Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With contact or lead
Reexamination Certificate
2000-07-31
2003-05-13
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With contact or lead
C257S666000, C257S676000
Reexamination Certificate
active
06563209
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lead frame for use in a semiconductor device.
2. Description of the Background Art
Hitherto, it has been popular to use a QFP (Quad Flat Package) type semiconductor device in which external leads are arranged on four sides of a semiconductor device using a lead frame as a wiring base member. Recently, under the background of high density integration of semiconductor chips, multiple pins are arranged in the semiconductor device, and instead of the QFP type semiconductor device, a ball grid array (Ball Grid Array, hereinafter referred to as BGA) type semiconductor device in which external leads are arranged over a surface, and a non lead (Quad Non Lead Package, hereinafter referred to as QFN) type semiconductor device have been increasingly used. Generally, in the BGA type semiconductor device, a printed circuit board is popularly used as a wiring base member. However, in such a conventional BGA type semiconductor device, a wiring line is connected by way of a through hole, which is a high-priced structure. Therefore, recently a BGA type semiconductor device and a QFN type semiconductor device using a low-priced lead frame as a wiring base member have been put into practical use.
A semiconductor device using a conventional lead frame a wiring base member is hereinafter described with reference to the accompanying drawings.
FIG. 9A
is a sectional view showing a construction of a conventional BGA type semiconductor device disclosed in the Japanese Laid-Open Patent Publication (unexamined) No. Hei. 11-74404, and
FIG. 9B
is a bottom view of the semiconductor device shown in FIG.
9
A.
FIG. 10A
is a plan view showing a lead frame used in the conventional BGA type semiconductor device and arranged in a single line.
FIG. 10B
is a sectional view taken along the line Xb—Xb indicated by the arrows in FIG.
10
A.
FIG. 10C
is a sectional view taken along the line Xc—Xc indicated by the arrows in FIG.
10
A.
In
FIGS. 9A
,
9
B,
10
A,
10
B and
10
C, the conventional BGA type semiconductor device uses a lead frame
50
as a wiring base member, and a semiconductor chip
1
provided with a pad electrode is mounted on a die pad
2
with a junction material
3
. The semiconductor device has a soldering ball mounting portion (hereinafter referred to as external electrode portion)
4
. A lead electrode
5
of which an inside end portion is arranged proximate the die pad
2
and a pad electrode of the semiconductor chip
1
are connected to each other through a connecting lead
6
and sealed with a resin layer
7
. Portions
4
a
and
4
b
continued underneath the lead electrode
5
are made thin by etching, except the external electrode portion
4
. Accordingly, the die pad
2
, the external electrode portion
4
and a suspension lead
8
for supporting the die pad
2
are exposed on the same surface as the under surface of the resin layer
7
. A soldering ball
9
is mounted on the external electrode portion
4
, and an end of the lead electrode
5
and that of the suspension lead
8
are finally cut along the resin seal line
7
a.
A manufacturing method is hereinafter described with reference to
FIGS. 9
to
11
C.
FIGS. 11A
,
11
B and
11
C are explanatory views showing a manufacturing method of the conventional BGA type semiconductor device using a conventional type lead frame as a wiring base member.
FIG. 11A
is a sectional view of the lead frame shown in FIG.
10
C.
FIG. 11B
is a sectional view showing molds applied at the time of sealing with the resin layer.
FIG. 11C
is a sectional view showing an assembling step before mounting the soldering ball has completed.
First, the lead frame
50
shown in
FIGS. 10A
,
10
B and
10
C is manufactured. More specifically, after forming a resist film not shown on the upper surface
50
a
and the under surface
50
b
of the lead frame
50
and patterning it as shown in
FIG. 10A
, it is etched from the upper surface
50
a
and the under surface
50
b
. Thus, the die pad
2
, the external electrode portion
4
, the lead electrode
5
, the suspension lead
8
and a dam bar
50
c
are formed and continue one another across openings
50
d
and
50
e
. Then, after forming a resist film (not shown) on to the under surface
50
b
side of the lead frame
50
, except the portions
4
a
and
4
b
on the underside of the lead electrode
5
, the portions
4
a
and
4
b
are formed by half etching.
Subsequently, the semiconductor chip
1
provided with the pad electrode is mounted on the die pad
2
by applying the junction material
3
. The pad electrode of the semiconductor chip
1
and the inside end of the lead electrode
5
are then connected through the connection lead
6
. Then, as shown in
FIG. 11B
, after mounting a lower mold
10
in contact with the die pad
2
and the external electrode portion
4
, an upper mold
11
is positioned to the resin seal line
7
A and mounted on the upper surface of the lead frame
50
. After tightening the two molds
10
and
11
, the semiconductor chip
1
, the die pad
2
, the lead electrode
5
and the connecting lead
6
are sealed with the seal resin layer
7
by transfer molding. Thereafter, when removing the upper mold
11
and the lower mold
10
, a non lead type semiconductor device, before mounting the soldering ball
9
, is obtained, as shown in FIG.
11
C.
Then, by applying a soldering paste to the external electrode portion
4
, the soldering ball
9
is mounted on the external electrode portion
4
. When the lead electrode
5
protruding from the resin sealing line
7
a
, and the seal resin layer
7
gets into the underside portions
4
a
and
4
b
of the lead electrode
5
that is thin, are cut along the resin seal line
7
a
with a cutter, the conventional BGA type semiconductor device shown in
FIGS. 9A and 9B
is obtained.
In the mentioned semiconductor device using the conventional lead frame as the wiring base member, since the die pad
2
, the external electrode portion
4
, the lead electrode
5
, the suspension lead
8
and dam bar
50
c
are continuous across the openings
50
d
and
50
e
, when sealed with the seal resin layer
7
after mounting the two molds
10
and
11
, the molten resin having a low viscosity is formed also in the opening portion
50
d
. As a result, there has been a problem that the resin molten intrudes into a small space between contact surfaces, where the die pad
2
, the external electrode portion
4
, the suspension lead
8
are in contact with the lower mold
10
, and comes to form a thin resin film (hereinafter referred to as thin burr).
It is certainly possible to prevent the thin burr formed between the external electrode portion
4
and the lower mold
10
if contact pressure between the external electrode portion
4
and the lower mold
10
is large. However, the lead electrode
5
is thin and supported like a cantilever at a part held between the lower mold
10
and the upper mold
11
at the position of the resin seal line
7
a
. Therefore, if the external electrode portion
4
is pressed by the lower mold
10
, the lead electrode
5
is deformed by the pressure. As a result, it has been heretofore impossible to secure a contact pressure capable of preventing the formation of the thin burr between the external electrode portion
4
and the lower mold
10
.
The formation of the thin burr varies depending on the degree of roughness in surface finishing (hereinafter referred to as surface roughness) of the contact surface where the die pad
2
and the external electrode portion
4
are in contact with the lower mold
10
. Generally, the thin burr does not adhere to any die or mold having a good surface roughness, but adheres to the die pad
2
, the external electrode portion
4
, etc. having poor surface roughness. Therefore, it is necessary to remove the thin burr adhered, for example, to the external electrode portion
4
. To remove the thin burr, hydraulic pressure trimming, chemical trimming, chemical and hydraulic pressure trimming, etc. are performed,
Chaudhuri Olik
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
Nguyen DiLinh
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