Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Metallic housing or support
Reexamination Certificate
2002-08-29
2004-02-17
Picardat, Kevin M. (Department: 2822)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Metallic housing or support
C438S111000, C438S112000, C438S124000, C438S126000, C438S127000
Reexamination Certificate
active
06692991
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a resin-encapsulated semiconductor device called “QFN” (Quad Flat Non-leaded package), and a method for manufacturing the same. More particularly, the present invention relates to a resin-encapsulated semiconductor device and a method for manufacturing the same in which a lead frame is machined so as to reduce the thickness of the device and to improve the reliability thereof.
In recent years, in order to reduce the size of portable electronic devices, there is a demand for high-density mounting of semiconductor components such as resin-encapsulated semiconductor devices. Along with this trend, semiconductor packages have been reduced in size and thickness. QFN type package is known in the art as one type of resin-encapsulated semiconductor device that can meet such a demand. In a QFN type package, an outer lead, which is otherwise protruding sideways from the package, is eliminated, with external electrodes for electrical connection to the mother board being provided on the bottom surface.
A conventional QFN type resin-encapsulated semiconductor device and a method for manufacturing the same will now be described.
FIG.
6
A and
FIG. 6B
are a cross-sectional view and a bottom view, respectively, illustrating a structure of the conventional resin-encapsulated semiconductor device, wherein
FIG. 6A
is a cross-sectional view taken along line VIa-VI′a-VIa in FIG.
6
B.
As illustrated in FIG.
6
A and
FIG. 6B
, the conventional resin-encapsulated semiconductor device includes a die pad
102
, a semiconductor chip
101
mounted on the die pad
102
and having an electrode pad on the upper surface thereof, a plurality of leads
103
for passing electric signals to the semiconductor chip
101
, thin metal wires
104
made of, for example, Au (gold) for connecting the semiconductor chip
101
and leads
103
with each other, suspension leads
108
connected to the die pad
102
, and an encapsulation resin
105
for encapsulating therein the semiconductor chip
101
, the thin metal wires
104
and the die pad
102
. Note that the bottom surface of the conventional resin-encapsulated semiconductor device illustrated herein is in a rectangular or square shape, and the leads
103
provided along the four sides of the bottom surface are exposed on the bottom surface and the side surface of the semiconductor device. Moreover, at each corner of the bottom surface, the suspension lead
108
is exposed. The die pad
102
, the lead
103
and the suspension lead
108
are made of a metal containing Cu (copper), and the thickness thereof is substantially in the range of 200 &mgr;m to 300 &mgr;m. Moreover, the thickness of the semiconductor device including the encapsulation resin is about 800 &mgr;m (0.8 mm) when the thickness of the semiconductor chip
101
is 200 &mgr;m.
As described above, the conventional resin-encapsulated semiconductor device is a lead-less type resin-encapsulated semiconductor device, in which the leads
103
exposed on the bottom surface are used as external electrodes.
Moreover, the upper surface of the die pad
102
is located higher than the upper surface of the lead
103
, as illustrated in
FIG. 6A
, whereby the semiconductor chip
101
can overlap with the lead
103
as viewed from above, thus increasing the chip area proportion in the resin-encapsulated semiconductor device. Therefore, the conventional resin-encapsulated semiconductor device is reduced in size and thickness as compared with a QFP (Quad Flat Package) in which the leads are protruding outwards.
Next, a method for manufacturing the conventional resin-encapsulated semiconductor device will be described.
FIG. 7A
to
FIG. 7D
are cross-sectional views illustrating a process of manufacturing the conventional resin-encapsulated semiconductor device, taken along line VIa-VII in FIG.
6
B.
First, in the step shown in
FIG. 7A
, a lead-frame-forming metal plate made of a copper (Cu)-based material and having a thickness of 200 to 300 &mgr;m is prepared, and the metal plate is stamped or etched so as to form a lead frame including the die pad
102
, semi-finished leads
103
a
, the suspension leads
108
for supporting the die pad
102
at their tips, and an outer frame (not shown) to which the ends of the semi-finished leads
103
a
and the suspension leads
108
are connected.
Then, the lead frame is pressed so as to bend the suspension leads
108
upwards, thereby upsetting the upper surface of the die pad
102
to be located higher than the upper surface of the semi-finished lead
103
a
. Since the pressing process requires a “grip margin”, the raised portion of the suspension lead
108
is necessarily provided inside the outer frame.
Then, in the step shown in
FIG. 7B
, the semiconductor chip
101
is mounted on, and adhered to, the upper surface of the die pad
102
by using an adhesive such as a silver paste.
Then, in the step shown in
FIG. 7C
, the electrode pad of the semiconductor chip
101
mounted on the die pad
102
is electrically connected to the upper surface of the semi-finished lead
103
a
by using the thin metal wire
104
such as a gold wire.
Then, in the step shown in
FIG. 7D
, the mounted semiconductor chip
101
, the die pad
102
and the thin metal wires
104
are encapsulated together with the encapsulation resin
105
. In this process, the lower surface (opposing the upper surface) of the semi-finished lead
103
a
is left exposed.
Then, a portion of each semi-finished lead
103
a
connected to the outer frame of the lead frame that is protruding out of the encapsulation resin
105
is cut off, thereby forming the leads
103
. Thus, the resin-encapsulated semiconductor device of a QFN type is obtained, in which the cut surface of each lead
103
is exposed on, and flush with, the side surface of the encapsulation resin
105
.
When the upper surface region of the lead frame is encapsulated with the encapsulation resin
105
, a sheet seal method is used, in which the resin encapsulation process is performed with a seal sheet being closely attached to the lower surface of the lead frame, thereby preventing the encapsulation resin from creeping onto the reverse surface of the lead frame. With this method, it is ensured that the lower surface of each lead is left exposed, thus realizing a one-side-encapsulated structure.
Note that in an actual manufacturing process, a plurality of resin-encapsulated semiconductor devices are formed on the same surface of a single lead frame.
In this way, the conventional resin-encapsulated semiconductor device, which are small and thin, is manufactured.
However, in the conventional resin-encapsulated semiconductor device, the upper surface of the die pad
102
is located higher than the upper surface of the lead
103
, and thus the thickness of the upset is added, whereby it is difficult to further reduce the thickness thereof.
Moreover, in the conventional resin-encapsulated semiconductor device, the die pad
102
is located higher than the leads
103
by bending the suspension leads
108
, whereby a bending stress is applied during the bending process to the suspension leads
108
and the die pad
102
contained in the encapsulation resin
105
. Furthermore, a stress is also applied during the injection and curing of the encapsulation resin
105
. Thus, the stress applied to the suspension leads
108
and the die pad
102
remains unremoved even after the resin encapsulation process, whereby the operating lifetime of the conventional resin-encapsulated semiconductor device may possibly be shortened under certain operating environments.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a resin-encapsulated semiconductor device and a method for manufacturing the same, in which the thickness is further reduced and the stress applied to lead members in an encapsulation resin is reduced, thereby realizing a high reliability.
A resin-encapsulated semiconductor device of the present invention includes: a die pad provided by thinning a lower portion of a lead fra
Minamio Masanori
Nomura Toru
LandOfFree
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