Wave transmission lines and networks – Coupling networks – Electromechanical filter
Reexamination Certificate
2001-09-04
2003-09-30
Summons, Barbara (Department: 2817)
Wave transmission lines and networks
Coupling networks
Electromechanical filter
C333S150000, C310S31300R, C310S348000
Reexamination Certificate
active
06628179
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a flip-chip mounted surface acoustic wave (SAW) device and a method of producing the same.
2. Description of Related Art
Conventionally, surface-acoustic-wave (SAW) devices are fabricated through a series of steps of adhesively fixing a SAW chip on the inside bottom surface of a package and then interconnecting the bonding pads formed in the package and the bonding pads on the surface of the SAW chip through the wire bonding. However, these wire-bonded-type SAW devices have a problem in that the adhesive agent used for fixing the SAW chip leads to variations in characteristic after fabrication. In contrast, flip-chip mounted-type SAW devices are fabricated through the following steps. That is, bumps made of a conductor such as gold are placed on conductive pads of a SAW chip. The SAW chip is placed on the bottom surface inside the package, with the bump formed surface (electrode formed surface) facing the bottom surface inside the package (die attachment surface). The intermediate structure is subjected to heating, pressure, or ultrasonics. Thus, the conductive pads on the die attachment surface and those on the electrode formed surface are electrically connected and mechanically fixed by the bumps. This process does not require any adhesive agent. Hence, the resultant SAW device has less variation in characteristics than do conventional wire-bonded-type SAW devices.
FIG. 7
illustrates the configuration of a flip-chip mounted SAW device. Referring to
FIG. 7
, electrodes or various conductive layers (not shown) are formed on the electrode formed surface
10
a
of a SAW chip
10
. The electrodes may be ones that excite a surface of a Piezoelectric substrate of, e.g. quartz crystal, by applied electrical signals to generate surface acoustic waves. The electrodes may receive surface acoustic waves and produce electrical signals or may reflect surface acoustic waves in a specific direction. Moreover, conductive pads (not shown) electrically connected with the electrodes on the electrode formed surface
10
a
are connected to and fixed to the package
12
. The package
12
has a recess to accommodate the SAW chip
10
. Conductive pads (not shown) are formed on the bottom surface, or the die attachment surface
12
a
, so as to face bumps
14
when the chip
10
is accommodated in the recess. Footprints
12
b
, being conductors for external connection, are formed on the package
12
. The footprints
12
b
are electrically connected to conductive pads on the die attachment surface
12
b
through conductors (not shown) penetrating the package
12
.
In the fabrication of the SAW device in
FIG. 7
, bumps
14
made of a metal such as gold are first placed on the conductive pads formed on the electrode formed surface
10
a
. The SAW chip
10
is placed in the recess of the package
12
, with the electrode formed surface
10
a
downward in FIG.
7
. The intermediate structure is subjected to heating, pressure, or ultrasonics. Thus, the conductive pads of the SAW chip
10
are electrically connected and mechanically fixed to the conductive pads on the die attachment surface
12
a
via the bumps
14
. Thereafter, the lid (cover)
12
c
seals the recess to house the SAW chip
10
. The sealing portion
12
d
, which is a sealing member intervening between the lid
12
c
and the package
12
, is formed by applying heat or pressure. Gold or tin, resin, soldering, glass and so on are among the substances that may be used for the sealing member.
With the package
12
connected and fixed with the bumps
14
, the characteristics of the SAW device
10
can be measured with an external measuring device via the footprints
12
b
before sealing the opening of the package
12
. One of the inventors of the present invention also invented the method disclosed in Japanese Patent Laid-Open Publication No. Hei NO. 10-145167 (hereinafter referred to as a previous proposal). According to this method, before the opening of the package
12
is covered with the lid
12
c
after the bump connection and fixture, focused radiation such as laser light is irradiated from above the back surface of the SAW chip
10
(from the upper orientation in FIG.
7
), to adjust the characteristics of the SAW chip
10
. Thus, the radiation evaporates the conductive layer or the insulating layer on the electrode formed surface
10
a
while the characteristics of the in-process item is being measured. Though this process, the device characteristics can be adjusted to suppress and prevent characteristic variations due to conditional deviations in fabrication.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a flip-chip mounted surface-acoustic-wave device, the characteristics of which can be adjusted during fabrication to suppress changes in characteristics due to fabrication.
Another object of the present invention is to provide a surface-acoustic-wave device that adopts a devised characteristic adjusting method so that variation in characteristics can be suppressed to a larger degree, compared with the previous proposal.
In order to achieve the above mentioned objectives, a method of fabricating a surface-acoustic-wave device according to the present invention comprises (1) a mounting step of flip-chip mounting a surface-acoustic-wave (SAW) chip within a package, the package having a window for characteristics adjustment in its die attachment surface, and (2) a first adjustment step of adjusting characteristics of an in-process item by an adjustment operation. The adjustment operation may be the introduction of a gas into the package through the window, or may be the beam irradiation onto the electrodes or insulation films on the surface of the SAW chip, or may be the combination thereof.
The gas is introduced, for example, into the package to etch the substrate or electrodes of a SAW chip, or, onto the electrode formed surface of a SAW chip to form (e.g. by CVD) a film relating to surface acoustic wave propagation, or, onto the electrode or insulation film formed on the surface of the SAW chip to change or adjust the quality of the electrode or insulation film. Gas introduction in the preferable embodiment of the present invention can be defined as the introduction of gases which affect the surface-acoustic-wave propagation and thus the characteristics of a SAW device. That is, according to the present invention, since the substrate conditions and the electrode properties of a SAW chip can be changed, characteristics variations such as center frequency variations can be further suppressed and the center frequency can precisely be set to the target frequency. The gas to be introduced may be selected according to whether the substrate is to be etched or not, whether the electrode is to be etched or not, whether the quality of the electrodes or insulation films or not, whether a new film is to be formed, and so on.
According to the present invention, a window for characteristics adjustment is formed on the die attachment surface. Because the die attachment surface must be provided with an area for connecting a SAW chip to the package side, such as a conductive pad area, the window must be smaller than the opening for introducing a SAW chip into the package. The present invention may preferably embodied by effectively utilizing the relationship between the opening area and the window area.
In an example employing a method with a relatively high etching rate, like reactive ion etching wherein a fluorine series gas is used as an etching gas, a case can be considered wherein the substrate or electrodes of a SAW chip is etched to perform the device characteristics adjustment related to the feature of the present invention and wherein the in-process item to be adjusted in characteristics is a SAW device in process for a relatively high frequency band, that is, with fine electrodes. If plasma as used in this specification, comprehensively including excited active species such as ions, electrons, atoms, and radicals in this appli
Iijima Hiroaki
Mineshima Nobuhiro
Yatsuda Hiromi
LandOfFree
Surface acoustic wave device with a window for adjustment of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Surface acoustic wave device with a window for adjustment of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Surface acoustic wave device with a window for adjustment of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3057098