Flash-free mold structure for integrated circuit package

Details Flash-free mold structure for integrated circuit package Flash-free mold structure for integrated circuit package

2000-05-19

2001-09-18

Davis, Robert (Department: 1722)

Plastic article or earthenware shaping or treating: apparatus

Distinct means to feed, support or manipulate preform stock...

Opposed registering coacting female molds

C264S272170, C264S328900, C425S544000, C425S588000

Reexamination Certificate

active

06290481

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention:
This invention relates to mold structures, and more particularly, to a mold structure for use in the molding of an encapsulant for encapsulating a semiconductor chip.
2. Description of Related Art:
Molding process is an important step in IC packaging, in which a set of specially-shaped molding pieces are used for the molding of an encapsulant for encapsulating semi-conductor dies. In use, the molding pieces are attached to each other to define a cavity therewithin; and then, an encapsulating material, typically resin, can be filled into the cavity to form the intended encapsulant.
Conventionally, there are many various kinds of patented mold structures that can be used in the molding of encapsulants, such as the U.S. Pat. No. 5,971,734.
One drawback to the conventional mold structures, however, is that flash would easily occur at the junction between the two molding pieces. This is because that the junction between the two molding pieces would hardly reach the level of absolute airtightness, and consequently, a fissure would be left at the junction. During the molding process, flash occurs if the melted resin enters this fissure. This drawback is further illustratively depicted in the following with reference to
FIGs. 1A-1B
.
FIG. 1A
shows a schematic top view of the mold structure disclosed in the U.S. Pat. No. 5,971,734. As shown, this patented mold structure includes a bottom molding piece
10
and an upper molding piece
20
; and when these two molding pieces
10
,
20
are attached to each other, it defines a cull
11
, a runner
12
, a subrunner
13
, and a molding cavity
14
therewithin (for detailed description of these parts, please refer to the specification of U.S. Pat. No. 5,971,734). During molding process, melted resin is introduced into the cull
11
and which will then flow through the runner
12
and the subrunner
13
to be guided into the respective molding cavity
14
for the purpose of forming an encapsulant (not shown) in each molding cavity
14
.
However, as shown in
FIG. 1B
, the junction between the bottom molding piece
10
and the upper molding piece
20
would hardly reach the level of absolute airtightness; and consequently, a fissure
30
would be left in the junction. Although this fissure
30
is very small in dimension, it would nevertheless allow a small part of the melted resin used in the molding process to enter therein, thus causing undesired flash into the fissure
30
. As roughly illustrated in
FIG. 1A
, after the molding process is completed, flashed resin would be left around the rims of the cull
11
, the runner
12
, and the subrunner
13
(the flashed resin is indicated by the reference numeral
15
).
To remove the flashed resin, it is required to perform a cleaning process prior to the next round of molding process. However, this cleaning process would undesirably cause the removed resin to be scattered away, thus causing contamination to the nearby fabrication tools, making the removed resin easily attached to the molded encapsulants during the next round of molding process. This would degrade the IC packaging quality.
SUMMARY OF THE INVENTION
It is therefore an objective of this invention to provide a flash-free mold structure, which can help prevent flash during molding process.
It is another objective of this invention to provide a flash-free mold structure, which can help ensure the IC packaging quality.
It is still another objective of this invention to provide a flash-free mold structure, which can prevent the fabrication tools from being contaminated during molding process.
In accordance with the foregoing and other objectives, the invention proposes a flash-free mold structure. The flash-free mold structure of the invention includes: (a) a first molding piece having a junction side; and (b) a second molding piece having a junction side for coupling with the junction side of the first molding piece during molding process; the second molding piece being formed with a resin passage for an encapsulating material to flow therethrough during molding process. It is a characteristic feature of the invention that a cutaway portion is formed at the rim of the resin passage, which is dimensioned significantly smaller than the resin passage so as to allow the encapsulating material flowing into the cutaway proportion to accelerate the speed of absorbing the heat of the molding pieces and then make the capsulating material increased in viscosity; as a result, the flow speed of the encapsulating material is retarded, thereby preventing the encapsulating material from entering the fissure between the first molding piece and the second molding piece during the molding process.
The foregoing flash-free mold structure of the invention can help prevent flash from occurring at the rims of the cull, the runner, and the subrunner defined by a first molding piece and a second molding piece, so that IC packaging quality can be assured and fabrication tools can be prevented from contamination. The invention is therefore more advantageous to use than the prior art.


REFERENCES:
patent: 4126292 (1978-11-01), Saeki et al.
patent: 4779835 (1988-10-01), Fukushima et al.
patent: 5556647 (1996-09-01), Abe et al.
patent: 5928595 (1999-07-01), Knapp et al.
patent: 5971734 (1999-10-01), Moon
patent: 63-10533-A (1988-01-01), None
patent: 1-315148-A (1989-12-01), None

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