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Dokumentenidentifikation EP1653613 25.10.2007
EP-Veröffentlichungsnummer 0001653613
Titel In Keramikpackung eingekapseltes akustisches Oberflächenwellenfilter mit darin eingebauter Kapazität
Anmelder Oki Electric Industry Co., Ltd., Tokio/Tokyo, JP
Erfinder Shimamura, Hajime, 1-chome Minato-ku 105, Tokyo, JP
Vertreter derzeit kein Vertreter bestellt
DE-Aktenzeichen 69738146
Vertragsstaaten DE, FR, GB
Sprache des Dokument EN
EP-Anmeldetag 07.02.1997
EP-Aktenzeichen 051105138
EP-Offenlegungsdatum 03.05.2006
EP date of grant 12.09.2007
Veröffentlichungstag im Patentblatt 25.10.2007
IPC-Hauptklasse H03H 9/05(2006.01)A, F, I, 20060330, B, H, EP

Beschreibung[en]
BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a SAW (surface acoustic wave) filter encapsulated in a ceramic package, and a ceramic package therefore.

Description of the Background Art

It is common practice with a ceramic package for encapsulating a SAW filter to form pads on one of its opposite major surfaces. A SAW filter chip or wafer chip is affixed to the package by adhesion or similar technology with its one major surface carrying a pattern of electrodes facing upward. The pattern of electrodes, i.e., electrode strips are connected to the pads of the package by bonding wires. A lid is mounted on the top of the package and sealed by solder. The electrodes are printed on a substrate of piezo-electric material, such as LiTaO3.

The above-mentioned conventional ceramic package has a problem that the adjustment of impedance is extensively difficult partly because the surface of the filter chip carrying the electrode pattern and facing upward is hermetically sealed in the package and partly because the electrode pattern itself is printed on LiTaO3 or similar fragile material.

EP-A-0 637871 discloses a SAW device comprising a ceramic package wherein the SAW filter chip is mounted such that the pattern of electrodes face down towards the pads on the surface of the ceramic package. Metallic bumps form the connections between the SAW filter chip and the electrode pads. In one embodiment, the ceramic package comprises a grounded counter electrode pattern formed on the surface of the ceramic package and facing the surface of the SAW filter chip comprising the patter of electrodes. The grounded counter electrode is connected in a manner that reduces the effect of directly propagated electromagnetic waves between input and output electrodes on the surface of the SAW filter.

JP 07 212180 A discloses another SAW device wherein the SAW filter chip is mounted such that the pattern of electrodes face down towards the electrode pads on the surface of the ceramic package and wherein metallic bumps are used to connect the chip and the ceramic package. The SAW filter chip is placed in a recess in the ceramic package and is further attached with an epoxy adhesive to insulating glass elements positioned in the periphery of the recess. The epoxy adhesive provides shock resistance to the device.

JP 05 335 878 A discloses another SAW device wherein the chip is mounted on bumps on the plateau region of a shoulder formed in the recess.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a ceramic package for a SAW filter capable of promoting easy adjustment of impedance.

According to the invention, there is provided a SAW filter comprising a SAW filter made of piezoelectric material and having a major surface on which a pattern of electrodes is formed to propagate surface acoustic waves. The SAW filter further comprises a ceramic package having a recess formed for encapsulating said SAW filter chip therein. The SAW filter chip is mounted to said ceramic package such that at least part of the pattern of electrodes faces a bottom of the recess. Moreover, bumps, formed on the bottom of the recess, are provided between the bottom of the recess and the major surface of the SAW filter chip for connecting and supporting said SAW filter chip to said ceramic package. The SAW filter, according to the invention, is characterised by further comprising a conductive pad formed on the bottom of the recess, the bumps being arranged to define an air gap between the part of the pattern of electrodes and part of said conductive pad, and a shoulder with a plateau region formed in the recess, said SAW filter chip and said shoulder being arranged such that the plateau region of said shoulder faces and is spaced from end regions of the major surface.

A capacitance is thereby established between the conductive pad and the propagation paths on the major surface of the SAW filter chip. The shoulder may be provided as part of a stepped structure that surrounds the SAW filter chip.

BRIEF DESCRIPTION OF THE DRAWINGS

The object and features of the present invention will become more apparent from consideration of the following detailed description taken in conjunction with the accompanying drawings in which:

  • FIG. 1A is a plan view showing a ceramic package for encapsulating a SAW filter and embodying the present invention;
  • FIG. 1B is a front view of the package shown in FIG. 1A;
  • FIG. 1C is a rear view of the package shown in FIG. 1A;
  • FIG. 2 is a plan view, similar to FIG. 1, showing an alternative embodiment of a ceramic package in accordance with the present invention;
  • FIG. 3 shows a section of the package of the embodiment shown in FIGS. 1A, 1B and 1C, cut along a dot-and-chain line III-III in FIG. 1A, together with a SAW filter mounted thereon;
  • FIG. 4 is a fragmentary, enlarged view of a portion designated with a circle A included in the assembly shown in FIG. 3;
  • FIG. 5 shows an equivalent circuit to a SAW filter encapsulated in a conventional ceramic package;
  • FIGS. 6, 7 and 8 are equivalent circuit diagrams, similar to FIG. 5, each showing part of a specific circuit configuration available with the SAW filter encapsulated in the package of FIGS. 1A, 1B and 1C;
  • FIGS. 9 and 10 are equivalent circuit diagrams, similar to FIG. 5, each showing part of a specific configuration available with the SAW filter included in the package shown in FIG. 2; and
  • FIG. 11 is a section partially showing a conventional ceramic package and a SAW filter mounted thereon.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

To better understand the present invention, a brief reference will be made to a conventional ceramic package for encapsulating a surface acoustic wave (SAW) filter, shown in FIG. 11. As shown, the package, generally designated with a reference numaral 1, has metal pads 2 formed on one of its opposite major surfaces. A SAW filter chip or wafer chip 3 is affixed to the package 1 by, e.g., adhesive 5 with its surface 4 carrying a pattern of electrodes facing upward. The electrode pattern, i.e., electrodes 6 are connected to the pads 2 of the package 1 by bonding wires 7. A lid, not shown, is mounted on the top of the package 1 and sealed by solder. The electrodes 6 are printed on a substrate of piezoelectric substance such as LiTaO3.

The problem with the afore-mentioned conventional package 1 is that the adjustment of impedance is extensively difficult partly because, on one hand, the patterned surface 4 is hermetically sealed in the package 1 and, on the other hand, partly because the electrode pattern itself is printed on LiTaO3 or similar fragile material, as stated earlier.

Referring now to FIGS. 1A, 1B and 1C, a ceramic package for encapsulating a SAW filter in accordance with an embodiment of the present invention will be described. As shown in FIG. 1A, the package, generally designated with a reference numeral 10, is generally of a rectangular box. The package 10 includes an input terminal 11, an output terminal 12, and four ground terminals 13-16 formed in a recess 10C cut therein. The ground terminals are to be connected to ground. As shown in FIG. 1B, the output terminal 12 and ground terminals 15 and 16 are respectively connected to terminal pads 12A, 15A and 16A, which are formed on one or front side face 10A of the package 10. Likewise, as seen from FIG. 1C, the input terminal 11 and ground terminals 13 and 14 are respectively connected to other terminal pads 11A, 13A and 14, which are also formed on another side, or rear face 10B of the package 10 opposite to the front side face 10A.

A generally rectangular pad 17 is formed of metal and positioned on the generally flat bottom 10D of the recess 10C formed in the package 10. The metal pad 17 is surrounded by the input terminal 11, output terminal 12, and ground terminals 13-16 as depicted. It is to be noted that the pad 17 may be provided with any desired shape and may be located at any desired position on the bottom surface 10D of the package 10 shown in FIG. 1A. In FIG. 1A, a SAW filter chip 31 and bumps 32 to which the filter chip 31 is connected are indicated by phantom lines. How to support the chip 31 by the bumps 32 will be described later.

FIG. 2 shows an alternative embodiment of the present invention. In FIG. 2, the structural elements like those shown in FIGS. 1A, 1B and 1C are designated by the same reference numerals, and a detailed description thereof will not be made in order to avoid redundancy. As shown, this embodiment may be the same as what is shown in and described with reference to FIGS. 1A, 1B and 1C except that with the FIG. 3 embodiment the metal pad 17 is connected to the ground terminals 13-16 by connections, such as wires or metal strips, 18-21, respectively.

How the SAW filter chip 31 is mounted to the ceramic package 10 shown in FIGS. 1A-1C will be described with reference to FIGS. 3 and 4. As shown in FIG. 3, the filter chip 31 is mounted to the package 10 face down, i.e., with one of its primary surface 31A carrying an electrode pattern 33 facing downward in the figure. The filter chip 31 is connected to the bottom surface 10D of the package 10 by the bumps 32. The package 10 includes a shoulder 34 for forming an appropriate air gap between the electrode pattern or propagation paths 33 of the filter chip 31 and the pad 17 of the package 10. As shown in FIG. 3, the shoulder has a steep slope 34A and a plateau region 34B. Moreover, when the SAW filter chip is mounted with its primary surface 31A facing downward, as shown in FIG. 3, it overlaps the plateau region 34B of the shoulder 34 such that the plateau region 34B of the shoulder faces and is spaced from the end regions 31B of the primary surface. The shoulder 34 has a height, as measured from the bottom 10D of the recess 10C formed in the package 10, so selected as not to affect the connection using the bumps 32. The electrode pattern or propagation paths 33 are printed on the primary surface 31A of the chip 31 in the form of metal, comb-like strips, for example, which are adapted to propagate surface acoustic waves over the surface of the piezoelectric substrate 31 along the paths 33.

A lid, shown with a phantom line 50, FIG. 3, is fitted on the top of the recess 10C of the package 10 in order to seal the package 10. In this configuration, as imaginarily shown in FIG. 4, a capacitance C is produced between the propagation paths 33 of the filter chip 31 and the pad 17 of the package 10 due to the above-mentioned gap. By adjusting the height of the bumps 32 to vary the capacitance C, it is possible to control the impedance and phase of the propagation paths 33. This is also true with the alternative embodiment shown in FIG. 2.

Assume that a three-stage SAW filter is mounted on a conventional ceramic package by way of example. Then, the SAW filter encapsulated in the package in the conventional way is usually represented by an equivalent circuit shown in FIG. 5. It is noted that a capacitance is not formed in the circuitry. By contrast, when such a SAW filter is now mounted on the ceramic package of the type shown in FIGS. 1A, 1B and 1C, a capacitance or capacitances can be added, as shown in FIG. 6, 7 or 8. Specifically, a capacitance C, (FIG. 6), a capacitance C2 (FIG. 7) or capacitances C3-C11 (FIG. 8) can be added, as desired, by appropriately providing, positioning and shaping the metal pads 17, as well as adjusting the height of the bumps 32. The application shown in FIG. 8 is of a maximum number of capacitances available with this specific circuit configuration. With the FIG. 8 application, the capacitances C3, C4, C5, C7, C8, C9 and C11 are inserted in serial to the propagation paths 33. The remaining capacitances C6 and C10 have one electrodes thereof grounded, established by grounding metal pads 17 by connection wires 18, 19, 20 and 21 to the ground terminal 12, 14, 15 and 16, as shown in FIG. 2.

Likewise, as shown in FIG. 9, when the above filter is mounted on the ceramic package 10 of the type shown in FIG. 2, a capacitance C12 can be added in a parallel connection. Alternatively, as shown in FIG. 10, capacitances C13, C14 and C15 may be added in a plurality of parallel connections. In any case, the capacitance or capacitances allow the impedance of the SAW filter encapsulated in the package to be varied and thereby allow the frequence of the filter to appropriately be adjusted. Moreover, because the patterned surface of the filter chip 31 faces downward, namely directed to the botom 10D, it is protected from solder which may fly in the event of sealing of the package.

In summary, it will be seen that the present invention provides a ceramic package for encapsulating a SAW filter and having various unprecedented advantages, as follows. Because the package includes a metal pad, a capacitance can be varied with ease on the bases of the shape of the pad. As a result, the impedance and phase of propagation paths can be varied, as desired. Further, bumps allow a SAW filter chip to be readily mounted to the package and reduce the cost of the package. Moreover, a shoulder formed in the recess of the package and surrounding the filter chip further promotes easy mounting of the chip and implements automated production. In addition, the capacitance added to the packaged SAW filter varies the impedance and thereby allows the frequency of the SAW filter to be adjusted.

While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention. For example, while the illustrative embodiments have concentrated on a ceramic package for a SAW filter, they are similarly applicable to an RF (Radio Frequency) module using bumps if the chip wafer is replaced with a monolithic module.


Anspruch[de]
Akustisches Oberflächenwellen (SAW)-Filter mit: einem SAW-Filterchip (31), der aus einem piezoelektrischen Material besteht und eine Hauptoberfläche (31A) aufweist, auf der ein Elektrodenmuster (33) zur Ausbreitung von akustischen Oberflächenwellen gebildet ist; eine Keramikeinheit (10) mit einer darin ausgebildeten Ausnehmung (10C) zum Einkapseln des SAW-Filterchips (31); wobei der SAW-Filterchip (31) an der Keramikeinheit (10) derart befestigt ist, dass wenigstens ein Teil des Elektrodenmusters einem unteren Ende (10D) der Ausnehmung gegenüber liegt,

auf dem unteren Ende der Ausnehmung gebildete Erhebungen (32), die zwischen dem unteren Ende (10D) der Ausdehnung und der Hauptoberfläche (31A) des SAW-Filterchips zum Verbinden mit und Tragen des SAW-Filterchips (31) auf der Keramikeinheit (10) vorgesehen sind,

dadurch gekennzeichnet, dass das SAW-Filter weiter aufweist: einem auf dem unteren Ende (10D) der Ausnehmung (10C) gebildeten, leitfähigen Anschlussfeld (17), wobei die Erhebungen angeordnet sind, um einen Luftspalt zwischen dem Teil des Elektrodenmusters (33) und einem Teil des leitfähigen Anschlussfelds (17) zu bestimmen; und eine Schulter (34) mit einem in der Ausnehmung (10C) gebildeten Plateaubereich (34B), wobei der SAW-Filterchip (31) und die Schulter (34) derart angeordnet sind, dass der Plateaubereich der Schulter gegenüber liegt und von Endbereichen (31B) der Hauptoberfläche (31A) beabstandet ist.
Filter gemäß Anspruch 1, wobei die Schulter (34) Teil einer abgestuften Struktur ist, die den SAW-Filterchip (31) umgibt. Filter gemäß Anspruch 1 oder 2, weiter mit einem Anschluss (11-16), der auf der Keramikeinheit (10) zum Verbinden des Elektrodenmusters (33) mit der Außenwelt gebildet ist. Filter gemäß einem der vorhergehenden Ansprüche, weiter mit

einem Anschluss (13-16), der auf der Keramikeinheit (10) gebildet und mit Masse verbunden ist; und

einem Verbindungsdraht (18-21) zum Zusammenschalten des leitfähigen Anschlussfelds (17) mit dem Anschluss (13-16).
Filter gemäß einem der vorhergehenden Ansprüche, wobei das leitfähige Anschlussfeld Metall aufweist.
Anspruch[en]
A surface acoustic wave (SAW) filter comprising: a SAW filter chip (31) made of a piezoelectric material and having a major surface (31A) on which a pattern of electrodes (33) is formed to propagate surface acoustic waves; a ceramic package (10) having a recess (10C) formed for encapsulating said SAW filter chip (31) therein; said SAW filter chip (31) being mounted to said ceramic package (10) such that at least part of the pattern of electrodes faces a bottom (10D) of the recess, bumps (32), formed on the bottom of the recess, which are provided between the bottom (10D) of the recess and the major surface (31A) of the SAW filter chip for connecting and supporting said SAW filter chip (31) to said ceramic package (10) characterised by the SAW filter further comprising: a conductive pad (17) formed on the bottom (10D) of the recess (10C), the bumps being arranged to define an air gap between the part of the pattern of electrodes (33) and part of said conductive pad (17); and a shoulder (34) with a plateau region (34B) formed in the recess (10C), said SAW filter chip (31) and said shoulder (34) being arranged such that the plateau region of said shoulder faces and is spaced from end regions (31B) of the major surface (31A). A filter in accordance with claim 1, wherein said shoulder (34) is part of a stepped structure that surrounds said SAW filter chip (31). A filter in accordance with claim 1 or 2, further comprising a terminal (11-16) formed on said ceramic package (10) for connecting the pattern of electrodes (33) to outside. A filter in accordance with any one of the preceding claims, further comprising

a terminal (13-16) formed on said ceramic package (10) and connected to ground; and

a connecting wire (18-21) for interconnecting said conductive pad (17) to said terminal (13-16).
A filter in accordance with any one of the preceding claims, wherein the conductive pad comprises a metal.
Anspruch[fr]
Filtre d'ondes acoustiques de surface (SAW) comprenant : une plaquette de filtre SAW (31) faite d'un matériau piézoélectrique et ayant une surface principale (31A) sur laquelle un motif d'électrodes (33) est formé pour propager des ondes acoustiques de surface ; un ensemble en céramique (10) ayant un creux (10C) formé pour y intégrer ladite plaquette de filtre SAW (31) ; ladite plaquette de filtre SAW (31) étant montée sur ledit ensemble en céramique (10) de sorte qu'au moins une partie du motif d'électrodes soit face à un fond (10D) du creux, des bosses (32), formées sur le fond du creux, qui sont fournies entre le fond (10D) du creux et la surface principale (31 A) de la plaquette de filtre SAW pour connecter et soutenir ladite plaquette de filtre SAW (31) audit ensemble en céramique (10) caractérisé en ce que le filtre SAW comprend en outre: un pavé conducteur (17) formé sur le fond (10D) du creux (10C), les bosses étant disposées pour définir un espace d'air entre la partie du motif d'électrodes (33) et une partie dudit pavé conducteur (17) ; et un épaulement (34) avec une région de plateau (34B) formé dans le creux (10C), ladite plaquette de filtre SAW (31) et ledit épaulement (34) étant disposés de sorte que la région de plateau dudit épaulement soit face à et espacée des régions d'extrémité (31B) de la surface principale (31A). Filtre selon la revendication 1, dans lequel ledit épaulement (34) fait partie d'une structure en gradins qui entoure ladite plaquette de filtre SAW (31). Filtre selon la revendication 1 ou 2, comprenant en outre une borne (11-16) formée sur ledit ensemble en céramique (10) pour connecter le motif d'électrodes (33) à l'extérieur. Filtre selon l'une quelconque des revendications précédentes, comprenant en outre

une borne (13-16) formée sur ledit ensemble en céramique (10) et reliée à la terre ; et

un fil de connexion (18-21) pour interconnecter ledit pavé conducteur (17) à ladite borne (13-16).
Filtre selon l'une quelconque des revendications précédentes, dans lequel le pavé conducteur comprend un métal.






IPC
A Täglicher Lebensbedarf
B Arbeitsverfahren; Transportieren
C Chemie; Hüttenwesen
D Textilien; Papier
E Bauwesen; Erdbohren; Bergbau
F Maschinenbau; Beleuchtung; Heizung; Waffen; Sprengen
G Physik
H Elektrotechnik

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