Patent Publication Number: US-6988310-B2

Title: Method of assembling an interconnect device assembly

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to electrical interconnects and, more particularly, relates to the assembly of electrical interconnects incorporating an interposer having resilient wire bundles that provide a conductive path between two electronic substrates. The present invention further particularly relates to apparatus involved in the assembly of such electrical interconnects. 
   Electrical interconnect devices having resilient wire bundles for providing a conductive path between two electronic substrates are well known to those skilled in the art. Such resilient wire bundles are also known as fuzz buttons, button contacts, button wads or contact wads and shall be collectively referred to hereafter as resilient wire bundles. 
   One such device is the electrical interconnect device shown in Hopfer, III et al., the disclosure of which is incorporated by reference herein. There, it can be seen that resilient wire bundles are held in a carrier. In use, the carrier is placed between two circuit boards and the resilient wire bundles provide the conductive path between the two circuit boards, As noted in Hopfer, III et al., the resilient bundles wire (contact wads) are held in place in the carrier in their corresponding holes by compressive radial frictional engagement with the side walls of each of the holes. 
   Metreaud et al. IBM Technical Disclosure Bulletin, vol. 20, no. 7, p. 2695 (December 1977) discloses another use of a resilient wire bundle (fuzz button) in which a depression is formed in the resilient wire bundle to accommodate a chip. The compressed portion of the resilient wire bundle enhances the thermal conductivity of the resilient wire bundle for better cooling of the chip. 
   Leahy et al. U.S. Pat. No. 5,359,488, the disclosure of which is incorporated by reference herein, discloses another use of a resilient wire bundle (fuzz button) which interconnects a radio frequency package to a ceramic motherboard. 
   The inherent difficulty with such interconnect devices that use a resilient wire bundle for a conductive path is that the resilient wire bundle is frequently jarred loose from the carrier during transit or handling such that when the interconnect device is placed between two electronic substrates, an open results due to the missing resilient wire bundle. This unfortunate circumstance occurs notwithstanding the teachings of Hopfer, III et al. that the resilient wire bundles are force fitted into the holes in the carrier. When such an open occurs, the interconnect device has to be replaced at some additional cost. Instead of being jarred loose from the carrier, the resilient wire bundle instead could be partially jarred from the carrier such that when the resilient wire bundle is compressed between the two electronic substrates, the resilient wire bundle bends over and makes contact with an adjacent resilient wire bundle causing a short circuit which can result in damage to one of both of the electronic substrates being interconnected. In this latter situation as well, the resilient wire bundle, and possibly also one or both of the electronic substrates being interconnected, would have to be replaced at some additional cost. 
   In order to remedy the shortcomings of the prior art, it is a purpose of the present invention to have a method of assembling the interconnect device in which the resilient wire bundles are prevented from being jarred loose during handling and transit of the interconnect device. 
   It is a further purpose of the present invention to have an apparatus for assembling an interconnect device in which the resilient wire bundles are prevented from being jarred loose during handling and transit of the interconnect device. 
   These and other purposes of the present invention will become more apparent after referring to the following description of the invention considered in conjunction with the accompanying drawings. 
   BRIEF SUMMARY OF THE INVENTION 
   The purposes of the invention have been achieved by providing, according to a first aspect of the present invention, a method of assembling an interconnect device, the method comprising the steps of:
         obtaining a resilient wire bundle having first and second ends and a carrier having a perforation for receiving the resilient wire bundle and a resilient wire bundle in the perforation; and   contacting the first and second ends of the resilient wire bundle with a shaping die so as to increase a cross-sectional area of the resilient wire bundle to thereby form the resilient wire bundle into a dog bone shape and retain the resilient wire bundle in the perforation.       

   According to a second aspect of the present invention, there is provided an interconnect device assembly fixture comprising:
         a first die assembly comprising a first stripper plate having a perforation therein and a first shaping die slidably engaged in the first stripper plate perforation wherein the first shaping die is capable of extending past a working side of the first stripper plate;   a second die assembly comprising a second stripper plate having a perforation therein and a second shaping die slidably engaged in the second stripper plate perforation wherein the second shaping die is capable of extending past a working side of the second stripper plate;   the first and second die assemblies being in opposed, spaced apart relation such that the working side and shaping die of the first die assembly face and do not contact the working side and shaping die of the second die assembly;   wherein, in operation, a carrier having resilient wire bundles is placed between the respective working sides of the first and second die assemblies and the respective shaping dies are caused to contact the resilient wire bundles so as to increase a cross-sectional area of the resilient wire bundles and thereby retain them in the carrier.       

   According to a third aspect of the present invention, there is provided a method of assembling a plurality of shaping dies, the method comprising the steps of:
         placing a plurality of shaping dies in perforations in a die block so that the plurality of shaping dies protrude from the die block;   adjusting the shaping dies so that they all protrude the same amount from the die block;   permanently fixing the shaping dies in the die block.       

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of the invention believed to be novel and the elements characteristic of the invention are set forth with particularity in the appended claims. The Figures are for illustration purposes only and are not drawn to scale. The invention itself, however, both as to organization and method of operation, may best be understood by reference to the detailed description which follows taken in conjunction with the accompanying drawings in which: 
       FIG. 1  is a partial cross-sectional view of an interconnect device assembly fixture according to the present invention in a first position. 
       FIG. 2  is a partial cross-sectional view of the interconnect device assembly fixture of  FIG. 1  in a second position. 
       FIG. 3  is a partial cross-sectional view of a fixture for assembling a plurality of shaping dies according to the present invention. 
       FIG. 4  is a partial cross-section of a fixture for testing the shaping dies. 
       FIG. 5  is a schmatical illustration of sample output from the testing of shaping dies in the fixture of  FIG. 4 . 
       FIG. 6  is a partial cross-sectional view of a second fixture for use in the assembly of interconnect devices. 
       FIG. 7A  illustrates a resilient wire bundle in a carrier,  FIG. 7B  illustrates the resilient wire bundle of  FIG. 7A  formed into a dog bone shape according to one method step of the invention, and  FIG. 7C  illustrates the resilient wire bundle of  FIG. 7A  formed into a dog bone shape according to another method step of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to the Figures in more detail, and particularly referring to  FIGS. 7A to 7C , there is shown in  FIG. 7A  an interconnect device assembly  34  comprising carrier  36  having a perforation  44  for receiving a resilient wire bundle  38 . A portion  46  of perforation  44  may be tapered for the purpose of inserting resilient wire bundle  38  in the perforation  44 . Typically, the carrier  36  and resilient wire bundle  38  are purchased as an interconnect device assembly  34  from a manufacturer, of which there are many. One such manufacturer is Cinch Connectors Inc., Lombard, Ill. Further, while  FIG. 7A  only shows one resilient wire bundle in the carrier  36 , it should be understood that there will usually be many such resilient wire bundles  38  in the carrier  36  to make up interconnect device assembly  34 . 
   A problem with interconnect device assembly  34  is that the normally cylindrically-shaped resilient wire bundle  38  may be partially or totally dislodged from the carrier  36  during handling or transit as mentioned previously. The present invention, therefore, is directed to securing the resilient wire bundles  38  in carrier  36 . 
   Turning now to  FIG. 7B , it can be seen that resilient wire bundle  38  has been flattened at first end  40  and second end  42 , by means to be discussed hereafter, into a dog bone shape that is now retained in the perforation  44  of carrier  36 . 
   In  FIG. 7C , resilient wire bundle  38  has been indented at first end  40  and second end  42 , by means to be discussed hereafter, into a dog bone shape that is now retained in the perforation  44  of carrier  36 . 
   While the process steps necessary to form the shape of resilient wire bundle  38  shown in  FIG. 7B  or  7 C may be sufficient if used alone in one preferred embodiment of the present invention, it is another preferred embodiment of the present invention to use them in combination as will be explained in more detail hereafter. 
   Referring now to  FIG. 1 , there is shown a first preferred embodiment of an interconnect device assembly fixture  10  according to the present invention which will shape the resilient wire bundles  38  into the form represented by  FIG. 7C .  FIG. 1  shows the interconnect device assembly fixture  10  in the rest position. An interconnect device assembly  34  is placed in cavity  32  of die assembly  14 . Die assembly  14  comprises a stripper plate  16  and die block  28 . Contained within stripper plate  16  and die block  28  are shaping dies  30  which are slidably moveable in perforations  18  of stripper plate  16  but are fixed in die block  28  as will be explained in more detail hereafter. Shaping dies  30  preferably are round in cross-section and have pointed tips  52 . Stripper plate  16  and die block  28  are spaced apart a distance  26  by biasing means  24  such as springs. Stripper plate  16  has a working side  20  which faces the interconnect device assembly  34 . 
   Still referring to  FIG. 1 , interconnect device assembly fixture  10  further comprises die assembly  12  which is identical to die assembly  14  except that die assembly  12  does not contain a cavity for receiving the interconnect device assembly  34 . Die assemblies  12  and  14  are spaced apart a distance  22 . 
   Interconnect device assembly fixture  10  sits on table  54  or other rigid surface. Schematically shown as arrow  56  is a force mechanism, for example a press comprising an air cylinder and regulator, which will apply a downward force to interconnect device assembly fixture  10 . As an illustration, such a press may exert a force of about 1000 pounds on an interconnect die assembly having 1500 resilient wire bundles. The interconnect device assembly fixture  10  may be assembled by placing die assembly  14  on table  54 , inserting interconnect device assembly  34  into cavity  32 , then placing die assembly  12  over die assembly  14 . Alignment of die assemblies  12 ,  14  is accomplished by dowel pins (not shown) which run vertically through die assemblies  12 ,  14 . 
   Referring now to  FIG. 2 , the interconnect device assembly fixture  10  is shown in operation. Upon application of force mechanism  56 , stripper plates  16  of die assemblies  12 ,  14  move toward each other until contact is made with the interconnect device  34 . During this part of the operation, biasing means  24  keep the respective die blocks  28  apart from the stripper plates  16 . Once contact of the stripper plates  16  is made with the interconnect device assembly  34 , continued application of force mechanism  56  overcomes biasing means  24  such that the die blocks  28  now move toward each other and interconnect device assembly  34 . Shaping dies  30  consequently also move toward and into contact with the resilient wire bundles  38 . In one preferred embodiment of the present invention, the shaping dies each move about 6 mils which is sufficient to clear the stripper plate and make substantial contact with the resilient wire bundles  38  so as to effectively indent each end  40 ,  42  of the resilient wire bundles  38  as shown in  FIG. 7C . The stroke of the die blocks  28  and hence also shaping dies  30  can be further regulated by the inclusion of shims  50  between respective die blocks  28  and stripper plates  16 . 
   Once contact of the shaping dies  30  is made with the resilient wire bundles  38 , the force mechanism  56  is relieved such that the interconnect device assembly fixture returns to its position as shown in  FIG. 1 . Die assembly  12  is then removed, interconnect device assembly  34  removed, another interconnect device assembly  34  is put into cavity  32  and die assembly  12  replaced to begin the process all over again. 
   It is advantageous for the present invention that all of shaping dies  30  extend the same distance from die block  28  so that contact with the resilient wire bundles  38  is uniform. Accordingly, a method for assembling the shaping dies  30  in die block  28  will now be described. Referring now to  FIG. 3 , stripper plate  16  and die block  28  are assembled on flat plate  58 . Shims  50  may be inserted between stripper  16  and die block  28  if desired. Shaping dies  30  are inserted into die block  28  and then stripper plate  16  so that the tips  52  of shaping dies  30  rest on flat plate  58 . Adhesive  60 , preferably epoxy, is then applied to the tops  68  of shaping dies  30  followed by release layer  62  (e.g., Saran wrap) and then elastomeric pad  64 . Because these shaping dies  30  can be small (on the order of 20 mils in diameter), they will float up into the adhesive  60 , thereby destroying the planarity of the shaping dies  30  on flat plate  58  unless they are forced down during the curing of the adhesive  60 . Thus, a force  66  is applied to elastomeric pad  64  which holds the shaping dies  30  in place. Upon curing of the adhesive  60 , the force  66 , elastomeric pad  64  and release layer  62  are removed. Thereafter, a second adhesive  70  (shown in  FIGS. 1 and 2 ), preferably also epoxy, is added to fill the die block  28 . 
   From time to time, it is desirable to check the operation of the interconnect device assembly fixture  10  to make sure it is working properly. For example, the tips  52  of the shaping dies  30  could become bent, worn or broken or there could be some other problem with the device assembly fixture  10  such that there would be insufficient contact of the shaping dies  30  with resilient wire bundles  38 . Accordingly, the present inventors have proposed a method of testing the interconnect device assembly fixture  10  as shown in  FIG. 4 . A metal sheet  72  is placed in cavity  32  of stripper plate  16  of die assembly  14 . Thereafter, carrier  36  (without any resilient wire bundles) is placed on top of metal sheet  72  followed by a second metal sheet  72 . Die assembly  12  is then placed over die assembly  14  and force mechanism  56  activated (as shown in  FIG. 2 ) to move shaping dies  30  into contact with metal sheets  72 . Die assembly  12  is then removed followed by removal of metal sheets  72  and carrier  36 . Metal sheets  72  are then examined. The examination of the metal sheets  72  will provide information as to whether the tips  52  are defective, bent, deformed, broken, worn out or contain debris or whether there is a problem with the die assemblies  12 ,  14  that would allow for over-or under-penetration of the tips  52  into the resilient wire bundles. A schematical illustration of one of these tested metal sheets is shown in  FIG. 5 . As can be seen in  FIG. 5 , the shaping dies  30  have mostly made impressions or indentations  74  indicating that the tips  52  of those shaping dies  30  are in good working order. However, two shaping dies did not made contact with metal sheet  72 , indicated by phantom impressions  76 , thereby indicating at least those shaping dies corresponding to phantom impressions  76  need to be repaired or replaced. 
   The metal sheet  72  utilized could be any thin metal sheet such as a 0.5 to 5 mil thick sheet of copper, tin, aluminum, gold or lead, just to name a few. However, it is preferred that a MYLAR polycarbonate material sandwich consisting of clear MYLAR (e.g., 2 mil thick) and aluminized MYLAR (e.g., comprising a clear MYLAR sheet 0.5 mil thick with a 50–250 Å coating of aluminum) be used as the thin metal sheet. The aluminized MYLAR may additionally be replaced by a thin (e.g., 0.5 mil thick) layer of opaque material. The sandwich should be assembled such that the clear MYLAR is against the interconnect device assembly  34  and the aluminized MYLAR is against the working side  20  of the stripper plate  16 . To avoid contamination of the shaping dies  30  with aluminum residue, it is most preferred that the aluminized side of the aluminized MYLAR is placed against the clear MYLAR which serves as a backup material allowing the thin aluminized MYLAR sheet to be penetrated by the tips  52  of the shaping die  30  instead of just being stretched out of planarity. 
   The advantage of the aluminized MYLAR is that it can be easily inspected using a microscope with bottom illumination, giving a dark background with bright spots appearing where the tips  52  have penetrated the aluminized MYLAR. This inspection could be performed using automatic image recognition equipment. As an interconnect device assembly  34  can have 1500 or more resilient wire bundles  38 , thereby requiring a corresponding number of shaping dies  30 , inspection of the aluminized MYLAR by automatic image recognition equipment would be preferred. 
   Referring now to  FIG. 6 , there is shown an alternative interconnect device assembly fixture  110  comprising die block  114  having a cavity  116  for receiving interconnect device assembly  34 , die block  112  having a cavity  118  for receiving flat plate  120 . Die block  114  sits on table  124  or other rigid surface. Once the interconnect device assembly fixture  110  is fully assembled as shown in  FIG. 6 , there is a gap  124  between die blocks  112  and  114 . In operation, a force  122  is exerted on the interconnect device assembly fixture  110  which causes resilient wire bundles  38  to be compressed between flat surface  126  of cavity  116  and flat plate  120 , thereby flattening the ends  40 ,  42  of resilient wire bundles  38  into a dog bone shape as shown in  FIG. 7B  as well as centering the resilient wire bundles  38  within carrier  36  in the Z (vertical) direction so that the resilient wire bundles  38  protrude by equal amounts above and below the surface of the carrier  36 . 
   While the interconnect device assembly fixtures  10 ,  110  can be used separately, in a preferred embodiment of the present invention, the interconnect device assembly fixtures  10 ,  110  can be used together to achieve the most advantageous results. Thus, interconnect device assembly  34  may first be worked on in interconnect device assembly fixture  110 , followed by interconnect device assembly fixture  10  and, most preferably, another application of interconnect device assembly fixture  110 . 
   It has been found that retention of resilient wire bundles  38  within carrier  36  of interconnect device assembly  34  is improved by the application of interconnect device assembly fixture  110 , is improved more so by the application of interconnect device assembly fixture  10  and is improved most by the combined application of interconnect device assembly fixtures  10 ,  110  as explained above. 
   It will be apparent to those skilled in the art having regard to this disclosure that other modifications of this invention beyond those embodiments specifically described here may be made without departing from the spirit of the invention. Accordingly, such modifications are considered within the scope of the invention as limited solely by the appended claims.