Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2002-07-05
2004-05-04
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S363000, C310S364000
Reexamination Certificate
active
06731046
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to surface acoustic wave elements, and more specifically, it relates to a surface acoustic wave element to be bonded to a package with metallic bumps and a manufacturing method thereof.
2. Description of the Related Art
Along with increases in the frequency of mobile radio communications, a surface acoustic wave apparatus used for the mobile radio communications is also required to be usable in a high-frequency range. The surface acoustic wave apparatus includes a surface acoustic wave element having a piezoelectric substrate and a package for accommodating the surface acoustic wave element. Because an acoustic velocity of the surface acoustic wave element on the surface of the piezoelectric substrate is several thousands m/second, the wavelength of an interdigital electrode of the surface acoustic wave element is as small as several &mgr;m, when forming the surface acoustic wave element operating at approximately 800 MHz, for example. Therefore, there has been a problem that the absolute value of the electrode film thickness for optimizing characteristics of the surface acoustic wave element is reduced so that a loss due to an electrode resistance, i.e., an ohmic loss, increases.
In order to solve such a problem, a surface acoustic wave apparatus as shown in
FIGS. 5A and 5B
is disclosed in Japanese Unexamined Patent Application Publication No. 7-212175. In addition,
FIG. 5B
is a schematic sectional view along the lines of
FIG. 5A
connecting the dash-dot lines P—P, Q—Q, and R—R, and the dash-dot lines S and T of
FIG. 5B
indicate boundaries of the connection. In addition, in the drawings attached to this specification, in the same way as
FIGS. 5A and 5B
, the sections shown along the lines P—P, Q—Q, and R—R in the plan view are shown in the sectional view corresponding to the plan view by connecting them along the dash-dot lines S and T.
In a surface acoustic wave apparatus
201
in the prior art, on a piezoelectric substrate
202
, an interdigital electrode
203
and reflector electrodes
204
and
205
disposed on both sides of the interdigital electrode
203
are arranged. Also, relay electrodes
206
and
207
are arranged to be electrically connected to the interdigital electrode
203
. Furthermore, electrode pads
208
and
209
are arranged so as to be electrically connected to the relay electrodes
206
and
207
, respectively. The electrode pads
208
and
209
correspond to parts to be electrically connected to electrodes of a package, and metallic bumps are arranged on the electrode pads
208
and
209
. The surface acoustic wave apparatus
201
includes the interdigital electrode
203
and the reflector electrodes
204
and
205
among various electrodes mentioned above and conductive films
212
shown in FIG.
5
B. As shown by the electrode pads
208
and
209
in
FIG. 5B
as representatives, on at least portions of the electrode pads
208
and
209
or the relay electrodes
206
and
207
, second conductive films
213
are deposited. That is, in comparison with the interdigital electrode
203
, portions of the relay electrodes
206
and
207
and the electrode pads
208
and
209
have an increased thickness, so that an ohmic loss due to an electrode resistance is reduced, thereby improving electrical characteristics.
By the way, because electronic components have recently been required to have a reduced size and height, a surface acoustic wave apparatus using a flip chip bonding technique is put into practical use. In the surface acoustic wave apparatus using the flip chip bonding technique, an electrode forming portion of the surface acoustic wave element opposes a mounting surface of a package, and electrodes of the surface acoustic wave element and electrodes of the package are bonded with metallic bumps. In this case, in order to increase the bonding strength between the metallic bump and the electrode pad, metallic films such as AU are disposed on the electrode pads of the surface acoustic wave element. On the metallic film made of AU, a metallic bump made of AU is disposed, which in turn is bonded to the package electrode surface. Alternatively, on the electrode pad, a metallic film made of Ag and having excellent solder wettability is disposed, so that a method in which solder bumps that are formed in the package in advance are bonded to the metallic films having excellent solder wettability is used.
When using the method described above, bonding wire is not required. Therefore, since the surface acoustic wave element is not required to have wire pads to be connected to the bonding wire, the planar area and height of the surface acoustic wave apparatus can be reduced.
Also, in the surface acoustic wave apparatus obtained by using the flip chip bonding technique, when a surface acoustic wave is actually vibrated, while the film thickness of electrodes other than electrodes to be propagated is increased, the ohmic loss is reduced, and losses and the reduction in Q of a resonator can be suppressed. In this case, first, the electrodes, in which a surface acoustic wave is vibrated and propagated, i.e., the interdigital electrode, reflector electrodes, bus bar electrodes, relay electrodes, and electrode pads are formed of the same conductive film. Next, in electrodes disposed in portions other than where a surface acoustic wave is vibrated and propagated, the second conductive film is deposited or the first conductive film is increased in thickness.
Therefore, when performing the bonding with the metallic bumps, after depositing the metallic films such as Au on the thick conductive films on the electrode pads, the metallic bumps such as Au may be formed thereon. Also, when performing the bonding with the solder bumps, on the plurality of deposited conductive films or on the electrode pads thickly formed by the increase in the conductive film thickness, the metallic films made of Ag and having excellent solder wettability are provided.
FIGS. 6A and 6B
are a plan view and schematic sectional view for illustrating a conventional method using the flip chip bonding technique for manufacturing a surface acoustic wave apparatus operating at low frequencies, respectively.
According to the method, by patterning a conductive film
222
, an IDT electrode
223
, bus bar electrodes
224
and
225
, reflector electrodes
226
and
227
, relay electrodes
228
and
229
, and electrode pads
230
and
231
are formed. Next, as shown in
FIGS. 7A and 7B
, on each of the electrode pads
230
and
231
, a conductive film
232
and a metallic film
233
are deposited. The conductive film
232
is arranged for improving adhesion to the conductive film
222
, and the metallic film
233
is arranged for improving the bonding strength between a metallic bump
234
shown in
FIGS. 8A and 8B
and the electrode pad.
Therefore, according to the method, after patterning the conductive film
222
, the conductive film
232
and metallic film
233
have to be deposited.
On the other hand, when obtaining the surface acoustic wave apparatus operating at a high frequency range, as described above, in order to reduce the ohmic loss, on the conductive film
232
, a conductive film
241
made of the same material as that of the conductive film
222
is deposited, and on the conductive film
241
, the conductive film
232
and metallic film
233
have to be deposited, as shown in
FIGS. 9A and 9B
.
When manufacturing the surface acoustic wave apparatus operating at a low frequency range by bonding between the surface acoustic wave element and the package with the solder bumps disposed on the package instead of the metallic bumps made of Au, after the patterned conductive film
222
is formed on the piezoelectric substrate
221
as shown in
FIGS. 6A and 6B
, the metallic film
232
for improving the bonding strength to the conductive film
222
and a metallic film
242
to be a solder barrier are deposited on the electrode pads, and finally, a metallic film
243
having excellent solder wettability has to
Ieki Hideharu
Watanabe Hiroki
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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