Abstract:
An electrical interconnect system comprises: a flexible circuit having thereon a plurality of electrical contact pads; a contact strip comprising a plurality of electrical contacts aligned with respective pads on the flexible circuit; a compression member to engage the contacts with the pads; and, pierced areas on said pads to enhance the mechanical engagement between the contacts and the pads.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to the following U.S. Patent Applications, filed on even date herewith by the present inventors: Docket No. MAT-20A, entitled “Flexible circuit board and connection system”; Docket No. MAT-20B, entitled “Rigid circuit board with flexibly attached module”; Docket No. MAT-20C, entitled “Method for making an electrical circuit”; Docket No. MAT-20D entitled “Electronic module with heat spreading enclosure”; Docket No. MAT-20E entitled “Electronic interconnect system”; and Docket No. MAT-20G entitled “Compression connector system.” The entire disclosures of each of the foregoing are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to means for connecting microelectronic devices and systems. More particularly, the invention relates to improved flex-circuit based interconnect solutions for electronic circuits. 
         [0004]    2. Description of Related Art 
         [0005]    The evolution of smaller, lighter electronic devices with ever-increasing functionalities has increased the need for packaging, mounting, and interconnection architectures that will reduce size and weight while at the same time preserving interconnection characteristics that can handle the flow of large amounts of data between various circuits or modules in a device. Flex circuits are often used to provide a signal routing means that can be easily located in confined places within an equipment enclosure. They are also used to maintain electrical connections between two components that must move relative to one another; examples are the connections between the motherboard and the display on a laptop computer, or in many cell phones. 
         [0006]    Various approaches have been used to enable a long, flexible circuit to be reliably connected to a component such as a motherboard. In one case, a socket is permanently installed on the motherboard (typically by soldering). A mating plug is affixed to the end of the flex by mechanically clamping or crimping; this plug contains internal metal pins that pierce the flex to complete an electrical connection between the lines on the flex and the contacts on the plug that will mate with corresponding contacts on the socket. As the number of lines increases, and the pitch becomes correspondingly smaller, both the cost and reliability of this approach can suffer. 
         [0007]    Another approach, used particularly when the flex connection might need to withstand especially demanding mechanical forces, is to affix rigid circuit boards on both sides of the flex near the terminations. These boards typically have plated through holes and can be placed flat against the motherboard to secure a strong soldered connection. Connectors may also be further strengthened by potting in epoxy. 
       OBJECTS AND ADVANTAGES 
       [0008]    Objects of the present invention include at least the following: providing a flex circuit board and interconnect system having reduced size and complexity; providing a low-cost, highly reliable flex circuit board or module and associated interconnect system; providing a more reliable and manufacturable flex circuit board or module suitable for directly mounting on a motherboard without additional packaging; providing a motherboard with flex circuit boards mounted thereon via a compliant interconnect; and, providing a method for manufacturing flex circuits that is cost effective and suitable for mounting directly on a motherboard without a separate socket. 
       SUMMARY OF THE INVENTION 
       [0009]    In accordance with one aspect of the invention, a flexible circuit board comprises: a multilayer flex circuit having bifurcated extensions along one edge thereof and a plurality of electronic components mounted on at least one surface thereof; and a plurality of electrode pads positioned on the inner and/or outer surfaces of the two legs of the bifurcated extensions such that when the legs are spread apart by about 180° the electrode pads are alignable with respective contacts on a motherboard, and/or on a clamping connector and connectable thereto, so that a secure, mechanically flexible connection may be created between the flexible circuit board and the motherboard. 
         [0010]    In accordance with another aspect of the invention, an electrical circuit comprises: a rigid printed circuit board or motherboard having a plurality of electrical contacts on at least one surface thereof: a multilayer flexible circuit board having a plurality of electrical components on at least one surface thereof, and further having a bifurcated area along one edge thereof; electrode pads on the inner surfaces of the bifurcated area of said flexible circuit board that are aligned respectively with electrical contacts on the rigid circuit board when the legs of the bifurcation are spread apart by about 180°; and, electrical connections between the electrode pads and the respective electrical contacts sufficient to maintain electrical continuity and mechanical flexibility between the rigid printed circuit board and the flexible circuit board. 
         [0011]    In accordance with another aspect of the invention, a method for making an electrical circuit comprises the steps of: 
         [0012]    forming a rigid printed circuit board having a plurality of electrical contacts on at least one surface thereof; 
         [0013]    forming a multilayer flexible circuit board having a plurality of electrical components on at least one surface thereof, and further having a bifurcated area along one edge thereof; 
         [0014]    forming electrode pads on the inner surfaces of the bifurcated area of the flexible circuit board that are alignable respectively with the electrical contacts on the rigid circuit board when the bifurcated area is spread apart by about 180°; 
         [0015]    spreading the bifurcated area apart and aligning the electrode pads respectively with the electrical contacts; and 
         [0016]    forming an electrical connection between the electrode pads and the electrical contacts. 
         [0017]    In accordance with another aspect of the invention, an electronic subsystem comprises: a rigid circuit board daughter card or substrate having a plurality of electrical components on at least one surface thereof and electrical contacts along one edge thereof, one or more flexible circuit leads having a plurality of electrical contacts in electrical communication with the electrical contacts of the rigid printed circuit board thereof, and further extending at an angle along at least one edge thereof; electrode pads on at least one surface of said extension alignable with respective contacts on a motherboard, and/or clamping connector and connectable thereto, so that an electrical and secure, mechanically flexible connection may be created between said rigid circuit board daughter card and said motherboard. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  illustrates schematically a bifurcated flexible circuit having contact pads on the inner and outer surfaces of bifurcated extensions according to one aspect of the invention. 
           [0019]      FIG. 2  illustrates schematically a bifurcated flex circuit direct-mounted on a printed circuit board or motherboard. 
           [0020]      FIG. 3A  illustrates the flexible or compliant properties of bifurcated flexible circuits direct-mounted on a motherboard according to another aspect of the invention. 
           [0021]      FIG. 3B  illustrates the flexible or compliant properties of bifurcated flexible circuits direct-mounted on a motherboard within an enclosure according to another aspect of the invention. 
           [0022]      FIG. 4A  illustrates a supporting device to prevent excessive flexure between bifurcated flexible circuits that are vertically mounted on a motherboard according to another aspect of the invention. 
           [0023]      FIG. 4B  illustrates a supporting device to prevent excessive flexure between bifurcated flexible circuits that are mounted at an oblique angle to a motherboard according to another aspect of the invention. 
           [0024]      FIG. 5  illustrates schematically a rigid printed circuit board adapted with flexible circuit leads having contact pads on the inner surfaces for direct-mounting on a printed circuit board or motherboard according to one aspect of the invention. 
           [0025]      FIG. 6  illustrates schematically a bifurcated flex circuit direct-mounted on a printed circuit board or motherboard by means of conductive spheres or bumps, according to another aspect of the invention. 
           [0026]      FIG. 7  illustrates schematically a bifurcated flex circuit direct-mounted on a printed circuit board or motherboard by means of compression clamps, according to another aspect of the invention. 
           [0027]      FIG. 8A  illustrates schematically a bifurcated flex circuit direct-mounted on protruding pins, soldered to a printed circuit board or motherboard, by means of compression clamps, according to another aspect of the invention. 
           [0028]      FIG. 8B  illustrates schematically a bifurcated flex circuit direct-mounted on protruding pins, soldered to a printed circuit board or motherboard, by means of compression clamps that include flex circuit connectors, according to another aspect of the invention. 
           [0029]      FIG. 9  illustrates schematically a bifurcated flex circuit direct-mounted to a printed circuit board or motherboard, by means of compression clamps that include integral compression posts, according to another aspect of the invention. 
           [0030]      FIG. 10A  illustrates different patterns for piercing the electrode pads on the bifurcated extensions, according to one aspect of the invention. 
           [0031]      FIG. 10B  illustrates in cross-section the deformation of a pierced electrode pad when compressed by a post, according to one aspect of the invention. 
           [0032]      FIG. 10C  illustrates in cross-section a pierced electrode pad adjacent a layer of compliant material that enables a controlled deformation of the pad when a force is applied against a contact pin. 
           [0033]      FIG. 11A  illustrates schematically a bifurcated flexible circuit having contact pads on the inner surfaces of bifurcated extensions which are inserted through a slot within a clamping collar, according to one aspect of the invention. 
           [0034]      FIG. 11B  illustrates schematically a bifurcated flexible circuit having contact pads on the inner surfaces of bifurcated extensions which are inserted through a slot within a clamping collar and partially or fully reflexed against the bottom surface thereof, according to one aspect of the invention. 
           [0035]      FIG. 11C  illustrates schematically a bifurcated flexible circuit having contact pads on the inner surfaces of partially reflexed bifurcated extensions which are inserted through a slot within a clamping collar for attachment to a test socket, according to one aspect of the invention. 
           [0036]      FIG. 11D  illustrates schematically a bifurcated flexible circuit having contact pads on the inner surfaces of partially reflexed bifurcated extensions which are inserted through a slot within a clamping collar for attachment to a Zebra Strip Connector, according to one aspect of the invention. 
           [0037]      FIG. 11E  illustrates a bifurcated flexible circuit formed using two separate flexible films laminated to the outer surfaces of rigid PCB substrate, similar to  FIG. 5 , but which extend under the electronic components mounted to the sides. The bottom contacts include pads on both the inner and outer surfaces of the flexible films, which can interface with a socket connector. 
           [0038]      FIG. 12A  illustrates schematically the side-view of a bifurcated flexible circuit inserted through a slot within a clamping collar for attachment to a compression latch assembly, according to one aspect of the invention. 
           [0039]      FIG. 12B  illustrates schematically the bottom-view of the clamping collar of  FIG. 12A  with a center slot and alignment posts for attachment to a compression latch assembly, according to one aspect of the invention. 
           [0040]      FIG. 12C  illustrates schematically the bottom-view of the flexible bifurcated extensions of  FIG. 12A  with circuit leads and conductive bumps for attachment to a motherboard by means of a compression latch assembly, according to one aspect of the invention. 
           [0041]      FIG. 12D  illustrates schematically a side-view of an interposer board for adding gold-plated contacts onto the surface of a motherboard compatible with a compression latch assembly, according to one aspect of the invention 
           [0042]      FIG. 12E  illustrates schematically the side-view of a bifurcated flexible circuit inserted through a slot of a bowed clamping collar for attachment to a compression latch with integral, press-fitted, stamped metal contacts, according to one aspect of the invention. 
           [0043]      FIG. 12F  illustrates schematically the front and side-views of stamped metal straight contacts, according to one aspect of the invention. 
           [0044]      FIG. 12G  illustrates schematically a cross-section view of staggered, stamped metal straight contacts press-fitted into a compression latch assembly, according to one aspect of the invention. 
           [0045]      FIG. 12H  illustrates schematically a top-view of staggered, stamped metal straight contacts press-fitted into a compression latch assembly, according to one aspect of the invention. 
           [0046]      FIG. 12J  illustrates schematically the front and side-views of stamped metal “J-bend” contacts, according to one aspect of the invention. 
           [0047]      FIG. 12K  illustrates schematically a cross-section view of staggered, stamped metal “J-bend” contacts press-fitted into a compression latch assembly, according to one aspect of the invention. 
           [0048]      FIG. 12L  illustrates schematically a top-view of staggered, stamped metal “J-bend” contacts press-fitted into a compression latch assembly, according to one aspect of the invention. 
           [0049]      FIG. 12M  illustrates schematically the front and side-views of stamped metal spring contacts, according to one aspect of the invention. 
           [0050]      FIG. 12N  illustrates schematically a cross-section view of staggered stamped metal spring contacts press-fitted into a compression latch assembly, according to one aspect of the invention. 
           [0051]      FIG. 12P  illustrates schematically a top-view of staggered, stamped metal spring contacts press-fitted into a compression latch assembly, according to one aspect of the invention. 
           [0052]      FIG. 13  illustrates schematically a cross-section view of a bifurcated flexible circuit, protected within two metal heat spreaders having angled flanges, with bifurcated extensions bonded to the bottom of the angled flanges, according to one aspect of the invention. 
           [0053]      FIG. 14  illustrates schematically a cross-section view of a bifurcated flexible circuit, protected within two metal heat spreaders having diverging flanges, with bifurcated extensions bonded to the bottom of the diverging flanges, according to one aspect of the invention. 
           [0054]      FIG. 15A  illustrates schematically a cross-section view of a bifurcated flexible circuit, protected within two metal heat spreaders having angled flanges, clamped in compression against a motherboard with metal wedges, according to one aspect of the invention. 
           [0055]      FIG. 15B  illustrates the embodiment of  FIG. 15A  with a bifurcated flexible circuit having a folded extension with additional components, protected within metal heat spreaders without flanges, according to one aspect of the invention. 
           [0056]      FIG. 15C  illustrates schematically a cross-section view of a bifurcated flexible circuit, protected within two metal heat spreaders without flanges, clamped in compression horizontally against a motherboard with a clamping device, according to one aspect of the invention. 
           [0057]      FIG. 15D  illustrates the embodiment of  FIG. 15C , which includes a folded extension with additional components, protected within metal heat spreaders without flanges, clamped in compression horizontally to the top surface of a motherboard with a single clamping device, according to one aspect of the invention.  FIG. 15E  illustrates the embodiment of  FIG. 15C  clamped in compression horizontally on both sides of a motherboard with two clamping devices, according to another aspect of the invention. 
           [0058]      FIG. 16A  illustrates schematically a top-view of a direct connect socket for bifurcated flexible circuits protected within metal heat spreaders having angled flanges, according to one aspect of the invention. 
           [0059]      FIG. 16B  illustrates schematically a side-view of a direct connect socket for bifurcated flexible circuits protected within metal heat spreaders having angled flanges, according to one aspect of the invention. 
           [0060]      FIG. 16C  illustrates schematically a cross-section view of a pivoting compression clamp for metal heat spreaders having angled flanges, according to one aspect of the invention. 
           [0061]      FIG. 17A  illustrates schematically a top-view of a direct connect socket for bifurcated flexible circuits protected within metal heat spreaders having diverging flanges, according to one aspect of the invention. 
           [0062]      FIG. 17B  illustrates schematically a side-view of a direct connect socket for bifurcated flexible circuits protected within metal heat spreaders having diverging flanges, according to one aspect of the invention. 
           [0063]      FIG. 17C  illustrates schematically a cross-section view of a pivoting compression clamp for metal heat spreaders having diverging flanges, according to one aspect of the invention. 
           [0064]      FIG. 18A  illustrates schematically a cross-section view of an interposer board having bladed contacts and a concave dimpled clamping collar for mechanical forming and electrical mating with the electrode pads of a bifurcated flexible circuit, according to one aspect of the invention. 
           [0065]      FIG. 18B  illustrates schematically a close-up, cross-section view of  FIG. 18  A. 
           [0066]      FIG. 18C  illustrates schematically a cross-section view of a convex dimpled clamping collar for mechanical forming and electrical mating with the electrode pads of a bifurcated flexible circuit, according to one aspect of the invention. 
           [0067]      FIG. 18D  illustrates schematically a close-up, cross-section view of  FIG. 18  C. 
           [0068]      FIG. 19  illustrates schematically the bifurcated flex circuit of  FIG. 2  direct-mounted on both the top and bottom surface of a printed circuit board or motherboard using shared contacts of the motherboard by means of a contact translation board. 
           [0069]      FIG. 20  illustrates schematically the bifurcated flex circuit of  FIG. 2  direct-mounted to the edge of a printed circuit board or motherboard using a sliding compression connector. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0070]    The concept of a bifurcated flex circuit board is taught Applicants&#39; U.S. patent application Ser. No. 12/317,757, as well as in Applicants&#39; issued U.S. Pat. Nos. 7,796,399, and 7,724,530. The entire contents of all of the foregoing are incorporated herein by reference. The aforementioned disclosures are directed to various ways of making rigid modules, particularly DRAM modules, for rigidly mounting onto a motherboard via a rigidly-mounted socket or by soldering or adhesive bonding directly onto contacts on the motherboard The present invention is based on Applicants&#39; recognition that a multilayer, bifurcated flex circuit board can be mounted directly onto a motherboard in such a way that the mounting is flexible (i.e., it can allow the flex circuit to bend from side to side to some degree) and yet maintains electrical connectivity to the motherboard. As will be illustrated in the following examples, this structure provides numerous surprising advantages over conventional rigidly-mounted electronic modules. Some of these advantages include the following: 1. Size, weight, and cost of the entire system can be reduced by eliminating much of the module-level packaging. 2. Heat-generating components may be more effectively cooled by eliminating layers of packaging&#39; including surrounding socket structures which may impede air flow along the modules. 3. Assembly methods can take advantage of the compliant mounting of subsystems, allowing them to be folded sideways to reduce the height of the populated motherboard. 
         [0071]      FIGS. 1-3  illustrate electronic subsystems  1 ,  1 ′ and  1 ″ in which a centrally located, multilayer, bifurcated flexible circuit board or substrate  10  is populated on one or both sides with various electronic components  11 , which are connected by vias to circuit lines or traces on the inner and external surfaces of the individual dielectric plies. In the examples shown, two individual plies, with circuit traces on both surfaces, are bonded or laminated together with an adhesive or film  9  at the middle of the sandwich and interconnected with vias. Along one edge, the two flexible plies are bifurcated into two extensions or legs  13  by either selective application or removal of the middle bonding adhesive or by peeling the edges apart if the laminate plies are weakly bonded. In this example, electrode pads  12  are arranged along the inner surfaces of the bifurcated extension and electrode pads  12 ′ are arranged along the outer surfaces of the two bifurcated legs. Spreading the two legs of the bifurcated area apart, typically by about 180°, exposes pads  12  and enables them to be aligned with respective contacts  21  on a rigid printed circuit board or motherboard  20  as shown in  FIG. 2 . The pads are then bonded to the contacts using solder, anisotropic conductive adhesive, or isotropic conductive adhesive, or by clamping them in compression against the contacts, thereby functionally connecting the subsystem  1  to the motherboard. At the same time, there is a sufficient length of the legs  13  of the bifurcated flexible circuit board to allow the flex board to move from side to side by a useful amount. (As used herein, a useful amount of flexure might be as little as a few degrees or as much as +/−45° or even 90°, as shown generally in  FIG. 3 ). 
         [0072]    It will be appreciated that as used herein, the term “motherboard” is not limited specifically to a circuit board that includes a computer&#39;s CPU, but instead simply refers to any substantially rigid printed circuit board on which various components and subsystems may be mounted to form a higher-level electronic system. It will be further appreciated that the invention may be applied to desktop computers, mobile computers, tablet computers, smart phones, servers, and virtually any electronic system in which one needs to attach a multi-component subsystem to a larger system. 
       Example 
       [0073]      FIG. 1  illustrates schematically a bifurcated flexible circuit board  10 . The board may be constructed by forming two individual flexible dielectric sheets using polyimide or other suitable substrate material having selected metallization patterns as are well known in the art. Each sheet has electronic components  11  mounted on one side (which for clarity will be referred to as the outer surface) and a metallization pattern, including electrode pads  12  on the other side. Each sheet will typically have conductive vias that interconnect the two sides of the sheet, thereby allowing signals to move between the components  11  and pads  12 . 
         [0074]    In one embodiment of  FIG. 1 , the bifurcated flexible circuit board  10  consists of an Organic Light Emitting Diode display (OLED) adapted for direct connection to a PCB or motherboard  20  as explained below. 
         [0075]    The two sheets are bonded together with an adhesive film  9  over most of their surface area, leaving a bifurcated area forming two extensions  13  along one edge. The flexible board will also preferably extend for some distance between the mounted components  11  and the extensions  13  to create a compliant region  14 . 
       Example 
       [0076]      FIG. 2 . illustrates a subsystem  1  mounted onto motherboard  20 . Contacts  21  on motherboard  20  are spaced so that they will align with their respective electrode pads  12  on the flex board of subsystem  1 . Alignment holes may be located near the center and/or ends of the length of the bifurcated extensions or legs  13 , as shown at  57  in  FIG. 12C , to aid in the alignment of the electrode pads  12  with the contacts  21  on the motherboard. When pads  12  are bonded or compressed against contacts  21 , the subsystem  1  is securely attached to motherboard  20 , and yet has a degree of flexibility as shown schematically in  FIG. 3A . It will be appreciated that if pads  12 ′ are disposed on the outer surfaces of the legs  13  as shown in  FIG. 1 , another mounting option is available (not shown): In this option, the motherboard can have a slot through which compliant region  14  is passed. Legs  13  are then opened to bring pads  12 ′ into alignment with contacts on the underside of motherboard  20 . 
         [0077]    The contact pads on the motherboard of  FIG. 2  may be either of the Surface Mount Technology (SMT) type or through-hole type, as illustrated. 
       Example 
       [0078]    The inherent flexibility of the inventive interconnection system provides the system designer with many opportunities to optimize system-level layout and assembly as shown in  FIG. 3B . Here, motherboard  20 , having two subsystems  1 ′ and  1 ″ and another component  22  mounted thereon, must be packaged into housing  30 . After bonding to motherboard  20 , subsystem  1 ′ is flexed clockwise by about 45° and subsystem  1 ″ is flexed counterclockwise by about 90° to accommodate the geometrical constraints imposed by the system requirements. For applications requiring subsystems  1 ″ to be flexed up to 90° the adhesive or bonding film  9  used to laminated the flexible layers of plies together may be adjusted to lengthen the bifurcated area and legs  13 , as shown in  FIG. 3B . 
       Example 
       [0079]    The electronic components  11  mounted on the flex board may be of any type, such as, for example, logic devices and microprocessors, memory chips including DRAM or flash, buffer and timing circuits, analog, digital, and mixed-signal circuits, RF devices, optoelectronic devices including LEDs, and passive components including resistors, capacitors, inductors, and antennas. Furthermore, components  11  may be of any suitable size or form, such as, for example, bare die, packaged die, surface-mount, BGA, multichip module, etc., and the components may be attached to the flex board using any conventional technique such as solder, epoxy and wire bonds, or various conductive adhesives as are well known in the art. 
       Example 
       [0080]    The invention may be used for mounting one or more rows of DRAM chips onto a motherboard, where a key advantage of the invention is that the individual chips are more easily cooled by flowing air because much of the traditional package requirements of a conventional DRAM module is reduced or eliminated (e.g. module width/height or socket obstruction). It will be appreciated, however, that when a large flow of coolant is expected, it will in some cases be desirable to constrain the flexure of the subsystem  1  relative to the motherboard  20  so that unconstrained harmonic oscillations won&#39;t lead to fatigue and premature mechanical failure of the interconnects.  FIG. 4A  illustrates an enclosure  30 ′ having slots  40  along the top inner surface. Slots or other mechanical constraint structures may alternatively be attached to motherboard  20  instead of to enclosure  30 ′. 
       Example 
       [0081]    As noted earlier, in some cases, it is desirable to orient the subsystem  1  at some angle relative to motherboard  20  in order to reduce the system profile as shown generally in  FIG. 3B . In these situations, if flowing coolant is also used, a reduced-height enclosure  30 ″ may employ angled slots  40 ′ to hold the flex boards at a selected angle relative to motherboard  20 . A solution of this type might be appropriate for applications such as blade servers, for example. 
         [0082]    Those skilled in the art will appreciate that the invention is not limited to particular applications such as DRAM, but in fact is a general solution to many electronic systems and interconnection problems. 
       Example 
       [0083]    The inventive circuit is preferably manufactured as follows. First, two individual flexible circuit plies or laminates having conductive traces (typically on both surfaces) and vias connecting one surface to the other and one ply to another as needed, are formed by conventional means and bonded together over most of their surface area to form a multilayer flex panel or circuit board, leaving an unbonded strip (bifurcation) along one edge. The electrode pads intended to connect this circuit to a motherboard are located on the inner surfaces of the bifurcation. Next, the flex circuit is populated by microelectronic devices, which may be any combination of analog, digital, or mixed-mode semiconductor devices or passive components. This step will typically involve conventional “pick and place” assembly using solder or conductive adhesives as are known in the art. Then, the two legs of the bifurcated extensions or area are spread apart and the electrode pads are aligned with rows of contacts on a motherboard. The pads on the flex are then joined to the contacts using solder or conductive adhesive, by which the flex is securely held onto the motherboard but still able to bend from side to side by an amount that will be controlled to some degree by the rigidity of the flex and its overall geometry. 
         [0084]    Applicants contemplate that for some applications, a soldering bonding technique will be used to affix the flex circuit to the rigid circuit board. Alternatively, adhesive bonding using isotropic or anisotropic conductive adhesives may also be used as is well known in the art of electronic assembly. Each of the above mentioned techniques result in a permanent or semi-permanent mating of the flex circuit to the rigid circuit board or motherboard. In other cases, however, a detachable mating of the aligned pads and contacts will be the preferred method and various clamping devices, collars and compression latch assemblies are disclosed for this purpose. A variety of novel clamping devices are also disclosed herein to enable the flexible extensions to be temporarily, or semi-permanently compressed against various pads, plated through-holes, pins, compressible springs or conductors, and interposers. 
         [0085]    The invention may also be modified to use with rigid circuit boards. Referring now to  FIG. 5 , an electronic subsystem  2 , with a rigid circuit board or substrate  15  in place of a flexible circuit, is illustrated in cross-section with four rows of electronic components  11  in a standard-height DIMM memory module. In order to adapt the rigid circuit board for direct connection to the motherboard  20 , flexible circuit leads  16  are electrically and mechanically attached to the DIMM pads along the bottom sides and spread apart to about 180° to enable electrode pads  12  to connect to contacts  21  on the PCB or motherboard  20 . In this manner, a rigid printed circuit board module can be adapted for mounting at various angles with the respect to the motherboard as previously described in  FIG. 3A . 
         [0086]    In an alternative embodiment of  FIG. 5 , the rigid circuit board or substrate  15  consists of a Liquid Crystal Display (LCD) adapted for direct mounting to a PCB or motherboard  20  using bifurcated flexible circuit leads. In another alternative embodiment of  FIG. 5 , the rigid circuit board or substrate  15  consists of a Rigid-Flex Circuit Board adapted for direct mounting to a PCB or motherboard  20  using bifurcated flexible circuit leads. 
         [0087]      FIG. 6  illustrates a design for enabling electronic subsystem  1 , with a birfurcated flexible circuit board or substrate  10 , to be directly mated to a motherboard  20 . Electrode pads  12 , arrayed along the bottom, inside surfaces of the birfurcated area are exposed when legs  13  are bent apart in such a manner to form a 180° angle to mate with motherboard  20 . The angle illustrated here between each leg  13  and flexible circuit board  10  is approximately 90°; however, other angles may likewise be implemented. In this example, an array of conductive spheres or bumps  17  are disposed on electrode pads  12  to enable the pads to self-align and electrically mate with appropriately sized annular rings  19  of plated-through holes (PTHs)  18  arrayed on the motherboard  20 . Conductive spheres or bumps  17  may be fashioned from a large variety of materials, including; plated or partially reflowed solder balls, plated metal columnar bumps, gold thermo-compression bonded balls or stud bumps, stenciled or dispensed conductive epoxy or conductive elastomeric material, or anisotropic conductive adhesive and other means known for establishing electrical connection between flex circuit electrode pads  12  and PTH annular rings  19  or contacts  21  (not shown) of motherboard  20 . Conductive spheres made using solder alloys enable the electrode pads to be directly soldered to either the pads or plated-through holes of the motherboard. For example, if the flex circuit pads are simply coated with solder by plating or dipping in a molten bath, or if solder paste is stenciled or dispensed onto the motherboard contacts, the pads and contacts can then be subsequently soldered together by aligning them and using a heater-bar to simultaneously compress and melt the solder. Alternatively, if the conductive spheres are fashioned from either a rigid or compressible conductive material, they may be removably mated to the motherboard contacts using various means for applying a clamping force between the two surfaces. 
         [0088]    In many instances it will be preferable for electronics subsystem(s)  1  to be removably mounted to the motherboard  20 .  FIG. 7  illustrates an example of a clamping device  22  for applying a compressive force against the backside of the bifurcated extensions  13  to establish electrical contact between the PTH annular rings  19  and conductive spheres  17  on electrode pads  12  fashioned from plated metal bumps. Conductive spheres  17  are designed with a diameter slightly larger than the inside diameter of the PTH vias  18  such that when a compressive force is applied the plated metal conductive spheres  17  enter into intimate, gas tight, electrical contact with the inside perimeter of the PTH annular rings  19 . This electrical contact is maintained as long as the compressive force is maintained. Conversely, when the compressive force maintaining the electrical connection is removed, electronic devices or electronic subsystems  1  can be removed from the motherboard without need of a de-soldering process. Compressive force in  FIG. 7  is provided using a screw  23  and a lock nut  24  to apply a clamping force against the backside of the bifurcated extensions  13 . The plated metal conductive spheres  17  are positioned on electrode pads  12  to align and mate with the inside perimeter of the PTH annular rings  19  typically used for receiving and soldering the DIMM socket&#39;s pins. These sockets typically require four adjacent rows of staggered PTH vias  18  on the motherboard that receive the socket pins for soldering. The plated metal conductive spheres align with each via of the motherboard in a similar staggered configuration. For purposes of this compression contact, it is preferable that both the conductive spheres and PTH vias are plated with gold or other noble metal to ensure reliable electrical conductivity. Normal force is applied and maintained to these plated bumps using a clamping device  22 . One simple clamping device would consist of a metal bracket with a compliant material  25  on the bottom surfaces that is compressed against the surface of the motherboard  20  and flexible circuit extensions  13 . The compliant material  25  may be composed of rubber, silicone, or other material with elastomeric properties, which can be bonded to the surface of the metal clamping device. As noted earlier, other materials can be substituted for the plated metal conductive spheres  17 , such as a “Zebra Strip” (i.e., conductive elastomeric material), for achieving electrical connection when compressed between electrode pads  12  and PTH annular rings  19 . 
         [0089]      FIG. 8A  is similar to  FIG. 7 , but illustrates a different contact technique for the electronic subassembly  1 . In this embodiment, conductive spheres  17  are replaced with a “bed-of-nails” connector  26  that includes an array of pins extending from the bottom of motherboard  20 , through the PTH vias  18 , and projecting slightly above the PTH annular rings  19 . Connector  26  includes a molded plastic “rail” to hold the pins in proper alignment for simultaneous insertion into the motherboard vias and to set the correct stand-off height of the pins above the PTH annular rings. For this application the protruding pins  27  would preferably be made of stamped metal with pointed or blunt tips that are selectively gold plated and soldered from the bottom to form solder fillets  28  around the shaft of each pin and bottom annular rings if the PTH vias. The compliant material  25 , opposite the electrode pads of the bifurcated extensions, helps the pads to conform to the shape of the protruding pins and compensates for any non-uniformity in the height of the pins. Once the pins  27  are soldered to the motherboard, the plastic rail may optionally be removed. If the pins are wave soldered from the bottom side of the mother board, the solder would typically form solder fillets  28 , as shown. The advantage of this connector concept is that the electrical signal path from the motherboard into the subassembly is kept to a minimum distance and should therefore exhibit less parasitic capacitance and/or inductance with higher signal speeds. Although only two rows of connector pins are illustrated in cross-section for  FIG. 8 , it should be understood that there would preferably be four rows of staggered protruding pins  27  that match the mounting footprint of standard 240-pin DIMM memory module sockets as viewed from above the motherboard. 
         [0090]    In recent years there has been an increasing recognition for the need to increase the number of contact pins or pads on high-density, high-speed, memory modules to provide more power and ground connections to the modules. The additional power/ground connections aid in balancing the power and ground requirements for higher speed memory components and in providing better signal integrity of input/output signals. Normally this would be achieved by reducing the pad-to-pad pitch on the modules and correspondingly increasing the number of socket pins which contact these module pads. But, the number of contact pins on traditional DIMM sockets seems to have reached a practical limit at its current level of 240 pins due to the excessive insertion and extraction forces required. Many OEM manufacturers are experiencing problems with module and socket breakage during insertion of the modules and the problem is exacerbated if automated equipment is used for this manufacturing step. The embodiment shown in  FIG. 8B  is an attempt to help solve this problem. 
         [0091]    The electronic subsystem  1  and “bed-of-nails” connector  26 , as shown in  FIG. 8A , are similar to  FIG. 8B , but the bifurcations now include both bottom electrode pads  12  and top electrode pads  12 ′, similar to  FIG. 1 , and clamping device  22 ′ is modified to include an integrated flex circuit connector  50  with integrated conductive spheres or bumps  17 . The flex connectors  50  with conductive bumps  17  are clamped and held in compression against top electrode pads  12 ′ and contacts  21  on the motherboard  20  while simultaneously pressing the bottom electrode pads  12  against the protruding pins  27 . Flex connectors  50  also include circuit traces that are routed between the conductive bumps  17  which simultaneously contact the top electrode pads  12 ′ and PCB contacts  21 . This configuration effectively doubles the number of input/output contacts for electronic subsystem  1  without requiring a significant increase in the amount of compressive normal forces. It should be noted, however, that a similar increase in the number of input/output contacts can be achieved for the embodiments represented in  FIGS. 7 and 8A  by simply reducing the pad-to-pad pitch of electrode pads  12  and PTH vias  19  without requiring a significant increase in the amount of compressive normal forces. 
         [0092]    Turning now to  FIG. 9 , another configuration  22 ″ of the clamping device is illustrated. This clamping device integrates compression posts  29  opposite each electrode pad on the bifurcations to selectively deform the electrode pads  12  in a manner that causes them to protrude into the apertures of the PTH vias and against the interior edges of the PTH annular rings. The resulting formed electrode pads  31  and compressive posts  29  are engineered to provide reliable electrical connections by providing constant contact force between pads  12  and the PCB or motherboard vias during temperature cycling of the components. Since the posts will require constant force against the pads, it is preferable that they be fashioned from metal or a rigid plastic. It will be appreciated that the deformation process is aided by the thin cross-sectional thickness and inherently deformable characteristics of the bifurcations. However, additional modifications to the electrode pads  12  on the bifurcations, as represented in  FIGS. 10A-C , can improve and assist in the deformation of the formed electrode pads  31  to better engage the PTH on the motherboard  20 . 
         [0093]      FIG. 10A  illustrates a single electrode pad  12 , as viewed from above the pad, with four examples of various slitting patterns or shapes to produce a pierced electrode pad  32 . From left-to-right the patterns have either four or three slits with and without a center aperture. The slits would extend through the entire cross-sectional thickness of the electrode pad  12 , and allow a compression post  29  to more easily deform each slotted portion of the electrode pad  33  to conform with the interior aperture of each PTH via  18  as represented in  FIG. 10B . Referring then to  FIG. 10B , an enlarged cross-sectional view of the PTH via  18 , electrode pad  12 , pierced electrode pad  32 , and compression post  29  is illustrated. The figure on the left illustrates a view of the mating surfaces before the compression post engages with the pierced electrode pad, while the illustration to the right shows the mated surfaces after the post presses the pierced electrode pad down into the PTH via  18  and spreads and compresses the slotted portions of the electrode pad  33  against the interior edges of the PTH aperture ring. The inventive slits or other piercing features will help the flex conform to a dimpled surface in either a convex or concave direction. 
         [0094]      FIG. 10C  shows another cross-section example of pierced electrode pad  32  with a compliant material  25  placed on the opposite surface of the flexible circuit. When a force is applied from above, as illustrated by the bold arrow, the compliant material will allow the pads  12  to deform in a controlled manner against a metal contact pin  76 , similar to that as shown at  33  in  FIG. 10B . 
         [0095]    Applicants contemplate the principles described above for  FIGS. 10A-C  can be applied in general to other interconnect applications involving flexible circuits, including the examples illustrated in  FIGS. 12E-H ,  FIGS. 17A-B  and  FIGS. 18A-D . The principles described above allow flexible circuit connectors or sockets to be fashioned without the necessity for using piercing pins, thereby reducing cost, enabling lower profile connections and adding electrical redundancy. 
         [0096]    In the preceding “removable” electronic subsystems of  FIGS. 7 ,  8 A-B, and  9 , the clamping devices rely on threaded screws  23  and lock nuts  24  positioned to the sides of the devices to apply the required compressive normal forces to achieve electrical contact between the bifurcated electrode pads and PTH annular rings or vias of the motherboard. The extended portions of the clamping devices that hold these screws and lock nuts reduce the available mounting area on the motherboard for other adjacent subsystems such as parallel banks of memory modules. Ideally, manufacturers prefer to reduce the amount of space or pitch between components in order to increase the functionality of the motherboard for a given fixed board size or enclosure. Since memory requires a significant amount of the available space on most motherboards, it is highly desirable to place the individual memory modules as close as practical without impeding the air circulation or ability to insert and remove the modules from the DIMM sockets pre-soldered on the motherboard. Accordingly, a novel clamping collar  38  is integrated with the bifurcations  13  for the electronic subsystems illustrated in  FIGS. 11A-D ,  12 A, and  12 E to simplify the mounting/unmounting and reduce the width necessary for clamping the removable modules to the motherboard. 
         [0097]    Turning now to  FIG. 11A , a cross-section view is illustrated of an electrical subsystem  1 , similar to  FIG. 1 , with a multilayer flexible circuit  10 , four rows of components  11  and bifurcations  13 . Surrounding the compliant region  14  (refer to  FIG. 1 ) of the bifurcated leads is a clamping collar  38  with an open slot  47  along the centerline of the collar that allows the extensions to be inserted through the collar. The collar is preferably metal or a rigid molded plastic suitable for transferring the compression forces along its lateral length. On the bottom of the collar is a layer of compliant adhesive material  25  for bonding the bifurcations  13  to the bottom surface of the collar when they are spread apart ( FIG. 11B ). The resulting integrated clamping collar enables the electronic subsystem or module to be mated directly with the pads or PTH vias on the motherboard, as shown in  FIG. 12A-B , or to a variety of socket pins or springs, as shown in  FIG. 12E-P . 
         [0098]    Another novel clamping collar  38 ′ is illustrated in  FIG. 11C . The collar includes an open slot  47 ′ that is tapered towards the top and sized to mate with a narrow contact post  54 , the bottom leads of which are surface mount soldered to the motherboard  20 . The clamping collar  38 ′ is designed to apply a lateral, inward clamping pressure against both flexible legs of the bifurcation when the collar  38 ′ is pressed downward and over the contact post. When fully seated, the clamping collar locks the leads to the post and pinches the electrode pads  12  against the protruding spring pins  53  of the contact post  54 . One particular problem is resolved with this type of connector system. After components  11  are assembled to the flexible bifurcated circuit  10 , it is highly desirable to perform an electrical functional test of the components and assembly connections prior to proceeding to the next assembly steps. However, electrode pads  12  are typically disposed on the inner surfaces of the flexible plies making test probe access difficult. The clamping collar and contact post, as described above, therefore serve, among other things, as a novel solution to simplify electrical testing of electronic subsystems  1  or unpopulated, bare, bifurcated flexible circuits  10  prior to component attachment. In addition, clamping collar  38 ′ may also be implemented in a connector system for production mounting of modules to the motherboard. 
         [0099]    In the proceeding examples the flexible circuit leads were formed at an 180° angle. However, the flexible leads shown in  FIGS. 11C-D  and  FIG. 20  are opened slightly while keeping the two halves approximately parallel to engage contacts on both sides of a connector or edge of a PCB or motherboard. 
         [0100]      FIG. 11D  is similar to  FIG. 11C , but illustrates that a “Zebra-strip” elastomeric connector  55 , similar to those manufactured by Fujipoly America Corp., can replace or be integrated with the contact post  54  (not shown) to achieve the same results described above. 
         [0101]      FIG. 11E  is similar to  FIG. 5 , but includes two separate flexible circuits laminated to the external surfaces of a rigid printed circuit board (PCB) or substrate  15  and which extend under the attached electronic components  11 . The PCB or substrate and flexible circuits may be electrically connected across the interface of the laminated surfaces. Conversely, the PCB or substrate may serve only as a spacer to separate components  11  mounted to inner surfaces of the separate flexible circuits  10  (not shown). 
         [0102]    In this example, the two separate flexible circuits form equivalent bifurcated flexible leads at the bottom that may then be spread apart, as previously described for direct mating to a motherboard, or may be connected to a motherboard using a socket  54  or connector specifically designed to engage with the bifurcated leads. In the example shown n  FIG. 11E , the bifurcated leads include both inner  12  and outer  12 ′ electrode pads which engage with the socket contacts  53 . 
         [0103]    An elevation view of an electronic subsystem  1  with a clamping collar  38  installed is illustrated in  FIG. 12A . In this embodiment, a compression latch assembly  41  is also shown mounted to the PCB or motherboard  20 . Assembly  41  is designed to receive and latch the integrated clamping collar  38 , with attached electrode pads  12  as described for  FIG. 11B , into a slot (partially shown with dotted lines) and hold the integrated collar in compression directly against the PTH annular rings  19 , or vias  18 , or contact pads  21 , as previously described. The housing for assembly  41  would typically comprise a rigid, liquid crystal polymer (LCP) plastic or metal and would typically include threaded posts or holes at its ends and mid-point (not shown) for anchoring the housing to the motherboard using appropriate hardware. Metal spring latches or retention clips  39  located at the ends of the assembly are used to clamp the integrated clamping collar in compression against the motherboard contacts. These latches or clips  39  would preferably spring outward as the collar is pressed downward into at least a portion of the slot, and spring back to their original position to latch and hold the collar in compression against the surface of the motherboard once the collar is properly seated into the slot and sufficient compression is achieved to enable electrical function between all contact surfaces. 
         [0104]    The length of the slot and proportionately narrow side rails of the longer assembly housings  41 , may cause the housing and/or motherboard surface to bow if mated with an integrated collar that contains large numbers of contacts that require high normal forces to achieve reliable electrical connection with the motherboard. Consequently, the contact surfaces near the mid-point of the integrated collar  38  may not receive the same amount of compressive normal force as the contacts near the ends of the collar, causing potential open electrical connections in this area. To correct this problem, one solution is shown in  FIG. 12E  where collar  38 ″ is itself bowed in a convex manner near the mid-point of its length and in the direction of the motherboard contacts. When properly designed and assembled, the convex-bowed collar  38 ″ will bring the electrode pads  12  near the mid-point of its length into direct contact with the motherboard contacts first and enable higher compressive normal forces to be concentrated at this area of the motherboard. The amount of bowing required would be dependant on a number of factors, including the composition of the collar, whether metal or plastic, the length and thickness of the collar, the elastic properties of the complaint material  25 , the design of the assembly housing and method of anchoring to the motherboard, etc. The skilled artisan can determine the optimal bowing through routine experimentation for a particular application. 
         [0105]    Another solution for solving the tendency of the housing and/or motherboard surface to bow when mated in compression with the collar is to add an additional metal brace or stiffener plate  45  ( FIG. 15A ) directly beneath the assembly housing  41  on the opposite side of the motherboard. This metal stiffener plate would provide additional rigidity to the motherboard, which would be sandwiched in the middle between the plate on the bottom and assembly housing on the top surface. The stiffener plate and housing could be assembled together as a unit onto the motherboard using the same hardware (e.g., screws and threaded nuts) that clamp both pieces together onto the motherboard. Similar to the assembly housing described above, the stiffener plate would include an open slot along its length, to avoid metal contact with exposed PTH vias on the bottom of the motherboard, and a means at or near its mid-point to anchor the side rails of the stiffener plate together with the side rails of the assembly housing (not shown). 
         [0106]    In the embodiment shown in  FIG. 12A , the electrode pads include conductive bumps  17  arrayed across the bottom surface of the integrated clamping collar and are aligned with the PTH vias  18  and PTH annular rings  19  on motherboard  20  by means of alignment posts  58  located near the ends of the collar. These posts engage with orientation holes  59  (with or without different diameters) placed either on the motherboard or machined or molded into the compression latch assembly housing  41 . 
         [0107]      FIG. 12B  shows a bottom view of the collar  38  of  FIG. 12A , with the bifurcated extensions  13  removed for clarity, and  FIG. 12C  shows a bottom view of the same bifurcated extensions of  FIG. 12A  as they would appear with the leads spread apart and bonded to the bottom of the collar. A narrow open slot  47  is shown extending along the centerline for most of the length of collar  38  through which the bifurcations are inserted. Four alignment posts  58  are shown near the ends of the collar and are intended to engage with alignment holes  57  placed at the ends of the bifurcations  13 . These posts help align the flexible circuit leads  16  and conductive bumps  17  with the PTH annular rings  19  and vias  18  on the PCB motherboard, as described above. It will be understood that the dimensions as shown in  FIG. 12C  are exemplary only and representative of the conventional spacing between conductive bumps  17  to align and engage with the motherboard PTH vias for a standard 240-pin DIMM socket, although the number of leads and bumps illustrated are reduced for purposes of clarity. The terminal edge of the bonding adhesive or film  9 , which is selectively applied to produce bifurcated flexible circuit board  10 , is also shown. 
         [0108]    It is well known in the art of designing connector sockets that gold-plated contacts provide the most reliable electrical interfaces. However, to reduce costs, gold is typically used sparingly by selectively plating the surfaces of the contacts. Large PCB circuits, such as motherboards, are inherently expensive requiring multiple process steps during manufacture and risk costly yield losses with each additional process step. Therefore, adding even selectively plated gold directly to the contact pads or vias of a motherboard may be prohibitively expensive. Nevertheless, compression contacts, as described in these embodiments, would perform best when mated with gold-plated surfaces. To adapt the surface of an expensive motherboard for compatibility with the compression style contacts described herein, a gold-plated interposer board  42  is shown in cross-section in  FIG. 12D . This board consists of a thin PCB, flex circuit, or molded-plastic carrier with an array of plated through hole (PTH) vias  18  to match the footprint of pads or PTH vias on the motherboard  20  (e.g.  FIG. 12A ). The PTH vias  18  on the interposer electrically connect pads or via annular rings  19  from the bottom to the top surface of this carrier. The top pads or annular rings would be selectively gold-plated and would mate with the conductive spheres or bumps  17  of  FIG. 12C . The bottom pads or annular rings  19  would be solder coated and/or include solder balls  43  suitable for surface mount soldering to the same pattern of pads or PTH vias disposed on the motherboard. In this manner, motherboard contacts that are typically coated with a non-noble metal such as SnPb are converted to a gold-plated contact compatible with compression style connectors. These carriers can be mass-produced in large panel format and then cut or stamped to final size or, if manufactured from flexible circuits, could be produced in a reel-to-reel or roll-to-roll format and could be an inexpensive solution for providing an array of gold-plated contact pads or vias on the motherboard. The interposer  42 , as described herein, may also be used for mating other types of components that require gold-plated contacts for reliable connection to the motherboard (e.g. LCD displays, ribbon-connectors, etc.). 
         [0109]    Turning now to  FIG. 12E , a different example of a compression style connector is illustrated, which retains some features currently found on standard DIMM type sockets but makes a fundamental change in the location of the contacts and direction of the forces applied when inserting or removing the modules from the socket. 
         [0110]    Current DIMM sockets are designed to mate with contact pads arrayed along the bottom edges on both sides of the memory module&#39;s PCB substrate. DIMM socket pins apply a lateral normal force against these pads with approximately 6-8 grams per pin and are designed to rub both surfaces of the module&#39;s pads as the modules are inserted into the socket. This ensures that any surface contaminants or oxides present on the pads are abraded and the pins make good electrical contact with the pads. However, as noted earlier, the number of contact pads has increased in recent years to the point that the total amount of force required to insert or extract the modules from these standard sockets is causing frequent handling damage. The electronic industry currently forecasts a need to further increase the number of available contact pads for future memory modules assembled using newer generation DRAM components (e.g. DDR4, DDR5, etc.) to improve the signal-to-noise ratio on controlled-impedance PCB substrates by providing more power and ground connections. Many blade server computer OEMs also use very restricted enclosures and are straining to reduce the height of the socket-mounted modules while simultaneously increasing the total memory available on each module. As described below, the design shown in  FIG. 12E  is a major step in resolving these problems. 
         [0111]    The electronic subsystem  1  shown in  FIG. 12E  is similar to  FIG. 12A , except that it is integrated with a convex bowed collar  38 ″, as previously described, and includes an alignment post  58  near the center of its length. This post mates with an orientation hole  59  molded into the compression latch assembly  41 ′ and helps to align electrode pads  12 , disposed on the bifurcations  13 , with a variety of contact pins or springs, represented in  FIGS. 12F-P , that are press-fitted into molded slots within the base of the plastic-molded frame of assembly  41 ′. Socket assembly  41 ′ also includes two latches  51  that are designed to rotate about a pivot point and engage with the ends of the convex bowed collar  38 ″ to clamp and hold the integrated collar in a state of compression against stamped metal socket contacts  60 ,  61  or  62 , that are press-fitted into the plastic-molded frame or housing of the socket. 
         [0112]    Representative examples of the types of pins or spring contacts that can be incorporated within socket assembly  41 ′ are illustrated in  FIGS. 12F-P .  FIG. 12F  shows pin  60  terminated at its upper tip in a short rounded point. The same pin is shown in a side-view at  60 ′ and  60 ″. These two side-views are identical for this particular pin design, since there is no need to produce two versions of the upper contact for 180 degrees rotation as illustrated and described below for  FIGS. 12J and 12M . From the side-view  60 ′ (and  60 ″) it can be seen that there is an offset bend of the stamped-metal socket contact near the mid-point of its length. This offset bend is shaped such that when pin  60 ′ is placed in vertical alignment with adjacent pins  60 ″, which are rotated 180° in orientation as shown in  FIGS. 12G-H , the lower portion of the leads alternate in a staggered pattern when viewed from either the top or bottom (not shown) and are spaced apart by 1.90 mm.  FIG. 12G  is a cross-section view taken at location A-A′ of four staggered socket leads press-fitted into the plastic-molded frame or housing of socket  41 ′. The lower portion of the leads is staggered into four rows by rotating pin  60 ″ 180° and placing it immediately adjacent to pin  60 ′. The upper tips of adjacent contacts  60 ′ and  60 ″ then form two rows that are aligned along the length of the socket, as shown in  FIG. 12H .  FIG. 12H  is a view looking down onto a small section of the molded frame of socket  41 ′ showing that each individual contact tip extends into and is surrounded by a molded slot  40  which provides some freedom of deflection of the upper section on the contacts. As illustrated at  60  in  FIG. 12F , each individual pin includes a wide “anchoring” section near the mid-point of its length that is formed during the metal stamping process and which serves to lock the pin in position when press-fitted into a molded slot at the base of the plastic frame  41 ′. One embodiment of socket assembly  41 ′ would include a frame with 240 contact pins in four rows that are spaced apart the distances shown in  FIG. 12G  for compatible assembly onto motherboards with PTH vias  18  patterned to receive standard 240-pin DIMM sockets. 
         [0113]    Turning now to  FIG. 12J , contact pin  61  is shown, which appears similar to pin  60  in this view, but when rotated 90 degrees reveals a “J” shaped termination  61 ′ that is bent in the (normal) direction of its bottom lead. Pin  61 ″, though similar to pin  61 ′, has a reverse “J” bend that extends in the opposite direction, away from its bottom lead. FIG.  12 K is similar to  FIG. 12G  and is a cross-section view taken at location A-A′ of four staggered “J” bend leads press-fitted into the plastic-molded frame or housing of socket  41 ′. The lower portion of the leads is staggered into four rows by rotating pin  61 ″ 180° and placing it immediately adjacent to pin  61 ′. The upper rounded tips of adjacent contacts  61 ′ and  61 ″ then form two upper rows that are aligned along the length of the socket, as shown in  FIG. 12L .  FIG. 12L  is a view looking down onto a small section of the molded frame of socket  41 ′ showing that each individual contact tip extends into and is surrounded by a molded slot  40  which provides some freedom of deflection of the upper section on the contacts. Pins  61 ′ and  61 ″ are formed differently during the metal stamping process to enable the “J” bends to face in the same direction (i.e. towards the centerline of frame  41 ′) along both upper rows, as shown in  FIG. 12K . Depending on the cross-sectional dimensions, leaning angle for the upper-section, and type of metal from which the pins are stamped, the “J” bend contact pins  61 ′ and  61 ″ can be engineered to deflect when mating with electrode pads  12  to provide a wiping action against the pads as described earlier. 
         [0114]    Turning now to  FIG. 12M , spring contact pin  62  is shown, which when rotated 90° reveals a “folded” termination  62 ′ that is bent in the (normal) direction of its bottom lead. Pin  62 ″, though similar to pin  62 ′, has a reverse bend that extends in the opposite direction, away from its bottom lead.  FIG. 12N  is similar to  FIG. 12K  and is a cross-section view taken at location A-A′ of four staggered “folded” leads press-fitted into the plastic-molded frame or housing of socket  41 ′. The lower portion of the leads is staggered into four rows by rotating pin  62 ″ 180° and placing it immediately adjacent to pin  62 ′. The upper rounded tips of adjacent contacts  62 ′ and  62 ″ then form two upper rows that are aligned along the length of the socket, as shown in  FIG. 12P .  FIG. 12P  is a view looking down onto a small section of the molded frame of socket  41 ′ showing that each individual contact tip extends into and is surrounded by a molded slot  40  which provides some freedom of deflection of the upper section on the contacts. Pins  62 ′ and  62 ″ are likewise formed differently during the metal stamping process to enable the folded bends to face in the same direction (i.e. towards the centerline of frame  41 ′) along both upper rows, as shown in  FIG. 12N . Depending on the cross-sectional dimensions, folded angles for the upper-section, and type of metal from which the pins are stamped, the folded contact pins  62 ′ and  62 ″ can be engineered to deflect when mating with electrode pads  12  to provide a wiping action against the pads as described earlier. 
         [0115]    A preferred embodiment for each of the stamped-metal contacts  60 ,  61  and  62  described above would include selective gold plating over the upper contact surfaces. The compression latch assembly or socket  41 ′, as shown in  FIG. 12E , includes long leads intended to be inserted through PTH vias  18  formed on the motherboard and soldered to the bottom annular rings  19  of these vias. However, the leads may also be formed with right-angle bends to enable SMT soldering to staggered pads on the top surface of the motherboard. Assembly  41 ′, as shown in  FIG. 12E , also includes two anchor posts or threaded screws  65  to aid in securing the socket to the surface of the motherboard during soldering and when clamping the integrated collar  38 ″ into place. One preferred method for inserting subassembly  1  into socket  41 ′ would be (a) engage a first end of the integrated collar  38 ″ with a first latch  51  of the socket  41 ′, and (b) apply a downward, cantilever-force on the opposite second end of collar  38 ″ sufficient to engage the second latch of socket  41 ′ to clamp and hold the integrated collar in compression against the socket contacts. 
         [0116]    A cross-section of yet another example of the present invention is shown in  FIG. 13 . Whereas  FIGS. 11 and 12  illustrate a bottom clamping collar  38 ,  38 ′ or  38 ″ that does not enclose electronic subsystem  1  or  2 , this example integrates two metal heat spreaders with angled-flanges  34  that fully enclose electronic components  11  and passive chips  37  to provide a protected electronic subsystem  3 . The advantages for this design include; (a) a rigid enclosure for protecting fragile bare (unpackaged) silicon devices mounted onto flexible substrate  10 , (b) an adjacent heat spreading surface for the efficient removal of heat generated by the contained components  11 , (c) electrostatic and electromagnetic shielding of the contained components  11 , (d) a means for enabling a compressive force to be applied to contacts arrayed on the bottom surface, and (e) a means for supporting the module in direct electrical communication with contacts disposed on the motherboard. 
         [0117]    The angled-flange metal heat spreaders  34  comprise two thin, stamped-metal housings that are near mirror images of one another. The bottom surfaces of both heat spreaders are adhesively bonded respectively to one of the two bifurcations  13  and are spaced apart from one another by the thickness of flexible circuit  10 . Both legs are separated and spread apart from one another to form an angle of approximately 180°, but they remain joined together where the bonding adhesive or film  9  terminates, as previously shown in  FIGS. 1 ,  6 , and  11 A-B, which in this case is near the gap between the bottom flanges of the two heat spreaders shown in  FIG. 13 . The resulting structure allows the two metal heat spreaders to open and close in a clamshell fashion around the bifurcated flex circuit assembly by a means of a hinge consisting of flexible extensions  13  and bonding adhesive or film  9 . 
         [0118]    The angled flanges  34  formed at the bottom of the paired heat spreaders angle outward from the narrower sidewalls and then close back together at the base to (a) provide a surface against which a downward compression force can be applied by a mating clamping device, (b) provide a flat or slightly angled mounting surface for the flexible bifurcated extensions, with sufficient width to enable contact with a standard pattern of staggered PTH vias  18  or pads  19  on the motherboard intended for mounting DIMM sockets, (c) provide a means for transferring a compression force to an array of conductive bumps  17  or electrode pads  12  (not shown) located on the exposed surface of the bifurcated extensions  13 , (d) form a rigid, expanded cavity for mounting components onto the flexible substrate  10  which require greater stand-off height, and/or (e) enable the components  11  and/or passive chips  37  on flexible circuit  10  to be mounted in very close proximity to the surface of the motherboard. 
         [0119]    Examples of devices that mate with electronic subsystem  3 , for applying a downward compressive force, are disclosed below in  FIGS. 15A-B  and  16 A-C. In these examples, angled wedges contact the outward angled-flanges  34  of the heat spreaders and apply a clamping force against the flanges, which in turn compress conductive bumps  17  directly against the contact pads, vias or pins on the motherboard. The bottom surfaces of the flanges may be flat or angled slightly downward, near the beginning of the bifurcated extensions, to help compensate for lower compressive forces resulting from any flexing of the inner edges of the flanges near the bifurcated extensions  13 . The downward angled surfaces of the thin metal heat spreaders  34  also provide a means for establishing compliancy between the conductive spheres or bumps  17 , arrayed on the bottom of the folded bifurcated leads, and the contact pads  21  or annular rings  19  surrounding the Plated Thru Via Holes  18  of the motherboard. In addition, the adhesive chosen to bond the flexible leads to the bottom flanges of the heat spreaders can be selected to provide a measure of compliancy. 
         [0120]    The paired metal heat spreaders  34  of electronic subsystem  3  are held together in a closed position surrounding the bifurcated flex circuit assembly by two means; (a) an adhesive-backed Thermal Interface Material (TIM)  36 , and (b) interlocking clasps  67  located along the top edge of the heat spreaders (ref.  FIG. 13 ). The adhesive-backed TIM  36  is applied to the interior surface of the metal heat spreaders  34  in a thickness sufficient to contact and adhere to the backside surfaces of heat generating components  11  when the metal heat spreaders are folded together. A suitable TIM would be 3M™ Thermally Conductive Tape 8805, which is supplied with a contact adhesive on both sides of the tape for bonding components together. After cutting two pieces of tape to proper size, a first release liner is removed, exposing a first adhesive surface, and the tape is applied and pressed against the inside surface of both heat spreaders. When the subassembly is ready to be sealed, the second release liner is removed from both pieces of tape adhering to the inside surfaces of the heat spreaders, exposing the second adhesive surface, and the metal heat spreaders are folded and pressed together to adhere the second adhesive surfaces to the backside of the heat generating components  11 . When folded and pressed together, the thermally conductive interface material  36  bridges and joins the inside surfaces of the metal heat spreaders and backside surfaces of the heat generating components on both sides of the bifurcated flexible circuit  10  to form a unified assembly that can be opened, if necessary, for rework, but which otherwise adheres together tenaciously. Additional means for securing the subassembly together is provided by a series of interlocking clasps  67  spaced along the top edges of the heat spreaders. As shown in  FIG. 13 , the upper edges of the heat spreaders overlap one another and are formed with interlocking indentations that snap closed when the heat spreaders are folded together. Other embodiments of interlocking clasps (not shown) would include punched-metal, interdigitated “fingers” that alternate in height above and below a nominal midpoint along the top edge of the heat spreaders and which overlap and lock together when closed. 
         [0121]    In another preferred embodiment of  FIG. 13 , components  11  comprise memory devices positioned on both sides of the bifurcated flexible circuit  10 , and immediately above the bottom flange of both heat spreaders, to enable the detached module-height and overall system-height of subsystem  3 , when mated with motherboard  20 , to be reduced to a practical minimum. 
         [0122]      FIG. 14  is similar to the embodiment shown in  FIG. 13 , with exception that the flanges at the bottom of the stamped metal heat spreaders extend inward before flaring outward as two diverging-flanges  35 . The diverging-flanges provide access for applying a downward compressive force from directly above the conductive bumps  17 . 
         [0123]      FIG. 15A  is a cross-section view of the subassembly  3 , similar to  FIG. 13 , which is directly mated under compression to the DIMM socket PTH vias  18  of motherboard  20 . Two metal wedges  49  extend along both sides of the length of subassembly  3  and include compression pads  44  that contact the angled-flanges  34  and surface of the motherboard. The metal wedges may be constructed as separate pieces or from a single slotted collar that fits over the top of the subassembly  3 . A downward compressive force is exerted against the angled-flanges when multiple screws  23  are tightened into a metal stiffener plate  45 , similar to that as previously described that extends the length of subassembly  3  from the underside of the motherboard. Conductive bumps  17  align with and partially extend into the PTH vias  18  to make electrical contact with the inside perimeter of the annular rings  19 . 
         [0124]      FIG. 15B  is a cross-section view of another embodiment of a subassembly  3 ′, clamped in compression against motherboard  20  as previously described for  FIG. 15A , but which includes a folded extension  10 ′ of the bifurcated flexible circuit  10  with additional rows of components  11  mounted inside non-flanged metal heat spreaders  34 ′. This folded extension does not require any flanges on the heat spreaders and enables additional rows of components to be connected into circuit with the motherboard through the conductive bumps  17  of one pair of bifurcated extensions  13  held in compression through a single pair of metal wedges  49 . By folding the flex circuit extension  10 ′ over to one side, and inserting its end into a plastic or metal retention clip  74 , which is attached to a portion of the metal wedge  49 , the total height of the vertically mounted subassembly  3 ′ is held to a minimum. 
         [0125]    Yet another embodiment for a low-profile subassembly  4  is shown in  FIG. 15C . In this embodiment, subassembly  4  is clamped parallel to motherboard  20  and the bifurcated flex circuit  10  includes a first right-angle fold  68  towards the bottom edge of a non-flanged heat spreader  34 ′ and a second right-angle fold  69  of a first-portion of the bifurcated extensions  13  that is positioned between a lower portion of the heat spreader and PTH annular rings  19  of the motherboard. The other second-portion of the bifurcated extension includes a third right-angle fold  70  in the opposite direction from that of the first-portion. This second-portion of the bifurcated extension is positioned between a compression pad  44  of clamping device  22  and the PTH annular rings  19  of the motherboard  20 . In this embodiment, the clamping device  22  simultaneously applies a downward compressive force through compression pads  44  along (a) an upper-portion of the non-flanged metal heat spreader  34 ″, and (b) the second-portion of the bifurcated extension  13 . Screws  23  or other hardware devices can be fastened or threaded into a bottom metal stiffener plate  45  or tightened against the plate with a lock nut  24 . Since the second-portion of the bifurcated extension is positioned at a different height above the surface of the motherboard, a thicker layer of compression pad  44  or different compliant material  25  may be needed in areas of clamping device  22  that make direct contact with the motherboard. 
         [0126]      FIG. 15D  is similar to  FIG. 15B , and illustrates how the low-profile subassembly  4  of  FIG. 15  C can include a folded low-profile subassembly  4 ′ positioned above it. In this embodiment, folded low-profile subassembly  4 ′ is electrically connected to the bottom low-profile subassembly  4  by means of a folded extension  10 ′ of the bifurcated flexible circuit  10 . Subassembly  4 ′ is sufficiently spaced above subassembly  4  to enable adequate air flow between the adjacent subassemblies for efficient component cooling and is held in position with a plastic or metal retention clip  74 ′, similar to that shown in  FIG. 15B , that is attached to clamping device  22 . 
         [0127]    Turning now to  FIG. 15E , two low-profile subassemblies  4  are positioned above and below the surface of the motherboard  20 . The upper subassembly is clamped to the motherboard similar to  FIG. 15C  described above, but the lower subassembly is connected to the motherboard through a signal translation interposer board  56 . This board reroutes the signal functions coming from the bottom-side of the motherboard so that are correctly aligned with the electrode pads on the bifurcated extensions  13  of this lower subassembly. If the bifurcated flexible circuits  10  of the upper and lower subassemblies were exact mirror images of each other, the signal translation interposer board would not be required. However, using mirror imaged circuits may be a more expensive solution than using a simple signal translation interposed board. The signal translation interposer board  56  is preferably pre-attached to the bottom-side of the motherboard  20 . However, it may also be pre-attached to the bifurcated flex circuit  10  and held into compression against the PTH annular rings  19  of the motherboard. 
         [0128]    The additional stand-off height caused by the presence of the signal translation interposer board  56  may enable various electronic components  11  to be soldered to the bottom surface of the motherboard  20  that are thicker than otherwise allowed beneath the upper subassembly, as shown in  FIG. 15D . The clamping devices  22  may also use common hardware fasteners  23  for drawing the clamps together to provide the required compression forces against the upper and lower bifurcated extensions  13  of subassemblies  4 . 
         [0129]    A Direct Connect Socket  5 , for easy installment and removal of the protected electronic subassembly  3  (refer to  FIG. 13 ), is illustrated in  FIGS. 16  A-C. To avoid the manufacturing difficulties associated with assembling devices to motherboards using multiple clamps, screws and nuts, a simpler connector concept is shown here that uses a pivoting compression clamp  48  and compression latch assembly  41 ″ to simultaneously apply a downward compression force to both angled-flanges of the metal heat spreaders  34 .  FIG. 16A  is a top view, looking down onto the direct connect socket, while  FIG. 16B  is a side view of the same socket. The pivoting compression clamp is attached to the compression latch assembly with a pivot pin  46  that enables the clamp to rotate in a 180° arc in the direction of the arrow. The clamp is preferably made of a metal or rigid molded plastic as previously described for the clamping collar  38  of  FIG. 11A . However, in this example the compression clamp  48  includes two angled compression pads  44  that are shaped to conform to the surfaces of the angled-flanges on the heat spreaders. The cross-section A-A′, as shown in  FIG. 16C , shows the angled compression pads  44  bonded to the metal or plastic pivoting clamp  48 . 
         [0130]    For this embodiment, the compression latch assembly  41 ″ is fashioned from molded LCP plastic and includes an array of straight, stamped-metal, contact pins  60 ′ and  60 ″, as previously described for  FIGS. 12E-H , that are press-fitted into the base of the latch assembly. In  FIG. 16B , these pins are shown inserted through PTH vias placed on the motherboard  20  and soldered from the bottom side to the motherboard similar to a standard DIMM socket. A metal stiffener plate  45  may or may not be required, depending on the amount of compression force required for proper operation of the socket and the degree of flexing of the motherboard. It should be noted that the metal stiffener would either provide clearance slots or an insulating surface to prevent electrical shorting of the exposed pins exiting from the bottom of the motherboard. In this embodiment, two screws  23  extend up through the metal stiffener  45  and screw into a threaded hole or insert within the compression latch. 
         [0131]    To operate the Direct Connect Socket  5 , shown in  FIGS. 16A-C , subassembly  3  is first inserted into the base of the compression latch assembly  41 ″ and seated in alignment with the pins  60 ′ and  60 ″ arrayed across the bottom. The pivoting compression clamp  48  is then rotated over and down onto the angled-flanges  34 ′ of the metal heat spreaders. The open slot  47 , as shown in  FIGS. 16A and 16C , allows the upper sections of the heat spreaders  34  to pass between the two angled compression pads  44  and through the compression clamp  48  so that a collar, similar to  38 ′ of  FIG. 11C , extends around the bottom periphery of subassembly  3 . A downward compression force is then applied against the angled-flanges  34 ′ by pressing against the free-end of the compression clamp  48  until the latch  51  can be engaged to hold the clamp in place. 
         [0132]    In another embodiment, Direct Connect Socket  5 ′ (not shown) includes other press-fitted pins or contacts, such as “J-bend” contacts  61 ′ and  61 ″ or spring contacts  62 ′ and  62 ″ previously shown and described for  FIGS. 12J-P . In yet another embodiment, Direct Connect Socket  5 ″ (not shown) does not include any integrated, press-fitted, pins or contacts within the compression latch assembly  41 ″, but allows the electrode pads  12  or conductive spheres or bumps  17  arrayed on the bifurcated extensions  13  to directly contact the motherboard PTH vias  18  and/or annular rings  19  as previously shown and described (e.g.  FIGS. 6-7 ). In yet another embodiment, Direct Connect Socket  5 ′″ (not shown) allows the electrode pads  12  to directly contact an array of protruding pins  27  from separate “bed-of-nails” connector  26  soldered to the bottom of the motherboard as previously described in  FIG. 8A-B . 
         [0133]    Another Direct Connect Socket  6 , intended to mate with electronic subassembly  3 ′ (refer to  FIG. 14 ), is illustrated in  FIGS. 17  A-C. This embodiment includes many features similar to that described and shown in  FIGS. 16A-C . However, this socket uses a bifurcated compression clamp  52  that is slightly bowed near its center point and which includes an open-ended slot  47 ′ that is not closed at the end. The open-ended slot  47 ′ engages with the diverging-flanges  35  of subassembly  3 ′ by allowing the flanges to slide into the slot from the open-end after the bifurcated compression clamp  52  is rotated towards the top of its travel. The open-ended slot  47 ′, as shown in  FIGS. 17A  and C, allows the bifurcated clamp  52  to surround both sides of subassembly  3 ′ while sliding along the length of the divergent-flanges  35 . When fully engaged, the bifurcated clamp  52  appears similar to the collar  38  shown in FIGS.  11 A and  12 A-B, and extends almost completely around the bottom periphery of subassembly  3 ′. 
         [0134]    As the bifurcated compression clamp is lowered towards the compression latch assembly  41 ″, subassembly  3 ′ is seated within a molded cavity and is brought into alignment with protruding pins  27  of a “bed-of-nails” connector  26  arrayed across the bottom. The pivoting compression clamp  52  is then rotated down against the diverging-flanges  35  of both metal heat spreaders, applying a downward compression force as latch  51  is engaged to retain the clamp in compression. As noted earlier, the bottom of the bifurcated clamp may or may not include a layer of compliant material  25 . 
         [0135]    In the illustration shown in  FIG. 17B , the “bed-of-nails” connector  26  is preassembled onto the top surface of the motherboard  20  with the tails of the protruding pins  27  extending down through the PTH vias  18  and soldered from the bottom of the motherboard. As noted earlier for  FIG. 8A , the “bed-of-nails” connector may also be preassembled on the bottom surface of the motherboard with the protruding pins  27  extending up through the PTH vias. Various pins may also be press-fitted into the base of the latch assembly  41 ″ as previously described for  FIG. 16 . The bifurcated compression clamp  52 , viewed in this figure, is also slightly bowed near its center point in order to function as previously described for the bowed collar  38 ″ in  FIG. 12E . 
         [0136]    Turning now to  FIGS. 18A-B , a small section of interposer board  42  is shown in cross-section together with a new clamping collar  71  that includes a concave-dimpled surface. As previously described for  FIG. 12D , interposer board  42  is fashioned from a thin PCB, flexible circuit, or molded-plastic carrier. However, instead of containing an array of plated through hole (PTH) vias  18 , this embodiment includes bladed contacts  63 , fashioned from stamped metal with selectively gold-plated tips  72 , which are pressed fitted into a thin PCB or plastic molded interposer to match the footprint of pads or PTH vias on the motherboard  20 . The bladed contacts are pointed on the bottom-side of the interposer to aid in their alignment with the PTH vias of the motherboard and in penetrating the edges of the PTH annular rings  19  when collar  71  applies a downward compression force from above. The gold-plated tips  72  of contacts  63  are aligned with the concave dimples on the bottom surface of collar  71  and are rounded at their tips with a radius smaller than the radius of the concave dimples. When the thin electrode pads  12 , arrayed on the flexible bifurcated extensions  13 , are aligned and compressed between the tips of contacts  63  and concave dimples of collar  71 , the thin pads  12  are partially deformed into the concave dimples and create a “ball and socket” like connection, as shown in the close-up cross-section of  FIG. 18B . Electrode pads  12  are typically fashioned from thin copper films (≦40 μm thick and finished with a thin nickel-gold coating to resist tarnishing) bonded to thin polyimide films (≦50 μm thick) which can be easily deformed. This type of compression connection is intended to improve electrical reliability of the interposer contacts when (a) they are subject to temperature cycling during operation, or (b) the PTH annular rings  19  of motherboard  20  are solder-coated. 
         [0137]    Alternative materials that can be substituted for interposer board  42  include polyimide, Mylar, PVC, and PEC films, etc. Alternative compression-type contacts  63  that can be integrated with interposer  42  include gold-fuzz buttons (bumps), isotropic conductive epoxy bumps, copper-plated bumps, etc. (not shown), that are disposed directly above and below one another on both sides of the film, similar to that shown in  FIG. 18 , and are interconnected through small plated or non-plated vias within the film, as shown in  FIG. 12D . 
         [0138]      FIGS. 18A-B  indicate that the concave dimples are arrayed on the bottom surface of clamping collar  71 , which is similar to  38  shown in  FIGS. 11A  and B. However, it should be noted, the concave dimples can also be integrated into the compliant material  25  bonded to the bottom surface of collar  38 , or fashioned into the bottom surfaces of metal heat spreaders formed with either angled-flanges  34  or divergent-flanges  35  ( FIGS. 13 and 14 ). 
         [0139]    Turning now to  FIGS. 18C-D , a small section of a convex-dimpled clamping collar  73  is shown in cross-section together with thin electrode pads  12 , arrayed on a flexible bifurcated extension  13  and aligned above PTH vias  18  and annular rings  19  of motherboard  20 . As previously shown and described for  FIGS. 9 and 10B  and shown again in the close-up cross-section of  FIG. 18D , convex dimples will deform the thin bifurcated extension film  13  and bottom electrode pad  12  when a downward compressive force is applied through the clamping collar  73 , forcing the electrode pad into electrical contact with the annular ring  19  of the motherboard  20 . However, it is preferred with this embodiment and previously discussed, that the annular rings on the motherboard include a gold plated finish for this compression contact to form a reliable connection. In addition, it is desirable that convex dimple radius be smaller than the radius of the PTH via  18  in order for the electrode pad to be partially pressed into the via hole, as shown in  FIG. 18D . It should also be noted, these convex dimples can also be integrated into the compliant material  25  bonded to the bottom surface of collar  38 , or fashioned into the bottom surfaces of metal heat spreaders formed with either angled-flanges  34  or divergent-flanges  35  ( FIGS. 13-14 ). 
         [0140]    As previously described for  FIG. 2 , the electronic subsystem  1  can be electrically and mechanically connected to contacts  21  on the motherboard  20  by various means to electrode pads  12  on the flexible bifurcated extensions  13 . In  FIG. 15E , it was also demonstrated that two subassemblies  4 ′ could be mounted on both top and bottom surfaces of a motherboard  20  and share the same PTH via contacts  19  by means of a signal translation interposer board  56 . Turning now to  FIG. 19 , a similar embodiment is shown wherein two subsystems  1  are electrically and mechanically connected to contacts  21  from both sides of motherboard  20  by means of another contact translation circuit  66 . 
         [0141]    Another novel configuration for mounting the electronic subsystem  1  is illustrated in  FIG. 20 . In this example the bifurcated flexible leads are opened sufficient to straddle the edge of a PCB or motherboard  20  which includes contacts  21  arrayed along its edge. The inner electrode pads  12  of the flexible leads are aligned to these contacts and compressed together to mechanically and electrically connect the electronic subsystem in the plane of the motherboard. In the example shown, a sliding compression clamp or connector  75  can be moved from position A to A′ to lock the aligned bifurcated leads against the motherboard contacts and apply a pinching force that establishes electrical connections between the inner electrode pads and PCB contacts. It will be appreciated that once the two halves of the bifurcated flexible leads are aligned, any clamping device may suffice to enable electrical/mechanical mating of the module to the motherboard. 
       INDEX OF REFERENCE NUMERALS USED IN THE DRAWING FIGURES 
       [0000]    
       
           1  Electronic Subsystem (with bifurcated flexible circuit board or substrate) 
           1 ′ Flexed Electronic Subsystem (˜45° clockwise) 
           1 ″ Flexed Electronic Subsystem (˜90° counter-clockwise) 
           2  Electronic Subsystem (with rigid circuit board or substrate) 
           3  Protected Electronic Subsystem (with angled-flanges) 
           3 ′ Protected Electronic Subsystem (with divergent-flanges) 
           3 ″ Protected Electronic Subsystem (with angled-flanges and folded extension) 
           4  Low-Profile Protected Electronic Subsystem 
           5  Direct Connect Socket—Angled Flanges 
           6  Direct Connect Socket—Divergent Flanges 
           9  Bonding adhesive or film 
           10  Bifurcated flexible circuit 
           10 ′ Folded extension 
           11  Various electronic components 
           12  Inner electrode pads 
           12 ′ Outer electrode pads 
           13  Bifurcated extension or leg 
           14  Compliant region 
           15  Rigid printed circuit board (PCB) daughter card or substrate 
           16  Flexible circuit leads 
           17  Conductive spheres or bumps 
           18  Plated Through Hole (PTH) via 
           19  PTH annular ring 
           20  Printed Circuit Board (PCB) or motherboard 
           21  PCB or motherboard contacts 
           22  Clamping device 
           22 ′ Clamping device (with integrated flex circuit connector) 
           22 ″ Clamping device (with integrated compression posts) 
           23  Screw or fastener 
           24  Lock nut 
           25  Compliant material 
           26  “Bed-of-nails” connector 
           27  Protruding pins 
           28  Solder fillet 
           29  Compression post 
           30  Housing 
           30 ′ Enclosure (full-height) 
           30 ″ Enclosure (reduced-height) 
           31  Formed electrode pad 
           32  Pierced electrode pad 
           33  Slotted portion of the electrode pad 
           34  Angled-flange metal heat spreader 
           34 ′ Non-flanged metal heat spreader 
           35  Diverging-flange metal heat spreader 
           36  Thermal Interface Material (TIM) 
           37  Passive chip components 
           38  Clamping collar 
           38 ′ Collar with tapered slot 
           38 ″ Convex bowed collar 
           39  Spring latch or retention clip 
           40  Molded slot 
           40 ′ Angled slots 
           41  Compression latch assembly 
           41 ′ Compression latch assembly (with stamped metal leads) 
           41 ″ Compression latch assembly (with pivoting compression clamp) 
           42  Interposer 
           43  Solder ball 
           44  Compression pad(s) 
           45  Metal stiffener plate 
           46  Pivot pin 
           47  Open slot 
           47 ′ Open-ended slot 
           48  Pivoting compression clamp 
           49  Metal wedge 
           50  Flex circuit connector 
           51  Latch 
           52  Bifurcated compression clamp 
           53  Socket contact 
           54  Socket housing 
           55  Zebra-strip connector 
           56  Signal translation interposer board 
           57  Alignment hole 
           58  Alignment post 
           59  Orientation holes 
           60  Stamped metal socket contact—straight 
           60 ′ Stamped metal socket contact—straight side-view with normal bend 
           60 ″ Stamped metal socket contact—straight side-view with reverse bend 
           61  Stamped metal socket contact—J-bend 
           61 ′ Stamped metal socket contact—J-bend side-view with normal bend 
           61 ″ Stamped metal socket contact—J-bend side-view with reverse bend 
           62  Stamped metal socket contact—spring 
           62 ′ Stamped metal socket contact—spring side-view with normal bend 
           62 ″ Stamped metal socket contact—spring side-view with reverse bend 
           63  Interposer contacts 
           64  Bifurcated lead—partially reflexed 
           64 ′ Bifurcated lead—fully reflexed 
           65  Anchor post or screw 
           66  Contacts translation circuit 
           67  Interlocking clasp 
           68  First fold 
           69  Second fold 
           70  Third fold 
           71  Concave-dimpled clamping collar 
           72  Gold-plated tip 
           73  Convex-dimpled clamping collar 
           74  Plastic or metal retention clip 
           75  Sliding compression clamp 
           76  Metal contact pin