JP2001244785A - Surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave device that can be made small in size similar to the case with the size of element and manufactured easily. SOLUTION: In the surface acoustic wave device S1, a surface acoustic wave element 3, consisting of an excitation electrode 1 and lead electrodes 8, 9 (8 is a signal electrode and 9 is a ground electrode) connected to the electrode 1 formed on a lower side of a piezoelectric substrate 2, is placed on a base substrate 14, a recessed part 16 counterposed to the exciting electrode 1 and a through-hole 15 opposed to the lead electrodes 8, 9 are respectively formed to the base substrate 14 and a metallic film 17 which is a 1st conducting member and a 2nd conduction member 18 are filled into the through-hole 15 to form an external circuit connection section.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device which is a resonator or a frequency band filter incorporated in a mobile radio device such as a mobile phone and a mobile phone.

[0002]

2. Description of the Related Art In recent years, many surface acoustic waves have been used as electronic components such as frequency filters (hereinafter, referred to as filters), delay lines, and transmitters for electronic devices that communicate using radio waves. Resonators and surface acoustic wave filters are used. In particular, in the mobile communications field,
RF (Radio Frequency: radio frequency or high frequency) block and IF (Intermedia) of a mobile terminal device such as a mobile phone.
It is often used as a filter for te Frequency (intermediate frequency) blocks. In the future, it is desired to reduce the weight and size of components in a communication system using mobile wireless devices such as a mobile phone and a mobile phone.

[0003] Conventional surface acoustic waves (Surface Acoustic Wav)
e, hereinafter also referred to as SAW) The basic configuration of the device is that a pair of comb-shaped excitation electrodes (Inter Digital
Transducers, IDT electrodes) are mounted in a ceramic housing.

FIG. 5 shows an example of the related art. The excitation electrode 1
For example, on a piezoelectric substrate 2 made of 36 ° Y-cut X-propagation lithium tantalate single crystal or the like, A
1. After forming a conductive film such as an Al-Cu alloy, the conductive film is patterned by photolithography so as to be a fine electrode.

Further, a piezoelectric substrate 2 on which an excitation electrode 1 is formed
Is cut with a dicing saw to obtain a SAW element 3
Is produced. The SAW element 3 is placed in a casing 4 made of ceramic and fixed with an adhesive resin 5, and the input / output electrode 6 or the ground electrode 7 of the casing 4 is connected to the lead electrodes 8 and 9 by wires 10. Connect with. Then, in order to provide weather resistance, the housing 4 and the lid 11 are sealed by seam welding or a sealing material 12 made of solder or resin.

As described above, in the conventional SAW device, despite the demand for weight reduction and size reduction, the housing is larger than the element, and a space is secured in the housing by wire bonding. Because of the necessity, there is a problem that the size of the SAW device is increased.

On the other hand, in recent years, proposals have been made to perform flip-chip connection using bumps to reduce the weight and size of the entire device (for example, Japanese Patent Application Laid-Open No. H11-15044).
No. 0).

According to this method, the electrical connection is made by flip-chip connection, thereby eliminating the space required for wire bonding. For this reason, it is possible to make the SAW device smaller than a conventional SAW device by wire connection.

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 electrodes 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,
A large number of man-hours were required for manufacturing the base substrate or the package.

Accordingly, an object of the present invention is to provide a SAW device which can be reduced in size to the size of an element and can be easily manufactured.

[0011]

In order to achieve the above object, a surface acoustic wave device according to the present invention comprises an excitation electrode and a lead electrode connected to the excitation electrode on a lower surface of a piezoelectric substrate on a base substrate. The surface acoustic wave element was placed on the base substrate, and a concave portion facing the excitation electrode and a through hole facing the extraction electrode were formed in the base substrate, and the through hole was filled with a conductive material to form an external circuit connecting portion. Further, the external circuit connection portion is formed to be convex with respect to the lower surface of the base substrate. Further, the base substrate is made of a material that can be anisotropically etched, and the concave portions and the through holes are formed by anisotropic etching.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a surface acoustic wave device according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view of a surface acoustic wave device S1 according to the present invention. FIG. 2 is a top perspective view of the surface acoustic wave device S1. Here, FIG. 1 is a sectional view taken along line AA ′ of FIG.

The surface acoustic wave device S1 has an excitation electrode 1 and lead electrodes 8, 9 (8 is a signal electrode, 9 is a ground electrode) connected to the excitation electrode 1 on the lower surface of the piezoelectric substrate 2 on the base substrate 14. The surface acoustic wave element 3 on which is formed is mounted, a concave portion 16 facing the excitation electrode 1 and a through hole 15 facing the extraction electrodes 8 and 9 are respectively formed in the base substrate 14, and the first conductive material is formed in the through hole 15. A metal film 17 and a second conductive material 18 are filled to form an external circuit connection portion.

Here, on the functional surface of the surface acoustic wave element 3,
For example, a frame-shaped sealing material 12 made of a resin of an insulator material is applied and formed. The surface acoustic wave element 3 and the base substrate 14 are bonded and hermetically sealed by the sealing material 12.

The through hole 15 is filled with a conductive material 18, for example, a resin mixed with a solder or a metal filler. The conductive material 18 is printed and filled on the lower surface of the base substrate 14 so that the surface becomes convex. In this way, 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 board becomes extremely easy and good.

On the side surface of the through hole 15, the conductive material 18, the base substrate 14, and the extraction electrode 8 of the surface acoustic wave element 3,
In order to improve the adhesion with the metal film 9, a metal film 17 is formed by adhesion.

The concave portion 16 and the through hole 15 of the base substrate 14 can be formed by using, for example, a (100) plane or (110 plane) of a Si single crystal substrate capable of anisotropic etching as a main surface. (100) plane or (110) plane and (11) plane
1) Anisotropic etching utilizing a large difference in etching rate from the plane facilitates production of the recess 16 and the through-hole 15 having the inclined plane of the (111) plane. The alkaline etchant used for the anisotropic etching is preferably an alkaline aqueous solution such as KOH, NaOH, EPW (ethylenediamine + pyrocatechol + water), hydrazine, TMAH (tetramethylammonium hydroxide).

In the case where the sealing material 12 is sagged (deformed when heated or pressed) in the recess 16, the surface acoustic wave element 3
Although it may hinder the upper excitation electrode 1 and adversely affect the characteristics, by forming an inclined surface of a minute space at the resin sinking portion, the resin sinking amount 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.

Further, since the recess 16 is formed by anisotropic etching on the upper surface of the base substrate 14 at a portion facing the excitation electrode 1 of the surface acoustic wave element 3, the surface acoustic wave element 3
Irrespective of the electrode thickness, the vibration space 19 of the excitation electrode 1 can be sufficiently secured.

In addition, since the conductive material 18 and the like are printed and filled in the through hole 15, air bubbles are difficult to enter into the conductive material, and the conductive material is easily filled. Therefore, an anisotropic etching method capable of making the through hole 15 inclined is provided. Preferably, it is used.

Next, another embodiment shown in FIG. 3 will be described. Here, since the frame-shaped sealing material 12 is insulative, the lead-out electrode 8 serving as the input / output electrode and the lead-out electrode 9 serving as the ground electrode are not electrically short-circuited. The wiring on the piezoelectric substrate 2 can be freely performed. Accordingly, the wiring pitch of the input / output electrodes on the base substrate 14 and the lead electrodes 8 and 9 of the ground electrode has a degree of freedom, and additional circuits such as inductors and capacitors are formed on the piezoelectric substrate 2 and the base substrate 14. It is also possible. Thus, it is also possible to provide a ground electrode having a meandering (meandering) line 20 so as to constitute an inductor.

Further, the functional surface of the surface acoustic wave element 3 and the base substrate 14 can be hermetically sealed by bonding with a sealing material 12. However, when the surface acoustic wave device is mounted on an external circuit board, a manipulator of a chip mounter is used. The piezoelectric substrate 2 of the surface acoustic wave element 3 may be damaged by the pressure given by the surface acoustic wave device 3. Therefore, like the surface acoustic wave device S3 shown in FIG. It may be made by making.

The piezoelectric substrate 2 can be mainly made of lithium tantalate single crystal, lithium niobate single crystal, quartz, lithium tetraborate single crystal, langasite single crystal, potassium niobate single crystal, or gallium arsenide single crystal. .

The material of the excitation electrode 1 and the metal film 17 coated on the surface of the through hole is mainly aluminum, aluminum / copper alloy, aluminum / titanium alloy, aluminum / silicon alloy, gold, silver or silver / silver alloy. A palladium alloy can be mainly used, and when a base material is required to improve the degree of electrode adhesion and reduce electric resistance, chromium, titanium, copper, etc. can be mainly used.

The sealing material 12 and the protective resin 22 are made of a thermosetting resin (epoxy, silicone, phenol,
Polyimide, polyurethane, etc.), thermoplastic resin (polyphenylene sulfide, etc.), ultraviolet curable resin, low melting point glass, etc. can be mainly applied.

The conductive material 18 is made of a thermosetting resin (epoxy, silicone, phenol, polyimide,
Polyurethane-based resin, thermoplastic resin (polyphenylene sulfide, etc.), ultraviolet curable resin, low-melting glass, or the like mixed with a metal filler at an arbitrary ratio can be mainly used.

Further, in order to protect the excitation electrode 1 which is a fine electrode on the piezoelectric substrate 2 from foreign matter such as dust and metal migration, it is preferable to form a protective film 21 on the excitation electrode 1 within about 0.1 μm. General.

FIG. 1 shows a configuration diagram of a resonator ladder type filter in which an excitation electrode is used.
The operation may be performed by a double mode resonator type filter, a multi-IDT electrode type filter, or a combination thereof.

The present invention is not limited to the above-described embodiment. The present invention can be applied not only to a SAW filter but also to a SAW resonator and a SAW duplexer, and various modifications can be made without departing from the gist of the present invention. No changes can be made.

[0031]

EXAMPLE A 42 ° Y-cut X-propagation lithium tantalate single crystal wafer having a thickness of 0.35 mm and a diameter of about 80 mm was formed on an Al-Cu alloy as an electrode film by sputtering to a thickness of 0.2 μm.
Was formed. On top of that, a positive photoresist of 1 μm
Was applied by a spin coating method. After that, exposure and development are performed to pattern the photoresist, dry etching is performed to form the desired excitation electrode 1 and extraction electrodes 8 and 9, and the photoresist is removed by ashing to complete the electrode patterning. .

After that, the SiO2 film is formed to a thickness of 0.1 mm by the CVD method.
A film was formed with a thickness of 025 μm, and a positive photoresist was
It is applied by a spin coat method to a thickness of μm, is exposed and developed, is patterned by photoresist, is etched by dry etching, and the photoresist is removed by ashing. Was patterned.

A wafer on which a large number of patterned surface acoustic wave elements 3 are arranged is diced using a dicing saw to complete many 1 mm square surface acoustic wave elements 3.

Next, a positive photoresist is applied by a spin coating method to a substrate of 0.25 mm in thickness and a diameter of about 80 mm of Si single crystal (main surface is (100) plane) with a thickness of 1 μm. Developing, patterning the photoresist, immersing in a potassium hydroxide aqueous solution for 30 hours to etch the base substrate 14,
A through-hole of 0.2 mm square was formed on the surface opposite to the above, and a 0.55 mm square was formed on the connection terminal surface with the external circuit.

Similarly, in order to form the vibration space 19, a step having a 0.5 mm square bottom surface and a 0.64 mm square top surface was formed by anisotropic etching.

Thereafter, the surface acoustic wave element 3 is printed with a frame-shaped sealing resin of epoxy resin by mask printing to a thickness of 0.1 mm.
The epoxy resin is applied to a width of 0.15 mm,
Temporarily cured at 30 ° C. for 30 minutes. The surface acoustic wave element 3 and the base substrate 14 were slightly pressurized and heated (150 ° C., 2 hours) with the epoxy resin, and hermetically sealed.
Then, Ti is added to the through hole 15 by mask evaporation.
μm thick, a Ti metal film is formed on the side surface of the through hole, and a lead-free solder paste is mask-printed on the through hole 15.
Applied.

Next, with the solder paste applied side facing up, S
Melt and heat the i-wafer at 150 ° C for 1 minute for 23 minutes.
Solder balls were formed in the through holes at 0 ° C. for 5 seconds.

Then, the Si wafer was diced with a dicing saw to complete a number of 1.5 mm square surface acoustic wave devices.

By the above steps, the size is 1.5 mm in width,
An ultra-small surface acoustic wave device having a depth of 1.5 mm and a height of 0.7 mm was completed.

[0040]

As described in detail above, according to the surface acoustic wave device of the present invention, the electrical connection is made by flip-chip connection, so that it is not necessary to secure the space required for wire bonding. Therefore, a surface acoustic wave device smaller than a conventional surface acoustic wave device using a wire connection can be provided.

The base substrate of the present invention can eliminate the wiring of electrodes required for the base substrate for flip-chip connection or the package for wire connection, and provides a surface acoustic wave device that is very simple to manufacture and structure. it can.

Further, by forming the external circuit connecting portion in a convex shape with respect to the lower surface of the base substrate, the adhesion between the surface acoustic wave device and the external circuit mounting substrate becomes particularly excellent,
A surface acoustic wave device with excellent reliability can be provided.

Further, the base substrate is made of a material capable of anisotropic etching, and the recess and the through hole are formed by anisotropic etching. Can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically illustrating one embodiment of a surface acoustic wave device according to the present invention.

FIG. 2 is a top perspective view schematically illustrating one embodiment of a surface acoustic wave device according to the present invention.

FIG. 3 is a top perspective view schematically illustrating another embodiment of the surface acoustic wave device according to the present invention.

FIG. 4 is a cross-sectional view schematically illustrating another embodiment of the 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 (lead electrode) 9: Ground electrode (lead electrode) 10: Wire 11: lid 12: sealing material 14: base substrate 15: through hole 16: recess 17: first conductive material (metal film) 18: second conductive material 19: vibration space 20: signal wiring portion 21: Protective film 22: Protective resin S1 to S3: Surface acoustic wave device

Claims (3)

[Claims] 1. A surface acoustic wave device in which a surface acoustic wave element having an excitation electrode and a lead electrode connected to the excitation electrode formed on a lower surface of a piezoelectric substrate is mounted on a base substrate,
A concave portion facing the excitation electrode and a through hole facing the extraction electrode are formed in the base substrate, and the through hole is filled with a conductive material to form an external circuit connection portion. apparatus. 2. The surface acoustic wave device according to claim 1, wherein the external circuit connection portion is formed in a convex shape with respect to a lower surface of the base substrate. 3. The surface acoustic wave according to claim 1, wherein the base substrate is made of a material that can be anisotropically etched, and the recess and the through hole are formed by anisotropic etching. apparatus.