Abstract:
In one aspect, the present invention provides an electrical connector having a center conductor and means for preventing displacement of the center conductor, which displacement typically occurs in conventional connectors when the connector is heated and then cooled.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to electrical connectors. In some aspects, the present invention relates to electrical connectors having an inner or “center” conductor (i.e., a conductor surrounded by a dielectric and housed within a connector housing).  
         [0003]     2. Discussion of the Background  
         [0004]     In conventional electrical connectors having a center conductor, a dielectric (e.g., a polymer or other dielectric) mechanically supports the center conductor within a connector housing. A challenge to designers is how to design the connector to maintain critical interface dimensions and conductor path integrity during printed-circuit-board (PCB) wave solder and reflow, where temperatures can exceed 260 degrees Celsius.  
         [0005]     During this extreme heating that occurs during the process of connecting the connector to a printed-circuit-board (PCB), both the dielectric and connector housing expand. However, the dielectric typically expands at a rate significantly greater than the housing resulting in applied mechanical stresses on the conductor as well as changes in the final location of a contact socket interface after heating. The goal of any designer is to mitigate applied mechanical forces during the high temperature excursion and to hold within tolerance all critical contact and interface dimensions.  
         [0006]     As a specific example, consider an electrical connector having a brass housing, a Teflon® member housed within the brass housing, and a center conductor supported and surrounded by the Teflon member. The coefficient of thermal expansion (CTE) of Teflon is 122 μin/° F. and that of C160 brass is 11.1 μin/° F. Since the CTE of Teflon in the temperature range to which the connector will be subjected is an order of magnitude greater than that of the brass body that encapsulate it, there is a danger that the stresses induced by the expanding and contracting Teflon member will move the center conductor out of the desired position (i.e., displace the center conductor).  
         [0007]     In fact, after temperature cycling, the center conductor may translate toward the front of the connector resulting in a significant dimensional change at the mating interface (about 0.020 in). This shifting of the contact also appears to generate stresses on the solder joint, which can cause the rear contact, which is normally perpendicular to the plane of the PC board, to lean at an angle of between 1 and 1.5° of normal.  
         [0008]     The conductor displacement problem is exacerbated when lead-free solder is used as PCB connection means because using lead-free solder requires exposing the connector to a higher temperature during the solder reflow process, and exposing the connector to a higher temperature causes greater expansion of the dielectric member, which leads to a more noticeable displacement of the inner conductor.  
         [0009]     What is desired, therefore, is an electrical connector that does not suffer the above-described conductor displacement problem.  
       SUMMARY OF THE INVENTION  
       [0010]     It was discovered that the above described conductor displacement problem is particularly noticeable when an end of the dielectric body abuts a wall during assembly and the heating process. When subjected to high heat, the dielectric body moves away from this immovable surface, taking the center contact with it. As the connector cools, the dielectric body contracts symmetrically. The net affect is a translation of the center contact away from the wall equal to one-half the axial expansion of the dielectric body, and an air gap between the wall and the end of the body also equal to one-half the axial expansion of the body.  
         [0011]     Accordingly, the present invention provides an electrical connector having a center conductor and means for helping prevent displacement of the center conductor during a solder reflow process.  
         [0012]     In one embodiment, instead of positioning the dielectric body so that its end abuts the wall, the body is positioned so that a gap exists between the wall and the end of the body.  
         [0013]     In the same or another embodiment, a securing means for securing the dielectric body within the housing is used. The securing means may include a rib projecting outwardly from the dielectric body and a corresponding groove in the housing for receiving the rib. The securing means may also include one or more fasteners.  
         [0014]     The above and other features and advantages of the present invention, as well as the structure and operation of preferred embodiments of the present invention, are described in detail below with reference to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The accompanying drawings, which are incorporated herein and form part of the specification, help illustrate various embodiments of the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. In the drawings, like reference numbers indicate identical or functionally similar elements.  
         [0016]      FIG. 1  is a cross-sectional, side view of a connector according to an embodiment of the invention.  
         [0017]      FIG. 2  is a cross-sectional, side view of a connector according to another embodiment of the invention.  
         [0018]      FIGS. 3 and 4  are cross-sectional, side views of a connector according to another embodiment of the invention.  
         [0019]      FIG. 5  is a flow chart illustrating a process according to an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0020]     Referring now to  FIG. 1 ,  FIG. 1  is a cross-sectional, side view of a connector according to an embodiment of the invention. As shown in  FIG. 1 , connector  100  includes a housing  102  having a cavity  111  and a dielectric body  104  and a conductor or “contact”  106  housed in cavity  111  of housing  102 . More specifically, dielectric body  104  supports and electrically insulates conductor  106  from housing  102 . Housing  102  and conductor  106  may be made from brass and/or other electrically conducting material, and dielectric body  104  may comprise Teflon® and/or other dielectric materials.  
         [0021]     As further shown in  FIG. 1 , conductor  106  has a first end section  152 , a second end section  154  and an interim section  156 . Interim section  156  of conductor  106  is embedded within dielectric body  104 , while end sections  152  and  154  are not disposed within dielectric body  104 .  
         [0022]     As further shown in  FIG. 1 , connector  100  includes features that when used together or alone help prevent conductor  106  from being displaced during heating and subsequent cooling of connector  102 . For example, dielectric body  104  has a male member  130  projecting from a top surface thereof (male member  130  is referred to herein as “rib  130 ”) and body  102  has a corresponding female groove  132  for receiving rib  130 . Rib  130  may be machined into dielectric body  104  or otherwise attached thereto. Groove  132  is formed in the inner surface of housing  102 . In this embodiment, the location of rib  130  on dielectric body  104  is preferably at or near a first end  181  of dielectric body  104 . Rib  130  and groove  132  function to secure body  104  within cavity  111 .  
         [0023]     During assembly, dielectric body  104  is positioned such that rib  130  is located securely in groove  132 . Preferably, dielectric body  104  is positioned such that a gap  160  exists between a second end  182  of dielectric body  104  and a wall  170  of housing  102  that faces the second end  182  of dielectric body  104 . Wall  170  projects inwardly from the inner surface of housing  102 . Preferably, wall  170  is generally perpendicular to the inner surface of housing  102 . The length (L) of gap  160  is preferably about equal to or greater than the total amount of expected longitudinal expansion of dielectric body  104 . The expected longitudinal expansion of dielectric body  104  (“delta-L”) can be calculated using the following formula: 
 
delta− L =( CTE )( T 2− T 1)( L   i ), 
 
 where CTE is a known constant, T2 is the temperature at which the dielectric will be heated, T1 is the temperature of the dielectric prior to heating (e.g., room temperature) and L i  is the length of the dielectric at temperature T1. 
 
         [0024]     As connector  100  is heated, rib  130  provides a “pivot point.” That is, rib  130  provides a means for retaining the expanding dielectric body  104  and affecting the direction of the expansion of the dielectric body  104 . For example, rib  130  forces dielectric body  104  to expand longitudinally into gap  160 , since most of the expanding mass of dielectric body  104  is located between gap  160  and rib  130 . Further, as dielectric body  104  cools, rib  130  provides a point around which dielectric body  104  contracts, allowing dielectric body  104  and the embedded conductor  106  to return, as nearly as possible, to their initial position. In this manner, conductor  106  will not be displaced due to the expansion and contraction of body  104  due to the heating and subsequent cooling of connector  100 .  
         [0025]     As shown in  FIG. 1 , interim section  156  of conductor  106  may have a retention barb  192  on a surface thereof, which barb  192  functions to limit longitudinal movement of conductor in a direction away from wall  170 .  
         [0026]     Referring now to  FIG. 2 ,  FIG. 2  is a cross-sectional, side view of a connector  200  according to another embodiment of the invention. In the embodiment shown in  FIG. 2 , rib  130  is located generally midway between ends  181  and  182 .  
         [0027]     Preferably, contact  106  is designed such that when contact  106  is fully seated, retention barb  192  is concentric to the rib  130 ; i.e., barb  192  is in the same longitudinal position as rib  130  at assembly. The design intent is to affix dielectric body  104  such that, even during heating and cooling, it maintains its longitudinal position in the body. Expansion and contraction are allowed to take place symmetrically about rib  130  thus insuring that contact  106  undergoes no translations that might induce stress to the solder joint or otherwise affect the reference (mating) surfaces.  
         [0028]     Referring now to  FIG. 3 ,  FIG. 3  is a cross-sectional, side view of a connector  300  according to another embodiment of the invention. Connector  300  is similar to connectors  200  and  100 , with an exception that rib(s)  130  and groove(s)  132  are replaced with fasteners  301   a  and  301   b . In the embodiment shown, fasteners  301  are both placed at or near end  181  of dielectric body  104 . However, it is contemplated that, like the connector shown in  FIG. 2 , fasteners  301  may be located at a point midway between ends  181  and  182  of body  104 . Fasteners  301  provide the same functionality as the rib and groove combination. That is, fasteners help prevent conductor  106  from moving out of its initial position when body  104  expands and contracts due to heating and then subsequent cooling. Like ribs  130  and grooves  132 , fasteners  301  provide the “pivot point” functionality described above.  
         [0029]     Preferably, fasteners  301  are moveable from a first position to a second position. Placing fasteners  301  in the first position, which position is illustrated in  FIG. 3 , facilitates positioning body  104  within cavity  111  of housing  102 . Placing fasteners  301  in the second position, which position is illustrated in  FIG. 4 , facilitates fastening body  104  within cavity  111  of housing  102 . As illustrated in  FIG. 4 , fasteners  301  may be in the shape of a pin and may penetrate body  104  when moved from the first position to the second position. While only two fasteners  301  are shown, a housing  102  have more than two fasteners  301  is contemplated.  
         [0030]     Referring now to  FIG. 5 ,  FIG. 5  is a flow chart illustrating a process  500  according to an embodiment of the invention. Process  500  may begin in step  502 , where a connector housing, like housing  102 , is obtained. In step  504 , a dielectric body is obtained (e.g., dielectric body  104 ). The dielectric body surrounds an interim portion of a contact (e.g., contact  106 ).  
         [0031]     In step  506 , an expected longitudinal expansion of the dielectric body when the body is heated at a pre-determined temperature for a pre-determined amount of time is determined. The pre-determined temperature generally ranges between 150 and 300 degrees Celsius and the pre-determined amount of time generally ranges between ten seconds and ten minutes.  
         [0032]     In step  508 , dielectric body  104 , which houses the contact  106 , is placed in cavity  111  formed by a wall or walls of housing  102 . As discussed above, body  104  may be positioned in cavity  111  so that a gap  160  exists between end  182  and wall  170 . Preferably, the length (L) of gap  160  is about equal to or greater than the determined expected longitudinal expansion of body  104 .  
         [0033]     In step  510 , dielectric body  104  is secured within cavity  111 . Body  104  may be secured by fitting rib  130  into groove  132 , as shown in  FIGS. 1 and 2  or by moving fasteners  301  from the first position to the second position, as described above with respect to  FIGS. 3 and 4 .  
         [0034]     In step  512 , the assembly is heated at a temperature between about 150 and 300 degrees Celsius for an amount of time between about ten seconds and ten minutes.  
         [0035]     While various embodiments/variations of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. For example, depending on the specific requirements of a particular connector design, features of one or both of the above described embodiments may be employed to null the affects of dielectric expansion/shrinkage during heating.  
         [0036]     Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.