JPH03175713A - Piezoelectric resonator and its manufacture - Google Patents

Abstract

PURPOSE:To form a structure with sealing reliability higher than ever by extending a part of an adhesive on the inner wall plane of vibrating space composed of a piezoelectric substrate and a sealing substrate. CONSTITUTION:The adhesive 7 is applied to the lower side plane of the sealing substrate 4 and the upper side plane of the sealing substrate 5 leaving a part joining with the piezoelectric substrate 2 i.e., recessed parts 4a, 5a for the formation of vibrating space as it is. The sealing substrates 4, 5 on which the adhesive 7 is applied are stuck on the upper side and lower side of the piezoelectric substrate 2, which forms a stacked matter having the vibrating space. When the stacked matter is heated and also, is pressurized in a plate thickness direction, part of the adhesive 7 applied a little excessively is extended on the inner wall plane of the vibrating space from the terminal part of the joining part of the sealing substrates 4, 5 with the piezoelectric substrate 2. When the piezoelectric resonator is packaged on a printed board, etc., the adhesive 7 extending on the inner wall plane of the vibrating space functions as a packing material and no direct high internal pressure is applied to the adhesive 7 even when the internal pressure in the vibrating space is increased by adding heat due to reflow, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a piezoelectric resonator used in filter circuits, oscillation circuits, etc., and a method for manufacturing the same.

BACKGROUND ART Conventionally, energy trapping type three-terminal filters shown in FIGS. 4 to 6 have been known as piezoelectric resonators of this type. This filter 21 is composed of one piezoelectric substrate 22 and two sealing substrates 24 and 25. Piezoelectric substrate 2
2 has vibrating electrodes 23a, 23b, 2 on its central upper and lower surfaces.
3c is formed. The sealing substrates 24 and 25 each have a recess 24a for forming a vibration space at the center of the lower surface and the upper surface, respectively.
25a is formed. The sealing substrate 24 has a recess 24a.
Adhesive 26 is applied to the lower surface except for the area around the periphery. Similarly, an adhesive 26 is applied to the upper surface of the sealing substrate 25, leaving the recess 25a and the vicinity thereof.

Next, the piezoelectric substrate 22 and sealing substrates 24 and 25 stacked in the thickness direction of the substrate 22 are fixed to each other via an adhesive 26 to form a sealed vibration space.

FIG. 5 shows the appearance of the filter 21 fixed with adhesive 26. External electrodes (A), (B), and (C) are connected to vibrating electrodes 23a, 23b, and 23c, respectively.

By the way, the vibration space formed by the piezoelectric substrate 22 and the sealing substrates 24 and 25 is required to have a high sealing degree. Normally, even in the case of the conventional filter 21, the vibration space has a sealing degree sufficient for practical use. However, in order to meet specifications that require higher environmental resistance and reliability, there is a concern that conventional bonding methods may not be able to ensure sealing performance.

Therefore, an object of the present invention is to provide a piezoelectric resonator having a structure with better sealing reliability and a method for manufacturing the same.

Means for Solving the Problems In order to solve the above problems, a piezoelectric resonator according to the present invention is provided in which a piezoelectric substrate provided with a vibrating electrode and a sealing substrate provided with a recess for forming a vibration space are bonded with an adhesive. The piezoelectric substrate and the sealing substrate are bonded to each other via the piezoelectric substrate, and a portion of the adhesive extends to an inner wall surface of a vibration space formed by the piezoelectric substrate and the sealing substrate.

The manufacturing method includes: (a) applying an adhesive to at least one of a piezoelectric substrate provided with a vibrating electrode or a sealing substrate provided with a concave portion for forming a vibration space; (b) the piezoelectric substrate (c) applying pressure to the piezoelectric substrate and the sealing substrate to apply the adhesive to the inner wall surface of the vibration space; It is characterized by comprising a step of extending a part of.

Incidentally, the steps (b) and (e) are usually not performed side by side, but at the same time.

The adhesive extending on the inner wall surface of the vibration space formed by the working piezoelectric substrate and the sealing substrate functions as a packing, and is sandwiched between the piezoelectric substrate and the sealing substrate to bond them together. Protect the internal pressure of the vibration space from being applied directly to the adhesive being used.

Further, the extending adhesive increases the interfacial distance between the adhesive and the sealing substrate or the adhesive and the piezoelectric substrate.

EXAMPLES Hereinafter, examples of the piezoelectric resonator and the manufacturing method thereof according to the present invention will be described.

The energy trapping three-terminal filter 1 shown in FIG. 1 is composed of one piezoelectric substrate 2 and two sealing substrates 4.5. Vibrating electrodes 3a, 3b, and 3c are formed on the upper and lower surfaces of the piezoelectric substrate 2 at its center.

The piezoelectric substrate 2 is made of a crystal substrate or Pb(ZrTi)Os.
, Bal1Os ceramic substrates, etc. are used.

For the sealing substrates 4 and 5, insulating substrates such as heat-resistant ceramic substrates or resin substrates are used. A circular vibration space forming recess 4 a is provided in the center of the lower surface of the sealing substrate 4 . Similarly, a circular vibration space forming recess 5a is provided in the center of the upper surface of the sealing substrate 5. In the actual mass production process, these substrates 2, 4.5 have a wide area and are cut into predetermined dimensions after being bonded.

The sealing substrates 4 and 5 prepared in this way are bonded to the piezoelectric substrate 2, that is, the recesses 4-4a and 5a for forming the vibration space, and the adhesive 7 is applied to the lower surface of the sealing substrate 4 and the sealing substrate. Apply to the upper side of 5. At this time, the adhesive coating thickness is slightly thicker and the coating area is wider than the conventional adhesive coating thickness. As the adhesive 7, a thermosetting adhesive whose main component is diallyl resin, epoxy resin, etc., which has excellent heat resistance and reliability, is used.

Next, the sealing substrates 4 and 5 coated with the adhesive 7 are bonded to the top and bottom of the piezoelectric substrate 2 to form a laminate having a vibration space. When this laminate is heated and pressurized in the thickness direction, a portion of the slightly excessively applied adhesive 7 is released from the end of the joint between the sealing substrate 4.5 and the piezoelectric substrate 2 into the vibration space. Extends to the inner wall surface. The extended adhesive 7a has a fan-shaped cross section due to the surface tension of the adhesive itself. This extended adhesive 7a is formed over the entire circumference of the opening-side side wall surfaces of the circular recesses 4a, 5a. In this state, the adhesive 7 is thermoset and forms a sealed vibration space. Thereafter, external input/output electrodes (A) and (B) are formed in a state where they are electrically connected to the vibrating electrodes 3a and 3b, respectively. Similarly, the external common electrode (C) is formed in a state where it is electrically connected to the vibrating electrode 3c.

In this example, the process of bonding the piezoelectric substrate 2 and the sealing substrate 4°5 together to form a laminate having a vibration space, and the process of heating and pressurizing this laminate in the thickness direction are separated. Although explained separately, they are performed simultaneously in the actual manufacturing process.

When the obtained filter 1 is mounted on a printed wiring board or the like, even if the internal pressure of the vibration space increases due to the application of heat such as reflow, the adhesive 7a extending on the inner wall surface of the vibration space does not stick. The piezoelectric substrate 2 and the sealing substrates 4 and 5
High internal pressure is not directly applied to the adhesive 7 that is sandwiched between the two and joins them together.

In addition, the adhesive 7 and the sealing substrates 4 and 5 or the piezoelectric substrate 2
The interface distance with the filter is longer than that of a filter with a conventional structure. Therefore, the path through which moisture from the outside world enters the vibration space becomes longer.

Regarding the filter 1 manufactured in this way, experiments were conducted to examine the relationship between the amount of adhesive 7a extending on the inner wall surface of the vibration space and various electrical characteristics. The results are shown in the graph of FIG.

The filter 1 discharge center frequency used in the experiment was 10.7MH
Z is an energy trap type three-terminal filter, the thickness of the piezoelectric substrate is approximately 0.2 mm, and the diameter of the circular vibration space forming recesses 4a, 5a provided in the sealing substrates 4, 5 is 2.
It was 8 mm. The horizontal axis of the graph represents the diameter of the vibration space, and the vertical axis represents four types of electrical characteristics: 3 dB bandwidth, 20 dB bandwidth, spurious, and insertion loss. In the figure,
The solid line A1 shows the 3 dB bandwidth, the -dot chain line A2 shows the 20 dB bandwidth, the dotted line A3 shows the spurious, and the two-dot chain line A4 shows the experimental results of the insertion loss. Furthermore, the diameter of the vibration space is
The diameter of the inner circumference of the extended adhesive 7a (
(See Figure 1).

When the adhesive 7a does not extend (i.e., the diameter D of the vibration space
= 2.8 mmφ) and the extension amount T of the adhesive 7a (
(see Figure 1) is 0.1 mm (when D = 2.6 mmφ), the 3 dB bandwidth, 20 dB bandwidth, and insertion loss have hardly changed, while the spurious has increased from 31 dB to 39 dB. This shows that the amount of damping is extremely large.

- When the extension amount T of the adhesive 7a is further increased, 3d
The B bandwidth (solid line AI) gradually narrows, the 20 dB bandwidth (-dotted chain line A2) widens at an accelerating rate, and the insertion loss (
The two-dot chain line A4) also increases with acceleration. On the other hand, although the amount of damping of spurious components increases, the amount of change gradually decreases. According to this graph, in the case of this embodiment, it can be said that it is most preferable in terms of electrical characteristics to make the extension amount T of the adhesive 7a about 0.1 mm. In this way, although the adhesive extending on the inner wall surface of the vibration space slightly damps vibrations in the main frequency band,
Spurious damping is performed more than that.

Note that the piezoelectric resonator and the method for manufacturing the same according to the present invention are not limited to the above embodiments, and can be variously modified within the scope of the gist.

The shape of the adhesive extending on the inner wall surface of the vibration space changes variously depending on the bonding conditions of the adhesive 7. For example, in Figure 3 (a
) and (b) show the extended shape when the viscosity of the adhesive 7 is relatively low. In FIG. 3(a), the extended adhesive 7b is cured while flowing along the side wall of the vibration space forming recess 5a. In FIG. 3(b), the extended adhesive 7c flows along the upper surface of the piezoelectric substrate 2 and hardens with a long tail. FIG. 3(c) shows an extended shape when the adhesive 7 has a relatively high viscosity. Although the extended adhesive 7d flows along the upper surface of the piezoelectric substrate 2,
The amount of extension is small.

Further, in the embodiment described above, an example was shown in which the adhesive 7 was applied to the sealing substrate 4.5, but it may be applied to the piezoelectric substrate 2.

Further, in the above embodiment, a thermosetting adhesive having excellent heat resistance was used, but a room temperature curing adhesive may be used depending on the intended use of the piezoelectric resonator.

Further, in the above embodiment, the shape of the vibration space forming recesses 4a+5a provided in the sealing substrate 4.5 is circular, but the shape is not limited to this, and various shapes such as rectangular are possible. Can be adopted.

Effects of the Invention As described above, according to the present invention, even when heat stress is applied to the piezoelectric resonator body and the internal pressure in the vibration space increases when the piezoelectric resonator is mounted on a printed wiring board, the vibration space remains stable. The adhesive that extends over the inner wall of the piezoelectric substrate functions as a seal, so high internal pressure is not directly applied to the adhesive that is sandwiched between the piezoelectric substrate and the sealing substrate and joins them together. figure,
A piezoelectric resonator with higher sealing reliability can be obtained.

Additionally, since the interface distance between the adhesive and the sealing substrate or between the adhesive and the piezoelectric substrate becomes longer, the path through which moisture from the outside world enters the vibration space becomes longer, making it difficult to improve the sealing performance. can.

Furthermore, although the adhesive extending on the inner wall surface of the vibration space damps vibrations in the main frequency band, it damps spurious waves even more, so that the frequency characteristics are improved.

[Brief Description of the Drawings] Fig. 1 is a vertical cross-sectional view of a piezoelectric resonator according to an embodiment of the present invention, and Fig. 2 shows the amount of adhesive extending on the inner wall surface of the vibration space of the piezoelectric resonator. It is a graph showing the relationship between various electrical characteristics. FIGS. 3(a), 3(b), and 3(c) are vertical sectional views showing other shapes of the adhesive extending on the inner wall surface of the vibration space. Figures 4 to 6 show conventional piezoelectric resonators. Figure 4 is an exploded perspective view of the piezoelectric resonator, Figure 5 is a perspective view showing its appearance, and Figure 6 is the x of Figure 5. -x' is a vertical cross-sectional view. 1... Piezoelectric resonator (energy trap type 3-terminal filter), 2... Piezoelectric substrate, 3a, 3b, 3c.
... Vibration electrode, 4, 5... Sealing substrate, 4a, 5a...
・Vibration space forming recess, 7...Adhesive, 7a, 7b
, 7c, 7d...extended adhesive.

Claims (2)

[Claims] 1. A piezoelectric substrate provided with a vibrating electrode and a sealing substrate provided with a recess for forming a vibration space are bonded together via an adhesive,
A piezoelectric resonator characterized in that a portion of the adhesive extends on an inner wall surface of a vibration space formed by the piezoelectric substrate and the sealing substrate. 2. a step of applying an adhesive to at least one of a piezoelectric substrate provided with a vibrating electrode or a sealing substrate provided with a concave portion for forming a vibration space; and bonding the piezoelectric substrate and the sealing substrate via the adhesive. It is characterized by comprising the steps of bonding the piezoelectric substrate and sealing substrate together to form a vibration space, and applying pressure to the piezoelectric substrate and the sealing substrate to extend a portion of the adhesive onto the inner wall surface of the vibration space. A method for manufacturing a piezoelectric resonator.