JP4844855B2 - Tuning fork type piezoelectric vibrator - Google Patents

Description

  The present invention relates to a surface-mount type piezoelectric vibrator used for an electronic device, and more particularly to a package structure for supporting a tuning fork type piezoelectric vibrating piece in a cantilever manner and hermetically sealing the package.

  2. Description of the Related Art Conventionally, piezoelectric vibrators are widely used as clock sources for electronic circuits in various electronic devices including information communication devices such as bulletin phones and PHS, OA devices such as computers, and consumer devices such as electronic watches. Recently, especially with the downsizing and thinning of electronic devices such as portable devices, the piezoelectric vibrators have been further downsized and thinned.

  In general, surface-mount type piezoelectric vibrators have a widely adopted structure in which a piezoelectric vibrating piece such as crystal is supported at one end in a cantilevered manner and fixed in a package made of an insulating material such as ceramic, and hermetically sealed. Has been. FIG. 11 illustrates a configuration of a surface-mount type crystal resonator in which a tuning fork type crystal vibrating piece 4 is accommodated in a package 3 including such a thin rectangular box-shaped base portion 1 and a thin lid portion 2. The tuning-fork type crystal vibrating piece 4 having an excitation electrode formed on the surface of the crystal has a conductive adhesive on the electrode pad 5 provided on the inner bottom surface of the base portion 1 with a base end portion 4a provided with an extraction electrode from the excitation electrode. 6 is fixed in a cantilevered manner, and the lid portion 2 is joined to the upper end of the base portion 1 and hermetically sealed.

  However, the above-described conventional piezoelectric vibrator has a problem of impact resistance as the size and thickness thereof are reduced. In order to solve this problem, for example, one end of the piezoelectric vibrating piece is fixed to one of two steps opposed to the bottom surface inside the package, and the free end is fixed to a cantilever type with a slight separation from the other step. There is known a piezoelectric vibrator which is supported and in which the distance between the upper surface of the piezoelectric vibrating piece and the inner surface of the lid is reduced to a certain value or less (see Patent Document 1). When an impact such as dropping is applied, this piezoelectric vibrator contacts the upper surface of the step or the inner surface of the lid, and absorbs the impact and resists the vibration. Improve impact properties.

  Also known is a package structure of a piezoelectric device in which the bottom surface inside the package that supports the piezoelectric vibrating piece in a cantilever manner is an inclined surface, and the upside of the inclined surface and the free end of the piezoelectric vibrating piece are separated by a slight gap. (For example, refer to Patent Document 2). According to this package structure, impact from the outside is absorbed by the free end of the piezoelectric vibrating piece coming into contact with the bottom surface inside the package, thereby improving impact resistance and reducing the thickness of the package.

JP-A-9-186545 JP-A-11-214947

  The inventor of the present application has studied various causes of the frequency fluctuation when a large impact is applied to the piezoelectric vibrator due to dropping or the like. As a result, for example, as indicated by an imaginary line 4 ′ in FIG. 11, the free end 4 b of the vibrating arm of the tuning-fork type crystal vibrating piece 4 is greatly displaced up and down by impact, and the inner surface of the package 3, that is, the inner side of the base portion 1. It has been found that a change in the mass of the tip of the vibrating arm due to contact with the bottom surface or the inner surface of the lid portion 2 and missing corners is the main cause of frequency fluctuation. When the base end portion 4a of the piezoelectric vibrating piece is bonded onto the electrode pad 5, the free end portion 4b may be tilted somewhat upward or downward. There is a high possibility that it will easily collide with the bottom surface of the base portion 1 by an impact and break. And based on this knowledge, this invention is devised.

  Further, if a piece of material missing from the tip of the vibrating arm adheres to the tuning fork type quartz vibrating piece 4, its frequency changes, which may further deteriorate the vibrator characteristics. For this reason, conventionally, the piezoelectric vibrating reed is attached to the base portion so as to ensure a relatively large gap that does not contact the inner surface of the package even if the free end of the vibrating arm of the piezoelectric vibrating reed is greatly displaced up and down due to impact or the like. It was mounted at a high position from the inner bottom surface, and the lid portion was arranged at a higher position to ensure impact resistance. However, with such a configuration, there is a problem that the thickness of the entire piezoelectric vibrator increases, and it is impossible to meet the demands for miniaturization and thinning.

  In the case of a tuning fork type piezoelectric vibrator, after sealing the piezoelectric vibrating piece inside the package, the laser beam is irradiated from the outside through the transparent glass lid, and the metal weight part formed at the tip of the vibrating arm is partially Finally, a method of adjusting the frequency by finally melting and removing is employed. However, as the package becomes smaller and thinner, the gap between the piezoelectric vibrating piece and the package decreases, so the metal removed by the laser beam reattaches to the vibrating arm and affects the frequency, resulting in high accuracy. This may make it difficult to adjust the frequency.

  An object of the present invention is to provide a package structure capable of realizing excellent impact resistance without increasing the thickness of the package in response to the demand for miniaturization and thinning of the surface mount type piezoelectric vibrator. .

  Furthermore, an object of the present invention is to enable highly accurate frequency adjustment particularly in a tuning fork type piezoelectric vibrator.

In order to achieve the above object, the present invention provides a tuning fork type piezoelectric vibrator in which a tuning fork type piezoelectric vibrating piece is cantilever-mounted inside a package and hermetically sealed. A base portion for mounting a tuning fork type piezoelectric vibrating piece on one end of the electrode with a conductive adhesive in a cantilevered manner, and a lid portion joined to the upper portion of the base portion;
The mounting surface of the base portion has a recess formed in a portion adjacent to the free end of the vibrating arm of the tuning-fork type piezoelectric vibrating piece, and the surface facing the mounting surface in the middle portion of the vibrating arm is the full width of the vibrating arm When the tuning fork type piezoelectric vibrating piece is swung toward the mounting surface, the entire width of the flat surface facing the mounting surface at the middle portion of the vibrating arm contacts the corner portion of the recess on the connection electrode side. In order to obtain, it is characterized in that a recess is provided.

  In this way, when the piezoelectric vibrating reed is greatly swung up and down due to an impact such as dropping due to the recess formed on the mounting surface of the base portion, the impact is applied to the corner of the connection electrode side of the recess on the plane of the vibrating arm. It can be distributed and received over its entire width. Thereby, the possibility that the vibrating arm of the tuning-fork type piezoelectric vibrating piece is damaged or the material is lost can be minimized, and the frequency fluctuation caused thereby can be prevented or suppressed.

  Furthermore, when the vibrating arm of the tuning fork type piezoelectric vibrating piece swings up and down greatly due to an impact such as dropping, even if the free end of the vibrating arm enters the concave portion of the mounting surface of the base portion, the bottom surface of the concave portion The inventor of this application has confirmed that there is no possibility of the frequency fluctuating from a predetermined setting range due to lack of contact at the free end or loss of the tip of the free end or adhesion of the missing material to the piezoelectric vibrating piece. did. In addition, the gap between the piezoelectric vibrating piece and the mounting surface of the base portion can be narrowed to reduce the thickness of the entire package, thereby realizing a reduction in size and thickness.

  In one embodiment, the corner of the recess on the connection electrode side is an obtuse angle. As a result, even when the vibrating arm of the piezoelectric vibrating piece is displaced up and down, even if the middle portion contacts the corner of the recess, the impact can be reduced and the allowable amount of displacement of the vibrating arm can be increased. it can.

  The planar shape of the recess can be various shapes such as a rectangle, an ellipse, and a track shape (track shape of track and field) corresponding to the free end of the piezoelectric vibrating piece. In the case of a rectangle, the planar area of the recess can be increased. In addition, when each corner of the rectangle is rounded, stress concentration at the corner is reduced during processing of the recess, assembly and use of the vibrator, and cracks are prevented from occurring, and the package strength Can be improved, and processing of the concave portion is facilitated, which is preferable. In the case of an elliptical shape, the stress applied to the package itself can be alleviated from being concentrated in the vicinity of the recess, and the package strength can be improved. In particular, the track shape has both of these advantages, and a large planar area can be secured while reducing the stress concentration on the package.

  In addition, if a through-hole is formed in the recess formed on the mounting surface of the base portion to reduce the pressure inside the package in the final manufacturing process of the piezoelectric vibrator, the structure of the base portion can be simplified and the number of manufacturing steps can be reduced. Since it can reduce, it is preferable.

  The tuning fork type piezoelectric vibrator according to the present invention is joined to the mounting surface of the base portion and / or the base portion in a package in which the tuning fork type piezoelectric vibrating piece is cantilever-mounted at its end portion with a conductive adhesive. On the inner surface of the lid portion, a recess is formed in a portion adjacent to the free end of the crystal vibrating piece, and when the piezoelectric vibrating piece is swung toward the mounting surface, the intermediate portion of the vibrating arm is at its full width. By providing a flat surface in contact with the corner on the connection electrode side of the recess, the shock received by the vibrating arm is dispersed and relaxed over its entire width, preventing frequency fluctuations due to breakage of the vibrating arm and loss of material. Can do. In addition to this, even if the piezoelectric vibrating piece is greatly displaced up and down due to an external impact, the free end of the vibrating arm does not contact the mounting surface of the base part, so that the material at the tip or corner is missing or recycled. There is no risk of adhesion and deterioration of the vibrator characteristics, and since the gap between the piezoelectric vibrating piece and the mounting surface of the base portion can be narrowed, excellent impact resistance can be realized simultaneously with downsizing and thinning.

1 is a longitudinal sectional view of a piezoelectric vibrator showing a first embodiment of the present invention. It is a top view of the piezoelectric vibrator of FIG. It is a top view of the piezoelectric vibrator which shows the modification of 1st Example. It is a longitudinal cross-sectional view of the piezoelectric vibrator which shows 2nd Example of this invention. FIG. 5 is a plan view of the piezoelectric vibrator of FIG. 4. It is a top view of the piezoelectric vibrator which shows 3rd Example of this invention. It is a top view of the piezoelectric vibrator which shows 4th Example of this invention. It is a longitudinal cross-sectional view of the piezoelectric vibrator which shows 5th Example of this invention. Fig. A is a schematic perspective view showing a mounting state of a jig used for a drop impact test of a piezoelectric vibrator and a sample piezoelectric vibrator, and Fig. B is a diagram showing a direction of an impact force acting on a sample crystal vibrating piece. It is. It is a partial expanded sectional view which shows the internal dimension of the package structure of the sample used for a drop impact test. It is a longitudinal cross-sectional view which shows the structure of the conventional piezoelectric vibrator.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
1 and 2 show a first embodiment having a basic configuration of a piezoelectric vibrator according to the present invention. In this piezoelectric vibrator, a tuning fork type crystal vibrating piece 12 is mounted in a cantilever manner in a package including a thin rectangular box-shaped base portion 10 and a lid portion 11. The base portion 10 is formed by joining a rectangular frame-shaped side wall member 14 to the upper surface of a bottom plate portion 13 formed by laminating two generally rectangular thin plate members 13a and 13b made of an insulating material such as ceramics. The lid portion 11 is formed of a transparent glass thin plate or ceramic thin plate, and is joined to the upper end of the side wall member 14 with a metal brazing material such as sealing glass or solder, for example, and the tuning fork type crystal vibrating piece 12 is hermetically sealed inside the package. It has stopped.

  Two conductive electrodes 15 for connecting to an external circuit are wired on the upper surface of the bottom plate portion 13 constituting the mounting surface of the tuning-fork type crystal vibrating piece 12 and exposed to one end portion inside the base portion 10. A pair of electrode pads 16 are formed as connection electrodes for the tuning-fork type crystal vibrating piece 12 on the end portions of the conductive electrodes. The electrode pad 16 is bonded to the base end portion 12a on which the lead electrode of the tuning-fork type crystal vibrating piece 12 is formed using the conductive adhesive 17, so that the tuning-fork type crystal vibrating piece is attached to the mounting surface with a predetermined slight amount. It is mounted in a cantilever manner so as to extend in parallel with a distance. As the conductive adhesive 17, it is preferable to use a soft silicone adhesive that can absorb an external impact caused by dropping or the like.

  On the mounting surface inside the base portion 10, a planar rectangular recess 18 is provided in a portion adjacent to the free end 12 b of the tuning-fork type crystal vibrating piece 12, that is, the tip of the vibrating arm. The concave portion 18 can be easily formed by penetrating a rectangular hole in the upper thin plate member 13a constituting the bottom plate portion 13 and bonding the lower thin plate member 13b thereto. In addition, a through hole 19 for reducing the pressure in the package in the final manufacturing process of the quartz crystal unit after the frequency adjustment is formed in the approximate center of the bottom plate portion 13 and is closed with a filler 20.

  By providing the concave portion 18, even if the vibrating arm of the tuning fork type crystal vibrating piece 12 is greatly shaken downward, that is, toward the mounting surface, as indicated by an imaginary line 12 ′ in FIG. The intermediate portion of the vibrating arm contacts or does not contact the corner 18a on the electrode pad 16 side of the recess, and the free end 12b enters the recess 18 without contacting the bottom surface thereof. For this reason, there is no possibility that the tip of the free end portion 12b that has the greatest influence on the frequency is broken and missing, or the missing material is reattached to the tuning fork type crystal vibrating piece. Further, since the middle part of the vibrating arm of the tuning-fork type quartz vibrating piece is in contact with the corner 18a of the recess on the plane, there is little possibility of breakage or loss of material. Few.

  In this embodiment, the frequency of the crystal resonator is adjusted by passing the lid portion 11 joined to the base portion 10 and irradiating laser light from the outside, and the free end portion 12b of the tuning-fork type crystal vibrating piece 12, that is, the tip of the vibrating arm. This is performed by removing a weight part of metal such as Cr, Au, Ag, etc. At this time, since the metal scattered from the weight portion has a large gap below the tip of the vibrating arm due to the concave portion 18, most of the metal adheres to the bottom and side surfaces of the concave portion. Therefore, the amount of metal that adheres again to the vibrating arm is significantly less, and the frequency can be adjusted with high accuracy. Further, if the distance between the upper surface of the bottom plate portion 13 and the free end portion 12b is close, there is a possibility that the bottom plate portion 13b may be damaged by laser light irradiation. In this embodiment, the focal position of the laser light is the depth of the concave portion 18. There is no such a risk.

  As a modification, a through hole 19 ′ for depressurizing the inside of the package can be provided at the position of the recess 18 as indicated by an imaginary line in FIG. 1. Thereby, one process of drilling a through hole in the upper thin plate member 13a can be omitted, and the number of processing steps can be reduced.

  FIG. 3 shows a modification of the tuning fork type crystal resonator of the first embodiment. This modification differs from the first embodiment in that each corner 18b of the rectangular recess 18 is rounded. As a result, when the recess is processed in the upper thin plate member 13a made of relatively hard ceramic, and when the crystal resonator is assembled and used, the stress concentration at the corner is relaxed and breakage such as cracking is prevented. Therefore, the processing of the recess 18 is facilitated and the strength of the package structure is improved.

  4 and 5 show a second embodiment of a piezoelectric vibrator according to the present invention. This piezoelectric vibrator has substantially the same structure as that of the first embodiment, and the same parts are denoted by the same reference numerals and the description thereof is omitted. Also in this embodiment, a concave portion 23 is formed on the upper surface of the bottom surface portion 22 inside the base portion 21 made of an insulating material such as ceramics at a position corresponding to the free end portion 12b of the vibrating arm of the tuning fork type crystal vibrating piece 12. Yes. The concave portion 23 of the present embodiment is different from the first embodiment of FIG. 1 in that the wall surface 23a on the electrode pad 16 side is an inclined surface inclined downward toward the bottom of the concave portion.

  As a result, when the vibrating arm of the tuning-fork type crystal vibrating piece 12 swings downward, the middle portion of the tuning fork type quartz vibrating piece 12 contacts not the right angle as shown in FIG. Can be relaxed. Further, since the position of the middle portion of the vibrating arm of the tuning fork type crystal vibrating piece 12 that contacts the corner of the recess 23 on the electrode pad 16 side is shifted to the base end side as compared with the case of the first embodiment, the tuning fork type The quartz crystal vibrating piece 12 can be displaced more than in the case of the first embodiment. In this case as well, there is no possibility that the free end 12b of the vibrating arm contacts the inner surface of the package, and the impact resistance is further improved.

  In the first and second embodiments, the recesses 18 and 23 of the base portions 10 and 21 are formed in a planar rectangle so as to ensure a large planar area, but can be formed in various other shapes. In the third embodiment of the present invention shown in FIG. 6, the concave portion 25 of the base portion 24 is a plane ellipse. In the case of the first and second embodiments, the stress applied to the package itself tends to concentrate near the corners of the recess, but in the third embodiment, the stress concentration on the recess is relaxed and the package strength is improved. To do. Further, in the fourth embodiment of the present invention shown in FIG. 7, the concave portion 27 of the base portion 26 has a flat track shape, that is, a shape in which two opposing semicircular portions are joined by a straight portion, like a track for athletics. Is formed. Thus, by combining the advantages of both the first and second embodiments and the third embodiment, it is possible to increase the planar area of the recess while reducing the concentration of stress applied to the package on the recess.

  FIG. 8 shows a fifth embodiment of a piezoelectric vibrator according to the present invention. This embodiment differs from the above embodiments in that a recess 30 is formed on the inner surface of the lid portion 29 instead of the base portion 28 of the package. As a result, even if the free end portion 12b of the vibrating arm of the tuning-fork type crystal vibrating piece 12 is displaced upward due to an impact, it does not come into contact with the inner surface of the lid portion 29. There is no risk of material reattaching to the quartz crystal resonator element.

  In another embodiment, recesses as shown in FIGS. 1 and 8 can be provided in both the base portion and the lid portion constituting the package of the crystal vibrating piece. As a result, even if the quartz crystal resonator element is largely displaced up and down, there is no possibility that the free end portion contacts the inner surface of the package, and the impact resistance is further improved.

  Using the jig 31 shown in FIG. 9, a drop impact test was performed on the tuning fork type crystal resonator of FIG. The jig 31 is made of a stainless steel rectangular parallelepiped having a predetermined weight, and three sample tuning-fork type crystal resonators 32 are attached to the upper surface and one side surface thereof, and the floor surface from a certain height, for example, about 150 cm. Let fall. As shown in FIG. 9A, one crystal resonator 32 is on the upper surface of the jig 31, the remaining two are on the side surfaces, one with its longitudinal direction oriented in the horizontal direction and the other oriented in the vertical direction. Deploy. As a result, an impact force acts on the quartz crystal vibrating piece 33 in each quartz crystal resonator 32 in the X, Y, and Z directions orthogonal to each other as shown in FIG. 9B. After dropping the jig several times, each crystal resonator 32 is removed and its frequency is measured, and the occurrence rate is calculated assuming that the product is out of the predetermined frequency range as a defective product.

  As shown in FIG. 10, the dimensions of the tuning fork type crystal resonator 32 inside the package are fixed in the horizontal direction in the horizontal direction, ie, the front end of the electrode pad 16 on which the crystal vibrating piece 12 is fixed in a cantilever manner, that is, the crystal vibrating piece. The distance from the support point 16a to the free end tip 12b of the vibrating arm of the crystal vibrating piece is L0, and the distance from the fixed support point 16a to the edge of the recess 18 on the electrode pad side is L1, and the vertical direction is horizontal. The height between the supported crystal vibrating piece 12 and the lid portion 11, that is, the height from the top surface of the crystal vibrating piece to the lid portion is t 1, and the gap between the crystal vibrating piece 12 and the bottom surface of the concave portion 18, that is, the bottom surface of the concave portion. The height until is t2. The drop impact is applied to a large number of samples in which the height of the electrode pad is 50 μm, the thickness of the quartz crystal vibrating piece is 100 μm, L 0 = 3 mm, L 1 = 1.5 mm, t 1 = 100 μm, and t 2 is changed in the range of 50 to 150 μm. A test was conducted. As a result, it was confirmed that when t2 exceeds 75 .mu.m, the rate of occurrence of defective products is greatly reduced and becomes substantially zero at t2 .gtoreq.80 .mu.m, exhibiting excellent impact resistance.

  Next, the height of the electrode pad and the thickness of the quartz crystal vibrating piece were similarly set to 50 μm, 100 μm, L 0 = 3 mm, t 1 = t 2 = 100 μm, and L 1 was varied in the range of 0.6 to 2.4 mm. The drop impact test was performed on the sample. As a result, it was confirmed that when L1 exceeds 1.2 mm, the occurrence rate of defective products is greatly reduced and becomes almost zero when L1 ≧ 1.5 mm, and excellent impact resistance is exhibited.

  Since the rigidity of the quartz crystal resonator element is constant regardless of its dimension L0, if it is understood that its deflection rate is also constant, from the above test results, the package structure of the present invention has an internal dimension of 0.5 ≦ L1 / It can be said that excellent impact resistance is exhibited in the range of L0 <1 and t2 / t1 ≧ 0.8.

  The present invention is not limited to the tuning-fork type crystal vibrating piece of the above embodiment, and various piezoelectric materials such as lithium tantalate and lithium niobate other than quartz can be used, and a rectangular AT-cut crystal resonator Needless to say, the present invention can be similarly applied to any surface-mounting type in which the piezoelectric vibrating piece is mounted in a cantilever manner.

DESCRIPTION OF SYMBOLS 1,10,21,24,26,28 ... Base part, 2, 11, 29 ... Cover part, 3 ... Package, 4, 4 ', 12 ... Tuning fork type crystal vibrating piece, 4a, 12a ... Base end part, 4b , 12b: free end, 5, 16 ... electrode pad, 6, 17 ... conductive adhesive, 13 ... bottom plate, 13a, 13b ... thin plate member, 14 ... side wall member, 15 ... conduction electrode, 16a ... fixed support point , 18, 23, 25, 27, 30... Recess, 18 a... Corner, 19, 19 ′ through hole, 20... Filler, 22.

Claims (3)

In the tuning fork type piezoelectric vibrator in which the tuning fork type piezoelectric vibrating piece is mounted in a cantilever manner inside the package and hermetically sealed,
The package has a base part that cantilever-mounts the tuning-fork type piezoelectric vibrating piece at one end thereof with a conductive adhesive on a connection electrode on the mounting surface, and a lid that is joined to the upper part of the base part And having a part
The mounting surface of the base portion has a recess formed in a portion adjacent to the free end of the vibrating arm of the tuning fork type piezoelectric vibrating piece,
The surface facing the mounting surface of the middle part of the vibrating arm is a flat surface over the entire width of the vibrating arm,
When the tuning-fork type piezoelectric vibrating piece swings toward the mounting surface, the entire width of the flat surface facing the mounting surface of the intermediate portion of the vibrating arm comes into contact with the corner portion of the concave portion on the connection electrode side. A tuning fork type piezoelectric vibrator, wherein the concave portion is provided so as to obtain.   2. The tuning fork type piezoelectric vibrator according to claim 1, wherein a corner of the recess on the side of the connection electrode is an obtuse angle.   3. The tuning fork type piezoelectric vibrator according to claim 1, wherein a through hole for decompressing the inside of the package is formed in the concave portion formed on the mounting surface of the base portion.

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