JPH07131279A - Surface mount type crystal oscillator - Google Patents

Abstract

PURPOSE:To provide the surface mount type crystal oscillator which can have excellent resonance characteristics by being put in a box type insulating container and is suitable to, specially, a voltage-controlled oscillator. CONSTITUTION:A crystal piece 15 which has specific resonance characteristics and also has excitation electrodes 16a and 16b formed on the top and reverse plate surfaces is arranged in the box type container 11 which has an opening in the top surface; and the electrode on the reverse plate surface is set opposite the bottom surface of the container 11 and the excitation electrode 16a on the top plate surface is led out. Further, a capacity electrode 18 which forms specific electrostatic capacitance is provided on the bottom surface of the container 11 opposite the excitation electrode 16b on the reverse plate surface of the crystal piece 15, and then led out. The excitation electrode 16a on the top plate surface and capacity electrode 18 are connected to a mount electrode provided on the bottom surface of the container 11. Furthermore, the crystal piece is an AT-cut thickness-shear oscillator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface mount type crystal unit housed in a box-shaped container, and more particularly to improvement of resonance characteristics.

[0002]

2. Description of the Related Art Conventionally, a piezoelectric resonator using a piezoelectric crystal such as quartz has been widely used as a reference for time, frequency, etc. in various electronic devices. In particular, a crystal unit that uses a synthetic quartz crystal as a piezoelectric body has good electrical performance, extremely high frequency accuracy, can maintain a constant resonant frequency for a long time, and is inexpensive. Is used in many electronic devices for. With such a crystal unit, for example, in the manufacturing process of a thickness sliding crystal unit,
A crystal of artificial quartz is cut at a predetermined angle with respect to a crystal axis to be formed into a plate shape. Then, the outer shape is formed into a circle having a predetermined size, a strip shape, or the like, and further, a crystal piece is obtained by polishing to a thickness corresponding to a desired resonance frequency. Then, a conductive metal such as silver or aluminum is vapor-deposited on both side plates of the crystal piece to form an excitation electrode. Then, for example, a pair of terminals are planted in an oval base, and a holding member is provided at the tip of the terminals. Then, both side ends of the crystal piece are held by holding members, and a cylindrical cover having an oval cross section formed by pressing a thin metal plate on the base is further covered to hermetically seal.

On the other hand, in recent years, it has been desired to reduce the size and weight of various electronic devices and to automate the assembly process. For this reason, in the electronic parts used in such electronic devices, surface mount type parts without lead terminals tend to be frequently used. Such a surface mount type electronic component has a small shape, and the assembly process can be easily automated by automatically mounting it on a printed circuit board of an electronic device using a parts feeder or the like. There is. Therefore, there is also a demand for a surface mount type crystal resonator without a lead terminal.

An example of a conventional surface mount type crystal unit is
This will be described with reference to the side sectional view shown in FIG. 3 and the plan view shown in FIG. In the figure, reference numeral 1 is a box-shaped container having a substantially rectangular parallelepiped outer shape.
The container 1 is formed by molding an insulating material such as ceramic, glass, or molding resin, and has a hollow inside and an opening is formed in the upper surface, and a rectangular metal frame 2 is formed along the periphery of the opening.
Is embedded. At least a pair of mounting electrodes 3 are provided on the outer bottom surface of the container 1. Further, a pedestal 4 having an appropriate height is provided on the bottom of the container 1, and a holding electrode 5 electrically connected to the mounting electrode 3 is provided on the pedestal 4. The conductor 6 for electrically connecting the mounting electrode 3 and the holding electrode 5 is
It may be formed by metallization, or a metal thin plate or the like may be embedded to be electrically connected.

Reference numeral 7 is a so-called AT-cut crystal piece that excites, for example, thickness shear vibration. The crystal piece 7 is formed by cutting an artificial crystal crystal at a predetermined angle with respect to the crystal axis to form a strip shape, and polishing the crystal piece to a thickness corresponding to a desired resonance frequency. The excitation electrode 8 made of, for example, is vapor-deposited. The longitudinal end of the crystal piece 7 is placed on the pedestal 4 and fixed with a conductive adhesive so that the excitation electrode 8 of the crystal piece 7 is electrically connected to the holding electrode 5. The plate surface of the crystal piece 7 is held parallel to the bottom surface of the container 1, and the excitation electrode 8 is electrically connected to the mounting electrode 3. Then, a minute amount of metal is vapor-deposited on the electrode of the crystal plate 7 on the opening side of the container 1 to adjust the final frequency, and then the opening of the container 1 is hermetically sealed with the lid 9. I am trying to do it.

However, in such a structure, since the conductor 6 connecting the excitation electrode 8 and the mounting electrode 3 is disposed on the bottom surface of the container, the conductor 6 operates as a reactance and reacts in series with the crystal oscillator. In some cases, the Q value of the crystal unit was lowered because it became equivalent to that of connecting the. Also, the presence of the conductor 6 increases the equivalent parallel capacitance, so-called C0, which increases the capacitance ratio of the crystal unit. For example, when used as a voltage controlled oscillator (VCXO), oscillation is unstable when the oscillation frequency is changed. There is a problem that the frequency variable width becomes narrow.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and can be housed in a box-shaped insulating container to obtain good resonance characteristics, and is particularly suitable for a voltage controlled oscillator. The object is to provide a crystal oscillator of a mold.

[0008]

According to the present invention, a quartz piece having a predetermined resonance frequency and having excitation electrodes formed on front and back plate surfaces is provided in a box-shaped container having an opening on the top surface, and the back plate surface is provided. The electrode of (1) faces the bottom surface of the container and leads out the excitation electrode on the front plate surface to the outside, and further faces the excitation electrode on the back plate surface of the crystal piece to form a predetermined capacitance on the bottom surface of the container. It is characterized in that a capacitance electrode is provided and the capacitance electrode is led to the outside. Further, the present invention is characterized in that the excitation electrode and the capacitive electrode on the front plate surface are connected to a mounting electrode provided on the bottom surface of the container for surface mounting. Furthermore, the present invention is characterized in that the crystal piece is an AT-cut thickness slip oscillator.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the side sectional view shown in FIG. 1 and the plan view shown in FIG. Reference numeral 11 in the drawing is a box-shaped container having a substantially rectangular parallelepiped outer shape, for example, a width of 3.5 mm, a length of 6.0 mm and a thickness of 1.2 mm. The container 11 is formed by molding an insulating material such as ceramic, glass, or molding resin into a predetermined shape. The inside of the container 11 is hollow and an opening is formed in the upper surface. A metal frame 12 is embedded along the edge of the opening. There is. Further, at least a pair of mounting electrodes 13 are provided on the outer bottom surface of the container 11 along the longitudinal direction. Further, a pedestal 14 having an appropriate height is provided on one side of the bottom of the container 11 in the longitudinal direction.

Reference numeral 15 denotes a so-called AT-cut crystal piece that excites thickness shear vibration, for example, and cuts a crystal of artificial quartz at a predetermined angle with respect to the crystal axis, and measures, for example, 2.0 mm × 4.5 mm. Exciting electrodes 16a, 1 are formed by strip-forming and polishing to a thickness corresponding to a desired resonance frequency, and vapor-depositing aluminum, silver or the like on the front and back plate surfaces in a size of about 2.0 mm square.
6b is formed. Then, the crystal piece 15 has the excitation electrode 16b on the back plate surface facing the bottom surface of the container, and the end in the longitudinal direction is placed on the pedestal 14 and coated with a conductive adhesive to carry it to excite the front plate surface. The electrode 16a is led out to the mounting electrode 13 provided on one side in the longitudinal direction of the container 11. The base 14 and the mounting electrode 13 are electrically connected to each other by an appropriate conductor 17 such as metallization or a thin metal plate.

On the bottom surface of the container 11, the crystal piece 1 is attached.
5, the capacitive electrode 18 is formed to face the excitation electrode 16b of
The capacitance electrode 18 is electrically connected to the mounting electrode 13 on the other side in the longitudinal direction of the container 11. In addition, according to the height of the pedestal 14, the excitation electrode 16b and the capacitance electrode 18
And the height of the pedestal 14 can be set to 0.
It can be formed with an accuracy of about 05 mm. When the gap between the excitation electrode 16b and the capacitance electrode 18 is set to 0.5 mm, for example, a capacitance of several PF (picofarad) can be obtained. Then, the excitation electrode 1 on the front plate surface of the crystal piece 15
A slight amount of metal is vapor-deposited on 6a to perform final adjustment of the resonance frequency. Then, a lid 19 made of a metal plate is placed on the metal frame 12 having an opening on the upper surface of the container 11, and both are seam welded to hermetically seal them.

With such a structure, the excitation electrode 16a on the front plate surface of the crystal piece 15 is directly connected to the mounting electrode 13, and the excitation electrode 16b on the back plate surface is electrostatically coupled to the capacitive electrode 18. The capacitance electrode 18 is connected to the mounting electrode 13. Therefore, the crystal unit of the above embodiment is equivalent to a normal crystal unit in which a capacitor is connected in series. The excitation electrode 16b on the back plate surface of the crystal piece 15
The capacitor electrode 18 in the substantially central portion of the bottom surface of the container 11.
Are arranged. Therefore, the capacitive electrode 18 is connected to the container 11
When connecting to the mounting electrode 13 arranged on the outer bottom surface of the, the connection can be made in the shortest distance regardless of the position of the mounting electrode 13, and the increase of the equivalent parallel capacitance C0 can be extremely reduced. Therefore, if such a crystal oscillator is used in, for example, a voltage controlled oscillator (VCXO), stable oscillation can be maintained even when the frequency changes, and the oscillation frequency can be changed in a wide variable range.

FIGS. 3 to 5 are graphs showing the equivalent series resistance and capacitance ratio of the crystal unit of the above embodiment and the conventional crystal unit in comparison. This crystal oscillator has a resonance frequency of 89.545 MHz for the third overtone, and 20 samples were manufactured for each sample to examine the distribution of the equivalent series resistance and the capacitance ratio. 3 is the equivalent series capacitance of the conventional crystal unit, FIG. 4 is the capacitance ratio of the conventional crystal unit, FIG. 5 is the equivalent series capacitance of the crystal unit of the above embodiment, and FIG. 6 is the crystal vibration of the above embodiment. It is the capacity ratio of the child. As is clear from this graph, the equivalent series resistance of the conventional crystal unit is 3
The average value of 0 to 55Ω is 39.5Ω. On the other hand, the equivalent series resistance of the crystal unit of the above embodiment is 20 to 4
There is little variation at 0Ω, and the average value is 29.5Ω.
Regarding the capacitance ratio, the average value of the conventional vibrator is 30.
40, the average value is 276 in the vibrator of the above embodiment.
It is as small as 0, which is preferable.

The present invention is not limited to the above-mentioned embodiment. In the above-mentioned embodiment, a crystal piece is placed on a pedestal and a conductive adhesive is applied and carried. The crystal piece may be directly adhered to the bottom surface of the container by using an adhesive in which various beads and the like are kneaded. By doing so, it is not necessary to form a pedestal or the like on the bottom surface of the container, and when the adhesive is solidified, a gap can be surely provided between the plate surface of the crystal piece and the bottom surface of the container.

[0015]

As described in detail above, according to the present invention, there is provided a surface mount type piezoelectric vibrator having a good resonance characteristic and housed in a box-shaped insulating container suitable for a voltage controlled oscillator (VCXO). be able to.

[0016]

[Brief description of drawings]

FIG. 1 is a side sectional view showing an embodiment of the present invention.

FIG. 2 is a plan view showing an internal structure of the crystal unit shown in FIG.

FIG. 3 is a graph showing an equivalent series resistance of a conventional crystal unit.

FIG. 4 is a graph showing a capacitance ratio of a conventional crystal unit.

FIG. 5 is a graph showing an equivalent series resistance of a crystal unit according to an embodiment of the present invention.

FIG. 6 is a graph showing a capacitance ratio of a crystal resonator according to an example of the present invention.

FIG. 7 is a side sectional view showing an example of a conventional surface mount type crystal resonator.

8 is a plan view showing the internal structure of the crystal unit shown in FIG.

[Explanation of symbols]

 11 Container 15 Crystal Pieces 16a, 16b Excitation Electrode 18 Capacitance Electrode

Claims (3)

[Claims] 1. A box-shaped container having an opening on the upper surface, and excitation electrodes formed on the front and back plate surfaces having a predetermined resonance frequency and arranged in the container, the electrodes on the back plate surface being the bottom surface of the container. A quartz piece that faces the excitation electrode on the front plate and is led to the outside, and a capacitance electrode that is provided on the bottom surface of the container and faces the excitation electrode of the quartz piece to form a predetermined electrostatic capacitance and leads to the outside. And a surface mount type crystal unit. 2. The surface-mounted type crystal vibration according to claim 1, wherein the excitation electrode and the capacitive electrode on the front plate surface are connected to a mounting electrode provided on the bottom surface of the container for surface mounting. Child. 3. The surface mount type crystal resonator according to claim 1, wherein the crystal piece is an AT-cut thickness slip resonator.