Wire bonding method

Details Wire bonding method Wire bonding method

1999-09-07

2001-02-06

Ryan, Patrick (Department: 1725)

Metal fusion bonding

Process

Plural joints

C228S004500, C228S006200, C228S178000

Reexamination Certificate

active

06182885

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wire bonding method in which a wire that passes through a capillary is connected to a first bonding point and a second bonding point, and more particularly, to a wire bonding method which forms a low wire loop in low-step-height devices in which the step height between the first and second bonding points is small.
2. Prior Art
Various types of wire bonding methods have been proposed. The most common method is shown in FIGS.
8
(
a
) and
8
(
b
).
As seen from FIG.
8
(
a
), a capillary
2
is lowered with a damper (not shown), which is provided above the capillary
2
so as to hold a wire
1
, in an open state; and a ball formed on the tip end of the wire protruding from the tip end of the capillary
2
is bonded to a first bonding point A.
Japanese Patent Application Laid-Open No. H
10-
125715 discloses a method for forming a ball at the end of a bonding wire. In this prior art, a charging electrode is provided so as to be positioned on one side of a bonding wire, and a magnet is used so that the discharge spark from the electrode is applied to the wire from underneath the wire.
After the ball is bonded to the first bonding point A, the capillary
2
is raised to point B, delivering the wire
1
by an amount that corresponds to the wire length required to form a wire loop. Next, the clamper is closed, and the capillary
2
is moved to point D which is straight above the second bonding point C by performing a circular-arc motion as indicated by a curved arrow.
Then, as shown in FIG.
8
(
b
), the capillary
2
is lowered, and the wire
1
is bonded to the second bonding point C. Afterward, the damper is opened, and the capillary
2
and the damper are both raised. During this raising movement, the damper is closed so as to cut the wire
1
from its attachment root at the second bonding point C. The wire bonding of one wire is thus completed.
A wire bonding method of the type described above is disclosed in Japanese Patent Application Publication (Kokoku) No. HI-26531.
The conventional wire bonding method as described has problems when bonding is performed for a low-step-height device in which the step height between the first bonding point A and the second bonding point B is as small as, for instance, 50 microns or less. For instance, as shown in FIG.
8
(
a
), when the capillary
2
is moved to a point slightly above the second bonding point C, an excess portion of the wire
1
is suspended from the lower end of the capillary
2
, resulting in a wire shape
11
in which a bowed portion
10
is formed. Because of this bowed portion
10
, the wire length that is delivered from the capillary
2
is in fact longer than the ideal wire length of the wire shape
12
that is indicated by the two-dot chain line in FIG.
8
(
a
). As a result of this excess wire, the wire
1
undergoes a rebound due to plastic deformation when the wire
1
is bonded to the second bonding point C; and a wire loop shape
13
with an upward bow such as that shown in FIG.
8
(
b
) is formed.
In a low wire loop in which the apex of the loop is supposed to be the portion
14
above the first bonding point A, the wire loop shape
13
which has such a bow increases the overall height of the wire loop, and it also makes it difficult to control the height of the wire loop in the looping operation. Thus, an unstable wire loop shape is formed. The two-dot chain line shown in FIG.
8
(
b
) shows an ideal wire loop shape
19
.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to provide a wire bonding method which produces a stable wire loop shape by preventing bowing of the wire loop during bonding to a second bonding point, thus making it possible to form a low wire loop in low-step-height devices.
The above object is accomplished by unique steps in a wire bonding method in which a wire passed through a capillary is connected to a first bonding point and a second bonding point, and in the present invention: a ball formed on the tip end of the wire protruding from the tip end of the capillary is first bonded to the first bonding point; when the capillary is then moved toward the second bonding point the capillary is first lowered to a point that is slightly on the first bonding point side of the second bonding point so as to press the portion of the wire suspended from the tip end of the capillary against a horizontal surface; the capillary is then raised and moved to a point above the second bonding point; and the capillary is lowered; thus bonding the wire to the second bonding point.


REFERENCES:
patent: 3643321 (1972-02-01), Field et al.
patent: 4928871 (1990-05-01), Farassat
patent: 4951120 (1990-08-01), Hagiwara et al.
patent: 5024367 (1991-06-01), Terakado et al.
patent: 5111989 (1992-05-01), Holdgrafer et al.
patent: 5437405 (1995-08-01), Asanasavest
patent: 401057725 (1989-03-01), None
patent: 1-26531 (1989-05-01), None
patent: 05283463 (1992-03-01), None
patent: 405129357 (1993-05-01), None
patent: 5-60657 (1993-09-01), None
patent: 06310556 (1994-11-01), None
patent: 10-125715 (1998-05-01), None

Affiliated with

Also associated with

Rating

Wire bonding method does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Wire bonding method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Wire bonding method will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2613227