JP4510982B2 - Surface acoustic wave device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface acoustic wave device which is a resonator or a frequency band filter built in a mobile wireless device such as an automobile phone or a cellular phone.
[0002]
[Prior art and its problems]
In recent years, many surface acoustic wave resonators and surface acoustic wave filters have been used as electronic components such as frequency filters (hereinafter referred to as filters), delay lines, transmitters, etc. for electronic devices that communicate using radio waves. Is used. In particular, in the field of mobile communication, it is widely used as a filter for RF (Radio Frequency: radio frequency or high frequency) blocks and IF (Intermediate Frequency) blocks of mobile terminal devices such as mobile phones. In the future, it is desired to reduce the weight and size of parts in a communication system using mobile wireless devices such as automobile phones and mobile phones.
[0003]
The basic structure of a conventional surface acoustic wave (hereinafter also referred to as SAW) device is that a plurality of pairs of comb-like excitation electrodes (Inter Digital Transducers, IDT electrodes) are arranged on the surface of a piezoelectric substrate. The element is placed in a ceramic casing.
[0004]
FIG. 5 shows a conventional example. The excitation electrode 1 is formed by forming a conductive film such as an Al or Al-Cu alloy on a piezoelectric substrate 2 made of, for example, a 36 ° Y-cut X-propagating lithium tantalate single crystal by vapor deposition, sputtering, etc. It is formed by patterning a conductive film so as to be a fine electrode by lithography.
[0005]
Further, the SAW element 3 is manufactured by cutting the piezoelectric substrate 2 on which the excitation electrode 1 is formed with a dicing saw. Further, the SAW element 3 is placed in a case 4 made of ceramic and fixed with an adhesive resin 5, and the input / output electrode 6 or the ground electrode 7 of the case 4 is connected to the lead electrodes 8 and 9 with the wire 10. Connect with. And in order to give weather resistance, the housing | casing 4 and the cover body 11 are sealed with the sealing material 12 of seam welding or solder, or resin.
[0006]
As described above, in the conventional SAW device, although the weight and size are required, the housing is larger than the element, and it is necessary to secure a space in the housing by wire bonding. Therefore, there is a problem that the SAW device is increased in size.
[0007]
On the other hand, in recent years, proposals have been made to reduce the weight and size of the entire apparatus by performing flip chip connection using bumps (see, for example, JP-A-11-150440).
[0008]
According to this method, the space required for wire bonding becomes unnecessary by performing electrical connection by flip-chip connection. For this reason, it can be made smaller than a conventional SAW device by wire connection.
[0009]
However, in any of the above methods, it is necessary to form electrodes on the surface of the flip-chip base substrate or package. In addition, it is necessary to route the electrode from the connection portion with the SAW element to the lower surface of the base substrate to be flip-chip or the lower surface of the package, which requires a lot of man-hours for manufacturing the base substrate or the package.
[0010]
Therefore, an object of the present invention is to provide a SAW device that can be miniaturized to the same size as the element size and that is easy to manufacture.
[0011]
In order to achieve the above object, a surface acoustic wave device according to the present invention includes a surface acoustic wave device having an excitation electrode on a lower surface and a lead electrode electrically connected to the excitation electrode, and the excitation electrode. A base substrate that is disposed so as to face the surface acoustic wave element through an existing sealed space, and is joined to the surface acoustic wave element outside the sealed space in a plan view, and the upper part is the drawer A conductive material for connecting an external circuit electrically connected to the electrode, and for connecting the external circuit
The conductive material is located outside the sealing space in a plan view and does not exist inside the sealing space, and the base substrate is made of a material capable of anisotropic etching, A concave portion formed by anisotropic etching is provided in a portion of the base substrate facing the excitation electrode .
The surface acoustic wave device according to the present invention is characterized in that a lower portion of the conductive material is led out to a height position below the sealing space.
Further, in the surface acoustic wave device according to the present invention, the base substrate has a through hole at a position corresponding to a connection portion between the conductive material and the extraction electrode, and a lower portion of the conductive material is the through hole. It is derived | led-out to the height position below the said sealing space through this.
A mounting structure according to the present invention includes the surface acoustic wave device described above and an external circuit board on which the surface acoustic wave device is mounted.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of a surface acoustic wave device according to the present invention will be described in detail with reference to the drawings.
[0013]
FIG. 1 shows a cross-sectional view of a surface acoustic wave device S1 according to the present invention. FIG. 2 shows a top perspective view of the surface acoustic wave device S1. Here, FIG. 1 is a cross-sectional view taken along line AA ′ of FIG.
[0014]
In the surface acoustic wave device S1, the excitation electrode 1 and lead electrodes 8 and 9 (8 is a signal electrode and 9 is a ground electrode) connected to the excitation electrode 1 are formed on the lower surface of the piezoelectric substrate 2 on the base substrate 14. The surface acoustic wave element 3 is placed, and a recess 16 that faces the excitation electrode 1 and a through hole 15 that faces the extraction electrodes 8 and 9 are formed in the base substrate 14, respectively, and the through hole 15 is a first conductive material. The metal film 17 and the second conductive material 18 are filled to form an external circuit connection portion.
[0015]
Here, on the functional surface of the surface acoustic wave element 3, for example, a frame-shaped sealing material 12 made of an insulating material resin is applied and formed. The surface acoustic wave element 3 and the base substrate 14 are joined and hermetically sealed by the sealing material 12.
[0016]
The through-hole 15 is filled with a conductive material 18, for example, a resin mixed with solder or a metal filler, but the conductive material 18 is printed and filled so that the surface of the lower surface of the base substrate 14 is convex. Thus, by making the conductive material 18 convex, the adhesion of the surface acoustic wave device S1 particularly from the signal electrode to the electrode of the external circuit mounting substrate becomes extremely easy and good.
[0017]
A metal film 17 is deposited on the side surface of the through hole 15 in order to improve the adhesion between the conductive material 18 and the base substrate 14 and the extraction electrodes 8 and 9 of the surface acoustic wave element 3.
[0018]
In addition, the concave portion 16 and the through hole 15 of the base substrate 14 can be formed by using the (100) plane or the (110 plane) of the Si single crystal substrate capable of anisotropic etching as the main plane. Alternatively, the anisotropic etching using the large difference in etching rate between the (110) plane and the (111) plane facilitates the production of the concave portion 16 and the through hole 15 having the inclined surface of the (111) plane. The alkaline etchant used for anisotropic etching is preferably an alkaline aqueous solution such as KOH, NaOH, EPW (ethylenediamine + pyrocatechol + water), hydrazine, TMAH (tetramethylammonium hydroxide).
[0019]
When the sealing material 12 sags in the recess 16 (deforms during heating or pressurization), the excitation electrode 1 on the surface acoustic wave element 3 may be hindered and the characteristics may be adversely affected. By forming the inclined surface of the minute space at the site, the amount of resin sagging can be suppressed as much as possible by the surface tension of the resin. Therefore, it is preferable to use the anisotropic etching method as described above.
[0020]
Further, since the concave portion 16 is formed by anisotropic etching at a portion facing the excitation electrode 1 of the surface acoustic wave element 3 on the upper surface of the base substrate 14, the excitation electrode is independent of the electrode thickness of the surface acoustic wave element 3. A sufficient vibration space 19 can be secured.
[0021]
Further, since the conductive material 18 or the like is printed and filled in the through hole 15, bubbles are not easily contained in the conductor, and therefore, the anisotropic etching method capable of inclining the through hole 15 is used. preferable.
[0022]
Next, another embodiment shown in FIG. 3 will be described. Here, since the frame-shaped sealing material 12 is insulative, the extraction electrode 8 that is an input / output electrode and the extraction electrode 9 that is a ground electrode are not electrically short-circuited. The wiring on the piezoelectric substrate 2 can be freely performed. As a result, the wiring pitch between the input / output electrodes on the base substrate 14 and the lead electrodes 8 and 9 for the ground electrode is flexible, and additional circuits such as inductors and capacitors are formed on the piezoelectric substrate 2 and the base substrate 14. It is also possible to do. In this way, it is possible to provide a ground electrode having meandering (meandering) line 20 so as to constitute an inductor.
[0023]
Further, the functional surface of the surface acoustic wave element 3 and the base substrate 14 can be joined and hermetically sealed by the sealing material 12, but the pressure applied by the manipulator of the chip mounter when the surface acoustic wave device is mounted on the external circuit board. Can cause damage to the piezoelectric substrate 2 of the surface acoustic wave element 3. Therefore, as in the surface acoustic wave device S 3 shown in FIG. 4, the protective resin 22 is produced by resin potting from the upper surface side of the piezoelectric substrate 2. It doesn't matter.
[0024]
The piezoelectric substrate 2 is mainly applicable to lithium tantalate single crystal, lithium niobate single crystal, quartz, lithium tetraborate single crystal, langasite single crystal, potassium niobate single crystal, and gallium arsenide single crystal.
[0025]
The material of the excitation electrode 1 and the metal film 17 to be coated on the surface of the through hole is mainly aluminum, aluminum / copper alloy, aluminum / titanium alloy, aluminum / silicon alloy, gold, silver, or silver / palladium alloy. It can be mainly applied, and chromium, titanium, copper, etc. can be mainly applied when a base material is required for improving the adhesion of electrodes and reducing electric resistance.
[0026]
Further, the sealing material 12 and the protective resin 22 are a thermosetting resin (epoxy, silicone, phenol, polyimide, polyurethane, etc.), a thermoplastic resin (polyphenylene sulfide, etc.), an ultraviolet curable resin, or a low melting point. Glass etc. are mainly applicable.
[0027]
The conductive material 18 is made of a metal filler such as a thermosetting resin (epoxy, silicone, phenol, polyimide, polyurethane, etc.), a thermoplastic resin (polyphenylene sulfide, etc.), an ultraviolet curable resin, or a low-melting glass. Can be mainly applied.
[0028]
Further, in order to protect the excitation electrode 1, which is a fine electrode on the piezoelectric substrate 2, from foreign matters such as dust and metal migration, a protective film 21 is generally formed on the excitation electrode 1 within about 0.1 μm. is there.
[0029]
Although FIG. 1 shows a configuration diagram of a resonator ladder filter as an excitation electrode, it is performed by a resonator lattice filter, a dual mode resonator filter, a multi-IDT electrode filter, or a combination of these. It doesn't matter.
[0030]
The present invention is not limited to the above embodiment, and the present invention can be applied not only to the SAW filter but also to the SAW resonator and the SAW duplexer, and various modifications are possible without departing from the spirit of the present invention. There is no problem.
[0031]
【Example】
An Al—Cu alloy was formed as an electrode film on a 42 ° Y-cut X-propagating lithium tantalate single crystal wafer having a thickness of 0.35 mm and a diameter of about 80 mm to a thickness of 0.2 μm by sputtering. On top of that, a positive photoresist was applied by a spin coating method with a thickness of 1 μm. After that, exposure and development are performed to pattern the photoresist, etching is performed by a dry etching method so that the desired excitation electrode 1 and extraction electrodes 8 and 9 are formed, and the photoresist is removed by ashing to complete the electrode patterning. .
[0032]
After that, a SiO2 film is formed by a CVD method to a thickness of 0.025 μm, a positive photoresist is applied by a spin coating method with a thickness of 1 μm, exposure and development are performed, the photoresist is patterned, and dry etching is performed. The electrode was etched by the method, the photoresist was removed by ashing, and the protective film 21 was patterned on the excitation electrode 1.
[0033]
A wafer on which a large number of patterned surface acoustic wave elements 3 are arranged is diced using a dicing saw, and a large number of 1 mm square surface acoustic wave elements 3 are completed.
[0034]
Next, a positive photoresist is applied with a thickness of 1 μm by spin coating on a substrate of Si single crystal (main surface is (100) plane) having a thickness of about 0.25 mm and a diameter of about 80 mm, and exposure and development are performed. Then, the photoresist is patterned, immersed in an aqueous potassium hydroxide solution for 30 hours to etch the base substrate 14, 0.2 mm square on the surface of the Si substrate facing the SAW element 3, and on the connection terminal surface to the external circuit A 0.55 mm square through hole was formed.
[0035]
Similarly, in order to form the vibration space 19, a stepped portion having an inclination with a bottom surface of 0.5 mm square and an upper surface of 0.64 mm square was fabricated by anisotropic etching.
[0036]
Thereafter, an epoxy resin as a frame-shaped sealing material is applied to the surface acoustic wave element 3 by mask printing to a thickness of 0.1 mm and a width of 0.15 mm, and the epoxy resin is temporarily cured at 150 ° C. for 30 minutes. I let you. The surface acoustic wave element 3 and the base substrate 14 were finely pressurized and heated (150 ° C., 2 hours) with the epoxy resin, and hermetically sealed. Next, Ti was formed into a thickness of 0.1 μm in the through hole 15 by mask vapor deposition, a Ti metal film was formed on the side surface of the through hole, and a lead-free solder paste was mask printed on the through hole 15 and applied.
[0037]
Next, with the solder paste coating surface facing up, solder balls were formed in the through-holes under the conditions of preheating 150 ° C. for 1 minute, melt heating 230 ° C. for 5 seconds.
[0038]
The Si wafer was diced with a dicing saw to complete a number of 1.5 mm square surface acoustic wave devices.
[0039]
Through the above process, an ultra-small surface acoustic wave device having a width of 1.5 mm, a depth of 1.5 mm, and a height of 0.7 mm could be completed.
[0040]
【The invention's effect】
As described above in detail, according to the surface acoustic wave device of the present invention, it is not necessary to secure a space required for wire bonding by performing electrical connection by flip-chip connection. Therefore, it is possible to provide a surface acoustic wave device that is smaller than the conventional surface acoustic wave device using wire connection.
[0041]
Further, the base substrate of the present invention can eliminate the electrode routing required for the base substrate in the flip chip connection or the package in the wire connection, and can provide a surface acoustic wave device that is very simple to manufacture and structure.
[0042]
In addition, by forming the external circuit connection part in a convex shape with respect to the lower surface of the base substrate, the surface acoustic wave device particularly excellent in close contact between the surface acoustic wave device and the external circuit mounting substrate is provided. it can.
[0043]
Further, by forming the base substrate from a material that can be anisotropically etched and forming the recesses and the through holes by anisotropic etching, it is possible to provide a surface acoustic wave device that is easy to manufacture and has excellent reliability. .
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically illustrating an embodiment of a surface acoustic wave device according to the present invention.
FIG. 2 is a top perspective view schematically illustrating an embodiment of a surface acoustic wave device according to the present invention.
FIG. 3 is a top perspective view schematically illustrating another embodiment of a surface acoustic wave device according to the present invention.
FIG. 4 is a cross-sectional view schematically illustrating another embodiment of a surface acoustic wave device according to the present invention.
FIG. 5 is a cross-sectional view schematically illustrating a conventional surface acoustic wave device.
[Explanation of symbols]
1: Excitation electrode 2: Piezoelectric substrate 3: Surface acoustic wave element 4: Housing 5: Adhesive resin 6: Input / output electrode 7: Ground electrode 8: Input / output electrode (extraction electrode)
9: Ground electrode (lead electrode)
10: Wire 11: Lid 12: Sealing material 14: Base substrate 15: Through hole 16: Concave portion 17: First conductive material (metal film)
18: second conductive material 19: vibration space 20: signal wiring portion 21: protective film 22: protective resins S1 to S3: surface acoustic wave device

Claims (4)

A surface acoustic wave device having an excitation electrode on the lower surface and an extraction electrode electrically connected to the excitation electrode;
A base which is disposed so as to face the surface acoustic wave element through a sealing space existing between the excitation electrode and is joined to the surface acoustic wave element outside the sealing space in a plan view. A substrate,
A conductive material for connecting an external circuit, the upper part of which is electrically connected to the extraction electrode;
The conductive material for connecting the external circuit is located outside the sealing space in a plan view, and does not exist inside the sealing space .
The base substrate is made of a material capable of anisotropic etching, and a concave portion formed by anisotropic etching is provided in a portion of the base substrate facing the excitation electrode. apparatus.   The surface acoustic wave device according to claim 1, wherein a lower portion of the conductive material is led out to a height position below the sealing space. The base substrate has a through hole at a position corresponding to a connection portion between the conductive material and the lead electrode;
The surface acoustic wave device according to claim 1, wherein a lower portion of the conductive material is led out to a height position below the sealing space through the through hole. A surface acoustic wave device according to any one of claims 1 to 3,
A mounting structure comprising: an external circuit board on which the surface acoustic wave device is mounted.

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