Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2001-09-07
2004-03-02
Vo, Peter (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S600000, C029S832000, C029S840000, C029S841000, C174S256000, C174S260000, C228S180210, C228S180220, C310S348000, C310S344000, C310S31300R
Reexamination Certificate
active
06698084
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing radio frequency module components with a surface acoustic wave element of flip chip packaged type which is packaged on a ceramic multi-layer substrate, and more particularly to a method for manufacturing radio frequency module components with a surface acoustic wave element which can enhance the reliability during the use, improve the mounting capability, lower the product size, and increase the productivity.
In the electronic apparatuses, there is always a demand in the market to reduce the size of them, and the used components are required to be reduced in size and weight. In the radio frequency apparatuses represented by a portable telephone, this trend is remarkable, and can be also seen strikingly in the used components. The radio frequency apparatuses progressed along with the higher density of packaging the components, to cope with the demand for reducing the size and weight. A multi-layer substrate for mounting the elements in which a plurality of conductive layers are provided is principally employed in stead of a single layer substrate to cope with such miniaturization.
A ceramic multi-layer substrate has an insulating layer of the multi-layer substrate made of ceramic that is an electrical insulator, and a conductive layer made of silver. The ceramic multi-layer substrate has the features of smaller loss at high frequencies, better heat conductivity, higher dimensional precision, and higher reliability than the typical resin multi-layer substrate.
In the ceramic multi-layer substrate, the inner conductors are shaped like a coil, or opposed in parallel, to form an inductance or capacitance internally, and because of small loss and high dimensional precision, the elements having high Q value and less tolerance can be formed inside.
These features are effectively utilized, particularly in a radio frequency circuit for the portable telephone, as an aggregate element or a module in which various components are mounted on the surface, with high characteristics and small size.
On one hand, the radio frequency module having a circuit modularized for each function can provide a simpler structure of device with higher reliability and better characteristics than with the conventional method for forming a circuit having discrete components mounted. Also, in the conventional discrete components, the design becomes complex to fulfill the function in combination of the characteristics of each component, but the modularization allows the characteristic specifications to be determined for each module, and the design of device to be structured, resulting in shorter period and labor saving.
FIG. 9
is a block diagram of a radio frequency circuit for a GSM dual band type portable telephone. In the figure, reference sign ANT denotes an antenna for transmitting and receiving the electric wave, DPX denotes a diplexer (two frequency switching filter) as a multiple frequency separation filter, T/R SW denotes a transmission/reception changing switch as transmission/reception switching means, LPF denotes a low-pass filter as a transmitting stage harmonics suppression filter, and BPF denotes a band pass filter at the receiving stage.
In such a portable telephone circuit, several functions are modularized, including, for example, a power amplifier section within a transmitting system circuit, and an antenna switch section, in which the elements are practically mounted on the multi-layer substrate.
FIG. 10
shows an example of a module in the antenna switch section. In the figure, reference numeral
10
denotes a ceramic multi-layer substrate, internally provided with an inductor portion
11
and a capacitor portion
12
, and having an external electrode
13
. Also, a diode as a switching element and a chip component
15
such as resistor are mounted on the ceramic multi-layer substrate
10
, and a shield case
16
is provided to cover a whole upper part of the ceramic multi-layer substrate. The module in
FIG. 10
does not contain a surface acoustic wave element (hereinafter referred to as an SAW element), or has it in a package component mounted.
At present, the power amplifier or the antenna switch module is modularized with a single function, but if a wider range of functions are modularized, the advantages of the modularization can be drawn. Of course, it is important that the SAW element is added to the module.
The conventional SAW element employed a so-called package component. Of course, it is possible to make a module by mounting the package component, but if the element chips are directly mounted on the substrate as will be described later, the circuit can be reduced in size, and in height, with the lower costs.
The ceramic multi-layer substrate can contain an inductance and a capacitance, and therefore has a feature of smaller size, but on the other hand, is difficult to reduce the height. Therefore, in the typical module with a package further mounted on the substrate, it is not possible to meet the demand for smaller height which will further progress. Also, the package product will require a wider occupying area than the proper bear chip. Of the used components, the SAW element is highest, and widest in the occupying area. In these circumstances, it is desired that the SAW chip is directly mounted on the ceramic multi-layer substrate in some form, without the use of the package.
On the other hand, the manufacture of the SAW elements includes a step for producing the SAW chips and a step for mounting and sealing the SAW chips on the package, which are costed by the almost same amount. If the SAW elements can be directly mounted on the ceramic multi-layer substrate, no step of mounting and sealing the SAW chips on the package is undergone, whereby the circuit can be produced cheaply.
In the radio frequency module as above, it is desirable that the SAW elements are directly mounted as the chips, and other components are mounted onto the ceramic multi-layer substrate by soldering.
By the way, there are the following problems to realize the above-mentioned circuit.
(1) To hermetically seal the chip of SAW element.
(2) To realize a structure that can withstand variations in temperature by a supporting method having no influence on the surface acoustic waves to make a soldering step and an SAW element mounting step consistent.
(3) Flat module surface with small height.
(4) To process a plurality of ceramic multi-layer substrates collectively to increase the productivity.
(1) To hermetically seal the chip of SAW element
The SAW element is produced by forming a ladder electrode of aluminum at a precision of several &mgr;m on a substrate made of lithium tantalate, for example. This electrode pattern is precisely designed to obtain important characteristics such as resonance frequency, bandwidth, insertion loss, and out-of-band loss. For example, an error of 1 &mgr;m may not meet the design specification.
The element designed precisely is greatly affected by the outer air. The water content or dust adhering owing to humidity has fatal influence on the characteristics.
In these cases, it is required to seal the SAW element in some way, and for the module to which the invention is applied, it is required to be smaller, lower, and employ a process of mounting the SAW element with other components simultaneously, whereby a manufacturing method must be established.
(2) To realize a structure that can withstand variations in temperature by supporting method having no influence on the surface acoustic waves to make a soldering step and an SAW element mounting step consistent
In mounting the bear chips on the silicone based integrated circuit, the chips can be mounted firmly on the substrate by adhesives, with the entire face bonded. However, in case of the SAW element, the chips can not be fixed firmly over the entire face on the substrate by adhesives to obtain a resonance characteristic because the surface acoustic waves are present on the surface.
In case of the small SAW elements at present, the chips are fi
TDK Corporation
Trinh Minh
Vo Peter
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