WO2021175101A1

WO2021175101A1 - Electrically-conductive foam, ultrasonic fingerprint module, display screen assembly, and electronic apparatus

Info

Publication number: WO2021175101A1
Application number: PCT/CN2021/075723
Authority: WO
Inventors: 刘宣宣
Original assignee: 欧菲光集团股份有限公司; 江西欧迈斯微电子有限公司
Priority date: 2020-03-06
Filing date: 2021-02-07
Publication date: 2021-09-10
Also published as: CN111417295A

Abstract

The present invention relates to an electrically-conductive foam, an ultrasonic fingerprint module, a display screen assembly, and an electronic apparatus. The electrically-conductive foam comprises the following uniformly mixed components in percentage by mass: 1.5%-2.5% of a carbon powder; 3%-5% of a copper powder; 3%-5% of a nickel powder; the remainder being a resin, wherein the carbon powder particle size is less than or equal to 0.005 mm, the copper powder particle size is less than or equal to 0.01 mm, and the nickel powder particle size is less than or equal to 0.01 mm. The electrically-conductive foam of the present invention can be used to form a shielding layer attachable to a substrate of an ultrasonic fingerprint module. When the ultrasonic fingerprint module is in an operating state, the shielding layer can reflect an ultrasound wave emitted by a piezoelectric layer toward one side at which the substrate is located. The reflected ultrasound wave resonates with an ultrasound wave emitted by the piezoelectric layer toward one side at which an electrode layer is located so as to increase the signal strength of an ultrasound wave used to capture a fingerprint image, thereby obtaining a clear captured fingerprint image. In addition, the shielding layer has favorable electromagnetic shielding performance, thereby providing protection against EMI.

Description

Conductive foam, ultrasonic fingerprint module, display assembly and electronic equipment

This application claims the priority of a Chinese patent application filed with the Chinese Patent Office with the application number 202010151788.1 and the invention titled "conductive foam, ultrasonic fingerprint module, display assembly and electronic equipment" on March 6, 2020, and its entire contents Incorporated in this application by reference.

Technical field

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

Background technique

In the related art, the ultrasonic fingerprint module is attached to the display panel of the electronic device using glue, so that the display panel can have a fingerprint recognition function. However, the ultrasonic fingerprint module is very easy to radiate a large number of electromagnetic waves when it is working, and it becomes a radiation interference source. If the ultrasonic fingerprint module is not protected from EMI, it will not only affect the performance of the ultrasonic fingerprint module itself, if the signal strength may be reduced, the fingerprint image collected will not be affected. It is clear, and it will also cause electromagnetic interference to other electronic components in the electronic equipment, which will affect the normal operation.

Summary of the invention

Based on this, it is necessary to provide a conductive foam, an ultrasonic fingerprint module, a display assembly, and an electronic device to solve the problem of electromagnetic interference generated by electromagnetic waves radiated by the ultrasonic fingerprint module during operation.

The present invention provides a conductive foam. The conductive foam includes the following mass percentages of components uniformly mixed: 1.5% to 2.5% carbon powder, 3% to 5% copper powder, 3% to 5% nickel powder, and For the remainder of the resin, the particle size of the carbon powder is less than or equal to 0.005 mm, the particle size of the copper powder is less than or equal to 0.01 mm, and the particle size of the nickel powder is less than or equal to 0.01 mm.

The above-mentioned conductive foam can be used to make a shielding layer. The shielding layer can be attached to the substrate in the ultrasonic fingerprint module. When the ultrasonic fingerprint module is working, the shielding layer can reflect the ultrasonic waves emitted by the piezoelectric layer toward the side of the substrate. The ultrasonic waves emitted from the piezoelectric layer can resonate with the ultrasonic waves emitted from the piezoelectric layer toward the side of the electrode layer, thereby enhancing the signal strength of the ultrasonic waves used to collect fingerprint images, making the collected fingerprint images clearer. In addition, the shielding layer also has a good electromagnetic shielding effect and can realize EMI protection.

In one of the embodiments, the mass percentage of the carbon powder is 2% to 2.5%. In this way, the carbon powder of this mass percentage not only enables the conductive foam to have a good conductive effect, but also has a small influence on the foaming of the conductive foam.

In one of the embodiments, the particle size of the carbon powder is ≤ 0.001 mm. In this way, the shielding layer made of conductive foam made of carbon powder within the particle size range value can increase the SNR value of the ultrasonic fingerprint module, so that the fingerprint image collected by the ultrasonic fingerprint module is clearer.

In one of the embodiments, the mass percentage of the copper powder is 3%-4%. In this way, the copper powder of this mass percentage will not excessively increase the surface resistance value of the conductive foam, and the foaming effect of the conductive foam is also small.

In one of the embodiments, the particle size of the copper powder is less than or equal to 0.005 mm. In this way, the shielding layer made of conductive foam formed of copper powder in the particle size range value can increase the SNR value of the ultrasonic fingerprint module, so that the fingerprint image collected by the ultrasonic fingerprint module is clearer.

In one of the embodiments, the mass percentage of the nickel powder is 3%-4%. In this way, the nickel powder of this mass percentage will not excessively increase the surface resistance of the conductive foam, and it will have a small influence on the foaming of the conductive foam.

In one of the embodiments, the particle size of the nickel powder is less than or equal to 0.005 mm. In this way, the shielding layer made of conductive foam made of nickel powder in the particle size range value can increase the SNR value of the ultrasonic fingerprint module, so that the fingerprint image collected by the ultrasonic fingerprint module is clearer.

In one of the embodiments, the density of the conductive foam is less than or equal to 18 kg/m ³ . In this way, the impedance value of the conductive foam in this density range is closer to the impedance value of air. The shielding layer made of conductive foam and the substrate acoustic impedance of the ultrasonic fingerprint module have a large difference, and the ultrasonic signal can be greatly affected. reflection.

The present invention also provides an ultrasonic fingerprint module, including:

Substrate

A piezoelectric layer, which is attached to the substrate;

An electrode layer, which is attached to the side of the piezoelectric layer away from the substrate; and

The shielding layer is made of the above-mentioned conductive foam, the shielding layer is attached to the side of the substrate away from the piezoelectric layer, and the shielding layer can be grounded to shield electromagnetic signals.

According to the above-mentioned ultrasonic fingerprint module, the shielding layer can reflect the ultrasonic waves emitted by the piezoelectric layer toward the side of the substrate, and the reflected ultrasonic waves and the ultrasonic waves emitted by the piezoelectric layer toward the side of the electrode layer can form resonance, thereby enhancing the collection of fingerprint images. The signal strength of the ultrasonic wave makes the collected fingerprint image clearer. In addition, the shielding layer also has a good electromagnetic shielding effect and can realize EMI protection.

In one of the embodiments, the ultrasonic fingerprint module further includes a circuit board, the circuit board is electrically connected to the substrate and the electrode layer, and the shielding layer is electrically connected to the circuit board to pass The circuit board realizes the grounding of the shielding layer. In this way, the electrode layer can transmit and receive ultrasonic waves under the circuit board, and the shielding layer can be connected to the circuit board to realize convenient and fast grounding of the shielding layer, thereby realizing EMI protection.

The present invention also provides a display screen assembly, including:

Display panel

An adhesive layer disposed on the display panel; and

In the above ultrasonic fingerprint module, the electrode layer is attached to the display panel through the adhesive layer, and the piezoelectric layer can emit ultrasonic waves that penetrate the display panel and receive reflected ultrasonic waves.

According to the above display assembly, the shielding layer can reflect the ultrasonic waves emitted from the piezoelectric layer toward the side where the substrate is located, and the reflected ultrasonic waves and the ultrasonic waves emitted from the piezoelectric layer toward the side where the electrode layer is located can form resonance, thereby enhancing the fingerprint image collection. The signal strength of the ultrasound makes the captured fingerprint image clearer. In addition, the shielding layer also has a good electromagnetic shielding effect and can realize EMI protection.

In one of the embodiments, the display screen assembly further includes a protective cover plate connected to a side of the display panel facing away from the adhesive layer. In this way, the protective cover can enhance the structural strength.

In one of the embodiments, the adhesive layer is a black adhesive layer. In this way, the black adhesive layer can prevent light leakage of the display panel from causing different colors, and easily form an integrated black effect with the display panel.

The present invention also provides an electronic device, including:

Terminal body; and

The above-mentioned display screen assembly is connected with the terminal body.

According to the above electronic device, the ultrasonic fingerprint module can collect clear and uniform fingerprint images.

Description of the drawings

FIG. 1 is a schematic structural diagram of an electronic device provided by an embodiment of the present invention;

FIG. 2 is a schematic diagram of the structure of the display screen assembly in FIG. 1; and

Figure 3 shows the fingerprint image tested with the ultrasonic fingerprint function software.

Detailed ways

In order to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the following description, many specific details are explained in order to fully understand the present invention. However, the present invention can also be implemented in many other ways different from those described herein. Those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

It should be noted that when an element is referred to as being "fixed to" another element, it can be directly on the other element or a central element may also be present. When an element is considered to be "connected" to another element, it can be directly connected to the other element or an intermediate element may be present at the same time.

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

Referring to FIG. 1, the present invention will take a smart phone as an example to describe the electronic device 10. Those skilled in the art can easily understand that the electronic device 10 of the present invention can be any device with communication and storage functions, such as a smart phone, a tablet computer, a notebook computer, a portable phone, a video phone, a digital still camera, an e-book reader, The presentation form of the electronic device 10 such as a portable multimedia player (PMP), a mobile medical device, and other smart terminals is not limited in any way. Of course, for wearable devices such as smart watches, it is also applicable to the electronic device 10 of each embodiment of the present invention.

The electronic device 10 includes a terminal body 11 and a display screen assembly 12 connected to the terminal body 11. In one embodiment, the terminal body 11 includes a middle frame 13 and a back cover 14. The display screen assembly 12 and the back cover 14 are respectively connected to opposite sides of the middle frame 13 and enclosed to form a receiving space, which can be used for installation For the main board, power supply and other components of the electronic device 10, the middle frame 13 and the back cover 14 may be integrally formed or detachably connected. The side of the display screen assembly 12 facing away from the back cover 14 includes a displayable area 121. The displayable area 121 can constitute all or a part of the side of the display screen assembly 12 facing away from the back cover 14. The displayable area 121 is used for displaying image information.

As shown in FIG. 2, in an embodiment, the display screen assembly 12 includes a display panel 100 and a protective cover 200. The protective cover 200 is connected to a side of the display panel 100 facing away from the rear cover 14. The protective cover 200 may be A glass cover plate or a plastic cover plate is used to protect the display panel 100 from external interference. At this time, the displayable area 121 may be formed on all or a part of the protective cover plate 200 on the side facing the back cover 14. Of course, when the structural strength of the display panel 100 is not considered, the protective cover 200 may be omitted. In an embodiment, a light-shielding layer 110 is provided on the periphery of the display panel 100, and the light-shielding layer 110 is attached to the protective cover 200. The light-shielding layer 110 may be black graphite, and the black graphite may be formed on the protective cover 200 by printing. In order to absorb the light from the periphery of the display panel 100, the devices inside the containing space are shielded.

In one embodiment, the display panel 100 may adopt an LCD (Liquid Crystal Display) screen for displaying information. The LCD screen may be a TFT (Thin Film Transistor) screen or an IPS (In-Plane Switching) screen. Conversion) screen or SLCD (Splice Liquid Crystal Display) screen. In another embodiment, the display panel 100 may use an OLED (Organic Light-Emitting Diode, organic electro-laser display) screen for displaying information, and the OLED screen may be an AMOLED (Active Matrix Organic Light-Emitting Diode, active matrix organic light emitting diode). Diode) screen or Super AMOLED (Super Active Matrix Organic Light Emitting Diode) screen or Super AMOLED Plus (Super Active Matrix Organic Light Emitting Diode Plus, Magic screen) screen, here No longer.

Continuing to refer to FIG. 2, in one embodiment, the display screen assembly 12 includes an ultrasonic fingerprint module 300, and the ultrasonic fingerprint module 300 is disposed in the accommodating space and located below the display panel 100 in the drawing shown in FIG. 2. Specifically, in the process of manufacturing the electronic device 10 of the present invention, the ultrasonic fingerprint module 300 can be manufactured first, and after the manufacturing is completed, the ultrasonic fingerprint module 300 can be attached to the bottom of the display panel 100.

The ultrasonic fingerprint module 300 can scan a user's fingerprint using ultrasonic waves and recognize the fingerprint. Taking the embodiment shown in FIG. 2 as an example, the top surface of the ultrasonic fingerprint module 300 faces the display panel 100, and the ultrasonic fingerprint module 300 can transmit ultrasonic waves penetrating the display panel 100 and receive reflections from the user's finger touching the display panel 100 The ultrasonic waves, while converting the reflected ultrasonic waves into electrical signals. The top surface of the ultrasonic fingerprint module 300 is shown in FIG. 2 as the surface where the ultrasonic fingerprint module 300 and the display panel 100 are attached. Since the display panel 100 can conduct ultrasonic waves, when the user touches the position on the outer surface of the display panel 100 opposite to the ultrasonic fingerprint module 300, the ultrasonic waves emitted by the ultrasonic fingerprint module 300 are transmitted to the user's finger through the display panel 100. The reflected ultrasonic waves can be generated, and then the ultrasonic fingerprint module 300 receives the reflected ultrasonic waves and converts the reflected ultrasonic waves into electrical signals. The ultrasonic fingerprint module 300 can generate the collected fingerprint images according to these electrical signals and perform fingerprint identification. The above fingerprint recognition process uses the difference in acoustic impedance when the ultrasonic wave propagates between the fingerprint ridge (skin) and the fingerprint ridge (air), so that the location of the fingerprint ridge and the ridge can be distinguished, and the fingerprint recognition of the user can be realized.

Specifically, the ultrasonic fingerprint module 300 can compare the collected fingerprints with the standard fingerprints stored in the database. It is understandable that the standard fingerprint refers to the correct fingerprint stored in the database by the user himself. Wherein, the electronic device 10 is provided with a controller, which may be a central processing unit of the electronic device 10, and the controller is electrically connected to the ultrasonic fingerprint module 300. At this time, the ultrasonic fingerprint module 300 can send the comparison result to the controller, and the controller controls whether the display panel 100 is activated according to the comparison result, or whether the application software in the display panel 100 confirms the payment. For example, when the fingerprint collected by the ultrasonic fingerprint module 300 matches the standard fingerprint, the ultrasonic fingerprint module 300 sends the comparison result to the controller, and the controller controls the display panel 100 to light up. When the fingerprint collected by the ultrasonic fingerprint module 300 does not match the standard fingerprint, the ultrasonic fingerprint module 300 sends the comparison result to the controller, and the controller controls the display panel 100 to close. When the fingerprint collected by the ultrasonic fingerprint module 300 is the characteristic information of the user's fingerprint, at this time, the characteristic information of the user's fingerprint is collected by the ultrasonic fingerprint module 300, and the characteristic information of the collected fingerprint is combined with the standard characteristic information in the database. Comparison.

According to the above electronic device 10, when the user's finger touches the display panel 100, the ultrasonic waves emitted by the ultrasonic fingerprint module 300 can be reflected after passing through the display panel 100, and the ultrasonic fingerprint module 300 can perform fingerprint identification based on the reflected ultrasonic waves. , Achieve fingerprint recognition under the screen. Since the ultrasonic fingerprint module 300 does not need to be arranged in the frame of the electronic device 10, the area of the visible area of the electronic device 10 is increased.

With continued reference to FIG. 2, in one embodiment, the ultrasonic fingerprint module 300 includes a substrate 310, a piezoelectric layer 320, an electrode layer 330 and a circuit board 340. The substrate 310 may be a TFT substrate. The TFT substrate includes a base layer, a plurality of thin film transistors arranged in an array on the base layer, and lines for connecting the thin film transistors on the base layer. In addition, the TFT substrate can perform processing such as amplifying the electrical signal. Specifically, a thin film can be selected as the base layer for the TFT substrate. For example, when the display panel 100 is a flexible panel, the TFT substrate with a thin film as the base layer can meet the flexibility requirements of the entire electronic device 10.

The piezoelectric layer 320 is attached to the substrate 310. The piezoelectric layer 320 is composed of piezoelectric material and is used to transmit and receive ultrasonic waves through the piezoelectric effect. The material of the piezoelectric layer 320 is a ferroelectric polymer. For example, the material of the piezoelectric layer 320 can be It is P (VDF-TrFE) (polyvinylidene chloride and trifluoroethylene polymer). It can be understood that the material of the piezoelectric layer 320 is not limited to the above materials. For example, the material of the piezoelectric layer 320 may also be a homopolymer of polyvinylidene chloride (PVDC), a copolymer of polyvinylidene chloride, or polytetrafluoroethylene. Ethylene homopolymer, polytetrafluoroethylene copolymer, homo-vinylidene chloride or diisopropylamine bromide (DTPAB), etc.

The electrode layer 330 is attached to the side of the piezoelectric layer 320 away from the substrate 310, and the electrode layer 330 and the substrate 310 cooperate to accommodate the piezoelectric layer 320. The material of the electrode layer 330 may be silver. In a specific preparation process, the electrode layer 330 may be prepared by screen printing silver paste on one side of the piezoelectric layer 320 and then sintering. In various embodiments of the present invention, the electrode layer 330 is attached to the inner surface of the display panel 100, that is, the electrode layer 330 is attached to the side of the display panel 100 away from the protective cover 200. In an embodiment, the display screen assembly 12 includes an adhesive layer 400, the electrode layer 330 is attached to the display panel 100 through the adhesive layer 400, and the adhesive layer 400 may be a double-sided adhesive. In one embodiment, the adhesive layer 400 is a black adhesive layer, and the black adhesive layer can prevent the display panel 100 from leaking light and cause different colors, and it is easy to form an integrated black effect with the display panel 100.

The circuit board 340 is electrically connected to the substrate 310, and the circuit board 340 is also electrically connected to the electrode layer 330. For example, FIG. 2 illustrates that the circuit board 340 is electrically connected to the substrate 310 through the first anisotropic conductive adhesive 301, and the circuit board 340 is also electrically connected to the electrode layer 330 through the second anisotropic conductive adhesive 302. The circuit board 340 may specifically be a flexible circuit board, and the technical feature of the circuit board 340 may be applied to other embodiments. When assembling the display screen assembly 12, the circuit board 340 can be placed outside the path through which the ultrasonic wave is transmitted to the outer surface of the display panel 100, that is, the ultrasonic wave will not pass through the circuit board 340 during the process of transmitting the ultrasonic wave to the contact object, which can avoid The influence of the circuit board 340 on the conduction of ultrasonic waves.

In addition, a driver chip is provided on the circuit board 340, and the driver chip is, for example, an ASIC (Application Specific Integrated Circuit) chip. The driving chip provides a control signal to the piezoelectric layer 320, for example, sends a high-frequency electrical signal to the piezoelectric layer 320, so that the piezoelectric layer 320 emits ultrasonic waves. In addition, the driving chip also receives the electrical signal obtained by converting the reflected ultrasonic wave by the piezoelectric layer 320 to identify the fingerprint.

Both the substrate 310 and the electrode layer 330 are electrically connected to the driving chip. Take the example shown in FIG. The circuit board 340 is installed in this way to avoid interference with ultrasonic conduction.

The working principle of the above-mentioned ultrasonic fingerprint module 300 is: when performing fingerprint recognition, the user places a finger on the outer surface of the display panel 100, and the driving chip applies corresponding high-frequency electricity to the electrode layer 330 through the second anisotropic conductive glue 302 At the same time, a high-frequency electrical signal is applied to the substrate 310 through the first anisotropic conductive adhesive 301, and the piezoelectric layer 320 is activated under the excitation of the electrode layer 330 and the substrate 310, so that the piezoelectric layer 320 emits ultrasonic waves. The ultrasonic wave propagates upwards until it reaches the outer surface of the display panel 100 and is reflected after touching the user's finger. Then the piezoelectric layer 320 receives the reflected ultrasonic wave and converts it into an electrical signal, which is then processed (for example, amplified) by the substrate 310. It is transferred to the driver chip and converted into an image to identify the fingerprint. Due to the difference in ultrasonic acoustic wave impedance between the skin and the air, the location of the fingerprint ridge and the fingerprint valley can be distinguished, and the user's fingerprint can be collected according to the difference of the reflected ultrasonic waves.

It should be noted that the circuit board 340 in the ultrasonic fingerprint module 300 of each embodiment of the present invention can be omitted. In this case, in order to realize the fingerprint collection function of the ultrasonic fingerprint module 300, the substrate 310 and the electrode layer 330 can be directly connected to the electronic device. The circuit main board in 10 is electrically connected.

Although the ultrasonic fingerprint module 300 can realize fingerprint recognition under the screen, because the ultrasonic fingerprint module 300 emits ultrasonic waves under high-frequency and high-pressure conditions, it is extremely easy to generate a large number of electromagnetic waves and become a radiation interference source. If the ultrasonic fingerprint module 300 is not treated with EMI protection, the performance of the ultrasonic fingerprint module 300 may be easily affected, for example, the signal strength (SNR value) of the ultrasonic fingerprint module 300 may be reduced, and noise may be generated. In addition, the electromagnetic waves radiated by the ultrasonic fingerprint module 300 will affect the operation of other electronic components. Based on this, in an embodiment, the ultrasonic fingerprint module 300 further includes a shielding layer 350.

The shielding layer 350 is attached to the side of the substrate 310 away from the piezoelectric layer 320. The shielding layer 350 can reflect the ultrasonic waves emitted by the piezoelectric layer 320 toward the side where the substrate 310 is located, and the reflected ultrasonic waves and the piezoelectric layer 320 toward the electrode layer 330 The ultrasonic wave emitted from the side where it is located can form resonance, thereby enhancing the signal strength of the ultrasonic wave collecting the fingerprint image, making the fingerprint image collected more clear. In addition, the shielding layer 350 can be grounded to achieve EMI shielding protection and improve the quality of fingerprint images collected by the ultrasonic fingerprint module 300. In an embodiment, the shielding layer 350 is electrically connected to the circuit board 340, and the shielding layer 350 can be specifically connected to the bare copper area ground of the circuit board 340, so as to realize the grounding of the shielding layer 350 through the circuit board 340. For example, FIG. 2 illustrates that the shielding layer 350 is connected to the ground wire of the bare copper area of the circuit board 340 through the conductive member 360. The conductive member 360 may be a conductive cloth or a metal tape (such as a copper foil tape). The shielding layer 350 may also be connected to the ground wire of the bare copper area of the display panel 100 to realize the grounding of the shielding layer 350. Or the shielding layer 350 can also be connected to the terminal body 11 (for example, the middle frame 13 or the back cover 14) to realize the grounding of the shielding layer 350.

It should be noted that the shielding layer 350 of each embodiment of the present invention is made of conductive foam. The conductive foam includes the following mass percentages of components uniformly mixed: 1.5% to 2.5% carbon powder, 3% to 5% copper powder, 3% to 5% nickel powder, and the balance of resin. The particle size is less than or equal to 0.005mm, the particle size of the copper powder is less than or equal to 0.01mm, and the particle size of the nickel powder is less than or equal to 0.01mm. The resin can be, for example, polyurethane or acrylic resin. In order to obtain conductive foam, carbon powder, copper powder, and nickel powder in the above particle size range are added to the resin to be uniformly mixed with the resin during production, so that the resin is foamed to form conductive foam . And the formed conductive foam can realize all-round conductivity, that is, the conductive foam can conduct electricity in the three directions of X, Y, and Z. This is precisely because the resin is uniformly filled with carbon powder, copper powder, and nickel powder. Achievable.

Among them, carbon powder as a conductive material has low conductive resistance, and carbon powder is used for EMI protection. Since the surface roughness of the shielding layer 350 formed of conductive foam will affect the performance of the fingerprint test image, the particle size of the carbon powder is kept within 0.005 mm. Further, the particle size of the carbon powder is ≤0.001mm. The conductive foam with the above-mentioned particle size carbon powder can prepare a shielding layer 350 with a smooth surface and a small roughness, and the roughness can achieve Rz<0.001mm. If the mass percentage of the carbon powder filled in the conductive foam is too low, the surface impedance of the shielding layer 350 will be larger after the formation of the shielding layer 350, which cannot meet the conductive performance requirements. If the mass percentage of the carbon powder is too high, the conductive foam will be In the production process, it is more difficult to disperse the toner, and there is a risk of agglomeration. Therefore, the mass percentage of the carbon powder filled in the conductive foam of the present invention can be controlled at 1.5% to 2.5%. Further, in an embodiment, the mass percentage of the carbon powder can be controlled at 2% to 2.5%.

Copper powder and nickel powder can further improve the conductive performance of the conductive foam. In order to reduce the surface roughness of the shielding layer 350 formed by the conductive foam, the particle size of the copper powder and nickel powder is kept within 0.01 mm. In an embodiment, the particle size of the copper powder is less than or equal to 0.005 mm, and the particle size of the nickel powder is less than or equal to 0.005 mm. If the mass percentage of copper powder and nickel powder filled in the conductive foam is too low, the surface impedance of the shielding layer 350 will be large after the formation of the shielding layer 350, which cannot meet the conductive performance requirements, and if the mass percentage of copper powder and nickel powder is too high If it is high, it will affect the foaming process of the conductive foam, which is not conducive to the foaming of the conductive foam. The foaming of the conductive foam is affected and the density cannot be reduced. At this time, the impedance value of the conductive foam and the impedance value of the air are quite different That is, there is little difference in acoustic impedance between the shielding layer 350 made of conductive foam and the substrate 310 of the ultrasonic fingerprint module 300, and the ultrasonic signal cannot be well reflected. Therefore, the mass percentage of copper powder and nickel powder filled in the conductive foam of the present invention is controlled within a relatively small range. In one embodiment, the mass percentage of copper powder and nickel powder can be controlled between 3% and 5%. Further, the mass percentage of copper powder and nickel powder can be controlled within 3% to 4%.

After the shielding layer 350 made of the above conductive foam is attached to the substrate 310 in the ultrasonic fingerprint module 300, when the ultrasonic fingerprint module 300 is working, the shielding layer 350 can emit the piezoelectric layer 320 toward the side where the substrate 310 is located. The reflected ultrasonic waves can resonate with the ultrasonic waves emitted from the piezoelectric layer 320 toward the side of the electrode layer 330, thereby enhancing the signal strength of the ultrasonic waves used to collect fingerprint images, making the collected fingerprint images clearer. In addition, based on the content and particle size of the aforementioned metal powder, the formed shielding layer 350 also has a good electromagnetic shielding effect and can realize EMI protection.

In order to illustrate the influence of the density of the conductive foam on the clarity of the fingerprint test image, refer to Table 1 below. Table 1 lists the impact of the conductive foam on the clarity of the fingerprint test image when the density is different. The fingerprint test can be performed by attaching the shielding layer 350 to the substrate 310, and then attaching the electrode layer 330 to the display panel 100, by attaching a real finger or a fake finger with fingerprint lines to the display panel 100 for testing. The clarity of the fingerprint test image can be obtained by measuring the SNR value (signal-to-noise ratio). The larger the SNR value, the closer the fingerprint test image is to clear. The fingerprint test image clarity can also be obtained by visual observation.

Table 1. The influence of the density of conductive foam on the clarity of fingerprint test images

实验序号Experiment number	泡棉密度kg/m ³ Foam density kg/m ³	SNR值SNR value	测试背景Test background
11	9090	2.532.53	模糊Vague
22	4545	3.793.79	模糊Vague
33	1818	4.534.53	模糊Vague

It can be seen from Table 1 that when the density of conductive foam becomes smaller and smaller, the measured SNR value becomes larger. It should be noted that the SNR value (signal-to-noise ratio) is the ratio of the output signal power of the amplifier to the noise power output at the same time, usually expressed in decibels. The higher the signal-to-noise ratio of the device, the less noise it produces, that is, the larger the signal-to-noise ratio, which means that the smaller the noise mixed in the signal, the higher the sound quality of the sound playback, and the stronger the signal, otherwise the opposite is true. Referring to FIG. 3, under the influence of the shielding layer 350, the SNR value of the ultrasonic fingerprint module 300 is measured by the ultrasonic fingerprint function test software. The fingerprint ridge of the fake finger (the white area in the test image shown in FIG. 3) and the fingerprint The signal ratio of Yu (the black area in the test image in Figure 3) is the SNR value.

For experiment 3, the SNR value of experiment 3 is the largest. This is because the smaller the density of the conductive foam, the closer its acoustic impedance is to air, the greater the difference between the acoustic impedance and the substrate 310, and the ultrasonic signal is greatly affected. It reflects back, so the fingerprint test image is close to clear. But the final test result shows that the test image of Experiment 3 is still very blurry, and the test background is very dirty. This is because the clarity of the test images in the three sets of experiments is affected by the mass percentage and particle size of the carbon powder, copper powder and nickel powder filled in the conductive foam.

Based on this, in order to fully illustrate the influence of the mass percentage and particle size of carbon powder, copper powder and nickel powder, the present invention uses ^{conductive foam with a density of 18kg/m 2} to carry out multiple sets of experimental verification (in actual application, conductive foam The density can be ≤18kg/m ² ) to verify the surface impedance and electromagnetic shielding performance of the shielding layer 350 formed by conductive foam, and the clarity of the fingerprint image collected by the ultrasonic fingerprint module 200 during EMI protection.

It should be noted that the measurement of the electromagnetic shielding performance of the shielding layer 350 formed by the conductive foam of the present invention can be measured by the effectiveness of the shielding effectiveness SE, and the definition of the shielding effectiveness SE is as follows:

SE=20lg(E1/E2)(dB) (1)

In formula (1), E1 represents the field strength without shielding, and E2 represents the field strength with shielding. If the magnetic field strength is used in the shielding effectiveness calculation formula, it is called the magnetic field shielding effectiveness. If the shielding effectiveness calculation formula uses It is the electric field strength, which is called electric field shielding effectiveness, and the unit of shielding effectiveness is decibels (dB).

Please refer to the comparative examples and examples of each group listed in Table 2 below.

Table 2. Surface impedance, electromagnetic shielding performance and fingerprint test image clarity of the shielding layer formed by the conductive foams of Examples 1-12 and Comparative Examples 1-6

The results in Table 2 show that the shielding layer 350 formed by the conductive foams of Examples 1-12 has lower surface impedance and higher shielding performance, and the fingerprint test image measured therefrom has better clarity (high SNR value). ). Among them, when the particle size of the metal powder is 0.0001mm, it means that the metal powder is closest to 0 within the value range.

Comparing Example 1, Example 2 and Comparative Example 1, it can be seen that when the content of carbon powder is between 1.5% and 2.5%, the prepared shielding layer 350 has low surface impedance, high shielding performance, and little influence on the fingerprint test process.

Comparing Example 3, Example 4 and Comparative Example 2, it can be seen that when the content of copper powder is 3% to 5%, the prepared shielding layer 350 has low surface impedance, high shielding performance, and little influence on the fingerprint test process.

Comparing Example 5, Example 6 and Comparative Example 3, it can be seen that when the content of nickel powder is 3% to 5%, the prepared shielding layer 350 has low surface impedance, high shielding performance, and little influence on the fingerprint test process.

Comparing Example 7 and Example 8 with Comparative Example 4, it can be seen that when the particle size of the carbon powder is less than or equal to 0.005 mm, the prepared shielding layer 350 has low surface impedance, high shielding performance, and little impact on the fingerprint test process.

Comparing Example 9, Example 10 and Comparative Example 5, it can be seen that when the particle size of the copper powder is less than or equal to 0.01 mm, the prepared shielding layer 350 has low surface impedance, high shielding performance, and little impact on the fingerprint test process.

Comparing Example 11, Example 12 and Comparative Example 6, it can be seen that when the particle size of the nickel powder is less than or equal to 0.01 mm, the prepared shielding layer 350 has low surface impedance, high shielding performance, and little influence on the fingerprint test process.

The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the various technical features in the above-mentioned embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, all possible combinations are not described. It should be considered as the scope of this specification.

The above-mentioned embodiments only express several implementation modes of the present invention, and their descriptions are relatively specific and detailed, but they should not be understood as limiting the protection scope of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.

Claims

A conductive foam, which is characterized in that it comprises the following mass percentages of components uniformly mixed: 1.5% to 2.5% carbon powder, 3% to 5% copper powder, 3% to 5% nickel powder, and the balance For resin, the particle size of the carbon powder is less than or equal to 0.005 mm, the particle size of the copper powder is less than or equal to 0.01 mm, and the particle size of the nickel powder is less than or equal to 0.01 mm.
The conductive foam according to claim 1, wherein the mass percentage of the carbon powder is 2% to 2.5%.
The conductive foam according to claim 1, wherein the particle size of the carbon powder is ≤ 0.001 mm.
The conductive foam according to claim 1, wherein the mass percentage of the copper powder is 3% to 4%.
The conductive foam according to claim 1, wherein the particle size of the copper powder is ≤0.005mm.
The conductive foam according to claim 1, wherein the mass percentage of the nickel powder is 3% to 4%.
The conductive foam according to claim 1, wherein the particle size of the nickel powder is ≤0.005mm.
The conductive foam according to any one of claims 1 to 7, wherein the density of the conductive foam is ≤ 18 kg/m 3 .
An ultrasonic fingerprint module, characterized in that it comprises:

Substrate

A piezoelectric layer, which is attached to the substrate;

An electrode layer, which is attached to the side of the piezoelectric layer away from the substrate; and

The shielding layer is made of the conductive foam according to any one of claims 1 to 8. The shielding layer is attached to the side of the substrate away from the piezoelectric layer, and the shielding layer can be grounded to shield Electromagnetic signal.
The ultrasonic fingerprint module according to claim 9, wherein the ultrasonic fingerprint module further comprises a circuit board, the circuit board is electrically connected to the substrate and the electrode layer, and the shielding layer is electrically connected to the electrode layer. The circuit board is electrically connected to realize the grounding of the shielding layer through the circuit board.
A display screen assembly is characterized in that it comprises:

Display panel

An adhesive layer disposed on the display panel; and

The ultrasonic fingerprint module of claim 9 or 10, wherein the electrode layer is attached to the display panel through the adhesive layer, and the piezoelectric layer can emit ultrasonic waves penetrating the display panel and receive reflections. Ultrasound coming back.
11. The display screen assembly of claim 11, wherein the display screen assembly further comprises a protective cover plate, and the protective cover plate is connected to a side of the display panel facing away from the adhesive layer.
The display screen assembly of claim 11 or 12, wherein the adhesive layer is a black adhesive layer.
An electronic device, characterized in that it comprises:

Terminal body; and

The display screen assembly according to any one of claims 11 to 13, which is connected to the terminal body.