JPH10284975A - Package of surface mounting-type piezoelectric device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a package small in size, to prevent conductive defect owing to ultrasonic wave cleaning and to keep a frequency temp. characteristic by connecting an electrode formed on the other surface of a piezo-electric element to another internal terminal on a package inner base surface through the use of a conductive adhesive resin. SOLUTION: It is preferable that the electrode formed on the other surface of the piezo-electric element is connected to a seam ring which is positioned on the inner side surface of the package through the use of the conductive adhesive. A crystal substrate 1 is arranged so as to permit a surface where the division electrode 11 is formed in the crystal substrate 1 to be opposed to the upper surface of the substrate 21 and the division electrode 11 is electrically and mechanically connected to input/output lands 25 and 26 respectively by the conductive adhesive 4. A shared electrode 13 on the other main surface of the crystal substrate 1 is connected to an earth land 27 positioned just under its one end edge by the conductive adhesive 4. When the silicon-based adhesive with low hardness, for example, is used for at least two position among the three positions where conductive adhesive 4 is used, the frequency temp. characteristic of an <AT cut crystal substrate is kept.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a package structure of a surface mount type piezoelectric device, and more particularly, to a piezoelectric device used as a piezoelectric resonator (vibrator, filter), which electrically connects internal terminals in the package. The present invention relates to a package of a piezoelectric device capable of realizing a connection structure of a piezoelectric element that is mechanically connected without using a bonding wire.

[0002]

2. Description of the Related Art When a piezoelectric device used for a mobile communication device such as a mobile phone is mounted on a printed circuit board,
For reasons such as improvement in mounting workability, it is required to use a surface mount type, and for high-density mounting, it is necessary to reduce the size of the piezoelectric device, as well as the performance and price. Is getting stronger. Hereinafter, the structure of a conventional piezoelectric device will be described by taking a surface-mounted double mode filter using an AT-cut quartz substrate as an example. 6 (a) and (b)
FIG. 2 is a plan view and a bottom view of an AT-cut quartz substrate having electrodes formed on both sides. The crystal substrate 1 has divided electrodes 11 and 12 for input and output on one main surface as shown in FIG. 3A, and has a common electrode 13 for grounding on the other main surface as shown in FIG. FIG. 7 is a longitudinal sectional view showing a package structure of a surface mount type dual mode filter, and the quartz substrate 1 shown in FIG.
Is housed in a ceramic package 2, and the upper opening of the package is hermetically sealed with a metal upper lid 3. The ceramic package 2 includes a ceramic substrate 21
And a ceramic annular shelf 22 integrated on the outer periphery of the upper surface of the ceramic substrate 21, a ceramic annular frame 23 integrated on the shelf 22, and an annular fixed on the frame 23. It consists of a seam ring 24 for seam welding,
As a whole, it has a recess for accommodating quartz in the center, and has a box shape having an annular projection on the outer periphery. The input / output lands 25 and 26 are exposed on the upper surface of the substrate 21.
Grounding lands 27 are formed on the metallization 2 so as to be electrically connected to external terminals (not shown) by Au metallization.

When the crystal substrate 1 is housed in the package 2, the crystal substrate 1 is arranged so that the surface of the crystal substrate 1 on which the divided electrodes 11 and 12 are formed faces the upper surface of the substrate 21, and The outer ends of the divided electrodes 11 and the input / output lands 25 are electrically and mechanically connected to each other by the conductive adhesive 4. Similarly, the conductive adhesive 4 is also provided between the divided electrodes 12 and the input / output lands 26. Connect by. The common electrode 13 of the crystal substrate 1 facing the opening side of the upper surface of the package 2 is connected to the ground land 27 on the shelf 22 having almost the same height as the common electrode 13.
The connection is made by bonding a metal wire 5. However, when the common electrode 13 for grounding and the grounding land on the package side are connected by wire bonding as described above, a space S1 between the side surface of the crystal substrate 1 and the shelf 22 is used as a space for wire bonding. In addition, the space S2 corresponding to the upper surface of the quartz substrate 1 and the lower surface of the upper lid 4 needs to be secured in advance, and there is a problem that the size of the package is increased by these spaces. That is, it is necessary to add the shelf 22 to secure the space S1 in the width direction for bonding and the frame 23 to secure the space S2 in the height direction, and the package cannot be downsized. there were.

In addition, when the outer surface of the package is cleaned with an ultrasonic cleaner as a finish after hermetic sealing, there is a problem that the wires 5 that easily resonate with the ultrasonic waves of the ultrasonic cleaner break and become unable to conduct. Further, the quartz substrate 1 is firmly fixed on the substrate 21 by using, for example, an imide-based material having a high hardness as the conductive adhesive 4 so as to withstand a vertical shock applied to the upper surface during bonding. However, when the environmental temperature changes, as shown in FIG. 8A, the outer peripheral portion of the quartz substrate 1 cannot be freely expanded and contracted because it is restrained by the two conductive adhesives 4. Thermal distortion occurs inside the quartz substrate 1. Although the AT-cut quartz substrate has good frequency-temperature characteristics of a cubic curve, there is a problem that the characteristics are changed due to the thermal distortion and the performance of the product is significantly impaired. At the same time, as shown in FIG. 8 (b), a thermal stress is generated inside the conductive adhesive 4 due to a difference in thermal expansion coefficient between the quartz substrate 1 and the substrate 21. There was a drawback that bonding reliability was inferior because the stress could not be relaxed and it was easily broken. In order to eliminate such inconvenience, a surface mount type dual mode filter of the type not using wire bonding as shown in FIG. 9 has been devised. A folded portion 13 a extending from the side surface of the quartz substrate 1 to the opposite side surface is formed, and the ground land 27 formed on the upper surface of the substrate 21 and the folded portion 13 a are connected by the conductive adhesive 4. In addition,
In this figure, the land 26 is not shown because it is located behind the land 25.

[0005] Hermetic sealing after the crystal substrate 1 is housed in the package 2 is performed by seam welding or the like after placing the upper lid 3 on the seam ring 24. Note that the upper lid 3 may be configured to be electrically connected to an external ground terminal via the seam ring 24, the frame 23, and internal leads (not shown) of the shelf 22 to provide a shielding effect. In addition, contrary to the above example, the same grounding method is adopted in a filter of a type in which the common electrode 13 of the quartz substrate 1 is arranged so as to face the substrate 21.

As shown in FIG. 9, the common electrode 13 of the quartz substrate 1
Is folded back to the divided electrodes 11 and 12 side and connected with the conductive adhesive 4, bonding is not required, and therefore, for example, a silicon-based material having a low hardness can be used as the conductive adhesive 4. In addition, thermal distortion of the quartz substrate 1 can be reduced. However, in order to form a folded portion 13a in which the common electrode 13 is folded toward the divided electrodes 11 and 12, an oblique deposition process is required to form an electrode portion on the side surface of the quartz substrate 1. In particular, when performing so-called batch processing in which electrodes for a plurality of quartz substrates are collectively formed on a large-area wafer by photolithography and then cut and manufactured for each element, the above oblique vapor deposition is performed by dividing the quartz substrates into small pieces. However, there is a problem that the effect of the batch processing can be remarkably impaired and the cost cannot be reduced.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and reduces the size of a package by ensuring conduction between electrodes on a piezoelectric element such as a quartz substrate and electrodes in the package without using wire bonding. The use of a low-hardness silicon adhesive as a bonding means for the quartz substrate allows free expansion and contraction of the outer periphery of the quartz substrate and prevents the occurrence of thermal distortion inside the quartz substrate. It is possible to maintain the bonding reliability by relaxing the thermal stress generated inside the conductive adhesive due to the difference in the coefficient of thermal expansion between the quartz substrate and the substrate. An object of the present invention is to provide a low-cost surface-mount type piezoelectric resonator having frequency characteristics.

[0008]

In order to achieve the above object,
A first aspect of the present invention is a surface mount type piezoelectric device in which electrodes on one side of a piezoelectric element having electrodes on both front and rear sides are connected to the internal terminals on the bottom surface of the package by a conductive adhesive while facing the internal terminals. An electrode formed on the other surface is connected to another internal terminal on the bottom surface of the package using a conductive adhesive. According to the present invention, the connection between the electrode on the upper surface of the piezoelectric element and the internal terminal on the inner bottom surface of the package is achieved without using wire bonding. Can be. The invention according to claim 2 is a surface mount type piezoelectric device in which electrodes on one side of a piezoelectric element having electrodes on both front and back sides are connected by a conductive adhesive while facing the internal terminals on the inner bottom surface of the package. An electrode formed on the other surface is connected to a seam ring located on the inner side wall of the package by using a conductive adhesive. According to the present invention, since the electrode on the upper surface of the piezoelectric element is connected to the seam ring at the nearest position, various problems when a soft adhesive is used can be prevented. The invention according to claim 3 uses, as the piezoelectric element, an ultra-thin vibrating portion, a thick annular surrounding portion supporting the periphery of the vibrating portion, and a piezoelectric element having electrodes formed on both front and back surfaces. It is characterized by.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on a surface mount type dual mode filter as an example of a piezoelectric device using an AT-cut quartz substrate. FIG. 1 is a longitudinal sectional view showing a configuration of a surface mount type dual mode filter according to an embodiment of the present invention, and FIG. 2 is an ultra-thin wall as an example of a piezoelectric element used in the surface mount type dual mode filter. FIG. 5 is a perspective plan view of an AT-cut quartz substrate having a vibrating portion. This package has a structure in which a quartz substrate 1 is housed in a ceramic package 2 and the upper opening of the package is hermetically sealed with a metal upper lid 3. The quartz substrate 1 has divided electrodes 11 and 12 for input and output on one main surface as shown in FIG.
And the lead electrode 1 extending from each of the divided electrodes 11 and 12
6, 17 and pad electrodes 18 and 19, and the other main surface as shown in FIG.
Three. The other main surface is not a flat surface, but a rectangular recessed portion 14 in an appropriate place by etching or the like.
Is formed, the crystal portion remaining on the bottom surface of the concave portion 14 is an ultra-thin vibrating portion 14a. In this example,
The common electrode 13 is a full-surface electrode deposited on the entire surface of the other main surface including the inner wall and the inner bottom surface of the recess 14. The ceramic package 2 includes a ceramic substrate 21, an annular ceramic frame 23 integrated on the outer periphery of the upper surface of the ceramic substrate 21, and a seam ring 24 for seam welding fixed in an annular shape on the frame 23. The whole has a box shape having a recess for accommodating a quartz substrate or the like in the center and an annular projection on the outer periphery. On the upper surface of the substrate 21, input / output lands (internal terminals) 25 and 26 and ground lands (internal terminals) 27 are formed by Au metallization so as to be electrically connected to external terminals (not shown).

When the crystal substrate 1 is housed in the package 2, the crystal substrate 1 is arranged so that the surface on which the divided electrodes 11 and 12 of the crystal substrate 1 are formed faces the upper surface of the substrate 21. The pad electrode 18 of the divided electrode 11 and the input / output land 25 are electrically and mechanically connected by the conductive adhesive 4 and the pad electrode 1 of the other divided electrode 12 is electrically connected.
9 and the input / output lands 26 are also connected by the conductive adhesive 4. Common electrode 13 on other main surface of quartz substrate 1
Is connected by an electrically conductive adhesive 4 to a grounding land 27 located immediately below one end edge. That is,
In this embodiment, the grounding land 27 is formed so as to have a predetermined width immediately below one end of the quartz substrate 1 as shown in the figure, and is connected to one end of the common electrode 13 on the same side of the quartz substrate. The distance is set in advance so that the connection can be made with the conductive adhesive 4 at the shortest distance.

Hereinafter, embodiments of the present invention will be described in more detail.
First, regarding the quartz substrate 1, the resonance frequency of the piezoelectric resonator using the thickness shear vibration of the AT-cut quartz substrate is inversely proportional to the plate thickness. The other main surface is recessed by etching, and the bottom surface of the recess
a and an annular surrounding portion 15 that supports the periphery of the vibrating portion 14 is integrally formed. Thereafter, a common electrode 13 is formed on the other main surface by vapor deposition over the entire surface. On one main surface of the quartz substrate 1 are divided electrodes 11 and 12, lead electrodes 16 and 17 extending therefrom, and pad electrodes 18 and 19.
Is formed by photolithography. The above-described formation of the quartz substrate 1 is all performed by a batch process.

Next, the point that the package structure of the surface mount type dual mode filter of this embodiment is different from that of the above-mentioned conventional example is that the connection between the common electrode 13 of the quartz substrate 1 and the ground electrode on the package side. Is performed directly with the conductive adhesive 4 without using a bonding wire and without turning the common electrode 13 back to the divided electrodes 11 and 12. For this reason, in the present embodiment, the connection by the conductive adhesive 4 is facilitated by disposing the grounding land 27 disposed at an appropriate position on the substrate 1 immediately below the edge of the common electrode 13.

Next, FIGS. 3 (a), 3 (b) and 3 (c) are sectional views showing an assembling process of this surface mount type dual mode filter. First, as shown in FIG.
One input / output land 2 on 1 (bottom in package)
The conductive adhesive 4 is applied on the surfaces 5 and 26, respectively. Then (b)
And the lands 25 and 26 and the pad electrode 1
8 and 19 are adhered and fixed on each conductive adhesive 4 so that they are electrically connected to each other. Subsequently, the conductive adhesive 4 flows from the end of the common electrode 13 of the quartz substrate 1 as shown in FIG. 1C, and is connected to the ground land 27 on the substrate 21 via the side surface of the quartz substrate 1. That is, the quartz substrate 1 is housed in the package 2 in a cantilever structure that holds three places at the left end in the drawing. Thereafter, the upper lid 3 is hermetically sealed.

With the above configuration, it is not necessary to use a bonding wire for connecting the common electrode 13 of the quartz substrate 1, so that the package is reduced in size by the space conventionally required for bonding. On the other hand, a silicon adhesive having low hardness can be used as the conductive adhesive 4. That is, according to the present embodiment, the package 2 does not require a shelf for bonding, so that the area and the height can be reduced, and a package suitable for the size of the crystal substrate 1 can be constructed. Also,
There is no need to fear wire breakage during ultrasonic cleaning.
Further, if at least two of the three conductive adhesives 4 are made of, for example, a silicone-based material having low hardness, the frequency-temperature characteristics of the AT-cut quartz substrate can be maintained.

On the other hand, the common electrode 13 is divided into the divided electrodes 11 and 12
Since it is not folded back to the side and extended, the step of oblique deposition can be omitted. Therefore, when the quartz substrate 1 having the configuration shown in FIG. 2 is formed by batch processing, it is not necessary to perform oblique deposition on individual chips after the batch processing, so that productivity is not impaired. Further, since there is no wire bonding step and basically only one bonding point is added while applying the conventional mounting step of the quartz substrate 1 using the conductive adhesive 4, the overall man-hour is increased and the accompanying man-hour is increased. Problems such as cost increase do not occur. From the above, not only the cost can be reduced, but also the impact resistance is improved because the conductive adhesive 4 at three locations is held so as to sandwich the quartz substrate 1.

In the above embodiment, the common electrode 13 is connected to the grounding land 27 on the substrate 21. However, as shown in the modification of FIG. 23 and the conductive adhesive 4
May be connected to the seam ring (internal terminal for installation) 24 to ground. In other words, in the embodiment shown in FIG. 1 and the like, if the conductive adhesive 4 for the common electrode is made of an excessively low hardness, the conductive adhesive 4 for connecting the common electrode 13 and the ground land 27 is used. Although a part of the conductive adhesive may excessively enter between the bottom surface of the quartz substrate 1 and the top surface of the substrate and cause a problem such as restraining the quartz substrate 1, according to this modification, the common electrode 13 and the ring 24 Even if an adhesive having a lower hardness than the adhesive used for connecting the divided electrodes 11 and 12 is used as the conductive adhesive 4 for connecting the substrate and the substrate, the adhesive permeates between the quartz substrate 1 and the substrate 21. be able to. Alternatively, if it is not desired to form the ground land 27 on the substrate 21 in order to pursue the miniaturization of the package, the object of miniaturization can be achieved by employing the connection method of FIG.

In each of the above embodiments, the quartz substrate 1 is arranged so that the divided electrodes 11 and 12 face the substrate 21. On the contrary, the common electrode 13 faces the substrate 21. May be arranged. In this case,
Since the common electrode 13 is opposed to the ground land 27 on the upper surface of the substrate 1, the common electrode 13 may be directly connected using a conductive adhesive. Further, since the split electrodes 11 and 12 are located on the upper surface of the substrate, the common electrodes 1 and 12 in the package of FIG.
In the same manner as the method for connecting the ground 3 and the ground land 27, the connection is made by a method in which a conductive adhesive is dripped from the divided electrodes 11 and 12 on the substrate onto the input and output lands 25 and 26, respectively.
The effect of this embodiment is equivalent to the effect of the above embodiment.

In each of the above embodiments, an example in which the present invention is applied to a surface mount type double mode filter using an AT-cut quartz substrate having an ultra-thin vibrating portion formed by batch processing will be described. However, the present invention is not limited to this, and it is clear that the electrode formed on the quartz substrate 1 may be a vibrator having a double-sided common electrode. In this case, most of the conventional products use one common electrode folded back to the other as shown in FIG. 9, and the quartz substrate is restrained at two locations on the outer periphery on one side by a conductive adhesive. However, when the present invention is applied, as shown in FIG. 5, only the center of the outer peripheral portion on one side of the quartz substrate 1 is restricted by a conductive adhesive having a low hardness, and the AT-cut quartz crystal can be freely expanded and contracted. It is possible to maintain the frequency temperature characteristics inherent to the substrate, and a remarkable effect is exhibited. In addition, for quartz substrates that are not manufactured by batch processing, quartz substrates that do not have an ultra-thin vibrating part, and that have flat main surfaces, and that use cut-off angles other than AT-cut quartz or resonators that use piezoelectric elements other than quartz Also, the package structure of the present invention can be applied.

[0019]

Since the present invention is constructed as described above, there is no need to connect the piezoelectric element and the electrode in the package by a bonding wire, so that the size of the package can be reduced and conduction by ultrasonic cleaning can be achieved. Prevention of failure and maintenance of frequency temperature characteristics can be achieved. Further, since oblique deposition is not required, the effect of the batch processing is not impaired, and the assembling process is simple. Therefore, a remarkable effect is achieved in forming a small, high-performance, and low-cost surface-mount type piezoelectric resonator.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a package structure of a surface mount dual mode filter according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a quartz substrate used in an embodiment of the present invention.

FIGS. 3 (a), (b) and (c) are views for explaining an assembling process according to an embodiment of the present invention.

FIG. 4 is a cross-sectional view illustrating another embodiment of the present invention, illustrating a structure in which a common electrode of a quartz substrate is connected to a ring.

FIG. 5 is a diagram illustrating an application example of the present invention to a crystal resonator.

FIG. 6 is a plan view of a quartz substrate used in a conventional example;
(a) is a diagram showing one main surface, and (b) is a diagram showing the other main surface.

FIG. 7 is a cross-sectional view of a package of a surface mount type dual mode filter for explaining a conventional example.

FIG. 8 (a) is a diagram for explaining the generation of thermal stress inside the conductive adhesive due to the difference in the thermal expansion coefficient between the quartz substrate and the substrate, and FIG. 8 (b) is a diagram illustrating the inside of the quartz substrate due to preventing expansion and contraction of the quartz substrate. It is a figure explaining generation | occurrence | production of a thermal distortion.

FIG. 9 is a cross-sectional view illustrating a structure of a conventional example in which a common electrode of a quartz substrate is connected by being turned back to a divided electrode side.

[Explanation of symbols]

1 crystal substrate, 2 ceramic package, 3 lid,
4 conductive adhesive, 5 wires, 11 and 12 split electrodes, 13 common electrode, 14 vibrating part, 15 annular surrounding part, 16, 17 lead electrode, 18, 19 pad electrode 21 substrate, 22 shelf, 23 frame, 24 Ring (internal terminal), 25, 26 I / O land (internal terminal), 2
7. Land for grounding (internal terminal)

Claims (3)

[Claims] 1. A surface mount type piezoelectric device in which electrodes on one side of a piezoelectric element having electrodes on both front and back sides are connected to a terminal on a bottom surface of a package by a conductive adhesive while facing the internal terminals. A surface mount type piezoelectric device package, characterized in that the electrodes formed on the package are connected to other internal terminals of the bottom surface of the package using a conductive adhesive. 2. A surface mount type piezoelectric device in which electrodes on one side of a piezoelectric element having electrodes on both sides are connected by a conductive adhesive while being opposed to internal terminals on an inner bottom surface of the package. A surface mount type piezoelectric device package, characterized in that the electrodes formed above are connected to a seam ring located on the inner side wall of the package using a conductive adhesive. 3. The piezoelectric element according to claim 1, wherein an ultra-thin vibrating portion, a thick annular surrounding portion supporting the periphery of the vibrating portion, and a piezoelectric element having electrodes formed on both front and back surfaces are used. The package of the surface mount type piezoelectric device according to claim 1 or 2, wherein