Metal working – Piezoelectric device making
Reexamination Certificate
2001-12-26
2004-09-21
Budd, Mark (Department: 2834)
Metal working
Piezoelectric device making
C310S31300R
Reexamination Certificate
active
06792656
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a surface acoustic wave apparatus to be mounted using metal bumps by a flip chip bonding system and, also relates to the surface acoustic wave apparatus produced by such a method. In particular, the present invention relates to a method of manufacturing a surface acoustic wave apparatus in which at least one electrode for a surface acoustic wave element is formed by a lift-off method and, also relates to the surface acoustic wave apparatus.
2. Description of the Related Art
In recent years, in order to miniaturize surface acoustic wave apparatuses, the surface acoustic wave apparatuses assembled by a flip chip bonding system have been used widely. In this system, bumps made of Au or other material, are formed at electrode pads on a piezoelectric substrate constituting the surface acoustic wave apparatus, and the electrode pads and input and output electrode pads provided on the package or ground electrode pads are electrically connected via the bumps, and are mechanically joined at the same time.
When the aforementioned flip chip bonding system is used, the bumps not only electrically connect the surface acoustic wave apparatus and the package, but also mechanically fix the surface acoustic wave apparatus to the package. Therefore, it is required that the bumps have a high strength. In addition, the joining strength between the bumps and the electrode pads on the piezoelectric substrate must be high, and the adhesion between the electrode pads and the piezoelectric substrate must be high.
In order to increase the joining strength between the electrode pad and the bump, in general, a method, in which the thickness of the electrode pad is sufficiently increased, has been used. In order to increase the thickness of the electrode pad, a conventional method, in which a second electrode layer having a large film thickness is formed on a first electrode layer having a small film thickness, is known.
On the other hand, when the surface acoustic wave apparatus is formed, electrodes for the surface acoustic wave element, for example, an interdigital transducer, reflector, and wiring electrodes, and the aforementioned electrode pads are formed on the piezoelectric substrate. When the electrode pad includes the first and second electrode layers, in many cases, the electrodes for the surface acoustic wave element and the first electrode layer of the electrode pad are formed simultaneously. As the method for forming the electrode for surface acoustic wave element, (1) an etching method or (2) a lift-off method, has been used. In (1) the etching method, a conductive film primarily containing Al is formed over the entire surface of a substrate, and a desired resist pattern is formed by photolithography. Thereafter, the resulting metal film is processed by wet etching or dry etching, and then, the resist is removed. In (2) the lift-off method, the metal film portion adhered on the resist is removed together with the resist and, therefore, the electrode is formed from the remaining metal film portion.
In particular, regarding some surface acoustic wave filters for use in a 800 MHz band or in a 1 GHz to 2 GHz band, surface acoustic wave apparatuses are formed by the use of the aforementioned (2) lift-off method. An example of the method for manufacturing the aforementioned surface acoustic wave apparatus will now be described with reference to
FIGS. 22
to
24
.
As shown in
FIG. 23A
, a resist pattern
102
is formed on a piezoelectric substrate
101
by photolithography. A metal film
103
primarily containing Al is formed on the piezoelectric substrate
101
as shown in FIG.
23
B. Subsequently, the resist pattern
102
is removed together with the metal film portion adhered thereon by a lift-off process. Thus, a first electrode layer
103
a
for constituting an electrode pad and an electrode for the surface acoustic wave element
103
b
are simultaneously formed on the piezoelectric substrate
101
as shown in FIG.
23
C. Then, a resist pattern
104
is formed (FIG.
23
D). A metal film
105
is formed as shown in
FIG. 24A
, and the resist pattern
104
is removed by performing the lift-off process again. Consequently, as shown in
FIG. 24B
, a second electrode layer
105
a
is formed on the first electrode layer
103
a
and, therefore, electrode pads
106
having a double-layer structure can be produced.
Next, as shown in
FIG. 22
, bumps
107
are joined onto the electrode pads
106
. A surface acoustic wave apparatus
108
is joined with a package by a flip chip bonding system using the bumps
107
.
Regarding the above-described prior art shown in
FIGS. 22
to
24
, in the case where the first electrode layer
103
a
of the electrode pad
106
was formed by the lift-off method, since the adhesion between the piezoelectric substrate
101
and the first electrode layer
103
a
was relatively weak due to the effects of the resist used for the lift-off, when the formation was performed using bumps
107
by a wire bump bonding method concurrently using ultrasonic waves and heat, sometimes, peeling occurred between the first electrode layer
103
a
and the piezoelectric substrate
101
.
Furthermore, when the surface acoustic wave apparatus
108
was mounted on the package by the flip chip bonding system, and airtight sealing was performed by a covering member, sometimes cracks occurred in the piezoelectric substrate
101
in areas adjacent or near the electrode pads
106
due to the mechanical stress brought about by the residual stress. Therefore, the reliability, especially the reliability of the mechanical strength, of the surface acoustic wave apparatus was significantly degraded.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a method of manufacturing a surface acoustic wave apparatus and a surface acoustic wave apparatus produced by such a method, the apparatus having superior reliability, and in which the adhesion between the electrode pad and the piezoelectric substrate is very high, peeling of the electrode pad from the piezoelectric substrate is prevented from occurring, and cracks are prevented from being generated during the mounting on the package by the flip chip bonding system.
In addition, preferred embodiments of the present invention provide a method of manufacturing a surface acoustic wave apparatus and a surface acoustic wave apparatus, the apparatus having superior reliability in the electrical connection of electrode pads and electrodes for surface acoustic wave element with the wiring electrodes.
In accordance with preferred embodiments of the present invention, a surface acoustic wave apparatus is preferably a type that is mounted via bumps by a flip chip bonding system.
According to a first preferred embodiment of the present invention, a method of manufacturing a surface acoustic wave apparatus includes the steps of preparing a piezoelectric substrate, forming a first electrode layer of an electrode pad on the piezoelectric substrate, forming at least one electrode for a surface acoustic wave element after the step of forming the first electrode layer, forming a second electrode layer of the electrode pad after the step of forming the electrode for the surface acoustic wave element, and forming a wiring electrode for electrically connecting the electrode pad and the electrode for surface acoustic wave element. Therefore, an electrode forming process that is ideal for forming each of the electrode pad and the surface acoustic wave element is provided.
Regarding the method of manufacturing according to the first preferred embodiment of the present invention, the wiring electrode for electrically connecting the second electrode layer and the electrode for surface acoustic wave element may be simultaneously formed with the second electrode layer. In this case, since the wiring electrode can be simultaneously formed with the second electrode layer, the reliability in the elect
Marukawa Takashi
Shimoe Kazunobu
Yamato Shuji
Budd Mark
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
LandOfFree
Surface acoustic wave apparatus and manufacturing method... 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 apparatus and manufacturing method..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Surface acoustic wave apparatus and manufacturing method... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3197447