Silver paste for inhibiting electrode diffusion and method for preparing the same

Abstract

The application provides a silver paste for inhibiting electrode diffusion and a preparation method thereof. According to mass percentage, the silver paste comprises 50-90wt% silver powder, 0-20wt% glass powder, 0.05-15wt% hydrophobic filler, 0.01-5wt% dispersant, 0-10wt% adhesive, 8-30wt% solvent, 0-5wt% plasticizer and 0-1wt% adhesion aid. The hydrophobic filler is inorganic oxide particles after hydrophobic modification. The application forms a silver diffusion isolation layer between silver and green ceramic sheets through the principle that the polarity of the dispersant in the silver paste changes after heating, which causes the migration and precipitation of the hydrophobic filler, so that the silver ions in the silver layer and the glass phase in the ceramic layer cannot diffuse with each other, thereby improving the reliability of the LTCC, and the LTCC substrate which can effectively inhibit silver diffusion and maintain excellent conductivity of the silver electrode and has controllable cost can be prepared.

Description

Technical Field

[0001] This application belongs to the field of electronic materials technology, and specifically relates to a silver paste for suppressing electrode diffusion and its preparation method. Background Technology

[0002] Low-temperature co-fired ceramic (LTCC) technology, with its superior high-frequency characteristics, excellent thermal stability, and flexible three-dimensional wiring capabilities, has become a core technology in high-end fields such as RF modules, automotive electronics, aerospace, and medical implants. Meanwhile, silver, with its excellent conductivity (volume resistivity of only 1.59 × 10⁻⁶),... -8 Its low Ω·m, relatively low cost, and co-firing temperature (<900°C) that perfectly matches LTCC ceramics make it the preferred material for the internal electrode of LTCC.

[0003] Due to the chemical potential gradient (silver concentration difference) between the electrode region and the ceramic region, silver atoms diffuse into the adjacent ceramic dielectric layer during co-firing, driven by this concentration difference, through lattice interstices, grain boundaries, or surface pathways. When the temperature rises to the co-firing range (typically 850-900°C), the kinetic energy of silver atoms increases significantly, enabling them to overcome the lattice barrier. During lattice diffusion, silver atoms squeeze into the ceramic lattice interstices; during grain boundary diffusion, they rapidly advance along the grain boundary network of the polycrystalline ceramic; surface diffusion occurs at the interface between the ceramic and the electrode. The diffusion coefficient of silver follows the Arrhenius equation.

[0004] The macroscopic consequence of silver diffusion is passivation of the electrode morphology. Due to silver loss, electrodes originally designed with sharp edges and precise geometry become blurred in outline and have a reduced effective cross-sectional area. When high-frequency current flows through the electrode, the current density distribution is distorted, leading to increased resistance. Studies have shown that in cases of severe diffusion, the equivalent resistance of the electrode can increase by more than 30%, which is unacceptable for RF devices aiming for low insertion loss.

[0005] Furthermore, silver diffusion degrades the dielectric properties of ceramics. When silver ions enter the ceramic lattice, they introduce additional defect levels, becoming trapping centers for charge carriers. This directly leads to an increase in the dielectric loss tangent (tanδ) and a decrease in the quality factor (Q). At specific frequencies, the dielectric constant also drifts due to the polarization contribution of silver ions. For devices sensitive to dielectric parameters, such as filters and resonators, this change is sufficient to cause them to deviate from the design frequency, leading to system performance failure.

[0006] More seriously, silver diffusion reduces the insulation properties of ceramics. When silver diffuses in ceramics, it often forms dendritic conductive pathways along grain boundaries. These microscopic silver dendrites grow further under the influence of an electric field, eventually potentially building conductive bridges between two adjacent electrodes, leading to a decrease in insulation resistance and even short circuits. In high-voltage applications, this effect can be amplified dramatically, causing catastrophic failures.

[0007] Currently, commonly used methods for suppressing silver diffusion can be categorized as follows: ① On the one hand, adding one or more non-diffused metallic elements (such as Pd, Pt, Au) that can stabilize grain boundaries to silver to form a solid solution or composite phase; these added elements (especially Pd) have large atomic radii and high diffusion activation energies, which can significantly reduce the migration rate of silver ions; on the other hand, adding modifiers that can form stable compounds with silver or effectively block grain boundaries to LTCC ceramic powder. ② Adding metal oxides (such as Bi2O3, CuO, B2O3); during sintering, these additives form a low-melting-point glassy phase that flows and encapsulates silver particles, forming a physical barrier that blocks the rapid diffusion channels of silver ions through grain boundaries. ③ Adding oxides that can capture silver ions (such as MoO3, V2O5, etc.) or adding nanoscale ceramic particles (such as Al2O3) as fillers to silver paste to increase the tortuosity of the silver diffusion path.

[0008] Although the above methods alleviate the silver diffusion problem to some extent, they often come at the cost of sacrificing the conductivity of silver, increasing material costs, or complicating the preparation process. Summary of the Invention

[0009] The purpose of this application is to overcome the shortcomings of the prior art and provide a silver paste for suppressing electrode diffusion and a method for preparing the same.

[0010] To achieve the above objectives, in a first aspect, this application provides: a silver paste for inhibiting electrode diffusion, wherein, by weight percentage, the silver paste comprises: 50-90 wt% silver powder, 0-20 wt% glass powder, 0.05-15 wt% hydrophobic filler, 0.01-5 wt% dispersant, 0-10 wt% binder, 8-30 wt% solvent, 0-5 wt% plasticizer, and 0-1 wt% adhesive aid, wherein the hydrophobic filler is hydrophobically modified inorganic oxide particles.

[0011] In one feasible embodiment, the silver powder has a D50 particle size of 10 nm-5 μm and a tap density of 2-7 g / cm³. 3 The silver powder has one or more of the following morphologies: spherical, near-spherical, flake-like, dendritic, and flocculent.

[0012] In one feasible embodiment, the silver powder has a D50 particle size of 500nm-3μm, a tap density of 3-5g / cm³, and a morphology of spherical or near-spherical.

[0013] In one feasible embodiment, the glass powder has a D50 particle size of 10nm-5μm and a softening temperature of 300-700℃. The glass powder contains one or more of the following components: calcium oxide, silicon oxide, boron oxide, bismuth oxide, sodium oxide, potassium oxide, zinc oxide, aluminum oxide, magnesium oxide, and barium oxide.

[0014] In one feasible embodiment, the glass powder has a D50 particle size of 500 nm-3 μm and a softening temperature of 500-600 °C.

[0015] In one feasible embodiment, the hydrophobic filler is one or more of the following: hydrophobically modified silica, alumina, titanium oxide, zinc oxide, zirconium oxide, cerium oxide, lanthanum oxide, copper oxide, tin oxide, and magnesium oxide.

[0016] In one feasible embodiment, the hydrophobic filler is one or more of hydrophobically modified alumina, magnesium oxide, cerium oxide, and lanthanum oxide.

[0017] In one feasible embodiment, the D50 particle size of the hydrophobic filler is 50nm-800nm.

[0018] In one feasible embodiment, the dispersant is one or more of alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, sorbitan ester and their polyoxyethylene derivatives.

[0019] In one feasible embodiment, the dispersant is one or more of Span 85, Span 65, and Span 80, which are sorbitan esters and their polyoxyethylene derivatives.

[0020] In one feasible embodiment, the adhesive is one or more of polyethylene, polypropylene, polyisobutylene, polystyrene, polytetrafluoroethylene, and polyvinylidene fluoride.

[0021] In one feasible embodiment, the adhesive is polyethylene or polyisobutylene.

[0022] In one feasible embodiment, the number average molecular weight of the polyethylene or polyisobutylene is 1.0-5.0 × 10⁻⁶. 4 g / mol.

[0023] In one feasible embodiment, the solvent is one or more of alkanes and mixtures thereof, low-viscosity silicone oil, and low-polarity ethers.

[0024] In one feasible embodiment, the solvent is selected from C 10 -C 16 Alkanes or silicone oils with a boiling point range of 150-300℃.

[0025] In one feasible embodiment, the plasticizer is one or more of phthalates, aliphatic diesters, and citrates.

[0026] In one feasible embodiment, the plasticizer is one or more of diisononyl phthalate, dioctyl phthalate, diisodecyl phthalate, tributyl citrate, and acetylated tributyl citrate.

[0027] In one feasible embodiment, the adhesive aid is one or more of the following: aminosilane coupling agent, epoxysilane coupling agent, methacryloxysilane coupling agent, vinylsilane coupling agent, mercaptosilane coupling agent, and titanate coupling agent.

[0028] In one feasible embodiment, the adhesive aid is a methacryloyloxysilane coupling agent.

[0029] Secondly, this application provides: a preparation method for the silver paste of the technical solution of the first aspect, comprising the following steps:

[0030] S1, weigh out the solvent, binder, dispersant, plasticizer and adhesive aid, place them in a reactor, and after they dissolve, cool to room temperature to obtain solution A;

[0031] S2, Weigh out the hydrophobic filler and solution A, and place them in a ball mill jar for ball milling to obtain dispersion B;

[0032] S3, weigh silver powder and glass powder and place them in dispersion B. After ball milling, grind them using a three-roll mill to obtain silver paste.

[0033] The principle of this invention is based on the characteristic that the surface energy of green ceramic sheets is lower than that of Ag. Low-polarity solvents, binders, dispersants, and plasticizers are selected as the organic system, and hydrophobic fillers are used as silver diffusion inhibitors to prepare the silver paste. The silver paste is screen-printed onto the green ceramic sheet. During the drying process of the silver paste solvent, the dispersant undergoes a polarity change upon heating, leading to phase separation of the silver paste, and the hydrophobic filler migrates to the surface of the silver layer. During sintering, the high viscosity of the filler itself prevents silver ions in the silver layer and the glassy phase in the ceramic layer from diffusing with each other, ultimately inhibiting the silver diffusion phenomenon in LTCC.

[0034] This application has the following advantages compared with the prior art:

[0035] This application utilizes the principle that the polarity of the dispersant in the silver paste changes upon heating, leading to the migration and precipitation of hydrophobic fillers. The hydrophobic fillers form a silver diffusion isolation layer between the silver and the green ceramic sheet, preventing silver ions in the silver layer and the glass phase in the ceramic layer from diffusing with each other, thereby improving the reliability of LTCC. This enables the fabrication of LTCC substrates that can effectively suppress silver diffusion, maintain the excellent conductivity of the silver electrode, and have controllable costs. Specific Implementation

[0036] To illustrate the technical content, structural features, achieved objectives, and effects of the invention in detail, the technical solutions in the embodiments of this application will be described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. In the following description, for illustrative purposes, numerous specific details are set forth to provide a detailed description of various exemplary embodiments or implementations of the invention. However, various exemplary embodiments may also be implemented independently without these specific details or in one or more equivalent arrangements. Furthermore, the various exemplary embodiments may differ, but are not necessarily exclusive. For example, the specific shape, structure, and characteristics of the exemplary embodiments may be used or implemented in another exemplary embodiment without departing from the inventive concept.

[0037] This application provides a silver paste for inhibiting electrode diffusion. The silver paste uses a low-polarity solvent, binder, dispersant, and plasticizer as an organic system, and a hydrophobic filler as a silver diffusion inhibitor. By weight percentage, the silver paste comprises: 50-90 wt% silver powder, 0-20 wt% glass powder, 0.05-15 wt% hydrophobic filler, 0.01-5 wt% dispersant, 0-10 wt% binder, 8-30 wt% solvent, 0-5 wt% plasticizer, and 0-1 wt% adhesion promoter.

[0038] In this application, the D50 particle size of the silver powder is 10 nm-5 μm, and the tap density is 2-7 g / cm³. 3 Silver powder exhibits one or more morphologies, including spherical, near-spherical, flake-like, dendritic, and flocculent forms. As a host material for electrodes, silver powder provides excellent conductivity. Silver has a low bulk resistivity (1.59 × 10⁻⁶). -8 The particle size (Ω·m) is well matched with the co-firing temperature of LTCC ceramics. Particle size, morphology, and tap density affect the printability of the silver paste, the degree of sintering densification, and the conductivity of the final electrode. Preferably, the D50 particle size of the silver powder is 500 nm-3 μm, and the tap density is 3-5 g / cm³. 3The silver powder is spherical or near-spherical, allowing for an optimal balance between printability, sintering density, and conductivity. The silver powder content in the silver paste ranges from 50-90 wt%, for example: 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, etc.

[0039] In this application, the glass powder is composed of one or more of the following: calcium oxide, silicon oxide, boron oxide, bismuth oxide, sodium oxide, potassium oxide, zinc oxide, aluminum oxide, magnesium oxide, and barium oxide. The D50 particle size of the glass powder is 10 nm-5 μm, and its softening temperature is 300-700 °C. During sintering, the glass powder softens and melts, wetting the silver particles and the ceramic substrate, promoting the densification and sintering of the silver layer, and firmly bonding the silver electrode to the ceramic substrate. The composition of the glass powder is typically matched to the green ceramic sheet to ensure good interfacial bonding and thermal compatibility. Preferably, the glass powder is selected with a D50 particle size range of 500 nm-3 μm and a softening temperature of 500-600 °C. Glass powder within this particle size range matches the silver powder particle size, ensuring uniform mixing and avoiding localized enrichment of the glass phase. Glass powder within this softening temperature range does not flow excessively and can play a binding role without becoming a "carrier" for silver diffusion. The mass percentage of glass powder in silver paste can be 0, or it can be added between 0-20 wt%, such as 0.01 wt%, 0.1 wt%, 1 wt%, 5 wt%, 10 wt%, 15 wt%, etc.

[0040] This application preferably uses a low-polarity solvent, such as one or more alkanes and mixtures thereof, low-viscosity silicone oil, or low-polarity ethers, to match the surface properties of the hydrophobic filler. The solvent is used to dissolve organic components such as binders and dispersants, thereby adjusting the viscosity and rheological properties of the silver paste to make it suitable for screen printing. Preferably, the solvent is C... 10 -C 16 Alkanes or silicone oils with a boiling point range of 150-300 °C, C 10 -C 16 The alkanes have moderate boiling points and volatilize slowly during the drying stage (50-150℃), allowing sufficient time for the dispersant polarity transition and the migration of hydrophobic fillers. The same applies to silicone oils with boiling points in the 150-300℃ range, and their volatilization characteristics are matched to the process. The solvent content in the silver paste is 8-30 wt%, for example: 8.01 wt%, 8.1 wt%, 8.5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, etc.

[0041] This application preferably uses a non-polar or low-polarity adhesive, which is one or more of polyethylene, polypropylene, polyisobutylene, polystyrene, polytetrafluoroethylene, and polyvinylidene fluoride. The adhesive provides the necessary viscosity and thixotropy to the silver paste, ensuring the accuracy and shape integrity of the printed pattern. During the drying process, the adhesive forms a polymer film that fixes the solid particles onto the green ceramic sheet. Preferably, the adhesive is polyethylene or polyisobutylene, which are non-polar / low-polar polymers that match the surface properties of the hydrophobic filler and can form a uniform film at the drying temperature without premature decomposition interfering with filler migration. More preferably, the number average molecular weight of polyethylene or polyisobutylene is 1.0-5.0 × 10⁻⁶. 4 g / mol, when the number average molecular weight is less than 1.0 × 10 4 When the silver paste has poor film-forming properties, the silver layer is prone to cracking after printing; when the number average molecular weight is higher than 5.0×10⁻⁶, the silver paste is more prone to cracking. 4 If the silver paste viscosity is too high, printing will be difficult, and thermal decomposition residues may affect the conductivity of the electrodes. The binder content in the silver paste can be 0% by mass, or it can be added between 0-10 wt%, for example: 0.01 wt%, 0.1 wt%, 1 wt%, 5 wt%, 8 wt%.

[0042] In this application, the dispersant is one or more of alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, sorbitan ester, and their polyoxyethylene derivatives. During the silver paste preparation stage, the dispersant adsorbs onto the surface of the hydrophobic filler and silver powder, preventing particle agglomeration through steric hindrance or electrostatic repulsion, thus ensuring the uniformity and stability of the paste. However, during the drying and heating process, the selected dispersant undergoes a polarity change, shifting from initial oleophilicity to hydrophilicity (or increased polarity), leading to a decrease in its compatibility with low-polarity solvent systems. This drives the hydrophobic filler to migrate directionally from the interior of the silver layer to the surface and boundary layers. Preferably, the dispersant is one or more of sorbitan ester and its polyoxyethylene derivatives, specifically Span 85, Span 65, and Span 80. The hydrophilic-lipophilic balance of the Span series dispersants changes significantly during heating. The dispersant content in the silver paste is 0.01-5 wt%, for example: 0.02 wt%, 0.1 wt%, 1 wt%, 2 wt%, 3.5 wt%, 4 wt%, 4.5 wt%.

[0043] The plasticizer in this application is one or more of phthalate, aliphatic diester, and citrate. The plasticizer can lower the glass transition temperature of the adhesive, increase the flexibility of the dried silver film layer, and prevent cracking of the silver layer due to bending of the green ceramic sheet or lamination operations. Preferably, the plasticizer is selected from one or more of diisononyl phthalate, dioctyl phthalate, diisodecyl phthalate, tributyl citrate, and acetylated tributyl citrate. These plasticizers have the best compatibility with polyethylene / polyisobutylene, effectively lower the glass transition temperature of the adhesive, maintain the flexibility of the dried silver film layer, and prevent cracking during lamination. The plasticizer can be added at a mass percentage of 0% in the silver paste, or it can be added between 0-5 wt%, for example: 0.01 wt%, 0.1 wt%, 1 wt%, 1.5 wt%, 2.5 wt%, 4 wt%, and 4.5 wt%.

[0044] The adhesive aid in this application is one or more of the following: aminosilane coupling agent, epoxysilane coupling agent, methacryloxysilane coupling agent, vinylsilane coupling agent, mercaptosilane coupling agent, and titanate coupling agent. Silver powder and glass powder are inorganic powders, while the solvent, binder, dispersant, and plasticizer are organic carriers. The adhesive aid can react with the surface of the inorganic powders and is compatible with the organic carrier, enhancing the bonding force at the organic-inorganic interface, improving the stability of the silver paste, and increasing the adhesion between the sintered silver layer and the ceramic substrate. Preferably, the adhesive aid is a methacryloxysilane coupling agent. Methacryloxysilane coupling agents contain polymerizable double bonds, which can form a certain interaction with the carbon chains of the binder (such as polyisobutylene), enhancing wet adhesion. Furthermore, its thermal decomposition products are clean and will not introduce residual impurities after sintering, thus not affecting the electrode conductivity and the insulating layer effect. The adhesive can be added to the silver paste at a mass percentage of 0, or at a mass percentage of 0-1 wt%, such as 0.01 wt%, 0.1 wt%, 0.5 wt%, or 0.99 wt%.

[0045] The hydrophobic filler is an inorganic oxide particle that has been hydrophobically modified. In this application, the hydrophobic filler is one or more of the following: hydrophobically modified silica, alumina, titanium oxide, zinc oxide, zirconium oxide, cerium oxide, lanthanum oxide, copper oxide, tin oxide, and magnesium oxide. After hydrophobic modification, the filler surface exhibits low polarity, resulting in good initial dispersibility in a low-polarity organic carrier. During the drying process, as the polarity of the dispersant changes, the hydrophobic filler is "squeezed out" of the organic carrier system and migrates autonomously to the surface and edges of the silver layer, forming a dense layer of nano / submicron particles. During the high-temperature sintering stage, this layer of hydrophobic filler particles exhibits high viscosity and high stability, effectively blocking the diffusion path of silver ions from the electrode layer to the ceramic layer. It also blocks the penetration of the glass phase from the ceramic layer into the silver layer, thereby inhibiting silver diffusion and electrode passivation. Preferably, the hydrophobic filler is selected from one or more of hydrophobically modified alumina, magnesium oxide, cerium oxide, and lanthanum oxide. These four oxides, after hydrophobic modification, exhibit better compatibility with low-polarity organic carriers and can form a dense, high-viscosity isolation layer after sintering, providing optimal protection against silver ion diffusion. More preferably, the D50 particle size of the hydrophobic filler is 50nm-800nm. Hydrophobic fillers within this particle size range can be "driven" to migrate by the dispersant and better form a continuous physical barrier. The mass percentage content of the hydrophobic filler in the silver paste is 0.05-15wt%, for example: 0.06wt%, 0.1wt%, 1wt%, 5.5wt%, 10wt%, and 14.5wt%.

[0046] In the silver paste of this application, an appropriate amount of hydrophobic filler is required to form a continuous and effective isolation layer to suppress silver diffusion and electrode passivation without affecting the conductivity and printability of the silver paste. When the content of hydrophobic filler is too low (i.e., the mass percentage of hydrophobic filler is less than 0.05 wt%), a continuous and effective isolation layer cannot be formed; when the content of hydrophobic filler is too high (i.e., the mass percentage of hydrophobic filler is greater than 5 wt%), it will affect the conductivity and printability of the silver paste.

[0047] Solvents, binders, dispersants, and plasticizers act as organic carriers, providing excellent printing performance for the silver paste, and are removed through thermal decomposition in subsequent processes. The organic carriers and hydrophobic fillers work synergistically; the surface hydrophobicity of the fillers, combined with the low-polarity solvents, binders, and dispersants, forms a compatible system, ensuring uniform dispersion of the fillers in the paste. During drying, the polarity reversal of the dispersant acts as a "switch," driving the fillers to migrate directionally to the surface, forming a self-assembled isolation layer. This hydrophobic filler layer that migrates to the surface forms a physical barrier in the early stages of sintering, protecting the integrity and high conductivity of the silver layer and suppressing diffusion of the LTCC electrode.

[0048] Unlike existing technologies (such as adding Pd, Pt, or a large amount of glass phase), this application does not introduce a large amount of high resistivity material inside the silver phase, but instead suppresses diffusion through a surface isolation layer. Therefore, the sintered silver electrode can simultaneously achieve low sheet resistance (less than 4 mΩ / □) and extremely short silver diffusion distance (less than 30 μm), solving the technical problem of difficulty in achieving both conductivity and diffusion resistance in traditional technologies.

[0049] This application also provides a preparation method for the silver paste of the above-mentioned technical solution. The preparation method includes the following steps: S1, weighing solvent, binder, dispersant, plasticizer and adhesive aid, and placing them in a reactor, cooling to room temperature after dissolution to obtain solution A; S2, weighing hydrophobic filler and solution A, and ball milling them in a ball mill jar to obtain dispersion B; S3, weighing silver powder and glass powder and placing them in dispersion B, and grinding them using a three-roll mill after ball milling to obtain silver paste.

[0050] The prepared silver paste is screen-printed onto green ceramic sheets. The solvent in the silver paste is dried at 50-150℃ to promote the migration of hydrophobic fillers to the surface. Multiple green ceramic sheets are stacked and isostatically pressed at 20-60MPa, then sintered at 700-950℃. During the drying process of the silver paste solvent, the dispersant undergoes a polarity change, leading to phase separation in the silver paste and the migration of hydrophobic fillers to the surface of the silver layer. During sintering, the high viscosity of the filler itself prevents silver ions in the silver layer and the glass phase in the ceramic layer from diffusing with each other, ultimately inhibiting the silver diffusion phenomenon in LTCC. This preparation method is simple to operate, has low difficulty, controllable cost, and strong process compatibility.

[0051] The silver paste prepared by the above method is applied to the fabrication of LTCC substrates. The sheet resistance of the electrodes of the fabricated LTCC substrates is less than 4mΩ / □, and the silver diffusion distance is less than 30μm. The reliability of the LTCC substrates is effectively improved. The silver paste of this application can not only effectively suppress silver diffusion, but also maintain the excellent conductivity of the silver electrodes, and the cost is controllable.

[0052] The technical solutions provided in this application are further illustrated below through multiple comparative examples and embodiments.

[0053] Comparative Example 1

[0054] First, prepare solution A: Weigh 60g of dodecane and 20g of a solution with a number-average molecular weight of 3.0 × 10⁻⁶. 4 Polyisobutylene (g / mol), castor oil (6g), diisononyl phthalate (4g), and methacryloyloxysilane coupling agent (0.5g) were placed in a reactor. The mixture was dissolved at 80℃ and 200 rpm for 4 hours, then cooled to room temperature to obtain solution A.

[0055] Next, prepare dispersion B: Weigh 20g of hydrophobic alumina with a D50 particle size of 500nm and 60g of solution A, and place them in a ball mill jar. After ball milling at a speed of 200rpm for 6h, dispersion B is obtained.

[0056] Then, prepare the silver paste: weigh 312g of D50 with a particle size of 2μm and a tap density of 4g / cm³. 3 Spherical silver powder and 8g of Ca-Si-B-Al glass powder with a D50 particle size of 2μm and a softening temperature of 600℃ were placed in dispersion B and ball-milled for 6 hours at a speed of 200 rpm. Then, the powder was ground using a three-roll mill until the fineness was 8μm, thus obtaining silver paste.

[0057] Finally, the LTCC substrate was prepared: silver paste was screen-printed onto a Ca-Si-B-Al green ceramic sheet, and then the green ceramic sheet was placed at 100 °C to dry the dodecane in the silver paste and promote the migration of hydrophobic alumina to the surface and boundary layers; the green ceramic sheets were stacked and isostatically pressed at 40 MPa, and then the green ceramic sheets were sintered at 850 °C.

[0058] Comparative Example 2

[0059] First, prepare solution A: Weigh 60g of dodecane and 20g of a solution with a number-average molecular weight of 3.0 × 10⁻⁶. 4 A mixture of g / mol polyisobutylene, 6g Span 80, 4g diisononyl phthalate, and 0.5g methacryloyloxysilane coupling agent was placed in a reactor and dissolved for 4 hours at 80°C and 200 rpm. After cooling to room temperature, solution A was obtained.

[0060] Secondly, prepare the silver paste: weigh 312g of D50 with a particle size of 2μm and a tap density of 4g / cm³. 3 Spherical silver powder, 8g of Ca-Si-B-Al glass powder with a D50 particle size of 2μm and a softening temperature of 600℃, and 60g of solution A were ball-milled at 200rpm for 6h, and then ground using a three-roll mill until the fineness was 8μm, thus obtaining silver paste.

[0061] Finally, the LTCC substrate was prepared by screen printing silver paste onto a Ca-Si-B-Al green ceramic sheet, followed by drying the dodecane in the silver paste at 100°C; the green ceramic sheets were stacked and isostatically pressed at 40 MPa, and then sintered at 850°C.

[0062] Comparative Example 3

[0063] First, prepare solution A: Weigh 60g of dodecane and 20g of a solution with a number-average molecular weight of 3.0 × 10⁻⁶. 4A mixture of g / mol polyisobutylene, 6g Span 80, 4g diisononyl phthalate, and 0.5g methacryloyloxysilane coupling agent was placed in a reactor and dissolved for 4 hours at 80℃ and 200 rpm. After cooling to room temperature, solution A was obtained.

[0064] Next, prepare dispersion B: Weigh 20g of non-hydrophobic alumina with a D50 particle size of 500nm and 60g of solution A, and place them in a ball mill jar. After ball milling at a speed of 200rpm for 6h, dispersion B is obtained.

[0065] Then, prepare the silver paste: weigh 312g of D50 with a particle size of 2μm and a tap density of 4g / cm³. 3 Spherical silver powder and 8g of Ca-Si-B-Al glass powder with a D50 particle size of 2μm and a softening temperature of 600℃ were placed in dispersion B and ball-milled at 200rpm for 6h. Then, the powder was ground using a three-roll mill until the fineness was 8μm, thus obtaining silver paste.

[0066] Finally, the LTCC substrate was prepared by screen printing silver paste onto a Ca-Si-B-Al green ceramic sheet, followed by drying the dodecane in the silver paste at 100°C; the green ceramic sheets were stacked and isostatically pressed at 40 MPa, and then sintered at 850°C.

[0067] Comparative Example 4

[0068] First, prepare solution A: Weigh 60g of dodecane and 20g of a solution with a number-average molecular weight of 3.0 × 10⁻⁶. 4 A solution A was obtained by dissolving polyisobutylene (g / mol), Span 80 (6g), diisononyl phthalate (4g), and methacryloyloxysilane coupling agent (0.5g) in a reactor at 80°C and 200 rpm for 4 hours, followed by cooling to room temperature.

[0069] Next, prepare dispersion B: Weigh 20g of hydrophobic alumina with a particle size of 3μm and 60g of solution A, and place them in a ball mill jar. After ball milling at a speed of 200rpm for 6h, dispersion B is obtained.

[0070] Then, prepare the silver paste: weigh 312g of D50 with a particle size of 2μm and a tap density of 4g / cm³. 3 Spherical silver powder and 8g of Ca-Si-B-Al glass powder with a D50 particle size of 2μm and a softening temperature of 600℃ were placed in dispersion B and ball-milled at 200rpm for 6h. Then, the powder was ground using a three-roll mill until the fineness was 8μm, thus obtaining silver paste.

[0071] Finally, the LTCC substrate was prepared: silver paste was screen-printed onto a Ca-Si-B-Al green ceramic sheet, and then the green ceramic sheet was placed at 100°C to dry the dodecane in the silver paste and promote the migration of hydrophobic alumina to the surface and boundary layers; the green ceramic sheets were stacked and isostatically pressed at 40 MPa, and then the green ceramic sheets were sintered at 850°C.

[0072] Example 1

[0073] This embodiment fabricates an LTCC substrate using an inhibition method. First, solution A is prepared: 60g of dodecane and 20g of a number-average molecular weight compound (3.0 × 10⁻⁶) are weighed. 4 A solution A was obtained by dissolving polyisobutylene (g / mol), Span 80 (6g), diisononyl phthalate (4g), and methacryloyloxysilane coupling agent (0.5g) in a reactor at 80°C and 200 rpm for 4 hours, followed by cooling to room temperature.

[0074] Next, prepare dispersion B: Weigh 20g of hydrophobic alumina with a D50 particle size of 500nm and 60g of solution A, and place them in a ball mill jar. After ball milling at 200rpm for 6h, dispersion B is obtained.

[0075] Then, prepare the silver paste: weigh 312g of D50 with a particle size of 2μm and a tap density of 4g / cm³. 3 Spherical silver powder and 8g of Ca-Si-B-Al glass powder with a D50 particle size of 2μm and a softening temperature of 600℃ were placed in dispersion B and ball-milled at 200rpm for 6h. Then, the powder was ground using a three-roll mill until the fineness was 8μm, thus obtaining silver paste.

[0076] Finally, the LTCC substrate was prepared: silver paste was screen-printed onto a Ca-Si-B-Al green ceramic sheet, and then the green ceramic sheet was placed at 100°C to dry the dodecane in the silver paste and promote the migration of hydrophobic alumina to the surface and boundary layers; the green ceramic sheets were stacked and isostatically pressed at 40 MPa, and then the green ceramic sheets were sintered at 850°C.

[0077] Example 2

[0078] First, prepare solution A: Weigh 60g of silicone oil with a boiling point of 220-250℃ and 10g of silicone oil with a number average molecular weight of 4.0×10⁻⁶. 4 A solution A was obtained by dissolving 10 g / mol polyethylene, 10 g Span 85, 2 g tributyl citrate, and 0.5 g methacryloyloxysilane coupling agent in a reactor at 100 °C and 200 rpm for 6 h, followed by cooling to room temperature.

[0079] Next, prepare dispersion B: Weigh 30g of hydrophobic magnesium oxide with a D50 particle size of 800nm ​​and 60g of solution A, and place them in a ball mill jar. After ball milling at a speed of 200rpm for 6h, dispersion B is obtained.

[0080] Then, prepare the silver paste: weigh 280g of D50 with a particle size of 1μm and a tap density of 3g / cm³. 3 Spherical silver powder and 12g of Ca-Si-KB-Al glass powder with a D50 particle size of 800nm ​​and a softening temperature of 550℃ were placed in dispersion B and ball-milled for 6h at a speed of 200rpm. After grinding with a three-roll mill until the fineness was 6μm, silver paste was prepared.

[0081] Finally, the LTCC substrate was prepared: silver paste was printed onto a Ca-Si-KB-Al green ceramic sheet using a screen, and then the green ceramic sheet was dried at 100°C to remove the silicone oil in the silver paste and promote the migration of hydrophobic magnesium oxide to the surface and boundary layers; the green ceramic sheets were stacked and isostatically pressed at 30 MPa, and then the green ceramic sheets were sintered at 830°C.

[0082] The sintered silver layers from Comparative Examples 1-4 and Examples 1-2 were tested, and the results are summarized in the following table:

[0083] As shown in Example 1 and Comparative Examples 1 and 2, using the dispersant (Span 80) of this application alone can ensure good dispersibility of the silver paste and obtain a silver electrode with low sheet resistance, but it cannot suppress silver diffusion. As shown in Comparative Example 3, adding unmodified filler alone not only failed to suppress silver diffusion, but also significantly increased the electrode sheet resistance due to the poor dispersibility of the filler. As shown in Comparative Example 4, when the particle size of the hydrophobic filler is too large, although it has a certain inhibitory effect on electrode diffusion, it is not ideal and has a negative impact on resistance.

[0084] In contrast, Examples 1 and 2, by simultaneously using hydrophobic fillers of specific particle sizes and the dispersant described in this application, and by utilizing their phase separation and migration behavior during the drying process, successfully prepared low sheet resistance silver electrodes while significantly reducing the diffusion distance of silver to 15 μm and 5 μm, respectively, which is far superior to the four comparative examples, and achieved a significant diffusion inhibition effect.

[0085] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope. The scope of protection of the present invention is defined by the appended claims, specification, and their equivalents.

Claims

1. A silver paste for suppressing electrode diffusion, characterized in that, The silver paste, by weight percentage, comprises: 50-90 wt% silver powder, 0-20 wt% glass powder, 0.05-15 wt% hydrophobic filler, 0.01-5 wt% dispersant, 0-10 wt% binder, 8-30 wt% solvent, 0-5 wt% plasticizer, and 0-1 wt% adhesive aid, wherein the hydrophobic filler is a hydrophobically modified inorganic oxide particle.

2. The silver paste according to claim 1, characterized in that, The silver powder has a D50 particle size of 10 nm-5 μm and a tap density of 2-7 g / cm³. 3 The silver powder has one or more of the following morphologies: spherical, near-spherical, flake-like, dendritic, and flocculent.

3. The silver paste according to claim 2, characterized in that, The silver powder has a D50 particle size of 500nm-3μm, a tap density of 3-5g / cm³, and a morphology of spherical or near-spherical.

4. The silver paste according to claim 1, characterized in that, The glass powder has a D50 particle size of 10nm-5μm and a softening temperature of 300-700℃. The glass powder contains one or more of the following components: calcium oxide, silicon oxide, boron oxide, bismuth oxide, sodium oxide, potassium oxide, zinc oxide, aluminum oxide, magnesium oxide, and barium oxide.

5. The silver paste according to claim 4, characterized in that, The glass powder has a D50 particle size of 500nm-3μm and a softening temperature of 500-600℃.

6. The silver paste according to claim 1, characterized in that, The hydrophobic filler is one or more of the following: hydrophobically modified silica, alumina, titanium oxide, zinc oxide, zirconium oxide, cerium oxide, lanthanum oxide, copper oxide, tin oxide, and magnesium oxide.

7. The silver paste according to claim 6, characterized in that, The hydrophobic filler is one or more of hydrophobically modified alumina, magnesium oxide, cerium oxide, and lanthanum oxide.

8. The silver paste according to claim 7, characterized in that, The D50 particle size of the hydrophobic filler is 50nm-800nm.

9. The silver paste according to claim 1, characterized in that, The dispersant is one or more of alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, sorbitol ester and their polyoxyethylene derivatives.

10. The silver paste according to claim 9, characterized in that, The dispersant is one or more of Span 85, Span 65, and Span 80, which are sorbitol esters and their polyoxyethylene derivatives.

11. The silver paste according to claim 1, characterized in that, The adhesive is one or more of polyethylene, polypropylene, polyisobutylene, polystyrene, polytetrafluoroethylene, and polyvinylidene fluoride.

12. The silver paste according to claim 11, characterized in that, The adhesive is polyethylene or polyisobutylene.

13. The silver paste according to claim 12, characterized in that, The number average molecular weight of the polyethylene or polyisobutylene is 1.0-5.0 × 10⁻⁶. 4 g / mol.

14. The silver paste according to claim 1, characterized in that, The solvent is one or more of alkanes and their mixtures, low-viscosity silicone oil, and low-polarity ethers.

15. The silver paste according to claim 14, characterized in that, The solvent is selected from C 10 -C 16 Alkanes or silicone oils with a boiling point range of 150-300 ℃.

16. The silver paste according to claim 1, characterized in that, The plasticizer is one or more of phthalates, aliphatic diesters, and citrates.

17. The silver paste according to claim 16, characterized in that, The plasticizer is one or more of diisononyl phthalate, dioctyl phthalate, diisodecyl phthalate, tributyl citrate, and acetylated tributyl citrate.

18. The silver paste according to claim 1, characterized in that, The adhesive aid is one or more of the following: aminosilane coupling agent, epoxysilane coupling agent, methacryloxysilane coupling agent, vinylsilane coupling agent, mercaptosilane coupling agent, and titanate coupling agent.

19. The silver paste according to claim 18, characterized in that, The adhesive aid is a methacryloyloxysilane coupling agent.

20. A preparation method for preparing silver paste according to any one of claims 1-19, characterized in that, Includes the following steps: S1, weigh out the solvent, binder, dispersant, plasticizer and adhesive aid, place them in a reactor, and after they dissolve, cool to room temperature to obtain solution A; S2, Weigh out the hydrophobic filler and solution A, and place them in a ball mill jar for ball milling to obtain dispersion B; S3, weigh silver powder and glass powder and place them in dispersion B. After ball milling, grind them using a three-roll mill to obtain silver paste.

Images