Coating apparatus – Projection or spray type – With mask or stencil
Reexamination Certificate
1998-12-02
2001-05-22
Osele, Mark A. (Department: 1734)
Coating apparatus
Projection or spray type
With mask or stencil
C118S505000, C156S247000, C156S280000, C156S390000
Reexamination Certificate
active
06235113
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for manufacturing electrical device packages. More particularly, the invention relates to an apparatus for dispensing a liquid encapsulant to encapsulate a semiconductor chip that is attached to a tape.
2. Description of the Related Art
In a typical process for fabricating a plastic semiconductor package, a semiconductor chip after being attached and wire-boned to a lead frame is encapsulated with a molding compound by transfermolding. However, other packaging process can employ different encapsulation methods. For example, a micro ball grid array (&mgr;BGA) package, which includes a tape instead of a leadframe of the plastic package, is encapsulated by a liquid encapsulant coating process.
The tape typically has windows exposing parts of the beam leads for connection to the semiconductor chip. A fabrication method, which employs the tape with windows, is described below. A typical assembly process for assembling a &mgr;BGA package begins with providing a tape made of, for example, polyimide, and having windows and metal beam leads across the windows. A semiconductor chip is attached to the tape using an adhesive, and the beam leads are connected to bonding pads on the chip through the windows. Then the windows are filled with an encapsulant to protect the chip and the electrical connections.
FIG. 1
is a schematic diagram showing a conventional reel-to-reel dispensing apparatus
100
for filling the windows with an encapsulant. Apparatus
100
includes: a dispensing station
40
for coating a liquid encapsulant on a tape
10
to which a semiconductor chips
11
are attached; a reel-to-reel handling track
60
for moving tape
10
at dispensing station
40
; a tape feed station
20
for feeding tape
10
; and a tape take-up station
70
for unloading tape
10
from dispensing station
40
after the coating process. The structure of apparatus
100
will be explained based on the order of the movement of tape
10
.
A tape feed reel
22
of tape
10
is loaded into tape feed station
20
. A protection tape
30
which is wound with tape
10
in reel
22
to protect chips
11
is removed from the reel as tape
10
is supplied to dispensing station
40
. When removed, protection tape
30
is wound to a protection tape take-up reel
26
, while tape
10
moves to a support plate
50
in dispensing station
40
. In dispensing station
40
, a syringe
42
above support plate
50
dispenses a liquid encapsulant through a needle
44
to an upper surface
12
(
FIG. 2
) of tape
10
, which includes chips
11
. An actuator
46
coupled to syringe
42
controls the movement of syringe
42
. Tape
10
is then transferred to tape take-up station
70
which winds tape
10
on a reel
72
. At the same time, a protection tape
80
for protecting chips
11
on tape
10
is wound as an interleaf. Reel-to-reel handling track
60
controls the movement of tape
10
from tape feed station
20
to tape take-up station
70
.
Dispensing of the liquid encapsulant on the top of tape
10
is further described with reference to FIG.
2
. In
FIG. 2
, chip
11
is attached to tape
10
by an elastomer adhesive
18
, and beam leads
16
electrically connect chip
11
to tape
10
at windows
14
. For encapsulation, tape
10
is placed on support plate
50
. A suction port
52
connected to a vacuum pump (not shown) holds tape
10
to support table
50
.
Then, syringe
42
(
FIG. 1
) dispenses a liquid encapsulant
47
along periphery of chip
11
to protect the electrical connection area between chip
11
and beam leads
16
. When dispensed, liquid encapsulant
47
fills windows
14
(
47
b
), covers the periphery of chip
11
(
47
a
), and undesirably runs out through a gap between tape
10
and support table
50
(
47
c
). This may eventually contaminate support plate
50
and adversely affect dispensing encapsulant on following tapes.
To stop the encapsulant from running into the gap, several methods have been proposed. Two representative examples are depicted in FIG.
3
and FIG.
4
.
FIG. 3
shows a tape
10
covered with a photo solder resist (PSR) film
90
, which can be removed by etching after dispensing, and
FIG. 4
shows a piece of tape
10
temporarily held on a magazine substrate
94
.
With reference to
FIG. 3
, tape
10
having windows
14
and sprocket holes
19
has PSR film
90
formed on the bottom surface of tape
10
before the encapsulant coating step. PSR film
90
can prevent the liquid encapsulant from running onto support table
50
(FIG.
2
). After the encapsulant is cured, etching can remove PSR film
90
.
With reference to
FIG. 4
, tape
10
, which is cut to size, is placed on a magazine substrate
94
. Magazine substrate
94
has a surrounding lip that prevents the liquid encapsulant from running onto support table
50
(FIG.
2
).
However, the method of
FIG. 3
requires costly processing steps including forming PSR film
90
on the bottom of tape
10
before the encapsulant coating step, and partly removing PSR film
90
to expose windows
14
and solder ball pads (not shown). The method of
FIG. 4
reduces manufacturing efficiency by requiring an addition of tape cutting step, and because a batch-type process using tape strips is less efficient than a reel-to-reel process.
SUMMARY OF THE INVENTION
According to an aspect of the present invention an apparatus for dispensing a liquid encapsulant to encapsulate a semiconductor package includes: a dispensing station for dispensing the liquid encapsulant to a tape; a tape transfer station for transferring the tape to the dispensing station; a cover film attaching station for attaching a cover film to the bottom of the tape before transferring the tape to the dispensing station; and a cover film detaching station for separating the cover film from the tape after dispensing of the liquid encapsulant. The cover film prevents the liquid encapsulant from flowing into a gap between the tape and a stage with which the tape is in contact.
The cover film attaching station includes an attaching means which moves vertically with respect to the cover film. When the cover film is under the tape, the attaching means flattens the cover film and the tape, and uses a press roller to apply pressure to the cover film and attach the cover film to the tape. The cover film detaching station includes a separator which helps the cover film separate from the tape so that an excessive force is not applied to the cover film or the tape.
According to another aspect of the present invention, a method for dispensing a liquid encapsulant on the top of a tape of a semiconductor package employs a removable cover film attached to the tape to prevent leakage of encapsulant.
REFERENCES:
patent: 2056274 (1936-10-01), Holdsworth
patent: 2590557 (1952-03-01), Melsheimer
patent: 3635730 (1972-01-01), Sweitzer
Heid David W.
Osele Mark A.
Samsung Electronics Co,. Ltd.
Skjerven Morrill & MacPherson LLP
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