Abstract:
A cam-in DIMM card connector comprises camming protrusions provided on flexible side walls that rotationally guide a board into latching engagement with the connector. In the fully latched position the board is levered firmly between a top corner and opposing side wall of the board receiving slot in order to straighten any warping in the board. Greater dimensional tolerance can therefore be supported by the connector.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a connector for mating with a printed circuit board by means of a pivoting cam-in assembly, for applications such as Dual In-Line Memory Modules (DIMM). 
     SUMMARY OF THE PRIOR ART 
     In applications such as SIMM (Single In-Line Memory Module) and DIMM (Dual In-Line Memory Module) cards for computer systems, memory chips on a printed circuit are interconnected by circuit traces to a plurality of juxtaposed circuit pads arranged along the edge of the card, which can then be plugged into a connector, for interconnecting the memory modules to a computer. In many applications, the card must be unpluggable in order to exchange or replace the card. The contact pads arranged along the edge of the card are usually provided on either side of the card. 
     In SIMM cards, aligned contact pads on opposite sides of the board are electrically interconnected. The connector typically has edge-stamped contacts for contacting contact pads on both sides of the board, for example as shown in U.S. Pat. No. 4,575,172, where each contact has a pair of contact points abutting opposed aligned contact pads of the PCB. Adjacent contacts are closely spaced together, in order to have a large number of connections in one connector. Due to the high mating forces, low insertion force (LIF) plugging systems are therefore provided. One common LIF means is to cam-in the board by pivoting action as described in U.S. Pat. No. 4,575,1272. 
     In U.S. Pat. No. 4,747,790, an example of both direct plug-in and pivot cam-in is shown for a connector with leaf-spring contacts. Contacts used in DIMM connectors are electrically separate on either side of a printed circuit board. It is typical to use leaf-spring contacts that have a greater flexibility than the edge-stamped contacts often used in SIMM card connectors. In DIMM card connectors the contacts are usually gold plated. The gold plating permits lower contact forces as the formation of resistive oxide layers is avoided. Due to the lower contact forces, it is typical to simply plug-in edge-cards into DIMM connectors in a linear direction, although it is also known to pivotly cam-in the board if mating force reduction is required. 
     One of the problems of edge-card connector systems, in particular with a large number of contacts extending over a significant length, is that the contact may not be effected reliably if the printed circuit board is excessively warped. The longer the edge-card, the greater this problem becomes. The problem is aggravated by the desire to have a higher density of connections, which leads to smaller terminals, resulting in a reduction of their elastic displacement range. Such problems affect both DIMM and SIMM card connectors. 
     Manufacturing the boards within certain tolerances increases their costs. In view of the large number of applications, it is also difficult to ensure that boards with specified tolerances will always be used with a particular connector, therefore affecting the reliability of such connections. It would therefore be desirable to provide a connection system that accommodates the above mentioned problems in a more reliable, yet cost effective manner. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of this invention to provide an edge-card connector that provides a reliable connection to an edge card, in particular to overcome problems of tolerances in thickness or bending of the edge card. 
     It is an object of this invention to provide a low insertion force edge-card connector that ensures reliable and secure connection. 
     It would be advantageous to provide a reliable low insertion force edge-card connector that ensures reliable contact to an edge-card with tolerances in bending or thickness, in a cost effective manner. 
     Objects of this invention have been achieved by providing an edge-card connector according to the claims. In particular, by providing an edge card connector comprising a housing having a slot for receiving the edge of a printed circuit board therein and electrical terminals extending alongside the slot, wherein the latch is dimensioned with respect to opposing side walls of the slot in such a manner as to ensure resilient abutment of opposing sides of the board, against opposing sides of the slot in the fully mated position. Advantageously therefore, any excessive warpage in the board is straightened by resilient abutment with the opposing sides of the slot. 
     The slot can be dimensioned such that in the fully mated position, one side of the board is resiliently biased against a top edge of one side of the slot, the edge thereby concentrating the bending forces to improve the straightening effect. 
     The connector can be provided with a camming guide that engages the board shortly after rotation from the insertion position, guiding the board during pivotal movement to the fully mated position. In order to follow the pivotal movement, the camming guides could be provided with an arcuate shape. The camming guides have the advantage of not only preventing insertion of the board at an incorrect angle, but also maintain the board securely in the slot during the pivoting movement thereby assisting the mating operation and preventing damage to the connector by faulty insertion and rotation. 
     The arcuate camming members and latching means could advantageously be provided on both longitudinal ends of the connector, on sides walls extending above the connector slot and integrally formed with the connector housing for a cost effective solution. 
     Reliability of the connection can be further enhanced by increasing the elastic range of the terminals. The latter is achieved by positioning the retention features of the terminals, for retention to the connector housing proximate a mounting face of the connector remote from the edge-card receiving end. The aspects and advantages of this feature will be more apparent in the following description. 
     Further advantageous aspects of the invention are described in the claims or will be apparent from the following description and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of a connector according to this invention; 
     FIG. 2 is a cross-sectional view through a connector according to this invention; 
     FIG. 3 is a side view showing mounting portions of terminals of a conventional connector; 
     FIG. 4 is a side view of part of a terminal according to this invention; 
     FIG. 5a is an isometric view of part of a connector according to this invention and a board being plugged thereinto; 
     FIG. 5b is a schematic cross-sectional view illustrating a first insertion position of the board; 
     FIG. 6a is a view similar to FIG. 5a, but with the board in the fully mated position; 
     FIG. 6b is a schematic view similar to that of FIG. 5b, but showing the board in the fully mated position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 and 2, an edge-card connector 2 comprises an insulative housing 4 having a card receiving slot 6 extending longitudinally from the first end 8 to an opposed second end 10, and two rows 12,14 of electrical terminals 13,15 positioned either side of the slot 6 for electrically contacting circuit traces of a printed circuit board 16 (see FIGS. 5 and 6) inserted therein. The connector housing 4 has an upper card receiving face 18, a lower mounting face 20 opposed thereto for positioning on a printed circuit board, longitudinal side walls 22, and end walls 24 that extend upwards beyond the card receiving face 18 to upper free ends 26. The end walls 24 are attached to the housing on one side or attached end 28 only such that the end wall 24 is resiliently biasable outward in the direction D, as shown in FIG. 1, at an edge 30 opposed to the attachment end side 28. 
     Referring to FIG. 2, the card receiving slot 6 comprises a bottom face 32, a first side face 34 alongside the first row 12 of terminal 13, and a second side face 36 alongside the second row 14 of terminal 15. The housing 4 further comprises contact receiving cavities 38 extending from the mounting face 20 to the board receiving face 18 for receiving the contacts 13,15 therein. Both the contacts 13 and 15 comprise a connection section 40, in this embodiment comprising pins for mounting in a printed circuit board, a retention section 42 for secure retention to the housing 4, and a cantilever beam spring-arm 44 extending to a free end 46 proximate the board receiving face 18. The spring-arm comprises a contact section 45,47 respectively of the first and second contacts 13,15 protruding beyond the slot side faces 34,36 respectively. Between the retention section 42 and spring-arm 44 is a transition portion 48,49 that interconnects the contact arm to the retention section. 
     Referring to FIG. 3, the transition and retention sections 48&#39;,49&#39; and 42&#39; of first and second contacts 13&#39; and 15&#39; of a conventional connector are shown. The dotted line represents the mounting portion 40&#34; of the contact column adjacent to the contacts with the mounting portion 40&#39;. In other words, adjacent contacts have their mounting portions 40&#39;,40&#34; offset such that the contacts can be placed closer together whilst nevertheless having a large and sturdy retention section. The latter also enables a denser packing of the mounting portions on a printed circuit board. Switching the mounting portion 40&#39;,40&#34; either side of the contact spring arm for adjacent contacts, is termed hereinafter as &#34;joggling&#34;. In the conventional connector shown in FIG. 3, the joggling occurs below the retention portion 42&#39; which serves to securely fasten the terminals within a connector housing. The retention feature 42&#39; reduces the overall spring arm length and therefore its flexibility (i.e. elastic displacement range). 
     In the present invention, and in particular referring to FIG. 4, the retention section 42 is provided below the transition portion 48, the joggling occurring therefore above the retention section 42 such that the transition portion 48 adds to the elasticity of the spring-arm 44. A more flexible contact is thus provided (or the contact can be made more compact) than the prior art solution. The contacts 13,15 are assembled in the cavities 38 by stitching the contacts from the mounting face 20 through passages 50 (see FIGS. 2 and 5a), that communicate the cavities 38 with the mounting face 20. The retention portion 42 may comprise a retention barb 52 or 53 extending laterally from the plane of the contact that engages in an interference fit in a corresponding slot 54 in the housing. The slot 54 could be provided as a continuous longitudinal slot, whereby the barbs would be provided as in 52, projecting transversely out of the plane of the retention portion 42. In FIG. 2, one can see the mounting portions 41 of adjacent contacts that are joggled with respect to the mounting portions 40 of the terminals 13,15. 
     Referring mainly to FIGS. 5a and 2, the housing is shown comprising a latching member 52 comprising a portion 53 of the end wall 24 that extends above the board receiving face 18, and a latching protrusion 54 having a locking shoulder 55 engageable against an edge 58 of a printed circuit board 16 when fully mated therewith as shown in FIG. 6a. At the free end 26 of the resilient end wall 24, is provided a camming protrusion 60 protruding toward the connector and having an arcuate shape with shoulder 61 enabling rotational engagement with a corresponding shoulder 63 formed from a groove or recess 62 in the printed board 16. 
     The connector further comprises an insertion guide 64 projecting above the slot 6, to help guide the printed circuit board 16 into the slot 6, in conjunction with an insertion guide end 66 of the camming protrusion 60. Cooperation of the camming member insertion guide 66 and the insertion guide 64 ensures that the board 16 is positioned and guided at a specific angle when inserted into the connector slot 6. This prevents the board from being inserted at an incorrect angle that could damage the terminals 13,15 within the connector. When the board abuts the bottom face 32 of the slot 6 the groove 62 aligns with the camming protrusion 60. The board can then be pivoted, whereby the camming protrusion 60 engages in the groove 62 until latching of the protrusion 54 with the edge 58 of the board. The latching protrusion 54 is provided with resiliency (to enable engagement with the board) by the resiliency of the end wall portion 52, due to the cantilever attachment of the end wall. The resiliency of the end wall is further enhanced by separation of the end wall at the insertion end 30 from the connector body below the board receiving face 18. This gives the effect of pivotly &#34;hinging&#34; the latch member 52 at an attachment end 70 at one side 28 of the housing 4. 
     Referring mainly to FIGS. 5b and 6b, the board straightening effect of the invention will now be explained. Initially, as shown in FIG. 5b, the board is inserted into the slot 6 until abutment with the bottom face 32. The board is then pivoted, whereby the groove 62 engages the camming protrusion 60, to the fully mated position shown in FIG. 6b, where the latch protrusion 54 engages the board. In this fully mated position, the board is resiliently biased in abutment against an upper edge 72 of the slot 6 at the board receiving face 18, of the slot side face 36. Simultaneously, the lower end 17 of the board 16 abuts against the opposing slot side face 34. The latch protrusion is dimensioned in such a manner as to provide a resilient force (the elastic energy being stored in the connector and the board) that straightens any warping in the board by engagement thereof against the upper corner 72 and opposite side wall 34 of the connector slots 6. The lever arm between the position of the latch protrusion 54, the upper corner 72 and the lower end 17 provides sufficient force to straighten the board. 
     During the pivoting movement of the board, the cam protrusion also engages the groove 62 along the whole rotational movement, which prevents partial removal of the board from the slot which could damage the contacts or produce bad electrical connection. Furthermore, the guiding facilitates assembly of the board to the connector by an operator. The provision of latching members 52 and camming members 60 at both ends 8,10 of the connector ensures stable guiding and latching. 
     The effects of straightening the board and increasing the elastic range of the contacts significantly improves the ability to absorb dimensional tolerances, and/or provide a higher density of contacts per length of board. Furthermore, the cooperating guide features and camming member prevent incorrect installation of the board into the connector thereby protecting the contacts and in addition facilitating the coupling of a board to the connector by an operator. By integrally molding the latching member and camming member to the connector housing end walls, a particularly cost effective connector is provided. 
     Advantageously, therefore, a reliable edge-card connector is provided that can absorb greater dimensional tolerances in the board, and protects the contacts from damage, in a cost effective manner.