U.S. patent application number 13/571386 was filed with the patent office on 2013-08-15 for elastic wave device and method for manufacturing the same.
This patent application is currently assigned to MURATA MANUFACTURING CO., LTD.. The applicant listed for this patent is Atsushi KADOI, Hayami KUDO, Norihiko TAKADA. Invention is credited to Atsushi KADOI, Hayami KUDO, Norihiko TAKADA.
Application Number | 20130205586 13/571386 |
Document ID | / |
Family ID | 40985325 |
Filed Date | 2013-08-15 |
United States Patent
Application |
20130205586 |
Kind Code |
A1 |
TAKADA; Norihiko ; et
al. |
August 15, 2013 |
ELASTIC WAVE DEVICE AND METHOD FOR MANUFACTURING THE SAME
Abstract
An elastic wave device includes a substrate, a vibrating portion
located on a first main surface of the substrate, pads located on
the first main surface of the substrate and electrically connected
to electrodes of the vibrating portion, a supporting layer arranged
on the first main surface of the substrate so as to enclose the
vibrating portion, a sheet-shaped cover layer composed of resin
including synthetic rubber and disposed on the supporting layer so
as to form a hollow space around the periphery of the vibrating
portion, a protective layer composed of resin having resistance to
flux and disposed on a side of the cover layer remote from the
supporting layer, via conductors extending through the protective
layer, the cover layer, and the supporting layer and connected to
the pads, and external electrodes including solder bumps, disposed
at ends of the via conductors adjacent to the protective layer.
Inventors: |
TAKADA; Norihiko;
(Kanazawa-shi, JP) ; KADOI; Atsushi;
(Moriyama-shi, JP) ; KUDO; Hayami; (Kyoto-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TAKADA; Norihiko
KADOI; Atsushi
KUDO; Hayami |
Kanazawa-shi
Moriyama-shi
Kyoto-shi |
|
JP
JP
JP |
|
|
Assignee: |
MURATA MANUFACTURING CO.,
LTD.
Nagaokakyo-shi
JP
|
Family ID: |
40985325 |
Appl. No.: |
13/571386 |
Filed: |
August 10, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12850725 |
Aug 5, 2010 |
8461940 |
|
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13571386 |
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PCT/JP2009/050666 |
Jan 19, 2009 |
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12850725 |
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Current U.S.
Class: |
29/829 |
Current CPC
Class: |
H01L 2224/05569
20130101; H03H 9/1042 20130101; H03H 9/1085 20130101; H03H 9/059
20130101; H03H 9/1092 20130101; H01L 2224/05155 20130101; H03H
9/0523 20130101; Y10T 29/49005 20150115; H03H 3/00 20130101; H03H
9/105 20130101; H01L 2924/16235 20130101; H01L 2224/0558 20130101;
H01L 2224/02379 20130101; Y10T 29/49124 20150115; H01L 2924/181
20130101; H01L 2224/05001 20130101; H01L 2224/05147 20130101; H01L
2224/05008 20130101; H01L 2224/056 20130101; H01L 2224/16225
20130101; H01L 2224/05644 20130101; H01L 2924/181 20130101; H01L
2924/00012 20130101; H01L 2224/056 20130101; H01L 2924/00014
20130101; H01L 2224/05644 20130101; H01L 2924/00014 20130101; H01L
2224/05147 20130101; H01L 2924/00014 20130101; H01L 2224/05155
20130101; H01L 2924/00014 20130101 |
Class at
Publication: |
29/829 |
International
Class: |
H03H 3/00 20060101
H03H003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 18, 2008 |
JP |
2008-036396 |
Claims
1. A method for manufacturing an elastic wave device comprising: a
first step of forming a vibrating portion and a pad electrically
connected to an electrode of the vibrating portion on a first main
surface of a substrate; a second step of forming a supporting layer
having a thickness larger than a thickness of the vibrating portion
on the first main surface of the substrate so as to enclose the
vibrating portion; a third step of forming a sheet-shaped cover
layer composed of resin including synthetic rubber on the
supporting layer so as to cover the vibrating portion and so as to
form a hollow space around a periphery of the vibrating portion; a
fourth step of forming a protective layer composed of resin having
resistance to flux on a side of the cover layer remote from the
supporting layer; a fifth step of forming a via conductor extending
through the protective layer, the cover layer, and the supporting
layer and connected to the pad; and a sixth step of forming an
external electrode including a solder bump at an end of the via
conductor adjacent to the protective layer.
2. A method for manufacturing an elastic wave device comprising: a
first step of forming a vibrating portion and a pad electrically
connected to an electrode of the vibrating portion on a first main
surface of a substrate; a second step of forming a supporting layer
having a thickness larger than a thickness of the vibrating portion
on the first main surface of the substrate so as to enclose the
vibrating portion; a third step of forming a sheet-shaped multiple
layer formed of a sheet-shaped cover layer composed of resin
including synthetic rubber and a protective layer composed of resin
having resistance to flux stacked in advance on the supporting
layer such that the protective layer is located on a surface of the
cover layer remote from the supporting layer so as to cover the
vibrating portion and to form a hollow space around a periphery of
the vibrating portion; a fourth step of forming a via conductor
extending through the protective layer and the cover layer of the
multiple layer and the supporting layer and connected to the pad;
and a fifth step of forming an external electrode including a
solder bump at an end of the via conductor adjacent to the
protective layer.
3. The method for manufacturing the elastic wave device according
to claim 1, further comprising: a seventh step of forming a groove
in the substrate from the first main surface of the substrate to a
predetermined depth; and an eighth step of grinding a second main
surface of the substrate opposite to the first main surface so as
to reduce the thickness of the substrate and to divide the
substrate into chips.
4. The method for manufacturing the elastic wave device according
to claim 2, further comprising: a sixth step of forming a groove in
the substrate from the first main surface of the substrate to a
predetermined depth; and a seventh step of grinding a second main
surface of the substrate opposite to the first main surface so as
to reduce the thickness of the substrate and to divide the
substrate into chips.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to elastic wave devices and
methods for manufacturing the same, and in particular, relates to
elastic wave devices including vibrating portions such as
resonators and filters located on substrates and methods for
manufacturing the same.
[0003] 2. Description of the Related Art
[0004] To date, elastic wave devices including substrates,
vibrating portions formed on the substrates, and cover layers
covering the vibrating portions have been proposed.
[0005] FIGS. 9A to 9C illustrate an example configuration of an
elastic wave device. FIG. 9A is a cross-sectional view, FIG. 9B is
a cross-section taken along line X-X in FIG. 9A viewed from above,
and FIG. 9C is a cross-section taken along line X-X in FIG. 9A
viewed from below. As shown in FIGS. 9A to 9C, a surface acoustic
wave device 110 includes a piezoelectric substrate 111, a
conductive pattern including IDT electrodes 112, pads 113, and
wiring lines 118 formed on a first main surface 111a of the
piezoelectric substrate, a frame-shaped supporting layer 116
composed of resin formed so as to enclose a vibrating portion
including the IDT electrodes 112, and a cover layer 115 formed of
an insulating sheet formed on the supporting layer 116. External
electrodes 117 are formed on the cover layer 115, and the external
electrodes 117 and the pads 113 are electrically connected to each
other by via conductors 114 extending through the cover layer 115
and the supporting layer 116 (for example, see Japanese Unexamined
Patent Application Publication No. 2002-261582
[0006] When an elastic wave device having the above-described
structure is mounted on, for example, another circuit board using
solder bumps formed on the external electrodes, flux is applied to
the solder bumps so as to improve the solder wettability. However,
the flux often flows into a hollow space through the cover
layer.
SUMMARY OF THE INVENTION
[0007] Accordingly, preferred embodiments of the present invention
provide an elastic wave device having a structure with which flux
does not flow into a hollow space of the device during mounting of
the device using solder bumps.
[0008] An elastic wave device according to a preferred embodiment
of the present invention includes a substrate; a vibrating portion
located on a first main surface of the substrate; a pad located on
the first main surface of the substrate and electrically connected
to an electrode of the vibrating portion; a supporting layer having
a thickness larger than that of the vibrating portion and located
on the first main surface of the substrate so as to enclose the
vibrating portion; a sheet-shaped cover layer composed of resin
including synthetic rubber, arranged on the supporting layer so as
to cover the vibrating portion and to form a hollow space around
the periphery of the vibrating portion; a protective layer composed
of resin having resistance to flux and located on a side of the
cover layer remote from the supporting layer; a via conductor
extending through the protective layer, the cover layer, and the
supporting layer and being connected to the pad; and an external
electrode including a solder bump and located at an end of the via
conductor adjacent to the protective layer.
[0009] During mounting of the elastic wave device, flux is applied
to the solder bump so as to improve solder wettability. However,
the flux often flows into the hollow space in conventional devices.
The inventors discovered that the flux passed through the cover
layer since the cover layer was composed of resin including
synthetic rubber. Synthetic rubber needs to be added to resin so
that the cover layer has toughness and does not easily crack even
when the cover layer has a sheet-shaped configuration.
[0010] When the protective layer composed of resin having
resistance to flux is disposed on the sheet-shaped cover layer
composed of resin including synthetic rubber as in the
above-described structure, the flux does not pass through the
protective layer. Accordingly, the flux can be prevented from
flowing into the hollow space.
[0011] More specifically, the device can have various aspects as
described below.
[0012] According to an aspect of a preferred embodiment of the
present invention, the substrate may be a piezoelectric substrate.
The vibrating portion may include an IDT electrode. In this case,
the elastic wave device may be a surface acoustic wave device.
[0013] According to another aspect of a preferred embodiment of the
present invention, the substrate may be an insulating substrate.
The vibrating portion may include a piezoelectric thin film having
electrodes formed on both sides thereof. In this case, the elastic
wave device may be a bulk acoustic wave device such as a bulk
acoustic wave resonator (BAW resonator).
[0014] Preferably, the protective layer is composed of the same
material as the supporting layer such that the variety of materials
can be reduced, and manufacturing processes can be simplified.
[0015] Preferably, the protective layer is composed of
photosensitive polyimide resin. As a result, a difference in
brightness profile between the solder bump and the protective layer
becomes large, and it becomes easy for the solder bump to be
recognized. Accordingly, the elastic wave device can be mounted
with higher accuracy compared with when the external shape of the
elastic wave device is recognized.
[0016] Preferably, the cover layer is composed of
non-photosensitive epoxy resin so as to allow for a low temperature
curing process.
[0017] Preferably, the device further includes a nitride film or an
oxide film at least partially interposed between the substrate and
the supporting layer so that the nitride film or the oxide film has
a surface rougher than that of the piezoelectric substrate.
Therefore, adhesiveness can be improved by an anchoring effect. As
a result, problems that cause poor characteristics during processes
after the formation of the hollow space, for example, entering of
plating solution into the hollow space, can be prevented.
[0018] Moreover, another preferred embodiment of the present
invention provides a method for manufacturing an elastic wave
device including a first step of forming a vibrating portion and a
pad electrically connected to an electrode of the vibrating portion
on a first main surface of a substrate; a second step of forming a
supporting layer having a thickness larger than that of the
vibrating portion on the first main surface of the substrate so as
to enclose the vibrating portion; a third step of forming a
sheet-shaped cover layer composed of resin including synthetic
rubber on the supporting layer so as to cover the vibrating portion
and to form a hollow space around the periphery of the vibrating
portion; a fourth step of forming a protective layer composed of
resin having resistance to flux on a side of the cover layer remote
from the supporting layer; a fifth step of forming a via conductor
extending through the protective layer, the cover layer, and the
supporting layer and connected to the pad; and a sixth step of
forming an external electrode including a solder bump at an end of
the via conductor remote from the protective layer.
[0019] During mounting of the elastic wave device manufactured by
the above-described method, flux is applied to the solder bump so
as to improve solder wettability. The flux often flows into the
hollow space when only the cover layer is disposed on the hollow
space since the flux passes through the cover layer composed of
resin including synthetic rubber. In contrast, when the protective
layer composed of resin having resistance to flux is formed on the
cover layer as in a preferred embodiment of the present invention,
the flux does not pass through the protective layer composed of
resin having resistance to flux, and can be prevented from flowing
into the hollow space.
[0020] Preferably, the method includes a seventh step of forming a
groove in the substrate from the first main surface of the
substrate to a predetermined depth; and an eighth step of grinding
a second main surface of the substrate opposite to the first main
surface so as to reduce the thickness of the substrate and to
divide the substrate into chips.
[0021] In this case, a plurality of elastic wave devices having a
thinned substrate can be manufactured in a mother board at the same
time while cracking caused by warpage of the substrate is
prevented.
[0022] That is, in order to reduce the thickness of the substrate,
in general, chips are cut out by dicing after the second main
surface of the substrate remote from the hollow space is ground
until the substrate is reduced to a desired thickness. In this
method, stress remaining in, for example, the supporting layer and
the cover layer that form the hollow space disadvantageously causes
high warpage and cracking of the substrate when the thickness
thereof is reduced. In the case of the substrate having the hollow
space, the substrate does not significantly warp at the moment when
the thickness thereof is reduced when a groove is cut from the
first main surface of the substrate to a predetermined position in
advance and the thickness of the substrate is reduced by grinding
the second main surface. Therefore, cracking caused by the warpage
of the substrate can be prevented.
[0023] The supporting layer, the cover layer, and the protective
layer can be cut when the groove is formed in the substrate.
Moreover, the substrate can be divided into chips by reducing the
thickness of the substrate until the second main surface reaches
the groove or by folding the substrate along the groove after the
thickness of the substrate is reduced until the second main surface
reaches to just short of the groove.
[0024] In addition, another preferred embodiment of the present
invention provides a method for manufacturing an elastic wave
device. A method for manufacturing an elastic wave device includes
a first step of forming a vibrating portion and a pad electrically
connected to an electrode of the vibrating portion on a first main
surface of a substrate; a second step of forming a supporting layer
having a thickness larger than that of the vibrating portion on the
first main surface of the substrate so as to enclose the vibrating
portion; a third step of forming a sheet-shaped cover layer
composed of resin including synthetic rubber on the supporting
layer so as to cover the vibrating portion and to form a hollow
space around the periphery of the vibrating portion; a fourth step
of forming a protective layer composed of resin having resistance
to flux on a side of the cover layer remote from the supporting
layer; a fifth step of forming a via conductor extending through
the protective layer, the cover layer, and the supporting layer and
connected to the pad; and a sixth step of forming an external
electrode formed of a solder bump at an end of the via conductor
remote from the protective layer.
[0025] During mounting of the elastic wave device manufactured by
the above-described method, flux is applied to the solder bump so
as to improve solder wettability. The flux often flows into the
hollow space when only the cover layer is disposed on the hollow
space since the flux passes through the cover layer composed of
resin including synthetic rubber. In contrast, when the protective
layer composed of resin having resistance to flux is formed on the
cover layer as in a preferred embodiment of the present invention,
the flux does not pass through the protective layer composed of
resin having resistance to flux, and can be prevented from flowing
into the hollow space.
[0026] Preferably, the method further includes a sixth step of
forming a groove in the substrate from the first main surface of
the substrate to a predetermined depth; and a seventh step of
grinding a second main surface of the substrate opposite to the
first main surface so as to reduce the thickness of the substrate
and to divide the substrate into chips.
[0027] In this case, a plurality of elastic wave devices having a
thinned substrate can be manufactured in a mother board at the same
time while cracking caused by warpage of the substrate is
prevented.
[0028] That is, in order to reduce the thickness of the substrate,
in general, chips are cut out by dicing after the second main
surface of the substrate remote from the hollow space is ground
until the substrate is reduced to a desired thickness. In this
method, stress remaining in, for example, the supporting layer and
the cover layer that form the hollow space disadvantageously causes
high warpage and cracking of the substrate when the thickness
thereof is reduced. In the case of the substrate having the hollow
space, the substrate does not significantly warp at the moment when
the thickness thereof is reduced when a groove is cut from the
first main surface of the substrate to a predetermined position in
advance and the thickness of the substrate is reduced by grinding
the second main surface. Therefore, cracking caused by the warpage
of the substrate can be prevented.
[0029] The supporting layer, the cover layer, and the protective
layer can be cut when the groove is formed in the substrate.
Moreover, the substrate can be divided into chips by reducing the
thickness of the substrate until the second main surface reaches
the groove or by folding the substrate along the groove after the
thickness of the substrate is reduced until the second main surface
reaches to just short of the groove.
[0030] According to various preferred embodiments of the present
invention, a protective layer prevents flux from flowing into a
hollow space of an elastic wave device during mounting of the
device using solder bumps.
[0031] The above and other elements, features, steps,
characteristics and advantages of the present invention will become
more apparent from the following detailed description of the
preferred embodiments with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a cross-sectional view of an electronic component
including a surface acoustic wave device mounted thereon according
to a preferred embodiment of the present invention.
[0033] FIGS. 2A to 2C are cross-sectional views illustrating a
method for manufacturing a surface acoustic wave device according
to a preferred embodiment of the present invention.
[0034] FIGS. 3D to 3F are cross-sectional views illustrating a
method for manufacturing a surface acoustic wave device according
to a preferred embodiment of the present invention.
[0035] FIG. 4 is a cross-sectional view of a surface acoustic wave
device according to a preferred embodiment of the present
invention.
[0036] FIG. 5 is a cross-sectional view of another surface acoustic
wave device according to another preferred embodiment of the
present invention.
[0037] FIG. 6 is a cross-sectional view of an electronic component
including a bulk acoustic wave device mounted thereon according to
a preferred embodiment of the present invention.
[0038] FIG. 7 is a cross-sectional view of a bulk acoustic wave
device according to a preferred embodiment of the present
invention.
[0039] FIG. 8 is a perspective view of an elastic wave device.
[0040] FIGS. 9A to 9C are cross-sectional views of principal
portions of a conventional elastic wave device.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0041] Examples serving as preferred embodiments of the present
invention will now be described with reference to FIGS. 1 to 8.
Example 1
[0042] An electronic component 30 of Example 1 will now be
described with reference to FIGS. 1 to 4 and FIG. 8.
[0043] As shown in a cross-sectional view in FIG. 1, an electronic
component 30 of Example 1 includes two surface acoustic wave
devices 10 mounted on an upper surface 40a serving as a first main
surface of a common substrate 40. That is, lands 42 located in the
upper surface 40a of the common substrate 40 and the surface
acoustic wave devices 10 are electrically connected to each other
with solder bumps 18 interposed therebetween. A resin 32 is
disposed over the surface acoustic wave devices 10 so as to cover
the surface acoustic wave devices 10. External electrodes 44 used
for mounting the electronic component 30 on, for example, other
circuit boards are exposed at a lower surface 40b serving as a
second main surface of the common substrate 40. Via conductors 46
and internal wiring patterns 48 that electrically connect the lands
42 and the external electrodes 44 are located inside the common
substrate 40.
[0044] For example, the electronic component 30 can be a duplexer,
and can include the surface acoustic wave devices 10 as
surface-acoustic-wave filter elements for transmission and
reception mounted side by side on the common substrate 40.
[0045] As shown in a cross-sectional view in FIG. 4, the surface
acoustic wave devices 10 each include a piezoelectric substrate 11
and an element portion, for example, a SAW (surface acoustic wave)
filter located on the piezoelectric substrate. That is, an IDT
(interdigital transducer) electrode 12 serving as a comb-shaped
electrode of a vibrating portion 14, pads 13, and a conductive
pattern including wiring lines (not shown) that connect the IDT
electrode 12 and the pads 13 to each other are disposed on an upper
surface 11a serving as a first main surface of the piezoelectric
substrate 11. A frame-shaped supporting layer 20 is arranged so as
to enclose the vibrating portion 14 including the IDT electrode 12.
The thickness of the supporting layer 20 is larger than that of the
conductive pattern such as the IDT electrode 12 of the vibrating
portion 14. The supporting layer 20 is also located on the pads
13.
[0046] A cover layer 22 is disposed on the supporting layer 20, and
the periphery of the vibrating portion 14 disposed on the
piezoelectric substrate 11 is covered with the supporting layer 20
and the cover layer 22 serving as insulating members, thereby
forming a hollow space 19. Surface acoustic waves freely propagate
along the upper surface 11a of the piezoelectric substrate 11 in a
portion adjacent to the hollow space 19. A protective layer 24 is
located on the cover layer 22.
[0047] Via holes (through-holes) 15 extending to the pads 13
located on the upper surface 11a of the piezoelectric substrate 11
are formed in the protective layer 24, the cover layer 22, and the
supporting layer 20. Under-bump metals 16 serving as via conductors
are disposed in the via holes 15, and solder bumps 18 are located
on the under-bump metals 16 so as to be exposed to the outside.
[0048] Next, manufacturing processes of the electronic component 30
will be described.
[0049] First, manufacturing processes of the surface acoustic wave
device 10 will be described with reference to cross-sectional views
in FIGS. 2A to 3F. A plurality of surface acoustic wave devices 10
are manufactured in a mother board (wafer) at the same time.
[0050] As shown in FIG. 2A, the IDT electrode 12, the pads 13, and
the conductive pattern including wiring lines (not shown) that
connect the IDT electrode 12 and the pad 13 to each other are
located on the first main surface 11a of the piezoelectric
substrate 11, and the supporting layer 20 is arranged around the
periphery of the vibrating portion 14 including the IDT electrode
12. In order to form the supporting layer 20, photosensitive
polyimide resin, for example, is applied onto the entire first main
surface 11a of the piezoelectric substrate 11, and the resin is
opened (removed) at the periphery of the vibrating portion 14
including the IDT electrode 12 using a photolithographic
technique.
[0051] Next, as shown in FIG. 2B, the sheet-shaped cover layer is
formed on the supporting layer 20 by, for example, lamination. The
cover layer 22 is composed of, for example, non-photosensitive
epoxy resin which allows a low temperature curing process.
[0052] Next, as shown in FIG. 2C, the protective layer 24 is formed
on the cover layer 22. The protective layer 24 is composed of, for
example, photosensitive polyimide resin, which is the same material
as the supporting layer 20.
[0053] The cover layer 22 and the protective layer 24 can be formed
at the same time by placing a sheet-shaped multiple layer including
a sheet to be the cover layer 22 and a sheet to be the protective
layer 24 stacked in advance on the supporting layer 20 instead of
stacking the protective layer 24 after stacking the cover layer 22
on the supporting layer 20.
[0054] Next, as shown in FIG. 3D, the via holes 15 are formed by
laser processing so as to extend through the protective layer 24,
the cover layer 22, and the supporting layer 20 and such that the
pads 13 at the bottoms of the via holes are exposed
therethrough.
[0055] Next, as shown in FIG. 3E, the under-bump metals 16 serving
as via conductors are formed in the via holes 15 by electrolytic
plating (using, Cu, Ni, or the like), and Au for antioxidation
having a thickness of about 0.05 .mu.m to about 0.1 .mu.m, for
example, is formed on surfaces 16a of the under-bump metals 16, for
example.
[0056] Next, as shown in FIG. 3F, solder paste such as Sn--Ag--Cu
is printed immediately above the under-bump metals 16 with the
metal masks interposed therebetween, and is heated at, for example,
about 260.degree. C., at which the solder paste melts so that the
solder becomes fixed to the under-bump metals 16. Flux is removed
using a flux cleaner. With this, the spherical solder bumps 18 are
formed.
[0057] Next, grooves are cut from the protective layer 24 to a
predetermined depth in the piezoelectric substrate 11 by, for
example, dicing, and the bottom surface (second main surface) 11b
of the piezoelectric substrate 11 is ground so that the thickness
of the substrate is reduced and thereby that the board is divided
into chips. This completes the preparation of the surface acoustic
wave device 10 shown in FIG. 4. The supporting layer 20, the cover
layer 22, and the protective layer 24 can be cut when the grooves
are cut. Moreover, the board can be divided into chips by reducing
the thickness of the piezoelectric substrate 11 until the bottom
surface reaches the grooves or by folding the piezoelectric
substrate 11 along the grooves after the thickness of the
piezoelectric substrate 11 is reduced until the bottom surface
reaches to just short of the grooves.
[0058] In order to reduce the thickness of the piezoelectric
substrate 11, in general, the bottom surface 11b of the substrate
remote from the hollow space 19 is ground until the substrate is
reduced to a desired thickness before chips are cut out by dicing.
In this method, stress remaining in the resins such as the
supporting layer 20 and the cover layer 22 that form the hollow
space 19 disadvantageously causes high warpage and cracking of the
piezoelectric substrate 11 serving as a mother board when the
thickness thereof is reduced. In the case of the piezoelectric
substrate 11 having the hollow space 19, the piezoelectric
substrate 11 does not significantly warp at the moment when the
thickness thereof is reduced when grooves are cut from the first
main surface 11a of the piezoelectric substrate 11 to a
predetermined position in advance and the thickness of the
substrate is reduced by grinding the bottom surface 11b. Therefore,
cracking caused by the warpage of the piezoelectric substrate 11
can be prevented.
[0059] Next, processes of manufacturing the electronic component 30
by mounting the manufactured surface acoustic wave devices 10 will
be described. A plurality of electronic components 30 are
manufactured in a mother board at the same time.
[0060] First, the surface acoustic wave devices 10 are mounted on a
printed circuit board to be the common substrate 40. When the
devices are mounted, flux is applied to the solder bumps 18 so as
to improve the solder wettability.
[0061] Next, the surface acoustic wave devices 10 are embedded in
the resin 32 by, for example, lamination or resin molding while
being pressurized at about 2 Pa to about 5 Pa, for example, and
then the board is divided into chips. This completes the
fabrication of the electronic component 30 shown in FIG. 1.
[0062] For example, the thickness of the supporting layer 20 is
about 15 .mu.m, the thickness of the cover layer 22 is about 30
.mu.m, and the thickness of the protective layer 24 is about 3
.mu.m, for example.
[0063] The cover layer 22 can be a sheet of resin including
synthetic rubber, for example, a sheet of non-photosensitive epoxy
resin. The cover layer 22 has toughness even when it has a
sheet-shaped configuration due to the addition of the synthetic
rubber, and does not crack easily.
[0064] However, when the solder bumps 18 are formed immediately
above the cover layer 22 as in a surface acoustic wave device 10x
shown in a cross-sectional view in FIG. 8, flux often flows into
the hollow space 19 through the cover layer 22 composed of resin
including synthetic rubber such as acrylic rubber.
[0065] Therefore, the protective layer 24 composed of resin having
resistance to flux is formed on the cover layer 22 as shown in FIG.
4, and the solder bumps 18 are formed thereon. With this, flux does
not pass through the protective layer 24 composed of resin having
resistance to flux, and can be prevented from flowing into the
hollow space 19.
[0066] Although the material of the protective layer 24 can differ
from that of the supporting layer 20, the material of the
protective layer 24 is preferably the same as that of the
supporting layer 20 when the supporting layer 20 is composed of
resin having resistance to flux since the variety of materials is
not increased and thereby manufacturing processes can be
simplified.
[0067] During the process for mounting the surface acoustic wave
devices 10, accuracy in mounting the surface acoustic wave devices
10 can be improved by mounting the devices by recognizing the
solder bumps 18 rather than mounting the devices by recognizing the
external shapes of the devices, the shape being affected by dicing
accuracy. In particular, when the protective layer 24 is composed
of the same photosensitive polyimide resin as the supporting layer
20, a difference in brightness profile between the solder bumps 18
and the protective layer 24 becomes large, and it becomes easy for
the solder bump 18 to be recognized. Accordingly, the surface
acoustic wave devices 10 can be mounted with higher accuracy
compared with when the external shapes of the surface acoustic wave
devices 10 are recognized.
[0068] The hollow space 19 is hermetically sealed by the resin 32.
Openings for the via holes can be formed in the supporting layer 20
such that the pads 13 are at least partially exposed when the
supporting layer is formed. However, when the via holes that extend
through the cover layer and the protective layer are formed by
laser processing after the cover layer and the protective layer are
formed on the supporting layer having the openings for the via
holes, a portion of the material (for example, filler) of the cover
layer adheres to the bottoms of the via holes, i.e., the pads, and
adversely affects adhesiveness between the pads and the platings
subsequently disposed in the via holes.
[0069] When the openings for the via holes are not formed in the
supporting layer during the formation of the supporting layer and
the via holes are formed in the supporting layer, the cover layer,
and the protective layer by laser processing at the same time after
the formation of the cover layer and the protective layer, the
above-described problem does not occur, and adhesiveness between
the pads and the platings disposed in the via holes can be
improved.
[0070] When the surface acoustic wave devices 10 are embedded in
the resin 32, it is necessary to select the parameters of the
supporting layer 20 and the cover layer 22 so that the hollow space
19 does not collapse. The size of the hollow space 19 required to
realize a SAW filter used in an 800 MHz band, which requires the
largest size in frequency bands in which general SAW filters are
used, is approximately 400 .mu.m.times.1000 .mu.m, for example. In
order to form the hollow space 19 having the size of approximately
400 .mu.m.times.1000 .mu.m without it collapsing, the parameters of
the supporting layer 20 and the cover layer 22 can be selected so
as to satisfy the following conditions:
[0071] Thickness of cover layer.gtoreq.30 .mu.m
[0072] Elastic modulus of material of cover layer.gtoreq.3 GPa
[0073] Thickness of supporting layer.gtoreq.10 .mu.m
[0074] Elastic modulus of material of supporting layer.gtoreq.2.5
GPa
[0075] The thickness of the protective layer 24 and the elastic
modulus of the material of the protective layer 24 can be ignored
as conditions to be adjusted so that the hollow space 19 does not
collapse since the thickness of the protective layer 24 can be
smaller than that of the cover layer 22.
Example 2
[0076] A surface acoustic wave device 10a of Example 2 will now be
described with reference to FIG. 5.
[0077] The surface acoustic wave device 10a of Example 2 has the
same structure as the surface acoustic wave device 10 of Example 1
except for the following differences.
[0078] That is, as shown in a cross-sectional view in FIG. 5, an
intermediate layer 26 is formed between the supporting layer 20 and
the piezoelectric substrate 11. The intermediate layer 26 is formed
in an area except for the portions of a vibrating portion 14a
including the IDT electrode 12 and the pads 13 so as to enclose the
vibrating portion 14a and to be interposed between the
piezoelectric substrate 11 and the supporting layer 20. The
intermediate layer 26 can improve adhesiveness.
[0079] A SiO.sub.2 film serving as the intermediate layer 26 is
formed by, for example, forming the conductive pattern on the
LiTaO.sub.3 piezoelectric substrate 11 as in Example 1, forming the
SiO.sub.2 film on the substrate by sputtering, and then removing a
portion of the SiO.sub.2 film formed in portions from which the
SiO.sub.2 film is required to be removed, for example, the areas in
which the vibrating portion 14a and the pads 13 are formed, by dry
etching. A SiN film can be formed instead of the SiO.sub.2 film.
Subsequently, the supporting layer 20 and the like are formed as in
Example 1.
[0080] Adhesion strength can be improved by an anchoring effect
since the SiO.sub.2 film or the SiN film serving as the
intermediate layer 26 has a surface rougher than that of the
piezoelectric substrate 11. These films can be formed by sputtering
or CVD (chemical vapor deposition).
[0081] The hollow space 19 can be kept fluid-tight by forming the
intermediate layer 26 between the piezoelectric substrate 11 and
the supporting layer 20. With this, problems that cause poor
characteristics during processes after the formation of the hollow
space, for example, entering of plating solution into the hollow
space 19 during plating of the via holes, can be prevented.
[0082] The SiO.sub.2 film can be removed such that the areas to be
removed are larger than those of the pads 13. In this case,
portions of the supporting layer 20 are also formed on the
piezoelectric substrate 11 around the periphery of the pads 13.
However, the intermediate layer 26 only needs to be interposed
between the other portions of the supporting layer 20 and the
piezoelectric substrate 11 and to enclose the vibrating portion 14a
at a position closer to the IDT electrode 12 than the pads 13.
Example 3
[0083] An electronic component 30x of Example 3 will now be
described with reference to FIGS. 6 and 7.
[0084] As shown in a cross-sectional view in FIG. 6, the electronic
component 30x of Example 3 has substantially the same structure as
the electronic component 30 of the Example 1. Only differences from
Example 1 will be focused on in the following descriptions, and the
same reference sings are used for components common to those in
Example 1.
[0085] Unlike the electronic component 30 of Example 1, the
electronic component 30x of Example 3 includes the surface acoustic
wave device 10 and a bulk acoustic wave device 10x mounted on the
upper surface 40a serving as the first main surface of the common
substrate 40. That is, the lands 42 formed in the upper surface 40a
of the common substrate 40 are electrically connected to the
surface acoustic wave device 10 and the bulk acoustic wave device
10x with the solder bumps 18 interposed therebetween. The resin 32
is disposed over the surface acoustic wave device 10 and the bulk
acoustic wave device 10x so as to cover the surface acoustic wave
device 10 and the bulk acoustic wave device 10x. The external
electrodes 44 used for mounting the electronic component 30x on,
for example, other circuit boards are exposed at the lower surface
40b serving as the second main surface of the common substrate 40.
The via conductors 46 and the internal wiring patterns 48 that
electrically connect the lands 42 and the external electrodes 44
are formed inside the common substrate 40.
[0086] For example, the electronic component 30x can be a duplexer,
and can include the surface acoustic wave device 10 as a
surface-acoustic-wave filter element and the bulk acoustic wave
device 10x as a bulk-acoustic-wave filter element, one of which is
for transmission and the other is for reception.
[0087] The bulk acoustic wave device 10x has substantially the same
structure as the surface acoustic wave device 10 of Example 1
except that a vibrating portion 14x is formed on an insulating
substrate 11x composed of, for example, Si.
[0088] That is, the bulk acoustic wave device 10x has a package
structure similar to that of the surface acoustic wave device 10.
The bulk acoustic wave device 10x includes the frame-shaped
supporting layer 20 formed on a first main surface 11s of the
substrate 11x around the periphery of the vibrating portion 14x
formed on the surface. The thickness of the supporting layer is
larger than that of the vibrating portion 14x. The supporting layer
20 is formed also on the pads 13. The cover layer 22 is disposed on
the supporting layer 20, and the periphery of the vibrating portion
14x is covered with the supporting layer 20 and the cover layer 22
serving as insulating members, thereby forming the hollow space 19.
The protective layer 24 is formed on the cover layer 22. The via
holes (through-holes) 15 extending to the pads 13 are formed in the
protective layer 24, the cover layer 22, and the supporting layer
20. The under-bump metals 16 serving as via conductors are disposed
in the via holes 15, and the solder bumps 18 are formed on the
under-bump metals 16 so as to be exposed to the outside.
[0089] The above-described package structure is not limited to the
bulk acoustic wave device of the SMR type of Example 3, and can
also be applied to a bulk acoustic wave device in which a vibrating
portion is disposed above a hollow formed in a substrate or in
which a vibrating portion is supported while being suspended above
a substrate by, for example, removing a dummy layer.
[0090] As shown in a cross-sectional view of a principal portion in
FIG. 7, the bulk acoustic wave device 10x includes the vibrating
portion 14x including an upper electrode 12a, a lower electrode
12b, and a piezoelectric thin film 12s interposed therebetween
unlike the surface acoustic wave device 10 of Example 1. The
vibrating portion 14x is acoustically separated from the insulating
substrate 11x by an reflector 17 interposed therebetween.
[0091] The reflector 17 includes low acoustic impedance layers 17s
with a relatively low acoustic impedance and high acoustic
impedance layers 17t with a relatively high acoustic impedance
alternately stacked on the insulating substrate 11x. The upper
electrode 12a and the lower electrode 12b are electrically
connected to the pads 13 (not shown in FIG. 7).
[0092] Herein, the pads 13 can be directly formed on the main
surface 11s of the insulating substrate 11x, or can be formed on
the main surface 11s of the insulating substrate 11x with another
layer (for example, a low acoustic impedance layer 17s) interposed
therebetween.
[0093] As described above, flux can be prevented from flowing into
the hollow space 19 during mounting of the surface acoustic wave
devices 10 and 10a by forming the protective layer 24 on the cover
layer 22.
[0094] The present invention is not limited to the above-described
preferred embodiments, and various modifications are possible.
[0095] For example, not only the SAW filter but also an element
portion such as a SAW resonator can be formed on the piezoelectric
substrate. Moreover, not only the BAW filter but also an element
portion such as a BAW resonator can be formed on the insulating
substrate.
[0096] While preferred embodiments of the present invention have
been described above, it is to be understood that variations and
modifications will be apparent to those skilled in the art without
departing the scope and spirit of the present invention. The scope
of the present invention, therefore, is to be determined solely by
the following claims.
* * * * *