Patent Publication Number: US-7713067-B1

Title: Connector with a conductive shell with an extension to stradle a circuit board

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to connectors having a conductive shell and a center contact, and in particular, to connectors that are mounted on a circuit board. 
     2. Description of Related Art 
     Some connectors are designed to mount on circuit boards. These connectors are often soldered in place on the board. In many cases the connector will have a metal shell with a coaxial metal contact. The distal end of the connector may also have a male (female) fitting that is externally (internally) threaded to accept a mating threaded connector at the end of a cable. Instead of threads, other connectors may have a bayonet fitting, friction fitting, etc. 
     Connectors must deal with advancing technology that has allowed electronic equipment to handle much higher frequencies. Great advances have been achieved in digital electronics with ever faster clock rates and pulse rise times. With the advent of high-definition television, higher frequency demands have become routine. 
     In such a high-frequency environment, transferring signals between a cable and a circuit board is more demanding. To transfer electromagnetic energy efficiently, discontinuities ought to be avoided at the connection between the cable and circuit board. For example, cables such as coaxial cables have a characteristic impedance and should be terminated into a matching impedance to avoid reflections. Also, the geometry of the transition should be a designed carefully to avoid irregularities that can cause reflections as well. In addition, one must take into account the dielectric coefficient of intervening elements, including the dielectric coefficient of relevant volumes of air. 
     The geometry of the connector can determine whether there are discontinuities or other mismatching effects. This geometry is especially important since high-frequency connectors often include metal components and these metal bodies can have capacitive and inductive effects. The undesired presence of such capacitance and inductance may produce a mismatch that can adversely affect the transfer efficiency of the connector. 
     While high-frequency connectors ought to work well under these demanding conditions, their structure should also be simple, rugged and dependable. Further-more, and assembler should be able to easily and reliably install the connector on a circuit board. 
     See also U.S. Pat. Nos. 5,404,117; 5,823,790; 5,897,384; 6,106,304; 6,254,399; 6,407,652; 6,457,979; 6,682,354; 6,791,317; 6,811,405; 6,957,980; 7,042,318; 7,048,547; and 7,344,381, as well as U.S. Patent Application Publication Nos. 2004/0038587; 2008/0045043; and 2008/0102654. 
     SUMMARY OF THE INVENTION 
     In accordance with the illustrative embodiments demonstrating features and advantages of the present invention, there is provided a connector adapted for edge mounting on a circuit board. The connector includes a conductive shell having a proximal end with an extension adapted to extend proximally and attach to the circuit board. Also included is at least one insulating spacer mounted in the shell. The connector also has a center contact mounted in the at least one insulating spacer. This center contact and the extension are spaced to straddle the circuit board. The extension is disposed along most of its length entirely to the outside of a reference plane that is parallel to and spaced from the center contact. The extension for most of its length extends proximally beyond any portion of the shell located to the inside of the reference plane. 
     In accordance with another aspect of the invention, there is provided a connector adapted for edge mounting on a circuit board. The connector includes a conductive shell having a proximal end with an extension adapted to extend proximally and attach to the circuit board. Also included is at least one insulating spacer mounted in the shell. The connector also has a center contact mounted in the at least one insulating spacer. The center contact and the extension are spaced to straddle the circuit board. The connector has a sleeve lining the shell and polished to avoid reflections of electromagnetic energy passing through the shell. 
     In accordance with yet another aspect of the invention, a method employing a conductive shell is provided for connecting to a circuit board. The method includes the step of internally polishing a sleeve to avoid reflection of electromagnetic energy. Another step is fitting the sleeve inside the conductive shell. 
     In accordance with still yet another aspect of the invention, a method employing a conductive shell with a proximally extending extension is provided for connecting to a circuit board. The method includes the step of attaching a C-shaped clip to the outside of said extension. Another step is pressing the C-shaped clip into holes on the circuit board while compressing the clip to squeeze the extension. 
     By employing apparatus and methods of the foregoing type an improved connection can be achieved. In a disclosed embodiment a conductive shell contains a coaxial contact mounted in a spaced pair of insulating discs. At least one of these discs has a hollowed inside face that increases the volume of the air dielectric inside the shell in order to enhance the connector characteristics. 
     To avoid discontinuities, the inside of the disclosed conductive shell is fitted with a polished sleeve. By finely polishing the inside of this sleeve very little electromagnetic energy will be reflected due to internal irregularities. 
     The proximal end of this disclosed connector has an extension designed to attach the connector to a circuit board. The tip of this extension has an external groove for receiving a C-shaped clip. The free ends of this clip can have a bend, or bight, and are designed to clip into complementary holes on the circuit board. The free ends of the clip are slightly pressed together, which tends to squeeze the clip more securely into the external groove on the extension. Secured in this manner, the circuit board may lay on the extension and reach into an optional notch located at the root of the extension. 
     Accordingly, the extension will embrace the circuit board on one side, while the opposite side will fit under the coaxial contact that is projecting from the proximal end of the conductive shell. In a disclosed embodiment this coaxial (center) contact will project only a small distance upon the circuit board to avoid unnecessary capacitance and discontinuities. Also, the conductive shell does not extend significantly over the side of the circuit board that receives the center contact, again to avoid discontinuities and undesired capacitive effects. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above brief description as well as other objects, features and advantages of the present invention will be more fully appreciated by reference to the following detailed description of illustrative embodiments in accordance with the present invention when taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a longitudinal sectional view of a connector in accordance with principles of the present invention; 
         FIG. 2  is an axial view of the proximal end of the connector of  FIG. 1 ; 
         FIG. 3  is a perspective view of the connector of  FIG. 1  with a distal portion broken away for illustrative purposes; 
         FIG. 4A  is a top plan view of a circuit board adapted to receive the connector of  FIG. 1 ; 
         FIG. 4B  is a bottom plan view of the circuit board of  FIG. 4A ; 
         FIG. 5A  is a top plan view of the connector of  FIG. 1  installed on the circuit board of  FIG. 4A ; 
         FIG. 5B  is a bottom plan view of the connector and board of  FIG. 5A ; and 
         FIG. 6  is a top plan view of the circuit board of  FIG. 4A  fitted with a connector that is an alternate to that of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIGS. 1-3 , the illustrated connector has a conductive shell  10  in the form of a hollow cylinder with external threads  10 A located to the distal side of a low flange  10 B at the proximal end of the shell. In one embodiment threaded portion  10 A can have an overall outside diameter of 7/16 inch with 28 threads per inch (e.g., 7/16 28 UNEF  2 A), although other types of threading can be used in different embodiments. Shell  10  has at its distal end an inwardly projecting lip  10 C. 
     An integral pair of bars  14  extend proximately from flange  10 B to integral crosspiece  16  to form a hole  18 . Components  14  and  16  are herein referred to as a proximally extending extension with crosspiece  16  considered the remote tip of the extension. Crosspiece  16  has an axially spaced pair of parallel, flat transverse surfaces. The two other surfaces of crosspiece  16  are sections of a cylinder that are concentric with shell  10  with one facing radially inward and the other radially outward. Bars  14  each have a pair of parallel faces and two other faces that are also sections of a cylinder concentric with shell  10 , with one facing radially inward and the other facing radially outward. The portions of bars  14  adjacent to flange  10 B are referred to as the root support of the bars. 
     The flat inside faces  14 A of bars  14  are coplanar and define a reference plane indicated in  FIGS. 1 and 2  by reference line R-R. Extension  14 / 16  is located to the outside of reference plane R-R. Portions of shell  10  to the inside of reference plane R-R are herein referred to as the superior portion of the shell. 
     In one embodiment shell  10  and extension  14 / 16  are integral and are made of brass plated with nickel or tin (or some other tri-metal plating). 
     C-shaped clip  20  is pressed into an external arcuate groove running 120° on the outside cylindrical surface of crosspiece  16 . The exposed legs of clip  20  are bent into a Z-shaped configuration and each have a bight  20 A. In this embodiment clip  20  is made of a spring-type brass plated with tin, although different materials may be used in other embodiments. 
     Distal insulating spacer  24  is pressed into shell  10  to abut lip  10 C. Spacer  24  has an annular inside recess between rim  24 A and cylindrical hub  24 B. The floor of hub  24 B is pierced by a concentric circular hole  24 C whose outward portions flare, funnel-like. In one embodiment spacer  24  is made of Teflon™ material (polytetrafluoroethylene), although other materials may be used in different embodiments. 
     Cylindrical sleeve  22  is pressed into shell  10  with its distal end pressed, against rim  24 A of spacer  24  and with its proximal end flush with annular ledge  10 D of shell  10 . Sleeve  22  has at its proximal end an annular ridge  22 A that fits into the illustrated, matching annular recess on the inside of shell  10 . 
     The inside of sleeve  22  is polished to avoid discontinuities and reflections that can adversely affect the passage of electromagnetic energy through the sleeve. In this embodiment the inside of sleeve  22  is initially polished by pneumatically blasting through it a liquid abrasive; for example, tin oxide or aluminum oxide particles suspended in a liquid carrier. Thereafter, sleeve  22  can be internally polished with a soft, felt-like tube carrying a fine abrasive such as jeweler&#39;s rouge. Sleeve  22  can be readily polished in this fashion because, it lacks structure such as the large lip  10 C and extension  14 / 16  on shell  10 , which would interfere with the polishing process. Sleeve  22  can be made of a base material and plating similar to shell  10 , although in some embodiments different materials may be used depending upon the sleeve&#39;s desired strength, ease of polishing, electrical characteristics, etc. 
     The proximal end of sleeve  22  is fitted with a proximal insulating spacer  26 , shown as a washer-like device with a shoulder abutting internal ridge  22 B of sleeve  22 . In one embodiment spacer  26  is made of Teflon™ material, although other materials may be used in different embodiments. Center contact  28  has a cylindrical midsection and a smaller cylindrical pin  28 A pressed through a concentric hole in spacer  26 . Contact  28  may be phosphor-bronze with gold plating, although different materials may be used in other embodiments. 
     Pin  28 A is about 1.0 mm in diameter and extends beyond spacer  26  by about 1.35 mm and beyond flange  10 B by about 0.46 mm (and thus, flange  10 B extends 0.89 mm beyond spacer  26 ), although these dimensions will vary for other embodiments and applications. 
     For example, good results occur by keeping small the distance D that pin  28 A extends beyond the superior portion of shell  10  (i.e., the portion of shell  10  on the pin side of reference plane R-R). The distance D can be kept small in proportion to the overall width W of shell  10 . This width W is measured perpendicular to reference plane R-R at the root support of bars  14  of extension  14 / 16 . At the root support of bars  14  the overall width W is the outside diameter of flange  10 B. Good electrical characteristics can be achieved by keeping the pin extension D at most one tenth the overall width W. Superior electrical characteristics can be achieved by keeping the pin extension D at most one twentieth of the overall width W. 
     A distal portion of contact  28  has a coaxial bore  28 B forming a wall that is quadfurcated to form four flexible contact fingers  28 C that converge at hole  24 C. The tips of fingers  28 C are bevelled on the inside of their distal end to provide a flared opening for guiding an incoming pin into the space between the fingers. Fingers  28 C are shown in their neutral position, which provides clearance around the girth of the fingers relative to the inside surface of hub  24 B. Accordingly, fingers  28 C have clearance allowing them to spread. 
     An aligned pair of notches  30  cut into flange  10 B produce overhangs  28 E parallel to surfaces  14 A. The floor of notches  30  are substantially coplanar with ledges  10 D. 
     Circuit board  32  is shown in phantom in two different positions in  FIG. 1 : (1) an installed position where one side of board  32  lies along reference plane R-R; and (2) a pre-installed position where board  32  is tilted and its primary edge  32 A is inserted at an angle between pin  28 A and surfaces  14 A of bars  14 . In this pre-installed position a leg of clip  20  is shown about to slip into hole  34  in board  32 . It will be appreciated that board  32 , as shown in  FIGS. 4A and 4B  has a pair of holes  34  and that the two legs of clip  20  will simultaneously slip into these holes. To maintain compatibility with earlier or lower performing models of board-mounted connectors, holes  34  will be spaced inboard about 6 mm and separated about 10.2 mm, although other spacings are contemplated for other embodiments. 
     The legs of clip  20  are arranged so that they will compress slightly together upon installation into holes  34 . The converging slant at the tip of these legs accommodates this compression. The compression of the legs of clip  20  tends to tighten the clip inside the external groove around crosspiece  16 . Also, any force tending to separate crosspiece  16  from board  32  will also tend to pull clip  20  more firmly into this groove in the crosspiece thereby making the attachment more secure. 
     When being installed, board  32  rotates about edge  32 A in the direction indicated by arrow D. When Installed, edge  32 A will fit between and will be straddled by pin  28 A and bars  14 . 
     Under undisturbed, neutral conditions, center contact  28  is cantilevered perpendicularly on spacer  26  and the flexible fingers  28 C have clearance within hub  24 B of spacer  24 . It will be noticed that as board  32  is being rotated into position, it will act as a lever with a tendency to disturb the positioning of pin  28 A. To increase the support of contact  28 , the pin P of fixture F may be inserted between the fingers  28 C before installing board  32 . This insertion of pin P will spread fingers  28 C so they engage and receive support from the inside surface of hub  24 B. Also, keeping the cantilevered length of pin  28 A small reduces its effective lever arm and thereby reduces the likelihood of disturbing contact  28  when installing board  32 . 
     After board  32  is locked in place in alignment with extension  14 / 16  and reference plane R-R, pin P is then withdrawn. Improved performance can be achieved by reducing as far as possible any gap between primary edge  32 A and spacer  26 . In any event, board  32  will be held in position securely enough by slip  20  and notch  30  to accommodate surface soldering or reflow soldering. 
     As shown in  FIGS. 5A and 5B  the legs of C-shaped clip  20  pass through holes  34 , which are plated-through holes connecting to two annular conductive lands  34 A on one side, and on the other side to a rectangular conductive plane  34 B. 
     The connector may be soldered in place by filling hole  18  with molten solder ( FIG. 5B ). Filling hole  18  with solder will prevent components  10 B,  16 , and  18  from acting like an inductive loop. Simultaneously, solder will flow around the legs of clip  20  and through holes  34  to firmly attach the clip and thus the extension  14 / 16  to board  32 . 
     Also at this time, solder will flow between pin  28 A and trace  36  on board  32  to make an electrical connection. In some embodiments, trace  36  may descend over the edge  32 A of board  32 . 
     It will be noticed that a relatively small length of pin  28 A extends over the board  32  and trace  36  (1.35 mm in this embodiment). Accordingly, pin  28 A produces little inductive and capacitive effects and allows top mounting on board  32 . Also, connector  10 , including flange  10 B, does not extend significantly onto board  32  (0.89 mm in this embodiment), again to avoid unwanted inductive and capacitive effects. 
     Referring to  FIG. 6 , an alternate connector  110  is shown attached to previously mentioned circuit board  32 . Components in this Figure corresponding to those previously illustrated bear the same reference numerals but raised by 100. In particular, the structure of connector  110  around flange  110 B and to the right (proximal direction) is the same as before and will include the same previously mentioned extension (extension  14 / 16  of  FIG. 1 ) with a clip, shown herein as clip  120  inserted into holes  34 . To the left of flange  110 B (distal direction) the previously described threads (threads  10 A) are placed with a reduced diameter neck  138  having a groove  148 . An internally threaded hex nut  142  has a back collar  142 A with an inward lip (not shown) that fits into groove  140  allowing the nut to rotate 360° and slide axially a small amount. 
     Connector  110  has a central contact with a pin  128 A extending onto trace  36  as before. Also as before, the midsection of the central contact (not shown) is again a solid cylindrical shaft but now its distal end is formed into a slender contact pin  144 , which replaces the previously described flexible fingers (fingers  28 C of  FIG. 1 ). In a manner similar to that previously described in connection with  FIG. 1 , the central contact  128 A/ 144  will be supported inside connector  110  by a spaced pair of insulating spacers (not shown). The threaded connection provided by nut  142  and contact  144  is arranged much like a video-grade coax connector. In fact the connector of  FIG. 6  is the complementary mate to the connector of  FIG. 1 . 
     Referring again to  FIGS. 1-3 , once the illustrated connector has been installed on a circuit board  32  as shown in  FIGS. 5A and 5B , the connector can connect to a coaxial cable; for example, a cable carrying high definition television signals. Threads  10 A can threadably receive a cable fitting that is similar to that shown on the distal end of the connector  FIG. 6 . Such a cable fitting will have a pin and nut similar to pin  144  and nut  142  of  FIG. 6 . This pin will be inserted through hole  24 C and between fingers  28 C, prying them apart. The deflection of fingers  28 C produces a squeezing pressure as well as a wiping action on the incoming pin to establish a good electrical contact. 
     The nut on the cable fitting (see nut  142  of  FIG. 6 ) is then screwed in place to firmly secure the connection. The foregoing is a similar to the operation occurring with conventional RF connectors (e.g., threaded F-type connectors). 
     The separation of fingers  28 C gives the fingers an increased overall outside diameter thereby giving central contact  28  a consistent outside diameter over most of its length in order to reduce discontinuities and signal reflections. This enhances the radiation pattern and impedance characteristics of the connector. Also, the spreading of fingers  28 C bring them in proximity to the inside of hub  24 B to in order to stabilize contact  28  inside spacer  24 . 
     RF signals may now be conveyed through the connector of  FIGS. 1-3  in either direction. This connector has the advantage of being able to handle signals whose frequency content ranges from 0 Hz up to 10 GHz; although for some designs the tolerances and materials will be chosen to handle a maximum frequency to 8 GHz or less. The signals conveyed through the connector can be a modulated high frequency carrier, but in many embodiments the connector will convey digital pulses of short duration and fast rise time. 
     Signals passing through connector shell  10  will be affected by the dielectric constants of spacers  24  and  26 , as well as the dielectric constant of the air between the spacers inside sleeve  22 . It has been determined that better transfer characteristics are achieved with an air dielectric, but spacers  24  and  26  are needed to support central contact  28 . Accordingly, spacer  24  has an annular recess between rim  24 A and hub  24 B that increases the volume of the air dielectric between the two spacers. 
     Some surfaces of the connector may have small imperfections that constitute small discontinuities, but these can still produce a significant cumulative effect when many small imperfections are distributed over a significant distance. It has been discovered that polishing the inside surface of sleeve  22  in shell  10  reduces the cumulative effect of small irregularities and significantly improves the connector&#39;s ability to handle high frequency signals. (In some embodiments that lack a sleeve, the shell itself may be polished.) 
     In the disclosed embodiment the contributions of sleeve  22  are significant because the sleeve represents about 80% of the inside surface of the connector (extension  14 / 16  being excluded). As noted before, sleeve  22  can be finely polished because it lacks large ridges or large extraneous structures that can interfere with the polishing process. 
     Electromagnetic energy conveyed through connector shell  10  or the cable fitting attaching to threads  10 A are confined in a coaxial environment; that is, a conductive cylindrical shell around a slender concentric conductor. This coaxial environment is fairly immune to external interferences (external fields or conductors). Also, stray capacitive and inductive effects are not predominating concerns. 
     However, when transitioning from a coaxial environment to a circuit board, a signal can be significantly affected by external fields, external conductors, and stray capacitive and inductive effects. It has been discovered that these effects are most deleterious when they impinge on the non-grounded circuit traces on the associated circuit board, in this case trace  36  of  FIG. 5A . For this reason, pin  28 A extends over circuit board  32  a relatively short distance, in this embodiment, 1.35 mm. For the same reason, shell  10  and flange  10 B extend over board  32  a relatively short distance, in this embodiment, 0.89 mm. It will also be noted that trace  36  tapers down to a width corresponding to the diameter of pin  28 A in order to reduce transition discontinuities. 
     On the other side of board  32  extension  14 / 16  presents to trace  36  a relatively simple grounded plane whose effects can be anticipated and compensated for, without significant involvement of the bulk represented by the far side of extension  14 / 16 . Thus board  32  and its traces can be designed and tested without undue concern about the effect of any board-mounted connector. 
     It is appreciated that various modifications may be implemented with respect to the above described embodiments. For example, in some embodiments the illustrated extension maybe a solid block that is a portion of a cylinder, parallelepiped, ovoid, etc. Also, the legs of the clip may be straight, have a simpler bowed shape, have a non-uniform cross-section, etc. Instead of two spacers, other embodiments can have one spacer or more than two spacers. Also, every spacer may have a recess to increase the air dielectric. Furthermore, the various dimensions can be altered to accommodate different power ratings, strength requirements, temperature stability considerations, etc. In addition, the connector may have optional hardware for panel mounting, surface mounting, etc. 
     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.