Plastic and nonmetallic article shaping or treating: processes – With step of cleaning – polishing – or preconditioning...
Reexamination Certificate
1997-06-09
2001-03-13
Ortiz, Angela (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With step of cleaning, polishing, or preconditioning...
C264S272140, C264S272170, C264S328400
Reexamination Certificate
active
06200504
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an apparatus for encapsulating with plastic lead frame that carries at least one chip, comprising mutually movable mould halves which in the closed position bound a mould cavity for receiving a lead frame, a feed runner connecting onto the mould cavity for supplying encapsulating material and a plunger-cylinder connected onto this feed runner for carrying up encapsulating material under pressure. Such an apparatus is known from the European patent application 89.203003.2.
The problem with apparatus of this type is that despite a close fitting of the plunger in the cylinder there is the danger of liquid encapsulating material running along the wall of the plunger. The cylinder wall is hereby fouled, which results in interruptions in the encapsulating process.
SUMMARY OF THE INVENTION
The invention has the object of providing a solution to this problem. This is achieved according to the invention in that at a distance from the head end of the plunger a peripheral groove is arranged which is connected to the head end by means of at least one flow channel.
With the steps according to the invention the following is achieved. When a production stroke is performed and a pellet-shaped piece of encapsulating material is placed on the plunger head, which material becomes fluid through exerting of pressure and under the influence of heat, the encapsulating material will reach and fill the peripheral groove through the flow channels. The filled groove then serves as sealant of the plunger relative to the inner wall of the cylinder. At the end of the production stroke the plunger moves outside the upper edge of the cylinder. During the return movement the outer layer of the groove will be scraped off by the scraping edge of the cylinder. During a subsequent production stroke encapsulating material will be able to move through the clearance between the plunger and the inner wall of the cylinder and once again replenish the scraped-off outer layer of the encapsulating material in the groove.
A self-regulating sealing system is thus obtained.
The flow channel is preferably of swallowtail shape in order to ensure securing of the cured quantity of encapsulating material into the groove.
REFERENCES:
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patent: 6-21121 (1994-01-01), None
patent: WO 93/11925 (1993-06-01), None
Fico B.V.
Limbach & Limbach L.L.P.
Ortiz Angela
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