Ultralow-temperature sintering type silver paste for ultrasonic fingerprint module and preparation method and application of ultralow-temperature sintering type silver paste

Abstract

The invention discloses ultralow-temperature sintering type silver paste for an ultrasonic fingerprint module and a preparation method and application of the ultralow-temperature sintering type silver paste, and belongs to the technical field of ultrasonic fingerprint module transmission media. The ultralow-temperature sintered silver paste for the ultrasonic fingerprint module comprises the following components in percentage by mass: 2%-5% of saturated polyester, 0.1%-1% of a curing agent, 0.01%-0.5% of a saturated polyester modified additive, 80%-90% of nano silver powder, 2%-10% of a solvent, 0.1%-2% of a dispersing agent, 0.1%-0.5% of a silver paste sintering additive, 0.1%-1.2% of a coupling agent and 0.1%-1% of a thixotropic agent, wherein the saturated polyester is high-molecular-weight straight-chain saturated polyester with the weight-average molecular weight not lower than 20000. By optimizing the components of the sintered silver paste, the sintered silver paste has the advantages of low sintering temperature, high density, low thixotropy, low surface roughness, no layering after lamination, no large-size holes and the like.

Description

Technical Field

[0001] This invention belongs to the field of ultrasonic fingerprint module transmission medium technology, specifically relating to an ultra-low temperature sintering silver paste for ultrasonic fingerprint modules, its preparation method, and its application. Background Technology

[0002] Ultrasonic fingerprint modules are a type of biometric technology that uses ultrasonic waves to penetrate the skin of the finger and obtain 3D fingerprint images. They are characterized by high security and strong anti-interference capabilities and are widely used in high-end smartphones and smart devices. The conductive silver paste used in these modules includes sintered silver paste and cured silver paste. Compared with sintered silver paste, cured silver paste has many limitations, such as: (1) poor high temperature resistance, which can easily generate thermal stress between the piezoelectric layer and the substrate, leading to interface peeling or performance degradation; (2) due to the presence of resin and some organic additives, the low temperature during baking results in low density of the cured silver paste. Some solvent residues and air residues are difficult to remove during the curing process, which can form pores of 0.5 to 2 micrometers, causing attenuation of ultrasonic signals and directly affecting the clarity of the final image and the accuracy of fingerprint unlocking; (3) because the silver paste of low-temperature cured ultrasonic fingerprint modules inevitably needs to be laminated to meet the resistance and transmission path required for ultrasonic transmission, the presence of resin in low-temperature cured silver paste inevitably leads to the separation of some silver powder and resin, resulting in varying degrees of insulation; (4) moiré pattern problem.

[0003] Compared to solidified silver paste, sintered silver paste has superior conductivity, higher connection reliability, more efficient thermal management, stronger environmental adaptability, better long-term stability, and lower moiré pattern risk.

[0004] When used in ultrasonic fingerprint technology, ultra-low temperature sintered silver paste has high conductivity and low dielectric loss (tanδ<0.002), which can optimize the signal transmission between the sensor and the circuit. This increases the unlocking success rate of the module by more than 80% in environments such as wet hands, oil, and strong light, and also supports unlocking within 1 meter underwater.

[0005] Improving the performance of ultra-low temperature sintered silver paste for ultrasonic fingerprint modules is one of the research directions for ultrasonic fingerprint modules. Summary of the Invention

[0006] The purpose of this invention is to provide an ultra-low temperature sintering silver paste for ultrasonic fingerprint modules, its preparation method, and its application. By optimizing the composition of the sintering silver paste, it possesses advantages such as low sintering temperature (100-120℃), high density, low thixotropy (≤3), low surface roughness (Rz < 2μm), and no delamination or large-size pores (> 1μm) after lamination.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] One of the technical solutions of this invention is to provide an ultra-low temperature sintering silver paste for ultrasonic fingerprint modules, comprising, by mass percentage: 2%–5% saturated polyester, 0.1%–1% curing agent, 0.01%–0.5% saturated polyester modifying agent, 80%–90% nano silver powder, 2%–10% solvent, 0.1%–2% dispersant, 0.1%–0.5% silver paste sintering aid, 0.1%–1.2% coupling agent, and 0.1%–1% thixotropic agent; wherein the saturated polyester is a high molecular weight linear saturated polyester with a weight average molecular weight of not less than 20,000.

[0009] Preferably, the saturated polyester includes at least one of aromatic saturated polyester, aliphatic saturated polyester, and aromatic-aliphatic saturated polyester.

[0010] Preferably, the curing agent includes at least one of oxazoline, isocyanate, diisocyanate and dicyanate prepolymer.

[0011] Preferably, the saturated polyester modifying agent includes at least one of acid anhydride, organotin, and acetylacetone metal salt.

[0012] Preferably, the nano-silver powder includes at least one of the following: nano-silver powder 1 with an average particle size of 50-150 nm, an irregular polygonal structure, and a silver content of 90%-95%; nano-silver powder 2 with an average particle size of 200-300 nm, an irregular polygonal structure, and a silver content of 90%-95%; nano-silver powder 3 with an average particle size of 200-400 nm, a spherical structure, and a silver content of 90%-95%; and nano-silver powder 4 with an average particle size of 200-400 nm, a spherical structure, and a silver content of 99% or more.

[0013] Preferably, the solvent includes at least one selected from divalent ester (DBE), dimethyl adipate, 3-methoxybutyl acetate, diethyl adipate, 3-methoxybutyl acetate, and propylene glycol methyl ether acetate.

[0014] Preferably, the dispersant comprises at least one of quaternary ammonium salt, polyvinylpyrrolidone, sodium oleate, and TDO.

[0015] Preferably, the silver paste sintering aid includes at least one of sodium chloride (NaCl), hydrazine hydrate (N2H4), sodium borohydride (NaBH4), and tris(2-aminoethyl)amine.

[0016] Preferably, the coupling agent includes at least one selected from silane coupling agents, titanate coupling agents, aluminate coupling agents, bimetallic coupling agents, phosphate coupling agents, and borate coupling agents.

[0017] Preferably, the thixotropic agent comprises at least one of fumed silica, organobentonite, and polyamide wax.

[0018] The second technical solution of the present invention provides a method for preparing ultra-low temperature sintering silver paste for the above-mentioned ultrasonic fingerprint module, comprising the following steps:

[0019] Saturated polyester and solvent are dissolved at 90±5℃ to obtain a first mixture; saturated polyester modifier, silver paste sintering aid, coupling agent, dispersant and thixotropic agent are added to the first mixture, stirred evenly, and ground to obtain a second mixture; nano silver powder and curing agent are added to the second mixture, stirred evenly, ground, filtered and vacuum dispersed to obtain the ultra-low temperature sintering silver paste for the ultrasonic fingerprint module.

[0020] Preferably, the filtration is a high-mesh filtration of 1500 to 3500 mesh.

[0021] Preferably, the vacuum degree of the vacuum dispersion is 1-5 kPa, the stirring rate is 200-1000 rpm, and the time is 10-30 min.

[0022] The third technical solution of the present invention provides an application of the above-mentioned ultra-low temperature sintering silver paste for ultrasonic fingerprint modules in the preparation of ultrasonic fingerprint modules.

[0023] In the technical solution of this invention:

[0024] Saturated polyester is a linear saturated polyester with a large molecular weight. By controlling the molecular weight and optimizing the crystallinity, linear saturated polyester achieves a balance between strength and heat resistance. The intermolecular forces between linear molecular chains are weak, and the molecular chains are easy to slide, which minimizes the obstacles to the sintering of silver powder and lays the foundation for the low-temperature sintering of silver paste.

[0025] The mechanism by which silver paste sintering aids promote the sintering of silver nanoparticles is also known as ligand exchange reaction. This involves using a short-chain molecule or ion with better binding properties to the nanoparticle surface to replace the existing long-chain coating agent, thereby triggering the sintering of the nanoparticles at low temperatures. The key to triggering the low-temperature sintering of silver nanoparticles lies in the fact that the binding force between the silver paste and the silver particles is much greater than the adsorption between the coating agent and the silver particle surface. When silver nanoparticles come into contact with the sintering aid, the organic coating agent on their surface is replaced by a non-protective sintering aid. Therefore, driven by surface energy, low-temperature sintering occurs between the silver nanoparticles.

[0026] The saturated polyester modifier enables the saturated polyester to have a very large molecular weight after chain extension, with the maximum molecular weight reaching more than 10W. This achieves a high carrying capacity for silver powder, avoiding the sedimentation problem caused by the high density of silver powder. At the same time, due to the single functional group and the presence of the same polarity, there is an electrostatic repulsion effect between the silver powder particles, which helps the silver powder to be evenly distributed in the system and greatly reduces the possibility of agglomeration of nano silver powder.

[0027] In ultra-low temperature nano-sintered silver paste, the dispersant forms a protective layer on the surface of the silver nanoparticles by adsorbing onto them, preventing particle agglomeration through steric hindrance and thus ensuring the uniformity and sintering quality of the silver paste. Its mechanism of action is as follows: one end of the dispersant molecule has a polar carboxylic acid functional group, which can be adsorbed onto the surface of the silver nanoparticles; the other end has a hydrocarbon chain, which surrounds the particles through steric hindrance, preventing direct contact and aggregation between particles. It should also be noted that if the dispersant is not completely decomposed during low-temperature sintering, the residue will hinder the diffusion and bonding between silver particles, reducing the density and conductivity of the sintered body.

[0028] The coupling agent improves the dispersibility of silver powder, promoting closer contact and diffusion between silver particles during sintering, resulting in a denser conductive network. It gradually decomposes or desorbs during sintering, avoiding the problem of residues hindering the bonding of silver particles. Simultaneously, its molecular bridging effect promotes the diffusion and bonding between silver particles, contributing to the formation of a dense sintered structure.

[0029] The presence of the curing agent causes the silver nanoparticles to rearrange under the viscoelastic effect of the saturated polyester resin during the curing process, forming a denser conductive network. The curing agent improves the conductivity of the silver paste by adjusting the viscosity and flowability of the resin, promoting closer contact between particles, and reducing contact resistance.

[0030] Thixotropic agents enable silver paste to maintain high viscosity when at rest, preventing particle sedimentation. When subjected to shear force (such as the action of a printing squeegee), the viscosity decreases rapidly, achieving smooth printing. After the shear force disappears, the viscosity recovers quickly, maintaining the shape accuracy of the printed pattern. By improving the rheological properties of silver paste, thixotropic agents indirectly promote the uniform dispersion of nano-silver particles. Uniformly dispersed particles are more likely to form a dense conductive network during sintering, reducing contact resistance and improving conductivity. During sintering, silver paste regulated by thixotropic agents exhibits more complete diffusion and bonding between particles, which helps to form a dense sintered structure, reduces porosity, and improves sintering quality.

[0031] High-mesh filtration helps to obtain uniform, small-sized silver paste particles, improving the fineness of the silver paste and achieving a fineness of less than 1 μm (tested using a scraper fineness meter). Under an electron microscope, the silver paste particles after curing are less than 2 μm.

[0032] Vacuum dispersion helps to eliminate air bubbles introduced during the silver paste production process, reduces sintering resistance, and decreases the porosity (>0.5μm) of the sintered silver paste.

[0033] The beneficial technical effects of the present invention are as follows:

[0034] This invention optimizes the composition of sintering silver paste to achieve advantages such as low sintering temperature (100-120℃), high density, low thixotropy (≤3), low surface roughness (Rz<2μm), and no delamination or large-sized pores (>1μm) after lamination. Detailed Implementation

[0035] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0036] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0037] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0038] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0039] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0040] In the silver powders of this invention, Hashen Smart Materials TX-102 is a spherical silver powder with an average particle size of 280nm and a silver content of ≥99.9%; Texian LS0305 is a spherical silver powder with an average particle size of 240nm and a silver content of 91.4%; Texian KM120 is a polyhedral silver powder with an average particle size of 210nm and a silver content of 91.3%; and Sanzhixing MDOT-CF412 is a polyhedral silver powder with an average particle size of 150nm and a silver content of 90.1%.

[0041] Example 1

[0042] Preparation of ultra-low temperature sintering silver paste:

[0043] The raw materials by weight percentage are: 3.6% saturated polyester, 0.2% saturated polyester modifier, 0.2% curing agent, 0.2% silver paste sintering aid, 0.2% dispersant, 9.3% solvent, 0.8% coupling agent, 85% nano silver powder, and 0.5% thixotropic agent.

[0044] The saturated polyester is 100% Toyobo 270 saturated polyester (a linear saturated polyester with a weight-average molecular weight of 21,500).

[0045] The saturated polyester modifier is Aladdin's zirconium acetylacetonate;

[0046] The silver paste sintering aid is Aladdin's tri(2-aminoethyl)amine;

[0047] The curing agent is Asahi Kasei's K60X isocyanate;

[0048] The thixotropic agent is Wacker's H2O fumed silica;

[0049] The dispersant is Evonik's TDO;

[0050] The coupling agent is Dow Corning's 6040 silane coupling agent;

[0051] The solvent is a mixture of DBE and diethyl adipate (mass ratio 2:3);

[0052] The silver powder is silver (4): silver (3): silver (2) = 6.5: 2.3: 1.2, which corresponds to Harbin Shenzhi Materials TX-102, special line LS0305, and special line KM120 respectively;

[0053] Saturated polyester and solvent were heated and mixed in a glass stirred tank at 90±5℃ for 15 hours until the resin solution was uniform and fine, without large particles, which served as a primary carrier. The stirring speed was 450 rpm.

[0054] Saturated polyester modifier, silver paste sintering aid, coupling agent, dispersant and thixotropic agent are added to the obtained primary carrier. After mixing, the mixture is stirred at 70 / 1200 rpm on a double planetary mixer. The mixed slurry is then ground in a three-roll mill until the fineness of the slurry reaches below 1 μm, thus obtaining the secondary carrier.

[0055] After adding silver powder and curing agent to the obtained secondary carrier, the mixture is mixed at 70 / 1200 rpm on a double planetary mixer. The resulting mixture is then milled by three rollers, filtered through a filter press at 2000 mesh, and the silver paste is then vacuum dispersed at 500 rpm / 10 min / 1 kPa to obtain ultra-low temperature sintering silver paste.

[0056] The prepared ultra-low temperature sintered silver paste had a viscosity of 32500 cp, a thixotropy of 2.86, a fineness of 1.1 μm as measured by a scraper fineness meter, and a particle size of 2.4 μm as measured by a scanning electron microscope. After screen printing and drying at 100℃ for 60 min, its volume resistivity was found to be 1.5E-5 Ω·cm, its pencil hardness was ≥3H, and its adhesion was grade 5B.

[0057] After five layers of printing, the thickness is 15.5 μm, the surface roughness Rz is 1.8 μm, and there are clearly visible moiré patterns. After CP argon ion polishing, the silver paste does not separate into layers and there are no pores >1 μm.

[0058] Example 2

[0059] Preparation of ultra-low temperature sintering silver paste:

[0060] The raw materials by weight percentage are: 3.6% saturated polyester, 0.2% saturated polyester modifier, 0.2% curing agent, 0.2% silver paste sintering aid, 0.2% dispersant, 9.3% solvent, 0.8% coupling agent, 85% nano silver powder, and 0.5% thixotropic agent.

[0061] The saturated polyester is 100% Toyobo 270 saturated polyester (a linear saturated polyester with a weight-average molecular weight of 21,500).

[0062] The saturated polyester modifier is Aladdin's zirconium acetylacetonate;

[0063] The silver paste sintering aid is a 5% sodium chloride aqueous solution;

[0064] The curing agent is Asahi Kasei's K60X isocyanate;

[0065] The thixotropic agent is Wacker's H2O fumed silica;

[0066] The dispersant is Evonik's TDO;

[0067] The coupling agent is Dow Corning's 6040 silane coupling agent;

[0068] The solvent is a mixture of DBE and diethyl adipate (mass ratio 2:3);

[0069] The silver powder is silver (4): silver (3): silver (2) = 6.5: 2.3: 1.2, which corresponds to Harbin Shenzhi Materials TX-102, special line LS0305, and special line KM120 respectively.

[0070] Saturated polyester and solvent were heated and mixed in a glass stirred tank at 90±5℃ for 15 hours until the resin solution was uniform and fine, without large particles, which served as a primary carrier. The stirring speed was 450 rpm.

[0071] Saturated polyester modifier, silver paste sintering aid, coupling agent, dispersant and thixotropic agent are added to the obtained primary carrier. After mixing, the mixture is stirred at 70 / 1200 rpm on a double planetary mixer. The mixed slurry is then ground in a three-roll mill until the fineness of the slurry reaches below 1 μm, thus obtaining the secondary carrier.

[0072] After adding silver powder and curing agent to the obtained secondary carrier, the mixture is mixed at 70 / 1200 rpm on a double planetary mixer. The resulting mixture is then milled by three rollers, filtered through a filter press at 2000 mesh, and the silver paste is then vacuum dispersed at 500 rpm / 10 min / 1 kPa to obtain ultra-low temperature sintering silver paste.

[0073] The prepared ultra-low temperature sintered silver paste had a viscosity of 32400 cp, a thixotropy of 2.66, a fineness of 1.0 μm as measured by a scraper fineness meter, and a particle size of 2.1 μm as measured by a scanning electron microscope. After screen printing and drying at 100℃ for 60 min, its volume resistivity was tested to be 7.5E-6 Ω·cm, its pencil hardness was ≥3H, and its adhesion was grade 5B.

[0074] After five layers of printing, the thickness is 14.6 μm, the surface roughness Rz is 1.5 μm, and there are clearly visible moiré patterns. After CP argon ion polishing, the silver paste does not separate into layers and there are no pores >1 μm.

[0075] Example 3

[0076] Preparation of ultra-low temperature sintering silver paste:

[0077] The raw materials by weight percentage are: 3.6% saturated polyester, 0.2% saturated polyester modifier, 0.2% curing agent, 0.2% silver paste sintering aid, 0.2% dispersant, 9.3% solvent, 0.8% coupling agent, 85% nano silver powder, and 0.5% thixotropic agent.

[0078] The saturated polyester is 100% Toyobo 7000A saturated polyester (a linear saturated polyester with a weight-average molecular weight of 41295).

[0079] The saturated polyester modifier is Aladdin's zirconium acetylacetonate;

[0080] The silver paste sintering aid is Aladdin's tri(2-aminoethyl)amine;

[0081] The curing agent is Asahi Kasei's K60X isocyanate;

[0082] The thixotropic agent is Wacker's H2O fumed silica;

[0083] The dispersant is Evonik's TDO;

[0084] The coupling agent is Dow Corning's 6040 silane coupling agent;

[0085] The solvent is a mixture of DBE and diethyl adipate (mass ratio 2:3);

[0086] The silver powder is silver (4): silver (3): silver (2) = 6.5: 2.3: 1.2, which corresponds to Harbin Shenzhi Materials TX-102, special line LS0305, and special line KM120 respectively.

[0087] Saturated polyester and solvent were heated and mixed in a glass stirred tank at 90±5℃ for 15 hours until the resin solution was uniform and fine, without large particles, which served as a primary carrier. The stirring speed was 450 rpm.

[0088] Saturated polyester modifier, silver paste sintering aid, coupling agent, dispersant and thixotropic agent are added to the obtained primary carrier. After mixing, the mixture is stirred at 70 / 1200 rpm on a double planetary mixer. The mixed slurry is then ground in a three-roll mill until the fineness of the slurry reaches below 1 μm, thus obtaining the secondary carrier.

[0089] After adding silver powder and curing agent to the obtained secondary carrier, the mixture is mixed at 70 / 1200 rpm on a double planetary mixer. The resulting mixture is then milled by three rollers, filtered through a filter press at 2000 mesh, and the silver paste is then vacuum dispersed at 500 rpm / 10 min / 1 kPa to obtain ultra-low temperature sintering silver paste.

[0090] The prepared ultra-low temperature sintered silver paste had a viscosity of 31500 cp, a thixotropy of 2.52, a fineness of 1.0 μm as measured by a scraper fineness meter, and a particle size of 2.2 μm as measured by a scanning electron microscope. After screen printing and drying at 100℃ for 60 min, its volume resistivity was found to be 9.85E-6Ω·cm, its pencil hardness was ≥3H, and its adhesion was grade 5B.

[0091] After five layers of printing, the thickness is 15.6 μm, the surface roughness Rz is 1.4 μm, and there are clearly visible moiré patterns. After CP argon ion polishing, the silver paste does not separate into layers and there are no pores >1 μm.

[0092] Example 4

[0093] Preparation of ultra-low temperature sintering silver paste:

[0094] The raw materials by weight percentage are: 3.6% saturated polyester, 0.2% saturated polyester modifier, 0.2% curing agent, 0.2% silver paste sintering aid, 0.2% dispersant, 9.3% solvent, 0.8% coupling agent, 85% nano silver powder, and 0.5% thixotropic agent.

[0095] The saturated polyester is 100% Toyobo 270 saturated polyester (linear saturated polyester with a weight average molecular weight of 21,500);

[0096] The saturated polyester modifier is Aladdin's zirconium acetylacetonate;

[0097] The silver paste sintering aid is Aladdin's tri(2-aminoethyl)amine;

[0098] The curing agent is Asahi Kasei's K60X isocyanate;

[0099] The thixotropic agent is Wacker's H2O fumed silica;

[0100] The dispersant is Evonik's TDO;

[0101] The coupling agent is Dow Corning's 6040 silane coupling agent;

[0102] The solvent is a mixture of DBE and diethyl adipate (mass ratio 2:3);

[0103] The silver powder is silver (3): silver (2) = 6.5: 3.5, corresponding to special line LS0305 and special line KM120 respectively.

[0104] Saturated polyester and solvent were heated and mixed in a glass stirred tank at 90±5℃ for 15 hours until the resin solution was uniform and fine, without large particles, which served as a primary carrier. The stirring speed was 450 rpm.

[0105] Saturated polyester modifier, silver paste sintering aid, coupling agent, dispersant and thixotropic agent are added to the obtained primary carrier. After mixing, the mixture is stirred at 70 / 1200 rpm on a double planetary mixer. The mixed slurry is then ground in a three-roll mill until the fineness of the slurry reaches below 1 μm, thus obtaining the secondary carrier.

[0106] After adding silver powder and curing agent to the obtained secondary carrier, the mixture is mixed at 70 / 1200 rpm on a double planetary mixer. The resulting mixture is then milled by three rollers, filtered through a filter press at 2000 mesh, and the silver paste is then vacuum dispersed at 500 rpm / 10 min / 1 kPa to obtain ultra-low temperature sintering silver paste.

[0107] The prepared ultra-low temperature sintered silver paste had a viscosity of 33200 cp, a thixotropy of 2.76, a fineness of 0.9 μm as measured by a scraper fineness meter, and a particle size of 2.2 μm as measured by a scanning electron microscope. After screen printing and drying at 100℃ for 60 min, its volume resistivity was found to be 4.5E-6 Ω·cm, its pencil hardness was ≥3H, and its adhesion was grade 5B.

[0108] After five layers of printing, the thickness is 14.5 μm, the surface roughness Rz is 1.5 μm, and there are clearly visible moiré patterns. After CP argon ion polishing, the silver paste does not separate into layers and there are no pores >1 μm.

[0109] Example 5

[0110] Preparation of ultra-low temperature sintering silver paste:

[0111] The raw materials by weight percentage are: 3.6% saturated polyester, 0.2% saturated polyester modifier, 0.2% curing agent, 0.2% silver paste sintering aid, 0.2% dispersant, 9.3% solvent, 0.8% coupling agent, 85% nano silver powder, and 0.5% thixotropic agent.

[0112] The saturated polyester is 100% Toyobo 7000A saturated polyester (a linear saturated polyester with a weight-average molecular weight of 41,250).

[0113] The saturated polyester modifier is Aladdin's zirconium acetylacetonate;

[0114] The silver paste sintering aid is Aladdin's tri(2-aminoethyl)amine;

[0115] The curing agent is Asahi Kasei's K60X isocyanate;

[0116] The thixotropic agent is Wacker's H2O fumed silica;

[0117] The dispersant is Evonik's TDO;

[0118] The coupling agent is Dow Corning's 6040 silane coupling agent;

[0119] The solvent is a mixture of DBE and diethyl adipate (mass ratio 2:3);

[0120] The silver powder is silver (2): silver (3): silver (4) = 6.5: 2.3: 1.2, corresponding to special line LS0305, special line KM120, and Sanzhixing MDOT-CF412 respectively.

[0121] Saturated polyester and solvent were heated and mixed in a glass stirred tank at 90±5℃ for 15 hours until the resin solution was uniform and fine, without large particles, which served as a primary carrier. The stirring speed was 450 rpm.

[0122] Saturated polyester modifier, silver paste sintering aid, coupling agent, dispersant and thixotropic agent are added to the obtained primary carrier. After mixing, the mixture is stirred at 70 / 1200 rpm on a double planetary mixer. The mixed slurry is then ground in a three-roll mill until the fineness of the slurry reaches below 1 μm, thus obtaining the secondary carrier.

[0123] After adding silver powder and curing agent to the obtained secondary carrier, the mixture is mixed at 70 / 1200 rpm on a double planetary mixer. The resulting mixture is then milled by three rollers, filtered through a filter press at 2000 mesh, and the silver paste is then vacuum dispersed at 500 rpm / 10 min / 1 kPa to obtain ultra-low temperature sintering silver paste.

[0124] The prepared ultra-low temperature sintered silver paste had a viscosity of 32800 cp, a thixotropy of 2.36, a fineness of 0.8 μm as measured by a scraper fineness meter, and a particle size of 1.9 μm as measured by a scanning electron microscope. After screen printing and drying at 100℃ for 60 min, its volume resistivity was found to be 3.02E-6 Ω·cm, its pencil hardness was ≥3H, and its adhesion was grade 5B.

[0125] After five layers of printing, the thickness is 14.2 μm, the surface roughness Rz is 1.0 μm, and there are clearly visible moiré patterns. After CP argon ion polishing, the silver paste does not separate into layers and there are no pores >1 μm.

[0126] Example 6

[0127] Preparation of ultra-low temperature sintering silver paste:

[0128] The raw materials by weight percentage are: 3.6% saturated polyester, 0.2% saturated polyester modifier, 0.2% curing agent, 0.2% silver paste sintering aid, 0.2% dispersant, 9.3% solvent, 0.8% coupling agent, 85% nano silver powder, and 0.5% thixotropic agent.

[0129] The saturated polyester is 100% Toyobo 7000A saturated polyester (a linear saturated polyester with a weight-average molecular weight of 41,250).

[0130] The saturated polyester modifier is Aladdin's zirconium acetylacetonate;

[0131] The silver paste sintering aid is Aladdin's tri(2-aminoethyl)amine;

[0132] The curing agent is Asahi Kasei's K60X isocyanate;

[0133] The thixotropic agent is Wacker's H2O fumed silica;

[0134] The dispersant is Evonik's TDO;

[0135] The coupling agent is Dow Corning's 6040 silane coupling agent;

[0136] The solvent is a mixture of DBE and diethyl adipate (mass ratio 2:3);

[0137] The silver powder is 100% silver (4), namely, Three Star MDOT-CF412.

[0138] Saturated polyester and solvent were heated and mixed in a glass stirred tank at 90±5℃ for 15 hours until the resin solution was uniform and fine, without large particles, which served as a primary carrier. The stirring speed was 450 rpm.

[0139] Saturated polyester modifier, silver paste sintering aid, coupling agent, dispersant and thixotropic agent are added to the obtained primary carrier. After mixing, the mixture is stirred at 70 / 1200 rpm on a double planetary mixer. The mixed slurry is then ground in a three-roll mill until the fineness of the slurry reaches below 1 μm, thus obtaining the secondary carrier.

[0140] After adding silver powder and curing agent to the obtained secondary carrier, the mixture is mixed at 70 / 1200 rpm on a double planetary mixer. The resulting mixture is then milled by three rollers, filtered through a filter press at 2000 mesh, and the silver paste is then vacuum dispersed at 500 rpm / 10 min / 1 kPa to obtain ultra-low temperature sintering silver paste.

[0141] The prepared ultra-low temperature sintered silver paste had a viscosity of 33200 cp, a thixotropy of 2.16, a fineness of 0.6 μm as measured by a scraper fineness meter, and a particle size of 1.6 μm as measured by a scanning electron microscope. After screen printing and drying at 100℃ for 60 min, its volume resistivity was tested to be 2.4E-6 Ω·cm, its pencil hardness was ≥3H, and its adhesion was grade 5B.

[0142] After five layers of printing, the thickness is 13.8 μm, the surface roughness Rz is 0.8 μm, and there are clearly visible moiré patterns. After CP argon ion polishing, the silver paste does not separate into layers and there are no pores >1 μm.

[0143] Comparative Example 1

[0144] Preparation of ultra-low temperature sintering silver paste:

[0145] The raw materials by weight percentage are: 3.6% bisphenol A epoxy resin, 0.2% curing agent, 0.2% silver paste sintering aid, 0.2% dispersant, 9.3% solvent, 0.8% coupling agent, 85% nano silver powder, and 0.5% thixotropic agent.

[0146] The bisphenol A epoxy resin is 100% Mitsubishi Chemical JER1256 (bisphenol A epoxy resin with a weight average molecular weight of 49910).

[0147] The saturated polyester modifier is Aladdin's zirconium acetylacetonate;

[0148] The silver paste sintering aid is Aladdin's tri(2-aminoethyl)amine;

[0149] The curing agent is Asahi Kasei's Nenba Asahi 9322 microcapsule curing agent;

[0150] The thixotropic agent is Wacker's H2O fumed silica;

[0151] The dispersant is Evonik's TDO;

[0152] The coupling agent is Dow Corning's 6040 silane coupling agent;

[0153] The solvent is a mixture of DBE and diethyl adipate (mass ratio 2:3);

[0154] The silver powder is 100% silver (4), namely, Three Star MDOT-CF412.

[0155] Saturated polyester and solvent were heated and mixed in a glass stirred tank at 90±5℃ for 15 hours until the resin solution was uniform and fine, without large particles, which served as a primary carrier. The stirring speed was 450 rpm.

[0156] Saturated polyester modifier, silver paste sintering aid, coupling agent, dispersant and thixotropic agent are added to the obtained primary carrier. After mixing, the mixture is stirred at 70 / 1200 rpm on a double planetary mixer. The mixed slurry is then ground in a three-roll mill until the fineness of the slurry reaches below 1 μm, thus obtaining the secondary carrier.

[0157] After adding silver powder and curing agent to the obtained secondary carrier, the mixture is mixed at 70 / 1200 rpm on a double planetary mixer. The resulting mixture is then milled by three rollers, filtered through a filter press at 2000 mesh, and the silver paste is then vacuum dispersed at 500 rpm / 10 min / 1 kPa to obtain ultra-low temperature sintering silver paste.

[0158] The prepared ultra-low temperature sintered silver paste had a viscosity of 31600 cp, a thixotropy of 2.96, a fineness of 0.8 μm as measured by a scraper fineness meter, and a particle size of 2.1 μm as measured by a scanning electron microscope. After screen printing and drying at 100℃ for 60 min, its volume resistivity was found to be 3.82E-4Ω·cm, its pencil hardness was ≥3H, and its adhesion was grade 5B.

[0159] After five layers of printing, the thickness is 16.2 μm, the surface roughness Rz is 4.2 μm, and there are no obvious moiré patterns. After CP argon ion polishing, the silver paste does not separate into layers, but there are pores >1 μm (volume ratio >5%).

[0160] Comparative Example 2

[0161] Preparation of ultra-low temperature sintering silver paste:

[0162] The raw materials by weight percentage are: 3.6% saturated polyester, 0.2% saturated polyester modifier, 0.2% silver paste sintering aid, 0.2% dispersant, 9.5% solvent, 0.8% coupling agent, 85% nano silver powder, and 0.5% thixotropic agent.

[0163] The saturated polyester is 100% Toyobo 7000A saturated polyester (a linear saturated polyester with a weight-average molecular weight of 41,250).

[0164] The saturated polyester modifier is Aladdin's zirconium acetylacetonate;

[0165] The silver paste sintering aid is Aladdin's tri(2-aminoethyl)amine;

[0166] The curing agent is Asahi Kasei's K60X isocyanate;

[0167] The thixotropic agent is Wacker's H2O fumed silica;

[0168] The dispersant is Evonik's TDO;

[0169] The coupling agent is Dow Corning's 6040 silane coupling agent;

[0170] The solvent is a mixture of DBE and diethyl adipate (mass ratio 2:3);

[0171] The silver powder is 100% silver (4), namely, Three Star MDOT-CF412.

[0172] Saturated polyester and solvent were heated and mixed in a glass stirred tank at 90±5℃ for 15 hours until the resin solution was uniform and fine, without large particles, which served as a primary carrier. The stirring speed was 450 rpm.

[0173] Saturated polyester modifier, silver paste sintering aid, coupling agent, dispersant and thixotropic agent are added to the obtained primary carrier. After mixing, the mixture is stirred at 70 / 1200 rpm on a double planetary mixer. The mixed slurry is then ground in a three-roll mill until the fineness of the slurry reaches below 1 μm, thus obtaining the secondary carrier.

[0174] After adding silver powder and curing agent to the obtained secondary carrier, the mixture is mixed at 70 / 1200 rpm on a double planetary mixer. The resulting mixture is then milled by three rollers, filtered through a filter press at 2000 mesh, and the silver paste is then vacuum dispersed at 500 rpm / 10 min / 1 kPa to obtain ultra-low temperature sintering silver paste.

[0175] The prepared ultra-low temperature sintered silver paste had a viscosity of 31200 cp, a thixotropy of 2.06, a fineness of 0.9 μm as measured by a scraper fineness meter, and a particle size of 1.8 μm as measured by a scanning electron microscope. After screen printing and drying at 100℃ for 60 min, its volume resistivity was found to be 9.64E-6 Ω·cm, its pencil hardness was ≥3H, and its adhesion was grade 5B.

[0176] After five layers of printing, the thickness is 15.2 μm, the surface roughness Rz is 2.5 μm, and there are no obvious moiré patterns. After CP argon ion polishing, the silver paste does not separate into layers, but there are pores >1 μm (volume ratio >8%).

[0177] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A low-temperature sintering silver paste for ultrasonic fingerprint modules, characterized in that, The components, by mass percentage, include: 2%–5% saturated polyester, 0.1%–1% curing agent, 0.01%–0.5% saturated polyester modifying agent, 80%–90% nano silver powder, 2%–10% solvent, 0.1%–2% dispersant, 0.1%–0.5% silver paste sintering aid, 0.1%–1.2% coupling agent, and 0.1%–1% thixotropic agent; the saturated polyester is a high molecular weight linear saturated polyester with a weight average molecular weight of not less than 20,000.

2. The ultra-low temperature sintering silver paste for the ultrasonic fingerprint module according to claim 1, characterized in that, The saturated polyester includes at least one of aromatic saturated polyester, aliphatic saturated polyester, and aromatic-aliphatic saturated polyester.

3. The ultra-low temperature sintering silver paste for the ultrasonic fingerprint module according to claim 1, characterized in that, The curing agent includes at least one of oxazoline, isocyanate, diisocyanate, and dicyanate prepolymer.

4. The ultra-low temperature sintering silver paste for the ultrasonic fingerprint module according to claim 1, characterized in that, The saturated polyester modifying agent includes at least one of acid anhydride, organotin, and acetylacetone metal salt.

5. The ultra-low temperature sintering silver paste for the ultrasonic fingerprint module according to claim 1, characterized in that, The nano-silver powder includes at least one of the following: nano-silver powder 1 with an average particle size of 50-150 nm, an irregular polygonal structure, and a silver content of 90%-95%; nano-silver powder 2 with an average particle size of 200-300 nm, an irregular polygonal structure, and a silver content of 90%-95%; nano-silver powder 3 with an average particle size of 200-400 nm, a spherical structure, and a silver content of 90%-95%; and nano-silver powder 4 with an average particle size of 200-400 nm, a spherical structure, and a silver content of 99% or more.

6. The ultra-low temperature sintering silver paste for the ultrasonic fingerprint module according to claim 1, characterized in that, The solvent includes at least one of divalent esters, dimethyl adipate, 3-methoxybutyl acetate, diethyl adipate, 3-methoxybutyl acetate, and propylene glycol methyl ether acetate.

7. The ultra-low temperature sintering silver paste for the ultrasonic fingerprint module according to claim 1, characterized in that, The dispersant comprises at least one of quaternary ammonium salt, polyvinylpyrrolidone, sodium oleate, and TDO; and / or, the silver paste sintering aid comprises at least one of sodium chloride, hydrazine hydrate, sodium borohydride, and tris(2-aminoethyl)amine; and / or, the coupling agent comprises at least one of silane coupling agent, titanate coupling agent, aluminate coupling agent, bimetallic coupling agent, phosphate coupling agent, and borate coupling agent; and / or, the thixotropic agent comprises at least one of fumed silica, organobentonite, and polyamide wax.

8. A method for preparing ultra-low temperature sintering silver paste for an ultrasonic fingerprint module according to any one of claims 1 to 7, characterized in that, Includes the following steps: Saturated polyester and solvent are dissolved at 90±5℃ to obtain a first mixture; saturated polyester modifier, silver paste sintering aid, coupling agent, dispersant and thixotropic agent are added to the first mixture, stirred evenly, and ground to obtain a second mixture; nano silver powder and curing agent are added to the second mixture, stirred evenly, ground, filtered and vacuum dispersed to obtain the ultra-low temperature sintering silver paste for the ultrasonic fingerprint module.

9. The method for preparing ultra-low temperature sintering silver paste for ultrasonic fingerprint modules according to claim 8, characterized in that, The filtration is a high-mesh filtration of 1500-3500 mesh; and / or, the vacuum degree of the vacuum dispersion is 1-5 kPa, the stirring rate is 200-1000 rpm, and the time is 10-30 min.

10. The application of the ultra-low temperature sintering silver paste for ultrasonic fingerprint modules according to any one of claims 1 to 7 in the preparation of ultrasonic fingerprint modules.