. If there is no white substance, it means that no EBS has precipitated.

[0037] Thick flake silver powder is used, with a particle size of D50 = 1.0-4.0 μm, an aspect ratio of (1-3):1, and a thickness of approximately 0.5-2 μm. This type of silver powder uses spherical silver powder, which is flattened by physical pressure. It not only possesses the good printability of spherical silver powder but also the low surface resistivity of flake silver powder. Compared with traditional microcrystalline silver powder, the introduction of this type of silver powder results in a larger particle size and greater steric hindrance, forming a larger three-dimensional barrier network during the silver paste sintering process, which can inhibit silver migration to a certain extent. In terms of printing, it does not agglomerate like microcrystalline silver powder, which would cause the silver paste particle size to increase and thus affect printability. The addition of nano-zinc molybdate glass phase (ZnMoO4), with a particle size of approximately 10-100 nm and an addition content of approximately 0.5-1%, allows zinc molybdate (ZnMoO4) to form a composite glass network with other glass phases (B-Si-Bi glass) during sintering. When the resistor is energized, zinc ions (Zn²⁺) in the zinc molybdate are slowly released from the glass network, forming a dynamic ion source to capture silver ions and co-precipitate them to form stable compounds, thus blocking the migration channels of silver ions. Meanwhile, the residual MoO4²⁻ in the glass network can adsorb onto the silver surface to form a passivation layer, further inhibiting silver oxidation and thus playing a synergistic passivation role. Furthermore, the price of nano-zinc molybdate is only one-tenth that of silver and one-three-hundred-fiftieth that of palladium, significantly reducing raw material costs. Vinyl bis-stearamide (EBS) is a wax powder that is insoluble in most solvents at room temperature. It possesses dual functions of internal lubrication (reducing intermolecular friction) and external lubrication (reducing interfacial friction), exhibiting excellent release properties and superior dispersibility. It is widely used in the production of color masterbatches and filler masterbatches. Its excellent release properties significantly improve the printing characteristics of silver paste during screen printing (clean screen removal). However, due to its insolubility in most solvents and poor compatibility with the system, it tends to float to some extent during product storage, leading to silver paste stratification and deterioration, resulting in poor stability. Therefore, it is rarely used in the silver paste industry. This patent uses a silane coupling agent to modify vinyl bis-stearamide (EBS), retaining the lubricating properties of EBS while introducing Si-O functional groups that can bind to the surface of silver powder. This improves compatibility in cellulose resin and enhances the interfacial bonding between silver powder and resin, greatly improving product stability and completely solving the compatibility problem.

[0038] The above-described embodiments are merely illustrative of certain implementations of the present invention, and are described in a relatively specific and detailed manner. However, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A silver paste for resisting silver migration in chip resistors suitable for ultra-fine linewidth printing, characterized in that, The silver paste contains the following components: Thick flakes of silver powder; Nano zinc molybdate glass phase; and Vinyl bis-stearamide (EBS) modified with silane coupling agent.

2. The silver paste according to claim 1, characterized in that, The thick sheet-like silver powder has a particle size D50 of 1.0-4.0 μm, an aspect ratio of (1-3):1, and a thickness of 0.5-2 μm.

3. The silver paste according to claim 1, characterized in that, The nano-zinc molybdate glass phase has a particle size of 10-100 nm and is added to the silver paste at an amount of 0.5-2 wt%.

4. The silver paste according to claim 1, characterized in that, The silane coupling agent modified vinyl bis-stearamide is obtained by modifying vinyl bis-stearamide with an epoxy silane coupling agent.

5. The silver paste according to claim 1, characterized in that, The silver paste comprises, by weight percentage: Thick flake silver powder 60%-70%; 1-5% glass powder; Metal oxides 1-5%; Nano-zinc molybdate glass phase 0.5-2%; Resin material 5-10%; 0.5-2% vinyl bis-stearamide modified with silane coupling agent; Solvent 10-25%; and additives 1-5%.

6. The silver paste according to claim 5, characterized in that, The glass powder is a borosilicate bismuth system glass powder with a glass transition temperature Tg of 400-600℃ and a particle size D50 of 1.0-4.0 μm; and / or, the metal oxide is one or more of aluminum oxide, bismuth oxide, copper oxide, titanium oxide, and zinc oxide, with a purity >99.5% and a particle size D50 of 1.0-4.0 μm.

7. The silver paste according to claim 1, characterized in that, The silane coupling agent-modified vinyl bis-stearamide is prepared by a method comprising the following steps: S11. Add the dried EBS to the reactor, introduce N2 gas at a flow rate of 0.5 L / min, and slowly heat to 125°C while stirring at 350 rpm, then keep the temperature and stir for 30 min until the EBS is completely melted. S12. Slowly add dibutyltin dilaurate to molten EBS and stir at a constant temperature for 30 minutes. S13. Increase the temperature of the reactor to 140℃, increase the stirring speed to 500rpm, and add KH-560 coupling agent dropwise at a uniform rate. After the addition is completed, stir at a constant temperature for 2 hours. S14. After the reaction is complete, stop heating, keep nitrogen gas flowing in and stirring, and reduce the stirring speed to 200 rpm. Allow it to cool naturally to below 60°C, turn off the nitrogen gas and stirring, open the reactor, take out the block-shaped modified EBS product, put the product into a high-speed pulverizer for pulverization, and pass it through a 325-mesh sieve to obtain a white powdery epoxy silane modified EBS product.

8. The silver paste according to claim 7, characterized in that: In step S2, the ratio of dibutyltin dilaurate to EBS is 1:500, the ratio of KH-560 coupling agent to EBS is 1:25, and the dropping time is 30-40 minutes.

9. The silver paste preparation process according to any one of claims 1-8, characterized in that: Includes the following steps S21. Pour the required solvent into the mixing tank, and slowly heat it to 80°C at a stirring speed of 350 rpm. Stir at this constant temperature for 30 minutes. S22. Slowly add the resin material. After the addition is complete, increase the stirring speed to 500 rpm and stir at a constant temperature of 80°C for 4 hours until the final liquid is clear and transparent to obtain the intermediate product. S23. Place the intermediate product in a stirrer, and then add silver powder, glass powder, metal oxide, EBS-560, nano zinc molybdate glass phase, and dispersant in sequence, and stir at 10 rpm for 4 hours. S24. Grind 8-10 times, then pour into a mixer, add a certain proportion of diluent and stir for 4 hours to obtain the silver paste.

10. The use of the silver paste according to any one of claims 1-8 in the preparation of chip resistors.

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