Metal fusion bonding – Process – Plural joints
Reexamination Certificate
1999-06-25
2001-11-13
Dunn, Tom (Department: 1725)
Metal fusion bonding
Process
Plural joints
C228S004500, C228S179100
Reexamination Certificate
active
06315190
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wire bonding method in which a first bonding point and a second bonding point are connected by a wire, and more particularly to a wire loop formation method in wire bonding.
2. Prior Art
As seen from
FIG. 3
, in a semiconductor device assembly process, a pad
2
a
(first bonding point) on a semiconductor chip
2
mounted on a lead frame
1
and a lead
1
a
(second bonding point) on the lead frame
1
are connected by a wire
3
. The connected wire loop having the shape as shown in
FIG. 3
is called a trapezoidal loop. Wire loop formation methods of this type is disclosed, for example, in Japanese Patent Application Laid-Open (Kokai) Nos. H4-318943 and H7-176558.
The trapezoidal loop shown in
FIG. 3
is formed by the process shown in FIG.
4
.
In step (a), with a clamper (not shown) which holds the wire
3
opened, the capillary
4
is lowered, so that a ball formed on the tip end of the wire is bonded to the first bonding point A, after which the capillary
4
is raised in substantially vertical direction to point B, and the wire
3
is delivered. Next, in step (b), the capillary
4
is caused to move horizontally to point C in the opposite direction from the second bonding point G. Generally, such movement of the capillary
4
in the opposite direction from the second bonding point G is called a “reverse operation”. As a result of the reverse operation, the wire
3
assumes a shape that is inclined from point A to point C, and a kink
3
a
is formed in a portion of the wire
3
. The wire
3
delivered in this process from point A to point C forms the neck height part
31
shown in FIG.
3
.
Thereafter, in step (c) in
FIG. 4
, the capillary
4
is raised in substantially vertical direction to point D, and the wire
3
is delivered. Afterward, in step (d), the capillary
4
is again caused to move horizontally to point E in the opposite direction from the second bonding point G. In other words, a second reverse operation is performed. As a result, the wire
3
assumes a shape that is inclined from point C to point E, and another kink
3
b is formed in a portion of the wire
3
. This wire
3
delivered from point C to point E forms the trapezoidal length part
32
shown in FIG.
3
.
Next, in step (e), the capillary
4
is raised in substantially vertical direction to point F while the wire
3
is delivered. The amount of wire
3
delivered in this case forms the inclined portion
33
shown in FIG.
3
. Afterward, the clamper (not shown) is closed. When the clamper is closed, no wire
3
is delivered even of the capillary
4
is subsequently moved. Then, in steps (f) and (g), the capillary
4
is positioned at the second bonding point G by being caused to perform a circular-arc motion or by being lowered after being caused to perform a circular-arc motion, and the wire
3
is bonded to the second bonding point G.
In the trapezoidal loop formation process shown in
FIG. 4
, the first reverse operation in step (b) is performed with the capillary
4
in a position that is close to the height of the first bonding point A. Accordingly, a comparatively strong kink
3
a
can easily be formed. However, the second reverse operation in step (d) is performed with the capillary
4
in a high position away from the first bonding point A. Accordingly, the kink
3
b
is difficult to form and is unstable. As a result, the area of the kink
3
b
shown in
FIG. 3
is unstable, the shape retention strength of the wire loop is weak, and the height of the kink
3
b
is not aligned with the height of the kink
3
a
, forming an end-raised or end-lowered loop. Furthermore, if the shape retention strength of the portion in the vicinity of the kink
3
b
is weak, the bonded wire bends when pressure from the outside is applied to the wire. For example, wire bending tends to occur as a result of external forces such as shocks caused by capillary contact or ultrasonic oscillation during bonding to the second bonding point G, vibration of the wire
3
, or mold flow caused by injection of the molding material during molding.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to solve the problem of trapezoidal loops, and the main object of the present invention is to provide a wire bonding method which forms a stable wire loop shape and a wire loop shape which has a high shape retention strength.
The above object is accomplished by a set of unique steps of the present invention taken for a wire bonding method in which a first bonding point and a second bonding point are connected by a wire that passes through a capillary; and the present invention involves: a step in which the tip end of the wire is connected to the first bonding point; a step in which the capillary is raised and a reverse operation is performed so that the capillary is caused to move in the opposite direction from the second bonding point; a step in which the capillary is raised obliquely upward toward the second bonding point and then further raised; a step in which a reverse operation is performed so that the capillary is caused to move in the opposite direction from the second bonding point; and a step in which the capillary is raised and then caused to move toward the second bonding point, and the wire is connected to the second bonding point.
The above object is accomplished by another set of unique steps of the present invention taken for a wire bonding method in which a first bonding point and a second bonding point are connected by a wire that passes through a capillary; and the present invention involves: a step in which the tip end of the wire is connected to the first bonding point; a step in which the capillary is raised and a reverse operation is performed so that the capillary is caused to move in the opposite direction from the second bonding point; a step in which the capillary is raised obliquely upward toward the second bonding point; a step in which a reverse operation is performed so that the capillary is caused to move in the opposite direction from the second bonding point; and a step in which the capillary is raised and then caused to move toward the second bonding point, and the wire is connected to the second bonding point.
In the above methods, the step of raising the capillary obliquely upward toward the second bonding point and the successive step of raising the capillary and performing another reverse operation can be performed a plural number of times.
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Dunn Tom
Kabushiki Kaisha Shinkawa
Koda & Androlia
Pittman Zidia
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