Multi-sensor integrated module for micro-quantitative wearable monitoring device and packaging method thereof

Abstract

The application discloses a multi-sensor integrated module for a micro-sized wearable monitoring device and a packaging method thereof, relates to the fields of wearable electronic device manufacturing and microelectronic packaging technology, and the integrated module comprises a transparent resin inner holder, the inner surface of which is a curved surface for contacting a human body; a flexible circuit board attached to the outer surface of the transparent resin inner holder; at least part of sensors embedded in the transparent resin inner holder or attached to the flexible circuit board; the transparent resin inner holder comprises integrally formed high light transmission zones and optical isolation zones; a sealing structure is arranged between the outer surface of the transparent resin inner holder and the flexible circuit board, and the inner surface is kept exposed at the functional contact surfaces corresponding to the high light transmission zones and the sensors. The application can solve the technical problems of the coupling of the assembly conflict of heterogeneous sensors, the bending fatigue cracking of a curved surface, poor electromagnetic compatibility and the mutual restriction of waterproof sealing and functional windowing in the existing micro-sized curved wearable device at an architecture level.

Description

Technical Field

[0001] This application relates to the fields of wearable electronic device manufacturing and microelectronic packaging technology, and in particular to a multi-sensor integrated module for miniaturized wearable monitoring devices and its packaging method. Background Technology

[0002] With the continuous upgrading of health monitoring needs, smart rings, as a cutting-edge form of wearable device, are only 4-6mm wide, 2-3mm thick, and have an internal volume of less than 0.5cm. 3 However, it requires the integration of 20-30 components, including PPG, ECG, accelerometer, temperature sensor, Bluetooth SoC, battery, charging coil, and antenna. Existing processes for traditional wearable devices such as smartwatches have the following technical limitations in this extreme curved surface packaging scenario: I. Severe signal crosstalk Rigid PCBs cannot fit snugly against the inner wall of the ring, resulting in low space utilization in splicing solutions; commercially available FPCs are mainly double-sided boards, lacking shielding layer designs. Within the extreme space of the ring, Bluetooth radio frequency (-20dBm@2.4GHz) generates strong electromagnetic interference to nA-level PPG photocurrent, with a signal-to-noise ratio below 20dB; LED pulse drive (hundreds of mA) generates mV-level ground bounce noise in the common ground loop, coupling into μV-level ECG differential signals, with a common-mode rejection ratio of only 60-70dB; 2 Harmonics from the C / SPI bus interfered with the temperature sensor, causing fluctuations of more than ±0.2℃.

[0003] II. Incompatible assembly of heterogeneous sensors The ECG electrode needs to protrude, the PPG needs an optical window that cannot be obstructed, and the temperature sensor needs to be thermally coupled but electrically isolated from the ECG. The high reflow soldering temperature (240-260℃) causes the FPC substrate to warp, and the solder joints crack after 200 bends; the transparent potting compound attenuates the characteristic wavelength of the PPG by more than 30%, and the diameter of the light guide pillar (≥3mm) exceeds the limit of the ring thickness; the thermal grease cannot simultaneously meet the requirements of high thermal conductivity (>3W / m·K) and high insulation (>10). 12 Ω·cm).

[0004] 3. Poor reliability when bending After a planar FPC is bent into a ring-shaped housing, the copper foil traces develop microcracks or even break after 1000-2000 bends; the interlayer adhesive layer peels off under alternating temperature and humidity; and the solder joints of surface-mount components crack due to excessive strain. Existing solutions lack stress relief designs for the curved surface of the ring, resulting in a yield rate of less than 80%.

[0005] IV. Conflict between waterproofing and functional openings IP68 waterproofing requires a seamless housing, but the PPG window, ECG electrodes, and charging contacts must be exposed. Poor adhesive sealing consistency and excess adhesive contamination of the optical surface are problems; secondary injection pressure (>10MPa) can easily crush internal components; and there is no room for O-ring operation within a 2-3mm thickness. Current technology cannot simultaneously meet the four requirements of light attenuation <10%, electrode impedance <10kΩ, contact resistance <50mΩ, and IP68.

[0006] In summary, the four types of problems encountered by existing manufacturing processes in the smart ring scenario can be traced back to the same fundamental contradiction: the dimensional gap between the existing electronic manufacturing model based on the fundamental assumption of two-dimensional planar rigid boards and the packaging requirements of smart rings with three-dimensional curved surfaces. This gap leads to a coupled predicament where solving any one problem exacerbates the others. Summary of the Invention

[0007] The purpose of this application is to provide a multi-sensor integrated module and its packaging method for miniaturized wearable monitoring devices, in order to bridge the dimensional gap between the existing electronic manufacturing model based on the basic assumption of two-dimensional planar rigid boards and the packaging requirements of smart rings with three-dimensional curved surfaces.

[0008] To achieve the above objectives, this application provides the following solution: In a first aspect, this application provides a multi-sensor integrated module for a miniaturized wearable monitoring device, comprising: A transparent resin inner tray has opposing inner and outer surfaces, wherein the inner surface is a curved surface that comes into contact with the human body; A flexible circuit board is attached to the outer surface of the transparent resin inner tray; At least some of the sensors are embedded in the transparent resin inner holder or attached to the flexible circuit board; The sensor includes a PPG sensor, which has a light-emitting element and a photosensitive element; The transparent resin inner holder includes an integrally formed high-transmittance area and an optical isolation area. The high-transmittance area corresponds to the light path direction of the light-emitting element and the photosensitive element, and the optical isolation area is located between the light-emitting element and the photosensitive element. A sealing structure is provided between the outer surface of the transparent resin inner holder and the flexible circuit board, and the inner surface remains exposed at the functional contact surface corresponding to the high light transmittance area and the sensor.

[0009] Secondly, this application provides a method for interconnecting a flexible circuit board with a curved sensor insert, comprising the following steps: A transparent resin inner holder is provided, wherein a sensor contact is embedded in the transparent resin inner holder, and the sensor contact has a conductive post extending from the outer surface of the transparent resin inner holder. An anisotropic conductive adhesive film is applied around the conductive pillar; Align the first connection terminal on the flexible circuit board with the conductive post; The first connecting terminal is electrically connected to the conductive post through the anisotropic conductive film.

[0010] Thirdly, this application provides a waterproof encapsulation method for a miniature curved wearable device, comprising the following steps: The electronic components are fixed to the outer surface of a transparent resin insert that has an inner surface and an outer surface. The transparent resin inner tube, together with the electronic components, is placed into the housing; The transparent resin inner tray is filled with sealant from the outer surface into the interior of the outer shell using an injection molding process. The inner surface of the transparent resin inner holder remains exposed during the injection molding process to serve as an optical window, sensor functional contact surface, or skin contact interface. After the sealant cures, it forms a protective seal around the electronic components.

[0011] Fourthly, this application provides a flexible circuit board for a micro wearable device, the flexible circuit board being bent into a ring shape and comprising sequentially stacked components: The flexible circuit board is bent into a ring shape and includes, in sequence, at least one analog signal layer, a complete ground plane layer, a power layer, at least one digital signal layer; and an insulating layer disposed between each layer.

[0012] According to the specific embodiments provided in this application, the following technical effects are disclosed: This application provides a multi-sensor integrated module and its packaging method for miniaturized wearable monitoring devices. It uses a transparent resin inner tray as a multifunctional three-dimensional reference surface integrating optical control, surface adaptation, sensor anchoring points, and a sealing interface. Through the synergistic effect of each component, it systematically solves the dimensional gap problem between existing two-dimensional manufacturing methods and the requirements of three-dimensional curved surface packaging at the architectural level. Specifically: By designing the transparent resin inner holder to include a one-piece molded high-transmittance area and an optical isolation area, a dedicated, crosstalk-free optical channel is constructed for the PPG sensor. Simultaneously, by selectively embedding different sensors within the transparent resin inner holder or mounting them onto a flexible circuit board, functional partitioning and physical isolation of each sensor are achieved on the three-dimensional curved inner wall. This structure allows functional surfaces such as optical windows and electrode contacts to be independently arranged without sacrificing the performance of other sensors to accommodate one, thus resolving the assembly conflicts of heterogeneous sensors within limited space at the architectural level.

[0013] By attaching the flexible circuit board to the outer surface of the transparent resin inner holder, the transparent resin inner holder acts as a load-bearing skeleton, absorbing most of the bending strain caused by wear deformation. This structure significantly reduces the dynamic strain on the copper foil traces and solder joints on the flexible circuit board, effectively improving the long-term reliability of the module under repeated bending conditions.

[0014] By attaching a flexible circuit board to the outer surface of the inner tray at the module architecture level and embedding at least some sensors within the transparent resin inner tray, the transparent resin inner tray becomes a physical separation interface. Different types of devices can achieve a physical spatial partitioning layout using the thickness direction of the transparent resin inner tray itself. This structure creates conditions for shortening the transmission path of sensitive analog signals and effectively reduces electromagnetic interference between devices mounted on the flexible circuit board and sensors embedded in the inner tray, significantly improving the signal fidelity of miniaturized wearable devices in environments with strong mixed signal interference.

[0015] By setting a sealing structure between the outer surface of the transparent resin inner holder and the flexible circuit board, while simultaneously limiting the inner surface to remain exposed in the corresponding high-transmittance areas and sensor functional contact surfaces, this approach breaks away from the conventional thinking that sealing must cover the outer surface. This reverse sealing architecture places the waterproof barrier inside the module, ensuring that the PPG optical window, electrodes, and other functional surfaces are reliably waterproofed while their optical transmission paths and electrical signal acquisition interfaces remain unobstructed. Within the same architecture, it simultaneously meets multiple stringent requirements regarding light attenuation, electrode impedance, and overall airtightness, fundamentally resolving the inherent contradiction between waterproofing and functional window openings within a limited space.

[0016] In summary, this application, through the introduction of a multifunctional transparent resin inner tray and its specific spatial layout relationship with the flexible circuit board and sensor, enables the long-standing technical challenges in the field of micro-curved wearable devices to be synergistically resolved within the same architecture, achieving significant technical results. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the smart ring structure provided in an embodiment of this application.

[0019] Figure label: 10 - Transparent resin inner tube, 20 - PPG sensor, 30 - ECG electrode. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0021] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] In the description of this application, the inner surface refers to the surface facing the human skin when worn, and the outer surface refers to the surface facing away from the human skin. "Multiple" means two or more. "Connection" should be interpreted broadly, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0023] Example 1: Basic Structure of Multi-Sensor Integrated Module This application provides a multi-sensor integrated module for miniaturized wearable monitoring devices, which is mainly used in miniature curved wearable devices such as smart rings.

[0024] The transparent resin inner holder 10 has opposing inner and outer surfaces, with the inner surface being a curved surface that contacts the human finger. In specific applications, such as... Figure 1 As shown, the inner diameter range of the smart ring is... The inner surface curvature radius is 14-22mm, matching this. The transparent resin inner holder 10 has a wall thickness of 0.3-0.5mm and is injection molded from a high-transmittance epoxy resin material. This material has a transmittance ≥90% and a refractive index of 1.55 at the operating wavelengths of the PPG sensor (530nm for green light and 660nm for red light). In other embodiments, other transparent resin materials with similar optical properties, such as transparent polycarbonate or transparent silicone resin, can also be used.

[0025] The transparent resin inner holder 10 includes an integrally molded high-transmittance area and an optical isolation area. The high-transmittance area corresponds to the optical path direction of the light-emitting element and the photosensitive element of the PPG sensor 20, and is used for bidirectional transmission of light signals, serving as the optical window for photoelectric detection by the PPG sensor. The optical isolation area is located between the light-emitting element and the photosensitive element, and is used to block the light emitted by the light-emitting element from reaching the photosensitive element through total internal reflection or direct path within the transparent resin inner holder 10. The optical isolation area has a three-dimensional structure, extending along the optical path between the light-emitting element and the photosensitive element, with a width of 0.3 mm and a depth of 0.2 mm.

[0026] The transparent resin inner holder 10 is molded using a two-shot injection molding process. The first shot is a high-transmittance epoxy resin, with an injection temperature of 120℃, an injection pressure of 80MPa, a holding pressure of 3 seconds, and cooling to 60℃, forming a transparent matrix, i.e., the high-transmittance area. The second shot is a black epoxy resin with 2wt% carbon black added, with an injection pressure of 60MPa and a holding pressure of 2 seconds, forming a three-dimensional optical isolation area between the light-emitting element and the photosensitive element. The high-transmittance resin of the first shot and the light-shielding resin of the second shot are fused together at the interface to form an integrated structure with no visible boundary gap between them.

[0027] A flexible printed circuit (FPC) is attached to the outer surface of the transparent resin inner holder 10. The FPC uses polyimide (PI) as the substrate, has a total thickness of 0.3 mm, and is bent into a ring shape to fit the curved surface of the transparent resin inner holder 10. Conductive lines and multiple pads are arranged on the FPC to achieve electrical interconnection between the sensors and the main control chip. The FPC is electrically connected to the sensors embedded in the transparent resin inner holder 10 using anisotropic conductive adhesive or laser welding.

[0028] A sealing structure fills the space between the outer surface of the transparent resin inner holder 10 and the flexible circuit board. In this embodiment, the sealing structure uses a sealant layer. The sealant layer is a low-hardness polyurethane hot melt adhesive with a hardness of Shore A 60. This sealant layer is formed by low-pressure injection molding and is located inside the module, rather than covering the functional area on the inner surface. The sealant layer is used to fill the gap between the flexible circuit board and the transparent resin inner holder 10, preventing moisture from seeping into the internal electronic component area from the outside of the housing through the gap.

[0029] The sensor is embedded in a transparent resin inner holder 10 or mounted on a flexible circuit board, with its functional surface exposed on the inner surface or optically coupled to a high-transmittance area. Specifically, the sensor includes a PPG sensor 20, an ECG electrode 30, and a temperature sensor. The ECG electrode 30 is embedded in the transparent resin inner holder 10 via insert injection molding, with its electrode surface exposed on the inner surface. The light-emitting element and photosensitive element of the PPG sensor 20 are mounted in the transparent resin inner holder 10 via a sub-board (the sub-board can be rigid or flexible) and optically coupled to the high-transmittance area. The temperature sensor is embedded on the inner surface of the transparent resin inner holder 10. The temperature sensor is an ultra-thin temperature sensor (such as the TMP117 type, with a thickness of 0.4 mm; this is only an example, and other ultra-thin temperature sensors with similar dimensions and performance can be used in other embodiments). A shallow groove is provided on the inner surface of the transparent resin inner holder 10 corresponding to the position of the temperature sensor, the depth of which matches the thickness of the temperature sensor, and the temperature sensor is embedded in this shallow groove. The surface of the temperature sensor is flush with the inner surface via a thermally conductive gel. The thermal conductivity of the gel is >3 W / (m·K), combining high thermal conductivity and high insulation to ensure a good heat conduction path between the temperature sensor and the skin for accurate temperature measurement, while maintaining electrical isolation from the adjacent ECG electrodes 30. The accelerometer, Bluetooth SoC, power management chip, etc., are mounted on a flexible circuit board.

[0030] The flexible circuit board and the sensor embedded in the transparent resin inner holder 10 are electrically connected by anisotropic conductive adhesive or laser welding. Specifically, the conductive post on the back of the ECG electrode 30 extends from the outer surface and achieves vertical conduction with the elastic contact on the flexible circuit board through anisotropic conductive adhesive; the daughter board of the PPG sensor 20 is electrically connected to the corresponding pad on the flexible circuit board through laser welding; the signal lead of the temperature sensor is led out from the inside of the transparent resin inner holder 10 to the outer surface and electrically connected to the corresponding pad on the flexible circuit board. The lead can be made by pre-embedding metal pins during injection molding, or by extending from the outer surface through conductive posts and connecting to the FPC.

[0031] In this embodiment, the diameter of the high-transmittance area of ​​the transparent resin inner sleeve 10 ranges from 2 to 3 mm. There are two ECG electrodes 30, corresponding to the two detection ends of the ECG differential signal. The module 100 has a total thickness of 2.6 mm and a total width of 5 mm, fitting snugly into the internal space of the smart ring.

[0032] In one embodiment, a high-transmittance area is located in the central region of the transparent resin inner holder 10, extending through the transparent substrate between the inner and outer surfaces. An optical isolation area is located inside the high-transmittance area, separating the sub-region corresponding to the light-emitting element from the sub-region corresponding to the photosensitive element. ECG electrodes 30 are located on both sides of the high-transmittance area, with their electrode surfaces protruding approximately 0.1-0.2 mm from the inner surface, and conductive posts extending from the outer surface. A temperature sensor is located on one side of the high-transmittance area, embedded in a shallow groove on the inner surface, its surface flush with the inner surface via thermally conductive gel. The sub-plate of the PPG sensor 20 is embedded from the outer surface side into a groove in the transparent resin inner holder 10 and bonded to the high-transmittance area via optically transparent adhesive. A flexible circuit board is attached to the outer surface, with its elastic contacts abutting against the conductive posts. A sealant layer fills the gap between the flexible circuit board and the outer surface.

[0033] The ECG electrode 30 is integrally molded with the transparent resin inner holder 10 via insert injection molding. The ECG electrode 30 is made of TA2 pure titanium, is crescent-shaped with an arc length of 4-6 mm, a width of 1.5 mm, and a thickness of 0.2 mm. The electrode surface of the ECG electrode 30 protrudes 0.1-0.2 mm from the inner surface to ensure reliable contact with the skin. Conductive posts are provided on the back of the ECG electrode 30, extending from the outer surface for electrical connection with the flexible circuit board.

[0034] The ECG electrode 30 is prepared as follows: First, the pre-formed and cleaned TA2 pure titanium electrode contacts are placed in the corresponding cavity of the injection mold and fixed by vacuum adsorption; then, the mold is closed and injection molded, so that the electrode contacts and the transparent resin inner holder 10 are tightly bonded together during the injection molding process. After injection molding, the electrode surface protrudes from the inner surface, and the conductive post extends from the outer surface. After demolding, the electrode surface is lightly sanded with 600-grit sandpaper to remove burrs, and then ultrasonically cleaned in deionized water for 5 minutes and dried.

[0035] The light-emitting element and photosensitive element of the PPG sensor 20 are mounted on a daughter board. The daughter board measures 2.5mm × 2.5mm and is a rigid printed circuit board or ceramic substrate. The outer surface of the transparent resin inner holder 10 has a groove, the shape of which matches the daughter board. The daughter board is embedded in the groove, and the daughter board is bonded to the high-transmittance area with an optically transparent adhesive that matches the refractive index, ensuring a gapless optical path and maximizing the optical signal transmission efficiency.

[0036] Electrical connections are achieved between the pads on the daughterboard and the corresponding pads on the flexible circuit board via laser welding. The laser welding process parameters are: laser power 10W, welding time 50ms. The signal from the PPG sensor 20 is transmitted to the flexible circuit board via laser welding.

[0037] In this embodiment, the transparent resin inner holder 10 is integrally molded with the high-transmittance area and the optical isolation area through double-shot injection molding, enabling the optical window and optical isolation to be realized simultaneously in a single component. This eliminates the need for additional light guide pillars or light-shielding brackets, ensuring the structural integrity of the PPG optical path within the extremely limited space of only 2.6mm in ring thickness. The ECG electrode 30 is directly bonded to the transparent resin inner holder 10 via insert injection molding, eliminating the need for a secondary bonding process. After injection molding, the electrode surface precisely protrudes 0.1-0.2mm from the inner surface, ensuring reliable skin contact without subsequent machining. The temperature sensor is embedded in the inner surface through a shallow groove and filled with thermally conductive gel, achieving good thermal coupling with the skin. Simultaneously, the high insulation of the thermally conductive gel avoids electrical crosstalk between the sensor and the ECG electrode 30, allowing temperature measurement and ECG acquisition to work collaboratively without interference within the same curved surface. The PPG sensor 20's sub-plate is embedded in a groove on the outer surface and bonded to the high-transmittance area with optically transparent adhesive, eliminating air gaps in the optical path and avoiding the absorption and scattering of light signals by traditional potting compounds. The flexible circuit board is bonded to the outer surface of the transparent resin inner holder 10, making the transparent resin inner holder 10 the load-bearing structure of the entire module. Bending strain is borne by the transparent resin inner holder 10 rather than by the FPC alone. By spatially layering the sensors embedded in the transparent resin inner holder 10 with the devices mounted on the FPC (including accelerometers, Bluetooth SoCs, etc. mounted on the FPC), the transmission path of sensitive analog signals is shortened, reducing interference from digital / RF signals to analog signals. A sealant layer is filled between the transparent resin inner holder 10 and the FPC, placing the waterproof barrier inside the module. The high-transmittance area, electrode surface, and temperature sensor surface on the inner surface remain exposed during the sealing process. The above structures together form an integrated architecture with a transparent resin inner holder as a multifunctional three-dimensional reference surface, which allows heterogeneous sensors (including optical PPG sensors, electrical ECG electrodes, thermal temperature sensors, etc.) to be positioned on the curved inner wall without interfering with each other. Bending strain is shared by the inner holder instead of being borne solely by the FPC. Waterproofing and functional opening are transformed from external opposition to internal coexistence. This solves the coupling problem of heterogeneous sensor assembly, bending fatigue, signal crosstalk and waterproof sealing at the architectural level.

[0038] Example 2: Stack-up design of multilayer composite flexible circuit board This application provides a flexible circuit board for micro wearable devices. The flexible circuit board is bent into a ring shape and adapted to the internal space of micro curved wearable devices such as smart rings. The flexible circuit board includes a six-layer structure stacked sequentially, with a polyimide insulating layer (PI layer) between each layer.

[0039] From top to bottom, the six-layer structure is as follows: Analog signal layer L1 is used for mounting analog signal sensors. Analog signal layer L1 is made of electrolytic copper foil with a selective electroplating layer (Au / Ni / Ti) on its surface, and is used for mounting analog signal sensors such as the PPG sensor 20 and temperature sensors. The thickness of analog signal layer L1 is 18μm.

[0040] The first inner signal layer L2 is used for the PPG analog front-end signal lines and ECG differential signal lines. The first inner signal layer L2 is made of rolled copper foil with an ENIG (chemical nickel gold) surface treatment and a thickness of 18μm. Grounding protection rings are provided on both sides of the PPG analog front-end signal lines and ECG differential signal lines to reduce crosstalk between adjacent signal lines.

[0041] A complete ground plane layer L3 covers at least 90% of the board surface area. The complete ground plane layer L3 is made of rolled copper foil with a thickness of 35 μm. The complete ground plane layer L3 provides a low-impedance return path to isolate the analog signal layer L1 from the underlying power layer L4 and digital signal layer L5, reducing interlayer crosstalk. Preferably, the coverage of the complete ground plane layer L3 is ≥95% to ensure effective shielding.

[0042] Power layer L4 is used for routing power lines. Power layer L4 is made of rolled copper foil with a thickness of 18μm and a polyimide cover film. Power lines such as VBAT, VDD_3V3, and VDD_1V8 are routed on power layer L4. Below the LED driver circuit of the PPG sensor 20, power layer L4 has a partially cut-out structure that extends through the thickness of power layer L4. This cut-out structure is used to reduce parasitic capacitive coupling of the LED pulse drive current through power layer L4 to the sensitive signal lines below or above.

[0043] Digital signal layer L5 is used for routing digital signal lines. Digital signal layer L5 uses rolled copper foil with a thickness of 18μm and is used for routing I / O lines. 2 Digital signals such as C, SPI, and Bluetooth control lines.

[0044] The bottom device layer L6 is used for mounting radio frequency (RF) devices and digital devices. It uses electrolytic copper foil with an immersion gold finish and a thickness of 18μm, and is used to mount RF devices and digital devices such as accelerometers, Bluetooth SoCs, and power management chips.

[0045] The insulating layers between each layer are all polyimide (PI) films with a thickness of 25 μm. Electrical connections between adjacent metal layers are achieved through blind or buried vias. The thickness of each layer can be adjusted according to specific design requirements, but the overall thickness of the flexible circuit board is controlled within 0.3 mm to accommodate the narrow internal space of the smart ring.

[0046] In a preferred embodiment, the cutout structure of the power layer L4 is located directly below the LED driving circuit of the PPG sensor 20. Its shape is rectangular or circular, and its size is slightly larger than the projected area of ​​the LED driving circuit. This cutout structure reduces the electric field coupling of the LED pulse current through the power layer L4 plane to adjacent signal layers, further improving the anti-interference capability of the PPG analog front-end signal and the ECG differential signal. Alternatively, the cutout structure can also be a mesh cutout to maintain a certain continuity of the power layer L4 while reducing coupling.

[0047] A first polyimide insulating layer is provided between the analog signal layer L1 and the first inner signal layer L2. A second polyimide insulating layer is provided between the first inner signal layer L2 and the complete ground plane layer L3. A third polyimide insulating layer is provided between the complete ground plane layer L3 and the power layer L4. A fourth polyimide insulating layer is provided between the power layer L4 and the digital signal layer L5. A fifth polyimide insulating layer is provided between the digital signal layer L5 and the bottom device layer L6.

[0048] In a preferred embodiment of this application, the width of the grounding protection rings on both sides of the PPG analog front-end signal line and the ECG differential signal line in the first inner signal layer L2 is 0.1 mm, and the distance between the grounding protection rings and the signal lines is 0.1 mm. The grounding protection rings are electrically connected to the complete ground plane layer L3 through vias to form a coaxial cable-type shielding structure, further reducing crosstalk between signal lines.

[0049] In this embodiment, the overall stacked design of the six-layer flexible circuit board physically separates the analog signal layer L1 and the first inner signal layer L2 (analog signal area) from the power layer L4, digital signal layer L5 and the bottom device layer L6 (digital / RF signal area) through the vertical isolation of the complete ground plane layer L3, which significantly reduces electromagnetic interference between different types of signals.

[0050] In this embodiment, the six-layer FPC stack physically separates the analog signal layer L1, the first inner signal layer L2 (analog signal layer), the power layer L4, the digital signal layer L5, and the bottom device layer L6 (digital / RF signal layer) vertically through a complete ground plane layer L3. Combined with the grounding protection rings set on both sides of the signal lines in the first inner signal layer L2, the nA-level PPG photocurrent signal and the μV-level ECG differential signal achieve a shielding effect close to that of a rigid PCB on the flexible substrate. Crosstalk to the analog signal from Bluetooth RF (-20dBm@2.4GHz) and digital bus (several MHz harmonics) is effectively suppressed. The measured PPG signal-to-noise ratio is improved to over 45dB, the ECG common-mode rejection ratio reaches 100dB, and the temperature sensor reading fluctuation is controlled within ±0.1℃, solving the inherent problem of poor electromagnetic compatibility of micro FPCs in mixed signal environments. The power layer L4 has a partially hollowed-out structure below the LED driving circuit of the PPG sensor, which further reduces the parasitic coupling of large pulse currents through the power layer to adjacent signal lines, providing a physical basis for the above module architecture to achieve high-fidelity signal transmission.

[0051] Example 3: Interconnection method between flexible circuit board and curved sensor inner holder This application provides a method for interconnecting a flexible circuit board with a curved sensor insert.

[0052] First, a transparent resin inner holder 10 is provided, in which sensor contacts (e.g., conductive posts of ECG electrodes 30) are embedded by insert injection molding. The sensor contacts have conductive posts extending from the outer surface of the transparent resin inner holder 10. The conductive posts are made of TA2 pure titanium, with a diameter of 0.3 mm and a height of 0.5 mm.

[0053] Next, an anisotropic conductive film (ACF) is applied around the conductive pillars. The anisotropic conductive film used is a Hitachi HM-300 type ACF, with a thickness of 25 μm and a width of 2 mm. The ACF is applied by cutting it to a shape that matches the distribution area of ​​the conductive pillars and attaching it to the outer surface of the transparent resin inner holder 10 around the conductive pillars, ensuring the ACF covers the pillars. Further black silicone is dotted onto the black isolation wall of the optical isolation area to fill the tiny gaps between the light-emitting element and the photosensitive element, preventing total internal reflection crosstalk within the transparent resin inner holder 10.

[0054] Next, the elastic contacts on the flexible circuit board are aligned with the conductive posts. The flexible circuit board is provided with a first connection terminal, which in this embodiment uses elastic contacts, and the positions of the elastic contacts correspond one-to-one with the conductive posts. Alignment is performed using a CCD (Charge-Coupled Device) vision positioning system with a positioning accuracy of ±0.03mm, ensuring precise horizontal alignment of the elastic contacts and conductive posts.

[0055] Finally, the elastic contact and the conductive post are thermo-pressed together using an anisotropic conductive adhesive film, ensuring perpendicular conductivity between the elastic contact and the conductive post. The thermo-pressing temperature is 150-180℃, the pressure is 0.5-1.0MPa, and the time is 8-12 seconds.

[0056] After hot-pressing, the conductive particles in the anisotropic conductive film are compressed, forming a conductive path in the vertical direction, so that the conduction resistance between the elastic contact and the conductive post is less than 0.5Ω; in the horizontal direction, the conductive particles remain insulated from each other, and the insulation resistance between adjacent contacts is greater than 1GΩ.

[0057] After the anisotropic conductive adhesive film is thermo-pressed together, the flexible circuit board is fixed to the outer surface of the transparent resin inner holder 10 to achieve electrical and mechanical connection.

[0058] It should be noted that for the connection between the PPG sensor 20's daughterboard and the flexible circuit board, laser welding can be used instead of ACF hot pressing. Specifically, after embedding the daughterboard into the groove, laser welding is used to connect the pads on the daughterboard to the corresponding pads on the flexible circuit board. The laser power is 10W, and the welding time is 50ms. Laser welding is suitable for signal lines that need to withstand large currents or have extremely high connection impedance requirements, while ACF hot pressing is suitable for multi-pin, small-pitch array connections.

[0059] In this embodiment, an anisotropic conductive adhesive film (ACF) is used to thermopress the elastic contacts on the FPC to the sensor contact conductive posts embedded in the transparent resin inner holder 10, replacing the traditional soldering and reflow soldering process. Since the process temperature of ACF thermopressing (150-180℃) is much lower than the peak temperature of reflow soldering (240-260℃), the softening and warping effects of high temperatures on the polyimide substrate are avoided. Simultaneously, the cured ACF adhesive layer has flexible buffering properties, capable of absorbing the shear strain generated when a finger is bent, unlike brittle solder joints which experience stress concentration and cracking in the bending area. After 1000 finger bending cycles, the on-resistance change rate of the ACF connection point is less than 5%, while traditional solder joints exhibit fatigue cracking after approximately 200 bends, significantly improving the long-term reliability of the module in flexible curved surface scenarios.

[0060] Example 4: Waterproof Encapsulation Method for Miniature Curved Wearable Devices This application provides a waterproof encapsulation method for a miniature curved wearable device.

[0061] First, the electronic components are fixed to the outer surface of the transparent resin inner holder 10, which has inner and outer surfaces. The electronic components include a flexible circuit board and various electronic components (such as a Bluetooth SoC, power management chip, accelerometer, temperature sensor, etc.) mounted on the flexible circuit board. The flexible circuit board is electrically connected to the sensor (such as ECG electrode 30) embedded in the transparent resin inner holder 10 by ACF thermoforming (or laser welding). The daughter board of the PPG sensor 20 is embedded in the groove of the transparent resin inner holder 10 and bonded to the high-transmittance area with optically transparent adhesive.

[0062] Then, the transparent resin inner holder 10, along with the electronic components, is placed into the housing. The housing includes a lower housing and an upper housing, made of ABS or PC. The transparent resin inner holder 10 with the FPC components assembled is then placed into the corresponding cavity of the lower housing.

[0063] Before injection molding, silicone plugs are used to temporarily cover and protect the exposed optical window (i.e., the surface of the high-transmittance area), electrode surface, and charging interface on the inner surface of the transparent resin inner holder 10. The surface of the temperature sensor embedded in the shallow groove of the inner surface is also temporarily covered and protected with silicone plugs. The temperature sensor is flush with the inner surface via thermally conductive gel, and its surface needs to remain exposed during injection molding to ensure temperature measurement accuracy. The silicone plugs prevent sealant from contaminating its surface. The shape of the silicone plugs matches the shape of each functional surface, fitting tightly to the inner surface to prevent sealant from contacting or contaminating these functional surfaces during subsequent injection molding.

[0064] Then, using a low-pressure injection molding process, sealant is filled from the outer surface of the transparent resin inner holder 10 into the interior of the outer shell. The process parameters for low-pressure injection molding are: injection material is low-hardness polyurethane hot melt adhesive (Shore A 60), material temperature is 115-120℃, and injection pressure is 0.2-0.5MPa. The sealant is injected into the gaps between the transparent resin inner holder 10 and the outer shell, as well as the gaps between the transparent resin inner holder 10 and the flexible circuit board. During the injection molding process, the inner surface of the transparent resin inner holder 10 remains exposed due to the protective effect of the silicone plug. The silicone plug is removed after injection molding. The exposed high-transmittance area on the inner surface serves as an optical window for the transmission of PPG light signals, and the exposed electrode surface is used for contact with the skin to collect electrocardiogram signals.

[0065] After injection molding, the sealant cures to form a sealant layer, which encapsulates and seals the electronic components. The sealant layer fixes the flexible circuit board and the transparent resin inner holder 10 together, while filling the gaps between them to prevent moisture from seeping in from the outside.

[0066] Finally, the upper and lower housings are fastened together and sealed using ultrasonic welding. The ultrasonic welding parameters are: amplitude 65μm, pressure 0.25MPa, and welding time 0.6 seconds. After welding, the overall airtightness meets the IP68 standard.

[0067] To enhance sealing reliability, a second application of waterproof sealant (UV-cured) can be applied to the seam between the ECG electrode 30 and the housing, as well as around the magnetic charging port, to ensure no leakage during long-term immersion in water. Alternatively, laser welding can be used between the upper and lower housings instead of ultrasonic welding. The aforementioned magnetic charging port consists of a pair of annular magnets and two gold-plated pins. The gold-plated pins are passed through the corresponding pads on the FPC and fixed by reflow soldering; the annular magnets are fixed to the grooves on the side of the housing by a pressure ring or adhesive bonding. During low-pressure injection molding and housing sealing, the charging interface is temporarily protected by a silicone plug; the silicone plug is removed after injection molding is complete.

[0068] In this embodiment, the low-pressure injection molding process fills the sealant into the housing from the outer surface of the transparent resin inner insert 10, with an injection pressure of only 0.2-0.5 MPa, far lower than the conventional pressure (>10 MPa) of secondary injection molding, thus avoiding physical damage to the internal patch components caused by high-pressure injection molding. During the injection molding process, the high-transmittance area on the inner surface, the ECG electrode surface, and the charging interface are temporarily covered and protected by silicone plugs. After the injection molding is completed, the silicone plugs are removed, ensuring that these functional surfaces remain exposed and glue-free throughout the entire injection molding process and in the final product. This reverse sealing logic ensures that the PPG optical signal does not need to pass through any potting compound layer, with attenuation rate controlled within 10% and optical crosstalk <0.1%. There is no insulating adhesive layer between the ECG electrode surface and the skin, and the contact impedance is stable at 5-10kΩ. At the same time, the whole device passes the IP68 waterproof test (1.5 meters deep for 30 minutes), achieving simultaneous compliance with light attenuation, electrode impedance, and waterproof performance. This solves the inherent contradiction in traditional external dispensing or O-ring solutions where these three elements compete for limited outer surface area.

[0069] Example 5: Transparent resin inner tube double injection molding and ECG electrode insert molding This embodiment provides a specific manufacturing example for mass manufacturing transparent resin inner casing components for smart rings.

[0070] 1) Mold preparation: Design a double-shot injection mold. The first injection cavity is the transparent part of the entire inner tray (thickness 0.4mm), and the second injection cavity is a black optical isolation wall (width 0.3mm, depth 0.2mm). The mold also includes a pre-reserved slot for the ECG electrode insert.

[0071] 2) First injection: Heat medical-grade high-transmittance epoxy resin (refractive index 1.55, transmittance 92%@660nm) to 120℃, inject at a pressure of 80MPa, hold for 3 seconds to form a transparent matrix. Cool to 60℃.

[0072] 3) Insert placement: The robotic arm precisely places the pre-formed and cleaned TA2 pure titanium electrode contacts (crescent-shaped, 5mm in arc length, 1.5mm in width, 0.2mm in thickness, with conductive pillars welded on the back) into the electrode groove of the mold and fixes them by vacuum adsorption.

[0073] 4) Second injection: After mold closing, inject black epoxy resin (with 2wt% carbon black added) into the isolation wall area at an injection pressure of 60MPa and hold for 2 seconds. The black resin and the transparent matrix melt and bond at the interface, while firmly wrapping the electrode contacts, exposing only the electrode surface (protruding 0.15mm) and the back conductive post.

[0074] 5) Demolding and post-processing: Open the mold and remove the inner tray. Use 600-grit sandpaper to lightly sand the electrode surface to remove burrs. Then, ultrasonically clean it in deionized water for 5 minutes and dry it.

[0075] 6) Inspection: Under an optical microscope, check that the interface between the electrode and the resin is free of pores and cracks; the transmittance of the window area is ≥90% using a transmittance tester; the resistance between the two electrodes is >100MΩ using an insulation resistance tester (to ensure there is no short circuit).

[0076] The inner support component manufactured in this embodiment has a first-shot injection molding yield of 98.5%, an electrode pull-out force >45N, and no bubbles or excess adhesive in the optical window. Compared to the traditional secondary bonding method (yield of approximately 85%), this embodiment significantly improves production efficiency and consistency.

[0077] Example 6: ACF thermoforming connection between FPC and transparent resin inner tray and IP68 waterproof encapsulation of the whole machine This embodiment provides another specific manufacturing example for electrically connecting the FPC component to the inner tray manufactured in Embodiment 5 and completing the overall encapsulation.

[0078] 1) FPC fabrication: The FPC (dimensions: 45mm long, 5mm wide, 0.3mm thick) is fabricated according to a six-layer rigid-flex PCB stack. Gold finger pads (0.1μm gold plating thickness) are provided at corresponding positions for docking with the conductive posts of the transparent resin inner holder 10. Components such as accelerometers, Bluetooth SoCs, and battery protection ICs have been mounted on the FPC.

[0079] 2) ACF pre-application: An anisotropic conductive adhesive film (ACF, model Hitachi HM-300, thickness 25μm) with a width of 2mm is applied around the conductive pillars on the back of the transparent resin inner holder 10.

[0080] 3) Hot-press connection: Align the elastic contacts of the FPC with the conductive posts (using CCD vision positioning, accuracy ±0.03mm), heat the hot press head to 170℃, apply pressure of 0.8MPa, and hold for 10 seconds. After ACF curing, the conductive particles are compressed, with vertical conduction resistance <0.5Ω and horizontal insulation resistance >1GΩ.

[0081] 4) PPG sub-board welding: The small sub-board (2.5mm×2.5mm) pre-mounted with LEDs and PDs is embedded in the groove on the back of the transparent resin inner holder 10. The sub-board pads are connected to the corresponding pads of the FPC by laser welding (laser power 10W, welding time 50ms).

[0082] 5) Low-pressure injection molding: Place the connected inner tray-FPC assembly into the lower housing of the ring (ABS material), and after mold closing, perform low-pressure injection molding of polyurethane hot melt adhesive (material temperature 115℃, pressure 0.3MPa) to fill the internal gaps. During injection molding, use silicone plugs to protect the PPG optical window, electrode surface, and magnetic charging interface.

[0083] 6) Shell sealing: The upper shell (PC material) is fastened together and sealed with ultrasonic welding (amplitude 65μm, pressure 0.25MPa, welding time 0.6 seconds).

[0084] 7) IP68 test: Immerse the finished ring (weighing only 3.6g) in a 1.5-meter deep water tank for 30 minutes, remove it and wipe it dry. Test the internal circuit and find no water ingress (leakage rate <0.01sccm using a pressure leak detector); after immersion in fluorescent liquid, check under ultraviolet light and find no fluorescent penetration.

[0085] 8) Finished product testing: Test the continuity resistance between the ECG electrode contacts and the FPC to be <1Ω, the signal-to-noise ratio of the PPG sensor to be >45dB, and the contact resistance of the magnetic charging interface to be <50mΩ.

[0086] 9) Functional verification: When connected to the mobile APP, the ECG differential signal waveform can be clearly acquired after the ECG electrode contacts are in contact with the skin (signal-to-noise ratio > 30dB); the PPG sensor can measure blood oxygen saturation with a static finger and the deviation from the standard finger clip pulse oximeter is ≤ 1.5%; when the magnetic charging interface is connected to a 5V power supply, the charging current is stable at 100mA.

[0087] The 100 prototypes manufactured in this embodiment achieved a 100% pass rate in the IP68 waterproof test. The ACF connection reliability showed a conduction resistance change rate of less than 5% after 1000 finger bending cycles, and the first-time assembly yield of the entire machine exceeded 96%. This process allows for stable mass production, with unit processing costs controlled within a reasonable range.

[0088] Example 7: Fabrication and Signal Integrity Verification of a Six-Layer FPC This embodiment provides the specific manufacturing process and performance verification data for a six-layer FPC stack.

[0089] FPCs are fabricated using the following process: Using polyimide as the substrate, the following layers are stacked sequentially: bottom device layer L6, fifth polyimide insulating layer, digital signal layer L5, fourth polyimide insulating layer, power layer L4 (including a cutout structure), third polyimide insulating layer, complete ground plane layer L3, second polyimide insulating layer, first inner signal layer L2 (including a grounding protection ring), first polyimide insulating layer, and analog signal layer L1. Interlayer interconnection is achieved through laser drilling and electroplating to fill vias.

[0090] After FPC manufacturing is completed, signal integrity testing is performed: When the PPG analog front-end output terminal is continuously operating at maximum transmit power (-20dBm@2.4GHz) of the Bluetooth SoC, its peak-to-peak output noise is measured to be <50nA and its equivalent signal-to-noise ratio is >45dB. When a 1mV, 50Hz common-mode interference signal is applied to the differential input terminal of the ECG, and the LED driving pulse (200mA, 100Hz) is working simultaneously, the common-mode rejection ratio is measured to be ≥100dB. Temperature sensor (I) 2 When the digital bus is under full load transmission (C interface, clock frequency 1MHz), the temperature reading fluctuation range is ≤±0.1℃, which is better than the existing solution (±0.2℃ or more).

[0091] The data above demonstrates that the complete ground plane layer L3 and the grounding protection ring in the first inner signal layer L2 of the six-layer stack together constitute an effective electromagnetic shielding structure, ensuring sufficient physical isolation between signals of different natures and significantly improving the signal integrity of the micro FPC in mixed signal environments. This stack design provides the hardware foundation for achieving high-performance signal transmission in the aforementioned module architecture.

[0092] Example 8: Complete Process Flow Application Case of Multi-Sensor Integrated Module This embodiment provides a complete process flow application example from transparent resin inner mold to finished product inspection, for mass production of multi-sensor integrated modules for smart rings.

[0093] 1) Transparent resin inner holder double injection molding and sensor pre-embedding Mold preparation: Design a two-shot injection mold. The first injection cavity is the transparent part of the entire inner tray (0.4mm thick), and the second injection cavity is a black optical isolation wall (0.3mm wide, 0.2mm deep). The mold also includes pre-reserved slots for ECG electrode inserts, PPG sensor recesses, and shallow slots for temperature sensors.

[0094] First injection: Heat medical-grade high-transmittance epoxy resin (refractive index 1.55, transmittance 92%@660nm) to 120℃, inject at a pressure of 80MPa, hold for 3 seconds to form a transparent matrix, and then cool to 60℃.

[0095] ECG electrode insert placement: The robotic arm precisely places the pre-formed and cleaned TA2 pure titanium electrode contacts (crescent-shaped, 5mm in arc length, 1.5mm in width, 0.2mm in thickness, with conductive posts welded on the back) into the electrode groove of the mold and fixes them by vacuum adsorption.

[0096] Second injection: After mold closing, inject black epoxy resin (with 2wt% carbon black added) into the isolation wall area at an injection pressure of 60MPa and hold for 2 seconds. The black resin and transparent matrix fuse at the interface, firmly encapsulating the electrode contacts, exposing only the electrode surface (protruding 0.15mm) and the back conductive post. After demolding, lightly sand the electrode surface with 600-grit sandpaper to remove burrs, ultrasonically clean for 5 minutes, and then dry.

[0097] PPG sensor groove pre-reservation: A groove matching the sub-board (size 2.5mm×2.5mm) is formed on the outer surface side. The bottom of the groove is a transparent resin layer with high light transmittance and no black obstruction.

[0098] 2) Shallow Groove Pre-installation and Embedding of Temperature Sensor: A shallow groove is made on the inner surface of the transparent resin inner holder 10 corresponding to the position of the temperature sensor. The depth of the groove matches the thickness of the temperature sensor (in this example, the groove depth is 0.4 mm). A TMP117 ultra-thin temperature sensor (0.4 mm thick) is embedded in this groove. The signal lead of the temperature sensor is a metal pin pre-embedded in the inner holder, extending from the inside of the inner holder to the outer surface for subsequent electrical connection with the FPC. After the temperature sensor is embedded, its surface is coated with thermally conductive gel (thermal conductivity > 3 W / (m·K)), making the surface of the temperature sensor flush with the inner surface through the thermally conductive gel. The thermally conductive gel has both high thermal conductivity and high insulation, ensuring a good heat conduction path between the temperature sensor and the skin for accurate temperature measurement, while maintaining electrical isolation from the adjacent ECG electrode 30. It should be noted that the TMP117 ultra-thin temperature sensor is only an example; other ultra-thin temperature sensors with similar dimensions and performance can be used in other embodiments.

[0099] 3) Fabrication of six-layer flexible circuit boards The FPC (dimensions: 45mm long, 5mm wide, 0.3mm total thickness) is fabricated according to the six-layer stacked structure described in Example 2. Gold finger pads (0.1μm gold plating thickness) are provided at corresponding positions for docking with the conductive pillars of the inner holder. Components such as accelerometers, Bluetooth SoCs, and power management chips have been mounted on the FPC. Among them, the power layer L4 has a partially cut-out structure in the area below the LED driving circuit of the PPG sensor 20, and the cut-out structure extends through the thickness direction of the power layer L4.

[0100] 4) PPG sensor rigid sub-plate embedding and optical coupling The sub-board, pre-mounted with light-emitting elements (LEDs) and photosensitive elements (PDs), is embedded in the groove. The sub-board is bonded to the high-transmittance area using optically transparent adhesive with a matching refractive index, ensuring a gap-free optical path. After the optical path is aligned, black silicone is further applied to the black isolation wall of the optical isolation area to fill the tiny gaps between the light-emitting elements and the photosensitive elements, preventing total internal reflection crosstalk within the transparent resin inner holder 10.

[0101] 5) ACF hot pressing connection and laser welding An anisotropic conductive film (ACF, Hitachi HM-300, 25μm thick, 2mm wide) is applied around the conductive posts on the back of the inner tray. The flexible contacts of the FPC are aligned with the conductive posts (using CCD vision positioning, accuracy ±0.03mm), and the hot press head is heated to 170℃, pressure is applied at 0.8MPa, and held for 10 seconds. After ACF curing, the vertical conduction resistance is <0.5Ω, and the horizontal insulation resistance is >1GΩ.

[0102] For the PPG sensor 20's daughterboard, laser welding is used to connect the daughterboard pads to the corresponding FPC pads (laser power 10W, welding time 50ms) to ensure low impedance and high reliability of signal transmission.

[0103] Temperature sensor lead connection: The metal pins of the temperature sensor pre-embedded on the outer surface of the transparent resin inner holder 10 are electrically connected to the corresponding pads on the FPC by laser welding (laser power 10W, welding time 50ms), ensuring that the temperature signal is reliably transmitted to the signal processing circuit on the FPC.

[0104] 6) Integration of magnetic charging port The magnetic charging port consists of a pair of ring magnets and two gold-plated pins. The gold-plated pins are passed through the corresponding pads on the FPC and fixed by reflow soldering; the ring magnets are fixed in the grooves on the side of the housing by a clamping ring.

[0105] 7) Low-pressure injection molding internal filling The connected inner tray-FPC assembly is placed into the lower housing of the ring (ABS material). After mold closing, a low-pressure injection molding process is used to fill the internal gaps. The injection material is low-hardness polyurethane hot melt adhesive (Shore A 60), with a material temperature of 115℃ and an injection pressure of 0.3MPa. During injection molding, silicone plugs are used to temporarily cover and protect the PPG optical window (high-transmittance surface), electrode surface, temperature sensor surface, and magnetic charging port to ensure that these functional surfaces are not covered by adhesive.

[0106] 8) Housing seal The upper housing (PC material) is snapped together and sealed using ultrasonic welding (amplitude 65μm, pressure 0.25MPa, welding time 0.6 seconds). A second layer of UV-cured waterproof sealant is applied to the seams between the ECG electrode 30 and the housing, as well as around the magnetic charging port, to ensure no leakage even after long-term immersion in water.

[0107] 9) Finished product inspection Optical window sealing test: Immerse the finished product in fluorescent liquid, take it out and check it under ultraviolet light to confirm that there is no fluorescent penetration and no glue overflow in the optical window.

[0108] Electrical performance testing: The conduction resistance between the ECG electrode contacts and the FPC is <1Ω; the signal-to-noise ratio of the PPG sensor is >45dB when the Bluetooth SoC is continuously operating at maximum transmit power (-20dBm@2.4GHz); the contact resistance of the magnetic charging interface is <50mΩ.

[0109] Temperature sensor function test: Wear the finished ring on your finger and wait for the temperature reading to stabilize. Then compare it with a standard thermometer. The temperature measurement deviation should be ≤ ±0.2℃.

[0110] Functional verification: When connected to a mobile app, the ECG differential signal waveform can be clearly acquired after the ECG electrode comes into contact with the skin (signal-to-noise ratio > 30dB); the blood oxygen saturation measured by the PPG sensor deviates from that of a standard finger-clip pulse oximeter by ≤ 1.5%; when the magnetic charging interface is connected to a 5V power supply, the charging current is stable at 100mA.

[0111] The prototype manufactured using the above complete process has a 100% pass rate in the IP68 waterproof test (1.5 meters deep for 30 minutes), the ACF connection has a conductivity resistance change rate of less than 5% after 1000 finger bending cycles, and the overall assembly yield is over 96%.

[0112] The mounting structure of embedding the temperature sensor in a shallow groove and filling it with thermally conductive gel as described in this embodiment is also applicable to the temperature sensor in the multi-sensor integrated module described in Embodiment 1; the integration process of the magnetic charging port described in this embodiment is also applicable to the protection steps of the charging interface in the waterproof encapsulation method described in Embodiment 4. The technical features in each embodiment can be combined with each other where there is no contradiction.

[0113] The miniaturized wearable monitoring device (smart ring) of this application includes a Bluetooth SoC or microcontroller, which stores a computer program. When the computer program is executed, it performs the following functions: driving the light-emitting element of the PPG sensor to emit light signals; acquiring the photocurrent signal output by the photosensitive element and performing signal processing to calculate blood oxygen saturation and heart rate; acquiring the differential signal output by the ECG electrode to generate an ECG waveform; acquiring the signal output by the temperature sensor to convert it into a temperature value; acquiring the signal output by the accelerometer to identify the motion state; and interacting with external terminal devices via the Bluetooth communication protocol.

[0114] Those skilled in the art will understand that all or part of the above-described sensor signal processing and Bluetooth communication functions can be implemented by a computer program instructing related hardware. This computer program can be stored in a non-volatile computer-readable storage medium. The non-volatile computer-readable storage medium may include read-only memory, flash memory, magnetic storage, optical storage, etc. The volatile memory may include random access memory. The processor may be a general-purpose processor, microcontroller, digital signal processor, or programmable logic device.

[0115] It should be noted that the signal data processed by the above computer program (including PPG photoplethysmography signals, electrocardiogram signals, temperature signals, acceleration signals, etc.) are all physiological signals generated when the user wears the device. The collection, processing and use of the relevant data comply with the relevant regulations and standards in the field of medical devices and wearable devices.

[0116] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered to be within the scope of this specification.

[0117] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A multi-sensor integrated module for a miniaturized wearable monitoring device, characterized in that, include: A transparent resin inner tray has opposing inner and outer surfaces, wherein the inner surface is a curved surface that comes into contact with the human body; A flexible circuit board is attached to the outer surface of the transparent resin inner tray; At least some of the sensors are embedded in the transparent resin inner holder or attached to the flexible circuit board; The sensor includes a PPG sensor, which has a light-emitting element and a photosensitive element; The transparent resin inner holder includes an integrally formed high-transmittance area and an optical isolation area. The high-transmittance area corresponds to the light path direction of the light-emitting element and the photosensitive element, and the optical isolation area is located between the light-emitting element and the photosensitive element. A sealing structure is provided between the outer surface of the transparent resin inner holder and the flexible circuit board, and the inner surface remains exposed at the functional contact surface corresponding to the high light transmittance area and the sensor.

2. The multi-sensor integrated module for a miniaturized wearable monitoring device according to claim 1, characterized in that, The transparent resin inner holder is formed by a double injection molding process. The first injection is a high-transmittance resin to form the high-transmittance area, and the second injection is a light-shielding resin to form the optical isolation area. The optical isolation area is a three-dimensional structure that extends along the optical path between the light-emitting element and the photosensitive element.

3. The multi-sensor integrated module for a miniaturized wearable monitoring device according to claim 1, characterized in that, The sensor also includes an electrocardiogram (ECG) electrode, which is integrally molded with the transparent resin inner tube by insert injection molding. The electrode surface of the ECG electrode protrudes from the inner surface, and a conductive post is provided on the back of the ECG electrode. The conductive post extends from the outer surface and is electrically connected to the flexible circuit board.

4. The multi-sensor integrated module for a miniaturized wearable monitoring device according to claim 1, characterized in that, The light-emitting element and the photosensitive element of the PPG sensor are mounted on a sub-board. The sub-board can be a rigid sub-board or a flexible sub-board. The outer surface of the transparent resin inner holder is provided with a groove, and the sub-board is embedded in the groove. The sub-board and the high light transmittance area are bonded together with an optically transparent adhesive with a matching refractive index.

5. A method for interconnecting a flexible circuit board with a curved sensor inner holder, characterized in that, Includes the following steps: A transparent resin inner holder is provided, wherein a sensor contact is embedded in the transparent resin inner holder, and the sensor contact has a conductive post extending from the outer surface of the transparent resin inner holder. An anisotropic conductive adhesive film is applied around the conductive pillar; Align the first connection terminal on the flexible circuit board with the conductive post; The first connecting terminal is electrically connected to the conductive post through the anisotropic conductive film.

6. A waterproof encapsulation method for a miniature curved wearable device, characterized in that, Includes the following steps: The electronic components are fixed to the outer surface of a transparent resin insert that has an inner surface and an outer surface. The transparent resin inner tube, together with the electronic components, is placed into the housing; The transparent resin inner tray is filled with sealant from the outer surface into the interior of the outer shell using an injection molding process. The inner surface of the transparent resin inner holder remains exposed during the injection molding process to serve as an optical window, sensor functional contact surface, or skin contact interface. After the sealant cures, it forms a protective seal around the electronic components.

7. The waterproof encapsulation method for a micro-curved wearable device according to claim 6, characterized in that, Before injection molding, silicone plugs are used to temporarily cover and protect the exposed optical window, electrode surface, and charging interface on the inner surface of the transparent resin inner holder. After injection molding, the silicone plugs are removed.

8. The waterproof encapsulation method for a micro-curved wearable device according to claim 6, characterized in that, The pressure of the sealant is 0.2-0.5 MPa.

9. A flexible circuit board for a micro wearable device, characterized in that, The flexible circuit board is bent into a ring shape and includes, in sequence, at least one analog signal layer, a complete ground plane layer, a power layer, at least one digital signal layer; and an insulating layer disposed between each layer.

10. The flexible circuit board for a micro wearable device according to claim 9, characterized in that, The power layer has a partially hollowed-out structure in the area below the LED driving circuit of the PPG sensor, and the hollowed-out structure extends through the thickness direction of the power layer.

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