Patent Application
20070105406
The present invention generally relates to interconnection systems for high speed electronics systems, and more particularly to an electrical contact assembly and connector system that is adapted for use in electronic systems that are capable of high speed data transmission.
High density integrated circuit (IC) packages that house LSI/VLSI type semiconductor devices are well known. Input/output contacts for such IC packages are often arranged in such a dense pattern (sometimes more than five 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 as well as thermal expansion mismatch failures.
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. Referring to
Prior art LGA assemblies E are known which include an insulative housing and a plurality of resilient conductive contacts F received in passageways formed in the housing. The resilient conductive contacts typically have exposed portions at the upper and lower surfaces of the insulative housing for engaging flat contact pads B,C. When IC package A is accurately positioned in overlying aligned engagement with PCB D, such that conductive pads B engage conductive pads C, 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 LGA's have had a variety of shapes. A commonly used form of resilient conductive contact includes two free ends connected by a curved portion which provides for the storage of elastic energy during engagement with the IC package and PCB. Prior art resilient conductive contacts are usually 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. Typically, a combination of barrier metal and noble metal platings is 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 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; 5,232,372; and 5,473,510. The foregoing patents are hereby incorporated herein by reference.
A problem exists in the high density electrical interconnection art 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, is often not a good spring material. There is a need for a simplified resilient conductive contact which incorporates the seemingly opposing requirements of good spring properties and high conductivity. Additionally, attributes, missing from the prior art that are necessary for a universally applicable electrical contact include: (i) extendibility to a large contact array at fine pitch, i.e., five mils (thousandths of an inch) or less and (ii) spring members of relatively small size but high elastic compliance, i.e., spring members capable of deflections in the elastic range of as much as thirty percent of their uncompressed or undeflected height, and with low contact force, i.e., less than twenty grams per contact. In addition, such a universally applicable electrical contact will be capable of high frequency transmittance of signals greater than ten gigahertz, which would require a small self-inductance and therefore a short contact height. Also, a universally applicable electrical contact will be capable of high current capacity, i.e., having less than ten milliohm bulk resistance per contact and low contact resistance. Furthermore, a universally applicable electrical contact will be capable of high durability or high cycles of touchdowns, i.e., greater than five hundred thousand cycles, which requires a spring having a high elastic compliance to avoid permanent set in contact height under repeated compressive loadings as well as high fatigue strength. Additionally, a universally applicable electrical contact will be capable of high reliability with minimum degradation in contact resistance which often requires a noble metal contact surface and redundancy in contact points. Also, a universally applicable electrical contact will be capable of high service temperatures, i.e., often exceeding two hundred and fifty degrees centigrade, which requires the structural part of the electrical contact to be made of high melting temperature metals to prevent the relaxation of contact force. All of the foregoing will be essential, but will only help solve the problems in the art if achieved with low cost manufacturing, using conventional high volume tools and processes.
Therefore, an improved electrical contact system and assembly for use in a wide variety of electrical connector and interface sockets and interposers is needed which can overcome the drawbacks of conventional electrical contacts and exhibit the foregoing attributes.
The present invention provides an electrical contact formed from a compliant folded sheet that includes a top surface, a bottom surface, a first contact edge and a second contact edge. A plurality of corrugations are formed in the top surface and the bottom surface that terminate at the first contact edge and the second contact edge. In one embodiment, the compliant folded sheet includes at least one crest corresponding to a top surface of a fold in the sheet and at least one trough corresponding to a bottom surface of a fold in the sheet. A plurality of longitudinally oriented corrugations are formed in the top surface of the folded sheet and the bottom surface of the folded sheet so as to form a plurality of longitudinally oriented ridges that are transversely spaced from one another by a plurality of longitudinally oriented furrows and that terminate at the first contact edge and the second contact edge.
In another embodiment of the invention, an electrical contact is provided that includes a plurality of wires in the form of a compound spring arranged one next to another and fastened to one another along an intermediate portion of their length so as to form a compliant sheet defining a plurality of independent cantilevered wires projecting outwardly from that intermediate portion.
The present invention also provides a connector system having a housing that has a plurality of through openings. A plurality of electrical contacts, each being formed from a compliant folded sheet that includes a top surface, a bottom surface, a first contact edge and a second contact edge. A plurality of corrugations are formed in the top surface and the bottom surface that terminate at the first contact edge and the second contact edge. Each of the electrical contacts is arranged within a corresponding one of the plurality of through openings such that the first contact edge is positioned outside of the through-opening in which electrical contact is positioned, and the second contact edge is positioned outside of the through-opening in which electrical contact is positioned, but spaced from the first contact edge.
In one embodiment of connector system, a carrier assembly is provided that includes a top sheet and a bottom sheet each being formed from an insulator coated metal, a rigid polymer, or a polymer composite and having an array of through-holes. An inactivated layer of adhesive is disposed between the top sheet and the bottom sheet so that the top sheet and the bottom sheet slide over one another so as to move from a first position to a second position. In the first position, the array of through-holes are arranged in coaxially aligned relation to one another thereby defining a first opening size. In a the second position, the top sheet and the bottom sheet are transversely shifted relative to one another thereby defining a second opening size that is narrower than the first opening size thereby grasping and holding on of a plurality of electrical contacts, with one of the electrical contacts located in a corresponding one of the through-holes. Each of the electrical contacts includes a compliant folded sheet including a top surface, a bottom surface, a first contact edge and a second contact edge. A plurality of corrugations are formed in the top surface and the bottom surface that terminate at the first contact edge and the second contact edge.
In another connector system, a carrier assembly is provided including a top sheet and a bottom sheet that are each formed from an insulator coated metal, a rigid polymer, or a polymer composite and have an array of through-holes. An inactivated layer of adhesive is disposed between the top sheet and the bottom sheet so that the top sheet and the bottom sheet slide over one another so as to move from a first position to a second position. In the first position, the array of through-holes are arranged in coaxially aligned relation to one another thereby defining a first opening size. In a the second position, the top sheet and the bottom sheet are transversely shifted relative to one another thereby defining a second opening size that is narrower than the first opening size thereby grasping and holding on of a plurality of electrical contacts, with one of the electrical contacts located in a corresponding one of the through-holes. Each of the electrical contacts includes a plurality of wires in the form of a compound spring arranged one next to another and fastened to one another along an intermediate portion of their length so as to form a compliant sheet defining a plurality of independent cantilevered wires projecting outwardly from the intermediate portion. The intermediate portion of each of the electrical contacts is located within a through-hole that comprises the second opening size.
These and other features and advantages of the present invention will be more fully disclosed in, or rendered obvious by, the following detailed description of the preferred embodiments of the invention, which are to be considered together with the accompanying drawings wherein like numbers refer to like parts and further wherein:
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, if used, 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.
Referring to
More particularly, each base sheet 4 is often formed from hardened stainless steel, comparable other metal alloys having high melting temperature characteristics, hardened high temperature compatible copper alloys, or their equivalent. Importantly, the metal sheet 18 used to form electrical contacts 2 should exhibit a high yield strength in the range from about 275 ksi to about 325 ksi, and most preferably 300 ksi or more. In one preferred embodiment, a vacuum melted, 304V stainless steel having a highly conductive metal coating 19 has been used to form base sheet 4 so as to provide high service temperature capability on the order of two hundred and fifty degrees centigrade while at the same time exhibiting high durability and high cycles of touchdowns that will exceed five hundred thousand cycles. This preferred material (304V stainless steel and related alloys) also provides the high elastic compliance which avoids permanent set in contact height under repeated compressive loadings and also exhibits high fatigue strength. A highly conductive metal coating 19 that has been found to yield adequate results includes a two hundred microinch to four hundred microinch copper layer for conductivity/bulk resistivity improvement, followed by a fifty microinch nickel barrier layer, and finally a fifty microinch gold outer layer. Of course, base sheet 4 may be electroplated, clad, laminated or otherwise coated with the forgoing metals in ways known in the art. The plating or cladding is often about ten percent to forty percent of the thickness of base sheet 4, and covers all sides except the cut surface adjacent to top contact edge 6 and bottom contact edge 8.
The plurality of longitudinally oriented corrugations may be formed in the top and bottom surfaces of base sheet 4 by etching, stamping, pressing, or skiving the surface so as to form a plurality of longitudinally oriented ridges 17 that are spaced from one another by a plurality of longitudinally oriented furrows 21 in a transverse sinusoidal pattern. Corrugated base sheet 4 is further formed, by conventional methods known in the art, into a pleat-like, folded structure (
In one embodiment of the invention, as many as eight to ten of longitudinally oriented ridges 17 are formed in the top and bottom surfaces of base sheet 4. This arrangement, in turn, forms eight to ten contact pad interface regions 22 that, advantageously, provide contact redundancies for better reliability through the creation of parallel conduction paths between contact pads 23, 24. Thus, longitudinally oriented ridges 17 can be viewed as several conductive wires operating in parallel to achieve the same level of conductance as that of multiple wire spring electrical contacts. This structural arrangement provides for a relatively small size (i.e., relative to the center line spacing of contact pads 23 and contact pads 24, e.g., five mils or less) with a high but adjustable elastic compliance that allows for compressive deflections of as much as thirty percent of the undeflected or uncompressed height of each electrical contact 2, and with low contact forces that are routinely less than twenty grams per electrical contact assembly.
The redundant conductor structure of electrical contacts 2 enhances and improves both a mechanical and electrical engagement between the multiple longitudinally oriented ridges 17 and contact pads 23, 24. In particular, each electrical contact 2 provides a capability for high frequency transmittance of signals greater than ten gigahertz, due to the low self-inductance created by a highly conductive short contact height. In addition, electrical contacts 2 are capable of high current capacity due to a bulk resistance that is often less than ten milliohms. The less than ten milliohms that is achieved is produced by parallel contact and bulk resistances (through longitudinally oriented ridges 17) which reduce the total resistance of the electrical interconnection by dividing a normally single, high resistance by the number of contact interface resistances that are arranged in parallel, as a result of the multiple or redundant contact pad interface regions 22 that are engaged with contact pads 23, 24.
In one embodiment, a folded beam electrical contact 2 has two folds, where the two beam segments 26 that terminate along top contact edge 6 and bottom contact edge 8 of electrical contact 2 have only one-half the length of the long segments 28. This construction provides a contact point in the center of the folded structure. Alternatively, four folds can be provided with two short beam segments 26 and three long segments 28 located between them. The fold angle is a variable that determines the height and elastic compliance of the folded structure when the later is compressed along the longitudinal axis of the structure from either top contact edge 6 or bottom contact edge 8. Vacuum-melted 304 stainless steel may be rolled into a fully hardened sheet 18 of a required thickness, in the range from about 0.5 mils to about 1.5 mils. The fully hardened state is preferred so as to achieve a high yield strength providing a high fatigue strength especially when formed into thin cross-section sheets, on the order of one mil or less. Of course, other stainless steel alloys or other high melting temperature and high yield strength nonferrous alloys may be used with adequate results.
A folded electrical contact 2 may be formed in accordance with the present invention by first cutting a plated or clad base sheet 4 into narrow strips, e.g., having widths of from two mil to about three mils for center line spacing of five mils. Often, the width of the narrow strips is in the range from about five to ten times the thickness of base sheet 4. The thickness of the conductive metal cladding or plating is typically ten to forty percent of the thickness of a stainless steel sheet 18, often in the range from about 0.5 mils to 1.5 mils. After cutting, the cut sides of the narrow strip are often not covered by the conductive metal cladding or plating. Alternatively, the conductive metal can be applied to the narrow strips after cutting to cover all its sides. The narrow strips are then folded by using conventional CNC spring making machines or their equivalent, in high volume.
In one example of the present invention, an electrical contact is formed from vacuum melted stainless steel with a cross-section of 1.5 mils by fifteen-mils and a gold cladding of 0.3 to 0.4 mils thickness. Short beam segments 26 have a length of 7.5-10-mils and three long segments 28 have a length of 15-20-mil. Such an electrical contact 2 is capable of more than a ten mil elastic compliance under a contact force of less than thirty gram load, and a resistance of about ten milliohms or less. The elastic compliance can be increased when the number of folds is increased to four with a doubling of bulk resistance of the electrical contact. For chip or wafer level contact or interconnection a folded beam electrical contact 2 having two or four folds, a cross-section of 0.5 mils×three mils, a gold cladding of 0.1-0.15 mils thick, a short segment 26 of 2.5-mils length, and long segments 28 of 5-mils length, have been found to provide adequate compliance and electrical performance.
Referring to
Electrical contacts 2 are mounted to carrier assembly 30 as follow. Fixture 50 is formed including a top lamination stack 52, a bottom lamination stack 54, and a contact stop plate 56 (
Once in this position, an electrical contact 2 is positioned in each of through-holes 40, 58 so that bottom contact edge 8 abuts a portion of the surface of contact stop plate 56. From this arrangement, top sheet 33 is slid relative to bottom sheet 36, so that edges move toward one another and toward the top and bottom surfaces of electrical contact 2 while narrowing the size of through-holes 40. Once edges 42 engage electrical contact 2, the inactivated adhesive 45 that is resident along edges 42 contacts a portion of electrical contact 2. The lamination stack, under a compressive load, holds the array of electrical contacts 2 positioned in carrier assembly 30, which is then placed in an oven so as to activate and cure adhesive 45. Once the curing process is complete, the lamination stack is removed from its surrounding relation with electrical contacts 2 and carrier assembly 30 so as to release an electrical interconnection device or interposer 1 comprising a plurality of electrical contacts that are arranged so as to stand proud of the top and bottom surfaces of top sheet 33 and bottom sheet 36.
Referring to FIGS. 2, 13-14, 27-28, and 36-37, an IC package 13 may be electrically interconnected with a printed wiring board 16 using electrical interconnection device1 populated with electrical contacts 2 of the present invention. More particularly, with a plurality of electrical contacts 2 positioned projecting outwardly from carrier assembly 30, electrical interconnection device1 may be positioned between the bottom surface of IC 13 and a top or bottom surface of printed wiring board 16. In this arrangement, contact pads 23 of IC package 13 are positioned in confronting relation to top contact edge 6 and eight to ten contact pad interface regions 22. The eight to ten contact pad interface regions 22 advantageously provide contact redundancies for better reliability through the creation of parallel conduction paths between contact pads 23. Once in this position, carrier assembly 30 may be moved toward printed wiring board 16 such that cantilevered arms bottom contact edge 8 with its eight to ten contact pad interface regions 22 make electrical and mechanical contact and engagement with the top surfaces of each of contact pads 24. It will be understood that the off-set nature of top edge 6 and bottom edge 8 provide for a sliding or “wiping” engagement with the contact pads which will increase electrical engagement by removing dirt or light corrosion products from those surfaces. IC package 13 is then moved toward carrier assembly 30 so that contact pads 23, 24 engage top edge 6 and bottom edge 8.
Referring to
One alternative embodiment of electrical contact 2d comprises a compound spring shape that is formed from a plurality of pre-plated wires 90 that are adhesively fastened to one another along a common, intermediate section 92 (
Advantages of the Invention
Numerous advantages are obtained by employing the present invention. More specifically, an electrical contact assembly and connector system are provided which avoid the aforementioned problems associated with prior art devices. For one thing, an electrical contact assembly and connector system are provided that allows for a more simplified resilient conductive contact which incorporates the seemingly opposing requirements of good spring properties and high conductivity.
Additionally, an electrical contact assembly and connector system are provided that are extendible to a large contact array at fine pitch, i.e., five mils or less, with relatively small size, high elastic compliance, i.e., deflections of as much as thirty percent of the undeflected height of the electrical contact, and with low contact force, i.e., less than twenty grams per contact.
In addition, an electrical contact assembly and connector system are provided that are capable of high frequency transmittance of signals greater than ten gigahertz, due to low self-inductance created by a short contact height.
Also, an electrical contact assembly and connector system are provided that are capable of high current capacity, i.e., an electrical contact assembly having less than ten milliohm bulk resistance and low contact resistance.
Furthermore, an electrical contact assembly and connector system are provided that are capable of high durability or high cycles of touchdowns, i.e., greater than five hundred thousand cycles, utilizing a spring having a high elastic compliance that avoids permanent set in contact height under repeated compressive loadings and exhibits high fatigue strength.
Additionally, an electrical contact assembly and connector system are provided that are capable of high reliability with minimum degradation in contact resistance by employing a noble metal contact surface and redundancy in contact points via multiple, independent cantilevered beams, or folded grooved beams.
Also, an electrical contact assembly and connector system are provided that are capable of high service temperatures often exceeding two hundred and fifty degrees centigrade, by employing structural parts of the electrical contact formed of high melting temperature metals, such as 304V stainless steel, that prevent the relaxation of contact force at high temperatures.
Moreover, an electrical contact assembly and connector system are provided which avoid the aforementioned problems associated with prior art devices with low cost manufacturing, using conventional high volume tools and processes.
It is to be understood that the present invention is by no means limited only to the particular constructions herein disclosed and shown in the drawings, but also comprises any modifications or equivalents within the scope of the claims.
This application claims priority from co-pending Provisional Patent Application Ser. No. 60/734,607, filed Nov. 8, 2005, and entitled Electrical Contact And Connector System.
| Number | Date | Country | |
|---|---|---|---|
| 60734607 | Nov 2005 | US |
