Integrated chip, thick film pressure sensor and manufacturing method thereof

Abstract

The present invention provides an integrated chip, a thick-film pressure sensor, and a manufacturing method thereof. The integrated chip for the thick-film pressure sensor includes an elastic metal diaphragm and a conductive circuit. The elastic metal diaphragm has a deformation area for sensing pressure and a connection area connected to the deformation area. The conductive circuit includes a plurality of piezoresistors and thermistors. The plurality of piezoresistors are arranged on the upper surface of the elastic metal diaphragm and in the deformation area. The thermistor is arranged on the upper surface of the elastic metal diaphragm and in the connection area.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of thick film pressure sensors, and in particular to an integrated chip, a thick film pressure sensor and a manufacturing method thereof. Background Art

[0002] A thick-film pressure sensor is a device or apparatus that senses pressure signals and converts them into a usable electrical output signal according to a specific pattern. Conventional technology requires that a thick-film pressure sensor also sense temperature, but a separate temperature chip is typically integrated into the sensor. This increases the complexity of the packaging process and reduces environmental adaptability. Summary of the Invention

[0003] The purpose of the embodiments of the present invention is to provide an integrated chip, a thick-film pressure sensor and a manufacturing method thereof, aiming to solve the problem in the prior art that the temperature chip and the pressure chip are separately set in the thick-film pressure sensor, resulting in a complex packaging process and poor adaptability to the environment.

[0004] To solve the above technical problems, an embodiment of the present invention provides an integrated chip for a thick film pressure sensor, comprising:

[0005] an elastic metal diaphragm having a deformation region for sensing pressure and a connection region connected to the deformation region;

[0006] The conductive circuit includes a plurality of varistors and thermistors. The plurality of varistors are arranged on the upper surface of the elastic metal diaphragm and in the deformation zone. The thermistor is arranged on the upper surface of the elastic metal diaphragm and in the connection zone.

[0007] The present invention integrates a varistor and a thermistor on an elastic metal diaphragm, which can sense temperature and pressure at the same time, reduces the packaging process, and makes the integrated chip more adaptable to the environment. By arranging the varistor in the connection area of ​​the elastic metal diaphragm, the integrated chip can be prevented from being squeezed due to long-term pressure sensing, which affects the reliability of the varistor.

[0008] Preferably, in the integrated chip for the thick film pressure sensor, the plurality of piezoresistors are four, including a first piezoresistor, a second piezoresistor, a third piezoresistor, and a fourth piezoresistor, respectively, and the first piezoresistor, the second piezoresistor, the third piezoresistor, and the fourth piezoresistor are sequentially connected end to end in series to form a closed loop;

[0009] A first end of the thermistor is connected to a first end of the first varistor, and the other end is used to connect to a pad.

[0010] Preferably, in the integrated chip for the thick film pressure sensor, the first piezoresistor, the second piezoresistor, the third piezoresistor and the fourth piezoresistor form a Wheatstone bridge;

[0011] The first piezoresistor and the third piezoresistor are arranged at a middle position of the deformation zone, and the second piezoresistor and the fourth piezoresistor are arranged at an edge position of the deformation zone.

[0012] Preferably, the thickness of the elastic metal diaphragm is determined according to the pressure range and force analysis, and the determination process is as follows:

[0013] (1) Analysis of small deformation stress of elastic metal diaphragm

[0014] According to the small deformation theory, when the elastic metal diaphragm is under pressure, the maximum displacement of the elastic metal diaphragm does not exceed 30% of the thickness of the elastic metal diaphragm, that is:

[0015] y0≤0.3h; (1)

[0016] Under the action of uniform pressure P, the displacement of the circular elastic metal diaphragm 1 is as follows:

[0017]

[0018] Just like the displacement of a pressurized diaphragm, the stress distribution inside the metal diaphragm also changes with the thickness h of the diaphragm and the distance r from the center of the diaphragm. At a given distance r, one side of the diaphragm is subjected to tensile stress and the other side is subjected to compressive stress. At the same time, there are two stresses inside the diaphragm, namely the tangential stress σ t and radial stress σ r :

[0019]

[0020]

[0021] When the radial stress is zero:

[0022] r=a((1+v)(3+v)) 1 / 2 ; (5)

[0023] The shear stress at a distance r from the center of the diaphragm is:

[0024]

[0025]

[0026] (2) Relationship between displacement and pressure of elastic metal diaphragm 1

[0027] When the maximum displacement of the elastic metal diaphragm 1 under the pressure P is greater than 30% of the thickness of the elastic metal diaphragm 1, assuming that the elastic metal diaphragm 1 is still within the elastic range, the relationship between the pressure P and the displacement y of the elastic metal diaphragm 1 is as follows:

[0028]

[0029] Where E is the Young's modulus of the diaphragm material;

[0030] ν is the Poisson's ratio of the elastic metal diaphragm;

[0031] a is the radius of the elastic metal diaphragm;

[0032] h is the thickness of the elastic metal diaphragm;

[0033] r is the distance from the center of the diaphragm;

[0034] y0 is the maximum displacement of the elastic metal diaphragm;

[0035] σ t is the tangential stress inside the elastic metal diaphragm;

[0036] σ r is the radial stress inside the elastic metal diaphragm;

[0037] P is the pressure on the elastic metal diaphragm.

[0038] Based on the same inventive concept, the present invention also provides a thick film pressure sensor, comprising the above-mentioned integrated chip.

[0039] Preferably, the thick film pressure sensor further comprises a pressure connector, which is integrally provided with the elastic metal diaphragm of the integrated chip, and a stress isolation groove is formed between the pressure connector and the elastic metal diaphragm.

[0040] Preferably, in the thick film pressure sensor, the stress isolation groove is arranged in a ring shape and the diameter of the inner ring is D, 9.3 mm≤D≤9.6 mm.

[0041] Preferably, in the thick film pressure sensor, D is 9.5 mm.

[0042] Based on the same inventive concept, the present invention also provides a method for manufacturing the above-mentioned thick film pressure sensor, comprising sequentially screen printing a dielectric layer, screen printing a conductor, screen printing a varistor and a thermistor, and screen printing an encapsulation glaze on the elastic metal diaphragm.

[0043] Preferably, in the method for manufacturing the thick film pressure sensor, the screen printing of the dielectric layer includes the following steps:

[0044] Pretreatment of elastic metal diaphragm;

[0045] Performing dielectric slurry printing, deposition, leveling, and drying on the pretreated elastic metal diaphragm, wherein the dielectric slurry comprises Al2O3-SiO2-CaO;

[0046] The dried elastic metal diaphragm is sintered at a sintering temperature raised from room temperature to a preset sintering temperature, and maintained at the preset sintering temperature for 10 minutes to 12 minutes, wherein the preset sintering temperature is T, 840°C ≤ T ≤ 860°C, to form a dielectric layer;

[0047] And / or, the conductor screen printing includes:

[0048] Screen printing a conductor material on the dielectric layer, wherein the conductor material is palladium silver material;

[0049] Level the conductor paste after screen printing, eliminate the mesh pattern, and dry it;

[0050] The dried conductor is sintered at a sintering temperature of 850°C-860°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] One or more embodiments are exemplarily illustrated by pictures in the corresponding drawings. These exemplifications do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings are represented as similar elements. Unless otherwise stated, the figures in the drawings do not constitute proportional limitations.

[0052] Figure 1 A three-dimensional diagram of a portion of the structure of the thick film pressure sensor provided by the present invention;

[0053] Figure 2 for Figure 1 Top view in

[0054] Figure 3 for Figure 1 The main view;

[0055] Figure 4a This is a stress distribution diagram of the elastic metal diaphragm when the pressure load is 220MPa;

[0056] Figure 4b The stress distribution diagram of the elastic metal diaphragm in the X direction when the pressure load is 220MPa;

[0057] Figure 4c This is a stress distribution diagram of the elastic metal diaphragm under a pressure load of 400 MPa;

[0058] Figure 5 A flow chart of a method for manufacturing a thick film pressure sensor provided by an embodiment of the present invention;

[0059] Figure 6 This is a diagram showing the result of sintering the slurry and the elastic metal diaphragm provided in one embodiment of the present invention;

[0060] Figure 7 for Figure 6 The result diagram after sectioning.

[0061] Description of the accompanying drawings of the present invention:

[0062] Label name Label name 1 Elastic metal diaphragm 233 The third pad 11 deformation zone 234 Fourth pad 12 Connection Area 235 Fifth pad 2 Conductive circuit 3 Pressure connector 21 Varistor 31 Stress isolation groove 211 First varistor 4 dielectric layer 212 Second varistor 41 First dielectric layer 213 The third varistor 42 Second dielectric layer 214 Fourth varistor 43 The third dielectric layer 22 Thermistor 5 conductor 231 First pad 6 Encapsulated glaze 232 Second pad

[0063] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0064] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0065] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indications will also change accordingly.

[0066] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features specified as "first" and "second" may explicitly or implicitly include at least one of such features. In addition, the technical solutions between the various embodiments can be combined with each other, but this must be based on the fact that ordinary technicians in this field can implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0067] The present invention discloses an integrated chip for thick film pressure sensor. Figures 1 to 3The integrated chip for the thick film pressure sensor includes an elastic metal diaphragm 1 and a conductive circuit 2. The elastic metal diaphragm 1 has a deformation area 11 for sensing pressure and a connection area 12 connected to the deformation area 11. The conductive circuit 2 includes a plurality of piezoresistors 21 and a thermistor 22. The plurality of piezoresistors 21 are arranged on the upper surface of the elastic metal diaphragm 1 and are arranged in the deformation area 11. The thermistor 22 is arranged on the upper surface of the elastic metal diaphragm 1 and is arranged in the connection area 12.

[0068] The present invention integrates the varistor 21 and the thermistor 22 on the elastic metal diaphragm 1, thereby being able to sense temperature and pressure simultaneously, reducing the packaging process, and making the integrated chip more adaptable to the environment. By arranging the varistor 21 in the connection area 12 of the elastic metal diaphragm 1 (in this embodiment, the connection area 12 is the area on the elastic metal diaphragm 1 excluding the deformation area 11), the integrated chip can be prevented from being squeezed due to long-term pressure perception, thereby affecting the reliability of the varistor 21.

[0069] Furthermore, by integrating the varistor 21 and the thermistor 22 on the elastic metal diaphragm, the difficulties caused by the separate setting of the temperature sensor in the packaging are eliminated. Taking the integrated chip provided by the present invention in the packaging as an example, the protection effect can be achieved directly by coating the surface with a protective gel; while in the prior art, when the temperature sensor is set separately, factors such as the sensing medium are usually considered, and the pins connecting the pressure chip and the temperature sensor also need to consider issues such as the sealing between the pins and the substrate. When the substrate is a ceramic substrate, ceramic metallization and other technologies are also needed to ensure the sealing between the pins and the ceramic, which is costly, complex in process, and the separate setting of the temperature sensor increases the overall size.

[0070] Specifically, there are four varistors 21, namely a first varistor 211, a second varistor 212, a third varistor 213 and a fourth varistor 214. The first varistor 211, the second varistor 212, the third varistor 213 and the fourth varistor 214 are connected in series end to end to form a closed loop; the first end of the thermistor 22 is connected to the first end of the first varistor 211, and the other end is used to connect the pad. That is, the second end of the first varistor 211 is connected to the first end of the second varistor 212, the second end of the second varistor 212 is connected to the first end of the third varistor 213, the second end of the third varistor 213 is connected to the first end of the fourth varistor 214, and the second end of the fourth varistor 214 is connected to the first end of the first varistor 211. The first end of the thermistor 22 can be connected to the first end of the first varistor 211, or to the first end of the second varistor 212, or to the first end of the third varistor 213 or the fourth varistor 214. No specific restrictions are made here.

[0071] Furthermore, the first varistor 211, the second varistor 212, the third varistor 213 and the fourth varistor 214 form a Wheatstone bridge; the first varistor 211 and the third varistor 213 are arranged in the middle position of the deformation zone 11, and the second varistor 212 and the fourth varistor 214 are arranged at the edge position of the deformation zone 11. Both ends of each varistor are connected to pads interconnected with an external circuit, and also include a first pad 231, a second pad 232, a third pad 233, a fourth pad 234 and a fifth pad 235. The first pad 231 is connected to the first end of the first varistor 211 or the second end of the fourth varistor 214, the second pad 232 is connected to the second end of the first varistor 211 or the first end of the second varistor 212, the third pad 233 is connected to the second end of the second varistor 212 or the first end of the third varistor 213, the fourth pad 234 is connected to the second end of the third varistor 213 or the first end of the fourth varistor 214, and the fifth pad 235 is connected to the second end of the thermistor 22.

[0072] Because under the action of the pressure load, the pressure distribution on the surface of the elastic metal diaphragm 1 is as follows: the maximum tensile stress can be obtained in the middle area of ​​the elastic metal diaphragm 1 (i.e., the middle area of ​​the deformation zone 11), and the maximum compressive strain can be obtained in the edge area of ​​the deformation zone 11 of the elastic metal diaphragm 1. Unlike the anisotropic properties of semiconductor materials, the elastic metal diaphragm 1 (especially 17-4PH stainless steel treated with H900) exhibits isotropic behavior. Therefore, by arranging the first piezoresistor 211 and the third piezoresistor 213 in the middle position of the deformation zone 11 and the second piezoresistor 212 and the fourth piezoresistor 214 at the edge positions of the deformation zone 11, maximum sensitivity can be achieved; further, the first piezoresistor 211 and the third piezoresistor 213 are symmetrically arranged along the center of the deformation zone, and the second piezoresistor 212 and the fourth piezoresistor 214 are symmetrically arranged along the center of the deformation zone.

[0073] The elastic metal diaphragm 1 is the primary form factor of the sensor element. Pressure applied to one (or both) sides of the elastic metal diaphragm 1 causes the diaphragm to deflect until the elastic force balances the pressure. The material selection for the elastic metal diaphragm 1 is particularly important, especially for thick-film pressure sensors with high pressure ranges. Typically, ceramic materials are used for the thick-film piezoresistive effect. However, ceramic materials are inherently brittle and unsuitable for processing and welding during the packaging process, making them unsuitable for high-range thick-film pressure sensors. Compatible austenitic 304 and ferritic 430 stainless steels lack sufficient strength and are therefore unsuitable for high-range thick-film pressure sensors. Therefore, in this embodiment, the elastic metal diaphragm 1 is made of 17-4PH stainless steel treated with H900 (precipitation hardening at 900°F). A dielectric layer 4 is provided between the elastic metal diaphragm 1 and the conductive circuit 2. The yield strength of the stainless steel after such heat treatment is as high as 1379 MPa. Other materials may also be used. In this embodiment, the elastic metal diaphragm 1 is circular.

[0074] The thickness of the elastic metal diaphragm 1 also has a certain impact on its mechanical properties. Typically, at small deflections (<10% of the diaphragm thickness), the pressure-deflection relationship is linear. As pressure increases, the deflection rate and the pressure-deflection reduction relationship become nonlinear. A 12% deflection rate and a 0.2% thickness elastic metal diaphragm 1 will produce a nonlinearity, and so on. The suitability of the deflection range will depend on the required sensor specifications and the degree of compensation acceptable.

[0075] The surface of the elastic metal diaphragm 1 remains moderately flat and of uniform thickness. The material of the elastic metal diaphragm 1 is homogeneous and isotropic. The direction of pressure applied to the elastic metal diaphragm 1 is consistent with the normal direction of the metal diaphragm. The deformation of the elastic metal diaphragm 1 does not exceed the elastic range of the material. The thickness of the elastic metal diaphragm 1 cannot exceed 20% of the diaphragm diameter. The stress in the normal direction of the elastic metal diaphragm 1 is negligible. The thickness of the elastic metal diaphragm 1 is determined based on the pressure range and force analysis. The determination process is as follows:

[0076] (1) Analysis of the small deformation stress of the elastic metal diaphragm 1

[0077] According to the small deformation theory, when the elastic metal diaphragm 1 is under pressure, the maximum displacement of the elastic metal diaphragm 1 does not exceed 30% of the thickness of the elastic metal diaphragm 1, that is:

[0078] y0≤0.3h; (1)

[0079] Under the action of uniform pressure P, the displacement of the circular elastic metal diaphragm 1 is as follows:

[0080]

[0081] Just like the displacement of a pressurized diaphragm, the stress distribution inside the metal diaphragm also changes with the thickness h of the diaphragm and the distance r from the center of the diaphragm. At a given distance r, one side of the diaphragm is subjected to tensile stress and the other side is subjected to compressive stress. At the same time, there are two stresses inside the diaphragm, namely the tangential stress σ t and radial stress σ r .

[0082]

[0083]

[0084] When the radial stress is zero:

[0085] r=a((1+v)(3+v)) 1 / 2 ; (5)

[0086] The shear stress at a distance r from the center of the diaphragm is:

[0087]

[0088]

[0089] (2) Relationship between displacement and pressure of elastic metal diaphragm 1

[0090] When the maximum displacement of the elastic metal diaphragm 1 under the pressure P is greater than 30% of the thickness of the elastic metal diaphragm 1, assuming that the elastic metal diaphragm 1 is still within the elastic range, the relationship between the pressure P and the displacement y of the elastic metal diaphragm 1 is as follows:

[0091]

[0092] Where E is the Young's modulus of the diaphragm material;

[0093] ν is the Poisson's ratio of the elastic metal diaphragm;

[0094] a is the radius of the elastic metal diaphragm;

[0095] h is the thickness of the elastic metal diaphragm;

[0096] r is the distance from the center of the diaphragm;

[0097] y0 is the maximum displacement of the elastic metal diaphragm;

[0098] σ t is the tangential stress inside the elastic metal diaphragm;

[0099] σ r is the radial stress inside the elastic metal diaphragm;

[0100] P is the pressure on the elastic metal diaphragm.

[0101] The thickness of the elastic metal diaphragm 1 is determined based on the actual operating pressure range of the elastic metal diaphragm 1 and the above formula. High-range thick-film pressure sensors are commonly used in common rail injection systems for gasoline and diesel vehicles, as well as brake hydraulic pressure sensing in ESP systems. Gasoline common rail thick-film pressure sensors typically have an operating pressure range of 20 MPa and a burst pressure of up to 40 MPa. Diesel common rail thick-film pressure sensors have an operating range of up to 280 MPa and a burst strength of 400 MPa. Therefore, in this embodiment, the thickness of the elastic metal diaphragm 1 is 0.8 mm to 1.1 mm. Preferably, the thickness of the elastic metal diaphragm 1 is 0.8 mm, 0.9 mm, or 1 mm.

[0102] The following simulation is conducted for 17-4PH stainless steel treated with H900, with a working range pressure of 220MPa and a burst pressure of 400MPa. The thickness of the elastic metal diaphragm 1 is set to 1mm, the Young's modulus is 1.97e11Pa, the Poisson's ratio is 0.272, the material yield strength is 1379MPa, and the material ultimate strength is 1448MPa. See the figure, the simulation results are as follows: Figures 4a to 4c As shown in Figure 2, the maximum stress on the diaphragm under the uniform load of 220 MPa is 641.4 MPa. Figure 4a and 4b ; The maximum stress borne by the diaphragm under the bursting pressure mode is 1166 MPa, and the elastic metal diaphragm 1 has not entered the plastic deformation stage.

[0103] The present invention also provides a thick film pressure sensor, which includes the above-mentioned integrated chip.

[0104] The thick-film pressure sensor also includes a pressure connector 3, which is integrally integrated with the integrated chip's elastic metal diaphragm 1 and has a stress isolation groove 31 formed between the connector and the elastic metal diaphragm 1. By integrating the elastic metal diaphragm 1 and the pressure connector 3, the number of soldering steps required during the packaging process is significantly reduced. Furthermore, since the pressure connector 3 is susceptible to assembly stress during installation, which can cause product output drift after assembly, the stress isolation groove 31 provided between the elastic metal diaphragm 1 and the pressure connector 3 effectively achieves this stress isolation effect.

[0105] In addition, the size of the stress isolation groove 31 has a significant impact on the stress distribution on the surface of the elastic metal diaphragm 1. If the diameter of the stress isolation groove 31 is too large or too small, it will cause the output of the thick-film pressure sensor to drift, resulting in output instability and other problems. In this embodiment, the stress isolation groove 31 is arranged in an annular shape, and the inner ring diameter is D, 9.3mm≤D≤9.6mm. In this way, the stress generated by the piezoresistors on the elastic metal diaphragm 1 remains balanced, the Wheatstone bridge circuit is in a balanced state, and the output of the thick-film pressure sensor can remain relatively stable. Preferably, D is 9.3mm, 9.4mm, 9.49mm, 9.5mm, 9.55mm, or 9.6mm.

[0106] The present invention also provides a method for manufacturing the thick film pressure sensor. Figure 5 The manufacturing method of the thick film pressure sensor includes screen printing a dielectric layer, screen printing a conductor 5, screen printing a piezoresistor and a thermistor 22, and screen printing an encapsulating glaze 6 on the elastic metal diaphragm 1 in sequence.

[0107] The elastic metal diaphragm 1 is made of 17-4PH stainless steel treated with H900 (precipitation hardening treatment at 900°F).

[0108] In this embodiment, the dielectric layer screen printing includes screen printing of the first dielectric layer 41 , screen printing of the second dielectric layer 42 , and screen printing of the third dielectric layer 43 .

[0109] Specifically, the dielectric layer screen printing includes the following steps:

[0110] Step S710: pre-treating the elastic metal diaphragm 1;

[0111] In a specific implementation, the pretreatment of the elastic metal diaphragm 1 includes removing impurities and organic pollutants on the surface of the elastic metal diaphragm 1 .

[0112] Specifically, an ultrasonic cleaning machine and an ethanol organic solvent are used for cleaning, and then a plasma cleaning machine is used to activate the metal surface.

[0113] Step S720: performing dielectric slurry printing, deposition, leveling, and drying on the pre-treated elastic metal diaphragm 1, wherein the dielectric slurry includes Al2O3-SiO2-CaO;

[0114] A dielectric layer is formed between the elastic metal diaphragm 1 and the conductive circuit 2 to provide insulation and be compatible with both the elastic metal diaphragm 1 and the varistor / thermistor 22. In this embodiment, the dielectric slurry comprises Al2O3-SiO2-CaO, whose thermal expansion coefficient lies between that of the elastic metal diaphragm 1 and the varistor / thermistor 22. This provides a good transition effect, minimizing resistance drift caused by thermal expansion coefficient mismatch between the varistor / thermistor 22 and the elastic metal diaphragm 1, which can lead to cracks or even resistor shedding during high-temperature sintering and cooling.

[0115] Specifically, after the dielectric slurry is coated on the elastic metal diaphragm 1 , it is leveled for 10 minutes and then dried at 150° C. for 10 minutes.

[0116] Step S730: The dried elastic metal diaphragm 1 is sintered at a sintering temperature raised from room temperature to a preset sintering temperature, and maintained at the preset sintering temperature for 10 minutes to 12 minutes (in this embodiment, the holding time can be 11 minutes), wherein the preset sintering temperature is T, 840℃≤T≤860℃, to form a dielectric layer.

[0117] Specifically, the dried elastic metal diaphragm 1 is placed in a sintering furnace (usually a box-type sintering furnace), and the temperature of the sintering furnace is slowly raised from room temperature (i.e., normal temperature) to 850°C and maintained at 850°C for 10 minutes to allow the slurry to solidify. The temperature is then slowly lowered to 100°C. The results after sintering the slurry and the elastic metal diaphragm 1 (17-4PH stainless steel treated with H900) are as follows: Figure 6 As shown, the matching is good, the membrane layer is dense and complete. After repeated sintering, there is no crack on the surface of the layer, the dielectric layer is well bonded to the surface of the elastic metal diaphragm 1, and the dielectric layer does not fall off under temperature shock. Figure 7 The dielectric layer and the elastic metal diaphragm 1 after sectioning are shown. The dielectric layer after sintering is sectioned and the sectioned surface is polished with metallographic sandpaper to observe the bonding interface between the dielectric layer and the metal substrate. Figure 7 As shown in the figure, the bonding interface after sintering ( Figure 7 The position indicated by the arrow in the middle) is dense and has no holes.

[0118] The conductor 5 screen printing includes:

[0119] Step S810: screen printing a conductor 5 material on the dielectric layer, wherein the conductor 5 material is palladium silver material;

[0120] Conductor 5 is made of palladium-silver material. Silver ions in the silver conductor are prone to migration under the action of potential difference, leading to resistance or interconnect solder joint reliability problems. Adding a small amount of rare metal palladium can effectively prevent the silver ion migration problem.

[0121] Step S820: leveling the conductor 5 slurry after screen printing, eliminating the mesh pattern, and drying;

[0122] Step S830: the conductor 5 after drying is sintered at a sintering temperature of 850° C. to 860° C. (in this embodiment, the sintering temperature may be 855° C. or 860° C.).

[0123] The process of screen printing the varistor and thermistor 22 is similar to the process of screen printing the conductor 5 .

[0124] In addition, the entire upper surface is covered with a layer of encapsulating glaze 6, which is completed by high-temperature sintering at 400°C-500°C.

[0125] In this embodiment, the sintering temperature may be 420°C, 430°C, 440°C, or 450°C.

[0126] The above are only preferred embodiments of the present invention and are not intended to limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's description and drawings, or direct / indirect applications in other related technical fields, within the scope of the present invention are included in the patent protection scope of the present invention.

Claims

1. An integrated chip for a thick film pressure sensor, characterized in that: include: an elastic metal diaphragm having a deformation region for sensing pressure and a connection region connected to the deformation region; a conductive circuit comprising a plurality of varistors and thermistors, wherein the plurality of varistors are disposed on the upper surface of the elastic metal diaphragm and in the deformation zone, and the thermistor is disposed on the upper surface of the elastic metal diaphragm and in the connection zone; The thickness of the elastic metal diaphragm is determined according to the pressure range and force analysis, and the determination process is as follows: (1) Analysis of small deformation stress of elastic metal diaphragm According to the small deformation theory, when the elastic metal diaphragm is under pressure, the maximum displacement of the elastic metal diaphragm does not exceed 30% of the thickness of the elastic metal diaphragm, that is: y0≤0.3h; (1) Under the action of uniform pressure P, the displacement of the circular elastic metal diaphragm is as follows: Just like the displacement change of the pressurized diaphragm, the stress distribution inside the metal diaphragm also changes with the thickness h of the diaphragm and the distance r from the center of the diaphragm. At a given distance r, one side of the diaphragm is subjected to tensile stress and the other side is subjected to compressive stress. At the same time, there are two kinds of stress inside the diaphragm, namely radial stress σ r and its maximum value σ rmax for: When the radial stress is zero: r=a((1+v)(3+v)) 1 / 2 ; (5) Tangential stress σt and radial stress σr: The tangential stress σ at a distance r from the center of the diaphragm t and its maximum value σ tmax for: (2) Relationship between displacement and pressure of elastic metal diaphragm When the maximum displacement of the elastic metal diaphragm under pressure P is greater than 30% of the thickness of the elastic metal diaphragm, assuming that the elastic metal diaphragm is still within the elastic range, the relationship between pressure P and displacement y of the elastic metal diaphragm is as follows:

2. The integrated chip for thick film pressure sensor according to claim 1, characterized in that: The plurality of varistors are four, including a first varistor, a second varistor, a third varistor and a fourth varistor, respectively. The first varistor, the second varistor, the third varistor and the fourth varistor are connected in series end to end to form a closed loop; the first end of the thermistor is connected to the first end of the first varistor, and the other end is used to connect to the pad.

3. The integrated chip for thick film pressure sensor according to claim 2, characterized in that: The first varistor, the second varistor, the third varistor and the fourth varistor form a Wheatstone bridge; The first piezoresistor and the third piezoresistor are arranged at a middle position of the deformation zone, and the second piezoresistor and the fourth piezoresistor are arranged at an edge position of the deformation zone.

4. A thick film pressure sensor, characterized in that: The integrated chip comprises the integrated chip according to any one of claims 1 to 3.

5. The thick film pressure sensor according to claim 4, wherein: It also includes a pressure connector, which is integrally arranged with the elastic metal diaphragm of the integrated chip, and a stress isolation groove is formed between the pressure connector and the elastic metal diaphragm.

6. The thick film pressure sensor according to claim 5, wherein: The stress isolation groove is arranged in a ring shape, and the diameter of the inner ring is D, 9.3mm≤D≤9.6mm.

7. The thick film pressure sensor according to claim 6, wherein: D is 9.5mm.

8. A method for manufacturing a thick film pressure sensor according to any one of claims 1 to 7, characterized in that: The method includes screen printing the dielectric layer, the conductor, the varistor and thermistor, and the encapsulation glaze on the elastic metal diaphragm in sequence.

9. The method for manufacturing a thick film pressure sensor according to claim 8, wherein: The dielectric layer screen printing comprises the following steps: Pretreatment of elastic metal diaphragm; Performing dielectric slurry printing, deposition, leveling, and drying on the pretreated elastic metal diaphragm, wherein the dielectric slurry comprises Al2O3-SiO2-CaO; The dried elastic metal diaphragm is sintered at a sintering temperature raised from room temperature to a preset sintering temperature, and maintained at the preset sintering temperature for 10 minutes to 12 minutes, wherein the preset sintering temperature is T, 840°C ≤ T ≤ 860°C, to form a dielectric layer; And / or, the conductor screen printing includes: Screen printing a conductor material on the dielectric layer, wherein the conductor material is palladium silver material; Level the conductor paste after screen printing, eliminate the mesh pattern, and dry it; The dried conductor is sintered at a sintering temperature of 850°C-860°C.

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