WO2002031924A1

WO2002031924A1 - Compliant stacking connector

Info

Publication number: WO2002031924A1
Application number: PCT/US2001/032123
Authority: WO
Inventors: John Benham
Original assignee: Flexconn, Inc.
Priority date: 2000-10-12
Filing date: 2001-10-12
Publication date: 2002-04-18

Abstract

An electronic stacking connector and associated assembly comprises an insulating connector body (15) having top and bottom surfaces, each provided with an elongated channel (5) and a compliant force distribution member CFDM (4) is loacted, which projects from the respective surfaces. A flexible printed circuit FPC is wrapped around and affixed to the connector body and has contacts which overlie the top and bottom sides of CFDM. Two printed circuit boards PCBs (11, 12) are situated above and below the connector body and contacts (13, 16)) of the PCBs are connected to the contacts on FPC. Stiffener bars (9) are provided on the top and bottom of the PCBs.

Description

COMPLIANT STACKING CONNECTOR

Background of the Invention

The present invention relates to connectors for electronic circuits, in particular to connections between printed circuit boards and the like.

As electronic systems evolve in support of smaller, faster electronic devices, refinement of the interconnectivity of these devices presents an increasing challenge. Electrical characteristics, as well as the conflicting needs for increased contact density and miniaturization, are exceeding the capabilities of conventional connector technology.

Mechanical limitations have reached the threshold where discrete metal contact springs can no longer function reliably. The relative size, density, signal integrity and installed cost of a connector system are all of major importance. It is becoming clear that the effective and efficient delivery of force to the mating contacts is critical in achieving the inherent benefits of a flex circuit-based connector system.

Previous efforts have been made to address these problems, as exemplified by U.S. Patent No. 4,968,265, "Fluidly Actuated Electrical Connector"; International Application PCT/US97/1 1 1 01 , published as WO98/OO884, entitled "Button and Dovetail Connector Actuation

Mechanism"; and U .S. Patent No.5, 704, 793, " High Speed, High Density Connector for Electronic Signals" . Although these publications describe connectors which rely on the benefits of a highly compl iant member, such as a bladder or the like, which when energized provides hydrostatic-type uniformity in the normal force applied by each contact in mating relationship with another contact, the fundamental advantage of using such compl iant member cannot always be realized In practice. Summary of the Invention

The present invention relates primarily to a flexible printed circuit (FPC) electrical connector in a stacking configuration with the effective and efficient distribution of normal force being achieved via a compliant force distribution member (CFDM). The CFDM is energized by opposing stiffeners actuated by screws or the like at opposite ends of an insulative connector body. Compliant force or pressure against a very large number of connector contacts can be achieved on an FPC substrate, for the specified design life of the connector system. In a general, but not limited aspect of the invention, an electronic stacking connector assembly comprises an elongated insulating connector body having top and bottom surfaces, each surface having an elongated channel in which is located an elongated, compliant force distribution member which projects from the respective surface. The FPC is wrapped around and affixed to the connector body, and has top side contacts which overlie the top side of the CFDM and bottom side contacts which overlie the bottom side CFDM. A top printed circuit board (PCB) is situated over the top surface of the connector body and a bottom PCB is situated beneath the bottom surface of the connector body, whereby conducting contacts on the top PCB mate with the top side conductor contacts on the FPC and the conductor contacts on the bottom PCB mate with the bottom side conductor contacts on the FPC. Stand-off posts project from the top and bottom surfaces of the connector at each end thereof, a distance which is less than the distance by which the CFDM 's project from the top and bottom surfaces of the connector body. An elongated top stiffener bar spans the top PCB over the connector body and an elongated bottom stiffener bar spans the bottom PCB beneath the connector body. Means are provided for drawing the top stiffener and bottom stiffener toward each other to urge the PCB's toward each other until the PCB's bear upon the respective stand-off posts and thereby load the CFDM's, whereby the top side contacts are compliantly pressed against each other and the bottom side contacts are compliantly pressed against each other with a normal force transmitted from the respective PCB's, through the FPC's, to the CFDM's.

The foregoing configuration almost completely rigidly contains the CFDM, thereby achieving the near-hydrostatic property of the CFDM. This provides a very efficient technique to achieve the virtually infinite compliance along the array of opposing electrical circuit contacts.

Compliant materials include solid, elastomeric material such as silicone polymer materials or polyurethane, and fluid filled elastomers, which as a practical matter, retain their initial volume even under compressive loads. The stiffener according to the invention preferably incorporates a prebend or curvature which; when energized, creates a small, uniform, unsupported gap around the perimeter of the CFDM. The depth of the channel in the connector body for receiving the CFDM also varies in height to provide a commensurate curvature. This achieves a unique compression of the CFDM, which enhances the normal force of the inner connect.

The CFDM is covered with the FPC, which is mounted to the connector body. Preferably, CO₂ laser cut alignment holes in the FPC provide for the accurate registration of the FPC to the connector body. Means projecting from the connector body, preferably as integral posts or the like, engage holes in the FPC, for securing the two together and maintaining circuit alignment.

The FPC preferably has thieving of the copper circuit in the interconnect area, that reduces mechanical resistance and permits the efficient transfer of force. The FPC also features the added stability of copper framing around the active circuits, allowing for a more stable and precise circuit.

The PCB surface -reference standoffs (which preferably can slip relative to the connector body to facilitate force balance) enable the efficient use and control of the stiffener/spring deflection by providing a stop for screw or other means for drawing the top stiffener and bottom stiffener toward each other.

Brief Description of the Drawings

The preferred embodiment of the invention will be described below with reference to the accompanying drawings, in which:

Figure 1 is an exploded view looking at one end of the connector during assembly with parallel PCB's; Figure 2 is a longitudinal top view of the connector with FPC wrapped around and attached thereto, with partial cut-away showing the CFDM beneath the FPC;

Figure 3 is a longitudinal elevation view corresponding to Figure 2, with partial cutaway showing the CFDM beneath the FPC; Figure 4 is a longitudinal elevation view of a stiffener;

Figure 5 is a longitudinal top view of the connector with FPC omitted;

Figure 6 is a longitudinal section view taken along line 6-6 of Figure 5; Figure 7 is a cross-section view taken along line 7-7 of Figure 5;

Figure 8 is a cross-section view taken along line 8-8 of Figure 5;

Figure 9 is a longitudinal view of the CFDM;

Figure 1 0 is a longitudinal section view taken along line 1 0-1 0 of Figure 9; Figure 1 1 is a cross-section taken along line 1 1 - 1 1 of Figure 9;

Figure 1 2 is a detailed schematic cross-section view of a connector assembled with PCB, before actuation;

Figure 1 3 is a detailed schematic cross-section view of a connector assembled with PCB, after actuation;

Figures 1 4A and 14B are layout view and detail views of an FPC according to the invention;

Figure 1 5 is a cross-sectional view of an actuated connector assembly, taken through one of the stand-offs, looking from an end of the assembly;

Figure 1 6 is a longitudinal cross-section view of the actuated assembly, taken through the stand-offs;

Figure 1 7 is a perspective view of the connector body with FPC, shown without the top PCB and top stiffener; and Figure 1 8 is a schematic of the preferred array of conductor contacts on the PCB and FPC.

Description of the Preferred Embodiment

Figure 1 shows a connector 1 5 with associated flexible printed circuit 38 (FPC) carried thereon, parallel PCB's 1 1 1 2 situated above and below the connector, and a unitary stand-off 27 which is insertible through mounting holes 1 at the ends of the connector 1 5. The standoff 27 includes two spaced apart threaded bores 43, 44 which align with the bores 45 and counter bores 46 of the stiffeners 9 such that means fastener, such as head portion 47 of threaded bolts 35 or the like, engage the socket portion 46 of the counter bore, with the threaded portion passing through the PCB and into the threaded portion of the stand-offs 27.

Figures 2 and 3 show the connector including FPC 38 where the molded mounting holes 1 of the connector body 1 5 register with the respective al ignment holes 39 FPC. The cut-away portion of the FPC reveals the Complaint force distribution member (CDFM) 4 in an associated elongated channel 5 in the connector body, which extends below the contacts on the FPC in the inner, connection region 3. The

FPC is wrapped around the connector body and secured thereto via studs or the like 6 which protrude preferably integrally from the connector body to engage aligned holes along the longitudinal edges of the FPC. The studs are heated to flow and form enlarged "heads" which prevent relative movement between the overlapping edges of the

FPC.

Figure 4 shows the stiffeners 9 and 1 0 which have a pre- established arc or curvature 25 at least on the side which will bear against the PCB. The arc is substantially centered longitudinally and extends throughout the length of the stiffener. This arc would typically have a radius of curvature such that the deviation over the length of the stiffener bar (e.g., 4-6 inches} would be on the order of 0.0 D5 inch?\For

height is greater than about inch, it may be desirable to include a channel and respective CDFM, in the stiffener for bearing against the PCB along a region opposite to that where the CDFM in the connector body, bears against the PCB through the FPC.

Figures 5 through 8 show the connector body 1 5 with elongated channel 5 for receiving the CDFM. The channel width 37 is preferably slightly larger than the channel height or depth 36. The width 37 is mal ntafned constant along the channel length, whereas the depth 36 varies, preferably in an arc such that the greatest depth is at the center 33. This arc generally parallels, and therefore has approximately the same radius of curvature, as the arc 25 on the stiffener. Therefore, the channel depth 36' shown in Figure 8, taken at the squared off longitudinal ends 34 of the channel, is slightly less than the depth at 33.

Figures 9 through 1 1 illustrate the preferred CDFM 4 as a unitary, elongated strip of elastomeric material, preferably square in cross- section, and of uniform dimension 24 throughout its length.

Figure 1 2 shows the relationship of the connector member 1 5' including FPC 38, to the upper and lower PCB's 1 1 , 1 2, during make-up but prior to energization. In this view, it can be seen that the CDFM's 4 project from the top and bottom surfaces of the connector body 1 5, while in contact with the overlying FPC 38 in the circuit contact regions of the FPC. This projection is indicated via gap 1 9. Identifiers 1 3on PCB 1 1 , 1 4 on the top surface of the FPC 38, 1 6 on the PCB 1 2 and 1 7 on the bottom surface of FPC 38 show the locations of the mating circuit contacts.

As shown in Figure 1 3, when the fasteners are actuated to draw the stiffeners toward each other the CDFM's 4 are "squeezed" and, due to confinement of at l east about 75 % of the CDFM volume prior to actuation (i.e., via direct contact with the channel 5 and indirect contact with the PCB), the actuation-as shown reduces the gap 1 9 to a much smaller gap 41 . This is preferably less than about 1 0% of dimension 36 between the connector 1 5 and the FPC 38, as established by the stop means defined by the stand-offs 27. (see Figs. 7 and 1 5) . The compressive forces of actuation F1 and F2, cause the CDFM 4 to extrude slightly, in a direction parallel to the PCB's, as represented by dimension 1 8.

Figures 1 5 and 1 6 show other views of the actuated assembly (but with the CDFM not shown for clarity) . By maintaining a close tolerance on 25 the height dimension of the connector body 1 5, and the length of the stand-offs 27, the distance 23 between the upper surface of the connector body and the opposed PCB 1 1 , and the lower surface of the connector body and opposed PCB 1 2, can be very accurately established, regardless of the possible thickness variations in the PCB's. Similarly, by maintaining tight tolerances on the dimensions of the

CDFM 4 (see Figs. 7 and 8) and the channels 5 in the connector body for receiving the CDFM (see Figs. 5 and 6), one can reliably energize the CDFM by assuring full engagement of the fasteners 35 until the PCB's hit the stop surfaces 48, 49 defined by 5 the stand-offs 27. The energized CDFM thereby produces normal forces along the direction 42 which bear through the substrate of the FPC, onto the mating contacts carried by the FPC and the PCB. Preferably, a keying feature is located on the diameter of the stand-off 27 where engaged to the connector 1 5, to prohibit rotation of the stand-off 27 during Installation of the fastener 35. As shown in Figure 1 6, the connector 1 5 can slide axially relative to the stand-'off, enabling a self equalization of the CDFM 4 in axis 42. The CDFM 4 is energized to produce 75 to 200 grams normal force per mated contact, i.e., 1 3, 1 4 and 1 5, 1 6 as shown in Figure 1 3.

Figure 1 4A is a plan view showing the preferred construction and topography of the FPC 38, whereas Figure 14B shows greater detail of the portion of Figure 1 4A within the circle 50. As shown in layout, the FPC is preferably substantially rectangular. The FPC has a substantially thin, flexible insulating substrate material 7 on which a semi-rigid frame 2, preferably made of conductor material such as copper or the like is applied around the perimeter. A thin, insulative, inner region 3 of substrate 7 with contacts 1 3, 1 4 defines the connection top area, e.g. , two parallel rows 5 1 , 52 of electrical contacts 1 4 are spaced apart on one side of the longitudinal center line 53 of the FPC. In the connection area 3 of the FPC 38, extra copper is removed leaving only the substrate, thereby reducing the mechanical resistance of the FPC to the energized CDFM 4 A similar but bottom connection area is provided with two rows 54, 55 of contacts 1 7.

A plurality of relatively small reflow holes 20 are located in the frame, adjacent the longitudinal edges of the FPC, and preferably along the short edges as well. Two pair of relatively large alignment holes 39 are located in_the frame along the short edges. The FPC may also have a relieving feature 21 in the nature of weakened or meshed areas of the of the frame near the alignment holes 39, which allows a tailored fit of the FPC around the connector body 1 5. It should be appreciated that the size, shape and spatial relationships of the contacts, and the electrical conduction means within the substrate, can take 5 a variety of implementations according to the needs of the end user, and can be manufactured into the substrate according to well known techniques. When the FPC 38 is wrapped around and attached to the connector body 1 5, the reflow holes 20 along one longitudinal edge register with the respective reflow holes along the other longitudinal edge, such that the attachment posts 6 projecting from the connector body 1 5 engage the registered reflow holes. Each pair of the alignment holes 39 thus is also in registry, and in alignment with an alignment hole

1 in the connector and mounting holes 45 in the stiffeners 9. Preferably, the alignment holes 39 in the substrate of the FPC are precision cut with, for example, a CQ2 laser. The laser uses the art work of the FPC 38 as a template, cutting only the substrate and not the copper. By the use of a plurality of the holes 20 and 39, the FPC can be precisely and repeatedly positioned relative to mass produced connector bodies. Similarly, with the precision of the sizing and location of the holes 39 with associated stand-offs 27 when assembled with the connector body, the multiplicity of contacts 1 4, 1 7 on the FPC can be virtually exactly aligned in both the X and Y directions, with the contacts 1 3, 1 6 to be mated on the PCB's

Figure 1 4B shows an enlargement of the portion within the circle 50 indicated in Figure 1 4A. When the lower portion of the FPC shown in Figure 1 4A is folded around a connector body the holes 20 along the longitudinal edges will align along the side edges of the connector member, such that only that portion in the Y axis direction shown within the circle 50, would be visible from above. This is illustrated in Figure 1 7, and the enlarged detail thereof is shown in Figure 1 4B. Five signal pads are provided for each ground pad 64, on a substrate of, e.g.,

Kapton dielectric. In the illustrated embodiment, 1 00 traces 65 per inch are provided on the underside of the flex circuit, for the 1 00 total contact pads 1 4 per inch. These traces can be seen because of the thieving of the ground layer to increase the ability of the FPC to conform to the shape of the body.

Figure 1 7 is a perspective, illustrative view of the connector 1 5' including wrapped FPC 38 as secured to a lower PCB1 2, but without showing the upper PCB and associated stiffener. It should be understood that a stiffener is located substantially coextensively with the connector, but beneath the PCB 1 2. The stiffener and connector are drawn to each other via the fasteners. Thus, the center of the alignment hole on a first (top) side of the FPC centerline and the center of the other alignment hole on the first side of the FPC centerline lies on a first contact center line 56 that is parallel for the FPC center line 53. The center of one of the alignment holes on the second (bottom) side of the FPC centerline and the center of the other alignment hole on the second side of the FPC centerline lie on a second contact centerline that is parallel to the FPC centerline. When the FPC is wrapped around and attached to the connector body, the first contact centerline overlies one CFDM 4 and the second contact centerline overlies the other CFDM 4, as shown in Figures 1 2 and 1 3.

Figure 1 8 illustrates the preferred configuration of the contacts 1 4 in rows 51 and 52 on the PCB's and on the FPC. The contacts 1 4 on the FPC upper surface can be seen in Figure 1 7, whereas conductor leads 57, but not the contacts 1 6 themselves, can be seen on the

PCB1 2 in Figure 1 7.

As an indication of the precision which can be achieved with the present invention, representative (but not limiting) dimensions are shown for an alignment hole 39 having a diameter of 0.1 1 2 inch, in relation to the transverese centerline 58 of the FPC, which is 1 .327 inch from the center of the alignment hole 39. The contact centerline 56 between the two rows of contacts on, for example, the top surface as shown in Figure 1 7, passes through the centers of the alignment holes 39. As an example, the center to center spacing 60 of the individual contact pads can be on the order of 0.020 inch, with the leads thereto having a thickness 61 on the order of 0.005 inch. The exposed portions of the leads, on either side of the contact centerline 56, can be separated by a distance 62 on the order of 0.01 2 inch. The distance 63 between the midpoint of the space between adjacent contact pads, and the center of either of the adjacent contact pads, can be on the order of 0.010 inch. It can be appreciated with that with this contact pad size and density, at least 25 and preferably at least 50 contact pads can be situated side by side over a one inch span, and with two such rows on the upper surface (and the lower surface), the pad density on each surface is 1 00 pads per linear inch of connector.

Claims

CLAIMS:

1 . An electronic stacking connector assembly comprising: an elongated insulating connector body having top and bottom surfaces, each surface having an elongated channel in which is located an elongated, compliant force distribution member (CFDM) which projects from the respective surface; a flexible printed circuit (FPC) wrapped around and affixed to the connector member, and having top side contacts which overlie the top side CFDM and bottom side contacts which overlie the bottom side

CFDM; a top printed circuit board (PCB) over the top surface of the connector body and a bottom PCB beneath the bottom surface of the connector body, whereby contacts on the top PCB mate with said top side contacts on the FPC and contacts on the bottom PCB mate with said bottom side contacts on the FPC; standoff posts projecting from the top and bottom surfaces of the connector body at each end thereof, a distance which is less than the. distance by which the CFDM's project from the top and bottom surfaces of the connector body; an elongated top stiffener bar spanning the top PCB over the connector body and an elongated bottom stiffener bar spanning the bottom PCB beneath the connector body; means for drawing the top stiffener bar and bottom stiffener bar toward each other to urge the PC8's toward each other until the PCB's contact the respective standoff posts and thereby load the CFDM's, whereby the top side contacts are compliantly pressed against each other and the bottom side contacts are compliantly pressed against each other with a normal force transmitted from the respective PCB's, through the FPC's, to the CFDM's.

2. The stacking connector assembly of claim 1 , wherein the connector body has an alignment hole passing from the top to the bottom surface at each end of the connector body; each of said PCB's and stiffener bars has a mounting hole which registers with an alignment hole in the connector body; each said standoff post slidingly passes through a connector body alignment hole; and said means for drawing the stiffener bars toward each other pass through the mounting holes of the stiffener bars and the mounting holes of the PCB's into engagement with said standoff posts.

3. The stacking connector assembly of claim 1 , wherein each stiffener bar has a convex prebend toward a respective PCB and each connector body channel has a concave curvature which is substantially complementary to the stiffener bar prebend, such that upon assembly of the connector each CFDM extrudes into a uniform, unsupported gap around the perimeter of the CFDM.

4. The stacking connector assembly of claim 1 , wherein the CFDM is either a fluid-filled bladder of constant volume or a solid compliant material selected from the group consisting of elastomer, silicone polymer, or polyurethane.

5. The stacking connector assembly of claim 2, wherein the FPC has alignment holes cut by laser to provide for the accurate registration of the FPC to the connector body.

6. The stacking connector assembly of claim 2, wherein the FPC, when laid out flat prior to attachment to the connector body, is a substantially planar rectangle made of a thin, flexible insulating substrate material which supports conductors, said FPC having a longitudinal center line, a semirigid frame around the perimeter made of conductor material, an inner region on which rows of electrical contacts are located, spaced apart on either side of the longitudinal center line of the FPC, a plurality of relatively small reflow holes located in the frame and passing through the substrate situated at least along the longitudinal edges of the FPC, and one pair of relatively large alignment holes located in the frame and passing through the substrate situated along each of the short edges of the FPC, such that when the FPC is wrapped around and attached to the onnector body, the reflow holes along one longitudinal end register with respective reflow holes along the other longitudinal edge, attachment means projecting from the connector body engage the registered reflow holes whereby, each pair of the alignment holes is in registry, and in alignment with an alignment hole in the connector body and the mounting holes in the stiffener bars.

7, The stacking connector assembly of claim 6, wherein the alignment holes in the FPC are precision cut in the substrate with a laser before the frame with corresponding alignment holes is applied to the substrate.

8. The stacking connector assembly of claim 6, wherein the center of one of the alignment holes on a first side of the FPC centerline and the center of the other alignment hole on the first side of the FPC centerline lie on a first contact center line that is parallel to the

FPC center line, and the center of one of the alignment holes on the second side of the FPC centerline and the center of the other alignment hole on the second side of the FPC centerline lie on a second contact centerline that is parallel to the FPC centerline; such that when the FPC is wrapped around and attached to the connector body, the first contact centerline overlies one CFDM and the second contact centerline overlies the other CFDM.

9. The stacking connector assembly of claim 8, wherein a row of top side conductor contact pads extends in parallel on each side of the first contact centerline and a row of said bottom side contact pads extends on each side of the second contact centerline.

1 0. The stacking connector assembly of claim 9, wherein each row of contacts pads has a contact pad density of at least about 25 pads, preferably at least about 50 pads, per inch along the respective contact centerline.

1 1 . The stacking connector assembly of claim 1 , wherein the

FPC, when laid out flat prior to attachment to the connector body, is a substantially planar rectangle made of a thin, flexible insulating substrate material which supports conductors, said FPC having a longitudinal center line; a semirigid frame around the perimeter made of conductor material; an inner region on which two rows of electrical contacts are located on each side of the longitudinal center line of the FPC, one pair of relatively large alignment holes located in the frame and passing through the substrate situated along each of the short edges of the FPC, such that when the FPC is wrapped around and attached to connector body, each pair of the alignment holes is in registry, and in alignment with an alignment hole in the connector body and the mounting holes in the stiffener bars.

1 2. The stacking connector of claim 1 1 , wherein the center of one of the alignment holes on a first side of the FPC centerline and the center of the other alignment hole on the first side of the FPC centerline lie on a first contact center line that is parallel to the FPC center line, and the center of one of the alignment holes on the second side of the FPC centerline and the center of the other alignment hole on the second side of the FPC centerline lie on a second contact centerline that is parallel to the FPC centerline; such that when the FPC is wrapped around and attached to the connector body, the first contact centerline overlies one CFDM and the second contact centerline overlies the other CFDM.

1 3. The stacking connectors of claim 1 2, wherein a row of top side conductor contact pads extends in parallel on each side of the first contact centerline and a row of said bottom side contact pads extends on each side of the second contact centerline.

1 4. The stacking connector of claim 1 3, wherein each row of contacts pads has a contact pad density of at least about 25 pads, preferably at least about 50 pads, per inch along the respective contact centerline.

1 5. The stacking connector of claim 1 1 , wherein a plurality of relatively small reflow holes are located in the frame and pass through the substrate, along at least the longitudinal edges of the FPC, such that when the FPC is wrapped around and attached to the connector body, the reflow holes along one longitudinal edge register with respective reflow holes along the other longitudinal edge, attachment means projecting from the connector body engage the registered reflow holes whereby, each pair of the alignment holes is in registry, and in alignment with an alignment hole in the connector body and the mounting holes in the stiffener bars.

1 6. The stacking connector assembly of claim 1 5, wherein the reflow holes are situated along all four edges.

1 7. An electronic stacking connector comprising: an elongated insulating connector body having top and bottom surfaces, each surface having an elongated channel in which is located an elongated, compliant force distribution member (CFDM) which projects from the respective surface; a flexible printed circuit (FPC) wrapped around and affixed to the connector member, and having top side contacts which overlie the top side CFDM and bottom side contacts which overlie the bottom side CFDM; standoff posts projecting from the top and bottom surfaces of the connector body at each end thereof, a distance which is less than the. distance by which the CFDM's project from the top and bottom surfaces of the connector body; wherein the FPC, when laid out flat prior to attachment to the connector body, is a substantially planar rectangle made of a thin, flexible insulating substrate material which supports conductors, said FPC having a longitudinal center line, a semirigid frame around the perimeter made of conductor material a plurality of relatively small reflow holes located in the frame and passing through the substrate situated at least along the longitudinal edges of the FPC, and one pair of relatively large alignment holes located in the frame and passing through the substrate situated along each of the short edges of the FPC, an inner region on which two rows of electrical contacts are located on each side of the longitudinal center line of the FPC, such that when the FPC is wrapped around and attached to the connector body, the reflow holes along one longitudinal edge register with respective reflow holes along the other longitudinal edge, attachment means projecting from the connector body engage the registered reflow holes whereby, each pair of the alignment holes is in registry, in alignment with an alignment hole in the connector body.

1 8. The stacking connector of claim 1 7, wherein the center of one of the alignment holes on a first side of the FPC centerline and the center of the other alignment hole on the first side of the FPC centerline lie on a first contact center line that is parallel to the FPC center line, and the center of one of the alignment holes on the second side of the FPC centerline and the center of the other alignment hole on the second side of the FPC centerline lie on a second contact centerline that is parallel to the FPC centerline; such that when the FPC is wrapped around and attached to the connector body, the first contact centerline overlies one CFDM and the second contact centerline overlies the other CFDM.

1 9. The stacking connectors of claim 1 8, wherein a row of top side conductor contact pads extends in parallel on each side of the first contact centerline and a row of said bottom side contact pads extends on each side of the second contact centerline.

20. The stacking connector of claim 1 9, wherein each row of contacts pads has a contact pad density of at least about 25 pads, preferably at least about 50 pads, per inch along the respective contact centerline.