Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2002-06-14
2003-11-11
Arbes, Carl J. (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S840000, C228S180100, C228S180210
Reexamination Certificate
active
06643920
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electronic components and a method for producing the electronic components, and more particularly to an electronic component such as a surface acoustic wave device (SAW device), a high frequency device, and a module or sub-module including an SAW device and a method for producing these devices.
2. Description of the Related Art
(First Conventional Example)
The structure of a conventional surface acoustic wave device
1
is shown in FIG.
1
. In the surface acoustic wave device
1
, a surface acoustic wave element (chip)
3
is disposed and die bonded within a ceramic package
2
of a cavity structure with a recess formed therein. The surface acoustic wave element
3
is electrically connected to electrodes
5
disposed on the ceramic package
2
through wires
4
. The top surface of the ceramic package
2
is covered by a plate-shaped cap
6
, and the surface acoustic wave element
3
is hermetically sealed by welding the external peripheral portion of the cap
6
on the top surface of the ceramic package
2
via a KOVAR ring
7
.
In such a surface acoustic wave device
1
, since a material such as Al, which has a low degree of moisture tolerance, is used as the electrode material of the surface acoustic wave element
3
, corrosion of the electrodes is retarded by hermetic sealing of the surface acoustic wave element
3
. A space is formed between the surface acoustic wave element
3
and the cap
6
so that elastic oscillation of the surface acoustic wave element
3
is not prevented.
However, in such a surface acoustic wave device
1
, because the ceramic package
2
of a cavity structure with a recess formed thereon is required, the cost thereof is expensive. The mounting area and height (thickness) thereof are increased by the volume of the ceramic package
2
relative to the size of the surface acoustic wave element
3
, so that dense mounting of the surface acoustic wave devices
1
and so forth and miniaturizing of an apparatus in which the surface acoustic wave device
1
is assembled are prevented. Furthermore, since the ceramic package
2
is used, in addition to the manufacturing processes of the ceramic package
2
itself and the KOVAR ring
7
, the connecting process between the ceramic package
2
and the KOVAR ring
7
, die bonding of the surface acoustic wave element
3
, welding between the KOVAR ring
7
and the cap
6
, etc., are required, such that the manufacturing processes are complicated and expensive.
(Second Conventional Example)
The structure of another conventional surface acoustic wave device
11
is shown in FIG.
2
. In the surface acoustic wave device
11
, a surface acoustic wave element (bare chip)
13
is flip-chip mounted face down on a wiring substrate
12
; and a bump
14
disposed on the top surface of the surface acoustic wave element
13
is connected to a substrate electrode
15
disposed on the wiring substrate
12
. A space between the surface acoustic wave element
13
and the wiring substrate
12
is hermetically sealed by a sealing resin
18
so as to prevent corrosion of the bump
14
and the substrate electrode
15
and damage to the connecting portions due to thermal stress differences. Flowing of the sealing resin
18
before curing is also prevented by a resin-flow-preventing membrane
19
formed on the top surface of the wiring substrate
12
.
However, in the surface acoustic wave device
11
, the sealing resin
18
charged between the wiring substrate
12
and the surface acoustic wave element
13
has a specific dielectric constant of 3 to 4, so that the dielectric characteristic thereof considerably affects the transmission loss and reflecting characteristics of the surface acoustic wave device
11
. Also, the long time required for charging the sealing resin
18
between the wiring substrate
12
and the surface acoustic wave element
13
prevents the manufacturing process from being streamlined. Further, since the surface of the surface acoustic wave element
13
is sealed by the resin, the resulting restraint of the Mechanical Elastic Oscillation thereof may cause deterioration of the characteristics of the surface acoustic wave device
11
.
(Third Conventional Example)
In order to address the foregoing problems, a surface acoustic wave device
21
using both a ceramic package with a cavity structure, and a bump connection, is used without a sealing resin which would prevent elastic oscillation of a surface acoustic wave element and increase its transmission loss. Moreover, such a structure is capable of being miniaturized. Such a surface acoustic wave device
21
is shown in FIG.
3
. In the surface acoustic wave device
21
, a surface acoustic wave element
23
is disposed face down within the ceramic package
22
similar to the described one in
FIG. 1
; a bump
27
disposed on the top surface of the surface acoustic wave element
23
is connected to an electrode portion
24
; and the outer peripheral bottom surface of a cap
26
is connected on the ceramic package
22
via a KOVAR ring
25
.
In the surface acoustic wave device
21
of such structure, since the surface of the surface acoustic wave element
23
is not sealed by a resin, the surface oscillation of the surface acoustic wave element
23
is uninhibited and the characteristics of transmission, reflection, etc., in the surface acoustic wave device
21
are not deteriorated by a sealing resin. Although the ceramic package
22
is used, the need for a space for bonding the wire is eliminated by the bump connection so that the ceramic package
22
can be miniaturized.
However, in such a surface acoustic wave device
21
, although the ceramic package
22
is unitized with the surface acoustic wave element
23
by the bump connection, it is not different from the first conventional example in the respect that it also uses the ceramic package
22
, so that the surface acoustic wave device
21
cannot be miniaturized substantially more than the first conventional example.
(Fourth Conventional Example)
Accordingly, a structure shown in
FIG. 4
has been disclosed (Japanese Unexamined Patent Publication No. 9-162690) as a surface acoustic wave device
31
which neither uses the ceramic package nor has a sealing resin which restrains elastic oscillation of a SAW element's surface, thereby providing a highly reliable SAW device which can be miniaturized.
In the surface acoustic wave device
31
, interdigital electrodes (not shown) and an input-output electrode
33
are disposed on the surface of the surface acoustic wave element
32
and a bump
34
in turn is formed on the input-output electrode
33
. An element-side seal ring
35
is disposed on the periphery of the surface acoustic wave element
32
. This surface acoustic wave element
32
is laid face down on a mounting substrate
36
so that the bump
34
is connected to a pick-out electrode
37
disposed in the mounting substrate
36
and the element-side seal ring
35
is connected to a substrate-side seal ring
38
on the mounting substrate
36
as well. A space
39
between the surface acoustic wave element
32
and the mounting substrate
36
is sealed by the connection between the element-side seal ring
35
and the substrate-side seal ring
38
. The space
39
is sealed in addition by a sealing resin
40
which is coated from the back side of the surface acoustic wave element
32
so as to encapsulate the surface acoustic wave element
32
, and which further provides shock protection as well.
In the surface acoustic wave device
31
, the surface acoustic wave element
32
is sealed by coating the liquid sealing resin
40
on the entire surface acoustic wave element
32
and then curing the sealing resin
40
. As the sealing resin
40
, a conventional molding resin including a volatile solvent is used. (In the embodiment of the above-mentioned unexamined patent publication, a CRP series resin from Sumitomo Bakelite is used.) Such a sealing resin
40
is an insulator. However, in a surface acoustic wave device, a c
Arbes Carl J.
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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