Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Reexamination Certificate
2001-06-29
2004-07-27
Ortiz, Angela (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
C264S102000, C264S272150, C264S272170
Reexamination Certificate
active
06767484
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transfer molding apparatus and a method of manufacturing semiconductor devices.
2. Related Art
In the manufacture of semiconductor devices, transfer molding apparatuses for encapsulating semiconductor devices mounted on lead frames are conventionally used. As shown in
FIG. 7
, the transfer molding apparatus comprises a transfer pot
10
into which solid thermosetting resin (tablets) is loaded, a plunger
12
for transferring the thermosetting resin
28
(hereafter referred to as the resin
28
. See
FIG. 8
) that has been fluidified in the transfer pot, a position sensor
14
for detecting the position of the plunger
12
, a top-half mold
16
a
fixed to a top platen
26
a
, a bottom-half mold
16
b
fixed to a bottom-half platen
26
b
, heaters
18
for heating the top-half and bottom-half molds
16
a
,
16
b
to a predetermined temperature, and a suction pump
24
for reducing the pressure in the cavities
20
by extracting the air from a chamber
30
where the top-half and bottom-half molds
16
a
,
16
b
are disposed.
When the top-half and bottom-half molds
16
a
,
16
b
are closed, two cavities
20
each for setting up a molding space for a plastic IC package, and runners
22
and gates
23
as resin supply paths leading to the cavities
20
are formed.
When the top-half and bottom-half molds
16
a
,
16
b
are closed, air-vent slots
25
are also formed at the outer end positions of the two cavities
20
opposite the gates
23
located at the inner ends thereof. When the chamber
30
is placed at reduced pressure by extracting air by a suction pump
24
, the air is sucked out from the runners
22
and the gates
23
through the air-vent slots
25
, so that the cavities
20
are placed at reduced pressure. The runners
22
guide the resin
28
into the cavities
20
through the gates
23
that are open to the corresponding cavities
20
.
Referring to
FIG. 8
, description will be made of a method of manufacturing semiconductor devices on a transfer molding apparatus structured as described above.
FIG. 8
shows only the principal portions for convenience of explanation. First of all, a semiconductor-device-mounted lead frame (not shown) is set in the bottom-half mold
16
b
, a resin tablet is loaded in the transfer pot
10
, and by lowering the top platen
26
a
, the top-half mold
16
a
and the bottom-half mold
16
b
are closed, so that a cavity
20
, for example, is formed as shown in FIG.
8
(
a
). At this point in time, the semiconductor device has been placed almost in the center of the cavity
20
. In addition, the pressure in the chamber
30
has been reduced to about 30 to 99 Pa by the suction pump
24
.
While the resin tablet charged in the transfer pot
10
is being melted by heating it to 160° to 190° C. with the heaters
18
, the resin is extruded from the transfer pot
10
by raising the plunger
12
. By this operation, the molten resin
28
is introduced into the runner
22
as shown in FIG.
8
(
b
).
By the increasing the forcing pressure from the plunger
12
, the resin
28
in the runner
22
is guided through the gate
23
into the cavity
20
as shown in FIG.
8
(
c
). As shown in FIG.
8
(
d
), when the resin
28
has been filled into the cavity
20
, the forcing pressure from the plunger
12
is stopped, and the resin
28
in the cavity
20
, the runner
22
, and the gate
23
is cured. After the resin
28
is cured sufficiently, the top platen
26
a
(see
FIG. 7
) is raised, and the semiconductor device with a lead frame in a package of resin
20
that hardened around the semiconductor element is ejected. Subsequently, the excess resin is removed and whittled down to shape, and the lead-frame portion is cut off and the outer leads are formed to thereby produce a semiconductor package. Subsequently, the excess resin is removed, the package is whittled down to shape, the frame portion of the lead frame is trimmed, and the outer leads are formed. Thus, a semiconductor device is produced.
In the transfer molding apparatus constructed as described, there are possibilities of an unfilled region (voids)
29
being formed in the top-cavity portion or the bottom-cavity portion of the mold due to a difference in resin-filling speed between the top-cavity portion and the bottom-cavity portion, which partition is made by the semiconductor element loaded in the cavity
20
. Voids are unwanted because they give rise to a warp or deformation in the package or decreases its strength or humidity resistance.
There have been countermeasures against the voids. One is to provide a suction port communicating with the cavity, and directly reduce the pressure in the cavity by the use of a suction pump to decrease the remaining air in the top-cavity portion or the bottom-cavity portion to prevent the occurrence of voids.
The other is to place the chamber
30
itself in a reduced-pressure atmosphere so that the remaining air in the top-cavity portion or the bottom-cavity portion should be extracted through the air-vent slot
25
and to thereby prevent the occurrence of voids.
However, in the transfer molding apparatus constructed as described above, because the resin passes through the gate of a smaller diameter than that of the runner when it enters a cavity, the resin is subjected to pressure at the gate, and the resin in compressed state is injected into the cavity. Therefore, if the cavity is at reduced pressure when a specified amount of resin is introduced into the cavity, there is a relatively large pressure difference between the pressure in the cavity and the pressure in the resin. A problem here is that when there is such a large pressure difference, the air bubbles in the resin expand notably, and remain as voids in the package.
Thermosetting resins have a characteristic that curing does not progress in proportion to the passage of time, but curing occurs after the viscosity decreases once. Therefore, with some kinds of thermosetting resins, the viscosity sometimes drops temporarily while the cavity is being filled with a molding compound. Also in this case, there is a problem that the air bubbles expand remarkably in the resin and remain as voids in the package.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above problems, and has as its object to provide a transfer molding apparatus and a method for manufacturing semiconductor devices, which are free of voids remaining in a resin when filled in the cavities.
To achieve the above object, the transfer molding apparatus according to the present invention comprises:
a top-half mold and a bottom-half mold for forming a cavity as a molding space for a package and a transfer pot as a loading space, communicating with the cavity, for resin to be injected into the cavity;
a plunger for forcing the resin out of the transfer pot into the cavity; and
a pressure adjuster for reducing the pressure in the cavity when a specified amount of resin has been injected into the cavity.
Because the pressure adjuster reduces the pressure in a cavity after a specified amount of resin has been injected into the cavity, the cavity is at normal pressure at a point in time when the supply of a specified amount of resin is finished and the pressure difference between the pressure in the cavity and the pressure in the resin is relatively small. Therefore, the air bubbles in the resin can be prevented from expanding remarkably.
Because the pressure adjuster reduces the pressure in a cavity when a specified amount of resin has been injected into the cavity, the remaining air in the unfilled region of the top cavity portion or the bottom cavity portion can be decreased, so that the voids can be reduced, which occur due to a difference in filing rate between the top cavity portion and the bottom cavity portion.
In the transfer molding apparatus described above, the top-half mold and the bottom-half mold form a plurality of interconnected cavities, and the pressure adjuster reduces the pressure of the cavities every time any one
Nishi Hiroyuki
Sugai Akira
Oki Electric Industry Co. Ltd.
Ortiz Angela
Volentine & Francos, PLLC
LandOfFree
Transfer molding method for manufacturing semiconductor devices does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Transfer molding method for manufacturing semiconductor devices, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Transfer molding method for manufacturing semiconductor devices will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3254210