Method and apparatus for making a stretchable conductive interface

Abstract

The application provides a preparation method and device of a stretchable conductive interface. The method comprises the following steps: pouring a precursor mixture of a stretchable polymer solution or silica gel into a gradiently changed polytetrafluoroethylene mold placed on a water platform to form a stretchable polymer film with a thickness gradient; covering an electrode patterning mask on the surface of the stretchable polymer film, and depositing a conductive circuit on the surface of the stretchable polymer film by vacuum thermal evaporation or magnetron sputtering to form a micro-crack gold conductive layer covering the surface of the stretchable polymer film, so as to complete electrode patterning and obtain a gradiently changed flexible electrode; connecting one end of the stretchable polymer film with a large thickness of the gradiently changed flexible electrode to a flexible printed circuit board (FPCB), covering a polymer insulating layer film with a modulus matched with the substrate on the surface of the gradiently changed flexible electrode to perform encapsulation and protection, and completing the preparation of the stretchable conductive interface. The application can effectively disperse stress and improve the mechanical stability and durability of the interface.

Description

TECHNICAL FIELD

[0001] The embodiment of the application relates to the technical field of flexible electrodes, in particular to a preparation method and device of a stretchable conductive interface. BACKGROUND

[0002] Long-term dynamic monitoring of surface electrophysiological signals (such as electromyography, electroencephalography, and electrocardiography signals) requires that the sensing electrode has excellent stability and reliability. Traditional rigid electrodes are difficult to form conformal contact with the skin due to the mismatch of the mechanical modulus, and are prone to interface slip during movement, resulting in signal distortion and increased motion artifacts. Stretchable electrodes can achieve seamless fitting with the human body surface, significantly improving signal acquisition accuracy, and have become an important development direction for wearable electrophysiological monitoring.

[0003] However, existing flexible monitoring systems face serious challenges in dynamic deformation scenarios. With human movement, the monitoring device will undergo large-scale bending or stretching, and the monitoring device not only includes the front-end soft and stretchable electrode, but also includes the collection or transmission of the back-end hard circuit. Although the flexible and stretchable electrode can maintain stable performance under bending and stretching, the stress concentration phenomenon at the soft-hard interface will cause key performance degradation. This problem is particularly evident at the connection interface between the stretchable electrode and the FPCB. The electrode substrate is generally composed of a low-modulus polymer elastomer with a modulus of tens to hundreds of KPa, and the FPCB is composed of a high-modulus hard polymer with a modulus of hundreds of MPa to GPa. The mechanical properties of the two are obviously different, and dynamic deformation will cause non-uniform distribution of stress in the interface region, ① inducing stress concentration, leading to fracture of conductive materials or sudden change of circuit impedance, and even interruption of signal transmission; ② interface delamination or crack propagation under cyclic deformation, shortening the service life of the device, reducing mechanical durability, and further causing electrical performance failure; ③ interface micro-slip introduces noise, reduces the signal-to-noise ratio (SNR), and intensifies motion artifacts.

[0004] A commonly used solution in the prior art, such as a press-type interface based on anisotropic conductive adhesive (ACF, 3M Corporation), bonds the FPCB and the flexible film electrode with anisotropic conductive adhesive, and fixes them with a packaging film. The vertical direction is made conductive and the horizontal direction is made non-conductive by pressing. This solution is simple to operate, but the interface is difficult to withstand stress concentration during stretching, causing damage to the ACF adhesion, and is not suitable for long-term repeated stretching deformation application scenarios NatureFor example, a soft and hard interface based on a self-adhesive polymer film [Patent No.: CN202111510097, a method for connecting a soft and hard interface between a flexible conductive material and a hard conductive material] is used to alleviate the stress concentration problem between the soft and stretchable electrode and the FPCB due to the difference in material modulus. A layer of styrene-ethylene-butylene-styrene block copolymer (SEBS) is deposited at the non-metallic pin of the FPCB, and then the self-adhesive property of SEBS is used to press and bond with the SEBS stretchable circuit, thereby enhancing the mechanical connection strength at the interface. However, this method is only suitable for polymer films with self-adhesive properties, and there is no solution for stretchable polymer films that are not self-adhesive.

[0005] In the above prior art, the press-type interface based on ACF is unstable in stretching; the soft and hard interface based on a self-adhesive polymer film is limited in the type of stretchable substrate. Therefore, how to obtain a soft and hard interface connection scheme widely applicable to stretchable circuits has become a problem to be solved in the preparation of stretchable circuits. SUMMARY

[0006] Therefore, the embodiments of the present application provide a preparation method and device of a stretchable conductive interface to at least partially solve the above problems.

[0007] According to a first aspect of the embodiments of the present application, a preparation method of a stretchable conductive interface is provided, comprising: S1, pouring a precursor mixture of a stretchable polymer solution or silica gel into a gradiently changing polytetrafluoroethylene mold placed on a water platform to stand, to form a stretchable polymer film with a gradually changing thickness; S2, covering an electrode patterning mask on the surface of the stretchable polymer film, and depositing a conductive circuit on the surface of the stretchable polymer film by vacuum thermal evaporation or magnetron sputtering to form a micro-crack gold conductive layer covering the surface of the stretchable polymer film, thereby completing electrode patterning and obtaining a gradiently changing flexible electrode; S3, connecting one end of the stretchable polymer film of the gradiently changing flexible electrode with a large thickness to a flexible printed circuit board (FPCB), and covering a polymer insulating layer film with a modulus matching the substrate on the surface of the gradiently changing flexible electrode to encapsulate and protect, 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 connection end 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-crack gold conductive layer is less than 1 Ω / sq, and the resistance change rate is less than 10% when stretched by 30%.

[0010] Optionally, the thickness of the polymer insulation layer film is 20 microns.

[0011] Optionally, the flexible printed circuit board FPCB is connected to the stretchable polymer film through anisotropic conductive adhesive.

[0012] According to the second aspect of the embodiment of the present application, a preparation device of a stretchable conductive interface is provided, comprising: a gradient substrate preparation module for pouring a precursor mixture of a stretchable polymer solution or silica gel into a gradient polytetrafluoroethylene mold placed on a water platform to stand, forming a stretchable polymer film with a thickness gradient; an electrode patterning module for covering an electrode patterning mask on the surface of the stretchable polymer film, and depositing a conductive circuit on the surface of the stretchable polymer film through vacuum thermal evaporation or magnetron sputtering to form a micro-crack gold conductive layer covering the surface of the stretchable polymer film, thereby completing electrode patterning and obtaining a gradient flexible electrode; a connection and packaging module for connecting the end with a large thickness of the stretchable polymer film of the gradient flexible electrode to a flexible printed circuit board FPCB, and then covering a polymer insulation layer film with a modulus matching the substrate on the surface of the gradient flexible electrode for packaging and protection, thereby completing the preparation of the stretchable conductive interface.

[0013] Compared with the prior art, the beneficial effects of the present application are:

[0014] (1) Compared with the stretch-resistant conductive adhesive, the thickness gradient design of the present application can achieve more effective stress dispersion at the interface, reducing large deformation caused by stress concentration. In the face of frequent large stretching, the interface is less likely to appear cracks or micro-cracks, thereby enhancing the long-term reliability of the electrode and FPCB interface.

[0015] (2) Compared with pouring SEBS film at the FPCB interface, the present application completes electrode patterning first, and then connects the electrode to the FPCB, which can avoid the phenomenon that the SEBS film covers the wires at the interface, affecting the electrical path, etc., thereby ensuring the stability and consistency of the electrical connection.

[0016] (3) Compared with directly pouring on the surface of the FPCB and connecting to the stretchable circuit, the present application is more flexible and repeatable in controlling the thickness distribution and uniformity during electrode formation, and is not limited by the self-adhesive properties of the stretchable substrate. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments or prior art description. Obviously, the drawings in the following description only represent some of the embodiments of the present application, and those skilled in the art can also obtain other drawings from these drawings.

[0018] Figure 1 A flow chart of the steps of a preparation method of a stretchable conductive interface of the present application.

[0019] Figure 2 A schematic diagram of a gradient flexible electrode of the present application.

[0020] Figure 3 A specific operation flow chart of a preparation process of a gradient flexible electrode of the present application. DETAILED DESCRIPTION

[0021] In order to have a clearer understanding of the technical features, objectives and effects of the embodiments of the present application, the specific implementation manners of the embodiments of the present application will be described with reference to the drawings.

[0022] In this document, "exemplarily" means "serving as an example, instance or illustration", and any drawings, embodiments described as "exemplary" in this document should not be interpreted as a more preferred or more advantageous technical solution.

[0023] In order to make the drawings simple, only the parts related to the present application are schematically shown in the drawings, which do not represent the actual structure of the product. In addition, in order to make the drawings simple and easy to understand, in some drawings, only one or more of the parts with the same structure or function are schematically shown, or only one or more of them are indicated.

[0024] In order for those skilled in the art to better understand the technical solutions in the embodiments of the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the embodiments of the present application, all other embodiments obtained by those skilled in the art should belong to the scope of protection of the embodiments of the present application.

[0025] The flexible stretchable electrode with thickness gradient proposed in the present application aims to introduce a thickness gradient transition zone near the interface to slow down stress concentration, so that deformation is no longer concentrated at the interface connection, thereby effectively improving the mechanical stability and durability of the soft and hard interface. The present application can significantly reduce the damage and delamination risk at the interface in motion stretching, and meet the comprehensive needs of light, comfortable and stable signal acquisition of the electrode in long-term electrophysiological monitoring.

[0026] The embodiments of the present application are further illustrated below with reference to the accompanying drawings of the embodiments of the present application.

[0027] Referring to Figure 1 The preparation method of the stretchable conductive interface mainly includes:

[0028] S1, pour the precursor mixture of the stretchable polymer solution or silica gel into the gradiently changed polytetrafluoroethylene mold placed on the water platform to stand, forming a stretchable polymer film with gradually changed thickness;

[0029] S2, cover the electrode patterning mask on the surface of the stretchable polymer film, and deposit the conductive circuit on the surface of the stretchable polymer film by vacuum thermal evaporation or magnetron sputtering to form a micro-crack gold conductive layer covering the surface of the stretchable polymer film, thereby completing the electrode patterning and obtaining a gradiently changed flexible electrode;

[0030] S3, connect the end of the stretchable polymer film with large thickness of the gradiently changed flexible electrode to the flexible printed circuit board FPCB, cover the polymer insulating layer film with modulus matching the substrate on the surface of the gradiently changed flexible electrode to encapsulate and protect, and complete the preparation of the stretchable conductive interface.

[0031] 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°.

[0032] Optionally, the sheet resistance of the micro-crack gold conductive layer is less than 1 Ω / sq, and the resistance change rate is less than 10% when stretched by 30%.

[0033] Optionally, the thickness of the polymer insulating layer film is 20 μm.

[0034] Optionally, the flexible printed circuit board FPCB is connected to the stretchable polymer film through anisotropic conductive adhesive.

[0035] In summary, the present application realizes the flexible stretchable circuit design by constructing the stretchable film with gradually changing thickness, connecting the FPCB at one end of the film with thick thickness, and performing circuit patterning at the other end of the film with thin thickness. The present application constructs the stretchable film with gradually changing thickness based on common stretchable polymers, realizes the electrode patterning on the surface by vacuum thermal evaporation or metal magnetron sputtering, and prepares the stretchable electrode with gradually changing thickness, so as to form a stable soft-hard transition area at the interface between the electrode and the FPCB, thereby effectively relieving the stress concentration problem. By preparing the thickness gradient on the stretchable substrate and cooperating with the metal patterning process, the electrode of the present application can realize the dynamic stable monitoring of the electrophysiological signal while maintaining low impedance and good flexibility. This not only can improve the accuracy and reliability of the electrophysiological data acquisition, but also provides a new design idea for the application of wearable devices in the fields of medical monitoring and human-computer interaction.

[0036] Specifically, the scheme of the present application is further described according to the following examples:

[0037] The present application proposes a general soft-hard interface transition scheme based on structural design, aiming at the interface stress concentration problem between the stretchable electrode and the FPCB in the stretchable electronic device due to the too large modulus difference between the soft and hard materials. The scheme constructs a thickness gradually changing buffer structure in the interface area, effectively increases the stress cross-sectional area, realizes the gradient distribution of the stress, thereby significantly reduces the local strain and improves the connection stability. Compared with the traditional scheme which selects a high modulus substrate to enhance the interface stability, the present application creatively adopts a pure structural optimization strategy, completely without changing the intrinsic properties of the electrode material (maintaining the stretchable characteristic with Young's modulus <1MPa), and only through geometric design, the interface stress concentration problem is solved. The scheme has excellent material universality, can be compatible with various stretchable materials such as polyurethane and elastic silica gel, and can still maintain stable interface connection performance in more than 1000 stretching cycles. This innovative design not only solves the technical problem of soft-hard interface mismatch, but more importantly, it retains the original stretchable characteristics of the electrode material, providing a new idea for the reliability improvement of stretchable electronic devices.

[0038] The thickness gradually changing soft-hard interface, i.e., the stretchable conductive interface of the present application mainly consists of three parts:

[0039] Gradient transition area: the thickness gradually changes from 100-500μm at the FPCB connection end to 50-100μm at the electrode functional area, and the transition slope is controlled within 5°;

[0040] Metal patterning layer: a micro-crack gold conductive layer (sheet resistance <1Ω / sq, resistance change rate <10% when stretched by 30%) is prepared on the surface of the gradient transition area by vacuum thermal evaporation or magnetron sputtering;

[0041] Encapsulation protective layer: polymer insulating layer film (thickness 20 pm, modulus matching substrate) covering the conductive layer.

[0042] (1) Gradient substrate preparation:

[0043] Customized gradient PTFE mold was placed on a water platform. A precursor mixture of stretchable polymer solution or silicone was poured into it, and then it was placed in a fume hood for 24 hours to allow the solvent to evaporate or the silicone to solidify, forming a stretchable polymer film with a thickness gradient, as shown in Figure 2 The gradient flexible electrode schematic diagram is shown, in which the thick side of the film at the interface is three times the thickness of the thin side of the film at the electrode.

[0044] (2) Electrode patterning:

[0045] An electrode patterning mask was overlaid on the obtained stretchable film with a thickness gradient, and a conductive circuit was deposited on the film surface using vacuum thermal evaporation or magnetron sputtering, thereby completing the electrode patterning.

[0046] (3) Interface connection:

[0047] The thick end of the film was designed to be connected to the interface of the FPCB, so that the transition area effectively dispersed the stress concentration caused by the combination of soft and hard materials, thereby enhancing the mechanical stability at the interface, as shown in Figure 3 The gradient flexible electrode preparation process flowchart is shown, which includes solvent evaporation film formation, magnetron sputtering electrode patterning, and connection with FPCB interface in turn, and finally a gradient flexible electrode is prepared.

[0048] It should be understood that under the condition of constant Young's modulus, the thickness increases, the effective stress cross-sectional area increases, and the stress that can be borne also increases, so under the same stress, the thick place will deform less. Therefore, the transition area can effectively disperse the stress concentration caused by the combination of soft and hard materials.

[0049] Example 1: A 100 pm thick polyurethane film electrode with uniform thickness was connected to the FPCB through ACF after packaging and fixing. The stretchable film itself has a stretchability of ~150%, and the interface has a stretchability of ~50%.

[0050] Example 2: A 100 pm thick polyurethane film electrode with uniform thickness was connected to the FPCB through pressing, and the FPCB had a polyurethane surface. After packaging and fixing, the stretchable film itself had a stretchability of ~150%, and the interface had a stretchability of ~10%.

[0051] Example 3: The front end thickness was 50 pm, the back end thickness was 200 pm, and the gradient gradient was 1.5*10 -3The polyurethane film electrode is connected with the FPCB through the ACF and is fixed through packaging.

[0052] In one aspect, the present application realizes modulus gradient of soft and hard interfaces through the elastic body substrate with continuous thickness variation, and different levels of thickness gradient are designed at the interface between the stretchable electrode and the FPCB, so that stress can be effectively dispersed, and crack or fracture phenomenon at the combination part of the soft and hard materials can be reduced, and mechanical stability and durability at the interface can be significantly improved. In another aspect, the present application takes into account mechanical buffering and stretchable performance of the electrode, and the thickness ratio (FPCB end: electrode end) is 3:1 to 10:1.

[0053] It should be understood that if the thickness ratio is too large, the flexibility and stretchable performance of the electrode will be obviously reduced, and if the ratio is too small, stress concentration cannot be effectively relieved. Therefore, the thickness gradient interval of 3-10 times can balance between the interface stability and the stretchable performance of the electrode.

[0054] Alternative solutions and other uses of the present application include:

[0055] Gradient forming alternative process: 3D printing direct writing technology instead of mold deposition method, thickness gradient is realized by program control of nozzle speed.

[0056] Conductive layer alternative solution: the present application is not limited to the stretchable electrode of micro-cracked gold, and includes soft and stretchable conductive lines based on liquid metal or other noble metals and carbon materials.

[0057] Interface strengthening alternative design: the present application is not limited to ACF bonding materials, and is also applicable to other conductive bonding materials or bonding structure design.

[0058] The present application is not only applicable to the soft and hard interface of the flexible and stretchable electrode, but also can be popularized to the soft and hard interface of other flexible electronics.

[0059] In addition, the present application has been tested and used, and stable electromyography and electrocardiogram monitoring results have been obtained.

[0060] The present application also provides a preparation device of the stretchable conductive interface, comprising:

[0061] The gradient substrate preparation module is used for pouring a stretchable polymer solution or a precursor mixture of silica gel into a gradient polytetrafluoroethylene mold placed on a water platform to form a stretchable polymer film with a thickness gradient.

[0062] An electrode patterning module is used to cover an electrode patterning mask on the surface of the stretchable polymer film, and to deposit a conductive circuit on the surface of the stretchable polymer film by vacuum thermal evaporation or magnetron sputtering, so as to form a gold conductive layer covering the micro-cracks on the surface of the stretchable polymer film, thereby completing electrode patterning and obtaining a gradient flexible electrode.

[0063] A connection and packaging module is used to connect one end of the stretchable polymer film of the gradient flexible electrode with a large thickness to a flexible printed circuit board (FPCB), and then to cover the surface of the gradient flexible electrode with a polymer insulating layer film with a modulus matched with the substrate for packaging and protection, so as to complete the preparation of a stretchable conductive interface.

[0064] It should be understood that the device of the embodiment is used to implement the corresponding method in the foregoing plurality of method embodiments, and has the beneficial effects of the corresponding method embodiments, which will not be described here.

[0065] So far, specific embodiments of the present application 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 desirable results. In addition, the processes depicted in the figures do not necessarily require the particular order shown, or sequential order, to achieve the desired results. In some implementations, multitasking and parallel processing can be advantageous.

[0066] It should be understood that although the present specification is described in terms of various embodiments, not every embodiment contains only one independent technical solution, and the description of the specification is only for the sake of clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be combined appropriately to form other embodiments that those skilled in the art can understand.

[0067] Finally, it should be noted that: the above implementation manners are only used to illustrate the embodiments of the present application, and not to limit the embodiments of the present application. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the embodiments of the present application. Therefore, all equivalent technical solutions also belong to the scope of the embodiments of the present application, and the patent protection scope of the embodiments of the present application should be defined by the claims.

Claims

1. A method of making a stretchable conductive interface, the method comprising: The application relates to a stretchable conductive interface preparation method. S1, a precursor mixture of a stretchable polymer solution or silica gel is poured into a gradiently changed polytetrafluoroethylene mold placed on a water platform to form a stretchable polymer film with a thickness gradient; S2, an electrode patterning mask is covered on the surface of the stretchable polymer film, and a conductive circuit is deposited on the surface of the stretchable polymer film through vacuum thermal evaporation or magnetron sputtering to form a micro-crack gold conductive layer covering the surface of the stretchable polymer film, so that electrode patterning is completed, and a gradiently changed flexible electrode is obtained; S3, one end of the stretchable polymer film with a large thickness of the gradiently changed flexible electrode is connected with a flexible printed circuit board (FPCB), a polymer insulating layer film with a modulus matched with a substrate is covered on the surface of the gradiently changed flexible electrode to perform packaging protection, and the preparation of the stretchable conductive interface is completed.

2. The method of claim 1, wherein, The thickness of the stretchable polymer film gradually changes from 100-500 mu m at the connection end of the flexible printed circuit board (FPCB) to 50-100 mu m at the electrode functional area, and the transition slope is controlled within 5 degrees.

3. The method of claim 1, wherein, The sheet resistance of the micro-crack gold conductive layer is less than 1 omega / sq, and the resistance change rate is less than 10% when stretched by 30%.

4. The method of claim 1, wherein, The thickness of the polymer insulating layer film is 20 mu m.

5. The method of claim 1, wherein, The flexible printed circuit board (FPCB) is connected with the stretchable polymer film through anisotropic conductive adhesive.

6. An apparatus for preparing a stretchable conductive interface, characterized by, The application relates to a stretchable conductive interface preparation method. A gradient substrate preparation module is used for pouring a precursor mixture of a stretchable polymer solution or silica gel into a gradiently changed polytetrafluoroethylene mold placed on a water platform to form a stretchable polymer film with a thickness gradient; An electrode patterning module is used for covering an electrode patterning mask on the surface of the stretchable polymer film, and a conductive circuit is deposited on the surface of the stretchable polymer film through vacuum thermal evaporation or magnetron sputtering to form a micro-crack gold conductive layer covering the surface of the stretchable polymer film, so that electrode patterning is completed, and a gradiently changed flexible electrode is obtained; A connection and packaging module is used for connecting one end of a stretchable polymer film with a large thickness of the gradiently changed flexible electrode with a flexible printed circuit board (FPCB), covering a polymer insulating layer film with a modulus matched with a substrate on the surface of the gradiently changed flexible electrode to perform packaging protection, and completing the preparation of the stretchable conductive interface.

Images