Insert and rotate connector with improved latching means
BACKGROUND OF THE INVENTION 
     The present invention relates generally to electrical connectors for use in association with printed circuit boards and, more particularly, to a connector having an improved latching means. 
     Connectors are used in all types of electronic devices, and are widely used in the computer field. Many computers and other electronic devices have a main printed circuit board, referred to in the art as a &#34;mother&#34; board. Secondary electrical circuits are formed on different substrates as separate printed circuit boards which are added to the mother board, either subsequent to the installation of the mother board in a housing of the device, or prior to the final installation of the mother board into the component housing. These secondary circuits are typically designed to improve the performance of the device and are referred to in the art as &#34;daughter&#34; boards. 
     A connector is typically used in the computer art to connect a daughter board to the mother board. To provide an effective connection, connectors include a number of conventional features such as a longitudinal slot which receives an edge of the daughter board and a plurality of electrical terminals disposed in the slot in alignment with a like plurality of electrical contact pads arranged along the edge of the daughter board. The connection is effected along this edge of the daughter boards, and accordingly, daughter boards are often descriptively referred to as &#34;edge cards&#34;. 
     The connector terminals may typically include contact portions located in the connector housing which provide electrical contact between the connector and the edge card. The terminals also may include tail portions which extend out of the connector housing and which are received within corresponding holes in the mother board in order to provide a connection between the circuit(s) on the edge cards and the mother board. The electronics art and especially the computer art have noticed the desire of consumers for smaller computer devices as evidenced by the increase in popularity of &#34;laptop&#34; and &#34;sub-notebook&#34; computers, as well as smaller size desktop computers. In order to reduce space, connectors have been developed which are smaller than past connectors, and having a closer profile to the mother board. Sometimes, these low profile, or right angle connectors are designed in order to position the daughter board in a horizontal orientation, parallel to the mother board surface, rather than vertical and perpendicular to the mother board surface. 
     Right angle connectors are often used to provide electrical connections between memory modules, known in the art as either SIMMs (single in-line memory modules) or DIMMs (dual in-line memory modules). There is a primary difference between a SIMM and a DIMM which highlights the need for even more reliable connectors used with DIMMs. SIMMs typically contain their electrical contact pads along the opposing edges of the engagement edge of the SIMM in a redundant manner, i.e., a contact pad on one side of the SIMM has a corresponding contact pad disposed on the other side of the SIMM and the two contact pads are electrically connected to the same circuit. 
     The structure of a DIMM is different because each electrical contact pad on the opposing sides of the DIMM leads to a different circuit and, therefore requires a higher degree of certainty of contact between the connector terminal contact portions and the DIMM contact pads than a SIMM because of the lack of redundancy. If a break in contact occurs, disengagement of the connection established in the connector between the edge card contact pads and the terminal contact portions may result, potentially causing a computer failure. 
     Latching mechanisms have been developed for connectors in order to retain edge cards in place in the connector housing. Latching mechanisms for SIMMS are typically either directly formed in the structure of the connector housing at opposing ends, or they may be separately formed and inserted into the connector housing. These latching mechanisms may include different configurations for contacting the edge card and for retaining it in place within the connector housing. Examples of insertable latches are described in U.S. Pat. No. 4,995,825 issued Feb. 26, 1991 and U.S. Pat. No. 5,094,624, issued Mar. 10, 1992. The latches described in these patents are stamped and formed from a metal strip and are used in &#34;insert and rotate&#34; connectors wherein the engagement edge of the edge card is initially inserted into the connector slot and subsequently rotated to a second position in the connector slot into engagement with the terminals. 
     Another insert and rotate connector having a latching mechanism is described in European Patent Publication No. 0632542, published Jan. 4, 1994. The latching mechanism described in this patent includes latching members having a pair of wide shoulders which engage the ends of a circuit card and a tongue which is folded over the shoulders in order to contact the circuit card. Although these shoulders are illustrated as extending into opposing recesses positioned in the ends of an edge card, the entire latch arm is formed by stamping and forming the latching members over the shoulders. The tolerances in forming these latch members are not as accurate as may be obtained through blanking. 
     Small outline DIMM connectors of the type shown in European Patent Publication No. 0632542 are small in size and shape, and the latch members are likewise small. The difficultly in accurately stamping and forming a latch member increases as the overall size of the latch member decreases. In order to position the edge card accurately in the connector, such small outline DIMMs typically utilize a pair of notches or other style reentrant portions formed on the opposite ends of the edge card which engage an opposing surface of a latch member. The relatively small size of a DIMM and its lack of electrical redundancy requires that the latch member reliably hold the DIMM in place within the connector. It is desirable to engage the DIMM with the connector in a manner which will ensure accurate alignment and connection between the terminals and edge card contact pads and resist shock loading. 
     Accordingly, a need exists for a connector in which the edge card is inserted and rotated into position wherein the connector has a reliable latching mechanism which retains the edge card in place within the connector. 
     SUMMARY OF THE INVENTION 
     The present invention is therefore directed to an improved edge card connector of the insert and rotate style which offers significant advantages over the connectors described above, which is reliable and which offers improved resistance to shock loading and the like. 
     In one principal aspect, the present invention overcomes the aforementioned disadvantages by providing an edge card connector having an elongated housing with an edge card slot extending longitudinally therein between two opposing end portions. The housing has a plurality of contact-receiving cavities which intersect with and open into the edge card slot of the connector housing. Each contact-receiving cavity contains an individual terminal which engages an opposing contact pad formed on opposing surfaces of the edge card insertion edge, and the connector has a latching mechanism disposed at its opposite ends. The latching mechanism includes an insertable latch member held within a slot formed in an end portion of the connector housing. The latch member includes a projecting portion which engages a corresponding notch formed in an end of the edge card, the latch member having at least one retention member extending out from the projecting portion normal thereto which engages a surface of the edge card. The retention member further includes a cam surface disposed thereon which also extends generally normal to the card engaging projection and which a engages the edge card when the edge card rotated into place to move the latch members outwardly to accommodate the edge card. 
     In another principal aspect of the present invention, each of the latch members includes an insertable cantilevered latch which is held within the connector housing end portions. Each latch member includes a latch arm having an arcuate engagement portion having distinct upper and lower portions. The lower portion is received in an opposing notch portion of a DIMM edge card, while the upper portion includes a pair of blanked retention arms which extend outwardly therefrom over edges of the engagement portion lower portions to engage a surface of the edge card. The retention arms extend parallel to the edge card and apply a transverse force to it transverse to the edge card surfaces. The latch projecting engagement portions engage the lateral ends of the edge card and retain the edge card laterally within the connector housing card slot. 
     In still another principal aspect of the present invention, each latch member includes a ring projection formed in a body portion of the latch member, each ring projection having a pair of extensions blanked therefrom and extending outwardly from the ring projection. The ring extensions having inclined surfaces which extend away from the ring projection, the extrusions further extending past the outer radius of the ring projections to form an abutment which bears against the surface of the edge card. 
     In yet still another aspect of the present invention and as exemplified by a second embodiment thereof, the ring extensions are curved toward each other and a free end of each latch members is partially bent upon itself to form a manually manipulatable engagement portion by which the latch members may be spread apart from each other to release the edge card from its engagement position within the connector housing slot. 
     These and other objects and advantages of the present invention will be clearly understood through a consideration of the following detailed description and in which like reference numerals identify like parts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the course of this description, reference will be made to the attached drawings in which: 
     FIG. 1 is a perspective view of an improved circuit card connector constructed in accordance with the principals of the present invention; 
     FIG. 2 is a perspective view of the connector of FIG. 1 showing a second card in place within the connector; 
     FIG. 3 is top plan view of the connector of FIG. 2; 
     FIG. 4 is an end view of the connector of FIG. 3; 
     FIG. 5 is an end view of the connector of FIG. 3; 
     FIG. 6 is an enlarged perspective view of a latch means of the connector of FIG. 1; 
     FIG. 7 is an enlarged perspective view of the latch means of FIG. 1 showing a corresponding secondary circuit board in engagement with the latch means; 
     FIG. 8 is a partial plan view of the engagement of the latch means and secondary circuit board of the connector of FIG. 1; 
     FIG. 9 is a plan view of a second embodiment of a connector constructed in accordance with the principles of the present invention; 
     FIG. 10 is an enlarged perspective view of a latch means of the alternate embodiment of the connector illustrated in FIG. 9; 
     FIG. 11 is an enlarged perspective view of a latch means of the alternate embodiment of the connector but showing a secondary circuit card in engagement with the latch means; 
     FIG. 12 is an enlarged plan view of FIG. 11 illustrating the engagement of the latch means and secondary circuit board; 
     FIG. 13 is a perspective view of a latching mechanism of a conventional electrical connector; 
     FIG. 14 is a partial perspective view on the latch means of FIG. 13 in engagement with a corresponding opposing edge of a secondary circuit board in a latching condition; and 
     FIG. 15 is a plan view of the latch means and corresponding in opposing secondary circuit board edge engage in a latching condition. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 13-15 illustrate a conventional latch member 107 similar to that described in European Patent Publication No. 0632542 and utilized in a connector for retaining a DIMM in place within a connector (not shown) in order to establish a connection between the DIMM and a mother board. The latch member 107 includes an elongated latch arm 109 held within an elongated end portion 110 of a connector. The latch arm 109 includes a tongue, or retention member 108, which is stamped and formed from the same metal blank as the latch member 107. The tongue 108 is formed along the end 109a of the latch arm and is rolled more than 90° from the end 109a in order to confront the opposing surface 104b of an edge card 104. 
     FIG. 14 illustrates an edge card or DIMM 104 in engagement with the latch member 107 after the edge card 104 has been inserted into the connector card slot and rotated into place. In this position, the end 112 of the tongue 108 contacts the surface 104b of the edge card 104 in an area close to the edge card notch 104a and serves to retain it in place. It is important to note that the retention of the edge card 104 by the latch arm 109 is accomplished primarily by the tongue end 112, and as such, the tongue 108 merely exerts a normal force onto the edge card 104 (downward into the plane of FIG. 15). The tongue 108 has a generally curved exterior profile which the edge card notch 104a engages during rotation of the edge card into its proper position within the connector. The notch rides down on this surface until the edge card slips under the end 112 of the tongue 108. 
     In European Patent Publication No. 0632542 mentioned above, the latch member includes a pair of shoulders which are provided to fit into semi-circular recesses positioned in the ends of an edge card or DIMM. This structure is established by stamping and forming, and as such, it is difficult to obtain close tolerances by which movement of the DIMM within the connector socket may be kept to a minimum. 
     It is difficult to form such an engagement tongue 108 with accuracy. Additionally, when multiple insertions of an edge card are required, the tongue 108 may yieldingly deform as it allows the edge card notch 104a to repeatedly ride over it into engagement with its ends 112. When the edge card is removed from the connector, the tongue 108 may slightly deform as the edge card is rotated outwardly. In order to reliably perform this engagement function without excessive deformation, the tongue 108 must be accurately formed on the latch arm 109. 
     The present invention provides a latching mechanism for a connector which applies two retention forces to the edge card in different directions and which may be constructed with very low tolerances, in the order of 0.001 inches, to thereby better control the placement of the edge card or DIMM within the connector. An electrical connector constructed in accordance with the principles of the present invention is illustrated in FIG. 1 generally at 1. The connector 1 includes an elongated housing, or body portion 3, extending between two opposing ends, illustrated as posts 5 integrally formed with the housing 3 and extend outwardly therefrom, shown along direction E in FIG. 1. 
     The housing 3 includes a plurality of electrical terminals 2 disposed within a series of recesses 120 formed along opposite sides of a edge card receiving slot 6 formed in the connector housing 3. As is known in the art, the terminals 2 are disposed in a spaced-apart fashion along the slot and extend for the length N thereof. The slot 6 receives an engagement edge 4a of a secondary circuit board, such as the edge card 4 illustrated. The card slot 6 preferably has a width sufficient to receive the engagement edge 4a of the edge card 4 and permit the contact portions of the terminals 2 to engage opposing contact pads formed along the card edge 4a. The contact portions of one set of the connector terminals 2 may extend relatively far into the card slot 6 in order to provide a biasing force against the edge card 4 when it is engaged in place within the connector housing 3. The edge card engagement edge is, in effect, &#34;sandwiched&#34; between opposing rows of contact terminals 2 of the card slot 6. 
     Returning to FIG. 1, the connector end posts 5 have lower portions 15 which, on the bottom surfaces thereof, may engage an upper surface 20 of a mother board and, on the upper surfaces, may provide support to the edge card 4 when it is inserted into the connector 1. The insertion of the edge card 4 is illustrated generally in FIG. 2 wherein it can be seen that the edge card 4 (shown in phantom) is inserted into the card slot 6 of the connector housing 3 at a predetermined angle and subsequently rotated downwardly until the edge card is positioned between the connector end posts 5 and engaged with the latch members 7. 
     In order to retain the edge card 4 in place, the connector is preferably provided with a latching means which retains the edge card in place in at least two directions. This latching means is shown as taking the form of two flexible latch members 7 disposed at the ends of the connectors and partially received within corresponding slots 22 of the end posts 5. (FIGS. 1 &amp; 2.) Each latch member 7 is preferably formed from an elongated flexible and resilient metal strip 9. As shown in phantom in FIG. 1, the metal strip 9 has a lower portion 9c which is folded upon itself to define two interconnected arms 9c, 9e separated by an intervening space 10, which is received within the end post slots 22. Opposing sided of the end post slots 22 are closer together than the interconnected arms 9c, 9e in a relaxed condition. The lower portion 9c and the interconnected arm 9e of the latch member 7 are wedged into contact with the opposing sides of the end post slot 22 in order to bias the two arms 9c, 9e toward each other so that the latch member 7, when inserted into the end post slots 22, assumes a preloaded condition, wherein the two arms 9c, 9e resist their capture by the walls of the end post slots 22. A card-contacting projection 16 of the latch member 7 must be moved laterally outwardly along the path defined by line N to effect latching of the edge card 4 in the connector 1 to hold the edge card 4 in place within the card slot 6. 
     The latch member 7 further includes means by which the latch member may be manipulated by a user in order to release the edge card from the connector. This manipulating means is illustrated as a projecting end portion 9d which generally opposes the end 4d of the edge card 4 and extends along the end 4d up to the outermost edge 130 of the edge card 4. This end portion 9d includes, as illustrated in FIGS. 3 and 7, a tab 14 which is partially bent over the end portion 9d away from the edge card 4 about the axis P to provide a surface which facilitates engagement by the fingers of a user. In operation, the edge card 4 may be released from its engagement with the connector 1 when a user pulls the tabs 14 outwardly and away from the edge card ends 4d. 
     As illustrated in FIGS. 3 &amp; 6, the latch member 7 includes the arcuate card-engaging projection 16 which extends inwardly toward the edge card 4 in general alignment with the longitudinal axis N of the card slot 6. The connector of the present invention provides increased connection performance when used with the DIMM-type edge card 4 depicted in FIG. 2 DIMMs typically do not include the redundancy provided for by a SIMM (single in-line memory module) and thus needs a more accurate one to one alignment between its contact pads and a terminal contact portions of the connector. In this regard, the secondary printed circuit board which forms the substrate for a DIMM typically includes notches 4c formed in the opposing ends of the edge card 4. In this regard, the card-engaging projections 16 of the connector latch members 7 are aligned with the edge card notches 4c. DIMMs are usually smaller in size and more delicate than SIMMs and because of their low profile, they may be mounted closely to the surface 20 of the mother board. 
     The projections 16 preferably have a rounded profile as illustrated and importantly, preferably have radius which approximates that of the edge card notches 4c toward the center of the projections 16, but which is overall slightly less than the radius of the notches 4c. This is so that the projections 16 may fit within the notch 4c of the edge card 4 and ensure card-engaging contact at or near the centerline of the notch 4c. The projection 16 is nominally defined by two generally parallel opposing sidewalls 24, 25 and an intermediate portion, or card-contacting portion 16a, which interconnects the two sidewalls 24, 25 together. The distance between the sidewalls 24, 25 is less than the overall diameter of the edge card notch 4c (FIG. 8) so that the projection 16 will easily fit inside of its corresponding card notch 4c, and will concentrate its contact with the edge card 4 near the center of the notch 4c. The contact which occurs between the latch member 7 and the edge card 4 occurs along an arc φ. (FIG. 8.) 
     The card-contacting projection 16 is defined by forming its sidewalls 24, 25 in the latch member between the lower portion 9c and the tab portion 9d thereof and by further blanking the latch member 7. This blanking defines two distinct portions of the projection, which shall be referred to descriptively herein as &#34;upper&#34; and &#34;lower&#34; sections insofar as these sections have such an orientation with respect to the edge card 4 in the Figures. During the blanking, a slot 26 is formed between the retention arms 8 and the projection lower section 16 so that the projection upper section adopts the configuration of a pair of retention arms 8 in FIG. 6 and retention arms 8&#39; in FIG. 10. 
     By blanking the slots 26 to form the retention arms 8, the height of the slots 26, that is, the distance between the upper surface of the projection lower section 16 and the abutment surfaces 13 may be controlled to a much higher degree of precision (in the order of 0.001 inches or better) than if the retention arms 8 were stamped and formed from a tab, such as illustrated in FIGS. 13-15. This height control improves the ability of the connector to retain the edge card in place within the connector housing, thereby improving the overall performance of the connector. Additionally, by blanking the retention arms 8, it will be appreciated that the retention arms have a &#34;full&#34; cross-section to resist forces imparted or stresses developed by repeated insertion and removal of the edge card such as is commonly encountered in quality control testing. A full section means that the retention arms may utilize the entire depth of the latch member 7 within the projection sidewalls 24, 25 directly underneath the retention arms 8 and extending toward the junction of the sidewalls 24, 25 with the latch member sections 9c, 9d which structure is lacking in the connector illustrated in FIGS. 13-15 and that described in said European Patent Publication No. 0632542. The retention arms 8 extend above the projection lower section 16a generally along the axes of the two projection sidewalls 24, 25 and slightly outwardly therefrom. 
     In the embodiment illustrated in FIG. 6, the retention arms 8 terminate in ends 17 located slightly past the intersection of the sidewalls 24, 25 wherein they extend partially past the perimeter of the projection card-contacting portion 16a. The retention arm ends 17 define the outermost ends of lower abutment surfaces 13 which engage the confronting surface 4b of the edge card 4, when the edge card is installed in the housing 3 as illustrated in FIG. 7. The slot 26, in effect, bifurcates the projection 16 into two distinct portions which collectively engage the edge card 4 in two different planes of engagement. Consequently, the card-containing portions 16a of the lower projection sections 16 of the latch members 7 engages the lateral edges 4d of the edge card 4 at the interior confronting surface of the edge card slot 4c, while the retention arm abutment surfaces 13 of the latch member projection upper section engage the confronting surface 4b of the edge card 4. Accordingly, the edge card 4 is effectively retained in the connector 1 in two different planes which are coincident with the plane of the edge card and transverse thereto. 
     In another important aspect of the present invention, each retention arm 8 is provided with an inclined surface 12 which slopes downwardly in FIGS. 7 and 8 toward the projection lower section 16 and which terminates in an end 12a. These inclined surfaces serve as cam surfaces which the inner periphery of the edge card notches 4c engage when the edge card is rotated into place as illustrated in FIG. 2. As the edge card 4 is initially rotated into place within the connector, it will be seen that the inner peripheries of the edge card notches 4c contact the retention arm inclined surfaces 12. As the rotation of the edge card continues, the edge card rides upon the latch member inclined surfaces 12, applying a force opposite to their preloading and causing them to spread laterally outwardly in the direction indicated by the arrow M, thereby forcing the retention arm 8 and the latch members 7 laterally outwardly within the connector end slots 22 until the edge card snaps under the retention arms 8, whereupon the latch members 7 &#34;snap&#34; back toward the edge card 4 so that the retention arm abutment surfaces 13 contact the edge card surface 4b. 
     Another embodiment of a connector 1&#39; having a latch mechanism of the present invention is illustrated in FIGS. 10 &amp; 11. In this embodiment, the retention arms 8&#39; have a generally curved configuration and include curved inclined surfaces 12&#39; which incline gradually toward the edge card 4&#39; and which terminate at ends 12a&#39; to define a pair of retention arms with end portions 17&#39; that extend past the perimeter of lower contact portion 16a&#39; and the perimeter of the edge card notch 4c&#39;. The retention arms 8&#39; also include abutment surfaces 13&#39; on their lower surfaces which are defined in part by the slot which separates the upper and lower sections of the latch member projection 16&#39;. 
     Although in this description the connector 1 is described as being mounted to a mother board such that the connector assumes a generally horizontal position with respect to the mother board, it will be understood that the connector 1 may also be mounted on a mother board in a generally vertical orientation and still obtain the benefits and advantages of the invention. 
     For example, in a DIMM type edge card, as depicted in FIGS. 1-12, any rotation of the edge card 4 in and out of the connector 1 will impact upon the latch members 7. The use of two retention arms 8 for each latch member 7 will give better edge card retention with respect to the area of the circuit board engaged by the latch members 7. The notches 4c of the edge card 4 ride upon the blanked retention arm cam surfaces 12 which permits the latch members 7 to accommodate entry of the edge card 4 into engagement with the connector 1. Once the edge card 4 is engaged, the interior central portions of the projections 16 will engage the edge card and provide shock resistance to the connector to maintain the edge card in lateral alignment with the card slot terminals 2. 
     Additionally, it will be appreciated that the second embodiment of the invention depicted in the Figures, with its curved retention arm cam surfaces 12&#39; will provide more cam surface than with the straight cam surfaces of the first embodiment which, to a degree, will provide an easier force to press the edge card 4&#39; into engagement with the latch member 7&#39;. 
     Accordingly, it will be appreciated that the embodiments of the present invention have discussed herein are merely illustrative of a few applications of the principles of the invention. Numerous modifications may be made by those skilled in the art without departing from the true spirit and scope of the invention.