Electrical connector for printed circuit boards

Abstract: An electrical connector (14) includes an elongated dielectric housing (16) having an elongated slot (18) disposed generally along a longitudinal axis (20) of the housing for receiving, edgewise, a printed circuit board. A plurality of terminals (28) are inserted in a given insertion direction (C) into a plurality of passages (22) along at least one side of the slot. Each terminal includes a retention portion (36) press-fit in a retention section (30) of a respective passage. The retention section is tapered in the insertion direction from a wider terminal-receiving mouth (30d) for facilitating insertion of a respective terminal into the passage to a narrower retention area (30e) for embracing the respective terminal at least in a direction transverse to the longitudinal axis (20) of the housing.

Description: Field of the Invention This invention generally relates to the art of electrical connectors and, particularly, to an edgecard connector having spring arm contacts for engaging circuit traces on a printed circuit board. Background of the Invention One type of electrical connector commonly is called an "edgecard" connector in that it includes an elongated housing having an elongated slot for receiving, edgewise, a printed circuit board. The connector mounts a plurality of terminals along one or both sides of the slot for making electrical contact with circuit traces adjacent the edge of the circuit board. A very popular connector of this type is called a SIMM socket. The terminals which often are used in edgecard connectors are press-fit terminals having stamped and formed spring arm contacts for mechanically and electrically engaging the circuit traces on the printed circuit board. A problem which consistently surfaces in the design of such edgecard connectors is the dilemma of providing high normal forces which are associated with undesirably high insertion forces of the terminals into the connector housing. In order to provide satisfactory mating between the board and the spring arm contacts, a sufficient normal force must be created to assure the desired electrical contact. A typical edgecard connector includes parallel opposing rows of terminals having spring arm contacts extending toward each other and defining convex contact engaging surfaces engageable with the circuit board. The spring arms act as cantilever beams, so that when a board is slidably inserted therebetween, the ends of the spring arm contacts are forced laterally apart. Typically, the higher the normal force provided, the greater the insertion force. Document FR-A-2 120 409 discloses an apparatus for insertion contact terminals into terminal receiving cavities of a connector housing requiring high insertion forces. Each cavity has a tapered terminal retention recess adapted to receive a wedge-like bulge of a respective contact portion disposed between a spring contact portion and a tail portion. To avoid that the contact terminal is damaged or destroyed during insertion the apparatus comprises a first device for push-in the contact terminal in the insertion direction into the cavity till the tail portion projects at the opposite side from the housing, and a second device which subsequently catches the tail portion at that opposite side and pulls that contact terminal fully into the cavity till the wedge-like bulge becomes wedge within the tapered recess, so that the contact terminal is fixed and maintained. One solution to the above problem of balancing high normal contact forces with undesirable high insertion forces has bee n to "preload" the terminals, as disclosed for example in US-A-4,596,245. In other words, when the terminals are press-fit into respective passages in the connector housing, the cantilevered spring arms are preloaded or "cocked" against their resiliency and held or preloaded in that condition behind retaining shoulders of the connector housing. While preloaded terminals are effective to solve certain problems, as described above, they create still further, more serious problems, particularly when relatively long connector housings are exposed to relatively high processing temperatures. Specifically, an edgecard connector often interconnects a first printed circuit board received edgewise in the connector, as described above, with a second printed circuit board by soldering processes which require the application of heat. / When an elongated connector housing is exposed to high heat, the plastic material of the housing softens, and the high number of preloaded terminals apply pressure which tends to collapse the softened housing along the board-receiving slot. The housings could be fabricated of materials which do not collapse under the forces of the preloaded terminals, but such materials often are cost prohibitive. A further solution is disclosed in document US-A-3,497,952 by using a molded thermoplastic housing block with apertures for receiving terminal portions which are provided with detents and recesses. During insertion of the terminal portions into the apertures the side walls which are in direct surface engagement with the detents are subject to stress concentration and deformed. After insertion the stressed portions of the housing block are warmed by indirectly or directly heating the terminals portions, thereby reducing the induced stress and results in relaxation of the housing plastic, so that the terminal portions are fixed. However, indirectly heating requires for example an induction heating apparatus and directly heating requires for example an electrical resistance heating apparatus. The present invention is directed to solving the myriad of problems identified above by controlling the inserted location of the terminals and, thereby, avoiding the use of terminals having preloaded spring contact portions. Summary of the Invention An object, therefore, of the invention is to provide an electrical connector of the character described, particularly an edgecard connector having terminals with spring contact portions for engaging a printed circuit board. In the exemplary embodiment of the invention, an electrical connector includes an elongated dielectric housing having an elongated slot disposed generally along a longitudinal axis of the housing for receiving, edgewise, a printed circuit board. The board has circuit traces adjacent an inserted edge of the board. A plurality of terminal-receiving passages are provided along at least one side of the slot. A plurality of terminals are received in the passages, with each terminal including a spring contact portion projecting into the slot for engaging a circuit trace on the printed circuit board. Each terminal also includes a terminal portion projecting from the housing and a retention portion press-fit in a retention section of a respective passage. Each terminal is inserted into its passage in a given insertion direction. The invention contemplates that the retention section of each terminal-receiving passage be tapered in the insertion direction from a wider terminal-receiving mouth for facilitating insertion of a respective terminal into the passage to a narrower retention area for embracing the respective terminal at least in a direction transverse to the longitudinal axis of the housing. The retention section has an inner side wall means nearest the slot and located to define a reference surface against which the retention portion of the terminal is engageable. The reference surface provides a minimum normal contact force between the spring contact portion of the terminal and the respective circuit trace on the printed circuit board. Preferably, the terminals are stamped and formed of sheet metal material. The spring contact portions of the terminals form cantilevered spring contact arms, and the terminal portions of the terminals form solder tails projecting from the housing. Another feature of the invention is that the retention portion of each terminal is wider than immediately adjacent portions of the terminals, with the retention section of each passage including side walls for press-fittingly engaging opposite edges of the retention portion in a direction generally parallel to the longitudinal axis of the housing. Therefore, in essence, each terminal is gripped on all four sides thereof when inserted into its respective passage. Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings. Brief Description of the Drawings The features of this invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with its objects and the advantages thereof, may be best understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements in the figures and in which: FIGURE 1 is a perspective view of an electrical connector of the type for incorporating the invention; FIGURE 2 is a fragmented perspective view of the right-hand end of the connector of Figure 1, with a pair of the terminals removed to facilitate the illustration; FIGURE 3 is a view similar to that of Figure 2, with the terminals about to be inserted into their respective passages; FIGURE 4 is a view similar to that of Figures 2 and 3, with the terminals fully inserted into their passages; FIGURE 5 is an enlarged fragmented view of a pair of the terminals partially inserted into their respective passages; FIGURE 6 is a view similar to that of Figure 5, with the terminals fully inserted into the passages; FIGURE 7 is a fragmented section through the housing illustrating the configuration of the retention section of a terminal-receiving passage; FIGURES 8-11 are sequential views of a pair of terminals of similar inclinations being inserted into their respective passages on opposite sides of the card slot of the connector; FIGURE 12 is a schematic, fragmented sectional view taken generally along a horizontal line through a terminal and the terminal retention section of the housing adjacent the top of the retention section; FIGURE 13 is a schematic, fragmented sectional view taken generally along a horizontal line through a terminal and the terminal retention section of the housing adjacent the bottom of the retention section; and FIGURE 14 is an enlarged, fragmented perspective view of a terminal retention section. Detailed Description of the Preferred Embodiment Referring to the drawings in greater detail, and first to Figure 1, the invention is embodied in an edgecard electrical connector, generally designated 14, which includes a dielectric housing, generally designated 16, unitarily molded of plastic material. As can be seen, the housing is considerably elongated and defines an elongated slot 18 disposed generally along a longitudinal axis 20 of the housing for receiving, edgewise, a printed circuit board (not shown). The printed circuit board has a plurality of circuit pads or contacts spaced longitudinally adjacent an insertion edge of the board, as is known in the art. Connector 14, is shown as a "dual readout" connector in that the printed circuit board will have electrically distinct circuit pads on both sides thereof adjacent the insertion edge of the board. Correspondingly elongated housing 16 has a plurality of terminal-receiving passages 22 spaced longitudinally of the housing on each opposite side of longitudinal slot 18. The printed circuit board is inserted into the slot in the direction of arrow "A", whereupon a spring contact portion of each terminal within a passage 22 establishes mechanical and electrical contact with one of the circuit pads of the board at the edge thereof. The connector has an ejection lever 24 pivotally mounted at each end of housing 16, at 26, for facilitating removal or ejection of an inserted printed circuit board from slot 18. The ejection levers are generally known in the art and are effective for engaging the inserted edge of the printed circuit board, or a shoulder portion of the board, to eject the printed circuit board opposite the direction of arrow "A", when the ejection levers are pivoted in the direction of arrows "B". Figures 2-4 show a pair of terminals, generally designated 28, for insertion into respective terminal-receiving passages 22 in the direction of arrows "C". The terminals are stamped and formed of sheet metal material, and the terminals of each pair are identical but oriented in opposite directions so as to be mirror images of each other when inserted into a pair of passages 22 on diametric opposite sides of slot 18 in connector housing 16. Each terminal-receiving passage 22 includes a retention section or slot, generally designated 30, for purposes described hereinafter. Each terminal 28 includes a spring contact portion 32 which, when inserted into a respective passage 22, projects into slot 18 for engaging a respective circuit pad on the inserted printed circuit board. Each terminal includes a tail portion 34 projecting from housing 16, when the terminal is fully inserted as shown in Figure 4. In the disclosed embodiment, tail portions 34 form solder tails for insertion into holes in a second printed circuit board for solder connection to circuit traces on the board and/or in the holes. Lastly, each terminal 28 includes a retention portion 36 which is wider than spring contact portion 32 and tail portion 34. The retention portions of the terminals are press-fit into retention sections 30 of terminal-receiving passages 22. Figures 2-4 are sequential view of insertion of terminals 28 into passages 22. In Figure 2, the terminals are completely removed from the housing and the respective passages. In Figure 3, the tips of spring contact portions 32 of the terminals have begun to enter passages 22. In Figure 4, the terminals are completely inserted into passages 22, with retention portions 36 of the terminals press-fit into retention sections 30 of the passages. When fully inserted, as shown in Figure 4, spring contact portions 32 of the terminals project into slot 18 for engaging the respective circuit pads at the edge of the printed circuit board. Figures 5 and 6 are enlarged depictions somewhat similar to the illustrations depicted by Figures 2-4, in order to better illustrate the shapes of terminals 28, terminal-receiving passages 22 and retention sections 30. With the terminals being stamped and formed of sheet metal material, it can be seen that spring contact portions 32 are bent or formed to define convex contact engaging surfaces 32a. These surfaces will be exposed within slot 18 of contacting the circuit traces on the inserted printed circuit board. It also can be seen that retention portions 36 of the terminals are stamped to be wider than spring contact portions 32 and terminal portions 34. The retention portions have stepped edges 36a. Retention section 30 of passages 22 also have longitudinal end walls 30a which are molded with stepped configurations corresponding to the configurations of edges 36a of the terminal retention portions 36. The longitudinal width of retention sections 30 is slightly smaller than the width of retention portions 36 in order to establish a press-fit between end walls 30a of the retention sections and edges 36a of the terminal retention portions 36. Upon securing retention portions 36 within the housing, spring contact portions 32 are free to move within passages 22 transversely of slot 18 in order to provide normal forces between the spring contact portions and the circuit traces on the inserted printed circuit board. Figures 7 and 14 show an enlarged illustration of one of the retention sections 30 on each opposite side of each terminal-receiving passage 22 for receiving and establishing a press-fit with the retention portion 36 of one of the terminals 28. Figure 7 also shows one of a plurality of mounting pegs 40 and one of a plurality of standoffs 42 molded integrally with and projecting from a bottom surface 44 of housing 16. As is known in the art, mounting pegs 40 are inserted into appropriate mounting holes in the terminating printing circuit board, and standoffs 42 are provided to space the housing from the board for solder reflow processing purposes. Lastly, Figures 7 and 14 shows that the housing is formed with lead-in or guide surfaces 45 leading to a mouth 30d of retention section 30 to guide a terminal thereinto. More particularly, in referring to retention section 30 in Figure 7, the retention section has an inner lateral side wall 30b nearest board-receiving slot 18 and an outer lateral side wall 30c furthest from the slot. Side walls 30b and 30c are tapered between wider terminal-receiving mouth 30d and a narrower retention area 30e. While side wall 30b is generally vertical, side wall 30c is sloped approximately 2° from vertical. Mouth 30d is laterally wider than the thickness of the sheet metal material of terminal 28, particularly at retention portion 36 of the terminal. This facilitates easy insertion of the retention portion 36 into retention section 30 (i.e. easy insertion of the terminal into passage 22). On the other hand, retention area 30e is dimensioned to be slightly smaller than the thickness of the terminal to establish a press fit with the upper area of retention portion 36 of the terminal int he direction of arrows "D". Therefore, while mouth 30d allows for ready insertion of retention portion 36 of the terminal, retention area 30e essentially grips only the upper area of retention portion 36 to grip the terminal in a direction transverse to axis 20 (Fig. 1), i.e. in the direction of arrows "D". With side walls 30b and 30c gripping the retention portion at retention area 30e transverse to axis 20, end walls 30a of retention section 30 are also slightly tapered to grip edges 36a of retention portion 36 in a direction generally parallel to axis 20, i.e. longitudinally of the elongated connector. As a result, the terminals, at their retention portions, are gripped on all four sides transverse and parallel to the longitudinal axis of the connector. Figures 12 and 13 best show the manner in which the terminals are gripped. Figure 12 is taken generally adjacent retention area 30e. Because the distance between side walls 30b and 30c is less than the thickness "T" of the material of the retention portion 36 of the terminal, the retention portion is gripped between side walls 30b and 30c in an interference fit as at "a". The width between edges 36a of the retention portion 36 is greater than the distance between end walls 30a adjacent the top of the retention section and slightly less adjacent the lead-in area of the retention section. Accordingly, end walls 30a also grip the retention portion in the retention area 30e as a "b". However, referring to Figure 13, it can be seen that the distance between side walls 30b and 30c is greater than the thickness T of the retention portion 36. Since the distance between end walls 30a is less than the width between edges 36a, the retention portion is gripped only on its edges adjacent the bottom of retention section 30 as at "c". Such a structure results in accurate alignment of the terminals as they are inserted into their terminal-receiving passages as well as securely fixing the terminals therein. Lastly, Figures 8-11 show the concept of the invention in establishing a reference surface against which terminals 28 are engageable to provide a minimum normal contact force between the spring contact portions 32 of the terminals and the respective circuit traces on the printed circuit board inserted into slot 18. These views should be considered in conjunction with Figure 7. More particularly, terminals 28 can be inserted into passages 22 in a variety of orientations. In other words, looking at Figures 8-11, the right-hand terminal in each figure is shown with the bottom of the terminal (i.e., tail portion 34) canted to the left as indicated by arrow "E". Spring contact portion 32 of the right-hand terminal is canted outwardly away from slot 18 in the direction of arrow "F" (Fig. 8). Still referring to Figure 8, the left-hand terminal 28 is shown with the bottom or tail portion 34 thereof canted outwardly in the direction of arrow "G". Therefore, the top or spring contact portion 32 of the left-hand terminal is canted inwardly toward slot 18 in the direction of arrow "H". Of course, there can be other canted or oblique orientations of the terminals as they are inserted into their respective passages in the direction of arrows "C". The illustrations of the terminals in Figures 8-11 are representative of varying angles as might be encountered in a conventional gang-insertion process of inserting terminals. Regardless of the canted orientation of terminals 28 as represented by the right and left hand terminals in Figures 8-11, the terminals always will end up in a fully inserted position with inner side wall 30b (Fig. 7), which is nearest slot 18, being the inner limit position or reference surface against which the retention portion 36 of a respective terminal can be engageable. The reference surface defined by side wall 30b, therefore, establishes the outer extreme position of the spring contact portion 32 and its convex contact engaging surface 32a. By precisely locating inner surfaces 30b of retention sections 30, a minimum normal contact force can be established between the spring contact portions of the terminals and the respective circuit traces on the printed circuit board. In other words, looking at Figure 11, if it is assumed that retention portions 36 of terminals 28 are located in abutting engagement against inner side walls 30b of the retention sections, this establishes a given spacing between convex contact engaging surfaces 32a of spring arm portions 32 of the opposing terminals, as indicated by dotted lines 50. The inserted printed circuit board will always be thicker than this distance, but the distance, as established by the location of the reference surfaces defined by side walls 30b, will equal a minimum required normal contact force designed for the particular electrical connector. Of course, as retention portions 36 of the terminals move away from reference surfaces 30b toward side walls 30c, the distance between convex contact engaging surfaces 32a (i.e. between dotted liens 50) will be slightly smaller and create slightly larger normal forces, but the forces, of course, will be within the minimum established range.

Claims: An electrical connector (14) for receiving an edge of a printed circuit board having contact pads adjacent the edge of the board, the connector including an elongated dielectric housing (16) having an elongated slot (18) disposed generally along a longitudinal axis (20) of the housing for receiving said edge of the printed circuit board, and a plurality of webs extending generally perpendicular to said axis (20) to define terminal receiving passages (22) along at least one side of the slot (18), said terminal receiving passages (22) having pair of terminal retention recesses (30) along said webs into which a press-fit portion (36) of a terminal is inserted, each said terminal retention recess (30) having an end wall (30a) generally perpendicular to said longitudinal axis (20) and a pair of opposed side walls (30b, 30c) generally parallel to said longitudinal axis, said opposed side walls (30b, 30c) being generally planar; and a plurality of terminals (28), each being secured within one of said terminal receiving passages (22), each terminal (28) including a tail portion (34) projecting from the housing (16), a press-fit portion (36) press-fit into said terminal retention recesses (30) of a respective passage (22) in a given insertion direction, said press-fit portion (36) having a predetermined thickness, and a cantilevered spring contact portion (32a) extending between said press-fit portion (36) and a free end of said terminal (28), said free end being spaced from said housing (16) and said spring contact portion (32a) projecting into the slot (18) for engaging a contact pad on the printed circuit board and being spaced from said housing (16) along its entire length between said press-fit portion (26) and said free end; each said terminal retention recess (30) of a terminal receiving passage (22) being tapered in said insertion direction between said opposed side walls (30b, 30c) from a wider terminal-receiving mouth (30d) for facilitating insertion of a respective terminal (28) into the passage (22) to a narrower retention area (30e) for embracing the respective terminal (28) at least in a direction transverse to said longitudinal axis (20), one (30b) of said opposed side walls being located nearest said slot (18) to define a reference surface against which the press-fit portion (36) of the terminal is engageable to provide a minimum normal contact force between the spring contact portion of the terminal and the respective contact pad on the printed circuit board; characterized in that said predetermined thickness of said press-fit portion (36) of said terminal (28) being wider perpendicular to said axis (20) than said narrower retention area (30e) and being narrower perpendicular to said axis (20) than the distance between said side walls (30b, 30c) of a terminal retention recess (30) whereby said press-fit portion (36) of said terminal is press-fit between only a portion of at least one of said opposed side walls (30b, 30c) and is press-fit between essentially the entire length of the end walls (30a). An electrical connector (14) as set forth in claim 1 wherein said terminals (28) comprise stamped and formed sheet metal members. An electrical connector (14) as set forth in claim 2 wherein said retention portion (36) of each terminal (28) is wider than immediately adjacent portions of terminal (28), and each retention section (30) includes end wall (30a) for press-fittingly engaging edge walls (36a) of the retention portion (36) in a direction generally parallel to said axis. An electrical connector (14) as set forth in claim 2 wherein said spring contact portions (32) of the terminals (28) comprise formed spring contact arms and the terminal portions (34) of the terminals (28) comprise solder tails projecting from the housing.

Inventors: DIVIESTI ANTHONY M, REGNIER KENT E, DIVIESTI, ANTHONY M., REGNIER, KENT E.
Applicants: MOLEX INC, MOLEX INCORPORATED
Application year: 1995
Main classification: H01R23
IPC codes: H01R13, H01R12