Active solid-state devices (e.g. – transistors – solid-state diode – Lead frame
Reexamination Certificate
2000-02-24
2002-07-23
Jackson, Jr., Jerome (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Lead frame
C257S667000, C257S670000
Reexamination Certificate
active
06424023
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a lead frame used to make a semiconductor package. More particularly, the present invention relates to a lead frame capable of a superior resin filling profile in a molding process used to make the semiconductor package.
BACKGROUND OF THE INVENTION
Typically, lead frames for semiconductor packages are fabricated by processing a strip, made of copper (Cu), iron (Fe), aluminum (A
1
) or an alloy thereof, in accordance with a mechanical method such as a stamping method or a chemical method such as an etching method in such a fashion that it has a plurality of leads. Leads of such a lead frame serve as conductive lines for connecting a semiconductor chip mounted on the lead frame to external circuits. Such leads also serve as a support for holding a semiconductor package fabricated using the associated lead frame to a mother board. Lead frames formed on one strip are cut at their peripheral edges in a singulation process, so that they are separated from one another.
Referring to
FIG. 1
a
, a typical structure of a conventional lead frame is illustrated. As shown in
FIG. 1
a
, the lead frame, which is denoted by the reference numeral
10
′, has a structure including a central opening
14
′ having a substantially rectangular or square shape, and a plurality of leads extending radially around the central opening
14
′. Each of the leads has an inner lead
11
′ adapted to be encapsulated by a resin encapsulate (denoted by the reference numeral
4
in
FIG. 3
) subsequently molded, and an outer lead
12
′ disposed beyond the resin encapsulate. Each lead is connected to a dam bar
19
′ at the outer end of its inner lead
11
′ and at the inner end of its outer lead
12
′ so that it is supported by the dam bar
19
′. In addition to the support function for the leads, the dam bar
19
′ has a function for preventing melted encapsulating resin from being outwardly leaked between adjacent inner leads
11
′ during a molding process.
Adjacent ones of the inner leads
11
′ of the lead frame have a space defined therebetween in such a fashion that it increases gradually in width as it extends from the opening
14
′ to the dam bar
19
′. Also, all spaces defined for all inner leads
11
′ have the same width at the same radial position. In other words, all spaces of all inner leads
11
′ have the same size and shape.
Pseudo tie bars
15
′ are arranged at four corners of the lead frame
10
′, respectively. Each pseudo tie bar
15
′ extends diagonally while having a width larger than a typical width of the leads. Where a semiconductor chip mounting plate (not shown) is to be arranged within the central opening
14
′, the pseudo tie bars
15
′ serve as tie bars for supporting the semiconductor chip mounting plate by use of an adhesion means such as an adhesive tape. Otherwise, the pseudo tie bars
15
′ may be removed to simply leave spaces, respectively. In some cases, they may be used as inner leads or ground leads.
In
FIG. 1
, the reference numeral
18
′ denotes an initial encapsulating resin introduction region defined at a selected one of the pseudo tie bars
15
′ respectively arranged at the four corners of the lead frame
10
′ in order to allow melted encapsulating resin of high temperature and high pressure to be introduced into a molding region.
As apparent from the above description, the conventional lead frame
10
′ has a symmetrical structure in longitudinal, lateral, and diagonal directions.
On the other hand,
FIG. 1
b
is a schematic view illustrating a procedure for fabricating a conventional heat sink. As shown in
FIG. 1
b
, a pair of facing U-shaped slots
51
′ are formed through a metal strip
50
′ in accordance with a stamping process in such a fashion that a pair of facing support bars
52
′ are left therebetween. The support bars
52
′ have a reduced thickness as compared to that of the metal strip
50
′ because the metal material of the metal strip
50
′ is subjected to an elongation at regions corresponding to those support bars
52
′ during the stamping process. The reason why the support bars
52
′ are formed is because when a heat sink, which is denoted by the reference numeral
5
′, is completely cut from the metal strip
50
′ using a single stamping step, there is a high possibility for the heat sink
5
′ to be bent due to a relatively large thickness (typically, about 1.65 mm) of the metal strip
50
′. In order to planarize bent heat sinks, it is necessary to use an additional process. After the stamping process, the heat sink
5
′ is still held to the metal strip
50
′ while being supported by the support bars
52
′ between the slots
51
′. In this state, the support bars
52
′ are cut, so that the heat sink
5
′ is separated from the metal strip
50
′. The resultant heat sink
5
′ has a substantially square structure provided with two protrusions
5
b
′. The support bars
52
′ are cut in accordance with upward and downward pressing operations respectively conducted by two pressing tools. Since the support bars
52
′ are relatively thick, the elongation of the metal thereof occurring during the pressing operations proceeds in directions slightly inclined along an associated one of the support bars
52
′ from upward and downward directions, respectively. As a result, each protrusion
5
b
′ has a V-shaped cross-section at each side wall thereof.
Typically, the cut heat sink
5
′ is subsequently coated with nickel (Ni) in order to prevent its surface, exposed in a state integrated into a resin encapsulate, from being oxidized in air. The nickel-coated surface of the heat sink
5
′ is also subjected to a sand blast process for an easy marking thereof. The heat sink
5
′ is also subjected to a well-known black oxidation process (adapted to form a CuO thin film and/or a Cu
2
O thin film) at its surface, on which a semiconductor chip is mounted, and its surface contacting the resin encapsulate, in order to obtain an improved bonding force to the resin encapsulate at those surfaces.
FIG. 2
is a cross-sectional view illustrating a typical mold used in a molding process for the fabrication of semiconductor packages. As shown in
FIG. 2
, the mold, which is denoted by the reference numeral
20
, includes an upper mold
21
and a lower mold
22
. Typically, the lead frame
10
′ attached at its lower surface with the heat sink
5
′ and at its upper surface with a semiconductor chip
1
′ is laid on the lower mold
22
which is, in turn, coupled to the upper mold
21
in such a fashion that the lead frame
10
′ is received in a mold cavity
23
defined by the upper and lower molds
21
and
22
. A pressurized melted encapsulating resin
4
′ is injected into the mold cavity
23
via a mold runner
24
by a resin feeding ram
26
arranged at a pouring gate
25
of the mold
20
. The mold runner
24
is formed on the lower surface of the upper mold
21
in such a fashion that it communicates with the mold cavity
23
while communicating with a port
27
. The melted encapsulating resin of high temperature and high pressure is set as it is cooled, thereby forming a resin encapsulate (denoted by the reference numeral
4
in FIG.
3
).
FIG. 3
is a cross-sectional view illustrating a typical structure of a conventional semiconductor package fabricated using a lead frame such as the conventional lead frame
10
′ of
FIG. 1
a
and a heat sink such as the conventional heat sink
5
′ of
FIG. 1
b
. In
FIG. 3
, elements respectively corresponding to those in
FIGS. 1
a
and
1
b
are denoted by the same reference numerals. As shown in
FIG. 3
, the semiconductor package, which is denoted by the reference numeral
1
′, includes a heat sink
5
′ having a relatively la
Kim Gi Jeong
Kim Seung Mo
Lee Jin An
Amkor Technology Inc.
Cruz Lourdes
Jackson, Jr. Jerome
Parsons James E.
Skjerven Morrill LLP
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