A pressure sensor based on 3D printing and screen printing and its manufacturing method

Abstract

A pressure sensor based on 3D printing and screen printing and a manufacturing method thereof, the pressure sensor comprising: an annular groove formed on a sensitive film, the annular groove evenly connecting four short straight grooves, the four short straight grooves and the annular groove forming a stress concentration area; the sensitive film deforms in response to changes in air pressure, the short straight groove closest to the center of the circle has the maximum absolute value of strain, the piezoresistor at this position produces a resistance change, and a Wheatstone bridge outputs the resistance change through voltage, completing the conversion from pressure to voltage signal and realizing pressure measurement; the manufacturing method comprises: printing out and constructing the overall structure of the pressure sensor, cleaning and curing it, printing the piezoresistor on the upper surface of the short straight groove at the corresponding position, placing the overall structure of the pressure sensor in a dryer, completely curing the piezoresistor and leads, and the five leads of the cured overall structure of the pressure sensor leading to five circular contacts, which are externally connected to five wires; the present invention has the advantages of low cost and rapid manufacturing.

Description

Technical Field

[0001] The present invention relates to the field of sensor technology, and in particular to a pressure sensor based on 3D printing and screen printing and a manufacturing method thereof. Background Art

[0002] A pressure sensor is a sensor used to measure the pressure of liquids or gases. With the rapid development of the Internet of Things and Industry 4.0, sensors have become a research hotspot. Pressure sensors are currently one of the most widely used sensors and can be categorized by sensing mechanism into strain gauge, piezoresistive, capacitive, piezoelectric, and frequency-frequency pressure sensors. Traditional pressure sensors are primarily manufactured using MEMS technology. The sensitive element of a MEMS pressure sensor is an elastic film. When the diaphragm is subjected to pressure, it deforms. Using a piezoresistive effect, the pressure is converted into a change in its resistance to achieve pressure measurement. Although pressure sensors produced using this manufacturing technology offer excellent performance and are compact, the R&D cycle for MEMS pressure sensors generally takes 6-10 years and requires investments exceeding 100 million yuan. These sensors have disadvantages such as long R&D time, high manufacturing costs, and difficulty in processing complex structures to meet customized requirements.

[0003] Patent application number [CN202010240016.5], entitled "Pressure Sensor and Method of Manufacturing Pressure Sensor," provides a pressure sensor for determining the pressure of a fluid and a method for manufacturing the same. An exemplary pressure sensor includes a pressure sensor housing that is sealingly attached to a diaphragm at a first end. A pin header includes a lip configured to engageably mate with a second end of the pressure sensor housing to form an airtightly sealed component compartment. The pin header also includes pin header pins configured to transmit electrical signals between the interior and exterior of the airtightly sealed component compartment. A sensing element and a processor are disposed within the airtightly sealed component compartment and are in communication with each other. The sensing element is mounted to the processor within the airtightly sealed compartment, and a corresponding manufacturing method is also provided. However, due to the use of multiple processing techniques, the manufacturing process is relatively complex, and the sensor's integrity is poor. Therefore, this patent application suffers from the disadvantages of high cost, poor integrity, and a complex manufacturing process for the pressure sensor. Summary of the Invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a pressure sensor based on 3D printing and screen printing and a manufacturing method thereof. By combining 3D printing and screen printing technology, the advantages of low cost, high sensitivity and rapid integrated manufacturing of the pressure sensor are achieved.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A pressure sensor based on 3D printing and screen printing includes a shell 8, a sensitive film 3 is arranged inside the shell 8, an annular groove 4 is opened on the sensitive film 3, and the annular groove 4 is evenly connected with four short straight grooves 2. The four short straight grooves 2 and the annular groove 4 form a stress concentration area.

[0007] Four varistors are arranged at the intersection of the four short straight slots 2 and one annular slot 4, namely resistor R1, resistor R2, resistor R3 and resistor R4. Resistor R1 is connected to the endpoints of the first lead 6-1 and the fifth lead 6-5, the middle end of the first lead 6-1 and one end of the second lead 6-2 are connected to resistor R3, the other end of the second lead 6-2 and the endpoint of the third lead 6-3 are connected to resistor R4, and the middle end of the fifth lead 6-5 and the endpoint of the fourth lead 6-4 are connected to resistor R2; the connection method adopts pre-termination.

[0008] The housing 8 and the sensitive film 3 are both integrally formed by 3D printing.

[0009] One end of the housing 8 is provided with a mounting interface 5 , which is in communication with the air inlet 7 of the housing 8 .

[0010] The resistors R1, R2, R3 and R4 are made of conductive carbon paste and form a Wheatstone bridge circuit.

[0011] The shell 8 and the sensitive film 3 are both made of resin High Temp V2.

[0012] A method for manufacturing a pressure sensor based on 3D printing and screen printing comprises the following steps:

[0013] Step 1: Build the overall structure of the pressure sensor using 3D design software, and print the built pressure sensor overall structure using a light-curing 3D printer; the printing conditions are: printing resolution 20-50um;

[0014] Step 2: Clean the pressure sensor structure printed in step 1 with alcohol or isopropyl alcohol, and place the cleaned pressure sensor structure in a curing machine for curing for 15-30 minutes.

[0015] Step 3: Use a screen printer to print the conductive silver paste through the designed lead pattern onto the upper surface of the annular groove 4 at the corresponding position of the overall structure of the pressure sensor after curing in step 2;

[0016] Step 4: Use a screen printer to pass the conductive carbon paste through the designed piezoresistive pattern to print resistors R1, R2, R3, and R4 onto the upper surface of the short straight slot 2 at the corresponding position of the overall structure of the pressure sensor containing the lead pattern produced in step 3;

[0017] Step 5: Place the pressure sensor structure containing the lead pattern and the piezoresistor pattern prepared in step 4 into a dryer, heat to 130-150 degrees Celsius and bake for 20-30 minutes to completely solidify the piezoresistor and the lead, and then take it out and cool it to room temperature.

[0018] Step 6: The five leads of the solidified overall structure of the pressure sensor containing the lead pattern and the piezoresistor pattern produced in step 5 are led out to five circular contacts, and the five circular contacts are externally connected to five wires.

[0019] The lead pattern designed in step 3 is designed in the following steps:

[0020] Four varistors are arranged at the intersection of four short straight slots 2 and one annular slot 4, namely resistor R1, resistor R2, resistor R3 and resistor R4. Resistor R1 is connected to the endpoints of the first lead 6-1 and the fifth lead 6-5, the middle end of the first lead 6-1 and one end of the second lead 6-2 are connected to resistor R3, the other end of the second lead 6-2 and the endpoint of the third lead 6-3 are connected to resistor R4, and the middle end of the fifth lead 6-5 and the endpoint of the fourth lead 6-4 are connected to resistor R2; the connection method adopts pre-termination.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. By providing radial short straight grooves 2 and annular grooves 4 on the outside of the sensitive film 3, the maximum stress at the edge of the sensitive film 3 is increased without affecting the strength of the sensitive film 3, while also maintaining the feasibility of subsequent screen printing.

[0023] 2. In view of the special structure of four short straight grooves 2 and one annular groove 4, combined with the piezoresistive effect of the varistor, a corresponding varistor structure is designed to enable the varistor to fully exert the piezoresistive effect. The resistors are arranged in the maximum stress area, that is, the center of the intersection of the short straight groove 2 and the annular groove 4, and are all arranged radially. The leads are arranged along the annular groove 4, which can maximize the change in the resistance value of the varistor and has the characteristics of high sensitivity coefficient.

[0024] 3. The varistor is made of conductive carbon paste, which has a piezoresistive effect. The resistor printed with the conductive carbon paste is deformed by tension under the action of pressure, which reduces the volume fraction of carbon black in the carbon paste-based resistor, thereby increasing the resistance of the carbon paste-based resistor and having a high sensitivity coefficient.

[0025] 4. The present invention combines 3D printing and screen printing to produce a pressure sensor, thus having the characteristics of low manufacturing cost, high degree of integration, and rapid manufacturing.

[0026] 5. Since the present invention adopts a pre-terminated connection method to connect the resistor and the lead, it has the characteristic of high resistance performance stability.

[0027] In summary, the combined design of four straight grooves and annular grooves improves the sensor performance while avoiding the problem of pressure sensor failure caused by the sensitive film 3 being too thin. In addition, by combining 3D printing and screen printing technology, compared with the existing technology, the pressure sensor has the characteristics of low cost, high sensitivity, and rapid integrated manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0029] Figure 2 It is a schematic diagram of the internal structure of the present invention.

[0030] Figure 3 Schematic diagram of the Wheatstone bridge used for measurement in the present invention.

[0031] Among them, 1 is a fixing hole, 2 is a short straight groove, 3 is a sensitive film, 4 is an annular groove, 5 is a mounting interface, 6-1 is the first lead, 6-2 is the second lead, 6-3 is the third lead, 6-4 is the fourth lead, 6-5 is the fifth lead, 7 is the air inlet, and 8 is the shell. DETAILED DESCRIPTION

[0032] The structural principle and working principle of the present invention are further described in detail below with reference to the accompanying drawings.

[0033] See also Figure 1 A pressure sensor based on 3D printing and screen printing includes a shell 8 of the pressure sensor formed in one piece by 3D printing. A sensitive film 3 is provided inside the shell 8. The sensitive film 3 has an annular groove 4, and four short straight grooves 2 are evenly connected on the annular groove 4. The four short straight grooves 2 and the annular groove 4 form a stress concentration area. The air inlet 7 of the shell 8 is connected to the mounting interface 5. The mounting interface 5 is designed to be frustum-conical for easy connection to the device under test. Two fixing holes 1 are provided at the other end of the shell 8 to realize the positioning and installation of the sensor.

[0034] See also Figure 2Four varistors are arranged at the intersection of the four short straight grooves 2 and the annular groove 4, namely resistor R1, resistor R2, resistor R3 and resistor R4. Resistor R1 is connected to the end points of the first lead 6-1 and the fifth lead 6-5, the middle end of the first lead 6-1 and one end of the second lead 6-2 are connected to resistor R3, the other end of the second lead 6-2 and the end point of the third lead 6-3 are connected to resistor R4, and the middle end of the fifth lead 6-5 and the end point of the fourth lead 6-4 are connected to resistor R2; the connection method adopts pre-termination; the connection method adopts pre-termination, and the pre-termination is to first print the Wheatstone bridge lead on the sensitive film 3 of the sensor, and then print the varistor after low-temperature thermal curing. The two ends of the resistor are connected across the lead, and finally the varistor is thermally cured at low temperature to complete the connection between the resistor and the bridge.

[0035] The material of the wire is conductive silver paste.

[0036] The resistors R1, R2, R3 and R4 are made of conductive carbon paste and form a Wheatstone bridge circuit.

[0037] The working principle of the present invention is:

[0038] When the sensitive film 3 of the pressure sensor is deformed by changes in air pressure, the maximum absolute value of the strain appears at the short straight groove 2 closest to the center of the circle. The piezoresistor printed on the surface at this position will produce a change in resistance according to the strain, and the magnitude of the resistance change increases with the increase of strain. The resistance change is output as a voltage through the Wheatstone bridge, completing the conversion from pressure to voltage signal and realizing the measurement of pressure.

[0039] See also Figure 3 The Wheatstone bridge consists of four bridge arm resistors R1 to R4, which can convert the resistance change of the varistor into a voltage output, which is convenient for the back-end signal processing. When the ammeter shows that there is no current passing through, the bridge is in a balanced state, that is, R1·R2=R3·R4.

[0040] Example 1:

[0041] A method for manufacturing a pressure sensor based on 3D printing and screen printing comprises the following steps:

[0042] Step 1: Use the 3D design software SolidWorks to build the overall structure of the pressure sensor, and use a light-curing 3D printer Form3 to print the built overall structure of the pressure sensor. The main structural material of the pressure sensor is high-temperature resistant HighTempV2; the printing resolution is 20μm;

[0043] Build the overall structure of the pressure sensor, including the sensitive film 3. The following conditions must be met to manufacture the sensitive film 3:

[0044] According to the polar coordinates (r,θ), the stress σ of the sensitive film 3 r expression:

[0045]

[0046] Where: E represents the tensile elastic modulus of the thin plate material; μ represents the Poisson's ratio of the thin plate material; w(x, y) represents the deflection curve, z represents the distance from the neutral plane, and r represents the distance from the center of the circle;

[0047] Step 2: Clean the pressure sensor structure printed in step 1 with alcohol to remove the resin in the cavity inside the sensor. Place the cleaned pressure sensor structure in a curing machine and cure it for 15 minutes.

[0048] Step 3: Use a screen printer to print the conductive silver paste through the designed lead pattern onto the upper surface of the annular groove 4 at the corresponding position of the overall structure of the pressure sensor after curing in step 2;

[0049] The process of designing the designed lead pattern is specifically as follows: four varistors, namely resistor R1, resistor R2, resistor R3 and resistor R4, are arranged at the intersection of four short straight grooves 2 and an annular groove 4, respectively. Resistor R1 is connected to the endpoints of the first lead 6-1 and the fifth lead 6-5, the middle end of the first lead 6-1 and one end of the second lead 6-2 are connected to resistor R3, the other end of the second lead 6-2 and the endpoint of the third lead 6-3 are connected to resistor R4, and the middle end of the fifth lead 6-5 and the endpoint of the fourth lead 6-4 are connected to resistor R2; the connection method adopts pre-termination, which is to first print Wheatstone bridge leads on the sensitive film 3 of the sensor, and then print varistors after low-temperature thermal curing. The two ends of the resistors are connected across the leads, and finally the varistors are thermally cured at low temperatures to complete the connection between the resistors and the bridges;

[0050] Step 4: Use a screen printer to pass the conductive carbon paste through the designed piezoresistive pattern to print resistors R1, R2, R3, and R4 onto the upper surface of the short straight slot 2 at the corresponding position of the overall structure of the pressure sensor containing the lead pattern produced in step 3;

[0051] Step 5: Place the pressure sensor structure containing the lead pattern and the piezoresistor pattern produced in step 4 into a dryer, heat it to 130 degrees and bake it for 20 minutes to completely solidify the piezoresistor and the lead, then take it out and cool it to room temperature;

[0052] Step 6: Lead the five leads of the pressure sensor overall structure containing the lead pattern and the piezoresistor pattern after solidification produced in step 5 to five circular contacts, and connect the five circular contacts to five external wires.

[0053] Example 2:

[0054] A method for manufacturing a pressure sensor based on 3D printing and screen printing comprises the following steps:

[0055] Step 1: Use the 3D design software SolidWorks to build the overall structure of the pressure sensor, and use the light-curing 3D printer Form3 to print the built overall structure of the pressure sensor. The main structural material of the pressure sensor is high-temperature resistant HighTempV2; the printing resolution is 30μm;

[0056] Build the overall structure of the pressure sensor, including the sensitive film 3. The following conditions must be met to manufacture the sensitive film 3:

[0057] According to the polar coordinates (r,θ), the stress σ of the sensitive film 3 r expression:

[0058]

[0059] Where: E represents the tensile elastic modulus of the thin plate material; μ represents the Poisson's ratio of the thin plate material; w(x, y) represents the deflection curve, z represents the distance from the neutral plane, and r represents the distance from the center of the circle;

[0060] Step 2: Clean the pressure sensor structure printed in step 1 with alcohol to remove the resin in the internal cavity of the sensor. Place the cleaned pressure sensor structure in a curing machine and cure it for 30 minutes.

[0061] Step 3: Use a screen printer to print the conductive silver paste through the designed lead pattern onto the upper surface of the annular groove 4 at the corresponding position of the overall structure of the pressure sensor after curing in step 2;

[0062] The process of designing the designed lead pattern is specifically as follows: four varistors are arranged at the intersection of four short straight grooves 2 and one annular groove 4, namely resistor R1, resistor R2, resistor R3 and resistor R4, respectively; resistor R1 is connected to the endpoints of the first lead 6-1 and the fifth lead 6-5; resistor R3 is connected between the middle end of the first lead 6-1 and one end of the second lead 6-2; resistor R4 is connected between the other end of the second lead 6-2 and the endpoint of the third lead 6-3; resistor R2 is connected between the middle end of the fifth lead 6-5 and the endpoint of the fourth lead 6-4; the connection method adopts pre-termination, which is to first print Wheatstone bridge leads on the sensitive film 3 of the sensor, and then print varistors after low-temperature thermal curing, and the two ends of the resistors are connected across the leads; finally, the varistors are thermally cured at low temperatures to complete the connection between the resistors and the bridge;

[0063] Step 4: Use a screen printer to pass the conductive carbon paste through the designed piezoresistive pattern to print resistors R1, R2, R3, and R4 onto the upper surface of the short straight slot 2 at the corresponding position of the overall structure of the pressure sensor containing the lead pattern produced in step 3;

[0064] Step 5: Place the pressure sensor structure containing the lead pattern and the piezoresistor pattern produced in step 4 into a dryer, heat it to 140 degrees Celsius and bake it for 30 minutes to completely solidify the piezoresistor and the lead, and then take it out and cool it to room temperature;

[0065] Step 6: Lead the five leads of the pressure sensor overall structure containing the lead pattern and the piezoresistor pattern after solidification produced in step 5 to five circular contacts, and connect the five circular contacts to five external wires.

[0066] Example 3:

[0067] A method for manufacturing a pressure sensor based on 3D printing and screen printing comprises the following steps:

[0068] Step 1: Use the 3D design software SolidWorks to build the overall structure of the pressure sensor, and use a light-curing 3D printer Form3 to print the built overall structure of the pressure sensor. The main structural material of the pressure sensor is high-temperature resistant HighTempV2; the printing resolution is 50μm;

[0069] Build the overall structure of the pressure sensor, including the sensitive film 3. The following conditions must be met to manufacture the sensitive film 3:

[0070] According to the polar coordinates (r,θ), the stress σ of the sensitive film 3 r expression:

[0071]

[0072] Where: E represents the tensile elastic modulus of the thin plate material; μ represents the Poisson's ratio of the thin plate material; w(x, y) represents the deflection curve, z represents the distance from the neutral plane, and r represents the distance from the center of the circle;

[0073] Step 2: Clean the entire pressure sensor structure printed in step 1 with isopropyl alcohol to remove the resin in the internal cavity of the sensor, and place it in a curing machine for curing for 20 minutes;

[0074] Step 3: Use a screen printer to print the conductive silver paste through the designed lead pattern onto the upper surface of the annular groove 4 at the corresponding position of the overall structure of the pressure sensor after curing in step 2;

[0075] The process of designing the designed lead pattern is specifically as follows: four varistors, namely resistor R1, resistor R2, resistor R3 and resistor R4, are arranged at the intersection of four short straight grooves 2 and an annular groove 4, respectively. Resistor R1 is connected to the endpoints of the first lead 6-1 and the fifth lead 6-5, the middle end of the first lead 6-1 and one end of the second lead 6-2 are connected to resistor R3, the other end of the second lead 6-2 and the endpoint of the third lead 6-3 are connected to resistor R4, and the middle end of the fifth lead 6-5 and the endpoint of the fourth lead 6-4 are connected to resistor R2; the connection method adopts pre-termination, which is to first print Wheatstone bridge leads on the sensitive film 3 of the sensor, and then print varistors after low-temperature thermal curing. The two ends of the resistors are connected across the leads, and finally the varistors are thermally cured at low temperatures to complete the connection between the resistors and the bridges;

[0076] Step 4: Use a screen printer to pass the conductive carbon paste through the designed piezoresistive pattern to print resistors R1, R2, R3, and R4 onto the upper surface of the short straight slot 2 at the corresponding position of the overall structure of the pressure sensor containing the lead pattern produced in step 3;

[0077] Step 5: Place the pressure sensor structure including the lead pattern and the piezoresistor pattern prepared in step 4 into a dryer, heat to 150 degrees Celsius and bake for 15 minutes to completely solidify the piezoresistor and the lead, then take it out and cool it to room temperature.

[0078] Step 6: Lead the five leads of the pressure sensor overall structure containing the lead pattern and the piezoresistor pattern after solidification produced in step 5 to five circular contacts, and connect the five circular contacts to five external wires.

[0079] The pressure sensor was tested. Table 1 shows the test data of the output voltage corresponding to the measured gas pressure.

[0080] Table 1 is the pressure sensor test data

[0081]

[0082]

[0083] From the test results, it can be seen that in the first cycle, the second cycle, and the third cycle, the loading output pressure and the unloading output pressure are almost the same, which shows that the sensor can better reflect the output characteristic curve of the sensor.

[0084] In summary, the combined design of four straight grooves and annular grooves improves the sensor performance while avoiding the problem of pressure sensor failure caused by the sensitive film 3 being too thin. In addition, by combining 3D printing and screen printing technology, the advantages of low cost, high sensitivity, and rapid integrated manufacturing of the pressure sensor are achieved compared with the existing technology.

[0085] Those skilled in the art will appreciate that the above-mentioned embodiments are specific examples for implementing the present invention, and that in actual applications, various changes may be made thereto in form and detail without departing from the spirit and scope of the present invention.

Claims

1. A pressure sensor based on 3D printing and screen printing, comprising a housing (8), characterized in that: A sensitive film (3) is provided inside the housing (8), an annular groove (4) is formed on the sensitive film (3), and the annular groove (4) is evenly connected with four short straight grooves (2). The four short straight grooves (2) and the annular groove (4) form a stress concentration area. Four piezoresistors are arranged at the intersections of the four short straight slots (2) and the one annular slot (4), namely resistor R1, resistor R2, resistor R3 and resistor R4. Resistor R1 is connected to the endpoints of the first lead (6-1) and the fifth lead (6-5). Resistor R3 is connected between the middle end of the first lead (6-1) and one end of the second lead (6-2). Resistor R4 is connected between the other end of the second lead (6-2) and the endpoint of the third lead (6-3). Resistor R2 is connected between the middle end of the fifth lead (6-5) and the endpoint of the fourth lead (6-4). The connection method adopts pre-termination.

2. A pressure sensor based on 3D printing and screen printing according to claim 1, characterized in that: The housing (8) and the sensitive film (3) are both integrally formed by 3D printing.

3. The pressure sensor based on 3D printing and screen printing according to claim 1, characterized in that: One end of the housing (8) is provided with a mounting interface (5), and the mounting interface (5) is connected to the air inlet (7) of the housing (8).

4. The pressure sensor based on 3D printing and screen printing according to claim 1, characterized in that: The resistors R1, R2, R3 and R4 are made of conductive carbon paste and form a Wheatstone bridge circuit.

5. The pressure sensor based on 3D printing and screen printing according to claim 1, characterized in that: The shell (8) and the sensitive film (3) are both made of resin High Temp V2.

6. The method for manufacturing a pressure sensor based on 3D printing and screen printing according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1: Build the overall structure of the pressure sensor using 3D design software, and print the built overall structure of the pressure sensor using a light-curing 3D printer; Printing resolution is 20-50um; Step 2: Clean the pressure sensor structure printed in step 1 with alcohol or isopropyl alcohol, and place the cleaned pressure sensor structure in a curing machine for curing for 15-30 minutes. Step 3, using a screen printer to print the conductive silver paste through the designed lead pattern onto the upper surface of the annular groove (4) at the corresponding position of the overall structure of the pressure sensor after curing in step 2; Step 4, using a screen printer to pass the conductive carbon paste through the designed piezoresistive pattern, printing resistors R1, R2, R3, and R4 onto the upper surface of the short straight grooves (2) at corresponding positions of the overall structure of the pressure sensor containing the lead pattern produced in step 3; Step 5: Place the pressure sensor structure containing the lead pattern and the piezoresistor pattern prepared in step 4 into a dryer, heat to 130-150 degrees Celsius and bake for 20-30 minutes to completely solidify the piezoresistor and the lead, and then take it out and cool it to room temperature. Step 6: Lead the five leads of the pressure sensor overall structure containing the lead pattern and the piezoresistor pattern after solidification produced in step 5 to five circular contacts, and connect the five circular contacts to five external wires.

7. The method for manufacturing a pressure sensor based on 3D printing and screen printing according to claim 6, characterized in that: The lead pattern designed in step 3 is designed in the following steps: Four piezoresistors are arranged at the intersections of the four short straight slots (2) and the one annular slot (4), namely resistor R1, resistor R2, resistor R3 and resistor R4. Resistor R1 is connected to the endpoints of the first lead (6-1) and the fifth lead (6-5). Resistor R3 is connected between the middle end of the first lead (6-1) and one end of the second lead (6-2). Resistor R4 is connected between the other end of the second lead (6-2) and the endpoint of the third lead (6-3). Resistor R2 is connected between the middle end of the fifth lead (6-5) and the endpoint of the fourth lead (6-4). The connection method adopts pre-termination.

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