Edge card connector with biasing means

Abstract: An edge connector (20) is provided for a printed circuit board (94) having a mating edge (94a) and a plurality of contact pads adjacent the edge. The connector includes an elongated dielectric housing (22) having a board-receiving slot (24) for receiving the mating edge of the printed circuit board. A plurality of spring contact elements (48, 50) are mounted in the housing along at least one side of the slot. The spring contact elements have spring contact portions (48a, 50a) extending into the slot for contacting respective ones of the contact pads on the printed circuit board. A surface (52) on the housing at the one side of the slot defines a datum plane beyond which the spring contact portion of at least one of the spring contact elements extends into the slot. A biasing spring (58, 66, 78, 114) biases the printed circuit board against the surface, thereby deflecting the spring contact portion of the at least one spring contact element a predetermined amount.

Description: The invention relates to an edge card connector for receiving a printed circuit board according to the preamble of claim 1. In today's high speed electronic equipment, it is desirable that all components in an interconnection path be optimized for signal transmission characteristics, otherwise the performance of the system will be impaired or degraded. Such characteristics include risetime degradation or system bandwidth, crosstalk, impedance control and propagation delay. Ideally, the characteristics of an electrical connector would have little or no affect on the interconnection system. An ideal connector would be "transparent". In other words, the system would function as if the connector did not exist as part of the interconnection. However, such an ideal connector is generally impractical or impossible, and continuous efforts are made to develop electrical connectors which have as little effect on the system as possible. It has been found that inductance is one of the major concerns in designing an ideal connector. This is particularly true in electrical connectors for high speed electronic equipment, i.e. involving the transmission of high frequencies. A very popular type of electrical connector for such applications commonly is termed an "edge card" connector. In other words, an edge connector is provided for receiving a printed circuit board having a mating edge and a plurality of contact pads adjacent the edge. Such edge connectors have an elongated housing defining an elongated slot for receiving the mating edge of the printed circuit board. A plurality of terminals are spaced along one or both sides of the slot for engaging the contact pads adjacent the mating edge of the board. Most often, the terminals have some form or another of spring contact elements for biased engagement against the contact pads on the board and, most often, the spring contact elements are in one form or another of a cantilevered spring arm. With electrical connectors of the character described above, given electrical contacts of otherwise comparable geometry, the longer the spring contact arm or contact beam, the greater the inductance of the terminal and, cumulatively, the electrical connector itself. Therefore, it is desirable to have as short a contact beam as possible. Shortening the contact beam creates various problems. For instance, it is difficult to maintain constant contact pressures in a multiplicity of spring contact beams, particularly when the beams are relatively short. In addition, it is difficult to compensate for variances in the widths of printed circuit boards when the contact beams are short. In fact, such spring contacts can take a permanent set even when the contacts are displaced only a small amount. The contacts might take a permanent set after a relatively wide printed circuit board has been inserted into the connector. This permanent set of the contacts would make the connector ineffective when a relatively narrow board subsequently is inserted into the connector. If the contact beams do not make effective electrical connection with the contact pads on the edge of the printed circuit board, an unreliable or ineffective electrical connection results, rendering the connector effectively useless. This invention is directed to solving these problems by providing an edge card connector of the character described wherein the deflection of the spring contact elements is controlled, resulting in the ability to design very short spring contact beams. An edge card connector is known (EP-A-0 158 413 = US-A-4 575 172) wherein the terminals have spring contacts in the form of opposed spring arms, the ends thereof are offset from one another so as to offer a mouth for entering the edge of a circuit board. When the circuit board is pivoted into the slot of the connector, the opposed spring arms are biased and clamp the edge of the board therebetween. The surfaces are provided in the housing to limit the extent of bias to the spring arms. In an edge card connector DE-A-32 03 531) of the precharacterizing portion of claim 1 different surface means are provided to shift a datum plane according to the requirements given by the thickness of the circuit boards which are to be inserted into the edge card connector. The contact spring is provided to urge the circuit board against the respective datum plane. An object, therefore, of the invention is to provide a new and improved edge connector for a printed circuit board having a mating edge and a plurality of contact pads adjacent the edge. The invention is defined in claim 1. Generally, the edge connector includes a dielectric housing having a board-receiving slot for receiving the edge of the printed circuit board. A pair of spring contact elements is mounted in the housing along at least one side of the slot. The spring contact elements having spring contact portions extending into the slot for contacting respective ones of the contact pads on the printed circuit board. The invention contemplates that the housing include surface means at the one side of the slot defining a datum plane beyond which the spring contact portion of at least one of the spring contact elements extends into the slot. Biasing means is provided in the housing for biasing the printed circuit board against the surface means, thereby deflecting the spring contact portion of at least one spring contact element a predetermined amount. With the above structural combination of an edge connector of the character described, it has been found that the lengths of a spring contact arm or beam, from a rigid base portion of the contact element to a point of contact with a respective one of the contact pads on the printed circuit board, can be as small as on the order of 2.286 mm (0.09 inch). Such a spring contact arm can project into the slot means, beyond the surface means which defines the datum plane, approx. 0.127 mm (0.005 inch). Such short spring contact arms or beams result in very small inductance for the contact beam. Various embodiments of biasing means are illustrated herein. In one embodiment, the biasing means includes a second, unitary spring portion of the one spring contact element. In another embodiment, the biasing means may be provided by a spring contact portion of a spring contact element other than the one spring contact element. The biasing means may be provided by an integral portion of the housing, such as a unitarily molded portion of a plastic housing. The biasing means may be provided by a spring device mounted on the housing independent of the spring contact elements. Still further, the biasing means may be provided by a cam member, independent of the housing, positionable in the slot means for camming against a side of the printed circuit board opposite the datum plane. The invention also contemplates a feature wherein the surface means which define the datum plane be provided by a plurality of projections forming substantially line contact between the projections and the printed circuit board. The projections may be formed as rib portions of the housing located between the spring contact elements. Such line contacts define the datum plane and support the side of the printed circuit board opposite the biasing means. During insertion the contact pads travel parallel to these rib portions but not over them. Therefore, polymer contamination of the contact surface due to direct contact between the contact pads and the plastic housing is eliminated. Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings, in which like reference numerals identify like elements in the figures and in which: FIGURE 1 is a vertical section, with certain portions removed, through an elongated edge connector embodying the concepts of the invention; FIGURE 2 is a vertical section similar to that of Figure 1 of an alternative embodiment with the biasing means integral with the short contact element; FIGURE 3 is a vertical section through another alternative embodiment wherein the biasing means is provided by an independent spring beam member; FIGURE 4 is a vertical section through still another embodiment wherein the biasing means is integral with the housing; FIGURE 5 is a vertical section through still another embodiment wherein the biasing means is provided by a separate cam member; FIGURE 6 is a fragmented top plan view of a section of still another embodiment illustrating the feature of a ribbed surface defining the datum plane for the spring contact members; FIGURE 7 is a vertical section through still another embodiment which is similar to Figure 1, but with the terminals configured for application of the connector as a right-angled connector; FIGURES 8-10 are sequential views of an alternate form of connector involving a rotating and latch configuration for the printed circuit board; FIGURE 11 is a view similar to that of Figure 10, wherein the connector employs an auxiliary biasing spring independent of the housing; FIGURE 12 is a vertical section through a further embodiment of the invention incorporating a molded hinge and latch member for the connector; and FIGURE 13 is a perspective view, partly in section, of the connector of Figure 1 showing the long contact element and its integral biasing means. Detailed Description of the Preferred Embodiments Referring to the drawings in greater detail, and first to Figures 1 and 13, the invention is embodied in an edge connector, generally designated 20, for receiving a printed circuit board (not shown) having a mating edge and plurality of contact pads adjacent the edge. These types of connectors commonly are called "edge card" connectors in that they have receptacle means in the form of slots for allowing insertion of an edge of printed circuit boards into contact areas of the connectors. Such connectors are well known in the industry as exemplified by U.S. Patent No. 4,575,172, assigned to the assignee of this invention. Such connectors are elongated and have rows of spring contact elements spaced along one or both sides of an elongated card-receiving slot extending lengthwise of a dielectric housing. The spring contact elements engage contact pads spaced along a mating edge of the printed circuit board which is inserted into the slot. With this understanding, edge connector 20 includes a dielectric housing, generally designated 22, having a board receiving slot means 24 running the length of the connector for receiving the edge of the printed circuit board. A plurality of standoffs 26 depend from housing 22 for engaging a surface 28 of a second printed circuit board 30. Often, printed circuit board 30 is called a mother board and the printed circuit board which is inserted into slot means 24 is called a daughter board. Still further, housing 22 includes a plurality of transverse cavities 32 spaced longitudinally of slot means 24 for receiving alternating, differently configured terminals, as described below. Specifically, each cavity 32 has a cavity portion 32a on one side of slot means 24 (the left-hand side as viewed in Figure 1) and a cavity portion 32b on the opposite side of the slot means (the right-hand side as viewed in Figure 1). Cavities 32 are separated lengthwise of the elongated housing by wall means or partitions which include wall portions 34a separating cavity portions 32a and wall portions 34b separating cavity portions 32b. Wall portions 34a are formed so as to create an overhang portion 35 over cavity portions 32a in order to protect the top portion of the terminals 38 and 40 and to prevent inadvertent stubbing thereof. Housing 22 also includes a plurality of holes 36 outside cavities 32 and generally in transverse alignment therewith, for purposes described hereinafter. Each hole 36 includes a lower mouth 36a opening at the bottom of housing 22. The entire housing is unitarily molded of dielectric material such as plastic or the like. Generally, a plurality of terminals are mounted in housing 22, spaced longitudinally of the housing and corresponding to the plurality of transversely aligned cavities 32 and holes 36. Before describing the terminals in detail, it should be understood that the printed circuit board which is inserted into slot means 24 often has a plurality of contact pads defining two rows of pads parallel to and generally along the edge of the printed circuit board, i.e. the mating edge which is inserted into the slot means. One row of contact pads is located near the absolute edge of the board, and the other row of contact pads is spaced inwardly from the one row. Therefore, conventionally, terminals are located on housing 22 with contact elements alternating lengthwise of the housing for alternatingly engaging the contact pads in the two rows thereof along the mating edge of the printed circuit board. More particularly, terminals, generally designated 38 and 40, are mounted in housing 22 in an alternating array lengthwise of the housing. In other words, terminals 38 alternate between adjacent terminals 40. Both configurations of terminals 38 and 40 are similar to the extent that they have base portions 42, barb portions 44 projecting upwardly from the base portions and contact feet 46 projecting downwardly from the base portions. The terminals are mounted to the housing by inserting barb portions 44 through mouths 36a of holes 36 from the bottom of housing 22 to create an interference fit between the barbs and the side walls of their respective holes. If desired, serrations could be formed in the edges of barbs 44. Contact feet 46 engage circuit traces on top surface 28 of printed circuit board 30 (the mother board). Terminals 38 have cantilevered spring contact elements 48 projecting upwardly from their respective base portions 42, and terminals 40 have cantilevered spring contact elements 50 projecting upwardly from the respective base portions. If desired, contact feet 46 could be replaced as known in the art to provide solder tails that project through holes in the printed circuit board. It can be seen in Figure 1 that spring contact element 48 of terminal 38 is shorter than spring contact element 50 of terminal 40. Therefore, hereinafter, spring contact element 48 may be termed the "short" element, and spring contact element 50 may be termed the "long" element. Regardless, it can be seen that both configurations of spring contact elements 48 and 50 project into slot means 24 for engaging the contact pads along the mating edge of the printed circuit board (daughter board) inserted into the slot means. Generally, the invention contemplates that housing 22 be provided with surface means along the side of slot means 24 from which spring contact elements 48, 50 project, to define a datum plane beyond which portions of the spring contact elements extend into the slot means. In addition, biasing means are provided on the housing for biasing the printed circuit board against the surface means, thereby deflecting the spring contact elements a constant and predetermined amount. More particularly, still referring to Figure 1, wall portions 34a between cavity portions 32a have edges 52 which are in alignment lengthwise of housing 22 and which define one side (the left-hand side as viewed in the drawings) of slot means 24. These edges combine to define the datum plane beyond which portions of spring contact elements 48 and 50 project as seen in Figure 1. Therefore, it can be understood that if the daughter printed circuit board is biased against the datum plane in the direction of arrow "A", the datum plane provides an abutment or stop means to prevent further movement of the board and further deflection of the spring contact elements. With the board engaging spring contact elements 48 and 50, the spring contact elements will be deflected in the direction of arrows "B". Once the board engages the datum plane defined by edges 52 of wall portions 34a, the spring contact elements cannot be deflected any further. Consequently, the deflection of the spring contact elements is predetermined and constant, as indicated by arrows "C" for spring contact element 48 and arrows "D" for spring contact element 50. With the above-described concept, it can be understood that such problems as variations in the thicknesses of printed circuit boards are obviated. In other words, regardless of the thickness of the board, when it is biased against datum plane 52 in the direction of arrow "A", the spring contact elements can be deflected only the described predetermined amount. Therefore, the length of the spring contact elements do not have to be made excessively long to compensate for variances in board thicknesses. In addition, by effecting a constant deflection of the spring contact elements, the elements effectively exert constant contact pressure onto the contact pads of the board, which also has been a continuing problem with edge connectors heretofore available. By knowing the precise deflection of the spring contact elements, as described above, the length of the spring contact elements from base portion 42 to points of contact 48a and 50a for spring contact elements 48 and 50, respectively, can be made as short as possible. In fact, the length of short spring contact element 48 from base portion 42 to contact point 48a, as indicated by arrows "E", has been designed to be 2,26 mm (0.089 inch). It is anticipated that length could range from approximately 1,27 to 3,43 mm (.050 to .135 inches). The short spring contact element projects into slot means 24 (i.e. the distance from datum plane 52 as indicated by arrows "C") is approximately 0,127 mm (0.005 inch) and could range from approximately 0,06 to 0,254 mm (.002 to .010 inch). As generally stated above, biasing means are provided in housing 22 for biasing the daughter printed circuit board against datum plane 52 and deflecting spring contact elements 48 and 50. In the embodiment illustrated in Figure 1, spring contact elements 40 have base portions which project transversely across the respective cavities 32, as indicated at 54, with a spring arm 56 projecting upwardly into cavity portion 32b, and with a spring element 58 projecting outwardly into slot means 24 from the side of the slot means opposite datum plane 52. It can be seen that spring element 58 is significantly larger and, thereby, intended to have a greater biasing force than the reactionary deflection forces of a pair of spring contact elements 48 and 50. Therefore, when the daughter printed circuit board is inserted into slot means 24 in the direction of arrow "F", spring element 58, which is bent back from the distal end of spring arm 56, will bias the board in the direction of arrow "A", against datum plane 52 and deflecting spring contact elements 48 and 50 the predetermined amount indicated by arrows "C" and "D". Figure 2 shows an alternate form of biasing means, and like numerals have been applied to like components in Figure 2 corresponding to those components described in relation to the embodiment of Figure 1. More particularly, in the embodiment of Figure 2, a terminal 38' again includes a base portion 42, a barb portion 44 and a short spring contact element 48. However, the "short" terminal has its base portion extended, as at 60, with a spring arm 62 projecting upwardly therefrom and bent back downwardly to define a second spring portion 64 opposing spring contact element 48. Otherwise, the biasing means functions the same as described above in relation to spring arm 56 and spring element 58 of terminal 40. Figure 3 shows still another embodiment of a biasing means, wherein the biasing means is provided by a separate spring element, generally designated 66, mounted in a housing 22' on the side of slot means 24 opposite the terminals, such as the one terminal 38 shown. Biasing spring 66 again includes a spring arm 68 projecting upwardly into selected ones of cavity portions 32b, with a spring element 70 bent downwardly and projecting into the slot means. The spring element has a base portion 72, with a barb 74 projecting upwardly into a hole 76 in the housing. Again, this biasing spring is provided for biasing the daughter printed circuit board against datum plane 52 and deflecting the spring contact elements of the terminals, such as the one spring contact element 48 shown. Figure 4 shows a form of biasing means wherein an integral spring finger 78 is molded unitarily with a housing 22". Spring finger 78 projects into slot means 24, and a distal end 78a of the integral spring finger biases the daughter printed circuit board in the direction of arrow "G" against datum plane 52 to deflect spring contact element 48 of terminal 38. Figure 5 shows an embodiment of a biasing means wherein a cam member 80 is separate from the housing means and is inserted into slot means 24' in the direction of arrow "H". The cam member has a cam surface 80a for engaging a cam surface 82 on housing 22"' for biasing the daughter printed circuit board in the direction of arrow "I" against datum plane 52 to deflect spring contact element 48 of terminal 38. Figure 6 shows a fragmented, somewhat schematic illustration of a means for defining the datum plane of the connector to establish substantially line contacts with the daughter printed circuit board. As schematically illustrated, and referring back to Figure 1, it can be seen that spring elements 58 project into slot means 24 from one side thereof, and spring contact elements 48 and 50 project into the slot means from the opposite side thereof. Ribs 84 are formed integrally with housing 22 between the terminals which define spring contact elements 48 and 50. The inner edges of the ribs are rounded to provide a tangential line contacts 84a for engaging the printed circuit board. An imaginary plane drawn through the edges of the ribs define the datum plane against which the printed circuit board is biased. By providing line contacts between the datum plane and the printed circuit board, the surface area of the board, and the contact pads in particular, in contact with the plastic material of the housing is minimized to minimize polymer contamination of the contact pads on the board. Figure 7 shows an embodiment of the invention where, again, like numerals have been applied to designate like components described in relation to the embodiment of Figure 1. This illustration shows that the connector can be rotated 90° to provide a right-angled configuration with mother printed circuit board 30. In this embodiment, contact feet 46' of a "short" terminal 38' depend from the bottom of housing 22 which was the side of the housing as illustrated in Figure 1. Standoffs 86 projects downwardly from the housing for engaging top surface 28 of the printed circuit board. Otherwise, the connector functions the same as described above in relation to Figure 1, with the daughter printed circuit board being inserted into slot means 24 in the direction of arrow "J". Figures 8-10 show the invention embodied in an electrical connector, generally designated 88, which includes a housing, generally designated 90, defining a slot means 92 for receiving a mating edge 94a of a daughter printed circuit board 94. Housing 90 is mounted to the top of a mother printed circuit board by means of standoffs 96. Alternating "short" and "long" terminals are mounted on the housing, one short terminal, generally designated 98, being fully visible in the figures. The terminals define spring contact elements 100 and 102 projecting into slot means 92 beyond a datum plane defined by edges 104 of wall portions 106 disposed between alternating ones of the terminals. The terminals have contact feet 108 for engaging circuit traces on the mother printed circuit board. In operation of connector 88 (Figs. 8-10), mating edge 94a of daughter board 94 is inserted into slot means 92 as shown in Figure 8. With the slot means acting as a fulcrum, the board is rotated in the direction of arrow "K" as shown in Figure 9. The board is rotated until its side edges snap behind latches 110 at opposite ends of the connector, integral with the housing. In this fully mated condition, as with the other embodiments of the invention, the housing biases the daughter board against datum plane 104, effecting a predetermined and constant deflection of the spring contact elements 100 and 102. Again, housing cantilevered wall portion 112 which defines slot means 92 can deflect slightly to apply a biasing pressure. Figure 11 shows an embodiment which is substantially identical to that shown in Figure 10, with daughter board 94 in its fully latched condition. In the embodiment of Figure 11, a U-shaped auxiliary spring member 114 is used, embracing wall portion 112, for exerting biasing pressure against daughter board 94 in the direction of arrow "L" to deflect spring contact elements 100 and 102. Lastly, Figure 12 shows an embodiment of a connector, generally designated 88', which is somewhat similar to the configuration of connectors shown in Figures 8-10 and 11. Consequently, like numerals are applied in Figure 12 to designate like components described above in relation to Figures 8-11. In this embodiment, daughter board 94 is laid against datum plane 104. A separate hinge member or cover 116 is hingedly connected to housing 90 by a living integral hinge 118. A hooked latch 120 is formed on the distal end of hinge member 116. The hinge member is rotated in the direction of arrow "M" against daughter board 94 to bias the board against datum plane 104 and deflect spring contact elements 100 and 102. Latch 120 engages a complementary latch surface (not shown) on housing 90 to hold hinged member 116 in its operative position. In the alternative to the cover acting to bias the board against the datum plane, a secondary spring may also be added for biasing. It will be understood that the invention may be embodied in other specific forms without departing from the scope of the appended claims.

Claims: An edge card connector for receiving a printed circuit board (94) having a mating edge and a plurality of contact pads, adjacent the edge, said connector (20, 88, 88') comprising an elongated dielectric housing (22, 22', 22'', 22''', 90) having slot means (24, 92) for receiving the mating edge of the printed circuit board and surface means defining a datum plane (52, 104), terminals (38, 40; 98) having spring contact means for contacting respective ones of the contact pads on one side of the printed circuit board, characterized in that said terminals (38, 40; 98) include a plurality of first spring contact elements (48, 100) arranged for contacting a first row of contact pads on said printed circuit board, and a plurality of second spring contact elements (50, 102) arranged for contacting a second row of contact pads on the printed circuit board (94), said spring contact elements (48, 50, 100, 102) are arranged on the same side as said datum plane (52, 104) and extend a predetermined amount (C) beyond said datum plane into said slot means (24; 92), and in that biasing means (56/58; 62/64; 68/70; 78; 80; 112/114; 116/120) are provided for biasing the circuit board (94) against the datum plane (52, 104) thereby deflecting the spring contact elements (48, 50, 100, 102) said predetermined amount (C). The edge card connector of claim 1 wherein each said first and second spring contact elements (48, 50, 100, 102) are in the form of a spring arm extending from a base portion (42), the spring arms of the first contact elements (48) being shorter than the spring arms of the second contact elements (50). The edge card connector of claim 1 or 2 wherein said spring contact elements (48, 50, 100, 102) are shaped to include points of contact (48a, 50a) which are arranged by said predetermined amount (C) beyond said datum plane (52). The edge card connector of claim 3 wherein said predetermined amount (C) ranges from 0,05 to 0,254 mm. The edge card connector of claim 3 or 4 wherein the distance (E) between said point of contact (48a) of the respective shorter arm (48) to said base portion (42) is on the order of 2,3 mm. The edge card connector of any of claims 1-5 wherein said terminals (38, 40), further to said spring contact elements (48, 50; 100, 102), also include contact feet (46) arranged for engaging circuit traces of a further printed circuit board (30). The edge card connector of any of claims 1-6 wherein said biasing means include a resilient portion (78) of the housing (22"). The edge card connector of any of claims 1-6 wherein the said biasing means includes a movable cam member (80) engaging a cam surface (82) of the housing (22''') and said printed circuit board (94) so as to urge same against the datum plane (52). The edge card connector of any of claims 3-6 wherein said biasing means includes spring arms (56, 62, 68), each having a bent spring element (58, 64, 70) which projects into a region of the slot means (24) between said points of contact (48a, 50a) from the side opposite to said datum plane. The edge card connector of claim 9 wherein each of said spring arms (62) is integral to a respective one of said terminals (38) which include the first spring contact elements (48). The edge card connector of claim 9 wherein each of said spring arms (56) is integral to a respective one of said terminals which include the second spring contact elements (50). The edge card connector of claim 9 wherein each spring arm (68), together with its spring element (70), forms a separate spring member (66) which is anchored in the housing (22'). The edge card connector of any of claims 1-6 wherein the biasing means includes a cantilevered wall portion (112) and latch means (110) which are integral with the housing (90), said wall portion (112) forming a fulcrum for the mating edge (94a) of a circuit board (94) and can deflect slightly, when a circuit board (94) is inserted into said slot means, said latch means (110) receiving the side edges of the circuit board (94) when the same is rotated about the fulcrum and snaps behind the latch means (110). The edge card connector of claim 13 wherein said biasing means includes a U-shaped auxiliary spring member (114) which embraces the wall portion (112). The edge card connector of any of claims 1-6 wherein said biasing means includes a cover (116) hingedly (118) connected to the housing (90) and a hooked latch (120) which engages a complementary latch surface at the housing (90) so as to bias the circuit board (94) onto the datum plane (104), the cover (116) when being closed defining said slot means for receiving the mating edge of the circuit board (94).

Inventors: BRUNKER DAVID L, HARWATH FRANK A, REGNIER KENT E, BRUNKER, DAVID L., HARWATH, FRANK A., REGNIER, KENT E.
Applicants: MOLEX INC, MOLEX INCORPORATED
Application year: 1993
Main classification: H01R23
IPC codes: H01R24, H01R12