Preparation method of silk-screen printing flexible array pressure sensor

Abstract

The invention discloses a preparation method of a silk-screen printing flexible array pressure sensor, and relates to the technical field of flexible electronic sensor manufacturing, and the method comprises the steps: employing a printable insulating material to prepare an upper substrate layer and a lower substrate layer; printing and curing on the upper surface of the lower substrate layer to form an electrode layer, and forming an electrode wire layer on the lower surface; printing the planar pressure-sensitive layer on the lower surface of the upper substrate layer, overprinting the raised pressure-sensitive layer on the planar pressure-sensitive layer at least once, and curing to integrally mold the planar pressure-sensitive layer and the raised pressure-sensitive layer; printing a bonding layer on the upper surface of the lower substrate layer; the upper substrate layer and the lower substrate layer are aligned and bonded through the bonding layer, so that the functional layers are fixed into a whole; and finally, printing a conducting layer and a packaging layer on the upper surface of the upper substrate layer in sequence. The convex microstructure is directly constructed on the surface of the pressure-sensitive layer by adopting a secondary overprinting process, so that the sensitivity and the consistency of the sensor are improved; the method can be used for preparing a prong type sensor or a sandwich type sensor, an integrated flexible structure is realized, and the advantages of low cost, high efficiency and suitability for large-scale production of silk-screen printing are kept.

Description

Technical Field

[0001] This invention relates to the field of flexible electronic sensor manufacturing technology, and more specifically to a method for preparing a screen-printed flexible array pressure sensor. Background Technology

[0002] Flexible array pressure sensors, as key devices capable of converting pressure signals into electrical signals, have been widely used in various fields such as intelligent robot tactile sensing, medical and health monitoring, human-machine interfaces, wearable devices, and industrial automation control due to their flexibility (bendable and stretchable) and ability to detect spatial pressure distribution. With the continuous expansion and deepening of these applications, the market is placing higher demands on sensor performance (such as sensitivity, response speed, and stability), production costs, and large-scale manufacturing efficiency.

[0003] Among various fabrication processes, screen printing technology has become one of the mainstream technologies for the large-scale fabrication of flexible electronic devices, especially arrayed sensors, due to its relatively simple process flow, low equipment investment cost, high production efficiency, ease of large-area and mass production, and high material utilization. Typical flexible array pressure sensors usually adopt a stacked structure, and their core sensing mechanism relies on the change in contact resistance between the electrode layer and the pressure-sensitive functional layer as pressure changes.

[0004] However, the surface characteristics of the pressure-sensitive functional layer, especially its surface roughness, microstructure, and micro-morphology, are among the core factors determining the final performance of the sensor. An ideal surface morphology can produce a more significant and controllable change in contact area with the electrode layer under pressure, thereby outputting a stronger and more linear resistance change signal, directly improving the sensor's sensitivity, detection limit, and dynamic response performance.

[0005] Currently, the fabrication of flexible array pressure sensors based on screen printing technology mainly faces the following technical bottlenecks: The uncontrollable challenge of surface roughness and microstructure: Traditional screen printing processes have very limited ability to control the surface roughness and fine microstructure of the pressure-sensitive material film formed in a single printing step. Surface morphology is highly dependent on the complex interaction of ink rheological properties (such as viscosity and thixotropy), printing parameters (such as squeegee pressure, speed, and angle), and screen parameters (such as mesh count, wire diameter, and aperture shape). This multi-parameter coupling results in a narrow process window, cumbersome debugging processes, and strong reliance on experience, making it difficult to stably and repeatedly produce pressure-sensitive layers with specific and consistent surface roughness and microstructure across different batches, or even within the same batch. This directly leads to large dispersion in sensor performance, making it difficult to guarantee yield rates and hindering its widespread adoption in high-reliability applications.

[0006] The contradiction between performance and cost / efficiency: To address the aforementioned surface control issues, existing technologies employ supplementary or alternative processes beyond screen printing. For example, photolithography is used to pattern microstructures on the pressure-sensitive layer, or laser etching / processing, precision molding (casting), and 3D printing are used to construct specific surface morphologies. While these methods may offer advantages in microstructure forming precision, they generally suffer from inherent drawbacks such as complex processes, expensive equipment, long production cycles, high material costs, or difficulty in large-scale continuous production. They often contradict the core advantages of screen printing—low cost, high efficiency, and large-scale production—and fail to meet the market demand for high-volume, low-cost, high-performance sensors in consumer electronics, smart wearables, and other fields.

[0007] Therefore, how to provide a method for fabricating flexible array pressure sensors that can effectively regulate the surface microstructure of the pressure-sensitive layer, improve sensor sensitivity and consistency, and maintain the advantages of screen printing technology in terms of low cost, high efficiency, and suitability for large-scale production is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0008] In view of this, the present invention provides a method for fabricating a flexible array pressure sensor by screen printing, aiming to solve the above-mentioned technical problems.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A method for fabricating a flexible array pressure sensor using screen printing includes the following steps: Step 1) A flexible thin film substrate is prepared using a printable insulating material. The flexible thin film substrate includes an upper substrate layer and a lower substrate layer. An electrode layer is formed by curing printable conductive ink on the upper surface of the lower substrate layer, and an electrode wire layer is formed by curing on the lower surface of the lower substrate layer. Step 2): A planar pressure-sensitive layer is printed on the lower surface of the upper substrate layer using a printable pressure-sensitive material, and then a raised pressure-sensitive layer is overprinted on the planar pressure-sensitive layer, and then cured and integrally formed; a printable adhesive is printed on the upper surface of the lower substrate layer using a screen printing method to form an adhesive layer. Step 3), then the lower substrate layer formed in step 2) and the upper substrate layer formed are bonded and fixed together by the adhesive, so that the lower substrate layer and the electrode layer and electrode wire layer thereon, the upper substrate layer and the planar pressure-sensitive layer and the raised pressure-sensitive layer thereon are all fixed together as a whole; Step 4) Using a printable insulating material, a conductive layer is prepared on the upper surface of the prepared substrate layer by screen printing.

[0010] Through the above technical solution, this invention discloses a method for fabricating a flexible array pressure sensor using screen printing. It abandons the traditional method of manufacturing microstructures using complex and costly processes such as photolithography, molding, or chemical etching. By optimizing the screen printing process itself—specifically, directly overprinting a raised pressure-sensitive layer onto a planar pressure-sensitive layer—a microstructure with a specific roughness and morphology can be formed on the surface of the pressure-sensitive material. When under pressure, this raised structure causes a dramatic change in the contact separation area between itself and the electrode layer, resulting in a more significant and controllable change in resistance. This effectively solves the problem that the surface of the pressure-sensitive layer prepared by screen printing is usually relatively smooth and has limited sensitivity, thus stably improving the sensor's pressure detection lower limit, linearity, and resolution. The upper and lower substrates and their functional layers are precisely bonded and fixed by a printed adhesive layer, forming a stable, integrated flexible structure. This structure is not only thin, flexible, and stretchable, but also has fixed relative positions for each functional layer, effectively preventing interlayer misalignment and ensuring the independence and stability of the function of each array sensing point.

[0011] Preferably, the above-described method for fabricating a screen-printed flexible array pressure sensor further includes an encapsulation layer, which is fabricated on the upper surface of a substrate layer using a printable insulating material. Adding an encapsulation layer formed by printable insulating material to the outermost layer provides the sensor with crucial waterproof, moisture-proof, oxidation-proof, and physical protective barriers; this is particularly suitable for the complex operating environments that flexible sensors may face, extending the sensor's lifespan and maintaining the long-term stability of its core pressure-sensitive performance.

[0012] Preferably, in the above-described method for fabricating a flexible array pressure sensor using screen printing, the upper and lower surfaces of the lower substrate layer are connected by vias for positioning, with the vias located at one end of an electrode pin. By creating positioning vias in the lower substrate layer and filling them with conductive ink, electrical connection between the same fork-tooth electrode and the upper and lower surfaces of the substrate is achieved. This method replaces external flying wires or soldering, making the electrical connection internal and structured, thus improving the overall structural compactness, mechanical reliability, and signal transmission stability of the sensor.

[0013] This invention also provides a method for fabricating a flexible array pressure sensor using screen printing, wherein multiple raised pressure-sensitive patterns can be arranged on a single planar pressure-sensitive pattern of the planar pressure-sensitive layer. This increases the effective surface area and surface roughness of the pressure-sensitive functional layer, enhancing the sensitivity improvement effect brought about by the overprinting of the raised layer; at the same time, the number and arrangement of the raised patterns can be used as design variables, providing flexibility for finely controlling the pressure response curve of the sensor (such as sensitivity and range).

[0014] Preferably, in the above-described method for fabricating a flexible array pressure sensor using screen printing, the electrode layer includes multiple individual sensing point electrodes, which form an array electrode connected in n rows and m columns. Defining the sensor as an array structure formed by connecting n rows and m columns of individual sensing point electrodes is key to extending the pressure sensing capability of a single point to a two-dimensional plane. This allows the sensor to detect and map the magnitude and spatial distribution of pressure, making it suitable for advanced applications requiring multi-dimensional information input, such as robot tactile sensing, posture recognition, and human-computer interaction.

[0015] Preferably, in the above-described method for fabricating a screen-printed flexible array pressure sensor, the individual sensing point electrode is a circular or square forked electrode with a side length or diameter of D1. The size of the planar pressure-sensitive layer corresponding to the individual sensing point electrode is D2, where D2 > D1 to ensure that the pressure-sensitive layer of the individual sensing point can completely cover the electrode layer of that individual sensing point. By limiting the size of the pressure-sensitive layer to be larger than the size of the corresponding electrode layer, the design ensures that the entire effective sensing area of ​​the electrode can be completely covered by the pressure-sensitive material under any pressure. This avoids the inactivation of some areas of the electrode due to alignment deviation or pressure tilt, thereby ensuring the integrity, consistency, and accuracy of the output signal of each sensing point.

[0016] Preferably, in the above-described method for fabricating a screen-printed flexible array pressure sensor, the adhesive layer is located between each sensing point electrode, and the size D3 of the adhesive layer corresponding to a single sensing point electrode is smaller than the spacing between the planar pressure-sensitive layers corresponding to adjacent single sensing point electrodes. By limiting the adhesive layer to be located only between each sensing point electrode and its size to be smaller than the spacing between adjacent pressure-sensitive layers, it is ensured that the adhesive will not intrude into the pressure-sensitive functional area. This brings two major benefits: first, it prevents the adhesive from contaminating the pressure-sensitive material and affecting its performance; second, it physically isolates each sensing point, so that the film deformation generated when one point is pressed will not easily be transmitted to adjacent points, effectively reducing mechanical crosstalk and signal crosstalk between sensing points and improving the spatial resolution of the array.

[0017] Preferably, in the above-described method for fabricating a screen-printed flexible array pressure sensor, the size of the conductive layer corresponding to a single sensing point is D4, which is smaller than the spacing between the adhesive layers corresponding to adjacent single sensing points. This design, where the conductive layer size is smaller than the adhesive layer spacing, means that the conductive layer is precisely aligned with the sensing point area below. When external pressure is applied, the conductive layer can act as a force director, concentrating and transmitting the pressure to the pressure-sensitive area of ​​the target sensing point, rather than dispersing it to the non-functional adhesive area. This significantly improves the array's response to localized pressure and enhances its ability to distinguish adjacent pressure points.

[0018] Preferably, in the above-described method for fabricating a screen-printed flexible array pressure sensor, the square forked electrode includes a first connecting strip and a second connecting strip arranged in parallel, as well as a plurality of first insert strips and second insert strips. The plurality of first insert strips are vertically spaced and connected to the first connecting strip, and the plurality of second insert strips are vertically spaced and connected to the second connecting strip. The free ends of the plurality of first insert strips and the plurality of second insert strips are arranged in a relative insertion configuration. Specifically, the preferred structure of the forked electrode consists of staggered insert strips. This structure can create longer boundary lines and a more complex and uniform electric field distribution within a limited planar area. When the pressure-sensitive layer with the raised structure above is subjected to pressure contact, the forked electrode can provide more and more sensitive electrical contact change points, thereby further amplifying the resistance change signal brought about by the raised pressure-sensitive layer, achieving higher sensitivity and a better signal-to-noise ratio.

[0019] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a method for fabricating a screen-printed flexible array pressure sensor, which has the following beneficial effects: 1. In terms of core performance enhancement, this invention significantly improves the sensitivity and measurement accuracy of the sensor by using a secondary printing design that overlays a raised pressure-sensitive layer onto a planar pressure-sensitive layer. This method can form a controllable microstructure on the surface of the pressure-sensitive layer without introducing complex processes such as photolithography and etching, simply by optimizing the printing process. This makes the contact area of ​​the sensor change more significantly when it is under pressure, and the resistance response more sensitive, while maintaining the inherent advantages of screen printing in terms of low cost, high efficiency and large-scale production.

[0020] 2. In terms of structural integration and process compatibility, this invention achieves fully integrated printing fabrication from the substrate, electrodes, pressure-sensitive layer to the encapsulation layer. Each functional layer is sequentially formed by screen printing and finally bonded and fixed to form a thin, flexible, and structurally stable sensor assembly. The process chain is highly continuous, suitable for applications that are flexible and stretchable, and effectively avoids interlayer misalignment and signal interference. At the same time, the outer encapsulation layer provides the sensor with waterproof, moisture-proof, and oxidation-proof protection, enhancing its stability and service life in complex environments and ensuring long-term reliability of sensing performance.

[0021] 3. In terms of arraying and signal quality, this invention achieves accurate perception and independent detection of spatial pressure distribution through the design and size optimization of the fork-tooth electrode array. The fine layout of the adhesive layer and conductive layer effectively isolates mechanical and electrical crosstalk between adjacent sensing points, improving the spatial resolution and signal consistency of the sensor.

[0022] 4. Through the core design of secondary overprinting, this invention achieves simple and controllable preparation of the microstructure on the surface of the pressure-sensitive layer within the screen printing framework. It effectively solves the core contradiction of the difficulty in surface control in traditional screen printing processes and the fact that the pursuit of high performance often requires sacrificing mass production efficiency and cost. This provides a practical solution for the large-scale, low-cost manufacturing of high-sensitivity, high-consistency flexible array pressure sensors. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0024] Figure 1 The attached figure is a schematic diagram of the structure of the fork-tooth type flexible array pressure sensor provided by the present invention; Figure 2 The attached figure is a schematic diagram of the via structure of a single fork-tooth electrode provided by the present invention; Figure 3 The attached figure is a schematic diagram of the via structure of the array fork electrode provided by the present invention; Figure 4 The attached figure is a schematic diagram of the positioning relationship between the layers of the fork-tooth flexible array pressure sensor provided by the present invention; Figure 5 The attached figure is a schematic diagram of the sandwich-type flexible array pressure sensor provided by the present invention; Figure 6 The attached figure is a structural schematic diagram of the positioning relationship between the layers of the sandwich-type flexible pressure sensor provided by the present invention; Figure 7 The attached figure is a sample roughness statistics table before overprinting provided by the present invention; Figure 8 The attached figure is a roughness statistics table of the overprinted sample provided by the present invention.

[0025] Wherein: 1-upper substrate layer; 2-lower substrate layer; 21-via; 3-electrode layer; 31-sensing point electrode; 311-first connecting strip; 312-second connecting strip; 313-first insertion strip; 314-second insertion strip; 32-lower electrode layer; 33-upper electrode layer; 4-electrode wire layer; 5-planar pressure-sensitive layer; 51-lower planar pressure-sensitive layer; 52-upper planar pressure-sensitive layer; 6-raised pressure-sensitive layer; 61-lower raised pressure-sensitive layer; 62-upper raised pressure-sensitive layer; 7-adhesive layer; 8-conductive layer; 9-encapsulation layer. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Based on the method of this invention, two basic sensor structures can be fabricated: a forked flexible array pressure sensor and a sandwich-type flexible array pressure sensor. Those skilled in the art should understand that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0028] Example 1: Fork-tooth type flexible array pressure sensor This embodiment provides a specific structure and fabrication method for a fork-tooth type flexible array pressure sensor; such as... Figure 1 As shown, the sensor structure, from bottom to top, includes: an electrode wire layer 4 (located on the lower surface of the lower substrate layer 2 and connected to the electrode layer 3 through a via 21), a lower substrate layer 2, an electrode layer 3 (located on the upper surface of the lower substrate layer 2), an adhesive layer 7, a pressure-sensitive layer (composed of a planar pressure-sensitive layer 5 and a raised pressure-sensitive layer 6), an upper substrate layer 1, a conductive layer 8, and an encapsulation layer 9.

[0029] The specific preparation steps are as follows: Step S101: Prepare flexible thin film substrate 1 (upper substrate layer 1 and lower substrate layer 2) A printable, flexible insulating material (such as polyurethane, polyimide, or PDMS-based insulating inks) is selected as the substrate material. Using screen printing, wet films of the upper substrate layer 1 and the lower substrate layer 2 are formed on a flat glass, silicon wafer, or release film substrate. After printing, the films are sintered and cured in an oven or on a hot plate at 80-120°C for 20-60 minutes, resulting in a thin, independent film with a thickness of approximately 30-200 μm, a smooth surface, and good flexibility and bendability. The upper substrate layer 1 and the lower substrate layer 2 provide a printable and stable flexible platform for subsequent functional layers.

[0030] Step S102: Prepare electrode layer 3 On the upper surface of the cured substrate layer 2, a printable conductive ink (such as silver paste, carbon paste, or PEDOT:PSS conductive polymer) is printed using a screen printing stencil with a forked electrode pattern to form the electrode layer 3. Figure 2 and Figure 3As shown, the electrode layer 3 is composed of multiple individual sensing point electrodes 31 arranged in an n-row × m-column array (in this embodiment, there are 16 electrodes in a 4×4 array). Each individual sensing point electrode 31 is a forked electrode, and its structure includes a first connecting strip 311 and a second connecting strip 312 arranged in parallel with each other, and multiple first insert strips 313 connected to the first connecting strip 311 and multiple second insert strips 314 connected to the second connecting strip 312 respectively, which are perpendicular to each other and spaced apart. The free ends of the first insert strips 313 and the second insert strips 314 are interleaved and inserted relative to each other. The side length (square) or diameter (circular) of a single forked electrode is denoted as D1, and the distance between the centers of adjacent sensing points is denoted as L1. After printing, the lower substrate layer 2 is placed in an oven at 120-150°C for 15-30 minutes to cure the conductive ink fully and form a stable electrode pattern.

[0031] Step S103: Fabricate via 21 and electrode conductor layer 4 Fabrication of via 21: On the lower substrate layer 2 with the cured electrode layer 3, micro-holes penetrating the substrate, i.e., via 21, are fabricated at designated pin locations using methods such as laser ablation, mechanical drilling, or punching. The hole diameter is approximately 100-300 μm. This via is used to achieve electrical interconnection between the upper and lower surfaces of the substrate.

[0032] Electrode conductor layer 4: The lower substrate layer 2 is flipped over, and the electrode conductor layer 4 is prepared on its lower surface by screen printing. During printing, it is necessary to ensure that the ink fully fills the through hole 21 so that it forms a reliable electrical connection with the electrode layer 3 (the end of the first connecting strip 311) on the upper surface.

[0033] The array electrode shape consists of n rows and m columns of connected individual electrodes. The arrangement involves extending one end of each forked electrode from the top layer of the substrate, and the other end from the bottom layer of the substrate via a via. (e.g.) Figure 3 (As shown) For a forked electrode array arranged in n rows and m columns, each forked electrode has two lead wires. The m row-oriented (or column-oriented) forked electrodes on the same side are connected using wires to create n interfaces, which can be gold fingers or solder pads, etc. The other ends of the n vertical forked electrodes are led out from the back via vias, connected using wires to create m gold fingers or solder pads, etc. These n+m connection points are used to connect to subsequent acquisition circuits to transmit the acquired analog signals.

[0034] Step S104: Prepare pressure-sensitive layers (planar pressure-sensitive layer 5 and raised pressure-sensitive layer 6) On the lower surface of the upper substrate layer 1, a pressure-sensitive layer is prepared using a printable ink with piezoresistive properties (such as a polymer composite material doped with carbon black, graphene, or carbon nanotubes). This is one of the core steps of the present invention.

[0035] Printing the planar pressure-sensitive layer 5: First, a planar pressure-sensitive layer 5 is printed at positions corresponding to each sensing point of the lower substrate electrode layer 3 using a screen printing process. Its pattern shape typically corresponds to the electrode layer, and its size is denoted as D2. The design must satisfy D2 > D1 to ensure that, after assembly, the planar pressure-sensitive layer 5 completely covers and extends beyond the underlying forked electrode, avoiding misalignment that could result in some areas of the electrode not being covered.

[0036] Overprinting of the raised pressure-sensitive layer 6: On the cured planar pressure-sensitive layer 5, another screen printing plate with a micro-raised dot pattern (such as a circular or square dot matrix) is used for precise overprinting to form the raised pressure-sensitive layer 6. For example... Figure 1 As shown, multiple tiny raised pressure-sensitive patterns (dense dots in this embodiment; the actual number and spacing of the raised patterns can be freely designed) can be arranged on a single planar pressure-sensitive layer 5. After overprinting, the upper substrate layer 1 is placed in an oven at 100-130°C for final curing for 20-40 minutes. During this process, the materials of the planar pressure-sensitive layer 5 and the raised pressure-sensitive layer 6 are sintered and fused into a functional layer with integrity but a specific surface roughness and microstructure. This secondary overprinting process does not require complex photolithography or molding equipment; the surface characteristics of the pressure-sensitive layer can be effectively controlled by screen printing alone, making the contact area with the electrode change more drastically when under pressure, thereby significantly improving the sensitivity and response linearity of the sensor. The principle is that the pressure-sensitive material has piezoresistive characteristics; its resistance is large and stable when not under pressure, and decreases under pressure, and the resistance continues to decrease with increasing pressure. When the pressure-sensitive layer comes into contact with the electrode layer, the resistance value of the pressure-sensitive layer can be measured at both ends of the electrode. As the pressure increases, the measured resistance value decreases, thus achieving the effect of obtaining the current pressure value by measuring the resistance value. When a raised pressure-sensitive layer is printed after the planar pressure-sensitive layer is printed, the overall surface roughness of the pressure-sensitive layer increases, and the change in contact separation area between the pressure-sensitive layer and the electrode layer becomes more obvious under pressure, resulting in a more drastic change in resistance. Therefore, the pressure sensing sensitivity of the sensor is effectively increased.

[0037] Step S105: Prepare adhesive layer 7 and assemble Printed Adhesive Layer 7: On the upper surface of the lower substrate layer 2 (i.e., the side where the electrode layer 3 has been prepared), an adhesive layer 7 is prepared by screen printing using a printable flexible adhesive (such as silicone rubber, acrylate, or polyurethane adhesive). The pattern of the adhesive layer 7 is designed as a grid or ring, precisely located in the gap area between each sensing point and the outer edge of the sensor array, strictly avoiding covering the sensing point area (i.e., the forked electrode and the pressure-sensitive layer area above it). The width or size of the adhesive layer corresponding to the gap of a single sensing point is denoted as D3, and its design must satisfy: D3 < (L1 - D2), that is, less than the spacing between the edges of adjacent planar pressure-sensitive layers 5 (e.g., ...). Figure 4 (As shown).

[0038] Lamination Assembly: The upper substrate layer 1, with the pressure-sensitive layer already prepared, and the lower substrate layer 2, with the adhesive layer 7 already printed, are precisely aligned (ensuring the center of each sensing point is aligned). Then, lamination bonding is performed under appropriate temperature (e.g., 60-90°C) and pressure (e.g., 0.1-0.5 MPa). After the adhesive layer 7 cures, the upper and lower substrates and the functional layers in between are firmly bonded into a single unit. Simultaneously, due to the size limitation of D3, the sensing point area (between the pressure-sensitive layer and the electrode layer) remains a freely deformable cavity structure, unaffected by the adhesive.

[0039] Step S106: Prepare conductive layer 8 On the upper surface of the assembled sensor (i.e., the upper surface of the upper substrate layer 1), a conductive layer 8 is prepared by screen printing using the same or similar printable insulating material as the substrate layer. The shape of the conductive layer 8 corresponds to each sensing point, and is usually circular or square, with its dimension denoted as D4. The design must satisfy: D4 < (L1 - D3), that is, less than the spacing between adjacent adhesive layers 7 (e.g., ...). Figure 4 (As shown). The function of the conductive layer 8 is to conduct the pressure more concentratedly to the pressure-sensitive area of ​​the corresponding sensing point when external pressure is applied to the sensor surface, reducing the dispersion of pressure to the non-sensing adhesive area, thereby improving the pressure resolution of the array and the sensitivity of a single sensing point.

[0040] Step S107: Prepare encapsulation layer 9 Finally, a dense encapsulation layer 9 is applied to the entire outer surface of the sensor using a printable insulating material (which can be the same as the substrate) via screen printing, completely sealing the conductive layer 8 and the upper surface of the upper substrate layer 1. After printing, a final curing process is performed (e.g., 80-100°C, 30-60 minutes). The encapsulation layer 9 provides the sensor with necessary environmental protection, including waterproofing, moisture resistance, dustproofing, chemical corrosion protection, and prevention of oxidation of internal functional materials, thereby greatly improving the long-term stability and reliability of the sensor under complex operating conditions.

[0041] Working principle: When an external force is applied to a sensing point area on the sensor surface, the pressure is transmitted through the encapsulation layer 9 and the conductive layer 8, causing deformation of the upper substrate layer 1 and its attached raised pressure-sensitive layer 6 / planar pressure-sensitive layer 5 above that point, bringing them into contact with the corresponding toothed electrode. The initial contact point is located at the protrusion of the raised pressure-sensitive layer 6. As the pressure increases, the contact area (especially the contact between the protrusion and the toothed electrode insert strip) gradually increases. Since the resistance of the pressure-sensitive material decreases with increasing pressure, the pressure point can be accurately located and the pressure magnitude quantified by measuring the resistance change across the toothed electrode. The presence of the raised pressure-sensitive layer 6 greatly enhances the sensitivity of the initial contact and the dynamic range of resistance changes.

[0042] Example 2: Sandwich-type flexible array pressure sensor This embodiment provides a specific structure and fabrication method for a sandwich-type flexible array pressure sensor. For example... Figure 5 As shown, the sensor structure, from bottom to top, includes: a lower substrate layer 2, a lower electrode layer 32, a lower pressure-sensitive layer (composed of a lower planar pressure-sensitive layer 51 and a lower raised pressure-sensitive layer 61), an adhesive layer 7, an upper pressure-sensitive layer (composed of an upper planar pressure-sensitive layer 52 and an upper raised pressure-sensitive layer 62), an upper electrode layer 33, an upper substrate layer 1, a conductive layer 8, and an encapsulation layer 9.

[0043] The specific preparation steps are as follows: Step S201: Prepare flexible thin film substrates (upper substrate layer 1 and lower substrate layer 2) The materials and preparation process are the same as in step S101 of Example 1, and separate upper substrate layer 1 and lower substrate layer 2 are prepared respectively.

[0044] Step S202: Fabricate the lower electrode layer 32 and the upper electrode layer 33 Preparation of lower electrode layer 32: (see) Figure 5 and Figure 6 On the upper surface of the lower substrate layer 2, a lower electrode layer 32 is prepared by screen printing using printable conductive ink. The lower electrode layer consists of simple square, circular, or polygonal electrode pads arranged in n rows × m columns (e.g., 4×4), with a single electrode pad size of D1 and a center-to-center distance of L1 between adjacent electrodes. The array electrode shape is composed of n rows and m columns of connected individual electrodes. The arrangement is as follows: each electrode is vertically connected in the lower electrode layer 32, leading out n interfaces; and each electrode is horizontally connected in the upper electrode layer 33, leading out m interfaces. The interface type can be gold fingers or solder pads, etc. These n+m connection points are used to connect to subsequent acquisition circuits to transmit the acquired analog signals.

[0045] Fabrication of the upper electrode layer 33: The upper electrode layer 33 is fabricated on the lower surface of the upper substrate layer 1 using the same process and materials. The upper electrode layer 33 corresponds one-to-one with the lower electrode layer 32 (i.e., there is an electrode pad above and below each sensing point position).

[0046] It should be noted that the sandwich-type electrode layer is a simple planar electrode, without forked tooth structure or via requirements.

[0047] Step S203: Prepare the lower pressure-sensitive layer and the upper pressure-sensitive layer This is the application of the core process of the present invention in another structure, which needs to be performed on the upper and lower substrates respectively.

[0048] Fabrication of the lower pressure-sensitive layer: On the lower substrate layer 2 where the lower electrode layer 32 has been completed, firstly, a lower planar pressure-sensitive layer 51 with a size of D2 (D2 > D1) is printed at the position corresponding to each lower electrode pad. Subsequently, a lower raised pressure-sensitive layer 61 (such as a dot array) is overprinted on this planar layer.

[0049] Preparation of the upper pressure-sensitive layer: On the upper substrate layer 1 where the upper electrode layer 33 has been completed, the upper planar pressure-sensitive layer 52 and the upper raised pressure-sensitive layer 62 are printed sequentially using the same process, with the same dimensional requirements as above.

[0050] Curing: The upper and lower substrates with the printed pressure-sensitive layers are placed in an oven for curing, so that the planar layer and the raised layer are sintered together. The secondary overprinting process here serves the same purpose as in Example 1, aiming to improve the micro-roughness and morphology of the surface of each pressure-sensitive layer.

[0051] Step S204: Prepare adhesive layer 7 and assemble Adhesive layer 7: Adhesive layer 7 is prepared by screen printing on the surface of the pressure-sensitive layer (i.e., the lower raised pressure-sensitive layer 61) of the lower substrate layer 2. Its pattern design and size requirements are the same as in Example 1: a grid pattern distributed between the sensing points, with size D3 satisfying D3 < (L1 - D2) (e.g., ...). Figure 6 (As shown).

[0052] Lamination Assembly: The upper substrate layer 1, with the prepared upper electrode layer 33 and upper pressure-sensitive layer, is precisely aligned with the lower substrate layer 2, with the prepared lower electrode layer 32, lower pressure-sensitive layer, and adhesive layer 7. During alignment, it is essential to ensure that the upper and lower pressure-sensitive layers (especially the raised portions) are approximately aligned. Lamination is then performed under appropriate temperature and pressure. After the adhesive layer 7 cures, the upper and lower parts are bonded together, forming a sandwich core sensing structure with the adhesive layer mesh separating the layers and the upper and lower pressure-sensitive layers aligned.

[0053] Step S205: Fabrication of conductive layer 8 and encapsulation layer 9 On the upper surface of the assembled sensor (on the upper substrate layer 1), a conductive layer 8 and an encapsulation layer 9 are sequentially screen printed. The material selection, design dimensions (D4 < (L1 - D3)), functions, and preparation processes are exactly the same as steps S106 and S107 of Example 1.

[0054] Working Principle: When an external force is applied to a point on the sensor surface, the pressure is conducted through the layers, causing the upper and lower pressure-sensitive layers at that point to come into contact. Initial contact occurs at the protrusions of the upper and lower pressure-sensitive layers. As the pressure increases, the contact area between the upper and lower pressure-sensitive layers increases. At this point, the current path is: lower electrode → lower pressure-sensitive layer → upper pressure-sensitive layer → upper electrode. The resistance of this path depends on the contact resistance between the upper and lower pressure-sensitive layers, which decreases as the pressure increases. By measuring the resistance between the lower electrode row and the upper electrode row where the point is located, the pressure point can be located and sensed. Both the upper and lower pressure-sensitive layers employ a protruding structure, making the contact separation behavior more sensitive and significantly improving the response performance.

[0055] Both Example 1 (fork-tooth type) and Example 2 (sandwich type) adopt the core innovative process of overprinting a raised pressure-sensitive layer 6 on the planar pressure-sensitive layer 5 to improve sensitivity, and share the optimized design concept of full screen printing, flexible substrate, adhesive layer / conductive layer / encapsulation layer; the two structures each have their own advantages, and the choice can be made according to the specific application scenario, focusing on sensitivity, spatial resolution, process complexity and cost.

[0056] The working principle of flexible pressure sensors mainly consists of two aspects: Piezoresistive effect of materials: When a material is subjected to pressure, its resistance changes due to the tunneling effect.

[0057] Microstructure of materials: The microstructure of materials causes changes in resistance when subjected to pressure.

[0058] The microstructure of a material surface refers to the geometric shape and spatial distribution of the surface and near-surface regions, serving as the physical carrier of roughness. Roughness is a quantitative indicator, providing a measurable basis for the design and optimization of the microstructure. Therefore, effectively controlling the surface roughness of the pressure-sensitive layer is crucial for adjusting sensor performance.

[0059] This invention utilizes screen printing to overlay raised pressure-sensitive layers onto a planar pressure-sensitive layer, achieving effective adjustment of the microstructure. The advantages of this method are analyzed below from the perspectives of adjustable range, production efficiency, and production cost.

[0060] (1) Adjustable range 1. Only the flat pressure-sensitive layer is printed; the raised pressure-sensitive layer is not overprinted. The microstructure of the material is primarily determined by printing parameters, including but not limited to printing pressure, printing speed, squeegee angle, screen spacing, screen tension, mesh diameter, and photosensitive emulsion thickness. These various process parameters interact with each other, and their mechanisms of action are not fully understood. Therefore, adjusting the surface roughness of the material is difficult, and largely relies on repeated testing to obtain empirical results. (Appendix) Figure 7The roughness measurement results of the planar pressure-sensitive layer under different printing parameters are sorted from smallest to largest. The results show that the roughness Ra can be adjusted in the range of 0.921-1.485.

[0061] 2. Overprint a raised pressure-sensitive layer on the planar pressure-sensitive layer. The microstructure of the overprinted raised pressure-sensitive layer is mainly determined by the shape, size, and spacing of the raised material. The shape of the raised pressure-sensitive layer can be dots, squares, intersecting lines, etc., and its size and spacing can be freely set. These parameters can be determined during the preparation stage of the printing material, eliminating the need for repeated adjustments to printing pressure, printing speed, and other parameters during the printing process, thus simplifying the adjustment process. (Appendix) Figure 8 To statistically analyze the surface roughness of the printed samples under different parameters, the Ra values ​​were sorted from smallest to largest, with an adjustment range of 1.059-3.561.

[0062] As can be seen from the comparison, the method of overprinting the roughness of the raised pressure-sensitive layer can more effectively adjust the range of surface roughness.

[0063] (2) Production efficiency Taking a material processing range of 300mm*300mm as an example, the time required to prepare microstructures of the same size is compared as follows: 1. 3D printing For digital photopolymer 3D printing technology, curing is required layer by layer, and the classic processing time is 30 minutes.

[0064] For extrusion 3D printing technology, it takes about 10 hours, and the required accuracy cannot be achieved.

[0065] 2. Laser engraving For CO2 lasers, the line scanning speed is approximately 1000-2000 mm / s, and the classic processing time is 30-60 minutes.

[0066] For femtosecond lasers, it is suitable for small batch processing, with a classic processing time of 30 minutes.

[0067] 3. Mask etching For wet etching, the process involves spin coating of photosensitive emulsion, exposure, development, and etching, and takes about 2 hours.

[0068] 4. For dry etching, plasma dry etching requires a vacuum environment and the processing time is about 1 hour.

[0069] 5. Screen printing of raised pressure-sensitive layer The printing time is only about 10 seconds, and the processing and curing can be done simultaneously in large batches.

[0070] Compared to not using overprinting, the time increase from printing the raised pressure-sensitive layer is less than 10% of the overall sensor fabrication time. Compared to other methods, it requires less time and is more efficient.

[0071] (3) Production costs Taking a material processing range of 300mm*300mm as an example, a comparison of the costs required to fabricate microstructures of the same size: 1. The DLP / SLA process for 3D printing costs about 300,000 yuan per machine, has a long production cycle, and the cost of a single piece produced in batches is about 300 yuan.

[0072] 2. Laser engraving: femtosecond laser equipment costs approximately one million yuan, while the cost of a single sample is approximately 500 yuan.

[0073] 3. Mask etching: Etching equipment costs approximately 200,000 to 500,000 yuan, and the cost of a single sample is approximately 500 yuan.

[0074] 4. Screen printing: The equipment cost is approximately 10,000 to 300,000 yuan, but it is highly efficient in mass production, with a single sample costing approximately 10 to 30 yuan.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0076] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0077] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for fabricating a flexible array pressure sensor using screen printing, characterized in that, Includes the following steps: Step 1) A flexible thin film substrate is prepared using a printable insulating material. The flexible thin film substrate includes an upper substrate layer (1) and a lower substrate layer (2). An electrode layer (3) is formed by curing printable conductive ink on the upper surface of the lower substrate layer (2), and an electrode wire layer (4) is formed by curing on the lower surface of the lower substrate layer (2). Step 2), a planar pressure-sensitive layer (5) is printed on the lower surface of the upper substrate layer (1) using a printable pressure-sensitive material, and then a raised pressure-sensitive layer (6) is printed on the planar pressure-sensitive layer (5) at least once, and then cured and integrally formed; a printable adhesive is printed on the upper surface of the lower substrate layer (2) by screen printing to form an adhesive layer (7). Step 3), then the lower substrate layer (2) formed in step 2) and the upper substrate layer (1) formed are bonded and fixed together by the adhesive, so that the lower substrate layer (2) and the electrode layer (3) and electrode wire layer (4) on it, the upper substrate layer (1) and the planar pressure-sensitive layer (5) and the raised pressure-sensitive layer (6) on it are all fixed together. Step 4), using a printable insulating material, a conductive layer (8) is prepared on the upper surface of the prepared substrate layer (1) by screen printing.

2. The method for fabricating a screen-printed flexible array pressure sensor according to claim 1, characterized in that, It also includes an encapsulation layer (9) which is prepared on the upper surface of the upper substrate layer (1) using a printable insulating material.

3. The method for fabricating a screen-printed flexible array pressure sensor according to claim 1, characterized in that, The upper and lower surfaces of the lower substrate layer (2) are connected by vias (21) for positioning, and the vias (21) are located at one end of the electrode pin.

4. The method for fabricating a screen-printed flexible array pressure sensor according to claim 1, characterized in that, Multiple raised pressure-sensitive patterns can be arranged on a single planar pressure-sensitive pattern of the planar pressure-sensitive layer (5).

5. A method for fabricating a screen-printed flexible array pressure sensor according to any one of claims 1 to 4, characterized in that, The electrode layer (3) includes multiple individual sensing point electrodes (31), which form an array electrode formed by connecting n rows and m columns.

6. The method for fabricating a screen-printed flexible array pressure sensor according to claim 5, characterized in that, The single sensing point electrode (31) is a circular or square forked electrode with a side length or diameter of D1. The size of the planar pressure-sensitive layer (5) corresponding to the single sensing point is D2, where D2>D1 to ensure that the pressure-sensitive layer of the single sensing point electrode (31) can completely cover the electrode layer of the single sensing point.

7. The method for fabricating a screen-printed flexible array pressure sensor according to claim 5, characterized in that, The adhesive layer (7) is located between each sensing point, and the size D3 of the adhesive layer (7) corresponding to a single sensing point electrode (31) is smaller than the spacing between the planar pressure-sensitive layers (5) corresponding to adjacent single sensing point electrodes (31).

8. The method for fabricating a screen-printed flexible array pressure sensor according to claim 5, characterized in that, The size of the conductive layer (8) corresponding to a single sensing point electrode (31) is D4, which is smaller than the spacing between the adhesive layers (7) corresponding to adjacent single sensing point electrodes (31).

9. The method for fabricating a screen-printed flexible array pressure sensor according to claim 5, characterized in that, The square forked electrode includes a first connecting strip (311) and a second connecting strip (312) arranged in parallel with each other, and a plurality of first plug-in strips (313) and a plurality of second plug-in strips (314). The plurality of first plug-in strips (313) are vertically spaced and connected to the first connecting strip (311), and the plurality of second plug-in strips (314) are vertically spaced and connected to the second connecting strip (312). The free ends of the plurality of first plug-in strips (313) and the plurality of second plug-in strips (314) are arranged to be plugged into each other.

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