Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1997-02-06
2001-09-04
Young, Lee (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S850000, C228S180500, C228S004500
Reexamination Certificate
active
06282780
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bump forming method for forming a bump on the electrode of a workpiece.
2. Description of the Related Art
A method using the wire bonding technique is known as a method for forming a bump (protruded electrode) on the electrode of a workpiece such as an IC chip. A conventional bump forming method is described below.
FIGS. 19A
,
19
B,
19
C, and
19
D, and
FIG. 20
are illustrations showing a conventional bump forming method. As shown in
FIGS. 19A
, a ball
4
is formed at the bottom end of a wire
2
extended from a capillary tool
1
by making a torch
3
approach to the bottom end of the wire
2
and generating spark therebetween. Symbol
5
denotes a first clamper located above the capillary tool
1
to hold the wire
2
, and
6
denotes a second clamper located above the first clamper
5
to apply a tension to the wire
2
.
Then, as shown in
FIG. 19B
, the ball
4
is pressed against the electrode of a workpiece
7
by lowering the capillary tool
1
. Symbol
8
denotes a base on which the workpiece
7
is mounted. Then, as shown in
FIG. 19C
, the wire
2
(also referred to as tail) is conducted and extended from the bottom end of the capillary tool
1
by a length necessary to form the next ball by slightly raising the capillary tool
1
and thereafter, the wire
2
is securely held by the first clamper
5
. Then, as shown in
FIG. 19D
, the first clamper
5
and the capillary tool
1
are raised while holding the wire
2
to thereby cut the wire
2
immediately above the ball
4
and thus, a series of operations are completed and the bump
4
is formed on the electrode of the workpiece
7
.
FIG. 20
shows an enlarged state in which the ball
4
is bonded to the electrode of the workpiece
7
and then the wire
2
is cut off while holding the wire
2
by the first clamper
5
and raising the wire
2
in the step shown in FIG.
19
C. Symbol “A” denotes a cutting line and l
a
denotes the central hole of the capillary tool
1
through which the wire
2
is inserted. By raising the wire
2
, the wire
2
is forcibly cut at the cutting line “a” immediately above the ball
4
. In this case, a large tensile stress is produced on the joint surface between the ball (bump)
4
and the electrode
7
a
of the workpiece
7
. Therefore, there are problems that the ball (bump)
4
is easily removed from the electrode
7
a
and the joint surface between the ball (bump)
4
and the electrode
7
a
is easily damaged. In
FIG. 20
, a black portion at the bottom of the ball
4
is a damaged portion.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a bump forming apparatus and its forming method making it possible to firmly bond the bottom end of a wire to the electrode of a workpiece and prevent the joint surface between the ball (bump) and the electrode from damaging.
Therefore, a bump forming apparatus of the present invention includes a capillary tool for inserting a wire into the central hole, a bonding arm for holding the capillary tool at the front end, a vertical motion mechanism for vertically moving the capillary tool through the bonding arm, a first clamper provided above the capillary tool and capable of holding the wire, a second clamper provided with a clamp portion provided above the capillary tool, vertically moving integrally with the capillary tool, and holding the wire so as to be vertically slidable, a torch for forming a ball by sparks at the bottom end of the wire conducted and extended downward from the central hole of the capillary tool, and interval change means for changing the intervals between the second clamper and the capillary tool.
Moreover, a bump forming method of the present invention includes the step of making a torch approach to the bottom end of a wire inserted into the central hole of a capillary tool and extended downward and generating sparks between the bottom end of the wire and the torch to form a ball at the bottom end of the wire, the step of separating the ball from the wire by lowering the capillary tool relatively to the wire, and the step of further lowering the capillary tool and pressing the ball against the electrode of a workpiece to bond the ball onto the electrode.
Moreover, a bump forming method of the present invention includes the step of making a torch approach to the bottom end of a wire inserted into the central hole of a capillary tool and extended downward and generating sparks between the bottom end of the wire and the torch to form a ball at the bottom end of the wire, the step of making the ball approach the electrode of a workpiece by lowering the capillary tool, the step of holding the wire by a clamper so that the wire does not lower and simultaneously lowering the capillary to separate the ball from the wire, the step of further lowering the capillary tool and pressing the ball against the electrode of the workpiece to bond the ball onto the electrode, and the step of raising the capillary tool and taking out the bottom end of the wire from the bottom end of the capillary tool.
Furthermore, a bump forming method of the present invention includes the step of forming a ball at the bottom end of a wire inserted into the central hole of a capillary tool and extended downward, the step of holding the wire by a clamper so that the wire does not lower and simultaneously lowering the capillary tool to separate the ball from the wire, the step of further lowering the capillary tool and pressing the ball against the electrode of a workpiece to bond the ball onto the electrode, and the step of pressing the upside of the ball bonded onto the electrode of the workpiece by a pressing jig.
REFERENCES:
patent: 3357090 (1967-12-01), Tiffany
patent: 4860433 (1989-08-01), Miura
patent: 4955523 (1990-09-01), Calomagno et al.
patent: 5014419 (1991-05-01), Cray et al.
patent: 5438020 (1995-08-01), Grancher et al.
patent: 5616520 (1997-04-01), Nishiuma et al.
Haji Hiroshi
Takata Tsuyoshi
Waki Eisuke
Chang Rick Kiltae
Matsushita Electric - Industrial Co., Ltd.
Stevens Davis Miller & Mosher LLP
Young Lee
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