Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Flip chip
Reexamination Certificate
2003-02-11
2004-09-07
Potter, Roy (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Flip chip
C257S737000
Reexamination Certificate
active
06787922
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor chip-mounting board wherein a semiconductor chip is connected to a semiconductor chip-mounting face by a flip chip-mounting method, and electrodes formed on a circuit board-mounting face opposed to the semiconductor chip-mounting face are electrically connected to electrodes on a circuit board, and a method for mounting the semiconductor chip to the semiconductor chip-mounting board.
Wire bonding using metallic wires has been widely employed heretofore to electrically connect electronic microcircuit elements such as semiconductor chips or the like with electrode terminal parts on a circuit board. However, with the recent higher integration tendency in semiconductor chips and the increase of terminals, the narrowing of connection pitches has resulted. At the same time, personal computers, portable remote terminals, etc. need efficient use of a mounting area on the semiconductor chip. Because of this, a flip chip-mounting method is adopted lately whereby bumps (projecting terminals) are formed on electrode terminals on the semiconductor chip and are directly connected with electrodes on the circuit board by a bonding material, and besides, a minute bonding and mounting technique to resin circuit boards with low cost performance is required.
A semiconductor chip-mounting board having a semiconductor chip mounted according to the conventional flip chip-mounting method and a method for mounting a semiconductor chip to the semiconductor chip-mounting board will be described with reference-to the drawings.
FIG. 6
is a plan view of a conventional semiconductor chip-mounting board
4
with a semiconductor chip
1
mounted thereon.
FIG. 7
is a sectional view taken along the line III—III of
FIG. 6
, and
FIG. 8
is a sectional view taken along the line IV—IV of
FIG. 6. A
reference numeral
20
in
FIG. 6
is a through hole penetrating a semiconductor chip-mounting face
4
a
and a circuit board-mounting face
4
b
of the semiconductor chip-mounting board
4
to electrically connect the semiconductor chip with a circuit board.
On a circuit formation face
1
a
of the semiconductor chip
1
are formed electrode terminals
13
via an interval of 120 &mgr;m in a peripheral part of the semiconductor chip
1
. The electrode terminals
13
which are necessary for general functions of the semiconductor chip are provided with bumps
6
each having a two-step projection of a large diameter part
6
a
and a small diameter part
6
b
. The bump
6
is formed of gold of 75 &mgr;m larger diameter and 45 &mgr;m height.
On the other hand, the conventional semiconductor chip-mounting board
4
is formed of glass epoxy resin, having a thermal expansion coefficient of 13 ppm and a glass transition point of 115-120° C. Strip-shaped bonding lands
2
are formed every 120 &mgr;m at positions of the semiconductor chip-mounting face
4
a
of the board
4
corresponding to electrode terminals
13
formed on the semiconductor chip
1
. A width w
2
of the bonding land is 50 &mgr;m. As indicated in
FIG. 8
, the bonding land
2
extends a length L
2
from a contact point
6
c
thereof to the bump
6
towards a central part
107
of the semiconductor chip
1
. The above L
2
is conventionally 35 &mgr;m. Moreover, as shown in
FIG. 9
, a solder resist
9
is formed a distance r
2
separated from an end face
1
b
of the semiconductor chip
1
at the semiconductor chip-mounting face
4
a
of the board
4
. The r
2
is conventionally 200 &mgr;m.
A method for mounting the semiconductor chip
1
to the conventional semiconductor chip-mounting board
4
will be described.
In the first place, the above-described bumps
6
are formed at the electrode terminals
13
of the semiconductor chip
1
functionally required for the normal operation, that is, terminals necessary for inputting/outputting signals to the circuit board via the mounting board
4
. A bonding material
7
of conductive resin paste mainly composed of silver is previously transferred by a thickness of approximately 10 &mgr;m to the bumps
6
.
Then, as shown in
FIG. 6
, the semiconductor chip
1
having the bumps
6
to which the bonding material
7
is transferred is electrically bonded by the bonding material
7
via the bumps
6
to the bonding lands
2
formed at the semiconductor chip-mounting face
4
a
of the board
4
. After the bonding material
7
is dried at 120° C. for two hours to thereby be set, a sealing resin
8
is injected between the semiconductor chip
1
and the semiconductor chip-mounting face
4
a
, and set by heating at 120° C. for two hours.
FIG. 10
shows the semiconductor chip-mounting board
4
having a plurality of semiconductor chips
1
mounted thereon. The sealing resin
8
is applied from one side of the semiconductor chip
1
in a direction indicated by arrows
12
by a dispenser. Where to inject the sealing resin
8
is suitably selected depending on a shape of the semiconductor chip
1
or a distance to the peripheral lands.
The conventional semiconductor chip-mounting board
4
in the structure and the mounting method have the following disadvantages.
Since a bonding strength between the bump
6
of the semiconductor chip
1
and the bonding land
2
on the mounting board
4
is as small as about 3 g per bump, the semiconductor chip
1
with a small count of electrode terminals
13
is poorly bonded to the mounting board
4
. Moreover, the bonding material
7
cannot form a sufficient fillet due to a small area of the bonding land
2
, and rather spreads, on the semiconductor chip-mounting
4
a
, wide with a width w
12
larger than the width w
2
of the bonding land
2
as shown in FIG.
7
and with a length Lf
2
larger than the length L
2
of the bonding land
2
as shown in FIG.
8
. This causes short circuits and deteriorations in insulating resistance. The aforementioned width wf
2
is 100 &mgr;m and the length Lf
2
is 50 &mgr;m.
Further, since the thermal expansion coefficient of the conventional mounting board
4
is larger than that of silicon which is the material for the semiconductor chip
1
, when the sealing resin
8
is heated and set after the semiconductor chip
1
is mounted onto the mounting board
4
, a stress is generated due to a difference of thermal expansion coefficients of the mounting board
4
and the semiconductor chip
1
. This stress acts to a bonded part between the bump
6
and the bonding land
2
where the bonding strength is small as discussed above, and consequently, a resistance value at the bonded part might be increased or the bonded part might be disconnected.
The semiconductor chip-mounting board
4
uses the material mainly composed of glass epoxy resin as mentioned before. Therefore, when the temperature of the semiconductor chip-mounting board
4
rises to not lower than the glass transition point (Tg), a thermal expansion coefficient &agr;
1
before the glass transition point of the board
4
is increased by 5-7 times up to a thermal expansion coefficient &agr;
2
at the glass transition point, as is clearly shown in
FIG. 11
, whereby a deformation amount of the board
4
becomes large.
The semiconductor chip-mounting board
4
with the semiconductor chip
1
mounted is passed through the drying/setting process at 120° C. for two hours so as to dry and set the above bonding material
7
formed at the bumps
6
. At this time, when the temperature decreases from 120° C. after the bonding material
7
is set, the semiconductor chip-mounting board
4
warps to be a semiconductor chip-mounting board
4
′ shown in FIG.
12
.
Moreover, the sealing resin
8
injected between the mounting board
4
and the semiconductor chip
1
after the above drying/setting process is subjected to the setting process at 120° C. for two hours. When the temperature decreases from 120° C. after the sealing resin
8
is set, the semiconductor chip-mounting board
4
warps to be a semiconductor chip-mounting board
4
″ shown in FIG.
13
.
When the mounting board
4
is mounted to the circuit board by the SMT
Otani Hiroyuki
Yagi Yoshihiko
Yamamoto Ken-ichi
LandOfFree
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