1. Field of the Invention
The present invention relates to electrical interconnection (contact) elements and, more particularly, to contact elements which are resilient contact elements suitable for effecting readily demountable pressure connections between substrates, such as electronic components.
2. Description of Related Art
Readily demountable interconnections between electronic components include resilient contacts of one electronic component being received by another electronic component at, for example, pads or sockets. The spring contacts exert a contact force (optionally, with a wiping action) on the pad elements in an amount sufficient to ensure a reliable electrical connection. Resilient spring contacts or structures intended to make pressure contact with an electronic component, or other substrate, are referred to herein as xe2x80x9cspring contacts.xe2x80x9d Elements that are sized for direct demountable connection to semiconductor devices, such as semiconductor dice or wafers, are referred to as xe2x80x9cmicroelectronicxe2x80x9d springs, spring contacts, or spring structures.
Prior art techniques for making spring contacts generally involve stamping or etching a sheet of spring material, such as phosphor bronze, beryllium copper, steel or a nickel-iron-cobalt (e.g., kovar) alloy, to form individual spring contacts, shaping the spring contacts to have a spring shape, optionally plating the spring contacts 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 forming a plurality of such shaped, plated spring contacts into an array pattern. However, such techniques are not well suited for meeting the design requirements described below.
Stringent design requirements apply to microelectronic spring contacts. Generally, a certain minimum contact force is desired to achieve reliable electrical contact to electronic components. For example, a contact 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. Such terminals are often contaminated with organic films, corrosion, or oxides on their contact surfaces, and the tip of the spring contact must be applied with sufficient force to penetrate this barrier of contamination. Additionally, it is preferable for the tip of a spring contact to move in a direction parallel to the surface of the connecting terminal when it is depressed in a xe2x80x9czxe2x80x9d direction (i.e., perpendicular to the terminal surface), thereby providing xe2x80x9cwipe,xe2x80x9d which is useful for clearing contamination and ensuring a good connection. The tip should be disposed sufficiently above the substrate to which it is attached (i.e., the spring should have adequate xe2x80x9cz-extensionxe2x80x9d) to ensure that an electrical connection can be made without interfering with components, such as capacitors, which may be mounted to a surface of the components to be connected.
For any spring contact, the modulus of elasticity of the spring material in combination with the shape and size of the resilient working portion of the spring should be such that the spring contact reliably provides the minimum contact force needed to ensure debris removal and an electrical connection. Application and manufacturing considerations also constrain spring shape and size. When spring contacts are fabricated at ever-smaller microelectronic scales, it becomes increasingly difficult to fulfill these and other design requirements.
Various microelectronic spring contact structures have been developed for addressing the foregoing design requirements. Although a few of the prior art structures provide the desired combination of adequate z-extension and contact force, a shaped tip, and wiping action at the desired microelectronic scales, there remains an opportunity to improve upon the performance of these structures, and to extend their range of applicability, as disclosed herein.
The commonly-owned, co-pending application Ser. No. 09/746,716, filed Dec. 22, 2000, which is incorporated herein by reference, in its entirety, discloses a microelectronic spring structure comprising a group of column elements, a cantilevered beam secured transverse to the group of column elements, and a contact tip on a portion of the cantilevered beam distal from the column elements. In particular, Ser. No. 09/746,716 discloses column elements that are formed from a relatively soft wire core (such as a gold core) bonded to a substrate, and coated with a resilient structural material, (such as by plating the core with a nickel or nickel alloy layer). The resulting column elements, especially configured as a group of two or more columns, provide a relatively rigid and stable base for a cantilever beam element. Among other things, the column elements disclosed in Ser. No. 09/746,716 are used to space the cantilever beam apart from the substrate (i.e., provide high clearance for the beam). Column elements comprised of plated and ball-bonded wire are particularly useful for readily providing a relatively high beam clearance. Such cantilever beam-type spring structures, i.e., those with a relatively high beam clearance, are completely new to the field of microelectronic spring structures, insofar as they are structures that may be mass-produced cost-effectively, and correspondingly create opportunities for new improvements in the field, such as described herein.
The present invention improves upon cantilever beam-type microelectronic spring structures by providing additional structural features that modify the performance characteristics of the spring structures in useful ways. The additional features are especially suitable for use in structures having a relatively high beam clearance, for example, spring structures with column elements as described in Ser. No. 09/746,716 referenced above. However, the invention is not limited to such structures, and may be used with any microelectronic spring structure having enough beam clearance to accommodate the features described herein.
The added features provided by the present invention may be generally described as a protruding member mounted between the supporting substrate and the transverse cantilever beam of a microelectronic spring structure, at a distance spaced apart from the primary column elements (or equivalent structure) from which the beam is cantilevered. In embodiments of the invention, the height of the protruding member may be equal to the clearance under the beam, less than the clearance under the beam, or adjustable in height. In an embodiment of the invention, the protruding member is substantially rigid and incompressible. In an alternative embodiment, the protruding member is substantially xe2x80x9csoftxe2x80x9d and compressible. The protruding member may be comprised of a simple structural component, such as a beam, peg, cushion, or post; or may be comprised of a multi-component assembly, such as a truss or mechanical actuator. Additionally, the protruding member may be attached to both the substrate and the beam; attached to the substrate only; or attached to the beam only. These characteristics are combined in specific embodiments of the invention, as summarized below.
In an embodiment of the invention, the protruding member comprises a relatively rigid, incompressible post that is mounted to the substrate underneath the cantilever beam, at a position intermediate between a fixed end of the beam and its free end. In this embodiment, the post is shorter than the beam clearance. The post is positioned such that when the free end of the beam is deflected a desired distance towards the substrate (such as by contact with a mating electronic component), the beam contacts the top of the post. The post can be configured to act purely as a mechanical element, for increasing the contact force exerted at the free end of the beam. Alternatively, or in addition, the post can act as a component of an electrical switch that is activated when contacted by the beam. In a variation of this embodiment, the post is mounted to the underside of the beam, and is spaced apart from the substrate when the beam is in an undeflected position. As the beam is deflected, the post contacts the substrate, again serving as a mechanical element, an electrical element, or both. A protruding member mounted to the beam can optionally be configured to provide a reverse wiping action at a contact tip of the spring structure.
In an alternative embodiment, the protruding member comprises an electronic device, such as a capacitor. In this embodiment, the beam preferably extends from its support structure in at least two different directions. In one direction, the beam is cantilevered, and preferably has a contact tip located adjacent to its free end, for contacting the terminal of another electronic component, such as a semiconductor device. In a second direction, the beam is connected to the electronic device, which is in turn connected to a terminal on the substrate. Less preferably, the electronic device is connected to the beam at some other position, such as intermediate between the free end of the beam and the beam""s support structure.
In yet another embodiment, the protruding member is resilient and substantially compressible, comprising a compressible member or assembly, such as an elastic membrane or bellows enclosing a fluid. When the contact tip of the spring structure is deflected towards the substrate, the compressible assembly contacts the beam and exerts an upward force on the beam in proportion to the degree of compression. In an embodiment of the invention, the degree of compression of the compressible assembly (and hence, the force exerted by it) partially depends on the pressure of a fluid enclosed within it. The fluid pressure is optionally controlled by a fluid control device, such as a pump or cylinder, connected to the device. The adjustable pressure assembly is configured so that it can be expanded to press against the underside of the beam when the contact tip of the beam is adjacent to or contacting an electronic component. Thus, the adjustable pressure assembly can be used to provide or supplement the contact force exerted by the spring structure. Various alternative assemblies for performing this function are additionally disclosed herein.
A more complete understanding of the microelectronic spring structure with an additional protruding feature will be afforded to those skilled in the art, as well as a realization of additional advantages and objects thereof, by a consideration of the following detailed description of the preferred embodiment. Reference will be made to the appended sheets of drawings, which will first be described briefly.