JP2013088283A - Physical quantity detector and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a physical quantity detector for reducing the occurrence of a drift of a pressure detection value due to high temperature processing of reflow or the like, and the manufacturing method thereof.SOLUTION: A support frame part 206 of a diaphragm layer 20 of a pressure sensor 1 and a stationary part are connected by using a first bonding material 40, and a pair of base parts 16b of a pressure sensitive layer 10 and a pair of support parts 210 are connected by using a second bonding material 50 having a melting point higher than a melting point of the first bonding material 40.

Description

  The present invention relates to a physical quantity detector and a manufacturing method thereof, and more particularly to a physical quantity detector excellent in reflow resistance and a manufacturing method thereof.

  Conventionally, a physical quantity detector such as a diaphragm type pressure sensor including a piezoelectric vibrator used as a force detection element and a diaphragm that receives pressure (pressure of gas or liquid, etc.) or bends when pressed by an external force. Exists. For example, the diaphragm-type pressure sensor disclosed in Patent Documents 1 to 4 includes a diaphragm layer, a base layer (lid portion), and a pressure-sensitive element layer as an intermediate layer. A pressure sensitive element composed of a double tuning fork vibrator or the like is disposed at the center of the pressure sensitive element layer. The diaphragm layer is provided with a pair of support portions for fixing a pair of base portions disposed at both ends of the pressure-sensitive portion (vibration portion) of the pressure-sensitive element, and the pair of support portions causes the pair of base portions to be fixed. It is fixed and supported by a joining member such as an adhesive. In this diaphragm type pressure sensor, when the diaphragm layer receiving the pressure to be detected is deflected and displaced, the displacement is converted into force through the diaphragm layer and transmitted to the pressure sensitive element which is a physical quantity detecting element. The resonance frequency of the pressure-sensitive element changes due to internal stress (tensile stress or compression stress) generated inside due to the force, and the detected pressure is detected by measuring the fluctuation of the resonance frequency.

  When manufacturing a pressure sensor, a diaphragm layer and a pressure sensitive element layer are first joined, and then a pressure sensitive element layer and a base layer are joined. Patent Document 1 discloses a technique for bonding using an adhesive.

  Here, when the bonding material used for bonding and the diaphragm layer, the pressure sensitive element layer, and the base layer have different thermal expansion coefficients, thermal distortion occurs due to temperature changes, and the internal stress changes due to the thermal distortion. To do. This change in internal stress fluctuates the resonance frequency of the pressure-sensitive element, resulting in a problem that the detection accuracy of the pressure to be measured is lowered.

  In order to prevent such pressure degradation due to thermal strain, Patent Documents 2 to 4 describe the thermal expansion coefficient of the bonding material as a crystal when the diaphragm layer, the base layer, and the pressure-sensitive element layer are each formed of a quartz substrate. It has been proposed to make the coefficient of thermal expansion approximately equal.

  If the thermal expansion coefficients of the diaphragm layer, the pressure sensitive element layer, and the base layer are substantially equal to the thermal expansion coefficient of the bonding material, the temperature of the environmental atmosphere of the exposed pressure sensor changes, and accordingly, the temperature of each member is changed. Even if expansion or contraction occurs, the bonding material also expands and contracts at the same rate (expansion rate), so internal stress due to thermal strain does not occur, resulting in degradation of pressure detection accuracy. Will not.

JP 2008-275445 A JP 2010-117342 A JP 2010-164500 A JP 2010-164362 A

However, when the thermal expansion coefficient of the bonding material is substantially equal to the thermal expansion coefficient of each member of the pressure sensor, the following problems occur.
When each member of the pressure sensor is made of quartz, since quartz is a crystal material, the coefficient of thermal expansion is about 14 (ppm / K), which is larger than general PbO (lead oxide) -based low melting point glass used for bonding materials. . PbO-based low-melting glass can be mixed with fillers such as metal oxides to increase the thermal expansion coefficient and match the thermal expansion coefficient of quartz, but the melting point decreases. After joining the members of the pressure sensor using low-melting glass whose melting point has been lowered by matching the thermal expansion coefficient with quartz in this way, the pressure sensor is mounted on a mounting board such as a circuit board by high-temperature processing such as reflow. Then, the low melting point glass joining the pair of base portions of the pressure sensitive element and the diaphragm layer is remelted. Due to this remelting, the fixing point between the pair of base portions of the pressure-sensitive element and the pair of support portions of the diaphragm is displaced, and the low-melting glass is re-cured in a state where the displacement is generated. It becomes. Therefore, the degree (degree) of thermal strain that occurs when the temperature of the environmental atmosphere changes and the expansion and contraction of each member is accompanied by a difference, compared to the thermal strain before remelting. The internal stress generated in the pressure sensitive element changes due to the difference in thermal strain, which causes a problem such as drift in the pressure value to be detected.

Accordingly, the present invention has been made to solve the above-described problem, and an object thereof is to provide a physical quantity detector that reduces the occurrence of pressure detection value drift due to high-temperature processing such as reflow, and a method for manufacturing the same. To do.
It is another object of the present invention to provide a physical quantity detector that can prevent fluctuations in internal stress due to thermal strain of a pressure-sensitive element due to a temperature change and can realize highly accurate pressure detection, and a method for manufacturing the same.

It is another object of the present invention to provide a physical quantity detector capable of detecting pressure with higher accuracy and a method for manufacturing the same in consideration of the degree of influence of remelting of a bonding material and thermal expansion coefficient due to high-temperature treatment such as reflow. And
Moreover, it aims at providing the manufacturing method of the physical quantity detector which can join each member favorably with a joining material.

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.
Application Example 1 A pressure-sensitive element including a pair of base portions and a pressure-sensitive portion disposed between the pair of base portions, and a pair of supports in which the pair of base portions are bonded via a second bonding material A diaphragm including a flexible portion provided with a portion, a support frame portion that supports a periphery of the flexible portion, and a fixed portion in which the support frame portion is fixed via a first bonding material. And a physical quantity detector, wherein the melting point of the second bonding material is higher than the melting point of the first bonding material.

  According to the present invention, the support frame portion and the fixed portion of the diaphragm are bonded using the first bonding material, and the pair of support portions of the diaphragm and the pair of base portions of the pressure sensitive element are bonded using the second bonding material. In addition, since the melting point of the second bonding material is higher than the melting point of the first bonding material, the remelting of the second bonding material should be reduced when performing high-temperature processing such as reflow on the physical quantity detector after manufacture. It is possible to reduce the fluctuation of the internal stress due to the thermal strain of the pressure sensitive element due to the remelting of the second bonding material, and to reduce the drift of the detection value.

Application Example 2 The physical quantity detector according to Application Example 1, wherein a thermal expansion coefficient of the first bonding material and a thermal expansion coefficient of a portion bonded by the first bonding material are substantially equal.
The portion bonded by the first bonding material has a coefficient of thermal expansion between the first bonding material and the portion bonded by the first bonding material, rather than the influence of the drift of the pressure detection value due to remelting of the first bonding material. Since the influence of the drift of the pressure detection value due to the deviation is large, the above configuration can further reduce the drift of the detection value due to the temperature change and improve the accuracy of the detection value.

Application Example 3 The absolute value of the difference in coefficient of thermal expansion between the first bonding material and the portion bonded by the first bonding material is determined by the second bonding material and the portion bonded by the second bonding material. 3. The physical quantity detector according to application example 1 or 2, wherein the physical quantity detector is smaller than an absolute value of a difference in thermal expansion coefficient between the two.
According to the present invention, since the thermal expansion coefficient of the first bonding material can be made closer to the thermal expansion coefficient of the portion bonded by the first bonding material, the detection value drift due to temperature change can be further reduced. And the accuracy of the detected value can be improved.

Application Example 4 Any one of Application Examples 1 to 3 including a base having the function of the fixing portion, wherein the base and the diaphragm are laminated so as to cover the pressure sensitive element. The physical quantity detector described in one example.
According to the present invention, the physical quantity detector includes a base having the function of the fixed portion, and also in the case of a three-layer structure in which the base and the diaphragm are laminated so as to cover the pressure sensitive element. It is possible to reduce the fluctuation of the internal stress due to the thermal strain of the pressure sensitive element, to reduce the drift of the detected value, and to improve the accuracy of the detected value.

Application Example 5 includes a frame portion that surrounds the pressure-sensitive element, and a connection portion that connects the frame portion and the pressure-sensitive element, and the frame portion has a function of the fixing portion. The physical quantity detector according to any one of Application Examples 1 to 3.
According to the present invention, the physical quantity detector includes a frame portion that surrounds the pressure-sensitive element, and a connection portion that connects the frame portion and the pressure-sensitive element, and the frame portion functions as the fixing portion. Even in the case where it is provided, it is possible to reduce the fluctuation of the internal stress due to the thermal strain of the pressure-sensitive element, to reduce the drift of the detection value, and to improve the accuracy of the detection value.

Application Example 6 The diaphragm, the frame portion, and the base are laminated so as to cover the pressure-sensitive element, and the frame portion uses the first bonding material for the joint portion of the base that faces the frame portion. The physical quantity detector according to Application Example 5, wherein the physical quantity detector is bonded to each other.
According to the present invention, even in the case of a three-layer structure in which the diaphragm, the frame portion, and the base are laminated so as to cover the pressure sensitive element, the fluctuation of internal stress due to thermal strain of the pressure sensitive element is reduced. This can reduce the occurrence of drift of the detected value and improve the accuracy of the detected value.

[Application Example 7] The application example 1 is characterized in that the portion bonded by the first bonding material is quartz, and the thermal expansion coefficient of the first bonding material is larger than the thermal expansion coefficient of the second bonding material. The physical quantity detector as described in any one of thru | or 6.
Since the thermal expansion coefficient of quartz is relatively large, the thermal expansion coefficient between the first bonding material and the portion bonded by the first bonding material is set by making the thermal expansion coefficient of the first bonding material larger than that of the second bonding material. The difference between the second bonding material can be reduced and the melting point of the second bonding material is made higher than the melting point of the first bonding material, thereby reducing the remelting of the second bonding material when heating is performed during mounting on the substrate. Therefore, the detection value drift can be suppressed as a whole, and the accuracy of the detection value can be improved.

Application Example 8 The physical quantity detector according to any one of Application Examples 1 to 7, wherein the second bonding material is a glass material.
According to the present invention, by using a glass material as the second bonding material, the melting point of the second bonding material can be made higher than the temperature at the time of heating when mounted on the substrate.

Application Example 9 The physical quantity detector according to Application Example 8, wherein the glass material contains fine metal particles.
According to the present invention, the melting point and the coefficient of thermal expansion can be adjusted by adjusting the amount of metal fine particles contained in the glass material.

[Application Example 10] In the method of manufacturing a physical quantity detector according to any one of Application Examples 1 to 9, the melting point of the second bonding material is determined when the physical quantity detector is mounted on a substrate. The manufacturing method of the physical quantity detector characterized by being higher than heating temperature.
According to the present invention, it is possible to prevent remelting of the second bonding material when heating is performed when the physical quantity detector is mounted on the substrate, and it is possible to prevent thermal distortion of the pressure sensitive element due to remelting of the second bonding material. It is possible to suppress the fluctuation of the internal stress caused and prevent the detection value from drifting and to detect the physical quantity with high accuracy.

[Application Example 11] A pressure-sensitive element including a pair of base portions and a pressure-sensitive portion disposed between the pair of base portions, and a pair of supports in which the pair of base portions are bonded via a second bonding material. A diaphragm including a flexible portion provided with a portion, a support frame portion that supports a periphery of the flexible portion, and a first joint in which the support frame portion has a melting point lower than a melting point of the second bonding material. A method of manufacturing a physical quantity detector including a fixed portion fixed via a material, the step of applying the second bonding material to the pair of support portions of the diaphragm, and the pair of support portions. The step of pre-baking the applied second bonding material, and the support frame portion on the main surface side of the diaphragm where the support portion is provided, the first bonding material is made thicker than the thickness of the second bonding material. A step of thickly applying the first bonding material applied to the support frame portion; Firing, heating the first bonding material to a temperature equal to or higher than the melting point of the first bonding material and lower than the melting point of the second bonding material, and using the first bonding material, the support frame portion of the diaphragm and the In a state where the first bonding step for bonding the fixing portion and the second bonding material and the pair of base portions of the pressure-sensitive element are in contact with each other, the heating is performed to a temperature equal to or higher than the melting point of the second bonding material. A method of manufacturing a physical quantity detector, comprising: a second joining step for joining the pair of support portions of the diaphragm and the pair of base portions of the pressure sensitive element using two joining materials.
According to the present invention, since the melting point of the second bonding material is higher than the melting point of the first bonding material, remelting of the second bonding material is prevented in high-temperature processing such as reflow performed after manufacturing the physical quantity detector. It is possible to suppress the fluctuation of internal stress due to the thermal strain of the pressure sensitive element.
Further, by making the thickness of applying the first bonding material thicker than that of the second bonding material, the first bonding material having a low melting point is first melted and bonded in a state of being in contact with the bonding portion, and then the high melting point is bonded. Since the second bonding material is melted and bonded, the low melting point first bonding material is exposed to a temperature above the melting point for a long time without being in contact with the bonding portion, and avoids the problem that it cannot be bonded due to crystallization. can do.

Application Example 12 In the first bonding step, the first bonding material applied to the support frame portion of the diaphragm and temporarily fired, and a frame portion that surrounds the pressure-sensitive portion and functions as the fixing portion. , And the support frame portion and the frame portion are bonded using the first bonding material by heating to a temperature equal to or higher than the melting point of the first bonding material and lower than the melting point of the second bonding material. The manufacturing method of the physical quantity detector of the application example 11 characterized by these.
According to the present invention, by changing the thickness for applying the first bonding material and the second bonding material, the first bonding material having a low melting point is first melted and bonded in contact with the frame portion, and then joined. Since the high melting point second bonding material contacts and melts and joins the pair of base parts of the pressure sensitive element, the low melting point first bonding material is exposed to a temperature above the melting point for a long time without contacting the frame portion. The problem of crystallization and inability to join can be avoided.

It is an expansion perspective view of the pressure sensor concerning a 1st embodiment of the present invention. It is a schematic cross section explaining the operation of the pressure sensor according to the embodiment. It is an example of the graph which shows the relationship between melting | fusing point and a thermal expansion coefficient according to the quantity of the filler contained in low melting glass. It is a figure explaining the procedure which carries out temporary baking of the 1st joining material and the 2nd joining material to a diaphragm layer. It is a figure explaining the procedure which fuses the 1st bonding material and the 2nd bonding material which were calcinated, and joins a diaphragm layer and a pressure sensitive element layer. It is a sectional side view of the pressure sensor concerning a 2nd embodiment. It is AA sectional drawing of the pressure sensor shown in FIG. It is a sectional side view of the pressure sensor concerning a 3rd embodiment. It is an expansion | deployment perspective view of the pressure sensor which concerns on a modification. It is a figure which shows the pressure sensor which concerns on the other modification at the time of using an AT cut vibrator | oscillator as a pressure sensitive part, (a) is a disassembled perspective view of the pressure sensor, (b) is a model of the pressure sensor It is sectional drawing, (c) is a top view of the pressure sensitive element layer with which the same pressure sensor is provided.

Hereinafter, an embodiment in which a physical quantity detector according to the present invention is applied to a pressure sensor will be described in detail with reference to the accompanying drawings.
FIG. 1 is a developed perspective view of the pressure sensor according to the first embodiment, and FIG. 2 is a schematic cross-sectional view for explaining the operation of the pressure sensor. In FIG. 1, illustration of the bonding material is omitted.

  As shown in FIG. 1, the pressure sensor 1 includes a pressure-sensitive element layer 10 and a diaphragm layer (“diaphragm”) that covers one main surface side and the other main surface side of the pressure-sensitive element layer 10 so as to be hermetically sealed. ”) And a base layer (corresponding to“ base ”) 30. Each of the layers 10, 20, and 30 has a quartz substrate as a base material.

  The pressure-sensitive element layer 10 has a double tuning fork element 106 as a pressure-sensitive element and a frame-shaped frame part 108 surrounding the periphery thereof at the center. In the present embodiment, the frame portion 108 corresponds to a “fixed portion”. The double tuning fork element 106 has a pair of parallel columnar beams 16a as pressure-sensitive portions, and a pair of base portions 16b connected to both ends of both columnar beams 16a. The double tuning fork element 106 is a so-called double tuning fork type piezoelectric vibrator that changes its resonance frequency when a tensile stress or a compressive stress is applied to the columnar beam 16a.

The frame portion 108 is connected to the double tuning fork element 106 via a pair of beam-like connecting portions 110 extending from each base portion 16b in a direction orthogonal to the columnar beam 16a.
The double tuning fork element 106 is provided with an excitation electrode (not shown) and an extraction electrode (lead electrode) extending from the excitation electrode, and the extraction electrode is extracted to the frame portion 108 via the connection portion 110. Yes.

  The diaphragm layer 20 has a pressure receiving surface 204 that receives a pressure to be measured on one main surface side. The pressure receiving surface 204 is a flexible portion having flexibility, and deforms when receiving pressure from outside to be measured. A frame-shaped support frame portion 206 is formed on the periphery of the pressure receiving surface 204, and the support frame portion 206 is disposed so as to face the frame portion 108 of the pressure-sensitive element layer 10.

  A pair of base portions 16b of the double tuning fork element 106 is fixed to the other main surface side of the diaphragm layer 20 and the back surface of the pressure receiving surface 204, and the pressure receiving surface 204 is deformed by the deformation of the pressure receiving surface 204. A pair of support portions 210 are provided for converting the pressure to be measured received in step 1 into force and transmitting it to the double tuning fork element 106.

Each support part 210 of the diaphragm layer 20 and each base part 16 b of the double tuning fork element 106 are joined via a second joining material 50.
Further, the support frame portion 206 on the other main surface side of the diaphragm layer 20 and the frame portion 108 on the one main surface side of the pressure-sensitive element layer 10 are bonded via the first bonding material 40.

  In the present embodiment, low melting point glass containing metal fine particles is used for the first bonding material 40 and the second bonding material 50. Furthermore, the first bonding material 40 and the second bonding material 50 have different metal fine particle contents. In the present embodiment, PbO (lead oxide) is used as the metal fine particles contained in the bonding material. The metal fine particles to be contained are not limited to PbO but may be titanium, bismuth, silver oxide, or the like. In addition, when each of the first bonding material 40 and the second bonding material 50 is applied to the bonding portion, a material that is dissolved in an organic solvent into a paste material is used.

  FIG. 3 is an example of a graph showing the relationship between the melting point (° C.) and the thermal expansion coefficient (ppm / K) according to the amount of filler (metal fine particles) contained in the low-melting glass. As shown in FIG. 3, for example, when the content of the filler relative to the low-melting glass is small and the melting point is 330 ° C., the thermal expansion coefficient is slightly larger than 10 ppm / K. On the other hand, when the content of the filler with respect to the low-melting glass is increased and the melting point is 252 ° C., the thermal expansion coefficient is 13 ppm / K. Thus, the higher the filler content relative to the low-melting glass, the lower the melting point and the higher the thermal expansion coefficient. By utilizing such a relationship, it is possible to adjust the melting point and the coefficient of thermal expansion of the low-melting glass by adjusting the amount of filler contained in the low-melting glass.

  In the present embodiment, the melting point of the second bonding material 50 is 320 ° C., and the thermal expansion coefficient is 11 ppm / K. Since the reflow temperature when the pressure sensor 1 is mounted on a mounting substrate such as a circuit board is about 270 ° C., the second bonding material 50 is re-reflowed by reflow by setting the melting point of the second bonding material 50 to 320 ° C. Does not melt.

  The double tuning fork element 106 is easily affected by changes in internal stress due to thermal strain, and the pressure detection value drift is likely to occur. Therefore, the second bonding material 50 that joins the double tuning fork element 106 to the diaphragm layer 20 is remelted. By preventing this, drift of the detected pressure value can be prevented, and highly accurate pressure detection can be realized.

That is, when the pressure sensor according to the present invention is mounted on a circuit board by reflowing at a heating temperature of 270 ° C., the low melting point glass joining the pair of base portions of the pressure sensitive element and the diaphragm layer has a melting point temperature. Since it is 320 ° C., it does not melt.
Therefore, the fixing point between the pair of base portions of the pressure-sensitive element and the pair of support portions of the diaphragm layer can be prevented from being displaced due to melting of the low melting point glass.

  Therefore, in the pressure sensor according to the present invention, the degree (degree) of thermal strain that occurs when the temperature of the environmental atmosphere changes and the expansion and contraction of each member is accompanied by the change in the temperature (after the reflow). Therefore, the pressure value to be detected drifts due to the change in internal stress generated in the pressure-sensitive element due to the reflow. It exhibits an excellent effect of preventing the problem of fluctuations.

  In addition, the value of the melting | fusing point and thermal expansion coefficient of the 2nd joining material 50 mentioned above is only an example. By adjusting the amount of the metal fine particles contained in the low melting point glass and lowering the melting point of the second bonding material 50 within a range not lower than the reflow temperature, the thermal expansion coefficient is increased to increase the thermal expansion coefficient of the second bonding material 50. If the thermal expansion coefficient of the quartz is made closer, the drift of the pressure detection value can be further reduced.

  On the other hand, in the present embodiment, the melting point of the first bonding material 40 is 260 ° C., and the thermal expansion coefficient is 13 ppm / K. Since the first bonding material 40 has a larger amount of metal fine particles to be mixed than the second bonding material 50, the first bonding material 40 has a lower melting point and a higher thermal expansion coefficient than the second bonding material 50.

  The thermal expansion coefficient of quartz is a Z-cut substrate that is a substrate in which the plane including the X axis (electric axis) and the Y axis (mechanical axis) and the principal surface are generally used in a tuning fork type piezoelectric vibrator. (Substrate whose Z axis (optical axis) is orthogonal to the main surface) or the frequency temperature characteristics of a tuning-fork type piezoelectric vibrator, the peak temperature (vertical temperature) of a convex quadratic curve is the operating temperature In the quartz substrate cut out by the cut angle obtained by rotating the Z-cut substrate several times around the X axis of the quartz crystal so that it is in the middle of the range, in the temperature range from room temperature to 120 ° C., it is about 14 ppm / K. is there. According to the knowledge obtained from the results of experiments conducted by the inventor of the present application, it is confirmed that it is effective if the thermal expansion coefficients are matched within a range of ± 1 ppm / K. It was also found that when higher detection accuracy is required, it is preferable to match within a range of ± 0.1 ppm / K.

  The area of the frame portion 108 on one main surface side of the pressure-sensitive element layer 10 bonded by the first bonding material 40 (the area of the support frame portion 206 on the other main surface side of the diaphragm layer 20) is the second bonding. Since the area of the base portion 16b of the pressure-sensitive element layer 10 joined by the material 50 is larger than the area of the support portion 210 of the diaphragm layer 20, the decrease in pressure detection accuracy is first caused by the effect of remelting due to reflow. The influence on the deviation of the thermal expansion coefficient between the bonding material 40 and the portion bonded by the first bonding material 40 is greater. Therefore, for the first bonding material 40, even if the melting point is lower than the reflow temperature and there is a possibility of remelting during high temperature processing such as reflow, priority is given to matching the thermal expansion coefficient to the crystal. Thereby, the drift of the pressure detection value by a temperature change can be made small, and the precision of a pressure detection value can be improved.

  As described above, when the pressure-sensitive element layer 10 and the diaphragm layer 20 are based on a quartz substrate, the bonding between the support portion 210 and the base portion 16b is greatly affected by the drift of the pressure detection value caused by the remelting of the bonding material. The second bonding material 50 having a small coefficient of thermal expansion but a high melting point is used, and the frame part 108 of the pressure-sensitive element layer 10 and the support frame part 206 of the diaphragm layer 20 are greatly affected by the deviation of the coefficient of thermal expansion. For bonding, the accuracy of the pressure detection value can be improved as a whole by using the first bonding material 40 having a large thermal expansion coefficient and a low melting point.

  In this way, by using two types of bonding materials with different melting points and thermal expansion coefficients, pressure that does not cause pressure detection value drift due to high-temperature processing such as reflow, while preventing pressure detection accuracy from deteriorating due to temperature changes. A sensor 1 can be provided.

  When the base material of the pressure-sensitive element layer 10 and the diaphragm layer 20 is other than the quartz substrate, the thermal expansion coefficient is the portion joined by the first bonding material 40 and the first bonding material 40 (support frame). The absolute value of the difference between the thermal expansion coefficients of the portion 206 and the frame portion 108) is the thermal expansion coefficient between the second bonding material 50 and the portion (the support portion 210 and the base portion 16b) bonded by the second bonding material 50. By making it smaller than the absolute value of the difference, the same effect as described above can be obtained.

The base layer 30 is a member for sealing the internal space S that houses the double tuning fork element 106. The base layer 30 is disposed so as to cover the other main surface side of the pressure-sensitive element layer 10. A recess 302 for forming the internal space S is formed on the main surface of the base layer 30 on the pressure sensitive element layer 10 side. A frame-shaped outer peripheral frame portion 304 is provided so as to surround the recess 302. The outer peripheral frame portion 304 is bonded to the frame portion 108 on the other main surface side of the pressure-sensitive element layer 10 via the first bonding material 40, and the outer peripheral frame portion 304 is used as a bonding portion. In the present embodiment, the diaphragm layer 20, the frame portion 108 of the pressure sensitive element layer 10, and the base layer 30 constitute a container, and the internal space S is a frame of the diaphragm layer 20 and the pressure sensitive element layer 10. The space is surrounded by the portion 108 and the base layer 30.
A sealing hole 306 penetrating in the thickness direction is provided at the center of the base layer 30. The sealing hole 306 is used to evacuate the internal space S.

  Here, the area of the frame portion 108 on the other main surface side of the pressure-sensitive element layer 10 bonded by the first bonding material 40 (the area of the outer peripheral frame portion 304 of the base layer 30) is determined by the second bonding material 50. Since it is larger than the area of the base portion 16b of the pressure-sensitive element layer 10 being bonded (the area of the support portion 210 of the diaphragm layer 20), as described above, the drift of the pressure detection value due to remelting of the first bonding material 40 The influence of the drift of the pressure detection value due to the deviation of the thermal expansion coefficient between the first bonding material 40 and the portion bonded by the first bonding material 40 is greater than the influence. Therefore, when the outer peripheral frame portion 304 of the base layer 30 and the frame portion 108 on the other main surface side of the pressure-sensitive element layer 10 are joined, there is a possibility that the melting point is low and remelting occurs during high temperature processing such as reflow. By using the first bonding material 40 whose thermal expansion coefficient matches that of quartz, the drift of the pressure detection value due to temperature change can be reduced, and the accuracy of the pressure detection value can be improved.

  In addition, when the base material of the pressure-sensitive element layer 10 and the base layer 30 is other than the quartz substrate, the thermal expansion coefficient is the portion joined by the first bonding material 40 and the first bonding material 40 (the outer peripheral frame). The absolute value of the difference in thermal expansion coefficient between the second bonding material 50 and the second bonding material 50 (the support portion 210 and the base portion 16b) By making it smaller than the absolute value of the difference, the same effect can be obtained.

Although not shown, an electrode terminal is provided on the surface exposed to the outside of the base layer 30, and this electrode terminal inputs / outputs signals to / from the double tuning fork element 106 via a conductive pattern (not shown). I do.
The pressure sensor 1 configured as described above is hermetically sealed inside and kept in a vacuum state, and is a sensor that detects absolute pressure.

  Here, the basic operation of the pressure sensor 1 will be described with reference to FIG. As shown in FIG. 2, when the pressure sensor 1 receives pressure from the outside, the pressure receiving surface 204 of the diaphragm layer 20 bends in the arrow A direction. Due to the bending of the pressure receiving surface 204 of the diaphragm layer 20, the support portions 23 of the diaphragm layer 20 are displaced in the direction of arrow B in which the distance between them is increased.

  As a result, the columnar beam 16a, which is the pressure-sensitive portion of the double tuning fork element 106 that is joined in a state of being spanned between the support portions 210, is displaced by applying a tensile force in the direction of arrow B, so that a tensile stress is generated. As a result, the resonance frequency of the double tuning fork element 106 increases.

On the other hand, when the pressure from the outside is lower than the vacuum state inside the pressure sensor 1, the pressure receiving surface 204 of the diaphragm layer 20 bends in the direction opposite to the arrow A, and the respective support portions 210 are narrowed by the arrows B. Displaces in the opposite direction.
As a result, a compressive force is applied to the double tuning fork element 106 to cause displacement, and a compressive stress is generated, so that the resonance frequency of the double tuning fork element 106 is lowered.

  The double tuning fork element 106 is electrically connected to an oscillation circuit (not shown), and vibrates at an inherent resonance frequency by an AC voltage supplied from the oscillation circuit. The oscillation circuit outputs an electrical signal indicating the resonance frequency of the double tuning fork element 106, and a calculation means (not shown) calculates the pressure from the change in the resonance frequency indicated by the signal. The double tuning fork element 106 has a large change in resonance frequency with respect to the applied force, and can detect pressure with high sensitivity. In other words, the double tuning fork type piezoelectric vibrator has a significantly larger resonance frequency change due to the expansion / compression stress generated in the pressure sensitive part (columnar beam) than the thickness shear vibrator using AT cut quartz. Since the variable width of the frequency is large, a force sensor excellent in decomposing ability that detects a slight physical quantity difference (pressure difference) is a suitable pressure-sensitive element.

  Next, an example of a manufacturing method of the pressure sensor 1 will be described with reference to FIGS. First, with reference to FIG. 4, a procedure for temporarily firing the second bonding material 50 and the first bonding material 40 on the diaphragm layer 20 will be described. 4A shows a schematic cross-sectional view of the diaphragm layer 20, and FIG. 4B shows a plan view of the diaphragm layer 20 as viewed from the other main surface side. The diaphragm layer 20 is formed by a photolithography technique and a processing method such as an etching technique or a sand blast method.

First, using the screen mask A, the second bonding material 50 dissolved in an organic solvent and formed into a paste is applied to the surfaces of the pair of support portions 210 of the diaphragm layer 20 (step 1).
Next, the second bonding material 50 is temporarily fired at a temperature of about 390 ° C. At this time, the organic component is volatilized from the second bonding material 50 (step 2).

Next, using the screen mask B, the first bonding material 40 dissolved in an organic solvent and pasted into the support frame 206 on the other main surface side of the diaphragm layer 20 is applied thicker than the second bonding material 50. (Step 3).
Next, the first bonding material 40 is temporarily fired at 290 ° C. (step 4).

  Next, with reference to FIG. 5, the procedure for melting the temporarily fired first bonding material 40 and second bonding material 50 and bonding the diaphragm layer 20 and the pressure-sensitive element layer 10 will be described. 5A and 5B are schematic cross-sectional views of the diaphragm layer 20.

  First, the temporarily fired first bonding material 40 in the diaphragm layer 20 and the frame portion 108 of the pressure-sensitive element layer 10 are brought into contact with each other. Then, the first bonding material 40 is melted by heating at a temperature equal to or higher than the melting point (260 ° C.) of the first bonding material 40 and lower than the melting point (320 ° C.) of the second bonding material 50, for example, 280 ° C. Then, the support frame portion 206 of the diaphragm layer 20 and the frame portion 108 of the pressure-sensitive element layer 10 are bonded with the first bonding material 40 (step 5, first bonding step).

  When the first bonding material 40 is melted in Step 5, the second bonding material 50 of the diaphragm layer 20 and the base portion 16b of the pressure-sensitive element layer 10 come into contact with each other. In this state, the second bonding material 50 is heated at a temperature equal to or higher than the melting point (320 ° C.) of the second bonding material 50, for example, 330 ° C. for about 10 minutes to melt the second bonding material 50, and the second bonding material 50 forms the diaphragm layer 20. The support part 210 and the base part 16b of the pressure-sensitive element layer 10 are joined (step 6, second joining step).

  According to the manufacturing method of the pressure sensor 1 as described above, the first bonding material 40 having a low melting point is first melted and bonded in contact with the pressure-sensitive element layer 10, and then the second bonding material 50 having a high melting point is sensed. The pressure element contacts and melts and joins. Therefore, it is possible to avoid the problem that the first bonding material 40 having a low melting point is exposed to a temperature equal to or higher than the melting point for a long time without being in contact with the pressure-sensitive element layer 10 to be crystallized and cannot be bonded.

  The subsequent bonding of the pressure-sensitive element layer 10 and the base layer 30 with the first bonding material 40 is a process for bonding the pressure-sensitive element layer 10 and the diaphragm layer 20 with the first bonding material 40. It can be performed by combining the third step and the sixth step.

  Next, a second embodiment will be described. 6 is a side sectional view of the pressure sensor 1A according to the second embodiment, and FIG. 7 is a sectional view taken along line AA of the pressure sensor 1A shown in FIG. In these drawings, the same components as those described in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The second embodiment is different from the first embodiment in that the pressure sensor 1A according to the second embodiment includes the frame portion 108 that surrounds the double tuning fork element 106 described in the first embodiment, and the frame portion 108 and the double portion. The connection portion 110 that connects the tuning fork element 106 is not provided. Therefore, in the first embodiment, the frame portion 108 corresponds to the “fixed portion”, and the support frame portion 206 of the diaphragm layer 20 and the outer peripheral frame portion 304 of the base layer 30 facing the support frame portion 206 are sensed. The three-layer structure is formed by using the first bonding material 40 with the frame portion 108 of the pressure element layer 10 interposed therebetween. However, in the second embodiment, the base layer 30 corresponds to the “fixing portion”, and the diaphragm layer The 20 support frame portions 206 and the outer peripheral frame portion 304 of the base layer 30 facing the support frame portion 206 are bonded using the first bonding material 40 to form a two-layer structure.

  In the second embodiment, the diaphragm layer 20 and the base layer 30 constitute a container, and the internal space S is constituted by a space surrounded by the diaphragm layer 20 and the base layer 30.

As a manufacturing method of the pressure sensor 1A, the same method as in the first embodiment can be used. However, in the step of the second embodiment corresponding to step 5 shown in FIG. 5 in the first embodiment, the support frame portion 206 of the diaphragm layer 20 and the main surface of the diaphragm layer 20 face upward. When the outer peripheral frame portion 304 of the base layer 30 is brought into contact with the first bonding material 40, in the second embodiment, there is no frame portion around the double tuning fork element 106. I can't keep it inside. Therefore, in the second embodiment, the pair of base portions 16b of the double tuning fork element 106 are placed on the pair of support portions 210 of the diaphragm layer 20 with the other main surface of the diaphragm layer 20 facing upward. At the same time, the outer peripheral frame portion 304 of the base layer 30 may be placed on the support frame portion 206 of the diaphragm layer 20 and the steps 5 and thereafter may be performed.
Other configurations are the same as those of the first embodiment.

  Next, a third embodiment will be described. FIG. 8 is a side sectional view of a pressure sensor 1B according to the third embodiment. In the figure, the same components as those described in the above-described embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The difference between the pressure sensor 1B according to the third embodiment and the pressure sensor 1A according to the second embodiment is that the pressure sensor 1A according to the second embodiment is an absolute manometer, whereas the pressure sensor 1B according to the second embodiment relates to the third embodiment. The pressure sensor 1B is a relative pressure gauge.

  The pressure sensor 1B according to the third embodiment includes a diaphragm layer 30A instead of the base layer 30 included in the pressure sensor 1A according to the second embodiment. A strut 60 is provided between the diaphragm layer 20 and the diaphragm layer 30A to transmit the deformation of one diaphragm layer to the other. The struts 60 may be disposed on both sides of the double tuning fork element 106.

  In the pressure sensor 1B having such a configuration, when pressure is applied to the diaphragm layer 20 side, the pressure receiving surface 204 is deformed downward in the drawing. Thereby, the double tuning fork element 106 fixed to the support part 210 receives a tensile force, and the frequency increases. On the other hand, when pressure is applied to the diaphragm layer 30A side, the main surface of the diaphragm layer 30A is deformed upward in the drawing. By providing the column 60, the pressure receiving surface 204 of the diaphragm layer 20 is also deformed upward in the figure following the deformation of the diaphragm layer 30A. As a result, the pair of support portions 210 are inclined toward the center, so that the double tuning fork element 106 fixed to the support portion 210 receives a compression force, and the frequency thereof decreases. As described above, the pressure sensor 1B can detect the pressure even when the pressure is applied to any of the diaphragm layers 20 and 30A. Other configurations are the same as those of the second embodiment.

  In the above-described embodiment, the pair of columnar beams 16a is used as the pressure sensitive part, but the pressure sensitive part is not limited to this. For example, as shown in FIG. 9, the pressure-sensitive part may be composed of one columnar beam (also referred to as a single beam).

  Further, a thickness shear vibrator (hereinafter referred to as an AT cut vibrator) using an AT cut crystal may be used as the pressure sensitive portion. By using an AT-cut vibrator as the pressure-sensitive portion, frequency stability with respect to temperature can be improved, frequency temperature characteristics can be improved, and a pressure sensor that is strong against impact and can be made strong.

  FIG. 10A shows an example of an exploded perspective view of a pressure sensor 1C using an AT-cut vibrator as a pressure-sensitive part, and FIG. 10B shows a schematic cross-sectional view of the pressure sensor 1C. 10 (c) shows a plan view of the pressure-sensitive element layer 10A included in the pressure sensor 1C. In these drawings, the same components as those described in the above-described embodiment are denoted by the same reference numerals, and the description thereof is omitted. As shown in these drawings, the pressure sensor 1C has a configuration in which the pair of columnar beams 16a of the double tuning fork vibrator 106 included in the pressure sensor 1 according to the first embodiment is replaced with an AT cut vibrator 17. .

  The AT cut vibrator 17 includes a crystal piece 17a cut out at a cut angle called AT cut. The AT cut is a plane (Y plane) including the X axis and the Z axis, which are crystal axes of quartz, rotated about 35 degrees 15 minutes from the + Z axis to the −Y axis direction with the X axis as the rotation axis. It is a cut angle cut out so that the obtained surface becomes the main surface. An excitation electrode 17b for exciting the crystal piece 17a is provided at the center of the front and back surfaces (not shown) of the crystal piece 17a. An extraction electrode 17c is connected to the excitation electrode 17b, and is extracted toward the peripheral edge on one side in the length direction of the crystal piece 17a. The lead electrode 17c is electrically connected to the frame side mount electrode 94 provided on the frame portion 108 via the mount electrode 60 provided on the base portion 16b and the connection pattern 92 provided on the connection portion 110 and the frame portion 108. doing. When the pressure-sensitive element layer 10 </ b> A is sandwiched between the diaphragm layer 20 and the base layer 30, the frame-side mount electrode 94 is viewed in plan from the support frame portion 206 of the diaphragm layer 20 and the outer peripheral frame portion 304 of the base layer 30. It is provided at the overlapping position. The frame side mount electrode 94 is electrically connected to an electrode provided outside the pressure sensor 1A by a connection pattern (not shown).

  Such a pressure sensor 1C operates in the same manner as the pressure sensor 1 described with reference to FIG. 2 in the above-described embodiment. That is, when the diaphragm layer 20 receives the pressure to be detected and bends and displaces, the displacement is converted into a force through the diaphragm layer 20 and transmitted to the AT-cut vibrator 17. Internal stress (tensile stress, compressive stress) is generated in the AT-cut vibrator 17 to which the force is transmitted, and the resonance frequency changes. The change in resonance frequency can be measured to detect the detected pressure.

  As described above, when each member constituting the pressure sensor uses a quartz substrate as a base material, the second bonding material 50 for bonding the double tuning fork element 106 as a pressure sensitive element is made of quartz with a small thermal expansion coefficient. Although the difference in the thermal expansion coefficient is large, by making the melting point higher than that of the first bonding material 40 so as not to be re-melted by high-temperature processing such as reflow, the thermal strain of the pressure-sensitive element mounted on the diaphragm is reduced. It is possible to suppress the fluctuation of the internal stress caused.

  Further, the joining of the frame portions of the members constituting the pressure sensor is joined by the first joining material 40 and the first joining material 40 rather than the influence of the drift of the pressure detection value due to the remelting of the first joining material 40. Since the influence of the deviation of the thermal expansion coefficient with the portion that is being heated is large, the pressure detection value drift due to the deviation of the thermal expansion coefficient can be reduced by bonding using the first bonding material 40 having a thermal expansion coefficient close to that of the crystal. This can prevent the accuracy of the pressure detection value.

  In addition, when the pressure sensor is manufactured, the first bonding material 40 before heating is made thicker than the second bonding material 50 so that the first bonding material 40 having a low melting point is first formed into the pressure-sensitive element layer 10. The first bonding material 40 can be melted in contact with the second bonding material 50, and then the second bonding material 50 can be melted in the state where the high melting point second bonding material 50 is in contact with the pressure-sensitive element layer 10. It is possible to avoid the problem that the first bonding material 40 is exposed to a temperature equal to or higher than the melting point for a long time without being in contact with the bonding target portion, and is crystallized and cannot be bonded.

  In the above-described embodiment, the pressure sensor that detects the pressure of gas or liquid has been described. However, the physical quantity detector according to the present invention is not limited to this, and external force due to pressing of the finger when pressed directly with a finger or the like. Needless to say, the present invention can be widely applied to a force sensor for detecting the pressure and a sensor for detecting other physical quantities.

DESCRIPTION OF SYMBOLS 1, 1A ......... Pressure sensor 10, 10A ......... Pressure-sensitive element layer, 106 ......... Double tuning fork element, 16a ......... Columnar beam, 16b ......... Base, 17 ...... AT cut vibrator, 17a ......... crystal piece, 17b ......... excitation electrode, 17c ...... extraction electrode, 108 ......... frame portion, 110 ......... connection portion, 20 ......... diaphragm layer, 204 ...... pressure-receiving surface, 206 ......... Support frame part, 210 ......... Support part, 30 ......... Base layer, 302 ......... Recess, 304 ......... Outer frame part, 306 ......... Sealing hole, 40 ......... First joint Material: 50 ......... second bonding material, 60 ... support.

Claims (12)

A pressure-sensitive element including a pair of base portions and a pressure-sensitive portion disposed between the pair of base portions;
A diaphragm including a flexible portion including a pair of support portions to which the pair of base portions are bonded via a second bonding material; and a support frame portion that supports a peripheral edge of the flexible portion;
A fixing part in which the support frame part is fixed via a first bonding material;
With
The physical quantity detector, wherein the melting point of the second bonding material is higher than the melting point of the first bonding material. A coefficient of thermal expansion of the first bonding material;
The physical quantity detector according to claim 1, wherein a coefficient of thermal expansion of a portion joined by the first joining material is substantially equal. The absolute value of the difference in thermal expansion coefficient between the first bonding material and the portion bonded by the first bonding material is:
The physical quantity detector according to claim 1, wherein the physical quantity detector is smaller than an absolute value of a difference in thermal expansion coefficient between the second bonding material and a portion bonded by the second bonding material. Including a base having the function of the fixing portion;
The physical quantity detector according to claim 1, wherein the base and the diaphragm are stacked so as to cover the pressure-sensitive element. A frame portion surrounding the pressure sensitive element, and a connecting portion for connecting the frame portion and the pressure sensitive element,
The physical quantity detector according to claim 1, wherein the frame portion has a function of the fixing portion. The diaphragm, the frame part and the base are laminated so as to cover the pressure sensitive element,
The physical quantity detector according to claim 5, wherein the frame portion is bonded to the bonding portion of the base facing the frame portion using the first bonding material. The portion bonded by the first bonding material is quartz,
The physical quantity detector according to claim 1, wherein a thermal expansion coefficient of the first bonding material is larger than a thermal expansion coefficient of the second bonding material.   The physical quantity detector according to claim 1, wherein the second bonding material is a glass material.   The physical quantity detector according to claim 8, wherein the glass material contains metal fine particles. A method for manufacturing a physical quantity detector according to any one of claims 1 to 9,
The method of manufacturing a physical quantity detector, wherein the melting point of the second bonding material is higher than a heating temperature when the physical quantity detector is mounted on a substrate. A pressure-sensitive element including a pair of base portions and a pressure-sensitive portion disposed between the pair of base portions;
A diaphragm including a flexible portion including a pair of support portions to which the pair of base portions are bonded via a second bonding material; and a support frame portion that supports a peripheral edge of the flexible portion;
A method of manufacturing a physical quantity detector, comprising: a fixing portion in which the support frame portion is fixed via a first bonding material having a melting point lower than the melting point of the second bonding material,
Applying the second bonding material to the pair of support portions of the diaphragm;
Pre-baking the second bonding material applied to the pair of support parts;
Applying the first bonding material thicker than the second bonding material to the support frame portion on the main surface side of the diaphragm where the support portion is provided;
Pre-baking the first bonding material applied to the support frame part;
The first bonding material is heated to a temperature equal to or higher than the melting point of the first bonding material and lower than the melting point of the second bonding material, and the support frame portion and the fixing portion of the diaphragm are bonded to each other using the first bonding material. A first joining step to perform,
In a state where the second bonding material and the pair of bases of the pressure-sensitive element are in contact with each other, the second bonding material is heated to a temperature equal to or higher than the melting point of the second bonding material, and the pair of diaphragms is used by using the second bonding material. A method of manufacturing a physical quantity detector, comprising: a second joining step of joining a support part and the pair of base parts of the pressure-sensitive element.   In the first bonding step, the first bonding material applied to the support frame portion of the diaphragm and temporarily fired is brought into contact with the frame portion surrounding the pressure-sensitive portion and having the function of the fixing portion, The support frame portion and the frame portion are bonded to each other using the first bonding material by heating to a temperature equal to or higher than the melting point of the first bonding material and lower than the melting point of the second bonding material. Item 12. A method for producing a physical quantity detector according to Item 11.

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