U.S. patent application number 09/922384 was filed with the patent office on 2002-06-20 for mounting structure of a semiconductor device, and a process for mounting a semiconductor device on a mounting substrate.
Invention is credited to Kato, Masuo, Sasaki, Dai, Terasaki, Tohru, Tsurumi, Masami.
Application Number | 20020074163 09/922384 |
Document ID | / |
Family ID | 15073556 |
Filed Date | 2002-06-20 |
United States Patent
Application |
20020074163 |
Kind Code |
A1 |
Sasaki, Dai ; et
al. |
June 20, 2002 |
Mounting structure of a semiconductor device, and a process for
mounting a semiconductor device on a mounting substrate
Abstract
An acute tip is formed on each top of bump electrodes of a
semiconductor device to be mounted on a printed circuit board by
facedown bonding. Each acute tip is then applied a leveling process
as to form a small flat surface on its top. After that, each of the
bump electrode is depressed gradually with heat for transforming
the bump electrode against a conductor pattern of the printed
circuit board for mounting . Resultantly, the semiconductor device
is mounted on the printed circuit board firmly and without
including foreign body between the bump electrode of the
semiconductor device and the conductor pattern of the printed
circuit board.
Inventors: |
Sasaki, Dai; (Tokyo, JP)
; Terasaki, Tohru; (Aiichi, JP) ; Kato, Masuo;
(Aiichi, JP) ; Tsurumi, Masami; (Aiichi,
JP) |
Correspondence
Address: |
SONNENSCHEIN NATH & ROSENTHAL
P.O. BOX 061080
WACKER DRIVE STATION
CHICAGO
IL
60606-1080
US
|
Family ID: |
15073556 |
Appl. No.: |
09/922384 |
Filed: |
August 3, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09922384 |
Aug 3, 2001 |
|
|
|
09561941 |
May 1, 2000 |
|
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Current U.S.
Class: |
174/263 ;
174/260; 257/E21.503; 257/E23.021; 29/832; 29/840 |
Current CPC
Class: |
H01L 2924/01033
20130101; H01L 2924/01079 20130101; Y10T 29/49144 20150115; H01L
2224/13 20130101; H01L 24/83 20130101; H01L 2924/00013 20130101;
Y10T 29/53174 20150115; H01L 2224/05568 20130101; H01L 24/05
20130101; H01L 2924/01006 20130101; H01L 2224/45144 20130101; H01L
2224/32225 20130101; H01L 2924/01005 20130101; H01L 2224/11
20130101; H01L 21/563 20130101; H01L 2224/1134 20130101; Y10T
29/4913 20150115; H01L 2224/16225 20130101; H01L 2224/73204
20130101; H01L 2224/73203 20130101; H01L 24/13 20130101; H01L
2924/01004 20130101; H01L 2224/13144 20130101; Y10T 29/49146
20150115; H01L 2224/05573 20130101; H01L 24/11 20130101; H01L
2924/01082 20130101; H01L 2224/83192 20130101; H01L 2924/01013
20130101; H01L 2924/3511 20130101; H01L 24/29 20130101; H01L
2224/13144 20130101; H01L 2924/00014 20130101; H01L 2924/00013
20130101; H01L 2224/13099 20130101; H01L 2224/73204 20130101; H01L
2224/16225 20130101; H01L 2224/32225 20130101; H01L 2924/00
20130101; H01L 2224/16225 20130101; H01L 2224/13144 20130101; H01L
2924/00 20130101; H01L 2224/83192 20130101; H01L 2224/32225
20130101; H01L 2924/00 20130101; H01L 2224/13 20130101; H01L
2924/00 20130101; H01L 2224/11 20130101; H01L 2924/00 20130101;
H01L 2224/83192 20130101; H01L 2224/73204 20130101; H01L 2224/16225
20130101; H01L 2224/32225 20130101; H01L 2924/00 20130101; H01L
2224/45144 20130101; H01L 2924/00 20130101; H01L 2224/05624
20130101; H01L 2924/00014 20130101 |
Class at
Publication: |
174/263 ; 29/832;
29/840; 174/260 |
International
Class: |
H01R 012/04; H05K
001/11 |
Foreign Application Data
Date |
Code |
Application Number |
May 13, 1999 |
JP |
JP11-132104 |
Claims
What is claimed is:
1. A mounting structure of a semiconductor device mounted on a
mounting substrate, comprising; a semiconductor device having a
bump electrode which has an acute tip on top, a mounting substrate
on which said semiconductor device is mounted, and a conductor
pattern formed on said mounting substrate, wherein said acute tip
is gradually depressed on said conductor pattern of said mounting
substrate.
2. A mounting structure of a semiconductor device mounted on a
mounting substrate as claimed in claim 1, wherein said acute tip of
the bump electrode is treated with a leveling process as to form a
small flat surface before depressed on said conductor pattern of
the mounting substrate.
3. A mounting structure of a semiconductor device mounted on a
mounting substrate as claimed in claim 2, wherein heat is added to
said bump electrode of the semiconductor device so that said bump
electrode is transformed during depression of the bump electrode to
the conductor pattern of the mounting substrate.
4. A mounting structure of a semiconductor device mounted on a
mounting substrate as claimed in claim 3, wherein said mounting
substrate is a printed circuit board and said bump electrode is
depressed on the conductor pattern formed on the printed circuit
board.
5. A mounting structure of a semiconductor device mounted on a
mounting substrate as claimed in claim 4, wherein said
semiconductor device has an electrode pad and said bump electrode
is formed on this electrode pad.
6. A mounting structure of a semiconductor device mounted on a
mounting substrate as claimed in claim 1, wherein said acute tip of
the bump electrode has a shape of cone.
7. A process of mounting a semiconductor device on a mounting
substrate, said process comprising the steps of, bonding a
plurality of bump electrodes each having an acute tip on a pad
electrode formed on a semiconductor device, leveling all of said
acute tips of the bump electrodes as to have the same height,
positioning said tip of the bump electrode on a conductor pattern
of a mounting substrate, and mounting said acute tip of the bonding
electrode on said conductor pattern of the mounting electrode by
depressing gradually.
8. A process of mounting a semiconductor device on a mounting
substrate as claimed in claim 7, wherein heat is added to said bump
electrode in order to be transformed during said mounting step.
9. A process of mounting a semiconductor device on a mounting
substrate as claimed in claim 8, wherein said acute tip of the bump
electrode is formed to have a cone-shape at said bonding step.
10. A process of forming bump electrodes on a semiconductor device
to be mounted on a mounting substrate, said process comprising the
steps of, providing a conglobation on an end of a gold wire,
placing said conglobation of gold wire on electrode pads formed on
a semiconductor device, pulling off said gold wire from said
conglobation as to form bump electrodes having an acute tip on each
top of said bump electrodes, and leveling all of said acute tips of
said bump electrodes as to have a small flat surfaces on each top
of the bump electrodes.
11. A process of forming bump electrodes on a semiconductor device
to be mounted on a mounting substrate as claimed in claim 10,
wherein each of said electrode pads is made of aluminum and said
conglobation of the gold wire is heated by ultrasonic heating as to
make as alloy of the gold and the aluminum during said placing
step.
12. A process of mounting a semiconductor device on a mounting
substrate, said process comprising the steps of, providing a
conglobation on an end of a gold wire, placing said conglobation of
gold wire on an electrode pad formed on a semiconductor device,
pulling off said gold wire from said conglobation as to form a bump
electrode having an acute tip on its top, leveling all of said
acute tips of the bump electrodes as to have the same height,
positioning said tip of the bump electrode on a conductor pattern
of a mounting substrate, and mounting said acute tip of the bonding
electrode on said conductor pattern of the mounting electrode by
depressing gradually while transforming said bump electrode formed
on the electrode pad of the semiconductor device.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a mounting structure of a
semiconductor device, and a process for mounting a semiconductor
device on a mounting substrate such as a printed circuit board
having conductor patterns on which the semiconductor device with a
plurality of bump electrodes is mounted.
[0003] 2. Description of the Related Art
[0004] Conventionally, a flip chip bonding process is widely
employed, where a semiconductor device is mounted on a printed
circuit board (as a mounting substrate) by a facedown bonding
method. In this mounting process, as shown in FIG. 9, a plurality
of bump electrodes 14 having end surfaces 14A as shown in the
figure is bonded on aluminum electrode pads 12 provided on a
semiconductor device 10.
[0005] Namely, after the bump electrode 14 is bonded on the
aluminum electrode pad 12, each tip of the bump electrode 14 of the
semiconductor device 10 is treated a leveling process by a leveler
made of such as brass, so that all end surfaces 14A have the same
height and have relatively large area as shown in FIG. 9. The
leveling process is done with a load weight approximately expressed
by N.times.50 gram-force, where the N is the number of bonding pads
formed on the semiconductor device 10.
[0006] Then as shown in FIG. 10, when the semiconductor device 10
is mounted on a printed circuit board 20, the bump electrode 14 of
the semiconductor device 10 is positioned to conductor patterns 22
formed on the printed circuit board 20. Then heat and pressure are
added to the bump electrode 14 from backside of the semiconductor
device 10, thereby the bump electrode 14 is bonded on the conductor
pattern 22 of the printed circuit board 20.
[0007] A filler 30 of thermosetting resin is filled between the
semiconductor device 10 and the printed circuit board 20 to seal
gaps there-between.
[0008] In this conventional method of mounting a semiconductor
device on a printed circuit board as above described, there is a
defect that foreign body h as a resin particle or something like
that is easily put between the end face 14A (top surface) and the
conductor pattern 22 of the printed cuit board 20 during the
mounting process. Resultantly, the reliability of semiconductor
mounting process is degraded. For example, the foreign undesirably
put there-between deteriorates contact condition of the surface 14a
with the conductor pattern 22, and this degrades reliability nd
productivity of a final product that is installed thus processed
printed ircuit board.
SUMMARY OF THE INVENTION
[0009] An object of the invention is to provide a mounting
structure of a semiconductor device, and a process for mounting a
semiconductor device on a mounting substrate such as a printed
circuit board having conductor patterns on which the semiconductor
device with a plurality of bump electrodes is mounted.
[0010] Another object of the present invention is to provide a new
mounting structure of a semiconductor device, and a process for
mounting a semiconductor device on a printed circuit board, wherein
it is avoided for foreign bodies such as resin particles to be put
between a bump electrode of the semiconductor device and a
conductor pattern of the printed circuit board.
[0011] Further another object of the present invention is to
provide a new mounting structure of a semiconductor device, and a
process for mounting a semiconductor device on a mounting
substrate, wherein there is formed a bump electrode having an acute
tip such as cone-shaped top on the semiconductor device to be
mounted on the printed circuit board by a facedown bonding
method.
[0012] In order to overcome above-described defects existed in the
conventional mounting structure, it is proposed a new mounting
structure, wherein there is provided an acute tip at each bump
electrode of a semiconductor device when mounting the semiconductor
device having a plurality of bump electrodes on a mounting
substrate having conductor patterns.
[0013] These acute tips of the bump electrodes are slightly made
flat by a leveler with a relatively light load weight, then
depressed slowly on the conductor patterns of the mounting
substrate with heat and pressure. Resultantly, each bump electrode
and conductor pattern are joined with face contact by gradually
transforming the shape of the bump electrode including the acute
tip thereof.
[0014] In the process of mounting a semiconductor device having a
plurality of bump electrodes on the conductor pattern of the
mounting substrate according to the present invention, the process
comprises the steps of a bonding step for providing a plurality of
bump electrodes having acute tip on electrode pads of the
semiconductor device, a leveling step for slightly making flat the
acute tip of the bump electrodes by a leveler with relatively light
load weight, a positioning step for positioning the tip of the bump
electrode on the conductor pattern of the mounting substrate, and a
mounting step for depressing the tip of the bump electrode against
the conductor pattern slowly with heat and load weight. During this
mounting step, the bump electrode and the conductor pattern of the
mounting substrate are bonded with face contact while transforming
shape of the bump electrode gradually.
[0015] In the mounting structure for the semiconductor device
according to the present invention, each bump electrode of the
semiconductor device has an acute tip formed on top of the bump
electrode before mounting. Each acute tip of the bump electrode is
preferably flattened slightly with relatively light load weight.
And the tip of the bump electrode is positioned on the conductor
pattern of the printed circuit board and pressed slowly against the
conductor pattern with pressure and heat. Each tip of the bump
electrode is gradually transformed and joined to the conductor
electrode with face contact.
[0016] According to the present invention, each tip of the bump
electrode has only small top surface before mounting, so that
during mounting process it is avoidable to put foreign body between
the bump electrode and the conductor pattern of the printed circuit
board.
[0017] Namely the tip of bump electrode is gradually transformed by
being pressed against the conductor pattern of the mounting
substrate, and this transformation of the bump electrode pushes out
foreign body existed between the bump electrode and conductor
pattern from inside to outside, and finally the bump electrode is
transformed as to perform a face contact with the conductor pattern
while excluding foreign body.
[0018] Therefore, foreign bodies are seldom put between the
conductor pattern and the bump electrode.
[0019] According to the present invention, it is easily performed
to obtain a good contact condition between the bump electrode and
the conductor pattern, and thereby a reliability and productivity
of a final product are improved.
[0020] In the method for mounting the semiconductor device on the
mounting substrate according to the present invention, at first a
plurality of bump electrodes having acute tip is provided on each
of an electrode pad formed on a semiconductor device at a bonding
process. In the following leveling step, each tip of the bump
electrode is flattened slightly by a leveler with a light load
weight. Then each tip of the bump electrode of the semiconductor
device is positioned on a conductor pattern of a mounting substrate
in a positioning step. Then the semiconductor device is depressed
against the mounting substrate with load weight and heat in a next
mounting step. In this mounting step, each top of the bump
electrode is slowly depressed on the conductor pattern of the
mounting substrate, and is gradually transformed so as to perform
face contact condition between the transformed bump electrode and
the conductor pattern.
[0021] In order to make an acute tip at each top of the bump
electrode, a conglobation is formed at an end of a gold wire having
a diameter of about 25 .mu.m by an electric discharging at first.
Then thus formed conglobation of the gold wire is depressed on the
aluminum electrode pad 112 with an ultrasonic heating for making
alloy of gold and aluminum, and after that the gold wire is pulled
off as to form the acute tip on the bump electrode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a schematic cross sectional view of a
semiconductor device used in a mounting structure and a mounting
process of the present invention.
[0023] FIG. 2 is a schematic cross sectional view showing a
leveling process for a tip of a bump electrode of the semiconductor
device shown in FIG. 1.
[0024] FIG. 3 is a schematic cross sectional view of the bump
electrode of the semiconductor device shown in FIG. 1.
[0025] FIG. 4 is a schematic cross sectional view of one example of
a printed circuit board to be used in a mounting structure and a
mounting process of a semiconductor device according to the present
invention.
[0026] FIG. 5 is a schematic cross sectional view showing a
positioning step for positioning the semiconductor device in FIG. 1
and the printed circuit board in FIG. 4.
[0027] FIG. 6 is a schematic cross sectional view showing a
mounting step for mounting the semiconductor device in FIG. 1 and
the printed circuit board in FIG. 4.
[0028] FIG. 7A to FIG. 7C are a series of schematic cross sectional
views showing a transforming of a bump electrode in the mounting
step.
[0029] FIG. 8 is a schematic cross sectional view showing a
condition where the semiconductor device shown in FIG. 1 is mounted
on an up-curved printed circuit board.
[0030] FIG. 9 is a schematic cross sectional view showing one
example of a conventional semiconductor device having a plurality
of bump electrodes.
[0031] FIG. 10 is a schematic cross sectional view showing a
printed circuit board on which the semiconductor device as shown in
FIG. 9 is mounted.
PREFERRED EMBODIMENTS OF THE INVENTION
[0032] Preferred embodiments of a mounting structure and a process
for mounting a semiconductor device will be described in detail
below with reference to the accompanied drawings. In one example of
the present invention, a flip chip mounting process wherein a
semiconductor device is mounted a printed circuit board in a face
down condition is explained.
[0033] FIG. 1 through to FIG. 6 are schematic cross sectional views
for explaining one example of a mounting structure and a mounting
process of a semiconductor device on a mounting substrate, and a
mounting structure of a semiconductor device of the present
invention is explained at first.
[0034] A semiconductor device 110 of this embodiment has a
plurality of aluminum electrode pads 112 formed on a surface 110A
of the semiconductor device 110. A bump electrode 114 is bonded on
each of the aluminum electrode pad 112. This bump electrode 114 is
made of conductive material having characteristics such as plastic
and heat deposition. One example of this material is gold (Au).
Each bump electrode 114 is provided a cone shaped acute tip
114A.
[0035] This acute tip 114A is formed as follows. Namely, a
conglobation is formed at an end of a gold wire having a diameter
of about 25 .mu.m by an electric discharging at first. Then thus
formed conglobation of the gold wire is depressed on the aluminum
electrode pad 112 with an ultrasonic heating for making alloy of
gold and aluminum, and after that the gold wire is pulled off as to
form the acute tip 114A on the bump electrode 114.
[0036] FIG. 2 shows a leveling process applied to the tip 114A of
the bump electrode 114 of the semiconductor device 110. In case of
this example, thus formed acute tip 114A of the bump electrode 114
is treated a leveling process slightly with a light load weight by
a flat surface 132A of a brass leveler 132. Preferably a load
weight is N.times.(4.about.5) gram-force, where N is the number of
the tips 114A of the bump electrodes 114 formed on the
semiconductor device 110.
[0037] After this process, there is formed a small flat surface
114B at each tip 114A of the bump electrode 114 as shown in FIG. 3.
The size of the small flat surface 114B is 5 to 10 .mu.m as a
diameter. Namely, as shown in FIG. 3, each bump electrode 114 has a
size of about 60 .mu.m at bottom, 5 to 10 .mu.m at top and about 40
.mu.m in height after the leveling process.
[0038] According to the present invention, each tip 114A of the
bump electrode 114 has only small flat surface 114B before mounting
as described above, so that during mounting process it is avoidable
to put foreign body between the bump electrode 114 and a conductor
pattern of a printed circuit board.
[0039] FIG. 4 shows one example of a printed circuit board 120 on
which the semiconductor device 110 is mounted. And as shown in this
figure, on a surface of the printed circuit board 120, there is
formed a conductor pattern 122 on which the semiconductor device
110 is mounted. Further there is provided a filler (sealing
material) 130 of a thermosetting resin on the printed circuit board
120 in advance. This filler 130 is positioned between the conductor
patterns 122 as shown in FIG. 4.
[0040] FIGS. 5 to 6 show processes for mounting the semiconductor
device 110 on the printed circuit board 120 in facedown condition.
As shown in FIG. 5, at first, each bump electrode 114 of the
semiconductor device 110 and the conductor pattern 122 of the
printed circuit board 120 are positioned against each other. Then
the semiconductor device 110 is moved slowly toward the printed
circuit board 120, and thereby the top surface 114B of the bump
electrode 114 is depressed against the conductor pattern 122 of the
printed circuit board 120. In this condition, a load weight is
added to the semiconductor device 110 to move it toward the printed
circuit board 120, and simultaneously the bump electrode 114 is
heated up to a predetermined temperature to soften it. Resultantly
as shown in FIG. 6, each tip 114A of the bump electrode 114 is
gradually depressed and transformed, after that the bump electrode
114 and the conductor pattern 122 are joined each other. In this
process, the tip 114A of the bump electrode 114 is moved slowly
toward the conductor pattern 122 at a speed of 0.1 mm/sec., for
example.
[0041] FIGS. 7A to 7C show a series of transforming process of the
bump electrode 114 in the mounting process. FIG. 7A shows a step
wherein the tip 114A of the bump electrode 114 is contacted with
the conductor pattern 122, FIG. 7B shows a step wherein the tip
114A of the bump electrode 114 is started to transform by a load
weight and heat, and FIG. 7C shows a step where the bump electrode
114 is depressed enough against the conductor pattern 122 of the
printed circuit board 120. As shown in FIGS. 7B and 7C, the
transformation of the tip 114A of the bump electrode 114 operates
to exclude foreign bodies such as resin particles existed between
the bump electrode 114 and the conductor pattern 122 during this
process from inside to outside as depicted by arrows a.
[0042] As shown in FIG. 7C, by the depression of the bump electrode
114 to the conductor pattern 122, the height of the bump electrode
becomes about 20 .mu.m and the diameter becomes about 70 .mu.m,
respectively. In this process, the filler 130 placed on the printed
circuit board 120 is depressed and spread between the semiconductor
device 110 and the printed circuit board 120, and a space between
the semiconductor device 110 and the printed circuit board 120 is
filled with the filler 130 as shown in FIG. 6. This filler 130
seals the space between the semiconductor device 110 and the
printed circuit board 120 in insulating condition. According to the
present invention as described above, the tip 114A of the bump
electrode 114 and the conductor pattern 122 of the printed circuit
board 120 are gradually joined as to exclude foreign bodies such as
resin particles, and it is easy to have a good contacting condition
between the bump electrode 114 and the conductor pattern 122, and
the productivity of final product is improved with high
reliability.
[0043] Next, a process for mounting a semiconductor device
according to one embodiment of the present invention is explained
with reference to FIGS. 1 to 7. Firstly, FIG. 1 shows a step for
bonding the bump electrode 114 on the semiconductor device 110. As
described before, the semiconductor device 110 has a plurality of
aluminum electrode pads 112 on the top surface 110A, and the bump
electrode 114 is bonded on this aluminum electrode pad 112 of the
semiconductor device 120.
[0044] FIG. 2 shows a leveling step applied to each tip 114A of the
bump electrode 114 as depicted in FIG. 1. As shown in FIG. 2, a
brass leveler 132 is placed on the acute tip 114A of the bump
electrode 114 as to form a small flat surface 114B at every tip
114A of the bump electrode 114.
[0045] In case of this example, the acute tip 114A of the bump
electrode 114 is treated a leveling process slightly with a light
load weight by a flat surface 132A of a brass leveler 132.
Preferably a weight load is N.times.(4.about.5) gram-force, where N
is the number of the tip 114A of the bump electrode 114 formed on
the semiconductor device 110. Each flat surface 114B of the bump
electrode 114 has a circular area having a diameter of 5 to 10
.mu.m, resultantly.
[0046] Then the semiconductor device 110 provided thus formed the
bump electrode 114 with leveled acute tip 114A is mounted on the
conductor pattern 122 of the printed circuit board 120. Further
there is provided a filler (seal material) 130 of a thermosetting
resin on the printed circuit board 120 in advance.
[0047] FIG. 5 shows a step for positioning the semiconductor device
110 relative to the printed circuit board 120 in facedown
condition. In this positioning step, the bump electrode 114 of the
semiconductor device 110 and the conductor pattern 122 of the
printed circuit board 120 are positioned each other. Then the
semiconductor device 110 is slowly moved towards the printed
circuit board 120 so as to contact the small flat surface 110B of
the bump electrode 114 with the conductor pattern 122.
[0048] FIG. 6 shows a step for mounting the semiconductor device
110 on the printed circuit board 120 with a load weight. In this
mounting step, a load weight is added to the semiconductor device
110 to move it toward the printed circuit board 120, and
simultaneously the bump electrode 114 is heated up to a
predetermined temperature to soften it. Resultantly each tip 114A
of the bump electrode 114A is gradually depressed and transformed,
and finally the bump electrode 114 and the conductor pattern 122
are joined each other. In this process, the tip 114A of the bump
electrode 114 is moved slowly toward the conductor pattern 122 at a
speed of 0.1 mm/sec., for example.
[0049] As explained before in FIGS. 7A and 7C, the transformation
of the tip 114A of the bump electrode 114 operates to exclude
foreign bodies such as resin particles existed between the bump
electrode 114 and the conductor pattern 122 during this process
from inside to outside as depicted by arrows a.
[0050] In this step, besides depressed transformation of the bump
electrode 114, the filler 130 placed on the printed circuit board
120 is depressed and spread between the semiconductor device 110
and the printed circuit board 120, and a space between the
semiconductor device 110 and the printed circuit board 120 is
filled with the filler 130 as shown in FIG. 6.
[0051] Thus according to the mounting process of the present
invention, the acute tip 114A of the bump electrode 114 is joined
to the conductor pattern 122 of the printed circuit board 120 while
excluding foreign bodies during the mounting process, it is easily
obtain good contact relation between the bump electrode 114 and the
conductor pattern 122. Further in this embodiment, the bump
electrode 114 is transformed during the mounting process, so that
even if the printed circuit board 120 has a little bend as shown in
FIG. 8, it is easy to obtain good contact relation between the bump
electrode 114 of the semiconductor device 110 and the conductor
pattern 122 of the printed circuit board 120.
[0052] While we have described and shown the particular embodiments
of our invention, it will be understood that many modifications may
be made without departing from the spirit thereof, and we
contemplate by the appended claims to cover any modifications as
fall within the true spirit and scope of our invention.
* * * * *