Metal fusion bonding – Process – Plural joints
Reexamination Certificate
1999-07-26
2001-01-16
Ryan, Patrick (Department: 1725)
Metal fusion bonding
Process
Plural joints
C228S103000
Reexamination Certificate
active
06173885
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for forming a ball on a bonding wire and more particularly to a ball forming method in which a high voltage is applied across the tip end of a bonding wire and a discharge electrode so as to cause a discharge to take place, thus forming a ball on the tip end of the wire.
2. Prior Art
Conventionally, a fixed discharge electrode system is used for forming a ball at the end of a bonding wire. In this fixed discharge electrode system, a discharge electrode is positionally fixed. The discharge electrode is positioned as close as possible to the tip end of the wire that passes through a capillary. In addition, the discharge electrode is positioned to one side of the tip end of the wire so that the discharge electrode will not contact the capillary when the capillary is lowered.
Accordingly, in the fixed discharge electrode system, the ball is not formed when the discharge electrode is directly positioned beneath the tip end of the wire as in the case of a movable discharge electrode system. Thus, since the electric discharge is performed from the side of the wire, the ball may be distorted or an eccentric ball may be formed which deviates from the center of the wire in the direction of the wire diameter.
Japanese Patent Application Laid-Open (Kokai) No. H10-125714 (hereafter referred to as “Conventional Example 1”) and Japanese Patent Application Laid-Open (Kokai) No. H10-125715 (hereafter referred to as “Conventional Example 2”) disclose methods for avoiding an eccentric ball or a distorted ball in such fixed discharge electrode systems.
In Conventional Example 1, a gas is blown onto the discharge spark from the direction of the discharge electrode during ball formation, thus bending the discharge spark and causing the portion of the discharge spark that faces the wire to be positioned beneath the wire. In Conventional Example 2, a magnetic field is applied to the discharge spark, so that the portion of the discharge spark that faces the wire is bent beneath the wire.
However, Conventional Example 1 requires an auxiliary device which blows a gas onto the discharge spark, and in Conventional Example 2, an auxiliary device which applies a magnetic field to the discharge spark is required. Accordingly, both methods lead to an increase in equipment costs. Furthermore, in these prior arts, a precision control of the gas or electric field is required.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to provide a method for forming a ball in wire bonding which makes it possible to form a ball that does not show any distortion or deviation without any need for any auxiliary device and without performing any precision control.
It is another object of the present invention to provide a method for forming a ball which makes it possible to form the balls of a constant diameter.
The above objects are accomplished by unique steps of the present invention for a method which forms a ball at the tip end of a wire by using a discharge electrode installed on one side of the tip end of the wire that passes through a capillary and by applying a high voltage across the tip end of the wire and the discharge electrode so as to cause an electric discharge to take place; and in the present invention, the tail of the wire extending from the tip end of the capillary is bent toward the discharge electrode, the capillary is moved so that the tip end of this tail faces the discharge electrode, and an electric discharge is subsequently caused to take place from the discharge electrode so as to form the ball on the tip end of the wire.
The above objects are accomplished by further unique steps of the present invention for a method which forms a ball at the tip end of a wire by using a discharge electrode installed on one side of the tip end of the wire that passes through a capillary and by applying a high voltage across the tip end of the wire and the discharge electrode so that a discharge is caused to take place; and in the present invention:
after the wire has been bonded to the second bonding point, the capillary is raised obliquely in the opposite direction from the side on which the discharge electrode is installed,
when the amount of wire delivered during this raising of the capillary reaches the length required for the formation of the ball, a clamper is closed so as to cut the wire from the root of the second bonding point,
the capillary is then moved so that the tip end of the wire faces the discharge electrode, and
an electric discharge is subsequently caused to take place from the discharge electrode, thus forming a ball on the tip end of the wire.
REFERENCES:
patent: 4099663 (1978-07-01), Brill et al.
patent: 4912544 (1990-03-01), Onuki et al.
patent: 5897049 (1999-04-01), Nakamura et al.
patent: 5958259 (1999-09-01), Miyano et al.
patent: 5988482 (1999-11-01), Sasakura et al.
patent: 10-125714 (1998-05-01), None
patent: 10-125715 (1998-05-01), None
Mii Tatsunari
Takahashi Kuniyuki
Kabushiki Kaisha Shinkawa
Koda & Androlia
Pittman Zidia T.
Ryan Patrick
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