阅读说明：本技术 一种电容式压力传感器电极及后端电路封接方法 (Capacitive pressure sensor electrode and back end circuit sealing method ) 是由 乔冠军 王立朋 邵海成 刘桂武 陆浩杰 张相召 于 2021-09-30 设计创作，主要内容包括：本发明涉及传感器领域,尤其涉及一种电容式压力传感器电极及后端电路封接方法。采用陶瓷材料作为基底和敏感膜片,工艺过程包括电极图案制备、陶瓷片清洗、制备金电极、热处理金电极、丝网印刷浆料、封装、加压烧结以及电路连接与信号调理。本发明有效减少边缘效应的非线性问题,具有测量精度高、误差小、测量灵敏度高等特点,而且工艺成本低。(The invention relates to the field of sensors, in particular to a method for sealing an electrode and a back end circuit of a capacitive pressure sensor. The ceramic material is used as a substrate and a sensitive membrane, and the technological process comprises electrode pattern preparation, ceramic wafer cleaning, gold electrode preparation, gold electrode heat treatment, silk screen printing slurry, packaging, pressure sintering, circuit connection and signal conditioning. The invention effectively reduces the non-linear problem of the edge effect, has the characteristics of high measurement precision, small error, high measurement sensitivity and the like, and has low process cost.)

1. A method for sealing an electrode and a back end circuit of a capacitive pressure sensor is characterized by comprising the following specific steps:

the method comprises the following steps: designing electrodes by drawing software, wherein the lower electrode adopts double electrodes with the same coaxial area and comprises a measuring electrode lead, a reference electrode and a measuring electrode, and the reference electrode and the measuring electrode are coaxial and have the same area; the upper electrode adopts a single electrode and comprises an upper electrode and an electrode lead led out from the upper electrode; wherein, the black part is a hollow part, and a mask plate required by the magnetron sputtering process is designed according to the pattern;

step two: polishing, alkali washing, ultrasonic cleaning and drying the ceramic substrate and the ceramic membrane;

step three: placing the dried ceramic substrate and the ceramic membrane into a processed metal mold, then placing a mask, and preparing a gold electrode with uniform adhesion and strong binding force on the polished surfaces of the ceramic membrane and the ceramic substrate by adopting a high-precision magnetron sputtering instrument;

step four: placing the ceramic membrane plated with the gold electrode and the ceramic substrate in the muffle furnace for heat treatment;

step five: placing the ceramic membrane and the ceramic substrate which are subjected to the heat treatment in the step four in a metal mold, printing packaging slurry on the ceramic substrate with the electrode patterns and one surface of the ceramic membrane through a designed printing pattern by using a screen printing machine, and printing the packaging slurry on the ceramic substrate and the ceramic membrane through screen printing meshes;

step six: positioning the ceramic membrane and the ceramic substrate prepared in the fifth step according to the position of the positioning hole;

step seven: preparing a sensor sensitive element by bonding the ceramic membrane positioned in the sixth step and a ceramic substrate through pressurization and sintering;

step eight: designing a circuit and preparing a circuit board to be connected with the sensor sensitive element in the step seven.

2. The method as claimed in claim 1, wherein in the step one, the lower electrode is a dual electrode having the same coaxial area, the reference electrode and the measurement electrode have the same area, and the area of the lower electrode is 28-30mm²(ii) a The area of the upper electrode is 63-65mm²The radius of the upper electrode is designed to be the same as that of the reference electrode of the lower electrode.

3. The method of claim 1, wherein in step two, the ceramic diaphragm and the substrate are polished by a polishing machine, the surface roughness after polishing is 2.5 μm to 2.7 μm, so that the gold electrode is better bonded with the ceramic substrate, and the ratio of the mass ratio of the gold electrode to the substrate is NaOH: the tide laundry detergent is 1:2.5, an alkaline washing solution is prepared for heating alkaline washing, the purpose is to remove oil stains on the surface of the ceramic, finally the ceramic is subjected to alcohol ultrasonic treatment for 30-120min, and the ceramic is dried in an oven at 80-100 ℃ for 2-12 h.

4. The method for sealing an electrode and a back-end circuit of a capacitive pressure sensor according to claim 1, wherein in the third step, a high-precision dual-target magnetron sputtering apparatus is used to sputter a chromium target and a gold target with a purity of 99.99 wt% as electrode preparation materials, and the thickness of the electrode film of the ceramic diaphragm and the ceramic substrate is 250-300 nm.

5. The method as claimed in claim 1, wherein the ceramic diaphragm and the ceramic substrate coated with gold electrode are placed in a muffle furnace and heat treated at 400-600 deg.C for 10-60 min.

6. The method for sealing an electrode and a back-end circuit of a capacitive pressure sensor according to claim 1, wherein in the fifth step, the ceramic diaphragm and the ceramic substrate are packaged by screen printing packaging slurry, and the thickness of the screen printing is controlled by controlling different printing times, wherein the printing times are 1-8 times and the thickness is 10-40 μm; the printed pattern comprises three coaxial circular rings with the diameters of 20mm, 17.5mm and 15mm respectively, a measuring electrode lead hole corresponding to a measuring electrode lead of the lower electrode, a reference electrode lead hole corresponding to an electrode lead of the lower electrode, an upper electrode lead hole corresponding to an electrode lead of the upper electrode and a positioning hole; the aperture of the screen printing mesh is 200 meshes and 300 meshes.

7. The method for sealing an electrode and a back-end circuit of a capacitive pressure sensor according to claim 1, wherein in the sixth step, the ceramic substrate and the ceramic diaphragm are positioned by the positioning holes reserved therein, so as to ensure that the leads of the upper and lower electrodes correspond to the lead holes of the package pattern and the circuit is connected.

8. The method as claimed in claim 1, wherein in step seven, the packaging temperature is designed and the sealing is performed in a muffle furnace at 400-600 ℃ and 3-10kpa for 30-90min to form the sealed sensor.

9. The method as claimed in claim 1, wherein in step eight, a circuit matched with the sensor is designed, the CAV424 chip is used to convert the capacitance signal into a voltage signal, the measurement capacitor CR and the reference capacitor CL of the sensor are respectively connected to an integrator inside the chip, the charging and discharging currents of the measurement capacitor and the reference capacitor are adjusted by a 120k Ω resistor at pin 2 and a 120k Ω resistor at pin 3, the time of the charging and discharging process is determined by the frequency of the oscillator, the frequency of the oscillator is adjusted by a 15pF capacitor at pin 12 and a 120k Ω resistor at pin 1, the zero point and the full scale of the output voltage are adjusted by resistors R1-R5 of the circuit, wherein R3 and R1 are variable resistors, and the output terminal at pin 6 is connected to the single chip microcomputer to display the voltage output.

Technical Field

The invention relates to the field of sensors, in particular to a method for sealing an electrode and a back end circuit of a capacitive pressure sensor.

Background

With the gradual industrialization of the internet of things and intellectualization, the sensor is more and more widely applied to the fields of production, life, scientific research, military and the like. Among other things, the demand for capacitive pressure sensor applications has increased substantially. However, most of the capacitive pressure sensors with advanced technology at present are researched by large foreign companies, the capacitive pressure sensors begin to be early and mature in technology, and few capacitive pressure sensors capable of being produced and applied at present exist in China. Capacitive pressure sensor: the capacitance type pressure sensor based on the current variable-spacing principle has the characteristics of low power consumption, small temperature drift, simple structure and the like, but also has some problems. The first is the problem of leading out the electrodes of the upper and lower electrode plates, and the packaging is difficult and the reliability is poor. The second problem is non-linearity, and the non-linearity between the capacitance value and the pressure to be measured is caused by the edge effect generated by large middle deformation and small edge deformation when the ceramic sensitive membrane and the ceramic substrate are packaged under stress.

Disclosure of Invention

The invention aims to provide a sealing method of a ceramic diaphragm and a ceramic substrate structure, an electrode structure for reducing nonlinear errors, and a sensor electrode structure and a corresponding rear-end conditioning circuit for sealing, so that the nonlinear problem of edge effect is effectively reduced, and the sealing method has the characteristics of high measurement precision, small error, high measurement sensitivity and the like, and is low in process cost.

In order to achieve the purpose, the invention adopts the technical scheme that: a method for sealing an electrode and a back end circuit of a capacitive pressure sensor is characterized by comprising the following steps:

the method comprises the following steps: designing electrodes by drawing software, wherein the lower electrode is coaxial double-electrode with an electrode area of 28-30mm²As shown in fig. 2, the measuring electrode comprises a measuring electrode lead, a reference electrode and a measuring electrode, wherein the reference electrode and the measuring electrode are coaxial, and the area of the upper electrode is 63-65mm²The single electrode comprises an upper electrode and an electrode lead wire led out from the upper electrode, wherein the black part is a hollow part, and a mask plate required by a magnetron sputtering process is designed according to a pattern。

Step two: polishing, alkali washing, ultrasonic cleaning and drying the ceramic substrate and the ceramic membrane.

Step three: and putting the dried ceramic substrate and the ceramic diaphragm into a processed metal mould, then putting a mask, and preparing the gold electrode with uniform adhesion and strong binding force on the polished surfaces of the ceramic diaphragm and the ceramic substrate by adopting a high-precision magnetron sputtering instrument.

Step four: and C, placing the ceramic membrane plated with the gold electrode and the ceramic substrate in the muffle furnace for heat treatment.

Step five: placing the ceramic membrane and the ceramic substrate which are subjected to the heat treatment in the fourth step into a designed metal mold, printing the packaging slurry on one surface of the ceramic substrate with the electrode pattern and one surface of the ceramic membrane through a designed printing pattern by using a screen printer, wherein the printing pattern comprises three coaxial circular rings with the diameters of 20mm, 17.5mm and 15mm respectively, a measuring electrode lead hole corresponding to a measuring electrode lead of a lower electrode in the graph 2, a reference electrode lead hole corresponding to an electrode lead of a lower electrode in the graph 2, an upper electrode lead hole corresponding to an electrode lead of an upper electrode in the graph 3 and a positioning hole as shown in the graph 4, the packaging slurry passes through a screen printing mesh with the aperture of 200-300 meshes in the graph 4, and the packaging slurry pattern is printed on the ceramic substrate and the ceramic membrane.

Step six: and positioning the ceramic diaphragm and the ceramic substrate prepared in the fifth step according to the position of the positioning hole in the figure 4.

Step seven: and (4) bonding the ceramic diaphragm positioned in the sixth step with a ceramic substrate through pressurization and sintering to prepare the sensor sensitive element.

Step eight: designing a circuit as shown in FIG. 5, and preparing a circuit board to connect with the sensor sensitive element in step seven.

The method for sealing the electrode and the back-end circuit of the capacitive pressure sensor is characterized in that in the first step, the lower electrode of the capacitor is designed into two electrodes with the same coaxial area, such as a reference electrode and a measuring electrode shown in fig. 2, so that the edge effect caused by large middle deformation and small edge deformation is reduced, and the upper electrode is designed into a single electrode with the same radius as the reference electrode of the lower electrode, such as shown in fig. 3.

The method for sealing the electrode and the back-end circuit of the capacitive pressure sensor is characterized in that in the second step, a polishing machine is used for polishing the ceramic diaphragm and the substrate, the surface roughness after polishing is 2.5-2.7 microns, so that the gold electrode is better combined with the ceramic substrate, and the mass ratio of NaOH: the tide laundry detergent is 1:2.5, an alkaline washing solution is prepared for heating alkaline washing, the purpose is to remove oil stains on the surface of the ceramic, finally the ceramic is subjected to alcohol ultrasonic treatment for 30-120min, and the ceramic is dried in an oven at 80-100 ℃ for 2-12 h.

The method for sealing the electrode and the back end circuit of the capacitive pressure sensor is characterized in that in the third step, the ceramic substrate and the diaphragm are placed in a processed metal mold, a high-precision double-target magnetron sputtering instrument is used for taking a gold target material with the purity of 99.99 wt% and another chromium target material with the purity of 99.9 wt% as electrode preparation materials, the chromium target material is sputtered firstly, then the gold target material is sputtered, and the thickness of the electrode film of the ceramic diaphragm and the ceramic substrate is 250-300 nm.

The method for sealing the electrode and the back end circuit of the capacitive pressure sensor is characterized in that in the fourth step, the ceramic diaphragm and the ceramic substrate which are plated with the gold electrode are placed in a muffle furnace and are subjected to heat treatment at the temperature of 400-600 ℃ for 10-60 min.

The method for sealing the electrode and the back-end circuit of the capacitive pressure sensor is characterized in that in the fifth step, the ceramic diaphragm and the ceramic substrate are packaged by screen printing packaging slurry, and the thickness of the screen printing is controlled by controlling different printing times, wherein the pattern is shown in figure 4, the printing times are 1-8, and the thickness is 10-40 microns.

The method for sealing the electrode and the back-end circuit of the capacitive pressure sensor is characterized in that in the sixth step, the positioning is carried out through the ceramic substrate and the positioning holes reserved on the ceramic diaphragm, and the leads of the upper electrode and the lower electrode are ensured to correspond to the lead holes of the packaging patterns and to be communicated with the circuit.

The method for sealing the electrode and the back end circuit of the capacitive pressure sensor is characterized in that in the seventh step, the packaging temperature is designed, and the electrode and the back end circuit are sintered for 30-90min at the temperature of 400-600 ℃ and the pressure of 3-10kpa in a muffle furnace to form the sealed sensor sensitive element.

The method for sealing the electrode and the back-end circuit of the capacitive pressure sensor is characterized in that in step eight, a CAV424 chip is adopted to convert a capacitance signal into a voltage signal, a measurement capacitor CR and a reference capacitor CL of the sensor sensing element are respectively connected with an integrator inside the chip, charging and discharging currents of the measurement capacitor and the reference capacitor are adjusted through a 120k omega resistor at a pin 2 and a 120k omega resistor at a pin 3, time of a charging and discharging process is determined by frequency of an oscillator, frequency of the oscillator is adjusted through a 15pF capacitor at a pin 12 and a 120k omega resistor at a pin 1, zero point and full scale of output voltage are adjusted through resistors R1-R5 of the circuit, wherein R3 and R1 are variable resistors, and an output end Vout at a pin 6 is connected with a single chip microcomputer to display voltage output.

Compared with the prior art, the invention has the following advantages:

1. two electrodes of the capacitance pressure sensor are designed based on the performance of a ceramic material and a variable spacing principle, the upper electrode is designed to be a coaxial double electrode, the nonlinear problem caused by edge effect is reduced, the measurement precision is improved, and the error is smaller than 0.3%.

2. The packaging slurry is adopted for packaging at high temperature, so that the bonding strength between the ceramic plates is increased, and the corrosion resistance and the load resistance of the sensitive element are improved.

3. Compared with the traditional circuit, the adjustable circuit is designed, so that the measurement linearity is improved, the circuit is simple, the number of components is small, the adjustability is high, and very complicated steps are not needed in the adjusting process.

Drawings

Fig. 1 is a process flow diagram of a method for sealing an electrode and a back-end circuit of a capacitive pressure sensor according to the present invention.

Fig. 2 is a schematic view of the structure of the lower electrode of the present invention.

Fig. 3 is a schematic view of the upper electrode structure of the present invention.

Fig. 4 is a package pattern of the present invention.

Fig. 5 is a circuit diagram of the present invention.

Fig. 2 includes a measurement electrode lead 1, a reference electrode lead 2, a reference electrode 3, and a measurement electrode 4, fig. 3 includes an electrode lead 5 and an upper electrode 6, fig. 4 includes a measurement electrode lead hole 7, a reference electrode lead hole 8, an upper electrode lead hole 9, a printed pattern 10, and a positioning hole 11, fig. 5 is a schematic circuit diagram, and finally, a PCB is produced.

Detailed Description

Example 1

The method comprises the following steps: and designing electrodes comprising an upper electrode, a lower electrode and a packaging pattern by using drawing software.

Step two: roughly polishing and finely polishing the alumina ceramic substrate and the ceramic membrane on a polishing machine, wherein the roughness of the polished surface is 2.6 mu m, carrying out alkali washing in a prepared solution for 30min, carrying out ultrasonic cleaning with alcohol for 30min, and drying in an oven at 80 ℃ for 12 h.

Step three: a high-precision measurement and control sputtering instrument is used for sputtering 100nm of chromium and 200nm of gold on a ceramic membrane and a substrate at the temperature of 150 ℃.

Step four: and (4) placing the ceramic membrane and the ceramic substrate obtained in the step three in a muffle furnace for heat treatment at 600 ℃ for 20 min.

Step five: and (4) placing the ceramic membrane and the ceramic substrate which are subjected to the heat treatment in the step four in a designed metal mould, and printing the packaging slurry on one surfaces of the ceramic substrate with the electrode pattern and the ceramic membrane through a designed printing pattern by using a screen printer, wherein the printing frequency is 4 times, and the thickness is 20 microns.

Step six: and C, packaging the ceramic membrane printed in the step V and the ceramic substrate, enabling the upper electrode to correspond to the lead hole of the lower electrode, and positioning through the ceramic substrate and a positioning hole reserved on the ceramic membrane to ensure that the leads of the upper electrode and the lower electrode correspond to each other and the circuit is communicated.

Step six: and (4) bonding the ceramic diaphragm prepared in the fifth step and the ceramic substrate into a sensor sensitive element by applying pressure and pressure sintering, wherein the temperature of a muffle furnace is 500 ℃, the pressure is 5kpa, and the sintering time is 60 min.

Step seven: designing a circuit schematic diagram, and preparing a PCB (printed Circuit Board) to be connected with the sensor sensitive element in the fifth step.

The sensor based on the edge effect has the non-linear problem. The invention provides a method for solving the nonlinear problem, which designs two electrodes with equal areas, wherein at a certain temperature, when external pressure acts on a sensor, the deformation of a ceramic diaphragm can enable one of two capacitors formed by the two electrodes on the diaphragm to play a role in correcting a reference capacitor, when a capacitance value changes, a measurable voltage value is obtained by converting a capacitance signal through a rear-end processing circuit according to the two measured capacitance values, and the measurable voltage value is obtained by converting the capacitance signal through the rear-end processing circuit, so that the measurement of the pressure is realized, and the linearity is between 0.3% and 0.5% through a continuous dynamic test.

The foregoing has described the general principles, principal features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are given by way of illustration of the principles of the present invention, and that various changes and modifications may be made without departing from the scope of the invention as claimed.