Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Metallic housing or support
Reexamination Certificate
2001-05-16
2002-08-27
Ho, Hoai (Department: 2818)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Metallic housing or support
C257S666000, C257S667000, C257S712000, C257S787000
Reexamination Certificate
active
06440779
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to semiconductor packaging technology, and more particularly, to a semiconductor package based on window pad type of leadframe and method of fabricating the same.
2. Description of Related Art
A leadframe is a metal-made frame that includes a centrally-located die pad and a plurality of peripherally-located leads surrounding the die pad. The die pad is used for mounting a semiconductor chip thereon, while the leads are used to serve as external connecting means for the semiconductor chip. After the semiconductor chip is wire-bonded to the leads, the die pad together with the semiconductor chip are encapsulated in an epoxy-molded compound (EMC), or called encapsulation body.
A window pad type of leadframe is one of the many various kinds of leadframes that are used for construction of semiconductor packages. This type of leadframe is characterized by the provision of an opening (or called window) in the center of the die pad and can help to prevent delamination of the mounted chip. A conventional method for fabricating a semiconductor package based on a window pad type of leadframe is illustratively depicted in the following with reference to
FIGS. 1A-1D
.
FIG. 1A
shows a schematic diagram in top view of a window pad type of leadframe
100
, while
FIG. 1B
shows the same in sectional view cutting through the line
1
B—
1
B. As shown, this window pad type of leadframe
100
includes a plurality of peripherally-located leads
110
and a centrally-located die pad
120
having a solid ring portion
121
and a hollowed window portion
122
. The leadframe
100
is typically made of copper.
The leadframe
100
is used to serve as a chip carrier for a semiconductor chip
140
. It is to be noted that the width W
1
of the semiconductor chip
140
should be larger than the width W
0
of the window portion
122
of the die pad
120
.
Referring further to
FIG. 1C
, in the next step, a die-mounting process is performed to mount the semiconductor chip
140
over the die pad
120
by adhering the semiconductor chip
140
to the ring portion
121
of the die pad
120
with a thermally-conductive adhesive layer
141
, such as silver epoxy.
Referring further to
FIG. 1D
, in the next step, a wire-bonding process is performed to electrically couple the semiconductor chip
140
to the leads
110
of the leadframe
100
by means of a plurality of bonding wires
150
, such as gold wires. Finally, an encapsulation process is performed to form an encapsulation body
160
to encapsulate the semiconductor chip
140
. This completes the fabrication of the semiconductor package.
The reason for the provision of the window portion
122
in the die pad
120
of the leadframe
100
is that it can help prevent the delamination of the semiconductor chip
140
from the die pad
120
. Otherwise, since the die pad
120
is greatly different in coefficient of thermal expansion (CTE) from the semiconductor chip
140
(the CTE of the semiconductor chip
140
is typically from 3 ppm/° C. to 4 ppm/° C., while the CTE of the copper-made die pad
120
is typically from 16 ppm/° C. to 20 ppm/° C.), it would easily make the semiconductor chip
140
subjected to delamination from the die pad
120
while undergoing high-temperature process steps.
In practical applications, however, the foregoing method for fabricating a semiconductor package based on a window pad type of leadframe would have the following drawbacks.
First, each design of the leadframe
100
is only suited for the packaging of semiconductor chips of specific sizes that are larger than the width W
0
of the window portion
122
of the die pad
120
. For chips that are smaller in width than W
0
, a new leadframe design is apparently required, and which is quite cost-ineffective to implement. There exists therefore a need for a new method that allows one design of the leadframe
100
to be universally suited for packaging chips of various sizes, whether larger or smaller than the window size.
Second, the existence of the window portion
122
of the die pad
120
reduces the contact area between the semiconductor chip
140
and the die pad
120
, resulting in a reduced heat-dissipation efficiency through the die pad
120
.
Related patents, include, for example, the U.S. Pat. No. 5,140,404 entitled “SEMICONDUCTOR DEVICE MANUFACTURED BY A METHOD FOR ATTACHING A SEMICONDUCTOR DIE TO A LEADFRAME USING A THERMOPLASTIC COVERED CARRIER TAPE”. This patented technology, however, teaches no solutions to the above-mentioned two drawbacks.
SUMMARY OF THE INVENTION
It is therefore an objective of this invention to provide an improved semiconductor packaging technology for fabricating a semiconductor package based on a window pad type of leadframe, which allows one design of the window pad type of leadframe to be universally suited for packaging chips of various sizes.
It is another objective of this invention to provide an improved semiconductor packaging technology for fabricating a semiconductor package based on a window pad type of leadframe, which allows an increase in the heat-dissipation efficiency of the packaged chip as compared to the prior art.
In accordance with the foregoing and other objectives, the invention proposes a new semiconductor packaging technology for fabricating a semiconductor package based on a window pad type of leadframe.
In terms of method, the semiconductor packaging technology according to the invention comprises the following steps: (1) preparing a leadframe including a plurality of leads and a die pad having a solid ring portion and a hollowed window portion; the window portion of the leadframe having a predefined size; (2) mounting a window shim having a solid ring portion and a hollowed window portion over the die pad of the leadframe; (3) mounting a semiconductor chip over the window shim and (4) performing a wire-bonding process to electrically couple the semiconductor chip to the leads of the leadframe; and (5) performing an encapsulation process to form an encapsulation body to encapsulate the semiconductor chip.
In terms of structure, the semiconductor packaging technology according to the invention comprises the following constituent parts: (a) a leadframe including a plurality of leads and a die pad having a solid ring portion and a hollowed window portion; the window portion of the leadframe having a predefined size; (b) a window shim having a solid ring portion and a hollowed window portion, and whose ring portion is attached to the ring portion of the die pad of the leadframe; (c) a semiconductor chip mounted over the window shim; (d) a plurality of bonding wires for electrically coupling the semiconductor chip to the leads of the leadframe; and (e) an encapsulation body for encapsulating the semiconductor chip.
The semiconductor packaging technology according to the invention is characterized by the provision of the window shim over the die pad of the leadframe. The window shim is dimensioned in such a manner that the width of the ring portion thereof is larger than the width of the window portion of the die pad of the leadframe, while the width of the window portion of the window shim is smaller than the width of the semiconductor chip. This feature allows one design of the window pad type of leadframe to be universally suited for packaging semiconductor chips of various sizes. Moreover, the incorporation of the window shim additionally allows an increase in the heat-dissipation efficiency of the packaged chip.
REFERENCES:
patent: 5140404 (1992-08-01), Fogal et al.
patent: 5491362 (1996-02-01), Hamzehdoost et al.
patent: 6114752 (2000-09-01), Huang et al.
patent: 6191490 (2001-02-01), Huang
Chen Audi
Chiu Fly
Ho Tzong-Da
Corless Peter F.
Edwards & Angell LLP
Ho Hoai
Ho Tu-Tu
Jensen Steven M.
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