JP2010230592A - Gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To ensure a longer life by improving a corrosion resistance, and improve an electric connectivity between a pad portion and a lead pin of a sensor board. <P>SOLUTION: A gas sensor includes the corrosion-resistant sensor board 3 disposed in a measurement space S1, provided with a circuit element 33 for detecting a sample gas, and having the gold or platinum pad portion 34 serving as a wiring connection of the circuit element 33; the nickel alloy lead pin 5 wherein one end 5a is disposed in the measurement space S1 and electrically connected to the pad portion 34, and the other end 5b is disposed outside the measurement space; and a gold or platinum connection 6 which electrically connects between the pad portion 34 and the one end 5a of the lead pin 5. A first layer 7 comprising chromium, tungsten or titanium is formed at the one end 5a of the lead pin 5, and a second layer 8 comprising gold or platinum is formed on the first layer 7. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a gas sensor for detecting a sample gas, and particularly to a wiring structure of a sensor substrate of the gas sensor.

  As this type of gas sensor, as shown in Patent Document 1, the thermal conductivity of a sample gas is detected using a Wheatstone bridge circuit, and the concentration of a predetermined component in the sample gas is measured based on the thermal conductivity. There is a sensor.

  Conventionally, a sensor substrate on which circuit elements such as measurement resistors constituting a Wheatstone bridge circuit are formed is arranged in a measurement space. On this sensor substrate, a pad portion made of gold or platinum serving as a wiring connection portion of a circuit element is formed. One end is wire-bonded to a lead pin provided in the measurement space.

  Here, when the sample gas contains an acidic or alkaline corrosive component, the lead pin needs to have corrosion resistance. Conventionally, for example, iron (Fe) with low corrosion resistance is plated with copper (Cu). On top, nickel (Ni) plating and gold (Au) plating are used.

  However, if there is a pin hole (micro hole) in the plating, there is a problem that a corrosive component enters from the micro hole, the lead pin is corroded, a conduction failure occurs, and an error occurs in the detection signal.

  At this time, in order to eliminate the pinhole, it is conceivable to increase the thickness of the plating. However, if the plating is increased, there is a problem that the cost naturally increases.

JP 2003-42983 A

  Accordingly, the present invention has been made to solve the above-mentioned problems all at once, and it is possible to extend the life by improving the corrosion resistance and to electrically connect the pad portion of the sensor substrate and the lead pin. The main goal is to improve performance.

  That is, a gas sensor according to the present invention is provided in a measurement space, a circuit element for detecting a sample gas is formed, and a sensor substrate having a gold or platinum pad part that serves as a wiring connection part of the circuit element; A lead pin made of nickel alloy having one end portion provided in the measurement space and electrically connected to the pad portion, and the other end portion provided outside the measurement space, and the pad portion and one end portion of the lead pin electrically And a first layer made of chromium, tungsten, or titanium on one end of the lead pin, and a second layer made of gold or platinum on the first layer. It is formed.

  If this is the case, since the lead pin is made of nickel alloy, the lead pin can be made to have corrosion resistance, and it solves problems such as the occurrence of errors in detection signals by preventing poor conduction. It is possible to increase the service life. Further, a first layer made of chromium or the like and a second layer made of gold or the like are formed on one end of the lead pin, and the connection body is connected to the second layer, thereby electrically connecting the connection body and the lead pin. Can be improved.

  In order to improve the electrical connection between the external conductor and the lead pin, a first layer made of chromium, tungsten or titanium is formed on the other end of the lead pin, and a second layer made of nickel is formed on the first layer. It is desirable that a layer is formed and an external conductor is connected to the second layer.

  In order to relieve the stress generated in the sensor board due to the difference between the coefficient of thermal expansion of the member holding the sensor board and the coefficient of thermal expansion of the sensor board, and to prevent damage to the sensor board, the sensor board is preferably An intermediate body comprising a base body held in the measurement space, and having a thermal expansion coefficient between the base body and the sensor substrate, between the thermal expansion coefficient of the base body and the thermal expansion coefficient of the sensor substrate. It is desirable to intervene.

  According to the present invention configured as described above, it is possible to extend the life by improving the corrosion resistance and to improve the electrical connectivity between the pad portion of the sensor substrate and the lead pin.

It is a figure which shows the measurement circuit of the thermal conductivity sensor which concerns on one Embodiment of this invention. It is sectional drawing which shows the internal block body of the thermal conductivity sensor which concerns on the same embodiment. It is sectional drawing which shows the internal block body of the embodiment. It is a typical sectional view of a base body, a sensor board, and a lead pin of the embodiment. It is a top view which shows the sensor board | substrate of the embodiment. It is a simulation result which shows the temperature distribution of the thin film resistor of the embodiment.

  Hereinafter, an embodiment of a thermal conductivity sensor according to the present invention will be described with reference to the drawings.

The thermal conductivity sensor 100 according to the present embodiment detects the thermal conductivity of a sample gas containing a combustible and / or corrosive component, and measures the concentration of a predetermined component in the sample gas based on the thermal conductivity. is there. As combustible and / or corrosive components, water (H ₂ O), oxygen (O ₂ ) gas, sulfur oxide (SO _X ) gas, nitrogen oxide (NO _X ) gas, hydrochloric acid (HCl) gas Ammonia (NH ₃ ) gas, hydrogen sulfide (H ₂ S) gas, hydrogen (H ₂ ) gas, or the like.

First, a measurement circuit of the thermal conductivity sensor 100 will be described with reference to FIG.
This measurement circuit is configured by using two measurement resistors R1 and R2 provided in contact with the sample gas and two comparison resistors R3 and R4 provided in contact with the reference gas. The measurement circuit includes a Wheatstone bridge circuit WB configured by connecting two series circuit units formed in parallel by connecting one measurement resistor R1 or R2 and one comparison resistor R3 or R4 in series. It is configured using.

  At this time, the measurement resistors R1 and R2 of each series circuit unit are connected in parallel so that the comparison resistors R3 and R4 are located on opposite sides facing each other. Further, a constant current source CS for flowing a constant current is connected between the connection points of the series circuit portions. Note that a variable resistor R5 for offset adjustment is provided at one of connection points of the series circuit portions. In such a configuration, the calculation unit X detects the potentials of the connection points P1, P2 of the measurement resistors R1, R2 and the comparison resistors R3, R4 in each series circuit unit, and the potential difference between the connection points P1, P2 Is obtained as a detection signal, and the concentration of a predetermined component in the sample gas is calculated. Note that at least the thermal conductivity sensor 100, the constant current source CS, and the calculation unit X constitute a gas analyzer.

Next, the equipment configuration of the thermal conductivity sensor 100 will be described.
The thermal conductivity sensor 100 of the present embodiment includes the Wheatstone bridge circuit WB inside, and has a pressure- and explosion-proof structure in which an introduction port for introducing the sample gas into the interior and an outlet port for deriving the sample gas to the outside are formed. A casing (not shown), and an explosion-proof internal block body 2 (see FIG. 2) that is provided in the casing and communicates with the inlet and the outlet.

  As shown in FIG. 2, the internal block body 2 includes a block main body 21 in which an internal flow path 2A is formed, and is provided in the block main body 21 so as to communicate with the internal flow path 2A. And a lead-out pipe connecting portion 22 provided in the block main body 21 to communicate with the internal flow path 2A and connected to the lead-out port via a pipe. .

  A sintered metal element 24 is provided in the inlet pipe connecting part 22 and the outlet pipe connecting part 23 so as to partition the flow path in the connecting part into the block main body 21 side (ignition source side) and the pipe side. . Specifically, the sintered metal element has a bottomed cylindrical shape, and is provided along the flow path so that the bottom portion faces the block main body 21 side.

  Thus, by providing the sintered metal element 24 in each connection part 22,23, when a flame arises in the block main body 21, the said flame is prevented from reaching the connection parts 22,23, and piping There is no need to use a dedicated configuration based on the Industrial Electrical Equipment Explosion Proof Guidelines (Issued by the Occupational Safety and Health Research Institute) The configuration can be simplified and the manufacturing cost can be reduced.

  The block main body 21 is made of a corrosion-resistant material such as stainless steel, and the sensor substrate 3 on which the measurement resistors R1 and R2 are formed on the internal flow path 2A of the block main body 21 (hereinafter particularly distinguished). In this case, a measurement space S1 in which the “measurement substrate 3m” is disposed is formed.

  Specifically, the measurement space S1 is formed by the sensor holder 4 and the recess 21a by airtightly fitting the sensor holder 4 holding the measurement substrate 3m into the recess 21a that forms a part of the internal flow path 2A. A substrate 3m is provided in the measurement space S1.

  Further, the block body 21 is formed with a reference space S2 in which a sensor substrate 3 (hereinafter referred to as “comparison substrate 3r” when specifically distinguished) on which comparison resistors R3 and R4 are formed is disposed. Yes. In this reference space S2, a reference gas is enclosed and provided independently of the internal flow path 2A.

  Specifically, the sensor holder 4 holding the comparison substrate 3r is hermetically fitted into the recess 21b formed in the block body 21, whereby the reference space S2 is formed by the sensor holder 4 and the recess 21b, and the comparison substrate 3r. Are provided in the reference space S2. The sensor holder 4 that holds the comparison substrate 3r and the sensor holder 4 that holds the measurement substrate 3m have the same configuration.

  The sensor holder 4 is made of a corrosion-resistant material such as stainless steel and has a substantially cylindrical shape. As shown in FIG. 3, the sensor holder 4 includes a sensor board 3 and a substantially disc-shaped base body 41 to which lead pins 5 electrically connected to the sensor board 3 are fixed, and the base body 41. And a holder main body 42 fixed so as to be sandwiched from both sides. In addition, the base body 41 and the holder main body 42 are connected by all-around laser welding.

  Therefore, in the thermal conductivity sensor 100 of the present embodiment, the measurement resistors R1 and R2 arranged on one side of the Wheatstone bridge circuit WB are arranged in one measurement space S1, and arranged on the other side. The comparison resistors R3 and R4 are arranged in one reference space S2. That is, the measurement resistors R1 and R2 are provided on one measurement substrate 3m, the comparison resistors R3 and R4 are provided on one comparison substrate 3r, and the measurement substrate 3m is provided in one measurement space S1. The comparison substrate 3r is arranged in one reference space S2. One measurement space S1 is a space formed by one measurement cell, and is not formed by connecting two measurement cells by piping or the like. In this embodiment, one sensor cell 4 and one block body 21 constitute one measurement cell. One reference space S2 is a space formed by one reference cell, and is not formed by connecting two reference cells by piping or the like. In the present embodiment, one sensor cell 4 and the block main body 21 constitute one reference cell.

Here, the measurement substrate 3m and the comparison substrate 3r will be described.
As shown in FIG. 4, the measurement substrate 3m includes, for example, a silicon substrate 31 having a cavity 31a having a rectangular shape in plan view, and a resistor having a diaphragm structure provided on the silicon substrate 31 so as to block the cavity 31a. A holding film 32 (for example, composed of a SiO ₂ film and a Si ₃ N ₄ film formed on the SiO ₂ film), and a thin film resistor (made of platinum) formed on the resistor holding film 32 ( Circuit element) 33 and a pad portion 34 made of gold serving as a wiring connecting portion that contacts each end portion of the thin film resistor 33. The thin film resistor 33 and the resistor holding film 32 are partially covered with a surface protective film 35 such as a TEOS-SiO ₂ film. The comparison substrate 3r has the same configuration as the measurement substrate 3m.

  Specifically, the silicon substrate 31 constituting the measurement substrate 3m and the silicon substrate 31 constituting the comparison substrate 3r have the same shape, and in the present embodiment, both are rectangular in a plan view. Further, the pattern of the thin film resistor 33 constituting the measuring resistors R1 and R2 and the pattern of the thin film resistor 33 constituting the comparative resistors R3 and R4 are formed to be the same pattern, and their resistance values are To be the same. The other film configurations are also the same. Thus, by making the configuration of the measurement substrate 3m and the comparison substrate 3r the same, the temperature characteristics of the measurement substrate 3m and the comparison substrate 3r are made the same.

  Further, the measurement resistors R1 and R2 arranged on the opposite side of the Wheatstone bridge circuit WB are composed of two thin film resistors 33 patterned on one silicon substrate 31, and the comparison resistors arranged on the other opposite side. R3 and R4 are composed of two thin film resistors 33 patterned on one silicon substrate 31.

  Here, the pattern of the thin film resistor 33 constituting the measurement resistors R1 and R2 as a representative will be described with reference to FIG.

  One thin film resistor 33 constituting the measurement resistors R1 and R2 is formed for each region obtained by dividing the surface of the silicon substrate 31 into two equal parts. The thin film resistor 33 formed in each region is formed symmetrically with respect to the bisector.

  Specifically, each thin film resistor 33 has two pattern forming portions 33P that are patterned on the surface of the silicon substrate 31 (specifically, the resistor holding film 32). The pattern shape is such that the density of the peripheral portion is the largest and the density gradually decreases toward the central portion, and the vicinity of the pattern forming portion 33P can be heated to a substantially uniform temperature when the pattern forming portion 33P is energized.

  More specifically, the pattern forming portion 33P has a minimum line width of the thin film resistor 33 and a line interval (pitch) of the thin film resistor 33 at both ends in one direction (for example, the left and right direction). It is formed in a double zigzag pattern shape in which the line width of the thin film resistor 33 and the line interval (pitch) of the thin film resistor 33 gradually increase as it goes.

  In order to increase the sensor sensitivity in the thermal conductivity sensor 100 of the present embodiment, the temperature of the thin film resistor 33 (measurement resistors R1, R2 and comparison resistors R3, R4) is increased as much as possible. desirable. However, since the upper limit value of the temperature of the thin film resistor 33 is limited by the explosion-proof standard, a broad temperature distribution is desirable instead of a temperature distribution having a peak.

  From this point of view, the simulation result of the temperature distribution of the thin film resistor 33 of the present embodiment is shown in FIG. The temperature (Y axis) shown in FIG. 6 indicates the temperature along line C in FIG. Further, “after improvement” in FIG. 6 indicates a temperature distribution in the thin film resistor 33 of the present embodiment, and “before improvement” indicates a pattern of a pattern forming portion of the thin film resistor as a comparative example. However, both the end portions and the central portion are formed in a double zigzag pattern shape in which the line width of the thin film resistor and the line interval of the thin film resistor are the same, and the density of the peripheral portion is equal to the density of the central portion. .

  As can be seen from FIG. 6, the “before improvement” temperature has a peak in the center, the peak is limited to the explosion-proof standard temperature (specifically, 130 ° C.), and the temperature of other parts is further increased. I can't let you. On the other hand, it can be seen that the temperature after “improved” forms a uniform temperature distribution at an explosion-proof standard temperature (specifically, 130 ° C.) or less.

<Wiring structure of sensor substrate 3>
As shown in FIG. 4, the sensor holder 4 has one end portion 5a provided in the spaces S1 and S2 and electrically connected to the pad portion 34, and the other end portion 5b provided outside the spaces S1 and S2. Corrosion-resistant lead pins 5 are provided. An insertion hole 41a into which the lead pin 5 is inserted is formed in the base body 41 of the sensor holder 4, and the lead pin 5 is inserted into the insertion hole 41a and is airtightly fixed by glass sealing.

  The lead pin 5 is made of a material exhibiting corrosion resistance against a corrosive gas, and is specifically a rod member made of a nickel alloy. In addition, the nickel alloy in this embodiment has nickel (Ni) as a main component, cobalt (Co), chromium (Cr), molybdenum (Mo), tungsten (W), iron (Fe), silicon (Si), manganese It is an alloy containing (Mn), carbon (C) and the like.

  Further, one end portion 5 a (end portion on the measurement space S 1 side) of the lead pin 5 and the pad portion 34 of the measurement substrate 3 are electrically connected by the connection body 6. The connection body 6 is connected to the pad portion 34 and the one end portion 5a of the lead pin 5 by wire bonding, and is a gold wire in this embodiment.

  Thus, in order to electrically connect the nickel alloy and the gold wire 6 by wire bonding and to improve the corrosion resistance, the end portion 5a of the lead pin 5 is shown in the partially enlarged view of FIG. In addition, a first layer 7 (Cr layer) made of chromium (Cr) and a second layer 8 (Au layer) made of gold (Au) are formed on the first layer 7. Then, the Au wire 6 is connected by ultrasonic bonding. In the ultrasonic bonding, the gold wire 6 is pressed against the lead pin 5 with a jig and rubbed with ultrasonic vibration of about several tens of KHz, and bonded by frictional heat and pressure generated at that time.

  In this embodiment, the film thickness of the Cr layer 7 formed on the one end portion 5a of the lead pin 5 is, for example, 100 to 500 mm, and the film thickness of the Au layer 8 is, for example, 2000 mm or more.

  Where the Au layer 8 is difficult to deposit on the nickel alloy, the Au layer 8 is formed on the lead pin 5 by forming the Au layer 8 on the Cr layer 7 after forming the Cr layer 7 as described above. A film can be formed on the end portion (inner lead side) of the measurement space S1. Further, since the Cr layer 7 is easily oxidized, even if a pinhole (micro hole) is generated in the Au layer 8, the Cr layer 7 exposed to the outside by the pinhole forms an oxide film. The progress of oxidation can be suppressed, and the corrosion resistance can be improved.

  Further, in order to improve the connection between the nickel alloy and the external conductor 9 (for example, a lead wire made of copper (Cu)), the other end portion 5b of the lead pin 5 (the end portion on the opposite side to the measurement space S1) As shown in the partially enlarged view at the bottom of FIG. 4, a first layer 10 (Cr layer) made of chromium (Cr), a second layer 11 (Ni layer) made of nickel (Ni) on the first layer 10, A third layer 12 (Au layer) made of gold (Au) is formed on the second layer 11.

  In this embodiment, the film thickness of the Cr layer 10 formed on the other end 5b of the lead pin 5 is, for example, 100 to 500 mm, the film thickness of the Ni layer 11 is, for example, 8000 mm or more, and the film thickness of the Au layer 12 Is, for example, 500 mm or less.

  Although it is difficult to form the Ni layer 11 on the nickel alloy, the Ni layer 11 is formed on the lead pin 5 by forming the Ni layer 11 on the Cr layer 10 after forming the Cr layer 10 as described above. A film can be formed on the other end 5b (outer lead side). Then, by joining the external conductor 9 to the Ni layer 11 by soldering, the external conductor 9 and the nickel alloy (lead pin 5) can be electrically connected. Moreover, since the Au layer 12 is formed on the Ni layer 11, the oxidation of the Ni layer 11 can be prevented. In soldering the external conductor 9, the Au layer 12 is dissolved and the external conductor 9 and the Ni layer 11 are connected.

<Deposition method, etc.>
Next, an example of a method for forming each layer on the lead pin 5 will be described.

  First, the lead pin 5 is inserted into the insertion hole 41a provided in the base body 41 of the sensor holder 4, and the lead pin 5 is fixed to the base body 41 by glass sealing. Thereafter, the mask substrate having a through hole corresponding to the insertion hole 41a of the base body 41 is overlaid so that the lead pin 5 is inserted into the insertion hole 41a from the measurement space S1 side of the base body 41. At this time, a portion exposed from the mask substrate is a portion to be formed. In this state, the Cr layer 7 and the Au layer 8 are formed in this order on the exposed portion from the mask substrate by a thin film manufacturing technique such as sputtering, vacuum deposition, or CVD. Thereafter, the Cr substrate / Au layer is formed on the one end portion 5a of the lead pin 5 by removing the mask substrate.

  Further, a mask substrate having a through hole corresponding to the insertion hole 41a of the base body 41 is overlaid so that the lead pin 5 is inserted into the insertion hole 41a from the opposite side of the measurement space S1 of the base body 41. At this time, a portion exposed from the mask substrate is a portion to be formed. In this state, the Cr layer 10, the Ni layer 11, and the Au layer 12 are formed in this order on the exposed portion from the mask substrate by the thin film manufacturing technique. Thereafter, by removing the mask substrate, a Cr layer / Ni layer / Au layer is formed on the other end portion 5 b of the lead pin 5.

  After forming the film on both end portions 5 a and 5 b of the lead pin 5 in this way, a gold wire 6 for electrically connecting to the sensor substrate 3 is ultrasonically bonded to the one end portion 5 a of the lead pin 5. On the other hand, the external conductor 9 is soldered to the other end 5 b of the lead pin 5. Thereafter, the holder body 42 is laser welded to the base body 41. As a result, the sensor substrate 3 and the lead pins 5 are electrically connected, and they are fixed to the sensor holder 4 to form a sensor unit.

Next, the result of the corrosion resistance test of the sensor holder 4 using the lead pin 5 configured as described above will be described. The gas used in this corrosion resistance test contains 50% or more of nitric oxide (NO) or nitrogen dioxide (NO ₂ ). For comparison, the base body and the lead pins are made of iron, and a thermal conductivity sensor (hereinafter referred to as a conventional product 1) is plated with gold. The base body and the lead pins are made of iron, and they are plated with gold. A similar test was conducted on a thermal conductivity sensor coated with an epoxy resin (hereinafter referred to as conventional product 2).

  In the conventional product 1, the base body and the lead pin were corroded in 1 to 2 days, and in the conventional product 2, the base body and the lead pin were corroded in about 20 days. On the other hand, in the thermal conductivity sensor 100 of this embodiment, the corrosion of the base body 41 and the lead pin 5 was not observed even after about 250 days.

<Stress relaxation structure>
Further, in the thermal conductivity sensor 100 according to the present embodiment, between the base body 41 and the sensor substrate 3 of the sensor holder 4, between the thermal expansion coefficient of the base body 41 and the thermal expansion coefficient of the sensor substrate 3. The intermediate body 13 having a thermal expansion coefficient is interposed, and the base body 41 and the intermediate body 13 are bonded together by the adhesive 14, and the intermediate body 13 and the sensor substrate 3 are bonded together. As the adhesive 14, for example, an epoxy adhesive can be used.

The base body 41 of the present embodiment is made of stainless steel, the thermal expansion coefficient is about ^{16 × 10 -6 [/ ℃]} , are those sensor substrate 3 is a silicon substrate 31, the thermal expansion coefficient Since it is about 2.4 × 10 ⁻⁶ [/ ° C.], it is desirable that the thermal expansion coefficient of the intermediate 13 be in between. In particular, the intermediate 13 of the present embodiment has a high melting point, good chemical stability and low thermal conductivity, zirconia (ZrO ₂ ) (thermal expansion coefficient of about 10 × 10 ⁻⁶ [/ ° C.]), or room temperature strength, Although it is conceivable to use alumina (Al ₂ O ₃ ) (thermal expansion coefficient of about 8.1 × 10 ⁻⁶ [/ ° C.]) excellent in corrosion resistance and electrical insulation, it is applicable to corrosive gases. It is particularly preferable to use zirconia having a wide range.

  By interposing such an intermediate body 13, the stress generated in the sensor substrate 3 by the base body 41 can be relieved, and the problem that the resistor holding film 32 and the like are bent and cracked can be solved. .

  Further, the intermediate body 13 has a substantially spherical shape with a diameter of 400 μm or more, for example. As a result, when the base part 41 and the sensor substrate 3 are bonded with the intermediate body 13 interposed, the contact area between the adhesive 14 and the intermediate body 13 can be increased. The substrate 3 can be fixed firmly. That is, it is possible to prevent adhesion failure from occurring due to the stress caused by the difference in thermal expansion. Further, the sensor substrate 3 can be positioned with respect to the intermediate body 13 by the surface tension of the adhesive 14 applied to the intermediate body 13.

Finally, the combination of the base body 41 and the lead pin 5 will be described.
In the conventional configuration, the base body and the lead pins are made of iron, and gold plating is applied to facilitate wiring joining, and glass is used for glass sealing of the base body and the lead pins. Since the thermal expansion coefficient of iron is about 10 × 10 ⁻⁶ [/ ° C.] and the thermal expansion coefficient of glass is about 9.5 × 10 ⁻⁶ [/ ° C.], the base body and the lead pin are similar. Because of thermal expansion, the hermeticity of the glass sealing due to temperature fluctuation does not occur. However, as described above, if there is a pin hole (micro hole) in the gold plating, there is a problem that a corrosive component enters from the micro hole and the iron lead pin is corroded.

  Here, in order to give corrosion resistance, it can be considered that the base body and the lead pin are made of stainless steel.

However, even if glass is used for glass sealing of the stainless steel base body and the stainless steel lead pin, the thermal expansion coefficient of stainless steel is about 16 × 10 ⁻⁶ [/ ° C.], and the thermal expansion coefficient of glass. Is about 9.5 × 10 ⁻⁶ [/ ° C.], for example, there is a problem that a gap is likely to be formed between the lead pin and the glass due to a difference in temperature between glass melting and glass cooling in production. There is. Therefore, stainless steel cannot be used for the lead pin due to the problem of airtightness.

Therefore, in the thermal conductivity sensor 100 of the present embodiment, a nickel alloy (thermal expansion coefficient of about 10.0 × 10 ⁻⁶ [/ ° C.]) is used for the lead pin 5, and stainless steel is used for the base body 41. Glass-sealed with glass. As a result, not only can the base body 41 and the lead pin 5 have corrosion resistance, but the thermal expansion coefficients of the glass and the nickel alloy are close, so that the glass and the lead pin 5 have the same heat when the glass is cooled and solidified. When the base body 41 is made of stainless steel that is shrunk and hardly forms a gap between the glass and the lead pin 5 and has a large thermal expansion coefficient, higher airtightness can be secured at the time of the heat shrinkage.

<Effect of this embodiment>
According to the thermal conductivity sensor 100 according to the present embodiment configured as described above, since the lead pin 5 is made of a nickel alloy, the lead pin 5 can be provided with corrosion resistance and can prevent poor conduction. Problems such as an error in the detection signal can be solved. Moreover, since the lead pin 5 and the base body 41 have corrosion resistance, the lifetime of the thermal conductivity sensor 100 can be extended. Further, the Cr layer 7 and the Au layer 8 are formed on one end portion 5 a of the lead pin 5, and the gold wire 6 is connected to the Au layer 8, thereby improving the electrical connectivity between the gold wire 6 and the lead pin 5. Can be made.

<Other modified embodiments>
The present invention is not limited to the above embodiment.

  For example, in the above embodiment, the sensor substrate and the lead pin 5 are connected by Au wire bonding, but Pt wire bonding may also be used. At this time, the second layer formed on the Cr layer on one end face of the lead pin 5 is not an Au layer but a Pt layer.

  The first layer formed on one end or the other end of the lead pin is not limited to the Cr layer, and may be a tungsten layer or a titanium layer.

  Further, the connection body 6 is not limited to a wire, and may be, for example, a spherical member interposed between the tip surface of the lead pin 5 and the pad portion 34.

  Furthermore, in the above embodiment, one measurement space and one reference space are provided, and two measurement resistors are provided in the measurement space, and two comparison resistors are provided in the reference space. One measurement resistor may be provided in the space, one comparison resistor may be provided in the reference space, and other resistors constituting the Wheatstone bridge circuit may be provided as external resistors. Further, a measurement space may be provided for each measurement resistor, and a reference space may be provided for each comparison resistor.

  In addition, some or all of the above-described embodiments and modified embodiments may be combined as appropriate, and the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. .

100 ... Thermal conductivity sensor (gas sensor)
S1 ... Measurement space 3 ... Sensor substrate 33 ... Thin film resistor (circuit element)
34 ... pad part 41 ... base body 5 ... lead pin 5a ... one end part 5b ... other end part 6 ... connection body 7 ... first layer 8 at one end part ... Second layer 13 at one end ... Intermediate

Claims (4)

A sensor substrate provided in the measurement space, in which a circuit element for detecting a sample gas is formed, and having a pad portion made of gold or platinum that serves as a wiring connection portion of the circuit element;
A lead pin made of nickel alloy having one end portion provided in the measurement space and electrically connected to the pad portion, and the other end portion provided outside the measurement space;
A connection body made of gold or platinum that electrically connects the pad portion and one end of the lead pin;
A gas sensor in which a first layer made of chromium, tungsten, or titanium is formed at one end of the lead pin, and a second layer made of gold or platinum is formed on the first layer.   A first layer made of chromium, tungsten, or titanium is formed on the other end of the lead pin, and a second layer made of nickel is formed on the first layer, and an external conductor is connected to the second layer. The gas sensor according to 1. A base body for holding the sensor substrate in the measurement space;
The intermediate body having a thermal expansion coefficient between the thermal expansion coefficient of the base body and the thermal expansion coefficient of the sensor board is interposed between the base body and the sensor board. Gas sensor.   A gas analyzer using the gas sensor according to claim 1, 2 or 3.