Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2002-12-18
2004-11-09
Budd, Mark (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06815869
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface acoustic wave device having a structure in which a surface acoustic wave element is bonded to a substrate by a face-down mounting method, and more specifically, the present invention relates to a surface acoustic wave device having an improved structure including a substrate with a surface acoustic wave element laminated thereon.
2. Description of the Related Art
Miniaturization and low profile of a surface acoustic wave device accommodating a surface acoustic wave element has been strongly required of surface acoustic wave devices. To meet these requirements, a structure in which the surface acoustic wave element is bonded on the substrate via a bump, with a surface having an electrode for the surface acoustic wave element such as an IDT formed thereon defining a lower surface, i.e., a structure in which the surface acoustic wave element is mounted on the substrate by a so-called face-down mounting method, has been proposed.
In addition, the surface acoustic wave device accommodating the surface acoustic wave element and having an airtight or liquid-tight sealing structure has been required so as to stabilize the characteristics thereof, and so as to be less susceptible to fluctuations in the environment.
Japanese Unexamined Patent Application Publication No. 8-265096 discloses an example of the surface acoustic wave device of this type. In this example, the surface acoustic wave element is mounted on the substrate via the bump by the face-down mounting method, and, in order to seal the surface acoustic wave element, a metal cap is fixed to an upper surface of the substrate so as to surround the surface acoustic wave element. In addition, the surface acoustic wave element is bonded to the substrate also by insulating resin, and the bonding strength of the surface acoustic wave element to the substrate is increased. In order to prevent any flow casting of this insulating resin to the electrode side of the surface acoustic wave element, a guard layer is disposed on the upper surface of the substrate outside the surface acoustic wave element.
However, in the device disclosed in this Japanese patent publication, because the metal cap must be bonded to the substrate by using adhesive, etc. as described above, the number of parts is increased, and the assembly is complicated.
On the other hand, another structure has been known, in which the surface acoustic wave element is sealed in an airtight or liquid-tight manner by mounting the surface acoustic wave element on the substrate by the face-down mounting method, and sealing the surface acoustic wave element with resin except for a surface of the surface acoustic wave element having the electrode disposed thereon. In such a device, a metal cap need not be prepared separately, and an assembly process can be simplified.
FIG. 7
is a sectional view showing an example of a conventional surface acoustic wave device having a resin sealing layer. In a surface acoustic wave device
101
, a surface acoustic wave element
103
is mounted on a substrate
102
, and a resin sealing layer
104
is arranged so as to surround the surface acoustic wave element
103
. Electrode lands
102
a
and
102
b
are disposed on an upper surface of the substrate
102
. Via hole electrodes
102
c
and
102
d
are formed in the substrate
102
in a piercing manner through the substrate
102
. Upper ends of the via hole electrodes
102
c
and
102
d
are connected to the electrode lands
102
a
and
102
b
. In addition, mounting electrodes
102
e
and
102
f
are disposed on a lower surface of the substrate
102
so that the surface acoustic wave device
101
is mounted on a printed circuit board, etc. A shield ring
102
g
is disposed on the substrate
102
so as to provide an electromagnetic shield effect.
On the other hand, a schematically shown electrode
103
a
for the surface acoustic wave element is disposed on a lower surface of the surface acoustic wave element
103
. Bump pads
103
b
and
103
c
on the lower surface of the surface acoustic wave element
103
and the electrode lands
102
a
and
102
b
are connected to each other via metal bumps
105
and
106
.
In the surface acoustic wave device
101
, mounting electrodes
102
e
and
102
f
are disposed on the lower surface of the substrate
102
. The surface acoustic wave device
101
is surface-mounted on a printed circuit board or other substrate by using the mounting electrodes
102
e
and
102
f.
FIG. 8
is a sectional view of another example of a conventional surface acoustic wave device of this type.
In a surface acoustic wave device
111
shown in
FIG. 8
, unlike the surface acoustic wave device
101
, a substrate with the surface acoustic wave element
103
mounted thereon is a multi-layered substrate
112
. This means that the multi-layered substrate
112
has electrode lands
112
a
and
112
b
on an upper surface thereof in a manner similar to the substrate
102
. Via hole electrodes
112
c
and
112
d
are formed within the multi-layered substrate
112
. However, via hole electrodes
112
c
and
112
d
are formed in the multi-layered substrate
112
so that lower ends of the via hole electrodes
112
c
and
112
d
reach the position of the middle height of the substrate
112
, and connected to internal electrode
112
e
and
112
f
. Via hole electrodes
112
g
and
112
h
are formed on lower surfaces of the internal electrodes
112
e
and
112
f
. The distance between the via hole electrodes
112
g
and
112
h
is larger than the distance between the via hole electrodes
112
a
and
112
b.
In addition, the via hole electrodes
112
g
and
112
h
are arranged so as to reach the lower surface of the substrate
112
, and connected to mounting electrodes
112
i
and
112
j
disposed on the lower surface thereof.
FIG. 9
is a sectional view of yet another example of a conventional surface acoustic wave device of this type. In a surface acoustic wave device
121
, electrode lands
122
a
and
122
b
are disposed on an upper surface of a substrate
122
, and mounting electrodes
122
c
and
122
d
are disposed on a lower surface thereof. The electrode lands
122
a
and
122
b
on the upper surface and the mounting electrodes
122
c
and
122
d
on the lower surface are electrically connected to each other via the end surface electrodes
122
e
and
122
f
disposed on the other side of the substrate
122
.
In order to reduce the size and the cost of a surface acoustic wave device, it is necessary to obtain as many surface acoustic wave elements as possible from one wafer. Thus, the cutting margin when cutting individual surface acoustic wave elements out of the wafer is reduced, or the size of the surface acoustic wave elements themselves is reduced.
When the size of the surface acoustic wave elements is reduced, the distance between bump pads for bonding the surface acoustic wave elements via bumps is reduced. This means that surface bump pads
131
a
to
131
d
are disposed in a surface acoustic wave element
131
shown in FIG.
10
. Electrodes for surface acoustic wave elements such as IDTs are also formed on a surface with the bump pads
131
a
to
131
d
disposed thereon although this is not shown in FIG.
10
.
It is assumed that the surface acoustic wave element
131
is square in plan view, the length of one side is a, and the distance between bump pads is c. It is assumed that the size of the surface acoustic wave element
131
is reduced to obtain a surface acoustic wave element
132
shown in FIG.
11
. In this occasion, the length b of one side of the surface acoustic wave element
132
is smaller than the length a, and similarly, the distance d between the bump pads
132
a
to
132
d
is liable to be shorter than the distance c shown in FIG.
10
.
As described above, if the size of the surface acoustic wave element is reduced, the distance between the bumps must be smaller when the surface acoustic wave element is bonded on the substrate via bumps by the face-down mounting method. For
Baba Toshiyuki
Omura Masashi
Budd Mark
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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