JP4561521B2 - Piezoelectric vibration device - Google Patents

Description

  The present invention relates to a piezoelectric vibration device using a ceramic multilayer substrate, and more particularly to a structure of a conductive pad for holding a piezoelectric vibration plate by a conductive bonding material such as solder.

  Examples of piezoelectric vibration devices that require hermetic sealing include a crystal resonator, a crystal filter, and a crystal oscillator. All of these are hermetically sealed in order to form a metal thin film electrode on the surface of a crystal diaphragm (piezoelectric diaphragm) and protect the metal thin film electrode from the outside air.

  Due to the demand for surface mounting of parts for these crystal application products, for example, as shown in Patent Document 1, the configuration of hermetically accommodating a ceramic multilayer substrate as a package is increasing, and an appropriate hermetic sealing method is selected. By doing, favorable airtightness can be ensured. Such a ceramic multilayer substrate as a whole has a rectangular parallelepiped shape in which a concave storage portion is formed in the central portion, and a metal seal portion is formed on the upper surface of the bank portion around the storage portion. A stepped portion and a conductive pad formed on the upper surface of the stepped portion are formed at the bottom of the storage portion and led to an external terminal by a via or the like. One end portion of the crystal diaphragm is mounted on the conductive pad, and is electrically and mechanically connected by a conductive bonding material, and is covered and hermetically sealed.

JP-A-9-199972

  Recently, as electronic devices are further reduced in size and weight, piezoelectric vibration devices are also required to be ultra-miniaturized. Accordingly, the ceramic multilayer substrate that accommodates the piezoelectric diaphragm and the size of the piezoelectric diaphragm are also reduced. ing. In the piezoelectric vibration device configured as described above, a stress may be applied to the ceramic multilayer substrate due to thermal strain or warpage of a circuit board to be mounted, and a crack may be generated in the corner portion of the storage portion of the ceramic multilayer substrate. Therefore, a chamfer for relieving stress is indispensable. However, in the miniaturized piezoelectric vibration device, the area for holding the piezoelectric diaphragm is also reduced, and as a result, the chamfered portion for stress relaxation and the piezoelectric diaphragm are brought into contact with each other through a conductive bonding material. When the stress is locally concentrated and an impact such as a drop is applied, the piezoelectric diaphragm is cracked or chipped. In the worst case, the piezoelectric diaphragm may be broken starting from this portion. In particular, a small ceramic multilayer substrate having a short side dimension of 1.5 mm or less of the storage portion has a high risk of causing these problems. Furthermore, in the case where solder is used as the conductive bonding material, the stress tends to be concentrated at the boundary portion between the region bonded to the piezoelectric diaphragm and the region not bonded due to the hardness of the bonding material. It was. In addition, due to the downsizing of the ceramic multilayer substrate, the area for holding the piezoelectric diaphragm is also reduced, which may lead to a reduction in impact resistance and a risk of a short circuit.

  The present invention has been made to solve the above-described problems, and the chamfered portion is formed through a conductive bonding material as the ceramic multilayer substrate is reduced in size while suppressing the occurrence of cracks in the ceramic multilayer substrate by the chamfered portion. The first object is to eliminate stress concentration due to contact with the piezoelectric diaphragm and to eliminate the occurrence of cracks and chips in the piezoelectric diaphragm. Further, it is a second object of the present invention to suppress a reduction in impact resistance and reduce the risk of a short circuit as the ceramic multilayer substrate is miniaturized.

A bottomed storage part having a substantially square shape in plan view, a step part having a substantially square shape in plan view on which the piezoelectric diaphragm formed in the storage part is mounted, and a plurality of parts formed in parallel on top of the step part A ceramic multilayer substrate having a substantially square shape in plan view having a conductive pad and a bank portion surrounding the storage portion and the stepped portion, and one end portion side of the piezoelectric diaphragm is held on the upper surface of the conductive pad via a conductive bonding material The piezoelectric vibration device according to the present invention has a short side dimension of 1.5 mm or less , and a curved chamfered portion is formed at a corner portion of the storage portion and a connecting portion between the bank portion and the step portion. And the outer surface of the conductive pad is formed in a state along a ridge line on the free end side of the piezoelectric vibration plate of the stepped portion, and the bank portion is in contact with a ridgeline on the free end side of the piezoelectric vibration plate of the stepped portion It is formed in the state which does not contact the chamfering part of the connection part of a step part.

Further, in the above-described configuration, the remaining dimension W1 from each end portion at the most isolated position of the conductive pads formed in parallel to the end portion of the adjacent piezoelectric diaphragm is 0.1 mm or more and 0.2 mm or less. In this state , the piezoelectric diaphragm is held on the upper surface of the conductive pad through a conductive bonding material.

  In the above structure, the conductive bonding material is solder.

According to the first aspect of the present invention, the conductive bonding material is in contact with the ridge line on the free end side of the piezoelectric diaphragm of the stepped portion while suppressing the occurrence of cracks in the ceramic multilayer substrate by the curved chamfered portion. The conductive bonding material adheres along the ridge line on the free end side of the piezoelectric diaphragm of the stepped portion without spreading to the region of the chamfered portion existing at the connecting portion between the bank portion and the stepped portion. That is, the conductive bonding material does not partially protrude from the ridge line on the free end side of the piezoelectric vibration plate of the stepped portion toward the free end side of the piezoelectric vibration plate, and substantially linearly along the ridge line. To be attached. Therefore, the boundary portion between the region where the piezoelectric diaphragm is joined by the conductive bonding material and the region where the piezoelectric diaphragm is not joined is joined substantially linearly along the ridge line on the free end of the piezoelectric diaphragm of the stepped portion. Therefore, there is no local stress concentration on the piezoelectric diaphragm via the conductive bonding material, and the piezoelectric diaphragm is not cracked or chipped when subjected to an impact such as dropping.

In particular, in a small ceramic multilayer substrate having a short side dimension of 1.5 mm or less in the housing portion, a region for holding the piezoelectric diaphragm is narrowed, and the chamfered portion of the connecting portion between the bank portion and the step portion, the piezoelectric diaphragm plate, It becomes easy to contact through a conductive bonding material. As a result, there is an increased risk of cracking or chipping of the piezoelectric diaphragm when the stress is concentrated locally and subjected to an impact such as a drop. It becomes difficult to occur.

According to the second aspect of the present invention, in addition to the above-described effects, the dimensions (from the respective end portions at the most isolated positions of the conductive pads formed in parallel to the end portions of the adjacent piezoelectric diaphragms ( The piezoelectric diaphragm is held on the upper surface of the conductive pad via a conductive bonding material in a state where the excess dimension is 0.1 mm or more and 0.2 mm or less. While leaving the conductive bonding material in the direction of isolation, the conductive bonding material is fastened to the remaining region of the conductive pad, and the conductive bonding material acts so as to wrap around the side wall of the piezoelectric diaphragm. Therefore, it is possible to suppress a decrease in impact resistance and reduce the risk of a short circuit. At this time, if the excess dimension is less than 0.1 mm, the conductive bonding material cannot be released and the risk of short circuit increases. In addition, the amount of the conductive bonding material to be wound around the side wall of the piezoelectric diaphragm is reduced, and the impact resistance is lowered. If the excess dimension is larger than 0.2 mm, it is difficult to fasten the conductive bonding material, and it does not go around the side wall of the piezoelectric diaphragm, so that the impact resistance is lowered.

According to claim 3 of the present invention, by using solder as the conductive bonding material, it becomes easier for the solder to stay at the boundary between the electrode pad region and the ceramic substrate region where the stepped electrode pad is not formed. The effect of this can be obtained further.

  A first embodiment of the present invention will be described with reference to FIGS. 1 to 3 by taking a surface-mounted crystal resonator as an example. FIG. 1 is a plan view showing an embodiment of the present invention, and shows a state in which a crystal diaphragm (piezoelectric diaphragm) is mounted on a storage section. 2 is a cross-sectional view taken along the line XX of FIG. 1, and FIG. 3 is a plan view before the crystal diaphragm of FIG. 1 is mounted.

  The surface-mount type crystal resonator has a rectangular parallelepiped shape as a whole and a substantially multilayered ceramic multilayer substrate 1 having a concave storage portion 1a having an open top, and piezoelectric vibrations stored in the ceramic multilayer substrate. Although not shown, the crystal diaphragm 2 which is an element of the device and a metal lid bonded to the opening of the package are included.

  The crystal diaphragm 2 accommodated in the ceramic multilayer substrate 1 has a tuning fork shape, and an excitation electrode (not shown) formed on the leg portion and a lead electrode 21 from each excitation electrode formed on the base portion, 22 is formed. Each lead-out electrode 21 and 22 is electrically and mechanically joined to conductive pads 12 and 13 described later.

  When viewed in cross section, the ceramic multilayer substrate 1 is concave, and has a substantially rectangular shape in plan view and a bottomed storage portion 1a and a step portion having a substantially square shape in plan view on which a quartz diaphragm formed on the bottom of the storage portion is mounted. 1b, 1c, and the bank part (side wall) 10 surrounding the storage part and the step part. At this time, curvature chamfered portions R1 to R4 are formed at the corners of the storage portion 1a, and curvature chamfered portions R5 to R8 are formed at the connecting portion between the bank portion and the stepped portion. The storage part 1a has a short side dimension of 1.1 mm, the chamfered parts R1 to R4, R7 and R8 have a dimension of 0.25 mm, and the chamfered parts R5 and R6 have a dimension of 0.1 mm. .

Conductive pads 12 and 13 are formed in parallel with each other on the upper surface of each step. At this time, the conductive pads 12 and 13 are formed along the ridge lines 11b and 11c on the free end side of the stepped portions 1b and 1c of the piezoelectric diaphragm, and the chamfered portions R5 are in contact with the ridge lines 11b and 11c. , R6 is not contacted. These conductive pads 12 and 13 are composed of a metallized layer made of tungsten or the like using a ceramic lamination technique, and a metal film layer formed on the metallized layer. The metal film layer is composed of, for example, a nickel plating layer in contact with the metallized layer and an ultrathin gold plating layer formed on the nickel plating layer.

A circumferential metal seal portion 11 is formed on the top surface of the bank portion 10. The metal seal portion 11 includes a metallized layer made of tungsten or the like and a metal film layer formed on the metallized layer. The metal film layer is composed of, for example, a nickel plating layer in contact with the metallized layer and an ultrathin gold plating layer formed on the nickel plating layer.

  Then, the lead-out electrodes 21 and 22 of the quartz crystal plate 2 and the conductive pads 12 and 13 are electromechanically joined by solder D as a conductive joining material. At this time, the base side of the crystal vibrating plate 2 is fixed to the upper surfaces of the conductive pads 12 and 13 via the solder D, and is held on one side with the leg side of the crystal vibrating plate 2 being a free end. Further, as shown in FIGS. 1 and 2, the dimension W1 is set to 0 from each end portion of the conductive pads 12 and 13 formed in parallel to the end portion of the adjacent quartz diaphragm 2 from the end portion at the most isolated position. The crystal vibrating plate 2 is held on the upper surfaces of the conductive pads 12 and 13 through the solder D, with the area set to 1 mm to 0.2 mm, with this area as a surplus dimension. For this reason, as shown in FIG. 2, the solder D is fastened to the excess dimension W1 of the conductive pads 12 and 13 so that the solder D wraps around the side wall of the crystal diaphragm. Therefore, it is possible to suppress a decrease in impact resistance and reduce the risk of a short circuit.

Further, the metal lid (not shown) is mounted on the metal seal portion 11, and in this state, the metal lid and the metal seal portion are melted and sealed in an airtight manner by electron beam welding or laser beam welding.

In the embodiment of the present invention, the occurrence of cracks in the ceramic multilayer substrate 1 is suppressed by the chamfered portions R1 to R8. The solder D does not spread to the chamfered portions R5 and R6 of the step portions 1b and 1c, and adheres along the ridge lines 11b and 11c on the free end side of the crystal diaphragm of the step portions 1b and 1c. That is, the solder D adheres substantially linearly along the ridgelines 11b and 11c without protruding only partially from the ridgelines 11b and 11c of the step portion toward the free end side of the crystal diaphragm. For this reason, the crystal diaphragm 2 is joined substantially linearly along the boundary portion between the region joined by the solder D and the region not joined, that is, the ridge lines 11b and 11c of the step portions 1b and 1c. As a result, there is no local concentration of stress on the crystal diaphragm 2 via the solder D, and the crystal diaphragm 2 is not cracked or chipped when subjected to an impact such as dropping.

  Also, the ceramic multi-layer substrate 1 has a short side dimension of 1.1 mm (1.5 mm or less), and the chamfered portion of the connecting portion between the bank portion and the step portion contacting the ridge lines 11b and 11c of the step portion. Since the dimensions of R5 and R6 are set to 0.1 mm, the effect of suppressing the generation of cracks due to the chamfered portion on the ceramic multilayer substrate is not lowered while realizing miniaturization. The crystal vibrating plate 2 and the conductive pads 12 and 13 are not narrowed by the chamfered portions R5 and R6.

  Next, another embodiment according to the present invention will be described with reference to FIG. 4 using a surface-mount type crystal resonator as an example. FIG. 4 shows another embodiment of the present invention, and is a plan view showing a conductive pad of a ceramic multilayer substrate in a state where a quartz diaphragm is not mounted. The planar shape of the conductive pad is different from the above embodiment. Yes. Since the basic configuration is the same as that of the above embodiment, the same components are described using the same numbers, and a part of the description is omitted.

  The conductive pads 12 and 13 in FIG. 4A are formed wider on the base side than in the above embodiment, and narrow so that only portions close to the chamfered portions R5 and R6 do not contact each other. . That is, by forming an electrodeless region in which the electrode does not directly contact only around the chamfered portions R5 and R6, the same effect as the above embodiment can be obtained.

The conductive pads 12 and 13 shown in FIG. 4B are formed on the entire step 1b and 1c, and a part of the conductive pads 12 and 13 is covered with the alumina coat A. The alumina coat A is formed so as to be in contact with the chamfered portions R5 and R6 that are in contact with the ridge lines 11b and 11c on the free end side of the quartz plate of the stepped portions 1b and 1c and the bank portion adjacent thereto. That is, the outer surface of the conductive pads 12 and 13 is not in contact with the chamfered portions R5 and R6 by forming a film that keeps the conductive bonding material spread on the upper part of the electrodes around the chamfered portions R5 and R6. Therefore, the same effect as the above embodiment can be obtained. If the conductive bonding material is solder, a film that reduces wettability is preferable.

  The present invention can be implemented in various other forms without departing from the spirit or main features thereof. For example, the conductive bonding material is not limited to solder. It can also be applied to low melting point metal brazing filler metals and lead-free solder (tin copper solder, tin silver copper solder, tin silver solder, tin silver copper bismuth solder, etc.). Further, the chamfer is not limited to a curved shape. In the above description, a tuning fork type crystal resonator is illustrated as an example of the piezoelectric vibration device. However, a square crystal resonator that vibrates in a thickness-shear manner may be used. For example, in the above-described embodiment, an IC constituting an oscillation circuit may be attached to the lower space of the crystal diaphragm, and necessary wiring may be provided to constitute a crystal oscillator, or a single-element or multi-element crystal filter, etc. It can be applied to other piezoelectric vibration devices. Further, although beam welding is taken as an example of a sealing method, sealing by seam welding, glass sealing, resin sealing, or the like may be used. Therefore, the above-described embodiment is merely an example in all respects and should not be interpreted in a limited manner. The scope of the present invention is indicated by the claims, and is not restricted by the text of the specification. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

The top view in the state where the crystal diaphragm which shows the embodiment of the present invention was carried. Sectional drawing along the XX line of FIG. It is a top view before mounting the crystal diaphragm of FIG. The top view in the state where the crystal diaphragm which shows other embodiments of the present invention was carried.

DESCRIPTION OF SYMBOLS 1 Ceramic multilayer substrate 10 Bank part 11 Metal seal part 2 Crystal diaphragm (piezoelectric diaphragm)
12, 13 Conductive pad

Claims (3)

A bottomed storage part having a substantially square shape in plan view, a step part having a substantially square shape in plan view on which the piezoelectric diaphragm formed in the storage part is mounted, and a plurality of parts formed in parallel on top of the step part A ceramic multilayer substrate having a substantially square shape in plan view having a conductive pad and a bank portion surrounding the storage portion and the stepped portion, and one end portion side of the piezoelectric diaphragm is held on the upper surface of the conductive pad via a conductive bonding material A piezoelectric vibration device comprising:
The short side dimension of the storage part is 1.5 mm or less,
A curved chamfered portion is formed at each of the corner portion of the storage portion and the connecting portion between the bank portion and the step portion,
The outer surface of the conductive pad is formed in a state along the ridge line on the free end side of the stepped piezoelectric diaphragm, and is in contact with the ridge line on the free end side of the stepped piezoelectric diaphragm. A piezoelectric vibration device characterized in that the piezoelectric vibration device is formed so as not to contact the chamfered portion of the connecting portion. In the state where the extra dimension W1 from each end portion of the conductive pads formed in parallel to the end portion of the adjacent piezoelectric diaphragm is 0.1 mm or more and 0.2 mm or less, 2. The piezoelectric vibration device according to claim 1, wherein a vibration plate is held on the upper surface of the conductive pad via a conductive bonding material. The piezoelectric vibration device according to claim 1, wherein the conductive bonding material is solder.

Images