Miniature pressure sensor and manufacturing method thereof

Abstract

A miniature pressure sensor comprises a sensor body, the sensor body is of a center sunken structure, a boss is arranged at the center sunken position, and two half-bridge silicon strain gauges are symmetrically arranged on the periphery of the side, facing the sunken side of the sensor body, of the boss; and a compensation circuit board is arranged at the end part of one side, facing the recess of the sensor body, of the boss, and the compensation circuit board is connected with the two half-bridge silicon strain gauges through wires. According to the invention, the half-bridge silicon strain gauges are adopted, the design of a compensation circuit board is innovatively provided, and the design and manufacturing of the miniature pressure sensor are realized. The half-bridge silicon strain gauge is free of a polymer substrate material, so that the influence of the substrate material on the sensor is reduced. Meanwhile, a traditional surface mounting technology is improved, a repeated curing method without a pressurization mode is adopted, the connection reliability between the elastic body and the strain gauge is guaranteed, and then the stability of the sensor is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of sensors, and in particular to a micro pressure sensor and a manufacturing method thereof. Background Art

[0002] Miniature pressure sensors have a wide range of applications, such as robotics and new energy vehicles. These miniature pressure sensors are generally based on the strain gauge principle and primarily consist of an elastomer and a strain gauge. They range in diameter from a few millimeters to tens of millimeters and in height from 1 mm to 20 mm. These sensors face several challenges in practical use:

[0003] First, when such sensors are subjected to relatively small pressures, their signal output range is often only a few microvolts to a few millivolts. Such small signals generally cannot be directly collected and used by the back-end data processing system. High-precision signal transmission and acquisition technology is required to ensure the accuracy and stability of the signal, which increases the complexity and cost of the system.

[0004] Secondly, to increase the signal output of these sensors, the thickness of the elastomer beam must be reduced. This, on the one hand, requires sophisticated manufacturing processes to process these components, increasing costs. On the other hand, the thickness of the strain gauge and adhesive itself has a greater impact than the thickness of the elastomer, thereby increasing measurement errors.

[0005] Third, temperature sensitivity. Due to their tiny size and precise structure, sensors are often very sensitive to temperature changes. Existing technical solutions, limited by the sensor's small size, often place temperature compensation resistors on the leads rather than inside the sensor. As shown in the figure below, the balance module is where the various compensation resistors are located. This placement of temperature compensation resistors off the sensor itself inevitably affects the effectiveness of temperature error compensation.

[0006] In summary, the problems existing in existing micro pressure sensors are manifested in the following two aspects:

[0007] Question 1: Currently, the characteristics of this type of sensor are highly dependent on the strain gauge's substrate material and the adhesive bonding between the strain gauge and the elastomer. In particular, when the thickness of the elastic element is less than 0.3 mm, the strain gauge significantly affects measurement errors. This is because the substrate and adhesive are made of polymer materials, whose physical properties are often closely related to the environment. First, their Young's modulus decreases sharply with increasing temperature, causing the sensor's sensitivity to increase. Second, polymer materials experience significant creep, which in turn affects the strain gauge's perception of elastic element deformation. Third, the combined changes in temperature and humidity of the polymer material cause the elastic element to deform, resulting in sensor zero-point drift.

[0008] Question 2: The compensation circuit is not on the sensor body, which affects the compensation effect. Summary of the Invention

[0009] The purpose of the present invention is to provide a miniature pressure sensor and a manufacturing method thereof, which can achieve miniaturization (diameter <10mm, height <5mm) while being able to output a stable signal and having a body temperature compensation function. Through silicon strain gauge design, three-stage curing process and compensation circuit integration, the problems of weak signal, large temperature drift and complex process in the existing technology are solved.

[0010] A miniature pressure sensor includes a sensor body, which has a central recessed structure. A boss is provided at the central recess, and two half-bridge silicon strain gauges are symmetrically provided on the periphery of the boss facing the recessed side of the sensor body; a compensation circuit board is provided at the end of the boss facing the recessed side of the sensor body, and the compensation circuit board is connected to the two half-bridge silicon strain gauges by wires.

[0011] A method for preparing a micro pressure sensor comprises the following steps:

[0012] Step S1: The glue dispenser dispenses glue at the center depression of the sensor body;

[0013] Step S2: Place the glued sensor body into a high-temperature furnace for the first curing process, and the glass glue is cured and formed;

[0014] Step S3: placing the half-bridge silicon strain gauge on the cured glass glue;

[0015] Step S4: The sensor is cured for the second time. As the glass glue approaches its melting point and softens, the half-bridge silicon strain gauge is half-sunk in the glass glue.

[0016] Step S5: Take out the sensor, return it to room temperature, and then put it into the oven for the third curing;

[0017] Step S6: Paste the compensation circuit board into the inner cavity of the sensor, and connect the solder points of the compensation circuit board and the solder points of the strain gauge with welding metal wires by ultrasonic welding to form an electric bridge;

[0018] Step S7: Connect the wire to the compensation circuit board, and pass the other end of the wire through the cable hole of the sensor elastic body;

[0019] Step S8: the sensor performs zero point compensation;

[0020] Step S9: the sensor performs temperature zero point compensation;

[0021] Step S10: Preparation is completed.

[0022] The present invention innovatively proposes a design of a compensation circuit board by adopting a half-bridge silicon strain gauge, thereby realizing the design and manufacture of a micro pressure sensor.

[0023] This invention utilizes a half-bridge silicon strain gauge that lacks a polymer substrate, minimizing its impact on the sensor. Furthermore, it improves upon the traditional patching process by employing a multi-curing method without pressure, ensuring a reliable connection between the elastomer and the strain gauge, thereby improving sensor stability.

[0024] Traditional curing methods involve applying a layer of adhesive to the elastomer surface and strain gauge base, followed by pressurization and heat preservation, often referred to as primary curing. Sometimes, to improve sensor stability, a secondary curing step is performed after the primary curing step, followed by heating and heat preservation in an incubator.

[0025] The present invention designs a compensation circuit board and compensation method, which can realize zero point and temperature compensation in the microsensor body, which is superior to other sizes of microsensors. The body compensation makes the zero point temperature drift <0.02% FS / ℃, which is better than the traditional solution.

[0026] By adopting the preparation method of the micro pressure sensor of the present invention, the sensitivity of the half-bridge silicon strain gauge is improved, the output signal reaches above 20mV / V, and can be directly connected to a general acquisition system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the structure after the sensor body and the half-bridge silicon strain gauge are assembled.

[0028] Figure 2 This is a schematic diagram of the structure after the sensor body, half-bridge silicon strain gauge and compensation circuit board are assembled.

[0029] Figure 3 It is a schematic diagram of the overall structure of the micro pressure sensor of the present invention.

[0030] Figure 4 It is a structural schematic diagram of the compensation circuit board of the present invention.

[0031] Figure 5 It is a circuit principle diagram of the compensation circuit board of the present invention.

[0032] Figure 6 This is a schematic diagram of the structure of the half-bridge strain gauge used in the present invention. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is described in detail below with reference to the accompanying drawings:

[0034] like Figure 1 、 Figure 2 、 Figure 3As shown, a miniature pressure sensor includes a sensor body 1, which has a central recessed structure. A boss 2 is provided at the central recess, and two half-bridge silicon strain gauges 3 are symmetrically provided on the periphery of the boss 2 facing the recessed side of the sensor body 1; a compensation circuit board 4 is provided at the end of the boss 2 facing the recessed side of the sensor body 1, and the compensation circuit board 4 is connected to the two half-bridge silicon strain gauges by wires.

[0035] like Figure 4 As shown, the compensation circuit board 4 includes 6 solder points, V1 and V2 respectively connected to the positive signal O+ of the sensor cable are short-circuited with wires; the excitation positive of the cable is connected to V1 or V2; the excitation positive is the positive power supply V+; V3 and V4 respectively connected to the negative signal O- of the sensor cable are short-circuited with wires; the excitation negative of the cable is connected to V3 or V4; the excitation negative is the negative power supply V-.

[0036] like Figure 5 As shown, the half-bridge silicon strain gauge of the present invention has three pads in the middle and four thin sensitive gates on both sides.

[0037] A method for preparing a micro pressure sensor comprises the following steps:

[0038] Step S1: The glue dispenser dispenses glue at the center depression of the sensor body; the glue amount is 0.01-0.05mm 3 .

[0039] Step S2: Place the glued sensor body in a high-temperature furnace for the first curing process. The glass glue is cured and formed. The temperature is >500°C and the duration is 15-20 minutes.

[0040] Step S3: Place the half-bridge silicon strain gauge on the cured glass glue.

[0041] Step S4: The sensor is cured for the second time. As the glass adhesive softens near its melting point, the half-bridge silicon strain gauge is partially immersed in the adhesive. The temperature is 450-500°C and the duration is 10-18 minutes.

[0042] Step S5: Remove the sensor, return it to room temperature, and then place it in an oven for a third curing process. The temperature is 150-300°C for 12-72 hours. The thickness of the glass glue after curing is 0.01-0.05mm.

[0043] Step S6: Paste the compensation circuit board into the inner cavity of the sensor, and connect the solder points of the compensation circuit board and the solder points of the strain gauge with welding metal wires by ultrasonic welding to form an electric bridge.

[0044] Step S7: Connect the wire to the compensation circuit board, and pass the other end of the wire through the cable hole of the sensor elastic body;

[0045] Step S8: The sensor performs zero point compensation.

[0046] The specific process is: Figure 5 As shown, before the compensation zero point, V1 and V2 are short-circuited with a wire, and V3 and V4 are short-circuited with a wire; the six connection points of the two half-bridge strain gauges are connected to the numbers 1-6 on the compensation circuit board; the positive signal O+ of the cable is connected to pad 2; the positive signal O- of the cable is connected to pad 5; V1 is connected to pad 1, V2 is connected to pad 4, V3 is connected to pad 3, and V4 is connected to pad 6;

[0047] V1 and V2 constitute the positive excitation of the cable; the positive excitation is the positive power supply V+; V3 and V4, which are respectively connected to the negative signal O- of the sensor cable, are short-circuited with wires; V3 and V4 constitute the negative excitation of the cable; the negative excitation is the negative power supply V-;

[0048] The sensor cable has four conductors: the positive and negative excitation wires connect to an external power source to power the sensor, and the positive and negative signal wires transmit the sensor's output to the test instrument. The sensor's zero output is the voltage measured on the positive and negative signal wires.

[0049] Place the sensor horizontally with no load, connect the other end of the sensor cable to the test instrument, and obtain the initial output of the sensor without compensation from the test instrument, which is the sensor zero-point output (unit: mV / V);

[0050] At this time, if the zero-point output of the sensor is greater than 0, remove the short-circuit wire between V1 and V2 and replace it with a zero-point compensation resistor R0. The value of the zero-point compensation resistor R0 is positively correlated with the absolute value of the sensor zero-point output S, satisfying the following relationship:

[0051] R0=|S|*Rs / B

[0052] Where Rs is the resistance between the negative signal O- of the sensor cable and the positive signal O+ of the sensor cable when V1 and V2 are short-circuited; B is a constant with a value of 250;

[0053] Connect the positive excitation V+ of the sensor cable to V2; at this time, if the zero point output of the sensor is less than 0, the size and placement of the zero point compensation resistor are the same as above, connect the positive excitation V+ of the sensor cable to V1; complete the zero point compensation.

[0054] Step S9: The sensor performs temperature zero point compensation.

[0055] The specific process is: Figure 5 As shown, put the sensor that has completed zero point compensation into the temperature box without load, and record the zero point output S1 and S2 of the sensor at at least two different temperatures; let the temperatures corresponding to the zero point output S1 and S2 be T1 and T2, and T1 <T2;

[0056] At this time, if S1 < S2, the short-circuit wire between V3 and V4 is removed and replaced with a zero-temperature compensation resistor Rz. The magnitude of the zero-temperature compensation resistor Rz (unit: ohm) is positively correlated with the absolute value of the ratio P of (S2 - S1) / (t2 - t1), and satisfies the following relationship:

[0057] Rz = a*|P| or Rz = |4*Rs*(S2 - S1) / 1000 / (beta*(T2 - T1))|

[0058] Where a is a constant and beta is the temperature coefficient of resistance of the zero-temperature compensation resistor; the excitation negative V- of the sensor cable is connected to V3;

[0059] If S1 > S2, the method for obtaining the magnitude of the compensation resistor and the placement position are the same as above, and the excitation negative V- of the sensor cable is connected to V4; the zero-temperature compensation is completed.

[0060] Step S10: Preparation is completed.

[0061] Combined with Figure 4 、 Figure 5 , G1 and G2, G3 and G4 respectively form a half-bridge silicon strain gauge. Each half-bridge silicon strain gauge has a total of 3 connection points, and the common connection point is connected to the circuit through the pad numbered 2. The other connection point of G1 is connected to the circuit through pad 1, and so on.

[0062] The V+ terminal includes two pads V1 and V2, and a patch compensation resistor is connected between V1 and V2. A wire is led out from one of V1 or V2 as the excitation positive (power supply positive) of the sensor cable; the V- terminal includes two pads V3 and V4, and a patch compensation resistor is connected between V3 and V4. A wire is led out from one of V3 or V4 as the excitation negative (power supply negative) of the sensor cable.

[0063] O+ is connected to the signal positive of the sensor cable. O- is connected to the signal negative of the sensor circuit.

[0064] The compensation circuit board and pad layout of the present invention are basically as shown in the figure. Such a structural layout can better achieve zero and temperature compensation on the sensor body. The small groove on the sensor body 1 is convenient for passing the cable.

[0065] The half-bridge strain gauge structure used in the present invention is as Figure 6As shown, there are three pads in the middle and four thin sensitive grids on either side. The metal elastomer material is 17-4PH material, with an HRC of 38-42 after heat treatment. The surface is sandblasted (roughness Ra < 0.2μm) to achieve the best matching effect with the silicon strain gauge. Other optional elastomer materials include Inconel718, which has a thermal expansion coefficient close to that of the silicon strain gauge (approximately 12.5×10 -6 / ℃), which can reduce the stress mismatch caused by temperature gradient.

Claims

1. A miniature pressure sensor, characterized in that The sensor body (1) comprises a sensor body (1), wherein the sensor body (1) is a central recessed structure, a boss (2) is provided at the central recessed portion, and two half-bridge silicon strain gauges are symmetrically provided on the periphery of the boss (2) facing the recessed side of the sensor body (1); a compensation circuit board is provided at the end of the boss (2) facing the recessed side of the sensor body (1), and the compensation circuit board is connected to the two half-bridge silicon strain gauges via a wire.

2. The micro pressure sensor according to claim 1, characterized in that The above-mentioned compensation circuit board includes 6 solder points; V1 and V2 constitute the positive excitation of the cable line; the positive excitation is the positive power supply V+; V3 and V4 respectively connected to the negative signal O- of the sensor cable line are short-circuited with wires; V3 and V4 constitute the negative excitation of the cable line; the negative excitation is the negative power supply V-; one of V1, V2, V3, V4, the positive signal O+ of the cable line, and the positive signal O- of the cable line is connected to one of the solder points accordingly.

3. The micro pressure sensor according to claim 1, characterized in that The above-mentioned half-bridge silicon strain gauge has three pads in the middle and four thin sensitive gates on both sides.

4. A method for preparing the micro pressure sensor according to any one of claims 1 to 3, characterized in that The steps include: Step S1: The glue dispenser dispenses glue at the center depression of the sensor body; Step S2: Place the glued sensor body into a high-temperature furnace for the first curing process, and the glass glue is cured and formed; Step S3: placing the half-bridge silicon strain gauge on the cured glass glue; Step S4: The sensor is cured for the second time. As the glass glue approaches its melting point and softens, the half-bridge silicon strain gauge is half-sunk in the glass glue. Step S5: Take out the sensor, return it to room temperature, and then put it into the oven for the third curing; Step S6: Paste the compensation circuit board into the inner cavity of the sensor, and connect the solder points of the compensation circuit board and the solder points of the strain gauge with welding metal wires by ultrasonic welding to form an electric bridge; Step S7: Connect the wire to the compensation circuit board, and pass the other end of the wire through the cable hole of the sensor elastic body; Step S8: the sensor performs zero point compensation; Step S9: the sensor performs temperature zero point compensation; Step S10: Preparation is completed.

5. The preparation method according to claim 4, characterized in that Dispensing amount 0.01-0.05mm 3 The thickness of the glass glue after curing is 0.01-0.05mm.

6. The preparation method according to claim 4, characterized in that The requirements for the first curing in step S2 are: temperature>500°C, duration 15-20 minutes.

7. The preparation method according to claim 1, characterized in that The requirements for the second curing in the above step S4 are: temperature at 450-500° C., duration 10-18 minutes.

8. The preparation method according to claim 1, characterized in that The requirements for the third curing in step S5 are: a temperature of 150-300° C. and a duration of 12-72 hours.

9. The preparation method according to claim 1, characterized in that The above step S8 performs zero point compensation on the sensor, and the specific process is as follows: Before compensating the zero point, short-circuit V1 and V2 with a wire, and short-circuit V3 and V4 with a wire; connect the six connection points of the two half-bridge strain gauges to the numbers 1-6 on the compensation circuit board; connect the positive signal O+ of the cable to pad 2; connect the positive signal O- of the cable to pad 5; connect V1 to pad 1, V2 to pad 4, V3 to pad 3, and V4 to pad 6; V1 and V2 constitute the positive excitation of the cable; the positive excitation is the positive power supply V+; V3 and V4, which are respectively connected to the negative signal O- of the sensor cable, are short-circuited with wires; V3 and V4 constitute the negative excitation of the cable; the negative excitation is the negative power supply V-; Place the sensor flat and unloaded, connect the other end of the sensor cable to the test instrument, and obtain the initial output of the current sensor without compensation from the test instrument, which is the zero output of the sensor; Remove the short - circuit wire between V1 and V2 and replace it with the zero - point compensation resistor R0. The magnitude of the zero - point compensation resistor R0 is positively correlated with the absolute value of the zero - point output S of the sensor and satisfies the following relationship: R0 = |S| * Rs / B Where, Rs is the resistance between the negative signal O - and the positive signal O + of the sensor cable when V1 and V2 are short - circuited; B is a constant; Case A: If the zero - point output of the sensor is greater than 0, connect the excitation positive V + of the sensor cable to V1; Case B: If the zero - point output of the sensor is less than 0, connect the excitation positive V + of the sensor cable to V2; complete the zero - point compensation.

10. The preparation method according to claim 9, characterized in that The above step S9 performs temperature zero - point compensation on the sensor. The specific process is as follows: Place the sensor with zero - point compensation completed in the temperature chamber and unloaded, record the zero - point outputs S1 and S2 of the sensor at at least 2 different temperatures; let the temperatures corresponding to the zero - point outputs S1 and S2 be T1 and T2, and T1 < T2; At this time, if S1 < S2, remove the short - circuit wire between V3 and V4 and replace it with the zero - point temperature compensation resistor Rz. The magnitude (unit: ohm) of the zero - point temperature compensation resistor Rz is positively correlated with the absolute value of the ratio P of (s2 - s1) / (t2 - t1) and satisfies the following relationship: Rz = a * |P| or Rz = |4 * Rs * (S2 - S1) / 1000 / (beta * (T2 - T1))| Where, a is a constant, and beta is the resistance temperature coefficient of the zero - point temperature compensation resistor; connect the excitation negative V - of the sensor cable to V4; If S1 > S2, the method for obtaining the magnitude of the compensation resistor and the placement position are the same as above, and connect the excitation negative V - of the sensor cable to V3; complete the zero - point temperature compensation.

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