JP2006234463A - Inertial sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inertial sensor which assured leak vibration suppression effect and anti-shock performance against external shock vibration of a detection element and can reduce the size. <P>SOLUTION: A natural frequency of the flexible resin substrate 7 facing the mounting part 71 of a sensing element 8 by way of a spring 72 and having a substrate base 74 arranged so as to have a specific difference of level 73 to the mounting part 71 is constituted to be larger than the difference in the natural frequency in the sensing direction from the natural frequency in the drive direction of the sensing element 8 and smaller range than the lowest frequency excited by the sensing element 8 by external vibration. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a surface mount type inertial sensor.

  In recent years, systems that perform safety control and navigation of automobiles by detecting an inertia amount such as an angular velocity of a vehicle have become widespread.

  A detection element made up of a tuning fork type or columnar type vibrator that detects the angular velocity of an inertial sensor used in such a system, for example, is supported by an elastic material to suppress leakage of vibration to the outside. is doing.

  Such a conventional sensing element is shown in FIG. The detection element is composed of a cylindrical piezoelectric ceramic body 1, and concave portions 1 a are provided in two portions of the piezoelectric ceramic body 1. A ring-shaped support 2 is disposed in the recess 1a. Here, since the support tool 2 consists of an elastic body, it can be made to fit in the recessed part 1a. The piezoelectric ceramic body 1 is supported by fixing the support 2 to a case (not shown).

  With such a configuration, since the leakage of the vibration of the piezoelectric ceramic body 1 to the outside is absorbed by the support 2, the leakage vibration affects a mechanical transfer function such as an external structure (for example, a joint of a substrate or a case). As a result, offset drift due to “bounce”, temperature drift due to temperature change of transfer function, deterioration of member, and change with time are improved.

  Furthermore, the impact vibration from the outside of the inertial sensor accompanying the running of the automobile is absorbed by the elastic material, and the shock resistance can be ensured.

For example, Patent Document 1 is known as prior art document information relating to the present application.
Japanese Utility Model Publication No. 5-73518

  However, in view of the need for further downsizing as an inertial sensor in the future, with the conventional configuration, it becomes difficult to ensure a leakage vibration suppressing effect and impact resistance while downsizing the sensing element.

  This is a contradictory performance (for example, if the rigidity of the support part of the sensing element is lowered to suppress leakage vibration, the strength of the support part when applying an impact will be reduced). This is because the size of the part must also be reduced.

  Specifically, in order to reduce the size of the inertial sensor to a surface-mounting type having a high mounting area of several millimeters square, the sensing element is also required to have a size of several millimeters. It can be applied to such ultra-compact sensing elements, designing an elastic support member having a conventional configuration that ensures a leakage vibration suppressing effect and impact resistance, and using it, an inertial sensor with high yield can be used. Manufacturing is extremely difficult in practice.

  The present invention solves the above-described conventional problems, and an object of the present invention is to provide an inertial sensor that can be reduced in size while ensuring a leakage vibration suppressing effect and impact resistance.

  In order to solve the above-described conventional problems, the inertial sensor of the present invention may have a substrate base that is disposed so as to face the attachment portion of the detection element via a spring portion and have a predetermined step with respect to the attachment portion. The natural frequency of the flexible resin substrate is larger than the frequency difference between the natural frequency in the driving direction of the detection element and the natural frequency in the detection direction, and smaller than the lowest frequency excited in the detection element by external vibration. It is configured.

  With this configuration, the detection element is substantially elastically supported by the spring portion of the flexible resin substrate. As a result, the object can be achieved.

  According to the inertial sensor of the present invention, the leakage vibration of the detection element is attenuated by the intervention of the spring portion of the flexible resin substrate that is the support member. As a result, the influence of the leakage vibration from the detection element can be reduced, and the external impact can be reduced. Etc. are attenuated by the flexible resin substrate, so that it is possible to reduce the size while securing the leakage vibration suppressing effect and the impact resistance.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

(Embodiment 1)
1A and 1B show the inside of an inertial sensor according to Embodiment 1 of the present invention. FIG. 1A is a plan view and FIG. 1B is a cross-sectional view taken along line AA in FIG. FIG. 2 is a plan view of the flexible resin substrate of the inertial sensor according to Embodiment 1 of the present invention. 3A and 3B show a flexible resin substrate that supports the sensing element of the inertial sensor according to Embodiment 1 of the present invention. FIG. 3A is a top view and FIG. 3B is a side view. 4A and 4B show a detection element of the inertial sensor according to Embodiment 1 of the present invention. FIG. 4A is a perspective view at the time of stop, FIG. 4B is a drive time, and FIG. 5 shows a cross-sectional view of the inertial sensor according to Embodiment 1 of the present invention when an external impact vibration is applied. FIG. 5A is a cross-sectional view taken along the line AA in FIG. 1, and FIG. Each figure is shown. FIGS. 6A and 6B show output temporal characteristics when the external impact is applied to the inertial sensor according to the first embodiment of the present invention. FIG. 6A is an external impact waveform diagram, and FIG. An output waveform diagram is shown, and (c) is a sensor output waveform diagram when a spring portion is provided. FIG. 7 is a cross-sectional view showing a modification of the inertial sensor according to Embodiment 1 of the present invention.

  In FIG. 1 (a), the outer container 3 is made of a ceramic package, and the base walls 3a and 3b having different heights are provided on the inner wall thereof. Terminals 3c and 3d of a plurality of wiring conductors 30 that are integrally formed so as to be housed in the outer container 3 are formed on the upper surfaces of the bases 3a and 3b. All the terminals 3 c are electrically connected one-to-one by a part of the terminal 3 d and the wiring conductor 30. The remaining terminal 3d is connected to an external terminal (not shown) provided on the back surface of the outer container 3 so as to be used for power supply, sensor output, and digital calibration.

  A circuit IC 6 is fixed to the bottom surface of the outer container 3 by die bonding. The circuit IC6 is provided with a plurality of pads 6a. A wire 6b is connected between the pad 6a and the terminal 3d by wire bonding. Thereby, the circuit IC 6 is electrically connected to the wiring conductor 30.

  On the upper part of the circuit IC 6, the detection element 8 is supported by a mounting portion 71 provided on a part of the strip-shaped flexible resin substrate 7 so as not to contact the circuit IC 6.

  A substrate base portion 74 is disposed so as to face the attachment portion 71 via a spring portion 72 and to have a predetermined step 73 with the attachment portion 71. The step 73 is formed by bending the flexible resin substrate 7 into a crank shape.

  Here, since the detection element 8 is supported by the attachment portion 71 so as to face the substrate base portion 74, the detection element 8 is suspended in a hollow space except for a portion overlapping the attachment portion 71.

  Further, the terminals 7 b of the plurality of wiring patterns 7 a provided on the flexible resin substrate 7 are collected and arranged only at one end of the substrate base 74.

  The terminal 7b is electrically and mechanically connected and fixed by a terminal 3c provided on the base 3a and a conductive paste 9. Thereby, the flexible resin substrate 7 is fixed in a cantilever shape. At this time, as shown in FIG. 1B, the bases 3a and 3b are formed so that the former is higher, so that the flexible resin substrate 7 and the detection element 8 do not interfere with the circuit IC 6. Absent.

  Therefore, even if the detection element 8 is driven to vibrate, the amount of inertia can be detected without colliding with other members.

  The spring portion 72 was formed by cutting out a portion of the flexible resin substrate 7 excluding any of the substrate base 74, the attachment portion 71, and the step 73. As shown in FIG. 1, the spring portion 72 has a bent shape.

  As a result, as will be described later, leakage vibration can be suppressed and an external impact can be effectively absorbed.

  A metal lid (not shown) is seam welded to the opening 3e which is the uppermost end of the outer container 3 via a Kovar ring (not shown) brazed to the opening 3e. As a result, the inside of the outer container 3 contains the detection element 8 and the circuit IC 6 in a state where the airtightness is maintained.

  Here, the details of the flexible resin substrate 7 on which the detection element 8 is mounted will be described.

  The flexible resin substrate 7 is formed by processing polyimide into a shape as shown in FIG. That is, the flexible resin substrate 7 is provided with an attachment portion 71 and a spring portion 72, and the attachment portion 71 is configured by forming a step 73 by bending.

  The flexible resin substrate 7 is provided with a plurality of wiring patterns 7a, one terminal 7b of which is connected to the terminal 3c provided on the base 3a, and the other terminal 7c provided to the detection element 8. It connects with the terminal which is not illustrated with the method which is described below.

  FIG. 3 shows a state where the detection element 8 is mounted on the attachment portion 71 of the flexible resin substrate 7. The sensing element 8 is mounted with the terminals of the sensing element 8 overlapped so as to face the terminal 7c of FIG. Specifically, as shown in FIG. 3B, bumps 10 are provided between a plurality of terminals of the sensing element 8 and terminals 7c (shown by bold lines in the figure) of the flexible resin substrate 7. It is electrically connected by a face-down bonding method. Note that the thicknesses of the flexible resin substrate 7 and the bumps 10 in FIG. 3B are shown exaggerated for the sake of clarity.

  Here, as described above, the sensing element 8 must be miniaturized in order to meet the miniaturization needs of the inertial sensor, but the terminals are miniaturized accordingly. However, since the sensing element 8 vibrates as described later, the mechanical strength is insufficient due to the small area of the connecting portion if the two are fixed only by electrical connection between the terminal provided on the sensing element 8 and the terminal 7c. And may not be able to withstand vibration sufficiently.

  Therefore, in FIG. 3B, a portion other than the bump 10 is filled with the thermosetting one-component adhesive 11 in the gap between the detection element 8 and the attachment portion 71. Thereby, the detection element 8 and the flexible resin substrate 7 are firmly fixed electrically and mechanically.

  By adopting such a configuration, the conventional support 2 is not required and can be easily manufactured.

  Next, the operation will be described.

  In FIG. 4A, the detection element 8 has a tuning fork shape in which silicon is used as a base body and a piezoelectric thin film and electrodes (not shown) are formed on the surface thereof. These piezoelectric thin film and electrodes constitute a detection unit, a drive unit, and a terminal. The tuning fork is composed of two arms 8a and 8b and an element base 8c having terminals.

  When a voltage for driving and controlling the sensing element 8 is applied to the driving unit from the driving circuit built in the circuit IC 6 through the wire 6b, the wiring conductor 30, and the wiring pattern 7a, the coordinate system defined in the lower part of FIG. The arms 8a and 8b vibrate in the X direction at a speed Vx. FIG. 4B shows the state of the detection element 8 at this time.

  When rotation ω is applied in the Z-axis direction in this state, a force of m · Vx × ω (m: mass of the sensing element 8) acts in the Y direction, and the arms 8a and 8b generate vibration components in the Y direction. To do. The state of the detection element 8 at this time is shown in FIG. As shown in FIG. 4B, the driving vibration directions of the arms 8a and 8b are opposite to each other. Therefore, as shown in FIG. 4C, the vibration components in the Y direction have the same magnitude and the opposite directions.

  The deflection of the arms 8a and 8b is converted into electric charges by the detection unit provided in the detection element 8, and a signal corresponding to the deflection is obtained from the terminal provided in the element base 8c. The signals of the arms 8a and 8b are Since the magnitude is equal and the sign is opposite, the sensitivity is doubled by taking the difference between the two.

  This signal is input to the output circuit of the circuit IC 6 through the wiring pattern 7a, the wiring conductor 30, and the wire 6b. The output circuit processes the input signal, and finally adjusts and outputs the signal according to the amount of inertia due to the rotation ω.

  In addition, although the amplitude and the amount of bending of the arms 8a and 8b shown in FIGS. 4B and 4C are actually minute, they are exaggerated for easy understanding.

  Here, in order to efficiently obtain a charge signal according to the applied rotation, it is preferable that the natural frequency ωd in the driving direction (X direction) and the natural frequency ωs in the detection direction (Y direction) be appropriately close to each other. Therefore, in the first embodiment, ωd = 22 kHz and ωs = 21.3 kHz are set. The frequency difference between ωd and ωs is called a detuning frequency Δf, and Δf = 0.7 kHz in the first embodiment.

  In the inertial sensor driven in this way, the detection element 8 is suspended in a hollow space in the inner space of the outer container 3 by the flexible resin substrate 7, so that the drive vibration of the detection element 8 is applied only to the flexible resin substrate 7. Communicated. Since the flexible resin substrate 7 has the spring portion 72, the vibration of the detection element 8 is absorbed by the elasticity of the spring portion 72 in addition to the elasticity of the flexible resin substrate 7, thereby suppressing leakage vibration to the outside. it can.

  In addition, the influence on the sensor output with respect to external impact vibration was also examined.

  When the detection element 8 is firmly fixed without using the flexible resin substrate 7 or the spring portion 72, when various external impact vibrations are applied under the driving conditions, the vibration is excited in the detection element 8, and the driving vibration is generated. In some cases, it was greatly affected. As a result, an error is superimposed on the sensor output.

  Thus, as a result of investigating the frequency of the impact vibration that affects the sensor output signal, it was found that the driving condition affects at a plurality of frequencies in the range of 11 kHz to 135 kHz due to excitation. Therefore, by setting the shape of the spring portion 72 so as not to transmit a frequency up to 11 kHz, which is the lowest frequency, that is, to have a lower natural frequency, it is possible to absorb impact vibration from the outside. .

  From the above results, the upper limit of the natural frequency of the flexible resin substrate 7 was set to 10 kHz.

  On the other hand, when the natural frequency of the flexible resin substrate 7 is close to the detuning frequency Δf, the sensor output accuracy is deteriorated because it is amplified and superimposed on the detection element 8 when external shock vibration of that frequency is applied. Therefore, in order to avoid this influence, the natural frequency of the flexible resin substrate 7 must be larger than Δf.

  Since Δf = 0.7 kHz in the first embodiment, the lower limit of the natural frequency of the flexible resin substrate 7 may be larger than 0.7 kHz. However, the influence of external impact vibration is not sufficiently reduced in the vicinity of Δf. , Δf must be separated to some extent.

  Therefore, as a result of investigating the influence on the sensor output when changing the natural frequency of various flexible resin substrates 7 and the variation of Δf, it has been found that there is no significant effect at 2 kHz or more. Therefore, the lower limit of the natural frequency of the flexible resin substrate 7 is 2 kHz including the variation margin.

  From the above, the range of the natural frequency of the flexible resin substrate 7 is 2 kHz to 10 kHz. By setting the shape of the spring portion 72 of the flexible resin substrate 7 within this range, it is possible to effectively absorb impact vibration from the outside.

  Here, the shape of the spring part 72 is formed by cutting out a part of the flexible resin substrate 7 except for the terminal 7b of the wiring pattern 7a, the attachment part 71, and the step 73. Such a notch shape is not necessarily acceptable. Therefore, the optimum shape was determined as follows.

  First, FIG. 5 shows the state of the detection element 8 when impact vibration is applied in various directions from the outside to the inertial sensor in which the detection element 8 is mounted on the flexible resin substrate 7 not provided with the spring portion 72. 5A is a cross-sectional view taken along the line AA in FIG. 1, and FIG. 5B is a cross-sectional view taken along the line BB in FIG. Moreover, although the thickness and fluctuation | variation of the flexible resin substrate 7 are actually very small in any figure, all were exaggerated and shown for easy understanding.

  FIG. 5A shows a case where impact vibration in the vertical direction (Y direction) indicated by the arrow is applied to the inertial sensor. In this case, since the entire detection element 8 moves simultaneously in the Y direction, the arms 8a and 8b bend in the same direction. Accordingly, the signals generated in both detection units are the same in magnitude and sign.

  Here, as described above, since the signals of the arms 8a and 8b take the difference between the two, the signal due to the impact vibration in FIG. 5A becomes 0, and the influence on the output is cancelled. Therefore, there is no particular problem with respect to the impact vibration shown in FIG.

  On the other hand, when an impact vibration in the XY in-plane rotation direction of the inertial sensor is applied as indicated by the arrow in FIG. 5B, the detection element 8 also vibrates in the XY in-plane rotation direction as indicated by the dotted line in FIG. To do. As a result, the arms 8a and 8b bend as in FIG. Therefore, a signal due to shock vibration is superimposed, and an error occurs in the sensor output.

  Therefore, it is necessary to configure the spring portion 72 so that the detection element 8 absorbs the movement as shown in FIG. 5B and only the movement shown in FIG.

  Thus, as a result of producing spring portions 72 of various shapes and examining the influence of the impact vibration on the sensor output in FIG. 5B, the outer container 3 moves in the XY in-plane rotation direction in FIG. 5B. In order to prevent the detection element 8 from moving, it has been found that the spring 72 should be twisted. One example is the shape of the spring portion 72 shown in FIG.

  The spring portion 72 is configured to have a bent portion. As a result, even if the outer container 3 moves in the XY in-plane rotation direction of FIG. 5B, the bending portion is kinked so that vibration in the XY in-plane rotation direction is not transmitted to the detection element 8 and the sensor signal error Can be reduced.

  Thus, the shape of the flexible resin substrate 7 on which the optimum natural frequency was obtained and the spring portion 72 having the folded portion was formed was determined. In addition, as shown in FIG. 3, the natural frequency in the state which supported the detection element 8 in the attaching part 71 of the flexible resin board | substrate 7 was about 3 kHz.

  As a result of actually producing and evaluating a surface-mounting type small inertial sensor having the above configuration, it was confirmed that the influence on the output due to “bounce” due to leakage of the driving vibration of the sensing element 8 to the outside was reduced. .

  FIG. 6 shows the result of examining the influence on the output with respect to the impact vibration from the outside. In FIG. 6A, the horizontal axis represents time, and the vertical axis represents the impact vibration strength applied to the inertial sensor. 6B and 6C, the horizontal axis represents time, and the vertical axis represents sensor output.

  When the inertial sensor is subjected to the impact vibration shown in FIG. 6 (a), when the detection element 8 is firmly fixed without the flexible resin substrate 7 interposed therebetween, the impact vibration occurs in the sensor output as shown in FIG. 6 (b). It was found that the error was increased due to the superposition, and that it took a long time to attenuate.

  On the other hand, when the detection element 8 is supported on the flexible resin substrate 7 of the first embodiment, the influence of the impact vibration on the sensor output is extremely small as shown in FIG. I understood it.

  From the above, it was confirmed that the influence on the sensor output was sufficiently reduced even with external impact vibration.

  In the first embodiment, the outer container 3 is a ceramic package, but it may be made of plastic. As a result, the outer container 3 can be formed at a lower cost than a ceramic package. Therefore, the configuration of the first embodiment can be applied to a consumer inertial sensor that requires a low cost although its operating temperature range is narrow.

  Moreover, it is good also as a structure which provides a weight in the back surface in which the detection element 8 of the attaching part 71 provided in the flexible resin substrate 7 of this Embodiment 1 is mounted. A sectional view of the inertial sensor at this time is shown in FIG. The weight 12 is bonded to the back surface of the mounting portion 71. Note that the thickness of the flexible resin substrate 7 in FIG. 7 is exaggerated from the actual thickness for easy understanding.

  By configuring as shown in FIG. 7, the vibration in the XY in-plane rotation direction shown in FIG. 5B can be further reduced by the inertia of the weight 12, and a highly accurate inertial sensor can be realized.

  Furthermore, since the natural frequency of the flexible resin substrate 7 is changed by changing the weight of the weight 12 according to this configuration, the natural frequency can be easily set.

  With the configuration and operation described above, an inertial sensor that can be reduced in size while ensuring a leakage vibration suppressing effect and impact resistance can be realized.

  Since the inertial sensor according to the present invention can be reduced in size while ensuring a leakage vibration suppressing effect and impact resistance, it is useful as a surface mount type inertial sensor or the like.

(A) Top view which shows the inside of the inertial sensor in Embodiment 1 of this invention, (b) AA sectional drawing in Fig.1 (a). The top view of the flexible resin substrate of the inertial sensor in Embodiment 1 of this invention (A) Top view of flexible resin substrate supporting sensing element of inertial sensor in Embodiment 1 of the present invention, (b) Side view (A) The perspective view at the time of the stop of the detection element of the inertial sensor in Embodiment 1 of this invention, (b) The perspective view at the time of the drive, (c) The perspective view at the time of the detection (A) AA sectional view in FIG. 1 (a) at the time of external impact vibration application of the inertial sensor in Embodiment 1 of the present invention, (b) BB sectional view of the same (A) External impact waveform diagram when external impact is applied to the inertial sensor according to Embodiment 1 of the present invention, (b) Sensor output waveform diagram when no spring portion is provided, (c) Spring portion is provided The same sensor output waveform diagram Sectional drawing of the structure with the weight of the inertial sensor in Embodiment 1 of this invention Partial sectional view of the sensing element part of a conventional inertial sensor

Explanation of symbols

3 Outer container 3a, 3b Base 3c, 3d, 7b, 7c Terminal 3e Opening 30 Wiring conductor 6 Circuit IC
6a pad 6b wire 7 flexible resin substrate 7a wiring pattern 8 sensing element 8a, 8b arm 8c element base 9 conductive paste 10 bump 11 adhesive 12 weight 71 mounting portion 72 spring portion 73 step 74 substrate base

Claims (5)

A sensing element that detects the amount of inertia by driving vibration;
A circuit IC including a drive circuit that drives and controls the sensing element and an output circuit that processes a signal from the sensing element and adjusts and outputs the signal according to the amount of inertia;
The sensing element mounting portion, the mounting portion facing the mounting portion via a spring portion, and having a substrate base disposed so as to have a predetermined step with respect to the mounting portion, and so as to face the substrate base A strip-shaped flexible resin substrate on which a wiring pattern for electrically connecting the detection element supported by the mounting portion to the circuit IC is formed;
Including the circuit IC, and an outer container in which the substrate base is attached so that the detection element can detect the amount of inertia by driving vibration,
The natural frequency of the flexible resin substrate in a state where the detection element is supported is larger than a frequency difference between the natural frequency in the driving direction of the detection element and the natural frequency in the detection direction, and the detection element is caused by external vibration. An inertial sensor with a range smaller than the lowest frequency excited by The inertial sensor according to claim 1, wherein the detection element is supported on an attachment portion of the flexible resin substrate by an adhesive. The inertial sensor according to claim 1, wherein the natural frequency of the flexible resin substrate is set in a range of 2 kHz to 10 kHz depending on a shape of the spring portion. The inertial sensor according to claim 3, wherein the shape of the spring part is a folded shape. The inertial sensor according to claim 1, wherein a weight is provided on the mounting portion.

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