JP2002344278A - Piezoelectric resonator - Google Patents

Abstract

[PROBLEMS] To provide a Ni film, an Au film, a Ni film, and an A film on a surface of a crystal unit.
A pad electrode formed by vapor deposition in the order of the g film and an external connection electrode formed on the bottom surface inside the package of the vibrator are denoted by A.
When connected through a u-bump, a quartz substrate and a Ni film, Ag
Peeling occurs at the interface between the film and the Ni film. A pad electrode is formed by depositing a Cr film and an Au film on a quartz substrate, and further forming an Ag sputtered film thereon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric resonator, and more particularly to a surface mount type piezoelectric resonator using an Au bump as a means for connecting a piezoelectric vibrating element in a package.

[0002]

2. Description of the Related Art In recent years, various types of transmission communication equipment or OA
2. Description of the Related Art Along with high-speed processing and high performance of equipment, a piezoelectric resonator as a frequency control device is required to have a higher frequency, a smaller size, and higher reliability. FIG. 2 is a perspective view showing one example of two main surfaces of a conventional AT-cut quartz crystal vibrating element having an ultra-thin portion for high frequency. This crystal vibrating element
This is a vibrator utilizing the fundamental shear vibration wave of the AT-cut quartz crystal. Since the resonance frequency is inversely proportional to the plate thickness, in order to increase the frequency while maintaining the mechanical strength, the following quartz crystal is used. The vibrating part of the substrate is ultra-thin. That is, as shown in FIG. 2A, one main surface of the quartz substrate constituting the quartz vibrating element 3 is recessed by etching, and the bottom surface of the recess 11 is formed as an ultra-thin vibrating portion 11a. A thick annular surrounding portion 12 that supports the outer periphery of the vibrating portion 11a over the entire periphery is integrated. Furthermore,
On the one main surface (concave surface), Au with Ni as a base is used.
A main surface electrode 33, a lead electrode 34a extending from the main surface electrode 33, and a pad electrode 35a are formed by mask vapor deposition or photolithography. It is formed on the edge of the substrate.

Next, as shown in FIG. 1B, on the other main surface, that is, on the back surface (flat surface) of the main surface (concave surface), Au is formed by vapor deposition of Ni as a base. Back electrode 36 and a lead electrode 34 extending from the back electrode 36
b and the pad electrode 35c are formed. The pad electrode 35c and the pad electrode 35b are electrically connected via the through hole 37 at the end of the quartz substrate. Further, the pad electrodes 35a, 35b, 35c and the through-holes 37 are further increased in thickness by depositing Ag with Ni as a base on the Au film to increase the thickness of Au bumps 2a, 2b, 2c, 2d to be described later. This facilitates or improves the conductivity of the through hole 37. Au for connecting the signal of the vibrating element 3 to the outside is provided on each of the pad electrodes 35a and 35b.
The bumps 2a and 2b and the Au bumps 2c and 2d are formed. Here, the Au bumps 2a to 2d are bonded to the Ag film of the pad electrode by applying a wire bonding technique and by a diffusion phenomenon of Au by heating, pressurizing and applying ultrasonic waves.

FIG. 3 is a sectional view showing the structure of a surface-mount type crystal unit using the crystal unit 3. As shown in the figure, the present surface mount type crystal resonator has a structure in which the crystal resonator element 3 of FIG. 2 is housed in a ceramic package 4, and an opening thereof is hermetically sealed with a metal upper lid 5. . The ceramic package 4 is provided with a seam ring 41 fixed in an annular shape at the upper end of the opening of the ceramic package for seam welding the upper lid 5. Further, internal pad electrodes 42a, 42b formed by Au metallization are formed on the bottom surface inside the ceramic package 4.
Also, external pad electrodes 43a and 43b corresponding to the internal pad electrodes 42a and 42b are provided on the outer bottom surface of the ceramic package 4, and the corresponding internal and
An external pad electrode is connected (not shown).

[0005] The operation of housing the crystal vibrating element 3 in the package 4 and connecting them is performed by Au bumps 2a to 2d previously formed on the pad electrodes 35a and 35b of the crystal vibrating element 3 and the ceramic package. No. 4, the internal pad electrodes 42a and 42b are opposed to each other, and heating, pressurization and ultrasonic waves are applied by using a flip chip mounting technique, and the pad electrodes 35 are utilized by utilizing the diffusion phenomenon of the Au bumps 2a to 2d.
a, 35b and the internal pad electrodes 42a, 42b. Here, the reason for using the Au bumps for the connection is that the conductivity is improved, local bonding is possible, and the connection of the quartz vibrating element 3 is improved as compared with the case of using a conductive adhesive. It is a means that can reduce the occurrence of stress due to the occurrence and that there is no outgas, etc., and are means for contributing to higher frequency, smaller size, and higher reliability of the device.

[0006]

The deposited film thickness of the main surface electrode 33 on one main surface (concave surface) of the crystal vibrating element 3 determines the characteristics of the crystal vibrator, and depends on the characteristics. The main surface electrode 33 is formed of a deposited film of Au with Ni as a base. For example, in the case of a quartz oscillator having an oscillation frequency of 155 MHz, the thickness of the Ni film is about 7 nm, the thickness of the Au film is about 60 nm, and
In the case of a quartz oscillator having an oscillation frequency of 622 MHz, the thickness of the Ni film is about 7 nm, and the thickness of the Au film is about 30 nm.
It is. Therefore, when the lead electrode 34 a and the pad electrodes 35 a and 35 b are formed simultaneously and integrally with the main surface electrode 33, these electrodes have the same N as the main surface electrode 11.
It will be formed with a deposited film thickness of Au with i as a base. On the other hand, in the process of manufacturing the crystal resonator, as described above, the pad electrodes 35a and 35b are connected when the Au bumps are formed on the respective pad electrodes and when the crystal resonator element 3 and the ceramic package 4 are connected. Loads due to heating, pressurization and application of ultrasonic waves are applied twice, which causes cracks and peeling of the film layer. As described above, the pad electrodes 35a and 35b are formed in such a manner that the pad electrodes 35a and 35b are formed so as not to cause peeling when forming the Au bumps and to obtain a film thickness sufficient to withstand the load caused by heating, pressing and application of ultrasonic waves. Generally, the thickness is increased to 400 nm or more. On the surface of the Au film formed at the same time as the main surface electrode 11, an Ag vapor deposition film based on Ni is further formed to increase the thickness. For example, 155MH
In the case of a crystal oscillator having an oscillation frequency of z or 622 MHz, the thickness of the Ni film is generally about 7 nm, and the thickness of the Ag film is generally about 370 nm.

However, as described above, in a structure in which an Ag film based on Ni is further evaporated on an Au evaporated film based on Ni on a quartz substrate, a sufficiently thick A
The formation of the Au bumps is facilitated by the g film, but since the adhesion between the Ni film and the quartz substrate or the Ag film is weak, an external force such as a drop impact is applied when the quartz vibrating element 3 is connected to the ceramic package 4. The quartz substrate and Ni
Separation occurs at the interface with the film or at the interface between the Ag film and the Ni film, resulting in a problem that the electrical performance of the crystal unit cannot be obtained. Further, even if the quartz vibrating element 3 and the ceramic package 4 can be connected without the separation of the pad electrodes 35a and 35b, the stress generated at the connection portion of the Au bump during the connection work is mainly on the main surface. There is a problem that the frequency temperature characteristics and the long-term aging characteristics of the crystal unit are deteriorated by being transmitted to the surface electrode 33. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has a high reliability of a piezoelectric resonator that reduces peeling of a vapor-deposited film that occurs when a piezoelectric vibration element is connected to a package using an Au bump. The purpose is to provide.

[0008]

According to one aspect of the present invention, there is provided a piezoelectric resonator having a structure in which a piezoelectric vibrating element is sealed in a package, wherein the piezoelectric vibrating element is formed on a surface of the piezoelectric vibrating element. In a piezoelectric resonator in which electrical and mechanical connection between the pad electrode formed and an external connection electrode formed on the bottom surface of the package via an Au bump, the pad electrode has a Cr film and an Au film formed from the surface of the piezoelectric substrate. It is characterized by being formed of a metal multilayer film in which an Ag film and an Ag film are sequentially laminated.

According to a third aspect of the present invention, in the piezoelectric resonator according to the first or second aspect, an ultra-thin vibrating portion and an outer periphery of the vibrating portion are supported as a piezoelectric substrate constituting the piezoelectric vibrating element. It is characterized by using a piezoelectric substrate integrally formed with a thick annular surrounding portion. Claim 4
In the piezoelectric resonator according to any one of claims 1 to 3, the Ag film of the pad electrode has a thickness of at least 200 nm.
m or more, and the total thickness of the pad electrode is 400
less than nm.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings. FIG. 1 is a perspective view showing an embodiment of two main surfaces of an AT-cut quartz crystal resonator according to the present invention. As shown in FIG. 1A, one main surface (concave surface) of the quartz-crystal vibrating element 1 of the present invention includes a concave portion 11 formed by etching the main surface of a quartz substrate by etching, and a bottom surface of the concave portion 11. Ultra-thin vibrating part 11
a, an annular surrounding portion 1 for supporting the outer periphery of the vibrating portion 11a
2. The main surface electrode 13, a lead electrode 14a extending from the main surface electrode 13, a pad electrode 15a formed at the end of the lead electrode 14a, and a pad electrode 15b formed at the end of the quartz substrate facing the pad electrode 15a. It is composed of

As shown in FIG. 1B, a back electrode 16 is provided on the back surface (flat surface) of the main surface (concave surface).
It comprises a lead electrode 14b extending from the back electrode 16 and a pad electrode 15c formed at an end of the lead electrode 14b. The pad electrode 15c and the pad electrode 15b are electrically connected via the through hole 17 at the end of the quartz substrate. Further, Au bumps 2a, 2b and Au bumps 2c, 2d are formed on the pad electrodes 15a, 15b.

The quartz vibrating element 1 according to the present embodiment is shown in FIG.
Are assembled in a ceramic package in the same manner as the crystal resonator element 3 in the above, to constitute a surface-mount type crystal resonator.
Except for 5a, 15b, 15c and through-hole 17, the components are exactly the same as those of the crystal resonator element 3 of FIG.

The structure of the crystal resonator element 1 of this embodiment is different from that of the conventional example in that the pad electrodes 15a, 15b, 15c and the through holes 17 formed on the quartz substrate are formed on the quartz substrate. Then, a Cr film is formed as an underlayer, and an Au film is deposited thereon. Then, in order to obtain a required film thickness, Ag is directly sputtered on the Au film without passing through an underlayer of Ni or the like. It is to form a film. The particles of the Cr film are denser than the particles of the Ni film, and the anchor effect on the quartz substrate is improved, and the adhesion to the quartz substrate can be enhanced. In general, when an Ag vapor deposition film is formed on an Au film using a Ni film or a Cr film as an underlayer, an anchor effect can be obtained.
It was found that r and Ag were not alloyed, so that the adhesion was weak. In this embodiment, since the alloy is formed by forming Ag on the Au film, the above-described disadvantage can be compensated and the adhesion can be enhanced. Further, when the Ag film is formed by sputtering, the particles become denser than in the case of vapor deposition, and the Ag film is easily alloyed.

For example, in the case of a quartz oscillator having an oscillation frequency of 155 MHz, the thickness of the Ni film is about 7 nm, the thickness of the Au film is about 60 nm, and the thickness of the Ag film is about 200 n.
After bonding the pad electrodes 35a and 35b and the internal pad electrodes of the ceramic package by flip chip mounting as shown in FIG. 4 and visually confirming the bonding portion, the pad electrodes 35a and 35b were found to have cracks and peeling. No occurrence has been confirmed and normal operation has been confirmed. As described above, when the present vibration element 1 is connected to a ceramic package via an Au bump, or when external force such as a drop impact is applied, the occurrence of peeling of the pad electrode can be reduced, and the vibration occurs when the vibration element 1 is connected to the ceramic package. Deterioration of the frequency temperature characteristics and long-term aging characteristics of the crystal unit due to stress can be suppressed. In the case of a quartz oscillator having an oscillation frequency of 622 MHz, the thickness of the Ni film is set to about 7 n.
m, the thickness of the Au film was about 30 nm, and the thickness of the Ag film was about 200 nm.
No cracks, peeling, etc. occurred in a and 35b.

When various experiments were conducted, it was found that the Cr film and the Ag film
It was confirmed that sufficient strength could be obtained even if the total thickness of the pad electrode was less than 400 nm when the thickness of Ag was 200 nm or more regardless of the thickness of the film. In the above-described embodiment, the present invention has been described as applied to an AT-cut quartz-crystal vibrating element having an ultra-thin vibrating portion. However, the present invention is not limited to this, and may be applied to one side of a quartz substrate. Obviously, the electrode to be formed may be a split-mode dual-mode filter. Further, a quartz vibrating element having no ultra-thin vibrating portion may be used. Further, the cut angle of the quartz material may be a quartz substrate other than the AT cut or a piezoelectric substrate other than the quartz.

[0016]

As described above, according to the present invention, the electrode film formed on the quartz substrate is made of Cr, Au and Ag,
Since the g film is configured to be formed directly on the Au film by sputtering, when forming an Au bump on the Ag film,
It solves the problem that the pad electrode peels off when connected to a ceramic package or when an external force such as a drop impact is applied, and the frequency temperature characteristics and long-term aging characteristics are deteriorated due to the generation of stress due to the connection. be able to. Therefore, when manufacturing a small and high-frequency crystal resonator using Au bumps, the effects of Au bumps can be sufficiently exhibited. As a result, according to the present invention, a remarkable effect can be exhibited in providing a small and highly reliable surface mount type piezoelectric resonator. Further, the Ag film is
If the thickness is 0 nm or more, the total film thickness may be less than 400 nm, so that the Ag material and the film formation time can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of two main surfaces of an AT-cut quartz-crystal vibrating element according to the present invention, FIG. 1 (a) is a main surface (concave surface) having a concave portion, and FIG. The back surface (flat surface) of the main surface of a).

FIGS. 2A and 2B are perspective views showing an example of two main surfaces of a conventional AT-cut quartz-crystal vibrating element. FIG. 2A is a main surface (concave surface) having a concave portion, and FIG. Back side (flat side).

FIG. 3 is a cross-sectional view showing an example of the structure of a surface-mount type crystal unit using a conventional crystal unit.

[Explanation of symbols]

1 ··· quartz oscillator, 2a, 2b, 2c, 2d ···
Au bump, 3 ・ ・ Crystal vibrating element, 4 ・ ・ Ceramic package, 5 ・ ・ ・ Top cover, 11 ・ ・ Recess
11a: vibrating part, 12: annular surrounding part, 13:
.Principal surface electrodes, 14a, 14b .. Lead electrodes, 1
5a, 15b, 15c pad electrode, 16
..Back surface electrode, 33..Main surface electrode, 34a, 34
b lead electrode, 35a, 35b, 35c pad electrode, 36 back electrode, 37 through hole,
41 seam ring, 42a, 42b internal pad electrode, 43a, 43b external pad electrode

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 21/92 603A

Claims (4)

[Claims] A piezoelectric resonator having a structure in which a piezoelectric vibrating element is sealed in a package, wherein an electric connection between a pad electrode formed on a surface of the piezoelectric vibrating element and an external connection electrode formed on a bottom surface of the package is provided. In a piezoelectric resonator that performs mechanical connection via Au bumps, the pad electrode is formed of a metal multilayer film in which a Cr film, an Au film, and an Ag film are sequentially stacked from the surface of the piezoelectric substrate. Piezoelectric resonator. 2. The piezoelectric resonator according to claim 1, wherein the Ag film of the pad electrode is formed on the Au film by sputtering. 3. A piezoelectric substrate in which an ultra-thin vibrating portion and a thick annular surrounding portion supporting an outer periphery of the vibrating portion are integrally formed as a piezoelectric substrate constituting the piezoelectric vibrating element. The piezoelectric resonator according to claim 1, wherein: 4. The pad electrode has an Ag film of at least 20.
0 nm or more, and the total thickness of the pad electrode is 4
The piezoelectric resonator according to any one of claims 1 to 3, wherein the thickness is less than 00 nm.