JP2008124785A - Surface acoustic wave device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave device suppressing frequency variation during surface mounting. <P>SOLUTION: The surface acoustic wave device according to the present invention includes a piezoelectric substrate 11, an interdigital transducer 12 and a pad electrode provided on the piezoelectric substrate 11, a resin wall 14 provided to surround an excitation region of the interdigital electrode 12 on the piezoelectric substrate 11, a top plate 15 covering an opening portion of the resin wall 14 to seal the excitation region, an external electrode 16 provided on the top plate 15 and connected to the pad electrode 13, and a via electrode 17 provided in the top plate 15 and resin wall 14 and connecting the pad electrode 13 and external electrode 16 to each other, wherein the via electrode 17 is divided into a first via electrode 17a disposed on the side of the piezoelectric substrate 11 and a second via electrode 17b disposed on the side of the top plate 15, and the diameter of the first via electrode 17a is made smaller than the diameter of the second via electrode 17b. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surface-mount type surface acoustic wave device mainly used in mobile communication equipment.

  As a conventional surface acoustic wave device of this type, as shown in FIG. 4, in order to form the excitation region of the comb-shaped electrode 1, the excitation region of the comb-shaped electrode 1 is formed by the side wall 2 and the top plate 3 made of metal. I covered it.

As prior art document information relating to the invention of this application, for example, Patent Document 1 is known.
Japanese Patent Laid-Open No. 2004-364041

  In the conventional surface acoustic wave device described above, since the side wall 2 is formed of a hard metal, when stress is applied to the mounting surface of the surface acoustic wave device by mounting, the stress is transmitted via the side wall 2 to the piezoelectric substrate. Therefore, the piezoelectric substrate 4 is distorted to cause a frequency variation of the surface acoustic wave device.

  The present invention solves the above-described conventional problems, and an object thereof is to suppress frequency fluctuations during surface mounting in a surface acoustic wave device.

  To achieve the above object, the present invention provides a piezoelectric substrate, a comb electrode and a pad electrode provided on the piezoelectric substrate, and a resin wall provided on the piezoelectric substrate so as to surround the excitation region of the comb electrode. A top plate that covers the opening of the resin wall and seals the excitation area; an external electrode that is provided on the top plate and connected to the pad electrode; and a pad electrode that is provided in the top plate and the resin wall and connects to the external electrode The via electrode is divided into a first via electrode located on the piezoelectric substrate side and a second via electrode located on the top plate side, and the diameter of the first via electrode is set to the second via electrode. It is set as the structure made smaller than the diameter of this.

  According to the surface acoustic wave device of the present invention, it is possible to obtain an effect that frequency fluctuations during surface mounting can be suppressed.

  FIG. 1 is a cross-sectional view of a surface acoustic wave device according to an embodiment of the present invention. In the piezoelectric substrate 11, a comb electrode 12 and a pad electrode 13 provided on the piezoelectric substrate 11, and the piezoelectric substrate 11. The resin wall 14 provided so as to surround the excitation region of the comb-shaped electrode 12, the top plate 15 covering the opening of the resin wall 14 and sealing the excitation region, and the pad electrode 13 provided on the top plate 15 and connected to the pad electrode 13. And a via electrode 17 provided in the top plate 15 and the resin wall 14 to connect the pad electrode 13 and the external electrode 16, and the via electrode 17 is located on the piezoelectric substrate 11 side. 17a and the second via electrode 17b located on the top plate 15 side, and the diameter of the first via electrode 17a is made smaller than the diameter of the second via electrode 17b.

The piezoelectric substrate 11 is made of 39 ° Y-cut X-propagating LiTaO ₃ , and has a comb electrode 12 for exciting and receiving a surface acoustic wave on its surface, and a pad electrode 13 for extracting a signal from the comb electrode 12. Is formed. In addition, a resin wall 14 made of a photosensitive epoxy resin and having a thickness of 25 μm is provided on the piezoelectric substrate 11 so as to surround the outer peripheral portion of the comb-shaped electrode 12. Further, a first via electrode 17 a made of copper is formed in the resin wall 14 so as to be connected to the pad electrode 13.

  The top plate 15 covers the opening of the resin wall 14 and seals the excitation region of the comb-shaped electrode 12. In particular, a copper metal region 18 connected to the ground is provided at a portion facing the excitation region. A resin layer 19 for separating the metal region 18 and the via electrode 17 is provided in the via electrode 17 portion of the metal region 18.

  Hereinafter, a method for manufacturing a surface acoustic wave device according to an embodiment of the present invention will be described.

  First, as shown in FIG. 2A, the comb electrode 12 and the pad electrode 13 are formed on the piezoelectric substrate 11 by photolithography, and then the outer peripheral portion of the comb electrode 12 is surrounded on the piezoelectric substrate 11. In this manner, a photosensitive epoxy sheet having a thickness of 25 μm is laminated, exposed, and developed to form the resin wall 14. At this time, the first through hole 20 is formed in a portion corresponding to the first via electrode 17a.

  Next, as shown in FIG. 2B, a copper foil 21 is laminated on the upper end of the resin wall 14 and the entire opening so as to cover the opening of the resin wall 14 and seal the excitation region of the comb electrode 12. To do.

  Next, as shown in FIG. 2C, the copper foil 21 is etched to separate from the metal region 18 a portion of the through hole 20 that forms the via electrode 17 positioned at least in the signal path of the surface acoustic wave device.

  Next, as shown in FIG. 3A, a photosensitive resin is applied on the surface on which the copper foil 21 is formed, exposed and developed, and then heated and cured at 160 ° C. for 60 minutes to form the resin layer 19. Form. At this time, a second through hole 22 corresponding to the second via electrode 17b is also formed at the same time.

  Next, as shown in FIG. 3B, the exposed portion of the copper foil 21 is subjected to copper plating 21a to increase the thickness of the metal region 18 and fill the through holes 20 and 22 with copper. First, second via electrodes 17a and 17b are formed.

  Finally, as shown in FIG. 3C, the upper surface portion of the top plate 15 is polished and flattened, and then the external electrode 16 connected to the second via electrode 17b is formed.

  As described above, since the resin wall 14 is formed of a soft resin, the stress applied to the piezoelectric substrate 11 from the mounting surface can be relaxed compared to the side wall 2 using metal as in the past.

  Since the first and second via electrodes 17a and 17b are made of metal, stress is applied from the top plate 15 serving as a mounting surface, so that the first and second via electrodes 17a and 17b are interposed. Although stress is transmitted, the contact area between the piezoelectric substrate 11 and the first via electrode 17a is reduced by making the first via electrode 17a smaller than the diameter of the second via electrode 17b on the piezoelectric substrate 11 side. Thereby, since the stress which the 1st via electrode 17a gives to the piezoelectric substrate 11 can be relieved, the distortion amount in the piezoelectric substrate 11 reduces, and the frequency variation at the time of surface mounting can be suppressed.

  Further, in the above manufacturing process, the first via electrode 17a having a small diameter is provided in the resin wall 14 portion, and the second via electrode 17b having a large diameter is provided in the top plate 15 portion. Since the sizes of the through holes 20 and 22 are freely determined, the diameters of the via electrodes 17a and 17b can be easily adjusted.

  The via electrodes 17a and 17b not only function as an electric signal path, but also play a role of releasing heat generated by the excitation of the comb-shaped electrode 12 to the outside. However, the via electrodes 17a and 17b are arranged on the piezoelectric substrate 11 side. By reducing the diameter of the via electrode 17a, the amount of heat transfer is reduced. On the other hand, in the present invention, since the metal region 18 connected to the ground is provided in the top plate 15 corresponding to the excitation region, the radiant heat generated in the excitation region is released to the ground through the metal region 18. As a result, the heat dissipation of the surface acoustic wave device is enhanced, and the power durability of the surface acoustic wave device can be improved.

  The surface acoustic wave device according to the present invention has an effect of suppressing frequency fluctuations during surface mounting, such as a surface mounting type surface acoustic wave filter or a surface acoustic wave duplexer mainly used in mobile communication devices. This is useful in a surface acoustic wave device or the like.

Sectional drawing of the surface acoustic wave device in one embodiment of this invention Sectional drawing which shows the manufacturing process of the surface acoustic wave device Sectional drawing which shows the manufacturing process of the surface acoustic wave device Sectional view of a conventional surface acoustic wave device

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Piezoelectric substrate 12 Comb electrode 13 Pad electrode 14 Resin wall 15 Top plate 16 External electrode 17 Via electrode 17a 1st via electrode 17b 2nd via electrode

Claims (3)

A piezoelectric substrate; a comb electrode and a pad electrode provided on the piezoelectric substrate; a resin wall provided on the piezoelectric substrate so as to surround an excitation region of the comb electrode; and an opening of the resin wall. Covering the top plate for sealing the excitation region, an external electrode provided on the top plate and connected to the pad electrode, and provided in the top plate and the resin wall to connect the pad electrode and the external electrode A via electrode, and the via electrode is divided into a first via electrode located on the piezoelectric substrate side and a second via electrode located on the top plate side, and the diameter of the first via electrode is the first via electrode. A surface acoustic wave device characterized in that the surface acoustic wave device is smaller than the diameter of the via electrode. 2. The surface acoustic wave device according to claim 1, wherein the first via electrode is provided on the resin wall portion, and the second via electrode is provided on the top plate portion. 2. The surface acoustic wave device according to claim 1, further comprising a metal region that is grounded to a top plate portion corresponding to the excitation region portion.

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