U.S. patent application number 12/717171 was filed with the patent office on 2010-06-17 for circuit substrate, circuit module and method for manufacturing the circuit substrate.
This patent application is currently assigned to MURATA MANUFACTURING CO., LTD.. Invention is credited to Yutaka FUKUDA.
Application Number | 20100147573 12/717171 |
Document ID | / |
Family ID | 40428902 |
Filed Date | 2010-06-17 |
United States Patent
Application |
20100147573 |
Kind Code |
A1 |
FUKUDA; Yutaka |
June 17, 2010 |
CIRCUIT SUBSTRATE, CIRCUIT MODULE AND METHOD FOR MANUFACTURING THE
CIRCUIT SUBSTRATE
Abstract
A thin circuit substrate and a circuit module are arranged such
that the circuit module includes an IC mounted on a circuit
substrate, the IC includes an IC body and an solder bump located on
a mounting surface of the IC body, and the circuit substrate
includes a substrate including a recess formed by recessing a
portion of a mounting surface of the substrate on which the IC is
to be mounted, and a terminal protruding from the mounting surface
of the substrate. The terminal is to be electrically connected to
the solder bump.
Inventors: |
FUKUDA; Yutaka;
(Echizen-shi, JP) |
Correspondence
Address: |
MURATA MANUFACTURING COMPANY, LTD.;C/O KEATING & BENNETT, LLP
1800 Alexander Bell Drive, SUITE 200
Reston
VA
20191
US
|
Assignee: |
MURATA MANUFACTURING CO.,
LTD.
Nagaokakyo-shi
JP
|
Family ID: |
40428902 |
Appl. No.: |
12/717171 |
Filed: |
March 4, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/JP2008/065897 |
Sep 3, 2008 |
|
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12717171 |
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Current U.S.
Class: |
174/260 ;
174/267; 29/832; 29/837; 29/852 |
Current CPC
Class: |
H01L 2924/00011
20130101; H01L 23/16 20130101; H01L 2924/014 20130101; H05K 3/4697
20130101; H05K 3/4629 20130101; H05K 2203/0278 20130101; Y10T
156/1052 20150115; H01L 2224/81801 20130101; H01L 2924/01047
20130101; Y02P 70/611 20151101; H01L 2224/81193 20130101; H01L
2924/01006 20130101; H01L 2924/15153 20130101; H05K 3/4061
20130101; H01L 21/481 20130101; Y02P 70/50 20151101; H01L 21/4853
20130101; H01L 23/13 20130101; H01L 2924/1517 20130101; H05K 3/245
20130101; H01L 2924/01029 20130101; H01L 24/81 20130101; H01L
2224/81136 20130101; H05K 1/183 20130101; H01L 2924/01056 20130101;
H01L 23/49816 20130101; H01L 2924/01004 20130101; H05K 2203/308
20130101; H01L 2924/15151 20130101; H01L 2224/16225 20130101; H01L
2924/14 20130101; H01L 2924/01005 20130101; H01L 2924/01033
20130101; H05K 3/4611 20130101; Y10T 156/10 20150115; Y10T 29/49165
20150115; H01L 2924/00014 20130101; H05K 3/0014 20130101; H05K
2201/091 20130101; H05K 1/0306 20130101; H05K 2201/0367 20130101;
H01L 23/49827 20130101; Y10T 29/4913 20150115; H05K 3/4007
20130101; H05K 1/111 20130101; H01L 2924/12042 20130101; Y10T
29/49139 20150115; H05K 3/3436 20130101; H01L 2924/1517 20130101;
H01L 2924/15153 20130101; H01L 2924/12042 20130101; H01L 2924/00
20130101; H01L 2924/00014 20130101; H01L 2224/0401 20130101; H01L
2924/00011 20130101; H01L 2224/0401 20130101 |
Class at
Publication: |
174/260 ;
174/267; 29/832; 29/837; 29/852 |
International
Class: |
H05K 1/18 20060101
H05K001/18; H05K 1/11 20060101 H05K001/11; H05K 3/30 20060101
H05K003/30; H05K 3/42 20060101 H05K003/42 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 6, 2007 |
JP |
2007-231314 |
Mar 31, 2008 |
JP |
2008-092195 |
Claims
1. A circuit substrate on which a first electronic component
including a bump is to be mounted, the circuit substrate
comprising: a substrate including a mounting surface on which the
first electronic component is to be disposed, the mounting surface
including a recess defined by a recessed portion of the mounting
surface; and a terminal to be electrically connected to the bump of
the first electronic component, the terminal protruding from the
mounting surface within the recess.
2. The circuit substrate according to claim 1, further comprising
an electrode on the mounting surface outside the recess, the
electrode being to be joined to a second electronic component.
3. A circuit module comprising: a first electronic component; and a
circuit substrate on which the first electronic component is
mounted; wherein the first electronic component includes an
electronic component body and a bump on the electronic component
body, and the circuit substrate includes a substrate including a
mounting surface on which the first electronic component is
disposed and including a recess defined by a recessed portion of
the mounting surface, and a terminal protruding from the mounting
surface within the recess and electrically connected to the
bump.
4. The circuit module according to claim 3, wherein the electronic
component body is disposed within the recess when viewed in the
direction of the normal to the substrate.
5. The circuit module according to claim 3, wherein the electronic
component body covers the recess beyond edges of the recess when
viewed in the direction of the normal to the substrate and is in
contact with the substrate.
6. The circuit module according to claim 3, further comprising a
second electronic component, wherein the circuit substrate further
includes an electrode on the mounting surface outside the recess,
and the second electronic component is joined to the electrode via
a solder layer therebetween.
7. A method for manufacturing a circuit substrate on which a first
electronic component having a bump is to be mounted, the circuit
substrate including a terminal to which the bump of the first
electronic component is to be electrically connected, the method
comprising the steps of: forming a mask layer on a portion of a
main surface of a first sheet; forming a through-hole in the mask
layer; filling the through-hole with a conductive material;
stacking a plurality of second sheets and the first sheet having
the mask layer such that the mask layer defines an uppermost layer,
and compressing the stack to embed the mask layer in the first
sheet; and removing the mask layer from the stack of the first
sheet and the second sheets.
8. The method according to claim 7, wherein the mask layer is
formed by applying a resin paste onto the first sheet in the step
of forming the mask layer.
9. The method according to claim 7, wherein the through-hole is
formed by irradiating the mask layer with a laser beam in the step
of forming the through-hole.
10. The method according to claim 7, wherein the first sheet and
the second sheets are ceramic green sheets, and the mask layer is
made of a resin, and wherein the step of removing the mask layer is
performed by firing the first sheet and the second sheets together
with the mask layer, thereby consuming the mask layer.
11. The method according to claim 7, wherein the through-hole is
formed so as to pass through the first sheet and the mask layer in
the step of forming the through-hole.
12. The method according to claim 7, further comprising the steps
of forming an electrode to which a second electronic component is
to be joined, in a region other than the mask layer, and printing a
solder paste on the electrode through a mask pattern.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a circuit substrate, a
circuit module and a method for manufacturing the circuit
substrate, and more specifically, to a circuit substrate on which
electronic components are to be mounted, a circuit module and a
method for manufacturing the circuit substrate.
[0003] 2. Description of the Related Art
[0004] For mounting an electronic component, such as an IC, on a
circuit substrate, the following technique is generally applied.
Flat electrode pads are arranged in an array manner on the main
surface of a circuit substrate. On the main surface of an IC,
solder bumps are formed in an array manner. The IC is placed on the
circuit substrate in such a manner that the solder bumps are
aligned with the respective electrode pads, and the solder bumps
are reflowed. The solder bumps are melted to fix the electrode
pads, and the IC is thus mounted on the circuit substrate.
[0005] However, the circuit substrate and the IC have different
thermal expansion coefficients. Consequently, for example, the
circuit substrate may be warped by heat, and, thus, this mounting
technique may result in connection failure between the circuit
substrate and the IC. Accordingly, Japanese Patent No. 3203731 and
Japanese Unexamined Patent Application Publication No. 2005-45143
disclose a semiconductor device substrate on which columnar bumps,
but not flat electrode pads, are formed so as to protrude from the
main surface thereof.
[0006] The columnar bump has a larger height than the electrode pad
and is accordingly elastic. Even if the circuit substrate is warped
by heat, the columnar bump can absorb the warping. Thus, the
semiconductor device substrates disclosed in Japanese Patent No.
3203731 and Japanese Unexamined Patent Application Publication No.
2005-45143 can prevent the occurrence of connection failure between
the circuit substrate and the IC.
[0007] Such a semiconductor device substrate however increases the
height of the circuit substrate by the height of the columnar
bumps.
SUMMARY OF THE INVENTION
[0008] Accordingly, preferred embodiments of the present invention
provide a thin circuit substrate and circuit module that includes
protruding terminals, and a method for manufacturing the circuit
substrate.
[0009] A circuit substrate is provided on which a first electronic
component having a bump is to be mounted. The circuit substrate
includes a substrate including a mounting surface on which the
first electronic component is to be disposed. The mounting surface
includes a recess defined by a recessed portion of the mounting
surface. The circuit substrate also includes a terminal to be
electrically connected to the bump of the first electronic
component. The terminal protrudes from the mounting surface within
the recess. The circuit substrate may further include an electrode
to which a second electronic component is to be joined. The
electrode is disposed on the mounting surface outside the
recess.
[0010] A circuit module is provided which includes a first
electronic component, and a circuit substrate on which the first
electronic component is mounted. The first electronic component
includes an electronic component body and a bump located on the
electronic component body. The circuit substrate includes a
substrate including a mounting surface on which the first
electronic component is disposed and including a recess defined by
a recessed portion of the mounting surface, and a terminal
electrically connected to the bump and protruding from the mounting
surface within the recess.
[0011] According to a preferred embodiment of the present
invention, the recess is formed preferably by recessing a portion
of the mounting surface of the substrate. Consequently, the
distance from the lower surface of the circuit substrate to the top
of the terminal (that is, the height of the circuit substrate) can
be smaller than the height of a semiconductor device substrate
having a flat mounting surface. Thus, the thickness of a circuit
substrate and a circuit module including the circuit substrate can
be reduced.
[0012] The electronic component body may be disposed within the
recess when viewed in the direction of the normal to the
substrate.
[0013] Alternatively, the electronic component body may cover the
recess beyond the edges of the recess when viewed in the direction
of the normal to the substrate and be in contact with the
substrate.
[0014] The circuit module may further include a second electronic
component. In this instance, the circuit substrate further includes
an electrode on the mounting surface outside the recess. The second
electronic component is joined to the electrode with a solder layer
therebetween.
[0015] According to another preferred embodiment of the present
invention, a method of manufacturing a circuit substrate on which a
first electronic component having a bump is to be mounted and the
circuit substrate includes a terminal to which the bump of the
first electronic component is to be electrically connected,
includes the steps of forming a mask layer on a portion of a main
surface of a first sheet, forming a through-hole in the mask layer,
filling the through-hole with a conductive material, stacking a
plurality of second sheets and the first sheet having the mask
layer such that the mask layer acts as the uppermost layer, and
compressing the stack to embed the mask layer in the first sheet,
and removing the mask layer from the stack of the first sheet and
the second sheets.
[0016] The mask layer may be formed by applying a resin paste onto
the first sheet in the step of forming the mask layer.
[0017] The through-hole may be formed by irradiating the mask layer
with a laser beam in the step of forming the through-hole.
[0018] In the method, the first sheet and the second sheets may be
ceramic green sheets, and the mask layer may be made of a resin. In
this instance, the step of removing the mask layer is performed by
firing the first sheet and the second sheets together with the mask
layer, thereby consuming the mask layer.
[0019] The through-hole may be formed so as to pass through the
first sheet and the mask layer in the step of forming the
through-hole.
[0020] The method may further include the steps of forming an
electrode in a region other than the mask layer, and printing a
solder paste on the electrode through a mask pattern. The electrode
is to be joined to a second electronic component.
[0021] According to various preferred embodiments of the present
invention, the recess is formed preferably by recessing a portion
of the mounting surface of the substrate, and a terminal is formed
within the recess. Consequently, the height of the circuit
substrate can be lower than the height of a semiconductor device
substrate having a flat mounting surface. Thus, the thickness of a
circuit substrate and a circuit module including the circuit
substrate can be reduced.
[0022] 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
[0023] FIG. 1 is a sectional view of a structure in which an IC is
aligned on a circuit substrate according to a first preferred
embodiment of the present invention.
[0024] FIG. 2A is a sectional view of the structure of a circuit
module including an IC and a circuit substrate, and FIG. 2B is a
plan view of the circuit module.
[0025] FIGS. 3A-3C are sectional views showing a manufacturing
process of a circuit substrate.
[0026] FIGS. 4A-4C are sectional views showing the manufacturing
process of a circuit substrate.
[0027] FIGS. 5A and 5B are sectional views showing the
manufacturing process of a circuit substrate.
[0028] FIG. 6 is a sectional view showing the manufacturing process
of a circuit substrate.
[0029] FIG. 7 is a sectional view of the structure of a circuit
module according to a comparative example.
[0030] FIG. 8A is a sectional view of the structure of a circuit
module including an IC and a circuit substrate according to a
second preferred embodiment of the present invention, and
[0031] FIG. 8B is a plan view of the circuit module.
[0032] FIG. 9 is a sectional view of the structure of a circuit
module including an IC and a circuit substrate according to a third
preferred embodiment of the present invention.
[0033] FIG. 10A is a sectional view of the structure of a ceramic
green sheet, and FIG. 10B is a plan view of the ceramic green
sheet.
[0034] FIG. 11 is a sectional view showing a manufacturing process
of a circuit substrate.
[0035] FIG. 12 is a sectional view showing a manufacturing process
of a circuit substrate according to a comparative example.
[0036] FIG. 13 is a sectional view showing a manufacturing process
of a circuit substrate according to a comparative example.
[0037] FIG. 14 is a sectional view of the structure of a circuit
module including an IC and a circuit substrate according to a
fourth preferred embodiment of the present invention.
[0038] FIG. 15 is a sectional view of a circuit module in a
manufacturing process.
[0039] FIG. 16 is a sectional view of a circuit module in a
manufacturing process.
[0040] FIG. 17 is a sectional view of a circuit module in a
manufacturing process.
[0041] FIG. 18 is a sectional view of the structure of a circuit
substrate according to a comparative example.
[0042] FIG. 19 is a sectional view of a circuit module in a
manufacturing process.
[0043] FIG. 20 is a sectional view of a circuit module in a
manufacturing process.
[0044] FIG. 21 is a sectional view of a circuit module in a
manufacturing process.
[0045] FIG. 22 is a sectional view of a circuit module in a
manufacturing process.
[0046] FIG. 23 is a sectional view of the structure of a circuit
substrate according to a comparative example.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0047] The structures of a circuit substrate and a circuit module
according to a first preferred embodiment will now be described
with reference to related drawings. FIG. 1 is a sectional view of
the structure in which a semiconductor integrated circuit
(hereinafter referred to as IC) 50 is aligned on a circuit
substrate 10. FIG. 2A is a sectional view of the structure of a
circuit module 60 including the IC 50 and the circuit substrate 10.
FIG. 2B is a plan view of the circuit module 60. The plan view
mentioned herein refers to a structure viewed in the direction of
the normal to the circuit module 60.
[0048] The circuit substrate 10 is a base on which an electronic
component, or the IC 50, is to be surface-mounted, and includes a
substrate 12, terminals 14 and internal conductive layers 16, as
shown in FIG. 1. The substrate 12 includes a stack of a plurality
of insulating ceramic layers. The substrate 12 includes a recess 15
formed by recessing a portion of the mounting surface thereof on
which the IC 50 is to be mounted. In the description hereinafter,
the upper surface of the substrate 12 is referred to as the
mounting surface, and the surface of the substrate 12 opposing the
mounting surface is referred to as the lower surface. In the
present preferred embodiment, the mounting surface refers to the
visible surface in plan view. More specifically, the mounting
surface includes the surface defined by the region outside the
recess 15 and the surface defined by the region within the recess
15. The term recessing indicates that a portion of the circuit
substrate 10 is deformed by compression.
[0049] The internal conductive layers 16 are stacked with the
ceramic layers to form the substrate 12. The internal conductive
layers 16 are connected to each other through via conductors (not
shown) to form a circuit.
[0050] The terminals 14 are formed in an array manner in the recess
15 so as to protrude from the mounting surface of the substrate 12,
and serve to electrically connect the circuit including the
internal conductive layers 16 with the IC 50. Hence, first ends of
the terminals 14 are electrically connected to the internal
conductive layers 16. The level of the terminal is lower than the
level of the mounting surface of the substrate 12 outside the
recess 15.
[0051] The IC 50 includes an IC body 52 and solder bumps 54. The IC
body 52 includes a silicon substrate having a circuit (not shown).
The solder bumps 54 are arranged in an array on the lower surface
of the IC body 52, and serve to electrically connect the circuit of
the IC body 52 with the terminals 14. In the description
hereinafter, the upper surface of the IC body 52 is referred to as
the upper surface, and the lower surface of the IC body 52 is
referred to as the mounting surface.
[0052] The circuit substrate 10 and the IC 50 are aligned such that
the terminals 14 come in contact with the respective solder bumps
54, as shown in FIG. 1, and are then reflowed. The solder bumps 54
are thus melted to cover the terminals 14, as shown in FIG. 2A.
Consequently, the IC 50 is mounted on the circuit substrate 10.
[0053] The area of the recess 15 in plan view is smaller than that
of the IC body 52. Hence, the IC body 52 is mounted so as to cover
the recess 15 beyond the edges of the recess 15 when the circuit
module 60 is viewed from above, as shown in FIG. 2B. In this
instance, the mounting surface of the IC body 52 is in contact with
the mounting surface of the substrate 12, as shown in FIG. 2A.
[0054] A method for manufacturing the circuit substrate 10 will now
be described with reference to related drawings. FIGS. 3A to 6 are
sectional views of the circuit substrate 10 in a manufacturing
process.
[0055] First, a binder, a plasticizer and a solvent are mixed to a
ceramic material powder containing barium oxide, silicon oxide and
alumina to prepare a slurry. Subsequently, the slurry is formed
into a sheet on a carrier film to prepare a ceramic green sheet by
a doctor blade method or any other sheet forming technique. The
ceramic green sheet is cut into pieces having a predetermined
size.
[0056] After the completion of the ceramic green sheets, layers
constituting the substrate 12 are formed. As shown in FIG. 3A,
first, through-holes 24 are formed in one of the ceramic green
sheets 20 by stamping. Then, the through-holes 24 are filled with a
conductive paste mainly containing a conductive material, such as
Cu or Ag, to form via conductors 34, as shown in FIG. 3B.
[0057] Subsequently, a conductive paste mainly containing a
conductive material, such as Cu or Ag, is printed on the main
surface of the ceramic green sheet 20 to form an internal
conductive layer 16 having a predetermined pattern. One of the
layers constituting the substrate 12 is thus completed through the
steps shown in FIGS. 3A to 3C. The series of the steps shown in
FIGS. 3A to 3C is repeated until all the layers constituting the
substrate are completed.
[0058] Then, the uppermost layer of the substrate 12 is formed
using one of the ceramic green sheets. More specifically, a resin
paste mainly containing polypropylene, butyral or acrylic resin,
for example, is screen-printed on a portion of the main surface of
the ceramic green sheet 20 to form a mask layer 30, as shown in
FIG. 4A.
[0059] After the formation of the mask layer 30, the ceramic green
sheet 20 and the mask layer 30 are subjected to stamping together
to form through-holes 32 passing through the ceramic green sheet 20
and the mask layer 30, as shown in FIG. 4B. Then, the through-holes
32 are filled with a conductive paste mainly containing a
conductive material, such as Cu or Ag, to form terminals 14, as
shown in FIG. 4C.
[0060] Turning now to FIG. 5A, the mask layer 30 and a plurality of
ceramic green sheets 20 are stacked in such a manner that the mask
layer 30 overlies the ceramic green sheets 20 so as to act as the
uppermost layer. In practice, a carrier film 22 is removed from
each ceramic green sheet 20 before stacking the layers. Thus, a
multilayer green composite 40 is completed.
[0061] Subsequently, the multilayer green composite 40 is placed in
a base mold 42, and the multilayer green composite 40 is compressed
by applying a pressure using a mold cover 44 from above to bind the
ceramic green sheets 20 and the mask layer 30 together, as shown in
FIG. 5B. The compression is preferably performed under conditions
of a mold cover 44 temperature of about 70.degree. C. and a mold
cover 44 pressure of about 400 kg/cm.sup.2, for example. Thus, the
ceramic green sheets 20 under the mask layer 30 is compressed by
the mask layer 30 in the thickness direction, so that the mask
layer 30 is embedded in the uppermost ceramic green sheet 20, as
shown in FIG. 6. Thus, the recess 15 is formed. At this time, the
internal conductive layers 16 are bent in such a manner that the
portions of the internal conductive layers 16 under the mask layer
30 sink downwards, as shown in FIG. 6. In FIG. 6, the boundaries
between the ceramic green sheets 20, and the via conductors 34 are
omitted.
[0062] Finally, the multilayer green composite 40 including the
ceramic green sheets 20 is fired. At this time, the mask layer 30
is consumed (burned down) due to high temperature, and the recess
15 appears. The firing is performed at 990.degree. C. for 1 hour.
The circuit substrate 10 as shown in FIG. 1 is thus completed
through the above-described process.
[0063] The circuit substrate 10 includes a recess 15 formed by
recessing a portion of the mounting surface of the substrate 12,
and terminals 14 are formed in the recess 15. Consequently, the
distance from the lower surface of the circuit substrate 10 to the
top of the terminal 14 (that is, the height of the circuit
substrate) can be smaller than the height of a semiconductor device
substrate having a flat mounting surface as disclosed in Japanese
Patent No. 3203731. Thus, the thicknesses of the circuit substrate
10 and the circuit module 60 can be reduced. This will be described
in detail below.
[0064] The semiconductor device substrate disclosed in Japanese
Patent No. 3203731 has columnar bumps protruding from the
substrate, and a bump-forming sheet corresponding to the mask layer
30 is disposed as the uppermost layer over the entire surface of
the substrate. Accordingly, a force is substantially evenly placed
on the mounting surface of the substrate for compression, and a
recess is not formed in the mounting surface of the substrate.
[0065] On the other hand, for forming the circuit substrate 10, the
portions of the ceramic green sheets 20 under the mask layer
receive a higher pressure for compression than the other portions
of the ceramic green sheets 20. Consequently, the compression in
the stacking direction of the portions of the ceramic green sheets
20 under the mask layer 30 becomes larger by the thickness of the
mask layer 30 than that of the other portions of the ceramic green
sheets 20 and that of the substrate of Japanese Patent No. 3203731.
Thus, the height of the circuit substrate 10 is more reduced by the
thickness of the mask layer 30 than that of the semiconductor
device substrate. Hence, the thicknesses of the circuit substrate
10 and the circuit module 60 including the circuit substrate 10 can
be reduced.
[0066] Since the recess 15 is smaller than the IC body 52 when
viewed from above, as shown in FIG. 2B, the mounting surface of the
IC body 52 comes in contact with the mounting surface of the
substrate 12 when the IC 50 is mounted on the circuit substrate 10.
Consequently, the substrate 12 and the IC body 52 can maintain a
distance to some extent therebetween so as to prevent the solder
bumps 54 from being excessively compressed to cause a short circuit
between adjacent solder bumps 54. The reason will be described
below with reference to FIGS. 2A and 7. FIG. 7 is a sectional view
of the structure of a circuit module 360 according to a comparative
example. Let the distance between the mounting surface of the
substrate 12 and the mounting surface of the IC body 52 be h1 in
FIG. 2A. Also, in FIG. 7, let the distance between the mounting
surface of the substrate 312 and the mounting surface of the IC
body 352 be h2.
[0067] In the circuit module 360 shown in FIG. 7, an IC 350 is
mounted on a circuit substrate 310 whose mounting surface does not
have a recess. In this instance, since the mounting surface of the
IC body 352 does not come in contact with the mounting surface of
the substrate 312, the terminals 314 can be inserted in the solder
bumps 354 to a larger depth than those of the circuit module 60
shown in FIGS. 2A and 2B. Accordingly, the distance h2 between the
mounting surface of the substrate 312 and the mounting surface of
the IC body 352 is smaller than the distance h1 between the
substrate 12 and the IC body 52.
[0068] If the solder bump 54 and the solder bump 354 have the same
volume before mounting, the volume of the terminal 14 embedded in
the solder bump 54 in the circuit module 60 shown in FIGS. 2A and
2B is smaller than that in the circuit module 360 shown in FIG. 7.
Accordingly, the form of the solder bump 54 of the circuit module
60 shown in FIGS. 2A and 2B becomes smaller than that of the solder
bump 354 of the circuit module 360 shown in FIG. 7. Consequently,
the distances between the solder bumps in the circuit module 60
become larger than those in the circuit module 360, thus preventing
short-circuiting.
[0069] For the circuit module 60, the through-holes 32 are formed
in the ceramic green sheet 20 and the mask layer 30 at one time in
the step shown in FIG. 4B. This can prevent the misalignment
between the through-holes 32 formed in the ceramic green sheet 20
and the through-holes 32 formed in the mask layer 30. This will be
further described below.
[0070] If the mask layer 30 is formed of, for example, a resin
sheet, but not of a resin paste, the through-holes 32 of the mask
layer 30 and the through-holes 32 of the ceramic green sheet 20 are
formed in different steps. In this instance, the through-holes 32
are formed in the ceramic green sheet 20 and the mask layer 30
separately, and then the mask layer 30 is disposed on the ceramic
green sheet 20. Therefore, the through-holes 32 of the ceramic
green sheet 20 and the through-holes 32 of the mask layer 30 can be
misaligned unless the mask layer 30 is disposed on the ceramic
green sheet 20 with precise alignment. For the circuit module 60,
on the other hand, the through-holes 32 are formed in the ceramic
green sheet 20 and the mask layer 30 at one time, thus preventing
misalignment of the through-holes 32.
[0071] The structures of a circuit substrate and a circuit module
according to a second preferred embodiment will now be described
with reference to related drawings. FIG. 8A is a sectional view of
the structure of a circuit module 160 including an IC 150 and a
circuit substrate 110. FIG. 8B is a plan view of the circuit module
160. In the following description, differences of the circuit
module 160 from the circuit module 60 of the first preferred
embodiment will be mainly described.
[0072] In the circuit module 160, the area of the recess 115 in
plan view is larger than that of the IC body 152. Accordingly, the
IC body 152 is disposed within the recess 115 when the circuit
module 160 is viewed from above, as shown in FIG. 8B. In this
state, the level of the mounting surface of the IC body 152 is
lower than the level of the mounting surface of the substrate 112
outside the region of the recess 115, as shown in FIG. 8A. Thus,
the distance from the lower surface of the substrate 112 to the
upper surface of the IC body 152 (that is, the height of the
circuit module 160) is shorter than the distance from the lower
surface of the substrate 12 to the upper surface of the IC body
(that is, the height of the circuit module 60). Hence, the
thickness of the circuit module 160 can be more reduced than that
of the circuit module 60. It is preferable that the circuit module
160 be designed to have such a height as can maintain distances
between the solder bumps 154 so as to prevent short-circuiting.
[0073] The structures of a circuit substrate and a circuit module
according to a third preferred embodiment will now be described
with reference to related drawings. FIG. 9 is a sectional view of
the structure of a circuit module 260 including an IC 250 and a
circuit substrate 210. In the following description, differences of
the circuit module 260 from the circuit module 60 of the first
preferred embodiment will be mainly described.
[0074] The circuit substrate 210 includes a substrate 212 and a
frame portion 217 rising from the mounting surface along the sides
of the mounting surface. The frame portion 217 loops so as to
surround the mounting surface of the substrate 212. Also, the frame
portion 217 is formed such that the level of the upper surface
thereof is higher than that of the upper surface of the IC body
252. This structure allows the IC 250 to be sealed by filling the
region surrounded by the frame portion 217 with a resin. In the
present preferred embodiment, the mounting surface of the substrate
212 refers to the region surrounded by the frame portion 217, not
including the upper surface of the frame portion 217.
[0075] The upper surface of the frame portion 217 lies at a level
higher than the upper surface of the IC body 252. The structure of
the circuit substrate 210 allows the distance from the lower
surface of the substrate 212 to the upper surface of the IC body
252 to be reduced, as in the circuit substrate 10. Consequently,
the level of the upper surface of the frame portion 217 can be
lowered by the degree in which the level of the IC body 252 lowers.
In the circuit module 260, the distance from the lower surface of
the substrate 212 to the upper surface of the frame portion 217
(that is, the height of the circuit module 260) can thus be
reduced. Hence, the thicknesses of the circuit substrate 210 and
the circuit module 260 can be reduced.
[0076] The circuit substrate 210 can be manufactured by the
following method. A method for manufacturing the circuit substrate
210 will now be described with reference to FIGS. 10A, 10B and 11.
FIG. 10A is a sectional view of a ceramic green sheet 221. FIG. 10B
is a plan view of the ceramic green sheet 221. FIG. 11 is a
sectional view showing a step of the manufacturing process of the
circuit substrate 210.
[0077] The ceramic green sheet 221 defines the frame portion 217,
and has such a shape as is formed by stamping the center of a
rectangular sheet, as shown in FIG. 10B. A carrier film 222 is
bonded to the rear surface of the ceramic green sheet 221. The
ceramic green sheet 221 is disposed on the multilayer green
composite 40 shown in FIG. 6 after the carrier has been removed
therefrom, and then compression bonding is performed. The
compression bonding is performed at a pressure of about 200
kg/cm.sup.2, for example. The resulting composite is referred to as
a multilayer green composite 240. The multilayer green composite
240 includes two ceramic green sheets 221.
[0078] Subsequently, the multilayer green composite 240 is fired in
the same manner as in the method of the circuit substrate 10
according to the first preferred embodiment. In this step, the mask
layer 230 is burned down and removed due to high temperature and
the recess 215 appears. The circuit substrate 210 as shown in FIG.
9 is thus completed through the above-described process.
[0079] The above-described method of the present preferred
embodiment can provide a circuit substrate 210 including the frame
portion 217. The detail will be described below with reference to
FIGS. 12 and 13. FIGS. 12 and 13 are sectional views showing steps
of a manufacturing process of the circuit substrate 210 according
to a comparative example. In the process according to the
comparative example, a mask layer 430 is formed of a resin sheet,
but not a resin paste. This process will be described in detail
below.
[0080] In the method according to the comparative example, the mask
layer is formed so as to cover the entire surface of the uppermost
ceramic green sheet 220, as shown in FIG. 12. Then, additional
ceramic green sheets 221 intended for the frame portion 217 are
disposed on the mask layer 430. The ceramic green sheets 220, the
ceramic green sheets 221 and the mask layer 430 are compressed
together, thereby forming a multilayer green composite. The
multilayer green composite is fired. In this step, the mask layer
430 is burned down and removed due to high temperature. The ceramic
green sheets 221 disposed on the mask layer 430 as shown in FIG. 12
are separated from the substrate 212, as shown in FIG. 13, by
removing the mask layer 430. Hence, the circuit substrate
manufacturing method using the resin sheet cannot produce the
circuit substrate 210.
[0081] In the circuit substrate manufacturing method according to
the third preferred embodiment, on the other hand, the mask layer
230 is formed of a resin paste on a portion of the upper surface of
the ceramic green sheet 220. Thus, the mask layer 230 is not
present between the ceramic green sheet 220 and the ceramic green
sheets 221. Consequently, the frame portion 217 is not separated
from the substrate 212.
[0082] The structures of a circuit substrate and a circuit module
according to a fourth preferred embodiment will now be described
with reference to related drawings. FIG. 14 is a sectional view of
the structure of a circuit module 460 including an IC 450 and a
circuit substrate 410. In the following description, differences of
the circuit module 460 from the circuit module 60 of the second
preferred embodiment will be mainly described.
[0083] The difference between the circuit module 60 and the circuit
module 460 is that the circuit module 460 includes a circuit
substrate 410 including an IC 450 and an electronic component 470
while the circuit module 60 includes a circuit substrate 10
including only the IC 50. More specifically, the substrate 412
includes land electrodes 418 used for mounting an electronic
component 470 on the mounting surface outside the recess 415. The
electronic component 470 is disposed on the land electrodes 418
with a solder layer 472 therebetween.
[0084] A method for manufacturing the circuit module 460 will now
be described with reference to related drawings. FIGS. 15 to 17 are
sectional views of the circuit module 460 in steps of the
manufacturing process.
[0085] First, the steps shown in FIGS. 3A to 6 are performed in the
same manner as in the manufacturing process of the circuit
substrate 10 according to the first preferred embodiment, and the
same description will be omitted. Subsequently, land electrodes 418
are formed on the mounting surface outside the recess 415, as shown
in FIG. 15. The land electrodes 418 are formed by, for example,
applying an electroconductive paste mainly containing Cu, followed
by firing. The firing of the land electrodes 418 may be performed
simultaneously with the firing of the multilayer composite.
[0086] Turning now to FIG. 16, a metal mask 480 including openings
corresponding to the terminals 414 and the land electrodes 418 is
aligned on the circuit substrate 410. Then, a squeegee 482 is moved
on the metal mask 480 in the arrow direction to print a solder
paste 484 through the metal mask 480. Thus, solder layers 472 and
474 are printed on the terminals 414 and the land electrode 418, as
shown in FIG. 17. Subsequently, an electronic component 470 and an
IC 450 are mounted to complete the circuit module 460 shown in FIG.
14.
[0087] The circuit substrate 410 of the present preferred
embodiment can prevent the terminals 414 from breaking, and prevent
the solder layers 472 from being displaced and undesirably
spreading, as described below with reference to related drawings.
FIG. 18 is a sectional view of the structure of a circuit substrate
510 according to a comparative example.
[0088] The circuit substrate 510 shown in FIG. 18 is different from
the circuit substrate 410 shown in FIG. 14 in that the recess 415
is not formed. In order to print solder layers on the terminals 514
and the land electrodes 518 of such a circuit substrate 510, the
metal mask 580 is disposed on the circuit substrate 510, and a
solder paste 584 is printed using a squeegee 582.
[0089] In order to prevent the solder layers from being displaced
when the solder paste 584 is printed, the metal mask 580 should be
disposed close to the mounting surface of the substrate 510.
However, the circuit substrate 510 shown in FIG. 18 includes
terminals 514 protruding upward from the mounting surface of the
substrate 512. If the metal mask 580 is disposed excessively close
to the circuit substrate 510 to prevent the solder layers from
being displaced or undesirably spreading, the squeegee 582 may come
in contact with the terminals 514 to break the terminals 514. On
the other hand, if the metal mask 580 is disposed excessively
distant from the mounting surface of the circuit substrate 510 to
prevent the terminals 514 from being broken, the printed solder
layers are displaced or undesirably spread because of the large
distance between the metal mask 580 and the terminals 514 and land
electrodes 518.
[0090] On the other hand, in the circuit substrate 410 including
the recess 415, the terminals 414 are formed within the recess 415.
Consequently, the possibility that the squeegee 582 comes into
contact with the land electrodes 418 is low even though the metal
mask 480 is disposed close to the land electrodes 418. In addition,
the distance between the land electrodes 418 and the metal mask 480
in the circuit substrate 410 can be more reduced than that in the
circuit substrate 510, as shown in FIGS. 16 and 18. Accordingly,
the displacement and undesired spread of the printed solder layer
472 can be prevented particularly on the land electrodes 418.
[0091] The circuit substrate 410 and the circuit module 460
according to the fourth preferred embodiment may be produced by the
following manufacturing method. FIGS. 19 to 22 are sectional views
of the circuit module 460 in steps of the manufacturing
process.
[0092] First, the steps shown in FIGS. 3A to 6 are performed in the
same manner as in the manufacturing process of the circuit
substrate 10 of the first preferred embodiment, and the same
description will be omitted. Subsequently, land electrodes 418 are
formed on the mounting surface outside the recess 415, as shown in
FIG. 15. The land electrodes 418 are formed by, for example,
applying an electroconductive paste mainly containing Cu, followed
by firing. The firing of the land electrodes 418 may be performed
simultaneously with the firing of the multilayer composite.
[0093] Turning now to FIG. 19, a metal mask 480 having openings
corresponding to the land electrodes 418 is aligned on the circuit
substrate 410. This metal mask 480 does not have openings
corresponding to the terminals 414. Then, a squeegee 482 is moved
on the metal mask 480 in the arrow direction to print a solder
paste 484 through the metal mask 480. Thus, solder layers 472 are
printed on the land electrodes 418, as shown in FIG. 20.
[0094] Subsequently, an electronic component 470 is mounted on the
land electrodes 418 with the solder layers 472 therebetween, as
shown in FIG. 21. Then, an IC 450 having solder bumps 454 coated
with a flux 456 is disposed on the terminals 414, as shown in FIG.
22. The reflowing temperature for mounting the electronic component
470 and the IC 450 is, for example, about 260.degree. C. The
circuit module 460 is thus completed through the above-described
process.
[0095] The circuit substrate 410 of the present preferred
embodiment can prevent the top ends of the terminals 414 from being
crushed, and prevent the solder layers 472 from being displaced and
undesirably spreading, as described below with reference to related
drawing. FIG. 23 is a sectional view of the structure of a circuit
substrate 610 according to a comparative example.
[0096] The circuit substrate 610 shown in FIG. 23 is different from
the circuit substrate 410 shown in FIG. 14 in that the recess 415
is not formed. In order to print solder layers on the terminals 614
and the land electrodes 618 of such a circuit substrate 610, the
metal mask 680 is disposed on the circuit substrate 610, and a
solder paste 684 is printed using a squeegee 682.
[0097] In order to prevent the solder layers from being displaced
when the solder paste 684 is printed, the metal mask 680 should be
disposed close to the mounting surface of the substrate 610.
However, the circuit substrate 610 shown in FIG. 23 has terminals
612 protruding upward from the mounting surface of the substrate
614. If the metal mask 680 is disposed excessively close to the
circuit substrate 610 to prevent the solder layers from being
displaced or undesirably spreading, the metal mask 680 may be
pressed on the terminals 614 to crush the top ends of the terminals
614. On the other hand, if the metal mask 680 is disposed
excessively distant from the mounting surface of the circuit
substrate 610 to prevent the terminals 614 from being crushed, the
solder layers are displaced or undesirably spread because of the
large distance between the metal mask 680 and the terminals 614 and
land electrodes 618.
[0098] On the other hand, in the circuit substrate 410 having the
recess 415, the terminals 414 are formed within the recess 415.
Consequently, the possibility that the metal mask 480 comes into
contact with the land electrodes 418 is low even though the metal
mask 480 is disposed close to the land electrodes 418. In addition,
the distance between the land electrodes 418 and the metal mask 480
in the circuit substrate 410 can be more reduced than that in the
circuit substrate 610, as shown in FIGS. 19 and 23. Accordingly,
the displacement and undesired spread of the printed solder layer
472 can be prevented particularly on the land electrodes 418.
[0099] The solder bumps 454 may be coated with a solder paste
instead of the flux 456.
[0100] Although the through-holes 24 and 32 in the circuit
substrate 10 are preferably formed by stamping, for example, other
techniques may be applied to form the through-holes 24 and 32. For
example, the through-holes 24 and 32 may be formed by laser beam
machining. If the through-holes 32 are formed by laser beam
machining, it is preferable that laser beam be irradiated from the
mask layer 30 side. Since the energy of laser beam is consumed to
reduce the diameter of the beam while forming the through-holes 32
in the ceramic green sheet 20, the diameter of the through-hole 32
is increased upward.
[0101] As described above, various preferred embodiments of the
present invention are useful for circuit substrates, circuit
modules and methods for manufacturing circuit substrates, and are
particularly superior in that they reduce the thicknesses of
circuit substrates and circuit modules including circuit
substrates.
[0102] 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.
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