Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Making plural separate devices
Reexamination Certificate
2002-01-25
2003-09-30
Fahmy, Wael (Department: 2814)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Making plural separate devices
C438S123000, C438S124000
Reexamination Certificate
active
06627481
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods of manufacturing semiconductor packages, more particularly, to improved lead frames used in semiconductor packages.
2. Description of the Related Art
To meet the requirement of modem electric products being delicate, designs of semiconductor package are aiming at minimizing volume and thickness. However, such products tend to be multiple functions; thus sizes of semiconductor die to be packaged are enlarged. To make the semiconductor package have minimized volume and large dies is what persons skilled in this field expect.
Referring to
FIGS. 1
,
2
, or
3
, a conventional method of manufacturing semiconductor packages comprises steps of (a) providing a lead frame
11
which comprises a die pad
111
, a plurality of connecting parts
112
and a plurality of leads
113
, wherein the die pad
111
is lower than the leads
113
, and the connecting parts
112
connect the die pad
111
and the leads
113
; besides, the lead frame
11
made of copper retains appropriate flexibility; furthermore, inner fingers used in connecting circuits inside the package and/or outer fingers used in connecting circuits outside the package are etched in proper positions of the lead frame; (b) mounting a die
12
onto the die pad
111
and electrically connecting the lead frame
11
and die
12
by bonding wires
13
; (c) providing an upper mold
14
and a lower mold
15
, wherein the upper mold
14
and lower mold
15
are located at an upper side and a lower side of the leads
113
, respectively; the lead frame
11
, die
12
, and bonding wires
13
are enclosed in a mold cavity formed by the upper and lower molds
14
and
15
thereby, and the leads
113
are allowed to protrude outwards from the mold cavity. After fabricating such a construction, it can be proceeded with (d) applying an encapsulant through a filling hole co-formed by the upper mold
14
and the lower mold
15
; and (e) forming an encapsulant
16
after encapsulating and removing the upper and lower molds
14
and
15
to complete the package.
For the purpose of preventing the die pad
111
of the lead frame
11
from exposure out of the encapsulant
16
, an appropriate distance between the die pad
111
and the lower mold
15
should be kept. Therefore, the thickness of the semiconductor package cannot be reduced. In addition, when the dies to be packaged are too thick to fit the mold size, such dies should be grinded and cost and process rise as well.
In addition, in the process of applying the encapsulant, the encapsulant will form an upper flow F
1
and a lower mold flow F
2
, respectively, resulting from the separation of the lead frame
11
and the die
12
.
Referring to
FIG. 1
, when the upper and lower mold flows F
1
and F
2
distribute evenly in the mold cavity formed by the upper mold
14
and lower mold
15
, the lead frame
11
, die
12
and bonding wires
13
are forced equally, and relative positions thereof with the upper mold
14
and lower mold
15
would not be changed substantially. In this situation, electric elements are successfully enclosed in the mold cavity to achieve the desired package.
However, referring to
FIG. 2
, in the process of applying the encapsulant, when the lower mold flow F
2
is greater than the upper mold flow F
1
, a lifting force is applied to the flexible lead frame
11
, and such a force may change angles of the connecting part
112
between the die pad
111
and leads
113
. Extremely, the lifting force may even make the whole die pad
111
convex. The deformation of the lead frame
11
not only changes relative positions between elements but also may make the bonding wires
13
touch the upper mold
14
. Thus, such a product becomes defect in view of the exposure of the bonding wires
13
outside the encapsulant
16
.
On the other hand, if the upper mold flow F
1
is greater than the lower mold flow F
2
in the process of applying the encapsulant, as shown in
FIG. 3
, a pressing force is applied to the flexible lead frame
11
, and such a force may also change angles of the connecting part
112
between the die pad
111
and leads
113
. Extremely, the pressing force may even make the whole die pad
111
concave. The deformation of the lead frame
11
not only changes relative positions between elements but also may make the die pad
111
touch the lower mold
15
. Thus, the exposure of the lead frame
11
outside the encapsulant
16
occurs as well. Furthermore, the bonding wires
13
may be broken because of the deformation of the lead frame
11
, and such a product does not fit the requirement of packaging either.
The subject invention is to develop a novel method of manufacturing semiconductor packages to solve the problems of exposures of the bonding wires or lead frame and the semiconductor packages being over thick.
SUMMARY OF THE INVENTION
One objective of the present invention is to provide a method of manufacturing semiconductor packages and products thereof. The method of manufacturing comprises steps of: (a) providing a lead frame which comprises a die pad, a plurality of connecting parts and a plurality of leads, wherein the die pad is lower than the leads and connects the leads through the connecting parts, and wherein the die pad comprises at least one supporting structure to fix the lead frame substantially; (b) mounting a die onto the die pad and electrically connecting the lead frame and die by bonding wires; (c) providing an upper mold and a lower mold, wherein the upper mold and lower mold are located at an upper side and a lower side of the leads, respectively, wherein the supporting structures of the die pad are allowed to be supported on the lower mold, and the leads are allowed to protrude outwards from a mold cavity formed by the upper and lower molds; (d) setting the lead frame in steps (a) and (b) onto the lower mold in step (c) and making the supporting structures of the die pad to be supported on the lower mold and then combining the upper mold to the lower mold; (e) applying an encapsulant into the mold cavity formed by the upper and lower molds; and (f) removing the upper and lower molds after encapsulating.
Another objective of the present invention is to provide a lead frame used in a semiconductor package, which comprises a die pad, a plurality of connecting parts and a plurality of leads, wherein the die pad is lower than the leads and connects the leads through the connecting parts, and wherein the die pad comprises at least one supporting structure to fix the lead frame to the lower mold substantially. The present invention can enlarge ranges of the thickness of a die and avoiding the die from being grinded.
REFERENCES:
patent: 5389739 (1995-02-01), Mills
patent: 5578871 (1996-11-01), Fierkens
patent: 6303985 (2001-10-01), Larson et al.
patent: 405047979 (1993-02-01), None
patent: 410144853 (1998-05-01), None
Lee Meng-Tsang
Lo Kuang-Lin
Advanced Semiconductor Engineering Inc.
Fahmy Wael
Ladas & Parry
Pham Hoai
LandOfFree
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