JP4758197B2 - Surface acoustic wave device and communication device - Google Patents

Description

  The present invention relates to a surface acoustic wave device and a communication device such as a mobile phone and an in-vehicle sensor using the same.

Conventionally, dielectric filters have been mainly used for interstage filters and duplexers in mobile phones, but in recent years interstage filters and duplexers using surface acoustic wave devices that are advantageous for high performance and small size and weight have been used. It has been broken.
In such a surface acoustic wave device, the input level requirement ranges from 10 mW level for a conventional interstage filter to 1 to 3 W level required for a duplexer or the like as the operating frequency increases. Is spreading. For this reason, further improvement in power durability is desired as a surface acoustic wave device.

  In recent years, with the increase in the frequency band used in mobile phones, the line width of the IDT (Inter Digital Transducer) electrode of the resonator constituting the surface acoustic wave device has become smaller in inverse proportion to the frequency used. Yes. Conventionally, the electrode line width of the surface acoustic wave resonator is about 1 μm in the 800 MHz band, but becomes thinner to about 0.5 μm in the 1.9 GHz band. When surface acoustic waves are excited and received using such thin electrode fingers, if the signal power increases, the electrode finger and its finger due to the conversion of electrode finger vibration loss into heat and Joule heat due to electrode wiring resistance. The neighborhood generates heat from 100 ° C to 300 ° C. In a high temperature state, due to the effects of stress migration and heat generation, the synergistic effect promotes the destruction of the electrode fingers. Further, when the temperature becomes high, the temperature characteristics of the surface acoustic wave device are affected, and the characteristics change greatly.

Further, surface acoustic wave devices used for interstage filters and duplexers of mobile phones are required to be further reduced in size and weight as the various types of wireless communication devices become smaller. Therefore, in recent years, surface mount devices using flip chip mounting and surface acoustic wave devices having a CSP (Chip Scale Package) structure have been adopted.
FIG. 24 is a sectional view of a conventional surface acoustic wave device. The surface acoustic wave device includes a surface acoustic wave element in which at least a pair of IDT electrodes 102 and the like are formed on a piezoelectric substrate 101 such as a LiTaO ₃ single crystal, and a circuit board 105 that hermetically seals the surface acoustic wave device. The piezoelectric substrate 101 is mounted face-down on the circuit substrate 105, and the IDT electrode 102 and the like are bonded and fixed to the pad electrode 104 formed on the upper surface of the circuit substrate 105 via the bump connector. Thus, the surface acoustic wave element and the electrode of the circuit board 105 are electrically connected, and then hermetically sealed with the sealing resin 107.

When the flip chip mounting structure is adopted, the connection point with the circuit board 105 is only the bump connection body, and the space for radiating the generated heat is the main board of the piezoelectric substrate 101 on which the circuit board 105 and the surface acoustic wave element are formed. There is only a limited narrow space between the faces.
When the flip chip mounting structure is employed as described above, the structure is relatively unfavorable for heat dissipation, so that thermal design for reducing thermal resistance and measures for heat dissipation are problems.

With regard to heat dissipation countermeasures for such surface acoustic wave devices, a structure in which a metal piece for heat sink is brought into contact with the back surface of the piezoelectric substrate on which the surface acoustic wave element is formed, and further, a through hole is provided in the piezoelectric substrate to conduct with the metal piece. Such a structure has been proposed (see Patent Document 1).
Japanese Patent Laid-Open No. 2003-087093

However, in the above structure, it is necessary to dispose a metal piece on the piezoelectric substrate, which is disadvantageous for reducing the size and height of the surface acoustic wave device.
In the face-down mounting of a surface acoustic wave device, no proposal has been made that actively focuses on the arrangement of electrodes on the piezoelectric substrate as a heat dissipation measure for the surface acoustic wave device.
Accordingly, the present invention provides a surface acoustic wave device that reduces the influence of heat generated by the excitation electrode, has excellent heat dissipation, and provides stable desired characteristics when a surface acoustic device is configured by face-down mounting, and communication using the same. An object is to provide an apparatus.

The surface acoustic wave device according to the present invention has a structure in which a surface acoustic wave element is mounted face-down on a circuit board, and input / output pad electrodes are provided at portions of the main surface of the piezoelectric substrate between the surface acoustic wave resonators. The formed input / output pad electrode is connected to a connection electrode on a mounting surface of the circuit board by a bump connection body.
Alternatively, instead of the input / output pad electrode, a heat radiating pad electrode having no signal input / output function is formed at a portion between the surface acoustic wave resonators.

  According to these configurations, heat generated by the surface acoustic wave resonator can be efficiently radiated through the input / output pad electrode or the heat radiating pad electrode while being face-down mounted. Therefore, there is little change in characteristics due to temperature characteristics of the surface acoustic wave device, and stable characteristics can be obtained. As a result, it is possible to provide a surface acoustic wave device with excellent long-term reliability without causing destruction of electrode fingers of the IDT electrode.

In a structure in which a through conductor connected to the connection electrode is formed at a portion facing the input / output pad electrode or the heat dissipation pad electrode of the circuit board, the heat generated by the surface acoustic wave resonator is opposed. Heat can be efficiently radiated through the circuit board.
Further, if the surface of the piezoelectric substrate surrounds the surface acoustic wave element and a grounded annular electrode is formed, the structure can be sufficiently small and light and airtightness can be ensured. It is possible to provide a surface acoustic wave device having excellent properties.

  In addition, if the metal layer is formed on at least one of the back surface and the side surface of the piezoelectric substrate and the back surface and the side surface of the piezoelectric substrate are covered with a sealing resin, the outer periphery is a metal film. By covering with resin, it is excellent in moisture resistance and airtightness, and the element can be protected from destruction. As a result, it is possible to provide a surface acoustic wave device with excellent long-term reliability without causing destruction of electrode fingers of the IDT electrode.

   The surface acoustic wave device of the present invention has a structure in which a surface acoustic wave element is mounted face-down on a circuit board, and the surface acoustic wave element has a surface acoustic wave having an IDT electrode and a reflector electrode on the main surface of the piezoelectric substrate. A plurality of resonators are arranged and these surface acoustic wave resonators are connected to each other, and a heat dissipation pad electrode is formed at a portion between the surface acoustic wave resonators on the main surface of the piezoelectric substrate. In addition, an annular electrode surrounding the surface acoustic wave element is formed.

With this structure, it is compact and lightweight and can sufficiently secure airtightness, and heat generated by the surface acoustic wave resonator can be efficiently radiated through the heat radiating pad electrode and the annular electrode. It is possible to provide an excellent surface acoustic wave device.
The heat dissipation pad electrode is more preferably connected to the annular electrode via the main surface of the piezoelectric substrate or the mounting surface of the circuit board.

The heat dissipation pad electrode is connected to a heat dissipation bottom electrode formed on the bottom surface of the circuit board through a bump connector, a connection electrode formed on the circuit board, and a through conductor penetrating the circuit board. Is more preferable. The heat dissipation to the circuit board side can be improved using the heat conduction path using the heat dissipation pad electrode, the through conductor, and the annular electrode.
As the heat radiation electrode, a heat radiation inner layer electrode formed on the inner layer of the circuit board may be used in addition to the mounting surface and the bottom surface of the circuit board.

Further, if the heat conduction path is formed through the side conductor formed on the side surface of the circuit board, the heat dissipation efficiency can be further increased.
A ladder type circuit may be configured by connecting the plurality of surface acoustic wave resonators in series and in parallel. When a signal increases in a ladder-type surface acoustic wave device, heat generation particularly in a series resonator increases, which causes a problem. By arranging a pad electrode that actively dissipates heat in the vicinity of the resonator, the generated heat is opposed. Heat can be efficiently radiated through the circuit board.

  If the surface acoustic wave device described above is used as a filter circuit component of a communication device, a communication device that is small and light and has high transmission power can be realized.

Hereinafter, embodiments of a surface acoustic wave device and a communication device according to the present invention will be described in detail with reference to the drawings. In the following drawings, the size of each electrode, the distance between the electrodes, the number of electrode fingers, the interval, and the like are schematically illustrated for explanation.
The surface acoustic wave device includes a surface acoustic wave element and a circuit board for mounting the surface acoustic wave element.

FIG. 1 is a plan view showing an arrangement example of a surface acoustic wave element using input / output electrodes as heat radiation electrodes.
In addition, the “main surface” in this specification refers to the surface on which the IDT electrode and the reflector electrode are formed on the surface of the piezoelectric substrate.
As shown in FIG. 1, the surface acoustic wave element includes a piezoelectric substrate 1 made of a piezoelectric single crystal such as a lithium tantalate single crystal, a lithium niobate single crystal, or a lithium tetraborate single crystal; IDT electrodes 2a to 2g which are excitation electrodes connected to the surface by a system such as series connection or parallel connection, reflectors 9 positioned at both ends of the surface acoustic wave propagation direction of each IDT electrode 2a to 2g, and IDT electrode 2a The plurality of extraction electrodes 10a to 10f connected to 2g and internal connection electrodes 20a and 20b for connecting the IDT electrodes 2a to 2g are provided. The IDT electrodes 2a to 2g, the reflector electrode (hereinafter also referred to as “reflector”) 9, the extraction electrodes 10a to 10f, and the internal connection electrodes 20a and 20b are covered with a protective film (not shown).

Here, the IDT electrodes 2a to 2g are obtained by engaging a plurality of pairs of comb-like electrodes.
Input / output pad electrodes 3a and 3b are formed at the ends of the extraction electrodes 10a and 10b connected to the IDT electrodes 2a and 2b. The ends of the extraction electrodes 10c and 10e connected to the IDT electrodes 2d and 2f and the IDT electrode 2e , 2g, ground pad electrodes 4 are formed on the ends of the lead electrodes 10d, 10f.

The protective film is formed on the pad electrode with the pad electrode exposed.
In the embodiment of FIG. 1, the input / output pad electrodes 3a and 3b are surrounded by the region between the surface acoustic wave resonators, that is, the IDT electrodes 2a to 2c, 2e and 2g, the reflector 9, and the internal connection electrodes 20a and 20b. The configuration is arranged in each of the areas.

The IDT electrodes 2a to 2g, the reflector 9, the extraction electrodes 10a to 10f, the internal connection electrodes 20a and 20b, the input / output pad electrodes 3a and 3b, and the grounding pad electrode 4 are, for example, an Al alloy mainly composed of Al—Cu. Consists of.
An outline of the manufacturing method is as follows. An Al alloy thin film is formed by a thin film forming method such as a sputtering method, a vapor deposition method or a CVD (Chemical Vapor Deposition) method, and then a reduction projection exposure machine (stepper) and RIE (Reactive Ion Etching). Patterning is performed by photolithography using an apparatus to obtain a predetermined shape. Then, a protective film is formed by a thin film forming method such as a CVD method or a vapor deposition method. As the protective film, a SiO ₂ film, a SiN film, a Si film, or the like is used.

  The IDT electrodes 2a to 2g are generally made of an Al alloy containing Cu as described above, but Al containing one or more of Ti, Ta, Mg, W, Mb and the like other than Cu or together with Cu. An alloy may be used. For example, Al alloys such as Al—Ti, Al—Mg, and Al—Cu—Mg are available. Also, a structure in which a plurality of types of these alloys, for example, AlCu / Cu / AlCu, Ti / AlCu, and Ti / AlCu / Ti are laminated is applicable (/ indicates a laminated interface).

  The shapes of the IDT electrodes 2a to 2g are comb teeth formed so as to mesh with each other. The number of pairs of electrode fingers is about 50 to 300, the width of electrode fingers is about 0.1 to 10 μm, the distance between electrode fingers is about 0.1 to 10 μm, the crossing width of electrode fingers is about 10 to 200 μm, and the IDT electrodes 2a to 2g A thickness of about 0.1 to 0.5 μm is suitable for obtaining desired characteristics as a resonator or a filter.

Piezoelectric substrate 1 includes 36 ° ± 10 ° Y cut-X propagation LiTaO ₃ single crystal, 64 ° ± 10 ° Y cut-X propagation LiNbO ₃ single crystal, 45 ° ± 10 ° X cut-Z propagation Li It is preferable to use ₂ B ₄ O ₇ single crystal or the like because it has a large electromechanical coupling coefficient and a small group delay time temperature coefficient, and is especially a 36 ° ± 10 ° Y cut-X propagation LiTaO having a large electromechanical coupling coefficient. _Three single crystals are preferred. Further, the cut angle in the crystal Y-axis direction may be in the range of 36 ° ± 10 °, and in that case, sufficient piezoelectric characteristics can be obtained.

The thickness of the piezoelectric substrate 1 is preferably about 0.1 to 0.5 mm. If the thickness is less than 0.1 mm, the piezoelectric substrate 1 becomes brittle, and if it exceeds 0.5 mm, the material cost increases.
Moreover, in order to prevent the electrode destruction due to the pyroelectric effect of the piezoelectric substrate 1, there is no problem even if the piezoelectric substrate 1 subjected to the reduction treatment or the piezoelectric substrate 1 added with Fe element is used.
Further, when a duplexer is constituted by this surface acoustic wave element, a surface acoustic wave element for reception and a surface acoustic wave element for transmission may be formed on the main surface of one piezoelectric substrate 1. Alternatively, they may be formed on separate piezoelectric substrates 1 and individually mounted on a package.

FIG. 2 is a plan view of a surface acoustic wave element having another structure using a heat dissipation pad electrode as a heat dissipation electrode.
In this structure, IDT electrodes 2a to 2g, a reflector 9, a plurality of extraction electrodes 10a and 10b connected to the IDT electrodes 2a to 2g, and the IDT electrodes 2a to 2g are provided on the main surface of the piezoelectric substrate 1. The internal connection electrodes 20a and 20b to be connected and the ground pad electrode 4 are formed in the same manner as in FIG.

  1 is different from the structure of FIG. 1 in that the input / output pad electrodes 3a and 3b are arranged in the region between the surface acoustic wave resonators in the structure of FIG. In addition to the electrodes 3a and 3b and the grounding pad electrode 4, heat dissipating pad electrodes 16a and 16b that are not connected to anything are provided, and the heat dissipating pad electrodes 16a and 16b are formed between the surface acoustic wave resonators, That is, it is arranged in a region surrounded by the IDT electrodes 2a to 2c, 2e, 2g, the reflector 9, and the internal connection electrodes 20a, 20b. The input / output pad electrodes 3 a and 3 b are arranged along with the grounding pad electrode 4 on the outer peripheral portion of the surface acoustic wave resonator.

FIG. 3 is a schematic cross-sectional view of a surface acoustic wave device in which the surface acoustic wave element configured as described above is mounted on a circuit board.
The surface acoustic wave element is configured such that the principal surface of the piezoelectric substrate 1 provided with IDT electrodes 2a to 2g (generally referred to as “IDT electrode 2”) faces the upper surface (referred to as a mounting surface) of the circuit board 11. It is mounted face down.

Input / output pad electrodes 3a and 3b (collectively referred to as “input / output pad electrode 3”) formed on the main surface of the piezoelectric substrate 1 are bumped to the connection electrodes 12 formed on the mounting surface of the circuit substrate 11. The connection body 13 is connected.
The connection electrode 12 is connected to a heat radiation bottom electrode 21 formed on the bottom surface of the circuit board 11 through a through conductor 19 provided so as to penetrate the circuit board 11. Of course, the heat radiation bottom electrode 21 is connected to a predetermined electrode of the main board on which the surface acoustic wave device is mounted.

The circuit board 11 is produced, for example, by laminating a single ceramic substrate or a ceramic substrate and one or more frame-shaped ceramic substrates. A resin such as BT resin may be used instead of ceramic.
The connection electrode 12 and the heat radiation bottom electrode 21 provided on the circuit board 11 are formed by electrolytic plating or electroless plating.

The bump connection body 13 is formed simultaneously by forming a solder paste, an Au—Sn alloy paste or the like by a printing method such as screen printing, or by applying with a dispenser. Here, the bump connection body 13 is formed on the circuit board 11 side. However, the bump connection body 13 may be formed on the surface acoustic wave element side.
The through conductor 19 is formed by filling a hole provided in the circuit board 11 with a conductive paste and then curing by heating.

By reflow-melting the circuit board 11 on which the piezoelectric substrate 1 is placed in a reflow furnace, the surface acoustic wave element and the circuit board 11 are electrically and mechanically connected. Then, the sealing resin 15 is formed on the back surface and the peripheral surface of the surface acoustic wave element by the potting method or the printing method, and the surface acoustic wave device is completed by heat curing the resin.
In FIG. 3, low-humidity air may be sealed and sealed in the vibration space S formed between the opposing surfaces of the piezoelectric substrate 1 and the circuit substrate 11. This is preferable because deterioration due to oxidation or the like of the IDT electrode 2 can be suppressed. Further, if an inert gas such as nitrogen gas or argon gas is sealed instead of air and sealed, a more preferable effect can be obtained.

The heat generated by the surface acoustic wave element is generated from the input / output pad electrodes 3a and 3b (in the case of FIG. 1) or the heat dissipation pad electrodes 16a and 16b (in the case of FIG. 2) formed on the main surface of the piezoelectric substrate 1. The heat is transmitted to the connection electrode 12 through the bump connection body 13 and further transmitted to the heat-dissipating bottom electrode 21 formed on the bottom surface of the circuit board 11 through the through conductor 19 to be dissipated.
In particular, in the embodiment of the present invention, the input / output pad electrodes 3a and 3b or the heat radiation pad electrodes 16a and 16b are arranged on the piezoelectric substrate 1 in the region between the surface acoustic wave resonators. Heat can be easily collected by the output pad electrodes 3a and 3b and the heat radiation pad electrodes 16a and 16b, and the collected heat can be radiated to the bottom surface of the circuit board 11 so that efficient heat radiation can be performed. it can.

  By adopting such a structure that actively dissipates heat, it is possible to efficiently dissipate heat generated by the surface acoustic wave resonator while being face-down mounted with a small size and light weight. Therefore, there is little change in the characteristics of the surface acoustic wave device due to temperature, and stable characteristics can be obtained. As a result, it is possible to provide a surface acoustic wave device excellent in power durability and long-term reliability without causing electrode finger destruction.

Next, the structure of a surface acoustic wave element in which an annular electrode is provided on the piezoelectric substrate 1 will be described.
FIG. 4 is a plan view showing still another structure of the surface acoustic wave element of the present invention.
In this structure, an annular electrode 17 is formed on the outer peripheral portion of the surface acoustic wave resonator on the piezoelectric substrate 1 so as to surround the surface acoustic wave resonator. There is no grounding pad electrode 4 connected to the ground side of the IDT electrodes 2d to 2g, and the ground side of the IDT electrodes 2d to 2g is connected to the annular electrode 17. That is, instead of the grounding pad electrode 4, the annular electrode 17 performs the grounding function.

Also in FIG. 4, as in FIG. 1, the input / output pad electrodes 3a, 3b are regions between the surface acoustic wave resonators, that is, the IDT electrodes 2a to 2c, 2e, 2g, the reflector 9, the internal connection electrodes 20a, It is the structure arrange | positioned in the area | region enclosed by 20b.
FIG. 5 is a cross-sectional view showing a state where the surface acoustic wave element of FIG. 4 is mounted face-down on the circuit board 11.

  According to this structure, the piezoelectric substrate 1 is placed on the circuit board 11, and the input / output pad electrodes 3 a and 3 b formed on the main surface of the surface acoustic wave element and the mounting surface of the circuit board 11 are formed. The connection electrode 12 is connected via the bump connection body 13, the connection electrode 12 is connected to the bottom electrode 21 for heat dissipation of the circuit board 11 through the through conductor 19, and the annular electrode 17 is connected to the annular seal made of solder or the like. It is connected to an annular conductor 14 formed on the circuit board 11 side via a stopper 18.

  Thus, heat can be easily collected by the input / output pad electrodes 3a and 3b, and the heat can be efficiently dissipated by dissipating the heat to the bottom surface of the circuit board 11 through the through conductors 19. it can. Further, since the annular electrode 17 can be grounded through the annular conductor 14, electromagnetic noise can be cut off, and the gap between the main surface of the piezoelectric substrate 1 and the mounting surface of the circuit substrate 11 is hermetically sealed. It becomes easy to do.

FIG. 6 shows a cross-sectional view of a surface acoustic wave element according to another embodiment mounted on a circuit board 11.
The difference from FIG. 3 of this embodiment is that a metal film 22 is formed on the surface opposite to the main surface of the piezoelectric substrate 1 (referred to as the back surface) by sputtering or the like.
As the metal film 22, a structure in which Cr serving as an adhesion layer, Ni serving as a barrier metal layer, Au improving solder wettability, and the like are sequentially laminated can be used.

The metal film 22 provided on the back surface of the piezoelectric substrate 1 reduces the possibility that the piezoelectric substrate 1 is destroyed due to current collection even when a temperature history is applied during the manufacture of the element (reduction treatment is performed on the piezoelectric substrate 1 or Fe This is the same effect as adding elements).
The metal film 22 may be formed not only on the back surface of the piezoelectric substrate 1 but also on the side surface of the piezoelectric substrate 1 as shown in FIG.

  Further, in the structure of FIG. 6 in which the metal film 22 is formed on the back surface of the piezoelectric substrate 1 and the structure of FIG. 7 in which the metal film 22 is formed on the back surface and side surface of the piezoelectric substrate 1, as in FIG. An annular electrode 17 may be formed on the outer peripheral portion of the surface acoustic wave resonator of the substrate 1 so as to surround the surface acoustic wave resonator, and this annular electrode 17 may function as a grounding electrode. By mounting the surface acoustic wave resonator formed with the annular electrode 17 face-down on the circuit board 11, the annular electrode 17 formed on the outer peripheral portion of the surface acoustic wave resonator of the piezoelectric substrate 1 is placed on the circuit board 11 side. FIG. 8 is a sectional view showing a state in which the gap between the main surface of the surface acoustic wave element and the mounting surface of the circuit board 11 is hermetically sealed by connecting to the formed annular conductor 14 made of solder or the like.

FIG. 9 is a plan view showing a surface acoustic wave device according to another embodiment of the present invention. FIG. 10 is a schematic cross-sectional view showing a state in which this surface acoustic wave element is mounted on the circuit board 11.
As shown in FIG. 9, an IDT electrode 2 that is an excitation electrode for generating a surface acoustic wave, a plurality of extraction electrodes 10 connected to the IDT electrode 2, and the IDT electrodes 2 are formed on the main surface of the piezoelectric substrate 1. And an internal connection electrode 20 for connecting the two. An annular electrode 17 is formed on the outer peripheral portion of the surface acoustic wave resonator so as to surround the electrode.

  Further, at least one heat radiation pad electrode 16 a, 16 b (collectively referred to as “heat radiation pad electrode 16”) is disposed on the piezoelectric substrate 1. These heat radiation pad electrodes 16 are connected to the annular electrode 17 through the connection electrodes 24. Therefore, the heat generated in the heat dissipation pad electrode 16 is transmitted to the annular electrode 17 through the connection electrode 24. In FIG. 9, the connection electrode 24 connected to the heat radiation pad electrode 16 is joined to the ground electrode of the IDT electrode 2e and connected to the annular electrode 17, but extends separately from the ground electrode of the IDT electrode 2e, It may be connected to the annular electrode 17.

As shown in FIG. 10, the main surface of the piezoelectric substrate 1 on which the IDT electrodes 2 and the like are provided is mounted face-down so that the mounting surface of the circuit substrate 11 faces.
The piezoelectric substrate 1 is placed on the circuit board 11, and the annular electrode 17 is connected to the annular conductor 14 formed on the circuit board 11 correspondingly via the bump connector 13.
The annular conductor 14 is connected to the heat-dissipating bottom electrode 21 of the circuit board 11 through the through conductor 19 that penetrates the circuit board 11. A conductor layer (referred to as an inner layer conductor) 8 is formed in the circuit board 11, and a through conductor 19 is connected to the inner layer conductor 8. Therefore, the effect of diffusing heat by the inner layer conductor 8 is obtained. The planar shape of the inner layer conductor 8 is not shown, but it is needless to say that it is more advantageous in terms of heat dissipation if it is formed over as large an area as possible without contact with other electrodes.

Thus, by reflow-melting the circuit board 11 on which the piezoelectric substrate 1 is placed in a reflow furnace, the surface acoustic wave element and the circuit board 11 are electrically and mechanically connected. Then, the sealing resin 15 is formed on the back surface and the peripheral surface of the surface acoustic wave element by the potting method or the printing method, and the surface acoustic wave device is completed by heat curing the resin.
The feature of this surface-down surface acoustic wave device is that an annular electrode 17 surrounding the IDT electrode 2 and the like is formed on the main surface of the piezoelectric substrate 1, and the heat dissipating pad electrode 16 is connected to the annular electrode 17. is there. Since the annular electrode 17 is connected to the bottom electrode 21 for heat dissipation of the circuit board 11, the heat collected by the pad electrode 16 for heat dissipation passes through the annular electrode 17 and the bottom electrode 21 for heat dissipation of the inner layer conductor 8 and the circuit board 11. Easy to escape.

Therefore, when large signal power is input, sufficient heat dissipation is obtained by efficiently releasing the heat generated in the vicinity of the IDT electrode 2 through the annular electrode 17.
FIG. 11 is a cross-sectional view showing a structure in which the heat dissipation pad electrode 16 is directly connected to the connection electrode 12 of the circuit board 11 through the bump connection body 13 in addition to the structure of FIG. The connection electrode 12 of the circuit board 11 is connected to the inner layer conductor 8 in the circuit board 11 through a through conductor 19 that penetrates the circuit board 11.

In this structure, the heat collected by the heat dissipating pad electrode 16 is transmitted to the inner layer conductor 8 in the circuit board 11 through the bump connector 13, and is radiated to the heat dissipating bottom electrode 21 through the inner layer conductor 8. Since the heat dissipation path area is increased in addition to the heat dissipation path of FIG. 10, the heat dissipation efficiency is improved.
FIG. 12 shows a plan view of another embodiment of the surface acoustic wave device of the present invention. FIG. 13 is a schematic cross-sectional view thereof.

The surface acoustic wave device of FIG. 12 is provided with an annular electrode 17 surrounding the heat radiation pad electrode 16 and the IDT electrode 2 on the main surface of the piezoelectric substrate 1 as in the surface acoustic wave device of FIG.
The difference from FIG. 9 is that, on the main surface of the piezoelectric substrate 1, the input / output pad electrode 3a is disposed in the region between the surface acoustic wave resonators together with the heat dissipation pad electrode 16a, and the input / output pad electrode 3b is In other words, the heat dissipation pad electrode 16b is disposed in a region between the surface acoustic wave resonators. The input / output pad electrodes 3a and 3b and the heat dissipation pad electrodes 16a and 16b can easily collect heat, and the collected heat is dissipated to the bottom surface of the circuit board 11, thereby efficiently dissipating heat. It can be carried out.

A connection electrode facing the input / output pad electrode 3 is formed on the mounting surface of the circuit board 11, and this connection electrode is connected to the bottom electrode for heat dissipation of the circuit board through the through conductor as in FIG. is there.
13 to 18 are cross-sectional views showing examples of arrangement of heat radiation paths connected from the heat radiation pad electrode 16.

  In FIG. 13, the heat dissipation pad electrode 16 is connected to the connection electrode 23 on the circuit board 11 by the bump connection body 13. The connection electrode 23 is connected to the annular conductor 14 facing the annular electrode 17 on the circuit board 11. That is, as shown in FIG. 13, the heat radiation pad electrode 16 is connected to the annular conductor 14 on the circuit board 11 side. The annular conductor 14 is connected to the heat radiation bottom electrode 21 of the circuit board 11 through the through conductor 19 in the same manner as in FIG.

Also in this embodiment, the heat collected by the heat dissipating pad electrode 16 can be efficiently released to the heat dissipating bottom electrode 21 of the circuit board 11 through the connection electrode 23 and the annular conductor 14, and the embodiment of FIG. As with, high heat dissipation is obtained.
FIG. 14 is a cross-sectional view according to another modification.
In the structure of FIG. 14, in addition to the configuration of FIG. 13, the heat radiation pad electrodes 16a and 16b are connected to the connection electrode 12 and the through conductors 19a and 19b formed on the circuit board 11, and the through conductors 19a and 19b are connected. Is connected to the bottom electrode 21 for heat dissipation of the circuit board 11.

Also in this embodiment, the heat collected by the heat dissipating pad electrodes 16a and 16b is efficiently applied directly to the heat dissipating bottom electrode 21 of the circuit board 11 through the bump connector 13, the connecting electrode 12, and the through conductors 19a and 19b. Therefore, higher heat dissipation than that of the embodiment of FIG. 13 can be obtained.
FIG. 15 is a cross-sectional view according to another modification.

  In the structure of FIG. 15, the heat dissipation pad electrodes 16 a and 16 b are connected to the connection electrode 12 and the through conductors 19 a and 19 b formed on the circuit board 11, and the through conductors 19 a and 19 b are the bottom surface for heat dissipation of the circuit board 11. It is connected to the electrode 21. The difference from FIG. 14 is that the heat radiation bottom electrode 21 is formed over a wide range of the bottom surface of the circuit board 11. Similarly to FIG. 14, the heat radiation efficiency can be improved through the heat radiation bottom electrode 21 on the circuit board 11 side.

FIG. 16 is a cross-sectional view according to still another modification.
In the structure of FIG. 16, as in the surface acoustic wave device of FIG. 13, the annular electrode 17 surrounding the heat radiation pad electrodes 16 a and 16 b and the IDT electrode 2 is provided on the main surface of the piezoelectric substrate 1. On the mounting surface of the circuit board 11, an annular conductor 14 that faces the annular electrode 17 is formed, and a connection electrode 12 that faces the heat radiation pad electrodes 16 a and 16 b is formed.

The difference from FIGS. 14 and 15 is that the circuit board 11 has a laminated structure, and a conductor layer (referred to as an inner layer conductor) 8 is formed in the circuit board 11. The annular conductor 14 and the connection electrode 12 are connected by the inner layer conductor 8 on the inner layer surface of the circuit board 11 through the through conductors 19a and 19b, respectively.
Therefore, in the structure of FIG. 16, the heat radiation pad electrodes 16 a and 16 b are connected to the annular conductor 14 through the inner layer conductor 8 on the inner layer surface of the circuit board 11. Since the annular conductor 14 is connected to the heat radiation bottom electrode 21 of the circuit board 11 through the through conductor 19, the heat collected by the heat radiation pad electrodes 16 a and 16 b is transferred to the bump connector 13, the connection electrode 12, and the through conductor. 19. Through the inner layer conductor 8, it is possible to efficiently escape to the bottom electrode 21 for heat dissipation of the circuit board 11, and high heat dissipation is obtained as in the embodiment of FIG.

FIG. 17 shows a cross-sectional view of another embodiment of the surface acoustic wave device of the present invention.
This surface acoustic wave device is provided with heat radiation pad electrodes 16 a and 16 b and an annular electrode 17 on the main surface of the piezoelectric substrate 1 as in the surface acoustic wave device of FIG. 10. Correspondingly, an annular conductor 14 is formed on the circuit board 11, and the annular conductor 14 is connected to a heat radiation bottom electrode 21 of the circuit board 11 through a through conductor 19 that penetrates the circuit board 11.

In this structure, the annular conductor 14 is connected to a conductor pattern 21 a formed on the side surface of the circuit board 11, and the conductor pattern 21 a is connected to the bottom electrode 21 for heat dissipation of the circuit board 11.
The conductor pattern 21a formed on the side surface is similarly formed by printing a conductor paste and heating and curing, or by electroless plating.
In this structure, not only the mounting surface and the bottom surface of the circuit board 11 but also the side surfaces of the circuit board 11 are used as a path for releasing heat, so that heat dissipation can be further improved.

18A to 18C are sectional views of other embodiments of the surface acoustic wave device of the present invention.
This surface acoustic wave device is provided with heat radiation pad electrodes 16 a and 16 b and an annular electrode 17 on the main surface of the piezoelectric substrate 1 as in the surface acoustic wave device of FIG. 10. Correspondingly, an annular conductor 14 is formed on the circuit board 11, and the annular conductor 14 is connected to a heat radiation bottom electrode 21 of the circuit board 11 through a through conductor 19 that penetrates the circuit board 11.

In the structure of FIG. 18A, a good thermal conductor 21 b connected to the heat radiation bottom electrode 21 on the bottom surface of the circuit board 11 is coated on the side surfaces of the circuit board 11 and the sealing resin 15. The heat good conductor 21b is formed by applying a resin filled with Ag filler or the like and then heat-curing it. For this reason, the side surface of the surface acoustic wave device can also be used as a path for releasing heat.
FIG. 18B shows an example in which the heat good conductor 21 b is formed on the side surface of the sealing resin 15. Due to the presence of the good thermal conductor 21 b, the thermal resistance is reduced and heat is released from the side surface of the sealing resin 15.

FIG. 18C shows an example in which the good thermal conductor 21 c is formed on the upper surface of the sealing resin 15 instead of just the side surfaces of the sealing resin 15. By using the side surface and the upper surface of the sealing resin 15 as a path for releasing heat, the area of the heat good conductor can be further increased, so that heat dissipation is further enhanced.
Next, an embodiment of the communication apparatus of the present invention will be described by taking a mobile phone as an example.

In a communication apparatus including one or both of a reception circuit and a transmission circuit, the surface acoustic wave element of the present invention can be used as a bandpass filter included in these circuits.
FIG. 19 shows a block circuit diagram of a high-frequency circuit of a mobile phone. The unnecessary signal is removed from the high frequency signal transmitted from the cellular phone by the surface acoustic wave filter 41, amplified by the power amplifier 42, and then radiated from the antenna 34 through the isolator 43 and the surface acoustic wave demultiplexer 35. The

The high frequency signal received by the antenna 34 is separated by a surface acoustic wave demultiplexer 35, amplified by a low noise amplifier 36, unnecessary signals are removed by a surface acoustic wave filter 37, and then re-amplified by an amplifier 38. Then, it is converted into a low frequency signal by the mixer 39.
If the surface acoustic wave element of the present invention is employed, an excellent communication device with improved sensitivity can be provided.
Although the embodiments of the present invention have been described above, the embodiments of the present invention are not limited to the above-described embodiments. For example, hereinafter, the surface acoustic wave element is a ladder type surface acoustic wave filter, but may be a double mode surface acoustic wave resonator filter.

  In the present invention, in the case where at least one of the input / output pad electrodes and the heat dissipation pad electrode is formed in a portion between the surface acoustic wave elements on the main surface of the piezoelectric substrate, the IDT connected closest to the input / output terminals. Since the electrode generates the most heat, a configuration in which the area of the heat radiation pad electrode around the IDT electrode is maximized is preferable. In addition, various modifications can be made within the scope of the present invention.

The surface acoustic wave device shown in FIG. 4 was manufactured.
As the piezoelectric substrate 1, a 36 ° Y cut-X propagation LiTaO ₃ crystal was used, and its chip size was 1.1 mm × 1.5 mm. Further, as the circuit board 11, an LTCC (Low Temperature Co-fired Ceramics) board having a thickness of 70 mm × 70 mm and a thickness of 250 μm was used. An Ag electrode having a thickness of about 1 μm was formed on the LTCC substrate.

An Al—Cu electrode was formed as an IDT electrode 2 on the piezoelectric substrate 1 by sputtering. The electrode thickness of the Al—Cu electrode was 1800 mm. The input / output pad electrode 3 is disposed in a region between the surface acoustic wave resonators of the serial arm at the center of the surface acoustic wave element chip.
Also, a Cr film 1000 Å, a Ni film 1 μm, and an Au film 1000 に were formed on the back surface of the piezoelectric substrate 1 by sputtering.

  On the circuit board 11, a solder paste to be the annular conductor 14 was applied in advance by a screen printing method at a position where the input / output pad electrode 3 of the piezoelectric substrate 1 abuts and a position of the annular electrode 17. The line width of the applied solder paste was about 100 μm. Similarly, a solder paste was applied to the back surface of the piezoelectric substrate 1 by screen printing. For solder printing on the side surface of the piezoelectric substrate 1, a screen printing pattern larger than the size of the piezoelectric substrate 1 was used for application to the side surface.

  After face-down mounting at the position where the conductor pattern of the circuit board 11 and the input / output pad electrode 3 of the piezoelectric substrate 1 abut and the position of the annular electrode 17, solder after reflow melting at 240 ° C. for 5 minutes in a reflow oven. Cured. Further, an epoxy sealing resin 15 was applied by potting from the upper part of the back surface of the piezoelectric substrate 1 on which the surface acoustic wave element was formed, and then cured by heating in a drying oven at 150 ° C. for 5 minutes. Finally, individual chips were formed by dicing from the back surface of the circuit board 11 at separation positions between the chips. Through the above process, a small and highly reliable ladder-type surface acoustic wave filter having a width of 1.6 mm × 2.0 mm and a height of 0.6 mm was completed.

For the purpose of evaluating heat dissipation, the difference in temperature rise due to the placement of the pad electrode when signal power was applied to the surface acoustic wave device was determined by thermal analysis using the finite element method.
FIG. 20 shows a thermal analysis model (model) having the same structure as that of the present invention and having the input / output pad electrode 3 arranged in the region between the series arm surface acoustic wave resonators in the center of the surface acoustic wave element chip. (A)) is shown. For comparison with the present invention, FIG. 21 shows a thermal analysis model (model (b)) in the case where the input / output pad electrode 3 is arranged on the outer periphery of a conventional surface acoustic wave resonator. Note that the annular electrode on the outer periphery is evaluated as existing in both models. Furthermore, as an extreme model for comparison (model (c), not shown), the case where the pad electrode exists in all regions other than the surface acoustic wave resonator was also analyzed.

As analysis conditions, thermal conductivity (W / m · k) of each material is 4.1 for LiTaO ₃ substrate, 3.9 for LTCC substrate, 61 for solder connection material, 0.5 for epoxy resin, 150 for via Ag, and 2.6 for air. × 10 ^-2 was used.
As an analysis method, a signal power of 0.4 W is input to the surface acoustic wave device, and the heat generated in the vicinity of the surface acoustic wave resonator is conducted inside the surface acoustic wave device and is 25 ° C from the surface of the surface acoustic wave device. The temperature in the heat generating part during the process of transferring to the atmosphere was analyzed. Further, the thermal resistance from the heat generating part to the atmosphere was calculated. The results are shown in Table 1.

  The maximum temperature in the heat generating part near the surface acoustic wave resonator was 78.6 ° C. for the model (a) having the same structure as the present invention, 85.7 ° C. for the model (b) of the conventional structure, and 65.7 ° C. for the model (c). . The thermal resistance from the heat generating part to the atmosphere was 134.0 ° C. for model (a), 151.8 ° C. for model (b), and 101.8 ° C. for model (c). In the model (a) in which the input / output pad electrode 3 is arranged at a position closer to the heat generating portion as compared with the model (b) of the conventional structure, the thermal resistance is reduced by 12% (from Table 1, (151.8- 134.0) /151.8=0.117 (11.7%)). Further, in the model (c), the thermal resistance is reduced by about 33% as compared with the conventional structure (from Table 1, (151.8-101.8) /151.8=0.329 (32.9). %)).

From the above results, it can be seen that the heat dissipation is improved when the pad electrode is disposed between the surface acoustic wave resonators as close as possible to the surface acoustic wave resonator as the heat generating portion. Further, from comparison between the model (a) and the model (c), it can be seen that the heat dissipation is improved as the area of the pad electrode is as large as possible and the number of pad electrodes positioned between the surface acoustic wave resonators is increased.
Next, the evaluation of heat dissipation when the metal film 22 is formed on the back surface, back surface, and side surface of the piezoelectric substrate 1 is limited with respect to the difference in temperature rise due to the arrangement of the pad electrodes when signal power enters the surface acoustic wave device. It was obtained by thermal analysis using the element method.

  As a model for comparison, a thermal analysis model in which the metal film 22 is not formed on the back surface and side surface of the piezoelectric substrate 1 and the input / output pad electrode 3 is disposed on the outer peripheral portion of the conventional surface acoustic wave resonator. B1 was used. For model B1, the thickness of the metal film 22 on the back surface of the piezoelectric substrate 1 is 0.05 mm, model B2 is 0.1 mm, model B3 is 0.2 mm, model B4 is 0.2 mm, and piezoelectric substrate 1 A model B5 was obtained by forming a metal film 22 on the side surface of the piezoelectric substrate 1 with the thickness of the metal film 22 on the back surface of 0.1 mm.

The outer peripheral annular electrode 17 is evaluated as existing in all models. The same values as described above are used for the thermal conductivity of each material used as the analysis condition.
The results are shown in FIG.

  The maximum temperatures in the heat generating part near the surface acoustic wave resonator were 85.7 ° C for model B1, 75.5 ° C for model B2, 74.4 ° C for model B3, 72.7 ° C for model B4, and 66.6 ° C for model B5. The thermal resistance ratio from the heat generating part to the atmosphere decreases as the thickness of the metal film 22 increases. The thermal resistance is reduced by 19% compared to the model B1 which is 0.1 mm of the model B2 and does not have the metal film 22. Further, in the model B5 in which the metal film 22 is also formed on the side surface of the piezoelectric substrate 1, the thermal resistance ratio is reduced by 31%.

From the above results, it can be seen that the heat generated by the surface acoustic wave resonator can be efficiently dissipated by forming the metal film 22 on the back surface and side surfaces of the piezoelectric substrate 1 and depositing a predetermined film thickness.
Finally, the relationship between the thickness of the piezoelectric substrate 1 and the heat dissipation is similarly evaluated by thermal analysis using the finite element method for the difference in temperature rise due to the arrangement of the pad electrode when signal power enters the surface acoustic wave device. Asked. As a basic structure, a metal film 22 is not formed on the back and side surfaces of the piezoelectric substrate 1, and a conventional surface acoustic wave resonator having an input / output pad electrode 3 disposed on the outer peripheral portion thereof is used. The thickness of the LiTaO ₃ substrate used as the piezoelectric substrate 1 is 0.25 mm for the model C1, 0.35 mm for the model C2, and 0.45 mm for the model C3. The outer peripheral annular electrode 17 is evaluated as existing in all models. The same values as described above are used for the thermal conductivity of each material used as the analysis condition.

  The results are shown in FIG. The maximum temperatures in the heat generating part near the surface acoustic wave resonator were 85.7 ° C. for model C1, 81.7 ° C. for model C2, and 79.0 ° C. for model C3. The thermal resistance ratio from the heat generating part to the atmosphere decreases as the thickness of the piezoelectric substrate 1 increases. The thickness of the model C2 is 0.45 mm, and the thermal resistance is 11% lower than that of the model C1 having a thickness of 0.25 m.

From the above results, it can be seen that the heat dissipation of the heat generated by the surface acoustic wave resonator is improved as the thickness of the piezoelectric substrate 1 is increased.
As described above, when the structure of the present invention is adopted, the surface acoustic wave device is small and light, has excellent power durability, and can efficiently dissipate heat generated by the surface acoustic wave resonator while being face-down mounted. Can be provided. In addition, since a structure that actively dissipates heat is employed, there is little change in characteristics due to the temperature characteristics of the surface acoustic wave device, and stable characteristics can be obtained. As a result, it is possible to provide a surface acoustic wave device having excellent long-term reliability without causing destruction of electrode fingers of the IDT electrode 2.

It is a top view which shows the example of electrode arrangement | positioning of the surface acoustic wave element of this invention. It is a top view which shows the example of electrode arrangement | positioning including the pad electrode for thermal radiation of the surface acoustic wave element of this invention. It is sectional drawing which shows the surface acoustic wave apparatus which mounted the surface acoustic wave element of this invention in the circuit board. It is a top view which shows the example of electrode arrangement | positioning containing the annular electrode of the surface acoustic wave element of this invention. It is sectional drawing which shows the surface acoustic wave apparatus which mounted the surface acoustic wave element of this invention in the circuit board. 1 is a cross-sectional view illustrating a surface acoustic wave device according to the present invention in which a surface acoustic wave element having a metal film formed on the back surface of a piezoelectric substrate is mounted on a circuit board. 1 is a cross-sectional view illustrating a surface acoustic wave device according to the present invention, in which a surface acoustic wave element in which a metal film is also formed on a side surface of a piezoelectric substrate is mounted on a circuit board. It is sectional drawing which shows the surface acoustic wave apparatus which mounted the surface acoustic wave element of this invention in the circuit board. It is a top view which shows the example of electrode arrangement | positioning including the pad electrode for thermal radiation of the surface acoustic wave element of this invention. It is sectional drawing which shows the surface acoustic wave apparatus which mounted the surface acoustic wave element of this invention in the circuit board. It is sectional drawing which shows the surface acoustic wave apparatus which mounted the surface acoustic wave element of this invention in the circuit board. It is a top view which shows the example of electrode arrangement | positioning including the pad electrode for thermal radiation of the surface acoustic wave element of this invention. It is sectional drawing which shows the surface acoustic wave apparatus which mounted the surface acoustic wave element of this invention in the circuit board. It is sectional drawing which shows the surface acoustic wave apparatus which mounted the surface acoustic wave element of this invention in the circuit board. It is sectional drawing which shows the surface acoustic wave apparatus which mounted the surface acoustic wave element of this invention in the circuit board. It is sectional drawing which shows the surface acoustic wave apparatus which mounted the surface acoustic wave element of this invention in the circuit board. It is sectional drawing which shows the surface acoustic wave apparatus which mounted the surface acoustic wave element of this invention in the circuit board. It is each sectional drawing which shows the surface acoustic wave apparatus which mounted the surface acoustic wave element of this invention on the circuit board. It is a block diagram which shows the structure of the communication apparatus of this invention. It is a top view showing the input / output pad electrode position of the model used for the thermal analysis for evaluating the heat dissipation in the Example of this invention. It is a top view showing the input / output pad electrode position of the model used for the thermal analysis for evaluating the heat dissipation in the Example of this invention. It is a diagram which shows the relationship between the thickness of the metal film on a piezoelectric substrate and thermal resistance ratio which evaluated the heat dissipation in the Example of this invention by the thermal analysis. It is a diagram which shows the relationship between the thickness of the piezoelectric substrate which evaluated the heat dissipation in the Example of this invention by thermal analysis, and thermal resistance ratio. It is sectional drawing which shows the conventional surface acoustic wave apparatus.

Explanation of symbols

1: Piezoelectric substrate 2: IDT electrode 3: Input / output pad electrode 4: Grounding pad electrode 9: Reflector electrode 10: Lead electrode 11: Circuit board 12: Connection electrode 13: Bump connector 15: Sealing resin 16a, 16b: pad electrode for heat dissipation 17: annular electrode 18: annular sealing material S: vibration space

Claims (5)

In a surface acoustic wave device having a structure in which a surface acoustic wave element is mounted face-down on a circuit board,
The surface acoustic wave element includes a plurality of surface acoustic wave resonators each having an IDT electrode and a reflector electrode on a main surface of a piezoelectric substrate, and these surface acoustic wave resonators are connected to each other.
In the main surface of the piezoelectric substrate, a heat dissipation pad electrode is formed in a portion between the surface acoustic wave resonators , and an annular electrode surrounding the surface acoustic wave element is formed,
The heat dissipation pad electrode is not connected to any electrode on the main surface of the piezoelectric substrate,
An annular conductor facing the annular electrode is formed on the mounting surface of the circuit board,
The surface acoustic wave device according to claim 1, wherein the heat dissipating pad electrode is connected to the annular conductor via a bump connector and a connection electrode formed on the circuit board . 2. The surface acoustic wave device according to claim 1 , wherein the annular conductor is connected to a bottom electrode for heat dissipation formed on a bottom surface of the circuit board via a through conductor penetrating the circuit board . 2. The surface acoustic wave device according to claim 1 , wherein the annular conductor is connected to a bottom electrode for heat dissipation formed on a lower surface of the circuit board via a side conductor formed on a side surface of the circuit board . The surface acoustic wave device according to any one of claims 1 to 3, wherein the plurality of surface acoustic wave resonators constitute a ladder type circuit in which they are connected in series and in parallel . 5. A communication apparatus using the surface acoustic wave device according to claim 1 as a filter circuit component.

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