Abstract:
A connector utilized to electrically connect together conductive pads disposed on different substrates includes a flexible substrate having a plurality of conductive through-holes therein. A conductive line formed in the flexible substrate extends between at least two of the conductive through-holes. A plurality of contacts is mounted in the conductive through-holes of the flexible substrate. Each contact includes a post connected to a base of a crown-shaped head having a plurality of projections around the periphery of the base that extend away from the base in the direction opposite the post. The post of each contact is soldered into one of the plurality of conductive through-holes. A compression mat positioned on a side of the flexible substrate opposite the crownshaped heads includes a plurality of resilient cylinders that extend away from a resilient base. Each resilient cylinder has a distal end alignable in registration with a distal end of the post of one of the plurality of contacts. A compression fitting is positionable adjacent the resilient base of the compression mat. The compression fitting co-acts with one of the substrates to apply a clamping force therebetween that urges a projection of each contact into electrical contact with one of the conductive pads.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a divisional of application Ser. No. 08/963,401, filed Nov. 3, 1997 and entitled “Compression Connector,” now U.S. Pat. No. 5,899,757. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to electrical connectors and, more particularly, to high density electrical connectors utilized to electrically connect electronic devices disposed on two or more printed circuit boards. 
     2. Description of the Prior Art 
     Increased integration of electronic devices has created an interconnection problem for printed circuit boards receiving these devices. Specifically, the number of interconnections required to electrically connect together two or more printed circuit boards receiving these electronic devices has exceeded the connection densities of prior art pin-in-socket connectors. Moreover, these prior art pin-in-socket connectors typically have relatively long and unshielded lengths which have uncontrolled impedances resulting in less than desired electrical performance. 
     A high contact density connector utilizable for electrically connecting together electronic devices received on two or more printed circuit boards and overcoming the foregoing problems is disclosed in an article entitled “A High Density Edge Connector” by J. Campbell et al., Copyright 1995 IEEE. This article discloses a flex circuit formed of a 2 mil thick polyimide film having 3 mil wide copper lines plated onto one side thereof and 25 mil round contact pads plated on the side of the film opposite the circuit lines and along both edges of the film. 4 mil diameter plated through-holes, or vias, extend between the contact pads on one side of the film and the circuit lines on the other side. Palladium dendrites, or spires, are electro-deposited on surfaces of each contact pad. These dendrites straddle dust or fibers and puncture oils or films present on each contact pad prior to connector mating and produce on each contact pad a multitude of conductive connections. The connector includes a molded plastic force block to which elastomeric cylinders are molded. These cylinders act as springs which provide force, when compressed during assembly, to make and maintain an electrical connection between the contact pads on the film and the pads on a printed circuit board. One cylinder is provided for each contact and compensates for any variation in planarity and tolerance accumulation. Conical alignment pins are utilized to mate alignment holes in the flex circuit with alignment holes in the printed circuit board during assembly, thereby ensuring proper registration between the contact pads on the film and the pads on the printed circuit board. 
     Another flexible circuit connector for connecting a daughter card and a mother board is disclosed in an article entitled “A High Density Pad-On-Pad Connector Utilizing A Flexible Circuit” by R. S. Pokrzywa, Copyright 1993 IEEE. This connector utilizes a two-sided flex circuit having plated, spherical contacts contacting flat printed circuit pads on the daughter card and on the mother board. The spherical contacts on the flex circuit are 5 mils in diameter and have a copper base metal overplated with nickel and gold. Alignment pins are utilized to align the flex circuit, the daughter card and the mother board so that each spherical contact mates with a desired printed circuit pad. Precipitation hardened stainless steel curved beams provide contact force for reliable connection between the spherical contacts and the printed circuit pads. During actuation, the curved beam is flattened to produce a uniform load across the contact area. An elastomeric pad is positioned between the beam and the contact area to accommodate local discrepancies in load across the contact area and to focus the connector forces. In one embodiment, the elastomeric pad has a plurality of elastomeric cylinders utilized to back-up the spherical contacts. In another embodiment, where size does not permit molding individual cylinders for each spherical contact, an elastomeric rib is utilized to back a row of spherical contacts. 
     A problem with spherical contact pads and electro-deposited dendrites on contact pads is that they inconsistently break through contaminants, such as oxides, films or foreign materials, that may be present thereon or on the contact pad of a printed circuit board. Hence, inadequate electrical contact or, in some instances, no electrical contact is made between the contact pad of the flexible circuit and the contact pad of the printed circuit board. Moreover, the formation of dendrites on the contacts of the flexible circuit increases the cost of such connectors. 
     It is therefore an object the present invention to provide a connector which overcomes these drawbacks of the prior art connectors. It is an object of the present invention to provide a compression connector contact that promotes electrical contact with a conductive pad of a printed circuit board. It is an object of the present invention to provide a method for making a connector that utilizes the provided compression connector contact. It is an object of the present invention to provide a method of making a flexible circuit connector that is less costly to manufacture than the prior art flex circuit connectors. 
     SUMMARY OF THE INVENTION 
     Accordingly, we have invented a compression connector utilized to electrically connect together conductive pads disposed on one or more substrates. The compression connector includes a flexible substrate having a plurality of conductive through-holes therein and at least one conductive line thereon extending between at least two of the conductive through-holes. The compression connector also includes a plurality of contacts. Each contact has a post connected to a base of a crown-shaped head having a plurality of projections around the periphery of the base that extend away from the base in a direction opposite the post. The post of each contact is secured in one of the plurality of conductive through-holes. 
     A compression mat can be positioned on the side of the flexible substrate opposite the crown-shaped heads of the plurality of contacts. The compression mat can include a plurality of resilient cylinders extending away from a resilient base. Each resilient cylinder can have a distal end alignable in registration with a distal end of the post of one of the plurality of contacts secured in one of the plurality of conductive through-holes. 
     A transfer film can be utilized to transfer the plurality of contacts to the flexible substrate prior to securing each post in one of the plurality of conductive through-holes. The transfer film preferably has a plurality of elastically deformable receiving apertures which receive and secure the crown-shaped heads of the plurality of contacts. 
     The compression connector can also include a rigid substrate, such as a printed circuit board, which has a plurality of the conductive pads on a surface thereof and at least one conductive line connected to at least one of the conductive pads. The rigid substrate and the flexible substrate are alignable so that at least one projection of each contact on the flexible substrate is aligned in registration with one of the conductive pads on the surface of the rigid substrate. 
     A compression fitting can be positionable adjacent the resilient base of the compression mat. The compression fitting forces together at least one projection of each contact and the conductive pad in registration therewith. Each resilient column of the compression mat contacts the distal end of a post of a contact and functions as the spring when compressed to make and maintain good electrical connection between the projection and the conductive pad. 
     Preferably, a plurality of alignment holes in each of the flexible substrate, the rigid substrate and the compression fitting co-acts with a like plurality of alignment pins to align the flexible substrate, the rigid substrate and the compression fitting so that the heads of the plurality of contacts are in registration with the plurality of contact pads. Each alignment pin is preferably a bolt having a threaded end adapted to mate with a threaded nut. 
     We have invented a compression connector contact that includes a crown-shaped head having a base and a plurality of projections disposed around the periphery of the base and extending to one side thereof. A post extends from the side of the base opposite the projections. 
     The side of the base opposite the post can have a cavity formed therein in registration with a lengthwise axis of the post. The base can have a periphery having a generally rectangular outline. Each corner of the generally rectangular outline of the base can be rounded and can include one of the plurality of projections. Each projection can have a rounded edge formed continuous with the periphery of the base. 
     We have also invented a method of making a connector that includes providing a plurality of contacts, each contact having a post connected to a base of a crown-shaped head. Each crown-shaped head has a plurality of projections around the periphery of the base that extend away from the base in a direction opposite the post. The crown-shaped heads of the plurality of contacts are inserted into a plurality of receiving apertures in a transfer film so that the posts extend out of the plurality of receiving apertures. A flexible substrate is provided having a plurality of conductive through-holes therein and a plurality of conductive lines thereon. At least one conductive line extends between and electrically connects at least two of the conductive through-holes. The transfer film and the flexible substrate are mated so that the posts of the plurality of contacts are received in the plurality of conductive through-holes in the flexible substrate. The posts of the plurality of contacts are fused to the plurality of conductive through-holes in the flexible substrate. The transfer film is then separated from the flexible substrate and the plurality of contacts. 
     The plurality of contacts is formed from a strip of conductive material. Each contact is connected to an adjacent contact by a rib formed from the conductive strip. Each contact is excised from its connecting rib and inserted into one of the receiving apertures in the transfer film. Each receiving aperture elastically deforms to receive and retain the head of the contact therein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  is a cross section of a compression connector in accordance with the present invention; 
     FIG. 1 b  is an enlarged view of a portion of FIG. 1 a  within line  1   b;    
     FIG. 2 a  is a plan view of a compression mat of the compression connector in FIG. 1 a;    
     FIG. 2 b  is a side view of the compression mat of FIG. 2 a;    
     FIG. 3 a  is a plan view of a flexible substrate used in the compression connector of FIG. 1 a;    
     FIG. 3 b  is an enlarged view of a portion of FIG. 3 a  within line  3   b;    
     FIG. 4 a  is a plan view of a conductive strip that has been formed to include a plurality of contacts that are utilized in the compression connector of FIG. 1; 
     FIG. 4 b  is an enlarged view of a portion of the conductive strip of FIG. 4 a  within line  4   b;    
     FIG. 4 c  is a cross section taken along lines  4   c — 4   c  in FIG. 4 b;    
     FIG. 5 is a plan view of the conductive strip of FIG. 4 a  aligned with a transfer film; 
     FIG. 6 is a cross section of the aligned conductive strip and transfer film of FIG. 5 positioned between a transfer base and an excising tool; 
     FIG. 7 is a cross section of the contacts of the conductive strip of FIG. 4 a  received in receiving apertures of the transfer film of FIG.  6  and positioned in alignment with through-holes formed in the flexible substrate of FIG. 3 a;    
     FIG. 8 is a cross section similar to FIG. 7 showing the transfer film and flexible substrate mated together with the posts of the contacts received within and soldered to the through-holes of the flexible substrate; and 
     FIG. 9 is a cross section similar to FIGS. 7 and 8 showing the separation of the transfer film from the flexible substrate and contacts. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 a - 1   b , a rigid substrate  2 , such as a printed circuit board formed of FR- 4  or ceramic, has a plurality of conductive pads  4  formed thereon in a manner known in the art. The rigid substrate  2  may include one or more conductive lines that extend between one or more of the conductive pads  4  or between a conductive pad  4  and an electronic device connected to the rigid substrate  2 . The conductive lines and electronic device are not shown on the rigid substrate  2  in FIGS. 1 a - 1   b  for simplicity of illustration. 
     A flexible insulating substrate  6  having a plurality of contacts  8  secured thereon is positioned adjacent the rigid substrate  2 . The flexible substrate  6  is preferably formed of a polyimide film such as Kapton®. Kapton® is a registered trademark of E. I. DuPont DeNemours &amp; Company. The contacts  8  are secured on the flexible substrate  6  in a pattern matching the pattern of the conductive pads  4  on the rigid substrate  2 . Each contact  8  includes a head  10  that extends away from a surface of the flexible substrate  6 . Aligning the flexible substrate  6  and the rigid substrate  2  positions the heads  10  in registration with the conductive pads  4 . 
     A compression fitting  12  is positioned on the side of the flexible substrate  6  opposite the heads  10  of the contacts  8 . The compression fitting  12  includes a compression mat  14  received in an aperture  15  of an alignment sleeve  16 . As shown in FIGS. 2 a - 2   b , the compression mat  14  includes a resilient base  18 , preferably having a generally rectangular outline, and a plurality of resilient cylinders  20  extending from the resilient base  18 . The compression mat  14  and the flexible substrate  6  are positioned so that distal ends of the resilient cylinders  20  are aligned in registration with the contacts  8  on a surface of the flexible substrate  6  opposite the heads  10 . The compression fitting  12  includes a washer  22  positioned on a side of the alignment sleeve  16  opposite the resilient base  18  of the compression mat  14 . Preferably, the compression mat  14  is formed of a thermal silicon rubber, the alignment sleeve  16  is formed from a polyphenylene sulfide, UL 94 V-0, and the washer  22  is formed from stainless steel. 
     The compression fitting  12 , the flexible substrate  6  and the rigid substrate  2  each have a plurality of alignment apertures  24 ,  26  and  28 , respectively. Each alignment aperture  24 ,  26  and  28  is adapted to receive a shaft of an alignment pin  30 , such as a bolt having an externally threaded end  31  adapted to mate with internal threads of a nut  32 . Applying the nuts  32  to the alignment pins  30  urges together the compression fitting  12  and the rigid substrate  2 . This urging together forces into contact the conductive pads  4  and the heads  10  in registration therewith, and the distal ends of the resilient cylinders  20  in registration with contacts  8  on the surface of the flexible substrate  6  opposite the heads  10 . Continued application of the nuts  32  to the alignment pins  30  compresses the compression mat  14  between the flexible substrate  6  and the washer  22 . This compression causes the resilient cylinders  20  to deform against the contacts  8  on the side of the flexible substrate  6  opposite the heads  10 . This deformation causes each resilient cylinder  20  to apply a spring force between the head  10  and the conductive pad  4  in registration therewith. This spring force promotes between the head  10  and the conductive pad  4  in registration therewith the formation and maintenance of good electrical contact and compensates for any variations in planarity and tolerance accumulation. Preferably, double-sided tape  34  is utilized to adhere together adjacent surface of flexible substrate  6  and the sides of the alignment sleeve  16 . 
     The head  10  of each contact  8  has a base  40  and a plurality of projections  42  disposed around a periphery  43  of the base  40 . The projections  42  extend to one side of the base  40  and give the head  10  a crown-shaped appearance. Each contact  8  also has a post  44  that extends from a central part of the base  40  opposite the projections  42 . A cavity  46  is preferably formed in each base  40  opposite the post  44  and in alignment with a lengthwise axis  47  of the post  44 . 
     With reference to FIGS. 3 a - 3   b  and with ongoing reference to FIGS. 1 a - 1   b , the flexible substrate  6  has a plurality of through-holes  48  formed therein that are adapted to receive the posts  44  of the contacts  8 . The wall of each through-hole  48  includes metallization  50  formed therein to form a conductive through-hole. The metallization  50  in each through-hole  48  is preferably connected to a conductive line  52  or to one or more conductive ground planes  53  formed on the flexible substrate  6 . The one or more conductive ground planes  53  are formed on one or both surfaces of the flexible substrate  6  to reduce or eliminate cross-talk between conductive lines  52  and/or to reduce or eliminate the effect on one or more of the conductive lines  52  of electromagnetic interference from external sources. The metallization  50  in each through-hole  48 , the conductive lines  52  and the conductive ground planes  53  are formed on the flexible substrate  6  in a manner known in the art. To maintain the post  44  of each contact  8  received in a through-hole  48 , the metallization  50  of each through-hole  48  and the posts  44  of the contacts  8  received therein are fused together, preferably utilizing a solder  54 . 
     With reference to FIGS. 4 a - 4   c , an array of contacts  8  is formed by exposing a thin, flat strip  60  of conductive material to a stamping operation. The stamping operation also forms from the strip  60  a plurality of ribs  62  that extend between and secure together adjacent contacts  8 . 
     In a preferred embodiment, the periphery  43  of the base  40  of each head  10  has a generally rectangular outline. Each corner  66  of the generally rectangular outline of the base  40  is rounded and includes one of the projections  42 . Each projection  42  has a rounded edge  68  formed continuous with the periphery  43  of the base  40 . 
     With reference to FIG. 5, to install the contacts  8  in the flexible substrate  6 , the contacts  8  are first transferred to a flexible transfer film  70 , such as Kapton®. More specifically, the strip  60  having the array of contacts  8  formed therein is aligned with the transfer film  70  so that each contact  8  is aligned in registration with one of a plurality of receiving apertures  72  in the transfer film  70 . 
     As shown in FIG. 6, the transfer film  70  is positioned between the strip  60  and a transfer base  76  so that the posts  44  of the contacts  8  are positioned in opposition with the transfer base  76  through the receiving apertures  72  of the transfer film  70 . An excising tool  78  having a plurality of blades  80  and a plurality of push pins  82  is positioned on a side of the conductive strip  60  opposite the transfer film  70 . In use, the excising tool  78  is moved towards the base  76  so that the blades  80  excise the contacts  8  from the ribs  62 . The excised contacts  8  are then inserted into the receiving apertures  72  by the push pins  82  so that the lengthwise axes  47  of the posts  44  are substantially coaxial with lengthwise axes  83  of the receiving apertures  72 . 
     Before inserting the contacts  8 , each receiving aperture  72  has a diameter  84  that is less than a diagonal distance  86  (shown in FIG. 4 c ) between opposite corners  66  of the base  40 . As shown in FIG. 7, the receiving apertures  72  elastically deform to receive and secure the heads  10  of the contacts  8  therein. Preferably, each head  10  has a height  88  (shown in FIG. 4 c ) that is greater than a thickness  90  of the transfer film  70 . Hence, when the heads  10  are inserted in the receiving apertures  72 , the posts  44  of the contacts  8  are preferably positioned outside the receiving apertures  72 . When the heads  10  are received in the receiving apertures  72 , the transfer film  70  and the flexible substrate  6  are positioned so that the posts  44  are in registration with and receivable in the through-holes  48 . 
     As shown in FIG. 8, the flexible substrate  6  and the transfer film  70  are brought together so that the posts  44  are received within the metallization  50  of the through-holes  48 . The contacts  8  are secured to the flexible substrate  6  by fusing the posts  44  and the metallization  50  of the through-holes  48  together with the solder  54 . 
     As shown in FIG. 9, the flexibility of the transfer film  70  and the elastic deformability of the receiving apertures  72  enables the transfer film  70  to be separated, e.g., peeled away, from the contacts  8  secured to the flexible substrate  6 . When the transfer film  70  is separated, the flexible substrate  6  and contacts  8  can be utilized in the manner described above in connection with FIGS. 1 a - 1   b.    
     As shown in FIG. 3 a , a first plurality  96  of through-holes  48  and a second plurality  98  of through-holes  48  are preferably disposed on opposite sides of the flexible substrate  6 . When the contacts  8  are fused into the first and second plurality  96 ,  98  of through-holes  48 , the side of the flexible substrate  6  adjacent the first plurality  96  of through-holes  48  can be utilized to connect to one rigid substrate (not shown) and the side of the flexible substrate  6  adjacent the second plurality  98  of through-holes  48  can be utilized to connect to another rigid substrate (not shown) thereby effecting electrical connection between the rigid substrates. 
     In a preferred embodiment, each post  44  has a diameter between 7 and 8 mils and a length of 2 mils. The head  10  of each contact  8  has a height of 10 mils and the cavity  46  has a depth of 3 mils. The height of each projection  42  is 4 mils and a distance  94  (shown in FIG. 9) between rounded edges  68  of projections  42  on diagonally opposite corner  66  is 21.5 mils. The strip  60  and contacts  8  are formed from a strip of ¼ hard brass. The contacts  8  are plated with 5 micro-inches of soft gold over 30 micro-inches of palladium nickel over 50 micro-inches of sulfamate nickel. The conductors  52  and the ground planes  53  of the flexible substrate  6  are formed from ½ ounce copper which is deposited as a sheet on the flexible substrate  6  and then patterned and etched utilizing photolithographic and etching techniques known in the art. 
     Based on the foregoing, it can be seen that the contacts  8  are sufficiently small so that manual manipulation of contacts  8  into the through-holes  48  of the flexible substrate  6  is not practical. To this end, and in accordance with the present invention, forming the array of contacts  8  from the strip  60  enables the contacts  8  to be manipulated as an array. Similarly, the transfer film  70  enables the contacts  8  to be transferred as an array from the strip  60  to the flexible substrate  6 . The transfer film  70  also helps maintain the posts  44  of the contacts a in the through-holes  48  during fusing of the posts  44  to the metallization  50  of the through-holes  48 . Hence, the contacts  8  are manipulated as an array from the time they are formed from the strip  60  in the stamping operation until they are fused into the conductive through-holes in the flexible substrate  6 . This manipulation of the contacts  8  as an array enables the compression connector of the present invention to be manufactured efficiently and cost effectively. Moreover, the compression connector of the present invention avoids the prior art teaching of plating contacts on the flexible substrate. 
     Because the metallization  50  in the through-holes  48  and the conductive lines  52  are pre-formed on the flexible substrate  6 , it is preferable to avoid soldering the contacts  8  to the through-holes  48  prior to excising the contacts from the ribs  62  due to concerns over cutting with the blades  80  of the excising tool  78  the conductive lines  52  or the metallization  50  in the through-holes  48 . Hence, the contacts  8  are first transferred to the flexible transfer film  70  which is utilized to transfer the contacts  8  to the flexible substrate  6  and which may thereafter be disposed as justified by the condition thereof. 
     The contacts  8  of the present invention are believed to provide over prior contacts improved contact with conductive pads  4  on the rigid substrate  2 . Specifically, the rounded edge  68  of each projection  42  contacting one of the contact pads  4  cuts through oils or films that may be present on the conductive pad  4  and/or the contact  8  prior to mating, thereby enabling conductive paths to be formed between each projection  42  in contact with the conductive pad  4 . 
     As can be seen from the foregoing, the present invention provides a compression connector contact that promotes electrical contact with a conductive pad of a printed circuit board. The present invention also provides a method for making a flexible circuit connector that utilizes the provided compression connector contact and is less costly to manufacture than the prior art flexible circuit connectors. 
     The invention has been described with reference to the preferred embodiment. Obvious modifications and alterations will occur to others upon reading and understanding the preceding specification. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.