Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With contact or lead
Reexamination Certificate
1998-07-30
2001-03-27
Williams, Alexander O. (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With contact or lead
C257S684000, C257S666000, C257S675000, C257S676000, C257S693000, C257S692000, C257S690000, C257S698000, C257S707000, C257S730000
Reexamination Certificate
active
06208023
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a radio frequency powered semiconductor device using a surface-mounting resin-molded package and to a lead frame for the same.
Conventionally, a radio frequency semiconductor device was often assembled using a ceramic package. In recent years, however, a plastic package, molded with a molding resin material, is used more often than a ceramic package in order to reduce costs.
Hereinafter, a conventional method for fabricating a radio frequency powered semiconductor device using a lead frame for a plastic package will be described with reference to FIGS.
9
(
a
) through
9
(
c
).
FIG.
9
(
a
) illustrates a planar structure during a bonding process step in the conventional method for fabricating a radio frequency powered semiconductor device. As shown in FIG.
9
(
a
), a semiconductor chip
101
incorporating a radio frequency integrated circuit is adhered to the center portion of a square die pad
102
with a silver paste member
103
. Herein, the direction along the longer sides of the die pad
102
is assumed to be X-axis direction and the direction along the shorter sides of the die pad
102
is assumed to be axis direction. A pair of grounding leads
104
are connected to both ends of the die pad
102
in the X-axis direction. A plurality of leads
105
, extending in the Y-axis direction and being spaced apart from each other in the X-axis direction, are disposed to above and below the die pad
102
and to be spaced apart from the respective longer sides of the die pad
102
in the Y-axis direction. A grounding pad
101
a
formed on the semiconductor chip
101
for grounding the semiconductor chip
101
is electrically connected to a grounding point formed on the die pad
102
via a grounding wire
106
.
FIG.
9
(
b
) is a plan view of a semiconductor device formed by performing a step of integrally encapsulating the respective inner ends of the semiconductor chip
101
, the die pad
102
, the grounding leads
104
and the leads
105
with a molding resin
107
and then a bending step of molding the respective leads in predetermined shapes. FIG.
9
(
c
) is a cross-sectional view thereof taken along the line
9
C—
9
C of FIG.
9
(
b
). As shown in FIG.
9
(
c
), the grounding leads
104
are connected to a grounding land
108
such as a mounting substrate
109
and grounded. The molding resin material used as a plastic molding resin includes thermosetting epoxy resins and fillers of silica.
In the field of radio frequency powered semiconductor devices in general, it is strongly demanded to improve the heat radiation property of the molding resin
107
(i.e., to suppress the heat resistance thereof) and shorten the grounding wire
106
in order to stably operate the radio frequency powered semiconductor devices over the entire frequency regions ranging from a DC (direct current) region up to a radio frequency region.
As shown in FIG.
9
(
a
), in the conventional radio frequency powered semiconductor device, the heat generated from the semiconductor chip
101
is conducted to the grounding land
108
(formed on the mounting substrate
109
as shown in FIG.
9
(
c
)) through the die pad
102
and the grounding leads
104
. However, in this device, the heat is conducted over a long distance from the semiconductor chip
101
to the grounding land
108
also functioning as an radiator for radiating the heat to the outside of the molding resin
107
. In addition, it is difficult to secure sufficiently large grounding areas between the grounding leads
104
and the grounding land
108
. Thus, this type of device cannot efficiently radiate the heat generated from the semiconductor chip
101
. Accordingly, in the case of using the semiconductor chip
101
as a power converter, thermal runaway is adversely caused in the semiconductor chip
101
because the heat generated from the semiconductor chip
101
is not radiated sufficiently. As a result, the chip
101
is broken down and the reliability thereof is very low in such a case.
In a small-sized surface-mounting package, not only radiation properties but also mechanical strength thereof are problems. For example, if the thickness of the molding resin
107
is partially reduced on the bottom, on which the surface-mounting package is mounted, for the purpose of improving the radiation properties thereof, then the encapsulating strength of the molding resin
107
is disadvantageously decreased. Consequently, the leads
105
and the die pad
102
might be unintentionally detached from the molding resin
107
.
Moreover, when the semiconductor chip
101
is mechanically mounted at (or die-bonded to) a predetermined position on the die pad
102
as shown in FIG.
9
(
a
), positional misalignment of about 0.1 mm to about 0.5 mm is likely to be caused between the predetermined position and the actually mounted position of the semiconductor chip
101
on the die pad
102
in each of the X- and Y-axis directions. If such positional misalignment is caused in mounting the semiconductor chip
101
, a mounting margin of about 0.5 mm to about 1 mm should be provided in the Y-axis direction for the grounding point
102
a
to be located with respect to the longer side of the semiconductor chip
101
when the bonding pad
101
a
on the semiconductor chip
101
is connected to the grounding point
102
a
on the die pad
102
via the grounding wire
106
. Thus, the length of the grounding wire
106
becomes longer by the mounting margin. Accordingly, in the case of operating the semiconductor chip
101
as a power converter over a wide frequency region ranging from DC to radio frequency, oscillation adversely results from the parasitic inductance of the grounding wire
106
and the chip
101
cannot be operated stably any more.
Furthermore, when the bonding pad
101
a
is connected to the grounding point
102
a
via the grounding wire
106
in the same way after the semiconductor chip
101
has been adhered at the predetermined position of the die pad
102
with an adhesive such as the silver paste member
103
, a certain distance should be provided between the longer side of the semiconductor chip
101
and the grounding point
102
a
on the die pad
102
, considering the expansion of the silver paste member
103
to the periphery of the semiconductor chip
101
. In such a case, the length of the grounding wire
106
also needs some margin.
Moreover, in the bending step, the grounding leads
104
and the leads
105
are appropriately bent such that the bottoms of the grounding leads
104
and the leads
105
are located at substantially the same level as that of the bottom of the molding resin
107
when the packaged semiconductor device is mounted onto the mounting substrate. In this bending step, the extended portion of any of the grounding leads
104
and the leads
105
should have a length of about 2 mm to about 15 mm from the corresponding side of the molding resin
107
, from which the lead
104
or
105
extends. Thus, since none of these leads
104
and
105
can have a shortened length, the mounting area of the semiconductor device cannot be reduced.
SUMMARY OF THE INVENTION
In view of these conventional problems, the present invention was made to accomplish the objects of stably operating a radio frequency powered semiconductor device over a wide frequency region ranging from a DC region to a radio frequency region and reducing the mounting area of the radio frequency powered semiconductor device.
In order to accomplish these objects, according to the present invention, at least part of the bottom of a die pad for mounting a semiconductor element thereon and at least part of the bottom of a lead are exposed on the bottom of a molding resin as a package and the exposed bottom part of the die pad is made substantially flush with the exposed bottom part of the lead on the bottom of the molding resin.
A first semiconductor device according to the present invention includes: a die pad; a semiconductor element mounted on the die pad; a first lead having an inner end connected to the d
Fujiwara Toshio
Muramatsu Kaoru
Nakayama Masao
Tara Katsushi
Yoshida Noboru
Matsushita Electronics Corporation
McDermott & Will & Emery
Williams Alexander O.
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