Metal fusion bonding – With means to juxtapose and bond plural workpieces – Wire lead bonder
Reexamination Certificate
2000-04-28
2001-11-27
Dunn, Tom (Department: 1725)
Metal fusion bonding
With means to juxtapose and bond plural workpieces
Wire lead bonder
C228S001100
Reexamination Certificate
active
06321969
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to a tool for use in the bonding of wire to semiconductor devices and, more particularly to a bonding tool having efficient ultrasonic energy transfer characteristics.
DESCRIPTION OF THE RELATED ART
Modern electronic equipment relies heavily on printed circuit boards on which semiconductor chips, or integrated circuits (ICs), are mounted. The mechanical and electrical connections between the chip and the substrate have posed challenges for chip designers. Three well known techniques for interconnecting the IC to the substrate are: wire bonding, tape automated bonding (TAB) and flip-chip.
The most common of these processes is wire bonding. In wire bonding, a plurality of bonding pads are located in a pattern on the top surface of the substrate, with the chip mounted in the center of the pattern of bonding pads, and the top surface of the chip facing away from the top surface of the substrate. Fine wires (which may be aluminum or gold wires) are connected between the contacts on the top surface of the chip and the contacts on the top surface of the substrate. Particularly, the connecting wires are supplied and bonded to the chip and to the substrate through a capillary, a bonding tool further described below.
Capillaries are used for ball bonding the wire to electronic devices, particularly to bond pads of semiconductor devices. Such capillaries are generally formed from a ceramic material, principally aluminum oxide, tungsten carbide, ruby, zircon toughened alumina (ZTA), alumina toughened zircon (ATZ) and other materials. Very thin wire, generally on the order of about one mil gold, copper or aluminum wire, is threaded through an axial passage in the capillary with a small ball being formed at the end of the wire, the ball being disposed external of the capillary tip. The initial object is to bond the ball to a pad on the semiconductor device and then to bond a portion farther along the wire to a lead frame or the like. During the bonding cycle, the capillaries perform more than one function.
After the ball is formed, the capillary must first center the ball partly within the capillary for bond pad targeting. With a first bonding step, the ball is bonded to a pad on a semiconductor device. When the capillary touches the ball down on the bond pad, the ball will be squashed and flatten out. As the bond pads are generally made from aluminum, a thin oxide forms on the surface of the bond pad. In order to form a proper bond, it is preferable to break the oxide surface and expose the aluminum surface. An effective way of breaking the oxide is to “scrub” the surface of the oxide with the wire ball. The wire ball is placed on the surface of the aluminum oxide and the capillary rapidly moves in a linear direction based on the expansion and contraction of a piezo-electric element placed within the ultrasonic horn to which the capillary is attached. The rapid motion, in addition to heat applied through the bond pad, forms an effective bond by transferring molecules between the wire and the bond pad.
The capillary then handles the wire during looping, smoothly feeding the bond wire both out of the capillary and then back into the capillary. The capillary then forms a “stitch” bond and a “tack” or “tail” bond.
Presently, thermosonic wire bonding is the process of choice for the interconnection of semiconductor devices to their supporting substrates. The thermosonic bonding process is partially dependent upon the transfer of ultrasonic energy from the transducer, attached to a movable bondhead, through a tool, e.g. capillary or wedge, to the ball or wire being welded to the semiconducting device or supporting substrate.
In conventional capillaries (bonding tools), the geometry of the bonding tool is not engineered to modify energy transfer to the ball/wire interconnection pad interfacial area. The inventor of the present invention has determined that control of the ultrasonic attenuation of the stress/strain wave imposed upon the tool due to the ultrasonic transducer is crucial to controlling the bonding process and its performance.
Conventional bonding tool design is deficient, however, because conventional bonding tool design is based on interconnection pitch and wire bond loop height and does not consider controlling ultrasonic attenuation. As such, conventional bonding tools are not energy efficient.
FIG. 1
is an illustration of a conventional bonding tool. As shown in
FIG. 1
, bonding tool
100
has a cylindrical body portion
102
and a tapered portion
104
. An axial passage
108
extends from the end
110
to the tip
106
of the bonding tool
100
. A bonding wire (not shown) passes through axial passage
108
and through tip
106
for eventual bonding on a substrate (not shown).
SUMMARY OF THE INVENTION
To solve the aforementioned disadvantages of conventional bonding tools, the present invention relates to an energy efficient bonding tool for bonding a fine wire to a substrate.
The bonding tool comprises a first cylindrical section having a first diameter; a second cylindrical section coupled to an end of the first cylindrical section, the second cylindrical section having a second diameter less than the first diameter; and a tapered section coupled to an end of the second cylindrical section.
According to one aspect of the present invention, the second cylindrical section is a groove.
According to another aspect of the present invention, the second cylindrical section is a plurality of grooves.
According to a further aspect of the present invention, the grooves have a substantially rectangular cross section.
According to another aspect of the present invention, the groove is replaced by a slot.
According to yet another aspect of the present invention, the tapered section is immediately adjacent the second cylindrical section.
These and other aspects of the invention are set forth below with reference to the drawings and the description of exemplary embodiments of the invention.
REFERENCES:
patent: 3894671 (1975-07-01), Kulicke, Jr. et al.
patent: 3917148 (1975-11-01), Runyon
patent: 4315128 (1982-02-01), Matcovich et al.
patent: 4513190 (1985-04-01), Ellett et al.
patent: 5377894 (1995-01-01), Mizoguchi et al.
patent: 5558270 (1996-09-01), Nachon et al.
patent: 5890643 (1999-04-01), Razon et al.
patent: 5971248 (1999-10-01), Koduri
patent: 6006977 (1999-12-01), Koduri
patent: 6073827 (2000-06-01), Razon et al.
patent: 6112972 (2000-09-01), Koduri
F. Osterwald et al.,Increasing Bond Quality by Ultrasonic Vibration Monitoring, ISHM—Preceedings of SPIE—The International Society for Optical Engineering (Oct. 1996), pp. 426-431.
A. Wilson et al,Holographic Interferometry Applied to Motion Studies of Ultrasonic Bonders, IEEE Transaction on Sonics and Ultrasonics, New York , Institute of Electrical and Electronic Engineers (1972), SU-19 (4), pp. 453-461.
Dunn Tom
Kulicke & Soffa Investments
Pittman Zidia
Ratner & Prestia
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