Molded ball grid array package mold die

Details Molded ball grid array package mold die Molded ball grid array package mold die

1999-02-16

2001-02-13

Nelms, David (Department: 2818)

Semiconductor device manufacturing: process

Packaging or treatment of packaged semiconductor

C257S737000

Reexamination Certificate

active

06187612

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of forming a ball grid array (BGA) package.
2. Brief Description of the Prior Art
Molded ball grid array (BGA) packages are fabricated in accordance with the prior art by attaching one or more balls to a lead frame and placing the lead frame with ball attached into a mold having a depression in the lower mold die for receiving the ball and a depending finger in the upper mold die for each ball to force the associated ball into and against the depression in the lower die. The mold material is then injected into the mold to encase the lead frame. A problem that arises is that the mold material tends to cover a major portion and possibly all of the ball, thereby requiring that additional work be performed on the molded package to remove mold material from the ball. This is generally accomplished by an additional abrading process step which is both costly and time consuming and can lead to diminished yield.
SUMMARY OF THE INVENTION
In accordance with the present invention, the above described problem inherent in the prior art is minimized if not eliminated.
Briefly, there is provided an arrangement the same as in the prior art with an additional deformable plastic layer is disposed against the lower mold die inner surface including the cavity for reception of the ball and, optionally, against the upper mold die inner surface. The plastic film will have the property of being non-adherable to the die or the mold compound. Such a plastic film can be fabricated, for example, from ethylene fluorinated copolymer or any high temperature film with from about 100 to about 450 percent elongation. The plastic film is generally on a roll and indexed to be fed to the die cavity in an appropriate length for each molding operation with the used plastic film then preferably being taken up on a second roll downstream at which time the plastic film is separated from the ball and molding compound. The result is that, when the mold is closed and the upper and lower mold dies come together, the depending finger will force the ball against the deformable plastic on the lower mold die. This causes the ball to be pushed into the film and cause the film to extrude, thereby filling up an additional portion of the cavity around the lower portion of the ball and possibly all of the cavity. Accordingly, when the mold compound is injected into the mold cavity, such mold compound is prevented from movement under the ball and merely fills the cavity to the sides of the ball. When the package is then removed from the die cavity, the plastic film is merely removed as noted above with the ball surface being free of flash.


REFERENCES:
patent: 5293072 (1994-03-01), Tsuji et al.

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