Active solid-state devices (e.g. – transistors – solid-state diode – Lead frame – With dam or vent for encapsulant
Reexamination Certificate
2003-03-13
2004-09-14
Cao, Phat X. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Lead frame
With dam or vent for encapsulant
C257S787000
Reexamination Certificate
active
06791167
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Technical Field of the Invention
The present invention relates to a resin-molded device having a resin package holding together a plurality of electronic elements, lead frames (lead members), and metal blocks for radiating heat, and also relates to a manufacturing apparatus of the resin-molded device.
2) Description of Related Arts
An example of the resin-molded electronic devices is a power semiconductor device commonly used as a switching inverter device incorporated in an electronic appliance such as an air conditioner and a washing machine. As illustrated in
FIG. 22
, the power semiconductor device includes, in general, a plurality of lead frames
101
, a power element
102
, a metal block
103
serving as a heat sink for radiating heat. The power semiconductor device also includes a resin package
104
holding together those above-mentioned components.
The lead frame
101
includes a die pad portion
105
and an inner lead portion
106
. The power element
102
is bonded to the upper surface of the die pad portion
106
via solder
107
. Also, the power element
102
is electrically connected to the inner lead portion
106
via an aluminum wire
108
. A metal block
103
has a plateau portion
109
formed substantially in the middle region of the metal block
102
. The plateau portion
109
is arranged beneath the lower surface of the lead frame
101
so as to oppose to power element
102
and spaced from the lower surface of the lead frame
101
with a predetermined gap. A portion of the resin package
104
sandwiched between the plateau portion
109
of the metal block
103
and the lead frame
101
is referred to as a insulating resin layer
110
. The power element
102
, the lead frames
101
, and the metal block
103
are together held in the resin package
104
, while the bottom surface of the metal block
103
opposing to the top surface adjacent to the lead frame
101
is uncovered or exposed. Although not shown, an external radiator is secured on the exposed bottom surface of the metal block
103
.
In such a conventional power semiconductor device, heat generated by the power element
102
is radiated through the lead frame
101
, the insulating resin layer
110
, and the metal block
103
to the external radiator. The metal block
103
is made of metal such as aluminum and copper having thermal conductivity of 200 W/m·K and 390 W/m·K, respectively. Since the lead frame
101
is made of metal such as copper, it has thermal conductivity similar to one of the metal block
103
. Meanwhile, the insulating resin layer
110
has thermal conductivity of 1-3 W/m·K, which is approximately one-hundredth ({fraction (1/100)}) of those of the lead frame
101
and the metal block
103
. Therefore, the insulating resin layer
110
has a main controlling factor to the heat conductivity of the power semiconductor device. In other words, an internal heat resistance of the conventional power semiconductor device depends mostly upon the insulating resin layer
110
.
The heat resistance or heat radiating performance of a material is determined, in general, based upon a heat radiating thickness, a heat radiating area, and thermal conductivity of the material. Thus, the internal heat resistance of the power semiconductor device may be reduced by thinning the insulating resin layer
110
. However, since the dielectric breakdown voltage of the insulating resin layer
110
is required more than several thousands volts, it is known that it can not be thinner than approximately 0.3 mm. This limits improvement of the heat resistance by thinning the insulating resin layer
110
.
Thus, in order to further improve the heat radiating performance of the power semiconductor device, the metal block serving as a heat spreader has been proposed, which has a wider surface extending towards the upper stream, thereby increasing the heat radiating surface. In the power semiconductor device including a plurality of power elements, it should also includes a plurality of the metal blocks, which have to be electrically isolated from one another for the necessity of electrical isolation of the power elements from each other. Nonetheless, in a molding step of the resin package of the conventional power semiconductor device including several metal blocks, no special care has been taken to fill up the channels defined between the adjacent metal blocks with resin in a reliable manner. Thus, the conventional power semiconductor device including several metal blocks has several problems to be addressed as described hereinafter.
Referring to
FIGS. 23
to
26
, the above-mentioned problems will be described herein in detail.
FIG. 23
is a top plan view of the conventional semiconductor device before molding the resin package
104
. As described in JPA 2000-138343, fluid resin is injected from a plurality of resin runners
111
of a molding die through the corresponding resin inlet of the semiconductor device so as to form the resin package
104
.
FIG. 24
is a bottom plane view of the conventional semiconductor device schematically illustrating the plurality of the metal blocks
103
and the resin runners
111
while fluid resin is being injected from the resin runners
111
during the resin package molding step. A plurality of channels
112
a
to
112
c
are defined between the metal blocks
103
adjacent to each other, and the fluid resin reach into them at a different timing, as shown in FIG.
24
. Thus, the front-running resin reached in the channels
112
b
,
112
c
pushes the metal blocks
103
towards the channel
112
a
of the behind-running resin due to the resin injection pressure. The first problem of the conventional semiconductor device is that the metal blocks
103
are shifted so that the channels
112
b
,
112
c
of the front-running resin are expanded and the channel
112
a
of the behind-running resin is pinched.
As above, the fluid resin is filled in the channel
112
a
some time after filled in the channels
112
b
,
112
c
. Thus, the channels
112
b
,
112
c
become wider and the channel
112
a
is narrower than that before the molding step. Since the fluid resin is less likely to reach the narrower channel
112
a
, completion to fill in the narrower channel
112
a
is more delayed in comparison with the other channels
112
b
,
112
c
. Eventually, the adjacent metal blocks
103
sandwiching the narrower channel
112
a
may contact with each other so that the electric isolation (insulation) therebetween can not be secured, thereby resulting in the fatal defect of the semiconductor device. Also, in case where the adjacent metal blocks
103
sandwiching the narrower channel
112
a
have the substantial amount of stress applied thereto, the bonding layers between the lead frames and the metal blocks may have a critical damage.
Secondly, even where contact between the metal blocks are avoided, the fluid resin is less likely injected in the narrower channel
112
a
so that the resin-unfilled hollow portions are defined therein. This may also cause insufficiency of electrical isolation between the adjacent metal blocks, resulting in the fatal defect of the semiconductor device.
Thirdly, even where shift of the metal blocks is prevented, if air is trapped between the metal blocks and not evacuated, the remaining air forms so-called a “void” so that electrical isolation cannot be secured between the metal blocks. Thus, the usage of the conventional resin runners cause the resin injection timing for each of the channels different from one another, thus, the fluid resin turns around, thereby remaining air between the metal blocks, which is referred to as the void.
Also,
FIG. 25
is a schematic bottom view of the conventional semiconductor device similar to
FIG. 24
, but after the channels are completely filled up with the fluid resin. In this drawing, the running directions of the fluid resin are illustrated by the arrows. As above, the fluid resin is delayed to reach the channel
112
a
, the channel
112
a
is filled up not only with the fluid resin directly from the
Hayashi Ken-ichi
Kawafuji Hisashi
Shikano Taketoshi
Tajiri Mitsugu
Cao Phat X.
Mitsubishi Denki & Kabushiki Kaisha
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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