JP2001272292A - Pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the displacement of a chip when rotating around a rotary shaft of a screw-coupling from affecting workability in succeeding assembly, related to a pressure sensor where a stem comprising a diaphragm to which a chip for detecting a pressure is fixed is screw-coupled to a housing for pressure guidance. SOLUTION: A surface orthogonal to the rotary shaft of a screw-coupling in a stem 10 screw-coupled to a housing 30 is configured as a diaphragm for detecting a pressure, and a chip 40 of square plate is fixed on the diaphragm. The chip 40 comprises a bridge circuit 41 which converts a change in the resistance value corresponding to deformation of the diaphragm into an electric signal, and pads P1-P4 for a bridge circuit connected to a circuit board 60 using a bonding wire 64. The pads P1-P4 are repeatedly provided in a specified order around the rotary shaft of the screw-coupling at the peripheral part of the chip 40.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor in which a stem having a diaphragm on which pressure detecting means is formed is screw-connected to a housing capable of introducing pressure, and more particularly to detecting a high pressure of about 200 MPa. It is suitable to be used for

[0002]

2. Description of the Related Art As a pressure sensor of this type, the present applicant has proposed a pressure sensor described in Japanese Patent Application No. 11-82180. FIG. 5 shows a schematic cross section of a pressure sensor prototyped by the present inventors based on this prior application. This is, for example, a fuel injection system of an automobile (for example, common rail).
) Can be applied to a high pressure detection sensor for detecting a high pressure (fuel pressure) in the fuel pipe.

In FIG. 5, J1 is a hollow cylindrical metal stem having a thin diaphragm J2 as a closing part at one end of a shaft and an opening J3 at the other end of the shaft. This stem J1 has a sensor chip (detection means) J4 for pressure detection glass-bonded on a diaphragm J2, and an opening J3 is formed in a pressure introduction hole (pressure introduction passage) of a housing J5.
It is fixed to the housing J5 by a screw member J7 so as to communicate with J6. Thus, the end of the opening J3 of the stem J1 is pressed and sealed by the opening edge of the pressure introducing hole J6, so that airtightness is maintained even when a high pressure is introduced.

Here, a sensor chip J as a detecting means is used.
Reference numeral 4 has a bridge circuit (not shown) for converting a resistance change according to the deformation of the diaphragm J2 due to the pressure introduced from the pressure introduction hole J6 into an electric signal.
A circuit board J8 provided around the chip J4 in the housing J5 is connected to and electrically connected to a bonding wire J9 such as Al (aluminum).

In this sensor, the diaphragm J2 is deformed by the pressure introduced from the pressure introducing hole J6,
The distortion is converted into an electric signal by a chip J4, and the signal is converted to an external circuit (e.g., an automobile E) via a wire J9, a circuit board J8, a pin J10 and a connector terminal J11.
CU, etc.) to perform pressure detection.

[0006]

However, as in the above-mentioned prototype, the stem J1 is provided with a screw member J7 as a means for sealing the stem J1 and the pressure introducing hole J6 in order to maintain airtightness against high pressure. The following problem arises in the structure in which is screw-coupled to the housing J5.

In this structure, wire bonding is performed according to the outer shape of the housing J5,
Based on the orientation of the sensor chip J4 assembled in 5, the inspection of the chip characteristics by the probe and the assembly of the circuit board J8 are performed, and thereafter, the components such as the terminal J11 are assembled based on the circuit board J8.

However, in this structure, the stem J1
Since the sensor chip J4 is provided on the diaphragm J2 which is a surface orthogonal to the rotation axis of the screw connection in the above,
When screwing the stem J1 to the housing J5, the sensor chip J4 may rotate around the rotation axis of the screw connection and may be displaced from a proper position. In this case, the subsequent work such as wire bonding and assembly of the circuit board J8 must be corrected in accordance with the displaced chip J4.

In view of the above problems, the present invention provides a pressure sensor in which a stem having a diaphragm provided with detecting means for pressure detection is screw-connected to a housing capable of introducing pressure. It is an object of the present invention not to affect the workability of later assembly even if the position shifts due to rotation around the rotation axis.

[0010]

In order to achieve the above object, the invention according to claims 1 and 2 is characterized in that a housing (30) capable of introducing pressure is screwed to the housing, A stem (1) having a surface orthogonal to the rotation axis of the screw connection formed as the diaphragm (11).
0) and pressure detecting means (40) having a bridge circuit (41) for converting a change in resistance according to the deformation of the diaphragm into an electric signal on the diaphragm.
A circuit board (60) disposed around the detection means in the housing, and bonding wires (64) for connecting pads (P1 to P4) formed on the detection means and the circuit board. The pressure sensor has the following features.

In the present invention, the pads formed on the detecting means (40) are connected to the power supply terminal pads (P1, P3) and the output terminal pads (P2, P2, P3) of the bridge circuit (41).
P4) is repeatedly arranged in a predetermined order around the rotation axis of the screw connection, and when the detection means rotates around the rotation axis of the screw connection and displaces, the detection means Is characterized in that the bonding wire (64) can be connected so as to maintain the same circuit characteristics as those at the position.

That is, according to the present invention, the power supply terminal pad, the ground terminal pad, and the output terminal pad corresponding to the bridge circuit of the detecting means are arranged in a predetermined order to form one set. A plurality of sets may be continuously arranged around the rotation axis of the connection.

For example, in the present invention, when a detecting means is at a normal position, a set of pads arranged in the order of a power supply terminal pad, a ground terminal pad, and an output terminal pad in a clockwise direction is regarded as one set. It is assumed that each pad in (first set) is wire-bonded. In this case, even if the detection means rotates clockwise, for example, and the first set of output terminal pads is shifted to a position where wire bonding is not possible, the second set of output terminal pads next to the first set is not connected to the wire. Comes to a position where bonding is possible.

Therefore, according to the present invention, even when the detecting means is rotated around the rotation axis of the screw connection and displaced, the bonding is performed so as to maintain the same circuit characteristics as when the detecting means is at the regular position. Since the wires can be connected and there is no need to change the position of the circuit board, the workability of assembling based on the circuit board is not affected.

Here, when the detecting means (40) is formed in a general rectangular plate shape (for example, a chip having a rectangular plate shape) as in the second aspect of the present invention, each side is provided around the detecting means. , A set of pads including a power supply terminal pad (P1, P3) and an output terminal pad (P2, P4) is arranged one by one, and the order of the pads in each set of pads is set around the rotation axis of the screw connection. Configurations in the same order can be adopted.

The reference numerals in the parentheses of the above means are examples showing the correspondence with specific means described in the embodiments described later.

[0017]

FIG. 1 shows an overall sectional structure of a pressure sensor 100 according to an embodiment of the present invention. Pressure sensor 10
Numeral 0 is attached to a fuel pipe (not shown) in a fuel injection system (for example, a common rail) of an automobile, and detects the pressure of a liquid or a gas-liquid mixture as a pressure medium in the fuel pipe. FIG. 2 is a schematic view of a portion A surrounded by a circle in FIG. 1 (a cross section of a sensor chip and a metal stem).
It is a perspective view which expands and shows.

Reference numeral 10 denotes a metal stem having a hollow cylindrical shape, which is screwed and fixed to a housing 30 by a screw member 20. The metal stem 10 has a thin-walled diaphragm 11 as a closing part on one end side, and has an opening 12 on the other end side. Here, the diaphragm 11 forms a surface orthogonal to the rotation axis of the screw connection in the stem 10. The other end of the metal stem 10 (opening 1
On the second side), a stepped portion 13 having a larger outer diameter than one end side (diaphragm 11 side) is formed.

As shown in FIG. 2, a sensor chip 40 (detection means in the present invention) made of single crystal Si (silicon) is fixedly bonded to the outer surface of the diaphragm 11 of the metal stem 10 by a low melting point glass 50 as shown in FIG. ing. The sensor chip 40 functions as a detection unit (strain gauge) that detects distortion generated when the diaphragm 11 is deformed by the pressure of the pressure medium introduced into the metal stem 10 from the opening 12, and the deformation of the diaphragm 11 Has a bridge circuit (see FIG. 3) for converting a resistance value change according to the above into an electric signal. Note that a known bridge circuit can be employed. The diaphragm 11 and the sensor chip 40 determine the basic performance of the sensor.

The material of the metal stem 10 is required to have a high strength because of receiving an ultra-high pressure and a low thermal expansion coefficient for joining the sensor chip 40 made of Si with the glass 50. Typically, Fe, N
It can be formed by pressing, cutting, cold forging, or the like by selecting a material mainly composed of i, Co, Fe, or Ni and adding Ti, Nb, Al or Ti, Nb as a precipitation strengthening material.

The housing 30 is directly attached to the fuel pipe as an object to be attached, and has an attachment screw 31 formed on an outer peripheral surface thereof. Also, housing 3
A pressure introducing passage 32 communicating with the opening 12 of the metal stem 10 is formed in the inside of the metal stem 10. The pressure introducing passage 32 communicates with the inside of the fuel pipe in a state where the housing 30 is attached to the fuel pipe, and
A pressure medium is introduced into the inside.

The screw member (screw) 20 has a cylindrical shape that covers the outer periphery of the metal stem 10, and has a male screw portion 21 formed on the outer peripheral surface thereof. Is formed with a female screw portion 33 having a shape corresponding to the male screw portion 21.

By the screw connection of the two screw portions 21 and 33, the pressing force from the screw member 20 is applied to the step portion 13 in the metal stem 10, so that the metal stem 10 is pressed and fixed to the housing 30. Further, the communicating portion between the opening 12 and the pressure introducing passage 32, that is, the boundary K between the opening 12 side of the metal stem 10 and the pressure introducing passage 32 side of the housing 30 is sealed by the pressing force. .

As described above, the housing 30 is fixed to the fuel pipe (fuel pipe) (ultra high pressure seal and mechanical holding), and is fixed using the screw member 20 of the metal stem 10 (ultra high pressure seal). And mechanical holding) and a function of fixing (sealing and mechanical holding) the connector case 80 described later. Therefore, the required quality of the housing 30 includes corrosion resistance from the pressure medium and the actual vehicle environment, and screw strength for maintaining an axial force that generates a high sealing surface pressure at the boundary K.

In view of these required qualities, the material of the housing 30 may be carbon steel (for example, S15C or the like) having both high corrosion resistance and high strength, and may be subjected to Zn plating for increasing corrosion resistance, or XM7 or SUS43 having corrosion resistance.
0, SUS304, SUS630 and the like can be adopted.

The screw member 20 is required to have high strength in order to fix the metal stem 10 to the housing 30 and maintain an axial force for generating a high sealing surface pressure. Since it is housed inside a package, it does not need corrosion resistance unlike the housing 30, and can be made of carbon steel or the like.

Reference numeral 60 denotes a ceramic substrate as a circuit substrate, which is adhered to and fixed to the screw member 20.
It is arranged around the sensor chip 40 in the housing 30. An amplifier (Amp) IC chip 62 for amplifying the output of the sensor chip 40 and a characteristic adjusting IC chip 62 are fixed to the substrate 60 with an adhesive.

Here, the ceramic substrate 60 and the sensor chip 40 are connected by a bonding wire 64 which is a thin wire such as aluminum (Al) formed by ultrasonic wire bonding, and are electrically connected.
Details of the connection between the substrate 60 and the chip 40 by the wires 64 will be described later. Further, pins 66 for electrically connecting to the connector terminals 70 are joined to the ceramic substrate 60 by silver solder.

The connector terminal 70 is connected to the terminal 7
Reference numeral 2 denotes an assembly (ASSY) formed by insert molding the resin 74. The terminal 72 and the ceramic substrate 60 are joined to the pins 66 by laser welding. Thus, the output from the sensor chip 40 can be transmitted from the bonding wire 64 to the terminal 72 via the pin 66. Further, the connector terminal 70 is fixed and held to the connector case 80 by an adhesive 76, and the terminal 72 is electrically connectable to an ECU or the like of a vehicle via a wiring member.

The connector case 80 forms the outer shape of the connector terminal 70 and is integrated with the housing 30 assembled via an O-ring 90 to form a package. The sensor chip 40, various ICs,
It protects the electrical connection from moisture and mechanical external force. The material of the connector case 80 is P, which is highly hydrolyzable.
PS (polyphenylene sulfide) or the like can be employed.

A method of assembling the pressure sensor 100 having such a configuration will be described. First, the stem 10 to which the sensor chip 40 is joined by the glass 50 is screwed to the housing 30 via the screw member 20, and the stem 10 is fixed to the housing 30. Next, the ceramic substrate 60 is adhered to the screw member 20, and the ceramic substrate 60 and the sensor chip 40 are connected and electrically connected by wire bonding.

Next, the connector terminal 70 and the pin 66
Are joined by laser welding (YAG laser welding or the like).
Next, the connector case 80 is attached to the groove of the housing 30 via the O-ring 90, and the connector case 80 and the housing 30 are fixed by caulking the groove. Thus, the pressure sensor 100 shown in FIG. 1 is completed.

The pressure sensor 100 includes the housing 3
By directly connecting and attaching the No. 0 screw 31 to the screw portion formed on the fuel pipe (not shown), the fuel pipe is connected and fixed.

When the fuel pressure (pressure medium) in the fuel pipe is introduced from the opening 12 of the metal stem 10 into the interior (hollow portion) of the metal stem 10 through the pressure introduction passage 32, the pressure increases. The diaphragm 11 is deformed, the deformation is converted into an electric signal by the sensor chip 40, and this signal is processed by the ceramic substrate 60 or the like constituting a processing circuit portion of the sensor to detect pressure. And
The fuel injection control is performed by the ECU or the like based on the detected pressure (fuel pressure).

By the way, in this embodiment, in order to maintain the airtightness against the high pressure, the stem 1 is used by using the screw member 20.
As described above, when the stem 10 is screwed to the housing 30, the sensor chip 40 is rotated by the screw shaft of the stem 10 (hereinafter referred to as a screw rotation axis). ) It may rotate around and deviate from the normal position. In the present embodiment, the following unique configuration is adopted in the connection configuration between the substrate 60 and the chip 40 in order to prevent deterioration of the assembling workability due to the chip displacement.

FIG. 3 is a schematic diagram (viewed from the direction of the screw rotation axis) showing an example of a connection configuration of the ceramic substrate 60 and the sensor chip 40 by wires 64 in the present embodiment. In FIG. 3, (a) shows the case where the chip 40 is at the regular position, (b) shows the case where the chip 40 is rotated 22.5 ° counterclockwise from the regular position, and (c) shows that the chip 40 is at the regular position. This is a case where the camera is rotated counterclockwise by 45 °.

As shown in FIG. 3, the sensor chip 40 includes:
Pads P1 to P4 for wire bonding are formed by vapor deposition of Al (aluminum) or the like. In FIG. 3, the pads P1, P2, P3, and P4 are respectively represented by.
, Is indicated. In this example, the four pads P1 to P4 are set as a set of pads, and the order of the pads in each set is set to P1 counterclockwise with respect to the screw rotation axis around the chip 40 having a rectangular plate shape. , P2, P3, and P4, the sets of the pads are arranged one by one.

Here, each pad P1, P
2, P3 and P4 are a power supply terminal pad, an output (-) terminal pad of the bridge circuit 41 of the chip 40, respectively.
These correspond to power supply terminal pads and output (+) terminal pads. The power supply terminal pad P1 and the output (-)
Terminal pad P2, power supply terminal pad P3, output (+)
The terminal pad P4 is located at the regular position shown in FIG. 3A, and the power supply terminal T1 and the output (-) terminal T
2. The power supply terminal T3 and the output (+) terminal T4 are connected by wires 64, and the bridge circuit 41 of the chip 40 is in the connection state as shown.

In the state of displacement shown in FIG. 3B, the connection state at the regular position can be maintained by using the set (first set) of the pads P1 to P4 connected at the regular position. Wire bonding. However, FIG.
In the state shown in (c), since the displacement is large,
If an attempt is made to connect only the first set, the wires are too long in the first set of pads P1 and P2. For this reason, a problem such as disconnection of the wire or deterioration of bondability due to resonance at the time of wire bonding occurs, and it is practically impossible to connect.

However, according to the present embodiment, FIG.
In the sensor chip 40, the pads P1 to P4 adjacent to the first
Pads (P2 and P2) in the set (second set) are located at positions where wire bonding can be performed with the terminals T1 and T2 of the ceramic substrate 60.

Then, as shown in FIG. 3C, when the terminals T1 to T4 of the ceramic substrate 60 are wire-bonded to the pads P1 to P4 of the sensor chip 40, the symmetry of the bridge circuit 41 is used. Thus, the circuit characteristics when wire bonding is performed at a regular position can be maintained. That is, in all the bridge circuits 41 of FIGS. 3A to 3C, the resistance change direction between T1 and T4 and the resistance change direction between T2 and T3 both increase, and the equivalent circuit characteristics are maintained. I have.

Although not shown in FIG. 3, when the sensor chip 40 is rotated 90 ° counterclockwise from the normal position, the second set of pads P1 to P4 is replaced with the first set. Thus, wire bonding with each of the terminals T1 to T4 of the ceramic substrate 60 is possible so as to maintain the circuit characteristics at the regular position. Also, when the sensor chip 40 is displaced clockwise with respect to the screw rotation axis, it is needless to say that the same effect is obtained as in the case of counterclockwise rotation.

FIG. 4 is a diagram schematically showing a connection configuration of a bonding wire J9 in a conventional general sensor chip J4 as a comparative example. Conventionally, one pad P1, P2, P for each terminal of the bridge circuit of the chip J4, one at each of the four corners of the rectangular sensor chip J4.
3 and P4 are formed and connected by a wire J9 as shown.

With such a pad arrangement, the chip J4
Is rotated around the rotation axis (screw rotation axis) of the stem J1 from the normal position shown in FIG.
Depending on the direction of 4, a certain pad is too far from the bonding position on the ceramic substrate side, and the wires J9 cross each other or are too long. As a result, problems such as short-circuiting, wire breakage due to resonance during wire bonding, and deterioration of bondability occur, so that bonding becomes impossible or bonding is performed so as to maintain the circuit characteristics of the bridge circuit at a regular position. Or not.

In the example shown in FIG. 3, one set of power supply terminal pads P1 and P3 and one set of output terminal pads P2 per side are provided on the periphery of each side of the rectangular plate-shaped chip 40.
And P4 are arranged, and the order of the pads P1 to P4 in each set is the same order around the screw rotation axis, but it is not necessary to arrange one set on each side of the chip 40.

For example, two or more sets or 1
Set and half (eg, P1, P2, P3, P4, P1, P
(Six pads such as 2). The order in the set of pads is not limited to the illustrated example, and the chip 40 may not be a rectangular plate.

In short, in the present embodiment, the pads P1 and P3 for the power supply terminal and the pads P2 and P4 for the output terminal of the bridge circuit 41 in the chip 40 when the chip 40 is in the normal position are connected to the screw connection of the stem. If the chips 40 are repeatedly arranged in a predetermined order around the rotation axis (screw rotation axis), the bonding wires 64 can be connected so as to maintain the same circuit characteristics as when the chip 40 is at the normal position. it can.

Therefore, according to the present embodiment, the chip 40
In this case, wire bonding can be easily performed even if the position shift about the screw rotation axis occurs, and the position of the ceramic substrate 60 is not corrected. Therefore, when assembling the sensor,
In the process of assembling based on the ceramic substrate 60,
It is possible to prevent the displacement of the chip 40 from affecting the workability of these assembling steps.

The detecting means provided on the diaphragm and outputting an electric signal according to the deformation of the diaphragm is not limited to the above-mentioned sensor chip.
A strain gauge may be directly deposited on the diaphragm, and this strain gauge may be used as a detecting means.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating an entire configuration of a pressure sensor according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an enlarged part A surrounded by a circle in FIG. 1;

FIG. 3 is a schematic diagram illustrating details of connection between a ceramic substrate and a sensor chip.

FIG. 4 is a schematic diagram of a connection configuration of bonding wires in a conventional general sensor chip.

FIG. 5 is a schematic sectional view showing a pressure sensor as a prototype of the inventor.

[Explanation of symbols]

10: Stem, 11: Diaphragm, 30: Housing, 40: Sensor chip, 41: Bridge circuit, 60:
Ceramic substrate, 64 bonding wires, P1 to P
4: Sensor chip pad.

Claims (2)

[Claims] 1. A housing (30) capable of introducing a pressure, and a diaphragm which is screw-connected to the housing and whose surface orthogonal to a rotation axis of the screw connection can be deformed by pressure introduced into the housing. (11)
Pressure sensing means having a stem (10) configured as a bridge, and a bridge circuit (41) for converting a resistance value change according to the deformation of the diaphragm into an electric signal on the diaphragm of the stem. (40) a circuit board (60) disposed around the detection means in the housing; and a bonding wire (40) for connecting pads (P1 to P4) formed on the detection means and the circuit board. 64),
Wherein the pads are power terminal pads (P1, P3) and output terminal pads (P2, P4) of the bridge circuit.
Are arranged repeatedly in a predetermined order around the rotation axis of the screw connection, and when the detection means rotates around the rotation axis of the screw connection and is displaced, the detection means A pressure sensor, wherein the bonding wire is connectable so as to maintain the same circuit characteristics as in a normal position. 2. The detecting means (40) has a rectangular plate shape, and the power terminal pads (P1, P3) and the output terminal pads (P2) are provided around each side of the detecting means. , P4) are arranged one by one, and the order of the pads in each of these sets of pads is the same around the rotation axis of the screw connection. Pressure sensor.