Active solid-state devices (e.g. – transistors – solid-state diode – Lead frame
Reexamination Certificate
2003-06-16
2004-09-21
Potter, Roy (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Lead frame
C257S678000, C257S684000, C257S687000
Reexamination Certificate
active
06794736
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a resin-packaged semiconductor device.
2. Description of the Related Art
An example of prior art semiconductor device is shown in
FIGS. 9A and 9B
. The illustrated semiconductor device includes a semiconductor chip
9
, a pair of conductors
8
A,
8
B made of a metal plate, and a resin package
7
for sealing them. The semiconductor chip
9
is mounted on the conductor
8
A, and the conductor
8
A is electrically connected to a lower electrode (not shown) of the semiconductor device
9
. The semiconductor chip
9
includes an upper electrode
90
electrically connected to the conductor
8
B via a wire W. The paired conductors
8
A,
8
B respectively include a thicker portion
81
a
,
81
b
and a thinner portion
82
a
,
82
b.
The thicker portion
81
a
,
81
b
has a lower surface exposed at the bottom surface of the resin package
7
as a terminal
83
a
,
83
b
for surface-mounting. As shown in
FIG. 9B
, the terminal
83
a
,
83
b
is rectangular.
With this structure, the semiconductor device can be surface-mounted on a desired portion by utilizing the terminals
83
a
,
83
b
. Since each of the conductors
8
A,
8
B includes an upper surface having a larger area than that of the terminal
83
a
,
83
b
, the semiconductor chip
9
and the wire W can be appropriately bonded to these portions. The thinner portions
82
a
,
82
b
of the conductors
8
A,
8
B are sealed in the resin package
7
. Consequently, part of the resin content of the resin package
7
exists under the thinner portion
82
a
,
82
b
for fixing and supporting the conductors
8
A,
8
B.
However, the above-described prior art semiconductor device has the following disadvantages.
Due to a strong demand for an overall size reduction in the field of semiconductor devices, the semiconductor device needs to be reduced with respect to its length, width, and/or height. In realizing such a size reduction of the semiconductor device, it may be difficult for the conductor
8
B to have an enough size as a whole because the conductor
8
A must have a sufficient size for mounting the semiconductor chip. Even under such a situation, the terminal
83
b
must have a reasonable size for appropriate surface-mounting.
To increase the terminal
83
b
in size, the thicker portion
81
b
may have an increased dimension b, as shown in FIG.
9
A. However, the dimension a of the thinner portion
82
b
reduces due to this structure, resulting in a reduction of the resin content of the resin package
7
existing directly under the thinner portion
82
b
. As a result, the resin package
7
may not provide sufficient support for the conductor
8
B, which may easily cause crack formation at the corners of the resin package
7
.
Further, if the width c of the thicker portion
81
b
is increased to increase the area of the terminal
83
b
, the resin package
7
will have a correspondingly reduced width d on both sides of the thicker portion
81
b
. Consequently, crack formation may easily occur in these areas. Particularly, in molding the resin package
7
, the corners of the resin package
7
may be insufficiently filled with resin because of the reduced width d, which may easily leads to crack formation.
Thus, an attempt to reduce the overall size of the conventional semiconductor device will lead to higher likelihood of crack formation with respect to the resin package
7
, consequently posing a hinderance to a size reduction of the semiconductor device. While the above description is given only with respect to easier crack formation near the conductor
8
B which is reduced in size, the same problem may also apply to the relationship between the conductor
8
A and the resin package
7
.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a semiconductor device which, even if reduced in overall size, is unlikely to suffer crack formation with respect to a resin package, and which can be appropriately surface-mounted on a desired portion.
According to the present invention, a semiconductor device is provided which comprises a semiconductor chip, a plurality of conductors electrically connected to an electrode of the semiconductor chip, and a resin package for sealing the semiconductor chip and the conductors. Each of the conductors has a thicker portion and a thinner portion. The thicker portion includes a lower surface exposed at a bottom surface of the resin package as a terminal for surface-mounting. The thicker portion of at least one of the conductors is non-rectangular with partially or entirely uneven width.
According to the present invention, the non-rectangular thicker portion includes a relatively wide portion and a relatively narrow portion due to its partially or entirely uneven width. Due to the provision of the thicker portion and the thinner portion for the conductor, a width decrease of the thicker portion results in a corresponding size increase of the thinner portion. According to the present invention, therefore, even where the conductor cannot be made to have a sufficient overall size, the thicker portion and the terminal provided by the thicker portion for surface-mounting can retain a reasonable size for surface-mounting without unduly reducing the area of the thinner portion, as opposed to the prior art semiconductor. As a result, according to the present invention, the semiconductor device is unlikely to suffer crack formation with respect to the resin package while being capable of being appropriately surface-mounted on a desired portion, thereby contributing to an overall size reduction.
According to a preferable embodiment of the present invention, the resin package includes a pair of first side surfaces spaced in a direction x, and a pair of second side surfaces spaced in a direction y perpendicular to the direction x. The terminals of the conductors are paired with and spaced from each other in the direction x. The non-rectangular thicker portion includes a tapered portion having width increasing in the direction y toward a center of the resin package. The tapered portion may be generally trapezoidal, triangular, or semicircular.
With this structure, when the resin package is formed by utilizing a mold, the tapered portion functions as a guide for molding resin to smoothly flow into the corners of the resin package (where the first and the second side meet). Consequently, the corners of the resin package are prevented from remaining incompletely filled with resin, thereby reducing the possibility of crack formation.
Preferably, the conductor has an outer end projecting from a respective first side surface and formed with a recess. With this structure, solder flows into the recess to increase the bonding area of the solder relative to the conductor in surface-mounting the semiconductor device, which improves the mounting strength of the semiconductor device.
Preferably, the recess extends over an entire thickness of the thicker portion. This helps the solder smoothly flow into the recess.
Other features and advantages of the present invention will become clearer from the detailed description of the preferred embodiments given.
REFERENCES:
patent: 6198171 (2001-03-01), Huang et al.
patent: 6437429 (2002-08-01), Su et al.
patent: 6709892 (2004-03-01), Kobayakawa et al.
Merchant & Gould P.C.
Potter Roy
Rohm & Co., Ltd.
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