Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Flip chip
Reexamination Certificate
2000-07-12
2002-08-20
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Flip chip
C257S782000
Reexamination Certificate
active
06437450
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a method of mounting a semiconductor chip and an apparatus for mounting a semiconductor chip.
The method of mounting a semiconductor chip can be applied to mounting of a head IC chip
11
of a hard disk device
10
to a suspension
12
, as shown in
FIGS. 1A and 1B
, or to mounting of an IC chip
31
of a printed circuit board unit
30
to a substrate
32
, as shown in
FIGS. 3A
to
3
C.
As shown in
FIGS. 1A and 1B
, the hard disk device
10
has a hard disk
16
that rotates at high speed in a hermetically sealed housing
15
, and a head slider assembly
19
attached to the top end of an arm
18
. The head slider assembly
19
comprises a head slider
20
and the head IC chip
11
mounted on the suspension
12
, as shown in FIG.
2
. The head slider
20
has a magnetic head
21
formed by a thin film forming technique. The head IC chip
11
fimctions to control the magnetic head
21
by amplifying a weak signal read by the magnetic head
21
, for instance. As shown in the enlarged view in
FIG. 2
, the head IC chip
11
has Au bumps
22
on its lower surface joined to Au pads
24
at the edge of a wiring pattern
23
.
The printed circuit board unit
30
comprises a multi chip module
36
provided with a heat sink, a memory socket
38
, and an I/O connector
39
, all mounted on a mother board
35
, as shown in FIG.
3
A. The multi chip module
36
has a plurality of IC chips
31
mounted on the substrate
32
, as shown in FIG.
3
B. The head IC chip
31
has Au bumps
42
on its lower surface bonded to Au pads
43
formed on the substrate
32
. The head IC chip
31
is also bonded onto the substrate
32
by underfill
44
.
2. Description of the Related Art
FIGS. 4A
to
4
C illustrate a method of producing a conventional head slider assembly. The head IC chip
11
has Au bumps
51
on its lower surface. The suspension
12
has Au pads
61
on its upper surface. This head slider assembly is manufactured in the following manner.
First, the suspension
12
is fixed onto a stage
70
. A predetermined amount of insulating adhesive
71
functioning as “underfill” is then applied to the upper surface of the suspension
12
, using a precision dispenser (not shown). The head IC chip
11
is picked up by vacuum suction of a tool
75
having a suction hole
76
, and is moved onto the suspension
12
. The tool
75
then presses the head IC chip
11
by a force F, and ultrasonic vibration of several &mgr;m amplitude is applied to the head IC chip
11
for several seconds, as indicated by an arrow B. By doing so, the Au bumps
51
are bonded to the Au pads
61
. The vacuum suction of the tool
75
is then stopped, so that the tool
75
is separated from the head IC chip
11
. The suspension
12
is then moved to a heating furnace
80
, so that the adhesive
71
is hardened by heat. Here, underfill
72
is formed, and the head IC chip
11
is bonded to the suspension
12
by the underfill
72
. Thus, the head slider assembly
19
is completed.
The above method of producing a conventional head slider assembly exhibits at least the following disadvantages:
1. The shape of the fillet of the underfill is unstable.
The adhesive
71
functioning as the underfill is circular on the suspension
60
, as indicated by a two-dot chain line in FIG.
5
A. As the tool
75
presses the head IC chip
11
, the adhesive
71
is pressed by the lower surface of the head IC chip
11
, and is radially spread out. The spread adhesive
71
reaches the periphery of the lower surface of the head IC chip
11
, and forms a fillet
90
. The shape of the fillet
90
is determined by the spread state of the adhesive
71
to functions as the underfill. The spread state of the adhesive
71
varies with the applied amount and the applied position of the adhesive
71
. Depending on the situation, the adhesive
71
may significantly overflow on the upper surface of the suspension
12
, as indicated by reference numeral
91
in
FIGS. 5A and 5B
.
As the hard disk device becomes smaller, the width W
1
of the suspension
12
becomes smaller. On the other hand, as more functions are added, the head IC chip
11
becomes larger in the direction of L
1
shown in FIG.
5
A. Accordingly, the extra portion
92
outside the mounted head IC chip
11
on the suspension
12
becomes smaller in a width W
2
. Furthermore, the large amount of overflow of the adhesive has an adverse effect on the on the floating characteristic of the head slider
20
with respect to a hard disk.
As for the multi-chip module
36
shown in
FIGS. 3A
to
3
B, the large amount of overflow of the adhesive on the upper surface of the substrate
32
often hinders the mounting of other components.
2. The overflowing adhesive sticks to the tool
75
.
Depending on the applied amount and the applied position of the adhesive
71
, the adhesive
71
overflows onto the upper surface of the head IC chip
11
and sticks to the top end of the tool
75
, as indicated by reference numeral
93
in
FIGS. 6A and 6B
.
When the adhesive
71
sticks to the top end of the tool
75
, the suction operation of the tool
75
becomes unstable. Therefore, the top end of the tool
75
requires cleaning often. However, it is troublesome to clean the top end of the tool
75
every time the mounting of one head IC chip
11
is completed.
The applied adhesive
71
is applied in a circular pattern and spreads radially, when seen from above. Accordingly, the adhesive
71
overflows from the sides of the head IC chip
11
, and reaches the upper surface of the head IC chip
11
.
3. The transmission rate of ultrasonic waves from the tool
75
to the head IC chip
11
is low.
As shown in
FIG. 4B
, the tool
75
is brought into contact directly with the head IC chip
11
. The tool
75
is made of stainless steel, and the head IC chip
11
is made of silicon. The friction coefficient &mgr;
1
between the tool
75
and the IC chip
11
is in the range of 0.5 to 0.7, which is relatively low. Accordingly, the transmission rate of ultrasonic waves from the tool
75
to the head IC chip
11
is low, and the bonding of the Au bumps
51
to the Au pads
61
requires a long period of time.
4. The head IC chip often deviates at the time of mounting, and the deviation results in defective mounting.
As shown in
FIG. 4B
, the tool
75
and the head IC chip
11
are in contact with each other.
Due to the slight orientation of the end surface
75
a
of the tool
75
, the head IC chip
11
slightly deviates from the initial position shown in
FIG. 7A
in one direction of the ultrasonic oscillation (in the X
1
direction, for instance) every time the tool
75
ultrasonically oscillates. Depending on the situation, the Au bumps
51
might slip off the Au pads
61
, as shown in
FIG. 7B
, resulting in defective bonding.
In the multi-chip module
36
shown in
FIGS. 3A
to
3
C, the pads formed on the substrate
32
each have a rectangular shape, as indicated by reference numeral
43
A in FIG.
8
. However, the longitudinal direction of the horizontally aligned pads
43
A in
FIG. 8
is equivalent to the width direction of the vertically aligned pads
43
A in FIG.
8
. Accordingly, the pads on the substrate
32
are not always effective in preventing the head IC chip
11
from deviating when the tool
75
ultrasonically oscillates.
In view of this, the present invention is directed to providing a semiconductor chip mounting method and device, in which the above problems are eliminated.
SUMMARY OF THE INVENTION
To solve the problems mentioned above, the present invention provides a method of mounting a semiconductor chip, comprising the steps of:
bonding bumps formed on the semiconductor chip to pads formed on a substrate by pressing the semiconductor chip, with insulating adhesive being interposed between the semiconductor chip and the substrate; and
hardening the insulating adhesive spread out between the semiconductor chip and the substrate,
wherein the bonding step includes the step of hardening a peripheral portion of
Baba Shunji
Kainuma Norio
Kira Hidehiko
Kobae Kenji
Kobayashi Hiroshi
Armstrong Westerman & Hattori, LLP
Fujitsu Limited
Le B.
Nelms David
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