High density connector

Abstract: An electrical connector (10) for interconnecting a pair of circuit members (e.g., a circuit board and module), which, in one embodiment, includes a housing (11), at least one flexible circuit (15) within the housing (11) and a spring means (27) attached to the flexible circuit at two spaced locations for exerting force against the flexible circuit to cause the circuit to engage respective conductive pads on the circuit members when the circuit members are moved toward each other (e.g., compressed). The shape of the spring means conforms substantially to the portion of the flexible circuit between the locations of attachment. In another embodiment, a connector for interconnecting such circuit members includes a housing adapted for being located between both members and at least one elongated, compressible contact member in the housing and including conductive end portions for engaging the circuit members. The contact occupies a first, prestressed position before engagement and is adapted for moving to a second, compressed position during the engagement. The conductive end portions of the flexible circuit in the first embodiment and the contact member in the second embodiment preferably comprise a plurality of dendrites for providing enhanced connections.

Description: The invention relates to the field of electrical connectors and particularly to electrical connectors for interconnecting at least two electrical circuit members such as printed circuit boards, circuit modules or the like. Even more particularly, the invention relates to connectors of this type which may be used in the information handling system (computer) environment. In Ser. No. 901 054, filed under Attorney's Docket No. EN992079, and entitled "Method Of Forming A Conductive End Portion On A Flexible Circuit Member" (inventors: R. Busacco, et al.), there is defined a method of providing a plurality of dendritic elements on the ends of flexible circuit members such as may be used in the instant invention. The current trend in connector design for those connectors utilized in the computer field is to provide both high density and high reliability connections between various circuit devices which form important parts of the computer. High reliability for such connections is essential due to potential end product failure, should vital misconnections of these devices occur. Further, to assure effective repair, upgrade, and/or replacement of various components of the system (i.e., connectors, cards, chips, boards, modules, etc.), it is also highly desired that such connections be separable and reconnectable in the field within the final product, as well as tolerant of dust and fibrous debris. Such a capability is also desirable during the manufacturing process for such products, e.g., to facilitate testing. One prior technique for providing various interconnections is referred to as a wire bond technique, which involves the mechanical and thermal compression of a soft metal wire, e.g., gold, from one circuit to another. Such bonding, however, does not lend itself readily to high density connections because of possible wire breakage and accompanying mechanical difficulty in wire handling. Another technique involves strategic placement of solder balls or the like between respective circuit elements, e.g., pads, and reflowing the solder to effect interconnection. While this technique has proven extremely successful in providing high density interconnections for various structures, this technique does not allow facile separation and subsequent reconnection. In yet another technique, an elastomer has been used which included therein a plurality of conductive paths, e.g., small diameter wires or columns of conductive material, to provide the necessary interconnections. Known techniques using such material typically possess the following deficiencies: (1) high force necessary per contact which can be inherent in a particular design and exacerbated due to non-planarity of the mating surfaces; (2) relatively high electrical resistance through the interconnection between the associated circuit elements, e.g., pads; (3) sensitivity to dust, debris and other environmental elements which could readily adversely affect a sound connection; and (4) limited density, e.g., due to physical limitations of particular connector designs. Such prior art elastomeric structures also typically fail to provide effective wiping connections, which form of connection is highly desirable in many high density interconnection schemes. Attention is directed to U.S. Pat. Nos. 3,960,423, 3,960,424, 4,295,700, 4,636,018, 4,655,519, 4,793,814 and 5,049,084 for various techniques for providing electrical interconnections for a variety of electrical circuit members. As understood from a reading of these patents, the techniques as described therein include many of the aforedefined disadvantages, e.g., non-repeatability, potential misalignment, low density, etc. as well as others, e.g., relatively complex design, costly to manufacture, etc. In U.S. Pat. No. 5,061,192, assigned to the same assignee as the present invention, there is defined an electrical connector for interconnecting a pair of circuit members (e.g., circuit, module and printed circuit board) which assures highly reliable, yet separable connections for these members. The connector includes an electrically insulative (e.g., plastic) frame which defines an internal opening therein. Bridging this opening are a plurality of individual, resilient contact members which are maintained in a suspended and spaced orientation within the opening by a plurality of pairs of elongated insulative members (e.g., polymer rods). Each of the contacts is thus removable from the connector's frame to facilitate repair and/or replacement. As described, the connector is capable of providing wiping connections, thus assuring removal of debris or other contaminants from the respective conductive pads for each circuit member. In another embodiment, the connector includes a common carrier (e.g., plastic) having therein a plurality of cylindrical shaped resilient contact members (e.g., silicone) which further include a quantity of conductive (e.g., metallic) particles therein. To assure a wiping form of engagement with the respective conductive pads, each of the terminal ends of each contact member preferably includes a plurality of dendritic, interdigitated members thereon. This patent is incorporated herein by reference. It is believed that a high density electrical connector capable of providing effective, reliable connections (including providing a wiping type of connection), wherein such connections are repeatable (such that connection and reconnection can readily occur), and which provides the other advantageous features discernible from the following description would constitute a significant advancement in the art. Such a connector, as defined herein, also represents an improvement over the connector in U.S. Pat. No. 5,061,192, e.g., through elimination of the need for elongated insulative members for contact alignment and retention. US-A-4,655,519 discloses an electrical connector for positioning between and electrically interconnecting electrical components. The electrical connector includes a dielectric housing having compartments and contact elements freely disposed in the compartments and having cantilever spring arms supporting conductive contact areas at the free ends thereof for electrical engagement with conductive pads or the like on the electrical components. It is, therefore, a primary object of the present invention to enhance the electrical connector art. It is another object of the invention to provide an electrical connector capable of providing high density interconnections of a highly reliable and improved nature, which connections can be readily separated and repeated if desired. It is yet another object of the invention to provide such a connector which is relatively inexpensive to manufacture and also of a relatively simplistic design. In accordance with one aspect of the invention, there is provided a connector for electrically interconnecting first and second electrical circuit members according to claim 1. FIG. 1 is an exploded perspective view of a connector according to one aspect of the invention; FIG. 2 is a partial side view, in section, of the connector of FIG. 1, on a larger scale, and prior to circuit member engagement; FIG. 3 is a partial side view, in section, of the connector of FIG. 2, during circuit member engagement; FIG. 4 is a side view, in section, of the elongated flexible circuit member and spring means in accordance with the embodiment of FIG. 1, in a relaxed state prior to actuation thereof; FIG. 5 is a side view, in section, of the member and spring means of FIG. 4, in an actuated position; FIG. 6 is a perspective view of one embodiment of an elongated flexible circuit member adapted for use in the connector of FIG. 1, illustrating a plurality of conductive elements spacedly positioned thereon; FIGS. 7-10 represent the various steps in providing dendritic conductive elements on the end portions of a flexible circuit member such as may be used in both of the embodiments of FIGS. 4 and 13; For a better understanding of the present invention reference is made to the following preferred embodiment and the appended claims in connection with the above-described drawings. In FIG. 1, there is shown a connector 10 in accordance with one embodiment of the invention. Connector 10 comprises a housing 11 including, preferably, two parts 11a and 11b, each part preferably molded and of an electrically insulative, e.g., plastic, material and, as illustrated, preferably of substantially a rectangular configuration having a plurality (e.g., four) of walls 13a, 13b, 13c, 13d. In one example of the invention, housing 11 may possess a width (dimension "W") of about 1,27 x 10 -1 m (about five inches). This housing may also possess a combined thickness (dimension "T", FIG. 2) of only about 7,62 x 10 -3 m (about 0.30 inch). As stated, the preferred material for housing 11 is plastic, with suitable examples of such material being Vectra (a trademark of Hoechst Celanese Corporation), Ryton (a trademark of Phillips Petroleum Company), phenolic, and polyester. Connector 10, as illustrated in FIGS. 1-3, further includes a plurality of pairs 61 of elongated, electrically insulative members 63 and 63'. Each insulative member 63 and 63' preferably comprises a substantially trapezoidal-shaped rib of polymer material, suitable examples of such material being Vectra, Ryton, phenolic, and polyester, located within one or both of the housing parts 11a and 11b. Alternatively, these ribs may be formed as integral parts thereof (e.g., molded as part of each piece). Such construction may serve to enhance manufacturability. Other configurations, including octagonal, hexagonal, cylindrical, etc. may be used for members 63 and 63'. Electrically insulative members (ribs) 63 and 63' are specifically designed for holding respective elongated, resilient flexible circuit members 15 (defined in greater detail hereinbelow) in a suspended position between opposing walls 13b and 13d. Specifically, each pair 61 of two such members 63 and 63' is particularly designed for engaging the respective opposing end portions 23 and 25 respectively of each flexible circuit member 15. More specifically, and as best seen in FIG. 2, each opposing end 23 and 25 of the flexible circuit members 15 is preferably engaged on at least one side thereof. The aforedefined first pair 61 engages the ends along a first side (e.g., on the right side of the vertically oriented flexible circuit member 15 in FIG. 2), while a second pair 61 engages the flexible circuit member 15 from the other side (the left in FIG. 2). In Fig. 2, flexible circuit member 15 is shown to include only one conductive element on at least one side of the flexible circuit member's dielectric layer (described below). However, it is understood that the use of multiple conductors on each side of the dielectric layer is well within the scope of this invention, as further shown in FIG. 6, and is, in fact, preferred for use herein. Additionally, each pair 61 of members 63 and 63' serves to maintain each flexible circuit member 15 in a substantially upright orientation, as depicted in FIG. 2. Therein, each spring means 27 (defined in greater detail hereinbelow) is oriented in an upright manner such that a central curved portion 21 extends in a lateral direction (to the right in FIG. 2). Adjacent pairs of members 63 or 63' define a slot 65 therebetween for having one end of flexible circuit member 15 inserted therein. In effect, two pairs 61 of insulative members (which form a pair of slots 65) serve to guide each flexible circuit member 15 to provide location, both before and during engagement, with conductive pads 31 on circuit members 33 and 35 (also defined in greater detail hereinbelow). Significantly, under normal operating conditions, the opposing ends 23 and 25 exert minimal expansion (outward) force against the polymer ribs regardless of whether connector 10 is in an open (unactuated) or closed (actuated) position. The ends 23 and 25 exert this minimal expansion (outward) force in the unactuated state because flexible circuit member 15 is in a relaxed position and is essentially vertically free floating between the illustrated upper and lower ribs. When connector 10 is in a closed (actuated) position, ends 23 and 25 will still exert minimal expansion (outward) force on the ribs because the upper and lower conductive pads 31 (which engage opposing end portions 23 and 25) lock the location of the ends substantially as shown in FIG. 3 against the pads due to the frictional forces developed between the end portions and pads. In FIG. 2, connector 10 is shown prior to interconnecting the respective conductive pads 31 on the two circuit members (e.g., a circuit module 33 and printed circuit board 35). In this unactuated arrangement, the upper end portions 23 of each flexible circuit member 15 extend slightly above the upper surface of housing part lla while the opposing ends 25 extend below the lower, planar surface of the housing part llb. In one example, each of these end portions may extend a distance of about 3,81 x 10 -4 m (about 0.015 inch) beyond the respective planar, outer surfaces of these parts. In FIG. 3, the opposing circuit members 33 and 35 have been moved relative to each other (e.g., by an external clamping means, not shown but within the abilities of one skilled in the art) so as to compress the flexible circuit members 15 within housing parts lla and llb. That is, each of the arrays of conductive elements (41, 43, FIG. 6) for each flexible circuit member 15 engages a respective circuit member to provide electrical interconnection between such pads in the desired manner. Each extending end 23 and 25 is thus compressed such that the terminal end portions thereof lie substantially parallel to, but extend slightly above, the respective adjacent outer surfaces of parts lla and llb. Such compression results in slight displacement of the curvilinear central portions 21 of each flexible circuit member to cause further outward (to the right in FIG. 3) bowing thereof. Each flexible circuit member, however, maintains a spaced distance from the respective adjacent flexible circuit member so as not to electrically contact this member and thus possibly become electrically shorted thereto. Further assurance against this can be provided by the utilization of a layer 47 of dielectric material (FIG. 5) on at least one external surface of the flexible circuit member. Significantly, the compression of each flexible circuit member causes the outwardly extending end portions of each flexible circuit member to engage the respective conductive pad 31 in a vertically penetrating manner. This is highly desired in high density connections of the type defined herein, e.g., to penetrate films, remove debris and other contaminants which may affect these points of connection. The flexible circuit member 15 and spring means 27 are not shown in cross-section in FIGS. 2 and 3 for ease of illustration. Such cross-section is provided in the larger views in FIGS. 4 and 5. Housing 11, as defined, is adapted for being positioned between the pair of electrical circuit members 33 and 35 to thus form part of connector 10, which understandably serves to interconnect said circuit members. Examples of suitable circuit members for being interconnected by connector 10 include printed circuit boards, circuit modules, etc. By the term printed circuit board is meant to include a multilayered circuit structure including therein one or more conductive (e.g., signal, power and/or ground) layers. Such printed circuit boards, also known as printed wiring boards, are well known in the art and further description is not believed necessary. By the term circuit module is meant to include a substrate or the like member having various electrical components (e.g., semiconductor chips, conductive circuitry, conductive pins, etc.) which may form part thereof. Such modules are mentioned in U.S. Pat. Nos. 4,688,151 and 4,912,772 and further description is thus not believed necessary. The disclosures of these patents are thus incorporated herein by reference. Connector 10, as stated above, includes at least one (and preferably a plurality) of the described elongated, resilient flexible circuit members 15 positioned within housing parts 11a and 11b. Although five such flexible circuit members are shown in FIG. 1 for illustration purposes (and eight in FIGS. 2-3), it is understood that several additional such flexible circuit members may be used (and are preferably so) as part of the invention. In one embodiment of the connector of the invention, for example, a total of about 140 such members may be used. Each flexible circuit member 15 is located so as to substantially occupy an internal central opening 17 defined by the housing walls 13a-13d. It is understood, as shown in FIG. 1, that these flexible circuit members substantially about the internal surfaces of opposing walls 13b and 13d. By the term substantially abut is meant slight engagement by each flexible circuit member 15 at one or both opposite ends thereof with a respective, adjacent housing wall. These flexible circuit members 15 are thus arranged in substantially parallel, spaced orientation within central opening 17. Significantly, flexible circuit members 15 do not become located on or inserted within the housing's side walls but, as shown, remain substantially therebetween. A more detailed illustration of each flexible circuit member 15, taken in section, is seen in FIGS. 4-5. Each flexible circuit member 15 includes one or more conductive elements 41, 43 and 45 (FIG. 6), preferably of copper (or similar metallic material including e.g., phosphor bronze, beryllium-copper, etc.) on at least one side of a dielectric (e.g., polyimide) layer 19. Significantly, copper is the preferred material for the conductive elements 41, 43, and 45 because of its relatively low electrical and thermal resistivity compared to other metals commonly used in connectors. Preferably, conductive elements 41, 43 and 45 and end portions 23 and 25 are also plated with corrosion-resistant, sound conducting metallic material such as nickel, gold, silver, palladium, etc. Conductive elements 45 on the backside of dielectric layer 19 can be selectively commoned electrically to conductive elements 41, 43 on the opposite side of the dielectric layer 19 through end portions 23 and 25 (shown in FIGS. 4-5), although it is understood that alternate means of electrically connecting the two sides (e.g., vias, plated-through-holes, etc.) are possible and thus within the scope of this invention. As also shown in FIG. 4, each flexible circuit member 15 includes a substantially curved, central portion 21 with the first and second projecting end portions 23 and 25 extending in a substantially opposite manner from this central curved portion. Each opposing end 23 and 25 is designed for electrically contacting respective circuit elements (e.g., flat conductive pads 31) located on the respective surfaces of the circuit members 33, 35 in FIG. 2. As stated, these circuit members may be printed circuit boards (e.g., 35) having such flat conductive members (e.g., copper terminals) located on an outer surface thereof. These circuit members may also comprise the aforedefined circuit module 33 including a substrate 37 having a plurality of semiconductor elements 39 thereon and corresponding flat conductive pads (e.g., thin copper elements) 31 located on a bottom, external surface. The defined conductive pads 31 are, understandably, electrically coupled to corresponding circuitry which forms part of the respective electrical circuit members. These pads may provide signal, power or ground connections, depending on the operational requirements of the respective circuit member. Further shown in FIG. 4 is the aforementioned spring means 27, preferably of maraging or stainless steel, which is connected to the conductive element 45 on the backside of dielectric layer 19 (or directly to the dielectric layer 19 if conductive elements 45 are not present) in at least two separate locations, preferably near the ends 23 and 25 (e.g., at locations 29 and 29' in this embodiment), by attachment means such as soldering, welding, or use of either conductive or nonconductive adhesive. Such an adhesive is preferred if means 27 is connected directly to dielectric layer 19. During the process of attaching spring means 27, a space 28 is formed in the curved portion 21 between the spring means 27 and flexible circuit member 15 in order to reduce the maximum stress in the curved portion 21 of the flexible circuit member 15 both during and following actuation of connector 10. More specifically, this space allows spring means 27 and flexible circuit member 15 to deform independently (each with respect to its own neutral axis), thereby reducing the maximum bending stresses in each. In contrast, in a composite member (i.e. one in which spring means 27 and flexible circuit member 15 are laminated together along their entire length and are restrained from sliding with respect to each other at the lamination interface), a single neutral axis is developed such that the maximum distance of a point in the composite from the neutral axis will be greater than in the previous case, thereby increasing the maximum bending stresses in both spring means 27 and flexible circuit member 15. As can be seen in FIG. 5, which shows a single flexible circuit member 15 in its actuated state, the above-mentioned space between the spring means 27 and conductive element 45 is reduced but still preferably present. The space formed between spring means 27 and flexible circuit member 15 not only reduces the stress in both of these members, but also substantially reduces the combined stiffness as well. This occurs because the stiffness of spring means 27 is proportional to the cube of its thickness. In the case where a space is formed in the curved portion 21 between spring means 27 and flexible circuit member 15, the stiffness will be proportional to the sum of the cubes of the individual thicknesses of spring means 27 and flexible circuit member 15. In the case of a composite member as described above, the stiffness will be proportional to the cube of the sum of the thicknesses of spring means 27 and flexible circuit member 15. Clearly, for any value of thickness ("T1", FIG. 4) for the spring means and thickness ("T2", FIG. 4) for the flexible circuit member, T1 raised to the third power plus T2 raised to the third power will be less than the sum of T1 plus T2 raised to the third power. Therefore, the first combination cited above, which is incorporated in the preferred embodiment of the invention, is less stiff. Significantly, the use of maraging steel for spring means 27 to provide the vertically outward forces needed to support flexible circuit members (and especially the copper conductive elements thereof), both during and after actuation of connector 10, allows a separation of the mechanical and electrical functions of the flexible circuit member/spring means assembly, which allows optimization of each function both in terms of material and performance. Additionally, maraging steel is a preferable material for spring means 27 because of its high yield and tensile strengths compared to copper (which, as mentioned, is the preferred material of the conductive elements 41, 43 and 45). The tensile strength of maraging steel is at least twice that of the copper used for conductive elements 41, 43 and 45. Furthermore, the yield strength of maraging steel is at least fifteen times greater than that of the copper conductive elements 41, 43 and 45. For example, according to the December, 1990 issue of "Materials Engineering" magazine (which is hereby incorporated by reference), pages 41 and 82, at room temperature, the yield strength of annealed copper is approximately 10,000 p.s.i. while 18 percent nickel maraging steel is approximately 255,000 p.s.i. Each flexible circuit member 15, as shown in FIG. 1 and seen in greater detail in FIG. 6, includes both a plurality of first and second opposing end portions (23 and 25 respectively) fitted on or, preferably, formed as part of an array of conductive elements 41, 43 and 45. The array of elements 41, 43 and 45, as shown in FIG. 2, is adapted for engaging the defined individual flat conductive pads 31. The cross-sectional area (width and thickness) of individual conductive elements 41, 43 and 45 can be varied to optimize both the electrical and mechanical performance for the particular function (signal, power, or ground) that each performs. For example, because of the lower electrical resistance desired for these elements, wider conductive elements 41 may be better suited for use as power conductors than narrower elements 43. When used as signal conductors, narrower elements may have a lower coupled noise, provided the space between adjacent conductors is greater. The addition of one or more conductive elements 45 (which may serve either as a ground plane or as an additional conductive layer) on the back side of dielectric layer 19 (as best shown in FIG. 6), may enhance the electrical performance of corresponding elements 41, 43 on the front side of dielectric layer 19 in certain applications. The addition of connecting conductive means 49 (FIG. 6) to electrically connect one conductive element 45 on the back side of the dielectric layer 19 to a neighboring (preferably adjacent) conductive element 45 may further enhance the electrical performance of elements 43. The vertical location of conductive means 49 (relative to the closeness to the extreme ends 23 and 25) provides connector 10 with a means for modifying mechanical and electrical performance. Specifically, having the conductive means 49 closer to ends 23 and 25 is electrically superior since the ground plane current may more closely follow the path of the signal element 43. This may be less desirable mechanically, however since the ends of two adjacent elements are more tightly coupled, thereby reducing element-to-element compliance. The further the conductive means 49 is located toward central curved portion 21, the mechanical coupling between adjacent elements is reduced, but this may be less desirable, electrically, because the impedance of the section of element 43 that does not have a ground plane present may be higher than the impedance for the rest of element 43. In a preferred embodiment, conductive means 49 is substantially "V-shaped" (as opposed to a simple, straight horizontal bar) in order to have conductive means 49 mechanically act as a beam instead of a rigid plate. This further reduces the mechanical coupling between adjacent members that is due to variation in tip deflections which may be caused by component tolerances, differences in pad height, thermal expansion, etc.). The construction of conductive means 49 preferably occurs as part of the construction of the rest of the elements 45, although these may be added later through other means such as wire bonding, etc. The application of the two concepts described above to connector 10 can best be seen in the middle pair on conductors in FIG. 6. In this embodiment, the wider element 41, which is preferably at either ground or power voltage level, is electrically commoned to the conductive element 45 on the back side of the dielectric layer 19 through end portions 23 and 25. Conductive means 49 electrically commons element 45 behind the wider element 41 to the element 45 behind narrower element 43. This in effect provides a reference plane for a signal-carrying element 43, which in turn creates a microstrip transmission line structure that significantly improves the signal characteristics, such as controlling impedance, of element 43. This same concept can be applied to the situation where element 43 is a wider conductor to be used to carry power. In that situation, the effective inductance of element 43 is reduced due to the proximity of ground/reference elements 45. Alternatively, it is also possible to incorporate as part of member 15 one or more coupling metallic portions 51 (shown in phantom) which, like elements 41, 43 and 45 in FIG. 6, are capable of providing a common connection to two or more opposing pairs of conductive pads 31. Portion 51 in FIG. 6 is shown to couple two elements 41 as part thereof. Thus, in the embodiment of FIG. 6, it is possible to combine signal and power functions utilizing a singular flexible circuit member. Understandably, dielectric material 19 is of sufficient thickness to maintain the individual contacting sections in the desired spaced orientation so as to assume an overall, elongated configuration such as shown in FIG. 6. In such an embodiment, the conductive elements 41, 43 possess a thickness, preferably, of only about 7,11 x 11 -5 m (about 0.0028 inch) and a width of 7,62 x 10 -4 m and 1,01 x 10 -4 m (0.03 and 0.004 inch) respectively, while the corresponding dielectric layer (e.g., polyimide) possesses a thickness of about 7,62 x 10 -5 m (about 0.003 inch). Conductive elements 45 possess a thickness, preferably, of only about 8,89 x 10 -6 m (about 0.00035 inch) and a width of 7,62 x 10 -4 m (0.03 inch), and are thus slightly thinner than corresponding elements 41, 43. The presence of elements 45 functioning as a ground plane provides the additional benefit of essentially shielding elements 43 (if used as signal elements) from adjacent members 15, thereby reducing possible coupled noise generated from those members 15 to relatively low levels. Spring means 27, as shown in FIG.2, may be either partially or completely vertically segmented to enhance its mechanical properties (i.e. the compliancy of adjacent end portions 23 and 25). In the embodiment shown in FIG. 6, spring means 27 may comprise a plurality of individual spring elements, each of which is substantially equal in width to the respective dielectric layer 19 lying thereover as well as the wider, corresponding conductive element 41 in the region other than the curved central portion 21. In that region, such spring elements may be mechanically connected together to form an elongated, assembled structure. This may enhance the manufacturability of the spring means since it can be preferably formed as a single piece through a process such as stamping while still substantially minimizing the mechanical coupling between the end portions 23 and 25 of elements 41, 43 and 45 that would occur if the spring means were one solid piece. It is significant to note that spring means 27 should preferably be electrically commoned either to conductive elements 45 (if these are used) or to one or more conductive element 41, 43 (at a power or ground potential), preferably at one of the upper and lower locations 29 and 29', respectively, to ensure that the spring means is at a defined voltage level and does not impair the performance of elements used to carry signals. Additionally, in the embodiment show in FIG. 6, the shape of end portions 23 and 25 of elements 41 may narrow closer to the tip of the end portion, while the shape of narrower elements 43 may widen. This is done, significantly, to allow greater alignment tolerances between ends 23 and 25 and conductive pads 31 as well as to ensure that ends 23 and 25 of all width elements perform substantially the same from a mechanical point of view. Furthermore, additional conductive material (i.e. an additional layer of copper, etc.) may be added to ends 23 and 25 to offset the reduction of cross sectional area of especially the wider elements 41 that may be used as power conductors. However it is understood that the use of other shapes and/or contours of the end portions may be used and are well within the scope of this invention. In the embodiment shown in FIG. 6, the tips may possess a width (dimension "WT") of about 9,68 x 10 -6 m (about 0.015 inch). and a thickness (dimension "TT") of about 7,11 x 10 -5 m to 1,42 x 10 -4 m (about 0.0028 to 0.0056 inch). Alignment of the two circuit members 33 and 35 relative to interim connector 10 may be provided utilizing a pair of protruding pins 81 which extend from one of the circuit members (e.g., module 33), these pins being aligned with and positioned within corresponding openings 83 within housing parts lla and llb and openings 85 within the other of these circuit members. It is understood that other means of alignment are readily possible, including the provision of pins extending from opposing surfaces (upper and lower) of housing parts lla and llb for insertion within corresponding openings within the respective circuit members. To adjust for tolerancing, one of such openings within connector 10 may be of elongated configuration, as illustrated in FIG. 1. To enable cooling of the flexible circuit members 15 within housing 11, including during operation of connector 10, one or more slots 67 (when parts 11a and llb are combined) may be provided within at least one of the walls of the housing (FIG. 1). Preferably, these slots are provided in opposing walls 13b and 13d to enable fluid coolant (liquid or gas) to readily pass through the parallel aligned and closely spaced flexible circuit members and associated spring means. A preferred coolant is air. It is also possible to use nitrogen and oil for this purpose. It would be highly desirable to provide a sealed system through the use of bladders, tubes, etc. (not shown) if liquids are to be used as the coolant. Should connector 10 be utilized solely as a power connector, temperatures may be reduced by approximately fifty percent, thus enhancing the operation of the invention. To further assure prevention of accidental shorting with adjacent such flexible circuit members 15, each member 15 and spring means 27 may include the aforementioned relatively thin layer 47 of dielectric material (shown in phantom in FIG. 5) over a major portion thereof. Each layer, as stated, is of a dielectric material, a preferred example being polyimide. Although only member 15 is shown in FIG. 5 to include this layer, the layer may also be provided on the outer surface of spring means 27 (the left side in FIG. 5). In FIGS. 7-10, there is shown a method for making conductive end portions 23 and 25 of flexible circuit member 15 of connector 10 (and also conductive end portions 123 and 125 of the flexible circuit member 115 of connector 101) in accordance with a preferred embodiment of the invention. FIG. 7 shows an end portion of the dielectric layer 19 and the conductive elements 41 and 45, taken in cross section, prior to the formation of dendritic elements (77, described below) on the end portions of the flexible circuit member. FIG. 8 shows the end of flexible circuit member 15 after an opening 71 is provided near the tip of the end portion, this opening extending through both dielectric layer 19 and conductive elements 41 and 45. Opening 71 may be formed by means such as punching, drilling, etching or ablation (e.g., laser). Surface 73 of opening 71 is then made electrically conductive by adding a conducting layer 75 using a known method such as additive plating. Preferred materials for the conducting layer 75 are copper, nickel, gold, silver, palladium, etc. Significantly, and as previously described, the conducting layer may be used to electrically common conductive elements on one side of dielectric layer 19 to conductive elements on the other side. In one embodiment, a first layer of copper (e.g., 1,78 x 10 -5 m (0.0007 inch) thick) was added, followed by a thin layer (e.g., 1,40 x 10 -8 m (0.00002 inch)) of nickel (as a corrosive barrier to enhance dendrite adhesion), followed by a thin layer (e.g., 5,08 x 10 -7 m (0.0002 inch)) of palladium. Dendritic elements (77) were then added. FIG. 9 shows a conductive end portion after the conducting layer 75 (or layers, as defined above) of opening 71 has been plated with a plurality of dendritic elements 77 by a method such as electroplating. Preferred materials for the fabrication of the dendritic elements 77 are metals or combinations, composites or alloys of metals selected from the group palladium, nickel, gold, platinum, rhodium, ruthenium, irridium and osmium. The electroplating of such dendritic elements may, for example, be accomplished by the method as defined in Canadian Patent No. 1,121,011, which patent is incorporated herein by reference. The metal palladium has proven to provide a particularly favorable combination of electrical, mechanical and chemical properties (high electrical conductivity, ductility, yield strength and corrosion resistance) for the function of such elements when electroplated at a temperature near 30 degrees Celsius (C) at a current density near 60 milliamperes per square centimeter from an aqueous ammonia bath containing 15 millimolar palladium tetrammine chloride and 5 molar ammonium chloride, adjusted to a pH of 9 to 9.2. Preferably, these elements are then overplated for an additional time at a current density of 10 milliamperes per square centimeter in a bath of the same composition given above, except that the concentration of palladium is 150 millimolar. Significantly, this overplating with palladium metal is used to strengthen the dendritic elements. During both of these electroplating processes, the anodes should preferably be larger than opening 71 and placed perpendicular to the axis of said opening at a distance from said opening which is larger than the length and width of the said opening. Examples of such anodes (and placement) are shown in FIG. 8 and represented by the numerals 78. In one embodiment, anode 78 is of a thick screen-like construction and of a material such as titanium, niobium, or tantalum plated with platinum. To further enhance the electroplating process, agitation of the plating solution by means such as ultrasonic techniques and/or movement of the part being plated by mechanical means may be utilized. Such placement will result in the dendritic elements 77 growing on the conducting layer 75 predominantly in a direction perpendicular to said conducting layer and lying in the plane of said opening, as seen in FIGS. 9 and 10. Such orientation is particularly desired to provide enhanced connection between these elements and conductors (e.g., pads 31). FIG. 10 shows a conductive end portion after a portion of dielectric layer 19 and conductive elements 41 and 45 are removed, preferably by punching away undesired material. That is, the upper portion of the flexible circuit member's end (above part of the dendritic elements and conducting layer) is removed, such that some of these dendrites will remain, as seen in FIG. 10. Significantly, penetrating-type contact geometries such as dendritic elements 77 are included on the end portions of the flexible circuit member's contact interfaces to enhance the reliability of the connections by offering contact redundance, which in turn reduces contact resistance, heat dissipation, and the temperature in the contacts during operation. Furthermore, dendritic elements 77 can break through dust, films, and fibrous debris that may be present on such conductive pads 31 as those shown for circuit members 33 and 35. Thus there has been shown and described an electrical connector for providing highly dense interconnections between corresponding pluralities of conductive elements on opposing pairs of circuit members. Such connections are obtainable in a facile manner using the invention, which is of relatively simple construction and thus relatively inexpensive to manufacture and operate. It is understood from the foregoing that the described connections are readily separable such that the connector can be removed and repositioned, if necessary. Such a capability enables testing of the respective circuits on the described circuit members, if desired, in an overall connector scheme. While there have been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

Claims: A connector (10) for electrically interconnecting first and second electrical circuit members (33, 35), said connector comprising: a housing (11) adapted for being positioned between said first and second electrical circuit members (33, 35); elongated flexible circuit members (15) located within said housing (11) and each of which including a dielectric layer (19) and at least one conductive element (41, 43, 45) having first and second conductive end portions (23, 25) adapted for engaging said first and said second circuit members (33, 35), respectively when said housing (11) is positioned between said first and second electrical circuit members (33, 35); each elongated flexible circuit member (15) is supported by a pair of electrically insulative members (63, 63') in the area of said first and second conductive end portions (23, 25); said connector comprises spring means (27) operatively connected to each said flexible circuit member (15) for exerting a predetermined force against said flexible circuit member (15) to cause said first and second conductive end portions (23, 25) of said conductive element (15) to engage said first and second circuit members (33, 35); said spring means (27) being attached to said flexible circuit member (15) at spaced locations (29, 29') on said flexible circuit member (15) and having a shape conforming to the portion of said flexible circuit member (15) between said spaced locations (29, 29') along the entire length of said flexible circuit member (15), thus that said flexible circuit member (15) and said spring means (27) form a joint central curved portion (21) extending in a lateral direction, whereby said spring means (27) nestles into said flexible circuit member (15); said flexible circuit members (15) being arranged in rows, whereby the convex portions of said flexible circuit members nestles in the concave portions of said spring means of the adjacent row of flexible circuit members (15), thereby enhancing the packing density of said flexible circuit members, and whereby said spring means (27) and said flexible circuit member (15) define a first space therebetween prior to engagement between said first and second conductive end portions (23, 25) of said flexible circuit member (15) and said first and second circuit members (33, 35) and a second, narrower space therebetween during said engagement. The connector according to claim 1 wherein said housing is electrically insulative. The connector according to claim 2 wherein said housing is plastic. The connector according to claim 1 wherein said elongated flexible circuit includes a plurality of said conductive elements spacedly positioned thereon. The connector according to claim 4 wherein said conductive end portions of said conductive elements are of substantially similar width. The connector according to claim 5 wherein said conductive end portions of said conductive elements are of substantially similar thickness. The connector according to claim 1 wherein each of said conductive end portions comprises a plurality of dendrites. The connector according to claim 7 wherein said dendrites are comprised of palladium. The connector according to claim 1 wherein said dielectric layer is comprised of polymer material. The connector according to claim 9 wherein said polymer material is polyimide. The connector according to claim 1 wherein said conductive element is comprised substantially of copper. The connector according to claim 1 wherein said housing includes first and second parts. The connector according to claim 12 wherein said housing includes means for retaining said flexible circuit member in an aligned manner. The connector according to claim 13 wherein said means for retaining said flexible circuit member comprises at least two ribs, said ribs being located within at least one of said parts of said housing. The connector according to claim 14 wherein said ribs define a slot therebetween, said flexible circuit member being located within said slot. The connector according to claim 1 wherein said spring means is metallic. The connector according to claim 16 wherein said spring means is comprised of steel. The connector according to claim 1 wherein said spring means includes a tensile strength substantially greater than the tensile strength of said conductive element. The connector according to claim 18 wherein said tensile strength of said spring means is at least twice said tensile strength of said conductive element. The connector according to claim 1 wherein said spring means and said flexible circuit member each include a curved portion, said first and second spaces being located substantially between said curved portions.

Inventors: BUSACCO RAYMOND ARCHIE, CHANG CHI SHIH, CHAPIN FLETCHER WILLIAM, DRANCHAK DAVID WILLIAM, MACEK THOMAS GEORGE, PETROZELLO JAMES RALPH, SAXENMEYER GEORGE JOHN JR, SMITH ROD ALAN, BUSACCO, RAYMOND ARCHIE, CHANG, CHI SHIH, CHAPIN, FLETCHER WILLIAM, DRANCHAK, DAVID WILLIAM, MACEK, THOMAS GEORGE, PETROZELLO, JAMES RALPH, SAXENMEYER, GEORGE JOHN, JR., SMITH, ROD ALAN
Applicants: IBM, INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 1993
Main classification: H01R13
IPC codes: H01R12, H05K7, H01R4, H01R24