JP3911838B2 - Method for manufacturing piezoelectric vibrator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a piezoelectric vibrator such as a crystal vibrator used in an electronic apparatus, and more particularly to an electromechanical joint structure between a piezoelectric diaphragm and an electrode pad.
[0002]
[Prior art]
A piezoelectric vibrator has a piezoelectric diaphragm (electronic element) housed in a package. Since the element is a vibrating body, how it is supported is an important factor that determines its electrical characteristics. In particular, a support structure is important for a crystal unit having a high Q value.
[0003]
The connection between the piezoelectric diaphragm and the electrode for external derivation is performed by, for example, a conductive bonding material. FIG. 8 shows an example of a surface-mount type crystal resonator in which electromechanical bonding is performed using a conductive bonding material. An electrode pad 74 is formed on the upper surface of the ceramic substrate 7 and is electrically connected to the lead-out electrode 71 via the via electrode 73. The lead-out electrode 72 is electrically and mechanically connected to another electrode pad (not shown). The quartz diaphragm 8 having the excitation electrodes 81 and 82 formed on the front and back surfaces is mounted on the conductive bonding material S1, and further, the conductive bonding material S2 is applied on the top thereof, and the quartz diaphragm is electrically and mechanically connected. The The lid 9 covers the quartz diaphragm and the like, and the glass G is hermetically sealed to complete the piezoelectric vibrator.
[0004]
The conductive bonding material is, for example, a resin paste in which a conductive filler is kneaded, but handling has troublesome side surfaces. In other words, the supply of the conductive bonding material to the bonded portion is performed by a dispenser, but the viscosity and the like are easily affected by the ambient atmosphere of temperature and humidity, and depending on the surrounding environment, the supply of the bonding material is excessive, insufficient, or dripping. The problem occurs. Such instability of the bonding material supply leads to variations in the electrical characteristics of the crystal resonator, and dripping may cause a short circuit accident between the electrodes.
[0005]
Further, since a space for the conductive bonding material is required at the time of bonding, there is a problem that the distance h between the quartz crystal vibrating plate 8 and the lid 9 is inevitably large, and cannot cope with the low profile of the piezoelectric vibrator. It was.
[0006]
In order to solve such problems, for example, Japanese Patent Laid-Open No. 8-8684 discloses a method in which solder bumps or gold bumps are formed on electrode pads and the quartz diaphragm is electromechanically bonded by thermocompression bonding. ing. Since such a joining structure does not use a conductive joining material, it has the advantage that conventional problems such as excessive supply, insufficient supply, and dripping of the joining material do not occur.
[0007]
However, according to the above-described method, it is necessary to devise an electrode formed on the piezoelectric vibrator. That is, both of the two electrodes must be electrically joined on the electrode pad side (the back side of the piezoelectric vibrator). For example, in a piezoelectric diaphragm that excites thickness shear vibration, the main electrode for excitation is used. It was necessary to form on the front and back, and for this reason, the main electrode on the front surface had to be routed to the electrode pad side on the back surface. Such a lead-out electrode can be formed relatively easily by forming a lead-off mask shape used when forming an electrode thin film by a vacuum vapor deposition method or the like. However, the formed lead electrode may be cut at the edge portion of the piezoelectric vibrator, and particularly in a piezoelectric diaphragm that requires chamfering such as convex machining, the edge becomes sharper and the probability of a disconnection accident is high. It was.
[0008]
In addition, for the above-described configuration, a method of electrically connecting the electrode pad and the main electrode on the upper surface side by wire bonding is also conceivable, but the connection work is performed in a process different from the bonding of the electrode pad and the main electrode on the lower surface side Since it was necessary, there was a problem that the number of manufacturing steps increased. In addition, the presence of the bent portion of the wire has been an adverse effect of making the package thinner.
[0009]
[Problems to be solved by the invention]
The present invention has been made to solve the above problems, and can stably bond the electrode pad on the insulating substrate side and the electrode of the piezoelectric diaphragm, does not adversely affect various characteristics of the piezoelectric vibrator, and is complicated. An object of the present invention is to provide a piezoelectric vibrator that does not require a simple bonding method.
[0010]
[Means for Solving the Problems]
In the present invention, at least two electrode pads are formed on the upper surface, and the insulation is formed on the lower surface with two or more lead electrodes that are electrically connected to the electrode pads and connected to the outside. Place the board on the work stage,
A plurality of metal bumps are formed at a predetermined position of each electrode pad by using a wire bonding method, and a portion of each metal bump where the piezoelectric diaphragm is not mounted is cut in a state where the wire is extended. To form an extension,
After that, on the upper part of the metal bump, a piezoelectric diaphragm having electrodes formed on the front and back surfaces is mounted,
The extension portion and the electrode formed on the surface of the piezoelectric diaphragm, and the metal bump and the electrode formed on the back surface of the piezoelectric diaphragm are joined by an ultrasonic thermocompression bonding method or an ultrasonic welding method. It is said.
[0011]
By the above manufacturing method, the extension part and the electrode on the upper surface of the piezoelectric vibration plate, and the electrode located on the lower surface of the piezoelectric vibration plate and the metal bump are pressed or welded, so that each electrode and the like are firmly bonded to each other between metals. . In addition, since the space for the conductive bonding material is not required, the distance between the crystal diaphragm and the lid can be reduced, and the package can be made thinner.
[0012]
Furthermore, unlike the case where a conductive bonding material using a resin paste is used, there is no need to generate a problem due to the supply amount of the bonding material or to cure the bonding material.
[0013]
According to a second aspect of the present invention, in the method of manufacturing a piezoelectric vibrator, the uppermost layer of the electrode pad and the extraction electrode, and the extended portions of the metal bump and the metal bump are gold (Au). It is good also as a structure. As a result, bonding with the same metal can be performed, and gold, in particular, has the advantage that it has no problem of oxidation and has excellent bonding properties.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The embodiment of the present invention will be described with reference to FIGS. 1, 2, 3, 4, and 5, taking a surface-mounted crystal resonator as an example. FIG. 1 is an internal cross-sectional view of a surface-mounted crystal resonator, and is a cross-sectional view taken along line AA when a piezoelectric diaphragm is mounted and sealed with a lid in FIG. FIG. 2 is an exploded plan view of the quartz diaphragm and the insulating substrate, and FIGS. 3, 4, and 5 are diagrams showing the manufacturing process.
[0015]
The surface-mount type crystal resonator is mounted on the insulating substrate 1 and electrode pads 14 and 14 formed on the insulating substrate 1, and is electrically joined to the surface. The surface mounting type crystal resonator and the electrode pads 14 and 14 of the insulating substrate 1 are mounted. And metal bumps 31, 32, 33 interposed between the quartz diaphragm 2 and a lid 4 that hermetically seals the quartz diaphragm 2.
[0016]
The insulating substrate 1 is made of a rectangular ceramic thin plate such as alumina, and electrode pads 14 and 14 are formed on the surface side by side in the width direction (short side direction) of the insulating substrate. In addition, lead electrodes 11 and 12 are formed on the back surface, and are electrically connected to each other through the electrode pads 14 and 14 and via electrodes 13, respectively. Each of these electrodes is formed using a known metallization technique, plating technique, or the like. For example, a tungsten layer is provided as a lower layer and a gold layer is provided as an upper layer. Metal bumps 31, 32, and 33 made of wire bumps using gold wires are formed on the upper surface of each electrode pad. These wire bumps are also referred to as stud bumps. By using wire bonding technology, for example, the tip of a gold wire having a diameter of about 50 microns is heated to form a ball, and after being connected to the electrode pad, the wire is cut in the immediate vicinity of the bump. Can be obtained. The resulting metal bump has an outer dimension of, for example, a width of about 100 microns and a height of about 60 microns. This size is the wire diameter. The pressure can be changed as appropriate by selecting and adjusting the pressure, pressure and the like. Among these metal bumps, the metal bumps 31 and 32 are cut at the nearest portion of the bump, but the metal bump 33 on which the crystal diaphragm 2 is not mounted is cut by 0.5 to 2 mm above the wire, for example. In other words, an elongated portion 33a is formed by a wire.
[0017]
The quartz diaphragm 2 is a rectangular AT-cut quartz plate. For example, excitation electrodes 21 and 22 are formed on the front and back surfaces so as to excite thickness-shear vibration, and the extraction electrodes 21a and 22a are quartz-vibrated from the excitation electrodes 21 and 22, respectively. It is derived in the longitudinal direction of the plate. An extraction electrode 21b is formed on a part of the back surface corresponding to the extraction electrode 21a, and an extraction electrode 22b is formed on a part of the surface corresponding to the extraction electrode 22a. In this embodiment, the external dimensions of the quartz crystal plate are 4 mm long and 1.6 mm wide to obtain a frequency of 32 MHz, and each excitation electrode and extraction electrode has a lower layer made of chromium and an upper layer made of chromium. Composed of gold.
[0018]
The lid 4 is made of an insulating material such as ceramic and has a reverse concave shape in cross section, forming a space in which the quartz diaphragm 2 is hermetically sealed.
[0019]
Next, an example of a method of forming a metal bump on the insulating substrate 1 and mounting the electrode-formed crystal diaphragm 2 on the insulating substrate 1 and electrically and mechanically connecting it will be described with reference to FIGS. . As shown in FIG. 3, the insulating substrate 1 is placed on the work stage W, and a plurality of metal bumps (gold wire bumps) are continuously formed on the electrode pad 14 by a bump bonder using a wire bonding technique such as thermocompression bonding. It is formed. Among these, the extension part 33a is formed in the metal bump 33 of the longitudinal direction edge part side of a crystal diaphragm. The elongated portion 33a is formed by forming a metal bump, cutting the wire immediately above the bump, and cutting out a wire having a predetermined dimension and then fusing it. In FIG. 3, T is a bonding tool (capillary). Next, the crystal diaphragm 2 is mounted on the metal bumps 31 and 32 so that the extraction electrodes 21b and 22a are in contact with each other. When this operation is performed by an automatic mounting machine, for example, it is possible to control such that the number of bumps, the position, and the like are not mounted on the bumps having the extending portions using the markers.
[0020]
Thereafter, the extension portion 33a and the extraction electrode on the quartz diaphragm, and the metal bumps 31 and 32 and the extraction electrode of the quartz diaphragm are ultrasonically welded by an ultrasonic welder. More specifically, the elongating extension 33a is bent and brought into contact with the extraction electrode on the quartz diaphragm by the welding tip C of the ultrasonic welder, and the quartz diaphragm is pressed onto the bump as it is to apply a static pressure. Then, by vibrating the ultrasonic chip at a predetermined frequency, the extending portion 33a and the extraction electrode on the crystal diaphragm, and the metal bumps 31 and 32 and the extraction electrode of the crystal diaphragm are ultrasonically welded.
[0021]
In the configuration in which one main electrode is formed on each of the front and back surfaces as in this embodiment, it is not always necessary to form an extension corresponding to each extraction electrode, and the main electrode is on the surface (side without the electrode pad). It may be formed only on the side corresponding to the connection of the part in the.
[0022]
The crystal diaphragm 2 ultrasonically welded onto the electrode pad of the insulating substrate 1 is hermetically sealed by a lid 4. Joining to the insulating substrate 1 lid 4 is performed by the glass 41, but other airtight sealing means such as resistance welding may be used.
[0023]
Another embodiment of the present invention will be described with reference to FIG. FIG. 6 shows a modification of the bump configuration. Since the basic configuration is the same as that of the above-described embodiment, the same structural parts will be described using the same numbers, and a part of the description will be omitted.
[0024]
The electrode pad 14 is formed with a bump group 51 related to mounting of the piezoelectric diaphragm 2 and a bump group 52 composed of a plurality of bumps having extended portions related to electrical connection without being related to mounting. The bump group 51 has a configuration in which minute bumps are arranged in two rows, and the bump group 52 also has a plurality of extending portions 52a. Each of the plurality of extending portions is bent in the direction of arrow D and connected to the extraction electrode of the piezoelectric diaphragm. These elongated portions 52a are welded to the surface of the extraction electrode by an ultrasonic welder.
[0025]
Another embodiment of the present invention will be described with reference to FIG. FIG. 7 shows another modification of the bump configuration. Since the basic configuration is the same as that of the above-described two embodiments, the same structural parts will be described using the same numbers, and a part of the description will be omitted.
[0026]
The electrode pad 14 is formed so as to be located diagonally to the rectangular piezoelectric diaphragm. As described above, the present invention can be applied not only when the piezoelectric diaphragm is cantilevered but also when both ends are supported. In this embodiment, a bump group 53 related to mounting of the piezoelectric diaphragm 2 and a bump group 54 composed of a plurality of bumps having extended portions related to electrical connection without being related to mounting are formed, and the piezoelectric diaphragm is formed. Bump groups 53 and 54 are arranged in a biased manner at the end in the short side direction (width direction). The plurality of extending portions are bent in the directions of arrows D1 and D2, respectively, and connected to the extraction electrode of the piezoelectric diaphragm. These elongated portions 52a are welded to the surface of the extraction electrode by an ultrasonic welder.
[0027]
The metal bumps used in the above embodiments may be made of not only gold but also other materials such as copper and aluminum, but depending on the materials used, an oxidation-reduction atmosphere may be required. In addition, it is preferable to use the same material as the metal bump for the electrode to be connected such as an electrode pad and an extraction electrode. For example, in the first embodiment, the upper layer of the extraction electrode is made of silver, and bonding with a different metal using a gold bump It has been confirmed experimentally that this is possible.
[0028]
The metal bumps may be formed by a thermocompression bonding method, an ultrasonic thermocompression bonding method, an ultrasonic welding method, or the like. In each of the above embodiments, the piezoelectric diaphragm using the thickness shear vibration is illustrated. However, for example, when the tuning fork vibrator using bending vibration is cantilevered, the piezoelectric diaphragm can be applied to a piezoelectric diaphragm of another vibration mode. May be.
[0029]
【The invention's effect】
As described above, according to the present invention, the extension portion and the electrode on the upper surface of the piezoelectric vibration plate, and the electrode located on the lower surface of the piezoelectric vibration plate and the metal bump are bonded or welded. Combined. Further, it is not necessary to consider the problem of cutting the edge portion. Therefore, the instability of bonding that has occurred in the past is eliminated, and a piezoelectric vibrator having stable electrical characteristics can be obtained. In addition, the package can be made thinner, and a process for curing the bonding material is not required, so that the number of manufacturing steps is reduced and the productivity is improved.
[0030]
Then, a plurality of metal bumps are formed at predetermined positions of the respective electrode pads by using a wire bonding method, and the wires are extended with respect to the bumps in the portions where the piezoelectric diaphragm is not mounted in each electrode pad. Since it is a manufacturing method which forms an extended part by cut | disconnecting, formation of a metal bump and an extended part can be formed very efficiently and reliably. In addition, the wire extension and the electrode formed on the surface of the piezoelectric diaphragm, and the metal bump and the electrode formed on the back surface of the piezoelectric diaphragm are joined together by a thermocompression bonding method or an ultrasonic welding method. This can be performed reliably in a relatively small area.
[0031]
According to the second aspect, in addition to the above effect, bonding with the same metal can be performed. In particular, gold has no problem of oxidation, and the bonding property is improved.
[Brief description of the drawings]
FIG. 1 is an internal cross-sectional view according to a first embodiment.
FIG. 2 is a plan view according to the first embodiment.
FIG. 3 shows a manufacturing process.
FIG. 4 shows a manufacturing process.
FIG. 5 shows a manufacturing process.
FIG. 6 is a plan view showing another embodiment.
FIG. 7 is a plan view showing another embodiment.
[Fig. 8] Diagram showing a conventional example [Explanation of symbols]
1 Insulating substrate 2 Piezoelectric vibration plate (crystal vibration plate)
31, 32, 33 Metal bump (wire bump)
33a Extension part 4 Lid 51, 52, 53, 54 Bump group 52a Extension part

Claims (2)

An insulating substrate having at least two electrode pads formed on the upper surface and two or more lead electrodes formed on the lower surface and electrically connected to the electrode pads and connected to the outside;
A plurality of metal bumps are formed at a predetermined position of each electrode pad by using a wire bonding method, and a portion of each metal bump where the piezoelectric diaphragm is not mounted is cut in a state where the wire is extended. To form an extension,
After that, on the upper part of the metal bump, a piezoelectric diaphragm having electrodes formed on the front and back surfaces is mounted,
The extension portion and the electrode formed on the surface of the piezoelectric diaphragm, and the metal bump and the electrode formed on the back surface of the piezoelectric diaphragm are joined by an ultrasonic thermocompression bonding method or an ultrasonic welding method. A method for manufacturing a piezoelectric vibrator. 2. The method of manufacturing a piezoelectric vibrator according to claim 1, wherein the uppermost layer of the electrode pad and the extraction electrode, and the metal bump and the extended portion of the metal bump are gold.

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