JP2005315847A - Acceleration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acceleration sensor capable reducing the number of processes and a size, as to the acceleration sensor using a vibration detecting element comprising piezoelectric substrates. <P>SOLUTION: In this acceleration sensor, a fixing part 2 having a fixing through hole 2h is provided inside a rectangular parallelopiped-shaped case 1 having lead electrodes 1a, 1b, and having an opening part 1h formed in at least one end side, the vibration detecting element 3 bonded layeredly with the plurality of piezoelectric substrates 31, 32 via an adhesive 9 is inserted into the fixing through hole 2h, to be held, and the opening part 1h of the case is closed by a sealing resin 5. In the sensor, a pair of holding resins 4a, 4b opposed with the vibration detecting element 3 therebetween is attached to one end part of the vibration detecting element 3, and the paired holding resins 4a, 4b are brought into close contact with an inner face of the fixing through hole 2h. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an acceleration sensor using a vibration detecting element made of a piezoelectric substrate.

  An acceleration sensor detects a physical impact applied to a hard disk drive or the like from the outside, and many sensors using a vibration detection element made of a piezoelectric substrate have been proposed.

  For example, a through hole is provided in a support body in which a lead electrode is insert-molded, and one end of a vibration detecting element is press-fitted and held in the through hole, and the vibrating electrode element and the lead electrode are electrically connected via a conductive adhesive. An acceleration sensor has been proposed (see, for example, Patent Document 1). The vibration detection element is hermetically sealed by covering a separately prepared case, and the other end side is a vibration region. When an impact is applied to the acceleration sensor, a charge due to the piezoelectric effect of deformation is generated in the vibration detecting element and detected.

The acceleration sensor is also required to improve the sensitivity, and employs a vibration detecting element in which a plurality of piezoelectric substrates are bonded via an adhesive, and the signal electrodes attached to both main surfaces of the piezoelectric substrate are arranged in parallel. There has also been proposed an acceleration sensor having a structure connected to (see, for example, Patent Document 2).
JP-A-9-113533 Japanese Patent No. 3203523

  However, the conventional acceleration sensor described above requires a support for fixing the vibration detection element separately from the case in which the vibration detection element is hermetically sealed. Therefore, it is difficult to reduce the size of the acceleration sensor.

  Also in the process of manufacturing the acceleration sensor, the process of fixing the vibration detection element and the process of housing the vibration detection element in the case are required separately, which increases the number of processes and reduces the manufacturing cost. Hateful.

  The present invention has been devised in view of the above-described drawbacks, and an object thereof is to provide an acceleration sensor capable of reducing the number of processes and reducing the size.

  The acceleration sensor of the present invention is provided with a fixing portion having a fixing through hole in a rectangular parallelepiped case having a lead electrode and having an opening formed on at least one end side, and an adhesive is provided in the fixing through hole. An acceleration sensor in which a vibration detecting element formed by bonding a plurality of piezoelectric substrates is inserted and held, and the opening of the case is closed with a sealing resin, and one end of the vibration detecting element In addition, a pair of holding resins opposed to each other with the vibration detecting element interposed therebetween are attached, and the pair of holding resins are closely attached to the inner surface of the fixing through hole.

  The acceleration sensor of the present invention is characterized in that the other end portion of the vibration detecting element is a free end.

  Furthermore, the acceleration sensor of the present invention is characterized in that the adhesive is made of a glass cloth base epoxy resin.

  Furthermore, the acceleration sensor of the present invention is characterized in that both the sealing resin and the holding resin are made of an epoxy resin, and the both resins are bonded to each other in the vicinity of the opening of the case. To do.

  Furthermore, in the acceleration sensor of the present invention, a pair of signal electrodes are attached to both main surfaces of the piezoelectric substrate, and a part of the signal electrodes extends to the side peripheral edge of the piezoelectric substrate. The extending portion is electrically connected to the end portion of the lead electrode extending in the case near the side surface of the vibration detecting element via a conductive adhesive.

  Furthermore, the acceleration sensor according to the present invention is characterized in that a resin weir is provided from a predetermined region on the opening side of the case on the surface of the fixed portion to a predetermined region on the opening side of the case on the pair of holding resin surfaces. It is what.

  According to the acceleration sensor of the present invention, a pair of holding resins facing each other with the vibration detecting element interposed therebetween are attached to one end of the vibration detecting element, and the fixing portion provided with the pair of holding resins in the case Since the inner surface of the fixing through-hole is brought into close contact with each other, a complicated structure is not required at a portion where the vibration detecting element is fixed, and the acceleration sensor can be downsized. Also in the process of manufacturing the acceleration sensor, since the vibration detection element is fixed simultaneously with the process of housing the vibration detection element in the case, the number of processes is reduced, and the manufacturing cost can be reduced.

  Further, according to the acceleration sensor of the present invention, since the sealing resin and the holding resin are bonded to each other in the vicinity of the opening of the case, the fixing force of the vibration detecting element is enhanced by the sealing resin. Is done.

  Furthermore, according to the acceleration sensor of the present invention, a part of the signal electrode extends to the side peripheral edge of the piezoelectric substrate, and the extended portion extends in the case near the side surface of the vibration detecting element. Because it is electrically connected to the end of the wire through a conductive adhesive, it is fixed on the main surface and electrically connected on the side surface, so that the main surface of the vibration detecting element occupies the fixing of the vibration detecting element. Thus, the fixed area can be efficiently reduced, and the acceleration sensor can be made smaller.

  Furthermore, according to the acceleration sensor of the present invention, the resin weir is provided from the predetermined region on the opening side of the case on the surface of the fixed portion to the predetermined region on the opening side of the case on the pair of holding resin surfaces. Even if the conductive adhesive formed near one side of the vibration detection element flows, the flowed conductive adhesive is less likely to reach the other side, reducing the occurrence of short circuits between the lead electrodes. Can do.

  Hereinafter, an acceleration sensor according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is an external perspective view of an acceleration sensor according to an embodiment of the present invention, and FIG. 2 is a diagram excluding the sealing resin of the acceleration sensor shown in FIG. The acceleration sensor shown in the figure generally has a structure in which a vibration detecting element 3 is housed in a case 1 having lead electrodes 1a and 1b, and an opening 1h is sealed with a sealing resin 5. Yes.

  The rectangular parallelepiped case 1 that houses the vibration detecting element 3 is a container body having an opening 1h on one end side. Examples of the material include liquid crystal polymer (LCP), polyphenylene sulfide (PPS), polyether ether ketone ( PEEK) or the like is used.

  Lead electrodes 1a and 1b are attached to the case 1, and are electrically connected and fixed to an external circuit wiring board by solder or the like. The lead electrodes 1a and 1b are made of, for example, phosphor bronze, and the thickness thereof is set to 0.1 to 0.5 mm, for example. In the acceleration sensor of this embodiment, the lead electrodes 1a and 1b are integrally formed with the case 1 by insert molding.

  The sealing resin 5 is formed so as to close the opening 1h of the case 1, and as the material, for example, an epoxy resin or the like is used.

  FIG. 3 is an external perspective view of the fixing portion 2 used in the acceleration sensor of the present embodiment. The fixing portion 2 provided in the case 1 is made of the same material as the case 1 and is provided in the vicinity of the opening 1h as a part of the case 1, and is a fixing through-hole into which the vibration detecting element 3 is press-fitted. 2h is provided. Further, recesses 2a and 2b for potting conductive adhesives 6a and 6b described later are provided, and lead electrode ends 7a and 2b extending from the lead electrodes 1a and 1b are provided in the recesses 2a and 2b. 7b is exposed.

  FIG. 4 is an external perspective view of the vibration detecting element 3 used in the acceleration sensor of the present embodiment, and FIG. 5 is a perspective view partially showing a fixed end portion of the vibration detecting element of FIG. The vibration detection element 3 shown in the figure has a structure in which a plurality of strip-shaped piezoelectric substrates 31 and 32 having a pair of signal electrodes 31a, 31b, 32a and 32b attached to both main surfaces are bonded together with an adhesive 9. have. In the acceleration sensor of the present embodiment, a vibration detection element that forms a bimorph type by bonding two piezoelectric substrates is used.

  The piezoelectric substrates 31 and 32 are polarized in the thickness direction, and are made of, for example, a piezoelectric ceramic material such as lead zirconate titanate or lead titanate. The dimensions are 0.5 to 5.0 mm in length and width. Is set to a strip shape having a thickness of 0.2 to 1.0 mm and a thickness of 0.1 to 1.0 mm.

  The piezoelectric substrates 31 and 32 are manufactured by adding a binder to the raw material powder and pressing it, or mixing and drying the raw material powder with water and a dispersing agent using a ball mill, and adding a binder, a solvent, a plasticizer, and the like. A step of forming a sheet by a method such as molding by a doctor blade method, a step of baking at a peak temperature of 1100 ° C. to 1400 ° C. for several tens of minutes to several hours, and forming a substrate, in the thickness direction, for example, 60 ° C. to 150 ° C. A manufacturing method including a step of applying a polarization treatment by applying a voltage of 3 kV / mm to 15 kV / mm at a temperature is employed.

  The pair of holding resins 4a and 4b attached at one end of the vibration detecting element 3 so as to face each other with the vibration detecting element 3 interposed therebetween are made of epoxy resin or the like and have a thickness of 20 to 100 μm. Set to When forming the holding resins 4a and 4b, first, a sheet in which two piezoelectric mother substrates to be the piezoelectric substrates 31 and 32 are joined is prepared, and a resin paste is applied by screen printing to predetermined positions on both main surfaces of the sheet. Print and cure. If necessary, screen printing may be repeated a plurality of times, or the upper surface of the holding resin may be polished in order to obtain thickness accuracy. Then, the holding resins 4a and 4b were deposited by cutting the holding resin having a predetermined length and a position where a free length was obtained using a dicing saw or the like while checking the position of the cured resin paste. The vibration detection element 3 can be obtained. The shape of the vibration detection element 3 is, for example, a length of 3.0 mm, a width of 0.5 mm, a thickness of 0.25 mm, and a free length of 2.0 mm.

  The vibration detection element 3 described above is inserted into the fixing through hole 2h of the fixing portion 2 from the other end side, and is fixed by press-fitting one end portion into the fixing through hole 2h. The attached holding resins 4a and 4b realize high press-fitting properties in the process and strong fixing after press-fitting. The vibration detection element 3 that has been press-fitted has one end inserted earlier as a free end and the other end fixed.

  Since the pair of holding resins 4a and 4b are brought into close contact with the inner surface of the fixing through-hole 2h of the fixing portion 2 provided in the case 1, a complicated structure is not required at the portion where the vibration detecting element 3 is fixed. The acceleration sensor can be downsized. Also in the process of manufacturing the acceleration sensor, since the vibration detection element 3 is fixed simultaneously with the process of housing the vibration detection element 3 in the case 1, the number of processes is reduced, and the manufacturing cost can be reduced.

  When a physical shock is applied from the outside, the fixed vibration detecting element 3 bends at the free end with the fixed portion 2 as an axis, and a pair of signals attached to both main surfaces of the bonded piezoelectric substrates 31 and 32. Since charges are generated in the electrodes 31a, 31b, 32a, and 32b, the impact can be detected as vibration.

  6A to 6C are cross-sectional views taken along the line AA ′ of FIG. 1, and the free end of the region that is in close contact with the inner surface of the fixing through hole 2 h of the holding resins 4 a and 4 b from the free end. The free length L of the vibration detecting element 3 is up to the contact portion end X located on the side. As shown in FIG. 6B, even when the end portion of the holding resin 4a, 4b on the free end side is located on the free end side with respect to the inner surface of the fixing through hole 2h, the distance from the free end to the close contact portion end X is maintained. Since it becomes the free length L, it is preferable to arrange the end portions on the free end side of the holding resins 4a and 4b in a region in close contact with the inner surface of the fixing through hole 2h as shown in FIG. Even if there is some variation in the depth of press-fitting, the free length L can be made constant. As shown in FIG. 6C, the free length L is similarly set even when the holding resins 4a and 4b are tapered.

  The vibration detection element 3 is fixed so as to be inclined with respect to the horizontal direction, and can detect not only the vertical direction but also the stress from the horizontal direction. Specifically, the angle formed by the surface perpendicular to the main surface serving as the mounting surface of the case 1 and the main surface of the vibration detection element 3 (the angle on the acute side) is 20 to 50 ° depending on the application. It is set in the range.

  The signal electrodes 31a, 31b, 32a, 32b deposited on both main surfaces of the piezoelectric substrates 31, 32 are made of, for example, highly conductive materials such as gold, silver, copper, chromium, nickel, tin, lead, and aluminum. These metal materials are deposited and formed on both main surfaces of the piezoelectric substrates 31 and 32 by a conventionally known vacuum deposition or sputtering method, or a predetermined conductor paste containing the above-described metal material is used. It is applied to a predetermined pattern by a conventionally known printing method or the like, and is deposited and formed by baking at a high temperature.

  The adhesive 9 for bonding the piezoelectric substrates 31 and 32 is made of an insulating material such as a glass cloth base epoxy resin, inorganic glass or epoxy resin, or a conductive material such as a conductive adhesive or a metal sheet. In bonding with a glass cloth base epoxy resin, a piezoelectric substrate is superimposed on top and bottom with a prepreg material impregnated with an epoxy resin between glass fibers, and heated while being pressurized to a predetermined thickness. Compress and cure. In joining with inorganic glass, after glass paste is printed and applied, it is superposed and melted and integrated using a firing furnace while applying a load. In a baking furnace, it is heated to 300 to 700 ° C. If firing is performed in a vacuum furnace, it is possible to suppress the mixing of bubbles in the glass bonding intermediate layer. When bonding is performed at a high temperature of 300 ° C. or higher, the polarization of the piezoelectric substrate is depolarized, so that it is necessary to perform polarization processing after bonding.

  A part of the signal electrodes 31 a, 31 b, 32 a, and 32 b is extended to the side peripheral edges of the piezoelectric substrates 31 and 32, and the extension is extended in the case 1 to the vicinity of the side surface of the vibration detection element 3. Since the lead electrodes are electrically connected to the end portions 7a and 7b via the conductive adhesives 6a and 6b, a signal due to a current is output from the lead electrodes 1a and 1b to the outside due to the charge generated in the signal electrodes. Further, since the signal electrodes 31a and 32a and the signal electrodes 31b and 32b are connected in parallel, a highly sensitive acceleration sensor is obtained, and in addition, the main surface is fixed and the side surface is electrically connected. The fixed area of the vibration detecting element 3 can be efficiently reduced, and the acceleration sensor can be made smaller. The conductive adhesives 6a and 6b are formed in the recesses 2a and 2b, and the spread when potting is performed is suppressed.

  If the sealing resin 5 is formed so that the vibration detection element 3 is housed in the case 1 and fixed to the fixing portion 2 described later, and then poured into the opening 1 h of the case 1, the vibration detection element 3 is fixed.

  At this time, since both the sealing resin 5 and the holding resins 4a and 4b are made of an epoxy resin, the vibration detecting element 3 is fixed by being adhered to each other in the vicinity of the opening 1h of the case. Power is strengthened more.

  Resin weirs 8a and 8b are provided from a predetermined area on the opening 1h side of the case on the surface of the fixing portion 2 to a predetermined area on the opening 1h side of the case on the surface of the pair of holding resins 4a and 4b, and vibration detection is provided. Even if the conductive adhesives 6a and 6b formed in the vicinity of one side surface of the element 3 flow, the flowed conductive adhesive materials 6a and 6b rarely reach the other side surface, and short-circuit between the lead electrodes. Generation can be reduced. Specifically, even if the conductive adhesives 6a and 6b flow in the troughs constituted by the surface of the fixing portion 2 and the surfaces of the holding resins 4a and 4b exposed from the fixing through holes 2h, Resins weirs 8a and 8b are provided in an amount necessary to stop them.

  The present invention is not limited to the above-described embodiments, and various modifications and improvements can be made without departing from the gist of the present invention.

  For example, in the above-described embodiment, the vibration detection element 3 has a structure in which two piezoelectric substrates are bonded together, but three or more may be stacked. In this case, since the amount of generated charges can be increased, the sensitivity of the acceleration sensor can be increased.

  In the present embodiment, the fixed end of the vibration detecting element 3 is exposed from the fixed portion 2. However, the fixed end may be disposed in the fixing through hole 2h, and the fixed portion 2 has recesses 2a and 2b. Since it is provided, it can be connected to the conductive adhesives 6 a and 6 b on the side surface side of the vibration detecting element 3. In this case, the resin weirs 8a and 8b may cross over the vibration detecting element 3 and the holding resins 4a and 4b so as to cross between the conductive adhesives 6a and 6b.

1 is an external perspective view of an acceleration sensor according to an embodiment of the present invention. FIG. 2 is a diagram excluding a sealing resin of the acceleration sensor shown in FIG. 1. It is an external appearance perspective view of the fixing | fixed part used for the acceleration sensor which concerns on one Embodiment of this invention. It is an external appearance perspective view of the vibration detection element used for the acceleration sensor which concerns on one Embodiment of this invention. FIG. 5 is an external perspective view of a part of the fixed end portion of the vibration detection element in FIG. 4 seen through. (A)-(c) is the sectional view on the A-A 'line of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Case 1a, 1b ... Lead electrode 1h ... Opening part 2 ... Fixing part 2a, 2b ... Triangular level difference 2h ... Fixing through-hole 3 ... Vibration detection element 4a, 4b: Holding resin 5 ... Sealing resin 6a, 6b ... Conductive adhesive 7a, 7b ... Lead electrode ends 8a, 8b ... Resin weir 9 ... Adhesive Agents 31, 32 ... Piezoelectric substrates 31a, 31b, 32a, 32b ... Signal electrodes

Claims (6)

A fixing portion having a fixing through hole is provided in a rectangular parallelepiped case having a lead electrode and having an opening formed at least on one end side, and a plurality of piezoelectric substrates are placed in the fixing through hole via an adhesive. An acceleration sensor that inserts and holds the vibration detection element to be bonded and closes the opening of the case with a sealing resin,
A pair of holding resins facing each other across the vibration detecting element are attached to one end of the vibration detecting element, and the pair of holding resins are adhered to the inner surface of the fixing through-hole. An acceleration sensor. The acceleration sensor according to claim 1, wherein the other end of the vibration detection element is a free end. The acceleration sensor according to claim 1, wherein the adhesive is made of a glass cloth base epoxy resin. 4. The sealing resin and the holding resin are both made of an epoxy resin, and both resins are bonded to each other in the vicinity of the opening of the case. The acceleration sensor in any one. A pair of signal electrodes are attached to both main surfaces of the piezoelectric substrate, and a part of the signal electrode extends to a side peripheral edge of the piezoelectric substrate, and the extended portion is connected to the inside of the case. 5. The acceleration according to claim 1, wherein the acceleration is electrically connected to an end portion of a lead electrode extending in the vicinity of a side surface of the vibration detecting element via a conductive adhesive. Sensor. 6. The acceleration according to claim 5, wherein a resin weir is provided from a predetermined region on the opening side of the case on the surface of the fixed portion to a predetermined region on the opening side of the case on the pair of holding resin surfaces. Sensor.

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