Wave transmission lines and networks – Coupling networks – Electromechanical filter
Reexamination Certificate
2000-09-12
2002-06-11
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Electromechanical filter
C333S195000
Reexamination Certificate
active
06404303
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a surface acoustic wave element, in particular to a surface acoustic wave element such as a surface acoustic wave filter used for mobile communication. Further, the present invention relates to a surface acoustic wave element suitable for flip-chip assembling and a surface acoustic wave device in which a surface acoustic wave element is mounted on a package, in particular to a surface acoustic wave device such as a band pass filter in microwave stage in which a surface acoustic wave element is flip-chip assembled.
BACKGROUND ART
Recently, surface acoustic wave elements such as surface acoustic wave filters are much in use in mobile communication in which demand for miniaturization is strong. For this use, a piezoelectric substrate thereon a surface acoustic wave filter is formed is adhered to the inside of a ceramic package, and signal input/output terminals disposed inside of the package and bonding pads on the piezoelectric substrate are connected with bonding wires consisting of Au, Al or the like to mount. Thereafter, a metal cap is put thereon and welded to a metal frame at the upper portion of the package, thereby hermetic sealing the surface acoustic wave element in the package.
The signal terminal in the package is communicated with an external terminal of the package through a via-hole or a castellation. The package is mounted on for instance a printed wiring board, external circuit and the external terminal of the package being connected. Thus formed surface acoustic wave filter, being capable of surface mounting on a printed circuit board during assembling, can be assembled with high density. Accordingly, the surface acoustic wave filters thus formed are components suitable in miniaturizing an electronic instrument such as portable telephones or the like.
There is flip-chip assembly technique that is recently used as an assembly technique capable of further miniaturizing a surface acoustic wave element. In the flip-chip assembly technique, a surface acoustic wave element is face down bonded on a package called an envelope. In the flip-chip assembly technique, conductive bumps are formed of Au or the like on portions where electrical connection of the surface acoustic wave element is necessary, which is put opposite on a printed circuit board of the envelope thereon conductive patterns are formed, followed by heating or ultrasonic inputting to connect.
The conductive pattern of the printed circuit board is connected to an external terminal disposed on a bottom surface of the printed circuit board. After thus mounting the surface acoustic wave element on the envelope, a cap is put on the envelope to hermetic seal the surface acoustic wave element.
Thus, in the flip-chip assembly technique, since the bonding wire is not used, a portion for wire bonding is not necessary on the package. Further, in bonding due to the wire bonding, there is a necessity of ensuring an excess space in the envelope for introducing a tool that introduces the bonding wire and connects with the bonding pad. On the contrary, in the flip-chip connection, the bonding tool is not necessary to result in cutting down the excess space.
Thus, the flip-chip assembly technique is an assembling method suitable for miniaturization of a surface acoustic wave device.
A surface acoustic wave filter, having a steep rise frequency characteristic, is a device of excellent frequency selectivity suitable for the case where high attenuation characteristic is necessary particularly in the neighborhood of a pass band.
However, in the surface acoustic wave filter, in a frequency band far apart from the pass band, the frequency characteristics of the surface acoustic wave filter are largely affected by stray capacitance of the package thereon the surface acoustic wave element is mounted, inductance of bonding wire, mutual inductions between a plurality of bonding wires or the like. Accordingly, there are problems that attenuation characteristics intrinsic to the surface acoustic wave filter cannot be sufficiently obtained.
Accordingly, when for the surface acoustic wave filter, attenuation characteristic in a frequency band far apart from a pass band is demanded, a technique that another resonant system is formed in the surface acoustic wave device and a trap due to the resonant system is fitted in a frequency band far apart from the pass band has been frequently used.
With such a configuration, the surface acoustic wave filter, when used for a portable telephone for instance, can improve the attenuation characteristics at a frequency band of a local oscillator or image frequency that are apart from a transmitting band or a receiving band.
Usually, these bands are frequency bands several hundreds MHz apart from the pass band. At that time, to form a trap of a surface acoustic wave filter, a resonant system due to inductance of the bonding wires and that of routing electrode pattern, and stray capacitance in the package and that of the routing portion has been mostly used.
As mentioned above, to advance miniaturization of the surface acoustic device, the flip-chip assembly technique is preferably adopted. When flip-chip mounting is implemented, however, due to an absence of the bonding wire, there is no inductance pertaining to the bonding wire. In addition, in flip-chip assembling, the bump connecting between the surface acoustic wave element and the envelope has a magnitude of approximately several tens &mgr;m. As a result, compared with the bonding wire, the inductance is remarkably small. Accordingly, it was difficult to obtain a resonant system that forms a trap in a frequency band several hundreds MHz apart from the pass band due to inductance of the bump and that of the routing electrode pattern, and stray capacitance in the package and that of the routing portion.
In the case of the flip-chip assembling being adopted, there is no mutual induction between the bonding wires. As a result, there is an advantage that characteristics in a broad band, particularly in a high frequency region of 3 GHz or more, can be improved. Despite that, it is difficult to obtain an attenuation region such as the trap in the frequency band approximately several hundreds MHz apart from the pass band. As a result, there are problems that the flip-chip mounted surface acoustic wave devices cannot be used in various kinds of mobile communication systems including portable telephones, PHSs or the like.
DISCLOSURE OF THE INVENTION
The present inventions were carried out to solve these problems.
That is, an object of the present invention is to provide a surface acoustic wave element that can be miniaturized and can be improved of characteristics out of band.
Another object of the present invention is to provide a surface acoustic wave device that even when flip-chip assembling a surface acoustic wave element, can achieve both the miniaturization and the improvement of characteristics out of band. In particular, the object is to provide a surface acoustic wave filter having high attenuation characteristics even in a frequency band several hundreds MHz apart from a pass band.
Still another object of the present invention is to provide a surface acoustic wave element capable of adjusting attached capacitance with a high degree of freedom.
Still another object of the present invention is to provide a surface acoustic wave element that has large mechanical strength at a bump formation portion suitable for the flip-chip assembling and a structure of high connection reliability.
In order to solve these problems, the present invention adopts a configuration described in the following.
A surface acoustic wave element of the present invention comprises a piezoelectric substrate and a two-port surface acoustic wave resonator filter having input IDT (interdigital transducer) and output IDT. Here, one of a pair of interdigital electrodes constituting the input IDT is connected to an input side signal conductive pattern including an input side signal wiring and an input signal terminal, the other one bein
Kabushiki Kaisha Toshiba
Pascal Robert
Summons Barbara
LandOfFree
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