Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Wire contact – lead – or bond
Reexamination Certificate
1999-01-21
2001-06-26
Clark, Sheila V. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Wire contact, lead, or bond
C257S787000, C257S676000, C257S782000
Reexamination Certificate
active
06252306
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing a semiconductor device and a configuration thereof. More particularly, it relates to a method of producing a resin-sealed semiconductor device and a configuration thereof which make it possible to decrease the size, thickness, weight and cost of the device.
2. Description of the Related Art
FIGS. 15A and 15B
show a gull-wing type semiconductor device with the configuration of the prior art,
FIG. 15A
being a cross sectional view thereof and
FIG. 15B
being a top view thereof.
A semiconductor device of this configuration is generally produced in such steps as shown in
FIG. 16
, in a procedure described below. A semiconductor element
3
is bonded by means of a die bonding material
2
on an island
24
of a lead frame
6
which has the islands
24
and leads
1
as shown in FIG.
17
. Then after connecting an inner lead section of the lead
1
surrounding the island
24
to an electrode pad located on the semiconductor element
3
by wire bonding using a wire
4
such as gold wire, the elements are sealed individually on both sides of the lead frame
6
by using a sealing resin
5
.
FIG. 18
is a top view of the semiconductor device with the configuration of the prior art after being sealed with resin. In a last stage, an outer lead section of the lead
1
is plated with tin or the like, cut off from the lead frame
6
and formed in gull wing shape, thereby to obtain the semiconductor device as shown in
FIGS. 15A and 15B
.
In the production method of the prior art, it is necessary to prepare the lead frame
6
having the islands
24
matched to the size of the semiconductor elements
3
and molding dies (not shown) for sealing the individual semiconductor elements with a resin. Therefore, when semiconductor elements
3
of different specifications are used, it is necessary to prepare different lead frames
6
and different molding dies for the various specifications.
In the semiconductor device of the prior art shown in
FIGS. 15A and 15B
, there has been a limitation on the reduction of the size and weight because the resin covers both sides of the lead frame
6
.
Moreover, because heat generated by the semiconductor element
3
is dissipated through the lead
6
, it is difficult to apply the device to high-output power transistors which generated much heat. Because of the relatively long connection between the semiconductor element
3
and a mother board, it is also difficult to apply the device to high-frequency transistors or the like.
To counter such problems as described above, a molded transistor having only one side of a lead being molded with a resin is disclosed, for example, in Japanese Patent Kokai Publication No. 62-134945. However, since production of such a molded transistor requires different lead frames for different specifications as in the prior art and molding with the resin is carried out individually for each semiconductor element, different molding dies must be prepared according to different specifications and therefore the above problems are not solved.
Also the devices are mounted on the mother board by using flat leads according to this prior art technology, but it cannot be applied to devices which generate much heat because of relatively small lead area.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of producing the semiconductor device wherein semiconductor element are sealed with resin by using the same lead and independent of the specifications of the semiconductor elements, and a semiconductor device which can be reduced in size and weight and has good heat dissipation performance and high-frequency performance.
The present inventors have intensively studied. As a result, they found that semiconductor devices can be produced with a same lead frame regardless of the specifications of semiconductor elements when a plurality of the semiconductor elements are mounted on the lead frame having leads disposed substantially parallel to each other and, after sealing the whole with a resin, the individual semiconductor devices are cut off, and that the semiconductor device has improved heat dissipation performance and high-frequency performance. Thus, the present invention has been accomplished.
The present invention provides a method of producing a semiconductor device comprising a die bond pad, a wire bond pad, a semiconductor element mounted on the die bond pad, and a sealing resin for molding the semiconductor element, which comprises preparing a lead frame having a plurality of leads disposed substantially in parallel to each other at intervals in the longitudinal direction in the same plane; bonding a plurality of semiconductor elements in parallel on at least one lead surface of the lead frame; electrically connecting an electrode of each semiconductor element and another lead adjacent therewith in the longitudinal direction; molding the plurality of semiconductor elements together by means of the sealing resin applied from above the lead surface so that the back side of the lead is exposed; and cutting the lead and the sealing resin in the longitudinal direction between the semiconductor elements, thereby to take the lead with the semiconductor element being mounted thereon as a die bond pad, and to take the lead connected to the electrode of the semiconductor element as a wire bond pad.
With this method of producing the semiconductor element, because it is not necessary to prepare a plurality of lead frames for different sizes of the semiconductor elements to be mounted, the lead frame can be used in common, and therefore it becomes possible to simplify the production process and reduce the production cost.
Particularly with this method, since the semiconductor devices are made by cutting off the lead frame whereon the semiconductor elements are bonded consecutively, no part of the lead frame will be wasted, so that product yield per unit area of the lead frame is improved and the production cost can be reduced.
The present invention also provides a method of producing the semiconductor device, wherein the back surface of the lead is covered with a resin sheet thereby to mold with the sealing resin.
By providing such a step, the sealing resin is prevented from seeping through the space between the leads to the back surface of the lead during the sealing step, thus making it possible to prevent connection failure from occurring when connecting the semiconductor device to the mother board.
The resin sheet may be applied either to the entire back surface of the lead or to a part thereof.
Alternatively, the space between the leads may be filled with a masking material before applying the sealing resin.
Seeping of the sealing resin to the back of the leads can be prevented by filling the space between the leads with the masking material.
The present invention also provides a method of producing the semiconductor device, wherein the sealing resin which has seeped to the back surface of the lead is removed after applying the sealing resin.
By providing such a step, connection failure due to the sealing resin seeping to the back surface of the lead can be prevented.
The present invention also provides a method of producing the semiconductor device, wherein the leads are supplied in the form of a lead frame having electrically conductive leads fastened onto a frame substantially in parallel to each other at intervals in the same plane.
By using the lead frame having leads disposed parallel to each other, handling of the leads during the production process is made easier.
The size of the lead in the longitudinal direction whereon the semiconductor element is mounted is preferably equal to or less than the size of the semiconductor element in the longitudinal direction.
When the space between the leads is made equal to or less than the width of the semiconductor element, distance between the leads can be made larger even when the semiconductor device is made smaller, thus making it possible to prevent short
Fujihara Teruhisa
Ohgiyama Kenji
Ueda Tamotsu
Clark Sheila V.
Mitsubishi Denki & Kabushiki Kaisha
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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