JP3896585B2 - Tuning fork type piezoelectric vibrator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a tuning fork type piezoelectric vibrator used for a clock source of an electronic device or the like.
[0002]
[Prior art]
The tuning fork type piezoelectric vibrator uses a tuning fork type piezoelectric diaphragm having a pair of leg portions and a base portion connecting one end side as an element. One end of the leg portion is a free end and the lower portion of the base portion is fixed. It is electrically and mechanically connected to an electrode pad provided on the package as an end by a conductive bonding material. (See, for example, JP-A-11-312948)
[0003]
The tuning fork type piezoelectric vibrator obtains a predetermined frequency by mechanical resonance of the legs, but a commonly used vibration mode is a bending vibration in which a pair of legs starts from the base and the free end approaches and separates in a plane. Mode. In order to obtain such a vibration mode, an X-cut quartz plate is usually used, but the processing method from a quartz wafer to individual tuning-fork type quartz plates is based on mechanical processing using a wire saw or the like, and photolithography technology. There is a chemical processing method used. Regardless of whether the tuning fork type quartz diaphragm is obtained by a mechanical processing method or a chemical method, adjusting the vibration balance of the pair of legs is an important factor for improving the performance of the piezoelectric vibrator. It has become. That is, when the vibration balance of the leg is unbalanced, the vibration energy is not sufficiently attenuated at the base, and when the base is joined to the package, the deterioration of the CI (crystal impedance) value and the frequency fluctuation are remarkable. This is because they may appear and do not satisfy the required electrical performance.
[0004]
The method for adjusting the vibration balance varies depending on the manufacturing method. As an example of adjusting the electrical characteristics of the tuning fork type piezoelectric diaphragm obtained by the mechanical processing method, for example, as shown in Japanese Patent Laid-Open No. 59-5713, the tuning fork type After a predetermined excitation electrode is formed on the quartz diaphragm, the tip of one or both of the legs is ground with a rotating grindstone, and at the same time, the electrical characteristics such as CI (crystal impedance) value and frequency are monitored in real time. Thus, a predetermined vibration balance adjustment is performed, and further, the balance adjustment is further performed by attaching a metal film material having an additional mass to the tip portion of the leg portion by vacuum deposition or the like in a state of being incorporated in a package.
[0005]
In the chemical processing method, the adjustment with the rotating grindstone as described above is not normally performed, and a metal film material is added to the tip of the leg portion, or the adjustment metal film formed in advance is cut off. It was removed with a laser beam, etc., and the electrical characteristics changed by this work were monitored and predetermined adjustments were made. Japanese Patent Application Laid-Open No. 11-312948 also discloses that the frequency is adjusted with a laser beam or an electron beam.
[0006]
However, even when the vibration balance adjustment as described above is performed, there is a case where the balance is not completely achieved or an unbalance exceeding the detection capability of the adjustment device remains. In such an unbalanced tuning fork type piezoelectric diaphragm, the vibration energy of the leg portion is not attenuated as intended at the base portion, and the vibration energy remains in the base portion. When such a base is bonded to the electrode pad of the package, vibration energy may leak from the base to the package. Such vibration leakage is also called acoustic leakage, and vibration energy leaks through the entire tuning-fork type piezoelectric vibrator. Therefore, depending on the mounting state with the mounting board on which it is mounted, electrical characteristics such as frequency may be present. It sometimes fluctuated. In particular, when the main surface of the base portion of the tuning fork type piezoelectric diaphragm is bonded to the electrode pad of the ceramic package, the amount of vibration leakage and its probability tend to increase due to the wide bonding area.
[0007]
[Problems to be solved by the invention]
The present invention has been made to solve the above problems, and provides a tuning fork type piezoelectric vibrator having a stable electric characteristic by suppressing a decrease in electric characteristics due to vibration leakage as much as possible in the tuning fork type piezoelectric vibrator. It is intended.
[0008]
[Means for Solving the Problems]
In the present invention, a tuning fork type piezoelectric vibrator having a tuning fork type piezoelectric diaphragm housed in a package and hermetically sealed, and a mass ratio of the tuning fork type piezoelectric diaphragm is related to vibration leakage of the tuning fork type piezoelectric vibrator. It can be realized by the following configurations.
[0009]
A tuning fork type piezoelectric vibrator according to claim 1 has a pair of legs and a base for connecting the legs, a tuning fork type piezoelectric vibration plate having excitation electrodes formed on a main surface and side surfaces, and the tuning fork type piezoelectric vibration. A tuning fork type piezoelectric vibration comprising a ceramic package having an electrode pad on the inner bottom surface, a conductive bonding material for conductively bonding the ceramic package and the tuning fork type piezoelectric vibration plate, and a lid for hermetically sealing the package The leg portion of the tuning fork type piezoelectric diaphragm has a dimensional ratio (t / w) of the leg width w to the leg thickness t of 0.7 or less and a leg thickness t of 0. 1 mm or more, a part of one main surface of the tuning fork type piezoelectric diaphragm base is bonded to an electrode pad formed on the ceramic package by the conductive bonding material, and the mass A of the tuning fork type piezoelectric vibrator Before Is a tuning fork type piezoelectric vibrator, characterized in that the mass ratio of the mass B of the tuning-fork type piezoelectric vibrating plate (A / B) over 30. The mass B of the tuning fork type piezoelectric diaphragm is a mass including the tuning fork type quartz plate and the excitation electrode formed on the surface of the tuning fork type piezoelectric diaphragm. The mass A of the tuning fork type piezoelectric vibrator is the tuning fork type piezoelectric diaphragm in the package. It shows the mass mounted, bonded with a conductive bonding material, and hermetically sealed with a lid.
[0010]
In many cases, a surface-mounted tuning fork type piezoelectric vibrator usually joins a part of a main surface of a base portion with a relatively large area. As described above, the present invention functions effectively even with such a configuration, and deterioration of electrical characteristics due to vibration leakage can be suppressed.
[0011]
Next, the reason why the mass ratio of the mass B of the tuning fork type piezoelectric diaphragm to the mass A of the tuning fork type piezoelectric vibrator is set to 30 or more (A / B) will be described. FIG. 4 is a graph showing the rate of occurrence of acoustic leak (vibration leak) when the mass ratio is changed (A / B). The basic configuration of the sample used is the configuration shown in the first embodiment. The tuning fork type piezoelectric diaphragm is a tuning fork type crystal diaphragm on which an excitation electrode is formed, and the tuning fork type piezoelectric vibrator is used as a package. It is housed and bonded with a conductive bonding material and then hermetically sealed with a metal lid. Samples 1 to 3 use packages of the same outer size. Sample 1 has a mass A of the vibrator and sample 1 has a mass ratio of about 17 (the mass A of the vibrator is 0.026526 g, and the mass B of the diaphragm is 0). Sample 2 has a mass ratio of about 27 (oscillator mass A is 0.02599 g, diaphragm mass B is 0.000954 g), and sample 3 has a mass ratio (oscillator mass A is 0.005 g). 05247g, and the mass B of the diaphragm is about 33.00090g). Note that the difference in vibrator weight between samples 1 to 3 is due to the difference in the weight of the diaphragm and the difference in the amount and weight of the conductive bonding material. Samples 4 to 6 use packages having the same outer size, and have a larger outer size than the packages used in samples 1 to 3. Sample 4 has a mass ratio of about 32 (vibrator A is 0.05088 g, diaphragm B is 0.00001590 g), and sample 5 has a mass ratio of about 37 (vibrator A is 0.05883 g, diaphragm B is 0 Sample 6 has a mass ratio of about 66 (vibrator A is 0.05362 g, diaphragm B is 0.000813 g). In the measurement of the vibrator and the diaphragm, 1000 masses are measured, and the weight per one is calculated from this value.
[0012]
A verification experiment was performed on 100 samples arbitrarily selected from the above samples, and the frequency variation rate was confirmed in order to confirm the rate of occurrence of acoustic leakage. A package in which the hermetically sealed package was pressed at a predetermined pressure and the frequency changed by 5 ppm or more was defined as an acoustic leak generating product. Note that the tuning fork type piezoelectric diaphragm used in any of the samples is machined using a wire saw, and has been adjusted for characteristics by adjusting the tip of the leg portion by grinding. It can be understood from FIG. 4 that the acoustic leak, that is, the vibration leak is greatly reduced by setting the mass ratio to 30 or more regardless of the package size.
[0013]
Since the frequency of the tuning fork vibrator depends on the leg length (l) and leg width (w) of the diaphragm, the leg width (w) does not substantially vary. For this reason, the diaphragm is made thinner by reducing the dimensional ratio (t / w), and when it is 0.7 or less, the effect of reducing the weight of the diaphragm becomes obvious. However, in order to secure the electrode region formed on the side surface of the tuning-fork type piezoelectric diaphragm, the thickness t of the leg portion is required to be 0.1 mm or more, so the above-mentioned limited range is a preferable numerical range.
[0014]
Tuning fork type piezoelectric vibrators, particularly tuning fork type piezoelectric vibrators obtained by the above-mentioned mechanical processing method, tend to have variations in processing accuracy, and the vibration imbalance increases as the leg width w increases with respect to the leg width w. It is known that this is likely to occur. FIG. 5 is a graph showing the frequency change rate when t / w is varied, and a verification experiment was performed on three types of samples with different mass ratios. Sample A has a mass ratio of 27, and is plotted with crosses in FIG. Sample B has a mass ratio of 30 and is plotted with circles in FIG. Further, sample C has a mass ratio of 35, and is plotted with ◎ in FIG. Among these samples, samples B and C, that is, those having a mass ratio of 30 and 35 have a frequency change rate within a favorable range when t / w is 0.7 or less. Each diaphragm has a thickness of 0.15 mm.
[0015]
As can be seen from the graph of FIG. 5, the rate of frequency change increases as the leg thickness t becomes relatively large. In particular, when t / w is 0.7 or more, this is a practical problem. It is a value. Therefore, when the mass ratio (A / B) of the mass B of the tuning fork type piezoelectric diaphragm to the mass A of the tuning fork type piezoelectric vibrator is 30 or more, t / w is preferably 0.7 or less, and as described above. In order to secure the side surface electrode formation region, the thickness t of the leg portion is required to be 0.1 mm or more, so the above-mentioned limited range is a preferable numerical range.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
A first embodiment of the present invention will be described with reference to FIG. 2 and FIG. 2, taking a surface-mounted tuning fork type crystal resonator as an example. FIG. 1 is an exploded perspective view showing the present embodiment, FIG. 2 is a view schematically showing an internal cross-sectional view when FIG. 1 is assembled, and FIG. 3 is a cross-sectional view showing an electrode configuration of a tuning-fork type crystal plate leg. FIG. In FIGS. 1 and 2, the electrode film formed on the tuning fork type quartz diaphragm is not clearly shown. The tuning fork type crystal resonator includes a ceramic package 1 having a concave portion with an open top, a tuning fork type crystal vibration plate 3 which is a piezoelectric vibration plate housed in the package, and a metal bonded to the opening of the package. It consists of the lid 2 made from.
[0017]
In the concave ceramic package 1 as viewed in cross section, a circumferential metal layer 11 is formed on a bank portion 10a around the concave shape. Although not shown in detail, the metal layer 11 includes a metallized layer made of, for example, tungsten or molybdenum, and a plated layer made of nickel, gold, or the like formed on the metallized layer. Castellations C1, C2, C3, and C4 are formed at four corners of the outer periphery of the ceramic package. Of these, metal conductors 14 and 15 are formed below the castellations C1 and C2, and the metal conductors 14 and 15 are electrically connected to electrode pads described later. Further, metal conductors 16 and 17 are formed on the castellations C3 and C4 from the upper end to the lower end, and are electrically connected to the metal layer 11 and ground terminals E3 and E4 (E3 not shown) formed on the bottom surface of the ceramic package. Connected to.
[0018]
As shown in FIG. 2, the ceramic package 1 includes a rectangular flat plate-shaped package substrate 1a, a first ceramic frame 1b having a large central portion and substantially the same size as the package base, and the first ceramic package 1a. The ceramic frame 1b and a second ceramic frame 1c having substantially the same shape, these layers are laminated and fired integrally. The metal layer 11 described above is formed on the upper surface of the second ceramic frame 1c.
[0019]
Electrode pads 12 and 13 are formed on the inner bottom surface of the ceramic package 1. These electrode pads are connected to the device terminals E1 and E1 on the bottom surface outside the package via connection electrodes 12a and 13a (13a not shown). It is electrically drawn out as E2 (E2 is not shown).
[0020]
A tuning fork type quartz diaphragm 3 which is a piezoelectric diaphragm is mounted between the electrode pads 12 and 13. The tuning fork type quartz diaphragm 3 has a shape having a pair of leg portions 31 and 32 and a base portion 33 for connecting the leg portions 31 and 32 at one end side. Such tuning-fork type processing can be obtained from a quartz wafer by a mechanical cutting means such as a wire saw, or may be formed by chemical processing means by photolithography technology.
[0021]
As shown in FIG. 3, independent excitation electrodes are formed on the total four surfaces of the main surface and side surfaces of each leg portion of the tuning fork type quartz diaphragm. Main surface excitation electrodes 31a and 31b formed to face the main surface of one leg portion 31 and side surface excitation electrodes 32c and 32d formed to face the side surface of the other leg portion 32 are formed on the base 33. Side-exciting electrodes 31c, 31d formed opposite to the side surfaces of one leg 31 and side-exciting electrodes 32a formed opposite to the main surface of the other leg 32, 32b is commonly connected by wiring electrodes formed on the base 33. The electrode formed on the quartz plate has a structure in which, for example, the lower layer is a chromium layer, the upper layer is a chromium + silver layer, and the upper layer is a silver layer. These two commonly connected terminals are drawn out to positions corresponding to the electrode pads 12 and 13, respectively, and are conductively bonded by a conductive bonding material (not shown). As a result, the tuning fork type quartz diaphragm 3 is housed in the ceramic package in a cantilevered state with a part of the main surface base portion as a supporting portion.
[0022]
The metal lid 2 hermetically sealing the ceramic package has a configuration in which metal film layers are formed on the upper and lower surfaces of a metal base material 20 such as Kovar. A nickel layer 21 is formed on the upper surface of the metal lid, that is, the non-joint surface with the package, by means such as plating, and a copper layer 22 and a silver brazing layer 23 are formed in this order on the lower surface of the metal lid, that is, the ceramic package side. Has been. The copper layer 22 and the silver brazing layer 23 are formed using, for example, a rolling technique and are clad. By making the clad, there is an advantage that gas is not released at the time of melting, and adverse effects of the gas on the inside of the package can be avoided.
[0023]
The metal lid 2 and each metal film layer of the ceramic package 1 are joined by beam welding or seam welding in a vacuum atmosphere, which mainly melts the silver brazing of the metal lid and performs hermetic joining. Is called. The mass ratio (A / B) of the mass B of the tuning-fork type quartz diaphragm to the mass A of the completed tuning-fork type quartz vibrator is set to 30 or more. The mass of the tuning-fork type quartz diaphragm includes the electrode material formed on the surface thereof.
[0024]
As a method for adjusting the mass ratio, as described in the verification experiment, in addition to changing the size of the tuning fork type piezoelectric diaphragm, or changing the package size, for example, increasing the thickness of the package, Adjustment may be made such as using a material having a high specific gravity or reducing the specific gravity of the electrode material formed on the tuning-fork type piezoelectric diaphragm.
[0025]
【The invention's effect】
According to the present invention, the mass ratio (A / B) of the mass B of the tuning fork type piezoelectric diaphragm to the mass A of the tuning fork type piezoelectric vibrator is 30 or more. Even when there is vibration leakage, fluctuations in electrical characteristics can be suppressed. Therefore, a tuning fork type piezoelectric vibrator having stable electrical characteristics can be obtained.
[0026]
Further , even in a configuration in which the electrode pad formed on the package and a part of the main surface base portion of the tuning fork type piezoelectric diaphragm are joined, frequency fluctuation due to vibration leakage can be suppressed.
[0027]
Moreover, when the mass ratio (A / B) of the mass B of the tuning fork type piezoelectric diaphragm to the mass A of the tuning fork type piezoelectric vibrator is 30 or more, t / w is set to 0.7 or less, thereby causing vibration leakage. It is possible to obtain a tuning fork type piezoelectric vibrator capable of suppressing frequency fluctuations more favorably.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view according to a first embodiment.
FIG. 2 is an internal cross-sectional view when the components shown in FIG. 1 are assembled.
FIG. 3 is a diagram showing electrode wiring of a tuning fork type piezoelectric vibrator.
FIG. 4 is a graph showing verification experiment data.
FIG. 5 is a graph showing verification experiment data.
[Explanation of symbols]
1 Ceramic package 2 Metal lid 23 Metal brazing layer (silver brazing layer)
3 Tuning fork type quartz diaphragm (Tuning fork type piezoelectric diaphragm)
31, 32 Leg 33 Base

Claims (1)

A tuning fork-type piezoelectric diaphragm having a pair of legs and a base for connecting the legs, and an excitation electrode formed on the main surface and side surfaces, and housing the tuning-fork type piezoelectric diaphragm and electrode pads on the inner bottom surface a ceramic package having, a tuning fork type piezoelectric vibrator consisting of the with the ceramic package the tuning-fork type piezoelectric vibrating plate and a conductive bonding material to conductively joined, a cover for hermetically sealing the package,
The leg portion of the tuning fork type piezoelectric diaphragm has a dimensional ratio (t / w) of the leg width w to the leg thickness t of 0.7 or less and the leg thickness t of 0.1 mm or more. In addition, a part of one main surface of the tuning fork type piezoelectric diaphragm base is joined to an electrode pad formed on the ceramic package by the conductive joining material, and the tuning fork type with respect to the mass A of the tuning fork type piezoelectric vibrator. A tuning fork type piezoelectric vibrator characterized in that a mass ratio (A / B) of mass B of the piezoelectric diaphragm is 30 or more.

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