Abstract:
An electrical connector comprising: an insulative housing having at least one cavity; a retaining member removably securable to the insulative housing and occluding at least a portion of the cavity, the retaining member having at least one aperture in communication with the cavity; a conductive terminal having a first portion disposed in the cavity and a second portion disposed in the aperture; and a surface mount element mounted on the second portion of the terminal. The member retains the terminal within the insulative housing. A method of making an electrical connector comprising the steps of: inserting the terminal into the cavity; attaching the retaining member to the insulative housing, wherein the mounting portion of the terminal resides within the aperture; and securing the surface mount element to the mounting portion of the terminal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 60/068,664, filed on Dec. 23, 1997 and herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to electrical connectors. More specifically, the present invention relates to high density edge card connectors. 
     2. Brief Description of Earlier Developments 
     Edge card connectors have been used for a substantial period of time. As with many other connector types, there has been a continual evolution of these connectors in terms of size reduction, terminal pitch, and electrical performance. In order to reduce the size of the connector and in many cases increase the signal density, it is necessary to decrease the terminal pitch. 
     The decrease in terminal pitch necessitates a decrease in the amount of insulative material between terminals, thereby resulting in very thin walls between terminals. The insertion of terminals into the terminal cavities can result in rupturing these thin walls between terminal cavities. Also an accumulation of stress along the lengthwise dimension of the connector can occur. However, the decreased wall thicknesses in the connector housing render the housing less able to resist the stress accumulation. As a result, the connector tends to bow. This adversely affects conformance of the connector to the circuit board on which it is mounted and creates alignment difficulties, particularly in surface mount connectors, with contact pads on the printed circuit board. 
     In addition, many prior designs employ relatively long length contact arms in order to develop sufficient deflection to accommodate daughter board thickness tolerances and to obtain good contact normal forces between the contacts and the terminals of the connector. This increases the impedance of the connector and can unduly increase skew. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to minimize the accumulation of stresses in the connector housing. 
     It is a further object of the present invention to employ relatively light retention forces when inserting terminals into the housing. 
     It is a further object of the present invention to utilize an element secured to the housing after terminal insertion to hold the terminals in place within the housing. 
     It is a further object of the present invention to provide terminals having features to help retain the terminal within the insulative housing during handling. 
     It is a further object of the present invention to provide terminals that are movable with respect to the housing to accommodate differences in the coefficient of thermal expansion (CTE) of the connector body and the printed circuit board upon which the connector mounts. 
     It is a further object of the present invention to employ deformable elements, such as solder balls, to secure the terminals to the housing. 
     It is a further object of the present invention to provide a connector that can be closely stacked in an end-to-end configuration with another connector. 
     These and other objects of the present invention are achieved in one aspect of the present invention by an electrical connector comprising: an insulative housing having at least one cavity; a retaining member removably securable to the insulative housing and occluding at least a portion of the cavity, the retaining member having at least one aperture in communication with the cavity; a conductive terminal having a first portion disposed in the cavity and a second portion disposed in the aperture; and a surface mount element mounted on the second portion of the terminal. The member retains the terminal within the insulative housing. 
     These and other objects of the present invention are achieved in another aspect of the present invention by a card edge connector, comprising: an insulative housing, a conductive terminal, a retaining member and a surface mount element. The insulative housing has: a slot for receiving an edge of a card; a cavity in communication with the slot and a pair of posts, each having channels in communication with the slot for receiving the card. The conductive terminal has a mating portion residing within the cavity for engaging the card edge and a mounting portion extending from the cavity. The retaining member secures to the insulative housing and has an aperture in communication with the cavity that receives the mounting portion of the terminal. The retaining member preventing the terminal from exiting the cavity. The surface mount element attaches to the mounting portion of the terminal. 
     These and other objects of the present invention are achieved in another aspect of the present invention by a method of making an electrical connector, comprising the steps of: providing an insulative housing having a cavity; providing a conductive terminal having a mounting portion; providing a retaining member having an aperture; providing a surface mount element; inserting the terminal into the cavity; attaching the retaining member to the insulative housing, wherein the mounting portion of the terminal resides within the aperture; and securing the surface mount element to the mounting portion of the terminal. The retaining member keeps the terminal within the cavity. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other uses and advantages of the present invention will become apparent to those skilled in the art upon reference to the specification and the drawings, in which: 
     FIG. 1 is a side elevation of a connector embodying the invention; 
     FIG. 1 a  is a detailed view of a portion of FIG. 1; 
     FIG. 2 is an end view of the connector in FIG. 1; 
     FIG. 3 is a top view of the connector in FIG. 1; 
     FIG. 3 a  is a cross-sectional view taken along line IIIA—IIIA in FIG. 3 showing the terminals inserted into a main portion of the connector housing; 
     FIG. 3 b  is a cross-sectional view taken along IIIB—IIIB in FIG. 3 showing the terminals secured within the connector housing with a terminal retention element; 
     FIG. 4 a  is a detailed view of a portion of FIG. 3 a  showing a terminal retained within the connector; 
     FIG. 4 b  is a detailed view of a portion of FIG. 3 a  showing a terminal partially retracted from the connector housing; 
     FIG. 5 is a detailed view of a portion of FIG. 3 b  showing a feature of the terminal retention element; 
     FIG. 6 is a detailed view of a portion of FIG. 3 b  showing another feature of the terminal retention element; 
     FIG. 7 shows the connector of FIG. 1 together with a mating daughter board; 
     FIG. 8 is a detailed view of a portion of FIG. 7; and 
     FIG. 9 is a side view of two connectors according to the invention arranged end-to-end. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1-3 show various views of a connector  10  of the present invention. Connector  10  consists of three main components, a main body  11 , terminals  13  and a terminal retention member  15 . Generally speaking, assembly of connector  10  proceeds by inserting terminals  13  into main body  11 , then securing terminal retention member  15  to main body  11  which retains terminals  13  within main body  11 . Each component will now be described in detail. 
     Main body  11  is formed of a suitable dielectric material. Body  11  can have a generally planar base with two parallel, longitudinally oriented slots  17  (see FIG. 3) that receive daughter boards B (see FIG. 7) in an edge-wise configuration. 
     Body  11  includes upstanding, split guide posts  19  at one end. Guide posts  19  include a latch member  21  pivotally mounted via a pivot pin  23  in each guide post  19 . Latch member  21  can pivot between a substantially vertical position (shown in solid lines in FIG. 1) and an ejecting position (shown in phantom in FIG.  1 ). Latch member  21  includes an ejecting foot  25  at a bottom end and a pair of opposed cam tabs  27  for urging the portions of guide post  19  together against surfaces of inserted daughter board B. International publication number WO 97/08782, herein incorporated by reference, describes in more detail the aforementioned structure for retaining daughter board B in connector  10 . 
     Guide posts  29  oppose guide posts  19  on main body  11 . Guide posts  29  include a slot  31  aligned with slot  17  in body  11  to receive side edges of inserted daughter board B. As seen in FIG. 8, guide posts  29  have a surface  33  extending generally perpendicular to bottom surface  35  of main body  11  and an angled surface  37 . Angled surface  37  acts as a lead-in for inserting daughter board B into connector  10 . As will be described in more detail below, surface  33  helps retain daughter board B within connector  10 . 
     Preferably, the upper end of each guide post  29  is relieved to form a canted surface  39 . This allows end-to-end placement of several connectors  10  as seen in FIG.  9  and as will be described in more detail below. 
     Referring to FIGS. 1 and 3, a plurality of terminal cavities  41  flank each slot  17  in body  11 . Cavities  41  receive a respective terminal  13  that engage contact pads (not shown) disposed along the edge of daughter boards B inserted into slots  17 . 
     Cavities  41  includes side surfaces  43 ,  45  and upper surfaces  47 ,  49  that abut against corresponding portions of terminals  13  when terminals  13  reside within main body  11 . Surfaces  43 ,  47 ,  49  of cavities  41  form datum surfaces for the location of terminals  13  within main body  11 . This feature will be described in more detail below. 
     Main body  11  also includes a plurality of flanges  51  formed on opposed outer surfaces along bottom surface  35 . Flanges  51 , along with openings  53  in a central portion of main body  11 , help secure terminal retention member  15  to main body  11 . For example, terminal retention member  15  secures to main body  11  by positioning along bottom surface  35  and securing latch members with flanges  51  and openings  53 . 
     FIGS. 3 a ,  3   b ,  4   a  and  4   b  display terminals  13  positioned within main body  11 . Each terminal  13  includes a tapered cantilever beam  55  extending from a base portion  57 . Cantilevered beam  55  includes a contact surface  59  at a distal end opposite base portion  57 . 
     Base portion  57  includes side surfaces  61 ,  63 ; upper surfaces  65 ,  67 ; and lower surface  69  that interact with surfaces  43 ,  45 ,  47 ,  49  of cavities  41  and a mating surface of terminal retention member  15 . Interaction of the various surfaces help align and retain terminal  13  within main body  11 . 
     Side surface  61  has a retention barb  71  extending therefrom. Barb  71  pierces side surface  43  of cavity  41  to retain terminal  13  within main body  11  until terminal retention member  15  can secure to main body  11 . FIG. 4 a  displays terminal  13  properly seated within main body  11 . 
     Retention barb  71  is located towards a lower end of side surface  61  to prevent rotation of terminal  13  out of main body  11 . By locating barb  71  at a lower end of side surface  61 , an upper portion  97  of side surface  63  cannot exit main body  11 . As seen in FIG. 4 b , when terminal  13  rotates, upper portion  97  interferes with side surface  45  of cavity  41 . This feature additionally retains terminal  13  within main body  11  until terminal retention member  15  can secure to main body  11 . 
     Base portion  57  also includes a terminal tab  73  to receive, for example, a fusible element  75  such as a solder ball for surface mounting connector  10  to a substrate (not shown). Fusible elements  75  typically have a slightly greater transverse extent than the transverse extent of the openings  79  in terminal retention member  15 . Thus, fusible elements  75  also serve a retention function for securing terminals  13  in proper position and for holding terminal retention member  15  onto main body  11 . Fusible elements  75  form a connection between the terminals  13  and contact pads on the circuit substrate by conventional reflow techniques. 
     Fusible elements  75  secure to tabs  73  by applying a solder paste (not shown) into the openings  79 , then by placing individual fusible elements  75  over openings  79 . After placement of fusible elements  75  in openings  79 , connector  10  then undergoes a first reflow operation to melt the solder paste and to fuse the fusible element  75  to tab  73  of terminal  13 . A second reflow step attaches connector  10  to substrate S. 
     FIGS. 1 and 3 b  display terminal retention member  15 . Preferably, retention member  15  is made from a molded dielectric material. Retention member  15  includes a mating surface  77  that abuts bottom surface  35  of main body  11  and surfaces  69 ,  71  of terminal  13 . Retention member  15  includes a plurality of apertures  79  sized to receive terminal tab  73  of terminal  13  and at least a portion of fusible element  75 . Apertures  79  are preferably larger than tabs  73  to allow longitudinal movement of tab  73  without interference by the walls forming apertures  79 . 
     Terminal retention member  15  includes latches  81  located at opposite ends thereof to engage flanges  43  of main body  11  and centrally located latches  83  to engage openings  53  of main body  11 . Latches  81 ,  83  are preferably cantilevered members integrally molded with terminal retention member  15 . 
     Latches  81  include a flexible arm  85  and a catch  87  that engages flange  43 . Latches  83  comprise two pieces  89   a ,  89   b  in an opposed relationship. Each opposed portion  89   a ,  89   b  has a flexible arm  91   a ,  91   b  and a catch  93   a ,  93   b . Slightly different than catch  87  of latch  81 , catches  93   a ,  93   b  each include surfaces  95   a ,  95   b  angled opposite to that of conventional latches. Canted surfaces  95   a ,  95   b  engage opposite edges of opening  53  to retain member  15  in main body  11 . 
     The canting of surfaces  95   a ,  95   b  helps accommodate tolerance variations between main body  11  and terminal retention member  15 . The amount of potential tolerance absorption is represented by the dimension T, a dimension that is defined by the difference in elevation between the inside edge of surface  95   a  and the outside edge of surface  95   b . In essence, surfaces  95   a ,  95   b  serve as a camming surface, under the spring force generated by latches  83  to draw terminal retention member  15  against bottom surface  35  of main body  11 . Stated differently, the securing system for the terminal retention member  15  can absorb vertical tolerances between main body  11  and terminal retention member  15  and also the vertical dimension of the base  57  of terminal  13 . Preferably, surfaces  95   a ,  95   b  extends approximately 27° from the lateral axis of latch  83 . 
     The assembly of connector  10  will now be described. Initially, main body  11 , terminals  13  and terminal retention member  15  are separate elements. The first assembly step inserts terminals  13  into cavities  41  of main body  11 . FIG. 4 a  displays terminal  13  properly inserted into cavity  41 . When seated within cavity  41 , side wall  63  of terminal  13  abuts side surface  43  of cavity  41  and upper surfaces  65 ,  67  of terminal  13  abut upper surfaces  47 ,  49  of cavity  41 . 
     The points of contact between cavity  41  and terminal  13  constitute datum points, designated by arrows Z 1 , Z 2  and L 3 . The datum points help locate terminals  13  within main body  11 . Specifically, datum points Z 1  and Z 2  help position terminals  13  longitudinally within main body  11  (i.e. in the direction extending from the bottom to the top of FIG. 3 b ). Also, datum point L 3  helps position terminals  13  laterally within main body  11  (i.e. the direction extending from the left side to the right side of FIG. 3 a ). 
     As seen in FIG. 4 a , a clearance exists between side wall  61  (excluding barb  71 ) of terminal  13  and side surface  43  of cavity  41  when side wall  63  of terminal  13  abuts side surface  45  of cavity  41 . The length of barb  71 , however, is greater than the clearance between side wall  61  of terminal  13  and side surface  43  of cavity  41 . As a result, a portion of barb  71  pierces side surface  43  of cavity  41 . Barb  71  allows terminals  13  to move slightly in the longitudinal direction within main body  11  while still engaging side surface  43  of cavity  41 . This helps alleviate any stresses that might result from any mismatch in the coefficients of thermal expansion (CTE) between the materials of main body  11  and the substrate, such as a printed circuit board (not shown) on which the connector  10  is mounted. 
     Barb  71  creates a light retentive force sufficient to hold terminals  13  in housing  11  for subsequent handling prior to the attachment of terminal retention member  15 , but not for full retention under conditions of use. The light retentive force applies a relatively light stress to main body  11  at locations S 1 , S 2  than with conventional connectors. The light retentive force does not urge the main body to bow or cause the webs between adjacent cavities to crack as sometimes found with conventional connectors. The contact of surface  63  along surface  43  and the point contact of barb  71  with surface  45  allows for the movement of terminal  13  independent of housing  11 . 
     After terminals  13  are inserted within main body  11 , terminal retention portion  15  is secured to main body  11 . Specifically, terminal retention portion  15  is positioned to abut lower surface  35  of main body  11 . Latches  81 ,  83  on terminal retention portion engage corresponding flanges  51  and openings  53  on main body  11 . 
     When properly fastened to main body  11 , mating surface  77  of terminal retention member  15  abuts lower surface  69  of terminal  13 . The point of contact between cavity  41  and terminal  13  constitutes another datum point, designated by arrow Z 3  to help locate terminals  13  longitudinally within main body  11 . 
     The assembly of connector  10  is now complete. After assembly, connector  10  is attached to a substrate (not shown) using known surface mount techniques (SMT). Once attached to a substrate, connector  10  can receive daughter boards B as shown in FIG.  7 . 
     Generally perpendicular surface  33  helps retain daughter board B in slot  17 . In a manner similar to the arrangement of cavity  41 , perpendicular surface  33  inhibits rotation of daughter board B out of slot  17 . Upon rotation of daughter board B, the corner of daughter board B would interfere with perpendicular surface  33  as shown by the phantom line in FIG.  8 . Only upon actuation of lever  21  can daughter board B pass by perpendicular surface  33 . 
     As seen in FIG. 9, connectors  10  of the present invention can be closely stacked end-to-end. Canted surfaces  39  allow close end-to-end stacking because since they allow sufficient space for the outward swinging of the latch  21  to effect removal of daughter board B. 
     The advantages of the invention disclosed are many. A high density, fine-pitch connector can be achieved which maintains a reliable and repeatable terminal to insulator interface. Propagation delay through the connector is minimized by employing short electrical paths that have low inductance. The fine pitch connector of the present invention utilizes minimum printed circuit board space. The connector also has higher reliability in severe shock and vibration environments. 
     The structure as disclosed also allows the terminal to move longitudinally with the printed circuit board under conditions of thermal expansion, without being impeded by CTE differential. The terminal is retained at the ends of its base only and the terminal leg is allowed to follow the expansion and contraction of the printed circuit board relative to the housing, without resistance. This prevents the accumulation of terminal-to-housing stresses and subsequent forces on the solder ball-to-terminal and/or solder ball-to-printed circuit board interface. Manufacturing economies are realized by providing tolerance absorbing securing structures between assembled parts of the housing. 
     While the present invention has been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.