JP2008011125A - Surface acoustic wave device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain high reliability and high quality by improving mechanical strength and mounting strength, and by securing air-tightness and humidity resistance in a SAW device provided with a CSP-type SAW element. <P>SOLUTION: The SAW device 1 is provided with the CSP-type SAW element 2 which is formed by directly joining a SAW chip 5 with a cover 6, and a flat-plate-like base 3. The SAW element is flipchip-mounted on the base so as to directly connect its lead-out electrodes 17, 17 with connection terminals 19, 19 of the base. The SAW element is sealed with a mold resin 4 coating its outer face and the base surface, so as to be further firmly fixed mechanically while being protected from damages such as chipping and cracking. Even if the mold resin does not have sufficient air-tightness or humidity resistance, it is possible to sufficiently secure the air-tightness or the humidity resistance of the SAW element itself. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a SAW device such as a resonator, a filter, and an oscillator using surface acoustic wave (SAW).

  Conventionally, a resonator, a filter, an oscillator, etc. using a SAW element including an IDT (interdigital transducer) made of interdigitated electrodes formed on the surface of a piezoelectric substrate and a reflector and using a surface acoustic wave excited from the IDT SAW devices are widely used in various electronic devices. In particular, in recent years, in addition to higher frequency and higher accuracy of SAW devices that support higher speeds of information communication, further downsizing and thinning are required for use in small and thin information devices such as IC cards. It is requested.

  Conventional SAW devices generally hermetically seal the SAW element in a package in which a metal lid is joined to the base of a ceramic material by seam welding. In the SAW element, the bonding pad on the surface of the piezoelectric substrate is generally electrically connected to the connection terminal on the package side by wire bonding. Such a conventional structure has a large number of parts and a complicated structure, and requires a large space in the package for the bonding wire, which limits the reduction in thickness and size of the SAW device.

  Therefore, the piezoelectric substrate includes a SAW element having an IDT electrode, a takeout electrode and an anode junction on the surface of the piezoelectric substrate, and a cover substrate in which an external electrode is provided on a glass plate having a through hole, and the takeout electrode and the external electrode are electrically connected. A two-layered SAW device called a CSP type in which an IDT electrode is sealed by connecting and joining a cover substrate and an anodic bonding portion is known (see, for example, Patent Document 1). In this configuration, the base and the bonding wire for mounting the SAW element are omitted, the configuration of the entire apparatus can be made simple, small and thin, the manufacturing cost can be reduced, and the frequency characteristics can be stabilized.

  In addition, a SAW device is known in which a SAW chip is flip-chip mounted on a mounting substrate face down, and an outer surface of the SAW chip is sealed with a resin so as to define an airtight inner space in an area including the IDT (for example, , See Patent Documents 2 and 3). This provides a high-quality SAW device that is protected from breakage so that the outer surface of the SAW chip mounted on the substrate is not exposed, and is excellent in moisture resistance and airtightness.

  Further, in such a SAW device, in order to prevent the resin sealing the SAW chip mounted on the substrate from flowing in, a SAW device in which a dam made of resin is formed around the electrode forming surface of the SAW chip is known. (For example, see Patent Document 4). In addition, a SAW device is known in which a SAW chip is flip-chip mounted face down in a cavity provided in a package and resin-sealed so as to form a hollow portion in an IDT formation region of the SAW chip (for example, Patent Document 5). , 6).

Japanese Patent Laid-Open No. 8-213874 Japanese Patent No. 3689414 JP 2003-101383 A JP 2005-39331 A JP 2002-261177 A JP-A-2005-33280

  The above-described SAW device having the CSP structure is sufficiently airtight and exhibits excellent aging characteristics. However, when this is directly mounted on a circuit board or the like as an individual electronic component, both the SAW chip and the cover substrate are formed of a relatively fragile piezoelectric material and are exposed to the outside as they are. There is a risk of damage such as chipping, cracking, and chipping at the corners, which may impair airtightness and moisture resistance. For this reason, it is difficult to handle the SAW device during mounting and during use after mounting, resulting in a decrease in reliability.

  Further, the CSP-structured SAW device has the following problems when it is surface-mounted on a circuit board or the like by flip chip bonding or the like. That is, since the connection terminal formed on the outer surface of the SAW chip or the cover substrate is formed of a relatively thin electrode film, there is a problem that a cracking phenomenon occurs and the bonding strength tends to be lowered. For this reason, there is a possibility that it may be easily peeled off by an impact such as dropping, and high reliability cannot be obtained. In addition, since both the SAW chip and the cover substrate have relatively low rigidity, stress when mounted on a circuit board or the like directly acts on the SAW chip, which may adversely affect the vibration characteristics.

  Further, the SAW device described in Patent Document 2 and the like generally has difficulty in ensuring sufficient airtightness and moisture resistance due to the properties of the resin that seals the SAW chip. Therefore, practically necessary and sufficient quality cannot be obtained particularly when used as a resonator.

  Therefore, the present invention has been made in view of the above-described conventional problems, and the object thereof is not only provided with a SAW element having a so-called CSP type two-layer structure, thereby enabling miniaturization. An object of the present invention is to provide a SAW device having high reliability and quality by improving mechanical strength and mounting strength, ensuring excellent airtightness and moisture resistance, and preventing changes in characteristics due to external stress.

  According to the present invention, in order to achieve the above object, a SAW element and a base for supporting the SAW element are provided, and the SAW element is drawn from the IDT electrode and the IDT electrode on the main surface of the piezoelectric substrate. A SAW chip having an extraction electrode and a cover made of an insulating substrate that is integrally bonded to the piezoelectric substrate main surface of the SAW chip and defines a space for hermetically sealing the IDT electrode between the SAW chip and the SAW chip. A cover electrode formed on a surface of the insulating substrate facing the piezoelectric substrate and electrically connected to the extraction electrode of the SAW chip; and a cover formed on the surface of the insulating substrate opposite to the piezoelectric substrate. The connection electrode and the extraction electrode are electrically connected to each other by a conductive material provided in a through hole provided in the insulating substrate and hermetically sealed, and the base But SAW A connection terminal for electrically connecting the lead electrode and an external terminal electrically connected to the connection terminal for connecting to the outside, wherein the SAW element connects the lead electrode to the base. The SAW element outer surface and the base surface are electrically connected to the terminals and mounted on the base, and the SAW element and the base are coated mechanically by, for example, molding or potting or with a sheet-like resin material. A SAW device to be coupled is provided.

  By mounting the SAW element on the base and covering with the resin material in this way, the SAW chip and the cover made of a relatively fragile material are surely protected from damage such as chipping, cracking, and chipping, and the CSP structure originally has. Excellent airtightness and moisture resistance can be sufficiently secured, and the SAW element can be more firmly fixed to the base. Thereby, the mechanical strength and bonding strength of the SAW element can be improved, and a highly reliable and high quality SAW device can be obtained.

  In one embodiment, the base is formed of a flat substrate, a connection terminal is provided on one surface thereof, and an external terminal is provided on the other surface. As a result, the structure of the SAW device can be simplified, the number of parts can be reduced, and the size and cost can be reduced.

  In another embodiment, the base is formed in a box shape with an open top, and the SAW element is mounted therein, so that the SAW element can be more reliably protected from damage with a smaller amount of resin material and stronger. Can be fixed to the base. In this case, the SAW element can be mounted face-down by providing the connection terminal on the bottom surface inside the box-shaped base and providing the external terminal on the bottom surface.

  In one embodiment, the SAW element is mounted on the base by flip chip bonding, so that the SAW device can be made thinner. Even in this case, since the SAW element is covered with the resin material, sufficient bonding strength is ensured. In another embodiment, the SAW element can be electrically connected to the base by wire bonding, and the structure of the base can be simplified.

Hereinafter, preferred embodiments of a SAW device to which the present invention is applied will be described in detail with reference to the accompanying drawings.
FIG. 1 shows the configuration of a first embodiment of a SAW device according to the present invention. The SAW device 1 includes, for example, a SAW element 2 used as a resonator, and a base 3 for supporting the SAW element. The SAW element 2 is mounted on the base 3 as described later, and the whole is sealed with the mold resin 4.

  As shown in FIG. 2, the SAW element 2 has a so-called CSP type two-layer structure in which a SAW chip 5 and a cover 6 are directly joined. The SAW chip 5 comprises a rectangular piezoelectric substrate 7 as shown in FIGS. 1B and 1C, an IDT 8 comprising a pair of crossed finger electrodes is formed at the center of the upper surface, and reflectors are provided on both sides in the longitudinal direction. 9, 9 are formed. The interdigitated electrode is formed in the vicinity of the diagonal corner of the piezoelectric substrate, with the lead wires 10 and 10 being pulled out from the bus bar along the longitudinal edges of the piezoelectric substrate 7 in opposite directions. 11 and 11. In the periphery of the piezoelectric substrate 7, a metal joint 12 is provided over the entire circumference.

  In this embodiment, the piezoelectric substrate 7 is made of quartz, but other piezoelectric materials such as lithium tantalate and lithium niobate can also be used. The interdigitated electrodes, reflectors, and lead wires are formed of Al films from the viewpoint of their characteristics, workability, and cost, but other conductive metal materials such as commonly used aluminum alloys are used. You can also.

  The cover 6 is made of a rectangular substrate made of the same crystal as the piezoelectric substrate 7. When the piezoelectric substrate 7 is formed of a piezoelectric material other than quartz, it is preferable to form the cover 6 with the same piezoelectric material because the thermal expansion coefficient can be made equal. Alternatively, the cover 6 can be formed of a glass material or an insulating material having a thermal expansion coefficient similar to or close to that of the piezoelectric material of the piezoelectric substrate 7.

  The cover 6 is provided with tapered through holes 13 from the upper surface toward the lower surface. The through-holes are arranged diagonally corresponding to the extraction electrodes 11 and 11 so as to reduce the outer dimension of the SAW chip 5 while ensuring the pitch dimension. On the lower surface of the cover 6, connection electrodes 14 and 14 having a shape corresponding to the extraction electrode are formed on the peripheral edges of the respective through holes. Further, a metal joint 15 is provided on the entire periphery of the lower surface of the cover 6.

  The inner peripheral surfaces of the through-holes 13 and 13 and the connection electrode continuous therewith are covered with metal films 16 and 16 made of a conductive material. On the upper surface of the cover 6, extraction electrodes 17 and 17 are formed on the peripheral edges of the through holes. Each extraction electrode 17, 17 is electrically connected to the corresponding connection electrode 14, 14 of the SAW chip 5 via the metal film 16, 16 of the adjacent through hole.

  In this embodiment, the extraction electrodes 11 and 11 and the metal joint 12 are formed at the same height with a Cr / Au film or a Cr / Ni / Au film. Similarly, the connection electrodes 14 and 14 and the metal joint 15 are formed at the same height with a Cr / Au film or a Cr / Ni / Au film. Similarly, the metal films 16 and 16 and the extraction electrodes 17 and 17 are formed of a Cr / Au film or a Cr / Ni / Au film.

  The SAW chip 5 and the cover 6 are integrally joined to each other by the metal joint 12 and the metal joint 15 and the extraction electrodes 11 and 11 and the connection electrodes 14 and 14 by thermocompression bonding. Thus, the IDT 8 and the reflectors 9 and 9 are hermetically sealed in the space defined between the SAW chip 5 and the cover 6. In particular, when the thicknesses of the extraction electrode, the connection electrode, and the metal joints 9 and 13 are selected so as to be thicker than the Al film in a state where they are joined, the upper ends of the IDT and the reflector and the lower surface of the cover 3 are selected. A gap is defined between the two. Thereby, since the IDT and the reflector do not contact the cover 3, it is possible to ensure the excitation / reception operation of the SAW element expected in advance. In another embodiment, an AuSn alloy film is formed on the Cr / Au film of the connection electrodes 14 and 14 and the metal joint 15, and the SAW chip and the cover are similarly joined by thermocompression bonding or eutectic bonding. it can.

  The cross finger electrodes of the IDT 8 are electrically connected to corresponding extraction electrodes 17 and 17 of the cover 6 via extraction electrodes 11 and 11 and connection electrodes 14 and 14, respectively. Each through hole of the cover 6 is filled with a sealing material 18 made of a conductive material, whereby electric conduction between the extraction electrode and the connection electrode and the extraction electrode and airtight sealing in the through hole are achieved. High reliability. For the sealing material 18, for example, a conductive material such as AuSn, AuGe, a solder material, and high-temperature solder is used.

  In this embodiment, the base 3 for supporting the SAW element is formed of a flat plate made of a substrate material having a necessary rigidity, such as a ceramic substrate, a resin substrate, and a printed circuit board that are generally used for circuit boards and electronic components. . Connection terminals 19, 19 are formed on the upper surface of the base 3, that is, the surface facing the SAW element 2. External terminals 20, 20 are formed on the bottom surface of the base 3, that is, on the bottom surface of the SAW device 1. The external terminals 20 and 20 are electrically connected to the corresponding connection terminals 19 and 19 through via holes 21 and 21 that penetrate the base 3 vertically. Bumps 22 and 22 made of, for example, solder are formed on the connection terminals 19 and 19, for example.

  The SAW element 2 is positioned on the base 3 with the cover 6 side down, and the lead electrodes 17 and 17 are directly connected to the corresponding connection terminals 19 and 19 by flip chip bonding using the solder bumps 22 and 22, respectively. Thereby, the SAW element 2 is electrically connected to the base 3 and mechanically fixed while reducing the thickness of the entire device. Since the base 3 has rigidity, when the SAW device 1 is mounted on a circuit board or the like, the possibility that the stress acts on the SAW element 2 and affects the vibration characteristics is solved.

  The outer peripheral surface and upper surface of the SAW element 2 and the upper surface of the base 3 are completely encapsulated with the mold resin 4. The mold resin 4 protects the SAW element 2 from damage such as chipping, cracking, and chipping on the outer surface and corners thereof. In addition, since the mold resin 4 is provided so as to mechanically connect the outer surface of the SAW element 2 and the upper surface of the base 3, the SAW element 2 is mechanically firmly fixed on the base 3. In particular, in this embodiment, since the mold resin 4 is also filled in the gap between the SAW element 2 and the upper surface of the base 3, the SAW element 2 can be fixed more firmly on the base 3.

  Further, as described above, the SAW element 2 having the CSP structure in which the SAW chip 5 and the cover 6 are directly bonded has sufficient airtightness and moisture resistance of the CSP structure. Therefore, even when the sealing structure by the mold resin 4 does not have sufficient airtightness or moisture resistance, the airtightness and moisture resistance of the SAW element 2 are not affected at all. Therefore, the mold resin 4 can be provided at low cost, and the manufacturing cost of the SAW device 1 can be reduced.

  FIG. 3 shows a modification of the SAW device of the first embodiment shown in FIG. The SAW device 31 of this modification is different from the first embodiment in that a resin sheet 32 is used instead of the mold resin 4 in order to encapsulate the outer peripheral surface and upper surface of the SAW element 2 and the upper surface of the base 3. The resin sheet 32 is placed on the SAW element 2 so as to include the upper surface of the base 3 and is adhered to the outer surface of the SAW element 2 and the upper surface of the base 3. As a result, similarly, the outer surface and corners of the SAW element 2 can be protected from damage such as chipping, cracking, and chipping, and the SAW element 2 and the base 3 can be mechanically coupled to be firmly fixed mechanically. it can.

  FIG. 4 shows the configuration of a second embodiment of the SAW device according to the present invention. In the SAW device 41 of the second embodiment, a base 42 for supporting the SAW element 2 is a rectangular frame having an open top by laminating a rectangular frame-shaped ceramic thin plate 44 on a flat ceramic thin plate 43. It is formed in a box shape. Connection terminals 45, 45 are formed on the upper surface of the lower ceramic thin plate 43 so as to be exposed inside the box-type base 42 and overlap the upper ceramic thin plate 44. External terminals 46, 46 are formed on the lower surface of the ceramic thin plate 43, that is, the bottom surface of the SAW device 1. The external terminals 46 and 46 are electrically connected to the corresponding connection terminals 45 and 45 through via holes 47 and 47 provided at positions that penetrate the ceramic thin plate 43 in the vertical direction and overlap the upper ceramic thin plate 44, respectively. Has been. Bumps 48 and 48 made of, for example, solder are formed on the connection terminals 45 and 45, for example.

  The SAW element 2 is positioned on the ceramic thin plate 43 in the base 42 with the cover 6 side down, and the lead electrodes 17 and 17 are connected to the corresponding connection terminals 45 and 45 by flip chip bonding using the solder bumps 48 and 48. Connect directly with. Thereby, the SAW element 2 is electrically connected to the base 42 and mechanically fixed. Since the box-shaped base 42 described above has sufficient rigidity, when the SAW device 41 is mounted on a circuit board or the like, the possibility that the stress acts on the SAW element 2 and affects the vibration characteristics is eliminated. .

  The inside of the box-type base 42 is filled with, for example, a resin material 49 by potting in the gap between the inner surface and the outer surface of the SAW element 2. Further, the resin material 49 is provided so as to completely cover the upper surface of the SAW element 2. The combination of the resin material 49 and the box-type base 42 completely protects the outer surface and corners of the SAW element 2 from damage such as chipping, cracking, and chipping. Further, the SAW element 2 is mechanically and firmly fixed between the inner surface of the base 42 by the resin material 49.

  Further, the SAW element 2 having a CSP structure in which the SAW chip 5 and the cover 6 are directly bonded has sufficient airtightness and moisture resistance. Therefore, even when the sealing structure by the resin material 49 does not have sufficient airtightness or moisture resistance, the airtightness and moisture resistance of the SAW element 2 are not affected at all. Therefore, the mold resin 49 can be provided at low cost, and the manufacturing cost of the SAW device 41 can be reduced.

  FIG. 5 shows a modification of the SAW device of the second embodiment shown in FIG. In the SAW device 51 of this modification, the base 52 for supporting the SAW element 2 is formed by laminating a flat ceramic thin plate 53 and a rectangular frame thin ceramic plate 54 in the same manner as in the second embodiment, It is formed in an open rectangular box shape. Inside the box-type base 52, the SAW element 2 is bonded and fixed to the upper surface of the ceramic thin plate 53 with an adhesive 55 with the SAW chip 5 side down. Similarly, since the box-shaped base 52 has sufficient rigidity, when the SAW device 51 is mounted on a circuit board or the like, the possibility that the stress acts on the SAW element 2 and affects the vibration characteristics is eliminated. .

  Connection terminals 56 are formed on the upper surface of the upper frame-shaped ceramic thin plate 54. External terminals 57, 57 are formed on the lower surface of the lower ceramic thin plate 43, that is, on the bottom surface of the SAW device 51. The external terminals 57 and 57 are electrically connected to the corresponding connection terminals 56 and 56 by metal films 58 and 58 of conductive material formed on the side surfaces of the box-type base 52, respectively. The extraction electrodes 17 and 17 of the SAW element 2 are electrically connected to the corresponding connection terminals 56 and 56 by bonding wires 59 and 59, respectively.

  The resin material 60 is provided, for example, by potting so as to fill a gap between the inner surface of the box-type base 52 and the outer surface of the SAW element 2 and completely cover the upper surface of the SAW element 2 and the bonding wires 59 and 59. By the combination of the resin material 60 and the box-type base 52, the outer surface and corners of the SAW element 2 are completely protected from damage such as chipping, cracking, and chipping. Further, the SAW element 2 is mechanically and firmly fixed between the inner surface of the base 52 by the resin material 60.

  In this embodiment, the external terminal and the connection terminal are connected by the metal film formed on the side surface of the base 52, but the connection can be made using the via hole penetrating the base as in each of the embodiments described above. Conversely, in each of the embodiments described above, the external terminal and the connection terminal can be connected by a metal film formed on the side surface of the base.

  The present invention can be similarly applied to other SAW devices such as filters and oscillators using SAW elements. For example, a modularized SAW device can be configured by mounting electronic components such as an IC element for driving the SAW element on the base of each of the above embodiments.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention can be implemented by adding various modifications and changes to the above embodiments. For example, the SAW element is not limited to the CSP structure of the embodiment shown in FIG. 2, and can be similarly applied to various different CSP structures. Further, when the SAW element extraction electrode and the base connection terminal are connected face-down, another means such as a conductive adhesive may be used instead of the solder bump.

1 is a cross-sectional view showing a first embodiment of a SAW device according to the present invention. (A) is a plan view showing the SAW resonator of FIG. 1, (B) is a sectional view taken along the line II-II, and (C) is a plan view showing the SAW chip with the cover removed. Sectional drawing which shows the modification of 1st Example. Sectional drawing which shows 2nd Example of this invention. Sectional drawing which shows the modification of 2nd Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 31, 41, 51 ... SAW device, 2 ... SAW element, 3, 42, 52 ... Base, 4 ... Mold resin, 5 ... SAW chip, 6 ... Cover, 7 ... Piezoelectric substrate, 8 ... IDT, 9 ... Reflection 10 ... lead wire, 11 ... extraction electrode, 12 ... metal joint, 13 ... through hole, 14 ... connection electrode, 15 ... metal joint, 16, 58 ... metal film, 17 ... lead electrode, 18 ... sealing Material, 19, 45, 56 ... Connection terminal, 20, 46, 57 ... External terminal, 21, 47 ... Via hole, 22, 48 ... Bump, 32 ... Resin sheet, 43, 44, 53, 54 ... Ceramic thin plate, 49 , 60: Resin material, 59: Bonding wire.

Claims (6)

A surface acoustic wave (SAW) element, and a base for supporting the SAW element,
The SAW element is integrally bonded to the main surface of the piezoelectric substrate of the SAW chip, the SAW chip having an IDT electrode and a lead electrode drawn from the IDT electrode on the main surface of the piezoelectric substrate, and the SAW chip A cover made of an insulating substrate that defines a space for hermetically sealing the IDT electrode therebetween, and the cover is formed on a surface of the insulating substrate facing the piezoelectric substrate, and the SAW chip has the cover. A connection electrode electrically connected to the extraction electrode; and an extraction electrode formed on a surface of the insulating substrate opposite to the piezoelectric substrate, wherein the connection electrode and the extraction electrode are the insulating Electrically connected by a conductive material provided in a through hole provided in the conductive substrate and hermetically sealed,
The base includes a connection terminal for electrically connecting with the extraction electrode of the SAW element, and an external terminal for electrical connection with the connection terminal and for connection with the outside.
The SAW element is mounted on the base by electrically connecting the extraction electrode to the connection terminal, and the outer surface of the SAW element and the surface of the base are covered with a resin material, whereby the SAW element A surface acoustic wave device, wherein the base and the base are mechanically coupled.   2. The surface acoustic wave device according to claim 1, wherein the base is made of a flat substrate, the connection terminals are provided on one surface thereof, and the external terminals are provided on the other surface. .   The surface acoustic wave device according to claim 1, wherein the base has a box shape with an open top, and the SAW element is mounted therein.   The surface acoustic wave device according to claim 3, wherein the connection terminal is provided on an inner bottom surface of the base having a box shape, and the external terminal is provided on a lower surface thereof.   5. The surface acoustic wave device according to claim 1, wherein the SAW element is mounted on the base by flip chip bonding.   The surface acoustic wave device according to claim 3, wherein the SAW element is electrically connected to the base by wire bonding.

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