Active solid-state devices (e.g. – transistors – solid-state diode – Lead frame
Reexamination Certificate
1998-01-20
2001-04-10
Clark, Sheila V. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Lead frame
C257S676000
Reexamination Certificate
active
06215174
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lead frame having at least two leads and usable for resin-sealing a semiconductor chip, a mold for producing a resin-sealed semiconductor device using such a lead frame, a resin-sealed semiconductor device using such a lead frame, and a method for producing a resin-sealed semiconductor device using such a lead frame.
2. Description of the Related Art
Recently, semiconductor devices have an increased number of pins used for electrodes in accordance with an increase in complexity of the circuit structure mounted therein, the incorporation of various devices into a system, and the diversification of uses. The withstanding voltage characteristic (hereinafter, referred to as the “withstanding voltage”) of semiconductor devices has been increased. Therefore, a significantly high voltage may be applied between adjacent leads of a semiconductor device. Accordingly, the distance between such adjacent leads needs to be increased. For example, the minimum possible distance between two adjacent leads is generally considered to be 5 mm in the case of a semiconductor device having a withstanding voltage of 600 V. Such a trend in development requires development of special packages for semiconductor devices and new production facilities, which results in a higher cost for the semiconductor devices.
As one proposal for coping with the abovementioned development trend, common use of components such as packages and lead frames for semiconductors having different specifications have been researched.
FIG. 29
is a plan view of a conventional lead frame
1
for resin-sealing a semiconductor chip
2
. The lead frame
1
includes five leads, namely, two leads
1
a,
two leads
1
b
and one lead
1
c.
The semiconductor chip
2
is resin-sealed using the lead frame
1
in the following manner.
The semiconductor chip
2
is bonded on a die-mount portion
1
d
of the lead frame
1
, and the semiconductor chip
2
is connected to the leads
1
a
via thin metal wires
3
. The semiconductor chip
2
and the lead frame
1
are resin-sealed in a resin-seal body
6
except for the outer ends of the five leads
1
a,
1
b
and
1
c.
Then, the lead
1
c
which is not connected to the semiconductor chip
2
is cut along an outer peripheral surface of the resin-seal body
6
by appropriate machining.
Conventionally, a common lead frame is used for resin-sealing semiconductor chips having different manners of wire connection in order to allow for use of a common mold. After the semiconductor chip is resin-sealed, the unnecessary lead (such as
1
c
) which is not connected to the semiconductor chip is cut off in an appropriate manner. Consequently, circuits having complicated structures are produced with relative ease.
However, in the manner of resin-sealing described with reference to
FIG. 29
, after the unnecessary lead
1
c
is cut off, a part
1
c′
thereof is left on the outer peripheral surface of the resin-seal body
6
. During the flow-soldering or dip-soldering performed subsequent to the resin-seal, solder H adheres to the part
1
c′.
This causes the part
1
c′
to be a separate conductive part existing between the two respective leads
1
a,
resulting in potential electric connection of the two leads
1
a
to each other. When such a phenomenon (the solder adherence) gets too large, the withstanding voltage of the semiconductor device is lowered and sometimes the device does not function.
As the number of pins connected to a semiconductor chip increases, the distance between two adjacent leads is decreased. As the withstanding voltage of a semiconductor device rises, the voltage applied between the leads also rises. In order to cope with such a trend, a sufficient withstanding voltage should be obtained between the shortened lead distance.
In order to prevent the withstanding voltage between leads from decreasing, a lead frame and a mold specially used for each of various types of semiconductor devices are used. This raises the cost of the molds and also increases the number of mold replacements, thus raising the production cost of the semiconductor devices.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a lead frame used for a resin-sealed semiconductor device includes a die-mount portion on which a semiconductor chip rests; and a plurality of leads arranged along a common portion of the lead frame. The plurality of leads include at least one adjusting lead, and the adjusting lead has a length that is less than the others of the plurality of leads such that a tip of the adjusting lead is sufficiently proximate to an outer peripheral surface of a resin-seal body to prevent resin flash during a formation of the semiconductor device and to allow the adjusting lead to be removed after the resin-seal body is formed over a portion of the lead frame.
In one embodiment of the invention, the adjusting lead projects into the resin-seal body.
In one embodiment of the invention, the tip of the adjusting lead is tapered.
In one embodiment of the invention, the tip of the adjusting lead is squared.
In one embodiment of the invention, the adjusting lead has a length that is less than the others of the plurality of leads such that a tip of the adjusting lead is located at one of a position outside an outer peripheral surface of the resin-seal body and a position in contact wit the outer peripheral surface of the resin-seal body during a formation of the semiconductor device.
In one embodiment of the invention, the tip of the adjusting lead is squared.
In one embodiment of the invention, an end surface of the tip of the adjusting lead and the outer peripheral surface of the resin-seal body is substantially parallel to each other.
In one embodiment of the invention, one or more of the leads other than the adjusting lead has a shape for preventing the one or more leads from removing from the resin-seal body after the resin-seal body is formed over the portion of the lead frame.
In one embodiment of the invention, the lead frame further includes a tie-bar for transversely connecting the plurality of leads, thereby substantially preventing a bending of the plurality of leads.
According to another aspect of the invention, a lead frame used for a resin-seal semiconductor device includes a die-mount portion on which a semiconductor chip rests; a plurality of leads which are arranged along a common portion of the lead frame, wherein at least two of the plurality of leads are spaced apart from each other a predetermined distance, wherein the predetermined distance is at least twice a distance between the others of the plurality of leads; a tie-bar for transversely connecting the plurality of leads, thereby substantially preventing a bending of the plurality of leads.
According to still another aspect of the invention, a mold for producing a resin-sealed semiconductor device using a lead frame is provided. The lead frame includes a plurality of leads arranged along at least one outer peripheral surface of the mold. The plurality of leads include at least one adjusting lead. The adjusting lead projects into the mold a predetermined distance which is sufficiently small to allow the adjusting lead to be easily removed from the resin-sealed semiconductor without resin flash after the resin-sealed semiconductor is formed. The mold has a part for holding the adjusting lead and extending to a vicinity of the tip of the adjusting lead during a formation of the semiconductor device.
According to still another aspect of the invention, a resin-sealed semiconductor device produced using a lead frame is provided, in which the resin-sealed semiconductor device includes a resin-seal body surrounding a portion of the lead frame for protecting a semiconductor chip thereon. The lead frame includes a plurality of leads arranged along at least one outer peripheral surface of the resin-seal body. The plurality of leads include at least one adjusting lead, which projects into the resin-seal body a sufficiently small distanc
Sakaguchi Shigeki
Takada Kouji
Yokozawa Masami
Yoshida Hiroyoshi
Clark Sheila V.
Matsushita Electronics Corporation
Snell & Wilmer L.L.P.
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