Metal fusion bonding – With means to juxtapose and bond plural workpieces – Wire lead bonder
Reexamination Certificate
2001-07-17
2004-04-06
Edmondson, Lynne (Department: 1725)
Metal fusion bonding
With means to juxtapose and bond plural workpieces
Wire lead bonder
C228S180500, C228S001100, C219S056210, C219S056220
Reexamination Certificate
active
06715658
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 for bonding of fine wire to bonding pads set at a very fine pitch.
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 (bonding tools) 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). 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 and the free air ball (FAB) formed thereby are such that the bonding tool can only be used to bond wires to bonding pads having an interpad spacing (pitch) of greater than 60 microns (0.060 mm; 15.34*10
−4
in.]. Thus, making them unsuitable for bonding wires to devices produced to meet the higher density requirements of the semiconductor industry. These prior art bonding tools are also unsuitable for handling wire bonds using wire as small a 0.4 mils (10 microns) in diameter. The inventors of the present invention have developed a bonding tool that meets the demands imposed by these high-density devices while maintaining structural integrity of the bonding tool.
FIG. 1A
is an illustration of a well-known prior art fine pitch bonding tool
100
. Bonding tool
100
has a cylindrical portion
101
, and a tapered potion
102
coupled between cylindrical portion
101
and working tip
104
. Working tip
104
(at an end of bonding tool
100
) has a tip angle of fifteen degrees relative to the longitudinal axis of bonding tool
100
. In other words, working tip
104
has an overall angle
106
of 30 degrees. The reduced width of working tip
104
relative to cylindrical portion
101
permits ball bonds to be made on pads having a pitch of about 0.0032 in. without working tip
104
touching an adjacent loop of a bonded wire as explained in U.S. Pat. No. 5,558,270.
FIG. 1B
is an illustration of an enlarged sectional view of working tip
104
. As shown in
FIG. 1B
, working face
111
has a face angle
108
of 4 degrees, and tapered portion
104
has an overall angle
118
of 10 degrees. In addition, adjacent working face
111
is first inner chamfer
110
, which, in turn, is adjacent second inner chamfer
112
. First inner chamfer
110
has chamfer angle
114
of 90 degrees, and connects or continues with second inner chamfer
112
having an angle greater than 60 degrees. These chamfers are designed to guide a fine wire (not shown) into wire hole
116
, having a diameter
106
, to accommodate wire with a diameter of about 1 mil.
These prior art bonding tool are deficient, however, in that their design is not able to accommodate the ultra fine pitch (30 microns or less) bonding pad requirements placed upon the industry by semiconductor manufacturers. Further, these bonding tools are formed from materials that are unable to withstand the forces and meet the elasticity requirements necessary to provide a bonding tool with working tip dimensions sufficient to meet the needs of the semiconductor industry.
SUMMARY OF THE INVENTION
To solve the aforementioned disadvantages of conventional bonding tools, the present invention relates to having a working tip with a diameter less than 39 microns.
The bonding tool comprises a working tip at an end of the bonding tool. The working tip including i) a tapered section having a predetermined angle with respect to the longitudinal axis of the first cylindrical section, ii) a working face with a first annular chamfer formed at an outside portion of an end of the working tip, and iii) a second annular chamfer formed at an inside portion of the end of the working tip, the first and second annular chamfer being adjacent one another; and a substantially cylindrical axial passage coupled to an upper portion of the second annular chamfer.
According to another aspect of the present invention, the second annular chamfer has an overall angle of less than 90°.
According to a further aspect of the present invention, the first annular chamfer has a face angle of greater than 8°.
According to another aspect of the present invention, the bonding tool is formed from a material containing at least 80% ZrO
2
by weight.
According to yet another aspect of the present invention, the bonding tool is formed from a material selected from one of group consisting of i) ZrO
2
+Y
2
O
3
and ii) Al
2
O
3
+ZrO
2
+Y
2
O
3
.
REFERENCES:
patent: 3917148 (1975-11-01), Runyon
patent: 3971499 (1976-07-01), Goodrich et al.
patent: 4405074 (1983-09-01), Levintov et al.
patent: 4821944 (1989-04-01), Tsumura
patent: 4974767 (1990-12-01), Alfaro et al.
patent: 5421503 (1995-06-01), Perlberg et al.
patent: 5437405 (1995-08-01), Asanasavest
patent: 5465899 (1995-11-01), Quick et al.
patent: 5558270 (1996-09-01), Nachon et
Atsmon Ziv
Bahalui Arie
Perlberg Gil
Sonnenreich Benjamin
Edmondson Lynne
Kulicke & Soffa Investments Inc.
RatnerPrestia
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