Patent Publication Number: US-6699054-B1

Title: Float mount coaxial connector

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a low profile surface mount coaxial connector that permits both axial and radial float relative to a mating connector. 
     2. Description of the Related Art 
     A coaxial cable includes an inner conductor and an outer conductor that surrounds the inner conductor. Insulating or dielectric material typically is disposed between the inner and outer conductors to maintain the substantially concentric relationship therebetween. The inner conductor is used for carrying a signal, and the outer conductor functions as a shield. Thus, the signal carried by the inner conductor will not affect nearby electronic equipment, and conversely nearby electronic equipment will not adversely affect the signal carried by the inner conductor. 
     A coaxial connector may be mounted to an end of a coaxial cable so that the conductors of the cable can be connected to another coaxial cable, to an apparatus or to a circuit board. The coaxial connector includes a center contact that is connected to the inner conductor of the cable and an outer contact that is connected to the outer conductor of the cable. An insulation or dielectric material may be disposed between the inner and outer contacts to maintain a substantially coaxial relationship. Coaxial connectors typically are provided as a male and female pair of connectors configured so that the inner and outer contacts of one connector in the pair telescope into electrical contact with the inner and outer contacts of the mating connector. 
     Connections often must be made between one or more coaxial connectors on one panel or circuit board and a corresponding number of coaxial connectors on another panel or circuit board. These connections typically are made by placing the panels or circuit boards in opposed relationship to one another so that the connectors on one panel or circuit board face the connectors on the opposed panel or circuit board. The panels and circuit boards then are moved toward one another so that the respective connectors mate. The ability to mate the opposed pairs of panel-mounted or board-mounted electrical connectors in this manner depends partly upon the precision of mounting the connectors on the panels or boards. Even small mounting errors can significantly complicate the connection and can significantly increase the forces required to achieve proper mating. Excessive force on either panel or board can damage the panel or board and the circuits thereon. Accordingly, some coaxial connectors are configured to float transversely and/or radially relative to the panel or circuit board to facilitate alignment for mating. Coaxial connectors that are configured to float relative to the panel or circuit board are shown in U.S. Pat. Nos. 4,358,174 and 5,769,652. 
     There have been substantial efforts in recent years to reduce the size of electrical and electronic components. The electronics industry also is very competitive and continually seeks ways to reduce costs. The above-described U.S. Pat. No. 4,358,174 and much of the other prior art achieves a panel-to-panel connection by providing separate mateable connectors on each panel and then urging the mateable connectors into connection with one another. Significant size and cost savings have been achieved in some electrical connection art areas by employing surface mounting (e.g., surface mounted IC chips). A surface mount connector enables a connector on one panel to be connected directly to conductive regions on a mating panel. The known surface mount technology is not well suited for coaxial connectors in view of the need to provide shielding across the connection. A few attempts have been made to mount a small coaxial receptacle to conductive regions on a board and then to mate a coaxial plug with the receptacle. Such a connection is shown in U.S. Pat. No. 5,662,480. The above-described alignment problems that exist for panel-to-panel connections of coaxial connectors also exist for surface mounted connections. 
     In view of the above, it is an object of the subject invention to provide a coaxial connector assembly that enables axial and/or radial float for achieving panel-to-panel coaxial connections. 
     It is also an object of the subject invention to provide a low profile coaxial connector that is well suited for panel-to-panel connections. 
     SUMMARY OF THE INVENTION 
     The subject invention relates to a coaxial connector for achieving connection between signal carrying circuits on first and second opposed circuit boards and for achieving a grounding connection and shielding between the first and second circuit boards. The first circuit board is provided with a plurality of conductive regions printed or otherwise disposed thereon. The conductive regions on the first circuit board include a first signal carrying region and a first ground that may substantially concentrically surround at least a portion of the signal carrying region. Similarly, the second circuit board may be provided with a plurality of conductive regions printed or otherwise disposed thereon. The conductive regions on the second circuit board may include a second signal carrying region and a second ground that may at least partly surround the signal carrying region. The signal carrying regions and the ground regions on the respective circuit boards are connected to other signal carrying circuit elements and ground circuit elements by techniques that are known to those skilled in this art. 
     The coaxial connector may be used with a short cylindrical electrically conductive guide sleeve that has a mounting end, a mating end and an inner circumferential surface extending between the ends. The mounting end of the guide sleeve is secured to the first circuit board and is connected electrically to the first ground region on the first circuit board. Additionally, the guide sleeve is mounted substantially concentrically around the first signal carrying region on the first circuit board. The inner circumferential surface of the guide sleeve may be substantially cylindrical at locations adjacent the mounting end of the guide sleeve. However, the inner circumferential surface of the guide sleeve may be chamfered to define an outward taper adjacent the mating end. 
     The coaxial connector includes an outer contact assembly with a generally tubular base. The base has a mounting end, a mating end and an inner circumferential surface extending between the ends. The mounting end of the base is fixed to the second circuit board and is connected electrically to the second ground. The mating end of the base may be characterized by an inwardly extending flange with an inside diameter less than the inside diameter of the inner circumferential surface of the base at locations spaced from the flange. 
     The outer contact assembly further includes a floating outer contact with a mounting end, a mating end and inner and outer circumferential surfaces extending between the ends. The floating outer contact preferably includes an outwardly extending flange at the mounting end. The outwardly extending flange of the floating outer contact is disposed between the second circuit board and the flange at the mating end of the base of the outer contact assembly. The flange at the mounting end of the floating outer contact defines an outside diameter that is greater than the inside diameter of the flange at the mating end of the base of the outer contact assembly. However, the outer diameter of the flange at the mounting end of the floating outer contact is less than the inside diameter of the inner circumferential surface of the base at locations adjacent the flange. The outside diameter of the floating outer contact at locations adjacent the flange are less than the inside diameter of the flange at the mating end of the base. Thus, the floating outer contact can float both radially and axially relative to the base of the outer contact assembly, but cannot be separated from the base of the outer contact assembly. 
     The mating end of the floating outer contact may have an inwardly extending flange. However, portions of the inner circumferential surface of the floating outer contact between the inwardly extending flange and the mating end preferably are substantially continuously cylindrical. The outer circumferential surface of the floating outer contact preferably is chamfered adjacent the mating end to facilitate alignment and to generate float during mating. 
     Portions of the floating outer contact between the mating end and the base of the outer contact assembly may include an outwardly extending bearing flange. The bearing flange defines an outside diameter that exceeds the inside diameter of the inwardly extending flange on the base of the outer contact assembly. 
     The outer contact assembly further may include also a spring between the inwardly extending flange of the base and the outwardly extending flange at the mounting end of the floating outer contact. The spring may be configured to urge the floating outer contact towards the second circuit board. The outer contact assembly may further include a spring between the bearing flange of the floating outer contact and the inwardly extending flange of the base of the outer contact assembly. The spring washer biases the floating outer contact away from the second circuit board. 
     The coaxial connector further includes an inner contact assembly that is disposed substantially concentrically within the outer contact assembly and that extends from the second circuit board substantially to the mating end of the floating outer contact. The inner contact assembly includes a plunger and a receptacle that are capable of axially floating relative to one another while achieving a sliding electrical contact therebetween. In a preferred embodiment, the plunger extends from the second circuit board, and the receptacle extends from the plunger to the mating end of the floating outer contact. At least one of the plunger and the receptacle may be configured to achieve radial float therein. Additionally, the inner contact assembly may be configured to achieve radial float relative to the second signal carrying circuit element on the second circuit board. 
     The coaxial connector further includes a plurality of non-conductive elements between the inner and outer contact assemblies. The non-conductive elements function to substantially center at least portions of the inner contact assembly relative to at least portions of the outer contact assembly. The non-conductive elements between the inner and outer contact assemblies preferably include at least one resilient O-ring, and preferably a stacked array of resilient O-rings. The number of O-rings and the combined axial dimensions of the O-rings are selected to bias the plunger and receptacle of the inner contact assembly into an extended position and toward the first circuit board. However, the O-rings can be compressed resiliently in response to forces generated during mating. 
     The coaxial connector is employed merely by positioning the first and second circuit boards in substantially juxtaposed relationship to one another and then urging the first and second circuit boards toward one another. The chamfer on the outer surface at the mating end of the floating outer contact will engage the chamfered entry to the guide sleeve on the first circuit board. The engagement of these chamfers will help to guide the first and second circuit boards into proper alignment with one another and will generate radial float of the floating outer contact to permit the floating outer contact to telescope into the guide sleeve. The outside diameter of the floating outer contact is significantly less than the inside diameter of the guide sleeve. Hence, there are minimal connecting forces created during mating. Movement of the first and second circuit boards toward one another will urge the mating end of the floating outer contact into engagement with the first ground circuit printed or otherwise disposed on the first circuit board. Substantially simultaneously, the mating end of the inner contact assembly will contact the first signal carrying circuit element on the first circuit board. 
     The receptacle and plunger of the inner contact assembly may telescope relative to one another in response to axial forces generated as the first and second circuit boards are moved into their final position. In all such positions, the resilient O-rings will exert biasing forces that urge the mating end of the inner contact assembly against the signal carrying circuit element on the first circuit board. The resilient force exerted by the inner contact assembly can be varied by providing more or fewer resilient O-rings, and replacing any such O-rings that are removed by non-resilient spacers. Thus, greater axial float can be achieved with a larger number of resilient O-rings. 
     Plural coaxial connector assemblies are likely to be used simultaneously at different locations on the first and second circuit boards. The radial and axial float of the floating contact members may vary from one coaxial connector assembly to another. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of a coaxial connector assembly according to a first embodiment of the invention. 
     FIG. 2 is a cross-sectional view taken along line  2 — 2  in FIG.  1 . 
     FIG. 3 is a cross-sectional view taken along line  3 — 3  in FIG.  2 . 
     FIG. 4 is a side elevational view of a coaxial connector assembly according to a second embodiment of the invention. 
     FIG. 5 is a cross-sectional view taken along line  5 — 5  in FIG.  4 . 
     FIG. 6 is a cross-sectional view taken along line  6 — 6  in FIG.  5   
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A coaxial connector in accordance with the subject invention is identified generally by the numeral  10  in FIGS. 1-3. The coaxial connector  10  is employed to connect circuit elements printed or otherwise disposed on a first circuit board  12  to corresponding circuit elements printed or otherwise disposed on a second circuit board  14 . More particularly, the first circuit board  12  is provided with a first signal carrying circuit element  16  and a first ground circuit elements  18  spaced from the first signal carrying circuit element  16 . The circuit elements  16  and  18  can take many different forms that known to those skilled in this art. As depicted herein, the first signal carrying circuit element  16  is a printed region on a surface of the first circuit board  12 , and the first ground circuit elements  18  represent four lands disposed on the circuit board. In other embodiments, the first ground circuit  18  may define a generally annular region surrounding the first signal carrying circuit element  16 . In still other embodiments, virtually all of the surface of the first circuit board  12  may be coated or laminated with a ground element, but the ground element may be removed or not applied to regions surrounding the signal carrying circuit element  16 . The first circuit board  12  is further provided with a short cylindrical guide sleeve  20  having a mounting end  22 , a mating end  24  and an inner circumferential surface  26  extending between the ends. Portions of the inner circumferential surface  26  adjacent the mounting end  22  define an inside diameter “a”. However, portions of the inner circumferential surface adjacent the mating end  24  define a chamfer  28  that flares outwardly for guiding the coaxial connector  10  into a mated position with the circuit elements on the first circuit board, as explained herein. The mounting end  22  is soldered or otherwise securely connected both mechanically and electrically to the first ground circuit elements  18  on the first circuit board  12 . 
     The second circuit board  14  similarly is provided with a second signal carrying circuit element  30  and second ground circuit elements  32 . The circuit elements  30  and  32  may be applied to the second circuit board  14  by any of the techniques described above with respect to the first circuit board  12  or by other technologies known to those skilled in this art. 
     The coaxial connector  10  includes an outer contact assembly  34  with a base  36  and a floating outer contact  38  that preferably are formed from brass or other alloy with appropriate mechanical and conductivity characteristics. The base  36  includes a mounting end  40 , a mating end  42  and a passage  44  extending continuously between the ends  40  and  42 . The mounting end  40  is characterized by lands  46  disposed symmetrically relative to one another substantially at the corners of a square. The lands  46  may be soldered or otherwise connected mechanically and electrically to the second ground elements  32  on the surface of the second surface board  14 . The mating end  42  of the base  36  is characterized by an inwardly extending flange  48 . Portions of the inner circumferential surface  44  of the base  36  at the flange  48  are cylindrically generated and define an inside diameter “b”. 
     The floating outer contact  38  of the outer contact assembly  34  includes a mounting end  50 , a mating end  52  and inner and outer circumferential surfaces  54  and  56 . A flange  58  extends outwardly from the outer circumferential surface  56  at locations adjacent the mounting end  50  of the floating outer contact  38 . The flange  58  defines an outside diameter “c” that exceeds the inside diameter “b” of the inwardly extending flange  48  on the base  36 . Portions of the floating outer contact  38  adjacent the flange  58  define a reduced diameter region  60  with an outside diameter that is significantly less than the inside diameter “b” defined by the inwardly extending flange  48  on the base  36 . The floating outer contact  38  is assembled with the base  36  so that the flange  58  of the floating outer contact  38  is trapped between the flange  48  of the base  36  and the second circuit board  14 . However, the axial dimension of the flange  58  of the floating outer contact  38  is selected relative to the dimensions of the base  36  to permit axial float of the floating outer contact  38  in directions to or away from the flange  48  and the second circuit board  14 . Additionally, the relative outside diameter of the reduced diameter portion  60  of the floating outer contact  38  and the inside diameter “b” of the flange  48  of the base  36  enable radial float of the floating outer contact  38  relative to the base  36 . 
     The mating end  52  of the floating outer contact  38  is characterized by an inwardly extending flange  62 . Portions of the inner circumferential surface  54  of the floating outer contact  38  adjacent the flange  62  are substantially uniformly cylindrical entirely to the mounting end  50  of the floating outer contact  38 . The outer circumferential surface  56  of the floating outer contact  38  defines a chamfer  64  at the mating end  52 . The chamfer  64  facilitates the guiding of the floating outer contact  38  into the guide sleeve  20  and will help to generate radial float. The outer circumferential surface  56  of the floating outer contact  38  is further characterized by an annular groove  66  at a location between the chamfer  64  and the reduced diameter portion  60 . A lock washer  68  is locked into engagement with the lock groove  66  and defines an outside cross-sectional dimension greater than the inside diameter “b” of the inwardly extending flange  48  at the mating end  42  of the base  36 . The lock washer  68  traps a flat washer  69  between the lock washer  68  and the base  36 . 
     The outer contact assembly  34  further includes a spring washer  70  between the lock washer  68  and the mating end  42  of the base  36 . The spring washer  70  may be formed from a stainless steel and exerts axial forces on the lock washer  68  for urging the floating outer contact  38  away from the second circuit board  14 . In certain embodiments, an annular spring may be disposed between the flange  48  of the base  36  and the flange  58  of the floating outer contact  38  for countering the biasing forces exerted by the spring washer  70  and substantially balancing the axial forces on the floating outer contact  38 . The annular spring between the flange  48  of the base  36  and the flange  58  of the floating center contact  38  also contributes to RF shielding and prevents the creation of gaps that could lead to signal leakage in certain relative axial positions of the spring biased assemblies. 
     The coaxial connector  10  further includes an inner contact assembly  72  that may be formed from the same material as the outer contact assembly  34 . However, contact regions of the inner contact assembly  72  preferably are gold plated. The inner contact assembly  72  includes a plunger  74  with a mounting end  76  and a mating end  78 . The mounting end  76  defines a substantially flat land for contacting the second signal carrying circuit element  30  on the second circuit board  14 . A flange  80  projects outwardly on the plunger  74  at locations between the mounting and mating ends  76  and  78 . The inner contact assembly  72  further includes a receptacle  82  having a receptacle end  84  and a mating end  86 . The receptacle end  84  is substantially hollow and dimensioned to slidably receive the mating end  78  of the plunger  74 . The mating end  86  of the receptacle  84  is substantially planar and is dimensioned to engage the first signal carrying circuit  16  on the first circuit board  12 . A flange  88  projects outwardly on the receptacle  82  at a location between the receptacle end  84  and the mating end  86 . 
     The coaxial connector  10  further includes a plurality of substantially annular insulators. More particularly, a first annular insulator  90  surrounds portions of the plunger  74  between the flange  80  and the mounting end  76 . The first insulator  90  engages the flange  80  of the plunger  74  and the mounting end  50  of the floating outer contact  38 . A second annular insulator  92  surround portions of the plunger  74  between the flange  80  and the receptacle  72 . A third annular insulator  94  surrounds the receptacle  72  between the flange  88  thereof and the receptacle end  84 . A fourth annular insulator  96  surrounds the receptacle  82  and extends between the flange  88  and the flange  62  of the floating outer contact  38 . The annular insulators  90 - 96  are substantially rigid. However, the coaxial connector  10  further includes a plurality of resilient O-rings  98  surrounding the inner contact assembly  72  and disposed between the annular insulators  92  and  94 . The resilient O-rings  98  urge the receptacle  82  of the inner contact assembly  72  in a mating direction MD relative to the plunger  74 . However, the resilient O-rings  98  permit the receptacle  72  to be collapsed axially over the plunger. Thus, the resilient O-rings  98  perform a function similar to the spring washer  70  of the outer contact assembly  34 . More particularly, the spring washer  70  urges the floating outer contact  38  in the mating direction MD relative to the base  36 , while the resilient O-rings  98  urge the receptacle  82  of the inner contact assembly  72  in the mating direction MD relative to the plunger  74  of the inner contact assembly  72 . 
     The coaxial connector  10  is employed by soldering or otherwise connecting the lands  46  at the mounting end  40  of the base  36  to the ground elements  32  on the second circuit board  14 . This fixed connection of the lands  46  to the ground elements  32  positions the mating end  76  of the plunger  74  adjacent the signal carrying circuit element  30  of the second circuit board  14 . However, this mounting end  76  of the plunger  74  is not soldered to the signal carrying circuit element  30 , and the plunger  70  is permitted to float both radially and axially. The first and second circuit boards  12  and  14  then are positioned in juxtaposed relationship to one another and are urged toward one another. This movement causes the mating end  52  of the floating outer contact  38  to move within the mating end  24  of the guide sleeve  20 . Any misalignment between the coaxial connector  10  and the guide sleeve  20  will be corrected by the chamfer  64  at the mating end  52  of the floating outer contact  38  and the corresponding chamfer  28  of the guide sleeve  20 . Thus, these cooperating chamfers  64  and  28  will cause the floating outer contact  38  and the receptacle  82  of the inner contact assembly  72  to float radially. Sufficient movement of the circuit boards  12  and  14  toward one another will bring the mating end  52  of the floating outer contact  38  into engagement with the ground elements  18  on the first circuit board  12  and substantially simultaneously will bring the mating end  86  of the receptacle  82  of the inner contact assembly  72  into contact with the signal carrying circuit element  16  of the first circuit board  12 . Movement of the first and second circuit boards  12  and  14  into their final disposition will cause the floating outer contact  38  to displace toward the second circuit board  14  and against the biasing forces exerted by the spring washer  70 . Similarly, the receptacle  82  will be biased over and further toward the plunger  74  and against the biasing forces exerted by the resilient O-rings  98 . Thus, the ends  76  and  86  of the inner contact assembly  72  are biased between the circuit boards  12  and  14  to achieve a high quality connection between the signal carrying circuit elements  16  and  30 . 
     The coaxial connector  10  described and illustrated above is intended for surface mount on the second circuit board  14 . FIGS. 4-6 show a very similar coaxial connector  110  that is intended for soldered mounting to through holes formed in a second circuit board  114 . The coaxial connector  110  include an outer contact assembly  134  with a base  136  and a floating outer contact  138 . The floating outer contact  138  is substantially identical to the floating outer contact  38  described and illustrated above. Hence, further description of the floating outer contact  138  is not provided. The base  136  of the inner contact assembly  134  is structurally and functionally very similar to the base  36  described and illustrated above. However, the base  136  does not include the lands  46 . Rather, the base  136  includes projections  146  that extend through holes (not shown) in the second circuit board  114 . Thus, as with the previous embodiment, the base  136  of the outer contact assembly  134  is fixed relative to the second circuit board  14  and achieves soldered electrical connection with the ground elements on the second circuit board. The floating outer contact  138  is permitted to move both axially and radially relative to the fixed base  136 , and is biased in the mating direction MD by a spring washer  170 . 
     The coaxial connector  110  further includes an inner contact assembly  172  with a receptacle  182  substantially identical to the receptacle  82  described and illustrated above. However, the second circuit board  114  is provided with a signal carrying pin  130  that projects through the second circuit board  114  and partly into the coaxial connector  110 . The pin  130  includes a mating end  131  spaced from the second circuit board  114 . 
     The inner contact assembly  172  includes a plunger  174  that has a mounting end  176  disposed in sliding contact with the mating end  131  of the pin  130 . Thus, the plunger  174  of the inner contact assembly  172 .can float radially relative to the pin  130 . 
     The coaxial connector  110  further includes annular insulators  190 - 196  that are substantially identical to the corresponding annular insulators on the coaxial connector  10  described and illustrated above. Additionally, the coaxial connector  110  includes resilient O-rings  198  at substantially the same locations and for performing substantially the same functions as the resilient O-rings  98  described and illustrated above. 
     The two embodiments described and illustrated above each show three resilient O-rings  98 ,  198  incorporated into the coaxial connector  10 ,  110 . However, more or fewer resilient O-rings  98 ,  198  can be provided in accordance with the amount of resiliency required and the range of axial float required. More or fewer resilient O-rings  98 ,  198  merely require changes in the dimensions of the annular insulators  92 ,  94 ,  192 ,  194 . Additionally, the preceding embodiments illustrate only a single coaxial connector  10 ,  110 , mounted to the second circuit board  14 ,  114 . However, several such coaxial connectors  10 ,  110  are likely to be mounted to the second circuit board  14 ,  114 . Manufacturing tolerances invariably lead to certain of the coaxial connectors  10 ,  110  being shifted slightly from their specified positions on the second circuit board  14 ,  114 . However, the radial float permitted by the coaxial connector  10 ,  110  is generated by the guide sleeves  20  and enables effective electrical connection to be made with minimal mating forces. 
     While certain preferred embodiments have been described and illustrated, it is apparent that various changes can be made without departing from the scope of the invention as defined by the appended claims.