Metal fusion bonding – With means to juxtapose and bond plural workpieces – Wire lead bonder
Reexamination Certificate
2000-08-16
2001-12-04
Elve, M. Alexandra (Department: 1725)
Metal fusion bonding
With means to juxtapose and bond plural workpieces
Wire lead bonder
C228S001100, C228S004100
Reexamination Certificate
active
06325269
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a capillary for bonding wires between a semiconductor chip and a leadframe, and the like. Particularly, it relates to an improved wire bonding capillary, which is capable of decreasing wire slide resistance (extraction resistance) and suitably applied for a long and low loop wire bonding process.
BACKGROUND ART
A wire bonding capillary is a tube made of ceramics, which is mounted to a tip of a wire-feeding portion of a wire bonding apparatus. In general, each wire bonding capillary has a through bore for feeding a bonding wire, a funnel-shaped bore for guiding the wire to the through bore, and a chamfer formed at an exit of the through bore. Here, the through bore is formed at the smallest diametered portion in each wire passage of a capillary. The chamfer is generally formed to taper having an opening angle of between 45° and 60° ( shown &thgr;1, &thgr;2 in FIG.
1
). Further, the corner between the chamfer and the through bore may be grounded to be round.
An embodiment of Japanese Unexamined Patent Publication No. Shou 59(1984)-191338 discloses the following wire bonding capillary. The capillary, according to the embodiment, has a through bore whose diameter (corresponding to d
1
in
FIG. 1
) is 43 &mgr;m and a chamfer whose opening angles( corresponding to &thgr;1, &thgr;2 in
FIG. 1
) are 45° and 15°.
In Japanese Examined Utility Model Publication No. Hei 1(1989)-42349, the following wire bonding capillary is disclosed as a preferable one; he through bore diameter (corresponding to d
1
in
FIG. 1
) is the wire diameter plus 8-12 &mgr;m; each of the opening angles of the chamfers (corresponding to &thgr;1, &thgr;2 in
FIG. 1
) is 40-50° and 10-20°, respectively; and the chamfer length ( corresponding to h
1
in
FIG. 1
) is the wire diameter×0.7-1.5.
However, none of the two prior arts discloses the through bore length and a technology trend for long and low loop wire bonding processes, as described below, and its associated problems.
Recently, in VLSI (Very Large Scale Integration) and the like, miniaturization of chips and multiplication of pins for high integration purposes have been advanced further, so that a need for long and low loop wire bonding processes becomes keen.
When a conventional wire bonding tool is used for carrying out a long and low loop wire bonding process, it is necessary to feed, from the through bore, the wire with a twice length longer than usual. Accordingly, the wire tends to twine and thus to yield a dispersion of the loop height due to sagging and excessive tautening. The sagging of the loop causes the wires to contact each other to lead to a short circuit failure. And also, the excessive tautening of the loop applies excess stress to a neck portion of a bonded ball to lead to a disconnection failure. Both failures are fatal defect on the wire bonding process and have to be completely dismissed.
In view of the above problems, the object of the present invention is to provide a wire bonding capillary, which is suitable for a long and low loop wire bonding process and is able to lower wire slide resistance.
DISCLOSURE OF THE INVENTION
In order to solve the above-mentioned problems, a wire bonding capillary according to the present invention has a through bore for feeding a bonding wire, a funnel-shaped bore for guiding the wire to the through bore, and a chamfer formed at an exit of the through bore, wherein the through bore is formed at the smallest diametered portion in each wire passage of a capillary and the bore has a length less than 1.5 times the through bore diameter.
As a result of experiment as mentioned below, it is fundamentally proven that the smaller the slide resistance of a wire, the shorter the length of the through bore. The through bore diameter, for the requirement of the positioning accuracy of the wire, is determined by adding some minute clearance to the through bore diameter, and the wire has to be drawn through a narrow place so that the slide resistance is high. Accordingly, it is desirable that the slide resistance will be lowered by making the through bore length as short as possible. From this view point, the through bore length is preferably less than 0.5 times the through bore diameter.
In the wire bonding capillary according to the present invention, it is preferable that a chamfer is so formed to widen an opening angle thereof toward an exit of the through bore. When a long and low loop wire is arranged, an angle between the axis of the capillary and the wire tends to get bigger so that the wire will sharply bent at the tip of the capillary to produce a large resistance against pulling out the wire here.
Therefore, at the tip of the capillary, the chamfer is formed to widen the opening angle thereof toward the exit of the through bore, whereby the wire can be smoothly introduced while being bent. Consequently, the resistance will be reduced.
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Mii Tatsunari
Sakurai Mamoru
Suzuki Takesi
Torihata Minoru
Elve M. Alexandra
Jones Day Reavis & Pogue
Pittman Zidia
Toto Ltd.
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