JP7630671B2 - Pressure Sensors - Google Patents

Description

The present invention relates to a pressure sensor having a sensor chip.

As shown in Patent Document 1, for example, the sensor unit built into the liquid-sealed semiconductor pressure sensor is composed of the following main elements: a metal diaphragm supported in the joint and isolating the pressure detection chamber from a liquid-sealed chamber described later, a liquid-sealed chamber formed above the metal diaphragm and storing silicone oil as a pressure transmission medium, a sensor chip arranged in the liquid-sealed chamber and detecting pressure fluctuations of the silicone oil through the metal diaphragm, a sensor chip mounting member supporting the sensor chip, hermetic glass sealing the periphery of the sensor chip mounting member in the through hole of the housing, a metal potential adjustment member arranged between the sensor chip and the metal diaphragm, and a group of terminals (lead pins) for sending output signals from the sensor chip and supplying power to the sensor chip. The withstand voltage of the internal circuit of the sensor chip of the above-mentioned sensor unit is relatively small, so that the internal circuit of the sensor chip may be damaged due to electrostatic discharge of several (kV) or more through the charged human body of a worker, for example. In such cases, it is effective to improve the dielectric strength by changing the material of the insulator that constitutes the sensor unit, or to ensure a sufficient insulation distance so that no discharge occurs. As a discharge prevention measure for the insulation distance, for example, as described in Patent Document 1, it has been proposed to set the distance between the welded part of the potential adjustment member and the inner circumference of the housing to a predetermined distance or more, or to form the welded part of the potential adjustment member further away from the pressure detection chamber.

JP 2018-179649 A

The discharge prevention measures for the insulation distance described above require the internal volume of the liquid-sealed chamber to be increased in order to ensure a sufficient distance between the welded part of the potential adjustment member and other parts.

However, increasing the internal volume of the liquid-sealed chamber and increasing the amount of silicone oil filled in the chamber reduces the response accuracy (sensitivity) of the pressure sensor, so there is a certain limit to increasing the internal volume of the liquid-sealed chamber and ensuring a sufficient distance between the welded part of the potential adjustment member and other components. Also, when it comes to improving the dielectric strength by changing the material of the insulator, there is a certain limit to changing the material, because if the voltage of static electricity becomes higher, it will eventually discharge. Another problem is that it is not known which of the above-mentioned terminals will generate an arc and be damaged, which means that countermeasures on the sensor chip side will be required over a wide area.

In consideration of the above problems, the present invention aims to provide a pressure sensor having a sensor chip that can significantly reduce the discharge current caused by electrostatic discharge without adversely affecting the internal circuitry of the sensor chip.

The pressure sensor according to the present invention is configured with a sensor unit that includes a conductive housing that supports a metal diaphragm that forms a liquid-sealed chamber in which a sensor chip that is filled with a pressure transmission medium, detects pressure, and sends out a detection output signal is placed, and that supports an input/output terminal group electrically connected to the sensor chip on the inside via an insulating member, a discharge terminal that is formed by bypassing the signal processing electronic circuit of the sensor chip and has a lower breakdown voltage with the conductive housing than the other terminals in the input/output terminal group, and a discharge path that releases static electricity applied between the input/output terminal group and the conductive housing to earth via a discharge section that discharges to the conductive housing.

The discharge terminal may be a ground terminal of the input/output terminal group, or may be a drive voltage terminal of the input/output terminal group. The discharge path may be formed by lowering the breakdown voltage by the insulation distance. In addition, a potential adjustment member may be provided that is disposed between one end face of the sensor chip and the diaphragm in the liquid chamber, blocks the electric field acting on the signal processing electronic circuit of the sensor chip, and is at the same potential as the ground part of the signal processing electronic circuit of the sensor chip.

The discharge portion may be formed between the potential adjustment member and the diaphragm via a pressure transmission medium, or between the conductive housing and a ground terminal disposed inside the conductive housing. Furthermore, the discharge portion may be formed between a protruding portion formed on a portion of the upper end of the conductive housing and the ground terminal, or between the upper end surface of the conductive housing and an extension portion of the ground connection terminal.

In the pressure sensor according to the present invention, a discharge path is formed that bypasses the signal processing electronic circuit of the sensor chip, and the static electricity from the ground terminal constituting part of the input/output terminal group connected to the potential adjustment member or the potential adjustment member is discharged to earth via a discharge section that discharges the static electricity from the potential adjustment member to the conductive housing, thereby making it possible to largely eliminate the discharge current caused by electrostatic discharge so as not to adversely affect the internal circuitry of the sensor chip.

FIG. 2A is a partial cross-sectional view showing a partially enlarged liquid-sealed chamber in a housing in a first embodiment of a pressure sensor according to the present invention, and FIG. 2B is a partially enlarged view of the main part shown in FIG. 1 is a cross-sectional view illustrating a schematic configuration of a pressure sensor according to a first embodiment of the present invention. FIG. 11 is a cross-sectional view showing a housing and an input/output terminal group in a second embodiment of a pressure sensor according to the present invention. 4A is a cross-sectional view showing a housing and an input/output terminal group in a third embodiment of a pressure sensor according to the present invention, and FIG. 4B is a partial cross-sectional view taken along line IVB-IVB in FIG. 4 is a diagram showing a schematic diagram of potential differences in the electric wires, the connection terminals, the terminals, the sensor chip, the potential adjustment member, and the like in the example shown in FIG. 3. 7A is a partial cross-sectional view of a housing and a connection terminal in a fourth embodiment of a pressure sensor according to the present invention, and FIG. 7B is a view seen in the direction indicated by arrow VIB.

FIG. 2 shows a schematic configuration of a first embodiment of a pressure sensor according to the present invention.
In FIG. 2, the pressure sensor includes a coupling member 30 that is connected to a pipe through which a fluid whose pressure is to be detected is guided, and a sensor unit accommodating section that is connected to a base plate 28 of the coupling member 30, accommodates a sensor unit described later, and supplies a detection output signal from the sensor chip to a specified pressure measuring device.

The metal joint member 30 has a female thread 30fs on the inside that screws into the male thread of the connection part of the above-mentioned piping. The female thread 30fs is connected to a port 30a of the joint member 30 that guides the fluid supplied from the direction indicated by the arrow P to a pressure chamber 28A described below. One open end of the port 30a opens toward the pressure chamber 28A formed between the base plate 28 of the joint member 30 and the diaphragm 32 of the sensor unit.

The outer shell of the sensor unit housing is formed by a cylindrical waterproof case 20 that serves as a cover member. The waterproof case 20 has an internal housing space 20A in which the sensor unit and the sealing material 26 that is filled around the sensor unit are disposed.

An opening 20b is formed at the bottom end of the resin waterproof case 20. The peripheral edge of the base plate 28 of the joint member 30 is bonded to the stepped portion on the inner periphery of the opening 20b.

A gas or liquid fluid, or a refrigerant, is supplied to the pressure chamber 28A through the port 30a of the joint member 30. The lower end surface of the sensor unit housing 12 is welded to the periphery of the base plate 28.

The sensor unit detects the pressure in the pressure chamber 28A and sends out a detection output signal. It is mainly composed of the following elements: a cylindrical housing 12, a metal diaphragm 32 that isolates the pressure chamber 28A from the inner circumference of the housing 12, a sensor chip 16 having a pressure detection element, a metal chip mount member 18 that supports one end of the sensor chip 16 via an adhesive layer 50, a group of input/output terminals 40ai (i = 1 to 8) electrically connected to the sensor chip 16, and hermetic glass 14 that fixes the group of input/output terminals 40ai and the oil filling pipe 45 between the outer surface of the chip mount member 18 and the inner surface of the housing 12.

The diaphragm 32 is supported on one of the lower end surfaces of the housing 12 facing the pressure chamber 28A. The diaphragm protective cover 34, which protects the diaphragm 32 disposed in the pressure chamber 28A, has multiple communication holes. The periphery of the diaphragm protective cover 34, together with the periphery of the diaphragm 32, is joined by welding to the lower end surface of the stainless steel housing 12.

The liquid-sealed chamber 13 formed between the metal diaphragm 32 and the end face of the sensor chip 16 and hermetic glass 14 facing it is filled with, for example, a predetermined amount of silicone oil PM as a pressure transmission medium via an oil filling pipe 45. One end of the oil filling pipe 45 is crushed and closed after filling with oil. The silicone oil is, for example, a silicone oil having a dimethylpolysiloxane structure consisting of a siloxane bond and an organic methyl group.

Between the sensor chip 16, which is disposed in a recess formed at the end of the hermetic glass 14, and the diaphragm 32, a metallic potential adjustment member 17 is further supported on the lower end surface of the hermetic glass 14. The potential adjustment member 17 includes a frame and a shield plate, as shown in Japanese Patent No. 3987386, for example, and is connected to a terminal connected to the zero potential of the internal circuit of the sensor chip 16. This provides an EMC (Electromagnetic Compatibility) countermeasure circuit for the sensor chip 16.

The ground potential of the potential adjustment member 17 and the potential of the metal diaphragm 32 and the joint member 30 are normally insulated by silicone oil PM, except in the unlikely event of insulation breakdown due to a discharge phenomenon as described below. In addition, the metal diaphragm 32, the housing 12, and the joint member 30 are electrically connected to a specified earth GND1.

The input/output terminal group 40ai (i = 1 to 8) is arranged at a predetermined interval on a common circumference and consists of one driving voltage terminal (Vcc), one ground terminal (GND), one output terminal (Vout), and five adjustment terminals. Both ends of each terminal protrude toward the recess formed at the end of the above-mentioned hermetic glass 14 and the hole 24b of the terminal block 24 described later. The driving voltage terminal (Vcc), the ground terminal (GND), and the output terminal (Vout) are each connected to the core wire 38a of each lead wire 38 via three metal connection terminals 36. The three connection terminals 36 are provided corresponding to the driving voltage terminal (Vcc), the ground terminal (GND), and the output terminal (Vout). The core wire 38a of the lead wire 38 is connected to each connection terminal 36. The three lead wires 38 are connected to, for example, a specified pressure measuring device. The ground terminal (GND) and the GND lead wire 38 are connected to the ground potential GND2 of a specified internal circuit.

The distance (insulation distance) Da between the shield plate of the potential adjustment member 17 and the diaphragm 32 is set to be a predetermined insulation distance, as shown in FIG. 1B. The minimum insulation distance Da is set, for example, so that static electricity is discharged from the shield plate as the discharge part of the discharge path to the diaphragm 32 through the silicone oil PM under a predetermined withstand voltage. In such a case, if static electricity is discharged from the shield plate to the diaphragm 32, it is considered that most of the discharge current will flow through a part with a locally low impedance. Therefore, since the insulation strength of the above-mentioned hermetic glass 14 and the coating layer 10b described later is stronger than the insulation strength of the potential adjustment member 17, the diaphragm 32, and the housing 12, and the impedance of the diaphragm 32 as the discharge part is low, most of the discharge current caused by the electrostatic discharge is reliably released to the earth GND1 via the diaphragm 32, the housing 12, the base plate 28, and the joint member 30 without flowing into the internal circuit in the sensor chip 16.

Note that in Figures 1 and 2, only four of the eight terminals are shown. The input/output terminal group 40ai is connected to the sensor chip 16, which will be described later, by bonding wires Wi.

The sensor chip 16 has a pressure detection element and is attached, for example, to one end of the chip mount member 18 via an adhesive layer 50.

The terminal block 24 that aligns or surrounds the input/output terminal group 40ai is molded mainly from a resin material, for example, polybutylene terephthalate (PBT). The terminal block 24 has a plurality of holes 24b into which the input/output terminal group 40ai is inserted, and a cavity 24A of a predetermined volume on the inside. The cavity 24A of a predetermined volume is surrounded by the inner peripheral surface of the cylindrical base end of the terminal block 24, the surface of the connecting part 24T that connects the base end facing the upper end surface 14UE of the hermetic glass 14, and the upper end surface 14UE of the hermetic glass 14.

A ring-shaped protrusion protruding toward the hermetic glass 14 is formed on the inner peripheral surface of the connecting portion 24T facing the upper end surface of the hermetic glass 14. The protruding length of the protrusion is set according to the viscosity of the coating layer 10b, which will be described later. By forming the ring-shaped protrusion in this way, when the coating layer 10b is formed, a part of the applied coating layer 10b is pulled and held by surface tension in the narrow space between the protrusion and the inner peripheral surface that forms the cavity 24A of the terminal block 24 and is approximately perpendicular to the upper end surface of the hermetic glass 14, so that the coating layer 10b is applied evenly without being biased to one side in the cavity 24A of the terminal block 24.

The position of the annular intersection line where the lower end surface of the base end of the terminal block 24 intersects with the inner peripheral surface of the base end is located closer to the input/output terminal group 40ai than the inner peripheral surface of the housing 12.

The bottom end surface 24TS of the base end of the terminal block 24, which serves as the adhesive surface, is adhered to the top end surface 12TS of the housing 12, which serves as the adherend surface, with a silicone adhesive. This results in an annular adhesive layer 10a having a predetermined thickness being formed on the top end surface 12TS of the housing 12.

A coating layer 10b made of a silicone adhesive is formed to a predetermined thickness on the entire upper end surface of the hermetic glass 14 from which the input/output terminal group 40ai protrudes. The silicone adhesive is the same as the silicone adhesive that forms the adhesive layer 10a described above. The thickness of the coating layer 10b gradually increases compared to the thickness around the input/output terminal group 40ai as it moves away from the periphery of the input/output terminal group 40ai and approaches the inner peripheral surface of the base end. An air layer is formed in the cavity 24A above the coating layer 10b.

A predetermined amount of sealant 26 is filled between the outer peripheral surface of the terminal block 24, the outer peripheral surface of the end cap 22 that is connected to the terminal block 24 and covers the hole 24b of the connecting portion 24T and the upper opening end of the terminal block 24, and the inner peripheral surface of the waterproof case 20, and also between the inner peripheral surface of the waterproof case 20 and the outer peripheral surface of the housing 12. The terminal block 24 and the end cap 22 are arranged in the waterproof case 20 facing the base plate 28 of the joint member 30 with the sensor unit in between.

The upper end surface of the end cap 22 protrudes upward from the open end of the waterproof case 20. In other words, the position of the upper end surface of the end cap 22 is higher than the position of the open end surface of the waterproof case 20.

Figure 3 shows the main parts of a second embodiment of the pressure sensor according to the present invention.

In the example shown in Fig. 1 and Fig. 2, the diameter of the ground terminal (GND) constituting part of the input/output terminal group 40ai is set to be the same as the diameter of the other terminals, but in the example shown in Fig. 3, the diameter R1 of the ground terminal 40'ai (GND) is set to be larger than the diameter R2 of the other terminals. Note that the example shown in Fig. 3 also includes the same components as the other components of the pressure sensor shown in Fig. 2, although they are not shown.

In FIG. 3, the input/output terminal group is arranged at predetermined intervals on a common circumference and is composed of one drive voltage terminal 40ai (Vcc), one ground terminal 40'ai (GND), one output terminal 40ai (Vout), and five adjustment terminals 40ai.
As a result, the mutual distance L1 between the inner circumferential surface of the housing 12 and the ground terminal 40'ai (GND) serving as a discharge terminal is smaller than the mutual distance L2 between the inner circumferential surface of the housing 12 and the other terminals 40ai.

Therefore, if a discharge current of electrostatic discharge flows through the ground terminal 40'ai (GND), for the reasons described below, the discharge current caused by the electrostatic discharge does not pass through the internal circuit of the sensor chip 16, but is released through the discharge part of the ground terminal 40'ai (GND) as a discharge terminal, the hermetic glass 14, the housing 12, the joint member 30, and the earth GND 1. Note that FIG. 5 shows a schematic diagram of the potential difference in the electric wire 38, the connection terminal 36, the terminals 40ai, 40'ai, the sensor chip 16, the potential adjustment member 17, etc.

5, the potential difference (Va1) between each electric wire 38 and the internal circuit of the sensor chip 16 is maximum, the potential difference (Va2) between the connection terminal 36 is slightly smaller than the potential difference (Va1) between each electric wire 38 and the internal circuit of the sensor chip 16, and the potential difference Va4 between the shield plate of the potential adjustment member 17 is even smaller than the potential difference (Va2) between the connection terminal 36. The potential difference (Va3) between the ground terminal 40'ai (GND), the other drive voltage terminal 40ai (Vcc), the output terminal 40ai (Vout), and the five adjustment terminals 40ai are the same. However, the potential difference Va3' between the discharge portion formed between the ground terminal 40'ai (GND) facing the inner circumferential surface of the housing 12 at a mutual distance L1 and the inner circumferential surface of the housing 12 is minimum. Therefore, the discharge current caused by electrostatic discharge does not pass through the internal circuitry of the sensor chip 16, but is instead discharged via the discharge part of the discharge path, which is a location with low impedance.

However, without being limited to this example, for example, the drive voltage terminal (Vcc) may be configured as a discharge terminal.

Figures 4(A) and (B) show the main parts of a third embodiment of the pressure sensor according to the present invention.

In the example shown in Fig. 3, the diameter of the ground terminal 40'ai (GND) is set larger than the diameter of the other terminals so that the mutual distance L1 between the inner peripheral surface of the housing 12 and the ground terminal 40'ai (GND) is smaller than the mutual distance L2 between the inner peripheral surface of the housing 12 and the other terminals 40ai, while in the example shown in Fig. 4 (A), the protruding portion 12'P as a discharge portion is formed on a part of the upper end of the inner peripheral portion of the housing 12' facing the ground terminal 40ai (GND). The arc-shaped protruding portion 12'P is radially spaced a predetermined distance from the central axis C of the housing 12' and protrudes a predetermined amount from the inner peripheral surface of the housing 12' toward the ground terminal 40ai (GND) as a discharge terminal. As a result, the mutual distance L1 between the protruding portion 12'P of the housing 12 and the ground terminal 40ai (GND) is smaller than the mutual distance L2 between the inner peripheral surface of the housing 12 and the other terminals 40ai. Therefore, if a discharge current due to electrostatic discharge flows through the ground terminal 40ai (GND), the discharge current caused by static electricity is released through the housing 12', the joint member 30, and the earth GND1 via the ground terminal 40ai (GND), the protruding portion 12'P, and the hermetic glass 14 without passing through the internal circuit of the sensor chip 16.

The example shown in FIG. 4(A) also includes components that are the same as the other components of the pressure sensor shown in FIG. 2, although these are not shown.

Figures 6(A) and (B) show the main parts of a fourth embodiment of the pressure sensor according to the present invention.

In the example shown in Figs. 4(A) and (B), the protruding portion 12'P as the discharge portion of the discharge path is formed on a part of the upper end of the inner periphery of the housing 12' facing the ground terminal 40ai (GND), while in the example shown in Figs. 6(A) and (B), the ground connection terminal 46 has a terminal portion 46Gb connected to the ground terminal 40ai (GND) and an extension portion 46Ga protruding toward the upper end surface of the housing 12. Note that the example shown in Fig. 6 also has the same components as the other components of the pressure sensor shown in Fig. 2, although they are not shown. In Fig. 6(A), the same components as those in the example shown in Fig. 2 are given the same reference numerals, and a duplicate description will be omitted.

The drive voltage terminal (Vcc), ground terminal (GND), and output terminal (Vout), which constitute part of the input/output terminal group, are connected to the core wire 38a of each lead wire 38 via two metal connection terminals 36 (not shown) and one ground connection terminal 46. The three lead wires 38 are connected to, for example, a predetermined pressure measuring device. The ground connection terminal 46 and the GND lead wire 38 are connected to the ground potential GND2 of a predetermined internal circuit.

The lower end of the extension portion 46Ga of the ground connection terminal 46, which is formed as a discharge portion between the ground connection terminal 46 and the housing 12, is separated by a predetermined distance L from the upper end surface of the housing 12. The predetermined distance L is set to an extent that ensures dielectric strength and insulation resistance.

Even in this configuration, if a discharge current due to electrostatic discharge flows through the ground terminal 40ai (GND), most of the discharge current due to electrostatic discharge does not pass through the internal circuitry of the sensor chip 16, but is released through the ground terminal 40ai (GND) and the extension portion 46Ga of the ground connection terminal 46, which serves as the discharge portion of the discharge path, through the housing 12, the joint member 30, and the earth GND1.

Therefore, in each of the above-mentioned embodiments, as shown in FIG. 5, by lowering the dielectric strength of only one terminal (ground terminal), it is possible to limit the circuits that require static electricity countermeasures, localize the countermeasures on the sensor chip 16 side, improve the resistance, and reduce the size. Also, by making that one terminal a GND terminal, it can be used as an electrostatic countermeasure circuit between the GND terminal and other terminals, and can be shared with other EMC countermeasure circuits, improving the resistance and reducing the size and cost.

In the above-mentioned example of the pressure sensor, the sensor unit is connected to a predetermined pressure measuring device by each lead wire 38 and a connection terminal, but this is not limited to the example. For example, the sensor unit may be configured to be connected to a predetermined pressure measuring device by a detachable male connector, a female connector, and a contact terminal.

Reference Signs List 12 Housing 12'P Projection 13 Liquid-sealed chamber 14 Hermetic glass 16 Sensor chip 17 Potential adjustment member 30 Joint member 32 Diaphragm 36, 46 Connection terminal 40ai Input/output terminal group 40ai (GND) Ground terminal 40'ai (GND) Ground terminal 46Ga Extension GND1 Earth

Claims (3)

a sensor unit including a conductive housing supporting a metal diaphragm that forms a liquid-sealed chamber in which a pressure transmission medium is filled and in which a sensor chip for detecting pressure is disposed, and supporting, via an insulating member, a group of input/output terminals electrically connected to the sensor chip;
the input/output terminal group includes a discharge terminal,
a discharge path that allows static electricity applied between the input/output terminal group and the conductive housing to escape to earth via a discharge portion that discharges static electricity to the conductive housing, so as to bypass the sensor chip;
Equipped with
a potential adjusting member that is disposed between one end face of the sensor chip and the diaphragm in the liquid-sealed chamber, blocks an electric field acting on the sensor chip, and has the same potential as a ground portion of the sensor chip ;
A pressure sensor characterized in that the discharge terminal is electrically connected to the potential adjustment member, and the discharge portion is formed between the potential adjustment member and the diaphragm via the pressure transmission medium . 2. The pressure sensor according to claim 1, wherein the discharge terminal is a ground terminal of the input/output terminal group. 2. The pressure sensor according to claim 1, wherein the discharge terminal is a drive voltage terminal among the group of input/output terminals.

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