Active solid-state devices (e.g. – transistors – solid-state diode – Lead frame – With structure for mounting semiconductor chip to lead frame
Reexamination Certificate
2000-12-14
2003-10-14
Clark, Sheila V. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Lead frame
With structure for mounting semiconductor chip to lead frame
C257S666000
Reexamination Certificate
active
06633077
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a resin-sealed semiconductor device for surface mounting and a method for manufacturing the same.
2. Description of the Related Art
The following is a description of a general method for manufacturing a resin-sealed semiconductor device, with reference to the accompanying drawings.
First, a metal sheet is processed into a desired shape of electrodes by etching or press working, thus producing a lead frame.
FIGS. 14A and 14B
show an example of the obtained lead frame, with
FIG. 14A
being a plan view and
FIG. 14B
showing a combinational cross-section taken stepwise along the alternate long and short dash line A—A in
FIG. 14A
seen in an arrow direction. In
FIGS. 14A and 14B
, numeral
900
denotes a frame, numeral
901
denotes a die pad on which a semiconductor chip is mounted, numeral
903
denotes bonding leads for a connection to the semiconductor chip, and numeral
910
denotes a pair of support leads for supporting the die pad
901
from both sides. As shown in the figure, the die pad
901
is displaced toward the side opposite to that on which the semiconductor chip is mounted with respect to a plane including the frame
900
and the bonding leads
903
, so as to be depressed stepwise.
Next, as shown in
FIGS. 15A and 15B
, a semiconductor chip
950
is mounted on and bonded to the die pad
901
with an adhesive or the like. Then, a bonding pad of the semiconductor chip
950
and the bonding leads
903
are connected by wires
905
(wire-bonded).
FIG. 15A
is a plan view, and
FIG. 15B
shows a combinational cross-section taken stepwise along the alternate long and short dash line A—A in
FIG. 15A
seen in an arrow direction.
Subsequently, as shown in
FIG. 16A
, the semiconductor chip
950
, the die pad
901
and the bonding leads
903
are sealed between an upper die
981
and a lower die
982
. As shown in
FIG. 16B
, a sealing resin
990
is injected in an injection direction
991
to form a resin-seal, then the dies
981
and
982
are opened to obtain a semiconductor device.
FIGS. 16A and 16B
show combinational cross-sections taken stepwise along a line corresponding to the alternate long and short dash line A—A in
FIGS. 14A and 15A
seen in an arrow direction.
Semiconductor devices are required to have still higher performance, smaller size, thinner structure and more pins. For achieving higher performance, current-driven bipolar semiconductor chips, for example, come to be used widely. Since the semiconductor chips of this type generate a large amount of heat, they need to be designed considering their heat radiation. For this purpose, as shown in
FIG. 16A
, the die pad
901
is depressed with respect to the frame
900
such that the lower surface of the die pad
901
contacts an internal wall surface of the lower die
982
. In this manner, after the resin-sealing, the lower surface of the die pad
901
is exposed to the lower surface of the semiconductor device. By packaging the semiconductor device so that this surface contacts closely to a circuit board, the heat generated by the semiconductor chip
950
can be conducted to the circuit board via the die pad
901
so as to be radiated.
For reducing the size and thickness of the semiconductor device and increasing the number of pins therein, it is desired that a metal sheet with which a lead frame is produced is made thinner and that the support lead
910
for supporting the die pad
901
is made narrower. However, this reduces the strength of the support lead
910
. Consequently, as shown in
FIG. 16B
, when the resin is injected, the die pad
901
floats up due to a resin flow and a press shape of the support lead
910
, so that the resin is injected also at the lower surface of the die pad
901
. As a result, the lower surface of the die pad
901
cannot be exposed to the lower surface of the semiconductor device, making it impossible to radiate heat sufficiently from the semiconductor chip
950
.
In addition, when the die pad
901
is displaced during the resin-sealing as described above, the semiconductor chip
950
mounted on the die pad
901
is somewhat distorted. Thus, if the die pad
901
is sealed while keeping the displacement, the semiconductor chip
950
maintains its distortion so that internal stress remains. This causes a change in the resistance of wiring in the semiconductor chip, leading to variations in characteristics. This also is a problem in those semiconductor devices in which the die pad
901
is not exposed to the lower surface of the semiconductor device because the heat-radiating characteristics are not as important.
SUMMARY OF THE INVENTION
Thus, it is an object of the present invention to prevent displacement of a die pad during a resin-sealing and residual distortion in a semiconductor chip, thereby providing a semiconductor device with a stable quality and the method for manufacturing the same.
In order to achieve the above-mentioned object, the present invention has the following structure.
A semiconductor device according to a first structure of the present invention includes a semiconductor chip, a die pad having a surface on which the semiconductor chip is mounted, and support leads formed in one piece with the die pad. The semiconductor chip, the die pad and the support leads are sealed with a resin. Protrusions are formed on the support leads on a same side as that of the die pad on which the semiconductor chip is mounted. With this structure, the protrusions provided in the support leads prevent the displacement of the die pad during the resin-sealing. Therefore, the die pad is arranged according to its initial design, making it possible to obtain the semiconductor device having the semiconductor chip in which distortion does not remain.
In the first semiconductor device described above, a second protrusion may be formed on a surface of the die pad opposite to that on which the semiconductor chip is mounted. With this structure, the protrusions (first protrusions) provided in the support leads and the second protrusion provided in the die pad can prevent the displacement of the die pad during the resin-sealing.
Also, in the first semiconductor device described above, it is preferable that tops of the first and second protrusions are formed close to a resin surface of the semiconductor device. It is especially preferable that the tops of the first and second protrusions are exposed to an outer surface of the semiconductor device. With this structure, these tops contact internal wall surfaces of dies for resin-sealing, thereby preventing the displacement of the die pad during the resin-sealing.
In addition, in the first semiconductor device described above, it is preferable that a surface of the die pad opposite to that on which the semiconductor chip is mounted is arranged close to a resin surface of the semiconductor device. It is especially preferable that that the surface of the die pad opposite to that on which the semiconductor chip is mounted is exposed to an outer surface of the semiconductor device. With this structure, heat generated by the semiconductor chip can be radiated easily via the die pad.
A method for manufacturing the semiconductor device according to a first structure of the present invention includes forming a die pad and support leads as one piece using a flat metal plate, as well as forming protrusions on a surface of the support leads, mounting a semiconductor chip on a surface of the die pad opposite to that on which the protrusions are formed, and enclosing the die pad, the support leads and the semiconductor chip in a die, so as to seal them with a resin while bringing the protrusions into contact with an internal wall surface of the die. With this structure, the protrusions provided in the support leads prevent the displacement of the die pad during the resin-sealing. Therefore, the die pad is arranged according to its initial design, making it possible to obtain the semiconductor device having the semiconductor chip in which distortion does not
Itoh Ken'ichi
Ogata Shuichi
Clark Sheila V.
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
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