Wire bonding method

In a wire bonding method in which a capillary is raised from a first bonding point after bonding and then moved in a direction opposite to a second bonding point, thus making a reverse action, such a reverse action is made in a circular-arc shape around a neck part of the wire at the first bonding point. Thus, an ideal wire-looping is accomplished, thus preventing wire damage which could be caused by reverse actions.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a wire bonding method that connects a 
first bonding point and a second bonding point with a wire, and more 
particularly, to a wire looping method used in wire bonding. 
2. Prior Art 
In wire bonding, it is preferable to keep the shape of wire loop constant 
during the bonding process. In the currently employed method, a capillary 
is raised after the wire is connected to a first bonding point, and then a 
reverse action is performed so that the capillary is moved horizontally by 
a small amount away from the second bonding point. These movements are 
performed with a clamp, which holds the wire, kept open. The Japanese 
Patent Application Publication ("Kokai") Nos. 57-87143 and 63-42135 
disclose these methods. 
In these prior art, the reverse action is an action of wire moving away 
from the second bonding point, forming a wire loop between the first and 
second bonding points. 
In this reverse action, the capillary moves horizontally. This action of 
the capillary, however, drags the wire, and a force greater than the force 
required to deform the wire is applied to the wire. This causes a damage 
to the neck part of the wire which is a part of the wire at the first 
bonding point. 
SUMMARY OF THE INVENTION 
Accordingly, the object of the present invention is to provide a wire 
bonding method which makes it possible to deform the wire in an ideal 
shape and perform wire-looping with a reverse action that causes no damage 
to the wire. 
The method of the present invention that accomplishes the object is 
characterized in that when a capillary is raised and a subsequent reverse 
action is performed after the wire is bonded to first bonding point, such 
a reverse action is made by a circular-arc movement of the capillary 
around the wire neck portion at the first bonding point or at a point near 
the wire neck portion. 
Since the reverse action is a circular-arc action, an ideal wire-loop is 
formed, and the capillary does not drag any portion of the wire or damage 
the wire.

DETAILED DESCRIPTION OF THE INVENTION 
One embodiment of the present invention will be described below with 
reference to FIGS. 1 and 2. 
With a clamp which holds a wire 1 open, a capillary 2 is raised to point B 
after the wire 1 is connected to first bonding point A. After being 
stopped temporarily (or for only an instant) at point B, the capillary 2 
is caused to make a reverse action, i.e., a circular-arc action with a 
radius of R centered at the wire neck portion 1a or at a point close to 
the wire neck portion 1a, and then moved to point C. 
Thus, since the reverse action is a circular-arc action (caused by the 
capillary) which is centered at the wire neck portion 1a or at a point 
near the wire neck portion 1a, the capillary 2 does not drag the wire 1 at 
all. As a result, except for the force necessary to deform the wire 1, no 
other force is applied to the wire 1. Accordingly, wire looping can be 
performed smoothly without damaging the wire 1. 
After the completion of the reverse action, the capillary 2 is raised from 
point C to point D. In other words, the capillary 2 is moved the distance 
required to form a wire loop, and the wire 1 is fed out. Afterward, the 
clamp is closed, and the capillary 2 is moved to point E, which is above 
the second bonding point F making a circular-arc movement with a radius of 
L centered at the wire neck portion 1a or on a point near the wire neck 
portion 1a. The capillary 2 is then lowered to the second bonding point F, 
and bonding is performed thereto. The movement of the capillary 2 from 
point C to the second bonding point F can be the same movement as that 
taken in the prior art. 
As described above, since the reverse action performed in the present 
invention is a circular-arc action, the capillary does not drag the wire. 
Thus, there is no damage to the wire, and an ideal wire loop is formed.