Silver paste for ultrasonic fingerprint module and preparation method thereof

Abstract

The present invention discloses a silver paste for ultrasonic fingerprint modules and a preparation method thereof, belonging to the field of fingerprint recognition technology. The silver paste comprises, by weight percentage, 2%-15% epoxy resin, 0.5%-2% curing agent, 0.01%-0.5% curing accelerator, 0.5%-2% dispersant, 2%-20% organic solvent, 0.1%-0.3% coupling agent, 65%-85% spherical silver powder, and 0.03%-1.35% thixotropic agent. The raw materials are graded, stirred, filtered, and vacuum dispersed to prepare the silver paste for ultrasonic fingerprint modules. The compounding of the raw materials results in the silver paste having the advantages of low curing temperature, low square resistance, low surface roughness, high density, and no delamination or large-sized holes after lamination.

Description

Technical Field

[0001] The present invention belongs to the technical field of fingerprint recognition, and in particular relates to a silver paste for an ultrasonic fingerprint module and a preparation method thereof. Background Art

[0002] Ultrasonic fingerprint modules utilize ultrasonic waves to detect the three-dimensional structure of fingerprints, providing higher levels of recognition accuracy and security. They penetrate the epidermis and capture deeper fingerprint details, effectively distinguishing genuine fingerprints from forgeries. This significantly improves system security compared to traditional fingerprint recognition technology. They also offer enhanced environmental adaptability. For example, they can accurately identify wet or stained hands and are unaffected by common contaminants such as water, oil, and hand cream. This ensures the ultrasonic fingerprint module maintains stable performance in a variety of application scenarios, such as outdoor environments and industrial production. Furthermore, with the continuous advancement of technology, consumers are demanding higher levels of security and convenience from smart devices. As an innovative biometric recognition technology, ultrasonic fingerprint modules meet the market's demand for higher performance and more convenient experiences. Their emergence provides more advanced unlocking solutions for products such as smartphones and smart door locks, enhancing the user experience.

[0003] Among them, silver paste plays a vital role in ultrasonic fingerprint modules, such as:

[0004] 1. High conductivity requirement: Ultrasonic fingerprint module silver paste has excellent electrical conductivity and can effectively transmit ultrasonic signals. In ultrasonic fingerprint modules, electrical signals are required to drive the ultrasonic transducer and receive the reflected ultrasonic signal. The high conductivity of silver paste ensures the efficiency and stability of signal transmission, improving the accuracy and response speed of fingerprint recognition.

[0005] 2. Good leveling and printability: Ultrasonic fingerprint module silver paste can be applied to specific areas of the fingerprint module through the printing process. It has good leveling properties, making the silver paste surface characterized by extremely low roughness, which can reduce the acoustic noise during the transmission of ultrasonic signals, thereby improving the timeliness and accuracy of ultrasonic signal transmission; and good printability enables the ultrasonic fingerprint module silver paste to adapt to complex geometric shapes, fine circuit designs and different degrees of lamination during the manufacturing process of ultrasonic fingerprint modules, thereby achieving high integration and miniaturization.

[0006] 3. Low-temperature curing and density: The silver paste of the ultrasonic fingerprint module needs to be cured at a high density at a lower temperature. This is mainly due to the non-heat-resistant material of the PVDF substrate, which determines that the curing temperature of the silver paste is lower than 100°C. In order to ensure fast and stable transmission of ultrasonic signals, the silver paste must be highly dense. Otherwise, it will cause signal attenuation, which will ultimately be reflected in poor unlocking sensitivity and accuracy.

[0007] However, existing silver pastes for ultrasonic fingerprint modules still have the following problems. For example, the materials used to make conductive electrodes are usually a mixture of large-grained silver particles, a film-forming carrier, and a solvent. The mixing is insufficient, resulting in uneven distribution of the cured material and low density. Alternatively, the raw material components are difficult to compound, resulting in delamination and large-sized holes after lamination. Alternatively, the silver paste has a high curing temperature and a large square resistance, which affects its conductive properties as a conductive material.

[0008] To sum up, in the application of ultrasonic fingerprint modules, silver paste needs to meet the characteristics of high conductivity, high leveling, low roughness, low temperature curing and high density. These high standards for silver paste make the development of an ultrasonic fingerprint module silver paste an indispensable key in ultrasonic fingerprint recognition technology. Summary of the Invention

[0009] In response to the above technical problems, the present invention proposes a silver paste for an ultrasonic fingerprint module and a preparation method thereof.

[0010] To achieve the above object, the present invention provides the following technical solutions:

[0011] One of the technical solutions of the present invention:

[0012] A silver paste for an ultrasonic fingerprint module, comprising, by weight percentage, the following raw materials:

[0013] Epoxy resin 2%-15%, curing agent 0.5%-2%, curing accelerator 0.01%-0.5%, dispersant 0.5%-2%, organic solvent 2%-20%, coupling agent 0.1%-0.3%, spherical silver powder 65%-85% and thixotropic agent 0.03%-1.35%;

[0014] Wherein, the epoxy resin is bisphenol A epoxy resin.

[0015] Preferably, the spherical silver powder is micron-sized silver powder, with a D50 of 1-2 μm and a D100 of 3-5 μm;

[0016] The mass ratio of the epoxy resin to the spherical silver powder is 7:74.

[0017] Preferably, the curing accelerator includes acetylacetonate metal salt; further, the acetylacetonate metal salt includes zirconium acetylacetonate, copper acetylacetonate or cobalt acetylacetonate; more preferably, zirconium acetylacetonate.

[0018] Beneficial effects: The present invention limits acetylacetonate metal salt as a curing accelerator to react with epoxy resin. The specific reaction mechanism is: the metal ions (zirconium ions) in zirconium acetylacetonate have empty orbitals and can form coordination complexes with epoxy groups in epoxy resin to carry out catalytic polymerization; during the reaction process, the metal ions not only participate in coordination catalysis, but can also act as catalysts through other mechanisms (such as ion effects, electronic effects, etc.) to significantly improve the reaction rate and curing efficiency of the epoxy resin, making the cured silver paste denser, and also causing the molecular structure of the epoxy resin to change, obtaining a more load-bearing network structure, and also making the silver powder more evenly distributed in the resin, which can effectively improve the stratification problem during the silver paste lamination process.

[0019] Preferably, the curing agent includes one or more of dicyandiamide, blocked isocyanate or latent imidazole modifier.

[0020] Preferably, the dispersant is one or more of polyether phosphate, oleic acid, TDO (Duomeen TDO colorant dispersant), or lauryl phosphate. More preferably, the dispersant is a mixture of TDO and oleic acid in a mass ratio of 1.2:1.

[0021] Beneficial effects: The addition of the above-mentioned dispersant during the preparation of the silver paste in the present invention enables the silver powder to have extremely high interfacial stabilization activity, can be evenly dispersed in the resin solution, and effectively solves the particle agglomeration effect (for example, the polymer chain segments in the TDO dispersant are fully expanded in the solvent to form a protective layer covering the surface of the silver powder particles. When two silver powder particles approach each other, the polymer chain segments on their surfaces will produce a steric hindrance effect, preventing further approach and agglomeration between the particles); and can effectively repel moisture adsorption at the interface of the substrate, improve the adhesion of the coating product, reduce the interfacial energy between the substrate and the silver paste, and between the silver pastes, and provide a good channel for ultrasonic transmission.

[0022] Preferably, the organic solvent is one or more of DBE (dibasic acid ester), dimethyl adipate, 3-methoxybutyl acetate, diethyl adipate, 3-methoxybutyl acetate or propylene glycol methyl ether acetate.

[0023] Preferably, the coupling agent is one or more of a silane coupling agent, a titanate coupling agent, an aluminate coupling agent, a bimetallic coupling agent, a phosphate coupling agent or a borate coupling agent.

[0024] Beneficial effects: The coupling agent defined in the present invention can enable the slurry to have good contact with the bottom substrate, thereby reducing the difficulty of electron transition, and the more frequent the bridging effect between the conductive silver powder particles, the better the conductive performance, and the better the transmission effect of the ultrasonic signal; and the synergistic effect with the curing accelerator defined in the present invention improves the curing degree of the slurry, reduces the porosity of the slurry, greatly improves the density of the silver paste, and greatly improves the transmission efficiency of the ultrasonic signal.

[0025] Preferably, the thixotropic agent includes one or more of fumed silica, organic bentonite, polyamide wax, asbestos, and kaolin.

[0026] Beneficial Effects: The thixotropic agent molecules (such as fumed silica and organobentonite) used in the present invention form a three-dimensional network structure through physical or chemical interactions with other raw materials in the system. This network structure is stabilized by interactions such as hydrogen bonds and van der Waals forces. When the system is subjected to external forces (such as stirring or coating), the network structure is disrupted, resulting in a decrease in viscosity and an increase in fluidity. Once the external force is removed, the network structure quickly recovers, and the viscosity of the system increases, returning to its original state.

[0027] The second technical solution of the present invention:

[0028] The preparation method of the silver paste comprises the following steps:

[0029] The epoxy resin and the organic solvent are mixed uniformly according to weight percentage to obtain a primary carrier;

[0030] Adding a curing agent, a curing accelerator, a coupling agent, a dispersant and a thixotropic agent to the primary carrier, stirring once, and then triple-roll grinding to obtain a secondary carrier;

[0031] Spherical silver powder is added to the secondary carrier, stirred twice, and then triple-rolled and ground. Then, the mixture is filtered in a filter press and then vacuum dispersed to obtain the silver paste.

[0032] Preferably, the conditions in the first stirring and the second stirring process are: placing the mixed material in a double planetary mixer and mixing at a speed of 50-100 / 1000-2000 rpm.

[0033] Preferably, the filtration is through 800-2000 mesh.

[0034] Beneficial effects: The preparation method of the present invention limits the filtration to a high mesh number of 800-2000 mesh, which helps to obtain uniform small-sized silver paste particles, improve the fineness of the silver paste, and obtain a silver paste fineness of less than 1 μm (test results using a scraper fineness meter). After the silver paste is solidified under an electron microscope, the silver paste particle size is less than 5 μm.

[0035] Preferably, the conditions during the vacuum dispersion process are: dispersion at a speed of 200-1000 rpm for 10-30 min under a pressure of 1-5 kPa.

[0036] Beneficial effect: The vacuum dispersion under the above conditions defined by the present invention helps to eliminate air bubbles introduced during the silver paste production process, so that the porosity (>1μm) of the silver paste after curing is reduced by 50-80%.

[0037] Compared with the prior art, the present invention has the following advantages and technical effects:

[0038] The present invention adds bisphenol A epoxy resin, epoxy resin curing agent, curing accelerator, conductive silver powder with a particle size of less than 5 μm, and compound multiple organic solvents and additives into the conductive silver paste, so that the silver paste finally prepared has the advantages of low curing temperature, low square resistance, low surface roughness, high density, no delamination after lamination, and no large-sized holes. DETAILED DESCRIPTION

[0039] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0040] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0041] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0042] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0043] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0044] The embodiment of the present invention discloses a low-temperature conductive silver paste for an ultrasonic fingerprint module, which comprises the following components, calculated by mass percentage:

[0045] Epoxy resin 2%-15%, curing agent 0.5%-2%, curing accelerator 0.01%-0.5%, dispersant 0.5%-2%, organic solvent 2%-20%, coupling agent 0.1%-0.3%, spherical silver powder 65%-85% and thixotropic agent 0.03%-1.35%;

[0046] The epoxy resin is bisphenol A epoxy resin purchased from Mitsubishi of Japan, model number JER1256.

[0047] In some preferred embodiments, the curing agent includes one or more of dicyandiamide, blocked isocyanate, or latent imidazole modifier.

[0048] In some preferred embodiments, the curing accelerator includes one or more of DBU octanoate, modified imidazole, acetylacetonate metal salt, or boron trifluoride complex.

[0049] In some preferred embodiments, the spherical silver powder is micron-sized silver powder, with a D50 of 1-2 μm and a D100 of 3-5 μm.

[0050] In some preferred embodiments, the organic solvent is one or more of DBE, dimethyl adipate, 3-methoxybutyl acetate, diethyl adipate, 3-methoxybutyl acetate, or propylene glycol methyl ether acetate.

[0051] In some preferred embodiments, the dispersant is one or more of polyether phosphate, oleic acid, TDO, or lauryl phosphate.

[0052] In some preferred embodiments, the coupling agent is one or more of a silane coupling agent, a titanate coupling agent, an aluminate coupling agent, a bimetallic coupling agent, a phosphate coupling agent, or a borate coupling agent.

[0053] In addition, an embodiment of the present invention further provides a method for preparing the low-temperature conductive silver paste for the ultrasonic fingerprint module, comprising the following steps:

[0054] Dissolving epoxy resin and organic solvent according to weight percentage at 70-80° C. and mixing uniformly to obtain a first mixture;

[0055] Adding a curing agent, a curing accelerator, a coupling agent, a dispersant, and a thixotropic agent to the first mixture, stirring evenly, and performing three-roll milling to obtain a second mixture;

[0056] After adding spherical silver powder to the above second mixture, stir evenly, perform three-roll grinding, and then filter it in a filter press with 800-2000 mesh. Then, the silver paste is vacuum dispersed at 200-1000rpm / 10-30min / 1-5kPa to finally prepare a low-temperature conductive silver paste for ultrasonic fingerprint module.

[0057] The raw materials used in the present invention are all purchased from the market.

[0058] The technical solution of the present invention is further illustrated by the following examples.

[0059] Example 1

[0060] A low-temperature conductive silver paste for an ultrasonic fingerprint module, comprising, by mass percentage, 8% epoxy resin, 1.2% curing agent, 0.2% curing accelerator, 0.55% dispersant, 11.6% organic solvent, 0.2% coupling agent, 78% spherical silver powder, and 0.25% thixotropic agent;

[0061] The epoxy resin is bisphenol A epoxy resin;

[0062] The curing agent is a latent imidazole modified substance, Asahi Kasei 9322;

[0063] The curing accelerator is zirconium acetylacetonate, CAS: 17501-44-9;

[0064] The dispersant is a mixture of TDO and oleic acid, with a mass ratio of 1.2:1;

[0065] The coupling agent is silane coupling agent, Dow Corning 6040;

[0066] The organic solvent is a mixture of DBE and diethyl adipate, with a mass ratio of 1:2;

[0067] Spherical silver powder has a D50 of 1-2μm and a D90 of 3-5μm.

[0068] The thixotropic agent is Wacker H20.

[0069] The method for preparing the low-temperature conductive silver paste for the ultrasonic fingerprint module comprises the following steps:

[0070] The epoxy resin and the organic solvent were mixed in a glass stirring kettle for 15 hours until the resin solution was uniform and fine without large particles, which was used as the primary carrier; wherein the stirring speed was 350 rpm;

[0071] Add a curing agent, a curing accelerator, a coupling agent, a dispersant, and a thixotropic agent to the prepared primary carrier, and then mix them evenly on a double planetary mixer at 70 / 1200 rpm; then grind the mixed slurry on a three-roll mill until the slurry fineness reaches less than 5 μm, thereby obtaining a secondary carrier;

[0072] After adding spherical silver powder to the above-mentioned secondary carrier, the mixture was mixed at 90 / 1500 rpm on a double planetary mixer, and the above-mentioned mixture was subjected to triple-roll milling, and then filtered through a 2000-mesh filter press. The silver paste was then vacuum dispersed at 500 rpm / 10 min / 2.5 kPa to obtain the desired silver paste.

[0073] The conductive silver paste was screen-printed and dried at 90°C for 60 minutes. The test showed that its pencil hardness was ≥3H, adhesion was 5B, and square resistance was 18mΩ / □ / mil.

[0074] After 3 layers of printing, the thickness is 16-20μm and the surface roughness Rz is 2.7μm. After CP argon ion polishing, the silver paste is not stratified and there are no pores larger than 3μm.

[0075] Example 2

[0076] A low-temperature conductive silver paste for an ultrasonic fingerprint module, comprising, by mass percentage, 7% epoxy resin, 1.2% curing agent, 0.2% curing accelerator, 0.55% dispersant, 15.6% organic solvent, 0.2% coupling agent, 75% silver powder, and 0.25% thixotropic agent;

[0077] The epoxy resin is bisphenol A epoxy resin;

[0078] The curing agent is Asahi Kasei K60X;

[0079] The curing accelerator is CAS: 17501-44-9;

[0080] The dispersant is a mixture of TDO and oleic acid, with a mass ratio of 1.2:1;

[0081] The coupling agent was Dow Corning 6040;

[0082] The solvent is a mixture of DBE and diethyl adipate, with a mass ratio of 1:2;

[0083] Silver powder has a D50 of 1-2μm and a D90 of 3-5μm, and is spherical;

[0084] The thixotropic agent is Wacker H20.

[0085] The method for preparing the low-temperature conductive silver paste for the ultrasonic fingerprint module comprises the following steps:

[0086] The epoxy resin and solvent were mixed in a glass stirring kettle for 15 h until the resin solution was uniform and fine without large particles, which was used as the primary carrier. The rotation speed was 350 rpm.

[0087] Add a curing agent, a curing accelerator, a coupling agent, a dispersant, and a thixotropic agent to the prepared primary carrier, mix them, and evenly mix them on a double planetary mixer at 70 / 1200 rpm; then grind the mixed slurry on a three-roll mill until the slurry fineness reaches less than 5 μm, thereby obtaining a secondary carrier;

[0088] After adding silver powder to the above-mentioned secondary carrier, mix it at 90 / 1500 rpm on a double planetary mixer, grind the above mixture with three rollers, and then filter it with 2000 mesh on a filter press. Then, vacuum disperse the silver paste at 500 rpm / 10 min / 2.5 kPa to obtain the required silver paste.

[0089] The conductive silver paste was screen-printed and dried at 90°C for 60 minutes. The test showed that its pencil hardness was ≥3H, adhesion was 5B, and square resistance was 35mΩ / □ / mil.

[0090] After 3 layers of printing, the thickness is 16-20μm and the surface roughness Rz is 1.8μm. After CP argon ion polishing, the silver paste is not stratified and there are no pores larger than 3μm.

[0091] Example 3

[0092] A low-temperature conductive silver paste for an ultrasonic fingerprint module, comprising, by mass percentage, 7% epoxy resin, 1.2% curing agent, 0.2% curing accelerator, 0.55% dispersant, 16.6% solvent, 0.2% coupling agent, 74% silver powder, and 0.25% thixotropic agent;

[0093] The epoxy resin is bisphenol A epoxy resin;

[0094] The curing agent is Asahi Kasei 9322;

[0095] The curing accelerator is CAS: 17501-44-9;

[0096] The dispersant is a mixture of TDO and oleic acid, with a mass ratio of 1.2:1;

[0097] The coupling agent was Dow Corning 6040;

[0098] The solvent is a mixture of DBE and diethyl adipate, with a mass ratio of 1:2;

[0099] Silver powder has a D50 of 1-2μm and a D90 of 3-5μm, and is spherical;

[0100] The thixotropic agent is Wacker H20.

[0101] The method for preparing the low-temperature conductive silver paste for the ultrasonic fingerprint module comprises the following steps:

[0102] The epoxy resin and solvent were mixed in a glass stirring kettle for 15 h until the resin solution was uniform and fine without large particles, which was used as the primary carrier. The rotation speed was 350 rpm.

[0103] Add a curing agent, a curing accelerator, a coupling agent, a dispersant, and a thixotropic agent to the prepared primary carrier, mix them, and evenly mix them on a double planetary mixer at 70 / 1200 rpm; then grind the mixed slurry on a three-roll mill until the slurry fineness reaches less than 5 μm, thereby obtaining a secondary carrier;

[0104] After adding silver powder to the above-mentioned secondary carrier, mix it at a speed of 901500 rpm on a double planetary mixer, grind the above mixture with three rollers, and then filter it with a 2000 mesh filter press. Then, vacuum disperse the silver paste at 500 rpm / 10 min / 2.5 kPa to obtain the required silver paste.

[0105] The conductive silver paste was screen-printed and dried at 90°C for 60 minutes. The test showed that its pencil hardness was ≥3H, adhesion was 5B, and square resistance was 20mΩ / □ / mil.

[0106] After 3 layers of printing, the thickness is 16-20μm and the surface roughness Rz is 0.7μm. After CP argon ion polishing, the silver paste is not stratified and there are no pores larger than 3μm.

[0107] Comparative Example 1

[0108] A low-temperature conductive silver paste for an ultrasonic fingerprint module, comprising, by mass percentage, 8% epoxy resin, 1.2% curing agent, 0.2% curing accelerator, 0.55% dispersant, 11.6% organic solvent, 0.2% coupling agent, 78% spherical silver powder, and 0.25% thixotropic agent;

[0109] The epoxy resin is 50wt% bisphenol A epoxy resin and 50wt% bisphenol F epoxy resin;

[0110] The curing agent is Asahi Kasei 9322;

[0111] The curing accelerator is CAS: 17501-44-9;

[0112] The dispersant is a mixture of TDO and oleic acid, with a mass ratio of 1.2:1;

[0113] The coupling agent was Dow Corning 6040;

[0114] The organic solvent is a mixture of DBE and diethyl adipate, with a mass ratio of 1:2;

[0115] Spherical silver powder has a D50 of 1-2μm and a D90 of 3-5μm.

[0116] The thixotropic agent is Wacker H20.

[0117] The method for preparing the low-temperature conductive silver paste for the ultrasonic fingerprint module comprises the following steps:

[0118] The epoxy resin and the organic solvent were mixed in a glass stirring kettle for 15 hours until the resin solution was uniform and fine without large particles, which was used as the primary carrier. The stirring speed was 350 rpm.

[0119] Add a curing agent, a curing accelerator, a coupling agent, a dispersant, and a thixotropic agent to the prepared primary carrier, mix them, and evenly mix them on a double planetary mixer at 70 / 1200 rpm; then grind the mixed slurry on a three-roll mill until the slurry fineness reaches less than 5 μm, thereby obtaining a secondary carrier;

[0120] After adding silver powder to the above-mentioned secondary carrier, mix it at 90 / 1500 rpm on a double planetary mixer, grind the above mixture with three rollers, and then filter it with 2000 mesh on a filter press. Then, vacuum disperse the silver paste at 500 rpm / 10 min / 2.5 kPa to obtain the required silver paste.

[0121] The conductive silver paste was screen-printed and dried at 90°C for 60 minutes. Testing showed that its pencil hardness was ≥3H, adhesion was 5B, and square resistance was 43mΩ / □ / mil.

[0122] After 3 layers of printing, the thickness is 16-20μm and the surface roughness Rz is 3.5μm. After CP argon ion polishing, the silver paste is not stratified and there are no pores larger than 3μm.

[0123] Comparative Example 2

[0124] A low-temperature conductive silver paste for an ultrasonic fingerprint module, comprising, by mass percentage, 7% epoxy resin, 1.2% curing agent, 0.2% curing accelerator, 0.55% dispersant, 15.6% solvent, 0.2% coupling agent, 75% silver powder, and 0.25% thixotropic agent;

[0125] Epoxy resin is 50wt% bisphenol A epoxy resin and 50wt% bisphenol F epoxy resin

[0126] The curing agent is Asahi Kasei K60X;

[0127] The curing accelerator is CAS: 17501-44-9;

[0128] The dispersant is a mixture of TDO and oleic acid, with a mass ratio of 1.2:1;

[0129] The coupling agent was Dow Corning 6040;

[0130] The solvent is a mixture of DBE and diethyl adipate, with a mass ratio of 1:2;

[0131] Silver powder has a D50 of 1-2μm and a D90 of 3-5μm, and is spherical;

[0132] The thixotropic agent is Wacker H20.

[0133] The method for preparing the low-temperature conductive silver paste for the ultrasonic fingerprint module comprises the following steps:

[0134] The epoxy resin and solvent were mixed in a glass stirring kettle for 15 h until the resin solution was uniform and fine without large particles, which was used as the primary carrier. The rotation speed was 350 rpm.

[0135] Add a curing agent, a curing accelerator, a coupling agent, a dispersant, and a thixotropic agent to the prepared primary carrier, mix them, and evenly mix them on a double planetary mixer at 70 / 1200 rpm; then grind the mixed slurry on a three-roll mill until the slurry fineness reaches less than 5 μm, thereby obtaining a secondary carrier;

[0136] After adding silver powder to the above-mentioned secondary carrier, mix it at 90 / 1500 rpm on a double planetary mixer, grind the above mixture with three rollers, and then filter it with 2000 mesh on a filter press. Then, vacuum disperse the silver paste at 500 rpm / 10 min / 2.5 kPa to obtain the required silver paste.

[0137] The conductive silver paste was screen-printed and dried at 90°C for 60 minutes. The test showed that its pencil hardness was ≥3H, adhesion was 5B, and square resistance was 65mΩ / □ / mil.

[0138] After 3 layers of printing, the thickness is 16-20μm and the surface roughness Rz is 3.5μm. After CP argon ion polishing, the silver paste is not stratified and there are no pores larger than 3μm.

[0139] Comparative Example 3

[0140] A low-temperature conductive silver paste for an ultrasonic fingerprint module, comprising, by mass percentage, 8% epoxy resin, 1.2% curing agent, 0.2% curing accelerator, 0.55% dispersant, 11.6% solvent, 0.2% coupling agent, 78% silver powder, and 0.25% thixotropic agent;

[0141] The epoxy resin is bisphenol A epoxy resin;

[0142] The curing agent is Asahi Kasei 9322;

[0143] The curing accelerator is SA-102;

[0144] The dispersant is a mixture of TDO and oleic acid, with a mass ratio of 1.2:1;

[0145] The coupling agent was Dow Corning 6040;

[0146] The solvent is a mixture of DBE and diethyl adipate, with a mass ratio of 1:2;

[0147] Silver powder has a D50 of 1-2μm and a D90 of 3-5μm, and is spherical;

[0148] The thixotropic agent is Wacker H20.

[0149] The method for preparing the low-temperature conductive silver paste for the ultrasonic fingerprint module comprises the following steps:

[0150] The epoxy resin and solvent were mixed in a glass stirring kettle for 15 h until the resin solution was uniform and fine without large particles, which was used as the primary carrier. The rotation speed was 350 rpm.

[0151] Add a curing agent, a curing accelerator, a coupling agent, a dispersant, and a thixotropic agent to the prepared primary carrier, mix them, and evenly mix them on a double planetary mixer at 70 / 1200 rpm; then grind the mixed slurry on a three-roll mill until the slurry fineness reaches less than 5 μm, thereby obtaining a secondary carrier;

[0152] After adding silver powder to the above-mentioned secondary carrier, mix it at 90 / 1500 rpm on a double planetary mixer, grind the above mixture with three rollers, and then filter it with 2000 mesh on a filter press. Then, vacuum disperse the silver paste at 500 rpm / 10 min / 2.5 kPa to obtain the required silver paste.

[0153] The conductive silver paste was screen-printed and dried at 90°C for 60 minutes. Testing showed that its pencil hardness was ≥3H, adhesion was 5B, and square resistance was 19.3 mΩ / □ / mil.

[0154] After 3 layers of printing, the thickness is 16-20μm and the surface roughness Rz is 2.6μm. After CP argon ion polishing, the silver paste is layered and there are no pores larger than 3μm.

[0155] Comparative Example 4

[0156] A low-temperature conductive silver paste for an ultrasonic fingerprint module, comprising, by mass percentage, 8% epoxy resin, 1.2% curing agent, 0.2% curing accelerator, 0.55% dispersant, 11.6% solvent, 0.2% coupling agent, 78% silver powder, and 0.25% thixotropic agent;

[0157] The epoxy resin is 50wt% bisphenol A epoxy resin and 50wt% bisphenol F epoxy resin;

[0158] The curing agent is Asahi Kasei 9322;

[0159] The curing accelerator is SA-102;

[0160] The dispersant is a mixture of TDO and oleic acid, with a mass ratio of 1.2:1;

[0161] The coupling agent was Dow Corning 6040;

[0162] The solvent is a mixture of DBE and diethyl adipate, with a mass ratio of 1:2;

[0163] Silver powder has a D50 of 1-2μm and a D90 of 3-5μm, and is spherical;

[0164] The thixotropic agent is Wacker H20.

[0165] The method for preparing the low-temperature conductive silver paste for the ultrasonic fingerprint module comprises the following steps:

[0166] The epoxy resin and solvent were mixed in a glass stirring kettle for 15 h until the resin solution was uniform and fine without large particles, which was used as the primary carrier. The rotation speed was 350 rpm.

[0167] Add a curing agent, a curing accelerator, a coupling agent, a dispersant, and a thixotropic agent to the prepared primary carrier, mix them, and evenly mix them on a double planetary mixer at 70 / 1200 rpm; then grind the mixed slurry on a three-roll mill until the slurry fineness reaches less than 5 μm, thereby obtaining a secondary carrier;

[0168] After adding silver powder to the above-mentioned secondary carrier, mix it at 90 / 1500 rpm on a double planetary mixer, grind the above mixture with three rollers, and then filter it with 2000 mesh on a filter press. Then, vacuum disperse the silver paste at 500 rpm / 10 min / 2.5 kPa to obtain the required silver paste.

[0169] The conductive silver paste was screen-printed and dried at 90°C for 60 minutes. The test showed that its pencil hardness was ≥3H, adhesion was 5B, and square resistance was 43.5mΩ / □ / mil.

[0170] After 3 layers of printing, the thickness is 16-20μm and the surface roughness Rz is 3.7μm. After CP argon ion polishing, the silver paste is layered and there are no pores larger than 3μm.

[0171] Comparative Example 5

[0172] A low-temperature conductive silver paste for an ultrasonic fingerprint module, comprising, by mass percentage, 7% epoxy resin, 1.2% curing agent, 0.2% curing accelerator, 0.55% dispersant, 15.6% solvent, 0.2% coupling agent, 75% silver powder, and 0.25% thixotropic agent;

[0173] The epoxy resin is bisphenol A epoxy resin;

[0174] The curing agent is Asahi Kasei K60X;

[0175] The curing accelerator is SA-102;

[0176] The dispersant is a mixture of TDO and oleic acid, with a mass ratio of 1.2:1;

[0177] The coupling agent was Dow Corning 6040;

[0178] The solvent is a mixture of DBE and diethyl adipate, with a mass ratio of 1:2;

[0179] Silver powder has a D50 of 1-2μm and a D90 of 3-5μm, and is spherical;

[0180] The thixotropic agent is Wacker H20.

[0181] The method for preparing the low-temperature conductive silver paste for the ultrasonic fingerprint module comprises the following steps:

[0182] The epoxy resin and solvent were mixed in a glass stirring kettle for 15 h until the resin solution was uniform and fine without large particles, which was used as the primary carrier. The rotation speed was 350 rpm.

[0183] Add a curing agent, a curing accelerator, a coupling agent, a dispersant, and a thixotropic agent to the prepared primary carrier, mix them, and evenly mix them on a double planetary mixer at 70 / 1200 rpm; then grind the mixed slurry on a three-roll mill until the slurry fineness reaches less than 5 μm, thereby obtaining a secondary carrier;

[0184] After adding silver powder to the above-mentioned secondary carrier, mix it at 90 / 1500 rpm on a double planetary mixer, grind the above mixture with three rollers, and then filter it with 2000 mesh on a filter press. Then, vacuum disperse the silver paste at 500 rpm / 10 min / 2.5 kPa to obtain the required silver paste.

[0185] The conductive silver paste was screen-printed and dried at 90°C for 60 minutes. Testing showed that its pencil hardness was ≥3H, adhesion was 5B, and square resistance was 36.2 mΩ / □ / mil.

[0186] After 3 layers of printing, the thickness is 16-20μm and the surface roughness Rz is 2.2μm. After CP argon ion polishing, the silver paste is layered and there are no pores larger than 3μm.

[0187] Comparative Example 6

[0188] A low-temperature conductive silver paste for an ultrasonic fingerprint module, comprising, by mass percentage, 7% epoxy resin, 1.2% curing agent, 0.2% curing accelerator, 0.55% dispersant, 16.6% solvent, 0.2% coupling agent, 74% silver powder, and 0.25% thixotropic agent;

[0189] The epoxy resin is 50wt% bisphenol A epoxy resin and 50wt% bisphenol F epoxy resin;

[0190] The curing agent is Asahi Kasei K60X;

[0191] The curing accelerator is SA-102;

[0192] The dispersant is a mixture of TDO and oleic acid, with a mass ratio of 1.2:1;

[0193] The coupling agent was Dow Corning 040;

[0194] The solvent is a mixture of DBE and diethyl adipate, with a mass ratio of 1:2;

[0195] Silver powder has a D50 of 1-2μm and a D90 of 3-5μm, and is spherical;

[0196] The thixotropic agent is Wacker H20.

[0197] The method for preparing the low-temperature conductive silver paste for the ultrasonic fingerprint module comprises the following steps:

[0198] The epoxy resin and solvent were mixed in a glass stirring kettle for 15 h until the resin solution was uniform and fine without large particles, which was used as the primary carrier. The rotation speed was 350 rpm.

[0199] Add a curing agent, a curing accelerator, a coupling agent, a dispersant, and a thixotropic agent to the prepared primary carrier, mix them, and evenly mix them on a double planetary mixer at 70 / 1200 rpm; then grind the mixed slurry on a three-roll mill until the slurry fineness reaches less than 5 μm, thereby obtaining a secondary carrier;

[0200] After adding silver powder to the above-mentioned secondary carrier, mix it at 90 / 1500 rpm on a double planetary mixer, grind the above mixture with three rollers, and then filter it with 2000 mesh on a filter press. Then, vacuum disperse the silver paste at 500 rpm / 10 min / 2.5 kPa to obtain the required silver paste.

[0201] The conductive silver paste was screen-printed and dried at 90°C for 60 minutes. Testing showed that its pencil hardness was ≥3H, adhesion was 5B, and square resistance was 72mΩ / □ / mil.

[0202] After 3 layers of printing, the thickness is 16-20μm and the surface roughness Rz is 3.6μm. After CP argon ion polishing, the silver paste is layered and there are no pores larger than 3μm.

[0203] Comparative Example 7

[0204] A low-temperature conductive silver paste for an ultrasonic fingerprint module, comprising, by mass percentage, 7% epoxy resin, 1.2% curing agent, 0.2% curing accelerator, 0.55% dispersant, 16.6% solvent, 0.2% coupling agent, 74% silver powder, and 0.25% thixotropic agent;

[0205] The epoxy resin is 50wt% bisphenol A epoxy resin and 50wt% bisphenol F epoxy resin;

[0206] The curing agent is Asahi Kasei 9322;

[0207] The curing accelerator is CAS: 17501-44-9;

[0208] The dispersant is a mixture of TDO and oleic acid, with a mass ratio of 1.2:1;

[0209] The coupling agent was Dow Corning 6040;

[0210] The solvent is a mixture of DBE and diethyl adipate, with a mass ratio of 1:2;

[0211] Silver powder has a D50 of 1-2μm and a D90 of 3-5μm, and is spherical;

[0212] The thixotropic agent is Wacker H20.

[0213] The method for preparing the low-temperature conductive silver paste for the ultrasonic fingerprint module comprises the following steps:

[0214] The epoxy resin and solvent were mixed in a glass stirring kettle for 15 h until the resin solution was uniform and fine without large particles, which was used as the primary carrier. The rotation speed was 350 rpm.

[0215] Add a curing agent, a curing accelerator, a coupling agent, a dispersant, and a thixotropic agent to the prepared primary carrier, mix them, and evenly mix them on a double planetary mixer at 70 / 1200 rpm; then grind the mixed slurry on a three-roll mill until the slurry fineness reaches less than 5 μm, thereby obtaining a secondary carrier;

[0216] After adding silver powder to the above-mentioned secondary carrier, mix it at a speed of 901500 rpm on a double planetary mixer, grind the above mixture with three rollers, and then filter it with a 2000 mesh filter press. Then, vacuum disperse the silver paste at 500 rpm / 10 min / 2.5 kPa to obtain the required silver paste.

[0217] The conductive silver paste was screen-printed and dried at 90°C for 60 minutes. The test showed that its pencil hardness was ≥3H, adhesion was 5B, and square resistance was 55mΩ / □ / mil.

[0218] After 3 layers of printing, the thickness is 16-20μm and the surface roughness Rz is 2.7μm. After CP argon ion polishing, the silver paste is not stratified and there are no pores larger than 3μm.

[0219] Comparative Example 8

[0220] A low-temperature conductive silver paste for an ultrasonic fingerprint module, comprising, by mass percentage, 7% epoxy resin, 1.2% curing agent, 0.2% curing accelerator, 0.55% dispersant, 16.6% solvent, 0.2% coupling agent, 74% silver powder, and 0.25% thixotropic agent;

[0221] The epoxy resin is bisphenol A epoxy resin;

[0222] The curing agent is hexafluoroantimonate;

[0223] The curing accelerator is CAS: 17501-44-9;

[0224] The dispersant is a mixture of TDO and oleic acid, with a mass ratio of 1.2:1;

[0225] The coupling agent was Dow Corning 6040;

[0226] The solvent is a mixture of DBE and diethyl adipate, with a mass ratio of 1:2;

[0227] Silver powder has a D50 of 1-2μm and a D90 of 3-5μm, and is spherical;

[0228] The thixotropic agent is Wacker H20.

[0229] The method for preparing the low-temperature conductive silver paste for the ultrasonic fingerprint module comprises the following steps:

[0230] The epoxy resin and solvent were mixed in a glass stirring kettle for 15 h until the resin solution was uniform and fine without large particles, which was used as the primary carrier. The rotation speed was 350 rpm.

[0231] Add a curing agent, a curing accelerator, a coupling agent, a dispersant, and a thixotropic agent to the prepared primary carrier, mix them, and evenly mix them on a double planetary mixer at 70 / 1200 rpm; then grind the mixed slurry on a three-roll mill until the slurry fineness reaches less than 5 μm, thereby obtaining a secondary carrier;

[0232] After adding silver powder to the above-mentioned secondary carrier, mix it at a speed of 901500 rpm on a double planetary mixer, grind the above mixture with three rollers, and then filter it with a 2000 mesh filter press. Then, vacuum disperse the silver paste at 500 rpm / 10 min / 2.5 kPa to obtain the required silver paste.

[0233] The conductive silver paste was screen printed and dried at 90°C for 60 minutes. Testing showed that its pencil hardness was ≥4H, adhesion was 0B, and sheet resistance could not be measured. Due to insufficient adhesion, lamination was not possible.

[0234] In summary, when the solid bisphenol A epoxy resin is limited, the ratio of silver powder with a certain uniform particle size and epoxy resin is 74:7, and the curing accelerator is zirconium acetylacetonate, the prepared low-temperature conductive silver paste for ultrasonic fingerprint module has the advantages of curing temperature <90°C, square resistance <30mΩ / □ / mil, high density, low surface roughness (Rz <1.5μm), no delamination after lamination, and no large-sized holes (>3μm).

[0235] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A silver paste for ultrasonic fingerprint module, characterized in that: In terms of weight percentage, the raw materials include: Epoxy resin 2%-15%, curing agent 0.5%-2%, curing accelerator 0.01%-0.5%, dispersant 0.5%-2%, organic solvent 2%-20%, coupling agent 0.1%-0.3%, spherical silver powder 65%-85% and thixotropic agent 0.03%-1.35%; Wherein, the epoxy resin is bisphenol A epoxy resin; The spherical silver powder is micron-sized silver powder, with a D50 of 1-2 μm and a D90 of 3-5 μm; and / or The mass ratio of the epoxy resin to the spherical silver powder is 7:74; The curing accelerator is zirconium acetylacetonate.

2. The silver paste for ultrasonic fingerprint module according to claim 1, characterized in that: The curing agent includes one or more of dicyandiamide, blocked isocyanate or latent imidazole modifier.

3. The silver paste for ultrasonic fingerprint module according to claim 1, characterized in that: The dispersant is one or more of polyether phosphate, oleic acid, TDO or lauryl phosphate.

4. The silver paste for ultrasonic fingerprint module according to claim 1, characterized in that: The organic solvent is one or more of DBE, dimethyl adipate, diethyl adipate, 3-methoxybutyl acetate or propylene glycol methyl ether acetate.

5. The silver paste for ultrasonic fingerprint module according to claim 1, characterized in that: The coupling agent is one or more of a silane coupling agent, a titanate coupling agent, an aluminate coupling agent, a bimetallic coupling agent, a phosphate coupling agent or a borate coupling agent.

6. A method for preparing silver paste for ultrasonic fingerprint module, characterized in that: The following steps are involved: According to the weight percentage of the silver paste raw material according to any one of claims 1 to 5, the epoxy resin and the organic solvent are mixed uniformly to obtain a primary carrier; Adding a curing agent, a curing accelerator, a coupling agent, a dispersant and a thixotropic agent to the primary carrier, stirring once, and then triple-roll grinding to obtain a secondary carrier; Spherical silver powder is added to the secondary carrier, stirred twice, and then triple-rolled and ground. Then, the mixture is filtered in a filter press and then vacuum dispersed to obtain the silver paste.

7. The method for preparing silver paste for ultrasonic fingerprint module according to claim 6, characterized in that: The conditions of the first stirring and the second stirring process are: placing the mixed material in a double planetary mixer and mixing at a speed of 50-100 / 1000-2000 rpm; and / or The conditions during the vacuum dispersion process are: dispersion at a speed of 200-1000 rpm for 10-30 minutes under a pressure of 1-5 kPa.