# Patent

## Title
Electrical contact and connector and method of manufacture

## Abstract

An electrical contact (2) and method of making the electrical contact (2), and a connector (11) and method making the connector (11), wherein the electrical contact (2) is an electrically conducting, nonwoven mesh (60), with edges of the mesh providing multiple contact points for edgewise electrical connection of the electrical contact (2), wherein the mesh (60) is annealed while restrained in the form of the electrical contact (2) wherein the mesh (60) is free of internal elastic strain, and wherein the connector (11) retains the electrical contact (2) for edgewise connection.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Patent Application No. 60/503,007, filed Sep. 15, 2003.
This application is a continuation in part of U.S. patent application Ser. No. 10/736,280, filed Dec. 15, 2003.
U.S. patent application Ser. No. 10/736,280, filed Dec. 15, 2003 claims the benefit of the following provisional applications; U.S. Provisional Patent Application No. 60/457,076, filed Mar. 24, 2003, U.S. Provisional Patent Application No. 60/457,258, filed Mar. 25, 2003, and U.S. Provisional Patent Application No. 60/462,143, filed Apr. 8, 2003.


FIELD OF THE INVENTION
The present invention generally relates to electrical interconnection devices, and more particularly to electrical contacts that are at the interface between a first electronic device and a substrate or between an electrical connector and the same.
BACKGROUND
High density integrated circuit (IC) packages that house LSI/VLSI type semiconductor devices are well known. Input/output pins for such IC packages are often arranged in such a dense pattern (sometimes more than two hundred closely spaced contacts) that direct soldering of the IC package to a substrate, such as a printed wiring or circuit board (PCB) creates several significant problems related to inspection and correction of any resulting soldering faults. Land grid array (LGA) connectors are known for interconnecting IC packages to PCB's. LGA's typically do not require soldering procedures during engagement with the PCB. Prior art LGA assemblies are used to interconnect an IC package having a plurality of flat contact pads or solder bumps formed on a bottom surface, to contact pads arranged in a regular pattern on a surface of PCB.
Prior art LGA assemblies are known which include an insulative housing and a plurality of resilient conductive contacts received in passageways formed in the housing.
Resilient conductive contacts typically have exposed portions at the upper and lower surfaces of insulative housing for engaging flat contact pads. When IC package is accurately positioned in overlying aligned engagement with PCB, such that conductive pads engage conductive pads, a normal force is applied to the exposed portions of each resilient conductive contact to electrically and mechanically engage the respective contact pads.
The resilient conductive contacts associated with prior art LGAs have had a variety of shapes. A commonly used form of resilient conductive contact includes two free ends connected by a curved, resilient portion which provides for the storage of elastic energy during engagement with the IC package and PCB. Prior art resilient conductive contacts may be a single metal structure in the form of a spring to provide the required elastic response during service while also serving as a conductive element for electrical connection. Alternatively, contact buttons have been developed in which a connector is wound around, embedded, or otherwise engaged with a dielectric core, which often provides for elastic energy storage during operation with the conductor merely providing an electrical conduction pathway. Typically, a combination of barrier metal and noble metal platings are applied to the surface of the spring for corrosion prevention and for electrical contact enhancement. It is often the case that these platings are not of sufficient thickness for electrical conduction along only the surface of the spring. Examples of such prior art resilient conductive contacts may be found in U.S. Pat. Nos. 2,153,177; 3,317,885; 3,513,434; 3,795,884; 4,029,375; 4,810,213; 4,820,376; 4,838,815; 4,922,376; 5,030,109; 5,061,191; 5,101,553; 5,127,837; 5,215,472; 5,228,861; 5,232,372; 5,308,252; 5,350,308; 5,385,477; 5,403,194; 5,427,535; 5,441,690;5,473,510; 5,495,397; 5,599,193; 5,653,598; 5,791,914; 5,800,184; 5,806,181; 5,810,607; 5,817,986; 5,823,792; 5,833,471; 5,949,029; 6,074,219; and 6,264,476. The foregoing patents are hereby incorporated herein by reference.
A problem in the art exists in that, a conductive contact in the form of a single conductor spring for attaining high compliance, has a high resistance and a high inductance. Further, a contact, in the form of multiple conductors in a bunched wire bundle, or in the form of a conductor structure embedded in a polymer core, is made with lower resistance and inductance than a single conductor spring, but requires a high contact force for deflection, and is unable to attain high compliance. Further, one problem in the art exists in that a good material for the construction of a spring, such as a high strength steel, is not a very good electrical conductor. On the other hand, a good electrical conductor, such as a copper alloy or precious metal, often does not provide adequate spring properties. There is a need for a more resilient conductive contact which incorporates the seemingly opposing requirements of good spring properties, temperature resistance, and high conductivity, but without the need for any integral supporting structure. Therefore, an improved electrical contact for use in an LGA socket or electrical connector is needed which can overcome the drawbacks of conventional electrical contacts.
Thus, it is desirable that a good electrical contact element possesses the following attributes: (a) usable for both a production socket, as well as, test and bum-in sockets, where the latter use requires high durability; (b) a large elastic compliance range and low contact forces; (c) capable of transmitting high frequency signals and high currents; (d) capable of withstanding high operating temperatures; and (e) exhibiting high durability, i.e. >500K repeated deflections.
The prior art has been devoid of at least one of the foregoing attributes necessary for a universally applicable electrical contact.
SUMMARY OF THE INVENTION
The present invention provides an electrical contact formed from a precursor material, such as an etched or stamped metal sheet. The terminology, electrical contact, is used herein interchangeably with the terminology, electrical contact element.
Embodiments of an electrical contact and the manufacture thereof are disclosed in U.S. application Ser. No. 10/736,280, filed Dec. 15, 2003, hereby, incorporated herein by reference, wherein, an electrical contact is formed from a precursor material made into a mesh, such as, an etched or stamped metal sheet, or a plurality of interlaced metal wires. The precursor materials may be formed into a tube or other appropriate shape, and annealed to set their structural form. The annealed structure may then be cut into short segments to form a plurality of individual electrical contacts. The precursor materials are often formed by photo-etching a sheet of conductive material into a mesh with openings of predetermined size and shape. The mesh may also be made by stamping with a conventional metal working die. Alternatively, the precursor material may be made by manipulating a plurality of wires so as to interlace the wires into a unitary structure in the form of a mesh. The desired form factor of the electrical contact can be made by first rolling a portion of the precursor material into a tube and followed by annealing under a constraint to set the form factor permanently. The tubular structure is then cut into short segments to form individual electrical contacts. The preferred structural forms include folded structures of one or more pleats formed from the precursor material. Such a structure can be made by pressing a unitary mesh structure in a die adapted to form pleated or folded structure in the mesh, followed by annealing the pleated or folded mesh while resident in the die to set permanently the structural form. It is then cut to form individual electrical contacts.
Such an electrical contact preferably has an all metal structure, is mechanically stable under large displacement, has a high compliance, low inductance and high electrical conductance.
An embodiment of an electrical contact in accordance with the present invention is an electrically conducting, nonwoven mesh, wherein the mesh comprises an unsupported electrical contact; and wherein the mesh is substantially free of elastic strain while in the form of the electrical contact.
According to another embodiment, the mesh is corrugated by having pleats. According to a further embodiment, each pleat comprises either a folded pleat or an unfolded pleat.
An electrical connector in accordance with the invention includes, but is not limited to, an interposer, a land grid array, a test fixture, and in accordance with the invention that has a carrier, wherein the carrier retains one or more electrical contacts arranged in an array. The array corresponds to a pattern of electrical contact pads on an electrical device or component. The contacts are interposed between the contact pads and opposing contact pads on another electrical device or component, such as, a substrate including, but not limited to, a PCB, a patterned semiconductor wafer and a patterned semiconductor transmission line.
An electrical connector in accordance with the invention includes a test fixture that has a carrier retaining electrical contacts arranged in an array, the carrier has a planar, polished surface for planarity testing, the carrier has a pattern of electrical contact pads on the planar, polished surface for electrical continuity testing, and the electrical contacts provide electrical interconnections with the electrical contact pads.
Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a front view of a mesh made by a perforated sheet having a pattern of diamond shaped openings, including, but not limited to, rhombic shaped openings and rhomboid shaped openings.
FIG. 1B is a front view of a mesh made by a perforated sheet having a pattern of round shaped openings, including, but not limited to, oval shaped openings and circular shaped openings.
FIG. 1C is an exploded perspective view of a photo-mask being applied to a sheet of conductive metal so as to form a mesh in accordance with an embodiment of the invention.
FIG. 1D is an alternative mesh forming a perforated sheet similar to that shown in FIGS. 1A and 1B, and showing a pattern of varying width openings between beam intersecting points.
FIG. 1E is a cross-sectional view of a beam section forming the electrical contact of the present invention.
FIG. 1F is a view similar to FIG. 1E and showing an insulation layer or a composite layer of a noble and/or highly conductive metal followed by an insulation covering the beam section of the electrical contact of the present invention.
FIG. 1G is a top view of a mesh and illustrating the process of being rolled into a tubular contact as one form of a cage in accordance with the present invention.
FIG. 1H is an isometric view of a cage configuration, including a tubular configuration.
FIG. 1J is an isometric view of a cage configuration, including a square.
FIG. 1K is an isometric view of a cage configuration, including a rectangle.
FIG. 1L is an isometric view of a mandrel and a mesh shaped over the mandrel.
FIG. 2A is an edgewise view of a perforated sheet during shaping thereof in a die to a shape of one or more electrical contacts.
FIG. 2B is a top view of a small piece of a pleated structure in the form of an electrical contact.
FIG. 2C is an isometric view of the small piece shown in FIG. 2B in the form of an electrical contact.
FIG. 2D is a top view of a small piece of a pleated structure in the form of an electrical contact.
FIG. 2E is an isometric view of the small piece shown in FIG. 2B in the form of an electrical contact.
FIG. 2F is an edgewise view of a small piece of a pleated structure during shaping thereof to the shape of a compact electrical contact.
FIG. 3A is a fragmentary side view or elevation view of an embodiment of an interposer with a retention hole having an exemplary contact element and an adhesive therein,
FIG. 3B is view similar to FIG. 3A, and disclosing an embodiment of an interposer with a retention hole having an exemplary contact element retained by elastic expansion of one or more protrusions in the retention hole.
FIG. 3C is a view similar to FIG. 3A, and disclosing an embodiment of an interposer with a retention hole having an exemplary contact element retained by elastic expansion of the contact element.
FIG. 3D is a side view or elevation view of an interposer, also referred to as a land grid array, as one form of an electrical connector.
FIG. 3E is a side view or elevation view of another embodiment of an interposer as one form of an electrical connector.



DETAILED DESCRIPTION
This description of preferred embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description of this invention. The drawing figures are not necessarily to scale and certain features of the invention may be shown exaggerated in scale or in somewhat schematic form in the interest of clarity and conciseness. In the description, relative terms such as “horizontal,” “vertical,” “up,” “down,” “top” and “bottom” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing figure under discussion. These relative terms are for convenience of description and normally are not intended to require a particular orientation. Terms including “inwardly” versus “outwardly,” “longitudinal” versus “lateral” and the like are to be interpreted relative to one another or relative to an axis of elongation, or an axis or center of rotation, as appropriate. Terms concerning attachments, coupling and the like, such as “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. The term “operatively connected” is such an attachment, coupling or connection that allows the pertinent structures to operate as intended by virtue of that relationship. In the claims, means-plus-function clauses are intended to cover the structures described, suggested, or rendered obvious by the written description or drawings for performing the recited function, including not only structural equivalents but also equivalent structures.
Each of FIGS. 1A and 1B discloses a precursor mesh 60 in the form of a nonwoven mesh, for example, a perforated sheet 60, shown with diamond shaped openings 3 in FIG. 1A and oval shaped openings 3 in FIG. 1B. The compliance of each contact element 2, interchangeably referred to herein as an electrical contact 2, is dependent on the shape and dimensions of the opening 3, and the dimensions of the side arm, also referred to as, either a beam or individual beam section 6, at the boundary of a corresponding opening 3, and its material construction. According to an embodiment, the mesh 60 includes a wide strip that can be divided into a number of narrow strips, wherein each of the narrow strips has a width equal to the height of an electrical contact 2, such as, the height disclosed by the contact 2 in FIG. 2C and FIG. 2E, respectively.
A connector system may be formed in accordance with the invention including a housing defining a plurality of openings that are each filled with an electrical contact of the present invention. In one embodiment, a connector system may be formed including a housing defining a plurality of openings that are each filled with an electrical contact comprising a unitary mesh made by a perforated sheet that is corrugated, wherein the perforated sheet is formed with corrugations having at least one pleat. Each pleat comprises either a folded pleat or an unfolded pleat.
The present invention provides an electrical contact 2 that comprises a large elastic range as a result of being formed so as to comprise an annealed metal structure that provides a plurality of individual beam-sections 6.
An electrical contact element 2 preferably has an all metal structure, is mechanically stable under large displacement, has a high compliance, low inductance and high electrical conductance. U.S. application Ser. No. 10/736,280, filed Dec. 15, 2003, has emphasized a cage-like structure, for example, a tube or other appropriate shape, made of weaved wires 8 which has been shown to amply meet the above requirements. Embodiments made of a perforated sheet 60 by wrapping, folding and a combination of the two were described. The high compliance achieved by the cage-like embodiment of weaved wires 8 is a result of the weaved open structure of the cage wall. For example, a mesh of weaved wires 8 structure typically offers a diamond shaped opening with sides of nearly straight wires 8.
A perforated sheet 60 can produce the same openness and offer more options for the pattern of the opening 3 made by a perforation 3. The perforation 3 of a sheet 60 can easily be produced with other shapes such as round or oval shaped openings 3 as required for engineering the compliance of the electrical contact element 2.
The perforation 3 can be produced by etching, stamping, deposition, plating and other processes. For obtaining fine structures, etching is a preferred method. A mesh or perforated sheet 60 can be formed in accordance with the present invention by casting, vapor deposition or other positive (additive) metal deposition processes. Whereas, a woven mesh 60 is made by individual beam sections that are interlaced, by weaving, braiding and the like, the nonwoven mesh 60 according to the invention has beam sections 6 surrounding the perforations 3, wherein the beam sections 6 are non-interlaced. Further, the beam sections 6 are unitary with one another to provide a unitary mesh 60. According to an embodiment, a mesh 60 may be formed through a photo-etching process in which a mask 64 is applied to a sheet of conductive material, e.g., stainless steel 68, and photo-etched in accordance with a conventional method (FIG. 1C). The resulting flat mesh 60 comprising an array of intersecting beams 6, or beam-sections 6, defining an array of openings 3 that are etched through the sheet 68. Alternatively the openings 3 are drilled, laser ablated or punched. The mesh 60 is then divided into individual contacts 2, wherein the individual contacts 2 may then be rolled or pleated as disclosed herein. Photo-etched mesh 60 must be annealed while either rolling or pleating in order to substantially eliminate the elastic strain stored within photo-etched mesh 60 so that slippage of the metal crystals occurs in a controlled manner. In this way, the metal is composed of regular crystals that have taken a set in their photo-etched and either rolled or pleated configuration. The compliance of the etched mesh structure will depend upon several factors, including its cross-sectional dimensions, openings that vary in size, wherein the size is measured by the ratio of the height and width of the mesh opening 3, e.g., an array of rhomboidally shaped or diamond shaped openings 3. A mesh 60 may be formed with an array of diamond shaped openings 3 having varying ratios of the height and width of the mesh opening 3 (FIG. 1A). The smaller the ratio, the higher will be the compliance at low applied force. Thus, compliance of the electrical contact is determined by a ratio of the long axis and the short axis of the openings 3 and the cross sectional dimensions of the beam sections 6.
The present invention provides an electrical contact 2 that comprises a large elastic range as a result of being formed as an annealed metal structure that provides a plurality of individual beam-sections 6.
Annealing is performed while the mesh 60 is being shaped to the shape of at least one electrical contact 2, and preferably while the mesh 60 is being shaped to the shape of one or more electrical contacts 2. Annealing substantially eliminates or substantially relieves internal elastic strain in each electrical contact 2. The substantial elimination or relief of internal elastic strain enables the contact 2 to maintain a compact shape without the contact 2 enlarging or warping by springing action to relieve internal elastic strain. Further, the substantial elimination or relief of internal elastic strain enables each electrical contact 2 to undergo relatively large amounts of deflection in the elastic range before reaching an elastic limit, which avoids permanent deformation of the contact 2 when the contact 2 deflects compliantly under compression while making an electrical connection. Further, the large range of deflection in the elastic range provides a wide range of compliancy when making an electrical connection.
Electrical contact 2 may be formed by forming an electrical contact precursor mesh 60 as a perforated sheet 60, wherein the perforated sheet 60 is shaped to the shape of an unsupported, stand alone electrical contact 2 by being formed in a cage configuration, including but not limited to, either a tubular or tube configuration, FIG. 1H, a square, FIG. 1J, a rectangle, FIG. 1K, or other form of cage configuration with open ends for edgewise electrical connection, or by being formed into a corrugated sheet 60 configuration that has one or more pleats, folded pleats or unfolded pleats, for edgewise electrical connection. Advantageously, the tubular or cage embodiments of the present invention, and the corrugated sheet 60 embodiments, of the present invention do not require there to be a central support structure around which the mesh 60 is wound or, an outer or inner support structure within which the mesh 60 resides in a formed electrical contact configuration, since the combination of a perforated sheet 60 or mesh 60 while annealing the mesh 60 removes the need for any additional integral or over-laid, co-extruded, or over-molded structural support. In other words, the electrical contacts 2 can be operated for their intended purpose while simply comprising a mesh 60 that has been manipulated to take a shape suitable for interconnecting two or more adjacent structures or opposing electronic components. It is in this sense then that electrical contacts 2 of the present invention are said to comprise an unsupported structure, also referred to herein as stand alone.
Typically, electrically-conductive beam-sections 6 suitable for use in the present invention will have a minimum cross sectional dimension in the range from about 0.025 to 0.1 millimeters. The diagonal dimensions of the diamond shaped openings 3 between adjacent beam-sections 6 are typically in the range from about 0.1 to 0.5 millimeters.
Advantageously, electrical contact 2 is subjected to an annealing process so as to substantially set each individual beam-section 6 in its shape free of internal strain and as a structural element or constituent of the mesh 60. Annealing for a stainless steel is conducted at temperatures ranging from about 500° C. to about 600° C., with about 550° C. being preferred for most applications. According to another preferred embodiment, annealing is conducted in a range of 550° C. to 650° C., with about 625° C. being preferred for most applications.
The perforated sheet 60 is first made into a corrugated sheet 60 of an appropriate amplitude which is of the order of the diameter of the retention hole in an interposer. A die of a top piece and a bottom is used to deform the sheet 60 into the desired shape. The deformation involves a combination of elastic deformation and plastic deformation. Under the constraint of the die the sheet 60 is annealed at an elevated temperature adequately to set the desired corrugated shape, and substantially relieve internal elastic strain. Referring to FIGS. 1E and 1F, the electrically-conductive beam-sections 6, shown as having etched circumferences, may either be bare, as in FIG. 1E, or have an insulation layer or a composite layer of noble and/or highly conductive layer followed by an insulation layer or coating 27 applied to their outer surfaces, as in FIG. 1F. According to another preferred embodiment, after annealing the sheet 60 is first cut into long strips the width of which is the height of the contact element 2. The strip is then cut into pieces of desired width to produce the electrical contact element 2.
In one embodiment, mesh 60 is wrapped upon itself so as to form a plurality of overlapping layers providing an individual contact 2 as a substantially helical wrap structure, as one form of a cage structure, FIG. 1G.
Advantageously, electrical contacts 2 of the present invention may be formed by constraining them in a precursor form, then annealing them at a sufficiently high temperature together with the stored elastic strain, and dislocations will be generated and moved to permanently set the shape of the electrical contacts 2 thus relaxing the stored elastic strain and substantially relieving the same. The extent of deformation in the elastic range is limited so that the shape of the beam section 6 cross-section, for example, will not be altered and it will be easier to design the die or other means of constraint. A folded or unfolded pleated structure may be formed by annealing the structure, while still elastically deformed in a properly designed die or other fixture which serves as the constraint. For a rolled electrical contact structure, a properly designed constraint to maintain the tubular form of the structure is necessary during annealing.
To maintain a good surface condition heat treatment should be carried out in a controlled atmosphere furnace at the appropriate temperature for the particular grade of stainless steel or, in a less preferred embodiment, alloy of copper which may also be oil quenched to achieve maximum hardness, and further oil quenched and strain hardened.
Suitable sheet material has a bulk resistivity below about 100 μΩ/cm, and preferably about 2 to 5 μΩ/cm. Typically, the sheet material will be conductive metal, such as, tungsten and its alloys, stainless steel or alloys of copper, that may have portions coated with highly conductive metals (identified by reference numeral 25 in FIG. 1A), such as, silver, palladium, rhodium, gold, and the various alloys thereof. Alternatively, suitable electrically conductive sheet material can be prepared by introducing a conductivity-imparting agent such as metal particles to a natural or synthetic polymer or other material, such as carbon. While polymer composites may not be able to withstand typical annealing temperature, a ceramic/metal composite may be used with good effect
FIG. 1H, FIG. 1J and FIG. 1K are illustrated with outlines along the edges of the electrical contacts 2. However, the outlines represent cutting lines, where the edges of the electrical contacts 2 are cut to provide multiple contact points. Just like the tube, FIG. 1H, or other cage-like structure, FIG. 1J and FIG. 1K, the folded pleated structure or unfolded, pleated structure thus produced will provide multiple electrical contact points along edges of the electrical contacts 2 from the top edge and from the bottom edge, the number of which contact points will depend on the size of the perforation 3, for edgewise electrical connection. Electrically it should also perform like a weaved structure in terms of inductance and electrical conductance.
The sheet material of the perforated sheet 60 preferably has a high yield strength. The yield strength is enhanced by hardening due to forming the sheet 60 with a limited amount of inelastic deformation, in addition to elastic deformation. It should be able to retain its yield strength after processing the hardened sheet 60 by annealing, which substantially relieves only the elastic deformation. For example, annealing is performed to set the shape of a corrugated structure, such as, the unsupported, stand alone electrical contact 2 in accordance with the present invention, including embodiments of the present invention, wherein a mesh 60 is made by a perforated sheet 60 that is formed in a tube or cage structure having folds, or is corrugated to form pleats. Each pleat comprises either a folded pleat or an unfolded pleat. The material can be a monolithic metallic alloy or a metal composite.
With reference to FIGS. 2B and 2C, an embodiment of an electrical contact 2 cut from a perforated sheet 60 of an appropriate width to height ratio can be folded into an unsupported, stand alone folded structure to produce mechanical stability under displacement. An unfolded embodiment is disclosed in FIGS. 2D and 2E.
When viewed from above, edgewise of the sheet 60, the sheet 60 can be formed into a tube shape according to the shape of an individual contact 2, wherein the individual contact 2 is an enclosure, an unsupported, stand alone structure, according to which the unsupported, stand alone structure can have a shape of a folded square, FIG. 1J, a folded rectangle, FIG. 1K, an unfolded rounded tube, FIG. 1H, or other cage configuration for edgewise electrical connection of the sheet 60. For example, the sheet 60 is formed by wrapping and folding the sheet 60 over a mandrel 20, FIG. 1L, that has a cross section shape to which the sheet conforms to assume the desired shape of at least one contact 2, and preferably one or more contacts 2. The tube shape of the sheet 60 has an axial or longitudinal open seam. The tube form of the sheet 60 comprises at least one electrical contact 2, and preferably one or more electrical contacts 2. The sheet 60 is annealed while being held in the tube shape to substantially relieve elastic strain. Further, the sheet 60 is easily formed by bending and folding the sheet to assume an M-shape, or other shapes. The M-shaped structure is easy to make, the method of manufacturing for which will be described. The method of manufacture applies for making the folded embodiment of FIGS. 2B and 2C, and for making the unfolded embodiment disclosed in FIGS. 2D and 2E.
A corrugated perforated sheet 60 is shown edgewise, having an edge 50 in FIG. 2A. The corrugated shape can be produced by compressing a perforated sheet 60 between mating or nesting die sections 71 and 73 of a forming die 75, wherein the nesting die sections 71 and 73 are two pieces having desired shapes at corrugated mating faces that close toward one another and form therebetween the perforated sheet 60 to a corresponding corrugated shape that conforms to the mating faces. The die sections 71 and 73 separate to permit removal of the perforated sheet 60 that has been formed or shaped into a corrugated shape, the shape of at least one electrical contact 2, and preferably to the shape of one or more electrical contacts 2. While constrained in the die 75, annealing at an elevated temperature is performed to set the shape or each electrical contact 2 in the perforated sheet 60 permanently, while such annealing substantially relieves solely the elastic strain. The annealing temperature is selected below a temperature that would reduce any yield strength. Thus, annealing retains substantial amounts of yield strength. To recover some of the lost yield strength due to annealing, the sheet 60 can be hardened by a controlled amount of inelastic deformation, by being formed a second time, to a more compact corrugated shape.
After annealing, the sheet 60 is in a strain relieved corrugated configuration, and is cut to the height of the contact element 2, as shown in FIG. 2C and FIG. 2E. For example, the sheet 60 comprises one or more strips, wherein the width of each strip equals the height of a contact element 2. Each strip comprises at least one electrical contact 2, and preferably one or more electrical contacts 2. Thereby, after being shaped to at least one electrical contact 2, and preferably one or more electrical contacts 2, while being annealed, the sheet 60 is divided into strips, and the width of each strip is the height of an contact element 2.
Alternatively, prior to being shaped in the die 75, the sheet 60 comprises one or more strips, wherein each strip is the height of the electrical contact 2. Each strip comprises at least one electrical contact 2, and preferably one or more electrical contacts 2, prior to being shaped and restrained in the die 75, while being annealed. Thereby, the sheet 60 is partly shaped to that of an individual contact 2 by being cut to the height of an individual contact 2.
Before each strip of the sheet 60 is further cut into smaller pieces 5, the edges 50 of each sheet 60 that has been cut to the height of the contact element 2 are applied with, for example, are plated with, nickel, serving as a barrier to formation of an inter-metallic due to metal migration. Then a coating of a highly conductive and noble metal is applied over the barrier of nickel. Alternatively each of the smaller pieces have their edges 50 applied with a barrier and a highly conductive and noble metal. The conducting edges 50 provide multiple points of electrical contact that are made highly conductive, when applied with the highly conductive and noble metal. Alternatively, the entire perforated sheet 60 is applied with a barrier and a highly conductive and noble metal to decrease the bulk resistivity.
Each of the strips is further cut into smaller pieces 5 of the sheet 60 to produce individual contact elements 2. The contact element 2, in FIG. 2C, is shown in its top view in FIG. 2B.
According to another embodiment, to recover or restore some of the lost yield strength due to annealing, the electrical contact 2 is hardened by a preconditioning operation, wherein the entire contact 2 is compressed axially in a direction, open end to open end, with sufficient deformation under compression to increase hardening due to a controlled amount of inelastic deformation, or plastic flow, substantially throughout the mesh 60. Thereby, the electrical contact 2 has an enhanced yield strength.
According to another embodiment, the small piece 5 may be given a second anneal under an elastic constraint to set the shape of a tighter structure compared to that of the sheet 60. For example, the tighter structure refers to an electrical contact 2 having a compacted cross-section to fit within a retention hole 8 of less than 10 mils cross-sectional dimension or diameter.
FIG. 2F discloses that the small corrugated piece 5 is further shaped into a more compact shape of an electrical contact 2, when the small piece 5 needs a more compact corrugated shape that can be produced by the die 75, in FIG. 2A. For example, the die 75 may have dimensional limitations that limit how small the corrugations can be made. To make a corrugated shape of a more compact electrical contact 2, first, the small piece 5 is shaped with a corrugated shape, in the manner, as disclosed by FIG. 2A, and is subjected to a first anneal by a first annealing process. Then the corrugated small piece 5 is removed from the die 75 and is further shaped to form a more compact electrical contact 2. The corrugated small piece 5 is inserted between mating or nesting die sections 77 and 79 of a forming die 81. For example, the corrugated small piece 5 is oriented sideways in a die cavity 77a of the die section 77. The mating die section 79 has a ram 79a that inserts along the die cavity 77a to compress and elastically deform the corrugated small piece 5 to a more compact shape of an electrical contact 2. In an alternative embodiment, a limited amount of permissible added compression produces a limited amount of inelastic deformation of the small piece 5 to a more compact shape, which supplements the elastic deformation. While remaining under elastic constraint in the die cavity, the corrugated small piece 5 is subjected to a second anneal by a second annealing process. The second annealing process sets the shape of the compact corrugated small piece 5 to the shape of a compact electrical contact 2, substantially free of only the elastic strain.
According to another embodiment, to recover some of the lost yield strength due to a second anneal, the electrical contact 2 is hardened by a preconditioning operation, wherein the entire contact 2 is compressed axially in a direction, open end to open end, with sufficient deformation under compression to cause a limited amount of inelastic deformation, or plastic flow, substantially throughout the mesh 60. Thereby, the electrical contact 2 has an enhanced yield strength.
FIGS. 2B and 2C disclose an embodiment of an individual electrical contact 2 in accordance with the present invention, wherein a mesh 60 made by a perforated sheet is corrugated to form the pleats 45 having at least one trough 47 and at least one peak 49. Each corrugation is doubled back on itself to form an adjacent pair of pleats. FIGS. 2B and 2C disclose a folded pleat, wherein each corrugation is doubled back on itself and folded, which defines a fold at each trough 47 between adjacent pleats 45, and another fold at each peak 49, between adjacent pleats 45. Thus the corrugations form folded pleats 45. FIGS. 2B and 2C are illustrated with outlines along the edges of the electrical contacts 2. However, the outlines represent cutting lines, where the edges of the electrical contacts 2 are cut to provide multiple contact points.
FIG. 2D and FIG. 2E disclose another embodiment of an individual electrical contact 2, wherein a mesh 60 made by a perforated sheet is corrugated to form the pleats 45 having at least one trough 47 and at least one peak 49. Each corrugation is doubled back on itself to form an adjacent pair of pleats. FIGS. 2D and 2E disclose an unfolded pleat, wherein each corrugation is doubled back on itself without being folded between adjacent pleats 45. Thus the corrugations form unfolded pleats 45. To form the unfolded pleats 45 in the mesh 60, the die sections 71 and 73 are modified to have corrugated mating faces with curved bends at the troughs 47 and the peaks 49, such that the mesh 60 is shaped therebetween with conforming unfolded pleats 4 having curved bends at the troughs 47 and the peaks 49. FIGS. 2D and 2E are illustrated with outlines along the edges of the electrical contacts 2. However, the outlines represent cutting lines, where the edges of the electrical contacts 2 are cut to provide multiple contact points.
Mesh 60 may be corrugated so as to create a plurality of pleats 45 defined by a plurality of troughs 47 and ridges 49. Pleated electrical contacts 2 may then be cut from mesh 60. A contact edge 50 is defined along each of the perimeter edges 50 of pleats 45 for edgewise electrical connection. The perimeter edges 50 are cut edges of the mesh 60. The cut edges of the mesh 60 intersect the beams or beam sections 6 at the boundaries of the mesh openings 3 to provide intersected beams or beam sections 6 along the edges 50. The intersected beams or beam sections 6 at and distributed along the edges 50 provide multiple contact points along the perimeter edges 50, which advantageously increase the number of electrical conduction paths through each contact 2. Thus, each contact 2 is a mesh 60 that provides multiple contact points along the perimeter edges 50 of the mesh 60, which contact points establish corresponding, multiple electrical connections with and for the contact 2.
Further, the pleated electrical contacts 2 are positioned within a plurality of passageways or openings 35 within housing E such that contact edge 50 is positioned in spaced confronting relation to contact pads B (FIG. 3E). In this way, pleats 45 act to support the contact within openings 35. Further, the multiple contact points along the perimeter edges 50 of the mesh 60 provide multiple contact points against the sides of the openings 35. Thus, each contact 2 is supported mechanically by multiple contact points against the sides of the openings 35.
In an alternative embodiment, the sides of the openings 35 are electrically conducting, for example, by being lined with plated conductors. Thereby, each contact 2 establishes multiple points of electrical connection with the conducting sides of the openings 35.
In operation, as IC package A is moved toward housing E, contact pads B engage contact edge 50 of each pleated electrical contact 2 thereby deforming the pleated electrical contact 2 to produce a resultant contact force. Further, the contact 2 resiliently deflects under compression in a direction inwardly of the opening 35 which makes the contact 2 compliant to different dimensions when compressed. Here again, annealing pleated contact 2 allows for a set to be created, substantially relieved from internal elastic strain.
Three preferred designs of an interposer 11 are shown in FIGS. 3A, 3B and 3C, respectively. A carrier 7 is shown with an array of retention holes 8, also referred to as passageways 8.
An interposer 11 has a carrier 7 retaining electrical contact elements 2 arranged in an appropriate array to connect corresponding contact pads of two mating components e.g. an electronic package and a substrate, for example, a printed-circuit-board, PCB to be interconnected. The substrate includes, but not limited to, a PCB, a patterned semiconductor wafer and a semiconductor transmission line. The contact elements 2 are interposed between the opposing contact pads, respectively, on the two mating components. The contact elements 2 are compressed inwardly relative to the thickness of the carrier 7. Further the contact elements 2 are resiliently deflected in the thickness plane of the mesh 60, and thereby, provide a contact force for interconnecting the two mating components. Accordingly, the thickness of the carrier 7 has to be minimal in order to avoid interfering with the deformation of the contact element 2, but should be adequate to support the alignment of the contact element 2 under repeated loading and unloading like in the case of a test socket making repeated interconnections and disconnects of the contact elements 2 with devices being tested by the test socket.
The coefficient of thermal expansion of the carrier 7 preferably matches that of the two mating components. The location of the holes in the carrier that retains the contact element 2 should match that of the contact pad of the mating components.
FIG. 3D discloses another embodiment of an interposer 11, also referred to as a land grid array, LGA, an assembly comprising electrical contacts 2 in a carrier 7. The carrier 7 is also referred to as a housing E, in accordance with the present invention. Each electrical contact 2 is positioned within a retention hole in the form of a passageway 8 formed in housing E such that a first end 31 of each electrical contact 2 is positioned above a surface of housing E, and a second end 33 is positioned below a surface of housing E.
FIG. 3E discloses another embodiment of an interposer 11, wherein the carrier 7, referred to as a housing E, has a plurality of retention holes in the form of blind openings 35 arranged in an array that corresponds with, for example, the array of contact pads B on IC package A such that connections can be made, for example, between IC package A and circuit traces, for example, located on or in PCB, printed circuit board D, thus, interconnecting the same. The PCB is one form of a substrate including, but not limited to, a PCB, a patterned semiconductor wafer and a patterned semiconductor transmission line. Each electrical contact 2 is positioned within a blind opening 35 such that a first end 31 of each electrical contact 2 is positioned above a surface of housing E, and a second end 33 is positioned at the bottom of a blind opening 35.
According to an embodiment of an interposer 11, disclosed by FIG. 3E, each of the blind openings 35 is covered at one end thereof by a conducting pad 37 that forms an area of electrical connection at a corresponding bottom surface 39 of the housing E or carrier 7. The second end 33 of a corresponding electrical contact 2 engages the conducting pad with multiple points of connection along the edge of the mesh that forms the electrical contact 2.
According to another embodiment of the interposer 11, disclosed by FIG. 3E, the bottom surface 39 of the housing E or carrier 7 is substantially planar, for example, by machining. The substantially planar bottom surface 39 has each conducting pad 37 thereon for establishing an electrical connection with a corresponding contact 2 in a blind opening 35. Further, the substantially planar bottom surface 39 is useful for a test fixture for engaging a printed circuit board, PCB, a patterned semiconductor wafer and a patterned semiconductor transmission line, respectively, to test for planarity thereof. For example, the substantially planar bottom surface 39 is placed against a PCB to test for non-planarity. A non-planar PCB will cause localized gaps to occur between the non-planar PCB and respective conducting pads 37, whereas, a planar PCB will engage such respective conducting pads 37. Electrical test signals are supplied to the electrical contacts 2 that connect with the respective conducting pads 37. The test signals will detect whether the pads 37 connect with the PCB or are open circuited by the localized gaps with the PCB.
According to another embodiment of the interposer 11, disclosed by FIG. 3E, the carrier 7 is a semiconductor substrate that is formed into a carrier 7 by semiconductor fabrication processes. For example, the conducting pads 37 are formed by first applying an etch resistant mask over the surface 39 of the carrier 7, followed by patterning the mask by photo lithographic patterning and photo-developing the mask, leaving a pattern of vias or trenches, followed by etching the vias or trenches in the surface 39 of the carrier 7, followed by filling the etched vias or trenches with electrolytically plated conductive material to form the conducting pads 37. Then, the opposite surface of the carrier 7 is photo-masked and selectively etched to form the blind openings 35 in the carrier 7. Then, the bottom surface 39 of the housing E or carrier 7 is formed substantially planar, for example, by CMP, chemical mechanical planarization, wherein a polishing pad and a fluid polishing composition polishes the surface 39. Each contact 2 is assembled in a blind opening 35. The contact 2 engages edgewise with a corresponding pad 37 to establish an electrical connection therewith.
The materials of construction for the carrier 7 begins with a substrate including but not limited to, epoxy/glass composite, a sheet or film, for example, of Kaepton (Kapton), filled polymer, photosensitive polymer, semiconductor wafer, and others. An epoxy/glass composite is a glass fiber reinforced epoxy substrate for a PCB. The holes can be produced by drilling, laser drilling or a selective photo etch process. In general the location of a hole 8 is more precisely located when produced by a photo etch process compared to being produced by mechanical drilling or laser drilling. A photosensitive polymer is useful in the case where high precision in retention hole 8 location is desired, and obtained by masking selected parts of the photo-exposure polymer, then, photo-exposure of unmasked parts of the photo-sensitive polymer to photo-develop the same, followed by washing away the undeveloped photo-sensitive polymer, leaving a patterned mask, followed by etching an under layer of the substrate exposed by the patterned mask. A semiconductor wafer or substrate is useful for making a carrier 7 with retention holes 8 and/or blind openings 35 according to semiconductor manufacturing processes. Further, planarization by CMP, chemical mechanical planarization provides a planar polished surface on the substrate with minimized surface roughness and minimized surface planarity variation.
There are three preferred method of retention for the contact element 2 in a retention hole 8, including but not limited to, the blind opening 35, of a carrier 7:
a) (FIG. 3A) Filling the retention hole 8 with a appropriate adhesive 13 to retain the contact element 2. In FIG. 3A the contact element 2 is shown to be retained by filling the retention holes with an adhesive 13. If the adhesive 13 fills the retention hole 8 completely it will prevent the top part of the contact element 2 from wetting by molten solder during reflow to solder the lower part of the contact element 2 to a printed-circuit board D.
b) (FIG. 3B) Use a pleated contact element 2, in the form of a folded pleats structure or unfolded pleats structure, with slightly larger horizontal profile dimensions compared to corresponding cross section dimensions of one of the retention holes 8. Compact the contact element 2 into a smaller horizontal profile by compacting the contact element in the end of a guide tube 15. Insert the compacted contact 2 into a retention hole 8, using guide tube 15. Removing the guide tube from the contact 2, such that the contact will expand resiliently in the hole 8, wherein the retention of the contact 2 in the hole 8 is achieved by the elastic expansion of the folded pleats structure or the unfolded pleats structure, after it has been compacted from its original size for insertion into the hole 8, followed by elastic expansion while being constricted in the hole 8. FIG. 3B shows the contact element 2, is slightly larger sized than the retention hole, 8. The contact element 2 is introduced with the aid of the guide tube 15. After the removal of the guide tube the retention of the contact element 2, is achieved by the elastic expansion of the contact element 2.
c) (FIG. 3C) Construct a carrier 7 with retention holes 8 containing elastic protrusions 19. Insert the folded structure also by a guide tube, not shown. After removal of the guide tube retention is achieved by constriction and the elastic expansion of the protrusions in the retention hole. FIG. 3C shows a carrier 7 having retention holes 8, containing elastic protrusions 19. Such protrusions 19 can be produced, for example, by laminating a polymer sheet 21 as an inner layer of the carrier 7, wherein the polymer sheet 21 has a hole 23 of a smaller hole diameter compared to that of the retention hole 8 in the carrier 7. A compacted contact element 2 in a guide tube can be inserted into the hole 8, while introduced with the aid of the guide tube, not shown, for the compacted contact element 2 to intercept the hole 23 in the polymer sheet 21, and to resiliently deflect the protrusions 19 protruding in the hole 23. After the removal of the guide tube the contact element 2 is retained by the resilient stored energy tending to cause elastic expansion of the protrusion 19 against the contact 2.
Although the invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the invention, which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.

## Claims

1. An electrical contact comprising:
an electrically conducting, nonwoven mesh, wherein the mesh comprises an unsupported electrical contact comprising folded pleats so as to form at least one trough and at least one peak that each extend across said mesh in substantially parallel relation to one another, with the peripheral edges of the mesh comprising edges of said pleats thereby defining multiple electrical contact points along said peripheral edges that are arranged for edgewise electrical connection; and wherein the mesh is substantially free of elastic strain while in the form of the electrical contact.

2. The electrical contact as in claim 1, further comprising: highly conductive and noble metal located on said multiple contact points formed by said edges of said mesh.

3. The electrical contact as in claim 1, wherein the mesh has diamond shaped openings.

4. The electrical contact as in claim 1, wherein the mesh has round shaped openings.

5. The electrical contact as in claim 1, wherein the mesh has openings that vary in size.

6. The electrical contact as in claim 1, wherein the electrical contact has a compacted cross section, and wherein the compacted cross section is substantially relieved of elastic strain.

7. The electrical contact as in claim 1, wherein the mesh has openings and beam sections encircling respective openings, and wherein corresponding beam sections at the edges of the mesh provide the multiple electrical contact points for the electrical contact.

8. The electrical contact as in claim 1, wherein the mesh is a perforated conducting sheet.

9. An electrical connector, comprising:
one or more electrical contacts, wherein each of the electrical contacts is in the form of an electrically conducting, nonwoven mesh, wherein the mesh comprises an unsupported electrical contact comprising folded pleats so as to form at least one trough and at least one peak that each extend across said mesh in substantially parallel relation to one another, with the peripheral edges of the mesh comprising edges of said pleats thereby defining multiple electrical contact points along said peripheral edges that are arranged for edgewise electrical connection; and wherein the mesh is substantially free of elastic strain while in the form of the electrical contact; and
a carrier holding each of the electrical contacts for edgewise electrical connection.

10. The electrical connector of claim 9, wherein the peripheral edges of the mesh have beam sections of the mesh, wherein the beam sections provide the multiple contact points.

11. The electrical connector of claim 9, wherein the mesh is corrugated.

12. The electrical connector of claim 9, wherein the mesh has openings, and beam sections encircling respective openings; and wherein the beam sections at the peripheral edges of the mesh provide multiple contact points for each of the electrical contacts.

13. The electrical connector of claim 9, wherein the carrier has openings through a thickness of the carrier, and the electrical contacts are in the openings.

14. The electrical connector of claim 9, wherein the carrier is a housing having blind openings, the electrical contacts are in the blind openings, a first end of each of the electrical contacts is positioned above a surface of the carrier, and a second end of each of the electrical contacts are in the blind openings.

15. The electrical connector of claim 9, wherein the carrier is a housing having blind openings, conducting pads cover the blind openings, and the electrical contacts are in the openings, wherein each electrical contact has a first end positioned above a surface of the carrier, and each electrical contact has a second end engaging one of the conducting pads.

16. The electrical connector of claim 9, wherein, the carrier is a housing having blind openings, conducting pads at a bottom surface of the carrier cover the blind openings, the electrical contacts are in the openings, each electrical contact has a first end positioned above a surface of the carrier, each electrical contact has a second end engaging one of the conducting pads, and the bottom surface of the carrier is substantially planar.

17. The electrical connector of claim 9, wherein each electrical contact is in a retention hole of the carrier, and wherein an adhesive in the retention hole retains the electrical contact.

18. The electrical connector of claim 9, wherein each electrical contact is in a retention hole of the carrier, and wherein one or more protrusions in the retention hole retain the electrical contact.

19. The electrical connector of claim 9, wherein each electrical contact is constricted in a retention hole of the carrier to retain the contact in the retention hole.