Abstract:
In a compression coaxial cable assembly, a housing has a contacting face and a coaxial cable has an end inserted into the housing, a signal conductor, and an outer shield. First and second members are mounted to and electrically coupled to the signal conductor and the outer shield, respectively, and each of the first and second members has a deflectable portion projecting from the housing at the contacting face. Upon coupling the housing to a substrate, the deflectable portions each electrically contact corresponding surfaces on the substrate. Upon urging the housing toward the substrate, the deflectable portions each deflect and withdraw into the housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/244,222, filed Oct. 30, 2000, hereby incorporated by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to an assembly for mounting a coaxial cable directly to a circuit substrate. In particular, the present invention relates to such an assembly for mounting one or more coaxial cables directly to a circuit substrate.  
         BACKGROUND OF THE INVENTION  
         [0003]    Under certain circumstances, it is desirable to bring one or more signals to a printed circuit board or the like by way of a coaxial cable. In many situations, each of the one or more coaxial cables is terminated by an appropriate termination device and is coupled by way of the termination device to a connector mounted to the printed circuit board. However, it is to be appreciated that such connector in particular can introduce unwanted parasitic effects such as resistive, capacitive, and/or inductive effects. Particularly in high-speed applications, and as should be appreciated, such parasitic effects are especially problematic.  
           [0004]    A need exists, then for an assembly that allows mounting of a coaxial cable to a printed circuit board or other substrate such that the coaxial cable electrically contacts the circuit board without the need for a connector interposed therebetween. Accordingly, unwanted parasitic effects resulting from the connector are eliminated.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention satisfies the aforementioned need by providing a compression coaxial cable assembly for being coupled to a substrate. In the assembly, a housing has a contacting face and a coaxial cable has an end inserted into the housing. The cable also has a signal conductor and an outer shield. First and second members are mounted to and electrically coupled to the signal conductor and the outer shield, respectively, at the end of the cable, and each of the first and second members has a deflectable portion projecting from the housing at the contacting face.  
           [0006]    Upon coupling the housing to the substrate, the contacting face of the housing faces toward and contacts the substrate, and the deflectable portions each electrically contact corresponding surfaces on the substrate. Upon urging the housing toward the substrate, the deflectable portions each deflect and withdraw into the housing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    The foregoing summary, as well as the following detailed description of preferred embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. As should be understood, however, the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings:  
         [0008]    [0008]FIG. 1 is a perspective view of a full compression coaxial cable assembly in accordance with one embodiment of the present invention, in which a plurality of coaxial cables enter a housing which is to be attached generally directly to a printed circuit board or substrate;  
         [0009]    [0009]FIG. 2A is a side view of the assembly of FIG. 1;  
         [0010]    [0010]FIG. 2B is a top view of the assembly of FIG. 1;  
         [0011]    [0011]FIG. 2C is an enlarged view of a portion of FIG. 2A;  
         [0012]    [0012]FIG. 2D is an enlarged view of a portion of FIG. 2B;  
         [0013]    FIGS.  3 A- 3 D are perspective views of a coaxial cable of FIG. 1, and show steps performed in terminating the end of such cable and elements employed therefor in accordance with one embodiment of the present invention;  
         [0014]    FIGS.  4 A- 4 C are perspective views of the elements employed in terminating the end of the cable in FIG. 3 and show a bellows contact (FIG. 4A), an insulator tube (FIG. 4B), and a ground spring/shield (FIG. 4C);  
         [0015]    [0015]FIG. 4D is a plan view of the ground spring/shield of FIG. 4C as stamped in sheet form;  
         [0016]    [0016]FIGS. 5A and 5B are broken-away perspective views of the housing of FIG. 1, and show an interior cavity for receiving the terminated cable of FIG. 3D (FIG. 5A) and the terminated cable received within the interior cavity (FIG. 5B);  
         [0017]    [0017]FIG. 6 is a plan view of a printed circuit board or substrate for having the assembly of FIG. 1 mounted thereto; and  
         [0018]    [0018]FIGS. 7A and 7B are exploded (FIG. 7A) and unexploded (FIG. 7B) perspective views of the coaxial cable of FIG. 1 terminated in an alternate embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0019]    Certain terminology may be used in the following description for convenience only and is not considered to be limiting. For example, the words “left”, “right”, “upper”, and “lower” designate directions in the drawings to which reference is made. Likewise, the words “inwardly” and “outwardly” are directions toward and away from, respectively, the geometric center of the referenced object. The terminology includes the words above specifically mentioned, derivatives thereof, and words of similar import.  
         [0020]    Referring now to FIGS.  1 - 7 B, in the present invention, one or more of coaxial cables  10  are coupled directly to a circuit board or substrate  12  (FIG. 6), where the end  14  of each cable  10  adjacent the circuit board or substrate (hereinafter ‘circuit board’)  12  resides within a housing  16 . As discussed in more detail below, the end  14  (FIGS.  3 A- 3 D) of each cable  10  is terminated with components necessary to retain such end  14  within the housing  16  and to ensure good quality compressive contact with the circuit board  12 , and such termination components reside substantially within the housing  16  when the cable  10  thereof is mounted to the housing  16 . Each of the one or more coaxial cables  10  preferably takes up a minimal amount of space within the housing  16 . Accordingly, the housing  16  with the cables  10  mounted thereto imparts a relatively small footprint as mounted to the circuit board  12 .  
         [0021]    As seen in FIGS. 1 and 2A, in one embodiment of the present invention, one or more of the coaxial cables  10  enter the housing  16  which is to be attached generally directly to the circuit board  12  (FIG. 6). As shown, the cables  10  are arranged in two rows of eight, one row staggered from the other to maximize available space. Of course, any number of cables  10  may be arranged in the housing  16  in any manner without departing from the spirit and scope of the present invention.  
         [0022]    The housing  16  may be constructed from a plastic, metal, or other appropriate material by machining, molding, or other appropriate process, all without departing from the spirit and scope of the present invention. Notably, in addition to holding the ends  14  of the cables  10 , the housing  16  is constructed and designed to align each end  14  with respect to the circuit board  12  when the housing  16  is mounted to such circuit board  12 . As seen, then, the housing  16  may define one or more apertures  18  therein that correspond to apertures  20  within the circuit board  12 . Accordingly, upon appropriately aligning the housing  16  with the circuit board  12  such that corresponding ones of the apertures  18 ,  20  also align, fasteners such as screws or bolts (not shown) may be placed through such aligned apertures  18 ,  20  to secure the housing  16  to the circuit board  12 .  
         [0023]    The housing  16  may have one or more keying features (not shown) for ensuring that the housing  16  is properly aligned with respect to and mounted to the circuit board  12 . For example, the keying feature may reside in one or more keying studs extend from the housing toward and through the printed circuit board. Such studs may define the apertures  18  of the housing  16 , or may be distinct from such apertures  18 .  
         [0024]    Each cable  10  may be any appropriate type or size of coaxial cable without departing from the spirit and scope of the present invention. As best seen in FIG. 3A, each cable  10  has an inner signal conductor  22  at the center, an insulative dielectric  24  surrounding the signal conductor  22 , an outer shield  26  surrounding the dielectric  24 , and a non-conductive jacket  28  surrounding the outer shield  26 . In the case of a plurality of the cables  10  mounted to the housing  16 , the cables  10  may be combined into one or more ribbons or the like, or may be distinct from one another.  
         [0025]    As mentioned above, each coaxial cable  10  is provided with termination components at the end  14  thereof to effectuate retention of the end  14  within the housing  16 . As will be appreciated, conductive ones of such termination components also directly contact the circuit board  12  to effectuate electrical contact between the circuit board  12  and the cable  10  of such end  14 . In one embodiment of the present invention, when the housing  16  is mounted to the circuit board  12 , each conductive terminating component extends from the housing  16  toward the circuit board  12  to contact such circuit board  12 .  
         [0026]    Such conductive termination components are preferably designed to deflect upon such contact, thus ensuring that all such conductive termination components achieve good electrical contact between the respective cables  10  and the circuit board  12 . As may be appreciated from FIGS. 2A and 2C, such components deflect at most to the point where the housing  16  as mounted to the circuit board  12  is flush therewith. As may be appreciated, the side of the housing  16  that faces the circuit board  12  as shown in FIGS. 2B and 2D is complementary to the circuit board  12  as shown in FIG. 6 in the region of contact therebetween such that a close contact is achieved. Thus, if the contacting surface of the circuit board  12  is generally planar, then so too is the contacting surface of the side of the housing  16  that faces the circuit board  12  generally planar. As may be appreciated, the housing  16  also protects such components from excess deflection and over-stressing.  
         [0027]    Referring to FIG. 3A, now, it is seen that prior to mounting the termination components to the end  14  of a cable  10 , such end  14  is stripped of, in decreasing lengths from the face of the end  14  (as best seen in FIG. 2D), the jacket  28 , the outer shield  26 , and the dielectric  24 . Thus, and starting at the face of the end  14 , a length of the signal conductor  22  is exposed, a length of the dielectric  24  is exposed, and a length of the outer shield  26  is exposed. As will be appreciated below, the respective lengths are based on and determined in conjunction with dimensions of the terminating components. Such respective lengths may nevertheless be any appropriate lengths without departing from the spirit and scope of the present invention.  
         [0028]    In one embodiment of the present invention, once the lengths have been exposed, and as best seen in FIGS. 3A and 3B, a contact  30  is conductively coupled to the signal conductor  22  at the end  14  as one of the termination components. As shown, the contact  30  is fitted over the length of the signal conductor  22  and contacts the dielectric  34  below. Of course, the contact  30  may also be fitted to the signal conductor in any other appropriate manner without departing from the spirit and scope of the present invention. The contact  30  may be appropriately constructed from any appropriate conductive material, may be soldered or brazed to the signal conductor  22 , or may be conductively coupled to the signal conductor  22  in another appropriate manner.  
         [0029]    As shown in FIGS. 3A, 3B, and  4 A, the contact  30  has a metal deflectable bellows-type portion  32  and has a cone  34  atop the bellows  32  that narrows to a point. As may be appreciated, the point on the cone  34  directly contacts the circuit board  12  at a contact pad  36  thereof (FIG. 6), and the bellows  32  deflects upon contacting the cone  34  to the circuit board  12 . As may also be appreciated, the cone  34  with the point is especially useful in that the cone  34  acts as a Hertzian bump that pierces through any dirt, debris or other materials on the corresponding contact pad without the need for any wiping. Such materials are merely pushed aside by such point and a good contact is achieved. Of course, the contact  30  may have any other appropriate deflecting design without departing from the spirit and scope of the present invention. For example, as seen in FIGS. 7A and 7B, the contact  30  may omit the cone  34  if not perceived necessary for a particular application.  
         [0030]    With the contact  30  mounted to the signal conductor  22 , and as best seen in FIG. 3C, an insulator tube  38  is fitted over the contact  30  so as to contact the dielectric  24  below. As shown, the insulator tube  38  exposes only the point of the cone  34  of the contact  30 . Of course, the insulator tube  38  may also be fitted over the contact  30  in any other appropriate manner without departing from the spirit and scope of the present invention. The insulator tube  38  may be held in place by way of an interference fit, by way of a cement or epoxy or the like, or may be coupled in another appropriate manner.  
         [0031]    As should be appreciated, the insulator tube  38  is akin to the dielectric  24  and therefore isolates the contact  30  from elements radially exterior thereto. Critically, such tube  38  is sized and formed from a material such that the impedance of the termination components at the end  14  of the coaxial cable  10  matches the impedance of the coaxial cable  10 .  
         [0032]    In one embodiment of the present invention, and as seen in FIGS. 3C and 4B, the tube  38  is designed with a plurality of generally axially extending ribs  40 . As may be appreciated, the ribs  40 , three of which are shown, function to space the contact  30  from elements radially exterior thereto, and also function to assist in defining the impedance of the termination components at the end  14  of the coaxial cable  10 . Of course, any appropriate material and design for the tube  38  may be employed without departing from the spirit and scope of the present invention. For example, as seen in FIGS. 7A and 7B, the tube  38  may omit the ribs  40  if not perceived necessary for a particular application. Also, any appropriate method of forming the tube  38 , such as, molding, extruding, or machining, may be employed without departing from the spirit and scope of the present invention.  
         [0033]    As may be appreciated, upon the point on the cone  34  directly contacting the circuit board  12  at a contact pad  36  thereof (FIG. 6), the tube  38  may also contact the circuit board  12 , although generally at or in the neighborhood of a buffer  42  surrounding the contact pad  36 . Note that absence of such contact between such tube  38  and the circuit board  12  may occur without departing from the spirit and scope of the present invention. As may be appreciated, the buffer  42  acts to isolate the contact pad  36  from conductive elements on the surface of the circuit board exterior to the buffer  42 . Such conductive elements may include a ground plane  44 , as shown. If contact between the tube  38  and circuit board  12  does occur, the tube  38  preferably deflects upon contacting the circuit board  12 .  
         [0034]    With the tube  30  fitted over the contact  30 , and as best seen in FIG. 3D, a ground spring/shield (hereinafter spring shield)  46  is fitted over the tube  30  so as to conductively contact the outer shield  26  of the cable  10  and to contact the jacket  28  below. As shown, the spring shield  46  substantially covers the length of the tube  38  and exposes only the point of the cone  34  of the contact  30 . Of course, the spring shield  46  may also be fitted over the contact  30  in any other appropriate manner without departing from the spirit and scope of the present invention. The spring shield  46  may be held in place by way of an interference fit, by way of being soldered or brazed to the outer shield  26 , or may be conductively coupled to the outer shield  26  in another appropriate manner. If solder is employed, such solder may be applied by way of a through-hole  47  in the spring shield  46  (FIG. 4D) to secure the spring shield  46  to the outer shield  26  and thus to the coaxial cable  10 .  
         [0035]    As should be appreciated, the spring shield  46  is akin to the outer shield  26  and therefore conductively couples the outer shield  26  to the circuit board  12 . Thus, upon the point on the cone  34  directly contacting the circuit board  12  at a contact pad  36  thereof (FIG. 6), the spring shield  46  also contacts the circuit board  12 , although at a region outside the buffer  42 , such as at the ground plane  44 .  
         [0036]    In one embodiment of the present invention, and as seen in FIGS. 3D, 4C, and  4 D, the spring shield  46  includes one or more spring arms  48  that directly contact the circuit board  12  such as at the ground plane  44  thereof (FIG. 6), and that deflects upon contacting the spring shield  46  to the circuit board  12 . Of course, the spring shield  46  may have any other appropriate deflecting design without departing from the spirit and scope of the present invention. For example, as seen in FIGS. 7A and 7B, the spring shield  46  may have a different style of spring arm  48 . As may be appreciated, each spring arm  48  of the spring shield  46  and the bellows portion  32  of the contact  30  in combination provide a linear normal force between the cable  10  and the circuit board  12 . Such linear normal force prevents the spring shield  46  and the contact  30  of each cable  10  from becoming overstressed.  
         [0037]    In one embodiment of the present invention, the spring shield  46  includes a retention feature  50  as seen in FIGS. 3D, 4C, and  4 D, the housing  16  defines a cable-receiving cavity  52  for receiving the end  14  of each cable  10  mounted thereto as seen in FIGS. 5A and 5B, and the housing  16  further defines a ledge  54  associated with and adjacent to each cavity  52  as also seen in FIGS. 5A and 5B. The retention feature  50  of the spring shield  46  includes a slot defined within the spring shield  46 , and an edge of the spring shield  46 . As best shown in FIG. 4D, such slot is generally L-shaped, and such edge is just above the horizontal portion of the slot.  
         [0038]    As may be appreciated, the retention feature  50  of the spring shield  46  co-acts with the ledge  54  of the cavity  52  to secure spring shield  46  and attached cable  10  within the housing  16 . More particularly, the cable  10  with termination components thereon is inserted into the housing  16  from the side of the housing opposite the side that faces toward the circuit board  12  such that the edge of the retention feature  50  of the spring shield  46  springs radially outwardly after passing by the ledge  54  of the cavity  52 , thus preventing withdrawal of the inserted cable  10  unless the cable  10  is rotated within the cavity  52  to disassociate the edge from the ledge  54 .  
         [0039]    Notably, upon inserting the cable  10  into a cavity  52  of the housing  16  and securing the cable  10  to such housing  16  by way of the associated ledge  54 , the end  14  of the cable as defined by the termination components protrudes through the side of the housing that faces toward the circuit board  12 , as best seen in FIGS.  2 A- 2 D. As shown, the length of such protrusion need not be very much, perhaps on the order of a millimeter or two.  
         [0040]    In one embodiment of the present invention, the spring shield  46  includes an impedance tuning feature  56  as seen in FIGS. 3D, 4C, and  4 D, the housing  16 . As seen, such tuning feature  56  includes a slot defined within the spring shield  46 , and a tab associated with the slot. As best shown in FIG. 4D, such slot is generally U-shaped, and such tab is generally defined by the slot. As may be appreciated, the tab of the impedance tuning feature  56  may be manipulated to fine-tune the impedance of the end  14  of the coaxial cable  10  so as to match the impedance of the remainder of the coaxial cable  10 . Such manipulation may be performed automatically or manually, before or after inserting the cable  10  within the housing  16 . Of course, if performed after insertion, the cable  10  is withdrawn from the housing to provide access to the tuning feature  56 .  
         [0041]    In one embodiment of the present invention, the spring shield  46  is stamped out of sheet metal or the like in a relatively flat state, as shown in FIG. 4D, and is rolled to its final form. Of course, any appropriate material and method of formation of the spring shield  46  may be employed without departing from the spirit and scope of the present invention. More generally, any appropriate design for the spring shield  46  may be employed without departing from the spirit and scope of the present invention.  
         [0042]    In the present invention, upon inserting each cable  10  into a cavity  52  of the housing  16  such that the cable  10  is locked to the housing  16  and protrudes at the side of the housing  16  facing the circuit board  12 , the housing  10  may then be appropriately positioned with respect to the circuit board  12  and secured to such circuit board  12 . Thus, the contact  30  of each cable  10  in the housing  16  directly conductively contacts a respective contact pad  36  of the circuit board  12  and the spring shield  46  of each cable  10  in the housing  16  directly conductively contacts the ground plane  44 . Upon securing the housing  16  to the circuit board  12 , the contacts  30  and spring shields  46  each deflect to exert a force normal to the circuit board  12 . Upon tightening the housing  16  down to the circuit board  12 , the deflecting components essentially disappear within the housing  16 , but yet continue to respectively contact the circuit board  12  at the aforementioned points.  
         [0043]    In the foregoing description, it can be seen that the present invention comprises a new and useful full compression coaxial cable module for being mounted normally and directly to a printed circuit board  12  or the like and for electrically contacting coaxial cables  10  mounted to a housing  16  of the module to the printed circuit board  12 . It should be appreciated by those skilled in the art that changes could be made to the embodiments described above and shown in the drawings without departing from the inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.