A fingerprint sensor based on hidden excitation ring

Abstract

The present invention discloses a fingerprint sensor based on a concealed excitation ring, which relates to the technical field of integrated circuits, and includes a fingerprint sensor chip, a substrate, a plastic sealing layer, and a concealed excitation ring; the fingerprint sensor chip is mounted on the substrate, and the substrate serves as a carrier of the fingerprint sensor chip to transmit the signal on the fingerprint sensor chip to the outside; the plastic sealing layer covers the fingerprint sensor chip to protect the fingerprint sensor chip from external physical damage, moisture invasion, and chemical corrosion; the fingerprint sensor is attached to a module PCB board, and the module PCB board serves as a carrier of the fingerprint sensor and is used to carry the fingerprint sensor; the concealed excitation ring is integrated into the fingerprint sensor. The present invention reduces the packaging cost of the fingerprint sensor, the installation difficulty and cost when embedded in the whole machine, avoids direct contact between human fingers and electrical signals, avoids interference introduced by the excitation ring, improves the acquisition quality of fingerprint images, and has stronger robustness of image acquisition performance.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated circuits, and in particular to a fingerprint sensor based on a hidden excitation ring. Background Art

[0002] In the current technology, fingerprint sensors have been widely used in various smart locks, electronic padlocks, mobile phones and other fingerprint recognition devices, using the fingerprint characteristics of the human body to identify personal identity. Fingerprint sensors are mainly divided into three types: optical fingerprint sensors, capacitive fingerprint sensors and ultrasonic fingerprint sensors. Among them, capacitive fingerprint sensors are widely used in fingerprint locks and various smart embedded devices due to their small size, low power consumption, easy integration, low cost, good product consistency and other advantages. According to most application scenarios, the fingerprint sensors used in mainstream fingerprint locks on the market have a ring on the outside, which is used to detect the placement of fingers and transmit the excitation signal inside the chip to the finger when collecting fingerprints. This ring is the excitation ring. In fingerprint sensors, the excitation ring is generally made of metal materials. In actual applications, the shells of many smart locks and electronic padlocks are metal shells. In order to shield static electricity, these metal shells are usually grounded. The excitation ring of the fingerprint sensor needs to be isolated from the shell of the fingerprint lock, otherwise the excitation ring close to the system ground will cause the finger detection to be insensitive and prone to short circuit failure. In addition, in order to obtain good robustness for different groups of people, the excitation signal is often designed as an electrical signal with high current and strong driving force. For sensitive people, when the finger directly touches the excitation ring and a large current signal is injected into the finger, there will often be an occasional tingling sensation, which reduces the comfort of using the product. At the same time, the existence of the excitation ring increases the cost of fingerprint sensor packaging. These factors limit the application of the excitation ring in fingerprint recognition devices.

[0003] Therefore, those skilled in the art are committed to developing a fingerprint sensor based on a hidden excitation ring. Summary of the invention

[0004] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to design a fingerprint sensor based on a hidden excitation ring, reduce the packaging cost of the fingerprint sensor, reduce the installation difficulty and cost when embedded in the whole machine, avoid direct contact between human fingers and electrical signals, avoid interference introduced by the excitation ring, improve the acquisition quality of fingerprint images, and make the acquisition performance more robust.

[0005] Fingerprint sensor mainly refers to the finished product of LGA package (Land Grid Array, i.e. grid array package). The inventor first analyzes the traditional capacitive fingerprint sensor, which includes a substrate, a fingerprint sensor chip, a plastic layer and a surface coating layer. The fingerprint sensor chip is mounted on the substrate, which acts as a carrier of the fingerprint sensor chip and transmits the signal on the fingerprint sensor chip to the outside. The fingerprint sensor chip is covered with a plastic layer to protect the fingerprint sensor chip from external physical damage, moisture intrusion and chemical corrosion. The surface coating layer is covered on the plastic layer, which is an insulating dielectric material to improve the anti-ESD (Electro-Staticdischarge) level of the fingerprint sensor and enhance the hardness of surface scratches. In order for the fingerprint sensor to work properly, it must also be equipped with a module PCB board and an excitation ring. The fingerprint sensor is attached to the module PCB board. The module PCB board acts as a carrier of the fingerprint sensor and is used to carry the fingerprint sensor. The excitation ring is a metal material and is fixed to the module PCB board by welding or conductive silver glue. The inner ring of the excitation ring is buckled above the fingerprint sensor.

[0006] When the finger touches the excitation ring, the excitation signal emitted by the fingerprint sensor chip is transmitted to the excitation ring through the wiring on the module PCB board, thereby forming an electric field inside the finger. The fingerprint sensor chip forms a fingerprint image by sensing the strength of the electric field at each point on the finger surface.

[0007] The inventors found that in order to avoid the insensitivity of finger detection and easy short-circuit failure caused by the excitation ring being close to the system ground, the excitation ring of the traditional capacitive fingerprint sensor needs to be isolated from the fingerprint lock housing; in order to obtain good robustness, the excitation signal is often designed as an electrical signal with high current and strong driving force. For sensitive people, when the finger directly touches the excitation ring and the high current signal is injected into the finger, occasional tingling sensation often occurs; in addition, the excitation ring of the traditional capacitive fingerprint sensor needs to be produced by a separate mold and then installed together, which increases the packaging cost, installation difficulty and installation cost.

[0008] In order to solve the above problems of traditional capacitive fingerprint sensors, in one embodiment of the present invention, a fingerprint sensor based on a hidden excitation ring is provided, including a fingerprint sensor chip, a substrate, a plastic sealing layer and a hidden excitation ring; the fingerprint sensor chip is mounted on the substrate, and the substrate serves as a carrier of the fingerprint sensor chip to transmit the signal on the fingerprint sensor chip to the outside; the plastic sealing layer covers the fingerprint sensor chip to protect the fingerprint sensor chip from external physical damage, moisture intrusion and chemical corrosion; the fingerprint sensor is attached to the module PCB board, and the module PCB board serves as a carrier of the fingerprint sensor and is used to carry the fingerprint sensor; the hidden excitation ring is integrated into the fingerprint sensor.

[0009] Optionally, in the fingerprint sensor based on the hidden excitation ring in the above embodiment, a surface coating layer is further included, and the surface coating layer covers the plastic packaging layer.

[0010] Optionally, in the fingerprint sensor based on the hidden excitation ring in the above embodiment, the surface coating layer adopts an insulating dielectric material with a thickness of about 20 um, which is used to improve the anti-ESD (Electro-Staticdischarge) level of the fingerprint sensor and enhance the hardness of surface scratches.

[0011] Optionally, in the fingerprint sensor based on the hidden excitation ring in the above embodiment, the hidden excitation ring is a conductive coating layer, which covers the plastic packaging layer, forms a ring around the surface coating layer, and is roughly flush with the surface coating layer and located on the same layer, and is connected to the internal excitation signal of the fingerprint sensor chip through a through hole.

[0012] Furthermore, in the fingerprint sensor based on the hidden excitation ring in the above embodiment, in response to the contact between the finger and the conductive coating layer, the fingerprint sensor chip sends an excitation signal, which is transmitted to the conductive coating layer through the through hole, forming an electric field inside the finger. The fingerprint sensor chip forms a fingerprint image by sensing the strength of the electric field at each point on the surface of the finger.

[0013] Optionally, in the fingerprint sensor based on the hidden excitation ring in the above embodiment, the hidden excitation ring is a metal wire surrounding the fingerprint sensor chip, attached to the surface of the substrate, located in the same layer as the fingerprint sensor chip, and covered by a plastic packaging layer and a surface coating layer.

[0014] Furthermore, in the fingerprint sensor based on the hidden excitation ring in the above embodiment, in response to the contact between the finger and the surface coating layer, the hidden excitation ring and the finger are coupled through the plastic packaging layer and the surface coating layer, and the excitation signal generated by the fingerprint sensor chip forms an electric field inside the finger. The fingerprint sensor chip forms a fingerprint image by sensing the strength of the electric field at each point on the finger surface.

[0015] Furthermore, in the fingerprint sensor based on the hidden excitation ring in the above embodiment, the fingerprint sensor chip is sunk into the interior of the substrate, the hidden excitation ring and the plastic packaging layer are located on the same layer and are roughly flush, and are covered by the surface coating layer, and the coupling distance from the hidden excitation ring to the finger is the thickness of the surface coating layer.

[0016] Optionally, in the fingerprint sensor based on the hidden excitation ring in the above embodiment, the fingerprint sensor is attached to the module PCB board in a flip-chip manner, the hidden excitation ring is made on the top of the substrate, and is connected to the excitation signal of the fingerprint sensor chip through the internal routing of the substrate. The module PCB board is hollowed out in the hidden excitation ring area to ensure the contact between the finger and the hidden excitation ring.

[0017] Furthermore, in the fingerprint sensor based on the hidden excitation ring in the above embodiment, in response to the contact between the finger and the hidden excitation ring, the fingerprint sensor chip sends an excitation signal which is transmitted to the hidden excitation ring through the through hole, thereby forming an electric field inside the finger. The fingerprint sensor chip forms a fingerprint image by sensing the strength of the electric field at each point on the surface of the finger.

[0018] Optionally, in the fingerprint sensor based on the hidden excitation ring in the above embodiment, the hidden excitation ring is placed on the top of the substrate and is connected to the excitation signal of the fingerprint sensor chip through internal wiring of the substrate.

[0019] Furthermore, in the fingerprint sensor based on the hidden excitation ring in the above embodiment, the middle part of the bottom of the substrate is thinned to place the fingerprint sensor chip, the fingerprint sensor chip collection surface faces upward, and the bottom surface of the substrate and the bottom surface of the fingerprint sensor core are roughly in the same plane.

[0020] Furthermore, in the fingerprint sensor based on the hidden excitation ring in the above embodiment, in response to the contact between the finger and the hidden excitation ring, the excitation signal of the fingerprint sensor chip is led out through the hidden excitation ring and injected into the finger, forming an electric field inside the finger. The fingerprint sensor chip forms a fingerprint image by sensing the strength of the electric field at each point on the surface of the finger.

[0021] Optionally, in the fingerprint sensor based on the hidden excitation ring in the above embodiment, it also includes a surface coating layer, the hidden excitation ring is integrated into the fingerprint sensor chip and covered by the plastic sealing layer, and the upper surface is roughly flush with the collection surface of the fingerprint sensor chip, and the surface coating layer covers the plastic sealing layer.

[0022] Furthermore, in the fingerprint sensor based on the hidden excitation ring in the above embodiment, in response to the contact between the finger and the hidden excitation ring, the excitation signal of the fingerprint sensor chip is led out through the hidden excitation ring, coupled to the finger through the plastic packaging layer and the surface coating layer, and an electric field is formed inside the finger. The fingerprint sensor chip forms a fingerprint image by sensing the strength of the electric field at each point on the surface of the finger.

[0023] The present invention integrates the external excitation ring into the chip package or the chip, and does not need to install an additional excitation ring outside the fingerprint sensor, which saves the packaging cost of the fingerprint sensor and reduces the difficulty of installation when it is embedded in the whole machine. At the same time, the present invention avoids direct contact between human fingers and electrical signals, is more convenient and comfortable to use, avoids interference introduced by the external excitation ring, improves the acquisition quality of fingerprint images, and has stronger robustness of image acquisition performance.

[0024] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a cross-sectional view of a fingerprint sensor illustrating a conventional excitation ring according to an exemplary embodiment;

[0026] Figure 2 is a top view of a fingerprint sensor illustrating a conventional excitation ring according to an exemplary embodiment;

[0027] Figure 3 is a structural diagram of a fingerprint sensor based on a hidden excitation ring according to an exemplary embodiment 1;

[0028] Figure 4 is a structural diagram of a fingerprint sensor based on a hidden excitation ring according to a second exemplary embodiment;

[0029] Figure 5 is a structural diagram of a fingerprint sensor based on a hidden excitation ring according to a third exemplary embodiment;

[0030] Figure 6 is a structural diagram illustrating a fingerprint sensor based on a hidden excitation ring according to a fourth exemplary embodiment;

[0031] Figure 7 is a structural diagram illustrating a fingerprint sensor based on a hidden excitation ring according to a fifth exemplary embodiment;

[0032] Figure 8 FIG. 2 is a diagram illustrating a structure of a fingerprint sensor based on a hidden excitation ring according to a sixth exemplary embodiment. DETAILED DESCRIPTION

[0033] The following describes several preferred embodiments of the present invention with reference to the drawings in the specification, so that the technical content is clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the protection scope of the present invention is not limited to the embodiments mentioned in the text.

[0034] In the drawings, components with the same structure are indicated by the same numerical reference numerals, and components with similar structures or functions are indicated by similar numerical reference numerals. The size and thickness of each component shown in the drawings are arbitrarily shown, and the present invention does not limit the size and thickness of each component. In order to make the illustration clearer, the thickness of the components is schematically exaggerated in some places in the drawings.

[0035] The inventors found that if Figure 1 and Figure 2 The conventional capacitive fingerprint sensor shown includes a substrate 106, a fingerprint sensor chip 105, a plastic sealing layer 104 and a surface coating layer 103; the fingerprint sensor chip 105 is mounted on the substrate 106, and the substrate 106 serves as a carrier of the fingerprint sensor chip 105 to transmit the signal on the fingerprint sensor chip 105 to the outside; the fingerprint sensor chip 105 is covered with a plastic sealing layer 104 to protect the fingerprint sensor chip 105 from external physical damage, moisture intrusion and chemical corrosion; the plastic sealing layer 104 is covered with a surface coating layer 103, and the surface coating layer 103 is an insulating dielectric material, which is used to improve the anti-ESD (Electro-Static discharge) level of the fingerprint sensor and enhance the hardness of the surface scratch. In order for the fingerprint sensor to work properly, it must also be equipped with a module PCB board 102 and an excitation ring 101. The fingerprint sensor is attached to the module PCB board 102. The module PCB board 102 serves as a carrier of the fingerprint sensor and is used to carry the fingerprint sensor. The excitation ring 101 is made of metal material and is fixed to the module PCB board 102 by welding or conductive silver glue. The inner ring of the excitation ring 101 is buckled above the four sides of the fingerprint sensor. In response to the contact between the finger and the excitation ring 101, the excitation signal emitted by the fingerprint sensor chip 105 is transmitted to the excitation ring 101 through the wiring on the module PCB board 102, thereby forming an electric field inside the finger. The fingerprint sensor chip 105 forms a fingerprint image by sensing the strength of the electric field at each point on the surface of the finger.

[0036] In order to prevent the excitation ring from being close to the system ground, which will lead to insensitive finger detection and easy short-circuit failure, the excitation ring 101 needs to be isolated from the fingerprint lock housing; in order to obtain good robustness, the excitation signal is often designed as an electrical signal with large current and strong driving force. For sensitive people, when the finger directly touches the excitation ring 101 and the large current signal is injected into the finger, occasional tingling sensation often occurs; in addition, the excitation ring 101 of the traditional capacitive fingerprint sensor needs to be produced by a separate mold and then installed together, which increases the packaging cost, installation difficulty and installation cost.

[0037] In order to solve the above problems of traditional capacitive fingerprint sensors, the inventors designed a fingerprint sensor based on a hidden excitation ring, including a fingerprint sensor chip, a substrate, a plastic sealing layer and a hidden excitation ring; the fingerprint sensor chip is mounted on the substrate, and the substrate serves as a carrier of the fingerprint sensor chip to transmit the signal on the fingerprint sensor chip to the outside; the plastic sealing layer covers the fingerprint sensor chip to protect the fingerprint sensor chip from external physical damage, moisture intrusion and chemical corrosion; the fingerprint sensor is attached to the module PCB board, and the module PCB board serves as a carrier of the fingerprint sensor and is used to carry the fingerprint sensor; the hidden excitation ring is integrated into the fingerprint sensor.

[0038] The inventor provides an embodiment 1 for the above scheme, such as Figure 3 As shown, it includes a fingerprint sensor chip 105, a substrate 106, a plastic layer 104, a hidden excitation ring 304 and a surface coating layer 103; the fingerprint sensor chip 105 is mounted on the substrate 106, and the substrate 106 serves as a carrier of the fingerprint sensor chip 105 to transmit the signal on the fingerprint sensor chip 105 to the outside; the plastic layer 104 covers the fingerprint sensor chip 105 to protect the fingerprint sensor chip 105 from external physical damage, moisture intrusion and chemical corrosion; the surface coating layer 103 covers the plastic layer 104, and the surface coating layer 103 is made of an insulating dielectric material with a thickness of about 20um, which is used to improve the anti-ESD (Electro-Static discharge) level to enhance the hardness of surface scratches; the fingerprint sensor is attached to the module PCB board 102, and the module PCB board 102 serves as a carrier of the fingerprint sensor and is used to carry the fingerprint sensor; the hidden excitation ring 304 is integrated in the fingerprint sensor, which is a conductive coating layer, covering the plastic packaging layer 104, surrounding the surface coating layer 103 to form a ring, and is roughly flush with the surface coating layer 103 and located in the same layer, and is connected to the internal excitation signal of the fingerprint sensor chip 105 through a through hole. In response to the contact between the finger and the hidden excitation ring 304 (i.e., the conductive coating layer), the fingerprint sensor chip 105 sends an excitation signal, which is transmitted to the hidden excitation ring 304 through the through hole, forming an electric field inside the finger, and the fingerprint sensor chip 105 forms a fingerprint image by sensing the strength of the electric field at each point on the surface of the finger.

[0039] The inventor provides a second embodiment of the above solution, such as Figure 4As shown, it includes a fingerprint sensor chip 105, a substrate 106, a plastic layer 104 and a hidden excitation ring 401; the fingerprint sensor chip 105 is mounted on the substrate 106, and the substrate 106 serves as a carrier of the fingerprint sensor chip 105 to transmit the signal of the fingerprint sensor chip 105 to the outside; the plastic layer 104 covers the fingerprint sensor chip 105 to protect the fingerprint sensor chip 105 from external physical damage, moisture invasion and chemical corrosion; the fingerprint sensor is attached to the module PCB board 102, and the module PCB board 102 serves as a carrier of the fingerprint sensor and is used to carry the fingerprint sensor; the hidden excitation ring 401 is integrated into the fingerprint sensor, which is a metal wire surrounding the fingerprint sensor chip, attached to the surface of the substrate 106, and is located on the same layer as the fingerprint sensor chip 105, and is covered by the plastic layer 104 and the surface coating layer 103. In response to the contact between the finger and the surface coating layer 103, the hidden excitation ring 401 is coupled to the finger through the plastic layer 104 and the surface coating layer 103, and the excitation signal generated by the fingerprint sensor chip 105 forms an electric field inside the finger. The fingerprint sensor chip 105 forms a fingerprint image by sensing the strength of the electric field at each point on the finger surface.

[0040] Considering that the coupling distance from the excitation ring 401 to the finger is limited by the thickness of the plastic layer 104 and the surface coating layer 103, the inventors have improved the above embodiment and provided embodiment 3, such as Figure 5 As shown, the portion of the substrate 106 in the middle where the fingerprint sensor chip 105 is placed is made thinner, the fingerprint sensor chip 105 is mounted on the substrate 106 and sunk into the inside of the substrate 106, the hidden excitation ring 401 is located in the thicker portion of the substrate 106, is located on the same layer as the plastic layer 104 and is roughly flush, and is covered by the surface coating layer 103, and the coupling distance from the hidden excitation ring 401 to the finger is the thickness of the surface coating layer 103.

[0041] The inventor provides a fourth embodiment of the above scheme, such as Figure 6As shown, it includes a fingerprint sensor chip 105, a substrate 106, a plastic layer 104 and a hidden excitation ring 401; the fingerprint sensor chip 105 is mounted on the substrate 106, and the substrate 106 serves as a carrier of the fingerprint sensor chip 105 to transmit the signal of the fingerprint sensor chip 105 to the outside; the plastic layer 104 covers the fingerprint sensor chip 105 to protect the fingerprint sensor chip 105 from external physical damage, moisture invasion and chemical corrosion; the fingerprint sensor is attached to the module PCB board 102 in a flip-chip manner, and the module PCB board 102 serves as a carrier of the fingerprint sensor and is used to carry the fingerprint sensor; the hidden excitation ring 401 is integrated into the fingerprint sensor, made on the top of the substrate 106, and connected to the excitation signal of the fingerprint sensor chip 105 through the internal wiring of the substrate 106. The module PCB board 102 is hollowed out in the hidden excitation ring 401 area to ensure the contact between the finger and the hidden excitation ring 401. In response to the contact between the finger and the hidden excitation ring 401, the fingerprint sensor chip 105 sends an excitation signal which is transmitted to the hidden excitation ring 401 through the through hole, forming an electric field inside the finger. The fingerprint sensor chip 105 forms a fingerprint image by sensing the electric field strength at each point on the finger surface.

[0042] In order to avoid hollowing out the module PCB board 102, the inventor has improved the above embodiment and provided a fifth embodiment. Figure 7 As shown, it includes a fingerprint sensor chip 105, a substrate 106, a plastic layer 104 and a hidden excitation ring 401; the fingerprint sensor chip 105 is mounted on the substrate 106, and the substrate 106 serves as a carrier of the fingerprint sensor chip 105 to transmit the signal on the fingerprint sensor chip 105 to the outside; the hidden excitation ring 401 is integrated into the fingerprint sensor, placed on the top of the substrate 106, and connected with the excitation signal of the fingerprint sensor chip 105 through the internal wiring of the substrate 106. The middle part of the bottom of the substrate 106 is thinned to place the fingerprint sensor chip 105, and the fingerprint sensor chip 105 is facing upward. The bottom surface of the substrate 106 and the bottom surface of the fingerprint sensor chip 105 are roughly in the same plane. In response to the contact between the finger and the hidden excitation ring 401, the excitation signal of the fingerprint sensor chip 105 is led out through the hidden excitation ring 401 and injected into the finger, forming an electric field inside the finger, and the fingerprint sensor chip 105 forms a fingerprint image by sensing the strength of the electric field at each point on the surface of the finger.

[0043] The inventor provides a sixth embodiment of the above scheme, such as Figure 8As shown, it includes a fingerprint sensor chip 105, a substrate 106, a plastic layer 104, a surface coating layer 103 and a hidden excitation ring 802; the fingerprint sensor chip 105 is mounted on the substrate 106, and the substrate 106 serves as a carrier of the fingerprint sensor chip 105 to transmit the signal on the fingerprint sensor chip 105 to the outside; the plastic layer 104 covers the fingerprint sensor chip 105 to protect the fingerprint sensor chip from external physical damage, moisture invasion and chemical corrosion; the fingerprint sensor is attached to the module PCB board, and the module PCB board 102 serves as a carrier of the fingerprint sensor and is used to carry the fingerprint sensor; the hidden excitation ring 802 is integrated into the fingerprint sensor chip 105, and the upper surface is roughly flush with the collection surface of the fingerprint sensor chip 105, and the surface coating layer 103 covers the plastic layer 104. In response to the contact between the finger and the hidden excitation ring 802, the excitation signal of the fingerprint sensor chip 105 is led out through the hidden excitation ring 802, coupled to the finger through the plastic packaging layer 104 and the surface coating layer 103, and an electric field is formed inside the finger. The fingerprint sensor chip 105 forms a fingerprint image by sensing the strength of the electric field at each point on the surface of the finger.

[0044] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A fingerprint sensor based on a hidden excitation ring, characterized in that: The invention comprises a fingerprint sensor chip, a substrate, a plastic sealing layer and a hidden excitation ring; the fingerprint sensor chip is mounted on the substrate, the substrate serves as a carrier of the fingerprint sensor chip, and transmits the signal on the fingerprint sensor chip to the outside; the plastic sealing layer covers the fingerprint sensor chip to protect the fingerprint sensor chip from external physical damage, moisture invasion and chemical corrosion; the fingerprint sensor is attached to the module PCB board, the module PCB board serves as a carrier of the fingerprint sensor, and is used to carry the fingerprint sensor; it also comprises a surface coating layer, the surface coating layer covers the plastic sealing layer; the hidden excitation ring Integrated into the fingerprint sensor, it is a conductive coating layer, covering the plastic sealing layer, forming a ring around the surface coating layer, and being roughly flush with the surface coating layer and located on the same layer, and connected to the internal excitation signal of the fingerprint sensor chip through a through hole; in response to the contact between the finger and the surface coating layer, the hidden excitation ring and the finger are coupled through the plastic sealing layer and the surface coating layer, and the excitation signal generated by the fingerprint sensor chip forms an electric field inside the finger, and the fingerprint sensor chip forms a fingerprint image by sensing the strength of the electric field at each point on the surface of the finger.

2. The fingerprint sensor based on the hidden excitation ring as claimed in claim 1, characterized in that: The surface coating layer is made of insulating dielectric material and has a thickness of about 20 um.

3. The fingerprint sensor based on the hidden excitation ring as claimed in claim 1, characterized in that: The hidden excitation ring is placed on the top of the substrate and is connected to the excitation signal of the fingerprint sensor chip through internal wiring of the substrate.

4. The fingerprint sensor based on the hidden excitation ring as claimed in claim 1, characterized in that: The middle part of the bottom of the substrate is thinned to place the fingerprint sensor chip, the fingerprint sensor chip collection surface faces upward, and the bottom surface of the substrate and the bottom surface of the fingerprint sensor chip are roughly in the same plane.

5. The fingerprint sensor based on hidden excitation ring as claimed in claim 1, characterized in that: It also includes a surface coating layer. The hidden excitation ring is integrated into the fingerprint sensor chip and covered by the plastic packaging layer. The upper surface is roughly flush with the collection surface of the fingerprint sensor chip. The surface coating layer covers the plastic packaging layer.

6. A fingerprint sensor based on a hidden excitation ring, characterized in that: It includes a fingerprint sensor chip, a substrate, a plastic sealing layer and a hidden excitation ring; the fingerprint sensor chip is mounted on the substrate, the substrate serves as a carrier of the fingerprint sensor chip, and transmits the signal on the fingerprint sensor chip to the outside; the plastic sealing layer covers the fingerprint sensor chip to protect the fingerprint sensor chip from external physical damage, moisture invasion and chemical corrosion; the fingerprint sensor is attached to the module PCB board, the module PCB board serves as a carrier of the fingerprint sensor, and is used to carry the fingerprint sensor; it also includes a surface coating layer, the surface coating layer covers the plastic sealing layer; the hidden excitation ring is integrated into the fingerprint sensor, which is a metal wire surrounding the fingerprint sensor chip, attached to the surface of the substrate, and is located on the same layer as the fingerprint sensor chip, and is covered by the plastic sealing layer and the surface coating layer; In response to the contact between the finger and the surface coating layer, the hidden excitation ring and the finger are coupled through the plastic packaging layer and the surface coating layer, the excitation signal generated by the fingerprint sensor chip forms an electric field inside the finger, and the fingerprint sensor chip forms a fingerprint image by sensing the strength of the electric field at each point on the finger surface.

7. The fingerprint sensor based on the hidden excitation ring as claimed in claim 6, characterized in that: The fingerprint sensor chip is sunk into the substrate, the hidden excitation ring and the plastic packaging layer are located in the same layer and are roughly flush, and are covered by the surface coating layer, and the coupling distance from the hidden excitation ring to the finger is the thickness of the surface coating layer.

8. A fingerprint sensor based on a hidden excitation ring, characterized in that: The invention comprises a fingerprint sensor chip, a substrate, a plastic sealing layer and a hidden excitation ring; the fingerprint sensor chip is mounted on the substrate, and the substrate serves as a carrier of the fingerprint sensor chip to transmit the signal on the fingerprint sensor chip to the outside; the plastic sealing layer covers the fingerprint sensor chip to protect the fingerprint sensor chip from external physical damage, moisture invasion and chemical corrosion; the fingerprint sensor is attached to the module PCB board in a flip-chip manner, and the module PCB board serves as a carrier of the fingerprint sensor for carrying the fingerprint sensor; the hidden excitation ring is integrated into the fingerprint sensor to surround the fingerprint sensor. The metal wire of the fingerprint sensor chip is attached to the surface of the substrate, the hidden excitation ring is made on the top of the substrate, and is connected to the excitation signal of the fingerprint sensor chip through the internal routing of the substrate. The module PCB board is hollowed out in the hidden excitation ring area to ensure the contact between the finger and the hidden excitation ring; in response to the contact between the finger and the hidden excitation ring, the fingerprint sensor chip sends an excitation signal that is transmitted to the hidden excitation ring through the through hole, forming an electric field inside the finger, and the fingerprint sensor chip forms a fingerprint image by sensing the strength of the electric field at each point on the surface of the finger.

9. A fingerprint sensor based on a hidden excitation ring, characterized in that: The invention comprises a fingerprint sensor chip, a substrate, a plastic sealing layer and a hidden excitation ring; the fingerprint sensor chip is mounted on the substrate, and the substrate serves as a carrier of the fingerprint sensor chip to transmit the signal on the fingerprint sensor chip to the outside; the plastic sealing layer covers the fingerprint sensor chip to protect the fingerprint sensor chip from external physical damage, moisture intrusion and chemical corrosion; the fingerprint sensor is attached to the module PCB board, and the module PCB board serves as a carrier of the fingerprint sensor and is used to carry the fingerprint sensor; the hidden excitation ring is made on the top of the substrate , connected with the excitation signal of the fingerprint sensor chip through the internal wiring of the substrate, the middle part of the bottom of the substrate is thinned to place the fingerprint sensor chip, the collection surface of the fingerprint sensor chip faces upward, and the bottom surface of the substrate and the bottom surface of the fingerprint sensor chip are roughly in the same plane; in response to the contact between the finger and the hidden excitation ring, the excitation signal of the fingerprint sensor chip is led out through the hidden excitation ring and injected into the finger, forming an electric field inside the finger, and the fingerprint sensor chip forms a fingerprint image by sensing the strength of the electric field at each point on the surface of the finger.

Images