JP4583188B2 - Acceleration sensor - Google Patents

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 detection element is press-fitted and held in the through hole, and the vibration 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 detection 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, since the conventional acceleration sensor described above requires a support for fixing the vibration detection element, in addition to the case in which the vibration detection element is hermetically sealed, 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 has a lead electrode, disposed at least one end rectangular having an opening formed on the casing, has a fixing through-hole, into said opening so as to close the opening a plate-shaped fixing part which is, Ri piezoelectric substrate in which a pair of signal electrodes on both principal surfaces are adhered the name is Awa bonding plural via an adhesive, which is inserted and retained in the fixing through-hole a vibration detecting element, attached to both main surfaces of the end portion of the vibration detecting element as the sealing resin disposed so as to close the opening of the case, facing each other across said vibration detecting element is, and, a pair of retaining resin which is brought into close contact with the inner surface of the fixing through-hole, a acceleration sensor wherein the signal electrodes extend up to the lateral side periphery of the piezoelectric substrate has an extension portion, the the extending portion, a pair of side surfaces near der of the vibration detecting element It is characterized in that the electrically connected via respective conductive adhesive to the ends of the pair of the lead electrode which extends in the vicinity of the fixing holes Te.

  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.

Further acceleration sensor of the present invention also, together with both the sealing resin and the pair of retaining resin is made of epoxy resin, the two resins are bonded to each other at the opening vicinity of the case It is characterized by.

Further acceleration sensor of the present invention also includes a predetermined region of the opening side of the casing of the stationary part surface, the resin dam provided to a prescribed region of the opening side of the case of the pair of retaining resin surface It is characterized by that.

  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. Since 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 the vibration detection element is fixed on the main surface of the vibration detection 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 for accommodating the vibration detecting element 3 is a container body having an opening 1h on one end side, and 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 detecting 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 a substrate at a peak temperature of 1100 ° C. to 1400 ° C. for several tens of minutes to several hours, and forming a substrate in a thickness direction, 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 impact is applied from the outside, the fixed vibration detecting element 3 bends on the free end side 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.

6 is a cross-sectional view along the longitudinal direction of the vibration detecting element of the acceleration sensor of the example of FIG. 1, and is in close contact with the inner surface of the fixing through-hole 2h of the holding resins 4a and 4b from the free end of the vibration detecting element 3. The free length L of the vibration detecting element 3 extends to the contact portion end X located closest to the free end in the region. Even when the end portion of the holding resin 4a, 4b on the free end side is located on the free end side from the inner surface of the fixing through hole 2h, the free end to the contact portion end X has a free length L. As shown in FIG. 6, 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. Even if there is some variation in the depth of press-fitting the vibration detecting element 3 into the fixing through hole 2h , the free length L can be made constant. Further, 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 stacked on top and bottom with a prepreg material impregnated with an epoxy resin between glass fibers, and the epoxy resin is heated to a predetermined thickness by heating. 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 periphery of the piezoelectric substrates 31 and 32, and the extending part is extended in the case 1 in 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. In addition, since the signal electrodes 31a and 32a and the signal electrodes 31b and 32b are connected in parallel, an acceleration sensor with high sensitivity can be obtained. 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 of the vibration detection element in FIG. (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 ... Concave part 2h ... Fixing through-hole 3 ... Vibration detection element 4a, 4b ... Holding resin 5 ... Sealing resin 6a, 6b ... Conductive adhesive 7a, 7b ... Lead electrode end 8a, 8b ... Resin weir 9 ... Adhesive 31, 32 ... Piezoelectric substrates 31a, 31b, 32a, 32b ... Signal electrodes

Claims (5)

A rectangular parallelepiped case having a lead electrode and having an opening formed at least on one end side, and a plate-shaped fixing portion having a fixing through hole and disposed in the opening so as to close the opening When both main surfaces piezoelectric substrate pair of signal electrodes are deposited on the Ri name is Awa bonding plural via an adhesive, a vibration detecting element inserted and held in the fixing through hole, said case And is attached to both main surfaces of one end of the vibration detection element so as to face the sealing resin disposed so as to close the opening of the vibration detection element, and for fixing An acceleration sensor comprising a pair of holding resins closely attached to the inner surface of the through hole ,
The signal electrode has an extending portion extending to a side peripheral edge portion of the piezoelectric substrate, and the extending portion is in the vicinity of the pair of side surfaces of the vibration detecting element and in the vicinity of the fixing through-hole. An acceleration sensor characterized in that it is electrically connected to the end portions of the pair of lead electrodes extended to each other via a conductive adhesive.   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.   2. The sealing resin and the pair of holding resins are both made of an epoxy resin, and the two resins are bonded to each other in the vicinity of the opening of the case. Item 4. The acceleration sensor according to any one of Items 3 to 4.   The resin weir is provided from a predetermined region on the opening side of the case on the surface of the fixing portion to a predetermined region on the opening side of the case on the pair of holding resin surfaces. The acceleration sensor according to claim 4.

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