Silver paste and preparation method thereof

Abstract

The invention discloses silver paste and a preparation method thereof. The silver paste comprises silver powder and an organic carrier. Wherein the organic carrier comprises a solvent, a metal complexing agent and silver salt; wherein the metal complexing agent and silver salt are subjected to a complexing reaction to generate a complex, and the complex has a polar group. In this way, diffusion of silver paste in the printing process can be reduced, and the precision and reliability of the semiconductor device are improved.

Description

Technical Field

[0001] This application relates to the field of semiconductor device technology, and in particular to a silver paste and its preparation method. Background Art

[0002] As modern electronic devices rapidly evolve towards higher power density, miniaturization, and high-temperature reliability, third-generation semiconductor devices and high-power modules, represented by silicon carbide (SiC) and gallium nitride (GaN), place increasingly stringent demands on packaging materials. These devices typically operate in high-temperature environments and must withstand extremely high current densities and frequent thermal cycling. Traditional tin-based solders, due to their inherent limitations—low melting point and low thermal conductivity—are prone to significant creep deformation, thermal fatigue cracking, and excessive growth of intermetallic compounds under high-temperature service conditions, severely restricting the reliability performance of devices in critical fields such as aerospace, electric vehicle control systems, and industrial frequency converters.

[0003] Against this backdrop, sintered silver technology has become a typical representative of the next generation of interconnect materials due to its unique material advantages. Its core technology lies in forming a dense silver sintered layer through a low-temperature sintering process (typically at 200-300℃) using nano / micro composite silver particles. This structure possesses excellent electrical and thermal conductivity approaching that of bulk silver, and can maintain long-term stability under extreme environments such as high temperature and high current density.

[0004] However, in chip mounting processes, the high fluidity of traditional silver paste can lead to a series of interface engineering challenges: First, low-viscosity silver paste is prone to three-dimensional diffusion after printing, which can easily cause bridging and short circuits between adjacent electrodes; second, excessive diffusion can change the preset silver layer thickness distribution, causing differences in sintering density in local areas, which in turn affects thermomechanical reliability; third, in multi-layer stacked packaging, the capillary climb phenomenon of silver paste may cause insulation failure of vertical interconnect structures. Summary of the Invention

[0005] The main technical problem addressed by this application is to provide a silver paste and its preparation method, which can reduce the diffusion of silver paste during the printing process and improve the precision and reliability of semiconductor devices.

[0006] To solve the above-mentioned technical problems, one technical solution adopted in this application is: to provide a silver paste, which includes silver powder and an organic carrier; wherein the organic carrier includes a solvent, a metal complexing agent and a silver salt; wherein the metal complexing agent reacts with the silver salt to form a complex, and the complex has polar groups.

[0007] The metal complexing agent is a crown ether.

[0008] The metal complexing agent is at least one of 18-crown-6, dibenzo-18-crown-6, and 15-crown-5.

[0009] The solvent is a polar solvent.

[0010] The solvent is at least one of ethylene glycol, dimethyl sulfoxide, and N-methylpyrrolidone.

[0011] The silver salt is at least one of silver acetate, silver nitrate, and silver citrate.

[0012] The silver powder includes flake-shaped silver powder of 1μm-5μm and submicron spherical silver powder of 0.2-2μm.

[0013] The silver particles in the silver powder are coated with surface ligands, which are at least one of organic acids, organic amines, and polyvinylpyrrolidone.

[0014] The organic carrier also includes dispersants and thixotropic agents; in the silver paste, the mass percentage of silver powder is 90%-94%, the mass percentage of solvent is 3%-7%, the mass percentage of metal complexing agent and silver salt is 0.1%-1%, the mass percentage of dispersant is 0-1%, and the mass percentage of thixotropic agent is 0-1%.

[0015] To solve the above-mentioned technical problems, another technical solution adopted in this application is: to provide a method for preparing silver paste, the method comprising: mixing a metal complexing agent, a silver salt and a solvent to obtain an organic carrier; adding the organic carrier to silver powder and stirring to obtain a mixture; grinding the mixture to obtain silver paste; wherein the metal complexing agent and the silver salt undergo a complexing reaction to generate a complex, the complex having polar groups.

[0016] The beneficial effects of this application are as follows: Unlike the prior art, the silver paste in this application comprises silver powder and an organic carrier; wherein the organic carrier comprises a solvent, a metal complexing agent, and a silver salt; wherein the metal complexing agent undergoes a complexation reaction with the silver salt to form a complex, and the complex has polar groups. In the above method, the metal complexing agent can complex silver ions to form a silver ion complex through a complexation reaction with the silver salt. During the subsequent sintering of the silver paste, the silver ion complex can release silver ions, which are reduced to silver atoms at high temperature, promoting the sintering process and thus improving the electrical performance of the bonding layer formed by the sintering of the silver paste, thereby improving the electrical performance of the semiconductor device. Furthermore, the metal complexing agent reacts with the silver salt to form a complex. This complex has polar groups, which can enhance the polarity of the solvent system in the silver paste, improve the cohesiveness of the silver paste, thereby reducing the diffusion of the silver paste on the chip surface during the printing process. This reduces the probability of bridging short circuits and capillary creep between adjacent electrodes, improves the uniformity of the silver layer thickness distribution, and ultimately improves the precision and reliability of semiconductor devices. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0018] Appendix Figure 1 This is a flowchart illustrating the preparation method of the silver paste of this application. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0020] This application provides a silver paste. This silver paste can be used for semiconductor device packaging and interconnection, specifically for chip bonding, attaching semiconductor chips to a packaging substrate or lead frame to provide electrical and thermal conduction pathways; it can also be used for interconnect lines and electrodes. In some thick-film hybrid circuits, flexible electronic products, and radio frequency devices, conductive silver paste can be directly printed as conductive lines, electrodes, and antennas; it can also be used in LED packaging, where conductive silver paste is used to bond LED chips, providing electrode connections and heat dissipation channels. Of course, the silver paste in this application can also be used in other areas, such as solar cells and sensors, and is not limited here.

[0021] In one embodiment, the silver paste comprises silver powder and an organic carrier.

[0022] Specifically, silver powder is the core conductive component of silver paste and can be composed of at least one of spherical silver powder, flake silver powder, etc. Spherical silver powder is easy to disperse, which helps improve the fluidity and printability of silver paste, as well as facilitating interfacial diffusion during sintering and enhancing sintering performance. Flake silver powder helps to increase the thixotropic value of silver paste, does not deform after printing, and due to its unique structure, it can form more overlapping points after curing or sintering, thus achieving better conductivity with lower filler content. In practical applications, the appropriate silver powder can be selected according to the specific application scenario and performance requirements.

[0023] In one embodiment, the silver powder in this application comprises flake silver powder and submicron spherical silver powder, specifically including flake silver powder of 1μm-5μm and submicron spherical silver powder of 0.2μm-2μm.

[0024] The size of flake silver powder (1μm-5μm) refers to the lateral dimension of the silver particles in the powder, which is the diameter or side length of the silver particles when they are spherical or polygonal flakes. The size of spherical silver powder (0.2μm-2μm) refers to the particle size of the silver particles in the powder, that is, the diameter of a single spherical or near-spherical silver particle.

[0025] Specifically, the size of the flake silver powder can be 1μm, 2μm, 3μm, 4μm, 5μm, etc., and the size of the spherical silver powder can be 0.2μm, 0.4μm, 0.6μm, 0.8μm, 1μm, 1.5μm, 2μm, etc., without any specific limitation here.

[0026] Furthermore, in this embodiment, the flake-shaped silver powder provides a large contact area, enhancing the conductivity of the silver paste; while the spherical silver powder fills the gaps, increasing the packing density of the silver paste. Mixing micron-sized flake-shaped silver powder with submicron-sized spherical silver powder further improves conductivity and mechanical strength by optimizing the packing density through size optimization. The combination of these two materials enhances the overall performance of the silver paste.

[0027] Furthermore, the silver particles in the silver powder can be ordinary silver particles or modified silver particles. Specifically, the surface properties, structure, or composition of the material can be altered through physical, chemical, or mechanical methods, thereby improving its overall performance or endowing it with new functions. In one embodiment, the silver particles in the silver powder are coated with surface ligands.

[0028] The ligands coated on the surface of the silver particles can be organic molecules, which can be adsorbed onto the surface of the silver particles through chemical bonding or physical adsorption to form a thin film, thereby improving the performance of the silver particles.

[0029] Specifically, in one embodiment, the surface ligand is at least one of an organic acid, an organic amine, and polyvinylpyrrolidone.

[0030] The aforementioned surface ligands can effectively prevent direct contact and aggregation between silver particles through steric hindrance or electrostatic repulsion, which is beneficial for maintaining good dispersibility of silver powder in solvents and increasing the solid content of silver paste. During the subsequent drying process, the high solid content of the silver paste helps reduce shrinkage and maintain the printed shape.

[0031] Furthermore, the organic carrier is the liquid matrix of the silver paste, used to hold the silver powder and ensure the stability and operability of the silver paste during processing and application.

[0032] The organic carrier may include a solvent to provide the rheological properties required for printing. In one embodiment, the solvent may be a polar solvent, specifically including at least one of ethylene glycol, dimethyl sulfoxide, N-methylpyrrolidone, etc.

[0033] It should be noted that highly polar solvents can control the wetting and spreading behavior of silver paste on the chip surface, reduce the diffusion of silver paste on the chip surface during subsequent printing, thereby reducing the probability of phenomena such as bridging short circuits and capillary creep between adjacent electrodes, improving the uniformity of silver layer thickness distribution, and thus improving the precision and reliability of semiconductor devices.

[0034] Furthermore, in one embodiment, the organic carrier further includes a metal complexing agent and a silver salt. Specifically, the metal complexing agent can complex silver ions to form a silver ion complex through a complexation reaction with the silver salt. During the subsequent sintering of the silver paste, the silver ion complex can release silver ions. The released silver ions are reduced to silver atoms at high temperature, promoting the sintering process and thereby improving the electrical performance of the bonding layer formed by the sintering of the silver paste, thus improving the electrical performance of the semiconductor device.

[0035] Furthermore, the metal complexing agent undergoes a complexation reaction with the silver salt to form a complex. This complex has polar groups, which can enhance the polarity of the solvent system in the silver paste and improve the cohesiveness of the silver paste, thereby reducing the diffusion of the silver paste on the chip surface during the printing process. Similarly, it can further reduce the probability of bridging short circuits and capillary creep between adjacent electrodes, improve the uniformity of the silver layer thickness distribution, and further improve the precision and reliability of semiconductor devices.

[0036] In one embodiment, the metal complexing agent is a crown ether. On one hand, the crown ether can selectively complex silver ions provided by the silver salt, reducing ion-induced silver particle aggregation, and simultaneously acting as a steric barrier, which is beneficial for the dispersion of silver particles. On the other hand, the crown ether has a strongly polar oxygen atom ring. When it complexes with silver particles to form a crown ether-silver complex, the polarity is significantly enhanced. Because the cations are exposed outside the cavity, they can interact strongly with the polar solvent, increasing the overall polarity of the system and further reducing the diffusion of silver paste on the chip surface.

[0037] In addition, crown ethers adsorbed on the surface of silver particles provide electron density through oxygen atoms, inhibiting oxidation and thus improving the long-term stability of silver paste.

[0038] In one embodiment, the complexing agent may be at least one of 18-crown-6, dibenzo-18-crown-6, 15-crown-5, etc.

[0039] In one embodiment, the silver salt may be at least one of silver acetate, silver nitrate, silver citrate, etc.

[0040] In this application, the organic carrier may also include additives to optimize the adhesion, mechanical strength and processing characteristics of the silver paste.

[0041] In one embodiment, the organic carrier may include a dispersant. The addition of a dispersant can help prevent silver powder agglomeration, improve the dispersibility of silver powder in the organic carrier, thereby enhancing the storage stability of the silver paste; in addition, it can also help improve the compatibility between silver powder and solvent, and increase the solid content of the silver paste.

[0042] In one embodiment, the dispersant may include at least one of BYK-111, Tween-80, citric acid, etc.

[0043] Among them, BYK-111, or DISPERBYK-111, is a wetting and dispersing agent produced by BYK GmbH in Germany. Tween-80, also known as polysorbate 80, can be prepared by ethoxylation of sorbitan and oleic acid.

[0044] In one embodiment, the organic carrier may further include a thixotropic agent. The thixotropic agent can adjust the rheological properties of the silver paste to adapt it to different printing or dispensing processes. Specifically, it can enhance the viscosity of the silver paste at rest, thereby helping the printed pattern maintain its shape and reducing diffusion or collapse.

[0045] In one embodiment, the thixotropic agent may include at least one of polyamide wax, hydrogenated castor oil, etc.

[0046] Of course, in some implementations, the organic carrier may not include additives. The specific choice can be made according to actual needs, and no limitation is made here.

[0047] Furthermore, in one embodiment, the silver paste comprises silver powder and an organic carrier, the organic carrier comprising a solvent, a metal complexing agent and a silver salt, a dispersant and a thixotropic agent. The silver powder comprises 90%-94% by mass, the solvent comprises 3%-7% by mass, the crown ether and silver salt comprise 0.1%-1% by mass, the dispersant comprises 0%-1% by mass, and the thixotropic agent comprises 0%-1% by mass.

[0048] Specifically, the mass percentage of silver powder can be 90%, 91%, 92%, 93%, 94%, etc., the mass percentage of solvent can be 3%, 4%, 5%, 6%, 7%, etc., the mass percentage of crown ether and silver salt can be 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, etc., the mass percentage of dispersant can be 0%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, etc., and the mass percentage of thixotropic agent can be 0%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, etc. The specific percentage can be determined according to the actual application and performance requirements, etc., and is not limited here.

[0049] This application also provides a method for preparing silver paste, which can be used at least to prepare the silver paste provided in the foregoing embodiments of this application.

[0050] In one embodiment, referring to the accompanying drawings, the method for preparing the silver paste may include:

[0051] Step S10: Mix the metal complexing agent, silver salt and solvent to obtain an organic carrier;

[0052] Specifically, metal complexing agents, silver salts, etc., can be added to the solvent and stirred evenly to obtain an organic carrier.

[0053] Step S20: Add an organic carrier to the silver powder and stir to obtain a mixture;

[0054] In this step, a high-speed centrifuge can be used to stir the silver powder and the organic carrier to obtain a homogeneous mixture.

[0055] Specifically, after mixing silver powder with liquid, the mixture is stirred using a high-speed rotating device to achieve preliminary and uniform mixing and dispersion of the silver powder in the organic carrier.

[0056] Step S30: Grind the mixture to obtain silver paste.

[0057] When grinding the mixture, a three-roll mill can be used to grind it 3-5 times, reducing the gap between the rollers to less than 10μm.

[0058] To ensure that the uniformity and fineness of the dispersion of solid particles, such as silver powder, in the silver paste meet the application requirements, the mixture of silver powder and organic carrier can be repeatedly passed through a three-roll mill 3 to 5 times. During each grinding process, the distance between the rollers can be gradually reduced until the final roller gap is set to less than 10 μm, thereby ensuring that the particles in the silver paste can be ground and dispersed to a size of less than 10 μm to meet the product's requirements for fineness, uniformity, and final performance.

[0059] In addition, the metal complexing agent reacts with the silver salt to form a complex, which has polar groups.

[0060] In other embodiments, additives such as dispersants and thixotropic agents may be added when preparing the organic carrier. The specific additions can be determined according to the application scenario and performance requirements of the prepared silver paste, and are not specifically limited here.

[0061] The substances involved in the above-mentioned silver paste preparation method, such as metal complexing agents, silver salts, solvents, silver powder, dispersants, thixotropic agents, etc., are the same as the corresponding components in the silver paste embodiments described above in this application. For details, please refer to the above embodiments, which will not be repeated here.

[0062] It should be noted that in the above method, the metal complexing agent can complex silver ions to form a silver ion complex through a complexation reaction with silver salt. During the subsequent sintering of the silver paste, the silver ion complex can release silver ions. The released silver ions are reduced to silver atoms at high temperature, which can promote the sintering process and improve the electrical performance of the bonding layer formed by the sintering of silver paste, thereby improving the electrical performance of the semiconductor device. In addition, the complex formed by the complexing reaction between the metal complexing agent and silver salt has polar groups, which can enhance the polarity of the solvent system in the silver paste, improve the cohesion of the silver paste, reduce the diffusion of silver paste on the chip surface during printing, and thus reduce the probability of bridging short circuits and capillary creep between adjacent electrodes, improve the uniformity of silver layer thickness distribution, and thus improve the precision and reliability of the semiconductor device.

[0063] The above-mentioned technical solutions of this application will be described below with reference to specific embodiments and comparative examples.

[0064] Example 1

[0065] (1) Preparation of silver paste: Solvent ethylene glycol, metal complexing agent crown ether 18-crown-6, silver salt silver acetate, dispersant BYK-111, and thixotropic agent polyamide wax are mixed in a mass ratio of 5:0.61:0.39:1:1 as an organic carrier; then, a mixture of 2μm flake silver powder and 0.4μm submicron spherical silver powder, and silver powder with surface modification by dodecanoic acid are selected, and the above organic carrier is added to the silver powder, wherein the mass ratio of silver powder to organic carrier is 92:8, and the mixture is stirred evenly using a high-speed centrifuge to obtain a mixture of silver powder and organic carrier; then, the mixture is ground 4 times using a three-roll mill to reduce the gap between the rollers to below 10μm to obtain silver paste.

[0066] (2) Sample measurement: The silver paste prepared in step (1) was printed onto the chip surface through a 3mm×3mm steel screen and dried in an oven at 80℃ for 30min. After drying, the sample side length was measured using a 3D profilometer and found to be 3.08mm×3.07mm.

[0067] Comparative Example 1

[0068] (1) Preparation of silver paste: Solvent ethylene glycol, dispersant BYK-111 and thixotropic agent polyamide wax are mixed in a mass ratio of 6:1:1 as an organic carrier; then, a mixture of 3μm flake silver powder and 0.5μm submicron spherical silver powder, and silver powder with surface modification by dodecanoic acid are selected, and the above organic carrier is added to the silver powder, wherein the mass ratio of silver powder to organic carrier is 92:8, and the mixture is stirred evenly using a high-speed centrifuge to obtain a mixture of silver powder and organic carrier; then, the mixture is ground 4 times using a three-roll mill to reduce the gap between the rollers to less than 10μm to obtain silver paste.

[0069] (2) Sample measurement: The silver paste prepared in step (1) was printed onto the chip surface through a 3mm×3mm steel screen and dried in an oven at 80℃ for 30min. After drying, the sample side length was measured using a 3D profilometer and found to be 3.21mm×3.19mm.

[0070] Example 2

[0071] (1) Preparation of silver paste: The solvent dimethyl sulfoxide (DMSO), the metal complexing agent crown ether dibenzo-18-crown-6, the silver salt silver nitrate, the dispersant Tween-80, and the thixotropic agent polyamide wax were mixed in a mass ratio of 3:0.68:0.32:1:1 as an organic carrier; then, a mixture of 3μm flake silver powder and 0.5μm submicron spherical silver powder, and silver powder with surface modification by dodecylamine were selected, and the above organic carrier was added to the silver powder, wherein the mass ratio of silver powder to organic carrier was 94:6, and the mixture was stirred evenly using a high-speed centrifuge to obtain a mixture of silver powder and organic carrier; then, the mixture was ground 4 times using a three-roll mill to reduce the gap between the rollers to less than 10μm to obtain silver paste.

[0072] (2) Sample measurement: The silver paste prepared in step (1) was printed onto the chip surface through a 3mm×3mm steel screen and dried in an oven at 80℃ for 30min. After drying, the sample side length was measured using a 3D profilometer and found to be 3.08mm×3.08mm.

[0073] Example 3

[0074] (1) Preparation of silver paste: The solvent N-methylpyrrolidone (NMP), the metal complexing agent crown ether 15-crown-5, the silver salt silver citrate, the dispersant citric acid, and the thixotropic agent hydrogenated castor oil were mixed in a mass ratio of 7:0.68:0.32:1:1 as an organic carrier; then, a mixture of 1μm flake silver powder and 0.2μm submicron spherical silver powder was selected, and the above organic carrier was added to the silver powder that was surface modified with polyvinylpyrrolidone, wherein the mass ratio of silver powder to organic carrier was 90:10, and the mixture was stirred evenly using a high-speed centrifuge to obtain a mixture of silver powder and organic carrier; then, the silver paste was ground three times using a three-roll mill to reduce the gap between the rollers to less than 10μm to obtain the silver paste.

[0075] (2) Sample measurement: The silver paste prepared in step (1) was printed onto the chip surface through a 3mm×3mm steel screen and dried in an oven at 80℃ for 30min. After drying, the sample side length was measured using a 3D profilometer and found to be 3.1mm×3.1mm.

[0076] It should be noted that the silver paste is printed onto the chip surface using a 3mm x 3mm stencil, and the change in its edge length during the drying process is a key indicator for measuring the degree of diffusion. As can be seen from Examples 1-3 and the comparative examples above, the edge length change of the sample corresponding to the silver paste with added metal complexing agent and silver salt is significantly smaller than that of the sample corresponding to the silver paste without added metal complexing agent and silver salt. This further illustrates that the metal complexing agent in this application undergoes a complexation reaction with the silver salt to form a complex. This complex has polar groups, which can enhance the polarity of the solvent system in the silver paste, improve the cohesiveness of the silver paste, and thus reduce the diffusion of the silver paste on the chip surface during the printing process.

[0077] The above are merely embodiments of this application and do not limit the scope of this patent application. Any equivalent structural or procedural changes made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of this application.

Claims

1. A silver paste, characterized in that, The invention comprises silver powder and an organic carrier; wherein the organic carrier includes a solvent, a metal complexing agent, and a silver salt; wherein the metal complexing agent reacts with the silver salt to form a complex, and the complex has polar groups.

2. The silver paste according to claim 1, characterized in that, The metal complexing agent is a crown ether.

3. The silver paste according to claim 2, characterized in that, The metal complexing agent is at least one of 18-crown-6, dibenzo-18-crown-6, and 15-crown-5.

4. The silver paste according to claim 1, characterized in that, The solvent is a polar solvent.

5. The silver paste according to claim 4, characterized in that, The solvent is at least one of ethylene glycol, dimethyl sulfoxide, and N-methylpyrrolidone.

6. The silver paste according to claim 1, characterized in that, The silver salt is at least one of silver acetate, silver nitrate, and silver citrate.

7. The silver paste according to claim 1, characterized in that, The silver powder comprises flake-shaped silver powder of 1μm-5μm and submicron spherical silver powder of 0.2-2μm.

8. The silver paste according to claim 1, characterized in that, The silver particles in the silver powder are coated with surface ligands, which are at least one of organic acids, organic amines, and polyvinylpyrrolidone.

9. The silver paste according to claim 1, characterized in that, The organic carrier also includes a dispersant and a thixotropic agent; In the silver paste, the mass percentage of the silver powder is 90%-94%, the mass percentage of the solvent is 3%-7%, the mass percentage of the metal complexing agent and the silver salt is 0.1%-1%, the mass percentage of the dispersant is 0%-1%, and the mass percentage of the thixotropic agent is 0%-1%.

10. A method for preparing silver paste, characterized in that, include: The organic carrier is obtained by mixing the metal complexing agent, silver salt and solvent; An organic carrier is added to silver powder and the mixture is stirred to obtain a mixture; The mixture is ground to obtain the silver paste; The metal complexing agent undergoes a complexing reaction with the silver salt to form a complex, and the complex has polar groups.

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