Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2001-06-01
2003-07-08
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06590314
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric resonator container for containing therein piezoelectric resonator pieces, such as quartz crystal resonators, to a piezoelectric resonator using the piezoelectric resonator container, to a circuit board having the piezoelectric resonator mounted thereon, and to a method for manufacturing a piezoelectric resonator. More particularly, the present invention relates to a technique for sealing an open end of an elliptical or nearly elliptical cylindrical case used in a piezoelectric resonator container.
2. Background of Related Art
Piezoelectric resonators used in various electronic devices are incorporated into the electronic devices in a state of being contained in containers. In some piezoelectric resonators, thin plate piezoelectric resonators are used in which electrodes are formed in predetermined patterns on piezoelectric resonator pieces, such as the tuning fork type or AT cut quartz crystal pieces. Therefore, if elliptical or nearly elliptical cylindrical cases are used corresponding to the shape of the piezoelectric resonator pieces, the piezoelectric resonator pieces can be efficiently contained, and the- thickness of the piezoelectric resonators can be reduced. An example of such containers is disclosed in Japanese Unexamined Utility Model Application Publication No. 2-55727. The piezoelectric resonator container has a structure such that a piezoelectric resonator is contained in a nearly elliptical case, and a stem is pressed into the open end of the case to be sealed.
However, according to the structure in which the nearly elliptical case is sealed by pressure as in the piezoelectric resonator container disclosed in Japanese Unexamined Utility Model Publication No. 2-55727, since the contact surface pressure between the case and the stem varies in a circumferential direction, leakage tends to occur at a portion of low contact surface pressure.
As a piezoelectric resonator container for solving such a problem, Domestic Republication of PCT international Publication for Patent Application No. WO97/08826 discloses a piezoelectric resonator container in which a pressure allowance is maximized between a minor axis portion and a major axis portion, when pressing a stem having an elliptical or nearly elliptical outer peripheral shape into a case having an elliptical or nearly elliptical inner peripheral shape. According to this arrangement, since the pressure allowance of a section where incomplete gas-tightness is empirically most likely to occur is maximized, the incomplete gas-tightness at this portion can be prevented.
However, in the piezoelectric resonator container in which the pressure allowance is maximized between the minor axis portion and the major axis portion, a portion is generated where stress (tensile stress) applied in the circumferential direction of the case during the application of pressure has a maximum. As a result, the case may break at this portion, and incomplete gas-tightness occurs.
SUMMARY OF THE INVENTION
It is an object of the present invention to realize a piezoelectric resonator container which solves the above problems and. in which incomplete gas-tightness does not occur even if an elliptical or nearly elliptical case is used, a piezoelectric resonator using the same, a circuit board having the piezoelectric resonator mounted thereon, and a method for manufacturing a piezoelectric resonator, and to realize a piezoelectric resonator container in which a piezoelectric resonator piece does not come into contact with the inner periphery of the case even if an oblate case, such as an elliptical or nearly elliptical case, is used.
In accordance with one aspect of the invention, there is provided a piezoelectric resonator container which may a consist of a cylindrical case, one end of which is an open end; and a stem for sealing the open end of the case, wherein, in a cross section of the stem in a direction perpendicular to an axial direction of the case at a portion contacting the case, an outer periphery of the stem includes a minor axis portion having a first radius of curvature, and a major axis portion having a second radius of curvature smaller than the first radius of curvature, and a tangent to the first radius of curvature coincides with a tangent to the second radius of curvature at a connection portion of the first radius of curvature and the second radius of curvature, wherein, in a cross section of the case in a direction perpendicular to an axial direction of the case at a portion contacting the stem, an inner periphery of the case includes a minor axis portion having a third radius of curvature, and a major axis portion having a fourth radius of curvature smaller than the third radius of curvature, and a tangent to the third radius of curvature coincides with a tangent to the fourth radius of curvature at a connection portion of the third radius of curvature and the fourth radius of curvature, and wherein a pressure allowance when pressing the stem into the open end of the case monotonically increases from the major axis of the case toward the minor axis.
In accordance with another aspect of the invention, there is provided a piezoelectric resonator in which a piezoelectric resonator piece is contained in a piezoelectric resonator container having a cylindrical case, one end of which is an open end, and a stem for sealing the open end of the case, wherein, in a cross section of the stem in a direction perpendicular to an axial direction of the case at a portion contacting the case, an outer periphery of the stem includes a minor axis portion having a first radius of curvature, and a major axis portion having a second radius of curvature smaller than the first radius of curvature, and a tangent to the first radius of curvature coincides with a tangent to the second radius of curvature at a connection portion of the first radius of curvature and the second radius of curvature, wherein, in a cross section of the case in a direction perpendicular to an axial direction of the case at a portion contacting the stem, an inner periphery of the case includes a minor axis portion having a third radius of curvature, and a major axis portion having a fourth radius of curvature smaller than the third radius of curvature, and a tangent to the third radius of curvature coincides with a tangent to the fourth radius of curvature at a connection portion of the third radius of curvature and the fourth radius of curvature, and wherein a pressure allowance when pressing the stem into the open end of the case monotonically increases from the major axis of the case toward the minor axis.
In the above aspect of the invention, since the outer periphery of the stem and the inner periphery of the case have a nearly elliptical shape formed of two types of large and small arcs, a flat piezoelectric resonator piece can be efficiently contained, and the thickness of the piezoelectric resonator can be reduced. Since the pressure allowance is increased at the minor axis portion where the vertical stress tends to decrease, the vertical stress is above the lower limit value over the entirety thereof. Therefore, incomplete gas-tightness due to inadequate sealing does not occur. Furthermore, since the pressure allowance is set to be small at the major axis portion where the tensile stress tends to increase, the tensile stress is below the upper limit value over the entirety thereof. For this reason, incomplete gas-tightness due to the breaking of the case does not occur. Therefore, according to the present invention, a piezoelectric resonator with a high degree of reliability can be constructed.
In accordance with an aspect of the invention, there is provided a piezoelectric resonator container which may consist of a cylindrical case, one end of which is an open end; and a stem for sealing the open end of the case, wherein, in a cross section of the stem in a direction perpendicular to an axial direction of the case at a portion contacting the case, an outer periphe
Arahari Hiroshi
Hama Setsuhiro
Karaki Eiji
Budd Mark O.
Oliff & Berridg,e PLC
Seiko Epson Corporation
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