WO2022021228A1

WO2022021228A1 - Conductive material, ultrasonic fingerprint module, and electronic device

Info

Publication number: WO2022021228A1
Application number: PCT/CN2020/105902
Authority: WO
Inventors: 刘宣宣
Original assignee: 欧菲光集团股份有限公司; 欧菲微电子技术有限公司
Priority date: 2020-07-30
Filing date: 2020-07-30
Publication date: 2022-02-03

Abstract

Disclosed is a conductive material, which is prepared from a formulated silver paste after curing, wherein the silver paste comprises: a silver powder with a mass ratio of 55-65%, the silver powder is formed by mixing a flaky silver powder and a spherical silver powder, and the mass ratio of the flaky silver powder to the spherical silver powder ranges from 7:3 to 8:2; a resin with a mass ratio of 16-20%; a solvent with a mass ratio of 10-14%; and an auxiliary. Compared with the prior art, the conductive material has good adhesion on the surface of the piezoelectric layer (typically a fluoride), the material has a low surface roughness, and there are no larger silver particles and no aggregation of silver particles in the material. Also provided is an ultrasonic fingerprint module and an electronic device.

Description

Conductive materials, ultrasonic fingerprint modules and electronic equipment

technical field

The invention relates to the technical field of fingerprint identification, in particular to a conductive material, an ultrasonic fingerprint module and an electronic device.

Background technique

In the field of ultrasonic fingerprint recognition technology, the conductive electrodes inside the fingerprint recognition module need to receive sinusoidal electrical signals sent by the driver IC, and ultrasonic waves will penetrate the conductive electrodes, so the electrode materials need to have excellent conductivity, the surface of the material must be flat, and it needs to be The surface of the piezoelectric layer has good adhesion.

In the process of realizing this application, the inventor found that there are at least the following problems in the prior art: the materials for making conductive electrodes are usually mixed large-grain silver particles, film-forming carriers and solvents, and these materials are first melted to form silver paste, and then The silver paste is cured to obtain conductive electrodes. However, due to the presence of large silver particles in the silver paste, the mixing of the silver paste is insufficient, and the distribution of the cured material is uneven, which makes the signal of the large silver particles in the ultrasonic wave when penetrating the conductive electrode is different from the signal in other areas. As a result, the recognition effect of the fingerprint module is deviated, and the recognition accuracy of the entire module is not high.

SUMMARY OF THE INVENTION

In view of this, it is necessary to provide a conductive material, an ultrasonic fingerprint module and an electronic device to solve the above problems.

The embodiment of the present invention provides a conductive material, which is obtained by curing a prepared silver paste, and the silver paste includes:

Silver powder with a mass ratio of 55%-65%, the silver powder is formed by mixing flake silver powder and spherical silver powder, and the mass ratio of the flake silver powder to the spherical silver powder is in the range of 7:3-8:2;

Resin with a mass ratio of 16%-20%;

10%-14% by mass of solvent; and

Auxiliary.

The silver paste is formed by using the mass ratio scheme provided in this application, and a conductive material is made. Compared with the prior art, the conductive material has good adhesion on the surface of the piezoelectric layer (usually fluoride), and the surface of the material is rough The degree of concentration is low, there are no larger silver particles in the material and no aggregation of silver particles. At the same time, the silver paste provided in this embodiment can be directly covered on the piezoelectric layer of the fingerprint module without the screen printing fine line process; compared with the screen printing fine line process, very low surface impedance is not required, which can further reduce The content of silver particles in the silver paste can reduce the cost.

In some embodiments, the flake silver powder satisfies 1 μm≤D50≤3 μm and D90≤6 μm;

Among them, D50 is the particle size corresponding to the cumulative particle size distribution percentage of silver particles at 50%, and D90 is the particle size corresponding to the cumulative particle size distribution of silver particles at 90%.

Satisfying the limits of the range requirements, the resulting conductive material has no larger silver particles and no silver particles agglomerated.

In some embodiments, the particle size of the spherical silver powder is less than or equal to 1 μm.

In some embodiments, the resin includes epoxy resin and polyurethane, and the mass ratio of the epoxy resin to the polyurethane ranges from 2:1 to 5:4.

Epoxy resin is used as the film-forming carrier of silver paste, which plays the role of bonding silver powder. Epoxy resin can be cured at lower temperature, which can meet the requirement of ultrasonic fingerprint processing temperature ≤120℃; at the same time, epoxy resin has good adhesion, and after adding coupling agent to silver paste, it has good adhesion with piezoelectric layer. Good adhesion. The use of polyurethane as the silver paste film-forming carrier plays the role of binding the silver powder. In this embodiment, a low molecular weight polyurethane resin is used, and the molecular weight is about 10,000, so that the polyurethane resin can effectively reduce the viscosity of the slurry, which is beneficial to the screen printing process.

In some embodiments, the solvent includes a divalent ester and isophorone, and the mass ratio of the divalent ester to the isophorone ranges from 2:1 to 1:1.

Using dibasic acid ester as the solvent of silver paste paste has good compatibility with resin and ensures good stability and fluidity of paste. The use of isophorone as the paste solvent of the silver paste has good compatibility with the resin, ensuring good stability and fluidity of the paste.

In some embodiments, the adjuvant includes:

A curing agent with a mass ratio of 3%-5%;

A coupling agent with a mass ratio of 5%-7%.

The curing agent is used to cure the silver paste so that the silver paste is solidified, and the coupling agent is used to assist the uniform dispersion of the silver powder and can improve the adhesion of the silver paste.

In some embodiments, the curing agent is hexahydrophthalic anhydride.

In some embodiments, the coupling agent is a silane coupling agent.

In some embodiments, the adjuvant further includes:

Accelerator with a mass ratio of 0.5%-1%.

Accelerators are used to promote the curing rate of silver pastes.

In some embodiments, the accelerator is 2,4,6-tris(dimethylaminomethyl)phenol.

The embodiment of the present invention also provides an ultrasonic fingerprint module, comprising:

TFT substrate;

TFT pixel array;

piezoelectric layer;

A conductive electrode, the conductive electrode includes the conductive material described in any of the above embodiments.

Using the silver paste provided in the above embodiment to form a conductive material, the silver powder particles in the material are uniformly distributed, and the silver powder particle size is small and does not aggregate, which has no obvious influence on the ultrasonic fingerprint sensor signal, and the signal-to-noise ratio of the detection result is low.

The embodiment of the present invention also provides an electronic device, including:

Body: and

In the ultrasonic fingerprint module according to any one of the above embodiments, the ultrasonic fingerprint module is arranged on the body.

The conductive material proposed in the embodiment of this application is used to replace the material of the conductive electrode in the traditional ultrasonic fingerprint identification module, and by selecting an appropriate ratio of silver powder, the conductive material has good adhesion on the surface of the piezoelectric layer, and the surface roughness of the material is low. , there are no larger silver particles and no aggregation of silver particles in the material. At the same time, the silver paste provided in this application can be directly covered on the piezoelectric layer of the fingerprint module without the screen printing fine line process; The content of silver particles in the paste can be reduced to achieve cost reduction.

Description of drawings

FIG. 1 is a schematic diagram of flake silver powder in the conductive material according to the first embodiment of the present invention.

FIG. 2 is a schematic diagram of spherical silver powder in the conductive material according to the first embodiment of the present invention.

FIG. 3 is a schematic structural diagram of an ultrasonic fingerprint module according to a second embodiment of the present invention.

FIG. 4 is a three-dimensional schematic diagram of an electronic device according to a third embodiment of the present invention.

Description of main component symbols

Ultrasonic fingerprint module 100

TFT substrate 10

TFT pixel array 20

Piezoelectric layer 30

Conductive electrode 40

Cover plate 50

Electronic equipment 200

Ontology 210

The following specific embodiments will further illustrate the present invention in conjunction with the above drawings.

detailed description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

It should be noted that when a component is said to be "electrically connected" to another component, it may be directly on the other component or there may also be an intervening component. When a component is considered to be "electrically connected" to another component, it can be a contact connection, e.g., by means of a wire connection, or a contactless connection, e.g., by a non-contact coupling.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terms used herein in the description of the present invention are for the purpose of describing specific embodiments only, and are not intended to limit the present invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Some embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The embodiments described below and features in the embodiments may be combined with each other without conflict.

Please refer to FIG. 1 and FIG. 2 at the same time. The first embodiment of the present invention provides a conductive material. The conductive material is obtained by curing a prepared silver paste. The silver paste includes: silver powder with a mass ratio of 55% to 65%, Silver powder is made by mixing flake silver powder and spherical silver powder. The mass ratio of flake silver powder and spherical silver powder ranges from 7:3-8:2; the mass ratio is 16%-20% of resin; the mass ratio is 10% -14% solvent and additives.

Among them, silver powder is the main component of silver paste, which is used for conduction. The resin is the film-forming carrier of the silver paste and plays the role of binding the silver powder. The solvent can mix the silver powder and the resin evenly, so that the material is evenly distributed after the silver paste is cured, and the silver particles are not easy to aggregate. The other ingredients contained in the additive help to promote the solidification of the silver paste or make the paste uniform.

It can be understood that the quality of the silver powder has an absolute effect on the conductivity of the silver paste, and the content of the silver powder, the particle size and the appearance of the silver powder have an influence on the conductivity. The silver paste of this embodiment uses silver powder with smaller particles in order to reduce the surface roughness of the material, and in order to further reduce the surface impedance, the scaly silver powder and spherical silver powder are mixed in a range ratio of 7:3-8:2, which can effectively reduce the surface resistance. At the same time, in order to reduce the cost of silver paste materials, the content of silver powder can be reduced as much as possible under the premise of meeting the conductive requirements of fingerprint modules.

Wherein, D50 is the particle size corresponding to the cumulative particle size distribution percentage of silver particles at 50%, and D90 is the particle size corresponding to the cumulative particle size distribution of silver particles at 90%.

Further, in some embodiments, the resin includes epoxy resin and polyurethane, wherein the mass ratio of epoxy resin to polyurethane ranges from 2:1 to 5:4.

Specifically, epoxy resin is used as the film-forming carrier of the silver paste, which plays the role of binding the silver powder. Epoxy resin can be cured at lower temperature, which can meet the requirement of ultrasonic fingerprint processing temperature ≤120℃; at the same time, epoxy resin has good adhesion, and after adding coupling agent to silver paste, it has good adhesion with piezoelectric layer. Good adhesion.

It can be understood that the use of epoxy resin will lead to high viscosity of silver paste, which is not conducive to subsequent screen printing and curing. It is necessary to add a low-viscosity solvent to reduce the viscosity of the resin, improve the fluidity of the resin, and enhance the wettability of the resin to the silver powder. When the epoxy resin content is too high, the viscosity of the paste is too large, and the leveling property during screen printing is poor; when the epoxy resin content is too low, the adhesion of the silver paste is poor, and the silver powder is prone to agglomeration, which leads to material resistance The rate of increase is higher.

Further, the use of polyurethane as the silver paste film-forming carrier plays the role of binding the silver powder. In this embodiment, a low molecular weight polyurethane resin is used, and the molecular weight is about 10,000, so that the polyurethane resin can effectively reduce the viscosity of the slurry, which is beneficial to the screen printing process. At the same time, polyurethane contains a large number of polar groups such as urethane groups and urea groups. The polar groups are easily adsorbed on the surface of the silver powder, and have a good wetting effect on the silver powder, which is conducive to the uniform dispersion of the silver powder in the slurry. The wetting property enables the binder phase to evenly coat the surface of the silver powder, effectively controlling the agglomeration of the silver powder, forming a good conductive path, and ensuring that the silver paste has a low resistivity. When the proportion of polyurethane resin is high, the adhesion of silver paste decreases, and when the proportion is low, the viscosity is high, the screen printing performance of the paste is poor, and the surface resistance increases significantly.

Specifically, using epoxy resin and polyurethane as the film-forming carrier at the same time, and formulating according to the mass ratio range, can make the silver particles of the conductive material after silver paste molding uniformly distributed, the overall surface impedance is low, and the leveling property is good.

Further, in other embodiments, the solvent includes divalent ester and isophorone, and the mass ratio of the divalent ester to isophorone ranges from 2:1 to 1:1.

Specifically, using a divalent ester as the solvent of the silver paste paste has good compatibility with the resin and ensures that the paste has good stability and fluidity. When the divalent ester content is too low, the viscosity of the silver paste increases, and the silver powder particles cannot be well wetted, resulting in uneven distribution of the silver powder in the paste, and the formed conductive network is not dense enough, so the resistivity increases; at the same time, the content is too high. When it is low, the viscosity of silver paste is high, the dispersion effect is poor, and the screen printing effect is not good. When the divalent ester content is too high, on the one hand, the silver paste paste is easy to settle and stratify during the storage process, which brings difficulties to the subsequent paste stirring. The resin phase cannot shrink in time, and the silver powder particles cannot be aggregated effectively, resulting in an increase in the porosity of the cured film, which in turn reduces the compactness of the conductive network, resulting in an increase in areal impedance.

Further, the use of isophorone as the paste solvent of the silver paste has good compatibility with the resin and ensures that the paste has good stability and fluidity. Isophorone is a solvent with a high boiling point and a low volatilization rate. It has less volatilization during printing and has little effect on the viscosity of the paste. When the ratio of isophorone is low, the viscosity of the paste is high, the thixotropic index is high, and the surface of the silver glue is prone to grid patterns, and the resin cannot wet the silver powder well, resulting in uneven distribution of the silver powder in the paste; When the isophorone ratio is high, the silver paste paste is easy to settle and stratify during storage, which brings difficulties to the subsequent paste stirring, and at the same time, the solid content of the paste is reduced, resulting in a low thickness of the silver paste after film formation.

It should be noted that, in the preparation process of silver paste, a solvent needs to be added to dissolve into paste and the subsequent screen printing process is carried out. During the process of screen printing, curing and film formation of silver paste, the solvent will gradually volatilize; The resin inside will be connected to form a resin network.

It can be understood that, the conductive material after the silver paste is cured and finally formed may not contain solvent components due to the volatilization of the solvent.

In other embodiments, the auxiliary agent in the silver paste for preparing the conductive material includes: a curing agent with a mass ratio of 3%-5%, which is used for curing the silver paste so that the silver paste is cured to form a film; and, the mass ratio is 5%-7% coupling agent is used to assist the uniform dispersion of silver powder and improve the adhesion of silver paste.

Specifically, the curing agent is preferably hexahydrophthalic anhydride. Hexahydrophthalic anhydride is a latent acid anhydride curing agent. It is used as a curing agent for polyurethane and epoxy resin. The content is calculated according to the weight of the resin. If the proportion of the curing agent is low, the curing will be incomplete, resulting in unqualified resin adhesion and resistance to alcohol wiping.

Further, the coupling agent is preferably a silane coupling agent, because the coupling agent can better connect inorganic materials (silver powder, etc.) and organic materials (resin, etc.), one end is combined with the surface of inorganic substances, and one end is chemically reacted with organic substances. or physical entanglement, thus forming an organically combined whole. Therefore, the use of a coupling agent can promote the uniform dispersion of the material and improve the leveling and wetting of the silver paste. At the same time, the adhesion of the silver paste to the piezoelectric layer can be further improved. When the content of the coupling agent is too low, the coating of the silver powder by the coupling agent is incomplete, so that the dispersion of the silver powder in the resin is not uniform, resulting in an increase in the resistivity of the silver paste; when the content of the coupling agent is too high, the silver particles The dispersion is uniform, but the coupling agent thickens on the surface of the silver particle coating layer, which makes the distance between the conductive particles larger, resulting in an increase in the resistance value of the material.

In other embodiments, the auxiliary agent further includes an accelerator in a proportion of 0.5%-1% by mass, and the accelerator is used to accelerate the curing rate of the silver paste.

Further, the accelerator is preferably 2,4,6-tris(dimethylaminomethyl)phenol.

Specifically, the use of accelerators can greatly increase the reaction speed of the curing agent and epoxy resin, and reduce the curing temperature without affecting the physical and chemical properties of the adhesive.

Further, the addition amount of the accelerator is generally 10% to 15% of the addition amount of the curing agent.

Please refer to FIG. 3 together. The second embodiment of the present application provides an ultrasonic fingerprint module 100 for identifying fingerprints. The ultrasonic fingerprint module 100 includes a substrate 10, a TFT pixel array 20, a piezoelectric layer 30, Conductive electrode 40 .

The TFT substrate 10 is a bottom plate, and the TFT pixel array 20 is disposed on one side of the TFT substrate. Specifically, TFT (Thin Film Transistor) is a thin film transistor, the TFT substrate 10 is used to generate electrical signals, and the TFT pixel array 20 is used to collect electrical signals and generate fingerprint images according to the electrical signals.

Further, the piezoelectric layer 30 is located on the side of the TFT pixel array 20 away from the TFT substrate 10 , and the conductive electrode 40 is located on the side of the piezoelectric layer 30 away from the TFT pixel array 20 .

Specifically, one end of the conductive electrode 40 is also electrically connected to the TFT substrate 10 , and the electrical signal from the TFT substrate 10 is transmitted through the conductive electrode 40 , thereby applying the electrical signal to the piezoelectric layer 30 from two directions. The piezoelectric layer 30 is a transducer for converting electrical signals into ultrasonic waves or converting ultrasonic waves into electrical signals. The piezoelectric layer 30 receives the electrical signals from the TFT substrate 10 and the conductive electrodes 40 to generate ultrasonic waves. The ultrasonic waves are reflected after encountering fingerprints. The piezoelectric layer 30 receives the reflected ultrasonic waves and converts the ultrasonic waves into electrical signals. The TFT pixel array 20 obtains After the electric signal, a fingerprint image is formed by the electric field strength of the electric signal.

It can be understood that by using the difference in acoustic impedance between the fingerprint ridges and the fingerprint valleys when ultrasonic waves are propagated, the positions of the fingerprint ridges and the valleys can be distinguished, and then the lines of the fingerprint can be calculated.

Further, the piezoelectric layer 30 is usually made of fluoride, preferably polyvinylidene fluoride (PVDF, Poly (vinylidene fluoride)).

Further, the conductive electrode 40 is selected from the conductive material in any of the above embodiments, and the conductive material is obtained by curing the prepared silver paste.

Specifically, according to the material ratio of the silver paste, materials such as silver powder, resin, solvent, and auxiliary agent are uniformly mixed by high-speed stirring, and the dispersed silver paste is fully ground; then the piezoelectric layer is cleaned by water washing and plasma cleaning. 30. Then screen-print the silver paste on the piezoelectric layer 30 through a screen printing process, and solidify it at a certain temperature to obtain a uniform and dense silver paste. The thickness of the silver paste needs to be controlled to be about 10 μm.

Further, the performance of the conductive electrode 40 can be analyzed by measuring the sheet resistance and surface roughness of the conductive material formed after the silver paste is cured.

Specifically, through testing, when the silver paste forming the conductive material meets the above-mentioned limitations, the conductive material has excellent leveling performance and screen printing performance, the surface of the material is flat and smooth, and the roughness Rz can reach 1.5 μm. The conductive material has excellent electrical conductivity. When the mass proportion of silver powder is 55% to 65% and the film thickness is 10 μm, the surface impedance of the conductive material is less than 50 mΩ/sq.

Further, after the silver paste is formed into a film to form a conductive material, the silver powder particles in the material are uniformly distributed, and the silver powder particle size is small and does not aggregate, which has no obvious impact on the ultrasonic fingerprint sensor signal, and the signal-to-noise ratio of the detection result is low.

In other embodiments, the ultrasonic fingerprint module 100 further includes a cover plate 50 located on the side of the conductive electrode 40 away from the piezoelectric layer 30 .

Specifically, the cover plate 50 is used to protect several components at the lower part to prevent fingerprints from directly contacting the conductive electrodes 40, and ultrasonic waves can penetrate the cover plate 50 and project on the fingerprints.

It can be understood that when the ultrasonic fingerprint module 100 is applied to an electronic device such as a mobile phone, the cover plate 50 may not be in direct contact with the conductive electrodes 40 , and other mechanisms such as a mobile phone display module can also be arranged between the cover plate 50 and the conductive electrodes 40 .

In order to obtain the proportioning ratio of the above-mentioned silver paste, the performance after the silver paste under different conditions is cured into a film is tested by the controlled variable method, and the test results are as shown in the following table:

Table 1

From the experimental data in the chart, in many test cases, when the total mass ratio of flake silver powder and spherical silver powder is within 55%-65% and the mass ratio of flake silver powder to spherical silver powder is in the range of 7:3- When the ratio is within 8:2, the surface resistance and roughness of the conductive material formed by the corresponding silver paste are at a low level.

Please also refer to FIG. 4 , a third embodiment of the present application provides an electronic device 200 , which includes a main body 210 and the above-mentioned ultrasonic fingerprint module 100 , and the ultrasonic fingerprint module 100 is disposed on the main body 210 .

Specifically, the electronic device 200 may be a mobile phone, a tablet computer, a notebook computer, an electronic book reader, a portable multimedia player (PMP), a portable phone, a video phone, a digital still camera, a mobile medical device, a wearable device, etc. Devices that require fingerprint recognition capabilities.

Using the conductive material proposed in the embodiment of the present application to replace the material of the conductive electrode in the traditional ultrasonic fingerprint identification module, and by selecting an appropriate ratio of silver powder, the conductive material has good adhesion on the surface of the piezoelectric layer 30, and the surface roughness of the material is relatively high. Low, there are no larger silver particles in the material and no aggregation of silver particles. At the same time, the silver paste provided in this application can be directly covered on the piezoelectric layer of the fingerprint module without the screen printing fine line process; The content of silver particles in the paste can be reduced to achieve cost reduction.

The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced. Neither should depart from the spirit and scope of the technical solutions of the present invention. Those skilled in the art can also make other changes within the spirit of the present invention to be used in the design of the present invention, as long as they do not deviate from the technical effects of the present invention. These changes made according to the spirit of the present invention should all be included within the scope of the claimed protection of the present invention.

Claims

A conductive material, characterized in that the conductive material is obtained by curing a prepared silver paste, the silver paste comprising:

Silver powder with a mass ratio of 55%-65%, the silver powder is formed by mixing flake silver powder and spherical silver powder, and the mass ratio of the flake silver powder to the spherical silver powder is in the range of 7:3-8:2;

Resin with a mass ratio of 16%-20%;

10%-14% by mass of solvent; and

Auxiliary.
The conductive material according to claim 1, wherein the flake silver powder satisfies 1 μm≤D50≤3 μm and D90≤6 μm;

Among them, D50 is the particle size corresponding to the cumulative particle size distribution percentage of silver particles at 50%, and D90 is the particle size corresponding to the cumulative particle size distribution of silver particles at 90%.
The conductive material according to claim 1, wherein the particle size of the spherical silver powder is less than or equal to 1 μm.
The conductive material according to claim 1, wherein the resin comprises epoxy resin and polyurethane, and the mass ratio of the epoxy resin to the polyurethane ranges from 2:1 to 5:4.
The conductive material according to claim 1, wherein the solvent comprises a divalent ester and isophorone, and the mass ratio of the divalent ester to the isophorone is in the range of 2:1 -1:1.
The conductive material according to claim 1, wherein the auxiliary agent comprises:

A curing agent with a mass ratio of 3%-5%;

A coupling agent with a mass ratio of 5%-7%.
The conductive material according to claim 6, wherein the curing agent is hexahydrophthalic anhydride.
The conductive material according to claim 6, wherein the coupling agent is a silane coupling agent.
The conductive material according to claim 6, wherein the auxiliary agent further comprises:

Accelerator with a mass ratio of 0.5%-1%.
The conductive material of claim 9, wherein the accelerator is 2,4,6-tris(dimethylaminomethyl)phenol.
An ultrasonic fingerprint module, characterized in that it comprises:

TFT substrate;

TFT pixel array;

piezoelectric layer;

A conductive electrode comprising the conductive material according to any one of claims 1-10.
An electronic device, comprising:

Body: and

The ultrasonic fingerprint module according to claim 11, wherein the ultrasonic fingerprint module is arranged on the body.