Patent Publication Number: US-4148537-A

Title: Zero insertion force connector for printed circuit boards

Description:
BACKGROUND AND OBJECTS OF THE INVENTION 
     The present invention relates to connectors for electrically connecting one circuit board with another, and more particularly to such a connector which facilitates entry and withdrawal of the circuit boards. 
     Connectors for the electrical interconnection of printed circuit boards have heretofore been proposed. Traditionally, connectors of this type include a housing which forms a slot sized to receive a daughter board. A plurality of contacts are retained in the housing and include flexible ends that can be spread apart to receive the daughter board and engage the conductors thereof. Other ends of the contacts project from the housing and are adapted for connection with a mother board. In some instances the flexible ends of the contacts are forcefully spread apart upon being contacted by the daughter board. However, the cumulative resistance offered by the contacts can be difficult to overcome and may result in damage occurring to the circuit boards. 
     With this difficulty in mind, connectors have been proposed in which the resilient ends of the contacts can be spread apart prior to insertion or withdrawal of the daughter board. This usually involves some sort of manually actuable camming member which urges the contacts open against an inherent closing bias, or urges them closed against an inherent opening bias. Exemplary of connectors of this type are those disclosed in Hartmann U.S. Pat. No. 3,665,370 issued May 23, 1972; Lightner U.S. Pat. No. 3,848,222 issued Nov. 12, 1974; Carter U.S. Pat. No. 3,865,457, issued Feb. 11, 1975; Pritulsky U.S. Pat. No. 3,897,991 issued Aug. 5, 1975; and Yeager et al. U.S. Pat. No. 3,899,234 issued Aug. 12, 1975. 
     Such connectors, often referred to as zero force insertion connectors, are intended to facilitate the entry and removal of the daughter boards and minimize the strain on the circuit boards. 
     It is desirable that connectors of this or any other type be of minimal dimension, especially in the lateral direction, or width, to maximize the number of connectors which can be mounted to a mother board. The presence of a camming mechanism may tend to produce an excessive increase in width. 
     It is further important that the durability of the connector be maintained. That is, any possible fatigue-induced breakage resulting from repeatedly camming the contacts open or closed, should be avoided. 
     For example, in one instance a connector has been heretofore proposed as described in an article presented at the Ninth Annual Connector Symposium Proceedings held Oct. 21, 1976 at Cherry Hill, N.J., the article entitled &#34;A new Zero-Insertion Force Card-Edge Connector&#34; by R. Cobaugh and A. Taylor, pages 400-401, and in an AMP Brochure designated as Data Sheet Number 76-376, Revised Oct., 1976, pages 15-20 to 15-24. In this connector, inwardly-biased flexible ends of the contacts are mounted in the upper portion of a pair of side walls of the connector. The lower end of each side wall is hooked beneath the underside of a stationary base part the connector to provide a hinge about which the side wall may swing. A camming bar is slidably mounted between the base and the side wall so that when the bar is slid longitudinally, the side wall is caused to swing outwardly about its hinge, thereby spreading the contacts apart. One characteristic of this type of connector is the increased width resulting from the presence of the swinging side wall, which is located laterally outwardly of the camming bar. Furthermore, in order to remove the side walls from the base for servicing purposes, it is necessary to separate the side walls from not only the contacts, but from the hooked connection with the base. 
     It is, therefore, an object of the present invention to provide a novel connector for facilitating entry and removal of a circuit board. 
     It is another object of the invention to provide such a novel connector of relatively narrow width. 
     It is a further object of the invention to provide such a novel connector which is highly durable and which minimizes the effort needed to actuate the contacts. 
     It is an additional object of the invention to provide a novel connector which is easily disassembled for servicing. 
     It is still another object of the invention to provide a zero force insertion connector which employs a camming bar that is both slidably and swingably mounted to a base. 
     BRIEF DESCRIPTION OF INVENTION 
     These objects are achieved by a circuit board connector of the type including an aperture for receiving a circuit board. The connector includes a base retaining a row of longitudinally spaced contacts. The contacts include flexible portions adjacent one end. A camming bar is mounted on the base for longitudinal sliding movement and for swinging movement about a longitudinal axis. A contact actuating member is mounted on the camming bar and is engageable with the contacts. The base and the camming bar include cam means responsive to longitudinal sliding movement of the camming bar for swinging the camming bar and the contact actuating member about the longitudinal axis. In this manner, the flexible portions of the contacts are displaced away from the circuit board-receiving apertures to facilitate entry or removal of the circuit board. 
     The base includes a socket within which the camming bar is seated, to form the longitudinal swinging axis of the camming bar. 
    
    
     THE DRAWING 
     The advantages of the present invention will become apparent from the subsequent detailed description of a preferred embodiment thereof in connection with the accompanying drawing in which like numerals designate like elements and in which: 
     FIG. 1 is a plan view of a connector according to the present invention prior to the insertion of a daughter board; 
     FIG. 2 is a side view of an end portion of the connector; 
     FIG. 3 is a cross-sectional view of the connector, taken along line 3-3 in FIG. 1; 
     FIG. 4 is a perspective view of the connector, with a portion broken away to reveal the connector interior; 
     FIG. 5 is a cross-sectional view similar to FIG. 3, after the camming bars have been pulled out to spread the contacts apart; 
     FIG. 6 is a longitudinal sectional view through the connector taken along a plane which is perpendicular to the contacts; and 
     FIG. 7 is a cross-sectional view similar to FIG. 3 of a modified connector. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION 
     A preferred connector 10 according to the present invention comprises a base 12, a pair of slidable camming bars 14, and a pair of contact actuating members 16. 
     The base 12 includes a pair of longitudinally extending inner walls 18 that are interconnected by longitudinally spaced bridge walls 20. Connected to and situated laterally outwardly of the inner walls 18 are short stub walls 22. The inner walls 18 and the sub walls 22 form open sockets 24 at each side of the base 12. These sockets are open in a direction toward the contact actuating member 16. 
     Retained in the base within slots 26 formed between the bridge walls 20 are a plurality of contacts 28. Each contact 28 is in mutually facing relationship with a laterally oppositely disposed contact in the slot. Each contact 28 includes, at one end, a terminal post portion 30 which projects from the base and is securable within apertures in a mother board in conventional press-fit fashion. At its other end the contact 28 includes a flexibly resilient portion 32. The flexibly resilient portion 32 is generally curvalinear in shape and includes a section 34 which is bowed toward an oppositely located contact 20 in the slot, and an enlarged head 36 which includes a pair of ears 38 extending parallel to the longitudinal axis of the base 12. 
     The contact actuating members 16 each comprise a longitudinally extending back wall 40, an overhang portion 42 which extends inwardly from the back wall 40, and a plurality of laterally projecting longitudinally spaced ribs 44 which form longitudinally spaced recesses 46 therebetween. Each rib 44 includes longitudinally extending flanges 48 which overlie a portion of each recess. The ribs 44 are spaced laterally of the longitudinal center plane of the base to form an aperture 50 for receiving a daughter board. 
     The heads 36 of the contacts 28 are received within the recesses 46 such that the ears 38 are disposed behind the flanges 48, the latter forming shoulders for engaging the ears 38. 
     In a normal, unflexed condition of the contacts 28 the curved resilient portions protrude into the aperture 50 beyond inner faces 52 of the ribs 44. 
     The camming bars 14 are seated in the base 12 and carry the contact-actuating members 16. Each camming bar 14 includes a main body portion 56 and a pair of outwardly extending legs 58, 60 projecting from an inner side thereof. The legs are coplanar and extend in opposite directions. A first of these legs 58 is seated within the sockets 24 formed by the internal wall 18 and the sub walls 22 to form a longitudinal swivel axis for the camming bar 14. The sockets are outwardly flared at 23 to enable the legs 58 to swing within the sockets without having to bend or flex to any appreciable degree. A second of the legs 60 is disposed within slots 62 (FIG. 3) formed in the ribs 44 and is situated laterally inwardly of the back wall 40 of the contact-actuating member 16. 
     The main body portion 18 of the camming bar 14 includes an outer surface 64 which is coplanar with outer surfaces 66, 68 of the sub wall 22 and contact-actuating member 16. 
     The camming bar 14 is longitudinally slidable relative to the base 12 and the contact-actuating portion 16. As will be discussed below, when such longitudinal sliding movement occurs, the resilient portions 32 of the contacts 28 are flexed laterally outwardly away from the aperture 50. 
     A plurality of longitudinally extending inwardly open cam channels 70 are formed in the main body portion 56 of each camming bar 14 (FIG. 6). These channels 70 are guided for sliding movement against respective ones of a plurality of guide blocks 72 that are carried on the backside of the internal wall 18. 
     Each channel 70 includes a ramp 74 which is inclined. laterally inwardly in a longitudinally inward direction. 
     The camming bars 14 project longitudinally from the housing and include enlarged gripping portions 76 at their outer ends, enabling the cam bars to be manually displaced longitudinally. When the camming bar 14 is slid longitudinally outwardly, the ramps 74 are displaced laterally outwardly by the blocks 72, thereby pivoting the camming bar 14 outwardly about the first leg 58. At the same time, the camming bar 14 acts against the back wall 40 of the contact actuating member 16 to displace the latter laterally outwardly. The flexible portions 32 of the contacts 28 are thus caused to flex laterally outwardly away from the aperture 50 as they are engaged by the flanges 48 of the contact-actuating members 16. Accordingly, a daughter board can be inserted into a aperture 50 with minimal effort. Once the daughter board has been inserted, the camming bars 14 are pushed longitudinally inwardly, enabling the contacts 28 to be released to their normal position and against the conductors of the daughter board. 
     In FIG. 7, a modified connector 10A is disclosed which is of somewhat narrower width than that earlier described. The legs 60A of the camming bars 14A are arranged to overlie the upper surfaces 80A of the inner walls 18A of the base 12A. Each leg 60A is inclined away from the aperture 50A to accommodate outward flexing of the contacts 28A. The legs 58A are somewhat shorter than the corresponding legs 58 of the earlier described embodiment, and the outer face 82A of each sub wall 22A is beveled outwardly to facilitate swinging motion of the camming bar within the socket 24A. 
     In operation, the contacts are normally disposed in an inwardly biased condition toward the aperture 50 (FIG. 3). When a daughter board is to be installed, the camming bars 14 are pulled longitudinally outwardly so that interaction between the ramps 74 and the blocks 72 causes the camming bars 14 to be swung laterally outwardly about the longitudinal axes defined by the leg-and-slot arrangements 58, 24. At the same time, each camming bar 14 displaces the contact-actuating member 16 laterally outwardly so that the contacts are flexed away from the aperture 50. Accordingly, a daughter board may be installed with minimal effort. Thereafter, the camming bars 14 are pushed longitudinally inwardly, allowing the contacts 28 to snap laterally inwardly into contact with conductors of the daughter board. 
     Although the illustrated connector is of the top entry type, it will be appreciated that the end of the connector could be open to permit side entry of the daughter board, as well. Also, the contacts could be of the type which are biased outwardly, rather than biased inwardly. 
     It will be realized that the connector 12 enables a daughter board to be inserted or removed with minimal effort. This is achieved without unduly enlarging the lateral dimension of the connector, i.e., there are no side walls located outwardly of the camming bars. Rather, the lateral dimension of the connector extends from the outer surface of one camming bar to the outer surface of the other camming bar. 
     Moreover, the effort required to actuate the contacts does not involve appreciable bending or flexing of the camming bar, so that such effort is minimized. 
     Although the invention has been described in connection with a preferred embodiment thereof, it will be appreciated by those skilled in the art that additions, modifications, substitutions and deletions not specifically described may be made without departing from the spirit and scope of the invention as defined in the appended claims.