Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Metallic housing or support
Reexamination Certificate
1999-07-21
2001-09-18
Graybill, David E. (Department: 2814)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Metallic housing or support
C438S124000, C438S126000, C438S127000
Reexamination Certificate
active
06291274
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a resin-molded semiconductor device, in which a semiconductor chip and a leadframe are molded with a resin encapsulant, and to a method for manufacturing such a device. In particular, the present invention relates to a device with the back surface of the leadframe partially exposed out of the resin encapsulant.
BACKGROUND ART
In recent years, in order to catch up with rapidly advancing downsizing of electronic units, it has become increasingly necessary to package semiconductor components for each of these electronic units at a higher and higher density. Correspondingly, sizes and thicknesses of semiconductor components have also been noticeably reduced.
Hereinafter, a conventional resin-molded semiconductor device will be described.
FIG.
23
(
a
) is a plan view of a conventional resin-molded semiconductor device, and FIG.
23
(
b
) is a cross-sectional view of the conventional resin-molded semiconductor device.
As shown in FIGS.
23
(
a
) and
23
(
b
), this conventional resin-molded semiconductor device is of the type including external electrodes on its back surface.
The conventional resin-molded semiconductor device includes a leadframe consisting of: inner leads
201
; a die pad
202
; and support leads
203
for supporting the die pad
202
. A semiconductor chip
204
is bonded onto the die pad
202
with an adhesive, and electrode pads (not shown) of the semiconductor to chip
204
are electrically connected to the inner leads
201
with metal fine wires
205
. And the die pad
202
, semiconductor chip
204
, inner leads
201
, support leads
203
and metal fine wires
205
are molded with a resin encapsulant
6
. In this structure, no resin encapsulant
206
exists on respective back surfaces of the inner leads
201
. In other words, the respective back surfaces of the inner leads
201
are exposed and respective lower parts of the inner leads
201
, including these exposed back surfaces, serve as external electrodes
207
.
In such a resin-molded semiconductor device, the respective back surfaces of the resin encapsulant
206
and those of the inner leads
201
are both located in the same plane, and the die pad
202
is located above the inner leads
201
. That is to say, by providing depressed portions
208
for the support leads
203
, the die pad
202
is elevated above the inner leads
201
. Thus, after the device has been molded with the resin encapsulant
206
, a thin layer of the resin encapsulant
206
is also formed on the back surface of the die pad
202
. In FIG.
23
(
a
), the resin encapsulant
206
is illustrated as being transparent such that the inside of the semiconductor device can be looked through. In FIG.
23
(
a
), the semiconductor chip
204
is indicated by the dashed line and the illustration of the metal fine wires
205
is omitted.
Also, conventionally, to secure a required standoff height from the back surface of the resin encapsulant
206
in bonding the external electrodes to the electrodes of a motherboard such as a printed wiring board, on which a resin-molded semiconductor device is mounted, ball electrodes
209
of solder are attached to the external electrodes
207
as shown in FIG.
24
. After the standoff height has been secured by these ball electrodes
209
, the device is mounted onto the motherboard.
Hereinafter, a method for manufacturing the conventional resin-molded semiconductor device will be described with reference to the drawings.
FIGS. 25 through 27
are cross-sectional views illustrating a manufacturing process for the conventional resin-molded semiconductor device.
First, as shown in
FIG. 25
, a leadframe
210
, including the inner leads
201
and die pad
202
, is prepared. It is noted that the die pad
202
is actually supported by the support leads, but the illustration of the support leads is omitted in FIG.
25
. Depressed portions are formed in the support leads and the die pad
202
is elevated above the plane on which the inner leads
201
are located. The leadframe
210
does not include any tie bar used for preventing the resin encapsulant from flowing out during resin encapsulation.
Next, as shown in
FIG. 26
, the semiconductor chip
204
is bonded, with an adhesive, to the die pad
202
of the lead-frame prepared. This process step is called “die bonding”.
Then, as shown in
FIG. 27
, the semiconductor chip
204
, which has been bonded onto the die pad
202
, is electrically connected to the inner leads
201
via the metal fine wires
205
. This process step is called “wire bonding”. As the metal fine wires
205
, aluminum (Al) or gold (Au) fine wires may be appropriately used, for example.
Subsequently, as shown in
FIG. 28
, the die pad
202
, semiconductor chip
204
, inner leads
201
, support leads and metal fine wires
205
are molded with the resin encapsulant
206
. In this case, the leadframe, on which the semiconductor chip
204
has been bonded, is introduced into a molding die assembly and transfer-molded. In particular, resin encapsulation is performed with the back surface of the inner leads
201
in contact with an upper or lower die of the die assembly.
Finally, the ends
211
of the inner leads
201
, protruding outward from the resin encapsulant
206
, are cut off after the resin encapsulation. By performing this cutting process step, the end faces of the inner leads
201
cut off are substantially flush with the side faces of the resin encapsulant
6
and the respective lower parts of the inner leads
201
are used as external electrodes
207
.
In the manufacturing process of this conventional resin-molded semiconductor device, the resin encapsulant
206
might overflow from the edges of the inner leads
201
, reach the back surfaces thereof and thereby form resin bur thereon (overflowing resin) during the resin encapsulation process step. Thus, a water jet process step is introduced for blowing off the resin bur after the resin encapsulation process step and before the process step of cutting off the inner leads
201
.
Also, if necessary, ball electrodes of solder are formed on the lower surfaces of the external electrodes
207
, thereby completing the resin-molded semiconductor device shown in FIG.
24
. As another alternative, a solder plating layer is sometimes formed instead of the solder balls.
PROBLEMS TO BE SOLVED
The conventional resin-molded semiconductor device, however, has the following drawbacks. First, since the lower surfaces of the external electrodes
207
are located in substantially the same plane as that of the resin encapsulant
206
on the back of the semiconductor device, no standoff height from the resin encapsulant
206
can be obtained. Thus, the device must be mounted onto a motherboard with the ball electrodes
209
of solder interposed therebetween. Accordingly, mounting cannot be carried out efficiently.
In addition, during the resin encapsulation step of the conventional process for manufacturing a resin-molded semiconductor device, a leadframe, on which a semiconductor chip has been bonded, is introduced into a molding die assembly and then molded with a resin by pressing the inner leads against the surface of the lower die such that the leads closely contact the die. Even so, there occurs a problem that the resin encapsulant reaches the back surface of the inner leads to form a resin bur (overflowing resin) on the surface of the external electrodes.
FIG. 30
is a partial plan view illustrating, on a larger scale, the external electrodes
207
and their surroundings on the back of the semiconductor device as illustrated within the circle in FIG.
23
(
a
). As shown in
FIG. 30
, resin bur
206
a
is sometimes formed on the respective lower surfaces of the external electrodes
207
during the conventional resin encapsulation process step. That is to say, the resin encapsulant
206
reaches the lower surfaces of the external electrodes
207
to form the resin bur
206
a
thereon during the resin encapsulation process step. In other words, part of each external electrode
207
is buried within the resin e
Oida Seishi
Suematsu Nobuhiro
Yamaguchi Yukio
Graybill David E.
Matsushita Electric - Industrial Co., Ltd.
Nixon & Peabody LLP
Robinson Eric J.
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