Patent Publication Number: US-9889586-B2

Title: Low pressure molded strain relief for coaxial connector interconnection

Description:
CROSS-REFERENCE TO PATENT APPLICATION 
     This patent application is a continuation of U.S. patent application Ser. No. 13/251,341, now U.S. Pat. No. 9,108,348, and entitled “Method for molding a low pressure molded strain relief for coaxial connector interconnection”, which was filed on Oct. 3, 2011, and is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to a strain relief for a Coaxial RF Connector. More specifically, the invention relates to a strain relief moldable about the cable to connector interconnection, providing sealing and strength characteristics which enhance the coaxial connector to coaxial cable interconnection. 
     Description of Related Art 
     Coaxial cables and coaxial connectors are used, for example, in communication systems requiring a high level of precision and reliability. To create a cost efficient electro-mechanical interconnection between the coaxial cable and the coaxial connector, it is often desirable to interconnect the cable and connector via soldering. 
     Solder pre-forms may be utilized to improve interconnection quality when soldering coaxial connectors to coaxial cables. The use of a solder pre-form standardizes the location and amount of solder applied. Representative of this technology is commonly owned U.S. Pat. No. 5,802,710 issued Sep. 8, 1998 to Bufanda et al (Bufanda). Bufanda discloses a solder pre-form with a planar connector side (outer surface) and a cable side (inner surface) dimensioned to key with corrugations of an annular corrugated outer conductor. 
     Other solder pre-forms, for example for soldering a coaxial connector with a smooth sidewall outer conductor coaxial cable, have been provided as a plurality of annular rings and/or a cylindrical tube. For ease of assembly prior to soldering, the solder pre-forms typically fit loosely within a desired interconnection area solder cavity formed between the connector body and the outer conductor. 
     Connector to cable interconnection soldering is typically performed with the connector and coaxial cable vertically oriented, for example as disclosed in U.S. Pat. No. 7,900,344 issued Mar. 8, 2011 to Ng, et al. Thereby, when heat is applied to the solder pre-form during the solder process, the solder liquefies and pools in the bottom of the interconnection area solder cavity. The solder pooling leaves an annular solder pre-form cavity between the outer conductor and the connector body that extends to the cable end of the connector body. 
     Coaxial cables may utilize aluminum material, for example to realize a cost of materials and/or weight savings advantage. However, use of aluminum may also introduce the disadvantages of reduced strength and/or bending resilience. Aluminum material exposed to air quickly oxidizes, forming an aluminum oxide coating that interferes with solder bonding. Special aluminum material specific soldering flux with a heat activated high acid content may be used to prepare aluminum material surfaces for soldering. However, such flux may be difficult to apply evenly within the interconnection area. 
     Heat shrink tubing has been utilized as a cosmetic and/or strain relief improvement for connector to coaxial cable terminations. However, heat shrink tubing may provide only a limited environmental seal that may allow moisture ingress/condensation which then pools under the heat shrink tubing, directly upon the interconnection. 
     Therefore, it is an object of the invention to provide an apparatus and method of manufacture that overcomes deficiencies in such prior art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
         FIG. 1  is a schematic partial cut-away view of a coaxial connector to coaxial cable solder interconnection. 
         FIG. 2  is a schematic partial cut-away side view of the coaxial connector to coaxial cable solder interconnection of  FIG. 1  with an exemplary strain relief applied. 
         FIG. 3  is a schematic isometric view of  FIG. 2 , with a partial cut-away portion to clarify details of the strain relief. 
         FIG. 4  is a close-up of area A of  FIG. 3 . 
         FIG. 5  is a schematic isometric cut-away end view of the coaxial connector to coaxial cable solder interconnection of  FIG. 2 , demonstrating a partial cross section of the interconnection area, with the connector body removed for clarity of understanding potential cavity and/or channel defects of the solder joint. 
         FIG. 6  is a schematic isometric view of the connector body of the coaxial connector of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The inventor has recognized that solder interconnections between coaxial connectors and coaxial cables, particularly where coaxial cables with aluminum material outer conductors are utilized, may have significant strength deficiencies due to the relative strength and resilience of aluminum outer conductors compared to the prior copper material outer conductors. Further, because the specialized flux used in preparation for soldering aluminum material is difficult to smoothly apply, an excess of flux may be applied resulting in flux residue at the completion of the solder operation that then requires additional steps to remove, where possible. 
     The residue of flux may be merged within the solder joint in the form of channels and/or cavities, making removal of all flux residue, particularly from the immediate area of the solder joint, impractical and/or impossible. The inventor has further recognized that this flux may also be hygroscopic and increasingly corrosive as water is absorbed. 
     The inventor has created a strain relief for coaxial connectors which improves both the overall strength of the joint and the seal sealing properties of the strain relief upon the interconnection. 
     As shown in  FIG. 1 , an interconnection between a coaxial connector  1  and a coaxial cable  3  utilizes a solder joint  2  between the outer diameter of the outer conductor  4  and an inner diameter of an interconnection area  6  of the bore  8  of a connector body  10 . A dielectric disc  12  may be applied to close the connector end of the interconnection area  6 , thereby reducing the chance of molten solder egress from the connection area  6 . As the solder pre-form melts and pools, an annular pre-form cavity  14  is formed between the resulting solder joint  2 , inner diameter of the bore  8 , outer diameter of the outer conductor  4  and a cable end of the connector body  10 . 
     A strain relief  16  for the coaxial cable and coaxial connector interconnection may be formed by injection molding a polymer material to surround the interconnection with at least one contiguous polymer portion  18 , for example as shown in  FIG. 2 . 
     The polymer material may be a thermoplastic material suitable for low temperature, low pressure injection molding, with resilient characteristics that is ultra-violet resistant and weatherproof. A suitable polymer material is polyamide; an exemplary polyamide material is Macromelt® OM 648, available from Henkel AG &amp; Co. KGaA of Dusseldorf, Germany. 
     Low pressure injection molding provides suitable cavity penetration, without otherwise damaging the existing coaxial cable and/or interconnection. A preferred pressure range for the low pressure injection molding is between 5 and 40 bar. Similarly, the heat of the injection molding should be low enough to avoid softening the solder joint, damaging the polymer insulation and/or outer jacket  20  of the coaxial cable  3 . A preferred temperature range of the injection molding is between 200 and 240 degrees Celsius. 
     The liquid injection of the polymer material during the low pressure injection molding fills the pre-form cavity  14 , and seals against the connector body  10  and outer jacket  20 , encapsulating any remaining flux and/or further filing any voids, channels  21  and/or cavities  23  that may be present in the solder joint, for example as shown in  FIGS. 3-5 . Thereby, the solder joint  2  and any flux residue is entirely encapsulated from moisture ingress that may corrode the metal surfaces and/or react with the flux residue to initiate accelerated corrosion of the metal surfaces and/or solder joint. 
     As best shown in  FIG. 2 , the strain relief  16  may be shaped to a desired coverage area, thickness and/or external surface configuration by the mold that is applied around the interconnection during the injection molding. 
     The strain relief  16  may be anchored upon a strain relief portion  22  of the connector body  10  of the coaxial connector  1 . The strain relief portion  22  may be provided with a plurality of retention features, such as grooves, protrusions or the like. As best shown in  FIG. 6 , where the retention features are non-cylindrical, such as raised segments  24 , an anti-rotation characteristic is provided which further increases the seal and/or retention of the strain relief  16  upon the strain relief portion  22 . The strain relief portion  22  may be provided adjacent to a tool face portion  26  of the connector body provided with tool faces for receiving a hand tool or the like to hold the connector stationary as a coupling nut is threaded during interconnection of the connector with another connector and/or device. One skilled in the art will appreciate that where the raised segments  24  and tool face portion  26  are applied with a common geometry, anti-rotation benefits of the raised segments  24  are realized and machining of the connector body  10  may be simplified. 
     The strain relief  16  may have a cable portion  28  extending over the coaxial cable  3  which tapers toward the cable end, providing reinforcement to the interconnection which also tapers, such that the reinforcement provided by the strain relief  16  does not abruptly terminate at a rigid edge where the coaxial cable  3  would likely buckle if subjected to excess bending forces near the interconnection. 
     A cable portion  28  of the strain relief  16  may extend away from the interconnection over the coaxial cable  3  a significant length, such as a distance greater than three diameters of the coaxial cable  3 . 
     In addition to and/or instead of a taper applied to the cable portion  28 , the cable portion  28  may be provided with a plurality of stress relief grooves  30 . The stress relief grooves  30  may be applied as generally elliptical grooves with a major axis of the stress relief grooves  30  arranged normal to a longitudinal axis of the coaxial connector  3 . A spacing, width and/or depth of the stress relief grooves  30  may be adjusted to progressively reduce a bending resistance toward the cable end, further enhancing a tapered support characteristic, which while significantly increasing the strength of the interconnection, also protects the coaxial cable  3  from buckling proximate the end of the strain relief  16  due to any excess bending forces that may be applied, thereby increasing both the overall strength and the flexibility characteristics of the interconnection. 
     One skilled in the art will appreciate that a strain relief  16  according to the invention may improve connector body to outer conductor interconnection strength and environmental seal. Thereby, prior concerns of flux residue contributing to accelerated degradation of the interconnection quality and/or environmental sealing of a solder joint  2  that may contain cavities and/or channels are reduced, especially where aluminum materials are being utilized. Thereby, the further adoption of aluminum material use in the coaxial connector and/or coaxial cable arts is enabled, which in turn may enable significant material cost savings for connector and coaxial cable manufacturers. 
     
       
         
           
               
             
               
                   
               
               
                 Table of Parts 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 1 
                 coaxial connector 
               
               
                 2 
                 solder joint 
               
               
                 3 
                 coaxial cable 
               
               
                 4 
                 outer conductor 
               
               
                 6 
                 interconnection area 
               
               
                 8 
                 bore 
               
               
                 10 
                 connector body 
               
               
                 12 
                 dielectric disc 
               
               
                 14 
                 pre-form cavity 
               
               
                 16 
                 strain relief 
               
               
                 18 
                 polymer portion 
               
               
                 20 
                 outer jacket 
               
               
                 21 
                 channel 
               
               
                 22 
                 strain relief portion 
               
               
                 23 
                 cavities 
               
               
                 24 
                 raised segment 
               
               
                 26 
                 tool face portion 
               
               
                 28 
                 cable portion 
               
               
                 30 
                 stress relief groove 
               
               
                   
               
            
           
         
       
     
     Where in the foregoing description reference has been made to ratios, integers or components having known equivalents then such equivalents are herein incorporated as if individually set forth. 
     While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus, methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of applicant&#39;s general inventive concept. Further, it is to be appreciated that improvements and/or modifications may be made thereto without departing from the scope or spirit of the present invention as defined by the following claims.