Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Ball or nail head type contact – lead – or bond
Reexamination Certificate
1999-05-28
2001-08-21
Wong, Don (Department: 2821)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Ball or nail head type contact, lead, or bond
C257S786000, C257S738000
Reexamination Certificate
active
06278191
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to wire bonding used in packaging semiconductor devices and the like. More particularly, the present invention relates to improved ball bonding techniques that may be used to protect device bond pads from oxidation after bonding.
BACKGROUND OF THE INVENTION
In the semiconductor industry, there are a number of different techniques that are used in the fabrication and packaging of integrated circuit devices. Although techniques vary extensively, most semiconductor devices have a number of bond pads on their top surface that serve as input/output (I/O) pads. The geometry of the bond pads is generally not considered critical, but the most common bond pad geometry is substantially square. A variety of different materials are used to form the bond pads, with one common material being aluminum. As is well known in the art, aluminum bond pads are somewhat prone to corrosion, especially if moisture penetrates to the bond pad.
During packaging of integrated circuits, the bond pads are typically electrically coupled to other components to facilitate connection to other integrated circuits or external devices. At the present time, wire bonding remains the dominant chip interconnection technology. In wire bonding, one end of a very fine wire is typically ultrasonically or thermosonically bonded to a bond pad and the other end is ultrasonically/thermosonically bonded to the component that the bond pad is to be electrically connected to (as for example a lead frame lead or a substrate trace). Generally the first end of the bonding wire is ball bonded to the bond pad using a wire bonding machine having a capillary that carries the bonding wire. During the ball bonding, it is generally considered important (if not imperative) that the capillary and thus the ball bond not contact the semiconductor passivation that surrounds the bond pad to avoid damaging the semiconductor device itself. Thus a portion of the bond pad remains exposed after wire bonding and the exposed portion of the bond pad is potentially subject to corrosion.
Currently, a number of techniques have been developed to seal or otherwise protect the bond pads from corrosion. However, there are always ongoing efforts to reduce the costs and improve the quality of packaging of semiconductor products. Accordingly improved techniques for sealing bond pads from corrosion would be desirable.
SUMMARY OF THE INVENTION
To achieve the foregoing and other objectives and in accordance with the present invention, a bond pad sealing arrangement and method that utilizes a ball bond to protect the bond pad is described. In a method aspect of the invention, a relatively large free air ball is formed at a distal end of the bonding wire used for ball bonding. The free air ball is pressed against a bond pad and ultrasonically welded to form a ball bond. The bonding parameters utilized during the ball bonding are selected such that excess ball material passes is squashed outward beyond the capillary tip and overflows the periphery of the bond pad thereby completely covering and sealing the bond pad. The described structure works well to protect aluminum and other bond pads that are subject to corrosion if left exposed.
In one preferred arrangement the capillary used to form the ball bond includes a cavity arrangement that molds a central portion of the ball bond to form a good intermetallic bond between the bond pad and the bonding wire.
REFERENCES:
patent: 4845543 (1989-07-01), Okikawa et al.
patent: 5186381 (1993-02-01), Kim
patent: 5839640 (1998-11-01), Kinnaird
patent: 5871141 (1999-02-01), Hadar et al.
patent: 5898226 (1999-04-01), Jeong et al.
patent: 5984162 (1999-11-01), Hortaleza et al.
patent: 5992725 (1999-11-01), Egawa et al.
Alemu Ephrem
Beyer Weaver & Thomas LLP
National Semiconductor Corporation
Wong Don
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