Abstract:
A method of forming a solder joint between a coaxial cable and a coaxial connector includes the steps of: positioning a solder element between an end of an outer conductor of the coaxial cable and a connector body of the connector, wherein the solder element is positioned within a vacuum chamber; melting the solder element to form a solder joint between the outer conductor and the connector body, the solder joint including a lower surface formed by contact with a mounting structure; and applying suction to the melting solder element to reduce the formation of bubbles within the solder joint.

Description:
RELATED APPLICATION 
       [0001]    The present application claims priority from and the benefit of U.S. Provisional Patent Application No. 62/131,105, filed Mar. 10, 2015, the disclosure of which is hereby incorporated herein in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    invention relates generally to a connector and cable interconnection, and more specifically to a connector and cable interconnection method and apparatus with improved manufacturing efficiency and electrical performance characteristics. 
       BACKGROUND OF THE INVENTION 
       [0003]    Coaxial connectors are commonly utilized in RF communications systems. A typical coaxial cable includes an inner conductor, an outer conductor, a dielectric layer that separates the inner and outer conductors, and a jacket that covers the outer conductor. Coaxial cable connectors may be applied to terminate coaxial cables, for example, in communication systems requiring a high level of precision and reliability. 
         [0004]    Coaxial connector interfaces provide a connect/disconnect functionality between a cable terminated with a connector bearing the desired connector interface and a corresponding connector with a mating connector interface mounted on an apparatus or on another cable. Typically, one connector will include a structure such as a pin or post connected to an inner conductor and an outer conductor connector body connected to the outer conductor; these are mated with a mating sleeve (for the pin or post of the inner conductor) and another outer conductor connector body of a second connector. Coaxial connector interfaces often utilize a threaded coupling nut or other retainer that draws the connector interface pair into secure electro-mechanical engagement when the coupling nut (which is captured by one of the connectors) is threaded onto the other connector. 
         [0005]    Commonly-owned U.S. Pat. Nos. 5,802,710 and 7,900,344, hereby incorporated by reference in their entireties, disclose a technique for attaching a coaxial connector to a coaxial cable. The connector utilizes an insulating disc retained upon the inner contact and against the dielectric layer and outer conductor of the cable. Induction heating of a solder preform wrapped around the outer conductor creates a molten solder pool in a cylindrical solder cavity formed between the outer conductor, the insulating disc and the connector body. The insulating disc prevents the molten solder from migrating out of the cavity, fouling the connector bore and/or shorting the outer and inner conductors. 
         [0006]    Commonly-owned U.S. Patent Publication No. 2014/0201989, also incorporated herein by reference in its entirety, illustrates a pedestal with an insulating seat on which the soldering of the outer conductor to the connector body can occur. One issue that can arise with this technique is the formation of air bubbles within the solder; if such bubbles form in locations along the signal path, the electrical performance of the connector interface can be compromised. 
       SUMMARY 
       [0007]    As a first aspect, embodiments of the invention are directed to a method of forming a solder joint between a coaxial cable and a coaxial connector. The method comprises the steps of: positioning a solder element between an end of an outer conductor of the coaxial cable and a connector body of the connector, wherein the solder element is positioned within a vacuum chamber; melting the solder element to form a solder joint between the outer conductor and the connector body, the solder joint including a lower surface formed by contact with a mounting structure; and applying suction to the melting solder element to reduce the formation of bubbles within the solder joint. 
         [0008]    As a second aspect, embodiments of the invention are directed to a method for attaching a connector to a coaxial cable, comprising the steps of: positioning a solder element between an end of an outer conductor of the coaxial cable and a connector body of the connector; positioning the connector body on a mounting structure; melting the solder element to form a solder joint between the outer conductor and the connector body, the solder joint including a surface formed by contact with the mounting structure, the melting step being performed as the solder element resides in a vacuum chamber; and applying suction to the melting solder element to reduce the formation of bubbles within the solder joint. 
         [0009]    As a third aspect, embodiments of the invention are directed to an apparatus for forming a solder joint between a coaxial cable and a coaxial connector, comprising: a mounting structure with an upper surface configured to receive a connector body and a coaxial cable; a heating element positioned to melt a solder element to form a solder joint between the connector body and the coaxial cable, the upper surface of the mounting structure positioned to form the lower surface of the solder joint; a vacuum chamber; and a vacuum source attached to the vacuum chamber and positioned to apply suction to the solder joint as it forms between the connector body and the coaxial cable, the solder joint forming in the vacuum chamber. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic perspective view of a cable-connector assembly apparatus and a cable, wherein electrical interconnections, supporting and enclosure structures are removed for clarity. 
           [0011]      FIG. 2  is a schematic section view of a connector body seated upon the interface pedestal of the apparatus of  FIG. 1 . 
           [0012]      FIG. 3  is an enlarged section view of the pedestal and connector body of  FIG. 2  with a cable and solder preform inserted therein for solder interconnection. 
           [0013]      FIG. 4  is a section view as in  FIG. 3  with the solder preform melted to form a solder joint. 
           [0014]      FIG. 5  is a front perspective view of an apparatus according to embodiments of the present invention, with the housing and the vacuum source illustrated schematically. 
           [0015]      FIG. 6  is a side perspective view of the apparatus of  FIG. 5 . 
           [0016]      FIG. 7  is a schematic front view of an apparatus according to alternative embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The present invention is described with reference to the accompanying drawings, in which certain embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments that are pictured and described herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. It will also be appreciated that the embodiments disclosed herein can be combined in any way and/or combination to provide many additional embodiments. 
         [0018]    Unless otherwise defined, all technical and scientific terms that are used in this disclosure have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the above description is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in this disclosure, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that when an element (e.g., a device, circuit, etc.) is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. 
         [0019]    Referring now to the figures, an apparatus  21  for soldering a connector body onto a coaxial cable such as is described in U.S. Patent Publication No. 2014/0201989, supra, is shown in  FIG. 1 . The apparatus includes a pedestal  19  mounted on a base  21 , a clamp  41  for holding a cable  1  in place, and an inductive heating element  37  for heating solder used to attach the connector body to the outer conductor of the cable  1 .  FIG. 2  shows a connector body  17  in place on the pedestal  19 , with a step in the connector body  17  resting on a shoulder  25  of the pedestal  19 . A cap  29 , formed of a dielectric, thermally insulative material, is mounted on the upper end of the pedestal  19  to provide thermal insulation to components of the cable  1  during soldering. As a result, the pedestal  19  and cap  29  act as a mounting structure for the connector body  17 . The pedestal  19  includes an inner conductor cavity  39  in its upper surface that is configured to receive the inner contact  11  of the cable  1  during soldering. 
         [0020]    As shown in  FIG. 3 , a solder preform  15  or other solder element circumscribes the end of the outer conductor  5  of the cable  1 . The connector body  17  is positioned on the pedestal  19 , with the solder cavity  27  of the connector body  17  (formed by the inner surface of the connector body  17 , the upper surface of the cap  29 , and the outer conductor  5 ) located above the pedestal  19 . The cable  1  with the solder preform  15  in place is lowered into the cavity  27  and onto the pedestal  19 , with the inner contact  11  of the cable  1  received in the inner conductor cavity  39 , and the end of the outer conductor  5  and the solder preform  15  abutting the cap  29 . The clamp  41  is applied to the connector body  17  to secure it in place. Heat is applied to the end of the cable  1  via the heating element  37 , such that the solder preform  15  melts, flows downwardly within the solder cavity  27  between the inner surface of the connector body  17 , the upper surface of the cap  29 , and the outer conductor  5 , and freezes, thereby forming a solder joint  18  between the outer conductor  5  and the connector body  17  ( FIG. 4 ). 
         [0021]    As described above, and as shown in  FIG. 4 , in many instances the flowing solder from the solder preform will create bubbles  22  that remain in the frozen solder joint  18 . Such bubbles  22  can adversely impact the electrical performance of the interface between the outer conductor  5  and the connector body  17 , particularly if the bubbles  22  are located in the electrical signal path. 
         [0022]    Referring now to  FIGS. 5 and 6 , an apparatus for forming solder joints between coaxial connectors and coaxial cables is shown therein and designated broadly at  101 . The apparatus  101  includes the components discussed above in connection with apparatus  1 . However, the apparatus  101  is contained within an airtight housing  102  that enables a vacuum to be generated within the housing  102 . As can be seen in  FIGS. 5 and 6 , the housing  102  includes a front wall  103 , a rear wall  104 , side walls  105 ,  106 , a floor  107  and a ceiling  108 . 
         [0023]    A vacuum source  110  is located externally from the housing  102 . Access to the interior of the housing  102  is available via a port  112  through which a hose  114  is routed. The port  112  is vacuum-sealed around the hose  114 . 
         [0024]    Also, as described above, the cable to be soldered is lowered into the pedestal  19  from above, and is clamped into place with the clamp  41 . The clamp  41  also includes a gasket, O-ring or the like that forms a vacuum seal with the connector body  17  and/or the cable. The clamp  41  also includes a seal with the ceiling  108 . As such, the interior of the housing  102  can be vacuum-sealed. 
         [0025]    In operation, the cable with the connector body  17  is lowered onto the pedestal  19  as described above. The clamp  41  clamps the connector body  17 , thereby forming a seal. The vacuum source  110  is activated, which draws a vacuum within the housing  102 . The heating element  37  is activated, which causes the solder preform  15  to melt; once melted, the solder is allowed to freeze to form the solder joint  18 . However, because the vacuum is present within the interior of the housing  102 , the tendency for bubbles to form in the molten solder is reduced or eliminated, which in turn reduces or eliminates voids in the solder joint  18  that can negatively impact electrical performance. 
         [0026]    The timing of the application of the vacuum may vary. In some embodiments, the vacuum may be activated prior to the application of heat via the heating element and maintained until the solder fully freezes. In other embodiments, the vacuum may be activated after the application of heat and maintained until freezing, and in other instances the vacuum may be deactivated prior to complete freezing of the solder joint  18 . 
         [0027]    Another apparatus directed to reducing the formation of voids in the solder joint is shown in  FIG. 7  and designated broadly at  201 . The apparatus  201  employs the components of the apparatus  1 , but also includes a small vacuum chamber  202  within which the connector body  17  resides during soldering. As shown in  FIG. 7 , the vacuum chamber  202  includes two halves  203 ,  204  that separate in a manner similar to a reciprocating mold. The meeting edges of the halves  203 ,  204  include a vacuum seal  205 . The halves  203 ,  204  also include a vacuum seal  206  that forms around the cable and a seal  207  that forms with the pedestal  19 . A vacuum source  208  is attached via a hose  209  to the half  204 . 
         [0028]    When a cable with a connector body  17  is mounted on the pedestal  19 , the halves  203 ,  204  close around it to provide an airtight cavity in which soldering can occur, with the seals  205 ,  206 ,  207  preventing leakage at the interfaces between components. As described above, the vacuum source  208  can be activated to before or during the melting of the solder preform  15  to reduce or eliminate the formation of voids in the solder joint  18 . 
         [0029]    Those skilled in this art will appreciate that concepts discussed above may be applied to other soldering operations. For example, surface mount and direct launch bulkhead connectors for antennas and filters may be suitable for use with these concepts. Other variations may also be apparent. 
         [0030]    The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. The invention is defined by the following claims, with equivalents of the claims to be included therein.