JP3870912B2 - Piezoelectric device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to piezoelectric devices such as piezoelectric vibrators, piezoelectric oscillators, and SAW devices that are widely used in various electronic devices, and in particular, a surface mount type in which a resonator element made of a piezoelectric material such as quartz is mounted and hermetically sealed. This relates to the piezoelectric device.
[0002]
[Prior art]
Recently, along with downsizing and thinning of electronic devices, piezoelectric devices are required to be further downsized and thinned, and surface mount devices suitable for mounting on circuit boards and the like are frequently used. In general, a surface-mount type piezoelectric device has a structure in which a piezoelectric vibrating piece and an electronic component are hermetically sealed in a package composed of a thin box-shaped base made of an insulating material and a thin plate-like lid. Things are known. Further, a package in which a gas is generated when the lid is joined to the base is exhausted or a sealing hole is provided in the base in order to maintain the inside of the package after sealing in a desired atmosphere, and this is closed after the lid is joined. The structure is known. An example of such a piezoelectric device is described in the following Patent Documents 1 and 2 by the present applicant.
[0003]
FIG. 4A shows a typical example of a conventional surface mount type crystal resonator in which a tuning fork type crystal vibrating piece 2 is mounted inside a package 1. The package 1 has a base 3 made of a ceramic material and a lid 4 made of a thin glass plate that is hermetically bonded to the base 3 using low-melting glass. The base 3 is formed in a box shape in which a frame portion 6 that defines a space for accommodating the resonator element 2 is laminated on a flat bottom plate portion 5 on which the tuning fork type crystal resonator element 2 is mounted. A sealing hole 7 that opens in the space is provided at the substantially center of the bottom surface, and is closed with a sealing material 8 made of a low melting point metal such as Au-Sn.
[0004]
As shown well in FIG. 4B, the sealing hole 7 is provided with a step 9 by enlarging the opening on the bottom side, and the surface of the step is metallized with an appropriate metal material. When the lid 9 is bonded to the base 3 on which the tuning-fork type crystal vibrating piece 2 is mounted in the final process and the inside of the package 1 is vacuum-sealed, the step 9 is placed with the metal ball 10 made of the low melting point metal. It is melted with a laser beam or the like, welded to the inner surface of the sealing hole 7 and used to close it. By providing the step 9, the metal ball 10 is positioned at the opening of the sealing hole 7 and welded to the vicinity of the opening on the bottom surface side of the sealing hole 9 to prevent elution into the package. In order to provide the step 9, the bottom plate portion 5 is formed in a laminated structure of at least two layers composed of the ceramic thin plate 5a on the bottom surface side provided with the large diameter hole 7a and the ceramic thin plate 5b on the void side provided with the small diameter hole 7b. The
[0005]
[Patent Document 1]
JP 2001-332952 A [Patent Document 2]
Japanese Patent Laid-Open No. 2002-76815 [0006]
[Problems to be solved by the invention]
However, in such a package in which the sealing hole is opened on the mounting surface of the piezoelectric vibrating piece, the base bottom plate portion 5 needs to have at least a two-layer structure in order to provide the step 9 described above. As described above, it is difficult to reduce the thickness and height. Also, when irradiating a metal ball with a laser beam or the like to fill the sealing material, the output must be finely adjusted so that it does not elute into the package and adversely affect the piezoelectric vibrating piece. However, there is a problem that the work is troublesome and the efficiency is lowered. Furthermore, if the sizes of the metal balls vary, the welded sealing material may protrude from the sealing hole to the outside of the package, which may hinder the surface mounting of the piezoelectric device.
[0007]
Accordingly, the present invention has been made in view of the above-described conventional problems, and the object thereof is to make it possible to further reduce the thickness and height of the package, and to reliably and satisfactorily improve the inside of the package in a desired atmosphere. An object of the present invention is to provide a surface-mount type piezoelectric device that can be hermetically sealed and has good workability.
[0008]
[Means for Solving the Problems]
According to the present invention, in order to achieve the above object, the piezoelectric vibrating piece, a box-shaped base made of an insulating material, and a flat lid joined to the upper part of the base are provided, and the piezoelectric vibration is contained therein. A package for hermetically sealing the piece, and the base includes a flat bottom plate portion and a frame portion stacked on the bottom plate portion to define a space for accommodating the piezoelectric vibrating piece. And a sealing hole penetrating from the back surface of the bottom plate portion to the upper surface of the frame portion, and the sealing hole includes a large-diameter portion provided in the base and a small-diameter portion provided continuously in the frame portion. A piezoelectric device hermetically sealed with molten metal in the vicinity of the step between the large diameter portion and the small diameter portion is provided.
[0009]
The lid is bonded to the upper part of the base using brazing material, low melting point glass, adhesive, etc. depending on the material, but there is inevitably a slight gap between the upper surface of the base and the back surface of the base by the thickness of the brazing material. A gap is generated, and the inside of the package communicates with the external atmosphere through the gap and the sealing hole even after the lid is joined. Therefore, after the lid is joined, the package is placed in a desired vacuum or an appropriate gas atmosphere, and the sealing hole is closed with a sealing material using the conventional method described above with reference to FIG. It can be hermetically sealed in a desired atmosphere.
[0010]
In an embodiment, when the surface of the step formed by the large diameter portion and the small diameter portion of the sealing hole is metallized with an appropriate metal material, the weldability of the sealing material is thereby increased, and the reliability is improved. This is advantageous because the sealing hole can be closed.
[0011]
In addition, since the sealing hole that opens on the upper surface of the frame portion is formed from the large-diameter portion of the base and the small-diameter portion of the frame portion, the base of the package has only one bottom plate, for example, only one ceramic thin plate And can be added to the frame portion to form a two-layer structure. Therefore, the package can be made thinner and lower than the conventional structure that requires at least three layers of bases. Further, by providing the sealing hole, the lid joining surface of the frame portion becomes larger than before, the joining strength of the lid is increased, and the rigidity of the entire package is improved.
[0012]
Furthermore, since the sealing hole opens not in the space in the package that accommodates the piezoelectric vibrating piece but in a narrow gap between the upper surface of the base and the back surface of the lid, the sealing hole is sealed when the sealing hole is closed. Even if the sealing material is so much in volume that it elutes from the sealing hole, there is no possibility that it will flow into the void and adversely affect the piezoelectric vibrating piece. Therefore, regardless of the size of the metal ball arranged at the level difference of the sealing hole, it is not necessary to finely adjust the output when melting it by laser beam irradiation or the like, and the workability is greatly improved. .
[0013]
The lid is formed of a thin plate made of metal, glass, ceramic or the like as in the prior art, and the piezoelectric vibrating piece can be mounted with either a thickness-shear mode piezoelectric vibrating piece or a tuning fork type vibrating piece as required. When the piezoelectric vibrating piece is a tuning fork type vibrating piece, a metal weight is attached to the surface of the vibrating arm in advance by irradiating a laser beam through the lid from the outside after sealing the package by using a transparent glass thin plate. The material can be partially removed to fine tune its oscillation frequency.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIGS. 1A and 1B schematically show a preferred embodiment of a surface-mounted crystal resonator to which the present invention is applied. In this quartz crystal resonator, a tuning fork type crystal vibrating piece 14 is mounted inside a package 13 including a base 11 made of a ceramic material and a lid 12. The base 11 has a space 17 for accommodating the crystal vibrating piece 14 by integrally joining a rectangular frame 16 made of a ceramic thin plate on a bottom plate portion 15 made of a single ceramic thin plate having a substantially rectangular shape. Are formed in a thin rectangular box shape. The quartz crystal vibrating piece 14 is fixed in a cantilever manner to the connection electrode 19 formed on the vibrating piece mounting surface in the space 17 by a conductive adhesive 18 at the base end portion 14a.
[0015]
The lid 12 is formed of a rectangular transparent glass thin plate and is airtightly joined to the upper end of the frame portion 16 using a low melting point glass 20. In another embodiment, a lid 12 formed of a thin plate of an insulating material such as ceramics or a metal material can be used in addition to glass, and a brazing material such as solder, a low melting glass, an adhesive, etc., depending on the material. To be joined to the upper end of the frame portion 16. When using a metal plate lid, a soldering material such as solder is used. Therefore, pre-metalizing the joint along the periphery of the upper surface of the frame portion 16 increases the adhesion of the brazing material to the upper surface of the frame portion 16, The lid 12 can be securely joined to the base 11.
[0016]
In the base 11, the frame portion 16 is enlarged in the width direction to one side of the void 17, and a sealing hole 21 penetrating to the back surface of the base is provided in the approximate center of the enlarged portion. As the frame portion 16 is enlarged in this manner, the bonding area with the lid 12 is increased, so that the bonding strength of the lid is improved. As shown in FIG. 1C, the sealing hole 21 has a large diameter portion 21 a provided in the bottom plate portion 15 and a small diameter portion 21 b provided in the frame portion 16, and thereby the bottom side of the base 11. A step is defined. A slight gap is defined between the upper surface of the base 11 and the rear surface of the lid 12 by the thickness of the low melting point glass 20 that joins the lid 12 to the base 11. However, the inside of the package 13 communicates with the external atmosphere.
[0017]
The sealing hole 21 is hermetically closed by filling an appropriate metal sealing material 22 in the vicinity of the opening on the bottom surface of the base 11, thereby hermetically sealing the inside of the package 13. The filling of the sealing material 22 is performed in the same manner as described above in relation to the prior art of FIG. As shown in FIG. 1C, after the lid 12 is bonded to the upper surface of the base 11 on which the crystal vibrating piece 14 is mounted, the package 13 is placed in a vacuum atmosphere with the bottom surface facing upward, and Au—Sn or Au— A metal ball 23 made of a low melting point metal such as Ge is placed on the step of the sealing hole 21, and this is irradiated with a laser beam or a halogen lamp to be welded to the sealing hole 21.
[0018]
The metallized portion 24 is formed on the surface of the step of the sealing hole 21 in advance by a known technique, for example, by screen printing an appropriate metal material and plating it as necessary, or by vapor deposition or sputtering. Has been. Since the metallized portion 24 provides good adhesion of the sealing material 22, the sealing hole 21 can be reliably sealed in the vicinity of the step. Further, since the sealing hole 21 is opened in the gap between the upper surface of the frame portion 16 and the back surface of the lid 12, the sealing material 22 even if the metal ball 23 is too large or the output of the irradiated laser beam is excessive. There is no possibility that the liquid crystal will be eluted directly into the void 17 and adversely affect the crystal vibrating piece 14.
[0019]
Finally, a laser beam is irradiated from the outside of the package 13 thus vacuum-sealed through the transparent lid 12, and the metal weight material for frequency adjustment previously attached to the surface of each vibrating arm of the crystal vibrating piece 14. Is partially evaporated and removed, and the oscillation frequency of the crystal vibrating piece 14 is finely adjusted. Thereby, the inside of the package is highly vacuum sealed, and a high-performance and high-quality crystal resonator that stably exhibits desired performance can be obtained.
[0020]
The sealing hole 21 of the present invention can be provided at any position of the frame portion 16 excluding the joint portion with the lid. In the modified example of FIG. 2, the frame portion 16 of the base 11 is widened in the longitudinal direction to one side of the void 17 and a sealing hole 21 is provided at the approximate center of the enlarged portion. Thereby, similarly to the said Example, the joining area with the lid | cover 12 of the frame part 16 expands, and the joining strength increases.
[0021]
In another modification shown in FIG. 3, a void 17 is provided along one diagonal direction of the rectangular base 11, and the crystal vibrating piece 14 is arranged. The frame portion 16 has a wide and generally triangular area on both sides of the space 17, and a sealing hole 21 is provided in the approximate center of one of the areas. Such a wide area on both sides of the void 17 increases the bonding strength by expanding the bonding area of the frame portion 16 with the lid 12 as in the above embodiments, and at the same time increases the rigidity of the base 11 and increases the package 13. Overall strength is improved.
[0022]
The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and various modifications and changes are made to the above-described embodiments within the technical scope thereof. can do. For example, the present invention is similarly applied to a resonator element made of various piezoelectric materials such as lithium tantalate and lithium niobate other than quartz, and a piezoelectric device having a resonator element of a thickness-shear vibration mode other than a tuning fork type. Can do.
[0023]
As described above, the piezoelectric device of the present invention has an opening on the upper surface of the frame portion of the box-type base of the package, and has a sealing hole including a large diameter portion of the base bottom plate portion and a small diameter portion of the frame portion, and these large diameters. The base can be made into a two-layer structure by sealing the inside of the package in an airtight manner by welding a sealing material in the vicinity of the step between the portion and the small diameter portion, so that the entire package can be made thin and low in profile. In the same sealing process as in the prior art, there is no possibility that the sealing material elutes into the package and adversely affects the piezoelectric vibrating piece, so that the workability can be greatly improved and the manufacturing cost can be reduced. Further, the enlargement of the frame portion increases the rigidity of the package itself and the bonding strength of the lid to the base, thereby improving the reliability and durability of the piezoelectric device.
[Brief description of the drawings]
FIG. 1A is a plan view showing a preferred embodiment of a crystal resonator according to the present invention, FIG. 1B is a cross-sectional view taken along the line I-I, and FIG. The partial expanded sectional view which shows the point to obstruct | occlude.
FIG. 2 is a plan view showing a modified example of a crystal resonator in which sealing holes are arranged at different positions.
FIG. 3 is a plan view showing another modified example of a crystal resonator in which sealing holes are arranged at different positions.
4A is a longitudinal sectional view showing an embodiment of a conventional crystal unit, and FIG. 4B is a partially enlarged sectional view showing a procedure for closing the sealing hole.
[Explanation of symbols]
1, 13 package; 2, 14 crystal vibrating piece; 3, 11 base; 4, 12 lid; 5, 15 bottom plate portion; 6, 16 frame portion; 7, 21 sealing hole; 7a, 21a large diameter portion; 21b Small diameter part; 8, 22 Sealing material; 9 Step; 10, 23 Metal ball; 17 Space; 20 Low melting point glass; 24 Metallized part

Claims (3)

A piezoelectric vibrating piece, a box-shaped base made of an insulating material, and a flat lid bonded to the upper part of the base, and a package for hermetically sealing the piezoelectric vibrating piece therein,
The base includes a flat bottom plate portion and a frame portion stacked on the bottom plate portion so as to define a space for accommodating the piezoelectric vibrating piece, and the frame extends from the back surface of the bottom plate portion. Having a sealing hole penetrating to the upper surface of the part,
The sealing hole is composed of a large-diameter portion provided in the base and a small-diameter portion continuously provided in the frame portion, and is formed by molten metal in the vicinity of a step between the large-diameter portion and the small-diameter portion. A piezoelectric device characterized by being hermetically sealed. The piezoelectric device according to claim 1, wherein a surface of the step of the sealing hole is metallized. The piezoelectric device according to claim 1 or 2, wherein the lid is a transparent glass thin plate, and the piezoelectric vibrating piece is a tuning fork type piezoelectric vibrating piece.

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