Preparation method and device of stretchable conductive interface

Abstract

The invention provides a preparation method and device of a stretchable conductive interface. The method comprises the following steps: pouring a stretchable polymer solution or a precursor mixture of silica gel into a gradient polytetrafluoroethylene mold on a horizontal table, and standing to form a stretchable polymer film with a gradient thickness; covering the surface of the stretchable polymer film with an electrode patterning mask, and depositing a conductive circuit on the surface of the stretchable polymer film through vacuum thermal evaporation or magnetron sputtering to form a microcrack gold conductive layer covering the surface of the stretchable polymer film, so as to complete electrode patterning and obtain a gradient gradient flexible electrode; and after one end, with the large thickness, of the stretchable polymer film of the gradient gradient flexible electrode is connected with a flexible printed circuit board FPCB, the surface of the gradient gradient flexible electrode is covered with a polymer insulating layer film with the modulus matched with that of the substrate for packaging protection, and preparation of the stretchable conductive interface is completed. Stress can be effectively dispersed, and the mechanical stability and durability of a connector are improved.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of flexible electrodes, and in particular to a method and device for preparing a stretchable conductive interface. Background Art

[0002] Long-term, dynamic monitoring of surface electrophysiological signals (such as electromyography, electroencephalography, and electrocardiography) requires excellent stability and reliability of sensing electrodes. Traditional rigid electrodes, due to mechanical modulus mismatch, have difficulty forming conformal contact with the skin. This makes interfacial slip during movement prone to signal distortion and increased motion artifacts. Stretchable electrodes, which seamlessly conform to the human body surface and significantly improve signal acquisition accuracy, have become a key development direction in wearable electrophysiological monitoring.

[0003] However, existing flexible monitoring systems face significant challenges in dynamic deformation scenarios. Human movement causes significant bending and stretching of monitoring devices, which consist not only of soft, stretchable electrodes at the front end but also rigid circuitry for data collection and transmission. While flexible, stretchable electrodes maintain stable performance under bending and stretching, stress concentration at the soft-hard interface can degrade key performance. This problem is particularly evident at the interface between the stretchable electrode and the FPCB. The electrode substrate is typically composed of a low-modulus polymer elastomer with a modulus ranging from tens to hundreds of kPa, while the FPCB is composed of a high-modulus, rigid polymer with a modulus ranging from hundreds of MPa to GPa. These two exhibit significant differences in mechanical properties. Dynamic deformation can lead to non-uniform stress distribution at the interface, ① inducing stress concentration, resulting in conductive material fracture, sudden changes in circuit impedance, and even interruption of signal transmission; ② interfacial delamination or crack propagation under cyclic deformation, shortening device lifespan, reducing mechanical durability, and ultimately leading to electrical failure; ③ interfacial microslip introduces noise, reducing the signal-to-noise ratio (SNR) and exacerbating motion artifacts.

[0004] Common solutions in existing technologies include a press-type interface based on anisotropic conductive adhesive (ACF, 3M). This adhesive bonds the FPCB to the flexible thin-film electrode and secures it with a packaging film. Pressing the interface allows for vertical conduction and horizontal conduction. This solution is simple to operate, but the interface cannot withstand the stress concentration caused by stretching, which can damage the ACF's adhesion and make it unsuitable for applications where long-term, repeated stretching and deformation are expected. Nature, 2023 614(7948), 456-462]. Another example is a soft-hard interface based on a self-adhesive polymer film [Patent No.: CN202111510097, A method for connecting a soft-hard interface between a flexible conductive material and a hard conductive material]. To alleviate the stress concentration problem caused by the material modulus difference between the soft stretchable electrode and the FPCB, this method deposits a layer of styrene-ethylene-butylene-styrene block copolymer (SEBS) on the non-metallic pins of the FPCB. The self-adhesiveness of SEBS is then used to press-bond the SEBS stretchable circuit, thereby enhancing the mechanical connection strength at the interface. However, this method is only applicable to polymer films with self-adhesive properties and no solution has been found for non-self-adhesive stretchable polymer films.

[0005] Among the existing technologies mentioned above, press-type interfaces based on ACFs can cause instability during stretching, while rigid-soft interfaces based on self-adhesive polymer films are limited in their applicability to a variety of stretchable substrates. Therefore, developing a flexible and rigid interface solution that is widely applicable to stretchable circuits has become a pressing challenge in the fabrication of stretchable circuits. Summary of the Invention

[0006] In view of this, embodiments of the present invention provide a method and apparatus for preparing a stretchable conductive interface to at least partially solve the above-mentioned problems.

[0007] According to a first aspect of an embodiment of the present invention, a method for preparing a stretchable conductive interface is provided, comprising: S1, pouring a stretchable polymer solution or a precursor mixture of silica gel into a gradient polytetrafluoroethylene mold placed on a horizontal platform and letting it stand to form a stretchable polymer film with a gradient thickness; S2, covering the surface of the stretchable polymer film with an electrode patterning mask, and depositing a conductive circuit on the surface of the stretchable polymer film by vacuum thermal evaporation or magnetron sputtering to form a micro-cracked gold conductive layer covering the surface of the stretchable polymer film, thereby completing electrode patterning and obtaining a gradient flexible electrode; S3, after connecting the end with a larger thickness of the stretchable polymer film of the gradient flexible electrode to a flexible printed circuit board (FPCB), covering the surface of the gradient flexible electrode with a polymer insulating layer film having a modulus matching that of the substrate for encapsulation and protection, thereby completing the preparation of the stretchable conductive interface.

[0008] Optionally, the thickness of the stretchable polymer film gradually changes from 100-500 μm at the end connected to the flexible printed circuit board (FPCB) to 50-100 μm at the electrode functional area, and the transition slope is controlled within 5°.

[0009] Optionally, the sheet resistance of the micro-cracked gold conductive layer is less than 1Ω / sq, and the resistance change rate is less than 10% when stretched by 30%.

[0010] Optionally, the polymer insulating layer film has a thickness of 20 μm.

[0011] Optionally, the flexible printed circuit board (FPCB) and the stretchable polymer film are connected via anisotropic conductive adhesive.

[0012] According to a second aspect of an embodiment of the present invention, a device for preparing a stretchable conductive interface is provided, comprising: a gradient substrate preparation module, for pouring a stretchable polymer solution or a precursor mixture of silica gel into a gradient-graded polytetrafluoroethylene mold placed on a horizontal platform and letting it stand to form a stretchable polymer film with a gradient thickness; an electrode patterning module, for covering the surface of the stretchable polymer film with an electrode patterning mask, and depositing a conductive circuit on the surface of the stretchable polymer film by vacuum thermal evaporation or magnetron sputtering to form a micro-cracked gold conductive layer covering the surface of the stretchable polymer film, thereby completing electrode patterning and obtaining a gradient-graded flexible electrode; a connection and packaging module, for connecting the end with the larger thickness of the stretchable polymer film of the gradient-graded flexible electrode to a flexible printed circuit board (FPCB), and then covering the surface of the gradient-graded flexible electrode with a polymer insulating layer film whose modulus matches the substrate for packaging and protection to complete the preparation of the stretchable conductive interface.

[0013] Compared with the prior art, the beneficial effects of the solution of the present invention are: (1) Compared to conductive adhesives with relatively low tensile strength, the thickness gradient design of the present invention can achieve more effective stress dispersion at the interface, reducing large deformations caused by stress concentration. When subjected to frequent and large stretching, the interface is less likely to crack or microcrack, thereby enhancing the long-term reliability of the electrode-FPCB interface.

[0014] (2) Compared with casting SEBS film at the FPCB interface, the present invention completes electrode patterning first and then connects the electrode to the FPCB. This can avoid the SEBS film from accidentally covering the wire at the interface and affecting the electrical path, thereby ensuring the stability and consistency of the electrical connection.

[0015] (3) Compared with directly casting on the FPCB surface and then connecting it to the stretchable circuit, the present invention has more flexible and repeatable control over the thickness distribution and uniformity during the electrode forming process, and is not limited by the self-adhesive properties of the stretchable substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the embodiments of the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0017] Figure 1 The present invention is a flowchart of the steps of a method for preparing a stretchable conductive interface.

[0018] Figure 2 Schematic diagram of the gradient flexible electrode of the present invention.

[0019] Figure 3 This is a specific operational flow chart of the gradient-varying flexible electrode preparation process of the present invention. DETAILED DESCRIPTION

[0020] In order to have a clearer understanding of the technical features, purposes and effects of the embodiments of the present invention, specific implementation methods of the embodiments of the present invention are now described with reference to the accompanying drawings.

[0021] In this document, “exemplary” means “serving as an example, instance or illustration”, and any illustration or implementation described as “illustrative” in this document should not be interpreted as a more preferred or more advantageous technical solution.

[0022] To simplify the drawings, only the parts relevant to the present invention are schematically shown in each figure, and they do not represent the actual structure of the product. In addition, to simplify the drawings and facilitate understanding, in some figures, only one or more components with the same structure or function are schematically depicted or labeled.

[0023] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments in the embodiments of the present invention should fall within the scope of protection of the embodiments of the present invention.

[0024] The flexible, stretchable electrode with a thickness gradient proposed in this paper aims to mitigate stress concentration by introducing a gradual thickness transition zone near the interface, preventing deformation from concentrating at the interface, thereby effectively improving the mechanical stability and durability of the soft-hard interface. This invention can significantly reduce the risk of damage and delamination at the interface during stretching and exercise, meeting the combined requirements of thin, comfortable electrodes and stable signal acquisition in long-term electrophysiological monitoring.

[0025] The specific implementation of the embodiment of the present invention is further described below with reference to the accompanying drawings of the embodiment of the present invention.

[0026] See also Figure 1 The present invention provides a method for preparing a stretchable conductive interface, which mainly comprises: S1. Pour a stretchable polymer solution or a precursor mixture of silica gel into a gradient polytetrafluoroethylene mold placed on a horizontal platform and let it stand to form a stretchable polymer film with a gradient thickness; S2. Covering the surface of the stretchable polymer film with an electrode patterning mask, and depositing a conductive circuit on the surface of the stretchable polymer film by vacuum thermal evaporation or magnetron sputtering to form a micro-cracked gold conductive layer covering the surface of the stretchable polymer film, thereby completing electrode patterning and obtaining a gradient flexible electrode; S3. After connecting the end with the larger thickness of the stretchable polymer film of the gradient-graded flexible electrode to the flexible printed circuit board FPCB, a polymer insulating layer film with a modulus matching the substrate is covered on the surface of the gradient-graded flexible electrode for encapsulation and protection to complete the preparation of the stretchable conductive interface.

[0027] Optionally, the thickness of the stretchable polymer film gradually changes from 100-500 μm at the end connected to the flexible printed circuit board (FPCB) to 50-100 μm at the electrode functional area, and the transition slope is controlled within 5°.

[0028] Optionally, the sheet resistance of the micro-cracked gold conductive layer is less than 1Ω / sq, and the resistance change rate is less than 10% when stretched by 30%.

[0029] Optionally, the polymer insulating layer film has a thickness of 20 μm.

[0030] Optionally, the flexible printed circuit board (FPCB) and the stretchable polymer film are connected via anisotropic conductive adhesive.

[0031] In summary, the present invention realizes a flexible stretchable circuit design by constructing a stretchable film with a gradual thickness, with the thick end of the film connected to the FPCB and the thin end of the film being patterned. The present invention uses a common stretchable polymer as a substrate to construct a stretchable film with a gradual thickness, and implements electrode patterning on its surface by vacuum thermal evaporation or metal magnetron sputtering to prepare a stretchable electrode with a gradual thickness, so as to form a stable soft-hard transition area at the interface between the electrode and the FPCB, thereby effectively alleviating the stress concentration problem. By preparing a thickness gradient on a stretchable substrate and coordinating the metal patterning process, the electrode of the present invention can achieve dynamic and stable monitoring of electrophysiological signals while maintaining low impedance and good flexibility. This not only improves the accuracy and reliability of electrophysiological data acquisition, but also provides a new design idea for the application of wearable devices in medical monitoring and human-computer interaction.

[0032] Specifically, the solution of the present invention is further described according to the following examples: This invention addresses the interfacial stress concentration problem between the stretchable electrode and the FPCB in stretchable electronic devices caused by the large difference in the modulus of the soft and hard materials. By proposing a universal soft-hard interface transition scheme based on structural design, this solution effectively increases the stress-bearing cross-sectional area by constructing a buffer structure with a gradually varying thickness at the interface, achieving a gradient stress distribution, thereby significantly reducing local strain and improving connection stability. Compared to traditional approaches that enhance interface stability by selecting a high-modulus substrate, this invention innovatively adopts a pure structural optimization strategy. Without changing the intrinsic properties of the electrode material (maintaining the stretchability of a Young's modulus <1 MPa), the interfacial stress concentration problem is solved solely through geometric design. This solution has excellent material universality and is compatible with various stretchable materials such as polyurethane and elastic silicone. It also maintains stable interfacial connection performance for more than 1000 stretching cycles. This innovative design not only solves the technical problem of soft-hard interface mismatch but, more importantly, preserves the original stretchability of the electrode material, providing new ideas for improving the reliability of stretchable electronic devices.

[0033] The thickness gradient soft-hard interface of the present invention, i.e., a stretchable conductive interface, mainly consists of three parts: Gradient transition zone: The thickness gradually changes from 100-500μm at the FPCB connection end to 50-100μm in the electrode functional area, and the transition slope is controlled within 5°; Metal patterned layer: A micro-cracked gold conductive layer (square resistance <1Ω / sq, resistance change rate <10% when stretched 30%) is prepared on the surface of the gradient transition zone by vacuum thermal evaporation or magnetron sputtering; Encapsulation protection layer: A polymer insulating film covering the conductive layer (20 μm thick, modulus matching the substrate).

[0034] (1) Gradient substrate preparation: Customize a gradient polytetrafluoroethylene mold and place it on a horizontal platform. Pour a stretchable polymer solution or a silicone precursor mixture into it, and then place it in a fume hood and let it stand for 24 hours to allow the solvent to evaporate or the silicone to solidify, forming a stretchable polymer film with a thickness gradient, such as Figure 2 Shown is a schematic diagram of a gradient-graded flexible electrode, where the thick side of the film at the interface is three times the thickness of the thin side of the film at the electrode.

[0035] (2) Electrode patterning: The obtained stretchable film with gradient thickness is covered with an electrode patterning mask, and a conductive circuit is deposited on the surface of the film by vacuum thermal evaporation or magnetron sputtering to complete the electrode patterning.

[0036] (3) Interface connection: The thick end of the film is designed as the interface connected to the FPCB, so that the transition area can effectively disperse the stress concentration caused by the combination of soft and hard materials, thereby enhancing the mechanical stability of the interface. Figure 3 The figure shows a specific operational flow chart of the gradient-graded flexible electrode preparation process, which includes solvent volatilization film formation, magnetron sputtering electrode patterning, and connection with the FPCB interface, and finally prepares a gradient-graded flexible electrode.

[0037] It should be understood that, with the Young's modulus remaining constant, increasing thickness effectively increases the cross-sectional area under load, and the stress it can withstand also increases. Therefore, under the same stress, the thicker areas will deform less. Therefore, this transition area can effectively disperse the stress concentration caused by the combination of soft and hard materials.

[0038] Example 1: A 100μm thick polyurethane film electrode with uniform thickness is connected to the FPCB via an ACF and then packaged and fixed. The stretchable film itself can stretch ~150%, and the interface can stretch ~50%.

[0039] Example 2: A 100μm thick polyurethane film electrode with uniform thickness is connected to a polyurethane-coated FPCB by pressing and then secured by encapsulation. The stretchable film itself has a stretchability of ~150%, and the interface has a stretchability of ~10%.

[0040] Example 3: The front thickness is 50 μm, the rear thickness is 200 μm, and the gradient is 1.5*10 -3 The polyurethane film electrode is connected to the FPCB via an ACF and then encapsulated and fixed. The stretchability of the interface is comparable to that of the film itself.

[0041] On one hand, this invention achieves a gradual modulus change at the soft-hard interface through a continuously varying thickness elastomeric substrate. By designing a layered thickness gradient at the interface between the stretchable electrode and the FPCB, this effectively disperses stress, reduces cracking or fracture at the junction of the soft and hard materials, and significantly improves the mechanical stability and durability of the interface. On the other hand, to balance mechanical buffering with electrode stretchability, this invention employs a thickness ratio (FPCB end:electrode end) of 3:1 to 10:1.

[0042] It should be understood that if the thickness ratio is too large, the flexibility and stretchability of the electrode will be significantly reduced; if the ratio is too small, stress concentration cannot be effectively alleviated. Therefore, a thickness gradient range of 3 to 10 times can achieve a balance between interface stability and electrode stretchability.

[0043] Alternatives and other uses of the present invention include: Alternative process for gradient formation: 3D printing direct writing technology replaces the mold deposition method, and the thickness gradient is achieved by program-controlled nozzle speed.

[0044] Conductive layer alternatives: The present invention is not limited to stretchable electrodes of microcracked gold, but also includes soft stretchable conductive circuits based on liquid metal or other precious metals and carbon materials.

[0045] Interface strengthening alternative design: The present invention is not limited to ACF bonding materials, but is also applicable to other conductive bonding materials or bonding structure designs.

[0046] The present invention is not only applicable to the soft and hard interfaces of flexible stretchable electrodes, but can also be promoted to the soft and hard interfaces of other flexible electronics.

[0047] In addition, the solution of the present invention has been tested and used, and stable electromyography and electrocardiogram monitoring results have been obtained.

[0048] An embodiment of the present invention further provides a device for preparing a stretchable conductive interface, comprising: A gradient substrate preparation module is used to pour a stretchable polymer solution or a precursor mixture of silica gel into a gradient polytetrafluoroethylene mold placed on a water platform and let it stand to form a stretchable polymer film with a gradient thickness; An electrode patterning module is used to cover the surface of the stretchable polymer film with an electrode patterning mask and deposit a conductive circuit on the surface of the stretchable polymer film by vacuum thermal evaporation or magnetron sputtering to form a micro-cracked gold conductive layer covering the surface of the stretchable polymer film, thereby completing electrode patterning and obtaining a gradient flexible electrode; The connection and packaging module is used to connect the end with the larger thickness of the stretchable polymer film of the gradient-graded flexible electrode to the flexible printed circuit board (FPCB), and then encapsulate and protect the surface of the gradient-graded flexible electrode with a polymer insulating layer film whose modulus matches the substrate to complete the preparation of the stretchable conductive interface.

[0049] It should be understood that the device of this embodiment is used to implement the corresponding methods in the aforementioned multiple method embodiments and has the beneficial effects of the corresponding method embodiments, which will not be described in detail here.

[0050] Thus far, specific embodiments of the present invention have been described. Other embodiments are within the scope of the appended claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve the desired results. Furthermore, the processes depicted in the accompanying drawings do not necessarily require the specific order shown or sequential order to achieve the desired results. In certain embodiments, multitasking and parallel processing may be advantageous.

[0051] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0052] Finally, it should be noted that the above implementation methods are only used to illustrate the embodiments of the present invention, and are not limitations on the embodiments of the present invention. Ordinary technicians in the relevant technical field can make various changes and modifications without departing from the spirit and scope of the embodiments of the present invention. Therefore, all equivalent technical solutions also fall within the scope of the embodiments of the present invention, and the scope of patent protection of the embodiments of the present invention should be defined by the claims.

Claims

1. A method for preparing a stretchable conductive interface, characterized in that: include: S1. Pour a stretchable polymer solution or a precursor mixture of silica gel into a gradient polytetrafluoroethylene mold placed on a horizontal platform and let it stand to form a stretchable polymer film with a gradient thickness; S2. Covering the surface of the stretchable polymer film with an electrode patterning mask, and depositing a conductive circuit on the surface of the stretchable polymer film by vacuum thermal evaporation or magnetron sputtering to form a micro-cracked gold conductive layer covering the surface of the stretchable polymer film, thereby completing electrode patterning and obtaining a gradient flexible electrode; S3. After connecting the end with the larger thickness of the stretchable polymer film of the gradient-graded flexible electrode to the flexible printed circuit board FPCB, a polymer insulating layer film with a modulus matching the substrate is covered on the surface of the gradient-graded flexible electrode for encapsulation and protection to complete the preparation of the stretchable conductive interface.

2. The method according to claim 1, characterized in that The thickness of the stretchable polymer film gradually changes from 100-500 μm at the end connected to the flexible printed circuit board (FPCB) to 50-100 μm at the electrode functional area, and the transition slope is controlled within 5°.

3. The method according to claim 1, characterized in that The sheet resistance of the micro-cracked gold conductive layer is less than 1Ω / sq, and the resistance change rate is less than 10% when stretched by 30%.

4. The method according to claim 1, wherein The thickness of the polymer insulating layer film is 20 μm.

5. The method according to claim 1, wherein The flexible printed circuit board (FPCB) and the stretchable polymer film are connected via anisotropic conductive adhesive.

6. A device for preparing a stretchable conductive interface, characterized in that: include: A gradient substrate preparation module is used to pour a stretchable polymer solution or a precursor mixture of silica gel into a gradient polytetrafluoroethylene mold placed on a water platform and let it stand to form a stretchable polymer film with a gradient thickness; An electrode patterning module is used to cover the surface of the stretchable polymer film with an electrode patterning mask and deposit a conductive circuit on the surface of the stretchable polymer film by vacuum thermal evaporation or magnetron sputtering to form a micro-cracked gold conductive layer covering the surface of the stretchable polymer film, thereby completing electrode patterning and obtaining a gradient flexible electrode; The connection and packaging module is used to connect the end with the larger thickness of the stretchable polymer film of the gradient-graded flexible electrode to the flexible printed circuit board (FPCB), and then encapsulate and protect the surface of the gradient-graded flexible electrode with a polymer insulating layer film whose modulus matches the substrate to complete the preparation of the stretchable conductive interface.

Images