Metal fusion bonding – Process – Plural joints
Reexamination Certificate
2000-03-01
2001-03-27
Ryan, Patrick (Department: 1725)
Metal fusion bonding
Process
Plural joints
C228S004500, C228S005100
Reexamination Certificate
active
06206275
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the bonding of wires to a substrate, and more particularly, to a method and apparatus enabling deep access, close proximity, fine pitch ultrasonic bonding of large wire.
2. Description of the Related Art
Wire bonding is the process of making electrical connections in semiconductor components by means of electrically conductive wire, typically wire with a diameter of from 12 microns to 500 microns. Examples of electrical connections which can be made using wire bonding techniques include connections between the contact surfaces of discrete or integrated chips and the contact leads of their packages, and, in the case of hybrid circuits, the connections between inserted monolithic elements and the film circuit which contains them.
A number of wire bonding techniques have been developed, and one which has been particularly successful is a microwelding technique using ultrasound. An automatic wire bonding apparatus on which such a technique can be operated is described in U.S. Pat. No. 4,619,397. Aluminum wire, for instance, in contact with the contact surface to which it is to be bonded, is moved vigorously along the surface to which it is to be bonded so that its oxide layer breaks open. The wire is then subjected to pressure, and a permanent junction is created between the two materials. Motion of the wire is generated by an ultrasonic transducer excited by an ultrasonic generator to produce high-frequency mechanical vibrations.
In the particular wire bonding process known as wedge bonding, the ultrasonic energy is supplied at a level correlated to the wire size used. The ultrasonic energy is directed to the aluminum or other type of wire by a special tool known as a “wedge.” The wire is fed through a guide at the bottom of the wedge. When the wedge with the wire touches the surface to which the wire is to be bonded, movement is stopped. The wire is pressed down with a small defined force, known as the bonding weight, and the wire is slightly deformed. This small deformation is known as the “pre-deformation.” Ultrasonic energy is now switched on, and the welding process starts. During this time, the diameter of the wire is reduced by a few microns, the actual reduction depending on the size, physical properties and the precise chemical nature of the wire.
Large wire bonding is defined as attaching about 0.005-0.020 inch (about 125 microns to 500 microns) electrical conductive wire to power devices as used in the semiconductor industry. Wires may be aluminum (Al), gold (Au) and copper (Cu), for instance, with aluminum wires being most prevalent. However, wires other than Al, Au and Cu may be used. Ultrasonic energy and elevated temperature of a work piece (in some cases) is the principle method of attaching these large wires to the power devices and/or semiconductors using a bonding tool or wedge.
Wire bonders, and especially large wire bonders, often require a cutter to terminate the wire. This cutter is typically positioned adjacent the bond wedge and brought down with a Z-axis motion to cut wire after a bond has been made. One example of a cutter positioned adjacent a bonding wedge is shown in U.S. Pat. No. 5,906,706.
Present wire bonders bring wire to the bonding tool, for example, by an independent wire guide of two types. In the first type, a separate member consisting of a wire guide capillary is held in place behind the wedge and at a specific angle to the bonding wedge. This wire guide capillary is disclosed, for instance, in U.S. Pat. No. 5,452,838. In the second type, a “clip on” wire guide member that separately attaches to the bonding wedge. The “clip on” wire guide member is disclosed, for instance, in U.S. Pat. No. 5,906,706.
In both wire guiding methods, the wire is held in position so as to locate the wire directly below the tip of the bond wedge. After the wire is brought to the work piece or substrate, loop forms are made with a combination of machine tool motion and friction within the two types of wire guides described above.
Unfortunately, the prior art tools require too much room to work with many emerging chips. As integrated circuits are made smaller, the resulting chips have less access space within which to bond wires. The combination of the bonding wedge or tool and separate wire guide described above precludes these wire bonders from being able to access newer power devices that call for deep-access, close proximity, and/or fine pitch wire bonding. Fine pitch wire bonding refers to wires bonded side-by-side as close as possible. Furthermore, when a wire cutter is used, the cutter adds additional dimension near the tip of the bonding tool making it even more difficult to access deep, tight spaces on a substrate.
SUMMARY OF THE INVENTION
Accordingly, what is needed is a wire bonder capable of performing deep access, close proximity, fine pitch wire bonding on a substrate. These and other needs are accomplished by satisfying one or more of the following objects of the present invention:
1. To eliminate the capillary and clip-on wire guides of present wire bonders;
2. To replace the known type of bond wedge with a type that incorporates a wire guide;
3. To replace the known type of wire cutter with a type that intersects with the shank diameter of the conventional wedge;
4. To reduce the size of a wire bonder with a cutter/wire guide/bond tool to less than one-half of the size of these components in techniques currently employed;
5. To reduce the need for extra machine control motions for certain loop forms and gain faster machine cycle rate;
6. To meet the challenges of deep access/close proximity/fine pitch wire bonding on new type power devices.
Briefly stated, the preferred embodiments of the present invention describe a wire bonding apparatus for bonding wire to a substrate wherein the components used to guide, bond and cut the wire have a reduced cross-sectional dimension near the substrate to enable close proximity, deep access, fine pitch bonding. This is accomplished in part by forming a wire guide integrally through a substantial portion of the bonding tool, thereby completely eliminating one component found in conventional wire bonding apparatus. This is further accomplished by tapering the size of the bonding tool toward the substrate such that the bonding tool in a lower or distal portion has a smaller cross-sectional area. A cutter extends adjacent the lower portion of the bonding tool and into the area that would otherwise be occupied by the lower portion of the bonding tool if not for the taper. Thus, both the cutter and the lower portion of the bonding tool occupy a minimal amount of space adjacent the substrate.
In one aspect of the present invention, a wire bonding apparatus for bonding wire to a substrate is provided. The apparatus comprises an ultrasonic bonding tool having an upper portion, a lower portion and a bottom tip. The bonding tool in the lower portion adjacent the tip has a reduced cross-sectional area compared to the cross-sectional area of the bonding tool in the upper portion. A cutter mounted adjacent the bonding tool extends along at least a portion of the bonding tool toward the tip. More particularly, the cutter extends at least partially into a projection of the cross-sectional area of the upper portion onto a plane perpendicular to the longitudinal axis of the bonding tool.
In another aspect of the present invention, the wire bonding apparatus comprises a bonding tool extending longitudinally between a proximal portion and a distal portion. The distal portion of the bonding tool includes a bonding tip for ultrasonically bonding wire to a substrate. A cutter mounted adjacent the bonding tool extending substantially longitudinally adjacent at least a portion of the bonding tool. The cutter has a proximal portion and a distal portion, the distal portion of the cutter including a cutting tip. At least the distal portion of the cutter extends adjacent the distal portion of the bonding tool. An undercut area is provided between the proximal
F & K Delvotec Bondtechnik GmbH
Johnson Jonathan
Knobbe Martens Olson & Bear LLP
Ryan Patrick
LandOfFree
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