Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2000-12-29
2004-03-09
Arbes, Carl J. (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S843000, C029S874000, C324S756010, C439S066000, C439S591000
Reexamination Certificate
active
06701612
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The invention relates to shaping bond wires, particularly Free-standing bond wires used as core elements for composite interconnection element such as are described in commonly-owned, copending U.S. patent application Ser. No. 08/452,255 filed May 26, 1995 (status: pending) and its counterpart PCT patent application number PCT/US95/14909 filed Nov. 13, 1995.
BACKGROUND OF THE INVENTION
Electronic components, particularly microelectronic components such as semiconductor devices (chips), often have a plurality of terminals (also referred to as bond pads, electrodes, or conductive areas). In order to assemble such devices into a useful system (or subsystem), a number of individual devices must be electrically interconnected with one another, typically through the intermediary of a printed circuit (or wiring) board (PCB, PWB).
Generally, interconnections between electronic components can be classified into the two broad categories of “relatively permanent” and “readily demountable”.
An example of a “relatively permanent” connection is a solder joint. Once two electronic components are soldered to one another, a process of unsoldering must be used to separate the components. A wire bond is another example of a “relatively permanent” connection.
An example of a “readily demountable” connection is rigid pins of one electronic component being received by resilient socket elements of another electronic component. The socket elements exert a contact force (pressure) on the pins in an amount sufficient to ensure a reliable electrical connection therebetween. Interconnection elements intended to make pressure contact with an electronic component are referred to herein as “springs” or “spring elements” or “spring contacts”.
Prior art techniques for making spring contact elements generally involve stamping (punching) or etching a “monolithic” spring material, such as phosphor bronze or beryllium copper or steel or a nickel-iron-cobalt (e.g., kovar) alloy, to form individual spring elements, shaping the spring elements to have a spring shape (e.g., arcuate, etc.) plating the spring elements with a good contact material (e.g., a noble metal such as gold, which will exhibit low contact resistance when contacting a like material), and molding a plurality of such shaped, plated spring elements into a linear, a peripheral or an array pattern. When plating gold onto the aforementioned materials, sometimes a thin (for example, 30-50 microinches, barrier layer of nickel is appropriate.
Generally, a certain minimum contact force is desired to effect reliable pressure contact to electronic components (e.g., to terminals on electronic components). For example, a contact (load) force of approximately 15 grams (including as little as 2 grams or less and as much as 150 grams or more, per contact) may be desired to ensure that a reliable electrical connection is made to a terminal of an electronic component which may be contaminated with films on its surface, or which has corrosion or oxidation products on its surface. The minimum contact force required of each spring element typically demands either that the yield strength of the spring material or that the size of the spring element are increased. However, generally, the higher the yield strength of a material, the more difficult it will be to work with (e.g., punch, bend, etc.). And the desire to make springs smaller essentially rules out making them larger in cross-section.
In commonly-owned, copending U.S. patent application Ser. No. 08/452,255 filed May 26, 1995 (and its counterpart PCT/US95/14909 filed Nov. 13, 1995), techniques are described for shaping elongate core elements (wire stems) of composite interconnection elements using a wirebonder. A one end of a supply wire is ball-bonded to an area (e.g., terminal) on a substrate (e.g., electronic component) by urging a capillary of a wirebonder downward (z-axis) onto the substrate. The capillary is then withdrawn (upward), and as the wire plays (feeds) out of the capillary, the substrate is moved in the x-y plane to impart a desired spring shape to the portion of the wire between the substrate and the capillary. The wire is then severed adjacent the capillary, resulting in a free-standing wire stem which is mounted to the substrate. The possibility of using external, mechanical instrumentalities to impart the desired shape to the wire stem is discussed, and is elaborated upon herein.
The following U.S. Patents are cited as being of interest:
5,386,344;
5,336,380;
5,317,479;
5,086,337;
5,067,007;
4,989,069;
4,893,172;
4,793,814;
4,777,564;
4,764,848;
4,667,219;
4,642,889;
4,330,165;
4,295,700;
4,067,104;
3,795,037;
3,616,532;
and
3,509,270.
Attention is also directed to U.S. Pat. No. 5,045,975 issued Sep. 3, 1991, entitled THREE-DIMENSIONALLY INTERCONNECTED MODULE ASSEMBLY, which discloses ball bonding a plurality of gold wires (leads) onto and substantially perpendicular to an integrated circuit die, and inserting the gold leads into plated through holes of printed circuit boards to effect an electrical and mechanical connection therebetween. The technique is also useful for interconnecting sandwiched assemblies of circuit boards. This patent illustrates the feasibility of adding a notching mechanism to a wirebonder (ball bonder), and also illustrates the technique
BRIEF DESCRIPTION (SUMMARY) OF THE INVENTION
It is an object of the invention to provide an improved technique for shaping core elements of a composite interconnection element to have an appropriate spring shape.
It is another an object of the invention to provide a technique for fabricating resilient interconnection elements (contact structures) for electronic components, particularly for microelectronic components.
It is another object of the invention to provide resilient contact structures (interconnection elements) that are suitable for making pressure contact to electronic components.
It is another object of the invention to provide a technique for securely anchoring interconnection elements to electronic components.
According to the invention, an external mechanical instrumentality (shaping tool) is used to impart a desired shape to portion of an elongate element (e.g., a bond wire).
In an embodiment of the invention, the shaping tool is a one-part tool, which urges (pushes) against a portion of the bond wire extending between an area (e.g., terminal) on a substrate (e.g., electronic component, sacrificial substrate, etc.) and a capillary of a wirebonder.
In another embodiment of the invention, the shaping tool is a two-part tool, comprising an anvil and a die. The anvil and die are brought together, with the elongate element (e.g., wire) therebetween, to impart the desired shape to the elongate element.
According to an aspect of the invention, the shaping tool is provided with a feature which can nick or completely sever the elongate element while performing shaping.
According to an aspect of the invention, the shaping tool can be biased (at an electrical potential, including ground) to control a spark (electrical discharge) which is used to sever the elongate element.
According to another aspect of the invention, regions of reduced diameter formed by the shaping tool can “attract” a spark during spark-severing (e.g., from an EFO electrode).
The present invention is particularly useful for, but is not limited to, shaping core elements of composite interconnection elements, which are fabricated by bonding a one end of a bond wire to a terminal on an electronic component (or to an area of a sacrificial substrate), imparting a spring shape to the wire, and severing the wire to be a free-standing wire stem (core element). The free-standing wire stem is overcoated with one or more layers of material to impart a desired resiliency and, optionally, electrical contact characteristics to the resulting composite interconnection element. It is within the scope of this invention that the core element is other than a wire having a circular cross-section. For example, the core element may have a rectangular cr
Dozier Thomas H.
Grube Gary W.
Khandros Igor Y.
Mathieu Gaetan L.
Arbes Carl J.
Burraston N. Kenneth
FormFactor Inc.
Merkadeau Stuart L.
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