Abstract:
A system for connecting circuit boards is provided. A plurality of overlapping spaced apart circuit boards have a plurality of conductive pins passing through holes in the circuit boards. A connector includes a flexible sheet insulator and a plurality of conductive surfaces separated and supported by the flexible insulator. At least one of the conductive surfaces has a hole there through and a bent compliant lead extending there from. The hole engages one of the pins, and the complaint lead connects to one of the circuit boards.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to interconnections for multiple-stacked printed circuit boards. More specifically, the present invention relates to a connector with compliant leads for multiple-stacked printed circuit boards. 
         [0003]    2. Discussion of Background Information 
         [0004]    In the manufacture of printed circuit boards and similar electrical devices, it is desirable to make connections to the device and between devices. One technique for making this connection is to employ pins which are mechanically and sometimes electrically connected to the devices. 
         [0005]    In the design of complicated electronic components, it is not uncommon to arrange circuit boards and other like devices in stacked relation with numerous electrical connections being made between the different boards. Typically this is done by providing a first circuit board with pins of either compliant or non-compliant types, moving a second circuit board into position such that the pins projecting from the first circuit board engage corresponding positions in the second circuit board, and then soldering the pins to the second circuit board to lock them in place. 
         [0006]    The above prior art design is adequate for standard commercial uses, but is not suitable for certain environments. For example, military and space environments may subject the solder joints to extreme temperatures, pressures (or vacuum) and/or mechanical shock. The solder joints between the pins and the boards may begin to crack and break under the continued stress of such intense military and/or space applications, and therefore do not provide a reliable connection for all environments. 
       SUMMARY 
       [0007]    According to a preferred embodiment of the invention, a system for connecting circuit boards is provided. A plurality of overlapping spaced apart circuit boards have a plurality of conductive pins passing through holes in the circuit boards. A connector includes a flexible sheet insulator and a plurality of conductive surfaces separated and supported by the flexible insulator. At least one of the conductive surfaces has a hole there through and a bent compliant lead extending there from. The hole engages one of the pins, and the complaint lead connects to one of the circuit boards. 
         [0008]    The above embodiment may have various features. The compliant lead may have a substantially S shape, C shape, or Z shape. The flexible insulator may be a polyimide film. The compliant lead may be made of copper covered with solder. The hole may be bordered by copper covered with solder. Solder may connect the hole to the one of the pins, or the hole and the one of the pins may form a press fit. 
         [0009]    According to another embodiment of the invention, a connector is provided. A plurality of conductive surfaces are separated and supported by a flexible insulator. Each of the conductive surfaces has a hole there through and a bent compliant lead extending there from. 
         [0010]    The above embodiment may have various features. The compliant lead may have a substantially S shape, C shape, or Z shape. The flexible insulator may be a polyimide film. The compliant lead may be made of copper covered with solder. The hole may be bordered by copper covered with solder. Solder may connect the hole to the one of the pins, or the hole and the one of the pins may form a press fit. 
         [0011]    According to yet another embodiment of the invention, a connector is provided. A plurality of conductive surfaces are separated and supported by a flexible insulator. Each of the conductive surfaces having a hole there through. A flex cable supports a plurality of conductive paths. Each path is connected to a different one of the plurality of conductive surfaces. 
         [0012]    The above embodiment may have various features. The flexible insulator may be a polyimide film. The hole may be bordered by copper covered with solder. 
         [0013]    According to still yet another embodiment of the invention, a method for manufacturing a connector is provided. A layer of conductive material and a layer of a flexible insulator are provided. Portions of the conductive material are removed to form distinct conductive regions supported by the flexible insulator. A hole is formed in each of the distinct regions. Portions of the distinct regions are plated. Bent compliant leads are attached to at least some of the distinct regions. 
         [0014]    The above embodiment may have various optional features. The attaching may include providing an array of leads connected to a common support, applying solder paste or flux to the array of leads, aligning the leads with corresponding ones of the distinct regions, heating at least the array and the district regions, and removing the support. The method may further include providing a circuit board and at least one pin passing through the circuit board, threading the at least one pin through corresponding ones of the holes, and connecting at least some of the leads to the circuit board. 
         [0015]    Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of certain embodiments of the present invention, in which like numerals represent like elements throughout the several views of the drawings, and wherein: 
           [0017]      FIG. 1  is a side view of an assembly of several circuit boards using connectors according to an embodiment of the invention. 
           [0018]      FIGS. 2(   a )-( e ) are top views of the formation of a flex board according to an embodiment of the invention. 
           [0019]      FIGS. 3(   a )-( e ) are side views of the flex board corresponding to  FIGS. 2(   a )-( e ), respectively. 
           [0020]      FIG. 4  is a perspective view of a lead array according to an embodiment of the invention. 
           [0021]      FIG. 5  is a side view of a connector according to another embodiment of the invention. 
           [0022]      FIGS. 6(   a ) and ( b ) are top views of a connector according to another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0023]    The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice. 
         [0024]    Referring now to  FIG. 1 , an illustrative side view of the implementation of an embodiment of the present invention is show. Three circuit boards  100 , individual labeled as modules # 1 , # 2 , and # 3 , are vertically stacked, although any number may be so stacked. Each circuit board  100  has holes  106  through which pass pins  108 . Although boards  100  and holes  106  are shown artistically in perfect alignment, in practice some variations and imperfections are expected within manufacturing tolerances. Holes  106  are preferably about 20 mils in diameter, and pins  108  are preferably about 8-10 mils in diameter. 
         [0025]    Pins  108  are mounted at their base to a connector  110 , which is preferably soldered to the underside of the bottom most circuit board  100  (module # 1 ). Holes  106  for this bottommost board are preferably substantially filed with solder to hold pins  108 . A non-limiting example of such solder (as discussed throughout the application) is made of 63% tin and 37% lead, although other solders could be used. 
         [0026]    Pins  108  connect to electronics on boards  100  for other modules through connectors  112 . Each connector  112  includes a flex board  116  and a plurality of complaint leads  114 . 
         [0027]    Referring now to  FIGS. 2(   a )-( e ) and  3 ( a )-( e ), the flex board  116  is manufactured as follows (dimensions exaggerated for illustrative purposes). A two-layer component  200  includes a conductor  202  on the top side and an insulator  204  on the bottom side, preferably cooper as the conductor and a polyimide film such as KAPTON as the insulator. Component  200  is preferably either manufactured to the specified size or cut to size from a larger lot. 
         [0028]    Copper is etched from conductor  202  using standard techniques to provide a plurality of separate copper pads  206 . The entire top surface is then covered with an insulator  208 , preferably of the same type as insulator  204 . Insulator material is then removed from insulator  204  and/or  208  ( 208  in the figures) to expose at least a portion of the underlying copper pad  206 , which will later form the attachment point for the compliant leads. Holes  210  for pins  108  are then drilled through the interior ends of copper pads  206 . The exposed underlying copper surfaces are then plated with solder  212  to form conductive pads  214 . 
         [0029]    Referring now to  FIG. 4 , an array  400  of compliant leads  402  is shown. Each lead  402  is preferably a copper core covered with a layer of solder. Array  400  is preferably either manufactured to the specified size or cut to size from a larger section. Each lead  402  is preferably  70  mils from top to bottom, and spaced apart so that each lead  402  corresponds to and will mate with a conductive pad  214 . Leads  402  are held in place by an integral support  404 . Support  404  may have holes  406  for stacking and/or retention purposes. Leads  402  are compliant, i.e., a semi-rigid characteristic that allows leads  402  to deform in response to changes in environment (e.g., bending under applied force, thermal expansion under increased temperature, thermal contraction due to decreased temperature) and substantially return to an original state upon removal of the change in the environment. 
         [0030]    Array  400  connects to flex board  116  as follows. Array  400  is placed into a fixture using holes  406 , and flux and/or solder paste is applied to leads  402  and conductive pads  214  using know methods (e.g., squeegee, stencils). Flex board  116  is then also loaded into an appropriate fixture to hold it in place relative to array  400  with the leads  402  in contact with the conductive pads  214  via the flux/solder paste. Array  400  and flex board  116  are then sent through a reflow oven, which melts the solder in leads  402  and conductive pads  214  to form conductive joints there between. The completed product forms connector  112 . 
         [0031]    Referring now also to  FIG. 1 , the completed connector  112  is slid over the pins  108  through holes  210  until connection  112  is at the desired location. The free ends of leads  114  are soldered to the underlying circuit board  100 . Connector  112  remains in place via a press fit, or solder  118  can be added above and/or below holes  210 . 
         [0032]    The flexible insulator  204 / 208  in connector  112  provides a certain degree of give relative to any minor production misalignment between the pins  108  and holes  210 , such that any perfect alignment will not place undue stress on the solder connections. The complaint characteristic of leads  402  also allows it absorb most of the force generated by a changing environment without placing undue stress on the solder joints themselves. The resulting solder joints were observed to remain intact for over three hundred (300) thermal cycles of −40° C. to +100° C. at a rate of one cycle per hour under induced misalignment of 10 mils, which simulates approximately twenty years of military use and ten years of space use. 
         [0033]    In the above embodiment, each conductive pad has one hole and one complaint lead, each defining an individual conductive path. However, the invention is not so limited, as not every pathway is necessary or desirable, and thus the electrical pathway need not be formed for each individual pad. For example, a different etching mask could be used to remove the connective copper between the hole and pad, such as shown in  FIGS. 6(   a ) and  6 ( b ). Various complaint leads could be removed, either broken off from the array before attachment or after attachment. Solder need not be applied to any particular pad or lead, such that there is an air gap between the pad/lead and/or lead/board. Copper pad  206  need never be formed in the first plane (e.g., the area is etched away) such that hole  108  passes through insulator  204 / 208  without providing a conductive path for pin  108 . 
         [0034]    As shown in  FIG. 1 , leads  114  are preferably S shaped, with the lower portion of the S facing inward to allow easier access to circuit board  100  for soldering. However, the invention is not so limited, as any desirable shape could be used. C and Z shapes are non-limiting examples of acceptable alternatives. U.S. Pat. No. 5,294,039 shows no-limiting examples of such shapes, and is incorporated by reference in its entirety. 
         [0035]    Referring now to  FIGS. 5(   a ) and  5 ( b ), another embodiment of a connector of the present invention is shown. The connector includes a flex board  502  substantially identical to  116  discussed above. The exposed contact pads of flex board  502  are soldered to exposed portions of a flex cable  504 . The flex cable  504  terminates in individual leads  505  which are electrically connected to circuits on the underlying board  506 , either by solder or an appropriate electrical connector. 
         [0036]    The embodiments herein show a single connector for a single side of a board. However, the invention is not so limited. Multiple connections can be used, either on either side of the board (or both sides). Connector  112  could also have two sets of leads  114 , one facing upwards and one facing downwards to connect with two different circuit boards. 
         [0037]    It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to certain embodiments, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims