Pressure sensitive element and manufacturing method thereof, and pressure sensor

Abstract

A low-cost pressure sensitive element includes: an integrally formed metal substrate, the substrate includes a longitudinally extending tube body, a pressure-sensitive diaphragm enclosed at the longitudinal proximal end of the tube body, and a ring of stoppers extending radially outward from the middle of the tube body; and a pressure sensing circuit arranged on the longitudinal proximal surface of the pressure-sensitive diaphragm, which includes at least one varistor. Its manufacturing method includes: obtaining a blank of the substrate by dry pressing or injection molding, drying the blank and sintering it to obtain an integrally formed metal substrate made by a powder metallurgy process; coating an inorganic insulating dielectric slurry on the longitudinal proximal surface of the pressure-sensitive diaphragm, and obtaining an insulating dielectric layer after sintering; coating a conductive slurry on the surface of the insulating dielectric layer, and obtaining a conductive circuit after sintering; coating a thick film slurry on the surface of the insulating dielectric layer, and obtaining a thick film resistor after sintering, so that the thick film resistor and the conductive circuit form a pressure measurement circuit.

Description

Technical Field

[0001] The present application relates to the field of sensor technology, and in particular to a pressure sensitive element and a manufacturing method thereof, and a pressure sensor. Background Art

[0002] Piezoresistive pressure sensors usually use diaphragms as the substrate of pressure-sensitive elements to receive the pressure of the pressure medium to be measured. These diaphragms can be metal diaphragms, semiconductor diaphragms, or ceramic diaphragms. One side surface of these diaphragms is combined with piezoresistors, which form measurement circuits in the form of, for example, Wheatstone bridges. The piezoresistors produce corresponding resistance changes according to the strain on the surface of the diaphragm, so that the measurement circuit outputs a corresponding electrical signal. Among them, these metal diaphragm-type pressure-sensitive elements are widely used due to their good welding and sealing properties and mechanical connection with the container of the pressure medium to be measured.

[0003] Since the diaphragm structure is made of metal material, it needs to be obtained through mechanical processing. In order to facilitate processing, its radial dimension cannot be too small. In addition, in order to avoid the adverse effects of installation stress on the diaphragm, it is usually necessary to set a stress isolation groove at the upper end of the pressure interface, so it cannot be processed integrally with the diaphragm. In this way, it and the metal pressure interface (used for mechanical connection with the container of the pressure medium to be measured) are usually processed separately and then welded together, as disclosed in CN219104249U. Even in some pressure sensors that do not have a stress isolation groove, the diaphragm structure and the pressure interface, the connecting threads of the pressure interface and other structures all need to be obtained through mechanical processing, which increases the processing cost. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present application provides a pressure sensitive element to solve at least one of the above technical defects.

[0005] To achieve the above objectives, the present application provides the following technical solution: a pressure sensitive element, comprising:

[0006] An integrally formed metal substrate made by powder metallurgy, the substrate comprising a longitudinally extending tube, a pressure-sensitive diaphragm sealed at the longitudinal proximal end of the tube, and a ring of stoppers extending from the middle of the tube toward the radial outside;

[0007] and a pressure sensing circuit disposed on the longitudinal proximal surface of the pressure-sensitive diaphragm, which includes at least one piezoresistor.

[0008] Preferably, an outer wall of the longitudinal distal end portion of the tube body is provided with an external thread.

[0009] Preferably, a sealing groove close to the stopper is provided on the outer wall of the longitudinal distal end portion of the tube body, and the sealing groove is used for installing a sealing ring.

[0010] Preferably, an annular stress isolation groove close to the stopper is provided on the outer wall of the longitudinal proximal end portion of the tube body.

[0011] Preferably, the raw material of the powder metallurgy process includes stainless steel powder.

[0012] Preferably, the varistor is a thick film resistor or a silicon strain gauge.

[0013] The present invention also claims protection for a pressure sensor, which includes the pressure sensitive element, and the longitudinal distal end of the tube body is connected to a container of a pressure medium to be measured.

[0014] The present invention also claims a method for manufacturing a pressure sensitive element, which comprises the steps of:

[0015] S1. A green body of the substrate is obtained by dry pressing or injection molding, and the green body is dried and then sintered to obtain an integrally formed metal substrate made by a powder metallurgy process; wherein the substrate comprises a longitudinally extending tube, a pressure-sensitive diaphragm closed at the longitudinal proximal end of the tube, and a ring of stoppers extending from the middle of the tube toward the radial outside;

[0016] S2, coating an inorganic insulating medium slurry on the longitudinal proximal surface of the pressure-sensitive diaphragm, and obtaining an insulating medium layer after sintering;

[0017] S3, coating a conductive slurry on the surface of the insulating dielectric layer, and obtaining a conductive circuit after sintering;

[0018] S4. Coating a thick film slurry on the surface of the insulating dielectric layer, and obtaining a thick film resistor after sintering, so that the thick film resistor and the conductive circuit form a pressure measurement circuit.

[0019] Preferably, the manufacturing method further comprises: forming an external thread on the outer wall of the longitudinal distal end portion of the tube body of the green body or the sintered base body by a machining method. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of a pressure sensitive element of a preferred embodiment;

[0021] Figure 2 is a flow chart of a method for manufacturing a pressure sensitive element in a preferred embodiment;

[0022] Figure 3 FIG. 4 is a flow chart of a method for manufacturing a pressure sensitive element in another preferred embodiment.

[0023] Explanation of the reference numerals in the accompanying drawings: 100, pressure sensitive element; 11a, longitudinal proximal portion; 11b, longitudinal distal portion; 11, tube body; 12, pressure-sensitive diaphragm; 13, stopper; 14, external thread; 1a, longitudinal proximal end; 1b, longitudinal distal end; 1c, sealing groove; 1d, stress isolation groove; 1, substrate; 21, varistor; 2, pressure sensing circuit. DETAILED DESCRIPTION

[0024] The technical solution of the present application will be clearly and completely described below in conjunction with the accompanying drawings. The following embodiments are exemplary and are only used to explain the present application, and cannot be interpreted as limiting the present application. In the following description, the same symbols are used to represent the same or equivalent elements, and repeated descriptions are omitted.

[0025] In the description of the present application, it should be understood that the terms "upper", "lower", "inside", "outside", "left", "right", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the products of the present application are conventionally placed when in use, or are the orientations or positional relationships conventionally understood by those skilled in the art. They are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0026] In addition, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0027] It should be further understood that the term “and / or” used in the specification and corresponding claims of this application refers to any and all possible combinations of one or more of the listed items.

[0028] like Figure 1 In a preferred embodiment of the present application, the pressure sensor includes a pressure sensitive element 100. The pressure sensitive element 100 includes a substrate 1, which is an integrally formed metal element. The substrate 1 includes a longitudinally extending tube 11, a longitudinal proximal end 1a ( Figure 1 The base 1 is made of a pressure-sensitive diaphragm 12 (upper end) and a ring of stopper 13 extending radially outward from the middle of the tube body 11. The longitudinal distal end 1b of the tube body 11 is used for connection with a connection hole on a container containing a pressure medium to be measured, and the stopper 13 is used for stopping on the outer wall of the container for positioning during connection. The base 1 is made by powder metallurgy.

[0029] The pressure sensitive element 100 further includes a pressure sensing circuit 2. The pressure sensing circuit 2 is disposed at the longitudinal proximal end 1a ( Figure 1 The lower end of the pressure sensing film 12 is formed on the surface of the pressure sensing film 12, which includes at least one piezoresistors 21, and more preferably, four piezoresistors 21 connected with the conductive traces 22 to form a Wheatstone bridge. One pair of piezoresistors 21 is arranged on one circumference of the pressure sensing film 12, and the other pair of piezoresistors 21 is arranged on the other circumference of the pressure sensing film 12, so that the two pairs of piezoresistors 21 respectively generate different degrees of strain and resistance changes after receiving the pressure of the medium to be measured on the far end side of the pressure sensing film 12, thereby converting the pressure into a corresponding electrical signal.

[0030] The pressure sensitive element 100 of this embodiment is configured as a metal element integrally formed by a powder metallurgy process by setting the metal elastic body in the prior art as a metal element, which can avoid the need to process various structures (such as Figure 1 As shown in the figure, there are multiple step surfaces for positioning with other components arranged at the longitudinal proximal end 1a of the tube body near the stopper 13).

[0031] The above-mentioned integrally formed metal matrix 1 can be obtained by mixing raw materials in powder form and then dry pressing, or by dispersing the raw materials in powder form into a slurry with a certain fluidity and then injecting it. The raw materials in powder form at least include metal powder and may also include a binder. When making the slurry, a suitable dispersant may also be added.

[0032] The outer wall of the longitudinal distal end portion 1b of the tube body 11 may be provided with a sealing groove 1c close to the stopper 13, and the sealing groove 1c is used to install a sealing ring (not shown) to ensure that the tube body 11 and the connecting hole of the container are reliably sealed. The outer wall of the longitudinal proximal end portion 1a of the tube body 11 may also be provided with an annular stress isolation groove 1d close to the stopper 13.

[0033] Preferably, an external thread 14 may be provided on the outer wall of the longitudinal distal end portion 1a of the tube body 11, so that the tube body 11 can be connected to the thread of the connecting hole by threaded connection.

[0034] In the above embodiments, the varistor 21 may preferably be a silicon strain gauge, or more preferably, the varistor 21 is a thick film resistor.

[0035] The present embodiment further provides a method for manufacturing a pressure sensitive element 100, which comprises the following steps:

[0036] S1. The raw material including metal powder is subjected to an integral molding method such as dry pressing or injection to obtain a green body of the substrate 1, and the green body is dried and sintered to obtain an integrally molded metal substrate 11. The substrate 1 includes a longitudinally extending tube 11, a pressure-sensitive diaphragm 12 enclosed at the longitudinal proximal end 1a of the tube 11, and a ring of stoppers 13 extending radially outward from the middle of the tube 11. The raw material may also include some toughening agents, such as SiC powder.

[0037] S2, coating a layer of inorganic insulating medium slurry on the surface of the longitudinal proximal end 1a of the pressure-sensitive diaphragm 12, and obtaining an insulating medium layer (not shown) after sintering;

[0038] S3. Coat the surface of the insulating dielectric layer with conductive slurry, and obtain a conductive circuit after sintering.

[0039] S4. Coat the surface of the insulating dielectric layer with thick film slurry, and obtain a thick film resistor after sintering, so that the thick film resistor and the conductive circuit form a pressure measurement circuit.

[0040] Among them, the above-mentioned coating method includes known methods such as screen printing and spray printing. Thick film resistors can be made by advanced thick film processes. Among them, the above-mentioned metal powder can include stainless steel powder, such as atomized 316L stainless steel powder, which can be sintered at a suitable temperature, such as 1050°C to 1450°C. The above-mentioned inorganic insulating medium slurry and its sintering can refer to the disclosure of CN112857635A, and its main oxide composition can be Al2O3-SiO2-CaO, and its sintering temperature can be selected at a suitable temperature, such as 840°C to 860°C.

[0041] When it is necessary to provide an external thread 14 on the outer wall of the longitudinal distal end portion 1b of the tube body 11, the pressure sensitive element 100 can be preferably obtained by injection. Figure 3 As shown, in some other embodiments, it is also feasible to form the above-mentioned pressure sensitive element 100 by dry pressing. In this case, pre-cutting (cutting) can be performed on the threaded portion of the blank to obtain a thread with a better degree of forming to avoid forming difficulties or forming defects.

[0042] like Figure 3 As shown, in some other embodiments, the inorganic insulating medium slurry can also be directly coated on the longitudinal proximal end 1a surface of the pressure-sensitive diaphragm 12 of the unsintered blank 1, and the metal blank 1 and the inorganic insulating medium slurry are sintered in the same sintering process. At this time, the sintering temperature of the inorganic oxide slurry can be appropriately increased and / or the sintering temperature of the stainless steel can be appropriately reduced by known methods, for example, the content of Al2O3 can be appropriately increased and / or a suitable sintering accelerator can be used when sintering the metal substrate 1 to increase the specific surface area of ​​the stainless steel powder.

[0043] More preferably, the manufacturing method may further include a step S5 after step S4, that is, cutting the external thread 14 on the outer wall of the longitudinal distal end portion 1b of the tube body 11 by a mechanical processing method.

[0044] The scope of the disclosure is defined not by the detailed description but by the claims and their equivalents, and all variations within the scope of the claims and their equivalents are construed as being included in the disclosure.

Claims

1. A pressure sensitive element (100), characterized in that: include: An integrally formed metal substrate (1) manufactured by a powder metallurgy process, the substrate (1) comprising a longitudinally extending tube (11), a pressure-sensitive diaphragm (12) sealed at a longitudinal proximal end (1a) of the tube (11), and a ring of stoppers (13) extending radially outward from the middle of the tube (11); and a pressure sensing circuit (2) arranged on the surface of the longitudinal proximal end (1a) of the pressure-sensitive diaphragm (12), which comprises at least one piezoresistor (21).

2. The pressure sensitive element (100) according to claim 1, characterized in that: An external thread (14) is provided on the outer wall of the longitudinal distal end portion (1a) of the tube body (11).

3. The pressure sensitive element (100) according to claim 1, characterized in that: A sealing groove (1c) close to the stopper (13) is provided on the outer wall of the longitudinal distal end portion (1b) of the tube body (11), and the sealing groove (1c) is used for installing a sealing ring.

4. The pressure sensitive element (100) according to claim 1, characterized in that: An annular stress isolation groove (1d) close to the stopper (13) is provided on the outer wall of the longitudinal proximal end portion (1a) of the tube body (11).

5. The pressure sensitive element (100) according to claim 1, characterized in that: The raw material of the powder metallurgy process includes stainless steel powder.

6. The pressure sensitive element (100) according to any one of claims 1 to 4, characterized in that: The varistor (21) is a thick film resistor or a silicon strain gauge.

7. A pressure sensor, characterized in that: The invention comprises a pressure sensitive element (100) according to any one of claims 1 to 6, wherein the longitudinal distal end (1b) of the tube body (11) is connected to a container of a pressure medium to be measured.

8. A method for manufacturing a pressure sensitive element (100), characterized in that: Includes steps: S1. A raw material including metal powder is subjected to dry pressing or injection molding to obtain a blank of the substrate (1), and the blank is dried and then sintered to obtain an integrally formed metal substrate (1) made by a powder metallurgy process; wherein the substrate (1) comprises a longitudinally extending tube (11), a pressure-sensitive diaphragm (12) sealed at the longitudinal proximal end (1a) of the tube (11), and a ring of stoppers (13) extending radially outward from the middle of the tube (11); S2, coating an inorganic insulating medium slurry on the surface of the longitudinal proximal end (1a) of the pressure-sensitive diaphragm (12), and obtaining an insulating medium layer after sintering; S3, coating a conductive paste on the surface of the longitudinal proximal end (1a) of the pressure-sensitive diaphragm (12), and obtaining a conductive circuit after sintering; S4, coating a thick film slurry on the surface of the longitudinal proximal end (1a) of the pressure-sensitive diaphragm (12), and obtaining a thick film resistor after sintering, so that the thick film resistor and the conductive circuit form a pressure measurement circuit.

9. A method for manufacturing a pressure sensitive element (100) according to claim 8, characterized in that: Also includes: An external thread (14) is formed on the outer wall of the longitudinal distal end portion (1b) of the tube body (11) of the green body or the sintered base body by a machining method.

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