Wave transmission lines and networks – Coupling networks – Electromechanical filter
Reexamination Certificate
2001-08-29
2003-09-30
Summons, Barbara (Department: 2817)
Wave transmission lines and networks
Coupling networks
Electromechanical filter
C333S133000, C310S349000, C257S728000, C257S778000, C257S779000, C361S760000
Reexamination Certificate
active
06628178
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to radio frequency module parts including surface acoustic wave elements of flip chip type which are mounted on a ceramic multi-layer substrate. In particular, this invention relates to radio frequency module parts including surface acoustic wave elements having increased reliability, improved element mounting efficiency, and reduced product size. The present invention also provides a manufacturing method for radio frequency module parts that enables increased productivity.
Miniaturization of electronic appliances is always increasing in the market. The size and weight of parts must also be reduced. These requirements are particularly remarkable in radio frequency appliances, such as mobile telephones. With respect to radio frequency appliances, electronic parts are mounted with high density, and the size and weight of the parts has been reduced. For miniaturization, a multi-layer substrate having plural conductor layers is mainly used in place of a conventional substrate having a single-layer conductor.
The ceramic multi-layer substrate is composed of an insulating layer formed of ceramics as an electrical insulator, and a conductive layer is formed with a metal, such as silver. In comparison to a general resin multi-layer substrate, the ceramic multi-layer substrate achieves low loss at radio frequency, good heat conductivity, dimensional high precision, and excellent reliability.
The ceramic multi-layer substrate is provided with internal conductors which are coiled or arranged opposite to each other in parallel so that inductance and capacitance may be formed therein. It is possible to form internal elements with low loss and high dimensional precision within the ceramic multi-layer substrate.
These ceramic multi-layer substrates are used as a module in radio frequency circuits such as mobile telephones. These ceramic multi-layer substrates are useful because various parts may be mounted on the surface to form small integrated elements.
Since radio frequency modules have circuits assembled based on each function, in comparison with a conventional technique of mounting discrete components one by one to form circuits, the structure of the module is simple and reliable. The present invention also enables modularization, which reduces manufacturing costs and simplifies device design.
FIG. 9
shows a block diagram of the radio frequency circuit of a mobile telephone of GSM dual band type which is most commonly used in the world. In
FIG. 9
, ANT is an antenna for transmitting and receiving electric waves, DPX is a diplexer (2-frequency filter) for separating a plurality of frequencies, T/R SW is a transmission/receiving switch for switching transmission and receiving, LPF is a low-pass filter for controlling the radio frequency at a transmission stage, and BPF is a band-pass filter at a receiving stage.
In such circuits of mobile telephones, the module is formed with a certain number of functions by actually mounting elements on the multi-layer substrate, for example, at the power amplifier portion in the transmission based circuit and at the antenna switch portion.
FIGS. 10 and 11
show the structures of the respective examples.
FIG. 10
shows an example of a power amplifier module, where reference numeral
1
designates a dielectric multi-layer substrate having an internal electrode
1
a
and external electrodes
1
b
. On the dielectric multi-layer substrate, there are mounted MMIC which is a main portion of power amplifier and chip members
2
of the peripheral circuits. The MMCI is protected by a protection coating
3
and the upper side of the dielectric multi-layer substrate is entirely covered with a shield case
4
.
FIG. 11
shows an example of a front-end module including the antenna switch portion, where reference numeral
10
is a ceramic multi-layer substrate having an internal inductance portion
11
, capacitor portions
12
, and external electrodes
13
. Further, on the ceramic multi-layer substrate
10
, there are mounted chip members
15
including diodes, resistors, and the like, and a shield case
16
for entirely covering the upper side of the ceramic multi-layer substrate. However, the front-end module of
FIG. 11
does not include the surface acoustic wave element (hereafter the “SAW element”).
Nowadays, module formation is realized in a single function such as a power amplifier and antenna switch module. Greater benefits of modularization may be obtained by including more functions in each module. It is a matter of course that the module formation including the SAW elements will be important.
The conventional SAW elements have been package members. It is possible to form the module by mounting the package members. However, as will be described in connection with the invention, mounting of element chips directly on the substrate enables a product which is miniaturized and reduced in thickness. Further, the production cost is reduced.
The ceramic multi-layer substrate, by having internal conductance and capacitance, achieves miniaturization. However, height reduction is more difficult. Therefore, the generally available module having the package mounted on the substrate will not satisfy the ever-increasing demand for reduction of height. Further, the package member occupies a wide area as compared to an original bear chip. Among the components to be used, the SAW element is one of the tallest components and occupies a broad area. Under these circumstances, the SAW element should be directly mounted to the ceramic multi-layer substrate without using the package.
On the other hand, for production of the SAW element, there is a process of forming the SAW chip and a process of mounting the SAW element to the package and sealing the same. Reduced costs for these processes are needed. If the SAW element may be directly mounted to the ceramic multi-layer substrate, the production cost will be reduced because the processes for mounting on the package and sealing may not be needed.
As has been described, regarding the radio frequency module, it is desirable to directly mount the SAW element to the ceramic multi-layer substrate to which other members are mounted by soldering.
In achieving the aforementioned goals, several problems arise, particularly:
(1) It is required to airtightly seal the SAW element chip;
(2) the structure should be resistant to temperature change without affecting the surface acoustic wave properties;
(3) the soldering process and the mounting process of the SAW element should be compatible.
(4) the module should have a flat surface while minimizing the module height;
(5) a plurality of ceramic multi-layer substrates should be mounted simultaneously, thereby increasing the production efficiency.
(1) Regarding the Requirement for Airtight-sealing the SAW Element:
The SAW element is made, for example, by forming a ladder-like electrode of aluminum at a precision of sub-micron (&mgr;m) order, for example, on a lithium tantalite substrate. The electrode pattern is precisely designed for obtaining important properties including resonance frequency, bandwidth, insertion loss, and out-of-band loss. For example, an error of 1 &mgr;m will not satisfy the design specification.
This precisely designed element is very likely to be influenced by external air. Contaminants such as water content from humidity and adherence of dust and the like damage the SAW element.
Accordingly, the SAW element mounting procedure should account for the above-described difficulties and should be compatible with miniaturization.
(2) Regarding the Requirement for Supporting the Element Free of Influence to the Surface Acoustic Waves:
When mounting the bear chips of a silicon based integrated circuit, the chips may be mounted to the substrate firmly and with entire surface adhered by, for example, an adhesive. However in the case of the SAW element, since the resonance property is obtained by the presence of elastic waves at the surface of the element, it is impossible to firmly fix the entire surface of the chips to the
Summons Barbara
TDK Corporation
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