JP2003229505A - Lid for piezoelectric device, piezoelectric device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lid for a piezoelectric device with which frequency shift amount of the piezoelectric device concurrent seam welding of the lid. <P>SOLUTION: A lid body 11 is formed from a super inver material or an inver material of small coefficient of cotton expansion. Meanwhile, a lower layer film 13 of electrolytic nickel plating is formed on the surface of the lid body 11. Further, an upper layer film 15 of electroless nickel plating is formed thereon. Consequently, if a temperature of the lid is raised up to a melting point of the electroless nickel plating, the lid can be seam-welded, and the amount of thermal expansion of the lid at seam welding is small. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric device lid, a piezoelectric device manufacturing method and a piezoelectric device, and more particularly to a piezoelectric device lid mounting a SAW chip, a piezoelectric device manufacturing method and a piezoelectric device. Is.

[0002]

2. Description of the Related Art Piezoelectric devices such as a piezoelectric vibrator and a piezoelectric oscillator are widely used to obtain a constant frequency in an electric circuit. The piezoelectric device has a piezoelectric vibrating piece mounted inside a package and an external terminal capable of conducting electricity to an excitation electrode of the piezoelectric vibrating piece formed outside the package.

3 and 4 show an example of the SAW device 1 in which the SAW chip 20 is mounted inside the package 30. 3 is a plan sectional view taken along the line AA of FIG. 4, and FIG. 4 is a front sectional view taken along the line BB of FIG. In the SAW device 1, the lid (lid member) 110 is fixed to the package 30 and the inside of the package 30 is sealed in a nitrogen atmosphere or a vacuum, so that the SA
This prevents the frequency of the W device 1 from changing with time. Figure 7
A cross-sectional view of a lid according to the related art is shown in FIG. Lid 110
In addition to forming the lid main body 111 with a metal material such as Kovar, electrolytic nickel plating or electroless nickel plating 113 is applied to the surface of the lid main body 111 to prevent leakage due to corrosion of the lid main body 111.

On the other hand, as shown in FIG.
The lid 110 is fixedly attached to the lid 110 by seam welding or the like. That is, the roller electrode 40 is brought into contact with the peripheral portion of the lid 110 to flow an electric current to raise the temperature of the lid 110 to melt the electrolytic nickel plating or the electroless nickel plating on the surface of the lid 110 and the lid 110 and the seam ring 34. And are fixed. The roller electrode 40 is rotated and moved along the peripheral edge of the lid 110 to fix the entire circumference of the lid 110 to the package.

[0005]

In the seam welding described above, for example, when the electrolytic nickel plating is melted, it is necessary to raise the temperature of the lid 110 up to about 1450 ° C. which is the melting point of the electrolytic nickel plating. . Since only the temperature of the lid 110 rises during seam welding and the temperature of the seam ring 34 and the package 30 does not rise so much, only the lid 110 is fixed to the seam ring 34 in a thermally expanded state as indicated by the arrow 18. As a result, as shown in FIG.
As described above, as the heat shrinks, a bending moment acts on the package 30. As a result, a bending moment also acts on the SAW chip 20 mounted on the package 30, and the pitch of the comb-teeth-shaped IDT electrodes 24 (see FIG. 3) formed on the surface of the SAW chip 20 is narrowed and the frequency is increased. There is a problem of shifting in the positive direction. Further, when electroless nickel plating having a low melting point (melting point 750 ° C.) is used to reduce this thermal deformation, there is a problem that the corrosion resistance of the lid is extremely lowered.

In view of the above problems, the present invention aims to provide a lid of a piezoelectric device, a method of manufacturing the piezoelectric device, and a piezoelectric device capable of reducing the frequency shift amount of the piezoelectric device due to seam welding of the lid. And It is another object of the present invention to provide a lid for a piezoelectric device, a method for manufacturing the piezoelectric device, and a piezoelectric device that can ensure the corrosion resistance of the lid.

[0007]

In order to achieve the above object, a lid of a piezoelectric device according to the present invention is a lid for encapsulating a package of a piezoelectric device, wherein a lower layer of a corrosion resistant material is formed on the surface of the lid body. While forming the film, the upper layer film was formed of a material having a lower melting point than the lower layer film.

In this case, seam welding is possible by raising the temperature of the lid to the melting point of the upper layer film. This reduces the amount of thermal expansion of the lid during seam welding,
The heat shrinkage of the lid after seam welding also decreases. Therefore, the frequency shift amount of the piezoelectric device due to the seam welding of the lid can be reduced. Further, even if the temperature of the lid is raised to the melting point of the upper layer film, the lower layer film having a higher melting point than this does not melt. Therefore, the corrosion resistance of the lid can be secured. Further, in a lid for sealing a package of a piezoelectric device, a lower layer film was formed on the surface of the lid body by electrolytic nickel plating, and an upper layer film was formed by electroless nickel plating.

In this case, if the temperature of the lid is raised to about 750 ° C., which is the melting point of electroless nickel plating, seam welding becomes possible. This reduces the amount of thermal expansion of the lid during seam welding, and also reduces the amount of thermal contraction of the lid after seam welding. Therefore, the frequency shift amount of the piezoelectric device due to the seam welding of the lid can be reduced. Even if the temperature of the lid is raised to 750 ° C. which is the melting point of the electroless nickel plating, the melting point is 14
Electrolytic nickel plating at 50 ° C does not melt. Therefore, the corrosion resistance of the lid can be secured.

The lid body may be made of Invar material or Super Invar material. Since the Invar material or Super Invar material has a smaller linear expansion coefficient than Kovar material used for conventional lids, the thermal expansion amount of the lid during seam welding decreases and the thermal contraction amount of the lid after seam welding also decreases. descend. Therefore, the frequency shift amount of the piezoelectric device due to the seam welding of the lid can be reduced.

On the other hand, a method of manufacturing a piezoelectric device according to the present invention uses the lid of the piezoelectric device according to any one of claims 1 to 3, and melts only the upper layer film to form the lid into the package. The structure is fixed. As a result, it is possible to reduce the frequency shift amount of the piezoelectric device due to seam welding of the lid. In addition, the corrosion resistance of the lid can be secured.

On the other hand, the piezoelectric device according to the present invention is manufactured by using the lid of the piezoelectric device according to any one of claims 1 to 3. Further, the piezoelectric device is manufactured by using the method for manufacturing a piezoelectric device according to claim 4. This makes it possible to provide a piezoelectric device having a predetermined frequency. Further, it is possible to provide a piezoelectric device having excellent corrosion resistance.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of a lid for a piezoelectric device, a method for manufacturing a piezoelectric device and a piezoelectric device according to the present invention will be described in detail with reference to the accompanying drawings. It should be noted that what is described below is only one aspect of the embodiment of the present invention, and the present invention is not limited thereto.

FIG. 1 is a sectional view of the lid of the piezoelectric device according to the embodiment. In the lid 10 of the piezoelectric device according to the present embodiment, while the lid body 11 is formed of the Invar material, the lower layer film 13 is formed on the surface of the lid body 11 by electrolytic nickel plating, and the upper layer film is formed by electroless nickel plating. 15 is formed.

Whereas the conventional lid body is made of Kovar material, the lid body 11 according to this embodiment is made of Invar material. Specifically, a blank is formed from a steel plate of an Invar material by press working, and then burryless working is performed to form the lid main body 11. The lid body 11 may be made of a Super Invar material. Table 1 shows the composition ratio and linear expansion coefficient of each material.

[Table 1]

Further, in the conventional lid, either the electrolytic nickel plating or the electroless nickel plating is applied to the surface of the lid main body, whereas in the present embodiment, the surface of the lid main body 11 is subjected to the electrolytic nickel plating. Underlayer film 1
3 and the upper layer film 15 is formed by electroless nickel plating. Electrolytic nickel plating is to deposit nickel ions in a solution on the surface of a lid by supplying electrons from an external power source through the lid. Nickel sulfate or the like is used as the nickel ion source. Electrolytic nickel plating has a high ductility of the deposits and can obtain a plating excellent in corrosion resistance, but has a problem that the melting point of the deposits becomes high.

On the other hand, the electroless nickel plating is to deposit nickel ions in the solution on the surface of the lid by supplying electrons from the reducing agent in the solution. Nickel sulfate or the like is used as the nickel ion source, and hypophosphite or the like is used as the reducing agent. Since electroless nickel plating reduces the ductility of precipitates, microcracks are more likely to occur and corrosion resistance is inferior to that of electrolytic nickel plating, but precipitates with a low melting point are obtained. Table 2 shows evaluation of corrosion resistance and melting point of electrolytic nickel plating and electroless nickel plating. The corrosion resistance in Table 2 is evaluated by a salt spray test (8 days) with 10 points when no rust was generated and 0 points when rust was generated on 50% of the surface area.

[Table 2]

Therefore, in this embodiment, after the lid body 11 formed as described above is washed and dried, the lower layer film 13 is formed on its surface by electrolytic nickel plating. The thickness of the lower layer film is about 2 to 3 μm, preferably 2.5 μm.
It is formed to about m. It is also possible to form the lower layer film by Zn-P plating. Further, after washing and drying this, the upper layer film 15 is formed on the surface by electroless nickel plating. The upper layer film is formed to a thickness of about 3 to 5 μm, preferably about 4 μm. in this way,
A lid 10 that is double-plated is formed. When impurities are present on the lid surface, the impurities are gasified due to the temperature rise during seam welding and adhere to the surface of the SAW chip, which causes the frequency of the SAW device to be shifted. Therefore, it is desirable to finally clean and dry the lid to remove impurities adhering to the surface.

Next, a method of manufacturing a SAW device using the lid according to this embodiment described above will be described. FIG. 2 shows a flowchart of the method for manufacturing the SAW device. First, a SAW chip is formed. Specifically, as shown in FIG. 3, the IDT electrode 24 is formed of a metal material such as aluminum on the SAW propagation surface 22 of the piezoelectric substrate made of a piezoelectric material such as quartz. The IDT electrode 24 is composed of a comb-teeth-shaped positive electrode side electrode and a negative electrode side electrode, and electrode fingers of both electrodes are alternately combined and arranged in parallel. In the SAW chip 20, surface acoustic waves having the same wavelength as the pitch of the electrode fingers of the IDT electrodes 24 are excited. In addition, an electrode pad 25 that conducts electricity to the IDT electrode 24 is formed on a side portion of the IDT electrode 24. Further, surface acoustic wave reflectors 26 are formed at both ends of the IDT electrode 24.

Further, a package for mounting the SAW chip is formed. As shown in FIG. 4, the package 30 is formed by stacking blank ceramic sheets in a predetermined shape and firing them. A cavity 32 for mounting the SAW chip 20 is provided at the center of the package 30.
To provide. In addition, a wiring pattern is formed on the inner surface of the cavity 32 to ensure electrical connection with external terminals (not shown) of the package. Then, at the opening edge of the cavity 32,
Secure the seam ring 34. The seam ring 34 is formed of Kovar material or the like, and is plated with Ni underlay Au.

Then, the SAW chip 20 is die-attached (S70). Specifically, SA is applied to the bottom of the cavity 32 in the package 30 via the adhesive 28.
The W chip 20 is mounted. As the adhesive 28, it is preferable to use a silicone-based or polybutadiene rubber-based adhesive that exhibits elasticity after curing. Also, the adhesive 28
Is preferably applied thickly. Further, the adhesive 28
It is preferable to apply a small area to a portion corresponding to the center of the back surface of the SAW chip 20. As a result, even if the package is deformed, the amount of deformation of the SAW chip accompanying it is reduced, and the amount of frequency shift can be reduced.

Next, the SAW chip 20 is wire-bonded (S72). Specifically, the electrode pad of the mounted SAW chip 20 and the wiring pattern of the package 30 are connected by an aluminum wire 29 or the like. This allows the SAW chip 2 to be connected to the external terminals (not shown) of the package 30.
It becomes possible to energize the IDT electrode of 0.

Next, the frequency of the SAW chip 20 is adjusted (S74). Specifically, while measuring the frequency of the SAW chip 20, by etching the piezoelectric substrate on which the IDT electrode is formed, the frequency is made to match the target value. The piezoelectric substrate is etched by dry etching.
As the etching gas, a gas containing fluorine, such as a CF-based gas such as C ₄ F ₈ or an SF-based gas such as SF ₆ , can be used. The etching gas is turned into plasma to generate fluorine radicals, and the piezoelectric substrate is treated with the fluorine radicals to perform etching.

Next, the inside of the package 30 is sealed in a nitrogen atmosphere (S76). Specifically, first, the seam welding apparatus is held in a nitrogen atmosphere, and the package 30 having the SAW chip 20 mounted thereon is set at the welding work position (S7).
8). Next, the lid 10 according to the present embodiment configured as described above is placed on the package 30 (S80). At that time, the entire periphery of the lid 10 is arranged on the surface of the seam ring 34 to close the opening of the cavity 32. The inside of the package 30 may be sealed in vacuum.

Next, the lid is seam welded (S8).
2). FIG. 5 shows an explanatory view of the seam welding process. Note that FIG.
[Fig. 5] is an enlarged view of a C portion of Fig. 4. Specifically, as shown in FIG. 5, the side surface of the roller electrode 40 is brought into contact with the peripheral portion of the lid 10, and an electric current is caused to flow from the roller electrode 40. Then,
A portion having a high electric resistance, such as a portion between the roller electrode 40 and the lid 10 or a portion between the lid 10 and the seam ring 34, generates heat to raise the temperature of the lid 10. The current of the roller electrode 40 is adjusted so that the temperature of the lid 10 rises to about 750 ° C., which is the melting point of electroless nickel plating. Due to this temperature rise, the upper layer film 15 formed on the surface of the lid 10 by electroless nickel plating is dissolved, and this serves as a sealing material to hermetically seal between the lid 10 and the seam ring 34. The lower layer film 13 formed by electrolytic nickel plating does not melt because its melting point is 1450 ° C. Further, since the lid main body 11 is formed of the Invar material or the Super Invar material having a small linear expansion coefficient, the lid 10 is fixed to the seam ring without being greatly expanded due to the temperature rise.

Then, while rotating the roller electrode 40,
By moving along the periphery of the lid 10, the space between the lid 10 and the seam ring 34 is hermetically sealed over the entire circumference. As described above, the inside of the package 30 is sealed in the nitrogen atmosphere. Finally, the SAW device is inspected for electrical characteristics and the like (S84). From the above,
The SAW device is completed.

The lid of the piezoelectric device according to this embodiment described above can reduce the frequency shift amount of the SAW device. In this respect, in the conventional lid, only the surface of the lid body is electrolytically nickel plated. Therefore, when seam welding the lid, it is necessary to raise the temperature of the lid to about 1450 ° C. which is the melting point of the electrolytic nickel plating. It was At this time, the temperature of the lid is 1450
Although the temperature rises to about 0 ° C, the seam ring remains at about 400 ° C and the package temperature hardly rises.
Therefore, only the lid is fixed to the seam ring in a thermally expanded state. As a result, as shown in FIG.
As the temperature of and decreases and heat shrinks as shown by arrow 19,
A bending moment acts on the package 30. As a result, a bending moment also acts on the SAW chip 20 mounted on the package 30, and the SAW chip 2
There is a problem that the pitch of the comb-teeth IDT electrodes formed on the surface of 0 becomes narrow and the frequency shifts in the positive direction.

However, in the lid of the piezoelectric device according to this embodiment, the lower layer film is formed on the surface of the lid body by electrolytic nickel plating and the upper layer film is formed by electroless nickel plating. In this case, seam welding is possible if the temperature of the lid is raised to about 750 ° C., which is the melting point of electroless nickel plating. This reduces the amount of thermal expansion of the lid during seam welding,
The heat shrinkage of the lid after seam welding also decreases, and SA
The bending moment acting on the W tip can be reduced. Therefore, the frequency shift amount of the SAW device can be reduced. Further, it is possible to reduce variations in the amount of frequency shift.

When only the electroless nickel plating is applied to the surface of the lid body, it becomes difficult to secure the corrosion resistance of the lid. That is, the electroless nickel plating is melted by seam welding, and only a thin film remains at the contact portion with the roller electrode, but since electroless nickel plating has low ductility, microcracks occur in the thin film portion, The lid itself may be corroded. If the corrosion penetrates the lid and leaks between the inside and the outside of the package, impurities adhere to the surface of the SAW chip and
The frequency of the device will change.

However, in the lid of the piezoelectric device according to the present embodiment, the lower layer film is formed on the surface of the lid body by electrolytic nickel plating and the upper layer film is formed by electroless nickel plating. As a result, at seam welding, the melting point of the electroless nickel plating is 75
Even if the lid temperature is raised to 0 ° C, the melting point is 1450.
Electrolytic nickel plating at ℃ does not dissolve. Therefore, the corrosion resistance of the lid can be secured.

Generally, in plating, pinholes are unavoidably generated, so there is a risk that the lid may be corroded through the pinhole reaching the lid body. However, in this embodiment, since the lid body is double-plated, the probability of pinholes reaching the lid body can be significantly reduced. Therefore, the corrosion resistance of the lid can be secured.

In the seam welding process, the lids are automatically supplied one by one from the laminated lid group to the package. However, if the lid is magnetized, the adjacent lids are in close contact with each other, which makes it difficult to automatically supply the lid. However, in the lid of the piezoelectric device according to the present embodiment, since the electroless nickel plating forming the upper layer film is a non-magnetic material, it is possible to prevent the adjacent lids from adhering to each other. This enables automatic supply of the lid.

The lid of the piezoelectric device according to the present embodiment has a structure in which the lid body is made of an Invar material or a Super Invar material. Since the Invar material or Super Invar material has a smaller linear expansion coefficient than Kovar material used for conventional lids, the thermal expansion amount of the lid during seam welding decreases and the thermal contraction amount of the lid after seam welding also decreases. The bending moment acting on the SAW chip can be reduced. Therefore, the frequency shift amount of the piezoelectric device can be reduced.

As shown in Table 1, since the Invar material and the Super Invar material contain a large amount of Fe, they have the property of being corroded more easily than the Kovar material. However, in this embodiment, since the lid body made of the Invar material or the Super Invar material is subjected to double plating, it is possible to effectively prevent corrosion of the lid body.

The present inventor measured a frequency shift amount by seam-welding a plurality of lids having different lid main bodies and different plating methods to the package. The result is shown in FIG. In the case of the conventional lid in which only the electrolytic nickel plating is applied to the surface of the lid body made of Kovar material in FIG. 6, the frequency is largely shifted to the plus side and is still varied. However, in the case of the lid according to the present embodiment in which the lower layer film is formed by electrolytic nickel plating on the surface of the lid body made of Super Invar material, and the upper layer film is formed by electroless nickel plating,
The amount of frequency shift is small and the variation is small. This confirmed the excellent effect of the lid according to the present embodiment described above.

In the above embodiment, the case where the lid of the piezoelectric device according to the present invention is applied to the lid of the SAW device has been described as an example. However, the lid of the piezoelectric device according to the present invention is, for example, AT cut. It is also possible to apply to a lid of a piezoelectric device mounted with a piezoelectric vibrating piece. In particular, in the case of a piezoelectric device in which both ends of the AT-cut piezoelectric vibrating piece are fixed to the package, the piezoelectric vibrating piece can also be deformed due to thermal contraction of the lid, so use the lid of the piezoelectric device according to the present invention. As a result, the frequency shift amount can be reduced.

[0037]

EFFECT OF THE INVENTION In a lid for sealing a package of a piezoelectric device, a lower layer film is formed on the surface of the lid body by a corrosion resistant material, and an upper layer film is formed by a material having a lower melting point than the lower layer film. It is possible to reduce the frequency shift amount of the piezoelectric device due to seam welding of the lid.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a lid of a SAW device according to an embodiment.

FIG. 2 is a flowchart of a method for manufacturing a SAW device.

FIG. 3 is an explanatory diagram of a SAW device, which is an A- of FIG.
It is a plane sectional view in the A line.

FIG. 4 is an explanatory diagram of a SAW device, and is a B- of FIG.
It is a front sectional view in the B line.

5 is an explanatory view of a seam welding process, and is an enlarged view of a C portion of FIG. 4.

FIG. 6 is a graph of measurement results of frequency shift amount.

FIG. 7 is a cross-sectional view of a lid of a SAW device according to a conventional technique.

FIG. 8 is an explanatory diagram of a frequency change due to thermal contraction of the lid.

[Explanation of symbols]

1 ………… SAW device, 10 ………… Lid, 11 ……
… Lid body, 13 ……… Lower layer film, 15 ……… Upper layer film,
18, 19 ......... Arrow, 20 ......... SAW chip, 22
……… SAW propagation surface, 24 ………… IDT electrode, 25 ……
… Electrode pad, 26 ……… Reflector, 28 ……… Adhesive,
29 ………… Aluminum wire, 30 ………… Package, 32 ……
... Cavity, 34 ... Seam ring, 40 Roller electrode, 110 ... Lid, 111 ... Lid body, 113 ... Electrolytic nickel plating.

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[Procedure amendment]

[Submission date] March 24, 2003 (2003.3.2
4)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0015

[Correction method] Change

[Correction content]

Whereas the conventional lid body is made of Kovar material, the lid body 11 according to this embodiment is made of Invar material. Specifically, a blank is formed from a steel plate of an Invar material by press working, and then burryless working is performed to form the lid main body 11. The lid body 11 may be made of a Super Invar material. Table 1 shows the composition ratio and linear expansion coefficient of each material.

[Table 1]

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Claims (6)

[Claims] 1. A lid for sealing a package of a piezoelectric device, wherein a lower layer film is formed of a corrosion-resistant material on the surface of the lid body, and an upper layer film is formed of a material having a melting point lower than that of the lower layer film. A lid for a piezoelectric device characterized by. 2. A lid for sealing a package of a piezoelectric device, wherein a lower layer film is formed on the surface of the lid body by electrolytic nickel plating and an upper layer film is formed by electroless nickel plating. Piezoelectric device lid. 3. The lid for a piezoelectric device according to claim 1, wherein the lid body is made of an Invar material or a Super Invar material. 4. A piezoelectric device manufacturing method, characterized in that the piezoelectric device lid according to any one of claims 1 to 3 is used, and only the upper layer film is melted to fix the lid to the package. Method. 5. A piezoelectric device manufactured by using the lid of the piezoelectric device according to claim 1. 6. A piezoelectric device manufactured by using the method for manufacturing a piezoelectric device according to claim 4.