Active solid-state devices (e.g. – transistors – solid-state diode – Lead frame – With structure for mounting semiconductor chip to lead frame
Reexamination Certificate
1998-04-17
2001-01-16
Tran, Minh Loan (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Lead frame
With structure for mounting semiconductor chip to lead frame
C257S675000, C257S692000, C257S720000, C257S666000, C361S710000, C361S707000, C361S709000
Reexamination Certificate
active
06175150
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device and more particularly, to a plastic-encapsulated semiconductor device having a good heat dissipation performance and a good moisture resistance, and a fabrication method thereof.
2. Description of the Prior Art
Conventionally, plastic-encapsulated semiconductor devices have been used in various electronic equipment. In the semiconductor devices of this sort, typically, an Integrated circuit (IC) or Large-Scale Integrated circuit (LSI) chip or pellet is encapsulated in a plastic package and electrically-conductive leads or terminals are protruded from the package. These leads are electrically connected to boding pads of the IC chips within the package. If the semiconductor device is mounted on a circuit board and the leads or terminals are electrically connected to wiring lines of the circuit board, various input signals may be applied to the IC chip or pellet and various output signals may be derived therefrom.
The semiconductor devices of this sort have been practically used in various application fields. With the semiconductor devices designed for outputting the electric wave in portable or pocket telephones, electric power consumption generates a lot of heat on operation and therefore, the heat thus generated needs to be efficiently dissipated or radiated.
FIGS. 1 and 2
show a conventional plastic-encapsulated semiconductor device
501
capable of efficient heat dissipation. This device is disclosed in the Japanese Non-Examined Patent Publication No. 61-144834 published in 1986.
As shown in
FIGS. 1 and 2
, this plastic-encapsulated semiconductor device
501
is equipped with an approximately square IC chip or pellet
503
having bonding pads
502
on its top face. The chip
503
is mounted on an island
504
. The island
504
is formed by a rectangular metallic plate and the chip
503
is fixed onto the center of an upper side of the island
504
. Leads or terminals
505
are arranged at regular intervals on the long sides of the island
504
. The leads
505
are electrically connected to the corresponding bonding pads
502
of the chip
503
through bonding wires
506
.
The IC chip or pellet
503
, the island
504
, the leads
505
, and the bonding wires
506
are encapsulated or molded in a rectangular parallelepiped-shaped plastic package
507
while the outer parts of the leads
505
and the short-side ends of the island
504
are protruded from the package
507
. The protruding outer parts of the leads
505
are located at the long sides of the package
507
. The protruding ends of the island
504
have penetrating circular holes
508
.
The conventional semiconductor device shown in
FIGS. 1 and 2
is mounted, for example, on an upper side of a wiring board (not shown) with the use of screws inserted into the penetrating holes
508
of the island
504
. The leads or terminals
505
are electrically connected to wiring lines formed on the upper side of the wiring board. Various electric signals are transferred between the chip
503
and the wiring lines through the terminals
505
. The heat generated in the chip
503
is dissipated at the protruding ends of the island
504
from the package
507
.
With the conventional semiconductor device
501
shown in
FIGS. 1 and 2
, the heat generated in the IC chip
503
is dissipated through the island
504
. However, the protruding parts of the island
4
from the package
507
are apart from the bottom of the package
507
. Therefore, conventionally, to improve the heat dissipation performance or capability, a proper thermally-conductive spacer is sandwiched between the protruding ends of the island
504
and the circuit board, or a proper heat-releasing plate is fixed onto the top of the package
507
. These additional members increase the number of parts and fabrication processes, thereby lowering the productivity and upsizing the semiconductor device
501
.
Also, since the IC chip or pellet
503
is located at the middle of the elongated island
504
, the protruding short-side ends of the island
504
are apart from the chip
503
at a comparatively long distance. Accordingly, the conventional semiconductor device
501
has no satisfactory heat-dissipation performance.
Further, although the semiconductor devices of this sort designed for the portable telephones have been required to be mounted on a wiring board as flat as possible in view of downsizing, the conventional semiconductor device
501
is not as flat as required.
FIGS. 3 and 4
show another conventional plastic-encapsulated semiconductor device
521
, which solves the above-described problems in the conventional plastic-encapsulated semiconductor device
501
. This device is disclosed in the Japanese Non-Examined Patent Publication No. 2-63142 published in 1990.
The explanation about the same configuration is omitted here by attaching the same reference numerals as those in
FIGS. 1 and 2
to the same or corresponding elements in
FIGS. 3 and 4
for the sake of simplification.
As shown in
FIGS. 3 and 4
, this plastic-encapsulated semiconductor device
521
is equipped with a heat-releasing plate
523
with a circular-ringed shape. The heat-releasing plate
523
is protruded from one side of a plastic package
522
from which the leads or terminals
505
are not protruded. The heat-releasing plate
523
is formed to be incorporated with an island
524
.
The heat-releasing plate
523
is located on a same plane as a middle part
525
of the island
524
on which the IC chip
503
is mounted. As clearly shown in
FIG. 4
, the middle part
525
of the island
524
is exposed from the bottom face of the package
522
. The inner parts of the leads or terminals
505
, which are arranged at each side of the island
524
, are also exposed from the bottom face of the package
522
.
Therefore, the conventional semiconductor device
521
is able to be mounted as flat as required for the portable telephones.
The heat-releasing plate
523
has a circular penetrating hole
526
. The conventional semiconductor device
521
is mounted on a wiring board (not shown) with the use of a screw inserted into the hole
526
.
With the conventional semiconductor device
521
shown in
FIGS. 3 and 4
, since the leads or terminals
505
are exposed from the bottom face of the package
522
, the leads
505
can be directly fixed onto the wiring lines of a wiring board by solder joints. The semiconductor device
521
is mounted on a wiring board by fixing the heat-releasing plate
523
protruding from the package
522
onto the wiring board with the use of a screw and fixing the island
524
onto a grounding wiring line of the wiring board.
If the middle part
525
of the island
524
is located on an electrically conductive pattern of the wiring board, the middle part
525
can be connected to the pattern by an adhesive with a good thermal conductivity. In this case, the heat generated in the IC chip
503
is efficiently transmitted to the pattern of the wiring board through the heat-releasing plate
523
and the middle part
525
of the island
524
. Thus, the heat-generating chip
503
is efficiently cooled.
However, the conventional semiconductor device
521
shown in
FIGS. 3 and 4
has the following problems.
Specifically, in the conventional semiconductor device
521
, not only the leads
505
but also the middle part
525
of the island
524
are exposed from the bottom face of the plastic package
527
in order to improve the heat dissipation capability. However, the heat dissipation capability is not practically improved unless the middle part
525
of the island
524
is connected to the wiring board by an adhesive with a good thermal conductivity. In this case, the thermally-conductive adhesive tends to flow toward the leads or terminals
525
before curing and therefore, contact or connection failure of the terminals
525
will occur.
To prevent the contact or connection failure of the terminals
525
, the terminals
525
may be connected to the wiring lines of the wiri
Ichikawa Seiji
Kitakoga Tooru
Miya Tatsuya
Nishibe Toshiaki
Nishimura Yoshikazu
NEC Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
Thai Luan
Tran Minh Loan
LandOfFree
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