Capacitive force sensor, preparation method and force measurement method

Abstract

The capacitive force sensor comprises a fixed polar plate and a movable polar plate which are oppositely arranged, the fixed polar plate comprises a first substrate, a first insulating layer locally arranged on the first substrate, a first conductive layer and a first pin / bonding pad layer; the movable pole plate comprises a second substrate, and a second insulating layer and a second conductive layer which are locally arranged on the second substrate; the first substrate and the second substrate are ceramic substrates; the first insulating layer and the second insulating layer are formed by sintering glass slurry; the first conductive layer and the second conductive layer are formed by sintering conductive slurry; the lead-out part of the first conductive layer extends to the surface of the first insulating layer. The shielding structure is matched with the carbon slurry, the problems that a traditional sensor is small in signal, poor in anti-interference capacity and the like are solved, and the sensor has the advantages of being simple in structure, resistant to high temperature, good in long-term stability, high in measurement precision and the like.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and in particular to a capacitive force sensor, its preparation method, and a force measurement method, specifically applicable to high-sensitivity detection of minute forces or pressures. Background Technology

[0002] In fields such as industrial automation, intelligent equipment, and precision testing, traditional resistance strain gauge force sensors serve as core sensing components, responsible for the accurate acquisition and conversion of force signals. Their performance directly determines the system's measurement accuracy, stability, and applicable scenarios, leading to continuously increasing industry requirements for their technical specifications. Currently, most widely used flat plate force sensors are designed based on the traditional resistance strain principle. However, these sensors suffer from numerous insurmountable technical defects, severely restricting their application in high-precision, high-stability, and special scenarios: On the one hand, they exhibit strong temperature sensitivity. Due to the material properties and working principle limitations of silicon resistance strain gauges, their temperature coefficient can reach as high as 2000 ppm / ℃. When the ambient temperature changes, the output signal is easily affected by temperature drift, resulting in significant fluctuations in measurement accuracy. This makes it difficult to meet the needs of outdoor testing equipment, high-temperature industrial production lines, and other scenarios with large temperature differences or frequent temperature changes. On the other hand, they exhibit significant hysteresis effects, with nonlinear errors typically exceeding 0.5%FS. When external forces change, the output signal cannot accurately follow the changes in real time, resulting in delays and deviations. In dynamic force detection scenarios, this can easily lead to data distortion, affecting system response judgment. Meanwhile, it has poor long-term stability. Affected by the creep of the adhesive and the aging of the structure, it is prone to performance drift after long-term use. The measurement accuracy decreases over time, requiring frequent calibration and maintenance, which increases costs and cannot guarantee the reliability of long-term continuous operation.

[0003] In contrast, capacitive force sensors measure force by detecting changes in capacitance caused by variations in the distance between electrodes. They offer advantages such as low power consumption, high sensitivity, and good structural scalability, making them promising for applications in precision measurement. However, existing capacitive force sensors still face challenges in practical applications, including difficulty in controlling the initial electrode spacing consistency, parasitic capacitance interference, complex manufacturing processes, and insufficient batch consistency.

[0004] Therefore, there is an urgent need to provide a capacitive force sensor with a reasonable structure, controllable manufacturing, and high measurement stability, as well as its supporting preparation method and force measurement method, to overcome the above-mentioned shortcomings in the existing technology. Summary of the Invention

[0005] The purpose of this invention is to provide a capacitive force sensor, a preparation method, and a force measurement method. The capacitive force sensor achieves controllable changes in the distance between the plates under external force by rationally setting the structure of the fixed plate and the movable plate and limiting their spacing, thereby obtaining a stable and repeatable capacitance change signal. The preparation method of the capacitive force sensor has clear process steps and controllable parameters, making it suitable for mass production. The force measurement method of the capacitive force sensor can achieve accurate measurement of external force.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: On one hand, a capacitive force sensor is provided, including a fixed electrode plate and a movable electrode plate disposed opposite to each other; the fixed electrode plate includes a first substrate, a first insulating layer, a first conductive layer and a first pin / pad layer partially disposed on the first substrate; the movable electrode plate includes a second substrate, a second insulating layer and a second conductive layer partially disposed on the second substrate; both the first substrate and the second substrate are ceramic substrates; the first insulating layer and the second insulating layer are formed by sintering glass paste; the first conductive layer and the second conductive layer are formed by sintering conductive paste; the lead-out portion of the first conductive layer extends to the surface of the first insulating layer; the first pin / pad layer is formed by sintering metal conductive paste, electrically connected to the first conductive layer, and constitutes a sensor first connection terminal, a sensor second connection terminal and a sensor shield connection terminal for external output; the fixed electrode plate and the movable electrode plate are connected and fixed by sintered glass paste in their peripheral regions to form a preset electrode plate spacing; the glass paste contains alumina microspheres to limit the preset electrode plate spacing and allow the movable electrode plate to displace under force, resulting in a change in capacitance. A capacitive sensor consists of two plates. When an external force is applied, the distance between the plates changes slightly, causing a change in capacitance. A high-precision detection circuit converts the capacitance change into a force output.

[0007] Preferably, the conductive paste is a carbon-based conductive paste, which includes conductive carbon fibers, carbon black, and an organic binder; the first conductive layer and the second conductive layer are sintered to form a carbon-based conductive layer containing a carbon fiber network. The conductive layer is formed by sintering the carbon-based conductive paste and is designed with coaxial annular shielding electrodes to suppress parasitic capacitance interference.

[0008] Preferably, the first pin / pad layer includes conductive bumps located within the region of the first insulating layer, the conductive bumps being overlaid on the lead-out portion of the first conductive layer; the lead-out portion of the second conductive layer extends to the surface of the second insulating layer to form a conductive contact area; when the fixed electrode and the movable electrode are connected relative to each other, the first insulating layer and the second insulating layer are fused together, causing the conductive bumps and the conductive contact area to form a press-fit connection, thereby leading the potential of the movable electrode to the fixed electrode. The conductive bumps have a certain thickness (10-30µm) to serve as press-fit contacts during subsequent packaging.

[0009] Preferably, the first conductive layer includes a central sensing electrode and a first peripheral shielding electrode surrounding the central sensing electrode; the second conductive layer includes a counter electrode corresponding to the central sensing electrode and a second peripheral shielding electrode surrounding the counter electrode; the first peripheral shielding electrode is connected to the shielding connection terminal of the first pin / pad layer via a lead-out portion of the first conductive layer; the second peripheral shielding electrode is connected to the shielding connection terminal of the fixed electrode plate via a press-fit connection between a conductive contact area and a conductive bump; wherein the outer diameter of the first peripheral shielding electrode is not equal to the outer diameter of the second peripheral shielding electrode, such that when the fixed electrode plate and the movable electrode plate are aligned, the peripheral shielding electrodes of the two form an interleaved electric field shielding structure at the edge.

[0010] Preferably, the main sensing area of ​​the first conductive layer is directly bonded to the first substrate, and its lead-out lines extend to the first insulating layer; the first pin / pad layer is printed with a metallic conductive paste, with one part located at the edge of the first substrate to form an external pad, and the other part located on the first insulating layer to form conductive bumps; the glass encapsulation material contains alumina microspheres to define a preset spacing and allow the movable electrode to displace under stress. During encapsulation sintering, the glass melts and flows, while the microspheres, acting as rigid supports, lock the spacing between the fixed electrode and the movable electrode at a preset value.

[0011] On the other hand, a method for fabricating a capacitive force sensor is also provided, comprising the following steps: S1. Preparation of conductive paste: The conductive paste is a carbon-based conductive paste. S2. Electrode printing and pretreatment: Glass insulating layers are printed and sintered on the ceramic substrates of both the fixed and movable electrodes. Then, conductive paste is printed on the glass insulating layer and the ceramic substrate, and cured or heat-treated to form a conductive layer. Metal conductive paste is printed on the fixed electrode to cover a portion of the conductive layer's lead-out area, and sintered to form the first pin / pad layer. S3. Encapsulation and sintering: A glass encapsulation material containing alumina microspheres is printed around the periphery of the movable electrode. The printed surfaces of the fixed and movable electrodes are aligned and bonded together. Pressure is applied and the material is heated to the softening temperature of the glass encapsulation material for sintering. After cooling, a capacitive force sensor is formed. The electrodes are sealed together by a glass paste containing alumina microspheres, with the microspheres defining the electrode spacing.

[0012] Preferably, in step S1, the preparation process of the conductive paste includes: mixing a dispersant with a solvent to dissolve an organic binder to form a matrix sol, adding graphite powder for grinding and dispersion, then adding chopped conductive carbon fibers for stirring and mixing, and finally obtaining the paste after vacuum degassing; in step S2, the curing or heat treatment includes: heat treatment at 300℃~600℃ under an inert atmosphere; the metal conductive paste for the first pin / pad layer is conductive silver paste. It is chemically stable in normal environments and is not easily oxidized or corroded. Even in extreme environments such as high temperature, high humidity, and strong radiation in the aerospace field, the conductive silver paste can maintain stable conductivity, extending the service life of electronic components.

[0013] On the other hand, a method for measuring a capacitive force sensor is also provided, for measuring the aforementioned capacitive force sensor, the steps of which are as follows: S1. Initialize the data information of the capacitive force sensor to obtain the initial capacitance value and the initial electrode spacing between the first conductive layer on the fixed electrode and the second conductive layer on the movable electrode; S2. Apply pressure to the capacitive force sensor in step S1, acquire the electrical signal representing the capacitance change between the second conductive layer and the first conductive layer, and obtain the changed capacitance; S3. Calculate the electrode spacing between the first conductive layer on the fixed electrode and the second conductive layer on the movable electrode based on the capacitance in step S2, and calculate the pressure applied to the sensor based on the obtained electrode spacing. This includes initializing and acquiring initial parameters, detecting capacitance changes after applying pressure, calculating the force value based on the nonlinear relationship between electrode spacing and capacitance, and pressure and electrode deformation, and converting the capacitance change into a force value output through a high-precision detection circuit.

[0014] Preferably, in step S3, the relationship between the capacitor and the distance between the fixed and movable plates is as follows: , :capacitance; : Correlation coefficient of the perimeter of a cylindrical structure; Relative permittivity; Vacuum permittivity; Points cap; : Integral variable; Initial spacing between the plates; The change in the distance between the plates caused by external force or displacement. This describes the capacitance. The change in electrode spacing and the radial dimension of the electrode. The quantitative relationship between them.

[0015] Preferably, in step S3, the relationship between the distance between the fixed electrode and the movable electrode and the magnitude of the pressure is as follows: , P: Pressure acting on the electrode plate; a: Characteristic dimension of the electrode plate; : Poisson's ratio of the electrode material; E: elastic modulus of the electrode material; h: electrode thickness; d: initial spacing between the electrodes; r: radial coordinate of a point on the electrode. By integrating material mechanical parameters and structural dimensional parameters, the influence of the electrode's own properties on deformation is demonstrated.

[0016] The beneficial effects of this invention compared to the prior art are: 1. The sensor consists of two plates: the fixed plate is made of a highly stable dielectric material and has a large thickness to maintain structural rigidity; the movable plate is designed as a micron-thin plate structure, which directly bears the external force as a force-sensitive element. When an external force is applied, the distance between the plates changes slightly, resulting in a change in capacitance. The change in capacitance is converted into a force output by a high-precision detection circuit.

[0017] 2. The outer diameters of the outer shielding electrodes of the fixed electrode and the movable electrode are designed to be different sizes. When the two electrodes are aligned, they form an overlapping edge covering structure, which can effectively reduce parasitic edge capacitance, increase the effective capacitance ratio at the center, and significantly improve the linearity, repeatability and zero-point stability of the sensor.

[0018] 3. Carbon-based conductive pastes are used instead of traditional metal pastes to reduce parasitic capacitance and improve electrode stability. Carbon-based materials such as graphite and carbon fibers form a continuous conductive network, resulting in lower surface effect parasitic capacitance and eliminating electrochemical migration issues. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the external shape of the capacitive force sensor of the present invention; Figure 2a This is a schematic diagram of the fixed electrode plate in the capacitive force sensor of the present invention; Figure 2b This is a schematic diagram of the movable plate in the capacitive force sensor of the present invention; Figure 3 This is a schematic diagram of the operation of the capacitive force sensor of the present invention; Figure 4 This is a schematic diagram of the cross-sectional structure of the capacitive force sensor of the present invention; Figure 5 This is a schematic diagram of the electric field distribution of the capacitive force sensor of the present invention without a shielding layer; Figure 6 A schematic diagram of the electric field distribution when a shielding layer is provided for the capacitive force sensor of the present invention; Figure 7 This is a schematic diagram of the pressure measurement process of the capacitive force sensor of the present invention. Detailed Implementation

[0020] The technical solutions of the present invention will now be described in detail with reference to the accompanying drawings. Example 1

[0021] like Figure 1 As shown, this application provides a capacitive force sensor, including a fixed electrode and a movable electrode. Both the fixed and movable electrodes use a ceramic material with an alumina content of 96% as the substrate material. This material exhibits outstanding compressive strength and deformation resistance, maintaining dimensional stability even under high and low temperature cycling or vibration environments, thus avoiding any impact on sensing accuracy.

[0022] like Figure 2a and Figure 2b As shown, the fixed electrode and the movable electrode are patterned using screen printing to form insulating layers, shielding layers, and conductive layers. The fixed electrode includes a first substrate, a first insulating layer, a first conductive layer, and a first pin / pad layer partially disposed on the first substrate. The first substrate uses ceramic material as the substrate material, and the first insulating layer serves as the first layer of the fixed electrode. Figure 2a The yellow pattern screen 1 shown has a mesh count of 150. It is printed onto the first substrate using a glass paste (DL151), and then sintered. The sintering temperature is 480℃ ~ 520℃, and the sintering time is 20 minutes. This sintering time does not include the heating and cooling time; the sintering environment must be strictly controlled to avoid oxidation affecting the adhesion strength and weather resistance of the glass paste. In this embodiment, the first insulating layer is distributed in a locally continuous mesa shape, mainly located in the lead-out wiring area above the first substrate, used to provide electrical isolation and elevate subsequent contact points.

[0023] The first conductive layer, serving as the second layer for fixing the electrode plate, uses a red patterned screen 1 with a mesh size of 150. A conductive paste, obtained by mixing graphite and carbon fiber in a specific ratio, is printed onto the first substrate and the first insulating layer, followed by sintering to fully solidify the binder in the paste, forming a conductive layer 1 with excellent conductivity and a strong bond to the electrode plate substrate. Using a conductive paste obtained by mixing graphite and carbon fiber in a specific ratio significantly improves the paste's conductivity and structural stability, while graphite ensures smooth printing and adhesion.

[0024] The first conductive layer has a predetermined pattern structure, including a central sensing electrode and a first peripheral shielding electrode surrounding the central sensing electrode, which are insulated from each other. The central sensing electrode is located in the center of the pattern and is circular; the first peripheral shielding electrode is annular and surrounds the outer periphery of the central sensing electrode along the same central axis to form an electric field shielding structure to reduce edge electric field distortion. The central sensing electrode is connected to the second connection terminal of the sensor through its lead-out electrode area; the first peripheral shielding electrode is connected to the sensor shielding connection terminal through its lead-out electrode area. The lead-out electrode area extends outward from the main electrode area, is arc-shaped or zigzag-shaped, and forms a continuous conductive path with the main electrode area after sintering.

[0025] The first conductive layer also includes conductive pattern regions connected to the first connection terminal, the second connection terminal, and the shielded connection terminal of the sensor. One end of the lead-out portion of each conductive pattern region is disposed on the first insulating layer, and the other end is disposed on the first substrate, for reliable lead-out of electrode signals.

[0026] The first pin / pad layer, serving as the third layer for fixing the electrode plate, uses a green patterned screen and conductive silver paste printed onto the first substrate, first insulating layer, and first conductive layer to form a conductive connection layer. This layer connects with the first conductive layer, creating a dense conductive film layer that ensures stable conductivity. Simultaneously, it forms a strong mechanical bond with the electrode plate surface, meeting the electrical connection and wear resistance requirements for subsequent use. The first pin / pad layer comprises two parts: external pads located at the edge of the substrate for soldering external conductors, and conductive bumps located within the first insulating layer area, directly overlaid on the ends of the lead lines of the first conductive layer. These conductive bumps have a certain thickness (10-30µm) to serve as press-fit contacts during subsequent packaging.

[0027] Structural reference of movable plate Figure 2b (Schematic diagram of movable electrode plate) The movable electrode plate and the fixed electrode plate are designed to mirror each other, including a second substrate, a second insulating layer and a second conductive layer partially disposed on the second substrate. The second insulating layer is also a partially printed glass paste platform, its position precisely corresponding to the first insulating layer of the fixed electrode plate. The second conductive layer is also a carbon-based conductive layer, including a counter electrode corresponding to the central sensing electrode and a second peripheral shielding electrode. The lead-out lines of the second conductive layer extend onto the second insulating layer, forming a flat conductive contact area at its end. The position of this contact area is vertically aligned with the "conductive bumps" on the fixed electrode plate. When the fixed electrode plate and the movable electrode plate are connected relative to each other, the first insulating layer and the second insulating layer fuse together, causing the conductive bumps and the conductive contact area to form a press-fit connection, thereby leading the potential of the movable electrode plate to the fixed electrode plate.

[0028] The manufacturing processes for movable and fixed electrodes are similar. First, glass paste is printed on the second insulating layer and then sintered. Then, a conductive paste made of graphite and carbon fiber mixed in a certain proportion is printed on the second conductive layer and then sintered.

[0029] The second substrate uses ceramic material as the base material, and the second insulating layer serves as the first layer of the movable electrode plate. A yellow patterned screen 2 is used, which is printed onto the second substrate using glass paste, and then sintered to form the second insulating layer. The yellow patterned screen 2 has a mesh size of 150 mesh. The glass paste is DL151, which is printed onto the second substrate and then sintered to form the second insulating layer. The sintering temperature is 480℃ ~ 520℃, and the sintering time is 20 minutes. The sintering time does not include the time for temperature rise and fall. During this period, the sintering environment must be strictly controlled to avoid oxidation affecting the adhesion strength and weather resistance of the glass paste, ultimately forming a dense and wear-resistant protective layer.

[0030] After the yellow glass paste is completely sintered and cooled, the printing of the conductive paste in the red area is started. The second conductive layer, as the second layer of the movable electrode plate, uses a red pattern screen 2. The conductive paste obtained by mixing graphite and carbon fiber in a certain proportion is printed on the second substrate and then sintered to form the conductive layer 2. The second conductive layer includes conductive pattern areas 2 that are respectively connected to the first connection terminal of the sensor and the shielding connection terminal of the sensor, and the conductive pattern areas 2 are set on the second insulating layer. The conductive paste obtained by mixing graphite and carbon fiber in a certain proportion can significantly improve the conductivity and structural stability of the paste, while graphite ensures the smoothness and adhesion of the paste printing.

[0031] To eliminate parasitic capacitance caused by edge effects, this embodiment employs an interleaved shielding design.

[0032] like Figure 4-6 As shown, the second conductive layer includes a counter electrode corresponding to the central sensing electrode and a second peripheral shielding electrode surrounding the counter electrode. The outer diameter of the first peripheral shielding electrode is not equal to that of the second peripheral shielding electrode. The outer diameter (width) of the first peripheral shielding electrode can be larger or smaller than that of the second peripheral shielding electrode. When the fixed electrode and the movable electrode are aligned and sintered, the first and second peripheral shielding electrodes form a conductive path, together constituting an edge-interlaced electric field shielding structure. When the outer diameters are not equal, the electric field gradient formed between the shielding electrodes can significantly reduce the edge electric field distortion, so that the equivalent measurement capacitance is mainly concentrated in the central effective area, thereby reducing the proportion of edge parasitic capacitance. The conductive pattern of the fixed electrode and the conductive pattern of the movable electrode are geometrically complementary or coaxially aligned. This includes the coaxial arrangement of the main electrode area and the corresponding positions of the lead-out electrode areas to stabilize the electric field distribution and improve sensitivity. Example 2

[0033] Sensor packaging and conductive interconnection between the two electrodes: Microsphere-controlled spacing encapsulation: A ring of glass encapsulation material is printed around the periphery of the movable electrode, containing spacer microspheres (such as alumina microspheres) with strictly selected diameters. The melting point of the microspheres (>2000℃) is much higher than the sintering temperature of the glass encapsulation material (approximately 500℃). During encapsulation sintering, the glass melts and flows, while the microspheres act as rigid supports, locking the spacing between the fixed and movable electrodes at a preset value: 30μm-100μm.

[0034] Fusion bonding interconnection: During the final encapsulation sintering process, in addition to the melting of the peripheral sealing ring, the first and second insulating layers (both made of glass) located in the lead-out area also soften and fuse together due to heat. As the glass layers fuse and shrink, the conductive bumps of the fixed electrode and the conductive contact area of ​​the movable electrode, which were originally only in physical contact, are forcibly pressed together. After cooling and solidification, the fused insulating layer forms a robust rigid enclosure, permanently sealing the conductive connection points inside. This structure enables reliable lead-out of the potential from the movable electrode to the fixed electrode, eliminating the need for fragile metal springs or conductive adhesives between the electrodes, and greatly improving the reliability of the sensor under vibration and shock environments. Example 3

[0035] This invention provides a method for fabricating a capacitive force sensor based on carbon-based slurry, comprising the following steps: Step S1: Preparation of carbon-based conductive paste, which solves the problems of high cost and easy ion migration of traditional silver / gold electrodes. The present invention provides a self-made carbon-based paste: 1. Raw materials 1.1 Conductive carbon fibers (short-cut, conductive type, length 50–300 μm, diameter ~7–10 μm), accounting for 10–35 wt% (adjusted according to the required conductivity) (main conductive phase).

[0036] 1.2 Graphite powder / conductive carbon black (to supplement the conductive network and reduce contact resistance): 5–20 wt%.

[0037] 1.3 Binder / film-forming agent: Ethyl cellulose or acrylic resin (to control viscosity and adhesion): 4–12 wt%.

[0038] 1.4 Dispersant / surfactant (to improve the dispersion of carbon fibers and graphite in solvents): Sorbitan trioleate (Span 85) or polyethylene glycol derivative: 1–3 wt.

[0039] 1.5 The remainder to 100% wt: Solvent (to dissolve the binder and adjust viscosity): Butyl carbitol, terpineol, or a mixture of xylene / butanone.

[0040] 2. Slurry preparation 2.1 Raw material pretreatment Carbon fiber stubs: If long fibers are used, they need to be stubbed to 50–300 μm and dried (80°C, 2 h) to remove moisture.

[0041] Graphite and carbon black are first sieved (<100 μm) to remove large agglomerates.

[0042] 2.2 Dispersion / Wet Milling Add the solvent (e.g., a mixture of butyl carbitol or terpineol) and dispersant to a mixing tank and heat to 60–90°C (if the binder used needs to be heated to dissolve).

[0043] Gradually add ethyl cellulose and allow it to dissolve completely (400–1000 rpm, 30–120 min) to form a matrix sol.

[0044] Add graphite powder and carbon black and wet-mill using a ball mill or three-roll mill to refine the particle size distribution of graphite / carbon black (specific process: three-roll mill 3-5 times, or ball mill 6-12 hours, depending on the equipment).

[0045] Finally, slowly add the chopped carbon fiber and stir at low speed to avoid the fibers breaking too short (300–600 rpm, 15–30 min).

[0046] 2.3 Degassing and Viscosity Adjustment Use vacuum degassing (-0.08 MPa, 10–30 min) to remove air bubbles and avoid porosity during printing.

[0047] Adjust the viscosity to the range required for screen printing (see printing parameters below). If the viscosity is too high, add an appropriate amount of solvent; if it is too low, add binder or increase the solids content.

[0048] 2.4 Screening and Packaging Pass through a 200–400 mesh sieve to remove large particles or agglomerates, then dispense into moisture-proof containers. Storage recommendations: Store in a dark, cool, inert, or dehumidified environment to prevent changes in viscosity and dispersibility.

[0049] Step S2: Electrode Printing and Pretreatment Throughout the entire printing process, environmental cleanliness must be controlled to prevent dust pollution from affecting printing quality; sufficient cooling time must be reserved between each step to prevent residual heat from the preceding process from adversely affecting subsequent printing materials; after printing, the electrode plates must be inspected for appearance, thickness, and conductivity to ensure that the product meets technical specifications.

[0050] A screen printing plate is a template used in screen printing processes to prepare sensor electrodes or other functional layers. The sintering process allows the coating to form a strong bond with the substrate, preventing peeling and wear. High-temperature sintering can eliminate pores and bubbles inside the printed layer, making the thickness and performance uniform.

[0051] Before printing on the fixed and movable electrode plates, the first and second substrates are ultrasonically cleaned with a water flow rate greater than 0.1 m. 3 The cleaning process is carried out at a rate of / h, with a cleaning time of 30 minutes. Then, the first and second substrates are dried at 80℃ for 30 minutes. The cavitation effect of ultrasound can remove stubborn impurities such as tiny oil stains and dust without damaging the substrate surface. No residue remains after drying, avoiding oxidation and corrosion caused by moisture or cleaning agent residue, extending the substrate's service life, improving its cleanliness and stability, and laying a solid foundation for subsequent processes (such as coating and bonding).

[0052] 3. Printing and curing / sintering processes 3.1 Mesh size: 150–300 mesh 3.2 Number of printing passes: 1–5 to achieve the desired thickness; after each printing, dry briefly (80–120°C) for 10–30 minutes to remove solvent.

[0053] 3.3 Bake at 120–200°C for 30–120 min to allow the organic binder to crosslink and evaporate residual solvents.

[0054] 3.4 Optional: First, heat treat in an inert atmosphere (N2 / Ar) at 300–600°C to remove a large amount of organic matter and make the contact between graphite / carbon fiber closer, forming a stable conductive layer after encapsulation sintering.

[0055] The target resistance of the printed electrode surface is 10 mΩ / cm² ~ 1 Ω / cm².

[0056] Using graphite or carbon fiber or a mixture thereof can achieve stable conductivity and eliminate metal migration issues (compared to gold paste, which may undergo electrochemical migration under high humidity / high pressure). Furthermore, graphite or carbon fiber or a mixture thereof has good flexibility, which can buffer thermal stress, especially on ceramic substrates, reducing thermal expansion mismatch. In addition, adjustable surface roughness can slightly increase the effective electric field area, thus achieving a low-cost, environmentally friendly alternative to precious metal electrodes.

[0057] Since both graphite and carbon fiber are excellent conductive materials, the conductive paste, after curing, forms a continuous conductive network, which is essentially a "conductor structure." When the conductor formed by this type of conductive paste is unshielded, divergent electric field lines will be generated on its surface. If other conductors are present nearby, such as adjacent conductive paste lines, metal components, or grounding structures, parasitic capacitance will form between them due to electric field coupling. Because the conductive paste has high conductivity and can have a large surface area, such as a large-area electrode, the electric field coupling with surrounding conductors is more significant, and the parasitic capacitance value may be even larger. This can lead to interference during signal transmission, such as high-frequency signal attenuation and noise coupling, or affect the capacitance accuracy in energy storage / sensor devices, such as parasitic capacitance superimposed on the target capacitance, causing measurement deviations. When the movable electrode plate is subjected to a certain pressure, using carbon in the conductive layer can reduce the influence of the electric field lines of the capacitor in the conductive layer on the capacitance.

[0058] Step S3: Alignment and Packaging A glass sealing paste containing alumina microspheres is printed around the periphery of the movable electrode plate.

[0059] Align the two plates face to face precisely, so that the "conductive protrusions" are aligned with the "conductive contact areas".

[0060] A certain pressure is applied, and the glass is heated to the sealing temperature (approximately 500°C). During this process, the peripheral glass is sealed, and the insulation layer in the lead-out area melts to achieve interconnection. Example 4

[0061] like Figure 7 As shown, this application also provides a force measurement method for a capacitive force sensor, used to measure the force of the aforementioned capacitive force sensor, the steps of which are as follows: S1. Initialize the data information of the capacitive force sensor to obtain the initial capacitance value, the initial electrode spacing of the first conductive layer on the fixed electrode and the second conductive layer on the movable electrode.

[0062] The core working principle of a capacitive flat plate force sensor is to change the electrode spacing / area / dielectric constant by external force, thereby changing the capacitance, and then converting the capacitance change into a measurable electrical signal. The core of the capacitive flat plate force sensor consists of two parallel conductive electrode plates, with air or a specific dielectric material usually present between the plates. When no force is applied, the plates maintain a fixed relative state, yielding the initial capacitance and the initial electrode spacing of the first and second conductive layers.

[0063] S2. Apply pressure to the capacitive force sensor in step S1, obtain the electrical signal characterizing the capacitance change between the second conductive layer and the first conductive layer, and obtain the changed capacitance.

[0064] like Figure 3As shown, when an external force is applied to the movable plate, the distance between the first conductive layer on the fixed plate and the second conductive layer on the movable plate decreases, and the capacitance increases as the distance decreases. The external force changes the relative overlapping area of ​​the plates, and the capacitance is proportional to the area. The change in area directly leads to the change in capacitance. The external force squeezes the dielectric material between the plates, causing its dielectric constant to change, which indirectly causes the change in capacitance. The capacitance after the change is measured.

[0065] S3. Based on the capacitance in step S2, calculate the electrode spacing between the first conductive layer on the fixed electrode and the second conductive layer on the movable electrode, and calculate the pressure applied to the sensor based on the obtained electrode spacing.

[0066] Based on the measured change in capacitance, the distance between the first conductive layer on the fixed electrode and the second conductive layer on the movable electrode is calculated using the formula relating capacitance and electrode spacing. The formula is as follows: , :capacitance; : Correlation coefficient of the perimeter of a cylindrical structure; Dielectric constant; Vacuum permittivity; : Radial dimension of the electrode (e.g., radius of a circular electrode); : The radial coordinate of a point on the electrode plate; Initial spacing between the plates; The change in the distance between the plates caused by external force or displacement.

[0067] By describing the capacitance in a capacitive force sensor Change in distance between the plates Radial dimensions of the electrode plates The quantitative relationship between them. When an external force reduces the distance between the plates... At that time, capacitor The capacitance will increase accordingly, and the magnitude of the external force or displacement can be inferred by detecting the change in capacitance.

[0068] Then, based on the electrode spacing, the pressure is calculated using the following formula: ,

[0069] : Pressure (or external force) acting on the electrode plate; Characteristic dimensions of the electrode (e.g., the radius of a circular electrode); Poisson's ratio of the electrode material; E: Elastic modulus of the electrode material; h: The thickness of the electrode plate; d: Initial spacing between the plates; r: Radial coordinate of a point on the electrode plate (used to describe the deformation difference at different radial positions); By integrating material mechanical parameters and structural dimensional parameters ( This demonstrates the influence of the plate's own characteristics on deformation; through The item describes the deformation differences at different radial positions of the electrode (the deformation at the edge and the center are different), and is an accurate model of the actual elastic electrode deformation (non-ideal uniform deformation).

[0070] The feasibility of the "force-physical parameter-capacitance" conversion was verified, which is the fundamental basis for the sensor's ability to measure force. This demonstrates the sensor's quantitative measurement capability; because the two have a stable correspondence, the magnitude of the external force can be inferred from the change in capacitance. Under the same force, the more significant the capacitance change, the higher the sensor's sensitivity. In practice, circuit calibration is needed to correct nonlinear errors and ensure measurement accuracy. The stability of the relationship (unaffected by environmental interference) determines the sensor's reliability; structural design is necessary to reduce the influence of temperature and humidity on this relationship.

[0071] The above embodiments are merely illustrative of the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solutions based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. A capacitive force sensor, characterized in that, This includes fixed and movable electrode plates that are positioned opposite each other; The fixed electrode plate includes a first substrate, a first insulating layer, a first conductive layer and a first pin / pad layer partially disposed on the first substrate; the movable electrode plate includes a second substrate, a second insulating layer and a second conductive layer partially disposed on the second substrate; Both the first substrate and the second substrate are ceramic substrates; The first and second insulating layers are formed by sintering glass slurry. The first conductive layer and the second conductive layer are formed by sintering conductive paste; the lead-out portion of the first conductive layer extends to the surface of the first insulating layer. The first pin / pad layer is formed by sintering a metal conductive paste, is electrically connected to the first conductive layer, and constitutes the sensor first connection terminal, sensor second connection terminal and sensor shield connection terminal for external output; The fixed electrode and the movable electrode are connected and fixed by sintered glass slurry in their peripheral areas to form a preset electrode spacing; the glass slurry contains alumina microspheres to limit the preset electrode spacing and allow the movable electrode to displace under force, resulting in capacitance change.

2. The capacitive force sensor according to claim 1, characterized in that, The conductive paste is a carbon-based conductive paste, which contains conductive carbon fibers, carbon black and organic binders; the first conductive layer and the second conductive layer are sintered to form a carbon-based conductive layer containing a carbon fiber network.

3. The capacitive force sensor according to claim 1, characterized in that, The first pin / pad layer includes conductive bumps located within the region of the first insulating layer, the conductive bumps being overprinted on the lead-out portion of the first conductive layer; the lead-out portion of the second conductive layer extends to the surface of the second insulating layer to form a conductive contact area.

4. The capacitive force sensor according to claim 3, characterized in that, The first conductive layer includes a central sensing electrode and a first peripheral shielding electrode surrounding the central sensing electrode; the second conductive layer includes a counter electrode corresponding to the central sensing electrode and a second peripheral shielding electrode surrounding the counter electrode; the first peripheral shielding electrode is connected to the shielding connection terminal of the first pin / pad layer via the lead-out portion of the first conductive layer; the second peripheral shielding electrode is connected to the shielding connection terminal of the fixed electrode plate via the crimping connection between the conductive contact area and the conductive bump.

5. The capacitive force sensor according to claim 1, characterized in that, The main sensing area of ​​the first conductive layer is directly bonded to the first substrate, and its lead-out lines rise to the first insulating layer; the first pin / pad layer is printed with metal conductive paste, part of which is located at the edge of the first substrate to form an external pad, and the other part is located on the first insulating layer to form a conductive bump.

6. A method for manufacturing a capacitive force sensor as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Prepare a conductive paste, wherein the conductive paste is a carbon-based conductive paste; S2. Electrode printing and pretreatment: Glass insulating layers are printed and sintered on the ceramic substrates of the fixed electrode and the movable electrode, respectively. Subsequently, conductive paste is printed on the glass insulating layer and the ceramic substrate, and then cured or heat-treated to form a conductive layer. A metallic conductive paste is printed on a fixed electrode plate to cover part of the lead-out area of ​​the conductive layer, and then sintered to form the first pin / pad layer. S3. Encapsulation and sintering: A glass encapsulation material containing alumina microspheres is printed around the movable electrode. The printed surfaces of the fixed electrode and the movable electrode are aligned and bonded together. Pressure is applied and the glass encapsulation material is heated to its softening temperature for sintering. After cooling, a capacitive force sensor is formed.

7. The preparation method according to claim 6, characterized in that, In step S1, the preparation process of the conductive paste includes: mixing the dispersant with the solvent, dissolving the organic binder to form a matrix sol, adding graphite powder for grinding and dispersion, adding short-cut conductive carbon fibers for stirring and mixing, and obtaining the paste after vacuum degassing; in step S2, the curing or heat treatment includes: heat treatment at 300℃~600℃ under an inert atmosphere; the metal conductive paste of the first pin / pad layer is conductive silver paste.

8. A method for fabricating and measuring a capacitive force sensor, characterized in that, For measuring the capacitive force sensor as described in any one of claims 1-5, the following steps are included: S1. Initialize the data information of the capacitive force sensor to obtain the initial capacitance value, the initial electrode spacing of the first conductive layer on the fixed electrode and the second conductive layer on the movable electrode. S2. Apply pressure to the capacitive force sensor in step S1, obtain the electrical signal representing the change in capacitance between the second conductive layer and the first conductive layer, and obtain the changed capacitance. S3. Based on the capacitance in step S2, calculate the electrode spacing between the first conductive layer on the fixed electrode and the second conductive layer on the movable electrode, and calculate the pressure applied to the sensor based on the obtained electrode spacing.

9. The measurement method of the capacitive force sensor according to claim 8, characterized in that, In step S3, the relationship between the capacitor and the distance between the fixed and movable plates is as follows: , C :capacitance; : Correlation coefficient of the perimeter of a cylindrical structure; Relative permittivity; Vacuum permittivity; Points cap; : Integral variable; d: Initial spacing between the plates; The change in the distance between the plates caused by external force or displacement.

10. The measurement method of the capacitive force sensor according to claim 8, characterized in that, In step S3, the relationship between the distance between the fixed and movable plates and the magnitude of the pressure is as follows: ， P The pressure acting on the electrode plates; Characteristic dimensions of the electrode plate; Poisson's ratio of the electrode material; E: Elastic modulus of the electrode material; h: The thickness of the electrode plate; d: Initial spacing between the plates; r: Radial coordinate of a point on the electrode plate.

Images