JP2004104719A - Electrode structure for piezoelectric vibrator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode structure for a piezoelectric vibrator in which electrical and mechanical strengths are improved in the case of bonding a piezoelectric vibrating element to a ceramic package. <P>SOLUTION: A full electrode 11 is formed all over a principal surface of a crystal substrate 9 on the side of a recess by a means of deposition, and a main electrode 12 having a predetermined size as well as a lead electrode 13 extending from the main electrode 12 are similarly formed approximately in the middle of a thin portion formed with the recess on the principal surface of the crystal substrate 9 on the side of the recess by the means of deposition. Next, a pad electrode 17a is formed by sputtering to be thick in comparison with the other main electrode 12 and lead electrode 13, and conducted through the lead electrode 13. The pad electrode 17a secures the strength of the electrodes in the case of flip chip packaging using a bump 15a stuck on the pad electrode 17a and a Cr film is formed as a base when forming the pad electrode 17a to improve the bonding strength of the pad electrode and the crystal substrate. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrode structure of a piezoelectric vibrator, and more particularly to a piezoelectric vibrator having a structure in which a piezoelectric vibrating element such as a quartz vibrating element is hermetically sealed in a ceramic package, wherein the piezoelectric vibrating element is bumped on internal pad electrodes of the ceramic package. The present invention relates to an electrode structure of a piezoelectric vibrator provided with a method of connecting and fixing using such methods.
[0002]
[Prior art]
Due to the rapid progress of cost reduction and miniaturization accompanying the spread of mobile communication devices such as mobile phones, high-speed processing and high performance of OA devices, crystal units used in these communication devices and OA devices For piezoelectric devices such as these, there is a growing demand for higher frequency, smaller size, higher reliability, lower cost, and the like.
In general, as a miniaturized piezoelectric vibrator, a surface mount type (hereinafter, referred to as SMD) piezoelectric vibrator is the mainstream. A piezoelectric vibrating element is housed in a predetermined ceramic package, and the ceramic package is placed on a lid. And hermetically sealed.
[0003]
FIG. 5 is a cross-sectional view showing a structural example of a conventional SMD type crystal resonator. As shown in FIG. 5, the SMD type crystal resonator 1 has a crystal resonator element 5 connected and fixed to an internal pad electrode 3 provided on the inner bottom surface of a ceramic package 2 using a bump 4. Are electrically connected to a predetermined external connection terminal 6 via a wiring conductor that penetrates the wall of the ceramic package 2 in an airtight manner. On the other hand, the ceramic package 2 is hermetically sealed by seam welding the lid 8 to the upper end of the opening of the ceramic package 2 using a ring-shaped seam ring 7.
[0004]
As the crystal resonator element, one utilizing the fundamental wave thickness shear vibration wave of an AT-cut crystal substrate is usually used, and its resonance frequency is inversely proportional to the thickness of the crystal substrate. In order to cope with a high frequency such as 200 MHz, a thin quartz substrate is required. Therefore, in order to prevent the quartz substrate from becoming thin and mechanical strength from deteriorating, for example, a recess is formed by etching a part of the quartz substrate having a thickness of about 80 μm, and the thin portion of the recess having a thickness of about several ten μm is formed. There is known a method of obtaining a high-frequency resonance frequency by vibrating a vibrating part.
[0005]
FIG. 6 shows an example of the external structure of a conventional quartz vibrating element. FIG. 6A is a perspective view of the concave side main surface. After forming a concave portion 10 at a predetermined position of the quartz substrate 9 by etching, an entire surface electrode 11 is formed on the entire concave side main surface by means such as vapor deposition. Has formed. On the other hand, FIG. 6B is a perspective view of the flat portion-side main surface, and the main electrode 12 having a predetermined area is provided substantially at the center of the thin portion where the concave portion of the concave side main surface of the quartz substrate 9 is formed. The lead electrode 13 and the pad electrode 14a extending from the main electrode 12 and the pad electrode 14b extending from the entire surface electrode 11 are formed by means such as vapor deposition. Also, bumps 15a and 15b used for connecting and fixing the crystal resonator element to the ceramic package are attached to the pad electrodes 14a and 14b.
[0006]
FIG. 7 is a cross-sectional view of the crystal resonator shown in FIG. FIG. 7 is a cross-sectional view of the pad electrode 14a extending from the main electrode. A concave portion 10 is formed at a predetermined position on a quartz substrate 9 having a thickness of about 80 μm. Is a vibrating portion, and a full-surface electrode 11 having an electrode film thickness of about 0.1 μm is formed on the concave-side main surface. On the other hand, a main electrode 12, a lead electrode 13, and a pad electrode 14a having the same electrode thickness of about 0.1 μm are formed on the flat main surface, and a bump 15a is attached to a predetermined position of the pad electrode 14a. I have.
[0007]
[Problems to be solved by the invention]
When the thickness of the vibrating portion provided in the concave portion is reduced with the increase in the frequency of the crystal resonator, the electrode film thickness also needs to be reduced in order to obtain a desired resonance frequency. The thickness is about 0.1 μm, but when the flip-chip mounting is performed using the bump formed on the pad electrode when connecting and fixing the crystal resonator element to the ceramic package, the thickness of the pad electrode is small. There is a disadvantage that the bonding strength between the crystal resonator and the ceramic package is reduced, and the crystal resonator is easily peeled off.
Therefore, in order to eliminate such a defect, a method is used in which the electrode is processed to be a thick film in addition to only the pad electrode.
[0008]
FIG. 8 shows a state in which a thick film processing is added to a pad electrode in a conventional crystal resonator. FIG. 8 is a cross-sectional view of the pad electrode 14 a extending from the main electrode. A thick film portion 16 a of the pad electrode 14 a is additionally formed on the pad electrode 14 a provided on the quartz substrate 9.
Here, a method of forming an electrode will be described. First, a Ni film is formed on a quartz substrate, and then the formed Ni film is used as a base, and then an Au film is formed as an electrode. This is because, when the Ni film is used as a base, it is possible to prevent the electrode film from being deteriorated even during heating such as soldering performed in a later step when assembling the crystal oscillator, and it is excellent as a material of the electrode. by.
[0009]
However, if Ni is used as a base when forming the electrodes, it is less likely to be peeled off than if Au is directly formed on a quartz substrate, but flip-chip mounting is performed by using bumps on internal pad electrodes provided on the ceramic package of the quartz vibrating element. In such a case, there has been a problem that the quartz vibrating element often peels off from the internal pad electrode. Therefore, the manufacturing yield of the crystal unit is reduced, the cost is increased, and the reliability of the crystal unit is poor.
[0010]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and has been made in consideration of the fact that a quartz vibrating element is mounted on an internal pad electrode provided in a ceramic package by flip-chip mounting using a bump. It is an object of the present invention to provide an electrode structure of a piezoelectric vibrator in which electric and mechanical strength between a ceramic package and a ceramic package is enhanced.
[0011]
[Means for Solving the Problems]
To achieve the above object, the electrode structure of the piezoelectric vibrator according to the present invention has the following configuration.
The electrode structure of a piezoelectric vibrator according to claim 1, wherein the piezoelectric vibrator has a structure in which a piezoelectric vibrating element is hermetically sealed in a package, and a pad electrode formed on the piezoelectric vibrating element and an internal pad formed on the package. In a piezoelectric vibrator having a structure in which electrodes are electrically and mechanically connected, a pad electrode formed on the piezoelectric vibrator has a predetermined thickness of Cr as a base on a piezoelectric substrate and a predetermined thickness on the surface of the Cr film. It is configured to deposit Au with a film thickness.
[0012]
The electrode structure of the piezoelectric vibrator according to claim 2 is configured such that the Cr film and the Au film constituting the pad electrode are formed by a sputtering method.
[0013]
4. The electrode structure of a piezoelectric vibrator according to claim 3, wherein the electrodes other than the pad electrodes constituting the piezoelectric vibrating element are based on a Ni film having a predetermined thickness formed at a predetermined position on a piezoelectric substrate, and It is configured so that Au of a predetermined thickness is formed on the surface of the film.
[0014]
According to a fourth aspect of the present invention, the electrode structure of the piezoelectric vibrator is configured such that the Ni film and the Au film constituting electrodes other than the pad electrode are formed by a vapor deposition method.
[0015]
The electrode structure of the piezoelectric vibrator according to the fifth aspect is configured such that the pad electrode is formed after the other electrodes are formed.
[0016]
In the electrode structure of a piezoelectric vibrator according to claim 6, the piezoelectric substrate constituting the piezoelectric vibrating element has a concave portion formed by etching at a predetermined position on one surface, and the concave portion functions as a thin vibrating portion. The configuration is as follows.
[0017]
According to a seventh aspect of the present invention, the electrode structure of the piezoelectric vibrator is configured such that a pad electrode connected to the main excitation electrode of the piezoelectric vibrating element and a pad electrode inside the package are connected via a bump.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.
In the present invention, in order to strengthen the electrical and mechanical bonding between the crystal vibrating element and the ceramic package, when forming a pad electrode on the crystal vibrating element, the base of the pad electrode is made of Cr with strong bonding strength, Further, a feature is that the Au film is processed to be a thick film on the basis of the formed Cr film. When Cr is used as the base of the electrode film, the electrode film is deteriorated when the electrode film is heated, so that the excitation electrode film leads to the deterioration of the characteristics of the crystal unit. It is not suitable for use as a base, but if it is an electrode intended to electrically and mechanically join a crystal resonator element to a ceramic package, such as a pad electrode, the Cr film used as the base has been altered by overheating. However, the electrical and mechanical strength when the crystal resonator is connected and fixed to the ceramic package is improved without affecting the characteristics of the crystal resonator.
[0019]
FIG. 1 is a cross-sectional view of an external structure showing an embodiment of a crystal resonator element according to the present invention, and shows a cross-sectional view of a pad electrode 17a extending from a main electrode. FIG. 1 shows that after a concave portion 10 is formed at a predetermined position of a quartz substrate 9 by etching so that the thickness of the vibration substrate on the bottom surface of the concave portion becomes a desired thickness, an entire surface electrode 11 is vapor-deposited on the entire main surface on the concave side. It is formed by means. On the other hand, on the flat portion side main surface which is the other surface of the quartz substrate 9, an excitation main electrode having a predetermined size is provided substantially at the center of the thin portion where the concave portion is formed on the concave portion side main surface of the quartz substrate 9. The lead electrode 12 and the lead electrode 13 extending from the main electrode 12 are integrally formed by means of vapor deposition.
[0020]
Next, a pad electrode 17 a for electrically and mechanically connecting the crystal resonator element to an internal pad electrode provided on the inner bottom surface of the ceramic package is formed, and is electrically connected to the lead electrode 13. The pad electrode 17a is thicker than the other main electrodes 12 for excitation and the lead electrode 13, and is attached to the pad electrode 17a when the crystal resonator element is connected and fixed to the ceramic package. When the flip-chip mounting is performed using the bumps 15a, the strength of the electrodes is ensured. When the pad electrode 17a is formed, a Cr film is formed as a base to enhance the bonding strength between the pad electrode and the quartz substrate. Further, as described above, the bumps 15a used for connecting and fixing the crystal resonator to the ceramic package are attached to the pad electrodes 17a.
[0021]
FIG. 2 is an enlarged view of a portion surrounded by a circle A shown in FIG. 1 in a cross-sectional view of an external structure showing an embodiment of a crystal resonator element according to the present invention. 3 shows details of a pad electrode formed on a quartz substrate. Referring to FIG. 2, the quartz vibrating element is formed by forming a concave portion 10 at a predetermined position of a quartz substrate 9 by etching so that the thickness of the vibration substrate on the bottom surface of the concave portion becomes a desired thickness. Next, an entire surface electrode is formed by means of vapor deposition. For the full-surface electrode, a full-surface electrode Ni film 18 is formed as a base, and a full-surface electrode Au film 19 is formed on the surface of the full-surface electrode Ni film 18 by means of vapor deposition.
[0022]
Similarly, in the main electrode and the lead electrode, a main electrode Ni film 20 is formed as a base of the main electrode, and a main electrode Au film 21 is formed on the surface of the main electrode Ni film 20 by means of vapor deposition. A lead electrode Ni film 22 is formed as a base of the lead electrode, and a lead electrode Au film 23 is formed on the surface of the lead electrode Ni film 22 by means of vapor deposition.
[0023]
On the other hand, in the pad electrode, after the formation of the main electrode and the lead electrode is completed, the pad electrode Cr film 24a is formed as a base of the pad electrode in order to improve the mechanical strength when the crystal resonator is connected and fixed to the ceramic package. The pad electrode Au film 25a is formed into a thick film on the surface of the pad electrode Cr film 24a by sputtering. The sputtering method used for forming the pad electrode has a larger adhesion of the Cr film to the quartz substrate than the vapor deposition method, and improves the mechanical strength when the quartz vibrating element is connected and fixed to the ceramic package. . When Cr is used as a base, the pad electrode may be degraded when the crystal resonator is heated, but it does not affect the characteristics of the crystal resonator, and only the mechanical strength is enhanced. Also, bumps 15a used for connecting and fixing the crystal resonator element to the ceramic package are attached to the pad electrodes.
[0024]
FIG. 3 is a cross-sectional view of the external structure showing one embodiment of the crystal resonator element according to the present invention, and shows a cross-sectional view of the pad electrode 17b extending from the entire surface electrode. In FIG. 3, a pad electrode 17b is formed on the flat portion-side main surface of the quartz substrate 9 so as to extend from the entire surface electrode 11 formed on the concave-side main surface of the quartz substrate 9 and to interpose the side electrode 26 therebetween.
Like the pad electrode 17a, the pad electrode 17b is processed to be thicker than the other main electrodes 12 for excitation and the lead electrode 13, and when connecting and fixing the crystal resonator element to the ceramic package, When the flip-chip mounting is performed using the bump 15b attached to the pad electrode 17b, the strength of the electrode is ensured. When the pad electrode 17b is formed, a Cr film is formed as a base to enhance the bonding strength between the pad electrode and the quartz substrate.
[0025]
FIG. 4 is an enlarged view of a portion surrounded by a circle B shown in FIG. 3 in a cross-sectional view of an external structure showing an embodiment of a crystal resonator element according to the present invention. 3 shows details when each electrode is formed. Referring to FIG. 4, the full-surface electrode is formed by forming a full-surface electrode Ni film 18 as a base, and forming a full-surface electrode Au film 19 on the surface of the full-surface electrode Ni film 18 by means of vapor deposition. As the side electrode, a side electrode Ni film 27 is formed as a base, and a side electrode Au film 28 is formed on the surface of the side electrode Ni film 27 by means of vapor deposition. On the other hand, in the case of the pad electrode, after the formation of the main electrode and the lead electrode is completed, the pad electrode Cr film 24b is used as a base of the pad electrode in order to improve the mechanical strength when the crystal resonator is connected and fixed to the ceramic package. A pad electrode Au film 25b is formed into a thick film on the surface of the pad electrode Cr film 24b by means of a sputtering method.
Also, bumps 15b used for connecting and fixing the crystal resonator element to the ceramic package are attached to the pad electrodes.
[0026]
Regarding the method of forming the main electrode for excitation, since the thickness of the quartz substrate at the position where the main electrode is formed is thin, the quartz substrate is distorted when the film is formed by the sputtering method, and the characteristics of the quartz oscillator, especially over time The fluctuation may be deteriorated, and the film is formed by using the evaporation method as described above.
[0027]
Next, an example of the thickness of each of the above-described electrode films will be described. The underlayers formed when forming each of the electrodes include a front electrode Ni film 18, a main electrode Ni film 20, a lead electrode Ni film 22, and a side electrode. The Ni film 27 and the pad electrode Cr films 24a and 24b are both about 70 °, and the metal layers formed on the surface of each underlayer are a front electrode Au film 19, a main electrode Au film 21, a lead electrode Au film 23, and a side surface. The thickness of each of the electrode Au films 28 is about 0.1 μm, and the pad electrode Au films 25a and 25b processed to be thick are formed to be about 0.2 to 0.4 μm.
[0028]
Further, according to this embodiment, the pad electrode is formed last after the main electrode for excitation is formed. Therefore, it is possible to prevent a phenomenon in which the surface of the pad electrode is contaminated during a film forming process of another process such as another main electrode, so that it is difficult for a bump to be attached to the pad electrode to adhere. The bumps are desirably attached to the pad electrode immediately after the pad electrode is formed.
[0029]
Further, in the present embodiment, the pad electrode is electrically conductively fixed via the bump. However, the bonding strength can be enhanced even with another conductive connection member, for example, a conductive adhesive.
[0030]
Further, in this embodiment, one electrode is used as the whole surface electrode, but any electrode may be used as long as it is disposed opposite to the other electrode via the piezoelectric substrate.
[0031]
【The invention's effect】
As described above, according to the present invention, the following excellent effects can be obtained.
According to the first aspect of the present invention, the pad electrode of the piezoelectric vibrating element is made of Cr of a predetermined thickness as a base and Au of a predetermined thickness is formed on the surface of the Cr film. This has an excellent effect that the mechanical bonding strength can be extremely improved.
[0032]
According to the second aspect of the present invention, the Cr film and the Au film constituting the pad electrode are formed by the sputtering method, so that the adhesion at the interface between the piezoelectric substrate and the Cr film and the interface between the Cr film and the Au film. Is extremely improved.
[0033]
According to the third aspect of the present invention, the electrodes other than the pads of the piezoelectric substrate are formed on the surface of the Ni film with the Au film having the predetermined thickness on the basis of the Ni film having the predetermined thickness. In the treatment, there is an excellent effect that deterioration of the electrode film can be prevented.
[0034]
According to the fourth aspect of the present invention, the electrodes other than the pads of the piezoelectric substrate are formed by depositing Au of a predetermined thickness on the surface of the Ni film by a vapor deposition method on the basis of a Ni film of a predetermined thickness. An excellent effect is obtained in that distortion of the substrate is prevented from occurring, and furthermore, deterioration due to aging of the electrical characteristics can be prevented.
[0035]
Since the pad electrode is formed after the other electrodes are formed, the invention described in claim 5 has an excellent effect that the thick film processing of the pad electrode can be performed under optimum conditions.
[0036]
According to the sixth aspect of the present invention, since the piezoelectric substrate is a depressed type piezoelectric substrate having a thin vibrating portion, an excellent effect that an ultra-thin piezoelectric vibrator realizing a high frequency can be provided.
[0037]
According to the seventh aspect of the present invention, since the piezoelectric vibration element is bonded to the package via the bump, an excellent effect of being able to provide a flip-chip mounted piezoelectric vibrator having improved mechanical bonding strength is provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an external structure showing a crystal vibrating element according to an embodiment of the present invention, showing a cross-sectional view of a pad electrode 17a extending from a main electrode.
FIG. 2 is an enlarged view of a portion surrounded by a circle A shown in FIG. 1 in a cross-sectional view of an external structure showing one embodiment of a crystal resonator element according to the present invention.
FIG. 3 is a cross-sectional view of an external structure showing an embodiment of a crystal resonator element according to the present invention, and shows a cross-sectional view of a pad electrode 17b extending from an entire surface electrode.
FIG. 4 is an enlarged view of a portion surrounded by a circle B shown in FIG. 3 in a cross-sectional view of an external structure showing one embodiment of a crystal resonator element according to the present invention.
FIG. 5 is a cross-sectional view illustrating a structural example of a conventional SMD type crystal resonator.
FIG. 6 shows an example of an external structure of a conventional crystal resonator element.
7 is a cross-sectional view of the quartz-crystal vibrating element shown in FIG.
FIG. 8 shows a state in which a thick film processing is added to a pad electrode in a conventional crystal resonator element.
[Explanation of symbols]
1. Crystal oscillator, 2. Ceramic package,
3. Internal pad electrode, 4. Bump,
5. Crystal oscillator, 6. External connection terminal,
7. Seam ring, 8. Lid,
9 ··· quartz substrate, 10 ··· recess
11 ・ ・ Overall electrode 、 12 ・ ・ Main electrode 、
13. Lead electrode, 14a, 14b Pad electrode,
15a, 15b, bump, 16, thick film part,
17a, 17b ··· pad electrode, 18 · · · full surface electrode Ni film,
19 ・ ・ Full-surface electrode Au film, 20 ・ ・ Main electrode Ni film,
21 ·· Main electrode Au film, 22 ·· Lead electrode Ni film,
23 ··· Lead electrode Au film, 24a, 24b · · Pad electrode Cr film,
25a, 25b ··· Pad electrode Au film 26 ··· Side electrode 27 ··· Side electrode Ni film
28 ・ ・ Side electrode Au film

Claims (7)

A piezoelectric vibrator having a structure in which a piezoelectric vibrating element is hermetically sealed in a package, wherein a pad electrode formed on the piezoelectric vibrating element and an internal pad electrode formed on the package are electrically and mechanically connected. In the piezoelectric vibrator,
A pad electrode formed on the piezoelectric vibrating element is formed by depositing a predetermined thickness of Au on a surface of the Cr film with a predetermined thickness of Cr as a base on a piezoelectric substrate. Child electrode structure. 2. The electrode structure of a piezoelectric vibrator according to claim 1, wherein the Cr film and the Au film constituting the pad electrode are formed by a sputtering method. Electrodes other than the pad electrodes constituting the piezoelectric vibrating element are based on a Ni film having a predetermined thickness formed at a predetermined position on a piezoelectric substrate, and a Au film having a predetermined thickness is formed on the surface of the Ni film. The electrode structure of a piezoelectric vibrator according to claim 1, wherein: 4. The electrode structure of a piezoelectric vibrator according to claim 3, wherein the Ni film and the Au film constituting electrodes other than the pad electrode are formed by a vapor deposition method. 5. The electrode structure for a piezoelectric vibrator according to claim 1, wherein the pad electrode is formed after other electrodes are formed. 6. The piezoelectric substrate constituting the piezoelectric vibrating element includes a concave portion formed by etching at a predetermined position on one surface, and the concave portion functions as a thin vibrating portion. The electrode structure of the piezoelectric vibrator according to any one of the above. 7. The electrode structure of a piezoelectric vibrator according to claim 1, wherein a pad electrode connected to the main excitation electrode of the piezoelectric vibrating element and a pad electrode inside the package are connected via a bump.

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