JP2009141641A - Piezoelectric device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric device that surely prevents the occurrence of defective electrical continuity, especially, that effectively prevents frequency shifting. <P>SOLUTION: The piezoelectric device is provided with a storage container 40, formed internally with a connecting electrode part; a piezoelectric vibration piece 31, having an extraction electrode electrically connected with the connecting electrode part, first electrical-connection parts 37, 38 wherein the piezoelectric vibration piece is bonded to the connecting electrode part of the storage container via a conductive adhesive, and a second electrical connecting part 53, wherein the connecting electrode part of the storage container and the extraction electrode of the piezoelectric vibration piece are connected to each other through wire bonding. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an improvement of a piezoelectric device in which a piezoelectric vibrating piece is housed in a container.

Piezoelectric vibrators and piezoelectrics in small information devices such as HDDs (hard disk drives), mobile computers, IC cards, mobile communication devices such as mobile phones, car phones, and paging systems, and piezoelectric gyro sensors Piezoelectric devices such as oscillators are widely used.
Many of these piezoelectric devices have a structure in which a piezoelectric vibrating piece is housed and sealed in a container such as a ceramic package, and a conductive adhesive is applied to an electrode part for connection formed inside the container. Thus, the piezoelectric vibrating reeds are joined together, and electrical and mechanical joining are simultaneously performed, so that the piezoelectric vibrating reeds can be supported in the storage container and a driving voltage can be supplied from the outside.

For example, the following configuration examples are known.
Patent Document 1 is a method in which a piezoelectric vibrating piece is bonded with a silicone-based conductive adhesive, and a metal component of a base metal layer when an extraction electrode is formed on the piezoelectric vibrating piece is used as an Au layer thereon. It is intended to improve the electrical conductivity of the electrode by depositing on the surface.
Patent Document 2 also joins a piezoelectric vibrating piece with a silicone-based conductive adhesive. A terminal electrode is formed by laminating a metal, and diffuses a metal component adjacent between layers to lower a conduction resistance. .

Patent Document 3 also joins a piezoelectric vibrating piece with a silicone-based conductive adhesive, but attempts to improve conductivity by forming a surface deposition layer on which the underlying metal layer is partially deposited on the electrode surface. To do.
In Patent Document 4, a piezoelectric vibrating piece is joined with a conductive adhesive, and the surface of an electrode portion is formed of a silicone-based conductive adhesive and a metal having good adhesion, that is, Ag.
In Patent Document 5, a piezoelectric vibrating piece is joined with a non-conductive adhesive, and electrical conduction is attempted by wire bonding.
Patent Document 6 joins a piezoelectric vibrating piece with a silicone-based conductive adhesive, and the connection electrode and excitation electrode of the piezoelectric vibrating piece are connected as a chromium layer, a gold layer, a gold layer, or a silver layer. By simultaneously forming the electrode and the excitation electrode, it is intended to improve the conduction performance without increasing the number of steps.

JP 2000-151345 A JP 2002-33569 A JP 2003-78383 A JP2003-224444 JP-A-2005-94461 JP2006-13900

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
A container having a connection electrode portion; and a piezoelectric vibrating piece having a lead electrode electrically connected to the connection electrode portion, and a conductive adhesive on the connection electrode portion. A first electrical connection portion to which the piezoelectric vibrating piece is bonded via a wire, a second electrical connection portion to which the connection electrode portion and the extraction electrode are connected by wire bonding. A piezoelectric device characterized by that.
According to the above configuration, the piezoelectric vibrating reed is electrically and mechanically joined to the electrode portion for connection of the storage container by the conductive adhesive at the first electrical connection portion. As a result, the drive voltage from the container side is not only applied to the piezoelectric vibrating piece, but also the mechanical joining is performed by the conductive adhesive, and as in the case of the non-conductive adhesive. A large amount of outgas is not generated at the time of curing, and the risk of frequency fluctuation due to adhesion of the gas to the surface of the piezoelectric vibrating piece is reduced.
In addition, since the lead electrode of the piezoelectric vibrating piece is connected by wire bonding in the second electrical connection portion, the first electrical connection portion and the second electrical connection portion The electrical connection between the storage container and the piezoelectric vibrating piece is achieved at two locations, and it is possible to reliably prevent the occurrence of poor conduction, and in particular, it is possible to effectively prevent frequency shift.

[Application Example 2]
In the above configuration, the extraction electrode is formed on the front and back surfaces of the piezoelectric vibrating piece, and in the first electrical connection portion, the extraction electrode on the back surface is connected to the connection electrode portion by the conductive adhesive. In the second electrical connection portion, the wire bonding is performed on the extraction electrode on the surface.
According to the above configuration, the extraction electrode on the back surface of the piezoelectric vibrating piece is bonded to the connection electrode portion of the housing container by the conductive adhesive, and the extraction electrode on the surface of the piezoelectric vibrating piece at the bonding position. On the other hand, the wire bonding is performed. Thereby, it is possible to make a reliable connection without escaping the ultrasonic wave during the bonding operation.

[Application Example 3]
In the above configuration, a stud bump is formed on the extraction electrode on the surface.
In the above configuration, wire bonding directly above the portion of the piezoelectric vibrating piece to which the conductive adhesive is applied is more effective than the case where wire bonding is performed at a location where the conductive adhesive is not present. For example, if the conductive adhesive is soft and has a low elastic modulus, ultrasonic waves may be absorbed by the conductive adhesive. Then, it can connect reliably by bonding with respect to the stud bump formed on the extraction electrode of the surface of a piezoelectric vibrating piece.

[Application Example 4]
In the above structure, the conductive adhesive is a soft adhesive having a low elastic modulus in a cured state.
According to the above configuration, when the conductive adhesive is a soft adhesive having a low elastic modulus in a cured state, the stress relaxation capability with respect to the piezoelectric vibrating piece joined thereby is high, and frequency fluctuation is unlikely to occur.

[Application Example 5]
In the above configuration, the conductive adhesive is a silicone-based conductive adhesive.
According to the above configuration, the silicone-based conductive adhesive has an extremely low elastic modulus of about 0.2 GPa and a high stress relaxation capability, so that it is difficult for frequency fluctuations to occur.

[Application Example 6]
In the above-described configuration, the conductive adhesive is a bismaleimide conductive adhesive.
According to the above configuration, the bismaleimide-based conductive adhesive has an elastic modulus of about 3.4 GPa and is slightly harder than the silicone-based conductive adhesive. Ultrasonic waves are less likely to escape and easier to bond. In addition, compared with a hard conductive adhesive such as an epoxy type, the stress relaxation ability is excellent, and therefore the frequency fluctuation is smaller.

[Application Example 7]
In the above configuration, the piezoelectric vibrating piece is integrally joined to the base portion via a connecting portion, a base portion formed of a piezoelectric material, a plurality of vibrating arms extending from one end side of the base portion, and A supporting arm that extends in the width direction on the other end side that is a predetermined distance away from the one end side of the base, and extends in the same direction as the vibrating arm on the outside of the vibrating arm. The lead electrodes are formed on the front surface and the back surface, and the first and second electrical connection portions are provided on the support arm.
According to the above configuration, since the supporting arm extending from the base portion, not the base portion of the piezoelectric vibrating piece, is joined to the receiving container to form the first electrical connection portion, a change in ambient temperature or a drop impact For example, the stress change produced at the joint location hardly affects the vibrating arm via the base.
Moreover, on the contrary, vibration leakage from the vibrating arm that bends and vibrates hardly reaches the supporting arm across the base. In addition, since the supporting arm of the present invention extends in the width direction from the other end of the base and extends in the same direction as the vibrating arm outside the vibrating arm, the overall size can be made compact. .

1 and 2 show a first embodiment of a piezoelectric device according to the present invention. FIG. 1 is a schematic plan view thereof, and FIG. 2 is a sectional view taken along line AA of FIG.
In these drawings, the piezoelectric device 30 shows an example in which a piezoelectric vibrator is configured. The piezoelectric device 30 houses a piezoelectric vibrating piece 31 in a package 40 that is a housing container.

As shown in FIGS. 1 and 2, the package 40 as a container is formed in, for example, a rectangular box shape, and includes a first substrate 41, a second substrate 42, and a third substrate 43. It is formed by stacking three substrates. These substrates are formed by, for example, forming an aluminum oxide ceramic green sheet as an insulating material into a shape shown in the figure and then sintering.
The package 40 is hermetically sealed by housing a piezoelectric vibrating piece 31 and then bonding a transparent glass lid 45 using a sealing material 44. As a result, after the lid 45 is sealed, the frequency can be adjusted by trimming the electrodes of the piezoelectric vibrating piece 31 by irradiating laser light from the outside.
Note that the lid 45 is not a transparent material, and may be a structure in which a metal plate such as Kovar is joined by seam sealing or the like.

The bottom of the package 40 has a through hole 46 for degassing in the manufacturing process. The through hole 46 is formed in the first hole 46a formed in the first substrate 41 and the second substrate 42, has an outer diameter smaller than that of the first hole 46a, and the first hole 46a. The second hole 46b communicates with the second hole 46b.
The through hole 46 is sealed with a metal sealing material 47 so that the inside of the package 40 is airtight.
Here, as shown in FIG. 2, the package 40 forms a space of the internal space S by removing the material inside the third substrate 43. This internal space S is a housing space for housing the piezoelectric vibrating piece 31.

Connection electrode portions (hereinafter referred to as “electrode portions”) 48 and 49 are formed on the surface of the second substrate 42 of the package 40.
These electrode portions 48 and 49 are connected to mounting terminals 55 and 55 formed on the bottom surface of the package 40. That is, each of the electrode portions 48 and 49 receives the drive voltage supplied from the outside when the piezoelectric device 30 is mounted on various devices, and the piezoelectric electrodes in which the drive electrodes are accommodated in the package 40 from the mounting terminals 55 and 55. This is for transmitting to the vibrating piece 31.
The electrode portions 48 and 49 and the mounting terminals 55 and 55 are connected by, for example, a conductive through hole penetrating through the package 40 or a conductive pattern provided using a castellation (not shown) formed on the outer surface of the package 40. .

The piezoelectric vibrating piece 31 is made of, for example, quartz, and a piezoelectric material such as lithium tantalate or lithium niobate can be used in addition to quartz. As shown in FIG. 1, the piezoelectric vibrating piece 31 includes a base portion 32 and a pair of vibrating arms 35 and 36 that extend in parallel from the base portion 32 in a bifurcated manner toward the right.
Excitation electrodes (not shown) are formed on the front and back surfaces of the main surfaces of the vibrating arms 35 and 36. Preferably, each of the vibrating arms 35 and 36 is formed with long grooves extending in the length direction on the front and back surfaces up to the vicinity of each tip, and the excitation electrode is formed on the inner wall and bottom of these grooves. May be.

Furthermore, with respect to the piezoelectric vibrating piece 31 of the present embodiment, as shown in FIG. 2, the base portion 32 further has a connecting portion extended in the width direction, and at positions on both outer sides of the vibrating arms 35 and 36. Supporting arms 33 and 34 extending in parallel with the vibrating arms 35 and 36 are provided in the extending direction of the vibrating arms 35 and 36 (rightward in FIG. 2) from the connecting portion.
The tuning fork-shaped outer shape of the piezoelectric vibrating piece 31 and the long groove provided in each vibrating arm are formed by wet etching a material such as a quartz wafer with a hydrofluoric acid solution or dry etching using plasma, for example. It can be formed precisely.
The piezoelectric vibrating piece is not limited to the one provided with a supporting arm as shown in the figure, but a thin rectangular piezoelectric vibrating piece, a mesa-type or reverse mesa-type piezoelectric vibrating piece, or a tuning-fork type piezoelectric device without a supporting arm. A vibrating piece or the like can be used.

  The excitation electrodes are formed in the long grooves on the front and back surfaces of the vibrating arms 35 and 36 and the side surfaces of the vibrating arms, and the electrodes provided in the long grooves and the electrodes provided on the side surfaces of each vibrating arm are paired. Has been. Each excitation electrode extends the electrode film and is led to the front and back surfaces of the supporting arms 33 and 34 as an extraction electrode (not shown). In the case where no long groove is formed in each of the vibrating arms 35 and 36, excitation electrodes are formed on the front and back surfaces of the vibrating arms, respectively.

A joining structure between the supporting arms 33 and 34 and the electrode portions 48 and 49 will be described.
Since the support arms 33 and 34 have the same structure and are joined to the corresponding electrode portions 48 and 49, only the support arm 34 which is one support arm will be described, and the other support will be described. Description of the arm 33 is omitted.
For example, as shown in FIG. 1, the support arm 34 is electrically conductive on the electrode portion 49 on the imaginary line G passing through the midpoint of the weight in the length direction of the piezoelectric vibrating piece 31, that is, the center of gravity of the piezoelectric vibrating piece 31. It is possible to apply a bonding adhesive and join at one point.
However, from the viewpoints of bonding stability, bonding strength, and the like, in this embodiment, conductive adhesives 37 and 38 are disposed on the electrode portion 49 by selecting positions symmetrical to each other in the length direction with respect to the virtual line G. The conductive adhesives 37 and 38 are bonded by applying the piezoelectric vibrating piece 31 and curing the conductive adhesives 37 and 38 thereon. That is, it is preferable to select and join two points that are equidistant from each other with the position of the imaginary line G between them, since the joining structure is further strengthened and stabilized.
The portion joined by the conductive adhesives 37 and 38 mechanically and electrically connects the piezoelectric vibrating piece 31 and the electrode portion 49 to form a first electrical connection portion.

Further, a metal bump 51 is formed on the electrode portion 49, a bonding wire 52 is extended therefrom, and the excitation electrode on the surface side of the piezoelectric vibrating piece 31 is formed at the same position as the application portion of the conductive adhesive 38 described above. The wire bonding portion 53 is bonded to the wire. As the metal bump 51, a gold (Au) bump is suitable.
That is, for example, a metal ball is formed at the tip of a capillary for performing wire bonding work, and this is hit on the electrode portion 49, and the wire is extended by extending the wire while hitting a second at the position of reference numeral 53. In this way, electrical connection is made. The joint portion 53 corresponds to a second electrical connection portion.
Here, in the wire bonding, the wire bonding is performed on the lead electrode on the surface of the piezoelectric vibrating piece 31 at the bonding position of the conductive adhesive 38. Thereby, it is possible to make a reliable connection without escaping the ultrasonic wave during the bonding operation.

The present embodiment is configured as described above, and the piezoelectric vibrating piece 31 is placed at the positions 37 and 38 by the conductive adhesive that is the first electrical connection portion with respect to the electrode portion 49 of the package 40. Electrically and mechanically joined. Accordingly, the drive voltage from the mounting terminal 55 of the package 40 is applied to the piezoelectric vibrating piece 31 via the electrode portion 49.
Further, since the mechanical bonding is performed by the conductive adhesives 37 and 38, a large amount of outgas is not generated at the time of curing unlike the case of the nonconductive adhesive. The risk of frequency fluctuation due to adhesion to the surface of the piezoelectric vibrating piece 31 is reduced.
Further, since the second electrical connection portion 53 is connected to the lead electrode of the piezoelectric vibrating piece 31 by wire bonding, the conductive adhesives 37 and 38 which are the first electrical connection portions described above, The electrical connection between the package 40 side and the piezoelectric vibrating piece 31 is achieved at two locations of the second electrical connection portion 53, and it is reliably prevented that a conduction failure occurs, and in particular, the frequency shift is effective. Can be prevented.

Here, the conductive adhesive for forming the first electrical connection portion is obtained by mixing conductive particles such as silver particles in a binder component using a synthetic resin or the like. Can be performed simultaneously. In this embodiment, the conductive adhesives 37 and 38 in FIG. 1 are preferably soft adhesives having a low elastic modulus in a cured state.
Thereby, in the piezoelectric device 30, the stress relaxation capability with respect to the piezoelectric vibrating piece 31 joined is high, and it is hard to raise | generate a frequency fluctuation.
More preferably, a silicone-based conductive adhesive is used as the conductive adhesives 37 and 38. The silicone-based conductive adhesive has an extremely low elastic modulus of about 0.2 GPa and has a high stress relaxation capability, so that it is difficult for frequency fluctuations to occur.

In addition, as the conductive adhesive for forming the first electrical connection portion and the conductive adhesives 37 and 38 in FIG. 1, a bismaleimide conductive adhesive can be used.
This bismaleimide-based conductive adhesive has an elastic modulus of about 3.4 GPa and is slightly harder than a silicone-based conductive adhesive. For this reason, ultrasonic waves are less likely to escape than the silicone-based conductive adhesive during bonding in wire bonding, and bonding is easy. In addition, since the stress relaxation ability is excellent as compared with a hard conductive adhesive such as an epoxy-based adhesive, the frequency variation is smaller when the piezoelectric device 30 is formed.

FIG. 3 is a graph showing the characteristics of a silicone-based conductive adhesive, and FIG. 4 is a graph showing the characteristics of a bismaleimide-based conductive adhesive. The vertical axis represents weight and the horizontal axis represents temperature. In each figure, A indicates a change in weight, and B indicates a differential value of the weight change value indicated by A.
In mounting the piezoelectric device 30, the reflow temperature peak is about 260 ° C. (260 degrees Celsius).
On the other hand, as shown in FIG. 3, the silicone-based conductive adhesive is reduced in weight from above 400 ° C., so outgas is generated from this temperature. Therefore, there is almost no outgassing at the reflow temperature as in the case of epoxy conductive adhesives.
Similarly, the bismaleimide-based conductive adhesive shows a decrease in weight when the temperature exceeds 350 ° C., and the weight rapidly decreases when the temperature exceeds 400 ° C. Therefore, it can be seen that even when a bismaleimide conductive adhesive is used, outgas is hardly generated during reflow.

FIG. 5 is a schematic cross-sectional view showing a second embodiment of the present invention.
In FIG. 5, the portions denoted by the same reference numerals as those in FIGS. 1 and 2, which are the first embodiment, have a common configuration, and thus redundant description will be omitted, and hereinafter, differences will be mainly described.
In FIG. 5, the second electrical connection portion 53-1 is obtained by previously forming a stud bump on the extraction electrode on the surface side of the piezoelectric vibrating piece 31.

As described in the first embodiment, wire bonding via the piezoelectric vibrating piece 31 directly above the portion where the conductive adhesive 38 is applied is the extraction electrode in the portion where the conductive adhesive 38 is not present. Compared to the case of wire bonding, there is less escape of ultrasonic waves, and bonding is more reliable.
However, for example, if the conductive adhesive 38 is soft and has a low elastic modulus, ultrasonic waves may be absorbed by the conductive adhesive. Therefore, as shown in FIG. 5, a more reliable electrical connection can be realized by wire bonding to the stud bump 53-1 formed on the lead electrode on the surface of the piezoelectric vibrating piece 31. Can do.

The stud bump is formed by forming the outer shape by etching from the quartz substrate (outer shape etching step) and then forming the excitation electrode and the extraction electrode (electrode forming step) when the piezoelectric vibrating piece 31 is formed. The
After the stud bumps are formed, a mounting process for bonding the piezoelectric vibrating piece 31 into the package 40 is performed, and the conductive adhesives 37 and 38 are heated and cured (curing process). After joining the piezoelectric vibrating piece 31, for example, a metal ball is formed at the tip of the capillary, and this is hit on the electrode portion 49, and a second is applied to the previously formed stud bump 53-1 while extending the wire. By hitting, the electrical connection can be realized more reliably.
Subsequently, the lid body 45 is heat-sealed (primary sealing process) and degassed (degassing process) from the through hole 46 which is a gas vent hole, and then the through hole 46 is sealed with a metal sealant 47. By stopping (secondary sealing step), the piezoelectric device 30-1 can be completed.

The present invention is not limited to the above-described embodiment. Each configuration of each embodiment can be appropriately combined or omitted, and can be combined with other configurations not shown.
Further, the present invention is not limited to the case where the piezoelectric vibrating piece is accommodated in the box-shaped package, the case where the piezoelectric vibrating piece is accommodated in the cylindrical container, the piezoelectric vibrating piece functioning as a gyro sensor, Furthermore, the present invention can be applied to any piezoelectric device using a piezoelectric vibrating piece regardless of the name of a piezoelectric vibrator, a piezoelectric oscillator, or the like. Furthermore, although the piezoelectric vibrating piece 31 forms a pair of vibrating arms, the present invention is not limited to this, and the number of vibrating arms may be three or four or more.

1 is a schematic plan view showing a first embodiment of a piezoelectric device of the present invention. The AA line schematic sectional drawing of FIG. The graph which shows the characteristic of a silicone type conductive adhesive. The graph which shows the characteristic of a bismaleimide type conductive adhesive. The schematic sectional drawing which shows 2nd Embodiment of the piezoelectric device of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 30 ... Piezoelectric device, 31 ... Piezoelectric vibrating piece, 32 ... Base, 33, 34 ... Supporting arm, 35, 36 ... Vibrating arm, 37, 38 ... First electric Connection part, 53 ... 2nd electrical connection part

Claims (7)

A container in which an electrode part for connection is formed;
A piezoelectric vibrating reed comprising a lead electrode electrically connected to the connecting electrode part,
A first electrical connection portion in which the piezoelectric vibrating piece is bonded to the connection electrode portion via a conductive adhesive;
A piezoelectric device comprising: the connection electrode portion and a second electrical connection portion in which the lead electrode is connected by wire bonding. The extraction electrodes are formed on the front and back surfaces of the piezoelectric vibrating piece,
In the first electrical connection portion, the extraction electrode on the back surface is joined to the connection electrode portion by the conductive adhesive,
2. The piezoelectric device according to claim 1, wherein in the second electrical connection portion, the wire bonding is performed with respect to the lead electrode on the surface. 3.   The piezoelectric device according to claim 2, wherein a stud bump is formed on the extraction electrode on the surface.   4. The piezoelectric device according to claim 1, wherein the conductive adhesive is a soft adhesive having a low elastic modulus in a cured state.   The piezoelectric device according to claim 4, wherein the conductive adhesive is a silicone-based conductive adhesive.   The piezoelectric device according to claim 4, wherein the conductive adhesive is a bismaleimide-based conductive adhesive. The piezoelectric vibrating piece is
A base formed of piezoelectric material;
A plurality of vibrating arms extending from one end of the base;
It is integrally joined to the base portion via a connecting portion, extends in the width direction on the other end side separated from the one end side of the base portion by a predetermined distance, and on the outside of the vibrating arm, the vibrating arm A support arm extending in the same direction as
With
7. The lead electrode is formed on a front surface and a back surface of the support arm, and the first electrical connection portion and the second electrical connection portion are provided on the support arm. The piezoelectric device according to any one of the above.

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